AIM (Advanced Integrated Materials, 차세대융합소재연구실)

The practical utilization of Si electrodes is hindered by their substantial volume expansion during alloying and dealloying processes, which causes mechanical damage and separation from Cu current collectors. To alleviate the problem of Si composite detachment from Cu current collectors, the surface of the Cu current collectors is modified using atmospheric oxygen plasma. Plasma treatment improves the wetting ability of the Cu current collectors and, consequently, the coating quality of the Si electrodes. The uniform distribution of the Si electrode components reduces the sheet resistance and improves the adhesion properties of the Si electrodes containing surface-modified Cu current collectors. As a result, the volume expansion of Si during alloying and dealloying is reduced; this results in an excellent rate capability of 1584 mA h g–1 at a current density of 3.6 A g–1 (135% that of bare Cu) and excellent cycle performance of 1545 mA h g–1 after 300 cycles (Si electrodes with bare Cu exhibit 930 mA h g–1). Therefore, the developed plasma treatment method for Cu current collectors is expected to be an economical and efficient approach for improving the Li–ion battery performance.

In this study, a stable solid electrolyte interface (SEI) and a Ag–Li alloy were formed through a simple slurry coating of silver (Ag) nanoparticles and Li nitrate (LiNO3) on a Li metal surface (AgLN-coated Li). The Ag–Li alloy has a high Li diffusion coefficient, which allowed the inward transfer of Li atoms, thus allowing Li to be deposited below the alloy. Moreover, the highly conductive SEI enabled the fast diffusion of Li ions corresponding to the alloy. This inward transfer resulted in dendrite suppression and improved the Coulombic efficiency (CE). The AgLN-coated Li exhibited an initial capacity retention >81% and CE > 99.7 ± 0.2% over 500 cycles at a discharge capacity of 2.3 mA h cm–2.

A simple, eco-friendly, and effective additive-free technique for stabilizing a coating slurry, using alumina (Al2O3) inorganic particles and aqueous dual polymers—sodium carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) is developed. The slurry preparation process is optimized by determining the polymer binders (CMC/PVA) content in the ceramic slurry and studying the interaction between the polymer binders and Al2O3 ceramic particles by changing the mixing order of the slurry components. CMC effectively controls the viscosity of the slurry to maintain a stable slurry dispersion. In contrast, PVA significantly influences the formation of a uniform ceramic coating layer on the polyethylene (PE) separator. This results in a synergistic effect to produce an optimal ceramic-coated composite separator (CCS). Compared to the bare PE separators, the prepared Al2O3 CCSs display improved physical properties, such as high adhesion strength of the ceramic coating layer, thermal stability, electrolyte wettability, and increased ionic conductivity. Moreover, the CCSs exhibit enhanced electrochemical performance. Half cells (LiMn2O4/Li metal) comprising CCSs retained 96.5% (144.8 mAh g− 1) of the initial discharge capacity even after 200 cycles, while bare PE separators lose their capacity rapidly after 150 cycles, retaining only 22.62% (33.5 mAh g− 1) at the 200th cycle.

Lithium nitrate (LiNO3) is attracting attention as a promising additive for dendrite suppression owing to its formation of Li3N during electrochemical decomposition and the formation of a spherical-like Li deposition morphology. However, LiNO3 has very low solubility in carbonate electrolytes, and it is continuously decomposed during cycling; thus, we infuse it into a ceramic composite protective layer coated on a thin Li metal surface (thickness: 20 μm) to act as a reservoir during battery cycling. This allows for a slow release of LiNO3 into the electrolyte during cycling, the formation of a Li3N-infused solid electrolyte interface layer, and dendrite suppression. Here, this results in enhanced Li/Li symmetric cell cycling performance for ∼345 h at 0.5 mA cm–2 (0.25 mAh cm–2) and ∼250 cycles, with ∼96% initial discharge capacity retention and ∼99% Coulombic efficiency for Li/LMO cells. Because of the facile nature and effectiveness of the process, the LiNO3 embedded protective layer has the potential to enhance the performance of thin Li metal anodes in Li metal batteries.

Ceramic-polymer hybrids promise to form composite electrolytes with high ionic conductivity, good stability, and electrode compatibility that conventional ceramic or polymer electrolytes cannot achieve. Using ceramic fillers in polymer electrolytes frequently results in significantly improved ion conduction. This study employs a representative composite electrolyte based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), Li zeolite Li2(Al2Si4O12) (bikitaite, BKT) ceramics, and an ether-based dual salt containing Li nitrate (EDSN) electrolyte as a plasticizer. The resulting composite electrolyte composed of PVdF, EDSN, and BKT has a superior ionic conductivity of 1.03 × 10–3 S cm−1, a broader electrochemical window of 4.8 V, and a high Li transference number of 0.61. The assembled solid-state LiFePO4/Li metal battery demonstrates a long lifespan, with an outstanding capacity retention of 86% after 450 cycles at 0.3C. The developed electrolyte with long cycling stability may serve as a model for developing solid electrolytes for Li metal secondary battery applications.

The practical applications of Li-metal batteries (LMBs) are limited by dendrite formation. Thus, a synergistic approach for enhancing the cycling performance of LMBs by combining dual salts with lithium nitrate as an additive in an ether-based electrolyte system is presented. The dual salts, lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and lithium bis(oxalate)borate (LiBOB), and lithium nitrate (LiNO3), are dissolved in a dual etherbased solvent composed of 1,2-dimethoxyethane and 1,3-dioxane. The electrolyte shows high electrochemical stability of up to ∼ 4.6V, circumventing the drawback of ether-based solvents, which are known to exhibit an oxidation potential of <4V. Moreover, dendrite inhibition is enhanced by the formation of a robust and passivating solid-electrolyte interface (SEI). Additionally, the rate capability and cycling performance are enhanced up to 1000 cycles, with a 90.0% discharge capacity retention at 1C for the lithium iron phosphate (LFP)/Li battery. Furthermore, Li/Li symmetric cells exhibit a high stability with >2300 h of repeated stripping and plating at 0.5 mA cm− 2, which is an enhancement of approximately 300% compared with the reference

The manufacturing of flexible electronics requires flexible batteries. However, the development of high-performance flexible batteries has been rather slow. A majority of the available techniques are impractical and too expensive for industrial applications because of the type of equipment needed for preparing these flexible electrodes. Therefore, in this study, we developed a simple approach for fabricating free-standing flexible cathodic electrodes. The process involves the slurry casting of a well-dispersed electrode mixture comprising the active material, carbon fibers, polymer, plasticizer, and lithium salts. By adjusting the weight ratios, we realized the best trade-off between flexibility and specific capacity. The prepared free-standing flexible cathodic electrodes of lithium manganese oxide exhibited remarkably long cycling performance over 5000 cycles at 10 C versus Li metal anode with a coulombic efficiency (C.E.) > 99% The pouch cell also had excellent cycling performance of over 500 cycles at 5C with a C.E. > 99%. This method is simple and uses current battery production line equipment without the need for new specialized equipment. This could be cost-effective and efficient for manufacturing freestanding electrodes.

Lithium metal is considered a next-generation anode material for high-voltage, high-energy-density batteries; however, its commercialization is limited because of dendrite formation during charging, which leads to short-circuiting and fire. Li metal is coated with a lithium zeolite Li2(Al2Si4O12) (bikitaite - BKT) for dendrite suppression. The BKT-coated Li metal anode exhibits enhanced cycle performance for both Li/LMO (over 982 cycles) and Li/Li cells (over 2000 h at 0.52.0 mAh cm−2 and 693 h at 2.0 mAh cm−2 ). Moreover, the voltage profile of the Li/Li cells deviates from the conventional Li plating behavior. We hypothesize that this is due to the Li wetting of the BKT particles during plating, which leads to the formation of an interconnected three-dimensional (3D) Li network. Furthermore, BKT, a Li conductor, promotes even Li + -ion distribution during plating, resulting in the uniform deposition of Li and, consequently, suppressed dendrite formation. This work provides evidence that BKT can be potentially used in Li metal batteries.

We demonstrate that dispersion stability and excellent coating quality are achieved in polyethylene (PE) separators by premixing heterogeneous ceramics such as silica (SiO 2 ) and alumina (Al 2 O 3 ) in an aqueous solution, without the need for functional additives such as dispersing agents and surfactants. Due to the opposite polarities of the zeta potentials of SiO2 and Al2O3, SiO2 forms a sheath around the Al2O3 surface. Electrostatic repulsion occurs between the Al2O3 particles encapsulated in SiO2 to improve the dispersion stability of the slurry. The CCSs fabricated using a dual ceramic (SiO2 and Al2O3 )-containing aqueous coating slurry, denoted as DC-CCSs, exhibit improved physical properties, such as a wetting property, electrolyte uptake, and ionic conductivity, compared to bare PE separators and CCSs coated with a single ceramic of Al2O3 (SC-CCSs). Consequently, DC-CCSs exhibit an improved electrochemical performance, in terms of rate capability and cycle performance. The half cells consisting of DC-CCSs retain 93.8% (97.12 mAh g−1 ) of the initial discharge capacity after 80 cycles, while the bare PE and SC-CCSs exhibit 22.5% and 26.6% capacity retention, respectively. The full cells consisting of DC-CCSs retain 90.9% (102.9 mAh g−1 ) of the initial discharge capacity after 400 cycles, while the bare PE and SC-CCS exhibit 64.7% and 73.4% capacity retention, respectively.

Developing uniform ceramic-coated separators in high-energy Li secondary batteries has been a challenging task because aqueous ceramic coating slurries have poor dispersion stability and coating quality on the hydrophobic surfaces of polyolefin separators. In this study, we develop a simple but effective strategy for improving the dispersion stability of aqueous ceramic coating slurries by changing the mixing order of the ceramic slurry components. The aqueous ceramic coating slurry comprises ceramics (Al2O3), polymeric binders (sodium carboxymethyl cellulose, CMC), surfactants (disodium laureth sulfosuccinate, DLSS), and water. The interaction between the ceramic slurry components is studied by changing the mixing order of the ceramic slurry components and quantitatively evaluating the dispersion stability of the ceramic coating slurry using a Lumisizer. In the optimized mixing sequence, Al2O3 and DLSS premixed in aqueous Al2O3 -DLSS micelles through strong surface interactions, and they repel each other due to steric repulsion. The addition of CMC in this state does not compromise the dispersion stability of aqueous ceramic coating slurries and enables uniform ceramic coating on polyethylene (PE) separators. The prepared Al2O3 ceramic coated separators (Al2O3–CCSs) exhibit improved physical properties, such as high wettability electrolyte uptake and ionic conductivity, compared to the bare PE separators. Furthermore, Al2O3–CCSs exhibit improved electrochemical performance, such as rate capability and cycling performance. The half cells (LiMn2O4/Li metal) comprising Al2O3–CCSs retain 90.4% (88.4 mAh g−1) of initial discharge capacity after 150 cycles, while 27.6% (26.4 mAh g−1) for bare PE. Furthermore, the full cells (LiMn2O4/graphite) consisting of Al2O3–CCSs exhibit 69.8% (72.2 mAh g−1) of the initial discharge capacity and 24.9% (25.0 mAh g−1) for bare PE after 1150 cycles.

Silicon is an attractive anode material for lithium-ion batteries (LIBs) because of its natural abundance and excellent theoretical energy density. However, Si-based electrodes are difficult to commercialize because of their significant volume changes during lithiation that can result in mechanical damage. To overcome this limitation, we synthesized an eco-friendly water-soluble polyimide (W-PI) precursor, poly(amic acid) salt (W-PAmAS), as a binder for Si anodes via a simple one-step process using water as a solvent. Using the W-PAmAS binder, a composite Si electrode was achieved by low-temperature processing at 150 °C. The adhesion between the electrode components was further enhanced by introducing 3, 5-diaminobenzoic acid, which contains free carboxylic acid (–COOH) groups in the W-PAmAS backbone. The –COOH of the W-PI binder chemically interacts with the surface of Si nanoparticles (SiNPs) by forming ester bonds, which efficiently bond the SiNPs, even during severe volume changes. The Si anode with W-PI binder showed improved electrochemical performance with a high capacity of 2061 mAh g−1 and excellent cyclability of 1883 mAh g−1 after 200 cycles at 1200 mA g−1. Therefore, W-PI can be used as a highly effective polymeric binder in Si-based high-capacity LIBs.

Lithium ion conducting polymer electrolytes with broad electrochemical stability, good mechanical strength, high thermal stability, and easy processability are necessary for all-solid-state and shape-variant lithium secondary batteries. Hybrid gel polymer electrolytes incorporating an ionic liquid have been attracting attention for application in solid-state lithium secondary batteries owing to their superior thermal properties compared to conventional electrolyte systems. In this study, a variety of polymer electrolytes based on poly(vinylidene fluoride-co-hexafluompropylene) (PVdF-HFP), lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PMPyrrTFSI) are prepared, and an in-depth study of their composition dependence and electrical properties is conducted to develop the optimum composition. The composition dependent ionic conductivity of the polymer electrolyte increases with increasing LiTFSI and PMPyrrTFSI and reaches a maximum value of 6.93 x 10(-4) S cm(-1) at mom temperature (25 degrees C) when the polymer electrolyte contains 30 wt% LiTFSI and 60 wt% PMPyrrTFSI. In addition, the optimized gel polymer electrolytes consisting of PVdF-HFP/LiTFSI/PMPyrrTFSI (70/30/60 by weight, i.e., 70PVdF-HFP/30LiTFSI/60PMPyrrTFSI) look transparent and exhibit high mechanical stability and excellent thermal stability up to 420 degrees C. Finally, the lithium iron phosphate (LiFePO4)/lithium metal solid-state cells coupled with the optimized gel polymer electrolyte are prepared, and their discharge characteristics are studied. The 70PVdF-HFP/30LiTFSI/60PMPyrrTFSI based solid-state cell delivered a maximum discharge capacity of 151 mAh g(-1) at room temperature with a good rate capability and cycling performance.

The ceramic coating layer (CCL) on a polyolefin separator plays a pivotal role in securing the safety of lithium-ion batteries (LIBs) by suppressing the thermal shrinkage of the separator even under abnormal circumstances. However, an additional CCL inevitably leads to energy density loss and electrochemical performance degradation. To mitigate these weaknesses, we designed a new chemical crosslinking between ceramic particles and polymeric binders to minimize the thickness of the CCL while maintaining its thermal stability. For this purpose, a polydopamine (PD) nanolayer is preliminarily introduced on the surface of ceramic particles using a simple solution polymerization method. Then, a poly(acrylic acid) binder, which can react with the amine groups in the PD, is chosen for the aqueous ceramic coating slurry. Thus, this combination can create a number of crosslinking points within the CCL, which leads to higher adhesion within the CCL after electrolyte impregnation. As a result, the crosslinked PD ceramic-coated separator (xPD-CCS) can maintain its original dimension even at 160 ◦C for 1 h with a 9-μm polyethylene base film. In addition, a full cell (LiNi0.8Co0.1Mn0.1O2/graphite) with the xPD-CCS can show a comparable cycle performance (capacity retention of 89.2% after 400 cycles) to those of bare polyethylene and non-crosslinked PD-CCS cases.

The multilayered membrane for lithium rechargeable batteries based on poly (vinylidene fluoride) (PVdF) is prepared with the coated layer containing nano-sized filler. The prepared membranes were subjected to studies of mechanical strength, morphology, interfacial stability, impedance spectroscopy, ionic conductivity, and cycle performance. The localized inorganic filler in the PVdF composite membrane rendered mechanical strength much reduced because of its low stretching ratio and it results in around half value of the mechanical strength of highly stretched PVdF membrane. In order to achieve high ionic conductivity and interfacial stability without sacrificing high mechanical strength, coating layer with nano-filler was newly introduced to PVdF membrane. The ionic conductivity of the coated membrane was 1.03 mS/cm, and the interface between the coating layer and PVdF membrane was stable when the membrane was immersed into liquid electrolyte. The discharge capacity of the cell based on nano-filler coated PVdF membrane was around 91% of the initial discharge capacity after 250 cycles, which is an improvement in cycle performance compared to the case for the non-coated PVdF membrane.

In order to overcome severe capacity fading of LiMn2O4/graphite Li-ion cells at high temperature at 60 °C, fluoroethylene carbonate (FEC) was newly evaluated as an electrolyte additive. With 2 wt.% FEC addition into the electrolyte (EC/DEC/PC with 1 M LiPF6), the capacity retention at 60 °C after 130 cycles was significantly improved by about 20%. To understand the underlying principle on the capacity retention enhancement, the electrochemical properties of the cells including cell performance, impedance behavior as well as the characteristics of the interfacial properties were examined. Based on these results, it is suggested that the improved capacity retention of LiMn2O4/graphite Li-ion cells with addition of FEC especially at high temperature is mainly originated from the thin and stable SEI layer formed on the graphite anode surface.

The effect of an electrolyte additive, succinic anhydride (SA), on the electrochemical performances of a silicon thin-film electrode, which is prepared by radio-frequency magnetron sputtering, is investigated. The introduction of SA into a liquid electrolyte consisting of ethylene carbonate/diethyl carbonate/1 M LiPF6 significantly enhances the capacity retention and coulombic efficiency of the electrode. This improvement in the electrochemical performance of the electrode is attributed to modification of the solid/electrolyte interphase (SEI) layer by the introduction of SA. The differences in the characteristic properties of SEI layers, with or without SA, are explained by analysis with scanning electron microscopy, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy.

Anion receptor-coated separators were prepared by coating poly(ethylene glycol) borate ester (PEGB) as an anion receptor and poly(vinyl acetate) (PVAc) as a good adhesive material towards electrodes onto microporous polyethylene (PE) separators. Gel polymer electrolytes were fabricated by soaking them in an liquid electrolyte, 1 M LiPF6 in EC/DEC/PC (30/65/5, wt.%). As the weight ratio of PEGB to PVAc in a coating layer increased, gel polymer electrolytes showed higher cationic conductivity and electrochemical stability. The cationic conductivity and electrochemical stability of the gel polymer electrolyte based on coated separator with PVAc/PEGB (2/5, weight ratio) could reach 2.8 × 10–4 S cm–1 and 4.8 V, respectively. Lithium-ion polymer cells (LiCoO2/graphite) based on gel polymer electrolytes with and without PEGB were assembled, and their electrochemical performances were evaluated.

We report N-(triphenylphosphoranylidene) aniline (TPPA) as a new electrolyte additive for high performance lithium cobalt oxide (LiCoO2) electrodes during high voltage operations. When cycled in the voltage range of 3.0–4.4 V, graphite-LiCoO2 full cells with 0.2 wt% TPPA exhibited 10% increased discharge capacities after 200 cycles compared to those of control cells with no such additive. The enhanced cycling performance is attributed to the additive effect toward the modified surface films on LiCoO2 electrodes that suppress the decomposition of both solvent and salt in the electrolyte. This additive effect was characterized by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS).

Polydopamine-treated polyethylene (PE) separators for high-power lithium ion batteries are developed. A simple dipping process makes the PE surfaces hydrophilic and thus enhances the power capabilities remarkably compared to those of the control cases with bare PE separators. The original mechanical and thermal properties of the PE separators are preserved.

Lithium ion capacitors (LICs) have recently drawn considerable attention because they utilize the advantages of supercapacitors (high power) and lithium ion batteries (high energy). However, the energy densities of conventional LICs, which consist of a pair of graphite and activated carbon electrodes, are limited by the small capacities of the activated carbon cathodes. To overcome this limitation, we have engaged urea-reduced graphene oxide. The amide functional groups generated during the urea reduction facilitate the enolization processes for reversible Li binding, which improves the specific capacity by 37?% compared to those of conventional systems such as activated carbon and hydrazine-reduced graphene oxide. Utilizing the increased Li binding capability, when evaluated based on the mass of the active materials on both sides, the LICs based on urea-reduced graphene oxide deliver a specific energy density of approximately 106 Wh?kgtotal-1 and a specific power density of approximately 4200 W?kgtotal-1 with perfect capacity retention up to 1000 cycles. These values are far superior to those of previously reported LICs and supercapacitors, which suggests that appropriately treated graphene can be a promising electrode material for LICs.

Highly ion-conductive gel polymer electrolyte (GPE) with mechanical flexibility is developed by incorporating liquid electrolyte into polymer films that are fabricated by initiator-free photopolymerization of poly(ethylene glycol) dimethacrylate (acrylate monomer) and pentaerythritol tetrakis (3-mercaptopropionate) (thiol monomer) blend. When UV is irradiated on the blend, the thiol monomers themselves produce radicals to initiate the polymerization. GPEs with 40–50 wt.% of thiol monomer content show mechanically free standing characteristics with sufficient flexibility. The ionic conductivity of the GPE reaches1.1 × 10−3 S cm−1 at 25 °C and is thus high enough to be applied for lithium secondary batteries. The GPE is electrochemically stable up to 4.4 V versus Li/Li+ and the unit cells consisting of LiCoO2/GPE/lithium metal show good cycling performance. This GPE is thus considered a good electrolyte candidate for future flexible and wearable lithium secondary batteries.

An excellent cycle life (150 cycles with 80% retention) for lithium‐metal anodes in lithium‐ion batteries is achieved by employing mussel‐inspired polydopamine‐treated‐polyethylene separators. This originates from the polydopamine coating, which enables a uniform ionic flux, as well as mussel‐inspired catecholic adhesion of the separators onto the lithium surfaces. Additionally, the polydopamine coating improves the thermal‐shrinkage properties of polyethylene separators.

In this study, we developed an integrative bioinspired approach that improves the power and safety of Li-ion batteries (LIBs) by the surface modification of polyethylene (PE) separators. The approach involves the synthesis of a diatom-inspired silica layer on the surface of the PE separator, and the adhesion of the silica layer was inspired by mussels. The mussel- and diatom-inspired silica coating increased the electrolyte wettability of the separator, resulting in enhanced power and improved thermal shrinkage, resulting safer LIBs. Furthermore, the overall processes are environmentally friendly and cost-effective. The process described herein is the first example of the use of diatom-inspired silica in practically important energy storage applications. The improved wetting and thermal properties are critical, particularly for large-scale battery applications.

With the aim of attaining a better understanding of the thermal stabilities of solid electrolyte interphase (SEI) layers with lithium salts, a series of lithium alkyl carbonates, including lithium methyl carbonate (LMC) and lithium ethyl carbonate (LEC), were synthesized as model reference SEI components. The effects of the lithium salts, lithium hexafluorophosphate (LiPF6) and lithium bis(oxalate) borate (LiBOB), on the thermal stabilities of the lithium alkyl carbonates were then investigated via the differential scanning calorimetry (DSC) method. It was demonstrated that small and broad exothermic peaks near 100 °C for pure lithium alkyl carbonates were drastically increased, likely due to vigorous synergic exothermal reactions between the lithium alkyl carbonates and LiPF6. In contrast, LiBOB did not show increased peaks.

The thermal shrinkage of the widely adopted polyethylene (PE) separators has become a very critical issue for safety in lithium ion batteries, especially for electrical vehicle applications. As an effort to minimize the thermal shrinkage of PE separators, in this study, we coat PE separators with a substance from the polyimide family by engaging a simple dipping method. A polymer coating at the optimal concentration endows PE separators with improved mechanical strength and thus remarkably increased resistance against thermal shrinkage at elevated temperatures. Despite the coating layers, the cells with the polyimide-coated separators exhibit almost identical electrochemical properties to those of the cells with the bare PE separators, thus proving that the polymer coating does not affect the battery performance. The preserved electrochemical properties can be explained by morphology and porosity characterization.

Li-rich layered cathode materials are very promising candidates for next generation high energy lithium ion batteries. One of the Li-rich layered cathode materials, Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 is prepared by a co-precipitation method. In this report, we focus on anomalous changes upon cycling in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material in a voltage range of 2.0–4.55 V at room temperature. The structural transitions upon cycling are analyzed by ex situ X-ray diffraction. In addition, the changes in local structure during cycling are studied by X-ray absorption near edge structure. With differential capacity plots by controlling the cut-off voltage, the voltage decay during cycling is intensively studied. The continuous activation process of the residual Li2MnO3 component during cycling is correlated with voltage decay during cycling, and increasing capacity during the initial several cycles. Also, the electrochemical performance in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material below 4.4 V is discussed. Furthermore, cycle performance is improved by reassembling Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 into another cell after washing.

We report an alginate, extracted from brown seaweed as a polymeric binder for spinel LiMn2O4. The exceptional Mn2+ capture of the alginate extracted from brown seaweed resolves the chronic issue of a promising lithium battery cathode, LiMn2O4, upholding the feasibility of its use for emerging large-scale applications including electric vehicles.

Conjugation of mussel-inspired catechol groups to various polymer backbones results in materials suitable as silicon anode binders. The unique wetness-resistant adhesion provided by the catechol groups allows the silicon nanoparticle electrodes to maintain their structure throughout the repeated volume expansion and shrinkage during lithiation cycling, thus facilitating substantially improved specific capacities and cycle lives of lithium-ion batteries.

Aiming at improving the capacity retention abilities of LiMn2O4/graphite based Li-ion batteries (LIBs) at high temperatures, we report on 2-(triphenylphosphoranylidene) succinic anhydride (TPSA) as a new electrolyte additive. The unit cells with 0.1 wt.% of TPSA achieved a 43% capacity retention increase at high temperature operation (55 °C, 100 cycles, C/2 rate) compared to a control group without the additive. To understand the underlying principle on the enhanced capacity retention ability of the unit cells, the effect of TPSA was investigated by cyclic voltammetry, X-ray photoelectron spectroscopy, auger electron spectroscopy, and galvanostatic measurements. The results suggest that the electrochemical decomposition of TPSA takes place on both surfaces of the LiMn2O4 and graphite during precycling, thereby reducing the decomposition reaction of the electrolyte during subsequent cycles.

The rice husk is the outer covering of a rice kernel and protects the inner ingredients from external attack by insects and bacteria. To perform this function while ventilating air and moisture, rice plants have developed unique nanoporous silica layers in their husks through years of natural evolution. Despite the massive amount of annual production near 108 tons worldwide, so far rice husks have been recycled only for low-value agricultural items. In an effort to recycle rice husks for high-value applications, we convert the silica to silicon and use it for high-capacity lithium battery anodes. Taking advantage of the interconnected nanoporous structure naturally existing in rice husks, the converted silicon exhibits excellent electrochemical performance as a lithium battery anode, suggesting that rice husks can be a massive resource for use in high-capacity lithium battery negative electrodes.

We report a simple process to coat silicon monoxide (SiO) particles with nitrogen-doped carbon layers (NC-SiO) by using a nitrogen-containing ionic liquid. The nitrogen-doping addresses the moderate electric conductivity of SiO particles as large as 20 μm and thus enables NC-SiO to exhibit substantially improved specific capacity and rate performance as compared to those of bare carbon-coated SiO (C-SiO) and bare SiO counterparts. Due to the simplicity of the coating procedure, the current approach should be readily applicable to other lithium battery electrodes that suffer from low electronic conductivities.

Mesoporous silicon nanofibers (m-SiNFs) have been fabricated using a simple and scalable method via electrospinning and reduction with magnesium. The prepared m-SiNFs have a unique structure in which clusters of the primary Si nanoparticles interconnect to form a secondary three-dimensional mesoporous structure. Although only a few nanosized primary Si particles lead to faster electronic and Li+ ion diffusion compared to tens of nanosized Si, the secondary nanofiber structure (a few micrometers in length) results in the uniform distribution of the nanoparticles, allowing for the easy fabrication of electrodes. Moreover, these m-SiNFs exhibit impressive electrochemical characteristics when used as the anode materials in lithium ion batteries (LIBs). These include a high reversible capacity of 2846.7 mAh g–1 at a current density of 0.1 A g–1, a stable capacity retention of 89.4% at a 1 C rate (2 A g–1) for 100 cycles, and a rate capability of 1214.0 mAh g–1 (at 18 C rate for a discharge time of ∼3 min).

The effects of cathode/anode area ratio on the electrochemical performance of lithium-ion batteries are investigated using 2032-type coin full cells. As the anode area is increased from 1.13 (ø12 mm) to 2.54 cm2 (ø18 mm) while maintaining the cathode area as 1.13 cm2 (ø12 mm), both coulombic efficiency and discharge capacity at the first formation step become increasingly worse, probably owing to greater formation of solid electrolyte interphase (SEI). Moreover, rate capability also declined with increased anode area, whereas discharge capacity retention behavior during 1C/1C charge/discharge cycling appeared similar except for a slightly decreased capacity of coin cells with larger anode areas. The findings indicate that cathode/anode area ratio should be carefully evaluated to achieve reliable data on electrochemical performance.

This study demonstrates the effect of polydopamine coating on separator membranes used in liquid electrolyte batteries as a function of membrane porosity. We select two typical separators that differed only in porosity. High-porosity (16H) and low-porosity (16L) separators are coated with polydopamine by simple dip-coating. Their properties are evaluated via scanning electronic microscopy (SEM) and determining the water contact angle, Gurley number, ionic conductivity, and uptake volume of liquid electrolyte. In addition, the effect of polydopamine coating on electrochemical properties is tested using CR2032 coin-type half-cells (LiMn2O4/Li metal). With enhanced hydrophilic properties of surfaces as keeping pore structures, both of polydopamine coated high and low porous separators show enhanced rate capability and cell performance compared to uncoated versions. The effect of polydopamine coating is greatly enhanced in the low-porosity separators, with up to 40% increase in power capability (at 5 C rate) and a 290% increase in cycle performance (after 500 cycles, at C/2 rate), compared to the high-porosity type (13% increase in power capability, 43% increase in cycle performance).

The effect of succinic anhydride (SA) as an electrolyte additive on the cycling performance of Li electrode is discussed. As the SA content in the electrolyte increased from 2 to 5 to 10 wt%, the capacity retention of LiCoO2/Li cell is greatly improved owing to the modification of the solid electrolyte interphase (SEI) layer and the suppression of dendrite growth on the Li electrode. In particular, when 10 wt% SA is introduced into the electrolyte, the Li electrode thickness increases only about 45 μm (from 100 to 145 μm) after 40 cycles, whereas an increase of about 210 μm occurs without SA. This amazing enhancement in cycling performance is also augmented by a much smaller increase in the bulk resistance of the LiCoO2/Li cell after cycling with 10 wt% SA.

We report a simple fabrication process for a stainless steel metal fibril-supported Fe2O3 (Fe2O3/SF) material as a lithium battery anode. Utilizing the well-developed 3D structure of Fe2O3/SF, the material shows not only a superior rate capability but also extremely long cycle life (2000 cycles), even at a high current density.

The demand for lithium ion batteries (LIBs) in various flexible mobile electronic devices is continuously increasing. With this in mind, a vast number of smart approaches, such as implementation of conductive nanomaterials onto paper and textiles, have been recently demonstrated. Most of them were, however, limited to the single-cell level. In the present study, large area flexible battery modules were developed in an attempt to expand the knowledge and design accumulated from the single-cell level approaches to larger-scale applications. A multi-stacked configuration was adopted to produce a high areal energy density in each single-cell. Meanwhile textile-based electrodes on both sides grant mechanical stability, even on the module level, by efficiently releasing the stress generated during aggressive folding and rolling motions. Moreover, the connection between and stacking of the single-cells allow the wide tuning of the overall voltage and capacity of the module. This battery design should be immediately applicable to a broad range of outdoor, building, and military items.

The adhesion strength of lithium-ion battery (LIB) electrodes consisting of active material, a nanosized electric conductor, and a polymeric binder is measured with a new analysis tool, called the Surface and Interfacial Cutting Analysis System (SAICAS). Compared to the conventional peel test with the same electrode, SAICAS gives higher adhesion strength owing to its elaborate cutting-based measurement system. In addition, the effects on the adhesion property of the polymeric binder type and content, electrode density, and measuring point are also investigated to determine whether SAICAS provides reliable results. The findings confirm SAICAS as an effective and promising tool to measure and analyze the adhesion properties of LIB electrodes.

Lithium–oxygen batteries are of great interest because of their very high-energy density; however, they present many challenges, one of which is the low cycling stability of a lithium (Li) metal anode. Here, we report a composite protective layer (CPL) comprising Al2O3 and polyvinylidene fluoride-hexafluoro propylene for a Li metal anode that resulted in a dramatic enhancement of the cycling stability of a lithium–oxygen battery. A cell with the CPL-coated Li metal anode exhibited more than 3 times higher discharge capacity at the 80th cycle compared to a cell without the CPL. X-ray photoelectron spectroscopy measurements for the cycled lithium metal anodes confirm that the CPL effectively suppressed electrolyte decomposition at the surface of the Li metal anode.

The chemical stability of Li metal in a rechargeable Li–O2 cell was examined by investigating the physicochemical changes that occurred during storage of Li in an electrolyte comprising dimethyl sulfoxide (DMSO) with dissolved O2. During prolonged storage of Li in the oxygenated electrolyte, the Li surface became moss-like and its interfacial resistance increased. Analyses of reaction products using XPS and FT-IR revealed that the bis(trifluoromethyl sulfonyl) imide (TFSI) anions and DMSO solvent could have decomposed significantly through a further reaction path induced by O2. Furthermore, the formation of an unstable solid-electrolyte interphase by O2 causes degradation of the Li metal and deterioration of the electrolyte. This investigation shows that the Li anode should be protected from O2 by modification of Li and the separator to ensure long-term stability of the Li–O2 cell.

The effects of a thermally stable co-polyimide-based polymeric binder on the performance of a cathode electrode are investigated. The introduction of co-polyimide (P84) into a conventional polymeric binder system based on polyvinylidene fluoride (PVdF) enhances the cycle performance under high-temperature conditions (60 °C). Because of the inherent mechanical and thermal stabilities of the co-polyimide, P84 retains outstanding adhesive/cohesive strength within the electrode composite, as well as between the electrode composite and the aluminum current collector. These findings are further supported by electrochemical impedance spectroscopic analysis, scanning electron microscope, and studies using a Surface and Interfacial Cutting Analysis System (SAICAS®).

A mussel-inspired polydopamine (PDA) coating turns radio-frequency (RF) Al2O3 sputtering – which thus far has not been appropriate for the surface treatment of porous polyolefin-based separators – into a damage-free, reliable, and cost-efficient process. Due to the thermally resistive PDA layers, polyethylene (PE) separators can sustain high-power Al2O3 sputtering conditions over 75 W, which significantly reduces processing time. Furthermore, compared to the as-prepared separators, PDA/Al2O3-coated PE separators also reveal improved thermal stability and cycle performance for lithium secondary batteries. PDA/Al2O3-coated PE separators retained their original size when exposed to temperatures of 145 °C over 30 min, while the bare PE separators shrank to 9% of their original size. At a temperature of 25 °C, the unit cell (LiMn2O4/separator/Li metal) employing the PDA/Al2O3-coated PE separators maintained 94.8% (103.4 mA h g−1) of the initial discharge capacity after 500 cycles at C/2 rate and 51.7% (56.7 mA h g−1) at 25 C rate, while the corresponding values for the bare PE separators were 89% (98.6 mA h g−1) at C/2 rate and 24.5% (27.2 mA h g−1) at 25 C rate.

To investigate the synergistic effect of different types of conductive additives on the cathode performance of lithium-ion batteries, various types of cathode materials containing different ratios of vapor-grown carbon fibers (VGCFs) and carbon black (Super-P) are investigated. The pillar-like morphology of the VGCFs enabled them to efficiently connect to the active materials and hence, the highest electrical conductivity of LiCoO2 and LiFePO4 (both of which are composed of primary particles) was achieved with the VGCFs. On the other hand, for LiNi0.6Co0.2Mn0.2O2, composed of micro-sized secondary particles embedded with nano-sized primary particles, improved electrical conductivity was achieved with a mixture of VGCF and Super-P via synergistic action.

In order to investigate the effect of back-side coating of cathodes and anodes upon electrochemical performances of lithium-ion batteries (LIBs), four different pouch-type lithium cobalt oxide (LiCoO2, LCO)/graphite unit cells with different coating conditions are prepared and compared in a systematic manner. Their electrochemical performance, in terms of Coulombic efficiency, capacity realization, capacity retention ability, and rate capabilities, is investigated. From the results, we confirm an opposing relationship existing between back-side-coated cathodes and anodes, in that the coated cathodes provide improved cell performance, while the coated anodes impede it. This is attributed to the fact that, as is generally understood, cathodes act as noble lithium (Li) ion suppliers for LIBs, while anodes consume a large portion of Li ions to form surface layers during the first charging process. Furthermore, we also confirm that the magnitude of the back-side coating effect for LCO and graphite are somewhat different. The double-side-coated cathodes have a notable positive effect on cell performances in contrast to the negative effect seen with the double-side-coated anodes. As a result, unit cells employing double-side-coated cathodes with single-side-coated anodes show the best performance, followed by those based on double-side-coated cathodes with double-side-coated anodes rather than single-side-coated cathodes with single-side coated anodes.

In order to investigate the effects of electrode density and thickness on the room temperature electrochemical performance of lithium metal polymer batteries (LMPBs), four LiFePO4 cathodes with different electrode density/thickness (1.6 g cm−3/20 μm, 1.6 g cm−3/40 μm, 2.0 g cm−3/20 μm, and 2.0 g cm−3/40 μm) are prepared. Several types of unit cells employing each cathode are prepared using in situ thermally cross-linked polymer electrolytes controlled under the same manufacturing condition. The unit cells employing the thinnest cathode with highest density achieve the most improved rate capability and cycle life, which seems to be attributed to the higher electrical conductivity of the cathode and shorter diffusion length of Li+ ions within the cathode pores. In addition, the LMPB with an optimized LiFePO4 cathode (2.0 g cm−3, 20 μm) and polymer electrolyte (5 vol% of the crosslinking agent with non-volatile liquid electrolytes) delivers a high and stable charge/discharge capacity under very fast charging and discharging conditions (at a 2 C rate) at room temperature.

The effect of mechanical surface modification on the performance of lithium (Li) metal foil electrodes is systematically investigated. The applied micro-needle surface treatment technique for Li metal has various advantages. 1) This economical and efficient technique is able to cover a wide range of surface area with a simple rolling process, which can be easily conducted. 2) This technique achieves improved rate capability and cycling stability, as well as a reduced interfacial resistance. The micro-needle treatment improves the rate capability by 20% (0.750 mAh at a rate of 7C) and increases the cycling stability by 200% (85% of the initial discharge capacity after 150 cycles) compared to untreated bare Li metal (0.626 mAh at a rate of 7C, 85% of the initial discharge capacity after only 70 cycles). 3) This technique efficiently suppresses Li formation of high surface area Li during the Li deposition process, as preferred sites for controlled Li plating are generated.

In order to improve the safety of lithium-ion batteries (LIBs), composite separators were developed using two typical metal hydroxides, aluminum hydroxide (Al(OH)3) and magnesium hydroxide (Mg(OH)2). The composite separators were prepared by adding ceramic coating layers comprising one of the chosen metal hydroxides and a poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) binder to polyethylene (PE) separators. Both the metal hydroxide-composite separators exhibited promising fire-retardant properties, which resulted in a significant self-extinguishing time (SET) reduction and also helped to suppress any thermal dimensional changes in the PE separators that may occur at high temperatures. Due to the hydrophilic properties of metal hydroxides, unit cells employing the composite separators achieved significant improvements in rate capability that were closely associated with their improved wettability for liquid electrolytes. The electrochemical stability of the Mg(OH)2-composite separators was verified to be comparable to that of PE separators; however, the Al(OH)3-composite separators were electrochemically unstable over the same voltage range. This highlights the highly improved capacity retention of the developed unit cells that employ Mg(OH)2-composite separators.

We introduce 2-(triphenylphosphoranylidene) succinic anhydride (TPSA) as a lithium (Li) metal anode surface-stabilizing electrolyte additive for improving the cycle performance of Li metal secondary batteries. We verified that TPSA is readily decomposed on Li metal anodes before the decomposition of liquid electrolytes, and forms stable surface layers, i.e., a solid electrolyte interface (SEI). Consequently, TPSA was found to improve the cycle performance of unit cells consisting of LiCoO2/Li metal. The unit cells containing 3 wt.% of TPSA retain 85% of the initial discharge capacity after 100 cycles, whereas the unit cells that do not contain TPSA showed catastrophic failure after only 50 cycles. Each unit cell was operated at C/2 rate (0.8 mA cm−2) in the voltage range 3.0–4.2 V vs. Li/Li+. The TPSA-derived SEI suppresses continuous electrolyte decomposition, and thereby Li dendrite formation as well. The effect of TPSA was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy.

A highly adhesive and thermally stable copolyimide (P84) that is soluble in organic solvents is newly applied to silicon (Si) anodes for high energy density lithium-ion batteries. The Si anodes with the P84 binder deliver not only a little higher initial discharge capacity (2392 mAh g–1), but also fairly improved Coulombic efficiency (71.2%) compared with the Si anode using conventional polyvinylidene fluoride binder (2148 mAh g–1 and 61.2%, respectively), even though P84 is reduced irreversibly during the first charging process. This reduction behavior of P84 was systematically confirmed by cyclic voltammetry and Fourier-transform infrared analysis in attenuated total reflection mode of the Si anodes at differently charged voltages. The Si anode with P84 also shows ultrastable long-term cycle performance of 1313 mAh g–1 after 300 cycles at 1.2 A g–1 and 25 °C. From the morphological analysis on the basis of scanning electron microscopy and optical images and of the electrode adhesion properties determined by surface and interfacial cutting analysis system and peel tests, it was found that the P84 binder functions well and maintains the mechanical integrity of Si anodes during hundreds of cycles. As a result, when the loading level of the Si anode is increased from 0.2 to 0.6 mg cm–2, which is a commercially acceptable level, the Si anode could deliver 647 mAh g–1 until the 300th cycle, which is still two times higher than the theoretical capacity of graphite at 372 mAh g–1.

To improve the safety of lithium-ion batteries (LIBs), co-polyimide (PI) P84 was introduced as a polymeric binder for Al2O3/polymer composite surface coatings on polypropylene (PP) separators. By monitoring the dimensional shrinkage of the PP separators at high temperatures, we verified a synergistic thermal stabilization effect between the Al2O3 ceramic and the PI polymeric binder. Although PI was thermally stable up to 300 °C, a coating consisting solely of PI did not impede the PP separator dimensional changes (−22% at 150 °C). On the other hand, the Al2O3/PI-coated PP separators efficiently impeded the thermal shrinkage (−10% at 150 °C). In contrast, an Al2O3/poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) combination lowered the thermal stability of the PP separators (−33% at 150 °C). As a result, the Al2O3/PI-coated PP separators remarkably suppressed the internal short-circuit of the unit half-cells associated with separator thermal shrinkage (100 min at 160 °C), whereas the PVdF-HFP retained only 40 min under identical conditions. The Al2O3/PI-coated PP separators achieved rate capabilities and cell performances similar to those of the bare PP separators.

We simulate the electrochemical properties of Li-ion cells consisting of a blended cathode composed of LiMn2O4 and LiNi0.6Co0.2Mn0.2O2 and an artificial graphite anode using the Li-ion battery model available in COMSOL MULTIPHYSICS 4.4 along with a capacity fade model. The discharge profiles of the pure and blended cathodes at various current rates obtained through simulations and experimental results are well matched. By combining two capacity fade models available in literature, namely the solid electrolyte interphase (SEI) growth model and the Mn2+ dissolution model, the cycling performance of the pure LiMn2O4 cells at 25 °C are successfully simulated and found to be in a good agreement with the experimental results. The blended cathode exhibits better capacity retention than the pure LiMn2O4 during cycling. We also observed that at high powers, the gravimetric energy density of the LiMn2O4 cathode exceeds that of the LiNi0.6Co0.2Mn0.2O2 cathode; the reverse effect is seen at low powers. Further, we were able to easily modulate the energy and power densities of the blended cathode system by changing the blend ratio in our simulation model.

To develop an environmentally friendly and cost-effective water-based inorganic coating process for hydrophobic, polyolefin-based microporous separators, the effect of surfactants in an aqueous inorganic coating solution comprising alumina (Al2O3) on polyethylene (PE)-based microporous separators is investigated. By using a selected surfactant, i.e., disodium laureth sulfosuccinate (DLSS), the aqueous Al2O3 coating solution maintained a dispersed state over time and facilitated the formation of a uniform Al2O3 coating layer on PE separator surfaces. Due to the hydrophilic nature of the Al2O3 coating layers, the as-prepared, ceramic-coated PE separators had better wetting properties, greater electrolyte uptake, and larger ionic conductivities compared to those of the bare PE separators. Furthermore, half cells (LiMn2O4/Li metal) containing Al2O3-coated PE separators showed improved capacity retention over several cycles (93.6% retention after 400 cycles for Al2O3 coated PE separators, compared to 89.2% for bare PE separators operated at C/2) and rate capability compared to those containing bare PE separators. Moreover, because the Al2O3-coated layers are more thermally stable, the coated separators had improved dimensional stability at high temperatures (140 °C).

Significant acceleration in the speed of polydopamine coating is achieved by optimizing various physicochemical conditions. Using these conditions, sufficient amounts of polydopamine layers are deposited onto various surfaces within a minute. Moreover, the coating process is improved by combining it with a spray system, which allows the system to be used for large-scale surface modifications.

Repressing uncontrolled lithium (Li) dendrite growth is the top priority for enabling the reliable use of Li metal secondary batteries. On the other hand, the technique controlling the metal plating behavior during metal plating indeed has been considered very difficult to achieve. For instance, how can one plate metal ions on the favored selected region during plating? The present study describes how to achieve this goal, i.e., dendrite-free Li deposition, by mechanical surface modification using a simple stamping technique, where finite-element method simulation using COMSOL Multiphysics was used to design the micro-patterns of the stamp. After stamping, the transferred micro-patterns on Li metal anodes suppress dendrite growth during repeated Li deposition/stripping processes and exhibit improved long-term cycling stability of Li metal anodes. During the repeated Li plating processes, the pattern holes are filled by the liquid-like and/or granular forms of Li metal without resulting Li dendrite growth. These holes are then reversibly drained during the Li stripping process, reverting to their original dimension. This study investigated the correlation of this unique Li plating/stripping behavior as a function of the current density.

LiNi0.6Co0.2Mn0.2O2 cathodes of different thicknesses and porosities are prepared and tested, in order to optimize the design of lithium-ion cells. A mathematical model for simulating multiple types of particles with different contact resistances in a single electrode is adopted to study the effects of the different cathode thicknesses and porosities on lithium-ion transport using the nonlinear least squares technique. The model is used to optimize the design of LiNi0.6Co0.2Mn0.2O2/graphite lithium-ion cells by employing it to generate a number of Ragone plots. The cells are optimized for cathode porosity and thickness, while the anode porosity, anode-to-cathode capacity ratio, thickness and porosity of separator, and electrolyte salt concentration are held constant. Optimization is performed for discharge times ranging from 10 h to 5 min. Using the Levenberg-Marquardt method as a fitting technique, accounting for multiple particles with different contact resistances, and employing a rate-dependent solid-phase diffusion coefficient results in there being good agreement between the simulated and experimentally determined discharge curves. The optimized parameters obtained from this study should serve as a guide for the battery industry as well as for researchers for determining the optimal cell design for different applications.

Ceramic composite separators (CCSs) play a critical role in ensuring safety for lithium-ion batteries (LIBs), especially for mid- and large-sized devices. However, production of CCSs using organic solvents has some cost and environmental concerns. An aqueous process for fabricating CCSs is attractive because of its cost-effectiveness and environmental-friendliness because organic solvents are not used. The success of an aqueous coating system for LIBs is dependent upon minimizing moisture content, as moisture has a negatively impact on LIB performance. In this study, CCSs were fabricated using an aqueous coating solution containing Al2O3 and an acrylic binder. Compared with polyethylene (PE) separators, CCSs coated with an aqueous coating solution showed improved thermal stability, electrolyte uptake, puncture strength, ionic conductivity, and rate capability. In addition, our new approach of introducing a small amount of an oily liquid to the aqueous coating solution reduced the water adsorption by 11.7% compared with coatings that do not contain the oily liquid additive.

Dopamine, which can be electrochemically oxidized to polydopamine on cathode surface, was introduced as an electrolyte additive for high-voltage lithium-ion batteries (LIBs). The addition of 0.1 wt % dopamine to the electrolyte led to the formation of a polydopamine-containing layer on the cathode, thereby resulting in suppression of the oxidative decomposition of the electrolyte during high-voltage operation (up to 4.5 V) of a LiNi1/3Co1/3Mn1/3O2/artificial graphite cell. The addition of dopamine to the electrolyte improved the capacity retention of the cell from 136 to 147 mAh g–1 after 100 cycles at a rate of 1 C and a cutoff voltage of 4.5 V, while the cycle performance and rate capability with a cutoff voltage of 4.3 V were comparable to those of the cell without dopamine. Further evidence of the positive impact of dopamine on high-voltage LIBs was the lower DC-IRs and AC impedances, as well as the retention of the cathode morphology even after operation at 4.5 V.

The study has developed a facile polydopamine (PD) surface coating method for a typical conductive additive, Super-P. This method is efficient, economical, and environmentally friendly, and it can be used for the mass production of Super-P. PD treatment converts the hydrophobic surfaces of Super-P into hydrophilic surfaces, facilitating slurry preparation, and slurry coating for the fabrication of Si-based electrodes. Furthermore, the unique adhesion properties of PD and its ability to form a cross-linking network with polymeric binders such as poly(acrylic acid) improve the cycle performance of Si anodes containing PD-treated Super-P (1395.1 mAh g–1 after 1000 cycles, and 1200 mA g–1 for charging and discharging processes). A postmortem scanning electron microscopy study reveals that PD-treated Super-P efficiently reduces the mechanical stress of Si anodes caused by large volumetric changes that occur during lithiation and delithiation.

To establish an accurate correlation between a separator’s pore structure and the electrochemical performance of a lithium-ion battery (LIB), we fabricate well defined polyethylene (PE) separators on the same production line while maintaining most processing variables, except for composition. Four PE separators having different thicknesses and porosities (16 μm/37%, 16 μm/40%, 16 μm/47%, 22 μm/47%, respectively) are physically and electrochemically evaluated in detail. Although thickness and porosity remain good parameters by which to represent the separators’ characteristics, both the normalized Gurley number and ionic conductance are found to have much stronger relationships with the rate capability.

To meet the high requirements of future lithium secondary batteries based on lithium metal anodes for large-scale applications, we develop a cost-effective and environmentally friendly water-based method to prepare inorganic/polymer composite coating layers on commercial hydrophobic polyolefin-based microporous separators. To this end, we utilize a plasma-treatment technique. After the plasma treatment, the surface of the polyethylene (PE) separators changes from hydrophobic to hydrophilic, and the pore structures of the separators widen. These changes improve the affinity of the PE separators for polar liquid electrolytes and their ionic conductivities compared to those of bare PE and other ceramic-coated control systems. The polar functional groups derived from plasma treatment interact with the hydroxyl groups of water-soluble polymeric binders in the ceramic (Al2O3) coating layers, thereby improving the adhesion strength between the PE substrate and the ceramic coating layer. This improvement impedes hydrophobic recovery phenomena. As a result, plasma-treated ceramic-coated separators (plasma CCSs) exhibit superior power capability and cycle performance (plasma CCS maintained 94.7% of the initial discharge capacity up to the 1000th cycle at C/2, whereas bare PE’s remained high only up to the 300th cycle) in unit cells based on lithium metal anodes.

Using a surface and interfacial cutting analysis system (SAICAS) that can measure the adhesion strength of a composite electrode at a specific depth from the surface, we can subdivide the adhesion strength of a composite electrode into two classes: (1) the adhesion strength between the Al current collector and the cathode composite electrode (FAl–Ca) and (2) the adhesion strength measured at the mid-depth of the cathode composite electrode (Fmid). Both adhesion strengths, FAl–Ca and Fmid, increase with increasing electrode density and loading level. From the SAICAS measurement, we obtain a mathematical equation that governs the adhesion strength of the composite electrodes. This equation revealed a maximum accuracy of 97.2% and 96.1% for FAl–Ca and Fmid, respectively, for four randomly chosen composite electrodes varying in electrode density and loading level.

A mathematical model is developed for the cyclic aging of a spinel LiMn2O4/graphite lithium-ion cell in this study. The proposed model assumes the formation and dissolution of the solid electrolyte interphase (SEI) in the anode, Mn(II) dissolution of the LiMn2O4 cathode active material due to the Mn(III) disproportionation reaction, the effect of deposition of the reduced Mn on the SEI at the anode, and the formation of a cathode-electrolyte interphase (CEI) layer on the cathode. The decrease of the Li-ion diffusion coefficient in the cathode due to the formation of a passive film and the dissolution of the active material are introduced as factors that lead to capacity fading. Temperature effects on the capacity fade parameters and chemical reactions are integrated into this model. The developed model is incorporated into the Newman's Porous Composite Electrode (PCE) framework and implemented in the battery module of COMSOL Multiphysics. The proposed model is used to investigate the effect of variations in the ambient temperature, and of the voltage range of cycling on the capacity fade. In addition, the effect of changes in the volume fraction of cathode active material, the resistance in the cell, and the state of charge of the anode are also studied.

Unstable and deficient supplies of lithium resources have led to the development of alternative battery systems such as sodium-ion batteries. Herein, P-type Na 0.6 Mn 0.65 Ni 0.25 Co 0.10 O 2 cathode materials were synthesized by a co-precipitation and solid-state reaction method. When the calcination temperature was changed from 700 to 1000 C, Na 0.6 Mn 0.65 Ni 0.25 Co 0.10 O 2 had a different morphology and crystalline structure; however, a P3-type structure was formed only at 700 C, and P2-type structured cathodes could be obtained at 800, 900, and 1000 C. Their electrochemical performances were evaluated with 2032 coin-type half cells. Among them, the P2-type cathode calcinated at 900 C, exhibited a high specific discharge capacity of 148 mAh g− 1, and a stable cycling performance at a 0.2 C rate for 150 cycles.

To investigate the effects of the exposure of battery tabs to humidity on the self-discharge properties of full-cell type lithium-ion batteries (LIBs), we assembled two different types of LIBs, composed of NCM/graphite or LCO/graphite, and compared their discharge retention abilities after storage in humid conditions (90% relative humidity (RH)) with and without battery tab protection. Regardless of the type of cathode active materials, tab protection improved the calendar lives of LIBs. For NCM/graphite, battery tab protection shows an approximate 50% improvement in the discharge capacity compared to the case without battery tab protection after storage in humid conditions (51.1% and 34.6% of the initial discharge capacity for tab-protected and non-protected LIBs, respectively). In contrast, LCO/graphite reveals a smaller change in the discharge capacity retention for the same experimental condition because they show superior capacity retention abilities regardless of battery tab protection (85.6% and 82.0% retention of the initial discharge capacity for tab-protected and non-protected LIBs, respectively). We suggested that these results come from the induction effect of polar water molecules, which pulls electrons to the battery tab side, resulting in lithium ion loss from the graphene layers to the liquid electrolyte.

Two types of Cu foil, conventional flat Cu foil and rough Cu foil, are used to fabricate silicon (Si) electrodes for flexible and high-energy-density lithium-ion batteries (LIBs). Confocal microscopy and cross-sectional SEM images reveal the roughness of the very rough Cu foil to be approximately 3 μm, whereas the conventional flat Cu foil has a smooth surface and a roughness of less than 1 μm. This difference leads to the improvement of the interfacial adhesion strength between the Si electrode and the Cu foil from 89.7 (flat Cu foil) to 135.7 N m−1 (rough Cu foil), which is measured by a versatile peel tester. As a result, the Si electrode with high Si content (80 wt%) can deliver a significantly higher discharge capacity of 1500 mA h g−1 after 200 cycles, even at a current rate of 1200 mA g−1. Furthermore, when the corresponding Si electrode is assembled into a pouch-type cell and cycled in the rolled conformation with a radius of 6.5 mm, the Si electrode with rough Cu foil shows a stable cycle performance due to better interfacial adhesion.

A stable electrolyte system at a charge voltage over 4.5 V is the key to successfully obtaining higher energy density by raising the charging cutoff voltage. We demonstrate a fluorinated electrolyte (1 M LiPF6 fluoroethylene carbonate (FEC) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) (FEC/FEMC = 1/9, v/v)) for a high-voltage LiNi0.5Mn0.3Co0.2O2/graphite system. The stability of the fluorinated electrolyte for the LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode was investigated using scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The charge-discharge performance of the fluorinated electrolyte was superior to the corresponding non-fluorinated electrolyte system at a charging cutoff voltage of 4.7 V.

Owing to the natural abundance of sodium resources and their low price, next-generation batteries employing an Na metal anode, such as Na–O2 and Na–S systems, have attracted a great deal of interest. However, the poor reversibility of an Na metal electrode during repeated electrochemical plating and stripping is a major obstacle to realizing rechargeable sodium metal batteries. It mainly originates from Na dendrite formation and exhaustive electrolyte decomposition due to the high reactivity of Na metal. Herein, we report a free-standing composite protective layer (FCPL) for enhancing the reversibility of an Na metal electrode by mechanically suppressing Na dendritic growth and mitigating the electrolyte decomposition. A systematic variation of the liquid electrolyte uptake of FCPL verifies the existence of a critical shear modulus for suppressing Na dendrite growth, being in good agreement with a linear elastic theory, and emphasizes the importance of the ionic conductivity of FCPL for attaining uniform Na plating and stripping. The Na–Na symmetric cell with an optimized FCPL exhibits a cycle life two times longer than that of a bare Na electrode.

Because of the constantly increasing demand for highly safe lithium-ion batteries (LIBs), interest in the development of ceramic composite separators (CCSs) is growing rapidly. Here, an in-depth study of the adhesion properties of the Al2O3 ceramic composite coating layer of CCSs is conducted using a peel test and a surface and interfacial cutting analysis system (SAICAS). Contrary to the 90 and 180° peel tests, which resulted in different adhesion strengths even for the same CCS sample, the SAICAS is able to measure the adhesion properties uniformly as a function of depth from the surface of the coating layer. The adhesion strengths measured at the midlayer (Fmid) and interface (Finter, interlayer between the separator and the ceramic coating layer) are compared for various types of CCS samples with different amounts of polymeric binder, and it is found that Finter is higher than Fmid for all CCSs. Compared with Fmid, Finter is significantly affected by storage in the liquid electrolyte (under wet condition).

To improve the rate capability and safety of lithium-ion batteries (LIBs), we developed an integrated separator/electrode by gluing polyethylene (PE) separators and electrodes using a polymeric adhesive (poly(vinylidene fluoride), PVdF). To fabricate thin and uniform polymer coating layers on the substrate, we applied the polymer solution using a spray-coating technique. PVdF was chosen because of its superior mechanical properties and stable electrochemical properties within the voltage range of commercial LIBs. The integrated separator/electrode showed superior thermal stability compared to that of the control PE separators. Although PVdF coating layers partially blocked the porous structures of the PE separators, resulting in reduced ionic conductivity (control PE = 0.666 mS cm–1, PVdF-coated PE = 0.617 mS cm–1), improved interfacial properties between the separators and the electrodes were obtained due to the intimate contact, and the rate capabilities of the LIBs based on integrated separators/electrodes showed 176.6% improvement at the 7 C rate (LIBs based on PVdF-coated and control PE maintained 48.4 and 27.4% of the initial discharge capacity, respectively).

A new composite polymer electrolyte (CPE) containing a flame-retardant material, Mg(OH)2, is fabricated via a two-step process: porous poly(vinylidene-co-hexafluoropropylene) films composited with different Mg(OH)2 contents are first prepared via casting and extraction steps, and they are then impregnated with a liquid electrolyte. As the Mg(OH)2 content in the CPEs increases, their flame-retardant properties are greatly improved compared to those of the bare polymer electrolyte. Moreover, the better wettability of Mg(OH)2 toward a liquid electrolyte leads to higher ionic conductivities of CPEs, thereby resulting in a better rate capability in LiCoO2/graphite lithium-ion polymer batteries (LiPBs). However, the Mg(OH)2 content must be limited to less than 40 wt% to maintain the mechanical properties of the corresponding CPEs.

Carbon materials have enjoyed wide applications in supercapacitors because of their high surface area which guarantees a high power output through the formation of an electric double layer (EDL). However the energy stored by this EDL mechanism is often insufficient and as such there is the need to upgrade them for higher energy applications. Quinone materials are attracting interest because of their pseudocapacitance contributions which help to boost the energy density of supercapacitors. In this study, composite supercapacitor electrodes are prepared by mechanically mixing 2,3,5,6-tetrachloro-1,4-benzoquinone (TCBQ) and activated carbon. An investigation of 5% w/w and 10% w/w of this quinolic material as a pseudocapacitance material to activated carbon in 1 M HCl aqueous electrolyte delivers a specific capacitance of 236 F g−1 and 240 F g−1 comparable to 190 F g−1 of just activated carbon over a potential range of −0.3 V–0.9 V vs Ag+/Ag. Contrary to what is commonly observed, this material is highly insoluble in the electrolyte medium and remains stable with cycling, recovering 99.57% (for 10% w/w addition) and 99.13% (for 5% w/w addition) of its initial capacitance after cycling at 500 mV s−1 scan rate. The findings in this report potentially provides a cheaper yet efficient route to boost the energy density of activated carbon using TCBQ for high energy supercapacitor applications.

We introduce a novel approach for the high-value production of nano/micro hierarchical structured Sn anodes for lithium-ion batteries (LIBs) by utilizing microalgal biomass residues that collaterally form during oil extraction for biofuel production. The Sn/C composites made from the oil-extracted microalgal biomass residues (the extracted Sn/C) exhibit the following advantages as high-energy-density anodes: 1) a homogeneous distribution of Sn nanoparticles in the carbon matrix (Sn/C), which efficiently relieves the strain caused by volume changes of the active materials; 2) a high porosity of Sn/C composites; and 3) a homogeneous distribution of the hetero elements N and P in the carbon matrix. Overall, the extracted Sn/C exhibit improved electrochemical performance in LIBs compared with the Sn/C composites made from the microalgal biomass residues without oil extraction (non-extracted Sn/C). The extracted Sn/C have improved rate capabilities (160.0 and 72.9 mAh g−1 for the extracted Sn/C and the non-extracted Sn/C, respectively, at the 80th cycle, 3.5 A g−1) and improved cycle performances (511.7 and 493.2 mAh g−1 for the extracted Sn/C and the non-extracted Sn/C, respectively, at the 300th cycle, 200 mA g−1).

To overcome the limitation of simple empirical cycle life models based on only equivalent circuits, we attempt to couple a conventional empirical capacity loss model with Newman's porous composite electrode model, which contains both electrochemical reaction kinetics and material/charge balances. In addition, an electrolyte depletion function is newly introduced to simulate a sudden capacity drop at the end of cycling, which is frequently observed in real lithium-ion batteries (LIBs). When simulated electrochemical properties are compared with experimental data obtained with 20 Ah-level graphite/LiFePO4 LIB cells, our semi-empirical model is sufficiently accurate to predict a voltage profile having a low standard deviation of 0.0035 V, even at 5C. Additionally, our model can provide broad cycle life color maps under different c-rate and depth-of-discharge operating conditions. Thus, this semi-empirical model with an electrolyte depletion function will be a promising platform to predict long-term cycle lives of large-format LIB cells under various operating conditions.

Herein, we improved the performance of Si/graphite (Si/C) composite anodes by introducing a highly adhesive co-polyimide (P84) binder and investigated the relationship between their electrochemical and adhesion properties using the 90° peel test and a surface and interfacial cutting analysis system. Compared to those of conventional poly(vinylidene fluoride) (PVdF)-based electrodes, the cycling performance and rate capability of P84-based Si/C anodes were improved by 47.0% (372 vs 547 mAh g–1 after 100 cycles at a 60 mA g–1 discharge condition) and 33.4% (359 vs 479 mAh g–1 after 70 cycles at a 3.0 A g–1 discharge condition), respectively. Importantly, the P84-based electrodes exhibited less pronounced morphological changes and a smaller total cell resistance after cycling than the PVdF-based ones, also showing better interlayer adhesion (Fmid) and interfacial adhesion to Cu current collectors (Finter).

Lithium (Li) metal is one of the most promising candidates for the anode in high-energy-density batteries. However, Li dendrite growth induces a significant safety concerns in these batteries. Here, a multifunctional separator through coating a thin electronic conductive film on one side of the conventional polymer separator facing the Li anode is proposed for the purpose of Li dendrite suppression and cycling stability improvement. The ultrathin Cu film on one side of the polyethylene support serves as an additional conducting agent to facilitate electrochemical stripping/deposition of Li metal with less accumulation of electrically isolated or “dead” Li. Furthermore, its electrically conductive nature guides the backside plating of Li metal and modulates the Li deposition morphology via dendrite merging. In addition, metallic Cu film coating can also improve thermal stability of the separator and enhance the safety of the batteries. Due to its unique beneficial features, this separator enables stable cycling of Li metal anode with enhanced Coulombic efficiency during extended cycles in Li metal batteries and increases the lifetime of Li metal anode by preventing short-circuit failures even under extensive Li metal deposition.

To enhance the uniformity and adhesion properties of water-based ceramic coating layers on hydrophobic polyethylene (PE) separators, their surfaces were treated with thin and hydrophilic polydopamine layers. As a result, an aqueous ceramic coating slurry consisting of Al2O3 particles, carboxyl methyl cellulose (CMC) binders, and water solvent was easily spread on the separator surface, and a uniform ceramic layer was formed after solvent drying. Moreover, the ceramic coating layer showed greatly improved adhesion properties to the PE separator surface. Whereas the adhesion strength within the bulk coating layer (Fmid) ranged from 43 to 86 N m−1 depending on the binder content of 1.5–3.0 wt%, the adhesion strength at the interface between the ceramic coating layer and PE separator (Fsepa-Al2O3) was 245–360 N m−1, a value equivalent to an increase of four or five times. Furthermore, an additional ceramic coating layer of approximately 7 μm did not degrade the ionic conductivity and electrochemical properties of the bare PE separators. Thus, all the LiMn2O4/graphite cells with ceramic-coated separators delivered an improved cycle life and rate capability compared with those of the control cells with bare PE separators.

To improve the electrochemical properties of LiNi1/3Co1/3Mn1/3O2 (NCM) under the high-voltage operating condition of 4.5 V, 0.5 wt.% of alumina (Al2O3) was introduced as a ceramic filler during NCM cathode preparation. Uniformly dispersed Al2O3 over the entire area of the NCM cathodes efficiently stabilized the oxidative decomposition of the liquid electrolyte up to 5.3 V. This behavior hindered the formation of a thick surface film on the NCM cathodes after high-voltage operation (4.5 V). The Al2O3-containing NCM cathodes (NCM/Al2O3) revealed much smaller total cell resistance compared to the bare NCM cathodes, resulting in improved cycle performance and rate capabilities, which were identified as a facilitated Li+ diffusion in presence of the Al2O3 particles. NCM/Al2O3 showed a 29.4% improvement over the bare NCM (79.3 and 112.3 mAhh g−1 for bare NCM and NCM/Al2O3, respectively, after the 100th cycle) at 3C (4.3 V cutoff, C/2 for charging and 3C for discharging processes) and a 53.5% improvement (35.0 and 75.3 mAhh g−1 for NCM/Al2O3 and bare NCM, respectively) at 5C (4.5 V cutoff).

The commercialization of Li metal electrodes is a long-standing objective in the battery community. To accomplish this goal, the formation of Li dendrites and mossy Li deposition, which cause poor cycle performance and safety issues, must be resolved. In addition, it is necessary to develop wide and thin Li metal anodes to increase not only the energy density, but also the design freedom of large-scale Li-metal-based batteries. We solved both issues by developing a novel approach involving the application of calendared stabilized Li metal powder (LiMP) electrodes as anodes. In this study, we fabricated a 21.5 cm wide and 40 μm thick compressed LiMP electrode and investigated the correlation between the compression level and electrochemical performance. A high level of compression (40% compression) physically activated the LiMP surface to suppress the dendritic and mossy Li metal formation at high current densities. Furthermore, as a result of the LiMP self-healing because of electrochemical activation, the 40% compressed LiMP electrode exhibited an excellent cycle performance (reaching 90% of the initial discharge capacity after the 360th cycle), which was improved by more than a factor of 2 compared to that of a flat Li metal foil with the same thickness (90% of the initial discharge capacity after the 150th cycle).

Polymeric binder distribution within electrodes is crucial to guarantee the electrochemical performance of lithium-ion batteries (LIBs) for their long-term use in applications such as electric vehicles and energy-storage systems. However, due to limited analytical tools, such analyses have not been conducted so far. Herein, the adhesion properties of LIB electrodes at different depths are measured using a surface and interfacial cutting analysis system (SAICAS). Moreover, two LiCoO2 electrodes, dried at 130 and 2308C, are carefully prepared and used to obtain the adhesion properties at every 10 μm of depth as well as the interface between the electrode composite and the current collector. At high drying temperatures, more of the polymeric binder material and conductive agent appears adjacent to the electrode surface, resulting in different adhesion properties as a function of depth. When the electrochemical properties are evaluated at different temperatures, the LiCoO2 electrode dried at 1308C shows a much better high-temperature cycling performance than does the electrode dried at 2308C due to the uniform adhesion properties and the higher interfacial adhesion strength.

One possible way to increase the energy density of Li secondary batteries is to replace the commercialized carbonaceous anodes (such as graphite ones) with Li anodes due to their extremely high theoretical specific capacities, low densities, and lowest negative values of electrochemical potential. Despite these advantages of Li metal anodes, the uncontrolled deposition of dendritic, mossy, and granular Li particles decreases the Coulombic efficiency of Li batteries and causes various safety issues, which limits their scope of practical applications. To solve this problem, a surface-patterned Li metal anode covered with an alumina-based composite protection layer is developed in this work. Subsequently, the composite protection layer composition is optimized, and the electrochemical properties of the resulting micro-patterned Li metal anode are investigated. Due to the existence of a synergistic effect between the surface-patterned Li metal anode and the composite protection layer coating, the deposition of Li ions is effectively controlled, which prevents the formation of dendritic, granular, and moss-like Li particles after multiple deposition cycles even at relatively high current densities (up to 2.4 mA cm−2).

Uncontrolled lithium (Li) deposition has hampered the evolution of Li-metal electrode-based Li-batteries. In this work, we report the differences of a guided Li deposition with a size change of the square hole micro-patterns carved on the Li-metal surface with two different dimensions using a simple stamping method. Li deposition is preferentially initiated on the top edge for the smaller pattern and on the bottom for the larger pattern. Although the two patterns lead to a more uniform utilization of the Li, the larger pattern shows a higher cycling stability within a LiFePO4/Li cell than that of the smaller one indicating that initiating the Li deposition from the bottom of the hole is more efficient in confining the deposited Li. Based on the impedance analysis of the compressed Li electrodes, we suggest that the guided Li deposition on the bottom of the hole is attributed to a large contrast in the resistance of native surface passivation layer between the top and hole surfaces. This improved understanding can further advance guided Li deposition induced by surface patterns for high performance Li-metal batteries.

The capacity fading behavior of a LiMn2O4/graphite lithium ion cells at different temperatures is analyzed using a physics-based porous composite electrode model and a parameter estimation technique. The parameter estimation technique is used to extract capacity fade dependent model parameters from experimental cycling data. Although the capacity fading mechanism of the LiMn2O4/graphite lithium ion cells are greatly influenced by temperature, major capacity fading mechanism is closely related to the trapping of Li ions into solid electrolyte interphase on the graphite negative electrode and the reduction in the volume fraction of the active material in the LiMn2O4 positive electrode. At 25°C, the dominant capacity fading mechanisms is the formation of the solid electrolyte interphase while at 60°C the dominant capacity fading mechanism is the reduction in the volume fraction of the positive active material. The efficacy of the physics-based composite electrode model is validated with experimental discharge profiles obtained from cells cycled at 25 and 60°C.

A coupled chemo-mechanical model which considers the contact resistance as well as the influence of the attractive forces inside the contact area between the electrode and current collector was developed to evaluate the effects of the adhesive strength of a binding material on the electrochemical performance of silicon-based lithium-ion batteries. The increase in contact resistance between the electrode and current collector was introduced as a factor that reduces the electrochemical performance of the cell. The model predictions were validated with experimental data from coin-type half-cells composed of Li metal, Si electrodes, and Cu current collectors coated with binding materials with different adhesive strengths. The contact resistance increased with an increasing number of cyclic current rate. The adhesive strength decreased with cyclic current rate. The proposed model was used to investigate the effects of adhesive strength and various cell design parameters on the specific capacity of the Si-based Li-ion cells.

Two micro-patterns of different sizes (50 and 80 μm) are designed to have equivalent capacities of 1.06 and 2.44 mAh cm−2 by building a computational battery model. After preparing two stamps each possessing a micro-pattern design, the corresponding pattern is properly imprinted on the surface of 100 μm lithium metal, which is confirmed by scanning electron microscopy. When both micro-patterned lithium metals are electrochemically reduced and oxidized up to 1 mAh cm−2 in Li/Li symmetric cells at 1 or 2 mA cm−2, the 80 μm-patterned lithium shows a more stabilized lower overpotential during long-term cycling than the 50 μm-patterned and bare lithium, probably due to the lithium anchoring effect and a larger empty volume in the patterns. Additionally, an overflow of lithium deposits is easily observed in the 50 μm-patterned lithium metal, while the 80 μm-patterned lithium metal holds most of the lithium deposits within the patterns. When both micro-patterned lithium metals are assembled to full cells with a LiNi0·6Co0·2Mn0·2O2 cathode of 2 mAh cm−2, the 80 μm-patterned lithium metal shows much better electrochemical performances with stable plating/stripping behavior within the patterns.

An electrochromic (EC) device based on a thin and porous polymer membrane was newly fabricated for large-area applications such as smart windows. The pore structure of the poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) membrane was generated by extracting the pore generation material, dibutyl phthalate (DBP), from the cast film consisting of PVdF-HFP and DBP. The thickness of the porous polymer membrane was controlled to be very thin (approximately 30 μm), and the membrane was used to assemble WO3/W-NiO EC devices with 1 M LiClO4 in propylene carbonate as liquid electrolyte. Since the porous polymer membrane has a higher ionic conductivity than the non-porous one, the EC device with the porous polymer membrane showed a much higher current density in cyclic voltammetry even at a high scanning rate, faster color changing speed, and better stability after 500 cycles.

As the loading level or thickness of LIB composite electrodes increases, it becomes more difficult to uniformly distribute all components within the electrode. Because electric conductors are very small and light, they tend to rise upwards during drying process. Especially, to speed up the electrode fabrication process, not only drying temperature but also coating speed is maximized for reducing production costs. In this harsh condition, the polymeric binder tends to be unevenly distributed depending on the depth of electrode. Nevertheless, due to limited analysis tools, it had been left as research area to explore. Meanwhile, since a new tool, surface and interfacial cutting analysis system (SAICAS), was developed, the adhesion properties of the composite electrodes could be measured deliberately while changing the depth. Herein, we attempted to unveil the polymeric binder distribution by measuring the adhesion strength at different depths. In order to increase the reliability of the analytical results, composite electrode samples having different binder compositions and distributions were prepared and used for this study. At the same time, the compositional analysis with x-ray photoelectron spectroscopy were also conducted to confirm the binder distribution as a function of electrode depth. Finally, we investigated the effect of binder distribution on the electrochemical properties as well.

All-solid-state batteries (ASSBs) are promising secondary batteries which have been studied for high energy density and safety. However, ASSBs have not had excellent electrochemical performance owing to using solid electrolyte instead of liquid electrolyte. Two main reasons are very low ion conduction property due to complex pathway made with the solid electrolytes and the large decline of the contact area between active materials and the solid electrolytes. In spite of distinct faults were already recognized, there have hardly been the studies because of the difficulty of obtaining the value by using the experiment. In this study, we tried to gain the values from the simulation technics, which helped us draw the three-dimension electrode structure and check essential properties such as the contact area, tortuosity, and conductivity etc. with the variable electrochemical performance. In order to verify the appropriacy of our computational approach, the component ratio experiment that had been rudimentary for the electrode design was simulated under condition changing the ratio of natural graphite as the active material and LSTP (Li2O-SiO2-TiO2-P2O5) as the oxide-based solid electrolyte and then were compared and discussed with the data that anyone could confirm as the experiment.

Unexpected Li deposition during plating, which causes low Coulombic efficiency and safety issues, limits the use of Li metal as an anode in commercial secondary batteries. With the recently developed micro-patterned Li metal anodes, dendrite formation during high current Li plating (2.4 mA cm−2) has successfully been reduced, as Li ions are guided into the patterned holes. However, the uncontrolled formation of granular Li is still observed in this material. To overcome these shortcomings, we have introduced cesium hexafluorophosphate into micro-patterned Li metal anodes. This additive employs the self-healing electrostatic shield mechanism to effectively reduce the formation of granular Li and Li dendrites, thereby significantly improving the electrochemical performance of the anodes even when only small amounts (0.05 M) of electrolyte are used. Our experiments revealed that batteries employing surface-patterned Li metal anodes with cesium hexafluorophosphate maintained 88.7% (96.6 mAh g−1) of their initial discharge capacity after the 900th cycle (Charging current density: C/2, 0.6 mA cm−2, Discharging current density: 1C, 1.2 mA cm−2), which is three times higher than the capacity observed with surface-patterned Li metal anodes without the additive (discharge capacity starts to decrease from 300 cycles).

The development of safe and high-performance lithium (Li) metal anodes has been a challenging issue that has not been addressed for decades. In this study, we have developed a thermally stable polydopamine-treated three-dimensional (3D) carbon fiber-coated separator (P3D-CFS) using an economical and environment-friendly process. P3D-CFS has a conductive coating layer that is used as a 3D hosting structure, which does not cause morphological changes in the Li metal anode. As a result, the unit cells (LiMn/Li metal) employing P3D-CFS improve the cycle performance and rate capability compared to commercial polyethylene (PE) separators. P3D-CFS maintained 83.1% of the initial discharge capacity at the 400th cycle, whereas bare PE maintains only 74.3% of the initial discharge capacity after the 250th cycle (C/2 = 0.5 mA cm/graphite) that employed P3D-CFS is maintained for over 60 min at 140 °C, whereas the unit cells that employed bare PE show a sudden voltage drop after only 3 min.

The use of surface-patterned lithium (Li) metal has been proposed as a promising strategy for inhibiting the formation of Li dendrites during repeated Li plating/stripping processes. Nevertheless, the conventional Li metal patterning process is complex, expensive, incompatible with mass production, and incapable of producing finely controlled patterns on the Li metal surface. A large, flexible patterning stamp capable of large-area patterns is developed using a silicon (Si) wafer-based chemical etching process, and its effect on the electrochemical performance of a Li metal anode is investigated. The newly developed stamps have 5,000% larger patterning area compared to the conventional stainless-steel stamps. Furthermore, when compared to conventional surface-patterned Li metal fabricated with conventional stainless-steel stamps (SP-LM), the surface-patterned Li metal fabricated with large and flexible patterning stamps (LAP-LM) demonstrates improved electrochemical performance and stable morphological properties. As a result, the LAP-LM is able to retain up to 85.2% of its initial discharge capacity (85.9 mAh g−1) after 200 cycles at 3C (3.96 mA cm−2), while the SP-LM shows a severe capacity decay after 150 cycles (94.0 mAh g−1 and 13.0 mAh g−1 at the 150th cycle and 200th cycle, respectively).

Due to the high theoretical energy density and lowest negative potential, Li metal is being revalued as a candidate for large-scale battery systems, such as electric vehicles (EVs) and energy storage systems (ESSs). Nevertheless, the Li metal suffer from several issues that the formation of dendrite and continuous side reactions during repeated cycling. In our previous contribution, we tackled this problem by using Li powder (LMP), because the simple manufacturing using slurry coating, flexible cell design, reduced exchanged current density. However, the LMP-based electrode also has severe morphological drawback, which induced the imperfect Li2CO3 passivation layer. During the long-term cycling, the spherical shape can be completely lost due to extensive Li loss at individual LMPs, leading to a failure of the conformal Li distribution. Herein, we report a pre-planted nitrate LMP composite electrode (LN-LMP). The LiNO3 additives play important roles not only allowed chemically induced homogeneous nitration on surfaces but also released toward electrolytes as additives. Therefore, due to the significant features of the LN‐LMP composite design, LMBs with 20 µm‐thick LN‐LMP composite anodes demonstrated excellent cycling performances compared to cells with conventional LMPs and LiNO3‐containing electrolytes. Furthermore, we further verified that the LN‐LMP electrode with compatible electrolytes consistently exhibits better performances under practical cell design conditions.

Today, lithium secondary batteries are heavily involved in our daily life. The electric vehicle market is gradually expanding, and the demands for electric vehicles with increased driving mileage are also increasing. To meet the requirements of long-mileage electric vehicles, a battery with a large energy density must be adopted. Considering this, metallic Li, which has a high theoretical capacity and lowest potential, is the most promising anode material. Nevertheless, Li metal anodes have several problems, such as the formation of dendritic Li and deterioration of Li metal battery capacity in repeated cycles. Internal short circuit and explosion of the battery can occur by dendritic Li resulting from non-uniform deposition on the Li metal electrode. Therefore, recent research has been conducted regarding the effective methods to control the electrodeposition behavior of Li. Lithium metal powder (LiMP) with a large surface area effectively suppresses dendritic growth. Here, we try to maximize the performance of LiMP electrodes by adding AgNO3. Ag forms uniform electrodeposition of Li by setting nucleation sites across the broad LiMP electrode surface. Also, an excellent Li-ion conductor, Li3N particles are formed by Li metal and AgNO3 reactions. When dendritic Li is formed and comes into contact with Li3N, it controls the growth direction of the dendrite. To confirm the effect of AgNO3 on the performance of the electrodes, the symmetric cell test, impedance test, SEM (Scanning Electron Microscopy), and XPS (X-ray Photoelectron Spectroscopy) were implemented. In the case of the electrode with AgNO3, we confirm that dendritic Li growth was relatively suppressed, and the overpotential also decreased in the Li/Li symmetry cell test.

Li metal thickness has been considered a key factor in determining the electrochemical performance of Li metal anodes. The use of thin Li metal anodes is a prerequisite for increasing the energy density of Li secondary batteries intended for emerging large-scale electrical applications, such as electric vehicles and energy storage systems. To utilize thin (20 μm thick) Li metal anodes in Li metal secondary batteries, we investigated the synergistic effect of a functional additive (Li nitrate, LiNO3) and a dual-salt electrolyte (DSE) system composed of Li bis(fluorosulfonyl)imide (LiTFSI) and Li bis(oxalate)borate (LiBOB). By controlling the amount of LiNO3 in DSE, we found that DSE containing 0.05 M LiNO3 (DSE–0.05 M LiNO3) significantly improved the electrochemical performance of Li metal anodes. DSE–0.05 M LiNO3 increased the cycling performance by 146.3% [under the conditions of a 1C rate (2.0 mA cm–2), DSE alone maintained 80% of the initial discharge capacity up to the 205th cycle, whereas DSE–0.05 M LiNO3 maintained 80% up to the 300th cycle] and increased the rate capability by 128.2% compared with DSE alone [the rate capability of DSE–0.05 M LiNO3 = 50.4 mAh g–1, and DSE = 39.3 mAh g–1 under 7C rate conditions (14.0 mA cm–2)]. After analyzing the Li metal surface using scanning electron microscopy and X-ray photoelectron spectroscopy, we were able to infer that the stabilized solid electrolyte interphase layer formed by the combination of LiNO3 and the dual salt resulted in a uniform Li deposition during repeated Li plating/stripping processes.

Making Li metal batteries (LMBs) with thinner Li is necessary to improve the cell energy density in practice. Li metal powders (LMPs) are beneficial for the facile manufacturing of thin Li, flexible cell design, and the 3D control of Li plating/stripping. However, the inhomogeneous surfaces of commercial LMPs limit their practical use in LMBs. Herein, a 20 µm-thick, LiNO3 preplanted LMP (LN-LMP) composite electrode, rationally designed for LMP surface stabilization, is presented. The addition of LiNO3 into the slurry uniformly modified the LMP surface by N-rich solid-electrolyte interphase (SEI). Preplanted LiNO3 further acts as a reservoir for the sustainable release into the electrolyte, thereby repairing the SEI upon cycling. The LMBs with LN-LMP exhibited excellent cycling performances (450 cycles at 87.3% retention) compared to the control cells, and even outperformed the cells with LiNO3-containing electrolytes. Further verification with high loading of a LiNixMnyCo1–x–yO2 (NMC) cathode demonstrated the feasibility of the practical cells and the versatility of the thin, LN-LMP anode combined with advanced electrolytes.

Lithium ion conducting polymer electrolytes with broad electrochemical stability, good mechanical strength, high thermal stability, and easy processability are necessary for all-solid-state and shape-variant lithium secondary batteries. Hybrid gel polymer electrolytes incorporating an ionic liquid have been attracting attention for application in solid-state lithium secondary batteries owing to their superior thermal properties compared to conventional electrolyte systems. In this study, a variety of polymer electrolytes based on poly(vinylidene fluoride-co-hexafluompropylene) (PVdF-HFP), lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PMPyrrTFSI) are prepared, and an in-depth study of their composition dependence and electrical properties is conducted to develop the optimum composition. The composition dependent ionic conductivity of the polymer electrolyte increases with increasing LiTFSI and PMPyrrTFSI and reaches a maximum value of 6.93 x 10(-4) S cm(-1) at mom temperature (25 degrees C) when the polymer electrolyte contains 30 wt% LiTFSI and 60 wt% PMPyrrTFSI. In addition, the optimized gel polymer electrolytes consisting of PVdF-HFP/LiTFSI/PMPyrrTFSI (70/30/60 by weight, i.e., 70PVdF-HFP/30LiTFSI/60PMPyrrTFSI) look transparent and exhibit high mechanical stability and excellent thermal stability up to 420 degrees C. Finally, the lithium iron phosphate (LiFePO4)/lithium metal solid-state cells coupled with the optimized gel polymer electrolyte are prepared, and their discharge characteristics are studied. The 70PVdF-HFP/30LiTFSI/60PMPyrrTFSI based solid-state cell delivered a maximum discharge capacity of 151 mAh g(-1) at room temperature with a good rate capability and cycling performance.

Inorganic polyhedral oligomeric silsesquioxane with epoxy functional groups (ePOSS) is newly presented as a co-binder for the ceramic-coated separator (CCS) for safe Li-ion batteries. The ePOSS-incorporated coating layer significantly improved the dimensional stability of the CCS at 140 degrees C and maintained the original form even after an ignition test. Although the permeability of the CCS was slightly decreased due to the crosslinked structure of the silsesquioxane coating layer, it showed high electrochemical stability up to 5 V. Moreover, the improved liquid electrolyte wettability by ePOSS co-binder enhanced the ionic conductivity and showed 93% of cycle capacity at 0.5C rate in Li-ion batteries. (C) 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Thermostable polymers offer excellent thermal and mechanical stabilities, and in this study, an organosoluble polyimide (PI) was employed to fabricate high-performance separators for use in advanced lithium-ion batteries (LIBs). The organosoluble PI was synthesized and its nanofibrous membrane was fabricated via electrospinning. A subsequent heat treatment induced thermal crosslinking between the PI nanofibers to improve the heat resistance of the separators. PI nanofibrous membrane exhibited excellent wettability toward the liquid electrolyte, resulting in a greatly improved rate capability and cycle life. These results suggest that organosoluble PI nanofibrous membranes have a high potential for use as separators in high-performance LIBs. (C) 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

The key challenge in all-solid-state batteries is to construct well-developed ionic and electric conductive channels within an all-solid-state electrode, with an extensive contact area between electrode components. Hence, a new design methodology is proposed for all-solid-state electrodes utilizing a 3D geometry interpretation tool and electrochemical simulator. Firstly, the 3D structures of all-solid-state electrodes are generated using the voxel array formation. Secondly, with these structures, not only physical properties such as the specific contact area of the active materials, but also conductivity values can be identified. Subsequently, the main parameters derived from the 3D structures are utilized to build an electrochemical model to predict the cell performance. This three-step process will provide key insights on how 3D structures of all-solid-state electrodes must be constructed by predicting their preliminary physical and electrochemical properties with the help of computational simulations.

Lithium-sulfur (Li-S) batteries are expected to be very useful for next-generation transportation and grid storage because of their high energy density and low cost. However, their low active material utilization and poor cycle life limit their practical application. The use of a carbon-coated separator in these batteries serves to inhibit the migration of the lithium polysulfide intermediate and increases the recyclability. We report the extent to which the electrochemical performance of Li-S battery systems depends on the characteristics of the carbon coating of the separator. Carbon-coated separators containing different ratios of carbon black (Super-P) and vapor-grown carbon fibers (VGCFs) were prepared and evaluated in Li-S batteries. The results showed that larger amounts of Super-P on the carbon-coated separator enhanced the electrochemical performance of Li-S batteries; for instance, the pure Super-P coating exhibited the highest discharge capacity (602.1 mAh g(-1) at 150 cycles) with a Coulombic efficiency exceeding 95%. Furthermore, the separators with the pure Super-P coating had a smaller pore structure, and hence, limited polysulfide migration, compared to separators containing Super-P/VGCF mixtures. These results indicate that it is necessary to control the porosity of the porous membrane to control the movement of the lithium polysulfide.

We developed a 3D electrochemical model for simulating the electrochemical properties and revealing the internal properties of a single LiFePO4 secondary particle during cycling. The main model parameters, such as the diffusion coefficient and rate constant, were optimized using rate capability data, which have been measured experimentally with a unique single particle measurement technique. We simulated voltage profiles at different c-rates from 2 to 20C, which were approximately equivalent to the experimental voltage profiles. The model estimated real-time overpotential, lithium ion concentration, and state-of-charge within the single particle, which have not been obtained experimentally, while changing design parameters and operating conditions. We validated the reliability and applicability of the model by comparing and analyzing the electrochemical results of various LiFePO4 secondary particles with variable design parameters (i.e., solid volume fraction, secondary particle size, and primary particle size).

We used a cesium hexafluorophosphate (CsPF6)-containing liquid electrolyte for surface-patterned Li metal anodes and confirmed that there is a synergistic improvement in the electrochemical performance such as cycle performance and rate capability. For instance, the surface-patterned Li metal maintains 91.4% of the initial discharge capacity after the 1000th cycle (C/2 = 0.8 mA cm(-2) for charging, 1C for discharging). When a large quantity of the CsPF6-containing liquid electrolyte (600 mu L) is used, the bare Li metal and surface-patterned Li metal are more effectively stabilized in comparison with the case where 80 mu L of electrolyte is used, resulting in improved electrochemical performance. Through systematic testing, we recognize that these results are because of the self-healing electrostatic shield mechanism, which is mainly dependent on the amount of Cs+ ions. A small amount of Cs+ ions cannot effectively counteract the incoming Li+ ions because they cannot form an effective electrostatic shield on the protrusions present on the Li metal surface.

We present a synergistic strategy to boost the cycling performance of Li-metal batteries. The strategy is based on the combined use of a micropattern (MP) on the surface of the Limetal electrode and an advanced dual-salt electrolyte (DSE) system to more efficiently control undesired Li-metal deposition at higher current density (similar to 3 mA cm(-2)). The MP-Li electrode induces a spatially uniform current distribution to achieve dendrite-free Li-metal deposition beneath the surface layer formed by the DSE. The MP-Li/DSE combination exhibited excellent synergistic rate capability improvements that were neither observed with the MP-Li system nor for the bare Li/DSE system. The combination also resulted in the LillLiMn(2)O(4) battery attaining over 1000 cycles, which is twice as long at the same capacity retention (80%) compared with the control cells (MP-Li without DSE). We further demonstrated extremely fast charging at a rate of 15 C (19.5 mA cm(-2)).

Li metal experiences significant morphological changes during operation, resulting in rapid electrochemical performance degradation. In this study, a traditional balloon trick is applied to the Li metal surface to release mechanical stress and hinder morphological changes during operation. Polymer separators directly attach to the Li metal surface using a polymeric adhesive to fabricate a separator/Li metal integrated assembly. The separator/Li metal assembly improves not only the electrochemical performance but also safety issues related to Li metal anodes. This approach has three main advantages: (i) Li metal surface stabilization. The separator/Li metal assembly mechanically stabilize the Li metal surface, resulting in improved rate capability and cycle performance [85.0% of initial discharge capacity (90.2 mAh g(-1)) at a 7C condition for rate capability and 87.6% of discharge capacity (95.5 mAh g(-1)) at the 220th cycle] compared with the bare Li metal without separator integration [82.6% of initial discharge capacity (84.5 mAh g(-1)) at a 3C condition for rate capability and 58.0% of discharge capacity (62.6 mAh g(-1)) at the 120th cycle]. (ii) Suitability for high energy density battery implementation. The thickness of the polymeric adhesive is less than 1 mu m, which is one-tenth of the coating layer of conventional thermally stable separators, but exhibits similar thermal shrinkage characteristics (0% shrinkage at 140 degrees C for 30 min). By reducing the thickness of inactive components, a larger volume of active material can be loaded into the battery system to increase the energy density of the battery. (iii) Simple process for mass production. The separator/Li metal integration process ("stick" and "dry") is very simple and can be easily applicable across industries.

Metallic sodium is regarded as a promising anode material for sodium rechargeable batteries. However, sodium dendrite growth and exhaustive electrolyte decomposition cause the poor reversibility of the sodium metal electrode. Here, we present that, by forming a mixed surface of carbon and sodium metal, the sodium electrodeposition mode and stripping mechanism can be tuned. In order to systematically investigate sodium plating/stripping behavior on a mixed surface of carbon and sodium, we fabricate a carbon nanotube-sodium composite electrode with a simple rolling and folding method. As the carbon nanotube content is increased, the overpotentials for sodium nucleation and pit-formation are remarkably reduced. Postmortem and chronoamperometry analysis elucidate that sodium and sodiated carbon nanotube have a different sodium nucleation mode, and sodium nucleation is preferred on the sodiated carbon nanotube surface with lower nucleation energy, inducing a more uniform sodium deposition. Furthermore, the embedded carbon nanotube appears to help sodium stripping by providing a channel for a more facile sodium ion transport. As a result, the carbon nanotube-sodium composite electrode exhibites a 5 times higher cycling stability. The tuning of the nucleation and stripping behaviors by forming a mixed surface can be a viable approach for enhancing the reversibility of metal electrode.

We propose a time-effective framework for accelerated cyclic aging analysis of lithium-ion batteries. The proposed framework involves the coupling of a physico-chemical capacity-fade model that considers the cyclic aging mechanisms of the LiMn2O4/graphite cell, with a physics-based porous-composite electrode model to predict cycling performance at different temperatures. A one-dimensional simple empirical life model is then developed from the coupled physico-chemical capacity-fade model and the physics-based porous-composite electrode model predictions. An accelerated cyclic aging analysis based on the principle of time-temperature superposition is performed using the developed one-dimensional simple life empirical model. The proposed framework is used to predict the maximum number of cycles and the highest temperature required for accelerated cyclic aging analysis of LiMn2O4/graphite cells. The efficacy of the proposed framework is validated with experimental cycle-performance data obtained from LiMn2O4/graphite coin cells at 25 and 60 degrees C.

In this study, we present nanodomes-combined surface relief gratings (SRGs) of azopolymer films with controlled shapes and sizes. We investigate the effect of the polarization mode of light interference on leading nanodomes in the conventional SRG patterns. In addition, we also systematically study the relationship between Bragg distance of light interference and shapes of nanodomes. From this, we explain the anisotropic self-assembled behavior nanodomes in photoaddressable azopolymer films regarding polarization modes as well as spatial confinement effect. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 731-737

To understand the effect of a polydopamine interlayer between a copper current collector and a silicon composite electrode, a physics-based model is used to analyze the cycle performance of silicon-based lithium-ion half-cells with bare and polydopamine-treated copper current collectors. We investigate the capacity-fading mechanisms of the two cell configurations by analyzing the model parameters that change with cycling. The major capacity-fading mechanisms in the silicon-based anodes are the increase in film resistance (solid electrolyte interphase resistance and contact resistance) and the isolation of silicon active material. The polydopamine interlayer reduced the contribution of the film resistance and isolation of the silicon active material to the capacity fade by 22 % and 10 %, respectively. The insulating-nature of the polydopamine interlayer resulted in an increase in the charge transfer resistance contributing to 15 % reduction in the capacity retention. The efficacy of the physics-based model is validated with experimental data obtained from silicon-based half-cells with bare and polydopamine-treated copper current collectors.

All-solid-state lithium secondary batteries have never shown both higher energy and power density than them of conventional lithium-ion batteries. Herein, on the basic of well-established percolation theory, we expected what includes a dimension-controlled solid electrolyte in an electrode can improve the electrochemical properties, such as ionic conduction and capacity retention. The behavior of electrodes is systematically demonstrated via computational simulations of virtual electrodes with various dimension-controlled solid electrolytes. In particular, the effective ionic conductivity and the specific contact area are investigated as key parameters that determine cell performance. We confirmed that the dimension-controlled solid electrolyte can improve the electrochemical performance of all-solid-state batteries by enhancing the effective ionic conductivity, which is facilely realized via percolation of the solid electrolyte with an increased dimensional geometry. This simulation prediction suggests a clue to be able to overcome poor performance of present all-solid-state batteries.

Li dendrite formation deteriorates cyclability and poses a safety hazard, hindering the widespread use of Li metal as the ultimate anode material for post-Li-ion batteries. Hence, the underlying reasons of this phenomenon and ways to suppress it have been extensively investigated, which has resulted in the establishment of corresponding theoretical models and their practical applications. Herein, several representative models (e.g., the Chazalviel model) of Li dendrite growth are explained, and the key technologies of structure-controlled framework and Li metal usage allowing to realize low local current densities and improved electrochemical performance are covered with the practical (dis)advantages due to material characteristics, electrode and cell design, and even manufacturing processes. In particular, the use of Li metal powder and patterned Li metal is discussed in conjunction with corresponding applications (e.g., protection layers, functional additives, and salts in the electrolyte) and advantages.

Short cycle life of the lithium metal secondary battery (LMSB) is largely ascribed to the dendritic growth of lithium metal during the charging process followed by continuous electrolyte decomposition. To make up for this intrinsic drawback of lithium metal, two pioneering techniques, micropatterning on lithium metal and three dimensionally ordered microporous polyimide (3DOM PI) separator, are combined to ascertain their hybrid effect on the cycle performance of LMSB. When a unit cell consisting of LiNi0.6Mn0.2Co0.2O2/3DOM PI separator/patterned lithium metal is cycled at the charging and discharging c-rates of 0.3C and 1C (1C = 2.5 mA), respectively, above 80% of the initial discharge capacity is maintained even after 400 cycles, while a control cell with polyethylene separator survives only for 130 cycles. This tremendous improvement is ascribed to the combination effect of inducing preferential lithium electrodeposition reaction into the micropattern and the uniform distribution of lithium ions on the nonpatterned lithium surface region by the 3DOM PI separator. Thus, combining these two technologies is very promising for LMSB commercialization in the future.

Power measurement has become as important as capacity to ensure stable operating conditions for batteries at different temperatures, states of charge (SOCs), and states of health (SOHs). Unlike capacity, the power of a lithium-ion battery (LIB) is quite sensitive to temperature. However, there have been few systematic works on the measurement of power at different temperatures with various LIB types. Herein, the power of two types of LIB (cylindrical and pouch), which are normally used in traction applications, are measured at different temperatures (15, 25 and 35 degrees C) using the hybrid pulse power characterization (HPPC) method. When LIB reaches to each thermal equilibrium, the battery is discharged and charged for 10 s at a specific SOC by applying constant current. And then, power value could be obtained through calculating some simple equations. In normal operating conditions, capacity change little (similar to 0.47% per degrees C) regardless of temperature change, but power increase by about 3% per degrees C. Considering that each cell type has a totally different cell configuration, the similarity of this trend between LIB types is quite noticeable. Consequently, when measuring the power of LIB, the temperature must be controlled precisely, or at least calibrated if temperature differences are observed.

Effects of soluble polyimide (PI) binders on large-sized Li anodes (width =21.5 cm; thickness =40 mu m) prepared using Li-metal powder (LiMP) have been investigated. PI binders form a uniform protective layer on exposed Li-powder-coated surfaces, thereby resulting in formation of scaffold-structured LiMP-based anodes. Uniform PI surface films favor realization of Li plating on Li-metal surfaces by forming a smooth surface structure, and the three-dimensional insulating PI matrix functions as a buffer layer that absorbs volume change. Moreover, PI binders facilitate enhanced cohesion between LiMP particles. The above described triple action of PI binders significantly reduces Li dendrites. Consequently, PI-containing LiMPbased metal anodes demonstrate enhanced electrochemical performance compared to both polymeric binders and bare Li-metal foils. Results obtained in this study reveal that LiMP-based anodes containing PI binders exhibit 89% (98.2 mAh g(-)1) discharge-capacity retention during the 200th cycle, whereas bare Li-metal foil demonstrates sudden degeneration during the 65th cycle. Furthermore, PI containing LiMP-based anodes exhibit improved rate capability compared to other polymeric binders considered in this study. (C) 2020 Elsevier Ltd. All rights reserved.

To inhibit Li-dendrite growth on lithium (Li)-metal electrodes, which causes capacity deterioration and safety issues in Li-ion batteries, we prepared a porous polyimide (PI) sponge using a solution-processable high internal-phase emulsion technique with a water-soluble PI precursor solution; the process is not only simple but also environmentally friendly. The prepared PI sponge was processed into porous PI separators and used for Li-metal electrodes. The physical properties (e.g., thermal stability, liquid electrolyte uptake, and ionic conductivity) of the porous PI separators and their effect on the Li-metal anodes (e.g., self-discharge and open-circuit voltage properties after storage, cycle performance, rate capability, and morphological changes) were investigated. Owing to the thermally stable properties of the PI polymer, the porous PI separators demonstrated no dimensional changes up to 180 degrees C. In comparison with commercialized polyethylene (PE) separators, the porous PI separators exhibited improved wetting ability for liquid electrolytes; thus, the latter improved not only the physical properties (e.g., improved the electrolyte uptake and ionic conductivity) but also the electrochemical properties of Li-metal electrodes (e.g., maintained stable self-discharge capacity and open-circuit voltage features after storage and improved the cycle performance and rate capability) in comparison with PE separators.

A method of microalgae-templated spray drying to develop hierarchical porous Fe3O4/C composite microspheres as anode materials for Li-ion batteries was developed. During the spray-drying process, individual microalgae serve as building blocks of raspberry-like hollow microspheres via self-assembly. In the present study, microalgae-derived carbon matrices, naturally doped heteroatoms, and hierarchical porous structural features synergistically contributed to the high electrochemical performance of the Fe3O4/C composite microspheres, enabling a discharge capacity of 1375 mA.h.g(-1) after 700 cycles at a current density of 1 A/g. Notably, the microalgal frameworks of the Fe3O4/C composite microspheres were maintained over the course of charge/discharge cycling, thus demonstrating the structural stability of the composite microspheres against pulverization. In contrast, the sample fabricated without microalgal templating showed significant capacity drops (up to similar to 40% of initial capacity) during the early cycles. Clearly, templating of microalgae endows anode materials with superior cycling stability.

The mechanical robustness of highly loaded composite electrodes is important for ensuring the long-term reliability of high-energy-density secondary batteries. Considering that in real state, the electrodes in batteries are completely impregnated with electrolyte, the swelling of the polymeric binder must be carefully observed and controlled to maintain the electric connectivity within the electrode. However, the decrease in the cohesion/adhesion of electrodes caused by electrolyte impregnation has not been directly measured due to the absence of appropriate tools. Here, the surface and interfacial cutting analysis system and a specifically designed sample holder are well combined to realize this breakthrough measurement. When electrode is impregnated with a liquid electrolyte, not only the 12% increase in electrode thickness but also the greater than 74% decrease in cohesion/adhesion, which is caused by the swelling of the amorphous phase of the polymeric binders, is clearly observed. The large decrease in cohesion/adhesion can be greatly ameliorated by controlling both the degree of crystallinity and crystallite size of the polymeric binder through a simple annealing process. Thus, it believes that the measurement of the real cohesion and adhesion of composite electrodes can provide an innovative and practical way to secure the reliability of high-energy-density batteries. (C) 2020 Elsevier Ltd. All rights reserved.

To investigate the correlation between the molecular weight of the polymeric binder in Li-ion battery electrodes and their adhesion properties, polyvinylidene fluoride (PVdF) with three different molecular weights of 500,000, 630,000, and 1,000,000 are selected for LiCoO2 electrode fabrication. Using a surface and interfacial cutting analysis system, it is observed that, as the molecular weight of the PVdF increases, the adhesion strength not only in the electrode composite, but also at the electrode/current collector interface increases. This enhancement can be attributed to the increased polymeric chain entanglement and higher crystallinity of PVdF with higher molecular weight, which is confirmed using a microfluidic viscometer and differential scanning calorimeter, respectively. In summary, regardless of slightly higher electrode resistance, the LiCoO2 electrode with a PVdF binder of high molecular weight shows better electrochemical performance during cycling test even at 60 degrees C due to its stable mechanical integrity. (C) 2019 Elsevier Ltd. All rights reserved.

To enhance delamination limitations in silicon electrode, a thin-film interlayer between silicon electrode and copper current collector is designed using a chemo-mechanical degradation model. The chemo-mechanical degradation model considers the formation of the solid electrolyte interphase on the surface and within the cracks of the silicon electrode, the physical isolation of active materials and the resistance due to loss of contact between the silicon composite electrode and the copper foil as the main capacity fading mechanisms. The model is validated with experimental data collected from coin cells made of silicon electrode with a bare and an adhesive thin film laminated copper foil. The reduction in the delamination limitations depends on the interplay of the adhesion strength, conductivity, coverage and thickness of adhesive thin film on the surface of the copper foil. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

The surface area of the lithium metal electrode must be considered when attempting to suppress dendritic growth of lithium metal, as surface area can lower the effective current density. For this reason, lithium metal powder (LiMP) has attracted much attention for use in electrodes because of its higher surface area. However, repeated cycling, even in aging time, leads to delamination of lithium particles from flat metal current collectors and results excess dead lithium particles, even in LiMP electrodes. Herein, this problem is addressed by coating submicron-thickness carbon interlayers on copper current collectors for LiMP electrodes. This thin carbon layer plays important roles in both maintaining the interfacial contact between Cu foil and LiMP particles and lowering overpotential in Li/Li symmetric cells, which leads to improve electrochemical performance in thin LiMP (40 mu m) based cell. These enhancements are related to the enlarged surface area, as confirmed by higher adhesion of the electrode after precycling. Furthermore, the carbon materials are also believed to contribute to seeding for efficient lithium nucleation. Thus, thin carbon layers on current collectors can provide simple but powerful enhancements to the electrochemical performance of high-energy-density LMSBs.

리튬 이차전지의 4 대 구성요소에 포함되는 양극은 배터리의 에너지 밀도를 담당하는 중요한 구성요소에 속하며, 보편적으로 제작되는 양극의 습식 제작 공정에는 활물질, 도전재, 고분자 바인더의 혼합 과정이 필수적으로 이루어지게 된다. 하지만, 양극의 혼합 조건의 경우 체계적인 방법이 갖추어져 있지 않기 때문에 제조사에 따라 성능의 차이가 발생하는 경우가 대다수이다. 따라서, 양극의 슬러리 제작 단계에서 정돈되지 않은 혼합 방법의 최적화를 진행을 위해 보편적으로사용되는 THINKY mixer와 homogenizer를 이용한 LiMn2O4 (LMO) 양극을 제조해 각각의 특성을 비교하였다. 각 혼합 조건은 2000 RPM, 7 min으로 동일하게 진행하였으며, 양극의 제조 동안 혼합 방법의 차이 만을 판단하기 위해 다른 변수 조건들은 차단한 후, 실험을 진행하였다(혼합 시간, 재료 투입 순서 등). 제작된 THINKY mixer LMO (TLMO), homogenizer LMO (HLMO) 중 HLMO는 TLMO보다 더 고른 입자 분산 특성을 가지며, 그로 인한 더 높은 접착 강도를 나타낸다. 또한, 전기화학적 평가 결과, HLMO는 TLMO와 비교하여 개선된 성능과 안정적인 수명 주기를 보였다. 결과적으로 수명특성평가에서 초기 방전 용량 유지율은 HLMO가 69 사이클에서 TLMO와 비교하여 약 4.4 배 높은 88%의 유지율을 보였으며, 속도성능평가의 경우 10, 15, 20 C의 높은 전류밀도에서 HLMO가 더 우수한 용량 유지율과 1C에서의용량 회복률 역시 우수한 특성을 나타냈다. 이는 활물질과 도전재 및 고분자 바인더가 포함된 슬러리 특성이 homogenizer를 사용할 때, 정전기적 특성이 강한 도전재가 뭉치지 않고 균일하게 분산되어 형성된 전기 전도성 네트워크를 생성할 수 있기 때문으로 간주된다. 이로 인해 활물질과 도전재의 표면 접촉이 증가하고, 전자를 보다 원활하게 전달하여 충전 및 방전 과정에서 나타나는 격자의 부피변화, 활물질과 도전재 사이의 접촉저항의 증가 등을 억제하는 것에 기인한다.

The microblade cutting method, so-called SAICAS, is widely used to quantify the adhesion of battery composite electrodes at different depths. However, as the electrode thickness or loading increases, the reliability of adhesion values measured by the conventional method is being called into question more frequently. Thus, herein, a few underestimated parameters, such as friction, deformation energy, side-area effect, and actual peeing area, are carefully revisited with ultrathick composite electrodes of 135 ㎛ (6 mAh cm-2). Among them, the existence of side areas and the change in actual peeling area are found to have a significant influence on measured horizontal forces. Thus, especially for ultrahigh electrodes, we can devise a new SAICAS measurement standard: 1) the side-area should be precut and 2) the same actual peeling area must be secured for obtaining reliable adhesion at different depths. This guideline will practically help design more robust composite electrodes for high-energy-density batteries.

Various steps in the electrode production process, such as slurry mixing, slurry coating, drying, and calendaring, directly affect the quality and, consequently, mechanical properties and electrochemical performance of electrodes. Herein, a new method of slurry coating is developed: Double-coated electrode. Contrary to single-coated electrode, the cathode is prepared by double coating, wherein each coat is of half the total loading mass of the single-coated electrode. Each coat is dried and calendared. It is found that the double-coated electrode possesses more uniform pore distribution and higher electrode density and allows lesser extent of particle segregation than the singlecoated electrode. Consequently, the double-coated electrode exhibits higher adhesion strength (74.7 N m−1) than the single-coated electrode (57.8 N m−1). Moreover, the double-coated electrode exhibits lower electric resistance (0.152 Ω cm−2) than the single-coated electrode (0.177 Ω cm−2). Compared to the single-coated electrode, the double-coated electrode displays higher electrochemical performance by exhibiting better rate capability, especially at higher C rates, and higher long-term cycling performance. Despite its simplicity, the proposed method allows effective electrode preparation by facilitating high electrochemical performance and is applicable for the large-scale production of high-energy-density electrodes.

A polymer electrolyte was prepared by using polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) or poly(ethylene glycol) dimethacrylate (PEGDMA) as polymer matrices, succinonitrile as an additive, and lithium perchlorate as a lithium salt. Compared to the polymer electrolyte employing PVdF-HFP, the PEGDMA-based polymer electrolyte exhibits substantially superior thermal stability when exposed to high temperatures. Nonetheless, the ionic conductivity of the PEGDMA-based polymer electrolyte was preserved in a wide temperature range between −20∘C and 80∘C.

The consequences of electrode density and thickness for electrochemical performance of lithium-ion cells are investigated using 2032-type coin half cells. While the cathode composition is maintained by 90:5:5 (wt.%) with LiCoO2 active material, Super-P electric conductor and polyvinylidene fluoride polymeric binder, its density and thickness are independently controlled to 20, 35, 50 um and 1.5, 2.0, 2.5, 3.0, 3.5 g cm−3, respectively, which are based on commercial lithium-ion battery cathode system. As the cathode thickness is increased in all densities, the rate capability and cycle life of lithium-ion cells become significantly worse. On the other hand, even though the cathode density shows similar behavior, its effect is not as high as the thickness in our experimental range. This trend is also investigated by cross-sectional morphology, porosity and electric conductivity of cathodes with different densities and thicknesses. This work suggests that the electrode density and thickness should be chosen properly and mentioned in detail in any kinds of research works.

1991 년 일본의 SONY 사에 의해 시장에 등장한 리튬이온전지 (lithium-ion battery, LIB) 는 기존 이차전지 대비 높은 에너지밀도 (중량당 에너지밀도를 기준으로 납축전지 대비 5 배, Ni-MH 전지 대비 3 배 이상임) 를 구현함으로써 휴대전자기기 대중화의 기틀을 마련했다. 그러나, 3 V 이상의 높은 작동 전압으로 인해 기존 수계 전해질 대신 유기계 전해질 (non-aqueous electrolyte) 을 적용해야만 했고, 이로 인한 높은 전지 저항과 안전성 문제는 큰 이슈가 되었다. 특히, 유기계 전해질 사용으로 야기된 높은 전지 저항은 리튬이온전지 상용화에 큰 걸림돌이었고, 이에 대한 해결책으로 양극과 음극의 간격을 획기적으로 줄일 수 있는 박막 분리막의 도입은 필수적이었다. 이를 위해, 기존 수백 마이크로미터의 분리막 (separator) 두께를 수십 마이크로미터로 낮춰야 했고, 또한 박막 분리막의 충분한 절연 특성을 확보하기 위해 기공의 크기 역시 마이크로미터 이하로 제어해야만 했다. 그 결과, 미세다공성 폴리올레핀 계열 분리막이 개발되어 최근까지도 큰 문제없이 사용되고 있다. 그러나, 2000 년대 후반 리튬이온전지가 전기자동차용 전원으로 적용됨에 따라, 중대형 리튬이온전지의 안전성 확보를위한 기술적 이슈로 폴리에틸렌 분리막의 열적 안정성 개선이 주목받게 되었다. 이로 인해, 리튬이온전지 분리막용 내열 고분자 소재에 대한 연구가 급격히 증가하였다. 따라서, 본 특집의 앞 부분에서는 분리막 내열 특성을 개선하기 위한 연구 동향을 고분자 소재 관점에서 정리하고자 한다. 여기에 포함될 수 있는 분야는 분리막원단 소재뿐만 아니라 내열 코팅 고분자 소재, 그리고 세라믹 코팅층 형성을 위한 바인더 소재 (binder materials) 를 포함한다.

In this study, we demonstrated the effects of aluminum oxide (Al2O3)-based ceramic coatings deposited by radio-frequency (RF) magnetron sputtering on commercial polyethylene (PE) microporous separators. Due to the superb thermal stability of the ceramic materials themselves, the Al2O3 coatings solved the chronic thermal shrinkage problem of PE separators. Separators with sputtered Al2O3 coatings maintained their initial dimensions even after high temperature exposure at 140 °C for 30 min. The sputtered Al2O3 layer effectively changed the surface of a PE separator from being hydrophobic to hydrophilic too, improving its wettability with liquid electrolyte. Additionally, a sputtered Al2O3 coating can improve the rate capability (~130%) compared with a bare PE separator under a high current density (7.75 mA cm-2, 5 C rate) because the layer does not require additional use of polymeric binder materials, which usually inhibit the formation of pore structures in microporous membranes.

리튬이차전지 실리콘 전극에 활용하기 위해, 유기용매에 용해성이 있는 폴리이미드(Polyimide, PI) 고분자 바인더를 두 단계 반응을 이용해 합성하였다. 두 가지 단량체(Bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic Dianhydride (BCDA)와 4,4-oxydianiline (ODA))의 개환 반응 및 축합 반응을 통해 PI 고분자 바인더를 합성하였다. 합성된 PI 고분자 바인더를 이용해 실리콘(silicon, Si) 음극 전극을 제조하였다. 또한 비교군으로써, Polyvinylidene Fluoride (PVDF)을 고분자 바인더로 사용하는 동일 조성을 가진 실리콘 전극을 제조하였다. PI 바인더를 사용한 Si 전극(2167mAhg−1)의 초기 쿨롱 효율은 기존 PVDF 바인더 조성의 Si 전극(1,740mAhg−1)과 유사했지만, 방전용량은 크게 개선되었다. 특히 수명 특성에서는 PI 바인더를 사용한 Si 전극이 우수한 특성을 나타내었는데, 이는 PI 바인더를 사용한 Si 전극접착력(0.217kNm−1)의 전극 접착력이 PVDF를 사용한 Si 전극(0.185kNm−1)보다 높아, 실리콘 부피팽창에 의한 전극 구조 열화가 적절히 제어되었기 때문이라고 판단된다. Si 전극 내의 접착력은 surface and interfacial cutting analysis system (SAICAS) 장비를 통해 검증하였다.

음극 표면에 solid electrolyte interphase (SEI)를 형성하는 전해질 첨가제인 lithium bis(oxalate) borate (LiBOB), fluoroethylene carbonate (FEC), vinylene carbonate (VC), 2-(triphenylphosphoranylidene) succinic anhydride (TPSA)를 Li(Ni1/3Co1/3Mn1/3)O2(NCM)/graphite 전지에 도입하여 고온 저장 특성을 비교하였다. 각 전지를 50%의 충전상태(stage of charge, SOC)에서, 고온 저장(60∘C, 20일) 시킨 이후의 용량 유지율을 확인한 결과, LiBOB 1 wt.%가 가장 우수한 용량 유지 특성(초기 방전용량 대비 86.7%)을 나타내었다. LiBOB 1 wt.%의 경우 고온 저장 전후의 전지 저항 증가 및 SEI 두께 변화가 가장 적었고, 이는 음극 SEI에 포함된 다량의 semi-carbonate 물질과 연관성이 높다고 판단된다. 또한, LiBOB 1 wt.%가 포함된 NCM/graphite 전지의 상온(25∘C) 및 고온수명(60∘C) 특성도 기준 전해액(1.15 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate/ethyl methyl carbonate (EC/EMC, 3/7 by volume))보다 각각 6%와 9% 향상된 결과를 보여주었다. 따라서, LiBOB이 상온 성능을 동등 이상으로 유지하면서도 고온 특성을 개선할 수 있는 우수한 전해액 첨가제로 판단된다.

시간대별 효율적인 전력 운영과 전력품질 향상을 위해 ESS (Energy Storage System)의 보급이 세계적으로 활발하게 이루어지고 있다. 이러한 ESS용 전원소자로 리튬이차전지의 채용이 급격히 늘어남에 따라, 리튬이차전지의 수명 및 출력 열화 거동을 측정 및 예측하는 기술이 시급히 요구되고 있다. 특히, ESS 운영에 있어 핵심 특성인 리튬이차 전지 출력은 측정이 어려울 뿐만 아니라, 정확한 측정을 위해서는 많은 시간이 소요되는 문제점이 있다. 따라서, 본 연구에서는 ESS용 리튬이차전지 단전지를 전산 모델링 한 후, 펄스 측정법을 적용하여 충전상태에 따른 방전 및 충전시의 직류저항(DC-IR)과 출력을 예측한다. 또한, 두 가지 펄스 측정법인 HPPC (Hybrid Pulse Power Characteristics)와 J-Pulse (JEVS D 713, Japan Electric Vehicle Association Standards)의 결과를 비교 분석한다.

6M의 KOH 수계 전해액에 potassium polyacrylate (PAAK)가 3 wt.% 포함된 하이드로겔 전해질을 제조하고, 이에 친수성 실리카 OX50을 1 wt.% 포함시킨 하이드로겔 전해질을 함께 제조하고, 이를 Scimat 분리막에 코팅 및 건조하여 활성탄 수퍼커패시터의 자기지지체 전해질/분리막으로 사용하여 그 실리카 첨가효과를 조사하였다. 실리카 입자는 다공성 분리막 지지체의 표면기공에 균일하게 분포하여 하이드로겔의 이온전도도와 전기화학적 안정성을 향상시켰으며 이에 따라 고속스캔 조건에서도 활성탄 수퍼커패시터의 비축전용량이 비교적 높게 유지되었는데, 이는 실리카가 포함된 하이드로겔 전해질이 활성탄 전극과 분리막 사이에서의 계면저항이 감소하기 때문이다.

폴리올레핀 분리막의 내열성을 향상시키면서도 전기화학특성 개선을 위해 RF Magnetron Sputter기반으로 수십 나노미터 수준의 세라믹 층이 코팅된 내열 분리막을 제조하였다. 분리막 원단의 열적 손상없이 코팅 시간을 최소화하기 위한 증착 조건을 최적화 하였고, 이를 기반으로 제조된 내열 분리막의 물리적, 전기화학적 평가를 진행하였다. 약 20 nm의 Al2O3가 코팅된 Polypropylene(PP) 분리막은 원단 분리막 대비 통기 특성 (원단: 211.3 sec/100 mL, 코팅 분리막: 250.8 sec/100 mL)은 떨어졌으나, 열 수축율 (원단: 19.4%, 코팅 분리막: 0.0% @ 140∘C & 30 min), 전해액 Uptake(원단: 176%, 코팅 분리막: 190%) 및 이온전도도 (원단: 0.700 mS/cm, 코팅 분리막: 0.877 mS/cm)는 모두 향상되었다. 그 결과, 2032-type Half-cell(LiMn2O4/Li)을 이용한 전기화학적 평가에서도, 향상된 율별 특성과 유사한 수명 특성을 나타내었다.

많은 실험실 기반의 리튬이차전지 실험결과는 코인셀로부터 얻어진다. 이는 조립의 용이성, 저렴한 가격, 실험 결과의 우수한 재연성 등에 기인한다. 코인셀은 케이스(case), 가스켓(gasket), 스페이서(spacer disk), 스프링(wave spring)로 구성되어 있으며, 이러한 구조적인 특성으로 인하여 코인셀은 상용화된 파우치, 각형 및 원통형 전지에 비하여 전극 무게 대비 많은 양의 전해질을 포함하게 된다. 하지만 과량의 전해액이 셀의 성능에 미치는 영향에 대한 연구는 현재까지 이루어지지 않은 상황이다. 본 연구에서는 액체 전해액의 양을 다르게 제어하여 코인셀에 미치는 영향을 알아보고자 하였다. 전해액의 양은 전극 용량 대비(전해액의 양/전극용량)로 제어하였으며, 조립된 셀의 전해액 함량에 따른 전기화학적 특성을 확인하기 위해 초기 충 방전 곡선과 상온 (25∘C), 고온 (60∘C) 및 고전압(4.5 V)에서의 수명특성평가를 진행하였다. 30mgmAh−1의 전해액을 포함하는 단위 전지의 경우, 고온 및 고전압 조건에서 100mgmAh−1의 경우에 비해 매우 우수한 방전 용량 유지 특성을 나타내었다. 전자는 후자보다 더 큰 내부저항 증가를 보였으며, 이를 통해 전해액의 양이 전지의 방전 용량 유지 특성에 매우 큰 영향을 미치고 있음을 확인하였다.

복합전극의 결착특성은 리튬이차전지의 장기신뢰성 확보와 고에너지밀도 구현을 위한 중요한 물성임에도 불구하고, 측정 기술의 한계로 관련 연구가 제한적이었다. 하지만, 두께의 코팅층을 절삭 및 박리하면서 결착특성을 측정할 수 있는SAICAS(Surface And Interfacial Cutting Analysis System)란 장비의 출현으로 전극 결착특성 연구가 활발해지고 있다. 따라서, 본 총설에서는 SAICAS를 이용한 복합전극의 결착특성 분석 원리 및 측정 방법뿐만 아니라, Peel Test와 같은 기존 결착특성 분석 방법과 비교함으로써 SAICAS를 이용한 분석 방법의 신뢰성 검증 결과를 제시한다. 또한, 전극 설계의 최적화, 신규 바인더 도출 연구, 복합전극 내 바인더 분포 등의 연구에서 SAICAS가 적용된 사례를 소개한다. 이를 통해 SAICAS를 이용한 분석 방법이 리튬이차전지용 복합전극의 결착특성 분석에 용이하게 적용될 수 있음을 제안한다.

동일 전극 로딩 조건에서 면적당 용량을 극대화하기 위해, 고분자 바인더의 함량을 4, 2, 1 wt%로 줄인 전극을 제조하였다. 바인더 함량이 1 wt%로 낮춘 경우, 압연 후 펀칭 과정에서 전극 코팅층이 부분적으로 박리되는 문제가 발생하여 추가 분석은 진행되지 않았다. 전극 내 바인더 함량을 4 wt%에서 2 wt%로 줄이면, 계면 접착력은 0.4846에서 약 46% 감소하고, 전극 코팅층의 강도도 3.847에서 2.013 MPa로 약 48%가 떨어졌다. 그러나, 두 전극을 리튬 전극과 반쪽 전지로 구성하여 전기화학적 특성을 살펴보면, 초기 방전 용량과 충방전 효율은 유사하였다. 하지만, 단기 수명 평가에서 2 wt% 바인더 전극은 수명 특성이 떨어질 뿐만 아니라, 전지를 분해하는 과정에서 전극 코팅층이 집전체에서 박리되는 현상이 관찰되었다. 반면, 4 wt% 바인더 전극은 높은 전극 로딩조건에서도 전극 코팅층과 집전체 계면이 잘 유지되고 있음이 확인되었다.

Li metal exhibits considerable morphological changes during its plating/stripping, and in particular, the formation of needle-like Li or “dead Li” during plating/stripping has limited the widespread the use of Li metal as a secondary battery anode material. In recent attempts to suppress dead-Li formation during Li plating/stripping, the method of hosting Li metal in a stable structure in plating process has attracted considerable attention. Although many types of conductive Li host materials have been introduced to improve the electrochemical properties of Li metal anodes, the mechanism by which conductive Li hosting materials inhibit dead Li in each system has not been precisely investigated. In this study, we introduce a vapor-grown carbon-nanofiber-based protective layer on the Li metal surface and investigate the effects of the protective layer on the formation of dead Li. To this end, we investigate the adhesion properties of the plated Li and the morphological changes of the Li metal anodes with the protective layer during plating. Furthermore, the effects of the protective layer on the electrochemical properties of Li metal anodes are investigated. The protective layer firmly holds the plated Li over entire area, which results in reduced amounts of dead Li during repeated cycling.

리튬이차전지(Lithium Secondary Batteries)를 에너지원으로 채용하는 분야가 다양해짐에 따라, 기존 요구 특성뿐만 아니라 각 분야에 특화된 성능 평가 결과까지 요구하고 있다. 이에 대응하기 위해 각 전지 제조사는 연구 인력을 충원하고 고가의 장비를 지속적으로 도입해서 다수의 전지를 오랜 기간 평가해야 하는 어려움을 겪고 있다. 이를 해소하기 위해, 전지 모델링(Modeling)을 기반으로 한 모사(Simulation) 기법을 도입하여, 실험 횟수를 최소화하고 실험 시간도 단축하려는 시도를 지속하고 있다. 현재까지 다양한 리튬이차전지 모델링 기법이 보고되고 있으며, 목적에 따라 최적 기법이 선택 및 활용되어 왔다. 본 리뷰 논문에서는 뉴만(Newman) 모델을 기반으로 한 전기화학적 모델링(Electrochemical Modeling) 기법을 상세히 설명한다. 특히, 전극 반응속도를 나타내는 버틀러-볼머식(Butler-Volmer Equation), 각 상(Phase)에서 전자와 이온의 균형 방정식 (Material and Charge Balance Equations), 그리고 전지의 온도 변화를 설명할 수 있는 에너지 균형 방정식 (Energy Balance Equation)의 물리적 의미를 쉽게 설명하고, COMSOL Multiphysics를 이용한 간단한 해석 과정과 결과를 제시한다.

리튬 금속 음극은 낮은 환원 전위, 고에너지 밀도로 인해 흑연을 대체할 차세대 음극재로 재조명 받고 있다. 하지만, 충방전시 리튬 금속 표면에서의 반복적인 산화/환원 반응에 의해 리튬 덴드라이트가 형성되며 이로 인해 수명특성이 급격하게 저하되고 더 나아가 내부 단락(Internal Short-circuit)과 같은 안전성 문제로 인해 상용화되기에는 어려운 실정이다. 이를 해결하기 위해 본 연구 그룹에서는 리튬 금속에 미세 패턴을 형성하여 전류 밀도를 제어함으로써 덴드라이트 형성을 제어하였으나, 고전류밀도에서는 리튬 덴드라이트의 형성을 완벽하게 제어할 수는 없었다. 본 연구에서는 미세 패턴화된 리튬 금속 전극에 전해질 첨가제 Vinylene Carbonate(VC)를 도입하여 고율 충방전 시 미세 패턴화된 리튬 금속 전극의 덴드라이트 형성 억제를 극대화하고자 하였다. 미세 패턴화된 리튬 금속 전극과 VC 첨가제의 시너지 효과로 인해 높은 전류 밀도에서의 리튬 덴드라이트가 비교적 치밀하게 형성되는 것을 확인할 수 있었다. 이로 인해 300사이클 동안 88.3%의 용량유지율을 보였으며, 기존의 미세 패턴화된 리튬 금속 전극에 대비하여 수명특성이 약 6배 이상 향상된 것을 확인할 수 있었다.

이차전지용 전극은 일반적으로 전극 활물질, 도전재, 그리고 고분자 바인더가 혼합된 복합 전극의 형태를 갖는다. 따라서, 크기나 형태가 다른 각 성분의 조성 및 전극 내 분포에 따라 전극의 전기화학적 활성이 달라지게 되나, 이를 효율적으로 예측하고 설계하는 3차원 전극 구조 모델링 기술은 아직 활발히 연구되고 있지 못하다. 따라서, 본 논문에서는 3차원 구조 모델링 툴인 GeoDict를 이용하여, LiCoO2 전극 활물질 입자 크기와 복합 전극 밀도에 따른 입자 간 접촉 면적과 전기전도특성을 예측한 결과를 제시한다. 전극의 조성과 로딩은 LiCoO2 : Super P Li® : Polyvinylidene Fluoride (PVdF) = 93 : 3 : 4 (wt%)과 13 mg cm-2로 고정하고, LiCoO2 평균 입경은 10 μm과 20 μm로 전극 밀도는 2.8 g cm-3, 3.0 g cm-3, 3.2 g cm-3, 3.5 g cm-3, 4.0 g cm-3로 제어하여 가상의 3차원 전극 구조를 만들었다. 이 구조를 활용하여 LiCoO2 입경증가에 따른 입자 간 접촉 면적 감소와 전기전도특성 증가 경향성이 정량화되었다. 또한, 전극밀도가 증가함에 따라 입자 간 접촉 면적 및 전기전도특성 향상도 수치화 된 값으로 예상될 수있다. 따라서, 본 논문에서는 3차원 전극 구조 분석 기법을 이용하면, 더 효율적인 복합 전극설계가 가능함을 제시한다.