The cover art is attributed to an article entitled “Moisture Stability of Sulfide Solid Electrolytes: Systematic Comparison and Mechanistic Insight” by Dr. Yusuke Morino et al. selected as an Editor’s Choice for the 71^st Special Feature, “New Progress of Batteries and Fuel Cells” recommended jointly by the guest editors from The Committee of Battery Technology and the editorial board. In this article, the authors systematically investigate the moisture stability of various sulfide solid electrolytes (SEs) and elucidate distinct mechanisms responsible for the degradation of lithium ionic conductivity upon exposure to moisture. A quantitative comparison was conducted for SEs with different crystal structures, including Li₆PS₅Cl, Li₃PS₄, and Li₄SnS₄, in order to offer a more comprehensive understanding of their respective degradation behaviors. This comparative study revealed that the SEs undergo two different degradation pathways: hydrolysis and hydration. Notably, both Li₃PS₄ and Li₄SnS₄ exhibited a comparable decline in lithium ionic conductivity to that of Li₆PS₅Cl, despite generating significantly less H₂S gas. This observation suggests that the underlying deterioration mechanisms differ among the materials.

This cover art was created and published with financial support from The Committee of Battery Technology.

The cover art is attributed to an article entitled “Chemical Composition-Driven Machine Learning Models for Predicting Ionic Conductivity in Lithium-Containing Oxides” by Yudai Iwamizu et al. selected as an Editor’s Choice for the 71st Special Feature, “New Progress of Batteries and Fuel Cells” recommended jointly by the guest editors from The Committee of Battery Technology and the editorial board. In this article, the authors present machine learning models that predict the ionic conductivity of lithium-ion conductive solid oxide electrolytes based solely on their chemical composition. High ionic conductivity is essential for the development of high-performance all-solid-state batteries (ASSBs), making solid electrolytes a critical component. The proposed models, trained on over 2,200 data entries, significantly outperform previous approaches. Notably, configurational entropy emerged as a key feature in predicting ionic conductivity. The models also generalize well to previously unseen systems, facilitating the efficient discovery of promising solid electrolytes for ASSBs.

This cover art was created and published with financial support from The Committee of Battery Technology.

The cover art is attributed to an article entitled “Measurement of Side-Reaction Currents in Lithium-Ion Batteries with Different Capacity Ratios” by Prof. Kingo Ariyoshi et al. selected as an Editor’s Choice for the 71^st Special Feature, “New Progress of Batteries and Fuel Cells” recommended jointly by the guest editors from The Committee of Battery Technology and the editorial board. The side-reaction current (ISR) significantly contributes to capacity fading, primarily due to state-of-charge imbalances between the positive and negative electrodes in lithium-ion batteries. In this study, the authors conducted a detailed analysis of three types of ISR based on electrochemical behavior, using electrodes with different loadings and varying positive/negative capacity ratios. The results revealed that an additional ISR, caused by internal crosstalk within the battery, depends on the concentration of side-reaction products. Controlling this ISR by adjusting its magnitude is essential for extending battery life. This study provides valuable insights into strategies for improving the longevity of lithium-ion batteries.

This cover art was created and published with financial support from The Committee of Battery Technology.

The cover art is attributed to an article entitled “Mechanistic Insights into Electrooxidative Allylation of a Carbamate in the Presence of Solid-Supported Acids” by Ms Haruka Homma et al. as an Editor’s Choice. In this work, the authors successfully demonstrated electrooxidative carbon–carbon bond formation of a carbamate with allyltrimethylsilane, aided by in-situ generated HBF₄ species. Electrochemical oxidation of organic compounds is a highly promising strategy for generating reactive and versatile carbocations in organic synthesis. To effectively control subsequent nucleophilic reactions with these carbocations, the authors introduced a solid-supported acid, which generated HBF₄ and promoted the desired C–C bond formation. Detailed mechanistic analysis revealed that in-situ generated HBF₄ plays a crucial role in enabling carbon-carbon bond formation of a carbamate with allyltrimethylsilane.

This special issue of Electrochemistry features selected papers from the 65th Battery Symposium in Japan, held in November 2024, which marked a full return to in-person meetings after the COVID-19 pandemic. The symposium saw record participation, highlighting strong interest in lithium-ion batteries, all-solid-state batteries, and emerging chemistries such as sodium-ion and lithium–sulfur systems. Progress in electrolyte design, interfacial science, and data-driven approaches was also emphasized. Additionally, several contributions focused on fuel cell research, reflecting the expanding scope of electrochemical energy technologies. We hope this collection stimulates further innovation in energy storage and conversion.

Current status and trends of automotive lithium-ion batteries are reviewed from the viewpoints of important performance by showing their energy density, power density, life, safety, operating temperature range, and cost in current electric vehicles around the world. This kind of information is very limited and useful, because many battery researchers in academia are unaware of the current situation of automotive lithium-ion batteries, and they can evaluate the performance of next generation batteries in comparison with the current lithium-ion batteries.

The Center for Advanced Battery Collaboration (ABC) was established at the National Institute for Materials Science with the support of COI-NEXT, Japan Science and Technology Agency (JST). ABC aims to create a platform for collaboration between academia and industry for battery research and development with a special focus on developing battery simulation protocols through advanced characterization, data science and theoretical calculations. These protocols not only support the development of advanced Li batteries, Li-air batteries, sodium batteries, magnesium batteries, and all-solid-state batteries but also promote the innovation of new battery technologies in collaboration with industries. This article provides an overview of the projects in ABC and highlights the efforts and achievements of each research team.

The Global warming caused by greenhouse gas emissions was increasingly recognized in the world, and international congresses have been held to discuss what we in the world should do against the critical issue. With the restriction targets set, various Japanese ministries and agencies are creating programs to achieve them. The Ministry of Education, Culture, Sports, Science and Technology (MEXT) and the Japan Science and Technology Agency (JST) are creating programs to develop specific devices based on natural science theories established in academia. As for developing storage batteries, they launched ALCA-SPRING program where the first team-based research on storage batteries with a top-down approach was conducted. Learning from the success of the ALCA-SPRING program, GteX program was created based on the similar concept. In the battery area of GteX program, there are eight teams that are Advanced Lithium-ion batteries team, Sulfide-based Solid-State batteries team, Oxide-based Solid-State batteries team, Sodium-ion batteries team, Magnesium batteries team, Lithium-sulfur batteries team, Lithium-air batteries team, and Battery Research Platform team. In this program, active research works are underway to significantly improved existing storage batteries and to create next-generation batteries.

All-solid-state batteries with sulfide solid electrolytes are promising next-generation energy storage devices owing to their longer lifetimes compared with liquid-type lithium-ion batteries. However, their practical application is hindered by low moisture stability. Few studies have quantitatively compared their moisture stability and underlying mechanisms among electrolyte species. This study systematically evaluates the moisture stability of sulfide solid electrolytes by standardizing particle size and varying electrolyte species, moisture content (dew point), and atmospheric conditions. Sulfide solid electrolytes with different crystal structures, such as Li₆PS₅Cl, Li₃PS₄, and Li₄SnS₄, were exposed to Ar gas flows with dew points from −30 to 0 °C (H₂O concentrations: 0.45–4.8 g m⁻³). H₂S generation followed the order: Li₆PS₅Cl ≫ Li₃PS₄ > Li₄SnS₄. At 0 °C dew point, H₂S gas release was ∼22.7 ml g⁻¹ for Li₆PS₅Cl, ∼0.44 ml g⁻¹ for Li₃PS₄, and ∼0.17 ml g⁻¹ for Li₄SnS₄. Despite variations in H₂S generation, lithium ionic conductivity retention was similar. X-ray photoelectron spectroscopy showed surface hydrolytic decomposition species were observed on Li₆PS₅Cl, whereas Li₃PS₄ and Li₄SnS₄ showed minimal changes. Thermogravimetric analysis revealed clearer hydration in Li₃PS₄ and Li₄SnS₄, causing lower ionic conductivity without H₂S generation. Differences in conductivity reduction are attributed to sulfide unit structures.

The formation of solid-electrolyte interphase (SEI) on a Pt electrode was investigated in ethylene carbonate (EC) and diethyl carbonate (DEC) containing LiPF₆ and lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) using the redox probe method. The formation and properties of the SEI were examined in the electrolytes containing ferrocene as a redox probe. Inhomogeneous and rigid SEI was found to form in 1 M (= mol dm⁻³) LiPF₆/EC+DEC, probably due to the conversion of decomposition products to LiF by the reaction with HF derived from LiPF₆. On the other hand, the formation of homogeneous and soluble (or dispersible) SEI was suggested in 1 M LiTFSA/EC+DEC.

Lithium-ion batteries are used on an increasingly large scale, making their lifetime prediction a critical issue. Especially, a rapid decrease in capacity after the mild degradation period, referred to as the knee point, is often observed, and thus understanding the knee point and its mechanism is a critical issue. Although numerous studies have been dedicated to the analysis of this phenomenon, studies on a commercial large-format lithium-ion battery are lacking. Further studies are required to continuously track changes over time and elucidate the source of knee points during operation. Herein, we conduct degradation cycle tests using a large-format commercial lithium-ion battery (> 50 Wh, LiNi_0.5Co_0.2Mn_0.3O₂/graphite) and analyze the knee points during cycling by employing electrochemical impedance spectroscopy (EIS) at different states of charge (SOCs) to track the degradation state over time, in combination with differential analysis and post-mortem methods. As a result, two knee points appear during degradation, caused by increases in resistance that are mainly derived from electrolyte depletion and Li plating at the anode. These observations are described based on the SOC dependency of the EIS results, which can be leveraged to identify the cause of knee points.

This study investigated the stability of the surface film of the negative electrode by investigating how temperature affects the morphology of the surface film of the negative electrode using in-situ electrochemical atomic force microscope (AFM) in LiPF₆-based electrolytes with the addition of vinylene carbonate (VC) or by replacing LiPF₆ with lithium bis(fluorosulfonyl)imide (LiFSI). AFM measurements revealed that, in the case of the LiPF₆-based electrolyte, blisters were generated by the reductive decomposition of the electrolyte at the step edge of the negative electrode, grew larger as the storage temperature increased up to 45 °C, and collapsed at 55 °C. The surface film with blisters was partially broken down at 65 °C. Conversely, with VC addition or LiFSI substitution, no blister collapse and film dissolution were observed, even when the temperature was raised to 65 °C.

In this study, the cathode properties of αLi₂MnO₃–(1 − α)Li(Mn_10/24Ni_7/24Co_7/24)O₂ (α = 0.5, 0.4) with Li metal and TiNb₂O₇ (TNO) as the negative electrode and the average and electronic structures after five charge–discharge cycles were investigated using neutron diffraction and synchrotron X-ray diffraction data. Charge–discharge tests of αLi₂MnO₃–(1 − α)Li(Mn_10/24Ni_7/24Co_7/24)O₂ (α = 0.5, 0.4)//Li and TNO were conducted at 0.1C, and a capacity of ∼200 mAh g⁻¹ was obtained in the range between 2.0 V and 4.8 V vs. Li/Li⁺ for the cell with Li. By contrast, a capacity of ∼180 mAh g⁻¹ was obtained in the range between 0 V and 3.3 V for the cell with TNO, and the capacity increased with each cycle for approximately 15 cycles. To clarify the cause of the change in electrode characteristics, electrodes in a 5-cycle charge–discharge state were fabricated and the average structure was investigated by Rietveld analysis using neutron diffraction and synchrotron X-ray diffraction. The results of the average structure analysis showed that the transition metal migrates to the transition-metal site and that the distortion parameter for the MO₆ octahedron is high after the five-cycle charge. In addition, from an electron density analysis, in αLi₂MnO₃–(1 − α)Li(Mn_10/24Ni_7/24Co_7/24)O₂ (α = 0.4)//Li, which showed excellent positive electrode characteristics, the difference in electron density between the pristine and charged/discharged conditions was small at the 2b site. These results indicate that the crystal structure changes between charging and discharging depending on the anode, which affects the battery properties.

A machine learning model that can predict the ionic conductivity of lithium-containing oxides using chemical composition and ionic conductivity data was previously developed. However, this model revealed several limitations, leading to less-than-ideal prediction accuracy. Thus, new models demonstrating improved prediction ability must be developed. This study presents the development of machine learning models for the accurate prediction of ionic conductivity in lithium-containing materials based solely on their chemical composition. The models constructed using the NGBoost and LightGBM algorithms show high compatibility with the training and test data, resulting in high predictive accuracy. The constructed models identify “entropy,” which is considered a key factor in developing ionic conductors, as an important feature. This finding highlights the potential utility of this property from a solid-state chemistry perspective. The developed models demonstrate high predictive accuracy even for previously reported lithium superionic conductor-type materials that were not included in the training dataset. The established models are expected to facilitate efficient material discovery for the development of all-solid-state lithium batteries.

CH₄ production by CO₂ reduction using a membrane electrode assembly containing a Pt/C electrocatalyst was recently demonstrated. Because this CO₂ reduction reaction occurs at approximately its theoretical electrode potential, it is possible to generate electric power as an H₂-CO₂ fuel cell by the reduction reaction occurring in combination with the H₂ oxidation reaction. However, the CH₄-generation reaction deactivated in a short time (∼5 min) due to the influence of the CO adsorbed on the Pt surface (CO_ads) as a reaction intermediate. In this study, we investigated the CO₂ reduction using a Pt_0.5Ru_0.5/C electrocatalyst in order to realize a continuous CH₄ production. As a result, steady CH₄ generation for more than 15 min with a faradaic efficiency of 12.0 % was observed at 0.22 V vs. RHE under a 4 vol% CO₂ atmosphere. In other words, an improved continuous CH₄ production was achieved by employing a Pt_0.5Ru_0.5/C electrocatalyst instead of Pt/C, and their faradaic efficiencies were equivalent. This result was obtained because the adsorption energy of CO_ads decreased due to the alloying of Pt and Ru based on the changes in the onset potential of the CH₄ production. In addition, power generation as an H₂-CO₂ polymer electrolyte fuel cell was observed while converting CO₂ to CH₄.

An organic electrolyte solution of 1.0 mol dm⁻³ LiCl/dimethyl sulfoxide (DMSO) was investigated for a fluorine-free battery with an electrode using 2,5-dimethoxy-1,4-benzoquinone (DMBQ) as the n-type active material and styrene butadiene rubber (SBR) as the binder. The DMBQ electrodes showed the initial discharge capacities of 222 mAh g⁻¹ and 164 mAh g⁻¹ for the DMSO solution of the LiCl system and the LiPF₆ system, respectively. Moreover, they showed similar working voltages of 2.6–2.7 V, even though their plateau slopes had slight differences. In addition, the chemical bonding and crystallinity changes of DMBQ were confirmed during discharge-charge, suggesting that it reacted electrochemically with Li⁺ in the LiCl/DMSO solution. The results of cycle properties suggested that a gradual decrease in the discharge capacities would result from denaturation and dissolution of DMBQ during the redox process in the electrolyte solution.

All-solid-state batteries (ASSBs) are expected to be next-generation batteries owing to their safety and suitability for high-temperature operation. While traditional lithium-ion batteries use liquid electrolytes that enable easy electrolyte filling after electrode fabrication, ASSBs use solid electrolyte particles. Thus, electrolyte particles must be dispersed alongside the active materials and additives during electrode preparation. The dispersion state of the electrolyte influences subsequent electrode formation and structure; however, experimentally quantitatively controlling and evaluating the dispersion states remains challenging. This study used powder simulation to control the dispersion state quantitatively, based on the aggregation size of solid electrolyte particles. It also evaluated the compression process and the resulting electrode structure.

In this paper, we investigated the effects of Ga substitution and preparation process on the negative-electrode properties of Wadsley–Roth phase TiNb₂O₇. We also investigated the crystal structures of the samples with different Ga compositions via the Rietveld refinements and then discussed the relationship between the electrode properties and the structure. We demonstrated that the Ga substitution to TiNb₂O₇ was successful based on the diffraction patterns and X-ray absorption near-edge structure (XANES) spectra. The investigation of the electrode properties showed that the capacities associated with the insertion and deinsertion of Li⁺ were improved by the Ga substitution, and that excellent electrode properties could be achieved by optimizing the preparation process. Furthermore, by performing Rietveld analysis using both neutron and synchrotron X-ray diffraction data, it was revealed that the distortion of the crystal structure was suppressed by the Ga substitution. Such a structural change by the Ga substitution was considered to be one of the factors for improving the electrode properties.

To extend the lifetime of lithium-ion batteries, determining the side-reaction current (I_SR) is essential because capacity fading is mainly caused by the state-of-charge imbalances of positive and negative electrodes. Among the three types of I_SR (intrinsic, additional, and actual), the additional I_SR resulting from crosstalk reactions exhibits complex behavior owing to its dependence on the opposing electrode. In this study, the effect of the opposing electrode on additional I_SR was examined by measuring the three types of I_SR in Li[Li_1/3Ti_5/3]O₄/Li[Li_0.1Al_0.1Mn_1.8]O₄ cells with different capacity ratios of the positive and negative electrodes. The results indicate that additional I_SR correlates with the weight of the opposing electrode, whereas intrinsic I_SR depends on the weight of each electrode. These findings suggest that additional I_SR is closely related to the amounts of side-reaction products generated at the opposing electrode owing to the intrinsic I_SR. The dependence of crosstalk reactions on the concentration of side-reaction products indicates that these concentrations must be considered to extend battery life by adjusting the actual I_SR.

Li-deficient argyrodite-type Li conductors are promising solid electrolytes for all-solid-state batteries because of their high ionic conductivity, favorable mechanical properties, and low synthesis cost. However, challenges such as incompatibility at the electrode/electrolyte interface must be addressed. In this study, Li-deficient argyrodite-type Li_5.5PS_4.5−xBr_1.5O_x (0 ≦ x ≦ 0.5) was synthesized by oxygen substitution and its crystal structure and electrochemical properties were investigated. Oxygen is soluble at specific crystallographic sites (16e), with substitution increasing systematically as the value of x in Li_5.5PS_4.5−xBr_1.5O_x increases. Furthermore, it was found that Li_5.5PS_4.5−xBr_1.5O_x (x = 0.1) showed relatively high ionic conductivity and improved compatibility with the positive electrode. The cells incorporating Li_5.5PS_4.5−xBr_1.5O_x (x = 0.1) in the cathode composite demonstrate excellent cycle stability, retaining 71.5 % of their capacity after 100 cycles at a 0.1C-rate. These findings clarify the effects and mechanisms of oxygen substitution in argyrodite-type Li_5.5PS_4.5Br_1.5 and provide a strategy for advancing the practical application of all-solid-state batteries.

Owing to its high ionic conductivity, Li₁₀GeP₂S₁₂ (LGPS)-type Li-Si-P-S-Cl (LSiPSCl) solid electrolytes are promising candidates for all-solid-state batteries. This study introduces an LGPS-type LSiPSCl solid electrolyte synthesized rapidly via a solution method using excess sulfur and a solvent mixture of acetonitrile, tetrahydrofuran, and ethanol to enable large-scale production. X-ray diffraction patterns reveal an LGPS-type structure as the primary phase, while FE-SEM analysis confirms the presence of few large particles exceeding 5 µm. The LSiPSCl solid electrolyte synthesized via the solution method exhibits an ionic conductivity of 2.7 mS cm⁻¹, which is comparable to that of the sample synthesized using the mechanical milling method (3.1 mS cm⁻¹). In addition, the all-solid-state battery incorporating LSiPSCl synthesized using the solution method exhibits a slightly higher discharge capacity and similar cycle stability compared with the battery containing LSiPSCl synthesized using the mechanical milling method. These results confirm that the solution method successfully produces an LSiPSCl solid electrolyte. Raman and X-ray photoelectron spectroscopy analyses reveal a carbon surface layer on the particles originating from the solvent. This surface layer is identified as a key factor contributing to the higher discharge capacity of the all-solid-state battery containing the LSiPSCl solid electrolyte synthesized using the solution method. These findings suggest that the surface layer on the particles and/or particle characteristics are critical advantages of solution synthesis for improving battery performance.

PEO-based solid polymer electrolytes (SPEs) exhibit a narrow potential window and undergo decomposition when in contact with 4V-class cathode active materials. The objective of this study was to investigate the stability of the contact interface between the PEO electrolyte and the positive electrode material, coated with various inorganic compounds on the surface. The time variation for the impedance of the interface between the PEO-based SPE and the LiNi_0.6Mn_0.2Co_0.2O₂ (NMC) coated with various inorganic compounds was measured. The following coated materials were tested: the ionic crystal LiF, the covalent oxide Al₂O₃, the ferroelectrics BaTiO₃ and LiNbO₃, the lithium ion conductor La_0.45Li_0.45TiO₃ (LLTO), and the ferromagnetic and highly electron conductive La_0.7Sr_0.3MnO₃ (LSMO). They were coated on the surface of NMC electrode using the sputtering method. The impedance of the Li/SPE/coated NMC cell was measured while maintaining a potential of 4.2 V. In the non-coated NMC, the SPE/NMC interface resistance exhibited a notable increase over time. In all the coated NMCs, the increase in the interface resistance was suppressed, indicating an improvement in the interface stability. In particular, the interface resistance of LiF and Al₂O₃ remained unchanged for 40 h at 4.2 V, thereby demonstrating the formation of a highly stable SPE/NMC interface. The charge/discharge measurements of the Li/SPE/coated NMC cell revealed that the capacity retention rate of NMC coated with LiF and Al₂O₃ was significantly enhanced in comparison to that of NMC without coating.

This study focuses on the development of in-situ formed solid electrolyte anodes, specifically investigating TiH₂ as a promising candidate due to its high theoretical capacity, electronic conductivity, and low operating potential. Using SEM equipped with windowless Energy Dispersive X-ray Spectroscopy (EDS), the lithiation process and distribution of Ti and LiH were analyzed. Two cells (Cell A and Cell B) with differing lithiation capacities (980 mAh g⁻¹ and 623 mAh g⁻¹, respectively) were compared. Results revealed that the reaction in Cell B progressed uniformly throughout the electrode, while in Cell A, lithiation advanced further, forming a thicker LiH layer (0.5 µm) and fragmenting TiH₂ particles. Unlike MgH₂, which exhibited planar reaction progression, TiH₂ undergoes lithiation uniformly along the thickness direction of the electrode layer.

The increasing demand for cobalt reduction and high energy density in lithium-ion batteries has accelerated the development of cathode-active materials based on Ni-rich layered oxides. However, Ni-rich cathodes, such as LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811), suffer from capacity degradation due to factors including crystal structure changes, particle fractures, and the formation of surface resistive layers. While these degradation mechanisms have been extensively studied, the specific effects of high current density on capacity fading remains unclear. In this study, we investigate the degradation mechanisms of NMC811 cathodes cycled at 0.1C and 2C rates. Cycling at 2C rate results in severe capacity fading over 50 cycles. Synchrotron X-ray diffraction confirms the preservation of the crystal structure without evidence of Li–Ni site exchange. X-ray computed tomography reveals surface breakdown of primary particles following high-rate cycling. X-ray absorption spectroscopy and hard X-ray photoelectron spectroscopy indicate the formation of a thick resistive surface layer after the cycling at 2C rate. This layer, formed due to high polarization and intensified side reactions, impedes lithium-ion transport, leading to significant capacity degradation.

Recently, improving the performance and reducing the cost of lithium-ion batteries (LIBs) have become critical challenges. LiFePO₄ (LFP), in particular, has gained significant attention as a low-cost with high-performance cathode material, contributing to excellent cycle stability, safety, and environmental sustainability. The total cost of LIBs is not determined solely by material costs, and the manufacturing processes, such as production speed and yield rate, also have substantial impacts. To increase the production speed of electrodes, the improvements such as raising the drying temperature of the cathode slurry and manufacturing electrodes at high speeds have been investigated. Nonetheless, understanding the challenges associated with scaling up seems to be difficult from the laboratory scale.

In this paper, we focus on the physical property changes due to drying temperature, a factor with a significant impact on the manufacturing process, using the polyvinylidene difluoride (PVDF) and polyvinylidene difluoride-tetrafluoroethylene copolymer (NEOFLON VT-475) as fluoropolymer binders for LFP cathode. The results show that the electrodes with PVDF exhibited significant changes in peeling strength of electrode/current collector interface, as well as in electrode flexibility, depending on the drying temperature. On the other hand, the electrodes with VT-475 demonstrated minimal physical property changes with varying drying temperatures, and a reduction in binder quantity was feasible, suggesting a potential contribution to reducing battery costs.

Oxysulfides have the potential for battery electrodes to have durability and rate capability due to their rigid structures and electronic conductivity. Herein, we focus on the Ruddlesden-Popper phase oxysulfide Y₂Ti₂O₅S₂ and investigate the phase evolution of Y₂Ti₂O₅S₂ during electrochemical Li⁺ intercalation and deintercalation. The tetragonal structure is maintained down to 0.35 V during the lithiation process. A two-phase reaction between the tetragonal phase and the orthorhombic phase was observed at a voltage plateau region between 0.35 and 0.3 V. Subsequently, the tetragonal phase recovers for further lithiation process. The relatively low lattice volume change of 5 % compared with graphite anode leads to stable cycling performances.

The charge-discharge properties of all-solid-state batteries are affected by both chemical and physical factors. Physical issues mainly arise from the microstructure of the composites and the mechanical properties of the solid electrolytes themselves. However, physical issues have been investigated by focusing on the microstructures of the composites rather than the mechanical properties of the solid electrolytes themselves. In this study, composite cathodes with similar microstructures were fabricated using LiCoO₂ as the active material and either Li_9.81Sn_0.81P_2.19S₁₂ or Li₁₀GeP₂S₁₂ as the solid electrolyte. The composite with Li_9.81Sn_0.81P_2.19S₁₂ exhibited higher capacity retention and coulombic efficiency with increasing C-rates at 1.9–3.6 V vs. In-Li than that with Li₁₀GeP₂S₁₂. Moreover, when charging–discharging at 1.9–3.8 V, where the expansion and shrinkage of LiCoO₂ were greater those at 1.9–3.6 V, the composite with Li_9.81Sn_0.81P_2.19S₁₂ exhibited a higher capacity, capacity retention, and Coulombic efficiency than those of the composite with Li₁₀GeP₂S₁₂. These results are attributed to the high elastic modulus, high yield stress, and volumetrically-large elastic-deformability, which enable Li_9.81Sn_0.81P_2.19S₁₂ to reversibly deform while maintaining contact with LiCoO₂, unlike Li₁₀GeP₂S₁₂. These results demonstrate that solid electrolytes with low elastic moduli are not absolutely suitable for all-solid-state batteries, and that a high yield stress and volumetrically-large elastic-deformability are especially significant for reversible deformation. These findings provide new insights for the development of composite electrodes for all-solid-state batteries.

Mechanically rechargeable zinc-air batteries (MR-ZABs), in which the zinc anodes of the zinc-air batteries can be mechanically replaced, are attracting attention. The zinc anode of MR-ZAB must be easily replaceable, but with the conventional zinc anode using zinc powder, there is concern about clogging of the zinc powder, and it is difficult to remove the zinc oxide adhered inside the battery after use.

Therefore, we propose a method to make it easier to attach and remove the zinc anode by using the core as a zinc carrier and integrating it with the zinc. In addition, the zinc oxide that was produced by discharging reaction can be reused as a zinc anode by reducing it on the core metal with a separate plating tank. The results of this study show that the use of a metal core as a zinc carrier enables fuel replacement and repeated utilization of the metal core. It was also observed that the discharge performance was higher than with zinc powder due to better contact with the current collector. Furthermore, the amount of zinc produced can be varied by changing the feed rate and the length of the charging tank to match the amount of zinc used.

Anodes containing Si and SiOx are promising candidates for the fabrication of high energy density Li-ion batteries (LIBs). However, despite their specific capacity advantages, maintaining a sustainable cycling performance remains challenging due to their significant volume expansion and contraction. To enhance the interfacial stability of SiOx, this study uses an electrolyte containing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (D2) as an electrolyte additive and focuses on the solid electrolyte interphase (SEI) formed on the electrode surface. The reduction of D2 forms a robust LiF-based SEI along with a D2-specific fluoroalkyl component, which sufficiently stabilizes the SiOx interface. Therefore, the electrolyte containing D2 contributes not only to improving the charge-discharge cycle life and reducing resistance but also to suppressing gas generation within the battery system. To elucidate the mechanism of performance enhancement by D2, this study employs a wide range of analytical techniques, such as AC impedance spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and time of flight secondary ion mass spectrometry (TOF-SIMS), along with density functional theory (DFT) calculations to predict the reaction pathways of D2. These experimental and theoretical analyses demonstrate that D2 is an excellent additive for anode materials containing SiOx.

Garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZT) is one of the most promising solid electrolytes for all solid-state batteries due to its relatively high Li-ion conductivity and electrochemical stability against Li metal anode. However, the presence of pores and voids in the electrolyte causes short circuit due to lithium dendrites growth. In the present study, the effects of Li₂WO₄ (LWO) and Al₂O₃ sintering aids on the densification of LLZT were investigated to decrease the pores and voids and thereby to improve the tolerance for Li dendrite growth. Both sintering aids were effective for improving the densification; however, their effects were totally different. While 2 wt% Al₂O₃ significantly enhanced the grain growth, 4 wt% LWO gave smaller grains of uniform size distribution (3–5 µm). Simultaneous addition of 4 wt% LWO and 2 wt% Al₂O₃ gave relatively larger grains (5–20 µm) with very few voids, and a very high relative density of 99.3 % was obtained. The critical current density (CCD) was improved from 0.2 to 0.4 mA cm⁻². Reducing the amount of lanthanum in LLZT led to the formation of lithium zirconate as a self-forming sintering aid and achieved a higher relative density (99.7 %) for La-deficient (6 %) LLZT with 4 wt% LWO and 2 wt% Al₂O₃. The CCD was further improved to 0.6 mA cm⁻².

Lithium–sulfur (Li–S) rechargeable batteries, LSBs, have been reported to possess high gravimetric energy densities (GEDs) of over 500 Wh kg_(cell)⁻¹ at the single-cell level (including weights of battery tabs and cases) and are greatly anticipated as one of the next-generation lightweight batteries. However, GED and safety demonstrations of the LSBs with practical battery cell designs are limited, and their commercialization has been slow. Here, we created newly designed LSB pouch cells named LiLiSPRing-model ADETAMA, using practical approaches, combining sulfurized polyacrylonitrile (SPAN; ADEKA AMERANSA SAM series) as the cathode active material and an Al-resin film (trilayer Al/PET/Al) as the cathode current collector, which have been reported to exert remarkable rechargeable battery performances. The LSB (Li–SPAN) pouch cell, SPAN/Al-resin film cathode | high-concentrated ether-based electrolyte solution | Li–metal anode (Li–SPAN/Al-resin film), weighing 25.2 g (including weights of battery tabs and pouch cases), exhibited discharge characteristics of 9.27 Ah capacity and 1.50 V average voltage at 3rd cycle in 0.05C-rate, 0.30 V cut-off, 25 °C, and cell pressurization of 507 kPa (5.0 atm). We have succeeded in achieving a high GED of 552 Wh kg_(cell)⁻¹, well above the GEDs of lithium-ion rechargeable batteries in commercial use or under development. While 9 Ah, 550 Wh kg_(cell)⁻¹-class SPAN cells cannot yet sustain stable long-term charge-and-discharge cycling, similar <1 Ah single-layer pouch cells indicate potential for several dozen cycles. In addition to the lightweight characteristic, the Li–SPAN/Al-resin film pouch cell with 503 Wh kg_(cell)⁻¹ (9.21 Ah and 14.1 Wh) exhibited a high ignition safety property in a nail-penetration test for a short-circuit. These results obtained by the state-of-the-art technology would contribute to the practical application of next-generation LSBs and lead to the adoption of lightweight batteries in flying vehicles such as high-altitude platform station (HAPS) or others.

Proton-coupled electron transfer (PCET) plays a critical role in processes ranging from biological energy conversion to catalysis and materials science. In this study, the effect of a phenyl substituent on hydroquinone reactivity is examined through the PCET reaction between 2-phenylbenzene-1,4-diol (Ph-H₂Q) and electrogenerated superoxide radical anion (O₂^•−) in N,N-dimethylformamide. Using cyclic voltammetry (CV) and in situ electrolytic electron spin resonance (ESR) spectroscopy, it was demonstrated that Ph-H₂Q undergoes a concerted two-proton-coupled electron transfer (2PCET) process. The CV profiles show that in the presence of Ph-H₂Q the usual reversible dioxygen/O₂^•− redox couple becomes irreversible, indicating that the initial proton transfer (PT) from Ph-H₂Q to O₂^•− is followed by an electron transfer and a subsequent PT to yield the quinone radical anion (Ph-Q^•−). The ESR spectra confirmed the formation of Ph-Q^•− via characteristic hyperfine splitting, with no significant spin delocalization onto the phenyl ring. Density functional theory calculations revealed that the frontier orbital energy variations along the 2PCET pathway for Ph-H₂Q closely resemble those of unsubstituted hydroquinone, indicating minimal inductive or resonance effects from the phenyl group. Although the phenyl substituent is electronically similar to hydrogen in terms of PCET mechanism, its larger steric bulk slightly diminishes reactivity at higher concentrations. The thermodynamic analysis further confirmed that the overall 2PCET process is exergonic. These findings elucidate the subtle role of the phenyl substituent in PCET reactions, with implications for the rational design of hydroquinone-based redox systems.

Thiosulfate leaching of gold is a promising alternative to cyanidation due to its low toxicity and reduced environmental impact. We proposed displacement deposition (cementation) onto silicon powder for gold recovery from ammonium thiosulfate leaching solutions. However, the overall process from the leaching of solid gold to the separation of recovered gold has not been demonstrated. In this study, we present the leaching of a commercially available gold foil (94.43 wt% gold, 4.90 wt% silver, and 0.66 wt% copper) as a model of gold metal, the cementation of gold onto silicon powder in the pregnant solution, and the dissolution of silicon to separate the gold deposits. The gold metal dissolved completely in the leaching solution, and 100 % of dissolved gold was recovered via silicon powder cementation, while avoiding the co-recovery of copper used as an oxidizing agent for gold dissolution. The silicon powder was removed by potassium hydroxide treatment, yielding metal particles mainly composed of gold with minor silver originating from the gold foil. We further investigated silver deposition behavior using both gold and silver foils, indicating the formation of gold-silver mixed particles. This study demonstrates the applicability of a clean and sustainable gold recovery process from urban mine resources.

The electrooxidative allylation of a carbamate was successfully demonstrated using 3-propylsulfonic acid-functionalized silica gel (Si-SCX-2). It was shown that the electrochemical oxidation of the carbamate as a first step yields the corresponding N-acyliminium ion equivalent at room temperature, and the reaction of the N-acyliminium ion equivalent with allyltrimethylsilane as a next step leads to allylation without the use of Lewis acids. It was also found that the HBF₄ generated by the cation exchange reaction between the Si-SCX-2 and the supporting electrolyte plays an important role in this reaction system.

Polymer electrolyte fuel cells (PEFCs) need to achieve long-term durability for widespread commercialization. Chemical degradation of the perfluorosulfonic acid (PFSA) membrane caused by radical species (·OH) can be mitigated by adding cerium ions as radical scavengers; however, cerium ions migrate within the membrane, potentially reducing their effectiveness. In this study, we have developed an operando high-energy microbeam X-ray fluorescence (XRF) system to visualize the distribution of cerium ions in the electrolyte membrane and catalyst layers under fuel cell operating conditions. Scanning across the membrane and catalyst layers with sub-micron spatial resolution directly observes rapid migration of cerium ions from the membrane to the cathode side immediately after current loading. Conversely, when the cell is returned to open-circuit voltage (OCV), the cerium ions diffuse back into the membrane. The amount of migrated cerium ions depends on the current density, suggesting that higher current loads accelerate cerium ion transport toward the cathode.