Sodium-ion batteries (SIBs) are promising next-generation energy-storage systems, yet their low energy density remains a major challenge. An effective strategy to utilizing low-potential anodes is tuning their electrode potentials with respective to an electrolyte potential window. Herein we propose a molecular framework design of electrolyte solvents to rationally tune sodium electrode potential (E_Na). Extending the alkyl chains of phosphate ester solvents upshifted E_Na by up to 0.32 V (tripropyl phosphate vs. trimethyl phosphate) despite similar donor numbers, indicating a dominant steric effect to weaken the Na⁺ solvation. In contrast, cyclic crown ether 15-crown-5 downshifted E_Na by 0.16 V compared to its linear counterpart (tetraglyme) via the formation of a more stable chelate coordination. Furthermore, the magnitude of these steric/structural effects depended strongly on the cation species, leading to large variations in the Na-Li electrode potential difference (ΔE_Na–Li), from 0.53 V in tripropyl phosphate to 0.10 V in 18-crown-6. Machine-learning-based molecular dynamics simulations revealed that the changes in the cation solvation structure, induced by the solvent molecular framework engineering, are responsible for the observed potential shifts. These findings establish solvent molecular framework engineering as a versatile strategy to tune electrode potentials in battery electrolytes.

Electrochemical conversion of CO₂ into calcium carbide in molten salts has emerged as a promising route for carbon capture and utilization, enabling the production of acetylene, an important industrial chemical. However, continuous operation requires a stable oxygen evolution reaction (OER) at the anode while suppressing competing oxidation of carbonate and carbide species that regenerate CO₂. The anodic reaction mechanism in carbide-containing molten salts remains poorly understood. Here, the anodic behavior and durability of the perovskite oxide La_0.7Sr_0.3FeO_3−δ are investigated in molten NaCl–CaCl₂ at 873 K under controlled anionic environments containing O²⁻, CO₃²⁻, and C₂²⁻. Thermodynamic analysis using potential–pO²⁻ diagrams predicts that carbide oxidation occurs at the most negative potential, followed by carbon, oxide, and carbonate oxidation, which agrees with electrochemical measurements and gas analysis. When O²⁻ and CO₃²⁻ coexist, selective oxygen evolution is achieved with a Faradaic efficiency of 81.4 % and a low corrosion rate of 1.94 × 10⁻⁵ g cm⁻² h⁻¹. In contrast, dissolved C₂²⁻ undergoes anodic oxidation at lower potentials, producing amorphous carbon that accelerates electrode degradation and reduces OER efficiency. These results demonstrate that anodic stability is governed by the local anionic environment, highlighting the importance of maintaining O²⁻ and CO₃²⁻ coexistence while suppressing carbide transport to the anode.

Suppressing zincate crossover is necessary for rechargeable alkaline Zn-MnO₂ rechargeable batteries using electrolytic manganese dioxide (EMD). We benchmarked six commercial separators for their ability to block zincate ions while maintaining the transport of hydroxide ions. Among the separators, FAAM-75-PK (FP75), a commercial anion-exchange membrane, exhibited moderate conductivity (5.8 mS cm⁻¹) with the lowest diffusion coefficient of zincate ions (D_Zn = 2.0 × 10⁻⁸ cm² s⁻¹) and a moderate diffusion coefficient of hydroxide ions (D_OH = 3.5 × 10⁻⁵ cm² s⁻¹), leading to the highest permselectivity (D_OH/D_Zn = 1.7 × 10³). In the galvanostatic discharge–charge tests, FP75 exhibited the best capacity retention of 68 % at the 7th cycle. Characterization of the discharged EMD electrodes revealed that FP75 effectively suppressed ZnMn₂O₄ formation at the cathode, favoring Mn₃O₄ formation instead. The low Zn concentration of 6 ppm in the catholyte is consistent with the favored Mn₃O₄ formation. Beaker-cell tests identify a system-dependent zinc concentration threshold. When the Zn/Mn molar ratio exceeds ∼0.05–0.15, product formation shifts toward ZnMn₂O₄ from Mn₃O₄, and thus, the capacity decay accelerates.

It is important to develop a rechargeable battery that is safe and free from resource risk to replace the current lithium–ion battery in various application fields. We have been conducting research and development of aqueous electrolyte batteries with zinc as the negative electrode (anode) through national programs, Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING, RISING2 and RISING3), commissioned by the New Energy and Industrial Technology Development Organization (NEDO). In RISING2, we demonstrated a full cell that can achieve a target specific energy of 500 Wh kg⁻¹ for a zinc–air system through advancements in elemental technology and full-cell engineering. RISING3 aims to develop a sealed zinc-anode rechargeable battery by developing positive electrode (cathode) materials to replace air electrodes. A notable achievement of this study is proving that the manganese dioxide (MnO₂) prepared through electrolysis (EMD) has good rechargeability in alkaline electrolyte systems, in which the amount of structural water in the oxide determines the discharge capacity for the first one-electron reduction. We also found that the newly developed MnO₂ from the chemical reduction of permanganate (PMD) enables a reversible two-electron reaction even in the electrolyte containing zinc species, in which hetaerolite (ZnMn₂O₄) generally forms to inhibit further electrochemical reactions.

This study demonstrates that the acoustic emission (AE) methodology can be successfully applied to zinc-air battery systems. AE analysis provides real-time insights into mechanically induced events and enables qualitative correlation with electrochemical processes during different operating stages. The method shows high sensitivity to corrosion-driven hydrogen evolution under open-circuit conditions and to oxygen-evolution-related activity in catalyst-based gas diffusion electrodes during charging. In commercial cells, a pronounced increase in AE activity once the cell voltage exceeds 1.8 V indicates the onset of carbon-related degradation, while final AE spikes prior to failure reflect the mechanical manifestation of critical degradation events such as separator rupture or electrode collapse. Overall, the results highlight AE as a powerful diagnostic tool for identifying degradation phenomena in metal–air batteries. Consideration of the observed diffusion limitations and the future implementation of advanced analysis tools, including distribution of relaxation times, equivalent circuit models, and machine-learning approaches, will further refine the understanding of process contributions in next-generation rechargeable battery systems.