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In the Mn₃O₄electrode, chloride ions are reversibly converted into atomic chlorine species. Trapped Zn²⁺cations aid in stabilizing these chlorine atoms in polychloride species. 

Fluoride is a promising charge carrier for batteries due to its high charge/mass ratio and small radius. Here, we report commercial copper powder exhibits a reversible capacity of up to 222 mA h g −1 in a saturated electrolyte of 16 m KF. This electrolyte suppresses dissolution of CuF 2 , the charged product. Furthermore, the KF solid comprised in the Cu electrode facilitates a high initial capacity. Our results showcase the potential of aqueous fluoride batteries using copper as an electrode. 

Using elemental selenium as an electrode, the redox-active Cu 2+ /Cu + ion is reversibly hosted via the sequential conversion reactions of Se → CuSe → Cu 3 Se 2 → Cu 2 Se. The four-electron redox process from Se to Cu 2 Se produces a high initial specific capacity of 1233 mA h g −1 based on the mass of selenium alone or 472 mA h g −1 based on the mass of Cu 2 Se, the fully discharged product. 

Abstract Aqueous electrolytes typically suffer from poor electrochemical stability; however, eutectic aqueous solutions—25 wt.% LiCl and 62 wt.% H₃PO₄—cooled to −78 °C exhibit a significantly widened stability window. Integrated experimental and simulation results reveal that, upon cooling, Li⁺ions become less hydrated and pair up with Cl⁻, ice‐like water clusters form, and H⋅⋅⋅Cl⁻bonding strengthens. Surprisingly, this low‐temperature solvation structure does not strengthen water molecules’ O−H bond, bucking the conventional wisdom that increasing water's stability requires stiffening the O−H covalent bond. We propose a more general mechanism for water's low temperature inertness in the electrolyte: less favorable solvation of OH⁻and H⁺, the byproducts of hydrogen and oxygen evolution reactions. To showcase this stability, we demonstrate an aqueous Li‐ion battery using LiMn₂O₄cathode and CuSe anode with a high energy density of 109 Wh/kg. These results highlight the potential of aqueous batteries for polar and extraterrestrial missions. 

Abstract Most reported cathodes of nonaqueous dual‐ion batteries (DIBs) host anions via insertion reactions. It is necessary to explore new cathode chemistry to increase the battery energy density. To date, transition metals have yet to be investigated for nonaqueous DIBs, albeit they may offer high capacity in anodic conversion reactions. Here, we report that bulk copper powder exhibits a high reversible capacity of 762 mAh g⁻¹at 3.2 V vs. Li⁺/Li and relatively stable cycling in common organic electrolytes. The operation of the copper electrode is coupled with the transfer of anion charge carriers. An anion exchange membrane separator is employed to prevent Cu²⁺from crossing from the catholyte to the anode side. We designed an unbalanced electrolyte with a more concentrated anolyte than a catholyte. This addresses the concentration overpotential ensued during charge and facilitates the high specific capacity and enhanced reversibility. This finding provides a promising direction for high‐energy DIBs. 

Abstract Dual‐ion batteries that use anions and cations as charge carriers represent a promising energy‐storage technology. However, an uncharted area is to explore transition metals as electrodes to host carbonate in conversion reactions. Here we report the reversible conversion reaction from copper to Cu₂CO₃(OH)₂, where the copper electrode comprising K₂CO₃and KOH solid is self‐sufficient with anion‐charge carriers. This electrode dissociates and associates K⁺ions during battery charge and discharge. The copper active mass and the anion‐bearing cathode exhibit a reversible capacity of 664 mAh g⁻¹and 299 mAh g⁻¹, respectively, and relatively stable cycling in a saturated mixture electrolyte of K₂CO₃and KOH. The results open an avenue to use carbonate as a charge carrier for batteries to serve for the consumption and storage of CO₂.