Cu _<i>x</i> O as an ultra‐stable voltage plateaus and long‐life cathode material in aqueous ammonium‐ion batteries

Abstract Aqueous ammonium batteries (AAIBs) gain extensive attention because of their merits, such as cost‐effectiveness, eco‐friendliness, and safety. Nevertheless, the limited research on electrode materials impedes their further development. Here, we prepare Cu x O ( x = 1, 2) materials and apply them as cathode materials for AAIBs. The electrodes have a high discharge‐specific capacity and a long and stable charge–discharge plateau. In accordance with density functional theory, the mechanism of NH 4 + storage involves the reversible formation and breaking of hydrogen bonds. Simultaneously, CuO contributes additional electrons and facilitates the rearrangement of internal electrons, thereby enhancing the storage performance of NH 4 + . To further improve the chemical reaction kinetics and address the limited cycle stability of CuO, a composite material composed of CuO and carbon (CuO/C) is developed. The findings demonstrate that CuO/C exhibits superior rate capability, with an initial discharge‐specific capacity reaching 1851 mAh g –1 (0.1 A g –1 ) and improved reversible cycle performance (113 mAh g –1 after 400 cycles) . This study investigates the application of CuO as the cathode material in AAIBs and presents new opportunities for future industrial development.