<p>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_<i>x</i>O (<i>x</i> = 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 NH₄⁺ 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 NH₄⁺. 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. </p> Graphical abstract <p></p>