Enhancement of aqueous hydrogen proton batteries performance through the ineffective ion substitution effect of “overvoltage pre-cycling”

In this study, we discovered that Cu 31 S 16 , when used as the cathode in a battery, exhibits a significant “ineffective ion replacement” phenomenon during the first discharge cycle at low voltage. Specifically, Zn 2+ ions engage in an ion exchange reaction with the surface of the Cu 31 S 16 cathode material, irreversibly replacing Cu 2+ ions. Furthermore, we found that the Cu 2+ ions displaced in this process react with H + at the high voltage discharge plateau to form zinc hydroxysulfate (Zn 4 (OH) 6 SO 4 ·XH 2 O), which subsequently transforms into ZnxCu 4-x (OH) 6 SO 4 ·XH 2 O. The microstructure transitions from the characteristic hexagonal plate-like morphology of Zn 4 (OH) 6 SO 4 ·XH 2 O to the hexagonal prismatic cluster structure of ZnxCu 4-x (OH) 6 SO 4 ·XH 2 O. To address this issue, we propose and implement an “Overvoltage Pre-cycle” method, where trace amounts of Zn 2+ are introduced to replace Cu 2+ at the Cu 31 S 16 cathode. This approach stabilizes the surface structure of the cathode, significantly extending its operational lifespan, providing a more stable discharge plateau, and increasing the discharge duration. Comparative analysis reveals that the effective discharge plateau of AHPBs activated through the first cycle “Overvoltage Precycle” reaches 85.5 %, a 14.1 % improvement over the 71.4 % observed for conventionally activated AHPBs. Additionally, the charge-discharge energy conversion efficiency improves from 82.46 % to 83.35 %. Theoretical calculations indicate that the first cycle “Overvoltage Precycle” enhances the surface structure of Cu 31 S 16 as the cathode, and the Zn 2+ doping improves its electrochemical performance by facilitating efficient H + transport. This further deepens our understanding of the H + /Zn 2+ co-intercalation electrochemical behavior, offering new insights for optimizing cathode surface engineering.