Enhancing the kinetics and reversibility of copper batteries via anionic chemistry

Aqueous rechargeable batteries face the challenges of gas evolution side reactions on metal anodes. While copper metal offers a compelling candidate electrode due to its redox potential being above that of the hydrogen generation reaction, the role of coordinating anions in Cu-ion deposition/stripping is not clearly understood. Here, the influence of anions on the behavior of Cu during electrochemical processes is systematically investigated. Among various anions, perchlorate (ClO₄⁻) enables the best reversibility and fastest deposition/stripping kinetics by preventing the formation of the Cu₂O by-product. A Cu‖Cu symmetric cell with a 0.5 m Cu(ClO₄)₂ electrolyte achieves over 7000 hours of stable cycling at 1 mA cm⁻², outperforming as a new benchmark for Cu electrodes. Moreover, a 3 m Cu(ClO₄)₂ electrolyte lowers the freezing point to −112 °C by disrupting the hydrogen-bond network between water molecules. This electrolyte exhibits high ionic conductivity by the weak interaction between Cu²⁺ and ClO₄⁻ ions. Our assembled planar Cu–MnO₂ micro-battery through a dual-plating strategy demonstrates stable cycling for over 350 cycles and low-temperature performance down to −60 °C.