Building a Rechargeable Voltaic Battery via Reversible Oxide Anion Insertion in Copper Electrodes

The Voltaic battery (zinc-copper battery) is the very first battery built by humanity, which plays a critical role in battery development history. However, the inevitable copper ion dissolution-crossover issue leads to its primary battery nature. The ion-exchange membranes and alkaline electrolytes represent two leading approaches to mitigate this issue; however, they incur the disadvantages of complicated battery design, high cost, and zinc anode corrosion. Herein, we build a rechargeable zinc-copper Voltaic battery from simple and cost-effective electrode/electrolyte materials, where the cathode is a nano-sized copper, and the electrolyte is a near-neutral zinc sulfate solution. Interestingly, the copper electrode experiences a synergistic cation-anion insertion reaction, where copper transforms to zinc-copper alloy (Zn_xCu) during discharge and converts to copper (I) oxide (Cu₂O) during charge. Therefore, multivalent Zn²⁺ cations and multivalent O^2- anions participate in the redox reaction, giving a high capacity of ~370 mAh g^-1. Moreover, the structural similarity between Zn_xCu, Cu, and Cu₂O endows high reaction reversibility, leading to impressive cycling of ~500 cycles. Such a concerted cation-anion insertion is rarely reported in the battery field, which offers a mechanism-based approach for developing high-capacity and long-cycling multivalent-ion batteries.