Regulating the Intermediate Process of Zinc–Bismuth Batteries by Iodide Ions

Neutral aqueous electrolytes are more compatible with the anode of zinc metal batteries than alkaline electrolytes. Previous reports have shown that Zn||Bi 2 O 3 batteries with mild electrolytes have not been able to function effectively, though Bi 2 O 3 stands out as a promising cathode material with a low cost and potentially high capacity. Herein, iodide ions are introduced as a multifunctional electrolyte additive, allowing for a reversible multielectron conversion reaction of Bi(0) ↔ Bi(III) in mild aqueous electrolyte. Iodide ions significantly alter the intermediate reaction steps, leading to a kinetically favorable mechanism through coordination with Bi 3+ to continuously refresh and activate the interface. The resulting secondary neutral Zn||Bi 2 O 3 battery delivers a high specific capacity (1960 mAh cm –3 ), exceptional rate performance, and remarkable cycling stability (1225 mAh cm –3 at 10 A g –1, retaining 85% after 1500 cycles) with the conversion efficiency close to 100% per cycle. This work provides an energetic perspective for reversible battery chemistry.