Local pH regulation at zinc vanadate cathode by a hierarchical structure for long-life aqueous zinc batteries

Vanadium-based oxides are promising cathode candidates for aqueous zinc batteries, but their cycling stability is unsatisfactory. Herein, a unique hierarchical structured zinc vanadate material, with amorphous nanorod arrays standing on crystalline lamellar plates, is produced by the in-situ electrochemical conditioning from a H0.39V2O5 precursor. The hierarchical cathode achieves a high capacity of 536 mAh/g at 0.1 A/g and 344 mAh/g at 5 A/g. Importantly, a long life of 10,000 cycles with 88% capacity retention is realized at 5 A/g. Finite-element analysis shows that the tip effect of the nanorod arrays accumulates protons near the surface of the hierarchical cathode. The resulting locally low-pH environment prevents vanadium dissolution and formation of inactive Zn3V2O7(OH)2·nH2O during cycling, which ensures the high cycling stability. This work presents insights into local pH regulation to optimize the cycling stability of cathode materials in aqueous zinc batteries.