Uncovering and Retrieving the Internal Vanadium Migration Caused Voltage Fade in Vanadyl Phosphate Cathode for Aqueous Zinc Batteries
Hua‐Yu Shi, Quanwei Jiang, Tianshun He, Wanlong Wu, Sibo Wang, Xiaoxia Liu, Xiaoqi Sun
Abstract
Aqueous zinc batteries are expected to be applicable for large-scale energy storage. The polyanion cathode materials provide high voltage, but they experience fast voltage fade in the aqueous zinc system. Herein, we uncover the electrolyte-depending degradation mechanisms and propose the corresponding solutions with a representative layered hydrated VOPO 4 (VOP) polyanion cathode material. The voltage fade of VOP in the 10 m ZnCl 2 electrolyte is caused by the transition to VO x, which loses the inductive effect from phosphate. With further suppressed water activity with a “water in bi-salt” electrolyte, on the other hand, the voltage drops as a result of internal V migration from the VOP layer to the space between layers, the latter of which experiences a weakened inductive effect. Accordingly, a deep charging method is applied to retrieve the migrated V and recover the decayed voltage. As a result, the VOP cathode presents stable retention of both the voltage and capacity.