“Water-in-Salt” Electrolyte Suppressed MnVOPO4·2H2O Cathode Dissolution for Stable High-Voltage Platform and Cycling Performance for Aqueous Zinc Metal Battery

Abstract

Vanadium-based materials have the advantages of abundant valence states and stable structures, having great application potential as cathode materials in metal-ion batteries. However, their low voltage and vanadium dissolution in traditional water-based electrolytes greatly limit their application and development in aqueous zinc metal batteries (AZMBs). Herein, phosphate- and vanadium-based cathode materials (MnVOPO4·2H2O) with stacked layers and few defects were prepared via a condensation reflux method and then combined with a high-concentration electrolyte (21 m LiTFSI + 1 M Zn(CF3SO3)2) to address these limitations. The specific capacity and cycle stability accompanying the stable high voltage of 1.39 V were significantly enhanced compared with those for the traditional electrolyte of 3 M Zn(CF3SO3)2, benefiting from the suppressed vanadium dissolution. The cathode materials of MnVOPO4·2H2O achieved a high specific capacity of 152 mAh g−1 at 0.2 A g−1, with a retention rate of 86% after 100 cycles for AZMBs. A high energy density of 211.78 Wh kg−1 was also achieved. This strategy could illuminate the significance of electrolyte modification and provide potential high-voltage cathode materials for AZMBs and other rechargeable batteries.