VOSO ₄ Electrolyte Additive Enabling Ultrahigh Capacity and Superior Cycling Stability of Copper-Intercalated Vanadium Oxides in Aqueous Zinc-Ion Batteries

Vanadium oxides are promising cathode materials for aqueous zinc-ion batteries (AZIBs). However, their practical applications are restricted by rapid capacity decay and poor cycling stability. Herein, a composite electrolyte composed of Zn(OTF)2 and a VOSO4 additive is developed for Cu-intercalated V2O5 cathodes (Cu-VOH) in AZIBs. The as-fabricated batteries deliver an initial specific capacity of 551 mAh g–1 at a current density of 0.1 A g–1 and retain 376 mAh g–1 after 150 cycles. The cell demonstrates superior cycling stability with a capacity retention of 230 mAh g–1 after 5000 cycles at 2 A g–1. The systematic investigations on the charge storage mechanism reveal multifold functions induced by the VOSO4 additive. First, the VOSO4 in the electrolyte is cycle-by-cycle oxidized and deposited on the cathode as additional active materials, consequently enhancing the capacity during cycling. Second, the VOSO4 modifies the side reactions, in which the formation of inert Zn3(OH)2V2O7·2H2O precipitates is decelerated, and the Zn4SO4(OH)6·4H2O precipitates with better cycling reversibility are favored. The regulation on hydroxide precipitate formation consistently reconstructs the cathode surface and induces superior cycling stability. The VOSO4 additive initiates electrolyte-interface engineering, providing a creative strategy for designing high-performance vanadium oxide-based AZIBs.