Unveiling Electrochemically Induced Phase Transition of Hierarchical ZnV2O4@C Superstructures Toward Advanced Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries (AZIBs) are promising candidates for large-scale energy storage systems due to their high safety and low cost. Among diverse cathodes, spinel ZnV2O4 (ZVO) becomes more prominent thanks to its high storage capacity and long cycling life. However, the slow diffusion kinetics, vanadium dissolution, and ambiguous zinc-storage mechanism restrict its prospective applications. For this, herein, unique ZVO flower-shaped nano/micro-architectures with carbon coating (ZVO@C) are designed to enhance active electrode-electrolyte sur-/interfaces and reduce ion diffusion distance, while the nano-carbon shell improves electrical conductivity of cathodes and inhibits the active vanadium dissolution. Furthermore, the essential zinc-storage mechanism of ZVO@C is first clarified that the irreversible electrochemically-induced phase formation of ZnV3O8 and Zn3(OH)2V2O7·2H2O during the first cycle, rather than ZVO itself, which are the genuine electroactive phases for following zinc storage. Theoretical calculations reveal that the two newly-formed phases are intrinsically endowed with good conductivity and boosted diffusion kinetics for reversible co-(de)intercalation of Zn2+ and H+. The optimized ZVO@C shows superior cycling stability with 208.7 mAh g-1 after 5000 cycles even at 10 A g-1. Essentially, the contribution provides in-depth insights for intriguing phase transition involved zinc-storage mechanism and promotes commercial applications of vanadium-based cathodes for long-lifespan AZIBs.