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

Abstract

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.