Role of Defects on the Electrochemical Activity of ZnV2O4 Spinel Cathode for Secondary Zn-Ion Batteries.

Aqueous zinc-ion batteries are emerging as potential candidates to cater low-cost stationary energy storage due to the abundance, economic and ecological benignity of zinc. Among the various cathode materials, vanadium-based compounds have garnered significant attention owing to their structural diversity, Zn2+ storage capability, and high theoretical capacity. The electrochemical activities in these cathodes can be tuned by modulating their structure, particle morphology, surface coatings and local structural (dis)ordering. This study probes the role of disorder on the electrochemical performance of ZnV2O4 spinel cathodes. Without any surface or structural optimization, ZnV2O4 delivers a specific capacity of 150 mAh g-1 with stability over ≈1000 cycles at a current density of 1 A g-1. Using operando and ex situ techniques - including electron microscopy, X-ray diffraction, X-ray absorption, and Raman spectroscopy - it is revealed that initial cycling induces a conversion reaction, forming a disordered Zn-deficient vanadium oxide phase. This phase enables reversible Zn2+ (co)insertion, enhancing long-term performance. This findings highlight the critical role of disorder dynamics in tuning the electrochemical behavior of spinel ZnV2O4, offering valuable insights for designing advanced spinel cathodes for secondary zinc-ion batteries.