Enhanced Structural Transformation Enabled by Low-Crystalline Vanadium Oxides in Aqueous Zinc-Ion Batteries

Abstract

Aqueous batteries are gaining attention owing to their high safety and cost-effectiveness. Among these, Zn-based aqueous batteries excel because of Zn's low redox potential (−0.76 V vs. SHE), its abundance, and eco-friendliness. However, despite their advantages, challenges, such as low energy density and limited cycle life limit their usage. This study addresses these issues by employing low-crystalline V2O4.86 as a cathode material, enhanced with oxygen vacancies created by controlled annealing time. The structure of low-crystalline V2O4.86 facilitates rapid structural transformation into the highly active phase Zn3+x(OH)2V2O7·2(H2O). Electrochemical tests revealed a 22% capacity improvement for low-crystalline V2O4.86 (360 mAh g−1) over high-crystalline V2O5 (295 mAh g−1) at 0.8 A g−1, attributed to the presence of active oxygen vacancies. Comprehensive structural analysis, spectroscopy, and diffusion path/barrier studies elucidate the underlying mechanisms for the first time, highlighting the potential of oxygen-engineered V2O5. These findings indicate that electrodes engineered with oxygen vacancies offer promising insights in advancing cathode materials for high-performance secondary battery technologies.