Oxygen-Related Defect Engineering of Amorphous Vanadium Pentoxide Cathode for Achieving High-Performance Thin-Film Aqueous Zinc-Ion Batteries

Thin-film aqueous zinc-ion batteries are expected to serve as next-generation energy storage devices that are both low-cost and safe. However, to realize practical energy storage devices based on zinc-ion batteries, it is necessary to develop reliable, high-capacity cathode materials. In this study, we prepared a V₂O₅-based thin-film electrode and investigated the effect of varying the Ar pressure during radio frequency magnetron sputtering of V₂O₅, a representative cathode material in thin-film zinc-ion batteries, to control the number of oxygen vacancies in the oxide lattice. The optimized V₂O₅ thin-film electrode exhibited enhanced electrochemical activities, low degree of polarization, improved ion diffusion, and increased electrical conductivities. Specifically, an oxygen-deficient V₂O_5-x thin-film prepared by sputtering under high pressure exhibited a high rate capability (57.2 mAh g^-1 at 20 C) and superior electrochemical performance (105.2 mAh g^-1 for up to 1000 cycles at a current density of 5 C). The mechanism for the performance enhancement was revealed by density functional theory calculations, which showed that the oxygen-deficient V₂O_5-x had a lower Zn²⁺-ion diffusion energy barrier than that of pristine V₂O₅. This defect engineering strategy for tuning the oxidation state should aid in designing high-performance cathodes for advanced thin-film aqueous battery chemistry.