Chromium-doped tunnel-structured VO2(B) nanorods as high-capacity and stable cathode materials for aqueous zinc-ion batteries

Abstract

Vanadium-based oxides have gained significant attention as promising cathode materials for aqueous zinc-ion batteries, owing to their high theoretical capacities, the ability to undergo multi-electron transfer, and varied crystal structures. Despite these advantages, challenges related to structural instability and poor electrical conductivity remain significant barriers to their practical application. In this study, Cr-doped VO₂(B) nanorods were prepared using a hydrothermal treatment process as a promising candidate for aqueous zinc-ion battery cathodes. The multivalent nature of vanadium promotes a variety of redox reactions, resulting in high specific capacities. Chromium ion doping increases oxygen vacancy defects and provides efficient channels for electron transfer. The nanorod morphology offers an increased specific surface area, thereby promoting a higher density of active sites. Positron annihilation lifetime spectroscopy indicates that the generated defects exist in the form of single vacancies. Thanks to the unique tunnel structure and micro-morphology advantages, the CrVO cathode exhibits rapid electron transfer and superior reaction kinetics. Electrochemical performance is optimized at a chromium ion doping concentration of 6 at.%, achieving a high specific capacity of 312.8 mAh g⁻¹ at 0.1 A g⁻¹ and retaining 188.3 mAh g⁻¹ at 5 A g⁻¹ after 2000 cycles, with a remarkable capacity retention of 90.39 %, indicating exceptional long-term cycling stability. This work optimizes the electrochemical performance by introducing different concentrations of chromium ions into the monoclinic VO₂, thereby altering the Cr³⁺/Cr⁶⁺ and V⁴⁺/V⁵⁺ ratio, providing a feasible approach for developing high-performance vanadium-based aqueous zinc-ion battery cathodes.