Lowered Phase Transition Temperature of VO2(M) via Molybdenum Doping Toward Efficient Aqueous Zinc-Ion Batteries

Abstract

Rechargeable aqueous zinc-ion batteries have attracted considerable attention as large-scale energy storage systems owing to their safety, sustainability, and cost-effectiveness. However, their practical application has been hindered by limited energy density, primarily determined by cathode performance. Among transition metal oxides, vanadium dioxide (VO₂) is particularly appealing due to its layered structure, rich polymorphism, and ability to host Zn²⁺ ions reversibly. The thermally driven transition from insulating VO₂(M) to conductive VO₂(R) enhances charge transport through the metal–insulator transition (MIT). In this work, molybdenum doping is employed to lower the MIT temperature of VO₂(M). Doping reduces the MIT temperature of the VO₂(M) phase to 56.7 °C, resulting in the VO₂(R) phase. Electrochemical measurements reveal that Mo-VO₂(R) cathodes deliver up to ten times higher capacity than the pristine VO₂(M), with 3Mo-VO₂(R) reaching 404.8 mAh g^–1 at 0.1 A g^–1. These findings demonstrate that Mo doping serves as a practical approach to modify VO₂(M) and decrease the MIT temperature, while improving electrochemical performance. Moreover, the heteroatom doping strategy suggests a promising pathway for developing other VO₂ cathodes for efficient rechargeable batteries, which can leverage the heat dissipated in energy storage systems.