Lowered phase transition temperature of VO2(m) via molybdenum doping toward efficient aqueous zinc-ion batteries

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.