Keggin Bicapped-Type Polyoxovanadate as Cathode Material for High-Performance Quasi-Solid-State Zinc-Ion Batteries

Zinc-ion batteries have gained considerable attention owing to their cost-effectiveness, high energy density, and environmental friendliness compared with lithium-ion batteries. However, the development of suitable electrolytes and active materials remains a challenge that must be addressed. In this study, for the first time, Keggin bicapped-type polyoxovanadate K_xH₉(PV₁₄O₄₂) (KPV) was used as the active material for zinc-ion batteries. Owing to the multiple vanadium and oxygen atoms in KPV, the structure can accommodate and provide a fast kinetic reaction to store Zn²⁺, thus benefiting from a highly reversible capacity of 413.3 mAh g^–1 and high energy and power densities of 348.8 Wh kg^–1 and 42.15 kW kg^–1, respectively, and maintaining a Coulombic efficiency of nearly 97.96% after 2000 cycles. In addition, the fabricated cell was subjected to critical temperature testing ranging from −20 to 40 °C and the results showed a remarkably high reversible capacity of 375.5 mAh g^–1 (0.5 A g^–1) at 40 °C. This highlights the potential for designing active materials for high-energy storage devices.