Imidazole-Pillared Ammonium Vanadate as a High-Performance Cathode for Aqueous Zinc-Ion Batteries

Layered ammonium vanadates have attracted significant attention as promising cathode materials for aqueous zinc-ion batteries (AZIBs) owing to their high mass-specific capacity and rapid Zn²⁺ transport kinetics, which benefit from low molecular weight and expansive interlayer spacing. However, their practical application is hindered by irreversible structural degradation caused by strong Zn²⁺/V─O electrostatic interactions and weak interlayer N─H···O hydrogen bonding. Herein, we report an organic imidazole-intercalated (NH₄)₂V₄O₉ cathode where imidazole molecules function as robust structural pillars. This molecular pillar engineering strategy simultaneously expands the interlayer spacing and reinforces the host framework, effectively suppressing irreversible de-ammonization and enhancing structural integrity for Zn storage. The optimized cathode exhibits exceptional electrochemical performance, including a high reversible capacity of 431.9 mAh g^-1 at 0.5 A g^-1, outstanding cycling stability with 86.2% capacity retention after 5000 cycles at 10 A g^-1, and remarkable rate capability (155.6 mAh g^-1 at 20 A g^-1). This molecular-level pillar engineering not only resolves the intrinsic structural instability of ammonium vanadates but also offers a universal strategy for designing high-performance layered cathodes in next-generation energy-storage systems.