Dual-Modification of Ammonium Vanadate Cathodes for Aqueous Zinc-Ion Batteries

Abstract

The deployment of grid-level energy storage systems places stringent demands on battery technologies, particularly with respect to safety, cost, and long-term reliability. Aqueous zinc-ion batteries offer inherent advantages by employing nonflammable electrolytes and widely available materials. Even so, their practical operation is frequently hampered by slow electrochemical responses and progressive structural degradation of vanadium-based cathodes during repeated Zn²⁺ insertion. Layered ammonium vanadate (NH₄V₄O₁₀, NVO) possesses an interlayer-expanded architecture enabled by pre-intercalated ammonium ions, but its practical electrochemical performance remains limited by low electronic conductivity and gradual lattice deterioration. To address these challenges, nitrogen and polyvinylpyrrolidone incorporated ammonium vanadate cathode (N-NVO@PVP) was synthesized via a hydrothermal process followed by calcination. This dual modification simultaneously alters the interlayer environment and local electronic structure, leading to an expanded layered framework, as reflected by the shift of the (001) diffraction peak from 8.54° to 7.84°, and the formation of defect-associated domains. Spectroscopic characterization reveals an increased proportion of reduced vanadium species together with nitrogen-related chemical states, confirming effective modulation of the host lattice. As a result of these structural and electronic modifications, the N-NVO@PVP electrode delivers a reversible capacity of 415 mAh g⁻¹ at 0.1 A g⁻¹, along with enhanced rate capability and substantially improved cycling stability. After 2000 charge–discharge cycles, the modified electrode retains approximately 70% of its initial capacity, whereas pristine NVO retains only 35.7% under identical conditions. These findings indicate that concurrent interlayer regulation and defect engineering can effectively mitigate the intrinsic limitations of layered vanadate cathodes, suggesting N-NVO@PVP as a promising alternative cathode material for next generation energy storage applications.