Surface- and interlayer-modified ammonium vanadate cathode for high-performance aqueous Zn-ion batteries

Vanadium-based compounds suffer from the poor intrinsic conductivity, unstable structure, and sluggish reaction kinetics as the cathode materials for aqueous zinc ion batteries. In this work, conductive polymer (polypyrrole, PPy) coating/pre-intercalation is proposed to achieve stable and reversible Zn²⁺ storage in ammonium vanadates (NH₄V₄O₁₀, NVO). The PPy coating on the surface of the NVO nanobelts effectively suppresses material dissolution, and promotes the desolvation of hydrated zinc ions at the interface. The intercalated PPy within the layered structure expands the interlayer spacing, induces the formation of oxygen vacancies, and increases the electronic conductivity, thus accelerating zinc ion diffusion and electron transport kinetics. Benefiting from simultaneous optimization of the surface and interlayer structure, the PPy-NVO electrode demonstrates outstanding electrochemical properties, delivering a high discharge capacity of 455mAh g^-1 at 0.1 A g^-1 and 250mAh g^-1 at 5 A g^-1, maintaining 89 % of its initial capacity after 2500 cycles at 4 A g^-1. Ex situ characterization techniques demonstrate the reversible Zn ions insertion/extraction storage mechanism in the PPy-NVO cathode.