Deep dive into dQ/dV evaluation of NH₄V₄O₁₀ cathode for zinc-ion batteries toward understanding vanadium redox and rate-dependent challenges

Abstract

Aqueous zinc-ion batteries (AZIBs) face significant challenges in developing durable cathode materials with both high capacity and long-term stability, as vanadium-based oxides often exhibit limited rate capability and insufficient mechanistic understanding of their kinetic limitations. To address this issue, the present study provides deep insight into considering differential capacity (dQ/dV) analysis as a powerful diagnostic tool for evaluating NH₄V₄O₁₀ as a zinc-ion battery cathode, uncovering vanadium redox mechanisms and rate-dependent polarization effects that extend beyond prior work focused primarily on initial capacity or overall stability. The dQ/dV analysis provides detailed insights, identifying distinct peaks corresponding to the V5+ ↔ V4+ ↔ V3+ oxidation-state transitions. Critically, these findings are uniquely correlated with diffusion data obtained from galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS), and b-value calculations. This multifaceted correlation provides an unprecedented understanding of the intricate Zn2+ diffusion dynamics within the NH₄V₄O₁₀ structure, demonstrating that high-rate performance is governed not solely by diffusion-controlled mechanisms but is also significantly influenced by surface reactions. This analytical approach not only validates the potential of NH₄V₄O₁₀ as a promising cathode material-delivering a substantial initial capacity of 287.57 mAh g−1 at 0.1 A g−1 but also offers an innovative perspective on kinetic limitations and potential optimization strategies. Collectively, this research enhances mechanistic understanding and facilitates the rational design of advanced cathode materials for high-performance zinc-ion batteries.