Dual-Ion Co-Doped Ammonium Vanadate for Simultaneous Enhancement of Kinetics and Stability in Zn-Ion Batteries

Ammonium vanadates are promising for aqueous zinc-ion batteries due to their high capacity and low cost, yet their practical use is limited by slow ion kinetics and structural instability. Here, we develop a Na⁺/F^- codoping strategy to synergistically tailor the structure of (NH₄)₂V₆O₁₆, thereby achieving concurrent improvement in both Zn²⁺ diffusion kinetics and structural stability. The optimized NaNVOF cathode achieves 613 mAh g^-1 at 0.2 A g^-1 and retains 92.2% capacity after 4000 cycles at 10 A g^-1, surpassing most previously reported vanadium-based cathodes. Experiments and density functional theory (DFT) reveal that Na⁺ doping expands the interlayer spacing and weakens the electrostatic interaction with Zn²⁺, thereby enhancing ion transport kinetics. Meanwhile, F^- doping strengthens the structural stability through the formation of robust V-F bonds, while its strong electronegativity optimizes charge distribution and effectively facilitates electron transfer. Furthermore, the codoping induces a hydrophobic interface that provides additional protection against electrolyte corrosion. The synergistic effects of these mechanisms significantly improve the thermodynamic stability and cycling performance of the material. This work provides an effective strategy and theoretical foundation for resolving the inherent trade-off between kinetics and stability in layered cathode materials.