Sodium ion stabilized ammonium vanadate as a high-performance aqueous zinc-ion battery cathode

Aqueous zinc ion battery (AZIBs) has become a research hotspot because of its advantages of low cost, high safety and environmental protection. However, AZIBs still face challenges in achieving excellent rate performance, long service life, and wide temperature range due to slow Zn2+ diffusion kinetics. In this work, we developed a nonstoichiometric Na0.3(NH4)0.6V4O10·0.4H2O(NVO-Na) cathode material for AZIBs. The combined effects of pre-intercalated Na+ and structural water in NVO enhance the diffusion kinetic, reduce the electrostatic repulsion of Zn2+ (de)intercalation and keep the layer structure stable. The results show that NVO-Na cathode delivers an impressive specific capacity of 400.2 mAh g−1 at a current density of 0.1 Ag −1 and an excellent capacity retention of 97.2 % after 2000 cycles at 10 A g−1. In addition, the reversible intercalation mechanism of zinc ions in NVO-Na was investigated through ex-situ XRD and XPS analysis. The combined effect of pre-intercalated Na+, structural H2O molecules and remaining NH4+ keeps the layer structure stable during the reversible Zn2+ (de)intercalation reaction. This modification method provides a promising direction for the preparation of high-performance AZIBs cathode materials.