Mn²⁺-Modified Ammonium Vanadate as High Rate and Long Cycle Life Cathode for Aqueous Zinc Ion Batteries

Ammonium vanadate is a widely used cathode material in aqueous zinc ion batteries (AZIBs) due to its high specific capacity. Nevertheless, the cycling stability and performance at a high rate still need to be further improved. This study demonstrates that Mn²⁺ is an ideal doped ion to modify the rate and cycling performance of the ammonium vanadate. The calculated low energy barrier (peaking at 0.422 eV) along the migration pathway in Mn²⁺-modified (NH4)2V10O25·8H2O (MNVO) indicates the possibility of its superior rate performance. Incorporating a small amount of Mn²⁺ into (NH4)2V10O25·8H2O (NVO) to replace excess ammonium ions can effectively prevent structural collapse caused by the deamination process and has a positive effect on improving the diffusion rate of Zn²⁺ in NVO. The as-prepared cathode materials exhibit high-rate properties and stable cycling stability; they display a capacity retention of 85.6% over 10,000 cycles at 20 A g⁻¹ with a capacity of 162.3 mA h g⁻¹. The MNVO cathode displays high reversibility of rate performance when it is performed at various current densities of 0.5, 3, 6, 9, 12, 15, 18, 20, 17, 14, 11, 8, 5, 2, and 0.5 A g⁻¹. These results highlight the potential of MNVO for use in advanced energy storage devices.