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

Abstract

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 Mn 2+ 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 Mn 2+ -modified (NH 4 ) 2 V 10 O 25 •8H 2 O (MNVO) indicates the possibility of its superior rate performance. Incorporating a small amount of Mn 2+ into (NH 4 ) 2 V 10 O 25 •8H 2 O (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 Zn 2+ 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.