Mn<sup>2+</sup>-Modified Ammonium Vanadate as High\nRate and Long Cycle Life Cathode for Aqueous Zinc Ion Batteries

Ammonium vanadate is a widely used cathode material in\naqueous\nzinc ion batteries (AZIBs) due to its high specific capacity. Nevertheless,\nthe cycling stability and performance at a high rate still need to\nbe further improved. This study demonstrates that Mn<sup>2+</sup> is\nan ideal doped ion to modify the rate and cycling performance of the\nammonium vanadate. The calculated low energy barrier (peaking at 0.422\neV) along the migration pathway in Mn<sup>2+</sup>-modified (NH<sub>4</sub>)<sub>2</sub>V<sub>10</sub>O<sub>25</sub>·8H<sub>2</sub>O (MNVO) indicates the possibility of its superior rate performance.\nIncorporating a small amount of Mn<sup>2+</sup> into (NH<sub>4</sub>)<sub>2</sub>V<sub>10</sub>O<sub>25</sub>·8H<sub>2</sub>O (NVO)\nto replace excess ammonium ions can effectively prevent structural\ncollapse caused by the deamination process and has a positive effect\non improving the diffusion rate of Zn<sup>2+</sup> in NVO. The as-prepared\ncathode materials exhibit high-rate properties and stable cycling\nstability; they display a capacity retention of 85.6% over 10,000\ncycles at 20 A g<sup>−1</sup> with a capacity of 162.3 mA h\ng<sup>−1</sup>. The MNVO cathode displays high reversibility\nof rate performance when it is performed at various current densities\nof 0.5, 3, 6, 9, 12, 15, 18, 20, 17, 14, 11, 8, 5, 2, and 0.5 A g<sup>−1</sup>. These results highlight the potential of MNVO for\nuse in advanced energy storage devices.