Cathodes Based on Mg Ions Intercalated into Oxygen-Vacant Ammonium Vanadate Nanoribbons for Prolonged Cyclic Stability of Aqueous Zinc-Ion Batteries

Ammonium vanadate (NH 4 V 4 O 10, NVO) as a cathode for aqueous zinc-ion batteries (AZIBs) is receiving increasing attention owing to its high specific capacity, multielectron redox capability, and facile synthesis. However, its practical application is still restricted by its unstable structure and slow electrochemical kinetics. Here, we report Mg ion-intercalated ammonium vanadate nanoribbons with oxygen vacancies (Mg–NVO v ) cathodes prepared by a hydrothermal-annealing method. Mg 2+ ions intercalate into NVO, increasing the layer spacing from 10.7 to 11.87 Å, which weakens the charge force of lattice O and Zn ions, and play as pillar ions to improve structural stability. The annealing process is effective to eliminate the partial ammonium ion (NH 4 + ) between layers of NVO nanoribbons and generate oxygen vacancies, which improves the Zn ion storage sites and transport rate. The engineered Mg–NVO v nanoribbon cathode demonstrates excellent electrochemical performance, achieving a capacity retention of 82.5% after 3,500 cycles at 5 A g –1, along with a high specific capacity (411.44 mA h g –1 ) and energy density (320 W h kg –1 ) at 0.2 A g –1, which are significantly higher than those of NVO. The results provide a way for promoting the practical application of NVO cathodes in AZIBs.