Defect-engineered ammonium vanadate nanosheets with expanded interlayers for high-rate aqueous zinc ion batteries

Ammonium vanadate (NH₄V₄O₁₀), characterized by a stable bilayer structure and high theoretical mass capacity, is regarded as a promising cathode material for aqueous zinc ion batteries (AZIBs). Nevertheless, the poor intrinsic conductivity of ammonium vanadate and the propensity to form strong electrostatic interactions between Zn²⁺ ions and the V[sbnd]O layer during cycling result in inferior cycling stability and sluggish kinetics. Herein, a dual-strategy approach integrating glucose-assisted hydrothermal treatment and defect engineering is put forward to boost the specific surface area, enlarge the interlayer spacing, and generate oxygen defects. This exposes more active sites for ion- and electron-transport, promotes electrolyte infiltration, and offers extra space for reversible Zn²⁺ insertion/extraction. Consequently, due to the activation of the cathode after the first cycle, the capacity of NVO_0.3–350 escalates from 264.1 mAh g⁻¹ to 510.1 mAh g⁻¹ at 0.1 A g⁻¹. NVO_0.3–350 showcases excellent stability, with the battery capacity remaining at 214.0 mAh g⁻¹ after 2500 cycles, achieving a capacity retention of 84.2 %, which highlights its long cycle life feature. Subsequently, the storage mechanism of Zn²⁺ in NVO_0.3–350 is analyzed via several ex-situ characterization techniques.