Iodine‐Mediated Defect Engineering of Vanadyl Phosphate Cathodes for High‐Performance Aqueous Zinc‐Ion Batteries

Abstract Vanadyl phosphate (VOPO₄) is extensively studied as a cathode material for aqueous zinc‐ion batteries (AZIBs). However, due to sluggish ion migration and low electrical conductivity, VOPO₄ typically exhibits moderate specific capacity below 200 mAh g⁻¹. To address these issues, an iodine (I₂)‐mediated etching method is proposed to enhance the electrochemical performance of VOPO₄ for AZIBs. This method effectively regulates structural defects in VOPO₄. Initially, I₂ undergoes a disproportionation reaction with interlayer H₂O in VOPO₄, inducing crystal defects in the nanosheet structure. Additionally, the generated HI reduces V⁵⁺, further introducing oxygen vacancies in VOPO₄. Both experimental and computational results indicate that moderate structural defects in VOPO₄ can synergistically improve the electron transfer and ion diffusion kinetics of the electrode. However, excessive structural defects lead to crystalline amorphization and structural pulverization of VOPO₄, impeding Zn²⁺ migration within the material. Therefore, the iodine‐mediated etched VOPO₄ electrode (VOP‐I4) exhibits a high specific capacity of 249 mAh g⁻¹ at a current density of 0.2 A g⁻¹ and a large energy density of 300 Wh kg⁻¹ at a power density of 246.2 W kg⁻¹, outperforming most reported VOPO₄‐based materials for AZIBs. This study provides a new avenue for developing high‐performance VOPO₄ materials for energy storage applications.