Low-defect potassium vanadyl hexacyanoferrate cathode material with high specific capacity for aqueous zinc ion batteries

Prussian blue analogues (PBAs) are considered to be one of the most promising cathode materials for aqueous zinc-ion batteries (AZIBs). However, the low specific capacity due to defects and low activity has become the major problem limiting their application. In this work, a potassium vanadyl hexacyanoferrate K_0.37VO[Fe(CN)₆]_0.61·2.6H₂O was synthesized by ethanol-assisted co-precipitation. Controlled growth by ethanol addition results in smaller particle size and fewer defects in K_0.37VO[Fe(CN)₆]_0.61·2.6H₂O, leading to excellent zinc ion storage properties. The K_0.37VO[Fe(CN)₆]_0.61·2.6H₂O cathode material exhibits a high specific capacity of 190 mAh·g⁻¹ at 0.1 A·g⁻¹ and an outstanding rate performance of 160 mAh·g⁻¹ at 2 A·g⁻¹. Ex-situ characterization technologies reveal that the zinc-ion storage process is involve with redox reaction of Fe²⁺/Fe³⁺ and V³⁺/V⁴⁺/V⁵⁺, as well as phase transition.