Synergistic redox reaction of vanadium ions and phosphite ions dedrived high-performance Na₂[(VO)₂(HPO₃)₂(C₂O₄)]·2H₂O cathode material for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have good application prospects in the field of large-scale energy storage. The design and synthesis of high-performance cathode materials are key to promoting the development and application of AZIBs. In this work, the combination of redox active V 4+ cation and HPO 3 2− anion provides excellent zinc-ion (de)intercalation ability. In addition, HPO 3 2− and C 2 O 4 2− anion groups collaborate to construct a stable framework with multi-dimensional zinc-ion transport channels, providing fast and robust pathway for zinc-ion transport. Carbon composites further improve electronic conductivity, shorten ion transport distance, and increase the electrochemical reaction area of Na 2 [(VO) 2 (HPO 3 ) 2 (C 2 O 4 )]·2H 2 O@C (NVPCO@C) cathode material. As a result, NVPCO@C cathode material delivers a high specific capacity over 180 mAh·g −1 at a current density of 40 mA·g −1 . Moreover, NVPCO@30%C cathode material maintains 100 % capacity after 100 cycles. Ex-situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectra confirm the electrochemical activity of V 4+ /HPO 3 2− ions and reveal the zinc-ion storage mechanism.