Energy storage performance and mechanism of the novel copper pyrovanadate Cu3V2O7(OH)2·2H2O cathode for aqueous zinc ion batteries

Abstract Aqueous zinc ion batteries (ZIBs) are expected to be used in large-scale energy storage because of their major merits of high-safety, low cost as well as excellent energy density. However, the discovery of high-performance cathode materials and the exploration of zinc storage mechanism are still facing great challenges. Herein, a new cathode material of copper pyrovanadate Cu3V2O7(OH)2·2H2O (CuVO) is demonstrated to be potential in zinc ion storage. A series of ex-situ characterization results reveal a hybrid mechanism involving phase transitions and classical insertion/extraction reaction. First, zinc ions are embedded into CuVO and replace Cu2+ to form a new phase of Zn3(OH)2V2O7·2H2O (ZnVO), and then repeative intercalation of Zn2+ in the ZnVO lattice dominates the subsequent electrochemical reactions. Meantime, a highly conductive Cu0 matrix is generated upon cycling, which effectively enhance the electronic transport. In addition, electrochemical reaction kinetics demonstrate that the CuVO electrode has a significant capacitance contribution and a fast zinc ion solid-state diffusion rate. As a consequence, the CuVO electrode delivers a high specific discharge capacity of 216 mA h g−1 at 0.1 A g−1, and a high capacity retention of 89.3% after 500 cycles at 0.5 A g−1.