In-Depth Understanding of the Electrochemical Behavior of Vse2 Cathode in Aqueous Zn-Ion Batteries and its Zinc Ion Storage Mechanism

Aqueous Zn-ion batteries (ZIBs) become the promising candidates for large-scale energy storage due to their low cost, high theoretical capacity and intrinsic safety. The develpomet of cathode materials with high specific capacity and long cycle life is still the mian bottleneck, which seriously restricts the application of ZIBs. Layered VSe2 with high electronic conductivity, low ion migration barriers and large interlayer spacing is theoretically a potential host material for zinc ion storage. However, the electrochemical process of VSe2 cathode is complicated over large voltage range, especially at the high potential. In this light, herein, the electrochemical behavior of the VSe2 electrodes were verified at different potential window. Experimental results and material characterizations show that with the intercalation/deintercalation of Zn2+/H+ in the host material, VSe2 elecrtodes undergo an in-situ electrochemical activation process at higher potential during the first charge. The activation process caused a obviously valence state change and induced an in-situ phase transformation from VSe2 to ZnxV2O5·nH2O. In the subsequent cycles, the electrochemical activated VSe2 (ZnxV2O5·nH2O) electrode with high valence state and subordinated porous structure become the new host for Zn-ion storage, significantly enhancing the capacity of the as-prepared ZIBs.