Why does the capacity of vanadium selenide based aqueous zinc ion batteries continue to increase during long cycles?

At present, rechargeable aqueous zinc ion batteries (RZIBs) have become a rising star and highly sought after in the field of new energy. While vanadium-based RZIBs often exhibit an anomaly of increased long-cycle capacity, which has not been explored in depth. Nevertheless, it is critical to understand this phenomenon to develop high-performance RZIBs. Therefore, this study investigated the growth mechanism of VSe2-based RZIBs using VSe2/MXene as the cathode material via in-situ and ex-situ characterization techniques and electrochemical measurements. Experimental results indicated that with the interaction/extraction of Zn2+/H+ in the host material during cycling, an obvious oxidation reaction occurs at high voltage, and the formed vanadium oxide further reacts with Zn2+ from the electrolyte. As a result, Zn0.25V2O5·H2O is continuously produced and accumulated, contributing to the increasing capacity of the prepared RZIBs.