Energy storage mechanism and electrochemical performance of Cu2O/rGO as advanced cathode for aqueous zinc ion batteries

Aqueous zinc-ion batteries (AZIBs) are expected to be used for large-scale energy storage, due to their environmentally friendly, low cost, abundant global stockpile, high capacity. However, the development of high-performance cathodic materials still faces huge challenges. Herein, cuprous oxide (Cu2O) and Cu2O/reduced graphene oxide (rGO) are first reported as a cathode for AZIBs respectively. Simultaneously, the Zn//Cu2O/rGO battery exhibits significantly enhanced electrochemical performance with a high rate performance and an excellent cycle lifespan (139 mAh g−1 after 500 cycles at 1 A g−1 with 95.9% capacity retention), which is extremely excellent in copper-based zinc-ion battery cathode materials. Moreover, ex-situ XRD and XPS results have revealed a hybrid mechanism involving conversion reactions and classical insertion/extraction reaction. when the Zn//Cu2O/rGO battery discharged from the initial state to 0.2 V, part of Cu2O will be reduced to Cu0 with the insertion of zinc ions; when the Zn//Cu2O/rGO battery charged to 1.1 V, Cu0 is completely oxidized to Cu2O with the deintercalation of zinc ions, and only Cu+ is existing at this time. The results reveal the energy storage mechanism of the Cu2O/rGO electrode, which will provide significant help for the research on copper based cathodic materials and expect to be further explored in other ion-batteries.