Oxygen vacancies enhance supercapacitive performance of CuCo2O4 in high-energy-density asymmetric supercapacitors

Although the emerging CuCo2O4 electrode material proves to be promising for use in energy-storage applications, its slow reaction kinetics and poor conductivity limit its broad utilisation. To address this challenging fundamental issue, herein, oxygen-vacancy-enriched CuCo2O4 nanoflowers is prepared using a facile hydrothermal method followed by thermal treatment in a hypoxic atmosphere. Because of the presence of oxygen defect sites and impurity bands, such flower-like CuCo2O4 nanomaterials with large specific surface areas demonstrate much superior electrical conductivity and favourable hydrophilic properties, which are highly encouraging for supercapacitor applications. Impressively, when evaluated as an active electrode material, it exhibits a remarkable specific capacitance (1006 F g(-1) at 1 A g(-1), i.e., 1.2 F cm(-2) at 1.2 mA cm(-2)), excellent rate capability (69.4% capacitance retention at 20 A g(-1)) and ultra-long cycling lifespan (85.5% specific capacitance retention after 10,000 cycles). Moreover, when being paired with activated carbon, the quasi-solid-state asymmetric supercapacitors provide a maximum energy density of 58.7 Wh kg(-1) at a power density of 800 W kg(-1) and extraordinary cycling stability (71.2% retention after 10,000 cycles). These results firmly verify that the proper incorporation of oxygen vacancies into metal oxides provides a new efficient pathway to advance electrode behaviours.