The partial replacement of Co by Cu in cobaltite to give Cu0.27Co2.73O4 with unique flower-like morphology is found to be very beneficial for supercapacitor–battery hybrid applications. The 3D architecture of the material on a conductive substrate resulted in outstanding supercapattery performance. Asymmetric assembly of the material with activated carbon in a two-electrode system delivered high energy and power densities as well as a high specific capacity. The device also showed excellent cycling stability over 20 000 cycles, with a capacity
retention value of 86.9%
