Construction of sandwich‐structured Co ₃ O ₄ –Fe ₃ O ₄ composite electrode with free binder for high‐performance all‐solid‐state supercapacitor

Abstract With the rapid development of flexible equipment, high‐energy/‐power requirements have been proposed for energy storage devices. Nevertheless, the poor conductivities of metallic oxides and their low levels of transmission of electrons/ions hinder their widespread application. Here, a sandwich‐structured Co 3 O 4 –Fe 3 O 4 (CFO) composite with binder‐free was synthesized on a carbon cloth substrate via co‐precipitation and partial ion exchange. The appropriate substitution of Co 3 O 4 with Fe 3 O 4 is favorable in promoting the rapid transfer of electrolyte ions and alleviating changes in volume during the electrochemical studies. When the duration of the substitution reaction is 20 min, the obtained electrode delivers a maximum specific capacitance of 1196.2 F g −1 at a current density of 1 A g −1 and a superior capacity retention of ~ 71% when the current density varies from 1 to 30 A g −1 . Furthermore, the fabricated CFO//activated carbon flexible all‐solid‐state supercapacitor exhibits a respective maximum energy and power density of 68.7 Wh kg −1 and 16,000 W kg −1 and excellent flexibility. It also displays a specific capacity retention of 81.3% under four continuous bending states at a current density of 6 A g −1 over 10,000 cycles. These remarkable electrochemical characteristics suggest that the sandwich‐structured CFO composite displays considerable potential for application in flexible high‐energy/‐power supercapacitors.