Design of metal phosphite decorated sponge materials for high-performance flexible battery-type supercapacitors

In this work, iron and zinc phosphite [FeP and Zn3P2 (ZnP)] crystals were individually decorated on a flexible, freestanding, and three-dimensional (3D) graphene sponge material (GSM) through a facile and cost-effective electrodeposition method. With the synergistic effect between metal phosphite (MP) particles and graphene, 3D FeP/GSM and ZnP/GSM electrodes displayed excellent electrochemical performances with high specific capacitances of 1872 and 908 F/g at a current density of 1 A/g and remarkable cycling stabilities (85% and 70% retention after 10 000 cycles), respectively. Owing to their superior properties, two asymmetric supercapacitor (ASC) circuits were assembled by employing FeP/GSM and ZnP/GSM as the positive electrodes and GSM as the negative electrode. The FeP/GSM//GSM and ZnP/GSM//GSM ASCs exhibited high energy densities of 265 and 62 Wh/kg with high power densities of 5545 and 3050 W/kg, respectively. Furthermore, as-designed devices showed great stability as retaining 80% and 70% of their initial capacitance after a consecutive 10 000 cycles of galvanostatic charge-discharge processes. These results demonstrated that MP/GSMs can be used as promising electrode materials for flexible ASC applications.