Valence modulation in hollow carbon nanosphere/manganese oxide composite for high performance supercapacitor

A hollow graphitized carbon nanosphere/mixed-valence manganese oxide composite (HMO) was successfully synthesized via a SiO2 template and impregnation-reduction method. The chemical valence and content of manganese species were controlled by the reaction time of impregnation-reduction process. The HMO composite obtained by impregnation-reduction for 6 h (HMO-6) shows a large specific capacitance (292.5 F g(-1) at 0.5 A g(-1)), excellent cycling stability (96.8% after 5000 cycles at 1 A g(-1)) and rate performance (155.3 F g(-1) at 10 A g(-1)). The interior graphitized carbon shell, hollow porous structure, higher surface area, and appropriate percentage of Mn2+, Mn3+ and Mn4+ species are responsible for the superior electrochemical performance. The asymmetric supercapacitor composed of HMO-6 and hollow graphitized carbon nanosphere (HCS) also shows a superior electrochemical performance in all-solid-state asymmetric supercapacitor. The design and synthesis strategy of electrode materials offers a promising approach to develop high-performance manganese oxide supercapacitors.