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

Abstract A hollow graphitized carbon nanosphere/mixed-valence manganese oxide composite (HMO) was successfully synthesized via a SiO 2 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. Graphical abstract Unlabelled Image Highlights • A new strategy for designing hollow graphitized carbon nanosphere/mixed-valence manganese oxide composites • The electrodes exhibited high specific capacitance, excellent cycle stability and rate capability. • The aqueous and all-solid-state asymmetric supercapacitors deliver high energy and power density. • This multistage design and valence modulation strategy could be extended to other electrode materials. [ABSTRACT FROM AUTHOR]