▎ 摘　　要

To enhance the energy density of supercapacitors, an asymmetric supercapacitor was prepared by well-matched graphene@MnO2 nanosheets (G@MnO2) as cathode material and porous graphene as anode material. The hierarchical MnO2 ultrathin nanosheets uniformly decorating on graphene sheets were prepared by polyaniline-assisted growth method. The obtained G@MnO2 composite can provide fast electron transfer rate and efficient space to decrease the length of ion diffusion during energy storage. Therefore, the G@MnO2 electrode exhibits a high specific capacitance reaching 245.0 F g(-1) at 0.5 A g(-1), 74.5% of retention ratio at 20 A g(-1). Meanwhile the assembled asymmetric supercapacitor delivers a high energy density of 30.6 W h kg(-1), and a remarkable energy density of 7.9 W h kg(-1) at ultrahigh power density of 11,804 W kg(-1) due to the well-assembly of G@MnO2 and porous graphene with the similar capacitance and rate performance. Moreover, the asymmetric supercapacitor also shows an excellent cycle life with 8.5% loss of the initial specific capacitance after 10,000 cycles. The excellent electrochemical performance of the asymmetric supercapacitor of G@MnO2//porous graphene makes it an attractive candidate for high power and energy storage systems.