Polyaniline-assisted growth of MnO2 ultrathin nanosheets on graphene and porous graphene for asymmetric supercapacitor with enhanced energy density

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.