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[Display omitted] • Biomass activated carbon was designed and prepared from expired bread and Ganoderma spores and then composited with graphene. • The specific capacitance of the biomass activated carbon based composite is 290.4F/g at 1 A/g. • The AC improvement can be more effective than a pseudocapacitive material in improving the full device performance. We prepared expired bread activated carbon (AC), ganoderma spore AC and mixed biomass AC by charring and chemical activation methods. The biomass AC based composite was obtained by simple mechanical compounding of graphene and biomass AC. The specific capacitance was 290.47F/g at a current density of 1 A/g. It retained a 99.92% specific capacitance value after 5000 cycles at a current density of 10 A/g. Assembled with hollow NiCo 2 S 4 micron spheres into devices, the specific capacitance of the device was 148.40F/g at a current density of 1 A/g, and the energy density reached 56.11Wh/kg at a power density of 807.98 W/kg. The biomass composite AC based supercapacitor material not only shows a higher specific capacitance value than that of a commercial activated carbon by itself, it also demonstrated significant importance in improving the overall performance of the assembled supercapacitor devices. [ABSTRACT FROM AUTHOR]