Hierarchically structured spherical nickel cobalt layered double hydroxides particles grown on biomass porous carbon as an advanced electrode for high specific energy asymmetric supercapacitor

•BPC with a high specific surface area is used as a conductive carbon layer.•Hierarchically structured spherical NiCo-LDHs are successfully anchored on the surface of BPC.•The effects of nickel-cobalt molar ratio (R) on the NiCo-LDHs/BPC composite are detailedly studied.•The ASC device shows superhigh specific energy and excellent cycle stability.