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

Nickel cobalt layered double hydroxides (NiCo-LDHs) as electroactive material of supercapacitor have attracted a lot of attention during the recent years because of their high theoretical specific capacitance (3000 F g−1), environmental friendliness, and low cost. However, the low electrical conductivity of the NiCo-LDHs and thus leading to low rate capability and poor cycling stability limit their commercial application in practical supercapacitor. Herein, biomass porous carbon (BPC) with a high specific surface area is used as a conductive carbon layer, and the NiCo-LDHs/BPC composite, in which nickel-cobalt layered double hydroxides (NiCo-LDHs) with hierarchically structured spherical morphology which is consisted of self-assembled homogeneous nanosheets, are anchored on the surface of BPC by a facile solvothermal method. At the same time, the effects of nickel-cobalt molar ratio (R) on the electrochemical properties of the NiCo-LDHs/BPC composite are detailedly studied. It has been found that the NiCo-LDHs-1/BPC electrode (R = 1:0.5) possesses a high specific capacitance of 2047 F g−1 at 1 A g−1 due to synergistic effect between LDHs and BPC. And even at a high current density of 20 A g−1, NiCo-LDHs/BPC electrode still has a high specific capacitance of 1539 F g−1. Besides, the asymmetric supercapacitor based on the NiCo-LDHs-1/BPC cathode and the BPC/PPy anode delivers a high specific capacitance of 139 F g−1 at 1 A g−1, a high specific energy of 49 W h kg−1 at 1 A g−1, and good cycling performance (∼75.8% retention after 6000 cycles).