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

Abstract

Abstract 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).