Core-shell carbon@Ni2 (CO3 )(OH)2 particles as advanced cathode materials for hybrid supercapacitor: The key role of carbon for enhanced electrochemical properties

Three-dimensional porous Ni2(CO3)(OH)2 compounds were grown on carbon nanopowder using a facile hydrothermal method for the production of core-shell carbon@Ni2(CO3)(OH)2 compounds. This work successfully overcame the shortcomings related to the low electrical conductivity and poor electrical stability caused by the presence of hollows in the Ni2(CO3)(OH)2 structure. The hollow spaces were filled with carbon powder, which acted as a seed material, yielding an ideal electrode material with a large specific surface area, high electrical conductivity, and good stability. A Ni2(CO3)(OH)2 electrode containing 50 mg of carbon powder could store more energy than a Ni2(CO3)(OH)2 electrode without carbon seed materials. The Ni2(CO3)(OH)2 electrode comprising 50 mg of carbon powder has a considerably high specific capacity (181.7 mAh g-1 at 3 A g-1) and excellent cycling stability (77.9 % capacity retention after 5000 cycles), which is 1.5 times higher than that of the Ni2(CO3)(OH)2 electrode without carbon powder. Moreover, an asymmetric supercapacitor using Ni2(CO3)(OH)2 containing 50 mg of carbon powder as the positive electrode and graphene as the negative electrode exhibits a high energy density of 34.2 Wh kg- 1 and a power density of 176.1 W kg- 1 at a current density of 2 A g-1. Using a combination of carbon and a Ni2(CO3)(OH)2 nanowire compound to increase the electrochemical property and specific surface area, respectively, a suitable synergistic effect can be obtained, which may pave the way for efficient electrode design for high-performance supercapacitors.