Multidimensional Carbon-Modified NiCo2O4/Ni–Co–S Nanocomposite Electrode Material for High-Energy Asymmetric Supercapacitors

The synergistic effect of the electrochemical double-layer and pseudocapacitance electrode materials has been extensively used to improve the performance of composite electrodes for supercapacitors (SCs). However, the energy density of SCs is still unsatisfactory for practical utilization. Herein, a C-NiCo2O4/C@Ni–Co–S electrode is ingeniously devised through coupling the interior of 0D/2D carbon-modified NiCo2O4 and the external sheath of Ni–Co–S nanosheets. The 0D carbon quantum dot doping can effectively avoid the agglomeration of NiCo2O4 nanoparticles and improve the electronic conductivity. 2D carbon as the intermediate layer can ameliorate the physical/chemical stability of the electrode. Ni–Co–S nanosheets can improve the area-specific capacitance of the electrode and thus enhance the energy density of the device. As expected, the C-NiCo2O4/C@Ni–Co–S electrode delivers an outstanding specific capacitance of 2396 F g–1 (7.9 F cm–2) at 3 A g–1 and excellent cycling stability (92% after 10 000 cycles). Furthermore, a quasi-solid-state asymmetric supercapacitor (ASC) using C-NiCo2O4/C@Ni–Co–S as positive electrode and active carbon (AC) as negative electrode exhibits a high energy density of 95 Wh kg–1 at 0.9 kW kg–1 and an excellent cycle performance. Our work reveals that this reasonable structure design is very effective for achieving a high-performance positive electrode for practical SC applications.