Cathode of Co9S8/NiMn-LDH with enhanced cycle stability and anode of carbon gels for asymmetric supercapacitors

Nickel‑manganese layered double hydroxide (NiMn-LDH) is used for supercapacitors due to its high redox activity and theoretical capacity, while with the disadvantages of low conductivity and unstable structure. Here, we report a Co9S8/NiMn-LDH composite electrode material with a core-shell heterostructure grown in situ on a carbon cloth (CC). NiMn-LDH nanosheets are uniformly and densely grown in the outer layer of Co9S8 nanorods, and this structure design makes full use of the high activity of NiMn-LDH. Meanwhile, the internal electric field formed at the heterogeneous interface is shown by density functional theory (DFT) calculations to effectively accelerate the diffusion of OH− in the electrode. The core-shell heterostructure makes it exhibit better electrochemical performance than NiMn-LDH as a positive electrode (178.7 mA h g−1 specific capacity at 1 A g−1, 80.6 % capacity retention after 5000 cycles). In addition, a carbon gels anode was prepared by the sol-gel method and subsequent carbonization steps, which has excellent performance (specific capacitance of 145.6 F g−1 at 1 A g−1). The assembled Co9S8/NiMn-LDH//C-gel asymmetric supercapacitor provides an energy density of 35.2 Wh kg−1 at 850 W kg−1. Further assembled into a quasi-solid-state flexible supercapacitor, two devices in series can light an LED lamp, showing its potential application prospects in energy storage systems.