Fabrication of nickel foam/MXene/CoAl-layered double hydroxide by electrodeposition as electrode material for high-performance asymmetric supercapacitor

Layered double hydroxides (LDH) have become one of the highly promising electrode materials due to large specific area, excellent cycling stability and high energy density. However, the large internal resistance limits their applications in energy storage. The introduction of highly conductive materials is expected to solve this problem. In here, nickel foam (NF)/MXene/CoAl-LDH is prepared by electrodepositing CoAl-LDH on the surface of MXene-coated NF, and the effects of Co:Al ratio on the electrochemical properties are investigated in detail. The best electrochemical performance of the composite is obtained when Co:Al=2:1, with a specific capacitance of 646.7 F g-1 at 0.5 A g-1 and 450.8 F g-1 at 5 A g-1. Furthermore, the asymmetric supercapacitor is assembled with NF/MXene/CoAl-LDH as the positive electrode and activated carbon (AC) as the negative electrode. The voltage window of the device can reach 1.6 V. The specific capacitance of the device is 126.87 F g-1 at a current density of 0.5 A g-1. At the power density of 400 W kg-1, the energy density of 45.11 Wh kg-1 is provided. Even at the high power density of 4000 W kg-1, the energy density can still reach 17.88 Wh kg-1. After 5000 cycles at a current density of 5 A g-1, it still maintains a capacity retention rate of 92.9%. The asymmetric device with its high specific capacitance, long term stability and good power density and energy density has a great potential in energy storage applications.