Nitrogen-doped activated carbon (NAC) with a high specific surface area was successfully fabricated through graphitization derived from cotton and ammonia doping. The obtained NAC exhibits an enhanced specific capacitance of 156.4 F g−1 at 0.5 A g−1 and good cycling stability with capacitance retention of 95% after 5000 cycles. Hydrothermal route was used to synthesize CuCo2O4 nanoneedles with diameter of 20 to 50 nm. CuCo2O4 electrode showed good electrochemical performance with specific capacitance of 390 F g−1 at 0.5 A g−1 and high stability. Based on the two electrodes, an all-solid-state asymmetric supercapacitor (ASC) was assembled, which can achieve specific capacitance of 26.2 F g−1 at 1 A g−1, energy density of 8.2 Wh kg−1 at a power density of 750 W kg−1 and still retains 5.6 Wh kg−1 at power density of 7500 W kg−1. Two ASCs in series successfully illuminated 52 LEDs connected in parallel, indicating the practical application of the device.
This work was financially supported by the National Natural Science Foundation of China (No. 51601220 and 51671214), the Science and Technology Planning Project of Jiangsu Province (No. BY2016026-05) and the Laboratory Open Fund (II and III Project) of China University of Mining and Technology (No. 20180212).