Cellulose-derived carbon-based electrodes with high capacitance for advanced asymmetric supercapacitors

Asymmetric supercapacitor as a promising energy storage system utilizes both redox-type and electric doublelayer type electrodes in one single device, but it is urgent to design sustainable electrodes with low-cost and high-performance. Herein, hybrid NiCo2S4/carbon and porous carbon electrodes are prepared by using carboxylated cellulose nanofibers as the carbon source due to the carbon-rich backbone and abundant hydroxyl groups on the surface. The NiCo2S4/carbon electrode displays a large specific capacity/capacitance of 783C g(-1)/ 1569 F g(-1)- at 0.5 A g(-1) with the capacity retention ratio of 78% after 5000 cycles. The specific capacitance of porous carbon material is 376 F g(-1) at 1 A g(-1). With the utilization of the different electrochemical potential windows, an asymmetric device is fabricated by using the NiCo2S4/carbon hybrid and porous carbon as the positive and negative electrodes, showing a high energy density of 53.7 W h kg(-1) at 184.4 W kg(-1). The asymmetric device maintains an excellent capacity retention rate of 97% after 10,000 cycles. These promising properties are related with the synergistic effect from the high-performance positive and negative electrodes. Considering the advantage in terms of sustainability, this work paves the way for the design of advanced electrodes for high-efficiency energy storage equipment.