Preparation of cellulose-based carbon nanofibers/NiCo2S4 composites for high-performance all-solid-state symmetric supercapacitors

Carbon fiber-based electrodes hold great potential application in flexible supercapacitors, however most of carbon fibers are fabricated by nonrenewable polyacrylonitrile. In this work, a 3D flexible cellulose-based carbon nanofiber (C-CNFs) networks were prepared by electrospinning and multi-step heat treatment using renewable cellulose as precursor; then NiCo2S4 nanosheets and nanospheres were uniformly coated on C-CNFs through onestep solvothermal method to obtain flexible C-CNFs/NiCo2S4 electrodes for supercapacitor. Compared with the C-CNFs/NiCo2S4 nanospheres, C-CNFs/NiCo2S4 nanosheets achieve a higher specific capacitance of 1784 F g(-1) at the current density of 1 A g(-1) and possess lower resistance, which attributes to high specific surface area and low resistance of C-CNFs/NiCo2S4 nanosheets. Meanwhile, the C-CNFs/NiCo2S4 nanosheets show excellent cyclic stability with 79.3% capacitance retention after 10,000 cycles at the large current density of 10 A g(-1). Finally, all-solid-state symmetric supercapacitor (ASSC) assembled from C-CNFs/NiCo2S4 nanosheets exhibits the large energy density of 85.53 Wh kg(-1) at the power density of 1200 W kg(-1) and good cyclic stability with 63.4% capacitance retention after 5000 cycles at the current density of 4 A g(-1). Four ASSCs in series can power a 'DHU' Logo consisted of 36 light emitting diodes, confirming the as-prepared flexible CNFs/NiCo2S4 nanosheets have promising application in portable electronic devices and smart wearable devices.