N/S co-doped carbon nanosheets derived from sugarcane processing by-products for flexible solid-state supercapacitors

[Display omitted] •N/S co-doped carbon nanosheets derived from sugarcane processing by-products are synthesized.•Sulfonated potassium fulvic acid is used as both carbon source and heteroatom dopant.•The symmetric supercapacitor delivers a maximum energy and power density of 0.92 mW cm−2 and 184.5 μWh cm−2, respectively. Developing sustainable carbon materials from biomass for supercapacitors is a promising solution to alleviate energy and environmental pressures. In this paper, novel N/S co-doped carbon nanosheets derived from sugarcane processing by-products are proposed. Flexible and binder-free electrodes based on carbon felt and sulfonated potassium fulvic acid were prepared by a simple impregnation-carbonization method. The maximum areal specific capacitance, power density and energy density of the symmetric supercapacitor are 409.9 mF cm−2 (1 mA cm−2), 0.92 mW cm−2 and 184.5 μWh cm−2, respectively. The operating voltage of the device increases to 1.8 V by using LiCl electrolyte. After 10,000 cycles, the capacitance remains 90 % of its initial value. Besides, the device possesses good flexibility, which can be bent at different angles and has a capacitance retention of 92.3 % after 5000 bending cycles. The supercapacitor is of great significance for the recovery of crop processing by-products to prepare flexible electronic devices.