Designed synthesis of nickel-cobalt-based electrode materials for high-performance solid-state hybrid supercapacitors

Supercapacitors with high security, excellent energy and power densities, and superior long-term cycling performance are becoming increasingly essential for flexible devices. Herein, this study has reported a novel method to synthesize CoNi₂S₄, which delivered a high specific capacitance of 1836.6 F g^-1 at 1 A g^-1, with a slight fluctuation in the testing temperature rising up to 50 °C (1855.2 F g^-1) or decreasing to 0 °C (1587.6 F g^-1). In addition, the corresponding solid-state CoNi₂S₄//AC HSC could achieve a high energy density of 35.8 W h kg^-1 at a power density of 800.0 W kg^-1, with nearly no change when tested at 0 °C and 50 °C, and possessed excellent long-term electrochemical cycling stability of 132.3% after 50;000 cycles; the solid-state hybrid supercapacitor using biomass-derived carbon (BC) as the negative electrode (CoNi₂S₄//BC HSC) could also deliver a high energy density of 38.9 W h kg^-1 at a power density of 850.0 W kg^-1 and the specific capacitance retention was 101.2% after cycling for 50;000 times. This work has provided a promising method to prepare high-performance electrode materials for solid-state hybrid supercapacitors with superior cycling stability and energy density.