One-step solvothermal synthesis of nickel–cobalt sulfides in a low coordination 1,4-dioxane solvent for supercapacitors

Renowned for their exceptional specific capacity, high rate performance and good cycling stability, nickel–cobalt sulfides (NCSs) are highly promising electrode materials for supercapacitors. Unlike previous hydrothermal or solvothermal techniques that rely on solvents with strong polarity, high coordination ability and good solubility for synthesizing NCSs, this study employs solvents with low coordination and solubility ability for metal ions. These differences subsequently influence the macroscopic characteristics of the resultant materials. Specifically, the common solvent 1,4-dioxane with low coordination ability was employed. NCSs were synthesized using a straightforward one-step solvothermal method at different temperatures. NCS-180, synthesized at 180 °C, displays a sea urchin-like crystalline structure with aggregated linear nickel cobalt sulfide and demonstrates superior electrochemical performance. At a current density of 1 A g⁻¹, it exhibits a specific capacity of 664.30 C g⁻¹. Moreover, after enduring 5000 cycles at 10 A g⁻¹, its capacity retention rate remains at 97.99%. Additionally, a dual-electrode configuration was constructed, utilizing NCS-180 as the cathode and activated carbon (AC) as the anode. The findings reveal that the NCS-180//AC system demonstrates a notable energy density of 50.35 Wh kg⁻¹ at a power density of 750 W kg⁻¹. Furthermore, after enduring 6000 cycles at 10 A g⁻¹, the system retains a capacitance retention rate of 93.30%.