One-step synthesis of nickel cobalt sulphides particles: tuning the composition for high performance supercapacitors

Abstract

NiS₂–CoS₂ composites with different Ni and Co molar ratios for supercapacitors (SCs) were synthesized by one-step hydrothermal co-deposition method using cheap Na₂S₂O₃·5H₂O as sulfur source. With the increase of Ni content, the composites particle size increases gradually and the hollow sphere structure becomes more obvious. The electrochemical measurements demonstrate that these composites possess a high specific capacitance (C_m) performance, good rate capability and long cycle stability. To be specific, the C_m of Ni/Co/S-1 composite is the largest, up to 954.3 F g⁻¹ at 1 A g⁻¹, and as high as 309.5 F g⁻¹ even at large current density of 20 A g⁻¹. Furthermore, the Ni/Co/S-1 maintains 99.9% of its initial C_m after 1000 cycles at 5 A g⁻¹. Moreover, the asymmetric supercapacitors with Ni/Co/S-1 as positive electrode and active carbon as negative electrode are of prominent energy density of 29.3 W h⁻¹ kg⁻¹ at the power density of 0.7 kW kg⁻¹, and superior cycling stability of 99.1% initial value retention after 1000 cycles.