High mass loading porous CoNi2S4 nanosheets with ultrahigh areal capacity for flexible supercapacitors

Abstract

Ternary nickel–cobalt sulfides with excellent electrical conductivity and high electrochemical activity can serve as ideal cathode materials for flexible hybrid supercapacitors. The electrochemical performance of the nickel–cobalt sulfides can be well tuned by different Ni and Co contents. Herein, nickel–cobalt sulfides with different Ni/Co ratios have been successfully prepared on carbon cloth (CC) by applying a two-step method: first the electrodeposition of hydroxide precursors on CC and then the subsequent sulphuration using a hydrothermal method. By systematically investigating the ratio effects of Ni and Co ions on the growth and capacity contribution of materials, the CoNi₂S₄/CC electrode presented a high utilization of electrochemically active sites, showing excellent electrochemical performance. The effect of different mass loadings of up to 18.80 mg cm⁻² of CoNi₂S₄/CC on electrochemical performance was further investigated, and it was observed that the areal capacity is positively correlated with the mass loading. A high areal capacity of 11.11 C cm⁻² at 2 mA cm⁻² was observed for the synthesized CoNi₂S₄/CC with excellent rate capability and long cycle life. Furthermore, flexible hybrid supercapacitors with CoNi₂S₄-1000/CC as the positive electrode and activated carbon as the negative electrode deliver a maximum power density of 2.99 mW cm⁻² at a 0.252 mW h cm⁻² energy density and an outstanding cyclic stability. The results provide a novel route for preparing high-mass loading nickel–cobalt sulfide electrodes with outstanding areal capacity.