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

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.