Charge/discharge activation of CoS/NiMn-hydroxide composite for enhancing the electrochemical performance

Electrochemical activation tactics have been adopted to enhance the electrochemical performance of electrodes. To reveal the charge/discharge activation mechanism of sulfides/hydroxides composites, herein, self-supporting NF/CoS/NiMn-hydroxides (NF/CoS/NiMn-OH) composite is prepared with NiMn-OH nanosheets wrapped rod-like CoS. The activation mechanism is revealed in 1 M KOH electrolyte, as well as the relationship between the charge/discharge cycles, microstructure/composition transition and electrochemical performance. During a charging process, the S2− anions are replaced by OH－ to generate active Co-hydroxides, accompanied by the dissolution of rod-like CoS. When activated for 10 cycles, the capacitance reaches the maximum value of 2980 F g−1 (8.046 F cm−2) at 1 A g−1, much higher than the initial capacitance of 2160 F g−1. The resulting product is verified as highly active CoNiMn–OH. A possible activation mechanism of CoS/NiMn–OH is proposed as the anion exchange reaction of S2−, followed by the generation and reconstruction of CoNiMn–OH nanosheets. Compared with initial composite, the inner CoS is converted into Co-hydroxide. Meanwhile, newly generated tri-metallic CoNiMn-hydroxide contributes to much more pseudocapacitance by playing a synergistic effect. When acting as a positive electrode, the asymmetric supercapacitor with activated carbon negative electrode presents a capacitance of 63.6 F g−1 at 1 A g−1, with a high capacitance retention of 90.6% over 6000 cycles.