Synthesis of mesoporous nickel-cobalt-manganese sulfides as electroactive materials for hybrid supercapacitors

Nickel-cobalt-manganese sulfide (NiCoMn-S) with a mesoporous structure was synthesized as the electroactive battery materials for hybrid supercapacitors. The synergy between transition metals of NiCoMn-S was investigated theoretically by performing density functional theory calculations and experimentally by comparing the charge storage properties of sulfides with different transition metals. It is found that the Mn composition can activate the 3d electrons of Co and enhance affinity of NiCo–S with electrolyte ions, leading to synergy between transition metals for enhanced electrochemical activity and rate performance. The Mn composition also increases the specific area for more electroactive sites and reduces the charge transfer resistance of sulfides. In addition, it is found that the Mn and Ni compositions can greatly enhance the charge storage activity of sulfide, and the Co composition greatly improves the rate performance. The strong synergy between Ni, Co and Mn results in enhanced specific capacity, high rate performance and excellent cycling stability. The NiCoMn-S exhibits a specific capacity of 661 C g−1 at 1 A g−1, which retains 440 C g−1 at 50 A g−1. More significantly, the NiCoMn-S demonstrates well matched performance with the capacitive RGO electrode, and the resulting hybrid supercapacitor (HSC) demonstrates both high power and high energy performances. The HSC exhibits a specific energy of 42.1 Wh kg−1 at a specific power of 750 W kg−1, and showing a specific energy of 13.2 Wh kg−1 at a specific power of 22.5 kW kg−1.