Supercapacitors can deliver high power density and long cycle stability, but the limited energy density due to weak electronic and ionic conductivity has been a bottleneck in many applications. In this study, NiMn layered double hydroxides (LDH) with sulfidation is used to reduce the charge transfer resistance of energy storage electrodes. Fast reversible redox reactions with notably enhanced specific capacitance can be achieved. The incorporation of graphite oxide (GO) in NiMn LDH during sulfidation leads to simultaneous reduction of GO with enhanced conductivity, lower defects and doping of S into the graphitic structure. Cycling stability of the sulfidized composite electrode is enhanced due to the alleviation of phase transformation during electrochemical cycling test.
On the other hand, Mn-doped Ni sulfide (NMS) nanoparticles can be obtained by similar sulfidation process. The NMS nanoparticles deliver higher electronic conductivity and larger sodium diffusion coefficient compare to Ni sulfide (NS) nanoparticles. NMS/reduced graphene oxide composites (NMGS) can be obtained with the reduction of GO during synthesis. Conversion-based electrochemical mechanism of NMGS in carbonate-based electrolyte was confirmed using ex-situ transmission electron microscopy technology. With the use of ether-based electrolyte, the NMGS electrode maintains a capacity of 229.2 mAh/g at high current density of 5 A/g, and retain capacity of 206.1 mAh/g at 0.5 A/g after 2000 cycles. The high specific capacity, high rate performance with excellent cycling stability emphasizes the promising potential of NMGS as sodium ion battery anodes.