Gradually sulfurized Co-Ni LDH as electrode for highly-stable asymmetric supercapacitor

To break the bottleneck of poor rate performance and low cycling stability of metal hydroxides based electrode materials for supercapacitor resulted from their inferior inherent poor conductivity and instable microstructure, herein, a scalable method based on successive cation/anion exchange reaction from low cost magnesium hydroxide was developed to prepare CoNi based sulfides with different sulfurization degree and magnesium doping. Systematically investigation demonstrates that after sulfurization, the morphology can be maintained while the textual parameters like surface area, pore volume have a gradual decrease. Due to the sulfurization and magnesium doping, as electrode for supercapacitor, the resultant sulfide achieves a greatly enhanced rate capability of 71.9 % (vs 52.7 % of parent CoNi LDH), high energy density of 37.8 Wh/kg@750 W/kg and superior cycling stability with about 92.2 % capacitance retention after repeated charge/discharge at large current density for 10,000 cycles. A comprehensive comparison indicates that the resultant sulfide (CoNiS-50) achieves a higher energy storage level than those of parent CoNi LDH and some recently reported sulfides, promising a great potential for practical energy storage. Importantly, the developed cation/anion ion-exchange method is easily-operated thus offers a wide applicability towards the preparation of various sulfides with adjustable metal species and sulfurization degree.