Self-assembly and controllable synthesis of high-rate porous NiCo2S4 electrode materials for asymmetric supercapacitors

Because of high electrical conductivity, theoretical capacity, and numerous redox pairs, NiCo2S4 has sparked a lot of interest in energy storage. In the paper, with citric acid as inductive agent, NiCo2S4 mesoporous microspheres have been successfully prepared via solvothermal approach by regulating the solvent ratio (water/ethanol ratio = 1/3). It reveals that citric acid dominate in the nucleation and orientated growth of NiCo2S4 and the morphology of NiCo2S4 with different submicron structures can be tuned by the ratio of water/ethanol. The morphology, structure, and electrochemical properties of all NiCo2S4 samples have been investigated. Among these samples, NiCo2S4 mesoporous microspheres display the best electrochemical properties due to their unique mesoporous structure and high specific area. It has a high discharge capacity of 857C/g at a current density of 1 A/g, and exhibit exceptional rate capability (80 % retention even at 20 A/g). Additionally, when employed as positive of an asymmetric NiCo2S4//active carbon (AC) supercapacitor, it yields an energy density of 48.7 Wh kg(-1) at 801 W kg(-1) and 81 % capacity retention after 10,000 cycles at a current density of 5 A/g. The work describes a quick and easy way to increase the performance of NiCo2S4 electrode materials and demonstrates its potential in practical application.