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

Abstract

• Control of microscopic morphology by modulation of the water-to-alcohol ratio. • The high capacitance of NCS-3 (857C/g) and the capacitance retention rate is 80% (20 A g −1 ). • Asymmetric supercapacitor shows high energy density 48.7 Wh kg −1 at a power density of 801 W kg −1 . Because of high electrical conductivity, theoretical capacity, and numerous redox pairs, NiCo 2 S 4 has sparked a lot of interest in energy storage. In the paper, with citric acid as inductive agent, NiCo 2 S 4 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 NiCo 2 S 4 and the morphology of NiCo 2 S 4 with different submicron structures can be tuned by the ratio of water/ethanol. The morphology, structure, and electrochemical properties of all NiCo 2 S 4 samples have been investigated. Among these samples, NiCo 2 S 4 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 NiCo 2 S 4 //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 NiCo 2 S 4 electrode materials and demonstrates its potential in practical application.