Ethanol driven Ni, Co and S elements generate NiCo2S4 crystal phases for high-performance asymmetric supercapacitors

Abstract

NiCo 2 S 4 has excellent electrochemical properties, but its synthesis process is cumbersome and costly. The coexistence of Ni, Co and S elements in the reaction system is difficult to spontaneously form the NiCo 2 S 4 phase. For this purpose, a one-step solvothermal method was adopted, and alcohol was used to drive Ni, Co and S elements to form the NiCo 2 S 4 phase with a spinel structure, thereby simplifying the preparation process of NiCo 2 S 4 . Various alcohols can induce the synthesis of NiCo 2 S 4 , but ethanol has more advantages. This process is only related to the C-OH group and has nothing to do with the state of the central C. The occurrence of phase transition is attributed to the fact that alcohols change the ion diffusion rate and the surface energy of crystal plane growth. When the ratio of ethanol to water is 1:1, the prepared NiCo 2 S 4 material (NiCoS@E20) has a high specific surface area and the best electrochemical performance. The asymmetric supercapacitor constructed with NiCoS@E20 achieved a high energy density of 31.3 Wh kg −1 . These results provide a simple and effective method for regulating the microstructure of metal sulfides and reducing the cost of supercapacitors.