Tuning the solubility of polysulfides for constructing practical lithium-sulfur battery

Abstract

Li-S batteries are regarded as one of the most promising candidates for next-generation battery systems with high energy density and low cost. However, the dissolution-precipitation reaction mechanism of the sulfur (S) cathode enhances the kinetics of the redox processes of the insulating sulfur, which also arouses the notorious shuttle effect, leading to serious loss of S species and corrosion of Li anode. To get a balance between the shuttle restraining and the kinetic property, a combined strategy of electrolyte regulation and cathode modification is proposed via introducing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoroprpyl ether (HFE) instead of 1,2-dimethoxyethane (DME), and SeS7 instead of S8. The introduction of HFE tunes the solvation structure of the LiTFSI and the dissolution of intermediate polysulfides with Se doping (LiPSSes), and optimize the interface stability of the Li anode simultaneously. The minor Se substitution compensates the decrease in kinetic due to the decreased solubility of LiPSs. In this way, the Li-SeS7 batteries deliver a reversible capacity of 1062 and 1037 mAh g−1 with 2.0 and 5.5 mg SeS7 cm−2 loading condition, respectively. Besides, an electrolyte–electrode loading model is established to explain the relationship between the optimal electrolyte and cathode loading. It makes more sense to guide the electrolyte design for practical Li-S batteries.