Two-Stage Solvation of Lithium Polysulfides in Working Lithium–Sulfur Batteries

Abstract

Lithium–sulfur (Li–S) batteries are promising in achieving high energy density but inferior in cycling lifespan since Li polysulfides (LiPSs) corrode Li metal anode. Weakening the electrolyte solvating power (ESP) for LiPSs effectively mitigates anodic corrosion but inevitably retards cathodic reaction kinetics. Herein, the correlation between the ESP and the LiPS redox kinetics in weakly solvating electrolyte is unveiled for achieving high-performance Li–S batteries. The ESP exhibits a two-stage variation tendency as the weakly solvating solvent (WSS) content increases, where the transition depends on whether the WSS enters the LiPS inner solvation shell. Once the WSS directly coordinates with LiPSs, the LiPS charge-transfer kinetics deteriorate dramatically, with a rapid increase in activation polarization. To overcome the kinetic sluggishness, advanced electrocatalysts are introduced to endow Li–S batteries with reduced polarization and prolonged cycling lifespan. An ultrahigh energy density of 607 W h kg^–1 is realized in 10 Ah-level pouch cells with a stable cycling lifespan. This work deepens the current understanding of LiPS solvation and kinetics, highlighting the significance of weakly solvating electrolytes toward high-energy-density and long-cycling Li–S batteries.