Incorporating Solvate and Solid Electrolytes for All-Solid-State Li₂S Batteries with High Capacity and Long Cycle Life

The development of all-solid-state lithium–sulfur batteries is hindered by the poor interfacial properties at solid electrolyte (SE)/electrode interfaces. The interface is modified by employing the highly concentrated solvate electrolyte, (MeCN)₂−LiTFSI:TTE, as an interlayer material at the electrolyte/electrode interfaces. The incorporation of an interlayer significantly improves the cycling performance of solid-state Li₂S batteries compared to the bare counterpart, exhibiting a specific capacity of 760 mAh g⁻¹ at cycle 100 (330 mAh g⁻¹ for the bare cell). Electrochemical impedance spectroscopy shows that the interfacial resistance of the interlayer-modified cell gradually decreases as a function of cycle number, while the impedance of the bare cell remains almost constant. Cross-section scanning electron microscopy (SEM)/ energy dispersive X-ray spectroscopy (EDS) measurements on the interlayer-modified cell confirm the permeation of solvate into the cathode and the SE with electrochemical cycling, which is related to the decrease in cell impedance. In order to mimic the full permeation of the solvate across the entire cell, the solvate is directly mixed with the SE to form a “solvSEM” electrolyte. The hybrid Li₂S cell using a solvSEM electrolyte exhibits superior cycling performance compared to the solid-state cells, in terms of Li₂S loading, Li₂S utilization, and cycling stability. The improved performance is due to the favorable ionic contact at the battery interfaces.