Mechanistic Investigation of Polymer‐Based All‐Solid‐State Lithium/Sulfur Battery

Abstract Although employing solid polymer electrolyte (SPE) in all‐solid‐state lithium/sulfur (ASSLS) batteries is a promising approach to obtain a power source with both high energy density and safety, the actual performance of SPE‐ASSLS batteries still lag behind conventional lithium/sulfur batteries with liquid ether electrolyte. In this work, combining characterization methods of X‐ray photoelectron spectroscopy, in situ optical microscopy, and three‐electrode measurement, a direct comparison between these two battery systems is made to reveal the mechanism behind their performance differences. In addition to polysulfides, it is found that the initial elemental sulfur can also dissolve into and diffuse through the SPE to reach the anode. Different from the shuttle effect that causes uniform corrosion on the anode in a liquid electrolyte, dissolved sulfur species in SPE unevenly passivate the anode surface and lead to the inhomogeneous Li + plating/stripping at the anode/SPE solid‐solid interface. Such inhomogeneity eventually causes void formation at the interface, which leads to the failure of SPE‐ASSLS batteries. Based on this understanding, a protection interlayer is designed to inhibit the shuttling of sulfur species, and the modified SPE‐ASSLS batteries show much‐improved performance in cycle life.