Diagnosing and Correcting the Failure of the Solid‐State Polymer Electrolyte for Enhancing Solid‐State Lithium–Sulfur Batteries

Abstract Solid‐state polymer electrolytes (SPEs) attract great interest in developing high‐performance yet reliable solid‐state batteries. However, understanding of the failure mechanism of the SPE and SPE‐based solid‐state batteries remains in its infancy, posing a great barrier to practical solid‐state batteries. Herein, the high accumulation and clogging of “dead” lithium polysulfides (LiPS) on the interface between the cathode and SPE with intrinsic diffusion limitation is identified as a critical failure cause of SPE‐based solid‐state Li–S batteries. It induces a poorly reversible chemical environment with retarded kinetics on the cathode–SPE interface and in bulk SPEs, starving the Li–S redox in solid‐state cells. This observation is different from the case in liquid electrolytes with free solvent and charge carriers, where LiPS dissolve but remain alive for electrochemical/chemical redox without interfacial clogging. Electrocatalysis demonstrates the feasibility of tailoring the chemical environment in diffusion‐restricted reaction media for reducing Li–S redox failure in the SPE. It enables Ah‐level solid‐state Li–S pouch cells with a high specific energy of 343 Wh kg −1 on the cell level. This work may shed new light on the understanding of the failure mechanism of SPE for bottom‐up improvement of solid‐state Li–S batteries.