Visualizing the Dynamic Wetting and Redistribution of Electrolyte in Lean‐Electrolyte Lithium‐Sulfur Pouch Cells via Operando Neutron Imaging

Abstract The lean electrolyte in lithium‐sulfur (Li‐S) batteries commonly presents inhomogeneous distribution and inadequate electrolyte wetting, resulting in uneven electrochemical reaction interface, suboptimal performance, and cell failure or accelerated degradation. Non‐destructive operando /in situ methods that can visualize electrolyte wetting and dynamics during cell operation in liquid metal‐sulfur batteries have unfortunately not been described. In this study, the operando neutron tomography technique is employed to non‐destructively visualize and analyze the electrolyte distribution in practical lean‐electrolyte double‐layer Li‐S pouch cells. Through real‐time electrolyte observation across different pouch‐cell layers, we unambiguously reveal conglomeration and diminishment of unwetted areas during cell rest, leading to localized electrolyte redistribution. Remarkably, discharge/charge processes can enhance electrolyte homogeneity remarkably, boosting the electrochemical activation of sulfur. Unique periodic “breath‐in” and “breath‐out” behaviors of electrolyte wetting are observed in the dynamic evolution with the status of discharge and charge, which is correlated to the dissolution and precipitation of sulfur species. These results provide solid evidence of an inhomogeneous distribution of lean electrolyte in practical Li‐S pouch cells and offer insights into the correlation between electrolyte redistribution and lithium‐sulfur (electro‐)chemistry. This work develops valuable guidelines for optimizing testing protocols and strategies for electrolyte wetting in Li‐S pouch cells and other metal‐sulfur batteries.