Localized Electrolyte Grain Engineering to Suppress Li Intrusion in All‐Solid‐State Batteries

Li intrusion is the primary factor contributing to the undesirable cycling durability and rate capability of all-solid-state lithium metal batteries. However, conventional engineering methodologies for solid electrolytes (SEs) that focus on crystalline scales, such as doping, have limited efficacy in addressing this issue, as they not only involve cumbersome trial-and-error processes but also struggle to simultaneously optimize the multiple macroscopic properties necessary for effectively suppressing Li intrusion. Herein, rather than following the conventional practice of SE engineering, it is concentrated on optimizing SEs at the grain-aggregate level. A highly scalable chemical approach based on a thermodynamic-favored anion exchange reaction is first developed to engineer an amorphous metal compound layer on the surface of argyrodite-type electrolyte grains. Further, a novel localized grain engineering concept is introduced, which combines engineered and pure electrolyte grains to enable aggregates with favorable macroscopic properties for suppressing Li intrusion. The localized grain-engineered electrolyte aggregates greatly enhance Li reversibility and are able to suppress Li intrusion under practical working conditions. Notably, the 20 µm-Li||LiNi_0.83Co_0.12Mn_0.05O₂ cell using localized grain-engineered electrolyte aggregates can stably cycle for over 2000 cycles at a high current density of 1.6 mA cm^-2.