Uniformization of Electron Distribution at Grain Boundaries via Work Function Adjusting Interlayer to Prevent Li‐Filament Formation Within Solid Electrolytes

Abstract With the increasing demand for safe all‐solid‐state lithium metal batteries (ASSLMBs), preventing Li‐filament formation has become a critical issue in inorganic solid‐electrolytes (ISEs). Fundamentally, uniformizing electronic properties at the microstructure is key to preventing the reduction of Li‐ions, which strongly induces Li‐filament formation. However, little information on the electronic properties of ISEs makes interpreting the source of Li‐filament formation difficult. Herein, a mechanism for Li‐filament formation is revealed by confirming that work function differences at the interface between the grain interiors (LLZO) (≈ 4.2 eV) and grain boundaries (LixAlOy) (≈ 4.32 eV), cause localized currents, reducing Li‐ions at the grain boundaries of ISEs. Introduction of a work function adjusting interlayer, a thin LiF layer that uniformizes the work function evenly across t…