Revealing a novel origin of solid-state battery failure: electrolyte damage from interface engineering.

Interfacial engineering is a widely adopted strategy for mitigating dendrite growth in solid-state lithium (Li) metal batteries (SSLMBs). This strategy typically involves depositing a thin-film interlayer on the solid electrolyte (SE) surface to enhance lithiophilicity, mechanical compliance, and uniform current distribution. However, whether the process of constructing a thin-film interlayer damages the SE remains unclear. If so, how can a systematic deposition protocol be established to construct a damage-free interlayer/SE interface? Here, we deposited W and Cu thin-film interlayers on the surface of the SE by magnetron sputtering and thermal evaporation, respectively, two commonly used techniques in interface engineering. Cryogenic focused ion beam (cryo-FIB) and transmission electron microscopy (TEM) analyses reveal that both processes can severely damage the near-surface crystal structure of the SE, inducing surface amorphization and forming an additional Li-containing compound layer at the interface. More importantly, we show that proper selection of deposition techniques and interlayer materials enables a damage-free interlayer/SE interface. In situ TEM observation reveals distinct Li deposition behaviors at damaged and damage-free interfaces, highlighting the importance of interfacial structural integrity in regulating Li deposition. This work reveals the interfacial damage mechanism during interlayer construction, providing important guidance for optimizing interfacial engineering toward long-cycle-life SSLMBs.