A LiODFP‐Derived Multifunctional Interphase Enables Chemo‐Mechanical Stability and Fast Interfacial Kinetics in Sulfide‐Based All‐Solid‐State Batteries

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The lithium argyrodite‐type electrolyte exhibits excellent ion transport properties for all‐solid‐state batteries (ASSBs). However, their practical implementation is limited by poor cycle stability, arising from the coupled chemo‐mechanical degradation. To address these issues, we developed an effective interfacial engineering strategy by constructing the lithium difluoro(bisoxalato)phosphate (LiODFP)‐derived conformal LiF/fluorophosphate‐rich layer on the Li 5.5 PS 4.5 Cl 1.5 (LPSC1.5) surface. The multifunctional interface layer acts as an electron‐blocking barrier to suppress parasitic interfacial oxidation, and as a bridging agent to fill interparticle voids in composite cathodes, thereby reinforcing chemo‐mechanical integrity during cycling. Consequently, the LiIn|LPSC@1%LP|NCM83‐based cells retain 90% of their initial capacity after 2000 cycles at 1 C and 86% after 800 cycles at 2 C, enabling the ultra‐stable operation at high‐rate capabilities. It provides further insights into the chemical‐mechanical coupling failure evolution at the electrolyte/cathode interface, and extends the electrolyte‐centered interfacial functionalization engineering strategy for high‐energy solid‐state energy storage.