Enhancing the Interfacial Stability between Li6PS5cl Argyrodite Sulfide Solid Electrolyte and Lithium Anode through in-Situ Formed Lif-Rich SEI Layer and a Flexible Sulfide Composite Solid Electrolyte

The sulfide-type solid electrolyte (SE) is a promising candidate for realizing all-solid-state batteries (ASSBs) due to its good mechanical properties and high ionic conductivity. However, challenges such as limited electrochemical stability, inadequate solid-solid contact with the electrode, and reactivity with lithium often lead to dendrite growth and electrolyte reduction. A simple, solvent-free method was developed to form a robust artificial interphase between lithium metal and the solid electrolyte to address these issues. This was achieved by incorporating a composite electrolyte composed of Li 6 PS 5 Cl, polyethylene glycol (PEG), and lithium bis(fluorosulfonyl)imide (LiFSI), leading to the in-situ formation of a LiF-rich interfacial layer. This interphase effectively suppresses electrolyte reduction and enhances lithium-ion diffusion. Notably, the PEG additive improves the mechanical strength of the electrolyte by enhancing adhesion between sulfide particles. It also increases the flexibility of the Li 6 PS 5 Cl solid electrolyte, improving physical contact with the lithium anode and acting as a protective barrier to prevent direct SE-Li interaction, thus reducing electrolyte decomposition. As a result, Li/Li symmetric cells exhibited excellent cycling stability, maintaining performance for over 3000 hours at a current density of 0.1 mA cm -2 , while the composite solid electrolyte achieved a critical current density of 4.75 mA cm -2 . This study underscores the synergistic benefits of combining an artificial solid electrolyte interphase (SEI) with composite solid electrolytes, paving the way for high-performance all-solid-state lithium metal batteries (ASSLBs).