Tuned Reactivity at the Lithium Metal–Argyrodite Solid State Electrolyte Interphase

Abstract Thin intermetallic Li 2 Te–LiTe 3 bilayer (0.75 µm) derived from 2D tellurene stabilizes the solid electrolyte interphase (SEI) of lithium metal and argyrodite (LPSCl, Li 6 PS 5 Cl) solid‐state electrolyte (SSE). Tellurene is loaded onto a standard battery separator and reacted with lithium through single‐pass mechanical rolling, or transferred directly to SSE surface by pressing. State‐of‐the‐art electrochemical performance is achieved, e.g., symmetric cell stable for 300 cycles (1800 h) at 1 mA cm −2 and 3 mAh cm −2 (25% DOD, 60 µm foil). Cryo‐stage focused ion beam (Cryo‐FIB) sectioning and Raman mapping demonstrate that the Li 2 Te–LiTe 3 bilayer impedes SSE decomposition. The unmodified Li–LPSCl interphase is electrochemically unstable with a geometrically heterogeneous reduction decomposition reaction front that extends deep into the SSE. Decomposition drives voiding in Li metal due to its high flux to the reaction front, as well as voiding in the SSE due to the associated volume changes. Analysis of cycled SSE found no evidence for pristine (unreacted) lithium metal filaments/dendrites, implying failure driven by decomposition phases with sufficient electrical conductivity that span electrolyte thickness. DFT calculations clarify thermodynamic stability, interfacial adhesion, and electronic transport properties of interphases, while mesoscale modeling examines interrelations between reaction front heterogeneity (SEI heterogeneity), current distribution, and localized chemo‐mechanical stresses.