Interphases and Electrode Crosstalk Dictate the Thermal Stability of Solid-State Batteries

Solid-state batteries, because of their high energy density, are promising candidates for long-range electric vehicles and electric aviation. While the enhanced safety potential of solid-state batteries has been typically ascribed to the nonflammability of solid electrolytes, an extensive interrogation of their thermal stability is still required. In this work, we reveal how the thermal stability in sulfide-based solid-state batteries is critically dependent on the interphase interactions at the solid electrolyte/Li interface, thereby illustrating the drastically different thermal signature of Li₁₀SnP₂S₁₂ when compared with Li₃PS₄ and Li₆PS₅Cl. Our study shows that thermal runaway occurs even for a pristine Li₁₀SnP₂S₁₂/Li interface and is severely exacerbated with cycling, which exhibits a massive thermal spike at the melting point of Li; this shift in thermal response uniquely correlates to the Li₁₀SnP₂S₁₂ interphase evolution. On the basis of these distinct thermal signatures, cell-level mechanistic safety maps cognizant of the Li/interphase interaction, cathode/Li crosstalk, and specific energy are delineated.