Stack Pressure Measurements to Probe the Evolution of the Lithium–Solid-State Electrolyte Interface

Although solid-state batteries with lithium metal could enable higher energy density and better safety characteristics than Li-ion batteries, the complex electro-chemo-mechanical evolution of the Li–solid-state electrolyte interface can diminish performance. Here, we measure the stack pressure in real time to provide new insights into the effects of applied stack pressure and electrolyte processing on the interfacial behavior of two representative solid-state electrolytes, Li₁₀SnP₂S₁₂ and Li₆PS₅Cl; these materials exhibit different degradation mechanisms through either interphase formation or Li filament growth. We find that stack pressure evolution sensitively depends on interphase formation and that tracking stack pressure coupled with impedance can distinguish between various reaction phenomena and degradation mechanisms within cells. Furthermore, Li filament growth exhibits distinct stack pressure signatures that depend on electrolyte density. The findings advance our understanding of the interfacial evolution of two important classes of solid-state electrolytes, and they demonstrate the utility of electro-chemo-mechanical measurements to understand solid-state battery behavior.