In Situ Investigation of Chemomechanical Effects in Thiophosphate Solid Electrolytes

Solid-state batteries can suffer from catastrophic failure at high current densities due to solid electrolyte fracture, interface decomposition, or lithium filament growth. Failure is linked to chemomechanical material transformations that can manifest during electrochemical cycling. We systematically investigate how solid electrolyte microstructure and interfacial decomposition (e.g., interphase) affect failure mechanisms in lithium thiophosphates (Li₃PS₄, LPS) electrolytes. Kinetically metastable interphases are engineered with iodine doping, and microstructural control is achieved using milling and annealing processing techniques. In situ transmission electron microscopy reveals iodine diffusion to the interphase, and upon electrochemical cycling, pores are formed in the interphase region. In situ synchrotron tomography reveals that interphase pore formation drives edge fracture events, which are the origin of through-plane fracture failure. Fractures in thiophosphate electrolytes actively grow toward regions of higher porosity and are affected by heterogeneity in microstructure (e.g., porosity factor). This work provides fundamental design guidelines for high-performance solid-state batteries. Li filament growth and solid electrolyte fracture are key technical challenges limiting the commercial application of solid-state batteries. Electrical shorting, irreversible Li cycling, and the formation of dead Li at high current density limits the Coulombic efficiency and rate capability of solid electrolytes. A fundamental understanding regarding fracture mechanisms will inform materials design and system operating strategies for next-generation solid-state batteries. This work leverages advanced characterization techniques to investigate material transformation pathways in sulfide-containing solid electrolytes. We highlight the importance of microstructural heterogeneity in dictating degradation in solid electrolytes and offer insight into fracture onset and growth mechanisms. These results offer vital information required to rationally engineer solid-state battery systems that can mitigate Li filament growth and enable high energy density and high rate capability. Solid electrolytes can realize high-energy-density batteries by use of a lithium metal anode. However, filament growth and electrolyte fracture limit the solid-state battery performance. In this work, we investigate the impact of interphase chemistry and microstructure on chemomechanical degradation of thiophosphate solid electrolytes. Achieving metastable interphases and dense solid electrolytes are key to high-energy-density solid-state batteries.