Quantifying the Structural Properties of the Lithium-Solid Electrolyte Interface
Authors: Uselton Kelsey , Hamilton Dylan , Allan-Cole Elizabeth , Ferreira de Menezes Rafael , Marks Samuel , Maughan Annalise , Toney Michael F 
Published: December 2024

All-solid-state batteries (ASSBs) are poised to meet the rising demand for high energy density electrochemical energy storage and safety in lithium-ion battery technology, a crucial aspect for the widespread adoption of electric vehicles [1]. However, the solid-electrolyte interphase (SEI) layer arising from chemical incompatibility and a narrow solid electrolyte electrochemical window poses a significant hurdle. The SEI contributes high resistance to ion transfer resulting in poor performance and cyclability of promising solid-state electrolyte materials [1]. Therefore, probing interfacial properties between the lithium and solid-state electrolyte is paramount to assess the interfacial changes that adversely impact battery performance through multiple charge–discharge cycles [2]. According to a review from Paul et al. there have been several studies characterizing the chemical composition of the SEI in ASSBs, but there is limited evidence probing the Li-SSE interphase structure [3]. Structural properties impact interfacial transport and are difficult to assess due to the limited quantity of material available for examination and for the “buried” nature of the interphase [4]. We implemented a Li/Li symmetric cell system to isolate the interactions between lithium and an argyrodite (Li6PS5Cl) solid electrolyte. To understand and quantify the structure of reaction layers that form and evolve at Li-SSE interfaces during cycling, we have performed interface-sensitive operando transmission X-ray Diffraction (XRD) experiments with high energy, high flux synchrotron radiation. Electrochemical cycling and electrochemical impedance spectroscopy paired with XRD measurements quantified SEI formation, degradation, and specific resistance contributions. Our results show evidence for crystalline reaction layers that evolve with time and potential providing insight into the formation and evolution of dominant crystalline phases throughout the interphase region.
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