Room-temperature sintering of amorphous thiophosphate solid electrolyte (Li${}_3$PS${}_4$). Coupling morphological evolution to electrochemical properties

Thiophosphate solid electrolytes (Li${}_3$PS${}_4$, hereafter denoted LPS) have the advantage of presenting a reasonable ionic conductivity at room temperature (≈ 0.3 mS cm${}^{-1}$) and an easy manufacturing, meaning that they can be sintered at room temperature. Unfortunately, during cycling, several chemo-mechanical degradations quite often attributed to the electrochemical activities occur, but they could also be linked to the sintering process. To date, a fundamental understanding of room-temperature sintering and its impact on the microstructure, the ionic conductivity, and the link between electrochemistry and structure/morphology remains imprecise. In this study, a comprehensive study of homemade amorphous 75% Li${}_2$S - 25% P${}_2$S${}_5$ (Li${}_3$PS${}_4$) is presented, investigating the influence of pressure and time of room temperature sintering. Focused ion beam-scanning electron microscopy coupled to electrochemical techniques such as electrochemical impedance spectroscopy, Li plating/ stripping and coupled to structural techniques such as wide-angle X-ray scattering are used to establish the link between structure, morphology, and electrochemical properties. It is demonstrated that the room temperature sintering of solid electrolytes is not that trivial and that the commonly accepted rule "less porosity = better ionic conductivity" is not always true and that many additional parameters should be considered to properly sinter the solid electrolyte. (© 2023 The Authors. Advanced Functional Materials published by Wiley‐VCH GmbH)