Mechanical Milling - Induced Microstructure Changes in Argyrodite Lpscl Solid-State Electrolyte Critically Affect Electrochemical Stability

In the early stages of sulfide solid-state electrolyte (SSE) research, sulfides like Li 6 PS 5 Cl (LPSCl) were primarily synthesized in laboratories using fine precursors such as Li 2 S, LiCl, and P 2 S 5 , employing meticulous synthetic procedures involving milling and sintering. This approach resulted in grams of as-synthesized SSE materials with a uniform particle size distribution and well-controlled morphology. Consequently, large-scale synthesis methods for LPSCl SSE have been developed, leading to the availability of commercial LPSCl SSE. Nonetheless, compared to lab-scale synthesis, commercial production of LPSCl SSE often yields a wide range of particle sizes and particle distributions. In-depth understanding is needed regarding how microstructural features such as the average particle size and distribution, and pore size and distribution, affect the compressed SSE's electrochemical performance. In this presentation, we investigate mechanical milling – induced microstructure changes of LPSCl SSE and their influence on electrochemical performance. Planetary mechanical milling in wet media (m-xylene) is employed to alter commercial LPSCl powder. Quantitative stereology demonstrates how extended milling progressively refines grain and pore size/distribution, increases compact density, and geometrically smoothens the SSE-Li interface. Microstructure, in turn, profoundly influences electrochemical behavior. It is shown that an optimized SSE microstructure enables state-of-the-art electrochemical performance without the need for any artificial SEI layers or other secondary modifications. Combined cryogenic focused ion beam (cryo-FIB) and X-ray photoelectron spectroscopy (XPS) demonstrate that milled microstructures promote uniform early-stage electrodeposition on foil collectors and stabilize solid electrolyte interphase (SEI) reactivity. For the first time, short-circuiting Li metal dendrite is directly identified, employing 1.5 mm diameter "mini" symmetrical cell and cryo-FIB. Site-specific analysis highlights that the lithium metal dendrite has the following features: a) a sheet-like morphology with branching sections; b) traverses the compact intergranularly, moving around large grains rather than through them; c) fills the interparticle voids and reacts with the contacting SSE to form reduction decomposition products, i.e. the dendrite is surrounded by an SEI. Figure 1