Session:

In the early stages of sulfide solid-state electrolyte (SSE) research, sulfides like Li₆PS₅Cl (LPSCl) were primarily synthesized in laboratories using fine precursors such as Li₂S, LiCl, and P₂S₅, 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. Mechanical indentation demonstrates that these changes lead to reduced site-to-site variation in the compact's hardness. Microstructure, in turn, profoundly influences electrochemical behavior. For example, symmetric cells with 8 and 24-hour milled electrolytes remain stable after 190 cycles at 1 mA cm^-2/2 mAh cm^-2, while the unmilled baseline cells short-circuit during initial activation. The Li/Ni asymmetric half-cells with milled electrolytes allow for stable electrodeposition of approximately 20 mAh cm^-2 (100 μm Li thickness), while the baseline shorts at 1.2 mAh cm^-2. 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. Mesoscale modeling reveals the relationship between Li-SSE interface morphology and the onset of electrochemical instability, based on underlying reaction current distribution.

Co-Author(s): David Mitlin (The University of Texas at Austin)

Yixian Wang

Appearances