Facile mechanical refinement of sulfide solid electrolytes for stable all-solid-state Li metal batteries

All-solid-state lithium metal batteries offer high energy density and enhanced safety, yet mechanical instability at both positive electrode/solid electrolyte and Li metal/solid electrolyte interfaces severely limits cycling stability and rate performance, particularly at a low stacking pressure. Here, we report a facile, industry-compatible strategy to refine polycrystalline Li_5.5PS_4.5Cl_1.5 grains using Al₄C₃ abrasives. The resulting Al₄C₃-engineered Li_5.5PS_4.5Cl_1.5 exhibits reduced average particle size and a narrowed size distribution. The refined electrolyte grains enable a high relative density in both anolytes and composite positive electrodes. Beyond particle refinement, Al₄C₃ in the anolyte stabilizes the Li/electrolyte interface through its high modulus, low electronic conductivity, and favorable interfacial mechanics, enabling a high critical current density/capacity of 3.2 mA cm^‒2/3.2 mAh cm^-2. Leveraging our designed electrolyte as both anolyte and catholyte, the all-solid-state lithium metal batteries demonstrate stable cycling performance under a low stack pressure of 4 MPa and a positive electrode loading of 1.4 mAh cm^-2, sustaining over 1500 cycles at 1.4 mA cm^‒2. This study provides a potentially simple and scalable approach to optimize solid electrolyte particles and interfacial mechanics.