Li_1.6AlCl_3.4S_0.6: a low-cost and high-performance solid electrolyte for solid-state batteries

Solid electrolytes (SEs) are crucial for advancing next-generation rechargeable battery technologies, but their commercial viability is partially limited by expensive precursors, unscalable synthesis, or low ionic conductivity. Lithium tetrahaloaluminates offer an economical option but exhibit low Li⁺ conductivities with high activation energy barriers. This study reports the synthesis of lithium aluminum chalcohalide (Li_1.6AlCl_3.4S_0.6) using inexpensive precursors <i>via</i> one-step mechanochemical milling. The resulting Cl-S mixed-anion sublattice significantly improves the ionic conductivity from 0.008 mS cm^-1 for LiAlCl₄ to 0.18 mS cm^-1 for Li_1.6AlCl_3.4S_0.6 at 25 °C. Structural refinement of the high-resolution XRD patterns and ⁶Li magic-angle-spinning (MAS) NMR quantitative analysis reveals the formation of tetrahedrally-coordinated, face- and edge-shared LiCl _<i>x</i> S _<i>y</i> octahedra that facilitate 3D Li⁺ transport. <i>Ab initio</i> molecular dynamics (AIMD) simulations on Li_1.6AlCl_3.4S_0.6 support an enhanced 3D network for Li⁺ migration with increased diffusivity. All-solid-state battery (ASSB) half-cells using Li_1.6AlCl_3.4S_0.6 exhibit high-rate and long-term stable cycling performance. This work highlights the potential of Li_1.6AlCl_3.4S_0.6 as a cost-effective and high-performance SE for ASSBs.