Li ₂ CO ₃ ‐Derived Low‐Cost Li ₂ S for Sulfide Solid Electrolytes Exceeding 11 mS cm ⁻¹

ABSTRACT Sulfide solid electrolytes (SSEs) hold great promise for all‐solid‐state batteries (ASSBs), owing to their high ionic conductivity and excellent deformability. However, their practical application is severely hindered by high cost, primarily originating from lithium sulfide (Li 2 S), which accounts for ∼90% of the total SSE cost. Here, we report a novel strategy to produce low‐cost Li 2 S from lithium carbonate (Li 2 CO 3 ) via its reaction with ammonium thiocyanate (NH 4 SCN). This reaction generates only gaseous by‐products, eliminating purification procedures and enabling scalable production of high‐quality Li 2 S. The resulting Li 2 S enables the synthesis of representative SSEs, Li 5.4 PS 4.6 Cl 0.8 Br 0.8 (LPSCB) and Li 5.4 PS 4.6 Cl 1.6 (LPSC), with room‐temperature ionic conductivities of 11.33 and 7.94 mS cm −1 , respectively. When coupled with LiNbO 3 ‐coated LiNi 0.895 Co 0.077 Mn 0.028 O 2 cathode, ASSBs deliver discharge capacities of 192.2 and 198.8 mAh g −1 at 0.1C, and retain 94.85% and 94.89% of initial capacities after 800 cycles at 1C, respectively. Cost analysis reveal that the total cost of SSEs synthesized from this Li 2 CO 3 ‐derived Li 2 S is reduced by 86.6% and 88.5%, highlighting its significant techno‐economic advantages for commercializing SSEs toward ASSBs.