Enhancing Long Stability of Solid‐State Batteries Through High‐Energy Ball Milling‐Induced Decomposition of Sulfide‐Based Electrolyte to Sulfur

Abstract Metal sulfides are increasingly favored as cathode materials in all‐solid‐state batteries (ASSBs) due to their high energy density, stability, affordability, and conductivity. Metal sulfides often exhibit capacities exceeding their theoretical limits, a phenomenon that remains not fully understood. In this study, it reveals that this phenomenon is primarily due to the sulfur decomposition from sulfide‐based electrolyte. By employing the high‐energy ball milling (HEBM) technique, the deposition of sulfide‐based electrolyte onto sulfur is intentionally promoted, resulting in higher charge capacities compared to the discharge capacities and surpass theoretical limits of metal sulfides. Using chromium sulfide (Cr ₂ S ₃ ) as the active material, the sulfur decomposed from sulfide‐based electrolyte transforms into lithium sulfide (Li ₂ S) after discharge, resulting in an increased capacity by ≈439.6 mAh g ⁻¹ and improved cycling stability. Consequently, it demonstrates a specific capacity surpassing 1200 mAh g ⁻¹ with a capacity retention of over 80% after 650 cycles, maintaining cycling stability for more than 1900 cycles and achieving a Coulombic efficiency exceeding 99.9%. This versatile HEBM approach enables the fabrication of ASSBs utilizing various transition metal sulfides, such as molybdenum disulfide (MoS ₂ ), niobium disulfide (NbS ₂ ), and iron disulfide (FeS ₂ ), all exhibiting over theoretical limited capacities and prolonged cycling capabilities.