Li ₂ TaS _{1– <i>x</i>} O _<i>x</i> Cl ₅ : Triple-Anion Glassy Superionic Conductors for High-Performance Solid-State Batteries

The development of stable, high-performance solid electrolytes is critical for advancing all-solid-state lithium batteries (ASSLBs). We report a series of triple-anion electrolytes, Li2TaS1–xOxCl5 (0 ≤ x ≤ 0.9), synthesized via a rapid 2-hour mechanochemical process. The optimal composition, Li2TaS0.4O0.6Cl5 (LTSOC), achieves a room-temperature ionic conductivity of ∼4.2 mS cm–1, over 15 times that of Li2TaSCl5. XRD confirms its amorphous nature, while 6/7Li NMR reveals one magnetically equivalent lithium environment due to fast ion-exchange dynamics. Raman spectroscopy shows extensive anion mixing within Ta-centered octahedra, where O2– and S2– occupy axial positions, linking Ta–O–S–Cl units, while Li+ primarily migrates along equatorial Cl–-lined pathways. Nanoindentation reveals a reduced elastic modulus with oxygen incorporation. When employed with commercial NMC811, LTSOC delivers an initial capacity of 187 mAh g–1 at 0.1C, with ∼81.8% retention after 100 cycles and Coulombic efficiency exceeding 99%. These results demonstrate the promise of amorphous, mixed-anion solid electrolytes for scalable, high-performance ASSLBs.