Sulfur-Induced Lattice Disordering in Halide Electrolytes Enables Superionic Sodium-Ion Conduction

Amorphous solid electrolytes provide a promising route to overcoming the ion-transport limitations of crystalline halide frameworks, yet achieving superionic Na+ conduction remains challenging. Herein, we report a mixed-anion amorphous Na-ion solid-state electrolyte, TaCl5-0.5Na2S (NTSC), synthesized via high-energy ball-milling, which exhibits an ultrahigh room-temperature ionic conductivity of 2.9 mS/cm and a low activation energy of 0.276 eV. Structural analyses reveal a highly disordered framework composed of Ta-centered bipolyhedra interconnected via corner-sharing sulfur atoms [Ta2Cl10S], [TaCl5S], [TaCl4S], and [TaCl4S2], evidenced by comprehensive characterizations, forming a flexible, disordered amorphous network. Ab initio molecular dynamics (AIMD) simulations identify continuous Na+-diffusion pathways with low migration barriers. Complementary topological analyses further indicate that sulfur incorporation leads to local lattice distortions, shortens Na–Na hopping distances, and enhances framework flexibility, collectively enabling fast, multidimensional Na+ transport. When applied in all-solid-state sodium-ion batteries (ASSNIBs), NTSC enables high reversible capacity (111.95 mAh/g with a Coulombic efficiency of 92.6% at 0.1 C) and excellent cycling stability (76.9% initial capacity retention after 200 cycles at 0.2 C) at room temperature. This work establishes mixed-anion amorphization as an effective design strategy for high-performance Na-ion solid electrolytes.