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

Abstract

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.

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