Halogen Doping Mechanism and Interface Strengthening in the Na₃SbS₄ Electrolyte via Solid-State Synthesis

Good-performing sodium solid electrolytes (SSEs) are essential for constructing all-solid-state sodium-ion batteries operating at ambient temperature. Sulfide solid electrolyte, Na₃SbS₄ (NBS), an excellent SSE with good chemical stability in humid air, can be synthesized with low-cost processing. However, Na₃SbS₄-based electrolytes with liquid-phase synthesis exhibit conductivities below milli-Siemens per centimeter. Thus, a series of halogen-doped samples formulated as Na_3-SbS_4-M (0 ≤ x ≤ 0.3, M = Cl, Br, and I) were experimentally prepared in this study using the solid-state method to improve the battery performance. X-ray diffraction with refinement analysis and Raman spectroscopy were employed to understand deeply the connection between the crystal structure and conductivity of Na⁺ ions. In addition, symmetric sodium batteries with Na_2.85SbS_3.85Br_0.15 were tested at room temperature, and pristine Na₃SbS₄ was used as the control group. The result showed that the symmetric sodium battery assembled with the Na_2.85SbS_3.85Br_0.15 electrolyte can stably cycle for longer than 100 h at a current density of 0.1 mA/cm². This research provides a method to manufacture novel SSEs by elaborating the effect of halogen doping in NBS.