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

Abstract

Good-performing sodium solid electrolytes (SSEs) are essential for constructing all-solid-state sodium-ion batteries operating at ambient temperature. Sulfide solid electrolyte, Na 3 SbS 4 (NBS), an excellent SSE with good chemical stability in humid air, can be synthesized with low-cost processing. However, Na 3 SbS 4 -based electrolytes with liquid-phase synthesis exhibit conductivities below milli-Siemens per centimeter. Thus, a series of halogen-doped samples formulated as Na 3−x SbS 4−x M x (0 ≤ x ≤ 0.3, M = Cl, Br, and I) were experimentally prepared in this study using the solidstate 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 2.85 SbS 3.85 Br 0.15 were tested at room temperature, and pristine Na 3 SbS 4 was used as the control group. The result showed that the symmetric sodium battery assembled with the Na 2.85 SbS 3.85 Br 0.15 electrolyte can stably cycle for longer than 100 h at a current density of 0.1 mA/cm 2 . This research provides a method to manufacture novel SSEs by elaborating the effect of halogen doping in NBS.

Tungsten and Boron Codoping toward High Ionic Conductivity and Stable Sodium Solid Electrolyte for All-Solid-State Sodium Batteries

“…Recently, an even higher conductivity of 10.37 mS cm –1 with a W-doped Na 3 SbS 4 solid electrolyte was achieved by melt-quenching. However, the capacity of the resulting all-solid-state battery deteriorated owing to the instability at the Na/solid electrolyte interface. − The high-valence W is easily reduced by metallic sodium, , forming a solid electrolyte interface layer that increases the interface impedance and thus leading to a rapid battery failure. , One of the commonly used strategies to improve the stability of the interface is to optimize the composition of the solid electrolyte by doping. , For instance, the W and O-codoped Na 3 SbS 4 can form passivation decomposition products of Na 2 O at the Na/solid electrolyte interface, thus improving the interfacial stability. It is reported that the introduction of boron in solid electrolytes can form stable compounds, which can inhibit undesirable chemical reactions at the interface.…”