Effects of Substituting S with Cl on the Structural and Electrochemical Characteristics of Na₃SbS₄ Solid Electrolytes

Herein, we report the synthesis of Na3–xSbS4–xClx (0 ≤ x ≤ 0.1) solid electrolytes using a liquid-phase method and describe their structural and electrochemical characteristics. A maximum room-temperature conductivity of 9.0 × 10–4 S cm–1 was achieved in the case of Na2.95SbS3.95Cl0.05 (Cl content = 1.25%). Rietveld analysis based on the X-ray diffraction data indicated that the altered structure due to Cl-substitution involved looser local bonding between Na and S (or Cl) around the Na1 site (Wyckoff 4d position); this site was also the underlying site for a three-dimensional ion-transport network, which comprised a structure that promoted fast ion transport. A bond valence sum mapping technique revealed that the specific crystal structure generated following Cl-substitution enabled the expansion of bottlenecks for Na+ conduction, especially along the c-axis. To investigate the effect of Cl doping in Na3SbS4 on the overall cell performance, the electrochemical performances of symmetric Na15Sn4/Na2.95SbS3.95Cl0.05 and Na2.90SbS3.90Cl0.10/Na15Sn4 cells were evaluated and compared with that of Na3SbS4. The introduction of NaCl into Na3SbS4 suppressed the increase in interfacial resistance that accompanied stripping/plating, thereby enhancing the cell’s electrochemical stability at 0 V versus Na/Na+.