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 x 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 cells electrochemical stability at 0 V versus Na/Na+.

Automated summary

Solid electrolytes Na3-xSbS4-xClx were synthesized using a liquid-phase method, with Na2.95SbS3.95Cl0.05 showing the highest room-temperature conductivity. The introduction of Cl substitution altered the structure to promote fast ion transport, as evidenced by Rietveld analysis and bond valence sum mapping. The addition of NaCl enhanced the electrochemical stability of Na3SbS4 cells by suppressing interfacial resistance during stripping/plating cycles.