Herein, we report the synthesis of Na3–x SbS4–x Cl x (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+.

The decomposition behavior of electrolytes affects the cycle stability and electrochemical redox activity in all-solid-state lithium−sulfur batteries (ASSLSBs). However, there is a sparse understanding of the electrochemistry of ASSLSBs involving the oxidative decomposition of sulfide solid electrolytes (SEs) due to the lack of fundamental studies. Herein, we unveil the redox chemistry related to Li 2 S/S conversion reaction, electrolyte decomposition, and redox reaction of the decomposition product, based on differential capacity curves. The oxidation reaction of Li 2 S proceeds simultaneously with a continuous oxidative decomposition of sulfide SEs. Raman spectroscopy of the cell after cycling shows that SEs in the cathode convert the thiophosphates with a S−S thiol bond via the decomposition behavior of the electrolytes. The implication of this reaction chemistry is expanded toward understanding the Li 2 S activation process in ASSLSBs. Additionally, we demonstrate that Li 2 S/SE interface modification by different rotation speeds of ball milling in SE mixing allows us to control the decomposition kinetics of electrolytes. The severe decomposition of electrolytes causes cycle fading instead of increasing the electrochemical redox activity in the early period. The findings of this work highlight the need for interface engineering to avoid severe degradation of electrolytes in the cathode and enhance the ability of SEs as a redox mediator.

Synthesis technology for sulfide-based solid electrolytes based on liquid-phase processing has attracted significant interest in relation to achieving the optimal design for all-solid-state batteries. Herein, guidelines to solvent selection for the liquid-phase synthesis of superionic conductor Li7P3S11 are described through systematic examination. 70Li2S–30P2S5 system, a source of Li7P3S11, is treated via a wet chemical reaction using eight organic solvents with different physical and chemical properties (i.e., dielectric constant, molecule structure, and boiling point). We reveal that the solvent’s polarity, characterized by the dielectric constant, plays an important role in the formation of crystalline Li7P3S11 via wet chemical reaction. In addition, acetonitrile (ACN) solvent with a high dielectric constant was found to lead to high-purity crystalline Li7P3S11 and intrinsically high ionic conductivity. Further, solvents with a high boiling point and ring structures that cause steric hindrance were found to be unfavorable for the wet chemical synthesis of Li7P3S11 solid electrolyte. Overall, we demonstrate that ACN solvent is the most suitable for the liquid-phase synthesis of a crystalline Li7P3S11 solid electrolyte with high purity based on its dielectric constant, molecular structure, and boiling point.

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Solution processing technology for the manufacturing of all‐solid‐state batteries (ASSBs) holds great promise of scalability and low cost over ball milling and solid‐state methods. However, conventional liquid‐phase synthesis for solid electrolytes has yet to translate into large‐scale manufacturing to address commercialization challenges. Herein, solution processing via dynamic sulfide radical anions is developed, providing rapid and scalable manufacturing of Li7P3S11 solid electrolytes (SEs). A mixture of Li2S, P2S5, and excess elemental sulfur in a mixed solvent of acetonitrile, tetrahydrofuran, and ethanol forms a homogenous precursor solution containing the S3 ·− radical anion. The presence of ethanol enhances the chemical stability of S3 ·−. The resulting sulfide radical anions serve as a mediator with two strategies: the soluble polysulfide formation and activation of P2S5, and thus allows the generation of the precursor solution in 2 min. The Li7P3S11 is prepared in 2 h without the need for ball milling or high‐energy treatment, which shows higher ionic conductivity (1.2 mS cm−1 at 25 °C) and excellent cell performance of ASSBs cells than Li7P3S11 prepared by ball milling. The solution processing technology reported here paves the way for the accelerated adoption of practical ASSBs manufacturing.