Sulfide Electrolyte Suppressing Side Reactions in Composite Positive Electrodes for All-Solid-State Lithium Batteries

Long-lasting all-solid-state batteries can be achieved by preventing side reactions in the composite electrodes comprising electrode active materials and solid electrolytes. Typically, the battery performance can be enhanced through the use of robust solid electrolytes that are resistant to oxidation and decomposition. In this study, the thermal stability of sulfide solid electrolytes Li 3 PS 4 and Li 4 SnS 4 toward oxide positive electrode active materials was estimated by investigating the occurrence of side reactions at the electrolyte–electrode interfaces when the composite electrodes are heated in an accelerated aging test: Li 4 SnS 4 showed higher thermal stability because of the suppression of the substitution reaction between S and O. Moreover, thermally stable sulfide solid electrolytes are amenable to an improved cell construction process. The sintering (pelletizing and subsequent heating) of the composite electrodes with Li 4 SnS 4 as the solid electrolyte allowed the manufacture of dense electrodes that exhibited increased ionic conductivity, thereby enhancing the battery performance.