The electrochemical window of solid electrolytes (SEs) plays a crucial role in designing active material-SE interfaces in high-energy-density all-solidstate batteries (ASSBs). However, the suitable electrochemical window for individual active materials is not yet investigated, as the electrochemical window of SEs is overestimated. In this study, the oxidation onset voltages (OOVs) of several SEs, namely those compatible with Li 2 S as a high-capacity positive electrode material are determined. Results reveal that SEs with low OOVs decrease the capacity and increase the interfacial resistance of the corresponding ASSBs. The OOVs of SEs must exceed that of Li 2 S by more than 0.2 V to achieve high capacity, which in turn depends on SE ionic conductivity. Therefore, an Li 2 S positive electrode is combined with pseudobinary Li-oxyacid salts as SEs, exhibiting high OOVs and ionic conductivities, to afford a high-capacity (500 Wh kg −1 ) ASSB with high Li 2 S content.

No abstract

All-solid-state batteries using oxide electrolytes are regarded as safe batteries. However, most crystalline oxide solid electrolytes require high-temperature sintering for densification. Oxide electrolytes with high formability, which enable the construction of high-performance batteries, are thus required. In this study, Li 4 SiO 4 Li 2 SO 4 glasses and glass-ceramics were prepared by mechanochemical treatment and subsequent heat treatment at 270°C to achieve electrolytes with high formability. As the Li 2 SO 4 content was increased, the formability of the electrolyte increased. The 90Li 4 SiO 4 •10Li 2 SO 4 glass-ceramic electrolyte with a hexagonal structure (a P6 3 /mmc space group) showed the highest ionic conductivity of 2.2 © 10 ¹6 S cm ¹1 at 25°C. In this crystal structure, oxygen anions form a hexagonal close-packed structure, and silicon and sulfur cations randomly occupy the tetrahedral sites formed by oxygen anions. An all-solid-state LiIn/LiNi 1/3 Mn 1/3 Co 1/3 O 2 cell using a 90Li 4 SiO 4 •10Li 2 SO 4 glass-ceramic electrolyte operated at 100°C as a secondary battery without high-temperature sintering. These oxide materials are promising solid electrolytes for oxide-type all-solid-state batteries.

Li 4 GeO 4 -based solid electrolytes can be synthesized at low temperatures, and their formability is improved by adding Li 2 SO 4 . Glass ceramic Li 4 GeO 4 exhibits a relatively high ionic conductivity of approximately 10 ¹6 S cm ¹1 at room temperature, which is higher than that of glass Li 4 GeO 4 . Thus, Li 4 GeO 4 has promising applications in all-solid-state lithium ion batteries. To understand the correlation between the ionic conductivity, formability, and microstructure of the synthesized materials, the microstructures and crystallization process of glass and glassceramic Li 4 GeO 4 and 80Li 4 GeO 4 •20Li 2 SO 4 (Li 3.6 Ge 0.8 S 0.2 O 4 ) were observed by transmission electron microscopy (TEM). Since Li 3.6 Ge 0.8 S 0.2 O 4 glass exhibits a halo diffraction pattern, the addition of Li 2 SO 4 to Li 4 GeO 4 stabilizes its amorphous phase. In addition, glass ceramic samples were found to be characterized by an amorphous state containing nanocrystallites with a crystallinity degree of approximately 40%, which improves the ionic conductivity of the material.