Structure and particle surface analysis of Li2S–P2S5–LiI-type solid electrolytes synthesized by liquid-phase shaking

Abstract Li 2 S–P 2 S 5 –LiI-type solid electrolytes, such as Li 4 PS 4 I, Li 7 P 2 S 8 I, and Li 10 P 3 S 12 I, are promising candidates for anode layers in all-solid-state batteries because of their high ionic conductivity and stability toward Li anodes. However, few studies have been conducted on their detailed local structure and particle surface state. In this study, Li 7 P 2 S 8 I (Li 2 S: P 2 S 5 :LiI = 3:1:1) solid electrolytes as the chemical composition were synthesized by mechanical milling and liquid-phase shaking, and their local structures were analyzed by transmission electron microscopy. The particle surface states were analyzed by X-ray photoelectron spectroscopy, high-energy X-ray scattering measurements, and neutron total scattering experiments. The results showed that Li 7 P 2 S 8 I solid electrolytes are composed of nanocrystals, such as Li 4 PS 4 I, LiI, Li 10 P 3 S 12 I and an amorphous area as the main region, indicating that the crystalline components alone do not form ionic conductive pathways, with both the amorphous and crystalline regions contributing to the high ionic conductivity. Moreover, the ionic conductivity of the crystalline/amorphous interface of the glass-ceramic was higher than that of the Li 2 S–P 2 S 5 –LiI glass. Finally, an organic-solvent-derived stable surface layer, which was detected in the liquid-phase shaking sample, served as one of the factors that contributed to its high stability (which surpassed that of the mechanically milled sample) toward lithium anodes. We expect these findings to enable the effective harnessing of particle surface states to develop enhanced sulfide solid electrolytes.