No abstract

Solid electrolytes (SEs) are promising candidates for enhancing the energy density and safety of conventional lithium-ion batteries. Recently, lithium thioantimonate iodide argyrodites have been regarded as promising SEs because of their high ionic conductivities and air-stability. In this study, we utilized highenergy ball milling to synthesize Ge-substituted thioantimonate argyrodites and achieved an ionic conductivity of 16.1 mS cm −1 for Li 6.5 Sb 0.5 Ge 0.5 S 5 I, which is the highest value among the reported cold-pressed SE pellets. First-principles calculations reveal that concerted Li-ion migrations through the inter-cage paths substantially improve the ionic conductivity. Li 6.5 Sb 0.5 Ge 0.5 S 5 I shows good compatibility with LiNi 0.5 Co 0.2 Mn 0.3 O 2 -based all-solid-state batteries (ASSBs) after applying Li 3 YCl 6 as a catholyte, which exhibits a high discharge capacity of 164 mAh g −1 and good cycle stability. Ge-substituted thioantimonate argyrodites exhibit excellent air-stability, which facilitates reducing the synthesis and fabrication costs of ASSBs with hygroscopic P-based sulfide SEs. The superionic conductors with high air-stability reported in this study demonstrate substantial promise for the development of ASSBs.

Lithium-based solid electrolytes have been investigated in many studies for improving the energy density and safety of conventional Li-ion batteries. Recently, Li argyrodites (Li6+x Sb1–x Si x S5I) have been reported as promising superionic conductors, exhibiting an ionic conductivity above 10 mS cm–1. This study examined the high ionic conductivities of Li6+x Sb1–x Si x S5I using first-principles calculations and subsequent experiments. The calculation results demonstrate that the Li ionic conductivities increase with the Si content in Li6+x Sb1–x Si x S5I due to the concerted Li-ion migration. Li6+x Sb1–x Si x S5I compounds synthesized using high-energy ball milling exhibit a high-symmetry argyrodite structure. The Li6.75Sb0.25Si0.75S5I phase demonstrates a favorable combination of a high ionic conductivity of 13.1 mS cm–1 and a low activation energy of 0.17 eV, which was achieved for the first time for cold-pressed pellets, leading to a high ionic conductivity at low temperatures (1.4 mS cm–1 at −20 °C). In addition, Li6.75Sb0.25Si0.75S5I exhibits good electrochemical stability, compatibility with Li metal anodes, high critical current density (1.5 mA cm–2), and hydrolysis stability. Based on the lightweight, low-cost, and non-toxic features of Si, the high Si content in superionic conductor Li6.75Sb0.25Si0.75S5I shows substantial promise for practical use in all-solid-state Li batteries.