High-performance sulfide electrolyte based on tin (Sn) element replacement for all-solid-state lithium metal batteries

High-performance sulfide electrolyte based on tin (Sn) element replacement for all-solid-state lithium metal batteries
In order to solve the current problems of low energy density and low safety of liquid electrolyte-based lithium-ion batteries, researchers have proposed the development of new all-solid-state lithium-metal batteries based on sulfide-based electrolytes. However, for sulfide electrolytes, there are two major problems that are currently hindering their further development. First, poor compatibility of lithium metal cathodes. Almost all of the reported sulfide electrolytes are reduced by lithium metal. In addition, because of the unstable lithium deposition at the sulfide/lithium metal interface, the same will produce lithium dendrites, and make the battery failure. Second, air instability. Because the sulfide electrolyte in the positive pentavalent phosphorus (P) has a very strong affinity for oxygen (O) in the air, so the sulfide electrolyte can react with water in the air, thus releasing hydrogen sulfide (H2S) gas. To alleviate the incompatibility of the sulfide/Li cathode interface, researchers have repeatedly reported that the I- or F-rich Li cathode interface layer is beneficial for stable deposition/deposition of Li metal. In particular, when the electrolyte itself contains I, the in situ formation of I-containing interfacial layer can provide very good lithium cathode protection through electrochemical reactions. However, at present, the synthesis of sulfide electrolytes with excellent room temperature ionic conductivity (>10-4 S/cm) and at the same time good air stability is still a great challenge. From the literature reported so far, a class of electrolytes based on the Li-Sn-S system (Li4SnS4 and Li2SnS3) is the only class of sulfide electrolytes that can be stable in air (conductive to lithium ions), but their room-temperature ionic conductivity lies only in the 10-5 S/cm level. The Li6PS5I (LPSI) sulfide electrolyte of the sulfur-silver-germanite type, which is itself rich in I, is considered to have good lithium metal compatibility. However, its room temperature ionic conductivity is only ~10-6 S/cm. In addition, like other sulfides, it is unstable in air.

Professor Xueliang Sun's group at the University of Western Ontario, Canada, used tin (Sn) to partially replace phosphorus (P) in a sulfur-silver-germanium ore type LPSI sulfide electrolyte to prepare a new solid-state electrolyte with Sn replacement: LPSI-xSn (x is the Sn replacement percentage). Multiple test results show that the room-temperature ionic conductivity of the LPSI-20Sn electrolyte is 125 times higher than that of the LPSI electrolyte, reaching 3.5 × 10-4 S/cm. The high ionic conductivity allows this iodine (I)-rich electrolyte to be used as a stable lithium metal cathode interlayer, allowing the all-solid-state lithium metal battery to operate smoothly at room temperature. More importantly, the air stability of the sulfide electrolyte is also significantly improved thanks to the Sn-S bond that is stable in air. This three-in-one element replacement strategy provides a new guideline for us to continue exploring and developing new high-performance sulfide electrolytes.