Sodium Halide Solid State Electrolyte with High Ionic Conductivity | Laisuo Su

All-solid-state batteries (ASSBs) are a promising next-generation energy storage technology, offering enhanced safety by replacing flammable liquid electrolytes with non-flammable solid electrolytes (SEs). The robust mechanical strength of SEs also enables the use of metal anodes for high energy density. Among various SEs, halide-based materials have gained attention due to their high ionic conductivity, oxidative stability, deformability, and moisture tolerance. However, most reported halide SEs are lithium-based, with sodium counterparts still underdeveloped. In particular, Na halide SEs often exhibit low ionic conductivity, typically less than 0.1 mS/cm, limiting their practical application. Here, we report a new Na halide-based SE with room-temperature Na⁺ conductivity exceeding 1 mS/cm and an activation energy of just 0.23 eV. The material exhibits a mixed amorphous-crystalline structure, and its conductivity decreases with increasing crystallinity. This conductivity rivals that of some organic liquid electrolytes, making it viable for real-world applications. Our synthesis strategy offers a pathway to improve ionic conductivity in other halide-based SEs, advancing the development of sodium ASSBs.

Keywords: Sodium; Solid-state electrolyte; Amorphous-crystalline structure; All-solid-state batteries.

This presentation is part of the Power-to-X for a Sustainable Future Workshop 2025, taking place on 14–16 September 2025 at the Montien Hotel Surawong, Bangkok, Thailand. The Power-to-X initiative is supported by the Royal Academy of Engineering.