Stable all-solid-state Li-Te battery with Li₃TbBr₆ superionic conductor

Rare-earth (RE) halide solid electrolytes (HSEs) have been an emerging research area due to their good electrochemical and mechanical properties for all-solid-state lithium batteries (ASSBs). However, only very limited types of HSEs have been reported with high performance. In this work, tens of grams of RE-HSE Li₃TbBr₆ (LTbB) was synthesized by a vacuum evaporation-assisted method. The as-prepared LTbB displays a high ionic conductivity of 1.7 mS·cm⁻¹, a wide electrochemical window, and good formability. Accordingly, the assembled solid lithium-tellurium (Li-Te) battery based on the LTbB HSE exhibits excellent cycling stability up to 600 cycles, which is superior to most previous reports. The processes and the chemicals during the discharge/charge of Li-Te batteries have been studied by various in situ and ex situ characterizations. Theoretical calculations have demonstrated the dominant conductivity contributions of the direct [octahedral]–[octahedral] ([Oct]–[Oct]) pathway for Li ion migrations in the electrolyte. The Tb sites guarantee efficient electron transfer while the Li 2s orbitals are not affected during migration, leading to a low activation barrier. Therefore, this successful fabrication and application of LTbB have offered a highly competitive solution for solid electrolytes in ASSBs, indicating the great potential of RE-based HSEs in energy devices.