Superior room-temperature cycling stability of fluoride-ion batteries enabled by solid electrolytes synthesized by the solid-state reaction

All-solid-state fluoride-ion batteries (ASSFIBs) exhibit ultrahigh theoretical energy densities up to 5000 W h L-1, and thus receive increasing attention. However, due to the difficulty of identifying appropriate solid electrolytes, it was commonly believed that ASSFIBs cannot exhibit satisfactory long-term cycling performance at 25 degrees C. Recently, this situation is changed by the discovery of CsPb0.9K0.1F2.9, which shows a rare combination of high ionic conductivity and excellent electrochemical stability. Here, we discover that the performance of this material can be further improved by simply altering the reported mechanochemical synthesis approach with the solid-state reaction. The resulting material shows a room-temperature conductivity of 2.2 mS cm(-1), outperforming the most conductive F-ion solid electrolyte reported so far (PbSnF4, 1.6 mS cm(-1)). More importantly, it enables 100 cycles of stable ASSFIB operation at 25 degrees C for the first time, with a final capacity (152.5 mA h g(-1) after 100 cycles) also surpassing all the other room-temperature bulk-type ASSFIBs in literature (below 80 mA h g(-1) after no more than 20 cycles).

Automated summary

All-solid-state fluoride-ion batteries (ASSFIBs) with high theoretical energy densities have attracted increasing attention. However, the difficulty in finding suitable solid electrolytes has hindered their long-term cycling performance. A recent study discovered a new material with high ionic conductivity and excellent electrochemical stability, and by modifying the synthesis approach, its performance was further improved. This material exhibited stable battery operation for over 100 cycles at room temperature, with high capacity and conductivity.