Investigation the electrochemical properties of LiCl-LiBr-LiF-doped Li7La3Zr2O12 electrolyte for lithium thermal batteries

Li7La3Zr2O12 (LLZO) has been considered as one of the most promising electrolytes for lithium batteries due to its high safety and wide electrochemical window. However, few reports were observed for the application of LLZO on lithium thermal batteries. In this paper, LLZO was studied as the electrolyte of lithium thermal battery. To further improve the performance of LLZO, LLZO-LiCl-LiBr-LiF composite electrolyte was designed by mechanical mixing LiCl-LiBr-LiF eutectic salt with LLZO. The doping content of LiCl-LiBr-LiF was also investigated, and the results showed that the optimize content was 15% (in weight) LiCl-LiBr-LiF. For instance, the specific capacity of the battery using LLZO-(LiCl-LiBr-LiF)x (x = 15%) as electrolyte was 224.6 mAh g−1, the active material utilization rate was 85.08%, and the service life of lithium thermal battery can be extended to 25 min under 80 mA cm−2 at 550 °C. The superior electrochemical properties of LLZO-(LiCl-LiBr-LiF)x (x = 15%) were ascribed to the larger ionic conductivity (2.802 × 10−2 S cm−1 at 550 °C). Our study not only successfully improves the electrochemical properties of LLZO by compositing with LiCl-LiBr-LiF electrolyte but also paves the way for the practical application of LLZO-LiCl-LiBr-LiF composite in the lithium thermal batteries.