Smart Deep Eutectic Electrolyte Enabling Thermally Induced Shutdown Toward High-Safety Lithium Metal Batteries

摘要

Severe safety concerns and uncontrollable lithium dendrites are major challenges for commercializing high-voltage lithium metal batteries (LMBs) utilizing state-of-the-art carbonate-based electrolytes. Herein, a new type of deep eutectic electrolyte (succinonitrile/1,3,5-trioxane/lithium difluoro(oxalato) borate (DFOB), abbreviated as DEE) with a thermally induced smart shutdown function is presented to ameliorate the aforementioned issues. In this delicately designed DEE, 1,3,5-trioxane (TXE) can participate in the Li+ primary solvation shell and form an unique solvation structure (Li~+-SN-TXE-DFOB~?), which is favorable to enhance the Li/electrolyte interfacial compatibility. It is demonstrated that a 4.45 V LiCoO_2/Li battery using the as-prepared DEE electrolyte delivers a high Coulombic efficiency (99.5%), remarkable cyclability (capacity retention of 81% after 100 cycles) at 25 ℃. Furthermore, thermal abuse tests of LiCoO_2/Li batteries using the as-prepared DEE display a rapid thermal shutdown function to terminate Li-ion transportation and subsequent battery operation when they are exposed to environment temperatures exceeding 150 ℃. This thermally induced shutdown function is achieved via the polymerization of TXE to polyformaldehydes possessing ultra-low ionic conductivity at elevated temperatures. The as-reported smart, thermallyinduced shut-down DEE opens new avenues for designing next-generation high-performance LMBs with enhanced safety properties.