Weakly Solvating Cyclic Ether-Based Deep Eutectic Electrolytes for Stable High-Temperature Lithium Metal Batteries.

Deep eutectic electrolytes (DEE) have emerged as an innovative approach to address the instability and safety issues of lithium metal batteries at elevated temperatures. However, in practice, there is often an undesirable incompatibility between the eutectic mixture and electrodes, and also an insufficient reduction stability of DEE due to the increased Li concentration. Herein, we designed a new DEE by utilizing weakly solvating tetrahydropyran (THP) solvent. Due to the high reduction resistance of THP and concentrated lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), this DEE demonstrates enhanced compatibility with Li metal anode and high temperature tolerance with LiMnO cathode. The Li||LiMnO cell (1.6 mAh cm) shows a high capacity retention of 96.02 % after 600 cycles at room temperature. More importantly, this Li||LiMnO cell achieves a remarkable high-temperature performance with a high capacity retention of 91.72 % after 120 cycles and low self-discharge after storage for 240 hours at a high temperature of 55 °C, which is critical for LiMnO cathode. Overall, this electrolyte design provides an alternative pathway for the development of DEEs for high-temperature and high-voltage lithium metal batteries, which can also be expanded to other batteries.