Electrolyte Design via Hydrogen Bonding Between Solvent and Non-Solvating Cosolvent Enabling Stable Lithium Metal Batteries at −20°C

Lithium metal batteries (LMBs) have great significance in enhancing energy density. However, low ion diffusion in bulk electrolytes, high desolvation energy of Li⁺, and sluggish ion transport kinetics in electrode interphases at low temperatures cause LMBs to have a short cycle life (usually below 300 cycles). In this study, we designed a low-temperature electrolyte to overcome these issues. The medium-chain length isopropyl formate (IPF) was employed as main solvent in the designed electrolyte. Especially, the hydrogen bonding between non-solvating cosolvent (1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether [TFE]) and IPF can be formed, leading to the weakened interaction between Li⁺ and the solvents. Thus, a fast Li⁺ desolvation can be achieved. Additionally, the designed electrolyte can maintain a high conductivity (6.37 mS cm⁻¹) at −20°C and achieve higher Li⁺ transference numbers (0.62). Finally, Li||LiFePO₄ full cells using the designed electrolyte exhibit a capacity of 113 mAh g⁻¹ after 480 cycles at 0.1C under −20°C. Meanwhile, Li||LiFePO₄ can deliver 150 mAh g⁻¹ after 120 cycles at 50°C. This study provides a novel pathway for optimizing electrolytes for next-generation LMBs during low-temperature operations.