A Carboxylic Ester-Based Electrolyte with Additive to Improve Performance of Lithium Batteries at Ultra-Low Temperature

Lithium metal batteries (LMBs) are the promising battery system to push energy density to high level at low temperatures. In this work, the linear carboxylic esters methyl propionate (MP)-based electrolyte with 4 wt% fluorinated ethylene carbonate (FEC) is reported. The low melting point and viscosity of MP makes it the candidate solvent for the low temperature field. Assisted with FEC, the optimized electrolyte shows quite high ionic conductivity and better compatibility with separator and lithium metal anode, resulting in stable cycling performance at room temperature. Besides, it keeps liquid state at −70 °C and exhibits lower binding energy with lithium ion, enabling the Li/LiCoO 2 batteries to cycle at −40 °C for 60 cycles. Apart from that, this battery can retain 88.6% discharge capacity at −70 °C of that at room temperature, reaching the highest discharge capacity retention at this ultra-low temperature to the best of our knowledge. This work demonstrates a simple but effective way to design the electrolytes with excellent low temperature performance.