Molecular Design of Mono-Fluorinated Ether-Based Electrolyte for All-Climate Lithium-Ion Batteries and Lithium-Metal Batteries

Abstract

Fluorinated-ethers are promising electrolyte solvents in lithium metal batteries, for their high antioxidant and excellent reductive stability on Li anode. However, fluorinated-ethers with high fluorination degree suffer from low ionic conductivity and narrow temperature adaptibility. Herein, we synthesize a mono-fluorinated linear ether of bis(2-fluoroethoxy) methane (BFME) with enhanced solvated ability. The −OCH₂O− structure and fluoride substitution on the β-C position endows the BFME electrolyte with moderate affinity to Li⁺, thereby improving the ionic conductivity and decreasing the Li⁺-desolvation energy barrier at a wide temperature range of −60–60 °C. Additionally, the electrolyte with anion-participated solvation structure demonstrates high film-forming ability by forming LiF-rich interfacial film on the electrode surfaces, rendering the graphite anode with an initial Coulombic efficiency (CE) of 94.9 % and a Li plating/stripping CE of 99.8 % by Aurbach method. Consequently, the Graphite||LiFePO₄ pouch cells delivered 83.2 %, 92.5 % and 81.2 % capacity retention after 1250, 200 and 300 cycles at 25, −20 °C and 60 °C, respectively. Moreover, the Li||LFP pouch cell with 3 Ah capacity can operate for 65 cycles with 99 % capacity retention, verifying the effectiveness of the BFME electrolyte in stabilizing the interfaces and broadening the temperature adaptibility of lithium-ion and lithium metal batteries.