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 oC. 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 oC and 60 oC, 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.