Development of Non-fluorinated Hybrid Ester Solvents for Wide-Temperature Operation of Lithium-Ion Batteries

Abstract

In the pursuit of wide-temperature operable Li-ion batteries (LIBs), novel electrolytes have been explored to support fast charge (Li-ion) transfer at low temperatures to overcome the low melting point of ethylene carbonate solvent. Although ester-based solvents have garnered attention due to their relatively low melting points and high ionic conductivity, they suffer from high affinity to Li-ions in electrolytes, resulting in large interfacial resistances at the graphite anodes. Herein, we propose a novel approach of hybridization of ester solvents with ether functional groups into intra-molecular structures. Methyl 3-methoxypropionate (MMP), a hybrid solvent with the opposite orientation of functional groups, showed an increased electron-withdrawing effect on the oxygen in carbonyl group (C=O). This results in low binding and solvation energies in electrolytes, confirmed by DFT, MD simulations, Raman spectra, and electrochemical analysis. The MMP electrolytes showed superior rate capabilities and cyclability at a wide temperature range from −30 to 45^oC. The strategy of manipulating the molecular structure to reduce the de-solvation energy shows promise in achieving fast charging and widening the range of operation temperature.