Development of non-fluorinated hybrid ester solvents for wide-temperature operation of lithium-ion batteries†

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 the carbonyl group (CO). This results in low binding and solvation energies in electrolytes, confirmed by DFT, MD simulations, Raman spectra, and electrochemical analyses. The MMP electrolytes showed superior rate capabilities and cyclability in a wide temperature range from −30 to 45 °C. 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.