Rational Design of Fluorinated Electrolytes for Low Temperature Lithium-Ion Batteries

摘要

Nonaqueous carbonate electrolytes are commonly used in commerciallithium-ion battery (LIB). However, the sluggish Li~+ diffusivity and highinterfacial charge transfer resistance at low temperature (LT) limit theirwide adoption among geographical areas with high latitudes and altitudes.Herein, a rational design of new electrolytes is demonstrated, which cansignificantly improve the low temperature performance below ?20 ℃. Thiselectrolyte is achieved by tailoring the chemical structure, i.e., altering thefluorination position and the degree of fluorination, of ethyl acetate solvent.It is found that fluorination adjacent to the carbonyl group or high degreeof fluorination leads to a stronger electron-withdrawing effect, resultingin low atomic charge on the carbonyl oxygen solvating sites, and thus lowbinding energies with Li~+ ions at LT. The optimal electrolyte 2,2,2-trifluoroethylacetate (EA-f ) shows significantly improved cycle life and C-rate of aNMC622/graphite cell when cycled at ?20 ℃ and ?40 ℃, respectively. Inaddition to superior LT performance, the electrolyte is nonflammable andtolerant for high voltage charging all owing to its fluorine content. This workprovides guidance in designing next-generation electrolytes to address thecritical challenge at subzero temperatures.