Poor low-temperature performance is one of the major challenges hindering the widespread use of lithium-ion batteries. Modulation of Li+ solvation structure to facilitate desolvation process is an important strategy in electrolyte engineering under low temperature. Herein, different electronic effect groups including electron-withdrawing groups (CH2Cl) and electron-donating groups (CH3), are introduced in the weakly solvated solvent tetrahydrofuran (THF), respectively, to compare their effects on the ion-dipole interaction in the electrolyte and thus the regulation of Li+ solvation structure. Theoretical calculations combined with characterization demonstrates that the introduction of electron-withdrawing groups CH2Cl in the solvent can reduce the electron cloud density of oxygen in the THF solvent molecule, weaken the binding energy between Li+ and the solvent, and lead to more anions participating in solvation shell of Li+ and coordinating with Li+, thus accelerating the desolvation kinetics of Li+. This electrolyte-design strategy based on electronic effect tuned ion-dipole interactions has notably increased the cycling stability of the LiFePO4||Li half-cell at −20 °C, that is, it not only increases the capacity by about 10 mAh g−1 at the rate of 0.2 C, but also maintains the capacity retention rate at 97.4 % after 100 cycles. This study reveals an important electrolyte design strategy at the molecular level.
Read full abstract