Electronic effect tuned ion-dipole interactions for low-temperature electrolyte design of LiFePO4-based lithium-ion batteries

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 ( CH 2 Cl) and electron-donating groups ( CH 3 ), 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 CH 2 Cl 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 LiFePO 4 ||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.