Ion-Dipole Chemistry Drives Rapid Evolution of Li Ions Solvation Sheath in Low-Temperature Li Batteries

摘要

Sluggish evolution of lithium ions' solvation sheath induces large charge-transfer barriers and high ion diffusion barriers through the passivation layer, resulting in undesirable lithium dendrite formation and capacity loss of lithium batteries, especially at low temperatures. Here, an ion-dipole strategy by regulating the fluorination degree of solvating agents is proposed to accelerate the evolution of the Li+ solvation sheath. Ethylene carbonate (EC)-based fluorinated derivatives, fluoroethylene carbonate (FEC) and di-fluoro ethylene carbonate (DFEC) are used as the solvating agents for a high dielectric constant. As the increase of the fluorination degree from EC to FEC and DFEC, the Li+-dipole interaction strength gradually decreases from 1.90 to 1.66 and 1.44 eV, respectively. Consequently, the DFEC-based electrolyte displays six times faster ion desolvation rate than that of a non-fluorinated EC-based electrolyte at -20 degrees C. Furthermore, LiNi0.8Co0.1Mn0.1O2||lithium cells in a DFEC-based electrolyte retain 91% original capacity after 300 cycles at 25 degrees C, and 51% room-temperature capacity at -30 degrees C. By bridging the gap between the ion-dipole interactions and the evolution of Li+ solvation sheath, this work provides a new technique toward rational design of electrolyte engineering for low-temperature lithium batteries.