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

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.

Automated summary

The sluggish evolution of lithium ions' solvation sheath can lead to dendrite formation and capacity loss in lithium batteries, especially at low temperatures. However, by using an ion-dipole strategy to regulate the fluorination degree of solvating agents, it is possible to accelerate the evolution of Li+ solvation sheath and improve battery performance. The DFEC-based electrolyte demonstrates significantly faster ion desolvation rate at low temperatures, allowing for better capacity retention in LiNi0.8Co0.1Mn0.1O2||lithium cells after cycling. This work provides a new technique towards rational design of electrolyte engineering for low-temperature lithium batteries.