Understanding the Role of Fluorination on the Interaction of Electrolytic Carbonates with Li⁺ through an Electronic Structure Approach

Abstract

The donor-acceptor orbital interaction between the unoccupied orbital of Li + and the lone pair of oxygen atoms in the carbonyl group of Li + -carbonate complexes shows significant decrease on fluorination. This has been investigated through molecular orbital formalism based density functional theory. The fluorination process lowers the binding energy (reduced up to 13.8 kcal/mol), and widens the HOMO-LUMO gap (enhanced up to 0.7 eV), which is essential for achieving electrolytes with high potential window in Li-ion battery. Furthermore, the impact of fluorination on few critical factors has been observed, i. e. dipole moment (drastic enhancement), IR spectra (most affected C=O vibrational mode shows blue shift in the spectra) and Raman active mode (carbonyl group stretching mode doublet (n C<C¼>O ) shifted to higher frequency) which have been probed by vibrational frequency analysis.

Reaction Mechanisms of the Degradation of Fluoroethylene Carbonate, an Additive of Lithium‐Ion Batteries, Unraveled by Radiation Chemistry

“…Its melting point is around 293 K. The FEC molecular weight is 106.05 g mol À 1 , and its mass density at 298 K is 1.410 g cm À 3 (neat FEC thus corresponds to 13.3 mol L -1 ). [36] The FEC dielectric constant was experimentally determined around 110, [27] but calculated to be 91 at 298 K. [36] Its dipole moment was calculated to be 4.67 D. [37] As in the case of propylene carbonate (PC), [17] the high static dielectric constant may be a consequence of the large value of the dipole moment. The dynamic viscosity of FEC is 4 mPa.s at 20°C.…”

“…The FEC dielectric constant was experimentally determined around 110, [27] but calculated to be 91 at 298 K [36] . Its dipole moment was calculated to be 4.67 D [37] . As in the case of propylene carbonate (PC), [17] the high static dielectric constant may be a consequence of the large value of the dipole moment.…”

trans-Difluoroethylene Carbonate as an Electrolyte Additive for Microsized SiOx@C Anodes

“…In order to obtain insights into the electrochemical properties of the three additives (EC, FEC, and DFEC), the interaction between them and lithium ions is essential to be investigated comprehensively. As shown in Figure a, the binding energies ( E b , kcal mol –1 ) of Li + [EC], Li + [FEC], and Li + [DFEC] were calculated to evaluate the effect of additives on the solvation of lithium ions by density functional theory (DFT, conducted with the B3LYP functional and cc-pVTZ basis sets) . The binding energy value of Li + [DFEC] (−43.26 kcal mol –1 ) is significantly lower than those of Li + [FEC] (−48.26 kcal mol –1 ) and Li + [EC] (−53.09 kcal mol –1 ), revealing that Li + have weaker interaction with DFEC in comparison with FEC and EC .…”

Influences and Mechanisms of Water on a Solid Electrolyte Interphase Film for Lithium-Ion Batteries

“…As shown in Figure 4a, the distinct peaks arising around 1149 cm −1 (δCH 2 , marked as "▲"), 1060 cm −1 (ν s O−C−O marked as "▼"), and 1645 cm −1 (νO−H, marked as "◆") are the characteristic transmittance peaks of EC solvent. 26,27 Moreover, blue shifts of δCH 2 and ν s O−C−O can be observed with the introduction of water impurity, indicating that water has a weak structure influence on EC solvent through CH 2 − and −OCO− groups. 28,29 When LiBOB is dissolved in the EC solvent, in addition to the characteristic peak of the EC solvent, a new peak emerges at 1285−1300 cm −1 (ν as Li + −OC, marked as "★"), implying the presence of the solvation structure of Li + (EC) 4 .…”