Theoretical study of interactions of a Li⁺(CF₃SO₂)₂N⁻ ion pair with CR₃(OCR₂CR₂)_nOCR₃ (R = H or F)

Abstract

Interactions of a lithium bis(trifluoromethane sulfonyl)imide (Li(+)Tf2N(-)) ion pair with oligoethers are investigated via density functional theory (DFT). As a model for polymer electrolytes polyethyleneoxide (PEO) and perfluoropolyether (PFPE), CR3(OCR2CR2)n=1-5OCR3 (R = H or F) is considered. Topographical analysis of the molecular electrostatic potential (MESP) is performed to determine preferential binding sites of Li(+). Our study shows that the MESP value near the oxygen sites of the polymer backbone is more negative for PEO than for PFPE. This result indicates that substitution of hydrogen by fluorine in polyethers leads to reduction in Li(+)-polymer interactions, in concert with the experimental ionic conductivity results. S-O stretching vibrations of Tf2N(-) are calculated for the lithium salt in the presence and absence of electrolytes. The blue and red shifts predicted for S-O stretching are further explained by natural bond orbital analysis and molecular electron density topography. The S-O stretching vibrations can be used as a useful tool to understand the ion pair interactions and thus ion transport phenomena in polymer electrolytes.

Predicting Ion Association in Sodium Electrolytes: A Transferrable Model for Investigating Glymes

“…Regarding the role of ion association, Jónsson and Johansson performed ab initio calculations with solvation models to emphasize the general importance of anion structure and charge delocalization on ion association . Inclusion of explicit solvation was considered by Dhumal et al in a series of gas-phase ab initio DFT studies of the coordination structure of sodium salts by glymes of varying chain length. − By accounting for the chelation effect, they validated the notion that cation–anion binding weakens as the glyme length increases. This work was extended recently by Tsuzuki et al with a detailed study of the electrostatic interactions between a TFSA counteranion, sodium cations, and glymes within MP2 .…”

Structural, energetic and dynamic investigation of poly(ethylene oxide) in imidazolium-based ionic liquids with different cationic structures

“…The end bits of PEO 3 were modeled as methyl groups. 57,58 Limited by the computation time, the conformation search program Molclus 59 combined with MOPAC2016 60 was used to pre-optimize and screen the initial structures. The initial PEO/MIL and PEO/DIL structures were optimized by MOPAC2016 at the semiempirical PM6-DH+ theoretical level.…”

Homogeneous and Fast Ion Conduction of PEO‐Based Solid‐State Electrolyte at Low Temperature

“…[ 19 ] The distance between adjacent Li + binding sites (two adjacent oxygens) in a PEO molecule is the chain length of OCH 2 CH 2 O and Li + transported gradually with the length of OCH 2 CH 2 O in the intramolecular and intermolecular. [ 21–23 ] (Figure S1c and S1d, Supporting Information). Accordingly, this added filler should meet two requirements: (1) the size of the filler should be close to the chain length of OCH 2 CH 2 O and (2) the additive must effectively optimize the chemical environment of Li + .…”