First-Principles Study of the Solvation Structure of Tetraglyme based Electrolytes

Glyme based electrolytes for rechargeable Li secondary batteries are of great interest, due to the high oxidative stability, low vapor pressure, and non-flammability. Here we employ the first-principles molecular dynamics simulation to study the lithium bis(trifluoromethylsulfonyl)-amide (LiTFSA) and tetraglyme (G4) electrolyte system. For the case of equimolar Li salt concentration, a positive correlation between the total coordination number of Li⁺ ions and the phase stability is clearly established. At the ground state of equimolar LiTFSA-G4 electrolyte, most of Li⁺ ions are coordinated to four O atoms of a curled G4 molecule and one O atom of a TFSA⁻ anion. By contrast, Li⁺ ions prefer to be coordinated by two G4 molecules and not in direct contact with TFSA⁻ anions at a low concentration of the Li salt. The significantly increased probability of pairing between the Li-G4 complexes and TFSA⁻ anions at the equimolar ratio could be highly relevant to its ionic-liquid-like properties [1].
[1] Y. Sun and I. Hamada, J. Phys. Chem. B, Article ASAP DOI: 10.1021/acs.jpcb.8b07098