Density functional theory study on structure information and modification design of solid polymer electrolytes containing ester-thioether groups

Poly (ethylene glycol dimethacrylate-1,2-ethanedithiol) (P(EDGMA-EDT)) and poly (ethylene glycol dimethacrylate-3,6-dioxy-1,8-octanedithiol) (P(EDGMA-DODT)) are excellent solid polymer electrolytes synthesized experimentally. The coordination structure, redox properties, and modification design of P(EDGMA-EDT)-LiTFSI and P(EDGMA-DODT)-LiTFSI are investigated by density functional theory. The theoretical simulation of infrared spectra and the coordination structure information show that the ester carbonyl group in P(EDGMA-EDT) and the ester carbonyl group and ether oxygen in P(EDGMA-DODT) interact with Li⁺ ions. Li⁺ ion coordination numbers in these two electrolytes are 4 and 5; thioether and ester groups in polymers are their redox active sites, respectively. Modified sulfone oxide P(EDGMA-EDT)2-SO₂ and P(EDGMA-DODT)2-SO₂ cannot only maintain the reduction stability but also greatly improve the oxidation potential. LiPF₆, LiDFBOP, and LiBF₃Cl are good candidates for sulfone-based polymers. The electron-withdrawing groups (− 4Br, − 4Cl, − 4F, − NO₂, and − CN) substitution can improve the oxidation potential of P(EDGMA-EDT) but have little effect on the oxidation potential of P(EDGMA-DODT) and reduce the reduction stability of both polymers. These findings provide theoretical guidance for the coordination structure as well as the molecular design of solid electrolytes containing ester groups and thioether.