Theoretical study on oxidation-reducing properties of polyacetal solid electrolytes

Abstract

Density functional theory (DFT) is used to study the redox properties of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and polyacetal [P(2EO-MO), P(EO-MO), P(EO-2MO)] electrolyte system. It is found that the oxidation potential is mainly controlled by the polymer, the reduction potential depends on the salt anion. Among three polyacetal electrolytes, P(EO-MO) has the most excellent electrochemical window, can be used as a high-pressure electrolyte material. Another six lithium salts (LiCF₃SO₃, LiDFSI, LiPDI, LiTDI, LiBOB, LiDFOB) and five substituents (–CN, –F, –CF₃, –NH₂, –CH₃) are selected to modify the polyacetal electrolyte in order to design a new solid electrolyte with better electrochemical performance. It is found that the electrolyte composed of LiCF₃SO₃ and polyacetal has good electrochemical stability. The introduction of electron-absorbing groups improves the oxidation potential of the three polyacetals, the introduction of electron-donating groups can improve the reduction stability of the polymers. Based on this, three substituent-functional polymers, P(EO-MO)-CN, P(EO-MO)-F and P(EO-MO)-CH₃, are designed to pair LiCF₃SO₃ to form electrolytes. These three electrolytes have a wide electrochemical window and can be used as high-voltage cathode resistant materials. These results enrich the theoretical research of redox properties of polyacetal electrolytes and provide theoretical guidance for the design of polyacetal electrolytes.