DFT analysis of structural and optoelectronic properties of (PEO)8-LiFSI complexes

Abstract

Computational tools for studying the atomic and molecular structures of complex systems are very useful. This work uses the first principle method to investigate the structural and optoelectronic properties of a polyethylene oxide (PEO)-based solid polymer electrolyte including lithium salt (LiFSI) as an ion-conducting species. Density functional theory (DFT) has been used for the analysis of electrolyte conducting properties. The band gap of the polymer electrolyte (PEO)₈-LiFSI system has been quantitatively examined by the HOMO–LUMO concept. It is verified that (PEO)₈ exhibits insulator properties with a wide band gap of 6.27 eV, whereas the bandgap of (PEO)₈-LiFSI slightly drops to 6.00 eV. These findings suggest that the current polymer electrolyte system (PEO)₈-LiFSI could be a viable option for the electrolyte in next-generation energy storage devices. The low electronic conductivity, confirmed through electronic analysis, is essential in maintaining high safety standards by preventing electronic leakage, which could lead to short circuits in solid-state batteries. Raman and IR spectra reveal crucial interactions between the Li⁺ ions and the PEO matrix, specifically the coordination of Li⁺ with the ether oxygen of PEO and the FSI⁻ anion. These interactions significantly affect the ionic conductivity by influencing ion transport mechanisms in the electrolyte. NMR analysis provides detailed insights about the (PEO)₈ and (PEO)₈-LiFSI structures that in turn help to estimate the mobility and dynamics of lithium ions within the polymer matrix. The UV–vis-nir analysis offers insights into the optical and electronic properties. This is important for understanding the lifetime and reliability of the electrolyte in solid-state battery applications. Therefore, the results collectively provide a comprehensive understanding of the (PEO)₈-LiFSI system, for using it as a solid polymer electrolyte for next-generation solid-state batteries.