Solid Poly(2-alkyl/Aryl-2-oxazoline) Electrolytes: A Molecular Dynamics Study of Structure and Ionic Conductivity

Abstract

This study employed molecular dynamics (MD) simulations to investigate the structure and ionic conductivity of 5 solid polymer electrolytes (SPEs), poly(ethylene oxide) (PEO), poly(2-ethyl-2-oxazoline) (PEOZ), poly(2-propyl-2-oxazoline) (PPrOZ), poly(2-pentyl-2-oxazoline) (PPeOZ), and poly(2-phenyl-2-oxazoline) (PPhOZ), complexed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Key parameters, including Li+ transport number, radial distribution functions (RDF), density functional theory (DFT), degree of independent ion motion, mean-square displacements (MSD), and coordination numbers, were analyzed. In all electrolytes, the Li:O ratio was kept at 1:16, with polymer molecular weights set at 5 kDa. Comparing DFT and coordination number results reveals that PPhOZ can have high Li+ diffusivity because of low binding energy and low coordination with the O of the polymer. PEO also has a low coordination number and binding energy, which makes it favorable for Li+ hopping without causing a caging effect. These findings suggest that, alongside PEO, PPhOZ is a promising candidate for solid-state electrolyte applications in lithium-ion batteries due to its efficient Li-TFSI separation and favorable Li-O and Li-N interactions.