Molecular dynamics simulation of the LiBF4–PEO system containing Al2O3 nanoparticles

Abstract

The amorphous LiBF4(PEO)20 system has been simulated alone and containing a ca. 14-Å diameter Al2O3 nanoparticle and in juxtaposition with a ca. 65-Å thick α-Al2O3 slab at a nominal temperature of 293 K by Molecular Dynamics (MD) methods. Li-ion mobility in the poly(ethylene oxide) (PEO) host is found to increase on the addition of the nanoparticle; the effect is also noticeable for the alumina slab. This can be seen as theoretical confirmation of the positive influence of nanoparticles on ion mobility in a PEO–salt system, as observed earlier experimentally. Other effects observed are related to this Li-ion mobility enhancement: PEO forms an immobilised coordination sphere around the particle and an immobilised layer at the surface of the α-alumina slab. No Li ions are found near the particle or at the slab surface. Instead, two to three unpaired BF4− anions are found attached to the particle within the region of immobilised PEO and at least one is found immobilised on the slab surface, leaving free Li ions in the regions away from the particle and slab surfaces. No more than 60% of the Li ions form ion pairs and ion clusters in the regions away from the particle surface and up to 87% of the Li ions form ion pairs and ion clusters in the regions away from the slab surface.