Molecular dynamics simulation of the effect of adding an Al2O3 nanoparticle to PEO–LiCl/LiBr/LiI systems

The effect of adding ca. 20 Å diameter quasi-spherical nanoparticles of α-Al2O3 (corundum) to LiCl, LiBr and LiI salts in amorphous PEO has been simulated at a nominal 360 K by molecular dynamics (MD) methods; the Li∶EO ratio studied was 1∶10, along with salt-free and particle-free reference cases. The PEO forms an immobilised coordination sphere around the particle. Li-ion mobility in PEO is found to decrease on the addition of particles; the effect is greatest near the particle surface in the region of the PEO. LiX pairing/clustering (for X = Cl, Br, I) was observed away from the particle surface; the effect was greatest for LiBr and least for LiCl. The ion-clustering tendency would appear to be dependent on the particle size; it is noticeably larger for the case of smaller particles. A number of unpaired Li ions were found attached to the particle within the region of the immobilised PEO. Corresponding “free” anions were located somewhat further away from the particle surface in the more mobile PEO regions, along with charged and uncharged ion-clusters.