Molecular dynamics study of nanocomposite polymer electrolyte based on poly(ethylene oxide)/LiBF4

Interactions of Li+ and BF4- ions with TiO2 clusters were investigated using ab initio quantum chemistry methods. Classical force fields have been developed for poly(ethylene oxide)/LiBF4/TiO2, and molecular dynamics simulations have been performed on poly(ethylene oxide)/LiBF4 polymer electrolyte with and without embedded TiO2 nanoparticles using the developed force field. Addition of a TiO2 nanoparticle to PEO/LiBF4 solid polymer electrolyte resulted in the formation of a highly structured layer with a thickness of 5-6 Angstrom that had more than an order of magnitude slower mobility than that of bulk PEO/LiBF4. The PEO and ions in the layers extending from 6 to 15 Angstrom from the TiO2 nanoparticle also revealed some structuring and reduced dynamics, whereas the PEO/LiBF4 located further than 15 Angstrom was basically unaffected by the presence of the TiO2 nanoparticle. Both cations and anions tended to form a region with an increased concentration in the interfacial layers extending from 5 to 15 Angstrom. No ions were dissolved by the first interfacial layer of PEO. Addition of a nanoparticle with soft-repulsion interactions with PEO resulted in the formation of a PEO interfacial layer with reduced PEO density but increased ion concentration. The PEO and ion mobility in the interfacial layer next to the soft-repulsive nanoparticle were higher than those of bulk PEO/LiBF4 by 20-50%, whereas the conductivity of the nanocomposite electrolyte with the soft-repulsive particle increased only by 10%.