Interactions of Li⁺ and 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 Å 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 Å from the TiO₂ nanoparticle also revealed some structuring and reduced dynamics, whereas the PEO/LiBF₄ located further than 15 Å 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 Å. 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%.