The aim of this work was the preparation and characterization of solid nanocomposite polymer electrolytes consisting of a polymer matrix (poly(ethylene oxide) (PEO)), nanofiller (aminopropyl hepta- isobutyl polyhedral oligomeric silsesquioxane (APHIB-POSS)) and salt (lithium bis(oxalate )borate (LiBOB)). Nanocomposite polymer electrolytes were prepared by static melt intercalation method with different molar ratios of oxygen atoms and lithium ions (EO/Li) and different proportions of APHIB-POSS. The interactions of the added LiBOB and APHIB-POSS with the PEO polymer matrix were analyzed by Fourier transform infrared spectroscopy (FT-IR) and confirmed by differential scanning calorimetry (DSC). It was found that Li salt has a much greater influence on the reduction of the crystalline phase of PEO compared to the nanofiller. The results of the research showed that the addition of APHIB-POSS nanofillers by physical mixing with the PEO polymer matrix does not show a significant impact on reducing the PEO crystallinity as in the case of the chemical connection of the POSS molecule with the polymer macromolecule. Thermogravimetric analysis (TG) was carried out for the purpose of testing thermal stability and has showed a decrease in the thermal stability of the prepared samples compared to pure PEO. However, polymer nanocomposite electrolytes remain thermally stable enough for their application in electrochemical devices.