Size effect of cubic ZrO₂ nanoparticles on ionic conductivity of polyethylene oxide-based composite

A solvent free solid composite polymer electrolyte (SCPE) film consisting of high molecular mass polyethylene oxide (PEO) with sodium perchlorate (⁠$NaClO4$⁠) as electrolytic salt and cubic zirconium oxide (⁠$ZrO2$⁠) nanoparticles as the filler has been prepared by solution casting technique to influence the transport properties. X-ray diffraction and Fourier transform infrared spectroscopy confirm the formation of the SCPE film, whereas atomic force microscopy reveals the presence of a network of interconnected nanoparticles forming uniform surface feature of relatively low roughness. The highest ionic conductivity (⁠$σ$ = 6.96 $×$ $10-5$ S-$cm-1$⁠) for $PEO25$ - $NaClO4$ with 5 wt. % $ZrO2$ nanoparticles of the smallest size 4.5 nm is an order of magnitude higher than the pure $PEO25$ - $NaClO4$ at room temperature. The conductivity enhancement is due to the creation of additional sites and favorable conduction pathways for ionic transport through Lewis acid-base type interactions between the polar surface groups of the ceramic filler and the electrolyte ionic species.