Influence of Fe₂O₃ Nanofiller Shape on the Conductivity and Thermal Properties of Solid Polymer Electrolytes: Nanorods versus Nanospheres

The influence of nanofiller shape on the ionic conductivity and thermal properties of solid polymer electrolytes is investigated. Electrolytes of polyethylene oxide (PEO) and LiClO 4 filled with 1–20 wt % spherical Fe 2 O 3 nanoparticles and 0.5–10 wt % Fe 2 O 3 nanorods are measured at an ether oxygen to Li ratio of 10:1. Nanorods improve the ionic conductivity to a similar extent as spherical nanoparticles, except at concentrations 10–20 times lower. The maximum conductivity improvement occurs at a spherical metal oxide nanoparticle loading of 10 wt %; however, an equivalent nanorod loading decreases the conductivity below that of the unfilled electrolyte. This result suggests that the long-range morphology of the two nanocomposites differs widely, where high concentrations of nanorods will inhibit instead of enhance Li transport. The shape of the nanofiller also affects the crystallization rate and resulting crystal structure. Differential scanning calorimetry measurements show that samples containing nanorods crystallize faster than those containing spherical nanoparticles, and nanorods favor formation of the (PEO) 6:LiClO 4 crystal phase. Previous studies have shown that this channel-like structure is more conductive than the amorphous phase. If nanorods could be used to induce the formation and alignment of this conductive structure normal to the electrode surface, perhaps ionic conductivity could be further enhanced in nanofilled solid polymer electrolytes where the nanoscale structure is precisely controlled.