Structure and Mobility of PEO/LiClO4 Solid Polymer Electrolytes Filled with Al2O3 Nanoparticles

The mechanism for improved ionic conductivity in nanoparticle-filled solid polymer electrolytes containing polyethylene oxide [PEO], LiClO4, and Al2O3 is investigated using differential scanning calorimetry [DSC], dielectric spectroscopy, small-angle neutron scattering [SANS], and quasi-elastic neutron scattering [QENS]. We measure samples with ether oxygen to lithium ratios ranging from 14:1 to 8:1 and Al2O3 nanoparticle concentrations ranging from 5 to 25 wt %. The T g and pure PEO crystal fraction are unaffected by nanoparticle addition, and SANS reveals nanoparticle aggregation, with the extent of aggregation similar in all samples regardless of LiClO4 or Al2O3 concentration. Despite the similarity between samples, nanoparticles improve conductivity at all temperatures, but only at the eutectic concentration (ether oxygen to lithium ratio of 10:1). Our QENS results indicate that a rotation is present in both filled and unfilled samples at all concentrations and is consistent with the rotation of (PEO)6:LiClO4, a channel-like structure that is more conductive than the amorphous equivalent. The rotation becomes more restricted in the presence of nanoparticles.