Preparation and Characterization of Poly(ethylene-oxide)/Kaolinite Composite Electrolyte

Kaolinite-urea intercalation complex was prepared using kaolinite as intercalation host and urea as intercalating agent. The kaolinite-urea intercalation complex was used as precursor to prepare exfoliated kaolinite by deintercalating urea molecules from the interlayers of kaolinite through ultrasonic treatment. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the as-prepared exfoliated kaolinite. A broad 001 diffraction of kaolinite with weak intensity showed the random orientation of kaolinite platelets. SEM micrograph confirmed the exfoliation of kaolinite particles with layer thickness of no more than 50 nm. The exfoliated kaolinite particles were used as filler to poly(ethylene-oxide)/LiClO4 (PEO/LiClO4) system to prepare PEO/kaolinite composites, with the aim to improve the ion conductivity and mechanical property of the PEO matrix. SEM, transmission electron microscopy (TEM), XRD and Fourier transform infrared spectroscopy (FTIR) were used to characterize the PEO/kaolinite composites. SEM and TEM micrographs exhibited a good dispersion of exfoliated kaolinite in PEO matrix. XRD results showed that the crystallinity of PEO was gradually decreasing with increased exfoliated kaolinite content. FTIR analysis indicated that the hydrogen bonding was formed between the oxygen atoms of PEO segments and the hydroxyl groups on kaolinite surface, and this interaction between PEO and kaolinite was beneficial to the decrease in crystallinity of PEO. In order to evaluate the effect of the exfoliated kaolinite on ion conductivity and mechanical property of PEO matrix, AC impedance measurement and mechanical test were carried out. The results indicated that the ion conductivity of the composites gradually increased with increased exfoliated kaolinite content and reached 6.0 x 10(-5) S/cm at filler concentration of 20 wt%. The formation of amorphous region around the exfoliated kaolinite was beneficial for the Li+ ion conduction in PEO matrix. When the exfoliated kaolinite content reached 10 wt%, the formed amorphous regions were connected to each other to form a network for the transport of Li+ in the interconnected amorphous regions, leading to a sharp increase in ion conductivity. Moreover, the prepared composites under different drying temperature exhibited different ion conductivity. The reason was attributed to the change of PEO crystallinity with drying temperature, and the change trend of the ion conductivity was consistent with that of PEO crystallinity. Under the drying temperature of 95 degrees C, the as-prepared composite possessed high ion conductivity (6.8 x 10(-5) S/cm). In addition, the Young's modulus and tensile strength of the composites were improved because of the introduction of the exfoliated kaolinite into EPO matrix. The composites showed the maximal increase of 256% and 121% in Young's modulus and tensile strength, i.e., to 165.1 MPa and 6.743 MPa respectively, compared to PEO/LiClO4 (46.3 and 3.047 MPa). Therefore, the exfoliated kaolinite was a promising filler to prepare PEO based polymer electrolyte.