Characterization of (PEO)LiClO₄‐Li_1.3Al_0.3Ti_1.7(PO₄)₃ composite polymer electrolytes with different molecular weights of PEO

Abstract

Abstract A group of polyethylene oxide (PEO)LiClO 4 ‐Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 composite polymer electrolyte (CPE) films was prepared by the solution‐cast method. In each film, EO/Li = 8 and the Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 content of 15 wt % were fixed, but the number averaged molecular weight of PEO ( M n ) was altered from 5 to 7 × 10 4 to 10 6 , 2.2–2.7 × 10 6 , 3–4 × 10 6 , 4–5 × 10 6 , and 5.5–6 × 10 6 , respectively. Several techniques including X‐ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and electrical impedance spectroscopy (EIS) were used to characterize the CPE films. LiClO 4 was found to have a strong tendency to complex with PEO, but Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 was rather dispersed in PEO matrix. DSC analysis revealed that the amorphous phase was dominant in the CPE films although the PEOs before‐use was considerably crystalline. SEM study showed smooth and homogeneous morphologies of the films with low molecular weight PEO and a dual phase characteristic for those with high molecular weight PEO. EIS results indicated that the CPE films are all ionic conductor and the conducting behavior obeys Vogel‐Tamman‐Fulcher (VTF) equation. The parameters in VTF equation were obtained and discussed by taking into considerations PEO molecular weights and crystallinities of the CPE films. Of all the films, the one with PEO with the smallest M n = 5–7 × 10 4 had the maximum conductivity, i.e., 1.590 × 10 −5 S cm −1 at room temperature and 1.886 × 10 −3 S cm −1 at 373 K. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4269–4275, 2006