Solid-state polymer nanocomposite electrolyte of TiO₂/PEO/NaClO₄ for sodium ion batteries

A free-standing transparent film for sodium-ion conduction in PEO-based solid polymer electrolyte (additionally comprising NaClO₄ and nano-sized TiO₂) has been fabricated for use in Na-ion batteries by using a solution casting technique. The crystallinity of the solid polymer electrolyte and the interactions between PEO and the Na-ions is characterized by X-ray diffraction (XRD) and Fourier transformed infra-red (FTIR) spectra, which reveals the degree of Na⁺ ion solvation by PEO oxygen atoms (EO:Na). The ionic conductivities of the films are investigated by impedance analysis from 1 MHz to 1 Hz within the temperature range 303-363 K. A solid polymer electrolyte with anatomic ratio EO:Na = 20 exhibits a maximum ionic conductivity of 1.35 × 10^-4 S cm^-1, which increases to 2.62 × 10^-4 S cm^-1 by the addition of TiO₂ (3.4 nm, 5 wt%) at temperature 60 °C. The performance of a Na_2/3Co_2/3Mn_1/3O₂ half cell with a polymer electrolyte is compared to a similar cell with a liquid electrolyte.