Bi-continuous phases structured nanocomposite polymer electrolytes: Facile preparation and electrochemical properties

摘要

In this paper, inspired by the cubic bi-continuous gyroid structure self-assembled by block copolymers, we start with the application of a novel and more facile approach, compared to the tedious synthetic procedures of block copolymers, to prepare the bi-continuous phases structured nanocomposite electrolytes. The bi-continuous phase structure is composed of a hard phase of the electrospun poly vinylidene fluoride (PVDF) non-woven scaffold providing the mechanical support for the electrolyte membranes and another soft phase built up then by the infiltration of polyethylene oxide (PEO) electrolyte into the PVDF scaffold membrane to be the ionic conducting phase. Therefore, the nanocomposite polymer electrolytes of the bi-continuous phase structure are prepared with addition of the different amounts of TiO_2 nanoparticles into the PEO electrolyte (containing LiClO_4). The nanocomposite electrolyte membranes have systematically been characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), X-ray diffraction (XRD), and tensile test. The tensile results indicate that the infiltration of PEO phase into the PVDF scaffold can greatly improve the elongation of the electrolyte membrane at break, but the tensile strength of the electrolyte membrane is substantially dependent on the electrospun PVDF scaffold. The ionic conductivity measurements show that addition of TiO_2 nanoparticles with an appropriate amount of ca. 10wt% enhances the ionic conductivity of the nanocomposite electrolytes to 7.60 × 10~(-5) S cm~(-1) at 60℃, compared to 8.33 × 10~(-6) S cm~(-1) at 60℃ of the PEO-LiClO_4 electrolyte. The effect of TiO_2 nanoparticles on the enhancement of Li~+ ion conductivity has been investigated by attenuated total reflectance-Fourier transform infrared spectra (ATR-FTIR), and the results show that a competitive interaction between TiO_2 nanoparticles and Li~+ ions weakens to some extent the existing complexing action of ether-O...Li~+, allowing Li~+ ions faster transfer. However, we have found by high-resolution transmission electron microscopy (HRTEM) that the real dispersion state of TiO_2 nanoparticles in the nanocomposite electrolytes is in the form of large aggregates instead of the individual primary nanoparticles, which would tremendously depress the surface effect of the individual nanoparticles and greatly impact on the enhancement of the ionic conductivity.