Novel composite polymer electrolyte comprising mesoporous structured SiO₂ and PEO/Li

Novel composite polymer electrolytes comprise of hexagonal array of mesoporous structured MCM-41, and poly(ethylene oxide) (PEO)/Li show that the conductivity and mechanical properties are improved simultaneously. The comparison of small angle X-ray diffraction (XRD) of mesoporous MCM-41 and blended films of PEO:Li/MCM-41 shows that the nano-porous SiO₂ channels were not destroyed in PEO/Li. Solid-state ⁷Li NMR spectra identified two major lithium species attributed to the Li⁺ ions associated with PEO, and intercalation or penetration of polymer and Li⁺ ions both within and outside the channels of mesoporous MCM-41. The scanning electron microscopy (SEM) photographs indicated that the electrolytes are miscible and homogeneous up to 8 wt.% of MCM-41, and an optimal conductivity is reached at this composition. However, at higher weight ratios (>10 wt.%), the Li/MCM-41-rich domain developed, and the conductivity decreased with increasing mesoporous material. Apart from the fundamental random diffusion within the amorphous PEO, additional conducting mechanism is established by replacing the nearby vacancy ("hole") with lithium ion on MCM-41 surface, which bears lower activation energy E_a. As a result, enhancement of conductivity is observed when the polymer and oxide are well miscible. This additional mechanism is absent in the case of spherical fillers such as TiO₂, Al₂O₃ or SiO₂ nano-particles in PEO-based electrolytes.