Stable polymer electrolytes based on polyether-grafted ZnO nanoparticles for all-solid-state lithium batteries

Abstract

Solid polymer nanocomposite electrolytes composed of polyethylene oxide (PEO) macromolecules, LiN(CF₃SO₂)₂ (LiTFSI) and polyether-grafted nano-ZnO (designated ZnO(PEGME)), are prepared and characterized in comparison with the prototypical PEO–LiTFSI film and that doped with conventional acetate group modified ZnO nanoparticles (designated ZnO(Ac)). High resolution transmission electron microscopic (HRTEM) results show that ZnO nanoparticles are dispersed homogeneously in the present PEO–LiTFSI–ZnO(PEGME) films, while those particles in PEO–LiTFSI–ZnO(Ac) aggregate badly. Atomic force microscopic (AFM) analyses prove that after storage at room temperature for a month, PEO–LiTFSI forms large dendrites while only a small amount of tiny crystals can be observed in the PEO–LiTFSI–ZnO(PEGME) film. In contrast, ZnO(Ac) particles agglomerate around the PEO–LiTFSI dendrites and separate from the original phase. This is the first direct observation on the micromorphology of the SPE films after long-term storage, which elucidates why the PEO–LiTFSI–ZnO(PEGME) electrolyte is much more stable than its counterparts. Conductivity evolutions, Li⁺ transport number measurements and cycle performances of the above-mentioned three typical films in all-solid-state lithium batteries also suggest that the structural merits of the polyether-grafted nanoparticles render this type of SPEs attractive in the future applications.