Understanding the role of nanoparticles in PEO-based hybrid polymer electrolytes for solid-state Lithium-polymer batteries

Nano-ZnO-PEO (poly(ethylene oxide)) hybrid polymers have been synthesized and successfully investigated as a solid-state electrolyte for application in lithium-polymer batteries. Three compositions containing 2, 5, and 7 wt % of ZnO nanoparticles covalently grafted to PEO chains have been prepared. The chemical structure of these materials has been characterized via Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and X-ray photoelectron spectroscopy. The surface morphology and elemental distribution of the materials have been investigated by means of atomic force microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results reveal a uniform distribution of the ZnO nanoparticles within the smooth electrolyte films, prepared by dissolving in these materials lithium bis(trifluoromethanesulfonyl)imide as the Li-conducting salt and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid as plasticizer. Such volatile solvent-free polymer electrolytes possess the high thermal stability and suitable electrochemical stability required for solid-state lithium-metal batteries. In fact, the material with 7 wt % ZnO exhibits a rather good lithium plating/stripping performance at 40 degrees C and the highest ionic conductivity (4.2 X 10(-4) S cm(-1)) at room temperature, benefiting from the well-dispersed inorganic nanoparticles due to the polymer grafting and hybrid polymer approach.