Preparation and characterization of composite electrolytes based on PEO(375)-grafted fumed silica

Abstract Recent developments in polymer electrolytes have focused on preparation of composites using nano/micron size ceramic particles such as SiO 2 , TiO 2 , Al 2 O 3 , BaTiO 3 , and MgO. We report here the preparation and characterization of an all-solid state polyethylene oxide (PEO) composite electrolyte from PEO(375)–SiO 2 , high molecular weight PEO (MW = 600 K) and LiClO 4 (O/Li = 16/1). Oligomeric PEOs, with ethylene oxide (EO) repeat units 6–9 (  = 375 g/mol), were chemically grafted (~ 30 wt.%) to fumed silica (A380) using a trimethoxy PEO(375)-silane. The surface grafted PEO chains were disordered (no crystallization) and less mobile than the free chains, with the glass transition temperature ( T g ) increasing from − 90 °C [PEO(375)-silane] to − 54 °C [PEO(375)–SiO 2 ]; addition of LiClO 4 (O/Li = 8/1) further raised T g to − 34 °C. Nanocomposite electrolytes with good dimensional stability were obtained by blending 14-wt.% PEO(375)–SiO 2 with semicrystalline PEO(600 K)/LiClO 4 (O/Li = 16/1). Conductivities ( σ ) were 10 to 4 times greater [between 10 °C ( σ  = 2.1 × 10 − 8  S/cm) and 40 °C ( σ  = 1.1 × 10 − 5  S/cm), respectively] than for neat PEO(600 K) or for composite electrolytes having the same amount of native fumed silica, SiO 2 . No conductivity improvements were observed above T m or for amorphous PEO(600 K)/LiClO 4 (O/Li = 8/1) with addition of SiO 2 or PEO(375)–SiO 2 .