A series of poly(ethylene oxide) (PEO)/lithium trifluoromethanesulfonate (LiTf)/ethylene carbonate (EC)/sepiolite composite electrolytes have been prepared by melt compounding, using neat sepiolite (Sep), sepiolite coated with polyethylene glycol (PEG-Sep) and with D-alpha-tocopherol polyethylene glycol 1000 succinate (TPGS-Sep) as fillers. The composites (weight ratio EC:PEO similar to 1) present ionic conductivity close to 10(-3) S cm(-1) at 30 degrees C, i.e. close to liquid electrolytes. Their crystallization and viscoelasticity were investigated evidencing a very complex phase structure and rheological behaviour, both of which dramatically depend on the type of nanofiller introduced in the blend. In the absence of TPGS-Sep as filler, the composites slowly separate into EC-rich and PEO-rich macrophases, what is visually evident in a two month time scale. With TPGS-Sep, the electrolytes are solid-like even at temperatures well above the PEO melting temperature range and do not phase separate in at least two years, constituting a homogeneous and stable blend which keeps its properties for long time periods. (C) 2014 Elsevier B.V. All rights reserved.