Variation of the mesh size of PEO-based networks filled with TFSILi: from an Arrhenius to WLF type conductivity behavior

The properties of ionically conducting membranes based on polyethylene oxid e (PEO) networks crosslinked with urethane functions, containing lithium bi s(trifluoromethane sulfone imide) (TFSILi) were studied. The temperature an d salt concentration influence on the ionic conductivity of these materials was analyzed. The best conductivity value measured at 30 degrees C was 7 x 10(-5) S cm(-1) at O/Li = 43 for a PEO molecular weight between crosslinks of 2000 g mol(-1). The curves obtained in the Arrhenius coordinates were t ypical of a William Landel Ferry (WLF) like behavior when the molecular wei ght of the PEO between crosslinks was 1000 or 2000 g mol(-1). However, the network based on PEO600 followed an Arrhenius behavior, typical of a networ k where segmental movements are prevented, A strong interaction between TFS ILI, ethylene oxide units and urethane crosslinks functions at high urethan e concentration explains these results, This finding demonstrates that the two types of conductivity behavior (Arrhenius or WLF) can be found for the same type of polymer electrolyte depending on the predominant elementary co nductivity process. (C) 1999 Elsevier Science Ltd. All rights reserved.