Novel lithium salts exhibiting high lithium ion transference numbers in polymer electrolytes

A variety of lithium aluminates containing two oligoether groups and two electron-withdrawing groups, CF3CO2, CF3SO3, (CF3SO2)2N or C6F5O, on aluminum atom were prepared. Viscous liquid salts were obtained by incorporation of oligoether substituents containing an average of 7.2 and 11.8 ethylene oxide repeating units. Ionic conductivity of the liquid salt was enhanced by incorporation of electron withdrawing groups on the aluminate center and was dependent on the chain length of oligoether groups. Temperature dependence of ionic conductivity was well fitted to Vogel–Tammann–Fulcher equation, indicating that ion motion was coupled to segmental motion of oligoether chains. Polymer electrolytes were prepared by mixing of the salt and poly(ethylene oxide) and exhibited a high ionic conductivity, a high lithium transference number, a wide potential window, and a good thermal stability.