Lewis acidity and hardness of group 13/III metal centered alkoxides and their effects on ionic conductivity of polymer electrolytes

We have focused on 13/III group alkoxides, Ga(OC2H5)3, Al(OC2H5)3 and B(OC2H5)3 as novel anion receptors and investigated their effects on the ionic conductivity of polymer electrolytes containing LiClO4. Addition of the alkoxides into the polymer electrolytes brought increases in the ionic conductivities. The order concerning the effect of the alkoxides on the increases in the ionic conductivities was Ga(OC2H5)3>Al(OC2H5)3>B(OC2H5)3. Differential scanning calorimetry (DSC) studies about glass transition temperatures of the polymer electrolytes implied that the increases in the ionic conductivities by the addition of these alkoxides were due to an increase in the concentration of carrier ions; in other words, due to enhancement of the dissociation constant of the lithium salt by the interaction between the alkoxides and the anions. Ab initio calculations indicated that the order of the Lewis acidity is Ga(OC2H5)3>Al(OC2H5)3>B(OC2H5)3, meanwhile, the order of hardness is B(OC2H5)3>Al(OC2H5)3>Ga (OC2H5)3, and accordingly, Ga(OC2H5)3 is a soft and strong Lewis acidic alkoxide which should reflect the tendentious increases in the ionic conductivity of the polymer electrolytes.