COMPARISON OF PROPERTIES OF COMPOSITE POLYMERIC ELECTROLYTES BASED ON THE OXYMETHYLENE-LINKED POLY(ETHYLENE OXIDE) NACLO4 ELECTROLYTE WITH POLYACRYLAMIDE OR ALPHA-AL2O3 ADDITIVES

A comparison is made between two, amorphous, composite polyether electrolytes; one with an inorganic filler (alpha-Al2O3 and the other with an organic filler, poly(acrylamide) (PAAM). Oxymethylene-linked poly(ethylene oxide) (OMPEO) is used as the polyether and NaClO4 as the salt. Differential scanning calorimetry (DSC), impedance spectroscopy, FT-IR, Na-23 NMR, and energy-dispersive X-ray (EDX) were used. Unlike the OMPEO-PAAM-LiClO4 electrolytes which had ionic conductivities considerably enhanced over the basic OMPEO-LiClO4 system, these composite electrolytes show only slightly enhanced conductivity below 300 K. The increase in conductivity in the OMPEO-PAAM-LiClO4 is due to enhanced flexibility in the amorphous phase as indicated by the detection of two T-g's, one at 205 K associated with a clearly detectable amorphous uncomplexed OMPEO phase. The OMPEO-NaClO4-based composites discussed herein exhibit only one T-g, so that there is no highly flexible amorphous phase to promote a higher conductivity than the OMPEO-NaClO4 electrolyte except at temperatures below 300 K. The ionic conductivities for the OMPEO-PAAM-NaClO4 system are slightly lower than the OMPEO-alpha-Al2O3-NaClO4 system at equal mass percent of filler. EDX spectra show that alpha-Al2O3 is homogeneously distributed whereas PAAM is nonuniformly distributed; the sodium cations follow the filler particles. A discussion of the complexes formed is given based upon FT-IR results. In the case of the PAAM filler the competition between ion-dipole interactions and hydrogen bonding is discussed where the Na+ cation and the ether oxygens and N-H moieties are involved. It is found that bonding due to the Na+ cation competes favorably with hydrogen bonding but does not dominate as was the case for Li+ in the OMPEO-PAAM-LiClO4 system. In the alpha-Al2O3 case a Lewis acid (Na+)-base (alpha-Al2O3) discussion is used which relates to the active surface centers of alpha-Al2O3. Here strong interaction between surface oxygens and the Na+ cation are evident; these reduce the number of transient cross-links between Na+ cations and ether oxygens. Assuming that the increase in conductivity of these composite polymer electrolytes is associated with interphase phenomena, the conductivity results were analyzed in terms of a model based on effective medium theory.