An infrared spectroscopic study on the effect of plasticizers such as ethylene carbonate and propylene carbonate on the PEO-LiCF3SO3 system is reported. It has been observed that the additives seem to favor less associated ionic species when present in large amounts. A few differences between ethylene carbonate and propylene carbonate as plasticizers have been noted and discussed. The ionic conductivity of the plasticized polymer complexes are about 3-4 magnitudes higher than that of (PEO)(9)LiCF3SO3. The plasticizers seem to preferentially interact with the crystalline PEO phase, thereby rendering the electrolytes amorphous.