EFFECT OF CROWN-ETHER ON THE IONIC-CONDUCTIVITY OF THE POLY(ETHYLENE OXIDE) LITHIUM SALT ELECTROLYTE

The addition of small amounts of crown ethers was observed to enhance the conductivity of the system PEO(20)LiCF(3)SO(3) (PEO: poly(ethylene oxide)). Optimum conductivity enhancement was observed for the system PEO(20)LiCF(3)SO(3)(crown ether)(0.003) when 12-crown-4 and benzo-12- crown-4 were used and for the system PEO(20)LiCF(3)SO(3)(crown ether)( 0.03) containing the corresponding azacrown ether (cyclen) and thiacro wn ether. Maximum conductivity enhancement was observed for PEO(20)LiC F(3)SO(3) (cyclen)(0.03). Over the temperature range studied, the cond uctivity of this system was 1 - 1.5 orders of magnitude higher than fo r the system PEO(20)LiCF(3)SO(3). The Li+ diffusion coefficient for th e system PEO(20)LiCF(3)SO(3)(cyclen)(0.03) was determined to be 1.5 . 10(-9) cm(2) . s(-1) at 90 degrees C. This is lower than the values ob tained by other workers in the absence of cyclen using pulsed field gr adient NMR techniques. The presence of cyclen thus appeared to have th e effect of suppressing the Li+ motion. The presence of small quantiti es of 18-crown-6 in PEO(8)Ca(CF3SO3)(2) electrolytes was also associat ed with a conductivity enhancement. This showed that this effect was n ot limited to systems containing monovalent cations.