Electrochemical insertion of alkaline ions into polyparaphenylene: effect of the crystalline structure of the host material

The intercalation of lithium and sodium ions into different materials deriv ed from polyparaphenylene (PPP) (as synthesized PPP without a thermal treat ment, PPP annealed for 36 h at 400 degreesC and PPP pyrolyzed at 700 degree sC for half an hour in argon atmosphere) was studied using the electrolyte composed of ethylene carbonate (E and propylene carbonate (PC) and MC10, as the alkaline salt (M = Li or Na). These materials exhibit various degrees of crystallinity: PPP is a semi-crystalline polymer with about 30% of crist allinity, whereas pyrolyzed PPP exhibits a totally disorganized structure. Spectroscopic characterization indicates that the configurations of the pol ymer chains are similar in these two materials. Then, we present in this wo rk a comparative study of the intercalation of alkaline ions into these mat erials in order to specify the effect of the crystalline structure on the i ntercalation processes. The electrochemical capacities are close whatever t he degree of crystallinity contrary to the potentials profiles of the galva nostatic curves. That indicates different intercalation processes into thes e materials. A two-step mechanism of the intercalation into PPP is proposed . First, the intercalation of the alkaline ions into the crystalline parts of the polymer occurs and secondly the insertion of Li+ and Na+ into the am orphous regions takes place at very low potentials. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.