Influence of calix[2]-p-benzo[4]pyrrole on the electrochemical properties of poly(ethylene oxide)-based electrolytes for lithium batteries

Poly(ethylene oxide) based electrolytes comprising LiCF₃SO₃ and calix[2]-p-benzo[4]pyrrole (CBP) as anion binder were prepared and subjected to DSC, ionic conductivity, cationic transport number and FTIR analyses. Symmetric cells of the type Li/PEO+LiCF₃SO₃+CBP/Li were assembled with these electrolytes and evolution of interfacial resistance as a function of time was analyzed. The cationic transference number, t Li+, was found to increase from 0.23 to 0.78 on incorporation of CBP in the polymer electrolyte (PE). The incorporation of CBP as an anion trap does not enhance ionic conductivity below 60°C although it improves the interfacial properties. FTIR study revealed the formation of Li-C compounds on the lithium surface upon contact with the CBP added membranes. The CBP added PE was found to be optimal in terms of ionic conductivity and transport number, t Li+, above 70°C, which were found to be higher for a system previously reported with calix[6]pyrrole.