Investigation of novel, redox-active organic materials for lithium-ion and lithium-oxygen batteries

Abstract: This thesis encompasses the successful synthesis, characterization (NMR, IR, TGA) and electrochemical testing of novel, potentially redox-active organic materials. These were destined as electrodes for Li-organic cells and/or as catalysts for Li–O2 cells. The electrochemical performance of the dilithiated and tetralithiated salts of 2,5-dialkylamide hydroquinones (with ethyl, isopropyl or benzyl as the alkyl group) and of a partially lithiated polymer with a backbone of alternating 2,5-dicarbonylhydroquinone and 1,4-benzyl diaminophenylene units was evaluated. The small organicsalts exhibited redox-activity around 1.0 V vs Li/Li+ (the terephthaloyl redox system) and 2.8 V vs Li/Li+ (the quinone redox system). These values drifted depending on lithiation degree and alkyl substituent. Redox irreversibility featured these materials which decomposed and dissolved. The polymer exhibited multiple redox-activity in the region of 2.5-3.6 V vs Li/Li+, which was however also irreversible. Further on, the small organic salts were tested as to their impact on the dischargeproduct (Li2O2) yield in Li-O2 cells. Discharge profiles of cells with and without the inclusion of the salts were contrasted to each other; the former having a jagged appearance, indicative of side-reactions. The O2 electrode was studied by XRD todetect the formed products and the amount of Li2O2 present was quantified throug htitration and UV-vis spectroscopy. Organic salt inclusion was found to negatively affect the Li2O2 formation and also attack the Li-electrode.