Singlet oxygen in non-aqueous oxygen redox chemistry

Life demonstrates powerful energy storage using the redox chemistry of main group elements. The redox chemistry of oxygen plays hereby a central role and may as well be used for human-made electrochemical energy storage. Exploiting oxygen redox chemistry in batteries may enable a step change in energy storage employing either transition metal oxide intercalation materials or metal-air cells. However, both life and these families of battery chemistries suffer from irreversible reactions originating from reactive oxygen species, which form in the course of oxygen redox. Oxygen occurs in two states, which differ in how electrons occupy molecular orbitals and their reactivity towards other substances: First the so-called triplet oxygen, which constitutes the majority of oxygen in our environment and which has rather low reactivity. Second, excited so-called singlet oxygen, which has high reactivity towards most organic materials found in life and in batteries. Singlet oxygen formation has only recently been recognized as (at least in large part) the cause of these irreversible reactions. The exceptional importance of singlet oxygen occurring in battery chemistry involving O-redox arises from its high reactivity towards, and degradation of, vital organic cell components, leading to cell failure. Along with others, the project leader has shaped the topic and knowledge of singlet oxygen in in non-aqueous redox chemistry. However, knowledge about effects, formation, and mitigation mechanisms is still critically underdeveloped. We aim to close these critical knowledge gaps with relevance to both energy storage and pure chemistry. This proposal directly targets the fundamental understanding of singlet oxygen as a major determinant of the long-term cyclability of important electrochemical systems. To do so we expand our suite of methods. Detailed understanding of singlet oxygen formation and deactivation is paramount to improve energy efficiency, rate capability, capacity, and cycle life of oxygen-redox based batteries. Work so far has shown that practical perspectives for both batteries involving oxygen redox may even stand or fall with mastering singlet oxygen-induced parasitic processes. Apart from the importance of our research questions for energy storage, the proposal develops new methodology and covers uncharted terrain in physical chemistry