Reversible and irreversible reaction mechanisms of Li-CO2 batteries.

Abstract

Li-CO2 batteries are considered a versatile solution for CO2 utilization. However, their development, including reversibility and efficiency, is impeded by an inadequate understanding of Li-CO2 electrochemistry, particularly the decomposition of carbon and the generation of by-product O2. Here, using typical Ru(0001) (reversible) and Ir(111) (irreversible) as model catalysts and employing state-of-the-art first-principles calculations, the rechargeable/reversible reaction mechanisms of Li-CO2 batteries are disclosed. We find that electrolyte, often neglected or oversimplified in Li-CO2 modelling, plays an essential role in CO2 activation and C-C coupling affects the generation pathways of discharge intermediates due to the sluggish kinetics. The results rationalize experimental observations, which are also examined by constant-potential modelling. Specifically, by exploring the kinetics of the charging process, we discover that the reversibility of Ru(0001) is attributed to its ability to suppress O-O coupling while co-oxidizing Li2CO3 and carbon. In contrast, Li2CO3 decomposition on Ir(111) preferentially produces O2, during which carbon can only be partially decomposed. These findings solve long-standing questions and highlight the necessity of describing the explicit solvent effect in modelling, which can promote further studies on Li-CO2 batteries.