The use of redox mediators (RMs) has shaped up as a promising strategy to face some of the main unsolved criticalities which hamper the development of aprotic lithium-oxygen batteries. RMs can promote the oxidation of the discharge products at significantly lower voltage, thus limiting the large overpotentials requested during charging, which in turn leads to a reduced impact of harmful side reactions. Currently, the effectiveness of many different classes of RMs has been tested; nevertheless, the mechanisms of RMs reactivity is still largely unknown, and this poses limitations on their use as a general means to boost the performance of lithium-oxygen batteries.
The project we propose tackles the topic of RMs reactivity from a theoretical standpoint.
Our aim is to use state-of-the-art ab-initio computational techniques in order to elucidate from a mechanistic point of view the reactive processes which RMs can undergo in lithium-oxygen batteries. We expect to obtain valuable results for rationalizing the complex amount of uneven experimental observations, thus providing general criteria which could be helpful to improve the design of future electrochemical cells.
RMs are likely to play a key role for the future development of durable and fully reversible metal-oxygen batteries. In this context, a true mechanistic understanding of their reactivity will be required to help the cell design and the choice of the mediator. This research project aims to fill some of the gaps in the current theoretical picture of RM reactions.
Computational simulations can represent an extremely useful tool to predict data which are hardly accessible to experimental techniques, especially for such complicated systems as electrochemical cells. The expected data on the energies of the various processes during the cycling operations would represent a complete novelty in the present state of the research. Moreover, such data should provide a possible general criteria to rationalize the often inconsistent set of experimental observations.
Apart from the specific application to metal-oxygen batteries, the approach we propose contains elements of novelty also in the development of computational methods for the study of ET processes. This is particularly true due to the planned calculation being directly targeting both the reaction coordinate and the activation barrier of the ET, without relying on traditional semi-classical Marcus theory [15][16]. In addition, the use of nonadiabatic molecular dynamics itself in this field is certainly not common.
[15] A. Amini, A. Harriman, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2003, 4, 155-177
[16] G. Jeanmairet, B. Rotenberg, M. Levesque, D. Borgis, M. Salanne, Chem. Sci. 2019, 10, 2130-2143