Cathodes based on layered LiMO2 are the limiting components in the path toward Li-ion batteries with energy densities suitable for electric vehicles. Introducing an overstoichiometry of Li increases storage capacity beyond a conventional mechanism of formal transition metal redox. This unconventional activity is commonly termed "oxygen redox", which obscures the possibility of a diversity of mechanisms that could fall under this simple umbrella. Taking a step away from application, the ability of 4d and 5d metals to undergo unconventional redox transitions has been highlighted in the literature, providing a playground for understanding that could eventually be translated to base metals with greater technological feasibility. In this talk, I will summarize our recent effort at carefully describing the mechanisms of charge compensation in a suite of materials based on Ru and Ir, perhaps the two metals where most evidence of unconventional redox exists. Central to our research has been the use of a suite of X-ray methods, especially spectroscopy. By comparing Li2RuO3, Li3RuO4 and Li7RuO6, the role of crystal structure on the ability of Ru to get oxidized and for O to undergo redox was elucidated. Within the Li3MO4 stoichiometry, stark differences were found between the behavior of M=Ru and Ir. The results shed new light into our ability to tap the chemical bond in solids to conduct electrochemical reactions that could surpass the current frontiers of reversible exchange of charge.

Definition of redox centers in reactions of lithium intercalation in Ru and Ir oxides

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.