Abstract
Anionic redox processes play a key role in determining the accessible capacity and cycle life of Li-rich cathode materials for batteries. We present a framework for investigating the anionic redox processes based on data readily available from standard DFT calculations. Our recipe includes a method of classifying different anionic species, counting the number of species present in the structure and a preconditioning scheme to promote anionic redox. The method is applied to a set of LixMnO3 (1 ≤ x ≤2) structures, with cationic disorder, to identify the evolution of anionic redox processes during cycling. Additionally, we investigate how different choices of exchange-correlation functionals affect the formation of anionic redox species. The preconditioning of the structures is shown to promote the formation of peroxo-like species. Furthermore, the choice of exchange-correlation functional has a large impact on the type of anionic redox species present, and thus care must be taken when considering localization in anionic species.
Highlights
Anionic redox processes are currently an intensely studied topic in battery research as it allows a significant increase in the accessible energy capacity in Li-rich cathodes in lithium-ion batteries[1,2]
We propose an algorithm for determining the types of anionic species present in the structures based on data readily accessible from standard density functional theory (DFT) calculations
The presented method is capable of estimating the amount of localized anionic redox and the trends in the evolution of anionic redox during cycling, all based on data readily available from standard DFT calculations
Summary
Anionic redox processes are currently an intensely studied topic in battery research as it allows a significant increase in the accessible energy capacity in Li-rich cathodes in lithium-ion batteries[1,2]. Li2MnO3 is one of the Li-rich cathode materials where the anionic redox is known to make a dominant contribution to its high theoretical capacity of around 460 mAh g−13–5. Many possible explanations for the cyclability were suggested, and anionic redox is regarded as one of the main contributors[5,9]. Li2MnO3 suffers from a fast capacity fading, in the initial cycling step[10]. Its fast capacity fading is attributed to the anionic redox process, which leads to an irreversible and potentially dangerous evolution of oxygen gas[7,10]
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