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The role of O2 in O-redox cathodes for Li-ion batteries


The energy density of Li-ion batteries can be improved by storing charge at high voltages through the oxidation of oxide ions in the cathode material. However, oxidation of O2− triggers irreversible structural rearrangements in the bulk and an associated loss of the high voltage plateau, which is replaced by a lower discharge voltage, and a loss of O2 accompanied by densification at the surface. Here we consider various models for oxygen redox that are proposed in the literature and then describe a single unified model involving O2− oxidation to form O2, most of which is trapped in the bulk and the remainder of which evolves from the surface. The model extends the O2 formation and evolution at the surface, which is well known and well characterized, into the electrode particle bulk as caged O2 that can be reversibly reduced and oxidized. This converged understanding enables us to propose practical strategies to avoid oxygen-redox-induced instability and provide potential routes towards more reversible, high energy density Li-ion cathodes.

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Fig. 1: Layered Li-rich cathodes.
Fig. 2: Previously proposed forms of oxidized O.
Fig. 3: Experimental evidence for molecular O2.
Fig. 4: Relationship between structural change and voltage hysteresis.
Fig. 5: Surface and bulk O2 formation.
Fig. 6: Strategies to develop stable O-redox materials.


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P.G.B. is indebted to the Engineering and Physical Sciences Research Council (EPSRC), Henry Royce Institute for Advanced Materials (under grant IDs EP/R00661X/1, EP/S019367/1, EP/R010145/1) and the Faraday Institution Next Generation Li-ion Cathodes project CATMAT (under grant ID FIRG016) for financial support.

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The manuscript was written by R.A.H., J.-J.M. and P.G.B. with contributions and revisions from all authors.

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Correspondence to Peter G. Bruce.

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House, R.A., Marie, JJ., Pérez-Osorio, M.A. et al. The role of O2 in O-redox cathodes for Li-ion batteries. Nat Energy (2021).

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