Abstract
The electrification of heavy-duty transport and aviation will require new strategies to increase the energy density of electrode materials1,2. The use of anionic redox represents one possible approach to meeting this ambitious target. However, questions remain regarding the validity of the O2-/O- oxygen redox paradigm, and alternative explanations for the origin of the anionic capacity have been proposed3, because the electronic orbitals associated with redox reactions cannot be measured by standard experiments. Here, using high-energy X-ray Compton measurements together with first-principles modelling, we show how the electronic orbital that lies at the heart of the reversible and stable anionic redox activity can be imaged and visualized, and its character and symmetry determined. We find that differential changes in the Compton profile with lithium-ion concentration are sensitive to the phase of the electronic wave function, and carry signatures of electrostatic and covalent bonding effects4. Our study not only provides a picture of the workings of a lithium-rich battery at the atomic scale, but also suggests pathways to improving existing battery materials and designing new ones.
Highlights
Electrification of heavy-duty vehicles and aviation requires batteries with much higher specific energy than the current Li-ion batteries.[1,2] substantial progress has been made with lithium metal anodes[3] and silicon,[4,5] there is a need to move beyond the current layered cathodes to meet these demanding targets
The area under the Compton profile difference (CPD) gives the difference in the number of electrons for the two Li concentrations and we renormalize the CPD to one when we consider it as a projection of the momentum density of a redox orbital[29]
We have provided conclusive evidence in support of the anionic redox mechanism in LTMO and rule out alternative explanations based on the Mn oxidation number
Summary
Electrification of heavy-duty vehicles and aviation requires batteries with much higher specific energy than the current Li-ion batteries.[1,2] substantial progress has been made with lithium metal anodes[3] and silicon,[4,5] there is a need to move beyond the current layered cathodes to meet these demanding targets. Li-rich oxides present a promising cathode materials class to move closer towards these targets with a high capacity of about 300 mAh/g 6–12. The anionic redox mechanism underlying their electrochemical operation, has been difficult to understand fully with the current probes and techniques. It has proven difficult to detect significant oxygen activity[16] via x-ray Raman spectroscopy, even though it is more bulk sensitive
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