Journal
ADVANCED ENERGY MATERIALS
Volume 11, Issue 30, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.202100892
Keywords
pi interaction; anionic redox; metal-ligand Interactions; Li-ion batteries
Categories
Funding
- National Natural Science Foundation of China [U1764255]
- International Science & Technology Cooperation of China [2019YFE0100200]
- National Key R&D Program of China [2016YFB0100200]
- Beijing Municipal Natural Science Foundation [2181001]
- China Postdoctoral Science Foundation [2020T130004]
- High-Performance Computing Platform of Peking University
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Understanding the anionic redox behavior with respect to metal-ligand interactions in Li-rich oxide cathodes is crucial for developing high-capacity battery materials. By analyzing the orbital combinations of transition metals and oxygen in LROs, it was found that a pi-type oxygen redox mode can be achieved at low voltages, expanding the fundamental theories of anionic redox and providing a new design route for high-capacity cathode materials. The interaction between oxygen and central Rh in Li2RhO3 demonstrates high reactivity in the occupied anti-bonding state, showing a novel low-voltage oxygen redox mechanism.
Li-rich oxide (LRO) cathodes that exhibit anionic redox activity can boost the energy density of Li-ion batteries. Oxygen redox in LROs can originate from the charge compensation of pure O 2p nonbonding (NB) states; however, the high charging voltages cause much safety concerns in practical applications. Exploiting new anionic redox modes that can be used at low voltages is thus imperative. In view of this, a further understanding of the anionic redox behavior with respect to metal-ligand interactions in LROs is highly desired. In this study, by analyzing the orbital combinations of transition metals (TMs) and O in LROs, the prevalence of pi-type, sigma-type, and NB states is investigated. Highly covalent Li2RhO3 with strong pi-type interactions is selected as a model material. Owing to the closer energy levels of O and Rh and the orbital vacancy of Rh-4, oxygen acts as a pi-electron donor to central Rh and exhibits high reactivity in the occupied anti-bonding state, showing a novel low-voltage O redox which is distinct from high-voltage NB O redox. This pi-type oxygen redox mode expands the fundamental theories of anionic redox and provides a new design route to achieve high-capacity Li-rich cathode materials.
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