Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 9, Issue 42, Pages 36463-36472Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.7b09835
Keywords
battery; cathode; transition-metal oxides; oxygen-redox reaction; molecular-orbital method; orphaned oxygen orbital
Funding
- Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan [15H05701]
- Iketani Science and Technology Foundation
- Grants-in-Aid for Scientific Research [15K13798, 15H05701] Funding Source: KAKEN
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Lithium-ion batteries are key energy-storage devices for a sustainable society. The most widely used positive electrode materials are LiMO2 (M: transition metal), in which a redox reaction of M occurs in association with Li+ (de)intercalation. Recent developments of Li-excess transition-metal oxides, which deliver a large capacity of more than 200 mAh/g using an extra redox reaction of oxygen, introduce new possibilities for designing higher energy density lithium-ion batteries. For better engineering using this fascinating new chemistry, it is necessary to achieve a full understanding of the reaction mechanism by gaining knowledge on the chemical state of oxygen. In this review, a summary of the recent advances in oxygen-redox battery electrodes is provided, followed by a systematic demonstration of the overall electronic structures based on molecular orbitals with a focus on the local coordination environment around oxygen. We show that a 7r-type molecular orbital plays an important role in stabilizing the oxidized oxygen that emerges upon the charging process. Molecular orbital principles are convenient for an atomic-level understanding of how reversible oxygen-redox reactions occur in bulk, providing a solid foundation toward improved oxygen-redox positive electrode materials for high energy-density batteries.
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