Department of Chemical System Engineering, School of Engineering, The University of Tokyo , Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.
ACS Appl Mater Interfaces. 2017 Oct 25;9(42):36463-36472. doi: 10.1021/acsami.7b09835. Epub 2017 Oct 10.
Lithium-ion batteries are key energy-storage devices for a sustainable society. The most widely used positive electrode materials are LiMO (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 π-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.
锂离子电池是可持续社会的关键储能设备。最广泛使用的正极材料是 LiMO（M：过渡金属），其中 M 的氧化还原反应与 Li（脱）插层相关联。使用额外的氧氧化还原反应来实现超过 200 mAh/g 的大容量的富锂过渡金属氧化物的最新发展为设计更高能量密度的锂离子电池带来了新的可能性。为了更好地利用这种引人入胜的新化学，有必要通过了解氧的化学状态来实现对反应机制的全面理解。在这篇综述中，提供了对氧氧化还原电池电极的最新进展的总结，然后系统地展示了基于分子轨道的整体电子结构，重点是氧周围的局部配位环境。我们表明，π 型分子轨道在稳定充电过程中出现的氧化氧方面起着重要作用。分子轨道原理便于从原子水平上理解如何在体相发生可逆的氧氧化还原反应，为改善高能密度电池的氧氧化还原正极材料提供了坚实的基础。
