Unraveling Oxygen Evolution in Li-Rich Oxides: A Unified Modeling of the Intermediate Peroxo/Superoxo-like Dimers
Unraveling Oxygen Evolution in Li-Rich Oxides: A Unified Modeling of the Intermediate Peroxo/Superoxo-like Dimers
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DOI：
10.1021/jacs.9b03710
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发表时间：
2019-07-10
影响因子：
15
通讯作者：
Zeng, Xiao Cheng
中科院分区：
文献类型：
--
作者：
Chen, Zhenlian;Li, Jun;Zeng, Xiao Cheng
过氧/超氧是电催化中析氧/还原反应的关键中间体。然而，过氧/超氧类似物引起了关于氧阴离子氧化还原起源的争议。具体来说，在氧氧化过程中，大块材料中O-O键长度的大小等一些特性一直令人困惑，过氧/超氧中间体与氧释放之间的关系也是如此。后者是氧阴离子氧化还原在锂离子电池中应用的主要安全问题。本文采用第一性原理计算方法，对模型体系Li2MnO3的全分解过程进行了统一建模。我们发现阳离子反位缺陷和电子缺乏是阴离子氧化的两个主要限制因素，随着氧化程度的增加，阴离子氧化的状态可以从电子/空穴，通过过氧样O-2（δ -）二聚体的形成，到最终释放气相氧分子。在分解过程中，悬垂氧（即与Mn单配位）对在中间二聚体的形成中起关键作用。同时，我们确定了5种O-2（δ -）二聚体与Mn离子的一般结合模式，它们的O-O键长度从过氧态的1.45埃到气相氧分子的1.22埃不等。此外，三个分子轨道sigma(c), pi(a)和pi(b)的主要特征被区分开来，由于与主晶格的相互作用，相应的能级高度离域和混合。这项工作提供了对阴离子氧化还原中间状态的深刻理解，并为设计高效安全的富锂阴极材料提供了减少氧释放的新策略。
Peroxo/superoxo is a key intermediate in oxygen evolution/reduction reactions in (electro)catalysis. However, peroxo/superoxo analogues have aroused controversies relevant to the origin of oxygen-anion redox. Specifically, some characteristics such as the magnitude of the O-O bond length in bulk materials have been puzzling during oxygen oxidation, as has the relationship between the peroxo/superoxo intermediate and the release of oxygen. The latter is a major safety concern to the application of oxygen-anion redox in lithium ion batteries. Herein, we present a unified modeling of the full delithiation process for model system Li2MnO3 by using first-principles calculations. We find that the cationic antisite defects and the electron deficiency are two major limiting factors in the anionic oxidation whose state can evolve, as the degree of delithiation increases, from the electron/hole, through peroxo-like O-2(delta-) dimer formation, to the eventual release of gas-phase oxygen molecule. During the delithiation process, the dangling oxygen (i.e., singly coordinated with Mn) pairs play a critical role in intermediate dimer formation. Meanwhile, we identify five generic binding patterns of O-2(delta-) dimers with Mn ions for which the O-O bond length varies from 1.45 angstrom in the peroxo state to 1.22 angstrom in the gas-phase oxygen molecule. Moreover, the dominant features of the three molecular orbitals, sigma(c), pi(a), and pi(b), are distinguished, with the corresponding energy levels being highly delocalized and mixed as a result of the interplay with the host lattice. This work provides a deep understanding of the intermediate states of the anionic redox and suggests new strategies that mitigate oxygen release for the design of highly efficient and safe Li-rich cathode materials.