Anionic and Cationic Redox Processes in β-Li2IrO3 and Their Structural Implications on Electrochemical Cycling in a Li-Ion Cell,The Journal of Physical Chemistry C

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Anionic and Cationic Redox Processes in β-Li2IrO3 and Their Structural Implications on Electrochemical Cycling in a Li-Ion Cell
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-01-22 , DOI: 10.1021/acs.jpcc.9b10195
Paul E. Pearce _{1,

2,

3} , Gaurav Assat _{1,

2,

3} , Antonella Iadecola ₂ , François Fauth ₄ , Rémi Dedryvère _{2,

5} , Artem Abakumov ₆ , Gwenaëlle Rousse _{1,

2,

3} , Jean-Marie Tarascon _{1,

2,

3}

Affiliation

The recent discovery of anionic redox as a means to increase the energy density of transition-metal oxide positive electrodes is now a well-established approach in the Li-ion battery field. However, the science behind this new phenomenon pertaining to various Li-rich materials is still debated. Thus, it is of paramount importance to develop a robust set of analytical techniques to address this issue. Herein, we use a suite of synchrotron-based X-ray spectroscopies as well as diffraction techniques to thoroughly characterize the different redox processes taking place in a model Li-rich compound, the tridimensional hyperhoneycomb β-Li₂IrO₃. We clearly establish that the reversible removal of Li⁺ from this compound is associated with a previously described reductive coupling mechanism and the formation of the M-(O–O) and M-(O–O)* states. We further show that the respective contributions to these states determine the spectroscopic response for both Ir L₃-edge X-ray absorption spectroscopy and X-ray photoemission spectroscopy. Although the high covalency and the robust tridimensional structure of this compound enable a high degree of reversible delithiation, we found that pushing the limits of this charge compensation mechanism has significant effects on the local as well as average structure, leading to electrochemical instability over cycling and voltage decay. Overall, this work highlights the practical limits to which anionic redox can be exploited and sheds some light on the nature of the oxidized species formed in certain lithium-rich compounds.

中文翻译：

阴离子和阳离子氧化还原过程中β-栗₂的IrO ₃和在锂离子电池上电化学循环及其结构的启示

阴离子氧化还原作为增加过渡金属氧化物正电极能量密度的一种手段，最近的发现是锂离子电池领域公认的方法。但是，与各种富含锂的材料有关的这种新现象背后的科学仍在争论中。因此，开发一套强大的分析技术来解决此问题至关重要。在这里，我们使用了一套基于同步加速器的X射线光谱的以及衍射技术彻底表征发生在一个模型富含锂化合物不同的氧化还原过程，立体hyperhoneycombβ-李₂的IrO ₃。我们清楚地确定，可逆地去除Li ⁺该化合物的化合物与先前描述的还原偶联机理以及M-（O-O）和M-（O-O）*状态的形成有关。我们进一步表明，对这些状态的各自贡献决定了两个Ir L ₃的光谱响应边缘X射线吸收光谱和X射线光发射光谱。尽管该化合物的高共价性和稳固的三维结构能够实现高度可逆的脱氢，但我们发现，突破这种电荷补偿机制的极限，会对局部结构和平均结构产生重大影响，从而导致循环和循环过程中电化学不稳定电压衰减。总体而言，这项工作突出了可以利用阴离子氧化还原的实际限制，并为某些富含锂的化合物中形成的氧化物种的性质提供了一些启示。

更新日期：2020-01-23

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