正极材料Li 2 FeSiO 4中阳离子和阴离子氧化还原活性之间精确过渡的机理,The Journal of Physical Chemistry Letters

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正极材料Li ₂ FeSiO _4中阳离子和阴离子氧化还原活性之间精确过渡的机理
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2018-10-16 00:00:00 , DOI: 10.1021/acs.jpclett.8b02725
Jiaxin Zheng ₁ , Gaofeng Teng ₁ , Jinlong Yang ₁ , Ming Xu ₁ , Qiushi Yao ₂ , Zengqing Zhuo _{1,

3} , Wanli Yang ₃ , Qihang Liu ₂ , Feng Pan ₁

Affiliation

阴离子氧化还原活性的发现有望提高锂离子电池（LIB）阴极的容量。然而，仍然缺乏对引发阴离子氧化还原的机理的基本了解。在这里，使用混合密度泛函研究与实验性软X射线吸收光谱（sXAS）测量相结合，我们明确地证明了Li _{（2– x）} FeSiO ₄通过脱锂而具有后续的阳离子和阴离子氧化还原活性。具体而言，Fe ²⁺被氧化为Fe ³⁺在第一次按公式单位（fu）提取锂离子时，而第二次提取锂离子则专门触发了氧的氧化还原。阳离子和阴离子氧化还原分别导致电子和空穴极化子态，这解释了先前实验中指出的Li _{（2– x）} FeSiO _4的电导率很差。相反，该族中的其他阴极材料表现出氧化还原过程的多样性。Li ₂ MnSiO ₄在整个脱锂过程中显示出双阳离子氧化还原（Mn ²⁺ -Mn ⁴⁺），而Li ₂ CoSiO ₄显示同时发生的阳离子和阴离子氧化还原。本发现不仅为可再充电电池的聚阴离子化合物中的氧还原活性提供了新的见解，而且为高容量可再充电电池的未来设计提供了启示。

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Mechanism of Exact Transition between Cationic and Anionic Redox Activities in Cathode Material Li2FeSiO4

The discovery of anion redox activity is promising for boosting the capacity of lithium ion battery (LIB) cathodes. However, fundamental understanding of the mechanisms that trigger the anionic redox is still lacking. Here, using hybrid density functional study combined with experimental soft X-ray absorption spectroscopy (sXAS) measurements, we unambiguously proved that Li_(2–x)FeSiO₄ performs sequent cationic and anionic redox activity through delithiation. Specifically, Fe²⁺ is oxidized to Fe³⁺ during the first Li ion extraction per formula unit (f.u.), while the second Li ion extraction triggered the oxygen redox exclusively. Cationic and anionic redox result in electron and hole polaron states, respectively, explaining the poor conductivity of Li_(2–x)FeSiO₄ noted by previous experiments. In contrast, other cathode materials in this family exhibit diversity of the redox process. Li₂MnSiO₄ shows double cationic redox (Mn²⁺–Mn⁴⁺) during the whole delithiation, while Li₂CoSiO₄ shows simultaneous cationic and anionic redox. The present finding not only provides new insights into the oxygen redox activity in polyanionic compounds for rechargeable batteries but also sheds light on the future design of high-capacity rechargeable batteries.

更新日期：2018-10-16

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