Activity of Metal-Fluorine States upon Delithiation of Disordered Rocksalt Oxyfluorides
Activity of Metal-Fluorine States upon Delithiation of Disordered Rocksalt Oxyfluorides
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DOI：
10.1021/acs.chemmater.2c03680
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发表时间：
2023-02
影响因子：
8.6
通讯作者：
Indrani Roy;Khagesh Kumar;Haifeng Li;Neelam Sunariwal;Grant C. B. Alexander;J. Freeland;F. Rodolakis;J. Cabana
中科院分区：
文献类型：
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作者：
Indrani Roy;Khagesh Kumar;Haifeng Li;Neelam Sunariwal;Grant C. B. Alexander;J. Freeland;F. Rodolakis;J. Cabana
过渡金属氧化物作为锂离子电池阴极的容量受到高电荷状态时产生的不稳定性的限制。具有无序岩盐结构的氟氧化物已成为有吸引力的替代品，但F在其电化学功能中的作用，特别是当阳离子氧化还原产生高形式氧化态时，仍有待确定。利用x射线吸收光谱，我们证实了在Li2MnO2F和Li2Mn2/3Nb1/3O2F中存在Mn-F共价相互作用。当相减少时，特别是在Mn（IV）的存在下，Mn - f和Mn - o键的杂化3d-2p态演变成新的未占据态。结果挑战了F作为阴离子的假设，其与金属的共价态在非常高的电位下被挖掘，取而代之的是提供了一幅细致入微的氟氧化物氧化还原补偿图。他们提出，通过操纵过渡金属和两种不同阴离子之间的共价相互作用，电池阴极设计中存在独特的旋钮。
The capacity of transition-metal oxides as Li-ion battery cathodes is limited by instabilities that arise when high states of charge are achieved. Oxyfluorides with a disordered rocksalt structure have emerged as attractive alternatives, but the role of F in their electrochemical function, particularly when cationic redox produces high formal oxidation states, remains to be ascertained. Using X-ray absorption spectroscopy, we confirm the existence of Mn–F covalent interactions in Li2MnO2F and Li2Mn2/3Nb1/3O2F. New unoccupied states evolve from hybrid 3d-2p states of both Mn–F and Mn–O bonds when the phases are delithiated, particularly in the presence of Mn(IV). The results challenge the assumption of F as anion whose covalent states with the metal are tapped at very high potentials, providing instead a nuanced picture of redox compensation in oxyfluorides. They suggest the existence of unique knobs of design of battery cathodes by manipulating the covalent interactions between transition metals and two different anions.