法国法兰西学院Tarascon, Jean-Marie团队报道了显示阴离子氧化还原的富锂岩盐化合物中配体金属电荷转移与电压滞后的关系。相关研究成果发表在2021年9月16日出版的《自然—化学》。

对于锂离子阴极来说，阴离子氧化还原是一把双刃剑，因为它提供了能量密度的转换性增加，同时被其实际应用中的一些不利缺点所抵消。其中，电压滞后是最麻烦的，因为其来源仍然不清楚，并存在争论。

该文中，研究人员通过设计一种典型的富锂阳离子无序岩盐化合物Li1.17Ti0.33Fe0.5O2来解决该问题，该化合物表现出阴离子氧化还原活性和异常大的电压滞后，同时在八面体和四面体位置之间表现出部分可逆的铁迁移。通过结合原位和非原位光谱技术，研究人员证明了非平衡（绝热）氧化还原途径（包括Fe³⁺/Fe⁴⁺和O氧化还原）的存在，而非平衡（非绝热）氧化还原途径仅涉及O氧化还原。

进一步研究表明，从O（2p）孤对态到Fe（3d）态的电荷转移（包括缓慢的结构畸变）是电压滞后的原因。

该研究提供了对富锂岩盐化合物大家族中各种电压滞后特征的一般认识。

附：英文原文

Title: Correlating ligand-to-metal charge transfer with voltage hysteresis in a Li-rich rock-salt compound exhibiting anionic redox

Author: Li, Biao, Sougrati, Moulay Tahar, Rousse, Gwenalle, Morozov, Anatolii V., Dedryvre, Rmi, Iadecola, Antonella, Senyshyn, Anatoliy, Zhang, Leiting, Abakumov, Artem M., Doublet, Marie-Liesse, Tarascon, Jean-Marie

Issue&Volume: 2021-09-16

Abstract: Anionic redox is a double-edged sword for Li-ion cathodes because it offers a transformational increase in energy density that is also negated by several detrimental drawbacks to its practical implementation. Among them, voltage hysteresis is the most troublesome because its origin is still unclear and under debate. Herein, we tackle this issue by designing a prototypical Li-rich cation-disordered rock-salt compound Li1.17Ti0.33Fe0.5O2 that shows anionic redox activity and exceptionally large voltage hysteresis while exhibiting a partially reversible Fe migration between octahedral and tetrahedral sites. Through combined in situ and ex situ spectroscopic techniques, we demonstrate the existence of a non-equilibrium (adiabatic) redox pathway enlisting Fe3+/Fe4+ and O redox as opposed to the equilibrium (non-adiabatic) redox pathway involving sole O redox. We further show that the charge transfer from O(2p) lone pair states to Fe(3d) states involving sluggish structural distortion is responsible for voltage hysteresis. This study provides a general understanding of various voltage hysteresis signatures in the large family of Li-rich rock-salt compounds.

DOI: 10.1038/s41557-021-00775-2

Source: https://www.nature.com/articles/s41557-021-00775-2