Capturing dynamic ligand-to-metal charge transfer with a long-lived cationic intermediate for anionic redox
Capturing dynamic ligand-to-metal charge transfer with a long-lived cationic intermediate for anionic redox
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DOI：
10.1038/s41563-022-01278-2
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发表时间：
2022-06-20
期刊：
影响因子：
41.2
通讯作者：
Tarascon, Jean-Marie
中科院分区：
文献类型：
--
作者：
Li, Biao;Kumar, Khagesh;Tarascon, Jean-Marie
可逆的阴离子氧化还原反应代表了为锂离子电池创造先进的高能量密度正极材料的转型变化。这些反应的活化机制通常与配体-金属电荷转移（LMCT）过程有关，由于缺乏合适的模型材料，该过程尚未得到充分的实验验证。在这里，我们表明，在阳离子无序岩盐Li 1.17Ti 0.58Ni 0.25 O2的阴离子氧化还原的激活涉及一个长寿命的中间Ni 3 +/4+物种，它可以完全演变为Ni 2+在松弛过程中。结合电化学分析和光谱技术，我们定量地确定了Ni ~（3 +/4+）物种的还原经历了一个动态LMCT过程（Ni ~（3 +/4+）-O_2-> Ni ~（2+）-On-）。我们的研究结果提供了以前的理论假设的实验验证，并有助于合理化与阴离子氧化还原，如阳离子-阴离子氧化还原反转和电压滞后的几个特点。这项工作也提供了额外的指导，设计高容量的电极，通过筛选适当的阳离子物种介导LMCT.了解可逆的阴离子氧化还原反应是关键，设计高能量密度的锂离子电池阴极。在阳离子无序岩盐Li1.17Ti0.58Ni0.25O2中的阴离子氧化还原活化被证明涉及中间Ni 3 +/4+物种，其可以在弛豫期间演变为Ni 2+。
Reversible anionic redox reactions represent a transformational change for creating advanced high-energy-density positive-electrode materials for lithium-ion batteries. The activation mechanism of these reactions is frequently linked to ligand-to-metal charge transfer (LMCT) processes, which have not been fully validated experimentally due to the lack of suitable model materials. Here we show that the activation of anionic redox in cation-disordered rock-salt Li1.17Ti0.58Ni0.25O2 involves a long-lived intermediate Ni3+/4+ species, which can fully evolve to Ni2+ during relaxation. Combining electrochemical analysis and spectroscopic techniques, we quantitatively identified that the reduction of this Ni3+/4+ species goes through a dynamic LMCT process (Ni3+/4+-O2- -> Ni2+-On-). Our findings provide experimental validation of previous theoretical hypotheses and help to rationalize several peculiarities associated with anionic redox, such as cationic-anionic redox inversion and voltage hysteresis. This work also provides additional guidance for designing high-capacity electrodes by screening appropriate cationic species for mediating LMCT.Understanding reversible anionic redox reactions is key to designing high-energy-density cathodes for lithium-ion batteries. Anionic redox activation in cation-disordered rock-salt Li1.17Ti0.58Ni0.25O2 is shown to involve intermediate Ni3+/4+ species that can evolve to Ni2+ during relaxation.