Chemical Modulation of Local Transition Metal Environment Enables Reversible Oxygen Redox in Mn-Based Layered Cathodes
Chemical Modulation of Local Transition Metal Environment Enables Reversible Oxygen Redox in Mn-Based Layered Cathodes
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DOI：
10.1021/acsenergylett.1c01071
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发表时间：
2021-05
影响因子：
22
通讯作者：
Muhammad Mominur Rahman;S. McGuigan;Shaofeng Li;Lina Gao;D. Hou;Zhijie Yang;Zhengrui Xu;Sang-Jun Lee;Cheng-Jun Sun;Jue Liu;Xiaojing Huang;Xianghui Xiao;Y. Chu;Sami Sainio;D. Nordlund;X. Kong;Yijin Liu;Feng Lin
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作者：
Muhammad Mominur Rahman;S. McGuigan;Shaofeng Li;Lina Gao;D. Hou;Zhijie Yang;Zhengrui Xu;Sang-Jun Lee;Cheng-Jun Sun;Jue Liu;Xiaojing Huang;Xianghui Xiao;Y. Chu;Sami Sainio;D. Nordlund;X. Kong;Yijin Liu;Feng Lin
氧氧化还原对提高锰基层状阴极的能量密度有显著作用。然而，由于复杂的同时发生的结构和化学转化，理解影响氧氧化还原可逆性的因素是不容易的。在这里，我们证明了局域Mn-O对称性引起的结构和化学演化主要决定了Na细胞中NaxLiyMn1-yO2氧氧化还原的可逆性。我们发现，具有Jahn-Teller扭曲的MnO6八面体的NaxLiyMn1-yO2在循环过程中经历了严重的Mn溶解，这破坏了过渡金属层的稳定性，导致Li保留率低和氧氧化还原不可逆。通过Mg/Ti双掺杂来调节Mn的局域电荷和Mn-O距离，可以抑制MnO_6八面体的Jahn-Teller失真。这会减少锰的溶解，从而产生更可逆的氧氧化还原。这样的稳定化显著提高了镁/钛双掺杂NaxLiyMn1-yO2的电化学性能。通过这项工作，我们表明，促进可逆的氧氧化还原可以受益于局部长度尺度上的结构稳定，而通过掺杂化学来改变化学环境是促进局部结构稳定从而促进氧氧化还原的有效策略。
Oxygen redox plays a prominent role in enhancing the energy density of Mn-based layered cathodes. However, understanding the factors affecting the reversibility of oxygen redox is nontrivial due to the complicated concurrent structural and chemical transformations. Herein, we show that local Mn‒O symmetry induced structural and chemical evolutions majorly dictate the reversibility of oxygen redox of NaxLiyMn1-yO2 in Na cells. We find that NaxLiyMn1-yO2 with Jahn-Teller distorted MnO6 octahedra undergoes severe Mn dissolution during cycling, which destabilizes the transition metal layer resulting in poor Li retention and irreversible oxygen redox. Jahn-Teller distortion of MnO6 octahedra can be suppressed by modulating the local charge of Mn and Mn‒O distance through Mg/Ti dual doping. This leads to reduced Mn dissolution resulting in more reversible oxygen redox. Such stabilization significantly improves the electrochemical performance of Mg/Ti dual doped NaxLiyMn1-yO2. Through this work, we show that promoting reversible oxygen redox can benefit from structural stabilization at local length scale, and that modifying the chemical environment through doping chemistry is an efficient strategy to promote local structural stability and thus, oxygen redox.