Fundamental Linkage Between Structure, Electrochemical Properties, and Chemical Compositions of LiNi1-x-yMnxCoyO2 Cathode Materials
Fundamental Linkage Between Structure, Electrochemical Properties, and Chemical Compositions of LiNi1-x-yMnxCoyO2 Cathode Materials
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DOI：
10.1021/acsami.0c18942
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发表时间：
2021-01-07
影响因子：
9.5
通讯作者：
Hu, Enyuan
中科院分区：
文献类型：
--
作者：
Hu, Jiangtao;Wang, Qinchao;Hu, Enyuan
LiNi1-x-yMnxCoyO2（NMC）是一类重要的高能量密度正极材料。改变化学式中的 x 和 y 的可能性为许多材料提供了不同的电化学和结构特性。非常需要获得有关 NMC 结构和电化学特性与其化学成分的相关性的指导，以进行材料设计和筛选。在这里，利用基于同步加速器的X射线衍射、X射线吸收光谱、电化学表征和文献调查，Mn和Co之间的含量差异（在NMC中表示为x-y）被确定为估计Li/过渡金属（Li/TM）阳离子混合比和第一循环库仑效率（CE）的有效指标。此外，还发现了氧位置“z”与Li+和TM阳离子之间的尺寸差（通过c轴长度归一化）之间的线性关系，并且通过考虑平均TM阳离子尺寸和c轴长度，这种线性可用于准确预测NMC材料中的氧位置。还得出结论，即使在高电荷状态下，大部分 NMC 材料的最短 O-O 距离也不能短于 2.5 埃。因此，如果结构保持 R (3) 超过巴 m 对称性，则不可能从本体中释放氧。
LiNi1-x-yMnxCoyO2 (NMC) is an important class of high-energy-density cathode materials. The possibility of changing both x and y in the chemical formula provides numerous materials with diverse electrochemical and structural properties. It is highly desirable to have guidance on correlating NMC structural and electrochemical properties with their chemical composition for material designing and screening. Here, using synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, electrochemical characterization, and literature survey, the content difference between Mn and Co (denoted as x-y in NMC) is identified as an effective indicator to estimate Li/transition metal (Li/TM) cation mixing ratio and first-cycle Coulombic efficiency (CE). In addition, a linear relationship between oxygen position "z" and the size difference between Li+ and TM cation (normalized by the c-axis length) is found, and such linearity can be used to accurately predict the oxygen position in NMC materials by considering the average TM cation size and c-axis length. It is also concluded that the shortest O-O distance in the bulk of NMC materials could not be shorter than 2.5 angstrom even at a highly charged state. Therefore, oxygen release is not likely to take place from the bulk if the structure maintains the R (3) over bar m symmetry.