Elucidating the Factors That Cause Cation Diffusion Shutdown in Spinel-Based Electrodes
Elucidating the Factors That Cause Cation Diffusion Shutdown in Spinel-Based Electrodes
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DOI：
10.1021/acs.chemmater.1c01668
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发表时间：
2021-08
影响因子：
8.6
通讯作者：
S. Kolli;A. Van der Ven
中科院分区：
文献类型：
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作者：
S. Kolli;A. Van der Ven
我们系统地研究了客体阳离子(即Li、Na或Mg)在尖晶石插层化合物中的扩散，尖晶石插层化合物是一类很有前途的锂、钠和镁离子电池材料。利用动力学蒙特卡罗模拟，我们确定了导致阳离子扩散系数强烈的浓度依赖性的因素。我们关注的是尖晶石，其中的客体阳离子倾向于八面体位置，其中的扩散是由空位团簇介导的。从MgyTiS2开始，我们预测，由于高度相关的镁扩散的开始，镁扩散系数将突然下降，大约在≈0.5时跨越几个数量级。这一预测与之前的实验研究是一致的，这些实验研究只能达到MgyTiS2理论容量的一半。接下来，我们使用动力学蒙特卡罗模拟对尖晶石中的扩散进行了参数研究，应用于晶格模型哈密顿量，并确定了尖晶石晶体结构的关键拓扑弱点，使其在中到高客体阳离子浓度下容易发生高度关联的阳离子扩散。我们发现，随着客体阳离子对之间的近邻排斥变得更强，这种高度关联扩散的开始变得更加明显，因为这增加了长程阳离子扩散对三位空位团簇的依赖。这项研究的结果为调整尖晶石中阳离子扩散系数的浓度依赖关系以减少高阳离子浓度下的缓慢扩散提供了指导。这项研究得出的结论也适用于其他紧密堆积的阴离子主体，如无序的岩盐电极和偏序的尖晶石。
We report on a systematic study of guest cation (i.e., Li, Na, or Mg) diffusion within spinel intercalation compounds, a promising class of materials for Li-, Na-, and Mg-ion batteries. Using kinetic Monte Carlo simulations, we identify factors that are responsible for a strong concentration dependence of the cation diffusion coefficient. We focus on spinels in which the guest cations prefer the octahedral sites and where diffusion is mediated by vacancy clusters. Starting with MgyTiS2, we predict an abrupt drop in the Mg diffusion coefficient that spans several orders of magnitude aroundy≈ 0.5 due to the onset of highly correlated Mg diffusion. The prediction is consistent with previous experimental studies that are only able to achieve half the theoretical capacity of MgyTiS2. We next perform a parametric study of diffusion in spinels using kinetic Monte Carlo simulations applied to lattice model Hamiltonians and identify a critical topological weakness of the spinel crystal structure that makes it prone to highly correlated cation diffusion at intermediate-to-high guest cation concentrations. We find that the onset of this highly correlated diffusion becomes more pronounced as the nearest-neighbor repulsion between pairs of guest cations becomes stronger, since this increases the dependence of long-range cation diffusion on triple-vacancy clusters. The results of this study provide guidance with which the concentration dependence of cation diffusion coefficients in spinel can be tailored to reduce the onset of sluggish diffusion at high cation concentrations. The conclusions drawn from this study also apply to other close-packed anion hosts such as disordered rocksalt electrodes and partially ordered spinels.