Structure and Dynamics of the Lithium-Ion Solvation Shell in Ureas
Structure and Dynamics of the Lithium-Ion Solvation Shell in Ureas
复制标题
DOI：
10.1021/acs.jpcb.9b07623
复制
发表时间：
2019-11-21
影响因子：
3.3
通讯作者：
Kuroda, Daniel G.
中科院分区：
文献类型：
--
作者：
Chen, Xiaobing;Fulfer, Kristen D.;Kuroda, Daniel G.
锂离子电池由于其在我们日常生活的能量存储需求中的使用而在现代生活中变得无处不在。在过去的几十年里，人们对有机碳酸盐电解质的分子结构进行了大量的研究。然而，其他具有类似性质但热稳定性更好的溶剂，如叔酰胺，尚未受到同等程度的审查。在这项工作中，锂盐在脲中的溶液，具有结构RR 'N-CO-NR ''R''的叔酰胺，具有不同的尺寸和连接性进行了研究。尿素是一个有趣的案例研究，因为与有机碳酸酯不同，酰胺键是平面的，并限制了构象变化。此外，脲不能通过其氮原子结合锂离子。通过使用稳态和时间分辨的红外光谱和从头计算方法，详细描述了锂离子溶剂化结构的变化，作为结果的尿素结构，来自三个脲轴承一个非常相似的常用的有机碳酸酯。这些结果表明，脲类化合物的溶剂化壳层具有与其他有机溶剂相似的四面体结构。虽然这些脲中酰胺键的结构与碳酸酯分子的结构相似，但原子连接性不同。此外，由脲形成的阳离子溶剂化壳层的动力学表现出皮秒运动，这归因于四面体结构的变形。我们的研究还表明，由于这些分子中酰胺键的刚性，变形动力学直接由脲的大小控制。总的来说，这项工作表明，脲类化合物与它们的有机碳酸酯类似物具有相似性，但刚性脲结构提供了一个更容易的框架，用于解释溶剂分子结构方面的振动观测。
Lithium-ion batteries have become ubiquitous to modern life because of their use in the energy storage needs of our daily lives. In past several decades, much effort has been put into studying the molecular structure of electrolytes composed of organic carbonates. However, other solvents with similar properties but better thermal stabilities, such as tertiary amides, have not received the same level of scrutiny. In this work, solutions of lithium salts in ureas, tertiary amides with the structure RR'N-CO-NR '' R''', with different sizes and connectivity are studied. Ureas present an interesting case study because unlike organic carbonates, the amide bond is planar and has restricted conformational change. In addition, ureas cannot bind the lithium ion through their nitrogen atoms. By using steady-state and time-resolved infrared spectroscopies and ab-initio computational methods, detailed descriptions of the changes to the lithium-ion solvation structure as a result of the urea structure were derived for three ureas bearing a strong resemblance to commonly used organic carbonates. These results show that the solvation shell of ureas has a tetrahedral structure similar to that of other organic solvents. Although the structure of the amide bonds in these ureas is similar to that of carbonate molecules, the atomic connectivity differs. In addition, the dynamics of the cation solvation shell formed by ureas shows a picosecond motion, which is attributed to deformation of the tetrahedral structure. Our investigations also indicate that the deformation dynamics is controlled directly by the size of the urea because of the rigidity of the amide bond in these molecules. Overall, this work shows that ureas share similarity with their organic carbonate analogues, but the rigid urea structure provides an easier framework for interpreting the vibrational observations in terms of the solvent molecular structure.