Investigating the Mechanism of Lithium Transport at Solid Electrolyte Interphases
Investigating the Mechanism of Lithium Transport at Solid Electrolyte Interphases
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DOI：
10.1021/acs.jpcc.0c03018
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发表时间：
2020-07-30
影响因子：
3.7
通讯作者：
Peart, Shaniya
中科院分区：
文献类型：
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作者：
Jorn, Ryan;Raguette, Lauren;Peart, Shaniya
在锂离子存储设备中，碳酸盐电解质和石墨电极之间的反应会产生一种称为固体电解质界面（SEI）的副产物表面膜。在评估这些界面的组成和结构方面取得了重大进展;然而，它们对充电和放电过程中锂传输的影响缺乏分子细节。在过去的十年中，电化学阻抗谱（EIS）已经表明，锂的传输受到离子去溶剂化和通过SEI的离子传导的组合的限制，但是哪一步是速率限制仍然没有解决。在这项工作中，我们模拟了这个过程的第一步，即，离子去溶剂化，进入和离开两个模型SEI，所述模型SEI由与碳酸亚乙酯电解质界面连接的碳酸亚乙酯锂（LEDC）和Li 2CO 3组成。通过关联自由能的变化与溶剂化结构，我们表明，所采取的路径Li+插入是一个两步机制，包括克服两个能量障碍的吸附，然后吸收。两者中最大的测量势垒为59.2 kJ/mol，在从EIS测量获得的估计值内。然而，从LEDC的离子提取遵循由表面基团延伸到电解质中的灵活性所确定的不同的自由能曲线。从LEDC提取的依赖性的表面基团的性质，强调通过比较从更刚性的Li 2CO 3表面的离子提取，突出了SEI组合物和锂传输之间的复杂关系。
Reactions between carbonate electrolytes and graphite electrodes in lithium-ion storage devices produce a surface film of byproducts known as the solid electrolyte interphase (SEI). Significant progress has been made in assessing the composition and structure of these interphases; however, their impact on lithium transport during charge and discharge lacks molecular detail. Over the past decade, electrochemical impedance spectroscopy (EIS) has shown that lithium transport is limited by a combination of ion desolvation and ion conduction through the SEI, however which step is rate limiting remains unresolved. In this work, we simulate the first step in this process, i.e., ion desolvation, both into and out of two model SEI's comprised of lithium ethylene dicarbonate (LEDC) and Li2CO3 interfaced with an ethylene carbonate electrolyte. By correlating free-energy changes with solvation structure, we show that the path taken for Li+ insertion is a two-step mechanism consisting of overcoming two energy barriers to adsorption and then absorption. The largest measured barrier of the two is 59.2 kJ/mol, within the estimates obtained from EIS measurements. Ion extraction from the LEDC, however, follows a different free-energy profile determined by the flexibility of the surface groups to extend into the electrolyte. The dependence of extraction from LEDC on the nature of the surface groups, emphasized by comparison with ion extraction from the more rigid Li2CO3 surface, highlights the complex relationship between SEI composition and lithium transport.