Graphite Electrodes Immersed in Nonaqueous Li+ Electrolytes Studied with a Combined Ultrahigh Vacuum-Electrochemistry Approach
Graphite Electrodes Immersed in Nonaqueous Li+ Electrolytes Studied with a Combined Ultrahigh Vacuum-Electrochemistry Approach
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采用超高真空-电化学相结合的方法研究浸没在非水锂电解质中的石墨电极
DOI：
10.1021/acs.jpcc.1c03645
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Kim Yousoo
中科院分区：
文献类型：
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作者：
Wong Raymond A.;Yokota Yasuyuki;Kazuma Emiko;Oniki Motoyuki;Kim Yousoo
我们报告了一种结合超真空电化学（UHV-EC）的方法，用于探测高取向热解石墨（HOPG）电极的化学和形态学的变化浸没在含锂离子的非水电解质。UHV-EC提供了一个“快照式”的电极表面分析，而不会受到洗涤或冲洗的干扰。这是通过进行电化学，然后清洁转移到真空中进行X射线光电子能谱（XPS）和扫描隧道显微镜（UHV-STM）来实现的。采用这种方法与HOPG作为模型系统的石墨负极在锂离子电池中，我们专注于阴极极化引起的电极表面的变化。在相对于Li/Li+的约1.75 V下极化后的XPS鉴定出少量的残余电解质和来自包括LiF的Li盐（LiPF 6）的分解的产物。同时，高分辨率UHV-STM成像显示石墨剥离的发生，并且在更高的放大倍数下，边缘平面显示聚集结构，同时还表明存在残余电解质和分解产物。我们的工作表明，石墨电极表面的显着变化之前已经存在的电位，其中发生显着的表面膜（固体电解质界面）的形成。
We report on a combined ultrahigh vacuum–electrochemistry (UHV-EC) approach used to probe the chemical and morphological changes of highly oriented pyrolytic graphite (HOPG) electrodes immersed in Li+-containing nonaqueous electrolytes. UHV-EC provides a “snapshot-like” analysis of electrode surfaces without perturbation from washing or rinsing. This is accomplished by performing electrochemistry, followed by clean transfer into vacuum for X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (UHV-STM). Employing this approach together with HOPG serving as a model system for the graphite negative electrode in lithium-ion batteries, we focus on the changes to the electrode surface induced by cathodic polarization. XPS following polarization atca.1.75 V vs Li/Li+identifies a low amount of the residual electrolyte and products from the decomposition of the Li salt (LiPF6) including LiF. Meanwhile, high-resolution UHV-STM imaging shows the occurrence of graphite exfoliation, and at higher magnifications, the edge planes show aggregated structures while also suggesting the presence of residual electrolyte and decomposition products. Our work shows that notable changes to the graphite electrode surface are already present prior to the potentials, where significant surface film (solid electrolyte interphase) formation occurs.