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Degradation and Speciation of Li Salts during XPS Analysis for Battery Research
ACS Energy Letters ( IF 19.3 ) Pub Date : 2022-09-06 , DOI: 10.1021/acsenergylett.2c01587
Weilai Yu 1 , Zhiao Yu 1 , Yi Cui 2 , Zhenan Bao 1
Affiliation  

X-ray photoelectron spectroscopy (XPS) is one of the most common techniques to characterize the solid–electrolyte interphase (SEI) in battery research. However, residual salt or solvent can produce spectroscopic artifacts that complicate the evaluation of actual SEI chemistry. Herein, we present a systematic XPS study of three different Li salts, namely lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium hexafluorophosphate (LiPF6). A side-by-side comparison reveals that the binding energies of constituent elements sensitively shift in response to their distinct chemical environments. Strikingly, all three Li salts consistently transformed into LiF under Ar+ sputtering, pointing out the importance of complete salt removal before XPS analysis. Residue from organic solvent or impurities from sample surface to bulk were found specific to the solvent–salt combination, which should be distinguished from the real organic SEI. Overall, this set of benchmark studies not only offers a valuable reference for peak assignment but also emphasizes the significance of control experiments to avoid potential pitfalls while identifying actual SEI components.

中文翻译:

用于电池研究的 XPS 分析过程中锂盐的降解和形态形成

X 射线光电子能谱 (XPS) 是电池研究中表征固体电解质界面 (SEI) 的最常用技术之一。然而,残留的盐或溶剂会产生光谱伪影,使实际 SEI 化学的评估变得复杂。在此,我们对三种不同的锂盐进行了系统的 XPS 研究,即双(氟磺酰)亚胺锂(LiFSI)、双(三氟甲磺酰)亚胺锂(LiTFSI)和六氟磷酸锂(LiPF 6)。并排比较表明,组成元素的结合能响应于它们不同的化学环境而敏感地变化。引人注目的是,所有三种 Li 盐在 Ar +下始终转化为 LiF溅射,指出在 XPS 分析之前完全去除盐分的重要性。发现有机溶剂的残留物或样品表面到本体的杂质是溶剂-盐组合特有的,应与真正的有机 SEI 区分开来。总体而言,这组基准研究不仅为峰值分配提供了有价值的参考,而且还强调了对照实验的重要性,以避免在识别实际 SEI 组件时出现潜在的陷阱。
更新日期:2022-09-06
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