Understanding the SEI Formation at Pristine Li‐Ion Cathodes: Chemisorption and Reaction of DEC on LiCoO2 Surfaces Studied by a Combined SXPS/HREELS Approach
Understanding the SEI Formation at Pristine Li‐Ion Cathodes: Chemisorption and Reaction of DEC on LiCoO2 Surfaces Studied by a Combined SXPS/HREELS Approach
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DOI：
10.1002/admi.201700567
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发表时间：
2017-12
影响因子：
5.4
通讯作者：
Th Späth;D. Becker;N. Schulz;R. Hausbrand;W. Jaegermann
中科院分区：
文献类型：
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作者：
Th Späth;D. Becker;N. Schulz;R. Hausbrand;W. Jaegermann
电极-电解质界面的反应和固体电解质界面（SEI）的形成对锂离子电池的稳定性和性能至关重要，但在基础层面上仍未完全理解。为了提高电池性能，需要详细了解这些降解过程。本文介绍了薄膜LiCoO2正极材料与碳酸二乙酯（DEC）作为典型电池电解质溶剂之间的界面形成。采用表面科学方法，在低温下将DEC逐步吸附到LiCoO2上。利用同步加速器X射线光发射光谱（SXPS）和高分辨率电子能量损失光谱对每一步后的界面进行了研究。结果表明，吸附实验中观察到的碳酸盐溶剂与完全锂化正极材料接触时的分解是复杂的，包括溶剂的还原、后续的分解反应以及催化效应。在本例中，碳酸乙基锂、氧化锂和氧化锂被指定为反应产物。光谱提供了部分电子转移耦合到涉及表面氧O2p轨道和DEC最低未占据分子轨道（LUMO）态的共价相互作用的指示。
Reactions and solid electrolyte interface (SEI) formation at electrode–electrolyte interfaces are crucial for the stability and performance of Li‐ion batteries, but are still not fully understood on a fundamental level. For improving battery properties, a detailed understanding of these degradation processes is needed. In this contribution, the interface formation between a thin film LiCoO2 cathode material and diethyl carbonate (DEC) as typical battery electrolyte solvent is presented. A surface‐science approach is used performing a stepwise adsorption of DEC onto LiCoO2 at low temperatures. The interface is studied after each step by synchrotron‐based X‐ray photoemission spectroscopy (SXPS) and high‐resolution electron energy loss spectroscopy. The results demonstrate that the decomposition of carbonate solvents in contact with fully lithiated cathode materials as observed in adsorption experiments is complex, including the reduction of solvent, subsequent decomposition reactions, and also catalytic effects. In the present case, lithium ethyl carbonate, lithium ethoxide, and lithium oxides are assigned as reaction products. The spectra provide indications for partial electron transfer coupled to covalent interaction involving surface oxygen O2p orbital and DEC lowest unoccupied molecular orbital (LUMO) states.