The formation of passive films on electrodes due to electrolyte decomposition significantly affects the reversibility of Li-ion batteries (LIBs); however, understanding of the electrolyte decomposition process is still lacking. The decomposition products of ethylene carbonate (EC)-based electrolytes on Sn and Ni electrodes are investigated in this study by Fourier transform infrared (FTIR) spectroscopy. The reference compounds, diethyl 2,5-dioxahexane dicarboxylate (DEDOHC) and polyethylene carbonate (poly-EC), were synthesized, and their chemical structures were characterized by FTIR spectroscopy and nuclear magnetic resonance (NMR). Assignment of the vibration frequencies of these compounds was assisted by quantum chemical (Hartree–Fock) calculations. The effect of Li-ion solvation on the FTIR spectra was studied by introducing the synthesized reference compounds into the electrolyte. EC decomposition products formed on Sn and Ni electrodes were identified as DEDOHC and poly-EC by matching the features of surface species formed on the electrodes with reference spectra. The results of this study demonstrate the importance of accounting for the solvation effect in FTIR analysis of the decomposition products forming on LIB electrodes.

中文翻译：

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傅立叶变换红外光谱法鉴定2,5-二氧杂己烷二甲酸二乙酯和碳酸亚乙酯作为碳酸亚乙酯基电解质的分解产物

由于电解质分解，在电极上形成钝化膜会严重影响锂离子电池（LIB）的可逆性；但是，仍然缺乏对电解质分解过程的了解。本研究通过傅立叶变换红外光谱（FTIR）研究了碳酸亚乙酯（EC）基电解质在Sn和Ni电极上的分解产物。合成了参比化合物2,5-二氧杂己烷二甲酸二乙酯（DEDOHC）和聚碳酸亚乙酯（poly-EC），并通过FTIR光谱和核磁共振（NMR）对它们的化学结构进行了表征。这些化合物的振动频率分配得到了量子化学（Hartree-Fock）计算的帮助。通过将合成的参考化合物引入电解质中，研究了锂离子溶剂化对FTIR光谱的影响。通过将在电极上形成的表面物质的特征与参考光谱相匹配，可以将在Sn和Ni电极上形成的EC分解产物鉴定为DEDOHC和poly-EC。这项研究的结果证明了在LIB电极上形成的分解产物的FTIR分析中考虑溶剂化作用的重要性。