The use of functionalized electrolytes is effective in mitigating the poor cycling stability of silicon (Si), which has long hindered the implementation of this promising high-capacity anode material in next-generation lithium-ion batteries. In this Letter, we present a comparative study of gaseous byproducts formed by decomposition of fluoroethylene carbonate (FEC)-containing and FEC-free electrolytes using differential electrochemical mass spectrometry and infrared spectroscopy, combined with long-term cycling data of half-cells (Si vs Li). The evolving gaseous species depend strongly on the type of electrolyte; the main products for the FEC-based electrolyte are H₂ and CO₂, while the FEC-free electrolyte shows predominantly H₂, C₂H₄, and CO. The characteristic shape of the evolution patterns suggests different reactivities of the various Li_xSi alloys, depending on the cell potential. The data acquired for long-term cycling confirm the benefit of using FEC as cosolvent in the electrolyte.

中文翻译：

---

碳酸氟乙烯酯在锂离子电池硅阳极充气中的关键作用

功能化电解质的使用可有效减轻硅（Si）的不良循环稳定性，长期以来一直阻碍在下一代​​锂离子电池中采用这种有前途的高容量负极材料。在这封信中，我们提供了利用差分电化学质谱法和红外光谱结合半电池（Si）的长期循环数据，对含氟碳酸亚乙酯（FEC）和不含FEC的电解质进行分解而形成的气态副产物的比较研究。 vs李）。不断发展的气态物质在很大程度上取决于电解质的类型。基于FEC的电解质的主要产品是H ₂和CO ₂，而不含FEC的电解质主要显示H ₂，C ₂H ₄和CO。析出图案的特征形状表明，根据电池的电势，各种Li _x Si合金的反应性不同。长期循环获得的数据证实了在电解质中使用FEC作为助溶剂的好处。