The commercialization of the silicon (Si) anode has been hindered by the instability of its solid-electrolyte interphase (SEI), yet a comprehensive understanding of SEI properties remains underdeveloped owing to the challenge of characterizing this nanoscale passivation layer. In this work, we visualize the structure and chemistry of the SEI on silicon anodes using atomic-resolution cryogenic (scanning) transmission electron microscopy (cryo-(S)TEM) and electron energy loss spectroscopy (EELS), revealing its evolution over the first cycle. We discover the origin of the Si SEI instability in ethylene carbonate (EC) electrolytes, owing to the high reversibility of the SEI. The role of the critical electrolyte additive fluoroethylene carbonate is revealed, which extends the cyclability of the Si anode through deposition of an electrochemically irreversible polycarbonate layer on the anode surface. These findings provide a nuanced view into the Si anode instability in commercial EC-based electrolytes and the role of additives for SEI stabilization.

硅（Si）阳极的商业化已经受到其固体电解质中间相（SEI）的不稳定性的阻碍，但是由于表征这种纳米级钝化层的挑战，对SEI性能的全面了解仍未得到开发。在这项工作中，我们使用原子分辨率低温（扫描）透射电子显微镜（cryo-（S）TEM）和电子能量损失谱（EELS）可视化了SEI在硅阳极上的结构和化学性质，揭示了其在第一个过程中的演化循环。由于SEI的高度可逆性，我们发现了碳酸亚乙酯（EC）电解质中Si SEI不稳定性的起因。揭示了关键电解质添加剂氟代碳酸亚乙酯的作用，通过在阳极表面上沉积电化学不可逆的聚碳酸酯层，可扩展Si阳极的循环能力。这些发现为商业上基于EC的电解质中Si阳极的不稳定性以及添加剂对SEI稳定化的作用提供了细微的了解。