Physik-Department, Technische Universität München, James-Franck Straße 1, 85748 Garching, Germany.
Nanoscale. 2016 Aug 7;8(29):14004-14. doi: 10.1039/c6nr00825a. Epub 2016 May 3.
The SEI-formation on graphitic electrodes operated as an Li(+)-ion battery anode in a standard 1 M LiPF6 EC/DMC (1 : 1) electrolyte has been studied in situ by EC-STM. Two different modes of in situ study were applied, one, which allowed to follow topographic and crystallographic changes (solvent cointercalation, graphite exfoliation, SEI precipitation on the HOPG basal plane) of the graphite electrode during SEI-formation, and the second, which gave an insight into the SEI precipitation on the HOPG basal plane in real time. From the in situ EC-STM studies, not only conclusions about the SEI-topography could be drawn, but also about the formation mechanism and the chemical composition, which strongly depend on the electrode potential. It was shown that above 1.0 V vs. Li/Li(+) the SEI-formation is still reversible, since the molecular structure of the solvent molecules remains intact during an initial reduction step. During further reduction, the molecular structures of the solvents are destructed, which causes the irreversible charge loss. The STM studies were completed by electrochemical methods, like cyclic voltammetry, the potentiostatic intermittent titration technique and charge/discharge tests of MCMB electrodes.
在标准的 1 M LiPF6 EC/DMC（1:1）电解质中，作为锂离子电池阳极的石墨电极上的 SEI 形成已通过 EC-STM 进行了原位研究。应用了两种不同的原位研究模式，一种模式允许在 SEI 形成过程中跟踪石墨电极的形貌和结晶变化（溶剂共插层、石墨剥离、SEI 在 HOPG 基面的沉淀），另一种模式实时洞察 SEI 在 HOPG 基面的沉淀。从原位 EC-STM 研究中，不仅可以得出关于 SEI 形貌的结论，还可以得出关于形成机制和化学成分的结论，这些结论强烈依赖于电极电势。结果表明，在 1.0 V vs. Li/Li(+)以上，SEI 的形成仍然是可逆的，因为在初始还原步骤中溶剂分子的分子结构保持完整。在进一步还原过程中，溶剂的分子结构被破坏，导致不可逆的电荷损失。STM 研究通过电化学方法完成，如循环伏安法、恒电位间歇滴定技术和 MCMB 电极的充放电测试。
