Fig. 2.

Decomposition of selected molecules at the Li surface studied by DFT calculations and XPS. (A) Molecular structure of EC, FEC, DFEC, CF₃EC, and DTD. B and C are top and side views, respectively, of final decomposition products of EC, FEC, DFEC, CF₃EC, and DTD at Li (100) surface in the presence of LiPF₆, as predicted by DFT calculations. The purple atoms represent Li, red represent O, gray represent C, green represent P, blue represent F, yellow represent S, and silver represent H. FEC and DTD break down completely, while DFEC decomposes partially and CF₃EC does not undergo significant breakdown. DTD also catalyzes the decomposition of LiPF₆, leading to formation of LiF. (D) Wide-scan XPS spectra collected from the surface of the Li film deposited in 1 M LiPF₆ EC-DMC (EL-0), 1 M LiPF₆ FEC-DMC (EL-1), 1 M LiPF₆ DFEC-DMC (EL-2), 1 M LiPF₆ CF₃EC-DMC (EL-3), and 1 M LiPF₆ FEC-DMC + DTD (EL-4). (E) F content at the surface of the Li film deposited in different electrolytes. F content increases in the order of EL-3, EL-0, EL-1, EL-4, and EL-2. F–H are narrow-scan XPS spectra of F 1s, C 1s, and O 1s, showing that DFEC and CF₃EC decompose differently from FEC, despite their structural similarity. a.u., arbitrary units.