. (
a) The solvation energy and LUMO energy levels of solvated complexes in DME–based and VC–containing electrolytes were compared, and the relevant molecular structures are depicted in the figure. The atoms/ions of C, O, H, and Na are represented in gray, red, white, and purple, respectively. The orange and cyan ellipses serve as substrates for DME and VC molecules, respectively. Reproduced with permission of Ref [
31], Copyright 2020 Elsevier; (
b) The figure illustrates the possible potential mechanisms for the formation of cathodic passivation/surface layers. These include: 1. Nucleophilic attack originating from basic active cathodes. 2. Migration of reduced species from anodes, followed by deposition onto the cathode surface. 3. Interaction between HF and exposed cathode surfaces, leading to the formation of metal fluorides. 4. Formation of VC (poly VC). Reproduced with permission of Ref [
32], Copyright 2020 American Chemical Society; (
c) The schematic drawings in the figure depict the formation of SEI film during cycling, showing the initial nucleation of SEI at the first cycle and the final structure of SEI at the tenth cycle. Additionally, cryo-TEM images of the SEI film after ten cycles are provided for comparison between FEC-free EC: DMC and EC: DMC-FEC electrolytes. Reproduced with permission of Ref [
36], Copyright 2021 Nature; (
d) The figure displays a representative image of SEI films along with the NaPF
6/PC electrolyte solution. Two different concentrations of FEC additive, 1 vol% and 10 vol%, are included in the electrolyte. The solvent, PC, is represented by the color purple, while the gas molecules, namely C
3H
6 and CO
2, are depicted using stick models in gray. Reproduced with permission of Ref [
37], Copyright 2018 American Chemical Society; (
e) The proposed reduction reactions for (1) FEC and (2) VC. Reproduced with permission of Ref [
39], Copyright 2016 American Chemical Society.