The reaction mechanism of the new SEI additive 1-Fluoropropane-2-one in combination with the well-known SEI additive vinylene carbonate in propylene carbonate based electrolytes is investigated. Spectroscopic measurements support the proposition that 1-Fluoropropane-2-one is reduced first and that the reduced species then initiate vinylene carbonate decomposition. Cyclic voltammetry shows only a decomposition peak of the additive FA in the first cycle and does not show any evidence for subsequent vinylene carbonate decomposition at lower potential. NMR spectroscopy shows that after one cycle the signal representing the C-F bonds decreases. In situ Raman measurements show that the decomposition of vinylene carbonate occurs in the same potential range as 1-Fluoropropane-2-one, meaning that the VC decomposition is shifted to higher potentials. Finally, XPS measurements demonstrate that this electrolyte with two additives forms a LiF-rich SEI.