Combining experimental and computational techniques can provide a better understanding of surface film formation processes that occur in the lithium-ion battery. In this paper, we show that this joint approach can provide a mechanistic understanding of the effect of oxygen in the reduction of propylene carbonate (PC). We perform FTIR analysis, inside a glove box, after conducting linear sweep voltammetry (LSV) from an open-circuit voltage (OCV) to selected potential regions; subtraction between two successive IR spectra has been made to identify the reduction products formed within each potential range. FTIR analysis in the potential range from OCV to −0.1 V, in conjunction with density functional theory (DFT) calculations, confirm the formation of solvated Li2CO3 and (PC)2LiOC(O)OCH(CH3)CH2OLi(PC) due to PC reduction. Our experimental results and DFT calculations suggest that in the potential range from OCV to 1.6 V, PC, in the presence of O2, can easily decompose by the superoxide ion through a nucleophilic attack at the ethereal carbon atom.