In a previous study , we employed first-principles-based MD simulations to demonstrate the potential of sodium triflate (NaOTF) WiS electrolyte for use in Na-ion batteries. This study highlighted how NaOTF provides a balance between bulk transport properties and ion-ion correlations in the bulk liquid, with the latter playing a crucial role in enhancing electrochemical stability through the formation of a stable SEI. In the present study, we extend our research to investigate the initial stages of SEI formation in the same electrolyte. To this end, we apply the DFT approach proposed by Forster-Tonigold et al. to examine the interfacial interactions between the electrolyte and two distinct types of electrodes: graphite, typical of conventional carbon-based electrodes in sodium-ion batteries, and a reactive sodium metal electrode, representing either a bulk electrode or a thin film grown on the electrode surface. The primary objective of this study is to elucidate the potential mechanisms underlying the onset of SEI formation and the composition of the resulting interfacial layer covering the electrode surface. By separately analyzing aggregated and solvated ion structures, our results and conclusions can also be extended to similar ionic liquids.