Lack of understanding on the electrical properties of the solid electrolyte interface (SEI) has been one of the major hurdles for developing fast charging Li-ion batteries. Here, we report our preliminary experimental result on the measurement of the electrical resistivity of SEI using the direct-contact technique based on electron microscopy combined with 4-point-probe micro-electrical method. We observed that the SEI layer, which covers uniformly the surface of the graphite anode, exhibits a high resistivity (2.3 × 10⁵ Ω·m) comparable to those of typical insulators. In this study, using first principles calculations performed on the computational Li_xF_1-x (0.25 < x < 0.75) phases, we elucidate the structural origin responsible for the measured resistivity of SEI by analyzing the electronic structures. (Received September 4, 2018; Accepted September 19, 2018)