A comparative study on the passivation ability and ion transport property of two surface films was performed; one on a nickel-doped manganese spinel (LiNi0.5Mn1.5O4, LNMO) positive electrode and the other on a graphite negative electrode. The surface film on graphite is impermeable to electrolytemolecules and highly passivating; these are characteristic features of solid electrolyte interphase (SEI). In contrast, the surface film on LNMO is highly permeable to molecules and thus poorly passivating; this property is similar to that of the previously referred to solid permeable interface (SPI), which is also adopted in this work. The SPI layer, deposited as a result of electrolyte oxidation, is composed of cationic oligomers/polymers with anions. The SPI layer allows immersion of ions and solvent molecules, which easily access to the nearest surface on the LNMO electrode where electron tunneling is appreciable. Due to this highly permeable property, oxidative decomposition of electrolyte unceasingly occurs on LNMO electrode to cause continuous surface film growth. Due to the high ion permeability, the SPI film resistance is also influenced by the ionic conductivity of electrolyte solution. (C) 2018 The Electrochemical Society.