Although lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) has a high thermal stability and fine tolerance to water and is an outstanding candidate as an electrolyte, there is an urgent need to control aluminum corrosion. Here, we explain how we suppressed aluminum corrosion by controlling the LiTFSI concentration. SEM observations and XPS depth profiles of the electrode at high LiTFSI electrolyte concentrations showed that stable passivation film composed of LiF was formed on an aluminum electrode, which prevented the continuous decomposition reaction of the LiTFSI electrolyte. As a result, a lithium-ion battery with LiTFSI demonstrated excellent properties for several cycles without aluminum corrosion, which should accelerate progress in its applications to industry.