Metal corrosion is a serious problem that has beset various electrochemical systems. For lithium-ion batteries, oxidative corrosion of an Al current collector has been a great challenge in designing new electrolyte materials, and only a few lithium salts (e.g. LiPF6) are in practical use. The present work shows effective suppression of Al corrosion up to 4.5 V versus Li+/Li by using a highly concentrated electrolyte of lithium bis(fluorosulfonyl)amide (LiFSA). The corrosion prevention mechanism can be interpreted in relation to a remarkable change in solution structures at a certain threshold concentration. It is demonstrated that highly concentrated LiFSA/acetonitrile electrolyte enables highly reversible charge-discharge cycling of a 4V-class LiMn2O4/Li cell at a higher rate (ca. 50% capacity retention at 20 C compared to C/2) than a state-of-the-art commercial electrolyte (<20%), thus providing a new design strategy for electrolyte materials in high-rate lithium-ion batteries.