Embodiments of localized superconcentrated electrolytes (LSEs) for stable operation of electrochemical devices, such as rechargeable batteries, supercapacitors, and sensors, are disclosed. Electrochemical devices, such as rechargeable batteries, supercapacitors, and sensors, including the LSEs are also disclosed. The LSEs include an active salt, a solvent in which the active salt is soluble, and a diluent in which the active salt is insoluble or poorly soluble. In certain embodiments, such as when the solvent and diluent are immiscible, the LSE further includes a bridge solvent.