Abstract: Electrolyte is one of the most important factors determining the safety, energy density and cycle performance of supercapacitors.Water-in-salt electrolyte has been widely used in high-performance energy storage devices due to its non-flammability and wide operating voltage range.However, the low conductivity and high viscosity of water-in-salt electrolyte usually restrict the rate performance of supercapacitors.In this work, 1, 3-dioxopentane (DIOX) was introduced into the water-in-salt electrolyte system to form a “LiTFSI-DIOX/H₂O” hybrid electrolyte.Compared with the water-in-salt electrolyte, the electrolyte has the characteristics of low viscosity, high conductivity and low cost while ensuring a wide working potential window.The supercapacitor composed of 5 m LiTFSI-DIOX/H₂O electrolyte has a capacity retention rate of 98.5% and a coulombic efficiency of nearly 100% after 5000 cycles at a current density of 1 A g^-1.Even at a low temperature of -30 ℃, it can maintain 76.1% of the room temperature capacity, which indicates that the supercapacitor has good low temperature rate performance.