An electrolyte composition and a metal-ion battery employing the same are provided. The electrolyte composition includes a metal chloride, an imidazolium salt of Formula (I), an alkali halide, and an oxalate-containing borate wherein R1, R2, and R3 are independently C1-8 alkyl, C2-8 alkenyl, C2-8 alkynyl, C1-8 alkoxy, C2-8 alkoxyalkyl, or C1-8 fluoroalkyl; and X− is F−, Cl−, Br−, or I−. The metal chloride is aluminum chloride, iron chloride, zinc chloride, copper chloride, manganese chloride, chromium chloride, or a combination thereof.