A metal-ion battery, comprising: a positive electrode; a separator; a negative electrode, wherein the positive electrode is separated from the negative electrode by the separator; and an electrolyte disposed between the positive electrode and the negative electrode and contacting the positive electrode and the negative electrode, wherein the electrolyte comprises an ionic liquid with a melting point less than 100°C, aluminum halide, and metal halide, wherein the ionic liquid is selected from alkylimidazolium salt, alkylpyridinium salt, alkylfluoropyrazolium salt, alkyltriazolium salt, aralkylammonium salt, alkylalkoxyammonium salt, aralkylphosphonium salt, aralkylsulfonium salt, or a combination thereof; wherein the metal halide is silver halide, copper halide, cobalt halide, ferric halide, indium halide, cadmium halide, nickel halide, tin halide, chromium halide, lanthanum halide, yttrium halide, titanium halide, manganese halide, molybdenum halide, or a combination thereof, wherein the molar ratio of the total mole of the metal halide and the aluminum halide to the ionic liquid is from 1.1:1 to 2.1:1; wherein the positive electrode consists of a current-collecting layer and an active material; and wherein the current-collecting layer is conductive carbon substrate and the conductive carbon substrate is carbon cloth, carbon felt, or carbon paper; wherein the active material is layered active layer; wherein the active material is graphite, carbon nanotube, graphene, or a combination thereof; and/or wherein the graphite is natural graphite, artificial graphite, mesophase carbon microbead, pyrolytic graphite, foamed graphite, flake graphite, expanded graphite, or a combination thereof; the negative electrode comprises a metal or an alloy of the metal, a current-collecting layer, or a combination thereof; and wherein the metal or the alloy of the metal comprises silver, copper, iron, cobalt, aluminum, zinc, indium, cadmium, nickel, tin, chromium, lanthanum, yttrium, titanium, manganese, tungsten, tantalum, or molybdenum. a positive electrode; a separator; a negative electrode, wherein the positive electrode is separated from the negative electrode by the separator; and an electrolyte disposed between the positive electrode and the negative electrode and contacting the positive electrode and the negative electrode, wherein the electrolyte comprises an ionic liquid with a melting point less than 100°C, aluminum halide, and metal halide, wherein the ionic liquid is selected from alkylimidazolium salt, alkylpyridinium salt, alkylfluoropyrazolium salt, alkyltriazolium salt, aralkylammonium salt, alkylalkoxyammonium salt, aralkylphosphonium salt, aralkylsulfonium salt, or a combination thereof; wherein the metal halide is silver halide, copper halide, cobalt halide, ferric halide, indium halide, cadmium halide, nickel halide, tin halide, chromium halide, lanthanum halide, yttrium halide, titanium halide, manganese halide, molybdenum halide, or a combination thereof, wherein the molar ratio of the total mole of the metal halide and the aluminum halide to the ionic liquid is from 1.1:1 to 2.1:1; wherein the positive electrode consists of a current-collecting layer and an active material; and wherein the current-collecting layer is conductive carbon substrate and the conductive carbon substrate is carbon cloth, carbon felt, or carbon paper; wherein the active material is layered active layer; wherein the active material is graphite, carbon nanotube, graphene, or a combination thereof; and/or wherein the graphite is natural graphite, artificial graphite, mesophase carbon microbead, pyrolytic graphite, foamed graphite, flake graphite, expanded graphite, or a combination thereof; the negative electrode comprises a metal or an alloy of the metal, a current-collecting layer, or a combination thereof; and wherein the metal or the alloy of the metal comprises silver, copper, iron, cobalt, aluminum, zinc, indium, cadmium, nickel, tin, chromium, lanthanum, yttrium, titanium, manganese, tungsten, tantalum, or molybdenum.