NOVELTY - A gel electrolyte comprises polyurethane acrylate, conductive lithium salt, organic solvent, additive, and photoinitiator. The conductive lithium salt is lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, tris(trifluoromethylsulfonyl)methyl lithium, or lithium trifluoromethanesulfonate. The organic solvent is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, ethyl acetate, fluorobenzene, and/or ethyl acetoacetate.    USE - Gel electrolyte is used for lithium ion batteries.    ADVANTAGE - The gel electrolyte can be prepared by a method which eliminates the troubles and complex technical flows of forming a polymer film, extraction of pore, and electrolyte absorption. The preparation method is simple, reduces apparatus requirement, shortens process time, and improves productivity. The gel electrolyte satisfies the requirements of safety of lithium ion battery.    DETAILED DESCRIPTION - A gel electrolyte comprises polyurethane acrylate, conductive lithium salt, organic solvent, additive, and photoinitiator. The conductive lithium salt is lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, tris(trifluoromethylsulfonyl)methyl lithium, or lithium trifluoromethanesulfonate. The organic solvent is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, ethyl acetate, fluorobenzene, and/or ethyl acetoacetate. The additive is nano silica, ethylene carbonate, ethyl acetate, fluorobenzene, and/or cyclohexylbenzene. The molecular weight of polyethylene glycol used for polyurethane acrylate is 1000, 800 or 600. The photoinitiator is 1173 photoinitiator. An INDEPENDENT CLAIM is included for preparation of gel electrolyte, which involves placing isophorone diisocyanate and polyethylene glycol in a glass reactor under nitrogen protection, adding dibutyl tin dilaurate as catalyst, slowly adding hydroxyethyl methacrylate, introducing vinyl group at final molecule terminal to obtain polyurethane acrylate, preparing liquid electrolyte in a glove tank (less than 10 ppm of water and less than 10 ppm of oxygen) filled with argon gas, adding highly pure organic solvent, agitating for 5-15 minutes with magnetic agitator, adding conductive lithium salt and additive to the mixed solution, agitating for 5-13 minutes, mixing polyurethane acrylate and liquid electrolyte uniformly in glove tank, covering with glass or PTFE plate, adding photoinitiator, and irradiating UV light.