NOVELTY - A high-specific-energy lithium ion battery preparing method involves utilizing NCM / LFP mixed material, silicon carbon as cathode, electrolyte using high pressure electrolyte membrane using single-sided coated with a ceramic diaphragm with aluminum oxide. Cathode material is prepared. Negative electrode material is prepared followed by preparing electrolyte, separator, current collector, where the electrolyte is 1.5-2 mol/L ethylene carbonate and dimethyl carbonate solution, additive is 0.5-8% fluoro ethylene carbonate, separator is a ceramic separator, and preparing soft pack battery.    USE - Method for preparing high-specific-energy lithium ion battery for electric cars.    DETAILED DESCRIPTION - A high-specific-energy lithium ion battery preparing method involves utilizing NCM / LFP mixed material, silicon carbon as cathode, electrolyte using high pressure electrolyte membrane using single-sided coated with a ceramic diaphragm with aluminum oxide. Cathode material is prepared by using sol - gel method with lithium iron phosphate particles, Iron nitrate nonahydrate, lithium carbonate, Ammonium dihydrogen phosphate, citric acid at molar ratio of 2:1: 2: 1 dissolved in deionized water and ethylene glycol complexing agent, adjusting the pH to 5 with ammonia, stirring at 80 degrees C for 2 hours under constant stirring to 5-15% lithium iron phosphate sol A, weighing a certain quality of Li (Ni(0.6)Co(0.2)Mn(0.2)O2), adding to the sealed reactor with sol A, and stirring to obtain a uniform sol ? / ? mixture, after which the material is transferred to another reactor, the material placed at 600 degrees C under argon atmosphere, calcinising for 5 h, to obtain NCM/ LFP cathode material. Negative electrode material is prepared by using carbon negative electrode material for the negative electrode of silicon, multi-g capacity of 600mAh / g, for the first time more than 88% efficiency, particle diameter D50 of 5-15, Mm, specific surface area of 2-5m2/g, very sheet packing density 1.5-1.8g /cm3, followed by preparing electrolyte, separator, current collector, where the electrolyte is 1.5-2 mol/L ethylene carbonate and dimethyl carbonate solution, additive is 0.5-8% fluoro ethylene carbonate, separator is a ceramic separator, and preparing soft pack battery by using material, after co-pulp, coating, roll cutting, lamination, dry, liquid injection preparation, and packaging.