[0018] The preparation method of the electrolyte of the present invention is a conventionally used method. It is only necessary to dissolve the lithium salt and the weak acid salt of lithium in an organic solvent. The concentration of the lithium salt as an electrolyte is 0.5-2.0 mol/liter, preferably 0.5-1.5 mol/liter. Based on the total amount of the non-aqueous electrolyte, the content of the weak acid salt of lithium is 0.001 to 5% by weight, preferably 0.005 to 3% by weight.
[0019] Preferably, the weak acid salt of lithium is pre-baked at 120-180° C. for 5-24 hours before being mixed with the electrolyte, so that the water content of the weak acid salt of lithium is below 30 ppm. In order to sufficiently and efficiently remove the very small amount of moisture in the weak acid salt of lithium, the baking is preferably performed in a vacuum oven, and the vacuum pressure of the vacuum oven is less than atmospheric pressure.
[0020] The lithium ion secondary battery of the present invention includes an electrode group and an electrolyte, the electrode group and the electrolyte are sealed in a battery case, and the electrode group includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode.
[0021] The positive electrode may be various positive electrodes known to those skilled in the art, and usually includes a current collector and a positive electrode material coated and/or filled on the current collector. The current collector may be various current collectors known to those skilled in the art, such as aluminum foil, copper foil or nickel-plated steel strip. In the present invention, aluminum foil is used as the current collector. The positive electrode material may be various positive electrode materials known to those skilled in the art, and usually includes a positive electrode active material, a binder, and an optionally contained conductive agent.
[0022] The positive electrode active material may be a conventional positive electrode active material capable of inserting and deintercalating lithium ions, preferably one or more of the following materials: Li x M y Mn 2-y O 4 , Where 0.9≤x≤1.2, 0≤y≤1.0, M is one of lithium, boron, magnesium, aluminum, iron, cobalt, nickel, copper, gallium, yttrium, fluorine, iodine, sulfur and other elements; Li x Ni y Co 1-y O 2 , Where 0.9≤x≤1.1, 0≤y≤1.0; Li a Ni x Co y Mn z O 2 , Where 0≤a≤1.2, x+y+z=1, 0≤x≤0.5, 0≤y≤0.5, 0≤z≤0.5.
[0023] The binder can adopt all types of binders conventionally used in the prior art for preparing lithium ion secondary battery positive electrodes, for example, it can be polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) ), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), styrene butadiene rubber (SBR) and styrene butadiene rubber (SBR) latex. Based on the weight of the positive electrode active material in the positive electrode material, the content of the binder is 2-10% by weight, preferably 2-8% by weight.
[0024] The conductive agent may be a conventional positive electrode conductive agent in the art, such as at least one of acetylene black, conductive carbon black, and conductive graphite. The conductive agent in the second coating layer can be selected from one or more of the conductive agents defined by the positive electrode material coating. Based on the weight of the positive electrode active material in the positive electrode material, the content of the conductive agent in the positive electrode material coating is 0-20% by weight, preferably 2-15% by weight.
[0025] The negative electrode of the lithium ion secondary battery of the present invention is well known to those skilled in the art. Generally, the negative electrode includes a current collector and a negative electrode material coated and/or filled on a conductive substrate. The current collector is well known to those skilled in the art, and may be selected from aluminum foil, copper foil, nickel-plated steel strip or punched steel strip, for example. The negative active material is well known to those skilled in the art, and it includes a negative active material, a binder, and a conductive agent optionally contained.
[0026]The negative electrode active material is not particularly limited, and can be a conventional negative electrode active material capable of inserting and deintercalating lithium, such as natural graphite, artificial graphite, petroleum coke, organic pyrolysis carbon, mesophase carbon microspheres, carbon fiber, tin alloy, One or more of silicon alloys, preferably artificial graphite.
[0027] The binder of the negative electrode includes one or more of fluorine-containing resin and polyolefin compounds such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and styrene butadiene rubber (SBR). Based on the weight of the negative active material, the content of the binder is 0.1-10% by weight, preferably 0.5-5% by weight.
[0028] The conductive agent of the negative electrode is not particularly limited, and can be a conventional negative electrode conductive agent in the art, for example, it can be one or more of acetylene black, conductive carbon black and conductive graphite. Based on the weight of the negative electrode active material, the content of the conductive agent is 0-15% by weight, preferably 2-10% by weight.
[0029] The solvent used to prepare the positive electrode slurry and the negative electrode slurry of the present invention can be selected from conventional solvents, such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), and diethylformamide. (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and one or more of water and alcohols. The amount of solvent is such that the slurry can be coated on the current collector. Generally speaking, based on the weight of the negative electrode active material, the content of the solvent is 30-80% by weight, preferably 35-60% by weight.
[0030] The diaphragm layer has electrical insulation properties and liquid retention properties, is arranged between the positive electrode and the negative electrode, and is sealed in the battery case together with the positive electrode, the negative electrode and the electrolyte. The diaphragm layer may be various diaphragm layers commonly used in the field, such as modified polyethylene felt, modified polypropylene felt, ultrafine glass fiber felt, vinylon produced by various manufacturers in well-known manufacturers. A composite film made of felt or nylon felt and wettable polyolefin microporous film by welding or bonding.
[0031] The preparation method of the lithium ion secondary battery provided by the present invention includes preparing the positive electrode and the negative electrode of the battery, and preparing the positive electrode, the negative electrode and the separator between the positive electrode and the negative electrode into a pole core, and then placing the pole core in the battery case , Inject electrolyte to seal the battery case.
[0032] The preparation method of the positive electrode can adopt a conventional preparation method. For example, the positive electrode can be obtained by mixing the positive electrode active material, the conductive agent and the binder with the solvent, coating and/or filling it on the current collector, and drying, compression molding or no compression molding.
[0033] The preparation method of the negative electrode can adopt a conventional preparation method. For example, the negative electrode active material, the conductive agent, and the binder are mixed with a solvent, coated and/or filled on the current collector, dried, molded or not molded to obtain the negative electrode.
[0034] The preparation method of the lithium ion secondary battery of the present invention uses the non-aqueous electrolyte provided by the present invention for the electrolyte, and other steps are well known to those skilled in the art. The method for preparing a lithium ion secondary battery provided by the present invention includes disposing a separator layer between the prepared positive electrode and the negative electrode to form an electrode group, accommodating the electrode group in a battery case, injecting electrolyte, and then placing the battery case The lithium ion secondary battery can be prepared by sealing.
