Processing method of high-safety lithium manganese iron phosphate battery positive electrode material

Abstract

The invention relates to a processing method of a high-safety lithium iron manganese phosphate battery positive electrode material, and belongs to the technical field of lithium ion batteries. Comprising a positive plate, a negative plate, an isolating membrane, electrolyte and a battery shell, the positive plate comprises a positive current collector and a positive active material layer coated on the surface of the positive current collector, and the positive active material layer comprises the following components in percentage by weight: 90-96 wt% of a positive active material, 1.5-5 wt% of a positive conductive agent and 2-5 wt% of a positive binder. In order to solve the problem of poor safety of the nickel cobalt lithium manganate material, the lithium manganese iron phosphate battery is physically mixed with the nickel cobalt lithium manganate material, the particle size of the lithium manganese iron phosphate battery is only about 1 / 3 of that of the nickel cobalt lithium manganate, and the lithium manganese iron phosphate battery can be distributed among nickel cobalt lithium manganate particles after being mixed, so that chain reaction of the nickel cobalt lithium manganate material under the condition of thermal runaway can be inhibited, and the safety of the nickel cobalt lithium manganate material is improved. And the thermal stability is improved.

Description

Technical Field

[0001] The invention relates to a method for processing a high-safety lithium manganese iron phosphate battery positive electrode material, belonging to the technical field of lithium ion batteries. Background Art

[0003] Safety and energy density, as key indicators of power lithium-ion batteries, have always been the focus of research and solution in the industry. At present, the most widely used power lithium-ion battery systems at home and abroad are mainly lithium iron phosphate systems and ternary (nickel-manganese-cobalt or nickel-cobalt-aluminum three metal elements) systems, but both systems have obvious advantages and disadvantages and cannot fully meet the needs of the development of power lithium-ion batteries. The lithium iron phosphate system battery has excellent cycle life and safety performance, but the specific energy is difficult to exceed 1401,4-butane sultone / Kg. The specific energy of the ternary system battery can reach more than 1801,4-butane sultone / Kg, but while maintaining a high specific energy, the cycle life will be significantly worse than that of the lithium iron phosphate system battery, and there are major problems with safety performance. If a battery that combines the high safety, long life and high specific energy characteristics of lithium iron phosphate with ternary can be developed, it will have a huge impact on the development of power batteries. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art, to provide a high-safety processing method for lithium manganese iron phosphate battery positive electrode material, and to provide a lithium-ion battery that can both ensure the battery energy density and improve its safety performance in view of the shortcomings of current lithium iron phosphate and ternary system batteries.

[0005] To achieve the above object, the present invention is implemented by the following technical solutions:

[0006] A high-safety lithium manganese iron phosphate battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and a battery shell, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector, wherein the positive electrode active material layer has the following components in terms of weight percentage:

[0007] Positive electrode active material 90~96wt%

[0008] Positive electrode conductive agent 1.5~5wt%

[0009] Positive electrode binder 2~5wt%

[0010] Among them, the positive electrode active material includes two components, component A and component B, wherein component A is lithium manganese iron phosphate battery, and component B is lithium nickel cobalt manganese oxide.

[0011] Furthermore, the weight ratio of the lithium manganese iron phosphate battery to the lithium nickel cobalt manganese oxide is: lithium manganese iron phosphate battery: lithium nickel cobalt manganese oxide = 10:90 to 50:50.

[0012] Furthermore, the lithium manganese iron phosphate battery adopts surface carbon coating and bulk iron ion doping, and its molecular formula is LiMnxFe1-xPO4, wherein x ranges from 0.3 to 0.8; the molecular formula of the lithium nickel cobalt manganese oxide is LiNiyCozMn1-y-zO2, wherein y ranges from 0.3 to 0.8, and z ranges from 0.1 to 0.5.

[0013] Furthermore, the positive electrode conductive agent is a mixture of conductive carbon black and at least one of carbon nanotubes or graphene, and the ratio of the conductive carbon black to the at least one other conductive agent is 1wt%:0.5wt% to 4wt%:1wt% in terms of weight percentage in the positive electrode active material layer.

[0014] Furthermore, the positive electrode current collector is an aluminum foil with coatings on both the front and back surfaces, the coating is one of conductive carbon black, carbon nanotubes or graphene, and the total thickness of the coating is 2 μm to 5 μm.

[0015] Furthermore, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector. The components of the negative electrode active material layer are as follows, in terms of weight percentage:

[0016] Negative electrode active material 94~98wt%

[0017] Negative electrode conductive agent 0.5~2wt%

[0018] Negative electrode binder 1~5wt%

[0019] Wherein, the negative electrode active material is at least one of artificial graphite, natural graphite or mesophase carbon microspheres;

[0020] The negative electrode conductive agent is at least one of conductive carbon black, carbon nanotubes or graphene;

[0021] The negative electrode binder comprises two components: sodium carboxymethyl cellulose and styrene-butadiene rubber.

[0022] Furthermore, the isolation membrane is a polyolefin film or a non-woven fabric film, and the surface thereof contains a protective coating, and the protective coating is one of Al2O3, SiO2, TiO2, MgO or CaO.

[0023] Furthermore, the electrolyte is a high temperature resistant electrolyte, the main components of which are 11-14wt% of lithium salt, 84-88wt% of organic solvent, and 0.5-2wt% of high temperature additives, and the lithium salt is a mixture of at least one of lithium manganese iron hexafluorophosphate battery, lithium borate, lithium manganese iron difluorophosphate battery and lithium perchlorate.

[0024] Furthermore, the organic solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate or propylene carbonate.

[0025] Furthermore, the high temperature additive is a mixture of 1,4-butane sultone or 1,3-propane sultone and ethanolamine, and a linear polyphosphazene or a cyclic phosphazene trimer is added.

[0026] Beneficial effects of the present invention:

[0027] In order to improve the poor safety of lithium nickel cobalt manganese oxide materials in the present invention, lithium iron manganese phosphate batteries are physically mixed with them. Since the particle size of lithium iron manganese phosphate batteries is only about 1 / 3 of that of lithium nickel cobalt manganese oxide, they will be distributed between the particles of lithium nickel cobalt manganese oxide after mixing, which can inhibit the chain reaction of lithium nickel cobalt manganese oxide materials in the case of thermal runaway, and is conducive to improving and enhancing its thermal stability; in order to improve the poor conductivity of lithium manganese phosphate batteries in the present invention, on the one hand, they are mixed with lithium nickel cobalt manganese oxide materials with better conductivity, and lithium nickel cobalt manganese oxide plays a good conductive node role through physical mixing. On the other hand, in addition to using conductive carbon black and carbon nanotubes known to those skilled in the art, the positive electrode conductive agent also adds graphene solution, which can effectively improve the processing performance and conductive performance of the positive electrode active material layer. The positive electrode current collector uses coated aluminum foil to improve the conductive performance. At the same time, it can delay thermal runaway and improve safety performance during safety tests such as acupuncture, short circuit and extrusion; the isolation membrane described in the present invention is one of a polyolefin film or a non-woven film, and the surface contains a protective coating. The protective coating is one of Al2O3, SiO2, TiO2, MgO or CaO. The protective coating can effectively improve the oxidation and thermal shrinkage of the diaphragm surface, increase the battery life and improve the safety performance; the main purpose of using high temperature resistant electrolyte is to increase the decomposition temperature of the electrolyte and enhance its flame retardancy, so that the high temperature performance and safety performance of the battery are improved; the battery shell is one of aluminum plastic film soft packaging, aluminum shell, steel shell or plastic shell known to those skilled in the art. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with embodiments:

[0029] Example 1

[0030] This embodiment is manufactured using a laminated soft-package battery process.

[0031] In this embodiment, the content of the positive electrode active material is 20wt% for lithium manganese iron phosphate battery and 80wt% for lithium nickel cobalt manganese oxide.

[0032] The method for making the positive electrode sheet in this embodiment is as follows:

[0033] 1) Material baking: Weigh lithium manganese iron phosphate battery, lithium nickel cobalt manganese oxide, polyvinylidene fluoride, conductive carbon black and graphene solution according to 19wt%: 75.3wt%: 3wt%: 2wt%: 0.7wt%. Baste the lithium manganese iron phosphate battery, lithium nickel cobalt manganese oxide and conductive carbon black powder at 120℃ in a vacuum for 8 hours, and bake the polyvinylidene fluoride (molecular weight 1 million to 1.1 million) powder at 80℃ in a vacuum for 4 hours. Use a card furnace to measure the moisture content and cool it to below 40℃ for use.

[0034] 2) Preparation of adhesive solution: Add 1 part of polyvinylidene fluoride to 15 parts of nitrogen methyl pyrrolidone, stir at high speed under vacuum for 3 hours, and prepare an adhesive solution with a viscosity of 1000-2500 mPa·s.

[0035] 3) Preparation of positive electrode slurry: Add conductive carbon black to the glue solution, stir at high speed in vacuum for 2 hours, add graphene solution, and stir at high speed in vacuum for 1 hour. Then add the physically mixed lithium nickel cobalt manganese oxide and lithium iron manganese phosphate battery powder to the slurry, and stir at high speed in vacuum for 3 hours. Add nitrogen methyl pyrrolidone to adjust the slurry viscosity, stir at high speed for 0.5 hours after each addition, and measure the viscosity at 7000-9000mPa·s, and pass the glue through a 150 mesh sieve for use.

[0036] 4) Positive electrode roll coating: The positive electrode slurry is coated by an extrusion coater. The foil material is graphene-coated aluminum foil with a thickness of 20um and a coating double-sided density of 380g / m2. The coating machine runs at a speed of 8 to 12m / min. After the coating is qualified, it will proceed to the next step.

[0037] 5) Preparation of positive electrode sheets: The positive electrode rolls that have passed the coating and baking are rolled to a compacted density of 2.9-3.0 g / cc. The sheet is required to be tough and not fall off. The rolled positive electrode rolls are die-cut to obtain positive electrode sheets for subsequent battery lamination.

[0038] The method for making the negative electrode sheet in this embodiment is as follows:

[0039] Artificial graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber are prepared in a slurry at a ratio of 95wt%: 1wt%: 1.5wt%: 2.5wt%, and the solvent is deionized water. The final negative electrode slurry viscosity is 3000-5000mPa·s. Then coating, rolling and negative electrode sheet preparation are carried out.

[0040] The battery manufacturing method in this embodiment is as follows:

[0041] The positive electrode sheet and the negative electrode sheet are stacked and packaged with the protective coating diaphragm, and then vacuum-baked at 90°C until the moisture content is less than 500ppm. After the baking is qualified, the high-temperature resistant electrolyte is injected, and the finished battery is obtained after high-temperature aging, formation, high-temperature aging, and vacuum sealing.

[0042] The finished battery in this embodiment has been tested and the 1C discharge specific energy is 1701,4-butane sultone / Kg. The remaining capacity after 500 1C charge and discharge cycles is 96.3% of the initial capacity and can pass safety tests such as overcharge.

[0043] The description of the direction and relative position relationship of the structure in the present invention, such as the description of front, back, left, right, up, and down, does not constitute a limitation of the present invention, but is only for the convenience of description.

Claims

1. A method for processing a positive electrode material for a high-safety lithium manganese iron phosphate battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and a battery casing, Features: The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the surface of the positive electrode current collector. The composition of the positive electrode active material layer is as follows, in terms of weight percentage: Positive electrode active material 90~96wt% Positive electrode conductive agent 1.5~5wt% Positive electrode binder 2~5wt% Among them, the positive electrode active material includes two components, component A and component B, wherein component A is lithium manganese iron phosphate battery, and component B is lithium nickel cobalt manganese oxide.

2. A method for processing a high-safety lithium iron manganese phosphate battery positive electrode material according to claim 1, Features: The weight ratio of the lithium iron manganese phosphate battery to the lithium nickel cobalt manganese oxide is: lithium iron manganese phosphate battery: lithium nickel cobalt manganese oxide = 10:90 to 50:

50.

3. A method for processing a high-safety lithium manganese iron phosphate battery positive electrode material according to claim 1 or 2, Features: The lithium manganese iron phosphate battery is surface carbon coated and bulk iron ion doped, and its molecular formula is LiMnxFe1-xPO4, where x ranges from 0.3 to 0.8; the molecular formula of the lithium nickel cobalt manganese oxide is LiNiyCozMn1-y-zO2, where y ranges from 0.3 to 0.8 and z ranges from 0.1 to 0.

5.

4. A method for processing a high-safety lithium manganese iron phosphate battery positive electrode material according to claim 1, Features: The positive electrode conductive agent is a mixture of conductive carbon black and at least one of carbon nanotubes or graphene, and the ratio of the conductive carbon black to the at least one other conductive agent is 1wt%:0.5wt% to 4wt%:1wt% in terms of weight percentage in the positive electrode active material layer.

5. The method for processing the high-safety lithium manganese iron phosphate battery positive electrode material according to claim 1, Features: The positive electrode current collector is an aluminum foil with coating treatment on both the front and back surfaces, the coating is one of conductive carbon black, carbon nanotubes or graphene, and the total thickness of the coating is 2μm to 5μm.

6. The method for processing the high-safety lithium manganese iron phosphate battery positive electrode material according to claim 1, Features: The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector. The components of the negative electrode active material layer are as follows, in terms of weight percentage: Negative electrode active material 94~98wt% Negative electrode conductive agent 0.5~2wt% Negative electrode binder 1~5wt% Wherein, the negative electrode active material is at least one of artificial graphite, natural graphite or mesophase carbon microspheres; The negative electrode conductive agent is at least one of conductive carbon black, carbon nanotubes or graphene; The negative electrode binder comprises two components: sodium carboxymethyl cellulose and styrene-butadiene rubber.