Composite positive electrode material of lithium ion battery and preparation method of composite positive electrode material

Abstract

The invention provides a composite positive electrode material of a lithium ion battery. The composite positive electrode material comprises a ternary material matrix LiNixCoyM1-x-yO2 an iron phosphate transition layer which coats the surface of the matrix, and a lithium iron phosphate coating layer, wherein the lithium iron phosphate coating layer coats the surface of the iron phosphate transition layer; and the general formula of the composite positive electrode material is LiNixCoyM1-x-yO2.aFePOz.bLiFePO4. The invention further provides a preparation method of the composite positive electrode material of the lithium ion battery; the preparation method comprises the following steps that an iron salt and phosphate are added into water to obtain a uniform dispersion liquid; the ternary material is added into a dispersion medium to obtain a uniform turbid liquid; and slurry with uniformly mixed two liquids is further obtained, the slurry is dried to obtain a precursor, and the precursoris sintered to obtain an iron phosphate coated ternary material; and the iron phosphate coated ternary material is uniformly mixed with a lithium salt and a carbon source to be sintered under an inert atmosphere to obtain the composite positive electrode material of the lithium ion battery.

Description

technical field [0001] The invention belongs to the technical field of lithium ion battery materials, and in particular relates to a lithium ion battery composite cathode material with a core-shell structure and a preparation method thereof. Background technique [0002] At present, lithium iron phosphate and ternary materials are widely used in the preparation of lithium-ion battery cathode materials in electric vehicles. Although lithium iron phosphate has the advantages of high safety and long cycle life, its energy density is significantly lower. The nickel-cobalt-manganese ternary material has received more and more attention because of its higher specific energy, and with the increase of nickel content, the capacity of the ternary material is getting higher and higher. However, as the nickel content increases, its structural stability becomes worse and worse, while the cycle life will be shorter and the safety performance will be worse and worse. [0003] The modific...

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Problems solved by technology

[0006] The two Chinese invention patent applications with the publication numbers CN105406069A and CN105355880A synthesize lithium manganese iron phosphate or lithium iron phosphate in situ on the surface of the ternary material. The phosphate coating layer coated by this method is relatively uniform. The coating process needs to be carried out at a higher sintering temperature, and the ternary material is easy to react with lithium manganese iron phosphate or lithium iron phosphate and the carbon coating contained in the high temperature, thereby causing damage to the surface structure of the material. Therefore, this method is more difficult to realize industrial production

[0007] Kim et al. (Kim S B, Lee K J, Choi W J, et al. Preparation and cycle performance at high temperature for Li[Ni 0.5 co 0.2 mn 0.3 ]O 2 coated with LiFePO 4 [J].Journal of Solid State Electrochemistry,2010,14(6):919-922) through dry coating system coating lithium iron phosphate on the surface of the ternary material to improve the cycle performance of the material, although through this high-strength The instrument can improve the binding force between the two to a certain extent, but it needs to heat treat the two at high temperature, and there is a risk of reaction between the ternary material and lithium iron phosphate

[0008] None of the methods provided by the above patent documents can provide an effective coating method to improve circulation and safety issues

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