A kind of lithium-ion battery composite cathode material and preparation method thereof

Abstract

The invention provides a lithium-ion battery composite positive electrode material, including a ternary material matrix LiNi x co y m 1‑x‑y o 2 And the iron phosphate transition layer and the lithium iron phosphate coating layer coated on the surface of the substrate, the lithium iron phosphate coating layer is coated on the surface of the iron phosphate transition layer; the composite positive electrode material The general formula is expressed as: LiNi x co y m 1‑x‑y o 2 ·aFePO z · bLiFePO 4 . The present invention also provides a preparation method of a lithium-ion battery composite cathode material, the steps comprising: adding iron salt and phosphate into water to obtain a uniform dispersion; adding ternary materials to a dispersion medium to obtain a uniform suspension; Then obtain a slurry uniformly mixed with the two liquids, dry to obtain a precursor, and sinter to obtain a ternary material coated with iron phosphate; after uniformly mixing it with a lithium salt and a carbon source, sinter in an inert atmosphere to obtain a composite positive electrode material for a lithium-ion battery.

Description

Technical field [0001] The present invention belongs to the technical field of lithium ion battery materials, and more particularly to a lithium ion battery composite positive electrode material of a nuclear 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 the positive material of lithium ion battery in electric vehicles. Although lithium iron phosphate has the advantages of high safety and long cycle life, its energy density is significantly lower. Nickel-cobalt-manganese three-membered materials are increasingly concerned by higher than energy, and with the increase of nickel content, the capacity of the ternary material is getting higher and higher. However, with the improvement of nickel content, the structural stability is also getting worse, while the cycle life will be shorter, and the safety performance will be getting worse. [0003] For the modif...

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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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