A positive electrode active material, positive electrode sheet and electrochemical device

Abstract

The invention relates to a cathode active material. The cathode active material comprises a ternary material A and a ternary material B. The chemical formula of the ternary material A is Lia1(Nix1Coy1Mnz1)O2, wherein a1 is larger than or equal to 0.95 and smaller than or equal to 1.2, x1 is larger than 0.5 and smaller than 1, y1 is larger than 0 and smaller than 1, and x1+y1+z1=1, and the ternarymaterial A is of a polycrystalline structure; and the chemical formula of the ternary material B is Lia2(Nix2Coy2Mnz2)O2, wherein a2 is more than or equal to 0.95 and less than or equal to 1.2, x2 ismore than 0 and less than or equal to 0.5, y2 is more than 0 and less than 1, x2+y2+z2=1, and the ternary material B has a single crystal structure or a single crystal-like structure. A low-nickel single crystal material and a high-nickel polycrystalline material are mixed as the cathode active material, so that the gas production problem of the high-nickel material can be effectively solved, andthe cycle performance of the battery can be effectively improved.

Description

technical field [0001] The present application relates to the field of electrochemistry, and specifically relates to a positive electrode active material, a positive electrode sheet using the positive electrode active material, and an electrochemical device. Background technique [0002] With the application and promotion of lithium-ion battery technology in the field of pure electric passenger vehicles, people's requirements for the mileage and safety performance of pure electric vehicles are also continuously upgraded, so the requirements for positive active materials in lithium-ion batteries are also continuously increasing. Lithium-ion batteries are required to have higher gram capacity, good chemical stability, and long cycle life. Nickel cobalt lithium manganate ternary material is a kind of positive electrode active material with high gram capacity and long cycle life. The higher the relative content of nickel element, the higher the gram capacity of the formed ternar...

AI Technical Summary

Problems solved by technology

[0005] However, the method of coating the passivation film has high technical difficulties. This method generally covers the particle surface with a nano-scale coating layer, and the thickness and uniformity of the coating layer are not easy to control.

If the coating layer is not thick enough, as the charge-discharge cycle proceeds, the passivation film coating layer on the surface of the particles will gradually be consumed, and eventually the electrolyte will directly contact the positive electrode, and gas production will intensify, causing lithium precipitation or diving; if the coating layer is too thick , the dynamics are affected, and the gram capacity and DCR are very unsatisfactory; even if the coating layer of most materials is within the thickness specification, the current process cannot guarantee that the thickness of the coating layer of all particles is very uniform. The surface of the coated active material still has strong oxidation, which will also cause the above problems

The method of reducing the ambient humidity can effectively improve the gas production performance of the battery cell, but this method greatly increases the manufacturing cost, and this method cannot effectively directly reduce the storage gas production of the battery cell at high temperature and ease the cycle process. The rapid growth of DCR in China is a measure that treats the symptoms but not the root cause

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