Positive electrode active material and electrochemical device

Abstract

Provided are a positive electrode active material and an electrochemical device. The positive electrode active material is of a P63mc crystal structure and is a lithium transition metal composite oxide containing Co and an R element, wherein the M element includes at least one of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr, Y, or Zr, the R element includes at least one of F, Cl, and the R element is amolar content of nR; wherein the sum of the molar content of Co and the molar content of M is nCo+M, and the ratio delta of nR to nCo+M is larger than 0 and smaller than or equal to 0.01. The positiveelectrode active material disclosed by the invention is high in crystal structure stability, so that the cycle performance and the thermal stability of an electrochemical device are improved.

Description

technical field [0001] The present application relates to the technical field of cathode materials, in particular, to cathode active materials and electrochemical devices. Background technique [0002] Lithium-ion batteries are widely used in portable electronic products, electric transportation, national defense aviation, energy storage and other fields due to their advantages such as high energy density, good cycle performance, environmental protection, safety and no memory effect. In order to meet the needs of social development, it is an urgent problem to seek lithium-ion batteries with higher energy density and power density, which requires the cathode materials used to have higher specific capacity and higher voltage platform. [0003] In order to obtain higher specific energy, positive electrode active materials are developing towards high voltage. As the voltage increases, the current positive electrode active materials, Li + A large amount of desorption will cause ...

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Problems solved by technology

[0003] In order to obtain higher specific energy, positive electrode active materials are developing towards high voltage. As the voltage increases, the current positive electrode active materials, Li + A large amount of desorption will cause a series of irreversible phase transitions (O3 to H1-3, H1-3 to O1) in the crystal structure of the material, which will greatly reduce the cycle performance and safety performance of the material

Moreover, the interfacial side reactions are intensified at high voltages, such as LiCoO 2 The dissolution of Co metal in the material is serious, and the high-voltage electrolyte technology is difficult to match, and the decomposition and failure of the conventional electrolyte are accelerated under high voltage, so the capacity decay is very serious

In order to improve the stability of the crystal phase structure of the material, the irreversible phase transition can be delayed by metal cation doping, but this method has no obvious effect on the stability of the structure after the voltage is higher than 4.6V

In addition, as the doping amount increases, the theoretical capacity loss will increase

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