Positive electrode active material and preparation method therefor, secondary battery, and device

Abstract

Disclosed are a positive electrode active material and a preparation method therefor, a secondary battery, and a device. The positive electrode active material comprises a primary particle. The primary particle comprises: a core, which comprises LiaNibCocMndM1eOx; a first coating layer, which is applied on the surface of the core and is a continuous layer, wherein the first coating layer comprises a compound containing an element M2, and M2 comprises at least one of Co and Mn; and a second coating layer, which is applied on the surface of the first coating layer and is in the form of discrete islands, wherein the second coating layer comprises a compound containing an element M5, and M5 comprises at least one of Li, Na, Mg, Sr, Ba, Al, Y, B, Zr, Ti, Si, Sn, V, P, W and Mo; and the molar percentage content of Co and / or Mn in the first coating layer is greater than the molar percentage content of Co and / or Mn in the core. Thus, the positive electrode active material has excellent cycle performance and rate capability.

Description

Positive electrode active material and preparation method thereof, secondary battery and device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application CN202311693715.5, filed on December 6, 2023, with the invention name “Positive electrode active material, preparation method thereof, secondary battery and device”. The entire contents of the above Chinese patent application are incorporated into this application by reference. Technical Field

[0003] The present application relates to the field of energy storage, and in particular to a positive electrode active material and a preparation method thereof, a secondary battery, and a device. Background Art

[0004] In recent years, lithium-ion secondary batteries (Li-ion batteries) have been widely used in mobile phones, computers, energy storage, power tools, electric vehicles, and other fields due to their advantages such as high energy density, long cycle life, and low self-discharge rate. However, as the nickel content or cutoff voltage of the nickel-cobalt-manganese (NCM) ternary cathode active material in Li-ion secondary batteries increases, the structural stability of the material decreases during cycling, while thermal stability decreases, battery safety performance declines, and the accident rate increases. Therefore, to fully utilize the advantages of NCM ternary cathode active materials, one of the most commonly used methods is to surface-coat the ternary cathode active material.

[0005] However, current secondary batteries and devices still need improvement.

[0006] Summary of the Invention

[0007] The inventors have found that the traditional coating elements of the ternary positive electrode active materials in current secondary batteries are Mg, Al, Zr, and Ti, which eventually form oxides or lithium oxygen compounds on the surface of the ternary material core (kernel). In addition, considering the overall electrical performance, the amount added is small, and it is difficult to form a continuous and uniform coating layer. Usually, they are in a spotty or spherical form and are distributed on the surface of the ternary material core in the form of discrete islands (islands). As a result, the electrolyte can still contact the high-nickel material of the core through the uncoated area, accelerating the aging of its performance. Especially under high-voltage systems, the oxidation ability of the high-nickel positive electrode will be further enhanced, and its contact with the electrolyte through the uncoated area of ​​the core will lead to more intense side reactions. In response to the deficiencies in the prior art, the present application provides a positive electrode active material and its preparation method, a secondary battery and a device. The secondary battery of this application introduces a dense, continuous layered coating within the conventional discrete island coating of its positive electrode active material. This significantly improves the electrochemical performance of the positive electrode active material, particularly the electrochemical performance of high-nickel positive electrode active materials at high voltages, without significantly reducing the material's specific capacity. Based on these improvements, the positive electrode active material of this application has at least one of the following advantages: excellent material structural stability, electrical conductivity, cycling performance, rate capability, and electrochemical performance.

[0008] The first aspect of the present application provides a positive electrode active material, wherein the positive electrode active material includes primary particles, wherein the primary particles include: a core body, wherein the core body includes Li a Ni b Co c Mn d M1 e O x , wherein, 0.95≤a≤1.1, 0.5≤b≤0.96, 0≤c≤0.3, 0≤d≤0.4, 0≤e≤0.02, 1.5≤x≤2.5, b+c+d+e=1; M1 includes at least one of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; a first coating layer, the first coating layer is provided on the surface of the core body and is a continuous layer, the first coating layer includes a compound containing element M2, M 2 includes at least one of Co and Mn; a second coating layer, the second coating layer is arranged on the surface of the first coating layer and is in the form of discrete islands, the second coating layer includes a compound containing element M5, M5 includes at least one of Li, Na, Mg, Sr, Ba, Al, Y, B, Zr, Ti, Si, Sn, V, P, W and Mo; wherein the molar percentage content of Co and / or Mn in the first coating layer is greater than the molar percentage content of Co and / or Mn in the core body.

[0009] The second aspect of the present application provides a method for preparing a positive electrode active material, which comprises: mixing a core body precursor, a lithium salt and a first compound containing an element M1, and performing a first calcination treatment to obtain a core body; wherein M1 includes at least one of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; mixing the core body and a second compound containing an element M2, and performing a second calcination treatment to obtain a first product; wherein M2 includes at least one of Co and Mn; mixing the first product and a fifth compound containing an element M5, and performing a third calcination treatment to obtain the positive electrode active material; wherein M5 includes at least one of Li, Na, Mg, Sr, Ba, Al, Y, B, Zr, Ti, Si, Sn, V, P, W and Mo.

[0010] The present application also provides a secondary battery, which includes the positive electrode active material described above or the positive electrode active material formed by the preparation method described above.

[0011] The present application also provides a device, which includes the secondary battery described above.

[0012] The beneficial effects of this application are:

[0013] The positive electrode active material of the present application, wherein the primary particles include a core body, a continuous layered first coating layer arranged on the surface of the core body, and a discrete island-shaped second coating layer arranged on the surface of the first coating layer. By introducing a dense and continuous first coating layer between the core body and the discrete island-shaped second coating layer, the electrochemical performance of the positive electrode active material is greatly improved without significantly reducing the material's gram capacity. In addition, the setting of the two coating layers improves the stability of the material structure, effectively avoids direct contact between the core body and the electrolyte, reduces the side reaction between the core body and the electrolyte, and alleviates the problem of generating a large amount of gas due to the side reaction between the core body and the electrolyte. Specifically, on the one hand, the setting of the layered first coating layer utilizes a continuous layered first coating layer (shell layer) formed by modifying a large proportion of coating elements to completely coat the core, thereby avoiding contact between the electrolyte and the nickel-rich material of the core, inhibiting the side reaction between the positive electrode active material and the electrolyte, improving the stability of the positive electrode active material structure, and improving the conductivity of the positive electrode active material, thereby improving the cycle stability and rate performance of the positive electrode active material; and, the molar percentage content of Co and / or Mn in the first coating layer is greater than the molar percentage content of Co and / or Mn in the core. Thus, the first coating layer is rich in Co and Mn elements, and the reduction in its Ni content significantly reduces the reaction activity of the interface positive electrode active material and the electrolyte, further improving the electrochemical properties of the positive electrode active material, especially the electrochemical performance of the high-nickel positive electrode active material at high voltage. At the same time, the increase in Co and / or Mn in the first coating layer can reduce the Ni content, thereby reducing Li / Ni mixing, increasing the rate of Li ion diffusion, reducing diffusion polarization, and thus increasing the discharge capacity. On the other hand, the setting of the island-shaped second coating layer can have at least one of the following advantages by introducing a functional additive (element M5) into the second coating layer: modification of the fast ion conductor or the surface grain orientation, which increases the diffusion rate of surface lithium ions and improves the rate performance; preferential adsorption and reaction of HF, alleviates the attack of HF in the electrolyte, improves gas production, and improves storage and cycle life; improves the surface roughness of the positive electrode active material, increases the liquid retention capacity, and improves the electrochemical performance.

[0014] Therefore, based on the above improvements, the positive electrode active material of the present application has at least one of the following advantages: excellent material structure stability, electrical conductivity, cycle performance, rate performance, storage performance and safety performance. Description of the drawings:

[0015] FIG1 is a scanning electron microscope image of a cross section of a positive electrode active material in the prior art;

[0016] 2 and 3 are scanning electron microscope images of primary particles in a positive electrode active material according to one embodiment of the present application.

[0017] FIG4 is a scanning electron microscope image of a cross section of primary particles in a positive electrode active material according to one embodiment of the present application.

[0018] FIG5 is a graph showing the variation of the element content of each element in primary particles with the variation of the surface depth according to one embodiment of the present application. DETAILED DESCRIPTION

[0019] For the sake of clarity, this application only specifically discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0020] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0021] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0022] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0023] 1. Cathode Active Materials

[0024] The first aspect of the present application provides a positive electrode active material, wherein the positive electrode active material includes primary particles, wherein the primary particles include: a core body, wherein the core body includes Li a Ni b Co c Mn d M1 e O x, wherein, 0.95≤a≤1.1, 0.5≤b≤0.96, 0≤c≤0.3, 0≤d≤0.4, 0≤e≤0.02, 1.5≤x≤2.5, b+c+d+e=1; M1 includes at least one of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; a first coating layer, the first coating layer is provided on the surface of the core body and is a continuous layer, the first coating layer includes a compound containing element M2, M 2 includes at least one of Co and Mn; a second coating layer, the second coating layer is arranged on the surface of the first coating layer and is in the form of discrete islands, the second coating layer includes a compound containing element M5, M5 includes at least one of Li, Na, Mg, Sr, Ba, Al, Y, B, Zr, Ti, Si, Sn, V, P, W and Mo; wherein the molar percentage content of Co and / or Mn in the first coating layer is greater than the molar percentage content of Co and / or Mn in the core body.

[0025] The positive electrode active material of the present application, wherein the primary particles include a core body, a continuous layered first coating layer arranged on the surface of the core body, and a discrete island-shaped second coating layer arranged on the surface of the first coating layer. By introducing a dense and continuous first coating layer between the core body and the discrete island-shaped second coating layer, the electrochemical performance of the positive electrode active material is greatly improved without significantly reducing the material's gram capacity. In addition, the setting of the two coating layers improves the stability of the material structure, effectively avoids direct contact between the core body and the electrolyte, reduces the side reaction between the core body and the electrolyte, and alleviates the problem of generating a large amount of gas due to the side reaction between the core body and the electrolyte. Specifically, on the one hand, the setting of the layered first coating layer utilizes a continuous layered first coating layer (shell layer) formed by modifying a large proportion of coating elements to completely coat the core, thereby avoiding contact between the electrolyte and the nickel-rich material of the core, inhibiting the side reaction between the positive electrode active material and the electrolyte, improving the stability of the positive electrode active material structure, and improving the conductivity of the positive electrode active material, thereby improving the cycle stability and rate performance of the positive electrode active material; and, the molar percentage content of Co and / or Mn in the first coating layer is greater than the molar percentage content of Co and / or Mn in the core. Thus, the first coating layer is rich in Co and Mn elements, and the reduction in its Ni content significantly reduces the reaction activity of the interface positive electrode active material and the electrolyte, further improving the electrochemical properties of the positive electrode active material, especially the electrochemical performance of the high-nickel positive electrode active material at high voltage. At the same time, the increase in Co and / or Mn in the first coating layer can reduce the Ni content, thereby reducing Li / Ni mixing, increasing the rate of Li ion diffusion, reducing diffusion polarization, and thus increasing the discharge capacity. On the other hand, the setting of the island-shaped second coating layer, by introducing a functional additive (element M5) into the second coating layer, can have at least one of the following advantages: fast ion conductor or surface grain orientation modification, which increases the surface lithium ion diffusion rate and improves rate performance; preferential adsorption and reaction with HF, alleviates the attack of HF in the electrolyte, improves gas production, and increases storage and cycle life; improves the surface roughness of the positive electrode active material, increases the liquid retention capacity, and improves electrochemical performance. Therefore, based on the above improvements, the positive electrode active material of the present application has at least one of the following advantages: excellent material structure stability, conductivity, cycle performance, rate performance, storage performance, and safety performance.

[0026] It should be noted that the molar percentage content of Co and / or Mn in the first coating layer refers to the molar percentage content of Co and / or Mn in the first coating layer based on the total molar amount of all metal elements other than Li in the first coating layer. The molar percentage content of Co and / or Mn in the core body refers to the molar percentage content of Co and / or Mn in the core body based on the total molar amount of all metal elements other than Li in the core body.

[0027] In some embodiments, the core of the primary particle comprises Li a Ni b Co c Mn d M1 e O x , wherein 0.95≤a≤1.1, 0.5≤b≤0.96, 0≤c≤0.3, 0≤d≤0.4, 0≤e≤0.02, 1.5≤x≤2.5, b+c+d+e=1; M1 comprises at least one of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W, and Mo. In some embodiments, a is 0.95, 0.97, 0.99, 1, 1.05, 1.1, or any value therebetween. In some embodiments, b is 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.96, or any value therebetween. In some embodiments, 0.6≤b≤0.75. In some embodiments, 0.8≤b≤0.96. In some embodiments, c is 0, 0.1, 0.15, 0.2, 0.25, 0.3, or any value therebetween, d is 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, or any value therebetween, e is 0, 0.01, 0.015, 0.02, or any value therebetween, and x is 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, or any value therebetween.

[0028] In some embodiments, the first coating layer includes Li f Ni g Co h Mn i M2 j M3 k O y, wherein, 0.95≤f≤1.1, 0≤g≤0.96, 0≤h≤0.8, 0≤i≤0.8, 0<j≤1, 0≤k≤0.5, 1.5≤y≤4, g+h+i+j+k=1, and M3 includes at least one of Li, Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo. In some embodiments, f is 0.95, 0.96, 0.98, 0.99, 1, 1.05, 1.1 or any value therebetween, g is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.96 or any value therebetween, h is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or any value therebetween, i is 0, 0 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or any value therebetween, j is 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any value therebetween, k is 0, 0.1, 0.2, 0.3, 0.4, 0.5 or any value therebetween, y is 1.5, 2, 2.5, 3, 3.5, 4 or any value therebetween. In some embodiments, 0<j≤0.6. In some embodiments, 0≤k≤0.3.

[0029] In some embodiments, the second coating layer includes Li p M4 q M5 r O z , wherein 0≤p≤4, 0≤q≤1, 0<r≤1, 0≤z≤4, q+r=1; M4 comprises at least one of Ni, Co, and Mn. In some embodiments, p is 0, 0.01, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, or any value therebetween; q is 0, 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value therebetween; r is 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value therebetween; and z is 0, 0.01, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, or any value therebetween. In some embodiments, 0≤q≤0.5.

[0030] In some embodiments, M2 includes Co, c<h+j. Thus, when preparing the continuous layered first coating layer, the feed material contains Co element, and the molar percentage content of Co element in the formed first coating layer is greater than the molar percentage content of Co element in the core body. A continuous and dense layered first coating layer (shell layer) formed by modification with a large proportion of coating elements is used to completely coat the core body, effectively avoiding direct contact between the core body and the electrolyte, reducing the side reaction between the core body and the electrolyte, and alleviating the problem of generating a large amount of gas due to the side reaction between the core body and the electrolyte, thereby improving the stability of the positive electrode active material structure, improving the conductivity of the positive electrode active material, and thereby improving the cycle stability and rate performance of the positive electrode active material; and, the molar percentage content of Co in the first coating layer is greater than the molar percentage content of Co in the core body, the first coating layer is rich in Co elements, and the reduction of its Ni content significantly reduces the reaction activity of the interface positive electrode active material and the electrolyte, further improving the electrochemical properties of the positive electrode active material, especially the electrochemical performance of the high-nickel positive electrode active material under high voltage. At the same time, the increase in Co in the first coating layer can reduce the Ni content, thereby reducing Li / Ni mixing, increasing the rate of Li ion diffusion, reducing diffusion polarization, and thus increasing the discharge capacity.

[0031] In some embodiments, M2 includes Mn, d<i+j. Thus, when preparing the continuous layered first coating layer, the raw material contains Mn element, and the molar percentage content of Mn element in the formed first coating layer is greater than the molar percentage content of Mn element in the core body. A continuous and dense layered first coating layer (shell layer) formed by modification with a large proportion of coating elements is used to completely coat the core body, effectively avoiding direct contact between the core body and the electrolyte, reducing the side reaction between the core body and the electrolyte, and alleviating the problem of generating a large amount of gas due to the side reaction between the core body and the electrolyte, thereby improving the stability of the positive electrode active material structure, improving the conductivity of the positive electrode active material, and thereby improving the cycle stability and rate performance of the positive electrode active material; and, the molar percentage content of Mn in the first coating layer is greater than the molar percentage content of Mn in the core body, the first coating layer is rich in Mn elements, and the reduction of its Ni content significantly reduces the reaction activity of the interface positive electrode active material and the electrolyte, further improving the electrochemical properties of the positive electrode active material, especially the electrochemical performance of the high nickel positive electrode active material at high voltage (for example, >4.3V). At the same time, the increase of Mn in the first coating layer can reduce the Ni content, thereby reducing Li / Ni mixing, increasing the rate of Li ion diffusion, reducing diffusion polarization, and thus increasing the discharge capacity.

[0032] In some embodiments, M2 includes Co and Mn, and c+d<h+i+j. Thus, when preparing the continuous layered first coating layer, the raw materials contain Co and Mn elements, and the total molar percentage content of Co and Mn elements in the formed first coating layer is greater than the total molar percentage content of Co and Mn elements in the core. A continuous and dense layered first coating layer (shell layer) formed by modification with a large proportion of coating elements is used to completely coat the core body, effectively avoiding direct contact between the core body and the electrolyte, reducing the side reaction between the core body and the electrolyte, and alleviating the problem of generating a large amount of gas due to the side reaction between the core body and the electrolyte, thereby improving the stability of the positive electrode active material structure, improving the conductivity of the positive electrode active material, and thereby improving the cycle stability and rate performance of the positive electrode active material; and, the molar percentage content of Co and Mn in the first coating layer is greater than the molar percentage content of Co and Mn in the core body, the first coating layer is rich in Co and Mn elements, and the reduction of its Ni content significantly reduces the reaction activity of the interface positive electrode active material and the electrolyte, further improving the electrochemical properties of the positive electrode active material, especially the electrochemical performance of the high-nickel positive electrode active material under high voltage. At the same time, the increase of Co and Mn in the first coating layer can reduce the Ni content, thereby reducing Li / Ni mixing, increasing the rate of Li ion diffusion, reducing diffusion polarization, and thus increasing the discharge capacity.

[0033] In some embodiments, the second coating layer includes Li4SiO4, Al2O3, WO3, Li2WO4, Li2ZrO3, ZrO2, Li2SiO3, MgO, TiO2, Li4Ti5O 12 , at least one of MnO3, Li2MoO4, MoO3, Y2O3 and Li3PO4.

[0034] In some embodiments, based on the total mass of the primary particles, the mass percentage content of the first coating layer is 0.1 wt% to 4 wt%. In some embodiments, based on the total mass of the primary particles, the mass percentage content of the first coating layer is 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1 wt%, 1.3 wt%, 1.5 wt%, 1.7 wt%, 1.9 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, or any value therebetween.

[0035] In some embodiments, based on the total mass of the primary particles, the mass percentage content of the second coating layer is 0.05 wt% to 0.5 wt%. In some embodiments, based on the total mass of the primary particles, the mass percentage content of the second coating layer is 0.05 wt%, 0.07 wt%, 0.09 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, or any value therebetween.

[0036] In some embodiments, the Dv50 of the positive electrode active material is 2μm to 8μm. In some embodiments, the Dv50 of the positive electrode active material is 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8.0μm or any value therebetween. In some embodiments, the Dv50 of the positive electrode active material is 2.5μm to 4.5μm. It should be noted that the type of the positive electrode active material is a nickel-containing ternary material, and further a nickel-containing transition metal oxide. Dv50 is the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode active material reaches 50%, for example, obtained by testing with a laser particle size instrument. It should be noted that the positive electrode active material involved in this application includes primary particles, single crystal-like or spherical agglomerates formed by the agglomeration of primary particles. Primary particles refer to crystals with a particle size ranging from 0.2 μm to 8 μm, excluding grain boundaries, and whose crystallographic orientation remains basically consistent throughout the particle.

[0037] In summary, the positive electrode active material of the present application has at least one of the following advantages: excellent material structure stability, electrical conductivity, cycle performance, rate performance, storage performance and safety performance.

[0038] 2. Preparation Method of Positive Electrode Active Materials

[0039] This application also provides a method for preparing a positive electrode active material. The positive electrode active material prepared by this method can be the positive electrode active material described above. Thus, this method can have all the characteristics and advantages of the positive electrode active material described above, and will not be described in detail again. The preparation method includes:

[0040] S100: mixing a core precursor, a lithium salt, and a first compound containing an element M1, and performing a first calcination treatment to obtain a core; wherein M1 includes at least one of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W, and Mo;

[0041] S200: mixing the core body and a second compound containing an element M2, and performing a second calcination process to obtain a first product; wherein M2 includes at least one of Co and Mn;

[0042] S300: Mixing the first product and a fifth compound containing element M5, and performing a third calcination treatment to obtain the positive electrode active material; wherein M5 includes at least one of Li, Na, Mg, Sr, Ba, Al, Y, B, Zr, Ti, Si, Sn, V, P, W and Mo.

[0043] In some embodiments, the temperature of the first calcination treatment is 650° C. to 980° C., and the time is 6 hours to 15 hours. In some embodiments, the temperature of the first calcination treatment is 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 980° C., or any value therebetween, and the time is 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or any value therebetween.

[0044] In some embodiments, the second calcination treatment is performed at a temperature of 600° C. to 1050° C. for a time of 4 to 14 hours. In some embodiments, the second calcination treatment is performed at a temperature of 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C., 1050° C., or any value therebetween, and for a time of 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, or any value therebetween.

[0045] In some embodiments, the third calcination treatment is performed at a temperature of 200° C. to 800° C. for a time of 3 to 8 hours. In some embodiments, the third calcination treatment is performed at a temperature of 200° C., 300° C., 400° C., 500° C., 600° C., 700° C., 800° C., or any value therebetween, for a time of 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any value therebetween.

[0046] In some embodiments, the core precursor comprises Ni s Co t Mn u(OH)2, 0.5≤s≤0.96, 0≤t≤0.3, 0≤u≤0.4, s+t+u=1. In some embodiments, s is 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.96, or any value therebetween. In some embodiments, t is 0, 0.1, 0.15, 0.2, 0.25, 0.3, or any value therebetween, and u is 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, or any value therebetween.

[0047] In some embodiments, the lithium salt includes at least one of Li2CO3 and LiOH.

[0048] In some embodiments, the first compound includes at least one selected from the group consisting of carbonates, oxides, fluorides, and hydroxides of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W, and Mo.

[0049] In some embodiments, the second compound includes at least one of a cobalt source and a manganese source, wherein the cobalt source includes at least one of Co(OH)2, CoOOH, Co3O4, CoCo3, (CH3COO)2Co and CoCl2, and the manganese source includes at least one of MnO2, Mn2O3, Mn3O4, MnCO3, (CH3COO)2Mn and MnCl2.

[0050] In some embodiments, mixing the core and the second compound further includes adding a compound containing element M3 for mixing, and the third compound includes at least one selected from the group consisting of carbonates, oxides, fluorides and hydroxides of Li, Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo.

[0051] In some embodiments, the fifth compound includes at least one selected from the group consisting of carbonates, oxides, fluorides, and hydroxides of Li, Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W, and Mo.

[0052] In some embodiments, the molar ratio of the core precursor, the lithium salt, and the first compound is 1:(1.02-1.1):(0.001-0.005). In some embodiments, the mass ratio of the core precursor, the lithium salt, and the first compound is 1:1.02:0.001, 1:1.05:0.001, 1:1.1:0.001, 1:1.02:0.003, 1:1.05:0.003, 1:1.1:0.003, 1:1.02:0.005, 1:1.05:0.005, 1:1.1:0.005, or any value therebetween.

[0053] In some embodiments, the mass ratio of the core to the second compound is 1:(0.001-0.05). In some embodiments, the mass ratio of the core to the second compound is 1:0.001, 1:0.005, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, or any value therebetween.

[0054] In some embodiments, the mass ratio of the core, the second compound, and the third compound is 1:(0.001-0.05):(0.0005-0.01). In some embodiments, the mass ratio of the core, the second compound, and the third compound is 1:0.001:0.0005, 1:0.01:0.0005, 1:0.05:0.0005, 1:0.001:0.005, 1:0.01:0.005, 1:0.05:0.005, 1:0.001:0.01, 1:0.01:0.01, 1:0.05:0.01, or any value therebetween.

[0055] In some embodiments, the mass ratio of the first product to the fifth compound is 1:(0.0005-0.01). In some embodiments, the mass ratio of the first product to the fifth compound is 1:0.0005, 1:0.001, 1:0.005, 1:0.008, 1:0.01 or any value therebetween.

[0056] 3. Secondary batteries

[0057] The present application also provides a secondary battery comprising the aforementioned positive electrode active material or the positive electrode active material formed by the aforementioned preparation method. Thus, the device can have all the features and advantages of the aforementioned positive electrode active material or preparation method, which are not further described here.

[0058] In some embodiments, the secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector, wherein the positive electrode active material includes the positive electrode active material described above or the positive electrode active material prepared by the method described above.

[0059] In some embodiments, the positive electrode active material layer further includes a binder and a conductive material. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector. In some embodiments, the binder includes: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc. In some embodiments, the conductive material includes: carbon-based materials, metal-based materials, conductive polymers and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0060] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0061] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector. The negative electrode active material includes at least one of a carbon-based material, a silicon-based material, a tin-based material, a phosphorus-based material, and metallic lithium. In some embodiments, the carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, and graphene; the silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxide, and a silicon-carbon compound; the tin-based material includes at least one of tin, a tin oxide, and a tin alloy; and the phosphorus-based material includes phosphorus and / or a phosphorus-carbon complex. In some embodiments, the negative electrode active material includes a carbon-based material. In some embodiments, the negative electrode active material includes a carbon-based material and a silicon-based material, and the weight percentage of the silicon-based material is 0% to 30% based on the weight of the negative electrode active material. The weight percentage of the silicon-based material is 0%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, or any value therebetween, based on the weight of the negative electrode active material. Based on the mass of the negative electrode active material, the mass percentage content of the silicon-based material is 0% to 5%.Based on the mass of the negative electrode active material, the mass percentage content of the silicon-based material is 0% to 15%.

[0062] In some embodiments, the negative electrode active material layer further comprises a binder and a conductive agent. In some embodiments, the binder comprises: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc. In some embodiments, the conductive agent comprises: a carbon-based material, a metal-based material, a conductive polymer and a mixture thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0063] In some embodiments, the negative electrode current collector comprises: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0064] In some embodiments, the electrolyte includes a lithium salt, a solvent, and an additive.

[0065] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluorosulfonyl (LiTf), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium bis(fluoromalonate)borate (LiBFMB), lithium bisoxalatoborate (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorobisoxalatophosphate, and lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI).

[0066] In some embodiments, the weight percentage of the lithium salt is 4% to 25% based on the weight of the electrolyte. In some embodiments, the weight percentage of the lithium salt is 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any value therebetween. In some embodiments, the weight percentage of the lithium salt is 6% to 18%.

[0067] In some embodiments, the solvent includes at least one of a linear carbonate and a cyclic carbonate.

[0068] In some embodiments, linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate and fluorinated linear carbonate. In some embodiments, cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate. In some embodiments, organic solvent also includes non-fluorinated carboxylic acid ester, and non-fluorinated carboxylic acid ester is selected from at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and gamma-butyrolactone.

[0069] In some embodiments, the weight percentage of the solvent is 40% to 80% based on the weight of the electrolyte. In some embodiments, the weight percentage of the solvent is 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value therebetween. In some embodiments, the weight percentage of the solvent is 50% to 70%.

[0070] In some embodiments, the additive includes at least one of a cyclic carbonate containing a carbon-carbon double bond, a silyl-containing phosphate, and a nitrile compound salt. In some embodiments, the additive includes at least one of vinylene carbonate (VC), vinyl ethylene carbonate, tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), succinonitrile, adiponitrile, glutaronitrile, and hexanetrinitrile. In some embodiments, the additive further includes at least one of methylene methyl disulfonate (MMDS), ethylene ethyl disulfonate, 1,3-propane sultone (1,3-PS), 1-propylene-1,3-sultone (PST), 1,4-butane sultone (1,4-BS), vinyl sulfate (DTD), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST), propylene sulfate (TS), ethylene sulfite (DTO), dimethyl sulfite (DMS) and diethyl sulfite (DES).

[0071] In some embodiments, the weight percentage of the additive is 0.05% to 10% based on the weight of the electrolyte. In some embodiments, the weight percentage of the additive is 0.05%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, or any value therebetween. In some embodiments, the weight percentage of the additive is 0.1% to 5%.

[0072] In some embodiments, a separator is provided between the positive and negative electrode plates to prevent short circuits. The material and shape of the separator used in the embodiments of the present application are not particularly limited and may be any known prior art material. In some embodiments, the separator comprises a polymer or inorganic material, for example, formed from a material that is stable with the electrolyte of the present application.

[0073] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be used.

[0074] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0075] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0076] The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene).

[0077] In some embodiments, the method for preparing the secondary battery includes providing an electrode assembly, injecting liquid, packaging, and forming. In some embodiments, the forming temperature is 40° C. to 50° C., for example, 41° C., 42° C., 43° C., 44° C., 45° C., 46° C., 47° C., 48° C., or 49° C.

[0078] In some embodiments, the formation comprises: charging to 3.9V at 0.05C current and standing for 24 hours at a temperature of 40°C to 50°C, for example, 45°C, and a pressure of 150kgf to 750kgf, for example, 600kgf, followed by charging to 4.4V at 0.1C, and then discharging to 2.8V at 0.2C.

[0079] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0080] In some embodiments, the secondary battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0081] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0082] In some embodiments, the present application also provides a battery module. The battery module includes the aforementioned secondary battery. The battery module of the present application utilizes the aforementioned secondary battery and therefore has at least the same advantages as the aforementioned secondary battery. The battery module of the present application may include multiple secondary batteries, the specific number of which can be adjusted based on the application and capacity of the battery module.

[0083] In some embodiments, the present application further provides a battery pack comprising the above-mentioned battery module. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0084] 4. Device

[0085] The present application also provides a device comprising at least one of the aforementioned secondary battery, battery module, and battery pack. Thus, the device can have all the features and advantages of the aforementioned secondary battery, battery module, or battery pack, which are not further described here.

[0086] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. To meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0087] In other embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0088] Examples and Comparative Examples

[0089] Example 1

[0090] The steps for preparing the positive electrode active material are as follows: Step (1) weigh Ni 0.65 Co 0.05 Mn 0.30 (OH)2:LiOH:ZrO2=1:1.08:0.003, mixed by high speed mixer 1500rpm for 20min, calcined at 930℃ for 8h, cooled and crushed, sieved to obtain LiNi with single crystal morphology 0.649 Co 0.049 Mn 0.299 Zr 0.003 O2 core single crystal material, that is, core body; step (2) weighing the core single crystal material in step (1) according to the mass ratio: CoOOH = 1:0.02, mixing it with a high-speed mixer at 1500rpm for 20min, calcining it at 900℃ for 6h, cooling it down, crushing it, and sieving it to obtain a core body of LiNi 0.649 Co 0.049 Mn0.299 Zr 0.003 O2, containing the first coating layer LiNi 0.533 Co 0.221 Mn 0.246 O2 core-shell single crystal material, i.e. the first product; step (3) weighing the core-shell single crystal material in step (2) according to the mass ratio: MgO: Al2O3 = 1: 0.001: 0.001 to obtain a core body of LiNi 0.649 Co 0.049 Mn 0.299 Zr 0.003 O2, through a high-speed mixer at 1500 rpm, mixed for 20 minutes, calcined at 600 ° C for 4 hours, cooled and crushed, sieved, containing a continuous layered first coating layer of LiNi 0.533 Co 0.221 Mn 0.246 O2, a core-shell single crystal material containing a discrete island-shaped second coating layer of MgO and Al2O3, to obtain the primary particles in this application, that is, the positive electrode active material.

[0091] The preparation steps of the positive electrode sheet are as follows: the above-obtained positive electrode active material, CNT (conductive agent carbon nanotube) / Super-P (conductive carbon black), and binder polyvinylidene fluoride PVDF are mixed in N-methylpyrrolidone NMP at a weight ratio of positive electrode active material: CNT / Super-P:PVDF=95:(1.0 / 2.0):2, and after being fully homogenized, they are coated on a 12μm thick aluminum current collector, and then dried, rolled, hot pressed, and other steps to obtain the positive electrode sheet.

[0092] The preparation steps of the negative electrode plate are as follows: the negative electrode active material silicon oxide (SiOx, 0.5≤x≤1.5)-graphite composite (Si / C=5:95), the conductive agent acetylene black, the binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose CMCNa, and the polyacrylic acid PAA are added to deionized water in a weight ratio of 95:2:1.5:1:0.5, and after sufficient homogenization, they are coated on an 8μm thick copper current collector, and then dried, rolled, hot pressed and other steps to obtain the negative electrode plate.

[0093] Preparation of electrolyte: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the lithium salt LiPF6 was fully dissolved in a mixed solution of EC / DEC / EMC (ethylene carbonate / diethyl carbonate / ethyl methyl carbonate) = 25 / 20 / 55 to prepare a 1 mol / L solution.

[0094] Isolation film: PP / PE / PP (polypropylene / polyethylene / polypropylene) three-layer composite isolation film is used.

[0095] Preparation of lithium-ion secondary batteries: The positive electrode sheet, separator (PP / PE / PP three-layer composite film), and negative electrode sheet prepared above are overlapped in sequence, with the separator located between the positive electrode sheet and the negative electrode sheet to obtain a bare cell. The bare cell is placed in a punched aluminum-plastic film soft package shell. After sufficient drying, the electrolyte prepared above is injected. The battery is placed at 45°C for 48 hours and formed in a high-temperature fixture (the formation conditions are: temperature 45°C, pressure 600kgf, 0.05C current charging to 3.9V and standing for 24 hours, then 0.1C charging to 4.4V, and then 0.2C discharge to 2.8V. After secondary sealing, conventional capacity division is carried out.

[0096] Examples 2 to 9

[0097] Examples 2 to 9 are implemented on the basis of Example 1 by adjusting the core single crystal material, the feeding type and feeding amount of the coating material corresponding to the first coating layer, the feeding type and feeding amount of the coating material corresponding to the second coating layer, etc. Specific adjustment measures and detailed data are shown in Table 1.

[0098] Comparative Example 1

[0099] The other steps in Comparative Example 1 are the same as those in Example 1, except that the steps for preparing the positive electrode active material are different, as follows:

[0100] The preparation steps of the positive electrode active material are as follows: weigh Ni 0.65 Co 0.05 Mn 0.30 (OH)2:LiOH:ZrO2=1:1.08:0.003, mixed in a high-speed mixer at 1500 rpm for 20 minutes, calcined at 930°C for 8 hours, cooled, crushed and sieved to obtain a single crystal material.

[0101] Comparative Example 2

[0102] The other steps in Comparative Example 2 are the same as those in Example 1, except that the steps for preparing the positive electrode active material are different, as follows:

[0103] The steps for preparing the positive electrode active material are as follows: Step (1) weigh Ni 0.65 Co 0.05 Mn 0.30 (OH)2:LiOH:ZrO2=1:1.08:0.003, mixed by high speed mixer 1500rpm for 20min, calcined at 930℃ for 8h, cooled and crushed, sieved to obtain LiNi with single crystal morphology 0.649 Co 0.049 Mn 0.299 Zr 0.003O2 core single crystal material; step (2) weigh the core single crystal material in step (1) according to the mass ratio: MgO: Al2O3 = 1:0.001:0.001, mix it with a high-speed mixer at 1500rpm for 20min, calcine it at 600℃ for 4h, cool it down, crush it and sieve it to obtain a LiNi core single crystal material. 0.649 Co 0.049 Mn 0.299 Zr 0.003 Single crystal material of O2.

[0104] Comparative Example 3

[0105] The other steps in Comparative Example 3 are the same as those in Example 1, except that the steps for preparing the positive electrode active material are different, as follows:

[0106] The steps for preparing the positive electrode active material are as follows: Step (1) weigh Ni 0.65 Co 0.05 Mn 0.30 (OH)2:LiOH:ZrO2=1:1.08:0.003, mixed by high speed mixer 1500rpm for 20min, calcined at 930℃ for 8h, cooled and crushed, sieved to obtain LiNi with single crystal morphology 0.649 Co 0.049 Mn 0.299 Zr 0.003 O2 core single crystal material; step (2) weigh the core single crystal material in step (1): CoOOH = 1:0.02 according to the mass ratio, mix it with a high-speed mixer at 1500rpm for 20min, calcine it at 900℃ for 6h, cool it down, crush it and sieve it to obtain a LiNi core single crystal material. 0.649 Co 0.049 Mn 0.299 Zr 0.003 O2, containing coating layer LiNi 0.533 Co 0.221 Mn 0.246 Single crystal material of O2.

[0107] Test Method

[0108] 1. Determination of residual lithium content on the surface of positive electrode active materials

[0109] 30g of the resulting positive electrode active material was added to 100mL of water and stirred for 30 minutes. The free lithium in the sample was then titrated with a standard hydrochloric acid solution. Using a composite pH electrode as the indicator electrode, the titration endpoint was determined by the potential jump produced. The residual lithium on the surface of the positive electrode active material consisted of residual LiCO and / or LiOH.

[0110] 2. Gram capacity test

[0111] After the lithium-ion secondary battery was allowed to rest for 4 hours at 25°C, the initial charge and discharge capacity test was performed. The test conditions were: charge at 0.1C to 4.4V, charge at constant voltage to 0.05C, then rest for 5 minutes, and then discharge at 0.1C to 2.8V. The initial charge capacity (CC0 mAh / g) and the initial discharge capacity (DC0 mAh / g) were recorded. The initial coulombic efficiency performance test was calculated as (DC0 / CC0) × 100%. DC0 is the 4.4V-0.1C capacity.

[0112] 4. Capacity recovery rate at 60℃

[0113] Before storage, charge the battery to 4.4V at a constant current rate of 1C, then charge it at a constant voltage until the current is less than 0.05C. After standing for 5 minutes, discharge it to 2.8V at a rate of 1C, and record the discharge capacity C0. After storing it at 60°C for 30 days, remove the battery and place it at room temperature (more than 4 hours), discharge it to 2.8V at a rate of 1C, record the holding capacity C1, and then charge it to 4.4V at a constant current rate of 1C, then charge it to 2.8V at a constant voltage until the current is less than 0.05C. After standing for 5 minutes, discharge it to 2.8V at a rate of 1C, and record the discharge capacity. Repeat this charge and discharge cycle 3 times, take the average value of the three discharge capacities C2, and the capacity recovery rate after storing it at 60°C for 30 days is (C0-C2) / C0.

[0114] 5. Cycle life at 45℃

[0115] The lithium-ion secondary battery was cycled at a constant temperature of 45°C (cell capacity 150Ah, charged to 4.4V at a current of 150A, then discharged to 2.8V at a current of 150A, and so on) until the capacity retention rate decayed to 80%, and the total number of cycles was recorded.

[0116] 6. Cross-sectional scanning electron microscope test

[0117] The electrode pieces are cut to form electrode section, the electrode section is bombarded and polished by a plasma beam, and a cross-sectional image of the material is observed by imaging using a high-magnification scanning electron microscope (SEM).

[0118] 6. Energy Dispersive Spectrometer (EDS) test

[0119] The electrode pieces are cut to form electrode piece cross sections, which are bombarded and polished by a plasma beam. In conjunction with SEM, EDS is used to analyze the types and contents of micro-area components of the material profile in the cross section of the electrode piece to obtain the change in element content of each element in the primary particles with surface depth.

[0120] Test results

[0121] Table 1

[0122] Table 2

[0123] It can be seen from Examples 1 to 9 and Comparative Examples 1 to 3 that the present application greatly improves the electrochemical performance of the positive electrode active material without significantly reducing the material's gram capacity by introducing a dense and continuous first coating layer between the core and the discrete island-shaped second coating layer. In addition, the setting of the two coating layers improves the stability of the material structure, effectively avoids direct contact between the core and the electrolyte, reduces the side reactions between the core and the electrolyte, and alleviates the problem of generating a large amount of gas due to side reactions between the core and the electrolyte. Specifically, on the one hand, the setting of the layered first coating layer utilizes a continuous layered first coating layer (shell layer) formed by modifying a large proportion of coating elements to completely coat the core, thereby avoiding contact between the electrolyte and the nickel-rich material of the core, inhibiting the side reaction between the positive electrode active material and the electrolyte, improving the stability of the positive electrode active material structure, and improving the conductivity of the positive electrode active material, thereby improving the cycle stability and rate performance of the positive electrode active material; and, the first coating layer is rich in Co and / or Mn elements (Examples 1 to 6, 8 are rich in Co, Example 7 is rich in Mn, and Example 9 is rich in Co and Mn), and the reduction in its Ni content significantly reduces the reaction activity of the interface positive electrode active material and the electrolyte, further improving the electrochemical properties of the positive electrode active material. At the same time, the increase in Co and / or Mn in the first coating layer can reduce the Ni content, thereby reducing Li / Ni mixing, increasing the rate of Li ion diffusion, reducing diffusion polarization, and thus increasing the discharge capacity. On the other hand, the arrangement of the island-shaped second coating layer, by introducing a functional additive (element M5) into the second coating layer, can have at least one of the following advantages: modification of the fast ion conductor or surface grain orientation, which increases the surface lithium ion diffusion rate and improves the rate performance; preferential adsorption and reaction with HF, alleviating the attack of HF in the electrolyte, improving gas production, and increasing storage and cycle life; improving the surface roughness of the positive electrode active material, increasing the liquid retention capacity, and improving the electrochemical performance. As a result, the positive electrode active material of the present application has at least one of the following advantages: excellent material structure stability, conductivity, cycle performance, rate performance, storage performance, and safety performance.

[0124] Comparing Comparative Example 1 with Examples 1 to 6, it can be seen that in Comparative Example 1, the positive electrode active material is not provided with a coating layer, the surface residual alkali (Li2CO3 and / or LiOH) content increases, thereby causing gas production problems, and the first coulombic efficiency, capacity recovery rate and cycle life are all poor.

[0125] Comparing Comparative Example 2 with Examples 1 to 6, it can be seen that in Comparative Example 2, the positive electrode active material only forms an island-shaped coating layer, and the residual alkali content on the surface increases, which leads to gas production problems. Although the capacity recovery rate and cycle life are improved relative to Comparative Example 1, compared with the examples, the first coulombic efficiency, capacity recovery rate and cycle life are still poor.

[0126] Comparing Comparative Example 3 with Examples 1 to 6, it can be seen that in Comparative Example 3, the positive electrode active material only forms a layered coating layer. Compared with Comparative Examples 1 to 2, the surface residual alkali content is improved to a certain extent, and the capacity recovery rate and cycle life are improved relative to Comparative Example 1. However, compared with the examples, since the island-shaped second coating layer is not provided, the attack of HF in the electrolyte cannot be further slowed down or suppressed, and the capacity recovery rate and cycle life are still poor.

[0127] FIG1 is a cross-sectional scanning electron microscope image of the positive electrode active material in Comparative Example 1. It can be seen from the figure that no coating layer is formed on the surface of the positive electrode core structure in Comparative Example 1.

[0128] 2 and 3 are scanning electron microscope images of primary particles in the positive electrode active material according to Example 1 of the present application. It can be seen from the images that there is a discrete island-shaped coating layer on the surface of the primary particles.

[0129] Figure 4 is a cross-sectional scanning electron microscope image of the primary particles in the positive electrode active material according to Example 1 of the present application. It can be seen from the figure that the primary particles include a core body, a continuous layered first coating layer on the surface of the core body, and a discrete island-shaped second coating layer on the surface of the first coating layer, that is, the core body is double-coated, the continuous layered first coating layer first coats the core body, and the discrete island-shaped second coating layer is formed on the first coating layer.

[0130] Figure 5 shows the variation in the molar percentage content of various elements in the primary particles of Example 1 of the present application as the depth from the primary particle surface changes. Specifically, EDS was used to analyze the types and contents of the constituent elements in the primary particle cross-section along the lines indicated by the arrows in Figure 4 to obtain the variation in the elemental content of each element in the primary particles as the depth from the surface changes. In Figure 5 , the horizontal axis represents depth from the surface, the vertical axis on the left represents the molar percentage content of the elements Ni, Co, Mn, Al, and Mg at the corresponding depths, and the vertical axis on the right represents the molar percentage content of the element Zr at the corresponding depths.

[0131] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A positive electrode active material, characterized in that: The positive electrode active material includes primary particles, and the primary particles include: A core body, the core body comprising Li a Ni b Co c Mn d M1 e O x , wherein 0.95≤a≤1.1, 0.5≤b≤0.96, 0≤c≤0.3, 0≤d≤0.4, 0≤e≤0.02, 1.5≤x≤2.5, b+c+d+e=1; M1 includes at least one of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; A first coating layer, the first coating layer is disposed on the surface of the core body and is in a continuous layer, the first coating layer includes a compound containing an element M2, and M2 includes at least one of Co and Mn; A second coating layer, wherein the second coating layer is disposed on the surface of the first coating layer and is in a discrete island shape, wherein the second coating layer includes a compound containing an element M5, wherein M5 includes at least one of Li, Na, Mg, Sr, Ba, Al, Y, B, Zr, Ti, Si, Sn, V, P, W, and Mo; Wherein, the molar percentage content of Co and / or Mn in the first coating layer is greater than the molar percentage content of Co and / or Mn in the core body.

2. The positive electrode active material according to claim 1, characterized in that The first coating layer includes Li f Ni g Co h Mn i M2 j M3 k O y , wherein 0.95≤f≤1.1, 0≤g≤0.96, 0≤h≤0.8, 0≤i≤0.8, 0<j≤1, 0≤k≤0.5, 1.5≤y≤4, g+h+i+j+k=1, and M3 includes at least one of Li, Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; The second coating layer includes Li p M4 q M5 r O z , wherein 0≤p≤4, 0≤q≤1, 0<r≤1, 0≤z≤4, q+r=1; M4 includes at least one of Ni, Co and Mn.

3. The positive electrode active material according to claim 2, characterized in that M2 includes Co, c<h+j.

4. The positive electrode active material according to claim 2, characterized in that M2 includes Mn, d<i+j.

5. The positive electrode active material according to claim 2, characterized in that M2 includes Co and Mn, c+d<h+i+j.

6. The positive electrode active material according to claim 2, characterized in that 0<j≤0.6, 0≤k≤0.3, 0≤q≤0.5; and / or The second coating layer includes Li4SiO4, Al2O3, WO3, Li2WO4, Li2ZrO3, ZrO2, Li2SiO3, MgO, TiO2, Li4Ti5O 12 , at least one of MnO3, Li2MoO4, MoO3, Y2O3 and Li3PO4; and / or Based on the total mass of the primary particles, the mass percentage content of the first coating layer is 0.1wt% to 4wt%; and / or Based on the total mass of the primary particles, the mass percentage content of the second coating layer is 0.05wt% to 0.5wt%; and / or The Dv50 of the positive electrode active material is 2 μm to 8 μm.

7. A method for preparing a positive electrode active material, characterized in that: include: A core body precursor, a lithium salt and a first compound containing an element M1 are mixed, and a first calcination treatment is performed to obtain a core body; wherein M1 includes at least one of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; The core body and a second compound containing an element M2 are mixed and subjected to a second calcination treatment to obtain a first product; wherein M2 includes at least one of Co and Mn; The first product and a fifth compound containing element M5 are mixed and subjected to a third calcination treatment to obtain the positive electrode active material; wherein M5 includes at least one of Li, Na, Mg, Sr, Ba, Al, Y, B, Zr, Ti, Si, Sn, V, P, W and Mo.

8. The preparation method according to claim 7, characterized in that: The temperature of the first calcination treatment is 650° C. to 980° C. and the time is 6 h to 15 h; and / or The temperature of the second calcination treatment is 600°C to 1050°C, and the time is 4h to 14h; and / or The temperature of the third calcination treatment is 200°C to 800°C and the time is 3h to 8h; and / or The core precursor includes Ni s Co t Mn u (OH)2, 0.5≤s≤0.96, 0≤t≤0.3, 0≤u≤0.4, s+t+u=1; and / or The lithium salt comprises at least one of Li2CO3 and LiOH; and / or The first compound comprises at least one selected from the group consisting of carbonates, oxides, fluorides and hydroxides of Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; and / or The second compound comprises at least one of a cobalt source and a manganese source, wherein the cobalt source comprises at least one of Co(OH)2, CoOOH, Co3O4, CoCo3, (CH3COO)2Co and CoCl2, and the manganese source comprises at least one of MnO2, Mn2O3, Mn3O4, MnCO3, (CH3COO)2Mn and MnCl2; and / or Mixing the core body and the second compound further comprises adding a third compound containing element M3 for mixing, wherein the third compound comprises at least one selected from carbonates, oxides, fluorides and hydroxides of Li, Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; the mass ratio of the core body, the second compound and the third compound is 1: (0.001-0.05): (0.0005-0.01); and / or The fifth compound includes at least one selected from the group consisting of carbonates, oxides, fluorides and hydroxides of Li, Na, Mg, Sr, Ba, Al, Y, Zr, Ti, Si, Sn, V, P, W and Mo; and / or The molar ratio of the core precursor, the lithium salt and the first compound is 1:(1.02-1.1):(0.001-0.005); and / or The mass ratio of the core body to the second compound is 1:(0.001-0.05); and / or The mass ratio of the first product to the fifth compound is 1:(0.0005-0.01).

9. A secondary battery, characterized in that: The invention comprises the positive electrode active material according to any one of claims 1 to 6 or the positive electrode active material formed by the preparation method according to any one of claims 7 to 8.

10. A device, characterized in that: The secondary battery according to claim 10 is included.

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