Positive electrode active material, method for preparing the same, secondary battery, and electric device

Abstract

The present application relates to a positive electrode active material comprising a first positive electrode active material comprising a matrix of formula (I) which is doped with the element M1: Li A1 [Ni X1 Co Y1 Mn Z1 ]O2(I); and a second positive electrode active material comprising a matrix of formula (II) which is doped with the element M2: Li A2 [Ni X2 Co Y2 Mn Z2 ]O2(II); wherein the volume average particle size Dv 50 of the first positive electrode active material is greater than the volume average particle size Dv 50 of the second positive electrode active material, and 0

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a positive electrode active material, a preparation method thereof, a secondary battery and an electric device. BACKGROUND

[0002] In recent years, with the increasingly wide application of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their energy density, cycle performance and safety performance, etc. In addition, due to the increasingly limited selection of positive electrode active materials, high-nickel positive electrode active materials are considered to be the best choice to meet the requirement of high energy density.

[0003] However, with the continuous increase of nickel content, the structural stability becomes worse and worse. Coating or doping and other means to improve the rate performance and cycle performance of the material are currently effective means, but the existing methods will cause different degrees of damage to the performance of the secondary battery, for example, the specific capacity of the secondary battery decreases, the cycle performance becomes poor, etc. Therefore, the existing coated or doped positive electrode materials still need to be improved. SUMMARY

[0004] The present application is carried out in view of the above-mentioned problems, and aims to provide a positive electrode active material, so that the secondary battery containing the same has high volumetric energy density and good cycle performance and safety performance.

[0005] In order to achieve the above-mentioned purpose, the present application provides a positive electrode active material, a preparation method thereof, a secondary battery and an electric device.

[0006] The first aspect of the present application provides a positive electrode active material, which comprises:

[0007] The first positive electrode active material comprises a matrix of formula (I) doped with an element M1:

[0008] Li A1 [Ni X1 Co Y1 Mn Z1 ]O2(I),

[0009] In formula (I), 0.5≤X1<1, 0≤Y1<0.5, 0≤Z1<0.5, 0.9<A1<1.2, the element M1 includes at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y; and

[0010] a second positive electrode active material comprising a matrix of formula (II) doped with an element M2:

[0011] Li A2 [Ni X2 Co Y2 Mn Z2 ]O2(II),

[0012] In formula (II), 0.5≤X2<1, 0≤Y2<0.5, 0≤Z2<0.5, 0.9<A2<1.2, the element M2 comprises at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y;

[0013] wherein the volume average particle size Dv 50 of the first positive electrode active material is greater than the volume average particle size Dv 50 of the second positive electrode active material, and 0<X2-X1≤0.4, optionally 0<X2-X1≤0.1.

[0014] Thus, the present application, by matching the first positive electrode active material with a volume average particle size Dv 50 greater with the second positive electrode active material with a volume average particle size Dv 50 smaller, makes the positive electrode sheet comprising the positive electrode active material have a high compaction density, thereby significantly improving the volumetric energy density of the secondary battery; in addition, when the Ni content of the second positive electrode active material matrix is higher than the Ni content of the first positive electrode active material matrix and when the difference between the two Ni contents is within the range, the cycle performance and safety performance of the secondary battery can be improved while ensuring the capacity of the secondary battery.

[0015] In any embodiment, 0.9≤X2<1. When 0.9≤X2<1, the energy density of the secondary battery can be further improved.

[0016] In any embodiment, the weight ratio of the first positive electrode active material to the second positive electrode active material is 5:5 or more, optionally 6:4-9:1. When the weight ratio of the first positive electrode active material to the second positive electrode active material is within the given range, the compaction density of the positive electrode sheet can be further improved, thereby further improving the volumetric energy density of the secondary battery.

[0017] In any embodiment, the first positive electrode active material is a secondary particle with a volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 ≥0.5, optionally (Dv 90 -Dv 10 ) / Dv 50≥ 1.0.

[0018] In any embodiment, the first positive electrode active material has a volume average particle size Dv 50 of 6-20 pm.

[0019] When the volume average particle size Dv 50 of the first positive electrode active material and the volume particle size distribution span are within the given ranges, the first positive electrode active material has a higher gram capacity; and when paired with the second positive electrode active material, the compaction density of the positive electrode sheet can be further improved.

[0020] In any embodiment, the second positive electrode active material is secondary particles and / or primary particles, optionally primary particles, having a volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 ≥ 0.5, optionally (Dv 90 -Dv 10 ) / Dv 50 ≥ 1.0.

[0021] In any embodiment, the second positive electrode active material has a volume average particle size Dv 50 of 2-5 pm.

[0022] When the volume average particle size Dv 50 of the second positive electrode active material and the volume particle size distribution span are within the given ranges, the second positive electrode active material has a higher gram capacity and has good cycle performance and safety performance; and when paired with the first positive electrode active material, the compaction density of the positive electrode sheet can be further improved.

[0023] In any embodiment, in the first positive electrode active material, the doping amount of the element M1 is 500-7000 ppm, optionally 1000-5000 ppm, based on the total weight of the first positive electrode active material. When the element M1 is doped into the first positive electrode active material and when the doping amount of the element M1 is within the given range, the bulk structure stability of the secondary particles can be further improved.

[0024] In any embodiment, in the second positive electrode active material, the doping amount of the element M2 is 500-7000 ppm, optionally 1000-5000 ppm, based on the total weight of the second positive electrode active material. When the element M2 is doped into the second positive electrode active material and when the doping amount of the element M2 is within the given range, the bulk structure stability of the second positive electrode active material can be further improved.

[0025] In any embodiment, the surface of the first positive electrode active material further has a coating layer containing N1 elements, the N1 elements including at least one of Al, Co, Mn, B, La, Sr, P, F, Zr, Ti, and W. The coating layer containing N1 elements on the surface of the first positive electrode active material can further improve the interface stability of the secondary particles and reduce the side reaction between the secondary particles and the electrolyte.

[0026] In any embodiment, the coating amount of the N1 elements is 500-20000 ppm, optionally 1000-15000 ppm, based on the total weight of the first positive electrode active material. When the coating amount of the N1 elements is within the given range, the interface stability of the first positive electrode active material can be further improved without affecting other properties of the first positive electrode active material.

[0027] In any embodiment, the surface of the second positive electrode active material further has a coating layer containing N2 elements, the N2 elements including at least one of Al, Co, Mn, B, La, Sr, P, F, Zr, Ti, and W. The coating layer containing N2 elements on the surface of the second positive electrode active material can further improve the interface stability of the second positive electrode active material and reduce the side reaction between the second positive electrode active material and the electrolyte.

[0028] In any embodiment, the coating amount of the N2 elements is 500-20000 ppm, optionally 1000-15000 ppm, based on the total weight of the second positive electrode active material. When the coating amount of the N2 elements is within the given range, the interface stability of the second positive electrode active material can be further improved without affecting other properties of the second positive electrode active material.

[0029] The second aspect of the present application also provides a method for preparing a positive electrode active material, comprising the following steps:

[0030] Step A: preparing a first positive electrode active material, comprising:

[0031] Step A1: mixing a lithium salt, a ternary precursor of the first positive electrode active material, and a compound containing element M1, and sintering to obtain the first positive electrode active material;

[0032] Step B: preparing a second positive electrode active material, comprising:

[0033] Step B1: mixing a lithium salt, a ternary precursor of the second positive electrode active material, and a compound containing element M2, and sintering to obtain the second positive electrode active material;

[0034] Step C: mixing the first positive electrode active material and the second positive electrode active material to obtain the positive electrode active material;

[0035] wherein the first positive electrode active material comprises a matrix of formula (I) doped with an element M1:

[0036] Li A1 [Ni X1 Co Y1 Mn Z1 ]O2(I),

[0037] In formula (I), 0.5≤X1<1, 0≤Y1<0.5, 0≤Z1<0.5, 0.9<A1<1.2, and the element M1 comprises at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y;

[0038] The second positive electrode active material comprises a matrix of formula (II) doped with an element M2:

[0039] Li A2 [Ni X2 Co Y2 Mn Z2 ]O2(II),

[0040] In formula (II), 0.5≤X2<1, 0≤Y2<0.5, 0≤Z2<0.5, 0.9<A2<1.2, and the element M2 comprises at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y;

[0041] The volume average particle size Dv 50 of the first positive electrode active material is greater than the volume average particle size Dv 50 of the second positive electrode active material, and 0<X2-X1≤0.4, optionally 0<X2-X1≤0.1.

[0042] Thus, the method of the present application can synthesize a positive electrode active material with stable bulk structure, excellent material interface stability, and high capacity.

[0043] In any embodiment, in the step A1, the sintering temperature is 700-950℃, the time is 10-20h, and the atmosphere is air or O2. Using this initial sintering process, the first positive electrode active material with excellent crystal structure can be sintered, and uniform doping of the element M1 can be effectively performed.

[0044] In any embodiment, in the step B1, the sintering temperature is 750-1000℃, the time is 10-20h, and the atmosphere is air or O2. By using the initial sintering process, the second positive electrode active material with excellent crystal structure can be sintered, and the uniform doping of the element M2 can be effectively performed.

[0045] In any embodiment, the step A further comprises:

[0046] Step A2: mixing and sintering the first positive electrode active material obtained from the step A1 with a compound containing N1 to form a coating layer containing the element N1 on the surface of the first positive electrode active material.

[0047] In any embodiment, in the step A2, the sintering temperature is 250-700℃, the time is 5-15h, and the atmosphere is air or O2.

[0048] By using the coating sintering process, part of the element N1 can react with the impurity lithium on the surface of the first positive electrode active material, thereby reducing the content of the impurity lithium on the surface of the material; and the coating layer containing the element N1 can be firmly and uniformly coated on the surface of the first positive electrode active material, thereby greatly reducing the side reaction between the first positive electrode active material and the electrolyte.

[0049] In any embodiment, the step B further comprises:

[0050] Step B2: mixing and sintering the second positive electrode active material obtained from the step B1 with a compound containing N2 to form a coating layer containing the element N2 on the surface of the second positive electrode active material.

[0051] In any embodiment, in the step B2, the sintering temperature is 250-700℃, the time is 5-15h, and the atmosphere is air or O2.

[0052] By using the coating sintering process, part of the element N2 can react with the impurity lithium on the surface of the second positive electrode active material, thereby reducing the content of the impurity lithium on the surface of the material; and the coating layer containing the element N2 can be firmly and uniformly coated on the surface of the second positive electrode active material, thereby greatly reducing the side reaction between the second positive electrode active material and the electrolyte.

[0053] The third aspect of the present application provides a secondary battery comprising the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application.

[0054] The fourth aspect of the present application provides an electric device comprising the secondary battery of the third aspect of the present application.

[0055] The power consumption device of the present application comprises the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 A scanning electron microscope (SEM) image of the positive electrode active material prepared for Example 1-1 of the present application.

[0057] Figure 2 A first charge-discharge curve of the button cell made of the positive electrode active material prepared for Example 1-1 of the present application.

[0058] Figure 3 A 25℃ cycle comparison curve of the full cell made of the positive electrode active material prepared for Example 1-1 and Comparative Example 2-1 of the present application.

[0059] Figure 4 A 70℃ storage gas expansion comparison curve of the full cell made of the positive electrode active material prepared for Example 1-1 and Comparative Example 2-1 of the present application.

[0060] Figure 5 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0061] Figure 6 is a schematic diagram of a battery cell according to an embodiment of the present application. Figure 5

[0062] Figure 7 is a schematic diagram of a battery module according to an embodiment of the present application.

[0063] Figure 8 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0064] Figure 9 is a schematic diagram of a battery pack according to an embodiment of the present application. Figure 8

[0065] Figure 10 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.

[0066] REFERENCE SIGNS:

[0067] 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0068] ​​The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its preparation method, secondary battery, and power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0069] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0071] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0072] If not specified otherwise, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0073] If not specified otherwise, the terms "comprising" and "including" mentioned in the present application mean open and can also mean closed. For example, the terms "comprising" and "including" can mean that other components not listed can also be included or contained, or can mean that only the listed components are included or contained.

[0074] If not specified otherwise, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0075] The existing positive electrode active material is usually a single secondary particle material (large particle size) or a single primary particle material (small particle size), so that the compaction density of the positive electrode plate is low, and therefore the volumetric energy density of the positive electrode plate needs to be further improved. In addition, the cycle performance of the large particle secondary particle positive electrode active material is generally poor, and the storage and safety performance is poor, while the capacity of the single crystal primary particle positive electrode active material is low, and the rate performance is poor.

[0076] The present application provides a particle grading positive electrode active material, which can significantly improve the compaction density of the positive electrode plate, thereby improving the volumetric energy density thereof, and can effectively improve the cycle and safety performance of the secondary battery.

[0077] [Positive electrode active material]

[0078] In one embodiment of the present application, the present application provides a positive electrode active material, which comprises:

[0079] The first positive electrode active material comprises a matrix of formula (I) doped with an element M1:

[0080] Li A1 [Ni X1 Co Y1 Mn Z1 ]O2, (I),

[0081] In formula (I), 0.5≤X1<1, 0≤Y1<0.5, 0≤Z1<0.5, 0.9<A1<1.2, element M1 includes at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y; and

[0082] A second positive electrode active material comprising a matrix of formula (II) doped with element M2:

[0083] Li A2 [Ni X2 Co Y2 Mn Z2 ]O2, (II),

[0084] In formula (II), 0.5≤X2<1, 0≤Y2<0.5, 0≤Z2<0.5, 0.9<A2<1.2, element M2 includes at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y;

[0085] wherein the volume average particle size Dv 50 of the first positive electrode active material is greater than the volume average particle size Dv 50 of the second positive electrode active material, and 0<X2-X1≤0.4, optionally 0<X2-X1≤0.1.

[0086] Although the mechanism is not clear, the present applicant surprisingly found that the present application, by matching the first positive electrode active material with a volume average particle size Dv 50 greater with the second positive electrode active material with a volume average particle size Dv 50 smaller, makes the positive electrode sheet comprising the positive electrode active material have a high compaction density, thereby significantly improving the volumetric energy density of the secondary battery. In addition, when the second positive electrode active material with a smaller average particle size Dv 50 has a higher Ni content than the first positive electrode active material with a larger average particle size Dv 50 and when the difference between the two Ni contents is within the range, the cycle performance and safety performance of the secondary battery can be improved while ensuring the capacity of the secondary battery.

[0087] In some embodiments, element M1 is selected from at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y.

[0088] In some embodiments, element M2 is selected from at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y.

[0089] Figure 1 A scanning electron microscope image of the positive electrode active material prepared in Example 1-1 is shown. From the image, it can be seen that the volume average particle diameter Dv Figure 1 50 The larger first positive electrode active material and the volume average particle diameter Dv 50 The smaller second positive electrode active material is uniformly dispersed.

[0090] In some embodiments, the molecular formula of the first positive electrode active material is:

[0091] Li a1 [Ni x1 Co y1 Mn z1 M1 b1 ]O2(I’),

[0092] In formula (I), 0.5≤x1<1, 0≤y1<0.5, 0≤z1<0.5, 0.9<a1<1.2, 0<b1<0.2, and x1+y1+z1+b1=1;

[0093] The molecular formula of the second positive electrode active material is:

[0094] Li a2 [Ni x2 Co y2 Mn z2 M2 b2 ]O2(II’),

[0095] In formula (II), 0.5≤x2<1, 0≤y2<0.5, 0≤z2<0.5, 0.9<a2<1.2, 0<b2<0.2, and x2+y2+z2+b2=1.

[0096] In some embodiments, 0.9≤X2<1.

[0097] When 0.9≤X2<1, the energy density of the secondary battery can be further improved.

[0098] In some embodiments, the weight ratio of the first positive electrode active material to the second positive electrode active material is 5:5 or more, and optionally 6:4-9:1.

[0099] When the weight ratio of the first positive electrode active material to the second positive electrode active material is within the given range, the compaction density of the positive electrode sheet can be further improved, thereby further improving the volume energy density of the secondary battery.

[0100] In some embodiments, the first positive electrode active material is a secondary particle, and the volume particle size distribution span (Dv 90 -Dv​10 ) / Dv 50 ≥0.5, optionally (Dv 90 -Dv 10 ) / Dv 50 ≥1.0.

[0101] In some embodiments, the first positive electrode active material has a volume average particle size Dv 50 of 6-20 μm.

[0102] When the first positive electrode active material has a volume average particle size Dv 50 and a volume particle size distribution span within the given ranges, the first positive electrode active material has a higher gram capacity; and when paired with the second positive electrode active material, the compaction density of the positive electrode sheet can be further improved.

[0103] In some embodiments, the second positive electrode active material is a secondary particle and / or a primary particle, optionally a primary particle, having a volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 ≥0.5, optionally (Dv 90 -Dv 10 ) / Dv 50 ≥1.0.

[0104] In some embodiments, the second positive electrode active material has a volume average particle size Dv 50 of 2-5 μm.

[0105] When the second positive electrode active material has a volume average particle size Dv 50 and a volume particle size distribution span within the given ranges, the second positive electrode active material has a higher gram capacity and has good cycle performance and safety performance; and when paired with the first positive electrode active material, the compaction density of the positive electrode sheet can be further improved.

[0106] It should be noted that the secondary particle has a meaning known in the art. The secondary particle refers to an agglomerated particle formed by two or more primary particles. The primary particle has a meaning known in the art. The primary particle refers to a particle that has not formed an agglomerated state.

[0107] In the present application, the particle volume distribution particle size Dv 10 , Dv 50 , Dv 90 are known concepts in the art. Specifically, Dv 10 is the particle size, in units of μm, at which 10% of the cumulative volume of the powder particles is reached from the small particle size side in the volume-based particle size distribution. Dv 50Dv50 is the particle size in the volume-based particle size distribution of the powder particles, reaching 50% of the cumulative volume from the small particle size side. 90 Dv90 is the particle size in the volume-based particle size distribution of the powder particles, reaching 90% of the cumulative volume from the small particle size side. 10 Dv50 is the particle size in the volume-based particle size distribution of the powder particles, reaching 50% of the cumulative volume from the small particle size side. 50 Dv50 is the particle size in the volume-based particle size distribution of the powder particles, reaching 50% of the cumulative volume from the small particle size side. 90 The test method of Dv50, Dv90, Dv95 and Dv99 can be tested by a method known in the art. As an example, GB / T 19077-2016 / ISO 13320:2009 Particle size distribution - Laser diffraction method can be referred to, and the equipment Malvern 3000 can be used for determination.

[0108] In some embodiments, in the first positive electrode active material, the doping amount of the element M1 is 500-7000 ppm, and optionally 1000-5000 ppm, based on the total weight of the first positive electrode active material.

[0109] When the first positive electrode active material is doped with the element M1 and when the doping amount of the element M1 is within the given range, the bulk structure stability of the secondary particles can be further improved.

[0110] In some embodiments, in the second positive electrode active material, the amount of the element M2 is 500-7000 ppm, and optionally 1000-5000 ppm, based on the total weight of the second positive electrode active material.

[0111] When the second positive electrode active material is doped with the element M2 and when the doping amount of the element M2 is within the given range, the bulk structure stability of the second positive electrode active material can be further improved.

[0112] In some embodiments, the surface of the first positive electrode active material further has a coating layer, and the coating layer contains an N1 element, and the N1 element includes at least one of Al, Co, Mn, B, La, Sr, P, F, Zr, Ti, and W; optionally, the N1 element is selected from at least one of Al, Co, Mn, B, La, Sr, P, F, Zr, Ti, and W.

[0113] Providing the coating layer containing the N1 element on the surface of the first positive electrode active material can further improve the interface stability of the secondary particles and reduce the side reaction between the secondary particles and the electrolyte.

[0114] In some embodiments, the coating amount of the N1 element is 500-20000 ppm, and optionally 1000-15000 ppm, based on the total weight of the first positive electrode active material.

[0115] When the coating amount of the N1 element is within the given range, the interface stability of the first positive electrode active material can be further improved without affecting other properties of the first positive electrode active material.

[0116] In some embodiments, the surface of the second positive electrode active material further has a coating layer, and the coating layer comprises N2 elements, and the N2 elements comprise at least one of Al, Co, Mn, B, La, Sr, P, F, Zr, Ti and W; optionally, the N2 elements are selected from at least one of Al, Co, Mn, B, La, Sr, P, F, Zr, Ti and W.

[0117] The coating layer containing N2 elements arranged on the surface of the second positive electrode active material can further improve the interface stability of the second positive electrode active material and reduce the side reaction between the second positive electrode active material and the electrolyte.

[0118] In some embodiments, the coating amount of the N2 elements is 500-20000 ppm, and optionally 1000-15000 ppm, based on the total weight of the second positive electrode active material.

[0119] When the coating amount of the N2 elements is within the given range, the interface stability of the second positive electrode active material can be further improved without affecting other properties of the second positive electrode active material.

[0120] In one embodiment of the present application, the present application provides a method for preparing a positive electrode active material, comprising the following steps:

[0121] Step A: preparing a first positive electrode active material, comprising:

[0122] Step A1: mixing a lithium salt, a ternary precursor of the first positive electrode active material and a compound containing element M1, and sintering to obtain the first positive electrode active material;

[0123] Step B: preparing a second positive electrode active material, comprising:

[0124] Step B1: mixing a lithium salt, a ternary precursor of the second positive electrode active material and a compound containing element M2, and sintering to obtain the second positive electrode active material;

[0125] Step C: mixing the first positive electrode active material and the second positive electrode active material to obtain the positive electrode active material;

[0126] In some embodiments, the first positive electrode active material comprises a matrix of formula (I) doped with element M1:

[0127] Li A1 [Ni X1 Co Y1 Mn Z1 ]O2(I),

[0128] In formula (I), 0.5≤X1<1, 0≤Y1<0.5, 0≤Z1<0.5, 0.9<A1<1.2, element M1 includes at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y;

[0129] The second positive electrode active material comprises a matrix of formula (II) doped with element M2:

[0130] Li A2 [Ni X2 Co Y2 Mn Z2 ]O2(II),

[0131] In formula (II), 0.5≤X2<1, 0≤Y2<0.5, 0≤Z2<0.5, 0.9<A2<1.2, element M2 includes at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y;

[0132] The volume average particle size Dv 50 is greater than the volume average particle size Dv 50 of the second positive electrode active material, and 0<X2-X1≤0.4, optionally 0<X2-X1≤0.1.

[0133] Thus, the method of the present application can synthesize a positive electrode active material with stable bulk structure, excellent material interface stability, and high capacity.

[0134] In some embodiments, element M1 is selected from at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y.

[0135] In some embodiments, element M2 is selected from at least one of Ti, Zr, Al, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y.

[0136] In some embodiments, in step A1, the lithium salt is one or both of lithium carbonate and lithium hydroxide; the first positive electrode active material ternary precursor is [Ni X1’ Co Y1’ Mn Z1’](OH)2, wherein 0.5≤X1'<1, 0≤Y1'<0.5, 0≤Z1'<0.5, X1'+Y1'+Z1'=1; the compound containing element M1 includes one or more of a sulfate, a nitrate, an acetate, a carbonate, an oxide, a hydroxide, etc. of element M1; optionally, the compound containing element M1 is one or more of a sulfate, a nitrate, an acetate, a carbonate, an oxide, a hydroxide, etc. of element M1.

[0137] In some embodiments, in step A1, the molar ratio of Li to the sum of nickel, cobalt and manganese is (0.9-1.2):1.

[0138] In some embodiments, in step A1, the sintering temperature is 700-950°C, the time is 10-20h, and the atmosphere is air or O2.

[0139] Using this initial sintering process, a first positive electrode active material with excellent crystal structure can be sintered, and uniform doping of element M1 can be effectively performed.

[0140] In some embodiments, in step B1, the lithium salt is one or both of lithium carbonate and lithium hydroxide; the second positive electrode active material ternary precursor is [Ni X2’ Co Y2’ Mn Z2’ ](OH)2, wherein 0.5≤X2'<1, 0≤Y2'<0.5, 0≤Z2'<0.5, X2'+Y2'+Z2'=1; the compound containing element M2 includes one or more of a sulfate, a nitrate, an acetate, a carbonate, an oxide, a hydroxide, etc. of element M2; optionally, the compound containing element M2 is one or more of a sulfate, a nitrate, an acetate, a carbonate, an oxide, a hydroxide, etc. of element M2.

[0141] In some embodiments, in step B1, the molar ratio of Li to the sum of nickel, cobalt and manganese is (0.9-1.2):1.

[0142] In some embodiments, in step B1, the sintering temperature is 750-1000°C, the time is 10-20h, and the atmosphere is air or O2.

[0143] Using this initial sintering process, a second positive electrode active material with excellent crystal structure can be sintered, and uniform doping of element M2 can be effectively performed.

[0144] In some embodiments, step A further comprises:

[0145] Step A2: mixing the first positive electrode active material obtained from step A1 with a compound containing N1, sintering to form a coating layer containing N1 element on the surface of the first positive electrode active material.

[0146] In some embodiments, in step A2, the sintering temperature is 250-700°C, the time is 5-15h, and the atmosphere is air or O2.

[0147] Using this coating sintering process, part of the N1 element can effectively react with the impurity lithium on the surface of the first positive electrode active material to form a fast ion conductor material, improve the transmission speed of lithium ions, and reduce the content of impurity lithium on the surface of the material; it can also firmly and uniformly coat the coating layer containing N1 element on the surface of the first positive electrode active material, greatly reducing the side reaction between the first positive electrode active material and the electrolyte.

[0148] In some embodiments, in step A2, the compound containing N1 includes one or more of N1 sulfate, nitrate, acetate, carbonate, oxide, hydroxide, etc.; optionally, the compound containing N1 is one or more of N1 sulfate, nitrate, acetate, carbonate, oxide, hydroxide, etc.

[0149] In some embodiments, step B further comprises:

[0150] Step B2: mixing the second positive electrode active material obtained from step B1 with a compound containing N2, sintering to form a coating layer containing N2 element on the surface of the second positive electrode active material.

[0151] In some embodiments, in step B2, the sintering temperature is 250-700°C, the time is 5-15h, and the atmosphere is air or O2.

[0152] Using this coating sintering process, part of the N2 element can effectively react with the impurity lithium on the surface of the second positive electrode active material to form a fast ion conductor material, improve the transmission speed of lithium ions, and reduce the content of impurity lithium on the surface of the material; it can also firmly and uniformly coat the coating layer containing N2 element on the surface of the second positive electrode active material, greatly reducing the side reaction between the second positive electrode active material and the electrolyte.

[0153] In some embodiments, in step B2, the compound containing N2 includes one or more of N2 sulfate, nitrate, acetate, carbonate, oxide, hydroxide, etc.; optionally, the compound containing N2 is one or more of N2 sulfate, nitrate, acetate, carbonate, oxide, hydroxide, etc.

[0154] In some embodiments, in steps A1, A2, B1 and B2, the mixing is carried out in a plowshare mixer, a high-speed mixer or an inclined mixer.

[0155] In addition, a secondary battery and an electric device according to the present application are described below with appropriate reference to the accompanying drawings. The secondary battery can include a form of a battery cell, can include a form of a battery module, and can include a form of a battery pack.

[0156] In one embodiment of the present application, a battery cell is provided.

[0157] Generally, a battery cell includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. During charging and discharging of the battery, active ions are intercalated and deintercalated between the positive electrode tab and the negative electrode tab. The electrolyte functions to conduct ions between the positive electrode tab and the negative electrode tab. The separator is disposed between the positive electrode tab and the negative electrode tab and functions to prevent short circuiting between the positive electrode and the negative electrode while allowing ions to pass through.

[0158] [Positive electrode tab]

[0159] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material of the first aspect of the present application.

[0160] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0161] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material on a polymer material base material; the metal material can include, but is not limited to, aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like; and the polymer material base material can include, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0162] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0163] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0164] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the positive electrode current collector to drying, cold pressing, and the like to obtain the positive electrode sheet.

[0165] In some embodiments, the positive electrode sheet has a compaction density of ≥ 3.3 g / cc, and optionally ≥ 3.4 g / cc, when the positive electrode sheet is elongated by 0.7%.

[0166] [Negative electrode sheet]

[0167] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0168] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0169] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As a metal foil, for example, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material on a polymer material base layer; the metal material can include, but is not limited to, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like; and the polymer material base layer can include, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0170] In some embodiments, the negative electrode active material can be a negative electrode active material known in the art for use in a battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, and the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0171] In some embodiments, the negative electrode film layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0172] In some embodiments, the negative electrode film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0173] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

[0174] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, and the like, the negative electrode sheet can be obtained.

[0175] [Electrolyte]

[0176] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0177] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0178] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0179] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0180] In some embodiments, the electrolyte solution can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, and the like.

[0181] [Separator]

[0182] In some embodiments, a separator is further included in the battery cell. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0183] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0184] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a stacking process.

[0185] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte solution described above.

[0186] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, and the like can be listed.

[0187] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, Figure 5 is a square structure battery cell 5 as an example.

[0188] In some embodiments, with reference to Figure 6 , the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte solution is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0189] In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0190] Figure 7 is a battery module 4 as an example. Referring to Figure 7 In the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0191] Optionally, the battery module 4 can also include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0192] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0193] Figure 8 and Figure 9 is a battery pack 1 as an example. Referring to Figure 8 and Figure 9 In the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0194] In addition, the application also provides a power utilization device, which includes the secondary battery provided by the application. The secondary battery can be used as a power source of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0195] As the power utilization device, the secondary battery can be selected according to the use demand thereof.

[0196] Figure 10 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0197] As another example, the device can be a mobile phone, a tablet, a notebook computer, etc. The device generally requires thinness, and a battery monomer can be used as a power source.

[0198] Embodiment

[0199] Hereinafter, an embodiment of the present application will be described. The embodiment described below is exemplary and is for the purpose of explanation of the present application only and is not to be understood as a limitation of the present application. In the embodiment, unless a specific technique or condition is mentioned, the technique or condition described in the literature in the art or according to the product manual is used. Unless the manufacturer of the reagent or instrument is mentioned, it is a general product that can be obtained commercially.

[0200] Example 1-1

[0201] Step A: Preparation of the first positive electrode active material

[0202] Step A1: Lithium hydroxide, the first positive electrode active material ternary precursor [Ni 0.90 Co 0.05 Mn 0.05 ](OH)2, ZrO2are mixed in a plowshare mixer, wherein the volume average particle size Dv 50 of the first positive electrode active material ternary precursor is 10 μm, the molar ratio of lithium to the sum of nickel, cobalt and manganese is 1.01, the Zr doping amount is 5000 ppm, and the mixture is put into a kiln for sintering, the sintering temperature is 700°C, the sintering time is 20 h, and the sintering atmosphere is O2, to obtain the first positive electrode active material Li 1.01 [Ni 0.895 Co 0.050 Mn 0.050 Zr 0.005 ]O2,

[0203] Step A2: The first positive electrode active material is mixed with H3BO3 in a plowshare mixer, wherein the coating amount of B is 1000 ppm, the mixture is put into a kiln for sintering, the sintering temperature is 250°C, the sintering time is 15 h, and the sintering atmosphere is O2, to form a B-containing coating layer on the surface of the first positive electrode active material, the volume average particle size Dv 50 of the first positive electrode active material with the coating layer is 10 μm, and the volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 is 1.3;

[0204] Step B: Preparation of the second positive electrode active material

[0205] Step B1: Lithium hydroxide, the second positive electrode active material ternary precursor [Ni 0.92 Co 0.05Mn 0.03 ](OH)2, TiO2in a plowshare mixer, wherein the volume average particle size Dv 50 3 pm, the molar ratio of lithium to the sum of nickel, cobalt and manganese is 1.01, the Ti doping amount is 5000 ppm, the mixture is put into a kiln for sintering, the sintering temperature is 750°C, the sintering time is 20 h, and the sintering atmosphere is O2, to obtain the second positive electrode active material Li 1.01 [Ni 0.91 Co 0.05 Mn 0.03 Ti 0.01 ]O2,

[0206] Step B2: mixing the second positive electrode active material with H3BO3 in a plowshare mixer, wherein the coating amount of B is 1000 ppm, the mixture is put into a kiln for sintering, the sintering temperature is 250°C, the sintering time is 15 h, and the sintering atmosphere is O2, to form a coating layer containing B on the surface of the second positive electrode active material; the volume average particle size Dv 50 3 pm of the second positive electrode active material with the coating layer, and the volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 1.0;

[0207] Step C: mixing the first positive electrode active material with the coating layer and the second positive electrode active material with the coating layer in a ratio of 7:3 to obtain the positive electrode active material.

[0208] Example 1-2 to Example 1-3

[0209] The preparation of the positive electrode active material is generally referred to Example 1-1, except that,

[0210] In Step Al, the first positive electrode active material ternary precursor is respectively [Ni 0.50 Co 0.30 Mn 0.20 ](OH)2, [Ni 0.80 Co 0.10 Mn 0.10 ](OH)2, to obtain the first positive electrode active material Li 1.01 [Ni 0.497 Co 0.298 Mn 0.200 Zr 0.005 ]O2and Li 1.01 [Ni 0.796 Co 0.0995 Mn 0.0995 Zr 0.005 ]O2respectively;

[0211] In step B1, the second positive electrode active material ternary precursor is [Ni 0.90 Co 0.05 Mn 0.05 ](OH)2, thereby obtaining the second positive electrode active material Li 1.01 [Ni 0.891 Co 0.0495 Mn 0.0495 Ti 0.01 ]O2, respectively.

[0212] Comparative Example 1-1

[0213] The preparation of the positive electrode active material generally refers to Example 1-1, except that in step A1, the first positive electrode active material ternary precursor is [Ni 0.50 Co 0.30 Mn 0.20 ](OH)2, thereby obtaining the first positive electrode active material Li 1.01 [Ni 0.497 Co 0.298 Mn 0.200 Zr 0.005 ]O2.

[0214] Examples 2-1 to 2-4 and Comparative Example 2-1

[0215] The preparation of the positive electrode active material generally refers to Example 1-1, except that in step C, the mixing ratio of the first positive electrode active material with the coating layer and the second positive electrode active material with the coating layer is 5:5, 6:4, 9:1, 4:6 and 10:0, respectively.

[0216] Examples 3-1 to 3-4

[0217] The preparation of the positive electrode active material generally refers to Example 1-1, except that in step A1, the average particle size Dv 50 of the first positive electrode active material ternary precursor is 6 μm, 20 μm, 5 μm and 22 μm, respectively, thereby obtaining the first positive electrode active material with the coating layer having an average particle size Dv 50 of 6 μm, 20 μm, 5 μm and 22 μm, respectively.

[0218] Examples 3-5 to 3-8

[0219] The preparation of the positive electrode active material generally refers to Example 1-1, except that in step B1, the average particle size Dv 50 of the second positive electrode active material ternary precursor is 2 μm, 5 μm, 1 μm and 6 μm, respectively, thereby obtaining the second positive electrode active material with the coating layer having an average particle size Dv 502 pm, 5 pm, 1 pm and 6 pm, respectively, of the second positive electrode active material with a coating layer.

[0220] Example 3-9 to Example 3-10

[0221] The preparation of the positive electrode active material is generally in accordance with Example 1-1, except that in step A1, the volume distribution span (Dv 90 -Dv 10 ) / Dv 50 0.5 and 0.4, respectively, the volume average particle size Dv 50 remains unchanged, the first positive electrode active material with a coating layer is obtained in step A2, which has a volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 0.5 and 0.4, respectively.

[0222] Example 3-11 to Example 3-12

[0223] The preparation of the positive electrode active material is generally in accordance with Example 1-1, except that in step B1, the volume distribution span (Dv 90 -Dv 10 ) / Dv 50 0.5 and 0.4, respectively, the volume average particle size Dv 50 remains unchanged, the second positive electrode active material with a coating layer is obtained in step B2, which has a volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 0.5 and 0.4, respectively.

[0224] Example 4-1 to Example 4-3

[0225] The preparation of the positive electrode active material is generally in accordance with Example 1-1, except that in step A1, the Zr doping amount is 500 ppm, 1000 ppm and 7000 ppm, respectively.

[0226] Example 4-4 to Example 4-6

[0227] The preparation of the positive electrode active material is generally in accordance with Example 1-1, except that in step A1, ZrO2 is replaced by WO3, Nb2O5 and a mixture of WO3 and ZrO2 (wherein the doping amount of W and Zr is 2500 ppm, respectively), respectively.

[0228] Example 4-7 to Example 4-9

[0229] The preparation of the positive active material generally refers to Example 1-1, except that in step B1, the Ti doping amount is 500 ppm, 1000 ppm, and 7000 ppm, respectively.

[0230] Examples 4-10 to 4-12

[0231] The preparation of the positive active material generally refers to Example 1-1, except that in step B1, TiO2 is replaced by WO3, Nb2O5, and a mixture of WO3 and ZrO2 (wherein the doping amount of W and Zr is 2500 ppm, respectively).

[0232] Examples 5-1 to 5-2

[0233] The preparation of the positive active material generally refers to Example 1-1, except that in steps A2 and B2, H3BO3 is replaced by Al2O3 and Co(OH)2, respectively.

[0234] Examples 5-3 to 5-5

[0235] The preparation of the positive active material generally refers to Example 1-1, except that in steps A2 and B2, the coating amount of B is 500 ppm, 15000 ppm, and 20000 ppm, respectively.

[0236] Examples 6-1 to 6-2

[0237] The preparation of the positive active material generally refers to Example 1-1, except that in step A1, the sintering temperature is 800°C and 950°C, and the sintering time is 20h and 10h, respectively.

[0238] Examples 6-3 to 6-4

[0239] The preparation of the positive active material generally refers to Example 1-1, except that in step B1, the sintering temperature is 900°C and 1000°C, and the sintering time is 20h and 10h, respectively.

[0240] Examples 6-5 to 6-6

[0241] The preparation of the positive active material generally refers to Example 1-1, except that in step A2, the sintering temperature is 400°C and 700°C, and the sintering time is 10h and 5h, respectively.

[0242] Examples 6-7 to 6-8

[0243] The preparation of the positive active material refers to Example 1-1 as a whole, except that in step B2, the sintering temperature is 400°C and 700°C respectively, and the sintering time is 10h and 5h respectively.

[0244] Test method

[0245] 1. Volume distribution particle size

[0246] The test method of the volume distribution particle size is as follows: referring to GB / T 19077-2016 / ISO 13320:2009 Particle Size Distribution Laser Diffraction Method, the equipment is Malvern 3000. A clean beaker is taken, and an appropriate amount of the sample to be tested is added to an obscuration of 8%-12%, 20ml of deionized water is added, and at the same time, external ultrasonic is performed for 5min, and the particle size tester is started to test.

[0247] 2. Preparation of button cell

[0248] The positive active material, PVDF and conductive carbon are added to a certain amount of NMP, and the addition ratio is 90:5:5. The slurry is prepared by stirring in a dry room, the slurry is coated on an aluminum foil, and the positive electrode sheet is prepared by drying and cold pressing. Lithium sheet is used as the negative electrode, the electrolyte is 1mol / L LiPF6 / (EC+DEC+DMC) (volume ratio is 1:1:1), and the button cell is assembled in a button cell box.

[0249] Test method of initial gram capacity of button cell

[0250] Under 2.8-4.3V, charge at 0.1C to 4.3V, then charge at 4.3V to current≤0.05mA, stand for 2min, the charge capacity at this time is recorded as C0, then discharge at 0.1C to 2.8V, the discharge capacity at this time is the initial gram capacity, recorded as D0.

[0251] 3. Preparation of full cell

[0252] The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF) were mixed uniformly in a weight ratio of 96:2:2 in an N-methyl pyrrolidone solvent system, coated on an aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet. The negative electrode active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickening agent sodium carboxymethyl cellulose (CMC) were mixed uniformly in a weight ratio of 90:5:2:2:1 in a deionized water solvent system, coated on a copper foil, dried, and cold-pressed to obtain a negative electrode sheet. A PE porous polymer film was used as a separator. The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive and negative electrodes to play a separating role, and were wound to obtain a bare cell. The bare cell was placed in an outer package, injected with prepared base electrolyte, i.e. 1 mol / L LiPF6 / (EC+EMC+DMC) (volume ratio 1:1:1), and packaged to obtain a full cell.

[0253] Full cell initial gram capacity test method:

[0254] At 25°C in a constant temperature environment, stand for 5 min, discharge at 1 / 3C to 2.8V, stand for 5 min, charge at 1 / 3C to 4.25V, then charge at 4.25V until the current is less than or equal to 0.05mA, stand for 5 min, the charge capacity at this time is recorded as C0, then discharge at 1 / 3C to 2.8V, the discharge capacity at this time is the initial gram capacity, recorded as D0.

[0255] Full cell 25°C cycle performance test method:

[0256] At 25°C in a constant temperature environment, charge at 1C to 4.25V at 2.8-4.25V, then charge at 4.25V until the current is less than or equal to 0.05mA, stand for 5 min, then discharge at 1C to 2.8V, the capacity is D0, repeat the previous process and record the capacity D n (n=0,1,2……), calculate the capacity retention rate after 500 cycles: D 500 / D0×100%.

[0257] Full cell 70°C swelling test method

[0258] Store at 70°C at 100% SOC, measure the OCV, IMP, and volume (by drainage method) of the cell before and after storage and during storage, test the residual capacity and reversible capacity of the cell at the end of storage, take out the cell every 48h, stand for 1h, then test the OCV and IMP, cool to room temperature, then test the volume of the cell by the drainage method, test at the end of 40 days of storage, or stop storage when the volume expansion exceeds 50%, the protection voltage range is 2.7-4.3V, and the nominal capacity is 2.25Ah.

[0259] 4. Positive electrode sheet compaction density test method

[0260] The positive electrode active material was put into a 5L stirring tank, then conductive agent acetylene black (SP) and binder polyvinylidene fluoride (PVDF) were added for 30min premixing. Finally, solvent N-methyl pyrrolidone (NMP) was added under vacuum condition for rapid stirring to form a slurry. The mass ratio of positive electrode active material: acetylene black: polyvinylidene fluoride was 96:2:2, and the solid content of the slurry was 70wt%. The slurry was uniformly coated on both sides of the aluminum foil with a thickness of 12μm, and the coated electrode piece was taken out after drying in a 100-130℃ oven for half an hour. The positive electrode active material loading of the electrode piece was 21.5mg / cm 2 The removed positive electrode piece was cold-pressed by roller and then tested to obtain the data of the compaction density and the length direction elongation.

[0261] The compaction density PD of the positive electrode piece was calculated by the formula PD = M / (d x A). In the formula, M was the mass of the 40mm diameter small disc cut out from the positive electrode piece, which was averaged by 10 times of weighing; d was the thickness of the positive electrode piece, which was averaged by 10 times of measuring; and A was the area of the 40mm diameter small disc.

[0262] The length direction elongation of the cold-pressed electrode piece was calculated by the formula ΔEL% = (L2-L1) / L1 x 100%. In the formula, L1 was the distance between the marks before cold-pressing, which was 1000mm, and L2 was the distance between the marks after cold-pressing. The marks were formed by taking three 1000mm long line segments extending in the length direction of the electrode piece at different positions in the width direction of the electrode piece in the center region of the electrode piece, and marking the two end points of the line segments. L2 was recorded as the average value of the measured values of the distances between the two end points of each line segment after cold-pressing.

[0263] The compaction density value of the electrode piece under 0.7% elongation was taken as the compaction density of the positive electrode piece in this application.

[0264] The above examples and comparative examples were tested according to the above process, and the specific values were shown in Tables 1-6.

[0265] Table 1. Effect of the difference (X2-X1) between the nickel content of the second positive electrode active material and the first positive electrode active material matrix on the battery performance

[0266]

[0267] When the difference X2-X1 in the Ni content of the first positive electrode active material and the second positive electrode active material matrix satisfies 0 < X2-X1≤0.4, the secondary batteries all have good comprehensive performance; when the difference X2-X1 in the Ni content exceeds 0.4, the specific capacity or the cycle performance and / or the 70°C @ 40-day swelling of the secondary battery will deteriorate.

[0268] Table 2. Influence of the weight ratio of the first positive electrode active material to the second positive electrode active material on the battery performance

[0269]

[0270] When the weight ratio of the first positive electrode active material to the second positive electrode active material is 5:5 or more, the compaction density of the positive electrode sheet is relatively high, and the secondary battery has good comprehensive performance; when the weight ratio of the first positive electrode active material to the second positive electrode active material is 6:4-9:1, the compaction density of the positive electrode sheet is further improved; when the weight of the first positive electrode active material is lower than that of the second positive electrode active material, the compaction density of the positive electrode sheet will decrease significantly, as shown in Example 2-4; when there is only the first positive electrode active material, the compaction of the sheet decreases significantly, and the cycle and storage swelling performance of the secondary battery will deteriorate, as shown in Comparative Example 2-1. In addition, it can be seen that, compared with Comparative Example 2-1, the cycle performance and storage swelling performance of Example 1-1 are significantly improved. Figure 3 and Figure 4 It can be seen that, compared with Comparative Example 2-1, the cycle performance and storage swelling performance of Example 1-1 are significantly improved.

[0271] Table 3. Influence of the Dv 50 and (Dv 90 ) of the first positive electrode active material to the second positive electrode active material on the battery performance 10 50

[0272]

[0273] When the volume average particle size Dv 50 of the first positive electrode active material is in the range of 6-20 μm, the secondary battery has good comprehensive performance; when the volume average particle size Dv 50 of the first positive electrode active material is less than 6 μm, the compaction density of the positive electrode sheet will decrease significantly, and the cycle and storage swelling performance of the secondary battery will also decrease significantly, as shown in Example 3-3; when the volume average particle size Dv 50 of the first positive electrode active material is greater than 20 μm, the capacity of the secondary battery will decrease, and the cycle and storage swelling performance will also decrease, as shown in Example 3-4.​​

[0274] Comparative Example 1-1 and Examples 3-5 to 3-8, when the volume average particle size Dv 50 In the range of 2-5 pm, the secondary batteries all have good comprehensive performance; when the volume average particle size Dv 50 of the second positive electrode active material is less than 2 pm, the compaction density of the positive electrode sheet will be significantly reduced, and the cycle and storage gas production performance of the secondary battery will also be significantly reduced, as shown in Example 3-7; when the volume average particle size Dv 50 of the second positive electrode active material is greater than 5 pm, the capacity of the secondary battery will be reduced, and the cycle and storage gas production performance will also be reduced, as shown in Example 3-8.

[0275] Comparative Example 1-1 and Examples 3-9 to 3-12, when the particle volume distribution span (Dv 90 -Dv 10 ) / Dv 50 of the first positive electrode active material or the second positive electrode active material is greater than or equal to 0.5, the comprehensive performance of the secondary battery is good; when (Dv 90 -Dv 10 ) / Dv 50 of the first positive electrode active material or the second positive electrode active material is less than 0.5, the compaction density of the positive electrode sheet will be significantly reduced.

[0276] Table 4. Influence of doping elements and doping amounts on battery performance

[0277]

[0278] Comparative Example 1-1 and Examples 4-1 to 4-6, when the first positive electrode active material is doped with element M1, and the doping amount of element M1 is 500-7000 ppm, the comprehensive performance of the secondary battery is good; when the doping amount of element M1 is 1000-5000 ppm, the gram capacity or the cycle performance and / or 70°C @ 40 days of the secondary battery is further improved.

[0279] Comparative Example 1-1 and Examples 4-7 to 4-12, when the second positive electrode active material is doped with element M2, and the doping amount of element M2 is in the range of 500-7000 ppm, the secondary battery all has good comprehensive performance; when the doping amount of element M2 is 1000-5000 ppm, the gram capacity or the cycle performance and / or 70°C @ 40 days of the secondary battery is further improved.

[0280] Table 5. Influence of coating elements and coating amounts on battery performance

[0281]

[0282] Comparative Example 1-1 and Examples 5-1 to 5-5, when the first positive electrode active material and the second positive electrode active material are respectively coated with a coating layer containing N1 element and a coating layer containing N2 element, and when the coating amount of N1 element or N2 element is in the range of 500-20000ppm, the secondary batteries all have good comprehensive performance; when the coating amount of N1 element or N2 element is 1000-15000ppm, the specific capacity or the cycle performance and / or the 70℃@40 days swelling of the secondary battery is further improved.

[0283] Table 6. Influence of sintering temperature and sintering time of each step on battery performance

[0284]

[0285] Comparative Example 1-1 and Examples 6-1 to 6-8, the synthesis process using the method of the application, the obtained secondary batteries all have good comprehensive performance.

[0286] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, other ways constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material, characterized by, Comprising: a first positive electrode active material comprising a matrix of formula (I) doped with an element M1: Li A1 [Ni X1 Co Y1 Mn Z1 ]O2 (I), In formula (I), 0.5≤X1<1, 0≤Y1<0.5, 0≤Z1<0.5, 0.9<A1<1.2, the element M1 is selected from at least one of Ti, Zr, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y; and a second positive electrode active material comprising a matrix of formula (II) doped with an element M2: Li A2 [Ni X2 Co Y2 Mn Z2 ]O2 (II), In formula (II), 0.5≤X2<1, 0≤Y2<0.5, 0≤Z2<0.5, 0.9<A2<1.2, the element M2 is selected from at least one of Ti, Zr, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y; wherein the volume average particle diameter Dv 50 is greater than the volume average particle diameter Dv 50 and 0 < X2-X1≤ 0.

4.

2. The positive electrode active material according to claim 1, characterized by 0<X2-X1≤0.

1.

3. The positive electrode active material according to claim 1, characterized by 0.9≤X2<1。 4. The positive electrode active material according to claim 1, characterized by The weight ratio of the first positive electrode active material to the second positive electrode active material is 5:5 or more.

5. The positive electrode active material according to claim 4, characterized by The weight ratio of the first positive electrode active material to the second positive electrode active material is 6:4-9:

1.

6. The positive electrode active material according to claim 1, characterized by The first positive electrode active material is a secondary particle, a volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 ≥0.

5.

7. The positive electrode active material according to claim 6, characterized by (Dv 90 -Dv 10 ) / Dv 50 ≥1.

0.

8. The positive electrode active material according to any one of claims 1 to 7, characterized by, The volume average particle diameter Dv of the first positive electrode active material is 6 to 20 μm. 50 is 6 to 20 μm.

9. The positive electrode active material according to claim 1, characterized by The second positive electrode active material is secondary particles and / or primary particles.

10. The positive electrode active material according to claim 9, characterized by The second positive electrode active material is a primary particle, a volume particle size distribution span (Dv 90 -Dv 10 ) / Dv 50 ≥0.

5.

11. The positive electrode active material according to claim 10, characterized by (Dv 90 -Dv 10 ) / Dv 50 ≥1.

0.

12. The positive electrode active material according to any one of claims 1 to 7 and 9 to 11, characterized by, The volume average particle diameter Dv of the second positive electrode active material is 2 to 5 μm. 50 is 2 to 5 μm.

13. The positive electrode active material according to any one of claims 1 to 7 and 9 to 11, characterized by, In the first positive electrode active material, the doping amount of the element M1 is 500-7000 ppm based on the total weight of the first positive electrode active material.

14. The positive electrode active material according to claim 13, characterized by In the first positive electrode active material, the doping amount of the element M1 is 1000-5000 ppm based on the total weight of the first positive electrode active material.

15. The positive electrode active material according to any one of claims 1 to 7 and 9 to 11, characterized by, In the second positive electrode active material, the doping amount of the element M2 is 500-7000 ppm based on the total weight of the second positive electrode active material.

16. The positive electrode active material according to claim 15, characterized by In the second positive electrode active material, the doping amount of the element M2 is 1000-5000 ppm based on the total weight of the second positive electrode active material.

17. The positive electrode active material according to any one of claims 1 to 7 and 9 to 11, characterized by, The surface of the first positive electrode active material further has a coating layer, the coating layer contains an N1 element, the N1 element includes at least one of Al, Co, Mn, B, La, Sr, P, F, Zr, Ti, W.

18. The positive electrode active material according to claim 17, characterized by The coating amount of the N1 element is 500-20000 ppm based on the total weight of the first positive electrode active material.

19. The positive electrode active material according to claim 18, characterized by The coating amount of the N1 element is 1000-15000 ppm based on the total weight of the first positive electrode active material.

20. The positive electrode active material according to any one of claims 1 to 7 and 9 to 11, characterized by, The surface of the second positive electrode active material further has a coating layer, the coating layer contains an N2 element, the N2 element includes at least one of Al, Co, Mn, B, La, Sr, P, F, Zr, Ti, W.

21. The positive electrode active material according to claim 20, characterized by The coating amount of the N2 element is 500-20000 ppm based on the total weight of the second positive electrode active material.

22. The positive electrode active material according to claim 21, characterized by The coating amount of the N2 element is 1000-15000 ppm based on the total weight of the second positive electrode active material.

23. A method for producing a positive electrode active material, characterized by, Comprising the following steps: Step A: preparing a first positive electrode active material, comprising: Step A1: mixing a lithium salt, a first positive electrode active material ternary precursor, and a compound containing an element M1, sintering to obtain the first positive electrode active material; Step A1: mixing a lithium salt, a first positive electrode active material ternary precursor, and a compound containing an element M1, sintering to obtain the first positive electrode active material; Step B: preparing a second positive electrode active material, comprising: Step B1: mixing a lithium salt, a second positive electrode active material ternary precursor, a compound containing element M2, sintering to obtain the second positive electrode active material; Step C: mixing the first positive electrode active material and the second positive electrode active material to obtain the positive electrode active material; The first positive electrode active material comprises a matrix of formula (I) doped with element M1: Li A1 [Ni X1 Co Y1 Mn Z1 ]O2 (I), In formula (I), 0.5≤X1<1, 0≤Y1<0.5, 0≤Z1<0.5, 0.9<A1<1.2, the element M1 is selected from at least one of Ti, Zr, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y; The second positive electrode active material comprises a matrix of formula (II) doped with element M2: Li A2 [Ni X2 Co Y2 Mn Z2 ]O2 (II), In formula (II), 0.5≤X2<1, 0≤Y2<0.5, 0≤Z2<0.5, 0.9<A2<1.2, the element M2 is selected from at least one of Ti, Zr, Sb, W, Sr, Nb, Mo, Ca, K, Na, Mg, Si, Te, Cr, V, Y; The volume average particle diameter Dv of the first positive electrode active material 50 The volume average particle diameter Dv of the second positive electrode active material 50 and 0 < X2 - X1 ≤ 0.

4.

24. The method of claim 23, wherein, 0<X2-X1≤0.

1.

25. The method of claim 23, wherein, In the step A1, the sintering temperature is 700-950℃, the time is 10-20 h, and the atmosphere is air or O2.

26. The method of claim 23, wherein, In the step B1, the sintering temperature is 750-1000℃, the time is 10-20 h, and the atmosphere is air or O2.

27. The method of any one of claims 23-26, wherein, The step A further comprises: Step A2: mixing and sintering the first positive electrode active material obtained from the step A1 with a compound containing N1 to form a coating layer containing element N1 on the surface of the first positive electrode active material.

28. The method of claim 27, wherein, In the step A2, the sintering temperature is 250-700℃, the time is 5-15 h, and the atmosphere is air or O2.

29. The method of any one of claims 23-26, wherein, The step B further comprises: Step B2: mixing and sintering the second positive electrode active material obtained from the step B1 with a compound containing N2 to form a coating layer containing element N2 on the surface of the second positive electrode active material.

30. The method of claim 29, wherein, In the step B2, the sintering temperature is 250-700℃, the time is 5-15 h, and the atmosphere is air or O2.

31. A secondary battery, characterized by comprising: The positive electrode active material of any one of claims 1 to 22 or prepared by the method of any one of claims 23 to 30.

32. An electrical device, comprising: The secondary battery of claim 31.

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