Positive electrode active material, method for manufacturing the same, positive electrode sheet, secondary battery, and power using device

Abstract

A positive electrode active material and its preparation method are disclosed. The positive electrode active material includes a first positive electrode active material A and a second positive electrode active material B, wherein the chemical formula of the first positive electrode active material A is Li. a1 [Ni x1 Co y1 Mn z1 M1 b1 M3 c1 O2, where 0 < x1 < 1, 0 ≤ y1 < 0.5, 0 ≤ z1 < 0.5, 0.9 < a1 < 1.2, 0 < b1 < 0.2, 0 < c1 < 0.2, x1 + y1 + z1 + b1 + c1 = 1, where M1 is selected from at least one of W, Nb, and Mo, and M3 is selected from at least one of Zr, Ti, Mg, Al, Sb, B, and Co; the chemical formula of the second positive electrode active material B is Li a2 [Ni x2 Co y2 Mn z2 M2 b2 M4 c2 O2, where 0 < x2 < 1, 0 ≤ y2 < 0.5, 0 ≤ z2 < 0.5, 0.9 < a2 < 1.2, 0 < b2 < 0.2, 0 < c2 < 0.2, x2 + y2 + z2 + b2 + c2 = 1, where M2 is selected from at least one of Sr, Y and V, and M4 is selected from at least one of Zr, Ti, Mg, Al, Sb, B and Co.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a positive electrode active material and its preparation method, as well as a positive electrode sheet including the positive electrode active material, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on its energy density, cycle performance, and safety performance.

[0003] Cathode materials are a crucial component of lithium-ion batteries, influencing not only safety and cost but also directly determining electrochemical performance and lifespan. Common cathode materials include layered structures (such as lithium cobalt oxide, lithium manganese oxide, and lithium nickel oxide), spinel structures, polyanionic materials, and ternary materials. High-nickel ternary materials have attracted increasing attention due to their high energy density, low cost, and reliable safety. While high-nickel ternary materials offer significantly improved energy density compared to other materials, increasing nickel content leads to severe capacity decay and layered structure disruption during charge and discharge, hindering their further development. Therefore, strategies are needed to optimize high-nickel ternary materials to improve battery energy density, cycle performance, and safety. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material with good dispersibility, high compaction density, and improved structural stability, and to provide a method for preparing the positive electrode active material, as well as a positive electrode sheet, a secondary battery, and an electrical device comprising the positive electrode active material of this application.

[0005] To achieve the above objectives, a first aspect of this application provides a positive electrode active material, which includes a first positive electrode active material A and a second positive electrode active material B.

[0006] The chemical formula of the first positive electrode active material A is Li. a1 [Ni x1 Co y1 Mn z1 M1 b1 M3 c1O2, where 0 < x1 < 1, 0 ≤ y1 < 0.5, 0 ≤ z1 < 0.5, 0.9 < a1 < 1.2, 0 < b1 < 0.2, 0 < c1 < 0.2, and x1 + y1 + z1 + b1 + c1 = 1. Among them, M1 includes at least one of W, Nb, and Mo, and M3 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co; the chemical formula of the second cathode active material B is Li a2 [Ni x2 Co y2 Mn z2 M2 b2 M4 C2 O2, where 0 < x2 < 1, 0 ≤ y2 < 0.5, 0 ≤ z2 < 0.5, 0.9 < a2 < 1.2, 0 < b2 < 0.2, 0 < c2 < 0.2, and x2 + y2 + z2 + b2 + c2 = 1. Among them, M2 includes at least one of Sr, Y, and V, and M4 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co.

[0007] Therefore, compared with the prior art, the present application at least includes the following beneficial effects:

[0008] For the cathode active material of the present application, on the one hand, the co-doping of M1 element (i.e., W, Nb, or Mo) and M3 element can refine the grains of the first cathode active material A, making the grains tend to radial distribution. At the same time, the M1 element is enriched at the grain boundaries, which improves the compressive strength of the polycrystalline first cathode active material A, reduces cracking, and at the same time reduces the side reaction between the cracked part and the electrolyte, reducing oxygen release; on the other hand, the co-doping of M2 element (i.e., Sr, Y, or V) with a melting aid effect and M4 element is used to improve the structural stability of the second cathode active material B, which can increase the particle size of the single crystal second cathode active material B, thereby reducing the side reaction between its surface and the electrolyte and reducing oxygen release. Through the above two aspects of improvement, the cathode active material of the present application not only has a high packing density between particles, good dispersibility and high tap density, can effectively improve the energy density of the battery, but also has improved structural stability, effectively preventing side reactions of the electrolyte on the surface of the cathode active material, thereby improving the cycle performance and safety performance of the battery.

[0009] In any embodiment, the weight ratio of the first cathode active material A to the second cathode active material B is 10:1 - 1:1, and can be selected as 9:1 - 3:2. When the weight ratio of the first cathode active material A to the second cathode active material B in the cathode active material is within the above range, the cathode active material has a high tap density and can effectively improve the energy density of the battery.

[0010] In any embodiment, the (Dv90-Dv10) / Dv50 of the positive electrode active material is 1.5-2.5, and optionally 1.75-2.0. When the (Dv90-Dv10) / Dv50 of the positive electrode active material meets the above range, the positive electrode active material particles are continuously distributed, have good dispersion, and improve space utilization, which is beneficial to improving the processing performance of the positive electrode active material.

[0011] In any embodiment, the positive electrode active material satisfies the following formula:

[0012] K=ΔDv1 / Dv1*0.01+ΔDv3 / Dv3*0.03+ΔDv5 / Dv5*0.05,

[0013] And K≤7%, optionally, K≤5%.

[0014] Wherein, ΔDv1, ΔDv3, and ΔDv5 are the differences between Dv1, Dv3, and Dv5 of the positive electrode active material and Dv1', Dv3', and Dv5' of the positive electrode active material after being pressurized with 1 ton of weight, respectively. When the positive electrode active material satisfies the above formula, the positive electrode active material has good structural stability, high compressive strength, and fewer particle cracks, effectively preventing side reactions between the cracked areas and the electrolyte, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery.

[0015] In any embodiment, the electrochemically active specific surface area of ​​the positive electrode material is 1-8 cm². 2 / g, optional 2-6cm 2 / g. When the electrochemically active specific surface area of ​​the positive electrode active material meets the above range, the positive electrode active material has good structural stability, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, thereby improving the cycle performance and safety performance of the battery.

[0016] In any embodiment, the compaction density of the positive electrode active material under a pressure of 5 tons (T) is 3.4-4.0 g / cm³. 3 The selectable value is 3.7-3.9 g / cm³. 3 The positive electrode active material has high compaction density and high interparticle filling degree, which not only improves the processing performance of the positive electrode active material, but also effectively improves the energy density of the battery.

[0017] In any embodiment, the amount of M1 in the first positive electrode active material A is 500-8000 ppm, optionally 1000-4000 ppm, and the amount of M3 is 1000-20000 ppm, optionally 3000-15000 ppm. When the amounts of M1 and M3 in the first positive electrode active material A are within the above ranges, the compressive strength of the polycrystalline first positive electrode active material A can be improved, cracking can be reduced, and the side reactions between the cracked areas and the electrolyte can be effectively reduced, thereby improving the cycle performance and safety performance of the battery.

[0018] In any embodiment, the amount of M2 in the second positive electrode active material B is 500-8000 ppm, optionally 1000-4000 ppm, and the amount of M4 is 1000-20000 ppm, optionally 3000-15000 ppm. When the amounts of M2 and M4 in the second positive electrode active material B are within the above ranges, the structural stability of the single-crystal second positive electrode active material B can be improved, the single-crystal grain size can be increased, thereby reducing the side reactions between its surface and the electrolyte, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery.

[0019] In any embodiment, the molar ratio of M1 to M3 in the first positive electrode active material A is 1:80-4:1, or optionally 1:30-3:4. When the molar ratio of M1 to M3 in the first positive electrode active material A is within the above range, the first positive electrode active material A has high compressive strength, less particle cracking, effectively prevents side reactions of the electrolyte on the surface of the positive electrode active material, reduces oxygen release, and thus improves the cycle performance and safety performance of the battery.

[0020] In any embodiment, the molar ratio of M2 to M4 in the second positive electrode active material B is 1:40-8:1, optionally 1:20-3:2. When the molar ratio of M2 to M4 in the second positive electrode active material B is within the above range, the second positive electrode active material B has high structural stability, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, reducing oxygen release, thereby improving the cycle performance and safety performance of the battery.

[0021] In any embodiment, the first positive electrode active material A has a Dv50 of 7-15 μm and a (Dv90-Dv10) / Dv50 ratio of 0.5-1.5, optionally 1.0-1.45; the second positive electrode active material B has a Dv50 of 2-4 μm and a (Dv90-Dv10) / Dv50 ratio of 0.5-1.5, optionally 1.0-1.45. When the first positive electrode active material A and the second positive electrode active material B respectively meet the above ranges, the positive electrode active material of this application can have a high particle filling degree, good dispersibility and high compaction density, which can effectively improve the energy density of the battery.

[0022] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising the following steps:

[0023] S1) Prepare the first positive electrode active material A: Mix a lithium salt, a precursor of the first positive electrode active material A, a compound containing M1 element, and a compound containing M3 element according to a molar ratio, and sinter them;

[0024] S2) Prepare the second positive electrode active material B: Mix a lithium salt, a precursor of the second positive electrode active material B, a compound containing M2 element, and a compound containing M4 element according to a molar ratio, and sinter them;

[0025] S3) Mix the first positive electrode active material A and the second positive electrode active material B to obtain the positive electrode active material,

[0026] wherein, the chemical formula of the first positive electrode active material A is Li a1 [Ni x1 Co y1 Mn z1 M1 b1 M3 c1 O2, where 0 < x1 < 1, 0 ≤ y1 < 0.5, 0 ≤ z1 < 0.5, 0.9 < a1 < 1.2, 0 < b1 < 0.2, 0 < c1 < 0.2, and x1 + y1 + z1 + b1 + c1 = 1. Among them, M1 includes at least one of W, Nb, and Mo, and M3 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co,

[0027] The chemical formula of the second positive electrode active material B is Li a2 [Ni x2 Co y2 Mn z2 M2 b2 M4 C2 O2, where 0 < x2 < 1, 0 ≤ y2 < 0.5, 0 ≤ z2 < 0.5, 0.9 < a2 < 1.2, 0 < b2 < 0.2, 0 < c2 < 0.2, and x2 + y2 + z2 + b2 + c2 = 1. Among them, M2 includes at least one of Sr, Y, and V, and M4 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co.

[0028] Thus, the positive electrode active material prepared by the above method not only has a high filling degree between particles, good dispersibility and high tap density, can effectively improve the energy density of the battery, but also has improved structural stability, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, thereby improving the cycle performance and safety performance of the battery.

[0029] In any embodiment, in step S3), the first positive electrode active material A and the second positive electrode active material B are mixed at a weight ratio of 10:1 to 1:1, optionally 9:1 to 3:2. When the first positive electrode active material A and the second positive electrode active material B are mixed at the above weight ratio, a positive electrode active material with high compaction density can be obtained, which can effectively improve the energy density of the battery.

[0030] In any embodiment, the compound containing element M1 is one or more of an oxide, carbonate, or hydroxide containing element M1, wherein element M1 is one of W, Nb, or Mo; the compound containing element M3 is one or more of an oxide, carbonate, or hydroxide containing element M3, wherein element M3 is one of Zr, Ti, Mg, Al, Sb, B, or Co; the compound containing element M2 is one or more of an oxide, carbonate, or hydroxide containing element M2, wherein element M2 is one of Sr, Y, or V; the compound containing element M4 is one or more of an oxide, carbonate, or hydroxide containing element M4, wherein element M4 is one of Zr, Ti, Mg, Al, Sb, B, or Co. By selecting the source of each element M1, M2, M3, and M4, the structural stability of the positive electrode active material can be improved, thereby improving the performance of the positive electrode active material.

[0031] In any embodiment, the Dv50 of the precursor of the first positive electrode active material A is 7-15 μm; the Dv50 of the precursor of the second positive electrode active material B is 2-4 μm. By controlling the particle size distribution of the precursors, a positive electrode active material with the desired particle size distribution can be obtained, so that the resulting positive electrode active material has high interparticle filling degree, good dispersibility, high compaction density, and good material processing performance.

[0032] In any embodiment, in step S1), the sintering temperature is 700-850℃, optionally 700-800℃, the sintering time is 10-20h, and the sintering atmosphere is oxygen or air. By controlling the sintering temperature and sintering time, elements M1 and M3 can be enriched at the grain boundaries, improving the compressive strength of the first positive electrode active material A, reducing cracking, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, reducing oxygen release, thereby improving the cycle performance and safety performance of the battery.

[0033] In any embodiment, in step S2), the sintering temperature is 750-1000℃, optionally 750-850℃, the sintering time is 10-20h, and the sintering atmosphere is oxygen or air. By controlling the sintering temperature and sintering time, the M2 and M4 elements can be uniformly distributed, improving the structural stability of the second positive electrode active material, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery.

[0034] A third aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the positive electrode film layer comprises the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method of the second aspect of this application, and the coating amount of the positive electrode sheet is less than 0.025 g / cm³. 2 The compaction density of the positive electrode sheet is ≥3.3 g / cm³. 3 , can be ≥3.4g / cm 3 .

[0035] The fourth aspect of this application provides a secondary battery comprising the positive electrode active material of the first aspect of this application, or the positive electrode active material prepared by the method of the second aspect of this application, or the positive electrode sheet of the third aspect of this application.

[0036] A fifth aspect of this application provides an electrical device comprising a secondary battery selected from the fourth aspect of this application.

[0037] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0039] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0040] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0041] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0042] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0043] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0044] Explanation of reference numerals in the attached figures:

[0045] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0046] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its preparation method, secondary battery, battery module, battery pack, and electrical 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] 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 ​​of 1 and 2 are listed, and if maximum range values ​​of 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.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0050] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0052] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0053] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0054] High-nickel ternary cathode materials combine the synergistic effects of Ni, Co, and Mn elements. Ni effectively increases the specific capacity and energy density of the material; Co possesses excellent electrochemical activity, enhancing the Li-... + with Ni 2+ Reduced cation mixing improves the electronic conductivity and cycle performance of the material; while Mn can reduce material cost, improve battery safety and stability, and stabilize the crystal structure of the material. Although significant progress has been made in the research of high-nickel ternary cathode materials in recent years, many problems still need to be solved: 1) Over-Ni can occur during cycling of high-nickel ternary materials. 2+ and Li + Mixed arrangement, Ni 2+ Occupy Li + The position makes Li + 1) The material cannot embed lithium layers during discharge, resulting in a loss of capacity and a reduction in rate performance; 2) Due to Ni 4+ It has reducing properties and readily forms Ni. 3+, in order to maintain charge balance, oxygen is released in the material, resulting in the destruction of the material structure and a decrease in thermal stability; 3) Since the diffusion of Li + is affected by kinetic factors, the amount of Li extracted increases, reducing the transition metal ions. It is easy for the material to form new phases and pores on the surface to maintain its electrical neutrality, leading to the instability of the high-nickel cathode material structure. Under overcharge conditions, the structural instability is accelerated. Because it is accompanied by a partial structural transformation to the spinel-type and NiO-type rock salt phases, and the generation of oxygen, there are certain potential safety hazards in the battery.

[0055] Currently, the electrochemical performance of the material is usually improved by means such as surface coating, ion doping, and size grading of particles. Generally, for the size grading of particles, the large particles are polycrystalline, which are secondary large particles formed by the aggregation of small particle single crystals. They have a high discharge capacity and first-cycle efficiency. However, during the battery cycling process, microcracks are likely to occur in the large particles, resulting in side reactions with the electrolyte, and even expansion or collapse, causing the failure of the cathode material, and phenomena such as increased resistance, powder loss, and gas generation, leading to a rapid deterioration of the battery cycling performance and safety performance; the small particles are single crystal materials in which the primary grains are dispersed. They have good structural stability, but their discharge capacity is low and they are prone to side reactions with the electrolyte, reducing the battery life and safety performance. Therefore, it is hoped that the cathode active material with size grading can be further improved in order to obtain a cathode active material with both high energy density, excellent cycling performance and safety performance.

[0056] In view of the above problems, the present application provides a cathode active material, which includes a first cathode active material A and a second cathode active material B,

[0057] wherein, the chemical formula of the first cathode active material A is Li a1 [Ni x1 Co y1 Mn z1 M1 b1 M3 c1 O2, where 0 < x1 < 1, 0 ≤ y1 < 0.5, 0 ≤ z1 < 0.5, 0.9 < a1 < 1.2, 0 < b1 < 0.2, 0 < c1 < 0.2, x1 + y1 + z1 + b1 + c1 = 1, wherein, M1 includes at least one of W, Nb and Mo, and M3 includes at least one of Zr, Ti, Mg, Al, Sb, B and Co; the chemical formula of the second cathode active material B is Li a2 [Ni x2 Co y2 Mn z2 M2 b2 M4 C2O2, where 0 < x2 < 1, 0 ≤ y2 < 0.5, 0 ≤ z2 < 0.5, 0.9 < a2 < 1.2, 0 < b2 < 0.2, 0 < c2 < 0.2, and x2 + y2 + z2 + b2 + c2 = 1. Among them, M2 includes at least one of Sr, Y, and V, and M4 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co.

[0058] Although the mechanism is not yet clear, the applicant unexpectedly found that: the positive electrode active material of this application not only has a high degree of inter-particle filling, good dispersibility and high tap density, which can effectively improve the energy density of the battery, but also has improved structural stability, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material. Specifically, on the one hand, the positive electrode active material of this application can refine the grains of the first positive electrode active material A and make the grains tend to be radially distributed by co-doping with the M1 (i.e., W, Nb or Mo) element and the M3 element. At the same time, the M1 element is enriched at the grain boundaries, which improves the compressive strength of the first positive electrode active material A, reduces cracking, and at the same time reduces the side reaction between the cracked part and the electrolyte, reduces oxygen release, and thus improves the cycle performance and safety performance of the battery; on the other hand, the positive electrode active material of this application improves the structural stability of the second positive electrode active material B and increases the particle size of the second positive electrode active material B by co-doping with the M2 element (i.e., Sr, Y or V) with a fluxing effect and the M4 element, thereby reducing the side reaction between its surface and the electrolyte, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery.

[0059] In this application, the first positive electrode active material A can be a polycrystalline material, that is, a spherical or quasi-spherical secondary particle formed by aggregating a plurality of primary particles; the second positive electrode active material B can be a single crystal material, that is, in a state of a single particle without obvious agglomeration, and the primary particle has a size greater than 1 μm.

[0060] In some embodiments, M1 is selected from at least one of W, Nb, and Mo. In some embodiments, M3 is selected from at least one of Zr, Ti, Mg, Al, Sb, B, and Co. In some embodiments, M2 is selected from at least one of Sr, Y, and V. In some embodiments, M4 is selected from at least one of Zr, Ti, Mg, Al, Sb, B, and Co.

[0061] In some embodiments, the weight ratio of the first positive electrode active material A to the second positive electrode active material B is 10:1 - 1:1, and can be optionally 9:1 - 3:2. When the weight ratio of the first positive electrode active material A to the second positive electrode active material B in the positive electrode active material is within the above range, the positive electrode active material has a high tap density and can effectively improve the energy density of the battery.

[0062] In some embodiments, the (Dv90-Dv10) / Dv50 ratio of the positive electrode active material is 1.5-2.5, and optionally 1.75-2.0. When the (Dv90-Dv10) / Dv50 ratio of the positive electrode active material meets the above range, the positive electrode active material particles are continuously distributed, have good dispersion, and improve space utilization, which is beneficial to improving the processing performance of the positive electrode active material.

[0063] In this application, Dv10, Dv50, and Dv90 are the particle sizes of the positive electrode active material as measured by volumetric particle size distribution, wherein Dv10 is the particle size corresponding to a cumulative volume percentage of 10% of the sample, Dv50 is the particle size corresponding to a cumulative volume percentage of 50% of the sample, and Dv90 is the particle size corresponding to a cumulative volume percentage of 90% of the sample.

[0064] In some embodiments, the positive electrode active material satisfies the following formula:

[0065] K=ΔDv1 / Dv1*0.01+ΔDv3 / Dv3*0.03+ΔDv5 / Dv5*0.05,

[0066] And K≤7%, optionally, K≤5%.

[0067] Wherein, ΔDv1, ΔDv3, and ΔDv5 are the differences between Dv1, Dv3, and Dv5 of the positive electrode active material and Dv1', Dv3', and Dv5' of the positive electrode active material after being pressurized with 1 ton of weight, respectively. When the positive electrode active material satisfies the above formula, the positive electrode active material has good structural stability, high compressive strength, and fewer particle cracks, effectively preventing side reactions between the cracked areas and the electrolyte, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery.

[0068] In this application, Dv1 is the particle size corresponding to a cumulative volume distribution percentage of 1%; Dv3 is the particle size corresponding to a cumulative volume distribution percentage of 3%; and Dv5 is the particle size corresponding to a cumulative volume distribution percentage of 5%. Correspondingly, Dv1' is the particle size of the sample when pressurized with 1 ton of weight (i.e., using 1 ton of weight to pressurize a fixed area of ​​1.33 cm²). 2 The particle size at which the cumulative volume distribution percentage reaches 1% after pressurization for 30 seconds; Dv3' is the particle size of the sample after pressurization with 1 ton of weight (i.e., using 1 ton of weight to pressurize a fixed area of ​​1.33 cm²). 2 The particle size at which the cumulative volume distribution percentage reaches 3% after pressurization for 30 seconds; Dv5' is the particle size of the sample after pressurization with 1 ton of weight (i.e., using 1 ton of weight to pressurize a fixed area of ​​1.33 cm²). 2The particle size corresponding to a cumulative volume distribution percentage of 5% after pressurization for 30 seconds. Furthermore, ΔDv1 = Dv1 - Dv1', ΔDv3 = Dv3 - Dv3', ΔDv5 = Dv5 - Dv5'.

[0069] In this application, K = ΔDv1 / Dv1*0.01 + ΔDv3 / Dv3*0.03 + ΔDv5 / Dv5*0.05 can be used to represent the weighted fragmentation degree of the positive electrode active material. The lower the K value, the higher the compressive strength of the positive electrode active material, and the fewer particle cracks occur during battery cycling, thereby effectively improving battery cycle performance and safety performance. In this application, K can be ≤7%, ≤5%, ≤4.5%, ≤4%, ≤3.5%, ≤3%, ≤2.5%, ≤2%, ≤1.5%, ≤1%, or ≤0.5%.

[0070] In some embodiments, the electrochemically active specific surface area of ​​the positive electrode material is 1-8 cm². 2 / g, optional 2-6cm 2 / g. When the electrochemically active specific surface area of ​​the positive electrode active material meets the above range, the positive electrode active material has good structural stability, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, thereby improving the cycle performance and safety performance of the battery.

[0071] In this application, the electrochemically active specific surface area refers to the effective specific surface area of ​​electroactivity that reflects the electrical properties of the material. In this application, cyclic voltammetry is used with an electrochemical workstation (VMP3). A button cell is assembled using the positive electrode active material of this application. The CV of the electroactive probe is scanned four times at scan rates of 1.0 mV / s, 0.5 mV / s, 0.3 mV / s, and 0.1 mV / s. According to the Randles-Sevcik equation: Ip = 2.69 × 10⁻⁶ 5 n 3 / 2 AcD 1 / 2 v 1 / 2 The electrochemical active surface area of ​​the positive electrode material was obtained by combining the peak current Ip, diffusion coefficient D, scan rate v, electron transfer number n (which is 1), and concentration c (which is 50 mmol / L) from the test. In this application, the electrochemical active surface area of ​​the positive electrode material is, for example, 1-8 cm². 2 / g, 2-6cm 2 / g, 3-5.5cm 2 / g or 3.5-4.5cm 2 / g.

[0072] In some embodiments, the compaction density of the positive electrode active material under a pressure of 5 tons (T) is 3.4-4.0 g / cm³. 3The selectable value is 3.7-3.9 g / cm³. 3 The positive electrode active material has high compaction density and high interparticle filling degree, which not only improves the processing performance of the positive electrode active material, but also effectively increases the energy density of the battery. The compaction density can be measured according to GB / T24533-2009.

[0073] In some embodiments, the amount of M1 in the first positive electrode active material A is 500-8000 ppm, optionally 1000-4000 ppm, and the amount of M3 is 1000-20000 ppm, optionally 3000-15000 ppm. When the amounts of M1 and M3 in the first positive electrode active material A are within the above ranges, the compressive strength of the polycrystalline first positive electrode active material A can be improved, cracking can be reduced, and the side reactions between the cracked areas and the electrolyte can be effectively reduced, thereby improving the cycle performance and safety performance of the battery. In this application, the amounts of M1 and M3 elements in the first positive electrode active material are measured by detection techniques commonly used in the art to measure the content of doped elements, such as inductively coupled plasma atomic emission spectrometry (ICP).

[0074] In some embodiments, the amount of M2 in the second positive electrode active material B is 500-8000 ppm, optionally 1000-4000 ppm, and the amount of M4 is 1000-20000 ppm, optionally 3000-15000 ppm. When the amounts of M2 and M4 in the second positive electrode active material B are within the above ranges, the structural stability of the single-crystal second positive electrode active material B can be improved, the single-crystal grain size can be increased, thereby reducing the side reactions between its surface and the electrolyte, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery. The amounts of M2 and M4 elements in the first positive electrode active material are measured by detection techniques commonly used in the art to measure the content of doping elements, such as inductively coupled plasma atomic emission spectrometry (ICP).

[0075] In some embodiments, the molar ratio of M1 to M3 in the first positive electrode active material A is 1:80-4:1, or optionally 1:30-3:4. When the molar ratio of M1 to M3 in the first positive electrode active material A is within the above range, the first positive electrode active material A has high compressive strength, less particle cracking, effectively prevents side reactions of the electrolyte on the surface of the positive electrode active material, reduces oxygen release, and thus improves the cycle performance and safety performance of the battery.

[0076] In some embodiments, the molar ratio of M2 to M4 in the second positive electrode active material B is 1:40 - 8:1, optionally 1:20 - 3:2, and further optionally 1:2 - 1:1. When the molar ratio of M2 to M4 in the second positive electrode active material B is within the above range, the second positive electrode active material B has high structural stability, effectively prevents side reactions of the electrolyte on the surface of the positive electrode active material, reduces oxygen release, and thus improves the cycle performance and safety performance of the battery.

[0077] In some embodiments, the Dv50 of the first positive electrode active material A is 7 - 15 μm, and (Dv90 - Dv10) / Dv50 is 0.5 - 1.5, optionally 1.0 - 1.45; the Dv50 of the second positive electrode active material B is 2 - 4 μm, and (Dv90 - Dv10) / Dv50 is 0.5 - 1.5, optionally 1.0 - 1.45. When the first positive electrode active material A and the second positive electrode active material B respectively meet the above ranges, the packing density between the positive electrode active material particles of the present application is high, with good dispersibility, and the tap density of the positive electrode active material can be optimized, effectively improving the energy density of the battery.

[0078] The second aspect of the present application provides a method for preparing a positive electrode active material, including the following steps:

[0079] S1) Prepare the first positive electrode active material A: Mix a lithium salt, a precursor of the first positive electrode active material A, a compound containing the M1 element, and a compound containing the M3 element according to a molar ratio, and sinter.

[0080] S2) Prepare the second positive electrode active material B: Mix a lithium salt, a precursor of the second positive electrode active material B, a compound containing the M2 element, and a compound containing the M4 element according to a molar ratio, and sinter.

[0081] S3) Mix the first positive electrode active material A and the second positive electrode active material B to obtain the positive electrode active material.

[0082] Among them, the chemical formula of the first positive electrode active material A is Li a1 [Ni x1 Co y1 Mn z1 M1 b1 M3 c1 O2, where 0 < x1 < 1, 0 ≤ y1 < 0.5, 0 ≤ z1 < 0.5, 0.9 < a1 < 1.2, 0 < b1 < 0.2, 0 < c1 < 0.2, and x1 + y1 + z1 + b1 + c1 = 1. Among them, M1 includes at least one of W, Nb, and Mo, and M3 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co.

[0083] The chemical formula of the second positive electrode active material B is Li a2 [Ni x2 Co y2 Mn z2 M2 b2 M4 C2 O2, where 0 < x2 < 1, 0 ≤ y2 < 0.5, 0 ≤ z2 < 0.5, 0.9 < a2 < 1.2, 0 < b2 < 0.2, 0 < c2 < 0.2, and x2 + y2 + z2 + b2 + c2 = 1. Among them, M2 includes at least one of Sr, Y, and V, and M4 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co. The positive electrode active material prepared by the above method not only has a high filling degree between particles, good dispersibility and high tap density, can effectively improve the energy density of the battery, but also has improved structural stability, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, thereby improving the cycle performance and safety performance of the battery.

[0084] In this application, the precursors of the first positive electrode active material A and the second positive electrode active material B can be prepared by methods known in the prior art, such as the co-precipitation method of hydroxides, for example, prepared by the method described in CN111384372A. More specifically, the precursor of the first positive electrode active material A can be, including but not limited to, Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.9 Co 0.05 Mn 0.05 (OH)2, Ni 0.7 Co 0.1 Mn 0.2 (OH)2, Ni 0.96 Co 0.03 Mn 0.01 (OH)2, Ni 0.75 Co 0.1 Mn 0.15 (OH)2. The precursor of the second positive electrode active material B can be, including but not limited to, Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.9 Co 0.05 Mn 0.05 (OH)2, Ni 0.7 Co 0.1 Mn 0.2 (OH)2, Ni 0.96 Co 0.03 Mn 0.01 (OH)2, Ni 0.75 Co 0.1Mn 0.15 (OH)2.

[0085] In some embodiments, M1 is selected from at least one of W, Nb, and Mo. In some embodiments, M3 is selected from at least one of Zr, Ti, Mg, Al, Sb, B, and Co. In some embodiments, M2 is selected from at least one of Sr, Y, and V. In some embodiments, M4 is selected from at least one of Zr, Ti, Mg, Al, Sb, B, and Co. In some embodiments, in step S3), the first positive electrode active material A and the second positive electrode active material B are mixed at a weight ratio of 10:1 to 1:1, optionally 9:1 to 3:2. When the first positive electrode active material A and the second positive electrode active material B are mixed at the above weight ratio, a positive electrode active material with high compaction density can be obtained, which can effectively improve the energy density of the battery.

[0086] In some embodiments, the compound containing element M1 is one or more of an oxide, carbonate, or hydroxide containing element M1, wherein element M1 is one of W, Nb, or Mo; the compound containing element M3 is one or more of an oxide, carbonate, or hydroxide containing element M3, wherein element M3 is one of Zr, Ti, Mg, Al, Sb, B, or Co; the compound containing element M2 is one or more of an oxide, carbonate, or hydroxide containing element M2, wherein element M2 is one of Sr, Y, or V; and the compound containing element M4 is one or more of an oxide, carbonate, or hydroxide containing element M4, wherein element M4 is one of Zr, Ti, Mg, Al, Sb, B, or Co. By selecting the source of each of the elements M1, M2, M3, and M4, the structural stability of the positive electrode active material can be improved, thereby improving the performance of the positive electrode active material.

[0087] In some embodiments, the Dv50 of the precursor of the first positive electrode active material A is 7-15 μm; and the Dv50 of the precursor of the second positive electrode active material B is 2-4 μm. By controlling the particle size distribution of the precursors of the first positive electrode active material A and the second positive electrode active material B, a positive electrode active material with the desired particle size distribution can be obtained, resulting in a positive electrode active material with high interparticle filling degree, good dispersibility, high compaction density, and good material processing performance.

[0088] In some embodiments, in step S1), the sintering temperature is 700-850℃, optionally 700-800℃, the sintering time is 10-20h, and the sintering atmosphere is oxygen or air. By controlling the sintering temperature and sintering time, elements M1 and M3 can be enriched at the grain boundaries, improving the compressive strength of the first positive electrode active material A, reducing cracking, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, reducing oxygen release, thereby improving the cycle performance and safety performance of the battery.

[0089] In some embodiments, in step S2), the sintering temperature is 750-1000℃, optionally 750-850℃, the sintering time is 10-20h, and the sintering atmosphere is oxygen or air. By controlling the sintering temperature and sintering time, the M2 and M4 elements can be uniformly distributed, improving the structural stability of the second positive electrode active material, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery.

[0090] A third aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the positive electrode film layer comprises the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method of the second aspect of this application, and the coating amount of the positive electrode sheet is less than 0.025 g / cm³. 2 The compaction density of the positive electrode sheet is ≥3.3 g / cm³. 3 , can be ≥3.4g / cm 3 , can be ≥3.5g / cm 3 , can be ≥3.6g / cm 3 , can be ≥3.7g / cm 3 Alternatively, a concentration of ≥3.8g / cm³ can be selected. 3 .

[0091] In this application, the coating amount of the positive electrode sheet is less than 0.025 g / cm³. 2 For example, 0.015-0.02 g / cm³ 2 .

[0092] The fourth aspect of this application provides a secondary battery comprising the positive electrode active material of the first aspect of this application, or the positive electrode active material prepared by the method of the second aspect of this application, or the positive electrode sheet of the third aspect of this application.

[0093] A fifth aspect of this application provides an electrical device comprising a secondary battery selected from the fourth aspect of this application.

[0094] In this application, the secondary battery can be in the form of a single battery cell, a battery module, or a battery pack. Battery modules and battery packs contain single battery cells, and battery packs can also contain battery modules.

[0095] In some embodiments, the individual battery cells can be assembled into a battery module. In some embodiments, the individual battery cells can be assembled into a battery pack. In some embodiments, the battery modules can be assembled into a battery pack.

[0096] In addition, the secondary battery (in the form of a single battery cell), battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0097] In one embodiment of this application, a secondary battery is provided.

[0098] Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through. In this application, the battery pack margin is 90-95%.

[0099] [Positive electrode plate]

[0100] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0101] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0102] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0103] In some embodiments, the positive electrode active material may be the positive electrode active material of the first aspect of this application. The weight ratio of the positive electrode active material in the positive electrode film layer is 80-100% by weight, based on the total weight of the positive electrode film layer.

[0104] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0105] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0106] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; wherein the solid content of the positive electrode slurry is 40-80 wt%, the viscosity at room temperature is adjusted to 5000-25000 mPa·s, the positive electrode slurry is coated on a positive current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained, and the areal density of the positive electrode powder coating is 150-350 mg / m². 2 The compaction density of the positive electrode sheet is ≥3.3 g / cm³. 3 , can be ≥3.4g / cm 3 .

[0107] The formula for calculating the compaction density is as follows:

[0108] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0109] [Negative electrode plate]

[0110] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0111] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0112] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0113] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more. The negative electrode active material may have an average particle size (D0) of 1 μm-15 μm, preferably 4 μm-9 μm. 10 ), with an average particle size (D) of 12μm-22μm, preferably 14μm-17μm. 50 It has an average particle size of 26 μm to 40 μm, preferably 30 μm to 37 μm (D). 90 Dv10 is the particle size corresponding to a cumulative volume distribution percentage of 10% for the sample; Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for the sample; and Dv90 is the particle size corresponding to a cumulative volume distribution percentage of 90% for the sample. The weight ratio of the negative electrode active material in the negative electrode film layer is 70-100% by weight, based on the total weight of the negative electrode film layer.

[0114] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may 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). The binder accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0115] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0116] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The other additives constitute 0-15% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0117] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70 wt%, and the viscosity at room temperature is adjusted to 2000-10000 mPa·s; the negative electrode slurry is coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained. The areal density of the negative electrode powder coating is 75-220 mg / m³. 2 The compacted density of the negative electrode sheet is 1.2-2.0 g / m³. 3 .

[0118] [Electrolytes]

[0119] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0120] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0121] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0122] In some embodiments, the solvent may 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, butyl 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.

[0123] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0124] [Isolation membrane]

[0125] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0126] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0127] In some embodiments, the thickness of the isolation membrane is 6-40 μm, optionally 12-20 μm.

[0128] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0129] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0130] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0131] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0132] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0133] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0134] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0135] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0136] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0137] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0138] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0139] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0140] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0141] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0142] Example

[0143] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0144] Preparation of primary and secondary batteries

[0145] Example 1

[0146] 1. Preparation of positive electrode active materials

[0147] 1) Preparation of the precursor of the first positive electrode active material A

[0148] Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a 2 mol / L metal salt solution in a molar ratio of 8:1:1. This metal salt solution, along with 8 mol / L ammonia and 5 mol / L NaOH solution, were then continuously added to a reactor for reaction. The pH was controlled at 11.30, the ammonia concentration at 4.0 g / L, the reaction time at 20 h, and the stirring rate at 300 r / min. The precursor (Ni) of the first positive electrode active material A was prepared using a hydroxide co-precipitation method.0.8 Co 0.1 Mn 0.1 (OH)2), with a particle size Dv50 of 10 μm;

[0149] 2) Preparation of the precursor of the second positive electrode active material B

[0150] Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a 2 mol / L metal salt solution in a molar ratio of 8:1:1. This metal salt solution, along with 8 mol / L ammonia and 5 mol / L NaOH solution, were then continuously added to a reactor for reaction. The pH was controlled at 11.60, the ammonia concentration at 3.0 g / L, the reaction time at 20 h, and the stirring rate at 400 r / min. The precursor (Ni) of the second positive electrode active material B was prepared using a hydroxide co-precipitation method. 0.8 Co 0.1 Mn 0.1 (OH)2), with a particle size Dv50 of 3 μm.

[0151] 3) Preparation of the first positive electrode active material A

[0152] Lithium hydroxide, the precursor of the first positive electrode active material A, tungsten trioxide, and zirconium oxide were mixed evenly in a plow mixer at a molar ratio of 1.03:0.993:0.003:0.004. The mixture was then sintered in a kiln at 750℃ for 15 hours in an oxygen atmosphere. After cooling, the mixture was mechanically crushed to obtain the first positive electrode active material A (Li... 1.03 [(Ni 0.8 Co 0.1 Mn 0.1 ) 0.993 W 0.003 Zr 0.004 The tungsten doping content in the first positive electrode active material was determined to be 6000 ppm by inductively coupled plasma atomic emission spectrometry (ICP). The particle size Dv50 was 10 μm.

[0153] 4) Preparation of the second positive electrode active material B

[0154] Lithium hydroxide, the precursor of the second positive electrode active material B, strontium carbonate, and zirconium oxide were mixed evenly in a plow mixer at a molar ratio of 1.03:0.994:0.002:0.004. The mixture was then sintered in a kiln at 800℃ for 14 hours in an oxygen atmosphere. After cooling, the second positive electrode active material B (Li₂O₃) was obtained by air jet milling. 1.03 [(Ni 0.8 Co 0.1 Mn 0.1 ) 0.994Sr 0.002 Zr 0.004 The particle size Dv50 is 3 μm, and the strontium doping content in the second positive electrode active material is 2000 ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0155] 5) The first positive electrode active material A and the second positive electrode active material B are mixed in a mixer at a mass ratio of 8:2 for 1 hour to obtain the positive electrode active material.

[0156] 2. Preparation of button cells

[0157] [Positive Electrode Sheet] The obtained positive electrode active material, polyvinylidene fluoride (PVDF), and acetylene black were added to NMP at a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form the positive electrode sheet. The coating amount was 0.01 g / cm³. 2 The compacted density is 3.5 g / cm³. 3 .

[0158]

Negative Electrode

[0159] [Electrolyte] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1. Then, LiPF6 is uniformly dissolved in the above solution to obtain the electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0160]

Isolation Film

[0161] The separator membrane was purchased from Cellgard, model number Cellgard2400.

[0162] The positive electrode, negative electrode, separator and electrolyte prepared above are assembled into a CR2032 coin cell (hereinafter also referred to as "coin cell") in a coin cell box.

[0163] 3. Preparation of full cells

[0164] [Positive Electrode Sheet] The positive electrode active material obtained above is mixed evenly with acetylene black and polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solvent system at a weight ratio of 94:3:3. The mixture is then coated onto aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet. The coating amount is 0.02 g / cm³. 2 The compacted density is 3.5 g / cm³. 3 .

[0165] [Negative Electrode Sheet] The negative electrode active material, artificial graphite, hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are mixed evenly in deionized water at a weight ratio of 90:5:2:2:1. This mixture is then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet. The coating amount is 0.015 g / cm³. 2 The compacted density is 1.6 g / cm³. 3 .

[0166] [Electrolyte] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1. Then, LiPF6 is uniformly dissolved in the above solution to obtain the electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0167]

Separation membrane

[0168] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound to obtain a bare cell. The bare cell is placed in outer packaging, electrolyte is injected, and it is sealed to obtain a full cell (hereinafter referred to as "full cell"). The full cell has dimensions of 90mm × 30mm × 60mm (length × width × height) and a cell margin of 91.0%.

[0169] Example 2

[0170] Similar to Example 1, except that in the preparation of the first positive electrode active material A in 3), lithium hydroxide, the precursor of the first positive electrode active material A, niobium pentoxide, and zirconium oxide are in a molar ratio of 1.03:0.993:0.0015:0.004, the sintering temperature is 760℃, and the niobium doping content is 1500ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0171] Example 3

[0172] Similar to Example 1, except that in the preparation of the first positive electrode active material A in 3), lithium hydroxide, the precursor of the first positive electrode active material A, molybdenum trioxide, and zirconium oxide are prepared in a molar ratio of 1.03:0.993:0.003:0.004, the sintering temperature is 750℃, and the molybdenum doping content is 3000ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0173] Example 4

[0174] Similar to Example 1, except that in the preparation of the second positive electrode active material B in 4), lithium hydroxide, the precursor of the second positive electrode active material B, yttrium oxide, and zirconium oxide are prepared in a molar ratio of 1.03:0.994:0.001:0.004, the sintering temperature is 790℃, and the yttrium doping content is 2000ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0175] Example 5

[0176] Similar to Example 1, except that in the preparation of the second positive electrode active material B in 4), lithium hydroxide, the precursor of the second positive electrode active material B, vanadium pentoxide, and zirconium oxide are in a molar ratio of 1.03:0.994:0.001:0.004, the sintering temperature is 790℃, and the vanadium doping content is 1000ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0177] Example 6

[0178] Same as in Example 1, except that the first positive electrode active material A and the second positive electrode active material B are mixed at a mass ratio of 10:1.

[0179] Example 7

[0180] Same as in Example 1, except that the first positive electrode active material A and the second positive electrode active material B are mixed at a mass ratio of 9:1.

[0181] Example 8

[0182] Same as in Example 1, except that the first positive electrode active material A and the second positive electrode active material B are mixed at a mass ratio of 3:2.

[0183] Example 9

[0184] Same as in Example 1, except that the first positive electrode active material A and the second positive electrode active material B are mixed at a mass ratio of 1:1.

[0185] Example 10

[0186] Same as in Example 1, except that the precursor Dv50 of the first positive electrode active material A is 7 μm and the precursor Dv50 of the second positive electrode active material B is 4 μm.

[0187] Example 11

[0188] Same as in Example 1, except that the precursor Dv50 of the first positive electrode active material A is 9 μm and the precursor Dv50 of the second positive electrode active material B is 4 μm.

[0189] Example 12

[0190] Same as in Example 1, except that the precursor Dv50 of the first positive electrode active material A is 11 μm and the precursor Dv50 of the second positive electrode active material B is 3 μm.

[0191] Example 13

[0192] Similar to Example 1, except that the precursor Dv50 of the first positive electrode active material A is 13 μm, and the precursor Dv50 of the second positive electrode active material B is 2 μm. The first positive electrode active material A and the second positive electrode active material B are mixed at a mass ratio of 7:3.

[0193] Example 14

[0194] Similar to Example 1, except that in the preparation of the first positive electrode active material A in 3), lithium hydroxide, the precursor of the first positive electrode active material A, tungsten trioxide and zirconium oxide are in a molar ratio of 1.03:0.994:0.002:0.004, and the tungsten doping amount is 4000ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0195] Example 15

[0196] Similar to Example 1, except that in the preparation of the first positive electrode active material A in 3), lithium hydroxide, the precursor of the first positive electrode active material A, tungsten trioxide, and zirconium oxide are in a molar ratio of 1.03:0.9955:0.0005:0.004, and the tungsten doping amount is 1000 ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0197] Example 16

[0198] Similar to Example 1, except that in the preparation of the second positive electrode active material B in 4), lithium hydroxide, the precursor of the second positive electrode active material B, strontium carbonate, and zirconium oxide are in a molar ratio of 1.03:0.99:0.006:0.004, and the strontium doping amount is 6000ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0199] Example 17

[0200] Similar to Example 1, except that in the preparation of the second positive electrode active material B in 4), lithium hydroxide, the precursor of the second positive electrode active material B, strontium carbonate, and zirconium oxide are in a molar ratio of 1.03:0.992:0.004:0.004, and the strontium doping amount is 4000 ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0201] Example 18

[0202] Similar to Example 1, except that in the preparation of the second positive electrode active material B in 4), lithium hydroxide, the precursor of the second positive electrode active material B, strontium carbonate, and zirconium oxide are in a molar ratio of 1.03:0.995:0.001:0.004, and the strontium doping amount is 1000 ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0203] Example 19

[0204] Same as Example 1, except that in the preparation of the second positive electrode active material B in 4), lithium hydroxide, the precursor of the second positive electrode active material B, strontium carbonate, and zirconium oxide are in a molar ratio of 1.03:0.9955:0.0005:0.004, and the strontium doping amount is 500 ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0205] Example 20

[0206] Same as Example 1, except that: the first positive electrode active material A and the second positive electrode active material B are mixed at a mass ratio of 1:3.

[0207] Comparative Example 1

[0208] Similar to Example 1, except that in 3) the preparation of the first positive electrode active material A, lithium hydroxide, the precursor of the first positive electrode active material A, and zirconium oxide are in a molar ratio of 1.03:0.996:0.004. In 4) the preparation of the second positive electrode active material B, lithium hydroxide, the precursor of the second positive electrode active material B, and zirconium oxide are in a molar ratio of 1.03:0.996:0.004.

[0209] II. Testing of relevant parameters

[0210] (1) Particle size test

[0211] The particle size of the positive electrode active material was determined according to GB / T 19077.1-2016 / ISO 13320:2009 (Laser diffraction method for particle size distribution). A clean beaker was prepared, and an appropriate amount of the above-mentioned positive electrode active material was added, along with an appropriate amount of pure water. The mixture was sonicated at 120W / 5min to ensure complete dispersion of the material powder in the water. The solution was then poured into the sample column of a laser particle size analyzer (Malvin, model: Mastersizer3000) and circulated with the solution to the test optical path system. Under laser beam irradiation, the particle size distribution characteristics (opause level: 8-12%) were obtained by receiving and measuring the energy distribution of the scattered light. The corresponding values ​​of Dv1, Dv3, Dv5, Dv10, Dv50, and Dv90 were read.

[0212] Furthermore, based on the above testing process, the positive electrode active material was measured under pressure of 1 ton of weight (i.e., under pressure of 1 ton of weight on a fixed area of ​​1.33 cm²). 2 Dv1', Dv3', and Dv5' after pressurization for 30 seconds.

[0213] The results are shown in Table 1.

[0214] (2) Electrochemically active specific surface area test

[0215] The electrochemically active specific surface area was measured using cyclic voltammetry. An electrochemical workstation (VMP3) was used, and a button cell was assembled using the test material. The CV of the electroactive probe was scanned four times at four scan rates: 1 / 0.5 / 0.3 / 0.1 mV / s. According to the Randles-Sevcik equation: Ip = 2.69 × 10⁻⁶ mV / s. 5 n 3 / 2 AcD 1 / 2 v 1 / 2 By combining the peak current Ip, diffusion coefficient D, scan rate v, electron transfer number n (which is 1) and concentration c (which is 50 mmol / L) from the test, the electrochemically active specific surface area of ​​the material to be tested can be obtained.

[0216] The results are shown in Table 1.

[0217] (3) Compaction density test

[0218] A certain amount of powder is placed into a compaction mold, and then the mold is placed on a compaction density instrument. A pressure of 5 tons is applied (the compaction area is 1.33 cm²). 2 The thickness of the powder under pressure (the thickness after depressurization) is read on the equipment, and the compaction density is calculated using ρ = m / v.

[0219] The results are shown in Table 1.

[0220] III. Battery Performance Testing

[0221] (1) Initial capacity and first-efficiency test of button cell

[0222] At 2.8–4.3V, the button cell is charged at 0.1C to 4.3V, and then charged at 4.3V at a constant voltage until the current is ≤0.05mA. After resting for 2 minutes, the charging capacity at this time is recorded as C0. Then, it is discharged at 0.1C to 2.8V. The discharge capacity at this time is the initial specific capacity and is recorded as D0.

[0223] The initial effect is calculated as D0 / C0*100%.

[0224] The results are shown in Table 2.

[0225] (2) Initial capacitance test

[0226] Under constant temperature of 25℃, let stand for 5 minutes, discharge at 1 / 3C to 2.8V, let stand for 5 minutes, charge at 1 / 3C to 4.25V, then charge at 4.25V at constant voltage until the current is ≤0.05C, let stand for 5 minutes, and then discharge at 1 / 3C to 2.8V. The discharge capacity at this time is the initial specific capacity, denoted as D0.

[0227] The results are shown in Table 2.

[0228] (3) Full cell capacity retention rate at 25℃

[0229] At 25℃, the capacitor was charged to 4.25V with a constant current of 1C, then charged at a constant voltage of 4.25V until the current dropped to 0.05C, and finally discharged to 2.8V with a constant current of 1C. The first-cycle discharge specific capacity (C) was obtained. d1 Repeat this charge-discharge cycle until the 300th cycle. The discharge specific capacity of the lithium-ion battery after n cycles is denoted as C. dn Capacity retention rate = discharge specific capacity after n cycles (C dn ) / First-cycle discharge specific capacity (C d1 ).

[0230] The results are shown in Table 2.

[0231] (4) Full cell capacity retention rate at 45℃

[0232] At 45℃, the capacitor was charged to 4.25V with a constant current of 1C, then charged at a constant voltage of 4.25V until the current dropped to 0.05C, and finally discharged to 2.8V with a constant current of 1C. The first-cycle discharge specific capacity (C) was obtained. d1 Repeat this charge-discharge cycle until the 300th cycle. The discharge specific capacity of the lithium-ion battery after n cycles is denoted as C. dn Capacity retention rate = discharge specific capacity after n cycles (C dn ) / First-cycle discharge specific capacity (C d1 ).

[0233] The results are shown in Table 2.

[0234] (5) Full battery gas expansion test at 70°C

[0235] Full cells at 100% State of Charge (SOC) were stored at 70°C. The open-circuit voltage (OCV) and internal resistance (IMP) of the cells were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. Every 48 hours of storage, the full cells were removed, allowed to stand for 1 hour, and then OCV and IMP were tested. After cooling to room temperature, the cell volume was measured using the displacement method. The displacement method involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion from the dial readings, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the process, the weight F2 of the battery cell is measured at this time, and the buoyancy F_buoyancy of the battery cell is F1-F2. Then, according to Archimedes' principle F_buoyancy = ρgV_displaced, the volume of the battery cell V = (F1-F2) / ρg is calculated.

[0236] After each volume test, the battery cell is recharged with a constant current of 1C to 4.25V, and then charged with a constant voltage of 4.25V until the current drops to 0.05C. After the recharge is completed, the cell is put into the furnace for further testing.

[0237] After 30 days of storage, the cell volume is measured, and the increase in cell volume after storage is calculated relative to the cell volume before storage, i.e., the gas production.

[0238] The results are shown in Table 2.

[0239] Table 1. Composition and related parameters of the positive electrode active materials of Examples 1-20 and Comparative Example 1

[0240]

[0241] 1 SPAN is (Dv90-Dv10) / Dv50.

[0242] 2 K is ΔDv1 / Dv1*0.01+ΔDv3 / Dv3*0.03+ΔDv5 / Dv5*0.05.

[0243] Table 2 shows the performance test results of the secondary batteries in Examples 1-20 and Comparative Example 1.

[0244]

[0245] As can be seen from the results in Tables 1 and 2, compared with Comparative Example 1, the positive electrode active material of this application improves the structural stability of the positive electrode active material by using M1, M2, M3 and M4 elements for doping, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active material. In particular, by using M1 (i.e. W, Nb or Mo) element doping, the grains of the first positive electrode active material A tend to be radially distributed. At the same time, M1 element is enriched at the grain boundaries, which improves the compressive strength of the first positive electrode active material A and reduces cracking. Furthermore, by using M2 (i.e. Sr, Y or V) element doping with a fluxing effect, the structural stability of the second positive electrode active material B is improved and the particle size is increased, thereby greatly improving the cycle performance and safety performance of the secondary battery made from this positive electrode active material.

[0246] Compared with Example 20, the positive electrode active material in other embodiments of this application has high interparticle filling degree, good dispersibility, and high compaction density, thereby making the secondary battery prepared therefrom have a higher energy density.

[0247] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes a first positive electrode active material A and a second positive electrode active material B. Among them, the chemical formula of the first positive electrode active material A is Li a1 [Ni x1 Co y1 Mn z1 M1 b1 M3 c1 O2, where 0 < x1 < 1, 0 ≤ y1 < 0.5, 0 ≤ z1 < 0.5, 0.9 < a1 < 1.2, 0 < b1 < 0.2, 0 < c1 < 0.2, x1 + y1 + z1 + b1 + c1 = 1, where M1 includes at least one of W, Nb, and Mo, and M3 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co; the chemical formula of the second positive electrode active material B is Li a2 [Ni x2 Co y2 Mn z2 M2 b2 M4 C2 O2, where 0 < x2 < 1, 0 ≤ y2 < 0.5, 0 ≤ z2 < 0.5, 0.9 < a2 < 1.2, 0 < b2 < 0.2, 0 < c2 < 0.2, x2 + y2 + z2 + b2 + c2 = 1, where M2 includes at least one of Sr, Y, and V, and M4 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co.

2. The positive electrode active material according to claim 1, characterized in that, The weight ratio of the first positive electrode active material A to the second positive electrode active material B is 10:1 to 1:

1.

3. The positive electrode active material according to claim 2, characterized in that, The weight ratio of the first positive electrode active material A and the second positive electrode active material B is 9:1-3:

2.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The positive electrode active material satisfies the following formula: K=ΔDv1 / Dv1*0.01+ΔDv3 / Dv3*0.03+ΔDv5 / Dv5*0.05, And K≤7%, wherein ΔDv1, ΔDv3, and ΔDv5 are the differences between Dv1, Dv3, and Dv5 of the positive electrode active material and Dv1', Dv3', and Dv5' of the positive electrode active material after being pressurized with 1 ton of weight.

5. The positive electrode active material according to claim 4, characterized in that, K≤5%。 6. The positive electrode active material according to any one of claims 1-3, characterized in that, The specific surface area of ​​the positive electrode active material is 1-8 cm². 2 / g.

7. The positive electrode active material according to claim 6, characterized in that, The electrochemical active surface area of ​​the positive electrode material is 2-6 cm². 2 / g.

8. The positive electrode active material according to any one of claims 1-3, characterized in that, The compaction density of the positive electrode active material under 5 tons of pressure is 3.4-4.0 g / cm³. 3 .

9. The positive electrode active material according to claim 8, characterized in that, The compaction density of the positive electrode active material under 5 tons of pressure is 3.7-3.9 g / cm³. 3 .

10. The positive electrode active material according to any one of claims 1-3, characterized in that, The amount of M1 in the first positive electrode active material A is 500-8000 ppm, and the amount of M3 is 1000-20000 ppm.

11. The positive electrode active material according to claim 10, characterized in that, The amount of M1 in the first positive electrode active material A is 1000-4000 ppm.

12. The positive electrode active material according to claim 10, characterized in that, The amount of M3 in the first positive electrode active material A is 3000-15000 ppm.

13. The positive electrode active material according to any one of claims 1-3, characterized in that, The amount of M2 in the second positive electrode active material B is 500-8000 ppm, and the amount of M4 is 1000-20000 ppm.

14. The positive electrode active material according to claim 13, characterized in that, The amount of M2 in the second positive electrode active material B is 1000-4000 ppm.

15. The positive electrode active material according to claim 13, characterized in that, The amount of M4 in the second positive electrode active material B is 3000-15000 ppm.

16. The positive electrode active material according to any one of claims 1-3, characterized in that, The molar ratio of M1 to M3 in the first positive electrode active material A is 1:80-4:

1.

17. The positive electrode active material according to claim 16, characterized in that, The molar ratio of M1 to M3 in the first positive electrode active material A is 1:30-3:

4.

18. The positive electrode active material according to any one of claims 1-3, characterized in that, The molar ratio of M2 to M4 in the second positive electrode active material B is 1:40-8:

1.

19. The positive electrode active material according to claim 18, characterized in that, The molar ratio of M2 to M4 in the second positive electrode active material B is 1:20-3:

2.

20. The positive electrode active material according to any one of claims 1-3, characterized in that, The first positive electrode active material A has a Dv50 of 7-15 μm and a (Dv90-Dv10) / Dv50 ratio of 0.5-1.5; the second positive electrode active material B has a Dv50 of 2-4 μm and a (Dv90-Dv10) / Dv50 ratio of 0.5-1.

5.

21. The positive electrode active material according to claim 20, characterized in that, The ratio of (Dv90-Dv10) / Dv50 of the first positive electrode active material A is 1.0-1.

45.

22. The positive electrode active material according to claim 20, characterized in that, The ratio of (Dv90-Dv10) / Dv50 of the second positive electrode active material B is 1.0-1.

45.

23. A method for preparing a positive electrode active material, characterized in that, Includes the following steps: S1) Preparation of the first positive electrode active material A: Lithium salt, the precursor of the first positive electrode active material A, the compound containing element M1, and the compound containing element M3 are mixed in the molar ratio and sintered. S2) Preparation of the second positive electrode active material B: Lithium salt, precursor of the second positive electrode active material B, compound containing element M2, and compound containing element M4 are mixed in the molar ratio and sintered. S3) The first positive electrode active material A and the second positive electrode active material B are mixed to obtain the positive electrode active material. Among them, the chemical formula of the first positive electrode active material A is Li a1 [Ni x1 Co y1 Mn z1 M1 b1 M3 c1 O2, where 0 < x1 < 1, 0 ≤ y1 < 0.5, 0 ≤ z1 < 0.5, 0.9 < a1 < 1.2, 0 < b1 < 0.2, 0 < c1 < 0.2, x1 + y1 + z1 + b1 + c1 = 1, where M1 includes at least one of W, Nb, and Mo, and M3 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co The chemical formula of the second positive electrode active material B is Li a2 [Ni x2 Co y2 Mn z2 M2 b2 M4 C2 O2, where 0 < x2 < 1, 0 ≤ y2 < 0.5, 0 ≤ z2 < 0.5, 0.9 < a2 < 1.2, 0 < b2 < 0.2, 0 < c2 < 0.2, x2 + y2 + z2 + b2 + c2 = 1, where M2 includes at least one of Sr, Y, and V, and M4 includes at least one of Zr, Ti, Mg, Al, Sb, B, and Co.

24. The method for preparing the positive electrode active material according to claim 23, characterized in that, In step S3), the first positive electrode active material A and the second positive electrode active material B are mixed in a weight ratio of 10:1 to 1:

1.

25. The method for preparing the positive electrode active material according to claim 24, characterized in that, In step S3), the first positive electrode active material A and the second positive electrode active material B are mixed in a weight ratio of 9:1-3:

2.

26. The method for preparing the positive electrode active material according to any one of claims 23-25, characterized in that, The compound containing element M1 is one or more of oxides, carbonates, or hydroxides containing element M1, wherein element M1 is one of W, Nb, or Mo; the compound containing element M3 is one or more of oxides, carbonates, or hydroxides containing element M3, wherein element M3 is one of Zr, Ti, Mg, Al, Sb, B, or Co; the compound containing element M2 is one or more of oxides, carbonates, or hydroxides containing element M2, wherein element M2 is one of Sr, Y, or V; the compound containing element M4 is one or more of oxides, carbonates, or hydroxides containing element M4, wherein element M4 is one of Zr, Ti, Mg, Al, Sb, B, or Co.

27. The method for preparing the positive electrode active material according to any one of claims 23-25, characterized in that, The Dv50 of the precursor of the first positive electrode active material A is 7-15 μm; the Dv50 of the precursor of the second positive electrode active material B is 2-4 μm.

28. The method for preparing the positive electrode active material according to any one of claims 23-25, characterized in that, In step S1), the sintering temperature is 700-850℃, the sintering time is 10-20 h, and the sintering atmosphere is oxygen or air.

29. The method for preparing the positive electrode active material according to claim 28, characterized in that, In step S1), the sintering temperature is 700-800℃.

30. The method for preparing the positive electrode active material according to any one of claims 23-25, characterized in that, In step S2), the sintering temperature is 750-1000℃, the sintering time is 10-20 h, and the sintering atmosphere is oxygen or air.

31. The method for preparing the positive electrode active material according to claim 30, characterized in that, In step S2), the sintering temperature is 750-850℃.

32. A positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, said positive electrode film layer comprising the positive electrode active material according to any one of claims 1-22 or the positive electrode active material prepared by any one of claims 23-31, and wherein the coating amount of the positive electrode sheet is less than 0.025 g / cm³. 2 The compaction density of the positive electrode sheet is ≥3.3 g / cm³. 3 .

33. The positive electrode sheet as described in claim 32, characterized in that, The compacted density of the positive electrode sheet is ≥3.4 g / cm³. 3 .

34. A secondary battery, characterized in that, The positive electrode active material includes any one of claims 1-22, or a positive electrode active material prepared by any one of claims 23-31, or a positive electrode sheet as described in claim 32 or 33.

35. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 34.

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