Positive electrode active materials and their preparation methods, positive electrode sheets, secondary batteries and electrical devices

Abstract

This application provides a positive electrode active material, which satisfies the following formula: -1.912α 2 +2.207α+0.002β 2 -0.115β + 0.358γ + 0.123σ = K, and 0.34 ≤ K ≤ 0.66, optionally, 0.42 ≤ K ≤ 0.54, where α is the specific surface area of ​​the positive electrode active material, expressed in m². 2 / g; β is the Dv99 of the positive electrode active material, expressed in μm; γ is the value of the positive electrode active material at 1000kg / 1.33cm 2 The compaction density of powder under pressure, expressed in g / cm³ 3 σ is calculated as (Dv90-Dv10) / Dv50 of the positive electrode active material particles. The positive electrode active material of this application has high compaction density and improved structural stability, which can effectively improve the energy density of the battery and enhance its cycle performance and safety performance. This application also provides a positive electrode sheet including the positive electrode active material, a secondary battery, and a power-consuming device.

Description

Technical Field

[0001] This application relates to the field of 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. Lithium ions in the cathode material structure are the sole source of energy for the normal operation of a lithium-ion battery; therefore, the energy density of the cathode material largely determines the overall energy density of the battery. 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 a significant improvement in energy density compared to other materials, increasing nickel content leads to severe capacity decay and layered structure damage 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 having 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, the first aspect of this application provides a positive electrode active material, which satisfies the following formula:

[0006] -1.912α 2 +2.207α+0.002β 2 -0.115β+0.358γ+0.123σ=K,

[0007] And 0.34≤K≤0.66, optionally, 0.42≤K≤0.54.

[0008] Wherein, α is the specific surface area of ​​the positive electrode active material, expressed in m... 2 / g; β is the Dv99 of the positive electrode active material, expressed in μm; γ is the value of the positive electrode active material at 1000kg / 1.33cm 2 The compaction density of powder under pressure, expressed in g / cm³ 3 σ is the (Dv90-Dv10) / Dv50 of the positive electrode active material particles.

[0009] Therefore, compared with the prior art, this application has at least the following beneficial effects: the positive electrode active material of this application not only has a high interparticle filling degree and a high compaction 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, reducing oxygen release, thereby improving the cycle performance and safety performance of the battery.

[0010] In any embodiment, the positive electrode active material includes a first positive electrode active material A and / or a second positive electrode active material B.

[0011] The first positive electrode active material A is a polycrystalline material with the chemical formula LiNi. x1 Co y1 Mn z1 M1 a1 M2 b1 O 2-b1 Where 0.80≤x1≤1.0, 0≤y1≤0.20, 0≤z1≤0.02, 0≤a1≤0.02, x1+y1+z1+a1=1, 0≤b1≤0.02, and M1 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca and Ce, and M2 is selected from at least one of N, F, S and Cl; the second positive electrode active material B is a quasi-single crystal material with the chemical formula LiNi. x2 Co y2 Mn z2 M3 a2 M4 b2 O 2-b2 Wherein, 0.80≤x²≤1.0, 0≤y²≤0.20, 0≤z²≤0.02, 0≤a²≤0.02, x²+y²+z²+a²=1, 0≤b²≤0.02, and M3 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, and Ce, and M4 is selected from at least one of N, F, S, and Cl. When the positive electrode active material has the above-mentioned composition, the positive electrode active material has a high compaction density, which can effectively improve the energy density of the battery, and also has improved structural stability, which can effectively improve the cycle performance and safety performance of the battery.

[0012] In any embodiment, the weight ratio of the first positive electrode active material A to the second positive electrode active material B is 6:4-8:2, optionally 6.5:3.5-7.5:2.5. When the weight ratio of the first positive electrode active material A to the second positive electrode active material B is within the above range, the positive electrode active material has a high compaction density, which can effectively improve the energy density of the battery.

[0013] In any embodiment, the specific surface area of ​​the positive electrode active material is 0.3-0.85 m². 2 / g, can be selected as 0.5-0.7m 2 / g. This helps reduce 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.

[0014] In any embodiment, the Dv99 of the positive electrode active material is 6.0-30.0 μm, and optionally 7.0-25.0 μm. This increases the specific capacity of the positive electrode active material, thereby improving the energy density of the battery.

[0015] In any embodiment, the positive electrode active material is at 1000 kg / 1.33 cm⁻¹. 2 The compacted density of the powder under pressure is 2.9-3.5 g / cm³. 3 The concentration can be selected as 3.1-3.3 g / cm³. 3 This allows for an increase in the energy density of the battery.

[0016] In any embodiment, the (Dv90-Dv10) / Dv50 ratio of the positive electrode active material is 1.35-2.3, and can be optionally 1.9-2.25. Therefore, 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 and thus improving battery performance.

[0017] In any embodiment, the Dv50 of the positive electrode active material is 5.5-13 μm, optionally 6.0-8.8 μm. This increases the specific capacity of the positive electrode active material, thereby improving the energy density of the battery.

[0018] In any embodiment, the molar ratio of M1 to M2 in the first positive electrode active material A is 0.5-7:1, and can be selected as 2-4:1. This improves the structural stability of the positive electrode active material, 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.

[0019] In any embodiment, the molar ratio of M3 to M4 in the second positive electrode active material B is 0.5-7:1, and can be selected as 2-4:1. This improves the structural stability of the positive electrode active material, 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 specific surface area of ​​the first positive electrode active material A is 0.2-0.8 m². 2 / g; and / or, the specific surface area of ​​the second positive electrode active material B is 0.6-1.3m². 2 / g. This reduces the occurrence of side reactions, thereby improving the battery's cycle performance and safety.

[0021] In any embodiment, the Dv99 of the first positive electrode active material A is 13-30 μm; and / or, the Dv99 of the second positive electrode active material B is 6-23 μm. This increases the specific capacity of the positive electrode active material, thereby improving the energy density of the battery.

[0022] In any embodiment, the first positive electrode active material A is at 1000 kg / 1.33 cm⁻¹. 2 The compacted density of the powder under pressure is 2.7-3.3 g / cm³. 3 ; and / or, the second positive electrode active material B at 1000 kg / 1.33 cm 2 The compacted density of the powder under pressure is 2.2-3.2 g / cm³. 3 Therefore, the positive electrode active material has a high compaction density, which can improve the energy density of the battery.

[0023] In any embodiment, the (Dv90-Dv10) / Dv50 of the first positive electrode active material A is 0.4-1.8; and / or, the (Dv90-Dv10) / Dv50 of the second positive electrode active material B is 1.0-1.75. Therefore, the positive electrode active material particles are continuously distributed, have good dispersibility, and high interparticle filling density, which is beneficial for improving the processing performance of the positive electrode active material and improving battery performance.

[0024] In any embodiment, the Dv50 of the first positive electrode active material A is 6-15 μm, optionally 8.5-10.5 μm; and / or, the Dv50 of the second positive electrode active material B is 2-6 μm, optionally 2.5-4.0 μm. This improves the energy density of the battery.

[0025] A second aspect of this application provides a method for preparing a positive electrode active material, comprising mixing a lithium salt, a precursor of the positive electrode active material, and an additive containing modifying elements, followed by sintering to obtain the positive electrode active material.

[0026] The positive electrode active material satisfies the following formula:

[0027] -1.912α 2 +2.207α+0.002β 2 -0.115β+0.358γ+0.123σ=K,

[0028] And 0.34≤K≤0.66, optionally, 0.42≤K≤0.54.

[0029] Wherein, α is the specific surface area of ​​the positive electrode active material, expressed in m... 2 / g; β is the Dv99 of the positive electrode active material, expressed in μm; γ is the value of the positive electrode active material at 1000kg / 1.33cm 2 The compaction density of powder under pressure, expressed in g / cm³ 3 σ is the (Dv90-Dv10) / Dv50 of the particles of the positive electrode active material.

[0030] Therefore, the positive electrode active material prepared by the above method not only has high interparticle filling degree, good dispersibility and high compaction 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, thereby improving the cycle performance and safety performance of the battery.

[0031] In any implementation, the method includes:

[0032] S1) Preparation of the first positive electrode active material A: Lithium salt, the precursor of the first positive electrode active material A, a compound containing element M1, and a compound containing element M2 are mixed and sintered; and / or

[0033] S2) Preparation of the second positive electrode active material B: Lithium salt, precursor of the second positive electrode active material B, compound containing element M3, and compound containing element M4 are mixed and sintered;

[0034] When the method includes steps S1) and S2), the method further includes the following steps:

[0035] 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.

[0036] The first positive electrode active material A is a polycrystalline material with the chemical formula LiNi. x1 Co y1 Mn z1 M1 a1 M2 b1 O 2-b1Where 0.80≤x1≤1.0, 0≤y1≤0.20, 0≤z1≤0.02, 0≤a1≤0.02, x1+y1+z1+a1=1, 0≤b1≤0.02, and M1 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca and Ce, and M2 is selected from at least one of N, F, S and Cl; the second positive electrode active material B is a quasi-single crystal material with the chemical formula LiNi. x2 Co y2 Mn z2 M3 a2 M4 b2 O 2-b2 Where 0.80≤x²≤1.0, 0≤y²≤0.20, 0≤z²≤0.02, 0≤a²≤0.02, x²+y²+z²+a²=1, 0≤b²≤0.02, and M3 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, and Ce, and M4 is selected from at least one of N, F, S, and Cl. This allows for the attainment of high energy density and improved cycle performance and safety.

[0037] In any embodiment, 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 6:4-8:2, optionally 6.5:3.5-7.5:2.5. This yields a positive electrode active material with high compaction density, effectively improving the energy density of the battery.

[0038] In any embodiment, the compound containing element M1 is one or more of an oxide, carbonate, hydroxide, nitride, fluoride, sulfide, or chloride containing element M1, wherein element M1 is one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, or Ce; the compound containing element M2 is a metal salt containing element M2, wherein element M2 is one of N, F, S, or Cl; the compound containing element M3 is one or more of an oxide, carbonate, hydroxide, nitride, fluoride, sulfide, or chloride containing element M3, wherein element M3 is one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, or Ce; the compound containing element M4 is a metal salt containing element M4, wherein element M4 is one of N, F, S, or Cl. Therefore, the structural stability of the positive electrode active material can be improved, thereby improving the performance of the positive electrode active material.

[0039] In any embodiment, the Dv50 of the precursor of the first positive electrode active material A is 6-15 μm, optionally 8.5-10.5 μm; the Dv50 of the precursor of the second positive electrode active material B is 2-6 μm, optionally 2.5-4.0 μm. Thus, a positive electrode active material with the desired particle size distribution can be obtained, resulting in high interparticle filling density, good dispersibility, high compaction density, and good material processing performance.

[0040] In any embodiment, lithium salt, the precursor of the first positive electrode active material A, the compound containing element M1, and the compound containing element M2 are mixed in a molar ratio of 1.05:1:0-0.02:0-0.02; lithium salt, the precursor of the second positive electrode active material A, the compound containing element M3, and the compound containing element M4 are mixed in a molar ratio of 1.05:1:0-0.02:0-0.02. This improves the structural stability of the positive electrode active material, thereby enhancing the cycle performance and safety performance of the battery.

[0041] In any embodiment, in step S1), the sintering temperature is 700-850℃, the sintering time is 10-20h, and the sintering atmosphere is oxygen. This allows for the uniform distribution of elements M1 and M2, improving the structural stability of the first positive electrode active material, thereby enhancing the stability of the positive electrode active material, effectively reducing side reactions between the electrolyte and the positive electrode active material, reducing oxygen release, and thus improving the battery's cycle performance and safety performance.

[0042] In any embodiment, in step S2), the sintering temperature is 750-900℃, the sintering time is 10-20h, and the sintering atmosphere is oxygen. This enables the uniform distribution of M3 and M4 elements, improves the structural stability of the second positive electrode active material, and thus improves the stability of the positive electrode active material. It effectively reduces side reactions between the electrolyte and the positive electrode active material, reduces oxygen release, and thereby improves the cycle performance and safety performance of the battery.

[0043] In any embodiment, in steps S1) and S2), the oxygen concentration in the oxygen atmosphere is 80% or more, optionally 90% or more, or optionally 99.9% or more. This improves the stability of the positive electrode active material, thereby enhancing the battery's cycle performance and safety performance.

[0044] A third aspect of this application provides a positive electrode sheet, the 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, the positive electrode film layer 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.

[0045] In any embodiment, when the elongation of the positive electrode sheet is less than 0.8%, the compaction density of the positive electrode sheet is ≥3.6 g / cm³. 3 Preferably, it is ≥3.7g / cm³. 3 The positive electrode has a high compaction density, thereby increasing the energy density of the battery.

[0046] 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.

[0047] A fifth aspect of this application provides an electrical device comprising a secondary battery selected from the fourth aspect of this application.

[0048] 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

[0049] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0050] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0051] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0052] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0053] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0054] 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.

[0055] Explanation of reference numerals in the attached figures:

[0056] 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

[0057] 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 for a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0058] 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.

[0059] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0060] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0061] 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.

[0062] 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.

[0063] 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).

[0064] 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.

[0065] High-nickel ternary cathode materials possess an α-NaFeO2-type layered structure, belonging to the R-3m space group. They are solid solution oxides obtained by replacing some of the Ni element in LiNiO2 with metals such as Co and Mn. These materials combine the synergistic effects of Ni, Co, and Mn. Ni effectively increases the specific capacity and energy density of the material; Co exhibits 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+ To maintain charge balance, oxygen is released from the material, leading to structural damage and reduced thermal stability; 3) Due to Li + Diffusion is influenced by kinetic factors, leading to increased Li extraction and reduction of transition metal ions. To maintain electroneutrality, the material readily forms new phases and pores on its surface, resulting in structural instability in high-nickel materials. Overcharge conditions accelerate this instability, as it is accompanied by partial structural transformations to spinel-type and NiO-type rock salt phases, and the generation of oxygen, posing certain safety risks to the battery. Currently, surface coating and ion doping are commonly used to improve the electrochemical performance of materials. However, further improvements to high-nickel ternary cathode active materials are still desired to obtain cathode active materials that combine high energy density with excellent cycle performance and safety.

[0066] To address the aforementioned problems, the first aspect of this application provides a positive electrode active material, wherein the positive electrode active material satisfies the following formula:

[0067] -1.912α 2 +2.207α+0.002β 2 -0.115β+0.358γ+0.123σ=K,

[0068] And 0.34≤K≤0.66, optionally, 0.42≤K≤0.54.

[0069] Wherein, α is the specific surface area of ​​the positive electrode active material, expressed in m... 2 / g; β is the Dv99 of the positive electrode active material, expressed in μm; γ is the value of the positive electrode active material at 1000kg / 1.33cm 2 The compaction density of powder under pressure, expressed in g / cm³ 3 σ is the (Dv90-Dv10) / Dv50 of the positive electrode active material particles.

[0070] Although the mechanism is not yet clear, the applicant unexpectedly discovered that the positive electrode active material of this application not only has a high interparticle filling degree and a high compaction density, which can effectively improve the energy density of the battery, but also has improved structural stability, effectively preventing the electrolyte from undergoing side reactions on the surface of the positive electrode active material, thereby improving the cycle performance and safety performance of the battery.

[0071] In some embodiments, the positive electrode active material includes a first positive electrode active material A and / or a second positive electrode active material B.

[0072] The first positive electrode active material A is a polycrystalline material with the chemical formula LiNi. x1 Co y1 Mn z1 M1 a1 M2 b1 O 2-b1 Where 0.80≤x1≤1.0, 0≤y1≤0.20, 0≤z1≤0.02, 0≤a1≤0.02, x1+y1+z1+a1=1, 0≤b1≤0.02, and M1 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca and Ce, and M2 is selected from at least one of N, F, S and Cl; the second positive electrode active material B is a quasi-single crystal material with the chemical formula LiNi. x2 Co y2 Mn z2 M3 a2 M4 b2 O 2-b2 Wherein, 0.80≤x²≤1.0, 0≤y²≤0.20, 0≤z²≤0.02, 0≤a²≤0.02, x²+y²+z²+a²=1, 0≤b²≤0.02, and M3 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, and Ce, and M4 is selected from at least one of N, F, S, and Cl. When the positive electrode active material has the above-mentioned composition, the positive electrode active material has a high compaction density, which can effectively improve the energy density of the battery, and also has improved structural stability, which can effectively improve the cycle performance and safety performance of the battery.

[0073] In this application, the first positive electrode active material A can be a polycrystalline material, that is, a secondary particle formed by multiple primary particles agglomerated together to form spherical or near-spherical particles; the second positive electrode active material B can be a near-single crystal material, that is, a primary particle in the form of a single particle without obvious agglomeration, and with a size greater than 1 μm.

[0074] In some embodiments, the weight ratio of the first positive electrode active material A to the second positive electrode active material B is 6:4-8:2, optionally 6.5:3.5-7.5:2.5. When the weight ratio of the first positive electrode active material A to the second positive electrode active material B is within the above range, the positive electrode active material has a high compaction density, which can effectively improve the energy density of the battery.

[0075] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.3-0.85 m². 2 / g, can be selected as 0.5-0.7m 2 / g. When the specific surface area of ​​the positive electrode active material is within the above range, it is beneficial to reduce the side reactions between the electrolyte and the positive electrode active material, reduce oxygen release, and thus improve the cycle performance and safety performance of the battery.

[0076] In some embodiments, the Dv99 of the positive electrode active material is 6.0-30.0 μm, optionally 7.0-25.0 μm. When the Dv99 of the positive electrode active material is within the above range, the positive electrode active material has a high specific capacity, thereby improving the energy density of the battery.

[0077] In some embodiments, the positive electrode active material is at 1000 kg / 1.33 cm⁻¹. 2 The compacted density of the powder under pressure is 2.9-3.5 g / cm³. 3 The concentration can be selected as 3.1-3.3 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 / T 24533-2009.

[0078] In some embodiments, the (Dv90-Dv10) / Dv50 ratio of the positive electrode active material is 1.35-2.3, and optionally 1.9-2.25. 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.

[0079] In this application, Dv10, Dv50, Dv90, and Dv99 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, Dv90 is the particle size corresponding to a cumulative volume percentage of 90% of the sample, and Dv99 is the particle size corresponding to a cumulative volume percentage of 99% of the sample.

[0080] In some embodiments, the Dv50 of the positive electrode active material is 5.5-13 μm, optionally 6.0-8.8 μm. When the Dv50 of the positive electrode active material is within the above range, the specific capacity of the positive electrode active material can be increased, thereby increasing the energy density of the battery.

[0081] In some embodiments, the molar ratio of M1 to M2 in the first positive electrode active material A is 0.5-7:1, and can be selected as 2-4:1. By adjusting the molar ratio of M1 to M2 in the first positive electrode active material A, the structural stability of the first positive electrode active material A can be effectively improved, thereby improving the structural stability of the 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.

[0082] In some embodiments, the molar ratio of M3 to M4 in the second positive electrode active material B is 0.5-7:1, and can be selected as 2-4:1. By adjusting the molar ratio of M3 to M4 in the second positive electrode active material B, the structural stability of the second positive electrode active material A can be effectively improved, thereby improving the structural stability of the 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.

[0083] In this application, the amounts of elements M1, M2, M3, and M4 can be measured using detection techniques commonly known in the art for measuring the content of doped elements, such as inductively coupled plasma emission spectroscopy (ICP).

[0084] In some embodiments, the specific surface area of ​​the first positive electrode active material A is 0.2-0.8 m². 2 / g; and / or, the specific surface area of ​​the second positive electrode active material B is 0.6-1.3m². 2 / g. This reduces the occurrence of side reactions, thereby improving the battery's cycle performance and safety. By adjusting the specific surface area of ​​the first positive electrode active material A and / or the specific surface area of ​​the second positive electrode active material B, the positive electrode active materials can have good structural stability, effectively preventing side reactions of the electrolyte on the surface of the positive electrode active materials, thereby improving the battery's cycle performance and safety.

[0085] In some embodiments, the Dv99 of the first positive electrode active material A is 13-30 μm; and / or, the Dv99 of the second positive electrode active material B is 6-23 μm. By adjusting the Dv99 of the first positive electrode active material A and / or the Dv99 of the second positive electrode active material B, the specific capacity of the positive electrode active material can be increased, thereby increasing the energy density of the battery.

[0086] In some embodiments, the first positive electrode active material A is at 1000 kg / 1.33 cm. 2 The compacted density of the powder under pressure is 2.7-3.3 g / cm³. 3 ; and / or, the second positive electrode active material B at 1000 kg / 1.33 cm 2The compacted density of the powder under pressure is 2.2-3.2 g / cm³. 3 By adjusting the compaction density of the first positive electrode active material A and / or the compaction density of the second positive electrode active material B within the aforementioned range, the positive electrode active material can achieve a high compaction density and high interparticle filling degree. This 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 / T 24533-2009.

[0087] In some embodiments, the (Dv90-Dv10) / Dv50 ratio of the first positive electrode active material A is 0.4-1.8; and / or, the (Dv90-Dv10) / Dv50 ratio of the second positive electrode active material B is 1.0-1.75. By adjusting the (Dv90-Dv10) / Dv50 ratio of the first positive electrode active material A and / or the (Dv90-Dv10) / Dv50 ratio of the second positive electrode active material B to the above ranges, the positive electrode active material particles can be continuously distributed, with good dispersibility and high interparticle filling, which is beneficial to improving the processing performance of the positive electrode active material and improving the performance of the battery.

[0088] In some embodiments, the Dv50 of the first positive electrode active material A is 6-15 μm, optionally 8.5-10.5 μm; and / or, the Dv50 of the second positive electrode active material B is 2-6 μm, optionally 2.5-4.0 μm. By adjusting the Dv50 of the first positive electrode active material A and / or the Dv50 of the second positive electrode active material B to the above ranges, the compaction density of the positive electrode active material can be increased, thereby increasing the energy density of the battery.

[0089] A second aspect of this application provides a method for preparing a positive electrode active material, comprising mixing a lithium salt, a precursor of the positive electrode active material, and an additive containing modifying elements, followed by sintering to obtain the positive electrode active material.

[0090] The positive electrode active material satisfies the following formula:

[0091] -1.912α 2 +2.207α+0.002β 2 -0.115β+0.358γ+0.123σ=K,

[0092] And 0.34≤K≤0.66, optionally, 0.42≤K≤0.54.

[0093] Wherein, α is the specific surface area of ​​the positive electrode active material, expressed in m... 2 / g; β is the Dv99 of the positive electrode active material, expressed in μm; γ is the value of the positive electrode active material at 1000kg / 1.33cm 2The compaction density of powder under pressure, expressed in g / cm³ 3 σ is the (Dv90-Dv10) / Dv50 of the particles of the positive electrode active material.

[0094] Therefore, the positive electrode active material prepared by the above method not only has high interparticle filling degree, good dispersibility and high compaction 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, thereby improving the cycle performance and safety performance of the battery.

[0095] In some embodiments, the method includes:

[0096] S1) Preparation of the first positive electrode active material A: Lithium salt, the precursor of the first positive electrode active material A, a compound containing element M1, and a compound containing element M2 are mixed and sintered; and / or

[0097] S2) Preparation of the second positive electrode active material B: Lithium salt, precursor of the second positive electrode active material B, compound containing element M3, and compound containing element M4 are mixed and sintered;

[0098] When the method includes steps S1) and S2), the method further includes the following steps:

[0099] 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.

[0100] The first positive electrode active material A is a polycrystalline material with the chemical formula LiNi. x1 Co y1 Mn z1 M1 a1 M2 b1 O 2-b1 Where 0.80≤x1≤1.0, 0≤y1≤0.20, 0≤z1≤0.02, 0≤a1≤0.02, x1+y1+z1+a1=1, 0≤b1≤0.02, and M1 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca and Ce, and M2 is selected from at least one of N, F, S and Cl; the second positive electrode active material B is a quasi-single crystal material with the chemical formula LiNi. x2 Co y2 Mn z2 M3 a2 M4 b2 O 2-b2Wherein, 0.80≤x²≤1.0, 0≤y²≤0.20, 0≤z²≤0.02, 0≤a²≤0.02, x²+y²+z²+a²=1, 0≤b²≤0.02, and M3 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, and Ce, and M4 is selected from at least one of N, F, S, and Cl. When the positive electrode active material has the above-mentioned composition, the positive electrode active material has a high compaction density, which can effectively improve the energy density of the battery, and also has improved structural stability, which can effectively improve the cycle performance and safety performance of the battery.

[0101] 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 hydroxide co-precipitation. More specifically, the precursor of the first positive electrode active material A can be, but is 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, but is 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.

[0102] In some embodiments, 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 6:4-8:2, optionally 6.5:3.5-7.5:2.5. When the first positive electrode active material A and the second positive electrode active material B are mixed in 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.

[0103] In some embodiments, the compound containing element M1 is one or more of oxides, carbonates, hydroxides, nitrides, fluorides, sulfides, or chlorides containing element M1, wherein element M1 is one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, or Ce; the compound containing element M2 is a metal salt containing element M2, wherein element M2 is one of N, F, S, or Cl; the compound containing element M3 is one or more of oxides, carbonates, hydroxides, nitrides, fluorides, sulfides, or chlorides containing element M3, wherein element M3 is one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca, or Ce; and the compound containing element M4 is a metal salt containing element M4, wherein element M4 is one of N, F, S, or Cl. By selecting the sources of each of the M1, M2, M3 and M4 elements, the structural stability of the positive electrode active material can be improved, thereby improving the performance of the positive electrode active material.

[0104] In some embodiments, the Dv50 of the precursor of the first positive electrode active material A is 6-15 μm, optionally 8.5-10.5 μm; the Dv50 of the precursor of the second positive electrode active material B is 2-6 μm, optionally 2.5-4.0 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.

[0105] In some embodiments, lithium salt, precursor of the first positive electrode active material A, compound containing element M1, and compound containing element M2 are mixed in a molar ratio of 1.05:1:0-0.02:0-0.02; lithium salt, precursor of the second positive electrode active material A, compound containing element M3, and compound containing element M4 are mixed in a molar ratio of 1.05:1:0-0.02:0-0.02.

[0106] In some embodiments, in step S1), the sintering temperature is 700-850°C, the sintering time is 10-20 hours, and the sintering atmosphere is oxygen. By controlling the sintering temperature and sintering time, the M1 and M2 elements can be evenly distributed, improving the structural stability of the first positive electrode active material, thereby improving the stability of the positive electrode active material, effectively reducing side reactions between the electrolyte and the positive electrode active material, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery.

[0107] In some embodiments, in step S2), the sintering temperature is 750-900℃, the sintering time is 10-20h, and the sintering atmosphere is oxygen. By controlling the sintering temperature and sintering time, the M3 and M4 elements can be evenly distributed, improving the structural stability of the second positive electrode active material, thereby improving the stability of the positive electrode active material, effectively reducing side reactions between the electrolyte and the positive electrode active material, reducing oxygen release, and thus improving the cycle performance and safety performance of the battery.

[0108] In some embodiments, in steps S1) and S2), the oxygen concentration in the oxygen atmosphere is 80% or more, optionally 90% or more, or optionally 99.9% or more. By adjusting the oxygen concentration, the stability of the positive electrode active material can be further improved, thereby improving the cycle performance and safety performance of the battery.

[0109] A third aspect of this application provides a positive electrode sheet, the 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, the positive electrode film layer 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.

[0110] In some embodiments, when the elongation of the positive electrode sheet is less than 0.8%, the compaction density of the positive electrode sheet is ≥3.6 g / cm³. 3 Preferably, it is ≥3.7g / cm³. 3 The positive electrode has a high compaction density, thereby increasing the energy density of the battery.

[0111] In this application, the coating amount of the positive electrode sheet is less than 0.025 g / cm³. 2 For example, 0.0175-0.022 g / cm³ 2 .

[0112] 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.

[0113] A fifth aspect of this application provides an electrical device comprising a secondary battery selected from the fourth aspect of this application.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] In one embodiment of this application, a secondary battery is provided.

[0118] 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%.

[0119] [Positive electrode plate]

[0120] 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.

[0121] 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.

[0122] 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.).

[0123] In some embodiments, the positive electrode active material may be the positive electrode active material of the first aspect of this application. The weight percentage 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.

[0124] 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.

[0125] 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.

[0126] 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 The formula for calculating the compaction density is as follows:

[0127] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0128] [Negative electrode plate]

[0129] 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.

[0130] 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.

[0131] 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.).

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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 .

[0137] [Electrolytes]

[0138] 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.

[0139] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] [Isolation membrane]

[0144] 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.

[0145] 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.

[0146] In some embodiments, the thickness of the isolation membrane is 6-40 μm, optionally 12-20 μm.

[0147] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0148] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0159] 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.

[0160] 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.

[0161] Example

[0162] 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.

[0163] Preparation of primary and secondary batteries

[0164] Example 1

[0165] 1. Preparation of positive electrode active materials

[0166] A 2 mol / L metal salt solution was prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.93:0.05:0.02. This metal salt solution, along with 8 mol / L ammonia and 5 mol / L NaOH solution, was then continuously added to a reactor for reaction. The reaction was carried out by controlling the pH 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) for the positive electrode active material was prepared using a hydroxide co-precipitation method. 0.93 Co 0.05 Mn 0.02(OH)2), with a particle size Dv50 of 10 μm;

[0167] Lithium hydroxide, Ni 0.93 Co 0.05 Mn 0.02 (OH)₂, ZrO₂, and ZrF₄ were mixed uniformly in a plow mixer at a molar ratio of 1.05:1:0.005:0.0005. The mixture was then sintered in a kiln at 750℃ for 15 hours in an oxygen atmosphere (99.9% oxygen concentration). After cooling, the mixture was mechanically crushed to obtain the first positive electrode active material A (LiNi). 0.9245 Co 0.05 Mn 0.02 Zr 0.0055 F 0.002 O 1.998 The particle size Dv50 is 10 μm.

[0168] 2. Preparation of button cells

[0169] [Positive Electrode Sheet] The above-obtained positive electrode active material, polyvinylidene fluoride (PVDF), and acetylene black are added to N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry is then coated onto aluminum foil, dried, and cold-pressed to form the positive electrode sheet. The coating amount is 0.01 g / cm³. 2 The compacted density is 3.72 g / cm³. 3 .

[0170]

Negative Electrode

[0171] [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.

[0172]

Isolation Film

[0173] The separator membrane was purchased from Cellgard, model number Cellgard 2400.

[0174] 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.

[0175] 3. Preparation of full cells

[0176] [Positive Electrode Sheet] The positive electrode active material obtained above is mixed evenly with acetylene black and polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) 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 3.72 g / cm³. 3 .

[0177] [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 .

[0178] [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.

[0179]

Separation membrane

[0180] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation. The resulting assembly 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 90.5%.

[0181] Example 2

[0182] The battery was prepared in the same manner as in Example 1, and the positive electrode active material with the composition listed in Table 1 was prepared by a method similar to that used in Example 1. See Tables 1 and 2 for details.

[0183] Example 3

[0184] The battery was prepared in the same manner as in Example 1, and the positive electrode active material was prepared according to the following steps.

[0185] Preparation of positive electrode active materials

[0186] 1) Preparation of the precursor of the first positive electrode active material A

[0187] A 2 mol / L metal salt solution was prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.93:0.05:0.02. This metal salt solution, along with 8 mol / L ammonia and 5 mol / L NaOH solution, was then continuously added to a reactor for reaction. The reaction was carried out by controlling the pH 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. 0.93 Co 0.05 Mn 0.02 (OH)2), with a particle size Dv50 of 10 μm;

[0188] 2) Preparation of the precursor of the second positive electrode active material B

[0189] A 2 mol / L metal salt solution was prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 0.93:0.05:0.02. This metal salt solution, along with 8 mol / L ammonia and 5 mol / L NaOH solution, was then continuously added to a reactor for reaction. The reaction was carried out by controlling the pH 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. 0.93 Co 0.05 Mn 0.02 (OH)2), with a particle size Dv50 of 3 μm.

[0190] 3) Preparation of the first positive electrode active material A

[0191] Lithium hydroxide, Ni 0.93 Co 0.05 Mn 0.02 (OH)₂, ZrO₂, and ZrF₄ were mixed uniformly in a plow mixer at a molar ratio of 1.05:1:0.005:0.0005. The mixture was then sintered in a kiln at 750℃ for 15 hours in an oxygen atmosphere (99.9% oxygen concentration). After cooling, the mixture was mechanically crushed to obtain the first positive electrode active material A (LiNi). 0.9245 Co 0.05 Mn 0.02 Zr 0.0055 F 0.002 O 1.998 The particle size Dv50 is 10 μm.

[0192] 4) Preparation of the second positive electrode active material B

[0193] Lithium hydroxide, Ni 0.93 Co 0.05 Mn0.02 (OH)₂, SrO, and SrF₂ were mixed uniformly in a plow mixer at a molar ratio of 1.05:1:0.0005:0.0005. The mixture was then sintered in a kiln at 800℃ for 14 hours in an oxygen atmosphere (99.9% oxygen concentration). After cooling, the mixture was pulverized by airflow to obtain the second positive electrode active material B(LiNi). 0.929 Co 0.05 Mn 0.02 Sr 0.001 F 0.001 O 1.999 The particle size Dv50 is 3μm.

[0194] 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 7:3 for 1 hour to obtain the positive electrode active material.

[0195] Example 4-12

[0196] The battery was prepared in the same manner as in Example 1, and a first positive electrode active material A and a second positive electrode active material B with the composition listed in Table 1 were prepared according to a method similar to that used in Example 3. The positive electrode active materials listed in Table 2 were obtained therefrom. Please refer to Table 1 and Table 2 for details.

[0197] Examples 13-16

[0198] Similar to Example 3, except that the first positive electrode active material A and the second positive electrode active material B are mixed in different weight ratios to obtain the positive electrode active material, as detailed in Tables 1 and 2.

[0199] Examples 17-21

[0200] The battery was prepared in the same manner as in Example 1, and a first positive electrode active material A and a second positive electrode active material B with the composition listed in Table 1 were prepared according to a method similar to that used in Example 3. The positive electrode active materials listed in Table 2 were obtained therefrom. Please refer to Table 1 and Table 2 for details.

[0201] Comparative Examples 1-2

[0202] The battery was prepared in the same manner as in Example 1, and a first positive electrode active material A and a second positive electrode active material B with the composition listed in Table 1 were prepared according to a method similar to that used in Example 3. The positive electrode active materials listed in Table 2 were obtained therefrom. Please refer to Table 1 and Table 2 for details.

[0203] II. Testing of relevant parameters

[0204] (1) Particle size test

[0205] 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 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 Dv10, Dv50, Dv90, and Dv99 were read.

[0206] The results are shown in Tables 1 and 2.

[0207] (2) Specific surface area test

[0208] The specific surface area was tested in accordance with GB / T 19587-2017, using the nitrogen adsorption specific surface area analysis method, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis was performed using a Tri-Star3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0209] The results are shown in Tables 1 and 2.

[0210] (3) Compaction density test

[0211] Place a certain amount of powder into a compaction mold, then place the mold on a compaction density instrument. Apply 1000 kg / 1.33 cm². 2 The pressure is measured on the equipment, and the thickness of the powder under pressure (the thickness after depressurization) is read. The compaction density is then calculated using ρ = m / v.

[0212] The results are shown in Tables 1 and 2.

[0213] III. Battery Performance Testing

[0214] (1) Initial capacity and first-efficiency test of button cell

[0215] 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.

[0216] The initial effect is calculated as D0 / C0*100%.

[0217] The results are shown in Table 3.

[0218] (2) Initial capacitance test

[0219] 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.

[0220] The results are shown in Table 3.

[0221] (3) Full cell capacity retention rate at 25℃

[0222] 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 ).

[0223] The results are shown in Table 3.

[0224] (4) Full cell capacity retention rate at 45℃

[0225] 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 ).

[0226] The results are shown in Table 3.

[0227] (5) Full battery gas expansion test at 70°C

[0228] 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.

[0229] 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.

[0230] 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.

[0231] The results are shown in Table 3.

[0232]

[0233]

[0234]

[0235]

[0236]

[0237] As can be seen from the results in Tables 1-3, compared with Comparative Examples 1 and 2, whose K values ​​are not within the range of this application, the positive electrode active material of this application not only has high interparticle filling degree, good dispersibility and higher compaction density, and higher battery energy density, but also has improved structural stability, which can effectively prevent side reactions of electrolyte on the surface of the positive electrode active material, and has better cycle performance and safety performance.

[0238] 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 by, The positive electrode active material satisfies the following formula: -1.912a 2 +2.207a + 0.002b 2 -0.115b + 0.358g + 0.123s = K, and 0.34≤K≤0.66, optionally, 0.42≤K≤0.54, wherein a is the specific surface area of the positive electrode active material, in m 2 / g; β is the Dv99 of the positive electrode active material, in μm; γ is the powder compaction density of the positive electrode active material under a pressure of 1000 kg / 1.33 cm 2 , in g / cm 3 ; σ is (Dv90-Dv10) / Dv50 of the positive electrode active material particles, The positive electrode active material comprises a first positive electrode active material A and a second positive electrode active material B, wherein the first positive electrode active material A is a polycrystalline material with a chemical formula of LiNi x1 Co y1 Mn z1 M1 a1 M2 b1 O 2-b1 wherein 0.80≤x1≤1.0, 0≤y1≤0.20, 0≤z1≤0.02, 0≤a1≤0.02, x1+y1+z1+a1=1, 0≤b1≤0.02, wherein M1 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca and Ce, and M2 is selected from at least one of N, F, S and Cl; the second positive electrode active material B is a quasi-single crystal material with a chemical formula of LiNi x2 Co y2 Mn z2 M3 a2 M4 b2 O 2-b2 wherein 0.80≤x2≤1.0, 0≤y2≤0.20, 0≤z2≤0.02, 0≤a2≤0.02, x2+y2+z2+a2=1, 0≤b2≤0.02, wherein M3 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca and Ce, and M4 is selected from at least one of N, F, S and Cl.

2. The positive electrode active material according to claim 1, characterized by The weight ratio of the first positive electrode active material A and the second positive electrode active material B is 6:4-8:

2.

3. The polar active material according to claim 1 or 2, characterized in that, The weight ratio of the first positive electrode active material A and the second positive electrode active material B is 6.5:3.5-7.5:2.

5.

4. The positive electrode active material according to claim 1 or 2, characterized by The specific surface area of the positive electrode active material is 0.3-0.85 m 2 / g.

5. The positive electrode active material according to claim 1 or 2, characterized by The specific surface area of the positive electrode active material is 0.5-0.7 m 2 / g.

6. The positive electrode active material according to claim 1 or 2, characterized by The Dv99 of the positive electrode active material is 6.0-30.0 μm.

7. The positive electrode active material according to claim 1 or 2, characterized by The Dv99 of the positive electrode active material is 7.0-25.0 μm.

8. The positive electrode active material according to claim 1 or 2, characterized by The positive electrode active material has a powder compaction density of 2.9-3.5 g / cm 2 under a pressure of 1000 kg / 1.33 cm 3 .

9. The positive electrode active material according to claim 1 or 2, characterized in that, The positive electrode active material has a powder compaction density of 3.1-3.3 g / cm 2 under a pressure of 1000 kg / 1.33 cm 3 .

10. The positive electrode active material according to claim 1 or 2, characterized in that, The (Dv90-Dv10) / Dv50 of the positive electrode active material is 1.35-2.

3.

11. The positive electrode active material according to claim 1 or 2, characterized in that, The (Dv90-Dv10) / Dv50 of the positive electrode active material is 1.9-2.

25.

12. The positive electrode active material according to claim 1 or 2, characterized in that, The Dv50 of the positive electrode active material is 5.5-13 μm.

13. The positive electrode active material according to claim 1 or 2, characterized in that, The Dv50 of the positive electrode active material is 6.0-8.8 μm.

14. The positive electrode active material according to claim 1 or 2, characterized in that, The molar ratio of M1 to M2 in the first positive electrode active material A is 0.5-7:

1.

15. The positive electrode active material according to claim 1 or 2, characterized in that, The molar ratio of M1 to M2 in the first positive electrode active material A is 2-4:

1.

16. The positive electrode active material according to claim 1 or 2, characterized in that, The molar ratio of M3 to M4 in the second positive electrode active material B is 0.5-7:

1.

17. The positive electrode active material according to claim 1 or 2, characterized in that, The molar ratio of M1 to M2 in the first positive electrode active material A is 2-4:

1.

18. The positive electrode active material according to claim 1 or 2, characterized in that, The specific surface area of the first positive electrode active material A is 0.2-0.8 m 2 / g; and / or the specific surface area of the second positive electrode active material B is 0.6-1.3 m 2 / g.

19. The positive electrode active material according to claim 1 or 2, characterized in that, The Dv99 of the first positive electrode active material A is 13-30 μm; and / or, the Dv99 of the second positive electrode active material B is 6-23 μm.

20. The positive electrode active material according to claim 1 or 2, characterized in that, The first positive electrode active material A has a powder compaction density of 2.7 to 3.3 g / cm3under a pressure of 1000 kg / 1.33 cm2. 2 The second positive electrode active material B has a powder compaction density of 2.2 to 3.2 g / cm3under a pressure of 1000 kg / 1.33 cm2. 3 The second positive electrode active material B has a powder compaction density of 2.2 to 3.2 g / cm3under a pressure of 1000 kg / 1.33 cm2. 2 The second positive electrode active material B has a powder compaction density of 2.2 to 3.2 g / cm3under a pressure of 1000 kg / 1.33 cm2. 3 ​ 21. The positive electrode active material according to claim 1 or 2, characterized in that, The (Dv90-Dv10) / Dv50 of the first positive electrode active material A is 0.4-1.8; and / or, the (Dv90-Dv10) / Dv50 of the second positive electrode active material B is 1.0-1.

75.

22. The positive electrode active material according to claim 1 or 2, characterized in that, The Dv50 of the first positive electrode active material A is 6-15 μm; and / or, the Dv50 of the second positive electrode active material B is 2-6 μm.

23. The positive electrode active material according to claim 1 or 2, characterized in that, The Dv50 of the first positive electrode active material A is 8.5-10.5 μm; and / or, the Dv50 of the second positive electrode active material B is 2.5-4.0 μm.

24. A method for producing a positive electrode active material, characterized by, The method comprises mixing a lithium salt, a precursor of a positive electrode active material, an additive containing a modified element, sintering to obtain a positive electrode active material, The positive electrode active material satisfies the following formula: -1.912a 2 +2.207a + 0.002b 2 -0.115b + 0.358g + 0.123s = K, and 0.34≤K≤0.66, optionally, 0.42≤K≤0.54, wherein a is the specific surface area of the positive electrode active material in m 2 / g; β is the Dv99 of the positive electrode active material in μm; γ is the powder compaction density of the positive electrode active material under a pressure of 1000 kg / 1.33 cm 2 in g / cm 3 ; and σ is (Dv90-Dv10) / Dv50 of the particles of the positive electrode active material. The method comprises: S1) preparing a first positive electrode active material A: mixing a lithium salt, a precursor of the first positive electrode active material A, a compound containing an M1 element, a compound containing an M2 element, and sintering; and S2) preparing a second positive electrode active material B: mixing a lithium salt, a precursor of the second positive electrode active material B, a compound containing an M3 element, a compound containing an M4 element, and sintering; S3) mixing the first positive electrode active material A and the second positive electrode active material B to obtain the positive electrode active material, wherein the first positive electrode active material A is a polycrystalline material having a chemical formula of LiNi x1 Co y1 Mn z1 M1 a1 M2 b1 O 2-b1 wherein 0.80≤x1≤1.0, 0≤y1≤0.20, 0≤z1≤0.02, 0≤a1≤0.02, x1+y1+z1+a1=1, 0≤b1≤0.02, wherein M1 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca and Ce, and M2 is selected from at least one of N, F, S and Cl; the second positive electrode active material B is a quasi-single crystal material having a chemical formula of LiNi x2 Co y2 Mn z2 M3 a2 M4 b2 O 2-b2 wherein 0.80≤x2≤1.0, 0≤y2≤0.20, 0≤z2≤0.02, 0≤a2≤0.02, x2+y2+z2+a2=1, 0≤b2≤0.02, wherein M3 is selected from at least one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca and Ce, and M4 is selected from at least one of N, F, S and Cl.

25. The method of producing a positive electrode active material according to claim 24, characterized by, In the step S3), the first positive electrode active material A and the second positive electrode active material B are mixed in a weight ratio of 6:4-8:

2.

26. The method of producing a positive electrode active material according to claim 24, characterized by, In the step S3), the first positive electrode active material A and the second positive electrode active material B are mixed in a weight ratio of 6.5:3.5-7.5:2.

5.

27. The method of producing a positive electrode active material according to claim 24, characterized by, The compound containing the M1 element is one or more of an oxide, a carbonate, a hydroxide, a nitride, a fluoride, a sulfide or a chloride containing the M1 element, the M1 element being one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca or Ce; the compound containing the M2 element is a metal salt containing the M2 element, the M2 element being one of N, F, S or Cl; the compound containing the M3 element is one or more of an oxide, a carbonate, a hydroxide, a nitride, a fluoride, a sulfide or a chloride containing the M3 element, the M3 element being one of Zr, Y, Al, Ti, W, Sr, Ta, Sb, Nb, Na, K, Ca or Ce; the compound containing the M4 element is a metal salt containing the M4 element, the M4 element being one of N, F, S or Cl.

28. The method of producing a positive electrode active material according to claim 24, characterized by, The Dv50 of the precursor of the first positive electrode active material A is 6-15 μm, optionally 8.5-10.5 μm; the Dv50 of the precursor of the second positive electrode active material B is 2-6 μm, optionally 2.5-4.0 μm.

29. The method of producing a positive electrode active material according to claim 24, characterized by, The Dv50 of the precursor of the first positive electrode active material A is 8.5-10.5 μm; the Dv50 of the precursor of the second positive electrode active material B is 2.5-4.0 μm.

30. The method of producing a positive electrode active material according to claim 24, characterized by, The lithium salt, the precursor of the first positive electrode active material A, the compound containing the M1 element, the compound containing the M2 element are mixed in a molar ratio of 1.05:1:0-0.02:0-0.02; the lithium salt, the precursor of the second positive electrode active material A, the compound containing the M3 element, the compound containing the M4 element are mixed in a molar ratio of 1.05:1:0-0.02:0-0.

02.

31. The method of producing a positive electrode active material according to claim 24, characterized by, In the step S1), the sintering temperature is 700-850 °C, the sintering time is 10-20 h, and the sintering atmosphere is oxygen.

32. The method of producing a positive electrode active material according to claim 24, characterized by, In the step S2), the sintering temperature is 750-900 °C, the sintering time is 10-20 h, and the sintering atmosphere is oxygen.

33. The method of producing a positive electrode active material according to claim 24, characterized by, The sintering is performed in an oxygen atmosphere, the concentration of oxygen in the oxygen atmosphere being 80% or more.

34. The method of producing a positive electrode active material according to claim 33, characterized by, The concentration of oxygen in the oxygen atmosphere is 90% or more.

35. The method of producing a positive electrode active material according to claim 33, characterized by, The concentration of oxygen in the oxygen atmosphere is 99.9% or more.

36. A positive electrode sheet characterized by comprising: The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the positive electrode active material of any one of claims 1-23 or prepared by the method of any one of claims 24-35.

37. The positive electrode sheet according to claim 36, characterized by When the positive electrode sheet elongation is 0.8% or less, the positive electrode sheet has a compaction density of ≥ 3.6 g / cm 3 .

38. The positive electrode sheet according to claim 36, characterized by When the positive electrode sheet elongation is 0.8% or less, the positive electrode sheet has a compaction density of ≥ 3.7 g / cm 3 .

39. A secondary battery, characterized by comprising: The positive electrode active material of any one of claims 1-23 or prepared by the method of any one of claims 24-35 or the positive electrode tab of any one of claims 36 to 38.

40. An electrical device, comprising: The secondary battery of claim 39.

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