Positive electrode active material, positive electrode sheet, secondary battery, and electric device

Abstract

The invention provides a positive active material, a positive pole piece, a secondary battery and an electric device. The positive electrode active material exists in the form of secondary particles formed by gathering primary particles, and at least part of the secondary particles are provided with holes; and the particle size distribution diagram of the positive electrode active material measured by a laser diffraction method is in a double-peak shape, and the difference value between the second peak position and the first peak position is 1-13 [mu] m, so that the battery has excellent power performance and mechanical strength.

Description

[0001] This application is a divisional application based on the invention with application number 202310473126X, application date of April 27, 2023, applicant CATL, and invention title "Positive electrode active material, positive electrode sheet, secondary battery and power consumption device". Technical Field

[0002] This application relates to the field of secondary battery technology, and in particular to a positive electrode active material, a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0003] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0004] The performance of cathode active materials directly affects the performance of secondary batteries. Currently, cathode active materials have many defects and cannot meet the application needs of next-generation electrochemical systems. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material in which at least some of the secondary particles have pores and the particle size distribution of the positive electrode active material is bimodal, which can take into account both the power performance and mechanical strength of the battery.

[0006] A first aspect of this application provides a positive electrode active material, wherein the positive electrode active material exists in the form of secondary particles formed by the aggregation of primary particles, and at least a portion of the secondary particles have pores; and The particle size distribution of the positive electrode active material, as determined by laser diffraction, is bimodal, with the difference between the position of the second peak and the first peak being 1 μm to 13 μm.

[0007] On the one hand, the presence of pores is beneficial for the positive electrode active material to have three-dimensional channels, shortening the solid-phase mass transfer path of lithium ions and improving the power performance and energy density of the battery. On the other hand, the particle size distribution of the positive electrode active material is bimodal, meaning that the combination of positive electrode active materials with different particle sizes not only helps to improve the tap density of the positive electrode active material, but more importantly, the different particle sizes of the positive electrode active materials can provide a certain degree of support, which is beneficial to improving its mechanical strength, reducing the risk of breakage of the positive electrode active material during use, improving the shear strength of the positive electrode sheet, and improving the mechanical strength of the battery. In addition, controlling the difference between the peak positions of the first and second peaks in the particle size distribution of the positive electrode active material is 1 μm to 13 μm, which is beneficial to further improve the tap density of the positive electrode sheet and the electrical performance of the battery.

[0008] In any embodiment, the peak position of the first peak is located at 1 μm to 5 μm, optionally 1.5 μm to 4.5 μm; and / or The second peak is located at 6 μm to 14 μm, and can be selected as 8 μm to 12 μm.

[0009] By controlling the peak positions of the first and second peaks within a suitable range, the battery can achieve high volumetric energy density, excellent power performance, and mechanical strength.

[0010] In any embodiment, the secondary particle includes a plurality of pores formed by the space between the primary particles, the inner diameter of the pores being 0.1 μm to 0.6 μm, optionally 0.2 μm to 0.4 μm; or The secondary particle includes a single hollow pore surrounded by the primary particle at the center, the inner diameter of the pore being 0.5 μm to 3 μm, optionally 0.8 μm to 1.2 μm.

[0011] Pores with different distribution patterns have different inner diameters, both of which are conducive to the formation of three-dimensional channels in the positive electrode active material, shortening the solid-phase mass transfer path of lithium ions and improving the power performance of the battery.

[0012] In any embodiment, the positive electrode active material has the following chemical formula: Li a Ni x M1 y M2 1-x-y O2, Wherein, M1 and M2 include one or more of Co, Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb, with 0.8≤a≤1.2, 0.55≤x≤1.0, and 0≤y≤0.45, and optionally, 0.8≤a≤1.2, 0.95≤x≤0.995, and 0≤y≤0.05.

[0013] Using the above materials ensures that the positive electrode active material has a high specific capacity, resulting in a battery with a high energy density.

[0014] In any embodiment, the average particle size D of the primary particles of the positive electrode active material is 0.1 μm to 0.8 μm, and can be selected as 0.2 μm to 0.5 μm.

[0015] By controlling the average particle size of the primary particles of the positive electrode active material within a suitable range, secondary particles of the positive electrode active material with a suitable range can be formed, thereby enabling the battery to have high volumetric energy density, excellent power performance, and mechanical strength.

[0016] In any embodiment, the Dv50 of the secondary particles of the positive electrode active material is 9 μm to 15 μm, and can be selected as 10 μm to 12 μm.

[0017] The Dv50 of the positive electrode active material is controlled within a suitable range to enable the battery to have high volumetric energy density, excellent power performance and mechanical strength.

[0018] In any embodiment, the specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g~1.0 m 2 / g, can be selected as 0.2 m 2 / g~0.5 m 2 / g.

[0019] By controlling the specific surface area of ​​the positive electrode active material within a suitable range, the battery can achieve high volumetric energy density, excellent power performance, and mechanical strength.

[0020] In any embodiment, the positive electrode active material includes a first positive electrode material and a second positive electrode material.

[0021] The combination of the first and second cathode materials has a synergistic effect, which helps to improve the compaction density of the cathode sheet and enhance the mechanical and cycle performance of the battery.

[0022] In any embodiment, the first positive electrode material has the pores, and the second positive electrode material is a solid structure; or The first positive electrode material is a solid structure, and the second positive electrode material has the aforementioned pores; or Both the first positive electrode material and the second positive electrode material have the aforementioned pores.

[0023] The presence of pores can shorten the solid-phase mass transfer path of lithium ions, improve the power performance of the battery, and expose more 010 crystal planes, thereby generating more reactive sites and improving the specific capacity and energy density of the material.

[0024] In any embodiment, the mass ratio A of the first positive electrode material to the second positive electrode material and the porosity B of the positive electrode active material satisfy the following condition: 0≤|BA×0.4-(1-A)×0.2|≤1.

[0025] By controlling the mass ratio of the first cathode material and the second cathode material to satisfy the above-mentioned relationship with the porosity of the cathode active material, sufficient pores can be provided to shorten the solid-phase mass transfer path of lithium ions and improve the power performance of the battery. At the same time, the interaction force between the first cathode material and the second cathode material can be adjusted to improve the mechanical properties of the battery.

[0026] In any embodiment, the mass ratio A of the first positive electrode material to the second positive electrode material is 1.5 to 9, and can be selected as 2 to 8.

[0027] The mass ratio of the first positive electrode material and the second positive electrode material is controlled within a suitable range, taking into account both the compaction density of the positive electrode sheet and the mechanical strength of the battery.

[0028] In any embodiment, the porosity B of the positive electrode active material is 0.15%~0.45%, and can be selected as 0.25%~0.35%.

[0029] Controlling the porosity of the cathode active material within a suitable range can provide sufficient pores to shorten the solid-phase mass transfer path of lithium ions and improve the power performance of the battery, while avoiding or reducing the impact of the presence of pores on the mechanical strength of the cathode active material.

[0030] In any embodiment, the first cathode material and the second cathode material each independently have the following chemical formula: Li a Ni x M1 y M2 1-x-y O2, Wherein, M1 and M2 include one or more of Co, Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb, with 0.8≤a≤1.2, 0.55≤x≤1.0, and 0≤y≤0.45, and optionally, 0.8≤a≤1.2, 0.95≤x≤0.995, and 0≤y≤0.05.

[0031] Both the first and second cathode materials with the above chemical formulas can ensure that the cathode active material has a high specific capacity, thus enabling the battery to have a high energy density.

[0032] In any embodiment, the Dv50 of the first cathode material is 8 μm to 18 μm, and can be selected as 10 μm to 12 μm.

[0033] In any embodiment, the Dv50 of the second cathode material is 0.8 μm to 5 μm, and can be selected as 1 μm to 3 μm.

[0034] Controlling the Dv50 of the first cathode material and the Dv50 of the second cathode material to a suitable range is beneficial to the synergistic effect between the first cathode material and the second cathode material, and helps to improve the volumetric energy density and mechanical properties of the battery.

[0035] In any embodiment, the ratio of the difference between Dv90 and Dv50 of the first positive electrode material to Dv50 of the first positive electrode material satisfies 0.6~1.2, and can be optionally 0.8~1.0; and / or The ratio of the difference between Dv50 and Dv10 of the first positive electrode material to Dv10 of the first positive electrode material satisfies 1.2~2.5, and can be selected as 1.5~2.0.

[0036] In any embodiment, the ratio of the difference between Dv90 and Dv50 of the second positive electrode material to Dv50 of the second positive electrode material satisfies 0.8~1.5, and can be selected as 1.0~1.3; and / or The ratio of the difference between Dv50 and Dv10 of the second positive electrode material to Dv10 of the second positive electrode material satisfies 6~12, and can be selected as 8~10.

[0037] Controlling the particle size distribution of the first and second cathode materials within a suitable range is beneficial to both the synergistic effect between the first and second cathode materials, improving the mechanical properties of the battery, and increasing the compaction density of the cathode sheet.

[0038] A second 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 described in the first aspect of this application.

[0039] In any embodiment, the thickness of the positive electrode film is 200 μm to 400 μm, and can be selected as 220 μm to 300 μm.

[0040] By controlling the thickness of the positive electrode film within a suitable range, sufficient positive electrode active material can be provided to improve the energy density of the battery, while reducing the impact on lithium-ion solid-phase mass transfer. This balances the battery's energy density and power performance.

[0041] In any embodiment, the compaction density of the positive electrode film is 2.9 g / m³. 2 ~3.5 g / m 2 .

[0042] The compaction density of the positive electrode film is 2.9 g / m³. 2 ~3.5 g / m 2 This is beneficial for improving the energy density of batteries.

[0043] A third aspect of this application provides a secondary battery, including the positive electrode of the second aspect.

[0044] A fourth aspect of this application provides an electrical device including a secondary battery as described in the third aspect. Attached Figure Description

[0045] Figure 1 This is a particle size distribution diagram of the positive electrode active material shown in Example 3 of this application; Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application; Figure 3 yes Figure 2 An exploded view of a secondary battery according to an embodiment of this application is shown. Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application; Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application; Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown; Figure 7 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; Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0046] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its preparation method, secondary battery, and power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

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

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

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

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

[0052] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0053] Currently, ternary materials in the lithium battery field are popular cathode active materials due to their high theoretical specific capacity, high discharge platform, and low cost. However, the solid structure of commonly used ternary materials restricts the solid-phase mass transfer of metal ions. While preparing ternary materials with porous structures can shorten the solid-phase mass transfer path of metal ions and improve battery power performance, these porous materials may be prone to breakage during use, affecting the battery's electrical performance. Therefore, it is necessary to design a cathode active material that balances battery power performance and mechanical strength to meet the application needs of next-generation electrochemical systems.

[0054] [Positive electrode active material] Based on this, this application proposes a positive electrode active material, which exists in the form of secondary particles formed by the aggregation of primary particles, and at least some of the secondary particles have pores; and the particle size distribution of the positive electrode active material, as determined by laser diffraction, is bimodal, with the difference between the peak position of the second peak and the peak position of the first peak being 1 μm to 13 μm.

[0055] In this paper, the term "primary particle" refers to particles of the positive electrode active material before they agglomerate.

[0056] In this paper, the term "pore" refers to the cavity structure that exists inside the secondary particles of the positive electrode active material.

[0057] Understandably, the term "bimodal particle size distribution" means that the number of particles at the first and second peaks of the particle size distribution is significantly greater than the number of particles at other peaks in the particle size distribution, that is, there are a considerable number of particles of two different particle sizes in the positive electrode active material.

[0058] In some implementations, some of the secondary particles have pores.

[0059] In some implementations, all secondary particles have pores.

[0060] In some embodiments, the inner diameter of the hole can be selected as 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3 μm, or a value within the range formed by any two of the above points.

[0061] In some embodiments, the difference between the second peak position and the first peak position in the particle size distribution diagram can be selected as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, or a value within the range formed by any two of the above points.

[0062] In this paper, the particle size distribution map was constructed using data determined by laser diffraction. Following GB / T 19077-2016, Particle Size Distribution by Laser Diffraction, 0.1g–0.13g of the positive electrode active material sample was weighed into a 50 mL beaker, 5g of anhydrous ethanol was added, and a stir bar of approximately 2.5mm was placed inside. The beaker was then sealed with plastic wrap. After ultrasonic treatment for 5 minutes, the sample was transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were randomly selected from each batch for testing. The particle size distribution map was obtained using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, based on volume distribution.

[0063] On the one hand, the presence of pores is beneficial for the positive electrode active material to have three-dimensional channels, shortening the solid-phase mass transfer path of lithium ions and improving the power performance of the battery. On the other hand, the particle size distribution of the positive electrode active material is bimodal, meaning that the combination of positive electrode active materials with different particle sizes not only helps to improve the tap density of the positive electrode active material, but more importantly, the different particle sizes of the positive electrode active materials can provide a certain degree of support, which is beneficial to improving its mechanical strength, reducing the risk of breakage of the positive electrode active material during use, improving the shear strength of the positive electrode sheet, and improving the mechanical strength of the battery. In addition, controlling the difference between the peak positions of the first and second peaks in the particle size distribution of the positive electrode active material to be 3 μm to 13 μm is beneficial to further improving the tap density of the positive electrode sheet and the electrical performance of the battery.

[0064] In some embodiments, the first peak position is located at 1 μm to 5 μm, optionally 1.5 μm to 4.5 μm. In some embodiments, the first peak position is located at 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a value within the range formed by any two of the above points.

[0065] In some embodiments, the second peak is located at 6 μm to 14 μm, optionally 8 μm to 12 μm. In some embodiments, the second peak is located at 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, or a value within the range formed by any two of the above points.

[0066] By controlling the peak positions of the first and second peaks within a suitable range, the battery can achieve high volumetric energy density, excellent power performance, and mechanical strength.

[0067] In some embodiments, the secondary particles include a plurality of pores formed by the space between the primary particles, the inner diameter of which is 0.1 μm to 0.6 μm, optionally 0.2 μm to 0.4 μm.

[0068] In some embodiments, the secondary particles include a plurality of pores formed by the space between the primary particles, the inner diameter of which may be selected as 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, or a value within a range consisting of any two of the above.

[0069] In some embodiments, the secondary particle includes a plurality of pores formed by the space between the primary particles, the plurality of pores being distributed at intervals within the secondary particle, and the plurality of pores being distributed in a ring shape on a cross section passing through the center of gravity of the secondary particle.

[0070] In some embodiments, the secondary particles further include pores located within the primary particles, the inner diameter of which is 0.01 μm to 0.06 μm. In some embodiments, the secondary particles further include pores located within the primary particles, the inner diameter of which can be selected from 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, or a value within the range of any two of the above.

[0071] In some embodiments, the secondary particle includes a hollow single pore surrounded by primary particles at its center, the inner diameter of which is 0.5 μm to 3 μm, optionally 0.8 μm to 1.2 μm. In some embodiments, the secondary particle includes a hollow single pore surrounded by primary particles at its center, the inner diameter of which can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or a value within the range of any two of the above.

[0072] In this paper, the term "inner diameter of a cavity" refers to the longest straight-line distance between any two points on the perimeter of a single cavity inside the secondary particles of the positive electrode active material.

[0073] In this paper, the inner diameter of the pores can be tested using any method known in the art. As an example, conductive adhesive is applied to the sample stage, a powdered sample of the positive electrode active material is spread evenly on the adhesive, and any unadhered powder is blown away with a syringe. Gold is then sprayed onto the sample, and argon plasma is used to cross-sectionally cut the powder particles. Scanning electron microscopy (SEM) images of the powdered sample are obtained under conditions of 10 kV accelerating voltage and 10 mA emission current. The inner diameter of the pores is measured based on the SEM images. At least three samples are measured, with at least 50 pores measured for each sample. The average value is taken as the inner diameter of the pores in the sample.

[0074] Pores with different distribution patterns have different inner diameters, both of which are conducive to the formation of three-dimensional channels in the positive electrode active material, shortening the solid-phase mass transfer path of lithium ions and improving the power performance of the battery.

[0075] In some embodiments, the positive electrode active material has the following chemical formula: Li a Ni x M1 y M2 1-x-y O2, Wherein, M1 and M2 include one or more of Co, Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb, with 0.8≤a≤1.2, 0.55≤x≤1.0, and 0≤y≤0.45, and optionally, 0.8≤a≤1.2, 0.95≤x≤0.995, and 0≤y≤0.05.

[0076] Using the above materials ensures that the positive electrode active material has a high specific capacity, resulting in a battery with a high energy density.

[0077] In some embodiments, the average particle size D of the primary particles of the positive electrode active material is 0.1 μm to 0.8 μm, and optionally 0.2 μm to 0.5 μm. In some embodiments, the average particle size D of the primary particles of the positive electrode active material can be selected from 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, or a value within the range formed by any two of the above points.

[0078] In this paper, the average particle size D of the primary particles of the positive electrode active material can be tested using any method known in the art. As an example, after imaging with a 500x scanning electron microscope (ZEISS Sigma-02-33, Germany), 200 to 600 primary particles of the positive electrode active material with intact shapes and no obstructions were randomly selected from the electron micrographs, and the longest diameter of each pore in the primary particle in the micrograph was recorded, and the average value was taken as the average particle size D.

[0079] By controlling the average particle size of the primary particles of the positive electrode active material within a suitable range, secondary particles of the positive electrode active material with a suitable range can be formed, thereby enabling the battery to have high volumetric energy density, excellent power performance, and mechanical strength.

[0080] In some embodiments, the Dv50 of the positive electrode active material is 9 μm to 15 μm, and optionally 10 μm to 12 μm. In some embodiments, the Dv50 of the positive electrode active material can be selected as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, or a value within the range formed by any two of the above points.

[0081] In this paper, the Dv50 of the positive electrode active material can be tested using any method known in the art. As an example, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, 0.1g~0.13g of the positive electrode active material sample to be tested was weighed into a 50 mL beaker, 5g of anhydrous ethanol was added, and a stir bar of approximately 2.5mm was placed inside, followed by sealing with plastic wrap. After ultrasonic treatment for 5 minutes, the sample was transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were randomly selected from each batch for testing. The test was performed using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK. Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for secondary particles in the positive electrode active material.

[0082] The Dv50 of the positive electrode active material is controlled within a suitable range to enable the battery to have high volumetric energy density, excellent power performance and mechanical strength.

[0083] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g~1.0 m 2 / g, can be selected as 0.2m 2 / g~0.5 m 2 / g. In some embodiments, the specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g, 0.2 m 2 / g, 0.3m 2 / g, 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, or a value within the range formed by any two of the above points.

[0084] In this paper, the specific surface area of ​​the positive electrode active material can be tested using any method known in the art. As an example, GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" is referenced. The determination is performed using a TriStar II 3020 instrument. The positive electrode active material is dispersed in a dispersant (ethanol), sonicated for 30 minutes, and then dried in a vacuum drying oven. Finally, the specific surface area of ​​the positive electrode active material is measured using a specific surface area analyzer.

[0085] By controlling the specific surface area of ​​the positive electrode active material within a suitable range, the battery can achieve high volumetric energy density, excellent power performance, and mechanical strength.

[0086] In some embodiments, the positive electrode active material includes a first positive electrode material and a second positive electrode material.

[0087] It is understandable that the first and second cathode materials have different dimensions. The combination of the first and second cathode materials has a synergistic effect, which is beneficial to improving the compaction density of the cathode sheet and the mechanical and cycle performance of the battery.

[0088] In some embodiments, the first positive electrode material has pores, while the second positive electrode material has a solid structure.

[0089] In some implementations, the first positive electrode material is a solid structure, while the second positive electrode material has pores.

[0090] In some embodiments, both the first cathode material and the second cathode material have pores.

[0091] The presence of pores can shorten the solid-phase mass transfer path of lithium ions, improve the power performance of the battery, and expose more 010 crystal planes, thereby generating more reactive sites and improving the specific capacity and energy density of the material.

[0092] In some embodiments, the mass ratio A of the first positive electrode material to the second positive electrode material and the porosity B of the positive electrode active material satisfy the following relationship: 0 ≤ |BA×0.4-(1-A)×0.2| ≤ 1. In some embodiments, the relationship 0 ≤ |BA×0.4-(1-A)×0.2| ≤ 1 can satisfy values ​​of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any two of the above values ​​within a range.

[0093] In this paper, the relation “|BA×0.4-(1-A)×0.2|” is expressed as the absolute value of the numerical value of BA×0.4-(1-A)×0.2.

[0094] By controlling the mass ratio of the first cathode material and the second cathode material to satisfy the above-mentioned relationship with the porosity of the cathode active material, sufficient pores can be provided to shorten the solid-phase mass transfer path of lithium ions and improve the power performance of the battery. At the same time, the interaction force between the first cathode material and the second cathode material can be adjusted to improve the mechanical properties of the battery.

[0095] In some embodiments, the mass ratio A of the first positive electrode material to the second positive electrode material is 1.5 to 9, and can be selected as 2 to 8. In some embodiments, the mass ratio A of the first positive electrode material to the second positive electrode material is 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, or a value within the range formed by any two of the above points.

[0096] The mass ratio of the first positive electrode material and the second positive electrode material is controlled within a suitable range, taking into account both the compaction density of the positive electrode sheet and the mechanical strength of the battery.

[0097] In some embodiments, the porosity B of the positive electrode active material is 0.15% to 0.45%, and may be selected as 0.25% to 0.35%. In some embodiments, the porosity B of the positive electrode active material is 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or a value within the range formed by any two of the above points.

[0098] Controlling the porosity of the cathode active material within a suitable range can provide sufficient pores to shorten the solid-phase mass transfer path of lithium ions and improve the power performance of the battery, while avoiding or reducing the impact of the presence of pores on the mechanical strength of the cathode active material.

[0099] In some embodiments, the first cathode material and the second cathode material each independently have the following chemical formula: Li a Ni x M1 y M2 1-x-y O2, Wherein, M1 and M2 include one or more of Co, Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb, with 0.8≤a≤1.2, 0.55≤x≤1.0, and 0≤y≤0.45, and optionally, 0.8≤a≤1.2, 0.95≤x≤0.995, and 0≤y≤0.05.

[0100] Both the first and second cathode materials with the above chemical formulas have high volumetric energy density.

[0101] In some embodiments, the Dv50 of the first cathode material is 8 μm to 18 μm, and can be selected as 10 μm to 12 μm. In some embodiments, the Dv50 of the first cathode material is 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or a value within the range formed by any two of the above points.

[0102] In some embodiments, the Dv50 of the second cathode material is 0.8 μm to 5 μm, and can be selected as 1 μm to 3 μm. In some embodiments, the Dv50 of the second cathode material is 0.8 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a value within the range formed by any two of the above points.

[0103] In this paper, the testing methods for the Dv50 of the first cathode material and the Dv50 of the second cathode material are the same as those for the Dv50 of the cathode active material.

[0104] Controlling the Dv50 of the first cathode material and the Dv50 of the second cathode material to a suitable range is beneficial to the synergistic effect between the first cathode material and the second cathode material, and helps to improve the volumetric energy density and mechanical properties of the battery.

[0105] In some embodiments, the ratio of the difference between Dv90 and Dv50 of the first positive electrode material to Dv50 of the first positive electrode material satisfies 0.6 to 1.2, and can be selected as 0.8 to 1.0. In some embodiments, the ratio of the difference between Dv90 and Dv50 of the first positive electrode material to Dv50 of the first positive electrode material satisfies 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, or a value within the range formed by any two of the above points.

[0106] In some embodiments, the ratio of the difference between Dv50 and Dv10 of the first positive electrode material to Dv10 of the first positive electrode material satisfies 1.2 to 2.5, and can be selected as 1.5 to 2.0. In some embodiments, the ratio of the difference between Dv50 and Dv10 of the first positive electrode material to Dv10 of the first positive electrode material satisfies a value within the range of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or any two of the above points.

[0107] In some embodiments, the ratio of the difference between Dv90 and Dv50 of the second positive electrode material to Dv50 of the second positive electrode material satisfies 0.8 to 1.5, and can be selected as 1.0 to 1.3. In some embodiments, the ratio of the difference between Dv90 and Dv50 of the second positive electrode material to Dv50 of the second positive electrode material satisfies 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or a value within the range formed by any two of the above points.

[0108] In some embodiments, the ratio of the difference between Dv50 and Dv10 of the second positive electrode material to Dv10 of the second positive electrode material satisfies 6 to 12, and can be selected as 8 to 10. In some embodiments, the ratio of the difference between Dv50 and Dv10 of the second positive electrode material to Dv10 of the second positive electrode material satisfies 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, or a value within the range formed by any two of the above points.

[0109] In this paper, Dv90 is the particle size corresponding to a cumulative volume distribution percentage of secondary particles of the first cathode material / second cathode material reaching 90%, and Dv10 is the particle size corresponding to a cumulative volume distribution percentage of secondary particles of the first cathode material / second cathode material reaching 10%.

[0110] Controlling the particle size distribution of the first and second cathode materials within a suitable range is beneficial to both the synergistic effect between the first and second cathode materials, improving the mechanical properties of the battery, and increasing the compaction density of the cathode sheet.

[0111] [Positive electrode plate] 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 in some embodiments.

[0112] 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.

[0113] In some embodiments, the areal density of the positive electrode film is 24 mg / cm³. 2 ~46 mg / cm 2 In some embodiments, the areal density of the positive electrode film can be selected as 24 mg / cm³. 2 25 mg / cm 2 26 mg / cm 2 28 mg / cm 2 30 mg / cm 2 32mg / cm 2 34 mg / cm 2 35 mg / cm 2 36 mg / cm 2 38 mg / cm 2 40 mg / cm 2 42 mg / cm 2 44 mg / cm 2 45mg / cm 2 46 mg / cm2 The value within the range formed by any two of the above points.

[0114] The areal density of the positive electrode film is determined by measuring the coating weight (g) and coating area (cm²) of the positive electrode film on one side. 2 (The number of sampling points is greater than 14) This is the determination. Specifically, the coating density of the positive electrode film is calculated as: coating weight of the positive electrode film on one side (g) / coating area of ​​the positive electrode film (cm²). 2 ).

[0115] In some embodiments, the thickness of the positive electrode film is 200 μm to 400 μm, and optionally 220 μm to 300 μm. In some embodiments, the thickness of the positive electrode film can be selected from 200 μm, 220 μm, 240 μm, 250 μm, 260 μm, 280 μm, 300 μm, 320 μm, 340 μm, 350 μm, 360 μm, 380 μm, 400 μm, or a value within the range formed by any two of the above points.

[0116] Controlling the thickness of the cathode film within a suitable range can provide sufficient positive electrode active material to improve the battery's energy density while reducing the impact on lithium-ion solid-phase mass transfer. This balances the battery's energy density and power performance.

[0117] In some embodiments, the compaction density of the positive electrode film is 2.9 g / m³. 2 ~3.5 g / m 2 In some embodiments, the compaction density of the positive electrode film can be selected as 2.9 g / m³. 2 3.0 g / m 2 3.1 g / m 2 3.2 g / m 2 3.3 g / m 2 3.4 g / m 2 3.5 g / m 2 The value within the range formed by any two of the above points.

[0118] In this paper, the compaction density of the positive electrode film layer of the positive electrode sheet can be tested using any known testing method. As an example, the compaction density of the positive electrode film layer of the positive electrode sheet is measured by measuring the areal density (g / cm³) of the positive electrode film layer on one side. 2 The density of the positive electrode film is determined by the thickness of the positive electrode film layer on one side (cm) (number of sampling points > 14). Specifically, the compacted density of the positive electrode film layer = the surface density of the positive electrode film layer on one side (g / cm³). 2 ) / Positive electrode film thickness (cm).

[0119] Positive electrode sheets with high positive film compaction density are beneficial to improving volumetric energy density.

[0120] 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.).

[0121] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0122] 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), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0123] 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.

[0124] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0125] [Negative electrode plate] The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0126] 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.

[0127] 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.).

[0128] 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.

[0129] In some implementations, the negative electrode active material includes silicon suboxide.

[0130] In some embodiments, the mass content of silicon suboxide is 20% to 100% based on the total mass of the negative electrode active material, and can be selected as 50% to 100%.

[0131] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive 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).

[0132] 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.

[0133] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0134] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0135] [Isolation membrane] In some embodiments, the secondary battery also includes a separator. Any known porous separator with good chemical and mechanical stability can be selected.

[0136] 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. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0137] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0138] In some embodiments, the secondary battery includes a negative electrode, a separator, an electrolyte, and a positive electrode as described in some examples.

[0139] In some implementations, the secondary battery includes a lithium secondary battery.

[0140] In some implementations, the energy density of the secondary battery is 700 Wh / L to 900 Wh / L.

[0141] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0142] 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.

[0143] This application allows for a secondary battery that can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0144] In some implementations, refer to Figure 3 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.

[0145] 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.

[0146] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 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.

[0147] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0148] 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.

[0149] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 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.

[0150] 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.

[0151] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0152] Figure 7 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.

[0153] 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.

[0154] Example 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.

[0155] I. Preparation Method Example 1 1) Preparation of positive electrode active materials Preparation of the first cathode material: Prepare a nickel-cobalt-manganese solution with a nickel, cobalt, and manganese element molar ratio of 96:1:3, and adjust the concentration to 2 mol / L. The raw materials for soluble nickel, cobalt, and manganese are nickel sulfate, cobalt sulfate, and manganese sulfate, respectively, and the molar concentration of manganese ions is 0.25 mol / L. Prepare a 3 mol / L sodium hydroxide solution and a 5.5 mol / L ammonia solution.

[0156] Under a nitrogen atmosphere, the aforementioned nickel-cobalt-manganese solution, sodium hydroxide solution, and ammonia solution were simultaneously added to a reactor for a co-precipitation reaction. The reaction speed was controlled at 400 rpm, the temperature at 110°C, and the reaction time at 8 h. The pH of the system was controlled at 9.5, and the concentration of ammonia solution was 6 mol / L. After the co-precipitation reaction was completed, the reactants were transferred to a slurry tank for aging and washing. After dehydration, the mixture was dried in a 115°C oven for 9 h. After sieving and demagnetization, a precursor with multiple pores arranged in a ring was obtained.

[0157] The precursor and lithium hydroxide are mixed uniformly in a certain proportion, wherein the Li / Me molar ratio is 1.03; and Me is the total molar content of nickel, cobalt and manganese.

[0158] The uniformly mixed material is placed in a furnace for calcination at a heating rate of 3℃ / min. The temperature is maintained at 720℃ for 20 hours with an oxygen content of ≥98%. The material is then cooled in the furnace to obtain the matrix material.

[0159] Under a nitrogen atmosphere, the matrix material, cobalt boride, and titanium boride were mixed in a high-speed mixer at a mass ratio of 1:0.015:0.0041, and then calcined in a furnace at 320°C for 5 hours under a nitrogen atmosphere to obtain the product. The product was washed with water for 30 minutes, centrifuged, filtered, and then vibrated and dried to obtain the first cathode material comprising multiple pores formed by the spaces between the primary particles of the first cathode material.

[0160] Preparation of the second cathode material: Prepare a nickel-cobalt-manganese solution with a nickel, cobalt, and manganese molar ratio of 96:1:3 and adjust the concentration to 2.0 mol / L. The raw materials for the soluble nickel, cobalt, and manganese are nickel sulfate, cobalt sulfate, and manganese sulfate, respectively. Prepare a 2 mol / L sodium hydroxide solution and a 6 mol / L ammonia solution.

[0161] The aforementioned nickel-cobalt-manganese solution, sodium hydroxide solution, and ammonia solution were simultaneously added to a reaction vessel for co-precipitation reaction. The reaction speed was controlled at 850 rpm, the temperature at 55℃, and the reaction time at 5 h. The flow rates of the three solutions were adjusted as follows: sodium hydroxide solution at 0.6 L / min; ammonia solution at 0.6 L / min; and nickel-cobalt-manganese solution at 0.3 L / min. The pH of the system was controlled at 10.3.

[0162] After the coprecipitation reaction is completed, the precipitate is transferred to a slurry tank for aging and washing. After dehydration, it is placed in a 110 °C oven for 12 h to dry. After sieving and demagnetization, the precursor of the positive electrode active material is obtained.

[0163] The precursor and lithium hydroxide are mixed uniformly in a certain proportion, wherein the Li / Me molar ratio is 1.03; and Me is the total molar content of nickel, cobalt and manganese.

[0164] The uniformly mixed material is placed in a furnace for calcination at a heating rate of 3℃ / min and held at 700℃ for 15 hours. The atmosphere must have an oxygen content of ≥98%. The material is then cooled in the furnace to obtain the matrix material.

[0165] Under a nitrogen atmosphere, the matrix material, cobalt boride, and titanium boride were mixed in a high-speed mixer at a mass ratio of 1:0.015:0.0041, and then calcined in a furnace at 300℃ for 4 hours under a nitrogen atmosphere to obtain the product. The product was washed with water for 30 minutes, centrifuged, filtered, and then vibrated to dry, thus obtaining a solid-structured second cathode material.

[0166] Preparation of positive electrode active material: The first positive electrode material and the second positive electrode material are uniformly mixed at a mass ratio of 6:1 to obtain the positive electrode active material.

[0167] 2) Preparation of positive electrode sheet The above-mentioned positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone at a mass ratio of 97:1:2 and mixed and stirred for 0.5-6 h to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto the positive electrode current collector aluminum foil to prepare a positive electrode film. After drying, cold pressing, and slitting, a positive electrode sheet was obtained.

[0168] 3) Preparation of negative electrode sheet Silicon suboxide (SiO2)-doped artificial graphite, conductive carbon black, carbon nanotubes (CNTs), styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener were added to deionized water in a weight ratio of 94.5:1:0.375:2.8:1.325, with SiO2 comprising 30% by mass based on the mass of the artificial graphite. The mixture was stirred for 5 hours to obtain a negative electrode active material layer slurry. The negative electrode active material layer slurry was then uniformly coated onto a negative electrode current collector copper foil in layers. After drying, cold pressing, and slitting, the negative electrode sheet was obtained.

[0169] 4) Electrolyte In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), lithium salt LiPF6 / LIFSI was dissolved in an organic solvent of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / fluoroethylene carbonate (volume ratio 1:1:1:1), and stirred until homogeneous to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0170] 5) Separating membrane A polypropylene membrane is used as the base membrane, and a 1-micron alumina (CCS) + a 1-micron polyvinylidene fluoride (PCS) is coated on the base membrane.

[0171] 6) Battery manufacturing The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound together, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium battery product of Example 1.

[0172] Examples 2-4 The batteries in Examples 2-4 are prepared in a similar manner to those in Example 1, but the preparation method of the positive electrode active material is adjusted so that the pore inner diameter of the first positive electrode material is different. The specific parameters are shown in Table 1.

[0173] Example 5 The battery in Example 5 is prepared in a similar manner to the battery in Example 1, but the preparation method of the first positive electrode material is adjusted so that the first positive electrode material includes a hollow single pore surrounded by primary particles of the first positive electrode active material at the center. The specific preparation method is as follows: A nickel-cobalt-manganese solution with a nickel, cobalt, and manganese molar ratio of 96:1:3 was prepared and its concentration was adjusted to 1.9 mol / L. The soluble nickel, cobalt, and manganese raw materials were nickel sulfate, cobalt sulfate, and manganese sulfate, respectively. A 2 mol / L sodium hydroxide solution was prepared. A 6 mol / L ammonia solution was prepared. A 10 g / L carbon sphere dispersion was prepared and placed in a reaction vessel, stirred at 850 rpm for 120 min until uniformly dispersed. The carbon spheres had a diameter of 0.20 μm.

[0174] The aforementioned nickel-cobalt-manganese solution, sodium hydroxide solution, and ammonia solution were simultaneously added to a reaction vessel for co-precipitation reaction. The reaction speed was controlled at 850 rpm, the temperature at 55℃, and the reaction time at 5 h. The flow rates of the three solutions were adjusted as follows: sodium hydroxide solution at 0.6 L / min; ammonia solution at 0.6 L / min; and nickel-cobalt-manganese solution at 0.3 L / min. The pH of the system was controlled at 10.3. The weight ratio of the carbon spheres to the total weight of nickel, cobalt, and manganese in the nickel-cobalt-manganese solution was 2:18.

[0175] After the coprecipitation reaction is completed, the reaction material overflows into the aging kettle, a certain amount of washing additive is added, and the mixture is stirred for 1 hour. Then, the material is dehydrated, washed, dehydrated again, dried, sieved, and demagnetized to obtain a positive electrode active material precursor with carbon spheres at the center.

[0176] The positive electrode active material precursor and lithium carbonate are uniformly mixed in a certain proportion, wherein the Li / Me molar ratio is 1.02; and Me is the total molar content of nickel, cobalt and manganese.

[0177] The uniformly mixed material is placed in an oxygen atmosphere furnace, the heating rate is set to 5℃ / min, and it is held at 705℃ for 6 hours. The atmosphere requires an oxygen content of ≥98%, and then the furnace is cooled.

[0178] The material obtained after calcination is crushed by roller crushing, ultracentrifugal grinding and pulverizing, and then sieved through a 400-mesh sieve to obtain a first positive electrode material containing a hollow single pore formed by the primary particles of the first positive electrode active material at the center.

[0179] Examples 6-31 The batteries in Examples 6-31 are prepared in a similar manner to the battery in Example 5, but the preparation method of the positive electrode active material is adjusted. The specific parameters are shown in Table 1.

[0180] Example 32 The battery of Example 32 is prepared in a similar manner to the battery of Example 5, but the preparation method of the second positive electrode material is adjusted so that the second positive electrode material includes a hollow single pore surrounded by primary particles of the second positive electrode active material at the center position. The specific parameters are shown in Table 1.

[0181] Example 33 The battery of Example 33 is prepared in a similar manner to the battery of Example 32, but the preparation method of the second positive electrode material is adjusted so that the second positive electrode material includes multiple pores formed by the space between the primary particles of the second positive electrode material. The specific parameters are shown in Table 1.

[0182] Example 34 The battery of Example 34 is prepared in a similar manner to the battery of Example 2, but the preparation method of the second positive electrode material is adjusted so that the second positive electrode material includes a hollow single pore surrounded by primary particles of the first positive electrode active material at the center position. The specific parameters are shown in Table 1.

[0183] Example 35 The battery of Example 35 is prepared in a similar manner to the battery of Example 34, but the preparation method of the second positive electrode material is adjusted so that the second positive electrode material includes multiple pores formed by the space between the primary particles of the second positive electrode material. The specific parameters are shown in Table 1.

[0184] Example 36 The battery in Example 36 is prepared in a similar manner to the battery in Example 32, but the preparation method of the first positive electrode material is adjusted so that the first positive electrode material is a solid structure. The specific parameters are shown in Table 1.

[0185] Example 37 The battery in Example 37 is prepared in a similar manner to the battery in Example 33, but the preparation method of the first positive electrode material is adjusted so that the first positive electrode material is a solid structure. The specific parameters are shown in Table 1.

[0186] Comparative Example 1 The battery in Comparative Example 1 is prepared in a similar manner to the battery in Example 5, but the positive electrode active material only includes the first positive electrode material with a hollow structure and does not include the second positive electrode material. The specific parameters are shown in Table 1.

[0187] Comparative Example 2 The battery of Comparative Example 2 is prepared in a similar way to the battery of Example 33, but the positive electrode active material only includes a second positive electrode material with pores arranged in a ring, and does not include the first positive electrode material. The specific parameters are shown in Table 1.

[0188] Comparative Example 3 The battery of Comparative Example 3 is prepared in a similar manner to the battery of Example 2, but the positive electrode active material only includes a first positive electrode material with pores arranged in a ring, and does not include a second positive electrode material. The specific parameters are shown in Table 1.

[0189] Comparative Example 4 The battery in Comparative Example 4 is prepared in a similar manner to the battery in Example 32, but the positive electrode active material only includes the second positive electrode material with a hollow structure and does not include the first positive electrode material. The specific parameters are shown in Table 1.

[0190] Comparative Example 5 The battery of Comparative Example 5 is prepared in a similar way to the battery of Example 1, but the positive electrode active material includes a first positive electrode material and a second positive electrode material, both of which have a solid structure. The specific parameters are shown in Table 1.

[0191] Comparative Example 6 The battery of Comparative Example 6 is prepared in a similar manner to the battery of Example 1, but the parameters of the preparation method of the positive electrode active material are adjusted so that the difference between the second peak position and the first peak position in the particle size distribution diagram of the positive electrode active material is 15 μm. The specific parameters are shown in Table 1.

[0192] Comparative Example 7 The battery of Comparative Example 7 is prepared in a similar manner to the battery of Example 1, but the parameters of the preparation method of the positive electrode active material are adjusted so that the difference between the second peak position and the first peak position in the particle size distribution diagram of the positive electrode active material is 2 μm. The specific parameters are shown in Table 1.

[0193] II. Performance Testing 1. Performance testing of positive electrode active materials 1) Testing the inner diameter of the hole Conductive adhesive was applied to the sample stage. Powdered samples of the positive electrode active material from each embodiment and comparative example were spread evenly on the conductive adhesive. Unattached powder was blown away with a syringe, gold was sprayed, and the particles of the powdered sample were cross-sectionally cut using argon plasma. Scanning electron microscope (SEM) images of the powdered sample were obtained using an accelerating voltage of 10 kV and an emission current of 10 mA. The inner diameter of the pores was measured based on the SEM images. At least three samples were measured, with at least 50 data points for each sample. The average value of the data points was taken as the inner diameter of the pores in the sample.

[0194] 2) Test of the difference between the first and second peaks Particle size distribution was determined using laser diffraction method according to GB / T 19077-2016 / ISO 13320:2009, with the Malvern 3000 instrument. A particle size distribution map based on volume distribution was obtained, and the positions of the first and second peaks were determined from the particle size distribution map.

[0195] 3) Porosity test The porosity of the positive electrode active material can be tested using any method known in the art. As an example, it is measured using the gas displacement method according to GB / T24586. Porosity = (V1-V2) / V1*100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample.

[0196] 4) Average particle size D of primary particles test After imaging with a 500x scanning electron microscope (ZEISS Sigma-02-33, Germany), 200 to 600 primary particles of the positive electrode active material with complete shape and no obstruction were randomly selected from the electron micrographs, and the average value of the longest diameter of the primary particles in the micrographs was recorded as the average particle size D.

[0197] 5) Testing of Dv90, Dv50, and Dv10 Referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, 0.1g~0.13g of the sample of the positive electrode active material / first positive electrode material / second positive electrode material to be tested was weighed into a 50 mL beaker, 5g of anhydrous ethanol was added, and a stir bar of about 2.5mm was placed in the beaker and sealed with plastic wrap. After ultrasonic treatment for 5 minutes, the sample was transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were randomly selected from each batch for testing. The Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK, was used for testing. Among them, Dv90 is the particle size corresponding to a cumulative volume distribution percentage of secondary particles of the first positive electrode material / second positive electrode material reaching 90%, Dv50 is the particle size corresponding to a cumulative volume distribution percentage of secondary particles of the positive electrode active material / first positive electrode material / second positive electrode material reaching 50%, and Dv10 is the particle size corresponding to a cumulative volume distribution percentage of secondary particles of the first positive electrode material / second positive electrode material reaching 10%.

[0198] 6) Test method for tap density The tap density test of the positive electrode active material was conducted in accordance with GB / T 24533-2009 "Determination of Tap Density of Metal Powders", using a Dandong Baite BT-300 tap density meter.

[0199] Tapped density: The mass per unit volume of powder in a container after tapping under specified conditions. The calculation formula is: Pt=(m-m0) / V, where: Pt---- Tap density of powder, g / cm³ 3 ; m----Total mass of graduated cylinder and sample, in g; m0----The weight of the graduated cylinder, in grams; V---- Tap volume of powder, cm 3 .

[0200] 2. Positive electrode performance testing 1) Compacted density of the positive electrode film The compaction density of the positive electrode film layer of the positive electrode sheet is determined by measuring the areal density (g / cm³) of the positive electrode film layer on one side. 2 The density of the positive electrode film is determined by the thickness of the positive electrode film layer on one side (cm) (number of sampling points > 14). Specifically, the compacted density of the positive electrode film layer = the surface density of the positive electrode film layer on one side (g / cm³). 2 ) / Positive electrode film thickness (cm).

[0201] 2) Shear strength test Cut a piece of double-sided tape approximately 60mm in length and attach it along the longitudinal direction of the electrode. Use a blade to cut the electrode along the edge of the double-sided tape. Select a flat steel plate, sand its surface with sandpaper, wipe the surface with an alcohol-soaked cotton cloth, and dry it. Attach the double-sided tape to the steel plate, ensuring the bottom edge of the tape is more than 1cm from the bottom edge of the steel plate. Place the steel plate in a 60-80℃ oven for 5 minutes. Remove the steel plate and gently scrape off the release paper from the top of the tape with a blade. Attach the previously cut electrode to the double-sided tape on the steel plate, with the test surface facing down. Use a 2kg pressure roller to roll back and forth 3 times. Turn on the power of the Sansi tensile testing machine; the indicator light will illuminate. Adjust the limit block to the appropriate position. Fix the end of the steel plate without the electrode attached using the lower clamp, and hold the end of the steel plate without the electrode attached using the upper clamp. Then perform the test and read the values. The tensile speed is 10 mm / min.

[0202] 3. Battery performance test 1) Volumetric energy density test Battery cell capacity testing: The battery cell was left to stand at 25°C for 2 hours to ensure the temperature remained at 25°C. At 25°C, the battery cell was charged at 0.1C to the charging cutoff voltage, and then continued to be charged at this cutoff voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of the battery cell). The battery cell was then left to stand at 25°C for 1 hour. At 25°C, the battery cell was discharged at 0.1C to the discharge cutoff voltage, and the total discharge capacity C0 and total discharge energy E0 of the battery cell were recorded.

[0203] Battery cell volume measurement: The length, width and height of the battery cell are measured with calipers, and the volume V0 of the battery cell is obtained by multiplying the length, width and height of the battery cell.

[0204] Volumetric energy density calculation: The volumetric energy density of a battery cell is calculated as follows: Discharge energy of a single battery cell E0 / Volume of a single battery cell V0.

[0205] 2) Battery 40% SOC discharge time test The battery cells were discharged at a constant current of 0.33C to 2.8V and allowed to stand for 30 minutes; then charged at a constant current of 0.33C to 4.25V and then charged at a constant voltage of 0.05C until the voltage stabilized, and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 2.8V, at which point the initial capacity C0 was read, and allowed to stand for 30 minutes; charged at a constant current of 0.33C to 4.25V and then charged at a constant voltage of 0.05C until the voltage stabilized, and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 0.4C0Ah (40%) SOC and allowed to stand for 60 minutes; discharged at a constant current of 4.5C to 2.8V, and the discharge time was recorded.

[0206] 3) Cyclic performance test The secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 0.5C to the charging cutoff voltage of 4.25V, then charged at a constant voltage until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to the discharge cutoff voltage of 2.5V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge tests according to this method until the battery capacity decreased to 80%. The number of cycles at this point is the cycle life of the battery at 25°C.

[0207] III. Analysis of Test Results for Each Embodiment and Comparative Example Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Tables 1, 2, and 3 below. Table 1

[0208] Table 2

[0209] Table 3

[0210] As shown in the table above, the positive electrode active material in Examples 1 to 37 exists in the form of secondary particles formed by the aggregation of primary particles, and at least some of the secondary particles have pores; and the particle size distribution of the positive electrode active material determined by laser diffraction is bimodal, with the difference between the peak position of the second peak and the peak position of the first peak being 1 μm to 13 μm.

[0211] The particle size of the positive electrode active material in Example 1 was tested using a laser particle size analyzer. The test results are shown in [Figure 1]. Figure 1 As can be seen from the figure, the particle size distribution of the positive electrode active material is bimodal, with the difference between the peak position of the second peak and the peak position of the first peak being 1 μm to 13 μm.

[0212] A comparison of Examples 1-29, Examples 32-37, and Comparative Examples 1-4 shows that, compared to positive electrode active materials with a single-peaked particle size distribution, the positive electrode active material in this application, with a bimodal particle size distribution, exhibits higher shear strength, significantly improved battery volumetric energy density, and enhanced cycle performance. A comparison of Examples 1-29, Examples 32-37, and Comparative Example 5 shows that controlling at least some secondary particles to have pores is beneficial for improving the battery's discharge time and power performance. A comparison of Examples 1-29, Examples 36-37, and Comparative Examples 6-7 shows that controlling the difference between the second peak position and the first peak position to be 1 μm to 13 μm is beneficial for improving the compaction density of the positive electrode and the battery's cycle performance.

[0213] As seen in Examples 1-4, the secondary particles of the positive electrode active material include multiple pores formed by the spaces between the primary particles. The inner diameter of the pores is controlled to be 0.1 μm to 0.6 μm to give the positive electrode sheet excellent shear strength and the battery excellent volumetric energy density, discharge time, and cycle performance. Further controlling the inner diameter of the pores to 0.2 μm to 0.4 μm results in even higher cycle performance of the battery.

[0214] As seen in Examples 5-9, the secondary particles of the positive electrode active material include a hollow single pore surrounded by primary particles at the center. The inner diameter of the pore is controlled to be 0.5 μm to 3 μm to give the positive electrode sheet excellent shear strength and the battery excellent volumetric energy density, discharge time, and cycle performance. Further controlling the inner diameter of the pore to 0.8 μm to 1.2 μm is beneficial for further improving the discharge time.

[0215] As seen in Examples 5, 10-13, controlling the Dv50 of the first cathode material to be 8 μm to 18 μm results in excellent shear strength of the cathode sheet and excellent volumetric energy density, discharge time, and cycle performance of the battery. A comparison of Examples 5, 11-12 with Examples 10, 13 shows that further controlling the Dv50 of the first cathode material to 10 μm to 12 μm balances the shear strength of the cathode sheet, the volumetric energy density of the battery, discharge time, and cycle performance.

[0216] As can be seen from Examples 5 and 14-15, the ratio of the difference between Dv90 and Dv50 of the first positive electrode material to Dv50 of the first positive electrode material is controlled to satisfy 0.6 to 1.2, so that the positive electrode sheet has excellent shear strength and the battery has excellent volumetric energy density, discharge time and cycle performance.

[0217] As can be seen from Examples 5, 16-17, the ratio of the difference between Dv50 and Dv10 of the first positive electrode material to Dv10 of the first positive electrode material is controlled to satisfy 1.2 to 2.5, so that the positive electrode sheet has excellent shear strength and the battery has excellent volumetric energy density, discharge time and cycle performance.

[0218] A comparison of Examples 5 and 18-21 shows that controlling the Dv50 of the second cathode material to be 0.8 μm to 5 μm results in excellent shear strength for the cathode sheet and excellent volumetric energy density, discharge time, and cycle performance for the battery. A comparison of Examples 5 and 20 with Examples 18-19 and 21 shows that further controlling the Dv50 of the second cathode material to 1 μm to 3 μm is beneficial for further improving the volumetric energy density and cycle performance of the battery.

[0219] As can be seen from Examples 5, 22-23, the ratio of the difference between Dv90 and Dv50 of the second positive electrode material to Dv50 of the second positive electrode material is controlled to satisfy 0.8-1.5, so that the positive electrode sheet has excellent shear strength and the battery has excellent volumetric energy density, discharge time and cycle performance.

[0220] As can be seen from Examples 5, 24-25, the ratio of the difference between Dv50 and Dv10 of the second positive electrode material to Dv10 of the second positive electrode material is controlled to satisfy 6-12, so that the positive electrode sheet has excellent shear strength and the battery has excellent volumetric energy density, discharge time and cycle performance.

[0221] As seen in Examples 5, 26-29, controlling the mass ratio A of the first positive electrode material to the second positive electrode material to be 1.5-9 results in the positive electrode sheet exhibiting excellent shear strength, and the battery exhibiting excellent volumetric energy density, discharge time, and cycle performance. A comparison of Examples 5, 27-28 with Examples 26, 29 shows that further controlling the mass ratio A of the first positive electrode material to the second positive electrode material to be 2-8 can balance the shear strength of the positive electrode sheet, the volumetric energy density of the battery, discharge time, and cycle performance.

[0222] As can be seen from Examples 5, 30-31, the thickness of the positive electrode film is controlled to be 200 μm to 400 μm, so that the positive electrode sheet has excellent shear strength, and the battery has excellent volumetric energy density, discharge time and cycle performance.

[0223] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material exists in the form of secondary particles formed by the aggregation of primary particles, and at least some of the secondary particles have pores; and The particle size distribution of the positive electrode active material, as determined by laser diffraction, is bimodal, with the difference between the second peak and the first peak ranging from 1 μm to 13 μm.

2. The positive electrode active material according to claim 1, characterized in that, The first peak position is located at 1 μm to 5 μm, and can be selected as 1.5 μm to 4.5 μm; and / or The second peak is located at 6 μm to 14 μm, and can be selected as 8 μm to 12 μm.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The secondary particles include a plurality of pores formed by the spaces between the primary particles, wherein the inner diameter of the pores is 0.1 μm to 0.6 μm, optionally 0.2 μm to 0.4 μm; or The secondary particle includes a single hollow pore surrounded by the primary particle at the center, the inner diameter of the pore being 0.5 μm to 3 μm, optionally 0.8 μm to 1.2 μm.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that, The positive electrode active material has the following chemical formula: The a Nor x M1 y M2 1-x-y O2, Wherein, M1 and M2 include one or more of Co, Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb, with 0.8≤a≤1.2, 0.55≤x≤1.0, and 0≤y≤0.45, and optionally, 0.8≤a≤1.2, 0.95≤x≤0.995, and 0≤y≤0.

05.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that, The average particle size D of the primary particles of the positive electrode active material is 0.1 μm to 0.8 μm, and can be selected as 0.2 μm to 0.5 μm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that, The secondary particles of the positive electrode active material have a Dv50 of 9 μm to 15 μm, and can be selected as 10 μm to 12 μm.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that, The specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g~1.0 m 2 / g, can be selected as 0.2 m 2 / g~0.5 m 2 / g.

8. The positive electrode active material according to any one of claims 1 to 7, characterized in that, The positive electrode active material includes a first positive electrode material and a second positive electrode material.

9. The positive electrode active material according to claim 8, characterized in that, The first positive electrode material has the aforementioned pores, and the second positive electrode material is a solid structure; or The first positive electrode material is a solid structure, and the second positive electrode material has the aforementioned pores; or Both the first positive electrode material and the second positive electrode material have the aforementioned pores.

10. The positive electrode active material according to claim 8 or 9, characterized in that, The mass ratio A of the first positive electrode material to the second positive electrode material and the porosity B of the positive electrode active material satisfy the following condition: 0≤|BA×0.4-(1-A)×0.2|≤1.

11. The positive electrode active material according to any one of claims 8 to 10, characterized in that, The mass ratio A of the first positive electrode material to the second positive electrode material is 1.5 to 9, and can be selected as 2 to 8.

12. The positive electrode active material according to any one of claims 1 to 11, characterized in that, The porosity B of the positive electrode active material is 0.15%~0.45%, and can be selected as 0.25%~0.35%.

13. The positive electrode active material according to any one of claims 8 to 12, characterized in that, The first cathode material and the second cathode material each have the following independent chemical formulas: The a Nor x M1 y M2 1-x-y O2, Wherein, M1 and M2 include one or more of Co, Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg, and Nb, with 0.8≤a≤1.2, 0.55≤x≤1.0, and 0≤y≤0.45, and optionally, 0.8≤a≤1.2, 0.95≤x≤0.995, and 0≤y≤0.

05.

14. The positive electrode active material according to any one of claims 8 to 13, characterized in that, The Dv50 of the first cathode material is 8 μm to 18 μm, and can be selected as 10 μm to 12 μm.

15. The positive electrode active material according to any one of claims 8 to 14, characterized in that, The Dv50 of the second cathode material is 0.8 μm to 5 μm, and can be selected as 1 μm to 3 μm.

16. The positive electrode active material according to any one of claims 8 to 15, characterized in that, The ratio of the difference between Dv90 and Dv50 of the first positive electrode material to Dv50 of the first positive electrode material satisfies 0.6~1.2, and can be selected as 0.8~1.0; and / or The ratio of the difference between Dv50 and Dv10 of the first positive electrode material to Dv10 of the first positive electrode material satisfies 1.2~2.5, and can be selected as 1.5~2.

0.

17. The positive electrode active material according to any one of claims 8 to 16, characterized in that, The ratio of the difference between Dv90 and Dv50 of the second positive electrode material to Dv50 of the second positive electrode material satisfies 0.8~1.5, and can be selected as 1.0~1.3; and / or The ratio of the difference between Dv50 and Dv10 of the second positive electrode material to Dv10 of the second positive electrode material satisfies 6~12, and can be selected as 8~10.

18. A positive electrode plate, characterized in that, The positive electrode sheet 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 comprising the positive electrode active material according to any one of claims 1 to 17.

19. The positive electrode sheet according to claim 18, characterized in that, The thickness of the positive electrode film is 200 μm to 400 μm, and can be selected as 220 μm to 300 μm.

20. The positive electrode sheet according to claim 18 or 19, characterized in that, The compaction density of the positive electrode film is 2.9 g / m³. 2 ~3.5 g / m 2 .

21. A secondary battery, characterized in that, The positive electrode sheet includes any one of claims 18 to 20.

22. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 21.

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