Positive electrode active material and preparation method thereof, positive plate, battery, battery pack and electric equipment

Abstract

The embodiment of the invention provides a positive active material and a preparation method thereof, a positive plate, a battery, a battery pack and electric equipment. The positive electrode active material meets the following conditions: a difference value between a densest cumulative particle size distribution curve and a homogenized cumulative particle size distribution curve of the positive electrode active material is less than a preset value, and the preset value is less than or equal to 100. The positive electrode active material provided by the invention can realize higher bulk density, and is beneficial to improving the energy density of the battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery, a battery pack, and an electrical device. Background Art

[0002] With the rapid development of secondary batteries, people's requirements for secondary batteries are getting higher and higher. Not only is the demand for secondary batteries increasing rapidly, but also higher requirements are placed on the energy density of secondary batteries.

[0003] A higher compaction density in a positive electrode generally means more active material can be loaded per unit volume, which helps improve the volumetric energy density of the energy storage battery. The particle size distribution of the active material is one of the main factors affecting the compaction density of the positive electrode. Optimizing the particle size distribution of the active material to achieve the densest packing between particles, thereby helping the positive electrode achieve a high compaction density, is crucial for improving the energy density of energy storage batteries. Summary of the Invention

[0004] The present invention provides a positive electrode active material. Since the difference between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve of the positive electrode active material is less than a preset value, the positive electrode active material can achieve a higher packing density, which can significantly improve the compaction density of the positive electrode sheet, thereby facilitating the improvement of the energy density of the battery.

[0005] The present invention also provides a method for preparing a positive electrode active material. The method is simple to operate and can prepare a positive electrode active material with a higher bulk density.

[0006] The present invention also provides a positive electrode sheet. Since the positive electrode sheet includes the positive electrode active material, it has a higher compaction density, which helps to improve the energy density of the battery.

[0007] The present invention also provides a battery. Since the battery includes the positive electrode sheet, it can achieve higher energy output.

[0008] The present invention also provides a battery pack, which includes the battery and can achieve higher energy output.

[0009] The present invention also provides an electrical device. Since the electrical device includes the above-mentioned battery or battery pack, it has higher energy output and longer battery life.

[0010] In a first aspect, the present invention provides a positive electrode active material, wherein the positive electrode active material satisfies the following conditions:

[0011] The difference between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve of the positive electrode active material is less than a preset value, and the preset value is less than or equal to 100.

[0012] In an optional embodiment, the difference value is obtained by a method comprising the following process:

[0013] Obtaining the densest cumulative particle size distribution curve according to the maximum particle size, the minimum particle size and a preset model modulus of the positive electrode active material;

[0014] performing a homogenization process on the cumulative particle size distribution curve of the positive electrode active material to obtain a homogenized cumulative particle size distribution curve;

[0015] Difference processing is performed according to the densest cumulative particle size distribution curve and the uniformized cumulative particle size distribution curve to obtain the difference value.

[0016] In an optional embodiment, obtaining the densest cumulative particle size distribution curve according to the maximum particle size, the minimum particle size and the preset model modulus of the positive electrode active material includes: calculating the densest cumulative particle size distribution curve by formula 1:

[0017]

[0018] Among them, D L D is the maximum particle size of the positive electrode active material, unit: μm; S D is the minimum particle size of the positive electrode active material, unit: μm, j is the particle size of the most dense cumulative particle size distribution curve model, unit: μm, D S ≤D j ≤D L ; P(D j ) is the densest cumulative particle size distribution curve; n is the preset model modulus.

[0019] In an optional embodiment, 0.2≤n≤0.3.

[0020] In an optional embodiment, in Formula 1, D j The step length is Among them, 500≤a≤2000.

[0021] In an optional embodiment, the homogenization process includes the step of performing linear fitting according to Formula 2:

[0022]

[0023] Among them, D i 、D i+1 is the measured particle size of the positive electrode active material, unit: μm; Dj is the particle size of the most dense cumulative particle size distribution curve model, unit: μm; D i ≤D j ≤D i+1 ; U(D i )、U(D i+1 )、U(D j ) is the cumulative particle size distribution curve; U`(D j ) is the homogenized cumulative particle size distribution curve.

[0024] In an optional embodiment, the difference processing includes the step of calculating the mean square error by using Formula 3:

[0025]

[0026] Among them, S s is the mean square error between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve; m is D j The number of values ​​that can be taken, where m=a+1.

[0027] In an alternative embodiment, the maximum particle size of the positive electrode active material is D L , unit: μm, the minimum particle size of the positive electrode active material is D S , unit: μm, D L and D S Meet the following conditions: 5μm≤(D L -D S )≤60μm.

[0028] In an alternative embodiment, the maximum particle size of the positive electrode active material is 4 μm-65 μm.

[0029] In an optional embodiment, the minimum particle size of the positive electrode active material is 0.1 μm-5 μm.

[0030] In an alternative embodiment, the compaction density of the positive electrode active material is greater than 2.20 g / cm 3 .

[0031] In an alternative embodiment, the porosity of the positive electrode active material is no more than 15%.

[0032] In a second aspect, the present invention provides a method for preparing a positive electrode active material, comprising the following steps:

[0033] At least two positive electrode active material raw materials are obtained and blended. The blended positive electrode active material meets the following conditions:

[0034] The difference between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve of the blended positive electrode active material is less than a preset value, and the preset value is less than or equal to 100; the positive electrode active material is obtained.

[0035] In an optional embodiment, N groups of uniform cumulative particle size distribution weighted average curves are obtained based on K seed positive electrode active materials, so that the difference between the N groups of uniform cumulative particle size distribution weighted average curves and the densest cumulative particle size distribution curve is less than the preset value, and the optimized mass proportion of the K seed positive electrode active material is determined. According to the optimized mass proportion, the K seed positive electrode active materials are blended to obtain the positive electrode active material, wherein K>1,

[0036] In an optional embodiment, the N groups of uniform cumulative particle size distribution weighted average curves are obtained by a method comprising the following process:

[0037] Taking K seed positive electrode active materials, and obtaining a densest cumulative particle size distribution curve based on the maximum particle size, the minimum particle size and the preset model modulus of each seed positive electrode active material, wherein the K seed positive electrode active materials have different particle size compositions;

[0038] performing homogenization processing on the cumulative particle size distribution curve of each sub-positive electrode active material to obtain K homogenized cumulative particle size distribution curves;

[0039] The K uniform cumulative particle size distribution curves are subjected to N times of mass proportion optimization design to obtain N groups of uniform cumulative particle size distribution weighted average curves.

[0040] In an optional embodiment, the densest cumulative particle size distribution curve is obtained according to the maximum particle size, the minimum particle size and the preset model modulus of the K seed positive electrode active material.

[0041] In an optional embodiment, the method includes calculating the densest cumulative particle size distribution curve by formula 4:

[0042]

[0043] Among them, D L D is the maximum particle size of the K seed positive electrode active material, unit: μm; S is the minimum particle size of the K seed positive electrode active material, unit: μm, D j is the particle size of the most dense cumulative particle size distribution curve model of the K seed positive electrode active material, D S ≤D j ≤D L ; P(D j ) is the densest cumulative particle size distribution curve; n is the preset model modulus.

[0044] In an optional embodiment, 0.2≤n≤0.3.

[0045] In an optional embodiment, in Formula 4, D j The step length is

[0046] In an optional embodiment, the homogenization process includes the step of performing linear fitting according to Formula 5:

[0047]

[0048] Among them, D i 、D i+1 is the measured particle size of the K seed positive electrode active material, unit: μm; D j is the particle size of the most dense cumulative particle size distribution curve model, unit: μm; D i ≤D j ≤D i+1 ; U(D i )、U(D i+1 )、U(D j ) is the cumulative particle size distribution curve; U`(D j ) is the homogenized cumulative particle size distribution curve.

[0049] In an optional embodiment, performing N times of mass proportion optimization design on K uniformized cumulative particle size distribution curves includes:

[0050] Calculated by formula 6,

[0051]

[0052] Among them U h `(D j ) is the uniform cumulative particle size distribution curve of the hth seed positive electrode active material; R h is the weight percentage of the hth seed positive electrode active material, R h >0%, and

[0053] In an optional embodiment, determining the optimized mass proportion of the K seed positive electrode active material according to the difference between the N groups of uniform cumulative particle size distribution weighted average curves and the densest cumulative particle size distribution curve includes:

[0054] Calculate the mean square error of N groups using formula 7:

[0055] When the mean square error is less than a preset value, the mass proportion in the current uniform cumulative particle size distribution weighted average curve is the optimized mass proportion;

[0056]

[0057] Among them, S s is the mean square error between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve; m is D j The number of values ​​that can be taken, where m=a+1.

[0058] In an alternative embodiment, the maximum particle size of the positive electrode active material is D L , unit: μm, the minimum particle size of the positive electrode active material is D S , unit: μm, D L and D S Meet the following conditions: 5μm≤(D L -D S )≤60μm.

[0059] In an alternative embodiment, the maximum particle size of the positive electrode active material is 4 μm-65 μm.

[0060] In an optional embodiment, the minimum particle size of the positive electrode active material is 0.1 μm-5 μm.

[0061] In an alternative embodiment, the compaction density of the positive electrode active material is greater than 2.20 g / cm 3 .

[0062] In an alternative embodiment, the porosity of the positive electrode active material is no more than 15%.

[0063] In a third aspect, the present invention provides a positive electrode sheet, which includes the positive electrode active material described in the first aspect, or includes the positive electrode active material obtained by the preparation method described in the second aspect.

[0064] In a fourth aspect, the present invention provides a battery comprising the positive electrode sheet described in the third aspect.

[0065] In a fifth aspect, the present invention provides a battery pack comprising the battery described in the fourth aspect.

[0066] In a sixth aspect, the present invention provides an electrical device comprising the battery described in the fourth aspect or the battery pack described in the fifth aspect.

[0067] The positive electrode active material provided by the present invention can achieve a higher packing density because the difference between its densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve is less than a preset value. Therefore, the positive electrode active material can significantly improve the compaction density of the positive electrode sheet, thereby facilitating an increase in the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0069] Figure 1 A flowchart for determining whether the difference between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve of the positive electrode active material is less than a preset value in a specific embodiment of the present application;

[0070] Figure 2 This is a cumulative particle size distribution curve of component A, component B, and component C materials of Example 1 of the present application;

[0071] Figure 3 This is a graph showing the most dense cumulative particle size distribution curve of the positive electrode active material after the different component materials are blended in Application Example 1;

[0072] Figure 4 This is a graph showing the relationship between the proportion of each component and the mean square deviation of Example 1 of the present application;

[0073] Figure 5 This is a comparison diagram of the closest cumulative particle size distribution curve and the cumulative particle size distribution curve of the blended positive electrode active material of Example 1 of the present application;

[0074] Figure 6 This is a cross-sectional SEM image of component A, component B, and component C of Example 1 of the present application;

[0075] Figure 7 This is a SEM image of the positive electrode sheet 1 in Application Example 1 of this application;

[0076] Figure 8 This is a comparison diagram of the densest cumulative particle size distribution curve and the cumulative particle size distribution curve of the positive electrode active material peeled off from the coating of the positive electrode sheet 1 in Application Example 1 of this application;

[0077] Figure 9 This is a cumulative particle size distribution curve of component D and component E materials in Example 5 of the present application;

[0078] Figure 10 This is a relationship diagram of the proportion of each component and the mean square deviation of Example 5 and Example 8 of the present application. DETAILED DESCRIPTION

[0079] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0080] Throughout this application, references to "one embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment, embodiment, or example is included in at least one embodiment of the present invention. Therefore, appearances of the phrases "one embodiment," "an embodiment," "an example," or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and / or subcombinations in one or more embodiments or examples.

[0081] Existing solutions for optimizing the particle size distribution of positive electrode active materials generally improve the compaction density of the electrode sheet by mixing large and small particles in a certain ratio. However, the present invention has discovered through research that limiting and optimizing the particle size distribution of positive electrode active materials only by conventional particle size parameters such as D50, D90, and D10 is not comprehensive and holistic enough to optimize the particle size distribution curve. It is also impossible to define the shape of the particle size distribution curve of other parts. However, the influence of particle size distribution on compaction density is holistic. Therefore, the present invention proposes the following technical solutions:

[0082] In a first aspect, the present invention provides a positive electrode active material, which satisfies the following conditions:

[0083] The difference between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve of the positive electrode active material is less than a preset value, and the preset value is less than or equal to 100.

[0084] In the present invention, by making the difference between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve of the positive electrode active material less than a preset value, the pores between the particles of the positive electrode active material can be further reduced, which is beneficial to improving the ultimate compaction density of the positive electrode sheet, thereby effectively improving the energy density of the battery cell prepared based on the positive electrode active material.

[0085] When the preset value is less than or equal to 100, it indicates that the difference between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve of the positive electrode active material is smaller, that is, the uniform cumulative particle size distribution curve is closer to the densest cumulative particle size distribution curve. At this time, the ultimate compaction density of the positive electrode sheet can be increased, thereby effectively improving the energy density of the battery cell prepared based on the positive electrode active material.

[0086] Exemplarily, the preset value is less than or equal to any value among 90, 80, 70, 60, 50, 40, 30, 20, 10, 5, 0, etc., or a range consisting of any two of the values.

[0087] The above-mentioned positive electrode active material can be a positive electrode active material of any type of battery, including but not limited to: a positive electrode active material of a lithium ion battery, a positive electrode active material of a sodium ion battery, a positive electrode active material of a potassium ion battery, etc., wherein the positive electrode active material of the lithium ion battery includes but is not limited to: at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, lithium iron phosphate, lithium manganese iron phosphate, etc.; the positive electrode active material of the sodium ion battery includes but is not limited to: at least one of sodium iron phosphate, sodium cobalt oxide, sodium cobalt oxide, sodium vanadium fluorophosphate, sodium iron pyrophosphate, etc.; the positive electrode active material of the potassium ion battery includes but is not limited to: at least one of potassium cobalt oxide, potassium cobalt oxide, potassium iron phosphate, Prussian blue potassium iron compound, etc.

[0088] It should be noted that the particle size of the positive electrode active material can be measured by a PSA laser particle size analyzer, where D L is the maximum particle size, that is, the particle size of 100% of the particles is less than or equal to this particle size, D S The minimum particle size, that is, 100% of the particles have a particle size greater than or equal to this particle size.

[0089] For example, the PSA laser particle size analyzer may be Anton Paar's laser particle size analyzer Litesizer DIF500.

[0090] Furthermore, the wet dispersion-laser derivatization method was used for analysis and testing: 0.20±0.01 g of the positive electrode active material sample was weighed into a 100 mL beaker, 3 mL of surfactant was added dropwise, and deionized water was added to 20.0±0.1 mL. The beaker was sealed with a sealing film and placed in an ultrasonic machine (40 KHz / 210 W, output power 70%) for 5 minutes. The laser intensity was 70-90%, and the detector light energy was <100. When the shading degree reached 5-15%, the test was started to obtain the cumulative particle size distribution curve of the positive electrode active material, from which the D L and D s .

[0091] In some embodiments, the particle size parameters of the positive electrode active material can be directly tested, or can be tested after being disassembled from the positive electrode sheet.

[0092] Directly test the particle size parameters of the positive electrode active material: directly measure D using the PSA laser particle size analyzer L and D S .

[0093] If the positive electrode active material is located in the coating of the positive electrode sheet, the following disassembly process can be performed first:

[0094] The coating material on the surface of the positive electrode active material was scraped off, and the mixture was washed and ultrasonically dispersed multiple times using N-methylpyrrolidone (NMP). After centrifugation, the supernatant and precipitate were vacuum dried at 80°C. After the precipitate was dried, it was cooled to obtain the positive electrode active material to be tested.

[0095] In some embodiments, the cumulative particle size distribution curve of the positive electrode active material is a curve established with the particle diameter of the positive electrode active material as the X-axis and the volume percentage of the particle diameter of the corresponding positive electrode active material as the Y-axis, which can be directly obtained through PSA laser particle size analyzer testing.

[0096] For example, the PSA laser particle size analyzer can be an Anton Paar laser particle size analyzer Litesizer DIF500. Furthermore, a wet dispersion-laser derivatization method is used for analysis: 0.20±0.01 g of the positive electrode active material sample is weighed into a 100 mL beaker, 3 mL of a surfactant is added dropwise, and deionized water is added to 20.0±0.1 mL. The beaker is sealed with a sealing film and placed in an ultrasonic machine (40 kHz / 210 W, output power 70%) for 5 minutes. The laser intensity is 70-90%, and the detector light energy is <100. When the light shielding reaches 5-15%, the test is started to obtain the cumulative particle size distribution curve of the positive electrode active material.

[0097] In one embodiment, the difference value is obtained by a method comprising the following steps:

[0098] Obtaining the densest cumulative particle size distribution curve according to the maximum particle size, the minimum particle size and a preset model modulus of the positive electrode active material;

[0099] performing a homogenization process on the cumulative particle size distribution curve of the positive electrode active material to obtain a homogenized cumulative particle size distribution curve;

[0100] Difference processing is performed according to the densest cumulative particle size distribution curve and the uniformized cumulative particle size distribution curve to obtain the difference value.

[0101] In some embodiments, to determine whether the positive electrode active material meets the above conditions of the present invention, the following Figure 2 process,

[0102] S1: Obtain the densest cumulative particle size distribution curve based on the maximum particle size, minimum particle size and preset model modulus of the positive electrode active material;

[0103] S2: performing homogenization processing on the cumulative particle size distribution curve of the positive electrode active material to obtain a homogenized cumulative particle size distribution curve;

[0104] S3: performing difference evaluation processing based on the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve to obtain a difference value;

[0105] S4: Whether the difference between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve of the positive electrode active material is less than a preset value.

[0106] In a specific embodiment, the densest cumulative particle size distribution curve is obtained according to the maximum particle size, the minimum particle size and the preset model modulus of the positive electrode active material, including: calculating the densest cumulative particle size distribution curve by formula 1:

[0107]

[0108] Among them, D L D is the maximum particle size of the positive electrode active material, unit: μm; S D is the minimum particle size of the positive electrode active material, unit: μm, j is the particle size of the most dense cumulative particle size distribution curve model, unit: μm, D S ≤D j ≤D L ; P(D j ) is the densest cumulative particle size distribution curve; n is the preset model modulus.

[0109] When the actual cumulative particle size distribution curve of the material is the densest cumulative particle size distribution curve, the pores between the material particles are the smallest.

[0110] Among them, P(D j ) is a curve established with the particle size of the positive electrode active material as the X-axis and the volume percentage of the positive electrode active material with different particle sizes as the Y-axis.

[0111] The above-mentioned preset model modulus can be understood as a preset coefficient of the densest cumulative particle size distribution curve model. In a specific implementation manner, 0.2≤n≤0.3.

[0112] Among them, the preset model modulus affects the shape, smoothness and flexibility of the curve. The above-mentioned value range of n makes the curve smoother and more flexible, which is conducive to further reducing the pores between the positive electrode active material particles.

[0113] Dj D S to D L The adjustment range and step size thereof will affect the reliability of the most dense cumulative particle size distribution curve to a certain extent. Therefore, in a specific embodiment, in formula 1, D j The step length is Among them, 500≤a≤2000.

[0114] Among them, the step size will affect the calculation accuracy and convergence speed of the densest cumulative particle size distribution curve. A larger step size leads to rapid convergence, but may also cause oscillation or instability; a smaller step size may improve the accuracy, but the calculation time increases and the convergence speed slows down. The densest cumulative particle size distribution curve obtained by the above step size can better balance the convergence speed and accuracy of the curve, making it more reliable and conducive to further reducing the pores between the positive electrode active material particles.

[0115] In one embodiment, D j is the particle size of the positive electrode active material, which is also the particle size of the most densely packed model. j According to the step size of 0.05μm, from D S Start taking values ​​for calculation, and the intermediate values ​​are taken evenly according to the fixed step size, that is, D j =D s 、D s +0.05μm, D s +0.1μm, D s +0.15μm......D L .

[0116] In a specific embodiment, the homogenization process includes the step of performing linear fitting according to Formula 2:

[0117]

[0118] Among them, D i 、D i+1 、D j D is the particle size of the positive electrode active material, unit: μm; i ≤D j ≤D i+1 ; U(D i )、U(D i+1 )、U(D j ) is the cumulative particle size distribution curve; U`(D j ) is the homogenized cumulative particle size distribution curve.

[0119] In detail, D i is the measured particle size of the positive electrode active material, a sequence of numbers sorted by size, D i and D i+1The particle size value of the positive electrode active material represents the adjacent particle size.

[0120] Among them, the linear fitting through the above formula 2 can remove the random noise in the cumulative particle size distribution curve data, highlight the main trend or pattern of the data, and make the data more interpretable.

[0121] In a specific embodiment, the difference processing includes the step of calculating the mean square error by using Formula 3:

[0122]

[0123] Among them, S s is the mean square error between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve; m is D j The number of values ​​that can be taken, where m=a+1.

[0124] Among them, the calculation of the above-mentioned mean square deviation can obtain the difference between the densest cumulative particle size distribution curve and the uniformized cumulative particle size distribution curve of the positive electrode active material, thereby comparing the difference between the difference value and the preset value. If the difference value is less than the preset value, the positive electrode active material can further improve the ultimate compaction density of the electrode sheet.

[0125] In an alternative embodiment, the maximum particle size of the positive electrode active material is D L , unit: μm, the minimum particle size of the positive electrode active material is D S , unit: μm, D L and D S Meet the following conditions: 5μm≤(D L -D S )≤60μm; where D L and D S Satisfy: 5μm≤(D L -D S )≤60μm, the densest cumulative particle size distribution curve is more reliable, which is beneficial to further reduce the pores between the positive electrode active material particles and the particles.

[0126] For example, D L -D S = any value among 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc., or a range consisting of any two of them.

[0127] In a specific embodiment, the maximum particle size of the positive electrode active material is 4 μm-65 μm.

[0128] Illustratively, the maximum particle size of the positive electrode active material is any one of 4 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, etc., or a range consisting of any two of the values.

[0129] In a specific embodiment, the minimum particle size of the positive electrode active material is 0.1 μm-5 μm.

[0130] Illustratively, the minimum particle size of the positive electrode active material is any value among 0.1 μm, 0.5 μm, 0.7 μm, 1.0 μm, 1.5 μm, 1.7 μm, 2.0 μm, 2.5 μm, 2.7 μm, 3.0 μm, 3.5 μm, 3.7 μm, 4.0 μm, 4.5 μm, 4.7 μm, 5 μm, etc., or a range consisting of any two of the values.

[0131] When the maximum particle size and / or minimum particle size of the positive electrode active material is within the above range, the reliability of the densest cumulative particle size distribution curve can be further improved, thereby facilitating further reducing the pores between the positive electrode active material particles and improving the ultimate compaction density of the positive electrode sheet.

[0132] In a specific embodiment, the compacted density of the positive electrode active material is greater than 2.20 g / cm 3 ; The energy density of the battery cell prepared based on the positive electrode active material can be further improved.

[0133] For example, the compacted density of the positive electrode active material is 2.20 g / cm 3 , 2.21g / cm 3 , 2.22g / cm 3 , 2.23g / cm 3 , 2.24g / cm 3 , 2.25g / cm 3 , 2.26g / cm 3 , 2.27g / cm 3 , 2.28g / cm 3 , 2.29g / cm 3 , 2.30g / cm 3 , 2.31g / cm 3 , 2.32g / cm 3 , 2.33g / cm 3 , 2.34g / cm 3 , 2.35g / cm 3 , 2.36g / cm 3 , 2.37g / cm 3 , 2.38g / cm 3 , 2.39g / cm3 , 2.40g / cm 3 In a specific embodiment, the porosity of the positive electrode active material is not greater than 15%.

[0134] The porosity inside the positive electrode material particles is no more than 15%. This is mainly due to the excessive pores inside the material particles. Even if the particles can be perfectly filled with each other through particle grading, the excessive pores inside the particles will cause the overall porosity of the material to be too high, affecting the compaction density of the material.

[0135] It should be noted that the present invention does not specifically limit the preparation method of the above-mentioned positive electrode active material, and includes, but is not limited to: the positive electrode active material raw materials can be subjected to methods such as gas crushing, mechanical crushing, grinding, and blending of different positive electrode active material raw material components, so that the positive electrode active material raw materials meet the condition that the difference between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve is less than a preset value.

[0136] When different positive electrode active material raw material components are blended to prepare the positive electrode active material, the second aspect of the present invention provides a method for preparing the positive electrode active material, comprising the following steps:

[0137] At least two positive electrode active material raw materials are obtained and blended. The blended positive electrode active material meets the following conditions:

[0138] The difference between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve of the blended positive electrode active material is less than a preset value, and the preset value is less than or equal to 100; obtaining the positive electrode active material.

[0139] In a specific embodiment, N groups of uniform cumulative particle size distribution weighted average curves are obtained based on K seed positive electrode active materials, so that the difference between the N groups of uniform cumulative particle size distribution weighted average curves and the densest cumulative particle size distribution curve is less than a preset value, and the optimized mass proportion of the K seed positive electrode active material is determined. According to the optimized mass proportion, the K seeds of the positive electrode active materials are blended to obtain the positive electrode active material, wherein K>1,N.

[0140] Among them, the above preparation method uses the difference between the weighted average curves of N groups of uniformized cumulative particle size distribution and the densest cumulative particle size distribution curve to determine the optimized mass proportion of K seed positive electrode active material, and can prepare positive electrode active materials with higher stacking density.

[0141] Exemplarily, the preset value is less than or equal to any value among 90, 80, 70, 60, 50, 40, 30, 20, 10, 5, 0, etc., or a range consisting of any two of the values.

[0142] In some embodiments, the determination of N groups of solutions: setting R h is the weight percentage of the hth seed positive electrode active material (1≤h≤K), R h >0%, R h is a multiple of 0.1%, and Based on the above conditions, all the combinations of positive electrode active material ratios can be enumerated, and the cumulative number of combinations is

[0143] The above-mentioned positive electrode active material can be a positive electrode active material of any type of battery, including but not limited to: a positive electrode active material of a lithium ion battery, a positive electrode active material of a sodium ion battery, a positive electrode active material of a potassium ion battery, etc., wherein the positive electrode active material of the lithium ion battery includes but is not limited to: at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, lithium iron phosphate, lithium manganese iron phosphate, etc.; the positive electrode active material of the sodium ion battery includes but is not limited to: at least one of sodium iron phosphate, sodium cobalt oxide, sodium cobalt oxide, sodium vanadium fluorophosphate, sodium iron pyrophosphate, etc.; the positive electrode active material of the potassium ion battery includes but is not limited to: at least one of potassium cobalt oxide, potassium cobalt oxide, potassium iron phosphate, Prussian blue potassium iron compound, etc.

[0144] The K-seed positive electrode active material may be understood as a plurality of positive electrode active materials to be blended.

[0145] In one embodiment, the N groups of uniform cumulative particle size distribution weighted average curves are obtained by a method comprising the following steps:

[0146] Taking K seed positive electrode active materials, and obtaining a densest cumulative particle size distribution curve based on the maximum particle size, the minimum particle size and the preset model modulus of each seed positive electrode active material, wherein the K seed positive electrode active materials have different particle size compositions;

[0147] performing homogenization processing on the cumulative particle size distribution curve of each sub-positive electrode active material to obtain K homogenized cumulative particle size distribution curves;

[0148] The K uniform cumulative particle size distribution curves are subjected to N times of mass proportion optimization design to obtain N groups of uniform cumulative particle size distribution weighted average curves.

[0149] In some embodiments, the maximum particle size and minimum particle size of the positive electrode active material can be directly measured by a PSA laser particle size analyzer, wherein D L is the maximum particle size, that is, the particle size of 100% of the particles is less than or equal to this particle size, D S The minimum particle size, that is, 100% of the particles have a particle size greater than or equal to this particle size.

[0150] For example, the PSA laser particle size analyzer can be an Anton Paar laser particle size analyzer Litesizer DIF500. Furthermore, a wet dispersion-laser derivatization method is used for analysis: 0.20±0.01 g of the positive electrode active material sample is weighed into a 100 mL beaker, 3 mL of a surfactant is added dropwise, and deionized water is added to 20.0±0.1 mL. The beaker is sealed with a sealing film and placed in an ultrasonic machine (40 kHz / 210 W, output power 70%) for 5 minutes. The laser intensity is 70-90%, and the detector light energy is <100. The test is started when the obscuration reaches 5-15%, and the cumulative particle size distribution curve of the positive electrode active material can be obtained.

[0151] In some embodiments, the cumulative particle size distribution curve of the positive electrode active material is a curve established with the particle diameter of the positive electrode active material as the X-axis and the volume percentage of the particle diameter of the corresponding positive electrode active material as the Y-axis, which can be directly obtained through PSA testing.

[0152] In a specific embodiment, the method includes calculating the most dense cumulative particle size distribution curve using Formula 4:

[0153]

[0154] Among them, D L is the maximum particle size of the K seed positive electrode active material, unit: μm; D S is the minimum particle size of K seed positive electrode active material, unit: μm, D j is the particle size of the most dense cumulative particle size distribution curve model, D S ≤D j ≤D L ; P(D j ) is the densest cumulative particle size distribution curve; n is the preset model modulus.

[0155] The above-mentioned preset model modulus can be understood as a preset coefficient of the densest cumulative particle size distribution curve model. In a specific implementation, 0.2≤n≤0.3.

[0156] Among them, the preset model modulus affects the shape, smoothness and flexibility of the curve. The above-mentioned value range of n makes the curve smoother and more flexible, which is conducive to further reducing the pores between the positive electrode active material particles.

[0157] D j D to D L The adjustment range and step size thereof will affect the reliability of the most dense cumulative particle size distribution curve to a certain extent. Therefore, in a specific embodiment, in formula 1, D j The step length is Among them, 500≤a≤2000.

[0158] Among them, the step size will affect the calculation accuracy and convergence speed of the densest cumulative particle size distribution curve. A larger step size leads to rapid convergence, but may also cause oscillation or instability; a smaller step size may improve the accuracy, but the calculation time increases and the convergence speed slows down. The densest cumulative particle size distribution curve obtained by the above step size can better balance the convergence speed and accuracy of the curve, making it more reliable and conducive to further reducing the pores between the positive electrode active material particles.

[0159] In one embodiment, Dj is the particle size of the K seed positive electrode active material, which is also the particle size of the most densely packed model. j According to the step size of 0.05μm, from D S Start taking values ​​for calculation, and take intermediate values ​​evenly according to the fixed step size. j According to the step size of 0.05μm, from D S Start taking values ​​for calculation, that is, D j =D s 、D s +0.05μm, D s +0.1μm, D s +0.15μm......D L .

[0160] In a specific embodiment, the homogenization process includes the step of performing a linear fitting according to Formula 5:

[0161]

[0162] Among them, D i 、D i+1 is the measured particle size of the K seed positive electrode active material, unit: μm; D j is the particle size of the most dense cumulative particle size distribution curve model, unit: μm; D i ≤D j ≤D i+1 ; U(D i )、U(D i+1 )、U(D j ) is the cumulative particle size distribution curve; U`(D j ) is the homogenized cumulative particle size distribution curve.

[0163] Among them, the linear fitting through the above formula 5 can remove the random noise in the cumulative particle size distribution curve data, highlight the main trend or pattern of the data, and make the data more interpretable.

[0164] In a specific embodiment, performing N times of mass ratio optimization design on K uniform cumulative particle size distribution curves includes:

[0165] Calculated by formula 6,

[0166]

[0167] Among them U h `(D j )(h=1, 2, 3......K) is the uniform cumulative particle size distribution curve of the h-th seed positive electrode active material; R h (h=1, 2, 3.....K) is the weight percentage of the hth seed positive electrode active material, R h >0%, and

[0168] In a specific embodiment, the optimized mass proportion of the K seed positive electrode active material is determined according to the difference between the weighted average curves of the N groups of uniform cumulative particle size distributions and the densest cumulative particle size distribution curve, including:

[0169] Calculate the mean square error of N groups using formula 7:

[0170] When the mean square error is less than the preset value, the mass proportion in the current uniform cumulative particle size distribution weighted average curve is the optimized mass proportion;

[0171]

[0172] Among them, S s is the mean square error between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve; m is D j The number of values

[0173] Among them, the calculation of the above-mentioned mean square deviation can obtain the difference value between the densest cumulative particle size distribution curve and the homogenized cumulative particle size distribution curve of the positive electrode active material, so as to intuitively and reliably compare the difference between the difference value and the preset value, which is conducive to further reducing the pores between the obtained positive electrode active material particles, thereby improving the powder compaction density of the prepared positive electrode active material.

[0174] In a specific embodiment, the maximum particle size of the positive electrode active material is D L , the minimum particle size of the positive electrode active material is D S , D L and D S Meet the following conditions: 5μm≤(D L -D S )≤60μm; where D L and D S Satisfy: 5μm≤(D L -DS )≤60μm, the densest cumulative particle size distribution curve is more reliable, which is beneficial to further reduce the pores between the positive electrode active material particles and the particles.

[0175] For example, D L -D S = any value among 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc., or a range consisting of any two of them.

[0176] In a specific embodiment, the maximum particle size of the positive electrode active material is 4 μm-65 μm.

[0177] Illustratively, the maximum particle size of the positive electrode active material is any one of 4 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, etc., or a range consisting of any two of the values.

[0178] In a specific embodiment, the minimum particle size of the positive electrode active material is 0.1 μm-5 μm.

[0179] Illustratively, the minimum particle size of the positive electrode active material is any value among 0.1 μm, 0.5 μm, 0.7 μm, 1.0 μm, 1.5 μm, 1.7 μm, 2.0 μm, 2.5 μm, 2.7 μm, 3.0 μm, 3.5 μm, 3.7 μm, 4.0 μm, 4.5 μm, 4.7 μm, 5 μm, etc., or a range consisting of any two of the values.

[0180] When the maximum particle size and / or minimum particle size of the positive electrode active material is within the above range, the reliability of the densest cumulative particle size distribution curve can be further improved, thereby facilitating further reducing the pores between the positive electrode active material particles and improving the ultimate compaction density of the positive electrode sheet.

[0181] In a specific embodiment, the compacted density of the positive electrode active material is greater than 2.20 g / cm 3 ; The energy density of the battery cell prepared based on the positive electrode active material can be further improved.

[0182] For example, the compacted density of the positive electrode active material is 2.20 g / cm 3 , 2.21g / cm 3 , 2.22g / cm 3 , 2.23g / cm 3 , 2.24g / cm 3 , 2.25g / cm 3 , 2.26g / cm 3, 2.27g / cm 3 , 2.28g / cm 3 , 2.29g / cm 3 , 2.30g / cm 3 , 2.31g / cm 3 , 2.32g / cm 3 , 2.33g / cm 3 , 2.34g / cm 3 , 2.35g / cm 3 , 2.36g / cm 3 , 2.37g / cm 3 , 2.38g / cm 3 , 2.39g / cm 3 , 2.40g / cm 3 In a specific embodiment, the porosity of the positive electrode active material is not greater than 15%.

[0183] The porosity inside the positive electrode material particles is no more than 15%. This is mainly due to the excessive pores inside the material particles. Even if the particles can be perfectly filled with each other through particle grading, the excessive pores inside the particles will cause the overall porosity of the material to be too high, affecting the compaction density of the material.

[0184] In a third aspect, the present invention provides a positive electrode sheet, which includes the positive electrode active material of the first aspect, or includes the positive electrode active material obtained by the preparation method of the second aspect.

[0185] Illustratively, the above-mentioned positive electrode sheet includes a current collector and a positive electrode active material layer located on at least one surface of the current collector, the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder, the conductive agent includes the above-mentioned hard carbon material and, optionally, includes at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate; the material of the positive electrode current collector can be selected from any one or more of copper foil, titanium foil, tin foil, chromium foil, and composite foils of the above metals.

[0186] In a fourth aspect, the present invention provides a battery comprising the positive electrode sheet according to the third aspect.

[0187] Since the positive electrode active material of the present invention can be a positive electrode active material of any type of battery, the battery of the above-mentioned positive electrode sheet includes but is not limited to: lithium ion battery, sodium ion battery, magnesium ion battery, potassium ion battery, etc.

[0188] In some embodiments, the battery is a sodium ion battery and the positive electrode active material comprises sodium ferric pyrophosphate.

[0189] Illustratively, the battery further includes a separator. The present invention does not particularly limit the separator, and any known porous separator with electrochemical and chemical stability may be selected, such as at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator may be a single layer or multiple layers.

[0190] Exemplarily, the battery further comprises an electrolyte, which comprises an organic solvent and an electrolyte salt. The organic solvent acts as a medium for transporting ions in the electrochemical reaction, and can be any organic solvent known in the art for battery electrolytes; for example, the organic solvent can be at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0191] Illustratively, the battery of the present invention can be manufactured according to conventional methods in the art, such as stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, assembling them through a winding process or a stacking process to obtain a battery cell, and then packaging and baking them, injecting electrolyte, and then undergoing hot pressing and other processes to obtain a battery.

[0192] In a fifth aspect, the present invention provides a battery pack comprising the battery according to the fourth aspect.

[0193] Generally, a battery pack includes at least two of the above-mentioned batteries, which are connected as single cells to form a battery pack. The batteries can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods.

[0194] In a sixth aspect, the present invention provides an electrical device comprising the battery of the fourth aspect or the battery pack of the fifth aspect.

[0195] It should be noted that the above-mentioned electrical equipment can be any conventional equipment that requires electricity, such as but not limited to computers, electric cars, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0196] To further understand the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0197] Unless otherwise specified, all reagents involved in the embodiments of the present invention are commercially available products and can be purchased through commercial channels.

[0198] Example 1

[0199] This example provides a positive electrode active material, the preparation method of which includes the following steps:

[0200] 1) Three sodium iron pyrophosphate material components with different particle size distributions were selected and named as component A, component B, and component C. The internal porosity of the three materials was <15%, among which the maximum particle size D of component A was L -A is 4.6μm, the minimum particle size D S -A is 0.2μm; the maximum particle size of component B is D L -B is 35μm, the minimum particle size D S -B is 0.5μm; the maximum particle size of component C is D L -C is 32μm, the minimum particle size D S -C is 0.7 μm and the cumulative particle size distribution curves of the three components are as follows Figure 2 As shown, they are named U A (D j ), U B (D j ), U C (D j ), the weight percentage of each material is named R A 、R B 、R C The cumulative particle size distribution curve of the blended material can be considered as the weighted average of the three materials according to their weight proportions, that is, U 掺混 (D j )=U A (D j )×R A +U B (D j )×R B +U C (Dj )×R C , multiple groups of uniform cumulative particle size distribution weighted average curves are obtained by linear fitting through formula 5, where D j The step size is 0.0348 μm;

[0201] 2) Calculate the densest cumulative particle size distribution curve of the blended material by formula 4, where n is 0.23, and you can get Figure 3 The densest cumulative particle size distribution curve shown in the figure; where D L =D L -B=35μm,D S =D S -A=0.2μm, then D L -D S =34.8μm;

[0202] 3) R A 、R B 、R C ∈{1%, 2%, 3%......98%}, and R A +R B +R C = 100% combinations are arranged and combined, and the differences between these curves and the densest cumulative particle size distribution curve are calculated by formula 7. The above process is calculated using curve drawing software, and finally the following can be obtained: Figure 4 The relationship diagram of the proportion of each component and the mean square error is shown, where the X axis is the proportion of component A R A , the Y axis is the proportion of component B R B , component C accounts for R C =100-R A -R B , the Z axis is the mean square error S S From the data analysis, we can know that when R A =29%, R B =29%R C =42%, the mean square error S S The minimum is 7.5; that is, the optimization quality ratio is: R A =29%, R B =29%R C =42%, and sodium iron pyrophosphate materials of component A, component B, and component C were mixed according to the optimized mass ratio, and the materials were mixed by high-speed vibration in a mixer for 1 hour to obtain a positive electrode active material.

[0203] Example 2

[0204] This example provides a positive electrode active material, and its preparation method is basically the same as that of Example 1, except that: S =R when 37.5 A 、RB 、R C In order to optimize the mass ratio, the materials are mixed in a mass ratio of 20:20:60 among component A, component B and component C.

[0205] Example 3

[0206] This example provides a positive electrode active material, and its preparation method is basically the same as that of Example 1, except that: S = 78.6 when R A 、R B 、R C In order to optimize the mass ratio, the materials are mixed in a mass ratio of 15:15:70 among component A, component B and component C.

[0207] Example 4

[0208] This example provides a positive electrode active material, and its preparation method is basically the same as that of Example 1, except that: S = R when 67.5 A 、R B In order to optimize the mass ratio, the materials are mixed at a mass ratio of 25:75 between component A and component B.

[0209] Example 5

[0210] This example provides a positive electrode active material, the preparation method of which includes the following steps:

[0211] 1) Two sodium iron pyrophosphate material components with different particle size distributions are selected and named as component D and component E respectively. Among them, the maximum particle size of component D is D L -D is 5.1μm, the minimum particle size D S -D is 0.25 μm; the maximum particle size of component E is D L -E is 15.7μm, the minimum particle size D S -E is 1.3 μm; the cumulative particle size distribution curves of the two components are as follows Figure 9 As shown, according to the method of Example 1, multiple groups of uniform cumulative particle size distribution weighted average curves are obtained.

[0212] 2) Calculate the most dense cumulative particle size distribution curve of the blended material by formula 4, where n is 0.23; where D L =D L -E=15.7μm,D S =D S -D = 0.25 μm;

[0213] 3) R D and R E= 100% combinations are arranged and combined, and the differences between these curves and the most dense cumulative particle size distribution curve are calculated by formula 6. The above process is calculated using MATLAB, and finally the following can be obtained: Figure 10 The proportion of each component shown - mean square error S S From the data analysis, we can know that when R D =50, R E =50, the mean square error S S The minimum is 16.62, and the components D and E are mixed in a weight ratio of 50:50, and the materials are mixed by high-speed vibration in a mixer for 1 hour to obtain a positive electrode active material.

[0214] Example 6

[0215] This example provides a positive electrode active material, and its preparation method is basically the same as that of Example 1, except that: S =127.3 when R A 、R B 、R C In order to optimize the mass ratio, the materials are mixed in a mass ratio of 50:40:10 among component A, component B and component C.

[0216] Example 7

[0217] This example provides a positive electrode active material, and its preparation method is basically the same as that of Example 1, except that: S =536.4 when R A 、R B 、R C In order to optimize the mass ratio, the materials are mixed in a mass ratio of 80:10:10 among component A, component B and component C.

[0218] Example 8

[0219] This example provides a positive electrode active material, and its preparation method is basically the same as that of Example 5, with the following differences:

[0220] The small particle component D and the small particle component A in Example 1 are optimized to determine the ratio.

[0221] At this time, the densest cumulative particle size distribution curve of the blended material is calculated by formula 4, where n is 0.23; L =D L -D=0.51μm, D S =D S -A=0.2μm, then D L -D S =4.9μm;

[0222] According to the method of Example 1, RD and R E = 100% combinations are arranged and combined, and the differences between these curves and the most dense cumulative particle size distribution curve are calculated by formula 6. The above process is calculated using MATLAB, and finally the following can be obtained: Figure 10 The proportion of each component shown - mean square error S S From the data analysis, we can know that when R D =45, R E =55, mean square error S S The minimum is 154.9, and the components D and E are mixed in a weight ratio of 45:55. The materials are mixed by a mixer with high-speed vibration for 1 hour to obtain a positive electrode active material.

[0223] Example 9

[0224] This example provides a positive electrode active material, and its preparation method is basically the same as that of Example 1, with the following differences:

[0225] Three sodium iron pyrophosphate material components with different particle size distributions were selected and named as component F, component G, and component H. The particle size distributions of these three materials are basically consistent with the particle size distributions of component A, component B, and component H, respectively, but the internal porosity is relatively high. The specific internal porosity of the positive electrode active material particles after blending is shown in Table 1.

[0226] Based on the solution of Example 1, the ratio is optimized and the R F =29%, R G =29%R H =42%, the mean square error S S The minimum is 7.7.

[0227] Example 10

[0228] This example provides a positive electrode active material, and its preparation method is basically the same as that of Example 1, with the following differences:

[0229] Three sodium iron pyrophosphate material components with different particle size distributions were selected and named as component I, component J, and component K. The particle size distributions of these three materials are basically consistent with the particle size distributions of component A, component B, and component K, respectively, but the internal porosity is relatively high. The specific internal porosity of the positive electrode active material particles after blending is shown in Table 1.

[0230] Based on the solution of Example 1, the ratio is optimized and the R I =29%, R J =29%,R K =42%, the mean square error S S The minimum is 8.0.

[0231] Application Examples

[0232] This example provides a series of positive electrode sheets, each comprising the positive electrode active material of each embodiment or comparative example, and the preparation method thereof comprises the following steps:

[0233] The positive electrode active material, carbon nanotubes, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 100:5:4, and added to N-methylpyrrolidone to a solid content of 50%. Mechanical stirring is performed for 4 hours to prepare a conductive slurry. The conductive slurry is coated on an aluminum foil current collector and dried at 100°C to obtain a positive electrode sheet.

[0234] The positive electrode sheet prepared by using the positive electrode active material of Example 1 is named as positive electrode sheet 1. The positive electrode sheet 1 was subjected to SEM test. The results are shown in FIG. Figure 7 ,from Figure 7 It can be seen from the results that the material coating of the positive electrode sheet 1 is composed of large particles and small particles, and the particle distribution of the material has a certain span.

[0235] Test Example 1

[0236] Powder compaction density test: Use a powder compaction density tester and a 13mm diameter mold. After filling 1g of the powder sample to be tested, test the sample height when a pressure of 3T is applied to the sample and hold the pressure for 10s. Based on the sample weight, height and mold diameter, we can calculate the powder compaction density of the powder material under these pressures and record the powder compaction density under 3T.

[0237] Testing method for the average porosity inside particles: Use a scanning electron microscope (Scanning Electron Microscope) to test any cross-section of the positive electrode active material, adjust the contrast of the obtained image to the highest level, so that the pores appear black and the material entity appears white, and use ImageJ software to count the area ratio of the black area in the entire image to calculate the proportion of pores in the image. Repeat the sampling 20 times and measure according to the above method. Finally, take the average value to obtain the internal average porosity of the particles.

[0238] The above test results are recorded in Table 1.

[0239] Table 1:

[0240]

[0241]

[0242] As shown in Table 1, from Examples 1 to 8, it can be seen that the larger the mean square error between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve of the positive electrode active material, the lower the powder compaction, and the mean square error data and the powder compaction density show a very good negative correlation.

[0243] Furthermore, by comparing the data of Examples 1-5 and Examples 6-8, it can be seen that when the mean square error between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve of the positive electrode active material is less than 100, the compaction density of the powder will be higher.

[0244] By comparing Example 1, Example 9 and Example 10, we can find that when the average porosity inside the particles is smaller, the compaction density of the material can be further improved.

[0245] Test Example 2

[0246] The difference value S between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve of the positive electrode active material in the material coating of the test positive electrode sheet 1 is S , including the following steps:

[0247] 1) All the dressing materials in the coating of the positive electrode sheet 1 are scraped off, dissolved in NMP for cleaning and ultrasonic dispersion, and the dried powder is tested for particle size using a PSA laser particle size analyzer to obtain the most dense cumulative particle size distribution curve calculated by formula 1, wherein D j The step size is 0.05 μm, n is 0.23, D L =35μm, D S =0.2μm,

[0248] 2) Obtaining the cumulative particle size distribution curve of the dried powder, and performing linear fitting using Equation 2 to obtain a homogenized cumulative particle size distribution curve;

[0249] 3) Calculate the mean square error by formula 3 to obtain the difference value S between the densest cumulative particle size distribution curve and the homogenized cumulative particle size distribution curve of the powder S It is 11.5.

[0250] The difference S between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve of the positive electrode active material of Example 1 before and after being made into the positive electrode sheet S Both are smaller than the preset values, but there is a slight difference between the two. Analysis shows that this may be caused by particle breakage caused by ultrasound.

[0251] The present invention is intended to illustrate the technical solution of the present application rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solution from the scope of the technical solution of the embodiments of the present application.

Claims

1. A positive electrode active material, characterized in that The positive electrode active material meets the following conditions: The difference between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve of the positive electrode active material is less than a preset value, and the preset value is less than or equal to 100.

2. The positive electrode active material according to claim 1, characterized in that The difference value is obtained by a method comprising the following steps: Obtaining the densest cumulative particle size distribution curve according to the maximum particle size, the minimum particle size and a preset model modulus of the positive electrode active material; performing a homogenization process on the cumulative particle size distribution curve of the positive electrode active material to obtain a homogenized cumulative particle size distribution curve; Difference processing is performed according to the densest cumulative particle size distribution curve and the uniformized cumulative particle size distribution curve to obtain the difference value.

3. The positive electrode active material according to claim 2, characterized in that Obtaining the densest cumulative particle size distribution curve according to the maximum particle size, the minimum particle size and the preset model modulus of the positive electrode active material includes: calculating the densest cumulative particle size distribution curve by formula 1: Among them, D L D is the maximum particle size of the positive electrode active material, unit: μm; S D is the minimum particle size of the positive electrode active material, unit: μm, j is the particle size of the most dense cumulative particle size distribution curve model, unit: μm, D S ≤D j ≤D L ; P(D j ) is the densest cumulative particle size distribution curve; n is the preset model modulus.

4. The positive electrode active material according to claim 3, characterized in that 0.2≤n≤0.3； And / or, in Formula 1, D j The step length is Among them, 500≤a≤2000.

5. The positive electrode active material according to any one of claims 2 to 4, characterized in that: The homogenization process includes the step of performing linear fitting according to Formula 2: Among them, D i 、D i+1 is the measured particle size of the positive electrode active material, unit: μm; D j is the particle size of the most dense cumulative particle size distribution curve model, unit: μm; D i ≤D j ≤D i+1 ; U(D i )、U(D i+1 )、U(D j ) is the cumulative particle size distribution curve; U`(D j ) is the homogenized cumulative particle size distribution curve.

6. The positive electrode active material according to any one of claims 4-5, characterized in that The difference processing includes the step of calculating the mean square error using formula 3: Among them, S s is the mean square error between the densest cumulative particle size distribution curve and the uniform cumulative particle size distribution curve; m is D j The number of values ​​that can be taken, where m=a+1.

7. The positive electrode active material according to any one of claims 2 to 6, characterized in that The maximum particle size of the positive electrode active material is D L The minimum particle size of the positive electrode active material is D S , D L and D S Meet the following conditions: 5μm≤(D L -D S )≤60μm; And / or, the maximum particle size D of the positive electrode active material L 4μm-65μm; And / or, the minimum particle size D of the positive electrode active material S 0.1μm-5μm; And / or, the compaction density of the positive electrode active material is greater than 2.20 g / cm 3 ; And / or, the porosity of the positive electrode active material is not greater than 15%.

8. A method for preparing a positive electrode active material, characterized in that: The following steps are involved: At least two positive electrode active material raw materials are obtained and blended. The blended positive electrode active material meets the following conditions: The difference between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve of the blended positive electrode active material is less than a preset value, and the preset value is less than or equal to 100; the positive electrode active material is obtained.

9. The preparation method according to claim 8, characterized in that Obtain N groups of uniform cumulative particle size distribution weighted average curves based on K seed positive electrode active materials, make the difference between the N groups of uniform cumulative particle size distribution weighted average curves and the densest cumulative particle size distribution curve less than the preset value, determine the optimized mass proportion of the K seed positive electrode active material, and according to the optimized mass proportion, perform a blending process on the K seed positive electrode active materials to obtain the positive electrode active material, wherein K>1, 10. The preparation method according to claim 9, characterized in that The N groups of uniform cumulative particle size distribution weighted average curves are obtained by a method comprising the following steps: Taking K seed positive electrode active materials, and obtaining a densest cumulative particle size distribution curve based on the maximum particle size, the minimum particle size and the preset model modulus of each seed positive electrode active material, wherein the K seed positive electrode active materials have different particle size compositions; performing homogenization processing on the cumulative particle size distribution curve of each sub-positive electrode active material to obtain K homogenized cumulative particle size distribution curves; The K uniform cumulative particle size distribution curves are subjected to N times of mass proportion optimization design to obtain N groups of uniform cumulative particle size distribution weighted average curves.

11. The preparation method according to claim 10, characterized in that: The densest cumulative particle size distribution curve is obtained according to the maximum particle size, the minimum particle size and the preset model modulus of the K seed positive electrode active material.

12. The preparation method according to claim 10, characterized in that include: The densest cumulative particle size distribution curve is calculated by formula 4: Among them, D L is the maximum particle size of the K seed positive electrode active material, unit: μm; D S is the minimum particle size of the K seed positive electrode active material, unit: μm, D j is the particle size of the most dense cumulative particle size distribution curve model of the K seed positive electrode active material, unit: μm, D S ≤D j ≤D L ; P(D j ) is the densest cumulative particle size distribution curve; n is the preset model modulus.

13. The preparation method according to claim 12, characterized in that 0.2≤n≤0.3； And / or, in formula 4, D j The step length is Among them, 500≤a≤2000.

14. The preparation method according to claim 13, characterized in that The homogenization process includes the step of performing linear fitting according to Formula 5: Among them, D i 、D i+1 is the measured particle size of the positive electrode active material, unit: μm, D j is the particle size of the most dense cumulative particle size distribution curve model of the K seed positive electrode active material, unit: μm; D i ≤D j ≤D i+1 ; U(D i )、U(D i+1 )、U(D j ) is the cumulative particle size distribution curve; U`(D j ) is the homogenized cumulative particle size distribution curve.

15. The preparation method according to claim 14, characterized in that The N times of mass proportion optimization design of K uniform cumulative particle size distribution curves includes: Calculated by formula 6, Among them, U h `(D j ) is the uniform cumulative particle size distribution curve of the hth seed positive electrode active material; R h is the weight percentage of the hth seed positive electrode active material, R h >0%, and 16. The preparation method according to claim 15, characterized in that Determining the optimized mass proportion of the K seed positive electrode active material according to the difference between the weighted average curves of the N groups of uniform cumulative particle size distributions and the densest cumulative particle size distribution curve includes: Calculate the mean square error of N groups using formula 7: When the mean square error is less than a preset value, the mass proportion in the current uniform cumulative particle size distribution weighted average curve is the optimized mass proportion; Among them, S s is the mean square error between the uniform cumulative particle size distribution curve and the densest cumulative particle size distribution curve; m is D j The number of values ​​that can be taken, where m=a+1.

17. The preparation method according to claim 16, characterized in that The maximum particle size of the positive electrode active material is D L , unit: μm, the minimum particle size of the positive electrode active material is D S , unit: μm, D L and D S Meet the following conditions: 5μm≤(D L -D S )≤60μm; and / or, the maximum particle size of the positive electrode active material is 4 μm-65 μm; and / or, the minimum particle size of the positive electrode active material is 0.1 μm-5 μm; And / or, the compaction density of the positive electrode active material is greater than 2.20 g / cm 3 ; And / or, the porosity of the positive electrode active material is not greater than 15%.

18. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the positive electrode active material according to any one of claims 1 to 7, or comprises the positive electrode active material obtained by the preparation method according to any one of claims 8 to 17.

19. A battery, characterized in that: Including the positive electrode sheet according to claim 18.

20. A battery pack, characterized in that: Including the battery according to claim 19.

21. An electrical device, characterized in that: Comprising the battery according to claim 19 or the battery pack according to claim 20.

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