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

Abstract

The invention provides a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery and electric equipment, and the positive electrode active material comprises LiiMnxFe (1-x) MyPjO4 / C, x is less than or equal to 0.7, 0lt; y is less than or equal to 0.04, 0.9 lt; i is less than or equal to 1.2, 0.9 lt; j is less than or equal to 1.2, and M comprises at least one of Mg, Ca, Co, Al, Ti, V, W, Ni, Zr, B and La; the positive electrode active material comprises secondary particles formed by primary particles, in the primary particles of the positive electrode active material, the proportion of the primary particles with the particle size of 40-60 nm is 21%-35%, and the proportion of the primary particles with the particle size of 140-160 nm is 0.15%-5%. The positive electrode active material and the battery containing the positive electrode active material provided by the invention have excellent rate capability.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to positive electrode active materials and their preparation methods, positive electrode sheets, batteries, and electrical devices. Background Technology

[0002] With the rapid growth of global demand for clean energy and electric vehicles, the market demand for lithium-ion batteries continues to climb. At the same time, the market is placing higher demands on battery cost control, safety, and energy density. Phosphorus-based cathode materials, due to their wide availability of raw materials, low cost, and excellent thermal stability and safety, are gradually becoming one of the mainstream choices in the market. Among them, lithium iron phosphate (LiFePO4, LFP) has seen its market share increase year by year due to its high safety and long cycle life. However, the relatively low voltage platform of lithium iron phosphate (~3.4 V vs. Li / Li+) limits its further improvement in energy density, making it difficult to meet the needs of high-end applications. Therefore, lithium manganese iron phosphate (LMFP), which combines a high voltage platform (~4.1 V vs. Li / Li+) and high energy density, has attracted widespread attention as a next-generation phosphorus-based cathode material. LMFP not only inherits the high safety and low cost advantages of lithium iron phosphate, but also significantly improves the voltage platform and energy density of the material by introducing manganese, making it one of the ideal candidate materials for future high-energy-density lithium-ion batteries.

[0003] Lithium manganese iron phosphate (LMFP) is a new generation of high-voltage cathode material with significant advantages in theoretical capacity (170mAh / g) and safety. However, its insufficient rate performance (especially fast charging above 2C) severely restricts its application in power batteries. The current industry's main optimization directions include: (1) material nano-sizing: reducing particle size to shorten the Li+ diffusion path; (2) ion doping: introducing Mg 2+ Ti 4+ (2) Suppress Jahn-Teller distortion; (3) Carbon coating optimization: improve electronic conductivity.

[0004] Although some progress has been made in improving rate performance, the improvement is not significant. Summary of the Invention

[0005] This application aims to at least partially solve one of the technical problems in related technologies. This application proposes a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device. The positive electrode active material proposed in this application, and batteries containing it, exhibit excellent rate performance.

[0006] A first aspect of this application provides a positive electrode active material, the positive electrode active material comprising: Li i Mn x Fe1-x M y P j O4 / C, where 0.1 < x ≤ 0.7, 0 < y ≤ 0.04, 0.9 < i ≤ 1.2, 0.9 < j ≤ 1.2, and M includes at least one of Mg, Ca, Co, Al, Ti, V, W, Ni, Zr, B, and La; The positive electrode active material includes secondary particles formed by primary particles. Among the primary particles of the positive electrode active material, the proportion of primary particles with a particle size of 40 nm - 60 nm is 21% - 35%, and the proportion of primary particles with a particle size of 140 nm - 160 nm is 0.15% - 5%.

[0007] For the positive electrode active material proposed in this application, among the primary particles, the proportion of primary particles with a particle size of 40 nm - 60 nm is 21% - 35%, and the proportion of primary particles with a particle size of 140 nm - 160 nm is 0.15% - 5%. Under this particle size distribution characteristic of the primary particles, the positive electrode active material has a better size gradient, can form a continuous and unobstructed pore network, enabling the electrolyte to fully infiltrate the particle surface, reducing the transport resistance of lithium ions in the electrolyte, and can provide abundant Li + insertion / extraction active sites, thereby improving the constant current charging ratio, and further, the battery containing the positive electrode active material has excellent rate performance.

[0008] According to some embodiments of the present application, the positive electrode active material satisfies at least one of the following conditions: Among the primary particles of the positive electrode active material, the proportion of primary particles with a particle size of 40 nm - 60 nm is 28% - 33%; Among the primary particles of the positive electrode active material, the proportion of primary particles with a particle size of 140 nm - 160 nm is 0.15% - 2%.

[0009] According to some embodiments of the present application, the positive electrode active material satisfies at least one of the following conditions: The median particle size D50 of the number statistical distribution of the primary particles of the positive electrode active material is 65 nm - 75 nm; The particle size corresponding to 50% of the number distribution of the primary particles of the positive electrode active material is D50, the particle size corresponding to 90% of the number distribution is D90, and the particle size corresponding to 10% of the number distribution is D10. K90 = (D90 - D10) / D50, and K90 = 0.69 - 0.82.

[0010] According to some embodiments of the present application, the circularity of the primary particles of the positive electrode active material ≥ 0.75.

[0011] According to some embodiments of the present application, the unit cell volume of the positive electrode active material is 298.000 Å 3 -299.000 Å 3 .

[0012] According to some embodiments of this application, in the XRD pattern of the positive electrode active material, I (020) / I (311)= 0.68-0.69, where I (020) I is the diffraction intensity of the (020) crystal plane. (311) The diffraction intensity of the (311) crystal plane.

[0013] According to some embodiments of this application, the positive electrode active material satisfies at least one of the following conditions: the volume average particle size D of the positive electrode active material is... 50 The particle size is 7.0 μm-10 μm; the particle size corresponding to 50% of the particle size volume distribution of the positive electrode active material is D. 50 The particle size corresponding to 90% of the volume distribution is D. 90 The particle size corresponding to a volume distribution of 10% is D. 10 K 90 =(D 90 -D 10 ) / D 50 K 90 The mass ratio is 1.7-2.2; the positive electrode active material includes a carbon coating layer, and the mass ratio of carbon element is 1.7%-3.0% based on the total mass of the positive electrode active material.

[0014] The second aspect of this application provides a method for preparing the positive electrode active material provided in the first aspect of this application. The method includes: mixing a manganese iron phosphate precursor, a lithium source, optionally a phosphorus source, optionally a carbon source, and a grain growth inhibitor in a certain proportion to obtain a mixture; grinding the mixture for the first time and spray drying it to obtain first spray particles; subjecting the first spray particles to a first sintering to obtain a first sintering product; grinding the first sintering product for the second time to obtain a second-ground material; spray drying the second-ground material to obtain second spray particles; and subjecting the second spray particles to a second sintering to obtain the positive electrode active material.

[0015] The positive electrode active material prepared in this application achieves particle size distribution control based on a two-stage solid-state sintering process, so that the proportion of primary particles with a particle size of 40nm-60nm is 21%-35%, and the proportion of primary particles with a particle size of 140nm-160nm is 0.15%-5%, which enables the battery containing the positive electrode active material to have excellent rate performance.

[0016] According to some embodiments of this application, the method satisfies at least one of the following conditions: the grain growth inhibitor includes at least one of boric acid, magnesium oxide, and aluminum oxide; the volume average particle size of the material obtained from the first grinding is 0.1 μm-5 μm; the temperature of the first sintering is 300℃-500℃; the volume average particle size of the material from the second grinding is 0.1 μm-3 μm; the temperature of the second sintering is 500℃-700℃; and the mass of the grain growth inhibitor is 0.3%-0.8% of the mass of the manganese iron phosphate precursor.

[0017] The third aspect of this application provides a positive electrode sheet, including the positive active material provided in the first aspect of this application or the positive active material prepared by the method provided in the second aspect of this application.

[0018] The fourth aspect of this application provides a battery including the positive electrode provided in the third aspect of this application.

[0019] The fifth aspect of this application provides an electrical device, including the battery provided in the fourth aspect of this application. Attached Figure Description

[0020] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a SEM image of the positive electrode active material prepared in Example 1 of this application.

[0021] Figure 2 This is a SEM image of the positive electrode active material prepared in Example 2 of this application.

[0022] Figure 3 This is an analysis image obtained using the MetisVision 2.0 software, an intelligent particle microscopic image analysis system, of the positive electrode active material prepared in Example 1 of this application.

[0023] Figure 4 This is a 2C charge / discharge curve of the battery in Embodiments 1-2 of this application.

[0024] Figure 5 This is a 2C charge / discharge curve of the batteries used in Comparative Examples 1-2 of this application. Detailed Implementation

[0025] The embodiments of this application are described in detail below. 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 in accordance with 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.

[0026] In the first aspect of the present application, a cathode active material is provided. The cathode active material includes: Li i Mn x Fe 1- x M y P j O4 / C, where 0.1 < x ≤ 0.7, 0 < y ≤ 0.04, 0.9 < i ≤ 1.2, 0.9 < j ≤ 1.2, and M includes at least one of Mg, Ca, Co, Al, Ti, V, W, Ni, Zr, B, La; the cathode active material includes secondary particles formed by primary particles. Among the primary particles of the cathode active material, the proportion of primary particles with a particle size of 40 nm - 60 nm is 21% - 35%, and the proportion of primary particles with a particle size of 140 nm - 160 nm is 0.15% - 5%.

[0027] As an example, x can be 0.11, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or a range composed of any two of the above values; y can be 0.01, 0.02, 0.03, 0.04 or a range composed of any two of the above values; i can be 0.91, 0.95, 1, 1.05, 1.1, 1.15, 1.2 or a range composed of any two of the above values; j can be 0.91, 0.95, 1, 1.05, 1.1, 1.15, 1.2 or a range composed of any two of the above values.

[0028] For the cathode active material proposed in the present application, among the primary particles, the proportion of primary particles with a particle size of 40 nm - 60 nm is 21% - 35%, and the proportion of primary particles with a particle size of 140 nm - 160 nm is 0.15% - 5%. Under the particle size distribution characteristics of the primary particles, the cathode active material has a better size gradient, can form a continuous and unobstructed pore network, enabling the electrolyte to fully infiltrate the particle surface, reducing the transport resistance of lithium ions in the electrolyte, and providing abundant Li + insertion / extraction active sites, thereby increasing the constant current charging ratio, and further, the battery containing the cathode active material has excellent rate performance.

[0029] It is understandable that within the range of 21%-35% for primary particles with a particle size of 40nm-60nm, the proportion of primary particles in this range is significantly positively correlated with the 2C charge ratio of batteries containing positive electrode active materials. When the proportion of particles in this range is ≥22%, the 2C charge ratio increases to over 79%, which is more than 10% higher than existing methods. Within the range of 0.15%-5% for primary particles with a particle size of 140nm-160nm, the proportion of primary particles in this range is significantly negatively correlated with the 2C charge ratio of batteries containing positive electrode active materials. When the proportion of particles in this range is ≤5%, the 2C charge ratio remains stable at over 75%.

[0030] According to some embodiments of this application, the proportion of primary particles with a particle size of 40nm-60nm in the primary particles of the positive electrode active material is 21%-35%. For example, the proportion of primary particles with a particle size of 40nm-60nm can be 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or any combination of two of the above values. According to other embodiments of this application, the proportion of primary particles with a particle size of 40nm-60nm in the primary particles of the positive electrode active material is 28%-33%. Thus, the positive electrode active material can form a continuous and unobstructed porous network, allowing the electrolyte to fully wet the particle surface, reducing the transport resistance of lithium ions in the electrolyte, and providing abundant Li... + By inserting / extracting active sites, the constant current charge ratio is improved, thus giving batteries containing positive electrode active materials excellent rate performance.

[0031] According to some embodiments of this application, the proportion of primary particles with a particle size of 140nm-160nm in the primary particles of the positive electrode active material is 0.15%-5%. For example, it can be 0.15%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, or any range of two of the above values. According to other embodiments of this application, the proportion of primary particles with a particle size of 140nm-160nm in the primary particles of the positive electrode active material is 0.15%-2%. Thus, the positive electrode active material can form a continuous and unobstructed porous network, allowing the electrolyte to fully wet the particle surface, reducing the transport resistance of lithium ions in the electrolyte, and providing abundant Li... + By inserting / extracting active sites, the constant current charge ratio is improved, thus giving batteries containing positive electrode active materials excellent rate performance.

[0032] It can be understood that "the proportion of primary particles with a diameter of 40nm-60nm" and "the proportion of primary particles with a diameter of 140nm-160nm" refer to the percentage of primary particles with a diameter of 40nm-60nm and the percentage of primary particles with a diameter of 140nm-160nm in a specific number (e.g., 100) of primary particles. The diameter of the primary particles can be the average diameter. The proportion of primary particles of the above two diameters can be obtained by testing with a Hitachi S-4800 scanning electron microscope (SEM) at a voltage of 10kV. The primary particle size is statistically analyzed by taking SEM images at 30.0K magnification and using the Metis Vision 2.0 intelligent particle microscopy image analysis system to calculate the average primary particle size.

[0033] According to some embodiments of this application, the median particle size D50 of the primary particle number distribution of the positive electrode active material is 65nm-75nm. For example, it can be 65nm, 66nm, 67nm, 68nm, 69nm, 70nm, 71nm, 72nm, 73nm, 74nm, 75nm, or any range of two of the above values. The median particle size D50 refers to the particle size corresponding to a cumulative percentage distribution of 50%, meaning that particles larger than this size account for 50% of all particles, and particles smaller than this size also account for 50% of all particles. This allows the positive electrode active material to have a better size gradient, forming a continuous and unobstructed porous network, enabling the electrolyte to fully wet the particle surface, reducing the transport resistance of lithium ions in the electrolyte, and providing abundant Li-ion content. + Insertion / extraction of active sites improves the constant current charge ratio of the battery at high rates, thus giving batteries containing positive electrode active materials excellent rate performance; in addition, the shorter transport path of lithium ions in primary particles can further enhance the rate performance of the battery.

[0034] It is understandable that when the median particle size D50 of the positive electrode active material is 65nm-75nm, the 2C constant current charge ratio of the high-rate performance lithium manganese iron phosphate positive electrode material for lithium-ion batteries can reach 79%. A higher constant current charge ratio at high rates means that the battery can still maintain a high proportion of its capacity in constant current charging mode even under high current charging, which can significantly shorten the overall charging time and meet users' expectations for fast charging. On the other hand, high current charging can easily cause local polarization of the positive electrode active material (such as voltage shift and temperature rise). A higher constant current charge ratio indicates that the positive electrode active material can still maintain a stable crystal structure at high rates, and will not cause lattice collapse or active site failure due to polarization, thus ensuring a stable and efficient charging process.

[0035] According to some embodiments of this application, the particle size distribution of the primary particles of the positive electrode active material is as follows: 50% corresponds to the particle size D50, 90% corresponds to the particle size D90, and 10% corresponds to the particle size D10. K90 = (D90 - D10) / D50, and K90 = 0.69 - 0.82. For example, K90 can be 0.69, 0.7, 0.75, 0.8, 0.82, or a range of any two of the above values. D90 refers to the particle size corresponding to a cumulative distribution percentage of 90%, meaning that particles smaller than this size account for 90% of all particles. D10 refers to the particle size corresponding to a cumulative distribution percentage of 10%, meaning that particles smaller than this size account for 10% of all particles. This allows the positive electrode active material to have a better size gradient, forming a continuous and unobstructed pore network, enabling the electrolyte to fully wet the particle surface, reducing the transport resistance of lithium ions in the electrolyte, and providing abundant Li-ion content. + By inserting / extracting active sites, the constant current charge ratio of the battery at high rates is improved, thus giving batteries containing positive electrode active materials excellent rate performance.

[0036] It is understandable that the testing methods for D50, D90, and D10 of primary particles in positive electrode active materials are the same as those for the aforementioned testing methods for "the proportion of primary particles with a particle size of 40nm-60nm" and "the proportion of primary particles with a particle size of 140nm-160nm".

[0037] According to some embodiments of this application, the sphericity of the primary particles of the positive electrode active material is ≥0.75. For example, it can be 0.75, 0.8, 0.85, 0.9, 0.95, 1, or any combination of two of the above values. Controlling the sphericity of the primary particles of the positive electrode active material within the above range allows for the formation of a more complete and uniform carbon coating layer by the more rounded primary particles. This also helps to disperse stress concentration caused by volume changes during charging and discharging, reducing crack formation and thus improving the efficiency and stability of lithium-ion insertion / extraction. Consequently, it increases the constant current charge ratio of the battery containing the positive electrode active material at high rates, improving the battery's rate performance.

[0038] The sphericity of primary particles in positive electrode active materials can be determined using the following method: A clear two-dimensional projection image of the primary particle is obtained using a scanning electron microscope (SEM). The image analysis software Metis Vision 2.0 is used to accurately identify and extract the projection contour of each individual primary particle at the pixel level. Based on the extracted particle two-dimensional contour image, the actual area AP corresponding to the contour is calculated using the area calculation function of the analysis software. Using the outermost edge point of the particle projection contour as a reference, the smallest circle (i.e., the smallest circumcircle) that can enclose the contour is generated. The diameter of this circle is measured, and the area A0 of the circle is calculated using the circle area calculation formula: Circularity = AP / A0, with a value ranging from 0 to 1. The closer the value is to 1, the closer the particle projection is to a perfect circle, meaning the three-dimensional particle morphology is closer to an ideal sphere.

[0039] According to some embodiments of this application, the cell volume of the positive electrode active material is 298.000 Å. 3 -299.000Å 3 For example, it could be 298.000 Å. 3 298.1Å 3 298.2Å 3 298.3Å 3 298.4Å 3 298.5Å 3 298.6Å 3 298.7Å 3 298.8Å 3 298.9Å 3 299.000Å 3 Or any two of the above values ​​within a range, controlling the cell volume of the positive electrode active material within this range avoids channel compression caused by excessively small lattice volume, Li + The increased migration barrier prevents lattice disorder caused by excessively large cell volume, thus improving the rate performance and cycle performance of the battery.

[0040] It is understood that the cell volume of the positive electrode active material can be determined using the following method: The positive electrode active material is prepared as a flat powder sample, and an X-ray diffractometer is used with a Cu-Kα radiation source. Under certain voltage and current conditions, scanning is performed within a 2θ angle range of 10° to 80° to obtain a high-quality X-ray diffraction pattern. Structural refinement and calculation: The Rietveld full-spectrum structural refinement method is used, and professional software such as SmartLab Studio II x64 v4.6.671.0, GSAS, and FullProf are used to analyze the obtained diffraction patterns. Using the olivine structure (space group Pnma, a=10.407Å, b=6.067Å, c=4.725Å, α=β=γ=90°) as the initial model, the background, instrument zero point, peak shape parameters, lattice parameters (a, b, c), atomic coordinates, and site ratio were iteratively optimized during the refinement process until the calculated spectrum and experimental spectrum achieved the best agreement (the weighted residual factor Rwp was generally less than 15%). After the refinement converged, the final lattice parameters a, b, and c (in Å) output by the software were used to calculate the cell volume V (in Å) of the positive electrode active material according to the formula V=a×b×c. 3 ).

[0041] According to some embodiments of this application, in the XRD pattern of the positive electrode active material, I (020) / I (311) =0.68-0.69, where I (020) I is the diffraction intensity of the (020) crystal plane. (311) The diffraction intensity of the (311) crystal plane. For example, I (020) / I (311) The value can be 0.68, 0.682, 0.684, 0.686, 0.688, 0.69, or any range of two of the above values. Based on this characteristic, the positive electrode active material preferentially grows along the c-axis direction, exposing a large number of (020) active crystal planes. The (020) crystal plane is Li + The "entry face" of the one-dimensional diffusion channel, perpendicular to the lithium-ion migration direction (c-axis), directly exposes the channel port, shortening the Li-ion diffusion path. + The diffusion distance significantly reduces concentration polarization at high rates, thereby improving the cross-current charge ratio. At the same time, it avoids the negative effects of grain agglomeration and active site encapsulation caused by excessive orientation, resulting in a lower constant current charge ratio, which can further improve the rate performance of batteries containing positive electrode active materials.

[0042] Understandable, I (020) and I (311)It can be determined by the following method: the sample preparation and testing methods are consistent with the unit cell volume measurement method, and the results are directly used as the fitting results output by the structure refinement. In this invention, I (020) The angular range of the diffraction peaks used is 28.5°-30.5°, I (311) The angle range of the diffraction peaks used is 34.8°-35.8°.

[0043] According to some embodiments of this application, the volume average particle size D of the positive electrode active material 50 The particle size is 7.0μm-10μm. For example, it can be 7.0μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, or any combination of two of the above values. This shortens the lithium-ion transport path, improves the battery's rate performance, and prevents the volume-average particle size of the positive electrode active material from being too small, which would increase the contact area with the electrolyte and lead to more side reactions, resulting in excellent battery cycle performance.

[0044] According to some embodiments of this application, the particle size corresponding to 50% of the particle size volume distribution of the positive electrode active material is D. 50 The particle size corresponding to 90% of the volume distribution is D. 90 The particle size corresponding to a volume distribution of 10% is D. 10 K 90 =(D 90 -D 10 ) / D 50 K 90 For example, K is 1.7-2.2. 90 It can be 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, or any range of two of the above values, to determine the K of the positive electrode active material. 90 When controlled within the above range, the particle size of the positive electrode active material is uniform, and the channels and distances for lithium ion transport on the separator are similar, which improves the lithium ion transport efficiency and enhances the cycle performance of the secondary battery.

[0045] It is understood that in the embodiments of this application, D 90 This refers to the particle size at which the cumulative volume distribution percentage reaches 90%, meaning that particles smaller than this size account for 90% of the total particle volume; D 50 This refers to the particle size at which the cumulative volume distribution percentage reaches 50%, meaning that particles larger than this size account for 50% of the total particle volume, and particles smaller than this size also account for 50% of the total particle volume. 10Particle size refers to the particle size corresponding to a cumulative volume distribution percentage of 10%, that is, the volume content of particles smaller than this size accounts for 10% of all particles. The above three particle size values ​​can be determined using instruments and methods known in the art, such as using a laser particle size analyzer (e.g., MalvernMaster Size 3000) in accordance with standard GB / T 19077-2016.

[0046] According to some embodiments of this application, the positive electrode active material includes a carbon coating layer, and the mass percentage of carbon element is 1.7%-3.0% based on the total mass of the positive electrode active material. For example, the mass percentage of carbon element can be 1.7%, 1.9%, 2%, 2.2%, 2.4%, 2.5%, 2.7%, 2.9%, 3.0%, or any combination of two of the above values. This reduces the increased resistance to interparticle ion transport caused by excessively high carbon content, thus lowering the constant current charge ratio at high rates. Conversely, it reduces the low primary interparticle ion conductivity and even incomplete carbon network caused by excessively low carbon content, thereby lowering the constant current charge ratio at high rates. Within the above carbon content range, the constant current charge ratio of the battery containing the positive electrode active material can be improved at high rates, enhancing the battery's rate performance.

[0047] In a second aspect, this application provides a method for preparing the above-mentioned positive electrode active material. According to an embodiment of this application, the method includes: S1: Mix manganese iron phosphate precursor, lithium source, optional phosphorus source, optional carbon source and grain growth inhibitor in proportion to obtain a mixture; The manganese iron phosphate precursor includes phosphorus, manganese, and iron.

[0048] As an example, the lithium source may include at least one of lithium carbonate, lithium hydroxide, and lithium nitrate, and the phosphorus source may include at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid.

[0049] According to some embodiments of this application, the grain growth inhibitor includes at least one of boric acid, magnesium oxide, and aluminum oxide. The aforementioned grain growth inhibitor can ensure that the primary particle size in a specific range of the positive electrode active material meets the above requirements, facilitating the production of a positive electrode active material with a primary particle size of 40nm-60nm accounting for 21%-35% and a primary particle size of 140nm-160nm accounting for 0.15%-5%.

[0050] According to some embodiments of this application, the mass of the grain growth inhibitor is 0.3%-0.8% of the mass of the manganese iron phosphate precursor. For example, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or any combination of two of the above values. Thus, a positive electrode active material with a primary particle size of 40nm-60nm accounting for 21%-35% and a primary particle size of 140nm-160nm accounting for 0.15%-5% can be obtained.

[0051] According to some embodiments of this application, manganese iron phosphate precursor, lithium source, optional phosphorus source, optional carbon source and grain growth inhibitor are added to a mixing device in a preset ratio for preliminary mixing to obtain a mixture.

[0052] S2: The mixture is first ground and spray-dried to obtain the first spray particles.

[0053] According to some embodiments of this application, the volume average particle size of the material obtained from the first grinding is 0.1 μm-5 μm. For example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, or any combination of two of the above values, so as to obtain a positive electrode active material in which the proportion of primary particles with a particle size of 40 nm-60 nm is 21%-35% and the proportion of primary particles with a particle size of 140 nm-160 nm is 0.15%-5%.

[0054] According to some embodiments of this application, grinding can be wet or dry grinding.

[0055] According to some embodiments of this application, spray drying can be carried out under conditions of inlet air temperature of 180℃-250℃ and outlet air temperature of 80℃-120℃ to obtain spherical particles with a particle size of 10μm-50μm.

[0056] As an example, the inlet air temperature can be 180℃, 200℃, 220℃, 240℃, 250℃, or any combination of two of the above values; the outlet air temperature can be 80℃, 90℃, 100℃, 110℃, 120℃, or any combination of two of the above values; the particle size of the spherical particles can be 10μm, 20μm, 30μm, 40μm, 50μm, or any combination of two of the above values.

[0057] S3: Place the first sprayed particles in the first sintering to obtain a first sintering product.

[0058] According to some embodiments of this application, the temperature of the first sintering is 300℃-500℃, for example, it can be 300℃, 350℃, 400℃, 450℃, 500℃ or any combination of two of the above values. Controlling the temperature of the first sintering within the above range makes it easier to obtain a positive electrode active material with a primary particle size of 40nm-60nm accounting for 21%-35% and a primary particle size of 140nm-160nm accounting for 0.15%-5%.

[0059] According to some embodiments of this application, the obtained first spray particles are placed in a sintering furnace and heated to 300-500°C at a heating rate of 2-5°C / min under inert gas protection, and held at that temperature for 2-8 hours to complete the first sintering and obtain a first sintered product.

[0060] As an example, the heating rate can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or any combination of two of the above values; the holding time can be 2h, 4h, 5h, 7h, 8h or any combination of two of the above values.

[0061] According to some embodiments of this application, between step S3 and the second grinding, the following is also included: S31: Carbon supplementation treatment. After cooling the primary sintering product obtained in S3 to room temperature, a preset amount of carbon source (the carbon source is at least one of glucose, sucrose, polyethylene glycol, acetylene black or carbon black) is added and stirred to mix evenly to obtain the carbon-supplemented material.

[0062] S4: Grind the first sintering product (or the material after carbon supplementation) a second time to obtain the second-ground material.

[0063] According to some embodiments of this application, the volume average particle size of the secondary grinding material is 0.1μm-3μm, for example, it can be 0.1μm, 0.5μm, 1μm, 2μm, 3μm or any two of the above values. Thus, it is easy to obtain a positive electrode active material with a primary particle size of 40nm-60nm accounting for 21%-35% and a primary particle size of 140nm-160nm accounting for 0.15%-5%.

[0064] S5: Spray dry the secondary ground material to obtain second spray particles.

[0065] According to some embodiments of this application, the obtained secondary grinding material is added to a spray drying device and spray dried under the conditions of inlet air temperature of 160-220℃ and outlet air temperature of 70-100℃ to obtain secondary spherical particles with a particle size of 8-40μm.

[0066] As an example, the inlet air temperature can be 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃ or any two of the above values; the outlet air temperature can be 70℃, 80℃, 90℃, 100℃ or any two of the above values; and the particle size of the second spray particles can be 8μm, 10μm, 20μm, 30μm, 40μm or any two of the above values.

[0067] S6: The second spray particles are sintered a second time to obtain the positive electrode active material.

[0068] According to some embodiments of this application, the temperature of the second sintering is 500℃-700℃, for example, it can be 500℃, 550℃, 600℃, 650℃, 700℃, or any combination of two of the above values. This facilitates obtaining a positive electrode active material with a primary particle size of 40nm-60nm comprising 21%-35% and a primary particle size of 140nm-160nm comprising 0.15%-5%.

[0069] According to some embodiments of this application, the obtained second spray particles are placed in a sintering furnace and heated to 500-700°C at a heating rate of 1-3°C / min under inert gas protection, held at that temperature for 4-10 hours, and then naturally cooled to room temperature. As an example, the heating rate can be 1°C / min, 2°C / min, 3°C / min, or any combination of two of the above values; the holding time can be 4 hours, 5 hours, 7 hours, 9 hours, 10 hours, or any combination of two of the above values.

[0070] In summary, the method for preparing the positive electrode active material proposed in this application achieves particle size distribution control based on a two-stage solid-state sintering process. This results in primary particles with a diameter of 40nm-60nm accounting for 21%-35%, and primary particles with a diameter of 140nm-160nm accounting for 0.15%-5%, giving batteries containing the positive electrode active material excellent rate performance. It requires no complex equipment or special raw materials, has simple process steps, low cost, and is easy to scale up for industrial production.

[0071] In a third aspect, this application proposes a positive electrode sheet. According to embodiments of this application, the positive electrode sheet comprises the positive active material described in the first aspect of this application or a positive active material obtained using the method described in the second aspect of this application.

[0072] According to an embodiment of this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes the aforementioned positive active material. The positive current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). For example, the positive current collector can be an aluminum foil.

[0073] According to some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorinated acrylate resin.

[0074] According to some embodiments of this application, the positive electrode active material layer 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, or carbon nanofibers.

[0075] According to some embodiments of this application, 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 after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0076] It should be noted that the features and advantages described above for the positive electrode active material and its preparation method also apply to this positive electrode sheet, and will not be repeated here.

[0077] In a fourth aspect, this application discloses a battery. According to an embodiment of this application, the battery includes the positive electrode sheet described above.

[0078] As an example, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator located between the positive and negative electrodes. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0079] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). For example, the positive electrode current collector can be a copper foil.

[0080] According to some embodiments of the present invention, 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.

[0081] According to some embodiments of the present invention, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0082] According to some embodiments of the present invention, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0083] According to some embodiments of the present invention, 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, and binder, 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.

[0084] According to some embodiments of the present invention, the negative electrode sheet may also be a lithium metal sheet.

[0085] According to further embodiments of the present invention, the type of separator is not particularly limited, and any known porous separator with good chemical and mechanical stability can be selected. As an example, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0086] According to further embodiments of the present invention, there is no specific limitation on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be in a gel state or a completely solid state. According to some specific embodiments of the present invention, the electrolyte is an electrolyte solution comprising a lithium salt and a solvent.

[0087] According to some specific embodiments of the present invention, the lithium salt may include at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, or lithium bis(trifluoromethanesulfonyl)imide.

[0088] According to some specific embodiments of the present invention, the solvent may include at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0089] In some embodiments of this application, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0090] It should be noted that the features and advantages described above for the positive electrode also apply to this battery, and will not be repeated here.

[0091] In a fifth aspect, the present invention provides an electrical device. According to an embodiment of the invention, the electrical device includes the battery described above. According to an embodiment of the invention, the electrical device may include, but is not limited to, mobile phones, laptops, electric vehicles, etc.

[0092] It should be noted that the features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0093] 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.

[0094] Example 1 (1) The manganese iron phosphate precursor, lithium carbonate, glucose, and crystal inhibitor were mixed with pure water at a mass ratio of 100:26:1:3 (material:water = 7:13). The types of crystal inhibitors are shown in Table 1. The mixture was homogeneous by mechanical stirring milling and then ground to D50 = 0.20 μm by sand milling to obtain the first slurry. (2) The first slurry was pumped into a spray drying tower, with the inlet air temperature set at 245℃, the outlet air temperature at 100℃, and the atomization pressure at 0.2MPa, and spray drying was performed. The collected product was secondary spherical particles with a particle size D50 of 10μm; (3) The spherical particles obtained in step (2) are placed in a graphite crucible and placed in a tube sintering furnace. High-purity nitrogen is introduced as a protective gas at a flow rate of 400 mL / min. The temperature is increased from room temperature to 470°C at a rate of 1.5°C / min. After reaching the target temperature, the temperature is held for 6 hours to complete the first sintering. After naturally cooling to room temperature, the sintered product is taken out. (4) Add pure water to the primary sintering product obtained in step (3), glucose, and polyethylene glycol at a mass ratio of 100:4.6:11, with a material:water ratio of 2:3. Mix evenly using a mechanical stirring mill, and grind to D50=0.20μm using a sand mill to obtain the second slurry; (5) The second slurry obtained in step (4) is pumped into a spray drying tower. The inlet air temperature is set to 245℃, the outlet air temperature to 100℃, and the atomization pressure to 0.2MPa for spray drying. The collected product is secondary spherical particles with a particle size D50 of 10μm. (6) The spherical particles obtained in step (5) are placed in a graphite crucible and placed in a tube sintering furnace. High-purity nitrogen is introduced as a protective gas at a flow rate of 400 mL / min. The temperature is increased from room temperature to 650°C at a rate of 1.5°C / min. After reaching the target temperature, the temperature is maintained for 6 hours to complete the second sintering. After naturally cooling to room temperature, the secondary sintered product is taken out and sieved to obtain the high-rate performance lithium manganese iron phosphate cathode active material for lithium-ion batteries. The carbon content of the total mass of the cathode active material is 2.2%.

[0095] Example 2 The preparation method is the same as in Example 1, except that the secondary sintering temperature in step (6) is 675℃.

[0096] The differences between the remaining embodiments and comparative examples and Example 1 are shown in the table below. The data of the positive electrode active materials of each embodiment and comparative example are shown in the table below. If the subscripts of each element in the chemical formula or the composition changes, the amount added and the types of elements shall be adjusted accordingly.

[0097] Table 1

[0098] Performance testing In the above embodiments and comparative examples, the relevant parameters were obtained through testing using the following methods: (1) Primary particle size test: The primary particle size was obtained by scanning electron microscopy using a Thermo Fisher Scientific Apreo-2S model with an imaging voltage of 10kV. The primary particle size was statistically analyzed by taking 30.0K magnification scans and using the Metis Vision 2.0 intelligent particle microscopic image analysis system to statistically analyze the average primary particle size. The proportions of primary particles with a diameter of 40nm-60nm, the proportions of primary particles with a diameter of 140nm-160nm, the median particle size D50 of the primary particle quantity distribution, and the K90 of the primary particles were obtained.

[0099] Scanning electron microscope images of Examples 1 and 2 are shown below. Figure 1 and 2 It can be seen that the positive electrode active materials of Examples 1 and 2 have a higher content of primary particles with a particle size of 40nm-60nm and a lower content of primary particles with a particle size of 140nm-160nm.

[0100] The image obtained from the analysis by the Metis Vision 2.0 intelligent particle microscopic image analysis system in Example 1 is shown below. Figure 3 As shown, the different colors represent particles of different primary sizes.

[0101] (2) XRD test: The positive electrode active materials prepared in the examples and comparative examples, as well as the positive electrode active materials prepared in each example and comparative example, were prepared according to the method below and XRD test was performed. The equipment was a SmartLab 9kw X-ray diffractometer. The test target was Cu and the analysis was performed under Cu Kα radiation. The working voltage was 40kV and the working current was 200mA. The test angle range of the sample was 10° to 80°. The scanning mode was continuous scanning, the scanning rate was 2° / min, and the scanning step size was 0.02°.

[0102] Cell volume of positive electrode active material, I (020) I (311) The determination method is as follows: The Rietveld full-spectrum structure refinement method was employed, and professional software such as SmartLab Studio II x64 v4.6.671.0, GSAS, and FullProf were used to analyze the diffraction patterns obtained from the above scans. Using the olivine structure (space group Pnma, a=10.407Å, b=6.067Å, c=4.725Å, α=β=γ=90°) as the initial model, the background, instrument zero point, peak shape parameters, lattice parameters (a, b, c), atomic coordinates, and occupancy were iteratively optimized during the refinement process until the calculated spectrum and experimental spectrum achieved optimal agreement (the weighted residual factor Rwp was generally less than 15%). After refinement convergence, the final lattice parameters a, b, and c (in Å) output by the software were used to calculate the cell volume V (in ų) of the positive electrode active material using the formula V = a × b × c. (020) / I (311) The results obtained from the full spectrum refinement can be directly cited.

[0103] Table 2

[0104] The electrochemical performance of the positive electrode active material was tested using CR2025 coin cells. The specific fabrication process of the CR2025 coin cell is as follows: Positive electrode preparation: The positive electrode active material, conductive carbon black, and polyvinylidene fluoride (PVDF) of the above examples and comparative examples were thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 95:3:2 to form a uniform slurry. This slurry was coated onto aluminum foil and dried at 120°C for 12 h. Then, it was pressed into a positive electrode sheet with a diameter of 12 mm and a thickness of 3.2 mm using a pressure of 100 MPa. The loading of the positive electrode material was 15.5 mg / cm². 2 .

[0105] Battery Assembly: In an argon-filled glove box with both water and oxygen content less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into CR2032 coin cells and then allowed to stand for 6 hours. The negative electrode used a 15.8 mm diameter, 1 mm thick lithium metal sheet; the separator used a 25 μm thick polypropylene microporous membrane (Celgard 2325); and the electrolyte was a 1 mol / L LiPF6 solution, with equal volumes of ethylene carbonate (EC) and diethyl carbonate (DEC) as the solvent.

[0106] Electrochemical performance testing: In the following examples and comparative examples, the Shenzhen Xinwei Battery Testing System was used to test the electrochemical performance of CR2025 coin cells. The charge and discharge voltage range was controlled at 2.5-4.3V. At a constant temperature of 25°C, the coin cells were charged and discharged 4 times at 0.33C, then charged and discharged once at 0.5C, once at 1C, and once at 2C. The 2C constant current charge ratio of the positive electrode active material was evaluated, and the 0.33C charge and discharge capacity and the 1C discharge capacity were recorded respectively.

[0107] The 2C charge / discharge curves of the batteries in Examples 1 and 2 are as follows: Figure 4 As shown, the 2C charge / discharge curves of the comparative battery are as follows: Figure 5 As shown, the batteries of Examples 1-2 of this application exhibit excellent capacity and rate performance.

[0108] The test results of the batteries in the examples and comparative examples are shown in Table 3.

[0109] Table 3

[0110] Based on the performance data in Tables 1-3, it can be seen that in Examples 1-10 of this application, controlling the proportion of primary particles with a particle size of 40nm-60nm and the proportion of primary particles with a particle size of 140nm-160nm in the positive electrode active material results in batteries containing positive electrode active material exhibiting excellent rate performance. This effectively improves the 2C constant current charge ratio while simultaneously maintaining the battery's capacity and rate performance at their original levels. In Comparative Example 1, the proportion of primary particles with a particle size of 40nm-60nm is outside the range defined in this application, and in Comparative Example 2, the proportion of primary particles with a particle size of 140nm-160nm is also outside the range defined in this application, resulting in a significant decrease in the rate performance of the battery.

[0111] Compared with Example 1, Example 2 added the doping element Mg and increased the secondary sintering temperature, which reduced the proportion of primary particles with a particle size of 40nm-60nm in the positive electrode active material, reduced the smoothness of the internal pore network of the positive electrode active material, and decreased the electrolyte wetting performance. Although the specific capacity of the positive electrode active material increased, the rate performance of the battery decreased.

[0112] Compared with Example 1, the K90 of the primary particles in Example 5 was significantly increased, the uniformity of particle size distribution was reduced, and the smoothness of lithium-ion transport was reduced. Although the specific capacity of the positive electrode active material was increased, the rate performance of the battery was reduced.

[0113] Compared to Example 1, the median particle size D50 of the primary particle number distribution in Examples 6-8 was significantly increased, resulting in a longer lithium-ion transport path within the positive electrode active material and a decrease in battery rate performance. In Examples 7 and 8, the K90 of the primary particles was also significantly higher than in Example 1, leading to reduced particle size distribution uniformity and decreased smoothness of lithium-ion transport. Although the specific capacity of the positive electrode active material increased, the battery rate performance decreased.

[0114] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0115] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes: Li i Mn x Fe 1-x M y P j O4 / C, where 0.1 < x ≤ 0.7, 0 < y ≤ 0.04, 0.9 < i ≤ 1.2, 0.9 < j ≤ 1.2, and M includes at least one of Mg, Ca, Co, Al, Ti, V, W, Ni, Zr, B, and La; The positive electrode active material includes secondary particles formed by primary particles. Among the primary particles of the positive electrode active material, the proportion of primary particles with a particle size of 40 nm - 60 nm is 21% - 35%, and the proportion of primary particles with a particle size of 140 nm - 160 nm is 0.15% - 5%.

2. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material satisfies at least one of the following conditions: Among the primary particles of the positive electrode active material, the statistical proportion of primary particles with a particle size of 40 nm - 60 nm is 28% - 33%; Among the primary particles of the positive electrode active material, the statistical proportion of primary particles with a particle size of 140 nm - 160 nm is 0.15% - 2%.

3. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material satisfies at least one of the following conditions: The median particle size D50 of the statistical distribution of the primary particles of the positive electrode active material is 65 nm - 75 nm; For the positive electrode active material, the particle size corresponding to 50% of the particle size distribution of the primary particles is D50, the particle size corresponding to 90% of the particle size distribution is D90, the particle size corresponding to 10% of the particle size distribution is D10, and K90 = (D90 - D10) / D50, where K90 = 0.69 - 0.

82.

4. The positive electrode active material according to claim 1, characterized in that, The circularity of the primary particles of the positive electrode active material is ≥ 0.

75.

5. The positive electrode active material according to any one of claims 1-4, characterized in that, The cell volume of the positive electrode active material is 298.000 Å. 3 -299.000Å 3 .

6. The positive electrode active material according to any one of claims 1-4, characterized in that, In the XRD pattern of the positive electrode active material, I (020) / I (311) =0.68-0.69, where I (020) I is the diffraction intensity of the (020) crystal plane. (311) The diffraction intensity of the (311) crystal plane.

7. The positive electrode active material according to any one of claims 1-4, characterized in that, The positive electrode active material satisfies at least one of the following conditions: The volume average particle size D of the positive electrode active material 50 The thickness ranges from 7.0 μm to 10 μm. The particle size corresponding to 50% of the particle size volume distribution of the positive electrode active material is D. 50 The particle size corresponding to 90% of the volume distribution is D. 90 The particle size corresponding to a volume distribution of 10% is D. 10 K 90 =(D 90 -D 10 ) / D 50 K 90 It is 1.7-2.2; The positive electrode active material includes a carbon coating layer, and based on the total mass of the positive electrode active material, the mass proportion of carbon element is 1.7% - 3.0%.

8. A method for preparing the positive electrode active material according to any one of claims 1-7, characterized in that, It includes: Mixing a manganese iron phosphate precursor, a lithium source, an optional phosphorus source, an optional carbon source, and a grain growth inhibitor in proportion to obtain a mixed material; First grinding and spray drying the mixed material to obtain first spray particles; Placing the first spray particles in a first sintering to obtain a first sintered product; Second grinding the first sintered product to obtain a second grinding material; Spray drying the second grinding material to obtain second spray particles; Performing a second sintering on the second spray particles to obtain the positive electrode active material.

9. The method according to claim 8, characterized in that, The method satisfies at least one of the following conditions: The grain growth inhibitor includes at least one of boric acid, magnesium oxide, aluminum oxide, vanadium pentoxide, ammonium metavanadate, titanium dioxide, cobalt oxide, cobalt acetate, tungsten oxide, and nickel oxide; The volume average particle size of the material obtained by the first grinding is 0.1 μm - 5 μm; The temperature of the first sintering is 300°C - 500°C; The volume average particle size of the second grinding material is 0.1 μm - 3 μm; The temperature of the second sintering is 500°C - 700°C; The mass of the grain growth inhibitor is 0.3% - 0.8% of the mass of the manganese iron phosphate precursor.

10. A positive electrode plate, characterized in that, It includes the positive electrode active material according to any one of claims 1 - 7 or the positive electrode active material prepared by the method according to claim 8 or 9.

11. A battery, characterized in that, Includes the positive electrode sheet as described in claim 10.

12. An electrical appliance, characterized in that, Includes the battery as described in claim 11.

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