Positive electrode active material and preparation method therefor, positive electrode sheet, battery, and electric device

Abstract

The present disclosure relates to the technical field of secondary batteries, and in particular relates to a positive electrode active material and a preparation method therefor, a positive electrode sheet, a battery, and an electric device. The positive electrode active material comprises lithium iron phosphate, the lithium iron phosphate is secondary particles formed by aggregating primary particles, and the particle size number distribution curve of the primary particles presents three characteristic peaks, wherein the highest characteristic peak is a first characteristic peak, the peak position D1 of the first characteristic peak is 100-300 nm, and the corresponding number percentage N1 at the peak position D1 of the first characteristic peak is 25-35%; the peak position D2 of a second characteristic peak of the primary particles is 320-400 nm, and the corresponding number percentage N2 at the peak position D2 of the second characteristic peak is 4-9%; and the peak position D3 of a third characteristic peak of the primary particles is 450-620 nm, and the corresponding number percentage N3 at the peak position D3 of the third characteristic peak is 0.5-2%. Thus, this indicates that particles having various particle size distributions are present in the positive electrode active material, and work together to form step-by-step mixing, such that the positive electrode active material has a relatively high compaction density, and a secondary battery comprising same has a high capacity and excellent low-temperature performance.

Description

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

[0001] Priority information

[0002] This disclosure claims priority and benefits to patent application 202411752476.0, filed with the China National Intellectual Property Administration on November 30, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of secondary battery technology, specifically to a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device. Background Technology

[0004] Lithium iron phosphate (LFP) materials have become the most widely used cathode material in lithium-ion batteries due to their structural stability, good safety, and long cycle life. However, with the development of society and technology, people have placed higher demands on energy storage devices, including lithium-ion batteries. Their poor low-temperature performance has always been a bottleneck limiting their application in certain low-temperature environments. Therefore, improving the energy density and low-temperature performance of LFP batteries has become a research hotspot in the field in recent years. Particle size gradation is an effective method to improve powder compaction density. Currently, it is known to use dry mixing and gradation of LFP materials with different particle sizes to prepare high-compact LFP cathode materials. However, this method adds the preparation of LFP precursors with different particle sizes, and the materials need to be dry-mixed. The mixing uniformity cannot be guaranteed, and the cost increases significantly. In practice, it still cannot obtain high-performance LFP cathode materials that simultaneously achieve excellent low-temperature performance. Summary of the Invention

[0005] This disclosure aims to at least partially address one of the technical problems in the related art. To this end, one object of this disclosure is to provide a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device. This positive electrode active material achieves a graded structure, has a highly uniform carbon coating layer, and exhibits high conductivity and ion diffusion capability at low temperatures, combining high compaction and superior low-temperature performance. Furthermore, the preparation method of this positive electrode active material is simple and suitable for large-scale industrial production applications.

[0006] To this end, this disclosure provides a positive electrode active material, which includes lithium iron phosphate, wherein the lithium iron phosphate is secondary particles formed by the agglomeration of primary particles, and the particle size distribution curve of the primary particles exhibits three characteristic peaks.

[0007] Among them, the highest characteristic peak is the first characteristic peak, and the peak position D1 of the first characteristic peak is 100nm-300nm, and the quantity percentage N1 corresponding to the peak position D1 of the first characteristic peak is 25%-35%.

[0008] The second characteristic peak position D2 of the primary particle is 320nm-400nm, and the corresponding quantity percentage N2 at the second characteristic peak position D2 is 4%-9%.

[0009] The third characteristic peak D3 of the primary particle is located at 450nm-620nm, and the corresponding quantity percentage N3 at the third characteristic peak D3 is 0.5%-2%.

[0010] The positive electrode active material disclosed herein is a multi-stage blend, and the particle size distribution curve of the primary particles exhibits three characteristic peaks, corresponding to a large-to-small particle gradation of the primary particles in the positive electrode active material. This indicates that the positive electrode active material contains nanoscale single-crystal particles, which can fill the gaps between large particles step by step, thereby obtaining a high compaction density. At the same time, the method of multi-metal element co-doping modification is beneficial to the formation of vacancies and valence changes in the crystal structure of the positive electrode active material, widening the ion diffusion channels, promoting the mobility of lithium ions and electrons in the material, thereby improving the conductivity and ion diffusion ability at low temperatures, and enabling the secondary battery containing this positive electrode active material to obtain better low-temperature performance.

[0011] According to an embodiment of this disclosure, in the particle size distribution curve of the primary particles, there is a first minimum value D between the first characteristic peak and the second characteristic peak. 12 The first minimum value D 12 The corresponding particle size range is 270nm-320nm, and the first minimum value D 12 The corresponding quantity percentage N 12 It ranges from 3% to 6%.

[0012] According to embodiments of this disclosure, the peak splitting index γ of the positive electrode active material is 5%-40%;

[0013] Where γ=(N2-N 12 ) / N2×100%;

[0014] N 12 The first minimum value D between the first characteristic peak and the second characteristic peak 12 The corresponding percentage;

[0015] N2 is the percentage of the quantity corresponding to the peak position D2 of the second characteristic peak.

[0016] According to an embodiment of this disclosure, in the particle size distribution curve of the primary particles, there is a second minimum value D between the second characteristic peak and the third characteristic peak. 23 The second minimum value D 23 The corresponding particle size range is 400nm-500nm, and the second minimum value D 23The corresponding quantity percentage N 23 It ranges from 0.0% to 0.5%.

[0017] According to embodiments of this disclosure, the D of the primary particle 50 The range is 0.1μm-1.0μm.

[0018] According to embodiments of this disclosure, the D of the secondary particles 50 The range is 0.7μm-2.0μm.

[0019] According to embodiments of this disclosure, the compaction density of the positive electrode active material is 2.45 g / cm³. 3 -2.65g / cm 3 .

[0020] According to embodiments of this disclosure, the specific surface area of ​​the positive electrode active material is 10 m². 2 / g-13m 2 / g.

[0021] According to embodiments of this disclosure, the positive electrode active material includes a matrix and a carbon coating layer covering the surface of the matrix;

[0022] The matrix has the composition shown in Formula I: Li 1+a Fe b M c (PO4) d Formula I;

[0023] Where -0.1≤a≤0.1, 0≤b≤1, 0≤c≤0.5, 0≤d≤1;

[0024] M is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B, and Al.

[0025] According to embodiments of this disclosure, M is Nb, and at least one of Al, Nb, W, Co, V and Ti.

[0026] According to embodiments of this disclosure, the carbon coating content is 0.5wt%-2wt%, preferably 1wt%-1.5wt%, based on the total weight of the positive electrode active material.

[0027] The second aspect of this disclosure provides a method for preparing the positive electrode active material described in the first aspect, the method comprising:

[0028] A first mixed solution containing a first iron phosphate, a first lithium source, a first carbon source, and a first M source is prepared, ground to obtain a first slurry, and then subjected to a first spray drying treatment to obtain a first precursor;

[0029] A second mixture containing a second iron phosphate, a second lithium source, a second carbon source, and a second M source is prepared, ground to obtain a second slurry, and then spray-dried to obtain a second precursor.

[0030] The first precursor and the second precursor are mixed and sintered to obtain the positive electrode active material;

[0031] D of the first slurry 50 D is smaller than that of the second slurry 50 .

[0032] This disclosure prepares slurries with different particle sizes, obtaining precursors of different particle sizes, which are then blended to achieve a mixed gradation of particle sizes in the precursor stage. Subsequent sintering and crystallization further optimizes the particle size distribution of the material as the primary particles grow horizontally, resulting in tighter interparticle bonding and the preparation of a positive electrode active material that combines high capacity and high compaction density. Furthermore, this preparation method has a simple process flow and low equipment requirements, making it suitable for large-scale industrial production.

[0033] According to embodiments of this disclosure, the D of the first slurry 50 With the second slurry D 50 The difference is greater than 0.2 μm.

[0034] According to embodiments of this disclosure, the particle size of the first ferric phosphate is 80nm-200nm; the particle size of the second ferric phosphate is 50nm-160nm.

[0035] According to embodiments of this disclosure, the particle size D of the first precursor 50 The particle size D is smaller than that of the second precursor. 50 .

[0036] According to an embodiment of this disclosure, the specific surface area of ​​the first iron phosphate is 8 m². 2 / g-14m 2 / g.

[0037] According to an embodiment of this disclosure, the specific surface area of ​​the second iron phosphate is 6 m². 2 / g-10m 2 / g.

[0038] According to embodiments of this disclosure, the first iron phosphate satisfies an iron-to-phosphorus molar ratio Fe / P of 0.960-0.980.

[0039] According to embodiments of this disclosure, the second iron phosphate satisfies an iron-to-phosphorus molar ratio Fe / P of 0.950-0.970.

[0040] According to embodiments of this disclosure, the first lithium source and the second lithium source are independently selected from one of lithium hydroxide, lithium carbonate, and lithium acetate.

[0041] According to embodiments of this disclosure, the lithium iron molar ratio (Li / Fe) of the first lithium source and the first iron phosphate is 1.01-1.07.

[0042] According to embodiments of this disclosure, the lithium iron molar ratio (Li / Fe) of the second lithium source and the second iron phosphate is 1.01-1.07.

[0043] According to embodiments of this disclosure, the first carbon source is selected from at least one of glucose, sucrose, starch, polyethylene glycol, and citric acid.

[0044] According to embodiments of this disclosure, the amount of the first carbon source added satisfies the requirement that the mass ratio of carbon to the positive electrode active material is 1.0wt%-1.8wt%.

[0045] According to embodiments of this disclosure, the second carbon source is selected from at least one of glucose, sucrose, polyethylene glycol, and citric acid.

[0046] According to embodiments of this disclosure, the amount of the second carbon source added satisfies the requirement that the mass ratio of carbon to the positive electrode active material is 1.0 wt%-1.4 wt%.

[0047] According to embodiments of this disclosure, the solid content of the first slurry is 35wt%-50wt%.

[0048] According to embodiments of this disclosure, the solid content of the second slurry is 35wt%-50wt%.

[0049] According to embodiments of this disclosure, the D of the first slurry 50 The range is 0.25μm-0.45μm.

[0050] According to embodiments of this disclosure, the D of the second slurry 50 The range is 0.45μm-0.80μm.

[0051] According to embodiments of this disclosure, the inlet air temperature of the first spray drying process and the second spray drying process are independently 200°C-260°C, and the outlet air temperature is independently 80°C-110°C.

[0052] According to embodiments of this disclosure, the atomizer rotation speeds of the first spray drying process and the second spray drying process are independently 30-50 Hz.

[0053] According to embodiments of this disclosure, the particle size D of the first precursor and the second precursor is... 50 Independently, it has a size of 15μm-45μm and a water content of ≤3.0%.

[0054] According to embodiments of this disclosure, the first precursor and the second precursor are mixed in a mass ratio of (3:7) to (7:3).

[0055] According to embodiments of this disclosure, the sintering temperature is 750℃-850℃, and the sintering time is 6h-12h.

[0056] This disclosure provides a positive electrode sheet in a third aspect, the positive electrode sheet comprising the positive electrode active material described in the first aspect or the positive electrode active material prepared by the preparation method described in the second aspect. Therefore, this electrode sheet has a high core density and exhibits high capacity, high rate capability, and excellent low-temperature performance in electrochemical operation.

[0057] This disclosure provides a fourth aspect of a battery, which includes the positive electrode described in the third aspect. Therefore, the battery exhibits good electrochemical performance.

[0058] This disclosure provides a fifth aspect of an electrical device, the electrical device comprising the battery described in the fourth aspect.

[0059] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0060] The above and / or additional aspects and advantages of this disclosure will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0061] Figure 1 shows a SEM image of the lithium iron phosphate cathode active material prepared in Example 1 of this disclosure;

[0062] Figure 2 shows the XRD pattern of the lithium iron phosphate cathode active material prepared in Example 1 of this disclosure;

[0063] Figure 3 shows the particle size distribution curve of the primary particles of the lithium iron phosphate cathode active material prepared in Example 1 of this disclosure;

[0064] Figure 4 shows the particle size distribution curve of the primary particles of the lithium iron phosphate cathode active material prepared in Comparative Example 1 of this disclosure.

[0065] Detailed description of the invention

[0066] The embodiments of this disclosure are described in detail below. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure.

[0067] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0068] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0069] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0070] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0071] Unless otherwise specified, all steps in this disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0072] The first aspect of this disclosure provides a positive electrode active material, wherein the positive electrode active material is a secondary particle formed by the agglomeration of primary particles, and the particle size distribution curve of the primary particles exhibits three characteristic peaks.

[0073] Among them, the highest characteristic peak is the first characteristic peak, and the peak position D1 of the first characteristic peak is 100nm-300nm, and the quantity percentage N1 corresponding to the peak position D1 of the first characteristic peak is 25%-35%.

[0074] The second characteristic peak position D2 of the primary particle is 320nm-400nm, and the corresponding quantity percentage N2 at the second characteristic peak position D2 is 4%-9%.

[0075] The third characteristic peak D3 of the primary particle is located at 450nm-620nm, and the corresponding quantity percentage N3 at the third characteristic peak D3 is 0.5%-2%.

[0076] The particle size distribution curve of the primary particles of the cathode active material disclosed in this disclosure exhibits three characteristic peaks, indicating that the cathode active material contains primary particles with at least three particle size distributions. This indicates that the cathode active material contains single-crystal particles of different nanoscale sizes, which can fill the gaps between larger particles to significantly improve the overall powder compaction density. Simultaneously, the method of multi-metal element co-doping modification is beneficial for the formation of vacancies and valence changes in the crystal structure of the cathode active material, widening the ion diffusion channels, promoting the mobility of lithium ions and electrons in the material, thereby improving conductivity and ion diffusion capacity at low temperatures, resulting in superior low-temperature performance in secondary batteries containing this cathode active material.

[0077] The particle size distribution curve is obtained by plotting the particle size of primary particles on the horizontal axis and the percentage of the total number of particles of that size in the total number of all particles on the vertical axis.

[0078] According to a specific embodiment of this disclosure, the second characteristic peak position D2 of the primary particles is 320nm-400nm, and the corresponding quantity percentage N2 at the second characteristic peak position D2 is 4%-9%. This indicates that the primary particles have small particles within this particle size range, which can effectively fill the voids between large particles, enabling the positive electrode active material to achieve a high compaction density. When the particle size is too large, it will lead to an excessively long ion migration path, reducing capacity and charge / discharge efficiency; when the particle size is too small, it will affect the cycle life of the material. Therefore, when the second characteristic peak is in the 320nm-400nm range, it can balance the particle's own capacity, cycle balance, and better low-temperature performance.

[0079] According to a specific embodiment of this disclosure, the first characteristic peak and the second characteristic peak have a first minimum value D. 12 The first minimum value D 12The corresponding particle size range is 270nm-320nm, and the first minimum value D 12 The corresponding quantity percentage N 12 The value is 3%-6%. This results in a relatively obvious peak separation effect between the first and second characteristic peaks.

[0080] According to specific embodiments of this disclosure, the peak splitting index γ of the positive electrode active material is 5%-40%;

[0081] Where γ=(N2-N 12 ) / N2×100%;

[0082] N 12 The first minimum value D between the first characteristic peak and the second characteristic peak 12 The corresponding percentage;

[0083] N2 is the percentage of the quantity corresponding to the peak position D2 of the second characteristic peak.

[0084] When the particle size distribution of the first and / or second characteristic peaks is relatively wide, although the first and second characteristic peaks appear in the particle size distribution curve after mixing, the peak separation effect is not obvious. This is manifested in the fact that the volume percentage of the minimum value between the first and second characteristic peaks is close to the volume percentage of the maximum value of the second characteristic peak. At this time, the improvement effect on the compaction density of the particles is still small. Therefore, when the peak separation index γ meets the limitations of this disclosure, on the one hand, particles of different sizes can be effectively distributed in the structure to form a filling effect, so that the positive electrode active material can obtain a high compaction density; on the other hand, excessively large particles cannot be used for mixing, so that large particles can maintain good capacity and cycle performance.

[0085] According to a specific embodiment of this disclosure, the peak position D3 of the third characteristic peak of the primary particle is 450nm-620nm, and the percentage N3 corresponding to the peak position D3 is 0.5%-2%. This further improves the compaction density, enabling the positive electrode active material to be composed of small and large particles of a specific particle size, achieving the densest packing, thereby increasing the compaction density of the manufactured electrode sheet.

[0086] According to a specific embodiment of this disclosure, in the particle size distribution curve of the primary particles, there is a second minimum value D between the second characteristic peak and the third characteristic peak. 23 The second minimum value D 23 The corresponding particle size range is 400nm-500nm, and the second minimum value D 23 The corresponding quantity percentage N 23 It ranges from 0.0% to 0.5%.

[0087] According to specific embodiments of this disclosure, the D of the primary particles 50The size is 0.1 μm to 1.0 μm. As some specific examples, the D of the primary particles... 50 The sizes are 0.1μm, 0.5μm, 1.0μm, etc.

[0088] According to specific embodiments of this disclosure, the D of the secondary particles 50 The size ranges from 0.7 μm to 2.0 μm. As some specific examples, the D of the secondary particles... 50 The sizes are 0.7μm, 1μm, 1.5μm, 1.8μm, 2.0μm, etc.

[0089] According to a specific embodiment of this disclosure, the compaction density of the positive electrode active material is 2.45 g / cm³. 3 -2.65g / cm 3 As a specific example, the compaction density of the positive electrode active material is 2.45 g / cm³. 3 2.5g / cm 3 2.6g / cm 3 2.65g / cm 3 wait.

[0090] According to a specific embodiment of this disclosure, the specific surface area of ​​the positive electrode active material is 10 m². 2 / g-13m 2 / g. As some specific examples, the specific surface area of ​​the positive electrode active material is 10m². 2 / g、11m 2 / g、12m 2 / g、13m 2 / g etc.

[0091] According to specific embodiments of this disclosure, the positive electrode active material includes a matrix and a carbon coating layer covering the surface of the matrix;

[0092] The matrix has the composition shown in Formula I: Li 1+a Fe b M c (PO4) d Formula I;

[0093] Where -0.1≤a≤0.1, 0≤b≤1, 0≤c≤0.5, 0≤d≤1;

[0094] M is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B, and Al;

[0095] Preferably, M is selected from Nb, and also includes at least one of Al, Nb, W, Co, V and Ti.

[0096] According to specific embodiments of this disclosure, based on the total weight of the positive electrode active material, the content of the carbon coating layer is 0.5wt%-2wt%. As some specific examples, the content of the carbon coating layer is 0.5wt%, 1wt%, 1.5wt%, 2wt%, etc., preferably 1wt%-1.5wt%.

[0097] A second aspect of this disclosure provides a method for preparing the above-mentioned positive electrode active material, the method comprising:

[0098] (1) Prepare a first mixture containing a first iron phosphate, a first lithium source, a first carbon source and a first M source, and obtain a first slurry by first grinding, and obtain a first precursor by first spray drying.

[0099] According to specific embodiments of this disclosure, the particle size of the first iron phosphate is 80nm-200nm. As some specific examples, the particle size of the first iron phosphate can be 80nm, 100nm, 150nm, 200nm, etc.

[0100] According to a specific embodiment of this disclosure, the specific surface area of ​​the first iron phosphate is 8 m². 2 / g-14m 2 / g, as some specific examples, the specific surface area of ​​ferric phosphate can be 8m². 2 / g, 10m 2 / g、12m 2 / g、14m 2 / g etc. Further, the first iron phosphate satisfies an iron-to-phosphorus molar ratio Fe / P of 0.960-0.980, for example 0.960, 0.970, 0.980, etc.

[0101] According to specific embodiments of this disclosure, the specific type of the first lithium source is not particularly limited, and those skilled in the art can select it according to actual conditions. For example, the first lithium source may include at least one of lithium hydroxide, lithium carbonate, and lithium acetate, preferably lithium carbonate, and more preferably lithium carbonate with a purity ≥99.5%.

[0102] According to specific embodiments of this disclosure, the lithium iron molar Li / Fe ratio of the first lithium source and the first iron phosphate is 1.01-1.07, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, etc.

[0103] According to specific embodiments of this disclosure, the specific type of the first carbon source is not particularly limited, and those skilled in the art can select it according to actual needs. For example, the first carbon source may include at least one of glucose, sucrose, starch, polyethylene glycol, and citric acid. Further, the amount of the first carbon source added satisfies the requirement that the mass ratio of carbon to the positive electrode active material is 1.0wt%-1.8wt%, such as 1.0wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, etc.

[0104] According to specific embodiments of this disclosure, the specific type of the first M source is not particularly limited, and those skilled in the art can select it according to actual conditions. For example, the first M source may include at least one of the salts, hydroxides, and oxides of at least one element selected from La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B, and Al. Preferably, it may be aluminum oxide, titanium dioxide, ammonium metavanadate, tungsten trioxide, magnesium oxide, cobalt hydroxyl oxide, or niobium pentoxide. The addition amounts of titanium dioxide, ammonium metavanadate, tungsten trioxide, and niobium pentoxide meet the requirements that the contents of titanium, vanadium, tungsten, and niobium in the target positive electrode active material are 1000ppm-5000ppm, 1000ppm-2000ppm, 500ppm-2000ppm, and 500-2000ppm, respectively.

[0105] According to specific embodiments of this disclosure, the preparation method of the first mixture is not particularly limited and does not affect subsequent grinding, spray drying, or other steps. Specifically, the first mixture can be obtained by dissolving the first iron phosphate, the first lithium source, the first carbon source, and the first M source in a solvent, including but not limited to deionized water.

[0106] According to a specific embodiment of this disclosure, the solid content of the first slurry is 35wt%-50wt%, and the grinding results in a particle size D of the first slurry. 50 The particle size is 0.25μm-0.45μm. The grinding method is not particularly limited; it can be selected according to the specific circumstances to achieve a particle size within the target range for the slurry. This can be achieved through methods such as sand milling.

[0107] According to specific embodiments of this disclosure, the inlet and outlet air temperatures of the first spray drying process are not particularly limited, i.e., as long as the slurry is dried, preferably the water content of the spray-dried product (i.e., the first precursor) is ≤3.0%. As some specific examples, the inlet air temperature of the first spray drying process can be 200℃-260℃, and the outlet air temperature can be 80℃-110℃. Meanwhile, the atomizer rotation speed of the second spray drying process can be 30-50Hz.

[0108] According to a specific embodiment of this disclosure, the particle size D of the first precursor is... 50 Particle size D smaller than the second precursor 50 As some specific examples, the particle size D of the first precursor and the second precursor 50 It can be independently sized from 15μm to 45μm. This particle size can be achieved by pulverization after spray drying.

[0109] (2) Prepare a second mixture containing a second iron phosphate, a second lithium source, a second carbon source and a second M source, grind it to obtain a second slurry, and then spray dry it to obtain a second precursor.

[0110] According to specific embodiments of this disclosure, the particle size of the second ferric phosphate is 50nm-160nm. As some specific examples, the particle size of the first ferric phosphate can be 50nm, 70nm, 100nm, 130nm, 160nm, etc.

[0111] According to a specific embodiment of this disclosure, the specific surface area of ​​the second iron phosphate is 6 m². 2 / g-10m 2 / g, as some specific examples, the specific surface area of ​​ferric phosphate can be 6m². 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g etc. Further, the second iron phosphate satisfies an iron-phosphorus molar ratio Fe / P of 0.950-0.970, for example 0.950, 0.960, 0.970, etc.

[0112] According to specific embodiments of this disclosure, the specific type of the second lithium source is not particularly limited, and those skilled in the art can select it according to actual conditions. For example, the second lithium source may include at least one of lithium hydroxide, lithium carbonate, and lithium acetate, preferably lithium carbonate, and more preferably lithium carbonate with a purity ≥99.5%.

[0113] According to specific embodiments of this disclosure, the lithium iron molar Li / Fe ratio of the second lithium source and the second iron phosphate is 1.01-1.07, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, etc.

[0114] According to specific embodiments of this disclosure, the specific type of the second carbon source is not particularly limited, and those skilled in the art can select it according to actual needs. For example, the second carbon source may include at least one of glucose, sucrose, polyethylene glycol, and citric acid. Further, the amount of the second carbon source added satisfies the requirement that the mass ratio of carbon to the positive electrode active material is 1.0wt%-1.4wt%, such as 1.0wt%, 1.2wt%, 1.4wt%, etc.

[0115] According to specific embodiments of this disclosure, the specific type of the second M source is not particularly limited, and those skilled in the art can select it according to actual conditions. For example, the second M source may include at least one of the salts, hydroxides, and oxides of at least one element selected from La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B, and Al. Preferably, it may be aluminum oxide, titanium dioxide, ammonium metavanadate, tungsten trioxide, magnesium oxide, cobalt hydroxyl oxide, or niobium pentoxide. The addition amounts of titanium dioxide, ammonium metavanadate, and tungsten trioxide meet the requirements that the titanium, vanadium, and tungsten content of the target positive electrode active material is 1000ppm-5000ppm, 1000ppm-2000ppm, and 500ppm-2000ppm, respectively.

[0116] According to specific embodiments of this disclosure, the preparation method of the second mixture is not particularly limited and does not affect subsequent grinding, spray drying, or other steps. Specifically, the second mixture can be obtained by dissolving the second iron phosphate, the second lithium source, the second carbon source, and the second M source in a solvent, including but not limited to deionized water.

[0117] According to a specific embodiment of this disclosure, the D of the first slurry 50 D is smaller than that of the second slurry 50 D of the preferred first slurry 50 With the second slurry D 50 The difference is greater than 0.2 μm. By preparing slurries with different particle sizes, precursors of different particle sizes are obtained and blended to achieve a mixed gradation of particle sizes in the precursor stage. Subsequent sintering and crystallization further optimize the particle size distribution of the material as the primary particles grow horizontally, resulting in tighter interparticle bonding. This is beneficial for preparing positive electrode active materials that combine high capacity and high compaction density. When the D of the two slurries... 50 The difference must be greater than 0.2 μm to achieve a better mixing effect.

[0118] According to a specific embodiment of this disclosure, the solid content of the second slurry is 35wt%-50wt%, and the grinding results in a particle size D of the second slurry. 50The particle size is 0.45μm-0.80μm. The grinding method is not particularly limited; it can be selected according to the specific circumstances to achieve a particle size within the target range for the slurry. This can be achieved through methods such as sand milling.

[0119] According to specific embodiments of this disclosure, the inlet and outlet air temperatures of the second spray drying process are not particularly limited, i.e., as long as the slurry is dried, preferably the water content of the spray-dried product (i.e., the second precursor) is ≤3.0%. As some specific examples, the inlet air temperature of the second spray drying process can be 200℃-260℃, and the outlet air temperature can be 80℃-110℃. Simultaneously, the atomizer rotation speed of the second spray drying process can be 30-50Hz.

[0120] (3) The first precursor and the second precursor are mixed and sintered to obtain the positive electrode active material.

[0121] According to specific embodiments of this disclosure, the mixing ratio of the first precursor and the second precursor is not particularly limited, and those skilled in the art can make reasonable adjustments as appropriate. As some specific examples, the first precursor and the second precursor are mixed in a mass ratio of (3:7) to (7:3), such as 3:7, 2:3, 1:1, 3:2, 7:3, etc.

[0122] According to specific embodiments of this disclosure, the sintering temperature and time are not particularly limited, and those skilled in the art can make reasonable adjustments as needed. As some specific examples, the sintering temperature can be 750℃-850℃, and the sintering time can be 6h-12h. Further, the sintering is preferably carried out in an inert atmosphere, such as nitrogen.

[0123] A third aspect of this disclosure provides a positive electrode sheet comprising the positive active material described in the first aspect of this disclosure or the positive active material prepared by the method described in the second aspect of this disclosure.

[0124] The positive electrode typically includes a positive current collector and a positive active material layer disposed on the positive current collector, wherein the positive active material layer includes a positive active material.

[0125] The positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal materials on a polymer substrate). As an example, the positive electrode current collector may include at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil.

[0126] The positive electrode active material includes the positive electrode active material described in the first aspect of this disclosure or the positive electrode active material prepared by the method described in the second aspect of this disclosure.

[0127] The positive electrode active material layer may also optionally include a conductive agent and a binder. The conductive agent is used to improve the conductivity of the positive electrode active material layer, and the binder is used to firmly bond the positive electrode active material and the binder to the positive electrode current collector. This disclosure does not specifically limit the types of conductive agents and binders, which can be selected according to actual needs.

[0128] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may include at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers, or modified (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives thereof.

[0129] These materials can all be obtained through commercial means.

[0130] This disclosure provides a fourth aspect of a battery that includes the positive electrode as described in the third aspect of this disclosure. Therefore, the battery has excellent cycle life.

[0131] A battery is a device that can be recharged after being discharged, allowing its active materials to be reactivated and the device to continue functioning.

[0132] It is understandable that the battery proposed in this disclosure is a lithium-ion battery.

[0133] Typically, a battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, acting as a conductor of ions, lies between the positive and negative electrodes.

[0134] [Negative electrode plate]

[0135] In the battery, the negative electrode sheet can be lithium metal or a lithium-containing alloy.

[0136] In some embodiments, the negative electrode active material may include a silicon-based material in order to further improve the energy density of the battery.

[0137] The negative electrode active material layer may also optionally include binders, conductive agents, and other optional additives.

[0138] As an example, conductive agents may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0139] As an example, the adhesive may include one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0140] As an example, other optional additives may include thickeners and dispersants (such as sodium carboxymethyl cellulose CMC-Na) and PTC thermistor materials.

[0141] Electrolyte

[0142] The electrolyte may include an electrolyte salt and a solvent.

[0143] As an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0144] As an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0145] In some embodiments, the electrolyte may also include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0146] [Isolation membrane]

[0147] As the aforementioned separator, this disclosure does not impose any particular limitations. Any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, it may include a combination of at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0148] This disclosure provides a fifth aspect of an electrical device that includes the battery described in the fourth aspect. Specifically, the battery can serve as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, and energy storage systems.

[0149] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. 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 the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0150] The relevant parameters in the following embodiments and comparative examples were obtained through testing using the following methods:

[0151] (1) Morphological test: obtained by scanning electron microscope of model Regulus 8100 of Hitachi, Japan;

[0152] (2) X-ray diffraction (XRD) test: obtained by using a SmartLab 9kW X-ray diffractometer from Rigaku Corporation, Japan;

[0153] (3) Median particle size D 50 The particle size distribution was obtained using a Marvern Mastersizer 3000 laser particle size analyzer.

[0154] (4) Average primary particle size: The prepared lithium iron phosphate cathode active material was photographed at 30.0K magnification using a scanning electron microscope, and the average primary particle size was calculated using LIBMAS and Nano Measurer software.

[0155] (5) Specific surface area (BET) test: obtained by using a Micromeritics Tristar 3020 specific surface area analyzer;

[0156] (6) Powder compaction density test: Weigh 1g of the prepared lithium iron phosphate positive electrode active material and put it into the compaction mold. Put the mold into the compaction equipment and test the result under 30KN pressure.

[0157] (7) Particle size distribution test: The prepared lithium iron phosphate cathode active material was photographed at 30.0K magnification using scanning electron microscopy, and the statistical data was obtained using LIBMAS analysis software;

[0158] (8) Electrochemical performance test: Coin cell half-cells were used for testing. The test voltage was 2.5V-4.2V. The cells were charged to 4.2V using constant current and constant voltage charging, and discharged to 2.5V using constant current discharging. The charge and discharge current was 0.1C for 2 cycles; then 0.2C for 1 cycle; then 0.33C for 1 cycle; then 0.5C for 1 cycle; then 1C for 1 cycle; and then 2C for 1 cycle. The cutoff voltage condition was the same as 0.1C.

[0159] Example 1

[0160] Preparation of lithium iron phosphate cathode active materials

[0161] (1) Mix 5005.0g of ferric phosphate with a Fe / P molar ratio of 0.970 and a particle size of 110nm with 1235.10g of lithium carbonate, add 420g of glucose and 150g of polyethylene glycol, and simultaneously add 16.32g of titanium dioxide, 12.10g of ammonium metavanadate, 4.68g of niobium pentoxide and 11250g of pure water in a stirred mill to form a first mixture; feed the first mixture into a sand mill and sand mill at a temperature below 45℃, controlling the sand milling particle size D. 50 The particle size was 0.30 μm and the solid content was 38 wt%, resulting in the first slurry;

[0162] The first slurry was spray-dried, with the inlet air temperature controlled at 250℃, the outlet air temperature at 100℃, and the atomizer speed at 50Hz, to obtain a particle size D. 50 The first precursor is 15 μm in diameter and has a moisture content of ≤3.0%.

[0163] (2) Mix 4009.0g of ferric phosphate with a Fe / P molar ratio of 0.960 and a particle size of 150nm with 985.0g of lithium carbonate, add 305g of glucose, 120g of polyethylene glycol, 8.20g of titanium dioxide and 8830g of pure water in a stirred mill to form a second mixture; feed the second mixture into a sand mill and mill it at a temperature below 45℃, controlling the sand milling particle size D. 50 The particle size was 0.70 μm, and the solid content was 38 wt%, resulting in a second slurry;

[0164] The second slurry was spray-dried, with the inlet temperature controlled at 250℃, the outlet temperature at 100℃, and the atomizer speed at 34Hz, to obtain a particle size D. 50 A second precursor with a diameter of 40 μm and a moisture content of ≤3.0%;

[0165] (3) The first precursor and the second precursor were mixed in a high-speed mixer at a mass ratio of 7:3, and then calcined at high temperature under a nitrogen atmosphere, with the sintering temperature controlled at 790℃ and the sintering time controlled at 10h; then the mixture was pulverized, and the particle size D was controlled. 50 With a particle size of 1.4 μm and an average primary particle size of 172 nm, high-density lithium iron phosphate cathode active material was prepared.

[0166] Preparation of the positive electrode sheet

[0167] The lithium iron phosphate positive electrode active material prepared above, 50% Compressed Denka Black (acetylene black, compression ratio of 50%), and polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1.5:2. After ball milling and uniform dispersion, the mixture was coated on aluminum foil and vacuum dried to obtain the positive electrode sheet.

[0168] Preparation of the negative electrode sheet

[0169] The negative electrode uses a Li metal sheet.

[0170] Preparation of Electrolyte

[0171] A 1.1 mol / L LiPF6 solution was used as the electrolyte, with an equal volume mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) as the solvent.

[0172]

Isolation Film

[0173] Celgard polypropylene film was used as the separator.

[0174] The positive electrode, separator, negative electrode, and electrolyte are assembled into a coin cell.

[0175] The lithium-ion batteries containing positive electrode active materials in Examples 2-6 and Comparative Example 1 are basically the same as those in Example 1, except for some different parameters (see Table 1). Furthermore, by adjusting the type and amount of element M, the compounds have the compositions shown in Table 3.

[0176] In Example 4, “titanium dioxide, ammonium metavanadate, and niobium pentoxide” in step (1) of Example 1 are replaced with “titanium dioxide, Y-containing compound, and Mg-containing compound”; in Example 6, “titanium dioxide, ammonium metavanadate, and niobium pentoxide” in step (1) of Example 1 are replaced with “titanium dioxide, Zr-containing compound, and Sb-containing compound”.

[0177] Compared with Example 1, Comparative Example 1 adjusted the atomizer speed of the first and second spray dryers, and the D of the first and second precursors. 50 Size, D of the second slurry 50 size.

[0178] The specific scheme for Comparative Example 2 is as follows:

[0179] (1) 2785.0g of Fe / P molar ratio 0.970 and specific surface area 10.0m² 2 / g and iron phosphate with a particle size of 110nm, 1195.0g Fe / P molar ratio of 0.960, and a specific surface area of ​​8.0m². 2 / g of ferric phosphate with a particle size of 150nm and 984.30g of lithium carbonate were mixed together, along with 310g of glucose, 120g of polyethylene glycol, 16.80g of titanium dioxide, 13.50g of ammonium metavanadate, and 8870g of pure water. The mixture was then stirred in a mill to form a first mixture. This first mixture was then fed into a sand mill and milled at a temperature below 45℃, controlling the particle size D. 50 The particle size was 0.42 μm, and the solid content was 38 wt%, resulting in the first slurry;

[0180] The first slurry was spray-dried, with the inlet temperature controlled at 245℃, the outlet temperature at 95℃, and the atomizer speed at 35Hz, to obtain a first precursor with a particle size D50 of 25μm and a moisture content of ≤3.0%.

[0181] (2) The first precursor powder was calcined at high temperature under a nitrogen atmosphere, with the sintering temperature controlled at 790℃ and the sintering time controlled at 10h; then it was pulverized, with the particle size D controlled at 10h. 50 The particle size was 1.6 μm, and the average particle size of the primary particles was 200 nm, thus obtaining lithium iron phosphate cathode material.

[0182] The difference between Comparative Example 3 and Comparative Example 2 lies in the adjustment of the D of the first slurry and the first precursor. 50 size.

[0183] The particle size distribution data of the primary particles in the positive electrode active materials obtained in Examples 1-6 and Comparative Examples 1-3 are shown in Table 2, and the performance parameters of the positive electrode active materials are shown in Table 3.

[0184] In Example 2, the difference from Example 1 lies in the adjustment of the mixing ratio of the first and second slurries; in Example 3, the difference from Example 1 lies in the adjustment of the particle size of the second ferric phosphate and the D of the second slurry. 50 Size, and the atomizer speed of the second spray dryer; Example 4 differs from Example 1 in that the selection of the M source is adjusted (from V, Nb to Y, Mg); Example 5 differs from Example 1 in that the particle size of the first ferric phosphate, the D of the first slurry and the second slurry are adjusted. 50 Size, atomizer speed of the first and second spray dryers, D of the first and second precursors 50 Size; Example 6 differs from Example 1 in that the D of the second precursor is adjusted. 50 Size and the choice of M source has been adjusted (from V, Nb to Zr, Sb);

[0185] Comparative Example 1 differs from Example 1 in that the atomizer speeds of the first and second spray dryers were adjusted, and the D values ​​of the first and second precursors were also adjusted. 50 Size, D of the second slurry 50 Size; Comparative Example 2 differs from Example 1 in that the first slurry and the second slurry were not prepared separately, but rather the mixture containing the first ferric phosphate and the mixture containing the second ferric phosphate were mixed simultaneously, followed by grinding, drying, and calcination. The raw materials did not contain niobium pentoxide; Comparative Example 3 adjusted the D values ​​of the first slurry and the first precursor based on Comparative Example 2. 50 size.

[0186] Table 1

[0187] In Table 1, " / " indicates that it is not added or is not present.

[0188] Table 2

[0189] In Table 2, " / " indicates that it is not added or is not present.

[0190] Table 3

[0191] Results analysis:

[0192] Compared with Comparative Examples 1-3, the positive electrode active materials prepared by the method provided in this disclosure (i.e., Examples 1-6) have higher compaction density, higher capacity, higher rate capability, and better low-temperature performance.

[0193] Figure 1 shows the SEM image of the lithium iron phosphate cathode active material prepared in Example 1, revealing a mixture of particles with various sizes. Figure 2 shows the XRD pattern of the material, demonstrating its lithium iron phosphate structure. Figure 3 shows the particle size distribution curve of the primary particles, exhibiting three distinct characteristic peaks.

[0194] Similarly, the remaining embodiments exhibit the same excellent effects. In Embodiment 3, compared to Embodiment 1, the particle size of the second ferric phosphate and the D of the second slurry were adjusted. 50 Size, such that the D of the first slurry and the second slurry 50 The difference is small (0.15 μm), relative to the D of the first and second slurries. 50 For Examples 1-2 and 4 with larger differences, the gradation effect is reduced, but it is still better than Comparative Examples 1-3, indicating that the D of the first slurry and the second slurry is better. 50 A difference greater than 0.2 μm is more conducive to achieving high solid density and better electrochemical performance.

[0195] In Example 4, compared to Example 1, the choice of element M was changed (from V and Nb to Y and Mg). The results showed that the compaction density of the positive electrode active material decreased, and the capacity and low-temperature capacity retention of the battery containing this positive electrode active material both decreased, but it was still better than Comparative Examples 1-3, indicating that the preferred choice of M source is V or Nb. In Example 6, compared to Example 1, the choice of element M was changed (from V and Nb to Zr and Sb). The results showed that the compaction density of the positive electrode active material decreased, and the capacity and low-temperature capacity retention of the battery containing this positive electrode active material both decreased, but it was still better than Comparative Examples 1-3, also indicating that the preferred choice of M source is V or Nb.

[0196] Compared with Example 1, the difference lies in the adjustment of the atomizer speed of the first spray dryer and the second spray dryer, and the D of the first precursor and the second precursor. 50 Size, D of the second slurry 50 Size. The D values ​​of the first and second slurries in this comparative example. 50 The same, simultaneously produced precursor D 50 Similarly, although the preparation method used ferric phosphate with different particle sizes, it did not control the D of the slurry. 50 The limited range resulted in the material not achieving multi-stage mixing, thus reducing the compaction density of the resulting positive electrode active material and decreasing the capacity and low-temperature capacity retention of the battery containing it.

[0197] Compared with Example 1, Comparative Example 2 differs in that it directly mixes two materials with different particle sizes, followed by grinding, drying, and calcination. Therefore, this preparation method does not achieve particle size gradation in the slurry stage, resulting in only one type of precursor. This disadvantage is further amplified in the subsequent calcination process. As shown in Figure 4, the particle size distribution curve of the primary particles of this material has only one obvious characteristic peak, which also proves that the material has not achieved multi-stage mixing. This leads to a decrease in the compaction density of the obtained positive electrode active material, and a decrease in the capacity and low-temperature capacity retention of the battery containing it.

[0198] Comparative Example 3 is prepared similarly to Comparative Example 2, except that the D values ​​of the first slurry and the first precursor are adjusted. 50 The results showed that the material did not achieve multi-stage mixing, which led to a decrease in the compaction density of the prepared positive electrode active material, and a decrease in the capacity and low-temperature capacity retention of the battery containing it.

[0199] 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 disclosure. 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.

[0200] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A positive electrode active material, characterized in that, Including lithium iron phosphate, wherein the lithium iron phosphate is a secondary particle formed by the agglomeration of primary particles, and the particle size distribution curve of the primary particles exhibits three characteristic peaks. Among them, the highest characteristic peak is the first characteristic peak, and the peak position D1 of the first characteristic peak is 100nm-300nm, and the quantity percentage N1 corresponding to the peak position D1 of the first characteristic peak is 25%-35%. The second characteristic peak position D2 of the primary particle is 320nm-400nm, and the corresponding quantity percentage N2 at the second characteristic peak position D2 is 4%-9%. The third characteristic peak D3 of the primary particle is located at 450nm-620nm, and the corresponding quantity percentage N3 at the third characteristic peak D3 is 0.5%-2%.

2. The positive electrode active material according to claim 1, characterized in that, In the particle size distribution curve of the first-order particles, there is a first minimum value D between the first characteristic peak and the second characteristic peak. 12 The first minimum value D 12 The corresponding particle size range is 270nm-320nm, and the first minimum value D 12 The corresponding quantity percentage N 12 It is 3%-6%; Optionally, the peak splitting index γ of the positive electrode active material is 5%-40%; Where γ=(N2-N 12 ) / N2×100%; N 12 The first minimum value D between the first characteristic peak and the second characteristic peak 12 The corresponding percentage; N2 is the percentage of the quantity corresponding to the peak position D2 of the second characteristic peak.

3. The positive electrode active material according to claim 1 or 2, characterized in that, In the particle size distribution curve of the first-order particles, there is a second minimum value D between the second characteristic peak and the third characteristic peak. 23 The second minimum value D 23 The corresponding particle size range is 400nm-500nm, and the second minimum value D 23 The corresponding quantity percentage N 23 It ranges from 0.0% to 0.5%.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The primary particle's D 50 The range is 0.1μm-1.0μm; Optionally, the D of the secondary particles 50 Its thickness ranges from 0.7μm to 2.0μm. Optionally, the compaction density of the positive electrode active material is 2.45 g / cm³. 3 -2.65g / cm 3 ; Optionally, the specific surface area of ​​the positive electrode active material is 10 m². 2 / g-13m 2 / g.

5. The positive electrode active material according to any one of claims 1-4, characterized in that, The positive electrode active material includes a matrix and a carbon coating layer covering the surface of the matrix; The matrix has the composition shown in Formula I: Li 1+a Fe b M c (PO4) d Formula I; Where -0.1≤a≤0.1, 0≤b≤1, 0≤c≤0.5, 0≤d≤1; M is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Sb, Co, Ni, V, Mg, Na, B, and Al; Preferably, M is selected from Nb, and also includes at least one of Al, Nb, W, Co, V and Ti.

6. A method for preparing the positive electrode active material according to any one of claims 1-5, characterized in that, The preparation method includes: A first mixed solution containing a first iron phosphate, a first lithium source, a first carbon source, and a first M source is prepared, ground to obtain a first slurry, and then subjected to a first spray drying treatment to obtain a first precursor; A second mixture containing a second iron phosphate, a second lithium source, a second carbon source, and a second M source is prepared, ground to obtain a second slurry, and then spray-dried to obtain a second precursor. The first precursor and the second precursor are mixed and sintered to obtain the positive electrode active material; the D of the first slurry 50 D is smaller than that of the second slurry 50 .

7. The preparation method according to claim 6, characterized in that, D of the first slurry 50 With the second slurry D 50 The difference is greater than 0.2 μm; Optionally, the particle size of the first ferric phosphate is 80nm-200nm; the particle size of the second ferric phosphate is 50nm-160nm. Optionally, the particle size D of the first precursor 50 The particle size D is smaller than that of the second precursor. 50 .

8. The preparation method according to claim 6, characterized in that, D of the first slurry 50 The thickness ranges from 0.25μm to 0.45μm. Optionally, the D of the second slurry 50 The range is 0.45μm-0.80μm.

9. The preparation method according to claim 6, characterized in that, The atomizer rotation speeds for the first and second spray drying processes are independently 30-50 Hz; Optionally, the particle size D of the first precursor and the second precursor 50 Independently, it has a particle size of 15μm-45μm and a water content of ≤3.0%. Optionally, the first precursor and the second precursor are mixed in a mass ratio of (3:7) to (7:3); Optionally, the sintering temperature is 750℃-850℃, and the sintering time is 6h-12h.

10. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive active material according to any one of claims 1-5 or the positive active material prepared by the preparation method according to any one of claims 6-9.

11. A battery, characterized in that, The battery 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.

Images