Positive electrode active material and preparation method thereof, positive electrode plate and battery
By preparing lithium iron phosphate cathode active materials with optimized particle size distribution and combining them with titanium doping and carbon coating, the problems of compaction density and conductivity of lithium iron phosphate materials were solved, thereby improving battery energy density and cycle performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-05
- Publication Date
- 2026-03-17
AI Technical Summary
Lithium iron phosphate materials have low lithium-ion diffusion coefficients and electronic conductivity, and it is difficult to improve the compaction density under traditional processes, which limits the further improvement of their energy density.
A lithium iron phosphate cathode active material with three characteristic peaks in its particle size distribution curve was prepared, including 100nm-200nm, 200nm-300nm and 1μm-2μm particles. Combined with titanium doping and carbon coating, the particle size distribution was precisely controlled by a secondary sintering process to form a tightly packed structure.
It improves the compaction density and conductivity of lithium iron phosphate materials, enhances the lithium-ion transport path, and improves battery capacity utilization and low-temperature cycling performance.
Smart Images
Figure CN121687948A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery technology, specifically to positive electrode active materials and their preparation methods, positive electrode sheets, and batteries. Background Technology
[0002] Lithium iron phosphate (LFP) materials have become one of the preferred cathode active materials in lithium-ion batteries due to their excellent structural stability, high safety, long cycle life, and low cost. However, LFP has a low lithium-ion diffusion coefficient and low electronic conductivity, and its compaction density is difficult to improve under traditional processes, which severely limits its further energy density improvement. With the development of society and technology, people have placed higher demands on energy storage devices, including lithium-ion batteries. Therefore, improving the energy density of LFP batteries has become a research hotspot in the field in recent years, and developing LFP materials with both high compaction density and high specific capacity has become a technological bottleneck that urgently needs to be overcome.
[0003] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention
[0004] In a first aspect, this application proposes a positive electrode active material comprising lithium iron phosphate, wherein the lithium iron phosphate comprises secondary particles formed by the agglomeration of primary particles, and the particle size distribution curve of the primary particles exhibits three characteristic peaks; wherein the peak position of the first characteristic peak of the primary particles is 100nm-200nm, and the corresponding quantity percentage at the peak position of the first characteristic peak is 40%-60%; the peak position of the second characteristic peak of the primary particles is 200nm-300nm, and the corresponding quantity percentage at the peak position of the second characteristic peak is 20%-40%, and the corresponding quantity percentage at the peak position of the second characteristic peak is less than the corresponding quantity percentage at the peak position of the first characteristic peak; the peak position of the third characteristic peak of the primary particles is 1μm-2μm, and the corresponding quantity percentage at the peak position of the third characteristic peak is 0.5%-1%. Therefore, this positive electrode active material has a superior particle size distribution, higher compaction density, and better electron migration channels, resulting in better capacity utilization and low-temperature cycling performance.
[0005] In some embodiments of this application, the average particle size of the primary particles is 220 nm-240 nm; and / or, the median particle size D of the positive electrode active material is... 50 The surface area is 1.0 μm to 1.6 μm; and / or, the specific surface area of the positive electrode active material is 12.4 m². 2 / g-13.4m 2 / g. This helps to shorten the lithium-ion transport path and improve the processing performance of the positive electrode active material.
[0006] In some embodiments of this application, the powder compaction density of the positive electrode active material is 2.73 g / cm³ at 30 kN. 3 -2.75g / cm 3 Therefore, the positive electrode active material with a mixture of large and small particle sizes can fully fill the gaps between particles, forming a fully contacted conductive network. This results in a higher compaction density of the positive electrode active material and a lower overall resistance, which is beneficial for improving the battery's capacity.
[0007] In some embodiments of this application, the titanium doping amount in the positive electrode active material is 2000ppm-7000ppm. Therefore, by using an appropriate amount of Ti to dope lithium iron phosphate, the enhancing effect of Ti on the stability of lithium iron phosphate materials can be fully utilized, the dissolution of transition metals in lithium iron phosphate can be suppressed, and the negative impact on the specific capacity and structural integrity of lithium iron phosphate is minimal. Furthermore, during the preparation of the positive electrode active material, titanium helps to suppress primary particle growth, ensuring that some particles maintain their original morphology and keeping the original small and medium particle sizes in the primary sintering material unchanged.
[0008] In some embodiments of this application, the positive electrode active material includes a matrix and a carbon coating layer at least partially covering the surface of the matrix; wherein the matrix has the composition shown in Formula I: Li 1+a Fe b M c (PO4) d Formula I; -0.1≤a≤0.1, 0≤b≤1, 0≤c≤0.5, 0≤d≤1; M includes at least one of Ti, V, Zr, and Nb. Therefore, this positive electrode active material exhibits good conductivity and specific capacity, which helps to improve the rate performance of the battery.
[0009] In a second aspect, this application proposes a method for preparing a positive electrode active material, comprising: mixing iron phosphate, a lithium source, a phosphorus source, a carbon source, a dispersant, an M source, and a solvent; grinding the mixture to obtain a slurry; and spray-drying the slurry to obtain a spray-dried material. The iron phosphate comprises first iron phosphate and second iron phosphate, wherein the first iron phosphate has a particle size of 50 nm-200 nm, and the second iron phosphate has a particle size of 30 nm-160 nm. The spray-dried material is subjected to a first sintering treatment to obtain a primary sintered material. The primary sintered material, a titanium source, and a flux are mixed and subjected to a second sintering treatment to obtain the positive electrode active material. Thus, this application precisely controls the crystallization growth of primary particles during the material synthesis process through a secondary sintering treatment, obtaining a positive electrode active material with a superior particle size distribution. Furthermore, the process is simple, the production cost is low, and the parameters during production are easy to control, facilitating modern industrial production.
[0010] In some embodiments of this application, the specific surface area of the first iron phosphate is 8 m². 2 / g-16m 2 / g, and / or, the molar ratio of iron to phosphorus in the first ferric phosphate is 0.960-0.980; and / or, the specific surface area of the second ferric phosphate is 5m². 2 / g-12m 2 / g, and / or, the molar ratio of iron to phosphorus in the second ferric phosphate is 0.950-0.970; and / or, the mass ratio of the first ferric phosphate to the second ferric phosphate is (1-2):(1-3). This helps to obtain a primary sinter containing both small and medium particles.
[0011] In some embodiments of this application, the molar ratio of lithium in the lithium source to iron in the iron phosphate is 0.90-1.01, and the molar ratio of phosphorus to iron in the iron phosphate is 0.98-1.05. This facilitates a more complete reaction and reduces raw material waste and the generation of other impurities.
[0012] In some embodiments of this application, the solid content of the slurry is 40wt%-45wt%; and / or, the median particle size D of the slurry is... 50 The micrometer size is 0.30μm-0.50μm. This helps improve the stability of the slurry and reduces agglomeration and sedimentation.
[0013] In some embodiments of this application, the amount of carbon source added accounts for 1.0%-1.5% of the total mass of the positive electrode active material. This is beneficial for improving the conductivity of the positive electrode active material while suppressing abnormal grain growth.
[0014] In some embodiments of this application, the inlet air temperature of the spray drying process is 200℃-250℃, and the outlet air temperature is 80℃-120℃; and / or, the median particle size D of the spray material is... 50 The particle size is 15μm-50μm; and / or the moisture content of the aerosol is less than or equal to 3.0%. This helps to form aerosol powder with dense particles, smooth surface, and good sphericity.
[0015] In some embodiments of this application, the temperature of the first sintering treatment is 750℃-820℃, and the time is 10h-15h. This is beneficial for obtaining a primary sintered material with a specific particle size distribution.
[0016] In some embodiments of this application, the average particle size of the primary particles in the primary sintering material is 0.18 μm-0.22 μm, the proportion of primary particles with a particle size less than or equal to 100 nm is 8%-15%, and the proportion of primary particles with a particle size in the range of 100 nm-300 nm is 50%-60%. This helps to obtain a positive electrode active material with a specific particle size distribution.
[0017] In some embodiments of this application, the amount of flux added accounts for 0.1%-1.0% of the total mass of the positive electrode active material; and / or, the amount of flux added accounts for 0.5%-5% of the total mass of the primary sintering material. Therefore, the appropriate amount of flux added helps to control the crystallization growth of primary particles during material synthesis, promoting the growth of some primary particles to approximately 2 μm, and also reduces excessive growth of primary particles or the introduction of excessive impurities.
[0018] In some embodiments of this application, the temperature of the second sintering treatment is 750℃-800℃, and the time is 6h-10h. This helps to obtain a positive electrode active material with a specific particle size distribution.
[0019] In some embodiments of this application, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; and / or, the phosphorus source includes at least one of lithium dihydrogen phosphate and phosphoric acid; and / or, the carbon source includes at least one of glucose, sucrose, starch, and citric acid; and / or, the dispersant includes at least one of polyethylene glycol 3000, polyethylene glycol 6000, and polyvinyl alcohol 2000; and / or, the M source includes at least one of titanium dioxide, ammonium metavanadate, zirconium oxide, and niobium oxide; and / or, the solvent includes pure water or ethanol. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is convenient.
[0020] In some embodiments of this application, the titanium source includes at least one of titanium dioxide, titanium tetrachloride, and calcium titanate. This helps to suppress primary particle growth and ensures that some particles maintain their original morphology.
[0021] In some embodiments of this application, the flux includes at least one of lithium salts and ammonium salts; optionally, the flux includes at least one of LiCl, LiF, NH4Cl, and NH4F. This helps to promote the dissolution-recrystallization process of the particles.
[0022] In a third aspect, this application proposes a positive electrode sheet, comprising a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer comprises the positive active material described in the first aspect of this application or a positive active material prepared using the method described in the second aspect of this application. Therefore, this positive electrode sheet has high compaction density and mechanical strength, low overall resistance, and facilitates the formation of efficient electron migration channels, exhibiting better capacity utilization and cycle performance during charge and discharge.
[0023] In some embodiments of this application, the compaction density of the positive electrode active material layer is 2.8 g / cm³ at 30 kN. 3 -2.9g / cm 3 Therefore, this positive electrode has high specific capacity and high mechanical strength, low overall resistance, and fast electron migration rate.
[0024] In a fourth aspect, this application proposes a battery comprising the positive electrode sheet described in the third aspect. Thus, this battery possesses all the features and advantages of the aforementioned positive electrode active material, which will not be repeated here. Attached Figure Description
[0025] 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, wherein, Figure 1 Here is a SEM image of the lithium iron phosphate positive electrode active material prepared in Example 1 of this application; Figure 2 This is a particle size distribution diagram of the lithium iron phosphate cathode active material prepared in Example 1 of this application; Figure 3 The image shows the XRD pattern of the lithium iron phosphate cathode active material prepared in Example 1 of this application. Detailed Implementation
[0026] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.
[0027] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).
[0028] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.
[0029] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.
[0030] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
[0031] In the description of this application, the terms "first," "second," and "third" 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. "First feature" and "second feature" may include one or more of that feature.
[0032] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.
[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.
[0034] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.
[0035] In a first aspect, this application proposes a positive electrode active material comprising lithium iron phosphate, wherein the lithium iron phosphate comprises secondary particles formed by the agglomeration of primary particles, and the particle size distribution curve of the primary particles exhibits three characteristic peaks; wherein the peak position of the first characteristic peak of the primary particles is 100nm-200nm, and the corresponding quantity percentage at the peak position of the first characteristic peak is 40%-60%; the peak position of the second characteristic peak of the primary particles is 200nm-300nm, and the corresponding quantity percentage at the peak position of the second characteristic peak is 20%-40%, and the corresponding quantity percentage at the peak position of the second characteristic peak is less than the corresponding quantity percentage at the peak position of the first characteristic peak; the peak position of the third characteristic peak of the primary particles is 1μm-2μm, and the corresponding quantity percentage at the peak position of the third characteristic peak is 0.5%-1%. Therefore, this positive electrode active material has a superior particle size distribution, higher compaction density, and better electron migration channels, resulting in better capacity utilization and low-temperature cycling performance.
[0036] The particle size distribution curve of the primary particles of the positive electrode active material provided in this application shows three characteristic peaks, indicating that the positive electrode active material contains at least three types of primary particles. The positive electrode active material contains single crystal particles of different sizes. The smaller particles and the medium-sized particles fully fill the pores formed by the larger particles, achieving particle size distribution, improving the particle packing performance, and significantly improving the overall powder compaction density.
[0037] Specifically, in the positive electrode active material, larger particles with a diameter of 1μm-2μm are stacked together to form a three-dimensional framework structure of the positive electrode active material layer, thus providing the necessary mechanical strength and porosity. Furthermore, the porous structure formed by the stacked large particles is fully filled with smaller and moderately sized particles. This increases the compaction density of the positive electrode active material layer, while the larger particles act as key nodes in the conductive network, ensuring sufficient contact with the conductive agent. Electrons can preferentially pass through the larger particles for rapid transport, and then through the smaller and moderately sized particles filling the porous structure. This helps reduce the overall resistance of the positive electrode active material layer, forming efficient electron migration channels, resulting in superior low-temperature performance of the positive electrode active material. Therefore, the larger and smaller particles complement each other, jointly improving the specific capacity, conductivity, and cycle life of the lithium iron phosphate positive electrode active material.
[0038] As an example, the peak position of the first characteristic peak can be 100nm, 120nm, 140nm, 160nm, 180nm or 200nm, etc., and the percentage of the corresponding quantity at the peak position of the first characteristic peak can be 40%, 45%, 50%, 55% or 60%, etc.
[0039] As an example, the peak position of the second characteristic peak can be 200nm, 220nm, 240nm, 260nm, 280nm or 300nm, etc., and the corresponding percentage of the quantity at the peak position of the second characteristic peak can be 20%, 25%, 30%, 35% or 40%, etc.
[0040] As an example, the peak position of the third characteristic peak can be 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm or 2μm, etc., and the corresponding percentage of the number at the peak position of the third characteristic peak can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc.
[0041] The particle size distribution curve is obtained by plotting the particle size of primary particles on the x-axis and the percentage of the total number of particles of that size in the total number of particles on the y-axis.
[0042] In some embodiments of this application, the average particle size of the primary particles is 220 nm-240 nm; and / or, the median particle size D of the positive electrode active material is... 50 The surface area is 1.0 μm to 1.6 μm; and / or, the specific surface area of the positive electrode active material is 12.4 m². 2 / g-13.4m 2 / g.
[0043] As an example, the average particle size of primary particles can be 220nm, 222nm, 225nm, 228nm, 230nm, 232nm, 235nm, 238nm, or 240nm, etc.; the median particle size D of the positive electrode active material 50 The surface area can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or 1.6 μm, etc.; the specific surface area of the positive electrode active material can be 12.4 m². 2 / g, 12.6m 2 / g, 12.8m 2 / g, 13.2m 2 / g or 13.4m 2 / g etc.
[0044] Meeting the above conditions helps to shorten the lithium-ion transport path and improve the processing performance of the positive electrode active material.
[0045] As an example, the method for testing the average particle size of primary particles is as follows: A 10kx scanning electron microscope image of the prepared lithium iron phosphate cathode active material is taken, and the average primary particle size is calculated using LIBMAS and Nano Measurer software; the median particle size D of the cathode active material is... 50 The particle size distribution was obtained using a Marvern Mastersizer 3000 laser particle size analyzer; the specific surface area of the positive electrode active material was obtained using a Micromeritics Tristar 3020 specific surface area analyzer.
[0046] In some embodiments of this application, the powder compaction density of the positive electrode active material is 2.73 g / cm³ at 30 kN. 3 -2.75g / cm 3 .
[0047] As an example, at 30 kN, the powder compaction density of the positive electrode active material can be 2.73 g / cm³. 3 2.74 g / cm 3 Or 2.75g / cm 3 wait.
[0048] Therefore, the positive electrode active material with a mixture of large and small particle sizes can fully fill the gaps between particles, forming a fully contacted conductive network. This results in a higher compaction density and lower overall resistance of the positive electrode active material, which is beneficial for improving the battery's capacity.
[0049] As an example, the test method for the powder compaction density of positive electrode active material is as follows: weigh 1g of the prepared lithium iron phosphate positive electrode active material and put it into a compaction mold, then put the mold into a compaction device to test the result under a pressure of 30kN.
[0050] In some embodiments of this application, the titanium doping amount in the positive electrode active material is 2000ppm-7000ppm.
[0051] As an example, the titanium doping amount in the positive electrode active material is 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm or 7000ppm, etc.
[0052] By doping lithium iron phosphate with an appropriate amount of titanium (Ti), the stability-enhancing effect of Ti on lithium iron phosphate materials can be fully utilized, and the dissolution of transition metals in lithium iron phosphate can be suppressed, while having minimal negative impact on the specific capacity and structural integrity of lithium iron phosphate. Furthermore, during the preparation of the cathode active material, titanium doping within the aforementioned range helps to suppress primary particle growth, ensuring that some particles maintain their original morphology and preserving the original small and medium particle sizes in the primary sintering material.
[0053] In some embodiments of this application, the positive electrode active material includes a matrix and a carbon coating layer at least partially covering the surface of the matrix; wherein 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 includes at least one of Ti and V, Zr, and Nb. Therefore, this positive electrode active material exhibits good conductivity and specific capacity, which helps to improve the rate performance of the battery.
[0054] As an example, a can be -0.1, 0, 0.01, 0.02, 0.04, 0.06, 0.08, or 0.1, etc.; b can be 0, 0.1, 0.2, 0.4, 0.6, 0.8, or 1, etc.; c can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, or 1, etc.; and d can be 0, 0.1, 0.2, 0.4, 0.6, 0.8, or 1, etc.
[0055] In a second aspect of this application, a method for preparing positive electrode active materials is proposed. This method precisely controls the crystallization growth of primary particles during the material synthesis process through a secondary sintering treatment, resulting in a lithium iron phosphate positive electrode active material with a tightly packed structure of large, medium, and small particle sizes. Smaller particles (200nm-300nm) can effectively fill the pores formed by larger particles (1μm-2μm), forming a denser packing structure. This results in higher compaction density and lower overall resistance under the same rolling pressure. Furthermore, the process is simple, has low production costs, and the parameters are easy to control, making it suitable for modern industrial production. Specifically, it includes: S1: Iron phosphate, lithium source, phosphorus source, carbon source, dispersant, M source and solvent are mixed, ground to obtain slurry, and spray dried to obtain spray material. The iron phosphate includes first iron phosphate and second iron phosphate.
[0056] In some embodiments of this application, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; and / or, the phosphorus source includes at least one of lithium dihydrogen phosphate and phosphoric acid; and / or, the carbon source includes at least one of glucose, sucrose, starch, and citric acid; and / or, the dispersant includes at least one of polyethylene glycol 3000 (PEG3000), polyethylene glycol 6000 (PEG6000), and polyvinyl alcohol 2000 (PVA2000); and / or, the M source includes at least one of titanium dioxide, ammonium metavanadate, zirconium oxide, and niobium oxide; and / or, the solvent includes pure water or ethanol. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is convenient.
[0057] In some embodiments of this application, the particle size of the first ferric phosphate is 50nm-200nm, and the particle size of the second ferric phosphate is 30nm-160nm. Using ferric phosphate with different particle sizes as raw materials in this application helps to form small and large particle precursors, thereby increasing the material's bulk density and achieving a better particle size distribution.
[0058] As an example, the particle size of the first ferric phosphate can be 50nm, 80nm, 100nm, 130nm, 150nm, 180nm or 200nm, etc., and the particle size of the second ferric phosphate can be 30nm, 50nm, 70nm, 90nm, 110nm, 130nm or 160nm, etc.
[0059] In some embodiments of this application, the specific surface area of the first iron phosphate is 8 m². 2 / g-16m 2 / g, and / or, the molar ratio of iron to phosphorus in the first ferric phosphate is 0.960-0.980; and / or, the specific surface area of the second ferric phosphate is 5m². 2 / g-12m 2 / g, and / or, the molar ratio of iron to phosphorus in the second ferric phosphate is 0.950-0.970; and / or, the mass ratio of the first ferric phosphate to the second ferric phosphate is (1-2):(1-3). This helps to obtain a primary sinter containing both small and medium particles.
[0060] As an example, the specific surface area of iron phosphate can be 8 m². 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g or 16m 2 / g etc., the molar ratio of iron to phosphorus in ferric phosphate can be 0.960, 0.965, 0.970, 0.975 or 0.980, etc.
[0061] As an example, the specific surface area of the second ferric phosphate can be 5 m². 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g or 12m 2 / g, the molar ratio of iron to phosphorus in the second ferric phosphate can be 0.950, 0.955, 0.960, 0.965 or 0.970, etc.
[0062] As an example, the mass ratio of first ferric phosphate to second ferric phosphate can be 1:1, 1:2, 1:3, 2:1, or 2:3, etc.
[0063] In some embodiments of this application, the molar ratio of lithium in the lithium source to iron in the iron phosphate is 0.90-1.01, and the molar ratio of phosphorus to iron in the iron phosphate is 0.98-1.05. This facilitates a more complete reaction and reduces raw material waste and the generation of other impurities.
[0064] As an example, the molar ratio of lithium in the lithium source to iron in iron phosphate can be 0.90, 0.93, 0.95, 0.98, 1.00, or 1.01, etc., and the molar ratio of phosphorus to iron in iron phosphate can be 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, or 1.05, etc.
[0065] The mixing method of the raw materials is not particularly limited and does not affect subsequent grinding, spray drying and other steps. Specifically, the first ferric phosphate, the second ferric phosphate, the lithium source, the phosphorus source, the carbon source, the dispersant, and the M source can be dissolved in a solvent in a certain proportion to obtain a mixture.
[0066] In some embodiments of this application, the solid content of the slurry is 40wt%-45wt%, for example, it can be 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, or 45wt%; and / or, the median particle size D of the slurry is... 50The particle size is 0.30μm-0.50μm, for example, 0.30μm, 0.35μm, 0.40μm, 0.45μm, or 0.50μm. The grinding method is not particularly limited; it can be selected according to the situation to achieve the target particle size of the slurry. This can be achieved through methods such as sand milling. This helps improve the stability of the slurry and reduces agglomeration and sedimentation.
[0067] In some embodiments of this application, the amount of carbon source added accounts for 1.0%-1.5% of the total mass of the positive electrode active material, for example, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%. This is beneficial for improving the conductivity of the positive electrode active material while suppressing abnormal grain growth.
[0068] In some embodiments of this application, the inlet and outlet air temperatures of the spray drying process are not particularly limited, i.e., as long as the slurry is dried. In some specific examples, the inlet air temperature of the spray drying process is 200℃-250℃ (e.g., 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃, etc.), and the outlet air temperature is 80℃-120℃ (e.g., 80℃, 90℃, 100℃, 110℃, or 120℃, etc.), and the median particle size D of the spray-dried product (i.e., the spray material) is... 50 The particle size is 15μm-50μm (e.g., 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, or 50μm), and the moisture content of the aerosol is less than or equal to 3.0% (e.g., 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, or 3.0%). This helps to form aerosol powder with dense particles, smooth surface, and good sphericity.
[0069] S2: Perform a first sintering treatment on the sprayed material to obtain a primary sintered material.
[0070] In some embodiments of this application, the temperature of the first sintering treatment is 750℃-820℃ (e.g., 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, or 820℃), and the time is 10h-15h (e.g., 10h, 11h, 12h, 13h, 14h, or 15h). This is advantageous for obtaining a primary sinter with a specific particle size distribution. Furthermore, the first sintering treatment can be carried out in an inert atmosphere, such as nitrogen.
[0071] In some embodiments of this application, the average particle size of the primary particles in the primary sintering material is 0.18 μm-0.22 μm, the proportion of primary particles with a particle size less than or equal to 100 nm is 8%-15%, and the proportion of primary particles with a particle size in the range of 100 nm-300 nm is 50%-60%. This helps to obtain a positive electrode active material with a specific particle size distribution.
[0072] S3: Mix the primary sintering material, titanium source, and flux, and perform a second sintering process to obtain the positive electrode active material.
[0073] In some embodiments of this application, the titanium source includes at least one of titanium dioxide, titanium tetrachloride, and calcium titanate. This helps to suppress primary particle growth and ensures that some particles maintain their original morphology.
[0074] In some embodiments of this application, the flux includes at least one of lithium salt and ammonium salt; optionally, the flux includes at least one of LiCl, LiF, NH4Cl, and NH4F. The addition of the flux helps to promote the dissolution-recrystallization process of the particles, specifically by transforming a large number of fine primary particles smaller than 100 nm in the original material into particles in the range of 200 nm to 300 nm; and by growing larger primary particles in the range of 500 nm to 800 nm in the original material into more regular particles of 1 μm to 2 μm.
[0075] In some embodiments of this application, the amount of flux added accounts for 0.1%-1.0% of the total mass of the positive electrode active material, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, or 1.0%; and / or, the amount of flux added accounts for 0.5%-5% of the total mass of the primary sintering material, for example, 0.5%, 1%, 2%, 3%, 4%, or 5%. The flux forms a liquid phase at the sintering temperature, providing a medium for ion transport and particle rearrangement. The liquid phase environment formed by the flux promotes the melting of small particles and the growth of large particles, thereby reducing extremely small and medium-sized particles that are unfavorable for stacking, and forming a particle size system with a three-peak or more concentrated distribution, mainly within 100 nm, 200 nm-300 nm, and 1 μm-2 μm. The appropriate amount of flux can help regulate the crystallization growth of primary particles during the material synthesis process, promote the growth of some primary particles to about 2μm, and reduce the excessive growth of primary particles or the introduction of too many impurities.
[0076] In some embodiments of this application, the temperature of the second sintering treatment is 750℃-800℃ (e.g., 750℃, 760℃, 770℃, 780℃, 790℃, or 800℃), and the time is 6h-10h (e.g., 6h, 7h, 8h, 9h, or 10h). This helps to obtain a positive electrode active material with a specific particle size distribution. Furthermore, the second sintering treatment can be carried out in an inert atmosphere, such as nitrogen or argon.
[0077] During the second sintering process, the flux reacts with the attached particles, melting into agglomerated large particles (around 2 μm). The coating agent (i.e., the titanium source) inhibits particle surface growth, maintaining the stability of the original small and medium-sized particles in the primary sintering material. These smaller and medium-sized particles effectively fill the pores formed by the larger particles, effectively increasing the density of the lithium iron phosphate cathode active material. Furthermore, the larger particles act as key nodes in the conductive network, ensuring sufficient contact with the conductive agent. Electrons can preferentially pass through the larger particles for rapid transport, and then through the smaller and medium-sized particles filling the pore structure, helping to reduce the overall resistance of the cathode active material layer and forming efficient electron migration channels. Simultaneously, the second sintering process helps repair lattice defects that may have occurred during the first sintering process, optimizes the uniformity of carbon coating on the particle surface, repairs the carbon coating layer from the first sintering process, significantly improves the conductivity of lithium iron phosphate, enhances rate performance, and thus improves the overall electrochemical activity of the material. Furthermore, the second sintering process can further optimize the sphericity of the primary particles, which is beneficial to improving the packing density of lithium iron phosphate.
[0078] In some embodiments of this application, after the second sintering treatment, the material can be further crushed, sieved, and demagnetized to obtain lithium iron phosphate cathode active material.
[0079] The preparation method described in this application simplifies the secondary grinding and spray drying processes in the wet process, significantly reduces production costs, and can achieve mass production based on existing lithium iron phosphate production lines without the need for additional equipment investment, thus enabling rapid industrialization.
[0080] In a third aspect, this application proposes a positive electrode sheet, comprising a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer comprises the positive active material described in the first aspect of this application or a positive active material prepared using the method described in the second aspect of this application. Therefore, this positive electrode sheet has high compaction density and mechanical strength, low overall resistance, and facilitates the formation of efficient electron migration channels, exhibiting better capacity utilization and cycle performance during charge and discharge.
[0081] In some embodiments of this application, the compaction density of the positive electrode active material layer is 2.8 g / cm³ at 30 kN. 3 -2.9g / cm 3 .
[0082] As an example, at 30 kN, the compaction density of the positive electrode active material layer can be 2.8 g / cm³. 3 2.82 g / cm 3 2.84 g / cm 3 2.86 g / cm 3 2.88g / cm 3 Or 2.9g / cm 3 wait.
[0083] When the compaction density of the positive electrode active material layer is within the above range, the positive electrode sheet has a high specific capacity and high mechanical strength, low overall resistance, and fast electron migration rate.
[0084] In a fourth aspect, this application proposes a battery comprising the positive electrode sheet described in the third aspect. Thus, this battery possesses all the features and advantages of the aforementioned positive electrode active material, which will not be repeated here.
[0085] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.
[0086] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of 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 whose manufacturers are not specified are all conventional products that can be obtained commercially.
[0087] Example 1 (1) Mix 5000.0g of iron phosphate with a molar ratio of Fe / P of 0.975 and a primary particle size of 110nm, 5000.0g of iron phosphate with a molar ratio of Fe / P of 0.960 and a primary particle size of 150nm, and 2350g of lithium carbonate. Add 25g of phosphoric acid, 800g of glucose, 300g of polyethylene glycol 3000, 45g of titanium dioxide, V2O5, and 16kg of pure water in a stirred mill to form a dispersion. Pour the dispersion into a sand mill and sand mill at a temperature below 45℃, controlling the sand milling particle size D. 50 The particle size was 0.40 μm, and the solid content was 42 wt%. The obtained slurry was spray-dried, with the inlet temperature controlled at 245℃ and the outlet temperature at 95℃, to obtain a particle size D. 50A spray-dried material with a particle size of 20 μm and a moisture content of 2.0%; (2) The spray material was subjected to a first sintering treatment under a nitrogen atmosphere, with the sintering temperature controlled at 790℃ and the sintering time at 10h. (3) The obtained primary sintering material is mixed evenly with 20.7g of titanium dioxide and 12g of LiCl to obtain a coating material. The coating material is subjected to a second sintering treatment under a nitrogen atmosphere, with the sintering temperature controlled at 750℃ and the sintering time at 6h to obtain a secondary sintering material. (4) The secondary sintering material is crushed to control the particle size D. 50 The primary particle size ranges from 1.10 μm to 1.60 μm, with an average primary particle size of 220 nm, thus producing a lithium iron phosphate cathode active material.
[0088] The differences between other embodiments and comparative examples and embodiment 1 are shown in Tables 1-1 and 1-2.
[0089] Table 1-1
[0090] Table 1-2
[0091] The " / " indicates that the substance was not added.
[0092] The relevant parameters in the following examples and comparative examples were obtained by testing using the following methods. The test results are shown in Tables 2-1 and 2-2: (1) Morphological test: obtained by scanning electron microscope of model Regulus 8100 of Hitachi, Japan; (2) X-ray diffraction (XRD) test: obtained by testing with a Smart Lab 9kW X-ray diffractometer from Rigaku Corporation, Japan; (3) Median particle size D 50 The particle size distribution was obtained using a Marvern Mastersizer 3000 laser particle size analyzer. (4) Average particle size of primary particles: The prepared lithium iron phosphate cathode active material was photographed at 10k magnification using a scanning electron microscope, and the average primary particle size was calculated using LIBMAS and Nano Measurer software. (5) Specific surface area (BET) test: obtained by using a Tristar 3020 specific surface area analyzer from Micromeritics; (6) Powder compaction density test: Weigh 1g of the prepared lithium iron phosphate positive electrode active material and put it into the compaction mold. Place the mold into the compaction equipment and test the result under 30kN pressure. (7) Particle size distribution test: The prepared lithium iron phosphate cathode active material was photographed at 30.0k magnification and statistical data were obtained using LIBMAS analysis software.
[0093] Table 2-1
[0094] Table 2-2
[0095] Battery assembly and testing: The prepared lithium iron phosphate positive electrode active material, conductive agent (50% Compressed Denka Black), and binder (PVDF) were dispersed in 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. The electrolyte was 1.1 mol / L LiPF6, with the electrolyte solvent being EC:EMC:DMC = 1:1:1 (volume ratio). The separator was Celgard polypropylene membrane, and the lithium metal sheet was used as the negative electrode sheet. Together, they were assembled into a coin cell.
[0096] (1) 0.1C and 0.5C: Button 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 charging and discharging 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; then 2C for 1 cycle. The cutoff voltage condition was the same as for 0.1C.
[0097] (2) Low-temperature capacity retention rate at -10℃ and 0.3C: The test was conducted using coin cells with a test voltage of 2.5V-3.75V. At room temperature, the cells were charged to 3.75V using constant current and constant voltage charging, and then discharged to 2.5V using constant current discharging. The charge and discharge current was 0.3C for 4 cycles. In the fifth week, the cells were charged to 3.75V, and then the coin cells were placed at -10℃ for discharge. The ratio of the low-temperature discharge capacity in the fifth week to the low-temperature discharge capacity in the fourth week was the low-temperature capacity retention rate.
[0098] The test results are shown in Table 3.
[0099] Table 3
[0100] Results analysis: from Figure 1It can be seen that the primary particles of the lithium iron phosphate cathode active material exhibit three different particle size distributions, and are tightly connected with good particle roundness.
[0101] from Figure 2 It can be seen that the particle size distribution curve of the lithium iron phosphate cathode active material in Example 1 exhibits three characteristic peaks.
[0102] from Figure 3 As can be seen, the peak positions in the XRD spectrum of this lithium iron phosphate cathode active material are consistent with those of the standard PDF card for lithium iron phosphate, indicating the absence of impurities and high material purity.
[0103] As can be seen from Table 3, compared with Comparative Examples 1-5, the particle size distribution curve of the primary particles of the positive electrode active material prepared by the method provided in this application shows three characteristic peaks, indicating better particle size distribution, higher compaction density, and better capacity utilization and low-temperature cycling performance.
[0104] Compared with Example 1, Comparative Example 1 used only the first iron phosphate and Comparative Example 2 used only the second iron phosphate, resulting in the positive electrode active material not meeting the particle size distribution curve defined in this application, and having poor capacity utilization and low-temperature cycling performance.
[0105] Compared with Example 1, Comparative Example 3 did not introduce a titanium source during the preparation process, which could not effectively suppress primary particle growth. The particle size distribution curve also did not meet the requirements of this application, resulting in poor battery capacity performance and low-temperature cycling performance.
[0106] Compared with Example 1, Comparative Example 4 did not introduce flux during the preparation process, which could not effectively promote the dissolution and recrystallization of particles. There were fewer particles with larger particle sizes, resulting in poor battery capacity utilization and low-temperature cycling performance.
[0107] Compared with Example 1, Comparative Example 5 did not introduce titanium source and flux during the preparation process, and the particle size distribution curve did not meet the requirements of this application, resulting in poor battery capacity performance and low-temperature cycling performance.
[0108] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.
Claims
1. A positive electrode active material, characterized by, The lithium iron phosphate includes secondary particles formed by agglomeration of primary particles, and a particle size number distribution curve of the primary particles presents three characteristic peaks; The first characteristic peak of the primary particles has a peak position of 100nm-200nm, and a corresponding number ratio at the peak position is 40%-60%; The second characteristic peak of the primary particles has a peak position of 200nm-300nm, and a corresponding number ratio at the peak position is 20%-40%, which is less than the corresponding number ratio at the peak position of the first characteristic peak; The third characteristic peak of the primary particles has a peak position of 1um-2um, and a corresponding number ratio at the peak position is 0.5%-1%.
2. The positive electrode active material according to claim 1, characterized by The average particle size of the primary particles is 220nm-240nm; and / or, The median particle size D of the positive electrode active material 50 The micrometer diameter is 1.0 μm to 1.6 μm; and / or, The specific surface area of the positive electrode active material is 12.4 m 2 / g-13.4 m 2 / g.
3. The positive electrode active material according to claim 1, characterized by The powder tap density of the positive electrode active material is 2.73 g / cm3 at 30 kN 3 - 2.75 g / cm3 3 .
4. The positive electrode active material according to claim 1, characterized by The doping amount of titanium in the positive electrode active material is 2000ppm-7000ppm.
5. The positive electrode active material according to any one of claims 1 to 4, characterized by The positive electrode active material includes a substrate and a carbon coating layer at least partially coated on the surface of the substrate; The substrate has a composition shown in formula I: Li 1+a Fe b M c (PO4) d Formula I; -0.1≤a≤0.1, 0≤b≤1, 0≤c≤0.5, 0≤d≤1; M includes Ti and at least one of V, Zr, and Nb.
6. A method for producing the positive electrode active material according to any one of claims 1 to 5, characterized by, The method comprises: Mixing iron phosphate, a lithium source, a phosphorus source, a carbon source, a dispersant, an M source, and a solvent to obtain a slurry, and grinding to obtain a spray material through a spray drying process, wherein the iron phosphate includes first iron phosphate and second iron phosphate, the particle size of the first iron phosphate is 50nm-200nm, and the particle size of the second iron phosphate is 30nm-160nm; Performing first sintering treatment on the spray material to obtain a primary sintered material; Mixing the primary sintered material, a titanium source, and a fluxing agent and performing second sintering treatment to obtain the positive electrode active material.
7. The method of claim 6, wherein, said first iron phosphate has a specific surface area of 8 m 2 / g - 16 m 2 / g, and / or the molar ratio of iron to phosphorus in said first iron phosphate is 0.960 - 0.980; and / or, said second iron phosphate has a specific surface area of 5 m 2 / g-12 m 2 / g, and / or, the molar ratio of iron to phosphorus in said second iron phosphate is 0.950-0.970; and / or, The mass ratio of the first iron phosphate to the second iron phosphate is (1-2):(1-3).
8. The method according to claim 6 or 7, characterized in that, The molar ratio of lithium in the lithium source to iron in the iron phosphate is 0.90-1.01, and the molar ratio of phosphorus to iron in the iron phosphate is 0.98-1.05; and / or, The solid content of the slurry is 40wt%-45wt%; and / or, The median particle size D50 of the slurry is 0.30 μm - 0.50 μm; and / or, 50 0.30 μm - 0.50 μm; and / or, The addition amount of the carbon source accounts for 1.0%-1.5% of the total mass of the positive electrode active material.
9. The method according to claim 6 or 7, characterized in that, The inlet air temperature of the spray drying process is 200℃-250℃, and the outlet air temperature is 80℃-120℃; and / or, The median particle size D of the spray material 50 15μm-50μm; and / or, The water content of the spray material is less than or equal to 3.0%.
10. The method of claim 6 or 7, wherein, The first sintering treatment has a temperature of 750℃-820℃ and a time of 10h-15h.
11. The method of claim 10, wherein, The average particle size of the primary particles in the primary sintered material is 0.18um-0.22um, the number ratio of primary particles with a particle size less than or equal to 100nm is 8%-15%, and the number ratio of primary particles with a particle size in the range of 100nm-300nm is 50%-60%.
12. The method of claim 6 or 7, wherein, The addition amount of the fluxing agent accounts for 0.1%-1.0% of the total mass of the positive electrode active material; and / or, The adding amount of the fluxing agent accounts for 0.5%-5% of the total mass of the primary sintering material.
13. The method of claim 12, wherein, The temperature of the second sintering treatment is 750-800℃, and the time is 6-10h.
14. The method of claim 6 or 7, wherein, The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; and / or, The phosphorus source includes at least one of lithium dihydrogen phosphate and phosphoric acid; and / or, The carbon source includes at least one of glucose, sucrose, starch, and citric acid; and / or, The dispersant includes at least one of polyethylene glycol 3000, polyethylene glycol 6000, and polyvinyl alcohol 2000; and / or, The M source includes at least one of titanium dioxide, ammonium metavanadate, zirconium oxide, and niobium oxide; and / or, The solvent includes pure water or ethanol; and / or, The titanium source includes at least one of titanium dioxide, titanium tetrachloride, and calcium titanate; and / or, The fluxing agent includes at least one of lithium salt and ammonium salt; optionally, the fluxing agent includes at least one of LiCl, LiF, NH4Cl, and NH4F.
15. A positive electrode sheet characterized by comprising: The positive electrode active material includes the positive electrode active material according to any one of claims 1-4 or is prepared by the method according to any one of claims 5-14.
16. The cathode sheet of claim 15, wherein, The compacted density of the positive electrode active material layer is 2.8 g / cm3 at 30 kN 3 - 2.9 g / cm3 3 .
17. A battery, characterized by The positive electrode sheet includes the positive electrode sheet according to claim 15 or 16.