Lithium iron phosphate positive electrode material and preparation method therefor, and lithium-ion battery

Abstract

The present disclosure relates to the technical field of batteries and discloses a lithium iron phosphate positive electrode material and a preparation method therefor, and a lithium-ion battery. The lithium iron phosphate positive electrode material comprises primary particles and secondary particles. The secondary particles are formed by agglomeration of the primary particles. The lithium iron phosphate positive electrode material satisfies formula I and ρ% = 50% to 90%, where FSSS refers to the Fisher particle size of the lithium iron phosphate positive electrode material, DBET refers to the specific surface area particle size of the lithium iron phosphate positive electrode material, and ρ% refers to the relative density of the secondary particles. The present disclosure provides a lithium iron phosphate positive electrode material that satisfies both formula I and ρ% = 50% to 90%. The lithium iron phosphate positive electrode material has good dispersibility, a low degree of agglomeration, and a high compaction density. A positive electrode sheet prepared therefrom has the characteristics of a uniform areal density and a high peel strength, and therefore, a prepared battery has a high specific capacity and cycle stability.

Description

A lithium iron phosphate cathode material, its preparation method, and a lithium-ion battery

[0001] Cross-references to related applications

[0002] This disclosure claims priority to Chinese Patent Application No. 2025100084787, filed on January 3, 2025, entitled "A Lithium Iron Phosphate Cathode Material and Its Preparation Method and Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, and more specifically, to a lithium iron phosphate cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0004] Lithium iron phosphate (LFP) is one of the most competitive cathode active materials for lithium-ion batteries currently on the market. Compared with lithium cobalt oxide and ternary cathode materials, it has a longer lifespan and better safety performance. Furthermore, LFP has a capacity of 170 mAh / g. -1 With its theoretical specific capacity and a plateau discharge voltage of 3.4V, it possesses considerable energy density.

[0005] However, due to its crystal structure, lithium iron phosphate cathode materials have low ion diffusion rates and low conductivity. Therefore, techniques such as nano-sizing, coating, and doping are typically used to improve the Li- content of the material. + Diffusion rate and conductivity. However, these methods, to some extent, lead to or influence the agglomeration behavior of lithium iron phosphate cathode materials. For example, the smaller the particle size, the more the shape deviates from the standard spherical shape, and the wider the distribution of the cathode material, the easier it is for the cathode material to agglomerate. Also, when the coating layer is carbon material, if the carbon material is distributed in an island-like pattern on the surface of the active material, it will increase the surface roughness of the cathode material, thereby enhancing the interaction force between particles and promoting particle agglomeration. Furthermore, the preparation process affects the surface chemical properties of the obtained lithium iron phosphate cathode material, thus affecting the interaction between particles. The presence of agglomerates results in extremely noticeable scratches and particles during the cathode coating process, and also leads to uneven electrode surface density, making it difficult to maintain the uniformity of the cathode sheet, thus affecting the consistency of the battery.

[0006] In view of this, this disclosure is hereby made. Summary of the Invention

[0007] The purpose of this disclosure is to provide a lithium iron phosphate cathode material, a method for preparing the same, and a lithium-ion battery.

[0008] This disclosure is implemented as follows:

[0009] In a first aspect, this disclosure provides a lithium iron phosphate cathode material, comprising primary particles and secondary particles, wherein the secondary particles are agglomerated from the primary particles, and the lithium iron phosphate cathode material satisfies the following requirements: And ρ% = 50%~90%, where FSSS refers to the Fisher particle size of the lithium iron phosphate cathode material, in μm; and D BET The specific surface area particle size of the lithium iron phosphate cathode material is expressed in μm; ρ% = 1 - H%, where ρ% refers to the relative density of the secondary particles and H% refers to the porosity of the secondary particles.

[0010] In an optional implementation, the D BET The particle size of the lithium iron phosphate cathode material was measured and calculated using the nitrogen adsorption-desorption method. Wherein, BET refers to the specific surface area of ​​the lithium iron phosphate cathode material, and the value of BET is ≤20m². 2 / g, the ρ LFP This refers to the true density of lithium iron phosphate cathode material, where ρ... LFP The value range satisfies 3.3~3.6g / cm³. 3 .

[0011] In an optional embodiment, the FSSS is the average particle size of the lithium iron phosphate cathode material determined by steady-flow air permeation method, and the value of the FSSS is in the range of 0.4 to 5 μm.

[0012] And / or, the degree of aggregation N of the lithium iron phosphate cathode material is less than 25000, wherein the degree of aggregation is...

[0013] And / or, the compaction density of the lithium iron phosphate cathode material is 1.9–3.0 g / cm³. 3 .

[0014] In an optional embodiment, the lithium iron phosphate cathode material satisfies

[0015] And / or, the secondary particles of the lithium iron phosphate cathode material satisfy ρ% = 50% to 70%;

[0016] And / or, the lithium iron phosphate cathode material satisfies an agglomeration degree N of 200 to 12000;

[0017] And / or, the lithium iron phosphate cathode material satisfies FSSS = 1~2.5μm;

[0018] And / or, the lithium iron phosphate cathode material satisfies a BET of 9–15m. 2 / g.

[0019] In an optional embodiment, the lithium iron phosphate cathode material comprises an active material matrix and a carbon material, wherein the general formula of the active material matrix is ​​Li. 1-x A x Fe 1-y M y (PO 4-z )D z Wherein, A is selected from one or more of Na and Mg; M is selected from one or more of Al, Ni, Co, Mn, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn and Y; D is selected from one or more of F, S, N and Cl; 0≤x≤0.1; 0≤y≤0.1 and 0≤z≤0.1; the mass of the carbon material is 1% to 5% of the mass of the lithium iron phosphate cathode material.

[0020] Secondly, this disclosure provides a method for preparing a lithium iron phosphate cathode material as described in any of the foregoing embodiments, comprising:

[0021] Iron phosphate and lithium salt are mixed as materials, and the materials are mixed with carbon sources with different gasification temperatures to obtain a precursor.

[0022] The precursor was calcined in stages under an inert atmosphere, and then crushed, sieved, and demagnetized to obtain lithium iron phosphate cathode material.

[0023] In an optional embodiment, the step of mixing the iron phosphate and the lithium salt includes at least one of features I-IV;

[0024] Feature 1: Before the iron phosphate is mixed with the lithium salt, the iron phosphate is first added to an air jet mill for pulverization.

[0025] Feature II: The lithium salt is at least one of lithium carbonate, lithium oxalate, and lithium acetate;

[0026] Feature III: When the iron phosphate is mixed with the lithium salt, a dopant is also added, wherein the dopant is at least one of the salt, oxide and hydroxide of the dopant element;

[0027] Feature IV: The iron phosphate and the dopant are added in stoichiometric ratio.

[0028] In an optional embodiment, the carbon source with different vaporization temperatures includes a first carbon source with a vaporization temperature of 400 to 600°C, a second carbon source with a vaporization temperature of 200 to 400°C, and a third carbon source with a vaporization temperature of 100 to 200°C.

[0029] The first carbon source includes at least one of polyimide, polyphenylene ether, and polyetherimide;

[0030] The second carbon source includes at least one of glucose, polyethylene glycol, starch, sucrose, maltose, cellulose, chitosan, polyacrylonitrile, benzyl alcohol, and glycerol;

[0031] The third carbon source includes at least one of phenol, ethylene glycol, propylene glycol, butylene glycol, isopropanol, sorbitol, erythritol, fructose, malic acid, citric acid, and salicylic acid.

[0032] In an optional embodiment, the step of mixing the material with a carbon source having a different vaporization temperature includes at least one of features V to IX;

[0033] Feature V: The material and the carbon source with different gasification temperatures are mixed in an airflow pulverizer. An airflow is introduced during the mixing process. The pressure of the airflow is 0.5 to 1.5 MPa and the temperature is 25 to 120°C. The total mixing time is 15 to 60 minutes.

[0034] Feature VI: Before being mixed with the material, the carbon source with different vaporization temperatures is first prepared into a carbon source solution with a mass percentage concentration of 10% to 30%, and then the carbon source solution is atomized before being mixed with the material, wherein the atomization pressure is 0.1 to 1.5 MPa;

[0035] Feature VII: The material is first mixed with the first carbon source, then with the second carbon source, and finally with the third carbon source;

[0036] Feature VIII: The total mass of the carbon sources with different vaporization temperatures is 15% to 25% of the mass of the material;

[0037] Feature IX: When the material is mixed with carbon sources with different gasification temperatures, the mass ratio of the first carbon source, the second carbon source and the third carbon source is 0-15:2.5-15:2.5-10.

[0038] In an optional embodiment, the segmented calcination includes a first stage, a second stage, and a third stage. The first stage is heated to 180-220°C at a rate of 1-2°C / min and held for 1-2 hours. The second stage is heated to 380-420°C at a rate of 2-3°C / min and held for 2-4 hours. The third stage is heated to 650-750°C at a rate of 4-6°C / min and held for 4-8 hours.

[0039] Thirdly, this disclosure provides a lithium-ion battery comprising a lithium iron phosphate cathode material as described in any of the foregoing embodiments or a lithium iron phosphate cathode material prepared by a method for preparing a lithium iron phosphate cathode material as described in any of the foregoing embodiments.

[0040] This disclosure has the following beneficial effects:

[0041] (1) This disclosure provides a method that simultaneously satisfies The lithium iron phosphate cathode material has a p% content of 50% to 90%, and the lithium iron phosphate cathode material has good dispersibility, low agglomeration degree and high compaction density. The cathode sheet prepared by using it as the cathode active material has the characteristics of uniform surface density and high peel strength. Therefore, the battery prepared by it has high specific capacity and cycle stability.

[0042] (2) The method for preparing lithium iron phosphate cathode material provided in this disclosure utilizes carbon sources with different vaporization temperatures to perform vaporization and pore-forming at different calcination stages, resulting in loose bonding between material particles and inhibiting particle aggregation. This leads to a lower degree of agglomeration in the obtained cathode material. The preparation method provided in this disclosure can simultaneously meet the requirements of... Furthermore, the lithium iron phosphate cathode material has a ρ% content of 50% to 90%. This lithium iron phosphate cathode material has good dispersibility, low agglomeration degree, and high compaction density. The cathode sheet prepared from it has the characteristics of uniform surface density and high peel strength. Therefore, the battery prepared from it has high specific capacity and cycle stability. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 is a SEM image of the lithium iron phosphate cathode material provided in Embodiment 1 of this disclosure;

[0045] Figure 2 is a SEM image of the lithium iron phosphate cathode material provided in Embodiment 8 of this disclosure;

[0046] Figure 3 is a SEM image of the lithium iron phosphate cathode material provided in Comparative Example 4 of this disclosure;

[0047] Figure 4 shows the Raman spectra of the lithium iron phosphate cathode materials provided in Examples 1 and 4 of this disclosure. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0049] A lithium iron phosphate cathode material includes primary particles and secondary particles formed by the agglomeration of the primary particles. The lithium iron phosphate cathode material satisfies... And ρ% = 50%~90%, where FSSS refers to the Fisher particle size of lithium iron phosphate cathode material, in μm; D BET ρ% refers to the specific surface area and particle size of the lithium iron phosphate cathode material, in μm; ρ% = 1 - H%, where ρ% refers to the relative density of the secondary particles and H% refers to the porosity of the secondary particles.

[0050] This disclosure provides a method that simultaneously satisfies Lithium iron phosphate cathode materials with ρ% in a specific range have good dispersibility, low agglomeration degree and high compaction density. Cathode sheets prepared with them as cathode active materials have uniform surface density and high peel strength. Therefore, the batteries prepared with them have high specific capacity and cycle stability.

[0051] Specifically, This reflects the ratio of secondary particle size to primary particle size. Better dispersibility and lower agglomeration in lithium iron phosphate cathode materials indicate higher dispersion. The smaller the size. The lithium iron phosphate cathode material disclosed herein... The range is 5 to 40. Both excessively high and excessively low tap density will reduce the tap density of the cathode material, thereby decreasing the specific capacity of the lithium iron phosphate cathode battery. Excessively high density indicates a high degree of agglomeration in the lithium iron phosphate cathode material, with larger pores between the agglomerated secondary particles, resulting in low tap density. Insufficient density indicates that the lithium iron phosphate cathode material is mainly composed of dispersed primary particles. Since the porosity of secondary particles (agglomerates) is usually lower than that of primary particle powder in its tapped state, excessively low agglomeration will also cause a decrease in tap density.

[0052] In some implementations... The value range is from 10 to 30. For example, it can be any one of 10, 12, 15, 18, 20, 22, 25, 28, 30 or any two of them.

[0053] In some embodiments, the value of FSSS is in the range of 0.4 to 5 μm, for example, it can be any one or any two of 0.4 μm, 0.5 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, and 5 μm; in other embodiments, the value of FSSS is in the range of 1 to 2.5 μm.

[0054] The Fisher's Score (FSSS) is the average particle size of lithium iron phosphate cathode materials determined by a steady-flow air permeation method. The mechanism is as follows: constant pressure and constant flow air is passed through a powder sample tube, and the specific surface area and average particle size of the powder are calculated by measuring the gas pressure difference according to the formula. Since the airflow is constant pressure and constant flow, the measured specific surface area is the external specific surface area of ​​the powder. Therefore, the obtained average particle size can reflect the particle size of the agglomerates.

[0055] Specific surface area particle size (D) BET The volumetric surface area (BET) is defined as the specific surface area of ​​particles with this diameter, and is equal to the average specific surface area of ​​all particles. It is obtained by testing and calculating using the nitrogen adsorption-desorption method. The mechanism is as follows: by measuring the amount of nitrogen adsorbed on the powder sample under different pressures, the specific surface area (BET) of the powder is calculated according to the formula. Since the gas flow is pressurized and the collected data is the amount of gas adsorbed, the measured specific surface area is the total specific surface area of ​​the powder. Therefore, the particle size calculated using the BET specific surface area can reflect the particle size of primary particles. The calculation formula is as follows: Here, BET refers to the specific surface area of ​​the lithium iron phosphate cathode material, measured in m². 2 / g, ρ LFP This refers to the true density of lithium iron phosphate cathode material, expressed in g / cm³. 3 According to D BET definition, Right now at the same time, therefore

[0056] In some implementations, the value range of BET satisfies ≤20m 2 / g; In some implementations, the value of BET ranges from 9 to 15m. 2 / g, for example, can be 9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 A range of values ​​in / g or between any two of them; in some implementations, ρ LFP The value range satisfies 3.3~3.6g / cm3, for example, it can be 3.3g / cm3. 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 The range of values ​​between any one or any two of them.

[0057] The relative density of lithium iron phosphate secondary particles refers to the ratio of their apparent density to the true density of lithium iron phosphate. Apparent density is the ratio of the material's mass to its apparent volume, which is the sum of the solid volume and the pore volume. True density refers to the actual mass of a unit volume of solid material in an absolutely dense state, i.e., the density after removing internal pores. The relative density of secondary particles can be calculated using their porosity (H%), i.e., ρ% = 1 - H%. Higher porosity results in lower relative density, indicating a more porous structure, easier dispersion, and higher compaction density. This leads to more uniform surface density and higher peel strength in the prepared cathode material, resulting in higher specific capacity and cycle stability. In this disclosure, ρ% is taken as 50%–90%. Too high a value makes secondary particles difficult to disperse, while too low a value reduces the tap density of the lithium iron phosphate cathode material. In some embodiments, ρ% is taken as 50%–70%.

[0058] In some embodiments, the agglomeration degree N of the lithium iron phosphate cathode material is less than 25000, wherein the agglomeration degree...

[0059] In some embodiments, the degree of aggregation N of the lithium iron phosphate cathode material is 200–12000. Lithium iron phosphate cathode materials that meet the degree of aggregation range have better compaction density, and the prepared electrode sheet has a more uniform surface density, thus exhibiting higher specific capacity and cycle stability.

[0060] Agglomeration degree N reflects the number of primary particles contained in secondary particles in lithium iron phosphate cathode materials. Specifically, agglomeration degree... A smaller N value indicates lower aggregation and better electrode uniformity. However, an excessively low N value indicates a low relative density ρ% or... If the density is too small, the tap density of the material will be too low, resulting in a lower specific capacity.

[0061] In some embodiments, the compaction density of the lithium iron phosphate cathode material is 1.9–3.0 g / cm³. 3 The compaction density was obtained by testing under 3T pressure.

[0062] In some embodiments, the lithium iron phosphate cathode material includes an active material matrix and a carbon material, wherein the general formula of the active material matrix is ​​Li. 1-x A x Fe 1-y M y (PO 4-z )D zWherein, A is selected from one or more of Na and Mg; M is selected from one or more of Al, Ni, Co, Mn, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn and Y; D is selected from one or more of F, S, N and Cl; 0≤x≤0.1; 0≤y≤0.1 and 0≤z≤0.1; the mass of the carbon material is 1% to 5% of the mass of the lithium iron phosphate cathode material.

[0063] Furthermore, this disclosure provides a method for preparing a lithium iron phosphate cathode material, which includes the following steps:

[0064] S1. Iron phosphate and lithium salt are mixed and used as materials.

[0065] Before mixing with lithium salt, the iron phosphate is first added to an air jet mill for pulverization. This pulverization process refines the iron phosphate, making it easier to mix evenly with lithium salt later.

[0066] In this embodiment, the lithium salt includes, but is not limited to, at least one of lithium carbonate, lithium oxalate, and lithium acetate. When mixing iron phosphate with the lithium salt, a dopant may also be added according to actual product requirements, with the iron phosphate and dopant added in a stoichiometric ratio. The dopant includes, but is not limited to, at least one of salts, oxides, and hydroxides of the dopant element.

[0067] S2. Mix the material with carbon sources with different gasification temperatures to obtain a precursor.

[0068] Before mixing with the material, carbon sources with different vaporization temperatures are first prepared into carbon source solutions with a mass percentage concentration of 10% to 30%. The carbon source solutions are then atomized and mixed with the material. The atomization pressure is 0.1 to 1.5 MPa. The material and carbon sources with different vaporization temperatures are mixed in an airflow pulverizer. During mixing, airflow is introduced with a pressure of 0.5 to 1.5 MPa and a temperature of 25 to 120°C. The total mixing time is 15 to 60 minutes.

[0069] In this embodiment, the carbon sources with different vaporization temperatures include a first carbon source with a vaporization temperature of 400–600°C, a second carbon source with a vaporization temperature of 200–400°C, and a third carbon source with a vaporization temperature of 100–200°C. The material is first mixed with the first carbon source, then with the second carbon source, and finally with the third carbon source. The total mass of the carbon sources with different vaporization temperatures is 15%–25% of the mass of the material. When the material is mixed with the carbon sources with different vaporization temperatures, the mass ratio of the first carbon source, the second carbon source, and the third carbon source is 0–15:2.5–15:2.5–10. Wherein, when the mass of the first carbon source is 0, it means that the carbon sources only include the second and third carbon sources.

[0070] The first carbon source includes, but is not limited to, at least one of polyimide, polyphenylene ether, and polyetherimide; the second carbon source includes, but is not limited to, at least one of glucose, polyethylene glycol, starch, sucrose, maltose, cellulose, chitosan, polyacrylonitrile, benzyl alcohol, and glycerol; and the third carbon source includes, but is not limited to, at least one of phenol, ethylene glycol, propylene glycol, butanediol, isopropanol, sorbitol, erythritol, fructose, malic acid, citric acid, and salicylic acid.

[0071] The first carbon source has the characteristics of strong molecular chain rigidity, high degree of conjugation and large amount of solid residue after decomposition compared with the second or third carbon source. Therefore, its graphitization degree is higher, which is beneficial to improving the conductivity of the cathode material. On the one hand, since the first carbon source is more hydrophobic than the second or third carbon source, it can be better coated on the surface of the material particles when mixed with the material first. On the other hand, the first mixing can make the conductive carbon network formed by calcination tightly distributed on the surface of lithium iron phosphate particles.

[0072] S3. The precursor is calcined in stages under an inert atmosphere, and then crushed, sieved and demagnetized to obtain lithium iron phosphate cathode material.

[0073] The segmented calcination includes a first stage, a second stage, and a third stage. In the first stage, the temperature is increased to 180-220℃ at a rate of 1-2℃ / min and held for 1-2 hours. In the second stage, the temperature is increased to 380-420℃ at a rate of 2-3℃ / min and held for 2-4 hours. In the third stage, the temperature is increased to 650-750℃ at a rate of 4-6℃ / min and held for 4-8 hours.

[0074] The aforementioned lithium iron phosphate cathode material can be widely used in the preparation of batteries, and the resulting batteries exhibit excellent electrochemical performance. In this regard, this disclosure also provides a lithium-ion battery comprising the aforementioned lithium iron phosphate cathode material.

[0075] The battery disclosed herein typically includes a positive electrode, a negative electrode, a separator spaced between the positive and negative electrodes, and an electrolyte. Methods for preparing the battery should be known to those skilled in the art; for example, the positive electrode, separator, and negative electrode can each be a sheet, which can be cut to a target size and stacked sequentially, or wound to a target size to form a cell, and further combined with an electrolyte to form a battery.

[0076] In the battery provided in this disclosure, the negative electrode typically includes a negative current collector and a negative active material layer located on the surface of the negative current collector. The negative active material layer typically includes a negative active material. The negative active material can be any material suitable for lithium-ion batteries, including, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite can be selected from one or more combinations of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more combinations of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from one or more combinations of elemental tin, tin oxide compounds, and tin alloys. The negative current collector is typically a structure or component that collects current. The negative current collector can be any material suitable for use as a negative current collector in lithium-ion batteries, for example, the negative current collector can be, but not limited to, metal foil, and more specifically, copper foil.

[0077] In the battery provided by this disclosure, the separator can be any material suitable for lithium-ion battery separators in the art, such as, but not limited to, one or more combinations of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0078] In the battery provided in this disclosure, the electrolyte can be any electrolyte suitable for lithium-ion batteries in the art. For example, the electrolyte typically includes an electrolyte and a solvent. The electrolyte typically includes lithium salts, and more specifically, the lithium salt can be an inorganic lithium salt and / or an organic lithium salt. The lithium salt can be selected from one or more combinations of LiPF6, LiBF4, LiN(SO2F)2 (abbreviated as LiFSI), LiN(CF3SO2)2 (abbreviated as LiTFSI), LiClO4, LiAsF6, LiB(C2O4)2 (abbreviated as LiBOB), and LiBF2C2O4 (abbreviated as LiDFOB). For another example, the concentration of the electrolyte can be between 0.8 mol / L and 1.5 mol / L. The solvent can be any solvent suitable for lithium-ion batteries in the art. The solvent of the electrolyte is usually a non-aqueous solvent, preferably an organic solvent, specifically including but not limited to ethylene carbonate, propylene carbonate, butene carbonate, pentene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, etc., or one or more combinations of their halogenated derivatives.

[0079] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0080] This disclosure provides lithium iron phosphate cathode materials as shown in Tables 1, 2 and 3, and tests them.

[0081] Button cell assembly includes the following steps:

[0082] (1) Slurry preparation

[0083] PVDF binder was added to a portion of NMP and stirred in a dual planetary mixer at 80 rpm and 4500 rpm for 120 min to obtain a slurry with a solid content of 7%. Acetylene black was added to the slurry and stirred at 80 rpm and 4500 rpm for 60 min to obtain a conductive slurry. Lithium iron phosphate cathode material and the remaining NMP were added to the conductive slurry and stirred at 80 rpm and 6500 rpm for 90 min. Then, the mixture was stirred at 15 rpm for 30 min to defoam, resulting in a cathode slurry with a solid content of 65%.

[0084] The mass ratio of lithium iron phosphate cathode material, acetylene black, and PVDF is 97.2:0.8:2. The average particle size of acetylene black is 40 nm, and its specific surface area is 65 m². 2 / g.

[0085] (2) Electrode preparation

[0086] A double-sided reciprocating coating machine is used to coat the positive electrode slurry onto an aluminum foil substrate, which is then dried to obtain the positive electrode sheet. In the rolling process, the main roller temperature is set to 40℃, and the main roller pressure is controlled to achieve a compaction density of 2.55 g / cm³ for the electrode sheet. 3 .

[0087] (3) Button cell assembly

[0088] The negative electrode is a lithium sheet, the separator is a polypropylene porous membrane, and the electrolyte is prepared by dissolving 1 mol of LiPF6 in 1 L of a mixed solvent of EC and DMC (volume ratio 1:1). The positive electrode, negative electrode, electrolyte, and separator are assembled into a battery in an argon-protected glove box.

[0089] The testing methods include:

[0090] (1) Carbon content: The carbon content was obtained by high-frequency infrared carbon-sulfur analyzer according to YS / T 1028.4-2015.

[0091] (2) True density (ρ) LFP ): The measurement shall be performed in accordance with GB / T 24203-2024 helium method.

[0092] (3)Fischer size (FSSS): Measured in accordance with GB / T 3249-2022.

[0093] (4) Specific surface area (BET): Measured using a MacPherson strut physical adsorption analyzer according to the BET method of GB / T 19587-2017, and then based on... D was calculated BET Then, further calculations were performed to obtain...

[0094] (5) Relative density of secondary particles (ρ%): All or part of the secondary particles are separated from the sample to be tested, and their porosity (H%) is then tested. The relative density of the secondary particles is calculated by ρ% = 1 - H%.

[0095] The embodiments of this disclosure employ the following method to separate secondary particles: the sample to be tested is vibrated and sieved (the difference in mesh size between adjacent sieves is 10 mesh) to obtain multiple sub-samples with different particle size ranges. The sub-samples with different particle size ranges are separated by gravity sedimentation (water medium). The precipitate is dried at room temperature to obtain the secondary particles of the sub-sample. Then, the secondary particles of all sub-samples are combined.

[0096] In the embodiments of this disclosure, scanning electron microscopy (SEM) is used to observe and calculate the porosity of secondary particles: the magnification is adjusted until there is only one complete cross-section of secondary particles in the view and an SEM image is taken. Then, the SEM image is analyzed by Image-Pro Plus software and the porosity is calculated. Porosity = (sum of the areas of all pores of the secondary particles in the cross-section / cross-sectional area of ​​the secondary particles) × 100%.

[0097] (6) The formula for calculating the degree of aggregation N is:

[0098] (7) Compacted density (CD): Tested in accordance with GB / T 24533-2009, with the pressure endpoint being 3T (600MPa).

[0099] (8) Surface density test: The surface density of the electrode is tested by X-ray fluorescence spectroscopy (XRF). The electrode to be tested is cut into 20 small samples of the same size for testing. The content of each element is obtained, and the mass and surface density of the lithium iron phosphate cathode material are calculated. The average value is used as the average surface density, and the standard deviation of the surface density sample is calculated.

[0100] (9) Peel strength test: The 180° peel test method was used to test the strength on an Instron 3365 tensile tester at a pulling speed of 60 mm / min.

[0101] (10) Electrode resistance: The resistance was tested using the Yuaneng Technology BER2100 multi-functional electrode resistance meter at 10 different locations. The average value and the standard deviation of the sample were calculated.

[0102] (11) Electrochemical performance: The constant current charge-discharge and cycle performance of the battery were tested using the LAND battery test system. At 25°C, the charge-discharge voltage range was 2.5 to 4.2V.

[0103] The test results are shown in Tables 1, 2 and 3.

[0104] Table 1. Statistical table of general formulas and parameter detection for different samples

[0105] Table 2. Statistical table of physical property test results for different samples

[0106] Table 3. Statistical table of electrochemical performance of different samples

[0107] As can be seen from Tables 1, 2, and 3 above, the lithium iron phosphate cathode material of this disclosure embodiment has a higher compaction density and better overall performance compared to the comparative example. A density below 5 or above 40, or a ρ% greater than 90%, will result in an excessively low compaction density, thus affecting the charge / discharge specific capacity. Specifically, The ρ% ratio reflects the particle size distribution of secondary particles to primary particles, indicating the degree of agglomeration. ρ% reflects the compactness of the primary particles within the secondary particles. Insufficient agglomeration makes the particles easily crushed and rearranged during compaction, or excessive agglomeration leads to excessive pore volume between particles, hindering the improvement of compaction density. Conversely, excessive agglomeration or compaction makes it difficult to crush secondary particles during compaction, resulting in excessively large pore volumes formed by overlapping large particles, also hindering the improvement of compaction density. Therefore... The specific capacity and rate performance of the cathode material need to be maintained within a reasonable range to achieve a high compaction density. Compaction density affects the specific capacity and rate performance of the material, thus the comparative example exhibits poorer electrochemical performance compared to Example 1.

[0108] Example 2: Lithium iron phosphate cathode material conforms to Furthermore, the ρ% range is 50% to 90%, but this does not fall within the range where the agglomeration degree N is below 25000. In this case, compared to other embodiments, the lithium iron phosphate cathode material has a lower compaction density, resulting in lower electrode peel strength. Due to excessive agglomeration, both the areal density and electrode resistance sample standard deviations are large, leading to lower compaction density and specific surface area, thus reducing the lithium insertion / extraction rate. Therefore, it exhibits lower rate performance and poorer cycle stability. In other embodiments, the cathode material has an agglomeration degree N below 25000, and exhibits better performance across the board.

[0109] Compared to Example 6, Examples 1, 3, and 5 exhibit higher compaction density; furthermore, they possess higher electrode peel strength, lower areal density standard deviation, and lower electrode resistance standard deviation, resulting in higher rate performance and capacity retention. This indicates that lithium iron phosphate cathode materials have superior overall performance in the agglomeration degree range of 200–12000.

[0110] Compared to Examples 1, 3, and 5, Example 4 exhibits a lower compaction density. This is because the agglomeration degree of Example 4 is below 200, indicating a lower degree of agglomeration in the cathode material. Due to the low agglomeration degree, the number of primary particles is greater, resulting in a smaller overall particle size and thus a lower compaction density, further affecting the material's specific capacity. Because of the low agglomeration degree of the cathode material, both the sample standard deviation of the areal density and the sample standard deviation of the electrode resistance are lower. Furthermore, the lower agglomeration degree and the greater number of primary particles (i.e., smaller overall particle size) result in a larger specific surface area, thereby improving the adhesion of the cathode material coating to the current collector and increasing the peel strength.

[0111] Examples 1, 5, and Comparative Example 2 have similar chemical compositions and p%, but differ in... A comparison of the performance data of the three shows that, with As the density increases, the compaction density first increases and then decreases. This is because both excessive and insufficient agglomeration lead to increased porosity between particles, thus reducing compaction density. When ρ% is similar, as... An increase indicates that the number of primary particles contained in a single secondary particle increases, resulting in a higher overall compaction density; however, further increases... This indicates that a larger particle size of the secondary particles or a smaller particle size of the primary particles that make up the secondary particles will both disrupt the gradation balance, resulting in a decrease in compaction density; compaction density has a significant impact on the specific capacity of lithium iron phosphate cathode materials. The larger the value, the larger the areal density sample standard deviation, the smaller the peel strength, the larger the electrode resistance, and the larger the electrode resistance sample standard deviation. Ultimately, Example 1 exhibits superior electrochemical performance, indicating that the lithium iron phosphate cathode... It should be maintained within a certain range so that its aggregation degree N is maintained within a certain range.

[0112] Examples 2, 6, 7, and Comparative Example 3 have similar chemical compositions and However, comparing the performance data of the three materials with different ρ%, it can be seen that as ρ% increases, the compaction density first increases and then decreases. This is because secondary particles with higher relative density can increase the overall compaction density on the one hand, and are less likely to be crushed during the compaction process on the other hand. The increased porosity formed by the overlapping of larger secondary particles leads to a decrease in compaction density. In addition, as ρ% increases, the agglomeration degree N of the lithium iron phosphate cathode material increases, resulting in a decrease in peel strength. As ρ% increases, the agglomeration degree N increases, the resistance of the electrode increases, and both the standard deviation of the electrode areal density and the standard deviation of the electrode resistance sample increase. Finally, Example 7 has superior electrochemical performance, indicating that the ρ% or agglomeration degree N of the lithium iron phosphate cathode material should be maintained within a certain range.

[0113] In addition, this disclosure also provides preparation methods for the above-mentioned product embodiments and product comparative examples.

[0114] Method Example 1

[0115] A method for preparing lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Example 1 above, and the preparation method of this example includes the following steps:

[0116] (1) Air is introduced into the air jet milling device to pulverize anhydrous ferric phosphate with a Dv50 of 8.52 μm to obtain anhydrous ferric phosphate with a Dv50 of 0.4 to 0.5 μm.

[0117] (2) The anhydrous iron phosphate obtained in step (1) is mixed with lithium carbonate as materials to prepare a first carbon source solution, a second carbon source solution and a third carbon source solution; the atomized first carbon source solution, second carbon source solution and third carbon source solution are introduced into an airflow pulverizer to pulverize and coat the materials, respectively, to obtain a first precursor, a second precursor and a third precursor.

[0118] Anhydrous iron phosphate and lithium carbonate were mixed at a ratio of n(Fe):n(Li) = 1:1.05.

[0119] The first carbon source solution is a 10 wt% polyimide DMF solution; the second carbon source solution is a 20 wt% glucose aqueous solution; and the third carbon source solution is a 10 wt% ethylene glycol ethanol solution.

[0120] The feeding ratio of the material, the first carbon source solution, the second carbon source solution, and the third carbon source solution is 10g:5g:2.5g:5g.

[0121] The air pressure is 1±0.1MPa; the air temperature is 120℃ and the mixing time is 20min when the material is mixed with the first carbon source solution; the air temperature is 100℃ and the mixing time is 15min when the first precursor is mixed with the second carbon source solution; the air temperature is 80℃ and the mixing time is 15min when the second precursor is mixed with the third carbon source solution.

[0122] The atomization pressure is 1 MPa.

[0123] (3) The third precursor is placed in a rotary kiln and calcined in three stages under a nitrogen atmosphere. Then, it is mechanically crushed, sieved and demagnetized to obtain lithium iron phosphate cathode material.

[0124] The three-stage calcination process includes: the first stage involves heating to 200℃ at a rate of 1℃ / min and holding for 1 hour; the second stage involves heating to 400℃ at a rate of 2℃ / min and holding for 3 hours; and the third stage involves heating to 700℃ at a rate of 5℃ / min and holding for 6 hours.

[0125] Method Example 2

[0126] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Example 2 above, and the preparation method of this example includes the following steps:

[0127] (1) Anhydrous iron phosphate with a Dv50 of 8.52 μm is dry-mixed with lithium acetate, titanium oxysulfate, first carbon source, second carbon source and third carbon source to obtain material. The material is then put into a ball mill for grinding and crushing to obtain a precursor. The Dv50 of the precursor is controlled to be 0.4 to 0.5 μm.

[0128] Anhydrous ferric phosphate was mixed with titanium oxysulfate and lithium acetate in a ratio of n(Fe):n(Ti):n(Li) = 0.986:0.014:1.05.

[0129] The first carbon source is polyimide; the second carbon source is glucose; and the third carbon source is erythritol.

[0130] The total mass of anhydrous iron phosphate, lithium acetate, and titanium oxysulfate, and the feeding ratio of the first carbon source, the second carbon source, and the third carbon source are 10g:0.7g:0.7g:0.7g.

[0131] Ball milling conditions: frequency 30Hz, 1mm zirconia beads used in ball milling, volume ratio of bead size to material 1:1, rotation speed 600rpm, milling time 3h, temperature room temperature.

[0132] (2) The precursor is placed in a rotary kiln and calcined in three stages under a nitrogen atmosphere. Then, it is mechanically crushed, sieved and demagnetized to obtain lithium iron phosphate cathode material.

[0133] The three-stage calcination process includes: the first stage involves heating to 200℃ at a rate of 1℃ / min and holding for 1 hour; the second stage involves heating to 400℃ at a rate of 2℃ / min and holding for 2 hours; and the third stage involves heating to 700℃ at a rate of 5℃ / min and holding for 8 hours.

[0134] Method Example 3

[0135] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Example 3 above, and the preparation method of this example includes the following steps:

[0136] The difference from Method Example 1 is that:

[0137] The medium in the air jet pulverizer is nitrogen.

[0138] In step (2), lithium oxalate is used as the lithium source; sodium fluoride is also added to the material, and anhydrous iron phosphate is mixed with sodium fluoride and lithium oxalate in the ratio of n(Fe):n(Na):n(Li) = 0.988:0.002:1.05.

[0139] The first carbon source solution is a 10 wt% toluene solution of polyphenylene ether; the second carbon source solution is a 20 wt% ethanol solution of polyethylene glycol-400; the third carbon source solution is a 10 wt% ethanol solution of fructose; the feeding ratio of the materials, the first carbon source solution, the second carbon source solution, and the third carbon source solution is 10:2.5:2.5:7.5.

[0140] The air pressure is 0.8±0.1MPa; the air temperature is 120℃ and the mixing time is 15min when the material is mixed with the first carbon source solution; the air temperature is 70℃ and the mixing time is 15min when the first precursor is mixed with the second carbon source solution; the air temperature is 70℃ and the mixing time is 30min when the second precursor is mixed with the third carbon source solution.

[0141] The atomization pressure is 0.8 MPa.

[0142] Step (3) Three-stage calcination includes: the first stage is heated to 200℃ at 1℃ / min and held for 2h; the second stage is heated to 400℃ at 2℃ / min and held for 2h; the third stage is heated to 650℃ at 5℃ / min and held for 5h.

[0143] Method Example 4

[0144] A method for preparing lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Example 4 above, and the preparation method of this example includes the following steps:

[0145] The difference from Method Example 1 is that:

[0146] Step (2) uses lithium oxalate as the lithium source; no first carbon source is added, the second carbon source solution is a 20 wt% ethanol solution of polyethylene glycol-400; the third carbon source solution is a 10 wt% ethanol solution of ethylene glycol; the feeding ratio of the material, the second carbon source solution and the third carbon source solution is 10:5:8.

[0147] The air pressure is 1.5±0.1MPa; the air temperature is 80℃ and the mixing time is 30min when the material is mixed with the second carbon source solution; the air temperature is 80℃ and the mixing time is 20min when the second precursor is mixed with the third carbon source solution.

[0148] The atomization pressure is 1 MPa.

[0149] Step (3) Three-stage calcination includes: the first stage is heated to 200℃ at 1℃ / min and held for 2h; the second stage is heated to 400℃ at 2℃ / min and held for 4h; the third stage is heated to 650℃ at 5℃ / min and held for 5h.

[0150] Method Example 5

[0151] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Example 5 above, and the preparation method of this example includes the following steps:

[0152] The difference from Method Example 1 is that:

[0153] Step (2) The first carbon source solution is a 16 wt% DMF solution of polyimide; the second carbon source solution is a 10 wt% aqueous solution of amylose; the third carbon source solution is a 20 wt% ethanol solution of citric acid; the feeding ratio of the materials, the first carbon source solution, the second carbon source solution, and the third carbon source solution is 10:6.25:2.5:1.25.

[0154] The atomization pressure is 0.5 MPa.

[0155] Step (3) Three-stage calcination includes: the first stage is heated to 200℃ at 2℃ / min and held for 2h; the second stage is heated to 400℃ at 2℃ / min and held for 2h; the third stage is heated to 750℃ at 5℃ / min and held for 5h.

[0156] Method Example 6

[0157] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Example 6 above, and the preparation method of this example includes the following steps:

[0158] (1) Anhydrous iron phosphate with a Dv50 of 8.52 μm is mixed with lithium carbonate, titanium oxysulfate, a second carbon source and a third carbon source to obtain a material. The material is then placed in a ball mill for grinding and crushing to obtain a precursor. The Dv50 of the precursor is controlled to be 0.4 to 0.5 μm.

[0159] Anhydrous ferric phosphate was mixed with titanium oxysulfate and lithium carbonate in a ratio of n(Fe):n(Ti):n(Li) = 0.988:0.012:1.05.

[0160] The second carbon source is polyethylene glycol-400; the third carbon source is ethylene glycol.

[0161] The total mass of anhydrous iron phosphate, lithium carbonate, and titanium oxysulfate, the feed ratio of the second carbon source and the third carbon source is 10:1.5:1.

[0162] Grinding conditions: frequency 30Hz, 1mm zirconia beads used in ball milling, volume ratio of bead size to material 1:1, rotation speed 600rpm, ball milling time 3h, temperature room temperature.

[0163] (2) The precursor is placed in a rotary kiln and calcined in three stages under a nitrogen atmosphere. Then, it is mechanically crushed, sieved and demagnetized to obtain lithium iron phosphate cathode material.

[0164] The three-stage calcination process includes: the first stage involves heating to 200℃ at a rate of 1℃ / min and holding for 2 hours; the second stage involves heating to 400℃ at a rate of 2℃ / min and holding for 2 hours; and the third stage involves heating to 750℃ at a rate of 5℃ / min and holding for 6 hours.

[0165] Method Example 7

[0166] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Example 7 above, and the preparation method of this example includes the following steps:

[0167] The difference from Method Example 5 is that the materials in step (2) also include titanium oxysulfate, anhydrous iron phosphate, titanium oxysulfate, and lithium carbonate are mixed in the ratio of n(Fe):n(Ti):n(Li) = 0.988:0.012:1.05; the feeding ratio of the materials, the first carbon source solution, the second carbon source solution, and the third carbon source solution is 10:9.375:5:2.5.

[0168] Method Comparison Example 1

[0169] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Comparative Example 1 above, and the preparation method of this comparative example includes the following steps:

[0170] (1) Ferrous sulfate heptahydrate, lithium hydroxide, and phosphoric acid were mixed and dispersed in a mixed solvent (ethylene glycol to water volume ratio of 1:1) according to a solute to solvent ratio of 2g:40mL. After stirring evenly, the mixture was kept at 180℃ for 6h. After solid-liquid separation, the mixture was washed and dried to obtain lithium iron phosphate powder.

[0171] (2) Lithium iron phosphate powder was mixed with glucose and calcined in a rotary kiln under a nitrogen atmosphere. The resulting material was then mechanically crushed, sieved, and demagnetized to obtain the lithium iron phosphate cathode material. The calcination conditions were: heating to 650°C at a rate of 5°C / min and holding for 5 hours. The mass of the glucose was 15% of the mass of the lithium iron phosphate powder.

[0172] Method Comparison Example 2

[0173] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Comparative Example 2 above, and the preparation method of this comparative example includes the following steps:

[0174] (1) Ferrous sulfate heptahydrate, lithium hydroxide, and phosphoric acid were mixed and dispersed in a mixed solvent (ethylene glycol to water volume ratio of 1:1) according to a solute to solvent ratio of 2g:40mL. After stirring evenly, the mixture was kept at 180℃ for 6h. After solid-liquid separation, the mixture was washed and dried to obtain lithium iron phosphate powder.

[0175] (2) Mix lithium iron phosphate powder with a mixed carbon source and put it into a ball mill for grinding and crushing to obtain a mixture.

[0176] The mixed carbon source is a mixture of polyimide, glucose, and erythritol in a mass ratio of 1:1:1.

[0177] The mass of the mixed carbon source is 15% of the mass of the lithium iron phosphate powder.

[0178] Ball milling conditions: frequency 30Hz, 1mm zirconia beads used in ball milling, volume ratio of bead size to material 1:1, rotation speed 600rpm, milling time 3h, temperature room temperature.

[0179] (3) The mixture is placed in a rotary kiln and calcined in three stages under a nitrogen atmosphere. Then, it is mechanically crushed, sieved, and demagnetized to obtain lithium iron phosphate cathode material. The three-stage calcination includes: the first stage is heated to 200℃ at 2℃ / min and held for 1h; the second stage is heated to 400℃ at 2℃ / min and held for 2h; and the third stage is heated to 700℃ at 5℃ / min and held for 8h.

[0180] Method Comparison Example 3

[0181] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Comparative Example 3 above, and the preparation method of this comparative example includes the following steps:

[0182] The difference from Method Example 1 is that the materials in step (2) also include titanium oxysulfate, and anhydrous iron phosphate is mixed with titanium oxysulfate and lithium carbonate in a ratio of n(Fe):n(Ti):n(Li) = 0.986:0.014:1.05. Step (3) adopts a single-stage calcination, that is, heating to 700℃ at 2℃ / min and holding for 8h to obtain lithium iron phosphate cathode material.

[0183] Method Comparison Example 4

[0184] A method for preparing a lithium iron phosphate cathode material, wherein the product obtained corresponds to the product of Comparative Example 4 above, and the preparation method of this comparative example includes the following steps:

[0185] The difference from Method Example 1 is that only the second carbon source solution is added in step (2), and step (3) involves a single-stage calcination, specifically including the following steps:

[0186] (1) Same as method embodiment 1;

[0187] (2) The anhydrous iron phosphate obtained in step (1) is mixed with lithium carbonate as material, and the atomized second carbon source solution is introduced into the airflow pulverizer to pulverize and coat the material to obtain the precursor.

[0188] Anhydrous iron phosphate and lithium carbonate were mixed at a ratio of n(Fe):n(Li) = 1:1.05.

[0189] The second carbon source solution is a 20 wt% glucose aqueous solution.

[0190] The feed ratio of the material and the second carbon source solution is 10g:7.5g.

[0191] The air pressure was 1 ± 0.1 MPa; the air temperature was 100 °C and the mixing time was 15 min when the material was mixed with the second carbon source solution.

[0192] The atomization pressure is 1 MPa.

[0193] (3) The precursor was placed in a rotary kiln and calcined under a nitrogen atmosphere. Then, it was mechanically crushed, sieved, and demagnetized to obtain lithium iron phosphate cathode material. Calcination conditions: The temperature was increased to 700℃ at 2℃ / min and held for 8 hours.

[0194] Based on the products and preparation methods disclosed herein, and the product performance shown in Tables 1-3 above, it can be seen that in Method Example 2, because the mixing method of anhydrous ferric phosphate with lithium acetate, titanium oxysulfate, the first carbon source, the second carbon source, and the third carbon source is a dry mixing process, the agglomeration degree of the product prepared in this way is significantly higher than that of other method examples. This results in lower compaction density and peel strength, larger standard deviations of areal density and electrode resistance, and poorer rate performance and cycle stability. Method Example 3, however, changes the reaction parameters within the scope of this disclosure and still achieves good results. In Method Example 4, because the first carbon source is not added, compared with Example 1, its... The sample standard deviations for areal density and electrode resistance are both low, and the specific capacity of the material also decreases slightly, but it is still significantly better than Comparative Examples 1-4, fully demonstrating that the carbon source disclosed in this invention can achieve superior results even with only two types. Method Example 5 adjusted the type and amount of carbon source and the reaction conditions, and it still achieved good performance. In Method Example 6, all raw materials were directly ball-milled and mixed, which resulted in a decrease in the FSSS and specific capacity of the prepared product. The p% and aggregation degree are significantly increased, leading to increased aggregation. Method Example 7 prepared a chemical composition similar to that of Method Example 6 according to the method of Method Example 5, but its overall performance is better because the p% and aggregation degree of Method Example 7 are better than those of Method Example 6.

[0195] Comparative Examples 1 and 2 prepared lithium iron phosphate powder using conventional methods, then mixed it with a carbon source and calcined it. Whether calcined in one stage or three stages, the overall performance of the prepared lithium iron phosphate cathode material was significantly worse than that of the aforementioned method examples. Comparative Example 3, compared to Method Example 1, used a single-stage calcination in step (3), and its effect was significantly worse than that of Method Example 1. Comparative Example 4 performed even worse than Comparative Example 3, because it only added one carbon source, resulting in lower FSSS and lower performance of the prepared lithium iron phosphate cathode material. Significant improvement, ρ ％ Both the degree of aggregation and the degree of cohesion exceed the scope of this application, resulting in a significant reduction in the electrical performance of the product.

[0196] In addition, this disclosure also provides method embodiments 8-14 and method comparative example 5, which vary a certain parameter or step of method embodiment 1.

[0197] Specifically, the specific steps of method embodiments 8-14 and method comparative example 5 are as follows:

[0198] Method Example 8

[0199] The difference from Method Example 1 is that the carbon source and the material are dry-mixed in a ball mill, including the following steps:

[0200] Anhydrous iron phosphate with a Dv50 of 8.52 μm was mixed with lithium carbonate, a first carbon source, a second carbon source, and a third carbon source to obtain a material. The material was then placed in a ball mill for grinding and crushing to obtain a precursor. The Dv50 of the precursor was controlled to be 0.4–0.5 μm.

[0201] Anhydrous iron phosphate and lithium carbonate were mixed at a ratio of n(Fe):n(Li) = 1:1.05.

[0202] The first carbon source is polyimide; the second carbon source is glucose; and the third carbon source is ethylene glycol.

[0203] The total mass of anhydrous iron phosphate and lithium carbonate, and the feeding ratio of the first carbon source, the second carbon source, and the third carbon source are 10g:0.5g:0.5g:0.5g.

[0204] Ball milling conditions: frequency 30Hz, 1mm zirconia beads used in ball milling, volume ratio of bead size to material 1:1, rotation speed 600rpm, milling time 3h, temperature room temperature.

[0205] The precursor is calcined in the same way as step (3) of Method Example 1.

[0206] Method Example 9

[0207] The difference from Method Example 1 is that the carbon source and the material are mixed together in an airflow crusher, including the following steps:

[0208] (1) Same as method embodiment 1

[0209] (2) Prepare a carbon source mixed solution, wherein the mass percentages of polyimide, glucose, ethylene glycol and solvent DMF in the carbon source mixed solution are 10%: 10%: 10%: 70% respectively; mix the anhydrous iron phosphate obtained in step (1) with lithium carbonate as the material, and introduce the atomized carbon source mixed solution into the airflow pulverizer to pulverize and coat the material to obtain the precursor.

[0210] Anhydrous iron phosphate and lithium carbonate were mixed at a ratio of n(Fe):n(Li) = 1:1.05.

[0211] The feeding ratio of the mixed solution of materials and carbon source is 10g:5g.

[0212] The air pressure was 1 ± 0.1 MPa; the air temperature was 120 °C and the mixing time was 20 min when the material was mixed with the carbon source solution.

[0213] The atomization pressure is 1 MPa.

[0214] (3) Same as in Method Example 1.

[0215] Method Example 10

[0216] The difference from Method Example 1 is that the atomized third carbon source solution, second carbon source solution and first carbon source solution are introduced into the airflow pulverizer in sequence to pulverize and coat the material, thereby obtaining the first precursor, second precursor and third precursor respectively.

[0217] Method Example 11

[0218] The difference from Method Example 1 is that the feeding ratio of the material, the first carbon source solution, the second carbon source solution and the third carbon source solution in step (2) is 10g:8g:2.5g:2g.

[0219] Method Example 12

[0220] The difference from Method Example 1 is that the feeding ratio of the material, the first carbon source solution, the second carbon source solution and the third carbon source solution in step (2) is 10g:2g:2.5g:8g.

[0221] Method Example 13

[0222] The difference from Method Example 1 is that in step (2), the material and carbon source solution are mixed at room temperature (25°C).

[0223] Method Example 14

[0224] The difference from Method Example 1 is that a ball mill is used instead of an air jet mill for wet mixing. The specific steps are as follows:

[0225] (1) Same as method embodiment 1;

[0226] (2) The anhydrous iron phosphate obtained in step (1) is mixed with lithium carbonate as material to prepare a first carbon source solution, a second carbon source solution and a third carbon source solution; the atomized first carbon source solution is sprayed onto the material under stirring, stirred evenly and then placed in a ball mill for a first ball mill to obtain a first precursor; the atomized second carbon source solution is sprayed onto the first precursor under stirring, stirred evenly and then placed in a ball mill for a second ball mill to obtain a second precursor; the atomized third carbon source solution is sprayed onto the second precursor under stirring, stirred evenly and then placed in a ball mill for a third ball mill to obtain a third precursor;

[0227] Anhydrous iron phosphate and lithium carbonate were mixed at a ratio of n(Fe):n(Li) = 1:1.05. The atomization pressure was 1 MPa.

[0228] The first carbon source solution is a 10 wt% polyimide DMF solution; the second carbon source solution is a 20 wt% glucose aqueous solution; and the third carbon source solution is a 10 wt% ethylene glycol ethanol solution.

[0229] The feeding ratio of the material, the first carbon source solution, the second carbon source solution, and the third carbon source solution is 10g:5g:2.5g:5g.

[0230] Ball milling conditions: frequency 30Hz, 1mm zirconia beads used in the ball mill, volume ratio of bead size to material 1:1, rotation speed 600rpm; ball milling temperature of the first ball mill 120℃, time 1h; ball milling temperature of the second ball mill 100℃, time 1h; ball milling temperature of the third ball mill 80℃, mixing time 1h.

[0231] (3) Same as in Method Example 1.

[0232] Method Comparison Example 5

[0233] The difference from Method Example 1 is that only the second carbon source solution is added in step (2).

[0234] The products of the above method examples 8-14 and method comparison example 5 were tested, and the test results are shown in Table 4.

[0235] Table 4. Statistical table of parameter detection for different samples

[0236] As can be seen from the table above, in Method Example 8, anhydrous ferric phosphate was mixed with lithium carbonate, a first carbon source, a second carbon source, and a third carbon source and ball-milled to obtain a precursor. At this time, its FSSS and The increase is significant, leading to increased aggregation that exceeds the scope of this disclosure. In method example 9, all carbon sources were mixed together instead of added sequentially, which resulted in a slight increase in FSSS, but... ρ% and aggregation degree N remain within the ranges defined in this application. In Method Example 10, the order of carbon source addition is reversed compared to Method Example 1. This results in a slight increase in FSSS, but... ρ% and aggregation degree N remain within the ranges defined in this application. In method examples 11-12, the amounts of the first, second, and third carbon sources were adjusted. It can be seen that changes in the amounts of the first and third carbon sources also have a certain impact on product performance parameters. Specifically, increasing the amount of the first carbon source and decreasing the amount of the third carbon source leads to an increase in FSSS and a decrease in BET. Increased ρ% and aggregation degree N. Conversely, a decrease in the amount of the first carbon source and an increase in the amount of the third carbon source lead to a decrease in FSSS and an increase in BET. The decrease in ρ% and agglomeration degree N indicates that these parameters can be controlled within a reasonable range by adjusting the amount of carbon source added. In Method Example 13, the mixing temperature of the material and carbon source solution was changed, resulting in a significant increase in ρ%. Method Example 14 uses a ball mill instead of an air jet mill for wet mixing, demonstrating that both air jet milling and ball milling can prepare materials that simultaneously meet the required parameters. While the ρ% of lithium iron phosphate cathode materials are within a specific range, mixing the materials using air jet milling can improve the dispersion of the components in the precursor, ensuring the carbon source is uniformly dispersed on the surface of anhydrous iron phosphate or lithium source particles. This facilitates subsequent uniform gasification and pore formation, resulting in lithium iron phosphate cathode materials with uniform carbon material distribution. Through the above method embodiments, it can be seen that adjustments within the parameter range disclosed herein can simultaneously achieve the desired results. The lithium iron phosphate cathode material with ρ% in a specific range has good dispersibility, low agglomeration degree and high compaction density. The cathode sheet prepared from it has the characteristics of uniform surface density and high peel strength. Therefore, the battery prepared from it has high specific capacity and cycle stability.

[0237] However, in Comparative Example 5, only a second carbon source was added, which would cause the FSSS to exceed the scope of this disclosure. The degree of aggregation increases significantly, ultimately leading to a degree of aggregation exceeding the scope of this disclosure. This fully demonstrates that it is impossible to obtain lithium iron phosphate cathode materials with an aggregation degree of less than 25,000 by adding only one carbon source.

[0238] This disclosure also includes electron microscopy scans of the products of Embodiments 1, 8 and Comparative Example 4 above. Please refer to Figures 1, 2 and 3 for SEM images.

[0239] A comparison of Figures 1, 2, and 3 shows that the dispersion is: Example 1 > Example 8 > Comparative Example 4.

[0240] Furthermore, this disclosure also includes Raman spectroscopy tests on the lithium iron phosphate cathode materials provided in Examples 1 and 4: the graphitization degree of the lithium iron phosphate cathode materials was characterized using a Burker RFS100 / S Raman spectrometer (Germany), with an excitation wavelength of 458 nm. After background subtraction, a Gaussian function was used for fitting, with wavelengths ranging from 1300 to 1400 cm⁻¹. -1 The corresponding D-band characteristic peak represents sp 3 A of hybrid carbon atoms 1g Vibrations reflect defects or disordered structures in carbon materials, with corresponding peak intensities of I. D 1500~1600cm -1 The corresponding G-band characteristic peak represents sp 2 E of hybrid carbon atoms 2g Vibrations reflect the ordered structure of carbon materials, and the corresponding peak intensity is I.G ,by The degree of graphitization of carbon materials in lithium iron phosphate cathode materials was evaluated. The test results are shown in Figure 4.

[0241] The higher the degree of graphitization, the better the electrical conductivity of the carbon material. The Raman spectra of Examples 1 and 4 are shown in Figure 4. Example 1's I... G / I D =1.22, I of Example 4 G / I D =1.09, indicating that adding the first carbon source is beneficial to improving the graphitization degree of the lithium iron phosphate cathode material. Furthermore, the amount of carbon source fed in Method Example 4 is greater than that in Method Example 1, but the carbon content in Example 1 is higher, indicating that adding the first carbon source is beneficial to increasing the solid residue of the carbon source, thereby increasing the conductive carbon content.

[0242] The above are merely preferred embodiments of this disclosure and are not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure. Industrial applicability

[0243] This disclosure provides a method that simultaneously satisfies Furthermore, the lithium iron phosphate cathode material comprises 50%–90% lithium iron phosphate, which exhibits good dispersibility, low agglomeration, and high compaction density. The cathode sheet prepared using this material as the positive electrode active material has uniform areal density and high peel strength, resulting in a battery with high specific capacity and cycle stability. The preparation method is simple and easy to implement, possessing good industrial applicability.

Claims

1. A lithium iron phosphate cathode material, characterized in that, It comprises primary particles and secondary particles formed by agglomeration of the primary particles, and satisfies and p% = 50% to 90%, wherein the FSSS refers to the Fisher particle size of the lithium iron phosphate positive electrode material, in units of μm; the D BET refers to the specific surface area particle size of the lithium iron phosphate positive electrode material, in units of μm; the p% = 1-H%, wherein the p% refers to the relative density of the secondary particles, and the H% refers to the porosity of the secondary particles.

2. The lithium iron phosphate cathode material of claim 1, wherein, The D BET The particle size of the lithium iron phosphate positive electrode material is measured and calculated by the nitrogen adsorption-desorption method, and the The BET refers to the specific surface area of the lithium iron phosphate positive electrode material, and the value range of the BET satisfies ≤20 m 2 / g, the ρ LFP The true density of the lithium iron phosphate positive electrode material, and the value range of the ρ LFP satisfies 3.3-3.6 g / cm3. And / or, the FSSS is the average particle size of the lithium iron phosphate cathode material determined by steady-flow air permeation method, and the value of the FSSS is in the range of 0.4 to 5 μm; and / or the agglomeration degree N of the lithium iron phosphate positive electrode material is below 25000, wherein the agglomeration degree N is defined as the number of particles having a size of 5-20 pm divided by the total number of particles of the lithium iron phosphate positive electrode material. and / or the compaction density of the lithium iron phosphate positive electrode material is 1.9-3.0 g / cm3 3 .

3. The lithium iron phosphate cathode material of claim 2, wherein, The lithium iron phosphate positive electrode material satisfies And / or, the secondary particles of the lithium iron phosphate cathode material satisfy ρ% = 50% to 70%; And / or, the lithium iron phosphate cathode material satisfies an agglomeration degree N of 200 to 12000; And / or, the lithium iron phosphate cathode material satisfies FSSS = 1~2.5μm; And / or, the lithium iron phosphate positive electrode material satisfies BET of 9~15m 2 / g.

4. The lithium iron phosphate cathode material according to any one of claims 1 to 3, characterized in that The lithium iron phosphate positive electrode material comprises an active material matrix and carbon material, the general formula of the active material matrix is Li 1-x A x Fe 1-y M y (PO 4-z )D z , wherein A is selected from one or more of Na and Mg; M is selected from one or more of Al, Ni, Co, Mn, Ti, La, Ce, Cr, Mo, Ca, Ga, V, Nb, Zr, In, Zn and Y; D is selected from one or more of F, S, N and Cl; 0≤x≤0.1; 0≤y≤0.1 and 0≤z≤0.1; the mass of the carbon material is 1% to 5% of the mass of the lithium iron phosphate positive electrode material.

5. A method of producing a lithium iron phosphate cathode material as claimed in any one of claims 1 to 4, characterized in that, It includes: Iron phosphate and lithium salt are mixed as materials, and the materials are mixed with carbon sources with different gasification temperatures to obtain a precursor. The precursor was calcined in stages under an inert atmosphere, and then crushed, sieved, and demagnetized to obtain lithium iron phosphate cathode material.

6. The method of claim 5, wherein the lithium iron phosphate cathode material is prepared by the steps of: The step of mixing the iron phosphate and the lithium salt includes at least one of features I-IV; ​ Feature 1: Before the iron phosphate is mixed with the lithium salt, the iron phosphate is first added to an air jet mill for pulverization. Feature II: The lithium salt is at least one of lithium carbonate, lithium oxalate, and lithium acetate; Feature III: When the iron phosphate is mixed with the lithium salt, a dopant is also added, wherein the dopant is at least one of the salt, oxide and hydroxide of the dopant element; Feature IV: The iron phosphate and the dopant are added in stoichiometric ratio.

7. The method of producing a lithium iron phosphate cathode material according to claim 5 or 6, characterized in that, The carbon sources with different vaporization temperatures include a first carbon source with a vaporization temperature of 400-600°C, a second carbon source with a vaporization temperature of 200-400°C, and a third carbon source with a vaporization temperature of 100-200°C. The first carbon source includes at least one of polyimide, polyphenylene ether, and polyetherimide; The second carbon source includes at least one of glucose, polyethylene glycol, starch, sucrose, maltose, cellulose, chitosan, polyacrylonitrile, benzyl alcohol, and glycerol; The third carbon source includes at least one of phenol, ethylene glycol, propylene glycol, butylene glycol, isopropanol, sorbitol, erythritol, fructose, malic acid, citric acid, and salicylic acid.

8. The method of claim 7, wherein the lithium iron phosphate cathode material is prepared by the steps of: The step of mixing the material with a carbon source having a different vaporization temperature includes at least one of features V to feature IX; ​ Feature V: The material and the carbon source with different gasification temperatures are mixed in an airflow pulverizer. An airflow is introduced during the mixing process. The pressure of the airflow is 0.5 to 1.5 MPa and the temperature is 25 to 120°C. The total mixing time is 15 to 60 minutes. Feature VI: Before being mixed with the material, the carbon source with different vaporization temperatures is first prepared into a carbon source solution with a mass percentage concentration of 10% to 30%, and then the carbon source solution is atomized before being mixed with the material, wherein the atomization pressure is 0.1 to 1.5 MPa; Feature VII: The material is first mixed with the first carbon source, then with the second carbon source, and finally with the third carbon source; Feature VIII: The total mass of the carbon sources with different vaporization temperatures is 15% to 25% of the mass of the material; Feature IX: when the material is mixed with carbon sources having different gasification temperatures, the mass ratio of the first carbon source, the second carbon source and the third carbon source is 0-15:2.5-15:2.5-10.

9. The method of producing a lithium iron phosphate cathode material according to any one of claims 5 to 8, characterized in that, The segmental calcination comprises a first segment, a second segment and a third segment, the first segment is heated to 180-220℃ at a rate of 1-2℃ / min and kept for 1-2h; the second segment is heated to 380-420℃ at a rate of 2-3℃ / min and kept for 2-4h; the third segment is heated to 650-750℃ at a rate of 4-6℃ / min and kept for 4-8h.

10. A lithium-ion battery, characterized by, It comprises the lithium iron phosphate cathode material prepared by the preparation method of the lithium iron phosphate cathode material according to any one of claims 1-4.

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