Preparation method of lithium iron phosphate material and application thereof

Abstract

The application provides a preparation method of a lithium iron phosphate material, and the method comprises the following steps: mixing first iron phosphate, lithium carbonate, a first carbon source and deionized water in a certain proportion to obtain a first mixed solution, stirring and dispersing, first wet grinding, spray drying, first sintering and first crushing to obtain a lithium iron phosphate intermediate; mixing the lithium iron phosphate intermediate, second iron phosphate, lithium carbonate, a second carbon source, a dopant and deionized water in a certain proportion to obtain a second mixed solution, stirring and dispersing, second wet grinding, spray drying, second sintering, second crushing to obtain the lithium iron phosphate material; wherein the average particle size of the lithium iron phosphate intermediate is larger than that of the lithium iron phosphate material. The process flow is simple, and the material has high compactness. The application further provides the lithium iron phosphate material and a lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, more particularly, to a preparation method of lithium iron phosphate material, lithium iron phosphate material, and lithium ion battery. BACKGROUND

[0002] As the most excellent secondary battery representative in current comprehensive performance, the commercialization of lithium ion battery can be traced back to the 1990s. After years of research, lithium iron phosphate cathode material has become a good performance technology route in the field of lithium ion battery.

[0003] As a lithium ion battery cathode material, lithium iron phosphate has the advantages of high voltage, high specific capacity, long cycle life, small volume, low cost, etc., and has become a strong competitor for electric vehicle batteries. However, the traditional lithium iron phosphate material has low compaction density, resulting in low battery energy density, which limits its application in the field of power batteries.

[0004] Therefore, it is necessary to provide a lithium iron phosphate cathode material with high compaction density and a preparation method thereof, which has a milestone significance for expanding its development in the field of power batteries. The conventional preparation methods of lithium iron phosphate and its precursor include high-temperature solid-phase method, sol-gel method and co-precipitation method, etc. The compaction density of the prepared precursor or lithium iron phosphate cathode material is low by using a conventional single preparation method, resulting in low electrochemical specific capacity of the cathode material and the corresponding battery, which cannot meet the high-performance application requirements.

[0005] The known preparation scheme of lithium iron phosphate cathode material using secondary distribution of precursor, however, adds a grinding process to prepare different particle size precursor, which increases the process complexity and cannot guarantee the element uniformity of the material. In fact, it still cannot actually obtain lithium iron phosphate cathode material meeting high performance requirements. SUMMARY

[0006] In view of the above, the present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a preparation method of lithium iron phosphate material and its application. The lithium iron phosphate intermediate is prepared by first mixing, grinding, drying and sintering, and then the lithium iron phosphate material is prepared by second mixing, grinding, drying and sintering. The materials prepared by the first preparation step and the second preparation step can realize the grading structure, and have high uniformity of lithium iron phosphate element distribution, metal doping, and dense and uniform carbon coating layer, which can optimize the electrochemical performance of the material. At the same time, the preparation method of the lithium iron phosphate material has a simple process flow and is suitable for large-scale industrial production.

[0007] Therefore, in a first aspect, embodiments of the present invention provide a method for preparing lithium iron phosphate material, the method comprising:

[0008] S10. Take a first iron phosphate, lithium carbonate, a first carbon source and deionized water in a certain proportion to obtain a first mixture, and then disperse it by stirring, perform a first wet grinding, spray drying, a first sintering and a first pulverization to obtain a lithium iron phosphate intermediate.

[0009] S20. According to a certain proportion, lithium iron phosphate intermediate, second iron phosphate, lithium carbonate, second carbon source, dopant and deionized water are mixed to obtain a second mixture. The mixture is then stirred and dispersed, subjected to second wet grinding, spray drying, second sintering and second pulverization to obtain the lithium iron phosphate material.

[0010] The average particle size of the lithium iron phosphate intermediate is greater than the average particle size of the lithium iron phosphate material.

[0011] Preferably, the first iron phosphate satisfies the following condition: specific surface area is 4 m² / g. 2 / g-20m 2 / g, particle size is 40nm-300nm; iron phosphate bisphosphate meets the following requirements: specific surface area is 8m². 2 / g-20m 2 / g, with particle size ranging from 40nm to 150nm.

[0012] Preferably, the iron-to-phosphorus molar ratio (Fe / P) of the first ferric phosphate is 0.955-0.980, and the iron-to-phosphorus molar ratio (FE / P) of the second ferric phosphate is 0.970-0.985; and / or,

[0013] The lithium carbonate has a purity ≥99.5%, and the corresponding lithium-iron molar ratio (Li / Fe) of the first or second ferric phosphate is between 1.01 and 1.07; and / or,

[0014] The first carbon source includes at least one selected from glucose, sucrose, polyethylene glycol, and citric acid; preferably, the amount of the first carbon source added satisfies the requirement that the carbon content accounts for 0.1 wt% to 0.4 wt% of the target lithium iron phosphate material by mass; and / or,

[0015] The second carbon source includes at least one selected from glucose, sucrose, polyethylene glycol, and citric acid; preferably, the amount of the second carbon source added satisfies the requirement that the carbon content accounts for 1.1 wt% to 1.5 wt% of the target lithium iron phosphate material mass ratio; and / or,

[0016] The dopant comprises a mixture of titanium dioxide, ammonium metavanadate and niobium pentoxide; preferably, the titanium dioxide, ammonium metavanadate and niobium pentoxide are added in an amount such that the titanium, vanadium and niobium content of the target lithium iron phosphate material is 3000-5000 ppm, 1000-2000 ppm, 300-1000 ppm; and / or,

[0017] The solid content of the first mixed solution is 30-50 wt%; and / or,

[0018] The solid content of the second mixed solution is 30-50 wt%.

[0019] Preferably, the first wet-ground sand has a particle size larger than that of the second wet-ground sand; preferably, the first wet grinding satisfies: sand particle size D50 is 0.5-0.9 μm; the second wet grinding satisfies: sand particle size D50 is 0.3-0.5 μm.

[0020] Preferably, the spray drying has an inlet air temperature of 180-260°C, an outlet air temperature of 80-140°C, a dry product particle size D50 of 20-60 μm, and a water content of ≤1.5%; and / or,

[0021] The first crushed material has a particle size D50 of 1.0-1.8 μm, and the second crushed material has a particle size D50 of 0.7-1.5 μm.

[0022] Preferably, the first sintering has a sintering temperature of 750-850°C and a sintering time of 4-10 h; and / or, the second sintering has a sintering temperature of 720-780°C and a sintering time of 4-10 h.

[0023] Preferably, the mass ratio of the lithium iron phosphate intermediate to the second iron phosphate is 3:7-7:3.

[0024] In a second aspect, the embodiments of the present application also provide a lithium iron phosphate material, which is prepared by the preparation method of the first aspect.

[0025] Preferably, the lithium iron phosphate material comprises first lithium iron phosphate particles having an average particle size of 500-1000 nm and second lithium iron phosphate particles having an average particle size of 120-220 nm.

[0026] In a third aspect, the embodiments of the present application also provide a lithium ion battery, which comprises a battery anode prepared from the lithium iron phosphate material of the second aspect.

[0027] The application provides a preparation method of a lithium iron phosphate positive electrode material, which is synthesized by a two-step method, i.e., a first step of sintering is used to prepare large lithium iron phosphate particles, and a second step of sintering is used to prepare small lithium iron phosphate particles on the basis of the particles prepared in the first step. The method optimizes the particle size distribution of the material, solves the problem of poor combination of positive electrode material particles in the traditional method, and prepares the lithium iron phosphate positive electrode material with high capacity and high compaction density. Meanwhile, the preparation method has a simple process flow and low equipment requirement, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A preparation method flow chart of the lithium iron phosphate material provided by an embodiment of the application is shown in the figure.

[0029] Figure 2 An SEM image of the lithium iron phosphate positive electrode material prepared in Example 1 of the application is shown in the figure.

[0030] Figure 3 An XRD spectrum of the lithium iron phosphate positive electrode material prepared in Example 1 of the application is shown in the figure.

[0031] Figure 4 A charge-discharge performance curve of the lithium iron phosphate positive electrode material prepared in Example 1 of the application is shown in the figure. DETAILED DESCRIPTION

[0032] The embodiments of the application are described in detail below, and examples of the embodiments are shown in the drawings, in which the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the application, and cannot be understood as limiting the application.

[0033] The following disclosure provides many different embodiments, or examples, for implementing different structures of the application. For the purpose of simplicity, the elements and settings of the particular examples in the following description are depicted by referring to drawings. Of course, they are merely examples and are intended to explain the application, and are not intended to limit the application. In addition, the application can repeatedly refer to reference numerals and / or letters in different examples. Such repetition is for the purpose of simplicity and clarity, and does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the application provides examples of various specific processes and materials, but those skilled in the art can realize the applicability of other processes and / or the use of other materials.

[0034] Please refer to Figure 1 In a first aspect, the embodiments of the application provide a preparation method of a lithium iron phosphate material, which comprises:

[0035] S10, a first iron phosphate, lithium carbonate, a first carbon source and deionized water are mixed in a certain proportion to obtain a first mixed solution, which is stirred and dispersed, first wet ground, spray dried, first sintered, and first crushed to obtain a lithium iron phosphate intermediate;

[0036] S20, the lithium iron phosphate intermediate, second iron phosphate, lithium carbonate, second carbon source, dopant and deionized water are mixed in a certain proportion to obtain a second mixed solution, which is stirred and dispersed, second wet ground, spray dried, second sintered, and second crushed to obtain the lithium iron phosphate material.

[0037] The average particle size of the lithium iron phosphate intermediate is greater than the average particle size of the lithium iron phosphate material.

[0038] It can be understood that the step S10 is a first step sintering preparation process, and the step S20 is a second step sintering preparation process. In the first step sintering preparation process, the first iron phosphate, lithium carbonate, first carbon source and other raw materials are used to prepare the lithium iron phosphate material. By preparing relatively large particles of lithium iron phosphate material first, the second step sintering process retains the lithium iron phosphate intermediate prepared in the first step, and the second iron phosphate, lithium carbonate, second carbon source, dopant and other raw materials are used to supplement the preparation of relatively small particles of lithium iron phosphate material. In the final product, the large particles and small particles of lithium iron phosphate material achieve a gradation structure, and the large particle material is closely combined with the small particle material. The lithium iron phosphate intermediate prepared in step S10 only contains large particles of lithium iron phosphate, while the lithium iron phosphate material product prepared in step S20 includes large and small particles of lithium iron phosphate. Therefore, the average particle size of the lithium iron phosphate intermediate is greater than the average particle size of the lithium iron phosphate material.

[0039] Further, the first iron phosphate satisfies: specific surface area of 4m 2 / g-20m 2 / g, particle size of 40nm-300nm; the second iron phosphate satisfies: specific surface area of 8m 2 / g-20m 2 / g, particle size of 40nm-150nm.

[0040] Specifically, the step S10 selects a larger particle size of iron phosphate raw material, and the step S20 selects a smaller particle size of iron phosphate raw material.

[0041] Further, the first iron phosphate has a molar ratio of iron to phosphorus Fe / P of 0.955-0.980, and the second iron phosphate has a molar ratio of iron to phosphorus FE / P of 0.970-0.985.

[0042] Further, the purity of the lithium carbonate is ≥99.5%, and the molar ratio of lithium to iron Li / Fe of the corresponding first iron phosphate or second iron phosphate is 1.01-1.07.

[0043] Further, the first carbon source includes at least one of glucose, sucrose, polyethylene glycol, and citric acid; preferably, the first carbon source is added in an amount such that the carbon content accounts for 0.1wt%-0.4wt% of the target lithium iron phosphate material.

[0044] Further, the second carbon source includes at least one of glucose, sucrose, polyethylene glycol, and citric acid; preferably, the second carbon source is added in an amount such that the carbon content accounts for 1.1wt%-1.5wt% of the target lithium iron phosphate material.

[0045] Further, the dopant includes a mixture of titanium dioxide, ammonium metavanadate, and niobium pentoxide; preferably, the titanium dioxide, ammonium metavanadate, and niobium pentoxide are added in an amount such that the titanium, vanadium, and niobium content of the target lithium iron phosphate material accounts for 3000ppm-5000ppm, 1000ppm-2000ppm, and 300ppm-1000ppm.

[0046] Further, the solid content of the first mixed solution is 30wt%-50wt%.

[0047] Further, the solid content of the second mixed solution is 30wt%-50wt%.

[0048] Further, the first wet grinding has a sand grinding particle size greater than that of the second wet grinding; preferably, the first wet grinding satisfies: sand grinding particle size D50 is 0.5μm-0.9μm; and the second wet grinding satisfies: sand grinding particle size D50 is 0.3μm-0.5μm.

[0049] Specifically, the preparation method can first prepare a large-particle lithium iron phosphate material, and then prepare a small-particle lithium iron phosphate material; accordingly, the wet grinding in step S10 corresponds to a larger grinding particle size, and the wet grinding in step S20 corresponds to a smaller grinding particle size.

[0050] Further, the spray drying has an inlet air temperature of 180℃-260℃, an outlet air temperature of 80℃-140℃, a dry product particle size D50 of 20μm-60μm, and a water content of ≤1.5%.

[0051] Further, the first crushed material has a particle size D50 of 1.0μm-1.8μm, and the second crushed material has a particle size D50 of 0.7μm-1.5μm.

[0052] Further, the first sintering has a sintering temperature of 750℃-850℃ and a sintering time of 4h-10h; and / or, the second sintering has a sintering temperature of 720℃-780℃ and a sintering time of 4h-10h.

[0053] Further, the mass ratio of the lithium iron phosphate intermediate to the second lithium iron phosphate is 3:7-7:3.

[0054] In a second aspect, the embodiments of the present application further provide a lithium iron phosphate material, which is prepared by the preparation method of the first aspect.

[0055] Further, the lithium iron phosphate material includes first lithium iron phosphate particles with an average particle size of 500-1000 nm and second lithium iron phosphate particles with an average particle size of 120-220 nm. Specifically, the particle size of the first lithium iron phosphate particles is prepared in step S10, and the particle size is not greatly affected even if the first lithium iron phosphate particles are further coated with carbon in step S20. The second lithium iron phosphate particles are prepared in step S20.

[0056] In a third aspect, the embodiments of the present application further provide a lithium ion battery, which includes a battery anode prepared from the lithium iron phosphate material of the second aspect.

[0057] The embodiments of the present application are described by taking the preparation of large-particle lithium iron phosphate material in the first step and small-particle lithium iron phosphate material in the second step as examples.

[0058] In the first step, the large-particle lithium iron phosphate is prepared by low-temperature sintering. In the second step, the large-particle lithium iron phosphate is not consumed by additional carbon source, and the stability of the carbon content of the finished product is ensured.

[0059] In the first step, the large-particle lithium iron phosphate is prepared by low-temperature sintering. In the second step, the large-particle lithium iron phosphate is not consumed by additional carbon source, and the stability of the carbon content of the finished product is ensured.

[0060] The specific process and effects of the preparation method of the lithium iron phosphate anode material of the present application are further described in detail in combination with some specific embodiments, but are not limited to the protection scope of the present application.

[0061] Embodiment 1

[0062] The lithium iron phosphate material is prepared, and the specific steps include the following steps:

[0063] (1) 4000 g of Fe / P molar ratio is 0.980 and specific surface area is 4.0 m 2The 1052.9 g of lithium carbonate, 40 g of glucose, 40 g of sucrose and 11500 g of water were mixed in a ball mill to form a dispersion; the dispersion was moved to a sand mill and sand-milled at 45°C, with the sand-milling granularity D50 controlled to be 0.8 μm and the solid content controlled to be 30 wt%, to obtain a slurry; the slurry was spray-dried, with the inlet temperature controlled to be 180°C and the outlet temperature controlled to be 80°C, to obtain a precursor powder with the granularity D50 controlled to be 60 μm and the moisture content controlled to be ≤1.5%; the precursor powder was calcined at a high temperature under a nitrogen atmosphere, with the sintering temperature controlled to be 750°C and the sintering time controlled to be 10 h; and then the precursor powder was crushed, with the granularity D50 controlled to be 1.0 μm and the average primary particle size controlled to be 500 nm, to obtain the lithium iron phosphate one-sintered material.

[0064] (2) 2800 g of the one-sintered material and 1200 g of iron phosphate with the molar ratio Fe / P of 0.970 and the specific surface area of 20.0 m 2 / g and 298.16 g of lithium carbonate, 600 g of polyethylene glycol and 400 g of citric acid were mixed, and 22.73 g of titanium dioxide, 22.22 g of ammonium metavanadate, 5.72 g of niobium pentoxide and 11500 g of water were added to a ball mill to form a dispersion; the dispersion was moved to a sand mill and sand-milled at 45°C, with the sand-milling granularity D50 controlled to be 0.5 μm and the solid content controlled to be 30 wt%, to obtain a slurry; the slurry was spray-dried, with the inlet temperature controlled to be 240°C and the outlet temperature controlled to be 140°C, to obtain a precursor powder with the granularity D50 controlled to be 20 μm and the moisture content controlled to be ≤1.5%; the precursor powder was calcined at a high temperature under a nitrogen atmosphere, with the sintering temperature controlled to be 780°C and the sintering time controlled to be 4 h; and then the precursor powder was crushed, with the granularity D50 controlled to be 0.7 μm and the average primary particle size controlled to be 120 nm, to finally obtain the high-capacity high-compactness lithium iron phosphate positive electrode material with the carbon content of 1.5%.

[0065] Figure 2 The SEM image of the lithium iron phosphate positive electrode material prepared in Example 1 is shown in the figure, from which it can be seen that the primary particles are distributed in different sizes and are closely connected with each other.

[0066] Figure 3 The XRD spectrum of the lithium iron phosphate positive electrode material prepared in Example 1 is shown in the figure, from which it can be seen that the peak position of the spectrum is consistent with the standard PDF card of lithium iron phosphate, and there is no impurity phase, so the material has high purity.

[0067] Figure 4 The further prepared discharge voltage of the lithium iron phosphate positive electrode material prepared in Example 1 is shown in the figure, from which it can be seen that the discharge specific capacity reaches 159.6 mAh / g at the 0.1 C rate in the voltage range of 2.0 V-3.75 V. Figure 4 The further prepared discharge voltage of the lithium iron phosphate positive electrode material prepared in Example 1 is shown in the figure, from which it can be seen that the discharge specific capacity reaches 159.6 mAh / g at the 0.1 C rate in the voltage range of 2.0 V-3.75 V.

[0068] Example 2

[0069] This embodiment prepares a lithium iron phosphate material, specifically including the following steps:

[0070] (1) 4000g of Fe / P with a molar ratio of 0.967 and a specific gravity of 12.0m 2 =1023.38g of lithium iron phosphate and 120nm primary particle size were mixed with 40g of glucose, 40g of polyethylene glycol and 7500g of water in a ball mill to form a dispersion. The dispersion was transferred to a sand mill and milled at 30℃, controlling the particle size D50 to be 0.65μm and the solid content to be 40wt%, to obtain a slurry. The slurry was spray dried, controlling the inlet temperature to be 210℃ and the outlet temperature to be 110℃, to obtain a precursor powder with a particle size D50 of 40μm and a moisture content ≤1.5%. The precursor powder was calcined at high temperature under a nitrogen atmosphere, controlling the sintering temperature to be 800℃ and the sintering time to be 7h. Then it was pulverized, controlling the particle size D50 to be 1.4μm and the average primary particle size to be 750nm, to obtain lithium iron phosphate calcined material.

[0071] (2) Take 2000g of raw material and 2000g of material with a molar ratio of Fe / P of 0.977 and a specific gravity of 14.0m. 2 / g of ferric phosphate with a primary particle size of 90nm and 516.61g of lithium carbonate were mixed, along with 240g of sucrose and 200g of citric acid. Simultaneously, 30.31g of titanium dioxide, 16.67g of ammonium metavanadate, 3.72g of niobium pentoxide, and 7500g of water were added and mixed in a ball mill to form a dispersion. The dispersion was then transferred to a sand mill and milled at 30℃, controlling the particle size D50 to be 0.4μm and the solid content to be 40wt%, to obtain a slurry. The slurry was then further processed... Spray drying was performed with the inlet temperature controlled at 210℃ and the outlet temperature at 110℃ to obtain precursor powder with a particle size D50 of 40μm and a moisture content ≤1.5%. The precursor powder was then calcined at high temperature under a nitrogen atmosphere with a sintering temperature controlled at 750℃ and a sintering time of 7h. After pulverization, the particle size D50 was controlled at 1.1μm, and the average particle size of the primary particles was 170nm, finally yielding a high-capacity, high-density lithium iron phosphate cathode material with a carbon content of 1.3%.

[0072] Example 3

[0073] This embodiment prepares a lithium iron phosphate material, specifically including the following steps:

[0074] (1) 4000g of Fe / P with a molar ratio of 0.955 and a specific gravity of 20.0m 2 / g of iron phosphate with a primary particle size of 40nm and 993.86g of lithium carbonate were mixed, and 40g of glucose, 40g of citric acid and 5000g of water were added to form a dispersion in a ball mill. The dispersion was then transferred to a sand mill and milled at 10℃, controlling the milled particle size D50 to be 0.5μm and the solid content to be 50wt%, to obtain a slurry. The slurry was spray-dried, controlling the inlet temperature to be 240℃ and the outlet temperature to be 140℃, to obtain a precursor powder with a particle size D50 of 20μm and a moisture content ≤1.5%. The precursor powder was calcined at high temperature under a nitrogen atmosphere, controlling the sintering temperature to be 850℃ and the sintering time to be 4h. Then it was pulverized, controlling the particle size D50 to be 1.8μm and the average primary particle size to be 1000nm, to obtain lithium iron phosphate calcined material.

[0075] (2) Take 1200g of raw material and 2800g of material with a molar ratio of Fe / P of 0.985 and a specific gravity of 8.0m. 2 / g of ferric phosphate with a primary particle size of 150nm and 737.03g of lithium carbonate were mixed, and 200g of sucrose and 175g of polyethylene glycol were added. Simultaneously, 37.88g of titanium dioxide, 11.11g of ammonium metavanadate, 1.72g of niobium pentoxide, and 5000g of water were added and mixed in a ball mill to form a dispersion. The dispersion was then transferred to a sand mill and milled at 10℃, controlling the particle size D50 to be 0.3μm and the solid content to be 50wt%, to obtain a slurry. The slurry was then further processed... Spray drying was performed with the inlet temperature controlled at 180℃ and the outlet temperature at 800℃ to obtain precursor powder with a particle size D50 of 60μm and a moisture content ≤1.5%. The precursor powder was then calcined at high temperature under a nitrogen atmosphere with a sintering temperature controlled at 720℃ and a sintering time of 10h. After pulverization, the particle size D50 was controlled at 1.5μm, and the average particle size of the primary particles was 220nm, finally yielding a high-capacity, high-density lithium iron phosphate cathode material with a carbon content of 1.1%.

[0076] Comparative Example 1

[0077] The difference between this comparative example and Example 2 is that the mass ratio of lithium iron phosphate intermediate to second iron phosphate is 9:1.

[0078] Comparative Example 2

[0079] The difference between this comparative example and Example 2 is that the mass ratio of lithium iron phosphate intermediate to second iron phosphate is 1:9.

[0080] Further tests were conducted on Examples 1-3 and Comparative Examples 1-2. Specifically, the lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 were photographed using a 20kx scanning electron microscope, and the average primary particle size was statistically analyzed using Nano Measurer software. 1g of the lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 was weighed and placed into a compaction mold. The mold was then placed in a compaction device for testing, and the powder compaction density was determined under a pressure of 30kN. The lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 were dispersed in NMP with Super-P and PVDF at a mass ratio of 80:10:10. After ball milling and uniform dispersion, the dispersion was coated onto aluminum foil and vacuum dried to obtain the cathode electrode. The electrolyte was 1mol / L LiPF6, with a solvent volume ratio of EC:DMC:EMC = 1:1:1 (volume ratio). The separator was a Celgard polypropylene membrane, and the lithium metal sheet was used as the anode. All these components were assembled into a coin cell. The test voltage range was 2.0V-3.75V. The voltage was charged to 3.75V using a constant current / constant voltage charging method, and then discharged to 2.0V using a constant current discharging method. The charge / discharge current was 0.1C for 1 cycle; then, a 1C charge / discharge current was used for 3 cycles, with the cutoff voltage condition the same as at 0.1C. The test results are shown in Table 1 below.

[0081] Table 1 Test Results

[0082]

[0083] As can be seen from the above results, the lithium iron phosphate cathode material prepared by the method of the present invention has better capacity and higher powder compaction density.

[0084] This invention proposes a method for preparing lithium iron phosphate (LFP) cathode materials. The method employs a two-step synthesis: the first step involves sintering to prepare large LFP particles individually, and the second step involves mixing and sintering to prepare small LFP particles. This method optimizes the particle size distribution of the material and solves the problem of loose particle bonding in traditional methods, resulting in LFP cathode materials with both high capacity and high compaction density. Furthermore, this preparation method has a simple process flow and low equipment requirements, making it suitable for large-scale industrial production.

[0085] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0086] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing lithium iron phosphate material, characterized in that, The preparation method includes: S10. Take a first iron phosphate, lithium carbonate, a first carbon source and deionized water in a certain proportion to obtain a first mixture, and then disperse it by stirring, perform a first wet grinding, spray drying, a first sintering and a first pulverization to obtain a lithium iron phosphate intermediate. S20. A second mixture is prepared by mixing lithium iron phosphate intermediate, second iron phosphate, lithium carbonate, second carbon source, dopant and deionized water in a certain proportion. The mixture is then dispersed by stirring, wet milling, spray drying, sintering, and pulverizing to obtain the lithium iron phosphate material. The average particle size of the lithium iron phosphate intermediate is larger than the average particle size of the lithium iron phosphate material. First ferric phosphate satisfies the following condition: specific surface area is 4m². 2 / g-20m 2 / g, particle size is 40nm-200nm; iron phosphate meets the following requirements: specific surface area is 8m². 2 / g-20m 2 / g, with particle size ranging from 40nm to 150nm; The mass ratio of the lithium iron phosphate intermediate to the second iron phosphate is 3:7-7:3; The first carbon source includes at least one of glucose, sucrose, polyethylene glycol, and citric acid; the amount of the first carbon source added satisfies that the carbon content accounts for 0.1wt%-0.4wt% of the target mass of the prepared lithium iron phosphate material. The second carbon source includes at least one of glucose, sucrose, polyethylene glycol, and citric acid; the amount of the second carbon source added satisfies that the carbon content accounts for 1.1wt%-1.5wt% of the target mass of the prepared lithium iron phosphate material.

2. The method for preparing lithium iron phosphate material according to claim 1, characterized in that, The first ferric phosphate has an iron-to-phosphorus molar ratio (Fe / P) of 0.955-0.980, and the second ferric phosphate has an iron-to-phosphorus molar ratio (FE / P) of 0.970-0.985; and / or, The lithium carbonate has a purity ≥99.5%, and the corresponding lithium iron phosphate molar ratio (Li / Fe) is between 1.01 and 1.07; and / or, The dopant comprises a mixture of titanium dioxide, ammonium metavanadate, and niobium pentoxide; the amounts of titanium dioxide, ammonium metavanadate, and niobium pentoxide added meet the target requirements for preparing lithium iron phosphate materials with titanium, vanadium, and niobium contents of 4000ppm-6000ppm, 1000ppm-3000ppm, and 300ppm-1000ppm, respectively; and / or, The solid content of the first mixture is 30wt%-50wt%; and / or, The solid content of the second mixture is between 30wt% and 50wt%.

3. The method for preparing lithium iron phosphate material according to claim 1, characterized in that, The abrasive particle size of the first wet grinding is greater than that of the second wet grinding; the first wet grinding satisfies the following: abrasive particle size D50 is between 0.5μm and 0.9μm; the second wet grinding satisfies the following: abrasive particle size D50 is between 0.3μm and 0.5μm.

4. The method for preparing lithium iron phosphate material according to claim 1, characterized in that, The spray dryer has an inlet air temperature of 180℃-260℃, an outlet air temperature of 80℃-140℃, a dried product particle size D50 of 20μm-60μm, and a water content ≤1.5%; and / or, The particle size D50 of the first pulverized material is 1.0μm-1.8μm, and the particle size D50 of the second pulverized material is 0.7μm-1.5μm.

5. The method for preparing lithium iron phosphate material according to claim 1, characterized in that, The sintering temperature of the first sintering is 750℃-850℃, and the sintering time is 4h-10h; and / or, the sintering temperature of the second sintering is 720℃-780℃, and the sintering time is 4h-10h.

6. A lithium iron phosphate material, characterized in that, The lithium iron phosphate material is prepared by the preparation method according to any one of claims 1-5.

7. The lithium iron phosphate material according to claim 6, characterized in that, It includes first lithium iron phosphate particles with an average particle size of 500nm-1000nm and second lithium iron phosphate particles with an average particle size of 120nm-220nm.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode made of lithium iron phosphate material as described in claim 6 or 7.

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