Lithium iron phosphate cathode materials, their preparation methods and applications

Abstract

This invention relates to the field of lithium-ion battery cathode material preparation technology, specifically to a multi-stage gradation process for lithium iron phosphate (LFP) materials, and particularly to a method for preparing high-density, high-capacity LFP cathode materials through multi-stage gradation based on secondary milling and feed pump speed control. The LFP cathode material preparation method provided by this invention achieves multi-stage gradation through milling feed speed control, prepares high-density LFP cathode materials through multi-stage gradation, and achieves LFP cathode materials with uniform carbon layer coating through appropriate carbon source content. This method can produce high-density, high-capacity LFP cathode materials. Furthermore, the milling mill, mixer, and other equipment used are all commonly used equipment in existing industrial mass production, requiring no new equipment and can be directly upgraded from existing LFP production lines, demonstrating strong process compatibility.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material preparation technology, specifically to a multi-stage gradation process for lithium iron phosphate materials, and particularly to a method for preparing high-pressure, high-density, high-capacity lithium iron phosphate cathode materials through multi-stage gradation based on secondary milling and feed pump speed control. Background Technology

[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, is widely used in power batteries, large-scale energy storage batteries, and other fields due to its advantages such as high safety, long cycle life, and low cost. Increasing the compaction density of lithium iron phosphate materials is one of the core ways to improve the energy density of lithium-ion batteries, and particle gradation (achieving close packing of particles through a reasonable ratio of particles of different sizes) is a key technical means to improve the compaction density of powder materials.

[0003] Currently, the mainstream industrial route for preparing high-density lithium iron phosphate is the iron phosphate method (carbothermic reduction solid-state method). This method typically uses finished iron phosphate directly as raw material, combined with lithium and carbon sources, and involves mixing, grinding, and calcination to prepare the final product. Multi-stage gradation processes often rely on particle size classification mixing of the slurry and parallel grinding with multiple devices. The core principle is to achieve the preparation and mixing of particles of different sizes through the control of grinding parameters. While the application of two-stage gradation (a reasonable ratio of large and small particle sizes) is relatively mature in industry, the application of multi-stage gradation is still relatively rare. Multi-stage gradation using the two-stage gradation method involves dividing the well-dispersed slurry into three parts, grinding them separately to large, medium, and small particle sizes, and then mixing them. This method involves multiple grinding batches, complex processes, difficulties in slurry matching, and high costs. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide lithium iron phosphate cathode material, its preparation method and application. The preparation method of lithium iron phosphate cathode material provided by the present invention can prepare lithium iron phosphate cathode material with high pressure density and high capacity, and the process is simple.

[0005] This invention provides a method for preparing lithium iron phosphate cathode material, comprising the following steps:

[0006] S1) The phosphorus source, iron source, lithium source, carbon source, water and metal-containing additives are coarsely ground, and then the resulting material is sintered for the first time under a protective atmosphere to obtain the lithium iron phosphate precursor.

[0007] S2) The carbon source, metal additive, water and lithium iron phosphate precursor mentioned in step S1 are coarsely ground. The coarse grinding is a segmented coarse grinding achieved by adjusting the feed rate. Then, a portion of the material obtained from the coarse grinding is finely ground. The finely ground material is then mixed with the remaining material obtained from the coarse grinding in a slurry. The resulting material is then sintered a second time under a protective atmosphere to obtain a secondary sintered material.

[0008] The particle size distribution of the material obtained by mixing the slurry includes a first particle size peak, a second particle size peak and a third particle size peak. The peak particle size of the first particle size peak ranges from 0.2 μm to 0.6 μm, the peak particle size of the second particle size peak ranges from 1 μm to 3 μm, and the peak particle size of the third particle size peak ranges from 8 μm to 15 μm.

[0009] S3) The secondary sintering material described in step S2 is post-processed to obtain lithium iron phosphate cathode material.

[0010] The method for preparing lithium iron phosphate cathode material provided by the present invention includes, in step S1, firstly, coarsely grinding a phosphorus source, an iron source, a lithium source, a carbon source, water, and a metal-containing additive. Specifically, the phosphorus source, iron source, lithium source, carbon source, water, and metal-containing additive are mixed to obtain a primary mixture; then, the primary mixture is coarsely ground to obtain a coarsely ground slurry; finally, the coarsely ground slurry is dried to obtain the coarsely ground material.

[0011] This invention mixes a phosphorus source, an iron source, a lithium source, a carbon source, water, and a metal-containing additive to obtain a primary mixture, wherein the mixing time is 0.5 h to 4.0 h. In some embodiments of this invention, the phosphorus source, iron source, lithium source, carbon source, water, and metal-containing additive are mixed in a stirred tank to obtain a primary mixture. In the primary mixture preparation process of step S1, this invention incorporates metal-containing additives for metal doping, thereby improving intrinsic electronic conductivity and thus enhancing rate performance.

[0012] After obtaining a primary mixture, the present invention performs coarse grinding on the primary mixture, and the D50 particle size of the material obtained by coarse grinding is 1.0 μm to 2.0 μm. Specifically, the present invention performs coarse grinding on the primary mixture to obtain a coarsely ground slurry, and the D50 parameter characterizing the particle size of the coarsely ground slurry is between 1.0 μm and 2.0 μm; then the coarsely ground slurry is dried to obtain the coarsely ground material, and the D50 particle size of the coarsely ground material is 1.0 μm to 2.0 μm. In some embodiments of the present invention, the diameter of the grinding beads used in step S1 of the present invention is 0.6 mm to 1.0 mm, and the rotation speed of the coarse grinding is 1000 rpm to 1200 rpm. In other embodiments of the present invention, the coarse grinding in step S1 of the present invention is performed using a sand mill.

[0013] In this invention, the primary mixture is coarsely ground to obtain a coarsely ground slurry, and then the coarsely ground slurry is dried to obtain the coarsely ground material. Preferably, the drying is spray drying. In some embodiments of this invention, the drying is spray drying, the inlet air temperature of the spray drying is 200℃~260℃, preferably 240℃, and the outlet air temperature of the spray drying is 90℃~110℃, preferably 95℃.

[0014] After obtaining the coarsely ground material, the present invention performs a first sintering under a protective atmosphere to obtain a lithium iron phosphate precursor. Specifically, the first sintering is performed at 550℃~750℃ for 5 h~15 h. More specifically, the first sintering is performed by increasing the temperature to 550℃~750℃ at a rate of 2℃ / min~5℃ / min and sintering for 5 h~15 h. The protective gas used in this invention is preferably an inert atmosphere.

[0015] In step S1 of this invention, phosphorus source, iron source, lithium source, carbon source, water, and metal-containing additives undergo a pretreatment process including mixing in a stirred tank, coarse grinding in a sand mill, and drying. The resulting material is then subjected to a first sintering under a protective atmosphere to obtain a large-particle, one-time sintered lithium iron phosphate precursor. Preferably, in step S1), the molar ratio of the lithium source, iron source, and phosphorus source is Li:Fe:P = (1.0~1.05):1:(1.010~1.036), and the amount of metal element in the metal-containing additive accounts for 0.2%~0.6% of the mass of the lithium iron phosphate precursor. Preferably, in step S1, the phosphorus source is selected from one or more of ferric phosphate, phosphoric acid, and ammonium dihydrogen phosphate; the iron source is selected from one or more of ferric phosphate, iron oxide, and ferrous oxalate dihydrate; the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; the carbon source is selected from one or more of glucose, sucrose, starch, and polyethylene glycol; and the metal-containing additive is selected from one or more of titanium dioxide, tetrabutyl titanate, magnesium oxide, magnesium acetate, magnesium hydroxide, magnesium nitrate, zirconium nitrate, zirconium hydroxide, zirconium oxide, vanadium pentoxide, or niobium pentoxide. Preferably, the water is pure water.

[0016] After obtaining the lithium iron phosphate precursor in step S1, the present invention first performs coarse grinding on the carbon source, metal additive, water and the lithium iron phosphate precursor obtained in step S1 in step S2. The coarse grinding is a segmented coarse grinding achieved by adjusting the feed rate. Then, a portion of the material obtained from the coarse grinding is finely ground, and then the material obtained from the fine grinding is mixed with the remaining material obtained from the coarse grinding into a slurry.

[0017] In step S2 of this invention, the carbon source, metal-containing additive, water, and the lithium iron phosphate precursor described in step S1 are first coarsely ground. Specifically, the carbon source, metal-containing additive, water, and the lithium iron phosphate precursor described in step S1 are mixed to obtain a secondary mixture; then, the secondary mixture is coarsely ground. The particle size D50 of the material obtained by coarse grinding in step S2 of this invention is 1.0 μm to 2.0 μm. In some embodiments of this invention, after coarse grinding in step S2, the parameter D50 characterizing the particle size of the resulting slurry is between 1.0 μm and 2.0 μm.

[0018] More specifically, a portion of the material obtained by coarse grinding in step S2 of the present invention accounts for 40% to 60% of the weight of the material obtained by coarse grinding, preferably accounting for 1 / 2 of the weight of the material obtained by coarse grinding. In some embodiments of the present invention, the coarse grinding in step S2 is performed using a sand mill, the diameter of the grinding beads used in the coarse grinding is 0.6 mm to 1.0 mm, and the rotation speed of the coarse grinding is 1000 rpm to 1200 rpm.

[0019] The coarse grinding in step S2 of this invention is a segmented coarse grinding achieved by adjusting the feed rate. Specifically, the feed rate for the first 40% to 60% of the feed weight segment in step S2 is 3 kg / min to 5 kg / min, preferably 3.5 kg / min to 5 kg / min; the feed rate for the remaining feed weight segment is 0.5 kg / min to 2 kg / min, preferably 1 kg / min to 2 kg / min. Preferably, the feed rate for the first half of the feed weight segment in step S2 is 3 kg / min to 5 kg / min, preferably 3.5 kg / min to 5 kg / min; the feed rate for the remaining feed weight segment is 0.5 kg / min to 2 kg / min, preferably 1 kg / min to 2 kg / min. The feeding weight segment mentioned in this invention refers to the feeding process calculated based on the total weight of the material after coarse grinding. Specifically, the first 40% to 60% feeding weight segment refers to the feeding process of 40% to 60% of the total weight of the material after coarse grinding, the first half feeding weight segment refers to the feeding process of half the total weight of the material after coarse grinding, and so on. Step S2 of this invention employs a secondary sand mill coarse grinding feed rate control method, eliminating the need to divide the slurry into multiple portions. Compared to the common method of grinding large, medium, and small slurries in parallel, this greatly simplifies the operation process and avoids particle size contamination caused by media residue. Simultaneously, by precisely controlling the pump speed, a clear pump speed-particle size correspondence is established, achieving precise control and stable reproduction of the three-stage particle size distribution, resulting in a more stable gradation effect.

[0020] In step S2 of this invention, after coarsely grinding the carbon source, metal-containing additive, water, and the lithium iron phosphate precursor described in step S1, a portion of the material obtained from the coarse grinding is then finely ground. The particle size D50 of the material obtained from the fine grinding in step S2 of this invention is 0.3 μm to 0.6 μm. Specifically, after the fine grinding in step S2 of this invention, the parameter D50 characterizing the particle size of the resulting slurry is between 0.3 μm and 0.6 μm. In some embodiments of this invention, the fine grinding is performed using a sand mill, the diameter of the grinding beads used in the fine grinding is 0.2 mm to 0.35 mm, and the grinding speed is 900 rpm to 1200 rpm.

[0021] In step S2 of this invention, a portion of the material obtained from coarse grinding is finely ground, and then the finely ground material is mixed with the remaining coarsely ground material to form a slurry. This means that in step S2, a portion of the material obtained from coarse grinding is finely ground, and the remaining coarsely ground material is set aside. After the fine grinding is completed, the finely ground material is mixed with the remaining coarsely ground material.

[0022] The slurry obtained after mixing according to this invention exhibits a three-peak distribution, meaning the particle size distribution of the material includes a first peak, a second peak, and a third peak. The peak particle size range of the first peak is 0.2 μm to 0.6 μm, the peak particle size range of the second peak is 1 μm to 3 μm, and the peak particle size range of the third peak is 8 μm to 15 μm. This three-peak distribution optimizes particle packing and significantly improves compaction density. Specifically, due to the high precision of particle size control, the particle size gradient matching degree among coarse, medium, and fine particles is higher. Fine particles can fully fill the tiny gaps between coarse and medium particles, while medium particles fill the gaps between coarse particles, minimizing the internal porosity of the material and increasing the compaction density of the subsequently prepared lithium iron phosphate material to ≥2.60 g / cm³. 3 This can meet the needs of high-energy-density batteries.

[0023] After mixing the slurry in step S2, the present invention further includes drying the material obtained after mixing the slurry. Preferably, the drying is spray drying. In some embodiments of the present invention, the drying is spray drying, the inlet air temperature of the spray drying is 200℃~260℃, preferably 240℃, and the outlet air temperature of the spray drying is 90℃~110℃, preferably 95℃.

[0024] In step S2 of this invention, the secondary mixture comprising a carbon source, a metal-containing additive, water, and the lithium iron phosphate precursor described in step S1 undergoes a secondary pretreatment process including coarse grinding, fine grinding, slurry mixing, and drying. The carbon source, metal-containing additive, and water are the same as described above and will not be repeated here.

[0025] In step S2 of this invention, after mixing the slurry, the resulting material is sintered a second time under a protective atmosphere to obtain a secondary sintered material. Specifically, the second sintering is performed at 700℃~800℃ for 5 h~15 h. More specifically, the second sintering is performed by heating to 700℃~800℃ at a rate of 2℃ / min~5℃ / min and sintering for 5 h~15 h. Preferably, the protective atmosphere is an inert atmosphere.

[0026] After obtaining the secondary sintered material in step S2, the present invention performs post-processing on the secondary sintered material in step S3 to obtain lithium iron phosphate cathode material. Specifically, the post-processing includes sequential crushing, sieving, and iron removal.

[0027] The method for preparing lithium iron phosphate cathode material provided by this invention achieves multi-stage gradation by controlling the feed rate of sand milling, and prepares lithium iron phosphate cathode material with high compaction density through multi-stage gradation. In step S1, an appropriate carbon source content is used to prepare lithium iron phosphate precursor through carbothermal reduction during the first sintering, forming a lithium iron phosphate crystal phase structure containing a small amount of carbon source, which controls particle growth, so that the subsequent second coarse grinding only needs one grinding to achieve the particle size required for coarse grinding of large and medium particles. In the second sintering process, carbon coating is performed on the surface of lithium iron phosphate precursor, which helps to achieve uniform carbon layer coating, reduce the generation of free carbon, and improve the conductivity of cathode material.

[0028] This invention provides a lithium iron phosphate cathode material, obtained by any of the preparation methods described above. The preparation method provided by this invention is a method for preparing lithium iron phosphate cathode material by controlling the pump speed at the milling end to achieve multi-stage gradation during the grinding process, thus solving the problem of multiple batches in multi-stage gradation milling. The final lithium iron phosphate cathode material obtained has high compaction density and high capacity.

[0029] This invention provides a lithium-ion battery positive electrode, comprising a current collector and a positive electrode material layer disposed on the current collector; the positive electrode material layer is formed of the aforementioned lithium iron phosphate positive electrode material. This invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes; the positive electrode is the aforementioned lithium-ion battery positive electrode.

[0030] This invention provides lithium iron phosphate cathode materials, their preparation methods, and applications. The preparation method for the lithium iron phosphate cathode material provided by this invention achieves multi-stage gradation through controlled feed rate adjustment in a sand mill. This multi-stage gradation prepares lithium iron phosphate cathode materials with high compaction density. By using an appropriate carbon source content, a lithium iron phosphate cathode material with a uniform carbon layer coating is achieved. This method can produce high-component, high-capacity lithium iron phosphate cathode materials. Furthermore, the sand mill, mixer, and other equipment used are all commonly used equipment in existing industrial mass production, requiring no new equipment. It can be directly upgraded from existing lithium iron phosphate production lines, demonstrating strong process compatibility. Attached Figure Description

[0031] Figure 1 This is a schematic flowchart illustrating an embodiment of the preparation method of the lithium iron phosphate cathode material of the present invention;

[0032] Figure 2 This is a particle size distribution diagram of the final graded slurry in step A2 of Embodiment 1 of the present invention;

[0033] Figure 3 This is a SEM image of the lithium iron phosphate cathode material obtained in Example 1 of the present invention;

[0034] Figure 4 This is a particle size distribution diagram of the final graded slurry in step A2 of Embodiment 2 of the present invention;

[0035] Figure 5 This is a particle size distribution diagram of the final graded slurry in step A2 of embodiment 3 of the present invention;

[0036] Figure 6 This is a particle size distribution diagram of the final graded slurry in step C2 of Comparative Example 1 of the present invention. Detailed Implementation

[0037] This invention discloses lithium iron phosphate cathode materials, their preparation methods, and applications. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0038] This invention involves mixing a phosphorus source, iron source, lithium source, carbon source, and additives in a stirred tank to obtain a primary mixture. This primary mixture undergoes a pretreatment and a sintering process to obtain a lithium iron phosphate precursor. A carbon source and additives are then added, and the mixture is further mixed in a stirred tank to obtain a secondary mixture. This secondary mixture undergoes a second pretreatment, a second sintering, and a second post-treatment to obtain the lithium iron phosphate cathode material. Figure 1 As shown, Figure 1 This is a schematic flowchart illustrating an embodiment of the preparation method of the lithium iron phosphate cathode material of the present invention.

[0039] The present invention will be further described below with reference to the embodiments:

[0040] Example 1

[0041] (1) Preparation of lithium iron phosphate precursor:

[0042] Material preparation was carried out according to the raw material molar ratio Li:Fe:P = 1.036:1:1.032.

[0043] S1. Mix 6.5 kg of glucose, 625.5 g of titanium dioxide, 25 kg of lithium carbonate, 100 kg of ferric phosphate, and 150 kg of pure water in a mixing tank for 1 hour. The stirring frequency is 12 Hz to obtain a primary mixture.

[0044] S2. The primary mixture is fed into a sand mill for coarse grinding (zirconium bead diameter 0.6mm) until the grinding particle size D50=1.25μm; then spray drying is performed with an inlet air temperature of 240℃ and an outlet air temperature of 95℃; then sintering is performed under an inert atmosphere, with the temperature increased to 650℃ at a rate of 2.5℃ / min and held for 7.5 hours, and finally cooled down to obtain the lithium iron phosphate precursor.

[0045] (2) Preparation of high-pressure, high-capacity lithium iron phosphate cathode material:

[0046] A1. Mix 100 kg of the lithium iron phosphate precursor prepared above, 3.5 kg of glucose, 6.0 kg of polyethylene glycol (molecular weight 6000), and 144 kg of pure water until homogeneous to obtain a secondary mixture.

[0047] A2. The secondary mixture is fed into a sand mill for coarse grinding (zirconium bead diameter 0.6mm) until the particle size D50 = 1.45μm. The feed rate of the first half of the coarse grinding slurry is 3.5kg / min, and the feed rate of the second half is 1.5kg / min. The grinding speed is 1200rpm. Half of the slurry is then fed into a sand mill for fine grinding (zirconium bead diameter 0.3mm) until the particle size D50 = 0.42μm. The finely ground slurry and the coarsely ground slurry are mixed to obtain the final graded slurry. Figure 2 As shown, Figure 2 This is a particle size distribution diagram of the final graded slurry in step A2 of Embodiment 1 of the present invention.

[0048] The final graded slurry is then spray-dried at an inlet air temperature of 240°C and an outlet air temperature of 95°C. It is then sintered under an inert atmosphere, with the temperature increased to 780°C at a rate of 2.5°C / min and held for 7.5 hours. Finally, it is cooled down to obtain the secondary sintered material.

[0049] A3. The secondary sintered material was subjected to air jet milling, sieving, and iron removal to obtain the lithium iron phosphate cathode material of Example 1. Figure 3 As shown, Figure 3 This is a SEM image of the lithium iron phosphate cathode material obtained in Example 1 of the present invention.

[0050] Example 2

[0051] The difference from Example 1 is that in step A2, the feed rate for the first half of the coarse grinding is 3.0 kg / min, while the other steps are the same, ultimately yielding the lithium iron phosphate cathode material of Example 2. Figure 4 As shown, Figure 4 This is a particle size distribution diagram of the final graded slurry in step A2 of Embodiment 2 of the present invention. Since the feed rate has reached its lower limit, the third peak is weakened, but a small peak can still be seen near scale 10 in the diagram.

[0052] Example 3

[0053] The difference from Example 1 is that in step A2, the feed rate for the first half of the coarse grinding is 4 kg / min, ultimately yielding the lithium iron phosphate cathode material of Example 3. Figure 5 As shown, Figure 5 This is a particle size distribution diagram of the final graded slurry in step A2 of embodiment 3 of the present invention.

[0054] Comparative Example 1

[0055] Unlike the examples, Comparative Example 1 uses the conventional two-stage gradation route of the iron phosphate process. The specific process is as follows:

[0056] (1) Preparation of lithium iron phosphate precursor:

[0057] Material preparation was carried out according to the raw material molar ratio Li:Fe:P = 1.036:1:1.032.

[0058] B1. Mix 6.5 kg of glucose, 625.5 g of titanium dioxide, 25 kg of lithium carbonate, 100 kg of ferric phosphate, and 150 kg of pure water in a mixing tank for 1 hour. The stirring frequency is 12 Hz to obtain a single-phase mixture.

[0059] B2. The primary mixture is fed into a sand mill for coarse grinding (zirconium bead diameter 0.6mm) until the grinding particle size D50=1.28μm; then spray drying is performed with an inlet air temperature of 240℃ and an outlet air temperature of 95℃; then sintering is carried out under an inert atmosphere protection condition, with the temperature increased to 650℃ at a rate of 2.5℃ / min and held for 7.5 hours, and finally cooled down to obtain the lithium iron phosphate precursor.

[0060] (2) Preparation of high-pressure, high-capacity lithium iron phosphate cathode material:

[0061] C1. Mix 100 kg of the lithium iron phosphate precursor prepared above, 3.5 kg of glucose, 6.0 kg of polyethylene glycol (molecular weight 6000), and 144 kg of pure water until homogeneous to obtain a secondary mixture.

[0062] C2. The secondary mixture is fed into a sand mill for coarse grinding (zirconium bead diameter 0.6 mm) until the particle size D50 = 1.42 μm. The feed rate of the coarse grinding slurry is 2 kg / min, and the grinding speed is 1200 rpm. Half of the slurry is then fed into a sand mill for fine grinding (zirconium bead diameter 0.3 mm) until the particle size D50 = 0.41 μm. The finely ground slurry and the coarsely ground slurry are mixed to obtain the final graded slurry. Figure 6 As shown, Figure 6 This is a particle size distribution diagram of the final graded slurry in step C2 of Comparative Example 1 of the present invention.

[0063] Next, spray drying is carried out with an inlet air temperature of 240℃ and an outlet air temperature of 95℃. Then, sintering is carried out under an inert atmosphere protection condition, with the temperature increased to 780℃ at a rate of 2.5℃ / min and held for 7.5 hours. Finally, the material is cooled down to obtain the secondary sintered material.

[0064] C3. The secondary sintering material is subjected to air jet milling, sieving, and iron removal to obtain the lithium iron phosphate cathode material of Comparative Example 1.

[0065] Comparative Example 2

[0066] The difference in Comparative Example 1 is that in step C2, the material is finely ground to D50 = 0.36 μm, while the other steps are the same, ultimately yielding the lithium iron phosphate cathode material of Comparative Example 2.

[0067] Comparative Example 3

[0068] The difference in Comparative Example 1 is that in step C2, the material is finely ground to D50 = 0.50 μm, while the other steps are the same, ultimately yielding the lithium iron phosphate cathode material of Comparative Example 3.

[0069] The performance of the products obtained in the examples and comparative examples was compared. Specifically, the carbon content, specific surface area, powder compaction, and resistivity of the cathode materials of Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3 were measured, and coin cells were fabricated in the same manner. Then, the parameters characterizing the electrical performance (0.1C specific capacity and 1.0C specific capacity) were measured using methods disclosed in the prior art. The results are shown in Table 1.

[0070] Table 1

[0071]

[0072] As shown in Table 1, the material prepared using the milling parameters of Example 1 exhibits the highest powder compaction and also a high coin cell capacity. Reducing the feed rate in the first half of the coarse milling (Example 2) increases the coin cell capacity, but the powder compaction decreases from 2.65 to 2.55. This is because the overall particle size of the slurry produced by reducing the feed rate is smaller, ultimately increasing the active sites in the powder and thus increasing the capacity. However, the smaller size of the large particles prevents them from fully filling the voids, resulting in a decrease in powder compaction. Increasing the feed rate in the first half of the coarse milling (Example 3) decreases the coin cell capacity, with a powder compaction of 2.60. This is because the slurry produced by increasing the feed rate contains oversized particles, affecting electrochemical performance. Excessively large particles also negatively impact powder compaction. Compared to Comparative Examples 1, 2, and 3, the lithium iron phosphate cathode material prepared in Example 1 shows significantly improved compaction and electrochemical performance. Furthermore, the added step only requires adjusting the feed rate once, making the operation simple.

[0073] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing lithium iron phosphate cathode material, characterized in that, Includes the following steps: S1) The phosphorus source, iron source, lithium source, carbon source, water and metal-containing additives are coarsely ground, and then the resulting material is sintered for the first time under a protective atmosphere to obtain the lithium iron phosphate precursor. S2) The carbon source, metal additive, water and lithium iron phosphate precursor mentioned in step S1 are coarsely ground. The coarse grinding is a segmented coarse grinding achieved by adjusting the feed rate. Then, a portion of the material obtained from the coarse grinding is finely ground. The finely ground material is then mixed with the remaining material obtained from the coarse grinding in a slurry. The resulting material is then sintered a second time under a protective atmosphere to obtain a secondary sintered material. The particle size distribution of the material obtained by mixing the slurry includes a first particle size peak, a second particle size peak and a third particle size peak. The peak particle size of the first particle size peak ranges from 0.2 μm to 0.6 μm, the peak particle size of the second particle size peak ranges from 1 μm to 3 μm, and the peak particle size of the third particle size peak ranges from 8 μm to 15 μm. S3) The secondary sintering material described in step S2 is post-processed to obtain lithium iron phosphate cathode material.

2. The method according to claim 1, characterized in that, In step S1, the D50 particle size of the material obtained by coarse grinding is 1.0 μm to 2.0 μm; In step S2, the particle size D50 of the material obtained by coarse grinding is 1.0 μm to 2.0 μm; In step S2, the particle size D50 of the material obtained by fine grinding is 0.3 μm to 0.6 μm.

3. The preparation method according to claim 1, characterized in that, In step S2, the diameter of the grinding beads used in the coarse grinding is 0.6 mm to 1.0 mm, and the rotation speed of the coarse grinding is 1000 rpm to 1200 rpm; In step S2, the diameter of the grinding beads used in the fine grinding is 0.2 mm to 0.35 mm, and the rotation speed of the fine grinding is 900 rpm to 1200 rpm.

4. The preparation method according to claim 1, characterized in that, In step S2, the feeding rate for the first 40% to 60% of the material weight of the coarse grinding is 3 kg / min to 5 kg / min, and the feeding rate for the remaining material weight of the coarse grinding is 0.5 kg / min to 2 kg / min. In step S2, a portion of the material obtained by coarse grinding accounts for 40% to 60% of the weight of the material obtained by coarse grinding.

5. The method according to claim 1, characterized in that, In step S1, the first sintering specifically involves sintering at 550℃~750℃ for 5 h~15 h. In step S2, the second sintering specifically involves sintering at 700℃~800℃ for 5 h~15 h.

6. The method according to claim 1, characterized in that, In step S1, the molar ratio of the lithium source, iron source, and phosphorus source is Li:Fe:P = (1.0~1.05):1:(1.010~1.036), and the amount of metal element in the metal additive accounts for 0.2%~0.6% of the mass of the lithium iron phosphate precursor.

7. The method according to claim 1, characterized in that, In step S1, the phosphorus source is selected from one or more of ferric phosphate, phosphoric acid, and ammonium dihydrogen phosphate; In step S1, the iron source is selected from one or more of ferric phosphate, ferric oxide, and ferrous oxalate dihydrate; In step S1, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; In steps S1 and S2, the carbon source is independently selected from one or more of glucose, sucrose, starch, and polyethylene glycol; In steps S1 and S2, the metal-containing additive is independently selected from one or more of titanium dioxide, tetrabutyl titanate, magnesium oxide, magnesium acetate, magnesium hydroxide, magnesium nitrate, zirconium nitrate, zirconium hydroxide, zirconium oxide, vanadium pentoxide, or niobium pentoxide.

8. A lithium iron phosphate cathode material, characterized in that, It is obtained by the preparation method according to any one of claims 1 to 7.

9. A lithium-ion battery positive electrode, characterized in that, Includes a current collector and a positive electrode material layer disposed on the current collector; The cathode material layer is formed from the lithium iron phosphate cathode material as described in claim 8.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the positive electrode is the positive electrode of the lithium-ion battery according to claim 9.

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