Preparation method of lithium iron phosphate

Abstract

The invention discloses a preparation method of lithium iron phosphate, which comprises the following steps: homogenizing and dispersing a lithium iron phosphate raw material to form primary slurry; sequentially carrying out coarse grinding and fine grinding on the primary slurry to form slurry turbid liquid; performing spray drying on the slurry turbid liquid to form a spray material; carrying out rolling and granulation on the spray material; the rolled and granulated particles are screened, and selected particles are screened out; the selected particles are sequentially subjected to bowl loading, sintering and crushing, and the lithium iron phosphate material is obtained. According to the preparation method of the lithium iron phosphate disclosed by the invention, on one hand, relatively high bowl loading quantity can be obtained, so that the productivity is increased; and secondly, the prepared product is good in consistency and excellent in electrical property.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate preparation, and in particular to a method for preparing lithium iron phosphate. Background Art

[0002] At present, the mainstream process for preparing olivine-type lithium iron phosphate uses a carbon thermal reduction method. In this process, after the wet stage ball milling is completed, the water slurry needs to use a spray drying process, and then the spray material is sintered in a nitrogen atmosphere furnace. However, on the one hand, the loading amount of the spray material particles itself is low, resulting in a low kiln production capacity, and the energy consumption of the sintering process of the lithium iron phosphate positive electrode material accounts for a large proportion, about 70%-80% of the total power consumption, which will increase the preparation cost of the lithium iron phosphate positive electrode material; on the other hand, although the existing technology attempts to produce positive electrode materials by granulating the spray material, it is not suitable for the preparation of lithium iron phosphate positive electrode materials, because the particles prepared based on the existing granulation process are not subjected to a post-processing process. If they are directly used in the sintering process of the lithium iron phosphate positive electrode material, there will be problems such as high residual alkali content and low constant current charging ratio, thereby reducing the quality of the lithium iron phosphate positive electrode material.

[0003] Therefore, there is an urgent need to find a low-cost large-scale preparation method for the production of lithium iron phosphate positive electrode materials, which can not only improve the sintering capacity of the kiln and significantly reduce the sintering power consumption cost, but also ensure the production quality of lithium iron phosphate positive electrode materials. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for preparing lithium iron phosphate, which can firstly obtain a higher filling volume, thereby increasing production capacity; and secondly, the obtained product has good consistency and excellent electrical properties.

[0005] The present invention also provides a preparation device, which is applied to the above-mentioned preparation method of lithium iron phosphate.

[0006] The method for preparing lithium iron phosphate according to an embodiment of the present invention comprises:

[0007] homogenously dispersing the lithium iron phosphate raw material to form a preliminary slurry;

[0008] The preliminary slurry is subjected to coarse grinding and fine grinding in sequence to form a slurry turbid liquid;

[0009] The slurry turbid liquid is spray-dried to form a spray material;

[0010] Rolling and granulating the spray material;

[0011] Screening the particles after rolling and granulation to select the particles;

[0012] The selected particles are successively potted, sintered and crushed to obtain lithium iron phosphate material.

[0013] According to the preparation method of lithium iron phosphate of the embodiment of the present invention, the lithium iron phosphate raw material is dispersed homogeneously to form a preliminary slurry; the preliminary slurry is subjected to coarse grinding and fine grinding in sequence to form a slurry turbid liquid; the spray material is rolled and granulated; the particles after rolling and granulation are screened to select selected particles; the selected particles are successively filled, sintered and crushed to obtain lithium iron phosphate material; the spray material is rolled and granulated to make the spray material denser, so that the density of the formed particles is larger, so that the particle filling density is high, and a higher filling amount can be obtained, thereby increasing production capacity. After screening the particles, the selected particles whose equivalent diameter is within the preset range can be screened out. On the one hand, particles with equivalent diameters that are too large or too small can be screened out to prevent uneven reaction during the sintering process due to large differences in particle size. For example, when using too small materials or too large materials, the total surface alkali content of the lithium iron phosphate positive electrode material obtained under the same sintering process is relatively high, the discharge capacity and efficiency in the first week of 0.5C / 0.5C are relatively low, and the constant current charging ratio is low, which will reduce the production quality of the lithium iron phosphate positive electrode material. On the other hand, the equivalent diameters of the selected particles are relatively small, thereby improving the uniformity of the particles and making the product more consistent.

[0014] In some embodiments of the present invention, screening the particles after rolling and granulation includes:

[0015] The particles after rolling and granulation are passed through a first-stage sieve and a second-stage sieve in sequence, wherein the sieve hole diameter of the first-stage sieve is larger than the sieve hole diameter of the second-stage sieve, and the sieve-surface material of the second-stage sieve is taken as the selected particles.

[0016] In some embodiments of the present invention, the method for preparing lithium iron phosphate further includes:

[0017] The undersize material from the second-stage screen is then rolled and granulated.

[0018] And / or, the method for preparing lithium iron phosphate further comprises:

[0019] The material on the first-stage screen is granulated again.

[0020] In some embodiments of the present invention, the mesh diameter of the first-stage sieve is 4-5 mm; and / or, the mesh diameter of the second-stage sieve is 1-2 mm; and / or, the mesh diameter of the first-stage sieve is 2-4 mm larger than the mesh diameter of the second-stage sieve; and / or, the mesh diameter of the first-stage sieve is 2-5 mesh; and / or, the mesh diameter of the second-stage sieve is 10-20 mesh.

[0021] In some embodiments of the present invention, roller pressing the spray material comprises:

[0022] The spray material is delivered through a feeding device;

[0023] The delivered spray material is rolled by a roller, the roller is driven to rotate by a driving motor, and the pressure of the roller is provided by a hydraulic cylinder.

[0024] In some embodiments of the present invention, the frequency of the driving motor is 25-35Hz; and / or, the feeding frequency of the feeding device is P1, the frequency of the driving motor is P2, P1:P2=0.5-2.0; and / or, the pressure provided by the hydraulic cylinder for roller pressing is 10-15MPa.

[0025] In some embodiments of the present invention, granulating the spray material comprises:

[0026] The spray material after rolling is cut and granulated by a cutter roller, and the rotation speed of the cutter roller is 300-500RPM.

[0027] In some embodiments of the present invention, the outer peripheral wall of the roller has a groove extending along the axis direction of the roller.

[0028] In some embodiments of the present invention, the groove width gradually decreases along the radial inward direction of the roller; and / or the groove is a plurality of grooves arranged at equal intervals along the circumference of the roller; and / or the depth of the groove is 4-8 mm.

[0029] In some embodiments of the present invention, the temperature during sintering of the selected particles is 750-850° C.; and / or the sintering time of the selected particles is 20-24 hours.

[0030] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0032] Figure 1 is a front view of a preparation device of a method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0033] Figure 2 is a side view of a preparation device of a method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0034] Figure 3is a three-dimensional view of a rolling roller of a rolling roller device of a preparation device of a method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0035] Figure 4 is a top view of a rolling roller of a rolling device of a preparation device of a method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0036] Figure 5 is a front view of a rotary cutting machine of a rotary cutting granulation device of a preparation device of a method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0037] Figure 6 is a side view of a cutting blade roller of a rotary cutting machine of a rotary cutting granulation device of a preparation device of a method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0038] Figure 7 is a stereoscopic diagram of a grading and screening device of a preparation device of a method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0039] Figure 8 is a stereogram of a grading and screening device of a preparation device of a method for preparing lithium iron phosphate according to an embodiment of the present invention from another perspective;

[0040] Fig. 9 is a schematic flow chart of a method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0041] Fig.10 is a particle size volume distribution curve diagram of LFP1-LFP7 according to the method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0042] Fig.11 is a particle size distribution curve diagram of LFP1-LFP7 according to the method for preparing lithium iron phosphate according to an embodiment of the present invention;

[0043] Fig.12 is a scanning electron microscope morphology image of lithium iron phosphate materials LFP1-LFP3 according to the method for preparing lithium iron phosphate in an embodiment of the present invention;

[0044] Fig.13 This is a scanning electron microscope morphology image of lithium iron phosphate materials LFP4-LFP7 according to the method for preparing lithium iron phosphate in an embodiment of the present invention;

[0045] Fig.14 It is a distribution diagram of the capacity of LFP1-LFP7 according to the preparation method of lithium iron phosphate in an embodiment of the present invention at 25° C., 2.5-4.2V, 1.0C / 1.0C buckling cycle for 200 cycles;

[0046] Fig.15It is a distribution diagram of the capacity retention rate of LFP1-LFP7 according to the preparation method of lithium iron phosphate according to an embodiment of the present invention at 25° C., 2.5-4.2V, 1.0C / 1.0C buckling cycle for 200 cycles.

[0047] Reference numerals:

[0048] 10. Preparation device;

[0049] 1. Feeding device; 11. Elevator; 12. Spray material feeding hopper; 13. First buffer device; 131. First buffer bin; 14. Stirring device; 15. Material level meter; 16. Feeder;

[0050] 2. Roller device; 21. Conveying device; 22. Roller; 221. Groove; 23. Driving motor; 24. Hydraulic cylinder;

[0051] 3. Peeling granulation device; 31. Second buffer device; 311. Second buffer bin; 312. Return port; 313. Sight glass; 32. Peeling machine; 321. Cutter roller; 3211. Roller body; 3212. Blade; 322. Vibration structure; 33. Connecting pipe; 34. Control valve;

[0052] 4. Grading screening device; 41. Grading screen body; 411. Screening space; 412. Feed inlet; 413. First discharge outlet; 414. Second discharge outlet; 415. Third discharge outlet; 42. First-stage screen; 44. Vibration device;

[0053] 5.PLC control module. DETAILED DESCRIPTION

[0054] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0055] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0056] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0057] Reference below Fig. 9 A method for preparing lithium iron phosphate according to an embodiment of the present invention is described.

[0058] like Fig. 9 As shown, the method for preparing lithium iron phosphate according to an embodiment of the present invention includes:

[0059] The lithium iron phosphate raw materials are dispersed homogeneously to form a preliminary slurry; wherein the lithium iron phosphate raw materials include a preset proportion of an iron phosphate precursor, a lithium source, water, additives and auxiliary materials, the additives include a surfactant, a stabilizer, a structure directing agent and a conductive agent, and the auxiliary materials include a binder, a dispersant, a desiccant and a sintering aid, etc.

[0060] The preliminary slurry is subjected to coarse grinding and fine grinding in sequence to form a turbid slurry; specifically, in the present application, a ball mill with a zirconium ball particle size of 2 mm is first used for coarse grinding until the dispersed particle size Dv50 of the slurry is 1-1.2 μm; after the coarse grinding particle size is qualified, a ball mill with a zirconium ball particle size of 1 mm is used for fine grinding to obtain a finely ground slurry with a dispersed particle size Dv50 of 0.38-0.41 μm.

[0061] The slurry turbid liquid is spray dried to form a spray material; during the spray drying process, the liquid material is atomized into fine droplets, and these droplets come into contact with hot air in a drying tower and are quickly dried into solid powder. Spray drying can ensure the uniformity of mixing of various raw materials of lithium iron phosphate.

[0062] The spray material is rolled and granulated; wherein, by controlling the parameters of the roller 22 during rolling (such as the rotation frequency and the rolling pressure), the thickness of the sheet material formed by rolling the spray material can be better defined. Since the thickness of the sheet material is related to the equivalent diameter of the particles after granulation, the equivalent diameter of the particles after granulation is better defined, avoiding excessive differences in the equivalent diameters of multiple particles after granulation, improving the uniformity of the particles, and making the product more consistent.

[0063] In addition, the spray material is more compact after roller pressing, so that the formed particles have a higher density, which makes the particle filling and stacking density high, and a higher filling volume can be obtained, thereby increasing production capacity.

[0064] The particles after rolling and granulation are screened to select the selected particles; it can be understood that the selected particles whose equivalent diameter is within the preset range can be screened out by screening (for example, the equivalent diameter of the selected particles in the present invention is 2-4mm). On the one hand, particles with an equivalent diameter that is too large or too small can be screened out to prevent uneven reaction degree during the sintering process due to large differences in particle size. For example, when using too small materials or too large materials, the total surface alkali content of the lithium iron phosphate positive electrode material obtained under the same sintering process is relatively high, the discharge capacity and efficiency in the first week of 0.5C / 0.5C are relatively low, and the constant current charging ratio is low, which will reduce the production quality of the lithium iron phosphate positive electrode material. On the other hand, the equivalent diameters of the selected particles are relatively small, thereby improving the uniformity of the particles and making the product more consistent.

[0065] The selected particles are filled, sintered and crushed in sequence to obtain lithium iron phosphate material.

[0066] The following describes the improvement of the production capacity and performance of the product by sintering the sprayed material after rolling, granulation and screening through Examples 1-3 and Comparative Examples 1-4.

[0067] Among them, Examples 1-3 and Comparative Examples 1-4 were sintered in a nitrogen atmosphere at a sintering temperature of 795° C. and a sintering time of 22 h. The material was loaded in a sagger with a depth of 130 mm. After the material was taken out of the furnace, it was crushed to obtain a lithium iron phosphate positive electrode material with a D50 of 1.05 μm.

[0068] Example 1 is labeled LFP-1, Example 2 is labeled LFP-2, Example 3 is labeled LFP-3, Comparative Example 1 is labeled LFP-4, Comparative Example 2 is labeled LFP-5, Comparative Example 3 is labeled LFP-6, and Comparative Example 4 is labeled LFP-7.

[0069] Table 1

[0070]

[0071] As shown in Table 1, the production capacity of Example 1 can reach 484 kg / h, and the density after granulation can reach 0.930 g / cm 3 In Example 2, as the feeding frequency is reduced to 20 Hz, the granulation capacity is reduced to 257 kg / h. On the other hand, in Example 3, with the same 45 Hz feeding frequency, as the roller frequency is reduced to 25 Hz, part of the material is accumulated on the roller, resulting in a certain degree of increase in the density after granulation to 0.934 g / cm 3 As can be seen from Table 1, the bulk density of the spray material without granulation is only 0.690 g / cm 3 , its filling capacity under normal circumstances is only 8.0Kg. Further, it can be seen from Examples 1-3 and Comparative Examples 2-4 that regardless of whether screening is performed, as long as granulation is performed, the bulk density can be improved to varying degrees, and granulation can at least increase the density by more than 33.2%. Therefore, granulation can significantly increase the filling capacity, and the density improvement rate here = (bulk density after tableting - bulk density before tableting) / bulk density before tableting * 100%.

[0072] Table 2

[0073]

[0074]

[0075] From the comparison of physical and chemical properties in Table 2, it can be seen that the product performance of Examples 1-3 is close to that of Comparative Example 1, for example, the density is 2.5 g / cm 3 , resistivity: 8.0-9.0Ω·cm, specific surface area: 12.41-12.60m 2 / g, total alkali: 1700-1800ppm, half-cell first charge and discharge efficiency is about 93.0%, constant current charge ratio: 97.0%, wherein the specific surface areas of Examples 1-3 are all higher than those of Comparative Example 1. However, in Comparative Example 2, which did not undergo a screening process, its resistivity increased significantly to 15.27Ω·cm, and its specific surface area was also relatively small, only 9.81. The total surface alkali content was increased by 27.05% compared with that in Example 1, and the electrical performance was significantly inferior to that of Examples 1-3 and Comparative Example 1. On the other hand, the difference between Comparative Examples 3 and 4 lies in the different particle screening ranges. Comparative Example 3 selects materials with an average particle size of less than 4 mm, and Comparative Example 4 selects materials with an average particle size of more than 2 mm. It can be seen from Table 2 that whether granulated particles with an average particle size that is too large or granulated particles with an average particle size that is too small are selected, the total alkali content on the surface of the positive electrode material will be increased, which will affect the charge and discharge performance of the positive electrode material to a certain extent. For example, the first-week discharge capacity of Comparative Examples 3-4 is only 146.6-147.5 mA / h, and the 0.5C / 0.5C first-week charge and discharge efficiency of Comparative Example 4 is only 89.8%, which is much lower than that of Examples 1-3 and Comparative Example 1.

[0076] In summary, after roller granulation, the particles are screened and then sintered to prepare lithium iron phosphate positive electrode material, which can effectively ensure the physical and chemical properties of the material. The performance of Examples 1-3 and Comparative Example 1 (traditional process) are basically the same, and the performance of Comparative Example 2 (unscreened) is worse than that of Examples 1-3 and Comparative Example 1, which fully demonstrates that after roller granulation, the particle size range screening process for the preparation of lithium iron phosphate positive electrode is indispensable.

[0077] The lithium iron phosphate positive electrode materials of Examples 1-3 and Comparative Examples 1-4 were observed by SEM, and the particle micromorphology was as follows: Figure 12-13As shown, the preparation processes of Examples 1-3 and Comparative Example 1 can generate spherical lithium iron phosphate particles, and Comparative Example 2-3 is non-spherical lithium iron phosphate particles. It can be seen from Table 2 that the spherical lithium iron phosphate particles generated by Examples 1-3 and Comparative Example 1 have lower internal resistance and excellent rate performance. Compared with the non-spherical lithium iron phosphate particles of Comparative Example 2-3, the internal resistance of the lithium iron phosphate battery with spherical morphology is reduced by 8.8mΩ, and the charge transfer impedance and lithium ion diffusion impedance are also lower. The electrical properties of the button battery are as follows: the first discharge capacity: 152.5mA / h, the first charge and discharge efficiency is about: 93%, and the constant current charging ratio: 97.0%. On the contrary, in Comparative Example 2-4, the packing density of the granular lithium iron phosphate particles is higher, but the electronic conductivity and ion diffusion rate are lower, resulting in a lower specific capacity. The first discharge capacity of Comparative Example 4 is only: 146.6mA / h, the first charge and discharge efficiency is only: 89.8%, and the constant current charging ratio is as low as: 95.7%. This shows that the introduction of roller cutting screen is feasible in the preparation of lithium iron phosphate positive electrode materials. While improving the overall production capacity, optimizing the screening of the particle range before sintering can effectively ensure that the physical, chemical and electrical properties of the material are not lost.

[0078] Table 3

[0079]

[0080] Calculating the kiln production line capacity and unit consumption, it can be seen from Table 3 that the capacity of Comparative Example 1 (traditional process) is about 7000Kg / d, while the output of the same equipment in Examples 1-3 can reach (equal to or higher than) 9400Kg / d, and the capacity is increased by about 35.0%; on the other hand, the power consumption per Kg of Comparative Example 1 is about 2.21KWh / Kg, and the unit power consumption of Examples 1-3 is about 1.93KWh / Kg. By comparison, it is found that the power consumption per Kg is saved by 13.1%.

[0081] In the present invention, the lithium-ion battery is a CR2025 battery. The present invention preferably mixes the positive electrode material of the above technical solution with a conductive agent (supper-P) and an adhesive (6% PVDF solution, the solvent is N-methyl-2-pyrrolidone) in a mass ratio of 80:10:10, and then supplements a small amount of N-methyl-2-pyrrolidone according to the viscosity of the slurry. The obtained electrode slurry is coated, dried, rolled and punched; the negative electrode is a lithium sheet; 1mol / L LiPF6 is used as an electrolyte, and a polyolefin diaphragm is selected as the diaphragm. The positive electrode, diaphragm, and negative electrode are assembled using a stacking process. After the button battery is assembled, it is placed in a constant temperature box at (25±2)℃ for 12h to test its electrical performance. The lithium-ion button batteries assembled in the above embodiments 1-3 and comparative examples 1-4 are tested at 25℃, 2.5-4.2V, and the 0.5C / 0.5C first charge and discharge efficiency and the 1C / 1C cycle 200 weeks are tested for their capacity retention rate.

[0082] like Fig.14 and Fig.15 As shown, through the test of the retention rate of the buckle batteries of Examples 1-3 and Comparative Examples 1-4 at 25°C, 2.5-4.2V, 1.0C / 1.0C buckle power cycles for 200 cycles, the cycle performance of the buckle batteries of Examples 1-3 and Comparative Example 1 is significantly better than that of Comparative Examples 2-4. After 200 cycles, the capacity retention rates of Examples 1-3 and Comparative Examples 1-4 are 99.88%, 99.72%, 99.75%, 99.89%, 95.84%, 97.53%, and 97.78%, respectively. Compared with Examples 1-3 and Comparative Example 1, the comparative cycle retention rates are basically the same, maintained at 99.88%, but Comparative Example 2 has not been screened for particles, and its capacity retention is only 95.84%, and the battery capacity decay rate is significantly faster than that of Examples 1-3 and Comparative Example 1 (traditional process); similarly, due to the high residual alkali, the residual alkali will change the acid-base balance inside the battery, affect the chemical reaction, and thus affect the performance and life of the battery. The positive electrode materials (LFP-6 and LFP-7) prepared without particle screening have residual alkali contents of 1905ppm and 1983ppm, which are significantly higher than Examples 1-3 and Comparative Example 1 (see Table 2), and the capacity retention rates of LFP-6 and LFP-7 are at 97.53% and 97.78%, respectively, which are also significantly lower than Examples 1-3 and Comparative Example 1.

[0083] The particle size distribution of the positive electrode materials of Examples 1-3 and Comparative Examples 1-4 was tested respectively, and the results are shown in Table 4. Fig.10 and Fig.11 As shown. From the number distribution of particle size, it can be seen that the distribution and particle size of the curves of Examples 1-3 and Comparative Example 1 (traditional process) are basically the same, while the particle size volume distribution peak of LFP-5 in Comparative Example 2 can be seen to have an obvious tail, corresponding to its Dmax: 9.78μm, which is significantly larger than that of Examples 1-3 and Comparative Example 1; similarly, the particle size number distribution diagram of Comparative Example 3, which has not been thoroughly screened, is clearly visible on the left side of Comparative Example 1, and the overall particle size is small; on the contrary, the particle size distribution of Comparative Example 4 is larger as a whole. It can be explained that only when the lithium iron phosphate positive electrode material prepared through the sintering process is screened by granulation and the particle size after granulation is controlled to be in the range of 2μm-4μm, can the particle size distribution of the lithium iron phosphate positive electrode material obtained by direct spray sintering be consistent, thereby ensuring the stability and controllability of the batch finished product.

[0084] Table 4

[0085]

[0086] According to the preparation method of lithium iron phosphate of the embodiment of the present invention, the lithium iron phosphate raw material is dispersed homogeneously to form a preliminary slurry; the preliminary slurry is subjected to coarse grinding and fine grinding in sequence to form a slurry turbid liquid; the spray material is rolled and granulated; the particles after rolling and granulation are screened to select selected particles; the selected particles are successively filled, sintered and crushed to obtain lithium iron phosphate material; the spray material is rolled and granulated to make the spray material denser, so that the density of the formed particles is larger, so that the particle filling density is high, and a higher filling amount can be obtained, thereby increasing production capacity. After screening the particles, the selected particles whose equivalent diameter is within the preset range can be screened out. On the one hand, particles with equivalent diameters that are too large or too small can be screened out to prevent uneven reaction during the sintering process due to large differences in particle size. For example, when using too small materials or too large materials, the total surface alkali content of the lithium iron phosphate positive electrode material obtained under the same sintering process is relatively high, the discharge capacity and efficiency in the first week of 0.5C / 0.5C are relatively low, and the constant current charging ratio is low, which will reduce the production quality of the lithium iron phosphate positive electrode material. On the other hand, the equivalent diameters of the selected particles are relatively small, thereby improving the uniformity of the particles and making the product more consistent.

[0087] In some embodiments of the present invention, screening the particles after rolling and granulation includes:

[0088] The particles after rolling and granulation are passed through the first-stage sieve 42 and the second-stage sieve in sequence, wherein the sieve hole diameter of the first-stage sieve 42 is larger than the sieve hole diameter of the second-stage sieve, and the sieve-surface material of the second-stage sieve is taken as the selected particles.

[0089] It can be understood that the first-stage screen 42 can remove particles with an equivalent diameter that is too large, thereby ensuring the reaction rate during sintering and improving production capacity. The second-stage screen can screen out particles with an equivalent diameter that is too small, thereby avoiding a large difference in the equivalent diameters of multiple particles, improving the uniformity of the particles, and making the product more consistent.

[0090] In some embodiments of the present invention, the method for preparing lithium iron phosphate further includes:

[0091] The undersize material from the second-stage screen is then rolled and granulated.

[0092] Therefore, the screened material of the second-stage screen after rolling and granulation can be screened again to obtain selected particles, so that the screened material of the second-stage screen can be recycled, thereby improving the utilization rate of the material and reducing the production cost.

[0093] In some embodiments of the present invention, the method for preparing lithium iron phosphate further includes:

[0094] The oversize material of the first-stage screen 42 is further granulated.

[0095] Therefore, the screened material of the first-stage screen 42 after granulation can be further screened to obtain selected particles, so that the screened material of the first-stage screen 42 can be recycled, thereby improving the utilization rate of the material and reducing the production cost.

[0096] In some embodiments of the present invention, the mesh diameter of the first-stage screen 42 is 4-5 mm, such as 4 mm, 4.2 mm, 4.5 mm or 5 mm, so that particles with larger equivalent diameters can be easily screened out. For example, in the present invention, the mesh diameter of the first-stage screen 42 is 4 mm, so that particles with equivalent diameters greater than 4 mm can be easily screened out.

[0097] In some embodiments of the present invention, the mesh diameter of the second-stage screen is 1-2 mm, such as 1 mm, 1.5 mm, 1.8 mm or 2 mm, etc. Thus, it is convenient to screen out particles with smaller equivalent diameters. For example, in the present invention, the mesh diameter of the second-stage screen is 2 mm, so that it is convenient to screen out particles with equivalent diameters less than 2 mm.

[0098] In some embodiments of the present invention, the mesh diameter of the first-stage sieve 42 is 2-4 mm larger than the mesh diameter of the second-stage sieve; for example, 2 mm, 2.5 mm, 3 mm or 4 mm.

[0099] In some embodiments of the present invention, the mesh size of the first-stage sieve 42 is 2-5 meshes, such as 2 meshes, 3 meshes, 4 meshes or 5 meshes.

[0100] In some embodiments of the present invention, the mesh size of the second-stage screen is 10-20 meshes, such as 10 meshes, 11 meshes, 15 meshes or 20 meshes.

[0101] In some embodiments of the present invention, roller-pressing the spray material comprises:

[0102] The spray material is conveyed by the feeding device 1 , thereby improving the conveying efficiency and ensuring the uniformity of the spray material during conveying.

[0103] The spray material delivered is rolled by roller 22, the roller 22 is driven to rotate by driving motor 23, and the pressure of roller 22 is provided by hydraulic cylinder 24. Thus, the spray material is rolled and granulated.

[0104] In some embodiments of the present invention, the frequency of the drive motor 23 is 25-35 Hz, such as 25 Hz, 30 Hz, 32 Hz or 35 Hz, etc. Thus, the frequency of the drive motor 23 is appropriate, so that the equivalent diameter of the particles is appropriate, the proportion of the selected particles output is increased, the output of the screen material of the first-stage screen 42 and the screen material of the second-stage screen is reduced, and the production efficiency is improved.

[0105] In some embodiments of the present invention, the feeding frequency of the feeding device 1 is P1, the frequency of the driving motor 23 is P2, and P1:P2=0.5-2.0; for example, P1:P2 can be 0.5, 1, 1.5 or 2.0. Thus, on the one hand, a higher frequency of the driving motor 23 can be ensured, thereby increasing the density of the granulated particles, thereby increasing the filling amount and increasing the production capacity. On the other hand, it can ensure that the spray material has good fluidity, and there is no material blockage during roller pressing, thereby increasing the production capacity.

[0106] In some embodiments of the present invention, the pressure of the hydraulic cylinder 24 is 10-15 MPa, such as 10 MPa, 11 MPa, 12 MPa or 15 MPa, etc. Thus, the pressure of the hydraulic cylinder 24 is appropriate, which can improve the density of the granules after granulation and avoid the breakage of the granules or the generation of obvious cracks.

[0107] In some embodiments of the present invention, granulating the spray material comprises:

[0108] The spray material after rolling is cut and granulated by the cutter roller 321, and the rotation speed of the cutter roller 321 is 300-500RPM, such as 300RPM, 400RPM, 450RPM or 500RPM. Thus, on the one hand, the cutting rate is guaranteed, thereby improving the production capacity, and on the other hand, it can avoid the particles being too small, ensure the proportion of the selected particles output, and reduce the output of the undersize material of the second-stage screen.

[0109] In some embodiments of the present invention, Figure 3 and Figure 4 As shown, the outer peripheral wall of the roller 22 has a groove 221 extending along the axis direction of the roller 22; it can be understood that, through the provision of the groove 221, on the one hand, the friction and grip of the roller 22 when rolling the spray material can be improved to prevent slipping, and on the other hand, the shape of the granulated particles can be made irregular, thereby increasing the surface area of ​​the particles, increasing the reaction rate, and also facilitating the reduction of the gaps between the particles, further making the particle filling and stacking density high, and obtaining a higher filling amount, thereby increasing production capacity.

[0110] In some embodiments of the present invention, Figure 3 and Figure 4 As shown, the width of the groove 221 gradually decreases along the radial inward direction of the roller 22; thereby, the shape of the granulated particles is further made irregular, thereby increasing the surface area of ​​the particles, increasing the reaction rate, and also facilitating the reduction of the gaps between the particles, further making the particle filling density high, and obtaining a higher filling volume, thereby increasing production capacity.

[0111] In some embodiments of the present invention, Figure 3 and Figure 4As shown, the grooves 221 are arranged at equal intervals along the circumference of the roller 22; thereby, the friction and grip of the roller 22 when rolling the spray material are further improved to prevent slipping, and the shape of the granulated particles is further made irregular, thereby increasing the surface area of ​​the particles and the reaction rate. At the same time, it is also convenient to reduce the gaps between the particles, further making the particle filling density high, and obtaining a higher filling volume, thereby increasing production capacity.

[0112] In some embodiments of the present invention, Figure 3 and Figure 4 As shown, the depth of the groove 221 is 4-8 mm, such as 4 mm, 5 mm, 6 mm or 8 mm. Thus, the depth of the groove 221 is appropriate, and the groove 221 is prevented from being too deep or too shallow. On the one hand, the friction and gripping force of the roller 22 when rolling the spray material are ensured, and on the other hand, the spray material can be prevented from remaining in the groove 221.

[0113] In some embodiments of the present invention, the temperature for sintering the particles is 750-850°C, for example, 750°C, 770°C, 800°C or 850°C, etc. Thus, the temperature for sintering the particles is appropriate, the reaction rate is guaranteed, and the production capacity is improved.

[0114] In some embodiments of the present invention, the particle sintering time is selected to be 20-24 hours, such as 20 hours, 21 hours, 22 hours or 24 hours, etc., thereby making the particle sintering time appropriate, thereby ensuring the product yield.

[0115] Reference below Figure 1-Figure 8 A preparation apparatus 10 according to an embodiment of the present invention is described.

[0116] like Figure 1-Figure 8 As shown, the preparation device 10 according to the embodiment of the present invention comprises: a feeding device 1, a roller device 2, a rotary cutting granulation device 3, a grading and screening device 4 and a PLC control module 5.

[0117] Specifically, Figure 1-Figure 2 As shown, the preparation device 10 is applied to the above-mentioned preparation method of lithium iron phosphate. The spray material is rolled, granulated and screened through the preparation device 10. The feeding device 1 is used to input the spray material; the roller device 2 is arranged below the feeding device 1 and is used to roll the spray material; the rotary cutting granulation device 3 is arranged below the roller device 2 and is used for rotary cutting and granulation of the spray material; the grading and screening device 4 is used to screen the particles after rolling and granulation to obtain selected particles.

[0118] It can be understood that by feeding the spray material into the feeding device 1, the spray material enters the roller device 2 for rolling, and then passes through the rotary cutting granulation device 3 for rotary cutting granulation, and finally the selected particles are screened out by the grading and screening device 4, thereby realizing the rolling, granulation and screening of the spray material.

[0119] Furthermore, if Figure 1 and Figure 2 As shown, the PLC control module 5 is connected in communication with the feeding device 1, the roller device 2, the rotary cutting granulation device 3 and the grading screening device 4. Among them, the PLC control module 5 (Programmable Logic Controller) is connected in communication with the feeding device 1, and can control the feeding process speed of the feeding device 1. The PLC control module 5 is connected in communication with the roller device 2, and can control the rolling parameters (such as frequency and pressure, etc.) of the roller device 2. The PLC control module 5 is connected in communication with the rotary cutting granulation device 3, and can control the rotary cutting parameters (such as frequency, etc.) of the rotary cutting granulation device 3. The PLC control module 5 is connected in communication with the grading screening device 4, so that the vibration frequency of the grading screening device 4 can be controlled.

[0120] Therefore, the PLC control module 5 is connected to the feeding device 1, the roller device 2, the rotary cutting granulation device 3 and the grading and screening device 4 in communication, thereby realizing the refined preparation of lithium iron phosphate and ensuring the yield and efficiency of the production product.

[0121] According to the preparation device 10 of the embodiment of the present invention, by applying the above-mentioned preparation method of lithium iron phosphate, the lithium iron phosphate raw material is homogeneously dispersed to form a preliminary slurry; the preliminary slurry is successively subjected to coarse grinding and fine grinding to form a slurry turbid liquid; the spray material is rolled and granulated; the particles after rolling and granulation are screened to screen out selected particles; the selected particles are successively filled, sintered and crushed to obtain lithium iron phosphate material; the spray material is rolled and granulated to make the spray material denser, so that the density of the formed particles is larger, so that the particle filling density is high, and a higher filling amount can be obtained, thereby increasing production capacity. After screening the particles, the selected particles whose equivalent diameter is within the preset range can be screened out. On the one hand, particles with equivalent diameters that are too large or too small can be screened out to prevent uneven reaction during the sintering process due to large differences in particle size. For example, when using too small materials or too large materials, the total surface alkali content of the lithium iron phosphate positive electrode material obtained under the same sintering process is relatively high, the discharge capacity and efficiency in the first week of 0.5C / 0.5C are relatively low, and the constant current charging ratio is low, which will reduce the production quality of the lithium iron phosphate positive electrode material. On the other hand, the equivalent diameters of the selected particles are relatively small, thereby improving the uniformity of the particles and making the product more consistent.

[0122] In some embodiments of the present invention, Figure 1 and Figure 2 As shown, the feeding device 1 includes: an elevator 11, a spray material feeding hopper 12, a first buffer device 13 and a level meter 15. The spray material feeding hopper 12 is connected to the elevator 11, and the elevator 11 is used to transport the spray material to the spray material feeding hopper 12; the first buffer device 13 is arranged below the spray material feeding hopper 12 and is connected to the spray material feeding hopper 12, and the first buffer device 13 has a first buffer bin 131 for accommodating the spray material; the level meter 15 is arranged in the first buffer bin 131, and is used to detect the height position of the spray material, and the PLC control module 5 is connected to the level meter 15 for communication.

[0123] It is understandable that the provision of the first buffer bin 131 can prevent the spray material from being excessively accumulated in the roller device 2, thereby ensuring the fluidity of the spray material in the preparation device 10 and ensuring production efficiency. The material level meter 15 is provided in the first buffer bin 131 to detect the height position of the spray material, thereby playing a role of detection and alarm, and can prevent the spray material from being excessively accumulated in the first buffer bin 131.

[0124] Furthermore, if Figure 1 and Figure 2 As shown, there is a feeder 16 between the spray material hopper 12 and the first buffer device 13, and the PLC control module 5 is communicatively connected with the feeder 16. When the level meter 15 detects that the spray material accumulates to a preset height, the signal is transmitted to the PLC control module 5. The PLC control module 5 controls the conveying speed of the feeder 16, reduces the speed at which the spray material enters the first buffer bin 131, thereby avoiding excessive accumulation of the spray material in the first buffer bin 131, ensuring the fluidity of the spray material in the preparation device 10, and ensuring production efficiency.

[0125] In some embodiments of the present invention, Figure 1 and Figure 2 As shown, the feeding device 1 further includes: a stirring device 14, which is arranged in the first buffer bin 131 and is used to stir the spray material. Thus, the spray material can be prevented from bridging in the first material buffer bin 131, further ensuring the fluidity of the spray material in the preparation device 10 and ensuring production efficiency.

[0126] In some embodiments of the present invention, Figure 1 and Figure 2As shown, the roller device 2 includes: a conveying device 21, a roller 22, a driving motor 23 and a hydraulic cylinder 24. The conveying device 21 is arranged below the feeding device 1 and connected to the feeding device 1; the roller 22 is arranged at the material output end of the conveying device 21, and there are two rollers 22, which are respectively arranged at the upper and lower sides of the material output end. The arrangement of the conveying device 21 can provide a stable conveying speed, which is conducive to ensuring the uniformity of the spray material, wherein the conveying device 21 can be a screw conveyor.

[0127] Furthermore, if Figure 1 and Figure 2 As shown, the drive motor 23 is used to drive the roller 22 to rotate around the axis of the roller 22; wherein, the output shaft of the drive motor 23 is connected to the two rollers 22 through a belt transmission, so that the drive motor 23 drives the two rollers 22 to rotate synchronously around the axis of the roller 22, and the two rollers 22 have the same rotation speed, thereby avoiding uneven rolling pressure of the upper and lower rollers 22 on the spray material.

[0128] Furthermore, if Figure 1 and Figure 2 As shown, the hydraulic cylinder 24 is connected to the roller 22, and is used to drive the two rollers 22 to move toward each other, and the PLC control module 5 is in communication connection with the hydraulic cylinder 24, the drive motor 23 and the conveying device 21. The hydraulic cylinder 24 is connected to both rollers 22, and drives the two rollers 22 to move toward each other, thereby generating pressure on the spray material, so that the spray material can be compacted, and the particle density after granulation is improved.

[0129] In some embodiments of the present invention, Figure 1 , Figure 2 , Figure 5 and Figure 6 As shown, the peeling granulation device 3 includes: a second buffer device 31 and a peeling machine 32. The second buffer device 31 is arranged below the roller device 2 and connected to the roller device 2. The second buffer device 31 has a second buffer bin 311; the peeling machine 32 is arranged below the second buffer device 31 and connected to the second buffer device 31. The PLC control module 5 is communicatively connected to the peeling machine 32, and the peeling machine 32 is provided with an excitation structure 322.

[0130] It can be understood that the setting of the second buffer bin 311 can prevent the spray material after rolling from directly entering the rotary cutter 32 and causing the rotary cutter 32 to be blocked, thereby ensuring the smooth flow of the spray material after rolling and the working efficiency of the rotary cutter 32, thereby ensuring production efficiency.

[0131] Furthermore, if Figure 1 , Figure 2 , Figure 5 and Figure 6As shown, the rotary cutter 32 has a rotatable cutting roller 321, and the cutting roller 321 includes: a roller body 3211 and a blade 3212, the blade 3212 is perpendicular to the axis of the roller body 3211, so as to reduce the residue of the spray material on the blade 3212, and the blade 3212 is a plurality of blades spaced apart along the axis direction of the roller body 3211, so as to improve the efficiency of rotary cutting and granulation.

[0132] Furthermore, if Figure 5 and Figure 6 As shown, there are multiple cutter rollers 321 spaced apart from each other. For example, in the present invention, there are two cutter rollers 321 spaced apart from each other in the up-down direction. The multiple blades 3212 on each cutter roller 321 are staggered with the multiple blades 3212 on the adjacent cutter roller 321, thereby improving the efficiency of rotary cutting and granulation.

[0133] Among them, the excitation structure 322 can be mechanical excitation, electromagnetic excitation, hydraulic excitation, etc. The excitation structure 322 can vibrate the spray material after rolling in the peeling machine 32, thereby improving the fluidity of the spray material and ensuring production efficiency. At the same time, it can also reduce the particles remaining on the cutting roller 321 of the peeling machine 32.

[0134] In some embodiments of the present invention, Figure 1 and Figure 2 As shown, a return port 312 connected to the second cache bin 311 is provided on the peripheral wall of the second cache device 31; thereby, the screened material of the first-stage screen 42 can be put in from the return port 312 and then re-rotary cut and granulated, so that the screened material of the first-stage screen 42 can be utilized, reducing production costs.

[0135] In some embodiments of the present invention, Figure 1 and Figure 2 As shown, a mirror 313 is provided on the peripheral wall of the second buffer device 31 for observing the height position of the spray material in the second buffer bin 311. It is understandable that the mirror 313 can be used to observe whether the spray material after rolling exceeds the preset height. If it exceeds the preset height, the rate at which the spray material enters the second buffer bin 311 is reduced or the rate at which the spray material enters the rotary cutter 32 is increased, thereby avoiding excessive accumulation of the spray material after rolling in the second buffer bin 311, thereby ensuring the fluidity of the spray material and ensuring production efficiency.

[0136] In some embodiments of the present invention, Figure 1 As shown, the rotary cutting granulation device 3 also includes: a connecting pipe 33, the two ends of the connecting pipe 33 are respectively connected to the second buffer device 31 and the rotary cutter 32, a control valve 34 is provided on the connecting pipe 33, and the PLC control module 5 is communicatively connected with the control valve 34.

[0137] It is understandable that the PLC control module 5 is connected to the control valve 34 in communication, so that the opening of the control valve 34 can be controlled. When there is too much spray material in the peeling machine 32, the opening of the control valve 34 can be reduced to avoid excessive accumulation of the spray material in the peeling machine 32, thereby ensuring the smoothness of the production line and the peeling performance of the peeling machine 32. When there is too much spray material in the second buffer bin 311, the opening of the control valve 34 can be increased to avoid excessive accumulation of the spray material in the second buffer bin 311, thereby ensuring the smoothness of the production line and ensuring production efficiency.

[0138] In some embodiments of the present invention, Figure 7 As shown, the rotary cutting granulation device 3 has a material outlet, and the grading screening device 4 includes: a grading screen body 41, a first-stage screen 42 and a second-stage screen, the grading screen body 41 has a screening space 411, and the grading screen body 41 has a feed port 412, a first discharge port 413, a second discharge port 414 and a third discharge port 415 that are interconnected with the screening space 411, and the first discharge port 413, the second discharge port 414 and the third discharge port 415 are sequentially arranged in the middle from top to bottom. The first-stage screen 42 and the second-stage screen are arranged in the screening space 411, and the first-stage screen 42 is arranged above the second-stage screen. The first-stage screen 42 and the second-stage screen divide the screening space 411 into a first screening area, a second screening area and a third screening area from top to bottom. The first discharge port 413 is connected to the first screening area, the second discharge port 414 is connected to the second screening area, and the third discharge port 415 is connected to the third screening area.

[0139] It can be understood that the first-stage screen 42 is arranged above the second-stage screen, and the aperture of the first-stage screen 42 is larger than the aperture of the second-stage screen. The particles after rolling and granulation will first fall on the first-stage screen 42, and the screened material (larger particles) of the first-stage screen 42 will come out from the first discharge port 413 and return to the rotary cutting granulation device 3 for re-granulation, so as to realize the recycling of the screened material of the first-stage screen 42; the screened material of the first-stage screen 42 will fall on the second-stage screen, and the screened material of the second-stage screen, i.e., the selected particles, can come out from the second discharge port 414, and be successively potted, sintered and crushed to obtain lithium iron phosphate material; and the screened material (smaller particles) of the second-stage screen will come out from the third discharge port 415, and then be put into the feeding device 1 for re-rolling and granulation, so as to realize the recycling of the screened material of the second-stage screen. In this way, the particles after rolling and granulation are screened and the selected particles are screened out.

[0140] Furthermore, if Figure 8As shown, a vibration device 44 is provided on the grading screen body 41, and the vibration device 44 is used to vibrate the grading screen body 41, thereby improving the screening effect and screening efficiency. Among them, the vibration device 44 can be a vibration motor, etc., and the vibration device 44 is connected to the PLC control module 5 in communication, so that the PLC control module 5 can control the vibration frequency of the vibration device 44, etc., to better improve the screening effect and screening efficiency.

[0141] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0142] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing lithium iron phosphate, characterized in that: include: homogenously dispersing the lithium iron phosphate raw material to form a preliminary slurry; The preliminary slurry is subjected to coarse grinding and fine grinding in sequence to form a slurry turbid liquid; The slurry turbid liquid is spray-dried to form a spray material; Rolling and granulating the spray material; Screening the particles after rolling and granulation to select the particles; The selected particles are successively potted, sintered and crushed to obtain lithium iron phosphate material.

2. The method for preparing lithium iron phosphate according to claim 1, characterized in that: Screening of the granules after rolling and granulation includes: The particles after rolling and granulation are passed through a first-stage sieve and a second-stage sieve in sequence, wherein the sieve hole diameter of the first-stage sieve is larger than the sieve hole diameter of the second-stage sieve, and the sieve-surface material of the second-stage sieve is taken as the selected particles.

3. The method for preparing lithium iron phosphate according to claim 2, characterized in that: The preparation method of the lithium iron phosphate further includes: The screened material of the second-stage screen is further rolled and granulated; And / or, the method for preparing lithium iron phosphate further comprises: The material on the first-stage screen is granulated again.

4. The method for preparing lithium iron phosphate according to claim 2, characterized in that: The mesh diameter of the first-stage sieve is 4-5 mm; And / or, the mesh diameter of the second-stage sieve is 1-2 mm; and / or, the mesh diameter of the first-stage sieve is 2-4 mm larger than the mesh diameter of the second-stage sieve; And / or, the mesh size of the first-stage screen is 2-5 meshes; And / or, the mesh size of the second-stage screen is 10-20 meshes.

5. The method for preparing lithium iron phosphate according to claim 1, characterized in that: Rolling the spray material comprises: The spray material is delivered through a feeding device; The delivered spray material is rolled by a roller, the roller is driven to rotate by a driving motor, and the pressure of the roller is provided by a hydraulic cylinder.

6. The method for preparing lithium iron phosphate according to claim 5, characterized in that: The frequency of the driving motor is 25-35 Hz; And / or, the feeding frequency of the feeding device is P1, the frequency of the driving motor is P2, P1:P2=0.5-2.0; And / or, the pressure provided by the hydraulic cylinder for rolling the rollers is 10-15 MPa.

7. The method for preparing lithium iron phosphate according to claim 5, characterized in that: The outer peripheral wall of the roller is provided with a groove extending along the axis direction of the roller.

8. The method for preparing lithium iron phosphate according to claim 7, characterized in that: Along the radial inward direction of the roller, the groove width of the groove gradually decreases; And / or, the grooves are multiple and are arranged at equal intervals along the circumference of the roller; And / or, the depth of the groove is 4-8 mm.

9. The method for preparing lithium iron phosphate according to any one of claims 1 to 8, characterized in that: Granulating the spray material comprises: The spray material after rolling is cut and granulated by a cutter roller, and the rotation speed of the cutter roller is 300-500RPM.

10. The method for preparing lithium iron phosphate according to claim 1, characterized in that: The temperature of the selected particles during sintering is 750-850°C; And / or, the selected particles have a sintering time of 20-24 hours.

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