A method for preparing lithium iron phosphate and a mixing and pulverizing device

Abstract

The present application provides a method for preparing lithium iron phosphate and a hybrid pulverizing device, comprising the following steps: S1: Mixing the raw materials for preparing the precursor in a predetermined ratio; S2: Feeding the mixed raw materials into the hybrid pulverizing device for pulverization treatment; wherein, the hybrid pulverizing device includes a vertically arranged housing and a classification wheel rotatably arranged coaxially inside it; S3: Feeding the pulverized materials into a homogenizing device for re-mixing to obtain a precursor; S4: Feeding the precursor into a calciner for calcination treatment, and the calcination temperature is 500°C to 800°C; S5: Pulverizing and classifying the calcined precursor to obtain the finished lithium iron phosphate powder. This solution can effectively reduce production energy consumption and improve production efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of raw materials for lithium batteries, and particularly relates to a method for preparing lithium iron phosphate and a mixing and grinding device. Background Art

[0002] Since the emergence of lithium-ion battery materials, their high capacity and renewable characteristics have enabled people to see the prospects of new energy in the new century. As a cathode material with high safety, good cycle performance, and environmental friendliness, lithium iron phosphate has always been a popular research object in the lithium battery industry, and its application fields involve various commercial vehicle batteries, energy storage base stations, and many electrical equipment.

[0003] In the prior art, there is a method for preparing lithium iron phosphate powder by using a wet process. The process mainly includes raw material preparation, wet grinding, spray drying, calcination, grinding and other processes. In the spray drying process of preparing lithium iron phosphate by the wet process, hot air quickly removes the moisture in the droplets, so that the droplets are dried into solid particles in a short time. The inlet air temperature of the hot air in this process is generally 200°C - 250°C, and the energy consumption for heating the air to this temperature is extremely high. Summary of the Invention

[0004] To solve the deficiencies of the prior art, the present invention provides a method for preparing lithium iron phosphate and a mixing and grinding device, which can effectively reduce production energy consumption and improve production efficiency.

[0005] In order to achieve the purpose of the present invention, the following scheme is proposed:

[0006] A method for preparing lithium iron phosphate includes the following steps:

[0007] S1: Mix the raw materials for preparing the precursor in a predetermined ratio;

[0008] S2: Feed the mixed raw materials into a mixing and grinding device for grinding; wherein, the mixing and grinding device includes a vertically arranged shell and a classification wheel coaxially rotating inside it;

[0009] When grinding, the precursor mixed raw materials are coaxially fed from the feed pipe at the top of the shell, and the upper nozzles arranged along the circumference at the upper end of the shell perform the first grinding on the raw materials; part of the materials directly fall through the middle of the classification wheel below the upper nozzles, and the lower nozzles arranged along the circumference at the lower end of the shell perform grinding on the falling materials;

[0010] After grinding, the qualified powder is sucked through the blades of the classification wheel under the suction of the negative pressure pipe arranged on the side wall of the shell and discharged through the negative pressure pipe.

[0011] S3: Feed the ground materials into a homogenizing device for re-mixing to obtain the precursor.

[0012] S4: Feed the precursor into a calciner for calcination at a temperature of 500°C to 800°C.

[0013] S5: Crush and classify the calcined precursor to obtain the finished lithium iron phosphate powder.

[0014] A mixing and crushing device is used to perform the crushing process in step S2 of the above lithium iron phosphate preparation method;

[0015] The mixing and crushing device includes a vertically arranged housing and a classification wheel rotatably arranged coaxially inside it;

[0016] During crushing, the precursor mixed raw material is coaxially fed into the housing from the feed pipe at the top of the housing, and the upper nozzles arranged along the circumference at the upper end of the housing perform the first crushing on the raw material; part of the material directly falls through the middle of the classification wheel below the upper nozzles, and the lower nozzles arranged along the circumference at the lower end of the housing perform crushing on the falling material;

[0017] After crushing, the powder with qualified particle size passes through the blades of the classification wheel under the suction of the negative pressure pipe arranged on the side wall of the housing and is discharged through the negative pressure pipe.

[0018] The beneficial effects of the present invention are as follows: In the traditional wet method for preparing lithium iron phosphate, spray drying is required. Spray drying quickly removes the moisture in the droplets by hot air, so that the droplets are dried into solid particles in a short time. This process consumes a large amount of energy to heat the air to a predetermined temperature. This solution replaces wet grinding and spray drying with a dry mixing and crushing method, which can effectively reduce energy consumption; and this solution mixes and crushes the raw materials simultaneously, reducing the complicated processes of separately crushing the raw materials, which helps to improve production efficiency. Brief Description of the Drawings

[0019] The drawings described herein are only for illustrating the selected embodiments, not all possible implementation schemes, and are not intended to limit the scope of the present invention.

[0020] Figure 1 Shows a flowchart of the lithium iron phosphate preparation method of the present application.

[0021] Figure 2 Shows an external structural schematic diagram of the mixing and crushing device used in step S2.

[0022] Figure 3 Shows a structural sectional view of the mixing and crushing device used in step S2.

[0023] Figure 4 Shows a preferred structural schematic diagram of the classification wheel used in step S2.

[0024] Markings in the figure: housing - 1, feed pipe - 11, negative pressure pipe - 12, grading wheel - 2, annular chamber - 201, upper ring - 21, lower ring - 22, material suction hole - 221, baffle - 222, funnel - 23, strip hole - 231, gear ring - 24, upper nozzle - 3, lower nozzle - 4, motor - 5. Detailed implementation mode

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following describes the implementation modes of the present invention in detail with reference to the accompanying drawings. However, the embodiments described herein are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0026] Example 1, as Figure 1 shown, a method for preparing lithium iron phosphate includes the following steps:

[0027] S1: Mix the raw materials for preparing the precursor in a predetermined ratio.

[0028] S2: Feed the mixed raw materials into a mixing and grinding device for grinding; the raw materials for the precursor mainly include a lithium source, a phosphorus source, an iron source, a carbon source, and various additives, etc. Using the same mixing device to grind the mixed raw materials simultaneously can not only effectively improve the preparation efficiency of lithium iron phosphate and reduce the energy consumed by the grinding process, but also mix the ground materials in this way; the traditional dry method for preparing lithium iron phosphate is to first grind various raw materials and then mix them. The separate grinding process is not only more complex but also has higher energy consumption. The mixing and grinding device used in this step is a jet mill or a steam mill. In this step, the particle size of the ground material is 0.4μm to 0.6μm.

[0029] S3: Feed the ground material into a homogenizing device for re - mixing to obtain the precursor. This mixing is the third mixing in the whole preparation process, effectively ensuring the uniformity of the mixing of various raw materials in the precursor. The homogenizing device is a stirred mill or other equipment that can play a role in uniform mixing of materials.

[0030] S4: Feed the precursor into a calciner for calcination, the calcination temperature is 500°C to 800°C, and the calciner is one of a rotary kiln or a fluidized bed rapid calciner.

[0031] S5: Grind and classify the calcined precursor to obtain the finished lithium iron phosphate powder. Specifically, in this step, a jet mill is used to grind the calcined precursor, and a dust collector is used to collect the ground powder.

[0032] This solution replaces wet grinding and spray drying with a dry - mixing and grinding method, which can greatly reduce energy consumption.

[0033] As a further preferred solution, the waste heat in the calcination process is used to heat compressed air, and the heated compressed air is used as the medium of the jet mill to crush materials. This can not only improve the crushing kinetic energy of the energy-efficient mill, but also preheat the materials in the current crushing stage, reduce the moisture content of the materials, and thus reduce the energy consumption of the calcination process.

[0034] Example 2, as Figures 2 to 4 shown, the hybrid crushing device includes a vertically arranged housing 1 and a classification wheel 2 rotatably arranged coaxially inside it.

[0035] Specifically, a plurality of upper nozzles 3 are arranged in a circumferential array above the classification wheel 2 of the housing 1, and a plurality of lower nozzles 4 are arranged in a circumferential array below the classification wheel 2. Both the upper nozzles 3 and the lower nozzles 4 are used to crush the mixed precursor raw materials. Specifically, the intersection points of the axes of the plurality of upper nozzles 3 and the intersection points of the axes of the plurality of lower nozzles 4 both pass through the axis of the housing 1. A feed pipe 11 is coaxially arranged at the top of the housing 1 for adding the mixed precursor raw materials into the interior of the housing 1.

[0036] A negative pressure pipe 12 communicating with the annular chamber 201 is provided on the side wall of the housing 1. The negative pressure pipe 12 is connected to a negative pressure device for generating suction inside the housing 1 so that qualified materials can smoothly enter the negative pressure pipe 12.

[0037] A gear ring 24 is coaxially arranged at the upper end of the classification wheel 2. A through hole is formed in the side wall of the housing 1, and a gear meshing with the gear ring 24 is provided outside the housing 1 corresponding to the through hole. The gear is driven by a motor 5.

[0038] Specifically, in step S2 of Example 1, the mixed raw materials are simultaneously crushed using the hybrid crushing device described in the example. The specific process is as follows:

[0039] During crushing, the precursor mixed raw materials are coaxially fed from the feed pipe 11 at the top of the housing 1, and the upper nozzles 3 arranged circumferentially at the upper end of the housing 1 perform the first crushing on the raw materials; some of the materials directly pass through the middle of the classification wheel 2 below the upper nozzles 3 and fall down, and the lower nozzles 4 arranged circumferentially at the lower end of the housing 1 crush the falling materials.

[0040] After crushing, the powder with qualified particle size passes through the blades of the classification wheel 2 under the suction of the negative pressure pipe 12 arranged on the side wall of the housing 1 and is discharged through the negative pressure pipe 12.

[0041] Since the precursor mixed raw materials include various materials with different textures and particle sizes, after the mixed raw materials are put into the mixing and pulverizing equipment, most of the materials can collide with each other under the action of the high-pressure air flow of the upper nozzle 3, so as to achieve the pulverizing effect. For the pulverized materials, those with qualified particle sizes will pass through the blades of the classification wheel 2 under the suction force generated by the negative pressure pipe 12 and be discharged smoothly from the negative pressure pipe 12, while the unqualified materials with larger particle sizes will fall through the middle of the classification wheel 2; there is also another part of the materials, which will directly fall from the middle of the classification wheel 2 because of their large density or too fast falling speed, resulting in that this part of the materials has no time to be pulverized at the upper nozzle 3; but no matter which kind of materials falling from the middle of the classification wheel 2; the materials falling from the classification wheel 2 will be pulverized by the lower nozzle 4 below, so as to improve the material pulverizing efficiency, and all the falling materials will be completely pulverized under the action of the lower nozzle 4, avoiding partial materials depositing at the bottom of the housing 1 and causing deviation in the proportion of the precursor mixture.

[0042] Preferably, in step S2, the used classification wheel 2 includes an upper ring 21 and a lower ring 22 coaxially arranged with the housing 1 as shown in Figure 3 , Figure 4 . A plurality of blades are arranged in a circumferential array between the inner circles of the upper ring 21 and the lower ring 22, the distance between adjacent blades is the same, and an annular chamber 201 is formed between the outer side of the blades and the inner wall of the housing 1 and between the upper ring 21 and the lower ring 22. The negative pressure pipe 12 is communicated with the annular chamber 201.

[0043] Preferably, the blades of the classification wheel 2 form an inverted conical hole structure. In step S2, the materials falling from above the classification wheel 2 as shown in Figure 3 , Figure 4 fall through the inverted conical holes formed by the blades of the classification wheel 2; the classification wheel 2 in this solution not only increases the contact area between the materials falling from above and the classification wheel 2, making it easier for the materials above to participate in the classification process of the classification wheel 2, but also can make the materials falling from the middle of the classification wheel 2 more concentrated towards the axis of the equipment, improving the pulverizing effect of the lower nozzle 4 on the materials. At the same time, this structural design makes the lower ring 22 have a larger width dimension, which is convenient for arranging the suction holes 221.

[0044] Preferably, as shown in Figure 3 , Figure 4 , the lower ring 22 is of an annular plate structure, and a plurality of suction holes 221 are arranged in a circumferential array on it. The suction holes 221 are communicated with the annular chamber 201. In step S2, the materials with qualified particle sizes pulverized by the lower nozzle 4 enter the annular chamber 201 through the suction holes 221 opened on the lower ring 22. This solution can increase the channels for the materials below the classification wheel 2 to enter the negative pressure pipe 12 and improve the classification efficiency of the materials pulverized by the lower nozzle 4.

[0045] Preferably, asFigure 4 As shown, a funnel 23 is coaxially arranged below the classification wheel 2, and the axis convergence point of the lower nozzle 4 is on the axis of the funnel 23. In step S2, the material falling from the middle of the classification wheel 2 is converged at the axis convergence point of the lower nozzle 4 under the action of the funnel 23 coaxially arranged below the classification wheel 2. This solution uses the funnel 23 to gather the material falling from the classification wheel 2, so that the falling material falls more concentratedly within the crushing area formed by the lower nozzle 4, so as to improve the crushing effect of the lower nozzle 4 on the material.

[0046] Further preferably, as Figure 4 shown, strip-shaped holes 231 are provided on the side wall of the funnel 23. In step S2, among the materials falling from the middle of the classification wheel 2, the materials with qualified particle sizes are transferred to below the lower ring 22 through the strip-shaped holes 231 provided on the side wall of the funnel 23, and enter the annular chamber 201 through the material suction holes 221. Specifically, as Figure 3 , Figure 4 shown, the strip-shaped holes 231 are arranged in the horizontal direction, and the extending direction of the strip-shaped holes 231 faces the lower end of the axis of the funnel 23. This structural design enables the materials with qualified particle sizes in the materials falling from the classification wheel 2 to pass through the strip-shaped holes 231 and move smoothly below the lower ring 22. In this way, this part of the qualified materials can smoothly enter the annular chamber 201 through the material suction holes 221, thereby reducing the workload of the lower nozzle 4 and preventing the lower nozzle 4 from further refining the materials with qualified particle sizes and resulting in extremely fine materials; and setting the strip-shaped holes 231 horizontally and limiting their extending direction aims to prevent large-particle materials from being discharged out of the strip-shaped holes 231 and affecting the smooth entry of large-particle materials into the crushing area of the lower nozzle 4. Moreover, the strip-shaped holes 231 arranged in this structure are more conducive to the suction force generated by the negative pressure pipe 12 to form a streamlined material suction trajectory through the strip-shaped holes 231 and the material suction holes 221, so that the materials with qualified particle sizes are more likely to pass through the strip-shaped holes 231 and the material suction holes 221 under the action of the suction force and enter the annular chamber 201.

[0047] Preferably, as Figure 3 , Figure 4 shown, a plurality of baffle plates 222 are arranged in a circumferential array on the bottom surface of the lower ring 22, and the perpendicular line of the side facing the rotation direction of the classification wheel 2 faces the crushing area formed by the lower nozzle 4. By providing the baffle plates 222, the materials lifted below can be slapped again into the crushing area of the lower nozzle 4, improving the crushing efficiency, and the airflow formed when the baffle plates 222 rotate can prevent the lifted materials from gathering below the lower ring 22.

[0048] Preferably, a hopper is provided above the feed pipe 11. A stirring shaft is provided inside the hopper. A stirring paddle is provided at the upper end of the stirring shaft. A spiral push plate is provided on the outer wall of the lower end of the stirring shaft. The spiral push plate penetrates into the feed pipe 11. The stirring paddle is driven by a driving motor. With this structural design, various raw materials can be directly added into the hopper, and the hopper is used to mix the raw materials. Or the mixed raw materials are put into the hopper, and the stirring shaft in the hopper is used to continuously stir and mix the raw materials, so that the raw materials are in a uniform mixed state when they are put into the housing 1. Moreover, during feeding, the spiral push plate can be used to control the falling speed of the raw materials to avoid excessive concentration of the raw materials during falling.

[0049] The above are only the preferred embodiments of the present invention and do not represent the only or limiting the present invention. Those skilled in the art should understand that various changes or equivalent replacements made to the present invention without departing from the scope of the present invention all fall within the scope of protection of the present invention.

Claims

1. A hybrid grinding device, characterized in that, It includes a vertically arranged housing (1) and a classification wheel (2) rotatably arranged coaxially inside it; During pulverization, the precursor mixed raw materials are coaxially fed from the feed pipe (11) at the top of the housing (1). The upper nozzles (3) arranged along the circumference at the upper end of the housing (1) perform the first pulverization on the raw materials; part of the materials directly pass through the middle of the classification wheel (2) below the upper nozzles (3) and fall down. The lower nozzles (4) arranged along the circumference at the lower end of the housing (1) perform the second pulverization on the falling materials; After pulverization, the qualified powder with the required particle size passes through the blades of the classification wheel (2) under the suction of the negative pressure pipe (12) arranged on the side wall of the housing (1) and is discharged through the negative pressure pipe (12); The classification wheel (2) includes an upper ring (21) and a lower ring (22) arranged coaxially with the housing (1). A plurality of blades are arranged in a circumferential array between the inner circles of the upper ring (21) and the lower ring (22). An annular chamber (201) is formed between the outer sides of the blades and the inner wall of the housing (1) as well as between the upper ring (21) and the lower ring (22). The negative pressure pipe (12) is communicated with the annular chamber (201); The blades of the classification wheel (2) form an inverted conical hole structure, and a material suction hole (221) communicated with the annular chamber (201) is also arranged on the lower ring (22); A funnel (23) is arranged coaxially below the classification wheel (2), and the axis convergence point of the lower nozzles (4) is on the axis of the funnel (23); Strip-shaped holes (231) are formed in the side wall of the funnel (23). Among them, the strip-shaped holes (231) are arranged in the horizontal direction, and the extending direction of the strip-shaped holes (231) faces the lower end of the axis of the funnel (23).

2. The hybrid grinding device according to claim 1, characterized in that, A plurality of baffle plates (222) are arranged in a circumferential array on the bottom surface of the lower ring (22), and the vertical line on the side facing the rotation direction of the classification wheel (2) faces the pulverization area formed by the lower nozzles (4).

3. A method for preparing lithium iron phosphate, characterized in that, It is realized by using the hybrid pulverization equipment according to any one of claims 1 to 2. The preparation method includes the following steps: S1: Mix the raw materials for preparing the precursor in a predetermined proportion; S2: Feed the mixed raw materials into the said hybrid pulverization equipment for pulverization treatment; S3: Feed the pulverized materials into a homogenizing device for re-mixing to obtain a precursor; S4: Feed the precursor into a calciner for calcination treatment, and the calcination temperature is 500°C to 800°C; S5: Perform pulverization and classification treatment on the calcined precursor to obtain the finished lithium iron phosphate powder.

4. The preparation method of lithium iron phosphate according to claim 3, wherein, In step S5, a jet mill is used to perform pulverization treatment on the calcined precursor, and a dust collector is used to collect the pulverized powder.

5. A method for preparing lithium iron phosphate according to claim 4, characterized in that, In step S2, the particle size of the pulverized materials is 0.4μm to 0.6μm.

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