A lithium iron phosphate precursor ultrafine grinding method and device

Abstract

This invention provides a method and equipment for ultrafine grinding of lithium iron phosphate precursor. The method includes the following steps: adding raw materials and additives to a continuous dry grinding system to obtain powder; drawing the powder and water into a continuous liquid-solid mixing and dispersion device to obtain a premixed slurry; and sending the premixed slurry to a continuous ultrafine grinding system to obtain the target slurry. The equipment used incorporates wire mesh packing and employs a sand mill, with ultrasonic devices installed on the grinding rod pins of the sand mill. This method allows for continuous operation, high production efficiency, narrow precursor particle size distribution, and low energy consumption, making it suitable for large-scale industrial continuous production.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, specifically relating to a method and equipment for ultrafine grinding of lithium iron phosphate precursor. Background Technology

[0002] Currently, the energy density of lithium iron phosphate batteries has been significantly improved, making up for their shortcomings and accelerating their application in passenger vehicles.

[0003] The mainstream lithium iron phosphate (LFP) production process currently on the market involves obtaining a precursor through ultrafine grinding, followed by high-temperature sintering to form LFP. The yield of the high-temperature sintering reaction and the stability of the LFP product largely depend on the particle size and particle size distribution of the precursor. A precursor particle size D50 of 100nm-200nm (which can vary within this range depending on the application of the LFP product) and a particle size distribution range <1 generally result in high-quality LFP products.

[0004] In recent years, the energy consumption required in the grinding stage has accounted for approximately 35% of the entire lithium iron phosphate production process. In order to reduce costs and increase efficiency, finding new and efficient ultrafine grinding processes has become a current research focus.

[0005] The existing grinding process for lithium iron phosphate precursors is intermittent wet grinding: materials and water are intermittently mixed (about 2-3 hours) to prepare a premixed slurry, and the premixed slurry is intermittently ground several times (about 6-8 hours) to obtain the product. This grinding method is time-consuming, has low production capacity, produces precursors with a wide particle size distribution (span of about 1.5-3), and has high energy consumption (energy consumption per ton of product is about 400-500 kWh).

[0006] In summary, the urgent needs in this field are to solve the problems of production efficiency and energy consumption in grinding processes, as well as the problem of preparing precursors with narrow particle size distribution. Summary of the Invention

[0007] To address the problems existing in the prior art, one of the objectives of this invention is to provide an ultrafine grinding method for lithium iron phosphate precursors. This method is a continuous operation with high production efficiency, narrow precursor particle size distribution (span < 1), and low energy consumption (energy consumption per ton of product is approximately 200-280 kW·h), making it suitable for large-scale industrial continuous production.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for ultrafine grinding of lithium iron phosphate precursor, the method comprising the following steps:

[0010] S1: Add raw materials and additives to a continuous dry grinding system to obtain powder;

[0011] S2: The powder and water are drawn into a continuous liquid-solid mixing and dispersing device to obtain a premixed slurry;

[0012] S3: The premixed slurry is fed into a continuous ultrafine grinding system to obtain the target slurry;

[0013] In S2, the equipment uses built-in wire mesh filler, and in S3, a sand mill is used, with the grinding rod pin of the sand mill equipped with an ultrasonic device.

[0014] In one embodiment of the present invention, the D50 of the raw materials and additives in S1 is 10-100 μm.

[0015] In one embodiment of the present invention, the raw materials in S1 are iron phosphate and lithium carbonate.

[0016] In one embodiment of the present invention, the adjuvant in S1 is an organic carbon source, preferably maltose and / or sucrose.

[0017] In one embodiment of the present invention, S1 employs a dry stirring ball mill; preferably, the mass ratio of grinding media to material is (2-15):1.

[0018] In one embodiment of the present invention, the D50 of the powder obtained in S1 is 2-5 μm.

[0019] In this invention, dry grinding is employed in step S1, and the process is continuous. In this grinding method, the energy of the grinding media acts directly on the material itself, resulting in lower grinding energy consumption.

[0020] In this invention, the heat transfer coefficient is improved by directly contacting the cold grinding media with the solid material. An ultrasonic vibrating screen is installed at the outlet of the stirred ball mill. The ground material enters the downstream system, and the grinding media enters the hopper and is transported to the inlet of the stirred ball mill by cold air (fresh air is heat exchanged through a finned tube heat exchanger and chilled water). A dust collector is installed on the top of the equipment, and the gas is discharged directly into the atmosphere after dust removal.

[0021] In one embodiment of the present invention, the solid content of the premixed slurry in S2 is 10wt%-60wt%.

[0022] In one embodiment of the present invention, S2 employs a continuous solid-liquid mixing and dispersion device. The internal structure of the device consists of an impeller at the front stage, followed by a homogenizing dispersion disc, a wire mesh packing, and another homogenizing dispersion disc in sequence. All internal components are connected by a main shaft.

[0023] In this invention, the impeller rotation of S2 generates negative pressure, which can uniformly draw powder and water into the equipment. Because the equipment is equipped with a loss-in-weight scale on the powder feed line and a flow regulating valve on the water feed line, it can quantitatively draw in powder and water to prepare a slurry with a specific solid content. The series connection of the dispersing disc and the packing material allows for rapid mixing of solid and liquid materials into a uniform slurry state. The wire mesh packing is composed of corrugated plates, and baffles are installed on the packing material, with an angle of 60-120° between the baffles and the packing material. The packing material shears the liquid into a liquid film, increasing the solid-liquid contact area, and achieving a mixing uniformity of up to 99.5%.

[0024] In one embodiment of the present invention, a slurry with a D50 of 100nm-200nm is obtained in S3, and the particle size range is <1.

[0025] In one embodiment of the present invention, a semi-circular protrusion is provided on the surface of the pin in S3 to increase the contact area between the pin and the grinding medium; preferably, the radius of the semi-circular protrusion is 0.3cm-1cm.

[0026] In one embodiment of the present invention, the frequency of the ultrasonic device in S3 is 30kHz-70kHz.

[0027] In this invention, S3 employs a series operation of four to six sand mills. The first-stage sand mill yields a slurry with a D50 of 0.8-1 μm, the second-stage sand mill yields a slurry with a D50 of 0.4-0.5 μm, the third-stage sand mill yields a slurry with a D50 of 0.25-0.3 μm, the fourth-stage sand mill yields a slurry with a D50 of 0.18-0.25 μm, the fifth-stage sand mill yields a slurry with a D50 of 0.13-0.18 μm, and the sixth-stage sand mill yields a slurry with a D50 of 0.1-0.13 μm.

[0028] In this invention, the grinding material in the sand mill in S3 will experience a temperature rise. In order to prevent the material from deteriorating at high temperatures, a slurry heat exchanger is installed at the inlet of each stage of the sand mill to control the temperature inside the grinding chamber below 40°C.

[0029] In this invention, a specially structured sand mill is used in step S3. Several grinding rods of the sand mill are equipped with ultrasonic devices, and the surfaces of the rods have semi-circular protrusions to increase the contact area between the rods and the grinding media. The semi-circular protrusions on the rod surfaces allow the grinding media to acquire higher kinetic energy, resulting in better grinding performance. Furthermore, due to the synergistic effect of the ultrasonic waves during the grinding process, the specified grinding particle size can be achieved within a shorter residence time.

[0030] Another object of the present invention is to provide an apparatus for ultrafine grinding of lithium iron phosphate.

[0031] An apparatus for ultrafine grinding of lithium iron phosphate, the apparatus being used in the above-mentioned preparation method, the apparatus comprising a continuous dry grinding section, a continuous mixing and slurry preparation section, and a continuous ultrafine grinding section; wherein, the grinding rod pins of the sand mill in the continuous ultrafine grinding section are equipped with ultrasonic devices; wherein, after being processed in the continuous dry grinding section, the material enters the continuous mixing and slurry preparation section to obtain a premixed slurry, and the slurry is pumped to the continuous ultrafine grinding section for grinding.

[0032] In one embodiment of the present invention, the continuous dry grinding section uses a dry stirred ball mill to grind the material.

[0033] In one embodiment of the present invention, the outlet of the dry stirring ball mill is equipped with a vibrating screen to separate the grinding media and materials.

[0034] In one embodiment of the present invention, the continuous mixing and pulping section employs a continuous solid-liquid mixing and dispersion device, the internal structure of which is an impeller at the front stage, followed by a homogenizing dispersion disc, a wire mesh packing, and another homogenizing dispersion disc in sequence; preferably, the wire mesh packing is composed of corrugated plates, and a baffle is provided on the packing, with the baffle and the packing having an angle of 60-120°.

[0035] In one embodiment of the present invention, the continuous ultrafine grinding section adopts 4-6 stages of sand mills connected in series, and a slurry heat exchanger is provided at the inlet of each stage of sand mill.

[0036] Another object of the present invention is to provide an ultrafine ground lithium iron phosphate precursor.

[0037] An ultrafine ground lithium iron phosphate precursor, wherein the lithium iron phosphate precursor is prepared by the above-described preparation method or by the above-described equipment, and the average particle size of the lithium iron phosphate precursor is 100nm-200nm, with a particle size range of <1.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) The precursor obtained by this invention has a particle size D50 of 100-200nm and a narrow particle size distribution (span <1).

[0040] (2) The present invention has low energy consumption, with an energy consumption of about 200-280 kw·h per ton of product, making it economical and practical. Attached Figure Description

[0041] Figure 1 A schematic diagram of the ultrafine grinding process for lithium iron phosphate precursor;

[0042] Figure 2 This is a schematic diagram of the internal structure of a continuous solid-liquid mixing and dispersion device.

[0043] Figure 3This is a schematic diagram of the packing structure for a continuous solid-liquid mixing and dispersion device.

[0044] Figure 4 This is a schematic diagram of the packing structure for a continuous solid-liquid mixing and dispersion device.

[0045] Figure 5 This is a schematic diagram of the inner cylinder structure of a sand mill;

[0046] Figure 6 This is a schematic diagram of the pin structure of a sand mill. Detailed Implementation

[0047] Raw material information:

[0048]

[0049]

[0050] Note: Iron phosphate and lithium carbonate are insoluble in water, while maltose and sucrose are soluble in water.

[0051] Analytical characterization instruments:

[0052] Malvern laser particle size analyzer (manufacturer: Malvern, model: Mastersizer 3000+), halogen moisture analyzer (manufacturer: Mettler Toledo, model: HS153)

[0053] Analytical characterization methods:

[0054] The particle size distribution of the material was tested using a Malvern laser particle size analyzer, and the moisture content of the material was tested using a halogen moisture analyzer.

[0055] Span = (D90 - D10) / D50

[0056] Equipment 1: A dry-mixed ball mill (with a vibrating screen at the outlet to separate the grinding media and materials), a continuous solid-liquid mixing and dispersing device 1 (internal structure: initial stage is an impeller, followed by a homogenizing dispersion disc, wire mesh packing, and another homogenizing dispersion disc; the wire mesh packing is composed of corrugated plates, and baffles are installed on the packing with an angle of 60° between the baffles and the packing), and a sand mill 1 (four-stage sand mills connected in series; the grinding rod pins have semi-circular protrusions with a radius of 0.3cm on the surface, and an ultrasonic device with a frequency of 70kHz is installed inside; each stage of the sand mill has a slurry heat exchanger at the inlet). After being processed by the dry-mixed ball mill, the material enters the continuous solid-liquid mixing and dispersing device 1 to form a premixed slurry, which is then ground by the sand mill 1 to obtain the target product.

[0057] Equipment 2: Employs a dry-mixed ball mill (with a vibrating screen at the outlet to separate the grinding media and materials), a continuous solid-liquid mixing and dispersing device 2 (its internal structure consists of an impeller at the front, followed by a homogenizing disc, wire mesh packing, and another homogenizing disc; the wire mesh packing is composed of corrugated plates, and baffles are installed on the packing with an angle of 120° between the baffles and the packing), and a sand mill 2 (six-stage sand mills connected in series; the grinding rods have semi-circular protrusions with a radius of 1cm on their surface, and an internal ultrasonic device with a frequency of 30kHz; each stage of the sand mill has a slurry heat exchanger at its inlet). After being processed by the dry-mixed ball mill, the material enters the continuous solid-liquid mixing and dispersing device 2 to form a premixed slurry, which is then ground by the sand mill 2 to obtain the target product.

[0058] Example 1

[0059] Ferric phosphate (D50 = 10 μm), lithium carbonate (D50 = 50 μm), maltose (D50 = 70 μm), and sucrose (D50 = 100 μm) were added to equipment one for ultrafine grinding. In the dry stirred ball mill, the mass ratio of grinding media to materials was 15:1, and the resulting dry powder had a D50 of 2 μm.

[0060] The dry powder material is then mixed with water to make a slurry. The premixed slurry at the outlet of the continuous solid-liquid mixing and dispersion equipment has a solid content of 30 wt%.

[0061] The slurry then enters a sand mill for grinding. The D50 of the slurry at the outlet of the first-stage sand mill is 0.9μm, the D50 of the slurry at the outlet of the second-stage sand mill is 0.4μm, the D50 of the slurry at the outlet of the third-stage sand mill is 0.28μm, and the D50 of the slurry at the outlet of the fourth-stage sand mill is 0.18μm, with a span of 0.6.

[0062] The energy consumption per ton of product in this process is approximately 230 kWh.

[0063] Example 2

[0064] Ferric phosphate (D50 = 90 μm), lithium carbonate (D50 = 20 μm), maltose (D50 = 20 μm), and sucrose (D50 = 50 μm) were added to equipment two for ultrafine grinding. In the dry stirred ball mill, the mass ratio of grinding media to materials was 3:1, and the resulting dry powder had a D50 of 5 μm.

[0065] The dry powder material is then mixed with water to make a slurry. The premixed slurry at the outlet of the continuous solid-liquid mixing and dispersion equipment has a solid content of 15 wt%.

[0066] The slurry then enters a sand mill for grinding. The D50 of the slurry at the outlet of the first-stage sand mill is 1 μm, the D50 of the slurry at the outlet of the second-stage sand mill is 0.47 μm, the D50 of the slurry at the outlet of the third-stage sand mill is 0.3 μm, the D50 of the slurry at the outlet of the fourth-stage sand mill is 0.23 μm, the D50 of the slurry at the outlet of the fifth-stage sand mill is 0.15 μm, and the D50 of the slurry at the outlet of the sixth-stage sand mill is 0.1 μm, with a span of 0.7.

[0067] The energy consumption per ton of product in this process is approximately 270 kWh.

[0068] Example 3

[0069] Ferric phosphate (D50 = 50 μm), lithium carbonate (D50 = 90 μm), maltose (D50 = 50 μm), and sucrose (D50 = 20 μm) were added to equipment one for ultrafine grinding. In the dry stirred ball mill, the mass ratio of grinding media to materials was 10:1, and the resulting dry powder had a D50 of 3 μm.

[0070] The dry powder material is then mixed with water to make a slurry. The premixed slurry at the outlet of the continuous solid-liquid mixing and dispersion equipment has a solid content of 60 wt%.

[0071] The slurry then enters a sand mill for grinding. The D50 of the slurry at the outlet of the first-stage sand mill is 0.95μm, the D50 of the slurry at the outlet of the second-stage sand mill is 0.45μm, the D50 of the slurry at the outlet of the third-stage sand mill is 0.3μm, and the D50 of the slurry at the outlet of the fourth-stage sand mill is 0.2μm, with a span of 0.8.

[0072] The energy consumption per ton of product in this process is approximately 210 kWh.

[0073] Comparative Example 1

[0074] Compared with Example 1, the difference is that the existing intermittent wet grinding method is used.

[0075] Ferric phosphate (D50 = 10 μm), lithium carbonate (D50 = 50 μm), maltose (D50 = 70 μm), sucrose (D50 = 100 μm), and water were added to a mixing tank. Mixing was performed using a stirrer (double-layered four-bladed inclined paddle) for 2 hours to form a stable slurry with a solid content of 30 wt%. The slurry was then ground in a conventional sand mill without protrusions on the pins or ultrasonic devices. After intermittent cyclic grinding for 7 hours, a slurry with a D50 of 0.2 μm and a span of 2.5 was obtained.

[0076] The energy consumption per ton of product in this process is approximately 450 kWh.

[0077] Comparative Example 2

[0078] Compared with Example 1, the difference is that the sand mill pin is not equipped with an ultrasonic device.

[0079] Ferric phosphate (D50 = 10 μm), lithium carbonate (D50 = 50 μm), maltose (D50 = 70 μm), and sucrose (D50 = 100 μm) were added to equipment one for ultrafine grinding. In the dry stirred ball mill, the mass ratio of grinding media to materials was 15:1, and the resulting dry powder had a D50 of 2 μm.

[0080] The dry powder material is then mixed with water to make a slurry. The premixed slurry at the outlet of the continuous solid-liquid mixing and dispersion equipment has a solid content of 30 wt%.

[0081] The material then enters a sand mill for grinding. The slurry output D50 of the first-stage sand mill is 1.5μm, the slurry output D50 of the second-stage sand mill is 1μm, the slurry output D50 of the third-stage sand mill is 0.8μm, and the slurry output D50 of the fourth-stage sand mill is 0.5μm. The span is 2.8, and the product particle size and span do not meet the requirements.

[0082] Comparative Example 3

[0083] Compared with Example 2, the difference is that the surface of the sand mill pin does not have a semi-circular protrusion.

[0084] Ferric phosphate (D50 = 90 μm), lithium carbonate (D50 = 20 μm), maltose (D50 = 20 μm), and sucrose (D50 = 50 μm) were added to equipment two for ultrafine grinding. In the dry stirred ball mill, the mass ratio of grinding media to materials was 3:1, and the resulting dry powder had a D50 of 5 μm.

[0085] The dry powder material is then mixed with water to make a slurry. The premixed slurry at the outlet of the solid-liquid mixing and dispersion equipment has a solid content of 15 wt%.

[0086] The slurry then enters a sand mill for grinding. The D50 of the slurry exiting the first-stage sand mill is 1.2μm, the D50 of the slurry exiting the second-stage sand mill is 0.7μm, the D50 of the slurry exiting the third-stage sand mill is 0.5μm, the D50 of the slurry exiting the fourth-stage sand mill is 0.45μm, the D50 of the slurry exiting the fifth-stage sand mill is 0.4μm, and the D50 of the slurry exiting the sixth-stage sand mill is 0.32μm. The span is 1.8, and the product particle size and span do not meet the requirements.

[0087] Comparative Example 4

[0088] Compared with Example 3, the difference is that no packing material is used in the continuous solid-liquid mixing and dispersion equipment.

[0089] Ferric phosphate (D50 = 50 μm), lithium carbonate (D50 = 90 μm), maltose (D50 = 50 μm), and sucrose (D50 = 20 μm) were added to equipment one for ultrafine grinding. In the dry stirred ball mill, the mass ratio of grinding media to materials was 10:1, and the resulting dry powder had a D50 of 3 μm.

[0090] Subsequently, the dry powder material is mixed with water to make a slurry. However, due to the lack of filler, a uniform and stable slurry cannot be formed, resulting in an imbalance in the material ratio and making it impossible to carry out subsequent ultrafine grinding operations.

[0091] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for ultrafine grinding of lithium iron phosphate precursor, characterized in that, The method includes the following steps: S1: Add raw materials and additives to a continuous dry grinding system to obtain powder; S2: The powder and water are drawn into a continuous liquid-solid mixing and dispersing device to obtain a premixed slurry; S3: The premixed slurry is fed into a continuous ultrafine grinding system to obtain the target slurry; In S2, the equipment uses built-in wire mesh filler, and in S3, a sand mill is used, with the grinding rod pin of the sand mill equipped with an ultrasonic device.

2. The method according to claim 1, characterized in that, The D50 of the raw materials and additives in S1 is 10-100 μm; And / or, the raw materials in S1 are iron phosphate and lithium carbonate; And / or, the adjuvant in S1 is an organic carbon source, preferably maltose and / or sucrose; And / or, S1 uses a dry stirred ball mill; Preferably, the mass ratio of grinding media to material is (2-15):1; And / or, the D50 of the powder obtained by S1 is 2-5 μm.

3. The preparation method according to claim 1, characterized in that, The solid content of the premixed slurry in S2 is 10wt%-60wt%; And / or, S2 uses a continuous solid-liquid mixing and dispersion device. The internal structure of the device consists of an impeller at the front, followed by a homogenizing dispersion disc, wire mesh packing, and another homogenizing dispersion disc in sequence. All internal components are connected by a main shaft.

4. The preparation method according to claim 1, characterized in that, S3 yields a slurry with a D50 of 100nm-200nm and a particle size range of <1; And / or, the surface of the pin in S3 is provided with a semi-circular protrusion to increase the contact area between the pin and the grinding media; Preferably, the radius of the semi-circular protrusion is 0.3cm-1cm; And / or, the frequency of the ultrasonic device in S3 is 30kHz-70kHz.

5. An apparatus for ultrafine grinding of lithium iron phosphate, said apparatus being used in the preparation method according to any one of claims 1-4, characterized in that, The equipment includes continuous dry grinding, continuous mixing and pulping, and continuous ultrafine grinding sections; Among them, the grinding rod pin of the sand mill in the continuous ultrafine grinding section is equipped with an ultrasonic device; The material is processed in the continuous dry grinding section and then enters the continuous mixing and pulping section to obtain premixed slurry. The slurry is then pumped to the continuous ultrafine grinding section for grinding.

6. The device according to claim 5, characterized in that, The continuous dry grinding section uses a dry stirred ball mill to grind the materials; And / or, the outlet of the dry stirring ball mill is equipped with a vibrating screen to separate the grinding media and materials.

7. The device according to claim 5, characterized in that, The continuous mixing and pulping section uses a continuous solid-liquid mixing and dispersion device, whose internal structure consists of an impeller at the front stage, followed by a homogenizing dispersion disc, wire mesh packing, and another homogenizing dispersion disc in sequence. Preferably, the wire mesh packing is composed of corrugated plates, and baffles are provided on the packing, with the included angle between the baffles and the packing being 60-120°.

8. The device according to claim 5, characterized in that, The continuous ultrafine grinding section uses four to six sand mills connected in series, with a slurry heat exchanger installed at the inlet of each sand mill.

9. An ultrafine ground lithium iron phosphate precursor, wherein the lithium iron phosphate precursor is prepared by the preparation method of any one of claims 1-4, or by the equipment of any one of claims 5-8, wherein the average particle size of the lithium iron phosphate precursor is 100nm-200nm and the particle size range is <1.

Images