Lithium iron phosphate slurry filtering method, system and device

Abstract

The invention provides a lithium iron phosphate slurry filtering method, system and device.The method comprises the step that slurry is screened in an ultrasonic vibrating screen, at least two layers of screen mesh assemblies are arranged in the ultrasonic vibrating screen in the vertical direction, and the space where screen meshes are located is in a basically closed state; the method further comprises the step of spraying and cleaning all the screens after screening or during screening. During screening, the ultrasonic frequency is larger than 35 KHZ and smaller than 45 KHZ.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy material preparation, and is particularly suitable for online filtration, washing and anti-clogging of slurry in the production process of lithium iron phosphate, a positive electrode material for lithium-ion batteries, and specifically relates to a lithium iron phosphate slurry filtration method, system and device. Background Art

[0002] Currently, magnetic particles and large foreign matter may have a significant negative impact on the performance and safety of lithium iron phosphate batteries (LiFePO4 batteries), as shown below:

[0003] 1. Impact on battery performance:

[0004] 1) Internal Short Circuit Risk: Magnetic particles (such as iron filings and nickel particles) can aggregate into electrodes or separators, forming a conductive bridge. This can penetrate the separator, leading to direct contact between the positive and negative electrodes and causing micro or severe short circuits. Large foreign matter (such as metal fragments and dust) can penetrate the separator or damage the electrode coating, increasing the probability of a short circuit. Consequences: Increased self-discharge, capacity decay, and even thermal runaway.

[0005] 2) Damage to the electrode structure: When foreign matter is embedded in the electrode (such as the positive electrode lithium iron phosphate material or the negative electrode graphite), it will hinder the insertion and extraction of lithium ions, causing localized failure of the active material and reducing the battery capacity and rate performance. If the foreign matter is hard (such as silicon particles), it may continuously wear the electrode during the charge and discharge cycle, accelerating structural collapse.

[0006] 3) Electrolyte contamination: Some metal particles (such as copper and iron) may dissolve in the electrolyte, triggering redox reactions, consuming active lithium ions, and causing capacity loss. Magnetic particles (such as Fe 3 +) may catalyze the decomposition of the electrolyte, generating gases (such as CO2, CH4) and solid by-products (Li2CO3), increasing the internal resistance.

[0007] 2. Impact on security:

[0008] 1) Thermal runaway risk: Local overheating at the short-circuit point can trigger a chain reaction of exothermic reactions (such as SEI film decomposition and electrolyte combustion), especially under high-temperature or high-current conditions. Although lithium iron phosphate has good thermal stability, localized high temperatures caused by foreign matter can still cause thermal runaway.

[0009] 2) Mechanical damage: Large foreign particles may squeeze the pole pieces or diaphragms during battery assembly or charging and discharging, causing deformation and rupture, and increasing the risk of failure after long-term cycling.

[0010] 3. Peculiarities of magnetic particles:

[0011] 1) Magnetic Aggregation Effect: Magnetic particles tend to aggregate under the influence of magnetic fields or electric currents, forming larger conductive clusters and increasing the risk of short circuits. During battery production, it is crucial to strictly avoid the wear of iron-containing tools and environmental dust contamination.

[0012] 2) Electrochemical corrosion: Magnetic metals such as iron may undergo oxidation and dissolution on the high-voltage positive electrode side, migrate to the negative electrode, and then undergo reduction and deposition, destroying the SEI film (such as forming dendrites).

[0013] Magnetic particles and large foreign matter can damage lithium iron phosphate batteries from multiple perspectives: electrochemical, mechanical, and thermal stability. This must be avoided through rigorous production processes and material handling. While lithium iron phosphate batteries are more tolerant to thermal runaway than ternary batteries, short circuits and side reactions caused by foreign matter cannot be ignored.

[0014] At present, the lithium iron phosphate slurry filtration section generally adopts the following two forms:

[0015] A. Traditional rotary vibrating screen + mechanical scraper: The vibrating motor generates low-frequency (25-50Hz) mechanical vibration, which is combined with the scraper to move the slurry on the screen surface to achieve solid-liquid separation.

[0016] B. Ultrasonic vibrating screen: A piezoelectric transducer is attached to the bottom of the screen to generate 20-35kHz longitudinal vibration to reduce clogging, but regular shutdown for manual cleaning is still required.

[0017] The prior art has the following shortcomings:

[0018] (1) For lithium iron phosphate slurry with a viscosity greater than 500 mPa·s, traditional low-frequency vibration cannot overcome the van der Waals force between particles, and the screen clogging rate is greater than 20% / h, requiring the machine to be shut down for cleaning every 2 hours;

[0019] (2) The ultrasonic vibrating screen lacks the function of forced liquid online cleaning, and the downtime for maintenance accounts for more than 10% of the total production time, resulting in low production line utilization rate;

[0020] (3) The traditional equipment has a semi-open structure. The water in the slurry evaporates at 30-50°C, generating lithium iron phosphate dust. The on-site dust concentration is >3mg / m 3 , does not comply with the requirements of GB 15577-2017 "Safety Specification for Dust Explosion Prevention";

[0021] (4) The filtration accuracy is greatly affected by the scraper linear speed. When the scraper linear speed is greater than 0.8m / s, the agglomerated particles larger than 45μm are easily broken and penetrate the screen, resulting in the D50 fluctuation of the finished product greater than 0.5μm. Summary of the Invention

[0022] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a lithium iron phosphate slurry filtration method with high cleaning efficiency and slurry filtration accuracy.

[0023] The technical problem to be solved can be implemented through the following technical solutions.

[0024] A method for filtering lithium iron phosphate slurry, comprising the steps of screening the slurry in an ultrasonic vibrating screen, wherein the ultrasonic vibrating screen is provided with at least two layers of screen assemblies in the upper and lower directions, and the space where the screens are located is in a substantially closed state, and the method further comprises the steps of spraying and cleaning each screen after or during screening; during screening, the ultrasonic frequency is greater than 35 kHz. Z And less than 45KH Z .

[0025] Furthermore, when the screen is sprayed and cleaned, the nozzle provides at least two water jets at different angles to the screen, and the angle between one of the water jets and the screen is 30°±5°.

[0026] Furthermore, the viscosity of the lithium iron phosphate slurry is greater than 500 mPa·s.

[0027] Furthermore, during screening, the amplitude of the vibrating screen frame is 15-25 μm.

[0028] Furthermore, when the screen is spray-cleaned, the ultrasonic system operates in a sweep frequency mode of 33-37 kHz and a period of 1-3 s.

[0029] Another technical problem to be solved by the present invention is to provide a lithium iron phosphate slurry filtration system for realizing the aforementioned filtration method.

[0030] The technical solution is as follows

[0031] A lithium iron phosphate slurry filtration system includes a tank for storing slurry to be sprayed, a water storage tank, a buffer tank, and an ultrasonic vibrating screen. The ultrasonic vibrating screen is a substantially sealed tank body with at least two layers of screen structures, one upper and one lower. The feed port at the upper end of the tank body is connected to the discharge port for the material to be sprayed, and the finished product discharge port at the lower end of the tank body is connected to the feed port of the buffer tank.

[0032] The cleaning water provided by the water storage tank is respectively connected to the cleaning spray system of the ultrasonic vibrating screen and the spray system of the buffer tank through the delivery branch provided by the cleaning water pipeline;

[0033] The outlet pipeline of the buffer tank leads to the material spray drying process, and the buffer tank is provided with a stirring device that can stir the internal material.

[0034] Furthermore, the connecting pipes between the spray tank, water storage tank, buffer tank and ultrasonic vibrating screen are provided with several valves for controlling the opening and closing of the pipes and fluid pressure and flow monitoring devices; the ultrasonic vibrating screen and buffer tank are also respectively provided with material level sensors that can monitor the thickness of the internal material accumulation.

[0035] Another technical problem solved by the present invention is to provide a lithium iron phosphate slurry filtering device for implementing the above-mentioned filtering method.

[0036] The device adopts the following technical solutions.

[0037] A filtering device for lithium iron phosphate slurry, used for filtering lithium iron phosphate slurry with a viscosity greater than 500mPa·s, includes an ultrasonic vibrating screen. The device is characterized in that at least two layers of screen assemblies are provided inside the ultrasonic vibrating screen along the upper and lower directions, and the space in which the screens are located is in a basically closed state. A spray cleaning system is also introduced into the ultrasonic vibrating screen to spray water to act on the screens.

[0038] Furthermore, the spray cleaning system provides at least two water jets with different angles to the screen, wherein the angle between one of the water jets and the screen is 30°±5°.

[0039] Furthermore, the spray cleaning system includes multiple spray water inlet pipes that can reach different screens, and the upper part of the outer shell of the ultrasonic vibrating screen is provided with a respirator that can empty or adjust the gas storage in the equipment; it also includes a material level sensor that can monitor the thickness of the material retained on each screen, and the material level sensor is electrically connected to the opening and closing control circuit of the spray cleaning system.

[0040] Furthermore, in each screen of the at least two layers of screen assembly, the aperture of the lower screen is not larger than the aperture of the upper screen; the screen is selected from 304 plain mesh or nylon 66 electrospinning membrane.

[0041] The lithium iron phosphate slurry filtration method, system and device using the above technical solution have the following characteristics and beneficial effects:

[0042] 1. Without dismantling the machine, it can achieve continuous operation for ≥24h and the screen clogging rate is <1%;

[0043] 2. Improve the filtration accuracy of lithium iron phosphate slurry from the current ≥80μm to ≥30μm, and the D50 fluctuation is ≤0.2μm;

[0044] 3. Reduce the amount of dust leakage inside the equipment to ≤0.5mg / m 3 , meet the requirements of dust-free workshop;

[0045] 4. The single cleaning time is shortened from the current ≥40min to ≤10min, and the cleaning fluid consumption is reduced by ≥50%.

[0046] 5. Magnetic particles of 5-200μm and larger than 200μm are 50-100pcs / kg before screening and 5-20pcs / kg after screening.

[0047] 6. For non-magnetic particles of 5-200μm and larger than 200μm, the rate is 100-300pcs / kg before screening and 30-60pcs / kg after screening. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a process flow chart of the filtration method of the present invention;

[0049] Figure 2 This is a schematic diagram of the structure of the ultrasonic vibrating screen of the present invention;

[0050] Figure 3 for Figure 2 sectional view of

[0051] Figure 4 for Figure 3 Stereoscopic image of

[0052] Figure 5 for Figure 2 A top view of

[0053] In the figure: 1. First pressure transmitter; 2. Second pressure transmitter; 3. Third pressure transmitter; 4. Material level sensor; 5. Spray ball; 6. Tank breather; 7. First flow meter; 8. Water pump; 9. Second flow meter; 10. Third flow meter; 11. Stirring device; 12. Pump;

[0054] 21. Feed inlet; 22. Upper screen discharge port; 23. Ultrasonic transducer; 24. Material level sensor; 25. Vibrating screen frame; 26. Lower screen discharge port; 27. Process observation port; 28. Sight glass with brush; 29. ​​Respirator; 30. Spring; 31. Vibrating motor; 32. Distributor; 33. Lower spray inlet; 34. Upper spray inlet; 35. Spray ring; 36. Nozzle; 37. Finished product discharge port; 38. Base; 39. Upper cover; 40. Locking ring; 41. Valve cylinder;

[0055] 100, can to be sprayed; 110, manual valve; 120, pneumatic valve; 130, slurry pipeline;

[0056] 200, water storage tank; 210, cleaning water pipe;

[0057] 300, cache tank; 310, tank bottom valve;

[0058] 400, ultrasonic vibrating screen; 410, finished product pipeline;

[0059] 500. Sewage pipe. DETAILED DESCRIPTION

[0060] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0061] Reference Figures 1 to 5 The present invention provides a method, system and device for filtering lithium iron phosphate slurry.

[0062] like Figure 1 As shown, this process utilizes a pre-spray tank 100, a water storage tank 200, a buffer tank 300, and a modified ultrasonic vibrating screen 400. The ultrasonic vibrating screen 400 is a relatively sealed tank structure. The lower outlet of the pre-spray tank 100 is connected to the feed port 21 at the top of the ultrasonic vibrating screen 400 via a slurry pipe 130. The water storage tank 200 delivers clean water via a clean water pipe 210 to the interior of the ultrasonic vibrating screen 400 and the spray system of the buffer tank 300.

[0063] Several valves are installed on each pipeline to control the opening and closing of the corresponding pipeline to determine the direction of the material.

[0064] further,

[0065] The pump 12 provided on the slurry pipeline 130 is used to provide power to the slurry to ensure that the slurry can be delivered to relevant equipment at a certain flow rate.

[0066] The first pressure transmitter 1 provided on the slurry pipeline 130 can detect the feed pressure in real time to prevent the screen from being damaged by excessive pressure.

[0067] The first flow meter 7 provided on the slurry pipeline 130 can detect the feed flow in real time to meet the requirements of different batch production processes.

[0068] The water pump 8 provided on the cleaning water pipeline 210 can provide the delivery pressure of the cleaning water and control the flow rate of the cleaning water.

[0069] The second flow meter 9 provided on the cleaning water pipeline 210 can monitor the cleaning water flow in real time to meet the requirements of different batch production processes.

[0070] The second pressure transmitter 2 provided on the cleaning water pipeline 210 can monitor the cleaning water pressure in real time to avoid damage to the screen or pipeline caused by excessive pressure.

[0071] The third flow meter 10 provided on the finished material pipeline 410 can monitor the outlet flow of the finished material in real time to meet the requirements of different batch production processes.

[0072] Since the interior of the buffer tank 300 is sealed, a tank respirator 6 is provided on the top of the buffer tank 300 in order to exhaust the gas in the equipment when feeding or taking in water.

[0073] In order to prevent the finished materials from sinking to the bottom after entering the buffer tank 300 and to ensure that the finished materials have a certain fluidity, the buffer tank 300 is further provided with a stirring device 11, which can stir the materials inside the tank.

[0074] The upper part of the cache tank 300 is provided with a spray system (such as the spray ball 5 shown in the figure) connected to the external cleaning water pipeline 210 to facilitate cleaning of the inside of the cache tank after production is completed.

[0075] The cache tank 300 is also equipped with a third pressure transmitter 3 that can monitor the internal pressure of the cache tank in real time to avoid damage to the tank body due to abnormal pressure.

[0076] Similarly, the buffer tank 300 is also equipped with a material level sensor 4 that can monitor the material level inside the buffer tank in real time, for example, to avoid excessive accumulation of materials.

[0077] The setting of the tank bottom valve 310 at the bottom of the buffer tank 300 must ensure that the bottom of the tank bottom is level with the bottom of the finished material to avoid material accumulation in dead corners of the tank body.

[0078] The tank body of the ultrasonic vibration screen 400 and the buffer tank 300 are also connected to the sewage pipe 500 to facilitate the discharge of waste.

[0079] Reference Figures 2 to 5 The ultrasonic vibrating screen 400, which is an overall tank structure, is mainly composed of a sealing frame, a screen assembly, an ultrasonic system and a cleaning system; its main body adopts a fully sealed frame structure, and the main tank body is supported by the bracket structure of the base 38; the upper cover 39 of the tank body, in order to increase and ensure the sealing, a locking ring 40 is set between the openable cover 39 and the tank body.

[0080] A feed port 21 is provided at the top of the tank body, and a finished product discharge port 21 is provided at the bottom of the tank body; at least two layers of screen assemblies are provided at the upper and lower positions inside the tank body (two layers are used in the embodiment of the present invention), and an upper screen discharge port 22 and a lower screen discharge port 26 are provided on the side of the tank body for discharging waste materials and waste liquids during cleaning and discharging overflow materials.

[0081] The upper and lower layers of screens are each provided with a corresponding cleaning system. The cleaning system of the present invention mainly includes an annular cleaning main pipe (corresponding to the spray ring 35 in the figure), from which several nozzles 36 are drawn. The water flow sprayed by the nozzles 36 can be sprayed onto the circular screen of the ultrasonic vibrating screen 400. The nozzles 36 of the present invention provide at least two types of spray water flow, one of which is provided at a spray angle of 30°±5° with the screen. The nozzle aperture can be selected to be 0.8mm, and the opening rate is 0.3%. A spray water flow perpendicular to the screen can also be provided; the water flow sprayed by the nozzle acts on the screen from the bottom of the screen. In order to meet the needs of the circular structure of the screen, the multiple nozzles provided can be arranged as a whole to form a circle, so the nozzles 36 can also be regarded as fan-shaped nozzles. The spray systems of the upper and lower layers of screens are respectively provided with corresponding water inlets, such as the upper spray water inlet 34 provided on the upper cover 39 and the lower spray water inlet 33 provided on the side wall of the tank body.

[0082] further,

[0083] The state of the material inside the equipment can be observed in real time through the process observation port 27 opened on the upper cover 39 of the tank body.

[0084] The material accumulation inside the tank body and the internal conditions of the lower screen and the following components can be manually checked by using the brush sight glass 28 provided on the side of the tank body.

[0085] The ultrasonic vibrating screen's ultrasonic transducer 23 acts directly on the inner ring of the screen (i.e., the annular support portion of the screen's support body near the center), generating resonance to accelerate slurry screening and facilitate screen cleaning. Specifically, the transducer in the ultrasonic system of the ultrasonic vibrating screen 400 is fixed to the inner ring nodes of the ultrasonic mesh (vibrating screen mesh frame 25 in the figure) via node locking, with the node amplitude typically controlled to 15-25 μm.

[0086] The material level sensor 24 positioned on the side wall of the tank is used to automatically identify the material level to help determine when to open the cleaning system for cleaning.

[0087] Since the interior of the tank is sealed, a respirator 29 is provided on the tank cover 39 in order to exhaust the gas in the equipment when feeding or water is taken in.

[0088] The upper end of a coil spring 30 provided at the lower part of the tank body is supported at the lower part of the tank body, and the lower end of the spring abuts against the bracket body of the base 38 of the ultrasonic vibration screen.

[0089] A group of vibration motors 31 positioned on the outer side wall of the tank body is used to provide a vibration source for the ultrasonic vibrating screen equipment and can also accelerate the slurry to pass through the screen.

[0090] The distributor 32 located below the feed port 21 in the tank body can ensure that the slurry is evenly spread on the screen and avoid the uneven feed pressure on the local screen causing damage to the screen; wherein, the upper and lower layers of the screen are equipped with corresponding distributors.

[0091] Based on actual needs, a screen with a diameter of 400-2000mm can be selected.

[0092] Description of the working status of the ultrasonic vibrating screen stand-alone equipment;

[0093] In the first step, the vibration motor 31 of the ultrasonic vibrating screen 400 is started. After the ultrasonic wave is started, the slurry is introduced through the feed port 21 to start screening and filtering;

[0094] In the second step, the material enters the screening and filtration state. The material passes through the upper and lower layers of screens, and the finished product is discharged from the finished product outlet 37 at the bottom of the tank body. The retained material on the screen continues to remain on the screen;

[0095] In the third step, after the slurry is screened and filtered, cleaning water is introduced. At the same time, the valve is opened under the control of the valve cylinder 41, and the cleaning water drives the retained matter to be discharged from the upper screen discharge port 22 and the lower screen discharge port 26 respectively; at the same time, the cleaning water cleans the inside of the ultrasonic vibrating screen 400 and the screen, so there is no need to manually disassemble the equipment for cleaning.

[0096] The work of ultrasonic vibrating screen can also be divided into filtering stage and cleaning stage.

[0097] Filtration stage: The slurry enters from the feed port 21, and the ultrasonic transducer 23 generates high-frequency vibrations to disperse the agglomerated particles into monomers <10μm and form a micro-suspension layer on the screen surface to avoid clogging; the filtrate passes through the screen and is discharged from the finished product discharge port 37, and the coarse particles are discharged from the upper screen discharge port 22.

[0098] Cleaning stage: When the material level sensor 24 detects that the slurry thickness on the screen surface is ≥5mm and the running time reaches the set value, the system automatically switches to the cleaning mode:

[0099] Step 1: Close the feed valve and drain the slurry;

[0100] Step 2: Start water inlet, and the nozzle sprays cleaning liquid at a pressure of 0.2MPa. At the same time, the ultrasonic system works in sweep frequency mode (33→37kHz, cycle 1-3s, preferably 2s), and the cavitation effect removes the residual particles in the sieve holes;

[0101] Step 3: The cleaning liquid is discharged through the bottom reflux port;

[0102] Step 4: After 10 minutes of cleaning and detecting that the slurry thickness on the screen surface is less than 5mm, the system automatically ends cleaning and resumes filtration.

[0103] Description of the overall working status of the process system:

[0104] In the first step, after the ultrasonic vibrating screen 400 is started, the valves (manual valve 110 and pneumatic valve 120) at the bottom of the spray tank 100 are opened, and the slurry enters the tank body of the ultrasonic vibrating screen 400 along the slurry pipe 130 and the feed port 21 through the action of the pump 12, and screening and filtration are started.

[0105] The second step is to open the bottom valve of the ultrasonic vibration screen 400, and the slurry is transported to the buffer tank 300 along the finished product discharge port 37 and the finished product pipeline 410.

[0106] The third step is to open the tank bottom valve 310 at the bottom of the buffer tank 300 and deliver the material in the buffer tank 300 to the spray drying process along the relevant pipeline.

[0107] Part 4: Open the bottom valve of the water storage tank 200. The cleaning water can be selectively sent into the ultrasonic vibration screen tank body and / or the cache tank along the cleaning water pipeline 210 through the action of the water pump 8 to further complete the relevant cleaning operations.

[0108] The following are more specific examples.

[0109] Example 1:

[0110] Screen specifications: upper layer 38μm 304 plain mesh, lower layer 30μm 304 plain mesh;

[0111] Ultrasonic parameters: frequency 36 kHz, power 200 W, continuous mode;

[0112] Cleaning parameters: cleaning liquid temperature 20-25℃, circulation flow 3m 3 / h.

[0113] According to the test, the filtration flux of lithium iron phosphate slurry with a solid content of 30% and a viscosity of 800mPa·s is 20m 3 / h, the screen has no obvious blockage.

[0114] Example 2:

[0115] The difference from Example 1 is that the screen is replaced with a 20 μm nylon 66 electrospinning membrane, and the ultrasonic frequency is changed to 38 kHz, which is suitable for ultra-high solid content slurry with a viscosity of 2000 mPa·s, and the filtration flux is maintained at 12 m 3 / h, particle retention rate>99.5%.

[0116] Working process:

[0117] 1. The slurry enters from the feed port and the vibration motor frequency is set to 50Hz;

[0118] 2. The transducer converts electrical energy into mechanical vibration and transmits it to the screen, causing the particles to suspend in the low altitude under ultrasonic acceleration;

[0119] 3. The material level sensor detects the screen load → triggers the cleaning process:

[0120] The gate closes the inlet / outlet; the nozzle sprays 20-25℃ purified water for 10 minutes;

[0121] 4. The cleaning waste liquid is discharged from the discharge port and the system automatically resets to production mode.

[0122] Effect verification:

[0123] Filtration efficiency: 20m 3 / h (more than 11 times higher than traditional equipment); screen blockage rate: <5% (traditional equipment> 50%);

[0124] Product impurity content: 0.008% (national standard requirement: ≤ 0.02%). Table 1 below compares the effects of the technical solution of the present invention with those of the prior art.

[0125] Table 1:

[0126]

Claims

1. A method for filtering lithium iron phosphate slurry, comprising the step of screening the slurry in an ultrasonic vibrating screen, characterized in that: At least two layers of screen assemblies are provided inside the ultrasonic vibrating screen along the upper and lower positions, and the space where the screens are located is in a basically closed state. The method also includes the step of spraying and cleaning each screen after or during screening; during screening, the ultrasonic frequency is greater than 35KH Z And less than 45KH Z .

2. The lithium iron phosphate slurry filtering method according to claim 1, characterized in that: When spray cleaning the screen, the nozzle provides at least two water jets at different angles to the screen, and the angle between one of the water jets and the screen is 30°±5°.

3. The lithium iron phosphate slurry filtering method according to claim 1, characterized in that: The viscosity of the lithium iron phosphate slurry is greater than 500 mPa·s.

4. The lithium iron phosphate slurry filtering method according to claim 1, characterized in that: During screening, the amplitude of the vibrating screen frame is 15-25μm.

5. The lithium iron phosphate slurry filtering method according to claim 1, characterized in that: When spray cleaning the screen, the ultrasonic system operates in a sweep frequency mode of 33-37kHz and a period of 1-3s.

6. A lithium iron phosphate slurry filtration system, characterized in that: It includes a tank for storing slurry to be sprayed, a water storage tank, a buffer tank and an ultrasonic vibrating screen; the ultrasonic vibrating screen is a substantially sealed tank structure, and at least two layers of screen structures are provided inside the tank; the feed port at the upper end of the tank is connected to the discharge port for the material to be sprayed, and the finished product discharge port at the lower end of the tank is connected to the feed port of the buffer tank; The cleaning water provided by the water storage tank is respectively connected to the cleaning spray system of the ultrasonic vibrating screen and the spray system of the buffer tank through the delivery branch provided by the cleaning water pipeline; The outlet pipeline of the buffer tank leads to the material spray drying process, and the buffer tank is provided with a stirring device that can stir the internal material.

7. The lithium iron phosphate slurry filtration system according to claim 6, characterized in that: The connecting pipes between the spray tank, water storage tank, buffer tank and ultrasonic vibrating screen are equipped with several valves for controlling the opening and closing of the pipes and fluid pressure and flow monitoring devices; the ultrasonic vibrating screen and buffer tank are also respectively provided with material level sensors that can monitor the thickness of the internal material accumulation.

8. A filtering device for lithium iron phosphate slurry, used for filtering lithium iron phosphate slurry with a viscosity greater than 500 mPa·s, comprising an ultrasonic vibrating screen, characterized in that: At least two layers of screen assemblies are provided inside the ultrasonic vibration screen along the upper and lower directions. The space where the screens are located is in a basically closed state. A spray cleaning system for spraying water to act on the screens is also introduced inside the ultrasonic vibration screen.

9. The filtering device for lithium iron phosphate slurry according to claim 8, characterized in that: The spray cleaning system provides at least two water jets with different angles to the screen, wherein the angle between one of the water jets and the screen is 30°±5°.

10. The filtering device for lithium iron phosphate slurry according to claim 8, characterized in that: The spray cleaning system includes multiple spray water inlet pipes that can reach different screens. The upper part of the outer shell of the ultrasonic vibrating screen is provided with a respirator that can empty or adjust the gas storage in the equipment; it also includes a material level sensor that can monitor the thickness of the material retained on each screen. The material level sensor is electrically connected to the opening and closing control circuit of the spray cleaning system.

11. The filtering device for lithium iron phosphate slurry according to claim 8, characterized in that: In each screen of the at least two layers of screen assembly, the aperture of the lower screen is not larger than the aperture of the upper screen; the screen is selected from 304 plain mesh and nylon 66 electrospinning membrane.

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