Method for purifying lithium dihydrogen phosphate by reverse temperature difference washing and dissolving equipment

Abstract

This invention provides a method and dissolution equipment for purifying lithium dihydrogen phosphate using reverse temperature difference washing, relating to the field of lithium dihydrogen phosphate preparation for battery materials. Step S1, low-temperature dissolution: Deionized water is added to the dissolution equipment and pre-cooled to 0-5°C. Then, crude lithium dihydrogen phosphate is added to the deionized water, and the system temperature is maintained at 0-5°C. Under stirring conditions, the crude lithium dihydrogen phosphate is fully dissolved in the deionized water to obtain a low-temperature solution. The method for purifying lithium dihydrogen phosphate using reverse temperature difference washing provided by this invention relies on the temperature difference characteristics of lithium dihydrogen phosphate solubility. It removes soluble impurities at low temperatures and promotes directional crystallization at higher temperatures, refining low-purity crude products into high-purity battery-grade products. Using only deionized water as the medium, it eliminates the need for added acids, alkalis, organic solvents, or other additives, preventing the introduction of external impurities. The process is simple, easy to control, and avoids the flammability and explosiveness associated with organic solvents, as well as the difficulty in separating viscous solutions from saturated solutions.

Description

Technical Field

[0001] This invention relates to the field of lithium dihydrogen phosphate preparation for battery materials, and particularly to a method and dissolution equipment for purifying lithium dihydrogen phosphate by reverse temperature difference washing. Background Technology

[0002] Lithium dihydrogen phosphate (LiH2PO4) is a key raw material for preparing lithium iron phosphate (LFP), the cathode material for lithium-ion batteries. Its purity directly affects the electrochemical performance and batch stability of the cathode material. During the preparation of LiH2PO4, whether obtained through the neutralization of lithium hydroxide with phosphoric acid or through a metathesis reaction, the initial product often contains unreacted raw materials, byproducts such as sulfate, sodium ions, or potassium ions, and other water-soluble impurities. Therefore, efficient washing and purification are essential steps in obtaining battery-grade LiH2PO4.

[0003] Currently, the washing and purification methods for lithium dihydrogen phosphate mainly have the following technical solutions and drawbacks:

[0004] Firstly, existing conventional processes typically employ rinsing with organic solvents such as anhydrous ethanol or acetone, utilizing the extremely low solubility of lithium dihydrogen phosphate in these solvents to minimize product loss and remove impurities. For example, Chinese Patent Publication No. CN104445128A, entitled "A Process for Reaction and Crystallization Using Ethanol as a Medium," utilizes the low solubility of lithium dihydrogen phosphate in ethanol to directly precipitate the product, avoiding the high energy consumption issues of traditional evaporation concentration and cooling crystallization processes. Similarly, Chinese Patent Publication No. CN101311108B, entitled "A Method for Separation and Preparation of Lithium Dihydrogen Phosphate," also uses ethanol washing and drying after cooling crystallization. However, these methods have significant industrial drawbacks: organic solvents are flammable and explosive, requiring production workshops to possess Class A explosion-proof qualifications, resulting in extremely high equipment investment and safety maintenance costs; furthermore, organic solvents are volatile, making exhaust gas treatment and solvent recovery systems complex, leading to persistently high overall production costs.

[0005] Secondly, some processes use saturated lithium dihydrogen phosphate solution as the washing medium. For example, Chinese Patent Publication No. CN101638225B, entitled "Method for Preparing Battery-Grade Lithium Dihydrogen Phosphate and Battery-Grade Lithium Dihydrogen Phosphate Obtained Therefrom," provides a washing scheme: after dehydrating the lithium dihydrogen phosphate slurry to obtain a crude product, it is washed with a saturated lithium dihydrogen phosphate solution, and the washing is repeated 2 to 6 times. Chinese Patent Publication No. CN102351160A, entitled "Method for Preparing Battery-Grade Lithium Dihydrogen Phosphate Using High-Purity Lithium Carbonate Precipitating Mother Lithium," also uses a saturated washing method. Although this type of scheme avoids the introduction of an organic phase, the saturated lithium dihydrogen phosphate solution has a high viscosity, especially in high-concentration environments, resulting in low solid-liquid separation efficiency, poor mass transfer during washing, and difficulty in effectively removing mother liquor impurities encapsulated inside the crystals. This leads to incomplete product washing, and the viscous solution is prone to clogging in pipeline transportation and centrifugal separation, affecting continuous production.

[0006] Thirdly, as illustrated by Chinese Patent Publication No. CN101327919A, entitled "A Cooling Crystallization Separation Process," this method involves cooling the high-temperature lithium dihydrogen phosphate solution generated in the reaction to 0–20°C, causing the product to crystallize and precipitate, followed by solid-liquid separation. This method utilizes conventional forward solubility characteristics (high-temperature dissolution, low-temperature precipitation), and the purpose of cooling crystallization is to separate the product from the reaction solution, not to wash and purify the existing crude solid. This process still requires a subsequent washing step to obtain a high-purity product.

[0007] Therefore, there is still room for improvement in how to enhance the safety of lithium dihydrogen phosphate purification, simplify the operation, and improve the purification effect.

[0008] Therefore, it is necessary to provide a method for purifying lithium dihydrogen phosphate using reverse temperature difference washing to solve the above-mentioned technical problems. Summary of the Invention

[0009] This invention provides a method for purifying lithium dihydrogen phosphate using reverse temperature difference washing, which solves the problems of existing technologies that rely on flammable and explosive organic solvents and have viscous solutions that are difficult to separate.

[0010] To solve the above-mentioned technical problems, the present invention provides a method for purifying lithium dihydrogen phosphate using reverse temperature difference washing, comprising the following steps:

[0011] S1. Low-temperature dissolution: Deionized water is added to the dissolution equipment and pre-cooled to 0-5°C. Then, crude lithium dihydrogen phosphate is added to the deionized water, and the system temperature is maintained at 0-5°C. Under stirring conditions, the crude lithium dihydrogen phosphate is fully dissolved in the deionized water to obtain a low-temperature solution.

[0012] S2: Heating crystallization: The low-temperature solution is heated to 20-30°C at a heating rate of 0.5-3°C / min, so that the dissolved lithium dihydrogen phosphate precipitates again in the form of crystals, resulting in a solid-liquid mixture;

[0013] S3: Separation and drying: The liquid mixture is separated into solid and liquid components. The separated solid is dried at 60-110°C for 4-12 hours to obtain battery-grade lithium dihydrogen phosphate product.

[0014] Preferably, the solid-liquid mass ratio of the crude lithium dihydrogen phosphate to deionized water is 1:3 to 1:6.

[0015] Preferably, the deionized water is pre-cooled to 0-2°C.

[0016] Preferably, in step S3, the mother liquor after solid-liquid separation is treated by cooling and reuse or by evaporation and concentration.

[0017] The present invention also provides a dissolution apparatus for use in step S1 of the method for purifying lithium dihydrogen phosphate by washing with reverse temperature difference;

[0018] Includes: a dissolving tank, wherein a temperature regulating sleeve is fitted onto the dissolving tank;

[0019] A stirring device is installed in the dissolving tank and is used to stir and mix the solution in the dissolving tank.

[0020] A feeding assembly includes a first feeding tray, a second feeding tray, a rotating sleeve, a support ring, and a driving component. The first feeding tray, the second feeding tray, the rotating sleeve, and the support ring are all concentrically arranged and sleeved on the outside of the stirring rod of the stirring device. The inner and outer diameters of the second feeding tray are larger than those of the first feeding tray. The top of the first feeding tray is fixedly connected to the second feeding tray via a first guide plate. The rotating sleeve is fixedly connected to the top of the second feeding tray via a second guide plate. The support ring is fixed to the inner wall of the dissolving tank via a support rod. The rotating sleeve is sleeved on and rotatably mounted on the support ring.

[0021] The driving component is used to drive the first and second material trays to rotate.

[0022] The feed pipe has its bottom end penetrating the melting tank and extending above the support ring.

[0023] Preferably, the dissolving equipment further includes a storage cylinder and a valve. The storage cylinder is suspended above the dissolving tank. The feed pipe is connected to the discharge end of the storage cylinder. The valve is used to control the connection state of the feed pipe. A spiral feeder is provided inside the feed pipe.

[0024] Preferably, the top of the dissolving tank is equipped with multiple weighing columns, the top of which is equipped with a weighing sensor. A support plate is installed on the feed pipe, and the weighing sensor is used to support the support plate.

[0025] Preferably, the valve includes a lifting cylinder, a valve housing, and a valve plate. The valve housing is connected to the feed pipe, the lifting cylinder is mounted on the support plate, the valve plate is slidably disposed inside the valve housing, and the output end of the lifting cylinder is connected to the valve plate.

[0026] Preferably, the driving component is a transmission tube, which is sleeved on the stirring rod. The bottom end of the transmission tube passes through the first material tray and forms a circumferential fixed and axial sliding fit with the first material tray. A square groove is provided at the top of the transmission tube, and a square part is provided on the stirring rod above the transmission tube. The square part is aligned with the square groove.

[0027] The transmission pipe is equipped with a bearing housing, and the dissolving device also includes a connecting rod that connects the bearing housing and the valve plate.

[0028] Preferably, the bottom end of the auger shaft of the spiral feeder passes through the feed pipe, a gear is installed at the bottom end of the auger shaft, and an external gear ring is installed at the top of the rotating sleeve, the gear meshing with the rotating sleeve.

[0029] Compared with related technologies, the method for purifying lithium dihydrogen phosphate using reverse temperature difference washing provided by the present invention has the following advantages:

[0030] This invention provides a method for purifying lithium dihydrogen phosphate using reverse temperature difference washing. The process of this invention relies on the temperature difference characteristics of lithium dihydrogen phosphate solubility. Soluble impurities are washed away at low temperature, and crystallization is carried out at high temperature. This method can refine low-purity crude products into battery-grade high-purity products with high purity and low impurity content.

[0031] The entire process uses only deionized water as the medium, without the need to add acids, alkalis, organic solvents or other additives, and without the introduction of external impurities. The process is simple, easy to operate and control, and suitable for laboratory and industrial continuous production. It avoids the flammable and explosive situation of organic solvents and the problem of viscous and difficult separation of saturated solutions. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the steps of the method for purifying lithium dihydrogen phosphate using reverse temperature difference washing provided by the present invention.

[0033] Figure 2 This is a schematic diagram of the dissolving device provided by the present invention;

[0034] Figure 3 for Figure 2The diagram shows a partial structural schematic of the dissolving equipment.

[0035] Figure 4 A partial cross-sectional view of the dissolving apparatus provided by the present invention;

[0036] Figure 5 for Figure 4 A partial schematic diagram of the dissolving equipment is shown.

[0037] Figure 6 A schematic diagram of the transmission tube sleeved on the square portion according to the present invention;

[0038] Figure 7 A cross-sectional view of the gear meshing with an external gear ring provided by the present invention;

[0039] Figure 8 A top view of the gear meshing with an external gear ring provided by the present invention.

[0040] Numbering on the map:

[0041] 1. Dissolving tank; 101. Temperature control jacket; 102. Positioning rod;

[0042] 2. Stirring device; 21. Motor; 22. Stirring rod; 23. Stirring blade;

[0043] 221. Square part;

[0044] 3. Storage cylinder; 31. Feed pipe; 32. Support plate; 33. Diverter plate;

[0045] 311. Strip-shaped opening;

[0046] 4. Weighing column; 41. Weighing sensor;

[0047] 5. Spreading assembly; 51. First material tray; 52. Second material tray; 53. Rotating sleeve; 54. Support ring; 55. Transmission pipe; 551. Bearing seat; 552. Square groove; 511. First guide plate; 521. Second guide plate; 541. Support rod;

[0048] 6. Valve components; 61. Lifting cylinder; 62. Valve housing; 63. Valve plate;

[0049] 7. Spiral feeder; 71. Screw shaft; 72. Gear;

[0050] 8. Connecting rod; 9. External toothed ring; 10. Bracket. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0052] This invention provides a method for purifying lithium dihydrogen phosphate using reverse temperature difference washing.

[0053] Please refer to the following: Figure 1 In one embodiment of the present invention, the method for purifying lithium dihydrogen phosphate by reverse temperature difference washing includes the following steps:

[0054] S1. Low-temperature dissolution: Deionized water is added to the dissolution equipment and pre-cooled to 0-5°C. Then, crude lithium dihydrogen phosphate is added to the deionized water, and the system temperature is maintained at 0-5°C. Under stirring conditions, the crude lithium dihydrogen phosphate is fully dissolved in the deionized water to obtain a low-temperature solution.

[0055] S2: Heating crystallization: The low-temperature solution is heated to 20-30°C at a heating rate of 0.5-3°C / min, so that the dissolved lithium dihydrogen phosphate precipitates again in the form of crystals, resulting in a solid-liquid mixture;

[0056] S3: Separation and drying: The liquid mixture is separated into solid and liquid components. The separated solid is dried at 60-110°C for 4-12 hours to obtain battery-grade lithium dihydrogen phosphate product.

[0057] The process of this invention relies on the temperature difference characteristics of lithium dihydrogen phosphate solubility. Soluble impurities are washed away at low temperature and crystallized in a directional manner by heating. This process can refine low-purity crude products into battery-grade high-purity products with high purity and low impurity content.

[0058] The entire process uses only deionized water as the medium, without the need to add acids, alkalis, organic solvents or other additives, and without the introduction of external impurities. The process is simple, easy to operate and control, and suitable for laboratory and industrial continuous production. It avoids the flammable and explosive situation of organic solvents and the problem of viscous and difficult separation of saturated solutions.

[0059] Set the temperature to a slow gradient of 0.5~3℃ / min to avoid rapid crystallization, resulting in regular and uniform crystal grains, and better product flowability and performance.

[0060] Furthermore, the mother liquor separated after crystallization can be cooled and reused or evaporated and concentrated to recover residual lithium components, realizing material recycling, significantly reducing lithium loss, effectively improving the overall lithium yield, and reducing wastewater discharge, making it green and environmentally friendly.

[0061] The solid-liquid mass ratio of the crude lithium dihydrogen phosphate to deionized water is 1:3 to 1:6.

[0062] The preferred solid-liquid mass ratio of crude lithium dihydrogen phosphate to deionized water is 1:5.

[0063] Preferably, the deionized water is pre-cooled to 0-2°C.

[0064] Preferably, in step S3, the mother liquor after solid-liquid separation is treated by cooling and reuse or by evaporation and concentration.

[0065] After the mother liquor is cooled, it is returned to the low-temperature dissolution and washing process to participate in the washing of crude products again; the excess water in the mother liquor is heated and evaporated to increase the lithium salt concentration in the mother liquor. The high-concentration mother liquor can be sent back to the heated dissolution and crystallization process to recrystallize and produce high-purity products.

[0066] The present invention also provides the following embodiments, specifically the results of experiments using different parameter data:

[0067] Example 1:

[0068] A method for purifying lithium dihydrogen phosphate using reverse temperature difference washing includes the following steps:

[0069] S1: Low-temperature dissolution. Take 100 g of crude lithium dihydrogen phosphate (purity approximately 96.5%) to be washed, and measure 400 mL of deionized water. Place the water in a dissolution apparatus and cool it to 0°C beforehand. Add the crude product to the ice water, maintain the temperature at 0–2°C, and stir at 250 rpm for 40 minutes to ensure that the crude product is completely disintegrated and that impurities are fully diffused into the water.

[0070] S2: Heating crystallization. The above low-temperature solution was removed from the ice bath and naturally heated to 25°C at a rate of approximately 1.5°C / min. During the heating process, as the temperature increased, the solubility of lithium dihydrogen phosphate gradually decreased from approximately 1260 g / L to approximately 700 g / L. A large number of fine, shiny crystals were observed to begin to precipitate. After reaching 25°C, the solution was allowed to stand and age for 30 minutes.

[0071] S3: Separation and drying. The heated slurry is vacuum filtered, and the filter cake is quickly rinsed once with a small amount of cold deionized water (about 10 mL) at 0°C to replace the residual mother liquor on the surface. The filter cake is placed in a forced-air drying oven and dried at 105°C for 6 hours to obtain the purified lithium dihydrogen phosphate product.

[0072] Example 2:

[0073] A method for purifying lithium dihydrogen phosphate using reverse temperature difference washing includes the following steps:

[0074] S1: Low-temperature dissolution. Take 200 g of crude lithium dihydrogen phosphate to be washed and add it to 1000 mL of deionized water pre-cooled to 0℃ (solid-liquid ratio 1:5). Dissolve under stirring for 25 minutes. No obvious large solid particles are visible.

[0075] S2: Heating crystallization. The above low-temperature solution is placed in a constant-temperature water bath and heated to 30°C at a rate of approximately 2°C / min. During this heating process, driven by the decrease in solubility, crystals precipitate rapidly, forming a loose flocculent slurry;

[0076] S3: Separation and drying. Centrifugation separates the solid and liquid phases. The wet solid material is dried at 80°C for 6 hours to obtain the purified product.

[0077] Example 3:

[0078] A method for purifying lithium dihydrogen phosphate using reverse temperature difference washing includes the following steps:

[0079] S1: Low-temperature dissolution. Take 100 g of crude recovered lithium dihydrogen phosphate with a high impurity content, add 300 mL of deionized water (solid-liquid ratio 1:3), and place in a dissolution device and cool to 0℃. Stir and dissolve for 60 minutes;

[0080] S2: Heating crystallization, controlling the heating rate to 1℃ / min up to 22℃. During the heating process, a small amount of undissolved crystals can act as seed crystals, promoting more uniform crystal growth.

[0081] S3: Separation and drying. After filtration, the product is dried at 60°C for 6 hours to obtain purified lithium dihydrogen phosphate.

[0082] Example 4:

[0083] A method for purifying lithium dihydrogen phosphate using reverse temperature difference washing includes the following steps:

[0084] S1: Dissolve at low temperature. Take 150 g of crude lithium dihydrogen phosphate (purity about 97.2%), add it to 600 mL of deionized water pre-cooled to 2°C, and stir to dissolve for 50 minutes.

[0085] S2: Heating crystallization: Heating the solution to 25°C at a rate of 1°C / min, precipitating crystals, and then letting it stand for 40 minutes to age.

[0086] S3: Separation and drying: Filter the filter cake, rinse it with 10 mL of cold pure water at 5℃, and dry it at 105℃ for 6 hours to obtain the purified product.

[0087] Through Examples 1 to 4 above, it can be seen that lithium dihydrogen phosphate exhibits a unique reverse temperature difference effect, that is, its solubility changes in an anomalous manner with temperature. Measurements showed that its solubility is as high as approximately 126 g / 100 mL water (i.e., 1260 g / L) at 0°C, while at 25°C, the solubility significantly decreases to approximately 700 g / L. In other words, the solubility of lithium dihydrogen phosphate decreases with increasing temperature from 0 to 25°C, thus achieving the purpose of purifying lithium dihydrogen phosphate.

[0088] The present invention also provides a dissolution device for use in step S1 of a method for purifying lithium dihydrogen phosphate by washing with reverse temperature difference; the dissolution device is not limited to the dissolution of crude lithium dihydrogen phosphate with deionized water in step S1, but can also be used in step S2 to raise the temperature of the dissolution tank 1 by temperature control jacket 101 for crystallization; it can also be used in other dissolution processes or solid-liquid reactions, such as in the preparation of sodium hydroxide solution or sodium carbonate solution, to dissolve the corresponding solid powder in deionized water.

[0089] Please see Figures 2 to 3 A dissolving device includes: a dissolving tank 1, wherein a temperature regulating sleeve 101 is fitted onto the dissolving tank 1;

[0090] Stirring device 2, which is installed in the dissolving tank 1, is used to stir and mix the solution in the dissolving tank 1;

[0091] The feeding assembly 5 includes a first feeding tray 51, a second feeding tray 52, a rotating sleeve 53, a support ring 54, and a driving component. The first feeding tray 51, the second feeding tray 52, the rotating sleeve 53, and the support ring 54 are all concentrically arranged and sleeved on the outside of the stirring rod 22 of the stirring device 2. The inner diameter and outer diameter of the second feeding tray 52 are larger than the inner diameter and outer diameter of the first feeding tray 51. The top end of the first feeding tray 51 is fixedly connected to the second feeding tray 52 through a first guide plate 511. The rotating sleeve 53 is fixedly connected to the top of the second feeding tray 52 through a second guide plate 521. The support ring 54 is fixed to the inner wall of the dissolving tank 1 through a support rod 541. The rotating sleeve 53 is sleeved on and rotatably mounted on the support ring 54.

[0092] The driving component is used to drive the first material tray 51 and the second material tray 52 to rotate.

[0093] The bottom end of the feed pipe 31 passes through the melting tank 1 and extends above the support ring 54.

[0094] Here, the inner diameter and outer diameter are respectively the inner diameter of the first material tray 51 and the inner diameter of the second material tray 52, as well as the radius from the center to the edge.

[0095] In this invention, a temperature regulating chamber is provided inside the temperature regulating sleeve 101. A liquid outlet pipe is provided at the top of the temperature regulating sleeve 101, and a liquid inlet pipe is provided at the bottom. The liquid outlet pipe and the liquid inlet pipe are staggered. A partition is provided inside the regulating chamber to separate the liquid outlet pipe and the liquid inlet pipe. The liquid inlet pipe is connected to the output end of the water pump through a pipe, and the input end of the water pump is connected to the cold source through a pipe. The liquid outlet pipe is connected to the collection container through a pipe, so that the cooling medium (liquid or gas) after heat exchange flows back into the collection container.

[0096] When used in step S2, the input end of the water pump is connected to the heat source through a three-way pipe, and both ends of the three-way pipe are equipped with electric valves. The valves control whether the medium entering the temperature control chamber is a cooling medium or a heating medium, thereby achieving cooling or heating.

[0097] The temperature control jacket 101 has an internal insulation layer, the dissolving tank 1 has an internal temperature sensor for detecting the solution temperature, and the top is also equipped with a water inlet for adding deionized water;

[0098] In use, first, deionized water is added to the dissolving tank 1. The temperature-regulating sleeve 101 and a temperature sensor are used to cool the deionized water to a preset temperature. Then, crude lithium dihydrogen phosphate powder is added to the dissolving tank 1 through the feed pipe 31. During this process, some of the crude lithium dihydrogen phosphate powder entering through the feed pipe 31 falls onto the second material tray 52, and the other part falls onto the first material tray 51 through the central hole of the second material tray 52. ​​The driving component drives the first material tray 51 and the second material tray 52 to rotate, causing centrifugal force to be generated in the first material tray 51 and the second material tray 52. ​​The material on them is dispersed in the deionized water along the first material tray 51 and the second material tray 52. ​​Since the diameter of the second material tray 52 is larger than that of the first material tray 51, ... Figure 6 The materials dispersed from the two trays enter the deionized water at different locations;

[0099] At the same time, the stirring device 2 stirs the material, thereby dispersing the material in deionized water, which can accelerate the dissolution rate of the material and improve the dissolution efficiency and quality.

[0100] The number of first material trays 51 can be one or more. In this embodiment, there are two. When there are multiple first material trays 51, they are connected by first guide plates 511, and their diameters decrease from top to bottom. The second material tray 52 is set in the same way as the first material tray 51, so that multiple layers can be formed during material feeding, allowing the material to enter the deionized water more evenly.

[0101] Among them, such as Figure 4 The bottom end of the feed pipe 31 is an arc-shaped pipe extending above the support ring 54, and the outlet faces the first material tray 51 and the second material tray 52.

[0102] Among them, such as Figure 4and Figure 5 Preferably, a diverter plate 33 is provided in the outlet of the feed pipe 31. One end of the diverter plate 33 extends outside the feed pipe 31 to the top of the first material tray 51, corresponding to the center hole of the second material tray 52. ​​When material is discharged from the outlet of the feed pipe 31, the material below the diverter plate 33 falls directly onto the second material tray 52, and the material on the diverter plate 33 is guided to the first material tray 51 through the diverter plate 33, so that the material can enter the first material tray 51 and the second material tray 52 relatively evenly.

[0103] The support ring 54 is connected to the inner wall of the dissolving tank 1 by multiple support rods 541. The support ring 54 is provided with a flange, and the rotating sleeve 53 is fitted on the flange to form a rotating assembly. Ball bearings are embedded at the top and bottom of the flange to make the relative rotation smoother.

[0104] The dissolving tank 1 is mounted on the support 10, and an output pipe is provided at the bottom of the dissolving tank 1, with a valve installed on the output pipe.

[0105] In this embodiment, the stirring device 2 includes a motor 21, a stirring rod 22, and a stirring blade 23. The motor 21 is installed on the top of the dissolving tank 1. The top end of the stirring rod 22 passes through the top of the dissolving tank 1 and is fixedly connected to the output shaft of the motor 21. The bottom end passes through the support ring 54, the second material tray 52, and the first material tray 51 in sequence and is fixedly connected to the stirring blade 23.

[0106] Please see Figure 2 and Figure 4 In this embodiment, the dissolving device further includes a storage cylinder 3 and a valve 6. The storage cylinder 3 is suspended above the dissolving tank 1. The feed pipe 31 is connected to the discharge end of the storage cylinder 3. The valve 6 is used to control the connection state of the feed pipe 31. A spiral feeder 7 is provided inside the feed pipe 31.

[0107] The top of the storage cylinder 3 is equipped with a feeding pipe, and a sealing cap is threaded onto the feeding pipe. Lithium dihydrogen phosphate powder can be added into the storage cylinder 3 by unscrewing the sealing cap.

[0108] By setting up a storage cylinder 3, lithium dihydrogen phosphate powder is pre-loaded. When dissolving, the valve 6 is opened, and the screw feeder 7 is used to uniformly introduce the lithium dihydrogen phosphate powder into the spreading component 5, which then spreads it into the deionized water.

[0109] When continuous dissolution is performed;

[0110] In one embodiment, valve 6 is a metering valve, which is used to quantitatively add lithium dihydrogen phosphate powder.

[0111] Please refer to it again. Figure 2 and Figure 4In another embodiment, a plurality of weighing columns 4 are installed on the top of the dissolving tank 1, and a weighing sensor 41 is provided on the top of the weighing column 4. A support plate 32 is installed on the feed pipe 31, and the weighing sensor 41 is used to support the support plate 32.

[0112] By setting a weighing sensor 41 to support the dissolving tank 1, the weighing sensor 41 detects the weight of the material in the dissolving tank 1. Each time dissolving is performed, when the weighing sensor 41 detects a decrease in weight by a preset value, the valve 6 is closed, blocking the feed pipe 31, thereby enabling the quantitative addition of lithium dihydrogen phosphate powder.

[0113] The top of the dissolving tank 1 is equipped with multiple positioning rods 102. The top of the positioning rods 102 passes through the support plate 32, which limits the horizontal movement of the dissolving tank 1 and does not provide support for the dissolving tank 1. The feed pipe 31 is clearance-fitted to the top of the dissolving tank 1 and also does not provide support.

[0114] There are at least two weighing columns 4 and weighing sensors 41, and in this embodiment there are three.

[0115] The dissolving equipment also includes a control module. Weighing sensor 41 and temperature sensor are connected to the input end of the control module, while motor 21, valve 6, and water pump for temperature regulation are connected to the output end of the control module. The control module controls the operating status of each device based on the detected information, and allows staff to turn the equipment on or off or set the operating mode of the entire equipment.

[0116] Please see Figure 5 As an optional embodiment, the valve 6 includes a lifting cylinder 61, a valve housing 62, and a valve plate 63. The valve housing 62 is connected to the feed pipe 31, the lifting cylinder 61 is mounted on the support plate 32, the valve plate 63 is slidably disposed in the valve housing 62, and the output end of the lifting cylinder 61 is connected to the valve plate 63.

[0117] When the feed pipe 31 is opened, the lifting cylinder 61 raises the valve plate 63, thereby opening the outlet of the feed pipe 31, so that the material can be discharged through the feed pipe 31 and the valve 6.

[0118] When closed, the lifting cylinder 61 pushes down the valve plate 63 to block the feed pipe 31 again.

[0119] The lifting cylinder 61 can be a pneumatic cylinder, a hydraulic cylinder, or an electric push cylinder.

[0120] Please see Figure 4 and Figure 5As an optional embodiment, the driving component is a transmission tube 55, which is sleeved on the stirring rod 22. The bottom end of the transmission tube 55 passes through the first material tray 51 and forms a circumferential fixed and circumferential sliding fit with the first material tray 51. A square groove 552 is provided at the top of the transmission tube 55. A square part 221 is provided on the stirring rod 22 above the transmission tube 55, and the square part 221 is aligned with the square groove 552.

[0121] The transmission pipe 55 is equipped with a bearing seat 551, and the dissolving device also includes a connecting rod 8, which connects the bearing seat 551 and the valve plate 63.

[0122] When material needs to be discharged, the lifting cylinder 61 raises the valve plate 63. The valve plate 63 raises the transmission tube 55 through the connecting rod 8 and the bearing seat 551. The transmission tube 55 moves upward accordingly. When the valve plate 63 is raised to the preset height, the square groove 552 at the top of the transmission tube 55 is fitted onto the square part 221 of the stirring rod 22. At this time, when the motor 21 drives the stirring rod 22 to rotate, the stirring rod 22 drives the stirring blade 23 to rotate. At the same time, the square part 221 drives the transmission tube 55 to rotate. The transmission tube 55 drives the first material tray 51 to rotate. The first material tray 51 drives the second material tray 52 to rotate through the first guide plate 511. Thus, the first material tray 51 and the second material tray 52 rotate simultaneously, so that the lithium dihydrogen phosphate powder can be dispersed into deionized water for dissolution and mixing.

[0123] After a single feeding of lithium dihydrogen phosphate powder is completed, the motor 21 stops, the lifting cylinder 61 lowers the valve plate 63 to block the feed pipe 31 again, and at the same time the connecting rod 8 drives the transmission pipe 55 to descend through the bearing seat 551, so that the transmission pipe 55 separates from the square part 221. The motor 21 drives the stirring rod 22 to rotate again, which drives the stirring blade 23 to rotate to carry out the dissolution work. At this time, the feeding component 5 will not be driven to work.

[0124] Therefore, in one state, the motor 21 drives the feeding assembly 5 to disperse the material into the deionized water and simultaneously perform stirring. In another state, it is only used to drive the stirring blade 23 to rotate and perform stirring and mixing.

[0125] Motor 21 is a geared motor, or a servo motor, or a regular motor with a speed reduction device, etc., and the preferred speed is 20 to 60 r / min.

[0126] Preferably, a strip-shaped opening 311 is provided at the top of the feed pipe 31, so that when the valve plate 63 is raised to the upper side of the inner wall of the feed pipe 31, the transmission pipe 55 is sleeved on the square part 221, such as... Figure 6 Ensure that the valve plate 63 opens and closes sufficiently.

[0127] Meanwhile, a strip-shaped opening is correspondingly provided on the upper part of the diversion plate 33, and one end of the connecting rod 8 passes through the strip-shaped opening and connects to the valve plate 63. Since the diversion plate 33 is located at a position slightly below the center inside the feed pipe 31, it ensures that the materials entering the first material tray 51 and the second material tray 52 are as close as possible.

[0128] In the initial state, the square part 221 is aligned with the square groove 552. Each time, the motor 21 drives the stirring rod 22 to rotate an integer number of revolutions, thereby ensuring that the square part 221 can be aligned with the square groove 552 each time, which facilitates subsequent assembly.

[0129] Preferably, an abutment rod is horizontally installed on the inner wall of the support ring 54, with an arc-shaped abutment joint (not shown) at the end of the abutment rod. A rubber ring is fitted and fixed on the transmission tube 55. When the valve plate 63 blocks the feed tube 31, the abutment rod abuts against the rubber ring. When the valve plate 63 opens, the abutment rod separates from the rubber ring. By abutting against the rubber ring, the transmission tube 55 can be limited and rotation can be prevented, thereby keeping the square groove 552 aligned with the square part 221.

[0130] The transmission tube 55 and the stirring rod 22 are in clearance fit.

[0131] In this embodiment, the lower end of the transmission tube 55 has a square cross-section, and the center of the first material tray 51 has a square through groove, so that the bottom end of the transmission tube 55 passes through the square through groove to form a circumferentially fixed and axially sliding fit.

[0132] In other embodiments, strip-shaped sliding keys are provided on both sides of the transmission tube 55, and corresponding keyways are opened on both sides of the inner wall of the central hole of the first material tray 51. The transmission tube 55 passes through the central hole, and the strip-shaped sliding keys slide into the keyways to form a circumferential fixed and axial sliding fit.

[0133] As an optional embodiment, the bottom end of the auger shaft 71 of the spiral feeder 7 passes through the feed pipe 31, a gear 72 is installed at the bottom end of the auger shaft 71, and an external gear ring 9 is installed at the top of the rotating sleeve 53. The gear 72 meshes with the rotating sleeve 53.

[0134] By setting a gear 72 at the bottom end of the auger shaft 71 and an external gear ring 9 on the rotating sleeve 53, when the stirring rod 22 drives the transmission tube 55 to rotate through the square part 221, the transmission tube 55 drives the first material plate 51 and the second material plate 52 to rotate in sequence. The second material plate 52 drives the rotating sleeve 53 to rotate along the support ring 54, and at the same time drives the external gear ring 9 to rotate. The external gear ring 9 meshes with the gear 72, driving the gear 72 to rotate. The gear 72 drives the auger shaft 71 to rotate, thereby driving the conveying screw located on the auger shaft 71 to rotate, and the material is fed out by the conveying screw.

[0135] The bottom end of the auger shaft 71 passes through the feed pipe 31 and is sealed by a mechanical seal to ensure the sealing of the connection.

[0136] As another optional method in this embodiment, the gear 72 can be replaced with a drive motor. The drive motor can be installed in the dissolving tank 1 through a mounting bracket, and the output end of the drive motor is fixedly connected to the bottom end of the auger shaft 71; or the drive motor can be installed on the inner wall or the top sealing cover of the storage cylinder 3 through a mounting bracket, and the top end of the auger shaft 71 is fixedly connected to the output end of the drive motor.

[0137] Compared with related technologies, the dissolving device provided by the present invention has the following beneficial effects:

[0138] In use, first, deionized water is added to the dissolving tank 1. The temperature-regulating sleeve 101 and a temperature sensor are used to cool the deionized water to a preset temperature. Then, crude lithium dihydrogen phosphate powder is added to the dissolving tank 1 through the feed pipe 31. During this process, some of the crude lithium dihydrogen phosphate powder entering through the feed pipe 31 falls onto the second material tray 52, and the other part falls onto the first material tray 51 through the central hole of the second material tray 52. ​​The driving component drives the first material tray 51 and the second material tray 52 to rotate, causing centrifugal force to be generated in the first material tray 51 and the second material tray 52. ​​The material on them is dispersed in the deionized water along the first material tray 51 and the second material tray 52. ​​Since the diameter of the second material tray 52 is larger than that of the first material tray 51, ... Figure 6 The materials dispersed from the two trays enter the deionized water at different locations;

[0139] At the same time, the stirring device 2 stirs the material, thereby dispersing the material in deionized water, which can accelerate the dissolution rate of the material and improve the dissolution efficiency and quality.

[0140] Specifically, when material needs to be discharged, the lifting cylinder 61 raises the valve plate 63, and the valve plate 63 raises the transmission pipe 55 through the connecting rod 8 and the bearing seat 551. The transmission pipe 55 moves upward accordingly. When the valve plate 63 is raised to the preset height, the square groove 552 at the top of the transmission pipe 55 is fitted onto the square part 221 of the stirring rod 22. At this time, when the motor 21 drives the stirring rod 22 to rotate, the stirring rod 22 drives the stirring blade 23 to rotate, and at the same time, drives the transmission pipe 55 to rotate through the square part 221. The transmission pipe 55 drives the first material tray 51 to rotate, and the first material tray 51 drives the second material tray 52 to rotate through the first guide plate 511, thereby driving the first material tray 51 and the second material tray 52 to rotate simultaneously, so that the lithium dihydrogen phosphate powder can be dispersed into deionized water for dissolution and mixing.

[0141] After a single feeding of lithium dihydrogen phosphate powder is completed, the motor 21 stops, the lifting cylinder 61 lowers the valve plate 63 to block the feed pipe 31 again, and at the same time the connecting rod 8 drives the transmission pipe 55 to descend through the bearing seat 551, so that the transmission pipe 55 separates from the square part 221. The motor 21 drives the stirring rod 22 to rotate again, which drives the stirring blade 23 to rotate to carry out the dissolution work. At this time, the feeding component 5 will not be driven to work.

[0142] Therefore, in one state, the motor 21 drives the feeding assembly 5 to disperse the material into the deionized water and simultaneously perform stirring. In another state, it is only used to drive the stirring blade 23 to rotate and perform stirring and mixing.

[0143] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for purifying lithium dihydrogen phosphate using reverse temperature difference washing, characterized in that, Includes the following steps: S1. Low-temperature dissolution: Deionized water is added to the dissolution equipment and pre-cooled to 0-5°C. Then, crude lithium dihydrogen phosphate is added to the deionized water, and the system temperature is maintained at 0-5°C. Under stirring conditions, the crude lithium dihydrogen phosphate is fully dissolved in the deionized water to obtain a low-temperature solution. S2: Heating crystallization: The low-temperature solution is heated to 20-30°C at a heating rate of 0.5-3°C / min, so that the dissolved lithium dihydrogen phosphate precipitates again in the form of crystals, resulting in a solid-liquid mixture; S3: Separation and drying: The liquid mixture is separated into solid and liquid components. The separated solid is dried at 60-110°C for 4-12 hours to obtain battery-grade lithium dihydrogen phosphate product.

2. The method for purifying lithium dihydrogen phosphate by reverse temperature difference washing according to claim 1, characterized in that, The solid-liquid mass ratio of the crude lithium dihydrogen phosphate to deionized water is 1:3 to 1:

6.

3. The method for purifying lithium dihydrogen phosphate by reverse temperature difference washing according to claim 1, characterized in that, The deionized water is pre-cooled to 0–2°C.

4. The method for purifying lithium dihydrogen phosphate by reverse temperature difference washing according to claim 1, characterized in that, In step S3, the mother liquor after solid-liquid separation is treated by cooling and reuse or by evaporation and concentration.

5. A dissolving apparatus, characterized in that, Used in step S1 of the method for purifying lithium dihydrogen phosphate by reverse temperature difference washing as described in any one of claims 1-4; Includes: a dissolving tank, wherein a temperature regulating sleeve is fitted onto the dissolving tank; A stirring device is installed in the dissolving tank and is used to stir and mix the solution in the dissolving tank. A feeding assembly includes a first feeding tray, a second feeding tray, a rotating sleeve, a support ring, and a driving component. The first feeding tray, the second feeding tray, the rotating sleeve, and the support ring are all concentrically arranged and sleeved on the outside of the stirring rod of the stirring device. The inner and outer diameters of the second feeding tray are larger than those of the first feeding tray. The top of the first feeding tray is fixedly connected to the second feeding tray via a first guide plate. The rotating sleeve is fixedly connected to the top of the second feeding tray via a second guide plate. The support ring is fixed to the inner wall of the dissolving tank via a support rod. The rotating sleeve is sleeved on and rotatably mounted on the support ring. The driving component is used to drive the first and second material trays to rotate. The feed pipe has its bottom end penetrating the melting tank and extending above the support ring.

6. The dissolving apparatus according to claim 5, characterized in that, The dissolving equipment also includes a storage cylinder and valves. The storage cylinder is suspended above the dissolving tank. The feed pipe is connected to the discharge end of the storage cylinder. The valves are used to control the connection status of the feed pipe. A spiral feeder is installed inside the feed pipe.

7. The dissolving apparatus according to claim 6, characterized in that, The top of the dissolving tank is equipped with multiple weighing columns, and the top of each weighing column is equipped with a weighing sensor. A support plate is installed on the feed pipe, and the weighing sensor is used to support the support plate.

8. The dissolving apparatus according to claim 7, characterized in that, The valve includes a lifting cylinder, a valve housing, and a valve plate. The valve housing is connected to the feed pipe, the lifting cylinder is mounted on the support plate, the valve plate is slidably disposed inside the valve housing, and the output end of the lifting cylinder is connected to the valve plate.

9. The dissolving apparatus according to claim 8, characterized in that, The driving component is a transmission tube, which is sleeved on the stirring rod. The bottom end of the transmission tube passes through the first material tray and forms a circumferential fixed and axial sliding fit with the first material tray. A square groove is opened at the top of the transmission tube, and a square part is provided on the stirring rod above the transmission tube. The square part is aligned with the square groove. The transmission pipe is equipped with a bearing housing, and the dissolving device also includes a connecting rod that connects the bearing housing and the valve plate.

10. The dissolving apparatus according to claim 9, characterized in that, The bottom end of the auger shaft of the spiral feeder passes through the feed pipe. A gear is installed at the bottom end of the auger shaft, and an external gear ring is installed at the top of the rotating sleeve. The gear meshes with the rotating sleeve.

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