Battery-grade lithium phosphate and preparation method thereof

Abstract

The preparation method comprises the following steps: firstly, preparing a lithium source solution and an ammonium phosphate salt phosphorus source solution, preheating a phosphorus source and a lithium source, adding the preheated lithium source into the phosphorus source solution in a spraying charging manner under a stirring condition, adding ammonia water into a system to adjust the pH value to 9.5 or above after feeding is completed, and then adding ammonium hydroxide into the system to obtain a lithium phosphate solution; stirring and aging under the condition of heat preservation to obtain lithium-containing slurry, finally separating solids in the obtained lithium-containing slurry, performing multi-stage washing and drying to obtain battery-grade lithium phosphate, and adjusting the pH gt of a first-stage washing solution by using a lithium hydroxide solution; 12.5, 12.5. The purity of the prepared battery-grade lithium phosphate is 99.5% or above.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery material technology, and particularly relates to a battery-grade lithium phosphate and its preparation method. Background Technology

[0002] Lithium phosphate, as an important lithium compound, has attracted much attention due to its unique optical, catalytic and electrochemical properties, and has been widely used in special glass, colored phosphors, catalysts and cathode materials for lithium-ion batteries.

[0003] In recent years, with the rapid development of the new energy vehicle and energy storage industries, the demand for lithium batteries has surged, driving a boom in demand across the entire industry chain, including lithium iron phosphate materials. According to brokerage research reports, global demand for lithium iron phosphate batteries is projected to reach 600 GWh by 2025, with demand for lithium iron phosphate materials reaching 2 million tons. As a key precursor raw material for lithium iron phosphate, the demand for lithium phosphate is showing strong growth, and its performance is a crucial factor affecting the performance of lithium iron phosphate batteries.

[0004] Currently, lithium phosphate is mainly prepared using hydrothermal synthesis and chemical precipitation methods, but these methods contain a large amount of SO4. 2- And Na + When lithium-containing solutions containing impurity ions are used as raw materials, these ions are easily encapsulated within the lithium phosphate during the reaction and crystallization process. They are difficult to remove effectively using conventional separation and purification methods, significantly reducing the purity of the lithium phosphate product. This makes it unable to meet the stringent requirements for impurity content in lithium-ion battery cathode materials, thus limiting its application in high-value-added fields. Chinese patent application CN110357055 A discloses a method for extracting lithium from salt lake brine and preparing lithium phosphate, along with its applications. This method uses oxalic acid to remove impurities such as calcium and magnesium, and combines microwave heating to regulate the precipitation rate and pore formation of lithium phosphate generated from the reaction of lithium liquid and phosphate ions, resulting in nanoscale porous lithium phosphate. However, this method involves microwave high-temperature heating and low-temperature freezing processes, leading to high energy consumption. Furthermore, the content of each impurity element is close to 200 ppm, failing to meet the purity requirements for battery-grade lithium phosphate. Chinese patent application CN 119240629 A discloses a method for preparing battery-grade lithium phosphate from lithium carbonate mother liquor after lithium extraction from salt lake brine. The method uses lithium carbonate mother liquor as raw material, adjusts the pH to 11-14, adds sodium phosphate for nucleation, aging and separation to obtain crude lithium phosphate; then the crude lithium phosphate is acid-dissolved, the pH is adjusted to 11-14 and a dispersant is added, and after aging, filtration, washing and drying, battery-grade lithium phosphate is obtained. However, this method has the problems of long process flow, large amount of acid and alkali used and high preparation cost.

[0005] Current technologies for preparing battery-grade lithium phosphate are not yet mature enough. Therefore, there is an urgent need to develop a new process for preparing battery-grade lithium phosphate, aiming to achieve economical, efficient and stable preparation of battery-grade lithium phosphate to meet the market demand for high-performance lithium phosphate materials in power batteries and energy storage systems. This process has great economic value. Summary of the Invention

[0006] To overcome the problems in the prior art, the present invention provides a battery-grade lithium phosphate and its preparation method, which is simple in process and yields battery-grade lithium phosphate with a purity of over 99.5%.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: This invention provides a method for preparing battery-grade lithium phosphate, comprising the following steps: S1. Prepare lithium source solution and ammonium phosphate source solution; S2. After preheating the phosphorus source and lithium source, the preheated lithium source is added to the phosphorus source solution by spray feeding under stirring conditions. After feeding is completed, ammonia water is added to the system to adjust the pH. The lithium-containing slurry is obtained by stirring and aging under heat preservation conditions. S3. After separating the solids from the lithium-containing slurry obtained in S2, the solids are washed and dried in multiple stages to obtain battery-grade lithium phosphate. The pH of the first-stage washing solution is adjusted to >12.5 using lithium hydroxide solution.

[0008] In this invention, the phosphorus and lithium sources are preheated, and then the lithium source is added to the phosphorus source in a highly dispersed manner via spray feeding. This avoids instantaneous nucleation caused by excessively high local concentrations, effectively inhibits particle aggregation, and reduces the entrainment and encapsulation of impurity ions such as sulfate and sodium in the lithium phosphate product. Using a phosphate-based phosphorus source while simultaneously utilizing ammonia as a pH adjuster allows the reaction system to form NH4+. + The NH3 buffer system helps maintain a stable pH environment, preventing crystal defects caused by localized over-acidity / over-alkaliness, and better controlling the crystal growth rate, which is beneficial for generating lithium phosphate crystals with uniform particle size and regular morphology. Further stirring and aging ensures complete reaction between the lithium and phosphorus sources, improving product yield. The first-stage washing uses lithium hydroxide solution as a pH adjuster to adjust the system pH to >12.5, ensuring that the precipitated lithium exists in a stable crystalline form of lithium phosphate, guaranteeing product purity meets battery-grade material standards.

[0009] As an optional implementation method, in the preparation method provided by the present invention, in step S3, the washing process is divided into 2 to 3 stages, and the temperature of the first-stage washing liquid is 85 to 100°C.

[0010] In this invention, the first-stage washing solution uses lithium hydroxide solution to adjust the pH to >12.5 and the temperature to 85-100℃, which can fully convert lithium dihydrogen phosphate and lithium hydrogen phosphate in the wet material into lithium phosphate.

[0011] As an optional implementation method, in the preparation method provided by the present invention, the liquid-to-solid ratio during the washing process is 2 to 5:1, and the washing time is 20 to 40 minutes.

[0012] As an optional implementation, in the preparation method provided by the present invention, in S2, the reaction device is a stirred reactor, and the stirred reactor is provided with baffles.

[0013] This invention adds baffles to the stirred reactor, which reconstructs the flow field, improves the mixing uniformity, reduces the central dead zone by more than 60%, and can also significantly increase the droplet collision frequency, promote the uniform dispersion of lithium phosphate particles, and reduce the encapsulation of impurity ions.

[0014] As an optional implementation method, in the preparation method provided by the present invention, in S2, the preheating temperature of the lithium source and the phosphorus source is 85-100°C.

[0015] The lithium precipitation reaction in this invention is an endothermic reaction. Increasing the reaction temperature can raise the activation energy, accelerate the reaction rate, and significantly improve the precipitation rate. Simultaneously, increasing the temperature can also improve the yield and purity of the lithium phosphate product.

[0016] As an optional implementation method, in the preparation method provided by the present invention, in step S2, the molar ratio of the phosphorus source to the lithium source is 0.33 to 0.40:1.

[0017] In this invention, controlling the molar ratio of phosphorus source to lithium source allows lithium in the solution to react fully to form lithium phosphate, increasing the lithium precipitation rate in the solution, i.e., improving the lithium phosphate recovery rate. When the ratio is less than this range, the lithium reaction in the solution is incomplete, affecting the lithium precipitation rate; when the ratio is greater than this range, the amount of phosphorus source used increases, which increases the preparation cost.

[0018] As an optional implementation, in the preparation method provided by the present invention, in S2, the atomized droplets of the spray feeding device are <40μm, and the lithium source feeding rate is 4-10mL / min.

[0019] In this invention, controlling the feeding rate of the atomized droplets and the lithium source in the spray feeding device can avoid instantaneous nucleation caused by excessively high local concentrations and effectively suppress particle aggregation. Particles larger than 40 μm are prone to aggregation, increasing the entrainment and encapsulation of impurity ions such as sulfate and sodium in the product, leading to reduced product purity. Excessive lithium source feeding rate results in higher local supersaturation in the system, a sharp increase in the nucleation rate, easy particle aggregation, and easy encapsulation of impurity particles, causing a decrease in the purity of lithium phosphate crystals.

[0020] As an optional implementation method, in the preparation method provided by the present invention, the concentration of ammonia in S2 is 25-28%.

[0021] As an optional implementation method, in the preparation method provided by the present invention, in step S2, the stirring and aging temperature is 85-100°C; and the stirring and aging time is 0.5-1.5 h.

[0022] As an optional implementation, in the preparation method provided by the present invention, in S2, the lithium source solution is a lithium extraction mixture from spodumene using the sulfuric acid method, wherein the lithium oxide concentration in the lithium source is 28-32 g / L, the sulfate content is 60-73 g / L, and the sodium content is 5-7 g / L.

[0023] As an optional implementation, in the preparation method provided by the present invention, the phosphate is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or ammonium phosphate, and the concentration of the phosphorus source is 0.5 to 1.0 mol / L.

[0024] This invention uses ammonium phosphate salts, which on the one hand block the introduction of sodium ions at the source, eliminating the risk of sodium pollution; on the other hand, the high water solubility of ammonium salts allows for the efficient removal of residual ammonium ions with just simple washing, which can significantly improve the purity of the product.

[0025] Based on the same technical concept, the present invention also provides lithium phosphate prepared by the above-mentioned method for preparing battery-grade lithium phosphate, wherein the lithium phosphate has a purity >99.5% and a D50 of 3-7 μm.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, ammonium phosphate salts are used as the phosphorus source and ammonia water is used as the pH adjuster, which can make the reaction system form NH4. + The NH3 buffer system helps maintain a stable pH environment, preventing crystal defects caused by localized over-acidity / over-alkaliness, and better controlling the crystal growth rate, which is beneficial for generating lithium phosphate crystals with uniform particle size and regular morphology. Meanwhile, the first-stage stirring process of this invention, by adjusting the system pH to >12.5, ensures that the precipitated lithium exists in a stable crystalline form of lithium phosphate, guaranteeing that the product purity meets battery-grade material standards.

[0027] (2) This invention integrates technologies such as flow field reconstruction, mixing enhancement and spray feeding through process innovation and raw material optimization (ammonium phosphate as phosphorus source), and achieves economical, efficient and stable preparation of battery-grade lithium phosphate by strengthening the process and controlling key parameters.

[0028] (3) The method for preparing battery-grade lithium phosphate in this invention uses ammonium phosphate salt phosphorus source solution as phosphorus source. The prepared lithium phosphate has a purity of >99.5% and a D50 of 3-7μm. It has the advantages of mild reaction conditions, high lithium recovery rate, high product purity, simple equipment operation, low cost, green environmental protection and no secondary pollution. It is suitable for large-scale industrial production and has good application prospects. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 SEM image of the battery-grade lithium phosphate prepared in Example 1; Figure 2 XRD pattern of battery-grade lithium phosphate prepared in Example 1; Figure 3 The image shows a SEM image of the battery-grade lithium phosphate prepared in Example 2. Detailed Implementation

[0031] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0034] Example 1 A method for preparing battery-grade lithium phosphate. In this embodiment, the raw material is a lithium extraction mixture obtained by the spodumene-sulfuric acid process. After filtration, the lithium source composition analysis is shown in Table 1 below: Table 1. Composition of Lithium Source Raw Materials

[0035] Includes the following steps: (1) Measure 2395 mL of 0.83 mol / L diammonium hydrogen phosphate solution and add it to the jacketed reactor, preheating it to 95°C; measure 2973 mL of lithium source and preheat it to 95°C.

[0036] (2) Under the condition of controlling the stirring rate at 375 rpm, the preheated lithium source was added to the phosphorus source at a rate of 4.3 mL / min using a spray feeding device. The atomized droplets of the spray feeding device were 15 μm. After the feeding was completed, 570 g of 25% ammonia water was added to adjust the pH of the system to 9.81. The system was stirred and aged at 95 °C for 1 h to obtain a lithium-containing slurry.

[0037] (3) The lithium-containing slurry was separated into solid and liquid by centrifuge. The solid was added to 800g of 95℃ deionized water and 66g of lithium hydroxide saturated solution was added to adjust the pH to 12.67. After stirring and reacting at 95℃ for 25min, the mixture was filtered. The solid was then subjected to second and third stage washing, with 1000g of deionized water used for each stage. The mixture was washed at room temperature for 25min and then filtered. The wet lithium phosphate was dried in an oven at 120℃ to prepare battery-grade lithium phosphate. Specifically, the purity of lithium phosphate was 99.82%, sodium was 45ppm, sulfate was 750ppm, and the product particle size D50 was 3.5μm.

[0038] Example 2 A method for preparing battery-grade lithium phosphate. In this embodiment, the raw material is a lithium extraction mixture obtained by the spodumene-sulfuric acid process. After filtration, the lithium source composition analysis is shown in Table 2 below: Table 2 Lithium Source Raw Material Composition Table

[0039] Includes the following steps: (1) Measure 3146 mL of 0.63 mol / L diammonium hydrogen phosphate solution and add it to the jacketed reactor, preheating it to 85°C; measure 3140 mL of lithium source and preheat it to 85°C.

[0040] (2) Under the condition of controlling the stirring rate at 320 rpm, the preheated lithium source was added to the phosphorus source at a rate of 6.0 mL / min using a spray feeding device. The atomized droplets of the spray feeding device were 20 μm. After the feeding was completed, 550 g of 25% ammonia water was added to adjust the pH of the system to 9.61. The system was stirred and aged at 85 °C for 1 h to obtain a lithium-containing slurry.

[0041] (3) The lithium-containing slurry was separated into solid and liquid by centrifuge. The solid was added to 800g of deionized water at 85℃ and 60g of saturated lithium hydroxide solution was added to adjust the pH to 12.53. After stirring and reacting at 85℃ for 30min, the mixture was filtered. The solid after the first stage of stirring and washing was added to 800g of deionized water and stirred and washed at room temperature for 30min. The mixture was then filtered. The wet lithium phosphate was placed in an oven at 105℃ to dry, and battery-grade lithium phosphate was prepared. Specifically, the purity of lithium phosphate was 99.69%, sodium was 56ppm, sulfate was 1013ppm, and the product particle size D50 was 5.4μm.

[0042] Example 3 A method for preparing battery-grade lithium phosphate. In this embodiment, the raw material is a lithium extraction mixture obtained by the spodumene-sulfuric acid process. After filtration, the lithium source composition analysis is shown in Table 3 below: Table 3. Composition of Lithium Source Raw Materials

[0043] Includes the following steps: (1) Measure 2829 mL of 0.70 mol / L ammonium phosphate solution and add it to the jacketed reactor, preheating it to 90°C; measure 2814 mL of lithium source and preheat it to 90°C.

[0044] (2) Under the condition of controlling the stirring rate at 250 rpm, the preheated lithium source was added to the phosphorus source at a rate of 8.0 mL / min using a spray feeding device. The atomized droplets of the spray feeding device were 10 μm. After the feeding was completed, 560 g of 25% ammonia water was added to adjust the pH of the system to 9.67. The system was stirred and aged at 90 °C for 1 h to obtain a lithium-containing slurry.

[0045] (3) The lithium-containing slurry was separated into solid and liquid by centrifuge. The solid was added to 1000g of 90℃ deionized water and 62g of saturated lithium hydroxide solution was added to adjust the pH to 12.60. After stirring and reacting at 90℃ for 30min, the mixture was filtered. The solid after the first stage of stirring and washing was added to 1000g of deionized water and stirred and washed at room temperature for 30min. The mixture was then filtered. The wet lithium phosphate was placed in a 120℃ oven to dry, and battery-grade lithium phosphate was prepared. Specifically, the purity of lithium phosphate was 99.62%, sodium was 68ppm, sulfate was 1205ppm, and the product particle size D50 was 6.5μm.

[0046] Comparative Example 1 The difference from Example 1 is that a spray feeding device is not used; instead, a peristaltic pump is used to add the preheated lithium source to the phosphorus source at a rate of 20 mL / min. All other steps are the same as in Example 1.

[0047] The specific indicators of the prepared lithium phosphate are as follows: lithium phosphate purity is 97.28%, sodium is 283 ppm, sulfate is 10039 ppm, and product particle size D50 is 4.8 μm.

[0048] Comparative Example 2 The difference from Example 2 is that neither the lithium source nor the phosphorus source is preheated, i.e., both are room temperature solutions, while the other steps are the same as in Example 2.

[0049] The specific indicators of the prepared lithium phosphate are as follows: lithium phosphate purity is 96.05%, sodium is 563 ppm, sulfate is 25867 ppm, and product particle size D50 is 7.5 μm.

[0050] Comparative Example 3 The difference from Example 1 is that in step (3), a saturated lithium hydroxide solution is not added to adjust the pH, while the other steps are the same as in Example 1.

[0051] The specific indicators of the prepared lithium phosphate are as follows: lithium phosphate purity is 98.52%, sodium is 51 ppm, sulfate is 783 ppm, and product particle size D50 is 4.0 μm.

[0052] Comparative Example 4 The difference from Example 1 is that after feeding is completed in step (2), ammonia water is not added to adjust the pH. All other steps are the same as in Example 1.

[0053] The lithium recovery rate decreased, and the specific indicators of the prepared lithium phosphate were: lithium phosphate purity of 97.63%, sodium content of 43 ppm, sulfate content of 741 ppm, and product particle size D50 of 3.9 μm. In Comparative Example 4, no ammonia was added to adjust the pH during the lithium precipitation stage, and the content of lithium dihydrogen phosphate and other components in the product was higher than that in Comparative Example 3. Therefore, the purity of the lithium phosphate product in Comparative Example 4 was lower.

[0054] Comparative Example 5 The difference from Example 1 is that after the lithium precipitation reaction slurry is separated into solid and liquid components, there is no washing treatment, and the wet material is directly dried. All other steps are the same as in Example 1.

[0055] The specific indicators of the prepared lithium phosphate are as follows: lithium phosphate purity is 98.12%, sodium is 146 ppm, sulfate is 990 ppm, and product particle size D50 is 3.7 μm.

[0056] Performance testing The lithium phosphate prepared in Example 1 was examined by electron microscopy, and the SEM image is shown below. Figure 1 As shown, by Figure 1 It can be seen that the lithium phosphate sample has a good morphology, exhibiting a relatively loose micron rod-shaped crystal structure with some attached nanoparticles.

[0057] The lithium phosphate prepared in Example 1 was subjected to XRD analysis, and the results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the diffraction peaks of the lithium phosphate sample are sharp, and their positions and intensities are consistent with those of the lithium phosphate standard card (PDF25-1030). There are no obvious impurity peaks, indicating that the prepared lithium phosphate has good crystallinity, complete cell structure, and good crystal structure order.

[0058] The lithium phosphate prepared in Example 2 was examined by electron microscopy, and the SEM image is shown below. Figure 3 As shown, by Figure 3 It can be seen that the lithium phosphate sample has a micron rod-like structure and the particles are relatively loose.

[0059] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing battery-grade lithium phosphate, characterized in that, Includes the following steps: S1. Prepare lithium source solution and ammonium phosphate source solution; S2. After preheating the phosphorus source and lithium source, the preheated lithium source is added to the phosphorus source solution by spray feeding under stirring conditions. After feeding is completed, ammonia water is added to the system to adjust the pH to above 9.

5. The lithium-containing slurry is obtained by stirring and aging under heat preservation conditions. S3. After separating the solids from the lithium-containing slurry obtained in S2, the solids are washed and dried in multiple stages to obtain battery-grade lithium phosphate. The pH of the first-stage washing solution is adjusted to >12.5 using lithium hydroxide solution.

2. The method for preparing battery-grade lithium phosphate according to claim 1, characterized in that, In S3, the washing process consists of 2 to 3 stages, with the temperature of the first-stage washing liquid being 85 to 100℃.

3. The method for preparing battery-grade lithium phosphate according to claim 2, characterized in that, The liquid-to-solid ratio during the washing process is 2–5:1, and the washing time is 20–40 minutes.

4. The method for preparing battery-grade lithium phosphate according to claim 1, characterized in that, In S2, the preheating temperature of the lithium source and phosphorus source is 85-100℃.

5. The method for preparing battery-grade lithium phosphate according to claim 1, characterized in that, In S2, the molar ratio of the phosphorus source to the lithium source is 0.33 to 0.40:

1.

6. The method for preparing battery-grade lithium phosphate according to claim 1, characterized in that, In S2, the atomized droplets of the spray feeding device are <40μm; the lithium source feeding rate is 4~10mL / min.

7. The method for preparing battery-grade lithium phosphate according to claim 1, characterized in that, In S2, the stirring and aging temperature is 85–100℃; the stirring and aging time is 0.5–1.5 h.

8. The method for preparing battery-grade lithium phosphate according to claim 1, characterized in that, In S2, the lithium source has a lithium oxide concentration of 28–32 g / L, a sulfate content of 60–73 g / L, and a sodium content of 5–7 g / L.

9. The method for preparing battery-grade lithium phosphate according to claim 1, characterized in that, The ammonium phosphate salt is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or ammonium phosphate, and the concentration of the phosphorus source is 0.5–1.0 mol / L.

10. Lithium phosphate prepared by the method for preparing battery-grade lithium phosphate according to any one of claims 1 to 9, characterized in that, The lithium phosphate has a purity of >99.5% and a D50 of 3–7 μm.

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