A method for preparing high-purity micron lithium phosphate powder

Abstract

The present invention relates to a method for preparing high-purity micron lithium phosphate powder, which comprises mixing phosphoric acid with an impurity remover and a dispersant, adding a lithium-containing substance to react at room temperature, adjusting the pH to neutral with an alkali solution after the reaction is completed, and then performing solid-liquid separation, washing the solid with deionized water by ultrasonic vibration, performing solid-liquid separation, and drying the solid to obtain high-purity micron lithium phosphate powder. The preparation method provided by the present invention is applicable to any lithium-containing substance, and high-purity lithium phosphate can be prepared by the proportion in the present invention. The preparation process is simple, convenient and fast, the reaction conditions are mild, and it is easy to realize industrial production. The purity of the obtained lithium phosphate is between 99.9-99.999%, and the particle size is less than 1-3 μm, which can be used for Li3PO4 target material, solves the problem that the material needs to rely on imports, and greatly reduces the production cost of Li3PO4 target material.

Description

Technical Field

[0001] The invention relates to a method for preparing high-purity micron lithium phosphate powder, and belongs to the technical field of high-performance target material preparation. Background Art

[0002] Lithium phosphate is a high temperature resistant material. It is an ideal raw material for producing color phosphors because it is non-radioactive, has the advantages of short illumination but long light effect and low cost. The LiPON solid electrolyte film prepared by lithium phosphate (Li3PO4) target is the most widely used electrolyte film in all-solid-state thin-film lithium batteries. The purity of lithium phosphate directly affects the performance of the LiPON solid electrolyte film sputtered from its target, and then affects the battery performance. At the same time, the particle size of lithium phosphate affects the density, strength and hardness of the target. The purity of lithium phosphate powder used for the most important Li3PO4 target needs to reach more than 99.9%, but the current existing technology for the research of high-purity Li3PO4 fine powder is not mature enough, which restricts the breakthrough of Li3PO4 target production technology. Therefore, the use of Li3PO4 target can only rely on imports, which greatly limits the development of all-solid-state lithium batteries.

[0003] The patent application publication number is CN110357055A, which discloses a method for extracting lithium from salt lake brine and preparing lithium phosphate and its use. Oxalic acid is used as a precipitant to remove impurity metal ions such as calcium and magnesium in the salt lake brine to obtain a filtrate containing lithium ions. The phosphate radicals in the filtrate interact with the lithium ions, and microwave heating is combined to adjust the precipitation rate of lithium phosphate and pore formation, thereby obtaining nano-scale porous lithium phosphate. The extraction rate of lithium from the salt lake brine is greater than 94%. The primary particle size of the prepared nano-scale porous lithium phosphate is 10-95nm, the secondary particle size is 100-1000nm, the porosity is 50-85%, and the content of each impurity element is below 200ppm. However, this method uses oxalic acid to remove impurities only for Ca and Mg ions, and the removal effect is limited. The content of each impurity element is as high as 200ppm, which can only reach the level of industrial-grade lithium phosphate, and the purity cannot meet the high purity requirements.

[0004] The patent application publication number is CN103435023A, which discloses a method for preparing ultrafine lithium phosphate powder. Phosphoric acid is diluted with deionized water and introduced into a reactor, a water-soluble nonionic surfactant is added, and a lithium hydroxide solution is slowly added under turbulent circulation conditions. The pH value is monitored, the product is centrifuged after being kept warm and aged, and the product is washed with deionized water and dried to obtain ultrafine lithium phosphate powder. The process is simple, stable, has a high specific surface area, and the particle size can be controlled at 3.6-8.9μm. However, the lithium phosphate product prepared is battery grade and does not reach the high-purity level. The product will have surfactant residues and cannot meet the preparation and use of high-performance target materials.

[0005] The patent application publication number is CN103754852A, which discloses a method for preparing lithium phosphate nanoparticles. An aqueous solution of lithium element and an aqueous solution containing phosphorus element are quickly mixed in a microreactor to react at 20-90°C. A lithium phosphate slurry is obtained at the reactor outlet. After solid-liquid separation, washing, drying and grinding, lithium phosphate particles in a nanoparticle state with good monodispersity are finally obtained. The method has mild conditions and is easy to operate. The particle size of the prepared lithium phosphate particles is between 50-200nm, and the yield is more than 90%. However, the reactor used is small and cannot be used for industrial mass production. The method does not remove impurities, and the purity of the product depends on the purity of the raw materials. At the same time, grinding will bring in pollution and increase the impurity content in the product, and a high-purity lithium phosphate product cannot be obtained. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] In order to solve the above problems in the prior art, the present invention provides a method for preparing high-purity micron lithium phosphate powder. The obtained lithium phosphate powder has a purity of 99.9-99.999% and a particle size of 1-3 μm.

[0008] (II) Technical solution

[0009] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0010] A method for preparing high-purity micron lithium phosphate powder comprises the following steps:

[0011] S1. Weighing a lithium-containing solid or a lithium-containing solution prepared from a lithium-containing solid.

[0012] S2, adding impurity remover and dispersant to the phosphoric acid solution, mixing and stirring to react;

[0013] S3, adding the lithium-containing solid or lithium-containing solution in step S1 to the phosphoric acid solution in step S2, and stirring the reaction at room temperature;

[0014] S4, adding alkali solution to the solution after the reaction in step S3 to adjust the pH to neutral;

[0015] S5, separating the solution from step S4 into solid and liquid, and washing the solid with deionized water by ultrasonic vibration for 1 to 3 times;

[0016] S6. The solution in step S5 is subjected to solid-liquid separation, and the solid is dried to obtain high-purity micron lithium phosphate powder.

[0017] In the preparation method as described above, the order of step S1 and step S2 can be adjusted.

[0018] In the preparation method as described above, preferably, in step S1, the lithium-containing solid is one or a mixture of lithium hydroxide, lithium carbonate, lithium bicarbonate, lithium iodide, lithium fluoride, lithium chloride or lithium tetrafluoroborate.

[0019] In the preparation method as described above, preferably, in step S1, the lithium-containing solution is an aqueous solution with a lithium element mass percentage of 0.1 to 3.5 wt%.

[0020] In the preparation method as described above, preferably, in step S2, the mass concentration of phosphoric acid in the phosphoric acid solution is 5-85%, and the amount of the phosphoric acid solution used is 0.05-0.3 times the mass of the lithium element in the lithium-containing substance in step S1 calculated as pure phosphoric acid.

[0021] In the preparation method as described above, preferably, in step S2, the impurity remover is ethylenediaminetetraacetic acid, and the amount of the impurity remover added is 0.01 to 0.5 times the mass of the lithium element;

[0022] The dispersant is one or more of ethanol, isopropanol, n-butanol, ethylene glycol, acetone, and polyacrylamide, and the added amount of the dispersant is 0.5 to 18 times the mass of the lithium element.

[0023] In the preparation method as described above, preferably, in step S3, the stirring reaction time is 15 to 60 minutes, and the stirring rate is controlled at 100 to 500 r / min.

[0024] In the preparation method as described above, preferably, in step S4, the alkali solution is one or a mixture of NaOH, ammonia water, LiOH, KOH, Ca(OH)2, Ba(OH)2 solution; the amount of alkali solution added is such that the pH of the solution is 7.

[0025] In the preparation method as described above, preferably, in steps S5 and S6, the solid-liquid separation is filtration or centrifugation.

[0026] In the above-mentioned preparation method, preferably, in step S5, the ultrasonic oscillation time is 5 to 15 minutes. In the above-mentioned preparation method, in step S6, the drying temperature is 80 to 220°C and the drying time is 2 to 5 hours. In the above-mentioned preparation method, the purity of lithium phosphate obtained is 99.9 to 99.999% and the particle size is 1 to 3 μm.

[0027] (III) Beneficial effects

[0028] The beneficial effects of the present invention are:

[0029] The method for preparing high-purity micron lithium phosphate powder provided by the present invention is applicable to any lithium-containing substance, and high-purity lithium phosphate can be prepared by the proportion in the present invention. The preparation process is simple, convenient and fast, the reaction conditions are mild, and industrial production is easy to achieve.

[0030] In the preparation method of the present invention, alkali solution is used to adjust pH, improve the stability of lithium phosphate, and promote the enrichment of reaction products to lithium phosphate; ethylenediaminetetraacetic acid is used to remove metal impurities in the solution, which can save a solid-liquid separation process compared with the precipitation method in the form of complexation, and the amount is small, and no extra impurities are introduced. The addition of a dispersant can prevent the impurity wrapping phenomenon caused by particle agglomeration, and can also refine the particle size. At the same time, ultrasonic vibration washing can fully wash away soluble impurities attached to the surface of lithium phosphate, and a high-purity micron-level lithium phosphate product can be obtained in one step. The dispersant used can be completely volatilized during the drying process, and there is no residue in the product. The purity of the obtained lithium phosphate is between 99.9-99.999%, and the particle size is 1-3μm, which can be used for Li3PO4 target materials, solving the problem of relying on imports of materials and greatly reducing the production cost of Li3PO4 target materials. DETAILED DESCRIPTION

[0031] The invention principle of the present invention is as follows: lithium ions react with phosphoric acid to generate solid lithium phosphate particles, an impurity remover is added during the reaction process, and the mass ratio of the impurity remover to lithium is maintained between 0.01 and 0.5 times. Before the solid particles are formed, the metal elements in the solution in an ionic state can be complexed to the maximum extent, and their enrichment in the solid particles (products) can be reduced to achieve the effect of purification and impurity removal. The complex remains in the liquid. Compared with the precipitation impurity removal method, the solid-liquid separation step can be reduced, and the impurity removal is completed in one step. The impurity remover is preferably ethylenediaminetetraacetic acid; at the same time, a dispersant is added during the reaction process. When small solid lithium phosphate crystals are generated, the dispersant wraps them, increases the steric hindrance, and controls the aggregation of particles. The dispersant is preferably one of ethanol, isopropanol, n-butanol, ethylene glycol, acetone or polyacrylamide, and a mixture of several thereof. When the mass ratio of the dispersant to lithium is maintained between 0.5 and 18 times, the obtained particles can be kept uniformly distributed at the level of 1-3 μm. Since phosphoric acid and lithium ions react to generate not only lithium phosphate, but also lithium dihydrogen phosphate and dilithium hydrogen phosphate, different amounts of phosphoric acid result in different product compositions. After a large number of experimental studies, it has been found that the product composition can be monitored by pH value. When the pH value is ≥7, the product contains only lithium phosphate, which is a white precipitate. During the reaction, in order to allow the lithium-containing substances to react fully, phosphoric acid is added in excess. When the phosphoric acid is kept at 0.05 to 0.3 times the mass of lithium, the lithium can be fully reacted, and the amount of phosphoric acid is minimized; in order to ensure that a stable lithium phosphate product is obtained, the excess phosphoric acid is neutralized with alkali solution. Considering the economic efficiency of the amount of alkali solution, the condition for judging the end of the reaction is preferably pH = 7. In order to further improve the purity of the product, the product is washed several times to wash the soluble impurities on the surface of the solid product and the residual impurity remover and dispersant. The dispersants used are all volatile substances, which can be completely removed at a suitable drying temperature to obtain a high-purity product.

[0032] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific embodiments. The raw materials used in the examples can all be commercially available products.

[0033] Example 1

[0034] Weigh 40g of 85wt% phosphoric acid solution, add 3.4g of ethylenediaminetetraacetic acid (accounting for 0.5 times the mass of the added lithium element) and 3.4g of polyacrylamide (accounting for 0.5 times the mass of the added lithium element), and stir at room temperature. Prepare 233g of 10wt% LiOH solution (the mass of the added lithium element (6.8g) is 0.2 times the mass of pure phosphoric acid), and slowly add it to the phosphoric acid solution with a separatory funnel, with a drop rate of 100 drops / min. After the dropwise addition is completed, stir the reaction at a rate of 100r / min for 60min, measure the pH, add ammonia water to adjust the pH to 7, stir for 15min and filter, add the solid back to 100g pure water, wash with ultrasonic vibration for 10min, filter, and dry the solid at 220℃ for 2h. The main content of lithium phosphate obtained (i.e., the purity of lithium phosphate) is 99.994%, and the particle size D50 is 1.05μm.

[0035] Example 2

[0036] Prepare 80g of 5wt% phosphoric acid solution, add 0.064g of ethylenediaminetetraacetic acid (accounting for 0.2 times the mass of added lithium element) and 5.76g of anhydrous ethanol (accounting for 18 times the mass of added lithium element), and stir at room temperature. Add 1.69g of Li2CO3 solid in small amounts and multiple times (the mass of lithium element added (0.32g) is 0.08 times the mass of pure phosphoric acid). After the solid powder added last time has reacted completely, add the next time, stir the reaction at a rate of 500r / min for 15min, measure the pH, add LiOH to adjust the pH to 7, stir for 15min and filter, add the solid to 100g of pure water again, wash with ultrasonic vibration for 15min, filter, repeat washing and filtering twice, and dry the solid at 80℃ for 5h. The main content of lithium phosphate obtained is 99.976%, and the particle size D50 is 2.98μm.

[0037] Example 3

[0038] Prepare 40g of 50wt% phosphoric acid solution, add 0.03g of ethylenediaminetetraacetic acid (0.01 times the mass of the added lithium element) and 30g of acetone (10 times the mass of the added lithium element), and stir at room temperature. Slowly drop 1.2L of LiHCO3 solution with a Li concentration of 2.5g / L after Li2CO3 carbonization (the mass of the added lithium element (3g) is 0.15 times the mass of pure phosphoric acid), and the drop rate is 100 drops / min. After the drop is complete, stir the reaction at a rate of 300r / min for 30min, measure the pH, add NaOH to adjust the pH to 7, stir for 15min and filter, add the solid back into 100g of pure water, wash with ultrasonic vibration for 5min, filter, repeat the washing and filtration once, and dry the solid at 150℃ for 3h. The main content of lithium phosphate obtained is 99.935%, and the particle size D50 is 2.30μm.

[0039] Comparative Example 1

[0040] Weigh 40g of 85wt% phosphoric acid solution and stir at room temperature. Prepare 233g of 10wt% LiOH solution (the added mass of lithium element (6.8g) is 0.2 times the mass of pure phosphoric acid), slowly add it to the phosphoric acid solution with a separatory funnel, the drop rate is 100 drops / min, after the drop is complete, stir the reaction at a rate of 100r / min for 60min, measure the pH, add ammonia water to adjust the pH to 7, stir for 15min and filter, add the solid back into 100g pure water, ultrasonically wash for 10min, filter, and dry the solid at 220℃ for 2h. The main content of lithium phosphate obtained is 99.648%, and the particle size D50 is 32.84μm.

[0041] Comparative Example 2

[0042] Prepare 80g of 5wt% phosphoric acid solution, add 0.064g of ethylenediaminetetraacetic acid (0.2 times the mass of the added lithium element), and stir at room temperature. Add 1.69g of Li2CO3 solid in small amounts and multiple times (the mass of the added lithium element (0.32g) is 0.08 times the mass of pure phosphoric acid). After the solid powder added last time has reacted completely, add the next time, stir and react at a rate of 500r / min for 15min, measure the pH, add LiOH to adjust the pH to 7, stir for 15min and filter, add the solid back into 100g of pure water, wash with ultrasonic vibration for 15min, filter, repeat washing and filtering twice, and dry the solid at 80℃ for 5h. The main content of lithium phosphate obtained is 99.993%, and the particle size D50 is 33.18μm.

[0043] Comparative Example 3

[0044] Prepare 40g of 50wt% phosphoric acid solution, add 30g of acetone (10 times the mass of added lithium element), and stir at room temperature. Slowly drop 1.2L of LiHCO3 solution with a Li concentration of 2.5g / L after Li2CO3 carbonization (the mass of lithium element added (3g) is 0.15 times the mass of pure phosphoric acid), the drop rate is 100 drops / min, after the drop is complete, stir the reaction at a rate of 300r / min for 30min, measure the pH, add NaOH to adjust the pH to 7, stir for 15min and filter, add the solid back into 100g pure water, ultrasonically shake and wash for 5min, filter, repeat washing and filtering once, and dry the solid at 150℃ for 3h. The main content of lithium phosphate obtained is 99.752%, and the particle size D50 is 2.16μm.

[0045] Comparative Example 4

[0046] Weigh 13.85g of 85wt% phosphoric acid solution, add 400g of deionized water to dilute, the phosphoric acid concentration after dilution is 0.3mol / L, stir and mix, heat to 55℃, add 0.18g of sodium dodecylbenzene sulfonate (accounting for 1% of the mass of phosphoric acid), stir and mix for 30min, prepare 1.8mol / L lithium hydroxide solution, slowly add it to the mixed solution, control the end point pH to 10.5; continue stirring and reacting for 35min, keep warm and stand for 240min. Centrifuge and filter, wash with 80℃ deionized water for 3 times, and dry at 120℃ for 4h to obtain lithium phosphate powder with a main content of 99.862% and a particle size D50 of 10.09μm.

[0047] The products prepared in the above examples and comparative examples were tested for main content and various impurity element contents by ICP, and particle size by laser particle size analyzer, wherein main content refers to the content of lithium phosphate. The results are shown in Table 1.

[0048] Table 1 Performance parameters of lithium phosphate prepared in each embodiment and comparative example

[0049]

[0050] It can be seen from the above that the purity of the lithium phosphate prepared in the embodiment of the present invention reaches between 99.9% and 99.999%, and the particle size is 1-3 μm, which can be used for Li3PO4 target material.

[0051] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any person skilled in the art can use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing high-purity micron lithium phosphate powder, characterized in that: It includes the following steps: S1. Weighing a lithium-containing solid or a lithium-containing solution prepared from a lithium-containing solid; S2, adding an impurity remover and a dispersant to the phosphoric acid solution, mixing and stirring to react; wherein the impurity remover is ethylenediaminetetraacetic acid, and the dispersant is one or more of ethanol, isopropanol, n-butanol, ethylene glycol, acetone, and polyacrylamide; S3, adding the lithium-containing solid or lithium-containing solution in S1 to the phosphoric acid solution in step S2, and stirring the reaction at room temperature; S4, adding alkali solution to the solution after the reaction in step S3 to adjust the pH to neutral; S5, separating the solution from step S4 into solid and liquid, and washing the solid with deionized water by ultrasonic vibration for 1 to 3 times; S6, subjecting the solid in step S5 to ultrasonic washing with deionized water, subjecting the solution to solid-liquid separation, and drying the solid to obtain high-purity micron lithium phosphate powder.

2. The preparation method according to claim 1, characterized in that In step S1, the lithium-containing solid is one or a mixture of lithium hydroxide, lithium carbonate, lithium bicarbonate, lithium iodide, lithium fluoride, lithium chloride or lithium tetrafluoroborate; and the lithium-containing solution is an aqueous solution with a lithium element mass percentage of 0.1 to 3.5 wt%.

3. The preparation method according to claim 1, characterized in that: In step S2, the mass concentration of phosphoric acid in the phosphoric acid solution is 5-85%, and the amount of the phosphoric acid solution used is 0.05-0.3 times the mass of the lithium element in the lithium-containing substance in step S1, calculated as pure phosphoric acid.

4. The preparation method according to claim 1, characterized in that: In step S2, the amount of the impurity remover added is 0.01 to 0.5 times the mass of the lithium element; The added amount of the dispersant is 0.5 to 18 times the mass of the lithium element.

5. The preparation method according to claim 1, characterized in that: In step S3, the stirring reaction time is 15 to 60 minutes, and the stirring rate is maintained at 100 to 500 r / min.

6. The preparation method according to claim 1, characterized in that: In step S4, the alkali solution is one of NaOH, ammonia water, LiOH, KOH, Ca(OH)2, Ba(OH)2 solution or a mixture of several thereof; the amount of alkali solution added is such that the pH value of the solution is 7.

7. The preparation method according to claim 1, characterized in that: In steps S5 and S6, the solid-liquid separation is filtration or centrifugation.

8. The preparation method according to claim 1, characterized in that: In step S5, the ultrasonic oscillation time is 5 to 15 minutes.

9. The preparation method according to claim 1, characterized in that: In step S6, the drying temperature is 80-220°C, and the drying time is 2-5 hours.

10. The preparation method according to claim 1, characterized in that: The purity of the obtained pure lithium phosphate is 99.9-99.999% and the particle size is 1-3 μm.

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