Preparation method of high-purity battery-grade lithium fluoride

Abstract

The invention discloses a preparation method of high-purity battery-grade lithium fluoride, which comprises the following steps: (1) adding industrial-grade lithium carbonate and deionized water into a reactor, and stirring and mixing to prepare a lithium carbonate suspension; (2) introducing supercritical carbon dioxide mixed fluid into the reactor in the step (1), controlling the pressure of the reactor to be 25-30MPa and the temperature to be 32-35 DEG C, performing carbonization reaction for 3-5 minutes under an ultrasonic condition, filtering, and removing impurities and uncarbonized lithium carbonate to prepare a purified lithium bicarbonate solution; (3) adding a metal impurity complexing agent into the purified lithium bicarbonate solution in the step (2), reacting for 3-5 minutes under an ultrasonic condition, filtering, further removing impurities, heating to 40-50 DEG C, and separating out high-purity lithium carbonate; and (4) adding high-purity lithium carbonate and an ammonium fluoride saturated solution into a reactor, heating to 70-80 DEG C, carrying out stirring reaction for 3-4 hours, carrying out solid-liquid separation, taking the solid, washing, and drying to obtain the high-purity battery-grade lithium fluoride.

Description

Technical Field

[0001] The invention relates to the field of lithium fluoride preparation, and in particular to a method for preparing high-purity battery-grade lithium fluoride. Background Art

[0002] Energy and environmental issues have always been the focus of attention of countries around the world. All countries are working hard to explore new green and environmentally friendly energy. At the same time, with the rapid development of electronic products such as mobile phones, digital cameras, notebooks and electric vehicles, the requirements for batteries are getting higher and higher. Lithium-ion batteries have been widely used because of their high operating voltage, high energy density, no memory effect, long life and safety.

[0003] Common lithium salts for lithium-ion battery electrolytes include lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)immonium, etc. Among them, lithium perchlorate is a lithium salt that has been studied for a long time. It is a strong oxidant with appropriate conductivity, good thermal stability and oxidation resistance stability, but poor safety. Therefore, it is basically not used for safety considerations. Lithium tetrafluoroborate has advantages such as good thermal stability and is not very sensitive to moisture, but it also has disadvantages such as low conductivity and cannot form a stable SEI film at the negative electrode when used alone. Although lithium hexafluoroarsenate has good performance, it is expensive and has strong carcinogenic toxicity, which can cause serious environmental pollution. Lithium trifluoromethanesulfonate and lithium bis(trifluoromethanesulfonyl)immonium both have the problem of corroding the positive electrode. Lithium hexafluorophosphate is currently the most widely used lithium salt. Although it has poor thermal stability and is easily hydrolyzed, it has good conductivity and electrochemical stability, and its waste battery treatment process is simple and has little impact on the environment. It is currently recognized as the best electrolyte for lithium-ion secondary batteries.

[0004] Lithium fluoride is an important chemical reagent that can be used in industrial fields such as enamel, glass, and ceramics. With the development of lithium battery technology in recent years, it has become an essential raw material for the preparation of lithium hexafluorophosphate, a common electrolyte in lithium-ion batteries. Therefore, the preparation of lithium hexafluorophosphate requires high-purity lithium fluoride that meets the requirements of batteries. Not only does it have relatively strict requirements for impurities, but the main content also needs to reach 99.95%.

[0005] In order to prepare high-purity lithium fluoride, high-purity lithium carbonate is required. In the prior art, carbon dioxide is introduced into a lithium carbonate suspension to prepare a soluble lithium bicarbonate carbonized liquid, which is then filtered to remove insoluble impurities and then purified by recrystallization. However, a small amount of impurity ions will still be dissolved in the carbonized liquid and retained with the subsequent recrystallization, which still has a certain impact on the quality of high-purity battery-grade lithium fluoride.

[0006] Therefore, there is an urgent need for a method for preparing high-purity battery-grade lithium fluoride that can further remove impurities in lithium carbonate and further improve product quality. Summary of the invention

[0007] Purpose of the invention: In view of the defects of the prior art, the purpose of the present invention is to provide a method for preparing high-purity battery-grade lithium fluoride which can further remove impurities in lithium carbonate and further improve product quality.

[0008] Technical solution:

[0009] A method for preparing high-purity battery-grade lithium fluoride comprises the following steps:

[0010] (1) adding industrial grade lithium carbonate and deionized water into a reactor, stirring and mixing to form a lithium carbonate suspension;

[0011] (2) introducing a supercritical carbon dioxide mixed fluid into the reactor of step (1), controlling the reactor pressure to 25-30 MPa and the temperature to 32-35° C., carbonizing under ultrasonic conditions for 3-5 minutes, and then filtering to remove impurities and uncarbonized lithium carbonate to obtain a purified lithium bicarbonate solution;

[0012] (3) adding a metal impurity complexing agent to the lithium bicarbonate solution purified in step (2), reacting under ultrasonic conditions for 3-5 minutes, filtering, further removing impurities, heating to 40-50° C., and precipitating high-purity lithium carbonate;

[0013] (4) Add high-purity lithium carbonate and saturated ammonium fluoride solution into the reactor, heat to 70-80° C., stir and react for 3-4 hours, separate the solid and liquid, wash and dry the solid to obtain high-purity battery-grade lithium fluoride.

[0014] The present invention uses a supercritical carbon dioxide mixed fluid to carbonize a lithium carbonate suspension, so that lithium carbonate that is insoluble in water is quickly converted into soluble lithium bicarbonate, and removes insoluble impurities and uncarbonized lithium carbonate by filtering, then adds a metal impurity complexing agent thereto, forms a precipitate after complexing with the metal impurities under ultrasonic conditions, further removes impurities after filtering, and then converts the lithium bicarbonate into insoluble lithium carbonate again by heating, thereby further purifying the lithium carbonate.

[0015] Furthermore, the mass concentration of the lithium carbonate suspension in step (1) is 10-30wt%.

[0016] Furthermore, in the step (2), the supercritical carbon dioxide mixed fluid is prepared by mixing supercritical carbon dioxide and a thickener in a mass ratio of (40-50): (1-2); the amount of the supercritical carbon dioxide mixed fluid introduced is 60-80% of the mass of the lithium carbonate suspension.

[0017] Furthermore, the thickener has a structure as shown in the following formula A:

[0018] Among them, n=20-25.

[0019] Furthermore, the metal impurity complexing agent in step (3) has a structure as shown in the following formula B:

[0020]

[0021] The metal impurity complexing agent of the present invention can effectively complex the metal impurities in lithium carbonate. On the one hand, a large amount of -COOH, -N=C and -C≡N in the metal impurity complexing agent can complex with the metal impurity ions to form a precipitate and then filter and remove impurities. In addition, -N=C and -C≡N have a great influence on Ca 2+ It has high selectivity for Fe ions and can significantly reduce Ca 2+ and Fe ion concentration, further improving product quality; on the other hand, the benzene ring structure with excellent stability and steric hindrance in the metal impurity complexing agent can effectively improve the stability and particle size of the complex precipitate, thereby quickly and stably removing impurities and avoiding re-dissolution of impurities.

[0022] Furthermore, the metal impurity complexing agent is prepared by the following steps: in a reactor, 4,6-diaminoisophthalic acid and p-cyanobenzoyl chloride are added, the catalyst is added after stirring evenly, the temperature is raised to 80-90° C., the reaction is performed for 4-6 hours, and then the metal impurity complexing agent is obtained after cooling, filtering, and recrystallization.

[0023] Furthermore, the catalyst is selected from one of acetic acid, propionic acid, citric acid or malic acid; and the mass ratio of the 4,6-diaminoisophthalic acid to p-cyanobenzoyl chloride is 10:8-9.

[0024] Furthermore, in step (2), the power of the ultrasound is 180-220 W and the frequency is 25-35 kHz.

[0025] Furthermore, in step (3), the power of the ultrasound is 230-250W and the frequency is 35-40kHz.

[0026] The present invention uses an ultrasonic device in the process of metal impurity complexing agent complexing metal ions, which can effectively induce complex precipitation to aggregate with each other to form impurities with larger particle size, and then can simply and effectively perform filtration separation, improve the removal effect of tiny impurities, and reduce production costs.

[0027] Furthermore, in step (4), the mass ratio of high-purity lithium carbonate to saturated ammonium fluoride solution is 1:5-8.

[0028] Beneficial effects:

[0029] (1) The method for preparing high-purity battery-grade lithium fluoride provided by the present invention can effectively complex the metal impurities dissolved in the lithium bicarbonate solution by adding a metal impurity complexing agent during the purification process of lithium carbonate, and further remove the impurities in the lithium carbonate, thereby further reducing the impurity content in the lithium fluoride and improving the quality of the lithium fluoride, so that it can be widely used in the preparation field of high-purity battery-grade lithium fluoride.

[0030] (2) The method for preparing high-purity battery-grade lithium fluoride provided by the present invention comprises the following steps: carbonizing a lithium carbonate suspension using a supercritical carbon dioxide mixed fluid, so that the lithium carbonate that is insoluble in water is quickly converted into soluble lithium bicarbonate, and removing insoluble impurities and uncarbonized lithium carbonate by filtering, and then adding a metal impurity complexing agent thereto, which forms a precipitate after complexing with the metal impurities under ultrasonic conditions, and further removing impurities after filtering, and then converting the lithium bicarbonate into insoluble lithium carbonate again by heating, thereby achieving further purification of the lithium carbonate.

[0031] (3) The preparation method of high-purity battery-grade lithium fluoride provided by the present invention, the metal impurity complexing agent can effectively complex the metal impurities in lithium carbonate. On the one hand, a large amount of -COOH, -N=C and -C≡N in the metal impurity complexing agent can be complexed with the metal impurity ions to form a precipitate and then filtered to remove impurities, and -N=C and -C≡N have a great influence on Ca 2+ It has high selectivity for Fe ions and can significantly reduce Ca 2+ and Fe ion concentration, further improving product quality; on the other hand, the benzene ring structure with excellent stability and steric hindrance in the metal impurity complexing agent can effectively improve the stability and particle size of the complex precipitate, thereby quickly and stably removing impurities and avoiding re-dissolution of impurities.

[0032] (4) The method for preparing high-purity battery-grade lithium fluoride provided by the present invention can effectively induce the complex precipitates to aggregate with each other by using an ultrasonic device during the complexation process of the metal impurity complexing agent with the metal ions, thereby forming impurity precipitates with a larger particle size, and then can be filtered and separated simply and effectively, thereby improving the removal effect of tiny impurities and reducing the production cost. DETAILED DESCRIPTION

[0033] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0034] Industrial-grade lithium carbonate and saturated ammonium fluoride solution were purchased from Aladdin Reagent Company; the remaining reagents and equipment were conventional reagents and equipment in the technical field.

[0035] Thickener preparation

[0036] Prepare the thickener by the following steps:

[0037] In a reactor, 2 g of 2-methylacrylic anhydride, 4 g of allyl tris(trimethylsiloxy)silane and 100 mL of deionized water were added, and nitrogen was introduced for 30 minutes after stirring evenly. 0.2 g of ammonium persulfate was added, and the reactor was sealed. After heating to 60° C. and reacting for 4 hours, the thickener was obtained after cooling, washing and drying.

[0038] Preparation of metal impurity complexing agent

[0039] The metal impurity complexing agent is prepared by the following steps:

[0040] In the reactor, 5 g of 4,6-diaminoisophthalic acid and 4 g of p-cyanobenzoyl chloride were added, stirred evenly, and then 0.2 g of acetic acid was added. The temperature was raised to 80° C., reacted for 6 hours, cooled, filtered, and recrystallized to obtain the metal impurity complexing agent.

[0041] Example 1

[0042] The preparation of high-purity battery-grade lithium fluoride is carried out by the following steps: by weight,

[0043] (1) adding industrial grade lithium carbonate and deionized water into a reactor, stirring and mixing to prepare a lithium carbonate suspension with a mass concentration of 25 wt %;

[0044] (2) introducing a supercritical carbon dioxide mixed fluid into the reactor of step (1), controlling the reactor pressure to 30 MPa and the temperature to 35° C., performing a carbonization reaction for 5 minutes under ultrasonic conditions of 200 W and 30 kHz, and then filtering to remove impurities and uncarbonized lithium carbonate to obtain a purified lithium bicarbonate solution;

[0045] (3) adding 3 wt % of a metal impurity complexing agent to the lithium bicarbonate solution purified in step (2), reacting the solution under ultrasonic conditions of 250 W and 40 kHz for 5 minutes, filtering the solution, further removing impurities, and heating the solution to 50° C. to precipitate high-purity lithium carbonate;

[0046] (4) Add 1 part of high-purity lithium carbonate and 7 parts of saturated ammonium fluoride solution into the reactor, heat to 70° C., stir and react for 3 hours, separate the solid and liquid, wash and dry the solid to obtain high-purity battery-grade lithium fluoride;

[0047] The supercritical carbon dioxide mixed fluid is prepared by mixing supercritical carbon dioxide and a thickener in a mass ratio of 45:1.

[0048] Example 2

[0049] The process is basically the same as Example 1, except that the power of the ultrasonic wave in step (3) is 230 W and the frequency is 35 kHz; and the amount of the metal impurity complexing agent added is changed to 5 wt%.

[0050] Example 3

[0051] The process is basically the same as Example 1, except that the power of the ultrasonic wave in step (3) is 240 W and the frequency is 35 kHz; and the amount of the metal impurity complexing agent added is changed to 4 wt%.

[0052] Comparative Example 1

[0053] The preparation of lithium fluoride is carried out by the following steps:

[0054] In the reactor, 1 part of industrial-grade lithium carbonate and 7 parts of saturated ammonium fluoride solution were added by weight. After heating to 70°C and stirring for 3 hours, the solid and liquid were separated. The solid was washed and dried to obtain lithium fluoride.

[0055] Comparative Example 2

[0056] The method is basically the same as Example 1, except that step (3) is not performed; the lithium bicarbonate solution purified in step (2) is heated to 50° C., and after the purified lithium carbonate is precipitated, the high-purity lithium carbonate in step (4) is replaced with an equal amount of purified lithium carbonate.

[0057] Comparative Example 3

[0058] The method is basically the same as Example 1, except that the metal impurity complexing agent in step (3) is replaced by an equal amount of ethylenediaminetetraacetic acid.

[0059] Comparative Example 4

[0060] The process is basically the same as Example 1, except that no ultrasonic device is provided in step (3).

[0061] Performance Testing

[0062] 1. Detect and record the purity of lithium carbonate and the content of major impurities in industrial grade lithium carbonate.

[0063] The test results are shown in the following table:

[0064] Element Content (wt%) <![CDATA[Li2CO3]]> 99.13 Fe 0.0316 <![CDATA[Ca 2+ ]]> 0.0247 <![CDATA[Mg 2+ ]]> 0.0154 <![CDATA[Na + ]]> 0.134 <![CDATA[SO4 2- ]]> 0.285 <![CDATA[Cl - ]]> 0.0168 Moisture 0.291

[0065] 2. The purified lithium carbonate in step (2) of Example 1-3 and Comparative Example 2-4 was dried to remove moisture, and the contents of main metal impurities after purification of lithium carbonate were respectively detected. The test results are shown in the following table:

[0066] Fe(ppm) <![CDATA[Ca 2+ (ppm)]]> <![CDATA[Mg 2+ (ppm)]]> <![CDATA[Na + (ppm)]]> Example 1 4.1 3.8 6.7 36.2 Example 2 4.3 3.7 6.5 36.5 Example 3 4.2 3.7 6.6 36.3 Comparative Example 2 12.8 12.1 19.8 126.7 Comparative Example 3 8.7 8.5 13.8 66.4 Comparative Example 4 5.8 5.2 9.1 49.3

[0067] According to the comparison of the test results of Examples 1-3 with the test results of industrial-grade lithium carbonate and Comparative Example 2, it can be seen that in the preparation method of high-purity battery-grade lithium fluoride provided by the present invention, after carbonizing the lithium carbonate in a supercritical carbon dioxide mixed fluid, a metal impurity complexing agent is used for impurity removal, thereby further reducing the impurity content in the lithium carbonate and improving the purity of the lithium carbonate.

[0068] According to the comparison of the test results of Examples 1-3 and Comparative Example 3, it can be seen that in the preparation method of high-purity battery-grade lithium fluoride provided by the present invention, the metal impurity complexing agent can more effectively complex the metal impurities in lithium carbonate for effective removal than the complexing agent in the prior art, and is more suitable for the removal of trace metal impurities.

[0069] According to the comparison of the test results of Examples 1-3 and Comparative Example 4, it can be seen that in the preparation method of high-purity battery-grade lithium fluoride provided by the present invention, by ultrasonically vibrating the complex, it can be induced to agglomerate to form a larger precipitate, which can then be simply and effectively removed, thereby further improving the purity of lithium carbonate.

[0070] 3. Detect and record the purity and main impurity content of lithium fluoride obtained in Examples 1-3 and Comparative Examples 1-4 respectively.

[0071] The test results are shown in the following table:

[0072]

[0073] According to the comparison of the test results of Examples 1-3 with those of Comparative Example 1, the method for preparing high-purity battery-grade lithium fluoride provided by the present invention, by using a supercritical carbon dioxide mixed fluid to carbonize and purify lithium carbonate, and then using a metal impurity complexing agent to remove impurities, has higher purity than the lithium fluoride prepared by industrial-grade lithium carbonate in the prior art, and can further reduce the content of metal impurities, and can be widely used in the field of preparation of high-purity battery-grade lithium fluoride.

[0074] According to the comparison of the test results of Examples 1-3 and Comparative Example 2, in the preparation method of high-purity battery-grade lithium fluoride provided by the present invention, by removing impurities from the carbonized and purified lithium carbonate using a metal impurity complexing agent, dissolved impurities can be further removed and the metal impurity content can be further reduced.

[0075] According to the comparison of the test results of Examples 1-3 and Comparative Example 3, it can be seen that in the preparation method of high-purity battery-grade lithium fluoride provided by the present invention, the metal impurity complexing agent can more effectively complex the metal impurities in lithium carbonate than the complexing agent in the prior art, and form a stable complex precipitate, thereby quickly and stably removing impurities and improving the purity of lithium carbonate.

[0076] According to the comparison of the test results of Examples 1-3 and Comparative Example 4, in the preparation method of high-purity battery-grade lithium fluoride provided by the present invention, by using ultrasonic oscillation in the complexation process, the complex precipitate can be effectively induced to agglomerate to form an impurity precipitate with a larger particle size, and then simply filtered and separated, thereby improving the removal effect of tiny impurities and further improving the purity of lithium carbonate.

[0077] The above implementation modes are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing high-purity battery-grade lithium fluoride, characterized in that: The following steps are involved: (1) adding industrial grade lithium carbonate and deionized water into a reactor, stirring and mixing to form a lithium carbonate suspension; (2) introducing a supercritical carbon dioxide mixed fluid into the reactor of step (1), controlling the reactor pressure to 25-30 MPa and the temperature to 32-35° C., carbonizing under ultrasonic conditions for 3-5 minutes, and then filtering to remove impurities and uncarbonized lithium carbonate to obtain a purified lithium bicarbonate solution; (3) adding a metal impurity complexing agent to the lithium bicarbonate solution purified in step (2), reacting under ultrasonic conditions for 3-5 minutes, filtering, further removing impurities, heating to 40-50° C., and precipitating high-purity lithium carbonate; (4) Add high-purity lithium carbonate and saturated ammonium fluoride solution into the reactor, heat to 70-80° C., stir and react for 3-4 hours, separate the solid and liquid, wash and dry the solid to obtain high-purity battery-grade lithium fluoride.

2. The method for preparing high-purity battery-grade lithium fluoride according to claim 1, characterized in that: The mass concentration of the lithium carbonate suspension in step (1) is 10-30wt%.

3. The method for preparing high-purity battery-grade lithium fluoride according to claim 1, characterized in that: In the step (2), the supercritical carbon dioxide mixed fluid is prepared by mixing supercritical carbon dioxide and a thickener in a mass ratio of (40-50): (1-2); the amount of the supercritical carbon dioxide mixed fluid introduced is 60-80% of the mass of the lithium carbonate suspension.

4. The method for preparing high-purity battery-grade lithium fluoride according to claim 3, characterized in that: The thickener has a structure shown in the following formula A: Among them, n=20-25.

5. The method for preparing high-purity battery-grade lithium fluoride according to claim 1, characterized in that: The metal impurity complexing agent in step (3) has a structure as shown in the following formula B:

6. The method for preparing high-purity battery-grade lithium fluoride according to claim 5, characterized in that: The metal impurity complexing agent is prepared by the following steps: adding 4,6-diaminoisophthalic acid and p-cyanobenzoyl chloride into a reactor, stirring evenly, adding a catalyst, heating to 80-90° C., reacting for 4-6 hours, cooling, filtering, and recrystallizing to obtain the metal impurity complexing agent.

7. The method for preparing high-purity battery-grade lithium fluoride according to claim 5, characterized in that: The catalyst is selected from one of acetic acid, propionic acid, citric acid or malic acid; the mass ratio of the 4,6-diaminoisophthalic acid to p-cyanobenzoyl chloride is 10:8-9.

8. The method for preparing high-purity battery-grade lithium fluoride according to claim 1, characterized in that: The power of the ultrasonic wave in step (2) is 180-220W and the frequency is 25-35kHz.

9. The method for preparing high-purity battery-grade lithium fluoride according to claim 1, characterized in that: In the step (3), the power of the ultrasonic wave is 230-250W and the frequency is 35-40kHz; the amount of the metal impurity complexing agent added is 3-5% of the mass of the purified lithium bicarbonate solution.

10. The method for preparing high-purity battery-grade lithium fluoride according to claim 1, characterized in that: In the step (4), the mass ratio of high-purity lithium carbonate to saturated ammonium fluoride solution is 1:5-8.

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