Preparation method of battery-grade lithium fluoride

Abstract

The invention discloses a preparation method of 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, removing impurities and uncarbonized lithium carbonate, heating to 40-50 DEG C, and separating out purified lithium carbonate; and (3) adding the purified lithium carbonate and ammonium fluoride saturated solution into a reactor, heating to 70-80 DEG C, stirring to react for 3-4 hours, carrying out solid-liquid separation, taking the solid, washing, and drying to obtain the battery-grade lithium fluoride. According to the method, the lithium carbonate suspension is carbonized by using the supercritical carbon dioxide mixed fluid, so that the purity of the prepared lithium fluoride can be remarkably improved, and the method can be widely applied to the field of preparation of 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 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] At present, the production methods of battery-grade lithium fluoride or high-purity lithium fluoride are divided into dry method and wet method according to different production methods. The dry method mainly dissolves lithium salt in water, purifies by leaching resin chromatography, concentrates, and spray-dries to obtain high-purity lithium hydroxide monohydrate, then grinds and mixes with ammonium fluoride at room temperature, and calcines under inert gas to obtain lithium fluoride. This preparation method has the disadvantages of complex process, cumbersome operation, high energy consumption and high production cost, and is difficult to industrialize. The wet method mainly uses the solution method to prepare lithium fluoride. In the early stage, it was prepared by reacting solid Li2CO3 with hydrofluoric acid solution. Although the principle is simple, it has high requirements on the quality of raw materials, and the particle size distribution of the generated LiF particles is uneven, so the raw materials need to be purified and impurities removed.

[0006] However, the degree of purification of raw material lithium carbonate and the effect of removing impurities in the prior art still need to be improved, and the purification process may introduce new impurities and the purification efficiency is low.

[0007] Therefore, there is an urgent need for a method for preparing battery-grade lithium fluoride that is efficient, pollution-free, and can significantly improve the purity of the product. Summary of the invention

[0008] 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 battery-grade lithium fluoride which is efficient, pollution-free and can significantly improve the purity of the product.

[0009] Technical solution:

[0010] A method for preparing battery-grade lithium fluoride comprises the following steps:

[0011] (1) adding industrial grade lithium carbonate and deionized water into a reactor, stirring and mixing to form a lithium carbonate suspension;

[0012] (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, filtering to remove impurities and uncarbonized lithium carbonate, and heating to 40-50° C. to precipitate purified lithium carbonate;

[0013] (3) Add purified 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 battery-grade lithium fluoride.

[0014] In the present invention, a supercritical carbon dioxide mixed fluid is used to carbonize a lithium carbonate suspension, so that lithium carbonate that is insoluble in water is quickly converted into soluble lithium bicarbonate, and insoluble impurities and uncarbonized lithium carbonate are removed by filtration. Then, the lithium bicarbonate is converted into insoluble lithium carbonate again by heating, thereby achieving purification of 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; the amount of the supercritical carbon dioxide mixed fluid introduced is 60-80% of the mass of the lithium carbonate suspension.

[0017] The present invention uses a supercritical carbon dioxide mixed fluid to carbonize lithium carbonate. On the one hand, supercritical carbon dioxide is used as a green solvent, which can avoid the environmental pollution problems of conventional solvents and the possible introduction of new impurities, thereby reducing production costs and improving the purification effect of lithium carbonate. On the other hand, supercritical carbon dioxide is used instead of gaseous carbon dioxide to carbonize lithium carbonate, which can avoid a complicated gas introduction process, reduce production costs, and significantly improve the conversion rate of lithium carbonate into lithium bicarbonate, significantly shorten the carbonization time, and improve production efficiency.

[0018] Furthermore, the thickener has a structure as shown in the following formula A:

[0019] Among them, n=20-25.

[0020] The present invention adds a thickener to supercritical carbon dioxide. On the one hand, the thickener can improve the consistency of the supercritical carbon dioxide and improve the carbonization efficiency and conversion rate of lithium carbonate; on the other hand, the polymer form of the thickener and its multi-branched silane structure can effectively adsorb metal impurities in industrial-grade lithium carbonate, so that fine impurities agglomerate with each other to form a large-volume precipitate, which can significantly improve the separation effect between the impurity precipitate and lithium bicarbonate, and further improve the purification degree of the prepared lithium carbonate.

[0021] Furthermore, the thickener is prepared by the following steps: adding 2-methacrylic anhydride, allyl tris(trimethylsiloxy)silane and deionized water into a reactor, stirring evenly and introducing nitrogen for 20-30 minutes, adding an initiator, sealing the reactor, heating to 50-60° C. and reacting for 4-6 hours, cooling, washing and drying to obtain the thickener.

[0022] Furthermore, the initiator is selected from one of ammonium persulfate or sodium bisulfite.

[0023] Furthermore, the mass ratio of the 2-methacrylic anhydride to allyltris(trimethylsiloxy)silane is 5:10-12.

[0024] Furthermore, the mass ratio of supercritical carbon dioxide to thickener in the supercritical carbon dioxide mixed fluid in step (2) is (40-50):(1-2).

[0025] Furthermore, in step (2), the power of the ultrasound is 180-220 W and the frequency is 25-35 kHz.

[0026] The present invention uses an ultrasonic device in the carbonization process of lithium carbonate, which can not only further improve the carbonization effect of supercritical carbon dioxide on lithium carbonate, but also induce nucleation of metal impurities, further improve the agglomeration effect, facilitate subsequent separation and impurity removal, and improve the purification effect of lithium carbonate.

[0027] Furthermore, the mass ratio of the purified lithium carbonate to the saturated ammonium fluoride solution in step (3) is 1:5-8.

[0028] Beneficial effects:

[0029] (1) The purity of industrial-grade lithium carbonate is about 99.0%, of which water accounts for about 0.3% of the impurities, and the remaining impurities are mostly metal ions, SO4 2- and Cl - Plasma impurities, the preparation method of battery-grade lithium fluoride provided by the present invention can purify industrial-grade lithium carbonate to separate metal impurities from SO4 2- and Cl - The formed precipitate is removed, the ionic impurity content in the lithium carbonate is reduced, and after the lithium carbonate is dried to remove moisture, the industrial-grade lithium carbonate can be further purified, and its purity can reach 99.99%. The metal impurity content can be controlled at the ppm level, further reducing the impact of metal impurities on the performance of battery-grade materials and improving the application value.

[0030] (2) The method for preparing battery-grade lithium fluoride provided by the present invention can significantly improve the carbonization rate of lithium carbonate and reduce the carbonization time and the amount of carbon dioxide introduced by using a fluid prepared by mixing supercritical carbon dioxide and a thickener to carbonize a lithium carbonate suspension, effectively remove impurities in industrial-grade lithium carbonate, improve the purity of the prepared lithium fluoride, and avoid the use of harmful solvents and the introduction of new impurities, thereby significantly improving the purity of the subsequently prepared lithium fluoride, so that it can be widely used in the field of preparation of battery-grade lithium fluoride.

[0031] (3) The preparation method of battery-grade lithium fluoride provided by the present invention uses a supercritical carbon dioxide mixed fluid to carbonize a lithium carbonate suspension, so that the lithium carbonate that is insoluble in water is quickly converted into soluble lithium bicarbonate, and the insoluble impurities and uncarbonized lithium carbonate are removed by filtration. Then, the lithium bicarbonate is converted into insoluble lithium carbonate again by heating, thereby purifying the lithium carbonate.

[0032] (4) The preparation method of battery-grade lithium fluoride provided by the present invention uses a supercritical carbon dioxide mixed fluid to carbonize lithium carbonate. On the one hand, supercritical carbon dioxide, as a green solvent, can avoid the environmental pollution problems existing in conventional solvents and the possible introduction of new impurities, thereby reducing production costs and improving the purification effect of lithium carbonate. On the other hand, using supercritical carbon dioxide instead of gaseous carbon dioxide to carbonize lithium carbonate can avoid the complicated gas introduction process, reduce production costs, and significantly improve the conversion rate of lithium carbonate to lithium bicarbonate, and significantly shorten the carbonization time, reduce the amount of carbon dioxide introduced, and improve production efficiency.

[0033] (5) The preparation method of battery-grade lithium fluoride provided by the present invention comprises adding a thickener to supercritical carbon dioxide. On the one hand, the thickener can increase the consistency of the supercritical carbon dioxide and improve its carbonization efficiency and conversion rate of lithium carbonate; on the other hand, the polymer form of the thickener and its multi-branched silane structure can effectively adsorb metal impurities in industrial-grade lithium carbonate, so that fine impurities agglomerate with each other to form a large-volume precipitate, which can significantly improve the separation effect between the impurity precipitate and lithium bicarbonate, and further improve the degree of purification of the obtained lithium carbonate.

[0034] (6) The preparation method of battery-grade lithium fluoride provided by the present invention can not only further improve the carbonization effect of supercritical carbon dioxide on lithium carbonate by using an ultrasonic device during the carbonization process of lithium carbonate, but also induce nucleation of metal impurities, further improve the agglomeration effect, facilitate subsequent separation and impurity removal, and improve the purification effect of lithium carbonate. DETAILED DESCRIPTION

[0035] 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.

[0036] 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.

[0037] Thickener preparation

[0038] Prepare the thickener by the following steps:

[0039] 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.

[0040] Example 1

[0041] Battery-grade lithium fluoride is prepared by the following steps: by weight,

[0042] (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 %;

[0043] (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, filtering to remove impurities and uncarbonized lithium carbonate, and heating to 45° C. to precipitate purified lithium carbonate;

[0044] (3) Add 1 part of purified 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 battery-grade lithium fluoride;

[0045] The supercritical carbon dioxide mixed fluid is prepared by mixing supercritical carbon dioxide and a thickener in a mass ratio of 45:1.

[0046] Example 2

[0047] The process is basically the same as Example 1, except that the power of the ultrasonic wave in step (2) is 180 W and the frequency is 35 kHz; and the mass ratio of supercritical carbon dioxide to thickener is changed to 40:1.5.

[0048] Example 3

[0049] The process is basically the same as Example 1, except that the power of the ultrasonic wave in step (2) is 220 W and the frequency is 25 kHz; and the mass ratio of supercritical carbon dioxide to thickener is changed to 40:2.

[0050] Comparative Example 1

[0051] The preparation of lithium fluoride is carried out by the following steps:

[0052] 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.

[0053] Comparative Example 2

[0054] Basically the same as Example 1, except that the ultrasonic process is not performed in step (2).

[0055] Comparative Example 3

[0056] The method is basically the same as Example 1, except that in step (2), supercritical carbon dioxide and thickener are replaced by carbon dioxide gas.

[0057] Comparative Example 4

[0058] The method is basically the same as Example 1, except that the thickener in step (2) is replaced by an equal amount of supercritical carbon dioxide.

[0059] Performance Testing

[0060] 1. Detect and record the purity of lithium carbonate and the content of major impurities of industrial grade lithium carbonate.

[0061] The test results are shown in the following table:

[0062] 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

[0063] 2. The purified lithium carbonate in step (2) of Example 1-3 and Comparative Example 2-4 was dried, and after removing the water, the carbonization rate of the lithium carbonate and the content of the main metal impurities after purification were respectively detected, and the carbonization time after the carbonization was completed was recorded;

[0064] The carbonization rate is the percentage of the carbonized lithium carbonate mass to the initial lithium carbonate mass after the carbonization reaction is completed. The test results are as follows:

[0065]

[0066]

[0067] According to the comparison between the test results of Examples 1-3 and the test results of industrial-grade lithium carbonate, it can be seen that in the preparation method of battery-grade lithium fluoride provided by the present invention, lithium carbonate is carbonized by a supercritical carbon dioxide mixed fluid. On the one hand, the carbonization rate of lithium carbonate can be significantly improved, and the impurity content in industrial-grade lithium carbonate can be significantly reduced, thereby improving the purity of lithium carbonate; on the other hand, the carbonization efficiency of lithium carbonate can be improved, the carbonization time and the amount of carbon dioxide introduced can be reduced, and the purification cost of lithium carbonate can be reduced.

[0068] According to the comparison of the test results of Examples 1-3 and Comparative Example 2, it can be seen that in the preparation method of battery-grade lithium fluoride provided by the present invention, by using an ultrasonic program during the carbonization process, the carbonization rate of lithium carbonate can be further improved, the impurity content can be further reduced, and the carbonization efficiency can be improved.

[0069] According to the comparison of the test results of Examples 1-3 and Comparative Examples 3-4, it can be seen that in the preparation method of battery-grade lithium fluoride provided by the present invention, by using supercritical carbon dioxide instead of carbon dioxide gas and adding a thickener, the carbonization rate and carbonization efficiency of lithium carbide can be significantly improved, which can not only further improve the purity of lithium carbonate, but also significantly reduce the carbonization time and the amount of carbon dioxide introduced.

[0070] 3. Detect and record the purity and main metal 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 battery-grade lithium fluoride provided by the present invention, by using a supercritical carbon dioxide mixed fluid to carbonize and purify lithium carbonate, has higher purity than the lithium fluoride prepared by industrial-grade lithium carbonate in the prior art, and can further reduce the impurity content, and can be widely used in the field of preparation of battery-grade lithium fluoride.

[0074] According to the comparison of the test results of Examples 1-3 and Comparative Example 2, it can be seen that in the preparation method of battery-grade lithium fluoride provided by the present invention, the purity of lithium carbonate can be further improved by using an ultrasonic program during the carbonization process, thereby improving the purity of the prepared lithium fluoride.

[0075] According to the comparison of the test results of Examples 1-3 and Comparative Examples 3-4, it can be seen that in the preparation method of battery-grade lithium fluoride provided by the present invention, by using supercritical carbon dioxide instead of carbon dioxide gas and adding a thickener, the purity of lithium carbide can be significantly improved, thereby significantly improving the purity of the obtained lithium fluoride and reducing the impurity content.

[0076] 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 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, filtering to remove impurities and uncarbonized lithium carbonate, and heating to 40-50° C. to precipitate purified lithium carbonate; (3) Add purified 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 battery-grade lithium fluoride.

2. The method for preparing 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 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; 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 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 battery-grade lithium fluoride according to claim 4, characterized in that: The thickener is prepared by the following steps: adding 2-methacrylic anhydride, allyl tris(trimethylsiloxy)silane and deionized water into a reactor, stirring evenly and introducing nitrogen for 20-30 minutes, adding an initiator, sealing the reactor, heating to 50-60° C., reacting for 4-6 hours, cooling, washing and drying to obtain the thickener.

6. The method for preparing battery-grade lithium fluoride according to claim 5, characterized in that: The initiator is selected from one of ammonium persulfate or sodium bisulfite.

7. The method for preparing battery-grade lithium fluoride according to claim 5, characterized in that: The mass ratio of the 2-methacrylic anhydride to allyl tris(trimethylsiloxy)silane is 5:10-12.

8. The method for preparing battery-grade lithium fluoride according to claim 1, characterized in that: The mass ratio of supercritical carbon dioxide to thickener in the supercritical carbon dioxide mixed fluid in step (2) is (40-50):(1-2).

9. The method for preparing 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.

10. The method for preparing battery-grade lithium fluoride according to claim 1, characterized in that: The mass ratio of the purified lithium carbonate to the saturated ammonium fluoride solution in step (3) is 1:5-8.

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