Method for producing lithium fluoride, method for producing lithium hexafluorophosphate, method for producing lithium tetrafluoroborate, and lithium fluoride

Abstract

The present disclosure provides, for example, a method for producing lithium fluoride, the method involving step 1 for preparing an aqueous solution of at least one of lithium chloride and lithium sulfate, step 2 for mixing the aqueous solution of at least one of lithium chloride and lithium sulfate with a hydrofluoric acid aqueous solution, and step 3 for mixing a base with the mixture liquid of the aqueous solution of at least one of lithium chloride and lithium sulfate and the hydrofluoric acid aqueous solution, wherein pH of the liquid obtained in step 3 is 3-6.

Description

Method for producing lithium fluoride, method for producing lithium hexafluorophosphate, method for producing lithium tetrafluoroborate, and lithium fluoride

[0001] One embodiment of the present disclosure relates to a method for producing lithium fluoride. Alternatively, one embodiment of the present disclosure relates to a method for producing lithium hexafluorophosphate using lithium fluoride obtained by the method. Alternatively, one embodiment of the present disclosure relates to a method for producing lithium tetrafluoroborate using lithium fluoride obtained by the method. Alternatively, one embodiment of the present disclosure relates to lithium fluoride obtained by the method.

[0002] Lithium fluoride (LiF) is a derivative of lithium hexafluorophosphate (LiPF ６ ) and lithium tetrafluoroborate (LiBF ４ LiF is widely used as a main raw material for lithium fluoride (LiF). The manufacturing method of LiF is to dissolve Li salt in an aqueous solution with hydrofluoric acid (HF) and ammonium fluoride (NH ４ A commonly used method is to fluorinate the resulting solution with ammonium fluoride (LiF) or acid ammonium fluoride, and then recover the resulting precipitate (LiF) by filtration (Patent Documents 1 to 6).

[0003] As a Li salt used in the production of LiF, for example, Patent Document 1 discloses lithium carbonate (Li ２ CO ３ ), lithium hydroxide (LiOH), lithium nitrate (LiNO ３ ), lithium chloride (LiCl), and lithium sulfate (Li ２ SO ４ On the other hand, as the Li salt, Li ２ CO ３ When LiF containing alkaline components is used as a raw material, a small amount of alkaline components is incorporated into the precipitated LiF, and washing after filtration recovery cannot sufficiently remove the alkaline components. ６ and LiBF ４ When the above is synthesized, the resulting LiPF ６ Solution and LiBF ４ In the solution, the alkaline component reacts with HF to produce water, which is called LiPF６ and LiBF ４ reacts with LiPF ６ Solution and LiBF ４ The problem is that the concentration of free acid in the solution increases.

[0004] One way to solve this problem is to use LiCl or Li ２ SO ４ It is conceivable to produce LiF using neutralized lithium salts such as LiCl as a raw material. For example, Patent Documents 1 to 3 describe the production of LiF using LiCl as a raw material.

[0005] Japanese Patent No. 6097111 Chinese Patent Application Publication No. 113697829 Chinese Patent Application Publication No. 101074103 Chinese Patent Application Publication No. 101462744 Chinese Patent Application Publication No. 1962445 Chinese Patent Application Publication No. 113716587

[0006] As a result of the investigations conducted by the present inventors, it was found that when LiF is produced using a neutralized lithium salt as a raw material, either the alkaline component or water in the LiF tends to remain. ６ and LiBF ４ When synthesized, LiPF ６ Solution and LiBF ４ It became clear that there was room for improvement, as the free acid concentration in the solution sometimes became too high.

[0007] An object of one embodiment of the present disclosure is to provide a method for producing LiF in which residual moisture and alkaline components are reduced in a balanced manner. Alternatively, an object of one embodiment of the present disclosure is to provide a method for producing lithium hexafluorophosphate in which the free acid concentration is reduced, using lithium fluoride obtained by the method. Alternatively, an object of one embodiment of the present disclosure is to provide a method for producing lithium tetrafluoroborate in which the free acid concentration is reduced, using lithium fluoride obtained by the method. Alternatively, an object of one embodiment of the present disclosure is to provide LiF in which residual moisture and alkaline components are reduced in a balanced manner, using the method.

[0008] One embodiment of the present disclosure provides a method for producing lithium fluoride, including Step 1 of preparing an aqueous solution of at least one of lithium chloride and lithium sulfate; Step 2 of mixing the aqueous solution of at least one of lithium chloride and lithium sulfate with an aqueous solution of hydrofluoric acid; and Step 3 of mixing the mixed solution of the aqueous solution of at least one of lithium chloride and lithium sulfate and the aqueous solution of hydrofluoric acid with a base, wherein the pH of the solution obtained in Step 3 is 3 to 6.

[0009] The step 2 may be carried out by adding dropwise an aqueous solution of at least one of lithium chloride and lithium sulfate to an aqueous solution of hydrofluoric acid, and the step 3 may be carried out by adding a base to the liquid obtained in the step 2.

[0010] An aqueous solution of at least one of lithium chloride and lithium sulfate may be added dropwise to the aqueous hydrofluoric acid solution at a rate of 0.010 eq / min to 0.20 eq / min.

[0011] The base may be at least one of an aqueous base and an organic base.

[0012] The basic aqueous solution may be an aqueous solution in which at least one selected from the group consisting of ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and potassium hydrogen carbonate is dissolved in water.

[0013] An aqueous solution of at least one of lithium hydroxide and lithium carbonate may be prepared, and the aqueous solution of at least one of lithium hydroxide and lithium carbonate may be mixed with at least one of hydrochloric acid and sulfuric acid to prepare an aqueous solution of at least one of lithium chloride and lithium sulfate.

[0014] The mixing of an aqueous solution of at least one of lithium hydroxide and lithium carbonate with at least one of hydrochloric acid and sulfuric acid may be carried out by adding at least one of hydrochloric acid and sulfuric acid to an aqueous solution of at least one of lithium hydroxide and lithium carbonate.

[0015] One embodiment of the present disclosure provides a method for producing lithium hexafluorophosphate, comprising mixing lithium fluoride obtained by any of the methods for producing lithium fluoride described above with a chain carbonate to prepare a lithium fluoride dispersion, and blowing phosphorus pentafluoride into the lithium fluoride dispersion to obtain lithium hexafluorophosphate.

[0016] The lithium fluoride dispersion may be prepared by adding lithium fluoride to a chain carbonate.

[0017] One embodiment of the present disclosure provides a method for producing lithium tetrafluoroborate, comprising mixing lithium fluoride obtained by any of the methods for producing lithium fluoride described above with a chain carbonate to prepare a lithium fluoride dispersion, and blowing boron trifluoride into the lithium fluoride dispersion to obtain lithium tetrafluoroborate.

[0018] The lithium fluoride dispersion may be prepared by adding lithium fluoride to a chain carbonate.

[0019] One embodiment of the present disclosure provides lithium fluoride containing 180 ppm or less of water, the pH of which is measured by adding 0.15 g of lithium fluoride to 50.0 g of water, stirring the mixture at 25°C ± 1°C for 10 minutes, and allowing the mixture to stand for 30 minutes, followed by measuring the supernatant.

[0020] One embodiment of the present disclosure provides a method for producing lithium hexafluorophosphate, which includes mixing the lithium fluoride and a chain carbonate to prepare a lithium fluoride dispersion, and blowing phosphorus pentafluoride into the lithium fluoride dispersion to obtain lithium hexafluorophosphate.

[0021] The lithium fluoride dispersion may be prepared by adding lithium fluoride to a chain carbonate.

[0022] One embodiment of the present disclosure provides a method for producing lithium tetrafluoroborate, which includes mixing the lithium fluoride and a chain carbonate to prepare a lithium fluoride dispersion, and blowing boron trifluoride into the lithium fluoride dispersion to obtain lithium tetrafluoroborate.

[0023] The lithium fluoride dispersion may be prepared by adding lithium fluoride to a chain carbonate.

[0024] According to one embodiment of the present disclosure, a method for producing LiF in which residual moisture and alkaline components are reduced in a balanced manner can be provided. Alternatively, according to one embodiment of the present disclosure, a method for producing lithium hexafluorophosphate in which the free acid concentration is reduced can be provided using lithium fluoride obtained by the method. Alternatively, according to one embodiment of the present disclosure, a method for producing lithium tetrafluoroborate in which the free acid concentration is reduced can be provided using lithium fluoride obtained by the method. Alternatively, according to one embodiment of the present disclosure, LiF in which residual moisture and alkaline components are reduced in a balanced manner can be provided using the method.

[0025] Hereinafter, a method for producing lithium fluoride, a method for producing lithium hexafluorophosphate, a method for producing lithium tetrafluoroborate, and lithium fluoride according to embodiments of the present disclosure will be described. However, the embodiments of the present disclosure should not be construed as being limited to the following embodiments and examples. In this specification, the notation "X to Y" in the description of a numerical range means X or more and Y or less, unless otherwise specified. In this disclosure, "room temperature" means 25°C ± 1°C. Furthermore, in this specification, the concentrations of each component ("%" and "ppm") represent concentrations on a mass basis ("mass %" and "mass ppm"), unless otherwise specified.

[0026] [Method for Producing LiF] The method for producing LiF according to this embodiment includes Step 1 of preparing an aqueous solution of at least one of lithium chloride and lithium sulfate, Step 2 of mixing the aqueous solution of at least one of lithium chloride and lithium sulfate with an aqueous HF solution, and Step 3 of mixing the mixed solution of the aqueous solution of at least one of lithium chloride and lithium sulfate with an aqueous HF solution, with a base, wherein the pH of the solution obtained in Step 3 is 3 to 6. According to the method for producing LiF according to this embodiment, when producing LiF using a neutralized lithium salt as a raw material, the aqueous lithium salt solution and the aqueous HF solution are mixed, and then a base is further added to adjust the pH of the aqueous solution to 3 to 6, thereby producing LiF with a balanced reduction in residual moisture and alkaline components. The method for producing LiF according to this embodiment will be described in detail below.

[0027] Aqueous solution of at least one of lithium chloride and lithium sulfate (Step 1). The aqueous solution of at least one of lithium chloride and lithium sulfate is typically an aqueous LiCl solution or Li ２ SO ４ Aqueous solutions of LiCl and Li ２ SO ４ The aqueous solutions were LiCl or Li ２ SO ４ It can be prepared by dissolving LiCl in water. ２ SO ４ The aqueous solution is preferably adjusted to a concentration of 5 to 40% by mass.

[0028] In one embodiment, an aqueous solution of LiCl and Li ２ SO ４ The aqueous solution is LiOH or Li ２ CO ３ It can also be prepared using LiOH or Li as a raw material. ２ CO ３ is dissolved in water and used as a LiOH solution or Li ２ CO ３ Prepare an aqueous solution, LiOH aqueous solution or Li ２ CO ３ Aqueous solution and hydrochloric acid (HCl) or sulfuric acid (H ２ SO ４) and LiCl aqueous solution or Li ２ SO ４ An aqueous solution can also be prepared. Preferably, an aqueous LiOH solution or Li ２ CO ３ The aqueous solution contains hydrochloric acid (HCl) or sulfuric acid (H ２ SO ４ ) was added to the solution of LiCl or Li ２ SO ４ An aqueous solution may be prepared.

[0029] Prepared LiCl aqueous solution or Li ２ SO ４ The aqueous solution of LiCl or Li is mixed with the aqueous solution of HF (Step 2). ２ SO ４ In step 2, the aqueous solution of LiCl or Li is mixed with the aqueous solution of HF to precipitate LiF. ２ SO ４ Preferably, the aqueous solution is added dropwise to the aqueous HF solution. ２ SO ４ The aqueous solution is added dropwise to the aqueous HF solution at a rate of 0.010 eq / min to 0.20 eq / min. ２ SO ４ The rate at which the aqueous solution is dropped is preferably 0.010 eq / min or more, 0.020 eq / min or more, 0.030 eq / min or more, 0.040 eq / min or more, 0.050 eq / min or more, 0.060 eq / min or more, 0.070 eq / min or more, 0.080 eq / min or more, 0.090 eq / min or more, 0.10 eq / min or more, 0.11 eq / min or more, 0.12 eq / min or more, 0.13 eq / min or more, or 0.14 eq / min or more, and is preferably 0.20 eq / min or less, 0.19 eq / min or less, 0.18 eq / min or less, 0.17 eq / min or less, 0.16 eq / min or less, or 0.15 eq / min or less.

[0030] In this embodiment, an aqueous LiCl solution or Li ２ SO ４The temperature of the aqueous HF solution to be dropped is preferably maintained at 5 to 50°C, more preferably at 30 to 40°C. ２ SO ４ After the dropwise addition of the aqueous solution is completed, the mixture is preferably stirred for 15 to 60 minutes to precipitate LiF.

[0031] LiCl aqueous solution or Li ２ SO ４ When the dropping rate of the aqueous solution is 0.010 eq / min or more, the deposited LiF crystals do not grow too much, so that it is possible to suppress the incorporation of HF and water during the crystal growth process, and as a result, it is easy to suppress the amount of HF and water remaining in LiF. ２ SO ４ When the dropping rate of the aqueous solution is 0.20 eq / min or less, good filterability is likely to be obtained when recovering the LiF particles.

[0032] In this embodiment, step 2 is performed by using an aqueous LiCl solution or Li ２ SO ４ The step 3 is preferably carried out by adding a base to the solution obtained in the step 2, as will be described later.

[0033] In this embodiment, an aqueous LiCl solution or Li ２ SO ４A base is mixed with the mixture of the aqueous solution and the HF aqueous solution (Step 3). The pH of the solution obtained in Step 3 is 3 to 6. That is, the aqueous solution from which LiF has been precipitated is mixed with the base to adjust the pH of the aqueous solution to 3 to 6. In Step 3, it is preferable to add a base to the aqueous solution from which LiF has been precipitated (the above-mentioned mixture). The base may be used by mixing as is, or may be used by mixing the base in a solution (aqueous solution). The concentration of the solution (aqueous solution) of the base may be 5 to 28% by mass. In one embodiment, the pH of the aqueous solution is preferably 3.0 or more, 3.5 or more, or 4.0 or more, and is preferably 6.0 or less, 5.5 or less, or 5.0 or less, and most preferably 4.5. When the pH of the aqueous solution after pH adjustment is 3 or more, it is easy to suppress the amount of residual HF in LiF and / or to reduce the moisture content of LiF after drying. Furthermore, if the pH of the aqueous solution after pH adjustment is 6 or less, it is easy to suppress the residual alkaline component in LiF. The LiF obtained by adjusting the pH of the aqueous solution to 3 to 6 is used as LiPF ６ and LiBF ４ When the pH is adjusted, it is preferable to maintain the temperature of the aqueous solution in which LiF is precipitated at 5 to 50°C.

[0034] The base may be an aqueous solution in which at least one selected from the group consisting of ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and potassium hydrogen carbonate is dissolved in water (hereinafter, this may be referred to as a "basic aqueous solution").

[0035] Alternatively, an organic base (primary amine, secondary amine, or tertiary amine), calcium hydroxide, or magnesium hydroxide, which has low solubility in water, may be used as is in place of the basic aqueous solution. The organic base may be at least one selected from the group consisting of methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, and pyridine, and triethylamine is preferred from the viewpoint of availability.

[0036] The base is preferably a basic aqueous solution or an organic base, since this facilitates reducing metal impurities in lithium fluoride produced using the base. Examples of the metal impurities include Ca, Na, K, Fe, Cr, Mg, Ni, Al, Cu, and Pb. The lower the content of metal impurities in lithium fluoride, the better, and it is preferable that the content of each of the above elements is less than 30 ppm.

[0037] The basic aqueous solution may be an aqueous solution in which at least one selected from the group consisting of ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and potassium hydrogen carbonate is dissolved in water. From the viewpoint of reducing residual Na in the obtained LiF, the basic aqueous solution is preferably an aqueous solution in which at least one selected from the group consisting of ammonia, lithium hydroxide, potassium hydroxide, lithium carbonate, lithium hydrogen carbonate, potassium carbonate, and potassium hydrogen carbonate is dissolved in water, and is more preferably an aqueous solution in which ammonia is dissolved in water, from the viewpoint of ease of preparation of the aqueous solution and ease of removal by drying the obtained LiF.

[0038] In this embodiment, the precipitated LiF may be collected by filtration (Step 4). The collected filter cake may be washed with pure water or dehydrated with a pressurized gas such as argon or nitrogen. The temperature during the dehydration may be 50°C to 200°C. The dehydrated filter cake may be dried at 100°C to 300°C for 6 to 48 hours.

[0039] By the above manufacturing method, LiPF ６ and LiBF ４ Even when used as a raw material for LiF, it is possible to obtain LiF in which the free acid concentration is easily suppressed.

[0040] [Characteristics of LiF] The present disclosure also relates to lithium fluoride containing 180 ppm or less of water, and having a pH of 8.8 or less when the supernatant liquid is measured after adding 0.15 g of lithium fluoride to 50.0 g of water, stirring at 25°C ± 1°C for 10 minutes, and allowing to stand for 30 minutes. The method for producing LiF according to this embodiment is not particularly limited, but it can be preferably obtained by the LiF production method described above. The characteristics of LiF according to this embodiment and LiF obtained by the above-mentioned production method will be described. The LiF according to this embodiment and LiF obtained by the above-mentioned production method contain 180 ppm or less of water. That is, the moisture content of the LiF after drying is 180 ppm or less. In one embodiment, the moisture content of the dried LiF is preferably 170 ppm or less, 160 ppm or less, 150 ppm or less, 140 ppm or less, 130 ppm or less, 120 ppm or less, 110 ppm or less, 100 ppm or less, 90 ppm or less, or 80 ppm or less. In one embodiment, the moisture content of the dried LiF may be, for example, 5 ppm or more, or 10 ppm or more, as long as it is within the above-mentioned range.

[0041] [Measurement of Water Content of LiF] In this specification, the water content of LiF is measured by extracting the water contained in LiF using a water vaporizer and measuring the water content by the Karl Fischer method.

[0042] Furthermore, in the LiF according to this embodiment and the LiF obtained by the above-described production method, when 0.15 g of LiF is added to 50.0 g of water, the mixture is stirred for 10 minutes at room temperature (25° C.±1° C.), and the resulting supernatant has a pH of 8.8 or less after being allowed to stand for 30 minutes. In one embodiment, the pH of the supernatant is preferably 8.5 or less, and may be 8.0 or less, 7.5 or less, or 7.0 or more.

[0043] [pH Measurement] In this specification, pH measurement is performed by adding LiF (0.15 g) to pure water (50.0 g), stirring at room temperature (25°C ± 1°C) for 10 minutes to extract the alkaline component, leaving it to stand for 30 minutes, and then recovering the supernatant liquid and measuring it with a pH meter.

[0044] In addition, the LiF according to this embodiment and the LiF obtained by the above-described manufacturing method can be used to produce LiPF６ or LiBF ４ LiPF when manufacturing ６ Solution or LiBF ４ It is preferred that the free acid concentration in the solution is 150 ppm or less. ６ Solution or LiBF ４ More preferably, the free acid concentration in the solution is 140 ppm or less, 130 ppm or less, 120 ppm or less, 110 ppm or less, 100 ppm or less, or 90 ppm or less. ６ Solution or LiBF ４ The free acid concentration in the solution may be, for example, 1 ppm or more, 2 ppm or more, 3 ppm or more, 4 ppm or more, 5 ppm or more, 6 ppm or more, 7 ppm or more, 8 ppm or more, 9 ppm or more, or 10 ppm or more, as long as it is within the above-mentioned range.

[0045] [Free Acid Concentration Measurement] In this specification, LiPF ６ Solution or LiBF ４ The free acid concentration in the solution is LiPF ６ Solution or LiBF ４ 20.0 g of the solution is weighed out and subjected to neutralization titration with 0.01 N triethylamine / acetone solution to quantify the free acid concentration. The free acid concentration is the mass concentration when the quantitative value (molar concentration) is converted to HF.

[0046] The LiF according to this embodiment and the LiF obtained by the above-described manufacturing method have the above-described properties, and therefore, LiPF ６ and LiBF ４ Even when used as a raw material for LiF, it is possible to obtain LiF in which the free acid concentration is easily suppressed.

[0047] [LiPF ６ LiPF using LiF according to this embodiment having the above-described properties ６ The manufacturing method of the LiPF according to this embodiment will be described below. ６ The method for producing the LiF dispersion liquid is prepared by mixing the LiF obtained by the LiF production method according to the present embodiment described above with a chain carbonate, and then adding phosphorus pentafluoride (PF ５) and LiPF ６ LiPF ６ In addition, the LiPF according to this embodiment is a method for producing the LiPF ６ The manufacturing method of the present invention is to prepare a LiF dispersion by mixing the LiF according to the present embodiment and a chain carbonate, and then add PF to the LiF dispersion. ５ Inject LiPF ６ LiPF ６ This is a manufacturing method.

[0048] A LiF dispersion is prepared by mixing the LiF according to this embodiment or the LiF obtained by the LiF production method according to this embodiment with a chain carbonate (step 11A). The LiF dispersion is preferably prepared by adding the LiF according to this embodiment or the LiF obtained by the LiF production method according to this embodiment to a chain carbonate. Examples of the chain carbonate used in step 11A include ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate, with ethyl methyl carbonate being preferred. The concentration of the LiF dispersion is preferably 1 to 20% by mass.

[0049] The LiF dispersion solution was treated with phosphorus pentafluoride (PF ５ ) and LiPF ６ (Step 12A). At this time, the LiF dispersion is kept at 5 to 35°C, preferably 25 to 30°C, while PF ５ It is preferable to inject PF ５ After the introduction of the above is completed, the mixture is preferably stirred at room temperature for 15 minutes to 2 hours.

[0050] LiPF produced by the reaction in step 12A ６ The reaction solution in which LiPF is dissolved is subjected to pressure filtration to remove excess LiF, and LiPF is obtained. ６ A solution can be obtained (Step 13A).

[0051] In this embodiment, by using LiF having the above-mentioned properties, LiPF with a reduced free acid concentration can be obtained. ６ can be manufactured.

[0052] [LiBF ４LiBF using LiF according to this embodiment having the above-described properties ４ The manufacturing method of LiBF according to this embodiment will be described below. ４ The method for producing the LiF dispersion liquid is prepared by mixing the LiF obtained by the LiF production method according to the present embodiment described above with a chain carbonate, and then adding boron trifluoride (BF ３ ) and LiBF ４ to obtain LiBF ４ In addition, the LiBF according to this embodiment is a method for producing the same. ４ The manufacturing method of the present invention is to prepare a LiF dispersion by mixing the LiF according to the present embodiment and a chain carbonate, and then adding BF to the LiF dispersion. ３ Blow in LiBF ４ to obtain LiBF ４ This is a manufacturing method.

[0053] A LiF dispersion is prepared by mixing the LiF according to this embodiment or the LiF obtained by the LiF production method according to this embodiment with a chain carbonate (step 11B). The LiF dispersion is preferably prepared by adding the LiF according to this embodiment or the LiF obtained by the LiF production method according to this embodiment to a chain carbonate. Examples of the chain carbonate used in step 11B include ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate, with ethyl methyl carbonate being preferred. The concentration of the LiF dispersion is preferably 1 to 20% by mass.

[0054] Boron trifluoride (BF ３ ) and LiBF ４ (Step 12B). At this time, the LiF dispersion is kept at 5 to 35°C, preferably 25 to 30°C, while BF ３ It is preferable to inject BF ３ After the introduction of the above is completed, the mixture is preferably stirred at room temperature for 15 minutes to 2 hours.

[0055] LiBF produced by the reaction in step 12B above ４ The reaction solution in which LiF was dissolved was filtered under pressure to remove excess LiF, and LiBF４ A solution can be obtained (Step 13B).

[0056] In this embodiment, by using LiF having the above-mentioned properties, LiBF having a reduced free acid concentration can be obtained. ４ can be manufactured.

[0057] Hereinafter, embodiments of the present disclosure will be described in detail with reference to examples, but the embodiments of the present disclosure are not limited to these examples.

[0058] Example 1 Preparation of LiCl Aqueous Solution 525 g of pure water and 225 g (5.31 mol) of LiCl (Honjo Chemical Co., Ltd.: purity ≥ 99.5%, metal components (Na, K, Mg, Ca, Si, Fe, Ni, Co, Cr, Cu, Pb, Al, Zn, S) each 20 ppm or less) were added to a 1 L glass flask and completely dissolved to prepare a 30 mass % LiCl aqueous solution. The LiCl aqueous solution was then filtered through a filter with a pore size of 1 μm to remove any undissolved matter.

[0059] <Fluorination> A 50% by mass aqueous solution of HF (H O ... ２ SiF ６ ≦0.05%, ignition residue≦0.05%, SO ４ ≦0.02%, As≦10ppm, Pb≦10ppm, Fe≦20ppm, Na ２ To the mixture was added 220 g (HF: 5.50 mol, 1.04 eq) of HF (0≦5 ppm, CaO≦10 ppm), and the filtered aqueous LiCl solution was added dropwise at a rate of 0.06 eq / min while stirring, while maintaining the liquid temperature at 45° C. or less. After the dropwise addition was completed, stirring was continued for 30 minutes to precipitate LiF.

[0060] <pH Adjustment> A 28% aqueous ammonia solution (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) was added dropwise to the aqueous solution in which LiF had been precipitated, and the mixture was stirred to adjust the pH to 4.5, while maintaining the liquid temperature at 45°C or lower.

[0061] <Filtration and Washing> The precipitate was collected by pressure filtration, and the collected filter cake was washed twice with 540 g of pure water. Dehydration was carried out with pressurized nitrogen.

[0062] <Drying> The residue was recovered from the filter and dried at 200° C. for 24 hours to obtain 135.1 g (5.21 mol, yield 98.1%) of LiF.

[0063] <LiPF ６ 225.0 g of ethyl methyl carbonate and dried LiF (13.1 g, 505.0 mmol, 1.02 eq) were added to a 1 L stainless steel vessel and stirred. PF ５ (62.2g, 493.8mmol, simply LiPF ６ (generated by thermal decomposition of PF at 200°C) was blown into the tank. ５ After the introduction of LiF was completed, stirring was continued for 1 hour at room temperature. After that, excess LiF was removed by pressure filtration, and LiPF with a concentration of 25% by mass was obtained. ６ A solution was obtained.

[0064] [Examples 2 to 4] The Li source was LiCl synthesized from LiOH (Tokyo Chemical Industry Co., Ltd., >98.0%) and hydrochloric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent, 35%), or Li ２ CO ３ (Fujifilm Wako Pure Chemical Corporation, special grade reagent, >99.0%) and hydrochloric acid. ２ SO ４ The LiFs of Examples 2 to 4 were produced by the same manufacturing method as in Example 1, except that the LiF was changed to a hydrate (FUJIFILM Wako Pure Chemical Industries, Ltd., special grade reagent, >99.0%). Furthermore, these LiFs were used to produce LiPFs of Examples 2 to 4 by the same manufacturing method as in Example 1. ６ A solution was obtained.

[0065] [Examples 5 to 8] LiF of Examples 5 to 8 was produced by the same production method as in Example 1, except that the dropping rate of the LiCl aqueous solution after filtration was changed. ５ The stirring time after the completion of the introduction was changed to 5 hours. In addition, using these LiFs, LiPF of Examples 5 to 8 were produced by the same manufacturing method as in Example 1. ６ A solution was obtained.

[0066] [Examples 9 to 10 and Comparative Examples 1 to 3] LiF of Examples 9 to 10 and Comparative Examples 1 to 3 was produced by the same production method as in Example 1, except that the pH of the aqueous solution obtained was changed by pH adjustment. In addition, using these LiF, LiPF of Examples 9 to 10 and Comparative Examples 1 to 3 was produced by the same production method as in Example 1. ６ A solution was obtained.

[0067] [Example 11] LiF of Example 11 was produced by the same production method as in Example 1, except that calcium hydroxide powder (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) was added and mixed instead of dropping the 28% aqueous ammonia solution. In addition, LiPF of Example 11 was produced by the same production method as in Example 1 using this LiF. ６ A solution was obtained.

[0068] [Example 10-1, Comparative Example 3-1] The LiF produced by the method of Example 10 was used, and the LiPF ６ The ethyl methyl carbonate described in the manufacturing procedure of 1) was converted into diethyl carbonate, and then PF ５ (62.2 g, 493.8 mmol) was dissolved in BF ３ (manufactured by Stella Chemifa, 33.5 g, 493.8 mmol) and LiBF of Example 10-1 ４ A solution was obtained. In addition, the LiF produced by the method of Comparative Example 3 was used to obtain the LiPF solution of Example 1. ６ The ethyl methyl carbonate described in the manufacturing procedure of 1) was converted into diethyl carbonate, and then PF ５ (62.2 g, 493.8 mmol) was dissolved in BF ３ (manufactured by Stella Chemifa, 33.5 g, 493.8 mmol) and LiBF of Comparative Example 3-1 ４ A solution was obtained.

[0069] [Comparative Examples 4 and 5] The Li source was LiOH or Li ２ CO ３ LiF of Comparative Examples 4 and 5 were produced by the same production method as in Example 1, except that the LiF was changed to: ６ A solution was obtained.

[0070] [Measurement of moisture content of LiF] After drying, the moisture content of the LiF samples of Examples 1 to 11 and Comparative Examples 1 to 5 was measured using a moisture vaporizer (Kyoto Electronics Manufacturing Co., Ltd., ADP-611) and a Karl Fischer moisture meter (Kyoto Electronics Manufacturing Co., Ltd., MKC-710S) (vaporization temperature: 300°C). The measurement results are shown in Tables 1 and 2.

[0071] [pH Measurement] LiF (0.15 g) from Examples 1 to 11 and Comparative Examples 1 to 5 after drying was added to pure water (50.0 g) and stirred at room temperature (25°C ± 1°C) for 10 minutes to extract the remaining alkaline component. After stopping the stirring and leaving it to stand for 30 minutes, the supernatant was recovered and the pH was measured using a pH meter (PH-SE, Horiba, Ltd.). The measurement results are shown in Tables 1 and 2.

[0072] [Metal Impurity Content] The dried LiF of Examples 1 to 11 and Comparative Examples 1 to 5 was mixed with perchloric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) and dissolved, and then the contents of the elements Ca, Na, K, Fe, Cr, Mg, Ni, Al, Cu, and Pb contained in the LiF were measured using an ICP optical emission spectrometer (ICPE-9800, Shimadzu Corporation).

[0073] [Free Acid Concentration Measurement] LiPF of Examples 1 to 11 and Comparative Examples 1 to 5 ６ Solution and LiBF ４ 20.0 g of the solution was weighed out and subjected to neutralization titration with a 0.01 N triethylamine (FUJIFILM Wako Pure Chemical Corporation, special grade reagent, >99.0%) / acetone (FUJIFILM Wako Pure Chemical Corporation, special grade reagent, >99.5%) solution to quantify the free acid concentration in the solution. The free acid concentration was reported as a mass concentration when the quantitative value (molar concentration) was converted to HF. The measurement results are shown in Tables 1 and 2.

[0074]

[0075]

[0076] In Example 4 and Comparative Examples 4 and 5 in Table 1, the "LiCl aqueous solution dropping rate" is ２ SO ４ "Aqueous solution dropping speed", "LiOH aqueous solution dropping speed", "Li ２ CO３ This shall be read as "aqueous solution drip rate."

[0077] <Comparison of Examples 1 to 4 and Comparative Examples 4 to 5> When a basic Li source was used, no difference in moisture was observed between the LiF of Examples 1 to 4, which used a neutralized Li source, but the LiF of Comparative Examples 4 and 5 had a large amount of residual alkaline components. As a result, the LiPF produced using these LiFs ６ In contrast, in the LiF of Examples 1 to 4, which used a neutralized Li source, the residual alkaline component was suppressed, and the LiF was converted into LiPF ６ Even when used as a raw material for the above, the increase in free acid was suppressed.

[0078] Comparison of Example 1 and Examples 5 to 8 In the LiF of Example 5, in which the dropping rate of the LiCl aqueous solution was reduced to 0.007 eq / min, a slight increase in moisture was observed (presumably due to the influence of moisture absorption caused by crystal growth). ６ The free acid concentration of the solution was less than 150 ppm, which was an acceptable level, but slightly higher than in other examples.

[0079] In the LiF of Example 6, in which the dropping rate of the LiCl aqueous solution was reduced to 0.02 eq / min, a slight increase in water content was observed (presumably due to the growth of crystals and the incorporation of water), but the LiPF ６ The effect on the free acid concentration of the solution was slight. In the LiF of Example 7, where the dropping rate was set to 0.10 eq / min, there was almost no difference in the effect on the free acid concentration compared to the LiF of Example 1, where the dropping rate was set to 0.06 eq / min. In addition, in the LiF of Example 8, where the dropping rate was set to 0.15 eq / min, a slight decrease in water content was observed, which is thought to be due to the decrease in the particle size of LiF.

[0080] <Comparison of Example 1 with Examples 9 and 10> In the LiF of Example 9, in which the pH after fluorination was lowered to 3.5, the adhesion of HF was increased, which is considered to be the influence of LiPF ６ A slight increase in the free acid concentration of the solution was confirmed. Conversely, in the case of LiF in Example 10, where the pH was increased to 5.5, the amount of residual alkaline components increased and the amount of LiPF６ The free acid concentrations in the solutions increased slightly, but both were below 150 ppm, which was within the acceptable level.

[0081] Comparison of Example 1 and Comparative Examples 1 to 3 In the LiF of Comparative Example 1, in which the pH was not adjusted after fluorination or the drop amount during pH adjustment was controlled to lower the pH to 1, or in the LiF of Comparative Example 2, in which the pH was lowered to 2, the residual alkali component was slightly reduced, but the moisture content increased, and the LiPF ６ The free acid concentration of the solution increased. This is thought to be due to an increase in the amount of HF attached to the LiF. Conversely, in the LiF of Comparative Example 3, where the pH was increased to 7, a slight increase in water content and an increase in the amount of residual alkaline components were confirmed, which resulted in the formation of LiPF ６ The free acid concentration of the solution increased significantly.

[0082] Comparison of Example 1 and Example 11 In the LiF of Example 11, in which the pH of the LiF aqueous solution was adjusted with calcium hydroxide, the LiPF ６ On the other hand, when LiF of Example 11 was used, calcium derived from calcium hydroxide was dissolved in LiPF 5 compared to when LiF of Example 1 was used. ６ However, the calcium concentration was slightly higher than that of LiPF ６ LiPF removed from solution ６ In this case, it is about 5 ppm, and furthermore, this LiPF ６ In the electrolyte prepared using LiPF, the concentration is about 1 ppm. ６ The calcium detected in the solution was at an acceptable level.

[0083] From the above results, LiPF ６It turns out that in order to suppress the free acid concentration of the solution to 150 ppm or less, it is important to keep the moisture content of the dried LiF to 180 ppm or less, reduce the alkaline component, and suppress the pH of the supernatant liquid measured after adding 0.15 g of LiF to 50.0 g of water, stirring for 10 minutes at 25° C.±1° C., and allowing to stand for 30 minutes to suppress the pH to 8.8 or less. To achieve these values, it is important to set the dropping rate of the LiCl aqueous solution during LiF production to 0.010 eq / min or more, and to keep the pH of the aqueous solution obtained in the above-mentioned step 3 within the range of 3 to 6.

[0084] The present disclosure provides a method for producing LiF with a balanced reduction in residual moisture and alkaline components. The present disclosure also provides a method for producing lithium hexafluorophosphate with a reduced free acid concentration, using lithium fluoride obtained by the method. The present disclosure also provides a method for producing lithium tetrafluoroborate with a reduced free acid concentration, using lithium fluoride obtained by the method. Furthermore, the present disclosure also provides LiF with a balanced reduction in residual moisture and alkaline components, using the method.

[0085] Although the present disclosure has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. This application is based on Japanese patent applications filed on August 16, 2023 (Patent Application No. 2023-132618) and May 7, 2024 (Patent Application No. 2024-075430), the contents of which are incorporated herein by reference.

Claims

1. A method for producing lithium fluoride comprising: step 1 of preparing an aqueous solution of at least one of lithium chloride and lithium sulfate; step 2 of mixing the aqueous solution of at least one of lithium chloride and lithium sulfate with an aqueous solution of hydrofluoric acid; and step 3 of mixing a mixed solution of the aqueous solution of at least one of lithium chloride and lithium sulfate and the aqueous solution of hydrofluoric acid with a base, wherein the pH of the solution obtained in step 3 is 3 to 6.

2. The method for producing lithium fluoride according to claim 1, wherein the step 2 is carried out by dropping an aqueous solution of at least one of the lithium chloride and lithium sulfate into an aqueous solution of hydrofluoric acid, and the step 3 is carried out by adding a base to the liquid obtained in the step 2.

3. The method for producing lithium fluoride according to claim 2, wherein the aqueous solution of at least one of lithium chloride and lithium sulfate is added dropwise to the aqueous hydrofluoric acid solution at a rate of 0.010 eq / min to 0.20 eq / min.

4. The method for producing lithium fluoride according to claim 1, wherein the base is at least one of a basic aqueous solution and an organic base.

5. The method for producing lithium fluoride according to claim 4, wherein the basic aqueous solution is an aqueous solution in which at least one selected from the group consisting of ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and potassium hydrogen carbonate is dissolved in water.

6. The method for producing lithium fluoride according to claim 1, comprising the steps of: preparing an aqueous solution of at least one of lithium hydroxide and lithium carbonate; and mixing the aqueous solution of at least one of lithium hydroxide and lithium carbonate with at least one of hydrochloric acid and sulfuric acid to prepare an aqueous solution of at least one of lithium chloride and lithium sulfate.

7. The method for producing lithium fluoride according to claim 6, wherein the mixing of the aqueous solution of at least one of lithium hydroxide and lithium carbonate with at least one of hydrochloric acid and sulfuric acid is carried out by adding at least one of hydrochloric acid and sulfuric acid to an aqueous solution of at least one of lithium hydroxide and lithium carbonate.

8. A method for producing lithium hexafluorophosphate, comprising mixing lithium fluoride obtained by the method for producing lithium fluoride according to any one of claims 1 to 7 with a chain carbonate to prepare a lithium fluoride dispersion, and blowing phosphorus pentafluoride into the lithium fluoride dispersion to obtain lithium hexafluorophosphate.

9. A method for producing lithium hexafluorophosphate according to claim 8, wherein the lithium fluoride dispersion is prepared by adding the lithium fluoride to the chain carbonate.

10. A method for producing lithium tetrafluoroborate, comprising the steps of: mixing lithium fluoride obtained by the method for producing lithium fluoride according to any one of claims 1 to 7 with a chain carbonate to prepare a lithium fluoride dispersion; and blowing boron trifluoride into the lithium fluoride dispersion to obtain lithium tetrafluoroborate.

11. The method for producing lithium tetrafluoroborate according to claim 10, wherein the lithium fluoride dispersion is prepared by adding the lithium fluoride to the chain carbonate.

12. Lithium fluoride containing 180 ppm or less of water, which has a pH of 8.8 or less when 0.15 g of lithium fluoride is added to 50.0 g of water, stirred at 25°C ± 1°C for 10 minutes, and allowed to stand for 30 minutes.

13. A method for producing lithium hexafluorophosphate, comprising mixing the lithium fluoride according to claim 12 with a chain carbonate to prepare a lithium fluoride dispersion, and blowing phosphorus pentafluoride into the lithium fluoride dispersion to obtain lithium hexafluorophosphate.

14. The method for producing lithium hexafluorophosphate according to claim 13, wherein the lithium fluoride dispersion is prepared by adding the lithium fluoride to the chain carbonate.

15. A method for producing lithium tetrafluoroborate, comprising mixing the lithium fluoride according to claim 12 with a chain carbonate to prepare a lithium fluoride dispersion, and blowing boron trifluoride into the lithium fluoride dispersion to obtain lithium tetrafluoroborate.

16. A method for producing lithium tetrafluoroborate according to claim 15, wherein the lithium fluoride dispersion is prepared by adding the lithium fluoride to the chain carbonate.

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