KR100288826B1 - A Manufacturing Method for Lithium Tetrafluoroborate - Google Patents

Abstract

The present invention relates to a method for producing lithium tetrafluoroborate (LiBF ₄ ) by reacting LiF with boron fluoride (BF ₃ ) in an organic solvent, wherein the solid phase obtained by reacting LiF with boron fluoride and etherate in an ether solvent LiBF ₄ )) was dissolved in hydrofluoric anhydride (HF) and cooled to -10 ~ -30 ℃, F ₂ gas was introduced, stirred and recrystallized at -80 ~ 0 ℃ to produce high purity LiBF ₄ in high yield It is about how to.

Crude LiBF ₄ is dissolved and recrystallized in hydrofluoric anhydride to dissolve the unreacted LiF contained in the crude LiBF ₄ to almost completely eliminate the metallic components contained in solid materials such as LiF and solvents and impurities such as lithium carbonate. It can be removed and the reaction system is treated with F ₂ gas to remove the side reactions and moisture such as lithium oxyborate, there is an advantage that can be produced in high yield LiBF ₄ in high yield.

Description

Manufacture method for lithium tetrafluoroborate {A Manufacturing Method for Lithium Tetrafluoroborate}

The present invention relates to a method for producing lithium tetrafluoroborate (LiBF ₄ ), which is one of essential components constituting a lithium ion secondary battery and a lithium polymer battery, with high yield and high purity.

Lithium ion battery or lithium polymer battery basically uses anode of Li metal oxide (LiCoO ₂ , NiNiO ₂ , LiMn ₂ O _4, etc.) and carbon cathode and electrolyte such as graphite. It is composed of an electrolyte solution dissolved in an organic solvent, and as an organic solvent, a mixed solvent of ethylene carbonate (hereinafter referred to as EC) and dimethyl carbonate (hereinafter referred to as DMC), or EC and diethyl carbonate (hereinafter referred to as A non-aqueous mixed solvent such as a mixed solvent of DEC) is used, and lithium tetrafluoroborate, lithium hexafluorophosphate, or the like is used as an electrolyte.

In these batteries, Li ions of the positive electrode are inserted into and attached between the pores of the carbon material of the negative electrode during charging, and Li ions of the negative electrode return to the positive electrode during discharge. At this time, since Li ions are moved through the electrolyte, the specifications such as purity of the electrolyte used here are very strictly limited in order to maintain performance such as battery life cycle.

By the production process of LiBF ₄ is a like non-aqueous solution method, an aqueous solution method, a gas phase method is known and non suyongbeop as is was dispersed lithium fluoride (LiF) in an organic solvent by introducing a boron trifluoride (BF ₃₎ gas for producing a LiBF ₄ The method is known (Japanese Patent Laid-Open No. 56-145113).

In this non-aqueous solution method, organic solvents such as ether and alcohol are used, and it is not easy to purify and remove water from the organic solvent used as a solvent. In particular, alkali metals used for water removal are likely to remain in the organic solvent. In addition, the metal component included in the raw material LiF and the organic solvent itself also has a problem of increasing the content of the metal component of the electrolyte.

Since these metal components are present in an ionic state in an organic solvent, no matter how precise distillation is, the distillation method cannot satisfy battery-level specifications, and the metal components contained in LiF are also very difficult to purify.

In addition, LiBF ₄ prepared by the organic solvent method is not suitable for use as an electrolyte because it forms a coordination bond in the form of an organic solvent and "LiBF ₄ solvent". Accordingly, pure LiBF ₄ should be produced by breaking the coordination bond of the solvent constituting the coordination bond, which is the only method up to now by vacuum drying while applying temperature. However, there is a disadvantage in that thermally unstable LiBF ₄ is decomposed during the heating vacuum drying process.

Pyrolysis results in the decomposition of LiF and BF ₃ gases, resulting in lower yield and purity.

A method of purifying LiBF ₄ using a solvent such as a lower alcohol is also known (Japanese Patent Laid-Open No. 58-190820), but since water in the alcohol forms a hydrogen bond with the alcohol to form an azeotropic mixture, water is distilled away. It is very difficult to remove, and after preparing LiBF ₄ , the alcohol, which is a solvent, must be removed again. In this case, LiBF ₄ is decomposed as described above because the vacuum drying is performed while heating to 100-130 ° C., so that the yield is reduced. There is a disadvantage.

Aqueous solution method is boric acid, hydrofluoric acid aqueous solution and reacted in an aqueous solution of lithium carbonate producing the LiBF _4, and do not use expensive BF ₃ gas as compared to the non-aqueous method using a concentrated, BF ₃ gas as a way of distilled water but is favorable advantage in cost, inherently is LiBF ₄ that even if performing a thorough drying, because it is the water produced is decomposed in the reaction system, the yield is not only very low, is difficult to the water content produced a 20PPM than LiBF ₄ there is a problem.

The gas phase method (J. Am. Chem. Soc 1953, 75, 1753) is a method for producing LiBF ₄ by reacting lithium carbonate and BF ₃ gas at a high temperature of 300 ℃, because it reacts at a high temperature, LiBF ₄ due to the thermal instability of LiBF ₄ Decomposition may occur with BF ₃ gas, and in particular, there is a disadvantage in that an expensive BF ₃ gas is used excessively.

Lithium metal and ionizing potential (Ionic potential) are different from the metal components contained in the raw materials used in the process of manufacturing lithium tetrafluoroborate or the corrosion of the device, so that the battery life if it is contained in the electrolyte Shorten (Cycle Life)

In addition, when moisture is contained in the final product, LiBF ₄ is decomposed into LiF, HF, and BF ₃ by moisture, and since they are transferred to a gas state, internal pressure is formed in the battery. In particular, HF not only reacts with an organic solvent, Because it affects the corrosion of the case surrounding the case (case) it will adversely affect the stability of the battery as a whole. Therefore, in the reaction system for producing LiBF ₄ , the less moisture, the better. For this reason, lithium tetrafluoroborate (LiBF ₄ ) used as an electrolyte strictly limits the specifications of purity, moisture, metal content, and free hydrofluoric acid.

An object of the present invention is to synthesize LiBF ₄ by reacting LiF and an ether compound of boron fluoride (Et ₂ O.BF ₃ : hereinafter referred to as boron fluoride etherate) in a solvent to remove the ether used as a solvent. Next, the LiBF ₄ obtained in this reaction was placed in a recrystallization bath coated with fluorine resin (hereinafter referred to as PTFE), dissolved in HF dried with F _2, and then introduced into the reaction with F ₂ gas. Unreacted LiF contained in LiBF ₄ by removing the lithium oxyborate fluoride (LiBO _x F _y ) produced by moisture and moisture contained in the raw material itself and recrystallizing LiBF ₄ at low temperature using hydrofluoric anhydride as a solvent. And it provides a method for producing a high purity LiBF ₄ by removing metal components contained in a solid raw material, a solvent and the like.

In particular, in the present invention, since it is intended to thoroughly remove not only moisture but also metal components, it is necessary to use hydrofluoric anhydride which completely removes moisture with F ₂ gas, and to use a reactor and a recrystallization apparatus in which all the apparatuses of the process are covered with fluorine resin. It has its features.

In the non-aqueous solution method, LiF is reacted with BF _{3 in} an organic solvent such as ether or alcohol to produce LiBF ₄ (LiF + BF ₃ → LiBF ₄ ) .After completion of the reaction, unreacted LiF remains in the reaction system, and Na, K, Metallic components, such as Fe, are contained in considerable quantity as an impurity. When LiBF ₄ is recrystallized in the state where the unreacted LiF and the metal component are contained in the reaction system, a considerable amount of impurities are contained in the LiBF ₄ product.

In the present invention, when the recrystallized LiBF ₄ with dried HF, the unreacted LiF and impurity metal components remain in the mother liquor, thereby reducing the amount of unreacted LIF and metal components contained in LiBF ₄ . At this time, impurities such as lithium carbonate contained in the reaction system react with HF to generate water (Li ₂ CO ₃ + HF → LiF + CO ₂ + H ₂ O).

The generated water can be completely removed by treatment with F ₂ gas.

The reason for using the hydrofluoric anhydride in the present invention is to use a low-cost industrial LiF to produce high-purity LiBF ₄ , which has a very high content of metal as an impurity to deteriorate the performance of the battery as described above It becomes a factor.

However, since all of these metal components are dissolved in hydrofluoric anhydride, they can be easily removed by filtration after recrystallization.In addition, in the organic solvent used in the present invention, LiF remaining as an unreacted substance does not dissolve and is present as an impurity. This is because it has the advantage of producing a high purity product by recrystallization.

However, in order to use general hydrofluoric acid for purification to produce battery-class products, there is a disadvantage in that the content of water and metal is high.

The reason for this is that in the hydrofluoric acid manufacturing process, there is a drying process that passes through anhydrous sulfuric acid in order to remove water. However, the dried hydrofluoric acid typically contains water of 100 PPM or more, and H _2, which is a heavy matter, is passed through sulfuric acid. SO ₄ is always included above a certain amount (50 PPM).

In addition, as described above, in the battery-grade electrolyte, the metal content is very important.

However, all the facilities in the HF manufacturing process are made of iron, so the hydrofluoric acid itself contains metals.

Hydrofluoric anhydride from the process due to its high moisture content, H ₂ SO ₄ , and metal content is not suitable for direct use as a raw material for battery-grade electrolytes, and once again needs drying and purification.

Therefore, in the present invention, using pure F ₂ gas obtained from the electrolytic cell, the hydrofluoric anhydride was thoroughly dried to the battery level, by drying and distillation was able to reduce the content of H ₂ SO ₄ and metal components to the maximum.

In the present invention, a reaction scheme in which residual moisture in hydrofluoric anhydride is dried is as follows.

H ₂ O (in HF) + 2F ₂ → 2HF + OF ₂ (↑)

Drying Condition: F ₂ Gas Bubbling Time: 1 ~ 3hr

Temperature: -10 ~ -30 ℃

Flow rate: 1 ~ 1000g / hr

Moisture in the hydrofluoric acid reacts with the F ₂ gas to be converted to hydrofluoric acid, releasing oxygen fluoride (OF ₂ ), and the oxygen fluoride has a very low boiling point (-145 ° C.) and is easily volatilized after the reaction.

A second feature of the present invention is the use of PTFE coated or P. F. resin (PFA resin) for the metal component management. First, all the devices are coated with fluorocarbon resin or PFA resin piping for the following reasons.

Conventional methods used reactors capable of withstanding hydrofluoric anhydride (HF), that is, alloy materials such as Monel metal, Ni, Cr, etc., but these materials are very expensive and are not only commercially disadvantaged. There is a high possibility that materials will meet moisture and be corroded by hydrofluoric anhydride, such as phase problems, ie leakage or exposure to air.

When the reactor is corroded, the product is inevitably contaminated by the corroded material, and these contaminants act as a factor to increase the metal content of the product.

If the equipment is contaminated, the maintenance cost of the whole process must be repaired again, which leads to a significant increase in organic maintenance costs, which in turn leads to inefficiency of the process.

The reaction scheme and purification conditions of the reaction are as follows.

end. Scheme

▶ Step 1: LiF / diethyl ether + Et ₂ O · BF ₃ → LiBF ₄

Step 2: LiBF ₄ solution + F ₂ gas

▶ Reaction condition: 1st step: Reaction temperature: -30 ℃ ~ Room temperature

Reaction pressure: Normal pressure

Reaction time: 1 ~ 10 hours

Stage 2: Reaction temperature: -10 ℃ ~ 0 ℃, F ₂ gas flow rate: 1 ~ 1000g / hr

Contact time: 10 minutes ~ 3 hours

I. Purification: Recrystallization of LiBF ₄ in hydrofluoric anhydride

The present invention, which has the two great features mentioned above, has high yield (more than 95%), high purity (more than 99.8%), low moisture (less than 20 ppm), low glass HF (150 ppm) and high purity lithium fluoride (LiBF ₄ ). It relates to a manufacturing method.

In contrast to the method of the present invention and known methods are shown in Table 1 below.

Comparison of the present invention with existing methods Characteristic Invention Japanese Laid-Open Patent (S56-145113) Japanese Laid-Open Patent (S58-190820) Aqueous solution method Meteorological law (J.Am. Chem. Soc, 1953, 75, 1753) Raw material ①F ₂ HF②LiF / Et ₂ O③Et ₂ O ・ BF ₃ ④F ₂ gas ①LiF②BF ₃ gas ③organic solvent ① LiBF ₄ · H ₂ O ② Low alcohol ①HBF ₄ solution②Li ₂ CO ₃ ③H ₂ O ①Li ₂ CO ₃ ②BF ₃ gas Core technology Use F ₂ gas (HF drying and F ₂ pass through reactant) Method of using organic solvent with high solubility of LiBF ₄ How to use lower alcohol Synthesis in aqueous solution Reaction method to gas phase, solid state yield More than 95% 41.5% 83.3% - - water 99.8% or more 99.8% - - - Advantages High yield, high purity LiBF ₄ can be manufactured, metal component can be controlled, moisture can be controlled - - Low cost LiBF ₄ can be manufactured - Disadvantages - Low yield, inflow and removal of metal components during organic solvent refining It is impossible to remove water from alcohol.Metal component.Decompose LiBF ₄ Low yield and moisture content cannot be controlled Inability to remove unreacted lithium carbonate, inability to remove metal components, decomposition of LiBF ₄

<Example 1>

<Drying of hydrofluoric anhydride>

20 kg of carbon steel (Caron steel) container inside the bubbling tube (Pubbling tube) made of PFA resin, and the hydrofluoric acid (Bp: 19.2 ℃, water content 100ppm) is added to 18kg.

The vessel is immersed in a water bath and kept between 0 ° C and 10 ° C.

The purity is caused to activate the electrolytic cell F ₂ greater than 99% and a concentration of 99% or higher F ₂ gas is brought into contact with hydrofluoric acid to ring introducing bubbles into the container.

The reaction conditions are F ₂ gas flow rate 61g / hr, the contact time is about 30 minutes.

<Distillation of hydrofluoric anhydride>

Heat the vessel containing HF dried with F ₂ to 20-130 ° C.

HF was evaporated and condensed by maintaining the pressure in the container at about 1 kg / cm ² G, and the water content of the distilled HF was analyzed by the turbidity method. The water content was less than 10 ppm, and the trace amount of metallic components (Fe, Mn, Ca) was less than 1 ppm. , Na, K, Pb, Zn, Cd, Ni, Mg, Ca, Al). Here, dried and purified HF was used as a solvent for recrystallization of LiBF ₄ in a purification process.

<Production of Lithium Tetrafluoride (LiBF ₄ )>

A magnetic stirring bar was placed in a 1.5 L reactor coated with PTFE, and 6.51 g (0.25 mol) of LiF was added thereto. After the reactor was assembled, the reactor atmosphere was replaced with nitrogen gas, and 60 g of diethyl ether was replaced. Inject and stir at a rate of 30-200 RPM to disperse.

In addition, 39.16 g (0.27 mol) of BF ₃ · etherate is added thereto, and 10 g of diethyl ether is added thereto to dilute the water, while preventing the inflow of water into the container prepared with PTFE in advance. Ether coordinated with BF ₃ is diethylether.

Here, reasons for using etherate (diethyletherate) to BF ₃ · diethyl is BF ₃ gas and the BF ₃ · etherate in the lower boiling point (-101 ℃) at room temperature because it is liquid at room temperature instead of BF ₃ BF ₃ · ethenyl This is because the use of the rate is easy to handle because it is used for the reaction.

This vessel is connected to the reactor with a tube coated with PFA and the reactor is cooled to -30 ° C. When the temperature of the reactor reaches −30 ° C., the valve of the vessel is opened and BF ₃ · etherate is fed over 10 minutes (feed rate: 4.92 g / min).

When the addition of BF ₃ · etherate is completed, the temperature is raised to room temperature in the air, and then the reaction is conducted at that temperature for 4 hours.

After the reaction was completed, the resultant was filtered, unreacted BF ₃ · etherate and solvent were removed, washed with diethyl ether, and then dried in vacuo to completely remove residual solvent.

The obtained compound was 22.74 g and the yield was 96.65%.

<Refining of lithium tetrafluoroborate (LiBF ₄ )>

The reactant obtained in the reaction is transferred to a recrystallization bath coated with fluorine resin again, and hydrofluoric anhydride is added through a PFA tube to dissolve the reactant.

The recrystallization bath was cooled to 0 ° C., and then F ₂ gas (35 L / hr, 30 minutes) was added thereto, stirred, and recrystallized at −40 ° C. to obtain pure LiBF ₄ , and LiBF ₄ remaining in the mother liquor was The mother liquor was concentrated and recrystallized again to give 85% or more.

The recrystallized LiBF ₄ was vacuum-dried and analyzed to obtain purity (99.8%), moisture content (13-18 ppm), HF (130 ppm) and high purity LiBF ₄ , which were prepared as an electrolyte and measured for electrical conductivity. Electrical conductivity was 5.6 ~ 5.8mS / cm. In addition, the structural analysis of the synthesized LiBF ₄ was performed by NMR ( ¹⁹ F-NMR, ¹¹ B-NMR, ⁷ Li-NMR), etc. As a result, it can be seen that it is in good agreement with the standard material.

Crude LiBF ₄ is dissolved and recrystallized in hydrofluoric anhydride to completely remove impurities such as unreacted LiF solvent contained in crude LiBF ₄ and metallic components or lithium carbonate contained in solid raw material LiF. By treating with F ₂ gas can remove the side reactions such as lithium oxyfluoride and water, there is an advantage that can be produced in high yield LiBF ₄ of high purity.

Claims (2)

In the method for producing lithium tetrafluoroborate (LiBF ₄ ) by reacting LiF and boron fluoride (BF ₃ ) in an organic solvent, solid LiBF obtained by reacting LiF with boron fluoride etherate in an ether solvent ₄ was bubbled into F ₂ gas and dissolved in dried hydrofluoric anhydride (HF), cooled to -10 to -30 ° C, and then F ₂ gas was introduced and stirred, and recrystallized at -80 to 0 ° C to form LiBF ₄ . How to manufacture. The method for producing LiBF ₄ according to claim 1, wherein the hydrofluoric anhydride is hydrofluoric anhydride dried by bubbling with F ₂ gas for 1 to 3 hours at a flow rate of 1 to 1000 g / hr at a temperature of -10 to 30 ° C.