JP5252908B2 - Method for producing tetrafluoroborate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing tetrafluoroborate where tetrafluoroborate can be produced at high yield and efficiently by a continuous process, an electrolyte containing tetrafluoroborate and a storage element with the electrolyte. <P>SOLUTION: The method for producing tetrafluoroborate is characterized by having a first step of dissolving boron trifluoride gas in an organic solvent, a second step of preparing a tetrafluoroborate solution by adding an equivalent or not more than stoichiometric amount of a fluoride (MFn wherein M is a metal or NH4; and 1&le;n&le;3) to boron trifluoride into the organic solvent and a third step of dissolving boron trifluoride gas in the tetrafluoroborate solution instead of the organic solvent by circulating the tetrafluoroborate solution to the first step. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for producing tetrafluoroborate and an apparatus for producing the same, and more specifically, a method for producing tetrafluoroborate applicable to an electrolytic solution of a power storage element, tetrafluoroborate The present invention relates to an electrolyte solution including the same and a power storage element including the electrolyte solution.

As a conventional method for producing tetrafluoroborate, for example, as a method for producing lithium tetrafluoroborate, for example, there is a method of obtaining lithium tetrafluoroborate by acting lithium carbonate on a borofluoric acid solution. It is done. Since the salt produced by this method is lithium borofluoride monohydrate represented by LiBF ₄ .H ₂ O, dehydration by heating at about 200 ° C. is required. However, heating at about 200 ° C. degrades the purity of lithium tetrafluoroborate because it decomposes lithium tetrafluoroborate. Moreover, several thousand ppmw of water remains. Therefore, this production method is not necessarily sufficient in terms of controllability of the reaction, purity of the product obtained, and the like.

  In order to solve this problem, for example, in Patent Document 1 below, boron trifluoride gas is blown into a non-aqueous organic solvent for lithium secondary battery electrolyte containing lithium fluoride, and lithium fluoride and boron trifluoride are injected. A method for producing lithium tetrafluoroborate by reacting is disclosed.

  However, in the above production method, since lithium fluoride has a low solubility in an organic solvent, the organic solvent is suspended (slurry). For this reason, it is difficult to circulate an organic solvent containing lithium fluoride in the production process, and it is difficult to produce tetrafluoroborate by a continuous process.

JP-A-11-157830

  The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a tetrafluoroborate production method that enables efficient production of tetrafluoroborate with high yield by a continuous process. It is another object of the present invention to provide an electrolytic solution containing tetrafluoroborate and a power storage device including the electrolytic solution.

  In order to solve the above-described conventional problems, the inventors of the present application have studied a method for producing tetrafluoroborate, an electrolytic solution containing tetrafluoroborate, and an electric storage element including the electrolytic solution. As a result, the inventors have found that the object can be achieved by adopting the following configuration, and have completed the present invention.

  That is, the method for producing tetrafluoroborate according to the present invention is equivalent to the first step of dissolving boron trifluoride gas in an organic solvent and the boron trifluoride in order to solve the above problems. Or a second stoichiometric amount of fluoride (MFn M is metal or NH4, 1 ≦ n ≦ 3) added to the organic solvent to form a tetrafluoroborate solution; A third step of dissolving boron trifluoride gas in the tetrafluoroborate solution instead of the organic solvent by circulating a solution of the fluoroborate in the first step, To do.

  Fluorides are generally poorly soluble in organic solvents. Therefore, when fluoride is added to the organic solvent prior to absorption of boron trifluoride gas, it enters a suspended (slurry) state. For this reason, at the time of absorption of boron trifluoride, clogging with solid fluoride occurs inside the apparatus, which hinders operation. However, in the above method, first, boron trifluoride gas is absorbed in the organic solvent in the first step, and then fluoride is added to the organic solvent in the second step. Thereby, tetrafluoroborate is synthesized in an organic solvent as shown in the following chemical reaction formula. Furthermore, since the amount of fluoride added is stoichiometrically equivalent to or less than boron trifluoride, all of the fluoride reacts with boron trifluoride. As a result, a non-slurry tetrafluoroborate solution with no unreacted fluoride remaining is obtained. Thereby, the tetrafluoroborate solution can be circulated to the first step, and boron trifluoride gas can be dissolved in the tetrafluoroborate solution instead of the organic solvent (third). Process). That is, in the above method, various apparatuses including an absorption tower can be used, and continuous operation is also possible, so that the productivity of tetrafluoroborate can be improved.

  The organic solvent is preferably a non-aqueous organic solvent or a non-aqueous ionic liquid. This makes it possible to absorb boron trifluoride without hydrolysis of boron trifluoride or tetrafluoroborate, and by-product of boron trifluoride or tetrafluoroborate hydrate. it can. In addition, when boron trifluoride or tetrafluoroborate is hydrolyzed, oxyfluoroborate, borate, etc. are used against acidic substances such as oxyfluoroboric acid, hydrofluoric acid and boric acid, or organic solvents. Produces insoluble components. When an electrolytic solution containing these acidic substances and insoluble components is used in a power storage element, it has adverse effects such as corrosion of the power storage element and deterioration of electrical characteristics. For this reason, it is preferable to use an organic solvent having a low moisture concentration. From such a viewpoint, the water concentration of the organic solvent is preferably 100 ppmw or less, more preferably 10 ppmw or less, and particularly preferably 1 ppmw or less.

  The first step and the third step can be performed using an absorption tower. In the production method of the present invention, the boron trifluoride gas is dissolved in the organic solvent and the tetrafluoroborate solution, and then the fluoride is added. Therefore, the suspension (slurry) state does not occur. For this reason, even if an absorption tower is used in the first step and the third step, it is possible to prevent clogging from occurring in the inside and to enable continuous operation. As a result, the productivity of tetrafluoroborate can be improved.

  In order to solve the above problems, an electrolytic solution according to the present invention includes tetrafluoroborate obtained by the above-described method for producing tetrafluoroborate.

  Moreover, in order to solve the said subject, the electrical storage element which concerns on this invention is equipped with the electrolyte solution as described above, It is characterized by the above-mentioned. A lithium ion secondary battery etc. are mentioned as an electrical storage element of this invention.

  The present invention has the following effects by the means described above.

  In other words, according to the present invention, a stoichiometric amount of a fluorine equivalent to or less than that of boron trifluoride in the reaction vessel is used in comparison with an organic solvent in which boron trifluoride gas is previously dissolved in the absorption tower. Since both compounds are reacted with each other, a tetrafluoroborate solution containing no fluoride is obtained. The obtained tetrafluoroborate solution was again supplied to the absorption tower and circulated, and after boron trifluoride gas was dissolved in this tetrafluoroborate, React with boron trifluoride. That is, according to the present invention, a high-purity tetrafluoroborate having no unreacted fluoride and impurities is produced by a continuous production process by circulating a tetrafluoroborate solution. be able to. Moreover, the filtration process for removing a fluoride becomes unnecessary, and it is economically excellent.

  An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is an explanatory view schematically showing a tetrafluoroborate manufacturing apparatus according to the present embodiment. However, parts that are not necessary for the description are omitted, and there are parts that are illustrated in an enlarged or reduced manner for ease of explanation.

  As shown in FIG. 1, the manufacturing apparatus according to the present embodiment includes a first absorption tower 1 and a second absorption tower 5, a first tank 2, a second tank 6, a third tank 10, a pump 3, 7 and 11, a first cooler 4 and a second cooler 8, a deaeration tower 9, an air pump 12, and a condenser 13.

A predetermined amount of organic solvent is put into the first tank 2 and the second tank 6. The pumps 3 and 7 supply the liquid in the first tank 2 and the second tank 6 to the first absorption tower 1 and the second absorption tower 5, respectively, and perform circulation operation. Next, boron trifluoride (BF ₃ ) gas is supplied to the bottom of the second absorption tower 5. Boron trifluoride may be 100%, or may be appropriately diluted by mixing an inert gas. Heat generation in the first absorption tower 1 and the second absorption tower 5 can be reduced by mixing the inert gas. Further, no particular limitation is imposed on the inert gas, for example N _2, Ar, dry air, carbon dioxide, and the like. Moisture in the inert gas used for dilution is not to hydrolyze boron trifluoride or tetrafluoroborate and to avoid by-product formation of boron trifluoride or tetrafluoroborate hydrate. In order not to induce hydrolysis of boron fluoride, the moisture content is preferably 100 ppmw or less, more preferably 10 ppmw or less, and particularly preferably 1 ppmw or less. Boron trifluoride gas is dissolved in the organic solvent by making countercurrent contact with the organic solvent in the second absorption tower 5 (first step). Absorption heat of boron trifluoride into the organic solvent is removed by the first cooler 4 and the second cooler 8 provided in the circulation line, and maintained at an appropriate operating temperature.

  Next, the organic solvent in which boron trifluoride gas is dissolved is supplied to the second tank 6. The second tank 6 is supplied with a stoichiometric amount of fluoride equivalent to or less than boron trifluoride. As a result, boron trifluoride and fluoride react to generate tetrafluoroborate (second step). The following reaction formula shows the reaction between boron trifluoride and lithium fluoride.

  The tetrafluoroborate solution produced in the second tank 6 is sent out by a pump 7 through a pipe and supplied to the top of the second absorption tower 5. Boron trifluoride supplied to the bottom of the tower is absorbed in the tetrafluoroborate solution in the second absorption tower (third step). Subsequently, the reaction with the fluoride is continuously performed in the second tank 6 to increase the tetrafluoroborate to a desired concentration. By performing such a circulation operation, when a predetermined concentration is reached, a part of the solution from the pump 7 is extracted as a product. Simultaneously with the extraction of the product, the supply of the organic solvent from the outside to the first absorption tower 1 is started, and the liquid supply destination of the pump 3 is switched from the first absorption tower 1 to the second absorption tower 5 to obtain tetrafluoroborate The continuous production of the solution is performed. At this time, the absorption liquid may be supplied to the second absorption tower 5 while continuing to circulate a part of the absorption liquid to the first absorption tower 1 at the same time.

  The amount of fluoride supplied to the second tank 6 is equivalent to that of boron trifluoride dissolved in the organic solvent in order to avoid the presence of a fluoride that is sparingly soluble in the organic solvent in the form of a slurry. Or a stoichiometric amount of less than that. Thereby, it is possible to avoid clogging or the like due to the slurry-like fluoride in the apparatus. A method of making the boron trifluoride stoichiometrically excessive with respect to the fluoride can be realized by always supplying a stoichiometric excess of boron trifluoride with respect to the fluoride. The excess boron trifluoride must be discharged out of the system in any step, which is not preferable because it causes loss of raw materials. A method by which boron trifluoride and fluoride are supplied in a stoichiometrically equivalent manner to a liquid in which an excessive amount of boron trifluoride suitable for operation in advance is absorbed is more preferable.

  The tetrafluoroborate solution in which boron trifluoride used in the second step is excessively dissolved is supplied to the top of the second absorption tower in the third step. 9 is also supplied. Further, the tetrafluoroborate solution sent to the deaeration tower 9 is depressurized by the air pump 12, and boron trifluoride is distilled off. Thereby, boron trifluoride and fluoride are adjusted to a solution of tetrafluoroborate in which the stoichiometric equivalent is obtained, and is extracted from the third tank 10 as a product. It is possible to adjust the solution of tetrafluoroborate by adding fluoride that is stoichiometrically equivalent to the excessively dissolved boron trifluoride, but from the viewpoint of continuous productivity, excess boron trifluoride is reduced in pressure. It is preferable to distill off. Moreover, in order to raise the removal efficiency of boron trifluoride by decompression, the deaeration tower 9 may be provided with a heater and heated.

  The distilled boron trifluoride is supplied to the bottom of the second absorption tower 5 by the air pump 12. Furthermore, it is recovered and reused by bringing it into countercurrent contact with the organic solvent and / or tetrafluoroborate solution in the second absorption tower 5. When boron trifluoride used as a raw material contains a small amount of hydrogen fluoride, the tetrafluoroborate solution is depressurized with an air pump 12 to distill off the hydrogen fluoride, and then the condenser 13 Hydrogen fluoride may be condensed and removed. The liquid (drain) condensed in the condenser 13 contains an organic solvent, hydrogen fluoride, and boron trifluoride. However, the liquid may be discarded after being subjected to waste liquid treatment, or hydrogen fluoride, boron trifluoride or The organic solvent may be recovered and reused as necessary. As a recovery method, a normal method such as distillation or extraction can be used.

  As described above, in the present invention, by circulating the tetrafluoroborate solution, high purity tetrafluoroborate can be continuously produced with high yield.

  In the present invention, it is preferable to use an absorption tower from the viewpoint of industrial production efficiency, but this does not exclude the use of surface absorption or bubbling. Further, the first absorption tower 1 and the second absorption tower 5 can use any type of tower-type absorber such as a packed tower, a plate tower, and a wet wall tower. Furthermore, the type of absorption may be either countercurrent or cocurrent.

  In the first and third steps, the concentration of boron trifluoride gas in the organic solvent and tetrafluoroborate solution is preferably 15% by weight or less, more preferably 10% by weight or less, and more preferably 5% by weight. % Or less is particularly preferable. If the boron trifluoride gas concentration in the organic solvent is high, the reaction between the organic solvent and boron trifluoride may occur, and the organic solvent may be colored, modified, or solidified. In addition, the heat of absorption becomes large and it may be difficult to control the liquid temperature.

  In the first step and the third step, the gas-liquid contact temperature between the boron trifluoride gas, the organic solvent and the tetrafluoroborate solution is preferably −40 to 100 ° C. More preferably, it is 60 ° C. If the gas-liquid contact temperature is less than -40 ° C, the organic solvent is solidified and continuous operation cannot be performed. On the other hand, when the gas-liquid contact temperature exceeds 100 ° C., the vapor pressure of boron trifluoride in the organic solvent and tetrafluoroborate solution becomes too high, and the absorption efficiency decreases. There is a disadvantage that a reaction of boron occurs.

  The organic solvent is preferably at least one of a non-aqueous organic solvent and a non-aqueous ionic liquid. Moreover, as the non-aqueous organic solvent, a non-aqueous aprotic organic solvent is more preferable. Since it is not capable of donating hydrogen ions when it is aprotic, the solution of tetrafluoroborate obtained by the production method of the present invention is applied as it is to the electrolytic solution of a storage element such as a lithium ion secondary battery. be able to.

  The non-aqueous organic solvent is not particularly limited. For example, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl acetate, ethyl acetate, γ-butyl lactone, acetonitrile, dimethyl Examples include formamide, 1,2-dimethoxyethane, methanol, isopropanol and the like. Among these organic solvents, from the viewpoint of continuous production, the generated tetrafluoroborate is difficult to precipitate, that is, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, which has high solubility of tetrafluoroborate, Methyl ethyl carbonate, acetonitrile and 1,2-dimethoxyethane are preferred. These non-aqueous organic solvents may be used alone or in combination of two or more.

Furthermore, examples of the non-aqueous aprotic organic solvent include a cyclic carbonate ester, a chain carbonate ester, a carboxylic acid ester, a nitrile, an amide, or an ether compound.
These non-aqueous aprotic organic solvents may be used alone or in combination of two or more.

  The non-aqueous ionic liquid is not particularly limited, and examples thereof include fluoride complex salts or fluoride salts such as quaternary ammonium or quaternary phosphonium. Among them, quaternary ammonium cations include tetraalkylammonium cations, imidazolium cations, pyrazolium cations, pyridinium cations, triazolium cations, pyridazinium cations, thiazolium cations, oxazolium cations, and pyrimidinium. A cation, a pyrazinium cation, etc. are mentioned. Furthermore, examples of the quaternary phosphonium cation include a tetraalkylphosphonium cation. These non-aqueous ionic liquids may be used alone or in combination of two or more, or may be used by dissolving in the non-aqueous organic solvent.

  The organic solvent may be a non-aqueous organic solvent or a non-aqueous ionic liquid, or a mixture of two or more.

The fluoride added in the second step (MF _n , M is metal or NH ₄ , 1 ≦ n ≦ 3) is not limited to LiF, but NaF, KF, RbF, CsF, NH ₄ F, AgF, CaF ₂ , MgF ₂ , BaF ₂ , ZnF ₂ , CuF ₂ , PbF ₂ , AlF ₃ , FeF _{3 and the} like. These fluorides may be used alone or in combination of two or more.

  The reaction temperature between the fluoride and boron trifluoride gas is preferably −50 ° C. to 200 ° C., more preferably −10 to 100 ° C., and particularly preferably 0 ° C. to 50 ° C. If the temperature is lower than -50 ° C, the organic solvent may be solidified or tetrafluoroborate may be precipitated. On the other hand, when it exceeds 200 ° C., the produced tetrafluoroborate may be decomposed.

  About the obtained tetrafluoroborate solution, tetrafluoroborate can also be taken out by precipitating tetrafluoroborate by concentrating and / or cooling and separating from the solvent. .

  About the obtained tetrafluoroborate solution, it may be used as an electrolytic solution of an electricity storage element as it is, or a non-aqueous aprotic organic solvent, a non-aqueous ionic liquid, or a mixture of two or more. May be used.

It is preferable that the boron component-containing gas used in the production of tetrafluoroborate, specifically boron trifluoride gas, is absorbed in an absorbent and recovered and reused. Examples of the absorbing solution include water, hydrofluoric acid aqueous solution, and M (M salt is selected from the group consisting of Li, Na, K, Rb, Cs, NH ₄ , Ag, Mg, Ca, Ba, Fe, and Al. And a solution containing a carbonate, a hydroxide or a halide containing at least one of the above. More specifically, 0 to 80% by weight of water or hydrogen fluoride aqueous solution, or M salt (M is Li, Na, K, Rb, Cs, NH ₄ , Ag, Mg, Ca, Ba, Fe, and Al. And a water or hydrogen fluoride aqueous solution of 0 to 80% by weight in which at least one selected from the group consisting of carbonates, hydroxides, and halides is dissolved. By absorbing boron trifluoride gas in the absorbing solution, M (BF ₄ ) n (wherein 1 ≦ n ≦ 3) and / or H _a BF _b (OH) _c · mH ₂ O (wherein 0 ≦ a ≦ 1, 0 ≦ b ≦ 4, 0 ≦ c ≦ 3, 0 ≦ m ≦ 8). Thereby, even when an excessive amount of BF ₃ gas is used, loss of raw materials can be suppressed.

  Further, boron trifluoride flowing out from the second absorption tower 5 during the production of tetrafluoroborate is converted to boron trifluoride in the first absorption tower 1 connected in series as shown in FIG. to recover. The organic solvent containing boron trifluoride obtained in the first absorption tower 1 is supplied to the second absorption tower 5. Boron trifluoride that could not be absorbed by the first absorption tower 1 may be recovered and reused by the absorption method described above. Thereby, even when an excessive amount of boron trifluoride gas is used, the entire amount is used, and loss of raw materials can be suppressed.

  Hereinafter, preferred embodiments of the present invention will be described in detail by way of example. However, the materials, blending amounts, and the like described in the examples and comparative examples are not intended to limit the scope of the present invention only to those described in the mere explanatory examples unless otherwise specified. Not too much.

Example 1
In this example, the apparatus shown in FIG. 1 was used. After 3L of commercially available battery grade diethyl carbonate (water concentration 9ppmw) was placed in fluororesin first tank 2 and second tank 6, respectively, circulation operation in each absorption tower and tank was started using pumps 3 and 7 did. At this time, the flow rates of the pump 3 and the pump 7 were both 1 L / min. Moreover, the 1st tank 2 and the 2nd tank 6 were made constant temperature of 20 degreeC using the 1st cooler 4 and the 2nd cooler 8, respectively.

  Next, supply of boron trifluoride gas to the tower bottom of the second absorption tower 5 was started at 3.41 g / min. After absorbing boron trifluoride gas in the organic solvent for 2 minutes, lithium fluoride was started to be supplied to the second tank 6 at 1.30 g / min. Sixty minutes after starting the supply of lithium fluoride, the product started to be extracted at 51.7 ml / min. Simultaneously with the extraction of the product, an organic solvent is supplied to the first absorption tower 1 at 50 ml / min, and the liquid supply destination of the pump 3 is switched from the first absorption tower 1 to the second absorption tower 5. did.

  By continuous operation for 60 minutes, 3,295.8 g of the solution was supplied to the deaeration tower 9, and the pressure was reduced by the air pump 12, whereby boron trifluoride gas excessively dissolved in the solution was distilled off. After the distillation, the solution was extracted from the third tank 10 to obtain 3,350 g of a lithium tetrafluoroborate solution. Diethyl carbonate accompanying the distilled boron trifluoride gas was removed by the condenser 13. Thereafter, it was merged with the raw material boron trifluoride gas and reused. The total supply amount of the distilled boron trifluoride gas and the raw material boron trifluoride gas was maintained at 3.41 g / min.

  The diethyl carbonate solution of lithium tetrafluoroborate thus obtained had an insoluble component of 10 ppmw or less, a free acid of 10 ppmw or less, and a water content of 10 ppmw or less. Moreover, the obtained diethyl carbonate solution of lithium tetrafluoroborate was further depressurized at 40 ° C. to distill off the diethyl carbonate to obtain a white solid. As a result of XRD analysis of the white solid, it was confirmed to be lithium tetrafluoroborate.

(Example 2)
In this example, the apparatus shown in FIG. 2 was used. Commercially available battery-grade diethyl carbonate 500 g (water concentration 9 ppmw) was put in a second tank 6 made of fluororesin, supplied to the top of the second absorption tower 5 with a pump 7 and circulated. The second tank 6 was kept constant at 20 ° C. using a cooler 8. Next, boron trifluoride gas was supplied to the bottom of the second absorption tower 5 at a flow rate of 0.5 L / min for 16.7 minutes, and 22.6 g was introduced (first step).

  Next, 8.0 g of lithium fluoride as a fluoride was gradually supplied to the second tank 6. Lithium fluoride quickly dissolved in an organic solvent containing boron trifluoride and reacted with boron trifluoride in the organic solvent. As a result, 530.6 g of a lithium tetrafluoroborate solution was obtained (second step).

  Furthermore, 500 g of diethyl carbonate was added to the second tank 6 and the same operation as described above was performed (third step). Of the obtained lithium tetrafluoroborate solution, 275 g was withdrawn into the third tank 10, brought to a constant temperature of 20 ° C., and 0.335 g of lithium fluoride stoichiometrically equivalent to the excessively dissolved boron trifluoride. Was added.

  The diethyl carbonate solution of lithium tetrafluoroborate thus obtained had an insoluble component of 10 ppmw or less, a free acid of 10 ppmw or less, and a water content of 10 ppmw or less. The obtained diethyl carbonate solution of lithium tetrafluoroborate was decompressed with an air pump 12 at 40 ° C. to distill off the diethyl carbonate to obtain a white solid. As a result of XRD analysis of the white solid, it was confirmed to be lithium tetrafluoroborate.

(Example 3)
In this example, the apparatus shown in FIG. 2 was used. Commercially available battery-grade diethyl carbonate 250 g (water concentration 9 ppmw) and ethylene carbonate 250 g (water concentration 7 ppmw) are placed in the second tank 6 made of fluororesin, and supplied to the top of the second absorption tower 5 by the pump 7 and circulated. It was. The second tank 6 was kept constant at 20 ° C. using a cooler 8. Next, boron trifluoride gas was supplied to the bottom of the second absorption tower 5 at a flow rate of 0.5 L / min for 25.5 minutes, and 34.6 g was introduced (first step).

  Next, 13.0 g of lithium fluoride as a fluoride was gradually supplied to the second tank 6. Lithium fluoride quickly dissolved in an organic solvent containing boron trifluoride and reacted with boron trifluoride in the organic solvent. As a result, a solution of 457.6 g of lithium tetrafluoroborate was obtained (second step).

  Furthermore, 250 g of diethyl carbonate and 250 g of ethylene carbonate were added to the second tank 6 and the same operation as described above was performed (third step). Of the obtained lithium tetrafluoroborate solution, 275 g was extracted into the third tank 10, brought to a constant temperature of 20 ° C., and reduced in pressure with the air pump 12 to distill away excessively dissolved boron trifluoride. The diethyl carbonate / ethyl carbonate solution of lithium tetrafluoroborate thus obtained had an insoluble component of 10 ppmw or less, a free acid of 10 ppmw or less, and a water content of 10 ppmw or less.

  Next, a coin-type non-aqueous electrolyte lithium secondary battery as shown in FIG. 3 was manufactured using the solution thus obtained, and the performance as an electrolyte was evaluated by a charge / discharge test. Specifically, the procedure was as follows.

<Creation of negative electrode 22>
Natural graphite and binder polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 9: 1, and N-methylpyrrolidone was added thereto to obtain a paste. This paste was uniformly applied onto a copper foil having a thickness of 22 μm using an electrode applicator. This was vacuum-dried at 120 ° C. for 8 hours, and a negative electrode 22 having a diameter of 16 mm was obtained with an electrode punching machine.

<Creation of positive electrode 21>
LiCoO ₂ powder, acetylene black as a conductive additive, and PVdF as a binder were mixed at a weight ratio of 90: 5: 5, and N-methylpyrrolidone was added to this mixture to obtain a paste. This paste was uniformly applied onto a copper foil having a thickness of 22 μm using an electrode applicator. This was vacuum-dried at 120 ° C. for 8 hours, and a positive electrode 21 having a diameter of 16 mm was obtained with an electrode punching machine.

<Creation of coin-type non-aqueous electrolyte lithium secondary battery>
After placing the positive electrode 21 on the bottom surface of the positive electrode can 24 and placing the porous porous separator 23 thereon, the non-aqueous electrolyte prepared in Example 2 was injected and the gasket 26 was inserted. After that, the negative electrode 22, the spacer 27, the spring 28, and the negative electrode can 25 are sequentially placed on the separator 23, and the opening of the positive electrode can 24 is bent inward using a coin type battery caulking machine. Sealed to prepare a non-aqueous electrolyte lithium secondary battery. Subsequently, charging was performed at a constant current of 0.4 mA. When the voltage reached 4.1 V, charging was performed at a constant voltage of 4.1 V for 1 hour. Discharging was performed at a constant current of 1.0 mA, and discharging was performed until the voltage reached 3.0V. When the voltage reached 3.0 V, 3.0 V was maintained for 1 hour, and a charge / discharge test was performed by a charge / discharge cycle. As a result, the charge / discharge efficiency was almost 100%, and the charge capacity did not change after 150 cycles of charge / discharge.

Example 4
In this example, the apparatus shown in FIG. 2 was used. 500 g of commercially available dehydrated methanol (water concentration 9 ppmw) was placed in a second tank 6 made of fluororesin and introduced into the top of the second absorption tower 5 with a pump 7 to circulate the organic solvent. The second tank 6 was kept constant at 20 ° C. using a cooler 8. Next, boron trifluoride gas was supplied to the bottom of the second absorption tower 5 at a flow rate of 0.5 L / min for 25.5 minutes, and 34.6 g was introduced (first step).

  Next, 13.0 g of lithium fluoride was gradually supplied to the second tank 6. Lithium fluoride quickly dissolved in an organic solvent containing boron trifluoride and reacted with boron trifluoride in the organic solvent. As a result, a solution of 457.6 g of lithium tetrafluoroborate was obtained (second step).

  Furthermore, 500 g of methanol was added to the second tank 6 and the same operation as described above was performed (third step). Of the obtained lithium tetrafluoroborate solution, 275 g was extracted into the third tank 10, brought to a constant temperature of 20 ° C., and reduced in pressure with the air pump 12 to distill away excessively dissolved boron trifluoride.

  The methanol solution of lithium tetrafluoroborate thus obtained had an insoluble component of 10 ppmw or less, a free acid of 10 ppmw or less, and a water content of 10 ppmw or less.

  Next, the obtained methanol solution of lithium tetrafluoroborate was bubbled with nitrogen at 5 L / min at a constant temperature of 60 ° C., and a part of the methanol was evaporated to deposit a white solid. This solution was filtered, and methanol was distilled off while purging the resulting white solid at 60 ° C. and nitrogen at 5 L / min. As a result of XRD analysis of the obtained white solid, it was confirmed to be lithium tetrafluoroborate.

(Example 5)
In this example, the apparatus shown in FIG. 2 was used. 500 g (water concentration 550 ppmw) of commercially available battery grade diethyl carbonate mixed with water was placed in a second tank 6 made of fluororesin, supplied to the top of the second absorption tower 5 with a pump 7 and circulated. The second tank 6 was kept constant at 20 ° C. using a cooler 8. Next, boron trifluoride gas was supplied to the bottom of the second absorption tower 5 at a flow rate of 0.5 L / min for 17 minutes, and 22.6 g was introduced (first step).

  Next, 8.0 g of lithium fluoride as a fluoride was gradually supplied to the second tank 6. Lithium fluoride quickly dissolved in an organic solvent containing boron trifluoride and reacted with boron trifluoride in the organic solvent. As a result, 530.6 g of a lithium tetrafluoroborate solution was obtained (second step).

  Furthermore, 500 g of diethyl carbonate was added to the second tank 6 and the same operation as described above was performed (third step). 275 g of the obtained lithium tetrafluoroborate solution was withdrawn into the third tank 10, brought to a constant temperature of 20 ° C., and excessively dissolved boron trifluoride was distilled off under reduced pressure. The diethyl carbonate solution of lithium tetrafluoroborate thus obtained has an insoluble component of 30 ppmw, a free acid of 130 ppmw, and a water content of 400 ppmw. A liquid lithium secondary battery was prepared and performance as an electrolyte was evaluated by a charge / discharge test. As a result, the initial charge / discharge efficiency induced water electrolysis. When 150 cycles of charge / discharge were repeated, the decrease in charge capacity could be suppressed to about 20%. Moreover, the coin cell after 150 cycles showed a slight expansion.

(Comparative Example 1)
This comparative example was performed using the apparatus shown in FIG. After charging 3L of commercially available battery grade diethyl carbonate (moisture concentration 9ppmw) into the first tank 2 and the second tank 6 made of fluororesin, start circulation operation in each absorption tower and tank using pumps 3 and 7 did. At this time, the flow rates of the pump 3 and the pump 7 were both 1 L / min. Moreover, the 1st tank 2 and the 2nd tank 6 were made constant temperature of 20 degreeC using the coolers 4 and 8, respectively.

  Next, supply of boron trifluoride to the bottom of the second absorption tower 5 was started at 3.41 g / min. After absorbing boron trifluoride gas in the organic solvent for 2 minutes, lithium fluoride was started to be supplied to the second tank 6 at 1.55 g / min. Sixty minutes after the start of the supply of lithium fluoride, the second absorption tower 5 was clogged with slurry-like lithium fluoride, making it difficult to operate.

It is explanatory drawing which shows roughly the manufacturing apparatus of the tetrafluoroborate which concerns on embodiment, Example 1, and Comparative example 1 of this invention. It is the schematic for demonstrating Examples 2-5 of this invention. It is explanatory drawing which shows roughly sectional drawing of the lithium secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st absorption tower 2 1st tank 3, 7, 11 Pump 4 1st cooler 5 2nd absorption tower 6 2nd tank 8 2nd cooler 9 Deaeration tower 10 3rd tank 12 Air pump 13 Condenser 21 Positive electrode 22 Negative electrode 23 Porous separator 24 Positive electrode can 25 Negative electrode can 26 Gasket 27 Spacer 28 Spring

Claims (4)

A first step of dissolving boron trifluoride gas in an organic solvent;
Adding the boron trifluoride paired tooth chemical stoichiometry following fluoride (MF _n M is a metal or _{NH 4, 1 ≦ n ≦ 3} ) in the organic solvent, produces a solution of tetrafluoroborate A second step of
Circulating the tetrafluoroborate solution in the first step to have a third step of dissolving boron trifluoride gas in the tetrafluoroborate solution instead of the organic solvent. A method for producing tetrafluoroborate, which is characterized.   The method for producing a tetrafluoroborate salt according to claim 1, wherein the organic solvent is at least one of a non-aqueous organic solvent and a non-aqueous ionic liquid.   The method for producing a tetrafluoroborate salt according to claim 1 or 2, wherein an organic solvent having a water concentration of 100 ppmw or less is used. The said 1st process and 3rd process are performed using an absorption tower, The manufacturing method of the tetrafluoroborate of any one of Claims 1-3 characterized by the above-mentioned .

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