TWI540097B - Preparation of Tetrafluoroborate - Google Patents

Description

Method for producing tetrafluoroborate

The present invention relates to a method for producing a tetrafluoroborate and a device for producing the same, and more particularly to a method for producing a tetrafluoroborate which is applicable to an electrolyte of a storage element, and a solution containing tetrafluoroborate a liquid and an electricity storage element including the electrolyte.

As a method for producing a conventional tetrafluoroborate, for example, a method for producing lithium tetrafluoroborate is, for example, a method in which lithium carbonate is allowed to act on a borofluoric acid solution to obtain lithium tetrafluoroborate. The salt produced by this method is a lithium borofluoride ‧1 hydrate represented by LiBF ₄ ‧H ₂ O, and is required to be dehydrated by heating at a temperature of about 200 °C. However, since heating at 200 ° C decomposes lithium tetrafluoroborate, the purity is lowered. Moreover, thousands of ppm of moisture remains. Therefore, the production method is not satisfactory in terms of the controllability of the reaction and the purity of the obtained product.

In order to solve this problem, for example, Patent Document 1 listed below discloses that boron trifluoride gas is blown into a non-aqueous organic solvent for a lithium secondary battery electrolyte containing lithium fluoride, and lithium fluoride and trifluoride are used. A method of producing boron tetrafluoride borate by boron reaction.

However, in the above production method, since the solubility of lithium fluoride in an organic solvent is small, the organic solvent is suspended (paste). Therefore, in the manufacturing process, it is difficult to circulate the organic solvent containing lithium fluoride, and there is a problem that it is difficult to produce a tetrafluoroborate in a continuous process.

Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. Hei 11-157830

The present invention has been made in view of the above problems, and an object thereof is to provide a method for producing a tetrafluoroborate which can be produced with high yield and high efficiency by a continuous process, an electrolyte containing tetrafluoroborate, and the like. The storage element of the electrolyte.

In order to solve the above-mentioned conventional problems, the inventors of the present application reviewed the method for producing a tetrafluoroborate, an electrolyte containing tetrafluoroborate, and a storage element including the electrolyte. As a result, it was found that the above object can be attained by adopting the following composition, and the present invention has been completed.

That is, the method for producing a tetrafluoroborate of the present invention solves the above-mentioned problems, and has a first step of dissolving a boron trifluoride gas in an organic solvent, and adding or substituting the boron trifluoride for the above or below. a stoichiometric amount of fluoride (MF _n , M-based metal or NH ₄ , 1≦n≦3) in the organic solvent, a second step of producing a solution of tetrafluoroborate, and by subjecting the tetrafluoride The borate solution is circulated in the first step described above, and is substituted for the third step of dissolving the boron trifluoride gas in the tetrafluoroborate solution in place of the organic solvent.

Fluoride is generally poorly soluble in organic solvents. Therefore, before the boron trifluoride gas is absorbed, if a fluoride is first added to the organic solvent, it will be in a suspended (paste) state. Therefore, when boron trifluoride is absorbed, clogging due to solid fluoride inside the apparatus causes an obstacle to operation. However, in the first step, after the boron trifluoride gas is absorbed in the organic solvent in the first step, the fluoride is added to the organic solvent in the second step. Thereby, a tetrafluoroborate represented by the following chemical reaction formula is synthesized in an organic solvent. Further, since the amount of the fluoride added is equivalent to or lower than boron trifluoride, all of the fluoride is reacted with boron trifluoride. As a result, no unreacted fluoride remained, and a non-paste tetrafluoroborate solution was obtained. Thereby, the solution of the tetrafluoroborate can be circulated in the first step, and an organic solvent is taken to dissolve the boron trifluoride gas in the solution of the tetrafluoroborate (step 3). That is, in the case of the above method, various devices including an absorption tower can be used, and continuous operation can be performed to improve the productivity of the tetrafluoroborate.

[Chemical 1]

nBF ₃ +MFn→M(BF ₄ ) _n

(However, when M is n=1, when Li, Na, K, Rb, Cs, NH ₄ or Ag, n=2, when Ca, Mg, Ba, Zn, Cu or Pb, n=3 , for Al or Fe.)

The organic solvent is preferably a non-aqueous organic solvent or a non-aqueous ionic liquid. Thereby, boron trifluoride or tetrafluoroborate is not hydrolyzed, and a hydrate of boron trifluoride or tetrafluoroborate is produced as a by-product, and boron trifluoride can be absorbed. Further, when boron trifluoride or tetrafluoroborate is hydrolyzed, an acidic substance such as oxyfluorinated boric acid, hydrofluoric acid or boric acid or an insoluble component such as oxyfluorinated borate or borate is generated in the organic solvent. When an electrolyte containing such an acidic substance or an insoluble component is used in a storage element, the corrosion of the storage element or deterioration of electrical characteristics is adversely affected. Therefore, as the organic solvent, it is preferred to use a low water concentration. From this point of view, the water concentration of the organic solvent is preferably 100 ppmw or less, more preferably 10 ppmw or less, and still more preferably 1 ppmw or less.

The first step and the third step described above can be carried out using an absorption tower. In the case of the production method of the present invention, since the boron trifluoride gas is dissolved in a solution of an organic solvent and a tetrafluoroborate, a fluoride is added, so that it does not become a suspended (paste) state. Therefore, even if the absorption tower is used in the first step and the third step, the internal clogging is prevented and the operation can be continued. This result enhances the productivity of tetrafluoroborate.

The electrolyte solution of the present invention is characterized by solving the above problems and comprising a tetrafluoroborate obtained by the method for producing a tetrafluoroborate described above.

Further, the electric storage device of the present invention is characterized in that the above-described problem is solved and the electrolytic solution described above is provided. A lithium ion secondary battery is exemplified as the electric storage device of the present invention.

The present invention achieves the following effects by means of the means as described above.

That is, according to the present invention, the organic solvent in which the boron trifluoride gas is previously dissolved in the absorption tower is added to the reaction tank to add a stoichiometric amount of fluoride to the boron trifluoride or the like, and the two are reacted. A solution of tetrafluoride borate having no residual fluoride can be obtained. The obtained solution of the tetrafluoroborate is again supplied to the absorption tower for circulation, and after the boron trifluoride gas is dissolved in the tetrafluoroborate, the fluoride is reacted with boron trifluoride in the reaction vessel. That is, according to the present invention, a high-purity tetrafluoroborate can be produced in a continuous manufacturing process by circulating a solution of tetrafluoroborate without unreacted fluoride or impurities. In addition, there is no need for a filtration step for removing fluoride, which is economically excellent.

The best form for implementing the invention

The embodiment of the present invention will be described below with reference to Fig. 1. Fig. 1 is an explanatory view schematically showing an apparatus for producing a tetrafluoroborate according to an embodiment of the present invention. However, unnecessary portions are omitted in the description, and for ease of explanation, there is a portion in which the schema is enlarged or reduced.

As shown in Fig. 1, the manufacturing apparatus of the present embodiment includes a first absorption tower 1 and a second absorption tower 5, and a first tank 2, a second tank 6, a third tank 10, and pumps 3 and 7, 11. The first cooler 4 and the second cooler 8, the degassing tower 9, the air pump 12, and the condenser 13.

A predetermined amount of an organic solvent is placed in the first tank 2 and the second tank 6. The liquids of the first tank 2 and the second tank 6 are supplied to the first absorption tower 1 and the second absorption tower 5 by the pumps 3 and 7, respectively, and are circulated. Next, boron trifluoride (BF ₃ ) gas is supplied to the bottom of the second absorption tower 5 at the bottom of the column. The boron trifluoride may be used in an amount of 100% or may be appropriately diluted with an inert gas. By mixing the inert gas, heat generation in the first absorption tower 1 and the second absorption tower 5 can be alleviated. Further, the inert gas is not particularly limited, and examples thereof include N ₂ and Ar, dry air, and carbon dioxide. The water in the inert gas used for dilution is based on hydrolyzed boron trifluoride or tetrafluoroborate, and the hydrate which does not produce boron trifluoride or tetrafluoroborate, and preferably has a low moisture of 100 ppmw or less. It is preferably 10 ppmw or less, more preferably 1 ppmw or less. The boron trifluoride gas is convectively contacted with the organic solvent in the second absorption tower 5, and is dissolved in the organic solvent (first step). The heat of absorption of the boron trifluoride in the organic solvent is removed by the first cooler 4 and the second cooler 8 provided in the circulation line, and is maintained at an appropriate operating temperature.

Next, an organic solvent in which boron trifluoride gas is dissolved is supplied to the second tank 6. In the second tank 6, a stoichiometric amount of fluoride equivalent to or less than boron trifluoride is supplied. Thereby, boron trifluoride reacts with the fluoride to produce a tetrafluoroborate (second step). The following reaction formula represents the reaction of boron trifluoride with lithium fluoride.

[Chemical 2] BF ₃ + LiF → LiBF ₄

The solution of the tetrafluoroborate produced in the second tank 6 is sent through a pipe, sent out by the pump 7, and supplied to the top of the tower of the second absorption tower 5. The boron trifluoride supplied to the bottom of the column is absorbed in the second absorption column for the solution of the tetrafluoroborate (step 3). Next, in the second tank 6, by continuously reacting with the fluoride, the tetrafluoroborate is raised to the desired concentration. By such a cycle operation, a predetermined concentration is achieved, and a part of the solution from the pump 7 is taken out as a product. At the same time as the product is taken out, the organic solvent is supplied to the first absorption tower 1 from the outside, and the liquid supply target of the pump 3 is converted from the first absorption tower 1 to the second absorption tower 5 to carry out the continuous operation of the tetrafluoroborate solution. produce. At this time, a part of the absorption liquid may be circulated to the first absorption tower 1 while the absorption liquid is supplied to the second absorption tower 5.

The amount of the fluoride to be supplied to the second tank 6 is such that the fluoride which is insoluble in the organic solvent is formed into a paste. Therefore, it is preferable to use a stoichiometric amount of boron trifluoride dissolved in the organic solvent in an equivalent or less. Thereby, clogging of the fluoride in the device due to the paste can be avoided. As a method for making the stoichiometric excess of boron trifluoride to fluoride, it can be realized by continuously supplying a boron fluoride having a stoichiometric excess of fluoride, but since the excess trifluoroboron must be present at a certain The step of discharging out of the system leads to the loss of raw materials, so it is not suitable. It is more preferable to supply a boron trifluoride and a fluoride by stoichiometrically supplying a liquid having a suitable excess amount of boron trifluoride in advance.

Further, the solution of the tetrafluoride borate in which the excess boron trifluoride is dissolved in the second step is supplied to the top of the second absorption tower in the third step, but the portion is also supplied to the deaeration column 9. Further, the solution of the tetrafluoroborate sent to the degassing column 9 is depressurized by the air pump 12 to distill off boron trifluoride. Thereby, a solution of boron trifluoride which is stoichiometrically equivalent to fluoride is adjusted, and the product is taken out from the third tank 10. Although it is possible to adjust the tetrafluoride borate solution by adding a stoichiometrically equivalent fluoride to the excess dissolved boron trifluoride, it is preferable to distill off the excess boron trifluoride under reduced pressure from the viewpoint of continuous productivity. . Further, in order to increase the efficiency of removing boron trifluoride by pressure reduction, the degassing tower 9 may be provided with heater heating.

The boron trifluoride exhausted is supplied to the bottom of the tower of the second absorption tower 5 by the air pump 12. Further, in the second absorption tower 5, the solution of the organic solvent and/or the tetrafluoroborate is convectively contacted, and recovered and reused. When a small amount of hydrogen fluoride is contained in the boron trifluoride used for the raw material, the solution of the tetrafluoroborate may be depressurized by the air pump 12, and the hydrogen fluoride may be distilled off, and then the hydrogen fluoride may be removed by coagulation. The liquid (drain) condensed by the condenser 13 contains an organic solvent, hydrogen fluoride, or boron trifluoride, but may be directly disposed of by waste liquid treatment, or may be hydrogen fluoride or boron trifluoride if necessary. The organic solvent is recycled and reused. As the recovery method, a usual method such as distillation or extraction can be used.

Thus, the present invention can continuously produce a high-purity tetrafluoroborate in a good yield by circulating a solution of a tetrafluoroborate.

Further, in the present invention, from the viewpoint of industrial production efficiency, although an absorption tower is preferably used, a method of using surface absorption or foaming is not excluded. Further, as the first absorption tower 1 and the second absorption tower 5, a tower type absorption device of any one of a packed column, a plate column, and a wet wall column may be used. In addition, the form of absorption can be either convection or cocurrent.

In the first step and the third step, the concentration of boron trifluoride in the solution of the organic solvent or the tetrafluoroborate is preferably 15% by weight or less, more preferably 10% by weight or less, and 5% by weight or less. better. When the concentration of the boron trifluoride gas in the organic solvent is high, the organic solvent reacts with boron trifluoride, which may cause coloring, denaturation, or solidification of the organic solvent. In addition, the absorption heat becomes large, and it is difficult to control the liquid temperature.

In the first step and the third step, the gas-liquid contact temperature of the boron trifluoride gas and the organic solvent or the tetrafluoroborate solution is preferably -40 to 100 ° C, more preferably 0 to 60 ° C. If the gas-liquid contact temperature is less than -40 ° C, the organic solvent will not work continuously due to solidification. On the other hand, when the gas-liquid contact temperature exceeds 100 ° C, the vapor pressure of boron trifluoride in the solution of the organic solvent and the tetrafluoroborate is too high, the absorption efficiency is lowered, and the organic solvent and boron trifluoride are generated. The unsuitable state of the reaction.

The organic solvent is preferably at least one of a non-aqueous organic solvent or a non-aqueous ionic liquid. Further, as the non-aqueous organic solvent, a non-aqueous aprotic organic solvent is further preferable. Since it is nonprotonic and has no ability to supply hydrogen ions, the solution of the tetrafluoroborate obtained by the production method of the present invention can be directly applied to an electrolyte of a storage element such as a lithium ion secondary battery.

The non-aqueous organic solvent is not particularly limited, and examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl carbonate. Ethyl ester, methyl acetate, ethyl acetate, γ-butyrolactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, methanol, isopropanol and the like. Among these organic solvents, the tetrafluoroborate produced is not easily precipitated from the viewpoint of continuous production, that is, ethylene carbonate, propylene carbonate, dimethyl carbonate, and carbonic acid having high solubility in tetrafluoroborate. Ethyl ester, methyl ethyl carbonate, acetonitrile, 1,2-dimethoxyethane are preferred. Further, these non-aqueous organic solvents may be used alone or in combination of two or more.

Further, examples of the non-aqueous aprotic organic solvent include a cyclic carbonate, a chain carbonate, a carboxylate, a nitrile, a guanamine or an ether compound.

These non-aqueous aprotic organic solvents may be used alone or in combination of two or more.

In addition, the nonaqueous ionic liquid is not particularly limited, and examples thereof include a fluoride salt or a fluoride salt such as a quaternary ammonium or a quaternary phosphonium. The fourth-order ammonium cation may, for example, be a tetraalkylammonium cation, an imidazolium cation, a pyrazolium cation, a pyridinium cation, a triazolium cation or a ruthenium. a phosphonium cation, a thiazolium cation, a oxazolium cation, a pyrimidine cation, a pyrazinium cation, or the like. Further, examples of the fourth-order phosphonium cation include a tetraalkyl phosphonium cation. These non-aqueous ionic liquid systems may be used singly or in combination of two or more kinds, or may be dissolved in the aforementioned non-aqueous organic solvent.

The organic solvent may be used by mixing one or more kinds of non-aqueous organic solvents and non-aqueous ionic liquids.

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

The reaction temperature of the fluoride and the boron trifluoride gas is preferably -50 ° C to 200 ° C, more preferably -10 ° C to 100 ° C, and more preferably 0 to 50 ° C. If it is less than -50 ° C, there is a possibility that the organic solvent is solidified or the tetrafluoroborate is precipitated. On the other hand, when it exceeds 200 ° C, the produced tetrafluoroborate decomposes.

Regarding the obtained tetrafluoroborate solution, the tetrafluoroborate is precipitated by concentration and/or cooling, and the tetrafluoroborate can be taken out by separation from the solvent.

The obtained tetrafluoroborate solution can be used as an electrolyte solution for an electric storage device, or can be used by mixing one or two or more kinds of non-aqueous aprotic organic solvents and non-aqueous ionic liquids.

In addition, the boron-containing component gas used in the manufacture of the tetrafluoroborate, specifically boron trifluoride gas, so as to be absorbed in the absorption liquid, for recycling. Reuse is appropriate. Examples of the absorption liquid include water, an aqueous solution of hydrofluoric acid, and an M salt (M system contains at least one selected from the group consisting of Li, Na, K, Rb, Cs, NH ₄ , Ag, Mg, Ca, Ba, Fe, and Al. A solution of a group of carbonates, hydroxides, halides). More specifically, it may be 0 to 80% by weight of water or an aqueous hydrogen fluoride solution, or a dissolved M salt (M system contains at least one selected from the group consisting of Li, Na, K, Rb, Cs, NH ₄ , Ag, Mg, Ca, Ba, 0 to 80% by weight of water or an aqueous solution of hydrogen fluoride in a carbonate, a hydroxide or a halide in which Fe and Al are grouped. By inhaling boron trifluoride gas in the absorption liquid, M(BF ₄ ) _n (wherein, 1≦n≦3) and/or H _a BF _b (OH) _{c can be used} . mH ₂ O (wherein, 0≦a≦1, 0≦b≦4, 0≦c≦3, 0≦m≦8) was recovered. Thereby, even if an excessive amount of BF ₃ gas is used, the loss of the raw material can be suppressed.

In addition, when the tetrafluoroborate is produced, it flows out from the second absorption tower 5. As shown in Fig. 1, boron trifluoride is obtained by collecting boron trifluoride in the first absorption tower 1 connected in series. The organic solvent containing boron trifluoride obtained in the first absorption tower 1 is supplied to the second absorption tower 5. The boron trifluoride that has not been completely absorbed by the first absorption tower 1 can also be recovered by the absorption method described above. Reuse. Thereby, even when an excessive amount of boron trifluoride gas is used, the total amount can be used to suppress the loss of the raw material.

Example

Suitable embodiments of the invention are described in detail below by way of example. However, the materials, blending amounts, and the like described in the examples and the comparative examples are not intended to limit the scope of the invention, and are not intended to limit the scope of the invention.

(Example 1)

This embodiment is carried out using the apparatus shown in Fig. 1. 3 L of commercially available battery grade diethyl carbonate (water concentration: 9 ppmw) was added to the first tank 2 and the second tank 6 made of fluororesin, and the pumps 3 and 7 were used to start the circulation of each absorption tower and tank. Running. At this time, the flow rates of the pump 3 and the pump 7 are both 1 L/min. In addition, the first tank 2 and the second tank 6 use the first cooler 4 and the second cooler 8, respectively, and have a constant temperature of 20 °C.

Next, boron trifluoride gas was supplied at the bottom of the tower of the second absorption tower 5 at 3.41 g/min. After the boron trifluoride gas was absorbed by the organic solvent for 2 minutes, lithium fluoride was supplied to the second tank 6 at 1.30 g/min. After the supply of lithium fluoride was started for 60 minutes, the product was taken out at 51.7 ml/min. At the same time as the product was taken out, the organic solvent was supplied to the first absorption tower 1 at 50 ml/min, and the liquid supply target was converted from the first absorption tower 1 to the second absorption tower 5 by the pump 3, and then continuously operated.

By continuously running for 60 minutes, 3,295.8 g of the solution was supplied to the degassing column 9, and the pressure was reduced by the air pump 12, and the excess boron trifluoride gas dissolved in the solution was distilled off. After distilling off, it was taken out from the third tank 10 to obtain a solution of 3,350 g of lithium tetrafluoroborate. The diethyl carbonate which is accompanied by the distilled boron trifluoride gas is removed by the condenser 13. Thereafter, the boron trifluoride gas of the combined raw materials is reused. Further, the total supply amount of the boron trifluoride gas to maintain the distilled boron trifluoride gas and the raw material was 3.41 g/min.

The diethyl carbonate solution of lithium tetrafluoroborate obtained in this manner has an insoluble content of 10 ppmw or less, a free acid of 10 ppmw or less, and a water content of 10 ppmw or less. Further, the obtained diethyl carbonate solution of lithium tetrafluoroborate was further reduced in pressure at 40 ° C to distill off diethyl carbonate to obtain a white solid. The result of analysis of a white solid by XRD (X-ray diffractometer) was confirmed to be lithium tetrafluoroborate.

(Example 2)

This embodiment is carried out using the apparatus shown in Fig. 2. 500 g of commercially available battery grade diethyl carbonate (water concentration: 9 ppmw) was added to the second tank 6 made of fluororesin, and supplied by the pump 7 and circulated to the top of the tower of the second absorption tower 5. The second tank 6 is a condenser 8 and is kept at a constant temperature of 20 °C. Next, boron trifluoride gas was supplied to the bottom of the tower 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 is rapidly dissolved in an organic solvent containing boron trifluoride and reacted with boron trifluoride in an organic solvent. Thus, 530.6 g of a solution of lithium tetrafluoroborate was obtained (second step).

Further, 500 g of diethyl carbonate was added to the second tank 6, and the same operation as described above was carried out (third step). 275 g of the obtained lithium tetrafluoroborate solution was taken out in the third tank 10 to maintain a constant temperature of 20 ° C, and 0.335 g of lithium fluoride equivalent to the dissolved excess boron trifluoride stoichiometric amount was added.

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

(Example 3)

This embodiment is carried out using the apparatus shown in Fig. 2. 250 g of diethyl carbonate (water concentration: 9 ppmw) and 250 g of ethylene carbonate (water concentration: 7 ppmw) were added to the second tank 6 made of fluororesin, and supplied by the pump 7 and recycled to the second tank. The top of the tower of the absorption tower 5. The second tank 6 is a condenser 8 and is kept at a constant temperature of 20 °C. 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 is rapidly dissolved in an organic solvent containing boron trifluoride and reacted with boron trifluoride in an organic solvent. Thereby, 457.6 g of a solution of lithium tetrafluoroborate was obtained (second step).

Further, 250 g of diethyl carbonate and 250 g of ethylene carbonate were placed in the second tank 6, and the same operation as described above was carried out (third step). 275 g of the obtained solution of lithium tetrafluoroborate was taken out in the third tank 10, and the temperature was kept constant at 20 ° C. The pressure was reduced by the air pump 12 to distill off the excess boron trifluoride gas. The diethyl carbonate/ethyl carbonate solution of lithium tetrafluoroborate thus obtained has an insoluble content of 10 ppmw or less, a free acid of 10 ppmw or less, and a water content of 10 ppmw or less.

Next, using the solution thus obtained, a button type nonaqueous electrolyte lithium secondary battery as shown in Fig. 3 was produced, and the performance as an electrolytic solution was evaluated by a charge and discharge test. Specifically, the following steps are performed.

<Making the negative electrode 22>

A natural graphite and an adhesive of 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 22 μm copper foil by an electrode coating applicator. This was dried under vacuum at 120 ° C for 8 hours, and a negative electrode 22 having a diameter of 16 mm was obtained by an electrode punch.

<Making the positive electrode 21>

The LiCoO ₂ and the conductive agent acetylene black and the PVdF of the adhesive were mixed at a weight ratio of 90:5:5, and N-methylpyrrolidone was added to the mixture to obtain a paste. This paste was uniformly applied onto a 22 μm copper foil by an electrode coating applicator. This was dried under vacuum at 120 ° C for 8 hours, and a positive electrode 21 having a diameter of 16 mm was obtained by an electrode punch.

<Production of button type nonaqueous electrolyte lithium secondary battery>

The positive electrode 21 was placed on the bottom surface of the positive electrode can 24, and a porous separator 23 made of polypropylene was placed thereon, and then the non-aqueous electrolyte solution prepared in Example 2 was injected, and the gasket 26 was inserted. Then, the negative electrode 22, the separator 27, the spring 28, and the negative electrode can 25 are placed in the upper portion of the separator 23, and the opening portion of the positive electrode can 24 is bent inward by a button-type battery fitting machine to be closed. Nonaqueous electrolyte lithium secondary battery. Next, charging was performed at a constant current of 0.4 mA, and when the voltage reached 4.1 V, 4.1 V was charged at a constant voltage for 1 hour. The discharge was performed at a constant current of 1.0 mA and discharged until the voltage was 3.0V. When the voltage reached 3.0 V, it was kept at 3.0 V for 1 hour, and a charge and discharge test was performed by a charge and discharge cycle. The result was that the charge and discharge efficiency was about 100%, and the charge capacity did not change when the charge and discharge were repeated for 150 cycles.

(Example 4)

This embodiment is carried out using the apparatus shown in Fig. 2. 500 g of commercially available dehydrated methanol (water concentration: 9 ppmw) was added to the second tank 6 made of fluororesin, and the pump 7 was introduced into the top of the second absorption tower 5 to circulate the organic solvent. The second tank 6 is a condenser 8 and is kept at a constant temperature of 20 °C. 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 is rapidly dissolved in an organic solvent containing boron trifluoride and reacted with boron trifluoride in an organic solvent. Thereby, 457.6 g of a solution of lithium tetrafluoroborate was obtained (second step).

Further, 500 g of methanol was added to the second tank 6, and the same operation as described above was carried out (third step). 275 g of the obtained solution of lithium tetrafluoroborate was taken out in the third tank 10, and the temperature was kept at 20 ° C, and the pressure was reduced by the air pump 12 to remove excess boron trifluoride.

The methanol solution of lithium tetrafluoroborate thus obtained has an insoluble content 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 kept at a constant temperature of 60 ° C, and 5 L/min of nitrogen was bubbled to partially evaporate methanol to precipitate a white solid. This solution was filtered, and the obtained white solid was distilled off at 60 ° C, 5 L / min of nitrogen to remove methanol. The result of the white solid obtained by XRD analysis was confirmed to be lithium tetrafluoroborate.

(Example 5)

This embodiment is carried out using the apparatus shown in Fig. 2. 500 g of commercially available battery grade diethyl carbonate (water concentration: 550 ppmw) was added to the second tank 6 made of fluororesin, and was supplied by the pump 7 and circulated to the top of the tower of the second absorption tower 5. The second tank 6 is a condenser 8 and is kept at a constant temperature of 20 °C. Next, boron trifluoride gas was supplied to the bottom of the tower 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 is rapidly dissolved in an organic solvent containing boron trifluoride and reacted with boron trifluoride in an organic solvent. Thus, 530.6 g of a solution of lithium tetrafluoroborate was obtained (second step).

Further, 500 g of diethyl carbonate was added to the second tank 6, and the same operation as described above was carried out (third step). 275 g of the obtained solution of lithium tetrafluoroborate was taken out in the third tank 10, and the temperature was kept constant at 20 ° C, and excess boron trifluoride was dissolved by distillation under reduced pressure. The diethyl carbonate solution of lithium tetrafluoroborate thus obtained has an insoluble content of 30 ppmw or less, a free acid of 130 ppmw or less, and a water content of 400 ppmw or less. Using this solution, the same button type nonaqueous electrolyte as in Example 3 was produced. A lithium secondary battery was evaluated for its performance as an electrolytic solution by a charge and discharge test. This result is that the initial efficiency of charge and discharge induces electrolysis of moisture. When the charge and discharge were repeated for 150 cycles, the reduction in the charge capacity was suppressed to 20%. In addition, it was found that the button groove after 150 cycles was slightly expanded.

(Comparative Example 1)

This comparative example was carried out using the apparatus shown in Fig. 1. 3 L of commercially available battery grade diethyl carbonate (water concentration: 9 ppmw) was added to the first tank 2 and the second tank 6 made of fluororesin, and the pumps 3 and 7 were used to start the circulation of each absorption tower and tank. Running. At this time, the flow rates of the pump 3 and the pump 7 are both 1 L/min. Further, in the first tank 2 and the second tank 6, the coolers 4 and 8 were used, respectively, so that the temperature was kept constant at 20 °C.

Next, boron trifluoride gas was supplied at the bottom of the tower of the second absorption tower 5 at 3.41 g/min. After the organic solvent absorbed the boron trifluoride gas for 2 minutes, lithium fluoride was supplied to the second tank 6 at 1.55 g/min. After the supply of lithium fluoride for 60 minutes, the second absorption tower 5 is blocked by the paste-like lithium fluoride, and the operation becomes difficult.

1. . . First absorption tower

2. . . First slot

3, 7, 11. . . Pump

4. . . 1st cooler

5. . . 2nd absorption tower

6. . . Second slot

8. . . 2nd cooler

9. . . Degassing tower

10. . . Third slot

12. . . Air pump

13. . . Condenser

twenty one. . . positive electrode

twenty two. . . negative electrode

twenty three. . . Porous separator

twenty four. . . Positive tank

25. . . Negative electrode tank

26. . . washer

27. . . Isolation board

28. . . spring

Fig. 1 is an explanatory view schematically showing an apparatus for producing a tetrafluoroborate of the embodiment of the present invention, and the first embodiment and the comparative example 1.

Fig. 2 is a schematic view for explaining Embodiments 2 to 5 of the present invention.

Fig. 3 is an explanatory view schematically showing a cross-sectional view of a lithium secondary battery of the present invention.

1. . . First absorption tower

2. . . First slot

3, 7, 11. . . Pump

4. . . 1st cooler

5. . . 2nd absorption tower

6. . . Second slot

8. . . 2nd cooler

9. . . Degassing tower

10. . . Third slot

12. . . Air pump

13. . . Condenser

Claims (9)

A method for producing a tetrafluoroborate characterized by the first step of dissolving a boron trifluoride gas in an organic solvent, and adding a stoichiometric fluoride (MF equivalent to or less than the boron trifluoride) _n , M-based metal or NH ₄ , 1≦n≦3) in the organic solvent, the second step of producing a solution of tetrafluoroborate, and the solution of the tetrafluoroborate in the first step The third step of circulating a boron trifluoride gas in a solution of tetrafluoroborate, wherein the organic solvent is at least one of a non-aqueous organic solvent or a non-aqueous ionic liquid. The method for producing a tetrafluoroborate according to the first aspect of the invention, wherein the organic solvent is a water concentration of 100 ppmw or less. A method for producing a tetrafluoroborate according to the first aspect of the invention, wherein the first step and the third step are carried out using an absorption tower. The method for producing a tetrafluoroborate according to the first aspect of the invention, wherein in the first step, the gas-liquid contact temperature of the boron trifluoride gas and the organic solvent is -40 to 100 °C. The method for producing a borofluoride borate according to the first aspect of the invention, wherein in the third step, the gas-liquid contact temperature of the boron trifluoride gas and the tetrafluoroborate solution is -40 to 100 ° C the following. The method for producing a tetrafluoroborate according to the first aspect of the invention, wherein the concentration of boron trifluoride in the organic solvent in the first step is 15% by weight or less. The method for producing a tetrafluoroborate according to the first aspect of the invention, wherein the concentration of boron trifluoride in the solution of the tetrafluoroborate in the third step is 15% by weight or less. An electrolyte characterized by containing a tetrafluoroborate obtained by a method for producing a tetrafluoroborate as in the first aspect of the patent application. An electric storage device characterized by having an electrolytic solution according to item 8 of the patent application.