TWI594489B - Electrolyte solution purification method and electrolyte solution manufacturing method - Google Patents

Description

Method for purifying electrolyte solution and method for producing electrolyte solution

The present invention relates to a method for purifying an electrolyte solution used as an electrolyte of an electrochemical device such as a lithium ion battery, a sodium ion battery, a lithium air battery, a lithium sulfur battery, or a lithium ion capacitor.

In batteries for electrochemical devices, in recent years, information-related machines, communication devices, such as computers, video cameras, digital cameras, mobile phones, smart phones, etc., are used for small-sized, high-energy-density power storage systems, or Power storage systems for large-scale, power-use applications such as electric vehicles, hybrid electric vehicles, auxiliary power supplies for fuel cell vehicles, and power storage have received much attention. As a candidate, non-aqueous electrolyte batteries such as lithium ion batteries, lithium batteries, and lithium ion capacitors are being actively developed.

A metal salt (except Li and Na) in which an ionic complex of a Lewis acid such as a hexafluorophosphate anion, a tetrafluoroborate anion, or a hexafluoroarsenate anion is bonded to a fluoride ion is highly soluble. From the standpoint of properties, high ion dissociation, and a wide range of potentials, it is used as a supporting electrolyte for electrochemical devices.

Among them, lithium hexafluorophosphate (hereinafter referred to as LiPF ₆ ) is particularly widely used because it is less toxic than lithium hexafluoroarsenate and has higher solubility than lithium tetrafluoroborate.

However, this LiPF ₆ also has a disadvantage of being low in thermal stability and decomposing into lithium fluoride (hereinafter referred to as LiF) and phosphorus pentafluoride (hereinafter referred to as PF ₅ ) due to heating. LiF is known to be a resistive component deposited on the surface of an electrode, so that the performance of a lithium-based electrochemical device represented by a lithium ion battery is lowered, and PF ₅ is accelerated by the Lewis acidity of the electrolyte solution.

Therefore, the industry is actively developing an ionic complex which is less toxic than hexafluoroarsenic acid, has higher solubility than lithium tetrafluoroborate, and has higher thermal stability than LiPF ₆ , for example, Patent Document 1 The use of an ionic complex compound obtained by substituting a part of fluorine of LiPF ₆ into a fluoroalkyl group (CF ₃ , C ₂ F _{5 ,} etc.) in an electrolytic solution is disclosed in Patent Document 2 and Non-Patent Document 1. 2 discloses the use of an ionic complex compound in which one or all of the fluorine of LiPF ₆ is substituted with oxalic acid in an electrolytic solution.

On the other hand, the fluorine-containing ionic complex compound may react with moisture in the air or in a liquid to generate hydrogen fluoride. Moreover, when producing a fluorine-containing ionic complex compound, there may be a case where excessive hydrogen fluoride remains or hydrogen fluoride is formed by-product. In general, hydrogen fluoride in the electrolyte causes dissolution of the electrode material or corrosion of the current collector, and even causes a decrease in the cycle characteristics of the battery, which in turn causes a decrease in battery characteristics such as charge and discharge capacitance and storage stability, so the content of hydrogen fluoride is higher. The lower the better, for example, the concentration of hydrogen fluoride in the electrolytic solution is set to be less than 30 ppm by mass (Patent Document 3).

Further, a method of reacting an acidic impurity such as hydrogen fluoride generated by hydrolysis of LiPF ₆ with a halide other than a fluoride to convert it into a hydrogen halide having a high vapor pressure and removing it is disclosed (Patent Document 4).

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. 2003-17118

Patent Document 2: Japanese Patent Laid-Open Publication No. 2002-110235 (Japanese Patent No. 3722685)

Patent Document 3: Japanese Patent Laid-Open No. Hei 10-270074

Patent Document 4: Japanese Patent Laid-Open No. Hei 10-092468 (Japanese Patent No. 3,034,202)

Non-patent literature

Non-Patent Document 1: ECS Transactions, 2009, 16 (35), 3-11

Non-Patent Document 2: Chem. Eur. J., 2004, 10, 2451-2458

However, if the hydrogen fluoride in the electrolytic solution is to be removed under reduced pressure, since hydrogen fluoride has a higher boiling point of 19.54 ° C under the influence of hydrogen bonding, the removal of hydrogen fluoride takes time and the concentration of hydrogen fluoride cannot be sufficiently lowered.

Further, in the method of reacting hydrogen fluoride with lithium chloride by adding lithium chloride as a purifying agent described in Example 1 of Patent Document 4, since lithium fluoride formed by the reaction is precipitated as a solid, it is necessary to In addition to the removal of the generated hydrogen chloride, the filtration step must be performed. Therefore, the production step becomes complicated, and the clogging of the filter cloth often occurs in the filtration step, and the removal of lithium fluoride is difficult. In the method of reacting hydrogen fluoride with ethyl hydrazine by adding ethyl hydrazine chloride as a purifying agent described in Example 5 of Patent Document 4, since no solid precipitate is generated, nitrogen gas is circulated at 70 ° C after the reaction. However, the hydrogen chloride generated by the reaction and the excess ethyl chloroform are removed, but the reaction time takes 12 hours, and the circulation of nitrogen takes 4 hours, and the removal of hydrogen fluoride takes time.

When the production described in Patent Document 2 or the like can be used in an electrolyte solution in which one or all of the fluorine of LiPF ₆ is partially substituted with oxalic acid, there is an unreacted oxalic acid or is produced during the production process. Oxalic acid remains in solution. Since such oxalic acid also adversely affects the battery characteristics due to deterioration of the cycle characteristics of the battery, it is necessary to remove it. However, in the usual crystallization method, oxalic acid is also precipitated together with the ionic complex, and in many cases, it is required. Repurification is performed, making it difficult to remove oxalic acid to a low concentration.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electrolyte solution capable of removing hydrogen fluoride in an electrolyte solution used as an electrolyte of an electrochemical device in a simple step and in a shorter period of time than before. Purification method. Further, it is more preferable to simultaneously remove oxalic acid remaining when the ionic complex compound in which one or all of the fluorine of LiPF ₆ is substituted with oxalic acid is produced.

The present inventors have conducted intensive studies in order to solve the above problems, and as a result, found that a hydrogen chloride-added purifying agent is used to form hydrogen fluoride into hydrogen chloride, and hydrogen sulfide is used together with a fluorinated purifying agent or an unreacted purifying agent by vapor pressure. The removal can thereby remove the hydrogen fluoride in a simple step. Further, if the fluorinated purification agent is retained in the system when the hydrogen fluoride is reacted with the purification agent, the reaction between the hydrogen fluoride and the purification agent does not become fast enough. The hydrogen fluoride contained in the solution can be used in a short period of time by using a purification agent such as a reaction product which is discharged to the reaction system at a normal temperature and a normal pressure, or a reaction product is removed from the reaction system during the reaction. The inside was removed to a low concentration, thereby completing the present invention. Specifically, in the present invention, a method for purifying an electrolyte solution as described below is provided.

A first aspect of the present invention is a method for purifying an electrolyte solution, comprising the steps of: adding a sulfoxide to a solution of an electrolyte containing at least hydrogen fluoride as an impurity in a non-aqueous solvent; a step of reacting the above-mentioned impurities with the above-mentioned purifying agent; and a step of removing the above impurities by removing hydrogen chloride as a reaction product, the above-mentioned purifying agent which is fluorinated, and the above-mentioned unpurified purifying agent.

A second aspect of the present invention provides a method for purifying an electrolyte solution, comprising the steps of: adding an electrolyte solution containing at least hydrogen fluoride as an impurity to a non-aqueous solvent; One of a group consisting of sulfonium chloride, sulfinium chloride, ruthenium chloride, and a carboxylic acid anhydride or a purification agent of the mixture, and the reaction product is extracted to the outside of the reaction system to make the above impurities and the above purification And a step of removing the impurities by removing hydrogen chloride as a reaction product, the fluorinated purification agent, and the unreacted purification agent.

A third aspect of the present invention is a method for producing an electrolyte solution, which comprises the step of purifying using a purification method using the electrolyte solution of the first or second aspect.

According to the purification method of the present invention, by using sulphur oxychloride as a purifying agent or removing the reaction product to the outside of the system during the reaction between hydrogen fluoride and a purifying agent, The hydrogen fluoride in the solution used as the electrolyte of the electrochemical device is removed to a low concentration before the simpler step and for a shorter period of time. Further, since the specific purifying agent reacts with both hydrogen fluoride and oxalic acid, hydrogen fluoride and oxalic acid can be simultaneously removed by removing the reaction product and the unreacted purifying agent.

Hereinafter, the present invention will be described in more detail.

(First embodiment)

According to a first aspect of the present invention, a method for purifying an electrolyte solution, comprising: a reaction step of adding an antimony chloride to an electrolyte solution in which an electrolyte is dissolved in a nonaqueous solvent containing at least hydrogen fluoride as an impurity; The purifying agent reacts the impurities with the purifying agent; and a removing step of removing the impurities by removing hydrogen chloride as a reaction product, the fluorinated purifying agent, and the unreacted purifying agent.

Since sulfinium chloride can also decompose and remove oxalic acid, oxalic acid can also be contained in the form of impurities in the electrolyte solution.

When sulfinium chloride (boiling point 76 ° C) and hydrogen fluoride (boiling point 19.54 ° C) are reacted, hydrogen chloride (boiling point - 85 ° C) and sulfoxide (boiling point - 43.8 ° C) are produced according to the following reaction formula, which is equal to At normal temperature and pressure, it is a gas, so the reaction product is quickly discharged to the outside of the reaction system, and the reaction cannot be intervened.

[Chemical 1] SOCl ₂ + 2HF → SOF ₂ + 2HCl

Further, there is also a case where sulfinium chlorofluoride (boiling point is about 12 ° C) is formed in place of sulfinium fluoride according to the following reaction formula, and sulphur chlorofluorocarbon is discharged to the outside of the reaction system or converted into a sub- Sulfur and fluorene, so the reaction product is quickly discharged to the outside of the reaction system, and the reaction cannot be intervened.

[Chemical 2] SOCl ₂ + HF → SOClF + HCl

In addition, the "fluorinated purification agent" means sulfoxide or sulfoxide.

Further, when sulfinium chloride is reacted with oxalic acid, hydrogen chloride, sulfur dioxide (boiling point - 10 ° C), carbon monoxide (boiling point - 192 ° C), and carbon dioxide (boiling point - -78.5 ° C) are produced according to the following reaction formula, which is equal to normal temperature. At normal pressure, it is a gas, so the reaction product is quickly discharged to the outside of the reaction system, and the reaction cannot be intervened.

[Chemical 3] SOCl ₂ + (COOH) ₂ → 2HCl + SO ₂ + CO + CO ₂

In addition, the "reaction decomposition product of a purifying agent and oxalic acid" means sulfur dioxide, carbon monoxide, carbon dioxide, etc. which are produced by the reaction of a purifying agent and oxalic acid.

In other words, in the first embodiment, when sulfite chloride is used as a purifying agent to react with hydrogen fluoride, the reaction product becomes a gas and is quickly discharged to the outside of the reaction system, so that the reaction cannot be intervened. The reaction rate of the reaction of hydrogen fluoride with sulfinium chloride, that is, the reaction rate of the positive reaction can be increased without the reverse reaction of the reaction formula, and the concentration of the hydrogen fluoride can be rapidly lowered to a low concentration.

Further, in the first embodiment, the reaction product or the unreacted sulfinium chloride can be removed while removing hydrogen chloride. Therefore, it is not necessary to carry out another step such as filtration, and is suitable for industrial purification.

If sulphur oxychloride is used, not only the hydrogen fluoride but also the oxalic acid in the solution can be removed.

Since sulphur chlorobenzene is a liquid at normal temperature and normal pressure, it is a liquid when it is added to the electrolyte solution before purification, and therefore it is easy to add compared with the case where a gas purifying agent is added.

The electrolyte contained in the solution is a salt, and the cation of the salt preferably comprises one of a lithium cation, a sodium cation, a potassium cation, a quaternary alkyl ammonium cation or a mixture thereof. The reason for this is that the cations can be used as a cation of a salt contained in an electrolyte for a non-aqueous electrolyte battery.

Further, the anion of the salt preferably comprises a hexafluorophosphate anion, a tetrafluoroborate anion, a bis(fluorosulfonyl) quinone imine anion, a bis(trifluoromethanesulfonyl) quinone imine anion, a double (two One of or a mixture of fluorophosphoryl) quinone imines. The reason for this is that the anions can be used as an anion of a salt contained in an electrolyte for a non-aqueous electrolyte battery.

The salt preferably comprises lithium hexafluorophosphate, sodium hexafluorophosphate, potassium hexafluorophosphate, lithium tetrafluoroborate, sodium tetrafluoroborate, potassium tetrafluoroborate, lithium bis(fluorosulfonyl) fluorene, bis(fluorosulfonyl) Sodium sulfoxide, potassium bis(fluorosulfonyl) phthalimide, lithium bis(trifluoromethanesulfonyl) phthalimide, sodium bis(trifluoromethanesulfonyl) sulfoxide, bis(trifluoro) Methanesulfonyl) sulfonium imide, lithium bis(difluorophosphate) ruthenium amide, sodium bis(difluorophosphate) ruthenium amide, potassium bis(difluorophosphate) ruthenium iodide, difluoro ionic One of the complexes (2a), (2b), (2c) or a mixture of such. The reason for this is that the salts can be used as a salt contained in an electrolyte solution for a non-aqueous electrolyte battery.

Further, the respective elements of the formula (2) of the difluoroionic complex compounds (2a), (2b), and (2c) are as follows. Further, the lithium salt of the difluoroionic complex (2a) is described as (2a-Li).

(2a) A = Li, Na, K or quaternary alkyl ammonium, M = P, Y = C, Z = C, p, q and s = 1, r = 0

(2b) A = Li, Na, K or quaternary alkyl ammonium, M = P, W = C (CF ₃ ) ₂ , Z = C, p and q = 0, r, s = 1

(2c) A = Li, Na, K or quaternary alkyl ammonium, M = P, W = C (CF ₃ ) ₂ , Z = C, p, q and s = 0, r = 2

Further, as the nonaqueous solvent of the electrolyte solution, the same as the nonaqueous solvent used in the synthesis method of the third embodiment described below can be used.

The reaction time of the impurity and the purifying agent can be appropriately selected in the range of 0.1 to 72 hours depending on the reaction rate. However, since the production cost is increased due to the occupation of the device for a long time, it is preferred to set the reaction time to 12 hours or less. More preferably, the reaction time is set to 6 hours or less. Further, in order to carry out the reaction of the entire system, it is preferred to stir the solution during the reaction.

The purifying agent is preferably used in a range of 10 mol or less relative to the molar amount of the free acid. Further preferably, the free acid and the purifying agent are in a range of a molar ratio of 1:0.1 to 1:10, and particularly preferably a range of a molar ratio of the free acid and the purifying agent of 1:1 to 1:5.

The addition of the purifying agent, the stirring, and the subsequent removal of the reaction product and the unreacted purifying agent are preferably carried out at a temperature of from -60 ° C to 150 ° C, more preferably from -20 ° C to 120 ° C. If it is less than -60 ° C, there is a case where the stirring is insufficient due to an increase in viscosity, or the reaction rate is lowered, and if it exceeds 150 ° C, there is a concern that the dissolved electrolyte is decomposed. In particular, the temperature at which the reaction product and the unreacted purifying agent are removed is preferably -20 ° C to 120 ° C which is easily carried out by heating or cooling.

Further, in the respective treatments in the first embodiment of the present invention, in order not to evaporate a large amount of the purifying agent or the solvent, it is preferred to use any of the boiling points of the purifying agent or the solvent. The degree is below. In particular, in order not to decompose the electrolyte contained in the solution, the addition of the purifying agent, the stirring, and the subsequent removal of the reaction product and the unreacted purifying agent are preferably carried out at 50 ° C or lower.

The removal of the reaction product and the unreacted purifying agent is removed by a method using a vapor pressure difference, specifically, a method of degassing under reduced pressure, or introducing an inert gas into the solution and It is removed by a method such as removal with an inert gas.

In the decompression, a vacuum pump, an aspirator, or the like can be used. The pressure reduction is carried out by setting the reactor to a sealed state and then maintaining the pressure in the system below atmospheric pressure. At this time, since a part of the nonaqueous solvent is also distilled off, the concentration of the electrolyte is concentrated. The pressure in the system varies depending on the temperature of the liquid to be purified and the vapor pressure, and therefore cannot be generalized. However, the pressure reduction is preferably such that the degree of vacuum in the tank is maintained at 80 kPa or less in absolute pressure. When the pressure maintained is more than 80 kPa, it is not possible to exclude the reaction product or the unreacted purification agent in the electrolyte solution to a desired concentration or less, or to remove it to a desired concentration or less, and it takes a long time. good. Further, if the pressure to be maintained is 50 kPa or less, the unreacted purifying agent can be excluded to a low concentration, which is further preferable. Further, in consideration of the load of the device, it is preferable to set the absolute pressure to 20 kPa or more.

The introduction of the inert gas into the solution is carried out by bubbling the solution with nitrogen, helium, neon, argon, helium or neon. Further, the pressure reduction of the reaction system and the introduction of the inert gas into the solution can also be carried out simultaneously.

(Second embodiment)

A second embodiment of the present invention provides a method for purifying an electrolyte solution, comprising: a reaction step of adding an electrolyte solution containing at least hydrogen fluoride as an impurity to a non-aqueous solvent in which an electrolyte is dissolved; One of a group consisting of chlorine, sulfonium chloride, sulfinium chloride, ruthenium chloride, and carboxylic acid anhydride or a purification agent of the mixture, and the reaction product is extracted to the outside of the reaction system to make the impurities and The above-mentioned purifying agent is subjected to a reaction; and a removing step by using hydrogen chloride as a reaction product and The above-mentioned purifying agent which is fluorinated and the above-mentioned unpurified purifying agent are removed to remove the above impurities.

As the electrolyte solution purified in the second embodiment, the same as in the first embodiment can be used.

In the second embodiment, by reacting hydrogen fluoride with a purifying agent or hydrogen fluoride and oxalic acid with a purifying agent while extracting the reaction product to the outside of the system, hydrogen fluoride or oxalic acid can be more efficiently decomposed and removed. . The method of extracting the generated reaction product out of the system is to decompress the reaction system or introduce an inert gas into the solution. The introduction of reduced pressure or an inert gas can be carried out in the same manner as the above method.

The reason is that the reaction between hydrogen fluoride and the purifying agent is reversible, so that the generated hydrogen chloride or the fluorinated purifying agent is continuously removed from the system by using a reduced pressure or an inert gas introduction, thereby restricting the reverse reaction. To accelerate the fluorination reaction of the purifying agent. Further, the reaction between oxalic acid and the purifying agent produces an irreversible reaction of carbon monoxide and carbon dioxide and is discharged to the outside of the system, and even if there is a case where the reaction is accelerated by introduction of a reduced pressure or an inert gas, there is no case where the reaction is decelerated.

Further, in the first embodiment in which ruthenium oxychloride is used, the reaction product may be taken out while the reaction product is extracted outside the system, and the fluorination reaction of sulfinium chloride may be accelerated to carry out hydrogen fluoride. Remove.

As the purifying agent, carboxy guanidine chloride, sulfonium chloride, sulfinium chloride, ruthenium chloride, carboxylic anhydride or the like can be used. Among them, as the purifying agent, grass chloroform, methyl chloroformate, ethyl chloroformate, ethyl hydrazine chloride, trifluoroacetamidine chloride, trifluoromethanesulfonium chloride, methylsulfonium chloride, sulfinium chloride, and the like are preferred. Trimethyl decane chloride, acetic anhydride, and trifluoroacetic anhydride are preferably grassy chlorinated, methyl chloroformate, ethyl chloroform, trifluoromethanesulfonate because of easy removal of the reaction product and unreacted purifying agent. Chlorine, methanesulfonium chloride, sulfoxide chloride, trimethylnonane chloride.

Carboxymethyl chloride, sulfonium chloride, sulfinium chloride and ruthenium chloride are reacted with hydrogen fluoride to form carboxyfluorene fluoride, sulfonium fluoride, sulfinium fluoride, cesium fluoride, and hydrogen chloride, respectively. Each fluoride has a lower atomic weight than the chloride, and has a lower boiling point than the chloride, in a reduced pressure or foaming environment. The next is easy to remove. Further, since the boiling point of hydrogen chloride is very low -85 ° C, it is easily removed. Similarly, the carboxylic acid anhydride is also reacted with hydrogen fluoride to obtain carboxyfluorene fluoride and a carboxylic acid, and thus is removed by volatilization under reduced pressure or a foaming environment.

For example, if ethyl chloroform (boiling point: 51 ° C) is reacted with hydrogen fluoride, hydrogen chloride (boiling point - 85 ° C) and acetamidine fluoride (boiling point: 20 ° C) are formed according to the following reaction formula, and the like are all under reduced pressure or foaming. It is removed under the environment.

[Chemical 5] CH ₃ COCl + HF → CH ₃ COF + HCl

In the case where acetoin is used as a purifying agent, the term "fluorinated purifying agent" means acetamidine fluoride or the like.

When the purifying agent is grass chloroform, methyl chloroformate, ethyl chloroformate, ethyl chloroform, trifluoroacetamidine chloride, trifluoromethanesulfonium chloride, methanesulfonate chloride or sulfoxide, it is not only The hydrogen fluoride is removed and the oxalic acid is decomposed and removed.

For example, when ethyl chloroform is reacted with oxalic acid, hydrogen chloride, acetic acid (boiling point: 118 ° C), carbon monoxide (boiling point - 192 ° C), and carbon dioxide (boiling point - -78.5 ° C) are produced according to the following reaction formula, and the like is reduced. Removed under pressure or blistering conditions.

[Chemical 6] CH ₃ COCl + (COOH) ₂ → HCl + CH ₃ COOH + CO + CO ₂

In the case where acetoin is used as a purifying agent, the term "reactive decomposition product of a purifying agent and oxalic acid" means acetic acid, carbon monoxide, carbon dioxide or the like which is formed by a reaction between a purifying agent and oxalic acid.

In the second embodiment, the reaction product is extracted to the outside of the system to cause a reaction. This is carried out so that the reaction of hydrogen fluoride with the purifying agent can be accelerated, and the hydrogen fluoride can be quickly removed to a low concentration.

The method and conditions of the reaction step or the removal step in the second embodiment are the same as those in the first embodiment.

(Third embodiment)

A third embodiment of the present invention provides a method for producing an electrolyte solution, which comprises the step of purifying using the purification method of the electrolyte solution of the first or second embodiment.

In other words, when a fluorine-containing ionic complex such as LiPF _{6 is} synthesized, excessive hydrogen fluoride or by-product hydrogen fluoride may remain, and the fluorine-containing ionic complex may react with moisture in the air or in the liquid. In the case where hydrogen fluoride is generated, the electrolyte of the first or second embodiment is incorporated in the step of producing an electrolyte solution containing a fluorine-containing ionic complex after synthesizing a fluorine-containing ionic complex or the like. As a method of purifying the solution, an electrolyte solution having less impurities such as hydrogen fluoride can be obtained.

In particular, the hexa-coordinate ionic complex (1) represented by the formula (1) is fluorinated in a nonaqueous solvent by a fluorinating agent to produce a difluoro group represented by the formula (2). In the step of the ionic complex compound (2), oxalic acid is formed as a by-product, so that both hydrogen fluoride and oxalic acid are removed. Therefore, after the preparation of the difluoro-ionic complex (2), the first or second is used. The purification steps of the purification method of the electrolyte solution of the embodiment are combined to produce an electrolyte solution containing the difluoro-ionic complex (2) having less acidic impurities.

In the step of producing the difluoroionic complex (2), a hexacoordinate ionic complex formed by coordinating a 3-molecular bidentate ligand represented by the following formula (1) (hereinafter, referred to as a hexa-coordinate ionic complex (1)), fluorine is introduced to produce a difluoro-ionic complex represented by the following formula (2) (hereinafter sometimes referred to as difluoro ion) Sexual complex (2)).

[Chemistry 7]

In the general formulae (1) and (2), A ⁺ is selected from the group consisting of metal ions, protons, and strontium ions, and functions to contribute to ion conduction in a nonaqueous electrolyte battery. From the viewpoint, lithium ion, sodium ion, potassium ion or quaternary alkyl ammonium ion is preferred. The quaternary alkyl ammonium ion is not particularly limited, and examples thereof include trimethylpropylammonium or 1-butyl-1-methylpyrrolidinium.

Further, in the general formulae (1) and (2), M is any one selected from the group consisting of P, As, and Sb. F is a fluorine atom. O is an oxygen atom. Y is a carbon atom or a sulfur atom. When Y is a carbon atom, q is 1. In the case where Y is a sulfur atom, q is 1 or 2. W represents a hydrocarbon group having a carbon number of 1 to 10 which may have a hetero atom or a halogen atom (in the case where the carbon number is 3 or more, a branched or cyclic structure may be used) or -N(R ¹ )-. In this case, R ¹ represents a hydrogen atom, an alkali metal, or a hydrocarbon group having 1 to 10 carbon atoms which may have a hetero atom or a halogen atom. When the carbon number is 3 or more, R ¹ may take a branched or cyclic structure. Z is a carbon atom. p represents 0 or 1, q represents an integer from 0 to 2, r represents an integer from 0 to 2, s represents 0 or 1, and is p+r≧1.

The above-mentioned six-coordinate ionic complex (1) and the diion-ionic complex (2) Each element of the sub-portion is preferably selected from the group consisting of at least one of (a), (b), and (c).

(a) M = P, Y = C, p, q, s = 1, r = 0 oxalic acid

(b) M=P, W=C(CF ₃ ) ₂ , p, q=0, r, s=1 hexafluorohydroxyisobutyric acid

(c) M=P, W=C(CF ₃ ) ₂ , p, q, s=0, r=2 perfluoropinacol

After dissolving or suspending the hexacoordinate ionic complex (1) in a nonaqueous solvent, it is used in an amount of 1.5 times or more and 50 moles or less relative to the hexacoordinate ionic complex (1). The fluorinating agent is selectively fluorinated, whereby a difluoroionic complex (2) is obtained. At this time, the amount of the fluorinating agent to be used is preferably 1.8 to 40 moles, and more preferably 2.0 to 20 moles.

As the fluorinating agent, an ionic fluorinating agent which generates fluoride ions when added to a nonaqueous solvent can be used, and among them, acidic potassium fluoride, acidic sodium fluoride, acidic ammonium fluoride, and hydrogen fluoride are preferably used in excess. The acidity such as an organic amine hydrogen fluoride salt or hydrogen fluoride is preferably hydrogen fluoride in terms of a faster reaction rate.

In the case of fluorination, an acid or a Lewis acid may be added in addition to the fluorinating agent. By adding an acid or a Lewis acid, the proton concentration in the reaction liquid can be increased, and fluorination can be performed. The reaction rate of the agent when fluorine is introduced is increased. Here, as the acid other than the fluorinating agent (protonic acid or blister acid), sulfuric acid, fluorosulfonic acid, hydrogen chloride, methanesulfonic acid, trifluoromethanesulfonic acid, trifluoroacetic acid, nitric acid, p-toluene may be used. As the Lewis acid other than the fluorinating agent, boron trifluoride, phosphorus pentafluoride, aluminum trichloride, antimony pentachloride, and metal triflate (cations of Li, Na, K, etc.) may be used. La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y). In particular, it is preferred to use trifluoromethanesulfonic acid, methanesulfonic acid or trifluoroacetic acid to increase the reaction rate.

The equivalent of the acid or Lewis acid other than the fluorinating agent is preferably 0.001 to 2.0 mol equivalents based on the hexacoordinate ionic complex (1). When the amount of the acid or the Lewis acid other than the fluorinating agent is too small, the effect of increasing the reaction rate is small, and if the amount is too large, not only the cost is increased but also the decomposition of the product proceeds.

A fluorinating agent other than the above acidic fluorinating agent may also be used by adding an acid or a Lewis acid. In this case, potassium fluoride, sodium fluoride, lithium fluoride, cesium fluoride, fluorination may be used. Nickel, calcium fluoride, barium fluoride, iron fluoride, zinc fluoride, manganese fluoride, fluorinated mirror, barium fluoride, cobalt fluoride, ammonium fluoride, tetrabutylammonium fluoride, etc., among which, It is potassium fluoride, sodium fluoride, lithium fluoride, barium fluoride, calcium fluoride, nickel fluoride, cobalt fluoride, iron fluoride, zinc fluoride, manganese fluoride, ammonium fluoride, and further, selectivity From the viewpoint, lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, calcium fluoride, nickel fluoride, iron fluoride, zinc fluoride, or ammonium fluoride is preferable.

The nonaqueous solvent used in the above-mentioned synthesis method may dissolve the hexacoordinate ionic complex (1) which is a raw material even if it is in a very small amount, and it is preferred that it does not react with a compound in the system. It is preferred that the relative dielectric constant is 2 or more. Here, in the case of using a non-aqueous solvent having no solubility at all, the fluorination becomes very slow, which is not preferable. As long as there is a slight solubility, the reaction is carried out because the solubility of the target difluoroionic complex (2) is high. For example, carbonates, esters, ketones, lactones, ethers, nitriles, guanamines, anthracenes, and the like can be used, and they may be a single solvent or a mixed solvent of two or more kinds.

Specific examples of the nonaqueous solvent include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl acetate, propyl acetate, and butyl acetate. , methyl propionate, ethyl propionate, butyl propionate, acetone, methyl ethyl ketone, diethyl ketone, γ-butyrolactone, γ-valerolactone, tetrahydrofuran, tetrahydropyran, dibutyl Ether, diisopropyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, acetonitrile, propionitrile, N,N-dimethylformamide, dimethyl alum And cyclodextrin, etc., among them, a solvent having a boiling point of 120 ° C or lower is preferred, and further preferably dimethyl carbonate, methyl carbonate, diethyl carbonate, ethyl acetate, methyl propionate, propionic acid Ethyl ester, acetone, tetrahydrofuran, 1,2-dimethoxyethane, acetonitrile.

The reaction temperature at the time of introducing fluorine using a fluorinating agent is -60 ° C to 150 ° C, preferably -20 to 120 ° C. When the temperature is lower than -60 ° C, the fluorine introduction may not be sufficiently performed. When the temperature is 150 ° C or higher, the hexa-coordinate ionic complex (1) which is a raw material may be present or may be produced as a product. The possibility of decomposition of the difluoro-ionic complex (2). In order to obtain a sufficient fluorine introduction speed and not cause decomposition, the range of -20 to 120 ° C is optimal.

Further, the reaction time can be appropriately selected depending on the reaction rate. However, if the device is occupied for a long period of time, the production cost is increased. Therefore, in practice, it is preferably 72 hours or less. Further, in order to carry out the reaction of the entire system, it is preferred to stir the solution during the reaction.

It is preferred to carry out a pressure reduction operation in order to reduce the residual free acid concentration after the fluorination, and to remove the precipitate by filtration as necessary. At this time, part of the nonaqueous solvent is also distilled off, so that the concentration of the difluoroionic complex (2) as a product is concentrated. In the decompression operation, a vacuum pump, an aspirator, or the like can be used. The pressure reduction operation is carried out by maintaining the pressure in the system at a pressure equal to or lower than atmospheric pressure after the reactor is sealed. The pressure in the system varies depending on the temperature of the liquid to be purified and the vapor pressure, and therefore cannot be generalized. However, the pressure reduction is preferably such that the degree of vacuum in the tank is maintained at an absolute pressure of 80 kPa or less. When the pressure to be maintained exceeds 80 kPa, it is not preferable until the residual free acid concentration is equal to or lower than the desired concentration, and it takes a long time. Again, if the pressure is maintained When the force is 50 kPa or less, the reaction product and the unreacted purifying agent can be excluded to a low concentration, which is further preferable. Further, in consideration of the burden on the device, it is preferable to set the absolute pressure to 20 kPa or more. In particular, when the ligand of the above-mentioned six-coordinate ionic complex (1) and the above-mentioned difluoro-ionic complex (2) is oxalic acid, it is preferred to carry out a pressure reduction operation after fluorination. One part of the solvent was distilled off to concentrate the difluoroionic complex (2), and the precipitated oxalic acid was separated by filtration.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the examples.

The treatment of any of the raw materials or products was carried out under a nitrogen atmosphere having a dew point of -50 ° C or lower. Further, the glass reactor and the fluororesin reactor used were each dried at 150 ° C for 12 hours or more, and then cooled to room temperature under a nitrogen gas stream having a dew point of -50 ° C or lower.

[Preparation of test solution]

The test liquid used in the deacidification treatment test shown in Table 1 was prepared by the following procedure as a solution in which an electrolyte was dissolved containing at least hydrogen fluoride as an impurity. Further, the free acid value is represented by a value obtained by converting the molar concentration of the acid into the mass of HF and using a salt (for example, (2a-Li) in the test liquid A) as a reference.

[Test solution A]

According to the method disclosed in Non-Patent Document 2, lithium oxalate lithium phosphate (1a-Li) as a hexacoordinate ionic complex compound having three molecules of oxalic acid is obtained. Into a 500 mL fluororesin reactor, (1a-Li) (30 g, 99.4 mmol) as an electrolyte was added, and methyl carbonate (hereinafter referred to as EMC) (120 mL) as a nonaqueous solvent was added and dissolved. Thereafter, hydrogen fluoride (hereinafter referred to as HF) (11.9 g, 596.2 mmol, 6.0 mol equivalent) as a fluorinating agent was added. After stirring at 25 ° C for 24 hours, the residual HF was removed and concentrated under reduced pressure. After the precipitated oxalic acid was removed by filtration, the conversion rate and the selectivity were determined by F, P-NMR (nuclear magnetic resonance), and the residue was determined by silver nitrate titration. The residual chlorine concentration was determined by free acid titration. As a result, the conversion ratio of the dichloro ionic complex (2a-Li) having 2 molecules of oxalic acid to the target was 71.0%, and the selectivity was selected. 95.4%, based on the difluoroionic complex (2a-Li), the residual chlorine concentration was less than 100 ppm by mass, and the residual free acid concentration was 2000 ppm by mass.

Conversion rate [%] = target mole %

Selection rate [%] = conversion rate / (100 - residual raw material mole %) × 100

The obtained (2a-Li)/EMC solution was adjusted to have a salt concentration of about 25% by mass to prepare Test Solution A. The details of the free acid (anion side) in the test liquid A were determined by ion chromatography, and as a result, the molar ratio of the fluoride anion to the oxalate anion was 1:1.5. From this, it is understood that the free acid of 2000 ppm by mass is derived from 500 ppm by mass of HF and 1500 ppm by mass derived from oxalic acid (in terms of HF).

In addition, it was confirmed that the addition amount of hydrogen fluoride was 2.0 mol equivalent, and trifluoromethanesulfonic acid (hereinafter referred to as TfOH) as an acid for accelerating the reaction was added at 0.02 mol equivalent, and stirred at 0 ° C. At 24 hours, the conversion to the difluoroionic complex (2a-Li) was 94.2%, the selectivity was 95.2%, and the reaction rate was increased by carrying out a fluorination reaction in the presence of TfOH.

[Test solution B]

The test liquid A was concentrated to a salt concentration of about 50% by mass, and the precipitated solid was removed by filtration. While stirring at a temperature of 25 ° C, 6 times by mass of chloroform was added to the mass of the obtained concentrate to precipitate a solid. The precipitated (2a-Li) was recovered by filtration. Here, the concentration of the free acid contained in the recovered (2a-Li) was less than 20 ppm by mass based on (2a-Li). This (2a-Li) was dissolved in EMC to prepare a 25% by mass EMC solution. Oxalic acid (0.11 g, 1.3 mmol) was added to 100 g of the EMC solution to prepare a test liquid B containing oxalic acid in an amount of 2,000 ppm by mass based on (2a-Li).

[Test solution C]

The test solution A was concentrated to a salt concentration of about 50% by mass, and the precipitate was removed by filtration. solid. The mixture was stirred at a temperature of 25 ° C, and 6 mass times of chloroform was added to the mass of the obtained concentrate to precipitate a solid. The precipitated (2a-Li) was recovered by filtration. Here, the concentration of the free acid contained in the recovered (2a-Li) was less than 20 ppm by mass based on (2a-Li). This (2a-Li) was dissolved in EMC to prepare a 25% by mass EMC solution. HF (0.05 g, 2.5 mmol) was added to 100 g of the EMC solution to prepare a test liquid C containing HF of 2000 mass ppm based on (2a-Li).

[Test solution D]

Test solution A (100 g) was concentrated under reduced pressure (50 ° C, 1.3 kPa) to remove EMC. When a dimethyl carbonate (hereinafter referred to as DMC) (70 g) is added to the residual solid residue (30 g) to prepare a (2a-Li)/DMC solution having a salt concentration of about 25% by mass, and the free acid concentration is measured, (2a-Li) was 1750 mass ppm as a standard. The details of the free acid (anion side) were determined by ion chromatography, and the molar ratio of the fluoride anion to the oxalate anion was 1:3. From this, it was found that 1750 ppm by mass of the free acid was derived from 250 ppm by mass of HF and 1500 ppm by mass derived from oxalic acid (in terms of HF). HF (0.006 g) was added to the (2a-Li)/DMC solution to prepare a test liquid D containing HF of 500 mass ppm based on (2a-Li) and oxalic acid of 1500 mass ppm in terms of HF. .

[Test solution E]

According to the preparation procedure of the test liquid C described above, the EMC was changed to DMC, thereby obtaining a test liquid E containing HF of 2000 mass ppm based on (2a-Li).

[Test solution F]

According to the preparation procedure of the test liquid D, DMC was changed to diethyl carbonate (hereinafter referred to as DEC), thereby obtaining HF containing 500 mass ppm based on (2a-Li) and 1500 in terms of HF. Test solution F of oxalic acid of mass ppm.

[Test solution G]

According to the preparation procedure of the test liquid C described above, the EMC was changed to DEC, whereby the test liquid G containing HF of 2000 mass ppm based on (2a-Li) was obtained.

[Test solution H]

According to the preparation procedure of the test liquid D, the DMC was changed to tetrahydrofuran (hereinafter referred to as THF), thereby obtaining HF of 500 ppm by mass based on (2a-Li) and 1500 ppm by mass in terms of HF. Oxalic acid test solution H.

[Test solution I]

According to the preparation procedure of the test liquid C described above, EMC was changed to THF, thereby obtaining a test liquid I containing HF of 2000 mass ppm based on (2a-Li).

[Test solution J]

According to the preparation procedure of the test liquid D described above, DMC was changed to ethyl acetate (hereinafter referred to as AcOEt), thereby obtaining HF of 500 ppm by mass based on (2a-Li) and 1500 mass in terms of HF. Phenolic acid test solution J.

[Test solution K]

According to the preparation procedure of the test liquid C described above, EMC was changed to AcOEt, thereby obtaining a test liquid K containing HF of 2000 mass ppm based on (2a-Li).

[Test solution L]

According to the preparation procedure of the test liquid D described above, DMC was changed to acetonitrile (hereinafter referred to as CH ₃ CN), thereby obtaining HF of 500 ppm by mass based on (2a-Li) and 1500 mass in terms of HF. Test solution L of oxalic acid of ppm.

[Test solution M]

According to the preparation procedure of the test liquid C described above, the EMC was changed to CH ₃ CN, whereby the test liquid M containing HF of 2000 mass ppm based on (2a-Li) was obtained.

[Test solution N]

According to the method disclosed in Non-Patent Document 2, lithium oxalate lithium phosphate (1a-Li) as a hexacoordinate ionic complex compound having three molecules of oxalic acid is obtained. 500 g of a strongly acidic cation exchange resin 252 (hereinafter referred to as an ion exchange resin) manufactured by Dow Chemical was weighed and immersed in a 0.1 equivalent aqueous sodium hydroxide solution (2.5 kg), and stirred at 25 ° C for 6 hours. The ion exchange resin was recovered by filtration, and sufficiently washed with pure water until the pH of the washing liquid became 8 or less. Thereafter, the water was removed by drying under reduced pressure (120 ° C, 1.3 kPa) for 12 hours. (1a-Li) (30 g, 99.4 mmol) was dissolved in EMC (270 mL), and 150 g of the dried ion exchange resin was added thereto, and stirred at 25 ° C for 6 hours. Thereafter, the ion exchange resin was removed by filtration, whereby a (1a-Na)/EMC solution in which a cation was converted from Li ⁺ to Na ⁺ was obtained. When performed by ion chromatography of cations quantitative, the Na ⁺ / Li ⁺ ratio of 99.4.

The concentration under reduced pressure was adjusted until the salt concentration of the (1a-Na)/EMC solution became about 20% by mass. Thereafter, HF (4.0 g, 198.7 mmol, 2.0 mol equivalent) and trifluoromethanesulfonic acid (hereinafter referred to as TfOH) (0.03 g, 0.2 mmol, 0.002 molar equivalent) were added. After stirring at a temperature of 25 ° C for 72 hours, the residual HF and the added acid were removed and concentrated under reduced pressure. After removing the precipitated oxalic acid by filtration, the conversion ratio and the selectivity were determined by F and P-NMR, and the residual chlorine concentration was determined by silver nitrate titration, and the residual free acid concentration was determined by free acid titration. The conversion rate to the target difluoro-ionic complex (2a-Na) was 94.8%, the selectivity was 96.0%, and the residual chlorine concentration was less than 100% based on the difluoro-ionic complex (2a-Na). The residual free acid concentration was 2,000 ppm by mass.

The obtained (2a-Na)/EMC solution was adjusted to have a salt concentration of about 25% by mass to prepare a test liquid N. The details of the free acid (anion side) in the test liquid N were determined by ion chromatography, and the molar ratio of the fluoride anion to the oxalate anion was 1:2. From this, it is understood that the free acid of 2000 ppm by mass is derived from 400 ppm by mass of HF and 1600 ppm by mass derived from oxalic acid (in terms of HF).

[Test solution O]

500 g of an ion exchange resin was weighed, immersed in a 0.1 N aqueous solution of sodium hydroxide (2.5 kg), and stirred at 25 ° C for 6 hours. The ion exchange resin was recovered by filtration and sufficiently washed with pure water until the pH of the washing liquid became 8 or less. Thereafter, the water was removed by drying under reduced pressure (120 ° C, 1.3 kPa) for 12 hours.

The test liquid A was concentrated to a salt concentration of about 50% by mass, and the precipitated solid was removed by filtration. While stirring at a temperature of 25 ° C, 6 times by mass of chloroform was added to the mass of the obtained concentrate to precipitate a solid. The precipitated (2a-Li) was recovered by filtration. Here, the concentration of the free acid contained in the recovered (2a-Li) was less than 20 ppm by mass based on (2a-Li). This (2a-Li) (25 g, 99.4 mmol) was dissolved in EMC (275 mL), and 150 g of the dried ion exchange resin was added thereto, and stirred at 25 ° C for 6 hours. Thereafter, the ion exchange resin was removed by filtration, whereby a (2a-Na)/EMC solution in which a cation was converted from Li ⁺ to Na ⁺ was obtained. If the cation is quantified by ion chromatography, the ratio of Na ⁺ /Li ⁺ is 99.3. After preparing a salt concentration of about 25% by mass, HF (0.05 g, 2.5 mmol) was added to 100 g of the EMC solution to obtain a test liquid O containing HF of 2000 mass ppm based on (2a-Na).

[Test solution P]

After dissolving LiPF ₆ (25 g) in EMC (75 g), HF (0.05 g, 2.5 mmol) was added to prepare a test liquid P containing HF of 2000 ppm by mass based on LiPF ₆ .

[Test solution Q]

After dissolving NaPF ₆ (25 g) in EMC (75 g), HF (0.05 g, 2.5 mmol) was added to prepare a test liquid Q containing HF of 2000 mass ppm based on NaPF ₆ .

[Test solution R]

After LiBF ₄ (25 g) was dissolved in EMC (75 g), HF (0.05 g, 2.5 mmol) was added to prepare a test liquid R containing HF of 2000 mass ppm based on LiBF ₄ .

[Test solution S]

After dissolving LiFSI (25 g) in EMC (75 g), HF (0.05 g, 2.5 mmol) was added to prepare a test liquid S containing HF of 2000 mass ppm based on LiFSI.

[Test solution T]

After dissolving LiDFPI (25 g) in EMC (75 g), HF (0.05 g, 2.5 mmol) was added to prepare a test liquid containing HF of 2000 ppm by mass based on LiDFPI. T.

The composition of each test liquid is shown in Table 1. In Table 1, PF ₆ represents a hexafluorophosphate anion, BF ₄ represents a tetrafluoroborate anion, FSI represents a bis(fluorosulfonyl) quinone imine anion, and DFPI represents a bis(difluorophosphate) quinone imine anion.

The concentration of the free acid in the electrolytic solution is usually required to be about 200 ppm by mass or less in terms of hydrogen fluoride. Since most of the ionic complexes are contained in the electrolytic solution in an amount of several to ten percent, in order to achieve such a hydrogen fluoride concentration, each test liquid containing an ionic complex must be used as a reference for the ionic complex. The hydrogen fluoride concentration is about 1000 ppm by mass or less.

[Example 1-1]

To the test liquid A (100 g), sulfoxide (0.36 g, 3.0 mmol, 1.2 eq. of 2000 mass ppm of free acid with respect to HF) was added as a purifying agent, and the mixture was stirred at a temperature of 25 ° C for 6 hours. Thereby, hydrogen fluoride and sulphur-thin chloride are converted into highly volatile hydrogen chloride and sulfoxide by reaction. Thereafter, at a temperature of 20 to 40 ° C and a pressure of 50 to 80 kPa under an absolute pressure, the pressure was reduced to remove the reaction product, and at the same time, 25 g of EMC was distilled off to concentrate the ionic complex. When the free acid concentration was measured, the value in terms of HF in terms of (2a-Li) was 200 ppm by mass.

[Example 1-2]

The treatment was carried out in the same manner as in Example 1-1 except that the temperature was changed from 25 ° C to 40 ° C. As a result, the free acid concentration was less than 100 ppm by mass.

[Example 1-3]

The temperature was changed from 25 ° C to 40 ° C, the stirring time was changed from 6 hours to 3 hours, and dry nitrogen gas (10 mL / min) was continuously blown into the solution while stirring, except for the examples. The same procedure as in 1-1 was carried out, and as a result, the free acid concentration was less than 100 ppm by mass.

[Example 1-4]

To the test liquid A (100 g), ruthenium chloride (0.36 g, 3.0 mmol, 1.2 eq. per 2,000 ppm by mass of HF in terms of HF) was added, and the pressure was reduced to a pressure at a temperature of 40 ° C to an absolute pressure of 50 Å. 80 kPa and stirring for 3 hours. The pressure was returned to atmospheric pressure by nitrogen, and 5 g of EMC was added to return to the initial test liquid weight of 100 g. Thereafter, the pressure was concentrated at a temperature of 20 to 40 ° C and the pressure was 50 to 80 kPa under absolute pressure, and 25 g of EMC was distilled off. When the free acid concentration was measured, the value in terms of HF converted to (2a-Li) was less than 100 ppm by mass.

[Example 1-5]

The test solution B was used to change the stirring time from 6 hours to 3 hours, except that the same procedure as in Example 1-2 was carried out, and the free acid concentration was less than 100%. Ppm.

[Example 1-6]

The test solution C was used to carry out the treatment in the same manner as in Example 1-2 except that the stirring time was changed from 6 hours to 3 hours. As a result, the free acid concentration was 600 ppm by mass.

[Examples 1-7]

The same procedure as in Example 1-6 was carried out, except that the amount of the addition of the sulphur sulphate was changed to 0.59 g and 5.0 mmol (2.0 eq. per 2,000 ppm by mass of the free acid in terms of HF). The free acid concentration was 200 ppm by mass.

[Examples 1-8]

In the same manner as in Example 1-4 except that the amount of the sulfite chloride was changed to 0.59 g and 5.0 mmol, the free acid concentration was less than 100 ppm by mass.

[Comparative Example 1-1]

The test liquid A (100 g) was stirred while being continuously blown into the solution at a temperature of 40 ° C for 3 hours while continuously blowing dry nitrogen gas (10 mL/min). Thereafter, the mixture was concentrated under reduced pressure at a temperature of 20 to 40 ° C, and 25 g of EMC was distilled off. The free acid concentration was measured and found to be 2000 ppm by mass.

[Comparative Example 1-2]

The test solution A (100 g) was kept at a reduced pressure (50 to 80 kPa) at a temperature of 40 ° C and stirred for 3 hours. Thereafter, the mixture was concentrated under reduced pressure at a temperature of 20 to 40 ° C, and 25 g of EMC was distilled off. When the free acid concentration was measured, the value in terms of HF in terms of (2a-Li) was 1900 ppm by mass.

[Comparative Example 1-3]

The test solution C (100 g) containing hydrogen fluoride but containing almost no oxalic acid was kept at a reduced pressure (50 to 80 kPa) at a temperature of 40 ° C and stirred for 3 hours. Thereafter, at temperature Concentrated under reduced pressure at 20 to 40 ° C, and distilled to remove 25 g of EMC. When the free acid concentration was measured, the value in terms of HF in terms of (2a-Li) was 1,700 ppm by mass.

[Comparative Example 1-4]

The free acid concentration was determined by the same procedure as in Example 1-1 except that acetamidine chloride (0.24 g, 3.0 mmol, 1.2 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as described above was 1300 ppm by mass.

[Comparative Example 1-5]

The free acid concentration was determined by the same procedure as in Example 1-6 except that acetamidine chloride (0.39 g, 5.0 mmol, 2.0 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as described above was 1100 ppm by mass.

[Example 2-1]

To the test liquid D (100 g), ruthenium chloride (0.36 g, 3.0 mmol, 1.2 eq. per 2,000 ppm by mass of HF in terms of HF) was added, and the pressure was reduced to 50 to 80 kPa at a temperature of 40 ° C, and stirred. hour. The nitrogen gas was returned to atmospheric pressure, and DMC, which is equivalent to the weight which was reduced by distillation during the operation, was added, and returned to the initial test liquid weight of 100 g. Thereafter, the mixture was concentrated under reduced pressure at a temperature of 20 to 40 ° C, and 25 g of DMC was distilled off. When the free acid concentration was measured, the value in terms of HF converted to (2a-Li) was less than 100 ppm by mass.

[Example 2-2]

To the test liquid E (100 g), ruthenium chloride (0.59 g, 5.0 mmol, 2.0 eq. of 2000 mass ppm of free acid in terms of HF) was added, and the pressure was reduced to 50 to 80 kPa at a temperature of 40 ° C, and stirred. hour. The nitrogen gas was returned to atmospheric pressure, and DMC, which is equivalent to the weight which was reduced by distillation during the operation, was added, and returned to the initial test liquid weight of 100 g. Thereafter, the mixture was concentrated under reduced pressure at a temperature of 20 to 40 ° C, and 25 g of DMC was distilled off. When the free acid concentration was measured, the value in terms of HF converted to (2a-Li) was less than 100 ppm by mass.

[Example 2-3]

The test solution was changed to F, DMC was changed to DEC, and the same procedure as in Example 2-1 was carried out. As a result, the free acid concentration (the same HF conversion value as described above) was less than 100%. Ppm.

[Example 2-4]

The test solution was changed to G, and the DMC was changed to DEC. Otherwise, the free acid concentration (the same HF conversion value as described above) was less than 100% by the same procedure as in Example 2-2. Ppm.

[Example 2-5]

The free acid concentration (the same HF conversion value as described above) was less than 100%, except that the test solution used was changed to H and the DMC was changed to THF, except that the same procedure as in Example 2-1 was carried out. Ppm.

[Example 2-6]

The free acid concentration (the same HF conversion value as described above) was less than 100 mass, except that the test liquid used was changed to I, and DMC was changed to THF, and the same procedure as in Example 2-2 was carried out. Ppm.

[Examples 2-7]

The test solution was changed to J, DMC was changed to AcOEt, and the same procedure as in Example 2-1 was carried out. As a result, the free acid concentration (the same HF conversion value as described above) was less than 100%. Ppm.

[Example 2-8]

The test solution was changed to K, the DMC was changed to AcOEt, and the same procedure as in Example 2-2 was carried out. As a result, the free acid concentration (the same HF conversion value as described above) was less than 100%. Ppm.

[Embodiment 2-9]

The free acid concentration (the same HF conversion value as described above) was not obtained by changing the test liquid to L and changing the DMC to CH ₃ CN, except that the same procedure as in Example 2-1 was carried out. 100 mass ppm.

[Example 2-10]

The free acid concentration (the same HF converted value as described above) was 100, except that the test liquid used was changed to M and the DMC was changed to CH ₃ CN. The same procedure as in Example 2-2 was carried out. Mass ppm.

The results of Examples 1-1 to 1-8, Comparative Examples 1-1 to 1-5, and Examples 2-1 to 2-10 are shown in Table 2. In Table 2, SOCl ₂ represents thiophosphorus chloride, and AcCl represents ethyl hydrazine chloride.

The free acid was reduced to 200 ppm by mass (Example 1-1) by treatment with a ruthenium chloride 1.2 molar equivalent at 25 ° C for 6 hours, and then the temperature was raised to 40 ° C. The free acid was reduced to less than 100 ppm by mass (Examples 1-2). Further, by performing a treatment operation using sulphur oxychloride chlorine under reduced pressure or introducing nitrogen gas, the rate of free acid removal is increased, and the free acid is less than 100 ppm by mass in 3 hours at 40 ° C (Examples 1-3) 1-4).

Although the free acid concentration is 2000 ppm by mass, when the main component is oxalic acid, the residual free acid concentration drops to less than 100 ppm under the conditions of 1.2 mol% of sulfoxide, and 3 hours at 40 °C ( In the case of Example 1-5), in the case where the main component of the free acid concentration of 2000 ppm by mass is HF, the free acid is only lowered under the conditions of 1.2 mol% of sulfinium chloride and 3 hours at 40 °C. Up to 600 ppm by mass (Examples 1-6). The free acid can be reduced to 200 ppm by mass (Examples 1-7) by increasing the sulfinium chloride to 2.0 molar equivalents, and further, by using 2.0 molar equivalents of sulfoxide and under reduced pressure. Treatment can reduce the free acid to less than 100 ppm by mass (Examples 1-8).

It is presumed that the reaction is that the reaction between HF and sulphur oxychloride is reversible relative to the reaction of oxalic acid with sulphide chloride being irreversible (carbon monoxide, carbon dioxide is produced and discharged outside the system). However, the produced sulfoxide or the like is discharged as a gas to the outside of the reaction system without being subjected to a reduced pressure or the like. Therefore, compared with the case where acetonitrile is used as a purifying agent as in Comparative Example 1-5, it can be quickly Ground removal of HF. It is considered that the generated HCl, sulfinium fluoride or sulfinium fluorochloride is continuously removed from the system by pressure reduction or nitrogen introduction, whereby the reaction of the reverse reaction is restricted, and the fluorination reaction of sulfinium chloride It is accelerated, and as a result, the rate of free acid removal becomes faster.

Test liquid having a free acid concentration of 2000 mass ppm (500 mass ppm derived from HF + 1500 mass ppm derived from oxalic acid and 2000 mass ppm derived from HF) in two kinds of HF, in DMC, DEC, THF, AcOEt, CH _{3 In} the system of CN, the de-free acid using sulphur sulphur chloride was studied, and as a result, almost no difference due to the solvent was observed, except for Example 2-10 using CH ₃ CN (Example 2-1~) 2-9) The residual free acid concentration was less than 100 ppm by mass.

It is almost impossible to use sulphur dioxide without pressure reduction or nitrogen introduction. The free acid concentration (the same HF converted value as described above) was lowered (Comparative Examples 1-1, 1-2, 1-3). Further, in the case where ethyl ruthenium chloride is used instead of ruthenium chloride as a purifying agent, the residual free acid concentration exceeds 1000 ppm by mass, and the reaction temperature and reaction time at 6 hours at 25 ° C or 3 hours at 40 ° C cannot be used. The hydrogen fluoride is removed to a sufficiently low concentration. It can be considered that the reason is that since the boiling point of the ethyl fluorinated fluorinated acetonitrile is about 20 ° C, and there is no decompression operation or nitrogen introduction in the reaction system, acetonitrile is retained in the reaction system, and hydrogen fluoride is stored. The reaction rate with the purifying agent was not sufficiently improved (Comparative Examples 1-4, 1-5).

[Example 3-1]

When the test liquid to be used was changed to N, the treatment was carried out in the same manner as in Example 1-4, and as a result, the free acid concentration (the same HF conversion value as described above) was less than 100 ppm by mass.

[Example 3-2]

When the test liquid to be used was changed to O, the treatment was carried out in the same manner as in Example 1-8, and as a result, the free acid concentration (the same HF conversion value as described above) was less than 100 ppm by mass.

[Example 3-3]

The test solution was changed to P, and the treatment was carried out in the same manner as in Example 1-8. As a result, the free acid concentration (the same HF conversion value as described above) was less than 100 ppm by mass.

[Example 3-4]

The test solution was changed to Q, and the treatment was carried out in the same manner as in Example 1-8. As a result, the free acid concentration (the same HF conversion value as described above) was less than 100 ppm by mass.

[Example 3-5]

The test solution was changed to R, and the same procedure as in Example 1-8 was carried out, and as a result, the free acid concentration (the same HF conversion value as described above) was less than 100. The amount is ppm.

[Examples 3-6]

The test solution was changed to S, and the treatment was carried out in the same manner as in Example 1-8. As a result, the free acid concentration (the same HF conversion value as described above) was less than 100 ppm by mass.

[Examples 3-7]

The test solution was changed to T, and the same procedure as in Example 1-8 was carried out, and as a result, the free acid concentration (the same HF conversion value as described above) was less than 100 ppm by mass.

The results of Examples 3-1 to 3-7 are shown in Table 3.

When the anion species of the salt dissolved in the test solution is changed from the difluoro ion complex (2a) to PF ₆ , BF ₄ , FSI, DFPI, and the cationic species is replaced with Li from Li, it is included in the test. The reaction of the free acid (only HF, or HF and oxalic acid) in the liquid with sulfoxide was carried out without any problem, and the residual free acid concentration after the treatment was less than 100 ppm by mass. Furthermore, in the example 3-1, the details of the free acid are mainly concentrated on oxalic acid, so the molar equivalent of thiocyanine chloride is 1.2, and the main components of the free acid in the examples 3-2 to 3-7 are HF, so 2.0 molar equivalents of sulfinium chloride were used.

[Example 4-1]

The free acid concentration was determined by the same procedure as in Example 1-4 except that acetamidine chloride (0.24 g, 3.0 mmol, 1.2 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as described above is less than 100 ppm by mass.

[Example 4-2]

The free acid concentration was determined by the same procedure as in Example 1-8 except that acetaminophen (0.39 g, 5.0 mmol, 2.0 eq. relative to the free acid) was used instead of sulphur. The same HF conversion value as described above is less than 100 ppm by mass.

[Example 4-3]

The free acid concentration was determined by the same procedure as in Example 1-4 except that chloroform (0.38 g, 3.0 mmol, 1.2 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as described above is less than 100 ppm by mass.

[Example 4-4]

The free acid concentration was determined by the same procedure as in Example 1-8 except that grass chlorobenzene (0.63 g, 5.0 mmol, 2.0 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as described above was 150 ppm by mass.

[Example 4-5]

The free acid concentration was obtained by the same procedure as in Example 1-4 except that methyl chloroformate (0.28 g, 3.0 mmol, 1.2 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as above is less than 100 ppm by mass.

[Examples 4-6]

The free acid concentration was obtained by the same procedure as in Example 1-8 except that methyl chloroformate (0.47 g, 5.0 mmol, 2.0 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as described above is 100 ppm by mass.

[Examples 4-7]

Trifluoromethanesulfonium chloride (0.51 g, 3.0 mmol, 1.2 eq. relative to the free acid) was used. In the same manner as in Example 1-4, the free acid concentration (the same HF conversion value as described above) was less than 100 ppm by mass.

[Examples 4-8]

The free acid was obtained by the same procedure as in Example 1-8 except that trifluoromethanesulfonium chloride (0.84 g, 5.0 mmol, 2.0 eq. relative to the free acid) was used instead of sulfinium chloride. The concentration (the same HF converted value as described above) was 100 ppm by mass.

[Examples 4-9]

The free acid concentration was obtained by the same procedure as in Example 1-4 except that methanesulfonium chloride (0.34 g, 3.0 mmol, 1.2 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as above is less than 100 ppm by mass.

[Examples 4-10]

The free acid concentration was obtained by the same procedure as in Example 1-8 except that methanesulfonium chloride (0.57 g, 5.0 mmol, 2.0 eq. relative to the free acid) was used instead of sulfinium chloride. The same HF conversion value as described above is 100 ppm by mass.

[Examples 4-11]

The free acid was treated by the same procedure as in Example 1-4 except that trimethyl decane chloride (0.33 g, 3.0 mmol, 1.2 eq. relative to the free acid) was used instead of sulfinium chloride. The concentration (the same HF converted value as described above) was 1000 ppm by mass.

[Examples 4-12]

The free acid was obtained by the same procedure as in Example 1-8 except that trimethyl decane chloride (0.54 g, 5.0 mmol, 2.0 eq. relative to the free acid) was used instead of sulphur. The concentration (the same HF converted value as described above) was 100 ppm by mass.

The results of Examples 4-1 to 4-12 are shown in Table 4. Table 4, AcCl represents acetyl chloride, (COCl) ₂ oxalyl represents acyl chloride, ClCO ₂ Me represents methyl chloroformate, TfCl represents trifluoromethanesulfonic acyl chloride, MsCl represents methanesulfonyl acyl chloride, TMSCl represents three chloride Base decane.

[Table 4]

In the case where acetoin is used as a purifying agent, the residual free acid concentration after the formation can be reduced to 100 ppm by mass by performing a pressure reduction during the reaction with the purifying agent, and in the reaction with the purifying agent. The residual free acid concentration can be greatly reduced as compared with the case where the pressure is not reduced (comparison of Examples 4-1 and 4-2 with Comparative Examples 1-4 and 1-5).

In the above study, the purification agent was changed from sulfinium chloride to other studies. In the system where oxalic acid became the main component of the free acid, the residual free acid concentration was reduced to the case where a purification agent other than TMSCl was used. Less than 100 ppm by mass. Relative to this (Examples 4-1, 4-3, 4-5, 4-7, 4-9), in the case of Example 4-11 where the purifying agent was TMSCl, the free acid concentration after the treatment was 1000. Mass ppm. The reason is that the reaction rate of TMSCl with oxalic acid is slow. In the case where the free acid is composed only of HF, the use of AcCl can achieve a concentration of free acid of less than 100 ppm by mass, whereas (COCl) ₂ or ClCO ₂ Me, TfCl, MsCl, TMSCl, Then, it was 100 to 150 mass ppm, and it was confirmed that the effect was slightly lowered.

Claims (13)

A method for purifying an electrolyte solution, comprising the steps of: adding an electrolyte solution containing at least hydrogen fluoride and oxalic acid as an impurity to an electrolyte dissolved in a nonaqueous solvent, comprising: selected from the group consisting of grass chloroform, methyl chloroformate, and chlorine One of a group consisting of ethyl formate, ethyl chloroform, trifluoroacetamidine chloride, trifluoromethanesulfonium chloride, methanesulfonyl chloride, and sulfinium chloride, or a purifying agent of the mixture, The impurities are reacted with the above-mentioned purifying agent to extract the reaction product out of the reaction system; and the reaction product hydrogen chloride, the fluorinated above-mentioned purifying agent, and the reaction product of the above-mentioned purifying agent with oxalic acid, and unreacted The above purifying agent is removed to remove the above impurities. The method for purifying an electrolyte solution according to claim 1, wherein the method of extracting the reaction product to the outside of the reaction system is a pressure reduction or introduction of an inert gas into the solution. The method for purifying an electrolyte solution according to claim 1 or 2, wherein the method of removing the above reaction product and the unreacted purification agent is a method of depressurizing or introducing an inert gas into the solution. The method for purifying an electrolyte solution according to claim 1 or 2, wherein the electrolyte is a salt, and the cation of the salt comprises one selected from the group consisting of a lithium cation, a sodium cation, a potassium cation, and a quaternary alkyl ammonium cation. Or a mixture of such. The method for purifying an electrolyte solution according to claim 1 or 2, wherein the electrolyte is a salt, and the anion of the salt comprises an anion selected from the group consisting of an hexafluorophosphate anion, a tetrafluoroborate anion, and a bis(fluorosulfonyl) quinone anion Bis(trifluoromethanesulfonyl) fluorene One of a group consisting of an anion, and an bis(difluorophosphate) quinone imine anion or a mixture thereof. The method for purifying an electrolyte solution according to claim 1 or 2, wherein the electrolyte is a salt, and the salt comprises a salt selected from the group consisting of lithium hexafluorophosphate, sodium hexafluorophosphate, potassium hexafluorophosphate, lithium tetrafluoroborate, sodium tetrafluoroborate, and tetrafluoroboric acid. Potassium, lithium bis(fluorosulfonyl) phthalimide, sodium bis(fluorosulfonyl) phthalimide, potassium bis(fluorosulfonyl) phthalimide, bis(trifluoromethanesulfonyl) quinone Lithium, sodium bis(trifluoromethanesulfonyl) sulfoximine, potassium bis(trifluoromethanesulfonyl) phthalimide, lithium bis(difluorophosphate) ruthenium hydride, bis(difluorophosphate) ruthenium One of a group consisting of sodium imide, potassium bis(difluorophosphate) phthalimide, and difluoroionic complexes (2a), (2b), and (2c) represented by the formula (2) And a mixture of the above; in addition, each element of the difluoroionic complex (2a), (2b), and (2c) is difluoroionic represented by the following formula (2) Complex, (2a) A = Li, Na, K or quaternary alkyl ammonium, M = P, Y = C, Z = C, p, q and s = 1, r = 0 (2b) A = Li , Na, K or quaternary alkyl ammonium, M = P, W = C (CF ₃ ) ₂ , Z = C, p and q = 0, r and s = 1 (2c) A = Li, Na, K or four alkylammonium, M = P, W = C (CF 3 ₂ , Z=C, p, q and s=0, r=2 The method for purifying an electrolyte solution according to claim 1 or 2, wherein a temperature at which hydrogen fluoride and the above-mentioned purifying agent or hydrogen fluoride and oxalic acid are reacted with the above-mentioned purifying agent is -60 ° C or more and 150 ° C or less. The method for purifying an electrolyte solution according to claim 1 or 2, wherein a temperature at which the reaction product and the unreacted purification agent are removed is -20 ° C to 120 ° C. The method for purifying an electrolyte solution according to claim 1 or 2, wherein the molar amount of the free acid in the solution before the reaction and the molar number of the above-mentioned purifying agent are in the range of 1:0.1 to 1:10. A method of producing an electrolyte solution, characterized by comprising a purification step using a purification method of the electrolyte solution according to any one of claims 1 to 9. A method for producing an electrolyte solution, which is a method for producing an electrolyte solution comprising a difluoro-ionic complex (2) represented by the formula (2), which method comprises: expressing the formula (1) a six-coordinated ionic complex (1) in which a fluorinating agent is fluorinated in a nonaqueous solvent to produce a difluoroionic complex (2) represented by the formula (2); and purification a step of using a purification method of the electrolyte solution of claim 1; [Chemistry 13] In the general formulae (1) and (2), A ⁺ is selected from the group consisting of metal ions, protons, and cesium ions, and M is selected from the group consisting of P, As, and Sb. One is; F is a fluorine atom; O is an oxygen atom; Y is a carbon atom or a sulfur atom; q is 1 when Y is a carbon atom; q is 1 or 2 when Y is a sulfur atom; W is carbon a hydrocarbon group having 1 to 10 which may have a hetero atom or a halogen atom (in the case where the carbon number is 3 or more, a branched or cyclic structure may be used), or -N(R ¹ )-; ¹ represents a hydrogen atom, an alkali metal, or a hydrocarbon group having 1 to 10 carbon atoms which may have a hetero atom or a halogen atom; when the carbon number is 3 or more, R ¹ may also take a branched or cyclic structure; Z is a carbon atom; p represents 0 or 1, q represents an integer from 0 to 2, r represents an integer from 0 to 2, s represents 0 or 1, and is p+r≧1. The method for producing an electrolyte solution according to claim 11, wherein the fluorinating agent is selected from the group consisting of acidic potassium fluoride, acidic sodium fluoride, acidic ammonium fluoride, hydrogen fluoride excess organic amine hydrogen fluoride, and hydrogen fluoride. More than one. The method for producing an electrolyte solution according to claim 11, wherein, in the case of fluorination, an acid other than the above fluorinating agent or a Lewis acid is added to the nonaqueous solvent, the fluorinating agent is hydrogen fluoride, and in addition to the fluorinating agent The acid is one or more selected from the group consisting of trifluoromethanesulfonic acid, methanesulfonic acid, and trifluoroacetic acid.