JP6093516B2 - Electrolytic solution, method for producing the same, and power storage device using the same - Google Patents

Description

  The present invention relates to an electrolytic solution, and more specifically, an electrolytic solution containing an ionic compound, an electrolytic solution with reduced free acid and / or moisture content, a method for producing the same, and It relates to the electricity storage device used.

  In addition to batteries with charging and discharging mechanisms such as primary batteries, lithium (ion) secondary batteries, fuel cells, etc., various power storage devices such as electrolytic capacitors, electric double layer capacitors, solar cells, etc. are equipped with an electrolyte. Many attempts have been made to reduce the amount of impurities in the electrolytic solution in order to prevent the decomposition of the electrolyte, the deterioration of electrochemical characteristics, and the deterioration of the performance of the electricity storage device due to the impurities contained in the solution.

For example, Patent Document 1, water contained in the electrolytic solution, HF, and the amount of potassium and sodium is defined, _{also, LiFSI, LiDCTA, LiPF 6,} TFSI, LiTFS
A method is described in which the amount of water in the electrolytic solution is reduced by bringing an electrolytic solution containing I or the like into contact with calcium carbide particles. Patent Documents 2 to 5 disclose methods for reducing the amount of acidic substances such as HF in the electrolyte solution for lithium batteries, and Patent Document 2 includes the content of alcohols that cause HF generation. In order to reduce the non-aqueous solvent used in the electrolytic solution, a method of treating by non-aqueous distillation, crystallization, or molecular sieve is described. In Patent Document 3, for removing acidic species such as HF in the electrolytic solution, A method of bringing an electrolytic solution into contact with a basic resin is described, and Patent Document 4 discloses a method of removing an acidic substance such as HF contained in an electrolyte as a hydrogen halide by reacting with a halide. Patent Document 5 discloses a method of reducing the amount of moisture in an electrolyte and fluorine derived from an electrolyte by mixing a moisture-absorbing substance and a substance that forms a sparingly soluble salt with fluorine in the electrolyte. Is described.

Special table 2009-506505 gazette JP-A-10-270076 JP 2000-505042 Japanese Patent Laid-Open No. 10-92468 JP 2010-257572 A

  Even if the content of the above acidic substances is low immediately after the production of the electrolytic solution, the amount thereof may increase over time, and such an electrolytic solution exhibits the initial electrochemical characteristics over a long period of time. It is difficult to realize an electric storage device that can be used.

  The present invention has been made paying attention to the circumstances as described above, and the purpose thereof is an electrolytic solution suitably used for an electricity storage device, and further, an amount of free acid that adversely affects the electrochemical characteristics of the electrolytic solution. It is an object of the present invention to provide an electrolytic solution in which an increase over time or the like is suppressed, and a method for producing the same.

The electrolytic solution of the present invention is characterized in that it contains an ionic compound represented by the following general formula (1) and a free acid, and the content of the free acid is less than 25 ppm (mass basis).
(XSO ₂ ) (X′SO ₂ ) N ⁻ Y ⁺ (1)
(In the formula, X and X ′ represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group, at least one of X and X ′ is a fluorine atom, and Y ⁺ represents an alkali metal cation or an onium cation. Represents.)

The free acid is preferably at least one free acid selected from the group consisting of HF, H ₂ SO ₄ and FSO ₃ H. Moreover, it is preferable that the moisture content contained in the electrolyte solution of this invention is 50 ppm or less (mass reference | standard). If the amount of free acid, or the amount of free acid and the amount of water are in the above ranges, it is preferable because these amounts hardly increase over time. In the above general formula (1), it is desirable that X and X ′ are fluorine atoms and Y ⁺ is a lithium cation.

  The present invention also includes an electricity storage device using the above electrolytic solution.

The production method of the present invention is a production method of the above electrolytic solution, and after mixing the ionic compound represented by the general formula (1) with a hydrocarbon solvent and / or an aprotic solvent,
(I) distilling off some or all of the solvent, and / or
(Ii) a step of contacting with the molecular sieve;
It has the characteristic in including.

  The electrolytic solution of the present invention has a reduced free acid content, is less prone to increase in free acid amount and water content over time, and has excellent storage stability. Therefore, if the electrolytic solution of the present invention is used for an electricity storage device, it is considered that a high-performance electricity storage device in which performance deterioration with time does not easily occur. Moreover, according to the method of the present invention, it is possible to produce an electrolytic solution in which an increase in the amount of free acid over time hardly occurs.

≪Electrolytic solution≫
The electrolytic solution of the present invention contains an ionic compound represented by the following general formula (1) (hereinafter sometimes referred to as ionic compound (1)) and a free acid, and the content of the free acid is less than 25 ppm. (Mass basis, the same applies hereinafter).
(XSO ₂ ) (X′SO ₂ ) N ⁻ Y ⁺ (1)
(In the formula, X and X ′ represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group, at least one of X and X ′ is a fluorine atom, and Y ⁺ represents an alkali metal cation or an onium cation. Represents.)

  The free acid in the electrolytic solution not only corrodes peripheral members of various power storage devices in which the electrolytic solution is used, but also increases the amount of free acid. When the amount of free acid in the electrolytic solution is less than 25 ppm, increase in the amount of free acid over time and corrosion of peripheral members of various power storage devices can be suppressed. Therefore, the content of the free acid is preferably 20 ppm or less in the electrolytic solution of the present invention. More preferably, it is 15 ppm or less. If the amount of free acid in the electrolyte is within the above range, the above-described problems are unlikely to occur.

  The amount of free acid in the electrolytic solution is preferably as small as possible. However, since the free acid is derived from the ionic compound (1) as described later, it is possible to reduce the content in the electrolytic solution to 0 ppm. It is difficult and may not be preferable for economic reasons. Therefore, the lower limit of the amount of free acid contained in the electrolytic solution of the present invention may be about 0.1 ppm. This is because if the content of the free acid is about 0.1 ppm, the influence on the characteristics of the electrolytic solution is small. The lower limit may be about 1 ppm. In this case, it is difficult to cause a remarkable deterioration in characteristics and hardly cause a practical problem. The free acid content in the present invention is, for example, a value measured by neutralization titration.

In the present invention, examples of the free acid whose content should be in the above range include one or more free acids selected from the group consisting of HF, H ₂ SO ₄ and FSO ₃ H. These free acids are inevitably contained in the electrolyte as starting materials, by-products during the synthesis of the ionic compound (1), or decomposition products of the ionic compound (1). Although it is difficult to reduce the amount to 0%, by setting the content within the above range, problems derived from these free acids can be suppressed. Among these free acids, it is recommended that the amount of HF, H ₂ SO ₄ and FSO ₃ H contained in the electrolytic solution be in the above range. The content of the free acid, HF, the total amount of one or more free acid selected from the group consisting of H ₂ SO ₄ and FSO ₃ H may be within the above range.

  In the electrolytic solution of the present invention, the amount of water contained in the electrolytic solution is desirably about 50 ppm or less (mass reference, the same applies hereinafter). The water contained in the electrolytic solution is, for example, the water mixed in the electrolytic solution manufacturing process due to moisture absorption from the environment such as water or solvent used in the synthesis reaction of the ionic compound (1) or purification, or in the air. It is thought that it remained. The use of the electrolytic solution of the present invention includes the above various electric storage devices. If the electrolytic solution contains moisture, the voltage resistance of the electrolytic solution is reduced, or the water is electrolyzed during operation of the electric storage device. As a result, hydrogen ions are generated and the pH of the electrolytic solution is lowered (acidic). As a result, the electrode material dissolves, reacts with the electrode material, corrodes, and the performance of the electricity storage device deteriorates. . In addition, the moisture contained in the electrolytic solution causes a hydrolysis reaction of the ionic compound (1), which not only decreases the amount of the ionic compound (1) in the electrolytic solution but also increases the amount of free acid. Also become. Furthermore, when water is electrolyzed, gas is generated, which may increase the internal pressure of various power storage devices having a sealed structure, leading to deformation or breakage. As a result, the device becomes unusable and may cause a safety problem.

  Therefore, the amount of water contained in the electrolytic solution of the present invention is more preferably about 30 ppm or less, and further preferably 10 ppm or less. If it is the said range, in addition to the deterioration suppression of a peripheral member, the increase in the amount of free acids with time can also be suppressed.

  In addition, although the moisture content in electrolyte solution is so low that it is good, it is technically difficult to reduce to 0 ppm, and it may be unpreferable for economical reasons. Therefore, the lower limit of the amount of water contained in the electrolytic solution of the present invention may be about 0.1 ppm. This is because if the water content is about 0.1 ppm, the influence on the characteristics of the electrolytic solution is small. The lower limit may be about 1 ppm. This is because a remarkable deterioration in characteristics is hardly seen and practical problems are unlikely to occur.

  The water content in the present invention is, for example, described in the examples described later using a Karl Fischer moisture measuring device (for example, a Karl Fischer moisture meter manufactured by Hiranuma Sangyo Co., Ltd.) by a coulometric titration method or a volumetric titration method. It is a value measured by the procedure.

<Ionic compound (1)>
Next, the ionic compound represented by the general formula (1): (XSO ₂ ) (X′SO ₂ ) N ⁻ Y ⁺ will be described. The electrolytic solution of the present invention contains an ionic compound (1) composed of an anion component: (XSO ₂ ) (X′SO ₂ ) N ⁻ and a cation component: Y ⁺ as an electrolyte. In general formula (1), X and X ′ represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group, and at least one of X and X ′ is a fluorine atom. The alkyl group having 1 to 6 carbon atoms is preferably a linear alkyl group, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, and a hexyl group. Examples of the fluoroalkyl group having 1 to 6 carbon atoms include those in which some or all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms, such as a fluoromethyl group, a difluoromethyl group, and a trifluoromethyl group. , Fluoroethyl group, difluoroethyl group, trifluoroethyl group, pentafluoroethyl group and the like. Among these, as X and X ′, a fluorine atom, a trifluoromethyl group, and a pentafluoroethyl group are preferable.

On the other hand, in the general formula (1), Y ⁺ represents an alkali metal cation or an onium cation. Examples of the alkali metal include lithium, sodium and potassium. Among these, lithium is preferable.

On the other hand, as the onium cation, the general formula (2): L ⁺ -R _s (wherein L represents C, Si, N, P, S or O. R is the same or different and represents a hydrogen atom, When R is an organic group and is a fluorine atom or an organic group, these may be bonded to each other, s is 2, 3 or 4, and is a value determined by the valence of the element L. , A bond between L and R may be a single bond or a double bond).

  The “organic group” represented by R means a group having at least one carbon atom. The “group having at least one carbon atom” may have at least one carbon atom, and may have another atom such as a halogen atom or a hetero atom, a substituent, or the like. . Specific examples of the substituent include an amino group, an imino group, an amide group, a group having an ether bond, a group having a thioether bond, an ester group, a hydroxyl group, an alkoxy group, a carboxyl group, a carbamoyl group, a cyano group, and a disulfide. Group, nitro group, nitroso group, sulfonyl group and the like.

  Specific examples of the onium cation represented by the general formula (2) include the following general formula:

  (Wherein R is the same as in general formula (2)) is preferred. Such onium cations may be used alone or in combination of two or more. Specific examples of the onium cation include a heterocyclic onium cation, an unsaturated onium cation, a saturated ring onium cation, and a chain onium cation described in WO2009 / 123328.

Preferred onium cations are those represented by the general formula (2): L ⁺ -R _s in which L is N, R is hydrogen, or a C _{1 to} C ₈ alkyl group, and a chain onium cation in which s is 4. There are 5 types of onium cations represented by the following general formula.

In the general formula, R ^{1 to} R ¹² are the same or different and are a hydrogen atom, a fluorine atom, or an organic group, and in the case of an organic group, these may be bonded to each other. As the organic group, a linear, branched, or cyclic C1-C18 saturated or unsaturated hydrocarbon group, a fluorocarbon group, or the like is preferable, and a C1-C8 saturated or unsaturated hydrocarbon group is more preferable. , A fluorocarbon group. These organic groups are hydrogen atom, fluorine atom, nitrogen atom, oxygen atom, sulfur atom, amino group, imino group, amide group, ether group, ester group, hydroxyl group, carboxyl group, carbamoyl group, cyano group, sulfone. A functional group such as a group or sulfide group may be contained. More preferably, R ^{1 to} R ¹² have one or more of a hydrogen atom, a fluorine atom, a cyano group, a sulfone group, and the like. When two or more organic groups are bonded, the bond may be formed between the main skeleton of the organic group, or between the main skeleton of the organic group and the functional group described above, or It may be formed between the functional groups.

Examples of the chain onium cation include tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, tetraheptylammonium, tetrahexylammonium, tetraoctylammonium, triethylmethylammonium, methoxyethyldiethylmethylammonium, and trimethylphenylammonium. , Benzyltrimethylammonium, benzyltriethylammonium, benzyltributylammonium, dimethyldistearylammonium, diallyldimethylammonium, (2-methoxyethoxymethyl) trimethylammonium, diethylmethyl (2-methoxyethyl) ammonium, tetrakis (pentafluoroethyl) ammonium, etc. No. 4 Ammonius , Tertiary ammonium such as trimethylammonium, triethylammonium, tributylammonium, diethylmethylammonium, dimethylethylammonium and dibutylmethylammonium, secondary ammoniums such as dimethylammonium, diethylammonium and dibutylammonium, methylammonium and ethyl ammonium, butyl ammonium, hexyl ammonium, primary ammonium such as octyl ammonium, N- methoxymethyl-trimethylammonium, N- ethoxymethyl trimethylammonium, ammonium compounds such as N- propoxymethyl trimethyl ammonium and NH ₄ and the like. Among these exemplified chain onium cations, preferred chain onium cations are ammonium, trimethylammonium, triethylammonium, tributylammonium, triethylmethylammonium, tetraethylammonium and diethylmethyl (2-methoxyethyl) ammonium.

  The ionic compound (1) may be a combination of the above cation and anion, but preferred ionic compound (1) includes lithium bis (fluorosulfonyl) imide.

<Medium>
The electrolyte solution of the present invention may contain a medium. Examples of the medium include aprotic solvents and polymers. As an aprotic organic solvent, the dielectric constant is large, the solubility of the electrolyte salt (alkali metal salt of fluorosulfonylimide, other electrolyte described later) is high, the boiling point is 60 ° C. or more, and the electrochemical stability A wide range of solvents is preferred. More preferred is a non-aqueous solvent. Non-aqueous solvents include ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, tetraethylene Ethers such as glycol dimethyl ether, 1,4-dioxane, 1,3-dioxolane; chains such as dimethyl carbonate, ethyl methyl carbonate (methyl ethyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, methyl phenyl carbonate -Like carbonates; ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), 2,3-dimethylethylene carbonate, butylene carbonate, carbonic acid Cyclic carbonates such as nylene and 2-vinylethylene carbonate; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate; methyl benzoate, benzoic acid Aromatic carboxylic acid esters such as ethyl; carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; phosphorous such as trimethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, triethyl phosphate Acid esters; nitriles such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile; N-methylformamide, N-ethyl Formamide, N, N Amides such as dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone, N-methylpyrrolidone, N-vinylpyrrolidone; dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, 2,4- Sulfur compounds such as dimethylsulfolane: alcohols such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; sulfoxides such as dimethyl sulfoxide, methyl ethyl sulfoxide and diethyl sulfoxide; aromas such as benzonitrile and tolunitrile Group nitriles; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone , 3-methyl-2-oxazolidinone and the like, and one or more of these are preferable. Among these, carbonic acid esters, aliphatic carboxylic acid esters, carboxylic acid esters, and ethers are more preferable, and carbonic acid esters are more preferable.

  Polymers used as a medium include polyether polymers such as polyethylene oxide (PEO) and polypropylene oxide, methacrylic polymers such as polymethyl methacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), and polyvinylidene fluoride ( PVDF), fluoropolymers such as polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof. In addition, a polymer gel obtained by mixing these polymers with another organic solvent can also be used as the medium according to the present invention. Examples of the other organic solvent include the aprotic solvents described above.

  As a method for producing an electrolytic solution using the polymer gel as a medium, a polymer formed by a conventionally known method, an aprotic solvent described above, an electrolyte (ionic compound (1) or other electrolyte described later) A solution in which the electrolyte and the aprotic solvent are impregnated and supported; the polymer and the electrolyte are melted and mixed at a temperature equal to or higher than the melting point of the polymer, and a film is formed. A method of impregnating an aprotic solvent; a method in which an electrolyte solution previously dissolved in an aprotic solvent and a polymer are mixed, and then a film is formed by a casting method or a coating method to volatilize the aprotic solvent (hereinafter referred to as a gel). Electrolyte); a method in which a polymer and an electrolyte are melted at a temperature equal to or higher than the melting point of the polymer, mixed and molded (intrinsic polymer electrolyte); and the like.

  The amount of the medium used is preferably 50 parts by mass to 99.9 parts by mass with respect to 100 parts by mass of the total amount of the electrolyte (ionic compound (1) and other electrolyte described later) and the medium. More preferably, they are 60 mass parts-99.5 mass parts, More preferably, they are 70 mass parts-99 mass parts. If the amount of the medium is too small, sufficient ionic conductivity may be difficult to obtain. On the other hand, if the amount is too large, the ionic concentration in the electrolytic solution is likely to change due to volatilization of the solvent, and stable ionic conductivity is obtained. It may be difficult.

<Other ingredients>
The electrolyte solution according to the present invention may contain only the ionic compound (1) as an electrolyte, but may contain other electrolytes. By using another electrolyte, the absolute amount of ions in the electrolytic solution can be increased, and the electrical conductivity can be improved.

As other electrolytes, those having a large dissociation constant in the electrolytic solution and having an anion that is difficult to solvate with the aprotic solvent are preferable. Examples of cation species constituting other electrolytes include alkali metal ions such as Li ⁺ , Na ⁺ and K ⁺ , alkaline earth metal ions such as Ca ²⁺ and Mg ²⁺ , and onium cations. Lithium ions are preferred. On the other hand, as anionic species, PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , AlCl ₄ ⁻ , C [(CN) ₃ ] ⁻ , N [(CN) ₂ ] ⁻ , B [(CN) ₄ ] ⁻ , N [(SO ₂ CF ₃ ) ₂ ] ⁻ , CF ₃ (SO ₃ ) ⁻ , C [
(CF ₃ SO ₂ ) ₃ ] ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ and dicyanotriazolate ion (DCTA). Among these, PF ₆ ⁻ and BF ₄ ⁻ are more preferable, and PF ₆ ⁻ is particularly preferable.

  The abundance of the other electrolyte is preferably 0.1% by mass or more and 99% by mass or less in a total of 100% by mass of the ionic compound (1) and the other electrolyte. If the amount of other electrolytes is too small, it may be difficult to obtain the effect of using other electrolytes (for example, the absolute amount of ions is not sufficient and the electrical conductivity is reduced). When there is too much quantity, there exists a possibility that the movement of ion may be inhibited greatly. More preferably, it is 1 mass% or more, More preferably, it is 5 mass% or more, More preferably, it is 95 mass% or less, More preferably, it is 90 mass% or less.

  In addition, the electrolyte concentration (the total amount of the ionic compound (1) and other electrolytes) in the electrolytic solution according to the present invention is preferably 0.1% by mass or more, and more preferably a saturation concentration or less. If it is less than 0.1% by mass, the ionic conductivity is lowered, which is not preferable. More preferably, it is 0.5 mass% or more, More preferably, it is 1 mass% or more. The electrolyte concentration in the electrolytic solution is more preferably less than 50% by mass, further preferably 40% by mass or less, and particularly preferably 30% by mass or less.

≪Electrolytic solution manufacturing process≫
The production method of the present invention is a method for producing the electrolytic solution, wherein the ionic compound represented by the general formula (1) is mixed with a solvent selected from a hydrocarbon solvent and / or an aprotic solvent. rear,
(I) a step of distilling off a part or all of the solvent, and / or (ii) a step of contacting with a molecular sieve,
It has the characteristic in including.

  When the present inventors synthesized the ionic compound (1) according to the present invention and then left it mixed with a medium or the like, the amount of free acid contained in the electrolytic solution increases with time. It has been found that the concentration of the ionic compound (1) in the electrolytic solution is lowered, and further, deterioration of peripheral members (electrode materials and the like) of the electricity storage device in which the electrolytic solution is used occurs. As described above, the free acid corresponds to a starting material and a by-product during the synthesis of the ionic compound (1), or a decomposition product of the ionic compound (1). Is difficult to completely prevent.

  Therefore, as a result of repeated studies to suppress the increase in the amount of free acid over time in the electrolytic solution, the present inventors have surprisingly found that the non-solvent used as a hydrocarbon solvent and / or a solvent for the electrolytic solution is also used. (I) a step of distilling off some or all of the solvent (hereinafter sometimes referred to as a solvent distilling step) and / or (ii) molecular in a state where the ionic compound is dissolved in the protic solvent. By performing the contact process with the sieve, not only the increase in the free acid amount over time can be suppressed, but also the amount of water that contributes to the generation of free acid can be reduced. The present inventors have found that an electrolytic solution that is considered to be less likely to decrease with time can be obtained. Hereinafter, the synthesis method of the ionic compound (1) will be described in order.

<Method for producing ionic compound (1)>
The method for producing an electrolytic solution of the present invention is characterized in that it includes the above (i) solvent distillation step and / or (ii) a step of contacting with a molecular sieve, and other steps are not particularly limited. Therefore, in the present invention, the method for synthesizing the ionic compound (1) is not particularly limited, and all conventionally known methods can be employed. For example, as described in JP-A-8-511274, a method for obtaining (fluorosulfonyl) imide by distillation of fluorosulfonic acid (HFSO ₃ ) in the presence of urea; fluorination from chlorosulfonylimide As a method for synthesizing fluorosulfonylimide using an agent and a method for obtaining a fluorosulfonylimide salt, the fluorosulfonylimide obtained by the above method or a salt thereof is a salt having a cation that gives a desired alkali metal or organic group. A method of exchanging cations by a reaction with (Patent Publication No. 2009/123328 pamphlet);

  In addition, in the term “fluorosulfonylimide” in the present invention, in the general formula (1), in addition to bis (fluorosulfonyl) imide in which both X and X ′ are fluorine atoms, one of X and X ′ is N- (fluorosulfonyl) -N- (fluoroalkylsulfonyl) imide which is a fluorine atom and the other is a fluorinated alkyl group is included. The same applies to “chlorosulfonylimide” as a starting material.

  In the present invention, in order to obtain an electrolytic solution, after mixing the ionic compound (1) with a hydrocarbon solvent and / or an aprotic solvent, (i) a step of distilling off a part or all of the solvent, and And / or (ii) performing the step of bringing the mixed solution into contact with the molecular sieve. Here, the ionic compound (1) may be in the state of an ionic compound (1) solution dissolved in a solvent, or may be a solid. In addition, when the ionic compound (1) solution contains a solvent other than the hydrocarbon solvent and / or the aprotic solvent, the hydrocarbon solvent and / or the aprotic solvent in advance by a conventionally known means. It is desirable to reduce the amount of solvent other than.

  Hydrocarbon solvents and aprotic solvents have higher solubility of the ionic compound (1) than other solvents. In addition, the aprotic solvent has a relatively high boiling point, while the hydrocarbon solvent includes an azeotrope with a solvent used in the production of the ionic compound (1), an aprotic solvent, and water. Since there is what can be formed, the use of a hydrocarbon solvent and / or an aprotic solvent can effectively reduce the water content while suppressing the precipitation of the ionic compound (1). Moreover, although the solvent used at the time of the synthesis | combination of electrolyte (ionic compound (1)) and remaining in electrolyte will be contained in electrolyte solution, the amount of the solvent can also be reduced in this process. In addition, since an aprotic solvent is used also as a solvent for the electrolyte solution of various electrical storage devices, even if it remains in an ionic compound (1) and electrolyte solution, the influence on the electrochemical property will be exerted. There are few things. In addition, after the synthesis of the ionic compound (1), the ionic compound (1) solution whose water content has been reduced through the step (i) and / or the step (ii) is used as it is for an electric storage device such as an electrolytic solution. Therefore, it is possible to obtain process advantages.

  Specific examples of the hydrocarbon solvent include aliphatic hydrocarbon solvents such as hexane and heptane; alicyclic hydrocarbon solvents such as cyclohexane and methylcyclohexane; aromatic hydrocarbons such as benzene. A hydrocarbon solvent may be used individually by 1 type, and may be used in combination of 2 or more type. Of the above exemplified solvents, cyclohexane is preferred.

  As the aprotic solvent, chain or cyclic carbonates, aliphatic carboxylic acid esters, carboxylic acid esters, and ethers exemplified as the medium of the electrolytic solution according to the present invention are more preferable. Are more preferred. Among chain or cyclic carbonates, dimethyl carbonate, ethyl methyl carbonate (methyl ethyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, methyl phenyl carbonate, ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), 2 , 3-dimethylethylene carbonate, butylene carbonate, vinylene carbonate, and 2-vinylethylene carbonate are preferred. An aprotic solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  The hydrocarbon solvent and aprotic solvent preferably have a low water content. The specific water content is preferably about 200 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less. A commercially available dehydrated solvent or the like can be used as the solvent having a low water content.

  As the ionic compound (1) to be mixed with these solvents, a solution of the ionic compound (1) containing the solvent used in the synthesis or other purification step may be used as it is, or a solid ionic compound (1) ) May be mixed with a hydrocarbon solvent and / or an aprotic solvent.

  The amount of the hydrocarbon solvent and / or the aprotic solvent used is 100 parts by mass to 1000000 parts by mass with respect to 100 parts by mass of the ionic compound (1) or the ionic compound (1) contained in the solution. More preferably, it is 100 mass parts-100,000 mass parts, More preferably, it is 100 mass parts -10000 mass parts. If the amount of the hydrocarbon solvent and / or aprotic solvent used is too small, the ionic compound (1) may precipitate and it may be difficult to remove moisture sufficiently. There are things to do.

  The mixed solution of the ionic compound (1) and the hydrocarbon solvent and / or the aprotic solvent may contain other solvents. The other solvent may be contained in the reaction solution, or may be mixed with the ionic compound (1) together with the hydrocarbon solvent and / or the aprotic solvent.

  The amount of the other solvent is not particularly limited, but in the process of performing the step (i) and / or the step (ii), it is preferable that the other solvent is distilled off. It is recommended that step (i) and / or step (ii) be performed in a state where the ionic compound (1) is dissolved in a hydrogen-based solvent and / or an aprotic solvent.

  Hereinafter, the steps (i) and (ii) will be described in order.

(I) Solvent distillation step In the present invention, the ionic compound (1) represented by the general formula (1) is mixed with a hydrocarbon solvent and / or an aprotic solvent, and then the mixed solution is used. The solvent is distilled off using a solvent distillation apparatus. In the solvent distillation step, the other solvent (such as a solvent used in the synthesis or purification step) and water contained in the mixed solution are distilled together with the hydrocarbon solvent and / or the aprotic solvent. is there. Solvent distillation operation that can be used in the present invention is not particularly limited, and is a simple distillation format, a format using a thin-film distiller, a fractional distillation format provided with a distillation column, and a distillate from the distillation column at a constant reflux ratio. Examples include a distillation system that is extracted while returning to the inside of the column, a distillation system in which the distillation column is held at total reflux, moisture is concentrated in the reflux tank, and components are extracted in a short time when the components in the reflux tank are stabilized. It is preferable that any apparatus used in the solvent distillation step is equipped with a known heating means.

  The heating temperature of the mixed solution is preferably 30 ° C. or more and 250 ° C. or less, more preferably 40 ° C. or more and 200 ° C. or less, and further preferably 50 ° C. or more and 150 ° C. or less. If the temperature is too low, it may be difficult to reduce moisture sufficiently. On the other hand, if the temperature is too high, the ionic compound (1) and the solvent may be decomposed. The solvent may be distilled off under reduced pressure. This is because the water content can be reduced efficiently even at low temperatures by controlling the degree of vacuum. The degree of reduced pressure is, for example, preferably 20 kPa or less, more preferably 10 kPa or less, and further preferably 5 kPa or less.

  The implementation time of the solvent distillation step is not particularly limited, and the solvent distillation operation may be performed until the predetermined solvent distillate amount or the concentration of the ionic compound (1) reaches a desired value. Thereby, the electrolyte solution containing the ionic compound (1) having a desired concentration can be obtained.

(Ii) Contacting step with molecular sieve In step (ii) according to the method of the present invention, the ionic compound represented by the general formula (1) and a hydrocarbon solvent and / or an aprotic solvent were mixed. Then, the contact process which makes this mixed solution contact with a molecular sieve is implemented.

Here, the molecular sieve, the general _{formula: M 2 / n O · Al} 2 O 3 · xSiO 2 · yH 2 O
(M is a metal cation such as an alkali metal or an alkaline earth metal, and n is a valence of M and represents 1 to 2). The shape of the molecular sieve is not particularly limited, and any of powder, sphere (bead), column (pellet type), trisive type in which a plurality of columns are combined, and the like can be used. The molecular sieve may contain a binder component as long as it does not affect the electrochemical properties of the ionic compound, if necessary. As the molecular sieve, a synthesized one may be used, or a commercially available one may be used. Furthermore, you may use it, after giving a baking processing as needed. Specific molecular sieves include molecular sieves having an average pore diameter of 3 to 10 mm (nominal value) based on 3A type, 4A type, 5A type, and 13X type. From the viewpoint of use in an electricity storage device, those having less elution components such as metal cations are preferred. Of these, those containing Li as the metal cation are preferably used because even if the metal cation derived from the molecular sieve remains after the contacting step, the performance of the electricity storage device is small. Moreover, in this invention, you may perform the process which replaces | exchanges the cation M contained in a molecular sieve for another metal cation as needed.

  The amount of molecular sieve used is not particularly limited, and can be appropriately determined according to the amount of water and the amount of free acid contained in the mixed solution of the ionic compound (1). The molecular sieve is preferably 0.01 parts by weight to 10,000 parts by weight, more preferably 0.05 parts by weight to 1000 parts by weight, and still more preferably 0.1 parts by weight to 100 parts by weight with respect to parts. . If the amount of molecular sieve used is too small, it may be difficult to sufficiently reduce the amount of water and the amount of free acid, and even if it is used in a large amount, it is difficult to see the effect of reducing the water content corresponding to the amount used.

  The contact mode between the mixed solution and the molecular sieve is not particularly limited as long as the ionic compound (1) and the molecular sieve are in contact with each other. However, in order to obtain good dehydration efficiency, the mixed solution in contact with the molecular sieve is renewed. Is preferred. Specific contact modes include, for example, a mode in which the mixed solution and the molecular sieve are mixed and stirred; a mode in which the ionic compound (1) solution is passed through the packed bed of the molecular sieve; and the like. In the embodiment in which the ionic compound solution is passed through the packed bed, if necessary, the same ionic compound (1) solution is repeatedly passed through the packed bed, thereby further increasing the content of moisture and the like in the solution. Can be reduced. Among the above embodiments, the embodiment in which the ionic compound (1) solution is passed through the packed bed of the molecular sieve is a solid-liquid process such as filtration, sedimentation separation, and centrifugal separation of the ionic compound (1) solution and the molecular sieve. It is not necessary to provide a separation step), the process is not complicated, and is particularly suitable for implementation at an actual operation level.

  The temperature at the time of bringing the mixed solution into contact with the molecular sieve is preferably -40 ° C to 200 ° C, more preferably -20 ° C to 100 ° C, and further preferably 0 ° C to 50 ° C. The contact time is not particularly limited, but is preferably 72 hours or less from the viewpoint of production efficiency, more preferably 24 hours or less, and even more preferably 6 hours or less.

  The used molecular sieve can be reused by heat treatment. The molecular sieve regeneration conditions include, for example, a method of heat treatment at 200 ° C. or higher under an inert gas flow such as nitrogen, a method of high temperature treatment after preheating at a lower temperature, and the like. It is not a thing.

  After the contact step with the molecular sieve, a solution containing the ionic compound (1) is obtained by performing solid-liquid separation as necessary.

  It is recommended that the above steps (i) and (ii) be carried out following the synthesis of the ionic compound and other purification steps. In addition, the water content reduction effect by the steps (i) and (ii) can be obtained even when the synthesis step is not performed. Therefore, when the solid ionic compound (1) contains water, it is obtained after being mixed with a hydrocarbon solvent and / or an aprotic solvent and dissolved or in a solution state. You may implement process (i) and (ii) about the solution of an ionic compound (1). In addition, although the reduction effect of moisture content is fully acquired by implementing either process (i) or (ii), you may implement combining these processes.

  By carrying out the above steps (i) and / or (ii), the free acid amount is reduced to the above range, or the free acid amount and the water content are reduced to a predetermined range (1) A solution containing is obtained. Since the solution containing the ionic compound (1) has a reduced water content, it can be used as an electrolytic solution for various electric storage devices as it is.

≪Usage≫
The electrolytic solution of the present invention has a reduced free acid and / or moisture content. Therefore, the electrolytic solution of the present invention is suitable for various electric storage devices such as electrolytic capacitors, electric double layer capacitors, solar cells, as well as batteries having charging and discharging mechanisms such as primary batteries, lithium (ion) secondary batteries, and fuel cells. Used for. Note that the structure of the electricity storage device is not particularly limited, and the electrolytic solution of the present invention can be applied to a known electricity storage device.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[NMR measurement]
¹ H-NMR and ¹⁹ F-NMR were measured using “Unity Plus-400” manufactured by Varian (internal standard substance: trifluoromethylbenzene, solvent: deuterated acetonitrile, integration number: 16 times). .

[Measurement of water content]
The sample solution obtained in the following experimental example and the amount of water contained in the organic solvent were measured using a Karl Fischer moisture measuring device “AQ-2100” manufactured by Hiranuma Sangyo Co., Ltd. A series of operations such as preparation of a measurement sample and measurement of water content were performed in a dry room (temperature: 25 ° C., dew point: −70 ° C. to −50 ° C.). The sample injection amount is 0.1 ml to 3 ml depending on the moisture content of the sample, and “Hydranal (registered trademark) Chromat AK” (manufactured by Sigma Aldrich) is used as the generation solution, while “Hydranal” is used as the counter electrode solution. "Nar (registered trademark) Chromat CG-K" (manufactured by Sigma Aldrich) was used. The sample was injected from the sample inlet using a syringe so as not to touch the outside air.

[Measurement of free acid content]
The total content of HF, H ₂ SO ₄ and FSO ₃ H was measured by neutralization titration.

Production Example 1 Synthesis of lithium bis (fluorosulfonyl) imide [fluorination step]
To a Pyrex (registered trademark) reaction vessel A equipped with a stirrer (internal volume 5 L), 900 g of butyl acetate was added under a nitrogen stream, and 100 g (467 mmol) of bis (chlorosulfonyl) imide was added thereto at room temperature (25 ° C.). It was dripped at.

  To the resulting bis (chlorosulfonyl) imide solution in butyl acetate, 50.5 g of zinc fluoride (491 mmol, 1.05 equivalents relative to bis (chlorosulfonyl) imide) was added in one portion at room temperature, and this completely dissolved. The mixture was stirred at room temperature for 6 hours.

[Cation Exchange Step 1-Synthesis of Ammonium Salt]
270 g (3964 mmol, 8.49 equivalents relative to bis (chlorosulfonyl) imide) of 25 mass% ammonia water was added to a Pyrex (registered trademark) reaction vessel B (internal volume: 1 L) equipped with a stirrer. The reaction solution in the reaction vessel A was added dropwise to the reaction vessel B at room temperature with stirring of aqueous ammonia. After completion of the addition of the reaction solution, stirring was stopped, and the aqueous layer containing by-products such as zinc chloride was removed from the reaction solution divided into two layers, an aqueous layer and a butyl acetate layer, and ammonium bis (fluoro A butyl acetate solution of sulfonyl) imide was obtained. ¹⁹ F-NMR (solvent: deuterated acetonitrile) was measured using the obtained organic layer as a sample. In the obtained chart, the amount of trifluoromethylbenzene added as an internal standard substance, and the comparison between the integrated value of the peak derived from this and the integrated value of the peak derived from the target product, was included in the organic layer. The crude yield of ammonium bis (fluorosulfonyl) imide was determined (378 mmol).
¹⁹ F-NMR (solvent: deuterated acetonitrile): δ 56.0

[Cation Exchange Step 2-Synthesis of Lithium Salt]
To the ammonium bis (fluorosulfonyl) imide contained in the obtained organic layer, 121 g of a 15% by mass lithium hydroxide aqueous solution (758 mmol as Li) was added so that the amount of lithium was 2 equivalents. Stir for minutes. Thereafter, the aqueous layer was removed from the reaction solution to obtain a butyl acetate solution of lithium bis (fluorosulfonyl) imide.

  Using the obtained organic layer as a sample, it was confirmed by ICP emission spectroscopic analysis that protons of fluorosulfonylimide were exchanged for lithium ions. Further, the organic layer was concentrated to dryness to obtain lithium bis (fluorosulfonyl) imide (yield: 63.5 g, yield: 73%).

Experimental Examples 1-4
In the flask, 18.71 g of lithium bis (fluorosulfonyl) imide and 101.21 g of an ethylene carbonate / ethyl methyl carbonate (30/70, volume ratio) solution were mixed and dissolved to obtain a sample solution. The obtained sample solution had a free acid amount of 25 ppm and a water content of 70.0 ppm.

  Add the sample solution and various molecular sieves (Union Showa Co., Ltd.) shown in Table 1 to a polypropylene screw tube with a capacity of 20 ml, and measure the water content of the sample solution at regular intervals while stirring with a shaker. And evaluated the transition. The results are shown in Table 2. Table 3 shows the amount of free acid contained in the sample solution before soaking (0 hour) and 24 hours after soaking.

Molecular sieve 1: Molecular sieve having sodium cation and calcium cation (model number “5A SDG”, average pore diameter (nominal value): 5 mm, spherical, made by Union Showa Co., Ltd.)
Molecular sieve 2: Molecular sieve having lithium cation and sodium cation (model number “Li-X SDG”, average pore size (nominal value): 10 mm, spherical, made by Union Showa Co., Ltd.)
Molecular sieve 3: Molecular sieve having sodium cation (model number “4A SDG”, average pore diameter (nominal value): 4 mm, spherical, made by Union Showa Co., Ltd.)
Molecular sieve 4: Molecular sieve having sodium cation and calcium cation (model number “3A SDG”, average pore size (nominal value): 3 mm, spherical, made by Union Showa Co., Ltd.)

From Tables 2-3, it can be seen that the amount of water and the amount of free acid in the sample solution can be reduced by contact with the molecular sieve. As confirmed by ¹⁹ F-NMR, no change was observed in the concentration of lithium bis (fluorosulfonyl) imide in the sample solution before and after contact with the molecular sieve.

Experimental Example 5
To the flask, 6.25 g of lithium bis (fluorosulfonyl) imide was added, and 33.74 g of an ethylene carbonate / ethyl methyl carbonate (30/70, volume ratio) solution was added and dissolved. The water content of the solution was 72.5 ppm, and the free acid content was 35 ppm. To the resulting solution, 11.20 g of cyclohexane was added and heated to 50 ° C. under reduced pressure to distill off the cyclohexane to obtain a sample solution. The sample solution obtained at this time had a water content of 8.0 ppm and a free acid content of 15 ppm. ^As confirmed by ¹⁹ F-NMR, no change was observed in the concentration of lithium bis (fluorosulfonyl) imide in the sample solution before and after heating.

Experimental Examples 6-10
The sample solutions obtained in Experimental Examples 1 to 5 were each sealed in a screw tube with a capacity of 20 ml to prevent moisture from entering from the outside. The screw tube containing each electrolyte solution was placed in an aluminum bag and shielded from light, and stored for 2 months in an environment at a temperature of 25 ° C., and the changes over time in the amount of water and the amount of free acid contained in the sample solution were evaluated. . The results are shown in Table 4. Note that no change in appearance was observed in the sample solution after storage for 2 months, and it was a colorless and transparent liquid.

Experimental Example 11
Except for using the sample solution (free acid amount: 25 ppm, water content: 70.0 ppm) before the contacting step with the molecular sieve prepared in Experimental Example 1, the same procedure as in Experimental Examples 6 to 10 was performed for 2 months. The sample was stored, and the change over time in the amount of water and the amount of free acid contained in the sample solution was evaluated. The results are shown in Table 4. Note that no change in appearance was observed in the sample solution after storage for 2 months, and it was a colorless and transparent liquid.

In Experimental Examples 6 to 10, both the amount of free acid and the amount of water were almost unchanged before and after storage for 2 months. On the other hand, in Experimental Example 11 in which the contact process with the molecular sieve and the solvent distillation process were not performed, the free acid amount was increased to 50 ppm. From this result, it was found that the electrolytic solution of the present invention was excellent in storage stability. Further, as confirmed by ¹⁹ F-NMR, no change was observed in the concentration of lithium bis (fluorosulfonyl) imide in the sample solution before and after storage.

Production Example 2 Synthesis of Potassium Bis (fluorosulfonyl) imide [Cation Exchange Step 2-Synthesis of Potassium Salt]
In the same manner as in Production Example 1, cation exchange step 2 was performed using a butyl acetate solution of ammonium bis (fluorosulfonyl) imide obtained by performing fluorination step and cation exchange step 1 (synthesis of ammonium salt). It was. To the ammonium bis (fluorosulfonyl) imide contained in the obtained organic layer, 283 g of a 15 mass% potassium hydroxide aqueous solution (758 mmol as K) was added so that the amount of potassium was 2 equivalents. Stir for minutes. Thereafter, the aqueous layer was removed from the reaction solution to obtain a butyl acetate solution of potassium bis (fluorosulfonyl) imide.

  Using the obtained organic layer as a sample, it was confirmed by ICP emission spectroscopic analysis that protons of fluorosulfonylimide were exchanged for potassium ions. Further, the organic layer was concentrated to dryness to obtain potassium bis (fluorosulfonyl) imide (yield: 74 g).

Experimental Examples 12-15
In the flask, 21.9 g of potassium bis (fluorosulfonyl) imide and 100.1 g of an ethylene carbonate / ethyl methyl carbonate (30/70, volume ratio) solution were mixed and dissolved to obtain a sample solution. The obtained sample solution had a free acid amount of 35 ppm and a water content of 53 ppm.

  Add the sample solution and various molecular sieves (made by Union Showa Co., Ltd.) shown in Table 5 to a polypropylene screw tube with a capacity of 20 ml, and measure the water content of the sample solution at regular intervals while stirring with a shaker. And evaluated the transition. The results are shown in Table 6. Table 7 shows the amount of free acid contained in the sample solution before soaking (0 hour) and 24 hours after soaking. In addition, the same molecular sieve as Experimental Examples 1-4 was used.

From Tables 6 to 7, it can be seen that the amount of water and the amount of free acid in the sample solution can be reduced by contact with the molecular sieve. Further, as confirmed by ¹⁹ F-NMR, no change was observed in the potassium bis (fluorosulfonyl) imide concentration in the sample solution before and after contact with the molecular sieve.

Experimental Example 16
To the flask, 7.3 g of potassium bis (fluorosulfonyl) imide was added, and 33.5 g of an ethylene carbonate / ethyl methyl carbonate (30/70, volume ratio) solution was added and dissolved. The water content of the solution was 52 ppm and the free acid content was 35 ppm. To the resulting solution was added 10.5 g of cyclohexane, and the mixture was heated to 50 ° C. under reduced pressure to distill off the cyclohexane to obtain a sample solution. The sample solution obtained at this time had a water content of 8.0 ppm and a free acid content of 9 ppm. ^As confirmed by ¹⁹ F-NMR, no change was observed in the potassium bis (fluorosulfonyl) imide concentration in the sample solution before and after heating.

Experimental Examples 17-21
The sample solutions obtained in Experimental Examples 12 to 16 were each sealed in a 20-ml screw tube to prevent moisture from entering from the outside. The screw tube containing each electrolyte solution was placed in an aluminum bag and shielded from light, and stored for 2 months in an environment at a temperature of 25 ° C., and the changes over time in the amount of water and the amount of free acid contained in the sample solution were evaluated. . The results are shown in Table 8. Note that no change in appearance was observed in the sample solution after storage for 2 months, and it was a colorless and transparent liquid.

Experimental Example 22
Except that the sample solution before the contact step with the molecular sieve prepared in Experimental Example 12 (free acid amount: 35 ppm, water content: 53 ppm) was used, the sample solution was prepared in the same manner as in Experimental Examples 17 to 21. The samples were stored for months, and the changes over time in the amount of water and the amount of free acid contained in the sample solution were evaluated. The results are shown in Table 8. Note that no change in appearance was observed in the sample solution after storage for 2 months, and it was a colorless and transparent liquid.

In Experimental Examples 17 to 21, both the amount of free acid and the amount of water were almost unchanged before and after storage for 2 months. On the other hand, in Experimental Example 22 in which the contact process with the molecular sieve and the solvent distillation process were not performed, the free acid amount was increased to 55 ppm. From this result, it was found that the electrolytic solution of the present invention was excellent in storage stability. Further, as confirmed by ¹⁹ F-NMR, no change was observed in the potassium bis (fluorosulfonyl) imide concentration in the sample solution before and after storage.

Production Example 3 Synthesis of Sodium Bis (fluorosulfonyl) imide [Cation Exchange Step 2-Synthesis of Sodium Salt]
In the same manner as in Production Example 1, cation exchange step 2 was performed using a butyl acetate solution of ammonium bis (fluorosulfonyl) imide obtained by performing fluorination step and cation exchange step 1 (synthesis of ammonium salt). It was. To the ammonium bis (fluorosulfonyl) imide contained in the obtained organic layer, 202 g of a 15% by mass aqueous sodium hydroxide solution (758 mmol as Na) was added so that the amount of sodium was 2 equivalents. Stir for minutes. Thereafter, the aqueous layer was removed from the reaction solution to obtain a butyl acetate solution of sodium bis (fluorosulfonyl) imide.

  Using the obtained organic layer as a sample, it was confirmed by ICP emission spectroscopic analysis that protons of fluorosulfonylimide were exchanged with sodium ions. Further, the organic layer was concentrated to dryness to obtain sodium bis (fluorosulfonyl) imide (yield: 69 g).

Experimental Examples 23-26
In the flask, 20.3 g of sodium bis (fluorosulfonyl) imide and 99.5 g of an ethylene carbonate / ethyl methyl carbonate (30/70, volume ratio) solution were mixed and dissolved to obtain a sample solution. The obtained sample solution had a free acid amount of 30 ppm and a water content of 55 ppm.

  Add the sample solution and various molecular sieves (Union Showa Co., Ltd.) shown in Table 9 to a polypropylene screw tube with a capacity of 20 ml, and measure the water content of the sample solution at regular intervals while stirring with a shaker. And evaluated the transition. The results are shown in Table 10. Table 11 shows the amount of free acid contained in the sample solution before soaking (0 hour) and 24 hours after soaking. In addition, the same molecular sieve as Experimental Examples 1-4 was used.

From Tables 10 to 11, it can be seen that the amount of water and the amount of free acid in the sample solution can be reduced by contact with the molecular sieve. As confirmed by ¹⁹ F-NMR, no change was observed in the concentration of sodium bis (fluorosulfonyl) imide in the sample solution before and after contact with the molecular sieve.

Experimental Example 27
To the flask, 6.8 g of sodium bis (fluorosulfonyl) imide was added, and 33.2 g of an ethylene carbonate / ethyl methyl carbonate (30/70, volume ratio) solution was added and dissolved. The water content of the solution was 53 ppm, and the free acid content was 30 ppm. To the resulting solution was added 10.8 g of cyclohexane, and the mixture was heated to 50 ° C. under reduced pressure to distill off the cyclohexane to obtain a sample solution. The sample solution obtained at this time had a water content of 7.8 ppm and a free acid content of 15 ppm. ^As confirmed by ¹⁹ F-NMR, no change was observed in the concentration of sodium bis (fluorosulfonyl) imide in the sample solution before and after heating.

Experimental Examples 28-32
The sample solutions obtained in Experimental Examples 23 to 27 were each sealed in a screw tube having a capacity of 20 ml to prevent moisture from entering from the outside. The screw tube containing each electrolyte solution was placed in an aluminum bag and shielded from light, and stored for 2 months in an environment at a temperature of 25 ° C., and the changes over time in the amount of water and the amount of free acid contained in the sample solution were evaluated. . The results are shown in Table 12. Note that no change in appearance was observed in the sample solution after storage for 2 months, and it was a colorless and transparent liquid.

Experimental Example 33
Stored for 2 months in the same manner as in Experimental Examples 28 to 32, except that the sample solution before the contacting step with the molecular sieve prepared in Experimental Example 23 (free acid amount: 30 ppm, moisture content: 55 ppm) was used. The time course of the amount of water and the amount of free acid contained in the sample solution was evaluated. The results are shown in Table 12. Note that no change in appearance was observed in the sample solution after storage for 2 months, and it was a colorless and transparent liquid.

In Experimental Examples 28 to 32, both the amount of free acid and the amount of water were almost unchanged before and after storage for 2 months. On the other hand, in Experimental Example 33 in which the contacting step with the molecular sieve and the solvent distillation step were not performed, the amount of free acid was increased to 44 ppm. From this result, it was found that the electrolytic solution of the present invention was excellent in storage stability. Further, as confirmed by ¹⁹ F-NMR, no change was observed in the concentration of sodium bis (fluorosulfonyl) imide in the sample solution before and after storage.

Production Example 4 Synthesis of Ethylmethylimidazolium Bis (fluorosulfonyl) imide [Cation Exchange Step 3-Synthesis of Ethylmethylimidazolium Salt]
Cation exchange using a butyl acetate solution of lithium bis (fluorosulfonyl) imide obtained by performing fluorination step, cation exchange step 1 (synthesis of ammonium salt) cation exchange step 2 in the same manner as in Production Example 1 Step 3 was performed. To the lithium bis (fluorosulfonyl) imide contained in the obtained organic layer, 453 g of ethyl methyl imidazolium bromide aqueous solution (ethyl methyl imidazole) was added so that the amount of ethyl methyl imidazolium was 1.05 equivalent. 356 mmol) was added as a lithium bromide and stirred at room temperature for 10 minutes. Thereafter, the aqueous layer was removed from the reaction solution to obtain a butyl acetate solution of ethylmethylimidazolium bis (fluorosulfonyl) imide.

Using the obtained organic layer as a sample, ¹ H-NMR confirmed a peak derived from ethylmethylimidazolium, and confirmed that the cation exchange reaction was completed. In addition, the organic layer was concentrated to dryness to obtain ethylmethylimidazolium bis (fluorosulfonyl) imide (yield: 94 g).

Experimental Examples 34 to 37
In the flask, 29.1 g of ethyl methylimidazolium bis (fluorosulfonyl) imide and 98.6 g of ethylene carbonate / ethyl methyl carbonate (30/70, volume ratio) solution were mixed and dissolved to obtain a sample solution. . The obtained sample solution had a free acid amount of 28 ppm and a water content of 51 ppm.

  The sample solution and various molecular sieves (Union Showa Co., Ltd.) shown in Table 13 are added to a polypropylene screw tube with a capacity of 20 ml, and the moisture content of the sample solution is measured at regular intervals while stirring with a shaker. And evaluated the transition. The results are shown in Table 14. Table 15 shows the amount of free acid contained in the sample solution before soaking (0 hour) and 24 hours after soaking. In addition, the same molecular sieve as Experimental Examples 1-4 was used.

From Tables 14 to 15, it can be seen that the amount of water and the amount of free acid in the sample solution can be reduced by contact with the molecular sieve. As confirmed by ¹⁹ F-NMR, no change was observed in the concentration of ethylmethylimidazolium bis (fluorosulfonyl) imide in the sample solution before and after contact with the molecular sieve.

Experimental Example 38
To the flask, 9.7 g of ethylmethylimidazolium bis (fluorosulfonyl) imide was added, and 32.7 g of an ethylene carbonate / ethyl methyl carbonate (30/70, volume ratio) solution was added and dissolved. The water content of the solution was 54 ppm, and the free acid content was 28 ppm. To the resulting solution was added 11.0 g of cyclohexane, and the mixture was heated to 50 ° C. under reduced pressure to distill off the cyclohexane to obtain a sample solution. The sample solution obtained at this time had a water content of 7.8 ppm and a free acid content of 13 ppm. ^As confirmed by ¹⁹ F-NMR, no change was observed in the concentration of ethylmethylimidazolium bis (fluorosulfonyl) imide in the sample solution before and after heating.

Experimental Examples 39-43
The sample solutions obtained in Experimental Examples 34 to 38 were each sealed in a 20-ml screw tube to prevent moisture from entering from the outside. The screw tube containing each electrolyte solution was placed in an aluminum bag and shielded from light, and stored for 2 months in an environment at a temperature of 25 ° C., and the changes over time in the amount of water and the amount of free acid contained in the sample solution were evaluated. . The results are shown in Table 16. Note that no change in appearance was observed in the sample solution after storage for 2 months, and it was a colorless and transparent liquid.

Experimental Example 44
Stored for 2 months in the same manner as in Experimental Examples 39 to 43, except that the sample solution before the contact step with the molecular sieve prepared in Experimental Example 34 (free acid amount: 28 ppm, water content: 51 ppm) was used. The time course of the amount of water and the amount of free acid contained in the sample solution was evaluated. The results are shown in Table 16. Note that no change in appearance was observed in the sample solution after storage for 2 months, and it was a colorless and transparent liquid.

In Experimental Examples 39 to 43, both the amount of free acid and the amount of water were almost unchanged before and after storage for 2 months. On the other hand, in Experimental Example 44 that did not undergo the contact step with the molecular sieve or the solvent distillation step, the amount of free acid was increased to 40 ppm. From this result, it was found that the electrolytic solution of the present invention was excellent in storage stability. Further, as confirmed by ¹⁹ F-NMR, no change was observed in the concentration of ethylmethylimidazolium bis (fluorosulfonyl) imide in the sample solution before and after storage.

  The electrolytic solution of the present invention is excellent in storage stability, and it is difficult for the free acid and moisture to increase with time. Therefore, if the electrolytic solution of the present invention is used for an electricity storage device, it is considered that a high-performance electricity storage device in which performance deterioration with time does not easily occur. Moreover, according to the method of the present invention, it is possible to produce an electrolytic solution in which the free acid amount and the water amount are hardly increased over time.

Claims (13)

A method for producing an electrolytic solution comprising an ionic compound represented by the following general formula (1) and a free acid, wherein the content of the free acid is less than 25 ppm (by mass),
Electrolysis characterized by including a step of distilling off part or all of a solvent after mixing an ionic compound represented by the following general formula (1) with a hydrocarbon solvent and / or an aprotic solvent Liquid manufacturing method.
(XSO ₂ ) (X′SO ₂ ) N ⁻ Y ⁺ (1)
(In the formula, X and X ′ represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group, at least one of X and X ′ is a fluorine atom, and Y ⁺ represents an alkali metal cation or an onium cation. Represents.)   The method for producing an electrolytic solution according to claim 1, wherein the step of distilling off part or all of the solvent is performed at a heating temperature of 30 ° C. or more and 250 ° C. or less and a degree of vacuum of 20 kPa or less. The method for producing an electrolytic solution according to claim 1 or 2, wherein the free acid is one or more free acids selected from the group consisting of HF, H ₂ SO ₄ and FSO ₃ H.   The method for producing an electrolytic solution according to any one of claims 1 to 3, wherein the amount of water in the electrolytic solution is 50 ppm or less (mass basis). In the said General formula (1), X and X 'are a fluorine atom, Y ^<+> is a lithium cation, The manufacturing method of the electrolyte solution in any one of Claims 1-4.   The method for producing an electrolytic solution according to claim 1, wherein a part of the solvent is distilled off.   The method for producing an electrolytic solution according to claim 1, wherein the electrolytic solution further contains a medium.   The method for producing an electrolytic solution according to claim 7, wherein the medium is a non-aqueous solvent.   The non-aqueous solvent comprises an ether non-aqueous solvent, a chain carbonate non-aqueous solvent, a cyclic carbonate non-aqueous solvent, an aliphatic carboxylate non-aqueous solvent and an aromatic carboxylate non-aqueous solvent. The method for producing an electrolytic solution according to claim 8, wherein the electrolytic solution is one or more selected from the group. The method for producing an electrolytic solution according to any one of claims 7 to 9, wherein the amount of the medium used is 50 parts by mass to 99.9 parts by mass with respect to 100 parts by mass of the total amount of the electrolyte and the medium. The electrolyte solution may contain an electrolyte in addition to the ionic compound (1), and the total amount of the ionic compound (1) and the other electrolyte in the electrolyte is 0.1% by mass or more. The manufacturing method of the electrolyte solution in any one of -10.   The aprotic solvent is selected from the group consisting of a cyclic carbonate aprotic solvent, an aliphatic carboxylic acid ester aprotic solvent, a carboxylic acid ester aprotic solvent, and an ether aprotic solvent. It is a seed | species or 2 or more types, The manufacturing method of the electrolyte solution in any one of Claims 1-11.   The amount of the hydrocarbon solvent and / or aprotic solvent used is 100 parts by mass to 1000000 parts by mass with respect to 100 parts by mass of the ionic compound (1). Manufacturing method of electrolyte solution.