JP2018052760A - Process for producing electrolyte material comprising alkali metal salt of bis(fluorosulfonyl)imide and organic solvent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing an alkali metal salt of bis(fluorosulfonyl)imide with decreased impurities generated in the production process.SOLUTION: The present invention provides a process for producing an electrolyte material comprising an alkali metal salt of bis(fluorosulfonyl)imide and an organic solvent (A). The process comprises: a cation exchange step in which cation exchange is performed in a solution containing an organic solvent (B), which differs from the organic solvent (A), an ammonium salt of bis(fluorosulfonyl)imide and an alkali metal compound to obtain an alkali metal salt of bis(fluorosulfonyl)imide; a step of alkali-washing and/or water-washing the obtained reaction solution; and a step that follows the washing step and is performed to distill away the organic solvent (B) and water in the presence of the organic solvent (A) under reduced pressure and/or with heating. The alkali metal compound is added in the cation exchange step in an amount of 0.90 molar equivalent or greater and 1.24 molar equivalent or less with respect to 1 mol of the ammonium salt of the bis(fluorosulfonyl)imide to produce the alkali metal salt of bis(fluorosulfonyl)imide. The alkali metal salt of bis(fluorosulfonyl)imide and the organic solvent (A) constitute the electrolyte material.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an electrolyte material containing an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent, and more specifically, an alkali metal salt of fluorosulfonylimide having reduced impurities and an organic material for a lithium ion secondary battery. The present invention relates to a method for producing an electrolyte material containing a solvent.

  The alkali metal salt of fluorosulfonylimide has attracted attention as a compound useful as an additive to electrolytes and electrolytes of fuel cells, and various production methods have been proposed.

  Improvements have been made in the method for producing an alkali metal salt of fluorosulfonylimide, and various techniques have been proposed. For example, Patent Document 1 discloses a technique for improving the cation exchange reaction efficiency in a method for producing a fluorine-containing sulfonylimide alkali metal salt or a fluorine-containing sulfonylimide ammonium salt.

  Patent Document 2 discloses a method for producing a high-purity disulfonylamine alkali metal salt with a low temperature history and at a low cost.

  Patent Document 3 discloses a method for producing an alkali metal salt of fluorosulfonylimide that can easily remove a reaction solvent from a reaction solution.

International Publication No. 2012/118063 Pamphlet International Publication No. 2014/148258 Pamphlet JP 2014-201453 A

  In examining the quality of the alkali metal salt of bis (fluorosulfonyl) imide, the inventors of the present invention have characteristics of products that require impurities from the production process of the alkali metal salt of bis (fluorosulfonyl) imide, For example, it has been found that this is a cause of deterioration of battery characteristics of a lithium ion secondary battery.

  The present invention has been made paying attention to the above-described circumstances, and an object of the present invention is to provide a production method capable of reducing impurities generated in the production process of an alkali metal salt of bis (fluorosulfonyl) imide. is there.

  The production method of the present invention that has solved the above problems is a method for producing an electrolyte material containing an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent (A), and is an organic material different from the organic solvent (A). A cation exchange step for obtaining an alkali metal salt of bis (fluorosulfonyl) imide by cation exchange in a solution containing a solvent (B), an ammonium salt of bis (fluorosulfonyl) imide, and an alkali metal compound was obtained. A step of washing the reaction solution with alkali and / or water, and a step of distilling off the organic solvent (B) and water by washing under reduced pressure and / or heating in the presence of the organic solvent (A) after the washing. The amount of the alkali metal compound added in the cation exchange step is 1 mol of the ammonium salt of the bis (fluorosulfonyl) imide. .90 molar equivalent or more, has the gist to containing 1.24 molar equivalent or less is bis alkali metal salt of (fluorosulfonyl) imide and an organic solvent (A).

  In the production method of the present invention, the alkali metal compound is added as a solid, the water content of the reaction solution after the cation exchange step is 4.5% by mass or less, the reaction solution after the cation exchange step Is subjected to a step of distilling ammonia from the reaction solution under reduced pressure and / or heating in the presence of the organic solvent (B), and then the alkali washing and / or the water washing, It is a preferred embodiment that the solvent (B) is an ester solvent and that the organic solvent (A) is a carbonate solvent.

  According to the production method of the present invention, impurities generated during the production of the alkali metal salt of bis (fluorosulfonyl) imide, specifically acetamide, ammonium, and acetic acid (hereinafter collectively referred to as “impurities”). Can be reduced). Therefore, when an electrolytic solution material containing an alkali metal salt of bis (fluorosulfonyl) imide obtained by the production method of the present invention and an organic solvent is used, deterioration of battery characteristics due to impurities can be suppressed, and the battery is superior to conventional batteries. Characteristics are obtained.

  As a result of the inventors' study on the improvement of the characteristics of the lithium ion secondary battery, the initial charge / discharge efficiency, the initial rate characteristics, and the cycle are attributed to impurities generated in the production process of the alkali metal salt of bis (fluorosulfonyl) imide. It was found that the capacity maintenance ratio (hereinafter, these may be collectively referred to as “battery characteristics”) is inhibited. And in the initial stage of the production process of the alkali metal salt of bis (fluorosulfonyl) imide, specifically, in the cation exchange process, if the amount of the alkali metal compound added is reduced as compared with the prior art, the alkalinity is low, so the decomposition of the ester solvent The present inventors have found that the production of the above-described impurities that deteriorate battery characteristics, such as the production of acetic acid and the production of acetamide, which is a dehydration condensate of acetic acid and ammonia, can be suppressed.

  Hereinafter, a method for synthesizing an alkali metal salt of bis (fluorosulfonyl) imide will be described.

The synthesis method of the present invention includes the following steps.
(I) A step of obtaining an alkali metal salt of bis (fluorosulfonyl) imide by cation exchange in a solution containing an organic solvent (B), an ammonium salt of bis (fluorosulfonyl) imide, and an alkali metal compound (hereinafter referred to as “a”). , "Cation exchange process")
(II) A step of washing the obtained reaction solution with alkali and / or water (hereinafter, “washing step”)

  In the present invention, as required, (i) a step of distilling ammonia from the reaction solution by reducing pressure and / or heating the reaction solution obtained in the cation exchange step in the presence of the organic solvent (B) (hereinafter referred to as “ The cleaning step may be performed after performing the “ammonia distillation step”.

  Furthermore, in the present invention, as a method for producing an electrolytic solution material containing an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent (A), (III) an alkali metal of bis (fluorosulfonyl) imide obtained through the above steps A step of distilling off the organic solvent (B) and water by reducing and / or heating the reaction solution containing the salt and the organic solvent (B) in the presence of the organic solvent (A) (hereinafter, “concentration step”) Is included).

(I) Cation Exchange Step In the present invention, an ammonium salt of bis (fluorosulfonyl) imide ((FSO ₂ ) ₂ N · NH ₄ ) is used as a starting material (hereinafter sometimes referred to as “compound (1)”). Compound (1) can be synthesized, for example, by adding a fluoride such as NH ₄ F, NH ₄ F · HF, NH ₄ F · 2HF to bis (chlorosulfonyl) imide, but is not limited thereto. These may be obtained by various known production methods, or may be commercially available products.

Cation exchange can be performed by reacting compound (1) with an alkali metal compound containing a desired cation (Li, Na, K, Rb, Cs). Examples of the alkali metal compound to be reacted include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH; carbonic acid such as Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , and Cs ₂ CO _3. Salts; carbonates such as LiHCO ₃ , NaHCO ₃ , KHCO ₃ , RbHCO ₃ , CsHCO ₃ ; chlorides such as LiCl, NaCl, KCl, RbCl, CsCl; fluorides such as LiF, NaF, KF, RbF, CsF; Alkoxide compounds such as CH ₃ OLi and EtOLi; alkyllithium compounds such as EtLi, BuLi, and t-BuLi; and the like (Et represents an ethyl group and Bu represents a butyl group). Among these, a compound containing lithium, sodium or potassium as an alkali metal is preferable. Specifically, LiOH, NaOH, KOH, Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , LiCl, NaCl, KCl, LiF NaF and KF are preferable, more preferably LiOH, NaOH, KOH, Li ₂ CO ₃ , Na ₂ CO ₃ and K ₂ CO ₃ , still more preferably LiOH, NaOH and KOH, and these compounds are hydroxides. It is preferable that

  In the present invention, the addition method of the alkali metal compound may be either an alkali metal compound aqueous solution or a solid alkali metal compound, but if a solid alkali metal compound is used, the water content in the reaction solution after the cation exchange step can be reduced. The yield of alkali metal salt of bis (fluorosulfonyl) imide can be improved as compared with the case where it is added as an aqueous solution. This is particularly desirable because the amount of ammonia dissolved in the reaction solution can be reduced by reducing the water content of the reaction solution. The solid alkali metal compound is preferably a hydrate of the above alkali metal compound. The solid shape is not particularly limited, such as flakes, powders, and beads.

  In this invention, by making the addition amount of an alkali metal compound into a predetermined range, the alkalinity of the reaction solution after a lithium exchange process can be suppressed low, and decomposition | disassembly of an organic solvent (B) can be suppressed. As a result, the formation of acetic acid, which is a decomposition product of the organic solvent (B), can be suppressed, and the formation of acetamide, which is a dehydration condensate of acetic acid and ammonia, can also be suppressed. Also, the smaller the amount of solid alkali metal compound added, the smaller the amount of water contained in the reaction solution after the cation exchange step compared to, for example, the conventional amount of 1.3 equivalents, and the alkalinity is also low. Since it is small, reverse reaction etc. are suppressed and generation | occurrence | production of the impurity which reduces battery characteristics can be suppressed. Therefore, by using the electrolytic solution material of the present invention, the amount of impurities in the non-aqueous electrolytic solution used for a lithium ion secondary battery or the like can be reduced, so that deterioration of battery characteristics can be suppressed as compared with the conventional case. The addition amount of the alkali metal compound is preferably 0.90 molar equivalent or more, more preferably 1.00 molar equivalent or more, and further preferably 1.01 molar equivalent, relative to 1 mole of the ammonium salt of bis (fluorosulfonyl) imide. It is above, Preferably it is 1.24 molar equivalent or less, More preferably, it is 1.20 molar equivalent or less, More preferably, it is 1.15 molar equivalent or less. When there is too much usage-amount of an alkali metal compound, decomposition | disassembly of an organic solvent (B) will occur easily. Even when a solid alkali metal is used, if the amount used is large, the amount of water contained in the reaction solution increases, and reverse reactions and the like are likely to occur. On the other hand, if the amount of alkali metal compound used is too small, an ammonium salt of bis (fluorosulfonyl) imide may remain. In the present invention, “equivalents” are all stoichiometric amounts.

  The compound (1) and the alkali metal compound are subjected to a cation exchange reaction in a solution containing an organic solvent (B) (an organic solvent different from the organic solvent (A)). As the organic solvent (B) that can be used in the cation exchange step, an aprotic solvent is preferably used. Specific examples of the aprotic solvent include ester solvents such as methyl acetate, ethyl acetate, isopropyl acetate, and butyl acetate. These solvents may be used alone or in combination of two or more. In particular, ethyl acetate, isopropyl acetate, and butyl acetate are preferable from the viewpoint of allowing the cation exchange reaction to proceed smoothly.

  The temperature of the solution at the time of cation exchange is not particularly limited, but if the temperature is too high, the organic solvent (B) may decompose to produce impurities such as acetic acid, while if the temperature is too low, the viscosity of the reaction solution May increase and handling may be complicated. Therefore, the temperature of the solution is preferably 40 ° C. or lower, more preferably normal temperature (25 ° C.) or lower, preferably −2 ° C. or higher, more preferably 0 ° C. or higher.

  In the present invention, it is desirable to distill off at least part of the ammonia produced as a by-product in the cation exchange reaction. Generation of impurities such as acetamide can be suppressed by distilling off ammonia. Further, it is preferable to distill off water together with ammonia because the amount of ammonia and the amount of water contained in the reaction solution after the cation exchange step can be further reduced. Since ammonia is produced as ammonia gas, it can be easily distilled off in the cation exchange step. Moreover, the temperature, pressure, etc. which water does not circulate in a cation exchange process may be employ | adopted for water. For example, the temperature is 40 ° C. or lower, preferably normal temperature or lower, preferably −2 ° C. or higher, more preferably 0 ° C. or higher, and the pressure is controlled so that water does not circulate within this temperature range (for example, 600 hPa or higher, 800 hPa or higher). The following is preferable.

Reducing the water content of the reaction solution after the cation exchange step can reduce the ammonium produced by suppressing the reverse reaction of water and ammonia (for example, LiFSI + NH ₃ + H ₂ O → NH ₄ FSI + LiOH) and is incorporated into the reaction solution. The amount of ammonia can be reduced. The water content of the reaction solution after the cation exchange step is preferably 4.5% by mass or less, more preferably 4.3% by mass or less, and still more preferably 4.0% by mass or less with respect to the total mass. From the viewpoint of reducing moisture, the cation exchange step is desirably performed in a low-humidity environment such as a dry room (temperature 25 ° C.) having a dew point of −40 ° C. or lower.

  The ammonia content in the reaction solution after the cation exchange step is preferably 3000 ppm by mass or less, more preferably 2500 ppm by mass or less, and still more preferably 2000 ppm by mass or less with respect to the total mass. In the present invention, various measuring methods such as the amount of water, the amount of impurities, the amount of alkali metal salt of bis (fluorosulfonyl) imide are based on the methods described in the examples (hereinafter the same).

  In the present invention, after the cation exchange step and before the washing step, (i) an ammonia distilling step may be performed as necessary.

(I) Ammonia distillation step By performing the ammonia distillation step, the ammonia content can be further reduced from the reaction solution. In addition, it is preferable to distill off at least a part of water and the organic solvent (B) together with ammonia because it is effective in suppressing the generation of impurities due to reverse reaction.

  The method for distilling off ammonia is not particularly limited, but it is preferable to control the temperature to be suitable for distilling off ammonia from the reaction solution under reduced pressure. By carrying out under reduced pressure, ammonia can be distilled off even at a low temperature. Therefore, it is preferably 50 hPa or less, more preferably 20 hPa or less, preferably 3 hPa or more, more preferably 5 hPa or more. If the temperature of the reaction solution becomes too high, acetamide due to the dehydration condensation reaction may increase. Therefore, the temperature of the reaction solution is preferably 60 ° C. or less, more preferably 55 ° C. or less, and further preferably 45 ° C. or less. The lower limit is not particularly limited, and may be room temperature (25 ° C.).

  By distilling off ammonia, the amount of impurities such as acetamide and ammonium contained in the electrolyte material can be reduced. Accordingly, the ammonia amount may be reduced by performing the ammonia distillation step a plurality of times. The ammonia content contained in the reaction solution after the distillation is preferably 500 ppm by mass or less, more preferably 300 ppm by mass or less, still more preferably 200 ppm by mass or less based on the total mass.

  In the present invention, after the cation exchange step or after the ammonia distilling step, at least one of (II-1) alkali washing step and (II-2) water washing step is performed. In addition, when performing both, it is an order of an alkali washing process and a water washing process.

(II-1) Alkali washing step By performing the alkali washing step, impurities such as water-soluble impurities contained in the compound (1) from the reaction solution and water-soluble by-products during cation exchange can be reduced. The alkali cleaning step is not limited as long as the reaction solution and the alkaline aqueous solution are in contact with each other. For example, an aspect in which the reaction solution is added to the alkaline aqueous solution and brought into contact with each other, and the reaction solution and the alkaline aqueous solution are simultaneously added to the reaction solution. For example, the contact may be made. As the alkaline aqueous solution, an aqueous solution of a basic substance may be used, and the basic substance is preferably the same alkali metal compound as the alkali metal compound used in the cation exchange step.

  In order to sufficiently remove impurities while suppressing the generation of acetic acid and acetamide, the alkaline aqueous solution is carried out in such a manner that the alkali washing step is performed with respect to 1 mol of the alkali metal salt of bis (fluorosulfonyl) imide. Contact with an alkali metal aqueous solution adjusted so that the amount is preferably 0.05 equivalents or more, more preferably 0.1 equivalents or more, preferably 1 equivalent or less, more preferably 0.6 equivalents or less. Is desirable. When the alkalinity increases, the organic solvent (B) may be decomposed to increase impurities such as acetamide and acetic acid. If the amount of the alkali metal is too small, the yield of the alkali metal salt of bis (fluorosulfonyl) imide may be lowered.

  The temperature of the reaction solution when contacting with the alkaline aqueous solution is not particularly limited, but is preferably 25 ° C. or less, more preferably 5 ° C. or less, and preferably 0 ° C. or more in order to suppress the generation of acetic acid and acetamide. .

  The contact time between the reaction solution and the alkaline aqueous solution is not particularly limited as long as the contact between the reaction solution and the alkaline aqueous solution is sufficient, but for example, preferably about 1 minute, more preferably 3 minutes from the end of the addition of the reaction solution. It is preferable to bring the reaction solution and the aqueous alkali solution into contact with each other while stirring. If the contact time is too short, impurities may remain.

(II-2) Water washing step Since the reaction solution contains impurities such as acetic acid, ammonia and acetamide, which are decomposition products of the organic solvent (B), the content of acetic acid and acetamide is reduced by washing with water. To reduce. In the present invention, since ammonia is reduced in the cation exchange step, the reverse reaction is suppressed, and the generation of ammonium ions due to the reverse reaction can also be suppressed. Moreover, the ammonium salt of bis (fluorosulfonyl) imide produced | generated by a reverse reaction can also be suppressed.

  The amount of water when washing with water is not particularly limited, but is preferably at least 1 time, more preferably at least 1.3 times and preferably at most 2 times the mass of the alkali metal salt of bis (fluorosulfonyl) imide. More preferably, it is 1.5 times or less. If the amount of water is too small, the cleaning effect is lowered and the removal of impurities becomes insufficient. On the other hand, if it is too much, it will be washed excessively and the yield of the alkali metal salt of bis (fluorosulfonyl) imide will be low.

  The temperature of water during washing is not particularly limited, but if the temperature is too low, it becomes difficult to handle the water, while if the temperature is too high, the alkali metal salt of bis (fluorosulfonyl) imide may be decomposed. Therefore, the temperature of water is preferably 0 ° C. or higher, preferably 45 ° C. or lower, more preferably 25 ° C. or lower.

  The washing time is not particularly limited, but is preferably 1 minute or more, more preferably 3 minutes or more, preferably 10 minutes or less, more preferably 5 minutes or less.

  The acetamide content is preferably 300 ppm by mass or less, more preferably 100 ppm by mass or less, and the acetic acid content is preferably 500 ppm by mass or less.

(III) Concentration step In the concentration step, the organic solvent (B) and water are separated from the washed reaction solution to obtain an electrolytic solution material containing an alkali metal salt of di (fluorosulfonyl) imide and the organic solvent (A). It is a process. Specifically, in the concentration step, water is removed for concentration, and the organic solvent (B) used as the reaction solvent is exchanged with an organic solvent (A) different from the organic solvent (B). As the organic solvent (A), a non-aqueous solvent is preferable, and any organic solvent generally used for an electrolyte solution for a non-aqueous electrolyte battery may be used. The dielectric constant is large, the solubility of the electrolyte is high, and the boiling point is 60 ° C. or higher. An organic solvent having a wide electrochemical stability range is more preferable, and a carbonate solvent is particularly preferable. Examples of carbonate solvents include chain carbonates such as dimethyl carbonate, ethyl methyl carbonate (ethyl methyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, and methyl phenyl carbonate; ethylene carbonate (ethylene carbonate), propylene carbonate (propylene Carbonates), saturated cyclic carbonates such as 2,3-dimethylethylene carbonate (2,3-butanediyl carbonate), 1,2-butylene carbonate, and erythritan carbonate; vinylene carbonate, methyl vinylene carbonate (MVC; 4-methyl- 1,3-dioxol-2-one), ethyl vinylene carbonate (EVC; 4-ethyl-1,3-dioxol-2-one), 2-vinylethylene carbonate (4-vinyl-1,3-dioxolane-2- ON) and phenylethylene carbonate Cyclic carbonates having an unsaturated bond such as Bonate (4-phenyl-1,3-dioxolan-2-one); Fluorine-containing cyclic carbonates such as fluoroethylene carbonate, 4,5-difluoroethylene carbonate and trifluoropropylene carbonate Examples thereof include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate. These can use 1 type (s) or 2 or more types.

  For example, when a plurality of organic solvents (A) having different boiling points are used, an organic solvent (A-1) having a boiling point of about 100 ° C. and an organic solvent (such as ethyl methyl carbonate, ethylene carbonate, polycarbonate, etc.) having a boiling point exceeding 200 ° C. By using the organic solvent (A-2) that does not azeotrope with B), the organic solvent (B) can be efficiently removed.

  The reaction apparatus that can be used in the concentration step is not particularly limited, and examples thereof include a rotary evaporator, a flask, a tank reactor, or a tank reactor that can be depressurized.

  The amount of the organic solvent (A) used may be appropriately determined according to the concentration of the alkali metal salt of bis (fluorosulfonyl) imide in the reaction solution. For example, the mass of the alkali metal salt of bis (fluorosulfonyl) imide On the other hand, it is preferably 0.8 times or more, more preferably 1.0 times or more, preferably 1.5 times or less, more preferably 1.2 times or less. When there is too little organic solvent (A), an alkali metal salt may precipitate. On the other hand, if the amount is too large, the composition range for dilution into the electrolyte solution becomes narrow.

  Further, in order to further increase the concentration efficiency of the alkali metal salt of bis (fluorosulfonyl) imide, the concentration step may be performed while heating the reaction solution. The heating temperature may be appropriately set according to the organic solvent (B) to be used, but in order to improve the removal efficiency of the organic solvent (B), it is preferably 45 ° C. or higher, more preferably 50 ° C. or higher. On the other hand, from the viewpoint of suppressing the decomposition of the alkali metal salt of bis (fluorosulfonyl) imide, it is preferably 70 ° C or lower, more preferably 60 ° C or lower.

  The concentration step may be performed under reduced pressure. By controlling the degree of vacuum, the organic solvent (B) can be efficiently removed even at a low temperature, and decomposition of the alkali metal salt of bis (fluorosulfonyl) imide by heat can also be prevented. The degree of vacuum may be appropriately adjusted according to the type of the organic solvent (B) and is not particularly limited, but is preferably 3 hPa or more, more preferably 5 hPa or more, preferably 50 hPa or less, more preferably 20 hPa or less. .

  Although the time of a concentration process is not specifically limited, Preferably it is 8 minutes or more, More preferably, it is 10 minutes or more, Preferably it is 5 hours or less, More preferably, it is 3 hours or less.

  In the concentration step, the water content is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, and the organic solvent (B) content is preferably 3000 ppm by mass or less, more preferably 1000 ppm by mass or less. Is preferred. The concentration step may be repeated a plurality of times, or the organic solvent (A-2) may be sequentially added to perform the concentration step.

  The organic solvent (B) and water are distilled off by the concentration step, and an electrolyte material containing an alkali metal salt of bis (fluorosulfonyl) imide and the organic solvent (A) is obtained.

  The obtained electrolyte material substantially contains an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent (A), and the balance is impurities. In the present invention, trace amounts of acetamide, ammonium, and acetic acid may be contained as impurities. Specifically, the content of acetamide is preferably 1000 ppm by mass or less (mass standard, the same applies hereinafter), more preferably 500 ppm by mass or less, and still more preferably 200 ppm by mass or less. The ammonium content is preferably 300 ppm by mass or less, more preferably 100 ppm by mass or less, and still more preferably 80 ppm by mass or less. The acetic acid content is preferably 750 mass ppm or less, more preferably 500 mass ppm or less. The lower the content of these impurities, the better the battery characteristics.

  An electrolyte material containing an alkali metal salt of di (fluorosulfonyl) imide obtained by the production method of the present invention and an organic solvent (A) has a charging / discharging mechanism such as a primary battery, a lithium (ion) secondary battery, or a fuel cell. It is suitably used as a material for ion conductors constituting electrochemical devices such as batteries, electrolytic capacitors, electric double layer capacitors, solar cells and electrochromic display elements.

  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.

Example 1
In the following procedure, the electrolyte material No. 1-3 were produced.

Example 1-1
Ammonium in butyl acetate 41.41g bis (fluorosulfonyl) imide (NH ₄ FSI) was prepared 10.63g charged with NH ₄ FSI20.4 wt% butyl acetate solution.

[Cation exchange process]
Lithium hydroxide monohydrate (LiOH · H ₂ O) powder having an ammonium salt ratio of 1.05 equivalents of bis (fluorosulfonyl) imide to the NH ₄ FSI 20.4% by mass butyl acetate solution obtained 2.36 g of the product was added, and the mixture was stirred at room temperature for 15 minutes, and ammonia gas generated during the stirring was distilled off from the reaction solution. The butyl acetate solution (reaction solution) of lithium bis (fluorosulfonyl) imide obtained by lithiation was 51.15 g. As a result of measuring the water content, butyl acetate content, lithium bis (fluorosulfonyl) imide (LiFSI) content, and ammonium content in the obtained reaction solution based on the following measurement methods, the water content was 4.00% by mass (2. 05 g), butyl acetate: 73.32 mass% (37.50 g), LiFSI: 22.02 mass% (yield: 11.26 g), and ammonium was 2370 mass ppm.

[Ammonia distillation step]
The reaction solution obtained by cation exchange was distilled under reduced pressure (20 hPa) at room temperature (25 ° C.) for 15 minutes to further distill off ammonia. At this time, water and butyl acetate were simultaneously distilled off together with the ammonia distillation. The mass of the reaction solution after the ammonia distillation step was 45.52 g. Further, the water content and the butyl acetate content in the reaction solution after the ammonia distillation step were measured based on the following measuring methods, respectively, and the water content was 2.30% by mass (1.05 g) and the butyl acetate was 73.84% by mass. (33.61 g).

[Water washing process]
After the ammonia distillation step, the butyl acetate solution (reaction solution) of lithium bis (fluorosulfonyl) imide was washed with pure water (14.64 g) 1.3 times the mass of lithium bis (fluorosulfonyl) imide (LiFSI). . After water washing, liquid separation was performed to remove the aqueous layer, and the obtained oil layer (44.44 g) was subjected to vacuum distillation for 10 minutes under the control of temperature (55 ° C.) and pressure (20 hPa).

[Concentration process]
Using a rotary evaporator ("REN-1000", manufactured by IWAKI), a butyl acetate solution as a reaction solvent and water were distilled from a butyl acetate solution of lithium bis (fluorosulfonyl) imide after the water washing step under reduced pressure. Left. Specifically, with respect to a butyl acetate solution of lithium bis (fluorosulfonyl) imide, ethylene carbonate (EC) of twice the mass of lithium bis (fluorosulfonyl) imide, and methyl ethyl carbonate (MEC) of 2 times the mass. In addition, the mixture was heated at 55 ° C. for 10 minutes under reduced pressure (20 hPa) and distilled under reduced pressure. Subsequently, twice the mass of methyl ethyl carbonate was added and the same vacuum distillation was performed. The same operation was repeated until the water content reached 50 mass ppm, and a total of 10 mass times of methyl ethyl carbonate was used. By distilling under reduced pressure, water and ethylene carbonate were distilled off together with butyl acetate to obtain 15.35 g of LiFSI / EC / MEC solution. The LiFSI amount of this solution was 53.74% by mass (8.25 g). The final yield of LiFSI (the mass of LiFSI in the solution / the amount of NH ₄ FSI input) was 77.61% by mass. The obtained lithium carbonate solution of lithium bis (fluorosulfonyl) imide was used as electrolyte material No. It was set to 1.

Example 1-2
[Cation exchange process]
LiOH · H ₂ O powder 2 having an ammonium salt ratio of 1.15 equivalents of bis (fluorosulfonyl) imide to a butyl acetate solution containing 20.4% by mass of NH ₄ FSI produced in the same manner as in Example 1-1 .59 g was added, and the mixture was stirred at room temperature for 15 minutes, and ammonia gas generated during the stirring was distilled off from the reaction solution. The obtained lithium bis (fluorosulfonyl) imide in butyl acetate (reaction solution) was 50.94 g. As a result of measuring the water content, butyl acetate content, LiFSI content, and ammonium content of the obtained reaction solution based on the following measurement methods, water: 4.24% by mass (2.16 g), butyl acetate: 73.38 Mass% (37.38 g), LiFSI: 22.06 mass% (11.24 g), and ammonium were 2420 mass ppm.

[Ammonia distillation step]
The ammonia solution was removed from the reaction solution obtained by cation exchange in the same manner as in Example 1-1. The mass of the reaction solution after the ammonia distillation step was 45.72 g. Further, the water content and the butyl acetate content in the reaction solution after the ammonia distillation step were measured based on the following measuring methods, respectively, water: 2.56% by mass (1.17 g), butyl acetate: 73.60% by mass. (33.65 g).

[Water washing process]
After the ammonia distillation step, the obtained reaction solution was subjected to a water washing step in the same manner as in Example 1-1. After water washing, liquid separation was performed to remove the aqueous layer, and the resulting oil layer (44.52 g) was subjected to vacuum distillation for 10 minutes under the control of temperature (55 ° C.) and pressure (20 hPa).

[Concentration process]
No. above. The concentration step was performed in the same manner as in 1 to obtain 15.41 g of LiFSI / EC / MEC solution. The LiFSI amount of this solution was 53.60% by mass (8.26 g). The final yield of LiFSI was 77.70% by mass. The obtained lithium carbonate solution of lithium bis (fluorosulfonyl) imide was used as electrolyte material No. 2.

Example 1-3 (comparative example)
[Cation exchange process]
Powder 2 of LiOH · H ₂ O having an ammonium salt ratio of 1.3 equivalents of bis (fluorosulfonyl) imide to a butyl acetate solution of 20.4% by mass of NH ₄ FSI produced in the same manner as in Example 1-1 .92 g was added and stirred at room temperature for 15 minutes, and ammonia gas generated during stirring was distilled off from the reaction solution. The obtained lithium bis (fluorosulfonyl) imide in butyl acetate (reaction solution) was 50.89 g. As a result of measuring the water content, butyl acetate content, LiFSI content, and ammonium content of the obtained reaction solution based on the following measurement methods, water: 5.01% by mass (2.55 g), butyl acetate was 72.44. The mass% (36.86 g), LiFSI was 22.11 mass% (11.25 g), and ammonium was 2530 mass ppm.

[Ammonia distillation step]
The ammonia solution was removed from the reaction solution obtained by cation exchange in the same manner as in Example 1-1. The mass of the reaction solution after the ammonia distillation step was 44.65 g. Further, the water content and the butyl acetate content of the reaction solution after the ammonia distillation step were measured based on the following measuring methods, respectively, water: 2.98% by mass (1.33 g), butyl acetate: 73.06% by mass. (32.62 g).

[Water washing process]
After the ammonia distillation step, the obtained reaction solution was subjected to a water washing step in the same manner as in Example 1-1. After water washing, liquid separation was performed to remove the aqueous layer, and the obtained oil layer (42.87 g) was subjected to vacuum distillation for 10 minutes under the control of temperature (55 ° C.) and pressure (20 hPa).

[Concentration process]
No. above. The concentration step was performed in the same manner as in 1 to obtain 15.31 g of LiSFI / EC / MEC solution. The LiFSI content of this solution was 53.81% (8.24 g). The final yield of LiFSI was 77.52%. The obtained lithium carbonate solution of lithium bis (fluorosulfonyl) imide was used as electrolyte material No. It was set to 3.

  The amount of acetamide, the amount of ammonium, and the amount of acetic acid contained in each obtained electrolyte solution material were measured based on the following measuring methods. The results are shown in Table 1.

[Measuring method]
(Measurement of water content)
The water content of each reaction solution was measured with a Karl Fischer moisture measuring device (AQ-2100 manufactured by Hiranuma Sangyo). The measurement sample was prepared by diluting 0.2 g of the reaction solution after cation exchange or ammonia distillation 10-fold with methanol. A series of operations such as sample preparation and measurement 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, “Hydranal (registered trademark) Chromat AK” (manufactured by Sigma Aldrich) is used as the generated liquid, and “Hydranal” is used as the counter electrode liquid. "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. Similarly, the water content of methanol used for dilution was measured, and the water content of the reaction solution was determined by subtracting the water content of methanol from the water content (measured value) of the sample solution.

(Measurement of LiFSI amount)
The amount of LiFSI contained in each reaction solution after the cation exchange step and after the concentration step was analyzed by ¹⁹ F-NMR. The concentration of LiFSI was measured by ¹⁹ F-NMR (solvent: deuterated acetonitrile) using the organic layer obtained from each reaction solution as a sample, and the amount of trifluoromethylbenzene added as an internal standard substance in the measurement result chart, and It was determined by comparing the integrated value of the peak derived therefrom with the integrated value of the peak derived from the target product.

(Measurement of acetic acid amount, acetamide amount, and butyl acetate amount)
Using a gas chromatograph mass spectrometer (GC-MASS), the amount of butyl acetate contained in each reaction solution after the cation exchange step and after the ammonia distilling step, and the electrolyte material No. Acetamide and acetic acid contained in 1 to 3 were measured. The analysis results are shown in Table 1.
The electrolyte material was diluted 40 times with ultra-dehydrated acetone to obtain an assumed solution.
The apparatus used was PolarisQ manufactured by ThermoQuest Co., Ltd., and was measured by the ionization method E / I method.
Gas-cooled condition constant temperature layer: 40 ° C. 5 minutes-250 ° C. 10 minutes Temperature rising rate 10 ° C./minute Flow rate: He 1.0 mL / minute Inlet port: 260 ° C., split injection method 1/10
Column: CP-VOLAMINE (0.25mm inner diameter x 30m)

(Measurement of ammonium content)
Using ion chromatography, electrolyte material No. The amount of ammonium ion contained in 1 to 3 was measured. The electrolyte solution material was diluted 1000 times with ultrapure water (over 18.2 Ω · cm) to obtain a measurement solution. The apparatus measured NH4 ⁺ in a measurement solution using ICS-2000 by Nippon Daionex Corporation.
Separation mode: Ion exchange eluent: 15-30 mM KOH aqueous solution Detector: Conductivity detector Column: Ion PAC OG16-CS16

  In Example 1-1 and Example 1-2, in which the amount of lithium hydroxide monohydrate added in the cation exchange step was within the range specified in the present invention, the water content in the reaction solution after the cation exchange step could be reduced. As a result, the amount of impurities (acetamide, ammonium, and acetic acid) contained in the electrolyte material could be reduced. On the other hand, in Example 1-3 in which the amount of added lithium hydroxide monohydrate was large, the water content of the reaction solution was large, and as a result, the amount of impurities contained in the electrolyte solution material was large.

  In Example 1-1 and Example 1-2, since the amount of lithium hydroxide monohydrate added in the cation exchange step was within the range specified in the present invention, the amount of lithium hydroxide monohydrate added was large. Compared with Example 1-3, the alkalinity after lithiation could be suppressed low, and decomposition of butyl acetate could be suppressed. As a result, the production of acetic acid, which is a decomposition product of butyl acetate, can be suppressed, and the formation of acetamide, which is a dehydration condensate of acetic acid and ammonia, can be suppressed. Acetic acid and acetamide contained in the electrolyte material are detected Reduced to below the limit. Moreover, in Example 1-1 and Example 1-2, the reverse reaction by water and ammonia can be suppressed by reducing the water content of the reaction solution after the cation exchange step, and the ammonium contained in the electrolyte material can be reduced. Reduced.

Example 2
(Preparation of non-aqueous electrolyte)
Electrolyte material No. EC and EMC were added after 1 to prepare a non-aqueous electrolyte I-1 having a LiFSI concentration of 1.2 mol / L EC / EMC = 3/7 (volume ratio).

Moreover, lithium hexafluorophosphate (LiPF ₆ , manufactured by Kishida Chemical Co., Ltd., electrolyte salt) is added to a non-aqueous solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 3: 7. By dissolving, a non-aqueous electrolyte solution II having a LiPF ₆ concentration of 1.2 mol / L was prepared.

The non-aqueous electrolyte solution I-1 and the non-aqueous electrolyte solution II are mixed, and the composition is LiFSI concentration 0.6 mol / L, LiPF ₆ concentration 0.6 mol / L, EC / EMC volume ratio = 3/7. Non-aqueous electrolyte No. 1 was prepared.

  Electrolyte material No. In place of electrolyte material No. 1 2 and 3 except that non-aqueous electrolytes I-2 and I-3 were prepared in the same manner as described above. 2, 3 were prepared.

Battery Evaluation Production of Laminate Type Lithium Ion Secondary Battery Positive Electrode Active Material (LiCoO ₂ ), Conductive Auxiliary 1 (Acetylene Black, manufactured by Denki Kagaku Kogyo), Conductive Auxiliary 2 (Graphite), and Binder (PVdF, Kureha Corporation・ A positive electrode mixture slurry prepared by mixing “Kureha L # 1120” manufactured by Battery Materials Japan in a mass ratio of 93: 2: 2: 3 and dispersed in N-methylpyrrolidone is an aluminum foil (positive electrode current collector). Both sides were coated on top, dried and compressed to produce a positive electrode sheet.

  Artificial graphite, conductive additive (VGCF, manufactured by Showa Denko KK), and binder (styrene butadiene rubber, carboxymethyl cellulose) are mixed as a negative electrode active material in a ratio of 100: 0.5: 2.6 (mass ratio). This was mixed with N-methylpyrrolidone to prepare a slurry solution. This negative electrode mixture slurry was coated on one side on a copper foil (negative electrode current collector), dried and compressed to prepare a negative electrode sheet.

  A negative electrode sheet (85 μm) was laminated so as to oppose both surfaces of the positive electrode sheet (150 μm), and a polyethylene separator (diameter 16 μm) was sandwiched between each sheet. The laminated body of the negative electrode sheet, the separator, the positive electrode sheet, the separator, and the negative electrode sheet is sandwiched between two aluminum laminates, and the aluminum laminate film is filled with 0.7 mL of the non-aqueous electrolyte 1 and sealed in a vacuum state ( Capacity 34 mAh), lithium ion secondary battery No. 1 was produced. Non-aqueous electrolyte No. 1 is a non-aqueous electrolyte No. 1 The lithium ion secondary battery No. 2 was changed in the same manner as described above except that it was changed to 2 or 3. 2 and 3 were produced.

  Lithium ion secondary battery No. The battery characteristics of (1) to (3) below were evaluated using 1 to 3.

(1) First-time charge / discharge efficiency For a lithium ion secondary battery, a charge / discharge test apparatus (ACD-01 manufactured by Asuka Electronics Co., Ltd., the same shall apply hereinafter) is used in an environment at a temperature of 25 ° C., and predetermined charge conditions (0. 5C (32mA), 4.35V, constant current constant voltage mode) was charged for 5 hours. Thereafter, discharge was performed under predetermined discharge conditions (0.2 C (12.8 mA), discharge end voltage 2.75 V, constant current discharge). The initial charge capacity per gram of the positive electrode active material and the initial discharge capacity per gram of the positive electrode active material were recorded, and the initial charge and discharge efficiency was calculated from the obtained value using the following formula. The results are shown in Table 2.
Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) × 100

(2) Initial rate characteristics Using a charge / discharge test apparatus ("ACD-01" manufactured by Asuka Electronics Co., Ltd.), a lithium ion secondary battery was measured at a current value of 1 C (64 mA) under an environment of a temperature of 25 ° C. The battery was charged at 0.05 V (1.28 mA) at a constant voltage of .35 V until the current dropped, and then discharged at a constant current of 0.2 C (12.8 mA) to 2.75 V. The discharge capacity per gram of the positive electrode active material at this time was 0.2 C capacity. Next, after charging again under the above conditions, constant current discharging was performed at 2.0 C up to 2.75 V. The discharge capacity per 1 g of the positive electrode active material at this time was 2.0 C capacity. The initial rate was calculated from the obtained discharge capacity value by the following formula. The results are shown in Table 2.
Initial rate characteristics (%) = (2.0 C capacity / 0.2 C capacity) × 100

(3) Cycle capacity maintenance rate Using a charge / discharge test device (ACD-01, manufactured by Asuka Electronics Co., Ltd.), the amount of current is 4.35V constant current constant voltage charge at a charge rate of 1C at a temperature of 45 ° C. Discharge until the voltage reaches 2.75 V at a discharge rate of 1 C, and perform a cycle characteristic test with a 10-minute charge / discharge pause time at each charge / discharge. The maintenance rate was calculated. The results are shown in Table 2.
Cycle capacity retention rate (%) = (discharge capacity at 50 cycles / discharge capacity at one cycle) × 100

  Electrolyte material No. obtained by the manufacturing method which satisfies the requirements of the present invention. 1 and 2, as described above, the impurity content is electrolyte material No. Compared to 3, it was reduced. Therefore, the electrolyte material No. Lithium ion secondary battery No. 1 and 2 are electrolyte material Nos. No. 3 lithium ion secondary battery No. 3 Compared to 3, the initial charge / discharge efficiency, the initial rate characteristics, and the capacity retention rate were improved.

  This shows that the battery characteristics can be improved by reducing the contents of acetamide, ammonium and acetic acid.

Claims (6)

A method for producing an electrolyte material comprising an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent (A),
Alkali metal of bis (fluorosulfonyl) imide by cation exchange in a solution containing an organic solvent (B) different from the organic solvent (A), an ammonium salt of bis (fluorosulfonyl) imide, and an alkali metal compound A cation exchange step to obtain a salt,
A step of washing the obtained reaction solution with alkali and / or water, and after the washing, the organic solvent (B) and water are distilled off by reducing pressure and / or heating in the presence of the organic solvent (A). Including steps,
The addition amount of the alkali metal compound in the cation exchange step is 0.90 mole equivalent or more and 1.24 mole equivalent or less with respect to 1 mole of the ammonium salt of the bis (fluorosulfonyl) imide. A method for producing an electrolyte material comprising an alkali metal salt of the organic solvent (A) and an organic solvent (A).   The method for producing an electrolyte material according to claim 1, wherein the alkali metal compound is added as a solid.   The method for producing an electrolyte material according to claim 1 or 2, wherein the water content of the reaction solution after the cation exchange step is 4.5 mass% or less.   The alkali solution and / or the water washing is performed after the reaction solution after the cation exchange step is subjected to a step of distilling off ammonia from the reaction solution by reducing pressure and / or heating in the presence of the organic solvent (B). The manufacturing method of the electrolyte material in any one of Claims 1-3.   The said organic solvent (B) is an ester solvent, The manufacturing method of the electrolyte material in any one of Claims 1-4.   The said organic solvent (A) is a carbonate type solvent, The manufacturing method of the electrolyte material in any one of Claims 1-5.