JP2018055882A - Method for manufacturing electrolyte material containing alkali metal salt of bis(fluorosulfonyl)imide and organic solvent, and electrolyte material containing alkali metal salt of bis(fluorosulfonyl)imide and organic solvent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method which can reduce impurities produced in a process of manufacturing an alkali metal salt of bis(fluorosulfonyl)imide.SOLUTION: A manufacturing method of the present invention is a method for manufacturing an electrolyte material including an alkali metal salt of bis(fluorosulfonyl)imide and an organic solvent (A). The method comprises: a cation exchange step of obtaining an alkali metal salt 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 step of depressurizing and/or heating a resultant reaction solution in the presence of the organic solvent (B), thereby removing ammonia from the reaction solution; a step of performing alkali cleaning and/or aqueous cleaning of the reaction solution with the ammonia removed therefrom; and a step of removing the organic solvent (B) and water from the resultant solution by depressurizing and/or heating it in the presence of the organic solvent (A) after the cleaning.SELECTED DRAWING: None

Description

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

  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.

  The process for producing an alkali metal salt of fluorosulfonylimide has been repeatedly improved, and a technique for improving the yield has 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 technique for easily removing a solvent from a reaction solution in a method for producing an alkali metal salt of fluorosulfonylimide.

International Publication No. 2012/118063 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.

  This invention which solved the said subject is a manufacturing method of the electrolyte material containing the alkali metal salt of bis (fluoro sulfonyl) imide, and the organic solvent (A), Comprising: The organic solvent (B) different from the said organic solvent (A) ), A cation exchange step in which an alkali metal salt of bis (fluorosulfonyl) imide is obtained by cation exchange in a solution containing an ammonium salt of bis (fluorosulfonyl) imide, and an alkali metal compound. A step of distilling ammonia from the reaction solution under reduced pressure and / or heating in the presence of an organic solvent (B), a step of washing the reaction solution after distilling off the ammonia with alkali and / or water, and after the washing, The present invention includes a step of distilling off the organic solvent (B) and water by reducing pressure and / or heating in the presence of the organic solvent (A).

  In the production method of the present invention, the temperature of the solution in the cation exchange step is 60 ° C. or lower, the ammonia distillation step is performed at 60 ° C. or lower, and the organic solvent (B) is an ester solvent. It is a preferred embodiment that the organic solvent (A) is a carbonate solvent.

  Moreover, the present invention is an electrolyte material containing an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent, and the ammonium ion contained in the electrolyte material is also preferably 500 ppm by mass or less.

  According to the production method of the present invention, impurities generated in the production process of an alkali metal salt of bis (fluorosulfonyl) imide, specifically, acetamide, ammonium, and acetic acid 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 study by the present inventors on the improvement of the characteristics of the lithium ion secondary battery, it was caused by impurities generated in the production process of the alkali metal salt of bis (fluorosulfonyl) imide, specifically, acetamide, ammonium, and acetic acid. It was found that the initial charge / discharge efficiency, the initial rate characteristics, and the cycle capacity retention ratio (hereinafter, these may be collectively referred to as “battery characteristics”) are hindered. And after the initial stage of the production process of the alkali metal salt of bis (fluorosulfonyl) imide, specifically, cation exchange, (A) Acetamide, which is a dehydration condensate of acetic acid and ammonia, is reduced by reducing ammonia as much as possible. (B) While reducing acetic acid and acetamide by washing after reducing ammonia, the reverse reaction from LiFSI to NH ₄ FSI (for example, LiFSI + NH ₃ + H ₂ O → NH ₄ FSI + LiOH) is suppressed. As a result, it was found that an electrolyte material having an extremely low impurity content can be obtained because the production of ammonium can be reduced, and the present invention has been achieved.

  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 distilling off ammonia from the reaction solution by reducing pressure and / or heating the obtained reaction solution in the presence of the organic solvent (B) (hereinafter referred to as “ammonia distilling step”),
(III) A step of alkali-washing the reaction solution after distilling off ammonia (hereinafter referred to as “alkali washing step”) and / or a step of washing with water (hereinafter referred to as “water washing step”) Sometimes referred to as “cleaning step”).

  Furthermore, in the present invention, as a method for producing an electrolyte material containing an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent (A), (IV) 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. Those obtained by various known production methods may be used. For example, the compound (1) may be obtained by the production method described in Patent Document 1 or Patent Document 2, or may be a commercially available product.

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, and more 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, LiOH, NaOH, KOH, Li ₂ CO ₃ , Na ₂ CO ₃ , and K ₂ CO ₃ are more preferable, and LiOH, NaOH, and KOH are more preferable. These compounds are hydroxylated. It is preferable that it is a thing.

  The alkali metal compound is preferably in a stoichiometric amount of 1.05 equivalents or more, more preferably 1.1 equivalents or more, preferably 3 equivalents or less, relative to 1 mol of the compound (1). More preferably, the amount used is adjusted so as to be 1.5 equivalents or less. If the amount of the alkali metal compound used is too large, the organic solvent B tends to be decomposed and acetic acid and acetamide increase. On the other hand, if the amount is too small, an ammonium salt of bis (fluorosulfonyl) imide may remain.

  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.

  By lowering the temperature of the solution at the time of cation exchange, it is possible to suppress the formation of acetic acid due to the decomposition of the organic solvent (B) such as butyl acetate, and it is possible to suppress the formation of acetamide due to dehydration condensation. On the other hand, when the temperature of the reaction solution is too low, the viscosity of the reaction solution increases and handling may be complicated. Therefore, the temperature of the reaction 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.

(II) Ammonia distillation step The reaction solution after the cation exchange reaction contains not only the produced alkali metal salt of bis (fluorosulfonyl) imide and the organic solvent (B) used, but also by-produced ammonia. . In the present invention, ammonia is distilled off from the reaction solution after the cation exchange step and before the washing step.

  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. When the temperature of the reaction solution is increased, the amount of acetamide produced by the dehydration condensation reaction tends to increase. Therefore, the temperature is 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.). Moreover, since ammonia can be distilled off at a low temperature by carrying out under reduced pressure, it is preferably 50 hPa or less, more preferably 20 hPa or less, preferably 3 hPa or more, more preferably 5 hPa or more.

  By distilling off ammonia, the amount of impurities such as acetamide and ammonium ions 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 addition, ammonia content is the quantity measured with the ion chromatograph as described in an Example.

  In the present invention, after the ammonia distillation step, at least one of (III-1) alkali washing step and (III-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.

(III-1) Alkali washing step The reaction solution after the ammonia has been distilled off may be subjected to an alkali washing (hereinafter sometimes referred to as an "alkali washing step") as necessary, followed by a water washing step. By contacting with an aqueous alkaline solution, impurities such as water-soluble impurities in the ammonium salt of bis (fluorosulfonyl) imide and water-soluble by-products during cation exchange are removed. 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 preferably the same alkali metal compound as the alkali metal compound selected in the cation exchange step is used as the basic substance.

  In order to sufficiently remove impurities while suppressing the generation of acetic acid and acetamide, the alkaline aqueous solution requires an amount of alkali metal relative to 1 mol of the alkali metal salt of bis (fluorosulfonyl) imide. 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. desirable. When the alkalinity increases, the organic solvent (B) may be decomposed to increase 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.

(III-2) Water washing step After the ammonia distilling step or after the alkali washing step, the reaction solution contains impurities such as acetic acid, ammonia, and acetamide that are decomposition products of the organic solvent (B). Therefore, the content of acetic acid and acetamide is reduced by washing with water. In the present invention, since ammonia is reduced in the ammonia distillation 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 bisfluorosulfonylimide 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.

  Although the temperature of the water at the time of water washing is not specifically limited, Preferably it is 0 degreeC or more and 45 degrees C or less, More preferably, it is 0 degreeC or more and 25 degrees C or less. If the temperature is too low, it becomes difficult to handle water, while if the temperature is too high, the alkali metal salt of bis (fluorosulfonyl) imide may be decomposed.

  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.

(IV) Concentration step The concentration step separates the organic solvent (B) and water 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 among these. These can use 1 type, or 2 or more types.
Yes.

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

  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.

  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 1500 ppm by mass or less (mass basis, the same applies hereinafter), more preferably 1000 ppm by mass or less, and still more preferably 500 ppm by mass or less. The ammonium content is preferably 500 ppm by mass or less, more preferably 300 ppm by mass or less, still more preferably 100 ppm by mass or less, and preferably 1 ppm by mass or more. The acetic acid content is preferably 800 ppm by mass or less, more preferably 750 ppm by mass or less, and still more preferably 500 ppm by mass 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
No. 1
To prepare a butyl acetate solution of NH4FSI 12.5 wt% with NH ₄ FSI powder made by a conventionally known method.

[Cation exchange process]
18% by mass of hydroxide so that the amount of lithium is 1.1 equivalents with respect to ammonium bis (fluorosulfonyl) imide in a butyl acetate solution of 12.5% by mass of ammonium bis (fluorosulfonyl) imide obtained. An aqueous lithium solution was added and stirred at room temperature for 15 minutes. Thereafter, the aqueous layer was removed from the reaction solution to obtain a butyl acetate solution of lithium bis (fluorosulfonyl) imide.

[Ammonia distillation step]
A butyl acetate solution of lithium bis (fluorosulfonyl) imide obtained by liquid separation was heated to 55 ° C. under reduced pressure (20 hPa) and stirred for 15 minutes to distill off ammonia.

[Alkali cleaning process]
After the ammonia was distilled off, a 0.45 mass% lithium hydroxide aqueous solution was added to the lithium bis (fluorosulfonyl) imide so that the amount of lithium was 0.2 equivalent, and the mixture was stirred at room temperature for 3 minutes. Then, alkali washing was performed. After alkali washing, the aqueous layer was removed, and the obtained organic layer was subjected to vacuum distillation for 10 minutes under the control of temperature (55 ° C.) and pressure (20 hPa).

[Water washing process]
To the organic layer obtained by distillation under reduced pressure, 1.3 times the mass of lithium bis (fluorosulfonyl) imide was added, and the mixture was stirred at room temperature for 3 minutes.

[Concentration process]
Using a rotary evaporator (“REN-1000” manufactured by IWAKI), the butyl acetate solution as a reaction solvent and water were distilled off from the butyl acetate solution of lithium bis (fluorosulfonyl) imide after water washing under reduced pressure. . 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) to distill off water, butyl acetate, and ethylene carbonate. Thereafter, the addition of twice the mass of methyl ethyl carbonate (MEC) was repeated 4 times until the water content was 50 ppm by mass or less, and the mixture was heated at 20 hPa and 55 ° C. for 10 minutes each, and water, butyl acetate, and methyl ethyl carbonate were Distilled off. The obtained lithium carbonate solution of lithium bis (fluorosulfonyl) imide was used as electrolyte material No. It was set to 1.

No. 2
Except that the temperature was changed from 55 ° C. to 25 ° C. in the ammonia distillation step, the electrolytic solution material No. 2 was obtained.

No. 3
In the cation exchange step, the temperature was changed from room temperature to 0 ° C., and an 18 mass% lithium hydroxide aqueous solution at 0 ° C. was used, and an alkaline washing liquid cooled to 0 ° C. was put into the reaction solution cooled to 0 ° C. In the same manner as in Example 1 except that the alkaline cleaning was performed, the electrolytic solution material No. 3 was obtained.

No. 4
A butyl acetate solution of lithium bis (fluorosulfonyl) imide was obtained in the same manner as in Example 1 except that the amount of lithium was 1.0 equivalent in the cation exchange step and a 13 mass% lithium hydroxide aqueous solution was used. It was. The obtained butyl acetate solution of lithium bis (fluorosulfonyl) imide was subjected to alkali cleaning without performing the ammonia distillation step. At that time, the alkali cleaning step was performed in the same manner as in Example 1 except that the amount of lithium was 0.6 equivalent and a 13 mass% lithium hydroxide aqueous solution was used. After the alkali cleaning, without performing the water washing step, the concentration step was performed under the same conditions as in Example 1, and the electrolyte material No. 4 was obtained.

No. 5
A butyl acetate solution of lithium bis (fluorosulfonyl) imide was obtained in the same manner as in Example 1 except that the amount of lithium was 1.0 equivalent in the cation exchange step and a 13 mass% lithium hydroxide aqueous solution was used. It was. The obtained butyl acetate solution of lithium bis (fluorosulfonyl) imide was subjected to alkali cleaning without performing the ammonia distillation step. At that time, the alkali cleaning step was performed in the same manner as in Example 1 except that the amount of lithium was 0.6 equivalent and a 13 mass% lithium hydroxide aqueous solution was used. After the alkali cleaning, the water washing step and the concentration step were performed under the same conditions as in Example 1 to obtain the electrolyte material No. 5 was obtained.

[Analysis by GC-MASS]
Using a gas chromatograph mass spectrometer, the electrolyte material No. Acetamide and acetic acid contained in 1 to 5 were measured. The analysis results are shown in Table 1.
The electrolyte material was diluted 40 times with ultra-dehydrated acetone to obtain a measurement 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)

[Analysis by ion chromatography]
Using ion chromatography, electrolytic solution material No. The amount of ammonium ions contained in 1 to 5 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

  Table 1 shows the following. After cation exchange, ammonia was distilled off before washing with alkali. In 1-1 to 1-3, no ammonia was distilled off. Compared with 1-4 and 1-5, acetamide, ammonium, and acetic acid content could be reduced. No. In 1-1 to 1-3, since ammonia was distilled off before alkali washing, the generation of acetamide was suppressed, and the reverse reaction during water washing was suppressed to reduce the amount of ammonium produced.

  No. When comparing 1-1 to 1-3, the ammonia distillation step was carried out at room temperature without heating. 1-2 and No. 1 in which the cation exchange step was performed at a temperature lower than room temperature. No. 1-3 is a No. 1-3 sample that was subjected to the cation exchange step at room temperature and the ammonia distillation step was heated to a temperature higher than room temperature. The generation of acetamide and acetic acid could be suppressed compared to 1-1. This shows that the amount of acetamide and acetic acid can be further reduced by controlling at least the temperature of at least one of the cation exchange step and the ammonia distillation step.

No. obtained by the conventional manufacturing method. 1-4 (no water washing step), No. No. 1-5 (with water washing step) was compared with No. 1 in which the water washing step was performed. In 1-5, the acetamide and acetic acid contents decreased, but the ammonium content increased. This is because ammonium was generated by reverse reaction from LiFSI to NH ₄ FSI during water washing.

  On the other hand, no. In 1-4, since the water washing process was not performed, there was no production of ammonium due to the reverse reaction, so the ammonium content was small, but the acetamide and acetic acid contents were large.

  As described above, it was difficult to reduce the content of acetamide and acetic acid without increasing the ammonia amount in the water washing step in the conventional manufacturing method, but by performing the ammonia distillation step, acetamide, acetic acid and ammonia The content can be reduced.

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

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 nonaqueous electrolytic solution I and the nonaqueous electrolytic solution II are mixed at a 1: 1 (volume ratio) to prepare a nonaqueous electrolytic solution No. 1 was prepared.

Electrolyte material No. In place of electrolyte material No. 1 Non-aqueous electrolyte No. 2 was prepared in the same manner as described above except that non-aqueous electrolyte I was prepared using 2-5. 2-5 were prepared. In addition, non-aqueous electrolyte No. The compositions of 1 to 5 are LiPF ₆ (concentration 0.6 mol / L), LiFSI (concentration 0.6 mol / L), and EC / MEC (volume ratio 3/7).

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 of 64 mAh), lithium ion secondary battery No. 1 was produced. Non-aqueous electrolyte No. The lithium ion secondary battery No. 2 was changed in the same manner as above except that it was changed to 2-5. 2-5 were produced.

  Lithium ion secondary battery No. The battery characteristics of the following (1) to (3) were evaluated using 1 to 5.

(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 / discharge efficiency was calculated from the following formula from the obtained values. 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 characteristic (%) = (2.0 C capacity / 0.2 C capacity) × 100

(3) Capacity maintenance rate Using a charge / discharge test apparatus (ACD-01, manufactured by Asuka Electronics Co., Ltd.), the current amount is 4.35V constant current constant voltage charging at a charging rate of 1C at a temperature of 45 ° C. The battery is discharged until the voltage reaches 2.75 V at a discharge rate of 1 C, and a cycle characteristic test is performed with a charge / discharge pause time of 10 minutes for each charge / discharge. The rate was calculated. The results are shown in Table 2.
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 to 3 manufactured from lithium ion secondary battery No. 1-3 are electrolyte material No. obtained by the conventional manufacturing method. Nos. 4 and 5 produced from lithium ion secondary battery No. 4 Compared with 4, 5, the initial charge / discharge efficiency, the initial rate characteristics, and the capacity retention ratio were improved.

  From this, it can be seen that the battery characteristics are 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 distilling off ammonia from the reaction solution by reducing the pressure and / or heating the obtained reaction solution in the presence of the organic solvent (B);
A step of washing the reaction solution after evaporation of ammonia with an alkali and / or water, and after the washing, the organic solvent (B) and water are reduced by heating under reduced pressure and / or in the presence of the organic solvent (A). A method for producing an electrolyte material comprising an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent (A), which comprises a step of distilling off.   The method for producing an electrolyte material according to claim 1, wherein the temperature of the solution in the cation exchange step is 60 ° C. or less.   The manufacturing method of the electrolyte material of Claim 1 or 2 which performs the said ammonia distillation process at 60 degrees C or less.   The method for producing an electrolytic solution material according to claim 1, wherein the organic solvent (B) is an ester solvent.   The said organic solvent (A) is a carbonate type solvent, The manufacturing method of the electrolyte material in any one of Claims 1-4. An electrolyte material comprising an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent, wherein the electrolyte material contains 500 ppm by mass or less of ammonium ions.