JP6806514B2 - A method for producing an electrolytic solution material containing an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent. - Google Patents

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 more specifically, an alkali metal salt of fluorosulfonylimide with reduced impurities and an organic for a lithium ion secondary battery. The present invention relates to a method for producing an electrolytic solution material containing a solvent.

Alkali metal salts of fluorosulfonylimides are attracting attention as compounds useful as additives for electrolytes and electrolytes of fuel cells, and various production methods have been proposed.

Improvements have been made to the method for producing alkali metal salts 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.

Further, 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.

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

International Publication No. 2012/118063 Pamphlet International Publication No. 2014/148258 Pamphlet Japanese Unexamined Patent Publication No. 2014-201453

In examining the quality of the alkali metal salt of bis (fluorosulfonyl) imide, the present inventors have developed the characteristics of the product in which impurities derived from the manufacturing process of the alkali metal salt of bis (fluorosulfonyl) imide are required at the time of use. For example, it has been found that it is a cause of deteriorating the battery characteristics of a lithium ion secondary battery.

The present invention has been made by paying attention to the above 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 solves the above problems is a method for producing an electrolytic solution material containing an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent (A), which is different from the organic solvent (A). A cation exchange step of 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. Includes a step of alkaline washing and / or washing the reaction solution with water, and a step of distilling off the organic solvent (B) and water by reducing the 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 0.90 mol equivalent or more and 1.24 mol equivalent or less with respect to 1 mol of the ammonium salt of the bis (fluorosulfonyl) imide. The gist is that it contains an alkali metal salt of 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, and the reaction solution after the cation exchange step. The organic solvent (B) is depressurized and / or heated to distill off ammonia from the reaction solution, and then the alkali washing and / or the water washing is performed. It is a preferred embodiment that the solvent (B) is an ester solvent and the organic solvent (A) is a carbonate solvent.

According to the production method of the present invention, impurities produced in the process of producing an alkali metal salt of bis (fluorosulfonyl) imide, specifically acetamide, ammonium, and acetic acid (hereinafter, these are collectively referred to as "impurities"). Yes) can be reduced. Therefore, when an electrolytic solution material containing an alkali metal salt of bis (fluorosulfonyl) imide and an organic solvent obtained by the production method of the present invention is used, deterioration of battery characteristics due to impurities can be suppressed, and the battery is superior to the conventional one. The characteristics are obtained.

As a result of studies on improving the characteristics of the lithium ion secondary battery, the present inventors have conducted initial charge / discharge efficiency, initial rate characteristics, and cycle due to impurities generated in the process of producing an alkali metal salt of bis (fluorosulfonyl) imide. It was found that the capacity retention rate (hereinafter, these are collectively referred to as "battery characteristics") is impaired. When the amount of the alkali metal compound added is reduced in the initial stage of the production process of the alkali metal salt of bis (fluorosulfonyl) imide, specifically, in the cation exchange step, the alkalinity is low, so that the ester solvent is decomposed. We have found that it is possible to suppress the formation of the above-mentioned impurities that deteriorate the battery characteristics, such as the formation of acetic acid and the formation of acetamide, which is a dehydration condensate of acetic acid and ammonia, and have reached the present invention.

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). , "Cation exchange process"),
(II) A step of alkaline washing and / or water washing of the obtained reaction solution (hereinafter, “washing step”).

In the present invention, if necessary, (i) a step of reducing the pressure and / or heating the reaction solution obtained in the cation exchange step in the presence of the organic solvent (B) to distill off ammonia from the reaction solution (hereinafter, "" The cleaning step may be performed after performing the ammonia distillation step).

Further, 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) the alkali metal of bis (fluorosulfonyl) imide obtained through the above steps. A step of distilling off the organic solvent (B) and water by reducing the pressure 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) Cationic 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, may be referred to as “compound (1)”). Compound (1) is NH ₄ F, for example, bis (chlorosulfonyl) imide, NH ₄ F · HF, can be synthesized by fluorination reaction by adding fluoride such NH ₄ F · 2HF, is not limited thereto , It may be obtained by various known production methods, or it may be a commercially available product.

The cation can be exchanged by reacting the 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; carbonates such as Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , and Cs ₂ CO _{3. salt; LiHCO 3, NaHCO 3, KHCO} 3, RbHCO 3, hydrogen carbonates such as _{CsHCO 3; LiCl, NaCl, KCl} , RbCl, chlorides such as CsCl; LiF, NaF, KF, RbF, fluorides such CsF; CH ₃ OLi, alkoxide compounds such EtOLi; etLi, BuLi, alkyl lithium compounds such as t-BuLi; etc. (Et represents an ethyl group, Bu is butyl group). Among these, compounds containing lithium, sodium or potassium as an alkali metal are preferable, and specifically, LiOH, NaOH, KOH, Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , LiCl, NaCl, KCl, LiF. , NaOH, KF are preferred, more preferably LiOH, NaOH, KOH, Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , and even more preferably LiOH, NaOH, KOH, these compounds being hydroxides. Is preferable.

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

In the present invention, by keeping the addition amount of the alkali metal compound within a predetermined range, the alkalinity of the reaction solution after the lithium exchange step can be suppressed to a low level and the decomposition of the 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. Further, the smaller the amount of the solid alkali metal compound added, the smaller the water content of the reaction solution after the cation exchange step and the alkalinity, for example, as compared with the case of using 1.3 equivalents which is the conventional addition amount. Since it is small, it is possible to suppress the generation of impurities that suppress the reverse reaction and deteriorate the battery characteristics. 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 amount of the alkali metal compound added is preferably 0.90 molar equivalent or more, more preferably 1.00 molar equivalent or more, still more preferably 1.01 molar equivalent, relative to 1 mol of the ammonium salt of bis (fluorosulfonyl) imide. The above is preferably 1.24 molar equivalents or less, more preferably 1.20 molar equivalents or less, still more preferably 1.15 molar equivalents or less. If the amount of the alkali metal compound used is too large, the organic solvent (B) is likely to be decomposed. 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 a reverse reaction or the like is likely to occur. On the other hand, if the amount of the alkali metal compound used is too small, the ammonium salt of bis (fluorosulfonyl) imide may remain. In the present invention, all "equivalents" are stoichiometric quantities.

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, it is preferable to use an aprotic solvent. 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. Ethyl acetate, isopropyl acetate and butyl acetate are particularly preferable from the viewpoint of facilitating the cation exchange reaction.

The temperature of the solution at the time of cation exchange is not particularly limited, but if the temperature becomes too high, the organic solvent (B) may be decomposed to generate impurities such as acetic acid, while if the temperature becomes too low, the viscosity of the reaction solution may be generated. May increase and the handling may become complicated. Therefore, it is desirable to control the temperature of the solution to preferably 40 ° C. or lower, more preferably room temperature (25 ° C.) or lower, preferably -2 ° C. or higher, and more preferably 0 ° C. or higher.

In the present invention, it is desirable to distill off at least a part of ammonia produced as a by-product in the cation exchange reaction. By distilling off ammonia, the formation of impurities such as acetamide can be suppressed. 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. Further, for water, the temperature and pressure at which water does not recirculate may be adopted in the cation exchange step. For example, the temperature is 40 ° C. or lower, preferably room temperature or lower, preferably -2 ° C. or higher, more preferably 0 ° C. or higher, and the pressure is controlled so that water does not recirculate within this temperature range (for example, 600 hPa or higher, 800 hPa or higher). The following) is preferable.

When the water content of the reaction solution after the cation exchange step is reduced, the reverse reaction between water and ammonia (for example, LiFSI + NH ₃ + H ₂ O → NH ₄ FSI + LiOH) can be suppressed to reduce the amount of ammonium produced, and it 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, still more preferably 4.0% by mass or less, based on the total mass. From the viewpoint of reducing water content, it is desirable that the cation exchange step be performed in a low humidity environment such as a dry room (temperature 25 ° C.) with a dew point of −40 ° C. or lower.

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

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

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

The method for distilling off ammonia is not particularly limited, but it is preferable to control the temperature from the reaction solution to a temperature suitable for distilling off ammonia under reduced pressure. By carrying out under reduced pressure, ammonia can be distilled off even at a low temperature, so that it is preferably 50 hPa or less, more preferably 20 hPa or less, preferably 3 hPa or more, and 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 lower, more preferably 55 ° C. or lower, still more preferably 45 ° C. or lower. The lower limit is not particularly limited and may be normal temperature (25 ° C.).

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

In the present invention, at least one of (II-1) alkali washing step and (II-2) water washing step is performed after the cation exchange step or the ammonia distillation step. When both are performed, the order is the alkaline cleaning step and the water cleaning step.

(II-1) Alkaline cleaning step By performing the alkaline cleaning step, impurities such as water-soluble impurities contained in compound (1) and water-soluble by-products during cation exchange can be reduced from the reaction solution. The alkaline washing step may be such that the reaction solution and the alkaline aqueous solution come into contact with each other. For example, 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 added to the reaction solution at the same time. It may be in a mode of contacting with each other. 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 above-mentioned cation exchange step.

In order to sufficiently remove impurities while suppressing the generation of acetic acid and acetamide in the alkaline aqueous solution, the alkali washing step is carried out in accordance with 1 mol of the alkali metal salt of the bis (fluorosulfonyl) imide. Contacting the 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 becomes strong, the organic solvent (B) may be decomposed and impurities such as acetamide and acetic acid may increase. If the amount of alkali metal is too small, the yield of alkali metal salt of bis (fluorosulfonyl) imide may decrease.

The temperature of the reaction solution when brought into contact with the alkaline aqueous solution is not particularly limited, but is preferably 25 ° C. or lower, more preferably 5 ° C. or lower, and preferably 0 ° C. or higher 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, it is preferably about 1 minute, more preferably 3 minutes after the addition of the reaction solution is completed. It is preferable to bring the reaction solution into contact with the alkaline aqueous solution while stirring to some extent. Impurities may remain if the contact time is too short.

(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), wash with water to reduce the content of acetic acid and acetamide. Reduce. In the present invention, since ammonia is reduced in the cation exchange step, the reverse reaction can be suppressed, and the generation of ammonium ions due to the reverse reaction can also be suppressed. In addition, the ammonium salt of bis (fluorosulfonyl) imide produced by the reverse reaction can also be suppressed.

The amount of water for washing with water is not particularly limited, but is preferably 1 time or more, more preferably 1.3 times or more, and preferably 2 times or less the mass of the alkali metal salt of bis (fluorosulfonyl) imide. , More preferably 1.5 times or less. If the amount of water is too small, the cleaning effect will be reduced and impurities will be removed insufficiently. 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 at the time of washing with water 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, and 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, and more preferably 5 minutes or less.

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

(III) Concentration Step In the concentration step, the organic solvent (B) and water are separated from the reaction solution after washing 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 and concentrated, and the organic solvent (B) used as the reaction solvent is replaced 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 electrolytic solution for a non-aqueous electrolyte battery may be used, and has a large dielectric constant, high solubility of the electrolyte, and a boiling point of 60 ° C. or higher. An organic solvent having a wide electrochemically stable range is more preferable, and a carbonate-based solvent is particularly preferable. Examples of the carbonate solvent include chain carbonate esters such as dimethyl carbonate, ethyl methyl carbonate (ethyl methyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate and methyl phenyl carbonate; ethylene carbonate (ethylene carbonate) and propylene carbonate (propylene carbonate). Saturated cyclic carbonates such as carbonate), 2,3-dimethylethylene carbonate (2,3-butanjiyl carbonate), 1,2-butylene carbonate and erythritan carbonate; vinylene carbonate, methylvinylene carbonate (MVC; 4-methyl- 1,3-Dioxol-2-one), ethyl vinylene carbonate (EVC; 4-ethyl-1,3-dioxol-2-one), 2-vinyl ethylene carbonate (4-vinyl-1,3-dioxolan-2-one) Cyclic carbonates having unsaturated bonds such as on) and phenylethylene carbonate (4-phenyl-1,3-dioxolan-2-one); fluoroethylene carbonate, 4,5-difluoroethylene carbonate, trifluoropropylene carbonate, etc. Fluorine-containing cyclic carbonates are mentioned, and among these, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate are preferable. These can be used alone or in combination of two or more.

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, or polycarbonate having a boiling point of more than 200 ° C. ( By using the organic solvent (A-2) that does not azeotrope with B), the organic solvent (B) can be efficiently removed.

The reactor that can be used in the concentration step is not particularly limited, and examples thereof include a rotary evaporator, a flask, a tank reactor, a tank reactor capable of depressurizing, and the like.

The amount of the organic solvent (A) to be 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 may be determined. 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, and more preferably 1.2 times or less. If the amount of the organic solvent (A) is too small, an alkali metal salt may be precipitated. On the other hand, if it is too much, the composition range of dilution into the electrolytic 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, the temperature is preferably 70 ° C. or lower, more preferably 60 ° C. or lower.

Further, the concentration step may be carried out under reduced pressure. By controlling the degree of reduced pressure, the organic solvent (B) can be efficiently removed even at a low temperature, and the decomposition of the alkali metal salt of bis (fluorosulfonyl) imide by heat can be prevented. The degree of reduced pressure 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, and more preferably 20 hPa or less. ..

The time of the concentration step is not particularly limited, but is preferably 8 minutes or more, more preferably 10 minutes or more, preferably 5 hours or less, and more preferably 3 hours or less.

In the concentration step, concentration is carried out until the water content is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, and the organic solvent (B) content is preferably 3000 mass ppm or less, more preferably 1000 mass ppm or less. Is preferable. The concentration step may be repeated a plurality of times, or the concentration step may be performed by sequentially adding the organic solvent (A-2).

The concentration step distills off the organic solvent (B) and water, 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 an impurity. In the present invention, acetamide, ammonium, and acetic acid may be contained in trace amounts as impurities. Specifically, the content of acetamide is preferably 1000 mass ppm or less (mass basis, the same applies hereinafter), more preferably 500 mass ppm or less, still more preferably 200 mass ppm or less. The ammonium content is preferably 300 mass ppm or less, more preferably 100 mass ppm or less, still more preferably 80 mass ppm or less. The content of acetic acid 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 can be obtained.

The electrolytic solution material containing the alkali metal salt of di (fluorosulfonyl) imide and the organic solvent (A) obtained by the production method of the present invention provides a charging / discharging mechanism for a primary battery, a lithium (ion) secondary battery, a fuel cell, or the like. It is suitably used as a material for an ionic conductor constituting an electrochemical device such as a battery, an electrolytic capacitor, an electric double layer capacitor, a solar cell, or an electrochromic display element.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples as well as the present invention, and appropriate modifications are made to the extent that it can be adapted to the gist of the above and the following. Of course, it is possible to carry out, and all of them are included in the technical scope of the present invention.

Example 1
Follow the procedure below to set the electrolyte material No. 1 to 3 were prepared.

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 equivalent of bis (fluorosulfonyl) imide to the obtained NH ₄ FSI 20.4 mass% butyl acetate solution. 2.36 g of the body was added, and the mixture was stirred at room temperature for 15 minutes, and the 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 lithium conversion was 51.15 g. As a result of measuring the water content, the butyl acetate amount, the lithium bis (fluorosulfonyl) imide (LiFSI) amount, and the ammonium amount of the obtained reaction solution based on the following measuring methods, the water content was 4.00% by mass (2. 05 g), butyl acetate: 73.32% by mass (37.50 g), LiFSI: 22.02% by mass (yield: 11.26 g), and ammonium was 2370% by mass.

[Ammonia distillation process]
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 distilled off at the same time as ammonia was distilled off. The mass of the reaction solution after the ammonia distillation step was 45.52 g. Further, as a result of measuring the water content and the butyl acetate amount of the reaction solution after the ammonia distillation step based on the following measurement methods, the water content was 2.30% by mass (1.05 g) and the butyl acetate: 73.84% by mass. It was (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 washing with water, the liquid was separated 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 the butyl acetate solution of lithium bis (fluorosulfonyl) imide after the water washing step under reduced pressure. I left. Specifically, for a butyl acetate solution of lithium bis (fluorosulfonyl) imide, 1 times the mass of ethylene carbonate (EC) and 2 times the mass of methyl ethyl carbonate (MEC) of lithium bis (fluorosulfonyl) imide In addition, under reduced pressure (20 hPa), the mixture was heated at 55 ° C. for 10 minutes and subjected to vacuum distillation. 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 times by mass of methyl ethyl carbonate was used. Water and ethylene carbonate were distilled off together with butyl acetate by distillation under reduced pressure to obtain 15.35 g of a LiFSI / EC / MEC solution. The amount of LiFSI in this solution was 53.74% by mass (8.25 g). The final yield of LiFSI (mass of LiFSI in solution / mass of NH ₄ FSI) was 77.61% by mass. The obtained ethylene carbonate solution of lithium bis (fluorosulfonyl) imide was used as an electrolytic solution 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 20.4 mass% butyl acetate solution of NH ₄ FSI prepared 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 the ammonia gas generated during the stirring was distilled off from the reaction solution. The obtained butyl acetate solution (reaction solution) of lithium bis (fluorosulfonyl) imide was 50.94 g. As a result of measuring the water content, butyl acetate amount, LiFSI amount, and ammonium amount of the obtained reaction solution based on the following measurement methods, water: 4.24% by mass (2.16 g), butyl acetate: 73.38. The mass% (37.38 g), LiFSI: 22.06 mass% (11.24 g), and ammonium were 2420 mass ppm.

[Ammonia distillation process]
The reaction solution obtained by cation exchange was subjected to an ammonia distillation step 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, as a result of measuring the water content and the butyl acetate content of the reaction solution after the ammonia distillation step based on the following measurement methods, water: 2.56% by mass (1.17 g) and butyl acetate: 73.60% by mass, respectively. It was (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 washing with water, the liquid was separated to remove the aqueous layer, and the obtained 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]
The above No. The concentration step was carried out in the same manner as in No. 1 to obtain 15.41 g of LiFSI / EC / MEC solution. The amount of LiFSI in this solution was 53.60% by mass (8.26 g). The final yield of LiFSI was 77.70% by mass. The obtained ethylene carbonate solution of lithium bis (fluorosulfonyl) imide was used as an electrolytic solution material No. It was set to 2.

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

[Ammonia distillation process]
The reaction solution obtained by cation exchange was subjected to an ammonia distillation step 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, as a result of measuring the water content and the butyl acetate content of the reaction solution after the ammonia distillation step based on the following measurement methods, water: 2.98% by mass (1.33 g) and butyl acetate: 73.06% by mass, respectively. It was (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 washing with water, the liquid was separated 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]
The above No. The concentration step was carried out in the same manner as in No. 1 to obtain 15.31 g of LiSFI / EC / MEC solution. The amount of LiFSI in this solution was 53.81% (8.24 g). The final LiFSI yield was 77.52%. The obtained ethylene carbonate solution of lithium bis (fluorosulfonyl) imide was used as an electrolytic solution material No. It was set to 3.

The amount of acetamide, the amount of ammonium, and the amount of acetic acid contained in each of the obtained electrolytic solution materials 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 water content measuring device (AQ-2100 manufactured by Hiranuma Sangyo Co., Ltd.). The measurement sample was prepared by diluting 0.2 g of the reaction solution after cation exchange or ammonia distillation with methanol 10-fold. 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 amount of sample injected should be 0.1 ml to 3 ml depending on the water content of the sample, "Hydranal (registered trademark) Cromat AK" (manufactured by Sigma-Aldrich) is used as the generated liquid, and "Hydra" is used as the counter electrode liquid. Nar (registered trademark) Clawmat CG-K ”(manufactured by Sigma-Aldrich) was used. The sample was injected from the sample injection port using a syringe so as not to come into contact with the outside air. Similarly, the water content of the 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 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 chart of the measurement results, and , It was obtained from the comparison between the integrated value of the peak derived from this and 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 the ammonia distillation step, and the electrolyte material No. Acetamide and acetic acid contained in 1-3 were measured. The analysis results are shown in Table 1.
The electrolyte material was diluted 40-fold with super-dehydrated acetone to prepare the assumed solution.
The apparatus was PolarisQ manufactured by Thermoquest, and the measurement was performed by the ionization method E / I method.
Gas chromatography conditions Constant temperature layer: 40 ° C. 5 minutes-250 ° C. 10 minutes Temperature rise rate 10 ° C./min Flow rate: He 1.0 mL / min Injection port: 260 ° C., split injection method 1/10
Column: CP-VOLAMINE (0.25 mm inner diameter x 30 m)

(Measurement of ammonium amount)
Using ion chromatography, the electrolyte material No. The amount of ammonium ion ions contained in 1-3 was measured. The electrolyte material was diluted 1000-fold with ultrapure water (more than 18.2 Ω · cm) to prepare a measurement solution. NH ⁴⁺ in the measurement solution was measured using ICS-2000 manufactured by Nippon Dionex Corporation.
Separation mode: Ion exchange eluent: 15-30 mM KOH aqueous solution detector: Electrical conductivity detector Column: Ion PAC OG16-CS16

In Examples 1-1 and 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 of 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 electrolytic solution material could be reduced. On the other hand, in Example 1-3 in which the amount of added lithium hydroxide / monohydrate was large, the amount of water contained in the reaction solution was large, and as a result, the amount of impurities contained in the electrolytic solution material was large.

In Examples 1-1 and 1-2, the amount of lithium hydroxide / monohydrate added in the cation exchange step was carried out within the range specified in the present invention, so that the amount of lithium hydroxide / monohydrate added was large. Compared with Examples 1-3, the alkalinity after lithium conversion could be suppressed to be low, and the decomposition of butyl acetate could be suppressed. As a result, the formation of acetic acid, which is a decomposition product of butyl acetate, can be suppressed, and the formation of acetamide, which is a dehydration condensation product of acetic acid and ammonia, can also be suppressed, and acetic acid and acetamide contained in the electrolytic solution material can be detected. It could be reduced to less than the limit. Further, in Examples 1-1 and 1-2, by reducing the water content of the reaction solution after the cation exchange step, the reverse reaction due to water and ammonia can be suppressed, and ammonium contained in the electrolytic solution material can be suppressed. I was able to reduce it.

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

In addition, lithium hexafluorophosphate (LiPF ₆ , manufactured by Kishida Chemical Co., Ltd., electrolyte salt) was added to a non-aqueous solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a ratio of 3: 7 (volume ratio). The mixture was dissolved to prepare a non-aqueous electrolyte II having a LiPF ₆ concentration of 1.2 mol / L.

The non-aqueous electrolytic solution I-1 and the non-aqueous electrolytic 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 solution No. 1 was prepared.

Electrolyte material No. Instead of No. 1, the electrolyte material No. Non-aqueous electrolyte solutions No. 2 and I-3 were prepared in the same manner as above except that the non-aqueous electrolyte solutions I-2 and I-3 were prepared using 2 and 3. A few were prepared.

Battery evaluation Fabrication of laminated lithium-ion secondary battery Positive electrode active material (LiCoO ₂ ), conductive auxiliary agent 1 (acetylene black, manufactured by Denki Kagaku Kogyo), conductive auxiliary agent 2 (graphite) and binder (PVdF, Kureha Co., Ltd.) -Aluminum foil (positive electrode current collector) is a positive electrode mixture slurry in which "Kureha L # 1120" manufactured by Battery Materials Japan) is mixed at a mass ratio of 93: 2: 2: 3 and dispersed in N-methylpyrrolidone. Both sides were coated on the surface, dried and compressed to prepare a positive electrode sheet.

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

The negative electrode sheets (85 μm) were laminated so as to face both sides of the positive electrode sheet (150 μm), and one polyethylene separator (diameter 16 μm) was sandwiched between them. A laminate in which the negative electrode sheet, the separator, the positive electrode sheet, the separator, and the negative electrode sheet are laminated in this order is sandwiched between two aluminum laminates, the inside of the aluminum laminate film is filled with 0.7 mL of non-aqueous electrolytic solution 1, and the mixture is sealed in a vacuum state ( Capacity 34mAh), Lithium-ion secondary battery No. 1 was produced. In addition, the non-aqueous electrolyte solution No. No. 1 is a non-aqueous electrolyte solution No. Lithium ion secondary battery No. 2 in the same manner as above except that it was changed to 2 and 3. A few were made.

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

(1) Initial charge / discharge efficiency For a lithium ion secondary battery, a charge / discharge test device (ACD-01 manufactured by Asuka Electronics Co., Ltd., the same shall apply hereinafter) is used in an environment of a temperature of 25 ° C., and predetermined charging conditions (0. Charging was performed at 5C (32mA), 4.35V, constant current constant voltage mode) for 5 hours. Then, the 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 1 g of the positive electrode active material and the initial discharge capacity per 1 g of the positive electrode active material were recorded, and the initial charge / discharge efficiency was calculated from the obtained values by the following formula. The results are shown in Table 2.
Initial charge / discharge efficiency (%) = (Initial discharge capacity / Initial charge capacity) x 100

(2) Initial rate characteristics Using a charge / discharge test device (“ACD-01” manufactured by Asuka Electronics Co., Ltd.), a lithium ion secondary battery with a current value of 1C (64mA), 4 After charging at a constant voltage of .35 V until the current dropped to 0.05 C (1.28 mA), constant current discharge was performed at 0.2 C (12.8 mA) to 2.75 V. The discharge capacity per 1 g of the positive electrode active material at this time was set to 0.2 C capacity. Then, after charging again under the above conditions, constant current discharge was performed at 2.0 C to 2.75 V. The discharge capacity per 1 g of the positive electrode active material at this time was set to 2.0 C capacity. The initial rate was calculated from the obtained discharge capacity value from the following formula. The results are shown in Table 2.
Initial rate characteristics (%) = (2.0C capacity / 0.2C capacity) x 100

(3) Cycle capacity retention rate Using a charge / discharge test device (ACD-01, manufactured by Asuka Electronics Co., Ltd.), the current amount is 4.35 V constant current constant voltage charging at a charging speed of 1 C at a temperature of 45 ° C. Perform until 0.02C, discharge until the voltage reaches 2.75V at a discharge rate of 1C, and perform a cycle characteristic test with a charge / discharge pause time of 10 minutes 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 1 cycle) x 100

Electrolyte material No. obtained by a production method satisfying the requirements of the present invention. As described above, 1 and 2 have an impurity content of the electrolytic solution material No. It was reduced as compared with 3. Therefore, the electrolyte material No. Lithium ion secondary battery No. 1 and 2 prepared from 1 and 2 are electrolyte material Nos. Lithium ion secondary battery No. 3 prepared from No. The initial charge / discharge efficiency, initial rate characteristics, and capacity retention rate were improved as compared with 3.

From this, it can be seen that the battery characteristics can be improved by reducing the contents of acetamide, ammonium, and acetic acid.

Claims (4)

A method for producing an electrolytic solution material containing 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. Cation exchange step to obtain salt,
The step of alkaline washing and / or water washing of the obtained reaction solution, and after the washing, the organic solvent (B) and water are distilled off by reducing the pressure and / or heating in the presence of the organic solvent (A). Including the process
The amount of the alkali metal compound in the cation exchange step, the bis (fluorosulfonyl) ammonium imide salt 1 mol per 1.01 mol equivalent or more, Ri 1.24 molar equivalents or less der,
The alkali metal compound is added as a solid,
A method for producing an electrolytic solution material, wherein 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 depressurized and / or heated in the presence of the organic solvent (B) to distill off ammonia from the reaction solution, and then the alkali washing and / or the water washing. The method for producing an electrolytic solution material according to claim 1 . The method for producing an electrolytic solution material according to claim 1 or 2 , wherein the organic solvent (B) is an ester solvent. The method for producing an electrolytic solution material according to any one of claims 1 to 3 , wherein the organic solvent (A) is a carbonate-based solvent.