JP5557010B2 - Electrolyte production method - Google Patents

Description

  The present invention relates to a method for producing an electrolytic solution useful as a component of an electrochemical device such as a lithium ion secondary battery or an electric double layer capacitor, and more particularly to a method for producing an electrolytic solution containing an ionic liquid.

  An electrolyte solution included in an electrochemical device such as a battery is required to have stability capable of withstanding a voltage applied to the electrolyte solution in the device. For example, in a battery (such as a lithium ion secondary battery) in which the electrolytic solution receives a voltage approximately equal to or higher than the decomposition voltage of water, an electrolytic solution (water-based electrolytic solution) containing water as a constituent component cannot be used. For this reason, as an electrolytic solution of a lithium ion secondary battery, generally, a lithium salt (supporting electrolyte) dissolved in an aprotic liquid is used. Representative examples of the aprotic liquid include carbonate solvents such as ethylene carbonate, propylene carbonate, and diethyl carbonate.

  The use of an ionic liquid (sometimes referred to as room temperature molten salt) as a constituent component of the electrolytic solution is also being studied. Representative examples of such ionic liquids include those in which the cation component is imidazolium (hereinafter sometimes referred to as “imidazolium-based ionic liquid”), and those in which the cation component is aliphatic cyclic ammonium (hereinafter referred to as “aliphatic cyclic”). And so on.) And the like. Patent Documents 1 and 2 describe an electrolytic solution using an aliphatic cyclic ammonium ionic liquid as an aprotic liquid. Patent Documents 3 and 4 describe electrolytes using aliphatic cyclic ammonium salts (but not necessarily ionic liquids), but these use the ammonium salts themselves as liquids. It is not intended, but is used by dissolving the ammonium salt in an organic solvent. For example, in the technique described in Patent Document 4, an electrolytic solution in which the ammonium salt is dissolved in an aprotic polar solvent (propylene carbonate or the like) is prepared, and the electrolytic solution is treated with activated carbon to thereby prepare an electrolytic solution for an electric double layer capacitor Is purified.

JP 2006-206457 A JP 2008-10613 A JP 2009-65062 A JP 2008-277401 A

  By the way, as a technique for improving the energy density of the secondary battery, there is a technique for increasing the operating voltage of the battery. For example, if the upper limit voltage is changed from 4.1 V to 4.4 V without changing the lower limit voltage in charging / discharging, the amount of current that can be extracted from the battery is increased, and the energy density is improved. If a material having higher voltage stability than a general aprotic solvent is provided, it is useful as an electrolytic solution or a component thereof in various fields including the electrolytic solution for a battery.

  Aliphatic cyclic ammonium-based ionic liquids have higher voltage stability than common aprotic solvents (for example, carbonate-based solvents) and tend to exhibit higher reduction stability than imidazolium-based ionic liquids. It is in. However, in general, the aliphatic cyclic ammonium ionic liquid has a higher viscosity than the imidazolium ionic liquid. As the viscosity increases, the ion transport number tends to decrease. Such a decrease in ion transport number can be a factor that reduces the performance as an electrolyte.

  Therefore, the present invention produces an electrolyte containing an aliphatic cyclic ammonium ionic liquid and having a lower viscosity (for example, an electrolyte for an electricity storage device such as a lithium ion secondary battery or an electric double layer capacitor). The purpose is to provide a method. Another related object is the provision of an electrochemical device comprising such an electrolyte.

  According to the present invention, a method for producing an electrolyte containing an ionic liquid is provided. The ionic liquid is a salt of a cation Ay and an anion By, and the cation Ay is pyrrolidinium or piperidinium. The electrolytic solution manufacturing method includes preparing a solution in which a first raw material that is a salt of a cation Ay and an anion Bx is dissolved in a solvent (typically a polar solvent such as water). The solution may be a solution prepared by dissolving the first raw material obtained through at least one crystallization in the solvent. The said manufacturing method also includes performing the process which contacts the said solution with adsorption material (for example, activated carbon). In addition, after the solution is separated from the adsorbent, the second raw material having an anion By and the first raw material are mixed to generate the ionic liquid.

  In such a production method, the first raw material is first treated with an adsorbent, and then the anion Bx of the first raw material is exchanged with an anion By to produce a target ionic liquid (typically AyBy). By this, compared with the case where the same adsorbent process is performed after anion exchange, the ionic liquid of lower viscosity (for example, gelatinization or the viscosity increase was suppressed) can be formed. Therefore, a low-viscosity electrolytic solution containing the ionic liquid (which can be an electrolytic solution composed only of the ionic liquid) can be produced.

  In this specification, the ionic liquid refers to a salt (sometimes referred to as a normal temperature molten salt, a room temperature molten salt, or the like) that can maintain the liquid properties in the normal temperature range. Here, the “normal temperature range” refers to a temperature range in which the upper limit is 80 ° C. (typically 60 ° C., in some cases 40 ° C.), and the lower limit is −30 ° C. (eg, −10 ° C.). Any salt may be used as long as the liquid property can be maintained in at least a part of the temperature range. A salt having a melting point lower than the above upper limit temperature is a typical example of the ionic liquid referred to herein. From the viewpoint that it can be suitably used alone (that is, without diluting with another organic solvent) as an electrolyte or a constituent material thereof, the melting point is 30 ° C. or lower, typically 20 ° C. or lower (more preferably 10 ° C. or lower). An ionic liquid having a temperature of 0 ° C. or lower, more preferably 0 ° C. or lower is preferable.

  A preferable application target of the method disclosed herein is an electrolytic solution in which the cation Ay is pyrrolidinium or piperidinium represented by the formula (I).

Here, R ¹ in the above formula (I) may be a substituted or unsubstituted alkyl group containing an ether bond. R ² in the above formula (I) may be a substituted or unsubstituted alkyl group containing or not containing an ether bond. P in the above formula (I) is a chemical bond in the case of pyrrolidinium, and an alkylene group having 1 carbon atom in the case of piperidinium. An ionic liquid having a cation Ay having such a structure is preferred because it tends to have a low viscosity.

As the anion component (anion Bx) in the first raw material, one in which the first raw material exhibits a solid state at room temperature (for example, 25 ° C.) can be preferably used. Such a first raw material may have good handleability (for example, handleability in operations such as washing, drying, and recrystallization performed as necessary). Preferred anions Bx are exemplified by halide ions (for example, chloride ions (Cl ⁻ )).

  In the technique disclosed herein, a preferred example of the anion component (anion By) constituting the ionic liquid is an anion represented by the formula (II).

Here, Rf ¹ and Rf ² in the above formula (II) may be the same or different perfluoroalkyl groups. An ionic liquid having an anion By having such a structure is preferred because it tends to have a low viscosity.

  According to this specification, there is also provided an electrochemical device comprising an electrolyte produced by any of the methods disclosed herein. A suitable example of such an electrochemical device is a secondary battery.

  In the present specification, the “secondary battery” is a term that generally indicates an electric storage device capable of storing and taking out electric energy, and is a lithium ion secondary battery, a metal lithium secondary battery, a nickel metal hydride battery, nickel cadmium. It is a concept encompassing so-called storage batteries such as batteries and power storage devices such as electric double layer capacitors. In this specification, the term “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of lithium ions between the positive and negative electrodes (typically metal lithium (single element ) Is not used as an electrode constituent material.

  According to this specification, the electrolyte solution for using as a component of a lithium ion secondary battery is also provided. The electrolytic solution contains an ionic liquid obtained by any of the methods disclosed herein and a lithium salt as a supporting electrolyte. According to such an electrolytic solution, a high-performance lithium ion secondary battery can be constructed because the electrolytic solution is excellent in voltage stability and has a low viscosity.

  A secondary battery provided with any of the electrolyte solutions disclosed herein (which may be an electrolyte solution produced by any of the methods disclosed herein) may be used alone or in series. In the form of an assembled battery, it can be preferably used as a battery mounted on a vehicle. For example, it is suitable as a power source for a motor (electric motor) of a vehicle such as an automobile. Therefore, according to the present invention, as schematically shown in FIG. 3, a vehicle (typically, which is provided with any of the secondary batteries (which may be in the form of an assembled battery) 10 disclosed herein as a power source (typically). Automobiles, in particular automobiles equipped with electric motors such as hybrid cars, electric cars, fuel cell cars, etc.) 1 can be provided.

It is a partial section perspective view showing typically the composition of the lithium ion secondary battery concerning one embodiment. It is a characteristic view which shows the relationship between a composition of electrolyte solution, and the amount of leakage current. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery which concerns on one Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The electrolytic solution in the technology disclosed herein includes an ionic liquid that is a salt of a cation Ay and an anion By, and the cation Ay is pyrrolidinium or piperidinium. In the cation Ay, the carbon atom constituting the aliphatic ring (pyrrolidine ring or piperidine ring) may or may not have a substituent. When it has a substituent, the substituent is a halogen atom (for example, F, Cl, Br, I, preferably F), an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, Etc. In a preferred embodiment, the aliphatic ring is a pyrrolidine ring or piperidine ring having no substituent (ie, unsubstituted) on the carbon atoms constituting the ring.

  Preferable examples of the cation Ay include cations represented by the above formula (I). The cation is pyrrolidinium when p is a chemical bond, and piperidinium when p is an alkylene group having 1 carbon atom (ie, methylene group).

R ¹ may be a substituted or unsubstituted alkyl group (referred to as “alkyl ether group”) containing one or more ether bonds. Thus, the cation Ay having a substituent containing ether oxygen on the nitrogen atom of the pyrrolidine ring or piperidine ring is weakened in the positive charge of the cation by the presence of the ether oxygen, and the lone pair on the ether oxygen and By ( The interaction between Ay and By can be weakened by the electrostatic repulsion effect with the counter anion in the ionic liquid. This can contribute to lowering the melting point and viscosity of the ionic liquid. An electrolytic solution containing such an ionic liquid is preferable because it can have higher properties (for example, a composition containing a lithium salt has a high lithium ion transport number and good low-temperature properties).

R ¹ may be an open-chain alkyl ether group and may form a ring structure. The term “open chain” as used herein means both an open chain having no branch (straight chain) and an open chain having a branch (branched chain) unless otherwise specified. When R ¹ has a substituent, the substituent may be a halogen atom (eg, F) such as F, Cl, or Br. Preferable examples of R ¹ include an alkyl ether group having 2 to 10 (preferably 2 to 5, for example, 2 to 3) carbon atoms and an open chain (preferably a straight chain). The cation Ay having R ¹ having such a structure can be an ionic liquid having a lower viscosity, and thus an electrolytic solution containing the ionic liquid. The number of ether bonds contained in R ¹ is preferably 2 or less (typically 1).

In a preferred embodiment, R ¹ is a substituted or unsubstituted alkyl ether group represented by —R ³ —O—R ⁴ . R ³ may be a substituted or unsubstituted alkylene group having 1 to 3 carbon atoms. R ⁴ may be a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms. When R ³ and / or R ⁴ have a substituent, a preferred example of the substituent is a halogen atom (eg, F, Cl, Br, I). For example, R ¹ having a structure in which neither R ³ nor R ⁴ has a substituent can be preferably used. Further, R ¹ having a structure in which R ³ and R ⁴ are both linear can be preferably used. This can provide a lower viscosity ionic liquid and an electrolyte containing the ionic liquid.

R ² is a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkyl ether group. When R ² is an alkyl ether group, preferred examples thereof include those similar to R ¹ . R ¹ and R ² may be the same or different from each other. When R ² is an alkyl group, the alkyl group may be an open chain or may form a ring structure. Preferable examples of R ² include an alkyl group having 1 to 10 (preferably 1 to 5, for example 1 to 3) carbon atoms and an open chain (preferably a straight chain).

Specific examples of the alkyl ether group that can be preferably employed as R ¹ and / or R ² include CH ₃ OCH ₂ CH ₂ —, CH ₃ CH ₂ OCH ₂ CH ₂ —, CH ₃ OCH ₂ CH ₂ OCH ₂ CH ₂ —, and _{CH 3 CH 2 OCH 2 CH 2} OCH 2 CH 2 - and the like. Specific examples of the alkyl group that can be preferably employed as R ² include CH ₃ —, CH ₃ CH ₂ —, and CH ₃ CH ₂ CH ₂ —. For example, a cation Ay in which R ¹ is any ^one of the above alkyl ether groups and R ² is any one of the above alkyl groups is preferable.

The anion By is an anion that can form an ionic liquid with the cation Ay as described above. Preferable examples include anions represented by the above formula (II). Rf ¹ and Rf ² in the above formula are the same or different perfluoroalkyl groups. The perfluoroalkyl group may be an open chain or may form a ring structure. An open chain (particularly linear) perfluoroalkyl group is preferred. The number of carbon atoms in Rf ¹ and Rf ² may be, for example, 1 to 10 (preferably 1 to 5, more preferably 1 to 3). A linear or branched (more preferably linear) perfluoroalkyl group satisfying the number of carbon atoms is preferred. Specific examples of such a perfluoroalkyl _{group, -CF 3, -CF 2 CF 3} , -CF 2 CF 2 CF 3, -CF 2 (CF 2) 2 CF 3, -CF 2 (CF 2) 3 CF 3, and _{-CF 2 (CF 2) 4 CF} 3 and the like. Among these, —CF ₃ , —CF ₂ CF ₃ and —CF ₂ CF ₂ CF ₃ are preferable. A particularly preferred anion is an anion (bis (trifluoromethanesulfonyl) imide; hereinafter may be referred to as “TFSI”) in which Rf ¹ and Rf ² are both —CF ₃ .

  As a particularly preferable application target of the technology disclosed herein, the cation Ay is N-methyl-N-methoxymethylpyrrolidinium, N-ethyl-N-methoxymethylpyrrolidinium, N-methyl-N-ethoxymethylpyrrolidi. Ni, N-ethyl-N-ethoxymethylpyrrolidinium, N-methyl-N-methoxymethylpiperidinium, N-ethyl-N-methoxymethylpiperidinium, N-methyl-N-ethoxymethylpiperidinium, And N-ethyl-N-ethoxymethylpiperidinium, and a salt in which the anion By is TFSI.

The technique disclosed herein may include crystallizing a first raw material that is a salt of a cation Ay and an anion Bx in the process of obtaining the ionic liquid. As the anion Bx, an anion different from the anion By is typically used. From the viewpoint of handling properties during recrystallization, washing, drying, and the like, an anion Bx such that the first raw material becomes solid at room temperature (typically 20 ° C. to 30 ° C.) can be preferably selected. . Specific examples of preferable anions Bx include halide ions such as chloride ions (Cl ⁻ ) and bromide ions (Br ⁻ ).

  The crystallized first raw material may be further recrystallized before preparing a solution to be brought into contact with the adsorbent in consideration of the quality (purity) of the starting raw material. When performing such recrystallization, the frequency | count may be only 1 time, and may be performed twice or more as needed. From the balance between quality and productivity, it is usually appropriate to set the number of recrystallizations to about 1 to 5 times (preferably 1 to 3 times). Recrystallization of the first raw material can be performed by a conventional method. For example, a method in which the first raw material is added to a small amount of solvent and heated to be completely dissolved, and the hot solution is filtered as necessary, and then slowly cooled (cooled) can be preferably used. What is necessary is just to select an appropriate thing as a recrystallization solvent according to the kind of 1st raw material. For example, a monoalcohol having about 1 to 4 carbon atoms (such as isopropyl alcohol) can be preferably used. As another recrystallization method, a method of adding a poor solvent little by little to a solution in which a first raw material is dissolved in a small amount of a good solvent is exemplified.

  In addition, when the sufficiently high-purity first raw material can be obtained (purchased, synthesized, etc.) in the form of crystals or solutions, the crystallization step can be omitted. That is, the technique disclosed in this specification includes a method for producing an electrolytic solution containing an ionic liquid that is a salt of a cation Ay and an anion By, wherein the cation Ay is pyrrolidinium or piperidinium: Preparing a solution in which the solution is dissolved in a solvent (eg water); performing a treatment of contacting the solution with an adsorbent (typically activated carbon); and separating the solution from the adsorbent, and then anion By A method of producing an electrolyte solution, comprising: mixing a second raw material having the first raw material with the first raw material to produce the ionic liquid. The technique disclosed herein also includes a method of producing an ionic liquid that is a salt of a cation Ay and an anion By: preparing a solution in which a first raw material is dissolved in a solvent (eg, water); Treating the solution with an adsorbent (typically activated carbon); and, after separating the solution from the adsorbent, mixing the second raw material having an anion By and the first raw material to Producing a ionic liquid can be included.

  The technique disclosed herein can also include preparing a solution in which the first raw material (typically, the first raw material obtained through at least one recrystallization) is dissolved in a solvent. A polar solvent is preferably used for the preparation of the solution, and usually water (ion exchange water, distilled water, etc.) is preferably used.

Next, the first raw material solution is brought into contact with the adsorbent. As the adsorbent, activated carbon, zeolite, molecular sieve, alumina, silica gel, diatomaceous earth, or the like can be preferably used. Of these, the use of activated carbon is preferred. Although the kind of activated carbon is not specifically limited, From a viewpoint of processing efficiency, normally, a specific surface area of about 1000-2000 m < ² > / g can be preferably used.

  As a contact method between the first raw material solution and the adsorbent, a method in which the first raw material solution is passed through a filter having an adsorbent, a method in which a particulate or powdered adsorbent is introduced into the first raw material solution and mixed and dispersed. , Etc. may be employed as appropriate. In the former case, the adsorbent and the solution can be separated by collecting the first raw material solution that has passed through the filter. In the latter case, the solution in which the adsorbent is dispersed is subjected to treatment such as filtration, decantation, and centrifugal separation (two or more treatments may be performed as necessary), and the adsorbent. The solution can be separated.

  In a preferred embodiment, a contact method in which a particulate or powdery adsorbent is introduced into the first raw material solution and mixed and dispersed is employed. In this case, the amount of adsorbent (for example, activated carbon) used is not particularly limited. Usually, it is appropriate to use activated carbon in an amount corresponding to 0.01 to 10% by mass (typically 0.05 to 5% by mass, for example, 0.1 to 2% by mass) of the first raw material. The time for bringing the first raw material solution into contact with the adsorbent is preferably about 10 seconds or longer. This contact time may be 1 hour or longer. On the other hand, from the viewpoint of productivity of the ionic liquid or the electrolytic solution, it is appropriate that the contact time is approximately 7 days or less.

In the technology disclosed herein, the first raw material solution treated with the adsorbent in this way is separated from the adsorbent, and then the second raw material having an anion By and the first raw material are mixed. Thereby, the anion Bx in the first raw material is exchanged (replaced) with the anion By to generate an ionic liquid that is a salt of the cation Ay and the anion By. As the second raw material, a salt of an arbitrary cation (which may be H ⁺ ) and an anion By can be used. As a specific operation, for example, the second raw material may be added to the first raw material solution as it is or in the form of a solution in which the second raw material is dissolved in an appropriate solvent and mixed. In a preferred embodiment, in order to increase the efficiency of anion exchange, an amount of an anion By containing an anion By in an excess amount (for example, 1.01 or more moles) relative to the number of moles of anion Bx contained in the first raw material. Use two raw materials. The upper limit of the amount of the second raw material used is not particularly limited, but from the viewpoint of easy removal of excess second raw material, the number of moles of anion By is 3 times or less (more preferably 1). .5 or less) is appropriate.

  In a preferred embodiment, the ionic liquid generated above is washed with a polar solvent (for example, water) that can be separated into two phases from the ionic liquid, thereby removing the anion Bx and the excess second raw material. Thereafter, the ionic liquid may be dried (depressurized drying, heat drying, etc. may be employed as appropriate), and the polar solvent mixed during washing may be more reliably removed from the ionic liquid.

The ionic liquid thus obtained can be suitably used as an electrolytic solution for various electrochemical devices in a form in which an appropriate material according to the purpose is blended (typically dissolved) if desired. For example, in the production of an electrolytic solution for a lithium ion secondary battery, an electrolytic solution may be prepared by dissolving an appropriate amount of a supporting electrolyte (supporting salt) in the ionic liquid. As the supporting electrolyte, LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ are used as in a general lithium ion secondary battery. Lithium salts such as F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ and LiClO ₄ can be preferably used. The concentration of the supporting electrolyte is not particularly limited, and can be, for example, the same level as that of a conventional lithium ion secondary battery. In a preferred embodiment, the electrolytic solution is prepared so that the supporting salt is contained in the ionic liquid at a concentration of about 0.1 mol / L to 5 mol / L (for example, about 0.8 mol / L to 1.5 mol / L) ( Manufacturing).

  When the ionic liquid is used as an electrolytic solution for an electric double layer capacitor, it is not essential to add the supporting electrolyte or the like. That is, the ionic liquid can be used as an electrolytic solution as it is. Alternatively, an electrolytic solution for an electric double layer capacitor may be produced by dissolving another appropriate salt in the ionic liquid. Examples of such salts include various quaternary ammonium salts that are solid at room temperature (for example, salts used in conventional electric double layer capacitors dissolved in an organic solvent such as propylene carbonate, which are solid at room temperature. Can be used.

  In the method disclosed herein, in the process of forming an ionic liquid that is a salt of a cation Ay and an anion By, the first raw material is first treated with an adsorbent as described above, and then the anion Bx of the first raw material. It is important to exchange for an anion By. According to such a method, for example, the anion Bx of the first raw material not treated with the adsorbent is exchanged with the anion By to generate an ionic liquid, and then the viscosity is lower than that of the method of treating the ionic liquid with the adsorbent. The ionic liquid can be obtained. Therefore, a lower viscosity electrolyte can be provided. Moreover, according to the method disclosed here, an ionic liquid can be manufactured with a higher yield compared with the method of performing an adsorbent treatment after exchanging the anion Bx with the anion By.

  In addition, the electrolyte solution disclosed here can contain other materials which are liquid at room temperature in addition to the ionic liquid (AyBy) which is a salt of the cation Ay and the anion By. For example, an ionic liquid that is a salt of a cation other than pyrrolidinium and piperidinium and any anion can be included. In addition to the ionic liquid AyBy, the technique disclosed herein can also be applied to an electrolytic solution containing a general organic solvent (a nonionic material that exhibits a liquid state at room temperature). According to the present invention, an ionic liquid AyBy having a lower viscosity than that of the conventional method can be obtained. Therefore, in the production of an electrolytic solution containing a general organic solvent in addition to the ionic liquid, the fluidity (viscosity of the electrolytic solution) ) To the desired value, the effect of reducing the amount of organic solvent used can be realized.

  The technique disclosed here can be preferably applied to the production of an electrolytic solution substantially free of a general organic solvent. Such an electrolyte is preferable because it can exhibit higher stability with respect to voltage. Here, “substantially free” means that at least a general organic solvent is not intentionally added to dilute the ionic liquid. Therefore, in the electrolytic solution, it can be allowed that a small amount of an organic solvent unintentionally mixed in the production process of the ionic liquid (for example, 1 part by mass or less with respect to 100 parts by mass of the ionic liquid).

The technology disclosed herein is an ionic liquid in which the cation Ay is pyrrolidinium represented by the above formula (I) (that is, a cation in which p is a chemical bond in the formula (I)), and production of an electrolytic solution containing the ionic liquid It can be preferably applied to. In this case, as a method for producing the first raw material in which the anion Bx is a chloride ion, for example, the following method can be preferably employed. That is, a starting material having a structure in which R ² is bonded to the nitrogen atom of the pyrrolidine ring (hereinafter also referred to as “N—R ² pyrrolidine”, 1-methylpyrrolidine in the production example described later) is prepared. If necessary, the raw material is purified by, for example, vacuum distillation. Next, this N—R ² pyrrolidine is reacted with the chlorinated product of R ¹ (in the production example described later, chlorodimethyl ether (CH ₃ OCH ₂ Cl)). Typically, a chlorinated product of R ¹ is dropped into a solution obtained by dissolving N—R ² pyrrolidine in a suitable reaction solvent (eg, acetone), and stirred at room temperature. Thereby, the target first raw material (N-methyl-N-methoxymethylpyrrolidinium in the production example described later) is generated. In the production of an ionic liquid using the first raw material thus synthesized (pyrrolidinium salt) and an electrolytic solution containing the ionic liquid, the presence or absence of activated carbon treatment and the timing of the treatment are the properties of the resulting ionic liquid. (Gelation, coloring, etc.) and yield are easily affected. Therefore, it is particularly meaningful to apply the method disclosed herein.

  Hereinafter, a configuration example of a lithium ion secondary battery including the electrolytic solution disclosed herein will be described with reference to the drawings. As shown in FIG. 1, the lithium ion secondary battery 10 includes an electrolytic solution 20 in which an electrode body 11 including a positive electrode 12, a negative electrode 14, and a separator 13 is manufactured by any of the methods disclosed herein. And it has the structure accommodated in the battery case (container) 15 of the shape which can accommodate this electrode body. At least a part of the electrolytic solution 20 is impregnated in the electrode body 11. As battery components other than the electrolytic solution 20, the same components as those of conventionally known lithium ion secondary batteries can be appropriately employed.

  The electrode body 11 includes a positive electrode (positive electrode sheet) 12 having a structure in which a positive electrode mixture layer 124 mainly including a positive electrode active material is provided on a long sheet-like positive electrode current collector 122, and a negative electrode active material as a main component. A negative electrode (negative electrode sheet) 14 having a configuration in which a negative electrode mixture layer 144 is provided on a long sheet-like negative electrode current collector 142 is superposed on two long sheet-like separators 13, It is formed by winding in a cylindrical shape. As the positive electrode current collector 122, an aluminum foil or the like can be preferably used, and as the negative electrode current collector 142, a copper foil or the like can be preferably used. As the separator 13, a porous polyolefin film or the like can be preferably used.

As the positive electrode active material, an oxide-based positive electrode active material having a layered structure, an oxide-based positive electrode active material having a spinel structure, and the like used in a general lithium ion secondary battery can be preferably used. Examples of the layered oxide positive electrode active material include lithium transition metal oxides having a layered rock salt type crystal structure, such as lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. In a preferred embodiment, a ternary lithium transition metal oxide containing at least Ni, Co, and Mn as transition metal elements (for example, containing these three kinds of transition metal elements in substantially the same atomic ratio) is used as a positive electrode active material. Used for substances. As a typical example of the oxide-based positive electrode active material having a spinel structure, lithium manganese oxide having a spinel crystal structure can be given. Examples of this type of lithium manganese oxide include LiMn ₂ O ₄ and compounds having a composition in which part of the Mn is replaced with another metal element. Other examples of the positive electrode active material include so-called polyanionic positive electrode active materials such as lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium cobalt phosphate, and lithium iron silicate. In a preferred embodiment, a positive electrode active material in which a carbon coating is applied to the particle surface of such a polyanionic positive electrode active material (for example, lithium iron phosphate) is used.

  As the negative electrode active material, an appropriate material can be adopted from various materials that are generally known to function as a negative electrode active material of a lithium ion secondary battery. As a suitable active material, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least partially may be mentioned.

  The battery case 15 includes a bottomed cylindrical case main body 152 and a lid 154 that closes the opening. The lid 154 and the case main body 152 are both made of metal and insulated from each other, and are electrically connected to the positive and negative current collectors 122 and 142, respectively. That is, in the lithium ion secondary battery 10, the lid body 154 also serves as a positive electrode terminal, and the case body 152 serves as a negative electrode terminal.

  On one edge along the longitudinal direction of the positive electrode current collector 122, a portion where the current collector 122 is exposed without providing the positive electrode mixture layer (positive electrode mixture layer non-forming portion) is provided. Similarly, on one edge along the longitudinal direction of the negative electrode current collector 142, a portion where the current collector 142 is exposed without the negative electrode mixture layer (a negative electrode mixture layer non-forming portion) is provided. . The lid 154 and the case main body 152 are connected to the exposed portions.

  In addition, although the cylindrical lithium ion secondary battery 10 is illustrated in FIG. 1, the shape (outer shape) of the lithium ion secondary battery disclosed here is not limited to the cylindrical shape, and for example, a rectangular shape, It may be a coin type or the like.

  The technology disclosed herein is for use under charge / discharge conditions in which the upper limit voltage between the positive and negative terminals is 4.3 V or higher (for example, about 4.4 V or higher, typically 7 V or lower, for example, 5 V or lower). It can be preferably applied to a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery). The lower limit voltage is not particularly limited, and can be, for example, about 3.0V. A positive electrode active material and a negative electrode active material may be combined so that such a voltage between terminals is obtained. Since the electrolytic solution produced by the method disclosed herein has high stability with respect to voltage, it is used as an electrolytic solution for a non-aqueous electrolyte secondary battery that is used under charge / discharge conditions with a relatively high upper limit voltage. Particularly preferred.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.

<Production Example 1: Production of N-methyl-N-methoxymethylpyrrolidinium-TFSI (1)>
(1) Distilled to purify 1-methylpyrrolidine.
(2) A solution obtained by dissolving 50 g (0.587 mol) of 1-methylpyrrolidine in 100 g of acetone was placed in a separable flask equipped with a stirrer, and 60 g (0.7 mol) of 95% chlorodimethyl ether was added dropwise thereto at room temperature. For 24 hours. As a result, white crystals of N-methyl-N-methoxymethylpyrrolidinium chloride (first raw material) were precipitated.
(3) The first raw material was filtered off and washed thoroughly with 100 g of cooled acetone.
(4) The first raw material was dissolved in 50 g of isopropyl alcohol and recrystallized twice, and then dried under reduced pressure for 1 hour. The yield was 68.07 g (0.4109 mol), and the yield was 70%.

(5) The 1st raw material obtained by performing the said operation was dissolved in 50 g of water, activated carbon powder was added to this aqueous solution, and it stirred for 24 hours. As the activated carbon powder, one having a specific surface area of 1500 m ² / g and an average particle diameter of 5 μm was used. The amount of the activated carbon powder used was an amount corresponding to 0.5% of the mass of the first raw material.
(6) The aqueous solution was filtered to remove activated carbon.
(7) HN (SO ₂ CF ₃ ) ₂ (hereinafter sometimes referred to as “HTFSI”) in pure water is 70% by mass in the obtained filtrate (the first raw material aqueous solution treated with activated carbon). A solution containing 175 g (0.448 mol) in a ratio was added dropwise and stirred at room temperature for 1 hour to generate an ionic liquid.
(8) The upper layer (aqueous phase) was removed by decantation.
(9) The remaining lower layer was washed with water to remove excess HTFSI. The washing with water was repeated until the pH of the aqueous phase reached 7.
(10) The lower layer after washing with water was heated to 120 ° C. for 24 hours to remove moisture.

  N-methyl-N-methoxymethylpyrrolidinium-TFSI was obtained through the above steps. The resulting product was an ionic liquid that was colorless and transparent at room temperature (23 ° C.). The yield was 151.6 g, and the yield relative to the amount of the first raw material used was 95%. Further, this resultant product had a clearly lower viscosity than the resultant products of Production Examples 3 and 4 to be described later, and no gelation tendency was observed.

<Production Example 2: Synthesis of N-methyl-N-methoxymethylpiperidinium-TFSI (1)>
N-methyl-N-methoxymethylpiperidinium-TFSI was obtained in the same manner as in Production Example 1 except that 1-methylpiperidine was used instead of 1-methylpyrrolidine. The resulting product was an ionic liquid that was colorless and transparent at room temperature (23 ° C.). The yield was 68 g, and the yield relative to the amount of the first raw material (N-methyl-N-methoxymethylpiperidinium chloride) used was 70%. Further, this resultant product had a low viscosity, and no tendency to gel was observed.

<Production Example 3: Synthesis of N-methyl-N-methoxymethylpyrrolidinium-TFSI (2)>
In this example, in (5) and (6) of Production Example 1, the operation of treating the aqueous solution of the first raw material with activated carbon powder was not performed. Instead, in the recrystallization process of the first raw material, more specifically, in the production example 1 (4), in the solution of the first raw material obtained in (3) dissolved in 50 g of isopropyl alcohol, An amount of activated carbon powder corresponding to 0.5% of the mass (the same as that used in Production Example 1) was added and stirred for 24 hours. The activated carbon powder was removed from the solution by filtration, and the first raw material was recrystallized (first recrystallization) from the filtrate. Next, the first raw material after recrystallization was dissolved in 50 g of isopropyl alcohol (no activated carbon powder was added), the first raw material was recrystallized (second recrystallization) from the solution, and then dried under reduced pressure for 1 hour. . Instead of the filtrate in (7) of Production Example 1, an aqueous solution (no activated carbon powder added) prepared by dissolving the first raw material obtained by performing the above operation in 50 g of water was used. About other points, it carried out similarly to manufacture example 1, and obtained N-methyl-N-methoxymethylpyrrolidinium-TFSI.
Unlike the product obtained in Production Example 1, the resulting product exhibits a yellow gel at normal temperature (23 ° C.) and can be used alone (ie, without being diluted with an organic solvent) as an electrolyte. It wasn't.

<Production Example 4: Synthesis of N-methyl-N-methoxymethylpyrrolidinium-TFSI (3)>
In this example, in (5) and (6) of Production Example 1, the operation of treating the aqueous solution of the first raw material with activated carbon powder was not performed. Instead, after the anion of the first raw material is replaced with TFSI, more specifically, the amount corresponding to 0.5% by mass of the first raw material used in the final round of water washing in (9) of Production Example 1 Activated carbon powder (same as that used in Production Example 1) was added and stirred for 24 hours. Then, it left still and was made to isolate | separate into two layers, the upper layer (water phase) was removed by decantation, and also the lower layer was filtered with the filter, and the activated carbon powder was removed. The filtrate was heated to 120 ° C. for 24 hours to remove moisture. About other points, it carried out similarly to manufacture example 1, and obtained N-methyl-N-methoxymethylpyrrolidinium-TFSI.
Unlike the product obtained in Production Example 1, the resulting product exhibits a yellow gel at normal temperature (23 ° C.) and can be used alone (ie, without being diluted with an organic solvent) as an electrolyte. It wasn't.

<Production of lithium ion secondary battery>
Lithium ion secondary batteries were produced using the ionic liquids obtained in Production Examples 1 and 2 and a conventional carbonate-based mixed solvent as a comparative example.
The following were used as the positive electrode. That is, the average particle size of about 0.7μm on the surface of the particulate LiFePO _4, carbon 2 parts by weight of the LiFePO ₄ particles per 100 parts by to prepare a carbon-coated with LiFePO ₄ coated. More specifically, the LiFePO ₄ particles are put into a polyvinyl alcohol aqueous solution to increase LiFePO ₄ -polyvinyl alcohol aggregates, which are baked in a reducing atmosphere to carbonize the polyvinyl alcohol to thereby form a carbon-coated LiFePO 4. ₄ was obtained.

The obtained carbon-coated LiFePO ₄ , acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder, and a carbon-coated LiFePO ₄ : AB: PVDF mass ratio of 85: It was mixed with N-methylpyrrolidone (NMP) so as to be 5:10 to prepare a paste or slurry-like composition (composition for forming a positive electrode mixture layer). The composition was applied to both sides of a 15 μm thick strip-shaped aluminum foil (positive electrode current collector) and dried to prepare a positive electrode sheet.

  The following were used as the negative electrode. That is, natural graphite as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener have a mass ratio of 95: 2.5: 2. It was mixed with ion-exchanged water so as to be 0.5, to prepare a paste or slurry-like composition (a composition for forming a negative electrode mixture layer). The above composition was applied to both sides of a 10 μm thick strip-shaped copper foil (negative electrode current collector) and dried to prepare a negative electrode sheet. The coating amount of the composition for forming a negative electrode mixture layer was adjusted so that the ratio of the theoretical capacity of the positive electrode to the theoretical capacity of the negative electrode was 1: 1.5.

The obtained positive electrode sheet and negative electrode sheet were wound together with two 20 μm-thick polypropylene / polyethylene composite porous sheets. The wound body was housed in a rectangular container (battery case) having an internal volume of 100 mL with a structure in which the positive electrode terminal and the negative electrode terminal can be taken out together with the electrolyte, and the container was sealed to construct a lithium ion secondary battery. As an electrolytic solution, a solution obtained by dissolving LiPF ₆ as a supporting salt in a concentration of 1 mol / L in N-methyl-N-methoxymethylpyrrolidinium-TFSI obtained in Production Example 1 (Sample 1), production LiPF ₆ dissolved in N-methyl-N-methoxymethylpiperidinium-TFSI obtained in Example 2 at a concentration of 1 mol / L (sample 2), and EC and DEC in a volume of 1: 1. A solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent mixed at a ratio (sample 3) was used.

  For these three types of batteries with different electrolyte solutions, as the initial charge / discharge treatment, constant current charging was performed at a rate of 1/5 C to 4.1 V, and then the rate was reduced to 1/10 of the initial current value. Voltage charging was performed. Here, 1C means the amount of current that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode in one hour. Next, the battery was discharged to 3 V at a rate of 1/5 C by a constant current method. After repeating this charging / discharging cycle 3 times, after sealing was released once and the internal pressure of the container was released, the container was resealed to obtain a lithium ion secondary battery. The obtained battery samples are referred to as samples B1 to B3 in association with the type of electrolyte used.

<Gas generation test>
The samples B1 to B3 produced above were charged with a constant current up to 4.5 V at a rate of 1/5 C, and then charged with a constant voltage until the rate reached 1/10 of the initial current value. The battery charged in this way was held at room temperature (23 ° C.) for 3 hours in a state where a constant voltage of 4.5 V was applied. Then, the internal pressure of the container was measured before and after the constant voltage of 4.5 V was applied, the pressure increase due to the voltage application for 3 hours was converted into the amount of gas generated inside the container, and this was applied to the voltage application time (here 3 hours). ) To determine the amount of gas generated per unit time. The obtained results are shown in Table 1.

  As shown in this table, samples B1 and B2 using only an ionic liquid as the solvent of the electrolytic solution (that is, using an electrolytic solution not containing an organic solvent) were electrolyzed using a general carbonate-based mixed solvent. It was confirmed that the stability to a voltage of 4.5 V was remarkably superior to that of Sample B3 using the liquid.

<Production of electric double layer capacitor>
Commercially available activated carbon (average particle size 5 μm, specific surface area 2000 m ² / g), AB as a conductive material, and CMC as a binder are ionized so that the mass ratio of these materials is 80:10:10. By mixing with exchange water, a paste or slurry-like composition (composite layer forming composition) was prepared. An electrode sheet having a total thickness of 60 μm is formed by applying the above composition to both surfaces of a 15 μm-thick strip-shaped aluminum foil (current collector) with a doctor blade and drying it. Two sheets were produced. These electrode sheets were overlapped and wound together with two 20 μm-thick polypropylene / polyethylene composite porous sheets. The wound body was housed in a container having a structure in which a pair of electrode terminals can be taken out together with the electrolytic solution, and the container was sealed to construct a capacitor cell. Here, as an electrolytic solution, N-methyl-N-methoxymethylpyrrolidinium-TFSI obtained in Production Example 1 was used as it was (Sample 4), and N-methyl-N obtained in Production Example 2 was used. -Methoxymethylpiperidinium-TFSI used as it is (Sample 5) and N-methyl-N-methoxymethylpyrrolidinium-TFSI obtained in Production Example 1 were added at 1 mol / min with propylene carbonate (PC). Those diluted to liters (sample 6) were used. These capacitor cell samples are referred to as samples C4 to C6 in association with the type of electrolyte used.

<Leakage current test>
For the samples C4 to C6 produced above, the leakage current was measured after applying a predetermined potential difference between the two electrodes and holding it for 5 minutes. A large amount of this leakage current indicates that many side reactions have occurred. The test was performed by changing the predetermined potential difference in the range of 2.25V to 3.65V. The obtained results are shown in FIG. In FIG. 2, a plot indicated by a white square indicates the result of sample C4, a plot indicated by a black triangle indicates the result of sample C5, and a plot indicated by a white circle indicates the result of sample C6.

  As is apparent from this figure, in the sample C6 using the electrolytic solution obtained by diluting the ionic liquid obtained in Production Example 1 with a carbonate-based solvent, the leakage current increases when the voltage applied between both electrodes exceeds 2.5V. In particular, when the voltage exceeds 3 V, the increase in leakage current becomes significant. On the other hand, in the samples C4 and C5 in which the ionic liquid obtained in Production Examples 1 and 2 was used as an electrolyte as it was (that is, without being diluted with an organic solvent), the voltage applied between both electrodes was 3.5 V. The leakage current did not increase even when the value exceeded, and it was confirmed that the voltage stability was excellent.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment is only an illustration and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

1 Vehicle (Automobile)
10 Lithium ion secondary battery (electrochemical device)
DESCRIPTION OF SYMBOLS 11 Electrode body 12 Positive electrode 122 Positive electrode electrical power collector 124 Positive electrode composite material layer 13 Separator 14 Negative electrode 142 Negative electrode electrical power collector 144 Negative electrode composite material layer 15 Battery case 20 Electrolyte

Claims (7)

An ionic liquid which is a salt of a cation Ay and an anion By, wherein the cation Ay is represented by the formula (I):

(R ¹ in the above formula (I) is an alkyl ether group represented by —CH ₂ —O—R ⁴ , and R ⁴ is a linear alkyl group having 1 to 5 carbon atoms. R ² Is a linear alkyl group having 1 to 5 carbon atoms, p is a chemical bond or an alkylene group having 1 carbon atom);
A process for producing an electrolyte solution that is pyrrolidinium or piperidinium represented by :
Crystallizing a first raw material that is a salt of a cation Ay and a halide ion ;
Recrystallizing the crystallized first raw material ;
Preparing a solution in which the first raw material obtained through the recrystallization is dissolved in a solvent;
Performing a treatment of contacting the solution with an adsorbent; and
After separating the solution from the adsorbent, mixing the second raw material having an anion By and the first raw material to produce the ionic liquid;
The manufacturing method of the electrolyte solution containing this. The cation Ay is N-methyl-N-methoxymethylpyrrolidinium, N-ethyl-N-methoxymethylpyrrolidinium, N-methyl-N-ethoxymethylpyrrolidinium, N-ethyl-N-ethoxymethylpyrrole. Dinium, N-methyl-N-methoxymethylpiperidinium, N-ethyl-N-methoxymethylpiperidinium, N-methyl-N-ethoxymethylpiperidinium, and N-ethyl-N-ethoxymethylpiperidinium The method of claim 1, wherein the method is any of nium . The method according to claim 1, wherein the anion By is an anion represented by the formula (II).

(Rf ¹ and Rf ² in the above formula (II) are perfluoroalkyl groups.) 4. The method according to claim 1, wherein the first raw material is synthesized by reacting a starting material having a structure in which R ² is bonded to a nitrogen atom of a pyrrolidine ring or piperidine ring and a chlorinated product of R ^1. The method according to claim 1.   The method according to any one of claims 1 to 4, wherein the adsorbent is activated carbon.   An electrochemical device comprising the electrolytic solution produced by the method according to any one of claims 1 to 5. An electrolyte for use in a lithium ion secondary battery,
An ionic liquid obtained by the method according to any one of claims 1 to 5;
A lithium salt as a supporting electrolyte;
An electrolyte for a lithium ion secondary battery, comprising:

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