JP2016119296A - Electrolyte for sodium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte for a sodium ion secondary battery, which achieves an improvement in non-flammability and nonvolatility, and alleviates a decrease in electric conductivity and an increase in the internal resistance of a battery during low-temperature operation.SOLUTION: There is provided an electrolyte for a secondary battery comprising an allylimidazolium salt represented by a formula (1). (In the formula, Rrepresents a substituted/unsubstituted linear, branched or cyclic 1-10C alkyl group, a substituted/unsubstituted linear, branched or cyclic 2-10C alkenyl group, a substituted/unsubstituted linear, branched or cyclic 2-10C alkynyl group, a substituted/unsubstituted aromatic hydrocarbon group, or a substituted/unsubstituted aromatic heterocyclic group; R-Reach represent H or a substituted/unsubstituted hydrocarbon group; and Xrepresents a counter anion)SELECTED DRAWING: Figure 1

Description

  Some aspects of the present invention relate to an electrolyte for a sodium ion secondary battery having a low viscosity, a high electrical conductivity, and a low melting point using an allylimidazolium salt.

Electrolytes made mainly of organic solvents that have been used in secondary batteries such as lithium ion batteries are flammable and volatile, so they generate heat when overcharged and short-circuited. There was a possibility of ignition and there was a problem with safety.
In recent years, attempts have been made to use an ionic liquid, which has been attracting attention in various fields, as an electrolytic solution due to its characteristics. An ionic liquid, which is an ionic substance in a liquid state, has nonflammability and non-volatility properties, and can improve safety, which has been a problem in the past.

No. 2013/141242

  However, an electrolytic solution using an ionic liquid generally has a high melting point and has a property of increasing viscosity at a low temperature, and the electrical conductivity is decreased during a low temperature operation, and the internal resistance of the battery is increased. For this reason, the usage environment is limited, which has been a major problem in the development of applications of secondary batteries using ionic liquid electrolytes.

  Some aspects of the present invention have been made in view of such circumstances. Non-flammable and non-volatile safety using an ionic liquid, reduction of electrical conductivity during low-temperature operation, and reduction of increase in battery internal resistance are achieved. The present invention provides an electrolyte for a sodium ion secondary battery.

According to some embodiments of the present invention, there is provided an electrolyte solution for a secondary battery including an allylimidazolium salt represented by the following general formula (1) and a sodium ion-containing electrolyte.
(In the formula (1), R ¹ is a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms which may be substituted with a substituent; Linear, branched or cyclic alkenyl group having 2 to 10 carbon atoms; linear, branched or cyclic alkynyl group having 2 to 10 carbon atoms which may be substituted with a substituent; substituted with substituent An aromatic hydrocarbon group that may be substituted; an aromatic heterocyclic group that may be substituted with a substituent; and a monovalent that includes a hetero atom in a part of the alkyl group, the alkenyl group, or the alkynyl group R ^{2 to} R ⁴ may be the same or different from each other, and each is a hydrogen atom or a hydrocarbon group that may be substituted with a substituent, and X ^- is a counter anion).

  The present inventor has studied to achieve reduction of electrical conductivity and reduction of battery internal resistance during low temperature operation of sodium ion secondary battery using ionic liquid electrolyte, and when using allylimidazolium salt, the above problem Has been achieved, and the present invention has been completed. The imidazolium salt introduced with the allyl group obtained by the method of the present invention has the properties of low viscosity, high electrical conductivity, and low melting point, and as an electrolytic solution for electrochemical devices, particularly at low temperature operation. Is excellent.

Hereinafter, various embodiments of the present invention will be exemplified. The following embodiments can be combined with each other.
Preferably, the counter anion of the allylimidazolium salt is an anion represented by the following general formula (2).

(In the formula (2), R ^{5 to} R ⁶ may be the same or different from each other, and are each a fluorine atom or a hydrocarbon group optionally substituted with a fluorine atom. .)
Preferably, R ¹ is an alkyl group having 1 to 10 carbon atoms.
Preferably, R ¹ is an alkyl group having 1 to 3 carbon atoms.
Preferably, the counter anion of the allylimidazolium salt is a bis (fluorosulfonyl) imide anion.
Preferably, the concentration of the sodium ion-containing electrolyte is 5 to 60 mol%.

  According to another viewpoint of this invention, the sodium ion secondary battery containing the said electrolyte solution for secondary batteries is provided.

  The electrolyte for sodium ion secondary batteries according to some embodiments of the present invention is nonflammable, non-volatile, and safe, and can reduce electrical conductivity during low temperature operation and increase in battery internal resistance.

The DSC curve of AEI-FSI and EPI-FSI is shown. The structure of a sodium ion secondary battery is shown. The graph of the electrical conductivity in each temperature of AEI-FSI and EPI-FSI is shown. The graph of the electrical conductivity in each temperature of AMI-FSI and AEI-FSI is shown. The graph of the viscosity in each temperature of AEI-FSI and EPI-FSI is shown. The graph of the viscosity in each temperature of AMI-FSI and AEI-FSI is shown. The graph of the electrical conductivity in each temperature of AEI-FSI and EPI-FSI which contain NaFSI in the density | concentration of 40 mol% is shown. The graph of the electrical conductivity in each temperature of AMI-FSI and AEI-FSI containing NaFSI at the density | concentration of 40 mol% is shown. The graph of the viscosity in each temperature of AEI-FSI and EPI-FSI which contain NaFSI in the density | concentration of 40 mol% is shown. The graph of the viscosity in each temperature of AMI-FSI and AEI-FSI which contains NaFSI in the density | concentration of 40 mol% is shown. The graph of the electric conductivity in 25 degreeC and the viscosity of AEI-FSI in each NaFSI density | concentration is shown.

  Embodiments of the present invention will be described below. Various characteristic items shown in the following embodiments can be combined with each other. In addition, the invention is independently established for each feature.

1. Allyl imidazolium salt The electrolyte for a sodium ion secondary battery obtained according to some embodiments of the present invention comprises an imidazolium salt. Preferably, it is an allylimidazolium salt in which the substituent on at least one nitrogen atom of the compound represented by the following general formula (1) is an allyl group.

In Formula (1), R ¹ is a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms which may be substituted with a substituent; a linear chain which may be substituted with a substituent Straight, branched or cyclic alkenyl groups having 2 to 10 carbon atoms; linear, branched or cyclic alkynyl groups having 2 to 10 carbon atoms which may be substituted with substituents; substituted with substituents An optionally substituted aromatic hydrocarbon group; an aromatic heterocyclic group optionally substituted with a substituent; and a monovalent group containing a hetero atom in a part of the alkyl group, the alkenyl group or the alkynyl group; It is one chosen from. R ^{2 to} R ⁴ may be the same as or different from each other, each of which is a hydrogen atom or a hydrocarbon group that may be substituted with a substituent, and X ⁻ is a counter anion.

<Substituents of allylimidazolium salts>
In the formula (1), the substituent R ¹ on the nitrogen atom which is not substituted with an allyl group out of the two nitrogen atoms is a hydrogen atom or a linear, branched or optionally substituted with a substituent. A cyclic alkyl group having 1 to 10 carbon atoms; a linear, branched or cyclic alkenyl group having 2 to 10 carbon atoms which may be substituted with a substituent; A chain, branched or cyclic alkynyl group having 2 to 10 carbon atoms; an aromatic hydrocarbon group optionally substituted with a substituent; an aromatic heterocyclic group optionally substituted with a substituent; and The alkyl group, the alkenyl group, the alkynyl group, and a monovalent group containing a hetero atom-containing group in the main chain or skeleton of the aromatic hydrocarbon group.
As the monovalent group containing a hetero atom in a part of the alkyl group, the alkenyl group or the alkynyl group, at least one of the methylene groups of the alkyl group, alkenyl group or alkynyl group is -O-, -CO-. , -COO-, -OCO-, -O-CO-O-, -NHCO-, -CONH-, -NH-CO-O-, -O-CO-NH-, -NH-, -S- and- And a group substituted with any heteroatom-containing group selected from the group consisting of CO—O—CH ₂ —CO—O—.

Examples of the linear, branched or cyclic alkyl group having 1 to 10 carbon atoms include linear alkyl groups having 1 to 10 carbon atoms such as methyl group, ethyl group, propyl group, butyl group and octyl group; isopropyl group Branched alkyl groups having 3 to 10 carbon atoms such as isobutyl group; cyclic alkyl groups having 3 to 10 carbon atoms such as cyclopentyl group and cyclohexyl group; and the like.
Examples of the alkenyl group or alkynyl group include groups in which at least one carbon-carbon single bond of the alkyl group is substituted with a carbon-carbon double bond or a carbon-carbon triple bond.
Examples of the aromatic hydrocarbon group include those having 6 to 10 carbon atoms such as a phenyl group, a naphthyl group, and an anthryl group.
Examples of aromatic heterocyclic groups include furan, thiophene, pyrrole, imidazole, pyran, pyridine, pyrimidine, pyrazine, indole, purine, quinoline, isoquinoline, chromene, chromone, coumarin, thianthrene, dibenzothiophene, phenothiazine, phenoxazine, xanthene, And groups having a skeleton such as acridine, phenazine and carbazole.

Examples of the substituent that the alkyl group of R ¹ may have include: an alkyl group such as a methyl group or an ethyl group; an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, or an anthryl group; an alkyloxy group such as a methoxy group Aryloxy groups such as phenoxy groups; alkylthio groups such as methylthio groups; arylthio groups such as phenylthio groups; acyl groups such as acetyl groups; aroyl groups such as benzoyl groups; acyloxy groups such as acetoxy groups; alloyoxy groups such as benzoyloxy groups; Further examples include nitrile groups and nitro groups.

The substituent R ¹ is preferably an alkyl group having 1 to 10 carbon atoms. More preferably, it is a C1-C3 alkyl group. More preferably, it is a C1-C3 linear alkyl group. Most preferably, it is a methyl group or an ethyl group, which is a linear alkyl group having 1 to 2 carbon atoms. The reason why R ¹ is preferably as described above is that when the volume of the cation is appropriately small, the electric conductivity tends to be improved.

In the formula (1), the substituents R ^{2 to} R ⁴ on the carbon may be the same or different from each other, and are each a hydrogen atom or a hydrocarbon group that may be substituted with a substituent. .

Examples of the hydrocarbon group include alkyl groups such as methyl, ethyl, propyl, butyl, and octyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; aromatic hydrocarbons such as phenyl, naphthyl, and anthryl groups. Groups and the like.
At least one of the methylene groups of the hydrocarbon group is —O—, —CO—, —COO—, —OCO—, —O—CO—O—, —NHCO—, —CONH—, —NH—CO—O. A group substituted with any heteroatom-containing group selected from the group consisting of —, —O—CO—NH—, —NH—, —S—, and —CO—O—CH ₂ —CO—O—. May be.

Examples of the substituent that the hydrocarbon group of R ^{2 to} R ⁴ may have include an alkyl group such as a methyl group and an ethyl group; an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, and an anthryl group; a methoxy group and the like An alkyloxy group such as a phenoxy group; an alkylthio group such as a methylthio group; an arylthio group such as a phenylthio group; an acyl group such as an acetyl group; an aroyl group such as a benzoyl group; an acyloxy group such as an acetoxy group; a benzoyloxy group And the like, and further examples thereof include a nitrile group and a nitro group.

The substituents R ^{2 to} R ⁴ are preferably a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms. This is because if the volume of the cation is moderately small, the electric conductivity tends to be improved.

Preferred examples of the allylimidazolium cation in which the substituents R ^{1 to} R ⁴ are combined include 1-allyl-3-methylimidazolium, 1-allyl-3-ethylimidazolium, 1-allyl-3-n-propylimidazolium. 1-allyl-3-isopropylimidazolium, 1-allyl-3-n-butylimidazolium, 1-allyl-3-isobutylimidazolium, 1-allyl-3-sec-butylimidazolium, 1-allyl-3 -Tert-butylimidazolium, 1-allyl-3-n-pentylimidazolium, 1-allyl-3-isopentylimidazolium, 1-allyl-3-n-hexylimidazolium, 1-allyl-3-n- Heptylimidazolium, 1-allyl-3-n-octylimidazolium, 1,3-diallylimidazolium, 1-a Ru-3-cyclopentylimidazolium, 1-allyl-3-methylcyclopentylimidazolium, 1-allyl-3-cyclohexylimidazolium, 1-allyl-3-vinylimidazolium, 1-allyl-3- (1- Propenyl) imidazolium, 1-allyl-3- (2-butenyl) imidazolium, 1-allyl-3- (3-butenyl) imidazolium and the like. Among them, electrolytes for sodium ion secondary batteries include 1-allyl-3-methylimidazolium (AMI), 1-allyl-3-ethylimidazolium (AEI), and 1-allyl-3-n-propylimidazolium. preferable. More preferred are 1-allyl-3-methylimidazolium (AMI) and 1-allyl-3-ethylimidazolium (AEI). More preferred is 1-allyl-3-ethylimidazolium (AEI).

  When used as a salt with a bis (fluorosulfonyl) imide anion, AEI has a lower viscosity than AMI and a higher electrical conductivity in the temperature range of 25-50 ° C. That is, AEI-FSI is superior to AMI-FSI as an ionic liquid electrolyte for reducing an increase in battery internal resistance during low-temperature operation of a sodium ion secondary battery. Thus, a more preferred example of an allylimidazolium cation is AEI.

<Counter anion of allylimidazolium salt>
The counter anion of the allylimidazolium salt is not particularly limited, and examples thereof include BF ₄ ⁻ and PF ₆ ⁻ .
The counter anion of the allylimidazolium salt is preferably an anion represented by the following general formula (2).

In the above formula (2), R ^{5 to} R ⁶ may be the same or different from each other, and each is either a fluorine atom or a hydrocarbon group optionally substituted with a fluorine atom. Preferably, it is either a fluorine atom or an alkyl group which may be substituted with a fluorine atom. More preferably, it is either a fluorine atom or an alkyl group having 1 to 5 carbon atoms substituted with a fluorine atom. More preferably, it is either a fluorine atom or a trifluoromethyl group. Most preferably, it is a fluorine atom.

  Specifically, bis (trifluoromethylsulfonyl) imide anion (TFSI), bis (pentafluoroethylsulfonyl) imide anion, trifluoromethylsulfonyl (nonafluorobutylsulfonyl) imide anion, bis (fluorosulfonyl) imide anion (FSI) ) Bis (sulfonyl) imide anion.

  FSI has a smaller anion volume than TFSI, and since the fluorine atom is directly bonded to the sulfur atom, the negative charge on the nitrogen atom is delocalized by conjugation via the p-orbital of the fluorine atom, Since interaction with a cation is relatively weak and ions are considered to be easily dissociated, it is preferable from the viewpoint of viscosity and electrical conductivity. In TFSI or the like in which a fluorine atom such as a trifluoromethyl group is bonded to a sulfur atom via a carbon atom, there is no bond (S—F) between the fluorine atom and the sulfur atom, and conjugation is unlikely to occur. The effect is presumed to be superior to FSI.

  The imidazolium salt according to some embodiments of the present invention can have a lower melting point and lower viscosity by having an allyl group. For example, 1-ethyl-3-n-propylimidazolium bis (fluorosulfonyl) imide (EPI-FSI) is 1-allyl-3-ethylimidazolium bis (fluorosulfonyl) imide (AEI-FSI) and the number of carbon atoms is Although the same, AEI-FSI has a melting point lower by 16 ° C. than EPI-FSI and is suitable for use in a lower temperature environment.

  Furthermore, AEI-FSI has a lower viscosity than EPI-FSI and higher electrical conductivity in the temperature range of -20 to 50 ° C. That is, AEI-FSI is superior to EPI-FSI as an ionic liquid electrolyte for reducing an increase in battery internal resistance during low-temperature operation of a sodium ion secondary battery.

<Viscosity of allylimidazolium salt>
In some embodiments of the present invention, the viscosity (mPa · s) of the allylimidazolium salt is preferably 25.0 or less at 25 ° C. More preferably, it is 22.0 or less. More preferably, it is 21.0 or less. Particularly preferably, it is 20.0 or less. This is because if it is 25.0 or less, the electrical conductivity at low temperature is increased.
In some embodiments of the present invention, the viscosity (mPa · s) of the allylimidazolium salt is preferably 12.0 or less at 50 ° C. More preferably, it is 11.5 or less. More preferably, it is 11.0 or less. Particularly preferably, it is 10.5 or less. This is because if it is 12.0 or less, the electrical conductivity at low temperature is increased.

2. Sodium Ion-Containing Electrolyte An electrolytic solution for a sodium ion secondary battery obtained according to some embodiments of the present invention includes an allylimidazolium salt and a sodium ion-containing electrolyte. The sodium ion-containing electrolyte is a sodium salt, and a sodium cation and various counter anions can be used in combination.

<Counter anion of sodium salt>
The counter anion of the sodium salt is fluoride ion, chloride ion, bromide ion, iodide ion, fluoroborate ion, hexafluorophosphate ion, trifluoromethanesulfonate ion, perchlorate ion, or the following general formula (2) An anion represented by You may use these individually or in mixture of 2 or more types.

In the above formula (2), R ^{5 to} R ⁶ may be the same or different from each other, and each is either a fluorine atom or a hydrocarbon group optionally substituted with a fluorine atom. Preferably, it is either a fluorine atom or an alkyl group which may be substituted with a fluorine atom. More preferably, it is either a fluorine atom or an alkyl group having 1 to 5 carbon atoms substituted with a fluorine atom. More preferably, it is either a fluorine atom or a trifluoromethyl group. Most preferably, it is a fluorine atom.

  Specifically, bis (trifluoromethylsulfonyl) imide anion (TFSI), bis (pentafluoroethylsulfonyl) imide anion, trifluoromethylsulfonyl (nonafluorobutylsulfonyl) imide anion, bis (fluorosulfonyl) imide anion (FSI) ) Bis (sulfonyl) imide anion.

  FSI has a smaller anion volume than TFSI, etc., and since the fluorine atom is directly bonded to the sulfur atom, the negative charge on the nitrogen atom is delocalized by conjugation via the p-orbital of the fluorine atom. Since the interaction with the cation is relatively weak and ions are considered to be easily dissociated, it is preferable from the viewpoint of viscosity and electrical conductivity. In TFSI or the like in which a fluorine atom such as a trifluoromethyl group is bonded to a sulfur atom via a carbon atom, there is no bond (S—F) between the fluorine atom and the sulfur atom, and conjugation is unlikely to occur. The effect is presumed to be superior to FSI.

3. Secondary Battery Electrolyte An electrolyte for a sodium ion secondary battery obtained according to some embodiments of the present invention includes the imidazolium salt and the sodium ion-containing electrolyte.
<Content of imidazolium salt>
The content of the imidazolium salt in the electrolytic solution is preferably 10 mol% or more, more preferably 30 mol% or more, further preferably 40 mol% or more, and particularly preferably 50 mol% or more. Moreover, 95 mol% or less is preferable, 80 mol% or less is more preferable, and 70 mol% or less is more preferable.

<Concentration of sodium ion-containing electrolyte>
Since some of the electrolyte solutions for sodium ion secondary batteries of the present invention can reduce the viscosity by using the imidazolium salt having a specific structure as a solvent, the concentration of the sodium ion-containing electrolyte can be increased. Thereby, the capacity | capacitance of a sodium ion secondary battery can be raised. However, when the concentration of the sodium ion-containing electrolyte is increased, the viscosity of the electrolytic solution tends to increase.
In order to satisfy both the viscosity reduction and the capacity increase of the electrolyte for sodium ion secondary batteries and satisfy the battery efficiency, the concentration (mol%) of the sodium ion-containing electrolyte is preferably 5 mol% or more, more preferably 20 mol% or more. 30 mol% or more is more preferable. Moreover, 90 mol% or less is preferable, 70 mol% or less is more preferable, 60 mol% or less is more preferable, 50 mol% or less is especially preferable.

<Other ingredients>
Some electrolyte solutions for sodium ion secondary batteries of the present invention may contain other components other than the imidazolium salt and the sodium ion-containing electrolyte as long as the effects of the present invention are not impaired.

<Ion battery>
FIG. 2 shows the configuration of an apparatus that uses an electrolyte for a sodium ion secondary battery that includes an allylimidazolium salt obtained according to some embodiments of the present invention and a sodium ion-containing electrolyte. A typical example of the device is a secondary battery, in which a positive electrode current collector, a negative electrode current collector, a positive electrode active material, a negative electrode active material, and an electrolyte layer are disposed in a battery case. The positive electrode active material, the negative electrode active material, and the electrolyte layer are disposed between the positive electrode current collector and the negative electrode current collector. The electrolyte layer is disposed between the positive electrode active material and the negative electrode active material. When such an electrolyte layer containing the sodium ion secondary battery electrolyte is used, an increase in battery internal resistance during low-temperature operation is reduced.

  Hereinafter, although the specific Example of this invention is shown, this invention is not limited to these.

<Synthesis of imidazolium salt>
Preparation examples of typical imidazolium salts represented by the following formulas (3-1) to (3-3) according to some embodiments of the present invention will be described.
[Preparation Example 1]
1-allyl-3-ethylimidazolium bis (fluorosulfonyl) imide (AEI-FSI)
To a dichloromethane solution of potassium bis (fluorosulfonyl) imide (KFSI), a dichloromethane solution of 1-allyl-3-ethylimidazolium chloride (AEI-Cl) and water are added and stirred for 1 hour. The organic layer is collected and washed with water to remove unreacted raw materials and potassium chloride. Subsequently, the organic layer is passed through a silica gel column to further remove metal ions such as potassium ions and halide ions such as chloride ions and fluoride ions. And dichloromethane is distilled off by heating at 70 degreeC under pressure reduction, and AEI-FSI is obtained.

[Preparation Example 2]
1-allyl-3-methylimidazolium bis (fluorosulfonyl) imide (AMI-FSI)
AMI-FSI is obtained in the same manner as in Preparation Example 1, except that 1-allyl-3-methylimidazolium chloride (AMI-Cl) is used instead of AEI-Cl.

[Preparation Example 3]
1-ethyl-3-n-propylimidazolium bis (fluorosulfonyl) imide (EPI-FSI)
EPI-FSI is obtained in the same manner as in Preparation Example 1 except that 1-ethyl-3-n-propylimidazolium chloride (EPI-Cl) is used instead of AEI-Cl.

<Melting point measurement of imidazolium salt>
The DSC measurement (DSC6220, manufactured by SII Nanotechnology Inc.) of AEI-FSI and EPI-FSI obtained by the preparation of the imidazolium salt was performed, and the melting point was measured. The results are shown in FIG. The melting point of AEI-FSI was -41 ° C, while the melting point of EPI-FSI was -25 ° C, and AEI-FSI was 16 ° C lower than EPI-FSI.

<Measurement of viscosity and electrical conductivity of imidazolium salt>
The imidazolium salt was set to −20 ° C., −10 ° C., and 0 ° C. using an ultra-low temperature water bath (Thomas Scientific Instruments Co., Ltd., TRL-080II type), and a digital rotary viscometer (Bisco Tech Co., Ltd., VISCO STAR +) and an electric conductivity meter (CM-30R, manufactured by Toa DK Corporation) were used to measure viscosity and electric conductivity. Viscosity at 25 ° C and 50 ° C was measured using a Canon Fenceke viscometer (manufactured by Shibata Scientific Instruments Co., Ltd. and Kusano Scientific Instruments Co., Ltd.) in a constant temperature bath (manufactured by Yamato Scientific Co., Ltd., BF-200) It was measured. The electrical conductivity measurement at 25 ° C. and 50 ° C. was performed using an electrical conductivity meter (same as above) while adjusting the temperature with a hot plate (PC-320, manufactured by Corning).

  For each of AEI-FSI, AMI-FSI, and EPI-FSI, the viscosity and electrical conductivity at each temperature were measured. These measurement results are shown in Table 1 and FIGS.

  The viscosity at each temperature was lower in Preparation Example 1 than in Preparation Example 2 and lower than Preparation Example 3. And as for the electrical conductivity in 25-50 degreeC which use is actually assumed, the preparation example 1 and the preparation example 2 were higher than the preparation example 3. FIG. That is, the electrical conductivity is superior when an allyl group is used as a substituent on the nitrogen atom, compared to when an n-propyl group is used. And Preparation Example 1 is excellent in electrical conductivity even at a lower temperature of -20 to 0 ° C.

<Measurement of viscosity and electrical conductivity of electrolyte containing NaFSI at a concentration of 40 mol%>
Electrolyte containing sodium bis (fluorosulfonyl) imide (NaFSI) at a concentration of 40 mol%, AEI-FSI (Na (40 mol%) / AEI-FSI), AMI-FSI (Na (40 mol%) / AMI-FSI), For each of EPI-FSI (Na (40 mol%) / EPI-FSI), the viscosity and electrical conductivity at each temperature were measured in the same manner as the imidazolium salt. These measurement results are shown in Table 2 and FIGS.

The viscosity at each temperature was lower in Example 1 than in Example 2 and lower than Comparative Example 1. And as for the electrical conductivity in 25-50 degreeC which use is actually assumed, Example 1 and Example 2 were higher than the comparative example 1. FIG. That is, the electrical conductivity is superior when an allyl group is used as a substituent on the nitrogen atom, compared to when an n-propyl group is used. And Example 1 is excellent in electrical conductivity also in -20-20 degreeC which is lower temperature.
Thereby, it is estimated that the electrolyte solution of Example 1 and 2 contributes to suppression of battery internal resistance compared with the electrolyte solution of the comparative example 1.

<Density and molecular volume calculation>
For each of AEI-FSI, AMI-FSI, and EPI-FSI, the density at 20 ° C. was measured, and the molecular volume was calculated (calculation level: B3LYP / 6-311 ++ G (d)). For each of Na (40 mol%) / AEI-FSI, Na (40 mol%) / AMI-FSI, and Na (40 mol%) / AEI-FSI, the density was measured. These results are shown in Table 3.

The density (g / cm ³ ) of the AEI-FSI and AMI-FSI at 20 ° C. is preferably 1.37 to 1.45. More preferably, it is 1.38 to 1.43. More preferably, it is 1.39 to 1.41. If it is in the above range, the interaction between ions is moderate and ion transport is sterically advantageous.
The molecular volume (calculation level: B3LYP / 6-311 ++ G (d)) is preferably 300 to 360 ³ . More preferably, it is 310-350 ³ . More preferably, it is 320-340 < ³ >. If it is in the above range, the interaction between ions is moderate and ion transport is sterically advantageous.

<Sodium ion-containing electrolyte concentration, viscosity and electrical conductivity>
The electric conductivity and viscosity were measured at 25 ° C. with the NaFSI concentration in AEI-FSI being 0 to 50 mol%. The electric conductivity and viscosity of AEI-FSI at each NaFSI concentration are shown in Table 4 and FIG.

Claims (7)

An electrolytic solution for a secondary battery comprising an allylimidazolium salt represented by the following general formula (1) and a sodium ion-containing electrolyte.
(In the formula (1), R ¹ is a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms which may be substituted with a substituent; Linear, branched or cyclic alkenyl group having 2 to 10 carbon atoms; linear, branched or cyclic alkynyl group having 2 to 10 carbon atoms which may be substituted with a substituent; substituted with substituent An aromatic hydrocarbon group that may be substituted; an aromatic heterocyclic group that may be substituted with a substituent; and a monovalent that includes a hetero atom in a part of the alkyl group, the alkenyl group, or the alkynyl group R ^{2 to} R ⁴ may be the same or different from each other, and each is a hydrogen atom or a hydrocarbon group that may be substituted with a substituent, and X ^- is a counter anion). The electrolyte solution for secondary batteries of Claim 1 whose counter anion of the said allyl imidazolium salt is an anion represented by following General formula (2).
(In the formula (2), R ^{5 to} R ⁶ may be the same or different from each other, and are each a fluorine atom or a hydrocarbon group optionally substituted with a fluorine atom. .) The electrolyte for a secondary battery according to claim 1, wherein R ¹ is an alkyl group having 1 to 10 carbon atoms. The electrolyte for a secondary battery according to claim 3, wherein R ¹ is an alkyl group having 1 to 3 carbon atoms. The secondary battery electrolyte solution according to any one of claims 1 to 4, wherein a counter anion of the allylimidazolium salt is a bis (fluorosulfonyl) imide anion. The electrolyte solution for a secondary battery according to any one of claims 1 to 5, wherein the concentration of the sodium ion-containing electrolyte is 5 to 60 mol%. The sodium ion secondary battery containing the electrolyte solution for secondary batteries as described in any one of Claims 1-6.