JP7005010B2 - Lithium ion conductive composition - Google Patents

Description

The present invention relates to a lithium ion conductive composition. More specifically, the present invention is a lithium ion conductive composition expected to be used for a lithium ion secondary battery used in, for example, transportation equipment such as aircraft, automobiles, railroad vehicles, ships, and electronic equipment. The present invention relates to an electrolyte for a lithium ion secondary battery containing the lithium ion conductive composition.

Lithium-ion secondary batteries are used as batteries having a high energy density. Lithium-ion secondary batteries are roughly classified into organic solvent-based lithium-ion secondary batteries and aqueous solution-based lithium-ion secondary batteries. Compared to aqueous solution-based lithium-ion secondary batteries, organic solvent-based lithium-ion secondary batteries generally have low ionic conductivity and ion diffusion rate, and have the disadvantage that it is difficult to efficiently discharge them at low temperatures. be.

As a lithium ion conductive polymer that can be used in an organic solvent-based lithium ion secondary battery that can efficiently discharge at a low temperature, it exhibits lithium ion conductivity, has a large number of pores, and has a large number of pores in the pores. A porous lithium ion conductive polymer has been proposed in which an organic electrolytic solution is retained and a passage through which ions are diffused is secured (see, for example, Patent Document 1).

The porous lithium ion conductive polymer is said to have good dischargeability at low temperature, a small amount of self-discharge at high temperature, and excellent long-term charge / discharge characteristics. However, since the porous lithium ion conductive polymer uses a polymer such as polyacrylonitrile, it has a drawback of being inferior in heat resistance.

JP-A-2002-373705.

The present invention has been made in view of the above-mentioned prior art, and is a lithium ion conductive composition having excellent heat resistance, excellent lithium ion conductivity, and a high lithium ion transport number, and the lithium ion conductive composition. It is an object of the present invention to provide an electrolyte for a lithium ion secondary battery containing.

The present invention
(1) Equation (I):

Repeat unit represented by and equation (II):

(In the formula, R ¹ , R ² and R ³ independently indicate an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms, respectively).
It contains a lithium ion conductive composition comprising a benzimidazole polymer having a repeating unit represented by the above and an ionic liquid, and (2) the lithium ion conductive composition according to (1) above. Regarding electrolytes for lithium-ion secondary batteries.

According to the present invention, a lithium ion conductive composition having excellent heat resistance and lithium ion conductivity and a high lithium ion transport rate, and an electrolyte for a lithium ion secondary battery containing the lithium ion conductive composition. Is provided.

It is a graph which shows the result of the Fourier transform infrared spectroscopic analysis of 2,5-polybenzimidazole used in Production Example 1. It is a graph which shows the ¹³ C-NMR spectrum of 2,5-polybenzimidazole used in Production Example 1. FIG. FIG. 3 is a wide-angle X-ray diffraction pattern of 2,5-polybenzimidazole used in Production Example 1. It is a graph which shows the stress-strain curve of 2,5-polybenzimidazole used in Production Example 1. FIG. It is a graph which shows the result of the Fourier transform type infrared spectroscopic analysis of the benzimidazole polymer obtained in the production example 2. It is a graph which shows the ^11B -NMR spectrum of the benzimidazole polymer obtained in the production example 2. FIG. It is a graph which shows the measurement result of the temperature dependence of the ion conductivity of the lithium ion conductive compositions A to E obtained in Examples 1-5. It is a graph which VFT plotted the measurement result of the temperature dependence of the ionic conductivity shown in FIG. 7. It is a schematic explanatory drawing which shows the structure of the half cell used in Experimental Example 2. It is a graph which shows the charge / discharge test result of the half cell used in Experimental Example 2.

As described above, the lithium ion conductive composition of the present invention has the formula (I):

Repeat unit represented by and equation (II):

(In the formula, R ¹ , R ² and R ³ independently indicate an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms, respectively).
It is characterized by containing a benzimidazole polymer and an ionic liquid having a repeating unit represented by.

The benzimidazole polymer used in the present invention can be synthesized using 3-amino-4-hydroxybenzoic acid as a raw material, which has an established biosynthetic pathway from the metabolic pathway of radioactive bacteria. Therefore, the benzimidazole polymer used in the present invention has an advantage that it can be prepared from 3-amino-4-hydroxybenzoic acid, which is a biomass-based compound that is friendly to the global environment.

Hereinafter, a method for preparing a benzimidazole polymer using 3-amino-4-hydroxybenzoic acid as a raw material will be described, but the present invention is not limited to this method alone.

(A) Preparation of benzimidazole homopolymer The benzimidazole homopolymer is, for example, the formula:

(In the formula, p indicates the degree of polymerization of the benzimidazole homopolymer)
As represented by, 3,5-diaminobenzoic acid is prepared by performing Smiles rearrangement of 3-amino-4-hydroxybenzoic acid, and the obtained 3,5-diaminobenzoic acid is polymerized. Can be prepared by.

Benzimidazole homopolymers have excellent heat resistance [for example, 10% weight loss temperature (T _d10 ): 689 ° C. in a nitrogen gas atmosphere by thermogravimetric analysis], excellent mechanical strength, and elongation at break. small. Therefore, since the benzimidazole polymer used in the present invention can be prepared by using the benzimidazole homopolymer as a production intermediate, it has the advantages of excellent heat resistance and mechanical strength and low elongation at break. Have.

The weight loss temperature (T _d ) by the thermogravimetric analysis is a value when measured under the following measurement conditions.

[Measurement conditions for thermogravimetric analysis]
・ Measuring device: Thermal weight-differential thermal simultaneous measuring device [Made by Hitachi High-Technologies Corporation, product name: STA7200]
The benzimidazole homopolymer was heated to 800 ° C. at a heating rate of 10 ° C./min in a nitrogen gas atmosphere or air, and the degree of weight loss was measured.

(B) Preparation of benzimidazole polymer The benzimidazole polymer is, for example, the formula:

(In the formula, R ¹ , R ² , R ³ and p are the same as above. Q indicates a repeating unit of benzimidazole, and r indicates a repeating unit of lithium benzimidazole).
As represented by, it can be prepared using a benzimidazole homopolymer. More specifically, a benzimidazole polymer can be prepared using a benzimidazole homopolymer as follows.

[Lithioization of benzimidazole homopolymer]
By lithiolating the benzimidazole homopolymer with a lithiolytic agent, some of the repeating units based on the benzimidazole homopolymer are lithiolated and formula (III) :.

(In the formula, q and r are the same as above)
It is possible to obtain a production intermediate of the benzimidazole polymer represented by.

In formula (III), the ratio of q and r can be appropriately adjusted by adjusting the lithiolation of the benzimidazole homopolymer. Lithioization of the benzimidazole homopolymer can be readily controlled by adjusting the amount of lithiolytic agent used.

Examples of the lithiating agent include lithium hydride, butyllithium, phenyllithium and the like, but the present invention is not limited to these examples.

Lithioization of the benzimidazole homopolymer can optionally be carried out in a non-aqueous organic solvent. Examples of the non-aqueous organic solvent include dimethyl sulfoxide, diethyl ether, tetrahydrofuran, dimethoxyethane and the like, but the present invention is not limited to these examples.

The temperature of the benzimidazole homopolymer to be lithiated is not particularly limited, but is usually preferably about 0 to 100 ° C. Lithioization of the benzimidazole homopolymer may be carried out in the air, for example, in the atmosphere of an inert gas such as nitrogen gas or argon gas.

By lithiolating the benzimidazole homopolymer as described above, an intermediate for producing the benzimidazole polymer represented by the formula (III) can be prepared.

[Boronization of intermediates for the production of benzimidazole polymers]
By boronizing the production intermediate of the benzimidazole polymer represented by the formula (III), a benzimidazole polymer having a repeating unit represented by the formula (I) and a repeating unit represented by the formula (II) can be obtained. ..

Boronizing agents are used to boronize the benzimidazole polymer production intermediates. Examples of the boronizing agent include the formula: BR ¹ R ² R ³ (in the formula, R ¹ , R ² and R ³ are independently alkyl groups having 1 to 12 carbon atoms or aryls having 6 to 12 carbon atoms, respectively. A boronizing agent represented by (indicating a group) can be used. Formula: In BR ¹ R ² R ³ , R ¹ , R ² and R ³ independently represent an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms, respectively. The aryl group may have a halogen atom or a substituent as long as the object of the present invention is not impaired.

The amount of the boronizing agent is usually 1. To ensure that the lithium atom contained in the benzimidazole polymer production intermediate is efficiently boronized, 1. It is preferably about 2 to 2 mol.

The temperature of boronization of the intermediate for producing the benzimidazole polymer is not particularly limited, but is usually preferably about 0 to 100 ° C. The boronization of the production intermediate of the benzimidazole polymer may be carried out in the atmosphere, or may be carried out in an atmosphere of an inert gas such as nitrogen gas or argon gas, for example.

By boronizing the manufacturing intermediate of the benzimidazole polymer as described above, the formula (IV):

(In the equation, R ¹ , R ² , R ³ , q and r are the same as above)
A benzimidazole polymer represented by, in other words, a benzimidazole polymer having a repeating unit represented by the formula (I) and a repeating unit represented by the formula (II) can be obtained.

In formula (IV), the repeating unit based on benzimidazole and the repeating unit based on boronified benzimidazole are described as blocks for convenience, but in the actually obtained benzimidazole polymer, benzimidazole is used. The repeating unit represented by the formula (I) based on the formula (I) and the repeating unit represented by the formula (II) based on the boronylated benzimidazole are randomly bonded.

The benzimidazole polymer has a repeating unit represented by the formula (I) and a repeating unit represented by the formula (II). The molar ratio of the repeating unit represented by the formula (I) to the repeating unit represented by the formula (II) [the repeating unit represented by the formula (I) [q in the formula (IV)] / the repetition represented by the formula (II). The unit [r] in the formula (IV)] is preferably 10/90 to 90 / from the viewpoint of obtaining a lithium ion conductive composition having excellent heat resistance, excellent lithium ion conductivity, and high lithium ion transport number. 10, more preferably 20/80 to 80/20, even more preferably 25/75 to 75/25, and even more preferably 20/80 to 80/20.

The number average molecular weight of the benzimidazole polymer is preferably 2000 to 100,000, more preferably 3000 to, from the viewpoint of obtaining a lithium ion conductive composition having excellent heat resistance, excellent lithium ion conductivity, and high lithium ion transport number. It is 100,000.

The number average molecular weight of the benzimidazole polymer and other polymers used in the present invention is a value measured by gel permeation chromatography (GPC) under the following measurement conditions.

〔Measurement condition〕
・ Equipment: Showa Denko KK, Product name: Shodex-101
-Concentration at the time of injection: 0.01% by mass
・ Injection amount: 100 μL
・ Flow velocity: 1 mL / min
-Solvent: N, N-dimethylformamide-Column: Made by Showa Denko KK, Product name: Shodex KD-803 and Product name: Shodex KD-804
-Column temperature: 40 ° C
-Standard: Polymethylmethacrylate

Next, the lithium ion conductive composition of the present invention can be obtained by mixing a benzimidazole polymer having a repeating unit represented by the formula (I) and a repeating unit represented by the formula (II) with an ionic liquid. can.

Examples of the ionic liquid include an ionic liquid having a cation portion and an anion portion.

Examples of the cation portion include a pyrrolidinium cation, a sulfonium cation, an imidazolium cation, a pyridinium cation, a quaternary ammonium cation, a piperidinium cation, a phosphonium cation, a morpholinium cation, and the like. It is not limited to illustrations only. Among these, from the viewpoint of obtaining a lithium ion conductive composition having excellent heat resistance, excellent lithium ion conductivity, and high lithium ion transport number, pyrrolidinium cation, sulfonium cation, imidazolium cation, pyridinium cation and A quaternary ammonium cation is preferred.

As a specific example of the cation portion, the formula (V):

(In the formula, R ⁴ and R ⁵ each independently represent an alkyl group having 1 to 8 carbon atoms).
Pyrrolidinium cation represented by, formula (VI):

(In the formula, R ⁶ , R ⁷ and R ⁸ each independently indicate an alkyl group having 1 to 8 carbon atoms).
Sulfonium cation represented by, formula (VII):

(In the formula, R ⁹ and R ¹⁰ each independently indicate an alkyl group having 1 to 8 carbon atoms, and R ¹¹ indicates a hydrogen atom or an alkyl group having 1 to 8 carbon atoms).
Imidazole cation represented by, formula (VIII):

(In the formula, R ¹² and R ¹³ each independently represent an alkyl group having 1 to 8 carbon atoms).
Pyridinium cation represented by, formula (IX):

(In the formula, R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ each independently indicate an alkyl group having 1 to 8 carbon atoms).
Examples thereof include quaternary ammonium cations represented by, but the present invention is not limited to these examples. These cation portions may be used alone or in combination of two or more.

As the anion portion, for example, the formula (X):

(In the formula, R ¹⁸ and R ¹⁹ independently indicate a fluorine atom, a trifluoromethyl group or a pentafluoroethyl group).
Examples thereof include bissulfonylimide anions represented by, but the present invention is not limited to these examples.

Specific examples of the ionic liquid having a cation part and an anion part include 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide, triethylsulfonium bis (trifluoromethylsulfonyl) imide, and 1-butyl. -3-Methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-butyl-3-methylpyridinium bis (trifluoromethylsulfonyl) imide, tetrabutylammonium bis (trifluoromethylsulfonyl) imide, tetraoctylammonium bis (tri) Fluoromethylsulfonyl) imide, 1,2-dimethyl-3-propylimidazolium bis (trifluoromethylsulfonyl) imide, 1-ethyl-3-methylpyridiniumbis (trifluoromethylsulfonyl) imide, 1-propyl-3-methyl Examples thereof include pyridinium bis (trifluoromethylsulfonyl) imide, but the present invention is not limited to such examples. These ionic liquids may be used alone or in combination of two or more.

The amount of ionic liquid per 100 parts by mass of the benzimidazole polymer having the repeating unit represented by the formula (I) and the repeating unit represented by the formula (II) is excellent in heat resistance, excellent lithium ion conductivity, and high lithium ion. From the viewpoint of obtaining a lithium ion conductive composition having an transport number, it is preferably 30 to 400 parts by mass, more preferably 40 to 300 parts by mass, and further preferably 50 to 200 parts by mass.

Mixing of a benzimidazole polymer having a repeating unit represented by the formula (I) and a repeating unit represented by the formula (II) with an ionic liquid is carried out at room temperature in the air or in an inert gas atmosphere such as nitrogen gas or argon gas. Can be done.

Since the lithium ion conductive composition obtained as described above has excellent heat resistance, excellent lithium ion conductivity, and a high lithium ion transport number, it is suitable for use as an electrolyte for a lithium ion secondary battery. Can be done.

The electrolyte for a lithium ion secondary battery of the present invention contains the lithium ion conductive composition of the present invention. The electrolyte for a lithium ion secondary battery of the present invention may be composed only of the lithium ion conductive composition of the present invention, and if necessary, other components such as a solvent may be added as long as the object of the present invention is not impaired. It may be contained.

Since the electrolyte for a lithium ion secondary battery of the present invention contains the lithium ion conductive composition of the present invention, it is excellent in heat resistance, excellent lithium ion conductivity, and has a high lithium ion transport rate. For example, it is expected to be used in a lithium ion secondary battery used in transportation equipment such as aircraft, automobiles, railroad vehicles, ships, and electronic equipment.

Next, the present invention will be described in more detail based on examples, but the present invention is not limited to such examples.

The physical characteristics of the compounds obtained in each of the following Examples and Comparative Examples were investigated based on the following methods.

[ ¹³ C-NMR spectrum and ¹¹ B-NMR spectrum]
-Measuring device: Nuclear magnetic resonance spectroscopy [manufactured by Bruker, trade name: AVANCE III]

[Fourier transform infrared spectroscopy (FT-IR)]
The infrared absorption spectrum was measured using a Fourier transform infrared spectroscope [manufactured by JASCO Corporation, product number: FT / IR6100].

Production Example 1
2,5-Polybenzimidazole obtained by polymerizing 2,5-benzimidazole was prepared in advance. The number average molecular weight of the 2,5-polybenzimidazole was 35,600.

The Fourier transform infrared spectroscopic analysis (FT-IR) of 2,5-polybenzimidazole is shown in FIG. FIG. 1 is a graph showing the results of Fourier transform infrared spectroscopic analysis of 2,5-polybenzimidazole. The ¹³ C-NMR spectrum of the 2,5-polybenzimidazole is shown in FIG. FIG. 2 is a graph showing the ¹³ C-NMR spectrum of the 2,5-polybenzimidazole. From these results, it was confirmed that the 2,5-polybenzimidazole has a repeating unit represented by the formula (I).

The 1% weight loss temperature (T _d1 ), 5% weight loss temperature (T _d5 ) and 10% weight loss temperature (T _d10 ) obtained by thermogravimetric analysis of 2,5-polybenzimidazole obtained above are set to a nitrogen gas atmosphere. It was measured in the medium or in the air under the measurement conditions of the thermogravimetric analysis. The results are shown in Table 1.

From the results shown in Table 1, 2,5-polybenzimidazole has a 10% weight loss temperature (T _d10 ) of 689 ° C. in a nitrogen gas atmosphere and a 10% weight loss temperature (T _d10 ) in the atmosphere. Since the temperature is 535 ° C, it can be seen that the heat resistance is significantly superior to that of the porous lithium ion conductive polymer in which the conventional polyacrylonitrile (glass transition temperature: 104 ° C) is used.

For reference, the measurement results of wide-angle X-ray diffraction of 2,5-polybenzimidazole are shown in FIG. FIG. 3 is a wide-angle X-ray diffraction pattern of 2,5-polybenzimidazole. From the results shown in FIG. 3, it is considered that 2,5-polybenzimidazole has low crystallinity because the peak is broad.

Next, using a tensile tester [Instron Japan Company Limited, trade name: INSTRON 3365], a plate of 2,5-polybenzimidazole (vertical) under the conditions of an initial distance between marked lines of 50 mm and a tensile speed of 200 mm / min. The breaking strength, elastic modulus and breaking elongation were measured (: 70 mm, width: 150 mm, thickness: 2 mm). The results are shown in FIG. FIG. 4 is a graph showing the stress-strain curve of 2,5-polybenzimidazole.

From the results shown in FIG. 4, it was confirmed that the breaking strength of 2,5-polybenzimidazole was 95 MPa, the elastic modulus was 9.5 GPa, and the breaking elongation was 0.027%. From these results, it can be seen that the 2,5-polybenzimidazole is rigid and has excellent mechanical strength.

Manufacturing example 2
The inside of the flask was replaced with nitrogen gas, 10 mL of dried dimethyl sulfoxide was placed in the flask, and then 2,5-polybenzimidazole 470 mg (1 equivalent) and 1.11 g of lithium hydride (3 equivalents) were placed in the flask. The reaction mixture was obtained by reacting 2,5-polybenzimidazole with lithium hydride for 24 hours at room temperature while stirring in a nitrogen gas atmosphere. By heating the reaction mixture obtained above at 80 ° C. for 1 hour, a deep red color was developed, and a production intermediate of the benzimidazole polymer represented by the formula (III) was obtained.

Next, the reaction mixture obtained above was allowed to cool to room temperature, and 40 mL (6 eq) of triethylborane was slowly added into the flask over 15 minutes with stirring to form a yellow precipitate. This precipitate was dissolved when the reaction temperature decreased and reached 80 ° C.

The reaction mixture obtained above is further stirred for 24 hours, allowed to cool to room temperature, and then added to a mixed solvent of toluene and acetone [toluene / acetone (volume ratio): 50/50]. This caused the resulting polymer to precipitate.

The polymer obtained above is dried in an atmosphere of 80 ° C. for 3 days, then added to N, N-dimethylformamide to dissolve it, and a mixed solvent of toluene and acetone [toluene / acetone (volume ratio): 50. Purification was performed by adding to / 50] and reprecipitating, and the obtained polymer was recovered. The polymer obtained above was dried at 80 ° C. for 3 days in a vacuum dryer.

The Fourier transform infrared spectroscopic analysis (FT-IR) of the polymer obtained above is shown in FIG. From the results shown in FIG. 5, it was confirmed that the polymer obtained above was a benzimidazole polymer having a repeating unit represented by the formula (I) and a repeating unit represented by the formula (II).

Further, in the polymer obtained above, gel permeation chromatography (GPC) indicates that the repeating unit represented by the formula (I) is 10200 and the number average molecular weight of the repeating unit represented by the formula (II) is 25400. ) Confirmed by. Further, from the measurement results of the ¹³ C-NMR spectrum, it was confirmed that the polymer obtained above was a compound having a mass ratio of q and r of 55/45 in the formula (IV).

The ¹¹ B-NMR spectrum of the benzimidazole polymer obtained above was examined. The results are shown in FIG. FIG. 6 is a graph showing the ¹¹ B-NMR spectrum of the benzimidazole polymer.

From the results shown in FIG. 6, in the benzimidazole polymer obtained above, the boron atom was introduced only in the place where the lithium atom of the production intermediate of the benzimidazole polymer was present, and the benzimidazole polymer was boronized. It was confirmed that the ratio of repeating units based on benzimidazole was 45 mol%.

Example 1
67 mg of the benzimidazole polymer and 33 mg of 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide obtained in Production Example 2 are placed in a vial and stirred at a temperature of 80 ° C. under reduced pressure for about 10 By drying for a time, a yellow paste-like lithium ion conductive composition A was obtained.

Example 2
Same as in Example 1 except that the amount of benzimidazole polymer was changed to 50 mg and the amount of 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide was changed to 50 mg. Obtained a lithium ion conductive composition B.

Example 3
Same as Example 1 except that the amount of benzimidazole polymer was changed to 33 mg and the amount of 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide was changed to 67 mg in Example 1. Obtained a lithium ion conductive composition C.

Example 4
Same as Example 1 except that the amount of benzimidazole polymer was changed to 25 mg and the amount of 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide was changed to 75 mg in Example 1. Obtained a lithium ion conductive composition D.

Example 5
Same as Example 1 except that the amount of benzimidazole polymer was changed to 20 mg and the amount of 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide was changed to 80 mg in Example 1. Obtained a lithium ion conductive composition E.

Experimental Example 1
The physical properties of the lithium ion conductive composition obtained in each example include ion conductivity, carrier ion number (A), ion transport activation energy (B), reliability (R2), lithium ion transport rate and lithium. The ionic conductivity was investigated based on the following method. The results are shown in Table 2.

[Ion conductivity]
The ion conductivity of the lithium ion conductive composition was evaluated by the AC impedance method using an impedance analyzer (manufactured by Solartron, product number: 1260). At that time, the temperature dependence of the ionic conductivity was evaluated by changing the measured temperature. The results are shown in FIG.

FIG. 7 is a graph showing the measurement results of the temperature dependence of the ionic conductivity of the lithium ion conductive compositions A to E obtained in Examples 1 to 5. In FIG. 7, A to E show the data of the lithium ion conductive compositions A to E, respectively, in order.

[Number of carrier ions (A), activation energy of ion transport (B) and reliability (R2)]
Based on the results shown in FIG. 7, the ion conduction behavior of the lithium ion conductive composition by the Vogel-Fulcher-Taman plot (hereinafter referred to as VFT plot) was analyzed. More specifically, the equation (1):
σT ^1/2 = Aexp (-B / (T-T ₀ )) (1)
(In the formula, A is the number of carrier ions, B is the activation energy of ion transport, and T ₀ is the glass transition temperature.)
Based on, a VFT plot was created. The results are shown in FIG. FIG. 8 is a graph in which the measurement results of the temperature dependence of the ionic conductivity shown in FIG. 7 are VFT plotted.

In FIG. 8, the vertical intercept is the number of carrier ions (A), and the slope of a straight line is the activation energy (B) of ion transport.

The reliability (R2) shown in Table 2 means the linearity of the graph shown in FIG. 8, and its value is preferably close to 1.

[Lithium ion transport number]
The lithium ion transport number was calculated from the diffusivity ratio of lithium ion and counter anion in the lithium ion conductive composition.

[Lithium ion conductivity]
A pair of stainless steel electrodes was prepared, and a lithium ion conductive composition was used as an electrolyte to prepare a bipolar evaluation cell. Using this bipolar evaluation cell, the lithium ion conductivity was measured by the AC polarization method.

For reference, the ionic conductivity of 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide is also shown in Table 2 (exhibitor: N. Matsumi et al., ChemElectroChem., 2015, 2, 1913-1916).

From the results shown in Table 2, the lithium ion conductive compositions obtained in each example all had ion conductivity, carrier ion number, activation energy, reliability, lithium ion transport number and lithium ion conduction. It turns out that it is excellent in degree.

Further, among the examples, the lithium ion conductive compositions obtained in Examples 3 to 5 are excellent in lithium ion transport number and lithium ion conductivity, and among them, the lithium ion conductive compositions obtained in Example 3 are obtained. It can be seen that the lithium ion conductive composition is also excellent in ionic conductivity.

Experimental Example 2
Using the lithium ion conductive composition D obtained in Example 4, a charge / discharge test was performed as follows.

A half-cell having the structure shown in FIG. 9 was used. FIG. 9 is a schematic explanatory view showing the structure of the half cell. As shown in FIG. 9, a metal anode container 1, a fixture 2, a spacer 3, a silicon plate (diameter: 15 mm, thickness: 100 μm) as an action electrode 4, and a circular polypropylene film (diameter:: diameter: 5) as a separator 5 are used in this order from the top. CR2025 in which a lithium metal plate (diameter: 15 mm, thickness: about 60 μm) as a counter electrode 6 and a lithium ion conductive composition D and a metal cathode container 8 as an electrolytic solution 7 are laminated in this order (16 mm, thickness: 25 μm). A type of coin-shaped half-cell was manufactured.

Using a compact charge / discharge device [manufactured by EC Frontier Co., Ltd., product number: ECAD-1000], at a current ratio of 0.1 C (0.0172 mA) and at the cutoff potential limit (2.1 to 0.03 V) above. Twenty cycles of charging and discharging the obtained half-cell were carried out at a constant current. The results are shown in FIG. FIG. 10 is a graph showing the results of the charge / discharge test of the half cell.

In FIG. 10, X is the discharge capacity in the first cycle, and the discharge capacity was 1118 mAh / g. Further, Y is the discharge capacity in the 20th cycle, and the discharge capacity was 1297 mAh / g.

From the above results, it can be seen that by using the lithium ion conductive composition, the battery can be reversibly charged and discharged, and the discharge capacity of 1000 mAh / g or more is maintained even after repeated charging and discharging. .. Further, since the discharge capacity is increased by repeating charging and discharging, it is considered that a good solid electrolyte interface is formed on the electrode by repeating charging and discharging.

Experimental Example 3
The lithium ion conductive composition A was applied onto the plate to form a film, which was then dried. The mass loss when the obtained film was heated was examined with a thermogravimetric analyzer (TGA). As a result, almost no mass decrease was observed until the heating temperature reached 250 ° C., and it was confirmed that the film had heat resistance of 250 ° C. or higher.

Experimental Example 4
The 5% weight loss temperature (T _d5 ) and the 10% weight loss temperature (T _d10 ) by thermogravimetric analysis of the lithium ion conductive compositions A to E were measured in the atmosphere under the measurement conditions of the thermogravimetric analysis. The results are shown in Table 3.

From the results shown in Table 3, all of the lithium ion conductive compositions have a 10% weight loss temperature (T _d10 ) of 340 ° C. or higher, and thus the conventional polyacrylonitrile (glass transition temperature: 104 ° C.). It can be seen that the heat resistance is significantly superior to that of the porous lithium ion conductive polymer in which) is used.

From the above results, the lithium ion conductive composition of the present invention is not only excellent in heat resistance as compared with the porous lithium ion conductive polymer in which the conventional polyacrylonitrile is used, but also has lithium ion conductivity. It can be seen that it is also excellent and has a high lithium ion transport number.

The lithium ion conductive composition of the present invention is not only excellent in heat resistance, but also excellent in lithium ion conductivity and has a high lithium ion transport rate, so that it is suitably used as an electrolyte for a lithium ion secondary battery. Therefore, it is expected to be used in applications that require these properties, such as lithium-ion secondary batteries used in transportation equipment such as aircraft, automobiles, railroad vehicles, ships, and electronic equipment. ..

1 Metal anode container 2 Fixture 3 Spacer 4 Working electrode 5 Separator 6 Counter electrode 7 Electrolyte solution 8 Metal cathode container

Claims (2)

Equation (I):

Repeat unit represented by and equation (II):

(In the formula, R ¹ , R ² and R ³ independently indicate an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms, respectively).
A lithium ion conductive composition comprising a benzimidazole polymer and an ionic liquid having a repeating unit represented by. An electrolyte for a lithium ion secondary battery comprising the lithium ion conductive composition according to claim 1.

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