JP2002358823A - Gel electrolyte and utilization of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gel electrolyte of which, ion conductivity is improved by lowering the ratio of polymer content, and to provide a cell and capacitor using the same. SOLUTION: The gel electrolyte is composed of an electrolyte salt, a solvent for the electrolyte salt, a polymer having gel forming nature in the solvent, an organic compound having reversible gel forming nature, and preferably, an oil gelatinizing agent expressed by formula 1 or formula 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gel electrolyte, and more particularly, to a gel electrolyte that can be suitably used as a solid electrolyte in, for example, batteries and capacitors.

[0002]

2. Description of the Related Art In recent years, solid electrolytes widely used in electrochemical devices are substances having a high ionic conductivity in a solid state. Among them, a solid polymer electrolyte using a polymer substance as a solid has recently been developed. As an electrolyte for a next-generation lithium-ion secondary battery, it has attracted special attention, and research is being promoted worldwide. Such a polymer solid electrolyte has a greater degree of freedom in terms of its shape, such as no risk of liquid leakage and a thin film, as compared with a conventional electrolyte solution.

[0003] However, conventionally known non-aqueous polymer solid electrolytes have a problem that their electric conductivity is remarkably lower than that of an electrolyte solution. For example, conventionally, a non-aqueous polymer solid electrolyte obtained by complexing a polymer material such as a chain polymer such as polyethylene glycol or polypropylene glycol or a comb polymer such as polyphosphazene with an electrolyte salt is known. Conductivity 10 ^-3 at room temperature
Nothing exceeding S / cm has been found.

Therefore, in recent years, it has been proposed to blend an organic solvent such as propylene carbonate or γ-butyrolactone as a plasticizer into the solid electrolyte.

[0005] For example, J. Electrochem. Soc., Vol.
7, 1657-1658 (1990) proposes a sheet-like gel electrolyte obtained by gelling an organic electrolytic solution comprising a mixed solvent of propylene carbonate and ethylene carbonate in which lithium perchlorate is dissolved with polyacrylonitrile. . JP-A-11-16579 proposes a gel electrolyte comprising polyacrylonitrile, an electrolyte salt and a non-aqueous solvent. JP-A-8-298126 proposes a gel electrolyte using polyethylene oxide or polypropylene oxide as a polymer component and using γ-butyrolactone as a solvent.

As described above, an electrolyte obtained by mixing an organic solvent with a conventional solid electrolyte is generally called a gel electrolyte. Such a gel electrolyte has some improvement in ionic conductivity as compared with the conventional solid electrolyte as described above, but it must be said that it is still lower than the liquid electrolyte.

Further, in such a gel electrolyte,
An electrolyte comprising an electrolyte salt and a solvent for dissolving the electrolyte salt, for example, as a self-supporting film, in order to sufficiently maintain a gel state, the mixing ratio of the polymer component, usually, It must be about 30% by weight or more, and when the mixing ratio of the polymer component is increased in this manner, there is a problem that the electric conductivity is lower than that of the liquid electrolyte.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional gel electrolyte, and has a low mixing ratio of the polymer component. It is an object of the present invention to provide a high gel electrolyte, and to provide a battery or a capacitor using such a gel electrolyte.

[0009]

According to the present invention, there are provided an electrolyte salt, a solvent for the electrolyte salt, a polymer having a gel-forming property with respect to the solvent, and an organic compound having a reversible gel-forming property. A gel electrolyte is provided.

Further, according to the present invention, there are provided a battery and a capacitor using the above gel electrolyte.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A gel electrolyte according to the present invention comprises an electrolyte salt, a solvent for the electrolyte salt, a polymer having a gel forming property with respect to the solvent, and an organic compound having a reversible gel forming property.

In the present invention, the organic compound having a reversible gel-forming property with respect to the solvent used refers to a solution (that is, an electrolytic solution) obtained by dissolving an electrolyte salt in a solvent (preferably a non-aqueous organic solvent). When this is blended into a composition,
The composition is brought to a temperature above room temperature (25 ° C.), for example,
While not limited, when heated to 40-100 ° C, a uniform solution is formed and the solution is heated to room temperature (25 ° C).
Refers to an organic compound that reversibly forms a gel-like composition when cooled. That is, in the present invention, an organic compound having a reversible gel-forming property means that, in principle, binding and dissociation, or mobility and immobilization are reversibly performed in accordance with changes in temperature, pressure, and the like. It is a substance capable of performing the above-mentioned bond and dissociation or mobility and immobilization reversibly by an intermolecular or intramolecular interaction such as hydrogen bond, coordinate bond, Van der Waals force, etc. Refers to organic compounds that can be formed.

In particular, according to the present invention, an organic compound which can be dissolved in a solvent in a temperature range higher than room temperature (25 ° C.), but solidifies at room temperature to form a gel-like composition reversibly. A group of organic compounds known as oil gelling agents are preferably used.

As described in "Polymer Processing", Vol. 45, No. 1, pp. 21-26 (1996), an oil gelling agent can be used to add a small amount of oil to oils so that the whole oil can be used. Various drugs that can be set in a jelly form are already known.

In the present invention, the organic compound having a gel-forming property is not particularly limited as long as it is known as an oil gelling agent.
Any of them can be used, but preferred specific examples include, for example, 12-hydroxystearic acid, N-lauroyl-L-glutamic acid-α, γ-bis-n-butylamide, 1,2,3,4-dibenzylidene- D-sorbitol, aluminum dialkylphosphate, 2,3-bis-n-hexadecyloxyanthracene, trialkyl-
Cis-1,3,5-cyclohexanetricarboxamide,

[0016]

Embedded image

Compound (1) represented by the formula:

[0018]

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Compound (2) represented by the following formula:

In particular, according to the present invention, the compound (1)
The compound (2) can be preferably used because it can be gelled by using a small amount of an electrolytic solution comprising an electrolyte salt and a solvent therefor. Hereinafter, in the present invention, an organic compound having a gel-forming property is represented by an oil gelling agent.

In the gel electrolyte according to the present invention, the ratio of the above-mentioned oil gelling agent depends not only on itself, but also on the desired sol-gel depending on the electrolyte salt and solvent used.
It is determined appropriately so as to form a gel composition,
Usually, it is in the range of 0.1 to 20% by weight of the obtained gel electrolyte. In addition, the ratio of the electrolyte salt is appropriately determined according to the oil gelling agent and the solvent used as well as the electrolyte salt itself, but is usually in the range of 1 to 20% by weight of the obtained gel electrolyte.

Next, in the present invention, the polymer having a gel-forming property with respect to the solvent to be used is preferably a polymer capable of swelling in the solvent to be used to form a gel.
Although not limited, for example, polyethylene oxide, polypropylene oxide, polyvinyl ether,
Polyphosphazene, polysiloxane, polyvinylidene fluoride, poly (vinylidene fluoride-hexafluoropropylene), poly (vinylidene fluoride-ethylene chloride trifluoride), polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyester, etc. Further, a polymer having a structure such as polyacrylate, polymethacrylate, polyethylene oxide, polypropylene oxide, polyphosphazene, polyvinyl ether, or polysiloxane in a main chain and a chain oligoalkylene oxide structure in a side chain may be mentioned. Can be.

In the present invention, the electrolyte salt may be a hydrogen ion, an ion of an alkali metal such as lithium, sodium or potassium, an ion of an alkaline earth metal such as calcium or strontium, or a tertiary or quaternary ammonium ion. Ingredients, hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid,
Anionic components include inorganic acids such as tetrafluoroboric acid, hydrofluoric acid, hexafluorophosphoric acid, and perchloric acid; and organic acids such as organic carboxylic acids, fluorine-substituted organic carboxylic acids, organic sulfonic acids, and fluorine-substituted organic sulfonic acids. Can be used. Among these, an electrolyte salt containing an alkali metal ion as a cation component is particularly preferably used.

Specific examples of such an electrolyte salt containing an alkali metal ion as a cation component include, for example, alkali metal perchlorates such as lithium perchlorate, sodium perchlorate and potassium perchlorate, and tetrafluoroboric acid. Lithium, sodium tetrafluoroborate, alkali metal tetrafluoroborate such as potassium tetrafluoroborate, lithium hexafluorophosphate, alkali metal hexafluorophosphate such as potassium hexafluorophosphate,
Examples thereof include alkali metal trifluoroacetates such as lithium trifluoroacetate and alkali metal trifluoromethanesulfonates such as lithium trifluoromethanesulfonate.

In the present invention, the solvent for the electrolyte salt is preferably a solvent which dissolves the electrolyte salt to be used and is gelled by the gel-forming polymer and the reversible gel-forming organic compound. Although it is appropriately selected without limitation, in the present invention, a non-aqueous organic solvent is preferably used. Such non-aqueous organic solvents include, for example, ethylene carbonate, propylene carbonate, butylene carbonate,
Examples thereof include cyclic esters such as γ-butyrolactone, ethers such as tetrahydrofuran and dimethoxyethane, and chain esters such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.
These can be used alone or as a mixture of two or more.

The gel electrolyte according to the present invention can be obtained by various methods. For example, a polymer is dissolved in an appropriate polymer solvent, and a mixture of an electrolyte salt, a solvent therefor, and a reversible gelling agent is added in a sol state to the obtained solution to prepare a casting liquid. Next, after casting the casting liquid on a glass plate, the polymer solvent is removed at an appropriate temperature to obtain a gel electrolyte according to the present invention.

As another method, for example, a polymer is dissolved in an appropriate polymer solvent, the resulting solution is cast on a glass plate, and then the polymer solvent is removed at an appropriate temperature to obtain a polymer comprising the polymer. Prepare a film. Next, the film is immersed in a sol (solution) composed of an electrolyte salt, a solvent therefor, and a reversible gelling agent to swell the film, and then the film is taken out and cooled to room temperature. Also, a gel electrolyte according to the present invention can be obtained.

In this method, if necessary, a solvent for dissolving the polymer is appropriately selected, and inorganic particles which can be extracted in the subsequent step are mixed in the polymer solution. The polymer film obtained by extraction can be made porous.

Further, as another method, an electrolyte salt is dissolved in a solvent therefor and heated to an appropriate temperature.
Add a polymer and a reversible gelling agent to this, stir,
A gel electrolyte according to the present invention can be obtained by preparing a uniform sol (solution) and cooling it to room temperature.

According to the present invention, a porous membrane can be used as a support to increase the strength of the gel electrolyte thus obtained. The porous membrane is not particularly limited as long as a channel for the gel electrolyte is formed in the thickness direction, but is used as a strong gel electrolyte in a battery or a capacitor. Is considered, the Gurley value is 1500 seconds / 10
Preferably, it is 0 cc or less, the needle penetration strength is 1 N or more, and the porosity is in the range of 30 to 90%.

The material of the porous membrane is not particularly limited as long as it is resistant to the solvent used for the gel electrolyte according to the present invention and is electrochemically stable in the potential range used. Those comprising polytetrafluoroethylene or the like are preferably used.

As described above, in order to obtain a gel electrolyte using a porous membrane as a support, for example, a polymer is dissolved in an appropriate polymer solvent, and the resulting solution is reversibly gelled with an electrolyte salt and a solvent therefor. A mixture of the agents is added in a sol state to prepare a casting liquid. Next, a porous film is placed on a glass plate, the casting liquid is cast on the porous film, and then the polymer solvent is removed at an appropriate temperature.

The gel electrolyte according to the present invention can be suitably used as a solid electrolyte in batteries and capacitors. FIG. 1 is a longitudinal sectional view of a coin-type lithium secondary battery using a gel electrolyte according to the present invention. In this lithium secondary battery, the positive electrode can 1 also serving as a positive electrode terminal is made of, for example, a nickel-plated stainless steel plate,
The battery case is combined with the negative electrode can 3 which also functions as a negative electrode terminal insulated from the positive electrode can via the insulator 2. The negative electrode can is also made of, for example, a nickel-plated stainless steel plate.

The positive electrode 4 is disposed in contact with the positive electrode can inside the battery container thus formed. The positive electrode 4 is made of, for example, a positive electrode active material such as a cobalt manganese composite oxide and a conductive material such as graphite made of polyethylene,
It can be obtained by mixing with a binder resin such as polypropylene or polytetrafluoroethylene, and then press-molding this. Similarly, the negative electrode 5 is provided in contact with the negative electrode can. The negative electrode, for example, stores lithium ions such as graphite,
It consists of something that can be released. Between these positive and negative electrodes,
The solid electrolyte 6 according to the present invention is provided to constitute a battery. In the case of a capacitor, both electrodes are carbon electrodes, but other materials are configured in the same manner as the battery.

[0035]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples. In the following, the physical properties of the used porous membrane and the properties of the gel electrolyte were evaluated as follows.

(Thickness of Porous Film) The thickness was measured from a 1 / 10,000 mm thickness gauge and a 10000 × scanning electron microscope photograph of a cross section of the porous film.

(Porosity of Porous Membrane) Weight W (g) per unit area S (cm ² ) of the porous membrane, average thickness t (μ)
m) and the density d (g / cm ³ ) of the resin constituting the film were calculated by the following equation.

Porosity (%) = (1- (10 ⁴ W / S / t)
/ D)) x 100

(Air permeability) Measured in accordance with JIS P 8117.

(Piercing Strength) A piercing test was performed using a compression tester KES-G5 manufactured by Kato Tech Co., Ltd. The maximum load was read from the obtained load displacement curve, and the piercing strength per 25 μm of the film thickness was determined. Use a needle with a diameter of 1.0 mm and a radius of curvature of 0.5 mm at the tip,
The test was performed at a speed of 2 cm / sec.

(Ion conductivity of gel electrolyte) The obtained gel electrolyte was held in a sealed cell with a platinum electrode sandwiched between
The complex impedance was measured in the range of 0 mHz to 100 kHz, and the ionic conductivity was obtained from the real axis piece of the Cole-Cole plot. Impedance measurement is Pote
ntiostat / Galvanostat Model 263A Lock-In Amplifier
Model 5210 (both EG & GPRINCETON APPLIED RESEARC
H) at a constant temperature of 25 ° C.

Example 1 Lithium perchlorate was dissolved in propylene carbonate to a concentration of 1 mol / L to form a solution.
Solution E was prepared by adding 2.5 parts by weight of the compound (1) as a gelling agent to 5 parts by weight and heating at 90 ° C. for 5 minutes.

Separately, 95 parts by weight of acetone were mixed with 2.5 parts of poly (vinylidene fluoride-hexafluoropropylene) (KYNAR2801 manufactured by Elf Atochem Japan KK).
A weight part was added, stirred and dissolved to obtain a solution P.

The above solutions E and P were stirred and mixed, cast on a glass plate, and heated at 80 ° C. for 1 hour to remove acetone to obtain a gel electrolyte as a self-supporting film.

In this gel electrolyte, the compounding ratio of the compound (1) was 2.5% by weight, and the compounding ratio of the polymer was 2.5% by weight.
% By weight, and the ionic conductivity was 4.5 × 10 ⁻³ S / cm.

Example 2 Example 2 was repeated except that poly (vinylidene fluoride-hexafluoropropylene) solution was replaced by polymethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight: 996000). In the same manner as in Example 1, a gel electrolyte as a self-supporting film was obtained.

In this gel electrolyte, as a gelling agent
The compounding ratio of the compound (1) is 2.5% by weight,
-2.5% by weight, ionic conductivity 4.7 ×
10 ^-3S / cm.

Example 3 Lithium perchlorate was dissolved in propylene carbonate to a concentration of 1 mol / L to form a solution.
5 parts by weight of polyacrylonitrile (Wako Pure Chemical Industries, Ltd.)
2.5 parts by weight of the compound (1) as a gelling agent
Add 2.5 parts by weight, stir while heating at 80 ° C,
Solution E was prepared.

After casting this solution E on a glass plate, it was cooled to room temperature to obtain a gel electrolyte as a self-supporting film.

In this gel electrolyte, the compounding ratio of the compound (1) was 2.5% by weight, and the compounding ratio of the polymer was 2.5% by weight.
% By weight, and the ionic conductivity was 4.3 × 10 ⁻³ S / cm.

Example 4 A microporous polyethylene membrane (15 μm thick,
The porosity was 40%, the Gurley value was 200 seconds / cc, and the needle penetration strength was 2N). The solutions E and P prepared in Example 1 were stirred and mixed, cast on this microporous membrane, and then heated at 80 ° C. for 1 hour to remove acetone to remove the autonomous gel electrolyte / A microporous membrane composite was obtained.

In the gel electrolyte in the gel electrolyte / microporous membrane composite, the compounding ratio of the compound (1) was 2.5% by weight, the compounding ratio of the polymer was 2.5% by weight, and the ion conductivity was 2.5%. × 10 ^-3 S / cm.

Example 5 In Example 1, the above compound (1) was used as a gelling agent.
In place of the compound (2), a gel electrolyte as a self-supporting film was obtained in the same manner as in Example 1.

In this gel electrolyte, the compounding ratio of the compound (2) was 2.5% by weight, and the compounding ratio of the polymer was 2.5% by weight.
% By weight, and the ionic conductivity was 4.4 × 10 ⁻³ S / cm.

Comparative Example 1 A solution E was prepared by dissolving lithium perchlorate in propylene carbonate at a concentration of 1 mol / L. Separately,
To 95 parts by weight of acetone, 5.0 parts by weight of poly (vinylidene fluoride-hexafluoropropylene) (ELN Atochem, KYNAR2801 manufactured by Japan) was added, and the mixture was stirred and dissolved to obtain a solution P.

The solution E95 was added to 100 parts by weight of the solution P.
After stirring and mixing parts by weight and casting the mixture on a glass plate, the mixture was heated at 80 ° C. for 1 hour to remove acetone. However, a self-supporting film could not be obtained, and a fluid electrolyte was obtained. Stayed.

In this electrolyte, the blending ratio of the polymer was 5.0% by weight, and the ionic conductivity was 4.0 × 10 ⁻³ S / c.
m.

Comparative Example 2 Comparative Example 1 was repeated, except that polymethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 996,000) was used instead of poly (vinylidene fluoride-hexafluoropropylene). In the same manner as in Example 1, a fluid electrolyte was obtained.

In this electrolyte, the blending ratio of the polymer was 5.0% by weight, and the ionic conductivity was 4.1 × 10 ⁻³ S / c.
m.

Comparative Example 3 Lithium perchlorate was dissolved in propylene carbonate (bromylene carbonate) at a concentration of 1 mol / L to form a solution. 95 parts by weight of this solution was mixed with polyacrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.). ) 5.0 parts by weight were added, and the mixture was stirred with heating at 80 ° C to prepare a solution E.

After the solution E was cast on a glass plate and cooled to room temperature, a self-supporting film could not be obtained, and only a fluid electrolyte was obtained.

In this electrolyte, the blending ratio of the polymer was 5.0% by weight, and the ionic conductivity was 3.8 × 10 ⁻³ S / c.
m.

Comparative Example 4 A solution E was prepared by dissolving lithium perchlorate in propylene carbonate) at a concentration of 1 mol / L.

Separately, a poly (vinylidene fluoride-hexafluoropropylene) copolymer (KYNAR2801 manufactured by Elf Atochem, Japan) was added to 30 parts by weight of acetone.
A weight part was added, stirred and dissolved to obtain a solution P.

30 parts by weight of the above solution E and 50 parts by weight of the above solution P were stirred and mixed, cast on a glass plate, and then heated at 80 ° C. for 1 hour to remove acetone, thereby removing a gel electrolyte as a self-supporting film. I got

In this gel electrolyte, the blending ratio of the polymer was 40.0% by weight, and the ionic conductivity was 0.9 × 10 ^−3.
S / cm.

[0067]

As described above, according to the present invention, the proportion of the polymer can be reduced by forming a gel electrolyte by using a reversible gelling agent together with a polymer having a gel forming property in the solvent used. As a result, it is possible to obtain a gel electrolyte having a sufficient gel state and a high ionic conductivity like a self-supporting film. On the contrary,
As shown in the comparative example, without using a reversible gelling agent, when using only a polymer as a gel-forming substance, depending on the use of a small amount, such as a self-supporting film,
A gel electrolyte having a sufficient gel state cannot be obtained,
On the other hand, when a large amount of polymer is used, a gel electrolyte having a sufficient gel state can be obtained like a self-supporting film, but such a gel electrolyte has low ionic conductivity.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a coin-type solid electrolyte secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode can also serve as a positive electrode terminal 2 ... Insulator 3 ... Negative electrode can also serve as a negative electrode terminal 4 ... Positive electrode 5 ... Negative electrode 6 ... Solid electrolyte

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4J002 BD041 BD141 BD161 BE041 BG061 BG101 CF001 CH021 CP031 CQ011 ET006 FD206 GQ00 GQ02 5G301 CA30 CD01 5H029 AJ02 AJ06 AK03 AL07 AM00 AM03 AM04 AM05 AM07 AM16 BJ03 BJ12 EJ03 DJ14

Claims (9)

[Claims] 1. A gel electrolyte comprising an electrolyte salt, a solvent for the electrolyte salt, a polymer having a gel-forming property with respect to the solvent, and an organic compound having a reversible gel-forming property. 2. The polymer is polyethylene oxide, polypropylene oxide, polyvinyl ether, polyphosphazene, polysiloxane, polyvinylidene fluoride, poly (vinylidene fluoride-hexafluoropropylene), poly (vinylidene fluoride-ethylene trifluoride chloride). 2. The gel electrolyte according to claim 1, wherein the gel electrolyte is polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate or polyester. 3. A polymer having a main chain structure of polyacrylate, polymethacrylate, polyethylene oxide, polypropylene oxide, polyphosphazene, polyvinyl ether or polysiloxane and a side chain having a chain oligoalkylene oxide structure. The gel electrolyte according to claim 1, which is: 4. The gel electrolyte according to claim 1, wherein the organic compound having a reversible gel-forming property is an oil gelling agent. 5. The method according to claim 1, wherein the oil gelling agent is represented by the following chemical formula (I): The gel electrolyte according to claim 4, which is a compound represented by the following formula: 6. The oil gelling agent is represented by the following chemical formula (II): The gel electrolyte according to claim 4, which is a compound represented by the following formula: 7. The gel electrolyte according to claim 1, which has a porous membrane as a support. 8. A battery comprising the gel electrolyte according to claim 1. 9. A capacitor using the gel electrolyte according to claim 1.