JP2000036218A - Reversible sol-gel composition and its application - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte that can be tightly attached to the surface of an electrode by forming this composition from a reversible gelatinization agent, an electrolytic salt and a solvent for the electrolytic salt. SOLUTION: It is preferable that a reversible sol-gel electrolyte composition is formed a reversible sol-gel composition, and a reversible gelling agent is an oil gelatinization agent, in particular, a 12-hydroxystearic acid. A composition into which the reversible gelling agent is mixed is formed into a uniform solution when heated to a temperature above room temperature, and reversibly formed into a gel form when cooled, and polyethylene glycol or the like is also used for the reversible gelling agent. An electrolytic salt is, in particular, lithium perchlorate, lithium tetrafluoroborate or the like. A nonaqueous organic solvent such as ethylene carbonate or dimethyl carbonate is used as a solvent for the electrolytic salt. The composition can retain good contact with a base material by being formed into a desired shape in a sol state and thereafter gelled. In addition, it has an excellent low temperature characteristic. For instance, it is useful for the solid electrolyte of a lithium secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible sol-gel composition and its use, and more particularly to a reversible sol-gel composition and a non-aqueous reversible sol-gel electrolyte composition using the same. And solid electrolyte laminates.

[0002]

2. Description of the Related Art A solid electrolyte refers to a substance having a high ionic conductivity in a solid state. Among them, a polymer solid electrolyte using a polymer substance as a solid has recently been used as an electrolyte for a next-generation lithium secondary battery. In particular, it is receiving attention and research is being promoted worldwide.

[0003] Such a polymer solid electrolyte has a greater degree of freedom in its shape, for example, without the risk of liquid leakage as compared with a conventional electrolyte solution, and can be formed into a thin film.
However, conventionally known non-aqueous polymer solid electrolytes have a problem that their electric conductivity is significantly 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. No conductivity of more than 10 ⁻³ S / cm at room temperature has been found.

Therefore, in recent years, various non-aqueous gel electrolytes have been studied for practical use. According to this study, a non-aqueous gel electrolyte having an electric conductivity of 10 ⁻³ S / cm or more at room temperature and being close to an electrolyte solution has been studied. Has been proposed. Such a gel electrolyte is obtained by dissolving an electrolyte salt in a gel formed by a polymer material and a non-aqueous organic solvent, and dissolving the polymer material or a precursor thereof in an organic solvent together with the electrolyte salt. , By solidification (gelation).

However, such a conventionally known gel electrolyte has poor contact with the surface of the electrode and a large resistance between the gel electrolyte and the surface of the electrode as compared with the electrolyte solution. There's a problem. As described above, when the resistance between the gel electrolyte and the surface of the electrode is large, the conductivity of the gel electrolyte itself cannot be effectively utilized, and the gel electrolyte cannot be practically used as an electrochemical element. In particular, when the surface of the electrode is not flat, it is difficult for the conventional gel electrolyte to make good contact with the surface of the electrode.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional solid electrolyte, and is a novel reversible sol-gel composition useful as a solid electrolyte. The purpose is to provide.
In particular, the present invention can be treated as a solid electrolyte,
An object of the present invention is to provide a reversible sol-gel composition which can be brought into close contact with the surface of an electrode and can be used as an electrochemical device having a desired shape.

[0007] Further, the present invention relates to such a reversible sol.
An object of the present invention is to provide a reversible sol-gel electrolyte composition comprising a gel composition and a solid electrolyte laminate containing the same.

[0008]

The reversible sol-gel composition according to the present invention is characterized by comprising a reversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt.

The reversible sol-gel electrolyte composition according to the present invention comprises such a gel composition.

[0010] Further, the solid electrolyte laminate according to the present invention comprises:
The reversible sol-gel composition layer is laminated on at least one surface of the solid electrolyte thin film.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a reversible gelling agent refers to a composition obtained by blending in a solution of a non-aqueous organic solvent in which an electrolyte salt is dissolved, at a temperature higher than room temperature (25 ° C.). High temperature, for example, but not limited to, 40-
A substance that forms a uniform solution when heated to 100 ° C and reversibly forms a gel composition when the solution is cooled to room temperature (25 ° C). In principle, temperature, pressure, etc. Is a substance capable of reversibly binding and dissociating, or mobility and immobilization according to the fluctuation of, for example, intermolecular or intramolecular such as hydrogen bond, coordinate bond, van der Waals force, etc. A substance that is capable of reversibly performing the above-mentioned binding and dissociation or mobility and immobilization by the interaction of is useful.

In particular, according to the present invention, polymers and oligomers which can be dissolved in a solvent in a temperature range higher than room temperature (25 ° C.) but solidify at room temperature to form a gel reversibly, especially In addition to polymers and oligomers having a polar group such as an ether group or a hydroxyl group in the molecule, a group of substances known as oil gelling agents are preferably used.

Examples of the polymer having a polar group such as an ether group or a hydroxyl group in the molecule include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, and polyvinyl alcohol.

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, any known oil gelling agent can be used without any particular limitation. Preferred examples thereof 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]

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Cholesterol derivatives such as

[0018]

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And cyclohexanediamino derivatives.

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. As 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 non-aqueous organic solvent for the electrolyte salt is appropriately selected without particular limitation as long as it dissolves the electrolyte salt to be used. Examples include cyclic esters such as propylene carbonate, butylene carbonate, and γ-butyrolactone; ethers such as tetrahydrofuran and dimethoxyethane; and chain esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. These, alone,
Alternatively, they can be used as a mixture of two or more.

In the present invention, the compounding amount of the reversible gelling agent is not limited to itself, but depends on the electrolyte salt and the solvent to be used so that these mixtures form the desired reversible sol-gel composition. Although it is determined as appropriate, it is usually in the range of 0.1 to 10% by weight of the obtained reversible sol-gel composition. Also, the amount of the electrolyte salt is not limited to itself,
It is appropriately determined according to the reversible gelling agent and the solvent to be used, but is usually 1 to 2 of the obtained reversible sol-gel composition.
The range is 0% by weight.

The reversible sol-gel composition according to the present invention comprises
A uniform solution (sol) can be obtained by adding an electrolyte salt and a reversible gelling agent to the above-mentioned solvent and heating and stirring the mixture at a temperature of 40 ° C. or higher, for example, and cooling it to room temperature (25 ° C.). Then, a gel can be obtained.

According to the present invention, the reversible sol-gel composition can have a core material such as a nonwoven fabric, a porous membrane, a split cloth, and a mesh. Thus, the reversible sol having a core material
The gel composition may be formed into a sol by, for example, converting a reversible sol-gel composition into a sol, and cooling the gel while keeping the core material immersed therein.

The reversible sol-gel composition according to the present invention comprises
Thus, it is a gel at room temperature (25 ° C.) and can be made into a sol by heating it to a high temperature of about 40 ° C. to 100 ° C., and the change between such a sol and the gel is reversible. It is a target. In addition, the reversible sol-gel composition according to the present invention can be formed into an arbitrary shape by molding in a sol state and gelling the sol.

The reversible sol-gel composition according to the present invention comprises
In other words, a reversible gelling agent is blended into an electrolyte solution comprising a non-aqueous organic solvent of an electrolyte salt, and is a gel at room temperature (25 ° C.) and a sol at a high temperature, usually at a temperature of 40 ° C. or higher, In addition, since the change between the sol and the gel is reversible, it is particularly useful as a gel electrolyte composition capable of forming a sol and a gel reversibly.

For example, when the electrolyte composition comprising such a reversible sol-gel composition is used as a solid electrolyte in a battery, the electrolyte composition is converted into a sol even when the surface of the electrode is not flat. After it is made to conform to the surface of the electrode and then gelled, it can be brought into close contact with the electrode. Further, even when the shape of the surface of the electrode changes, the reversible sol-gel electrolyte composition is heated, turned into a sol, and adhered to the surface of the electrode. Following the change in the shape of the electrode surface, the electrodes can be brought into close contact with each other and good contact therebetween can be maintained.

Further, the reversible sol-gel electrolyte composition according to the present invention converts the non-aqueous electrolyte solution into a gel by a relatively weak bond such as a hydrogen bond or van der Waals force of the reversible gelling agent. Since the non-aqueous electrolyte solution is retained, the electrical characteristics of the non-aqueous electrolyte solution are hardly impaired. Therefore,
The reversible sol-gel electrolyte composition according to the present invention has a small decrease in electric conductivity even at a low temperature, and thus, an electrochemical device constituted by using the electrolyte composition according to the present invention can be used as a conventional solid electrolyte or It has excellent low-temperature characteristics as compared with an electrochemical device using a gel-like solid electrolyte.

According to the present invention, the reversible sol-gel composition (electrolyte composition) of the present invention is applied to at least one surface of the solid electrolyte thin film in a sol state, and then cooled to form a gel. By doing so, a solid electrolyte laminate having a layer of the reversible sol-gel composition (electrolyte composition) according to the present invention as an interface layer on at least one surface of the solid electrolyte thin film can be obtained. Such a solid electrolyte laminate is preferably a thin film.

In such a solid electrolyte laminate, any conventionally known solid electrolyte can be used, and a conventionally known gel electrolyte can also be used as the solid electrolyte. . Such solid electrolyte, for example, lithium iodide, lithium iodide (alumina), and Li _x S _y P _z O, etc., polyethylene glycol, polypropylene glycol, polyacrylonitrile, polyphosphazene, the polymeric material of the polysiloxane Examples thereof include those obtained by dissolving an electrolyte salt.

Examples of the gel solid electrolyte include polyethylene glycol, polypropylene glycol, polyvinylidene fluoride, polyacrylonitrile, polymethacrylate, poly (meth) acrylate oligoethylene oxide, polyethylene imine, polyalkylene sulfide, and oligoethylene oxide. Crosslinking and curing of a polymer material such as a copolymer having a polymer in the side chain is performed, and an electrolyte salt is dissolved therein to form a gel, and if necessary, a plasticizer is added.

For example, by dissolving an electrolyte salt in a non-aqueous organic solvent, adding polyethylene propylene glycol diacrylate and a polymerization initiator to form a solution, and heating the solution to cross-link polyethylene propylene glycol diacrylate, A gel-like solid electrolyte can be obtained.

Such a solid electrolyte laminate can be used even when the surface of the electrode is not flat by using the interface layer composed of the reversible sol-gel electrolyte composition layer so as to contact the surface of the electrode. After the reversible sol-gel electrolyte composition is formed into a sol and formed along the surface of the electrode and then gelled, the solid electrolyte laminate can be brought into close contact with the surface of the electrode. Furthermore, even when the shape of the surface of the electrode changes, the reversible sol-gel electrolyte composition is heated, turned into a sol, adhered to the surface of the electrode, and then gelled, so that it is always gelled. The contact between the solid electrolyte laminate and the surface of the electrode can be favorably maintained following the change in the shape of the electrode surface.

As described above, the reversible sol-gel electrolyte composition and the solid electrolyte laminate according to the present invention can be suitably used, for example, as a solid electrolyte in a lithium secondary battery.

FIG. 1 is a longitudinal sectional view of a coin-type lithium secondary battery using such a solid electrolyte. In this lithium secondary battery, the positive electrode can 1 also serving as a positive electrode terminal is:
For example, the battery case is made of a nickel-plated stainless steel plate, and is combined with a negative electrode can 3 serving as a negative electrode terminal insulated from the positive electrode can via an 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, for example, a positive electrode active material such as a lithium manganese composite oxide or a lithium cobalt composite oxide and a conductive material such as graphite mixed with a binder resin such as polyethylene, polypropylene, and polytetrafluoroethylene; This can be obtained by pressure molding. Similarly, the negative electrode 5 is provided in contact with the negative electrode can. The negative electrode is made of, for example, a lithium plate or a lithium storage material.

The solid electrolyte laminate 6 according to the present invention is disposed between the positive electrode and the negative electrode to constitute a battery. The solid electrolyte laminate 6 has a layer 8 of a reversible sol-gel electrolyte composition as an interface layer on both surfaces of a solid electrolyte thin film 7, and the interface layer is in contact with the positive electrode and the negative electrode, respectively.

[0039]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples.

Example 1 A mixture of 36.6 g of ethylene carbonate and 55.6 g of ethyl methyl carbonate was used as a solvent, and 7.8 g of lithium tetrafluoroborate was dissolved as an electrolyte salt in the mixture.
An electrolyte solution was prepared. To 14.06 g of this electrolyte solution,
12-hydroxystearic acid as a reversible gelling agent
0.81 g were mixed and heated and stirred at 50 ° C. to obtain a uniform and transparent solution.

The above solution was spread on a glass plate having spacers at both ends for controlling the thickness, and then cooled to room temperature to obtain a white gel composition having a thickness of about 200 μm. This gel composition is heated to about 50 ° C. on a hot plate.
To a clear solution again. The conversion between such gel and solution was reversible.

Electric conductivity meter (CM manufactured by Toa Denpa Kogyo Co., Ltd.)
The conductivity of the gel composition was measured using -20S) and found to be 3.1 × 10 ⁻³ S / cm at 25 ° C. FIG. 2 shows the temperature dependence of the electric conductivity in the range of 50 ° C. to −20 ° C. The conductivity was measured at 25 ° C. and found to be 2.1 × 10 ⁻³ S / cm at 25 ° C. using metallic lithium as the electrode.

Comparative Example 1 A mixture of 36.6 g of ethylene carbonate and 55.6 g of ethyl methyl carbonate was used as a solvent, and 7.8 g of lithium tetrafluoroborate was dissolved as an electrolyte salt in the mixture.
An electrolyte solution was prepared.

When the electric conductivity of this electrolyte solution was measured in the same manner as in Example 1, it was found that at 25 ° C., 3.6 × 10
^-3 S / cm. FIG. 2 shows the temperature dependence of the electric conductivity in the range of 50 ° C. to −20 ° C. When the conductivity was measured by a DC four-terminal method using metallic lithium as an electrode, at 25 ° C., 2.5 × 10 ⁻³ S / cm.
Met.

Example 2 A mixture of 36.6 g of ethylene carbonate and 55.6 g of ethyl methyl carbonate was used as a solvent, and 7.8 g of lithium tetrafluoroborate was dissolved as an electrolyte salt in the mixture.
An electrolyte solution was prepared. To 14.06 g of this electrolyte solution,
Polyethylene glycol 2.43 as a reversible gelling agent
g was mixed and heated and stirred at 65 ° C. to obtain a uniform and transparent solution.

The above solution was spread on a glass plate having spacers at both ends for controlling the thickness, and then cooled to room temperature to obtain a transparent gel composition having a thickness of about 200 μm. This gel composition is heated to about 65 ° C. on a hot plate.
To a clear solution again. The conversion between such gel and solution was reversible.

This gel composition was prepared in the same manner as in Example 1.
Was measured at 25 ° C., 2.8 × 1
0^-3S / cm. In addition, metal lithium as an electrode
When the conductivity was measured by the DC four-terminal method using
At 25 ° C., 1.9 × 10 ^-3S / cm.

Example 3 A mixture of 36.6 g of ethylene carbonate and 55.6 g of ethyl methyl carbonate was used as a solvent, and 7.8 g of lithium tetrafluoroborate was dissolved therein as an electrolyte salt.
5.00 g and 0.05 g of 2,2′-azobisisobutyronitrile as a polymerization initiator were dissolved and stirred to obtain a uniform and transparent solution.

After the above solution was spread on a glass plate having spacers at both ends for controlling the thickness, the solution was heated at 90 ° C. for 2 hours.
By heating for a time, a self-supporting gel electrolyte thin film having a thickness of about 200 μm was obtained.

Separately, a mixture of 36.6 g of ethylene carbonate and 55.6 g of ethyl methyl carbonate was used as a solvent,
7.8 g of lithium tetrafluoroborate was dissolved therein as an electrolyte salt. 0.81 g of 12-hydroxystearic acid as a reversible gelling agent was mixed with 14.06 g of this solution, and the mixture was heated and stirred at 50 ° C. to obtain a uniform and transparent solution.

This solution was applied on both surfaces of the gel electrolyte thin film to a thickness of 50 μm, cooled to room temperature (25 ° C.) and gelled to form an interface layer. Thus, the solid electrolyte laminate was obtained. Obtained.

When this solid electrolyte laminate was heated to about 50 ° C. on a hot plate, only the surface interface layer became a sol. When this was cooled to room temperature (25 ° C.), the interface layer became gel-like again, and it was possible to reversibly convert between such a sol and a gel.

[0053]

The reversible sol-gel composition according to the present invention is in a gel state at room temperature (25 ° C.), and can be reversibly formed into a sol by heating.
Therefore, the reversible sol-gel composition according to the present invention can be formed into a desired shape in a sol state, and by gelling the same, the composition can be maintained in a stable shape while maintaining a stable shape of the composition. And good contact can be maintained between them.

The reversible sol-gel composition according to the present invention comprises
Particularly useful as a gel electrolyte composition, an electrochemical device containing the same has excellent low-temperature characteristics, even at low temperatures, as compared to conventional solid electrolytes and electrochemical devices using a gel solid electrolyte. Have.

Further, the reversible sol-gel electrolyte composition according to the present invention can be used, for example, even when the surface of the electrode is not flat, after the electrolyte composition is solified and formed along the surface of the electrode. By this, it can be brought into close contact with this. Furthermore, even when the shape of the surface of the electrode changes, the reversible sol-gel electrolyte composition is heated, turned into a sol, adhered to the surface of the electrode, and then gelled, so that it is always gelled. Following the change in the shape of the electrode surface, the electrodes can be brought into close contact with each other to maintain good contact therebetween.

Since the solid electrolyte laminate according to the present invention also has a layer composed of the reversible sol-gel electrolyte composition as an interface layer, similarly, the reversible sol-gel conversion is used to form an electrode. The electrode can be brought into close contact with the surface, and can follow the change in the shape of the surface of the electrode.

Therefore, the reversible sol-gel electrolyte composition and the solid electrolyte laminate according to the present invention, and furthermore, the electrochemical device containing them can be advantageously used, for example, as a solid electrolyte in a lithium secondary battery. it can.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the temperature dependence of the conductivity of a reversible sol-gel electrolyte composition according to the present invention and the temperature dependence of the conductivity of a conventional electrolyte solution as a comparative example.

[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 laminated body 7 ... Solid electrolyte thin film 8 ... Layer of reversible sol-gel electrolyte composition (Interface layer)

Claims (8)

[Claims] 1. A reversible sol comprising a reversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt.
Gel composition. 2. The reversible sol-gel composition according to claim 1, wherein the reversible gelling agent is an oil gelling agent. 3. The reversible sol-gel composition according to claim 1, wherein the reversible gelling agent is 12-hydroxystearic acid. 4. A reversible sol comprising a reversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt.
Gel electrolyte composition. 5. The reversible sol-gel electrolyte composition according to claim 4, wherein the reversible gelling agent is an oil gelling agent. 6. The reversible sol-gel electrolyte composition according to claim 4, wherein the reversible gelling agent is 12-hydroxystearic acid. 7. A solid electrolyte laminate comprising a layer of the reversible sol-gel electrolyte composition according to claim 4 laminated on at least one surface of a solid electrolyte thin film. body. 8. An electrochemical device comprising the reversible sol-gel electrolyte composition according to claim 4.