JP2001297626A - Reversible sol-gel electrolyte and electrochemical device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible sol-gel electrolyte composition of matter, having superior gelation ability, and a battery and a capacitor using it as the electrolyte. SOLUTION: In a reversible sol-gel electrolyte composition of matter, made of a reversible gelling agent; an electrolytic salt and a solvent for the electrolytic salt, an organic compound, which has an imino group and a carbonyl group but does not have a hydroxyl group in its molecule is used as the reversible gelling agent.

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 electrolyte composition having excellent ionic conductivity and gelling ability, and an electrochemical device using the same as a solid electrolyte, preferably a battery and a capacitor. About.

[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.

However, conventionally known non-aqueous polymer solid electrolytes have a problem that their ionic conductivity is lower than that of electrolyte solutions. 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, 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).

[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 is still lower than the liquid electrolyte.
Therefore, when such a gel electrolyte is used in a battery, the internal resistance is not sufficiently reduced, and when the shape of the electrode changes, the internal resistance is still low. Can't keep up with change.

Further, in general, in order to obtain a sufficient gel state in a gel electrolyte, the blending ratio of the above-mentioned polymer component needs to be about 20% by weight or more. For example, since the conductivity is lower than that of the liquid electrolyte, the internal resistance of the battery increases, and the charge / discharge characteristics deteriorate. This tendency is particularly remarkable at a low temperature of 0 ° C. or lower.

For example, when an electrode in a battery is made of an aggregate of granular or scaly active materials and has a gap between them, or when it is made of a porous material having a gap, the electrode is formed in such a gap. Due to the presence of the electrolyte,
For the first time, the transfer of reactants at the electrode-electrolyte interface is performed smoothly, and sufficient charge and discharge can be performed. Therefore, in general, when manufacturing an electrochemical element containing a solid electrolyte or a gel electrolyte together with an electrode, it is necessary to previously fill the electrolyte with a void in the electrode. Thus, conventionally, the production of an electrochemical device containing a solid electrolyte together with an electrode requires many steps, resulting in poor productivity and increased production cost.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional solid electrolyte, and it is an object of the present invention to provide a reversible gelling agent, an electrolyte salt, and In a reversible sol-gel electrolyte composition comprising a solvent, a reversible gelation of an organic compound characterized by having a molecular structure having a certain polar group and not having a certain polar group By using it as an agent, a reversible sol-gel electrolyte composition having excellent ion conductivity and gelling ability can be obtained.Furthermore, by using this as a solid electrolyte, batteries and capacitors having excellent properties can be obtained. The present inventors have found that they can be obtained, and have arrived at the present invention.

Accordingly, the present invention provides a reversible sol-gel electrolyte composition having excellent ion conductivity and gelling ability, and an electrochemical device using the same as a solid electrolyte, particularly,
It is intended to provide a battery and a capacitor.

[0011]

According to the present invention, there is provided a reversible sol-gel electrolyte composition comprising a reversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt. Is an organic compound having an imino group and a carbonyl group in the molecule, and a reversible sol-gel electrolyte is provided.

Further, according to the present invention, there is provided an electrochemical device, preferably a battery and a capacitor, using such a reversible sol-gel electrolyte as a solid electrolyte.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The reversible sol-gel electrolyte composition according to the present invention comprises a reversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt, that is, a solvent for dissolving the electrolyte salt,
Preferably, it consists of a non-aqueous (organic) solvent. in this way,
The reversible gelling agent is a substance that imparts reversible sol-gel properties to the obtained composition when the electrolyte is mixed with an electrolytic solution dissolved in a solvent.

That is, in the present invention, the term “reversible gelling agent” refers to a composition obtained when the compound is mixed with a solvent in which an electrolyte salt is dissolved, preferably a non-aqueous solvent solution (ie, a non-aqueous electrolyte solution). However, when this is heated to a temperature higher than room temperature (25 ° C.), for example, but not limited to, 50 ° C. or more, preferably 50-100 ° C., a uniform solution is formed, A substance that forms a gel composition reversibly when cooled to room temperature (25 ° C.), and in principle, reversibly binds and dissociates or changes mobility and immobilization according to changes in temperature, pressure, etc. It is a substance that can perform the bond and dissociation, or reversibility of mobility and immobilization by intermolecular or intramolecular interactions such as hydrogen bond, coordinate bond, van der Waals force, etc. Substances that can be performed

According to the present invention, as such a reversible gelling agent, a compound having an imino group and a carbonyl group in the molecule, in particular, the imino group and the carbonyl group form an amide bond in the molecule. Further, an organic compound having no hydroxyl group in the molecule is preferably used.

Conventionally, for example, various reversible gelling agents have been known as oil gelling agents. When such a reversible gelling agent has a hydroxyl group in the molecule, the hydroxyl group is not used. Since it is electrochemically unstable, when it is used as an electrolyte in a battery or a capacitor, sufficient characteristics cannot be obtained. For example, in a battery using an active material for transferring lithium metal or lithium ions to and from the negative electrode, when using an electrolyte containing a gelling agent having a hydroxyl group in the molecule as described above, this hydroxyl group Reacts with the above-mentioned lithium metal or lithium ion, and thus cannot obtain sufficient battery characteristics.

Preferred examples of the reversible gelling agent having the above-mentioned characteristic molecular structure used in the present invention include, for example, the following formula (1)

[0018]

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A compound represented by the following formula (2):

[0020]

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Compounds represented by the following formulas can be mentioned. These may be used alone or in combination. In the present invention, as the electrolyte salt, hydrogen ion, lithium, sodium, ions of alkali metals such as potassium, calcium, ions of alkaline earth metals such as strontium, tertiary or quaternary ammonium ions as a cation component, Inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, tetrafluoroboric acid, hydrofluoric acid, hexafluorophosphoric acid, perchloric acid, and organic carboxylic acids,
Salts using an organic acid such as a fluorine-substituted organic carboxylic acid, an organic sulfonic acid, or a fluorine-substituted organic sulfonic acid as an anion component 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 thereof include ethylene carbonate and ethylene carbonate. 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 blending amount of the reversible gelling agent in the reversible sol-gel electrolyte composition is not limited to itself, but also depends on the electrolyte salt and the solvent used, and the mixture of these reversible The sol-gel electrolyte composition is appropriately determined so as to form a typical sol-gel electrolyte composition, but is usually in the range of 0.1 to 20% by weight of the obtained reversible sol-gel electrolyte composition. In addition, the amount of the electrolyte salt is not limited to itself, but is appropriately determined depending on the reversible gelling agent and the solvent to be used, but is usually 1 to 3 of the obtained reversible sol-gel electrolyte composition. It is in the range of 20% by weight.

The reversible sol-gel electrolyte composition according to the present invention is prepared by adding an electrolyte salt and a reversible gelling agent to the above-mentioned solvent and heating the mixture to a temperature of 50 ° C. or more, for example, to obtain a uniform solution (sol-gel). ), And when this is cooled to room temperature (25 ° C.), a gel can be obtained.

That is, the reversible sol-gel electrolyte composition according to the present invention is a gel at room temperature (25 ° C.) and is converted into a sol by heating it to a high temperature of about 50 ° C. to 100 ° C. The change between such sols and gels is reversible. Moreover, the reversible sol-gel electrolyte composition can be formed into an arbitrary shape by molding in a sol state and gelling the sol.

Therefore, the electrolyte according to the present invention is, for example,
By making this into a sol state and impregnating it in a porous film and cooling it to room temperature (25 ° C.), it can be fixed as a gel in the porous film.

The reversible sol-gel electrolyte composition according to the present invention can be used in the manufacture of an electrochemical device, for example, a battery, a capacitor or a capacitor, in which a pair of electrodes are disposed to face each other via an electrolyte. It can be advantageously used as a non-aqueous electrolyte. That is, a work-in-progress of an electrochemical element is provided in which a pair of electrodes are disposed facing each other with a gap or through a porous sheet, and the reversible sol-gel electrolyte composition described above according to the present invention is prepared. After impregnating the in-process sol with the sol of the product, by gelling the sol,
Filling the gap between the electrodes with a solid electrolyte, or filling a porous sheet with a solid electrolyte, thus obtaining an electrochemical element using the reversible sol-gel electrolyte composition according to the present invention as a solid electrolyte Can be.

For example, in the case of a battery, a porous film for forming a battery separator is laminated with an electrode or combined by being wound together, for example, to form a pair of porous films via the porous film. The electrodes are arranged to face each other, and, for example, placed in a battery case, and after assembling a work-in-progress, a sol of a reversible sol-gel electrolyte composition is injected into the case, so After being impregnated in the porous membrane, it is cooled, and the gelled electrolyte is supported on the porous membrane. Thus, when a separator is formed, a battery is produced in which electrodes are provided through such a separator. It can be obtained easily and easily.

In particular, the reversible gelling agent is added to a non-aqueous electrolyte solution comprising a lithium salt as an electrolyte salt and a non-aqueous organic solvent to form a reversible sol-gel electrolyte composition,
Using this, a lithium ion battery can be obtained as described above. As the lithium salt, for example, as described above, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluoroacetate, lithium trifluoromethanesulfonate and the like can be used.

[0031]

As described above, according to the present invention, it comprises a reversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt. , Having an imino group and a carbonyl group forming an amide bond, and further preferably, by using an organic compound having no hydroxyl in the molecule, excellent reversibility with excellent gelling ability and ion conductivity. Sol-gel electrolyte composition can be obtained.

Further, according to the present invention, by using such a reversible sol-gel electrolyte composition as a solid electrolyte, it is possible to obtain an electrochemical device having excellent characteristics such as a battery and a capacitor. it can. In particular, the nonaqueous electrolyte battery according to the present invention does not cause liquid leakage, has low internal resistance, and has excellent charge / discharge characteristics.

[0033]

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

Example 1 (Preparation of positive electrode sheet) Lithium cobaltate (LiCoO
₂ , average particle size 15 μm), graphite powder and polyvinylidene fluoride resin were mixed at a weight ratio of 85: 10: 5, and the mixture was added to N-methyl-2-pyrrolidone, and stirred to obtain a solid content concentration of 15 wt. % Slurry was prepared. Using a coating machine, apply this slurry to the surface of a 20 μm-thick aluminum foil (current collector) to a thickness of 200 μm, dry at 80 ° C. for 1 hour, and further apply the slurry to the back of the aluminum foil. Was applied to a thickness of 200 μm and dried. Next, the thus treated aluminum foil was heated at 120 ° C. for 2 hours, dried, and then passed through a roll press to a thickness of 2 mm.
A 00 μm positive electrode sheet was produced.

(Preparation of Negative Electrode Sheet) Graphite powder and polyvinylidene fluoride resin were mixed at a weight ratio of 95: 5, and this was charged into N-methyl-2-pyrrolidone, and stirred to obtain a solid content of 15% by weight. % Slurry was prepared. Using a coating machine, apply this slurry to a surface of a 20 μm thick copper foil (current collector) to a thickness of 200 μm, heat at 80 ° C. for 1 hour, dry, and further apply The slurry was applied to a thickness of 200 μm, heated at 80 ° C. for 1 hour, and dried. Thereafter, the thus treated copper foil was heated at 120 ° C. for 2 hours, dried, and then passed through a roll press to produce a 200 μm-thick negative electrode sheet.

(Preparation of reversible sol-gel electrolyte composition)
Lithium perchlorate (LiClO ₄ ) was dissolved as an electrolyte in a solvent composed of a mixture of ethylene carbonate / ethyl methyl carbonate at a volume ratio of 1/1 so as to have a concentration of 1 mol / L to form an electrolytic solution. 5% by weight of the compound represented by the formula (1)
The mixture was heated to 0 ° C. and dissolved to prepare a reversible sol-gel electrolyte composition.

(Production of Battery) The above positive electrode sheet was 58 m wide.
m, cut into dimensions of 550 mm in length, and cut the negative electrode sheet to a width of 5 mm.
The sheet was cut into a size of 9 mm and a length of 600 mm, and a lead was attached to each current collector. These electrode sheet and width 60
mm polyethylene resin porous membrane (thickness 25 μm, porosity 50%, average pore diameter 0.1 μm) is alternately laminated, and this is wound into a coil so that the porous membrane is positioned on the outermost side. Into a cylinder. The outermost porous film was fixed on the inner porous film with an adhesive tape to prepare a work in process of an electrochemical element, and the work in process was inserted into an aluminum battery can. Separately, the in-process product was inserted into a battery bag made of polyethylene terephthalate film on which aluminum was deposited.

The above reversible sol-gel electrolyte composition is
The mixture was heated to ° C. to form a sol. The sol was poured into the battery can and the battery bag, sufficiently impregnated into the work-in-progress, and then cooled to gel the sol. Thereafter, the mouth of the battery can was covered with a lid, and the opening of the battery bag was heat-sealed and sealed. Thus, lithium ion secondary batteries were obtained as a can battery and a bag battery, respectively.

Example 2 A lithium ion secondary battery was obtained as a can battery and a bag battery in the same manner as in Example 1 except that the compound represented by the formula (2) was used as the gelling agent.

COMPARATIVE EXAMPLE 1 Lithium perchlorate (LiClO ₄ ) was dissolved as an electrolyte at a concentration of 1 mol / L in a solvent composed of a mixture of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1. Except for using as a liquid,
In the same manner as in Example 1, lithium ion secondary batteries were obtained as can batteries and bag batteries.

Comparative Example 2 Lithium perchlorate (LiClO ₄ ) was dissolved as an electrolyte in a solvent composed of a mixture of ethylene carbonate / ethyl methyl carbonate at a volume ratio of 1/1 so as to have a concentration of 1 mol / L to form an electrolyte. As a gelling agent,
1,2,3,4-dibenzylidene-D-sorbitol 5% by weight
In addition, the mixture was heated to 90 ° C. and dissolved to prepare a reversible sol-gel electrolyte composition. Using this electrolyte composition, a lithium ion secondary battery was obtained as a can battery and a bag battery in the same manner as in Example 1.

Comparative Example 3 Lithium perchlorate (LiClO ₄ ) was dissolved as an electrolyte in a solvent composed of a mixture of ethylene carbonate / ethyl methyl carbonate at a volume ratio of 1/1 to a concentration of 1 mol / L to form an electrolyte. As a gelling agent,
Add bis (p-methylbenzylidene-D-sorbitol 5% by weight, heat to 90 ° C., dissolve,
A gel electrolyte composition was prepared. Using this electrolyte composition, a lithium ion secondary battery was obtained as a can battery and a bag battery in the same manner as in Example 1.

Comparative Example 4 Lithium perchlorate (LiClO ₄ ) was dissolved in propylene carbonate at a concentration of 1 mol / L and heated to 100 ° C., and polymethyl methacrylate (manufactured by Aldrich, average molecular weight 120000) was added at 30% by weight. In addition, the mixture was dissolved to obtain a gel electrolyte sheet having a thickness of 50 μm by a casting method.

The gel electrolyte sheet obtained in this manner was replaced with a separator, and alternately laminated with an electrode sheet in the same manner as in Example 1, and this was wound so that the gel electrolyte sheet was positioned on the outermost side. It was a cylinder. The outermost gel electrolyte sheet was fixed on the inner gel electrolyte sheet with an adhesive tape to produce an electrochemical element. This electrochemical element was inserted into an aluminum battery can, and the above-mentioned in-process product was separately inserted into a polyethylene terephthalate battery bag on which aluminum was vapor-deposited. As obtained.

For each of the batteries thus obtained, the internal resistance was measured, and a charge / discharge test was performed.
In addition, a hole having a diameter of 1 mm was formed in the outer package, and the weight when the hole was allowed to stand for 30 minutes with the hole facing downward was compared with the initial weight to determine whether or not there was leakage of the electrolyte (quality).

The internal resistance of the battery was measured at a frequency of 10 kHz using an LCR meter (KC-546 manufactured by Kokuyo Electric Co., Ltd.).
It was measured at z. In the charge / discharge test, the battery was placed in a 25 ° C. thermostat, a charge / discharge terminal was connected thereto, the battery was allowed to stand for 3 hours, and then charged / discharged at 0.2 CmA. It is shown by the ratio (percentage) of the discharge capacity of each battery to the capacity (100%).

As shown in Table 1, the battery using the reversible sol-gel electrolyte composition according to the present invention has a low internal resistance and a low discharge capacity in both can batteries and bag batteries. It is substantially the same as that using a liquid, and has excellent charge / discharge characteristics. Also, there is no liquid leakage.

[0048]

[Table 1]

[0049]

The reversible sol-gel electrolyte composition according to the present invention uses an organic compound having a characteristic molecular structure as a reversible gelling agent, and therefore has excellent ionic conductivity and gelling ability. Therefore, such a reversible sol-
By using the gel electrolyte composition, an electrochemical element such as a battery, a capacitor, or a capacitor having excellent characteristics can be obtained.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 10/40 H01G 9/02 311 (72) Inventor Keisuke Kii 1-1-1 Shimohozumi, Ibaraki-shi, Osaka No. 2 Nitto Denko Corporation F term (reference) 5G301 CA30 CD01 5H029 AJ06 AK03 AL07 AM03 AM07 AM16 BJ02 BJ04 BJ14 CJ07 DJ09 DJ16 HJ02

Claims (8)

[Claims] 1. A reversible sol-gel electrolyte composition comprising a reversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt, wherein the reversible gelling agent has an imino group and a carbonyl group in the molecule. A reversible sol-gel electrolyte characterized by being an organic compound having: 2. The reversible sol according to claim 1, wherein the imino group and the carbonyl group form an amide bond in the molecule.
Gel electrolyte. 3. The reversible sol-gel electrolyte according to claim 1, wherein the imino group and the carbonyl group form an amide bond in the molecule and have no hydroxyl group in the molecule. 4. A reversible gelling agent represented by the following formula (1): And a compound represented by the following formula (2): The reversible sol-gel electrolyte according to claim 1, which is at least one selected from compounds represented by the following formula: 5. An electrochemical device in which a pair of electrodes are disposed to face each other with an electrolyte interposed therebetween, wherein the electrolyte comprises the reversible sol-gel electrolyte according to any one of claims 1 to 4. An electrochemical device, characterized in that: 6. An electrochemical device comprising a pair of electrodes disposed opposite to each other with an electrolyte interposed therebetween, wherein the electrolyte comprises the reversible sol-gel electrolyte according to any one of claims 1 to 4. A battery comprising: 7. An electrochemical device comprising a pair of electrodes opposed to each other with an electrolyte interposed therebetween, wherein the electrolyte comprises the reversible sol-gel electrolyte according to any one of claims 1 to 4. A capacitor characterized in that: 8. A lithium ion battery in which a pair of electrodes are arranged to face each other via an electrolyte made of the reversible sol-gel electrolyte according to any one of claims 1 to 4, wherein the electrolyte salt is A lithium-ion battery comprising a lithium salt.