JP2001200126A - Ionically conductive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ionically conductive composition having high ionic conductivity. SOLUTION: This ionically conductive composition comprises >=50 wt.% of an electrolyte and such a polyvinyl acetal derivative that the hydroxy group- contg. recurring unit in the polyvinyl acetal accounts for <=7 wt.% of the whole polyvinyl acetal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion conductive composition which can be used as an electrolyte for a primary battery, a secondary battery, an electric double layer capacitor, an electrochromic display device and the like, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, in the field of the electronics industry, not only high performance and miniaturization of electronic devices, but also high performance and miniaturization of electronic components, as well as high reliability as components are required. The requirements for a highly reliable electronic component include the following: First, the material used for the component is a solid, that is, an object that appears to be in a solid state under the conditions of use of the component, and flows like a liquid (hereinafter referred to as a fluid). (Hereinafter referred to as “solid body”). This is because, when a fluid material is used for an electronic component, liquid leaks frequently from the inside of the component to the outside of the component, causing performance degradation of the electronic component and adversely affecting other electronic components near the electronic component. And eventually cause the electronic device to fail. Therefore, when an ion conductive material is used for an electronic component, an electronic component using a solid ion conductive material has higher reliability than a fluid. On the other hand, using a fluid ionic conductive material,
In order to obtain a highly reliable component, there is a means for completely sealing the component. However, in many cases, the component is expensive and cannot be put to practical use.

As the solid ion conductive material, a ceramic material or a polymer material has been proposed. However, the former ion conductive ceramic material has fragile properties and cannot be formed or formed into an arbitrary shape. There is a disadvantage that mechanical properties such as workability are inferior. On the other hand, ionic conductive polymer materials have the advantage of being excellent in workability.

However, there is a problem that the ion conductivity of an ion-conductive polymer material containing a polymer as a matrix and containing a metal salt to form a solid solution is considerably smaller than the ion conductivity of an electrolytic solution.

[0005] At present, research on gel-type ionic conductive materials in which an electrolyte is contained in a solid ionic conductive material has been actively conducted. This is because as the amount of the electrolyte contained in the solid ionic conductive material increases, the mobility of ions increases and the conductivity increases. However, as the amount of the contained electrolytic solution increases, the solid ionic conductive material softens and eventually becomes a fluid. For this reason, an ionic conductive polymer material that does not soften even when a large amount of electrolyte is contained is required.

An electrolyte using polyvinyl acetal is disclosed in JP-A-57-143355 and JP-A-57-143355.
JP-A-143356 describes an ion-conductive solid composition using polyvinyl butyral and an organic solvent. JP-A-3-43909 describes a polymer solid electrolyte containing polyvinyl acetal and an organic solvent, and JP-A-3-43910 describes a polymer solid electrolyte containing polyvinyl butyral and an organic solvent. Have been. Furthermore, JP-A-10-50141 describes a polymer solid electrolyte containing polyvinyl acetal and an ion dissociable salt. However, all of the electrolytes described in the above publications have a low content of the electrolytic solution, so that the mobility of ions is small and sufficient ion conductivity cannot be obtained.

Further, US Pat. No. 3,985,574 describes a battery using a gel-type polymer electrolyte. However, in the gel-type polymer electrolyte described in the above specification, ammonium perchlorate is exemplified as the electrolyte, but the ammonium salt is compared with the lithium salt in electrochemical, thermochemical stability and conductivity as the electrolyte. It is not preferable because it is small. There are also problems with respect to liquid leakage and mechanical strength of the gel polymer electrolyte when using these electrolytes.

Further, polyvinyl acetal does not exist as a homopolymer, but includes a repeating unit having a hydroxyl group and a repeating unit having an acetyl group in addition to a repeating unit having an acetal group. As the number of repeating units having a hydroxyl group increases, the solubility in an organic solvent deteriorates. Furthermore, when an ion conductive material is used for a lithium battery, there is a problem that a side reaction in which a hydroxyl group is reduced by an electrochemical reaction to generate hydrogen is likely to occur.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an ion conductive composition having high ion conductivity. It is another object of the present invention to provide an ion conductive composition and a method for producing the same, which can reduce the time required for the production process by improving the poor solubility of the polyvinyl acetal in organic solvents.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems in consideration of the above problems, and as a result, have reached the present invention. That is, the present invention is as follows. (1) The proportion of the repeating unit containing a hydroxyl group in the polyvinyl acetal is 7% by weight of the entire polyvinyl acetal.
% Or less of the polyvinyl acetal derivative and an electrolytic solution, wherein the electrolytic solution contains the electrolytic solution in an amount of 50% by weight or more of the whole composition. (2) The above-mentioned ion-conductive composition wherein the electrolyte comprises a lithium salt and an alkyl carbonate. (3) A method for producing an ion-conductive material, comprising: a first step of chemically modifying hydroxyl groups of polyvinyl acetal, and a second step of molding and processing using the chemically modified polyvinyl acetal, electrolyte and alkyl carbonate.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polyvinyl acetal derivative used in the present invention is a polymer compound comprising an acetal group, an acetyl group, a hydroxyl group, and four types of repeating units each having a functional group obtained by chemically modifying the hydroxyl group as shown in the general formula (1). It is. General formula (1)

[0013]

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(Where R represents an alkyl group having 1 to 3 carbon atoms. X represents an organic residue other than a hydrogen atom and containing no hydroxyl group; p, q and r represent positive integers; The proportion of the repeating unit containing a hydroxyl group in the polyvinyl acetal is preferably 7% by weight or less, and more preferably 6% by weight, based on the entire polyvinyl acetal. The amount of the repeating unit having a hydroxyl group in the polyvinyl acetal can be adjusted by a chemical modification method described later for the hydroxyl group. When the repeating unit containing a hydroxyl group in the polyvinyl acetal is more than 7% by weight of the total amount of the polyvinyl acetal derivative, the solubility in the organic solvent is deteriorated.

The chemical modification in the present invention includes acylation, urethanization, esterification, etherification and the like, among which acylation and urethanization are preferred.
Among them, urethanization is recommended because it can contain more electrolyte solution. However, it is not limited to these as long as it reacts with a hydroxyl group.

The chemically modified polyvinyl acetal derivative of the ion conductive composition of the present invention may contain at least one repeating unit having an acetal group.
60 to 80 mol of repeating units having an acetal group
%, Especially 65 to 70 mol% is preferred. The general formula
R in (1) includes an alkyl group having 1 to 3 carbon atoms, that is, a methyl group, an ethyl group, a propyl group, and an isopropyl group. Particularly, R is preferably a propyl group. X in the general formula (1) is not particularly limited as long as it is an organic residue other than a hydrogen atom and containing no hydroxyl group. Specific examples include acyl groups such as acetyl group, propynyl group and butyryl group, alkyl groups such as methyl group, ethyl group and propyl group, and organic residues such as N-alkylcarbamoyl group. Further, the N-alkylcarbamoyl group may contain an ether group in the alkyl group, and may be a phenyl group, a 2-methacryloyloxyethyl group, or the like. The degree of polymerization of the polyvinyl acetal derivative is generally from 800 to 4000.
There is no particular problem in obtaining the ion conductive composition of the present invention as long as the degree is about the same, but a polymerization degree of 1200 to 2700 is particularly preferable. If the degree of polymerization is smaller than 800, the ion conductive composition becomes very brittle. On the other hand, when the degree of polymerization is larger than 4000, the solubility in an organic solvent is deteriorated.

Next, the electrolytic solution used in the present invention comprises an electrolyte and a plasticizer. The electrolytic solution accounts for 50% by weight or more based on the total amount of the ion conductive composition of the present invention. In particular, 70% by weight or more is preferable. If the amount of the electrolyte is less than 50% by weight, sufficient ion conductivity cannot be obtained.

As the electrolyte used in the present invention, any of inorganic salts, organic salts, inorganic acids, and organic acids can be used. As an electrolyte, for example, tetrafluoroboric acid, perchloric acid, nitric acid, sulfuric acid, phosphoric acid, inorganic acids such as hydrofluoric acid,
Organic acids such as trifluoromethanesulfonic acid, polyfluoropropylsulfonic acid, bis (trifluoromethanesulfonyl) imidic acid, acetic acid, trifluoroacetic acid, and propionic acid, and salts of these organic acids and inorganic acids. Further, mixtures of these organic acids, inorganic acids, and salts thereof can also be used as the electrolyte. As the cation of the salt-type electrolyte, protons, alkali metals, alkaline earth metals, transition metals, rare earth metals and the like can be used alone or in a mixed state, but alkali metals such as lithium and sodium are preferably used. In particular, when used as a lithium secondary battery, it is preferable to use an electrochemically stable lithium salt having a non-nucleophilic anion as a counter anion and exhibiting a wide potential window.LiBF ₄ , LiPF ₆ , (CF ₃ SO
₂ ) ₂ NLi. It is particularly preferable to use LiBF _4.

The plasticizer used in the present invention is used for accelerating the ion dissociation of the lithium salt in the ion conductive composition, improving the ion conductivity, and adjusting the strength such as processability and flexibility. Examples of the plasticizer include alkyl carbonate, ester compounds such as γ-butyrolactone and propiolactone, nitrile compounds such as acetonitrile and propionitrile, and amide compounds such as dimethylformamide. Preferably, it is an alkyl carbonate having a molecular weight of 120 or less. As this alkyl carbonate,
A cyclic carbonate compound such as ethylene carbonate and propylene carbonate, and a chain carbonate compound such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate can be used. Further, a mixture of the above alkyl carbonates can also be used.
In particular, it is more preferable to use propylene carbonate and ethylene carbonate.

In the case of molding and processing an ion-conductive composition using an electrolytic solution comprising a chemically modified polyvinyl acetal derivative, an electrolyte and a plasticizer as described above, various production methods are conceivable. The following methods are mentioned. However, it is not limited to these.

As a forming method, a chemically modified polyvinyl acetal derivative or a mixture of a chemically modified polyvinyl acetal derivative and an electrolytic solution is applied on a substrate and formed on a sheet. There is a method of performing cooling processing.

The first method is a method of dissolving a chemically modified polyvinyl acetal derivative in an organic solvent, adding an electrolytic solution, and evaporating and removing the organic solvent before or after molding. Examples of the organic solvent that dissolves the chemically modified polyvinyl acetal derivative include alcohols such as methanol, ethanol, and propanol; ketones such as acetone, methyl ethyl ketone and cyclohexanone; N, N-dimethylacetamide, and N and N-dimethylformamide. Examples include amides, dioxane, ethers such as tetrahydrofuran, chlorinated hydrocarbons such as methylene chloride, chloroform, aromatic solvents such as toluene, xylene, styrene, and pyridine, dimethyl sulfoxide, and acetic acid. The solvent is not limited to the above-mentioned organic solvents as long as it dissolves the acetal derivative.

The second method is a method of forming a mixture of a chemically modified polyvinyl acetal derivative, an electrolyte and an electrolytic solution comprising a plasticizer into a predetermined shape.

The third method is a method in which a chemically modified polyvinyl acetal derivative is formed into a film by a treatment such as a casting method or heat melting, and the film is impregnated with an electrolytic solution comprising an electrolyte and a plasticizer.

If necessary, other polymers, ceramics and metals can be added for improving mechanical strength, heat resistance and ionic conductivity.

[0026]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples. Production Example 1 In a reaction vessel, 4 g of polyvinyl acetal of general formula (1) in which R was a propyl group and X was a hydrogen atom (degree of polymerization: 1700), 100 ml of pyridine, and 2 ml of acetic anhydride were added and stirred at 100 ° C. for 2 hours. After the reaction, the reaction solution was poured into water to collect the precipitated solid, which was then dissolved in acetone again, dehydrated, and then reprecipitated by pouring into hexane to take out the desired product, which was dried to obtain 3.5 g of X. A white solid that was an acetyl group was obtained.
When the concentration of the repeating unit having a hydroxyl group was measured by the polyvinyl butyral test method of Japanese Industrial Standard K6728, the polyvinyl acetal before the reaction was 12.4%, whereas the obtained polyvinyl acetal derivative was 5.4%.
6%. Hereinafter, this reaction product is referred to as polymer A. Production Example 2 The target product was produced in the same manner as in Production Example 1 using polyvinyl acetal (degree of polymerization 2000) in which R in the general formula (1) was a methyl group and X was a hydrogen atom. Japanese Industrial Standard
When the concentration of the repeating unit having a hydroxyl group was measured by the K6728 polyvinyl butyral test method, the polyvinyl acetal before the reaction was 7.6%, whereas the obtained polyvinyl acetal derivative in which X was an acetyl group was 5. 4%. Hereinafter, this reaction product is referred to as polymer B
And Production Example 3 To a reaction vessel was added 4 g of polyvinyl acetal of general formula (1) in which R is a propyl group and X was a hydrogen atom (degree of polymerization 1700), and the inside of the vessel was sufficiently purged with nitrogen. Stir until After adding 0.1 phr of tin octylate to the homogeneous solution, 1.7 g of 2-isocyanatoethyl methacrylate is added, and the mixture is stirred at 50 ° C. for 5 hours. After completion of the reaction, the reaction solution was poured into hexane, and the precipitated solid was taken out and dried to obtain 5.1 g of a white solid in which X was 2-methacryloyloxyethyl group. When the concentration of the repeating unit having a hydroxyl group was measured by the polyvinyl butyral test method of Japanese Industrial Standard K6728,
While the polyvinyl acetal before the reaction was 12.4%, the obtained polyvinyl acetal derivative was 5.9%.
Met. Hereinafter, this reaction product is referred to as polymer C. Example 1 20 parts by weight of polymer A and 221 parts by weight of tetrahydrofuran were mixed and stirred for 1 hour to prepare a polymer solution. Separately, 11 parts by weight of LiBF ₄ and 6 parts of propylene carbonate
And 9 parts by weight to prepare an electrolytic solution. The prepared electrolyte solution and polymer solution were mixed and sufficiently stirred until they became uniform. Next, the whole amount of the mixed solution was poured into a Teflon container prepared in advance, and dried by heating at 50 ° C. for 5 hours, and then dried by heating under reduced pressure at 70 ° C. for 3 hours in a vacuum dryer to remove tetrahydrofuran. An ion conductive composition was prepared. Examples 2 to 7, Comparative Examples 1 to 3 Chemically modified polyvinyl acetal derivatives shown in Table 1,
An ion conductive composition was prepared in the same manner as in Example 1 by using the electrolyte, plasticizer, and tetrahydrofuran shown in Table 2 at the composition ratios shown in Table 2.

Table 2 shows the results of confirmation tests of strength and liquid leakage of the ion conductive composition produced by the above method.
Shown in Here, the strength is expressed as insufficient mechanical strength when the ion conductive composition breaks when peeling the ion conductive composition from the Teflon-made container, and sufficient mechanical strength when the ion conductive composition does not break. In addition, the presence of liquid leakage indicates a case where the surface of the ion conductive composition is wet. As is clear from the results in Table 2, when the chemically modified polyvinyl acetal derivative was used, an ion conductive composition having sufficient strength could be produced (Examples 2 to 8). However, when a polyvinyl acetal that had not been chemically modified was used, a uniform polymer solution could not be obtained under the conditions described in Example 1, so that an ion-conductive composition could not be prepared (Comparative Example). 1,2).

[0028]

[Table 1]

[0029]

[Table 2]

Examples 8 to 14, Comparative Example 4 Chemically modified polyvinyl acetal derivatives shown in Table 1
The ion conductivity of the ion-conductive composition prepared in the same manner as in Example 1 was measured using the electrolyte, plasticizer, and tetrahydrofuran shown in Table 3 at the composition ratio shown in Table 3.

The Teflon container containing the ion-conductive composition was transferred into a glove box filled with argon gas, and the ion-conductive composition was peeled off from the Teflon container, and then cut into a circular shape having a diameter of 1 cm. I got a piece. This measurement sample piece was sandwiched between stainless steel electrodes to produce a cell. This cell was connected to an impedance analyzer with a lead wire, and the resistance value of the sample was measured at 20 ° C. by the AC impedance method. The measurement is performed in an argon atmosphere, and the resistance and thickness (100 to 300 μm) of the measurement sample piece are measured.
In addition, the conductivity σ of the ion-conductive composition was calculated from the area of the stainless steel electrode.

Table 3 shows the measurement results of the ionic conductivity σ of the ionic conductive composition measured by the above method. As is clear from the results in Table 3, the electrolyte was 50% by weight of the whole composition.
It was found that when the amount was less than that (Comparative Example 4), sufficient ionic conductivity could not be obtained. In addition, when the urethane-modified polyvinyl acetal derivative is used, even if the electrolytic solution contains 90 wt% based on the total amount of the ion conductive composition, there is no liquid leakage and the mechanical strength is sufficient. It was a composition (Example 13).

[0033]

[Table 3]

[0034]

As described above, the present invention makes it possible to shorten the manufacturing process time of an ion conductive composition by chemically modifying the hydroxyl group of polyvinyl acetal, and furthermore, to provide an ion conductive material having a practical level of ion conductivity. Because of the composition and the production method thereof, it can be sufficiently practically used as an electrolyte for primary batteries, secondary batteries, electric double layer capacitors, electrochromic display elements, and the like.

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Claims (3)

[Claims] 1. An ion conductive composition comprising a polyvinyl acetal derivative in which the proportion of a repeating unit containing a hydroxyl group in polyvinyl acetal occupies 7% by weight or less of the entire polyvinyl acetal, and an electrolytic solution. An ion conductive composition comprising 50% by weight or more of the whole composition. 2. The ion conductive composition according to claim 1, wherein the electrolyte comprises a lithium salt and an alkyl carbonate. 3. A method for producing an ion-conductive material, comprising: a first step of chemically modifying hydroxyl groups of polyvinyl acetal, and a second step of molding and processing using the chemically modified polyvinyl acetal, electrolyte and alkyl carbonate.