JP3453158B2 - Gel electrolyte - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gel electrolyte having excellent ionic conductivity and suitable for forming a thin battery or the like. 2. Description of the Related Art Heretofore, a solid electrolyte in which an electrolyte is contained in a film made of polyvinyl alcohol or polyethylene oxide has been known. However, there is a problem that the ionic conductivity is generally low due to a problem that the material is brittle and easily broken and has poor practicality, a problem of poor adhesion to an electrode, a problem of poor mobility or solubility of metal ions, and the like. [0003] It is an object of the present invention to develop a polymer-based electrolyte having excellent practical strength and ionic conductivity. [0004] The present invention comprises an organogel containing an electrolyte, and the polymer forming the organogel is a mixed polymer of polyvinyl alcohol and polyethylene oxide or / and a vinyl alcohol / ethylene oxide copolymer. It is intended to provide a gel electrolyte characterized by the above. The organogel comprising the above-mentioned polymer containing vinyl alcohol and ethylene oxide has rubber-like properties and has practically sufficient mechanical strength such as tension, bending and torsion, and can easily form a thin film. And a film or sheet having excellent flexibility and deformability can be easily obtained (overcoming brittleness). As a result, a gel-like electrolyte can be formed by incorporating an electrolyte into such an organogel. The obtained gel electrolyte has excellent solubility of metal ions by a vinyl alcohol component and excellent conductivity of metal ions through vigorous segment movement by an ethylene oxide component. It exhibits excellent ionic conductivity because the amorphous property is improved by lowering the crystallinity, the organic solvent is contained, and the electrode can be brought into good contact with the electrode due to flexibility. DETAILED DESCRIPTION OF THE INVENTION The gel electrolyte of the present invention comprises an organogel of a mixed polymer of polyvinyl alcohol and polyethylene oxide and / or a polymer comprising a vinyl alcohol / ethylene oxide copolymer containing the electrolyte. The polyvinyl alcohol has a degree of polymerization of 500 to 5000 (weight average molecular weight of 22,000 to 22).
10,000), preferably 1000 to 3000, with a saponification degree of 80% or more, and especially 85% or more. If the degree of polymerization is too low, crystallinity is high and gelation is difficult. If it is too high, a homogeneous organogel is hardly formed due to an increase in solution viscosity. If the saponification degree is less than 80%, steric hindrance due to the acetic acid residue causes poor cohesion and makes it difficult to gel. The polyethylene oxide is not particularly limited and generally has a weight-average molecular weight of about 2,000,000 or less, especially 10,000 to 1,000,000. The proportion of polyethylene oxide to be used may be appropriately determined and is generally from 1 to 3000 parts by weight, preferably from 10 to 1000 parts by weight, especially from 30 to 300 parts by weight, per 100 parts by weight of polyvinyl alcohol. In the present invention, a practically sufficient organogel can be obtained even as a mixed polymer having a total weight average molecular weight of about 500,000. The vinyl alcohol / ethylene oxide copolymer has a weight average molecular weight of 20,000 or more from the viewpoint of gelation.
It is preferably 500,000, and the content of vinyl acetate units in the copolymer is 20% or less, particularly preferably 15% or less. The content ratio of vinyl alcohol units (including vinyl acetate units) is 1 to 3000 per 100 ethylene oxide units,
In particular, 10 to 1000, especially 30 to 300 is common. In the present invention, a practically sufficient organogel can be obtained even when the weight average molecular weight is about 500,000, as in the case of the above-mentioned mixed polymer. Vinyl alcohol
The form of the ethylene oxide copolymer is arbitrary, and may be a random copolymer or a block copolymer. When polyvinyl alcohol, polyethylene oxide and vinyl alcohol / ethylene oxide copolymer are used in combination, the composition ratio is preferably based on the above-mentioned mixed polymer based on vinyl alcohol units (including vinyl acetate units) and ethylene oxide units. .
The vinyl alcohol / ethylene oxide copolymer is
It is particularly preferably used because it is easy to obtain a homogeneous organogel, and it is easy to obtain a tough organogel due to entanglement of molecules through a long molecular chain due to a high molecular weight. The formation of the organogel can be carried out, for example, by freezing / thawing an aqueous solution of a polymer (a mixed polymer of polyvinyl alcohol and polyethylene oxide and / or a vinyl alcohol / ethylene oxide copolymer; the same applies hereinafter);
Drying, quenching, or the like may be performed to obtain a hydrogel, which may be dried, immersed in an organic solvent, and replaced with water and the organic solvent. The substitution of the hydrogel with the organogel is based on the fact that the hydrogel does not function as an electrolyte because the electrolysis of water takes precedence when producing a metal ion conductor that is less likely to be reduced than hydrogen ions. The organogel can also be formed by dissolving the polymer in a highly polar organic solvent such as dimethylsulfoxide, dimethylformamide, dimethylacetamide, or N-methylpyrrolidone and allowing it to stand. In this case, there is an advantage that the organogel can be directly formed. However, it can be replaced with another organic solvent such as propylene carbonate for the purpose of improving ionic conductivity and the like. The organogel obtained by the above method has an advantage that it is excellent in durability or electrical deterioration resistance, because it does not contain an unreacted cross-linking agent as compared with those obtained by light irradiation or heating using a cross-linking agent. In the above method, 30% by weight or less,
Preferably, the polymer concentration is from 10 to 20% by weight. On the other hand, by adding an alkali metal salt, a transition metal salt or / and a metal hydroxide that is hardly soluble in such an organic solvent to an aqueous solution or an organic solvent solution of a polymer, gelation can be promoted and the production efficiency of a hydrogel or an organogel can be improved. I can give it. Gelation can also be promoted by adding another type of metal salt that forms a hardly soluble metal hydroxide to the solution and immersing the solution in an alkaline solution such as sodium hydroxide or potassium hydroxide. In the latter case, a gelled product in a desired form can be formed by placing the metal salt additive solution in an open container and immersing it in an alkaline solution. Incidentally, specific examples of the above-mentioned gelling accelerator include halides and hydroxides of alkali metals such as sodium, potassium and lithium, and transition metals such as iron, copper, nickel, chromium, titanium, molybdenum and tungsten. Metal hydroxides that are hardly soluble in organic solvents such as halides and hydroxides, iron hydroxide, copper hydroxide, chromium hydroxide, calcium hydroxide and magnesium hydroxide, iron, copper, chromium, calcium and magnesium And halides such as chlorides of metals that form poorly soluble metal hydroxides. The amount of the gelling accelerator used is the amount of the polymer 100
It is generally 200 parts by weight or less, especially 5 to 150 parts by weight, especially 20 to 100 parts by weight per part by weight. In the case where a salt composed of a transition metal is used as the gelation accelerator,
There is an advantage that the toughness of the obtained organogel can be improved. The electrolyte to be contained in the organogel is not particularly limited. Generally, for example, cations such as Li ions, Na ions, and K ions, I ions, CF ₃ SO ₃
Ion, BF ₄ ion, ClO ₄ ion, AlCl ₄ ion,
An alkali metal salt or the like which is composed of a combination with an anion such as PF ₆ ion or AsF ₆ ion is used. The gel electrolyte of the present invention can also be formed by a method of including an electrolyte in a hydrogel or organogel of a polymer or a method of including an electrolyte when forming the hydrogel or organogel. Examples of the former method include a method in which an electrolyte is contained in an organic solvent when a hydrogel is replaced with an organogel, and a method in which an organic solvent in an organogel is replaced with an organic solvent containing an electrolyte. The latter method includes, for example, a method of blending an electrolyte with the polymer solution when forming a hydrogel or organogel of a polymer by the above-mentioned method. Accordingly, in this case, a gel electrolyte is obtained together with the formation of a hydrogel or organogel of the polymer. In the case of a hydrogel, an organogel can be formed while retaining the electrolyte by a solvent replacement operation. When the electrolyte added in the above-mentioned method also functions as a gelling accelerator such as a lithium salt, the portion does not contribute to ion conduction, so that the metal ions of the electrolyte are contained in the hydrogel or organogel of the obtained polymer. It is necessary to adjust so as to remain in a state that can contribute to conduction. Therefore, the amount of the electrolyte used is appropriately determined depending on whether or not another gelling accelerator is used in combination. In addition to the above-mentioned function as the gelling accelerator, the amount of the electrolyte in the hydrogel or the organogel of the polymer is also considered. Is added as an electrolyte and contributes to ion conduction. By the way, when a lithium salt is used as an electrolyte also serving as a gelling accelerator, 1 / to the hydroxyl group of the polymer is used.
By using a lithium salt having a ratio of 20 times or more (atomic ratio), characteristics as an ion conductor are exhibited. In the present invention, the mass of the electrolyte (contribution to ionic conduction) to be contained in the gel electrolyte is appropriately determined according to the desired ionic conductivity and the like, and is generally 100 parts by weight per 100 parts by weight of the polymer. The following 5
To 50 parts by weight. The gel electrolyte of the present invention can be formed in any form, and is generally in the form of a film or the like. By the way, when it is in the form of a film, its thickness can be appropriately determined, but 500 μm or less,
In particular, it can be as thin as 1 to 50 μm. The obtained gel electrolyte can be used for an appropriate purpose such as formation of a battery. In practical use, if necessary, excess organic solvent may be removed by, for example, a vacuum drying method for several hours to prevent bleeding. Example 1 10 parts by weight of polyvinyl alcohol having a degree of polymerization of 1400 and a saponification degree of 95% and 1 part by weight of polyethylene oxide having a weight average molecular weight of 60,000 were dissolved in 50 parts by weight of dimethyl sulfoxide, and 12 parts of LiClO ₄ was added to the solution. The mixture was stirred under heating, the viscosity increased sharply due to the dissolution of LiClO ₄ , and then developed and left in a glass petri dish. After about 10 hours, an electrolyte sheet composed of an organogel having silicon rubber-like behavior was obtained. Was. The electrolyte sheet was dried at 60 ° C. for 2 hours under reduced pressure by a vacuum pump to a thickness of 150 μm.
When the sheet was checked for ionic conductivity (impedance measurement, the same applies hereinafter).
It exhibited an excellent value of 4.0 / 10 ² S / cm. Example 2 10 parts by weight of polyvinyl alcohol having a polymerization degree of 1500 and a saponification degree of 85% and 10 parts by weight of polyethylene oxide having a weight average molecular weight of 60,000 were dissolved in 90 parts by weight of dimethyl sulfoxide, and 10 parts by weight of LiClO ₄ was added to the solution. The mixture was stirred under heating, and the viscosity increased sharply due to the dissolution of LiClO _{4. After} that, the mixture was developed in a glass Petri dish and allowed to stand. After about 3 hours, an electrolyte sheet composed of an organogel having a silicone rubber-like behavior was obtained. Was. The ionic conductivity of this sheet is:
It was excellent at 3/10 ³ S / cm. Example 3 20 parts by weight of a copolymer having a weight average molecular weight of 200,000 consisting of a polyvinyl alcohol block having a degree of polymerization of 1300 and a saponification degree of 95% and a polyethylene oxide block having a degree of polymerization of 130 was dissolved in 80 parts by weight of dimethylacetamide. Then, 30 parts by weight of LiClO ₄ was added to the solution, and the mixture was stirred under heating. After the viscosity increased sharply due to the dissolution of LiClO ₄ , the solution was developed and left in a glass petri dish. Was obtained. The ionic conductivity of this sheet is 4.5 / 10
It was excellent at ² S / cm. Example 4 A polyvinyl alcohol block having a degree of polymerization of 1000 and a saponification degree of about 87%, a polyethylene oxide block having a degree of polymerization of 2,000, and a weight average molecular weight of 500,000 comprising a polyvinyl alcohol block having a degree of polymerization of 1000 and a saponification degree of about 87% Was dissolved in 90 parts by weight of dimethylformamide, and 10 parts by weight of LiClO ₄ was added to the solution, dissolved under heating, frozen in an ice / ethanol bath, and thawed at room temperature twice. Thus, an electrolyte composed of an organogel having a silicone rubber-like behavior was obtained. The ionic conductivity of this electrolyte was as excellent as 2.0 / 10 ³ S / cm. Example 5 Instead of 12 parts by weight of LiCl _4, 9 parts by weight of ferric chloride and Li
In the same manner as in Example 1 except that 3 parts by weight of ClO ₄ was added, an electrolyte sheet made of a tough organogel having a silicone rubber-like behavior and having a thickness of 100 μm was obtained in about 5 hours after standing.
The ionic conductivity of this sheet was as excellent as 4.5 / 10 ² S / cm. Example 6 The procedure of Example 5 was repeated, except that ferric hydroxide was used instead of ferric chloride. A tough organogel exhibiting a silicone rubber-like behavior was formed with a thickness of 100 μm and an ionic conductivity of 4 μm. .0
An electrolyte sheet of / 10 ² S / cm was obtained. Example 7 15 parts by weight of polyvinyl alcohol having a degree of polymerization of 2,000 and a saponification degree of 99% and 5 parts by weight of polyethylene oxide having a weight average molecular weight of 150,000 were dissolved in 80 parts by weight of dimethyl sulfoxide. After adding 30 parts by weight and stirring under heating, the mixture was placed in a petri dish and allowed to stand in a 1N NaOH methanol solution, and after 15 hours, a tough 100 μm thick organogel sheet showing a silicone rubber-like behavior was obtained. It was immersed in a 20% by weight solution of LiClO ₄ in dimethyl sulfoxide to obtain an electrolyte sheet. The ionic conductivity of this sheet was excellent at 2.0 / 10 ³ S / cm. Example 8 A copolymer 20 having a weight average molecular weight of 300,000 comprising a polyvinyl alcohol block having a degree of polymerization of 2,000 and a degree of saponification of 90% and a polyethylene oxide block having a degree of polymerization of 1,000.
Parts by weight dissolved in 80 parts by weight of dimethylacetamide,
To the solution, 20 parts by weight of cupric chloride and 10 parts by weight of LiClO ₄ were added and stirred while heating.
(2) The procedure of placing in a test tube, freezing in dry ice / ethanol refrigerant and then thawing at room temperature is repeated, and 2 hours after the addition of cupric chloride, a tough hydrogel having a strength capable of being self-sustaining in the above-mentioned melting state. After dehydration treatment, it was re-swelled in dimethyl sulfoxide to obtain an organogel electrolyte. Its ionic conductivity was 1.5 / 10 ³ S / cm. Comparative Example 1 2 parts by weight of a polymer having a degree of polymerization of 1400 and a saponification degree of 95% and 3 parts by weight of LiCl ₄ were added to 20 ml of distilled water, stirred under heating to form an aqueous solution, which was developed in a glass dish and dried. Thus, a film having a thickness of 100 μm was obtained. Its ionic conductivity was 7.5 / 10 ⁵ S / cm. [0034] Comparative Example 2 Polymerization degree 1400, dissolved under heating and stirring of polyvinyl alcohol 11 parts by weight of LiClO ₄ 12 parts by weight of 95% degree of saponification in dimethyl sulfoxide 50 parts by weight, LiClO ₄
After the viscosity increased sharply due to the dissolution of the compound, the mixture was developed in a glass Petri dish and allowed to stand. After about 10 hours, an electrolyte sheet made of an organogel having silicon rubber-like behavior was obtained.
The sheet was dried under reduced pressure at a temperature of 2 ° C. for 2 hours to prevent bleeding of 150 μm in thickness, and the ionic conductivity of the sheet was determined to be 4.5 / 10 ³ S / cm. The gel electrolyte of the present invention is made of an organogel of a polymer containing vinyl alcohol and ethylene oxide, and is therefore excellent in amorphous properties, solubility of metal ions and conductivity. Further, it is excellent in flexibility and handleability, hardly causes cracks and the like due to brittleness, and can be brought into good contact with the electrode surface.

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Claims (1)

(57) [Claim 1] An organic gel containing an electrolyte, wherein the polymer forming the organogel is a mixed polymer of polyvinyl alcohol and polyethylene oxide or / and a vinyl alcohol / ethylene oxide copolymer. Characterized gel electrolyte.