JPH11121037A - Gel electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gel electrolyte excellent in ion conductivity, and good in heat stability. SOLUTION: A monomer expressed by a formula (where n=0 to 2, m=1 to 10) has an alkyl skeleton containing fluorine, and has a radiation polymerizing functional group as a functional group in a molecular structure. A polymer produced by polymerizing the monomer is formed into solid-like as a gel skeleton matrix so as to obtain a gel electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electrolyte used in a power storage technology.

[0002]

2. Description of the Related Art In recent years, with the development of the electronics field, miniaturization of electronic equipment has been remarkable. Especially mobile phones and PHS
The demand for portable devices such as portable computers and small personal computers has been remarkably increasing, and as these devices have become lighter, thinner and smaller, batteries that serve as power sources have been required to have not only higher functions but also smaller and thinner devices. Under such a background, a lithium battery that is small and can be expected to have a high capacity has attracted attention. Recently, lithium ion secondary batteries have been used in mobile phones and the like, and research has been actively conducted as a technology of interest in the information age.

[0003] Safety is considered important for lithium batteries, and separators, such as safety valves and PTC elements, are designed to cut off current at high temperatures. On the other hand, non-combustibility of solvents has been the subject of recent research. The use of a polymer having low flammability in the polymer solid electrolyte has attracted attention as a next-generation technology.

[0004]

Since small-sized electronic equipment must be operated at room temperature, a gel electrolyte having a solid shape is considered promising at present because of its characteristics. At present, gels using polyethylene oxide show an ionic conductivity of 1.5 × 10 ⁻³ Scm ⁻¹ at room temperature, according to Aihara et al., J. Power Sources 65 (1997).
143-147. In previous studies, the behavior of gel electrolytes of polyethylene oxide below the equilibrium swelling degree was completely different from that of liquid electrolytes, and the conductivity was not described by the Arrhenius equation, but was explained by a relational expression such as VTF. Therefore, it is necessary to consider the affinity between the polymer and the ion in addition to the structural interaction of the gel. When it is intended to improve bulk ion conduction, it can be said that the ether skeleton of the gel polymer does not require ether oxygen as a molecular skeleton structure, and a skeleton having little interaction with solvent molecules or solute molecules is preferable. From that viewpoint, fluoropolymers are currently being reviewed. Tsuchida for polyvinylidene fluoride
The authors reported the study in Electrochem. Acta, 28 (1983). However, there is a problem that it is thermoreversible, and since it becomes a solution state at high temperatures,
As such, it is difficult to use it alone.

[0005] The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a gel electrolyte having excellent ionic conductivity and good thermal stability.

[0006]

In order to solve the above problems, the present invention uses a monomer having a polymerizable functional group capable of easily undergoing radical polymerization in its molecular structure (Chemical Formula 1) to carry out the polymerization process and gelation. It is possible to simultaneously proceed with the conversion process.

[0007]

Embedded image

The term "polymerizable functional group" as used herein means a vinyl ketone or vinyl group, for example, an acryloyl group, a methacryloyl group, or an allyl group, but is not limited thereto. In addition, even when an alkyl monoacrylate monomer containing monofunctional fluorine is used, it is possible to make the polymer skeleton three-dimensional by using a polyfunctional acrylate as a cross-linking agent, thereby improving thermal stability. . The term “crosslinking agent” as used herein refers to an acrylate monomer having two or more functions. For example, 1,4-butanediol diacrylate, tetraethylene glycol diacrylate, polypropylene glycol diacrylate, bisphenol A-ethylene oxide adduct diacrylate, trimethylolpropane triacrylate,
Examples include, but are not limited to, trisacryloylethyl phosphate, pentaerythritol tetraacrylate, and the like. These chemical crosslinks make it possible to prevent the fluidization of the gel due to heat. Since a polymerization product obtained by polymerizing a monomer containing fluorine has an alkane containing fluorine in its skeleton, it has a small interaction with a solvent molecule or a solute molecule and is chemically and electrochemically stable. Also, an acid ester structure remains in the main skeleton,
It is thought that the presence of an appropriate polar group can prevent solvent syneresis.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a polymer formed by polymerizing from a monomer having a fluorine-containing alkyl skeleton and having a polymerizable functional group in a molecular structure as a functional group is formed in a solid state as a gel skeleton matrix. Characterized by a gel electrolyte, the monomer, having a polymerizable functional group in the molecular structure, a polymer formed by polymerizing a mixture of a monomer having a different structure from the monomer, as a gel skeleton matrix, Even when a monofunctional fluorine-containing alkyl monomer is used, the polymer skeleton can be made three-dimensional, and the thermal stability is improved. In addition, at the time of polymerization of the polymer, it is possible to simplify the production method by producing a gel electrolyte by polymerizing an organic solvent and a soluble electrolyte in a mixed state by radical polymerization. Becomes

[0010]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

(Invention 1) In a glass tube, 1.0 g of 5,5,5-trifluoroethyl acrylate and 0.2 g of trimethylolpropane triacrylate are dissolved in 4.0 g of γ-butyrolactone.
Lithium tetrafluoroborate was dissolved to 1 M in the solution, and 0.02 g of azoisobutyronitrile as a thermal reaction initiator was added and stirred. Thereafter, the glass tube was subjected to freeze degassing and vacuum sealed. The reaction was performed in a 60 ° C water bath for 24 hours.
Time went. The resulting gel was designated as Invention 1 and was cut into a predetermined thickness.

(Invention 2) In a glass tube, 1.0 g of 5,5,6,6-tetrafluoropropyl acrylate and 0.2 g of trimethylolpropane triacrylate are dissolved in 4.0 g of γ-butyrolactone, and lithium tetrafluoroborate is added to the solution. 1M
, And 0.02 g of azoisobutyronitrile was added as a thermal reaction initiator and stirred. Thereafter, the glass tube was subjected to freeze degassing and vacuum sealed. The reaction was performed in a 60 ° C. water bath for 24 hours. The resulting gel was designated as Invention 2 and was cut into a predetermined thickness.

(Invention 3) In a glass tube, 1.0 g of 5,5,5-trifluoroethyl methacrylate and 0.2 g of tetraethylene glycol dimethacrylate are dissolved in 4.0 g of γ-butyrolactone, and lithium tetrafluoroborate is added to the solution at a concentration of 1M. Then, 0.02 g of azoisobutyronitrile was added as a thermal reaction initiator and stirred. Thereafter, the glass tube was subjected to freeze degassing and vacuum sealed. The reaction was performed in a water bath at 80 ° C. for 24 hours. The resulting gel was designated as invention 3 and cut into a predetermined thickness.

Comparative Example 1 In a glass tube, 1.0 g of polyethylene glycol diacrylate having a molecular weight of about 11,000 was dissolved in 4.0 g of γ-butyrolactone, and lithium tetrafluoroborate was dissolved to 1 M with respect to the solution. Of azoisobutyronitrile was added and stirred. Thereafter, the glass tube was subjected to freeze degassing and vacuum sealed.
The reaction was performed in a 60 ° C. water bath for 24 hours. The resulting gel was used as Comparative Example 1 and cut into a predetermined thickness.

Comparative Example 2 As a comparison of thermal shape stability, a gel of polyvinylidene fluoride was prepared. The production method was such that 1.0 g of polyvinylidene fluoride was dispersed in 4.0 g of a 1 M solution of lithium tetrafluoroborate in γ-butyrolactone, and then heated and dissolved at 90 ° C. in an oil bath. The mixed solution was flowed on a metal foil and cooled slowly to form a polyvinylidene fluoride gel.

Each electrolyte was fixed in a predetermined cell for measuring ionic conductivity, and the ionic conductivity was measured from room temperature to -40 ° C. Measurements were made using Solartron's impedance analyzer model 1286 interface and model
Using 1255, 10000 Hz to 10 Hz was measured by AC measurement.

FIG. 1 shows the results of the ion conductivity measurement. It was found that the present inventions 1 to 3 exhibited higher ionic conduction than Comparative Example 1. Also in the present invention, a slight curvature is observed in a low temperature range, but the inclination is small, which indicates that the ionic conductivity is high in a wide temperature range.
Table 1 shows the results of heating the electrolytes of the present invention and the comparative examples to 110 ° C. on a hot plate.

[0018]

[Table 1]

As is clear from Table 1 comparing the thermal stability, the conventional fluoroalkyl polymer polyvinylidene fluoride was melted by heating. In the present invention and Comparative Example 1, no shape change was observed.

[0020]

According to the present invention, a polymer formed by polymerizing from a monomer having a fluorine-containing alkyl skeleton and having a radiation-polymerizable functional group in the molecular structure as a functional group is formed in a solid state as a gel skeleton matrix. Characterized by a gel electrolyte, a polymer formed by polymerizing a mixture of the monomer and a monomer having a polymerizable functional group in the molecular structure and having a different structure from the monomer is used as a gel skeleton matrix to form a polymer. Even when using an alkyl monomonomer containing functional fluorine, it is possible to make the polymer skeleton three-dimensional using a monomer having a polymerizable functional group,
As a result, the thermal stability is improved. In addition, at the time of polymerization of the polymer, it is possible to simplify the production method by producing a gel electrolyte by polymerizing an organic solvent and a soluble electrolyte in a mixed state by radical polymerization. Becomes

[Brief description of the drawings]

FIG. 1 is a diagram obtained by measuring the ionic conductivity of gel electrolytes of the present invention and a comparative example by Arrhenius plot.

Continuation of the front page (72) Inventor Hiroe Nakagawa 6-6 Josaicho, Takatsuki-shi, Osaka Inside Yu Asa Corporation

Claims (3)

[Claims] 1. A polymer formed by polymerizing from a monomer (chemical formula 1) having a fluorine-containing alkyl skeleton and having a polymerizable functional group in the molecular structure as a functional group, is formed in a solid state as a gel skeleton matrix. A gel electrolyte, characterized in that: Embedded image 2. A polymer formed by polymerizing a mixture of the monomer and a monomer having a polymerizable functional group in a molecular structure and having a different structure from the monomer, to form a polymer as a gel skeleton matrix in a solid state. The gel electrolyte according to claim 1, wherein: 3. The gel electrolyte according to claim 1, wherein an organic solvent and an electrolyte soluble in the organic solvent are mixed during the polymerization of the polymer.