JPH11176239A - Solid ion conductive composition - Google Patents

Abstract

(57) [Problem] To provide a solid ion conductive composition having high ion conductivity and excellent mechanical properties. SOLUTION: This polymer component 10 is made of a copolymer of vinylidene fluoride and hexafluoropropylene, and is rubbery at room temperature or has a melting point of 140 ° C. or less.
Provided is a solid ion-conductive composition comprising 50 to 400 parts by weight of a nonaqueous solvent and 0 parts by weight of an alkali metal salt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid used as an electrolyte which is used for a device such as a primary battery, a secondary battery, a capacitor and an electrochromic display, and also serves as a separator for preventing a short circuit between positive and negative electrodes of the device. A ionic conductive composition having a high ionic conductivity and excellent mechanical properties.

[0002]

2. Description of the Related Art Conventionally, an ion conductive material has been a liquid material obtained by dissolving an electrolyte salt in a solvent. For example, electrolytes such as nickel cadmium batteries, nickel metal hydride batteries, and lithium ion batteries include:
These ionic conductive liquids are used. But,
From a device using such an ion conductive liquid substance, there is a risk that the liquid may leak out in the long term, and there has been a problem in reliability. In recent years, in order to overcome this drawback, research and development of solid ion conductive materials have been carried out.

Among them, research on ion-conductive solid polymers originated from the fact that a complex of an alkali metal salt and polyethylene oxide (hereinafter abbreviated as PEO) was reported to exhibit ion conductivity. . The ionic conductivity of this complex was about 10 ⁻⁸ s / cm at room temperature. After that, a mixture of alkali metal salt and PEO, a report of a system blending polyvinyl denfluoride which is a highly polar polymer, and a mixture of alkali metal salt and PEO, a highly polar solvent,
There have been reports of systems plasticized by adding ethylene carbonate, propylene carbonate, or the like.

[0004] However, the ion conductivity of the improved ion-conductive solid polymer is 10 ^-5 s / cm.
The ionic conductivity of the ionic conductive liquid,
It is not enough compared to 0 ^-3 to 10 ^-2 s / cm,
It has not yet spread as a solid ion conductive composition. Also, by blending a large amount of a highly polar solvent, the ion-conductive solid polymer can be plasticized or gelled to improve the ion conductivity, but on the other hand, the mechanical strength is likely to decrease, Care must be taken not to apply unnecessarily large stress when manufacturing or using a device utilizing this, and this is not necessarily a good method.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid ionic conductive composition having high ionic conductivity and excellent mechanical strength. And

[0006]

An object of the present invention is to provide a copolymer of vinylidene fluoride and hexafluoropropylene, which is rubbery or has a melting point of 14 at room temperature.
100 parts by weight of a polymer component at 0 ° C. or less, 50 to 400 parts by weight of a non-aqueous solvent and an alkali metal salt are blended, and the polymer component is crosslinked to form a solid ion conductive composition. Will be resolved. In the solid ion conductive composition, the non-aqueous solvent is preferably propylene carbonate, ethylene carbonate, or a mixed solvent containing at least one of these.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The gist of the present invention is to stabilize a large amount of non-aqueous solvent in a copolymer by crosslinking a copolymer of vinylidene fluoride (hereinafter abbreviated as VDF) and hexafluoropropylene (hereinafter abbreviated as HFP). Focusing on the fact that a thin film having excellent elasticity and mechanical strength can be formed, and by adding an alkali metal salt thereto, the dissociation degree and the mobility of ions can be improved. It is in the point that it was found.

The solid ion-conductive composition of the present invention comprises 50 to 400 parts by weight of a non-aqueous solvent per 100 parts by weight of a VDF-HFP copolymer having a rubbery or melting point of 140 ° C. or less at room temperature. An alkali metal salt is blended, and the polymer component is crosslinked.

It is desirable that the VDF-HFP copolymer be rubbery at room temperature or have a melting point of 140 ° C. or less as determined by the DSC method. In this state, the non-aqueous solvent can be stably retained in a large amount by crosslinking the copolymer. Further, a thin film having excellent mechanical strength and elasticity can be obtained. As such a VDF-HFP copolymer, those having a HFP content of 15 to 50 mol% are preferably mentioned.

The non-aqueous solvent added to the VDF-HFP copolymer is used to promote the dissociation and movement of the alkali metal salt in the polymer component and to promote the movement of the alkali metal ion. It is. Specific examples include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethylsulfoxide, dimethylformamide, sulfolane and the like. Among these solvents, propylene carbonate, ethylene carbonate or a mixed solvent containing at least one of these is a highly polar solvent as compared with other solvents, and has a high effect of promoting dissociation and transfer of an alkali metal salt. It is preferably used because the ionic conductivity of the solid ionic conductive composition can be greatly improved.

These non-aqueous solvents are used in the above-mentioned polymer component 10
50 to 400 parts by weight, preferably 1 to 0 parts by weight
It is desirable to mix in a ratio of 00 to 200 parts by weight.
If the amount is less than 50 parts by weight, the ion conductivity of the solid ion conductive composition cannot be improved, which is inconvenient.
If the amount exceeds 400 parts by weight, the mechanical strength of the solid ion conductive composition cannot be kept high, which is disadvantageous.

The alkali metal salt used in the present invention includes, as cations, lithium ion, sodium ion, potassium ion and the like, and as anions, perchlorate ion, thiocyanate ion, trifluoromethanesulfonate ion, and the like. Examples thereof include tetrafluoroborate ion, hexafluorophosphate ion, and bistrifluoromethylsulfonylimide ion. The alkali metal salt is 2 to 100 parts by weight of the polymer component.
80 parts by weight, preferably 5 to 60 parts by weight, and more preferably 10 to 40 parts by weight.

[0013] The solid ion conductive composition of the present invention can be obtained by causing a crosslinking reaction to the polymer component blended in the above blend ratio. By cross-linking the polymer component, a large amount of non-aqueous solvent can be contained in the molecule, and high ion conductivity can be obtained. This polymer component can be cross-linked by chemical cross-linking, thermal cross-linking, high-energy radiation cross-linking, etc. In order to suppress this, high-energy beam irradiation crosslinking with an electron beam or γ-ray at a low temperature is preferably used.

When the solid ionic conductive composition of the present invention is used for a device such as a battery, it is used in the form of a thin film. In this case, the VDF-HFP copolymer, the non-aqueous solvent, and the alkali metal salt are blended in the above-described blending amounts, dissolved in an organic solvent, and the solution is cast into a desired shape, After drying to remove the organic solvent, it can be obtained by crosslinking the polymer component. Alternatively, it can be obtained by swelling the crosslinked polymer thin film by immersing it in a nonaqueous solvent in which an alkali metal salt is dissolved at a predetermined temperature for a predetermined time.

As described above, the solid ion conductive composition of the present invention can contain an appropriate amount of a non-aqueous solvent and an alkali metal salt in a polymer component comprising a VDF-HFP copolymer. Therefore, it shows high ionic conductivity, and is also excellent in mechanical strength, and can be thinned, and is suitably used as an electrolyte of devices such as primary batteries, secondary batteries, capacitors, and electrochromic displays. It can be suitably used as an electrolyte for a lithium secondary battery. In addition, since the VDF-HFP copolymer is a widely used polymer, the production process is easy and inexpensive, so that the solid ion conductive composition of the present invention can be reduced in cost.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. (Test Example 1) As a VDF-HFP copolymer, one having a melting point of 135 ° C. (Polymer 1) or a rubbery one at room temperature (Polymer 2) determined by the DSC method was used. Using a mixed solvent of carbonate, ethylene carbonate and diethyl carbonate, and using lithium tetrafluoroborate as an alkali metal salt, a solid ion conductive composition was prepared as follows.

First, 20 parts by weight of an alkali metal salt was added to 100 parts by weight of a VDF-HFP copolymer shown in Table 1.
A non-aqueous polar solvent was blended so as to have a blending amount shown in Table 1, and a solution in which these were dissolved in methyl ethyl ketone was prepared. The solution was then cast on a glass plate and
C. and dried in an argon atmosphere to prepare a thin film from which methyl ethyl ketone was removed. Then, these thin films were irradiated with an electron beam of 20 Mrad to crosslink the polymer component, thereby obtaining thin films of the solid ion conductive compositions of Examples 1 to 5 and Comparative Examples 1 to 4. The thickness of this thin film is 400 ± 10
It was 0 μm.

The ionic conductivity and mechanical strength of the thin film of the solid ion conductive composition were examined. The ionic conductivity was measured and evaluated as follows. From the thin films of the solid ionic conductive compositions of Examples 1 to 5 and Comparative Examples 1 to 4, circular samples each having an outer diameter of 20 mm were cut. An outer diameter of 20 mm and a thickness of 1
mm stainless steel was crimped to form an electrode. After the completion of these electrodes, the lead wires were taken out, and each electrode was sandwiched between two plastic films and heat-sealed to seal the electrodes so as not to come into contact with the atmosphere. All the above operations were performed in an argon atmosphere. The sealed electrode was taken out into the atmosphere, and the ionic conductivity was determined by measuring the AC impedance of each sample.

The mechanical strength was evaluated as follows. A sample was prepared by pressing a stainless steel plate on one side of the thin film of the solid ion conductive composition of Examples 1 to 5 and Comparative Examples 1 to 4. A tip radius of curvature of 5 mm and an outer diameter of 10
A 3 kg compressive force was applied for 10 seconds with a stainless steel rod of 10 mm, and the presence or absence of a short circuit between the stainless steel plate and the stainless steel rod was examined. Those having no short circuit were evaluated as having excellent mechanical strength. Table 1 shows the results.

[0020]

[Table 1]

From the results shown in Table 1, it can be seen that the solid ionic conductive composition of the present invention has both good ionic conductivity and sufficient mechanical strength.

[0022]

As described above, the solid ionic conductive composition of the present invention is a copolymer of vinylidene fluoride and hexafluoropropylene, and is rubbery at room temperature or has a melting point of 140 ° C. The following polymer components contain an appropriate amount of a non-aqueous solvent and an alkali metal salt, and are formed by crosslinking, so that they have high ionic conductivity and have excellent elasticity and mechanical strength. Become. Therefore, the solid ion conductive composition of the present invention is expected to be applied to various devices such as primary batteries, secondary batteries, capacitors, and electrochromic displays.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 6/18 H01M 6/18 E 10/40 10/40 B (72) Inventor Hiroshi Matsui 1-5 Kiba, Koto-ku, Tokyo No. 1 Inside Fujikura Co., Ltd.

Claims (2)

[Claims] 1. A polymer component 10 comprising a copolymer of vinylidene fluoride and hexafluoropropylene, which is rubbery at room temperature or has a melting point of 140 ° C. or lower.
A solid ion conductive composition in which 50 to 400 parts by weight of a nonaqueous solvent and an alkali metal salt are blended with respect to 0 parts by weight, and the polymer component is crosslinked. 2. The solid ion conductive composition according to claim 1, wherein the non-aqueous solvent is propylene carbonate, ethylene carbonate, or a mixed solvent containing at least one of them.