JPH0782450A - Electrolyte sheet - Google Patents

Abstract

PURPOSE:To provide an electrolyte sheet formable to a thin and large-area sheet, having excellent conductivity and usable as an electrochemical element such as battery, electric double layer capacitor, etc. CONSTITUTION:This electrolyte sheet is composed of a copolymer of acrylonitrile and methyl acrylate, methyl methacrylate or vinyl acetate, an aprotic solvent solution of a salt and powder of electrically insulating inorganic substance containing alumina or silica. The electrically insulating inorganic substance powder containing alumina or silica acts as cross-linking points in a gelatinous substance formed by the copolymer and the aprotic solvent containing a salt as a solute to give an electrolyte sheet having excellent shape-retaining property and high mechanical strength without lowering the conductivity.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a battery, a capacitor,
The present invention relates to an electrolyte sheet used in electrochemical devices such as sensors, display devices and recording devices.

[0002]

2. Description of the Related Art By using a sheet-shaped electrolyte, A4
It is possible to obtain a large-area and thin battery such as a plate and B5 plate, an electric double layer capacitor, or an electrochemical device such as an electrochromic display element. As an electrolyte suitable for such a purpose, (a) an electrolyte in which an organic solvent in which a lithium salt is dissolved is gelled with a copolymer of polyvinylidene fluoride (JP-A-58-75779), and (b) ion conduction An attempt to provide a solid electrolyte sheet which is made flexible by adding a plastic resin to a water-soluble inorganic compound and which is not easily damaged by mechanical impact (Japanese Patent Laid-Open No. 63-24587).
No. 1), (c) a film-processable polymer solid electrolyte composed of polyethylene oxide and an alkali metal salt ("Fast Ion Transport in Solid" P. Vanishsta et.a.
l., Eds. P. 131 (1979) North Holand Publishing Co.)
Have been proposed.

[0003]

In the case of (a) described above, if a sheet having a large area, for example, 100 cm ² and a thickness of about 200 μm is formed, it is difficult to maintain the shape by itself, and it is difficult to maintain the shape for a long time. If it is stored over a period of time, there is a drawback that the solvent seeps out and contracts, resulting in a change in shape. In addition, since (b) does not contain a solvent, it can have a large area and can be thinned like an ordinary plastic resin film, and there is no change in shape as described above, but it is an inorganic material mixed with a plastic resin. Even if the compound has a large ionic conductivity, it is about 10 ⁻³ S / cm at room temperature, and since a large amount of insulating plastic resin is mixed to give a sufficient sheet forming ability, the conductivity is further from one digit to two digits. digit decreases, 10 ^@ 4 -10 ^over 5 S / cm order of conductivity at room temperature is at most only obtained. Further, (c) has a sufficient sheet-forming ability and a large-area film can be obtained even when the thickness is 200 μm or less, but the ionic conductivity is lower than that of (b).
0 ^over 5 -10 ^over 6 S / cm only about it it is not obtained and referred drawbacks. Therefore, the object of the present invention is to provide a large area even if the thickness is 200 μm or less, to prevent solvent leaching during storage, to prevent change in shape, and to obtain 10 ⁻³ S / c at room temperature.
An object is to provide an electrolyte sheet having a high ionic conductivity of about m or more.

[0004]

Means for Solving the Problems The electrolyte sheet of the present invention which achieves the above objects, comprises a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate or vinyl acetate, and an aprotic solvent in which a salt is dissolved, It is characterized by being composed of powder of an electrically insulating inorganic substance containing alumina or silica.

[0005]

The electrolyte sheet of the present invention comprises a copolymer of acrylonitrile, which is a specific copolymer, and methyl acrylate or methyl methacrylate or vinyl acetate, and an electrically insulating inorganic substance powder containing alumina or silica. When an aprotic solvent containing a salt is gelled by the action of the copolymer, the powder of the electrically insulating inorganic substance containing alumina or silica in the gel is a cross-linking point of the copolymer. Acts as a solvent and develops a knitted structure in which the copolymer molecules are entangled, and effectively retains the aprotic solvent in which the salt is dissolved, so that the solvent does not seep out even when stored for a long period of time. Absent. The powder of electrically insulating inorganic material containing alumina or silica acts as a cross-linking point, so that the electrolyte is flexible and has high mechanical strength and excellent self-supporting property even if the area is 200 μm or less. It becomes a sheet.

To obtain the electrolyte sheet of the present invention, first,
A copolymer of acrylonitrile and methyl acrylate or methyl methacrylate or vinyl acetate (hereinafter referred to as PAN-MA or PAN-MMA or PAN) in an aprotic solvent in which a salt is dissolved (hereinafter referred to as an electrolytic solution)
-VA). A powder of an electrically insulating inorganic substance containing alumina or silica, which has been dried in advance, is added to the viscous liquid obtained by dissolution, and uniformly dispersed. It is prepared by spreading the obtained dispersion on a glass plate and then cooling it to 0 ° C. or lower.

PAN-MA or PAN-MMA is
Those having an average molecular weight of 20,000 to 100,000 are preferable. If it is less than 20,000, gelation does not occur even when cooled and a sheet having a self-supporting property cannot be obtained. If it is more than 100,000, the viscosity of the viscous liquid becomes high, and the powder of the electrically insulating inorganic substance containing alumina or silica is not uniformly dispersed, and a uniform film cannot be obtained. Heating and dilution with a solvent are effective in reducing the viscosity of viscous liquids, but when the molecular weight is 100,000 or more, thermal decomposition of the copolymer occurs before the viscosity decreases to the level required for dispersion if the heating temperature is raised. . Further, when a diluent is used, coagulation occurs and the copolymer and the solvent are separated. The copolymerization molar ratio of PAN-MA or PAN-MMA is preferably PAN: MA or MMA = 95: 5 to 60:40. Within this range, the copolymer will dissolve in the electrolytic solution, and a viscous liquid having a viscosity (about 500 to 3000 cps) suitable for dispersing the powder of the electrically insulating inorganic substance containing alumina or silica can be obtained.

PAN-VA has an average molecular weight of 10
It is preferably from 1,000,000 to 1,000,000. If it is less than 100,000,
Even if cooled, gelation does not occur and a sheet having a self-shape retention is not obtained. When it is more than 1,000,000, the viscosity of the viscous liquid becomes high, the powder of the insulating inorganic substance is not uniformly dispersed, and a uniform film cannot be obtained. Although heating and dilution with a solvent are effective in reducing the viscosity of viscous liquids, when the molecular weight reaches 1,000,000 or more, thermal decomposition of the copolymer occurs before the viscosity decreases to that required for dispersion if the heating temperature is raised. . Further, when a diluent is used, coagulation occurs and the copolymer and the solvent are separated.
The copolymerization molar ratio of PAN-MA is PAN: VA = 99 :.
1 to 80:20 is preferable. Within this range, the copolymer will dissolve in the electrolytic solution, and a viscous liquid having a viscosity (about 500 to 3000 cps) suitable for dispersing the insulating inorganic substance powder can be obtained.

LiClO is used as the salt for the electrolytic solution.
₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF
₃ SO ₃ , LiI, NaBF ₄ , (C ₂ H ₅ ) ₄ NBF ₄ ,
An alkali metal salt such as ammonium benzoate or ammonium tartrate, an alkaline earth metal salt, or an ammonium salt is used. A salt concentration of 0.5 M to 1.5 M is preferable because the highest ionic conductivity is obtained. As the aprotic solvent used for the electrolytic solution, butylene carbonate, propylene carbonate, ethylene carbonate,
Diethyl carbonate, dimethyl carbonate, sulfolane, methyl sulfolane, dimethoxyethane, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, acetonitrile or a mixture thereof is used.

As the powder of the electrically insulating inorganic substance containing alumina or silica, alumina powder, silica gel powder, porous glass powder, molten glass powder, aluminum silicate powder and the like are preferably used. The shape of these powders may be spherical, fibrous, or plate-like. Further, by using the powder of these inorganic substances whose surface is modified with a polymer of vinyl monomer, it is possible to effectively achieve the uniform dispersion of these powders in the viscous electrolytic solution in which the copolymer is dissolved, and The electrolyte sheet can be flexible and elastic. As the vinyl monomer, methyl methacrylate, acrylonitrile, styrene, vinyl acetate, vinyl chloride, butadiene, isoprene and the like can be used. Among them, PAN-MA, P that forms a gel
It is preferable to use methyl acrylate, methyl methacrylate or vinyl acetate, which is a component of the AN-MMA or PAN-VA copolymer, because higher homogeneity and mechanical strength can be obtained.

The surface of the inorganic substance powder is modified with a polymer of vinyl monomer as follows. The inorganic substance powder is suspended in an aqueous medium, and an alkylammonium quaternary salt and potassium persulfate or ammonium persulfate are added to form a sparingly soluble double salt on the surface of the inorganic substance powder. Next, when the vinyl monomer is added to the suspension, the double salt acts as a polymerization initiator, polymerization of the vinyl monomer occurs on the powder surface, and the surface is coated and modified by the vinyl monomer polymer. Alternatively, the vinyl monomer may be added to the suspension of the inorganic material powder without forming a double salt, and then a vinyl monomer polymer may be formed on the surface by using amines as a polymerization initiator. The addition amount of the inorganic powder is not particularly limited,
In order to obtain good mechanical strength and high ionic conductivity, it is preferably in the range of 0.5% to 10% based on the total weight of the electrolytic solution and the copolymer.

[0012]

The present invention will be described in more detail with reference to the following examples. Example 1 Ethylene carbonate (hereinafter referred to as EC) -sulfolane (hereinafter, referred to as EC) in which 4.6 g of LiBF ₄ was dissolved
(Hereinafter referred to as SL) (EC: SL = 1: 1 volume ratio) In 40 g of an electrolytic solution composed of a mixed solvent, a PAN-M having a copolymerization molar ratio of PAN and MA of 90:10 and an average molecular weight of 45,000.
After adding 6.0 g of A copolymer powder and heating to 150 ° C. to make a transparent viscous solution, 60 g of acetonitrile is added to dilute it to prepare a solution having a viscosity of 1550 cps. Next, porous silica gel powder (Syroid 404 manufactured by Fuji Devison Co., average particle size 5.2 μm, specific surface area 300 m ²
/ G) 2 g was dispersed in 50 ml of distilled water, and then 0.7 mmol of cetyltriethylammonium bromide was added,
Add 0.2 mmol of potassium persulfate and 3.5 mmol of methyl methacrylate, and then add 17
Polymerize for a period of time. After washing the precipitate with methanol, 8
Vacuum-dry at 72 ° C. for 72 hours to obtain surface-modified silica gel powder.

1.5 g of the silica gel powder thus prepared is added to the previously prepared solution and uniformly dispersed with a homogenizer to obtain a suspension. This suspension is
After casting on a glass petri dish of mm and heating to 60 ° C. under reduced pressure of 40 cmHg to dissipate acetonitrile,
By cooling to −20 ° C., an electrolyte sheet A having a thickness of 120 μm is obtained. The electrolyte sheet A is a flexible film that easily peels off from the glass petri dish and has a diameter of 50 mm.
Even after repeating the test of bending along the outer circumference of the column of 3000 times 3000 times, it did not break. This sheet has a diameter of 1
When punched into a 2.5 mm disc and sandwiched between lithium discs, the conductivity was measured and found to be 1 × 10 ⁻³ S / cm at 20 ° C.
It gave a high conductivity of 2 × 10 ⁻⁴ S / cm at −20 ° C.

[Comparative Example 1] In 40 g of an electrolytic solution composed of an EC-SL (EC: SL = 1: 1 volume ratio) mixed solvent in which 4.6 g of LiBF ₄ was dissolved, a copolymerization molar ratio of PAN and MA was 90. : 10, PAN-M having an average molecular weight of 45,000
After adding 6.0 g of A copolymer powder and heating to 150 ° C. to make a transparent viscous solution, 60 g of acetonitrile is added to dilute to prepare a solution having a viscosity of 1550 cps. This solution was cast on a glass petri dish having a diameter of 90 mm to obtain 40c.
Heat to 60 ° C under reduced pressure of mHg to dissipate acetonitrile, then cool to -20 ° C to obtain a thickness of 6
An electrolyte sheet B having a thickness of 70 μm is obtained. The electrolyte sheet B is
It can be peeled off from a glass petri dish as a film having a diameter of 90 mm, but it is more liable to break than the electrolyte sheet A and requires careful handling. We tried to reduce the casting amount to 1/5 and tried to form a thinner electrolyte sheet. However, the resulting membrane has poor self-holding property, is difficult to peel from a glass petri dish, and is easy to tear and is extremely difficult to handle. It was difficult.

[Example 2] EC-propylene carbonate (hereinafter referred to as PC) in which 4.6 g of LiBF ₄ was dissolved
(EC: PC = 1: 1 volume ratio) The copolymerization molar ratio of PAN and MA was 75: 2 in 40 g of an electrolytic solution containing a mixed solvent.
5. After adding 6.0 g of PAN-MA copolymer powder having an average molecular weight of 43,000 and heating to 150 ° C. to give a transparent viscous solution, 60 g of acetonitrile was added to dilute the solution to obtain a solution having a viscosity of 2950 cps. Prepare. Next, 150 ℃
Alumina powder vacuum-dried for 17 hours (Sumitomo Chemical Co., Ltd., low soda alumina powder AL-M41, central particle size 1.
9 μm) 3 g was dispersed in 50 ml of distilled water, and 0.7 ml of cetyltriethylammonium bromide was added.
1, 0.2 mmol of potassium persulfate and 3.5 mmol of styrene were further added, followed by polymerization at 60 ° C. for 17 hours. The precipitate is washed with methanol and then vacuum dried at 80 ° C. for 72 hours to obtain a surface-modified alumina powder.

Alumina powder 1.
5 g is added to the previously prepared solution and uniformly dispersed with a homogenizer to obtain a suspension. This suspension has a diameter of 90 mm
Cast on a glass Petri dish of 6 and under reduced pressure of 40 cmHg.
After heating to 0 ° C. to dissipate the acetonitrile, it is cooled to −20 ° C. to obtain an electrolyte sheet C having a thickness of 160 μm. The electrolyte sheet C was a film that was easily peeled off from the glass petri dish and was highly flexible, and did not break even after the test of bending along the outer periphery of a cylinder having a diameter of 50 mm was repeated 3000 times. This sheet has a diameter of 1
It was punched into a 2.5 mm disc, sandwiched between lithium discs, and the conductivity was measured to be 9 × 10 ⁻⁴ S / cm at 20 ° C.,
It gave a high conductivity of 8 × 10 ⁻⁵ S / cm at −20 ° C.

[Comparative Example 2] An electrolytic solution prepared by dissolving in the same manner as in Example 2 in which a PAN-MA copolymer powder was dissolved and diluted with acetonitrile was cast on a glass petri dish having a diameter of 90 mm, and the pressure was reduced to 40 cmHg. The mixture is heated to 60 ° C. below to dissipate acetonitrile, and then cooled to −20 ° C. to obtain an electrolyte sheet D having a thickness of 550 μm. The electrolyte sheet D can be peeled off from the glass petri dish as a film having a diameter of 90 mm, but it is more liable to break than the electrolyte sheet C and requires careful handling. We tried to reduce the casting amount to 1/5 and tried to form a thinner electrolyte sheet. However, the resulting membrane has poor self-holding property, is difficult to peel from a glass petri dish, and is easy to tear and is extremely difficult to handle. It was difficult.

[Comparative Example 3] A polyacrylonitrile powder having an average molecular weight of 51,000 was added to the same electrolytic solution as in Example 2 in place of the copolymer powder of PAN and MA, and heated to 150 ° C or higher. Even when heated, the powder did not dissolve and remained partly, and when continued heating, it began to turn yellow and decomposition of polyacrylonitrile occurred. When 60 ml of acetonitrile was added while partially undissolved, coagulation of polyacrylonitrile occurred and a white solid matter and a solution were separated.

[Example 3] A copolymerization molar ratio of PAN and VA was 97 in 40 g of an electrolytic solution containing an EC-SL (EC: SL = 1: 1 volume ratio) mixed solvent in which 4.6 g of LiBF ₄ was dissolved. : 3, PAN-V having an average molecular weight of 200,000
2.5 g of the A copolymer powder is added and heated to 150 ° C. to make a transparent viscous solution, and then 40 g of acetonitrile is added to dilute the solution to prepare a solution having a viscosity of 1250 cps. Next, porous silica gel powder (Syroid 244 manufactured by Fuji Devison Co., average particle size 1.8 μm, specific surface area 300 m ²
/ G) 2.5 g was dispersed in 50 ml of distilled water, and then 0.7 ml of cetyltriethylammonium bromide was added.
1, 0.2 mmol of potassium persulfate and 3.8 mmol of vinyl acetate were further added, followed by polymerization at 60 ° C. for 17 hours. After washing the precipitate with methanol, 80 ° C
After vacuum drying for 72 hours, a silica gel powder having a modified surface is obtained.

0.5 g of the silica gel powder thus prepared is added to the previously prepared solution and uniformly dispersed with a homogenizer to obtain a suspension. This suspension is
After casting on a glass petri dish of mm and heating to 60 ° C. under reduced pressure of 40 cmHg to dissipate acetonitrile,
By cooling to −20 ° C., an electrolyte sheet E having a thickness of 110 μm is obtained. The electrolyte sheet E is a flexible film that easily peels off from the glass petri dish and has a diameter of 50 mm.
Even after repeating the test of bending along the outer periphery of the column of 5000 times 5000 times, it did not break. This sheet has a diameter of 1
When punched into a 2.5 mm disc and sandwiched between lithium discs, the conductivity was measured to be 8 × 10 ⁻⁴ S / cm at 20 ° C.,
It gave a high conductivity of 8 × 10 ⁻⁵ S / cm at −20 ° C.

[Comparative Example 4] An electrolytic solution prepared in the same manner as in Example 3 and diluted with acetonitrile was cast on a glass petri dish having a diameter of 90 mm, and the pressure was reduced to 60 cm under a reduced pressure of 40 cmHg.
After heating to 0 ° C to dissipate the acetonitrile, it is cooled to -20 ° C to obtain an electrolyte sheet F having a thickness of 620 µm. The electrolyte sheet F can be peeled off from the glass petri dish as a film having a diameter of 90 mm, but it is more likely to be torn than the electrolyte sheet E and requires careful handling. We tried to reduce the casting amount to 1/5 and tried to form a thinner electrolyte sheet. However, the resulting membrane has poor self-holding property, is difficult to peel from a glass petri dish, and is easy to tear and is extremely difficult to handle. It was difficult.

Example 4 In 40 g of an electrolytic solution containing an EC-PC (EC: PC = 1: 1 volume ratio) mixed solvent in which 4.6 g of LiBF ₄ was dissolved, the molar ratio of copolymerization of PAN and VA was 95. : 5, PAN-V having an average molecular weight of 400,000
After adding 2.0 g of A copolymer powder and heating to 150 ° C. to make a transparent viscous solution, 40 ml of acetonitrile is added to dilute to prepare a solution having a viscosity of 1650 cps.
Next, alumina powder vacuum-dried at 150 ° C. for 17 hours (manufactured by Sumitomo Chemical Co., Ltd., low soda alumina powder AL-M4
3, the central particle size 3.0 μm) 3 g was dispersed in 50 ml of distilled water, and then 0.7 mmol of cetyltriethylammonium bromide, 0.2 mmol of potassium persulfate and 3.5 mmol of styrene were added, and then 60
Polymerization is carried out at ℃ for 17 hours. The precipitate is washed with methanol and then vacuum dried at 80 ° C. for 72 hours to obtain a surface-modified alumina powder.

Alumina powder 1.
5 g is added to the previously prepared solution and uniformly dispersed with a homogenizer to obtain a suspension. This suspension has a diameter of 90 mm
Cast on a glass Petri dish of 6 and under reduced pressure of 40 cmHg.
After heating to 0 ° C. to dissipate the acetonitrile, it is cooled to −20 ° C. to obtain an electrolyte sheet G having a thickness of 140 μm. The electrolyte sheet G was a film that was easily peeled off from the glass petri dish and was highly flexible, and did not break even after the test of bending along the outer periphery of a cylinder having a diameter of 50 mm was repeated 1000 times. This sheet has a diameter of 1
It was punched into a 2.5 mm disc, sandwiched between lithium discs, and the conductivity was measured to be 6 × 10 ⁻⁴ S / cm at 20 ° C.
It gave a high conductivity of 5 × 10 ⁻⁵ S / cm at −20 ° C.

[Comparative Example 5] An electrolytic solution prepared by dissolving in the same manner as in Example 4 in which PAN-VA copolymer powder was dissolved and diluted with acetonitrile was cast on a glass petri dish having a diameter of 90 mm, and the pressure was reduced to 40 cmHg. The mixture is heated to 60 ° C. below to dissipate acetonitrile, and then cooled to −20 ° C. to obtain an electrolyte sheet H having a thickness of 680 μm. The electrolyte sheet H can be peeled off from the glass petri dish as a film having a diameter of 90 mm, but it is more liable to break than the electrolyte sheet G and requires careful handling. We tried to reduce the casting amount to 1/5 and tried to form a thinner electrolyte sheet. However, the resulting membrane has poor self-holding property, is difficult to peel from a glass petri dish, and is easy to tear and is extremely difficult to handle. It was difficult.

[Comparative Example 6] A polyacrylonitrile powder having an average molecular weight of 51,000 was added to the same electrolytic solution as in Example 4 in place of the copolymer powder of PA and VA, and heated to 150 ° C or higher. Even when heated, the powder did not dissolve and remained partly, and when continued heating, it began to turn yellow and decomposition of polyacrylonitrile occurred. When 60 ml of acetonitrile was added while partially undissolved, coagulation of polyacrylonitrile occurred and a white solid matter and a solution were separated.

[0026]

INDUSTRIAL APPLICABILITY As described above, the electrolyte sheet according to the present invention has excellent self-shape retention, excellent flexibility, and high conductivity even when formed into a thin film having a large area and 200 μm or less. give. It is an electrolyte sheet having both excellent mechanical strength and electrical characteristics, and can be effectively used for thin and large area electrochemical devices such as batteries, electric double layer capacitors and electrochromic display devices.

Claims (6)

[Claims] 1. A copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, an aprotic solvent in which a salt is dissolved, and a powder of an electrically insulating inorganic substance containing alumina or silica. Electrolyte sheet. 2. The electrolyte sheet according to claim 1, wherein the electrically insulating inorganic powder contains alumina or silica whose surface is modified with a polymer of a vinyl monomer. 3. The electrolyte sheet according to claim 2, wherein the vinyl monomer is methyl acrylate or methyl methacrylate. 4. An electrolyte sheet comprising a copolymer of acrylonitrile and vinyl acetate, an aprotic solvent in which a salt is dissolved, and a powder of an electrically insulating inorganic substance containing alumina or silica. 5. The electrolyte sheet according to claim 4, wherein the electrically insulating inorganic powder contains alumina or silica whose surface is modified with a polymer of a vinyl monomer. 6. The electrolyte sheet according to claim 5, wherein the vinyl monomer is vinyl acetate.