JP3143273B2 - 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 batteries, capacitors,
The present invention relates to an electrolyte sheet used for an electrochemical device such as a sensor, a display device, and a recording device.

[0002]

2. Description of the Related Art By using a sheet-like electrolyte, A4
It is possible to obtain an electrochemical device such as a battery, an electric double layer capacitor, or an electrochromic display element having a large area and a thin shape such as a plate, a B5 plate or the like. Examples of electrolytes suitable for such purposes include (a) an electrolyte obtained by gelling an organic solvent in which a lithium salt is dissolved with a copolymer of polyvinylidene fluoride (JP-A-58-75779), and (b) an ion conductor. Attempts to provide a solid electrolyte sheet that is flexible by imparting flexibility by compounding a plastic resin with a non-reactive inorganic compound and that is hardly damaged by mechanical impact (Japanese Patent Laid-Open No. 24587/1988).
No. 1), and (c) a polymer solid electrolyte comprising polyethylene oxide and an alkali metal salt, which can be processed into a film ("Fast Ion Transport in Solid" P. Vanishsta et.a.
l., Eds. P. 131 (1979) North Holand Publishing Co.)
And so on.

[0003]

In the case of (a) described above, when 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, When stored over a period of time, there is a drawback that the solvent oozes out and shrinks to change the shape. Further, since (b) does not contain a solvent, it can have a large area and a thin film similarly to a normal plastic resin film, and there is no change in the shape as described above. Even if the ionic conductivity of the compound is large, it is about ^10-3 S / cm at room temperature, and a large amount of insulating plastic resin is mixed to give sufficient sheet forming ability. 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 ion 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, an object of the present invention is to provide a large area even if the thickness is 200 μm or less, no leaching of the solvent during storage, no change in shape, and 10 ⁻³ S / c at room temperature.
An object of the present invention is to provide an electrolyte sheet having a high ionic conductivity of about m or more.

[0004]

The electrolyte sheet of the present invention to achieve the above object, according to an aspect of the acrylonitrile and the copolymers of methyl acrylate or methyl methacrylate or vinyl acetate, made of aprotic solvent to dissolve the salt Electric
Solution solution and, Ri powder from forming the electrically insulating inorganic material containing alumina or silica, the powder crosslinking point of the copolymer
With respect to the total weight of the copolymer and the electrolytic solution
Characterized that you have included 0.5 to 10 wt%.

[0005]

The electrolyte sheet of the present invention comprises a copolymer of acrylonitrile and a copolymer of methyl acrylate or methyl methacrylate or vinyl acetate, and a powder of an electrically insulating inorganic substance containing alumina or silica. When the aprotic solvent in which the salt is dissolved is gelled by the action of the copolymer, the powder of the electrically insulating inorganic substance containing alumina or silica in the gel forms a cross-linking point of the copolymer. As a result, a stitch structure in which the copolymer molecules are entangled develops, and in order to effectively retain the aprotic solvent in which the salt is dissolved, no solvent seeps out even when stored for a long period of time. Absent. An electrically insulating inorganic substance powder containing alumina or silica acts as a cross-linking point, so that even if the area is 200 μm or less in a large area, the electrolyte is rich in flexibility, has high mechanical strength, and has excellent self-supporting properties. It becomes a sheet.

In order to obtain the electrolyte sheet of the present invention, first,
A copolymer of acrylonitrile and methyl acrylate or methyl methacrylate or vinyl acetate (hereinafter PAN-MA or PAN-MMA or PAN) is mixed with an aprotic solvent in which a salt is dissolved (hereinafter referred to as an electrolyte).
-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 cooling it to 0 ° C. or lower.

[0007] PAN-MA or PAN-MMA is
Those having an average molecular weight of 20,000 to 100,000 are preferred. If it is smaller than 20,000, gelling does not occur even when cooled, and the sheet does not become self-supporting. If it is larger 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, so that a uniform film cannot be obtained. Heating and dilution with a solvent are effective in lowering the viscosity of the viscous liquid, but when the molecular weight exceeds 100,000, thermal decomposition of the copolymer occurs before the viscosity required for dispersion decreases when the heating temperature is increased. . 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 dissolves in the electrolytic solution to obtain a viscous liquid (approximately 500 to 3000 cps) suitable for dispersing powder of an electrically insulating inorganic substance containing alumina or silica.

PAN-VA has an average molecular weight of 10
Thousands to one million are preferred. If it is smaller than 100,000,
Gelling does not occur even when cooled, and the sheet does not have self-shape retention. If it is larger than 1,000,000, the viscosity of the viscous liquid becomes high, and the powder of the insulating inorganic substance is not uniformly dispersed, so that a uniform film cannot be obtained. Heating and dilution with a solvent are effective in lowering the viscosity of the viscous liquid, but when the molecular weight exceeds 1,000,000, thermal decomposition of the copolymer occurs before the viscosity required for dispersion decreases when the heating temperature is increased. . 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:
1-80: 20 is preferred. Within this range, the copolymer dissolves in the electrolytic solution to obtain a viscous liquid having a viscosity suitable for dispersion of the insulating inorganic substance powder (about 500 to 3000 cps).

The salt used in the electrolyte is LiClO.
_{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. The salt concentration is preferably 0.5 M to 1.5 M because the highest ionic conductivity can be obtained. As the aprotic solvent used for the electrolyte, butylene carbonate, propylene carbonate, ethylene carbonate,
Diethyl carbonate, dimethyl carbonate, sulfolane, methylsulfolane, dimethoxyethane, dimethylformamide, dimethylsulfoxide, tetrahydrofuran, acetonitrile or a mixture thereof is used.

As a powder of an 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. In addition, by using powders of these inorganic substances whose surfaces are modified with a polymer of a vinyl monomer, uniform dispersion of these powders in a viscous electrolytic solution in which a copolymer is dissolved can be effectively achieved, and A flexible and elastic electrolyte sheet can be obtained. 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 which form 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 uniformity and mechanical strength can be obtained.

The surface of the inorganic substance powder is modified with a polymer of a vinyl monomer as follows. The inorganic material powder is suspended in an aqueous medium, and a quaternary alkyl ammonium salt and potassium persulfate or ammonium persulfate are added to form a hardly soluble double salt on the surface of the inorganic material powder. Next, when a vinyl monomer is added to the suspension, the double salt acts as a polymerization initiator, polymerization of the vinyl monomer occurs on the surface of the powder, and the surface is coated and modified with a polymer of the vinyl monomer. Alternatively, after a vinyl monomer is added to the suspension of the inorganic substance powder without forming a double salt, a polymer of the vinyl monomer may be formed on the surface by using an amine as a polymerization initiator. The amount of the inorganic powder added is not particularly limited,
In order to obtain good mechanical strength and high ionic conductivity, the content is preferably in the range of 0.5% to 10% with respect to 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] LiBF ₄ and 4.6g melted ethylene carbonate (hereinafter, referred to as EC) - sulfolane (hereinafter,
PAN-M having a copolymerization molar ratio of PAN and MA of 90:10 and an average molecular weight of 45,000 in 40 g of an electrolyte composed of a mixed solvent (referred to as SL) (EC: SL = 1: 1 volume ratio).
After adding 6.0 g of the A copolymer powder and heating to 150 ° C. to form a transparent viscous solution, 60 g of acetonitrile is added and diluted to prepare a solution having a viscosity of 1550 cps. Next, a porous silica gel powder (Syloid 404 manufactured by Fuji Devison, average particle size 5.2 μm, specific surface area 300 m ²⁾
/ G) After dispersing 2 g in 50 ml of distilled water, 0.7 mmol of cetyltriethylammonium bromide was added,
0.2 mmol of potassium persulfate was added, and 3.5 mmol of methyl methacrylate was further added.
The polymerization is carried out for a time. After washing the precipitate with methanol, 8
Vacuum drying at 0 ° C. for 72 hours gives a silica gel powder whose surface has been modified.

[0015] 1.5 g of the silica gel powder thus prepared is added to the previously prepared solution, and the mixture is uniformly dispersed with a homogenizer to obtain a suspension. This suspension is used for
and then heated 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 easily peeled off from the glass petri dish and is a flexible film having a diameter of 50 mm.
The test piece was not broken after repeating the bending test along the outer circumference of the column 3000 times. This sheet has a diameter of 1
When punched into a 2.5 mm disk and measured for conductivity by sandwiching it between lithium disks, 1 × 10 ⁻³ S / cm at 20 ° C.
At −20 ° C., a high conductivity of 2 × 10 ⁻⁴ S / cm was provided.

[Comparative Example 1] In 40 g of an electrolytic solution consisting of an EC-SL (EC: SL = 1: 1 volume ratio) mixed solvent in which 4.6 g of LiBF ₄ was dissolved, the 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 the A copolymer powder and heating to 150 ° C. to make a transparent viscous solution, 60 g of acetonitrile is added and diluted 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,
After heating to 60 ° C. under reduced pressure of mHg to dissipate acetonitrile, it is cooled to minus 20 ° C. to obtain a thickness of 6 μm.
An electrolyte sheet B of 70 μm is obtained. The electrolyte sheet B is
Although it can be peeled off from the glass petri dish as a film having a diameter of 90 mm, it is easily broken and requires careful handling as compared with the electrolyte sheet A. Although the casting amount was reduced to 1/5, an attempt was made to form a thinner electrolyte sheet. It was difficult.

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

The alumina powder thus prepared
5 g is added to the previously prepared solution, and the mixture is uniformly dispersed with a homogenizer to obtain a suspension. This suspension is 90 mm in diameter.
And cast under a reduced pressure of 40 cmHg.
After heating to 0 ° C. to dissipate acetonitrile, the mixture is cooled to −20 ° C. to obtain an electrolyte sheet C having a thickness of 160 μm. The electrolyte sheet C was easily peeled off from the glass petri dish, and did not break even after repeating a test of bending along the outer periphery of a cylinder having a diameter of 50 mm 3000 times. This sheet has a diameter of 1
When punched into a 2.5 mm disk and measured for conductivity by sandwiching it between lithium disks, 9 × 10 ⁻⁴ S / cm at 20 ° C.
At −20 ° C., a high conductivity of 8 × 10 ⁻⁵ S / cm was provided.

Comparative Example 2 An electrolyte solution prepared by dissolving a PAN-MA copolymer powder prepared in the same manner as in Example 2 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. After heating to 60 ° C. below to dissipate acetonitrile, it is cooled to −20 ° C. to obtain an electrolyte sheet D having a thickness of 550 μm. Although the electrolyte sheet D can be peeled off from the glass dish as a film having a diameter of 90 mm, the electrolyte sheet D is easily broken and requires careful handling as compared with the electrolyte sheet C. Although the casting amount was reduced to 1/5, an attempt was made to form a thinner electrolyte sheet. However, the resulting film has poor self-holding properties, is difficult to peel off from a glass Petri dish, and is easily broken and easily handled. It was difficult.

Comparative Example 3 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 PAN and MA copolymer powder, and heated to 150 ° C. or more. Even when heated, a part of the powder remained without dissolving, and when heating was continued, the powder began to turn yellow and decomposition of polyacrylonitrile occurred. When 60 ml of acetonitrile was added while partially undissolved, coagulation of polyacrylonitrile occurred, and the mixture was separated into a white solid and a solution.

Example 3 In a 40 g electrolyte composed of an EC-SL (EC: SL = 1: 1 volume ratio) mixed solvent in which 4.6 g of LiBF ₄ was dissolved, the copolymerization molar ratio of PAN and VA was 97 : 3, PAN-V having an average molecular weight of 200,000
After adding 2.5 g of A copolymer powder and heating to 150 ° C. to make a transparent viscous solution, 40 g of acetonitrile is added for dilution to prepare a solution having a viscosity of 1250 cps. Next, a porous silica gel powder (Syloid 244, manufactured by Fuji Devison, average particle size 1.8 μm, specific surface area 300 m ²⁾
/ G) After dispersing 2.5 g in 50 ml of distilled water, 0.7 ml of cetyltriethylammonium bromide was added.
After adding 0.2 mmol of potassium persulfate and 3.8 mmol of vinyl acetate, polymerization is carried out at 60 ° C. for 17 hours. After washing the precipitate with methanol,
For 72 hours to obtain a silica gel powder having a surface modified.

0.5 g of the silica gel powder thus prepared is added to the previously prepared solution, and the mixture is uniformly dispersed with a homogenizer to obtain a suspension. This suspension is used for
and then heated 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 easily peeled off from the glass petri dish and is a flexible film having a diameter of 50 mm.
The test piece was not broken even after the bending test along the outer periphery of the column was repeated 5000 times. This sheet has a diameter of 1
When punched into a 2.5 mm disk and measured for conductivity by sandwiching it between lithium disks, 8 × 10 ⁻⁴ S / cm at 20 ° C.
At −20 ° C., a high conductivity of 8 × 10 ⁻⁵ S / cm was provided.

[Comparative Example 4] An electrolytic solution diluted with acetonitrile prepared in the same manner as in Example 3 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 ℃ to dissipate acetonitrile, it is cooled to minus 20 ℃ to obtain an electrolyte sheet F having a thickness of 620 μm. Although the electrolyte sheet F can be peeled off from the glass dish as a film having a diameter of 90 mm, the electrolyte sheet F is easily broken and requires careful handling as compared with the electrolyte sheet E. Although the casting amount was reduced to 1/5, an attempt was made to form a thinner electrolyte sheet. However, the resulting film has poor self-holding properties, is difficult to peel off from a glass Petri dish, and is easily broken and easily handled. It was difficult.

Example 4 In 40 g of an electrolytic solution composed of a mixed solvent of EC-PC (EC: PC = 1: 1 by volume) in which 4.6 g of LiBF ₄ was dissolved, the copolymerization molar ratio of PAN and VA was 95. : 5, PAN-V having an average molecular weight of 400,000
After adding 2.0 g of the A copolymer powder and heating to 150 ° C. to make a transparent viscous solution, 40 ml of acetonitrile is added and diluted 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, 3 g of the center particle diameter is 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 are added.
The polymerization is carried out at 17 ° C. for 17 hours. The precipitate is washed with methanol and then dried under vacuum at 80 ° C. for 72 hours to obtain a surface-modified alumina powder.

The alumina powder thus prepared
5 g is added to the previously prepared solution, and the mixture is uniformly dispersed with a homogenizer to obtain a suspension. This suspension is 90 mm in diameter.
And cast under a reduced pressure of 40 cmHg.
After heating to 0 ° C. to dissipate acetonitrile, the mixture is cooled to −20 ° C. to obtain an electrolyte sheet G having a thickness of 140 μm. The electrolyte sheet G was easily peeled off from the glass Petri dish, and did not break even after repeating the bending test along the outer periphery of a cylinder having a diameter of 50 mm 1000 times. This sheet has a diameter of 1
When punched into a 2.5 mm disc and sandwiched between lithium discs and measured for conductivity, at 20 ° C., 6 × 10 ⁻⁴ S / cm,
At −20 ° C., a high conductivity of 5 × 10 ⁻⁵ S / cm was provided.

Comparative Example 5 An electrolyte solution prepared by dissolving a PAN-VA copolymer powder prepared in the same manner as in Example 4 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. After heating to 60 ° C. below to dissipate acetonitrile, the mixture is cooled to −20 ° C. to obtain an electrolyte sheet H having a thickness of 680 μm. Although the electrolyte sheet H can be peeled off from the glass dish as a film having a diameter of 90 mm, the electrolyte sheet H is easily broken and requires careful handling as compared with the electrolyte sheet G. Although the casting amount was reduced to 1/5, an attempt was made to form a thinner electrolyte sheet. However, the resulting film had poor self-holding properties, was difficult to peel off from the glass petri dish, and was easily broken and easily handled. It was difficult.

Comparative Example 6 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 more. Even when heated, a part of the powder remained without dissolving, and when heating was continued, the powder began to turn yellow and decomposition of polyacrylonitrile occurred. When 60 ml of acetonitrile was added while partially undissolved, coagulation of polyacrylonitrile occurred, and the mixture was separated into a white solid and a solution.

[0026]

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

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-3137 (JP, A) JP-A-61-189017 (JP, A) JP-A-51-147547 (JP, A) (58) Investigation Field (Int. Cl. ⁷ , DB name) C08L 33/00 H01G 9/022 H01M 6/18 WPI (DIALOG)

Claims (6)

(57) [Claims] And 1. A copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, an electrolyte solution comprising an aprotic solvent to dissolve the salt, electrolyte consisting of a powder of an electrically insulating inorganic material containing alumina or silica
A porous sheet, wherein the powder serves as a cross-linking point of the copolymer and the copolymer and the copolymer.
And 0.5 to 10% by weight based on the total weight of the electrolyte.
An electrolyte sheet characterized by being rare . 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 electrolytic solution comprising an copolymer of acrylonitrile and vinyl acetate, an aprotic solvent in which a salt is dissolved, and an electrolyte sheet comprising a powder of an electrically insulating inorganic substance containing alumina or silica. a is, the copolymer wherein the powder is as a crosslinking point of the copolymer Contact
And 0.5 to 10% by weight based on the total weight of the electrolyte.
An electrolyte sheet characterized by being rare . 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 said vinyl monomer is vinyl acetate.