JPH10321210A - Nonaqueous battery diaphragm - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery diaphragm showing high battery performance even at a large current density by comprising a vinylidene fluoride resin-made porous film having pores communicating with both sides and a permeating quantity of propylene carbonate of a specified value or more. SOLUTION: When a vinylidene fluoride resin-made porous film having a high permeating quantity of electrolytic solvent as a nonaqueous battery diaphragm, the capacity is hardly reduced when the current density is high. Therefore, a one having a permeating quantity of propylene carbonate of 50 kg/hr/m<2> / atm or more under the application of a static pressure of l atom at 23 deg.C is used. Since an excessively large permeating quantity causes possibilities of increased leaking property or short-circuit by dendrite of arborescent metal, the permeating quantity is preferably 10000 kg/hr/m<2> /atm or less. The vinylidene fluoride resin porous film suitable therefor is preferably cross-linked. The excessive deformation in swelling by electrolyte can be prevented by the cross-linked structure, and high high-temperature stability can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous battery diaphragm made of a vinylidene fluoride resin. More specifically, the present invention relates to a non-aqueous battery-use membrane capable of exhibiting high battery performance even at a large current density.

[0002]

2. Description of the Related Art Recently, miniaturization of mobile phones, personal computers, and the like,
A battery with a high energy density is required for weight reduction, and a non-aqueous lithium-ion battery has been developed as a corresponding battery. A polyolefin porous diaphragm that does not swell in the electrolytic solution is disposed between the positive electrode and the negative electrode of this battery. When the polyolefin diaphragm is used, leakage of the electrolyte is likely to occur. Therefore, the entire battery structure is packaged in a heavy metal container to prevent leakage of the electrolyte.

On the other hand, a solid-state battery using a solid electrolyte instead of a polyolefin diaphragm improves the reliability and safety of the battery because there is no leakage of the electrolyte, and adopts a nonmetallic package and makes the battery thinner. , Light weight is expected. In particular, a solid polymer electrolyte using an ion conductive polymer has a processing flexibility to form a laminated structure with a battery,
It is expected that the electrode has favorable properties such as the ability to maintain an interface following a change in volume due to ion occlusion and release of the electrode.

[0004] As an attempt of such a solid polymer electrolyte, an alkali metal salt complex of polyethylene oxide is disclosed by Wright as British Polymer.
Journal, Vol. 7, p. 319 (1975). Since then, polymer solid electrolyte materials based on polyphosphazene, polysiloxane, etc., as well as polyether-based materials such as polyethylene oxide and polypropylene oxide, have been actively studied. ing. Such a solid polymer electrolyte usually takes a form in which the electrolyte is uniformly dissolved in a polymer, and is known as a dry polymer solid electrolyte, but its ionic conductivity is remarkably higher than that of the electrolyte. However, the battery constituted by using such a battery has problems such as limited charge / discharge current density and high battery resistance.

[0005] Therefore, in an attempt to improve the ionic conductivity by forming a state closer to the electrolyte, it has been proposed to use a vinylidene fluoride resin as a base material. U.S. Pat. No. 5,418,091 discloses that a vinylidene fluoride resin is used as a base material as a material of this type, and a gel electrolyte in which an electrolyte is contained in the resin is used for a diaphragm portion. . Although this material is electrochemically stable and has an ionic conductivity far exceeding that of a conventional dry solid electrolyte, it is still insufficient compared with an electrolytic solution. Besides,
Such a gel electrolyte has a disadvantage that high battery performance cannot be obtained at a large current density.

Further, Japanese Patent Application Laid-Open No. 8-250127 discloses that a porous film made of a vinylidene fluoride resin is impregnated with an electrolytic solution, and the electrolytic solution-impregnated porous film is used for a diaphragm portion. However, even the method disclosed herein has a drawback that high battery performance cannot be obtained at a large current density, and a diaphragm material that provides excellent battery performance capable of rapid charge and discharge is still unknown. Absent.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-aqueous battery diaphragm which can exhibit high battery performance even at a large current density in a battery packaged in a non-metal container.

[0008]

Means for Solving the Problems In view of the above-mentioned problems of the prior art, the present inventors have conducted various studies and reached the present invention. The present invention and preferred embodiments thereof are as follows. 1) Has a communicating hole on the front and back, 1atm at 23 ° C
A membrane for non-aqueous batteries, comprising a porous membrane made of a vinylidene fluoride resin having a liquid permeability of propylene carbonate of 50 kg / hr / m ² / atm or more when a static pressure is applied.

2) The non-aqueous battery membrane according to 1 above, wherein the porous membrane made of a vinylidene fluoride resin is crosslinked. 3) The nonaqueous battery membrane according to the above 1, wherein the vinylidene fluoride resin-based porous membrane is a vinylidene fluoride-hexafluoropropylene copolymer and the content of hexafluoropropylene is 20% by weight or less.

4) The vinylidene fluoride resin-based porous membrane is a vinylidene fluoride-hexafluoropropylene copolymer having a hexafluoropropylene content of 20%.
2. The diaphragm for a non-aqueous battery according to the above item 1, wherein the diaphragm is made of a copolymer of not more than wt% and the copolymer is crosslinked. 5) The non-aqueous battery for a non-aqueous battery according to 1 above, wherein the porous membrane made of a vinylidene fluoride-based resin has at least one surface layer more dense than other portions and has huge pores and a three-dimensional network structure inside. diaphragm.

6) The nonaqueous battery-use membrane according to the above item 1, wherein the porous membrane made of a vinylidene fluoride resin has at least one surface layer which is denser than the other portions and the inside has a three-dimensional network structure. 7) The diaphragm for a non-aqueous battery according to 1 above, wherein the porous membrane made of a vinylidene fluoride resin has a three-dimensional network structure on both the surface and the inside.

8) When the ratio of the average pore diameter on one surface to the average pore diameter on the other surface is 2 in the vinylidene fluoride resin porous membrane.
20. The diaphragm for a non-aqueous battery according to 1 above, wherein Hereinafter, the present invention will be described in detail. In general, when the output current density of a battery is increased, the capacity may decrease due to internal resistance, concentration overvoltage, or the like. In particular, the tendency is remarkable in a non-aqueous battery having a diaphragm having a large internal resistance.

The feature of the membrane for a non-aqueous battery of the present invention is that when the membrane is used for a non-aqueous battery, the capacity is not easily reduced even at a large current density. For example, in a chargeable / dischargeable lithium ion secondary battery, it means that there is no large difference in discharge capacity between a low current density such as 1 mA / cm ² and a high current density such as 3 mA / cm ² . The present inventors have studied the requirements of the membrane to satisfy this property, and as a result, it was not possible to obtain satisfactory properties simply by increasing the ionic conductivity or reducing the resistance of the membrane, and the electrolyte solvent was not used. It has been found that this can be achieved only by using a membrane having high liquid permeability.

That is, when a static pressure of 1 atm is applied at 23 ° C., the liquid permeability of propylene carbonate is 50 kg / hr.
/ M ² / atm is a requirement. 50 kg
If it is less than / hr / m ² / atm, the capacity at a high current density decreases. The liquid permeation amount is preferably 75 kg / hr /
m ² / atm or more, more preferably 100 kg / hr
/ M ² / atm or more.

On the other hand, there is no upper limit to the amount of liquid permeation in order to obtain high battery performance. However, if the amount of liquid permeation is too large, liquid leakage will increase or short-circuiting due to dendritic dendritic metal deposits will occur. 10,000 kg / hr /
m ² / atm or less, preferably 5000 kg / hr / m
² / atm or less is more preferable, and 2000 kg / hr
/ M ² / atm or less is more preferred.

The amount of liquid permeation is measured by the following method. That is, the membrane is previously immersed in a propylene carbonate solution at room temperature to impregnate the inside of the membrane with propylene carbonate, and stored under a temperature environment of 23 ° C. ± 1 ° C. for 24 hours. Then, the diaphragm was 25 mm in diameter.
Into a membrane filter holder with an effective area of 3.5 cm ² , filled with propylene carbonate adjusted to 23 ± 1 ° C., and measured the permeation amount of propylene carbonate when a static pressure of 1 atm was applied for 5 minutes. From this value, the amount of liquid permeated per hour and per m ² is calculated. The measurement environment and the moisture and purity of the propylene carbonate and equipment used may affect the measured values and give erroneous evaluations. Therefore, the measurement operation of the liquid permeation amount is adjusted to 23 ± 1 ° C. and the relative humidity is set to 5%.
It is preferable to carry out under the following environment. The propylene carbonate used has a purity of 98 wt% or more, and preferably has a water content of 1000 ppm or less.

Generally, for a porous membrane such as an ultrafilter or a microfilter, the continuity of pores existing in the membrane is evaluated based on the amount of water permeation. However, as apparent from the comparison between Example 3 and Comparative Example 1 described later, a porous membrane made of a vinylidene fluoride resin has a higher water permeability but a higher liquid permeability of propylene carbonate. Absent. This is presumed to change depending on the polymer type and structure of the porous membrane. Therefore, the above liquid permeation amount does not directly correspond to the water permeation amount, and is a completely different concept.

In the present invention, the polymer species forming the porous membrane made of a vinylidene fluoride resin is preferably an electrochemically stable polymer. Specific examples of such polymer species include homopolymers of vinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, and vinylidene fluoride-tetrafluoroethylene. Copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-hexafluoroacetone Examples thereof include a copolymer, a vinylidene fluoride-perfluorovinyl ether copolymer, a vinylidene fluoride-ethylene-tetrafluoroethylene copolymer, and a vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer. These can be used alone or a mixture of these polymers can be used. In addition, as long as the battery performance is not adversely affected, a mixture with another polymer containing no vinylidene fluoride can be used. Among these polymer types, vinylidene fluoride-hexafluoropropylene copolymer is particularly preferred because of its good mechanical strength.

In the case of the above copolymer or mixture, the vinylidene fluoride component is preferably contained in an amount of 50% by weight or more, particularly preferably 75% by weight or more. If the vinylidene fluoride component is less than 50% by weight, the ion conductivity of the diaphragm may decrease, and if the electron beam crosslinking is performed, it is difficult to crosslink at less than 75% by weight. Furthermore, in the case of a vinylidene fluoride-hexafluoropropylene copolymer, the hexafluoropropylene content is preferably 20% by weight or less.
If it exceeds 20 wt%, the mechanical strength is not always sufficient.

These vinylidene fluoride resin porous membranes are preferably crosslinked. Generally, a vinylidene fluoride resin swells with an organic electrolyte used in a lithium ion secondary battery, but its degree is particularly remarkable at high temperatures. By having a crosslinked structure, excessive deformation at the time of swelling when immersed in an electrolytic solution can be prevented, and high high-temperature stability can be obtained. This crosslinked structure can be introduced at any stage during polymerization, before or after formation of the porous thin film.

Examples of the crosslinking method include a method of using a polyfunctional monomer during polymerization, a method of irradiating radiant energy such as an electron beam, a γ-ray, an X-ray, and an ultraviolet ray after polymerization, and a method of adding a radical initiator after polymerization. For example, a method of reacting by irradiation of heat or radiation energy can be used. When a crosslinked structure is introduced after the polymerization, a monofunctional or / and polyfunctional monomer component may be newly allowed to coexist. Among these methods, a method in which radiation energy such as an electron beam, γ-ray, X-ray, or ultraviolet ray is irradiated after polymerization is preferable since impurities and unreacted functional groups hardly remain.

In particular, when the thickness of the diaphragm is 100 μm or less, crosslinking by electron beam irradiation is economical and particularly preferable. When performing crosslinking by electron beam irradiation, the irradiation amount is preferably in the range of 5 to 100 Mrad,
More preferably, it is in the range of 8 to 50 Mrad. 5M
If it is less than rad, the effect of crosslinking is not always sufficient, and 10
If it exceeds 0 Mrad, there is a tendency that the disintegration of the polymer becomes remarkable.

The formation of the crosslinked structure can be confirmed by the solubility in a solvent in which the uncrosslinked polymer is soluble. That is, since the polymer having a crosslinked structure has a component that is insoluble in a soluble solvent and does not dissolve uniformly, formation of a crosslinked structure can be determined. In the present invention, as the porous membrane made of vinylidene fluoride resin, a porous material having communication holes is used, which has a high ionic conductivity when impregnated with the electrolytic solution, and has a high impregnation property of the electrolytic solution. By high. The porosity of the porous membrane is preferably in the range of 10 to 95%, more preferably 20 to 90%, and still more preferably 40 to 85%. If it is less than 10%, the ionic conductivity when impregnated with the electrolytic solution is not sufficiently high, and if it exceeds 95%, it is difficult to obtain sufficient strength.

The thickness of the porous film is generally 1 to 50.
About 0 μm is used, preferably 10 to 300
μm, more preferably 20 to 100 μm. 1μ
If the thickness is less than m, the strength is not necessarily sufficient, and short-circuiting between the electrodes is liable to occur. If the thickness exceeds 500 μm, the effective electric resistance of the entire film becomes too high, and the energy density per volume when used in a battery is reduced. Tends to be lower.

In the present invention, the porous membrane made of vinylidene fluoride resin has pores communicating with each other on the front and back, and it is necessary that the specific propylene carbonate has the liquid permeability as described above. The structure is not particularly limited. For example, (1) a film having a denser layer than the inside on at least one surface and having a huge hole and a three-dimensional network structure inside, and (2) a film having a denser than the inside on at least one surface. (3) a film having a three-dimensional network structure on both the surface and the inside,
(4) a film having a two-layer structure comprising a dense layer on one surface and a layer comprising huge holes below the surface layer;
(5) A film having a three-layer or five-layer structure having a dense layer on at least both surfaces and having a layer composed of huge holes inside is exemplified. Here, the huge pore refers to a pore whose maximum major axis is 10% or more of the film thickness. Among these structures, the films (1), (2) and (3) are particularly preferable because of their good mechanical strength.

The surface pore size of the porous membrane cannot be unequivocally limited because the appropriate range varies depending on the properties of the electrode in the battery to be used, but it must be sufficiently smaller than the particle size of the active material or the like constituting the electrode. Is desirable for preventing an internal short circuit. On the other hand, in order to facilitate the impregnation with the electrolytic solution, it is advantageous to increase the pore size. Therefore, the average pore diameter on one surface is different from the average pore diameter on the other surface, and the ratio (ΦL / Φ) of the larger average pore diameter (ΦL) and the smaller average pore diameter (ΦS) is different.
S) is preferably 1 or more, in particular, when the ratio is 2
It is preferably in the range of 20 to 20. Outside this range, the amount of liquid permeation becomes small, or ΦL becomes too large, so that an internal short circuit is likely to occur. Such a hole diameter ratio (ΦL
Among the films having a ratio of (/ ΦS) of 2 to 20, a film having a slope structure in which the opening hole diameter gradually increases from one surface side to the other surface side is easy to impregnate the electrolyte solution and at the same time, causes an internal short circuit. It is hard to cause and because the above liquid permeation amount is large,
Particularly preferred.

The method for producing such a porous membrane made of vinylidene fluoride resin is not particularly limited, and a known melting method or wet method can be applied. For example, the method described in JP-A-3-215535 and the method disclosed in
No. 38207, JP-A-54-1638.
The method described in JP-A-58-91732, the method described in JP-A-63-296940, and the like can be used.

In the melting method, a polymer is melted together with a plasticizer, an inorganic powder and the like, formed into a flat film, and thereafter the plasticizer, the inorganic powder and the like are extracted and removed. In the wet method, the polymer is dissolved in a solvent together with a surfactant and additives, and the solution is coagulated by immersing the solution in a thin film in a non-solvent.
Solvents, surfactants, additives and the like are to be removed by washing. In the latter case, a film having a dense layer on both sides of the film can be manufactured by directly extruding and immersing in a non-solvent in the form of a flat film. By immersing in a non-solvent, one having a dense layer on one side can be manufactured. Further, by appropriately selecting conditions such as the composition of the stock solution, the composition of the non-solvent solution, and the temperature thereof, a product having no dense layer can be produced.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples. In addition, the measurement was performed as follows using the sample which performed the following pre-processing as needed. [Pretreatment] An operation of immersing about 20 cm ² of the diaphragm in 50 ml of ethanol (special grade reagent) for washing was performed three times.
Thereafter, vacuum drying was performed at 60 ° C. for 4 hours.

(1) Permeate amount of propylene carbonate
(Referred to below as the amount of liquid permeated by PC) Measurement of propylene in a glass sample bottle that has been sufficiently dried
The carbonate was separated and the pre-treated membrane was removed.
Impregnated with propylene carbonate at room temperature
With the sample bottle sealed and a temperature of 23 ° C ± 1 ° C.
Stored for 24 hours in an environment. The septum is then moved to diameter 2
Punched into 5mm, effective area 3.5cm ^TwoMembrane
Installed in filter holder and adjusted to 23 ± 1 ° C
Fill with propylene carbonate and leave at 1 atm for 5 minutes
Permeate weight of propylene carbonate when water pressure is applied
The amount was measured. From this value per hour and 1m^TwoHit
Liquid permeation amount (kg / m^Two/ Hr / atm) was calculated.

The operation relating to the above measurement is performed at a relative humidity of 5%.
The test was performed under the following dry air environment. Propylene carbonate was a special grade reagent (manufactured by Tokyo Chemical Industry Co., Ltd.) and used immediately after opening. (2) Measurement of Water Permeation An operation of immersing about 20 cm ² of the diaphragm sample in 50 ml of ethanol (special grade reagent) and washing was performed three times. Next, the diaphragm was punched out to a diameter of 25 mm, and was immersed in ultrapure water to replace with pure water. Subsequently, the membrane was incorporated into a membrane filter holder having an effective area of 3.5 cm ² , filled with ultrapure water, and the weight of the permeated liquid was measured when a static pressure of 1 atm was applied for 5 minutes. At this time, the temperature of the ultrapure water was measured, and from the true density and the viscosity of the pure water at that temperature, the amount of water per hour and per m ^{2 at} 25 ° C. (liter / m ² / hr / atm, 25 ° C.) ) Was calculated.

(3) Measurement of thickness A diaphragm sample was placed on a glass plate (1 mm thick) having a smooth surface.
The thickness was measured with a digital micrometer. The thickness of the two glass plates was separately measured, and the thickness was obtained by subtracting the value of the glass plate from the measured value. (4) Measurement of Porosity The membrane sample was immersed in ethanol (special grade reagent) to perform a hydrophilization treatment, and then immersed in pure water at room temperature for 2 hours or more to completely replace the voids with pure water. Next, after the water on the membrane surface was wiped off, the weight (A) of the membrane containing pure water in the voids was measured. Subsequently, the membrane sample was placed in a vacuum at 60 ° C. for 4 hours.
After drying for more than an hour, water in the voids was removed, and the weight (B) of only the polymer portion was measured. From these weights and the true specific gravity (dp, dw) of the constituent polymer of the membrane and water, it was calculated by the following equation.

Porosity (%) = ((AB) / dw) /
(B / dp + (AB) / dw) × 100 The true specific gravity (dw) of water was 1.0. (5) Cross-sectional Structure and Surface Average Pore Diameter The cross-sectional structure was obtained by freezing a diaphragm sample using liquid nitrogen, cutting it, and then cross-sectioning the cross-section with an SEM (SE manufactured by Hitachi, Ltd.).
M; S-800).

The surface average pore diameter was determined by observing the membrane surface using an SEM in the same manner as described above, and calculating the area-based average value for pore diameters having a size of 0.05 μm or more. (6) Ion conductivity At room temperature, the membrane sample was subjected to an electrolytic solution (ethylene carbonate /
Propylene carbonate / γ-butyrolactone 1:
(A solution in which LiBF ₄ was dissolved in a 1: 2 mixed solvent at a concentration of 1.5 mol / liter) to impregnate the electrolyte. An electrochemical cell was constructed by sandwiching the electrolyte impregnated diaphragm between stainless steel electrodes. Based on the normal AC impedance method, an AC was applied between the electrodes to measure the resistance component, and the ionic conductivity was calculated from the real impedance intercept of the Cole-Cole plot.

Incidentally, the measurement of the impedance was performed by EG & G
Company, using a 389 type impedance meter, frequency 1
It was performed at kHz. The impregnation of the electrolyte and the measurement operation are performed at a dew point of
The test was performed in a dry environment of 0 ° C. or less. (7) Battery Performance (Current Density Dependency) A secondary battery using the following electrodes was constructed and evaluated from its charge / discharge characteristics.

First, a slurry is prepared by mixing and dispersing LiCoO ₂ powder having an average particle size of 10 μm and carbon black in an N-methylpyrrolidone solution (5% by weight) of polyvinylidene fluoride (KF # 1100, manufactured by Kureha Chemical Industry Co., Ltd.). did.
The solid content weight composition in the slurry was LiCoO
₂ (89%), carbon black (8%) and polymer (3%). This slurry was applied to an aluminum foil by a doctor blade method, dried, and then pressed to a thickness of 110 mm.
A μm positive electrode sheet was prepared.

Next, a needle coke powder having an average particle diameter of 10 μm was dispersed in a carboxymethyl cellulose solution and a styrene-butadiene latex (L1571 manufactured by Asahi Kasei Kogyo Co., Ltd.) mixture to prepare a slurry. The weight composition of the solid content in the slurry was as follows: needle coke / carboxymethyl cellulose / styrene butadiene = 100/0.
8/2. The slurry was applied to a metal copper sheet by a doctor blade method, dried, and then pressed to a thickness of 120 μm.
m of the negative electrode sheet was produced.

As in the case of the measurement of ionic conductivity,
A diaphragm impregnated with an electrolyte (electrolyte-impregnated diaphragm) was prepared.
The positive electrode sheet and the negative electrode sheet are each cut into 2 cm square,
The electrolyte impregnated diaphragm was cut into 2.3 cm squares. Two electrode sheets were laminated so as to face each other with the electrolytic solution-impregnated diaphragm interposed therebetween. At this time, the non-opposing portions of the positive and negative electrode sheets were not formed. Further, a battery was formed by sandwiching and adhering a glass plate from the outside of the positive electrode and the negative electrode. Next, stainless terminals were attached to the positive electrode and the negative electrode of the battery, and sealed in a glass container. The above battery assembly operation is performed with the dew point-
The test was performed in a dry environment of 60 ° C. or less.

The battery was charged / discharged (Hokuto Denko, 1
01SM6), and charging and discharging were repeatedly performed. Charging was performed at 4.2V constant potential charging after constant current charging, and discharging was performed at 2.7V constant current discharging with a cutoff voltage of 2.7V. First, 1mA /
Charge and discharge were repeated 10 times at a current density of ² cm ² ,
Charge / discharge was repeated 10 times at a current density of mA / cm ² .
At this time, the ratio of the discharge capacity at the 20th (3 mA / cm ² ) to the discharge capacity at the 10th (1 mA / cm ² ) was obtained. Battery performance (%) = (20th discharge capacity) / (10th discharge capacity) × 100

[0040]

Example 1 Vinylidene fluoride-hexafluoropropylene copolymer (manufactured by Elf Atochem, Kynar 280)
1: product containing 12% by weight of hexafluoropropylene) 17
Parts by weight, polyvinylpyrrolidone (manufactured by BASF, K-3
0) A solution consisting of 15 parts by weight and 68 parts by weight of N-methylpyrrolidone (special grade reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared and cast on a glass plate at 50 ° C. Immediately 62 ℃ at 30 ℃
Immersed in an aqueous solution of N-methylpyrrolidone for coagulation,
After washing with water and ethanol, it was dried. Next, the porous film was irradiated with an electron beam (irradiation amount: 30 Mrad) to prepare a crosslinked porous film.

Observation of the cross section of the crosslinked porous membrane revealed that both surfaces had relatively dense layers, and the inside had a three-dimensional network structure. The average pore diameter on both surfaces was 0.1 μm and 1.7 μm, respectively, and the ratio was 17. The porous membrane has a thickness of 65 μm, a porosity of 75%, and a water permeability of 2300 (liter / m ² / hr / at.
m, 25 ° C.) and the PC liquid permeation amount is 80 (kg / m ² / hr /
atm). When the porous membrane was immersed in an electrolytic solution at room temperature, the porous membrane was impregnated within several seconds and became completely transparent. The ionic conductivity of this electrolyte impregnated membrane was 1.3 mS /
cm, and its battery performance was 93%.

[0042]

Example 2 The polymer was vinylidene fluoride-hexafluoropropylene copolymer (manufactured by Elphatochem, Kyna
r2850: a product containing 3% by weight of hexafluoropropylene), and a porous membrane was obtained in the same manner as in Example 1 except that the coagulating solution was changed to an 82% by weight aqueous solution of N-methylpyrrolidone. Next, the porous film is irradiated with an electron beam (irradiation amount 10 M).
rad) to form a crosslinked porous membrane.

Observation of the cross section of the crosslinked porous membrane revealed that both surfaces had relatively dense layers, and the inside had a three-dimensional network structure. The average pore diameter on both surfaces was 0.9 μm and 4.8 μm, respectively, and the ratio was 5.3. The porous membrane had a thickness of 45 μm, a porosity of 77%, and a water permeability of 2070 (liter / m ² / hr / at.
m, 25 ° C.), PC liquid permeation amount 180 (kg / m ² / hr)
/ Atm).

When the porous membrane was immersed in an electrolytic solution at room temperature, it was impregnated within several seconds and became completely transparent. The ionic conductivity of the electrolyte-impregnated membrane was 1.2 mS / cm, and the battery performance was 95%.

[0045]

Example 3 Vinylidene fluoride polymer (Kureha Chemical, K
F # 1000: homopolymer) 17.2 parts by weight, polyethylene glycol # 200 (manufactured by Wako Pure Chemical Industries) 11.5
A solution consisting of 0.8 parts by weight of polyoxyethylene (20) sorbitan monooleate (manufactured by Wako Pure Chemical Industries, reagent) and 70.5 parts by weight of dimethylacetamide (special grade reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared. Cast on a glass plate at ° C. Immediately immersed in 70 ° C. water to solidify,
After washing with ethanol, it was dried. Next, the porous film was irradiated with an electron beam (irradiation amount: 30 Mrad) to prepare a crosslinked porous film.

Observation of the cross section of the crosslinked porous membrane revealed that both surfaces had a relatively dense layer, and had a huge pore and a three-dimensional network structure inside. The average pore sizes on both surfaces were 0.1 μm and 0.3 μm, respectively, and the ratio was 3.0. This porous membrane has a thickness of 50 μm.
m, porosity 81%, water permeability 1090 (liter / m ² / hr / atm, 25 ° C.), PC liquid permeability 250
(Kg / m ² / hr / atm).

When the porous membrane was immersed in an electrolytic solution at room temperature, it was impregnated within a few seconds and became completely transparent. The ionic conductivity of the electrolyte-impregnated membrane was 1.1 mS / cm, and the battery performance was 92%.

[0048]

Example 4 Average primary particle system 16 μm, specific surface area 110
m ² / g hydrophobic silica (Aerosil R-972) 30
Parts by weight, 37 parts by weight of dioctyl phthalate and 3 parts by weight of dibutyl phthalate were mixed with a Henschel mixer, and the mixture was mixed with a vinylidene fluoride polymer (KF # 1000, manufactured by Kureha Chemical Co., Ltd.).
30 parts by weight of a homopolymer) were added and mixed again with a Henschel mixer. The mixture was mixed into pellets using a 30 mm twin screw extruder (manufactured by Toshiba Machine Co., Ltd.). Next, a thin film was obtained from the pellets using a flat film production apparatus in which a T die and a cooling roll were attached to a 30 mm twin screw extruder. The thin film was immersed in 1,1,1-trichloroethane to extract dioctyl phthalate and dibutyl phthalate, and then dried. Then, immersed in 50% ethyl alcohol aqueous solution,
After further immersion in water to make it hydrophilic, it was immersed in a 20% aqueous sodium hydroxide solution at 70 ° C. to extract hydrophobic silica. Next, it was sufficiently washed with water and dried to obtain a porous membrane.

Observation of the surface and cross section of the above porous film revealed that both the surface and the inside had a three-dimensional network structure. The average pore diameter on both surfaces was 0.8 μm and 1.9 μm, respectively, and the ratio was 2.4. This porous membrane has a thickness of 8
0 μm, porosity 73%, water permeability 4400 (l / m ² / hr / atm, 25 ° C.), PC liquid permeability 9
20 (kg / m ² / hr / atm).

When the porous film was immersed in an electrolytic solution at room temperature, it was impregnated within several seconds and became completely transparent. The ionic conductivity of the electrolyte-impregnated membrane was 1.2 mS / cm, and the battery performance was 93%.

[0051]

Example 5 The porous film obtained in Example 4 was irradiated with an electron beam (irradiation amount: 30 Mrad) to prepare a crosslinked porous film.
The structure, thickness, and porosity of the crosslinked porous film were the same as in Example 4. The water permeability of this crosslinked porous membrane is
4500 (liter / m ² / hr / atm, 25 ° C.) and the PC liquid permeation amount is 970 (kg / m ² / hr / at
m).

When the porous film was immersed in an electrolytic solution at room temperature, it was impregnated within a few seconds and became completely transparent. The ionic conductivity of the electrolyte-impregnated membrane was 1.2 mS / cm, and the battery performance was 94%.

[0053]

Comparative Example 1 Vinylidene fluoride-hexafluoropropylene copolymer (manufactured by Elf Atochem, Kynar 280)
1: product containing 12% by weight of hexafluoropropylene) 17
A solution consisting of 83 parts by weight of N-methylpyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd., special grade reagent) was prepared and cast on a glass plate at 30 ° C. After being kept in an environment of 30 ° C. and a relative humidity of 95% for 10 minutes, it was immersed in water at 30 ° C. to coagulate, washed with water and ethanol, and dried. Next, the porous film was irradiated with an electron beam (irradiation amount: 30 Mrad) to prepare a crosslinked porous film.

Observation of the cross section of the crosslinked porous membrane revealed that both surfaces had relatively dense layers, and the inside had a three-dimensional network structure. The average pore diameter on both surfaces was 1.7 μm and 5.0 μm, respectively, and the ratio was 2.9. The porous membrane has a thickness of 66 μm, a porosity of 70%, and a water permeability of 1070 (liter / m ² / hr / at.
m, 25 ° C.) and the PC liquid permeation amount is 24 (kg / m ² / hr /
atm).

When the porous film was immersed in an electrolytic solution at room temperature, it was impregnated within several seconds and became completely transparent. The ionic conductivity of the electrolyte-impregnated membrane was 1.2 mS / cm, and the battery performance was 31%.

[0056]

Comparative Example 2 The same polymer solution as in Example 1 was formed into a thin film from a T-die through a gear pump and extruded into a 25 wt% aqueous solution of N-methylpyrrolidone to be coagulated. Next, the resultant was washed with water and ethanol and then dried to obtain a porous membrane.
Further, the porous film is irradiated with an electron beam (irradiation amount: 30 Mrad).
Then, a crosslinked porous membrane was prepared.

Observation of the cross section of the crosslinked porous membrane revealed that both surfaces had a relatively dense layer, and had a huge void and a three-dimensional network structure inside. The average pore diameter on both surfaces was 0.1 μm and 0.1 μm, respectively, and the ratio was 1.0. The porous membrane has a thickness of 57 μm,
The porosity is 80%, and the water permeability is 1100 (liter / m
² / hr / atm, 25 ° C.)
/ M ² / hr / atm).

When the porous film was immersed in an electrolytic solution at room temperature, it took about 10 minutes to be completely transparent. The ionic conductivity of this electrolyte impregnated membrane was 1.3 mS /
cm, and the battery performance was 28%.

[0059]

Comparative Example 3 Vinylidene fluoride polymer (Kureha Chemical, K
A solution consisting of 17 parts by weight of F # 1000: homopolymer) and 83 parts by weight of N-methylpyrrolidone (special grade reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared and cast on a glass plate at 30 ° C.
Immediately, it was immersed in water at 30 ° C. for coagulation, washed with water and ethanol, and dried. Next, the porous film was irradiated with an electron beam (irradiation amount: 30 Mrad) to prepare a crosslinked porous film.

Observation of the cross section of the crosslinked porous membrane revealed that both surfaces had a relatively dense layer, and had a huge pore and a three-dimensional network structure inside. 15000
No pores were observed on both surfaces even when magnified twice. It is presumed that there is probably a hole of 0.01 μm or less. The porous membrane has a thickness of 40 μm, a porosity of 79%, and a water permeability of 37 (liter / m ² / hr / atm, 2
5 ° C), PC liquid permeation amount is 2 (kg / m ² / hr / atm)
Met.

When the porous membrane was immersed in an electrolytic solution at room temperature, it took about 20 minutes to become completely transparent. The ionic conductivity of this electrolyte impregnated membrane was 1.1 mS /
cm, and its battery performance was 25%.

[0062]

The porous membrane made of vinylidene fluoride resin of the present invention exhibits high ionic conductivity and exhibits high battery performance even at a large current density when used in a non-aqueous battery.
Therefore, the porous membrane made of vinylidene fluoride resin of the present invention is useful as a constituent material for non-aqueous batteries such as primary batteries and secondary batteries such as lithium batteries, and polymer batteries.

Claims (1)

[Claims] 1. A vinylidene fluoride resin having a communicating hole on both sides thereof and having a liquid permeation amount of propylene carbonate of 50 kg / hr / m ² / atm or more when a static pressure of 1 atm is applied at 23 ° C. A diaphragm for a non-aqueous battery, comprising a porous membrane.