JPH11149912A - Separator and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve battery performance and improve reliability when used for a battery or capacitor by using a porous film of which thickness of a layer is less than a specified value. SOLUTION: A porous film thickness of a layer is less than 15 microns. Polyethylene, polkypropylene or the like is employed as a porous film and is preferred as a polymeric compound. A separator is composed of porous films of same or different two or more kinds. A break elongation percentage in widthwise direction of the porous film of one layer is preferred to be 20% or more, and thereby, breakage during manufacture or use of the film or internal shorting due to expansion of pore diameter can be avoided. Thickness of one porous film is very thin, and poor in filming properties and handling properties. Therefore, a film slit by being bonded to a carrier is released from the carrier, is wound with positive and negative electrodes immediately after the release, and the separator is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator which can be used as a separator, particularly a battery separator suitable for non-aqueous solvent batteries such as lithium batteries and a separator for electrolytic capacitors.

[0002]

2. Description of the Related Art Generally, a separator having a thickness in the range of 25 to 200 μm has been used for a battery.

[0003]

However, such a thick separator has the following disadvantages. That is, the electrical resistance of the separator itself increases, and because of the increase in the volume occupied by the separator,
The electrode plate area was reduced, leading to a decrease in battery performance.
Further, as described in JP-A-8-111238, an electrolyte having substantially no flash point has been proposed,
As the safety of batteries is greatly improved, demands for thinner separators are increasing.

Conventionally, the thickness of a separator is set to, for example, 20
When the thickness is less than μm, the handling properties such as winding are deteriorated due to the decrease in the mechanical properties of the porous film, and the internal short circuit increases due to the breakage of the porous film and the increase in the pore diameter. And has a fatal disadvantage of lacking reliability.

[0005] An object of the present invention is to realize a novel separator which has solved the problems caused by such a thickness, and a method for producing the same.

[0006]

According to the present invention, there is provided a separator comprising a porous film having a thickness of less than 15 μm.

[0007] The thickness of the one layer is preferably 10 µm or less, more preferably 5 µm or less. On the other hand, the separator of the present invention is a separator characterized by being composed of two or more kinds of porous films of the same type, or a separator characterized by being composed of two or more types of porous films of different kinds. is there.

[0008] The method for producing a separator according to the present invention is characterized in that the porous film adhered to the support is peeled off from the support, and then the porous film is wound together with the electrode to produce a separator. This is a method for producing a separator.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

In the separator of the present invention, the polymer compound suitable for use as the porous film includes polyethylene, polypropylene, ethylene-propylene copolymer, poly (4-methylpentene) 1, polyoxymethylene, polystyrene, and dicyclopentadiene. Polymer compounds selected from polyolefins represented by polymers, polyesters, polyamides, fluorine-based polymers and modified products thereof are preferred, and in the case of the present invention, especially polyethylene, polypropylene, ethylene-propylene copolymer Polyolefins represented by belts, poly (4-methylpentene) 1, polyoxymethylene, polystyrene, dicyclopentadiene-based polymers, etc. are low cost, solvent resistant,
It is preferable from the viewpoint of toughness, low-temperature melting property, low-temperature deformability, and the like. Needless to say, various additives such as a crystal nucleating agent, a slipping agent, a stabilizer, an antioxidant, a viscosity modifier, an antistatic agent, a coloring agent, a pigment, and the like can be arbitrarily used in these polymer compounds. For example, crystallization nucleating materials include talc, kaolin, silicon oxide, alumina oxide, antimony oxide, titanium oxide, zinc oxide, clay, calcium carbonate,
Inorganic compounds such as barium sulfate, strontium sulfate, zinc white, magnesium hydroxide, calcium silicate, diatomaceous earth and carbon black, and organic compounds such as liquid crystalline polyester compounds can be used.

As a method for producing a porous film, for example, (1) a large amount of an inorganic substance or another polymer compound incompatible with the polymer is added to a polymer compound such as polyolefin, and the polymer is stretched. A method of forming voids, (2) a method of adding and adding a large amount of an organic compound and then extracting and stretching the organic compound, (3) a method of changing the crystal structure in stretching, and (4) a ladder (ladder) A method of stretching a specific crystal structure such as a structure, (5) a method of penetrating with a specific light beam such as a laser, (6) a mechanical method of penetrating with a heating needle or the like, and (7) a method of combining them. , Etc.

The average pore size of the porous film as the separator of the present invention is preferably 5 μm or less, more preferably 2 μm or less, most preferably 1 μm or less, for example, as small as 0.05 μm or more. A thing with a small distribution is good. This is because when the hole diameter exceeds 5 μm, the occurrence rate of short circuit between the electrodes increases, and when the hole diameter is less than 0.05 μm, the equivalent series resistance increases. The higher the porosity is 30% or more, preferably 40 to 65%, the lower the equivalent series resistance, and a higher electromotive force can be obtained.

From such a viewpoint, the method for producing the porous film is not particularly limited, but the extraction method (2) (for example, Japanese Patent Publication No. 2625798, Japanese Patent Application Laid-Open No. 58-59072, and 58-59072
JP, JP-A 1-1113422, JP-A 6-2
No. 08849), the crystal transition method of (3),
The crystal deformation method (4) (for example, Japanese Patent Publication No. 50-2176, Japanese Patent Publication No. 46-40119) is preferable. In addition,
The outline of the extraction method (2) is as follows: 100 parts by weight of a polymer compound such as polyolefin is added to dicyclohexyl phthalate,
80 to 180 parts by weight of an organic solid such as triphenyl phosphate, phthalic acid ester such as dioctyl phthalate, sebacic acid ester, phosphoric acid ester such as tributyl phosphate, liquid paraffin, paraffin wax, and mineral oil are mixed. After melt extrusion, the organic solid contained in the polymer compound is converted into a good solvent, for example, trichloroethylene, trichloromethane, trichloroethane,
After extracting and drying 95% or more with an organic solvent typified by toluene, ethyl acetate, methyl ethyl ketone, acetone, methanol, etc., it is made porous by known stretching. The outline of the crystal transition method (3) is as follows. An additive that easily generates a β-crystal, which is a metastable crystal, is added to 100 parts by weight of a polymer compound such as polyolefin.
The film containing 10% by weight is cast at a relatively high temperature of 80 to 140 ° C., and a film containing as much fine and crystallized β crystal as possible is made porous by β → α transition by stretching. Further, the thickness of one porous film is 15 μm.
It is important that it is less than 10 m.
It is a separator having a thickness of not more than 5 μm, more preferably not more than 5 μm.

[0014] In such a thin porous film, the mechanical properties of the porous film are deteriorated, so that not only the handling property is deteriorated at the time of winding a capacitor or a battery, but also the porous film is not used in practical use. In reality, there is a fatal drawback that the internal short circuit increases due to breakage or an increase in the hole diameter, resulting in a lack of reliability.
One thick porous film of about 100 μm has been used, and the thin porous film was not used.
To remedy these drawbacks due to thin films,
Although the above-mentioned drawbacks cannot always be solved by simply using a single thin film, two or more, preferably five or more, more preferably ten or more thin films of the same type or different types, each having a total thickness of 20 μm Less than,
The problem can be solved by forming a laminated porous film having a thickness of preferably 15 μm or less.

[0015] As described above, the object of the present invention is to provide a separator composed of two or more kinds of porous films of the same kind, or a separator composed of two or more kinds of different kinds of porous films. More specifically can be achieved.

This means that, for example, the same type of
In the case of a separator having a total thickness of 5 μm by laminating sheets, even if one porous film of 1 μm is torn,
Even if the pore diameter increases, the probability that the remaining four porous films are damaged in the same manner is considered to be small, so that an internal short circuit occurs in the battery as a whole, and the internal short circuit increases. It is presumed that the reliability will increase because there is no such thing. Of course, such an adhesive layer between the layers of the laminated porous film may or may not be provided, but it is preferable that the adhesive film is adhered because the handleability is good.

Such an adhesive layer has a low yield strength,
A layer of a material having a large elongation at break is preferred. As described above, two or more films may be of the same type or different types. However, mechanical properties such as stiffness, elongation at break, tear propagation resistance, slippage, and handling properties, and thermal properties such as melting temperature and heat shrinkage temperature. Porous films having different characteristics such as mechanical properties are often better in terms of handleability, resistance to breakage, and difficulty in increasing the pore size. In particular, the elongation at break in the width direction of one porous film is 20% or more,
Preferably, the large value of 50% or more makes it difficult for the porous film to be broken or the pore diameter to be increased at the time of the pressing step or the winding step in the production of the porous film, and further to the time of use, so that an internal short circuit is unlikely to occur. It is because it becomes.

As described above, the thickness of one porous film is very thin, that is, 0.01 to 5 μm, so that the film forming property and the handling property are poor. Therefore, once a laminated film consisting of a porous film adhered to the support is formed, slitting, surface treatment, etc. are handled as the laminated film with the support, and then only the porous film is By removing the porous film from the support in a necessary step and using it, the handleability and the like are improved. Specifically, the present invention also provides a method for producing a separator in which a porous film which has been slit while being adhered to a support is peeled off from the support and immediately thereafter wound with positive and negative electrodes. The material of the support film is
Co-forming properties such as melt viscosity with the porous film, spinnability, stretchability, wetting tension, peeling tension, mechanical properties, surface properties,
Depends on the characteristics such as the price and the like, but when the porous film is a polyolefin such as polypropylene,
As a support, polyethylene terephthalate (PE
Polyesters such as T), polyamides such as nylon 6, and polyphenylene sulfide (PPS)
Materials are preferred. The thickness of the support is not particularly limited, but is preferably in the range of about 1 to 30 μm. Conversely, if the thickness exceeds 30 μm, the economics of film formation and winding may be deteriorated. Of course, the tension at the time of peeling (180-degree peel test) is preferably a small value of about 0.01 to 100 g.
Suitable release agents in the support film, for example, silicone oil and its modified products such as amino, carboxyl, oxyalkylene, paraffin wax, higher fatty acid,
Fatty acid compounds such as oxy fatty acids and fatty acid amides, and esters such as polyhydric alcohol esters and fatty acid lower alcohols are preferably added as necessary.

Next, an example of a method for producing the porous film for a separator of the present invention will be described.

As the porous film for a separator,
For example, a three-layer laminated film composed of PP / PEN / PP composed of a polypropylene (PP) film and a polyethylene naphthalate (PEN) film as a support is prepared. The electrical properties of the PP resin used at this time are emphasized. For this reason, the PP resin or the like usually used for capacitors is used. PP with low viscosity
And the melt index MI at 230 ° C. is 1
A relatively large value of about 50 g / min is better. of course,
It is better not to add any additives to the PP resin as much as possible. The material PEN of the support is selected from the viewpoints of co-stretchability with PP, peelability, handleability, surface smoothness, and the like. PP and PEN resins are supplied to a melt extruder, respectively, and melted at 260 to 310 ° C. so that three layers consisting of (PP + organic solid) / (PEN + release agent such as wax) / (PP + organic solid) are formed. The laminated sheet is laminated in a three-layer laminated adapter, supplied to a usual single-layer T-die die, and cooled while being in close contact with a cooling drum while applying an electrostatic charge to the molten sheet to obtain a cast sheet. The organic solid contained in the PP of both surface layers of the three-layer sheet is converted into a good solvent,
For example, after being almost completely extracted and dried with an organic solvent represented by trichloroethylene, trichloromethane, trichloroethane, toluene, ethyl acetate, methyl ethyl ketone, acetone, methanol, etc., it is supplied to a stretching machine to be 1.3 to 8%. The PP is made to be about 0.0 times longitudinally or horizontally uniaxially or biaxially vertically or horizontally to make the PP porous, and heat-fixed if necessary. At this time, in order to make the elongation at break in the width direction of the porous film 20% or more, preferably 50% or more, it is better to stretch the film in both longitudinal and transverse axes. Further, it is preferred that the PP porous layers on both surfaces are subjected to a hydrophilic treatment. As the hydrophilization treatment, various methods such as a nonionic surfactant treatment, a corona discharge treatment, a plasma treatment, and an ultraviolet treatment can be used in combination. When used as a separator for batteries or capacitors, the three-layer laminated sheet is slit in accordance with the outer diameter used. Immediately after the surface-layer PP porous film of the three-layer laminated film wound around the reel is peeled off from the support PEN, the film is wound so as to become a positive electrode thin film / PP porous film / negative electrode thin film / PP porous film. Sandwiched between the electrodes, as an electrolyte, substantially flash point of typical electrolytes such as propylene carbonate, diethyl carbonate, ethylene carbonate, dimethoxyethane, propylene carbonate and mixtures thereof, and trimethyl phosphate and mixtures thereof; It is impregnated with a non-flammable electrolyte that does not have it to make a separator for batteries. The thus obtained separator according to the present invention is effective as a compact and highly reliable electrical article, for example, as a separator for batteries and capacitors.

[0021]

[Measurement method of physical properties] (1) Intrinsic viscosity [η] (dl / g) of polyester resin: 25 ° C., and o-chlorophenol was used as a solvent and determined by the following equation.

[Η] = lm [ηsp / c] Specific viscosity ηsp
Is obtained by subtracting 1 from the relative viscosity ηr. c is the concentration.

(2) Melt index MI (g / 10
Min): measured at 230 ° C. for polypropylene (PP) and 190 ° C. for polyethylene (PE) under a load of 2 kg according to JIS K7210.

(3) Average pore size (μm): ASTM-F-
Evaluation was performed using ethanol according to 316-80. The measurement upper limit pressure is 10 kgf / cm ² .

(4) Average porosity (%): The pore size observed from SEM observation was calculated by calculating the pore area by an image analyzer and expressed as a ratio to the total area.

(5) Elongation at break (%): JIS K678
Measure at 23 ° C. according to 2.

(6) Thermal characteristics: using a scanning calorimeter DSC, sample weight 10 mg, heating rate 20 ° C. under nitrogen atmosphere
/ Min, and the starting temperature at which the baseline changes is Tg, the exothermic peak temperature due to crystallization is Tcc, and the endothermic peak temperature due to crystal melting is Tm. After the completion of the melting, the heating is continued as it is, and the temperature is maintained at Tm + 25 ° C. for 3 minutes, then cooled at a rate of 10 ° C./min, and the exothermic peak temperature due to crystallization is defined as Tmc.

(7) Film forming property: Judgment was made based on the frequency of breakage during stretching and the slit yield.

The criteria are as shown in Table 1.

[0030]

[Table 1] (8) Rollability: Judgment was made based on the ease of cutting and wrinkling of the separator when wound around the battery.

The criteria are as shown in Table 2.

[0032]

[Table 2] (9) Reliability as a battery: The battery was used continuously for a long period of 100 days, and was judged from the heat generation state of the battery.

The criteria are as shown in Table 3.

[0034]

[Table 3]

[0035]

EXAMPLES Examples and comparative examples are shown below.

Example 1 Polypropylene (PP) resin (MI: 15, tacticity index II: 98, dicyclohexyl phthalate (DCHP) as an additive contained 60% by weight), and polyethylene 2,6 naphthalate (PEN) resin ( Intrinsic viscosity [η]
0.75, and 0.15% by weight of a polyoxyethylene 80% modified silicone oil having a viscosity of 20 Pa · s as an additive) are supplied to a two-layer fusion laminating apparatus, and a two-layer film made of PP / PEN is subjected to T-die. The PP surface was extruded from a die, and the PP surface was tightly cooled and solidified while being applied with an electrostatic charge to a cast drum kept at 80 ° C. After almost completely extracting and drying the organic solid DCHP contained in the PP of the surface layer of the two-layer sheet with a trichloroethylene solvent that is a good solvent, the organic solid DCHP is supplied to a simultaneous biaxial stretching machine and fed in the longitudinal direction. The PP is stretched 4 times and 2.5 times in the width direction at 145 ° C., respectively, to make the PP porous, and then heat-fixed at 155 ° C. while relaxing 8% in the vertical direction to form a support having a thickness of 20 μm. On the PEN film layer, a 2 μm thick PP porous film 2
A 5 μm laminated film was obtained. Further, the PP porous layer was treated with a nonionic surfactant to perform a hydrophilic treatment.

In order to use the porous PP film of the two-layer laminated film as a separator for a lithium battery, the two-layer laminated sheet was slit to 35 mm in accordance with the outer diameter used. 2 wound on the reel
While peeling the surface PP porous film of the layer laminated film from the support PEN with a peeling force of 0.2 g / cm,
Immediately after the peeling, the positive electrode thin film electrode / PP porous film /
A negative electrode thin film electrode / PP porous film was wound and sandwiched between the electrodes, and was impregnated with a propylene carbonate electrolyte and a trimethyl phosphate electrolyte as an electrolyte to form a battery separator.

As a result, as shown in Table 4, the separator was excellent in handleability at the time of winding and the like and high in reliability as a battery.

Example 2 In Example 1, PEN was laminated and formed into a film. However, in this example, a 5 μm porous film made of only PP was formed in the same manner as in Example 1 except that the PEN support of Example 1 was not used. A film was formed and used as a battery separator.

As shown in Table 4, as shown in Table 4, although the handling property at the time of winding and film formation was poor, the reliability as a battery was slightly low when the battery was evaluated without considering the productivity. Was in a range that can be used sufficiently.

[0041]

[Table 4] Rather than using PP alone for film formation and winding,
It can be seen that, when the film is formed and wound together with a support such as PEN, not only the film forming property but also the performance as a battery is greatly different. The reason for this is not clear, but PE
It is considered that the N support plays an advantageous role in the electrical properties and surface properties of the PP porous film.

Example 3 The procedure of Example 1 was repeated, except that the thickness of the PP porous film formed in Example 1 was changed from 5 μm to 1 μm.
Porous film (1 μm) / PEN support (20 μm)
The 21 μm laminated film is subjected to film forming and hydrophilizing treatment,
A reel slit to 5 mm was prepared. From the five-layered two-layer laminated film reel wound around the reel, the surface PP porous film was each 0.1 g from the support PEN.
/ PP, and immediately after the peeling, five PP porous films are superimposed to form a positive electrode thin film electrode / 5.
Wound and sandwiched between electrodes so as to form a sheet of PP porous film / negative electrode thin film electrode / five sheets of PP porous film, and impregnated with propylene carbonate electrolyte and trimethyl phosphate electrolyte as electrolyte, For use as a separator.

As shown in Table 2, the results showed that the handleability during winding and the like and the reliability as a battery were high.

Example 4 Polypropylene PP Resin (MI = 2, Stereoregularity Index II)
Is 96, and dicyclohexyl phthalate (D
CHP)) and low-density polyethylene L
D-PE resin (MI: 0.1, melting point Tm: 102 ° C., density: 0.925 g / CC, containing 55% by weight of dicyclohexyl phthalate (DCHP) as an additive) and (P
P / PE) n (where n = 10) so that multiple layers could be stacked at once in a melt film forming process using a Kenix mixer. This melt and polyethylene 2,6 naphthalate PEN resin (intrinsic viscosity [η] 1.05, polyoxyethylene 80% having a viscosity of 15 Pa · s as an additive)
(Modified silicone oil added at 0.2% by weight) in two layers and extruded from a T-die die.
The PP surface was closely adhered to the cast drum kept at ℃ and cooled and solidified. The organic solid DCHP contained in the surface PP layer and PE layer of the two-layer sheet is almost completely extracted and dried with a good solvent, trichloroethylene solvent, and then supplied to a simultaneous biaxial stretching machine. After stretching at 4.5 and 2.0 times at 145 ° C. in the longitudinal and width directions, respectively, to make the PP film and the PE film porous, the material is relaxed by 5% in the longitudinal direction at 160 ° C. After heat setting, 5 μm thick on a support PEN film layer having a thickness of 20 μm.
To obtain a laminated film having a thickness of 25 μm, on which a porous film composed of PP / PE multilayers was laminated. Further, the porous layer composed of the PP and PE multilayers was treated with a nonionic surfactant to give a hydrophilic treatment.

The thickness of the PP layer of the laminated film is 0.4 μm.
In order to use a 10-layer multi-layer porous film having a thickness of 0.1 μm and a single layer of PE as a separator for a lithium battery, the laminated sheet with a support was slit to 45 mm in accordance with the outer diameter used. The 10-layer laminated film composed of PP and PE wound on the reel was peeled off from the PEN as a support with a peeling force of 0.1 g / cm or less.
P / PE porous film / negative electrode thin film electrode / PP / PE porous film, wound and sandwiched between electrodes, impregnated with propylene carbonate electrolyte and trimethyl phosphate electrolyte as electrolyte, for battery As a separator.

As a result, as shown in Table 5, the handleability at the time of winding and the like and the reliability as a battery were high.

[0047]

[Table 5]

[0048]

The separator of the present invention has a high performance such as a battery because it is thin, and can be miniaturized. Further, since the separator is a laminated / laminated film of two or more layers, it can be used as a battery or a capacitor. High reliability can be obtained.

Claims (12)

[Claims] 1. A separator comprising a porous film having a thickness of less than 15 μm. 2. A separator comprising two or more kinds of porous films of the same kind. 3. A separator comprising two or more different types of porous films. 4. The separator according to claim 2, wherein two or more types of porous films are adhered to each other. 5. The separator according to claim 1, wherein the porous film has a breaking elongation in the film width direction of 20% or more. 6. The separator according to claim 1, wherein the porous film is obtained by peeling the porous film adhered to the support from the support. . 7. The porous film is made of polyethylene, polypropylene, ethylene propylene copolymer, poly (4-methylpentene) 1, polyoxymethylene, polystyrene, polyolefin represented by dicyclopentadiene-based polymer, polyester, polyamide, fluorine-based. 7. A polymer compound film selected from a polymer and a modified product thereof, wherein the film is a polymer compound film.
The separator as described. 8. The method according to claim 1, wherein the separator is a separator for an electrolytic capacitor.
The separator according to 4, 5, 6 or 7. 9. The separator according to claim 1, wherein the separator is a battery separator. 10. The separator according to claim 9, wherein the separator is used with an electrolyte which does not ignite at least at 100 ° C. 11. The separator according to claim 1, wherein the separator is a separator for a separation membrane.
Or the separator according to 7. 12. A porous film adhered to a support,
A method for producing a separator, comprising peeling the porous film together with an electrode from the support, and then producing a separator.