JP4377553B2 - Electric double layer capacitor separator - Google Patents

Description

【００１６】
（内部抵抗の測定）
電極として、粒状活性炭、カーボンブラック及びポリテトラフルオロエチレンを混ぜて練り上げたもの、集電極としてアルミ箔、セパレータとして各実施例及び比較例のセパレータ、及び電解液としてテトラエチルアンモニウム・テトラフルオロボーレイトをプロピレンカーボネートに溶解させたものを用意した。
次いで、これら材料から各セパレータ毎にコインセル型の電気二重層キャパシタを作製した後、それらの内部抵抗を測定した。これらの結果は表１に示す通りであった。なお、内部抵抗が３．５Ω未満であれば、イオン透過性に優れていると判断した。
この表１から明らかなように、本発明のセパレータは抵抗値が３．２Ωよりも低い、イオン透過性の優れるものであった。
なお、比較例３のセパレータを使用したコインセル型の電気二重層キャパシタは、漏れ電流があり、不安定なものであった。
【００１７】
（引張り強度の測定）
各実施例及び比較例のセパレータから試験片（幅：１５ｍｍ、長さ：２００ｍｍ）を採取した後、ＪＩＳ Ｐ−８１１３に準じて引張り強度を測定した。この結果も表１に示す通りであった。なお、引張り強度は４Ｎ／１５ｍｍ幅以上あれば、実際に使用することができる。
この表１から明らかなように、本発明のセパレータは引張り強度が９Ｎ／１５ｍｍ幅以上の強度的にも優れるものであった。
【００１８】
【発明の効果】
本発明のセパレータは漏れ電流を生じることなく電極間の電気絶縁性、イオン透過性、及び強度的に優れている。また、電気二重層キャパシタの一定体積中におけるエネルギー密度を高めることができる。
本発明のセパレータを構成するフィブリルを有する繊維が、融解温度又は炭化温度が３００℃以上の樹脂から構成されていると、電気二重層キャパシタを製造する上で好適である。
本発明のセパレータを構成するいずれの成分も熱融着していないと、皮膜を形成していないためイオン透過性が更に優れている。
本発明のセパレータが湿式不織布からなると、繊維の均一分散性に優れているため、電気絶縁性に関して信頼性のより高いものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a separator for an electric double layer capacitor.
[0002]
[Prior art]
Electric double layer capacitors have a relatively large capacity, and have a long service life and quick charge / discharge. Therefore, in addition to conventional applications such as power supply smoothing and noise absorption, personal computer memory backup power supplies and secondary power supplies In recent years, it has been used as a secondary battery for electric vehicles.
This electric double layer capacitor has a structure in which a pair of electrodes are immersed in an ionic solution. When a voltage is applied to the electric double layer capacitor, ions having the opposite sign to the electrode are distributed in the vicinity of the electrode to form an ion layer, while charges having the opposite sign to the ion are accumulated inside the electrode. Next, when a load is connected between the electrodes, the charges in the electrodes are discharged, and at the same time, ions distributed in the vicinity of the electrodes are separated from the vicinity of the electrodes and return to the neutralized state.
In such an electric double layer capacitor, if a pair of electrodes come into contact with each other, it becomes difficult to form an ion layer in the vicinity of the electrodes. Therefore, a separator is usually disposed between the pair of electrodes. This separator needs to be excellent in ion permeability in addition to having electrical insulation between the electrodes as described above. In order to excel in the electrical insulation between the electrodes, which is the former requirement, the separator preferably has a high surface density and a large thickness. However, when the surface density of the separator is high and thick in this way, the ion permeability is hindered and the capacity tends to decrease, and the volume occupied by the separator in a certain volume increases, and it can exist in the certain volume. Since the amount of electrodes that can be reduced, it becomes difficult to increase the energy density in a certain volume, and it has not been possible to use in practice.
Conversely, if a separator with a low surface density and a low thickness is used to increase ion permeability, the electrical insulation between the electrodes will be reduced, leading to instability such as leakage current. Since the strength also tends to decrease, it is difficult to handle. For this reason, a method has been proposed in which a fiber that can be heat-sealed is included as a fiber constituting the separator in order to improve strength, and this heat-fusible fiber is heat-sealed. The separator is made of heat-sealable fibers that are heat-sealed, so that the surface density and thickness are reduced in order to improve ion permeability. The permeability was poor.
[0003]
[Problems to be solved by the invention]
The present invention has been made to solve the above-mentioned problems, and is an electric double layer capacitor that is excellent in electrical insulation, ion permeability and strength between electrodes, and can increase energy density in a constant volume. An object of the present invention is to provide a separator.
[0004]
[Means for Solving the Problems]
The separator for an electric double layer capacitor of the present invention (hereinafter referred to as “separator”) includes a fiber having a fibril made of para-type wholly aromatic polyamide (hereinafter referred to as “fibril fiber”) and a fineness of 0.11 dtex (decitex). fine and a polyester fiber, in areal density is 20 to 40 g / ^{m 2,} a thickness of 30 to 50 [mu] m, apparent density of fibers sheet of ^{0.56g / cm 3 ~0.8g / cm 3} . The separator of the present invention has a certain thickness of 30 μm or more, and since it can take a dense structure with fibril fibers and fine polyester fibers, it does not cause a leakage current, and can be electrically insulated between electrodes. Are better. It should be noted that, due to the presence of fine polyester fibers, the thickness is as thin as 30 to 50 μm, and the apparent density is 0.8 g / cm ³ or less and an extremely dense structure is not adopted, the ion permeability is reduced. Also excellent. In addition, since the fibrils of the fibril fibers are entangled, the surface density is 20 g / m ² or more, and the apparent density is 0.56 g / cm ³ or more, the structure is excellent in strength. Furthermore, since the surface density is 40 g / m ² or less and the thickness is 50 μm or less, the energy density in a constant volume can be increased. Since the fiber having the fibril is made of para-type wholly aromatic polyamide and the entire separator is excellent in heat resistance, when manufacturing an electric double layer capacitor, it is possible to remove moisture at a high temperature after assembling from each material. Therefore, it is suitable for manufacturing an electric double layer capacitor. Moreover, the fibril fiber which consists of para type | system | group fully aromatic polyamide is excellent also in affinity with electrolyte solution, and there exists an effect that it is excellent in ion permeability. If any of the components constituting the separator for an electric double layer capacitor is not heat-sealed, the film does not form and the ion permeability is further improved. When the fiber sheet is made of a wet nonwoven fabric, it is excellent in the uniform dispersibility of the fibers, and therefore has higher reliability in terms of electrical insulation.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Since the separator of the present invention can take a dense structure in which fibrils of fibril fibers are entangled, it is excellent in strength and also in electrical insulation.
This fibril fiber is a fiber in which an infinite number of fine fibers are generated from one fiber, and may be composed of only fine fibers, or a portion in which fine fibers are bundled in addition to fine fibers. It may be included, but if it contains fibril fibers including a portion in which fine fibers are bundled in addition to fine fibers as in the latter, it is excellent in strength, and the fine polyester fibers described later It can be suitably used because it exhibits excellent ion permeability due to its synergistic effect.
Although this fibril fiber may be comprised from what kind of resin, when it comprises from melting | fusing temperature or carbonization temperature 300 degreeC or more, it is suitable when manufacturing an electrical double layer capacitor.
For example, in an electric double layer capacitor using an organic electrolyte, if an individual material (for example, a collector electrode, an electrode, a separator, etc.) contains moisture, an electric double layer capacitor having a high withstand voltage or an electric double layer having a high energy density. Since it is difficult to manufacture a multilayer capacitor, each material needs to be sufficiently dried. Conventional separators made of polypropylene fibers and separators made of cellulose pulp have a lower heat-resistant temperature compared to other materials (eg, collectors, electrodes, etc.). If the separator is dried at a temperature of 150 ° C. or higher after assembling, the separator is significantly deteriorated such as melting or carbonizing. Therefore, it is difficult to simultaneously dry these materials after assembling. Therefore, it is sufficient to assemble the individual materials after sufficiently drying them, but there is a problem that it takes too much time to assemble the individual materials after they are sufficiently dried.
Therefore, when the fibril fiber constituting the separator is made of a resin having the melting temperature or the carbonization temperature as described above, after the collector electrode, the electrode and the separator are assembled, they are simultaneously dried at a temperature of 150 ° C. or more. Therefore, an electric double layer capacitor having a high withstand voltage and an electric double layer capacitor having a high energy density can be easily manufactured.
The “melting temperature” refers to a temperature obtained from a differential thermal analysis curve (DTA curve) obtained by differential thermal analysis defined in JIS K7121. The “carbonization temperature” refers to a temperature obtained by thermogravimetry as defined in JIS K 7120.
Examples of the “resin having a melting temperature of 300 ° C. or higher” include polytetrafluoroethylene, polyphenylene sulfide, and the like. Examples of the “resin having a carbonization temperature of 300 ° C. or higher” include meta-type wholly aromatic polyamide, para-type wholly aromatic polyamide, polyamideimide, aromatic polyetheramide, polybenzimidazole, wholly aromatic polyester, and the like. Can do. Among these, meta-type wholly aromatic polyamide or para-type wholly aromatic polyamide is excellent in affinity with the electrolyte solution, and can be preferably used, and para-type wholly aromatic polyamide having a higher carbonization temperature is more preferable. is there.
Such fibril fibers are preferably contained in the fiber sheet in an amount of 20% by mass or more, more preferably 50% by mass or more so as to be excellent in strength and excellent in electrical insulation. On the other hand, it is preferably 95% by mass or less, more preferably 90% by mass or less from the relationship with the fine polyester fiber described later.
In addition, the fibril fiber does not need to be one type and may include two or more types. When two or more kinds of fibril fibers are thus included, the total mass is preferably within the above range.
[0006]
In addition to the fibril fibers as described above, the separator of the present invention includes fine polyester fibers having a fineness of 0.45 dtex or less, thereby forming fine pores with excellent ion permeability.
If the fine polyester fiber has a fineness of more than 0.45 dtex, the diameter of the formed pores becomes large, and the electrical insulation tends to be remarkably deteriorated. A more preferred fineness is 0.35 dtex or less, a further preferred fineness is 0.25 dtex or less, and a most preferred fineness is 0.15 dtex or less. The lower limit is not particularly limited, but is preferably about 0.01 dtex. The “fineness” refers to a value obtained by the method A defined in JIS L 1015.
Since the softening temperature of the fine polyester fiber is about 240 ° C., if the fibril fiber is composed of a resin having a melting temperature or a carbonization temperature of 300 ° C. or more, individual materials (for example, collecting electrodes, electrodes, separators) Etc.) can be dried at the same time, which is suitable for manufacturing an electric double layer capacitor.
The “softening temperature” is a temperature that gives a starting point of a melting endothermic curve in a DSC curve obtained by heat flux differential running calorimetry (DSC, heating temperature 10 ° C./min) specified in JIS K 7121. Say.
The fiber length of the fine polyester fiber of this invention is not specifically limited, It changes with the aspects of a fiber sheet. When the fiber sheet of the present invention is made of a suitable wet nonwoven fabric, the fiber length is preferably about 1 to 25 mm, more preferably about 3 to 20 mm.
This fiber length refers to the length obtained by the method B (corrected staple diagram method) of JIS L 1015.
The cross-sectional shape of the fine polyester fiber does not need to be circular, and may be non-circular (for example, an ellipse, an ellipse, a star, an alphabet such as Y or X, or a plus).
Such fine polyester fibers are preferably contained in an amount of 5 mass% or more, more preferably 10 mass% or more in the fiber sheet so that the ion permeability is excellent. On the other hand, from the relationship with the above-mentioned fibril fiber, it is preferably 80 mass% or less, and more preferably 50 mass% or less.
The fine polyester fiber does not need to be one type, and may contain two or more types of fine polyester fibers that differ in terms of fiber diameter and / or resin composition. When two or more kinds of fine polyester fibers are thus included, the total mass is preferably within the above range.
[0007]
The separator of the present invention is composed of a fiber sheet containing fibril fibers and fine polyester fibers as described above, and the embodiment of the fiber sheet can be, for example, a woven fabric, a knitted fabric, a nonwoven fabric, or a composite thereof. Among these, it is preferable that it is a nonwoven fabric which can make thickness thin, and it is more preferable to consist of a wet nonwoven fabric excellent in the uniform dispersibility of a fiber, excellent in electrical insulation, and having high reliability.
In particular, the separator preferably has two or more fiber layers having the same fiber orientation or different fiber orientations so as to be excellent in denseness, electrical insulation, ion permeability and strength. Furthermore, it is more preferable that it is composed of two or more fiber layers and the fiber orientations of adjacent fiber layers are different so as to be excellent in electrical insulation.
[0008]
The separator of the present invention basically comprises fibril fibers and fine polyester fibers as described above, but may contain fibers other than these fibers as long as the function of these fibers is not impaired.
[0009]
It is preferable that none of the components (for example, fibril fibers, fine polyester fibers, etc.) constituting the separator of the present invention be heat-sealed. Since the film is not formed by not being thermally fused as described above, the ion permeability is excellent.
[0010]
The separator of the present invention is made of the fiber as described above, has a surface density of 20 to 40 g / m ² , a thickness of 30 to 50 μm, an apparent density of more than 0.5 g / cm ³ , and 0.8 g / cm. ³ or less.
When the surface density of the separator is less than 20 g / m ² , the strength tends to be weak, and when it exceeds 40 g / m ² , the thickness tends to increase, which is not only disadvantageous in terms of energy density, but also has a disadvantage. This is because the coating density tends to be high and the ion permeability tends to be poor, so a more preferable surface density is 25 to 35 g / m ² .
When the thickness of the separator is less than 30 μm, it becomes difficult to exhibit sufficient electrical insulation, and there is a tendency to become unstable such as leakage current. When the thickness exceeds 50 μm, in a constant volume This is because the volume occupied by the separator tends to increase and the energy density tends not to be increased, so a more preferable thickness is 35 to 45 μm.
When the apparent density of the separator is 0.5 g / cm ³ or less, the strength tends to be inferior. When the apparent density exceeds 0.8 g / cm ³ , the structure becomes too dense and the ion permeability is reduced. Since it tends to be inferior, a more preferable apparent density is 0.6 to 0.75 g / cm ³ .
“Area density” in the present invention refers to the basis weight obtained based on the method specified in JIS P 8124 (paper and paperboard—basis weight measurement method), and “thickness” is a value measured by the method specified in JIS B 7502. That is, the value measured by the outer micrometer at the time of 5N load. Further, the “apparent density (D)” is a value obtained by dividing the surface density (W, unit: g / cm ³ ) by the thickness (T, unit: cm), that is, a value obtained from the following equation.
D = W / T
[0011]
The separator of this invention can manufacture a fiber sheet by a conventional method, and can use the fiber sheet as a separator.
For example, a suitable wet nonwoven fabric can be produced as follows.
First, at least fibril fibers and fine polyester fibers are prepared. Since these fibril fibers and fine polyester fibers are both commercially available, they can be easily obtained.
Then, using these fibers, a conventional wet method (for example, a horizontal long net method, an inclined wire type short net method, a circular net method, a forward flow net / reverse flow net combination method, a forward flow net / circular net) Wet fiber webs with a surface density of 20 to 40 g / m ^{2 by} the former combination method, reverse flow net / circular net former combination method, short net / circular net combination method, or long net / circular net combination method). Form. When forming this wet fiber web, bubbles are generated by adding a thickener to maintain a uniform dispersion state of the fibers, adding a surfactant to increase the affinity between water and fibers, stirring, etc. An antifoaming agent may be added to remove the odor.
The wet fiber web can then be dried to remove the moisture and obtain a wet nonwoven fabric. The drying temperature is a temperature at which the fibers constituting the wet fiber web do not melt.
Next, pressure is applied to the wet nonwoven fabric produced in this way with a calender or the like so that the thickness is 30 to 50 μm and the apparent density is more than 0.5 g / cm ³ and 0.8 g / cm ³ or less. . By applying pressure in this manner, the thickness can be reduced, and the strength of the fibrils can be improved by advancing the fibrils of the fibril fibers to make them more dense or closely contacting the fibrils of the fibril fibers.
In addition, when applying a pressure, you may heat and it does not need to heat, but if it heats, it will be easy to exhibit the said effect. However, if heated to such an extent that the constituent fibers are softened, a film is formed and the ion permeability is deteriorated. Therefore, in the case of heating, among the resins constituting the constituent fibers, the softening temperature of the resin having the lowest softening temperature. It is preferable to heat at a lower temperature, more preferably at a temperature that is 10 ° C. or more lower than the softening temperature, and even more preferably at a temperature that is 20 ° C. lower than the softening temperature.
[0012]
A separator having two or more fiber layers having the same or different fiber orientation, which is suitable for the present invention, can be produced, for example, by laminating two or more wet fiber webs. More specifically, the wet fiber webs made by the same type of net are laminated, or the wet fiber webs made by different types of nets (for example, short net and circular net, long net and circular net) are laminated. Can be manufactured. Among these, when wet fiber webs made by different types of nets are laminated, a separator having two or more fiber layers having different fiber orientations can be easily produced.
The same separator can be produced by laminating the wet fiber web after drying and heating and pressurizing, but the same surface density, the same thickness, and the same are the same when the wet fiber web in the wet state is laminated. If it is a fiber orientation state, the separator which is excellent by ion permeability can be manufactured.
[0013]
The separator of the present invention can be used for an electric double layer capacitor, and can be used by being disposed between a pair of electrodes. In addition, when the fibril fiber which consists of resin whose melting temperature or carbonization temperature is 300 degreeC or more is included as a fiber which comprises a separator, the electric double layer which can dry the whole simultaneously after assembling from each material This is suitable for manufacturing a capacitor.
[0014]
Examples of the present invention will be described below, but the present invention is not limited to the following examples.
【Example】
(Examples 1-11, Comparative Examples 1-27)
Fibril fiber (registered trademark: Kevlar, manufactured by DuPont, carbonization temperature: 500 ° C. or higher) made of para-type wholly aromatic polyamide, and fine polyester fiber (melting temperature: 260) made of polyethylene terephthalate and having a fineness of 0.11 dtex and a fiber length of 3 mm. C., softening temperature: 253.degree. C., cross section: circular).
Next, a slurry containing fibril fibers and fine polyester fibers at a mass ratio of 1: 1 was formed, and then a wet fiber web was formed by an inclined wire type short net system.
Next, this wet fiber web was dried by a hot air circulation drier set at a temperature of 120 ° C.
Subsequently, the dried wet fiber web is pressed with various pressures by a pair of thermal calenders set at a temperature of 220 ° C., and is pressed wet nonwoven fabric with various surface densities, thicknesses and apparent densities as shown in Table 1, That is, a separator was manufactured. The fibril fibers constituting any of these separators also included a portion in which fine fibers are bundled. Moreover, although the thin polyester fiber which comprises any separator was somewhat crimped | bonded, it was not heat-seal | fused and the membrane | film | coat was not formed.
[0015]
[Table 1]

[0016]
(Measurement of internal resistance)
As an electrode, granular activated carbon, carbon black and polytetrafluoroethylene are mixed and kneaded, aluminum foil as a collecting electrode, separators of Examples and Comparative Examples as separators, and tetraethylammonium tetrafluoroborate as propylene carbonate as propylene carbonate What was dissolved in was prepared.
Next, after producing a coin cell type electric double layer capacitor for each separator from these materials, their internal resistance was measured. These results were as shown in Table 1. If the internal resistance was less than 3.5Ω, it was judged that the ion permeability was excellent.
As can be seen from Table 1, the separator of the present invention had excellent ion permeability with a resistance value lower than 3.2Ω.
In addition, the coin cell type electric double layer capacitor using the separator of Comparative Example 3 had a leakage current and was unstable.
[0017]
(Measurement of tensile strength)
After collecting a test piece (width: 15 mm, length: 200 mm) from the separator of each example and comparative example, the tensile strength was measured according to JIS P-8113. This result was also as shown in Table 1. In addition, if tensile strength is 4 N / 15mm width or more, it can actually be used.
As is apparent from Table 1, the separator of the present invention was excellent in tensile strength of 9 N / 15 mm width or more.
[0018]
【The invention's effect】
The separator of the present invention is excellent in electrical insulation between the electrodes, ion permeability, and strength without causing leakage current. In addition, the energy density in a constant volume of the electric double layer capacitor can be increased.
When the fiber having fibrils constituting the separator of the present invention is made of a resin having a melting temperature or a carbonization temperature of 300 ° C. or more, it is preferable for producing an electric double layer capacitor.
If any of the components constituting the separator of the present invention is not heat-sealed, a film is not formed, so that the ion permeability is further improved.
When the separator of the present invention is made of a wet nonwoven fabric, it is excellent in the uniform dispersibility of the fibers, and therefore has higher reliability in terms of electrical insulation.

Claims (3)

A surface density of 20 to 40 g / m ² and a thickness of 30 to 50 μm including a fiber having fibrils made of para-type wholly aromatic polyamide and a fine polyester fiber having a fineness of 0.11 dtex (decitex) electric double layer separators for capacitors apparent density is characterized by comprising a fiber sheet of ^{0.56g / cm 3 ~0.8g / cm 3} . The separator for an electric double layer capacitor according to claim 1, wherein none of the components constituting the separator for an electric double layer capacitor is thermally fused. The separator for an electric double layer capacitor according to claim 1 or 2, wherein the fiber sheet is made of a wet nonwoven fabric.