WO2014003192A1

WO2014003192A1 - Fine fiber structure

Info

Publication number: WO2014003192A1
Application number: PCT/JP2013/067960
Authority: WO
Inventors: 丈也出井; 航治岩崎; 恭介高野
Original assignee: 帝人株式会社
Priority date: 2012-06-25
Filing date: 2013-06-25
Publication date: 2014-01-03

Abstract

Provided is a fine fiber structure that will not suffer wrinkling or deformation of shape due to breaking or bending even if passed through a small-diameter roller or guide or wound about a wind-up bobbin during manufacture or processing steps, that simultaneously has excellent ion permeability, short circuit resistance, and the like, and that is suitable as a separator or insulating material for a battery, electric double layer capacitor, electric condenser, or the like. A fine fiber structure comprising a porous fine fiber layer made of polymeric fine fibers having a mean diameter of 50 to 3,000 nm, the fine fiber structure being characterized in that the bending resistance of the fine fiber structure according to a 45° cantilever method is 100 mm or less, and the mean pore size, thickness, porosity, basis weight, Frazier air permeability, and Macmillan number in the porous fine fiber layer are 0.01 to 15 μm, 0.0025 to 0.3 mm, 20 to 90%, 1 to 90 g/m², less than 46 m³/min/m², and 2 to 15, respectively.

Description

Fine fiber structure

The present invention relates to a fine fiber structure comprising a fine fiber layer composed of polymer fine fibers, and more specifically to a battery such as a lithium battery or an alkaline battery, a separator such as an electric double layer capacitor or a capacitor, or an insulating material. The present invention relates to a fine fiber structure that can be suitably used.

The battery includes a separator positioned between the anode and cathode to prevent electrical connection or short circuit between the anode and cathode. A short circuit occurs when the conductive particles bridge the separator, or when the separator is degraded to allow electrode contact. In rare cases, battery shorts may occur all at once, but rather due to the accumulation of very small conductive paths called “soft shorts” over time. “Dendrite short” is, for example, formed on one electrode of a battery with a dendrite containing a precipitate such as zincate in the case of an alkaline battery, or lithium metal in the case of a lithium battery, and through a separator. The other electrode is grown to provide an electrical connection between the anode and the cathode.
Primary alkaline batteries generally have a cathode, an anode, a separator disposed between the cathode and anode, and an alkaline electrolyte solution. The cathode is typically formed from MnO ₂ , carbon particles and a binder. The anode can be formed from a gel containing zinc particles. The electrolyte solution dispersed throughout the battery is most commonly an aqueous solution containing 30-40% potassium hydroxide. Battery separators used in alkaline batteries have certain performance requirements. For example, such a separator needs to be stable in the presence of a strong alkaline electrolyte (for example, 30 to 40% KOH). The lack of alkali chemical resistance can lead to internal shorts between the electrodes due to a loss of mechanical integrity. Good electrolyte absorption is also necessary, meaning that the separator is fully impregnated with the electrolyte solution needed for the electrochemical reaction of the cell. Another requirement of the separator is a barrier to the growing dendrites of conductive zinc oxide formed by electrochemical reactions in the cell that can cause a short circuit through the separator. The separator must also allow the movement of ions between the electrodes, in other words, the separator should exhibit a low resistance to ion flow.
Secondary alkaline zinc-MnO ₂ batteries have similar anode, cathode and electrolyte as primary alkaline batteries. Certain additives (eg, Bi ₂ O ₃ , BaSO ₄ , organic inhibitors, etc.) are often added to the anode and cathode to improve reversibility so that it can be charged after the battery is discharged and zinc corrosion Reduce. During charging and discharging, some of the additives can dissolve in the electrolyte and move to other electrodes. The use of a separator with good dendrite barrier properties will help extend the cycle life of the zinc-MnO ₂ secondary battery.
Battery separators for alkaline batteries conventionally have large pores with good (low) ionic resistance, but with a relatively poor barrier to growing dendrites (hereinafter sometimes referred to as “dendritic barriers”). Either a thick, multilayered nonwoven or a multilayered nonwoven with a microporous membrane having a very small pore on it with a good dendrite barrier but very high ionic resistance. It would be desirable to have an alkaline battery with a separator having an improved balance of dendrite barrier and ionic resistance.
U.S. Patent No. 6,057,031 discloses a composite battery separator that includes at least one nonwoven layer and a layer that reduces dendritic shorts, which can be a microporous layer made of cellophane, polyvinyl alcohol, polysulfone, grafted polypropylene or polyamide. The thickness of the composite separator is about 8.3 mil. The battery separator has an ionic resistance of less than 90 milliohm-cm ² when measured in a 40% potassium hydroxide (KOH) electrolyte solution at 1 KHz. The microporous layer is desirably mixed with a very high level of barrier to air, but it is not desirable to have high ionic resistance, poor electrolyte wettability, and poor electrolyte absorption properties.
U.S. Patent No. 6,057,049 PVA having 0.8 denier or less in combination with cellulose fibers having 1.0 denier or more to reduce thickness and improve barrier properties of battery separators for use in alkaline batteries. Disclose the use of fibers. However, if the fineness of the cellulose fibers is reduced below this, the higher surface area fibers will result in a faster degradation rate.
Lithium batteries belong to three general categories: lithium primary batteries, lithium ion secondary batteries and lithium ion gel polymer batteries. Lithium primary batteries use many different types of battery chemistries, each using lithium as the anode, but with different cathode materials and electrolytes. In lithium manganese oxide or Li-MnO ₂ cells, lithium is used as the anode and MnO ₂ is used as the cathode material; the electrolyte contains a lithium salt in a mixed organic solvent such as propylene carbonate and 1,2-dimethoxyethane. contains. Lithium iron sulfide or Li / FeS ₂ batteries use lithium as the anode, iron disulfide as the cathode, and lithium iodide in the organic solvent blend as the electrolyte. Lithium ion secondary batteries use lithium-inserted carbon as an anode, lithium metal oxide (eg, LiCoO ₂ ) as a cathode and an organic solvent blend with 1M lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte. Lithium ion gel polymer batteries use similar anode and cathode materials as lithium ion secondary batteries. The liquid organic electrolyte forms a gel with the polymer separator, which helps provide a good bond between the separator and the electrode. Although the ionic resistance of gel electrolytes is higher than that of liquid electrolytes, gel electrolytes offer several advantages with respect to safety and forming requirements (ie, the possibility of forming batteries in different shapes and sizes).
Patent Document 3 discloses an ultrafine fibrous porous polymer separator film for use as a battery separator in a lithium secondary battery, and the separator film has a thickness of 1 to 100 μm. The separator film is formed from fine fibers formed by electrospinning a polymer melt or polymer solution having a diameter of 1 to 3000 nm.
In recent years, due to the miniaturization of electronic devices, batteries must be miniaturized without sacrificing conventional battery performance. Nonwoven materials that are easily used as separators in alkaline batteries have large diameter fibers and therefore it is difficult to achieve thin separators. Such nonwoven fabric also has large pores, for example between 15 and 35 μm. The anode and cathode particles can move to each other through large pores, creating an internal short circuit. To compensate for the large pore size and improve the separator's dendrite barrier (ie, protection from short circuit), thicker separators are formed using multiple layers. However, such a thick separator is not preferable from the viewpoint of battery performance because it provides higher ionic resistance, and when used in coin cells and other small batteries that are useful in electronic devices, the separator is thick, and thus is not designed. The usage is limited. Therefore, it is desirable to have a thinner separator for a battery having a higher energy density, an electric double layer capacitor, or a capacitor. However, if the conventional separator is simply made thinner, a sufficient dendrite barrier can be obtained. I can't. Therefore, it is desirable to have a separator that can be formed thin and has low ionic resistance without sacrificing barrier properties.
In addition, as we studied, when manufacturing and processing materials such as separators, we manufactured separators and insulating materials through the process of passing rollers and guides with small diameters and winding them on winding bobbins, When this was incorporated into a battery, electric double layer capacitor, capacitor, etc., it was found that there was a problem that required performance could not be obtained.
WO99 / 53555 pamphlet US Pat. No. 4,746,586 International Publication No. 01/89022 Pamphlet

The present invention has been made in view of the above-described background art, and its purpose is to cause breakage or bending even when a roller or guide having a small diameter is passed or wound on a winding bobbin in the manufacturing or processing step. Providing a fine fiber structure suitable for separators and insulating materials for batteries, electric double layer capacitors, capacitors, etc., with excellent resistance to ion permeability and short circuit resistance, without causing wrinkles and deformation of the shape. There is to do.

As a result of the study by the present inventors, in a fine fiber structure made of fine fibers, when a roller or guide having a small diameter is passed or wound on a take-up bobbin in a manufacturing or processing step, it is caused by bending or bending. It has been found that wrinkles, deformation of the shape and the like are likely to occur, and that the cause is due to the hardness of the fine fiber structure, and that the above problem can be solved by the following configuration.
Thus, according to the present invention, a fine fiber structure comprising a fine fiber layer composed of polymer fine fibers having an average diameter of 50 to 3000 nm, wherein the fine fiber structure has a bending resistance by 45 ° cantilever method. 100 mm or less, average pore diameter of 0.01 to 15 μm, thickness of 0.0025 to 0.3 mm, porosity of 20 to 90%, basis weight of 1 to 90 g / m ² , fragile Provided is a fine fiber structure characterized by an air permeability of less than 46 m ³ / min / m ² and a Macmillan number of 2 to 15. In addition, a battery, an electric double layer capacitor, or a capacitor including the fiber structure as a separator or an insulating material is provided.

The fine fiber structure of the present invention is wrinkled or deformed due to bending or bending even when passing through a roller or guide with a small diameter or winding it on a winding bobbin in the manufacturing and processing steps. In addition, it has excellent ion permeability and short circuit resistance at the same time. For this reason, the fine fiber structure can be used as a separator or an insulating material, and can be fully utilized without being affected by wrinkles, deformation of the shape, etc., and high performance batteries, electric double layer capacitors, capacitors, etc. Can be manufactured.

The fine fiber structure of the present invention is excellent in thin, low ionic resistance and good dendrite barrier properties, soft short barrier properties, short circuit resistance, etc., and separators and insulating materials for batteries, electric double layer capacitors, capacitors, etc. Used for demonstrating excellent performance. That is, the fine fiber structure of the present invention has a high capacity for absorbing the electrolyte when used as a separator or insulating material for a battery, while the separator and the like are saturated even when saturated with an electrolyte solution. In order not to lose the dendrite barrier properties, it has excellent structure maintenance, chemical stability and dimensional stability in practical use. In addition, when used as a separator or an insulating material for an electric double layer capacitor or capacitor, the separator or the like has a high capacity for absorbing the electrolyte, and when the separator is saturated with the electrolyte solution, the soft short barrier In order not to lose the characteristics, it has excellent structure maintainability, chemical stability, and dimensional stability in practical use.
As the above-mentioned battery, electric double layer capacitor, capacitor separator and insulating material are all thinner, the materials used in the battery, electric double layer capacitor and capacitor (ie, anode, separator, insulating material, and cathode) Since the total thickness is reduced, a high electrochemically active material can be contained in a specific volume, and a large-capacity battery, an electric double layer capacitor, and a capacitor can be manufactured. The separator or the like has a low ionic resistance, and ions easily flow between the anode and the cathode. These performances are demonstrated by a Macmillan number of 2 to 15, preferably 2 to 6, but the present invention is realized by satisfying the average diameter of fine fibers, the structure of fine fiber structures, etc., which will be described later. it can.
The fine fiber structure of the present invention includes at least one fine fiber layer composed of polymer fine fibers having an average diameter of 50 to 3000 nm, preferably 50 to 1000 nm, and more preferably 100 to 800 nm. Such fine fibers can achieve good electrolyte absorbability and retention when used as separators or insulating materials for the above-mentioned batteries having a high surface area.
In the present invention, the crystallinity of the fine fibers is preferably 37% or more, more preferably 40% or more, still more preferably 45% or more, and particularly preferably 50% or more. If the degree of crystallinity is less than 37%, when the fine fiber structure including the fine fiber layer is used as a separator or the like and the electrolyte is infiltrated, the fiber tends to expand greatly and the pore diameter tends to be narrowed. In some cases, the battery becomes large, and sufficient performance cannot be obtained with a battery, capacitor, capacitor, or the like.
In the present invention, the average pore diameter of the fine fiber layer is 0.01 to 15 μm, preferably 0.01 to 5 μm, more preferably 0.01 to 1 μm. When the average pore diameter is smaller than 0.01 μm, the air permeability is low and the ionic resistance is high. On the other hand, if the average pore diameter is larger than 15 μm, short circuiting tends to occur, which is not preferable.
The porosity of the fine fiber layer is 20 to 90%, preferably 40 to 80%, more preferably 50 to 80%. By increasing the porosity, it is possible to achieve good electrolyte absorption and retention in a battery or the like as described above.
In the present invention, the thickness of the fine fiber layer is 0.0025 to 0.3 mm, preferably 0.0127 to 0.127 mm. When used in separators and insulating materials for batteries, etc., the thickness should be sufficient to prevent dendrite-induced shorts between the anode and cathode, while allowing ions to flow well between the cathode and anode. It is preferable that When the fine fiber structure including the thin fine fiber layer as described above is used as a separator or an insulating material, it can create a further space in the electrode in the cell, improve the performance as a battery, and extend the life. be able to.
In the present invention, the basis weight of the fine fiber layer is 1 to 90 g / m ² , preferably 5 to 30 g / m ² . When this basic weight exceeds 90 g / m < ² >, ionic resistance may become large too much. On the other hand, when the basis weight is less than 1 g / m ² , the separator may not be able to reduce the dendrite short and soft short barrier characteristics between the anode and the cathode.
In the present invention, the fragile air permeability of the fine fiber layer is less than 46 m ³ / min / m ² , preferably less than 8 m ³ / min / m ² , more preferably less than 1.5 m ³ / min / m ² . In general, the higher the fragile air permeability, the lower the ionic resistance of the separator, so a separator having a high fragile air permeability is desirable. In the present invention, it is important that the bending resistance of the fine fiber structure is 100 mm or less, preferably 90 mm or less, more preferably 80 mm or less. When the bending resistance exceeds 100 mm, in the process of manufacturing and processing a fine fiber structure, if it is passed through a roller or guide having a small diameter or wound on a winding bobbin, it will be wrinkled by bending or bending. When the shape is deformed, separators or insulating materials such as batteries, electric double layer capacitors and capacitors cannot be obtained. On the other hand, if the bending resistance is too low, the handleability deteriorates, so that it is preferably 10 mm or more, more preferably 20 mm or more, still more preferably 30 mm or more, still more preferably 38 mm, and particularly preferably 40 mm or more. desirable.
That is, according to the present invention, in the fine fiber structure as described above, wrinkles due to bending and bending in the manufacturing and processing steps, deformation of the shape, and the like greatly affect the performance of the battery, and JIS L1096 (2010). 8.21 A method (45 ° cantilever method) allows the above-mentioned problem to be improved by setting the bending resistance to 100 mm or less. In addition, the surface of the fine fiber structure and the internal hot-pressure treatment state are processed differently. The fiber having the above-mentioned bending resistance by improving the strength of the surface fiber and maintaining the softness of the inner fiber by the method and the method of carrying out calendering with a gap between the heat rolls of the calender device It has been found that a structure can be obtained, and has reached the fine fiber structure of the present invention. The present invention also achieves the above-mentioned bending resistance while maintaining the porosity, thickness, basis weight, etc. of the fine fiber layer.
In the present invention, when measuring the bending resistance by the 45 ° cantilever method described above, the measurement sample (test piece) is cut out from the fine fiber structure at any angle, for example, MD direction, CD direction, etc. Any of the collected samples may satisfy the above-mentioned requirements for the bending resistance.
In the present invention, the value obtained by dividing the tear strength of the fine fiber structure by the Elmendorf-type tear tester method by the basis weight, that is, the tear strength / basis weight is preferably 0.9 g / (g / m ² ) or more. Preferably it is 1.0 g / (g / m ² ) or more, more preferably 1.5 g / (g / m ² ) or more, particularly preferably 2.0 g / (g / m ² ) or more. If the tear strength / basis weight is less than 0.9 g / (g / m ² ), the fine fiber structure is wound between the electrodes, and the electrode burrs are used as the starting point for tearing and stable production. Tend to be difficult. Here, the tear strength and basis weight refer to the tear strength and basis weight of the fine fiber structure. Further, when measuring the tear strength, the measurement sample (test piece) may be cut out from the fine fiber structure at any angle, for example, MD direction, CD direction, etc. It is sufficient if the tear strength / basis weight requirement is satisfied.
In the present invention, the shock absorption value according to Charpy impact testing method of the fine fibrous structure is preferably 290 kJ / ^{m 2} or more, more preferably 300 kJ / ^{m 2} or more, more preferably 400 kJ / ^{m 2} or more, particularly preferably Is 450 kJ / m ² or more. If the shock absorption value is smaller than 290 kJ / m ² , when a vibration or impact is applied, the separator or insulating material cannot absorb the impact, and the internal members may be damaged or displaced. There is a tendency that performance degradation or failure of the battery including the separator or the insulating material is likely to be induced.
The fine fiber structure of the present invention has a low bending resistance of 100 mm or less, and at the same time has excellent tearing strength and impact absorption value, which are characteristics contrary to this, thereby producing a separator and an insulating material. The separator or the like is not deformed or damaged during the processing step, the manufacturing process of the battery using the same, or the use thereof, and a higher performance battery, capacitor, capacitor, or the like can be provided.
In the present invention, the penetration rate of the fine fiber structure is preferably 20 cm ² / min or more, more preferably 30 cm ² / min or more. When the penetration rate of the electrolytic solution is less than 20 cm ² / min, uniform penetration of the electrolytic solution into the interior of a battery, an electric double layer capacitor, a capacitor, or the like tends to be difficult. That is, in batteries, particularly lithium batteries, capacitors, capacitors, etc., the number of stacked electrodes and the area of the electrodes have increased due to the increase in capacity, and as a result, the penetration time of the electrolyte into the battery has increased and work efficiency has increased. However, when the above penetration rate is satisfied, a separator or an insulating material that can cope with these problems can be obtained.
In the present invention, it is preferable that the heat shrinkage rate at 280 ° C. of the fine fiber structure is less than 3%, preferably less than 2%, more preferably less than 1%. When the thermal shrinkage rate is 3% or more, shrinkage deformation at the time of abnormal heat generation becomes remarkable, the shape cannot be maintained, and an internal short circuit tends to occur. When measuring the heat shrinkage rate, the measurement sample (test piece) may be cut out from the fine fiber structure at any angle, for example, MD direction, CD direction, etc. It is only necessary to satisfy the above heat shrinkage requirement.
In the present invention, the residual solvent amount of the fine fiber structure is preferably less than 0.1% by weight, more preferably 0.05% by weight or less, and particularly preferably 0.03% by weight or less. When the residual solvent amount is 0.1% by weight or more, the solution retention at a high rate tends to be lowered.
In order to satisfy the above penetration rate of electrolyte, maximum compression rate, tear strength / basis weight, impact absorption value, residual solvent amount, crystallinity of fine fiber, etc. This can be realized by spinning and calendering, which will be described in detail later.
Suitable polymers that can be used in the fine fiber structure of the present invention include any thermoplastic and thermosetting that is substantially inert to the electrolyte solution used in batteries, electric double layer capacitors, capacitors, etc. Polymers. Polymers suitable for use in forming the separator fibers include, but are not limited to, polyvinyl alcohol, aliphatic polyamide, semi-aromatic polyamide, aromatic polyamide, polysulfone, cellulose acetate, cellulose, polyethylene terephthalate, polypropylene terephthalate, poly Butylene terephthalate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, polymethylpentene, polyacrylonitrile polyphenylene sulfide, polyacetyl, polyurethane, polyacrylonitrile, polymethyl methacrylate, polystyrene and copolymers or derivative compounds thereof, and these The combination of is mentioned.
In some embodiments of the invention, in order to maintain a porous structure and improve structural or mechanical integrity, thereby improving the dendrite barrier and thermal stability of separators formed therefrom, It is preferable to crosslink the polymer of the polymer fine fiber. Certain polymers, such as polyvinyl alcohol (PVA), polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, swell or gel in the electrolyte, plugging the pores of the fine fiber structure There is a tendency. It will also soften or decompose in the electrolyte and provide structural integrity to the snare of the fine fiber structure. Depending on the polymer of the battery separator, various crosslinking agents and crosslinking conditions can be used. All of the above polymers can be crosslinked by known means such as chemical crosslinking, electron beam crosslinking or UV crosslinking.
PVA can be crosslinked either by chemical crosslinking, electron beam crosslinking or UV crosslinking. Chemical cross-linking of the PVA fine fiber layer can be done by treating the PVA layer with dialdehyde and acid, then neutralizing the acid with NaHCO ₃ and washing the layer with water. Cross-linking of PVA makes it water-insoluble and increases its mechanical strength and its oxidation and chemical resistance.
A polyvinylidene fluoride-hexafluoropropylene separator is crosslinked by adding a crosslinking agent (PEGDMA oligomer) and a crosslinking initiator (2,2-azobisisobutyronitrile) and heating the separator at 80 ° C. for 12 hours. It is possible. Polyacrylonitrile separators can be crosslinked by adding a crosslinking agent (eg, ethylene glycol dimethacrylate or triethylene glycol dimethacrylate) and an initiator (eg, benzoyl peroxide) and heating at 60 ° C. .
One embodiment of the invention relates to an alkaline battery. The battery can be, for example, a zinc-manganese oxide or Zn-MnO ₂ battery in which the anode is zinc and the cathode is manganese oxide (MnO ₂ ), or a zinc-air battery in which the anode is zinc and the cathode is air. Can be an alkaline primary battery or, for example, a nickel cadmium battery in which the anode is cadmium and the cathode is nickel oxy-hydroxide (NiOOH), nickel zinc or the anode is zinc and the cathode is NiOOH or A Ni—Zn battery, the anode is a metal hydride (eg, LaNi ₅ ), and the cathode is NiOOH, a nickel metal hydride (NiMH) battery or the anode is hydrogen (H ₂ ), and Can be hydrogen or NiH ₂ alkaline secondary battery such as a battery - fine cathodes nickel is NiOOH. Other types of alkaline batteries include zinc / mercury oxide where the anode is zinc and the cathode is mercury oxide (HgO), the anode is cadmium and the cadmium / mercury oxide where the cathode is mercury oxide, the anode is Zinc / silver oxide, which is zinc and the cathode is silver oxide (AgO), cadmium / silver oxide where the anode is cadmium and the cathode is silver oxide. All these battery types use 30-40% potassium hydroxide as the electrolyte.
Another embodiment of the invention relates to a lithium battery. The lithium battery of the present invention can be a lithium primary battery, such as a Li—MnO ₂ or Li—FeS ₂ lithium primary battery, a lithium ion secondary battery, or a lithium ion gel polymer battery.
Lithium primary batteries utilize many different types of battery chemistry, each using lithium as the anode, but different cathode materials (SO ₂ , SOCl ₂ , SO ₂ Cl ₂ , CFn, CuO, FeS ₂ , MnO _2, etc. ) And an electrolyte. In lithium manganese oxide or Li-MnO ₂ cells, lithium is used as the anode and MnO ₂ as the cathode material; the electrolyte contains a lithium salt in a mixed organic solvent such as propylene carbonate and 1,2-dimethoxyethane. . Lithium iron sulfide or Li / FeS ₂ batteries use lithium as the anode, iron disulfide as the cathode, and lithium iodide in an organic solvent blend (eg, propylene carbonate, ethylene carbonate, dimethoxyethane, etc.) as the electrolyte.
Lithium ion secondary batteries use lithium-inserted carbon as an anode, lithium metal oxides (eg, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, etc.) as cathodes and blends of organic solvents (eg, propylene carbonate, ethylene carbonate, Diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc.) are used as an electrolyte together with 1M lithium hexafluorophosphoric acid (LiPF ₆ ).
Lithium ion gel polymer batteries use anodes and cathodes similar to lithium ion secondary batteries. The liquid organic electrolyte forms a gel with a polymeric separator (eg, PVdF, PVdF-HFP, PMMA, PAN, PEO, etc.), which helps to obtain a good bond between the separator and the electrode. Gel electrolytes have higher ionic resistance than liquid electrolytes, but offer additional advantages in terms of safety and formation requirements.
Another embodiment of the present invention is an electric double layer capacitor, wherein the carbon-based electrode is organic or non-aqueous such as, for example, a solution of acetonitrile or propylene carbonate and a 1.2 molar quaternary tetrafluoroammonium borate. The electric double layer capacitor can be used together with an electrolyte or an aqueous electrolyte such as a 30 to 40% KOH solution.
Moreover, in this invention, it can be set as the electric double layer capacitor depending on the reduction-oxidation chemical reaction which provides a capacitance. Such electric double layer capacitors are referred to as “pseudocapacitors” or “redox capacitors”. Pseudocapacitors can use carbon, noble metal hydrated oxides, modified transition metal oxides and conductive polymer based electrodes, as well as aqueous and organic electrolytes.
Another embodiment of the present invention is an aluminum electrolytic capacitor that includes an etched aluminum foil anode, an aluminum foil or film cathode, and a separator interposed therebetween. The separator and insulating material comprising the fine fiber structure of the present invention are impregnated with a liquid electrolytic solution or a conductive polymer. The liquid electrolyte solution contains a polar solvent and at least one salt selected from an inorganic acid, an organic acid, an inorganic acid salt, and an organic acid salt.
The capacitor of the present invention includes two conductive aluminum foils and a separator immersed in an electrolyte, and one of the conductive aluminum foils may be coated with an insulating oxide layer. The aluminum foil coated with the oxide layer is the anode, while the liquid electrolyte and the second foil function as the cathode. The multilayer assembly is rolled up, secured with a pin connector, and placed in a cylindrical aluminum case. The foil is high purity aluminum and billions of fine tunnels are chemically etched to increase the surface area in contact with the electrolyte. The anode foil supports the capacitor dielectric, which is a thin layer of aluminum oxide (Al ₂ O ₃ ) chemically grown on the anode foil. The electrolyte is a blend of components of different formulations according to voltage and operating temperature range. The main components are a solvent and a conductive salt as a solute that conducts electricity. Common solvents are ethylene glycol (EG), dimethylformamide (DMF) and gammabutyllactone (GBL). Common solutes are ammonium borate and other ammonium salts. A small amount of water is added to the electrolyte to maintain the integrity of the aluminum oxide dielectric. The separator can prevent the foil electrolytes from contacting each other or from being short-circuited, and can hold the electrolyte container.
The fine fiber structure layer of the present invention and the formation process of the fine fiber layer constituting the fine fiber structure layer may be a known electrospinning process, or WO 2003/080905 (US Patent Application No. 10 / 822,325). The electroblowing process disclosed in (1) can be employed.
In the present invention, for example, a single fine fiber layer (fiber web) is formed by passing once through the transport and collection means passing through the above process (that is, once through the transport and collection means under the spin pack). The fibrous web can also be multi-layered by passing under one or more spin packs arranged on the same conveying means.
The collected fine fiber layer can improve the tensile strength by bonding fibers, for example. In particular, by increasing the tensile strength in the longitudinal direction (longitudinal direction), the winding property of the cell is improved, and it contributes to good dendrite barrier properties when used as a separator in use. The bonding method between the fine fibers is not particularly limited, but a known method such as thermal calendering between heated and smooth nip rolls, ultrasonic bonding, point bonding, and bonding that can pass through a high-temperature atmosphere should be adopted. Can do. Due to the bonding between the fibers, the fine fiber layer is improved in handleability, and the strength of the fine fiber layer can be imparted to form a separator for a battery, an electric double layer capacitor, a capacitor, or an insulating material. In addition, physical properties such as thickness, density, hole diameter, and shape can be adjusted depending on the bonding method. When using thermal calendering, it is necessary that the fine fibers are melted and fused excessively until individual fiber forms are lost, so as not to form a complete film.
In the present invention, for example, first, a fine fiber layer (fine fiber web) obtained by electrospinning, electroblowing or the like or a multilayer fine fiber layer obtained by laminating the same is applied to a metal roll heated to 250 to 350 ° C. It is possible to preferably employ a method in which both surfaces are brought into contact with each other, and thereafter calendering is performed at a roll surface temperature of 100 to 200 ° C. and a linear pressure of 10 to 100 kg / cm. A fine fiber structure satisfying the bending resistance by the method can be produced. The above processing is not limited to polymers and the like, but it has been found that the processing is particularly effective in adjusting the bending resistance of fine fiber structures made of polyimide, aromatic polyamide, semi-aromatic polyamide, and the like.
The fine fiber structure of the present invention may be a single layer or a multilayer of fine fiber layers made of polymer fine fibers. When the fiber structure is composed of multiple layers, it may be composed of a fine fiber layer composed of the same polymer fine fiber, or may be composed of a fine fiber layer of different polymer fine fibers. In the case of a multilayer, although not particularly limited, a fine fiber layer different in at least one of polymer, thickness, basis weight, pore diameter, fiber size, porosity, air permeability, ionic resistance, tensile strength, etc. is laminated. May be. In addition, the fine fiber structure of the present invention only needs to include at least one fine fiber layer satisfying the requirements of the present invention, and does not satisfy the requirements of the present invention, for example, fibers, as long as the object of the present invention is not impaired. A fiber structure such as a wet nonwoven fabric or a dry nonwoven fabric having a diameter exceeding 3000 nm, a porous resin film, or the like may be included.

Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited by the following examples. In addition, each characteristic value in an Example was measured with the following method.
(1) Average diameter of fine fibers Arbitrary 50 fine fibers were sampled and measured with a scanning electron microscope JSM6330F (manufactured by JEOL) to obtain the average value of the fiber diameters. The measurement was performed at a magnification of 20,000 times.
(2) Basis Weight A fine fiber layer was cut into a square with a side of 25 mm, and the weight was measured using an electronic balance, and the basis weight was converted to a square with a side of 1 m.
(3) Thickness Ono Sokki Using a digital linear gauge DG-925 (diameter of measurement terminal portion 1 cm), thickness was measured at 20 arbitrarily selected locations, and an average value was obtained.
(4) Bending softness Using a fine fiber structure, it was measured by a bending softness tester manufactured by Yasuda Seiki Seisakusho Co., Ltd. according to JIS L1096 (2010) 8.21 A method (45 ° cantilever method).
(5) Average pore diameter The average pore diameter was calculated | required for the fine fiber layer using Capillary Flow Porometer CFP-1200-AEXL (made by Porous Materials, Inc.).
(6) Frazier air permeability A sample is cut out from the fine fiber layer, conforms to JIS L1096 (2010) 8.26 A method (Fragile format), and a measurement range is set to 5 cm ² using a Fragil type tester (FX3300 manufactured by TEXTEST). The measured value was shown in the unit m ³ / min / m ² .
(7) Porosity From the basis weight (g / m ³ ) of the fine fiber layer, the density (g / cm ³ ) of the polymer constituting the fine fiber, and the thickness (μm), the porosity was calculated by the following formula.
Porosity (%) = 100-basis weight / (polymer density × thickness) × 100
(8) Macmillan number A fine fiber layer is cut into 20 mmφ, sandwiched between two SUS electrodes, and calculated by dividing the ionic conductivity of the electrolyte by the conductivity calculated from the AC impedance at 10 kHz. The electrolyte used was 0.5 molar lithium trifluoromethanesulfonate (LiTFS), propylene carbonate: ethylene carbonate: dimethoxyethane (22: 8: 70), and the measurement temperature was 25 ° C.
Moreover, the sample measured the Macmillan number by said method using the sample before performing the process of the next winding cancellation | release, and the sample after performing this process. In the sample, if the Macmillan number is less than 1.5, even if a separator (fine fiber structure) is present, it indicates that the ionic conductivity is close to that of the electrolytic solution, and the separator tends to short-circuit or slightly short-circuit. Indicates.
The winding release treatment was released after applying a tension of 2.5 kgf to a fine fiber structure having a width of 25 mm and a length of 1 m and manually winding it on a metal rod having a diameter of 2 mm.
(9) Tearing strength (g)
According to JIS P8116 (tear strength), an Elmendorf-type tear tester manufactured by Toyo Seiki Seisakusho Co., Ltd. was used, and the sample size of the fine fiber structure was 70 mm width × 63 mm tear direction and 20 mm incision was measured.
(10) Impact absorption value Measured according to JIS K 7111-1 (2006) (unnotched Charpy impact strength). At this time, a test piece of 100 mm × 15 mm cut out from the fine fiber structure was used as the test piece, and this was made so that the striking blade of the pendulum hits the surface of the test piece so that the test piece did not become slack. Tension is applied, and it is installed on the test piece support with Cellophane tape (registered trademark) (manufactured by Nichiban Co., Ltd., ELPAC S LP-18S). The pendulum uses the 2J type.
(11) Penetration rate The fine fiber structure is cut into a 6 cm × 8 cm test sample, which is sandwiched between two glass plates of 20 cm × 30 cm × thickness 5 mm, and the surface of the test sample on the upper glass plate A weight is placed so that the pressure is 0.1 kgf / cm ² including the weight of the glass plate. At this time, a part of the test sample protrudes 6 cm × 1 cm from one side of the upper and lower glass plates, and the protruding portion is electrolyzed. It is immersed in a liquid bath, and the area (cm ² ) permeating the test sample in which the electrolyte is sandwiched between glass plates in 1 minute is measured. The electrolyte is measured at 25 ° C. using a mixed solution of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (weight ratio EC / EMC = 3/7).
(12) Thermal shrinkage The fine fiber structure was cut into a sample of length 25 mm × width 5 mm, and TMA4000SA (made by Bruker) was applied at a load of 1.5 g for 10 seconds at 280 ° C. The heat shrinkage was calculated using the following formula. At this time, the sample length before heat exposure was 20 mm.
Thermal contraction rate (%) = (sample length before heat exposure−sample length after heat exposure) / sample length before heat exposure × 100
[Example 1]
The target polymer was produced by the following interfacial polymerization method according to the method described in Japanese Patent Publication No. 47-10863.
25.13 g (99 mol%) of isophthalic acid dichloride and 0.25 g (1 mol%) of terephthalic acid dichloride as a third component were dissolved in 125 ml of tetrahydrofuran having a water content of 2 mg / 100 ml and cooled to −25 ° C. While stirring this, 13.52 g (100 mol%) of metaphenylenediamine was added over about 15 minutes as a trickle of a solution obtained by dissolving 125 ml of the above tetrahydrofuran to prepare a white emulsion (A). Separately, 13.25 g of anhydrous sodium carbonate was dissolved in 250 ml of water at room temperature, and this was cooled to 5 ° C. with stirring to precipitate sodium carbonate hydrate crystals to prepare a dispersion (B). The emulsion (A) and dispersion (B) were mixed vigorously. After further mixing for 2 minutes, 200 ml of water was added for dilution, and the resulting polymer was precipitated as a white powder. Filtration, washing with water and drying were carried out from the polymerization completed system to obtain the desired polymer (density: 1.38 g / cm ³ ).
The obtained aromatic copolyamide polymer was dissolved in N, N-dimethylacetamide so as to be 20% by weight to obtain a spinning solution for electrospinning. This polymer solution was discharged from a nozzle, an applied voltage was set to 20 kV by an electrospinning method, and fine fibers were molded. The fine fibers were collected by a transport net 20 cm below the nozzle to obtain a fine fiber web. Subsequently, in the step of hot pressing the fine fiber web, both surfaces of the obtained fine fiber web are brought into contact with and passed through a metal roll heated to 300 ° C., and then calendering is performed at a roll surface temperature of 150 ° C. The measurement was performed at a linear pressure of 75 kg / cm to obtain a fine fiber structure composed of one porous fine fiber layer. The results are shown in Table 1.
[Example 2]
In the process of hot-pressing the fine fiber web, both sides of the obtained fine fiber web are passed through a metal roll heated to 250 ° C., and then calendering is performed at a roll surface temperature of 100 ° C. and a linear pressure. A fine fiber structure shown in Table 1 was obtained in the same manner as in Example 1 except that the measurement was performed at 75 kg / cm. The results are shown in Table 1.
[Example 3]
In the process of hot-pressing the fine fiber web, both surfaces of the obtained fine fiber web are passed through a metal roll heated to 350 ° C., and then calendering is performed at a roll surface temperature of 200 ° C. and a linear pressure. A fine fiber structure shown in Table 1 was obtained in the same manner as in Example 1 except that the measurement was performed at 75 kg / cm. The results are shown in Table 1.
[Comparative Example 1]
In the process of hot-pressing the fine fiber web, the calendering process is performed only on the roll surface temperature of 300 ° C. and the linear pressure of 75 kg without passing the both sides of the obtained fine fiber web in contact with the heated metal roll. A fine fiber structure shown in Table 1 was obtained in the same manner as in Example 1 except that the measurement was performed at / cm. The results are shown in Table 1.
[Comparative Example 2]
In place of the fine fiber structure, the evaluation was performed using a cellulose separator for an electricity storage device (manufactured by Nippon Advanced Paper Industries, polymer density 1.5 g / cm ³ ). The results are shown in Table 1.

The fine fiber structure of the present invention is wrinkled or deformed due to bending or bending even when a roller or guide having a small diameter is passed or wound on a winding bobbin in the manufacturing or processing steps. In addition, it is excellent in ion permeability and short circuit resistance at the same time. For this reason, the fine fiber structure can be used for a separator or an insulating material, and can be fully utilized without being affected by wrinkles, etc., and a high performance battery, electric double layer capacitor, capacitor, etc. can be manufactured. it can.

Claims

A fine fiber structure comprising a fine fiber layer composed of polymer fine fibers having an average diameter of 50 to 3000 nm, wherein the fine fiber structure has a bending resistance of 100 mm or less by a 45 ° cantilever method, and the fine fiber layer The average pore diameter is 0.01 to 15 μm, the thickness is 0.0025 to 0.3 mm, the porosity is 20 to 90%, the basis weight is 1 to 90 g / m 2 , and the fragile air permeability is 46 m 3 / min / min. A fine fiber structure characterized by being less than m 2 and having a Macmillan number of 2 to 15.
2. The fineness according to claim 1, wherein the tear strength / basis weight is 0.9 g / (g / m 2 ) or more, which is a value obtained by dividing the tear strength by the Elmendorf-type tear tester method of the fine fiber structure by the basis weight. Fiber structure.
The fine fiber structure according to claim 1 or 2, wherein an impact absorption value measured by the following method is 290 kJ / m 2 or more.
<Shock absorption value>
Measurement is performed according to JIS K 7111-1 (notch-free Charpy impact strength). At this time, a test piece of 100 mm × 15 mm cut out from the fine fiber structure was used as the test piece, and this was made so that the striking blade of the pendulum hits the surface of the test piece so that the test piece did not become slack. Tension is applied, and it is installed on the test piece support with Cellophane tape (registered trademark) (manufactured by Nichiban Co., Ltd., ELPAC S LP-18S). The pendulum uses the 2J type.
The fine fiber structure according to any one of claims 1 to 3, wherein the penetration rate of the fine fiber structure measured by the following method is 20 cm 2 / min or more.
<Penetration rate>
The fine fiber structure is cut into a 6 cm × 8 cm test sample, which is sandwiched between two glass plates of 20 cm × 30 cm × 5 mm thickness, and the surface pressure applied to the test sample on the upper glass plate is A weight is placed so that the weight is 0.1 kgf / cm 2 including the weight. At this time, a part of the test sample protrudes 6 cm × 1 cm from one side of the upper and lower glass plates, and the protruding part is immersed in the electrolyte bath. And the area (cm < 2 >) which penetrated the test sample by which electrolyte solution was pinched | interposed into the glass plate in 1 minute is measured. The electrolyte is measured at 25 ° C. using a mixed solution of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (weight ratio EC / EMC = 3/7).
5. The fine fiber structure according to claim 1, wherein the fine fiber structure has a heat shrinkage rate at 280 ° C. of less than 3%.
6. The fine fiber structure according to claim 1, wherein the amount of residual solvent in the fine fiber structure is less than 0.1% by weight.
The fine fiber structure according to any one of claims 1 to 6, wherein the crystallinity of the polymer fine fiber is 37% or more.
Polymer fine fiber is aliphatic polyamide, semi-aromatic polyamide, aromatic polyamide, polyvinyl alcohol, cellulose, polyethylene terephthalate, polyethylene naphthalate, polyethylene, propylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, and blends and mixtures thereof. The fine fiber structure according to any one of claims 1 to 7, comprising a polymer selected from the group consisting of a copolymer and a copolymer.
A battery comprising the fine fiber structure according to any one of claims 1 to 8 as a separator or an insulating material.
An electric double layer capacitor comprising the fine fiber structure according to any one of claims 1 to 8 as a separator or an insulating material.
A capacitor comprising the fine fiber structure according to any one of claims 1 to 8 as a separator or an insulating material.
The battery according to claim 9, wherein the battery is a lithium battery, a lithium ion battery, or a lithium ion gel polymer battery.