JP2014007068A - Fine fiber structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine fiber structure that has an excellent ion permeability, short circuit resistance etc., that can deal with increase in a number of laminations of an electrode and in an electrode area, that can achieve increase in efficiency of a work of filling electrolytic solution, that enables uniform filling of permeation liquid, and that is suitable for a separator and an insulation material of a battery, an electric double-layer capacitor, a capacitor etc.SOLUTION: A fine fiber structure includes a porous fine fiber layer consisting of polymer fine fibers having an average diameter of 50-3,000 nm. With respect to the fine fiber structure, a permeation rate of an electrolytic solution obtained by mixing ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a weight ratio of EC/EMC=3/7 at the time when the electrolytic solution is made permeate in a state that a load of a surface pressure of 0.1 kgf/cmis applied, is 20 cm/min or more. With respect to the porous fine fiber layer, an average pore diameter is 0.01-15 μm, a thickness is 0.0025-0.3 mm, a porosity is 20-90%, a basis weight is 1-90 g/m, a Frazier permeability is less than 46 m/min/m, and a MacMillan number is 2-15.

Description

  The present invention relates to a fine fiber structure comprising a porous fine fiber layer made of polymer fine fibers, and more specifically, 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 insulation. The present invention relates to a fine fiber structure that can be suitably used for a material.

  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 (eg, 30-40% 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 traditionally have good (low) ionic resistance, but large pores with a relatively poor barrier to growing dendrites (also referred to herein as “dendritic barriers”). 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 between 1 and 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 nonwovens also have large pores, for example, between about 15 and about 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.

  On the other hand, in the case of a battery, particularly a lithium battery, the number of stacked electrodes and the electrode area are increased due to the increase in capacity, and not only the workability of electrolyte filling deteriorates, but also uniform penetration is not possible. It was found that such a problem occurred. In addition, it has been found that there are similar problems with electric double layer capacitors and capacitors.

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 excellent in ion permeability, short-circuit resistance, etc., and corresponds to the increase in the number of stacked electrodes and the electrode area, and the efficiency of the electrolyte filling operation. An object of the present invention is to provide a fine fiber structure that can be made uniform and can be uniformly filled with an osmotic solution, and is suitable as a separator or insulating material for batteries, electric double layer capacitors, capacitors and the like.

  The present inventor has increased the number of stacked electrodes and the electrode area in order to increase the capacity in a separator or an insulating material made of an ultrafine fiber structure composed of ultrafine fibers. As a result of repeated investigations, it was found that such problems can be solved by the following configuration.

Thus, according to the present invention, a fine fiber structure comprising a porous fine fiber layer comprising polymer fine fibers having an average diameter of 50 to 3000 nm, the penetration rate of the fine fiber structure measured by the following method Is 20 cm ² / min or more, and the average fine pore diameter is 0.01 to 15 μm, the thickness is 0.0025 to 0.3 mm, the porosity is 20 to 90%, and the basis weight is 1 to ^{2 in} the porous fine fiber layer. There is provided a fine fiber structure characterized by 90 g / m ² , a fragile air permeability of less than 46 m ³ / min / m ² , and a Macmillan number of 2 to 15.
<Penetration rate>
The 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 the weight of the glass plate And a weight of 0.1 kgf / cm ² , so that 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. The area (cm ² ) permeating the test sample in which the electrolytic solution is sandwiched between the 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).
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 used for separators and insulating materials for batteries, etc., and exhibits excellent performance in ion permeability, short-circuit resistance, etc., and the number of stacked electrodes and electrode area in recent years have increased. Therefore, the efficiency of the electrolyte filling operation can be improved, and the uniform permeation solution can be filled. For this reason, from the fine fiber structure, it is possible to manufacture a battery, an electric double layer capacitor, a capacitor and the like with high productivity and high performance.

  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 the fine fibers, the structure of the fine fiber structure, etc., which will be described later. it can.

  The fine fiber structure of the present invention includes at least one porous 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 average fine pore diameter of the porous 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 porous fine fiber layer is 20 to 90%, preferably 40 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 porous 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 The fine fiber structure including the thin porous fine fiber layer as described above can create more space in the electrode in the cell when used as a separator or an insulating material, improving performance as a battery, etc. Can be achieved.

In the present invention, the basis weight of the porous 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 permeability of the porous 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 batteries, particularly lithium batteries, the number of stacked electrodes and the electrode area 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 deteriorated. There is a problem that uniform penetration is not possible. Also, the same problem occurs in electric double layer capacitors and capacitors. The present invention focuses on such a problem and develops a separator and an insulating material with improved permeability of an electrolysis solution.

Therefore, in the present invention, it is important that the permeation rate of the fine fiber structure measured by the following method is 20 cm ² / min or more. When the penetration rate of the electrolytic solution is less than 20 cm ² / min, it is difficult to uniformly penetrate the electrolytic solution into the interior of a battery, an electric double layer capacitor, a capacitor, or the like.

<Penetration rate>
The 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 the weight of the glass plate And a weight of 0.1 kgf / cm ² , so that 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. The area (cm ² ) permeating the test sample in which the electrolytic solution is sandwiched between the 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).

  In the present invention, when the test sample is cut out from the fiber structure, it may be cut out at any angle as long as any of the collected test samples satisfies the requirements for the penetration rate.

In the calendering which is a heat treatment step of the fine fiber structure, the present invention further performs non-tensile heat treatment after processing at a low linear pressure, or after processing at the low linear pressure, further gaps between the hot rolls. A fine fiber structure having an unprecedented extremely high electrolyte solution penetration rate of 20 cm ² / min or more as described above is obtained by carrying out calendering and improving the porosity by thermal shrinkage of fine fibers. It was found that it was obtained. Therefore, when the treatment at a constant linear pressure is performed in the calendar process as in the conventional method, the gap between the fine fibers becomes small, and the target penetration rate of the electrolytic solution cannot be achieved.

  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, resulting in 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 It can be hydrogen or NiH ₂ alkaline secondary battery such as a battery - fine cathode 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. It can be an electric double layer capacitor used with an electrolyte or an aqueous electrolyte such as a 30-40% 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 porous fine fiber layer constituting the fine fiber structure layer can be performed by a known electrospinning process, or WO2003 / 080905 (US Patent Application No. 10 / 822,325). The electroblowing process disclosed in the specification can be employed.

  In the present invention, for example, a porous fine fiber layer (fiber web) composed of one layer is formed by passing once through the transport collection means passing through the above process (that is, once passing through the transport 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.

  As described above, in order to obtain a fine fiber structure having a permeation rate of the electrolytic solution of the present invention, in the calendering of the fine fiber structure, an additional heat treatment is performed after processing at a low linear pressure, and the fine fiber structure This can be achieved by, for example, a method for improving the porosity by heat shrinkage. Specifically, it may be possible to employ a method in which calendering is performed at a linear pressure of 10 to 60 kg / cm and a roll surface temperature of 250 to 350 ° C., and then subjected to tensionless heat treatment at 300 to 350 ° C. for 15 to 60 seconds. it can.

  The fine fiber structure of the present invention may be a single layer or a multilayer of porous fine fiber layers made of polymer fine fibers. When the fiber structure is composed of multiple layers, it may be composed of a porous fine fiber layer made of the same polymer fine fiber, or may be made of a porous fine fiber layer of different polymer fine fibers. In the case of multiple layers, although not particularly limited, a laminate of porous fine fiber layers that differ in at least one of polymer, thickness, basis weight, pore diameter, fiber size, porosity, air permeability, ionic resistance, tensile strength, etc. It may be. Further, the fine fiber structure of the present invention only needs to include at least one porous fine fiber layer that satisfies the requirements of the present invention and does not satisfy the requirements of the present invention as long as the object of the present invention is not impaired. For example, a fiber structure such as a wet nonwoven fabric or a dry nonwoven fabric made of fibers having a fiber 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.

<Average fiber diameter (nm)>
Arbitrary 50 nanofibers were sampled and measured with a scanning electron microscope JSM6330F (manufactured by JEOL), and the average value of the fiber diameters was determined. The measurement was performed at a magnification of 20,000 times.

<Basis weight (g / m ² )>
The porous fine fiber layer was cut into a square having a side of 25 mm, the weight was measured using an electronic balance, and the basis weight was converted into a square having a side of 1 m.

<Thickness (μm)>
Ono Sokki Using a digital linear gauge DG-925 (diameter of the measurement terminal part 1 cm), the thickness was measured at 20 arbitrarily selected locations, and the average value was obtained.

<Average pore diameter (μm)>
For the porous fine fiber layer, the average pore diameter was determined using Capillary Flow Porometer CFP-1200-AEXL (manufactured by Porous Materials, Inc.).

<Fragile air permeability>
A sample was cut out from the porous fine fiber layer, measured in accordance with JIS L1096 (2010) 8.26 A method (Fragile format), and measured using a Fragil tester (FX3300 manufactured by TEXTEST) with a measurement range of 5 cm ^2. Values are given in units of m ³ / min / m ² .

<Number of Macmillan>
A porous fine fiber layer is cut out to 200 mmφ, sandwiched between two SUS electrodes, and calculated by dividing the ionic conductivity of the electrolytic solution 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.

<Porosity (%)>
From the basis weight (g / m ³ ) of the porous fine fiber layer, the density (g / cm ³ ) of the polymer constituting the fine fiber, and the thickness (μm), the following formula was used.
Porosity (%) = 100-basis weight / (polymer density × thickness) × 100

<Penetration rate (cm ² / min)>
The porous fine fiber layer 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 the electrolyte solution osmose | permeated to the test sample pinched | interposed into the glass plate in 1 minute was measured. The electrolyte was measured at 25 ° C. using a mixed solution of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (weight ratio EC / EMC = 3/7).

[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 that the polymer concentration was 16% by weight to obtain a spinning solution. The spinning solution was discharged from a nozzle, an applied voltage was set to 20 kV by an electrospinning method, and fine fibers were formed. The fine fibers were collected by a transport net 20 cm below the nozzle to obtain a fine fiber web.
Subsequently, the obtained fine fiber web was calendered at a roll surface temperature of 300 ° C. and a linear pressure of 50 kg / cm, and then subjected to non-tensile heat treatment at 300 ° C. for 30 seconds. A structure was obtained. The results are shown in Table 1.

[Examples 2 and 3]
In Example 2, the spinning solution polymer was changed from 16% to 20% by weight, in Example 3, the spinning solution polymer was changed from 16% to 22% by weight, and the distance from the nozzle to the transfer net was changed from 20 cm to 15 cm. A fine fiber structure was obtained in the same manner as in Example 1 except for changing to. The results are shown in Table 1.

[Comparative Example 1]
A fine fiber structure was obtained in the same manner as in Example 1 except that no tension heat treatment was not performed. The results are shown in Table 1.

[Comparative Example 2]
In place of the fine fiber structure, evaluation was performed using a polyolefin microporous membrane (polymer density: 0.9 g / cm ³ ). The results are shown in Table 1.

  The fine fiber structure of the present invention is used for separators and insulating materials for batteries, etc., and exhibits excellent performance in ion permeability, short-circuit resistance, etc., and the number of stacked electrodes and electrode area in recent years have increased. Therefore, the efficiency of the electrolyte filling operation can be improved, and the uniform permeation solution can be filled. For this reason, from the fine fiber structure, it is possible to manufacture a battery, an electric double layer capacitor, a capacitor and the like with high productivity and high performance.

Claims (10)

A fine fiber structure comprising a porous fine fiber layer composed of polymer fine fibers having an average diameter of 50 to 3000 nm, and the penetration rate of the fine fiber structure measured by the following method is 20 cm ² / min or more. Yes, in the porous 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 Frazier ventilation A fine fiber structure having a degree of less than 46 m ³ / min / m ² and a Macmillan number of 2 to 15.
<Penetration rate>
The 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 the weight of the glass plate And a weight of 0.1 kgf / cm ² , so that 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. The area (cm ² ) permeating the test sample in which the electrolytic solution is sandwiched between the 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).   Polymer fine fiber is aliphatic polyamide, semi-aromatic polyamide, polyvinyl alcohol, cellulose, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polysulfone, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropene, polymethylpentene, polyacrylonitrile The fine fiber structure according to claim 1, comprising a polymer selected from the group consisting of polymethylmethacrylate, polyphenylene sulfide, polyacetyl, polyurethane, aromatic polyamide, and blends, mixtures and copolymers thereof.   The fine fiber structure according to claim 1 or 2, wherein a polymer constituting the polymer fine fiber is crosslinked.   The fine fiber structure according to any one of claims 1 to 3, wherein the fine fiber structure comprises a multilayer porous fine fiber layer.   The fine fiber structure according to claim 4, wherein the fine fiber structure comprises a multilayer porous fine fiber layer comprising two or more porous fine fiber layers containing different polymers.   A multilayer in which the fine fiber structure is composed of two or more porous fine fiber layers different in at least one of thickness, basis weight, average pore diameter, average diameter, porosity, fragile air permeability, ionic resistance, and tensile strength The fine fiber structure according to claim 4, comprising a porous fine fiber layer.   A battery comprising the fine fiber structure according to claim 1 as a separator or an insulating material.   An electric double layer capacitor comprising the fine fiber structure according to claim 1 as a separator or an insulating material.   A capacitor comprising the fine fiber structure according to claim 1 as a separator or an insulating material.   The battery according to claim 7, wherein the battery is a lithium battery, a lithium ion battery, or a lithium ion gel polymer battery.