JP2015193948A - fine fiber structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine fiber structure that can prevent ignition due to an abnormal heat generation, and can be suitably used as a separator or an insulation material to be made into a battery, a capacitor or the like with excellent safety.SOLUTION: There is provided a fine fiber structure comprising a fine fiber layer that is composed of a fine fiber. The fine fiber has an average diameter of 50 to 3000 nm and the porous fine fiber layer includes a gas generating agent that generates a non-flammable gas by heating. The porous fine fiber layer has an average pore diameter of 0.01 to 15 μm, a thickness of 0.0025 to 0.3 mm, a porosity of 20 to 90%, a basis weight of 1 to 90 g/m, a Frazier air permeability of less than 46 m/min./mand Macmillan number of 2 to 15. The fine fiber structure comprises a multi-layered fine fiber layer obtained by laminating 2 or more of fine fiber layers of which at least one of a thickness, a basis weight, an average pore diameter, an average diameter, a porosity, a Frazier air permeability, an ionic resistance and a tensile strength is different.

Description

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

Lithium secondary batteries are useful because of their small size, light weight, and high energy density. In recent years, lithium secondary batteries are expected to be applied to in-vehicle and stationary applications such as HEVs. In the battery, a separator is disposed between the anode and the cathode in order to prevent electrical connection or short circuit between the anode and the cathode.
For example, U.S. Patent No. 6,057,077 discloses a composite battery separator that includes at least one nonwoven layer and a layer that reduces dendritic shorts that can be a microporous layer made of cellophane, polyvinyl alcohol, polysulfone, grafted polypropylene or polyamide. To do. The thickness of the composite separator is about 8.3 mil. The battery separator has an ionic resistance of less than about 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).

On the other hand, since the battery uses a flammable non-aqueous electrolyte, heat generated by overcharging or the like causes thermal runaway, and many accidents such as fire and explosion have been reported.
For this reason, a conventional polyolefin microporous separator is used, and when the battery temperature rises to about 120-130 ° C due to abnormal heat generation, the separator melts and blocks the pores of the separator, thereby shutting down the charging current. However, depending on the charge rate, thermal runaway reaction between the positive electrode active material and the electrolyte proceeds and the separator further melts, depending on the charge rate. It may lose its shape, causing a meltdown phenomenon, causing a short circuit between the electrodes, which may cause battery rupture or ignition.
In addition, lithium cobaltate having a high energy density has been used as the positive electrode active material of a conventional lithium secondary battery, but it is easily decomposed by abnormal heat generation, releasing oxygen as a combustion-supporting gas into the battery, and May cause rupture or fire.

On the other hand, lithium manganate having a spinel structure has a characteristic that it is difficult to be decomposed even if abnormal heat is generated, and a battery using lithium manganate has an advantage that the safety of the battery is high. However, compared with lithium cobaltate, the capacity is low, and the battery characteristics are significantly deteriorated under high temperature conditions. These defects are fundamental weaknesses of lithium manganate. Cannot improve.
For this reason, there is a strong demand for the development of a high safety separator that can keep the electrodes separated without causing a meltdown phenomenon even when abnormal heat generation occurs, and that can safely cut off the current.

WO99 / 53555 pamphlet US Pat. No. 4,746,586

  The present invention has been made in view of the above-described background art, and its purpose is to provide a battery, a capacitor, a capacitor, and the like excellent in safety that can be used as a separator or an insulating material and can prevent ignition of abnormal heat generation. It is in providing the fine fiber structure which can be performed.

  The present inventor examined the cause of the decrease in safety in the use of a battery, etc., and ascertained that the separator caused the meltdown phenomenon due to abnormal heat generation and could not isolate the electrodes, and further investigation As a result, it has been found that a battery, a capacitor, a capacitor and the like exhibiting excellent safety can be obtained by the following configuration.

Thus, according to the present invention,
A fine fiber structure including a fine fiber layer composed of fine fibers, wherein the fine fiber has an average diameter of 50 to 3000 nm, and the fine fiber layer contains a gas generating agent that generates a nonflammable gas upon heating. A fine fiber structure is provided. In addition, a battery, an electric double layer capacitor, or a capacitor including the fine fiber structure as a separator or an insulating material is provided.

  The fine fiber structure of the present invention is used as a separator or an insulating material for batteries, capacitors, capacitors, etc., and extrudes the electrolyte contained in the separator in the event of abnormal heat generation, cuts off the charging current, and runs out of heat due to further heat generation. Can be prevented from igniting, and therefore, a battery with extremely high safety can be obtained.

  The fine fiber structure of the present invention is a fine fiber structure including a fine fiber layer composed of fine fibers (hereinafter sometimes referred to as a porous fine fiber layer), and the average diameter of the fine fibers is 50. It is ˜3000 nm, and the fine fiber layer contains a gas generating agent that generates a nonflammable gas by heating.

  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 the fact that the Macmillan number is preferably 2 to 15, more preferably 2 to 6, but the present invention satisfies the average diameter of the fine fiber, the structure of the fine fiber structure, etc., which will be described later. Can be realized.

  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 average pore diameter of the porous fine fiber layer is preferably 0.01 to 15 μm, more preferably 0.01 to 5 μm, and still 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.
Further, the porosity of the porous fine fiber layer is preferably 20 to 90%, more 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 preferably 0.0025 to 0.3 mm, more 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 preferably 1 to 90 g / m ² , more 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.

  Polymers that can be suitably used in the fine fiber structure of the present invention are substantially inert to electrolyte solutions used for batteries, electric double layer capacitors, capacitors and the like, have no melting point, or have a melting point of 120. Any thermoplastic and thermosetting polymer at or above ° C. 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 can 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. .

In the present invention, it is particularly preferable that the polymer constituting the fine fiber layer is an aromatic polyamide in that it contains a gas generating agent that generates heat resistance and the following non-combustible gas and exhibits excellent performance. It turned out to be preferable.
The aromatic polyamide is an aromatic polyamide fiber in which 80 mol% or more, preferably 90 mol% or more of the repeating units constituting the polyamide are composed of an aromatic homopolyamide or an aromatic copolyamide. Here, the aromatic groups to be the aromatic polyamide fibers may be the same or different aromatic groups. The hydrogen atom of the aromatic group may be substituted with a halogen atom, a lower alkyl group, or a phenyl group. Specific examples of the aromatic polyamide include para-type aromatic polyamides such as polyparaphenylene terephthalamide and copolymer type copolyparaphenylene, 3,4'-oxydiphenylene, terephthalamide, and polymetaphenylene terephthalamide. Examples of the meta-type aromatic polyamide such as a meta-type aromatic polyamide are excellent in heat resistance and moldability of a fine fiber layer containing a gas generating agent. This is preferable.

  In the present invention, it is important that the fine fiber layer has a gas generating agent that generates a noncombustible gas (hereinafter sometimes referred to as a noncombustible gas) by heating. As a result, when the fine fiber structure of the present invention is used as a separator or insulating material for a battery or the like, it pushes out the entire amount of electrolyte contained in the separator during abnormal heat generation, interrupts the charging current, and causes thermal runaway due to further heat generation. It becomes possible to prevent the battery or the like from firing. In addition, since the gas generated by heat is a non-combustible gas, the risk of fire of a battery or the like becomes extremely low.

  In the fine fiber structure of the present invention, when this is heated, preferably when heated to 50 ° C. or higher, a non-combustible gas, preferably carbon dioxide, is released in a volume greater than the void volume of the fine fiber layer. Is preferred. If the amount released is less than the void volume, it is not preferable in the above use because it is difficult to cut off the charging current by pushing out the entire amount of the electrolyte during abnormal heat generation.

  In the present invention, a gas generating agent is contained in at least a part of the fine fibers constituting the fine fiber layer, or a resin containing a gas generating agent in at least a part of the fine fibers constituting the fine fiber layer. It is preferable that it adheres. In particular, in the present invention, as described later, a gas generating agent can be easily incorporated into a heat-resistant polymer by adopting a method in which gas is blown into a polymer solution to which electrospinning, electroblowing, and meltblowing technology are applied. Can be contained.

  On the other hand, as a method for attaching a resin containing a gas generating agent to at least a part of the fine fibers constituting the fine fiber layer, the resin is dissolved in a solvent, and the gas generating agent is added thereto, and this is added to the fine fiber layer. Apply or spray. At this time, as the resin, those exemplified as the polymer constituting the fine fiber can be used. For example, when using fine fibers made of an aromatic polyamide, an aromatic polyamide resin may be used for the resin. Thereby, it can be set as the fine fiber structure which has high heat resistance.

  In the present invention, if the amount of the gas generating agent contained in the fine fiber layer is too small, the inert gas cannot be sufficiently generated at the time of heating. It tends to fall off from the layer, and when it is contained in the fine fiber, the spinning property tends to be poor. Therefore, the content of the gas generating agent is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, and further preferably 3 to 10% by weight based on the weight of the fine fiber layer.

  As the gas generating agent that can be suitably used for the fine fiber structure of the present invention, any thermally decomposable substance that is substantially inactive with respect to an electrolyte solution used for a battery, an electric double layer capacitor, a capacitor or the like is used. Can be mentioned. Examples of the thermally decomposable substance suitable as a separator include, but are not limited to, sodium hydrogen carbonate, potassium hydrogen carbonate, microcapsules enclosing a noncombustible gas, and combinations thereof. In particular, it has been found that sodium bicarbonate is effective in improving the performance of interrupting current when abnormal heat is generated when a separator such as a battery is used.

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 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. Further, it is possible to adopt a method in which a melt blown technique is applied, a polymer dope dissolved in a solvent is discharged from a plurality of discharge holes, a gas is injected into the polymer dope, the polymer dope is thinned, and a fine fiber layer is formed (US Pat. etc).
In this case, in the present invention, a gas generator is added to the polymer solution (dope) in any of the method applying the melt blowing technique, the electrospinning method, and the electroblowing method, and the polymer solution is used to By forming the fine fiber layer by the method, a fine fiber structure containing a gas generating agent in the fine fiber can be produced.

  In the present invention, the amount of the gas generating agent added to the polymer solution is not particularly limited. For example, a polymer solution in which 5 to 40% by weight of the polymer is dissolved contains 0.5 to 8% by weight of the gas generating agent. The fine fiber constituting the finally obtained fine fiber layer is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, and further preferably 3 to 10% by weight.

In the electrospinning method or the electroblowing method, for example, the polymer solution is discharged from a nozzle (spin pack), an applied voltage is set to 10 to 30 kV, a fine fiber is formed, and this is transferred with a transport net 5 to 50 cm below the nozzle. The recovered fiber web (fine fiber layer) can be formed.
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.

  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. As described above, even in the case of a fine fiber structure in which two or more porous fine fiber layers are laminated or a fine fiber structure in which other materials are laminated, the same heating and pressure treatment as described above is performed. Just do it.

  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 diameter of fiber>
Fifty fine fibers were arbitrarily 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>
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>
About the porous fine fiber layer, thickness was measured in 20 places arbitrarily selected using Ono Sokki digital linear gauge DG-925 (diameter of a measurement terminal part), and the average value was calculated | required.

<Average pore diameter>
The average fine pore diameter was calculated | required for the porous fine fiber layer using Capillary Flow Porometer CFP-1200-AEXL (made by Porous Materials, Inc.).

<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

<Shutdown test>
Preparation of electrode (positive electrode): 69.5 parts by mass of lithium cobaltate (LiCoO ₂ manufactured by Nippon Chemical Industry Co., Ltd.) powder, 4.5 parts by mass of acetylene black, and 6 parts by mass so that the dry weight of PVdF is 6 parts by mass. A positive electrode paste was prepared using an N-methyl-pyrrolidone (NMP) solution of PVdF in mass%. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.
Preparation of electrode (negative electrode): 6 masses so that 87 mass parts of mesophase carbon microbeads (manufactured by Osaka Gas Chemical Co., Ltd.), 3 mass parts of acetylene black, and 10 mass parts of PVdF are used as the negative electrode active material. A negative electrode paste was prepared using an NMP solution of% PVdF. The obtained paste was applied to a 18 μm thick copper foil, dried and pressed to obtain a 90 μm thick negative electrode.
Preparation of non-aqueous electrolyte: The electrolyte was prepared by dissolving lithium hexafluorophosphate at a concentration of 1M in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a weight ratio of 3: 7.
A laminate cell having a capacity of 40 mAh is prepared using the above-described electrode, electrolyte, and separator, and is charged with constant current and constant voltage at 10 V and 10 A after 0.2 C and 4.2 V constant current and constant voltage charging (8 hours). The battery was charged when the charging current was interrupted during charging and the battery voltage reached 10V, and the battery with the charging current continuously flowing was rejected.

<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 into 20 mmΦ, sandwiched between two SUS electrodes, and the ionic conductivity of the electrolyte is divided 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.

<Gas generation rate>
Cut the porous fine fiber layer into 20mm squares, pile up 10 sheets, immerse in electrolyte and heat at 100 ° C for 5 minutes to generate gas, collect by the upper displacement method using a precision graduated cylinder, and calculate as follows Calculated by the formula.
Gas generation rate (%) = gas generation amount (mm ³ ) / (porosity / 100 × area (mm ² ) × thickness (mm))

[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, and sodium hydrogen carbonate powder was added as a gas generating agent so as to be 1% by weight. A spinning solution (polymer solution) was obtained. 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, the obtained fine fiber web is subjected to heat and pressure treatment at a temperature of 45 ° C. and a linear pressure of 15 kgf / cm between a metal heating roll and a resin roll, and a fine fiber structure comprising one porous fine fiber layer. Got. The results are shown in Table 1.

[Example 2, Comparative Examples 1 and 2]
In Example 2, the gas generating agent was changed from sodium hydrogen carbonate to potassium hydrogen carbonate, Comparative Example 1 was changed from sodium hydrogen carbonate to sodium hypochlorite, and Comparative Example 2 was added with sodium hydrogen carbonate in an amount of 0.001. A fine fiber structure was obtained in the same manner as in Example 1 except that the weight percentage was changed. The results are shown in Table 1.

  The fine fiber structure of the present invention can be used as a separator or an insulating material to generate a non-flammable gas when abnormal heat is generated, and to prevent ignition. The industrial utility value is extremely high.

Claims (12)

  A fine fiber structure including a fine fiber layer composed of fine fibers, wherein the fine fiber has an average diameter of 50 to 3000 nm, and the fine fiber layer contains a gas generating agent that generates a nonflammable gas upon heating. A fine fiber structure characterized by:   Claims wherein the gas generating agent is contained in at least a part of the fine fibers constituting the fine fiber layer, or the resin containing the gas generating agent is attached to at least a part of the fine fibers constituting the fine fiber layer. Item 12. The fine fiber structure according to Item 1. In 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. The fine fiber structure according to claim 1 or 2, having a Macmillan number of 2 to 15 and less than / min / m ² .   The fine fiber structure according to any one of claims 1 to 3, wherein when the fine fiber structure is heated to 50 degrees or more, the gas generating agent generates an incombustible gas having a volume amount equal to or larger than the volume of the voids of the fine fiber layer. body.   The fine fiber structure according to any one of claims 1 to 4, wherein the gas generating agent is a thermally decomposable substance.   The fine fiber structure according to any one of claims 1 to 5, wherein the gas generating agent is an alkali metal hydrogen carbonate.   The fine fiber structure according to any one of claims 1 to 6, wherein the fine fiber structure comprises a multilayer fine fiber layer formed by laminating two or more fine fiber layers made of different polymers.   A multilayer in which a fine fiber structure is formed by laminating two or more fine fiber layers having 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 7, comprising a 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 9, wherein the battery is a lithium battery, a lithium ion battery, or a lithium ion gel polymer battery.