WO2014010753A1

WO2014010753A1 - Microfiber structure

Info

Publication number: WO2014010753A1
Application number: PCT/JP2013/069569
Authority: WO
Inventors: 丈也出井; 恵美佐藤; 航治岩崎; 恭介高野
Original assignee: 帝人株式会社
Priority date: 2012-07-11
Filing date: 2013-07-11
Publication date: 2014-01-16

Abstract

Provided is a microfiber structure with which short-circuiting does not occur easily and which is capable of exhibiting stable performance as a separator or insulating material for batteries, electric double layer capacitors, capacitors, etc. because pinholes due to electrode sheet burrs or bending, electrode swelling and contraction, etc. during manufacture or use do not occur easily. The microfiber structure obtained by comprising a microfiber layer obtained from polymer microfibers with a mean diameter of 50-3000 nm, is characterized in that: the maximum compressibility at a microfiber structure contact pressure of 5 MPa is 20% or more; the mean pore diameter in the microfiber layer is 0.01-15 µm; the thickness is 0.0025-0.3 mm; the porosity is 20-90%; the basis weight is 1-90 g/m²; the Frazier air permeability is less than 46 m³/min/m²; and the Macmillan number is 2-15.

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 a result of our investigation, it was found that there was a problem that pinholes were generated in the separator, etc. during the manufacture of the battery or when the battery was used, a short circuit was likely to occur, and stable battery performance could not be obtained. . In addition, it was found that the same problem occurs in 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-mentioned background art, and its purpose is that, during manufacture and use, pinholes due to burr and bending of the electrode sheet, bending, expansion and contraction of the electrode, etc. are unlikely to occur, so short-circuiting is unlikely to occur. An object of the present invention is to provide a fine fiber structure capable of exhibiting stable performance as a separator or insulating material for batteries, electric double layer capacitors, capacitors and the like.

As a result of the study by the present inventors, in the fine fiber structure composed of fine fibers, pinholes are likely to occur during the production and use of the battery, the cause of which is in contact with the burrs of the electrode sheet, The present inventors have found out that this occurs when an electrode material having a large expansion and contraction such as an alloy-based negative electrode is used, and found that the above problem can be solved by the following configuration.
Thus, the following invention is provided.
1. A fine fiber structure comprising a fine fiber layer composed of polymer fine fibers having an average diameter of 50 to 3000 nm, the maximum compression ratio at a surface pressure of 5 MPa measured by the following method of the fine fiber structure is 20% or more, 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. / Minute / m ² and a fine fiber structure having a Macmillan number of 2 to 15.
<Maximum compression ratio>
Using a test sample cut out from a fine fiber structure, the test sample is placed on a glass plate in a 25 ° C. atmosphere by a compression tester, and a test stress is 10 mN, that is, a surface pressure, with a flat indenter having a diameter of 50 μm. A compression test is performed in which a load of up to 5 MPa is applied, the load speed is 2.2 mN / sec, and load-unload is repeated three times, and the maximum change when the maximum thickness change occurs is the test before the compression test. The value divided by the thickness of the sample was taken as the “maximum compression rate”. The compression test is measured three times while changing the test sample, and the average value is obtained.
2. ^2. The fine fiber structure according to 1 above, 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 measured by the following method by the basis weight.
<Tear strength>
According to JIS P8116 (tear strength), an Elmendorf type tear tester is used, and the size of the test sample of the fine fiber structure is 70 mm wide × 63 mm tear direction, and the cutting length is 20 mm.
3. 3. The fine fiber structure according to 1 or 2 above, 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 sample of 100 mm × 15 mm cut out from the fine fiber structure was used as the test sample, and this was made so that the striking blade of the pendulum hits the surface of the test sample so that the test sample was not loosened. Tension is applied and it is installed on the test sample support with Cellophane tape (registered trademark) (manufactured by Nichiban Co., Ltd., Elpac S LP-18S). The pendulum uses the 2J type.
4). 4. The fine fiber structure according to any one of the above 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. 5. The fine fiber structure according to any one of 1 to 4 above, wherein the polymer fine fiber has a crystallinity of 30% or more.
6). Polymer fine fiber is aliphatic polyamide, semi-aromatic polyamide, aromatic polyamide, polyvinyl alcohol, cellulose, polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, and blends and mixtures thereof. 6. The fine fiber structure according to any one of 1 to 5 above, which comprises a polymer selected from the group consisting of copolymers.
7). A battery comprising the fine fiber structure according to any one of 1 to 6 as a separator or an insulating material.
8). 7. An electric double layer capacitor comprising the fine fiber structure according to any one of 1 to 6 as a separator or an insulating material.
9. A capacitor comprising the fine fiber structure according to any one of 1 to 6 as a separator or an insulating material.
10. 8. The battery according to 7 above, wherein the battery is a lithium battery, a lithium ion battery, or a lithium ion gel polymer battery.

The fine fiber structure of the present invention is in contact with a burr of an electrode sheet, is bent greatly, or used with an electrode material having a large expansion and contraction such as an alloy-based negative electrode during the production or use of a battery or the like. Even when the fine fiber structure has a predetermined compression characteristic, the fine fiber structure absorbs the burr of the electrode sheet and the volume change of the electrode, and it is difficult for a pinhole to occur, so that a short circuit hardly occurs. . For this reason, a high performance and stable performance can be exhibited as a battery, an electric double layer capacitor, a capacitor, or the like using the fine fiber structure as a separator or an insulating material.

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 30% or more, more preferably 35% or more, still 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 30%, 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, a capacitor, a 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 fine fiber layer has a porosity of 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 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 maximum compression rate of the fine fiber structure measured by the following method at a surface pressure of 5 MPa is 20% or more, preferably 25% or more, more preferably 30% or more. . When the maximum compression ratio is less than 20%, a pinhole is generated during the manufacture or use of a battery, an electric double layer capacitor, a capacitor, etc., and a short circuit is likely to occur. On the other hand, even if the maximum compression rate is too low, the handleability is poor, or the thickness of the fine fiber structure easily changes during the construction of the battery, so it is preferably 60% or less, more preferably 55% or less, Preferably it is 50% or less.
<Maximum compression ratio>
Using a sample cut out from the fine fiber structure, the sample was placed on a glass plate by a compression tester in an atmosphere at 25 ° C., and a test stress was 10 mN, that is, a surface pressure of 5 MPa with a flat indenter having a diameter of 50 μm. A compression test is performed in which the load speed is 2.2 mN / sec and load-unload is repeated three times. The maximum change when the maximum thickness change occurs is the thickness of the sample before the compression test. The value divided by this was taken as the “maximum compression rate”. The compression test is measured three times with different samples, and the average value is obtained.
That is, in the present invention, when the fine fiber structure is used as a separator or an insulating material, pinholes are generated during the production or use of a battery or the like, and stable performance may not be obtained. This occurs due to contact with the burr of the electrode sheet, bending it greatly, or using it with an electrode material having a large expansion and contraction such as an alloy-based negative electrode, and the maximum compressibility at a surface pressure of 5 MPa. It is important to be able to solve the above-mentioned problems corresponding to the stress due to such deformation by setting it to 20% or more, and for this purpose, it is important to increase the degree of crystallization by heat treatment of the fibers constituting the fine fiber structure. For example, as will be described later, a fine fiber web obtained by electrospinning or the like is subjected to preliminary drying in a hot press treatment step and then calendered. , It found that fine fiber structures with the maximum compression ratio is obtained, in which have reached the present invention.
In the present invention, the value obtained by dividing the tear strength by the Elmendorf-type tear tester method of the fine fiber structure by the basis weight, that is, the tear strength / basis weight is preferably 0.9 g / (g / m ² ) or more. More preferably, it is 1.0 g / (g / m ² ) or more, more preferably 1.5 g / (g / m ² ) or more, and particularly preferably 2.0 g / (g / m ² ) or more. When the tear strength / basis weight is smaller than 0.9 g / (g / m ² ), the fine fiber structure is wound between the electrodes, and the burrs of the electrodes are used as the starting point to stabilize the fine fiber structure. Manufacturing tends 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 test 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.
Furthermore, in the present invention, the impact absorption value by the Charpy impact test method of the fine fiber structure is preferably 290 kJ / m ² or more, more preferably 320 kJ / m ² or more, and further preferably 350 kJ / m ² or more. Particularly preferably, it is 400 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 high compression ratio of 20% or more at a surface pressure of 5 MPa, and at the same time has excellent tear strength and shock absorption value, which are characteristics contrary to this. Therefore, due to these synergistic effects, the separator and the like are not deformed or damaged in the manufacturing process of the separator and the insulating material, and further in the manufacturing process of the battery using the separator, or at the time of use. A high-performance battery, a capacitor, a capacitor, and the like having high liquid absorbability described below can be provided.
In the present invention, the permeation rate of the fine fiber structure is preferably 20 cm ² / min or more, more preferably 23 cm ² / min or more, further preferably 25 cm ² / min or more, and particularly 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, 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 simultaneously satisfy the penetration rate of the electrolyte solution, the tear strength / basis weight, the impact absorption value, the crystallinity of the fine fiber, etc. in the fine fiber structure, the above-mentioned and later details will be described. This can be realized by spinning and hot-pressure processing described below.
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, alicyclic polyamides, semi-aromatic polyamides, aromatic polyamides, polysulfones, cellulose acetates, cellulose, polyethylene terephthalate, polyethylene naphthalate. , Polypropylene terephthalate, polybutylene terephthalate, polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, polymethylpentene, polyacrylonitrile, polyphenylene sulfide, polyacetyl, polyurethane, polyacrylonitrile, polymethyl methacrylate, polystyrene , Polyimides and copolymers or derivative compounds thereof, and these Combinations thereof. In particular, consisting of aliphatic polyamide, semi-aromatic polyamide, aromatic polyamide, polyvinyl alcohol, cellulose, polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, and blends, mixtures and copolymers thereof. Those comprising a polymer selected from the group are preferred.
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 it is preliminarily dried with a hot air dryer at 250 to 350 ° C. And then calendering can be preferably adopted by a method in which the roll surface temperature is 150 to 250 ° C. and the linear pressure is 100 to 200 kg / cm, which satisfies the above-mentioned maximum compression rate at a surface pressure of 5 MPa. A fine fiber structure can be manufactured. Although the said process does not have limitation of a polymer etc., it turned out that it is effective in adjustment of the compression characteristic of the fine fiber structure which consists of polyimide, aromatic polyamide, a semi-aromatic polyamide etc. especially.
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) Average pore diameter The average pore diameter of the fine fiber layer was determined using Capillary Flow Porometer CFP-1200-AEXL (manufactured by Porous Materials, Inc.).
(5) Frazier permeability The sample is cut out from the fine fiber layer, conforms to JIS L1096 (2010) 8.26 A method (Fragile format), and the measurement range is 5 cm ² using a Fragil tester (FX3300 manufactured by TEXTEST). The measured value was shown in the unit m ³ / min / m ² .
(6) 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 fibers, and the thickness (μm), the porosity was calculated by the following formula.
Porosity (%) = 100-basis weight / (polymer density × thickness) × 100
(7) 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.
(8) Maximum compression rate Shimadzu microcompression tester Using MCT-W200, a test sample cut out from a fine fiber structure was placed on a glass plate in an atmosphere at 25 ° C., and a test stress was measured with a flat indenter having a diameter of 50 μm. 10 mN, that is, applying a load up to 5 MPa at a surface pressure, with a load speed of 2.2 mN / sec, conducting a compression test in which load-unload is repeated three times, and the maximum amount of change when the maximum thickness change occurs The value obtained by dividing by the thickness of the test sample before the compression test was defined as the “maximum compression rate”. The compression test was measured three times with different test samples, and the average value was obtained.
(9) Battery performance Preparation of electrode (positive electrode): 89.5 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 a dry weight of PVdF of 6 parts by mass Thus, a positive electrode paste was prepared using an N-methyl-pyrrolidone (NMP) solution of 6% by mass PVdF. 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 was produced using the above electrode, electrolyte, and separator, and the cell was compressed with a stress of 5 MPa. As a battery characteristic test, an initial charge / discharge test is performed. The initial charge / discharge test is 0.2C, 4.2V constant current / constant voltage charge (8 hours), and then 0.2C, 2.75V cut-off constant current discharge. The case where the short circuit did not occur was determined to be good, and the case where the short circuit occurred was determined to be defective.
(10) Tear strength In accordance with JIS P 8116 (Tear strength), the size of the test sample of the fine fiber structure is 70 mm wide × tear using an Elmendorf type tear tester (radius 24 cm) manufactured by Toyo Seiki Seisakusho Co., Ltd. Measurement was performed with a direction of 63 mm and a cutting length of 20 mm.
Specifically, the measurement was performed by the following method using an Elmendorf tear tester.
(11) Impact absorption value Measured in accordance with JIS K 7111-1 (2006) (unnotched Charpy impact strength). At this time, a test sample of 100 mm × 15 mm cut out from the fine fiber structure was used as the test sample, and this was made so that the striking blade of the pendulum hits the surface of the test sample so that the test sample was not loosened. Tension is applied and it is installed on the test sample support with Cellophane tape (registered trademark) (manufactured by Nichiban Co., Ltd., Elpac S LP-18S). The pendulum uses the 2J type.
(12) 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).
[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. The polymer solution was discharged from a nozzle, and an applied voltage was set to 40 kV by an electrospinning method to form fine fibers. The fine fibers were collected by a transport net 20 cm below the nozzle to obtain a fine fiber web.
Subsequently, in the process of hot-pressing the fine fiber web, a hot air dryer is used for 300 ° C. for 1 minute (preliminary drying), and then calendered at a roll surface temperature of 200 ° C. and a linear pressure of 150 kg / cm. Thus, a fine fiber structure composed of one fine fiber layer was obtained. The residual solvent amount of the fine fiber structure was 0.01% by weight. The results are shown in Table 1.
[Example 2]
In the process of hot-pressing the fine fiber web, Example 1 except that it was calendered at a roll surface temperature of 250 ° C. and a linear pressure of 200 kg / cm after drying at 350 ° C. for 1 minute with a hot air dryer. Similarly, the fine fiber structure shown in Table 1 was obtained. The residual solvent amount of the fine fiber structure was 0.01% by weight. The results are shown in Table 1.
[Example 3]
In the step of hot-pressing the fine fiber web, Example 1 except that it was dried at 250 ° C. for 1 minute with a hot air dryer and then calendered at a roll surface temperature of 150 ° C. and a linear pressure of 100 kg / cm. Similarly, the fine fiber structure shown in Table 1 was obtained. The residual solvent amount of the fine fiber structure was 0.02% by weight. The results are shown in Table 1.
[Comparative Example 1]
The fine fibers shown in Table 1 are the same as in Example 1 except that in the step of hot-pressing the fine fiber web, calendering was performed at a roll surface temperature of 300 ° C. and a linear pressure of 75 kg / cm without performing a preliminary drying treatment. A structure was obtained. The results are shown in Table 1.
[Comparative Example 2]
Instead of the fine fiber structure, evaluation was performed using a cellulose separator for an electricity storage device (manufactured by Nippon Advanced Paper Industries Co., Ltd., polymer density 1.5 g / cm ³ ). The results are shown in Table 1.

The fine fiber structure of the present invention is in contact with a burr of an electrode sheet, is bent greatly, or used with an electrode material having a large expansion and contraction such as an alloy-based negative electrode during the production or use of a battery or the like. Even when doing so, pinholes are unlikely to occur, and short circuits are unlikely to occur. For this reason, a high performance and stable performance can be exhibited as a battery, an electric double layer capacitor, a capacitor, or the like using the fine fiber structure as a separator or an insulating material.

Claims

A fine fiber structure comprising a fine fiber layer composed of polymer fine fibers having an average diameter of 50 to 3000 nm, the maximum compression ratio at a surface pressure of 5 MPa measured by the following method of the fine fiber structure is 20% or more, 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. / Minute / m 2 and a fine fiber structure having a Macmillan number of 2 to 15.
<Maximum compression ratio>
Using a test sample cut out from a fine fiber structure, the test sample is placed on a glass plate in a 25 ° C. atmosphere by a compression tester, and a test stress is 10 mN, that is, a surface pressure, with a flat indenter having a diameter of 50 μm. A compression test is performed in which a load of up to 5 MPa is applied, the load speed is 2.2 mN / sec, and load-unload is repeated three times, and the maximum change when the maximum thickness change occurs is the test before the compression test. The value divided by the thickness of the sample was taken as the “maximum compression rate”. The compression test is measured three times while changing the test sample, and the average value is obtained.
The fine fiber structure 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 measured by the following method by the basis weight.
<Tear strength>
According to JIS P8116 (tear strength), an Elmendorf type tear tester is used, and the size of the test sample of the fine fiber structure is 70 mm wide × 63 mm tear direction, and the cutting length is 20 mm.
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 sample of 100 mm × 15 mm cut out from the fine fiber structure was used as the test sample, and this was made so that the striking blade of the pendulum hits the surface of the test sample so that the test sample was not loosened. Tension is applied and it is installed on the test sample 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 crystallinity of the polymer fine fiber is 30% or more.
Polymer fine fiber is aliphatic polyamide, semi-aromatic polyamide, aromatic polyamide, polyvinyl alcohol, cellulose, polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, and blends and mixtures thereof. 6. The fine fiber structure according to claim 1, 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 6 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 6 as a separator or an insulating material.
A capacitor comprising the fine fiber structure according to any one of claims 1 to 6 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.