JP2002110130A - Battery separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery separator which can further reduce the occurrence of short circuit between electrodes when forming an electrode group and further suppress the occurrence of micro short circuit during long-term use. To provide. SOLUTION: The battery separator of the present invention has a total thickness of a mixed layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are entangled with each other by 3/3 of the total thickness. A non-woven fabric occupying at least one fiber, and further comprising ultra-fine short fibers having a fiber diameter of 8 μm or less and fused short fibers as the short fibers, wherein the long fibers have a tensile strength of 4.5 cN / dtex or more. It is characterized by being composed of fused long fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a battery separator.

[0002]

2. Description of the Related Art Conventionally, a separator capable of holding an electrolytic solution has been arranged between these electrodes so that a positive electrode and a negative electrode of an alkaline battery can be separated from each other to prevent a short circuit, and that an electromotive reaction can be carried out smoothly. Have been.

[0003] In recent years, with the miniaturization and weight reduction of electronic devices, development in the direction of increasing the battery capacity has been actively pursued. Under such circumstances, when forming the electrodes of a high-capacity battery in a group, it is necessary to use a separator having a small surface density or thickness as a separator, and to increase the winding pressure in the group configuration. As a result, many short-circuits occur between the electrodes, which has been a serious problem in the yield of battery production. Also, even if batteries could be manufactured without short-circuiting,
During use for a long period of time after charging and discharging, there have been problems such as causing a micro short circuit.

In order to solve such a problem, the applicant of the present invention has proposed a short fiber having a fiber length of less than 1 to 25 mm and a fiber length of 2 to 25 mm.
The total thickness of the mixed layer in which the long fibers of 5 mm or more are entangled,
It is an alkaline battery separator made of a nonwoven fabric having a thickness of 1/3 or more of the entire nonwoven fabric, and it is preferable that the fibers constituting the nonwoven fabric are made of ultrafine fibers, high-strength fibers, and fused fibers. (Japanese Unexamined Patent Publication No.
1-331495).

[0005]

This alkaline battery separator can reduce the occurrence of short circuits between the electrodes when forming the electrodes in groups, and can suppress the occurrence of minute short circuits during long-term use. However, a separator having further improved performance has been desired. The present invention has been made to improve the above points, and an object of this application is to further reduce the occurrence of a short circuit between electrodes when forming the electrodes in a group, and to reduce the use of the electrodes during long-term use. An object of the present invention is to provide a battery separator that can further suppress occurrence of a micro short circuit.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that (1) the use of ultrafine fibers having a long fiber length does not significantly affect the occurrence of micro short-circuits during long-term use. And (2) when a high-strength fiber having a long fiber length is used, it is particularly effective in preventing the occurrence of a short circuit when forming the electrodes in groups. The present invention has been made based on such knowledge, and the battery separator of the present invention (hereinafter simply referred to as “separator”) has a short fiber having a fiber length of less than 25 mm and a fiber length of 25 mm.
The total thickness of the mixed layer entangled with long fibers of not less than 1 mm is a nonwoven fabric occupying one third or more of the total thickness, and is fused with the ultrafine short fibers having a fiber diameter of 8 μm or less as the short fibers. And the short fibers have a tensile strength of 4.5 c.
It is characterized by comprising high-strength long fibers of N / dtex or more and fused long fibers. As described above, since the long fibers are composed of the two types of the high-strength long fibers and the fused long fibers, the amount of the high-strength long fibers can be increased. As a result, a tough skeleton is formed by the high-strength long fibers and the fused long fibers, so that when the electrodes are grouped, the separator is broken, the burr of the electrode plate penetrates through the separator, or the electrode plate It is difficult to be torn by the edge and short-circuit between the electrodes is less likely to occur when the electrodes are grouped. In addition, ultra-fine short fibers having a short fiber length have a high degree of freedom and can be densely and uniformly distributed between the skeletons formed by the high-strength long fibers and the fused long fibers. Excellent in nature. In addition, when the short fibers further include high-strength short fibers having a tensile strength of 4.5 cN / dtex or more, the high-strength short fibers are densely and uniformly distributed, so that the reliability of the performance is further improved. I do. The high-strength filament has a tensile strength of 9 cN / dtex or more,
When the Young's modulus is 800 kg / mm ² or more of polypropylene long fibers, the pressure applied when the electrodes are grouped,
Since the thickness of the nonwoven fabric (separator) can be maintained against the pressure during charge / discharge, the retention of the electrolyte is excellent, and the battery characteristics can be further improved.
Furthermore, when the ultrafine short fibers are derived from hollow split short fibers, the separators can be finer ultrafine short fibers, so that a more dense and uniform separator can be obtained. As a result, the battery is more excellent in preventing short circuits when the battery is used.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the separator of the present invention, the total thickness of a mixed layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are intertwined with each other is 3 minutes of the total thickness. Consisting of a nonwoven fabric occupying one or more of the following. This mixed layer has a more uniform distribution of the electrolytic solution, a lower internal resistance of the battery, and a battery excellent in discharge characteristics and high capacity as compared with a layer composed of only short fibers or a layer composed of only long fibers. The ratio of the mixed layer to the total thickness of the nonwoven fabric is preferably as high as possible, and the thickness of the mixed layer preferably occupies two-thirds or more of the total thickness of the nonwoven fabric, and the entire nonwoven fabric (separator) is composed of the mixed layer. Is most preferred. In addition, the mixed layer does not need to be one,
Two or more may exist. As in the latter case, when two or more are present, the total thickness should occupy one third or more of the thickness of the entire nonwoven fabric. In addition, layers other than the mixed layer contained in the nonwoven fabric (separator) (for example,
The presence or absence of a layer composed of only short fibers, a layer composed of only long fibers, and the like, and the arrangement of the mixed layer and the layers other than the mixed layer are not particularly limited.

In the present specification, the term "mixed layer" means a layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are entangled and mixed. Such a mixed layer can be formed by laminating a fiber web made of short fibers and a fiber web made of long fibers, and then performing at least one entanglement treatment. The layer composed of only short fibers, the layer composed of only long fibers, or the mixed layer can be clearly distinguished by, for example, observing a cross section of the nonwoven fabric (separator) with a microscope. Also, the thickness of this mixed layer is
It refers to the thickness under no load.

In the present invention, short fibers having a fiber length of less than 25 mm are included so that the formation is excellent. When the fiber length is 25 mm or more, the formation becomes worse, or the fiber web itself tends to be difficult to form. Therefore, the preferable fiber length is 5 to 20 mm, and the more preferable fiber length is 5 to 20 mm. 15 mm. The “fiber length” in the present invention means a length obtained by JIS L 1015 (chemical fiber staple test method) B method (corrected staple diagram method).

In the present invention, since the short fibers include ultrafine short fibers having a fiber diameter of 8 μm or less and fused short fibers, the ultrafine short fibers can be densely and uniformly dispersed, Since such a state can be maintained by the short fibers, the short-circuit prevention property during use of the battery is excellent.

The ultra-fine short fibers must have a fiber diameter of 8 μm or less, preferably 5 μm or less, more preferably 4 μm or less, so that they can be densely and uniformly dispersed. Although the lower limit of the fiber diameter of the ultrafine short fibers is not particularly limited, about 0.01 μm is appropriate. In the present invention, the "fiber diameter" refers to the diameter of the fiber when the cross-sectional shape is circular, and has the same area as the cross-sectional area when the cross-sectional shape of the fiber is non-circular. The diameter of a circle.

[0012] Such ultrafine short fibers can be used to divide splittable short fibers which can be split by a physical action such as a fluid stream such as a water stream, a needle or a calender, to dissolve and remove a resin component by a solvent, Thus, the split short fibers that can be split by a chemical action such as swelling the resin component can be obtained by splitting. Examples of the split short fibers that can be split by the former physical action include split short fibers having an orange cross-section as shown in FIGS. 1 to 4 and multi-bimetal cross-sections as shown in FIG. Split short fibers of the mold can be used. It is to be noted that hollow split short fibers as shown in FIGS. 6 to 14 can generate finer and ultra-fine short fibers, and can be split by weak physical action, disturbing formation. Therefore, a nonwoven fabric (separator) having a denser and more uniform formation can be obtained. As the split short fibers that can be split by the latter chemical action, for example, split short fibers having a sea-island cross section can be used.

Examples of the resin component constituting the split short fibers which can be split by a physical action or the split short fibers which can be split by a chemical action include, for example, polyamide resins (for example, nylon 6, nylon 66, nylon 12). , A nylon copolymer such as a copolymer of nylon 6 and nylon 12), an ethylene-based resin (for example, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ethylene and vinyl alcohol) , A copolymer of ethylene and acrylic acid, a copolymer of ethylene and methacrylic acid, and a propylene-based resin (for example, a copolymer of polypropylene, propylene and one or more other vinyl compounds) ), Butene-based resin (for example, polybutene, co-polymerization of butene with one or more other vinyl compounds) Coalescents), methylpentene resins (polymethylpentene, copolymers of methylpentene and one or more other vinyl compounds, etc.), and the split short fibers can be composed of one or more of these resins. .

[0014] Since short fibers constituting the separator of the present invention include fused short fibers, the fineness and uniformity of the ultrafine short fibers can be maintained. This fused short fiber completely melts other fibers (for example, ultra-fine short fiber, high-strength short fiber, high-strength long fiber, etc.) (except for fused long fiber) by heat at the time of fusion, and has a strength. It is preferable to have a resin component (low-melting point component) that does not lower the content on at least the fiber surface. In other words, when each of the other fibers is made of one type of resin component, a low melting point component having a lower melting point (preferably lower than 5 ° C, more preferably lower than 10 ° C) than any resin component is used. Preferably, it is a fused short fiber at least on the fiber surface. Also, 2
When containing other fibers composed of more than one kind of resin component, a low melting point component having a melting point lower than any resin component (preferably lower than 5 ° C., more preferably lower than 10 ° C.) At least a fused short fiber on the fiber surface may be used, or other fibers composed of two or more resin components may be fused so that other fibers composed of two or more resin components can be simultaneously fused. A fused short fiber having at least a low melting point component having a melting point similar to that of the resin component constituting the surface on the fiber surface may be used. In the present invention, the “melting point” refers to a temperature at which a maximum value of a melting endothermic curve obtained by using a differential calorimeter at a heating rate of 10 ° C./min from room temperature is obtained.

[0015] The fused short fibers can be composed of the same resin components as those constituting the above-mentioned split short fibers. That is, a polyamide resin (for example, nylon 6,
Nylon 66, Nylon 12, Nylon 6 and Nylon 1
2, a nylon copolymer such as a copolymer with 2, a low-density polyethylene, a medium-density polyethylene, a high-density polyethylene, a linear low-density polyethylene, a copolymer of ethylene and vinyl alcohol, Copolymers of ethylene and acrylic acid, copolymers of ethylene and methacrylic acid, propylene-based resins (eg, polypropylene, copolymers of propylene with at least one other vinyl compound, etc.), butene-based Resins (eg, polybutene, copolymers of butene with one or more other vinyl compounds, etc.), and methylpentene resins (polymethylpentene, copolymers of methylpentene, with one or more other vinyl compounds, etc.) ) And one or more resin components.

The fused short fiber may be composed of a single resin component or may be composed of two or more resin components. The latter is a nonwoven fabric (separator).
This is preferable because the tensile strength of the steel can be further improved. When the fused short fibers are composed of two or more resin components,
The fiber cross-sectional shape can be, for example, a core-sheath type, an eccentric type, a side-by-side type, a sea-island type, a multiple bimetal type, or an orange type.

The fiber diameter of the fused short fibers is not particularly limited, but is preferably 1 to 30 μm so as not to impair uniform formation, not to make the pore size of the nonwoven fabric too large, and to reduce the strength of the nonwoven fabric. Is preferably 3 to 20 μm
m is more preferable.

[0018] The tensile strength of the fused short fiber is 2.7c.
If it is more than N / dtex, the electrode plate group may be broken by tension, the burrs of the electrode plate may penetrate the separator, or the separator may be torn by the edge of the electrode plate, so that a short circuit is less likely to occur. It is suitable. More preferable tensile strength is 3.5 cN / dtex or more. Examples of such fused short fibers include, for example, fused short fibers containing high-density polyethylene, and more specifically, fused short fibers composed only of high-density polyethylene, and a core component composed of polypropylene. And a sheath-core fused short fiber whose sheath component is made of high-density polyethylene. "Tensile strength" in the present invention is defined by JIS L
1015 (chemical fiber staple test method).

The short fibers constituting the nonwoven fabric (separator) of the present invention have a tensile strength of 4.5 cN / dtex.
It preferably contains the above high-strength short fibers. Since the high-strength short fibers are densely and uniformly distributed, it is possible to further suppress occurrence of a short circuit between the electrodes when forming the electrodes in a group, and to manufacture a battery with a high yield.

The higher the strength of the short fiber, the higher the tensile strength, the better the above-mentioned effect.
It is preferably at least 3 cN / dtex, and 9 cN / d
tex or more, preferably 10.8 cN / dte
It is more preferable that the value be x or more. The upper limit of the tensile strength is not particularly limited, but is 50 cN / dtex.
The degree is appropriate.

The Young's modulus is preferably 800 kg / mm ² or more so that the thickness of the high-strength short fiber itself can be maintained against the pressure at the time of forming the electrode plate group or at the time of using the battery. More preferably, it is 850 kg / mm ² or more. The “Young's modulus” in the present invention is J
It refers to the value of apparent Young's modulus calculated from the initial tensile resistance measured by IS L 1015.

The high-strength staple fiber can be composed of one or more resin components similar to the resin component constituting the split staple fiber. However, from the viewpoint of electrolytic solution resistance, the fiber surface is made of a polyolefin resin. It preferably contains polypropylene or ultrahigh molecular weight polyethylene having an average molecular weight of 1,000,000 to 5,000,000. That is, it may be a high-strength short fiber composed of only polypropylene or ultrahigh-molecular-weight polyethylene having an average molecular weight of 1,000,000 to 5,000,000, or a polyolefin resin constituting the fiber surface, and polypropylene or an average molecular weight of 1,000,000 to 500,000. Ten thousand ultra-high molecular weight polyethylenes may be high-strength short fibers constituting the fiber interior.

Among these high-strength short fibers, particularly, the tensile strength is 9 cN / dtex or more and the Young's modulus is 800 kg.
It is preferably a high-strength short fiber made of polypropylene short fiber of / mm ² . Such a high-strength short fiber has, for example, an isotactic pentad fraction (IPF) of 95.
１００100%, the ratio of weight average molecular weight / number average molecular weight (Q
Value) is less than 4 and a pressurized water tank is arranged at the introduction part of the object to be drawn and the drawn part of the drawn object, and a drawing tank filled with high-temperature and pressurized steam is used. It can be obtained by stretching at a stretching bath temperature of 120 ° C. or more and a stretching ratio of 7 times or more by a stretching apparatus, and then cutting it to a length of less than 25 mm. The high-strength staple fiber obtained by such a method is highly oriented and crystallized in the fiber direction, and when the fiber side surface is observed in a crossed Nicol state under polarized light, the refractive index differs in the fiber direction, intermittent. It has a unique stripe pattern consisting of linear dark and light portions.

The fiber diameter of the high-strength staple fiber of the present invention is not particularly limited. However, the fiber diameter of the high-strength staple fiber should not be reduced so as not to impair uniform formation, not to increase the pore size of the nonwoven fabric, and to reduce the strength of the nonwoven fabric. Preferably 30 to 30 μm.
More preferably, it is 20 μm.

The short fibers constituting the nonwoven fabric (separator) of the present invention are composed of the above-mentioned ultrafine short fibers and fused short fibers, and are preferably composed of ultrafine short fibers, fused short fibers and high-strength short fibers. As in the former case, when the short fibers are composed of ultrafine short fibers and fused short fibers, the mass ratio is (ultrafine short fibers) :( fused short fibers) = 5-95: 95-5. Preferably, (extremely short fibers): (fused short fibers) = 20 to 8
0: 80-20 is more preferable. Further, as in the latter case, when the short fibers are composed of ultrafine short fibers, fused short fibers and high-strength short fibers, the mass ratio thereof is (ultrafine short fibers):
(Fused short fiber): (High strength short fiber) = 5-90: 5-9
0: 90 to 5, preferably (extremely short fiber):
(Fused short fiber): (High strength short fiber) = 10 to 80:10
-80: More preferably from 80 to 10, (extremely short fibers) :( fused short fibers) :( high-strength short fibers) = 20 to 6
The ratio is more preferably 0:20 to 60:60 to 20.
In addition, as the short fiber of the nonwoven fabric (separator) of the present invention,
It may contain undivided short fibers or short fibers having a fiber diameter exceeding 8 μm.

In the present invention, in addition to the short fibers as described above, long fibers having a fiber length of 25 mm or more are included in order to improve the tensile strength, tear strength and bending resistance of the nonwoven fabric (separator). If the fiber length is shorter than 25 mm,
This is because the tensile strength, the tear strength, and the bending resistance may not be sufficiently improved or may not be sufficiently entangled. Therefore, a preferable fiber length is 30 to 110 mm, and a more preferable fiber length is 30 to 60 mm.

In the present invention, since the long fibers are composed of two types of high-strength long fibers having a tensile strength of 4.5 cN / dtex or more and fused long fibers, the amount of high-strength long fibers can be increased. it can. As a result, a tough skeleton is formed by the high-strength long fibers and the fused long fibers, so that when the electrodes are grouped, the separator is broken, the burr of the electrode plate penetrates through the separator, or the electrode plate It is hard to be torn by the edge, and short circuit between the electrodes is less likely to occur when the electrodes are grouped.

Such a high-strength filament has a higher tensile strength, and the above-mentioned effect is more excellent. Therefore, the tensile strength is preferably 6.3 cN / dtex or more, and 9 c
N / dtex or more, preferably 10.8 cN /
It is more preferably at least dtex. Although the upper limit of the tensile strength is not particularly limited, it is 50 cN / d.
tex is appropriate.

The high-strength filaments serve to form a tough skeleton, so that the thickness of the nonwoven fabric (separator) can be maintained against the pressure when forming the electrode plate group or when using the battery. The Young's modulus is preferably 800 kg / mm ² or more, more preferably 850 kg / mm ² or more.

This high-strength long fiber can be composed of at least one resin component similar to the resin component constituting the split short fiber. However, from the viewpoint of electrolytic solution resistance, the fiber surface is made of a polyolefin resin. It preferably contains polypropylene or ultrahigh molecular weight polyethylene having an average molecular weight of 1,000,000 to 5,000,000. That is, it may be a high-strength long fiber consisting only of polypropylene or ultrahigh-molecular-weight polyethylene having an average molecular weight of 1,000,000 to 5,000,000, or a polyolefin resin constituting the fiber surface, and having a polypropylene or an average molecular weight of 1,000,000 to 500,000,000. Ten thousand ultra-high molecular weight polyethylenes may be high-strength long fibers constituting the inside of the fiber.

Among these high-strength filaments, the tensile strength is particularly 9 cN / dtex or more and the Young's modulus is 800 kg.
/ Mm ² is preferably a high-strength long fiber composed of a long polypropylene fiber. This high-strength long fiber can be produced in exactly the same manner as the high-strength short fiber except that it is cut into 25 mm or more.

It is preferable that the high-strength long fiber has a crimp, because the high-strength filament can further resist pressure and can maintain the thickness of the nonwoven fabric (separator). The number of crimps is preferably 3 pieces / inch or more, and more preferably 5 pieces / inch or more. On the other hand,
If the crimping is too large, the shape stability is deteriorated. Therefore, the number is preferably 30 pieces / inch or less, and more preferably 20 pieces / inch or less.

The high-strength long fibers preferably have a large fiber diameter so as to form the skeleton of the nonwoven fabric (separator) and to resist pressure. More specifically, it is preferably at least 1 μm, more preferably at least 3 μm. On the other hand, if the fiber diameter of the high-strength long fiber is too large, the entanglement with the short fiber deteriorates.
m or less, more preferably 20 μm or less.

Since the nonwoven fabric (separator) of the present invention contains fused long fibers as long fibers, the skeleton formed by high-strength long fibers can be fused and fixed. The fused long fibers are heated by the heat at the time of fusion to form other fibers (for example, ultrafine short fibers, high strength short fibers, high strength long fibers, etc.).
It is preferable that a resin component (low-melting point component) that does not lower the strength by completely melting (excluding the fused short fibers) is provided at least on the fiber surface. In other words, when each of the other fibers is made of one type of resin component, a low melting point component having a lower melting point (preferably lower than 5 ° C, more preferably lower than 10 ° C) than any resin component is used. ,
It is preferably a fused long fiber having at least a fiber surface. In the case where other fibers composed of two or more resin components are contained, a low melting point having a melting point lower than that of any of the resin components (preferably lower than 5 ° C., more preferably lower than 10 ° C.) The component may be a fused long fiber having at least a fiber surface, or another fiber composed of two or more resin components so that other fibers composed of two or more resin components can be simultaneously fused. A low melting point component having a melting point similar to that of the resin component constituting the surface of the fiber,
It may be a fused long fiber at least on the fiber surface. It is preferable that the low melting point component of the fused long fiber and the low melting point component of the fused short fiber have the same melting point, because the fused long fiber and the fused short fiber can be fused at the same time. is there.

The fused long fibers can be composed of the same resin components as those constituting the above-mentioned split short fibers. That is, a polyamide resin (for example, nylon 6,
Nylon 66, Nylon 12, Nylon 6 and Nylon 1
2, a nylon copolymer such as a copolymer with 2, a low-density polyethylene, a medium-density polyethylene, a high-density polyethylene, a linear low-density polyethylene, a copolymer of ethylene and vinyl alcohol, Copolymers of ethylene and acrylic acid, copolymers of ethylene and methacrylic acid, propylene-based resins (eg, polypropylene, copolymers of propylene with at least one other vinyl compound, etc.), butene-based Resins (eg, polybutene, copolymers of butene with one or more other vinyl compounds, etc.), and methylpentene resins (polymethylpentene, copolymers of methylpentene, with one or more other vinyl compounds, etc.) ) And one or more resin components.

The fused long fibers may be composed of a single resin component, or may be composed of two or more resin components. The latter is a nonwoven fabric (separator).
This is preferable because the tensile strength of the steel can be further improved. When the fused long fiber is composed of two or more resin components,
The fiber cross-sectional shape can be, for example, a core-sheath type, an eccentric type, a side-by-side type, a sea-island type, a multiple bimetal type, or an orange type.

Although the fiber diameter of the fused long fibers is not particularly limited, the fibers are firmly fused with the high-strength long fibers to maintain the skeleton formed by the high-strength long fibers and impart elasticity to the nonwoven fabric. Preferably, the thickness is 1 to 30 μm, more preferably 3 to 20 μm.

The tensile strength of the fused long fiber is 2.7 c.
If it is more than N / dtex, the electrode plate group may be broken by tension, the burrs of the electrode plate may penetrate the separator, or the separator may be torn by the edge of the electrode plate, so that a short circuit is less likely to occur. It is suitable. More preferable tensile strength is 3.5 cN / dtex or more. Examples of such fused long fibers include, for example, fused long fibers containing high-density polyethylene, and more specifically, fused long fibers composed only of high-density polyethylene, and a core component composed of polypropylene. And a core-sheath type fused long fiber whose sheath component is made of high-density polyethylene.

The long fibers of the present invention are composed of the high-strength long fibers and the fused long fibers as described above. The mass ratio is such that the high-strength long fibers can form a tough skeleton, and the high-strength long fibers can be used. (High-strength long fiber) :( fused long fiber) = 10-90: 90-10, preferably (high-strength long fiber) :( fused length) so that the skeleton can be maintained firmly. fiber)
= 20 to 80:80 to 20 is more preferable.

In the nonwoven fabric constituting the separator of the present invention, the ratio of short fibers to long fibers is excellent in the denseness and uniformity of short fibers, and the tensile strength, tear strength or softness of long fibers. It is preferable that (short fiber) :( long fiber) = 10-90: 90-10,
(Short fiber) :( long fiber) = 20-80: More preferably, 80-20.

The areal density of the nonwoven fabric (separator) of the present invention is preferably 30 to 100 g / m ² , and 40 to 80 g / m ^2.
g / m ² is more preferable. Area density 30g / m ²
If less than 100%, the tensile strength may be insufficient,
If it exceeds g / m ² , the nonwoven fabric becomes too thick and it is difficult to increase the capacity of the battery. The thickness is 0.08
It is preferably about 0.3 mm.

The nonwoven fabric (separator) of the present invention has an oxygen and / or sulfur-containing functional group (for example, sulfonic acid group, sulfonate group, sulfofluoride group, (A carboxyl group, a carbonyl group, etc.), a hydrophilic monomer is graft-polymerized, a surfactant is attached, or a hydrophilic resin is attached.

The tensile strength in the vertical direction (length direction) of the nonwoven fabric (separator) of the present invention is set to 100 N / 50 m so that the nonwoven fabric (separator) is not broken by the tension at the stage of manufacturing the electrode plate assembly.
m or more, and more preferably 140 N / 50 mm or more. This tensile strength refers to a value obtained by fixing a separator having a width of 50 mm to a tensile strength tester (manufactured by Orientec, Tensilon UTM-III-100) (distance between chucks: 100 mm) and measuring the tensile speed at 300 mm / min. .

The tear strength in the vertical direction (length direction) of the nonwoven fabric (separator) of the present invention is 50 N / 50 mm width or more so that the nonwoven fabric (separator) is not torn by the edge of the electrode plate at the stage of manufacturing the electrode group. Preferably 55
More preferably, the width is N / 50 mm or more. The tear strength refers to JIS L 1096 ^-1990 (general fabric test method, Torabezoido method) value measured by.

When the formation index of the nonwoven fabric (separator) of the present invention is 0.18 or less, short fibers are in a state of being densely and uniformly dispersed, and a micro short circuit is hard to occur, which is preferable. A more preferred formation index is 0.16 or less. The "formation index" refers to a value obtained by a method described in Japanese Patent Application No. 11-152139. That is, it means a value obtained as follows. (1) Light is emitted from a light source to an object to be measured (separator), and of the irradiated light, light reflected by a predetermined region of the object to be measured is received by a light receiving element to acquire luminance information. . (2) A predetermined area of the measured object has an image size of 3 mm square and 6 m
The image is equally divided into an m square, a 12 mm square, and a 24 mm square to obtain four divided patterns. (3) The luminance value of each of the equally divided sections for each of the obtained divided patterns is calculated based on the luminance information. (4) An average luminance (X) for each divided pattern is calculated based on the luminance value of each section. (5) Find the standard deviation (σ) for each divided pattern. (6) The coefficient of variation (CV) for each divided pattern is calculated by the following equation. Coefficient of variation (CV) = (σ / X) × 100 Here, σ indicates the standard deviation of each divided pattern, and X indicates the average luminance of each divided pattern. (7) A coordinate group obtained as a result of setting the logarithm of each image size as the X coordinate and the variation coefficient corresponding to the image size as the Y coordinate is regressed to a linear line by the least squares method, and its slope is calculated. Is defined as the formation index.

The separator of the present invention can be manufactured, for example, as follows.

When the ultrafine short fibers are obtained from physically splittable short fibers, physically splittable short fibers,
One or more short fiber webs (preferably including high-strength short fibers) containing fused short fibers are formed by, for example, a wet method. On the other hand, one or more long-fiber webs composed of high-strength long fibers and fused long fibers are formed by, for example, a dry method (for example, a card method, an air-lay method, a spun-bond method).

Next, one or more short fiber webs and one or more long fiber webs are laminated to form a laminated fiber web. When laminating at least one of the short fiber web and the long fiber web, two or more of the short fiber web and the long fiber web are combined so as to easily form a mixed layer in which the short fibers and the long fibers are entangled. It is preferred to alternately laminate.

Next, a fluid flow such as a water flow is jetted onto the laminated fiber web to perform an entanglement treatment. In the entanglement process, a fluid flow having higher energy than before is applied so that the long fibers and the short fibers are entangled. The split short fibers are entangled by the action of the fluid flow and split at the same time to generate ultrafine short fibers. Before applying a fluid flow or the like, the split short fibers may be split by calendering, needle punching, or the like.

More specifically, the action of the fluid flow having a higher energy than that of the prior art is defined as follows: when the nozzle diameter is R (unit: mm) and the internal pressure of the nozzle is P (unit: MPa), E) The E value derived from E = R × P ² is 10
Or more, preferably 15 or more, more preferably 18 or more,
Most preferably, it refers to applying at least one fluid stream at least once. In this equation, since the kinetic energy is proportional to the square of the mass and the velocity, the larger the nozzle diameter, the larger the mass of the fluid that is ejected and acts, and the higher the internal pressure of the nozzle, the greater the ejection. Since the velocity of the fluid is high, the kinetic energy of the fluid flow is represented in a pseudo manner.

The conditions for the fluid flow ejection are, for example, a nozzle diameter of 0.05 to 0.3 mm and a pitch of 0.2 to 3 m.
Using nozzle plates arranged in one or more rows at m, a fluid having an internal pressure of about 10 MPa to 30 MPa can be ejected and entangled. The jet of the fluid stream can be directed to one side or both sides of the laminated fiber web. The fluid flow is ejected twice or more, and is preferably ejected so that the total of the above E values is 30 or more, more preferably 40 or more, and more preferably 60 or more. It is more preferable to squirt, and it is most preferable to squirt so as to be 80 or more. Furthermore, when a coarse support is used as a support for supporting the laminated fiber web when the fluid flow is jetted out, a nonwoven fabric having openings is formed, and the possibility of short-circuiting increases. It is preferable to use a support having a finer texture than that of the support.

Next, the entangled non-woven fabric is formed.
By fusing at least the fused short fibers and the fused long fibers, the nonwoven fabric (separator) of the present invention can be obtained. In this fusion treatment, heating may be performed under no pressure, pressure may be applied simultaneously with heating, or pressure may be applied immediately after heating under no pressure. In addition, the heating temperature in the fusion process is, when heating under no pressure, the softening point of the higher melting point component of the higher melting point of the low melting point component of the fused short fiber and the low melting point component of the fused long fiber. From the melting point of the higher melting point of the low melting point component by 20
The temperature is preferably in a range up to a temperature as high as about ° C. The heating temperature when pressing at the same time as the heating is the lower melting point of the lower melting point component of the fused short fiber and the lower melting point component of the fused long fiber, the lower melting point of the higher melting point component. Preferably it is in the range up to the melting point of the components. Further, the pressurizing condition is preferably a linear pressure of 5 to 30 N / cm in each case. The “softening point” in the present invention refers to a temperature that gives a starting point of a melting endothermic curve obtained by using a differential scanning calorimeter and increasing the temperature from room temperature at a rate of 10 ° C./min.

On the other hand, when the ultrafine short fibers are obtained from the splittable short fibers that can be chemically split, first, the resin component of the split short fibers is dissolved and removed, or the resin component is swollen to split the ultrafine short fibers. Manufacture fiber. Next, one or more short fiber webs (preferably including high-strength short fibers) containing ultrafine short fibers and fused short fibers are formed by, for example, a wet method.
In addition, a long fiber web composed of a high-strength long fiber and a fused long fiber is subjected to, for example, a dry method (for example, a card method, an air-lay method,
One or more sheets are formed by a spun bond method or the like. Then, just like the method described above, formation of a laminated fiber web,
The non-woven fabric (separator) of the present invention can be obtained by performing an entanglement treatment by a fluid flow and a fusion treatment of the fusion short fibers and the fusion long fibers.

For a nonwoven fabric (separator) having a tensile strength in the vertical direction (length direction) of 100 N / 50 mm or more, a high-strength filament having a high tensile strength may be used.
Satisfies various conditions, such as increasing the amount of high-strength long fibers, firmly fusing with fusible short fibers and fusible long fibers, firmly entangled, and increasing the amount of fusible long fibers. Can be obtained.

For a nonwoven fabric (separator) having a tear strength in the vertical direction (length direction) of 50 N / 50 mm width or more, a high-strength long fiber having a high tensile strength may be used, or the amount of the high-strength long fiber may be reduced. It can be obtained by satisfying various conditions such as increasing the number of fibers, firmly fusing with the fused short fibers and the fused long fibers, firmly entangled, and increasing the amount of the fused long fibers.

Further, as for the nonwoven fabric (separator) having a formation index of 0.18 or less, when a fine short fiber having a smaller fiber diameter is used, or when the fine short fiber is generated from the divided short fiber, a hollow nonwoven fabric is used. It can be obtained by satisfying various conditions such as the use of split short fibers and the use of a fine-grained support (particularly a non-porous support) as a support for applying a fluid flow.

The non-woven fabric (separator) of the present invention is improved in the retention of the electrolytic solution by, for example, sulfonation treatment, fluorine gas treatment, graft treatment, surfactant treatment, and the like.
By performing at least one hydrophilization treatment such as a discharge treatment and a hydrophilic resin adhesion treatment, the surface of the fiber is subjected to an oxygen and / or sulfur-containing functional group (for example, a sulfonic acid group, a sulfonate group, a sulfofluoride group, It is preferable to introduce a carboxyl group, a carbonyl group, etc.), graft polymerize a hydrophilic monomer, attach a surfactant, or attach a hydrophilic resin. Such a hydrophilization treatment may be performed at the fiber stage (that is, at a stage before the formation of the nonwoven fabric), but the hydrophilization treatment after the formation of the nonwoven fabric is more excellent in workability. Hereinafter, a method of performing a hydrophilic treatment after forming the nonwoven fabric will be described. However, a case where the fibers are subjected to the hydrophilic treatment can be performed in exactly the same manner.

The sulfonation treatment includes, for example, a method of immersing the above-mentioned nonwoven fabric in a solution containing fuming sulfuric acid, sulfuric acid, chlorosulfuric acid, sulfuryl chloride or the like to introduce sulfonic acid groups, and a method of introducing sulfur trioxide gas. There is a method of introducing a sulfonic acid group by contacting the nonwoven fabric as described above, or a method of introducing a sulfonic acid group by causing discharge in the presence of a sulfur monoxide gas or a sulfur dioxide gas.

As the fluorine gas treatment, for example, fluorine gas diluted with an inert gas (eg, nitrogen gas, argon gas, etc.) and at least one selected from oxygen gas, carbon dioxide gas, sulfur dioxide gas, etc. The nonwoven fabric can be made hydrophilic by exposing the nonwoven fabric to a mixed gas with the above gas.

Examples of the graft polymerization treatment of a vinyl monomer include a method in which a nonwoven fabric is immersed in a solution containing a vinyl monomer and a polymerization initiator and heated, a method in which a vinyl monomer is applied to a nonwoven fabric, and then a radiation is applied. A method of contacting with a vinyl monomer after irradiation with radiation,
There is a method in which a vinyl monomer solution containing a sensitizer is applied to a nonwoven fabric and then irradiated with ultraviolet rays. As the vinyl monomer, for example, acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, vinylpyridine, vinylpyrrolidone or styrene can be used. In addition, when styrene is graft-polymerized, it is preferable to sulfonate so as to have an excellent affinity with an electrolytic solution. In addition, when the nonwoven fabric is modified by ultraviolet irradiation, corona discharge, plasma discharge, or the like before the vinyl monomer solution is brought into contact with the nonwoven fabric, affinity with the vinyl monomer solution is increased, so that graft polymerization can be performed efficiently.

The surfactant treatment includes, for example, an anionic surfactant (for example, an alkali metal salt, an alkyl sulfonate or a sulfosuccinate of a higher fatty acid), or a nonionic surfactant (for example,
The nonwoven fabric can be immersed in a solution of a polyoxyethylene alkyl ether or a polyoxyethylene alkylphenol ether, or the solution can be applied to the nonwoven fabric or sprayed on the nonwoven fabric.

[0062] Examples of the discharge treatment include corona discharge treatment, plasma treatment, glow discharge treatment, and electron beam treatment. In addition, under the atmospheric pressure in the air, between the pair of electrodes each carrying a dielectric, a nonwoven fabric is arranged so as to be in contact with both of these dielectrics, an AC voltage is applied between these two electrodes, With the method of generating discharge in the internal voids of the nonwoven fabric, the surface of the fiber inside the nonwoven fabric can be hydrophilized, so that a separator having excellent internal pressure characteristics can be manufactured.

In the treatment for imparting a hydrophilic resin, for example, a hydrophilic resin such as carboxymethylcellulose, polyvinyl alcohol, crosslinkable polyvinyl alcohol or polyacrylic acid can be attached. After dissolving or dispersing these hydrophilic resins in a suitable solvent, the nonwoven fabric can be immersed in the solvent, or the solvent can be applied or sprayed on the nonwoven fabric and dried to adhere.

As the crosslinkable polyvinyl alcohol, for example, there is polyvinyl alcohol in which a part of the hydroxyl group is substituted with a photosensitive group. More specifically, a styrylpyridinium-based photosensitive group, styrylquinolinium And polyvinyl alcohols in which some of the hydroxyl groups are substituted with styrylbenzothiazolium-based compounds.
This crosslinkable polyvinyl alcohol can also be crosslinked by irradiating light after adhering to the nonwoven fabric in the same manner as other hydrophilic resins. Such a polyvinyl alcohol in which a part of the hydroxyl group is substituted by a photosensitive group is excellent in alkali resistance and contains a large amount of a hydroxyl group capable of forming a chelate with an ion. It forms a chelate with ions before the metal is deposited, and can prevent short-circuiting between electrodes, so that it can be suitably used.

As described above, the separator of the present invention can further reduce the occurrence of short-circuits between the electrodes when forming the electrodes in groups, and can further suppress the occurrence of minute short-circuits during long-term use. For example, secondary batteries such as primary batteries such as alkaline manganese batteries, mercury batteries, silver oxide batteries, and air batteries, nickel-cadmium batteries, silver-zinc batteries, silver-cadmium batteries, nickel-zinc batteries, and nickel-hydrogen batteries. It can be suitably used for

Hereinafter, examples of the separator of the present invention will be described, but the present invention is not limited to these examples.

[0067]

(Example 1) As a split short fiber, as shown in FIG. 6, a polypropylene component (symbol 12 in the figure, a polypropylene ultra-fine short fiber having a fiber diameter of 3.6 μm (melting point: 160)
C)) and a high-density polyethylene component (symbol 11 in the figure, eight high-density polyethylene ultra-short fibers with a fiber diameter of 3.5 μm (melting point: 135 ° C.) can be generated), and the fiber axis Hollow section S with a circular cross section having a center corresponding to
And a certain angle (about 22.5) from the fiber axis.
°) divided short fibers (fineness: 1.) having a straight line extending every (°) as a boundary between the polypropylene component and the high-density polyethylene component.
43 dtex, fiber length: 5 mm, 16 divisions) were prepared.

Further, as the fused short fibers, low density polyethylene (melting point: 115 ° C.) is used as a sheath component, and polypropylene is used as a core component (melting point: 160 ° C.).
ex (fiber diameter: 13.1 μm), a core-sheath type composite fused short fiber having a fiber length of 10 mm and a tensile strength of 2.7 cN / dtex was prepared. Furthermore, as a high-strength short fiber, a tensile strength of 1
0.8 cN / dtex, Young's modulus 850 kg / mm ² ,
A polypropylene high-strength short fiber with a fineness of 1.32 dtex (fiber diameter: 13.7 μm) and a fiber length of 10 mm (melting point: 17
4 ° C.).

Next, the above-mentioned split short fiber, core-sheath type composite fused short fiber, and polypropylene high-strength short fiber were mixed with 60:
From the slurry mixed and dispersed at a mass ratio of 20:20, a short fiber web (area density: 30 g / m ² ) was formed by a wet papermaking method.

On the other hand, low-density polyethylene (melting point: 115 ° C.) is used as a sheath component and polypropylene is used as a core component (melting point: 160 ° C.) as a fused long fiber.
ex (fiber diameter: 15.3 μm), a core-sheath type composite fused long fiber having a fiber length of 51 mm, a number of crimps of 8 pieces / inch, and a tensile strength of 2.7 cN / dtex was prepared. Further, as a high-strength long fiber, tensile strength is 10.8 cN / dtex, Young's modulus is 8
50 kg / mm ² , fineness 1.32 dtex (fiber diameter: 1
3.7 μm), a polypropylene high-strength long fiber (melting point: 174 ° C.) having a fiber length of 38 mm and a crease number of 9.2 pieces / inch was prepared.

Next, after mixing the core-sheath type composite fused filament and the polypropylene high-strength filament in a mass ratio of 50:50, the mixture is opened by a carding machine to obtain a unidirectional filament web (area density). 20 g / m ² ).

Next, after laminating the unidirectional long fiber web and the short fiber web, the laminated fiber web was placed on a plain woven net having an opening of 0.175 mm, and the nozzle diameter was 0.15 mm and the pitch was 0 mm. A stream of water is jetted from a nozzle plate having an internal pressure of 12 MPa arranged in a line at 0.8 mm in the order of a unidirectional long fiber web, a short fiber web, a unidirectional long fiber web, and a short fiber web (one E value: 21). .6, the total E value: 86.4), and simultaneously entangled with each other to generate ultrafine short fibers to form an entangled nonwoven fabric.

Next, the entangled nonwoven fabric was heated at 115 ° C. for 10 minutes.
Immediately after heating for 2 seconds, pressure is applied by a calender roll having a linear pressure of 9.8 N / cm, and the core-sheath composite fused short fiber and the core-sheath composite fused long fiber are fused to form a fused entangled nonwoven fabric. did.

Thereafter, the fusion entangled nonwoven fabric was subjected to a fluorine gas treatment with a mixed gas of a fluorine gas, an oxygen gas and a sulfur dioxide gas diluted with a nitrogen gas to introduce a sulfofluoride group on the fiber surface. A separator having a thickness of 50 g / m ² and a thickness of 0.12 mm was formed. When an electron micrograph was taken of a cross section of the separator to observe the entangled state, a mixed layer in which short fibers and long fibers were entangled was present over the entire thickness of the separator.

Example 2 As split short fibers, an ethylene-vinyl alcohol copolymer component (symbol 12 in the figure, fiber diameter: 4.4 μm, ultra-fine ethylene-vinyl alcohol copolymer) as shown in FIG. 1 was used. Eight fibers (melting point: 155 ° C) can be generated) and a polypropylene component (symbol 1 in the figure)
1. A straight line extending from the fiber axis every fixed angle (about 22.5 °) with ethylene-vinyl alcohol, consisting of 8 ultra-fine polypropylene fibers (melting point: 160 ° C.) with a fiber diameter of 4.6 μm. Split short fiber (fineness: 3.3 dte) serving as a boundary between the copolymer component and the polypropylene component
x, fiber length: 6 mm, 16 divisions possible) 60 mass%
Except for using, a sulfofluoride group was introduced on the fiber surface in the same manner as in Example 1;
/ M ² , and a separator having a thickness of 0.12 mm was formed. When an electron micrograph was taken of a cross section of the separator to observe the entangled state, a mixed layer in which short fibers and long fibers were entangled was present over the entire thickness of the separator.

(Comparative Example) Split short fibers, core-sheath composite fusible short fibers, and polypropylene high-strength short fibers were mixed in a ratio of 50: 2.
Except for mixing and dispersing at a mass ratio of 5:25, a short fiber web (area density: 30 g /
m ² ).

On the other hand, as a split long fiber, as shown in FIG. 3, a polypropylene component (symbol 12 in the drawing, a polypropylene ultra-fine long fiber having a fiber cross section of substantially triangular shape and a fiber diameter of 3.5 μm (melting point: 160 ° C.) ), A single polypropylene ultra-short fiber (melting point: 160 ° C.) having a circular fiber cross section and a fiber diameter of 1.8 μm (melting point: 160 ° C.), and a high-density polyethylene component (symbol 11 in the figure, fiber crossing) The surface shape is substantially triangular, and the fiber diameter is 3.5 μm, and eight high-density polyethylene ultrafine fibers (melting point: 132 ° C.) can be generated.
Prepare split filaments (fineness: 1.43 dtex, fiber length: 25 mm, 17 splittable) with a straight line extending at a fixed angle (about 22.5 °) from the fiber axis as the boundary between the polypropylene component and the high-density polyethylene component. did. Further, the same core-sheath composite fused long fibers as in Example 1 and polypropylene high-strength long fibers were prepared. Next, the split filaments, the core-sheath composite fused filaments, and the polypropylene high-strength filaments were
After mixing at a mass ratio of 0:25:35, the fiber was opened by a carding machine, and a unidirectional long fiber web (area density: 20 g /
m ² ).

Next, in the same manner as in the example, lamination of a unidirectional long fiber web and a short fiber web, a water entanglement treatment, a fusion treatment, and a fluorine gas treatment are carried out, and the sulfofluoride is applied to the fiber surface. Having a surface density of 50 g / m ² ,
A separator having a thickness of 0.12 mm was formed. When an electron micrograph was taken of a cross section of the separator to observe the entangled state, a mixed layer in which short fibers and long fibers were entangled was present over the entire thickness of the separator.

(Tensile strength in vertical direction) width 50 m
m was fixed to a tensile strength tester (manufactured by Orientec, Tensilon UTM-III-100) (distance between chucks: 100 mm), and tensile speed: 300 mm
/ Min, and the tensile strength in the vertical direction was measured. The results were as shown in Table 1. As is clear from Table 1, the separator of the present invention was excellent in tensile strength, and thus it was found that the separator was not easily broken when constituting the electrodes.

[0080]

[Table 1]

[0081] The tear strength of the separator (tear strength in the longitudinal direction) was measured according to JIS L 1096 ^-1990 (general fabric test method, Torabezoido method).
The results were as shown in Table 1. As is clear from Table 1, the separator of the present invention was excellent in tear strength, so that it was found that the separator was not easily torn by the edge of the electrode plate when constituting the electrodes.

(Average penetration resistance) The separators were stacked on each other to a total thickness of about 2 mm, and the uppermost separator was placed on a handy compression tester (KES, manufactured by Kato Tech Co., Ltd., KES).
-G5) attached to a stainless steel jig (thickness:
0.5 mm, tip edge angle: 60 °) is 0.01c
The force required to pierce vertically at a speed of m / s and cut the uppermost separator was measured and defined as the penetration resistance. The measurement of the penetration resistance was performed for 50 places of each separator, the average value was calculated, and this value was defined as the average penetration resistance. The results were as shown in Table 1. The maximum and minimum values of the penetration resistance are also shown in Table 1. As is clear from Table 1, the separator of the present invention is hard to penetrate even a sharp stainless steel jig, so that when forming the electrodes in a group, the burr of the electrode plate is hard to penetrate. I understand. In addition, the difference between the maximum value and the minimum value of the penetration resistance of the separator of the present invention was small, and it was also found that the separator was hardly penetrated by the burr of the electrode plate and was highly reliable.

(Measurement of Formation Index) (1) A light source irradiates each separator with light, and among the irradiated light, reflected light reflected on a predetermined region of the separator is received by a light receiving element and brightness is obtained. Information obtained. (2) The predetermined area of the separator is set to an image size of 3 mm square, 6
By dividing equally into mm square, 12 mm square and 24 mm square, four divided patterns were obtained. (3) The luminance value of each section divided equally for each of the obtained division patterns was calculated based on the luminance information. (4) The average luminance (X) of each divided pattern was calculated based on the luminance value of each section. (5) The standard deviation (σ) for each divided pattern was determined. (6) The coefficient of variation (CV) for each divided pattern was calculated by the following equation. Coefficient of variation (CV) = (σ / X) × 100 Here, σ indicates the standard deviation of each divided pattern, and X indicates the average luminance of each divided pattern. (7) A coordinate group obtained as a result of setting the logarithm of each image size as the X coordinate and the variation coefficient corresponding to the image size as the Y coordinate is regressed to a linear line by the least squares method, and its slope is calculated. The absolute value of was defined as the formation index. The results were as shown in Table 1. As is apparent from these results, it was predicted that the separator of the present invention was excellent in formation, and that a micro short circuit was unlikely to occur during long-term use.

(Short Ratio) Using each separator,
The ratio at which the battery could not be manufactured when the electrode group was actually formed was defined as the short-circuit rate. The results were as shown in Table 1. From this result, it was found that the separator of the present invention is unlikely to cause a short circuit between the electrodes when forming the electrodes in a group.

(Battery life test) A paste-type nickel positive electrode (33
mm width, 182 mm length) and paste-type hydrogen storage alloy negative electrode (mesh metal alloy, 33 mm width, 247 mm length)
And created. Then, each separator was 33 mm wide, 4
After cutting to a length of 10 mm, each was sandwiched between a positive electrode and a negative electrode, spirally wound, and SC (sub-C)
An electrode group corresponding to the type was created. This electrode group was housed in an outer can, and 5N potassium hydroxide and 1N lithium hydroxide were injected into the outer can as an electrolytic solution, sealed, and the cylindrical nickel-
A hydrogen battery was created. Subsequently, for each cylindrical nickel-hydrogen battery, a charge / discharge cycle consisting of (1) charging at 150% at 0.2 C and (2) discharging to a final voltage of 1 V at 1 C is repeated, and the discharge capacity becomes the initial capacity. When the battery life reached 50%, it was determined that the battery life was over, and the number of cycles until the battery life was over was measured. Based on the number of cycles of the battery using the separator of the comparative example (10
Table 1 shows the ratio when 0) is set. From these results, it was found that a battery using the separator of the present invention hardly causes a micro short circuit, and thus has a long battery life.

(Battery internal pressure test) A cylindrical nickel-hydrogen battery formed in the same manner as that used in the battery life test was used.
The battery was charged at 0.5 ° C. at 20 ° C., and the internal pressure of the battery at 150% of the capacity was measured. Table 1 shows the ratio when the internal pressure of the battery using the separator of the comparative example is set as a reference (100). From these results, it was found that the battery using the separator of the present invention had a low internal pressure and was excellent in battery characteristics.

[0087]

According to the separator of the present invention, since a strong skeleton is formed by the high-strength long fibers and the fused long fibers, the separator may be broken or the burr of the electrode plate may be reduced when forming the electrodes in a group. , Or are not easily torn by the edge of the electrode plate, and a short circuit between the electrodes is less likely to occur when forming the electrodes in a group. In addition, ultra-fine short fibers having a short fiber length have a high degree of freedom and can be densely and uniformly distributed between the skeletons formed by the high-strength long fibers and the fused long fibers. Excellent in nature. In addition, when the short fibers further include high-strength short fibers having a tensile strength of 4.5 cN / dtex or more, the high-strength short fibers are densely and uniformly distributed, so that the reliability of the performance is further improved. I do. Further, when the high-strength filaments are made of polypropylene filaments having a tensile strength of 9 cN / dtex or more and a Young's modulus of 800 kg / mm ² or more, the pressure applied when forming the electrodes in groups and the pressure during charge / discharge are reduced. Against non-woven fabric (separator)
Can maintain the thickness of the electrolyte solution, so that the electrolyte can be kept excellent and the battery characteristics can be further improved. Furthermore,
When the ultrafine short fibers are derived from hollow split short fibers,
Since it can be a finer ultra-short fiber, it can be a more dense and uniform separator, and as a result, it is more excellent in preventing short-circuiting when a battery is used.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a split short fiber that can be used in the present invention.

FIG. 2 is a schematic cross-sectional view of another split short fiber that can be used in the present invention.

FIG. 3 is a schematic cross-sectional view of yet another split short fiber that can be used in the present invention.

FIG. 4 is a schematic cross-sectional view of yet another split short fiber that can be used in the present invention.

FIG. 5 is a schematic cross-sectional view of still another split short fiber that can be used in the present invention.

FIG. 6 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

FIG. 7 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

FIG. 8 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

FIG. 9 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

FIG. 10 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

FIG. 11 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

FIG. 12 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

FIG. 13 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

FIG. 14 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Split short fiber 11 1st component 12 2nd component S Hollow part

Claims (4)

[Claims] 1. A nonwoven fabric in which the total thickness of a mixed layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are entangled is 1/3 or more of the total thickness. Moreover, the short fibers include ultrafine short fibers having a fiber diameter of 8 μm or less and fused short fibers, and the long fibers are composed of high-strength long fibers having a tensile strength of 4.5 cN / dtex or more and fused long fibers. A separator for a battery, comprising: 2. The battery separator according to claim 1, wherein the short fibers further include high-strength short fibers having a tensile strength of 4.5 cN / dtex or more. 3. The high-strength continuous fiber has a tensile strength of 9c.
N / dtex or more, characterized by comprising a polypropylene filament having a Young's modulus of 800 kg / mm ² or more,
The battery separator according to claim 1 or 2. 4. The battery separator according to claim 1, wherein the ultrafine short fibers are derived from hollow split short fibers.