JP4450518B2 - Battery separator and battery - Google Patents

Description

【０１１９】
（単位面密度あたりの平均ニードル式耐貫通力の測定）
詳細な説明の欄に記載した方法により、単位面密度あたりの平均ニードル式耐貫通力を測定した。
【０１２０】
この結果は表１に示す通りであった。表１から明らかなように、実施例１〜４のセパレータのように、抽出した極細繊維をもとに繊維ウエブを形成した地合いの優れるセパレータは、単位面密度あたりの平均ニードル式耐貫通力が高く、実施例５及び実施例６のセパレータのように、やや地合いの劣るセパレータは、単位面密度あたりの平均ニードル式耐貫通力がやや悪く、比較例のセパレータのように、微細な貫通孔を有する地合いの劣るセパレータは、単位面密度あたりの平均ニードル式耐貫通力の悪いものであった。
【０１２１】
（電池製造時の不良率の評価）
電池の集電体として、水酸化ニッケルを発泡ニッケル支持体に充填した正極（３３ｍｍ幅、１８２ｍｍ長）と、ペースト式水素吸蔵合金負極（メッシュメタル系合金ＮｍＮｉ₅型、３３ｍｍ幅、２４７ｍｍ長）とを用意した。
【０１２２】
次いで、３３ｍｍ幅、４１０ｍｍ長に裁断した各セパレータをそれぞれ正極と負極との間に挟んだ後に渦巻状に巻回して、ＳＣ型対応の電極群を作製した。この時に、極板のバリや極板のエッジによってショートしてしまい、電池を製造することができなかった割合を電池製造時の不良率とした。この結果は表１に示す通りであった。
【０１２３】
この表１から、本発明のセパレータの中でも、特に抽出した極細繊維をもとに繊維ウエブを形成した実施例１〜４のセパレータは地合いが優れているため、不良率も低いものであった。実施例５及び実施例６のセパレータは地合いがやや悪いため、不良率もやや高いものであった。また、比較例のセパレータは地合いが悪いため、不良率も高いものであった。
【０１２４】
【発明の効果】
本発明の電池用セパレータは短絡が発生しにくく、しかも電池を歩留まり良く製造できるものである。
【０１２５】
本発明の電池は短絡が発生しにくく、歩留まり良く製造できるものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery separator and a battery.
[0002]
[Prior art]
Conventionally, a separator is used between the positive electrode and the negative electrode so that the positive electrode and the negative electrode of the alkaline battery are separated to prevent a short circuit and the electrolysis reaction can be performed smoothly while holding the electrolyte. ing.
[0003]
In recent years, the space occupied by batteries has become smaller as electronic devices become smaller and lighter. Has been. For that purpose, since the amount of the active material of the electrode needs to be increased, the volume occupied by the separator is inevitably reduced.
[0004]
Therefore, after forming a fiber web containing splittable fibers that can be mechanically split to generate ultrafine fibers, a high pressure water stream is applied to split the splittable fibers to generate ultrafine fibers at the same time. It has been proposed to use a non-woven fabric as a separator.
[0005]
[Problems to be solved by the invention]
However, the separator obtained by such a method is likely to cause a short circuit because a water flow is applied to easily form a hole penetrating from one surface to the other surface.
[0006]
Further, in order to reduce the volume of the separator, it is necessary to strongly wrap the separator around the electrode plate when forming the electrode plate group. However, as described above, the separator having the through hole is used when wrapping around the electrode plate. There was also a problem that the yield was deteriorated in battery production due to breakage due to tension, burr through the electrode plate, or tearing of the separator by the edge of the electrode plate.
[0007]
The present invention has been made to solve the above-described problems. A battery separator that is less likely to cause a short circuit and that can be manufactured with high yield, and a battery that uses this battery separator. The purpose is to provide.
[0008]
[Means for Solving the Problems]
  The above-described problems are high-strength polypropylene fibers having a tensile strength of 4.5 cN / dtex or more and ultrafine fibers having a fiber diameter of 5 μm or less, which are battery separators of the present invention (hereinafter sometimes simply referred to as “separators”). fiberMixed withIn addition, it has a non-woven fabric that maintains its form substantially only by fiber fusion.The entire cross-sectional shape of the ultrafine fibers is circular, and the ultrafine fibers are not present in bundlesIt can be solved by a separator.
[0009]
In other words, the separator of the present invention contains ultrafine fibers having a fiber diameter of 5 μm or less, and maintains a form substantially only by fusion between the fibers, and has undergone an entanglement effect such as conventional hydroentanglement. Therefore, there is no through hole and short circuit is unlikely to occur. In addition, because it contains high-strength polypropylene fiber with a tensile strength of 4.5 cN / dtex or more, it breaks due to the tension when it is wound around the electrode plate, or burr of the electrode plate penetrates, or due to the edge of the electrode plate Since the separator is difficult to tear, a battery can be manufactured with a high yield.
[0010]
Since the battery of the present invention uses the battery separator, a short circuit is unlikely to occur and the battery can be manufactured with a high yield.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The separator of the present invention has a tensile strength of 4.5 cN / dtex so that the separator is not broken by the tension when wound around the electrode plate, the burr of the electrode plate penetrates, or the separator is not torn by the edge of the electrode plate. The above high-strength polypropylene fibers are included. A more preferable tensile strength is 8 cN / dtex or more, a further preferable tensile strength is 8.9 cN / dtex or more, and a most preferable tensile strength is 10 cN / dtex. The upper limit of the tensile strength is not particularly limited, but about 50 cN / dtex is appropriate.
[0012]
The tensile strength in the present invention means a value measured by JIS L 1015 (chemical fiber staple test method).
[0013]
This high-strength polypropylene fiber has a Young's modulus of 800 kg / mm so that the above effect is more excellent.²Preferably, it is 850 kg / mm²The above is more preferable. The upper limit of Young's modulus is not particularly limited.
[0014]
This “Young's modulus” refers to the value of the apparent Young's modulus calculated from the initial tensile resistance measured by the method specified in JIS L 1015: 1999, paragraph 8.11. The initial tensile resistance is a value measured by a constant speed tension type testing machine.
[0015]
Further, if the heat shrinkage rate of the high-strength polypropylene fiber is 8% or less, even if heat is applied during the production of the separator, the dimensional change of the separator is small, and the uniform dispersibility of the fiber is excellent. Such performance is superior. More specifically, in addition to the high-strength polypropylene fiber, a high-strength polypropylene is used even if the heat-fusible fiber is melted by heat in order to improve the tensile strength and the bending resistance. Since the fiber is less likely to shrink, the dimensional change of the nonwoven fabric is less likely to occur. Therefore, the uniform dispersibility of the fibers is maintained and the above-described performance is excellent. A more preferable heat shrinkage rate is 7% or less. This heat shrinkage rate is a value of dry heat shrinkage rate measured using an oven dryer at a temperature of 140 ° C. based on JIS L 1015.
[0016]
In addition, it is preferable that the fiber cross-sectional shape of the high-strength polypropylene fiber is non-circular because the burrs of the electrode plate penetrate the separator or the separator is difficult to tear by the edge of the electrode plate. This is because even if the burrs and edges of the electrode plate come into contact with the high-strength polypropylene fibers, the high-strength polypropylene fibers are less slippery, the fiber contact misalignment is suppressed, and the forces from the burrs and edges are dispersed. It is thought that it is because it can be received. Thus, since the nonwoven fabric can take a dense structure because the cross-sectional shape of the high-strength polypropylene fiber is non-circular, a separator with a thinner thickness can be obtained. Specific cross-sectional shapes include, for example, an oval shape, a polygonal shape (for example, a triangular shape, a quadrangular shape, a pentagonal shape, a hexagonal shape, etc.), an alphabetic shape (for example, an X shape, a Y shape, an I shape, and a V shape). Etc.). Among these, a polygonal shape such as a pentagonal shape and a hexagonal shape is preferable.
[0017]
Further, when the high-strength polypropylene fiber can be fibrillated, it is preferable that the burrs of the electrode plate penetrate the separator or the separator is difficult to tear by the edge of the electrode plate. This is because when the burrs and edges of the electrode plate come into contact with this high-strength polypropylene fiber, the high-strength polypropylene fibers fibrillate and receive the force from the burrs and edges. This is considered to be because it is difficult to act.
[0018]
The high-strength polypropylene fiber may be already partially or entirely fibrillated, or may not be fibrillated. If part or all is fibrillated as in the former case, even if the burrs and edges of the electrode plate come into contact with the high-strength polypropylene fiber, the high-strength polypropylene fiber is difficult to slip and causes fiber contact misalignment. Therefore, it is preferable that the fiber can be further refined into a fibril shape to prevent a short circuit due to burrs or edges. In addition, since part or all of the high-strength polypropylene fiber is fibrillated, there is an effect that the retention of the electrolytic solution is further improved.
[0019]
The term “capable of fibrillation” means that an external force can generate a fibril in which one end is free and the other end is connected to a high-strength polypropylene fiber. This fibrillated state is an electron. It can be easily confirmed by a micrograph.
[0020]
The fiber diameter of such high-strength polypropylene fibers is preferably 13 to 35 μm, more preferably 15 to 30 μm, and most preferably 17 to 25 μm. When the fiber diameter of the high-strength polypropylene fiber is less than 13 μm, the absolute strength of the separator is weakened, and there is a tendency that the burrs of the electrode plate penetrate or are easily broken by the edge of the electrode plate. This is because if the fiber diameter exceeds 35 μm, the variation in penetration resistance tends to increase and short-circuiting easily occurs.
[0021]
“Fiber diameter” in the present invention refers to the diameter when the fiber cross-sectional shape is circular, and when the fiber cross-sectional shape is non-circular, it is a circle when converted to a circle having the same area. The diameter of
[0022]
The high-strength polypropylene fiber of the present invention may be composed of only a polypropylene component, or may further contain a resin component other than the polypropylene component (preferably a polyolefin resin component, particularly a polyethylene resin component). When the resin component other than the polypropylene component is included as in the latter, the cross-sectional shape of the fiber is, for example, a core-sheath type, an eccentric type, or a sea-island type, and the resin component constituting the surface is other than polypropylene. Is preferably a resin component having a low melting point (for example, a polyethylene resin component). In this case, it can be fused by the resin component constituting the fiber surface.
[0023]
The “melting point” in the present invention refers to a temperature that gives a maximum value of a melting endothermic curve obtained by using a differential scanning calorimeter at a temperature rising temperature of 10 ° C./min and raising the temperature from room temperature. When there are two or more maximum values, the highest temperature maximum value is taken as the melting point.
[0024]
Such a high-strength polypropylene fiber occupies 10 mass% or more of the mass of the nonwoven fabric so that the burrs of the electrode plate do not penetrate the separator or are torn by the edge of the electrode plate. It is preferable to occupy 20 mass% or more so that short-circuiting is more difficult. On the other hand, since it is necessary to contain extra fine fibers as will be described later, it is preferably 90 mass% or less in view of the balance.
[0025]
Such a high-strength polypropylene fiber has, for example, an isotactic pentad fraction (IPF) of 95 to 100% and a weight average molecular weight / number average molecular weight ratio (Q value) of less than 4. A fiber obtained by melt-spinning polypropylene is arranged at a stretched tank temperature of 120 ° C. or higher by a stretching apparatus using a stretched tank in which a pressurized water tank is arranged in the stretched product introduction part and the stretched product lead-out part and high-temperature pressurized steam is filled therein. It can be obtained by stretching at a stretching ratio of 7 times or more. The high-strength polypropylene fiber obtained by such a method is highly oriented and crystallized in the fiber direction, and when the side surface of the fiber is observed in a crossed Nicol state under polarized light, the refractive index varies intermittently in the fiber direction. It has a unique striped pattern consisting of a linear dark part and a bright part.
[0026]
In addition to the high-strength polypropylene fibers as described above, the separator of the present invention includes ultrafine fibers having a fiber diameter of 5 μm or less so as to form a uniform texture and prevent short-circuiting. The smaller the fiber diameter is, the more uniform the texture can be. Therefore, the fiber diameter of the ultrafine fiber is preferably 4 μm or less, more preferably 3 μm or less, and even more preferably 2 μm or less. . On the other hand, the lower limit of the fiber diameter of the ultrafine fibers is suitably about 0.01 μm so as to have a certain degree of strength.
[0027]
It is preferable that the ultrafine fibers have substantially the same fiber diameter so that a uniform pore diameter is formed by the ultrafine fibers and the texture is uniform. That is, the value (σ / d) obtained by dividing the standard deviation value (σ) of the fiber diameter distribution of the ultrafine fiber by the average value (d) of the fiber diameter of the ultrafine fiber is 0.2 or less (preferably 0.18 or less). Is preferred. When all the fiber diameters of the ultrafine fibers are the same, the standard deviation value (σ) is 0, so the lower limit value of the value (σ / d) is 0.
[0028]
This “average fiber diameter of ultrafine fibers (d)” is obtained by taking an electron micrograph of the nonwoven fabric constituting the separator and measuring the fiber diameter of 100 or more (n) ultrafine fibers in this electron micrograph. The mean value of the measured fiber diameter (χ). The “standard deviation value (σ)” of the ultrafine fiber is a value obtained by calculating the measured fiber diameter (χ) from the following equation.
Standard deviation = {(nΣχ²-(Σχ)²) / N (n-1)}^1/2
Here, n means the number of measured ultrafine fibers, and χ means the fiber diameter of each ultrafine fiber.
[0029]
In addition, when two or more types of ultrafine fibers are present, the above relationship is preferably established for each of the ultrafine fibers.
[0030]
Moreover, it is preferable that the ultrafine fibers have substantially the same diameter in the fiber axis direction so that the ultrafine fibers are excellent in texture.
[0031]
The resin component constituting the ultrafine fiber of the present invention can be composed of, for example, one or more types such as polyamide resin and polyolefin resin, but is excellent in electrolytic solution resistance and is said to cause self-discharge. It preferably consists essentially of a polyolefin resin that does not generate a nitrogen-containing compound. The term “substantially” means that the fiber surface is composed of a polyolefin-based resin because the portion that affects the resistance to electrolytic solution is mainly the fiber surface. For example, an ultrafine fiber that is composed of a polyamide resin and a polyolefin resin and only the polyolefin resin occupies the fiber surface is substantially a polyolefin ultrafine fiber.
[0032]
Examples of suitable polyolefin resins include polyethylene resins (for example, ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymers (ethylene-acrylic). Acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl alcohol copolymer, etc.), polypropylene resin (eg, polypropylene, propylene copolymer, etc.), polymethylpentene resin (eg, polymethyl). Pentene, methylpentene copolymer, etc.), and preferably made of polypropylene resin or polyethylene resin.
[0033]
The ultrafine fiber of the present invention can be suitably used because the texture of the separator can be further improved by having a circular cross-sectional shape.
[0034]
It should be noted that if the ultrafine fiber includes a resin component that can participate in fusion (hereinafter, also referred to as “fusion component”), and the fusion is performed by this fusion component, the ultrafine fiber is surely fixed and the ultrafine fiber is fixed. This is a preferred embodiment because the fibers do not fall off or become fuzzy.
[0035]
When the ultrafine fiber is fused, the ultrafine fiber can be composed of only one kind of resin component, or a component having a melting point higher than the melting point of the fusion component and the fusion component (hereinafter referred to as “non-fused”). It may also be composed of two or more types of resin components including “component”. If the ultrafine fiber is composed of two or more kinds of resin components including a fusion component and a non-fusion component as in the latter, the fiber form is maintained even if the fusion component is fused, and the texture of the separator is maintained. Since it does not worsen, it is more suitable.
[0036]
When the ultrafine fiber is composed of two or more kinds of resin components, it is preferable that the fusion component occupies part or all of the surface of the ultrafine fiber and can be fused. The cross-sectional shape of such an ultrafine fiber is preferably, for example, a core-sheath type, an eccentric type, or a sea-island type. The non-fusion component preferably has a melting point that is 10 ° C. or more higher than the melting point of the fusion component so that the fiber shape can be maintained, and more preferably 20 ° C. or more.
[0037]
The ultrafine fiber of the present invention can be obtained, for example, by removing at least one resin component from a composite fiber containing two or more resin components. That is, it can be obtained by decomposing and removing an easily removable resin component from a composite fiber including at least an easily removable resin component that can be easily decomposed and removed by a certain solvent and a difficultly removed resin component that is not easily decomposed and removed by this solvent. it can. For example, by immersing a composite fiber composed of a copolymerized polyester and polypropylene in a 10 mass% sodium hydroxide aqueous solution at a temperature of about 80 ° C., the copolymerized polyester component can be decomposed and removed to obtain an ultrafine fiber composed of polypropylene. it can. Thus, since the ultrafine fiber generated by removing at least one resin component from the composite fiber containing two or more kinds of resin components is very unlikely to be in a state where the ultrafine fibers are connected to each other, A separator containing ultrafine fibers is more excellent in texture.
[0038]
For example, the ultrafine fibers having substantially the same fiber diameter as described above, or the ultrafine fibers having substantially the same diameter in the fiber axis direction, extrude the island component by regulating the die into the sea component at the spinneret portion, for example. It can be obtained by removing the sea component of the sea-island type fiber obtained by a composite spinning method such as a composite method. In addition, the method of removing the sea component of the sea-island fiber obtained by the method of spinning after mixing the resin constituting the island component and the resin constituting the sea component, which is generally referred to as a mixed spinning method, or by the melt blow method It is difficult to obtain ultrafine fibers having substantially the same fiber diameter or ultrafine fibers having substantially the same diameter in the fiber axis direction.
[0039]
In addition, for the ultrafine fiber having a circular cross-sectional shape, for example, when the island component is extruded into the sea component, and the sea island-type fiber is spun together, the one having a circular cross section is used as a die for extruding the island component. If you can get.
[0040]
Furthermore, the ultrafine fiber composed of two or more kinds of resin components including the fusion component and the non-fusion component is used as a base for extruding the island component when the sea-island fiber is spun by a conventional composite spinning method. Two or more types are used when spinning using one that can form such a cross-sectional shape (for example, core-sheath type, eccentric type, sea-island type), or when spinning sea-island type fibers by a conventional composite spinning method It can be obtained by supplying a resin mixed with the above resin component to a die for extruding the island component, spinning sea-island type fibers, and removing the sea component.
[0041]
The total mass of such ultrafine fibers preferably accounts for 10% or more of the mass of the nonwoven fabric, and more preferably accounts for 15% or more so that the texture is excellent. On the other hand, it is preferable that it is 90 mass% or less from the balance with the above-mentioned high-strength polypropylene fiber.
[0042]
The ultrafine fibers are preferably short fibers having a high degree of freedom so as to be uniformly dispersed and excellent in texture. However, when cutting ultrafine fibers or composite fibers capable of generating ultrafine fibers, ultrafine fibers or ultrafine fibers are cut. When the resin components that are the basis of the pressure-bonding, the texture becomes poor, so when cutting, it is difficult to pressure-bond the ultra-fine fibers or the resin components that are the basis of the ultra-fine fibers. It is preferred to use a bicomponent fiber that can be generated.
[0043]
Examples of such an ultrafine fiber that is difficult to press or a composite fiber capable of generating an ultrafine fiber include a highly crystalline ultrafine fiber or a composite fiber containing a highly crystalline resin component. More specifically, when the ultrafine fiber or composite fiber contains polymethylpentene or polypropylene, the melting point of the polypropylene is preferably 166 ° C. or higher (preferably 168 ° C. or higher).
[0044]
It is preferable that the nonwoven fabric constituting the separator of the present invention further includes a heat-sealing fiber so as to be excellent in tensile strength and bending resistance.
[0045]
When this heat-fusible fiber is fused, the fiber other than the heat-fusible fiber is fused so that the fiber other than the heat-fusible fiber (for example, high-strength polypropylene fiber, ultrafine fiber, etc.) is not adversely affected. It is preferable to include a fusing component having a melting point that is 10 ° C. or more lower (more preferably 20 ° C. or more lower) than the melting point of the resin component that is not. For example, when fibers other than heat-sealing fibers include high-strength polypropylene fibers made only of polypropylene and ultrafine fibers made only of polypropylene resin, the fusing components of heat-sealing fibers are polyethylene-based. Resins (for example, ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymer (ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene -Vinyl alcohol copolymer and the like).
[0046]
This heat-fusible fiber may be composed of only the fusing component, or may contain a non-fusing component having a melting point higher than that of the fusing component in addition to the fusing component. When the non-fusion component is included as in the latter case, the strength of the separator can be further improved. In this case, the cross-sectional shape may be, for example, a core-sheath type, an eccentric type, or a sea-island type. The non-fusion component is preferably made of a resin that is higher by 10 ° C. or more than the melting point of the fusion component, and is preferably made of a resin that is higher by 20 ° C. or more.
[0047]
In addition, it is preferable that the heat sealing | fusion fiber is substantially comprised from the polyolefin resin for the same reason as the above-mentioned ultrafine fiber.
[0048]
Such heat-sealing fibers preferably occupy 20 mass% or more, more preferably 40 mass% or more, of the mass of the nonwoven fabric so that the strength of the separator can be improved. On the other hand, it is preferably 80% by mass or less in consideration of the above-described polypropylene-based high-strength fibers and ultrafine fibers.
[0049]
The fibers constituting the separator of the present invention (for example, polypropylene-based high-strength fibers, ultrafine fibers, heat-bonded fibers, etc.) can be in an unstretched state, but any fiber can be used so as to be superior in strength. It is preferably in the stretched state.
[0050]
Further, the fiber length of the fibers constituting the separator of the present invention (for example, polypropylene-based high-strength fibers, ultrafine fibers, heat-sealing fibers, etc.) is not particularly limited, but the shorter the fiber length, the more freedom of the fibers. The fiber length is preferably 0.1 to 25 mm (more preferably 0.1 to 20 mm), and more preferably 1 to 25 mm (more preferably 0.1 to 20 mm). It is preferable to use a fiber that has been cut.
[0051]
The fiber length is a length obtained by JIS L 1015 (chemical fiber staple test method) B method (corrected staple diagram method).
[0052]
As the fibers constituting the nonwoven fabric constituting the separator of the present invention, it is preferable not to contain fibrillated fibers except for polypropylene-based high-strength fibers. In particular, it is preferable that the ultrafine fiber that greatly affects the texture is not fibrillated. If the fibers thus fibrillated are not included, the texture becomes more uniform. Examples of the “fibrillated fiber” include a fiber obtained by beating a splittable fiber that can be mechanically split by a beater, a pulp, a fiber obtained by a flash spinning method, and the like.
[0053]
It is preferable that the bundle of ultrafine fibers as described above is substantially not present in the nonwoven fabric constituting the separator of the present invention. This is because if a bundle of ultrafine fibers is present, the texture is deteriorated despite the inclusion of ultrafine fibers. A nonwoven fabric in which bundles of such ultrafine fibers are formed, after forming a splittable fiber that can be divided by swelling the resin component with a solvent, or a fiber web containing splittable fibers that can be split by removing the resin component with a solvent, Although it is easy to form by dividing | segmenting a splittable fiber, if a fiber web is formed using an ultrafine fiber, the nonwoven fabric which does not have the bundle | flux of an ultrafine fiber substantially can be manufactured.
[0054]
Since the nonwoven fabric constituting the separator of the present invention is substantially maintained in shape only by fiber fusion, there is no through hole, excellent texture, short circuit is hardly caused, and the electrolyte is uniformly distributed. It is a separator that can reduce the internal resistance. For example, if the fibers are fixed by entanglement other than fusion, a through-hole is formed from the front surface to the back surface of the nonwoven fabric by an action for entanglement of the fibers (for example, fluid flow such as water flow, needle, etc.). Although formed and easily short-circuited, it is substantially fixed only by fusion, so that the arrangement of the fibers is not disturbed and the short-circuit hardly occurs.
[0055]
In addition, when manufacturing a nonwoven fabric, fibers may get entangled. For example, when a fiber web is formed by a wet method, the fibers are entangled more or less so that the shape of the fiber web can be maintained. However, since this entanglement does not disturb the fiber arrangement, it is considered that the entanglement is not substantially entangled. Thus, “substantially only fiber fusion” refers to a state in which the fibers are fixed only by fusion after the fiber web is formed. This fiber fusion is formed by fusion of at least one type of fiber selected from high-strength polypropylene fibers, ultrafine fibers, or heat-fusion fibers.
[0056]
The thickness of the nonwoven fabric of the present invention is preferably 0.11 mm or less, and preferably 0.10 mm or less so as to cope with the increase in capacity of the battery. The lower limit is not particularly limited, but about 0.02 mm is appropriate.
[0057]
The “thickness” in the present invention refers to a thickness measured by an outer micrometer (0 to 25 mm) defined in JIS B 7502: 1994.
[0058]
As an index of excellent texture of the separator of the present invention, “average texture index” can be mentioned. When the average formation index is 0.15 or less, the formation is excellent, short-circuiting is unlikely to occur, and the electrolyte can be kept uniform. A more preferable average formation index is 0.10 or less.
[0059]
This “average formation index” refers to a value obtained by the method described in Japanese Patent Application No. 11-152139. That is, the value obtained as follows.
(1) Light is irradiated from a light source to an object to be measured (nonwoven fabric), and of the irradiated light, reflected light reflected at a predetermined region of the object to be measured is received by a light receiving element to obtain luminance information. .
(2) A predetermined region of the object to be measured is equally divided into an image size of 3 mm square, 6 mm square, 12 mm square, and 24 mm square to obtain four divided patterns.
(3) The luminance value of each section equally divided for each obtained division pattern is calculated based on the luminance information.
(4) Based on the luminance value of each section, the average luminance (X) for each division pattern is calculated.
(5) A standard deviation (σ) for each division pattern is obtained.
(6) The coefficient of variation (CV) for each division pattern is calculated by the following equation.
Coefficient of variation (CV) = (σ / X) × 100
Here, σ indicates a standard deviation for each divided pattern, and X indicates a luminance average for each divided pattern.
(7) A coordinate group obtained as a result of taking the logarithm of each image size as the X coordinate and the coefficient of variation corresponding to the image size as the Y coordinate is regressed to a linear line by the least square method, and the inclination is calculated. The absolute value of is the formation index.
(8) This formation index measurement is repeated three times, and the average value is taken as the average formation index.
[0060]
The nonwoven fabric of the present invention has an average needle type penetration resistance unit density (g / m²) Is preferably 14 gf or more, more preferably 15 gf or more, and still more preferably 16 gf or more. If this value is 14 gf or more, the fibers constituting the separator are further separated by burrs or the like of the electrode plate, and short-circuiting is difficult when forming the electrode plate group. In addition, that this value is high also means that there is no through-hole and it is an excellent texture in which fibers are uniformly dispersed.
[0061]
This average needle type penetration resistance means the value obtained as follows.
One non-woven fabric is placed so as to cover the cylindrical through-hole of the support base having a cylindrical through-hole (inner diameter: 11 mm), and a fixing material having a cylindrical through-hole (inner diameter: 11 mm) is further formed on the non-woven fabric. The nonwoven fabric is fixed by being placed so as to coincide with the center of the cylindrical through hole of the support base. Thereafter, a needle (curvature radius at the tip: 0.5 mm, diameter: 1 mm, protrusion length from the jig: 2 cm) attached to a handy compression testing machine (KES-G5, manufactured by Kato Tech) for this nonwoven fabric. ) Is vertically stabbed at a speed of 0.01 cm / s, the force required for the needle to penetrate is measured, and this force is defined as a needle-type penetration resistance. This needle type penetration resistance is measured at 30 locations of the nonwoven fabric, and the average value is defined as the average needle type penetration resistance. In addition, the value per unit surface density is the average needle type penetration resistance expressed by surface density (g / m²The value divided by).
[0062]
The surface density of the nonwoven fabric of the present invention is 5 to 55 g / m.²Is preferable, and more preferably 10 to 40 g / m.²It is.
[0063]
The separator of the present invention is provided with the nonwoven fabric as described above, and can be composed only of the nonwoven fabric, or a porous film, a woven fabric, a knitted fabric, a net, a yarn, or the like can be laminated on the nonwoven fabric. In order to increase the capacity of the battery, it is preferable that the separator is made of only a non-woven fabric because it is advantageous that the separator is thin.
[0064]
The separator of the present invention has an oxygen and / or sulfur-containing functional group (for example, a sulfonic acid group, a sulfonic acid group, a sulfofluoride group, a carboxyl group, a carbonyl group so as to impart or improve the affinity with the electrolytic solution. Etc.), a hydrophilic monomer is graft-polymerized, a surfactant is applied, or a hydrophilic resin is applied.
[0065]
The separator of the present invention includes, for example, primary batteries such as alkaline manganese batteries, mercury batteries, silver oxide batteries, air batteries, nickel-cadmium batteries, silver-zinc batteries, silver-cadmium batteries, nickel-zinc batteries, nickel-hydrogen batteries. It can be suitably used as a separator for secondary batteries such as nickel-cadmium batteries or nickel-hydrogen batteries.
[0066]
The nonwoven fabric of this invention can be manufactured as follows, for example.
[0067]
First, the above-described high-strength polypropylene fiber, ultrafine fiber, preferably heat-bonded fiber is prepared.
[0068]
Next, a fiber web is formed using the prepared fibers. The method for forming this fiber web is not particularly limited, but it is preferably formed by a wet method in which fibers are easily dispersed uniformly. Examples of the wet method include a horizontal long net method, an inclined wire type short net method, a circular net method, a long net / circular net combination method, and a short net / circular net combination method.
[0069]
Subsequently, the nonwoven fabric which can be used as a separator can be manufactured by fixing the fiber which comprises this fiber web only by melt | fusion. Since it is fixed only by fusing as described above, the arrangement of the fibers is not disturbed, the texture is excellent, the short circuit is not easily generated, and the electrolyte can be uniformly distributed, and the internal resistance can be further reduced. It can be a separator. The fiber web may be fused under no pressure, under pressure, or after the fusion component is melted under no pressure and then pressurized (preferably immediately pressurized). Also good.
[0070]
Since the non-woven fabric of the present invention is preferably thin so that the capacity of the battery can be increased, if the non-woven fabric after fusion is thick, such as passing between a pair of rolls, It is preferable to adjust the thickness.
[0071]
In addition, the nonwoven fabric whose average formation index is 0.15 or less is a high-strength polypropylene fiber other than using ultrafine fibers as fibers or fixing the fibers only by fusing (not entangled). By adjusting these conditions, such as not using fibrillated fibers as other fibers, using short fibers with a fiber length of about 0.1 to 25 mm, or forming fiber webs by wet methods Can be manufactured.
[0072]
The nonwoven fabric having an average needle-type penetration resistance of 14 gf or more per unit surface density of the present invention not only uses high-strength polypropylene fibers, but also increases the amount of blending or high-strength polypropylene fibers by a wet method. It can be produced by adjusting various conditions such as uniformly dispersing, firmly fusing with heat-fusible fibers, or fusing the heat-fusible fibers and then immediately pressing and fusing.
[0073]
Since the nonwoven fabric of the present invention is preferably substantially composed only of polyolefin fibers so as to be excellent in alkali resistance, a hydrophilic treatment is performed in order to impart or improve the retention of the electrolytic solution. preferable. Examples of the hydrophilization treatment include sulfonation treatment, fluorine gas treatment, vinyl monomer graft polymerization treatment, surfactant treatment, discharge treatment, or hydrophilic resin application treatment.
[0074]
The sulfonation treatment is not particularly limited. For example, the sulfonic acid group is introduced by immersing the nonwoven fabric as described above in a solution composed of fuming sulfuric acid, sulfuric acid, sulfur trioxide, chlorosulfuric acid, or sulfuryl chloride. And a method of introducing a sulfonic acid group into a nonwoven fabric by applying an electric discharge in the presence of sulfur monoxide gas, sulfur dioxide gas, sulfur trioxide gas, or the like.
[0075]
The fluorine gas treatment is not particularly limited. For example, fluorine gas diluted with an inert gas (for example, nitrogen gas, argon gas, etc.), oxygen gas, carbon dioxide gas, and sulfur dioxide gas. The fiber surface of the nonwoven fabric can be hydrophilized by exposing the nonwoven fabric to a mixed gas with at least one gas selected from the above. In addition, after making sulfur dioxide gas adhere to a nonwoven fabric beforehand and making fluorine gas contact, permanent hydrophilicity can be provided more efficiently.
[0076]
In the graft polymerization of the vinyl monomer, for example, acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, vinyl pyridine, vinyl pyrrolidone, or styrene can be used as the vinyl monomer. When styrene is graft-polymerized, it is preferably sulfonated in order to impart affinity with the electrolytic solution. Among these, acrylic acid can be suitably used because of its excellent affinity with the electrolytic solution.
[0077]
As a method for polymerizing these vinyl monomers, for example, a method in which a nonwoven fabric is dipped in a solution containing a vinyl monomer and a polymerization initiator and heated, a method in which a vinyl monomer is applied to the nonwoven fabric and radiation is applied, and a radiation in the nonwoven fabric is irradiated. Then, there are a method of contacting with a vinyl monomer, a method of impregnating a nonwoven fabric with a vinyl monomer solution containing a sensitizer, and then irradiating with ultraviolet rays. If the surface of the nonwoven fabric is modified by ultraviolet irradiation, corona discharge, plasma discharge, etc. before contacting the vinyl monomer solution and the nonwoven fabric, the graft monomer can be efficiently graft-polymerized because of its high affinity with the vinyl monomer solution. .
[0078]
Examples of the surfactant treatment include an anionic surfactant (for example, an alkali metal salt of a higher fatty acid, an alkyl sulfonate, or a sulfosuccinate ester salt), or a nonionic surfactant (for example, a polyoxyethylene alkyl). The nonwoven fabric can be immersed in a solution of ether or polyoxyethylene alkylphenol ether), or this solution can be applied to or dispersed on the nonwoven fabric.
[0079]
Examples of the discharge treatment include corona discharge treatment, plasma treatment, glow discharge treatment, creeping discharge treatment, and electron beam treatment. Among these discharge treatments, under atmospheric pressure in air, a non-woven fabric is placed between a pair of electrodes each carrying a dielectric so as to be in contact with both of these dielectrics, and an AC voltage is applied between these two electrodes. When the method is applied and discharge is generated in the voids inside the nonwoven fabric, not only the outside of the nonwoven fabric but also the surface of the fibers constituting the inside of the nonwoven fabric can be treated. Therefore, it is excellent in the holding | maintenance of the electrolyte solution in the inside of a separator.
[0080]
As hydrophilic resin provision processing, hydrophilic resins, such as carboxymethylcellulose, polyvinyl alcohol, crosslinkable polyvinyl alcohol, or polyacrylic acid, can be made to adhere, for example. These hydrophilic resins can be dissolved or dispersed in a suitable solvent, and then the nonwoven fabric can be immersed in the solvent, or this solvent can be applied or dispersed on the nonwoven fabric and dried to be adhered. In addition, it is preferable that the adhesion amount of hydrophilic resin is 0.3-5 mass% of the whole separator so that air permeability may not be impaired.
[0081]
Examples of the crosslinkable polyvinyl alcohol include polyvinyl alcohol in which a part of the hydroxyl group is substituted with a photosensitive group. More specifically, the photosensitive group is a styrylpyridinium type or styrylquinolinium type. And polyvinyl alcohol substituted with a styrylbenzothiazolium-based one. This crosslinkable polyvinyl alcohol can also be cross-linked by light irradiation after being attached to the nonwoven fabric in the same manner as other hydrophilic resins. Polyvinyl alcohol in which a part of such hydroxyl groups is substituted with a photosensitive group is excellent in alkali resistance and contains many hydroxyl groups that can form chelates with ions, and is dendritic on the electrode plate during discharge and / or charge. This forms a chelate with the ions before the metal is deposited, and it is difficult to cause a short circuit between the electrodes.
[0082]
The battery of the present invention uses the separator as described above. Therefore, it is difficult to cause a short circuit and can be manufactured with a high yield.
[0083]
The battery of the present invention can be exactly the same as the conventional battery except that the separator as described above is used.
[0084]
For example, a cylindrical nickel-hydrogen battery has a structure in which an electrode plate group in which a nickel positive electrode plate and a hydrogen storage alloy negative electrode plate are wound in a spiral shape through a separator as described above is inserted into a metal case. As the nickel positive electrode plate, for example, a sponge-like porous porous material filled with an active material made of nickel hydroxide solid solution powder can be used. As the hydrogen storage alloy negative electrode plate, for example, a nickel plated perforated steel plate, For foamed nickel or nickel net, AB₅-Based (rare earth) alloy, AB / A₂B-based (Ti / Zr-based) alloy or AB₂Those filled with a (Laves phase) -based alloy can be used. As the electrolytic solution, for example, a potassium hydroxide / lithium hydroxide two-component system or a potassium hydroxide / sodium hydroxide / lithium hydroxide three-component system can be used. The case is sealed with an insulating gasket by a sealing plate provided with a safety valve. Furthermore, a positive electrode current collector and an insulating plate are provided, and if necessary, a negative electrode current collector is provided.
[0085]
Note that the battery of the present invention does not need to be cylindrical, and may be rectangular or button-shaped. In the case of a square type, it has a laminated structure in which a separator is disposed between a positive electrode plate and a negative electrode plate.
[0086]
Examples of the present invention will be described below, but the present invention is not limited to these examples.
[0087]
【Example】
Example 1
A sea-island type fiber (fineness: 1.), which is spun by a composite spinning method, in which 25 island components made of polypropylene are present in a sea component made of poly-L-lactic acid (hereinafter referred to as “PLLA”). 65 dtex, fiber length: 2 mm).
[0088]
Next, this sea-island type fiber is immersed in a bath composed of a 10 mass% sodium hydroxide aqueous solution at a temperature of 80 ° C. for 30 minutes to extract and remove PLLA, which is a sea component of the sea-island type fiber, to obtain a polypropylene extra fine fiber (fiber diameter: 2 μm, ρ / d: 0.083, melting point: 172 ° C., fiber length: 2 mm, unfibrillated, stretched, having substantially the same diameter in the fiber axis direction, and a cross-sectional shape: circular) It was.
[0089]
Moreover, as a heat-sealable fiber, a core-sheath type composite in which a core component (non-fusion component) is made of polypropylene (melting point: 168 ° C.) and a sheath component (fusion component) is made of high-density polyethylene (melting point: 135 ° C.). Fibers (fiber diameter: 12 μm, cut fiber length: 5 mm, mass ratio of core component to sheath component is 1: 1, not fibrillated, stretched) were prepared.
[0090]
Furthermore, high-strength polypropylene fiber (tensile strength: 10.7 cN / dtex, Young's modulus: 850 kg / mm², Heat shrinkage at 140 ° C .: 7%, fiber cross-sectional shape: almost pentagonal, melting point: 174 ° C., capable of fibrillation, fiber diameter: 22 μm, cut fiber length: 10 mm, stretched, polarized fiber side Below, when observed in a crossed Nicol state, a striped pattern composed of intermittent linear dark portions and bright portions having different refractive indexes in the fiber direction was prepared.
[0091]
Next, a fiber web was formed from the slurry obtained by mixing and dispersing 20 mass% of the above-mentioned polypropylene ultrafine fiber, 50 mass% of the core-sheath type composite fiber, and 30 mass% of the high-strength polypropylene fiber, by a wet method (horizontal long net method). .
[0092]
Next, this fiber web is left in a hot air circulation dryer set at a temperature of 135 ° C. for 3 minutes to dry the fiber web and heat-seal with the sheath component (high density polyethylene) of the core-sheath type composite fiber. Thus, a fused nonwoven fabric was formed.
[0093]
Next, the fused nonwoven fabric is supplied into a container filled with a mixed gas composed of fluorine gas (3 vol%), oxygen gas (5 vol%), sulfur dioxide gas (5 vol%) and nitrogen gas (87 vol%), The fused nonwoven fabric was brought into contact with the mixed gas for 120 seconds (temperature: 20 ° C.).
[0094]
Next, this fused non-woven fabric treated with fluorine gas was calendered at a linear pressure of 9.8 N / cm to obtain the separator of the present invention (surface density: 40 g / m², Thickness: 0.10 mm, bundles of ultrafine fibers are not substantially present, and fibers are arranged substantially two-dimensionally).
[0095]
(Example 2)
Except that the cut fiber length is 5 mm, the same high-strength polypropylene fiber as in Example 1 was used, and the polypropylene extra-fine fiber 20 mass%, the core-sheath type composite fiber 60 mass%, and the high-strength polypropylene fiber 20 mass% A fused nonwoven fabric was produced in exactly the same manner as in Example 1 except that the slurry was mixed and dispersed.
[0096]
Next, the fused nonwoven fabric was immersed in fuming sulfuric acid having a concentration of 15% and a temperature of 60 ° C. for 2 minutes to carry out sulfonation treatment. Subsequently, after sufficiently washing with water, it was dried at a temperature of 80 ° C.
[0097]
Next, the nonwoven fabric subjected to the sulfonated treatment was subjected to a calendar treatment at a linear pressure of 9.8 N / cm, and the separator of the present invention (surface density: 30 g / m², Thickness: 0.06 mm, bundles of ultrafine fibers are substantially not present, and the fibers are arranged substantially two-dimensionally).
[0098]
(Example 3)
The separator (surface) of the present invention was exactly the same as in Example 1 except that the same high-strength polypropylene fiber as in Example 1 was used except that the fiber diameter was 14 μm and the cut fiber length was 10 mm. Density: 40 g / m², Thickness: 0.10 mm, bundles of ultrafine fibers are not substantially present, and fibers are arranged substantially two-dimensionally).
[0099]
Example 4
The separator (surface) of the present invention was the same as in Example 1 except that the same high-strength polypropylene fiber as in Example 1 was used except that the fiber diameter was 31 μm and the cut fiber length was 10 mm. Density: 40 g / m², Thickness: 0.10 mm, bundles of ultrafine fibers are not substantially present, and fibers are arranged substantially two-dimensionally).
[0100]
(Example 5)
Split fiber (drawn) having an orange-like fiber cross section in which substantially triangular polypropylene components and substantially triangular high-density polyethylene components are alternately arranged, having a fiber diameter of 17 μm and a cut fiber length of 5 mm Eight polypropylene ultrafine fibers (melting point: 168 ° C.) having a substantially triangular fiber cross section and a fiber diameter of 4.5 μm, and high density polyethylene ultrafine fibers (melting point: 4.5 μm in fiber cross section). 135 ° C.) can be divided into 8).
[0101]
Moreover, as a heat-sealable fiber, a core-sheath type composite in which a core component (non-fusion component) is made of polypropylene (melting point: 168 ° C.) and a sheath component (fusion component) is made of low-density polyethylene (melting point: 115 ° C.). Fibers (fiber diameter: 12 μm, cut fiber length: 5 mm, mass ratio of core component to sheath component is 1: 1, not fibrillated, stretched) were prepared.
[0102]
Furthermore, the same high-strength polypropylene fiber as in Example 1 was prepared.
[0103]
Subsequently, the splittable fiber was split with a beater for 10 minutes to generate polypropylene ultrafine fibers and high density polyethylene ultrafine fibers.
[0104]
Next, from a slurry obtained by mixing and dispersing polypropylene fine fiber and high density polyethylene extra fine fiber 20 mass%, core-sheath type composite fiber 50 mass%, and high strength polypropylene fiber 30 mass% generated from splittable fibers, a wet method The separator of the present invention (surface density: 40 g / m) exactly as in Example 1 except that the fiber web was formed by (horizontal long mesh system).², Thickness: 0.10 mm, bundles of ultrafine fibers are not substantially present, and fibers are arranged substantially two-dimensionally).
[0105]
(Example 6)
The same sea-island type fiber, heat-sealing fiber, and high-strength polypropylene fiber as in Example 1 were prepared.
[0106]
Subsequently, 20 mass% of sea-island type fibers, 50 mass% of heat-sealing fibers, and 30 mass% of high-strength polypropylene fibers were mixed, and a fiber web was formed from the dispersed slurry by a wet method (horizontal long net method).
[0107]
Subsequently, this fiber web was heat-treated at 135 ° C., so that only the high-density polyethylene component of the heat-bonding fiber was fused to produce a fused nonwoven fabric.
[0108]
Next, this fused nonwoven fabric is immersed in a bath composed of a 10 mass% sodium hydroxide aqueous solution at a temperature of 80 ° C. for 30 minutes to extract and remove PLLA, which is a sea component of the sea-island fiber, to obtain polypropylene ultrafine fibers (fiber diameter: 2 μm, ρ / d: 0.083, melting point: 172 ° C., fiber length: 2 mm, unfibrillated, stretched, having substantially the same diameter in the fiber axis direction, cross-sectional shape: circular) An extracted nonwoven fabric was produced.
[0109]
Next, the extracted nonwoven fabric was heat-treated again at 135 ° C. to fuse only the high-density polyethylene component of the heat-sealing fibers to produce a re-bonded nonwoven fabric.
[0110]
Subsequently, this re-bonded nonwoven fabric was subjected to fluorine gas treatment and calendar treatment in the same manner as in Example 1 to obtain the separator of the present invention (surface density: 40 g / m², Thickness: 0.10 mm, bundle of ultrafine fibers, fibers arranged substantially two-dimensionally).
[0111]
(Comparative example)
The same splittable fiber, heat-fusible fiber, and high-strength polypropylene fiber as in Example 5 were prepared.
[0112]
Next, a fiber web was formed from a slurry obtained by mixing and dispersing 20 mass% of splittable fibers, 50 mass% of heat-sealing fibers, and 30 mass% of high-strength polypropylene fibers, and then dispersing the slurry.
[0113]
Next, this fiber web was heat-treated at 125 ° C., so that only the low-density polyethylene component of the heat-sealing fiber was fused. Next, the fused fiber web is placed on a net having a wire diameter of 0.15 mm, and a water flow having a pressure of 12.7 MPa is alternately ejected from the nozzle plate having a nozzle diameter of 0.13 mm and a pitch of 0.6 mm twice on both sides. Then, splitting and entanglement of the splittable fibers were performed.
[0114]
Thereafter, the fiber web treated with the water stream was heat-treated at 125 ° C., and only the low-density polyethylene component of the heat-sealed fiber was fused again to form a fused nonwoven fabric.
[0115]
This fused nonwoven fabric was subjected to a fluorine gas treatment and a calendar treatment exactly as in Example 1 to obtain a separator (surface density: 40 g / m², Thickness: 0.10 mm).
[0116]
(Measurement of average formation index)
The average formation index was measured by the method described in the detailed description column.
[0117]
The results are shown in Table 1. As is apparent from Table 1, among the separators of the present invention, the separators of Examples 1 to 4 in which the fiber web was formed based on the extracted ultrafine fibers were excellent in texture. The separator of Example 5 was slightly inferior in texture because the splittable fibers were not sufficiently split and fiber mass remained. Moreover, since the separator of Example 6 had a bundle of ultrafine fibers, the texture was slightly inferior. Furthermore, since the separator of the comparative example made the water flow act, it had a fine through-hole and was inferior in texture.
[0118]
[Table 1]

[0119]
(Measurement of average needle-type penetration resistance per unit surface density)
The average needle penetration resistance per unit surface density was measured by the method described in the detailed description column.
[0120]
The results are shown in Table 1. As is clear from Table 1, the separator having excellent texture formed from the extracted ultrafine fibers, such as the separators of Examples 1 to 4, has an average needle penetration resistance per unit surface density. High, like the separators of Example 5 and Example 6, the separator slightly inferior in texture has a slightly poor average needle type penetration resistance per unit surface density, and has fine through-holes like the separator of the comparative example. The separator having a poor texture has a poor average needle type penetration resistance per unit surface density.
[0121]
(Evaluation of defective rate during battery manufacturing)
As a battery current collector, a positive electrode (33 mm width, 182 mm length) filled with nickel hydroxide in a nickel foam support, and a paste type hydrogen storage alloy negative electrode (mesh metal alloy NmNi)_FiveMold, 33 mm width, 247 mm length).
[0122]
Next, each separator cut to a width of 33 mm and a length of 410 mm was sandwiched between the positive electrode and the negative electrode, and then wound in a spiral shape to produce an SC-type electrode group. At this time, the rate at which the battery could not be manufactured due to a short circuit due to the burr of the electrode plate or the edge of the electrode plate was taken as the defective rate at the time of battery manufacture. The results are shown in Table 1.
[0123]
From Table 1, among the separators of the present invention, the separators of Examples 1 to 4 in which the fiber web was formed based on the extracted ultrafine fibers were excellent in texture, so the defect rate was low. Since the separators of Example 5 and Example 6 had a slightly poor texture, the defect rate was slightly high. Moreover, since the separator of the comparative example was poor in texture, the defect rate was high.
[0124]
【The invention's effect】
The battery separator of the present invention is less likely to cause a short circuit and can be manufactured with a high yield.
[0125]
The battery of the present invention is less prone to short circuit and can be manufactured with good yield.

Claims (12)

Provided with a nonwoven fabric in which high-strength polypropylene fibers having a tensile strength of 4.5 cN / dtex or more and ultrafine fibers having a fiber diameter of 5 μm or less are mixed, and the shape is substantially maintained only by fiber fusion. A separator for a battery , wherein the cross-sectional shape of all of the ultrafine fibers is circular, and the ultrafine fibers are not present in a bundle .   The battery separator according to claim 1, wherein the high-strength polypropylene fiber has a fiber diameter of 13 to 35 μm. The battery separator according to claim 1 or 2, wherein a Young's modulus of the high-strength polypropylene fiber is 800 kg / mm ² or more.   The battery separator according to any one of claims 1 to 3, wherein the mass of the high-strength polypropylene fiber occupies 10 to 90% of the mass of the nonwoven fabric. The said ultra fine fiber is an ultra fine fiber obtained by removing at least 1 type of resin component from the composite fiber containing a 2 or more types of resin component, The any one of Claims 1-4 characterized by the above-mentioned. Battery separator. The ultrafine fibers entire mass, characterized in that it accounts for 10-90% of the mass of the nonwoven fabric, a battery separator according to any one of claims 1-5. The nonwoven fabric, characterized in that further includes a heat fusion fibers, battery separator according to any one of claims 1-6. The battery separator according to any one of claims 1 to 7 , wherein the nonwoven fabric does not include fibrillated fibers as fibers other than high-strength polypropylene fibers. The battery separator according to any one of claims 1 to 8 , wherein the nonwoven fabric has a thickness of 0.11 mm or less. The battery separator according to any one of claims 1 to 9 , wherein an average formation index of the nonwoven fabric is 0.15 or less. Wherein the average Needle penetration strength of the nonwoven fabric is unit surface density (g / m ²⁾ per 14gf or higher, the battery separator according to any one of claims 1-10. Battery using a battery separator according to any one of claims 1 to 11.