JP4776876B2 - Battery separator and battery equipped with the same - Google Patents

Description

  The present invention relates to a battery separator and a battery including the same.

  Conventionally, a separator is used between the positive electrode and the negative electrode in order to separate the positive electrode and the negative electrode of the battery to prevent a short circuit and to keep the electrolyte solution and to smoothly perform an electromotive reaction.

  In recent years, with the reduction in size and weight of electronic devices, the space occupied by batteries has become narrower. ing. 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. Therefore, it was also one method to reduce the volume of the separator by strongly pressing the separator against the electrode plate when assembling the electrode group. However, when the separator is strongly pressed against the electrode plate in this way, the separator is deformed and the pore diameter of the separator is changed, so that there is a problem that the active material dropped from the electrode easily enters the separator and causes a short circuit.

  As a separator for solving such a problem, the applicant of the present application stated that “a high strength fiber having a tensile strength of 5 g / d (denier) or more is included, a maximum pore diameter is 50 μm or less, and a 5% modulus strength in at least one direction is 60 N. "Separator for alkaline battery", characterized by comprising a nonwoven fabric having a width of / 5 cm or more (Patent Document 1). In addition, as one factor for producing a separator having a 5% modulus strength of 60 N / 5 cm width or more, the fiber orientation is controlled in one direction by adjusting the moving speed of the net for making up the fiber and the slurry flow rate. It was disclosed that it is preferable to set the state close to.

JP 2000-353509 A (Claim 1, paragraph number 0037, etc.)

In this way, the separator in which the fibers are oriented in one direction was not easily deformed and short-circuited by assembling the electrode group while applying tension in the orientation direction. The problem was that the sucking speed of the battery was slow and the battery manufacturing efficiency was poor. This problem was remarkable when the basis weight of the separator was lowered (for example, 40 g / m ² or less) and the volume of the separator was reduced in order to cope with the increase in capacity of the battery.

  The present invention has been made to solve this problem, and an object of the present invention is to provide a battery separator in which the sucked-up speed of the injected electrolyte is high and the battery manufacturing efficiency is excellent, and a battery including the same. .

  The inventors of the present invention have examined the cause of the slowed-up speed of the injected electrolyte solution. Generally, an electrode group in which the electrodes are insulated by a separator is used, and the winding direction of the separator is orthogonal to the depth direction of the metal case. After inserting the metal case into the metal case, the electrolyte is poured into the metal case, and then the metal case is sealed, and the fibers constituting the separator are oriented in one direction. It has been found that the capillary effect in the depth direction is difficult to act, so that the sucked-up speed of the injected electrolyte is slow and the battery manufacturing efficiency is poor. In particular, when the basis weight of the separator is lowered, the amount of the absolute fiber is decreased. Therefore, the phenomenon has been found to be remarkable due to the fact that the fibers are oriented in one direction in order to prevent breakage during electrode group production. The present invention has been made based on such knowledge.

The invention according to claim 1 of the present invention is the “longitudinal tensile strength (CD) with respect to the transverse tensile strength (CD) , which is fixed only by fiber fusion and is sulfonated. MD) ”is a battery separator made of a wet nonwoven fabric having a ratio (MD / CD) of 1.33 to 1.69 . The battery separator having such a ratio (MD / CD) has the fibers oriented not only in the vertical direction but also in the horizontal direction, and the capillary effect in the depth direction of the metal case is likely to act. , The sucked-up speed of the injected electrolyte is fast, and the battery manufacturing efficiency is excellent.

  The invention according to claim 2 of the present invention is the “battery separator according to claim 1, characterized in that the wet nonwoven fabric constituting fibers include ultrafine fibers having a fiber diameter of 4 μm or less”. By including such ultrafine fibers, the battery separator (wet non-woven fabric) can be thin, which not only contributes to an increase in capacity of the battery, but also can take a dense structure, so It also has excellent electrolyte retention and can extend battery life.

  The invention according to claim 3 of the present invention is “the battery separator according to claim 2, characterized in that it contains 30 mass% or more of ultrafine fibers”. When the amount of ultrafine fibers is 30 mass% or more, the battery separator (wet non-woven fabric) can be made thinner, which can contribute to an increase in battery capacity and a longer battery life.

  The invention according to claim 4 of the present invention is as follows: “The wet nonwoven fabric constituting fibers include high-strength fibers having a tensile strength of 4.5 cN / dteX or more. The battery separator according to any one of the above. When high-strength fibers are included, it is possible to prevent the battery separator from being cut by the electrode plate when the battery is manufactured (for example, at the time of forming the electrode plate group), or burr of the electrode plate can be prevented from penetrating the battery separator. A short circuit can be effectively prevented.

  The invention according to claim 5 of the present invention is “the battery separator according to claim 4, wherein the fineness of the high-strength fiber is 0.8 dtex or less”. If the fineness of the high-strength fiber is 0.8 dtex or less, the battery separator (wet non-woven fabric) can be thin, which not only contributes to the high capacity of the battery, but also has a dense structure. It also has excellent electrolyte retention under pressure and can extend the battery life.

  The invention according to claim 6 of the present invention is "the battery separator according to claim 4 or 5, wherein the high-strength fiber has a fusion component on the fiber surface". For high-strength batteries, the high-strength fibers themselves can act as adhesive fibers, and the high-strength fibers can be fused. It can be a separator.

The invention according to claim 7 of the present invention is the “battery separator according to any one of claims 1 to 6, wherein the basis weight is 40 g / m ² or less”. Such a basis weight can be a thin battery separator, which can contribute to an increase in battery capacity. Moreover, even if it is such a basis weight, the sucking speed of the injected electrolyte solution is high, and the battery manufacturing efficiency is excellent.

  The invention according to claim 8 of the present invention is “a battery including the battery separator according to any one of claims 1 to 7”. Therefore, the battery can be manufactured efficiently.

  The battery separator of the present invention has a high suction speed of the injected electrolyte and is excellent in battery production efficiency.

  The battery of the present invention is a battery that can be produced efficiently.

  The battery separator of the present invention (hereinafter sometimes simply referred to as a separator) has a ratio (MD / CD) of the tensile strength (MD) in the vertical direction to the tensile strength (CD) in the transverse direction. Since it is made of a wet nonwoven fabric of ˜1.8, the sucked-up speed of the injected electrolyte is fast and the battery manufacturing efficiency is excellent. That is, when the ratio (MD / CD) is in the range of 1 to 1.8, it means that there is a certain amount of tensile strength even in the transverse direction, and the fiber is oriented in the transverse direction as a separator structure. This means that the capillary effect easily acts in the lateral direction, and the electrolyte sucking speed is fast, so that the battery manufacturing efficiency is excellent.

  This means that the closer this ratio (MD / CD) is to 1, the smaller the tensile strength in the vertical direction and the tensile strength in the transverse direction, and the separator structure has a fiber orientation in the vertical direction and the transverse direction. The ratio (MD / CD) is preferably 1 to 1.6, and more preferably 1 to 1.4, because the electrolyte sucking speed is faster.

  The ratio (MD / CD) of the separator (wet nonwoven fabric) of the present invention is as described above, but if there is no strength to some extent, it tends to be difficult to form an electrode group. The strength (MD) is preferably 50 N / 5 cm width or more, and more preferably 70 N / 5 cm width or more. Accordingly, the tensile strength (CD) in the transverse direction is preferably 27.8 N / 5 cm width or more, more preferably 31.3 N / 5 cm width or more, and 35.7 N / 5 cm width or more. More preferably, it is 38.9 N / 5 cm width or more, more preferably 43.8 N / 5 cm width or more, and further preferably 50 N / 5 cm width or more.

  In addition, the “vertical direction” in the present invention means a flow direction at the time of manufacturing a wet nonwoven fabric, and the longitudinal direction corresponds to the vertical direction when the wet nonwoven fabric alone is seen. On the other hand, the “weft direction” in the present invention means a direction perpendicular to the vertical direction of the wet nonwoven fabric, and the width direction corresponds to the weft direction when the wet nonwoven fabric alone is seen.

  In addition, the “tensile strength” of the present invention is a 50 (mm) × 200 (mm) rectangular sample (one side coincides with the vertical direction or the horizontal direction of the wet nonwoven fabric) from a wet nonwoven fabric. According to JIS L1096-A method (strip method), it refers to the tensile strength measured by a constant speed extension type. Note that the tensile strength measured from the sample of 50 mm in the transverse direction and 200 mm in the longitudinal direction is the tensile strength in the longitudinal direction, and the tensile strength measured from the sample of 50 mm in the longitudinal direction and 200 mm in the transverse direction is satisfactory. The tensile strength in the direction.

  Since the battery separator of the present invention is made of a wet nonwoven fabric, it has excellent texture and electrical insulation. This wet nonwoven fabric means a nonwoven fabric produced by bonding fiber webs based on a fiber web formed by a wet method.

  The separator for a battery of the present invention, that is, the fiber constituting the wet nonwoven fabric is not particularly limited, but includes an ultrafine fiber having a fiber diameter of 4 μm or less and / or a high strength fiber having a tensile strength of 4.5 cN / dtex or more. It is preferable. By including the former ultrafine fibers, the battery separator (wet non-woven fabric) can be made thin, which not only contributes to higher capacity of the battery, but also can adopt a dense structure, so electrolysis under pressure This is because the liquid retainability is excellent and the battery life can be extended. In addition, by including the latter high-strength fiber, the battery separator is cut by the electrode plate during battery manufacture (for example, when forming the electrode plate group), or the burr of the electrode plate penetrates the battery separator. This is because a short circuit can be effectively prevented.

  The smaller the fiber diameter of the ultrafine fiber that can constitute the battery separator (wet nonwoven fabric) of the present invention, the smaller the fiber diameter of the ultrafine fiber is. More preferably, it is 2 μm or less. The lower limit of the fiber diameter of the ultrafine fiber is not particularly limited, but about 0.01 μm is appropriate.

The ultrafine fibers that can constitute the separator of the present invention are preferably distributed in a narrow fiber diameter range, and the fiber diameters of the ultrafine fibers are preferably substantially the same. This is because, when the fiber diameters of the respective ultrafine fibers are substantially the same, holes having a uniform pore diameter and a uniform internal space are formed by the ultrafine fibers, and the distribution of the electrolytic solution becomes uniform. Specifically, the value (σ / d) obtained by dividing the standard deviation value (σ) of the fiber diameter distribution of the ultrafine fiber by the average fiber diameter (d) 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. The “average fiber diameter (d) of the ultrafine fibers” is obtained by taking an electron micrograph of a separator (wet nonwoven fabric) sample, measuring the fiber diameter of 100 or more ultrafine fibers in the electron micrograph, and measuring the measured fiber. Arithmetic mean value of diameter. Further, the “standard deviation value (σ)” of the ultrafine fibers is a value calculated by the following equation from the measured fiber diameters (X) of the n (100 or more) ultrafine fibers.
Standard deviation = {(nΣX ² − (ΣX) ² ) / n (n−1)} ^1/2

  The “fiber diameter” in the present invention refers to a value obtained by converting the fiber cross-sectional shape into a circle. That is, when the fiber cross-sectional shape is non-circular, the diameter of a circle having the same area as the fiber cross-sectional area is regarded as the fiber diameter.

  In addition, when the ultrafine fibers having a fiber diameter of 4 μm or less are composed of two or more groups from the viewpoint of fiber diameter distribution, it is preferable that the above relationship is established for each group of ultrafine fibers. In addition, the diameter of each ultrafine fiber does not substantially change in the fiber axis direction (that is, substantially, so that a separator having a uniform pore diameter and a uniform internal space (wet nonwoven fabric) can be formed). Preferably have the same diameter).

  Thus, the ultrafine fiber whose diameter is substantially the same in the fiber axis direction in the individual ultrafine fibers, or the ultrafine fiber having substantially the same fiber diameter among the plurality of ultrafine fibers is, for example, a spinneret portion. The sea component can be obtained by removing the sea component of the sea-island type composite fiber obtained by a composite spinning method such as a method of extruding and compounding the island component into the sea component. In addition, depending on the method generally called the mixed spinning method, that is, 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. It is difficult to obtain ultrafine fibers whose diameters are substantially the same in the fiber axis direction in individual ultrafine fibers, and to obtain ultrafine fibers having substantially the same fiber diameter among a plurality of ultrafine fibers. . Also, by the melt-blowing method, it is possible to obtain an ultrafine fiber whose diameter is substantially the same in the fiber axis direction in each ultrafine fiber and does not change, or an ultrafine fiber having substantially the same fiber diameter among a plurality of ultrafine fibers. It is difficult to get.

  It is preferable that the cross-sectional shape of the ultrafine fibers is circular, since the texture of the separator (wet nonwoven fabric) can be further improved. In addition, if there is a bundle of ultrafine fibers (easily formed by dividing a splittable fiber after forming a wet fiber web containing splittable fibers), the texture of the separator (wet non-woven fabric) becomes worse. It is preferable that the individual ultrafine fibers are not dispersed but in a dispersed state.

  This ultrafine fiber is preferably composed of a polyolefin resin so as to be excellent in resistance to an electrolytic solution. For example, a polyethylene resin (for example, ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, Linear low density polyethylene or ethylene copolymer), polypropylene resin (eg, polypropylene or propylene copolymer), or polymethylpentene resin (eg, polymethylpentene or methylpentene copolymer). Etc.) and is preferably made of polypropylene resin or polyethylene resin. In addition, if the ultrafine fiber contains a resin component that can participate in fusion (hereinafter sometimes referred to as “fusion component”), and the ultrafine fiber is fused by this fusion component, the ultrafine fiber is dropped. Or fuzzing, which is preferable.

  When this ultrafine fiber is fused, the ultrafine fiber can be composed only of a fusion component made of the polyolefin resin as described above, or a component having a melting point higher than the melting point of the fusion component and the fusion component. (Hereinafter, it may also be referred to as “non-fused component”). If the ultrafine fiber is composed of two or more components such as a fusion component and a non-fusion component as in the latter, the fiber form is maintained by the non-fusion component even if the fusion component is fused. It is more preferable because the ultrafine fibers can form holes with a uniform pore diameter and a uniform internal space.

  When the ultrafine fiber is composed of two or more kinds of components, it is preferable that the fusion component occupies a part or all of the surface of the ultrafine fiber and can participate in the fusion. When this ultrafine fiber is composed of two or more types of components, the arrangement state in the cross section 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 has a melting point that is 20 ° C. or more. As described above, the composite ultrafine fiber composed of two or more kinds of resin components such as the fusion component and the non-fusion component extrudes the island component when the sea-island type composite fiber is spun by a conventional composite spinning method. As a die, a sea island type fiber is spun using a die capable of forming a cross-sectional shape (for example, a core-sheath type, an eccentric type, or a sea-island type) as described above, or a conventional composite spinning method When spinning the sea-island type composite fiber, the resin obtained by mixing two or more types of resin components is supplied to the island component extrusion die, and the sea-island type fiber is spun to remove the sea component. .

  The ultrafine fibers are preferably short fibers having a high degree of freedom so that they can be easily dispersed uniformly in the wet fiber web manufacturing process. Specifically, the fiber length is preferably 0.1 to 25 mm (more preferably 0.1 to 20 mm), and 0.1 to 25 mm (more preferably 0.1 to 20 mm). It is more preferable that the ultrafine fiber is cut into pieces. In addition, when ultrafine fibers or sea-island type composite fibers are cut, if the ultrafine fibers or island components are crimped together, the dispersibility decreases. It is preferable to use fiber or sea-island type fiber. For example, a highly crystalline resin can be used as the material of such ultrafine fibers or sea-island type composite fibers (island components) that are difficult to press. Specifically, polymethylpentene or polypropylene having a melting point of 166 ° C. or higher (preferably 168 ° C. or higher) is preferably used.

  Such ultrafine fibers preferably contain 30 mass% or more, more preferably 35% or more, in the fibers constituting the wet nonwoven fabric (separator) so that they can be dense even if thin. , 40% or more is more preferable. In addition, the wet nonwoven fabric (separator) of this invention may be comprised from ultrafine fiber 100%.

  The higher strength fiber that can constitute the separator (wet nonwoven fabric) of the present invention can effectively prevent short-circuiting as the tensile strength is stronger, and the separator (wet nonwoven fabric) can be thinner, so the tensile strength is 5 It is preferably not less than 0.0 cN / dtex, more preferably not less than 5.5 cN / dtex, still more preferably not less than 6.0 cN / dtex, and still more preferably not less than 6.2 cN / dtex. The upper limit of the tensile strength is not particularly limited, but about 50 cN / dtex is appropriate. The tensile strength in the present invention means a value measured by JIS L 1015 (chemical fiber staple test method).

  It is preferable that at least the fiber surface is provided with a polyolefin-based resin similar to the above-mentioned ultrafine fiber so that the high-strength fiber is also excellent in resistance to electrolyte. This high-strength fiber can be composed of a single resin component, or it can be composed of a plurality of resin components, but if the fiber surface has a fusion component, the high-strength fiber can function as an adhesive fiber. Since it is not necessary to use low-strength adhesive fibers or only a small amount can be used, a battery separator having higher strength can be used, which is preferable.

  The high-strength fiber (hereinafter, sometimes referred to as composite high-strength fiber) having a fusion component composed of a plurality of resin components, which is suitable, is a component other than the fusion component (non-fusion component) depending on the fusion component. ), The melting component preferably has a melting point of 10 ° C. or more lower than that of the non-fusion component, and more preferably 20 ° C. or more and the melting point is lower. Therefore, for example, when the composite high-strength fiber is made of only a polyolefin resin, the non-fusion component is made of a polypropylene resin (especially, an isotactic polypropylene homopolymer is preferable), and the fusion component is made of polyethylene (particularly, And high density polyethylene is preferred).

  The composite high-strength fiber only needs to have a fusion component on at least a part of the fiber surface. However, the higher the ratio of the fusion component on the fiber surface, the more fusion components that can participate in fusion. Since it can be a separator (wet non-woven fabric) with excellent mechanical strength, the fusion component preferably accounts for 50% or more of the fiber surface (excluding both ends of the fiber), and accounts for 70% or more ( More preferably 90% or more (excluding both ends of the fiber), and moreover covering the entire fiber surface (excluding both ends of the fiber). Most preferred. Therefore, the arrangement state of each component in the cross section of the composite high-strength fiber is preferably a core-sheath type, an eccentric type, or a sea-island type.

  Moreover, the volume ratio of the non-fusion component and the fusion component in the composite high-strength fiber is not particularly limited, but (non-fusion component) :( fusion component) = 15: 85 to 85:15. It is preferable that (non-fusion component) :( fusion component) = 30: 70 to 70:30.

  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.

  The high-strength fibers that can constitute the separator (wet nonwoven fabric) of the present invention preferably have a Young's modulus of 30 cN / dtex or more so that it can be a separator that is not easily deformed by pressure and has excellent electrolyte retention. 35 cN / dtex or more, more preferably 40 cN / dtex or more. The upper limit of Young's modulus is not particularly limited, but is preferably 110 cN / dtex or less. 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.

  Moreover, it is preferable that the high-strength fiber has a heat shrinkage rate of 10% or less. This is because the heat shrinkage rate is less likely to shrink due to heat during the production of the separator (wet nonwoven fabric), so that the uniform dispersibility of the fibers of the wet fiber web is maintained and the short circuit prevention property is excellent. . A more preferable heat shrinkage rate is 9% or less. This heat shrinkage rate is based on the heat shrinkage rate (Method B) of JIS L 1013 and is a value measured by heat treatment for 30 minutes using an oven drier at a temperature of 120 ° C.

  The fineness of the high-strength fibers that can be used in the present invention is not particularly limited, but can be a thin battery separator (wet nonwoven fabric), which not only contributes to a higher capacity of the battery, but also has a dense structure. It is preferably 0.8 dtex or less, more preferably 0.7 dtex or less, so that it can be taken, has excellent electrolyte retention under pressure, and can extend the battery life. More preferably, it is 0.6 dtex or less. On the other hand, the lower limit of the fineness of the high-strength fiber is not particularly limited, but about 0.1 dtex is appropriate. The “fineness” in the present invention refers to a value obtained by the A method defined in JIS L 1015.

  The fiber length of the high-strength fiber that can be used in the present invention is not particularly limited. However, the shorter the fiber length, the higher the degree of freedom of the fiber, and the more uniformly dispersible the separator (wet non-woven fabric) with better texture. Therefore, it is preferably 0.1 to 25 mm (more preferably 0.1 to 20 mm), and is a fiber cut to 0.1 to 25 mm (more preferably 0.1 to 20 mm). Is preferred. The fiber length is a length obtained by JIS L 1015 (chemical fiber staple test method) B method (corrected staple diagram method).

  In the wet nonwoven fabric constituting the separator of the present invention, the high-strength fibers may contain two or more types of high-strength fibers that differ in terms of fineness, tensile strength, and / or resin composition.

  The wet nonwoven fabric constituting the separator of the present invention has high strength fibers so that the burr on the electrode plate does not penetrate the separator or tear by the edge of the electrode plate during battery production (for example, when forming the electrode plate group). When it consists of one resin component, it is preferable to contain 5-70 mass%, and it is more preferable to contain 10-50 mass%. Moreover, when a high strength fiber consists of composite high strength fiber, it is preferable to contain 10-70 mass%, and it is more preferable to contain 20-70 mass%. Furthermore, when the wet nonwoven fabric includes composite high-strength fibers and ultrafine fibers, the mass ratio of (composite high-strength fibers) :( extrafine fibers) = 70 to 10:30 to 90 is preferable. Composite high-strength fiber): (extra fine fiber) = 70-20: 30 It is more preferable that the mass ratio is 30-80.

  In addition, the separator (wet non-woven fabric) of the present invention has a lower melting point (preferably a melting point lower by 10 ° C. or more, more preferably a melting point lower by 20 ° C. or more) than any of the fibers other than the ultrafine fibers and high-strength fibers as described above. It may further include an adhesive fiber having a resin having a fiber surface, or an adhesive fiber having a resin having a melting point comparable to that of at least one fusion component of an ultrafine fiber and a high-strength fiber on the fiber surface. For example, when both high-strength fibers and ultrafine fibers are made of polypropylene alone, a polyethylene resin (for example, ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, It is preferable to use an adhesive fiber having an ethylene copolymer or the like as a fusing component. When the high-strength fiber and / or ultrafine fiber is made of polypropylene and polyethylene, a polyethylene resin (for example, ultrahigh molecular weight polyethylene) It is preferable to use an adhesive fiber having a fusion component of high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene copolymer, or the like.

  Since this adhesive fiber has a fusion component on the fiber surface, the fibers can be fused together to improve the mechanical strength of the separator (wet nonwoven fabric). In this adhesive fiber, the fusion component preferably occupies 50% or more, more preferably 80% or more, of the fiber surface so that the adhesive force is excellent. Such an adhesive fiber may be composed of a single resin component (that is, only a fusion component) or may be composed of a plurality of resin components. In some cases, it is preferable to use a plurality of resin components.

  Examples of the cross-sectional shape of the adhesive fiber made of a plurality of resin components include a core-sheath type, an eccentric type, a bonded type, a sea-island type, an orange type, and a multiple bimetal type. Among these, a core-sheath type, an eccentric type, or a sea-island type adhesive fiber that can be fused by a fusing component constituting the entire fiber surface can be preferably used, and a core-sheath type adhesive fiber is particularly suitable. Can be used for The resin component other than the fusion bonding component of the adhesive fiber is preferably made of a resin that is higher by 10 ° C. or higher than the melting point of the adhesive component, and preferably made of a resin that is higher by 20 ° C. or higher so that the fiber shape can be maintained.

  The fineness of the adhesive fiber is not particularly limited, but is preferably 0.05 to 2 dtex. Further, the fiber length of the adhesive fiber is not particularly limited, but is preferably 0.1 to 25 mm, and more preferably 0.1 to 20 mm.

  Such an adhesive fiber can be contained in the fiber constituting the separator (wet nonwoven fabric) in an amount of 10 to 100 mass%, preferably 20 so that the mechanical strength of the separator (wet nonwoven fabric) can be improved. ~ 100 mass% may be included.

The basis weight of the separator (wet nonwoven fabric) of the present invention is not particularly limited, but if the basis weight is a low basis weight of 40 g / m ² or less, the thickness can be reduced, which contributes to an increase in battery capacity. It is possible and suitable. Moreover, even if it is such a basis weight, the ratio (MD / CD) is 1-1. A more preferable basis weight is 38 g / m ² or less. The lower limit of the basis weight is not particularly limited as long as the electrical insulation can be maintained, but about 15 g / m ² is appropriate. “Weight weight” means the basis weight obtained based on the method defined in JIS P 8124 (paper and paperboard—basis weight measurement method).

  Further, the thickness of the separator (wet nonwoven fabric) of the present invention is not particularly limited, but is preferably 0.12 mm or less because it can contribute to an increase in battery capacity. A more preferable thickness is 0.10 mm or less. The lower limit of the thickness is not particularly limited as long as the electrical insulation can be maintained, but about 0.03 mm is appropriate. “Thickness” is 10 points measured at random by the measuring method of JIS C2111 5.1 (1) using an outer micrometer (0 to 25 mm) defined in JIS B 7502: 1994. The average value of

  The separator (wet nonwoven fabric) of the present invention is preferably fixed only by fusing fibers (for example, ultrafine fibers, high-strength fibers, and / or adhesive fibers). In this way, when fixed only by fiber fusion, the texture is excellent, short-circuiting is unlikely to occur, and the electrolyte can be evenly distributed and can be a separator with low internal resistance. is there. For example, if it is fixed not only by fusion but also by entanglement, a through-hole from the surface to the back surface of the separator (wet nonwoven fabric) is formed by the action for entanglement (for example, fluid flow such as water flow). Therefore, there is a tendency that a short circuit is likely to occur. However, if it is fixed only by fusion, the arrangement of the fibers is not disturbed at the time of fusion, so that the short circuit is difficult to occur. Thus, “fiber fusion only” refers to a state where the wet fiber web is fixed only by fusion.

The separator (wet nonwoven fabric) of the present invention has a high electrolyte retention rate, and the separator preferably has a porosity of 40 to 75% so that the internal resistance and internal pressure of the battery can be kept low. % Is more preferable, and 50 to 65% is still more preferable. This “porosity (P)” is a value obtained from the following equation.
Porosity (P) = {1−W / (T × d)} × 100
Here, W means the basis weight of the separator (g / m ² ), T means the thickness (μm) of the separator, and d means the density (g / cm ³ ) of the resin (for example, fiber) constituting the separator. In addition, when resin which comprises a separator consists of 2 or more types of resin, the density of structural resin says the mass mean value of each structural resin. For example, when the resin A having a density d ₁ is a (mass%) and the resin B having a density d ₂ is b (mass%), the density (d) of the constituent resin is calculated by the following equation.
Density (d) = d ₁ × a / 100 + d ₂ × b / 100

  The separator (wet non-woven fabric) of the present invention preferably has a single layer structure so that the electrolyte is not unevenly distributed in the thickness direction of the separator. This “single-layer structure” means that the fibers are composed of the same fiber everywhere in the thickness direction of the separator.

  The separator (wet non-woven fabric) of the present invention has a sulfonation treatment, a fluorine gas treatment, a vinyl monomer graft polymerization treatment, a discharge treatment, a surfactant treatment, or a hydrophilic resin so that the electrolyte retainability is excellent. It is preferable that a hydrophilization treatment selected from the treatments is performed. Among these, sulfonation treatment, fluorine gas treatment, vinyl monomer graft polymerization treatment, or discharge treatment is preferable because the decrease in hydrophilicity is small and the electrolytic solution can be retained over a long period of time.

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

  First, a nonwoven fabric constituent fiber is prepared. Preferably, ultrafine fibers, high-strength fibers, and / or adhesive fibers as described above are prepared.

  Next, the prepared fibers are appropriately blended to form a fiber web by a wet method. Examples of the wet method include a conventionally known method, for example, a horizontal long net method, an inclined wire type short net method, a circular net method, or a long net / circular net combination method.

In order to easily produce a wet nonwoven fabric having a ratio (MD / CD) as in the present invention, the fiber web is formed under the papermaking conditions in which the flow rate of the slurry is higher than the moving speed of the porous support such as a net. Is preferred. This is considered to be because the fibers can be oriented in the thickness direction of the fiber web and the fibers can be entangled randomly. In particular, even if the basis weight is as low as 40 g / m ² or less, it is easy to form a fiber web by increasing the flow rate of the slurry rather than the speed of the porous support.

  Further, when two or more wet fiber webs are combined, it is preferable to combine the fiber webs composed of the same fibers so that a separator having a single layer structure can be manufactured.

  Then, the wet fiber web can be bonded to obtain a wet nonwoven fabric, that is, the separator of the present invention. As a bonding method, only fusion of fibers (ultrafine fibers, high-strength fibers, and / or adhesive fibers) is performed without performing entanglement or the like so as not to impair the uniform fiber dispersion state of the wet fiber web. It is preferable to combine by. The fiber web can be fused under pressure, can be carried out under no pressure, or can be carried out under pressure after heating.

  In addition, when it is preferable that the separator is hydrophilized, next, a hydrophilization process is implemented. Examples of the hydrophilic treatment include sulfonation treatment, fluorine gas treatment, vinyl monomer graft polymerization treatment, discharge treatment, surfactant treatment, and hydrophilic resin application treatment.

  The sulfonation treatment is not particularly limited. For example, the wet non-woven fabric produced as described above is immersed in a solution comprising fuming sulfuric acid, sulfuric acid, sulfur trioxide, chlorosulfuric acid, or sulfuryl chloride to sulphonate. There are a method of introducing an acid group, a method of introducing a sulfonic acid group into a wet nonwoven fabric by applying a discharge in the presence of sulfur monoxide gas, sulfur dioxide gas, sulfur trioxide gas or the like.

  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 wet nonwoven fabric can be hydrophilized by exposing the wet nonwoven fabric to a gas mixture with at least one gas selected from the above. In addition, after making sulfur dioxide gas adhere to a wet nonwoven fabric beforehand, when making fluorine gas contact, permanent hydrophilicity can be provided more efficiently.

  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. As a polymerization method of these vinyl monomers, for example, a method of immersing a wet nonwoven fabric in a solution containing a vinyl monomer and a polymerization initiator, a method of irradiating radiation after applying a vinyl monomer to a wet nonwoven fabric, a wet nonwoven fabric There are a method of contacting with a vinyl monomer after irradiation with radiation, a method of irradiating a wet non-woven fabric with a vinyl monomer solution containing a sensitizer and then irradiating with ultraviolet rays. In addition, if the wet nonwoven fabric surface is modified by ultraviolet irradiation, corona discharge, plasma discharge, or the like before contacting the vinyl monomer solution with the wet nonwoven fabric, the affinity with the vinyl monomer solution increases, which is efficient. Graft polymerization can be carried out.

  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 wet non-woven fabric can be immersed in a solution of ether or polyoxyethylene alkylphenol ether), or this solution can be applied to or sprayed on the wet non-woven fabric.

  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, a wet non-woven fabric is disposed between a pair of electrodes each carrying a dielectric under atmospheric pressure in the air so as to come into contact with both of these dielectrics, and an AC voltage is applied between these two electrodes. Is applied, and the surface of the fiber constituting the inside of the wet nonwoven fabric can be treated as well as the outside of the wet nonwoven fabric. Therefore, the separator hydrophilized by such a method is excellent in the retention of the electrolytic solution inside.

  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 an appropriate solvent, and a wet nonwoven fabric can be immersed in the solvent, or this solvent can be applied or sprayed onto the wet 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. Examples of the crosslinkable polyvinyl alcohol include polyvinyl alcohol in which a hydroxyl group is partially substituted with a photosensitive group, and more specifically, a styrylpyridinium-based photosensitive group, a styrylquinolinium-based photosensitive group, or There is polyvinyl alcohol substituted with a styrylbenzothiazolium-based photosensitive group. This crosslinkable polyvinyl alcohol can also be cross-linked by light irradiation after being attached to a wet 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 ions and chelates. It can be suitably used because it forms a chelate with the ions before the metal-like metal is deposited, and hardly causes a short circuit between the electrodes.

  In addition, when there is variation in the thickness of the separator, it is preferable to correct the variation in thickness by, for example, a method of passing between a pair of rolls.

  A separator having a porosity of 40 to 75% can be produced by a single means or a combination of means such as lowering the basis weight or increasing the thickness.

  The battery of the present invention can be exactly the same as the conventional battery except that it includes the separator of the present invention as described above.

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 spirally wound through the separator of the present invention as described above is inserted into a metal case. Have 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, A foamed nickel or nickel net filled with an AB ₅ (rare earth) alloy, an AB / A ₂ B (Ti / Zr) alloy, or an AB ₂ (Laves phase) 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.

  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. Moreover, a sealed type or an open type may be used.

  The battery of the present invention is, for example, a primary battery such as an alkaline manganese battery, a mercury battery, a silver oxide battery, or an air battery, or a nickel-cadmium battery, a silver-zinc battery, a silver-cadmium battery, a nickel-zinc battery, a nickel- The battery may be a secondary battery such as a hydrogen battery or a lead storage battery, and particularly preferably a nickel-cadmium battery or a nickel-hydrogen battery.

Examples of the present invention will be described below, but the present invention is not limited to the following examples. The height of liquid absorption in the horizontal direction is 25 mm and a sample of 180 mm in width is taken from the separator and placed in a 20 ± 2 ° C. environment with a potassium hydroxide aqueous solution with a density of 1.30 g / m ^3. The sample is hung so that the lower end of the sample is 5 mm so that the long side of the sample is perpendicular to the potassium hydroxide aqueous solution, and the height of the potassium hydroxide aqueous solution that has been absorbed and increased after 30 minutes. . If this liquid absorption height is 100 mm or more, battery manufacturing efficiency is excellent.

Example 1
Homopolypropylene (Q value: 3.2, MI: 14 g / 10 min, melting point: 168 ° C.) as a core component, high density polyethylene (Q value: 6.7, MI: 20 g / 10 min, melting point: 135 ° C.) Is a composite high-strength polypropylene fiber having a tensile strength of 6.5 cN / dtex (high-density polyethylene covers the fiber surface except for both ends, the volume ratio of the core component to the sheath component = 50: 50, Young's modulus: 45 cN / dtex, thermal shrinkage: 7%, fineness: 0.6 dtex, fiber diameter: 9.0 μm, cut fiber length: 5 mm) were prepared.

Further, in the sea component composed of poly-L-lactic acid, 25 island components composed of polypropylene are present, and a sea-island type composite fiber (fineness: 1.65 dtex, cut fiber length: 2 mm) manufactured by a composite spinning method is used. It is immersed in a bath (temperature: 80 ° C.) of 10 mass% sodium hydroxide aqueous solution for 30 minutes to extract and remove poly-L-lactic acid, which is a sea component of the sea-island type composite fiber, to obtain a polypropylene extra fine fiber (fiber diameter: 2 μm , Σ / d: 0.083, melting point: 172 ° C., cut fiber length: 2 mm, density: 0.91 g / cm ³ , cross-sectional shape: circular). This polypropylene ultrafine fiber was not fibrillated and stretched, and each fiber had substantially the same diameter in the fiber axis direction.

  Next, 70% by mass of the composite high-strength polypropylene fiber and 30% by mass of the polypropylene ultrafine fiber are dispersed in a slurry, and each polypropylene ultrafine fiber and composite high-strength polypropylene fiber are dispersed by a wet method (horizontal long net system). A fiber web with dispersed therein was formed. The fiber web was formed by setting the ratio (Vs / Vn) of the slurry flow rate (Vs) to the moving speed (Vn) of the papermaking net to 0.7.

  Next, the fiber web is transferred to a conveyor, and sucked from below the conveyor to bring the fiber web into close contact with the conveyor and blow hot air at a temperature of 137 ° C. for 10 seconds to a sufficient amount. A heat treatment was performed under no pressure allowing hot air to pass through, and at the same time as drying the fiber web, only the high-density polyethylene component of the composite high-strength polypropylene fiber was fused to form a fused fiber web.

Next, the fused fiber web was dipped in a fuming sulfuric acid solution (15% SO ₃ solution) at a temperature of 60 ° C. for 2 minutes, washed thoroughly with water, dried, and subjected to sulfonation treatment. A separator having a single layer structure of m ² and a thickness of 0.085 mm was manufactured. The physical properties of this separator were as follows.

Tensile strength in the vertical direction (MD): 80 N / 5 cm width Tensile strength in the transverse direction (CD): 60 N / 5 cm width Ratio (MD / CD): 1.33
Porosity: 55%
Liquid absorption height in the lateral direction: 130 mm / 30 min.

(Example 2)
Except that the fiber web was formed with a ratio (Vs / Vn) of 0.9, a single-layer separator having a basis weight of 35 g / m ² and a thickness of 0.085 mm was manufactured in the same manner as in Example 1. did. The physical properties of this separator were as follows.

Tensile strength in the vertical direction (MD): 88 N / 5 cm width Tensile strength in the transverse direction (CD): 52 N / 5 cm width Ratio (MD / CD): 1.69
Porosity: 55%
Liquid absorption height in the lateral direction: 125 mm / 30 min.

(Comparative Example 1)
Except that the fiber web was formed with a ratio (Vs / Vn) of 1.2, a single-layer separator having a basis weight of 35 g / m ² and a thickness of 0.085 mm was manufactured in the same manner as in Example 1. did. The physical properties of this separator were as follows.

Tensile strength in the vertical direction (MD): 95 N / 5 cm width Tensile strength in the transverse direction (CD): 45 N / 5 cm width Ratio (MD / CD): 2.11
Porosity: 55%
Absorption height in the horizontal direction: 95 mm / 30 min.

Claims (8)

The ratio (MD / CD) of the tensile strength (MD) in the vertical direction to the tensile strength (CD) in the transverse direction , which is fixed only by fusion of the fibers and is subjected to the sulfonation treatment, is 1. A battery separator comprising a wet nonwoven fabric of 33 to 1.69 . 2. The battery separator according to claim 1, wherein the wet non-woven fabric includes ultrafine fibers having a fiber diameter of 4 μm or less. The battery separator according to claim 2, further comprising 30 mass% or more of ultrafine fibers. The battery separator according to any one of claims 1 to 3, wherein the wet nonwoven fabric includes high-strength fibers having a tensile strength of 4.5 cN / dteX or more. The battery separator according to claim 4, wherein the fineness of the high-strength fiber is 0.8 dtex or less. The battery separator according to claim 4 or 5, wherein the high-strength fiber has a fusion component on the fiber surface. The battery separator according to any one of claims 1 to 6, wherein the basis weight is 40 g / m ² or less. A battery comprising the battery separator according to claim 1.