Battery electrolyte retaining materials

Abstract

To provide a liquid-retaining member for a battery, which is hardly displaced when wound to manufacture a battery, and is used by being provided between an electrode and a separator inside the battery for the purpose of retaining an electrolyte solution in the battery. [Solution] As a result of continued research, the present applicant has found that a battery electrolyte retaining member having a static friction coefficient of greater than 0.39, as defined in the present invention, is a battery electrolyte retaining member that exhibits high friction with the separator. In other words, even when a battery is manufactured by winding the battery electrolyte retaining member according to the present invention in the order of battery electrolyte retaining member-separator-electrode, unintended slippage between the separator and the battery electrolyte retaining member is unlikely to occur. As a result, the battery electrolyte retaining member according to the present invention can prevent significant misalignment of the battery during winding.

Description

[Technical Field]

[0001] The present invention relates to a liquid-retaining member for a battery, which is disposed between an electrode and a separator inside the battery for the purpose of retaining an electrolyte in the battery. [Background technology]

[0002] Conventionally, a separator has been provided between the positive and negative electrodes of a battery to separate them to prevent short circuits and to retain an electrolyte solution to facilitate an electromotive reaction. In addition, it is required to retain an electrolyte solution between the positive and negative electrodes to prevent an increase in the electrical resistance of the battery.

[0003] To meet this requirement, for example, Patent Document 1 (JP 2022-121195 A) discloses that a liquid-retaining member for a battery made of a nonwoven fabric with excellent electrolyte retention properties is further provided between the electrode and the separator inside the battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-121195 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a battery is manufactured using a battery liquid-retaining member according to the conventional technology disclosed in Patent Document 1 and by winding the stacked battery liquid-retaining member in the order of separator-battery liquid-retaining member-electrode-battery liquid-retaining member, unintended slippage can occur between the separator and the battery liquid-retaining member, resulting in significant misalignment in the winding.

[0006] In a battery in which a large misalignment has occurred, a region where no battery liquid retaining member exists is generated between the positive electrode and the negative electrode, which may increase the electrical resistance of the battery.

[0007] The present invention has been made in view of the above-mentioned problems, and has an object to provide a liquid retaining member for a battery that is less likely to cause significant misalignment when wound. [Means for solving the problem]

[0008] The present invention is a battery liquid-retaining member made of a nonwoven fabric and used between an electrode and a separator inside a battery, The static friction coefficient of the battery electrolyte retaining member measured by the following [measurement method] is greater than 0.39, Battery fluid retaining material. [Measurement method] (1) Prepare a friction measuring device (Static / Dynamic Friction Measuring Device TL201Tt, manufactured by Trinity Lab Co., Ltd.). (2) A piece measuring 20 cm in length and 5 cm in width is cut out from the battery liquid retaining material, and three pieces of this piece are prepared. (3) Double-sided adhesive tape is attached to both ends of one main surface of the piece in the vertical direction (within a range of 2 cm vertically and 5 cm horizontally at each end), and the piece is attached to the table of the friction measuring machine using the double-sided adhesive tape. (4) A tactile contactor (finger model, contact area with the measurement object: 1.5 mm) was placed in the center of the other main surface of the slice. 2 Then, a 100g weight is placed on the tactile contactor, and a load is applied in the thickness direction of the piece. (5) One minute after the weight is placed on the surface, the tactile contact is slid once on one of the main surfaces of the piece in the vertical direction at a speed of 10 mm / sec and a distance of 40 mm to measure the static friction coefficient. This measurement is carried out three times, once for each of the three pieces, and the average value of the three static friction coefficient measurements is regarded as the static friction coefficient of the battery liquid-retaining member. [Effects of the Invention]

[0009] The battery electrolyte retaining member according to the present invention, which has a static friction coefficient of more than 0.39, is less likely to cause unintended slippage between the separator and the battery electrolyte retaining member.

[0010] Therefore, the battery liquid retaining member according to the present invention can prevent the battery from being significantly misaligned when wound. DETAILED DESCRIPTION OF THE INVENTION

[0011] The battery liquid-retaining member (hereinafter sometimes simply referred to as "liquid-retaining member") made of a nonwoven fabric and used between an electrode and a separator inside the battery of the present invention has a static friction coefficient of greater than 0.39, measured by the [Measurement Method] described below.

[0012] Therefore, even when a battery is manufactured by winding the liquid retention member in the stacked state of separator-liquid retention member-electrode-liquid retention member in this order, unintended slippage is unlikely to occur between the separator and the liquid retention member. As a result, the liquid retention member according to the present invention can prevent significant misalignment between the separator and the liquid retention member inside the battery.

[0013] The static friction coefficient of the liquid-retaining member is determined by the following measurement method.

[0014] [Measurement method] (1) Prepare a friction measuring device (Static / Dynamic Friction Measuring Device TL201Tt, manufactured by Trinity Lab Co., Ltd.). (2) Cut a piece measuring 20 cm in length and 5 cm in width from the liquid-retaining material. (3) Double-sided adhesive tape is attached to both ends of one main surface of the piece in the vertical direction (within a range of 2 cm vertically and 5 cm horizontally at each end), and the piece is attached to the table of the friction measuring machine using the double-sided adhesive tape. (4) A tactile contactor (finger model, contact area with the measurement object: 1.5 mm) was placed in the center of the other main surface of the slice. 2 Then, a 100g weight is placed on the tactile contactor, and a load is applied in the thickness direction of the piece. (5) One minute after placing the weight, measure the static friction coefficient by sliding the tactile contactor once on one of the main surfaces of the piece in the vertical direction at a speed of 10 mm / sec and a distance of 40 mm. This measurement is carried out three times, and the average value of the three measured static friction coefficients is regarded as the static friction coefficient of the liquid-retaining member.

[0015] The higher the static friction coefficient of the liquid-retaining member, the less likely unintended slippage occurs between the separator and the battery liquid-retaining member. Therefore, the static friction coefficient is preferably 0.45 or higher, and even more preferably 0.50 or higher. The upper limit of the static friction coefficient of the liquid-retaining member is that if no slippage occurs between the separator and the liquid-retaining member, when a battery is manufactured by winding a stack of separator-liquid-retaining member-electrode-liquid-retaining member, the difference in length between the outer separator and the inner liquid-retaining member may cause slippage during winding. To prevent this slippage, some degree of slippage between the separator and the liquid-retaining member is necessary, so a realistic value is 2.0 or lower.

[0016] The liquid-retaining member of the present invention is composed of a nonwoven fabric. Examples of the nonwoven fabric that constitutes the liquid-retaining member include dry-laid nonwoven fabrics produced by a carding method or air-laying method, wet-laid nonwoven fabrics produced by papermaking, and directly spun nonwoven fabrics produced by accumulating directly spun (melt-blown, spun-bonded) fibers. Among these, wet-laid nonwoven fabrics are preferred because the fibers are uniformly dispersed within the nonwoven fabric, making it easy to uniformly retain the electrolyte, and enabling the realization of a battery with low electrical resistance.

[0017] Examples of resins contained in the constituent fibers of the nonwoven fabric constituting the liquid-retaining member of the present invention include polyolefin resins (polypropylene resin, polyethylene resin, polymethylpentene, polyolefin resins having a structure in which part of hydrocarbons is substituted with a cyano group or a halogen such as fluorine or chlorine, etc.), styrene resins, polyether resins (polyether ether ketone, polyacetal, phenolic resin, melamine resin, urea resin, epoxy resin, modified polyphenylene ether, aromatic polyether ketone, etc.), polyester resins (polyethylene terephthalate resin, polytrimethylene terephthalate resin, polybutylene terephthalate resin, polyethylene naphthalate resin, polybutylene naphthalate resin, polycarbonate resin, polyarylate resin, wholly aromatic polyester resin, unsaturated polyester resin, etc.), poly Examples of organic resins include imide resins, polyamideimide resins, polyamide resins (such as aromatic polyamide resins, aromatic polyetheramide resins, and nylon resins), resins containing nitrile groups (such as polyacrylonitrile resins), urethane resins, epoxy resins, polysulfone resins (such as polysulfone resins and polyethersulfone resins), fluorine-containing resins (such as polytetrafluoroethylene resins and polyvinylidene fluoride resins), cellulose resins (such as rayon fibers), polybenzimidazole resins, acrylic resins (such as polyacrylonitrile resins copolymerized with acrylic ester resins or methacrylic esters, and modacrylic resins copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride), vinylon resins (such as vinyl acetate resins and polyvinyl alcohol resins), and polyphenylene sulfide resins. Among the resins contained in the constituent fibers of the nonwoven fabrics described above, it is preferable to include polyolefin resins in the constituent fibers of the nonwoven fabrics described above, because they have excellent chemical resistance, are less likely to degrade inside the battery, and are highly versatile. It is more preferable that the constituent fibers of the nonwoven fabric are made of only polyolefin resin. The nonwoven fabric may be made of a single organic resin or two or more organic resins.

[0018] These organic resins may be either linear or branched polymers, may be block copolymers or random copolymers, and may have any three-dimensional structure or may be crystalline or non-crystalline.

[0019] The fibers constituting the nonwoven fabric may be monofilaments or composite fibers. The composite fibers may have, for example, a core-sheath, sea-island, side-by-side, orange, or bimetallic cross section. Furthermore, the fibers may be fibril fibers.

[0020] The nonwoven fabric constituting the liquid-retaining member of the present invention preferably contains fibers (hereinafter referred to as "fusible fibers") with a fusible component on at least a portion of the fiber surface. When the constituent fibers of the nonwoven fabric are fused together by the fusible component, the unevenness of the fused portions of the nonwoven fabric increases the static friction coefficient of the liquid-retaining member made of the nonwoven fabric. As a result, unintended slippage between the separator and the liquid-retaining member is more unlikely to occur, which is preferable. In addition, the increased mechanical strength of the nonwoven fabric contributes to dimensional stability, making the thickness of the nonwoven fabric less likely to collapse, and the nonwoven fabric's excellent electrolyte retention is preferable.

[0021] The area of ​​the fusible components on the fiber surface (excluding both ends) of the fusible fibers is not particularly limited, but the larger the area, the more irregularities caused by the fusion of the fusible components will be, and the higher the static friction coefficient of the liquid-retaining member made of a nonwoven fabric to which the fusible fibers are fused. Furthermore, the larger the fusible components that can participate in fusion, the more they will contribute to the dimensional stability of the nonwoven fabric. For these reasons, the fusible components preferably account for 50% or more of the area, more preferably 70% or more, and even more preferably 90% or more. It is most preferable that only the fusible components (100%) make up the fiber surface (excluding both ends).

[0022] The arrangement of the fusion component and the non-fusion component in the fiber cross section of such a fusion fiber may be, for example, a core-sheath, eccentric, sea-island, side-by-side, orange, or multi-layered configuration, and it is particularly preferred that the fiber surface (excluding both ends) is made up of only the fusion component (100%), such as a core-sheath, eccentric, or sea-island configuration.

[0023] The volume ratio of the fusion component to the non-fusion component in the cross section of the fusion fiber is not particularly limited, but so that there is a large amount of fusion component that can participate in fusion, it is preferable that the ratio of (fusion component):(non-fusion component) is 15:85 to 85:15, more preferably that the ratio of (fusion component):(non-fusion component) is 20:80 to 70:30, even more preferably that the ratio of (fusion component):(non-fusion component) is 23:77 to 55:45, and even more preferably that the ratio of (fusion component):(non-fusion component) is 25:75 to 45:55.

[0024] Furthermore, it is sufficient for the fusion component to have a lower melting point than the non-fusion component. However, even when only the fusion component is fused, the melting point of the fusion component is preferably at least 10°C lower than the melting point of the non-fusion component, more preferably at least 20°C lower, and even more preferably at least 30°C lower, so that the fiber form of the fiber having the fusion component on part of the fiber surface can be easily maintained.

[0025] The fusion fibers preferably contain a polyolefin resin because they have excellent chemical resistance, are less likely to degrade inside the battery, and are highly versatile. Examples of fusion fibers containing a polyolefin resin include polyethylene / polypropylene, polyethylene / polymethylpentene, polypropylene / polymethylpentene, propylene copolymer / polymethylpentene, ethylene copolymer / polymethylpentene, ethylene copolymer / polypropylene, and low-density polyethylene / high-density polyethylene. Among these polyolefin resins, polypropylene is preferred because it has relatively high rigidity, is resistant to crushing under pressure, and easily maintains the voids in the nonwoven fabric that constitutes the liquid-retaining member. Furthermore, the fusion fibers preferably contain polyethylene to facilitate fiber adhesion to the constituent fibers of the nonwoven fabric through fusion. Therefore, the fusion fibers preferably contain both polypropylene and polyethylene.

[0026] Polypropylene may be a propylene homopolymer or a copolymer of propylene and an α-olefin (e.g., ethylene, 1-butene, etc.). More specifically, examples include crystalline isotactic propylene homopolymers, ethylene-propylene random copolymers with a low ethylene unit content, propylene block copolymers composed of a homopolymer portion consisting of a propylene homopolymer and a copolymer portion consisting of an ethylene-propylene random copolymer with a relatively high ethylene unit content, and crystalline propylene-ethylene-α-olefin copolymers in which each homopolymer portion or copolymer portion of the propylene block copolymer is further copolymerized with an α-olefin such as 1-butene. Among these, isotactic propylene homopolymers are preferred in terms of strength, and such polypropylenes can be obtained by homopolymerizing propylene or copolymerizing propylene with other α-olefins using a Ziegler-Natta catalyst or a metallocene catalyst.

[0027] Polyethylene, for example, has a density of 0.942 g / cm 3High density polyethylene, density 0.930~0.942g / cm 3 Medium density polyethylene, density 0.910~0.930g / cm 3 The nonwoven fabric may be an ethylene polymer such as a low-density polyethylene or a linear low-density polyethylene. Among these, high-density polyethylene is preferred because it has a certain degree of hardness and can provide a nonwoven fabric with tension and stiffness, thereby enabling the nonwoven fabric and liquid-retaining member to be easily handled.

[0028] The higher the Young's modulus of the fusible fibers, the more likely they are to maintain their fiber shape even when pressure is applied, improving the shape stability of nonwoven fabrics containing fusible fibers and making it easier to realize nonwoven fabrics and liquid-retaining members with excellent electrolyte retention. Therefore, the Young's modulus of the fusible fibers is preferably 30 cN / dtex or more, more preferably 40 cN / dtex or more, and even more preferably 45 cN / dtex or more. There is no particular upper limit to the Young's modulus, but a value of about 110 cN / dtex is appropriate.

[0029] The Young's modulus in the present invention refers to the apparent Young's modulus calculated from the initial tensile resistance measured by the method specified in JIS L 1015 (Testing method for synthetic fiber staples): 2010, Section 8.11. The initial tensile resistance refers to the value measured using a constant-speed tension tester.

[0030] The higher the tensile strength of the fusible fibers constituting the nonwoven fabric, the greater the mechanical strength of the resulting nonwoven fabric. This also facilitates the realization of a nonwoven fabric and liquid-retaining member that are less likely to break during winding to manufacture a battery. Therefore, the tensile strength of the fusible fibers is preferably 5.0 N / dtex or more, more preferably 5.3 cN / dtex or more, and even more preferably 5.5 cN / dtex or more. While there is no particular upper limit to the tensile strength, a value of approximately 50 cN / dtex is appropriate.

[0031] Furthermore, the higher the elongation of the fusible fibers, the easier it is to realize a nonwoven fabric and a liquid-retaining member that are less likely to break during winding to manufacture a battery. Therefore, the elongation of the fusible fibers is preferably 10% or more, more preferably 15% or more, and even more preferably 18% or more. On the other hand, if the elongation of the fusible fibers is too high, the shape stability of the nonwoven fabric and the liquid-retaining member may be reduced, so the elongation is preferably 35% or less, more preferably 32% or less, and even more preferably 30% or less.

[0032] The tensile strength and elongation of the fiber in the present invention refer to values ​​measured by the method specified in JIS L 1015 (chemical fiber staple test method): 2010, section 8.7.1.

[0033] The average fiber diameter of the fusible fibers is not particularly limited, but when the fusible fibers are mixed with other fibers such as ultrafine fibers described below, the average fiber diameter of the fusible fibers is preferably 3 to 17 μm, more preferably 5 to 15 μm, and even more preferably 7 to 13 μm, so that the fusible fibers are uniformly dispersed, the nonwoven fabric and the liquid-retaining member containing the fusible fibers are less likely to break during winding to manufacture the battery, the electrolyte retention of the nonwoven fabric and the liquid-retaining member is excellent, and unintended slippage between the separator and the liquid-retaining member during winding to manufacture the battery is less likely to occur. Furthermore, when the nonwoven fabric constituting the liquid-retaining member of the present invention is composed only of fusible fibers, the smaller the fiber diameter of the fusible fibers, the larger the specific surface area of ​​the main surface of the nonwoven fabric constituting the liquid-retaining member. The average fiber diameter of the fused fibers is preferably 3 to 10 μm, so that the static friction coefficient of the liquid-retaining member made of the nonwoven fabric is high, unintended slippage between the separator and the liquid-retaining member is unlikely to occur, and the liquid-retaining member has excellent performance in various areas, such as electrolyte retention. In this invention, the "average fiber diameter" refers to the number-average fiber diameter of 50 randomly selected fibers. The "fiber diameter" refers to the diameter of a fiber when the cross-sectional shape of the fiber is circular; if the cross-sectional shape is not circular, the fiber diameter is considered to be the diameter of a circle with the same area as the cross-sectional area.

[0034] The fiber length of the fusible fibers is not particularly limited, but is preferably 0.1 to 25 mm, more preferably 1 to 10 mm, and even more preferably 2 to 5 mm, so that the fusible fibers are uniformly dispersed and the liquid-retaining member made of the nonwoven fabric containing the fusible fibers is less likely to break during winding to manufacture the battery. Note that the fiber length in the present invention refers to the length measured by the method specified in JIS L 1015 (Chemical Fiber Staple Testing Method): 2010, Section 8.4, Method B (Corrected Staple Diagram Method).

[0035] The nonwoven fabric may contain two or more types of fusible fibers that differ in one or more of the following: the number of resin components, resin components, Young's modulus, tensile strength, elongation, average fiber diameter, fiber length, and the like.

[0036] To maintain the nonwoven fabric structure by providing high adhesive strength between the constituent fibers, the fusible fibers preferably account for 20 mass% or more, more preferably 40 mass% or more, and even more preferably 50 mass% or more of the mass of the fibers constituting the nonwoven fabric. When the fibers constituting the nonwoven fabric include fibers other than fusible fibers, such as ultrafine fibers described below, the nonwoven fabric is made of fibers other than fusible fibers with a large specific surface area on the main surface, so that the static friction coefficient of the nonwoven fabric and the liquid-retaining member composed of the nonwoven fabric is high, unintended slippage between the separator and the liquid-retaining member is less likely to occur, and the liquid-retaining member has excellent performance in various areas, such as electrolyte retention. The fusible fibers are preferably 90 mass% or less, more preferably 80 mass% or less of the mass of the fibers constituting the nonwoven fabric.

[0037] The nonwoven fabric constituting the liquid-retaining member of the present invention may contain, in addition to fusible fibers, ultrafine fibers with a fiber diameter of 4.0 μm or less. The inclusion of ultrafine fibers allows the nonwoven fabric to have a dense structure. Furthermore, the inclusion of ultrafine fibers increases the specific surface area of ​​the main surface of the nonwoven fabric. As a result, the static friction coefficient of the liquid-retaining member made of this nonwoven fabric is high, reducing the likelihood of unintended slippage between the separator and the liquid-retaining member. Furthermore, the liquid-retaining member preferably has excellent performance, such as electrolyte retention. The smaller the diameter of the ultrafine fibers, the denser the nonwoven fabric can be, and the greater the static friction coefficient between the nonwoven fabric and the liquid-retaining member, reducing the likelihood of unintended slippage between the separator and the liquid-retaining member. Therefore, the fiber diameter of the ultrafine fibers is preferably 3.0 μm or less, and even more preferably 2.5 μm or less. The lower limit of the fiber diameter of the ultrafine fibers is not particularly limited, but approximately 0.1 μm is appropriate.

[0038] The fiber diameters of the ultrafine fibers constituting the nonwoven fabric are preferably approximately the same. This is because when the fiber diameters of the ultrafine fibers are approximately the same, it is easier to form voids of uniform size, and various performances such as the electrolyte retention ability of the nonwoven fabric and the liquid-retaining member are excellent. Specifically, the value (σ / d) obtained by dividing the standard deviation value (σ) of the fiber diameter distribution of the ultrafine fibers by the average fiber diameter (d) of the ultrafine fibers is preferably 0.2 or less (preferably 0.18 or less). Note that when the fiber diameters of the ultrafine fibers are all the same, the standard deviation value (σ) is 0, so the lower limit of the value (σ / d) is 0. Note that the standard deviation value (σ) of the ultrafine fibers is a value calculated from the fiber diameter (X) of each of the measured n (100) ultrafine fibers using the following formula: Standard deviation={(nΣX 2 -(ΣX) 2 ) / n(n-1)} 1 / 2

[0039] The ultrafine fibers of the present invention can be obtained, for example, by splitting external force-splittable fibers made of two or more resin components and splittable by external force, or by splitting chemically splittable fibers made of two or more resin components and splittable by chemical action. Examples of external forces that can split the external force-splittable fibers include fluid flows such as water, calendars, refiners, pulpers, mixers, and beaters. Chemical treatments include removing the resin components with a solvent and swelling the resin components with a solvent. Among these, ultrafine fibers obtained by splitting chemically splittable fibers are preferred because they have approximately the same fiber diameter in the length direction and even among multiple ultrafine fibers. They are uniformly dispersed in the nonwoven fabric, easily forming uniform-sized voids, and are excellent in various performances, such as the electrolyte retention of the nonwoven fabric and the liquid-retaining member.

[0040] Suitable chemically split fibers include fibers composed of two or more resin components and arranged in an islands-in-sea configuration in the fiber cross section. Such islands-in-sea fibers can be produced by a mixed spinning method or a composite spinning method. The individual ultrafine fibers composed of island components generated by removing the sea component from islands-in-sea fibers produced by a composite spinning method have approximately the same fiber diameter in the longitudinal direction, and the fiber diameter is also approximately the same among multiple ultrafine fibers. This facilitates the formation of uniform-sized voids within the nonwoven fabric, and is suitable for various performances such as the electrolyte retention of the nonwoven fabric and the liquid-retaining member. As described below, the ultrafine fibers preferably contain a polyolefin resin and / or a nylon resin, and therefore the island components of the chemically split fibers preferably contain a polyolefin resin and / or a nylon resin. In particular, chemically split fibers having island components composed only of a polyolefin resin component are preferred for their excellent chemical resistance.

[0041] The resin component constituting the ultrafine fibers is not particularly limited, but is preferably composed of a chemical-resistant resin component so as to have excellent chemical resistance, and is preferably composed of one or more of polyolefin resins such as polyethylene, polypropylene, and polymethylpentene, and nylon resins such as nylon 6, nylon 66, nylon 11, and nylon 12. Among these, it is preferable to contain a polyolefin resin that has particularly excellent chemical resistance, and polypropylene is particularly suitable because it has relatively high rigidity, is resistant to crushing under pressure, and makes it easy to maintain voids in the nonwoven fabric containing the ultrafine fibers and the liquid-retaining member, thereby realizing a battery with low electrical resistance.

[0042] The ultrafine fibers do not need to be composed of one type of resin component, but may be composed of two or more types of resin components with different melting points. If ultrafine fibers composed of two or more types of resin components with different melting points (preferably a difference of 10°C or more, more preferably 20°C or more) are bonded together with a low-melting-point resin component, this prevents the ultrafine fibers from shifting, maintains the dispersion of the ultrafine fibers, and provides excellent performance in various areas, such as the electrolyte retention of nonwoven fabrics and liquid-retaining members containing these ultrafine fibers. For example, the ultrafine fibers can be composed of polypropylene and polyethylene.

[0043] In addition, the ultrafine fibers are preferably in a stretched state so that they have excellent mechanical strength, are resistant to crushing under pressure, and can easily maintain the shape of a nonwoven fabric. This "stretched state" means that the fibers are mechanically stretched after fiber formation. Fibers formed by the melt-blowing method are stretched with heated air but are not mechanically stretched, so they are not in a stretched state. In addition, if external force split fibers or chemical split fibers are mechanically stretched before splitting, the ultrafine fibers generated from these split fibers are in a stretched state.

[0044] The fiber length of the ultrafine fibers of the present invention is not particularly limited, but is preferably 0.1 to 25 mm, more preferably 1 to 10 mm, and even more preferably 2 to 5 mm, so that the ultrafine fibers are uniformly dispersed and uniform-sized voids can be formed in the nonwoven fabric containing the ultrafine fibers. Note that, if bundles of ultrafine fibers are present, the ultrafine fibers cannot be uniformly dispersed and uniform-sized voids tend not to be formed, so it is preferable that the ultrafine fibers are not present in a bundled state, but in a state where individual ultrafine fibers are dispersed.

[0045] Such ultrafine fibers are contained in an amount of preferably 5 mass% or more, more preferably 15 mass% or more, and even more preferably 20 mass% or more of the mass of the fibers constituting the nonwoven fabric so that they are uniformly dispersed within the nonwoven fabric constituting the liquid-retaining member, thereby realizing a dense structure and increasing the static friction coefficient of the liquid-retaining member made of this nonwoven fabric. On the other hand, if the nonwoven fabric contains too many ultrafine fibers, the mechanical strength of the liquid-retaining member made of this nonwoven fabric may be weakened, so the ultrafine fibers are contained in an amount of preferably 80 mass% or less, more preferably 60 mass% or less, and even more preferably 50 mass% or less of the mass of the fibers constituting the nonwoven fabric.

[0046] The nonwoven fabric constituting the liquid-retaining member of the present invention may contain other fibers in addition to the fusible fibers and ultrafine fibers described above. Examples of such other fibers include nonfusible fibers with a fiber diameter exceeding 4.0 μm that are not involved in fusion, and single-fusible fibers composed of a single resin component with a fiber diameter exceeding 4.0 μm. The nonfusible fibers and single-fusible fibers preferably have a fiber diameter exceeding 4.0 μm and not exceeding 17 μm so as to be uniformly dispersed throughout the nonwoven fabric constituting the liquid-retaining member. The nonfusible fibers preferably have a resin component on their surface that has a melting point 10°C or more higher than the melting point of the fusible component of the fusible fibers. The single-fusible fibers preferably have a resin component with a melting point within ±10°C of the melting point of the fusible component of the fusible fibers. Both the nonfusible fibers and the single-fusible fibers are preferably composed of polyolefin resins. The fiber length of both the nonfusible fibers and the single-fusible fibers is preferably 0.01 to 25 mm so as to be uniformly dispersed.

[0047] The constituent fibers of the nonwoven fabric constituting the liquid-retaining member of the present invention are preferably fixed together solely by fusion of the fibers (e.g., fusion fibers). Fixation by fusion of the fibers (especially fusion fibers) in this manner is preferred because the nonwoven fabric and the liquid-retaining member have excellent ion permeability and an increase in the battery's electrical resistance is suppressed. Furthermore, it is not necessary to entangle the constituent fibers with each other through an entanglement process, such as a needle punching process or a fluid flow such as a water flow, and the resulting nonwoven fabric is preferably free from the disruption of fiber arrangement or the formation of through-holes that would otherwise result from the entanglement process. As a result, the electrolyte distribution within the nonwoven fabric is less likely to be uneven, and an increase in electrical resistance is suppressed by the liquid-retaining member composed of this nonwoven fabric, which is preferred.

[0048] It should be noted that, when manufacturing the nonwoven fabric constituting the liquid-retaining member, fibers may become entangled even without carrying out an entanglement treatment. For example, when a fiber web is formed by a dry method or a wet method, the fiber web can maintain its shape to some extent, so the fibers are at least entangled with each other. However, this entanglement does not disrupt the fiber arrangement, as in the entanglement caused by the above-mentioned fluid flow, and therefore is considered to be unentangled. Thus, "only fusion of fibers" refers to a state in which the constituent fibers in the nonwoven fabric are fixed to each other only by fusion resulting from the melting of the fibers.

[0049] The basis weight of the nonwoven fabric constituting the liquid-retaining member of the present invention is set to 30 g / m because the smaller the basis weight, the thinner the thickness of the liquid-retaining member can be, and the liquid-retaining member will have excellent ion permeability. 2 Less than 20 g / m is preferred 2 Less than 15 g / m is more preferable. 2 The lower limit of the basis weight is 3 g / m2 so as to provide a liquid-retaining member that is resistant to crushing in the thickness direction and has excellent mechanical strength. 2 It is preferable that the density is 5 g / m or more. 2 More preferably, it is 7 g / m or more. 2 It is more preferable that the "weight per unit area" is equal to or greater than 1000. Note that this "weight per unit area" refers to the basis weight obtained based on the method specified in JIS P 8124 (Paper and paperboard - Basis weight measurement method):2011.

[0050] The thickness of the nonwoven fabric constituting the liquid-retaining member of the present invention is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less, because the thinner the thickness, the thinner the liquid-retaining member can be, resulting in a liquid-retaining member with excellent ion permeability. The lower limit of the thickness is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more, so as to achieve excellent mechanical strength. In addition, the "thickness" in the present invention refers to the arithmetic average value of measurements taken at 10 randomly selected points under a load of 5 N using an outside micrometer (0-25 mm) as specified in JIS B 7502:1994.

[0051] The liquid-retaining member of the present invention may be composed of only nonwoven fabric, but may also contain inorganic particles in addition to the nonwoven fabric, since this increases the surface area of ​​the liquid-retaining member, allows the surface of the liquid-retaining member to have a dense structure, improves the liquid-retaining member's ability to retain electrolyte, and increases the static friction coefficient of the liquid-retaining member to prevent slippage during winding, resulting in various excellent performance characteristics.

[0052] Examples of the types of inorganic particles contained in the liquid-retaining member include inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), alumina-silica composite oxide, calcium oxide, titanium oxide, tin oxide, yttrium oxide, zirconium oxide, barium titanate, and tin-indium oxide.

[0053] The shape of the inorganic particles contained in the liquid-retaining member can be appropriately selected from, for example, spherical (nearly spherical or true spherical), fibrous, needle-like, polyhedral such as flat or cubic, and feather-like.

[0054] In order to improve the mechanical strength of the liquid-retaining member of the present invention, the nonwoven fabric constituting the liquid-retaining member preferably has a single-layer structure. This "single-layer structure" means that the nonwoven fabric is made of the same fiber blend.

[0055] The basis weight of the liquid-retaining member of the present invention is set to 35 g / m because the smaller the basis weight, the thinner the thickness and the better the ion permeability. 2 Less than 25 g / m 2 Less than 20 g / m is more preferable. 2 The lower limit of the basis weight is 5 g / m so that the liquid-retaining member is resistant to crushing and has excellent mechanical strength. 2 It is preferable that the density is 7 g / m or more. 2 More preferably, it is 9 g / m or more. 2 More preferably, it is equal to or greater than this.

[0056] The thickness of the liquid-retaining member of the present invention is preferably 120 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less, because thinner thicknesses result in better ion permeability. The lower limit of the thickness is preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more, so as to provide excellent mechanical hardness.

[0057] The liquid-retaining member of the present invention can realize a battery with low electrical resistance, and therefore can be suitably used, for example, as a member for retaining electrolyte to suppress an increase in the electrical resistance of a primary battery or a secondary battery (such as a nickel-metal hydride battery, a nickel-cadmium battery, a lithium-ion battery, or a nickel-zinc battery) by being disposed between an electrode and a separator inside the battery.

[0058] The separator to be combined with the liquid-retaining member of the present invention is a known separator such as a microporous membrane, a nonwoven fabric, etc. Among these, a microporous membrane has a lower coefficient of friction than a nonwoven fabric, and when a battery is manufactured, there is a high possibility that unintended slippage will occur between the separator and the liquid-retaining member, so the liquid-retaining member of the present invention is more effective when combined with a separator made of a microporous membrane.

[0059] The liquid-retaining member of the present invention can be produced, for example, as follows.

[0060] First, fibers are blended to form a fiber web. The blended fibers preferably contain the ultrafine fibers described above in addition to the fusible fibers described above. This increases the static friction coefficient of the nonwoven fabric and the liquid-retaining member formed from this nonwoven fabric, reduces slippage during winding to manufacture a battery, and improves the electrolyte retention of the nonwoven fabric and the liquid-retaining member formed from this nonwoven fabric. The method for forming this fiber web is not particularly limited, but it can be formed by, for example, a dry method (e.g., carding or air-laying) or a wet method. Among these, a wet method is preferred, as it allows for the production of a liquid-retaining member with uniformly dispersed fibers and minimal fiber irregularities. This wet method can be formed by conventionally known methods, such as a horizontal fourdrinier method, an inclined wire short-net method, a cylinder method, or a combination of a fourdrinier and a cylinder method. When two or more layers are combined, it is preferable to combine fiber webs having the same fiber blend so that a single-layer nonwoven fabric can be produced.

[0061] Next, the fibers constituting this fiber web are bonded to obtain a nonwoven fabric. Methods for bonding the fibers constituting the fiber web include fusing a fusible component composed of a low-melting-point resin contained in the fibers constituting the fiber web and applying a binder resin to the fiber web. However, because the nonwoven fabric has excellent ion permeability and suppresses an increase in electrical resistance in a battery having a liquid-retaining member made of this nonwoven fabric, it is preferable to bond the fibers constituting the fiber web by fusing a fusible component composed of a low-melting-point resin contained in the fibers constituting the fiber web. When bonding the fiber web by fusing a fusible component contained in the fibers constituting the fiber web, it is preferable to fuse the fusible component of the fusible fibers without performing an entanglement process or the like, so as not to disrupt the fiber arrangement and damage the texture.

[0062] The method for fusing the fusible components of the fusible fibers is not particularly limited, but examples include an air-through method in which a fiber web is supported by a conveyor and hot air is blown onto it, and a method in which heat is applied to the fiber web using a Yankee dryer or a calendar. In particular, when the fusible components of the fibers are fused using the air-through method, the pressure applied during drying tends to be lower than with other methods. This method makes it difficult for the thickness of the nonwoven fabric to collapse, increases the number of voids within the nonwoven fabric that can retain the electrolyte, and increases the amount of electrolyte retained by the nonwoven fabric. This makes it difficult for spaces without electrolyte to form within the battery, and thus allows for the realization of a liquid-retaining member with low electrical resistance, which is preferable.

[0063] The produced nonwoven fabric may be used as a liquid-retaining member as is. Alternatively, a nonwoven fabric that has been subjected to a hydrophilization treatment may be used as a liquid-retaining member. The hydrophilization method is not particularly limited, but examples thereof include sulfonation treatment, fluorine gas treatment, graft polymerization of a vinyl monomer, surfactant treatment, plasma treatment, and hydrophilic resin application treatment. Alternatively, the liquid-retaining member may be prepared by applying the inorganic particles described above to a nonwoven fabric by a known method (for example, by applying a dispersion of the inorganic particles to the nonwoven fabric). [Example]

[0064] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0065] (Preparation of composite polyolefin fusible fibers (fusible fibers)) A composite polyolefin fusion fiber with a core (non-fusion component) of homopolypropylene (melting point: 168°C) and a sheath (fusion component) of high-density polyethylene (melting point: 135°C), with a tensile strength of 6.0 cN / dtex, a Young's modulus of 47 cN / dtex, and an elongation of 20% (high-density polyethylene covers the fiber surface except for both ends, volume ratio of core component to sheath component = 60:40, average fiber diameter: 10.5 μm, fiber length: 5 mm, density: 0.94 g / cm). 3 ) was prepared.

[0066] (Preparing ultra-fine fibers) An islands-in-sea type composite fiber (fineness: 1.65 dtex, fiber length: 2 mm) produced by a composite spinning method, which has 25 island components made of polypropylene in a sea component made of copolymerized polyester, is immersed in a bath (temperature: 80°C) containing 10 mass% sodium hydroxide aqueous solution for 30 minutes to extract and remove the copolymerized polyester, which is the sea component of the islands-in-sea type composite fiber, and polypropylene ultrafine fibers (average fiber diameter: 2.0 μm, melting point: 172°C, fiber length: 2 mm, cross-sectional shape: circular, density: 0.91 g / cm) are obtained. 3 The polypropylene ultrafine fibers were not fibrillated and were in a stretched state, and each fiber had substantially the same diameter in the fiber axial direction.

[0067] Example 1 60 mass% of composite polyolefin fusible fibers and 40 mass% of polypropylene ultrafine fibers were dispersed in a slurry, and a fibrous web was formed using a wet method (horizontal fourdrinier method). Next, the fibrous web was supported by a conveyor, and while being transported by suction from below the conveyor so that the fibrous web was in close contact with the conveyor, it was subjected to an air-through method in which hot air at a temperature of 137°C and a wind speed of 8 m / s was blown onto the fibrous web for 10 seconds, allowing a sufficient amount of hot air to pass through, thereby performing a heat treatment under no pressure. By using the air-through method, only the high-density polyethylene of the composite polyolefin-based fusible fiber was fused at the same time as the fibrous web was dried, and the constituent fibers were fused together by the high-density polyethylene to form a nonwoven fabric. The nonwoven fabric thus prepared was used as a liquid-retaining member.

[0068] Example 2 Nonwoven fabrics were formed in the same manner as in Example 1, except that various fibers were blended and dispersed in the slurry according to the compositions shown in Table 1, and the basis weight of the nonwoven fabrics to be prepared was changed. The nonwoven fabric thus prepared was used as a liquid-retaining member.

[0069] (Example 3, Comparative Example 1) A nonwoven fabric was formed in the same manner as in Example 1, except that various fibers were blended in the compositions shown in Table 1 and dispersed in the slurry. The nonwoven fabric thus prepared was used as a liquid-retaining member.

[0070] Furthermore, the static friction coefficients of the liquid-retaining members prepared in the examples and comparative examples were measured by the method described in the above-mentioned [Measurement method], and the pressurized liquid retention rates and microporous membrane slippage were measured by the following methods to evaluate the physical properties of the liquid-retaining members.

[0071] (Measurement of pressurized liquid retention rate) (1) A circular test piece (30 mm in diameter) was taken from the liquid-retaining member. The test piece was allowed to reach moisture equilibrium at a temperature of 20°C and a relative humidity of 65%, and then the mass (M0) of the test piece was measured. (2) The test piece was immersed in propylene carbonate for 1 hour, thereby filling the voids in the test piece with propylene carbonate. (3) Two stacks of three sheets of filter paper (diameter: 30 mm) were prepared. Then, a test piece pulled out of the propylene carbonate was sandwiched between the stacks. Then, a pressure of 0.9 MPa was applied to the exposed filter paper surfaces for 30 seconds using a pressure pump. Thereafter, the test piece was removed from between the stacks, and the mass (M1) of the removed test piece was measured. (4) Enter the values ​​of M0 and M1 obtained above into the following formula and calculate R p The value of was calculated. R p =[(M1-M0) / M0]×100 Furthermore, the above-mentioned measurements (1) to (4) were also carried out on two test pieces separately taken from one liquid-retaining member. p The arithmetic mean of the values ​​was taken as the pressurized liquid retention rate (unit: %) of the liquid retention member.

[0072] (Microporous membrane slip evaluation) (1) The liquid-retaining member was cut into a rectangle measuring 150 mm in the vertical direction and 50 mm in the horizontal direction. A microporous membrane (Celgard® 2400 (Polypore)) was also prepared and cut into a rectangle measuring 150 mm in the vertical direction and 50 mm in the horizontal direction to prepare a separator. The vertical direction refers to the production direction during production of the liquid-retaining member (nonwoven fabric) and the microporous membrane, and the horizontal direction refers to the direction perpendicular to the vertical direction on the main surface. (2) The separator cut in (1) was placed on top of the acrylic plate, and the exposed main surface of the separator was completely overlapped with the main surface of the liquid-retaining member cut in (1) for which the static friction coefficient was measured, to prepare a measurement sample stacked in the order of acrylic plate - separator - liquid-retaining member. (3) At one of the two longitudinal ends of the measurement sample, only the rectangular liquid-retaining member was peeled off from the measurement sample, and the peeled liquid-retaining member was clamped with a clip. In addition, a 30 g weight (contact shape: circle, contact area: 3 cm) was placed on the exposed liquid-retaining member at the other longitudinal end of the measurement sample. 2 ) was placed on top. (4) The clips clamping the liquid-retaining member were pulled 100 mm in the longitudinal direction of the liquid-retaining member toward the end of the clip at a speed of 500 mm / min, applying a force to the clips and applying a longitudinal force only to the liquid-retaining member, thereby moving the liquid-retaining member 100 mm. The behavior of the separator at this time was evaluated using the following method. ○: Following the pulling of the liquid retaining member, the separator moved 50 mm or more in the direction in which the liquid retaining member was pulled. ×: The separator moved less than 50 mm in the direction in which the liquid retention member was pulled in response to the liquid retention member being pulled. Alternatively, even when the liquid retention member was pulled, the separator did not move in the direction in which the liquid retention member was pulled. Based on the above criteria, liquid-retaining members rated "Good" are less likely to experience unintended slippage between themselves and the separator than liquid-retaining members rated "Poor." On the other hand, liquid-retaining members rated "Poor" are more likely to experience unintended slippage between themselves and the separator.

[0073] The physical properties and measurement results of the liquid-retaining members prepared in the examples and comparative examples are shown in Table 1 below.

[0074] [Table 1]

[0075] Compared to the liquid retention member of Comparative Example 1, which had a static friction coefficient of 0.39, the liquid retention members of Examples 1 to 3, which had static friction coefficients exceeding 0.39, were less likely to slip on the separator. Therefore, it is considered that the liquid retention member according to the present invention is less likely to cause unintended slippage between the separator and the liquid retention member, even when a battery is manufactured by winding the separator-liquid retention member-electrode-liquid retention member stacked in this order. As a result, the liquid retention member according to the present invention can prevent significant misalignment in the battery. [Industrial Applicability]

[0076] The liquid-retaining member of the present invention can be suitably used, for example, as a member for retaining electrolyte to suppress an increase in the electrical resistance of a primary battery or a secondary battery (such as a nickel-metal hydride battery, a nickel-cadmium battery, or a lithium-ion battery) by being disposed between an electrode and a separator inside the battery.

Claims

[Claim 1] A battery liquid-retaining member made of nonwoven fabric, which is provided between an electrode and a separator inside a battery, The static friction coefficient of the battery electrolyte retaining member measured by the following [measurement method] is greater than 0.39, Battery fluid retaining material. [Measurement method] (1) Prepare a friction measuring device (Static / Dynamic Friction Measuring Device TL201Tt, manufactured by Trinity Lab Co., Ltd.). (2) Three pieces measuring 20 cm in length and 5 cm in width are cut out from the battery electrolyte retaining material. (3) Double-sided adhesive tape is attached to both ends in the vertical direction on one main surface of the slice (within an area of ​​2 cm vertical x 5 cm horizontal at each end), and the slice is attached to the table of the friction measuring machine using the double-sided adhesive tape. (4) A tactile contactor (finger model, contact area with the measurement object: 1.5 mm) was attached to the center of the other main surface of the slice. ２ Then, a 100 g weight is placed on the tactile contactor, and a load is applied in the thickness direction of the piece. (5) One minute after the weight is placed on the surface, the tactile contact is slid once on one of the main surfaces of the piece in the vertical direction at a speed of 10 mm / sec and a distance of 40 mm to measure the static friction coefficient. This measurement is carried out three times, once for each of the three pieces, and the average of the three measured static friction coefficients is defined as the static friction coefficient of the battery liquid-retaining member.

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