Separator for lead-acid battery and lead-acid battery including the same

Abstract

To provide a separator, the strength of which is enhanced so that permeation short-circuiting or similar other problems do not occur even when the thickness of a polar plate is thin.SOLUTION: This separator for lead storage batteries includes a crystalline region and an amorphous region. In the X-ray diffraction spectrum of the separator, the ratio R indicated by A1 / (A1+A2) is 0.60 or greater. A1 represents the area of a first diffraction peak, the peak height of which among the diffraction peaks equivalent to the crystalline region is maximum, and A2 represents the area of a second diffraction peak, the peak height of which among the diffraction peaks equivalent to the crystalline region is second highest.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a separator for a lead storage battery and a lead storage battery including the same.

Background Art

[0002] Lead storage batteries are used in various applications, including in-vehicle and industrial applications. A lead storage battery includes a positive electrode plate, a negative electrode plate, a separator interposed between these, and an electrolyte. Various performances are required for the separator of a lead storage battery.

[0003] Patent Document 1 discloses a lead storage battery including a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate, wherein the separator has a base portion, a negative electrode rib provided on a negative electrode surface of the base portion facing the negative electrode plate, and side end portions disposed on both sides of the base portion, the side end portions have a thick portion that is at least partially thicker than the base portion, and both ends of the negative electrode plate are located within the width of the thick portion when viewed from the thickness direction of the negative electrode plate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, when the thickness of the electrode plate is thin and the number of electrode plates per cell is large, if the electrode plate is deformed, the end portion of the electrode plate may strongly contact the separator, causing problems such as short circuit (including penetration short circuit due to dendrite generation).

[0006] As in Patent Document 1, when a thick portion is provided at the side end of the separator, the piercing strength of the thick portion can be increased, but the resistance of the separator increases. Therefore, in a high-performance lead-acid battery, it is difficult to adopt a configuration in which a thick portion is provided at the side end of the separator.

Means for Solving the Problems

[0007] One aspect of the present disclosure is a separator for a lead-acid battery, the separator includes a crystalline region and an amorphous region, in the X-ray diffraction spectrum of the separator, the ratio R represented by A1 / (A1 + A2) is 0.60 or more, A1 is the area of the first diffraction peak having the maximum peak height among the diffraction peaks corresponding to the crystalline region, A2 is the area of the second diffraction peak having the second highest peak height among the diffraction peaks corresponding to the crystalline region, and relates to a separator for a lead-acid battery.

Advantages of the Invention

[0008] In a lead-acid battery, the strength of the separator can be increased.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] One of the typical applications of lead-acid batteries is in automobiles. With the improvement of vehicle performance, the electrical equipment load is increasing, and further improvement in performance is required for lead-acid batteries. To enhance the performance of lead-acid batteries, it is common to increase the reaction area of the battery reaction. Therefore, in recent years, lead-acid batteries have a tendency that the thickness of the electrode plate becomes smaller and the number of electrode plates per cell increases compared to the past. Especially in idling stop (IS) applications such as idling stop system vehicles (hereinafter also referred to as ISS vehicles) where the engine is started frequently and large current discharge is repeated, a large number of thin electrode plates may be stacked to form an electrode plate group.

[0011] In lead-acid batteries, when charge and discharge are repeated, the negative electrode current collector bends at the end portion of the negative electrode plate. Conventionally, when the number of electrode plates per cell is small, since there is a certain gap between the electrode plates, even if the negative electrode current collector bends, it does not cause much problem. However, when the number of electrode plates per cell is large, since the gap between the electrode plates is quite small, when the negative electrode current collector bends, it may penetrate the separator and cause a short circuit. If the thickness of the separator is increased, the short circuit due to the breakage of the separator can be reduced. As in Patent Document 1, it is also conceivable to increase the thickness of the side end portion of the separator. Such a technique was a sufficiently effective means for suppressing short circuits in conventional lead-acid batteries. However, when the thickness of the separator increases, an increase in resistance is inevitable, so it is difficult to adopt for high-performance lead-acid batteries.

[0012] In view of the above, a separator for a lead-acid battery according to one aspect of the present invention includes a crystalline region and an amorphous region. In the X-ray diffraction (XRD) spectrum of the separator, the ratio R represented by A1 / (A1 + A2) is 0.60 or more. Here, A1 is the area of the diffraction peak with the largest peak height among the diffraction peaks corresponding to the crystalline region (the first diffraction peak). A2 is the area of the diffraction peak with the second highest peak height among the diffraction peaks corresponding to the crystalline region (the second diffraction peak).

[0013] The ratio R indicates the degree of crystallinity of the separator. In conventional separators, the ratio R tends to be relatively low, about 0.58 or less. In contrast, for the separator of the above aspect, the ratio R is 0.60 or more, and the crystallinity of the separator is improved compared to the prior art. By increasing the crystallinity of the separator, the strength of the separator itself (specifically, the piercing strength) can be improved. Therefore, unlike the case of increasing the thickness of the separator, there is almost no contradiction such as an increase in resistance. Therefore, the separator of the above aspect is also suitable for high-performance lead-acid batteries for ISS vehicles, and when used in such lead-acid batteries, excellent IS life performance can be ensured.

[0014] The separator for lead-acid batteries has a relatively large thickness, different from separators for lithium-ion secondary batteries and the like. In addition to the tendency that it becomes more difficult to increase the crystallinity as the thickness of the separator increases, when the crystallinity increases, the separator becomes hard and brittle. Therefore, in conventional separators for lead-acid batteries, the crystallinity has not been controlled. Against such conventional common sense, according to the above aspect of the present invention, by setting the ratio R to 0.60 or more, it is possible to ensure high strength of the separator while suppressing an increase in the resistance of the separator.

[0015] The thickness of the separator is preferably 100 μm or more and 300 μm or less. When the thickness is in such a range, higher strength of the separator can be ensured. In addition, since the resistance of the separator can be suppressed relatively low, excellent IS life performance is easily obtained.

[0016] The ratio R is preferably 0.9 or less. In this case, in addition to being able to easily ensure the flexibility of the separator, the manufacturing is easy.

[0017] The separator preferably contains oil. In this case, since the oxidative degradation of the separator can be suppressed, it is advantageous from the viewpoint of ensuring high high-temperature overcharge life performance.

[0018] In the separator, the tortuosity of the pores is preferably 5 or more. In this case, the strength of the separator can be further increased.

[0019] The separator preferably contains a polyolefin, more preferably contains a polyolefin containing at least an ethylene unit. Such a separator tends to have a relatively low strength, but the adjustment of the ratio R is relatively easy, and the strength of the separator can be increased by adjusting the ratio R. When the separator contains a polyolefin containing at least an ethylene unit, the first diffraction peak corresponds to the (110) plane due to the crystalline region, and the second diffraction peak corresponds to the (200) plane due to the crystalline region.

[0020] The present invention also includes a lead storage battery including the above-mentioned separator for a lead storage battery. The lead storage battery includes at least one cell including a plate group and an electrolyte, and the plate group includes a positive electrode plate, a negative electrode plate, and the above-mentioned separator interposed between the positive electrode plate and the negative electrode plate. By using the above-mentioned separator, the initial defect rate of the lead storage battery can be reduced, and the penetration short circuit or the short circuit associated with the bending of the electrode plate can be suppressed, so that the life performance can be improved. In addition, since the resistance of the separator is low, it is also useful for high-performance lead storage batteries such as IS applications, and excellent battery performance such as high IS life performance can be ensured.

[0021] The lead storage battery may be a controlled valve type battery (VRLA type battery), but a liquid type battery (vent type battery) is preferred.

[0022] In this specification, the vertical direction of the lead storage battery or the components of the lead storage battery (such as electrode plates, battery cases, separators, etc.) means the vertical direction in the vertical direction of the lead storage battery when the lead storage battery is in use. Each of the positive electrode plate and the negative electrode plate is provided with an ear portion for connecting to an external terminal. In the case of a liquid type battery, the ear portion is provided so as to protrude upward above the electrode plate.

[0023] Hereinafter, the separator and the lead storage battery according to the embodiments of the present invention will be described more specifically with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0024] (Separator) The separator includes a crystalline region in which the molecules of the constituent material of the separator are relatively regularly arranged (that is, the arrangement property is high) and an amorphous region with a low arrangement property. Therefore, in the XRD spectrum of the separator, diffraction peaks due to the crystalline region are observed, and scattered light due to the amorphous region is observed as a halo. In the XRD spectrum of the separator, a high strength of the separator can be obtained by the ratio R represented by A1 / (A1 + A2) being 0.60 or more. Here, A1 is the area of the diffraction peak with the maximum peak height among the diffraction peaks corresponding to the crystalline region (the first diffraction peak), and A2 is the area of the diffraction peak with the second highest peak height among the diffraction peaks corresponding to the crystalline region (the second diffraction peak).

[0025] For example, in the XRD spectrum of a separator containing a polyolefin containing ethylene units, a diffraction peak corresponding to the (110) plane of the crystalline region is observed in the range where 2θ is 20° or more and 22.5° or less, and a diffraction peak corresponding to the (200) plane of the crystalline region is observed in the range where 2θ is 23° or more and 24.5° or less. Also, the halo of the amorphous region is observed in the range where 2θ is 17° or more and 27° or less. Among the diffraction peaks due to the crystalline region, the diffraction peak corresponding to the (110) plane has the maximum peak height and corresponds to the first diffraction peak. The diffraction peak corresponding to the (200) plane has the second highest peak height and corresponds to the second diffraction peak.

[0026] The ratio R is 0.60 or more, and from the viewpoint of ensuring higher strength of the separator, it may be 0.65 or more, or may be 0.70 or more or 0.75 or more. The ratio R may be 0.9 or less, or may be 0.85 or less. When the ratio R is in such a range, in addition to being easy to ensure the flexibility of the separator, it is easy to manufacture.

[0027] The ratio R may be 0.60 or more and 0.9 or less (or 0.85 or less), 0.65 or more and 0.9 or less (or 0.85 or less), 0.70 or more and 0.9 or less (or 0.85 or less), or 0.75 or more and 0.9 or less (or 0.85 or less).

[0028] The area of the diffraction peak is obtained by fitting the diffraction peak due to the crystalline region in the XRD spectrum of the separator. Using the obtained area A1 of the first diffraction peak and the area A2 of the second diffraction peak, the ratio R is obtained from the above formula.

[0029] The separator contains a polymer material (hereinafter also referred to as the base polymer). Since the separator contains a crystalline region, the base polymer usually contains a crystalline polymer. The separator contains, for example, a polyolefin. A polyolefin is a polymer containing at least an olefin unit (that is, a polymer containing at least a monomer unit derived from an olefin).

[0030] As the base polymer, a polyolefin and another base polymer may be used in combination. The ratio of the polyolefin in the total base polymer contained in the separator is, for example, 50% by mass or more, may be 80% by mass or more, or may be 90% by mass or more. The ratio of the polyolefin is, for example, 100% by mass or less. The base polymer may be composed of only a polyolefin. When the ratio of the polyolefin is thus large, the strength of the separator tends to be low, but even in such a case, a high strength can be ensured in order to make the ratio R within the above range.

[0031] Polyolefins include, for example, homopolymers of olefins, copolymers containing different olefin units, and copolymers containing olefin units and copolymerizable monomer units. The copolymers containing olefin units and copolymerizable monomer units may contain one or more kinds of olefin units. Further, the copolymers containing olefin units and copolymerizable monomer units may contain one or more kinds of copolymerizable monomer units. The copolymerizable monomer unit is a monomer unit derived from a polymerizable monomer other than olefins and copolymerizable with olefins.

[0032] Examples of polyolefins include polymers containing at least C 2-3 polymers containing olefins as monomer units. C 2-3 Examples of olefins include at least one selected from the group consisting of ethylene and propylene. Examples of polyolefins include polyethylene, polypropylene, C 2-3 Copolymers containing olefins as monomer units (for example, ethylene-propylene copolymers) are more preferable. Among polyolefins, it is preferable to use polyolefins containing at least ethylene units (such as polyethylene and ethylene-propylene copolymers). Polyolefins containing ethylene units (such as polyethylene and ethylene-propylene copolymers) and other polyolefins may be used in combination.

[0033] The separator preferably contains oil. When the separator contains oil, oxidation degradation of the separator can be suppressed, so that high high-temperature overcharge life performance can be ensured. Oil refers to a hydrophobic substance that is liquid at room temperature (a temperature of 20°C or higher and 35°C or lower) and separates from water. Oils include naturally derived oils, mineral oils, and synthetic oils. As the oil, mineral oils, synthetic oils, etc. are preferable. Examples of the oil include paraffin oil and silicone oil. The separator may contain one kind of oil or a combination of two or more kinds.

[0034] The oil content in the separator is preferably 11% by mass or more and 18% by mass or less. When the oil content is within such a range, the effect of suppressing the oxidative degradation of the separator is further enhanced. Also, the resistance of the separator can be kept relatively low.

[0035] The separator may be in a sheet form. Also, a sheet bent in a bellows shape may be used as the separator. The separator may be formed in a bag shape. Either the positive electrode plate or the negative electrode plate may be wrapped with a bag-shaped separator.

[0036] The separator may or may not have ribs. A separator having ribs includes, for example, a base portion and ribs standing from the surface of the base portion. The ribs may be provided on only one surface of the separator or each base portion, or may be provided on both surfaces respectively. Note that the base portion of the separator is a portion excluding protrusions such as ribs among the constituent parts of the separator, and refers to a sheet-like portion defining the outer shape of the separator.

[0037] The thickness of the separator is, for example, 90 μm or more. From the viewpoint of obtaining higher strength, 100 μm or more or 150 μm or more is preferable. The thickness of the separator is, for example, 300 μm or less. From the viewpoint of keeping the resistance of the separator low, the thickness of the separator may be 250 μm or less or 200 μm or less. The thickness of the separator means the average thickness at the portion facing the electrode material of the separator. When the separator includes a base portion and ribs standing from at least one surface of the base portion, the thickness of the separator is the average thickness at the base portion. When an attachment member (mat, pasting paper, etc.) is attached to the separator, the thickness of the attachment member is not included in the thickness of the separator.

[0038] The thickness of the separator may be 90 μm or more and 300 μm or less (or 250 μm or less), 90 μm or more and 200 μm or less, 100 μm or more (or 150 μm or more) and 300 μm or less, 100 μm or more (or 150 μm or more) and 250 μm or less, or 100 μm or more (or 150 μm or more) and 200 μm or less.

[0039] When the separator has ribs, the height of the ribs may be 0.05 mm or more. Also, the height of the ribs may be 1.2 mm or less. The height of the ribs is the height of the portion protruding from the surface of the base portion (protrusion height).

[0040] The height of the ribs provided in the region of the separator facing the positive electrode plate may be 0.4 mm or more. The height of the ribs provided in the region of the separator facing the positive electrode plate may be 1.2 mm or less.

[0041] The separator is obtained, for example, by extruding a resin composition containing a base polymer, a pore former, and a penetrant (surfactant) into a sheet shape, performing a stretching treatment, and then removing at least a part of the pore former. By removing at least a part of the pore former, fine pores are formed in the matrix of the base polymer. The sheet-shaped separator is dried as necessary after removing the pore former. For example, the ratio R is adjusted by adjusting at least one selected from the group consisting of the cooling rate of the sheet during extrusion molding, the stretching ratio during the stretching treatment, and the temperature during the drying treatment. For example, when the sheet is rapidly cooled during extrusion molding, the stretching ratio is increased, or the temperature during the drying treatment is lowered, the ratio R tends to increase. The stretching treatment may be performed by biaxial stretching, but is usually performed by uniaxial stretching. The sheet-shaped separator may be bent in a bellows shape or processed into a bag shape as necessary.

[0042] In a separator having ribs, the ribs may be formed on the sheet when the resin composition is extrusion-molded. Further, the ribs may be formed by pressing the sheet with a roller having grooves corresponding to the respective ribs after the resin composition is formed into a sheet or after the pore-forming agent is removed.

[0043] Examples of the pore-forming agent include liquid pore-forming agents and solid pore-forming agents. The pore-forming agent preferably contains at least oil. By using oil, a separator containing oil can be obtained, and the effect of suppressing oxidative degradation can be enhanced. The pore-forming agent may be used alone or in combination of two or more kinds. Oil and other pore-forming agents may be used in combination. A liquid pore-forming agent and a solid pore-forming agent may be used in combination. Here, at room temperature (a temperature of 20°C or higher and 35°C or lower), a liquid pore-forming agent is classified as a liquid pore-forming agent, and a solid pore-forming agent is classified as a solid pore-forming agent.

[0044] As the liquid pore-forming agent, the above-mentioned oil is preferable. Examples of the solid pore-forming agent include polymer powder.

[0045] The amount of the pore-forming agent in the separator may vary depending on the type. The amount of the pore-forming agent in the separator is, for example, 30 parts by mass or more per 100 parts by mass of the base polymer. The amount of the pore-forming agent is, for example, 60 parts by mass or less per 100 parts by mass of the base polymer.

[0046] For example, by extracting and removing a part of the oil from the sheet formed using the oil as the pore-forming agent with a solvent, a separator containing oil is formed. The solvent is selected according to, for example, the type of the oil. For example, by adjusting the type and composition of the solvent, extraction conditions (extraction time, extraction temperature, supply rate of the solvent, etc.), the oil content in the separator is adjusted.

[0047] Examples of the surfactant as the penetrant include either an ionic surfactant or a nonionic surfactant. The surfactant may be used alone or in combination of two or more kinds.

[0048] The content rate of the penetrant in the separator is, for example, 0.01% by mass or more, and may be 0.1% by mass or more. The content rate of the penetrant in the separator may be 10% by mass or less.

[0049] The separator (or the resin composition used for manufacturing the separator) may contain inorganic particles.

[0050] As the inorganic particles, for example, ceramic particles are preferable. Examples of the ceramics constituting the ceramic particles include at least one selected from the group consisting of silica, alumina, and titania.

[0051] The content rate of the inorganic particles in the separator may be, for example, 40% by mass or more. The content rate of the inorganic particles may be, for example, 80% by mass or less, and may be 70% by mass or less.

[0052] In the separator, the tortuosity of the pores is, for example, 5 or more, and may be 20 or more. The tortuosity of the pores is, for example, 150 or less, and may be 70 or less. By having such a tortuosity, the strength of the separator can be further increased. In addition, a high effect of suppressing penetration short circuit can be obtained, and a high capacity can be obtained.

[0053] In the separator, the tortuosity of the pores may be 5 or more (or 20 or more) and 150 or less, or 5 or more (or 20 or more) and 70 or less.

[0054] The tortuosity of the pores is determined by the mercury intrusion method. The tortuosity is represented by the following formula.

[0055]

Equation

[0056] The degree of flexion can be adjusted by adjusting the affinity between the pore-forming agent and the base polymer, selecting the type and / or particle size of the inorganic particles, and / or adjusting the amount of functional groups and / or atoms present on the surface of the inorganic particles. Further, the degree of flexion can also be adjusted by adjusting the type and composition of the solvent, extraction conditions (extraction time, extraction temperature, rate of supplying the solvent, etc.) when extracting and removing the pore-forming agent.

[0057] (Analysis or size measurement of the separator) (Preparation of the separator) For the analysis or size measurement of the separator, an unused separator or a separator taken out from a fully charged lead-acid battery at the initial stage of use is used. The separator taken out from the lead-acid battery is washed and dried prior to analysis or measurement.

[0058] The washing and drying of the separator taken out from the lead-acid battery are performed in the following procedure. The separator taken out from the lead-acid battery is immersed in pure water for 1 hour to remove sulfuric acid in the separator. Then, the separator is taken out from the immersed liquid and left to stand for 16 hours or more in an environment of 25°C ± 5°C to dry.

[0059] In this specification, the fully charged state of the lead-acid battery is defined according to JIS D 5301:2019. More specifically, in a water tank of 25°C ± 2°C, the lead-acid battery is charged until the terminal voltage (V) during charging measured every 15 minutes at a current (A) that is 1 / 10 of the numerical value described as the rated capacity or the electrolyte density converted to 20°C shows a constant value for three consecutive times with three significant figures. The state of being charged until then is the fully charged state. The numerical value described as the rated capacity is a numerical value with the unit of Ah. The unit of the current set based on the numerical value described as the rated capacity is A.

[0060] A fully charged lead-acid battery is a lead-acid battery that has been fully charged after formation. The full charge of the lead-acid battery may be performed immediately after formation, or may be performed after a lapse of time from formation (for example, a lead-acid battery during use (preferably in the initial stage of use) after formation may be fully charged).

[0061] In this specification, a battery in the initial stage of use is a battery that has not elapsed much time since the start of use and has hardly deteriorated.

[0062] (XRD spectrum) The XRD spectrum of the separator is measured by irradiating X-rays from a direction perpendicular to the surface of the separator. A sample for measurement is prepared by processing a portion of the separator facing the electrode material into a strip shape. In the case of a separator having ribs, the sample is prepared by processing the base portion into a strip shape so as not to include the ribs. The measurement and fitting of the XRD spectrum are performed under the following conditions. (Measurement conditions) Measuring device: RINT-TTR2, manufactured by Rigaku Corporation Fitting: FT (step scan) method Measurement angle range: 15 - 35° Step width: 0.02° Measurement speed: 5° / min XRD data processing: Use XRD pattern analysis software (PDXL2, manufactured by Rigaku).

[0063] (Thickness of separator and height of rib) The thickness of the separator is obtained by measuring the thickness at five arbitrarily selected locations in the cross-sectional photograph of the separator and averaging them.

[0064] The height of the rib is obtained by averaging the height from one surface of the base portion of the rib measured at ten arbitrarily selected locations of the rib in the cross-sectional photograph of the separator.

[0065] (Oil content in separator) The portion of the separator facing the electrode material is processed into a strip shape to prepare a sample (hereinafter referred to as Sample A). In the case of a separator having ribs, Sample A is prepared by processing the base portion into a strip shape so as not to include the ribs.

[0066] Collect about 0.5 g of Sample A, accurately weigh it, and determine the mass (m0) of the initial sample. Put the weighed Sample A into a glass beaker of an appropriate size, and add 50 mL of n-hexane. Then, apply ultrasonic waves to the sample for about 30 minutes for each beaker to elute the oil content contained in Sample A into n-hexane. Next, take out the sample from n-hexane, dry it in the air at room temperature (a temperature of 20°C or higher and 35°C or lower), and then weigh it to determine the mass (m1) of the sample after oil removal. Then, calculate the oil content rate according to the following formula. Determine the oil content rate for 10 samples of Sample A and calculate the average value. The obtained average value is taken as the oil content rate in the separator. Oil content rate (mass %) = (m0 - m1) / m0 × 100

[0067] (Content rate of inorganic particles in the separator) Collect a part of Sample A prepared in the same manner as above, accurately weigh it, then put it into a platinum crucible, and heat it with a Bunsen burner until white smoke no longer appears. Next, heat the obtained sample in an electric furnace (in an oxygen stream, 550°C ± 10°C) for about 1 hour to incinerate it, and weigh the incinerated product. Calculate the ratio (percentage) of the mass of the incinerated product to the mass of Sample A, and take it as the content rate (mass %) of the above inorganic particles. Determine the content rate of inorganic particles for 10 samples of Sample A and calculate the average value. The obtained average value is taken as the content rate of inorganic particles in the separator.

[0068] (Content rate of penetrant in the separator) A part of Sample A prepared in the same manner as described above is collected, accurately weighed, and then dried for 12 hours or more at room temperature (a temperature of 20°C or higher and 35°C or lower) under a reduced pressure environment lower than atmospheric pressure. The dried product is placed in a platinum cell, set in a thermogravimetric analyzer, and heated from room temperature to 800°C ± 1°C at a heating rate of 10 K / min. The weight loss amount when heating from room temperature to 250°C ± 1°C is taken as the mass of the penetrant, and the ratio (percentage) of the mass of the penetrant in the mass of Sample B is calculated and used as the content rate (mass%) of the penetrant described above. As the thermogravimetric analyzer, Q5000IR manufactured by T.A. Instruments is used. The content rate of the penetrant is determined for 10 samples of Sample A, and the average value is calculated. The obtained average value is used as the content rate of the penetrant in the separator.

[0069] (Degree of Flexure) For the density, total pore volume, permeability, and differential pore distribution in the above formula of the degree of flexure, they are determined under the following conditions using a mercury porosimeter for a sample (Sample B) obtained by cutting the part of the separator facing the electrode material into a size of 20 mm in length and 5 mm in width. Mercury porosimeter: AutoPore IV9510, manufactured by Shimadzu Corporation Measurement pressure range: 4 psia (≈27.6 kPa) or higher and 60,000 psia (≈414 MPa) or lower Pore distribution: 0.01 μm or higher and 50 μm or lower

[0070] (Positive Electrode Plate) As the positive electrode plate, a paste-type positive electrode plate is used. The paste-type positive electrode plate includes a positive electrode current collector and a positive electrode active material. The positive electrode active material is held by the positive electrode current collector. The positive electrode active material is the part of the positive electrode plate excluding the positive electrode current collector. Note that members such as a mat and pasting paper may be attached to the electrode plate. Since such members (also referred to as attached members) are used integrally with the electrode plate, they are included in the electrode plate. When the positive electrode plate includes an attached member, the positive electrode active material is the part of the positive electrode plate excluding the positive electrode current collector and the attached member.

[0071] The positive current collector included in the positive electrode plate may be formed by casting lead (Pb) or a lead alloy, or may be formed by processing a lead or lead alloy sheet. Examples of the processing method include expansion processing or punching processing. It is preferable to use a grid-like current collector as the positive current collector because it is easy to carry the positive electrode material.

[0072] As the lead alloy used for the positive current collector, a Pb-Ca based alloy or a Pb-Ca-Sn based alloy is preferable in terms of corrosion resistance and mechanical strength. The positive current collector may have lead alloy layers with different compositions, and the alloy layer may be one layer or multiple layers.

[0073] The positive electrode material included in the positive electrode plate contains a positive electrode active material (lead dioxide or lead sulfate) that exhibits capacitance through an oxidation-reduction reaction. The positive electrode material may contain other additives (such as a reinforcing material) as necessary.

[0074] Examples of the reinforcing material include fibers (such as inorganic fibers and organic fibers). Examples of the resin (or polymer) constituting the organic fiber include at least one selected from the group consisting of acrylic resins, polyolefin resins (such as polypropylene resins and polyethylene resins), polyester resins (including polyalkylene arylates (such as polyethylene terephthalate)), and celluloses (such as cellulose and cellulose derivatives (such as cellulose ethers and cellulose esters)). Rayon is also included in the celluloses.

[0075] The content of the reinforcing material in the positive electrode material is, for example, 0.03% by mass or more. Also, the content of the reinforcing material in the positive electrode material is, for example, 0.5% by mass or less.

[0076] The unformed paste-type positive electrode plate is obtained by filling a positive electrode paste into a positive current collector and aging and drying it. The positive electrode paste is prepared by adding water and sulfuric acid to lead powder, an antimony compound, and other additives (such as a reinforcing material) as necessary and kneading them.

[0077] A positive electrode plate can be obtained by forming an unformed positive electrode plate. The forming can be carried out by charging a group of electrode plates including the unformed positive electrode plate while the group of electrode plates is immersed in an electrolyte containing sulfuric acid in the battery case of a lead-acid battery. However, the forming may be carried out before the assembly of the lead-acid battery or the group of electrode plates.

[0078] (Negative electrode plate) The negative electrode plate of a lead-acid battery is composed of a negative electrode current collector and a negative electrode active material. The negative electrode active material is the part of the negative electrode plate excluding the negative electrode current collector. Note that, in some cases, the above-described sticking member may be stuck to the negative electrode plate. In this case, the sticking member is included in the negative electrode plate. When the negative electrode plate includes the sticking member, the negative electrode active material is the part of the negative electrode plate excluding the negative electrode current collector and the sticking member.

[0079] The negative electrode current collector can be formed in the same manner as in the case of the positive electrode current collector. At least one of the positive electrode current collector and the negative electrode current collector may be a current collector formed by expansion processing. In an electrode plate using a current collector formed by expansion processing, in the manufacturing process of the electrode plate, the corners may be deformed due to interference with the manufacturing apparatus. When a lead-acid battery is manufactured using such an electrode plate, at an initial stage, the corners of the electrode plate are likely to break through the separator and cause a short circuit. Since the separator according to one aspect of the present invention has high strength, even when combined with an electrode plate using an expanded lattice, it is possible to suppress an initial short circuit associated with the deformation of the electrode plate, which is advantageous. At least one of the positive electrode plate and the negative electrode plate may include an expanded lattice.

[0080] The lead alloy used for the negative electrode current collector may be any of a Pb-Sb-based alloy, a Pb-Ca-based alloy, and a Pb-Ca-Sn-based alloy. These leads or lead alloys may further contain at least one selected from the group consisting of Ba, Ag, Al, Bi, As, Se, Cu, etc. as an additive element. The negative electrode current collector may have lead alloy layers with different compositions, and the alloy layer may be one layer or a plurality of layers.

[0081] The negative electrode material contained in the negative electrode plate contains a negative electrode active material (lead or lead sulfate) that exhibits capacitance through a redox reaction, and may contain an organic anti-shrinkage agent, a carbonaceous material, barium sulfate, etc. The negative electrode material may contain other additives (such as a reinforcing material) as necessary.

[0082] Examples of the organic anti-shrinkage agent include lignin, lignin sulfonic acid, synthetic organic anti-shrinkage agents (such as formaldehyde condensates of phenolic compounds), etc. The negative electrode material may contain one kind of organic anti-shrinkage agent or two or more kinds.

[0083] The content rate of the organic anti-shrinkage agent in the negative electrode material is, for example, 0.01% by mass or more. The content rate of the organic anti-shrinkage agent is, for example, 1% by mass or less.

[0084] Examples of the carbonaceous material include carbon black, graphite (artificial graphite, natural graphite, etc.), hard carbon, soft carbon, etc. The negative electrode material may contain one kind of carbonaceous material or two or more kinds.

[0085] The content rate of the carbonaceous material in the negative electrode material is, for example, 0.1% by mass or more. The content rate of the carbonaceous material may be, for example, 3% by mass or less.

[0086] The content rate of barium sulfate in the negative electrode material is, for example, 0.1% by mass or more. The content rate of barium sulfate is, for example, 3% by mass or less.

[0087] Examples of the reinforcing material include fibers (such as inorganic fibers, organic fibers (such as organic fibers composed of the resin described for the reinforcing material of the positive electrode material), etc.).

[0088] The content rate of the reinforcing material in the negative electrode material is, for example, 0.03% by mass or more. Also, the content rate of the reinforcing material in the negative electrode material is, for example, 0.5% by mass or less.

[0089] The negative electrode active material in the charged state is spongy lead, but the unformed negative electrode plate is usually produced using lead powder.

[0090] The negative electrode plate can be formed by filling a negative electrode current collector with a negative electrode paste, aging and drying to produce an unformed negative electrode plate, and then subjecting the unformed negative electrode plate to formation. The negative electrode paste is prepared by adding water and sulfuric acid to lead powder, an organic shrinkage inhibitor, and various additives as required and kneading them. In the aging process, it is preferable to age the unformed negative electrode plate at a temperature higher than room temperature and high humidity.

[0091] Formation can be carried out by charging the electrode plate group including the unformed negative electrode plate in a state where the electrode plate group including the unformed negative electrode plate is immersed in the electrolyte containing sulfuric acid in the battery case of the lead storage battery. However, the formation may be carried out before the assembly of the lead storage battery or the electrode plate group. Spongy lead is generated by the formation.

[0092] (Electrolyte) The electrolyte is an aqueous solution containing sulfuric acid. The electrolyte may be gelled as required.

[0093] The electrolyte may further contain at least one metal ion selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions, etc.

[0094] The specific gravity of the electrolyte at 20°C is, for example, 1.10 or more. The specific gravity of the electrolyte at 20°C may be 1.35 or less. These specific gravities are values for the electrolyte of a fully charged lead storage battery.

[0095] Hereinafter, the evaluation methods for each characteristic will be described. The strength of the separator is evaluated by the piercing strength.

[0096] (1) Piercing strength The piercing strength of the separator is measured by the following procedure. In accordance with "Puncture Strength Test" in 7.5 of JIS Z 1707:2019, a test piece including the edge of the separator (more specifically, the edges of both side ends of the separator) is fixed with a jig, the needle of the testing machine is pierced into the edge, and the maximum force (N) until the needle penetrates is measured. The same measurement is performed for five test pieces, and the average value is obtained and taken as the puncture strength. The test piece is produced by cutting the separator to a size of 50 mm in length × 50 mm in width so as to include the edge. In the case of a bag-shaped separator where crimping portions are formed at both side ends of the separator, the puncture strength is measured for the portion other than the crimping portion of the edge. As the testing machine, AGS-X, 10N - 10kN manufactured by Shimadzu Corporation is used. As the needle, one with a diameter of 1.0 mm and a semi-circular tip shape (radius 0.5 mm) is used, and the test speed is set to 50 ± 5 mm / min. As the jig for fixing the test piece, one with an upper surface of the measuring portion having a diameter of 10 mm and a lower diameter of 20 mm is used.

[0097] (2) IS life performance In the following procedure, the number of cycles until the terminal voltage reaches 7.2 V is used as an index of the IS life performance. Note that the micro current discharge in (e) simulates the dark current discharge when the engine is stopped in an ISS vehicle. (a) After completion of full charge, the battery is placed in a cooling chamber at 0°C ± 1°C for at least 16 hours, and then it is confirmed that the electrolyte temperature of any one of the cells in the center is 0°C ± 1°C. (b) The battery is discharged at a discharge current of 300 A for 1.0 second. (c) The battery is discharged at a discharge current of 25 A for 25 seconds. (d) The battery is charged at a voltage of 14.0 V for 30 seconds. (e) The discharges and charges in (b) to (d) above are repeated as one cycle. At this time, a micro current (20 mA) is discharged for 6 hours every 30 cycles. (f) The number of cycles when the terminal voltage becomes less than 7.2 V in (b) above is obtained.

[0098] Fig. 1 shows the appearance of an example of a lead storage battery according to an embodiment of the present invention. The lead-acid battery 1 includes a battery case 12 that houses a plate group 11 and an electrolyte (not shown). Inside the battery case 12, a plurality of cell chambers 14 are partitioned by a partition wall 13. One plate group 11 is housed in each cell chamber 14. The opening of the battery case 12 is closed by a lid 15 having a negative terminal 16 and a positive terminal 17. The lid 15 is provided with a liquid port plug 18 for each cell chamber. When replenishing water, the liquid port plug 18 is removed and replenishing liquid is supplied. The liquid port plug 18 may have a function of discharging gas generated in the cell chamber 14 to the outside of the battery.

[0099] The plate group 11 is constituted by stacking a plurality of negative plates 2 and positive plates 3 via separators 4 respectively. Here, a bag-shaped separator 4 for housing the negative plates 2 is shown, but the form of the separator is not particularly limited. In the cell chamber 14 located at one end of the battery case 12, a negative electrode rack portion 6 for connecting a plurality of negative plates 2 in parallel is connected to a through-connector 8, and a positive electrode rack portion 5 for connecting a plurality of positive plates 3 in parallel is connected to a positive electrode post 7. The positive electrode post 7 is connected to the positive terminal 17 outside the lid 15. In the cell chamber 14 located at the other end of the battery case 12, a negative electrode post 9 is connected to the negative electrode rack portion 6, and a through-connector 8 is connected to the positive electrode rack portion 5. The negative electrode post 9 is connected to the negative terminal 16 outside the lid 15. Each through-connector 8 passes through a through-hole provided in the partition wall 13 and connects the plate groups 11 of adjacent cell chambers 14 in series.

[0100] The matters described in this specification can be arbitrarily combined.

[0101] [Examples] Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

[0102] 《Lead-acid batteries E1 to E11 and C1 to C3》 Each lead-acid battery was manufactured according to the following procedure. (1) Manufacture of separator A resin composition containing 100 parts by mass of polyethylene, 160 parts by mass of silica particles, 80 parts by mass of paraffinic oil as a pore-forming agent, and 2 parts by mass of a penetrant was extruded into a sheet shape, stretched, and then a part of the pore-forming agent was removed to produce a microporous membrane having ribs on one side. At this time, the cooling rate of the extruded sheet and the stretching ratio were adjusted so that the separator ratio R obtained by the above-described procedure would be the values shown in Tables 1 and 2.

[0103] The oil content of the separator obtained by the above-described procedure was 11 to 18% by mass, the degree of bending was 5 to 70, and the content of silica particles was 60% by mass. The height of the rib obtained by the above-described procedure was 0.6 mm. The thickness (thickness of the base portion) of the separator obtained by the above-described procedure is shown in Tables 1 and 2.

[0104] Next, the sheet-shaped microporous membrane was folded in half so that ribs were arranged on the outer surface to form a bag, and both overlapping ends were crimped to obtain a bag-shaped separator.

[0105] The separator ratio R, oil content, silica particle content, base portion thickness, and rib height are values obtained for the separator before the production of the lead-acid battery, but are almost the same as the values measured by the above-described procedure for the separator taken out from the lead-acid battery after production.

[0106] (2) Production of positive electrode plate Lead oxide, a reinforcing material (synthetic resin fiber), water, and sulfuric acid were mixed to prepare a positive electrode paste. The positive electrode paste was filled into the mesh portion of an expanded grid made of a Pb-Ca-Sn alloy containing no antimony, and aged and dried to obtain an unformed positive electrode plate having a width of 100 mm, a height of 110 mm, and a thickness of 1.6 mm.

[0107] (3) Production of negative electrode plate A negative electrode paste was prepared by mixing lead oxide, carbon black, barium sulfate, lignin, reinforcing material (synthetic resin fiber), water and sulfuric acid. The negative electrode paste was filled into the mesh of an expanded lattice made of a Pb-Ca-Sn alloy not containing antimony, and aged and dried to obtain an unformed negative electrode plate with a width of 100 mm, a height of 110 mm and a thickness of 1.3 mm. The amounts of carbon black, barium sulfate, lignin and synthetic resin fiber used were adjusted so that the contents of each component in the negative electrode plate taken out of a fully charged lead-acid battery were 0.3 mass%, 2.1 mass%, 0.1 mass% and 0.1 mass%, respectively.

[0108] (4) Preparation of lead-acid battery The unformed negative electrode plates were housed in a pouch-shaped separator and stacked with the positive electrode plates to form an electrode plate group consisting of seven unformed negative electrode plates and six unformed positive electrode plates.

[0109] The lugs of the positive plates and the lugs of the negative plates were welded to the positive and negative shelf parts, respectively, using the cast-on-strap (COS) method. The plate group was inserted into a polypropylene battery case, electrolyte was poured in, and chemical formation was performed inside the battery case to assemble a flooded lead-acid battery with a rated voltage of 12V and a rated capacity of 30Ah (5-hour rate capacity (capacity when discharged at a current (A) that is 1 / 5 of the Ah value indicated on the rated capacity)). Note that six plate groups were connected in series inside the battery case.

[0110] The electrolyte used was an aqueous sulfuric acid solution. The specific gravity of the electrolyte after formation at 20°C was 1.285.

[0111] (5) Evaluation The XRD spectrum of the separator of Example 1 measured by the above-mentioned procedure is shown in Figure 1. As shown in Figure 1, the first diffraction peak corresponding to the (110) plane of the crystalline region of polyethylene was observed in the range of 2θ = 21.5 ° to 22.5 °, and the second diffraction peak corresponding to the (200) plane was observed in the range of 2θ = 23 ° to 24.5 °. Furthermore, a halo due to the amorphous region was observed broadly in the wide range of 2θ = 17 ° to 27 °.

[0112] Using the separator or the obtained lead storage battery, the piercing strength of the separator and the IS life performance of the lead storage battery were evaluated by the above-described procedure. The piercing strength was evaluated by the ratio of the value of the separator of each lead storage battery when the value of the separator in the lead storage battery C1 was set to 100. The IS life performance was evaluated by the ratio of the number of cycles of each lead storage battery when the number of cycles of the lead storage battery C1 was set to 100.

[0113] The evaluation results are shown in Tables 1 and 2. E1 to E11 are examples. C1 to C3 are comparative examples.

[0114]

Table 1

[0115] As shown in Table 1, when the ratio R of the separator was 0.60 or more, the piercing strength was improved as compared with the case where the ratio R corresponding to the prior art was 0.58. This is presumably because the strength was improved due to the increased crystallinity of the separator.

[0116]

Table 2

[0117] As shown in Table 2, when the thickness of the separator is 100 μm or more and 300 μm or less, higher strength can be ensured and higher IS life performance can be ensured.

Industrial Applicability

[0118] The separator for a lead storage battery according to the above aspect of the present invention is suitable for, for example, IS applications (such as lead storage batteries for ISS vehicles), starting power sources for various vehicles (such as automobiles and motorcycles), and the like. Further, the separator for a lead storage battery can also be suitably used for power sources such as industrial storage devices (such as forklifts) of electric vehicles. Note that these applications are merely examples. The applications of the separator for a lead storage battery and the lead storage battery according to the above aspect of the present invention are not limited to these.

Description of Symbols

[0119] 1: Lead storage battery, 2: Negative electrode plate, 3: Positive electrode plate, 4: Separator, 5: Positive electrode grid part, 6: Negative electrode grid part, 7: Positive electrode post, 8: Through-connection body, 9: Negative electrode post, 11: Electrode plate group, 12: Battery case, 13: Partition wall, 14: Cell chamber, 15: Cover, 16: Negative electrode terminal, 17: Positive electrode terminal, 18: Liquid port plug

Claims

1. A separator for a lead-acid battery, wherein the separator contains a polyolefin and includes a crystalline region and an amorphous region, In the X-ray diffraction spectrum of the separator, A １ / (A １ + A ２ ) is 0.60 or more, A １ is the area of the first diffraction peak with the maximum peak height among the diffraction peaks corresponding to the crystalline region, A ２ is the area of the second diffraction peak with the second highest peak height among the diffraction peaks corresponding to the crystalline region, wherein the first diffraction peak corresponds to the (110) plane of the crystalline region, and the second diffraction peak corresponds to the (200) plane of the crystalline region, a separator for a lead-acid battery.

2. The separator for a lead-acid battery according to claim 1, having a thickness of 100 μm or more and 300 μm or less.

3. The separator for a lead-acid battery according to claim 1 or 2, wherein the ratio R is 0.9 or less.

4. The separator for a lead-acid battery according to any one of claims 1 to 3, containing oil.

5. The separator for a lead-acid battery according to any one of claims 1 to 4, having a tortuosity of pores of 5 or more.

6. The separator for a lead-acid battery according to any one of claims 1 to 5, wherein the polyolefin contains at least an ethylene unit.

7. A lead-acid battery, wherein the lead-acid battery includes at least one cell containing a plate group and an electrolyte, the plate group includes a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate, and the separator is the separator for a lead-acid battery according to any one of claims 1 to 6, a lead-acid battery.

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