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

Abstract

To provide a separator with which it is possible to improve high temperature overcharge life performance in a lead storage battery.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 crystallinity index indicated by 100×Ic / (Ic+Ia) is 20% or greater. Ic represents the integrated intensity of diffraction peaks, the peak heights of which among the diffraction peaks equivalent to the crystalline region are maximum. Ia represents the integrated intensity of hollows equivalent to the amorphous region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a separator for a lead-acid battery and a lead-acid battery including the same. [Background technology]

[0002] Lead-acid batteries are used in a variety of applications, including automotive and industrial applications. Lead-acid batteries include positive and negative electrode plates, a separator interposed between them, and an electrolyte. Separators for lead-acid batteries are required to have various performance characteristics.

[0003] Patent Document 1 proposes a ribbed separator for lead-acid batteries containing 5 to 30 mass% of oil, which is obtained by heating and melting a raw material composition consisting of a mixture of 20 to 60 mass% polyolefin resin, 80 to 40 mass% inorganic powder, and 40 to 240 mass% mineral oil relative to the blend, and kneading the mixture while forming it into a ribbed sheet.The separator is then immersed in an immersion bath of an organic solvent that can dissolve the oil to extract and remove some of the oil, and then heated and dried.The separator is characterized in that the difference in oil content between the rib portion and the base portion of the separator is 5 mass% or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-338631 Summary of the Invention [Problem to be solved by the invention]

[0005] In lead-acid batteries, the positive plate contains lead dioxide, a highly oxidizing material, as a positive electrode active material. In an overcharged lead-acid battery, the potential of the positive plate is high. Therefore, the separator facing the positive plate is prone to oxidative degradation. Oxidative degradation of the separator during overcharge is particularly pronounced at high temperatures (e.g., temperatures above 75°C). In lead-acid batteries, oxidative degradation of the separator reduces its flexibility, causing cracks and short circuits, ultimately shortening the battery's life.

[0006] Separators for lead-acid batteries may have ribs on the surface facing the positive electrode plate or contain oil as a pore-forming agent. Such separators are advantageous in terms of ensuring high-temperature overcharge life performance because they can suppress oxidative degradation to some extent. However, with changes in the usage environment and usage patterns of lead-acid batteries, separators for lead-acid batteries are required to have even higher high-temperature overcharge life performance. [Means for solving the problem]

[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, 100×I c / (I c +I a ) is 20% or more, I c is the integrated intensity of the diffraction peak having the maximum peak height among the diffraction peaks corresponding to the crystalline region, I a is the integrated intensity of the halo corresponding to the amorphous region. [Effects of the Invention]

[0008] A separator capable of improving the high-temperature overcharge life performance of a lead-acid battery is provided. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a partially cutaway perspective view showing the appearance and internal structure of a lead-acid battery according to an embodiment of the present invention; [Figure 2] 1 is an X-ray diffraction spectrum of the lead-acid battery separator of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Lead-acid batteries are sometimes used under harsh conditions. One of the typical applications of lead-acid batteries is in automobiles. In recent years, the number of opportunities for lead-acid batteries to be exposed to overcharge has increased due to automobiles being caught in traffic jams or being used constantly like commercial vehicles. In addition, with global warming, there are more opportunities for lead-acid batteries to be used in higher temperature environments in the summer. Therefore, in recent years, there has been a growing demand for lead-acid batteries to have a higher level of high-temperature overcharge life performance than before.

[0011] Providing ribs on the separator surface facing the positive electrode plate tends to reduce oxidative degradation of the separator by forming a gap between the separator and the positive electrode plate. However, as lead-acid batteries have become more powerful, cells are increasingly containing a larger number of thin electrodes than before, so providing ribs alone is insufficient to prevent oxidative degradation of the separator. Even when the separator contains oil, oxidative degradation of the separator can be reduced to some extent. However, the insulating oil tends to clog the separator's pores, increasing the separator's resistance and reducing the reactivity of the electrodes. Therefore, it is difficult to increase the oil content in the separator for high-performance lead-acid batteries. As such, it is difficult to improve the high-temperature overcharge life performance of lead-acid batteries to a high level using conventional separators.

[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. c / (I c +I a ) is 20% or more.c is the integrated intensity of the diffraction peak with the largest peak height (hereinafter sometimes referred to as the first diffraction peak) among the diffraction peaks corresponding to the crystalline region. a is the integrated intensity of the halo corresponding to the amorphous region.

[0013] Because the separator has a crystallinity of 20% or more, the oxidation resistance of the separator itself can be improved. In this case, there is almost no trade-off between increased oxidation resistance and increased resistance, as is the case with conventional oil-containing separators. Therefore, even high-performance lead-acid batteries can ensure excellent high-temperature overcharge life.

[0014] Unlike separators for lithium-ion secondary batteries, separators for lead-acid batteries have a relatively large thickness. Furthermore, because lead-acid batteries have a lower positive electrode potential during overcharge than lithium-ion secondary batteries, sufficient oxidation resistance can be ensured in conventional operating environments or configurations using ribs or oil. Furthermore, the thicker the separator, the more difficult it tends to be to increase its crystallinity. Furthermore, as the crystallinity increases, the separator tends to become harder and more brittle. For these reasons, conventional separators for lead-acid batteries have not been designed to control their crystallinity. The crystallinity of conventional separators for lead-acid batteries tends to be relatively low, at approximately 18% or less. Contrary to this conventional wisdom, it has been revealed that a lead-acid battery separator according to one aspect of the present invention can significantly improve high-temperature overcharge life performance by achieving a crystallinity of 20% or more.

[0015] The thickness of the separator is preferably 100 μm or more and 300 μm or less. When the thickness is in this range, the effect of suppressing oxidation degradation of the separator is further enhanced, and the high-temperature overcharge life performance can be further improved.

[0016] The crystallinity is preferably 40% or less, which makes it easier to ensure the flexibility of the separator and also makes it easier to manufacture.

[0017] The separator preferably contains oil, which further enhances the effect of suppressing oxidation degradation of the separator and ensures higher high-temperature overcharge life performance.

[0018] The separator preferably contains a polyolefin, more preferably a polyolefin containing at least ethylene units. Such separators are prone to oxidative degradation, but their crystallinity can be increased relatively easily. When the separator contains a polyolefin containing at least ethylene units, the first diffraction peak corresponds to the (110) plane of the crystalline region.

[0019] The present invention also includes a lead-acid battery including the separator described above. The lead-acid battery includes at least one cell including a plate assembly and an electrolyte, and the plate assembly includes a positive plate, a negative plate, and the separator described above interposed between the positive plate and the negative plate. The inclusion of the separator described above can significantly improve the high-temperature overcharge life performance of the lead-acid battery.

[0020] The lead acid battery may be a valve regulated lead acid battery (VRLA type battery), but is preferably a flooded battery (vented type battery).

[0021] In this specification, the up-down direction of a lead-acid battery or its components (electrode plates, battery case, separator, etc.) refers to the up-down direction in the vertical direction of the lead-acid battery when the lead-acid battery is in use. Each of the positive and negative electrode plates has a lug for connecting to an external terminal, and in a flooded battery, the lug is provided on the top of the electrode plate so as to protrude upward.

[0022] Hereinafter, separators and lead-acid batteries according to embodiments of the present invention will be described in more detail with reference to the drawings, although the present invention is not limited to the following embodiments.

[0023] (separator) The separator contains crystalline regions where the molecules of the separator's constituent material are arranged in a relatively regular pattern (i.e., highly ordered), and amorphous regions where the ordering is low. Therefore, in the XRD spectrum of the separator, diffraction peaks due to the crystalline regions are observed, and scattered light due to the amorphous regions is observed as a halo. In the XRD spectrum of the separator, 100×I c / (I c +I a ) is 20% or more, excellent high-temperature overcharge life performance can be obtained. c is the integrated intensity of the diffraction peak with the largest peak height (first diffraction peak) among the diffraction peaks corresponding to the crystalline region, and I a is the integrated intensity of the halo corresponding to the amorphous region.

[0024] 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 2θ range of 20° to 22.5°, and a diffraction peak corresponding to the (200) plane of the crystalline region is observed in the 2θ range of 23° to 24.5°. Furthermore, a halo of the amorphous region is observed in the 2θ range of 17° to 27°. Among the diffraction peaks due to the crystalline region, the diffraction peak corresponding to the (110) plane has the highest peak height and corresponds to the first diffraction peak.

[0025] The crystallinity is 20% or more, and from the viewpoint of ensuring a higher high-temperature overcharge life performance, it may be 22% or more or 23% or more. The crystallinity may be 40% or less, 37% or less, or 35% or less. When the crystallinity is in this range, it is easy to ensure the flexibility of the separator and also easy to manufacture.

[0026] The crystallinity of the separator may be 20% or more (or 22% or more) and 40% or less, 20% or more (or 22% or more) and 37% or less, 20% or more (or 22% or more) and 35% or less, 23% or more and 40% or less (or 37% or less), or 23% or more and 35% or less.

[0027] The integrated intensities of the diffraction peaks and halos are determined by fitting the diffraction peaks due to the crystalline regions and the halos due to the amorphous regions in the XRD spectrum of the separator. The determined integrated intensity I of the first diffraction peak is c and the integrated intensity of the halo, I a The crystallinity can be calculated from the above formula using

[0028] The separator includes a polymer material (hereinafter also referred to as a base polymer). Because the separator includes a crystalline region, the base polymer typically includes a crystalline polymer. The separator includes, for example, a polyolefin. A polyolefin is a polymer that includes at least an olefin unit (i.e., a polymer that includes at least a monomer unit derived from an olefin).

[0029] The base polymer may be a combination of polyolefin and another base polymer. The proportion of polyolefin in the entire base polymer contained in the separator is, for example, 50% by mass or more, 80% by mass or more, or 90% by mass or more. The proportion of polyolefin is, for example, 100% by mass or less. The base polymer may be composed of polyolefin alone. When the proportion of polyolefin is this high, the oxidation resistance of the separator tends to be reduced. However, even in such a case, since the crystallinity is within the above range, high high-temperature overcharge life performance can be ensured.

[0030] Polyolefins include, for example, olefin homopolymers, copolymers containing different olefin units, and copolymers containing olefin units and copolymerizable monomer units. A copolymer containing olefin units and copolymerizable monomer units may contain one or more types of olefin units. Furthermore, a copolymer containing olefin units and copolymerizable monomer units may contain one or more types of copolymerizable monomer units. A copolymerizable monomer unit is a monomer unit derived from a polymerizable monomer other than an olefin that is copolymerizable with an olefin.

[0031] The polyolefin may, for example, be at least C 2-3 Polymers containing olefins as monomer units are also included. 2-3 The olefin may be at least one selected from the group consisting of ethylene and propylene. The polyolefin may be, for example, polyethylene, polypropylene, C 2-3 Copolymers containing olefins as monomer units (e.g., ethylene-propylene copolymers) are more preferred. Among polyolefins, polyolefins containing at least ethylene units (polyethylene, ethylene-propylene copolymers, etc.) are preferred. Polyolefins containing ethylene units (polyethylene, ethylene-propylene copolymers, etc.) may be used in combination with other polyolefins.

[0032] The separator preferably contains oil. When the separator contains oil, the effect of suppressing oxidative degradation of the separator can be further enhanced, thereby ensuring higher high-temperature overcharge life performance. 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 occurring oils, mineral oils, and synthetic oils. Preferred oils include mineral oils and synthetic oils. Examples of oils include paraffin oil and silicone oil. The separator may contain one type of oil or a combination of two or more types of oil.

[0033] The oil content in the separator is preferably 11% by mass or more and 18% by mass or less. When the oil content is in this range, the effect of suppressing oxidation degradation of the separator is further enhanced. In addition, the resistance of the separator can be kept relatively low.

[0034] The separator may be in a sheet form. Alternatively, a sheet folded into an accordion shape may be used as the separator. The separator may be formed in a bag form. Either the positive electrode plate or the negative electrode plate may be wrapped in the bag-shaped separator.

[0035] The separator may or may not have ribs. A separator with ribs includes, for example, a base portion and ribs extending from the surface of the base portion. The ribs may be provided on only one surface of the separator or each base portion, or on both surfaces. The base portion of the separator refers to the portion of the separator that excludes protrusions such as ribs, and is the sheet-like portion that defines the outer shape of the separator.

[0036] The thickness of the separator is, for example, 90 μm or more. From the viewpoint of obtaining higher high-temperature overcharge life performance, 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 of the portion of the separator facing the electrode material. When the separator has a base portion and ribs extending from at least one surface of the base portion, the thickness of the separator is the average thickness of the base portion. When an attachment member (such as a mat or pasting paper) is attached to the separator, the thickness of the attachment member is not included in the thickness of the separator.

[0037] 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.

[0038] When the separator has ribs, the rib height may be 0.05 mm or more. Alternatively, the rib height may be 1.2 mm or less. The rib height is the height of the part that protrudes from the surface of the base part (protrusion height).

[0039] The height of the ribs provided in the region of the separator facing the positive electrode plate may be 0.4 mm or more, or 1.2 mm or less.

[0040] The separator can be obtained, for example, by extruding a resin composition containing a base polymer, a pore-forming agent, and a penetrating agent (surfactant) into a sheet, stretching the extrusion, and then removing at least a portion of the pore-forming agent. Removing at least a portion of the pore-forming agent forms micropores in the base polymer matrix. After removing the pore-forming agent, the separator sheet is dried as needed. For example, the crystallinity can be adjusted by adjusting at least one of the following: the cooling rate of the sheet during extrusion, the stretch ratio during stretching, and the temperature during drying. For example, rapid cooling of the sheet during extrusion, increasing the stretch ratio, or decreasing the temperature during drying tends to increase the crystallinity. The stretching may be performed by biaxial stretching, but is usually performed by uniaxial stretching. The separator sheet may be folded into an accordion shape or processed into a bag shape as needed.

[0041] In a separator having ribs, the ribs may be formed on the sheet when the resin composition is extrusion-molded, or may be formed by pressing the sheet with a roller having grooves corresponding to each rib after molding the resin composition into a sheet or after removing the pore-forming agent.

[0042] 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 is obtained, which further enhances the effect of suppressing oxidative degradation. One type of pore-forming agent may be used alone, or two or more types may be used in combination. Oil may be used in combination with another pore-forming agent. A liquid pore-forming agent may be used in combination with a solid pore-forming agent. At room temperature (a temperature of 20°C or higher and 35°C or lower), liquid pore-forming agents are classified as liquid pore-forming agents, and solid pore-forming agents are classified as solid pore-forming agents.

[0043] The liquid pore-forming agent is preferably the above-mentioned oil, and the solid pore-forming agent may be, for example, a polymer powder.

[0044] The amount of pore-forming agent in the separator may vary depending on the type. The amount of 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 pore-forming agent is, for example, 60 parts by mass or less per 100 parts by mass of the base polymer.

[0045] For example, a separator containing oil can be formed by extracting and removing a portion of the oil from a sheet formed using oil as a pore-forming agent using a solvent. The solvent is selected, for example, depending on the type of oil. For example, the oil content in the separator can be adjusted by adjusting the type and composition of the solvent, extraction conditions (extraction time, extraction temperature, solvent supply rate, etc.), etc.

[0046] The surfactant used as the penetrating agent may be, for example, either an ionic surfactant or a nonionic surfactant. The surfactant may be used alone or in combination of two or more.

[0047] The content of the penetrant in the separator is, for example, 0.01% by mass or more, and may be 0.1% by mass or more, and may be 10% by mass or less.

[0048] The separator (or the resin composition used to produce the separator) may contain inorganic particles.

[0049] The inorganic particles are preferably, for example, ceramic particles, and examples of ceramics constituting the ceramic particles include at least one selected from the group consisting of silica, alumina, and titania.

[0050] The content of inorganic particles in the separator may be, for example, 40% by mass or more, and may be, for example, 80% by mass or less, or 70% by mass or less.

[0051] (Separator analysis or size measurement) (Preparing the separator) For separator analysis or size measurement, unused separators or separators removed from lead-acid batteries in a fully charged state after initial use are used. The separators removed from the lead-acid batteries are washed and dried prior to analysis or measurement.

[0052] The separator removed from the lead-acid battery is washed and dried using the following procedure: The separator is immersed in pure water for one hour to remove the sulfuric acid from the separator. The separator is then removed from the liquid and left to dry for at least 16 hours in an environment of 25°C ± 5°C.

[0053] In this specification, the fully charged state of a lead-acid battery is defined by JIS D 5301:2019. More specifically, the fully charged state is defined as a state in which a lead-acid battery is charged in a water tank at 25°C ± 2°C at a current (A) that is 1 / 10 of the value listed as the rated capacity, until the terminal voltage (V) during charging or the electrolyte density converted to a temperature of 20°C, measured every 15 minutes, shows a constant value to three significant digits three times in a row. The value listed as the rated capacity is in Ah. The unit of current set based on the value listed as the rated capacity is A.

[0054] A fully charged lead-acid battery is a lead-acid battery that has already been chemically formed and is fully charged. The lead-acid battery may be fully charged immediately after chemical formation, or after a certain period of time has passed since chemical formation (for example, a lead-acid battery that is in use (preferably in the early stages of use) after chemical formation may be fully charged).

[0055] In this specification, a battery in its early stages of use refers to a battery that has not been in use for a long time and has not deteriorated much.

[0056] (XRD spectrum) The XRD spectrum of a separator is measured by irradiating the separator with X-rays perpendicular to its surface. The measurement sample is prepared by cutting the separator's portion facing the electrode material into a strip. For separators with ribs, the base portion is cut into a strip to avoid including the ribs. The XRD spectrum measurement and fitting are performed under the following conditions: (Measurement conditions) Measurement 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: XRD pattern analysis software (PDXL2, Rigaku) ​​was used.

[0057] (Separator thickness and rib height) The thickness of the separator is determined by measuring the thickness at five arbitrarily selected points in a cross-sectional photograph of the separator and averaging the measurements.

[0058] The height of the rib is determined by averaging the heights of the base portion of the rib from one surface measured at 10 arbitrarily selected points on the rib in a cross-sectional photograph of the separator.

[0059] (oil content in separator) The portion of the separator facing the electrode material is cut into a strip to prepare a sample (hereinafter referred to as Sample A). For separators with ribs, Sample A is prepared by cutting the base portion into a strip so as not to include the ribs.

[0060] Approximately 0.5 g of sample A is taken and accurately weighed to determine the initial sample mass (m0). The weighed sample A is placed in an appropriately sized glass beaker and 50 mL of n-hexane is added. Next, ultrasonic waves are applied to the sample together with the beaker for approximately 30 minutes to dissolve the oil contained in sample A into n-hexane. Next, the sample is removed from the n-hexane and dried in the air at room temperature (a temperature between 20°C and 35°C), and then weighed to determine the mass (m1) of the sample after oil removal. The oil content is then calculated using the following formula. The oil content of 10 samples A is determined and the average value is calculated. The obtained average value is taken as the oil content in the separator. Oil content (mass%) = (m0 - m1) / m0 x 100

[0061] (Inorganic particle content in separator) A portion of Sample A prepared in the same manner as above was taken, accurately weighed, and placed in a platinum crucible. It was then heated with a Bunsen burner until no white smoke was emitted. The resulting sample was then heated in an electric furnace (in an oxygen stream at 550°C ± 10°C) for approximately 1 hour to incinerate it, and the incinerated material was weighed. The percentage of the mass of the incinerated material relative to the mass of Sample A was calculated, and this was taken as the inorganic particle content (mass%). The inorganic particle content was determined for 10 Samples A, and the average value was calculated. The average value obtained was taken as the inorganic particle content in the separator.

[0062] (Percentage of penetrant in separator) A portion of Sample A prepared in the same manner as above was taken, accurately weighed, and dried for at least 12 hours at room temperature (20°C to 35°C) under reduced pressure below atmospheric pressure. The dried material was placed in a platinum cell and placed in a thermogravimetric analyzer. The temperature was raised from room temperature to 800°C ± 1°C at a rate of 10 K / min. The weight loss upon raising the temperature from room temperature to 250°C ± 1°C was taken as the mass of the penetrant, and the ratio (percentage) of the mass of the penetrant to the mass of Sample B was calculated, giving the penetrant content (mass%). A TA Instruments Q5000IR thermogravimetric analyzer was used. The penetrant content was determined for 10 Samples A and the average value was calculated. The average value obtained was taken as the penetrant content in the separator.

[0063] (positive electrode plate) A paste-type positive electrode plate is used as the positive electrode plate. The paste-type positive electrode plate includes a positive electrode collector and a positive electrode material. The positive electrode material is held by the positive electrode collector. The positive electrode material is the portion of the positive electrode plate excluding the positive electrode collector. Note that a member such as a mat or pasting paper may be attached to the electrode plate. Such a member (also referred to as an attachment member) is used integrally with the electrode plate and is therefore included in the electrode plate. When the positive electrode plate includes an attachment member, the positive electrode material is the portion of the positive electrode plate excluding the positive electrode collector and the attachment member.

[0064] The positive electrode current collector included in the positive electrode plate may be formed by casting lead (Pb) or a lead alloy, or by processing a lead or lead alloy sheet. Examples of processing methods include expanding and punching. It is preferable to use a lattice-shaped current collector as the positive electrode current collector because it is easy to support the positive electrode material.

[0065] The lead alloy used for the positive electrode current collector is preferably a Pb-Ca alloy or a Pb-Ca-Sn alloy in terms of corrosion resistance and mechanical strength. The positive electrode current collector may have lead alloy layers with different compositions, and the alloy layer may be a single layer or multiple layers.

[0066] The positive electrode material contained in the positive electrode plate includes a positive electrode active material (lead dioxide or lead sulfate) that generates capacity through an oxidation-reduction reaction. The positive electrode material may also include other additives (such as reinforcing materials) as needed.

[0067] Examples of reinforcing materials include fibers (inorganic fibers, organic fibers, etc.). Examples of resins (or polymers) that constitute organic fibers include at least one selected from the group consisting of acrylic resins, polyolefin resins (polypropylene resins, polyethylene resins, etc.), polyester resins (including polyalkylene arylates (polyethylene terephthalate, etc.)), and celluloses (cellulose, cellulose derivatives (cellulose ether, cellulose ester, etc.)). Celluloses also include rayon.

[0068] The content of the reinforcing material in the positive electrode material is, for example, 0.03 mass % or more, and the content of the reinforcing material in the positive electrode material is, for example, 0.5 mass % or less.

[0069] Unformed paste-type positive electrode plates are obtained by filling a positive electrode current collector with a positive electrode paste, aging it, and drying it. The positive electrode paste is prepared by adding water and sulfuric acid to lead powder, an antimony compound, and optionally other additives (such as reinforcing materials), and kneading them.

[0070] A positive electrode plate can be obtained by chemically forming an unformed positive electrode plate. Chemical formation can be performed by immersing an electrode plate assembly including the unformed positive electrode plate in an electrolyte containing sulfuric acid in a battery container of a lead-acid battery and then charging the electrode plate assembly. However, chemical formation may also be performed before assembling the lead-acid battery or the electrode plate assembly.

[0071] (negative plate) The negative electrode plate of a lead-acid battery is composed of a negative electrode current collector and a negative electrode material. The negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector. Note that an adhesive member such as that described above may be attached to the negative electrode plate. In this case, the adhesive member is included in the negative electrode plate. When the negative electrode plate includes an adhesive member, the negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector and the adhesive member.

[0072] The negative electrode current collector can be formed in the same manner as 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 expanding.

[0073] The lead alloy used in the negative electrode current collector may be any of a Pb-Sb alloy, a Pb-Ca alloy, and a Pb-Ca-Sn alloy. These lead or lead alloys may further contain at least one additive element selected from the group consisting of Ba, Ag, Al, Bi, As, Se, and Cu. The negative electrode current collector may have lead alloy layers with different compositions, and the alloy layer may be a single layer or multiple layers.

[0074] The negative electrode material contained in the negative electrode plate contains a negative electrode active material (lead or lead sulfate) that generates capacity through an oxidation-reduction reaction, and may also contain an organic shrinkage inhibitor, a carbonaceous material, barium sulfate, etc. The negative electrode material may also contain other additives (such as a reinforcing material) as necessary.

[0075] Examples of the organic shrinkage inhibitor include lignin, lignin sulfonic acid, synthetic organic shrinkage inhibitors (such as formaldehyde condensates of phenol compounds), etc. The negative electrode material may contain one type of organic shrinkage inhibitor, or may contain two or more types.

[0076] The content of the organic shrinkage inhibitor in the negative electrode material is, for example, 0.01% by mass or more, and 1% by mass or less.

[0077] 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 type of carbonaceous material or two or more types of carbonaceous materials.

[0078] The content of the carbonaceous material in the negative electrode material is, for example, 0.1 mass % or more, and may be, for example, 3 mass % or less.

[0079] The content of barium sulfate in the negative electrode material is, for example, 0.1% by mass or more, and 3% by mass or less.

[0080] Examples of the reinforcing material include fibers (inorganic fibers, organic fibers (such as organic fibers made of resin as described above for the reinforcing material of the positive electrode material)).

[0081] The content of the reinforcing material in the negative electrode material is, for example, 0.03 mass % or more, and the content of the reinforcing material in the negative electrode material is, for example, 0.5 mass % or less.

[0082] The negative electrode active material in the charged state is sponge lead, but the unformed negative electrode plate is usually made using lead powder.

[0083] The negative electrode plate can be formed by filling a negative electrode current collector with a negative electrode paste, aging and drying the paste to produce an unformed negative electrode plate, and then chemically forming the unformed negative electrode plate. The negative electrode paste is produced by adding water and sulfuric acid to lead powder, an organic shrinkage inhibitor, and various additives as needed, and kneading them. In the aging process, the unformed negative electrode plate is preferably aged at a temperature higher than room temperature and at a high humidity.

[0084] The formation can be carried out by immersing an electrode plate assembly including unformed negative plates in an electrolyte containing sulfuric acid in a battery jar of a lead-acid battery and then charging the electrode plate assembly. However, the formation can also be carried out before assembling the lead-acid battery or the electrode plate assembly. The formation produces spongy lead.

[0085] (electrolyte) The electrolyte is an aqueous solution containing sulfuric acid, and may be gelled if necessary.

[0086] The electrolytic solution may further contain at least one metal ion selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions.

[0087] 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. Note that these specific gravities are values ​​for the electrolyte of a fully charged lead-acid battery.

[0088] The high-temperature overcharge life performance of a lead-acid battery is evaluated based on the life of the lead-acid battery at the time of a high-temperature overcharge durability test carried out according to the following procedure. (a) The battery shall be kept in an air chamber at 75°C ± 3°C throughout the entire test period. (b) Connect the storage battery to a life test device and continuously repeat the following discharge and charge cycles. This discharge and charge cycle is considered one life (1 cycle). Discharge: Discharge current 25.0A ±0.1A for 60 seconds ±1 second Charging: 600 seconds ±1 second at charging voltage 14.80V ±0.03V (limited current 25.0A ±0.1A) (c) During the test, leave the battery for 56 hours after every 480 cycles, then discharge the battery continuously for 30 seconds at the rated cold cranking current of 390A and record the voltage at the 30th second. Then, charge the battery as described in (b). These discharges and charges are also included in the life cycle (number of cycles). (d) The test is terminated when it is confirmed that the voltage measured at 30 seconds in the test (c) is 7.2 V or less and does not rise again, and the total number of cycles at this point is used as an index of life performance. The rated cold cranking current is a measure of engine starting performance, and is the discharge current determined so that the voltage after 30 seconds is 7.2V or higher when discharged at a temperature of -18°C ± 1°C.

[0089] FIG. 1 shows the appearance of an example of a lead-acid battery according to an embodiment of the present invention. The lead-acid battery 1 includes a battery case 12 that contains a plate group 11 and an electrolyte (not shown). The battery case 12 is divided into multiple cell chambers 14 by partition walls 13. Each cell chamber 14 contains one plate group 11. The opening of the battery case 12 is closed by a lid 15 that has a negative electrode terminal 16 and a positive electrode terminal 17. The lid 15 is provided with a vent plug 18 for each cell chamber. When rehydrating, the vent plug 18 is removed and rehydration liquid is added. The vent plug 18 may have the function of venting gas generated in the cell chambers 14 to the outside of the battery.

[0090] Each electrode plate group 11 is formed by stacking multiple negative electrode plates 2 and multiple positive electrode plates 3 with separators 4 interposed between them. Here, a pouch-shaped separator 4 is shown housing the negative electrode plates 2, but the shape of the separator is not particularly limited. In a cell chamber 14 located at one end of the battery case 12, a negative electrode shelf 6 that connects multiple negative electrode plates 2 in parallel is connected to a through-connector 8, and a positive electrode shelf 5 that connects multiple positive electrode plates 3 in parallel is connected to a positive electrode column 7. The positive electrode column 7 is connected to a positive electrode terminal 17 outside the lid 15. In a cell chamber 14 located at the other end of the battery case 12, a negative electrode column 9 is connected to the negative electrode shelf 6, and a through-connector 8 is connected to the positive electrode shelf 5. The negative electrode column 9 is connected to a negative electrode terminal 16 outside the lid 15. Each through-connector 8 passes through a through-hole provided in the partition wall 13 to connect the electrode plate groups 11 of adjacent cell chambers 14 in series.

[0091] The items described in this specification can be combined in any manner.

[0092] [Example] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0093] Lead-acid batteries E1 to E10 and C1 Each lead-acid battery was fabricated according to the following procedure. (1) Preparation of separator A resin composition containing 100 parts by weight of polyethylene, 160 parts by weight of silica particles, 80 parts by weight of paraffinic oil as a pore-forming agent, and 2 parts by weight of a penetrating agent was extruded into a sheet, stretched, and then partially removed to produce a microporous membrane with ribs on one side. The cooling rate and stretching ratio of the extruded sheet were adjusted so that the crystallinity of the separator, as determined by the procedure described above, would be the values ​​shown in Tables 1 and 2.

[0094] The oil content of the separator determined by the above-mentioned procedure was 11 to 18 mass %, and the silica particle content was 60 mass %. The rib height determined by the above-mentioned procedure was 0.6 mm. The separator thickness (thickness of the base portion) determined by the above-mentioned procedure is shown in Tables 1 and 2.

[0095] Next, the sheet-like microporous membrane was folded in half so that the ribs were disposed on the outer surface to form a bag, and the overlapping ends were crimped together to obtain a bag-like separator.

[0096] The crystallinity, oil content, silica particle content, base thickness, and rib height of the separator were values ​​determined for the separator before the lead-acid battery was fabricated, but were almost the same as the values ​​measured by the above-described procedure for the separator removed from the fabricated lead-acid battery.

[0097] (2) Preparation of the positive electrode plate A positive electrode paste was prepared by mixing lead oxide, reinforcing material (synthetic resin fiber), water, and sulfuric acid. The positive electrode paste was filled into the mesh of an expanded grid made of a Pb-Ca-Sn alloy containing no antimony, and then aged and dried to obtain an unformed positive electrode plate measuring 100 mm wide, 110 mm high, and 1.6 mm thick.

[0098] (3) Preparation of negative electrode plate A negative electrode paste was prepared by mixing lead oxide, carbon black, barium sulfate, lignin, a reinforcing material (synthetic resin fiber), water, and sulfuric acid. The negative electrode paste was filled into the mesh of an expanded lattice made of an antimony-free Pb-Ca-Sn alloy, and then aged and dried to obtain an unformed negative electrode plate measuring 100 mm wide, 110 mm high, and 1.3 mm thick. The amounts of carbon black, barium sulfate, lignin, and synthetic resin fiber were adjusted so that the respective component contents of the negative electrode plate removed from a fully charged lead-acid battery were 0.3%, 2.1%, 0.1%, and 0.1% by mass, respectively.

[0099] (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 assembly consisting of seven unformed negative electrode plates and six unformed positive electrode plates.

[0100] The lugs of the positive and negative plates were welded to the positive and negative shelf sections, respectively, using the cast-on-strap (COS) method. The plate assembly 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 12 V and a rated capacity of 30 Ah (5-hour rate capacity (capacity when discharged at a current (A) of 1 / 5 the Ah value listed on the rated capacity)). Six plate groups were connected in series inside the battery case.

[0101] The electrolyte used was an aqueous sulfuric acid solution, and the specific gravity of the electrolyte after formation at 20°C was 1.285.

[0102] (5) Evaluation The XRD spectrum of the separator of Example 1 measured using the procedure described above is shown in Figure 1. As shown in Figure 1, a 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 a diffraction peak corresponding to the (200) plane was observed in the range of 2θ = 23° to 24.5°. A broad halo due to the amorphous region was observed in the wide range of 2θ = 17° to 27°.

[0103] The obtained lead-acid batteries were evaluated for high-temperature overcharge life performance according to the procedure described above. The high-temperature overcharge life performance was evaluated by the ratio of the number of cycles of each lead-acid battery to the number of cycles of lead-acid battery C1, which was set to 100.

[0104] The evaluation results are shown in Tables 1 and 2. E1 to E10 are examples, and C1 is a comparative example.

[0105] [Table 1]

[0106] As shown in Table 1, when the separator crystallinity was 20% or higher, the high-temperature overcharge life performance was significantly improved compared to when the crystallinity was 18%, which corresponds to the conventional technology. This is thought to be because the increased crystallinity of the separator improved its oxidation resistance.

[0107] [Table 2]

[0108] As shown in Table 2, when the thickness of the separator is 100 μm or more and 300 μm or less, a higher high-temperature overcharge life performance can be ensured. [Industrial Applicability]

[0109] The lead-acid battery separator according to the above aspect of the present invention is suitable for, for example, IS applications (such as lead-acid batteries for ISS vehicles) and as a starting power source for various vehicles (such as automobiles and motorcycles). The lead-acid battery separator can also be suitably used as a power source for industrial power storage devices such as electric vehicles (such as forklifts). These applications are merely examples. The applications of the lead-acid battery separator and lead-acid battery according to the above aspect of the present invention are not limited to these. [Explanation of symbols]

[0110] 1: lead-acid battery, 2: negative electrode plate, 3: positive electrode plate, 4: separator, 5: positive electrode shelf, 6: negative electrode shelf, 7: positive electrode column, 8: through-connector, 9: negative electrode column, 11: electrode plate group, 12: battery case, 13: partition wall, 14: cell chamber, 15: lid, 16: negative electrode terminal, 17: positive electrode terminal, 18: liquid vent plug

Claims

1. A separator for a lead-acid battery, the separator contains at least a polyolefin and includes a crystalline region and an amorphous region; The separator contains oil, In the X-ray diffraction spectrum of the separator, 100×I ｃ / (I ｃ +I ａ ) has a crystallinity of 20% or more and 40% or less, I ｃ is the integrated intensity of the diffraction peak having the maximum peak height among the diffraction peaks corresponding to the crystalline region, I ａ is the integrated intensity of the halo corresponding to the amorphous region, A separator for a lead-acid battery having a thickness of 90 μm or more and 300 μm or less.

2. 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 polyolefin contains at least ethylene units, 3. The lead-acid battery separator according to claim 1, wherein the diffraction peak having the maximum peak height corresponds to a (110) plane of the crystalline region.

4. A lead-acid battery, The lead-acid battery includes at least one cell including a plate pack and an electrolyte; the electrode 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, A lead-acid battery, wherein the separator is the lead-acid battery separator according to any one of claims 1 to 3.

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