JP7739892B2 - Separator for lead-acid battery and lead-acid battery including same - Google Patents

Description

The present invention relates to a separator for a lead-acid battery and a lead-acid battery including the same.

Lead-acid batteries are used in a variety of applications, including automotive and industrial use. They contain positive and negative electrode plates, a separator between them, and an electrolyte. Separators for lead-acid batteries are required to have a variety of performance characteristics.

Patent Document 1 discloses a ribbed separator for lead-acid batteries containing 5 to 30% by mass of oil, obtained by heating and melting a raw material composition consisting of a mixture of 20 to 60% by mass of polyolefin resin, 80 to 40% by mass of inorganic powder, and 40 to 240% by mass of mineral oil relative to the blend, while kneading and forming the resulting mixture into a ribbed sheet. The sheet is then immersed in an immersion bath containing an organic solvent capable of dissolving the oil to extract and remove a portion of the oil, and then heated and dried. The difference in oil content between the rib portion and the base portion of the separator is 5% by mass or less.

Patent Document 2 discloses "a lead-acid battery separator, the lead-acid battery separator comprising a porous membrane and/or a fibrous mat, and one or more conductive elements or nucleating additives within or on top of the porous membrane and/or the fibrous mat."

Japanese Patent Application Laid-Open No. 2001-338631 Japanese Patent Application Laid-Open No. 2020-533741

Current lead-acid batteries, such as those used in vehicles with idle-stop systems, are required to perform under different usage conditions than lead-acid batteries of the past. To address this, there has always been a need to improve the lifespan and productivity of lead-acid batteries. Therefore, new technologies that can contribute to improving lifespan and productivity are needed.

One aspect of the present disclosure relates to a separator for a lead-acid battery, the separator comprising a porous membrane and a carbon material disposed on a surface of the porous membrane, the porous membrane comprising a crystalline region and an amorphous region, wherein an X-ray diffraction spectrum of the porous membrane has a ratio R expressed as _A1 /( _A1 + _A2 ) of 0.70 or more, _A1 being the area of a first diffraction peak having the largest peak height among the diffraction peaks corresponding to the crystalline region, and _A2 being the area of a second diffraction peak having the second largest peak height among the diffraction peaks corresponding to the crystalline region.

Another aspect of the present disclosure relates to a lead-acid battery. The lead-acid battery includes at least one cell containing an electrode plate assembly and an electrolyte, the electrode plate assembly including 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 lead-acid battery separator of the above aspect.

This disclosure provides a separator that can improve the life performance and productivity of lead-acid batteries.

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; 1 is an X-ray diffraction spectrum of an example of a separator for a lead acid battery produced in an example. 10 is a graph showing some of the results of Experimental Example 3. 10 is a graph showing another part of the results of Experimental Example 3.

The following describes examples of embodiments of the present disclosure, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be used as examples, but other numerical values and materials may be used as long as the effects of the present disclosure are achieved. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B." In the following description, when lower and upper limits are given for numerical values of specific physical properties or conditions, any of the exemplified lower limits can be combined with any of the exemplified upper limits, as long as the lower limit is not greater than or equal to the upper limit.

(Lead-acid battery separator)
A lead-acid battery separator according to one aspect of the present invention includes a porous membrane and a carbon material disposed on the surface of the porous membrane. Hereinafter, the porous membrane may be referred to as a "porous membrane (F)." The porous membrane (F) includes a crystalline region and an amorphous region. In an X-ray diffraction (XRD) spectrum of the porous membrane (F), the ratio R, expressed as _A1 /( _A1 + _A2 ), is 0.70 or greater. Here, _A1 is the area of the diffraction peak (first diffraction peak) having the largest peak height among the diffraction peaks corresponding to the crystalline region. _A2 is the area of the diffraction peak (second diffraction peak) having the second highest peak height among the diffraction peaks corresponding to the crystalline region.

Lead-acid batteries are sometimes used under harsh conditions. One of the most common uses for lead-acid batteries is in automobiles. In recent years, there have been increasing opportunities for lead-acid batteries to be exposed to overcharge due to automobiles being caught in traffic jams or being used constantly like commercial vehicles. Furthermore, with global warming, there are more opportunities for lead-acid batteries to be used in higher temperature environments in the summer. For this reason, there has been a growing demand for lead-acid batteries to have even higher levels of life performance (for example, high-temperature overcharge life performance) than before.

Oxidative degradation of the separator is one of the factors shortening the lifespan of lead-acid batteries. When ribs are provided on the surface of the separator facing the positive electrode plate, gaps are formed between the separator and the positive electrode plate. Therefore, providing ribs tends to reduce oxidative degradation of the separator. However, as lead-acid batteries have become more powerful, they are increasingly using a larger number of thinner electrodes per cell than before. Therefore, providing ribs alone is not sufficient to prevent oxidative degradation of the separator. Oxidative degradation of the separator can also be reduced to some extent when the separator contains oil. However, insulating oil tends to clog the pores of the separator, 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 lifespan of lead-acid batteries to a high level using conventional separators.

The ratio R indicates the crystallinity of the porous membrane (F). In other words, a high ratio R indicates high crystallinity of the porous membrane (F). Because the ratio R of the porous membrane (F) is 0.70 or higher, the oxidation resistance of the porous membrane (F) is high. Unlike increasing oxidation resistance using oil, increasing oxidation resistance by increasing crystallinity has almost no disadvantages, such as increased resistance. Therefore, even high-performance lead-acid batteries can ensure excellent life performance.

Unlike separators used in lithium-ion secondary batteries, separators for lead-acid batteries have a relatively large thickness. Furthermore, compared to lithium-ion secondary batteries, lead-acid batteries have a lower positive electrode potential during overcharge. Therefore, in conventional usage environments or configurations, sufficient oxidation resistance can be ensured by ribs, oil, etc. Furthermore, the thicker the separator, the more difficult it tends to be to increase crystallinity. Furthermore, as crystallinity increases, the separator tends to become harder and more brittle. For these reasons, the crystallinity of separators for lead-acid batteries has not been controlled in the past. The ratio R of conventional separators for lead-acid batteries has been at least 0.65 or less. Contrary to this conventional wisdom, the ratio R of the porous membrane (F) used in the separator of this embodiment is set to 0.70 or greater. This significantly improves life performance (e.g., high-temperature overcharge life performance).

The lifespan of lead-acid batteries is also significantly reduced by uneven electrolyte concentration (stratification). In lead-acid batteries, the concentration of electrolyte in the upper part of the battery can be lower than that in the lower part, which reduces the battery's lifespan performance.

The separator of this embodiment includes a carbon material disposed on its surface. This carbon material comes into contact with an electrode (positive electrode or negative electrode) within the lead-acid battery, and is therefore electrically connected to the electrode. As a result, when the lead-acid battery is charged (e.g., at the end of charging), water may be electrolyzed in the carbon material, generating gas. The generated gas agitates the electrolyte, thereby suppressing stratification of the electrolyte.

However, when water electrolysis occurs on the surface of the separator, it is important to prevent oxidation of the separator due to the oxygen gas that is generated. The separator of this embodiment uses a highly crystalline resin film (F), which makes it possible to prevent oxidation of the separator.

In addition, efforts are being made to improve the performance of lead-acid batteries by using multiple thin plates. Lead-acid batteries that use multiple thin plates have a high rate of defects during manufacturing due to insufficient separator strength. Therefore, increasing separator strength is particularly important for improving the reliability and productivity of high-performance lead-acid batteries.

The inventors of the present application have discovered that by combining a resin film (F) with a carbon material, a separator with strength beyond expectations can be obtained. In other words, the separator of this embodiment makes it possible to construct a high-performance lead-acid battery with long life and high productivity.

The thickness of the separator is preferably between 100 μm and 300 μm. When the thickness is within this range, the separator's oxidation degradation is further suppressed, further improving its lifespan.

The ratio R is preferably 0.90 or less. In this case, it is easy to ensure the flexibility of the separator and manufacturing is also easy.

It is preferable that the separator contains oil. In this case, the effect of suppressing oxidation degradation of the separator is further enhanced, ensuring a longer lifespan.

It is preferable that the tortuosity of the pores of the porous membrane (F) is 5 or more. In this case, the strength of the separator can be further increased.

The porous film (F) preferably contains a polyolefin, and more preferably contains a polyolefin containing at least ethylene units. Such porous films (F) tend to have relatively low strength, but the ratio R can be adjusted relatively easily, and adjusting the ratio R can increase the strength of the porous film (F). When the porous film (F) contains a polyolefin containing at least ethylene units, 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.

(carbon materials)
As the carbon material, a conductive carbon material can be used. Examples of conductive carbon materials include graphite, activated carbon, carbon black, carbon fiber, and carbon nanotubes. Examples of conductive carbon black include acetylene black, ketjen black, and high-surface-area carbon black. From the viewpoint of productivity, it is preferable to use carbon black, and for example, it is preferable to use acetylene black, high-surface-area carbon black, and ketjen black. The carbon material may be at least one selected from the group consisting of conductive carbon black and conductive carbon fiber. The carbon material may be arranged in the form of a layer on the surface of the porous membrane (F). The method of arranging the carbon material will be described later.

The carbon material may be disposed on only one of the two main surfaces of the porous membrane (F) (the main surface facing the positive electrode plate or the main surface facing the negative electrode plate), or on both main surfaces. In other words, the carbon material is present on at least one surface of the separator. In a preferred example, the carbon material is disposed on only one main surface of the porous membrane (F). As described below, the carbon material may be disposed on only the main surface of the porous membrane (F) facing the negative electrode plate.

The carbon material may be arranged in a layered form covering the main surface of the porous membrane (F), or may be arranged in a non-layered form. Examples of a non-layered form include a form in which the carbon material is arranged in the form of dispersed islands. When the carbon material is arranged in a layered form, the thickness may be 5 μm or more in order to increase the strength of the separator. The thickness of the carbon material layer may be in the range of 5 μm to 30 μm (e.g., in the range of 10 μm to 20 μm). The thickness of the carbon material layer can be measured in the same manner as the thickness of the separator.

The content of carbon material in the separator (carbon material disposed on the surface of the porous membrane (F)) may be 2% by mass or more, and preferably 3% by mass or more. By setting this content to 2% by mass or more, it is possible to particularly improve the oxidation resistance and strength of the separator. This content may be 40% by mass or less, or 30% by mass or less.

(Porous membrane (F))
The porous film (F) contains crystalline regions in which the molecules of the constituent materials of the porous film (F) are arranged in a relatively regular pattern (i.e., highly ordered), and amorphous regions in which the order is low. Therefore, in the XRD spectrum of the porous film (F), 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 porous film (F), excellent life performance can be obtained by having the ratio R expressed as _A1 /( _A1 + _A2 ) be 0.70 or more. Here, _A1 is the area of the diffraction peak (first diffraction peak) with the largest peak height among the diffraction peaks corresponding to the crystalline regions, and _A2 is the area of the diffraction peak (second diffraction peak) with the second highest peak height among the diffraction peaks corresponding to the crystalline regions.

For example, in the XRD spectrum of a porous film (F) 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°. Of the diffraction peaks due to the crystalline region, the diffraction peak corresponding to the (110) plane has the largest 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.

The ratio R is 0.70 or greater. From the perspective of ensuring higher separator strength, the ratio R may be 0.75 or greater. The ratio R may be 0.90 or less, 0.85 or less, or 0.80 or less. When the ratio R is within this range, it is easy to ensure the flexibility of the separator and manufacturing is also easy.

The ratio R may be 0.70 or greater and 0.90 or less, or 0.75 or greater and 0.90 or less. Within these ranges, the upper limit may be 0.85 or less, or 0.80 or less.

The area of the diffraction peaks is determined by fitting the diffraction peaks due to the crystalline region in the XRD spectrum of the porous film (F). The ratio R is determined from the above formula using the area _A1 of the first diffraction peak and the area _A2 of the second diffraction peak.

The porous membrane (F) contains a polymer material (hereinafter also referred to as a base polymer). Because the porous membrane (F) contains crystalline regions, the base polymer typically contains a crystalline polymer. The porous membrane (F) contains, for example, a polyolefin. A polyolefin is a polymer containing at least olefin units (i.e., a polymer containing at least monomer units derived from an olefin).

Polyolefins may be used in combination with other base polymers as the base polymer. The proportion of polyolefins in the total base polymers contained in the porous membrane (F) is, for example, 50% by mass or more, 80% by mass or more, or 90% by mass or more. The proportion of polyolefins is, for example, 100% by mass or less. The base polymer may be composed solely of polyolefins. When the proportion of polyolefins is this high, the oxidation resistance of the porous membrane (F) tends to be reduced. However, even in such cases, a long service life can be ensured by keeping the ratio R within the above range.

Polyolefins include, for example, olefin homopolymers, copolymers containing different olefin units, and copolymers containing olefin units and copolymerizable monomer units. Copolymers containing olefin units and copolymerizable monomer units may contain one or more types of olefin units. Copolymers containing olefin units and copolymerizable monomer units may contain one or more types of copolymerizable monomer units. Copolymerizable monomer units are monomer units derived from polymerizable monomers other than olefins that are copolymerizable with olefins.

Examples of polyolefins include polymers containing at least a C _2-3 olefin as a monomer unit. Examples of C _2-3 olefins include at least one selected from the group consisting of ethylene and propylene. Examples of polyolefins that are more preferred include polyethylene, polypropylene, and copolymers containing a C _2-3 olefin as a monomer unit (e.g., ethylene-propylene copolymer). Among polyolefins, it is preferable to use polyolefins containing at least ethylene units (polyethylene, ethylene-propylene copolymer, etc.). Polyolefins containing ethylene units (polyethylene, ethylene-propylene copolymer, etc.) may be used in combination with other polyolefins.

The separator (more specifically, the porous membrane (F)) preferably contains oil. When the separator contains oil, the effect of suppressing oxidative degradation of the separator can be further enhanced, ensuring a longer lifespan. Oil refers to a hydrophobic substance that is liquid at room temperature (a temperature between 20°C and 35°C) and separates from water. Oils include naturally occurring oils, mineral oils, and synthetic oils. Mineral oils, synthetic oils, etc. are preferred. 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.

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 this range, the effect of suppressing oxidative degradation of the separator is further enhanced. In addition, the resistance of the separator can be kept relatively low.

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

A separator may or may not have ribs. A separator with ribs, for example, has 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 a separator refers to the constituent parts of the separator excluding protrusions such as ribs, and is the sheet-like portion that defines the outer shape of the separator.

The thickness of the separator is 100 μm or more. From the perspective of achieving higher life performance, the thickness of the separator is preferably 150 μm or more. The thickness of the separator is, for example, 300 μm or less. From the perspective of keeping the separator's resistance low, the thickness of the separator may be 250 μm or less or 200 μm or less. The thickness of the separator refers to the average thickness of the portion of the separator facing the electrode material. If the separator has a base portion and a rib extending from at least one surface of the base portion, the thickness of the separator refers to the average thickness of the base portion. If 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.

The thickness of the separator may be 100 μm or more and 300 μm or less, 100 μm or more and 250 μm or less, or 100 μm or more and 200 μm or less. The lower limit of these ranges may be 120 μm or more, or 150 μm or more.

If 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 portion protruding from the surface of the base portion (protrusion height).

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.

The carbon material is disposed on the surface of the formed porous membrane (F). There are no particular limitations on the method for disposing the carbon material. For example, the carbon material may be formed by applying a carbon material, a composition containing a carbon material, or a dispersion containing a carbon material to the surface of the porous membrane (F). There are no particular limitations on the application method, and doctor blade methods, roller coating methods, spray coating methods, immersion methods, vapor deposition methods, and other printing methods may be used. Examples of dispersions containing a carbon material include dispersions in which a carbon material is dispersed in a dispersion medium (water and/or an organic solvent). The amount and thickness of the carbon material disposed on the surface of the porous membrane (F) can be adjusted by controlling the amount of carbon material applied.

Porous membrane (F) 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 sheet-shaped porous membrane (F) is optionally dried. For example, the ratio R can be adjusted by adjusting at least one of the following: the cooling rate of the sheet during extrusion, the stretching ratio during stretching, and the temperature during drying. For example, rapid cooling of the sheet during extrusion, increasing the stretching ratio, or decreasing the temperature during drying tends to increase the ratio R. Stretching can be performed by biaxial stretching, but is typically performed by uniaxial stretching. The sheet-shaped separator can be folded into an accordion shape or processed into a bag shape as needed. When a separator having a carbon material disposed on only one main surface of the porous membrane (F) is processed into a bag shape, the carbon material is disposed on either the inner or outer surface of the bag.

In separators with ribs, the ribs may be formed when the resin composition is extruded into a sheet. Alternatively, the ribs may be formed by pressing the sheet with a roller having grooves corresponding to each rib after the resin composition has been molded into a sheet or after the pore-forming agent has been removed.

Examples of pore-forming agents include liquid pore-forming agents and solid pore-forming agents. It is preferable that the pore-forming agent contains at least oil. By using oil, a separator containing oil is obtained, further enhancing 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. Liquid pore-forming agents may be used in combination with solid pore-forming agents. 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.

The above-mentioned oils are preferred as liquid pore-forming agents. Examples of solid pore-forming agents include polymer powders.

The amount of pore-forming agent in porous membrane (F) may vary depending on the type of pore-forming agent. The amount of pore-forming agent in porous membrane (F) is, for example, 30 parts by mass or more per 100 parts by mass of base polymer. The amount of pore-forming agent is, for example, 60 parts by mass or less per 100 parts by mass of base polymer.

For example, a porous membrane (F) containing oil is formed by extracting and removing some 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 porous membrane (F) can be adjusted by adjusting the type and composition of the solvent, extraction conditions (extraction time, extraction temperature, solvent supply rate, etc.), etc.

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

The content of the penetrant in the porous membrane (F) is, for example, 0.01% by mass or more, and may be 0.1% by mass or more. The content of the penetrant in the porous membrane (F) may be 10% by mass or less.

The porous membrane (F) (or the resin composition used to produce the porous membrane (F)) may contain inorganic particles. Note that these inorganic particles do not include carbon materials disposed on the surface of the porous membrane (F).

Ceramic particles are preferred as inorganic particles. Examples of ceramics that make up ceramic particles include at least one selected from the group consisting of silica, alumina, and titania.

The content of inorganic particles other than carbon materials in the porous membrane (F) may be, for example, 40% by mass or more. The content of inorganic particles may be, for example, 80% by mass or less, or 70% by mass or less.

The tortuosity of the pores of the porous membrane (F) 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 making the tortuosity of the pores 5 or more, the strength of the separator can be further increased. In addition, a high permeation short-circuit suppression effect can be obtained, and a high capacity can be obtained.

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.

The degree of tortuosity of pores can be determined using mercury intrusion porosimetry. The degree of tortuosity is expressed by the following formula:

(In the formula, ξ: degree of tortuosity, ρ: density, K: permeability, V _tot : total pore volume, and X: differential pore distribution.)

The degree of tortuosity 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. The degree of tortuosity can also be adjusted by adjusting the type and composition of the solvent used to extract and remove the pore-forming agent, as well as the extraction conditions (extraction time, extraction temperature, solvent supply rate, etc.).

(Separator analysis or size measurement)
(Preparing the separator)
For separator analysis or size measurement, an unused separator or a separator removed from a lead-acid battery in a fully charged state at the beginning of use is used. The separator removed from the lead-acid battery is washed and dried prior to analysis or measurement. The XRD spectrum of the porous membrane (F) may be measured using the porous membrane (F) before a carbon material is disposed on its surface. Furthermore, the XRD spectrum of the porous membrane (F) having a carbon material disposed on only one side may be measured using the surface on which the carbon material is not disposed.

Separators removed from lead-acid batteries are washed and dried using the following procedure. The separator is immersed in pure water for one hour to remove any 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. For separators with carbon material on both sides, the carbon material is removed by polishing before measuring the XRD spectrum.

In this specification, the fully charged state of a lead-acid battery is defined in accordance with 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 (ampere-hours). The unit of current set based on the value listed as the rated capacity is A (ampere).

A fully charged lead-acid battery is a lead-acid battery that has already been chemically formed and is fully charged. A lead-acid battery can be fully charged immediately after chemical formation, or after some 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 can be fully charged).

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

(XRD spectrum)
The XRD spectrum of the porous membrane (F) is measured by irradiating the surface of the porous membrane (F) with X-rays perpendicularly. The measurement sample is prepared by processing the portion of the porous membrane (F) facing the electrode material into a strip. For the porous membrane (F) having ribs, the base portion is processed into a strip so as not to include the ribs. The measurement and fitting of the XRD spectrum are performed under the following measurement 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, manufactured by Rigaku) was used.

(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. If the carbon material is layered, the thickness of the carbon material layer can be determined in the same manner.

The rib height is determined using the following procedure. First, ten random locations on the rib are selected in a cross-sectional photograph of the separator. Next, the rib height (height from the surface of the base) is measured at each of the ten selected locations. Next, the rib height is determined by averaging the heights measured at the ten locations.

(Oil content in porous membrane (F))
The portion of the separator facing the electrode material is processed into a strip to prepare a sample (hereinafter referred to as Sample A). At this time, the carbon material on the surface of the porous membrane (F) is removed by polishing to prepare the sample. For separators having ribs, Sample A is prepared by processing the base portion into a strip so as not to include the ribs.

Approximately 0.5 g of sample A is collected 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, thereby dissolving the oil contained in sample A into n-hexane. Next, the sample is removed from n-hexane, dried in the atmosphere at room temperature (a temperature of 20°C or higher and 35°C or lower), 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 porous membrane (F).
Oil content (mass%) = 100 x (m0 - m1) / m0

(Content of inorganic particles in porous membrane (F))
A portion of the sample A prepared in the same manner as above is taken, accurately weighed, placed in a platinum crucible, and heated with a Bunsen burner until no white smoke is emitted. Next, the obtained sample is heated in an electric furnace (in an oxygen stream, 550°C ± 10°C) for about 1 hour to incinerate, and the incinerated material is weighed. The mass ratio (percentage) of the incinerated material to the mass of sample A is calculated, and this is the inorganic particle content (mass%). The inorganic particle content is determined for 10 samples A, and the average value is calculated. The obtained average value is the inorganic particle content (inorganic particles other than carbon material) in the porous film (F).

(Content of penetrant in porous membrane (F))
A portion of sample A prepared in the same manner as above is taken and accurately weighed, and then dried for 12 hours or more at room temperature (a temperature of 20°C to 35°C) in a reduced pressure environment lower than atmospheric pressure. The dried product is placed in a platinum cell and set in a thermogravimetric measuring device, and the temperature is raised from room temperature to 800°C ± 1°C at a heating rate of 10 K/min. The weight loss when the temperature is raised 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 to the mass of sample B is calculated, and this is taken as the penetrant content (mass%). A Q5000IR manufactured by T.A. Instruments is used as the thermogravimetric measuring device. The penetrant content is determined for 10 samples A, and the average value is calculated. The obtained average value is taken as the penetrant content in the porous membrane (F).

(degree of curvature)
The terms in the above formula for determining the degree of tortuosity (density, total pore volume, permeability, and differential pore distribution) are determined by the following procedure. First, a portion of the porous membrane (F) facing the electrode material is cut into a size of 20 mm length x 5 mm width to prepare a sample (sample B). Next, the sample is measured using a mercury porosimeter under the following conditions to determine the above terms.
Mercury porosimeter: Autopore IV9510, manufactured by Shimadzu Corporation. Measurement pressure range: 4 psia (≒ 27.6 kPa) to 60,000 psia (≒ 414 MPa). Pore distribution: 0.01 μm to 50 μm.

(lead acid battery)
A lead-acid battery according to one aspect of the present invention includes at least one cell containing an electrode plate assembly and an electrolyte. The electrode plate assembly includes a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate. The separator is the lead-acid battery separator of this embodiment. Use of the separator of this embodiment can significantly improve the life performance and productivity of the lead-acid battery.

The lead-acid battery may be a valve-regulated (VRLA) battery, but a flooded (vented) battery is preferred.

The carbon material of the separator may be disposed on both of the two main surfaces of the porous membrane (F), or on the main surface facing the positive or negative electrode plate. For example, the carbon material of the separator may be disposed on the main surface facing the negative electrode plate, out of the two main surfaces of the porous membrane (F). When water electrolysis occurs during charging, oxygen gas is generated on the positive electrode side. By disposing the carbon material on the negative electrode plate side, it is possible to prevent oxygen gas from being generated within the separator and oxidizing the porous membrane (F).

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 positive and negative electrode plate has a lug for connecting to an external terminal, and in a liquid battery, the lug is provided on the top of the electrode plate so as to protrude upward. Examples of the components of a lead-acid battery are described below.

(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 current collector and a positive electrode material. The positive electrode material is held by the positive electrode current collector. The positive electrode material is the portion of the positive electrode plate excluding the positive electrode current 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.

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 grid-shaped current collector as the positive electrode current collector, as this makes it easier to support the positive electrode material.

In terms of corrosion resistance and mechanical strength, Pb-Ca alloys and Pb-Ca-Sn alloys are preferred as lead alloys for use in the positive electrode current collector. 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.

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

Examples of reinforcing materials include fibers (inorganic fibers, organic fibers, etc.). Examples of resins (or polymers) that make up 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 ethers, cellulose esters, etc.)). Celluloses also include rayon.

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

Unformed paste-type positive electrode plates are obtained by filling a positive electrode current collector with 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, if necessary, other additives (such as reinforcing materials), and kneading the mixture.

Positive plates are obtained by chemically forming unformed positive plates. Chemical formation can be carried out by immersing a group of plates including unformed positive plates in an electrolyte containing sulfuric acid in a lead-acid battery container and then charging the group of plates. However, chemical formation can also be carried out before assembling the lead-acid battery or the group of plates.

(negative electrode 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.

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. In electrode plates using current collectors formed by expanding, the corners of the electrode plate may be deformed due to interference with the manufacturing equipment during the electrode plate manufacturing process. When such electrode plates are used to manufacture a lead-acid battery, the corners of the electrode plate are likely to break through the separator in the early stages, causing a short circuit. Because the separator of this embodiment has high strength, it can suppress initial short circuits caused by electrode plate deformation, even when combined with electrode plates using expanded lattices. At least one of the positive electrode plate and the negative electrode plate may contain expanded lattices.

The lead alloy used in the negative electrode current collector may be any of a Pb-Sb alloy, a Pb-Ca alloy, or a Pb-Ca-Sn alloy. These lead or lead alloys may further contain at least one additional 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.

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 organic shrinkage inhibitors, carbonaceous materials, barium sulfate, etc. The negative electrode material may also contain other additives (such as reinforcing materials) as needed.

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

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

Examples of carbonaceous materials in the negative electrode material include carbon black, graphite (artificial graphite, natural graphite, etc.), hard carbon, and soft carbon. The negative electrode material may contain one type of carbonaceous material, or two or more types.

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

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

Examples of reinforcing materials include fibers (inorganic fibers, organic fibers (such as organic fibers made of resin as described for reinforcing materials for positive electrode materials)).

The reinforcing material content in the negative electrode material is, for example, 0.03 mass% or more. Also, the reinforcing material content in the negative electrode material is, for example, 0.5 mass% or less.

The negative electrode active material in a charged state is spongy lead, but unformed negative plates are usually made using lead powder.

A negative electrode plate can be formed by filling a negative electrode current collector with negative electrode paste, aging and drying it to produce an unformed negative electrode plate, and then chemically forming the unformed negative electrode plate. The negative electrode paste is made by adding water and sulfuric acid to lead powder, an organic shrinkage inhibitor, and various additives as needed, and kneading them. During the aging process, it is preferable to age the unformed negative electrode plate at a temperature higher than room temperature and at high humidity.

Formation can be performed by immersing a plate assembly containing unformed negative plates in an electrolyte containing sulfuric acid in a lead-acid battery container and then charging the plate assembly. However, formation can also be performed before assembling the lead-acid battery or plate assembly. Formation produces spongy lead.

There is no particular limit to the number of positive and negative electrode plates contained in one cell. However, the separator of this embodiment is particularly suitable for use in lead-acid batteries in which a single cell contains a large number of positive and negative electrode plates. When a single cell contains a total of 12 or more positive and negative electrode plates, the tensile strength of the separator becomes particularly important.

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

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.

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 in a fully charged lead-acid battery.

(1) Life Performance The life performance (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) The storage battery is connected to a life test device and the following discharge and charge cycles are continuously repeated. This discharge and charge cycle is considered to be one life (one cycle).
Discharge: 60 seconds ±1 second at a discharge current of 25.0 A ±0.1 A. Charge: 600 seconds ±1 second at a charge voltage of 14.80 V ±0.03 V (limited current of 25.0 A ±0.1 A). (c) During the test, leave the battery for 56 hours every 480 cycles, then discharge it continuously for 30 seconds at the rated cold cranking current of 390 A, and record the voltage at 30 seconds. Then, charge it as 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 time (hereinafter sometimes referred to as the "number of cycles N") is used as an index of life performance.
The rated cold cranking current is a measure of engine starting performance, and is a discharge current determined so that the voltage at 30 seconds after discharge at a temperature of -18°C ± 1°C is 7.2V or higher.

(2) Tensile Strength The tensile strength of a separator is measured by the following procedure. First, a separator is cut into a size of 10 mm x 40 mm to obtain a test piece. A tensile test is performed on this test piece using a precision universal testing machine (Shimadzu Corporation, product name: AGS-X) under conditions of a chuck distance of 20 mm, a tensile speed of 5 mm/min, and 25°C, and the stress at break is taken as the tensile strength.

Below, an example of a lead-acid battery according to this embodiment will be described in detail with reference to the drawings. The components described above can be applied to the components of the example lead-acid battery described below. Furthermore, the components of the example lead-acid battery described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment. Furthermore, in the embodiment described below, components that are not essential for the lead-acid battery according to this embodiment may be omitted.

Figure 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 assembly 11 and an electrolyte (not shown). The battery case 12 is divided into multiple cell chambers 14 by partitions 13. Each cell chamber 14 contains one plate assembly 11. The opening of the battery case 12 is closed by a lid 15 equipped with a negative terminal 16 and a positive 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 also have the function of venting gas generated in the cell chamber 14 to the outside of the battery.

Each electrode plate group 11 is constructed 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 separator's shape 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 pole 7. The positive electrode pole 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 pole 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 pole 9 is connected to a negative electrode terminal 16 outside the lid 15. Each through-connector 8 passes through a through-hole in the partition wall 13, connecting the electrode plate groups 11 of adjacent cell chambers 14 in series.

The items described in this specification may be combined in any manner.

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

(Experimental Example 1)
In Experimental Example 1, a plurality of separators and a plurality of lead-acid batteries were fabricated in the following procedure.

(1) Preparation and evaluation of separator The resin composition that comprises 100 mass parts of polyethylene, 160 mass parts of silica particles, 80 mass parts of paraffin oil as pore-forming agent, and 2 mass parts of penetrant is extruded into sheet, and then stretched, by removing part of pore-forming agent, prepare porous membrane with rib on one side.At this time, the cooling speed of extruded sheet and the stretching ratio are adjusted so that the ratio R of porous membrane that is obtained by the above-mentioned procedure is the value shown in Table 1.

Next, a carbon material was placed on one main surface (the main surface facing the negative electrode plate) of each of the formed porous membranes using the following procedure. First, a mixture of silica and carbon material was deposited on the separator, and then a pure carbon layer was deposited on top of that using roller coating or spray coating. In this way, the carbon material was placed. The thickness of the carbon material was the same for each porous membrane. Specifically, it was 10 μm. Using the above procedure, multiple separators with different porous membrane ratios R were produced.

The oil content of the separator determined using the procedure described above was 11-18% by mass, and the silica particle content was 60% by mass. The rib height determined using the procedure described above was 0.6 mm. The separator thickness (thickness of the base portion) determined using the procedure described above is shown in Table 1.

The sheet-like separator obtained by the above procedure was folded in half so that the ribs were located on the outer surface to form a bag. The overlapping ends were then crimped together to obtain a bag-like separator. The inner surface of the bag-like separator is the surface on which the carbon material is located.

The ratio R of porous membrane (F) in the separator, oil content, silica particle content, separator thickness, and rib height were determined for the separator before fabrication into a lead-acid battery. These values are approximately the same as those measured using the procedure described above for a separator removed from a fabricated lead-acid battery.

(2) Preparation of Positive Electrode Plate: A positive electrode paste was prepared by mixing lead oxide, a 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 the resulting plate was aged and dried to obtain an unformed positive electrode plate measuring 100 mm in width, 110 mm in height, and 1.6 mm in thickness.

(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, followed by aging and drying to obtain an unformed negative electrode plate measuring 100 mm in width, 110 mm in height, and 1.3 mm in thickness. 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.

(4) Preparation of lead acid battery Unformed negative electrode plates were housed in a pouch-shaped separator and stacked with positive electrode plates to form an electrode plate assembly of seven unformed negative electrode plates and six unformed positive electrode plates.

The positive and negative plate lugs 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) equal to 1/5 of the Ah value listed in the rated capacity)). Six plate groups were connected in series inside the battery case.

Aqueous sulfuric acid solution was used as the electrolyte. The specific gravity of the electrolyte after formation at 20°C was 1.285.

Figure 2 shows the XRD spectrum of the porous membrane used in the separator of Battery A1, measured using the procedure described above. As shown in Figure 2, a diffraction peak corresponding to the (110) plane of the polyethylene crystalline region was observed in the 2θ range of 21.5° to 22.5°, and a diffraction peak corresponding to the (200) plane was observed in the 2θ range of 23° to 24.5°. A broad halo due to the amorphous region was observed in the wide 2θ range of 17° to 27°.

The resulting lead-acid batteries were used to evaluate their lifespan performance (number of cycles N) using the procedure previously described. Lifespan performance was evaluated as the relative value of the number of cycles N for each lead-acid battery. The relative value of the number of cycles N is the value when the number of cycles N for battery CA1 is set to 90. The evaluation results are shown in Table 1. Batteries A1 to A4 are inventive examples, and battery CA1 is a comparative example.

As shown in Table 1, when the porous membrane ratio R was 0.70 or higher, the life performance was significantly improved compared to when the ratio R was 0.65. This is thought to be due to the high crystallinity of the porous membrane, which improved the oxidation resistance of the separator.

(Experimental Example 2)
In Experimental Example 2, lead-acid batteries were fabricated and evaluated in the same manner as in Experimental Example 1, except that the separator was changed. Specifically, a plurality of separators were fabricated in the same manner as in Experimental Example 1, except that the manufacturing conditions were changed to change the porous membrane ratio R and the separator thickness. The carbon material was arranged under the same conditions as in the separator of Experimental Example 1.

The produced separators and lead-acid batteries were evaluated in the same manner as in Experimental Example 1. The evaluation results are shown in Table 2. Batteries B1 to B12 are invention examples, and batteries CB1 to CB4 are comparative examples. The life performance (number of cycles N) in Table 2 is a relative value when the number of cycles N for battery B1 is set to 100.

As shown in Table 2, by making the separator thickness 100 μm or more, it was possible to significantly improve the lifespan performance. If the separator is thin (if the porous membrane is thin), it is thought that the resin does not flow well around the mold during resin molding to form the porous membrane, resulting in large variations in thickness and pore size, and partial cracking (separator tears). On the other hand, if the separator is 100 μm or thicker (porous membrane thickness is 90 μm or thicker), the resin flows better and a uniform porous membrane is obtained. In addition, by placing a carbon material on the surface of the porous membrane, the tensile strength of the separator is significantly improved, as described below. This is thought to be why the lifespan characteristics are significantly improved.

(Experimental Example 3)
In Experimental Example 3, multiple separators were produced under different production conditions. Specifically, multiple separators were produced using the same method as in Experimental Example 1, except that the production conditions were changed to change the porous membrane ratio R and the separator thickness, and the presence or absence of a carbon material was changed. The produced separators were evaluated in the same manner as in Experimental Example 1.

The tensile strength of the produced separators was also measured using the method described above. The separator evaluation results are shown in Tables 3 and 4. Separators S1 to S10 are inventive examples, and separators CS1 to CS12 are comparative examples. Note that the tensile strength is a relative value, with the tensile strength of separator CS1 set at 100.

The results of Table 3 are shown in Figure 3, and the results of Table 4 are shown in Figure 4. As shown in Table 3 and Figure 3, by placing a carbon material on the surface and setting the porous membrane ratio R to 0.70 or more, the tensile strength of the separator was significantly increased. As shown in Table 4 and Figure 4, by placing a carbon material on the surface and setting the thickness to 100 μm or more, the tensile strength of the separator was significantly increased.

As shown in Figure 3, the effect of increasing the ratio R on increasing tensile strength was greater in separators with carbon material disposed therein than in separators without carbon material disposed therein. As shown in Figure 4, the effect of increasing tensile strength on separators with carbon material disposed therein by increasing the separator thickness was greater than in separators without carbon material disposed therein. The reasons for these are not clear, but it is thought that disposing carbon material on the surface of the porous membrane has some kind of synergistic effect.

The present invention can be used for lead-acid batteries and separators used therein. The lead-acid battery separator of the present invention is suitable, for example, for 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). Note that these uses are merely examples. The uses of the lead-acid battery separator and lead-acid battery of the present invention are not limited to these.

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 pole, 8: Through-connector, 9: Negative electrode pole, 11: Plate group, 12: Battery case, 13: Partition, 14: Cell chamber, 15: Lid, 16: Negative electrode terminal, 17: Positive electrode terminal, 18: Vent plug

Claims (8)

A separator for a lead-acid battery,
a porous membrane containing polyolefin and a carbon material disposed on a surface of the porous membrane,
the porous film includes a crystalline region and an amorphous region;
In an X-ray diffraction spectrum of the porous film, the ratio R represented by A ₁ /(A ₁ +A ₂ ) is 0.70 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,
The polyolefin contains at least ethylene units,
the first diffraction peak corresponds to the (110) plane of the crystalline region;
The separator for a lead-acid battery , wherein the second diffraction peak corresponds to the (200) plane of the crystalline region . The lead-acid battery separator according to claim 1, having a thickness of 100 μm or more and 300 μm or less. The lead-acid battery separator according to claim 1 or 2, wherein the ratio R is 0.90 or less. The lead-acid battery separator according to any one of claims 1 to 3, containing oil. The lead-acid battery separator according to any one of claims 1 to 4, wherein the tortuosity of the pores of the porous membrane is 5 or more. 6. The lead-acid battery separator according to claim 1 , wherein the carbon material is at least one selected from the group consisting of conductive carbon black and conductive carbon fiber. 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 6 . The lead-acid battery according to claim 7 , wherein the carbon material of the separator is disposed on one of two main surfaces of the porous membrane that is closer to the negative electrode plate.