JP7703973B2 - Lead-acid battery separator 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 vehicles, industrial applications, and a variety of other applications. Lead-acid batteries 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 that contains 5 to 30% of the oil by weight, obtained by heating and melting a raw material composition consisting of a mixture of 20 to 60% by weight of polyolefin resin, 80 to 40% by weight of inorganic powder, and 40 to 240% by weight of mineral oil relative to the mixture, while kneading the raw material composition and forming it into a sheet having ribs. The sheet is then immersed in an immersion bath of an organic solvent capable of dissolving the oil to extract and remove a portion of the oil, and then heated and dried. The ribbed separator for lead-acid batteries contains 5 to 30% of the oil by weight, and the difference in the oil content between the rib portion and the base portion of the separator is set to 5% by weight 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 the porous membrane and/or the fibrous mat."

JP 2001-338631 A JP 2020-533741 A

Current lead-acid batteries, such as those used in vehicles with idling stop systems, are required to perform under different operating conditions than lead-acid batteries of the past. In response to this, there has always been a demand to improve the lifespan performance of lead-acid batteries and to improve productivity. Therefore, new technologies that can contribute to improving lifespan performance and productivity are required.

One aspect of the present disclosure relates to a separator for a lead-acid battery, the separator for a lead-acid battery 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, the porous membrane having a crystallinity of 20% or more, expressed as 100× _Ic /( _Ic + _Ia ), in an X-ray diffraction spectrum, where _Ic is the integrated intensity of a diffraction peak having a maximum peak height among the diffraction peaks corresponding to the crystalline region, and _Ia is the integrated intensity of a halo corresponding to the amorphous region.

Another aspect of the present disclosure relates to a lead-acid battery. The lead-acid battery includes at least one cell including an electrode plate group and an electrolyte, the electrode plate group 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 one 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. 13 is a graph showing some of the results of Experimental Example 3. 13 is a graph showing another part of the results of Experimental Example 3.

Below, examples of embodiments according to the present disclosure are described, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be exemplified, but other numerical values and other materials may be applied as long as the effects of the present disclosure are obtained. 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 "numerical value A or more and numerical value B or less." In the following description, when a lower limit and an upper limit are exemplified for numerical values of specific physical properties or conditions, any of the exemplified lower limits can be arbitrarily combined with any of the exemplified upper limits, as long as the lower limit is not equal to or greater than 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. The porous membrane may be referred to as a "porous membrane (F)" below. The porous membrane (F) includes a crystalline region and an amorphous region. In the X-ray diffraction spectrum of the porous membrane (F), the crystallinity expressed by 100×I _c /(I _c +I _a ) is 20% or more. I _c is the integrated intensity of a diffraction peak (hereinafter, sometimes referred to as a "first diffraction peak") having the maximum peak height among the diffraction peaks corresponding to the crystalline region. I _a is the integrated intensity of a halo corresponding to the amorphous region.

Lead-acid batteries are sometimes used under harsh conditions. One of the most common uses of 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. In addition, 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 a higher level of life performance (for example, high-temperature overcharge life performance) than before.

One of the factors that shorten the life of a lead-acid battery is the oxidation deterioration of the separator. If a rib is provided on the surface of the separator that faces the positive plate, a gap is formed between the separator and the positive plate. Therefore, by providing the rib, the oxidation deterioration of the separator tends to be reduced. However, as the performance of lead-acid batteries improves, it is becoming more common to accommodate a large number of thin plates per cell compared to the past. Therefore, simply providing the rib is not sufficient to suppress the oxidation deterioration of the separator. Even when the separator contains oil, the oxidation deterioration of the separator can be reduced to some extent. However, since the insulating oil blocks the pores of the separator, the resistance of the separator increases and the reactivity of the plate tends to decrease. Therefore, in a high-performance lead-acid battery, it is difficult to increase the oil content in the separator. Thus, with conventional separators, it is difficult to improve the life performance of a lead-acid battery to a high level.

The degree of crystallinity of the porous membrane (F) in this embodiment is 20% or more, so the porous membrane (F) has high oxidation resistance. Unlike the case where oxidation resistance is increased by oil, when oxidation resistance is increased by crystallinity, there is almost no disadvantage such as an increase in resistance. Therefore, even in high-performance lead-acid batteries, excellent life performance can be ensured.

Lead-acid battery separators have a certain degree of thickness, unlike separators for lithium-ion secondary batteries. In addition, lead-acid batteries have a lower positive electrode potential during overcharging than lithium-ion secondary batteries, so that sufficient oxidation resistance can be ensured by ribs, oil, etc. in conventional usage environments or forms. In addition, the thicker the separator, the more difficult it tends to be to increase the crystallinity, and as the crystallinity increases, the separator tends to become hard and brittle. From this perspective, the crystallinity of separators for lead-acid batteries has not been controlled in the past. The crystallinity of separators for conventional lead-acid batteries was relatively low, about 18% or less. In contrast to this conventional common sense, in this embodiment, the crystallinity of the porous film (F) is set to 20% or more. This allows the life performance (for example, high-temperature overcharge life performance) to be greatly improved.

The lifespan of a lead-acid battery is also significantly reduced by uneven electrolyte concentration (stratification). In a lead-acid battery, the electrolyte concentration at the top of the battery can be lower than that at the bottom, 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) in 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 to generate gas. The generated gas agitates the electrolyte, suppressing stratification of the electrolyte.

However, when water electrolysis occurs on the surface of the separator, it is important to suppress oxidation of the separator due to the oxygen gas that is generated. The separator of this embodiment uses a resin film (F) with a high degree of crystallinity, making it possible to suppress oxidation of the separator.

In addition, efforts are being made to improve the performance of lead-acid batteries by using many thin plates. Lead-acid batteries that use many thin plates have a high rate of defects during manufacturing due to insufficient separator strength. For this reason, 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 the 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 performance and high productivity.

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 deterioration of the separator is further enhanced, and the life performance can be further improved.

The degree of crystallinity of the porous membrane (F) is preferably 40% or less. In this case, it is easy to ensure the flexibility of the separator and it is easy to manufacture.

It is preferable that the separator (or porous membrane (F)) contains oil. In this case, the effect of suppressing oxidative deterioration of the separator is further enhanced, ensuring a longer life performance.

The porous film (F) preferably contains a polyolefin, and more preferably contains a polyolefin containing at least ethylene units. Such separators are prone to oxidative deterioration, but the crystallinity can be increased relatively easily. 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.

(Carbon materials)
As the carbon material, a carbon material having electrical conductivity can be used. Examples of the carbon material having electrical conductivity include graphite, activated carbon, carbon black, carbon fiber, carbon nanotube, etc. Examples of the conductive carbon black include acetylene black, ketjen black, high surface area carbon black, etc. From the viewpoint of productivity, it is preferable to use carbon black, for example, it is preferable to use acetylene black, high surface area carbon black, 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 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 on the positive electrode plate side or the main surface on the negative electrode plate side), 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) on the negative electrode plate side.

The carbon material may be arranged in a layer so as to cover the main surface of the porous membrane (F), or may be arranged in a non-layered form. Examples of non-layered forms include a form in which the carbon material is arranged in the form of dispersed islands. 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 the carbon material in the separator (the carbon material disposed on the surface of the porous membrane (F)) may be 2% by mass or more, and is preferably 3% by mass or more. By making the content 2% by mass or more, it is possible to particularly increase the oxidation resistance and strength of the separator. The content may be 40% by mass or less, or 30% by mass or less.

(Porous membrane (F))
The porous film (F) includes a crystalline region in which the molecules of the constituent material of the porous film (F) are arranged relatively regularly (i.e., highly ordered), and an amorphous region in which the molecules are arranged less ordered. Therefore, in the XRD spectrum of the porous film (F), a diffraction peak due to the crystalline region is observed, and scattered light due to the amorphous region is observed as a halo. In the XRD spectrum of the porous film (F), the crystallinity expressed by 100×I _c /(I _c +I _a ) is 20% or more, so that excellent life performance can be obtained. Here, I _c is the integrated intensity of the diffraction peak (first diffraction peak) with the maximum peak height among the diffraction peaks corresponding to the crystalline region, and I _a is the integrated intensity of the halo corresponding to the amorphous region.

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

The crystallinity is 20% or more, and from the viewpoint of ensuring higher life performance, it may be 23% or more or 25% or more. The crystallinity may be 40% or less, 35% or less, or 30% or less. When the crystallinity is in such a range, it is easy to ensure the flexibility of the separator, and it is easy to manufacture.

The crystallinity of the porous membrane (F) may be 20% or more and 40% or less, 20% or more and 35% or less, or 20% or more and 30% or less. In these ranges, the lower limit may be 23% or more or 25% or more.

The integrated intensities of the diffraction peak and the halo are obtained by fitting the diffraction peak due to the crystalline region and the halo due to the amorphous region in the XRD spectrum of the porous film (F). The crystallinity is calculated from the above formula using the obtained integrated intensity _Ic of the first diffraction peak and the integrated intensity _Ia of the halo.

The porous membrane (F) contains a polymer material (hereinafter also referred to as a base polymer). Since the porous membrane (F) contains a crystalline region, the base polymer usually contains a crystalline polymer. The porous membrane (F) contains, for example, a polyolefin. A polyolefin is a polymer that contains at least an olefin unit (i.e., a polymer that contains at least a monomer unit derived from an olefin).

As the base polymer, polyolefin may be used in combination with other base polymers. The ratio of polyolefin to the entire base polymer contained in the porous film (F) is, for example, 50% by mass or more, 80% by mass or more, or 90% by mass or more. The ratio of polyolefin is, for example, 100% by mass or less. The base polymer may be composed of polyolefin only. When the ratio of polyolefin is this high, the oxidation resistance of the porous film (F) tends to be low, but even in such a case, a high life performance can be ensured by setting the crystallinity within the above range.

Polyolefins include, for example, homopolymers of olefins, 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. 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 and copolymerizable with an olefin.

The polyolefin may be, for example, a polymer containing at least a C _2-3 olefin as a monomer unit. The C _2-3 olefin may be at least one selected from the group consisting of ethylene and propylene. The polyolefin may be, for example, polyethylene, polypropylene, or a copolymer containing a C _2-3 olefin as a monomer unit (for example, an ethylene-propylene copolymer). Among the polyolefins, it is preferable to use a polyolefin containing at least an ethylene unit (polyethylene, ethylene-propylene copolymer, etc.). A polyolefin containing an ethylene unit (polyethylene, ethylene-propylene copolymer, etc.) may be used in combination with another polyolefin.

The separator (more specifically, the porous membrane (F)) preferably contains oil. When the separator contains oil, the effect of suppressing oxidative deterioration of the separator can be further enhanced, and therefore a higher life performance can be ensured. Oil refers to a hydrophobic substance that is liquid at room temperature (a temperature between 20°C and 35°C) and separates from water. Oil includes naturally derived oils, mineral oils, and synthetic oils. Mineral oils, synthetic oils, etc. are preferred as 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.

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

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

The thickness of the separator is 100 μm or more. From the viewpoint of obtaining a 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 viewpoint of suppressing 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 part of the separator facing the electrode material. In the case where the separator has a base portion and a rib erected from at least one surface of the base portion, the thickness of the separator is the average thickness of the base portion. In the case where 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 height of the ribs may be 0.05 mm or more. The height of the ribs may be 1.2 mm or less. The height of the ribs is the height of the part that protrudes from the surface of the base part (protrusion height).

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

The carbon material is placed on the surface of the formed porous membrane (F). There is no particular limitation on the method of placing 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 liquid containing a carbon material to the surface of the porous membrane (F). There is no particular limitation on the application method, and a doctor blade method, a roller coating method, a spray coating method, a dipping method, a vapor deposition method, or other printing methods may be used. Examples of dispersion liquids containing a carbon material include dispersion liquids 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 placed on the surface of the porous membrane (F) can be adjusted by controlling the amount of carbon material applied.

The porous membrane (F) is 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 resin composition, and then removing at least a portion of the pore-forming agent. By removing at least a portion of the pore-forming agent, fine pores are formed in the matrix of the base polymer. After removing the pore-forming agent, the sheet-shaped porous membrane (F) is dried as necessary. For example, the crystallinity is adjusted by adjusting at least one selected from the group consisting of the cooling rate of the sheet during extrusion molding, the stretching ratio during stretching, and the temperature during drying. For example, the crystallinity tends to increase when the sheet is rapidly cooled during extrusion molding, the stretching ratio is increased, or the temperature during drying is decreased. The stretching process may be performed by biaxial stretching, but is usually performed by uniaxial stretching. The sheet-shaped separator may be folded into a bellows shape or processed into a bag shape as necessary. When a separator in which carbon material is placed on only one main surface of the porous membrane (F) is processed into a bag shape, the carbon material is placed on either the inner surface or the outer surface of the bag.

In a separator having 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 is molded into a sheet or after the pore-forming agent is removed.

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, and the effect of suppressing oxidative deterioration is further enhanced. The pore-forming agent may be used alone or in combination of two or more types. 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.

As a liquid pore-forming agent, the above-mentioned oil is preferable. As a solid pore-forming agent, for example, a polymer powder can be mentioned.

The amount of pore-forming agent in the porous membrane (F) may vary depending on the type of pore-forming agent. The amount of pore-forming agent in the porous membrane (F) 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.

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, according to 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, the extraction conditions (extraction time, extraction temperature, rate at which the solvent is supplied, etc.), etc.

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 types.

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 that are placed on the surface of the porous membrane (F).

As the inorganic particles, for example, ceramic particles are preferable. The ceramic constituting the ceramic particles is, for example, at least one selected from the group consisting of silica, alumina, and titania.

The content of inorganic particles other than the carbon material 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.

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

The separator removed from the lead-acid battery is washed and dried according to the following procedure. The separator removed from the lead-acid battery 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 stand for 16 hours or more in an environment of 25°C ± 5°C to dry. 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 by JIS D 5301:2019. More specifically, the fully charged state is a state in which a lead-acid battery is charged in a water tank at 25°C ± 2°C with a current (A) that is 1/10 of the value listed as the rated capacity until the terminal voltage (V) during charging measured every 15 minutes or the electrolyte density converted to a temperature of 20°C shows a constant value with three significant digits three consecutive times. 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 prepared and is fully charged. A lead-acid battery may be fully charged immediately after chemical preparation, or after a period of time has passed since chemical preparation (for example, a lead-acid battery that is in use (preferably in the early stages of use) after chemical preparation may be fully charged).

In this specification, a battery in its early stages of use is one 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 in a direction perpendicular to the surface. The measurement sample is prepared by processing the part of the porous membrane (F) facing the electrode material into a strip shape. For the porous membrane (F) having ribs, the base part is processed into a strip shape so as not to include the ribs to prepare the sample. The measurement and fitting of the XRD spectrum are performed under the following measurement conditions.

(Measurement conditions)
Measurement device: RINT-TTR2, manufactured by Rigaku 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.

(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 measured values. When the carbon material is layered, the thickness of the carbon material layer is determined in a similar manner.

The rib height is determined using the following procedure. First, 10 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 10 selected locations. Next, the rib height is determined by averaging the heights measured at the 10 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 a separator 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 mass (m0) of the sample. The weighed sample A is placed in a glass beaker of an appropriate size, and 50 mL of n-hexane is added. Next, ultrasonic waves are applied to the sample together with the beaker for about 30 minutes to dissolve the oil contained in sample A into n-hexane. Next, the sample is taken out of n-hexane, dried in air at room temperature (temperature of 20°C or higher and 35°C or lower), and then weighed to determine the mass (m1) of the sample after removing the oil. Then, the oil content is calculated by the following formula. The oil content of 10 samples A is calculated, 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 part of the sample A prepared in the same manner as above is taken, weighed accurately, and then placed in a platinum crucible and heated with a Bunsen burner until no white smoke is generated. Next, the obtained sample is heated in an electric furnace (in oxygen flow, 550°C ± 10°C) for about 1 hour to be incinerated, and the incinerated material is weighed. The ratio (percentage) of the mass of the incinerated material to the mass of sample A is calculated, and this is the content (mass%) of the inorganic particles. The content of the inorganic particles is calculated for 10 pieces of sample A, and the average value is calculated. The obtained average value is the content of inorganic particles (inorganic particles other than carbon materials) in the porous film (F).

(Content of penetrant in porous membrane (F))
A part of sample A prepared in the same manner as above is taken, accurately weighed, and then dried for 12 hours or more at room temperature (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 heated from room temperature to 800°C ± 1°C at a heating rate of 10K/min. The weight loss amount when heated 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 the content (mass%) of the penetrant is taken as the above. As the thermogravimetric measuring device, a Q5000IR manufactured by T. A. Instruments is used. The content of the penetrant is determined for 10 samples A, and the average value is calculated. The obtained average value is taken as the content of the penetrant in the porous membrane (F).

(lead acid battery)
A lead-acid battery according to one aspect of the present invention includes at least one cell including an electrode plate group 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. The separator is the separator for a lead-acid battery according to the present embodiment. By using the separator according to the present embodiment, the life performance and productivity of the lead-acid battery can be significantly improved.

The lead acid battery may be a valve regulated battery (VRLA type battery), but a flooded battery (vented type 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 on the positive or negative electrode plate side. For example, the carbon material of the separator may be disposed on the main surface on the negative electrode plate side 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 suppress the generation of oxygen gas in the separator and the oxidation of the porous membrane (F).

In this specification, the up-down direction of a lead-acid battery or the components of a lead-acid battery (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 electrodes 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 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 called 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 may be formed 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.

As the lead alloy used for the positive electrode current collector, a Pb-Ca alloy or a Pb-Ca-Sn alloy is preferred 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.

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

Examples of reinforcing materials include fibers (inorganic fibers, organic fibers, etc.). Examples of resins (or polymers) that make up the 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.

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 a positive electrode paste, and then aging and drying it. The positive electrode paste is prepared by adding water and sulfuric acid to lead powder, an antimony compound, and other additives (such as reinforcing materials) as necessary, and kneading them.

A positive plate is obtained by chemically forming an unformed positive plate. Chemical formation can be performed by charging a plate group including an unformed positive plate while the plate group is immersed in an electrolyte containing sulfuric acid in a lead-acid battery container. However, chemical formation may also be performed before assembling the lead-acid battery or the plate group.

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

The negative electrode collector can be formed in the same manner as the positive electrode collector. At least one of the positive electrode collector and the negative electrode collector may be a collector formed by expanding. In a plate using a collector formed by expanding, the corners of the plate may be deformed due to interference with the manufacturing equipment during the plate manufacturing process. When a lead-acid battery is manufactured using such a plate, the corners of the plate tend to break through the separator in the early stages, causing a short circuit. Since the separator of this embodiment has high strength, it is possible to suppress an initial short circuit caused by deformation of the plate even when combined with a plate using an expanded grid. At least one of the positive electrode plate and the negative electrode plate may include an expanded grid.

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

The negative electrode material contained in the negative plate contains a negative electrode active material (lead or lead sulfate) that develops 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 contain other additives (such as reinforcing materials) as necessary.

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, soft carbon, etc. The negative electrode material may contain one type of carbonaceous material, or two or more types.

The content of the carbonaceous material in the negative electrode material is, for example, 0.1 mass% or more. The content of the carbonaceous material may be, for example, 3 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 the reinforcing material of the positive electrode material)).

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

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

The negative electrode plate can be formed by filling a negative electrode current collector with a negative electrode paste, maturing 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 necessary, and kneading them. In the maturation process, it is preferable to mature the unformed negative electrode plate at a temperature higher than room temperature and at high humidity.

The chemical formation can be carried out by immersing the plate group, including the unformed negative plate, in an electrolyte containing sulfuric acid in a lead-acid battery container and then charging the plate group. However, chemical formation can also be carried out before assembling the lead-acid battery or the plate group. Chemical formation produces spongy lead.

There is no particular limit to the number of positive and negative 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 many positive and negative plates. When a total of 12 or more positive and negative plates are contained in one cell, the tensile strength of the separator becomes particularly important.

(electrolyte)
The electrolyte is an aqueous solution containing sulfuric acid. The electrolyte may be gelled as 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 of a lead-acid battery in a fully charged state.

(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 performed according to the following procedure.
(a) The battery shall be placed 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 25.0 A ± 0.1 A) (c) During the test, leave the battery for 56 hours every 480 cycles, then perform continuous discharge for 30 seconds at a rated cold cranking current of 390 A, and record the voltage at the 30th second. Then, perform charging as in (b). These discharges and charges are also added to 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) falls to 7.2 V or less and does not rise again, and the total number of cycles at this point (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 when discharged at a temperature of -18°C ± 1°C, the voltage at 30 seconds is 7.2V or higher.

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

Below, an example of a lead-acid battery according to this embodiment will be specifically described 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 group 11 and an electrolyte (not shown). The inside of the battery case 12 is divided into a plurality of cell chambers 14 by partitions 13. Each cell chamber 14 contains one plate group 11. The opening of the battery case 12 is closed by a lid 15 that includes a negative terminal 16 and a positive terminal 17. The lid 15 is provided with a liquid vent plug 18 for each cell chamber. When rehydrating, the liquid vent plug 18 is removed and rehydration liquid is replenished. The liquid vent plug 18 may have a function of discharging gas generated in the cell chamber 14 to the outside of the battery.

Each electrode plate group 11 is formed by stacking a plurality of negative electrode plates 2 and positive electrode plates 3 with separators 4 interposed therebetween. Here, a bag-shaped separator 4 that houses the negative electrode plates 2 is shown, but the shape of the separator is not particularly limited. In the cell chamber 14 located at one end of the battery case 12, the negative electrode shelf portion 6 that connects the plurality of negative electrode plates 2 in parallel is connected to the through connector 8, and the positive electrode shelf portion 5 that connects the plurality of positive electrode plates 3 in parallel is connected to the positive electrode column 7. The positive electrode column 7 is connected to a positive electrode terminal 17 outside the lid 15. In the cell chamber 14 located at the other end of the battery case 12, the negative electrode column 9 is connected to the negative electrode shelf portion 6, and the through connector 8 is connected to the positive electrode shelf portion 5. The negative electrode column 9 is connected to the 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 the adjacent cell chambers 14 in series.

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

[Example]
The present invention will be described in detail 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 produced in the following procedure.

(1) Preparation and evaluation of separator The resin composition containing 100 parts by weight of polyethylene, 160 parts by weight of silica particles, 80 parts by weight of paraffin oil as pore-forming agent, and 2 parts by weight of penetrant is extruded into sheet, stretched, and then a part of the pore-forming agent is removed to prepare a porous membrane with ribs on one side.At this time, the cooling speed of the extruded sheet and the stretching ratio are adjusted so that the crystallinity of the porous membrane 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 on the negative electrode plate side) of each of the formed porous films in 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 by roller coating or spray coating. In this manner, the carbon material was placed. The thickness of the carbon material was the same for each porous film. Specifically, it was 10 μm. Using the above procedure, multiple separators with different degrees of crystallinity of the porous film were produced.

The oil content of the separator determined by the above-mentioned procedure was 11-18% by mass, and the silica particle content was 60% by 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 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. Next, the overlapping ends were crimped together to obtain a bag-like separator. The inner surface of the bag-like separator was the surface on which the carbon material was located.

The crystallinity of the porous membrane (F) in the separator, the oil content, the silica particle content, the separator thickness, and the rib height are values determined for the separator before the lead-acid battery was fabricated. These values are approximately the same as the values measured by the procedure described above for the separator removed from the lead-acid battery after fabrication.

(2) Preparation of 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 lattice made of a Pb-Ca-Sn alloy not containing antimony, and aged and dried to obtain an unformed positive electrode plate having a width of 100 mm, a height of 110 mm and a thickness of 1.6 mm.

(3) Preparation of negative electrode plate Lead oxide, carbon black, barium sulfate, lignin, reinforcing material (synthetic resin fiber), water and sulfuric acid were mixed to prepare a negative electrode paste. The negative electrode paste was filled into the mesh of an expanded lattice made of an antimony-free Pb-Ca-Sn alloy, and aged and dried to obtain an unformed negative electrode plate with a width of 100 mm, a height of 110 mm and a thickness of 1.3 mm. The amounts of carbon black, barium sulfate, lignin and synthetic resin fiber used were adjusted so that the contents of each component in the negative electrode plate taken out of a fully charged lead-acid battery were 0.3 mass%, 2.1 mass%, 0.1 mass% and 0.1 mass%, respectively.

(4) Preparation of Lead Acid Battery Unformed negative plates were placed in a pouch-shaped separator and stacked with positive plates to form an electrode plate group of seven unformed negative plates and six unformed positive plates.

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

An aqueous solution of sulfuric acid 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 measured by the procedure described above for the porous film used in the separator of Battery A1. As shown in Figure 2, 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 halo due to the amorphous region was observed broadly in the wide range of 2θ = 17° to 27°.

The obtained lead-acid batteries were used to evaluate the life performance (cycle number N) using the procedure already described. The life performance was evaluated as the relative value of the cycle number N of each lead-acid battery. The relative value of the cycle number N is the value when the cycle number N of 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 crystallinity of the porous film is 20% or more, the life performance is significantly improved compared to when the crystallinity is 18%, which corresponds to the conventional technology. This is thought to be because the oxidation resistance of the separator is improved due to the high crystallinity of the porous film.

(Experimental Example 2)
In Experimental Example 2, a lead-acid battery was produced and evaluated in the same manner as in Experimental Example 1, except that the separator was changed. Specifically, a plurality of separators were produced in the same manner as in Experimental Example 1, except that the production conditions for changing the thickness of the separator and the crystallinity of the porous film were changed. The carbon material was disposed under the same conditions as the separator in Experimental Example 1.

The prepared 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 examples of the invention, 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 of battery B1 is set to 100.

As shown in Table 2, by making the separator thickness 100 μm or more, the life performance could be significantly improved. 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 pores, and that cracks (separator tears) may occur in some parts. On the other hand, if the separator is 100 μm thick or more (porous membrane thickness is 90 μm or more), the resin flows well and a homogeneous 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. It is thought that this is why the life characteristics have been significantly improved.

(Experimental Example 3)
In Experimental Example 3, a plurality of separators were produced by changing the production conditions. Specifically, a plurality of separators were produced by the same method as in Experimental Example 1, except that the production conditions for changing the crystallinity of the porous film and the thickness of the separator, and the presence or absence of the carbon material were changed. The produced separators were evaluated in the same manner as in Experimental Example 1.

The tensile strength of the produced separators was measured using the method described above. The evaluation results of the separators are shown in Tables 3 and 4. Separators S1 to S10 are separators of the invention, and separators CS1 to CS12 are separators of comparative examples. The tensile strength is a relative value when the tensile strength of separator CS1 is set to 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 making the crystallinity of the porous film 20% or more, the tensile strength of the separator could be significantly increased. As shown in Table 4 and Figure 4, by placing a carbon material on the surface and making the thickness 100 μm or more, the tensile strength of the separator could be significantly increased.

As shown in Figure 3, the effect of increasing the tensile strength by increasing the crystallinity was greater in the separator with the carbon material disposed therein than in the separator without the carbon material disposed therein. As shown in Figure 4, the effect of increasing the tensile strength by increasing the separator thickness was greater in the separator with the carbon material disposed therein than in the separator without the carbon material disposed therein. The reasons for this are unclear, but it is thought that disposing the 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 IS applications (such as lead-acid batteries for ISS vehicles) and as starting power sources 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 applications are merely examples. Applications 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 plate, 3: Positive plate, 4: Separator, 5: Positive shelf, 6: Negative shelf, 7: Positive pole, 8: Through connector, 9: Negative pole, 11: Plate group, 12: Battery case, 13: Partition, 14: Cell chamber, 15: Lid, 16: Negative terminal, 17: Positive terminal, 18: Liquid vent plug

Claims (7)

A separator for a lead-acid battery,
A porous membrane including a polymer material 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 crystallinity represented by 100×I _c /(I _c +I _a ) is 20% or more and 35% or less ;
_Ic is the integrated intensity of the diffraction peak having the maximum peak height among the diffraction peaks corresponding to the crystalline region,
_Ia is the integrated intensity of the halo corresponding to the amorphous region,
A separator for a lead-acid battery having a thickness of 100 μm or more and 300 μm or less . 2. The separator for a lead acid battery according to claim 1 , which contains oil. 3. The lead acid battery separator according to claim 1 , wherein the porous film comprises a polyolefin. The polyolefin contains at least ethylene units,
4. The lead acid battery separator according to claim 3 , wherein the diffraction peak having the maximum peak height corresponds to a (110) plane of the crystalline domain. 5. 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 group 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,
The separator is the separator for a lead-acid battery according to any one of claims 1 to 5 . The lead-acid battery according to claim 6 , wherein the carbon material of the separator is disposed on one of the two main surfaces of the porous membrane that is closer to the negative electrode plate.

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