JP7739739B2 - 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 proposes a flooded lead-acid battery having a positive electrode plate, a negative electrode plate, a separator separating the positive electrode plate and the negative electrode plate, and an electrolyte that immerses the positive electrode plate, the negative electrode plate, and the separator, characterized in that a porous layer is disposed between the top of the positive electrode plate and the top of the separator.

Patent Document 2 proposes a lead-acid battery that includes a positive electrode plate, a negative electrode plate, a perforated sheet that is disposed between the positive electrode plate and the negative electrode plate and has through holes formed in the thickness direction, and an electrolyte, in which the aperture ratio of the perforated sheet differs between the upper and lower portions.

Patent Document 3 proposes 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, kneading the mixture while forming it into a ribbed sheet, immersing the sheet in an immersion bath containing an organic solvent capable of dissolving the oil to extract and remove a portion of the oil, and then heating and drying the sheet. The difference in oil content between the rib portion and the base portion of the separator is 5% by mass or less.

International Publication No. 2017/042850 International Publication No. 2019/225389 Japanese Patent Application Laid-Open No. 2001-338631

Lead-acid batteries are sometimes used in a state of insufficient charge known as a partial state of charge (PSOC). For example, in idle-stop (IS) applications, such as idle-start-stop (ISS) vehicles, lead-acid batteries are used in PSOC. Repeated charge and discharge in PSOC easily leads to stratification, where the electrolyte density is low in the upper part of the battery and high in the lower part. Furthermore, in IS applications, the engine is started frequently, resulting in repeated high-current discharges. As a result, charge and discharge reactions tend to concentrate in the upper part of the plate, leading to significant softening and shedding of the positive electrode material in the upper part of the positive plate. Previous attempts have been made to improve life performance by reducing the reactivity of the upper part of the plate, making the reactivity of the entire plate more uniform. However, it would be advantageous to improve the life performance (hereinafter sometimes referred to as IS life performance) during repeated charge and discharge in PSOC and IS tests, which include high-current discharge.

Separators may also contain oil as a pore-forming agent. When a separator contains oil, the separator's resistance increases and the reactivity of the electrode plates decreases. Removing the oil from the separator reduces the separator's resistance and alleviates the decline in electrode plate reactivity. However, in this case, the life performance (hereinafter sometimes referred to as high-temperature overcharge life performance) when the lead-acid battery is overcharged at high temperatures (e.g., temperatures of 75°C or higher) decreases.

One aspect of the present invention is a separator for a lead-acid battery,
the separator contains oil and includes, in a main portion, a central portion, a first end portion and a second end portion located at both ends in a first direction, and a third end portion and a fourth end portion located at both ends in a second direction perpendicular to the first direction;
the oil content Ce1 at the first end portion and the oil content Cc at the central portion satisfy Ce1≧Cc,
The separator for a lead-acid battery relates to a separator for a lead-acid battery, wherein an oil content Ce at at least one of the second end, the third end, and the fourth end, and an oil content Cc at the central portion satisfy Ce<Cc.

In lead-acid batteries, high IS life performance and high high-temperature overcharge life performance can be ensured.

1 is a schematic plan view showing a state in which a separator according to an embodiment of the present invention is stacked on an electrode plate. 2 is a schematic plan view illustrating the portions of the separator of FIG. 1 from which samples are taken for measuring the oil content at the center and each end of the main portion. FIG. 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;

Generally, in IS tests for lead-acid batteries, stratification is likely to occur because the plates are unlikely to be overcharged and the electrolyte is unlikely to be agitated. When stratification occurs, charge/discharge reactions are concentrated at the top of the plate, increasing reactivity, while reactivity decreases at the bottom and sides of the plate. At the top of the positive plate, where charge/discharge reactions are concentrated, the positive electrode material is prone to deterioration, softening, and shedding. Shedding of the positive electrode material reduces capacity and IS life performance. In Patent Document 1 and Patent Document 2, variation in reactivity among the plates is reduced by reducing the reactivity of the top of the plate. However, it would be ideal to reduce variation in reactivity among the plates by increasing the reactivity of the less reactive parts of the plate.

When a lead-acid battery is overcharged, stratification and deterioration of the positive electrode material are reduced. However, the potential of the positive plate is high during overcharge, and the positive electrode material contains lead dioxide, a highly oxidizing positive electrode active material. As a result, the separator facing the positive plate is susceptible to oxidative deterioration. Oxidative deterioration of the separator during overcharge is particularly noticeable at high temperatures (e.g., temperatures above 75°C). In lead-acid batteries, oxidative deterioration of the separator reduces its flexibility, causing cracks and short circuits, ultimately shortening the battery's life.

Separators sometimes contain oil as a pore-forming agent. When a separator contains oil, oxidation degradation of the separator is suppressed, which is advantageous from the perspective of ensuring higher high-temperature overcharge life performance. However, because the insulating oil clogs the separator's pores, the separator's resistance increases and the reactivity of the electrode plates tends to decrease. Therefore, in lead-acid batteries, it is difficult to ensure high IS life performance while also ensuring high high-temperature overcharge life performance.

In view of the above, one aspect of the present invention provides a separator for a lead-acid battery that contains oil and includes, in its essential portion, a central portion, a first end and a second end located at both ends in a first direction, and a third end and a fourth end located at both ends in a second direction perpendicular to the first direction. The oil content Ce1 in the first end and the oil content Cc in the central portion satisfy Ce1 ≧ Cc. The oil content Ce in at least one of the second end, third end, and fourth end, and the oil content Cc in the central portion satisfy Ce < Cc.

In this specification, at least one of the second end, third end, and fourth end may be referred to as "at least one end other than the first end" or "end other than the first end." Furthermore, among the ends other than the first end, an end that satisfies Ce<Cc may be simply referred to as "an end that satisfies Ce<Cc."

The separator on the side surface has a lower oil content at at least one end other than the first end compared to the central portion and the first end, thereby reducing resistance and ensuring high electrolyte diffusibility. Furthermore, the separator retains a relatively large amount of oil at the first end and central portion. When such a separator is used in a lead-acid battery, the first end faces the upper end of the electrode plate, and the end satisfying Ce<Cc faces at least one of the side end and the lower end of the electrode plate. By facing the end of the separator satisfying Ce<Cc to the portion of the electrode plate that tends to have low reactivity (specifically, at least one of the side end and the lower end of the electrode plate), resistance can be reduced and electrolyte diffusibility can be increased. As a result, charge/discharge reactions can proceed more easily at at least one of the side end and the lower end of the electrode plate, increasing reactivity. This allows for more uniform reactivity throughout the electrode plate while maintaining high reactivity at the central portion and the upper end. In particular, in IS applications, where high-current discharges are performed, electrolyte diffusibility has a significant impact on life and discharge performance. By improving electrolyte diffusibility at the side or bottom ends, stratification is also reduced, resulting in high IS life. Furthermore, the first end and center of the separator, which face the naturally highly reactive portions of the electrode plates, contain more oil than the ends where Ce < Cc, resulting in high oxidation resistance. Therefore, high life (i.e., high-temperature overcharge life) can be ensured when the lead-acid battery is overcharged at high temperatures.

The present invention also includes a lead-acid battery including the above-described lead-acid battery separator. The lead-acid battery 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, and the separator is the above-described lead-acid battery separator. A first end of the separator faces the upper ends of both the positive electrode plate and the negative electrode plate.

The third and fourth ends of the separator are located outside the two ends of the central portion, and it is preferable that the oil content Ce at at least one of the third and fourth ends and the oil content Cc of the central portion satisfy the relationship Ce < Cc. When industrially manufacturing separators, the oil content can be easily adjusted at the third and fourth ends, which extend in a direction intersecting the first end. This makes it easier to ensure high IS life performance and high high-temperature overcharge life performance.

The ratio Ce/Cc of the oil content Ce to the oil content Cc is preferably 0.50 or greater and 0.95 or less. In this case, higher IS life performance can be achieved, and high-temperature overcharge life performance can be further improved.

The separator preferably contains inorganic particles. In this case, the separator's wettability with the electrolyte is increased, further reducing the separator's resistance. This results in higher IS life performance.

The separator preferably contains polyolefin. Separators containing polyolefin tend to have lower oxidation resistance. However, even in this case, the first end and central portion of the separator contain a relatively large amount of oil, ensuring high-temperature overcharge life performance.

In lead-acid batteries, the positive electrode plate typically includes a positive electrode current collector, and the negative electrode plate typically includes a negative electrode current collector. At least one of the positive electrode current collector and the negative electrode current collector may be formed by expanding. Current collectors formed by expanding do not have bones extending vertically or horizontally. Therefore, in plates including current collectors formed by expanding, the current collection path from the edge to the bottom end or side end is long, which tends to reduce reactivity at the bottom end or side end. Even in such cases, by controlling the oil content Ce at at least one end of the separator other than the first end to be smaller than the oil content Cc at the center, reactivity can be made more uniform throughout the plate, ensuring high IS life performance.

The electrolyte contained in the lead-acid battery may contain at least one of aluminum ions and lithium ions. In this case, the coarsening of lead sulfate produced during discharge is suppressed, improving charge acceptance and facilitating the reduction of lead sulfate to lead during charging. The increased effectiveness in suppressing stratification results in a longer IS life.

The concentration of aluminum ions in the electrolyte is preferably 0.02 mol/L or more and 0.2 mol/L or less. Furthermore, the concentration of lithium ions in the electrolyte is preferably 0.02 mol/L or more and 0.2 mol/L or less. In these cases, the IS life performance can be further improved.

In applications where charging and discharging is performed in PSOC (e.g., IS applications), repeated charging and discharging, including high-current discharge, results in a significant decrease in reactivity, particularly at the bottom and side edges of the plates. A lead-acid battery including a lead-acid battery separator according to one aspect of the present invention can ensure excellent life performance even in such applications.

(Explanation of terms)
(Main parts of the separator)
When the separator is interposed between a positive electrode plate and a negative electrode plate, the term "main portion of the separator" refers to the portion of the separator that faces both the region of the positive electrode plate where the electrode material is disposed and the region of the negative electrode plate where the electrode material is disposed. In an electrode plate assembly including a positive electrode plate and a negative electrode plate, in a separator that faces only each electrode plate located at the end of the electrode plate assembly, the term "main portion" refers to the portion of the main surface of each electrode plate that faces the region of the electrode material disposed. Note that the term "main surface of the electrode plate" refers to each of a pair of surfaces that occupy most of the surface of the electrode plate (i.e., a pair of surfaces excluding the end faces).

(Center, end, first and second directions of separator, and end of electrode plate)
When viewed from a direction perpendicular to the surface of the separator, the separator includes, in its main portion, a central portion and four end portions surrounding the central portion on all four sides. In the separator's main portion, the four end portions are composed of a first end portion and a second end portion located at both ends in a first direction, and a third end portion and a fourth end portion located at both ends in a second direction perpendicular to the first direction. In the separator's main portion, the central portion is sandwiched between the first end portion and the second end portion. In the separator's main portion, the central portion, the first end portion, and the second end portion are sandwiched between the third end portion and the fourth end portion. In other words, in the separator's main portion, the third end portion and the fourth end portion are located outside the both ends in the second direction of the central portion, the first end portion, and the second end portion.

In a lead-acid battery, the separator is positioned so that its first end faces the upper end of the electrode plate. Therefore, in a lead-acid battery, the separator's second end faces the lower end of the electrode plate, and its third and fourth ends face the side ends of the electrode plate.

The upper ends of the plates (positive and negative plates) correspond to the downstream ends in the current collection direction. Plates usually have lugs at their upper ends. The up-down direction of a plate is defined by the side with the lugs as the upper side and the side opposite the lugs as the lower side. The up-down direction of the plate is the same as the up-down direction of the lead-acid battery in the vertical direction. For a separator, the side opposite the upper side of the plate (i.e., the lug side) is the upper side of the separator, and the side opposite the lower side of the plate is the lower side of the separator. In a lead-acid battery, the first direction of the separator is the up-down direction in the vertical direction of the lead-acid battery, and the second direction is the horizontal direction of the lead-acid battery.

(Oil content in the center and edges of the main part)
The separator's main portion is divided into four equal parts in the first direction and four equal parts in the second direction, for a total of 16 regions. The oil content Cc in the central portion of the main portion is determined for the four central regions. The oil content Cc at each of the first and second ends is determined for two regions located outside the four central regions in the first direction. The oil content Cc at each of the third and fourth ends is determined for two regions located outside the four central regions in the second direction. If the separator has ribs, the sample for determining the oil content Cc is taken from a region without ribs.

The oil content is determined on a new separator or on a separator removed from a newly used lead-acid battery. If the separator is removed from a lead-acid battery, the separator is removed from a fully charged lead-acid battery.

(fully charged)
In this specification, the fully charged state of a lead-acid battery is defined by JIS D 5301:2019. More specifically, the fully charged state is defined as a state in which a lead-acid battery is charged in a water tank at 25°C ± 2°C at a current (A) that is 1/10 of the value given 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 given as the rated capacity is in Ah. The unit of current set based on the value given as the rated capacity is A.

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.

(oil)
Oil refers to a hydrophobic substance that is liquid at room temperature (a temperature of 20° C. or higher and 35° C. or lower) and separates from water. Oil includes naturally occurring oils, mineral oils, and synthetic oils.

(Polyolefin)
Polyolefins are polymers containing at least olefin units (i.e., polymers containing at least monomer units derived from olefins). Polyolefins include, for example, olefin homopolymers, copolymers containing different olefin units, and copolymers containing olefin units and copolymerizable monomer units. A copolymer containing olefin units and copolymerizable monomer units may contain one or more types of olefin units. Furthermore, a copolymer containing olefin units and copolymerizable monomer units may contain one or more types of copolymerizable monomer units. A copolymerizable monomer unit is a monomer unit derived from a polymerizable monomer other than an olefin and copolymerizable with an olefin.

Lead-acid batteries according to embodiments of the present invention will be described in more detail below with reference to the drawings. However, the present invention is not limited to the following embodiments.

(separator)
The separator includes a central portion facing the electrode material, a first end portion and a second end portion sandwiching the central portion in a first direction, and a third end portion and a fourth end portion sandwiching the central portion, the first end portion, and the second end portion in a second direction. In the separator's main portion, the first end portion is located outside the upper end of the central portion, and the second end portion is located outside the lower end of the central portion. In the separator's main portion, the third end portion and the fourth end portion are located outside the respective side ends of the central portion, the first end portion, and the second end portion.

The separator contains oil. The oil contained in the separator comes from, for example, a pore-forming agent used in the separator's manufacturing process.

The oil content Ce1 at the first end and the oil content Cc at the center satisfy Ce1 ≥ Cc. Because the first end faces the upper end of the electrode plate, it is preferable that the ratio Ce1/Cc of the oil content Ce1 to the oil content Cc be close to 1, in order to easily maintain high reactivity at the upper end of the electrode plate. The ratio Ce1/Cc is, for example, 1.1 or less, and preferably 1.05 or less. In particular, when the ratio Ce1/Cc = 1, separators can be easily manufactured industrially while maintaining high reactivity at the upper part of the electrode plate.

The oil content Ce at at least one end other than the first end and the oil content Cc at the center satisfy Ce < Cc. Because reactivity is particularly likely to decrease at the lower end of the electrode plate, the oil content Ce at the second end may be less than Cc to increase the reactivity of this lower end. From the perspective of facilitating industrial production of the separator, it is preferable that the oil content Ce at at least one of the third end and the fourth end satisfy Ce < Cc. From the perspective of increasing reactivity at both ends of the electrode plate and ensuring higher IS life performance, it is preferable that the oil content Ce at both the third end and the fourth end be less than Ce.

The ratio Ce/Cc of the oil content Ce to the oil content Cc is preferably 0.50 or greater, and more preferably 0.53 or greater. When the ratio Ce/Cc is within this range, the separator's oxidation resistance is enhanced, ensuring better high-temperature overcharge life performance. The ratio Ce/Cc should be less than 1. From the perspective of achieving a more uniform reactivity across the electrode plate and achieving better IS life performance, the ratio is preferably 0.95 or less, more preferably 0.93 or less, and even more preferably 0.9 or less.

The ratio Ce/Cc may be 0.50 or more (or 0.53 or more) but less than 1, 0.50 or more (or 0.53 or more) but 0.95 or less, 0.50 or more (or 0.53 or more) but 0.93 or less, or 0.50 or more (or 0.53 or more) but 0.9 or less.

The average oil content in the separator is, for example, 5% by mass or more. From the perspective of further enhancing the effect of suppressing oxidative degradation of the separator, the average oil content in the separator is preferably 10% by mass or more, and more preferably 12% by mass or more or 13% by mass or more. The average oil content in the separator is, for example, 20% by mass or less, and preferably 18% by mass or less. In this case, it is easier to further reduce the resistance of the separator.

The average oil content of the separator may be 5% by mass or more and 20% by mass or less (or 18% by mass or less), 10% by mass or more and 20% by mass or less (or 18% by mass or less), 12% by mass or more and 20% by mass or less (or 18% by mass or less), or 13% by mass or more and 20% by mass or less (or 18% by mass or less).

The separator has a portion outside the main portion that does not face the electrode material. More specifically, the separator has an upper end, a lower end, and both side ends outside the main portion. The oil content in these portions is not particularly limited. From the perspective of easily adjusting the oil content at each end of the separator's main portion, the portion outside the separator's main portion may have the same oil content as the end of the adjacent main portion. For example, the upper end of the separator is adjacent to the first end of the main portion and may have the same oil content as the oil content Ce1 of the first end. The both side ends of the separator are adjacent to the third and fourth ends of the main portion, respectively, and may have the same oil content as the third and fourth ends, respectively.

The separator may be in sheet form. Alternatively, a sheet folded into an accordion shape may be used as the separator. The separator may be formed in a bag shape, and either the positive electrode plate or the negative electrode plate may be wrapped in the bag-shaped separator. In either form, the center and each end of the essential part are determined by viewing the surface (specifically the top surface) of the separator from a direction perpendicular to the surface when the separator is placed on a flat surface.

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 separator can be obtained, for example, by extruding a resin composition containing a polymer material (hereinafter also referred to as the base polymer), a pore-forming agent containing at least oil, and a penetrating agent (surfactant) into a sheet, and then removing the pore-forming agent. By removing at least a portion of the pore-forming agent, micropores are formed in the base polymer matrix. The oil content in the center and each end can be adjusted by adjusting the amount of oil removed from the separator's main portion, the center, and each end. For example, by removing more oil from at least one end other than the first end than from the first end and the center, the oil content Ce can be adjusted to be less than the oil content Cc. The sheet-shaped separator may be folded into an accordion shape or processed into a bag shape, as needed.

In separators with ribs, the ribs may be formed on the sheet when the resin composition is extrusion-molded. 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.

The base polymer contained in the separator is not particularly limited as long as it is a base polymer used in separators for lead-acid batteries. Polyolefin is often used as the base polymer. Polyolefin may be used in combination with another base polymer. The proportion of polyolefin in the total base polymer contained in the separator is, for example, 50% by mass or more, 80% by mass or more, or even 90% by mass or more. The proportion of polyolefin is, for example, 100% by mass or less. The base polymer may be composed solely of polyolefin. When the proportion of polyolefin is this high, oxidation resistance tends to be low. However, even in such cases, a certain amount of oil is contained in the first end and central portion of the separator, ensuring high high-temperature overcharge life performance.

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.

Porosity-forming agents include liquid and solid pore-forming agents. The pore-forming agent contains at least oil. The use of oil further enhances the effect of suppressing oxidative degradation of the separator, resulting in high IS life performance. 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 between 20°C and 35°C), liquid pore-forming agents are classified as liquid pore-forming agents, and solid pore-forming agents are classified as solid pore-forming agents.

Preferred liquid pore-forming agents include mineral oil and synthetic oil. Examples of liquid pore-forming agents include paraffin oil and silicone oil. Examples of solid pore-forming agents include polymer powder.

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

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 separator 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 separator may be 10% by mass or less, or 5% by mass or less.

The content of the penetrant in the separator may be 0.01% by mass or more (or 0.1% by mass or more) and 10% by mass or less, or 0.01% by mass or more (or 0.1% by mass or more) and 5% by mass or less.

The separator (or the resin composition used to manufacture the separator) may contain inorganic particles. If the separator contains inorganic particles, the IS life performance can be further improved.

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 inorganic particle content in the separator is, for example, 40% by mass or more, and may be 50% by mass or more. When the inorganic particle content is within this range, higher IS life performance can be achieved. The inorganic particle content may be, for example, 80% by mass or less, 75% by mass or less, or 70% by mass or less.

The content of inorganic particles in the separator may be 40% by mass or more (or 50% by mass or more) and 80% by mass or less, 40% by mass or more (or 50% by mass or more) and 75% by mass or less, or 40% by mass or more (or 50% by mass or more) and 70% by mass or less.

The thickness of the separator's main portion is, for example, 0.15 mm or more. From the perspective of keeping the separator's resistance low, the separator's thickness is preferably 0.25 mm or less, and more preferably 0.20 mm or less. Note that the thickness of the separator's main portion refers to the average thickness of the main portion. If the separator has, in its main portion, a base portion and ribs extending from at least one surface of the base portion, the thickness of the separator's main portion 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.

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 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.

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

The separator removed from the lead-acid battery is washed and dried using the following procedure. The separator is immersed in pure water for one hour to remove 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.

(oil content in separator)
The separator's main portion is divided into 16 regions as described above. The four central regions are cut into strips to prepare samples for measuring the oil content Cc of the central region. The two upper regions of the four central regions are cut into strips to prepare samples for measuring the oil content Ce1 of the first end. The two lower regions of the four central regions are cut into strips to prepare samples for measuring the oil content of the second end. The two outer regions of the four central regions in the second direction are cut into strips to prepare samples for measuring the oil content of the third end and the fourth end. For separators with ribs, each sample is cut so as not to include the ribs.

Approximately 0.5 g of each sample is taken and accurately weighed to determine the initial sample mass (m0). The weighed sample is placed in an appropriately sized glass beaker, and 50 mL of n-hexane is added. Next, ultrasonic waves are applied to the sample together with the beaker for approximately 30 minutes to dissolve the oil contained in the sample into n-hexane. Next, the sample is removed from the n-hexane, dried in the air 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 is determined for each sample a total of 10 times, and the average value is calculated. The obtained average value is taken as the oil content at the center or each end.
Oil content (mass%) = (m0 - m1) / m0 x 100

The average oil content in the separator is determined from a sample cut into strips from the four regions in the second row from the top out of the 16 regions into which the separator's main part is divided. Except for using such a sample, the oil content is determined a total of 10 times in the same manner as for the oil content in the center or each end, and the average value is calculated. The resulting average value is used as the average oil content in the separator.

(Content of inorganic particles in separator)
A sample (hereinafter referred to as Sample A) is prepared by cutting a main portion of the separator into strips. For separators having ribs, Sample A is prepared by cutting the base portion into strips in the main portion of the separator so as not to include the ribs.

A portion of sample A is taken and accurately weighed, then placed in a platinum crucible and heated with a Bunsen burner until no more white smoke is emitted. The resulting sample is then heated in an electric furnace (in an oxygen stream, 550°C ± 10°C) for approximately 1 hour to incinerate it, and the ashes are weighed. The ratio (percentage) of the mass of the ashes to the mass of sample A is calculated, and this is taken as the inorganic particle content (mass %) in the separator. The inorganic particle content is determined a total of 10 times, and the average value is calculated. The resulting average value is taken as the inorganic particle content in the separator.

(Content of penetrant in separator)
A portion 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 (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 analyzer. 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 A is calculated, which is the penetrant content (mass%) in the separator. A Q5000IR manufactured by T.A. Instruments is used as the thermogravimetric analyzer. The penetrant content is determined a total of 10 times and the average value is calculated. The obtained average value is taken as the penetrant content in the separator.

(Separator thickness and rib height)
The thickness of the separator is determined by measuring the thickness at five arbitrarily selected points on the base portion of the main part in a cross-sectional photograph of the separator and averaging the thicknesses.

The rib height is determined by averaging the height from one surface of the rib's base measured at 10 randomly selected points on the rib in a cross-sectional photograph of the separator.

FIG. 1 is a schematic plan view showing a separator according to an embodiment of the present invention stacked on an electrode plate. A main portion 105 of the separator 104 faces a portion of the electrode plate 102 where the electrode material is present. The separator 104 contains oil. The main portion 105 of the separator 104 includes a central portion 110, a first end portion ₁₁₁ and a second end portion 112 located at both ends in a first direction D1, and a third end portion 113 and a fourth end portion 114 located at both ends in a second direction _D2 . The first direction _D1 is parallel to the vertical direction of the electrode plate. The second direction _D2 is perpendicular to the first direction _D1 and parallel to the horizontal direction of the electrode plate in a lead-acid battery. The first end portion 111 and the second end portion 112 are located outside the upper and lower ends of the central portion 110. The third end 113 and the fourth end 114 are located outside both side ends of the central portion 110, the first end 111, and the second end 112. The separator 104 is overlapped with the electrode plate 102 so that the first end 111 faces the upper end of the electrode plate 102. The oil content Ce1 in the first end 111 and the oil content Cc in the central portion 110 satisfy Ce1 ≧ Cc. The oil content Ce and the oil content Cc in at least one of the second end 112, the third end 113, and the fourth end 114 satisfy Ce < Cc. By controlling the oil content in this manner, a high IS life performance and a high high-temperature overcharge life performance can be ensured in the lead-acid battery.

FIG. 2 is a schematic plan view illustrating the areas where samples are taken to determine the oil content in the center and each end of the separator shown in FIG. 1 . The length of the main portion 105 of the separator 104 in the first direction _D1 is _L1 , and the length in the second direction _D2 is _L2 . As shown by dotted lines in FIG. 2 , the main portion 105 is divided into four equal parts in the first direction _D1 and four equal parts in the second direction _D2 , for a total of 16 regions. The oil content Cc in the center portion 110 is determined from samples taken from four regions 110a, 110b, 110c, and 110d near the center of the main portion 105. The oil content Ce1 in the first end portion 111 is determined from samples taken from two regions 111a and 111b located at the upper end of the main portion 105. The oil content at the second end 112 is determined for samples taken from two regions 112a and 112b located at the bottom of the main portion 105. The oil content at the third end 113 is determined for samples taken from two regions 113a and 113b located at the side ends of the main portion 105 (specifically, outside regions 110a and 110c of the four regions 110a to 110d from which samples are taken in the central portion 110). The oil content at the fourth end 114 is determined for samples taken from two regions 114a and 114b located at the side ends of the main portion 105 (specifically, outside regions 110b and 110d of the four regions 110a to 110d from which samples are taken in the central portion 110). The average oil content in the separator 104 is determined for samples taken from the four regions 113a, 110a, 110b, and 114a in the second row from the top.

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

The amount of reinforcing material in the positive electrode material can be determined using the following procedure. Reinforcing material analysis is performed using positive electrode material sampled from a positive plate removed from a fully charged lead-acid battery.

Positive electrode material is recovered from the positive electrode plate using the following procedure. First, a fully charged lead-acid battery is disassembled, and the obtained positive electrode plate is washed with water for 3 to 4 hours to remove the electrolyte from the positive electrode plate. The washed positive electrode plate is then dried in a thermostatic chamber at 60°C ± 5°C for at least 5 hours. After drying, if the positive electrode plate contains an adhesive material, the adhesive material is removed from the positive electrode plate by peeling it off. Positive electrode material for analysis (hereinafter referred to as sample B) is obtained by collecting positive electrode material from near the center of the positive electrode plate from the top, bottom, and left and right when viewed from the front. Sample B can be crushed and used for analysis, if necessary.

The crushed sample B is collected and accurately weighed. Next, sample B is added to a mixed solution of aqueous nitric acid (concentration: 25% by mass) and aqueous tartaric acid (concentration: 500 g/L) (mixing ratio (volume ratio) of aqueous nitric acid to aqueous tartaric acid = 7:2), and the soluble components are dissolved while stirring under heat. The resulting mixture is filtered using a membrane filter (average pore size: 0.45 μm or less). This leaves the reinforcing material contained in the positive electrode material as a solid on the filter paper. The resulting solid is washed with water and dried. The mass of the dried material is measured. The ratio (percentage) of the mass of the dried material to the mass of sample B is calculated. This ratio corresponds to the amount of reinforcing material in the positive electrode material.

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. Electrode plates using current collectors formed by expanding tend to have greater variations in reactivity. However, even in such cases, the use of a lead-acid battery separator according to one aspect of the present invention can make the reactivity of the entire electrode plate more uniform.

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 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 amount of reinforcing material in the negative electrode material is, for example, 0.03 mass% or more. Also, the amount of reinforcing material 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.

(Analysis of negative electrode materials or their constituents)
The following describes the method for quantifying the organic shrinkage inhibitor, carbonaceous material, barium sulfate, and reinforcing material in the negative electrode material. Quantitative analysis of the components of the negative electrode material is performed using negative electrode material sampled from a negative electrode plate removed from a fully charged lead-acid battery.

Negative electrode material is recovered from the negative plate using the following procedure. First, a fully charged lead-acid battery is disassembled to obtain the negative plate to be analyzed. The obtained negative plate is washed with water to remove sulfuric acid from the negative plate. The washing is continued until a pH test paper is pressed against the washed surface of the negative plate and no color change is confirmed. However, the washing time should be within two hours. The washed negative plate is then dried under reduced pressure at 60±5°C for approximately six hours. After drying, if the negative plate contains an adhesive material, the adhesive material is removed from the negative plate by peeling. Next, the negative electrode material is separated from the negative plate to obtain a sample (hereinafter referred to as Sample C). Sample C is then crushed as necessary and subjected to analysis.

<Quantitative determination of organic shrinkage inhibitor>
The crushed sample C is immersed in a 1 mol/L aqueous NaOH solution to extract the organic shrink-preventing agent. Insoluble components are removed by filtration from the aqueous NaOH solution containing the extracted organic shrink-preventing agent, and the filtrate (hereinafter also referred to as filtrate D) is recovered.

A predetermined amount of filtrate D is measured, desalted, concentrated, and dried to obtain a powder of organic shrinkage inhibitor (hereinafter also referred to as sample E). Desalting can be performed using a desalting column, by passing filtrate D through an ion exchange membrane, or by placing filtrate D in dialysis tubing and immersing it in distilled water.

The organic shrinkage inhibitor is identified by combining information obtained from the infrared spectrum of sample E, the ultraviolet-visible absorption spectrum of a solution obtained by dissolving sample E in distilled water or the like, the NMR spectrum of a solution obtained by dissolving sample E in a solvent such as heavy water, or pyrolysis GC-MS, which can provide information on the individual compounds that make up the substance.

Measure the ultraviolet-visible absorption spectrum of the above filtrate D. Quantify the content of the organic shrinkage inhibitor in the negative electrode material from the spectral intensity, the previously prepared calibration curve, the measured amount of filtrate D, and the mass of sample C. If the structural formula of the organic shrinkage inhibitor being analyzed cannot be precisely identified and a calibration curve for the same organic shrinkage inhibitor cannot be used, create a calibration curve using an available organic shrinkage inhibitor that exhibits a similar ultraviolet-visible absorption spectrum, infrared spectrum, NMR spectrum, etc. to the organic shrinkage inhibitor being analyzed.

Quantitative determination of carbonaceous materials, barium sulfate, and reinforcing materials
50 mL of 20% by mass nitric acid was added to 10 g of the crushed sample C, and the mixture was heated for about 20 minutes to dissolve the lead components as lead ions. The resulting solution was then filtered to separate out the carbonaceous material, barium sulfate, and other solids.

The resulting solids are dispersed in water to form a dispersion, and the reinforcing material is then recovered from the dispersion using a sieve. The reinforcing material is washed with water, dried, and its mass is measured. The ratio (percentage) of the mass of the dried material to the mass of Sample C is calculated. This ratio corresponds to the reinforcing material content in the negative electrode material.

The dispersion after removing the reinforcing material is subjected to suction filtration using a membrane filter whose mass has been measured in advance, and the membrane filter is dried together with the filtered sample in a dryer at 110°C ± 5°C. The resulting sample is a mixed sample of carbonaceous material and barium sulfate (hereinafter also referred to as sample F). The mass of sample F (M _m ) is measured by subtracting the mass of the membrane filter from the total mass of sample F and the membrane filter after drying. Then, dried sample F is placed in a crucible together with the membrane filter and incinerated at 1300°C or higher. The remaining residue is barium oxide. The mass of barium oxide is converted to the mass of barium sulfate to determine the mass of barium sulfate (M _B ). The mass of the carbonaceous material is calculated by subtracting the mass M _B from the mass M _m . The ratio (percentage) of the mass of the resulting barium sulfate and the mass of the carbonaceous material to the mass of sample C is determined. In this manner, the barium sulfate content and the carbonaceous material content in the negative electrode material are determined.

(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.

When the electrolyte contains at least one of Al ions and Li ions, charge acceptance is improved, ensuring higher IS life performance.

The concentration of Al ions in the electrolyte is preferably 0.02 mol/L or more, and may be 0.05 mol/L or more. When the Al ion concentration is in this range, higher charge acceptance is obtained. The concentration of Al ions in the electrolyte is, for example, 0.2 mol/L or less, and may be 0.15 mol/L or less. Even when the Al ion concentration is in this range, a sufficient improvement in charge acceptance can be achieved, and high IS life performance can be ensured.

The concentration of Al ions in the electrolyte may be 0.02 mol/L or more (or 0.05 mol/L or more) and 0.2 mol/L or less, or 0.02 mol/L or more (or 0.05 mol/L or more) and 0.15 mol/L or less.

The Li ion concentration in the electrolyte is preferably 0.02 mol/L or more, and may be 0.05 mol/L or more. When the Li ion concentration is in this range, higher charge acceptance is obtained. The Li ion concentration in the electrolyte is, for example, 0.2 mol/L or less, and may be 0.15 mol/L or less. Even when the Li ion concentration is in this range, a sufficient improvement in charge acceptance can be obtained, and high IS life performance can be ensured.

The concentration of Li ions in the electrolyte may be 0.02 mol/L or more (or 0.05 mol/L or more) and 0.2 mol/L or less, or 0.02 mol/L or more (or 0.05 mol/L or more) and 0.15 mol/L or less.

The concentration of metal ions in the electrolyte is determined by inductively coupled plasma (ICP) emission spectroscopy of the electrolyte removed from a fully charged lead-acid battery. More specifically, an ICP emission spectrometer is used to identify the type of metal ion in the electrolyte and measure the emission intensity of the metal ion. The concentration of metal ions in the electrolyte is determined from the measured emission intensity and a pre-created calibration curve. The ICP emission spectrometer used is an ICPS-8000 manufactured by Shimadzu Corporation.

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.

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

FIG. 3 shows an external 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 pack 11 and an electrolyte (not shown). The battery case 12 is divided into multiple cell chambers 14 by partition walls 13. Each cell chamber 14 contains one plate pack 11. The opening of the battery case 12 is closed with a lid 15 that includes a negative electrode terminal 16 and a positive electrode terminal 17. The lid 15 is provided with a vent plug 18 for each cell chamber. When rehydrating, the vent plug 18 is removed and rehydration solution is replenished. The vent plug 18 may 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 evaluation methods for each characteristic are explained below.

(1) IS Life Performance The IS life performance is measured by the number of cycles required for the terminal voltage to reach 7.2 V in the following procedure. Note that the minute current discharge in (e) simulates a dark current discharge when the engine is stopped.
(a) After the battery is fully charged, place it in a cooling room at 0°C ± 1°C for at least 16 hours, and then confirm that the electrolyte temperature of one of the central cells is 0°C ± 1°C.
(b) The storage battery is discharged at a discharge current of 300 A for 1.0 second.
(c) Discharge the battery at a discharge current of 25 A for 25 seconds.
(d) Charge the battery at a voltage of 14.0 V for 30 seconds.
(e) The discharge and charge cycles (b) to (d) are repeated, with a minute current (20 mA) being discharged for 6 hours every 30 cycles.
(f) In (b) above, find the number of cycles when the terminal voltage becomes less than 7.2 V.

(2) High-Temperature Overcharge Life Performance A high-temperature overcharge durability test is performed according to the following procedure to measure the life of the lead-acid battery.
(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) has fallen to 7.2 V or less and does not rise again, and the total number of cycles at this time 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.

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

Lead-acid batteries E1 to E6 and C1 to C4
Each lead-acid battery was fabricated according to the following procedure.
(1) Preparation of Separator A resin composition containing 100 parts by mass of polyethylene, 160 parts by mass of silica particles, 80 parts by mass of paraffinic oil as a pore-forming agent, and 2 parts by mass of a penetrating agent was extruded into a sheet, and then a portion of the pore-forming agent was removed to prepare a microporous membrane. The ratio of the oil content Ce at each of the third and fourth ends to the oil content Cc at the center was adjusted by adjusting the amount of pore-forming agent removed at the third and fourth ends of the separator. The ratios of the oil content Ce1 at the first end, the oil content Ce2 at the second end, the oil content Ce3 at the third end, and the oil content Ce4 at the fourth end to the oil content Cc at the center are shown in Table 1. The oil contents at the center and each end were determined using the procedure described above. The average oil content of the separator determined using the procedure described above is also shown in Table 1. The silica particle content in the separator was 60% by mass.

Next, the sheet-like microporous membrane was folded in half to form a bag, and the overlapping ends were welded together to obtain a bag-like separator. The bag-like separator had protruding ribs (external ribs) on its outer surface. The height of the external ribs was 0.6 mm, and the thickness of the base was 0.2 mm.

Note that the oil content at the center and each end of the separator, the average oil content, the thickness of the base, the height of the ribs, and the silica particle content were measured for the separator before it was fabricated into a lead-acid battery, but are almost the same as the values measured using 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, 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 wide, 110 mm high, and 1.3 m thick. The amounts of carbon black, barium sulfate, lignin, and synthetic resin fiber were adjusted so that the amounts of each component, measured using the previously described procedure for a negative electrode plate removed from a fully charged lead-acid battery, were 0.3 wt%, 2.1 wt%, 0.1 wt%, and 0.1 wt%, 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.

The electrolyte used was an aqueous sulfuric acid solution or an aqueous sulfuric acid solution with aluminum sulfate dissolved in it. The specific gravity of the electrolyte after formation at 20°C was 1.285. The concentration of aluminum ions in the electrolyte determined using the procedure described above is shown in Table 1.

(5) Evaluation The IS life performance and high-temperature overcharge life performance of the obtained lead-acid batteries were evaluated according to the procedure described above. The IS life performance and high-temperature overcharge life performance were evaluated as the ratio (%) of the number of cycles of each lead-acid battery to the number of cycles of lead-acid battery C1, which was set to 100.

The evaluation results are shown in Table 1. E1 to E6 are examples. C1 to C4 are comparative examples.

As shown in Table 1, when the oil content in key parts of the separator is uniform, as the average oil content decreases, IS life performance improves, while high-temperature overcharge life performance significantly decreases (C1 to C4).

In contrast, when Ce1 ≥ Cc is satisfied and the oil contents Ce3 and Ce4 at the third and fourth ends are less than Cc, high IS life performance is achieved while maintaining high high-temperature overcharge life performance (E1 to E6). When an electrolyte containing Al ions is used, even higher IS life performance is achieved (comparison between E1 and E6).

In the example, the case where the oil content at the third end and the fourth end is less than Cc is shown, but this is not limited to this case. The same effect as above can also be obtained when the oil content at either the third end or the fourth end is less than Cc. Furthermore, a similar effect to the above can also be obtained when the content at the second end is less than Cc.

The lead-acid battery separator according to the above aspect 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 according to the above aspect of the present invention are not limited to these.

102: electrode plate, 104: separator, 105: main part of separator, 110: center part of main part of separator, 111: first end part of main part of separator, 112: second end part of main part of separator, 113: third end part of main part of separator, 114: fourth end part of main part of separator, D ₁ : first direction, D ₂ : second direction, 110a, 110b, 110c, 110d: areas for taking samples to measure oil content Cc of the center part, 111a, 111b: areas for taking samples to measure oil content Ce1 of the first end part, 112a, 112b: areas for taking samples to measure oil content Ce1 of the second end part, 113a, 113b: areas for taking samples to measure oil content Ce1 of the third end part 114a, 114b: area for taking a sample to measure the oil content of the fourth end, 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: feedthrough connector, 9: negative electrode pole, 11: electrode plate group, 12: battery case, 13: partition wall, 14: cell chamber, 15: lid, 16: negative electrode terminal, 17: positive electrode terminal, 18: vent plug

Claims (10)

A separator for a lead-acid battery,
the separator contains oil and includes, in a main portion, a central portion, a first end portion and a second end portion located at both ends in a first direction, and a third end portion and a fourth end portion located at both ends in a second direction perpendicular to the first direction;
the oil content Ce1 at the first end portion and the oil content Cc at the central portion satisfy Ce1≧Cc,
an oil content Ce at at least one of the second end, the third end, and the fourth end and an oil content Cc at the central portion satisfy Ce<Cc;
the first end faces upper ends of both a positive electrode plate and a negative electrode plate of a lead-acid battery to which the separator is applied,
The separator for a lead-acid battery , wherein the first direction is parallel to a vertical direction of the positive electrode plate and the negative electrode plate . the third end and the fourth end are located outside both side ends of the central portion,
2. The lead-acid battery separator according to claim 1, wherein the oil content Ce and the oil content Cc in at least one of the third end and the fourth end satisfy Ce<Cc. The lead-acid battery separator according to claim 1 or 2, wherein the ratio Ce/Cc of the oil content Ce to the oil content Cc is 0.50 or more and 0.95 or less. The lead-acid battery separator according to any one of claims 1 to 3, containing inorganic particles. The lead-acid battery separator according to any one of claims 1 to 4, containing a polyolefin. 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 5. The positive electrode plate includes a positive electrode current collector,
The negative electrode plate includes a negative electrode current collector,
The lead-acid battery according to claim 6, wherein at least one of the positive electrode current collector and the negative electrode current collector is formed by expanding. The lead-acid battery according to claim 6 or 7, wherein the electrolyte contains at least one of aluminum ions and lithium ions. a concentration of the aluminum ions in the electrolytic solution is 0.02 mol/L or more and 0.2 mol/L or less;
9. The lead-acid battery according to claim 8, wherein the concentration of the lithium ions in the electrolyte is 0.02 mol/L or more and 0.2 mol/L or less. The lead-acid battery according to any one of claims 6 to 9, which is charged and discharged in a partially charged state.