JP7533474B2 - Lead-acid battery - Google Patents

Description

The present invention relates to a lead-acid battery.

Lead-acid batteries are used in vehicles, in industry, and for a variety of other applications. Lead-acid batteries are equipped with positive and negative electrode plates, a separator between them, and an electrolyte. Various performance requirements are placed on the components of a lead-acid battery.

Patent Document 1 proposes a ribbed separator for lead-acid batteries containing 5 to 30% by mass of oil, which is obtained by heating and melting a raw material composition consisting of a mixture of 20 to 69% 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 above blend, 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 that can dissolve the oil to extract and remove some of the oil, and then heated and dried, and the difference in oil content between the rib portion and the base portion of the separator is set to 5% by mass or less.

Patent Document 2 proposes a lead-acid battery in which both the positive and negative plates have expanded lattices, and plates of either the positive or negative polarity are stored in a bag-shaped separator made of a polyolefin synthetic resin sheet such as microporous polyethylene and stacked with plates of the other polarity, the bag-shaped separator has a surface facing the positive plate surface with a plurality of linear ribs in the vertical direction, and the height of battery case ribs provided in the vertical direction on the inner wall of a cell chamber that stores the plate group, which is parallel to the plate surface, is less than the height of the linear ribs.

Patent Document 3 proposes a separator for a lead battery that includes a polyolefin microporous member, the polyolefin microporous member including polyethylene, a particulate filler, and a plasticizer, the particulate filler being present in an amount of 40% by weight or more, the polyethylene including a shish-kebab-structured polymer including a plurality of elongated chain crystals and a plurality of folded chain crystals, and the average repetition or period of the kebab structure is 1 nm to 150 nm.

Patent Document 4 describes a bulky sheet obtained by wet papermaking of 30 to 90% by weight of synthetic pulp having a freeness of 0.1 sec/g or more and 1.0 sec/g or less, 5 to 30% by weight of a binder capable of bonding at a temperature lower than the melting point or decomposition temperature of the synthetic pulp, 5 to 60% by weight of three-dimensionally crimped eccentric sheath-core type or side-by-side type composite fiber, and 40% or less of a reinforcing agent, the bulky sheet having an apparent density of 0.15 g/cm3 or ^less under a load of 200 g/ ^cm2 .

Patent Document 5 describes a method for manufacturing a sealed lead-acid battery using a Pb-Ca alloy for the positive electrode grid, in which antimony or an antimony compound is added to the positive electrode active material so that the amount of Sb is 0.005% or more and 1.0% or less by weight of the positive electrode active material, and the time from injection to the start of cell formation is set to within 2 hours.

JP 2001-338631 A JP 2007-134109 A US Patent Application Publication No. 2017/0294636 Japanese Patent Application Publication No. 6-302313 Japanese Patent Application Publication No. 10-112311

Lead-acid batteries are required to have high output and a long life. In general, when the separator contains oil, oxidation degradation of the separator is suppressed, which is advantageous from the viewpoint of life performance. However, even when the separator contains oil, life performance may decrease in high-temperature deep discharge life tests.

One aspect of the present invention is a battery comprising a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate,
The positive electrode plate includes a positive electrode material,
The positive electrode material contains Sb element,
The content of the Sb element in the positive electrode material is 0.05 mass% or more,
The separator relates to a lead-acid battery, the separator including a polyolefin and an oil, and having an apparent density of 0.46 g/cm ³ or more and less than 0.57 g/cm ³ .

For lead-acid batteries, excellent life performance can be ensured in high-temperature deep discharge life tests.

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;

In lead-acid batteries, the specific gravity of the electrolyte generally increases during charging due to the charging reaction of the plate group, and the electrolyte with a higher specific gravity tends to drop. However, if the battery becomes overcharged toward the end of charging, gas is generated and the electrolyte is stirred, reducing the difference in specific gravity of the electrolyte.

Lead-acid batteries are sometimes used in a partially charged state (PSOC). For example, in idle-stop (IS) applications such as idle-start-stop (ISS) vehicles, lead-acid batteries are used in PSOC. When a lead-acid battery is charged and discharged in PSOC, it is less likely to become overcharged, so the electrolyte is not stirred. This makes it easy for stratification to occur, where the electrolyte density gradually becomes lower in the upper part of the battery and higher in the lower part of the battery. When electrolyte stratification occurs, the negative electrode material in the upper part of the negative plate deteriorates, the binding force in the negative electrode material decreases, and the capacity decreases. This reduces the life performance.

The positive electrode material of a lead-acid battery contains lead dioxide, which has strong oxidizing power, as a positive electrode active material. Separators containing polyolefin are often used in lead-acid batteries. Separators containing polyolefin are prone to deterioration when in contact with the positive electrode material for a long period of time due to the oxidation of the polyolefin. In a lead-acid battery, when the separator deteriorates due to oxidation, its flexibility decreases and cracks occur, causing a short circuit and thus terminating its life.

Separators containing polyolefins may contain oil as a pore-forming agent or additive. When the separator contains oil, oxidative deterioration of the separator containing polyolefin is suppressed, which is advantageous from the standpoint of life performance. However, because the insulating oil blocks the pores of the separator, the resistance of the separator tends to increase. When the resistance of the separator increases, it becomes difficult to increase output.

It is expected that the use of a separator with low density while containing oil will ensure the oxidation resistance of the separator due to the oil. In addition, the use of a separator with low density will ensure high output, and the improved diffusibility of the electrolyte will suppress stratification of the electrolyte, improving the battery's lifespan.

However, in reality, it has become clear that reducing the density of the separator can result in significant oxidation degradation of the separator, even though it contains oil, making it difficult to ensure high life performance in high-temperature deep discharge life tests.

It was also revealed that when the apparent density of the polyolefin-containing separator is 0.46 g/cm3 or ^more and less than 0.57 g/ ^cm3 , by adding a specific amount of Sb element to the positive electrode material, excellent life performance can be obtained in a high-temperature deep discharge life test.

In view of such findings, a lead-acid battery according to one aspect of the present invention includes a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive electrode material. The positive electrode material includes Sb element, and the content of Sb element in the positive electrode material is 0.05 mass% or more. The separator includes a polyolefin and an oil, and has an apparent density of 0.46 g/ ^cm3 or more and less than 0.57 g/ ^cm3 .

According to the above aspect of the present invention, by combining a separator having a relatively low apparent density with a positive electrode material containing Sb at a specific content, it is possible to obtain excellent life performance in a high-temperature deep discharge life test while ensuring high output in a lead-acid battery. In other words, it is possible to achieve both high output and excellent durability in a lead-acid battery.

Despite the use of a low-density separator containing polyolefin, excellent life performance was obtained in high-temperature deep discharge life tests for the following reasons.

Oxidation deterioration of the separator generally progresses when the positive electrode plate surface, which expands due to repeated charging and discharging of the lead-acid battery, comes into direct contact with the separator base surface (i.e., the area of the separator facing the positive electrode plate) (Patent Document 2, [0013]). Oxidation deterioration of the separator base surface is suppressed to some extent when the separator contains oil. However, when a separator with an apparent density of less than 0.57 g/ ^cm3 is used, it may be difficult to suppress the oxidative deterioration of the separator, even if the separator contains oil.

When a lead-acid battery is used in PSOC, stratification is likely to progress. When the apparent density is 0.57 g/cm ³ or more, ions in the electrolyte are difficult to diffuse, so stratification is likely to progress. Therefore, the charge/discharge reaction is concentrated at the top of the electrode plate, and the capacity decreases due to deterioration of the negative electrode material at the top of the negative electrode plate, resulting in the end of the battery life. In this case, the life performance does not depend on the content of Sb contained in the positive electrode material. In addition, in the high-temperature deep discharge life test, when the apparent density of the separator is less than 0.46 g/cm ³ , oil is likely to escape, and oxidation deterioration of the polyolefin contained in the separator is likely to occur in the region of the separator facing the positive electrode plate.

When the apparent density of the separator containing polyolefin is 0.46 g/cm ³ or more and less than 0.57 g/cm ³ , if the content of Sb element in the positive electrode material is less than 0.05 mass%, the oxidative deterioration of the separator becomes significant in the high-temperature deep discharge life test. It has become clear that such oxidative deterioration of the separator progresses near the lower end of the separator rather than in the area facing the positive electrode plate, and the life performance is reduced. It has not been known that such a problem occurs in the high-temperature deep discharge life test when the apparent density of the separator is within a specific range. It is believed that the oxidative deterioration of the lower end side of the separator in the high-temperature deep discharge life test progresses when the fallen positive electrode material comes into contact with the vicinity of the lower end of the separator.

In the above aspect of the present invention, when a separator having an apparent density of 0.46 g/cm ³ or more and less than 0.57 g/cm ³ is used, a positive electrode material containing 0.05 mass% or more of Sb element is used. By using such a positive electrode material, softening of the positive electrode material is suppressed. This suppresses the falling off of the positive electrode material, and therefore it is considered that oxidation deterioration of the separator near the lower end of the separator is suppressed. Therefore, high output and excellent life performance in high temperature deep discharge life test can be ensured.

The apparent density of the separator may be 0.56 g/cm ³ or less. When the apparent density is in this range, higher life performance can be ensured in a high-temperature deep discharge life test.

The oil content in the separator may be 5% by mass or more. In this case, the effect of suppressing oxidative deterioration in the area of the separator facing the positive electrode plate can be enhanced.

The total pore volume of the positive electrode material may be 0.08 cm ³ /g or more. In this case, a higher output of the lead-acid battery can be ensured. The total pore volume may be 0.18 cm ³ /g or less. In this case, the life performance in a high-temperature deep discharge life test can be further improved.

The positive electrode material may contain α-PbO ₂ crystallites and β-PbO ₂ crystallites. In a fully charged lead-acid battery, the ratio of α-PbO ₂ crystallites to β-PbO ₂ crystallites (=α-PbO ₂ crystallites/β-PbO ₂ crystallites=α/β) may be 0.55 or less. In this case, it is easy to ensure a high initial capacity.

Lead acid batteries are typically flooded (vented) lead acid batteries. They are particularly useful as lead acid batteries intended for charging and discharging in PSOC (e.g., IS lead acid batteries).

In IS lead-acid batteries, gassing is unlikely to occur because they are unlikely to be overcharged, and the positive electrode material is likely to soften and fall off. In the lead-acid battery according to the above aspect, even when used as such an IS lead-acid battery, oxidation degradation of the separator due to the fall off of the positive electrode material can be suppressed in a high-temperature deep discharge life test.

(Explanation of terms)
(Positive electrode material)
In a positive electrode plate, the positive electrode material is usually held by a positive current collector. The positive electrode material is the positive electrode plate excluding the positive current collector. A member such as a mat or pasting paper may be attached to the positive electrode plate. Such a member (also called an attachment member) is used integrally with the positive electrode plate, and is therefore included in the positive electrode plate. When the positive electrode plate includes an attachment member, the positive electrode material is the positive electrode material excluding the positive current collector and the attachment member.

(Total pore volume in positive electrode material)
The total pore volume of the positive electrode material is the sum of the volumes of all pores determined by mercury intrusion porosimetry.

(Separator apparent density)
The apparent density of a separator is the mass of the separator divided by the apparent volume of the separator (g/cm ³ ). The apparent density of a separator is determined using a sample obtained by cutting the separator. When the separator has ribs, the sample is cut from the base portion where the ribs are not formed.

(Polyolefin)
A polyolefin is a polymer containing an olefin as a monomer. For example, polyolefins include homopolymers of olefins, copolymers containing monomer units of different olefins, and copolymers containing an olefin and a copolymerizable monomer as a monomer unit. A copolymer containing an olefin and a copolymerizable monomer as a monomer unit contains one or more olefins as a monomer unit. A copolymerizable monomer is a polymerizable monomer other than an olefin that can be copolymerized with an olefin.

(oil)
The oil is a hydrophobic substance that is liquid at room temperature (a temperature between 20° C. and 35° C.) and separates from water. The oil includes naturally occurring oils, mineral oils, and synthetic oils.

(fully charged)
In this specification, the fully charged state of a lead-acid battery is defined by the definition of 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 with a current (A) that is 1/10 of the value described as the rated capacity until the terminal voltage 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 described as the rated capacity is a value in units of Ah. The unit of current set based on the value described as the rated capacity is A.

A fully charged lead-acid battery is a fully charged lead-acid battery that has already been chemically prepared. A lead-acid battery can 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 has been chemically prepared and is in use (preferably in the early stages of use) 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.

In this specification, the up-down direction of the electrode plate is defined as the side on which the ears are provided, and the side opposite the ears as the down-down direction. In addition, the side of the separator that faces the upper side of the electrode plate (i.e., the ear side) is defined as the upper side of the separator, and the side that faces the lower side of the electrode plate is defined as the lower side of the separator. The up-down direction of the electrode plate and the up-down direction of the separator are the same as the up-down direction in the vertical direction of a lead-acid battery.

The lead-acid battery according to the embodiment 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 embodiment.

(Separator)
The apparent density of the separator is 0.46 g/cm ³ or more. When the Sb element content of the positive electrode material is 0.05 mass% or more, if the apparent density of the separator is 0.46 g/cm ³ or more, high life performance can be ensured in the high-temperature deep discharge life test. From the viewpoint of ensuring even higher life performance in the high-temperature deep discharge life test, the apparent density of the separator is preferably 0.48 g/cm ³ or more or 0.49 g/cm ³ or more.

The apparent density of the separator may be less than 0.57 g/cm ³ and may be 0.56 g/cm ³ or less. With the apparent density in such a range, high output and high life performance in a high-temperature deep discharge life test can be obtained. When the Sb element content of the positive electrode material is 0.05 mass% or more, when the apparent density of the separator is 0.56 g/cm ³ or less, the life performance in a high-temperature deep discharge life test is significantly improved compared to when the apparent density is 0.57 g/cm ^3. In other words, when the Sb element content of the positive electrode material is 0.05 mass% or more, it can be said that the apparent density of the separator is critical at 0.56 g/cm ³ in the life performance of the high-temperature deep discharge life test.

The apparent density of the separator may be 0.46 g/ ^cm3 or more and less than 0.57 g/ ^cm3 (or 0.56 g/ ^cm3 or less), 0.48 g/ ^cm3 or more and less than 0.57 g/ ^cm3 (or 0.56 g/ ^cm3 or less), or 0.49 g/ ^cm3 or more and less than 0.57 g/ ^cm3 (or 0.56 g/ ^cm3 or less).

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, 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 matrix of the base polymer. The resin composition may further contain inorganic particles.

The apparent density of the separator can be adjusted, for example, by adjusting at least one (typically two or more) of the type of pore-forming agent, the amount of pore-forming agent, the mixing ratio of the base polymer and the pore-forming agent, and the amount of pore-forming agent removed.

At least a polyolefin is used as the base polymer. As the base polymer, polyolefin may be used in combination with another base polymer. The other base polymer is not particularly limited as long as it is used in a separator for a lead-acid battery. The ratio of polyolefin to the entire base polymer contained in the separator is, for example, 50% by mass or more, may be 80% by mass or more, or may be 90% by mass or more. The base polymer may be composed of only polyolefin.

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 more preferably be, for example, polyethylene, polypropylene, or a copolymer containing a C _2-3 olefin as a monomer unit (for example, an ethylene-propylene copolymer). Of the polyolefins, it is preferable to use at least polyethylene. Polyethylene may be used in combination with other polyolefins.

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

The content of inorganic particles in the separator may be, for example, 40% by mass or more, and may be 50% by mass or more. The content of inorganic particles may be, for example, 80% by mass or less, and may be 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.

Examples of the pore-forming agent include liquid pore-forming agents and solid pore-forming agents. At least oil is used as the pore-forming agent. 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 other pore-forming agents. 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.

Liquid pore-forming agents are preferably mineral oils, synthetic oils, etc. Examples of liquid pore-forming agents include paraffin oil and silicone oil. Examples of solid pore-forming agents include polymer powders.

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

The oil content in the separator is, for example, 5% by mass or more. From the viewpoint of suppressing oxidative deterioration in the region of the separator facing the positive electrode plate in a high-temperature deep discharge life test, the oil content in the separator is preferably 10% by mass or more, and more preferably 12% by mass or more. The oil content in the separator is, for example, 20% by mass or less, and preferably 18% by mass or less.

The oil content in 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), or 12% by mass or more and 20% by mass or less (or 18% by mass or less).

The surfactant 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 kinds.

The amount of the penetrant in the separator is, for example, 0.1 parts by mass or more, and may be 0.5 parts by mass or more, per 100 parts by mass of the base polymer. The amount of the penetrant is, for example, 10 parts by mass or less, and may be 5 parts by mass or less.

The amount of penetrating agent in the separator may be 0.1 parts by weight or more (or 0.5 parts by weight or more) and 10 parts by weight or less, or 0.1 parts by weight or more (0.5 parts by weight or more) and 5 parts by weight or less, per 100 parts by weight of base polymer.

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 is, for example, 5% by mass or less, and may be 10% by mass or less.

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

The thickness of the separator is, for example, 0.1 mm or more. The thickness of the separator may be 0.3 mm or less. However, if an attachment member (such as a mat or pasting paper) is attached to the separator, the thickness of the attachment member is included in the thickness of the separator.

The separator may have ribs or may not have ribs. The separator with ribs has, for example, a base portion and ribs erected from the surface of the base portion. The ribs may be provided only on one surface of the separator or each base portion, or on both surfaces. The separator may be sheet-shaped. 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 a bag-shaped separator. When a bag-shaped separator is used, the lower end of the separator is easily oxidized and deteriorated due to contact with the fallen positive electrode material. In the above aspect of the present invention, even when such a bag-shaped separator is used, oxidation deterioration at the lower end of the separator can be suppressed in a high-temperature deep discharge life test.

The ribs may be formed on the sheet when the resin composition is extruded. 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.

When 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 protruding from the main surface of the base portion (protruding 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.

When the separator has ribs, the thickness of the base portion is, for example, 0.15 mm or more. In this case, it is easy to ensure the strength of the separator. From the viewpoint of keeping the resistance of the separator low, it is advantageous for the thickness of the base portion to be, for example, 0.25 mm or less, and it may be 0.20 mm or less.

(Separator analysis or size measurement)
For separator analysis or size measurement, separators taken from lead-acid batteries in their early stages of use are used.

Once removed from the lead-acid battery, the separator is washed and dried prior to analysis or measurement.

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 in 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. Note that when removing the separator from the lead-acid battery, the separator is removed from a fully charged lead-acid battery.

(Separator apparent density)
The apparent density of the separator is determined by the following procedure. First, in the region of the separator facing the electrode plate, the base portion is processed into a strip of 100 mm x 10 mm so as not to include the ribs, to prepare a sample (hereinafter referred to as sample A). The vertical and horizontal sizes and thickness of sample A are measured, and the volume of sample A is calculated from these measurements. The mass of sample A is measured and divided by the volume to calculate the apparent density. The apparent density is determined for multiple samples (e.g., 20 samples), and the average value is calculated. The obtained average value is regarded as the apparent density of the separator.

(Oil content in separator)
Approximately 0.5 g of sample A is collected and accurately weighed to determine the initial mass (m ₀ ) 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 approximately 30 minutes to dissolve the oil contained in sample A into n-hexane. Next, the sample is removed from the n-hexane, dried in the air at room temperature (temperature of 20° C. or higher and 35° C. or lower), and then weighed to determine the mass (m ₁ ) of the sample after removal of the oil. The oil content is then calculated using the following formula:
Oil content (mass %)=(m ₀ −m ₁ )/m ₀ ×100

(Content of inorganic particles in separator)
A portion of sample A prepared in the same manner as above is taken, accurately weighed, and then placed in a platinum crucible and heated with a Bunsen burner until no white smoke is emitted. The obtained sample is then heated in an electric furnace (in oxygen gas flow, 550°C ± 10°C) for about 1 hour to be incinerated, and the incinerated product is weighed. The ratio (percentage) of the mass of the incinerated product to the mass of sample A is calculated to obtain the content (mass%) of the inorganic particles.

(Content of penetrant in separator)
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 the temperature is raised from room temperature to 800°C ± 1°C at a heating rate of 10K/min. The weight loss amount 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 to be the content (mass%) of the penetrant. A Q5000IR manufactured by T.A. Instruments is used as the thermogravimetric measuring device.

(Separator thickness, base 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 thicknesses.

The thickness of the base portion is determined by measuring the thickness of the base portion at five arbitrarily selected points on a cross-sectional photograph of the separator and averaging the measurements.

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

(Positive electrode plate)
As the positive electrode plate, a paste type positive electrode plate is used.

The positive electrode collector included in the positive electrode plate may be formed by casting lead (Pb) or a lead alloy, or by processing a lead or lead alloy sheet. Examples of processing methods include expanding and punching. It is preferable to use a lattice-shaped collector as the positive electrode 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 layers may be multiple. For the core metal, it is preferred to use a Pb-Ca alloy or a Pb-Sb alloy.

The positive electrode material contains a positive electrode active material (lead dioxide or lead sulfate) that exhibits capacity through an oxidation-reduction reaction. The positive electrode material contains Sb element. The positive electrode material may contain other additives (such as reinforcing materials) as necessary.

In a fully charged lead-acid battery, the positive electrode material usually contains α-PbO ₂ crystallites and β-PbO ₂ crystallites. At this time, the ratio of α-PbO ₂ crystallites to β-PbO ₂ crystallites (=α/β) may be 0.6 or less, 0.55 or less, 0.5 or less, or 0.2 or less. When the α/β ratio is in such a range, the proportion of active β-PbO ₂ crystallites is relatively high, so that the initial capacity decrease of the lead-acid battery can be suppressed and a high initial capacity can be ensured. The α/β ratio may be 0.05 or more or 0.1 or more. From the viewpoint of easily ensuring higher life performance in a high-temperature deep discharge life test, the α/β ratio may be 0.13 or more, 0.18 or more, or 0.2 or more. The α/β ratio can be controlled, for example, by adjusting at least one of the temperature during formation and the specific gravity of the electrolyte during formation.

In a fully charged lead-acid battery, the α/β ratio may be 0.05 or more (or 0.1 or more) and 0.6 or less, 0.13 or more (or 0.18 or more) and 0.6 or less, 0.2 or more and 0.6 or less, 0.05 or more (or 0.1 or more) and 0.55 or less, 0.13 or more (or 0.18 or more) and 0.55 or less, 0.2 or more and 0.55 or less, 0.05 or more (or 0.1 or more) and 0.5 or less, 0.13 or more (or 0.18 or more) and 0.5 or less, 0.2 or more and 0.5 or less, 0.05 or more (or 0.1 or more) and 0.2 or less, or 0.13 or more (or 0.18 or more) and 0.2 or less.

The content of Sb element in the positive electrode material is 0.05% by mass or more. By making the content of Sb 0.05% by mass or more, softening of the positive electrode material is suppressed, and excellent life performance in high-temperature deep discharge life test can be ensured. From the viewpoint of easily ensuring high capacity, the content of Sb element in the positive electrode material is, for example, 0.6% by mass or less, may be 0.5% by mass or less, or may be 0.3% by mass or less.

A positive electrode plate in which the positive electrode material contains Sb element can be formed, for example, by using an antimony compound (e.g., oxide, salt, etc.) as an additive.

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

The total pore volume of the positive electrode material is, for example, 0.08 cm ³ /g or more, and may be 0.09 cm ³ /g or more. When the total pore volume is in such a range, the diffusibility of sulfate ions is increased, so that it is easy to ensure a higher output. The total pore volume of the positive electrode material may be, for example, 0.2 cm ³ /g or less. When the total pore volume of the positive electrode material is 0.18 cm ³ /g or less, the contact between the particles of lead and lead sulfate is easy to be maintained even after repeated charging and discharging. Therefore, the effect of suppressing the softening and falling off of the positive electrode material by making the content of Sb element 0.05 mass% or more is further enhanced. Therefore, it is easy to ensure a higher life performance in the high temperature deep discharge life test.

The total pore volume of the positive electrode material may be 0.08 cm ³ /g or more (or 0.09 cm ³ /g or more) to 0.2 cm ³ /g or less, or alternatively 0.08 cm ³ /g or more (or 0.09 cm ³ /g or more) to 0.18 cm ³ /g or less.

Unformed paste-type positive plates are obtained by filling a positive electrode current collector with a positive electrode paste, aging it, and drying it. The positive electrode paste is prepared by adding water and sulfuric acid to lead powder, an antimony compound, and 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.

(Analysis of Positive Electrode Materials or Their Constituents)
The analysis of the positive electrode material or its constituent components is carried out using a positive electrode material sampled from a positive plate removed from a fully charged lead-acid battery.

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

(Amount of reinforcing material and Sb element content)
The crushed sample B is taken and accurately weighed. Then, sample B is added to a mixed solution of an aqueous nitric acid solution (concentration: 25% by mass) and an aqueous tartaric acid solution (concentration: 500 g/L) (mixture ratio (volume ratio) of the aqueous nitric acid solution and the aqueous tartaric acid solution = 7:2), and the soluble content is dissolved while stirring under heating. The resulting mixture is filtered using a membrane filter (average pore size: 0.45 μm or less). As a result, the reinforcing material contained in the positive electrode material is obtained as a solid on the filter paper. The obtained 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 determined. This ratio corresponds to the amount of the reinforcing material in the positive electrode material.

The filtrate obtained by filtering the solids is diluted with ion-exchanged water as necessary to a constant volume. The filtrate or the diluted filtrate is used as a solution for quantifying Sb, and the emission intensity of Sb in the solution is measured by inductively coupled plasma (ICP) emission spectroscopy. The mass of Sb contained in the solution is then calculated using a calibration curve created in advance. The proportion of the Sb mass to the mass of sample B used for analysis is calculated as the content of Sb element. Analysis by ICP emission spectroscopy is performed using a SPECTRO-ARCOS manufactured by Hitachi High-Tech Science Corporation.

(Total pore volume of positive electrode material)
The unground sample B is measured with a mercury porosimeter (Shimadzu Corporation, Autopore IV9510). The pressure range for the measurement is 1 psia (≒6.9 kPa) to 60,000 psia (≒414 MPa). The pore size distribution is in the range of 3 nm to 100 μm.

(α/β ratio)
The α/β ratio is determined from the intensity ratio of the peaks of each _PbO2 crystallite by measuring the X-ray diffraction (XRD) spectrum using the crushed sample B. In the XRD spectrum, the peaks near 2θ = 25.5° and 2θ = 28.5° are the peaks of β- _PbO2 crystallites and α- _PbO2 crystallites, respectively. The XRD measurement is performed using a fully automatic multipurpose X-ray diffractometer Smart Lab (horizontal goniometer θ-θ type, Cu-Kα ray) manufactured by RIGAKU Corporation.

(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 negative electrode plate excluding the negative current collector. Note that the negative electrode plate may have an attachment member as described above attached thereto. In this case, the attachment member is considered to be included in the negative electrode plate. In the case where the negative electrode plate includes an attachment member, the negative electrode material is the negative electrode plate excluding the negative current collector and the attachment member.

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

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 material contains a negative electrode active material (lead or lead sulfate) that exhibits capacity through an oxidation-reduction reaction, and may contain a shrinkage inhibitor (such as an organic shrinkage inhibitor), a carbonaceous material (such as carbon black), barium sulfate, etc. The negative electrode material may contain other additives (such as a reinforcing material) as necessary. Examples of reinforcing materials include fibers (inorganic fibers, organic fibers (such as organic fibers made of the resin described for the reinforcing material of the positive electrode material), etc.).

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.

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

(Electrolyte)
The electrolyte is an aqueous solution containing sulfuric acid. The electrolyte may further contain at least one selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions. The electrolyte may be gelled as necessary.

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 electrolyte in a preformed, fully charged lead-acid battery.

FIG. 1 shows the 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 group 11 and an electrolyte (not shown). The battery case 12 is divided into a plurality of cell chambers 14 by partitions 13. Each cell chamber 14 contains one of the plate groups 11. The opening of the battery case 12 is closed by 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 liquid is replenished. The 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 via a separator 4. 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 part 6 that connects the plurality of negative electrode plates 2 in parallel is connected to the through connector 8, and the positive electrode shelf part 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 part 6, and the through connector 8 is connected to the positive electrode shelf part 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 evaluation methods for each characteristic are explained below.

(Life performance in high temperature deep discharge life test)
In this specification, the life performance in a high-temperature deep discharge life test is evaluated based on the number of cycles that reach the life in the high-temperature deep discharge life test.

The high-temperature deep discharge life test is carried out on a fully charged lead-acid battery with a rated voltage of 12 V by repeatedly discharging and charging it under the following conditions: (a) to (c) are carried out in an air tank environment of 50°C ± 2°C.
(a) Discharge 1: Discharge for 59 seconds ±2 seconds at a current value of I _D ±1 A (I _D : current value (A) that is 1/3 of the 5-hour rate capacity)
(b) Discharge 2: Discharge for 1.0 seconds ±0.2 seconds at a current value of 300 A ±1 A (c) Charge: Charge for 60.0 seconds ±0.3 seconds at a limited current of 100.0 A ±0.5 A at 14.2 V ±0.03 V (d) Repetition: The above (a) to (c) constitute one cycle, and are repeated until the battery reaches its end of life. At this time, a break of 40 to 48 hours is taken every 3,600 cycles. The end of life is reached when it is confirmed that the discharge voltage during the test falls below 7.2 V.

(output)
The output of a lead-acid battery is evaluated by the terminal voltage 30 seconds after the start of discharge, measured according to the cold cranking current (CCA) test of JIS D 5301:2019, 10.3. The higher the voltage value, the higher the output. More specifically, the output of a lead-acid battery is measured by the following procedure.

After a fully charged lead-acid battery is fully charged, place it in a water bath at 25°C ± 2°C for 5 hours. Next, place the lead-acid battery in a cooling room at -18°C ± 1°C until the electrolyte temperature of one cell at or near the center reaches -18°C ± 1°C. After confirming that the electrolyte temperature of the above cell has reached -18°C ± 1°C, discharge the battery for 30 seconds at the rated cold cranking current (CCA) within 2 minutes. Record the terminal voltage 30 seconds after the start of discharge.

CCA is an index that indicates the performance of a lead-acid battery. For example, in the case of a lead-acid battery with a rated voltage of 12 V, it refers to the discharge current at which the terminal voltage after 30 seconds becomes 7.2 V when discharged at a temperature of -18°C ± 1°C.

(Initial capacity (20 hour rate))
The initial capacity of a lead-acid battery can be measured in accordance with the 20-hour rate capacity test of 10.1 of JIS D 5301: 2019. More specifically, the initial capacity of a lead-acid battery is measured by the following procedure.

After a fully charged lead-acid battery is fully charged, place it in a water bath at 25°C ± 2°C for approximately 1 hour. Confirm that the temperature of the electrolyte is 25°C ± 2°C. Place the lead-acid battery in a water bath at 25°C ± 2°C until the electrolyte temperature of one cell in the center or nearby reaches 25°C ± 2°C. Discharge the battery at a 20-hour rate current (A) until the terminal voltage of the lead-acid battery drops to 10.50 V ± 0.05 V, and calculate the discharge duration t (h) at this point. The initial capacity (Ah) can be calculated by multiplying the 20-hour rate current (A) by the discharge duration (h).

[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 E26 and R1 to R18
(1) 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 antimony-free Pb-Ca-Sn alloy expanded lattice, aged and dried to obtain an unformed negative electrode plate with a width of 100 mm, a height of 115 mm and a thickness of 1.2 mm. The amounts of carbon black, barium sulfate, lignin and synthetic resin fiber were adjusted to 0.3 mass%, 2.1 mass%, 0.1 mass% and 0.1 mass%, respectively, when measured in a fully charged state after formation.

(2) Preparation of Positive Electrode Plate Lead oxide, antimony trioxide, reinforcing material (synthetic resin fiber), water and sulfuric acid were mixed to prepare a positive electrode paste. At this time, the amount of antimony trioxide added was adjusted so that the Sb element content in the positive electrode material measured by the above-mentioned procedure was the value shown in Tables 1 to 3. In addition, the amount of water and sulfuric acid was adjusted so that the total pore volume of the positive electrode material measured by the above-mentioned procedure was the value shown in Tables 1 to 3. The amount of reinforcing material in the positive electrode material measured by the above-mentioned procedure was 0.15 mass%. The positive electrode paste was filled into the mesh part of an expanded lattice made of an antimony-free Pb-Ca-Sn alloy, aged, and dried to obtain an unformed positive electrode plate having a width of 100 mm, a height of 115 mm, and a thickness of 1.6 mm.

(3) Preparation of separator A resin composition containing polyethylene, silica particles, paraffin-based oil as a pore-forming agent, and a penetrant was extruded into a sheet, and then a part of the pore-forming agent was removed. The apparent density of the separator was adjusted by adjusting at least one selected from the mixture ratio of polyethylene, silica particles, and pore-forming agent, and the amount of pore-forming agent removed. The penetrant was used in a ratio of 2 parts by mass per 100 parts by mass of polyethylene. In this way, a microporous membrane having an apparent density obtained by the above-mentioned procedure and having the values shown in Tables 1 to 3 was prepared. A mold having a shape in which a plurality of striped ribs were formed was used for extrusion molding. Each sheet-shaped microporous membrane was folded in half to form a bag, and a bag-shaped separator was obtained.

The composition of the resin composition containing polyethylene, silica particles, a pore-forming agent, and a penetrating agent can be changed as desired, for example, depending on at least one of the separator design, manufacturing conditions, and how the lead-acid battery is used. Also, at least one of the amount of penetrating agent in the separator and the amount of pore-forming agent removed can be adjusted as necessary.

On the outer surface of the pouch-shaped separator, multiple stripe-shaped mini-ribs with a protruding height of 0.18 mm were provided at a pitch of 1 mm on both edges in the width direction of the pouch-shaped separator. On the outer surface of the pouch-shaped separator, multiple stripe-shaped main ribs with a protruding height of 0.6 mm were provided at a pitch of 9.8 mm in the area inside both edges where the mini-ribs were provided. The total thickness of the separator was 0.8 mm. The content of silica particles in the separator was 60 mass%. Note that the total thickness of the separator, the protruding height of the ribs, the rib pitch, and the content of silica particles are values obtained for the separator before the production of the lead-acid battery, but are almost the same as the values measured by the above-mentioned procedure for the separator removed from the lead-acid battery after production.

(4) Preparation of lead-acid batteries Each unformed negative plate was housed in a pouch-shaped separator, and seven unformed negative plates and six unformed positive plates were alternately stacked per cell to form a plate group. The ears of the positive plates and the ears of the negative plates were welded to the positive and negative shelf parts, respectively, by the cast-on-strap (COS) method. The plate group was inserted into a polypropylene battery case, an electrolyte was poured in, and formation was performed in the battery case to assemble flooded lead-acid batteries E1 to E26 and R1 to R18 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 of the value stated in the rated capacity)). In addition, six plate groups were connected in series in the battery case.

The electrolyte used was an aqueous sulfuric acid solution in which aluminum sulfate was dissolved. The Al ion concentration in the electrolyte after formation was 0.2 mass%. The specific gravity of the electrolyte during formation was adjusted to the range of 1.12 to 1.26 so that the α/β ratio in the positive electrode material would be the value shown in Tables 1 to 3.

The prepared lead-acid battery was fully charged using the procedure described above and used for the following evaluation.

[Evaluation 1: Output]
The output of the lead-acid battery was determined using the procedure described above.

[Evaluation 2: Life performance in high-temperature deep discharge life test]
Using the procedure described above, the number of cycles until the terminal voltage of the lead-acid battery reached 7.2 V was determined.

[Evaluation 3: Initial capacity]
The initial capacity of the lead-acid battery was determined using the procedure described above.

The results are shown in Tables 1 to 3. Each evaluation is expressed as a percentage, with the result for the lead-acid battery R7 being taken as 100%.

As shown in Table 1, when the apparent density of the separator is 0.57 g / cm ³ , even if the content of the Sb element in the positive electrode material is changed from 0 mass% to 0.30 mass%, the life performance in the high-temperature deep discharge life test does not change at all (R7, R9, R11 and R13). In addition, when the content of the Sb element in the positive electrode material is less than 0.05 mass%, if the apparent density of the separator is reduced to less than 0.57 g / cm ³ , the life performance in the high-temperature deep discharge life test decreases (comparison between R7 and R1 to R6). However, when the content of Sb element in the positive electrode material is 0.05 mass% or more, the life performance in the high-temperature deep discharge life test is improved by setting the apparent density of the separator to 0.46 g/cm ³ or more and less than 0.57 g/cm ³ (comparison between R8 and R9 and E1 to E6, comparison between R10 and R11 and E7 to E11, comparison between R12 and R13 and E12 to E16). Thus, when the content of Sb element in the positive electrode material is 0.05 mass% or more and when it is less than this, the influence (behavior) of the apparent density of the separator on the life performance in the high-temperature deep discharge life test is significantly different. In addition, in the lead-acid batteries E1 to E16, a high output of 100% or more can be ensured.

As shown in Table 2, from the viewpoint of ensuring higher output, the total pore volume of the positive electrode material is preferably 0.08 cm ³ /g or more, and more preferably 0.09 cm ³ /g or more. From the viewpoint of ensuring higher life performance in a high-temperature deep discharge life test, the total pore volume of the positive electrode material is preferably 0.18 cm ³ /g or less.

As shown in Table 3, when the α/β ratio in the positive electrode material is 0.55 or less, a higher initial capacity can be ensured. From the viewpoint of ensuring higher life performance in the high-temperature deep discharge life test, it is preferable that the α/β ratio is 0.18 or more or 0.2 or more.

The lead-acid batteries according to the above aspects of the present invention are suitable for use in IS (such as lead-acid batteries for ISS vehicles) and as starting power sources for various vehicles (such as automobiles and motorcycles). Lead-acid batteries can also be suitably used as power sources for industrial power storage devices (such as electric vehicles (such as forklifts)). Note that these uses are merely examples, and the lead-acid batteries according to the above aspects of the present invention are not limited to these uses.

1: Lead-acid battery, 2: Negative electrode plate, 3: Positive electrode plate, 4: Separator, 5: Positive electrode shelf, 6: Negative electrode shelf, 7: Positive electrode column, 8: Through connector, 9: Negative electrode column, 11: Plate group, 12: Battery case, 13: Partition, 14: Cell chamber, 15: Lid, 16: Negative electrode terminal, 17: Positive electrode terminal, 18: Liquid vent plug

Claims (6)

A battery comprising a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate,
The positive electrode plate includes a positive electrode material,
The positive electrode material contains Sb element,
The content of the Sb element in the positive electrode material is 0.05 mass% or more,
The separator of the lead-acid battery contains polyolefin and oil, and has an apparent density of 0.46 g/ ^cm3 or more and less than 0.57 g/ ^cm3 . 2. The lead-acid battery according to claim 1, wherein the apparent density is 0.56 g/ ^cm3 or less. A lead-acid battery as described in claim 1 or 2, wherein the oil content in the separator is 5 mass% or more. 4. The lead acid battery according to claim 1, wherein the positive electrode material has a total pore volume of 0.08 cm ³ /g or more and 0.18 cm ³ /g or less. In the lead-acid battery in a fully charged state,
The positive electrode material includes α-PbO ₂ crystallites and β-PbO ₂ crystallites,
The lead acid battery according to any one of claims 1 to 4, wherein the ratio of the α-PbO ₂ crystallites to the β-PbO ₂ crystallites is 0.55 or less. A lead-acid battery according to any one of claims 1 to 5, which is for use in an idling stop system.

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