lead-acid batteries

Abstract

Provided is a lead storage battery (1) comprising a positive electrode plate (3), a negative electrode plate (2), and a separator (4) interposed between the positive electrode plate (3) and the negative electrode plate (2), wherein: the positive electrode plate (3) contains a positive electrode material; the negative electrode plate (2) contains a negative electrode material; the negative electrode material contains elemental Bi; the content of the elemental Bi in the negative electrode material is not less than 100 ppm but less than 350 ppm by mass; the separator is porous; and in the separator, the cumulative volume A of pores of 0.005-10 μm is not less than 0.93 mL / g.

Description

Technical Field

[0001] The present invention relates to a lead-acid battery.

Background Art

[0002] Lead-acid batteries are used in various applications, including in-vehicle and industrial applications. A lead-acid battery includes a positive electrode plate, a negative electrode plate, a separator interposed between these, and an electrolyte.

[0003] Patent Document 1 proposes a lead-acid battery including a negative electrode plate composed of a negative electrode grid不含Sb, a positive electrode plate composed of a positive electrode grid不含Sb and having a layer containing 0.01 to 0.20 wt% of Sb with respect to the amount of the positive electrode active material on at least a part of the surface in contact with the positive electrode active material, a separator inserted between the positive and negative electrode plates, wherein the entire surfaces of the positive and negative electrode plates are immersed in the electrolyte, and the negative electrode active material contains Bi in an amount of 0.02 to 0.10 wt% with respect to the amount of the negative electrode active material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Lead-acid batteries may be used in a state called a partial state of charge (PSOC). For example, a lead-acid battery mounted in a vehicle controlled by an idle stop (IS) is used in a PSOC without being charged during engine stoppage. When a lead-acid battery is used in a PSOC, the impedance of the positive electrode plate tends to increase, and the charge acceptance of the negative electrode plate tends to decrease.

[0006] When the lead-acid battery described in Patent Document 1 is used in a PSOC (Power Storage Electron Cell), the reaction tends to proceed unevenly between the upper and lower plates. Specifically, the charge-discharge reaction and gas generation reaction tend to proceed locally in the upper part of the plate, resulting in insufficient improvement in lifespan. It is believed that the dissolution of Sb contained in the positive electrode plate into the electrolyte and subsequent deposition on the negative electrode plate is one of the causes of the uneven reaction. [Means for solving the problem]

[0007] One aspect of the present invention relates to a lead-acid battery comprising a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate, wherein the positive electrode plate contains a positive electrode material, the negative electrode plate contains a negative electrode material, the negative electrode material contains the element Bi, the content of the element Bi in the negative electrode material is 100 ppm or more and less than 350 ppm, the separator is porous, and the integrated pore volume A of the separator, which is 0.005 μm or more and 10 μm or less, is 0.93 mL / g or more. [Brief explanation of the drawing]

[0008] [Figure 1] This is a partially cutaway perspective view showing the external appearance and internal structure of a lead-acid battery according to one embodiment of the present invention. [Modes for carrying out the invention]

[0009] The lead-acid battery according to this embodiment comprises a positive electrode plate, a negative electrode plate, a separator interposed between the positive and negative electrode plates, and an electrolyte. The positive electrode plate contains a positive electrode material. The negative electrode plate contains a negative electrode material. The negative electrode material contains the element Bi (bismuth), and the Bi content in the negative electrode material is 100 ppm or more and less than 350 ppm by mass. The separator is porous, and the cumulative pore volume A of the separator, which is 0.005 μm or more and 10 μm or less, is 0.93 mL / g or more.

[0010] Lead-acid batteries are typically liquid-type (vented) lead-acid batteries, and this embodiment relates in particular to lead-acid batteries intended for charging and discharging in a PSOC (e.g., lead-acid batteries for vehicle applications with IS control). In PSOC charging and discharging, lead-acid batteries can be discharged to a depth of discharge (DOD) of, for example, 10% or more, and even 30% or more. The DOD is controlled to be, for example, between 10% and 40%.

[0011] In lead-acid batteries, generally, during charging, the specific gravity of the electrolyte increases due to the charging reaction of the electrode plates, and the electrolyte with the higher specific gravity tends to sink. However, in the case of lead-acid batteries not intended for use in PSOC (Power Storage Charge), charging and discharging are repeated while maintaining a high state of charge (SOC). Therefore, an overcharge state occurs towards the end of charging, generating gas that agitates the electrolyte and reduces the difference in specific gravity of the electrolyte.

[0012] On the other hand, lead-acid batteries used in PSOCs (i.e., lead-acid batteries for vehicle applications with IS control) are less prone to overcharging, so the electrolyte is not sufficiently agitated. In this case, stratification is likely to occur, and the specific gravity of the electrolyte at the top of the battery gradually decreases while the specific gravity of the electrolyte at the bottom of the battery increases. As stratification progresses, for example, the positive electrode material deteriorates at the top of the positive electrode plate and sulfation progresses at the bottom of the negative electrode plate. As a result, the impedance of the positive electrode plate increases and the charge acceptance of the negative electrode plate decreases, leading to a decrease in capacity and a shortened lifespan. Hereinafter, the lifespan of lead-acid batteries for vehicle applications with IS control, assuming use in a PSOC, will also be referred to as the "IS lifespan."

[0013] If the negative electrode material contains Bi (bicarbonate), and the Bi content in the negative electrode material is sufficient (e.g., 100 ppm or more), a considerable amount of gas will be generated even when a lead-acid battery is used in a PSOC (Potentially Activated Cellulose Oven), causing the electrolyte to flow to some extent and reducing the difference in specific gravity. Bi reduces the hydrogen overpotential of the negative electrode material, making it easier for hydrogen gas to be generated. However, in a PSOC, the degree of electrolyte flow is limited. Therefore, further measures are necessary.

[0014] Here, as in Patent Document 1, when a layer containing Sb is provided on the positive electrode plate, the Sb-containing layer has the effect of suppressing the deterioration of the positive electrode plate, but at the same time, Sb tends to dissolve from the positive electrode plate into the electrolyte and precipitate on the negative electrode plate. Sb mainly precipitates on the upper part of the negative electrode plate. As a result, the combined effects of Bi and Sb cause the charge-discharge reaction and gas generation reaction to proceed selectively on the upper part of the electrode plate. When the reaction proceeds non-uniformly between the upper and lower parts of the electrode plate in this way, it becomes difficult to suppress the deterioration of the positive electrode material on the upper part of the positive electrode plate and sulfation on the lower part of the negative electrode plate, making it difficult to mitigate the shortening of the IS life due to capacity reduction.

[0015] Therefore, in this embodiment, a separator that is even more porous than conventional separators is used in order to increase the electrolyte flow path. Specifically, the cumulative pore volume A of the separator, which is between 0.005 μm and 10 μm, is controlled to 0.93 mL / g or more. This significantly improves the balance between the driving force of Bi to cause the electrolyte to flow and the flow path through which the electrolyte can move, achieving electrolyte flow that is sufficient to suppress stratification. As a result, the charge-discharge reaction proceeds more uniformly across the electrode plate, suppressing the increase in impedance due to the deterioration of the positive electrode plate and the decrease in the charge acceptance of the negative electrode plate, and improving the shortening of IS life due to capacity reduction.

[0016] Separators generally contain oil. Materials used for separators include, for example, resin components and inorganic components. Polyolefins are commonly used as the main resin component. Oil may be included in the separator as a pore-forming agent or additive.

[0017] Separators (especially those containing polyolefins) tend to oxidize and degrade when in prolonged contact with the positive electrode material. On the other hand, the inclusion of oil in the separator suppresses oxidative degradation of the separator, which is advantageous in improving IS life. However, if the oil content in the separator is too high, the insulating oil tends to clog the pores of the separator, increasing the separator's resistance.

[0018] On the other hand, when a sufficient amount of Bi element is included in the negative electrode material and the integrated pore volume A of the separator is controlled to be 0.93 mL / g or more, even if the oil content in the separator is increased considerably, a flow path necessary for the flow of the electrolyte can be sufficiently secured. Therefore, the action as a resistance component of the oil is not manifested, and the charge-discharge reaction proceeds relatively uniformly over the entire electrode plate. The oil content in the separator may be, for example, 12 mass% or more and 20 mass% or less, or may be 15 mass% or more and 20 mass% or less. That is, it is possible to increase the oil content in the separator, and improve the antioxidant deterioration resistance of the separator by the oil, and further improve the IS life.

[0019] Hereinafter, the fully charged state of the liquid-type lead-acid battery is defined according to JIS D 5301:2019. More specifically, in a water tank at 25°C ± 2°C, with a current (A) of 0.2 times the numerical value described as the rated capacity (the numerical value with the unit of Ah), the terminal voltage (V) during charging measured every 15 minutes or the electrolyte density converted to 20°C is continuously measured three times until it shows a constant value with three significant figures, and the state of the lead-acid battery being charged is defined as the fully charged state.

[0020] The fully charged state refers to the state in which a preformed lead-acid battery is fully charged. The full charge of the lead-acid battery may be immediately after formation if it is after formation, or may be performed after a lapse of time from formation. For example, a lead-acid battery during use (preferably in the initial stage of use) after formation may be fully charged. The battery in the initial stage of use refers to a battery in which not much time has passed since the start of use and it has hardly deteriorated.

[0021] In this specification, in the electrode plate, the vertical direction is defined such that the side where the ear part is provided is the upper side, and the side opposite to the ear part is the lower side. In the separator, the side facing the upper side (that is, the ear part side) of the electrode plate is the upper side of the separator, and the side facing the lower side of the electrode plate is the lower side of the separator. The vertical directions of the electrode plate and the separator are the same as the vertical direction in the vertical direction of the lead-acid battery, respectively.

[0022] Hereinafter, each component of the lead-acid battery will be described more specifically. However, each component is not limited to the following description.

[0023] (Positive electrode plate) The positive electrode plate is composed of a positive electrode current collector and a positive electrode active material. The positive electrode plate may be a paste-type positive electrode plate. The positive electrode active material is held by the positive electrode current collector.

[0024] The positive electrode active material is the part of the positive electrode plate excluding the positive electrode current collector. Members such as mats and pasting papers may be attached to the positive electrode plate. Such members (also referred to as attached members) are included in the positive electrode plate because they are used integrally with the positive electrode plate. When the positive electrode plate includes an attached member, the positive electrode active material is the part of the positive electrode plate excluding the positive electrode current collector and the attached member.

[0025] The positive electrode active material contains a positive electrode active substance (lead dioxide or lead sulfate) that exhibits capacitance through an oxidation-reduction reaction. The positive electrode active material may contain a trace amount of Sb element, but it is desirable not to contain the Sb element. The content of the Sb element in the positive electrode active material is preferably less than 0.05% by mass. The positive electrode active material may contain other additives as required.

[0026] The positive electrode current collector is formed, for example, by processing a sheet of lead or a lead alloy. Examples of the processing method include expansion processing or punching processing. A lattice-shaped positive electrode current collector may be used.

[0027] As the lead alloy used for the positive electrode current collector, a Pb-Ca-based alloy or a Pb-Ca-Sn-based alloy having excellent corrosion resistance and mechanical strength is preferable. The positive electrode current collector may have lead alloy layers with different compositions, and there may be a plurality of lead alloy layers.

[0028] Positive electrodes are obtained by chemically transforming unformed positive electrodes. This chemical transformation can be carried out within the battery case of a lead-acid battery. For example, the transformation can proceed by immersing a group of electrodes containing unformed positive electrodes in an electrolyte (an aqueous solution containing sulfuric acid) and charging the electrode group. The chemical transformation may also be carried out before the assembly of the lead-acid battery or the electrode group.

[0029] Unformed positive electrode plates are obtained by filling a positive electrode current collector with positive electrode paste, followed by maturation and drying. The positive electrode paste contains lead powder, water, and sulfuric acid, and optionally includes additives such as reinforcing materials.

[0030] (Negative electrode plate) The negative electrode plate consists of a negative electrode current collector and a negative electrode material. The negative electrode material is held by the negative electrode current collector.

[0031] The negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector. The negative electrode plate may have an adhesive component attached. Since the adhesive component is used integrally with the negative electrode plate, it is included in the negative electrode plate. If the negative electrode plate includes an adhesive component, the negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector and the adhesive component.

[0032] The negative electrode material contains a negative electrode active material (lead or lead sulfate) that exhibits capacity through a redox reaction and element Bi, and may also contain shrinkage inhibitors (such as organic shrinkage inhibitors), carbonaceous materials (such as carbon black), barium sulfate, etc. The negative electrode material may also contain other additives as needed.

[0033] Bi (Bi) may be present in the negative electrode material in the form of oxides or compounds such as sulfates. The Bi content in the negative electrode material should be between 100 ppm and 350 ppm by mass, but preferably 300 ppm or less. If the Bi content is too high, the hydrogen generation potential at the negative electrode shifts to the noble side, increasing the amount of hydrogen generated by the electrolysis of water on the surface of the negative electrode material. This can lead to insufficient charging of the negative electrode material and, conversely, a decrease in IS (Isolation Stability) life. The Bi element content in the negative electrode material may be 100 ppm or more and 250 ppm or less, 100 ppm or more and 230 ppm or less, 150 ppm or more and 300 ppm or less, 150 ppm or more and 250 ppm or less, 150 ppm or more and 230 ppm or less, 170 ppm or more and 300 ppm or less, 170 ppm or more and 250 ppm or less, or 170 ppm or more and 230 ppm or less. Even if the Bi element is in the form of a compound, it is sufficient if the content considering only the mass of the bismuth element is within the above range.

[0034] The negative electrode current collector is formed, for example, by processing a sheet of lead or a lead alloy. Processing methods include, for example, expanding or punching. A grid-like negative electrode current collector may also be used.

[0035] Preferred lead alloys for the negative electrode current collector include Pb-Sb alloys, Pb-Ca alloys, and Pb-Ca-Sn alloys. The negative electrode current collector may also contain at least one additive element selected from the group consisting of Ba, Ag, Al, Bi, As, Se, Cu, etc.

[0036] The negative electrode plate is obtained by chemically transforming an unformed negative electrode plate. This chemical transformation can be carried out within the battery case of a lead-acid battery. For example, the transformation can proceed by immersing a group of plates containing unformed negative electrode plates in an electrolyte (an aqueous solution containing sulfuric acid) and charging the plate group. The chemical transformation may also be carried out before the assembly of the lead-acid battery or the plate group.

[0037] The unformed negative electrode plate is obtained by filling a negative electrode current collector with a negative electrode paste and subjecting it to aging and drying. The aging is preferably carried out at a temperature higher than room temperature and high humidity. The negative electrode paste contains lead powder, a Bi compound, an organic anti-shrinkage agent, water, and sulfuric acid, and may contain various additives as required. Spongy lead is generated by formation. As the Bi compound, for example, bismuth sulfate (Bi2(SO4)3) can be used. At least a part of the Bi compound remains as Bi element in the negative electrode material.

[0038] <Content of Bi element> The content of Bi element in the negative electrode material is determined by decomposing a fully charged lead storage battery at the initial stage of use, taking out the negative electrode plate, washing it with water, drying it, collecting the negative electrode material, pulverizing the sample, dissolving it in a (1 + 3) nitric acid solution heated to about 100 °C, filtering the insoluble matter, and performing ICP (Inductively Coupled Plasma) emission analysis on the solution.

[0039] The ratio of the mass of the positive electrode material to the mass of the negative electrode material (hereinafter, also referred to as the Mp / Mn ratio) may be 1.3 or more and 1.35 or less. The mass of the positive electrode material is the mass of the positive electrode material possessed by one positive electrode plate. The mass of the negative electrode material is the mass of the negative electrode material possessed by one negative electrode plate. Increasing the Mp / Mn ratio to 1.3 or more and 1.35 or less means reducing the amount of the negative electrode material used. In other words, the lead storage battery can be lightened by controlling the Mp / Mn ratio to 1.3 or more and 1.35 or less.

[0040] When the Mp / Mn ratio is 1.3 or more and 1.35 or less, the load on the negative electrode plate becomes considerably large, and the charge acceptance property is likely to deteriorate. On the other hand, when a sufficient amount of Bi element is contained in the negative electrode material and the integrated pore volume A of the separator is controlled to 0.93 mL / g or more, the flow of the electrolyte is easily ensured. Therefore, even if the Mp / Mn ratio is increased to 1.3 or more and 1.35 or less, the sulfation of the negative electrode plate hardly progresses.

[0041] (Separator) Porous separators can be obtained, for example, by extruding a resin composition containing a resin component (hereinafter also referred to as a base polymer), an inorganic component, an oil that functions as a pore-forming agent, and a penetrating agent (surfactant) into a sheet, and then removing a portion of the oil. By removing a portion of the oil, micropores are formed in the matrix of the base polymer. The oil remaining in the separator functions as an additive that improves the oxidation resistance of the separator.

[0042] The cumulative pore volume A of the separator, between 0.005 μm and 10 μm, is controlled to 0.93 mL / g or higher. This significantly improves the balance between the driving force of Bi to cause the electrolyte to flow and the available flow paths for the electrolyte, thereby mitigating the shortening of IS lifespan due to capacity reduction, as described above.

[0043] The cumulative pore volume A of the separator, which is between 0.005 μm and 10 μm in diameter, is the sum of the volumes of pores between 0.005 μm and 10 μm in the volume-based pore size distribution of the separator. The cumulative pore volume A accounts for, for example, 70% to 90% of the total pore volume B. The total pore volume B is the sum of the volumes of all pores in the separator.

[0044] The volume-based pore size distribution of separators often shows a peak with the highest frequency in the range of 2 μm to 3 μm. The cumulative pore volume A is preferably increased by increasing the number of pores with a smaller diameter than the pore size showing the highest frequency (for example, in the range of 0.1 μm or more and 0.2 μm or less). Increasing the number of pores within the range of 0.1 μm or more and 0.2 μm or less hardly reduces the strength of the separator and increases the flow paths suitable for the flow of the electrolyte.

[0045] The cumulative pore volume A of the separator, between 0.005 μm and 10 μm, should be 0.93 mL / g or more, but may also be 1.05 mL / g or more, 1.1 mL / g or more, or 1.2 mL / g or more. The larger the cumulative pore volume A, the greater the electrolyte flow path. However, if the cumulative pore volume A is excessively large, the durability of the separator may decrease. It is desirable that the cumulative pore volume A be, for example, 1.4 mL / g or less.

[0046] The pore size distribution of the separator can be controlled, for example, by adjusting at least one (typically two or more) of the type of oil, amount of oil, inorganic component content, and amount of oil removed from the resin composition.

[0047] The oil is a hydrophobic substance that separates from water, and may be a mineral oil or a synthetic oil. Mineral oils may include paraffin, petrolatum, or liquid paraffin (mineral oil). Synthetic oils may include silicone oil. One type of oil may be used, or two or more types of oils may be used in combination. The oil may be liquid or solid at room temperature (temperature between 20°C and 35°C), but is generally liquid.

[0048] The oil content in the separator may be, for example, 12% by mass or more and 20% by mass or less, 12% by mass or more and 18% by mass or less, 15% by mass or more and 20% by mass or less, or 15% by mass or more and 18% by mass or less. Within the above ranges, the resistance of the separator is low and the oxidation resistance due to the oil is sufficiently exhibited, which is even more advantageous for improving IS life.

[0049] Polyolefins are preferably used as the base polymer. Polyolefins may be used in combination with other polymers as the base polymer. The other polymers are not particularly limited as long as they are used in separators for lead-acid batteries. The ratio of polyolefins to the total 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.

[0050] Polyolefins are polymers that contain olefins as monomers. Polyolefins include, for example, homopolymers of olefins, copolymers containing monomer units of different olefins, and copolymers containing olefins and copolymerizable monomers as monomer units. Copolymers containing olefins and copolymerizable monomers as monomer units contain one or more olefins as monomer units. Copolymerizable monomers are polymerizable monomers other than olefins that can copolymerize with olefins.

[0051] Polyolefins are at least C 2-3 It may also be a polymer containing olefin as monomer units. 2-3 Examples of olefins include at least one selected from the group consisting of ethylene and propylene. Examples of polyolefins include polyethylene, polypropylene, and C 2-3 Copolymers containing olefins as monomer units (e.g., ethylene-propylene copolymers) are more preferred. Among polyolefins, at least polyethylene is preferred. Polyethylene may be used in combination with other polyolefins.

[0052] As the inorganic component, ceramic particles are preferred, for example. As the ceramics constituting the ceramic particles, at least one selected from the group consisting of silica, alumina, and titania can be cited.

[0053] The inorganic component content in the separator may be, for example, 40% by mass or more, and may be 50% by mass or more. The inorganic component content may be, for example, 80% by mass or less, and may be 75% by mass or less, or 70% by mass or less.

[0054] The penetrating agent (surfactant) may be either an ionic surfactant or a nonionic surfactant. The surfactant may be used alone or in combination of two or more types.

[0055] The content of the penetrant in the separator is, for example, 0.01% by mass or more, and may also be 0.1% by mass or more, and may also be, for example, 5% by mass or less, and may also be 10% by mass or less.

[0056] A minimum separator thickness of, for example, 0.12 mm or more makes it easier to ensure strength. Also, a minimum separator thickness of, for example, 0.25 mm or less makes it easier to keep the separator's resistance low. The minimum separator thickness can be 0.12 mm or more and 0.25 mm or less, 0.12 mm or more and 0.22 mm or less, 0.12 mm or more and 0.2 mm or less, 0.15 mm or more and 0.25 mm or less, 0.15 mm or more and 0.2 mm or less, 0.15 mm or more and 0.2 mm or less, 0.2 mm or more and 0.25 mm or less, or 0.2 mm or more and 0.22 mm or less. The minimum separator thickness is calculated as the average of the thicknesses measured at any five points in a cross-sectional photograph of the separator.

[0057] The separator may or may not have ribs. The separator comprises, for example, a base portion and ribs erected from the surface of the base portion. The ribs may be provided on only one surface of the base portion, or on both surfaces. The minimum thickness of a separator with ribs is the thickness of the base portion, and is calculated as the average of the thicknesses measured at any five locations on the base portion.

[0058] The separator may be in the form of a sheet, folded in an accordion shape, or formed into a bag shape. Either the positive electrode plate or the negative electrode plate may be wrapped in a bag-shaped separator.

[0059] The ribs may be formed on a sheet when the resin composition is extruded, or they may be formed by pressing the molded sheet with a roller having grooves corresponding to the ribs.

[0060] The height of the rib may be 0.05 mm or more, or 1.2 mm or less. The rib height is the height of the portion that protrudes from the main surface of the base (projection height). It is desirable that the height of the rib provided in the region facing the positive electrode plate of the separator be 0.4 mm or more. The rib height is calculated as the average value of the height from one main surface of the base, measured at any 10 points on the rib in a cross-sectional photograph of the separator.

[0061] For measuring and analyzing the thickness of the separator and the height of the ribs, separators removed from fully charged lead-acid batteries in their initial state of use are used. Prior to measurement and analysis, the separators removed from the lead-acid batteries are washed and dried. The washed and dried separators are referred to as Sample A.

[0062] The separators removed from the lead-acid battery are cleaned and dried using the following procedure: The separators removed from the lead-acid battery are immersed in pure water for 1 hour to remove sulfuric acid from the separators. Then the separators are removed from the liquid they were immersed in and allowed to stand at 25°C ± 5°C for at least 16 hours to dry, and this is designated as Sample A.

[0063] <Pore size distribution> The volume-based pore size distribution of the separator is determined by the mercury intrusion method. To determine the pore size distribution, first, sample A1 is prepared by processing the central region (key part) of separator sample A into a 20 mm x 5 mm strip. For separators with ribs, sample A1 is prepared by processing the base part (the part with the minimum thickness) into a 20 mm x 5 mm strip, excluding the ribs.

[0064] The pore size distribution of the separator is measured using sample A1 with a mercury porosimeter (e.g., Shimadzu Corporation, Autopore IV9510). The measurement pressure range is from 4 psia (≒27.6 kPa) to 60,000 psia (≒414 MPa). The pore size distribution used is the range of pores with a diameter of 0.005 μm to 50 μm. In other words, the total pore volume B is the sum of the volumes of pores with a diameter of 0.005 μm to 50 μm. The cumulative pore volume A is calculated for 10 samples of sample A1, and the average value of the cumulative pore volume A is calculated. The resulting average value is taken as the cumulative pore volume A of the separator.

[0065] <Oil content> To determine the oil content in the separator, approximately 0.5 g of the essential portion of sample A is taken as sample A2, accurately weighed, and the initial mass of sample A2 (m0) is determined. The weighed sample A2 is placed in a glass beaker of appropriate size, and 50 mL of n-hexane is added. Then, the beaker and sample are subjected to ultrasound for approximately 30 minutes to dissolve the oil contained in sample A2 into the n-hexane. Next, sample A2 is removed from the n-hexane, dried in the air at room temperature (temperature between 20°C and 35°C), and then weighed to determine the mass of sample A2 after oil removal (m1). The oil content is calculated using the following formula. Oil content (mass %) = (m0 - m1) / m0 × 100

[0066] <Content of inorganic components> A portion of the main part of Sample A, prepared in the same manner as described above, is taken as Sample A3, accurately weighed, placed in a platinum crucible, and heated with a Bunsen burner until no more white smoke is emitted. Next, the resulting residue is heated in an electric furnace (in an oxygen stream, 550°C ± 10°C) for about 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 expressed as the inorganic component content (mass %).

[0067] (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.

[0068] The specific gravity of the electrolyte at 20°C is, for example, 1.10 or higher. The specific gravity (density) of the electrolyte at 20°C may be 1.35 or lower. These specific gravity values ​​are for the electrolyte of a fully charged lead-acid battery.

[0069] The lead-acid battery according to an 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 embodiments.

[0070] Figure 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 comprises a battery case 12 that houses an electrode plate group 11 and an electrolyte (not shown). The inside of the battery case 12 is divided into a plurality of cell chambers 14 by a partition wall 13. Each cell chamber 14 houses one electrode plate group 11. The opening of the battery case 12 is closed with a lid 15 equipped with a negative electrode terminal 16 and a positive electrode terminal 17. The lid 15 is provided with a liquid inlet plug 18 for each cell chamber. When replenishing water, the liquid inlet plug 18 is removed and the water is replenished. The liquid inlet plug 18 may also have a function of discharging gas generated in the cell chamber 14 to the outside of the battery.

[0071] Each electrode plate group 11 is constructed by stacking multiple negative electrode plates 2 and positive electrode plates 3 via separators 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, a negative electrode shelf 6 that connects multiple negative electrode plates 2 in parallel is connected to a through connector 8, and a positive electrode shelf 5 that connects multiple positive electrode plates 3 in parallel is connected to a positive electrode column 7. The positive electrode column 7 is connected to a positive electrode terminal 17 on the outside of the lid 15. In the cell chamber 14 located at the other end of the battery case 12, a negative electrode column 9 is connected to the negative electrode shelf 6, and a through connector 8 is connected to the positive electrode shelf 5. The negative electrode column 9 is connected to a negative electrode terminal 16 on the outside of the lid 15. Each through connector 8 passes through a through hole provided in the partition wall 13 and connects the electrode plate groups 11 of adjacent cell chambers 14 in series.

[0072] The evaluation methods for each characteristic are described below. (IS life) IS life is evaluated based on the number of cycles required to reach the end of its lifespan, in accordance with JIS D5306:2021, in the following charge-discharge cycle test. A fully charged lead-acid battery with a rated voltage of 12V is subjected to repeated discharge and charging under the following conditions. Here, (a) to (c) are performed in a water bath at 40℃ ± 2℃. (a) Discharge 1:I D Discharge time of 59 seconds ± 0.2 seconds at a current of ±1A (I D =18.3I 20 (A), However I 20 This is the 20-hour rate current (A), which is 1 / 20th the current (A) of the value listed as the rated capacity (a value expressed in Ah). (b) Discharge 2: Discharge for 1.0 seconds ± 0.2 seconds at a current of 300A ± 1A (c) Charging: Charging at 14.0V ± 0.03V with a limited current of 100.0A ± 0.5A for 60.0 seconds ± 0.3 seconds. (d) Repetition: Repeat steps (a) to (c) above, which constitute one cycle, until the end of the lifespan. During this time, a 40-48 hour break is taken every 3600 cycles. The end of the lifespan is determined when the discharge voltage during testing falls below 7.2V.

[0073] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0074] Lead-acid batteries E1-E49 and R1-R12 (1) Fabrication of the negative electrode plate A negative electrode paste was prepared by mixing lead oxide, bismuth sulfate, carbon black, barium sulfate, lignin, water, and sulfuric acid. The negative electrode paste was filled into the mesh of an expanded grid (negative electrode current collector) made of antimony-free Pb-Ca-Sn alloy, and then 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, and lignin were adjusted so that they were 0.3 mass%, 2.1 mass%, and 0.1 mass%, respectively, when measured in the fully charged state after formation.

[0075] The amount of bismuth sulfate was adjusted so that the ppm value of element Bi in the negative electrode material, measured in the fully charged state of the pre-formed chemicals using the procedure described above, was as shown in Tables 1-3.

[0076] (2) Fabrication of the positive electrode plate A positive electrode paste was prepared by mixing lead oxide, reinforcing material (synthetic resin fiber), water, and sulfuric acid. The positive electrode paste was filled into the mesh of an expanded grid made of antimony-free Pb-Ca-Sn alloy, and after aging and drying, an unformed positive electrode plate with a width of 100 mm, a height of 115 mm, and a thickness of 1.6 mm was obtained.

[0077] (3) Fabrication of separators A resin composition containing polyethylene, silica particles, paraffin-based oil, and a penetrating agent was extruded into a sheet, and then a portion of the oil was removed to form a separator. The penetrating agent was used at a ratio of 2 parts by mass per 100 parts by mass of polyethylene.

[0078] The pore size distribution (cumulative pore volume A) and oil content of the separator were controlled to the values ​​shown in Tables 1-3 by adjusting at least one of the following: the mixing ratio of polyethylene, silica particles, and oil, and the amount of oil removed.

[0079] For extrusion molding, a mold with a shape that forms multiple striped ribs was used. A sheet-like separator was folded in half to form a bag, thereby obtaining a bag-shaped separator. By changing the slit width of the mold, the thickness of the base portion of the separator was controlled to the values ​​shown in Tables 1 to 3.

[0080] On the outer surface of the bag-shaped separator, multiple striped mini-ribs with a protrusion height of 0.18 mm were provided at a pitch of 1 mm on both edges in the width direction of the bag-shaped separator. On the outer surface of the bag-shaped separator, in the area inward from both edges where the mini-ribs are provided, multiple striped main ribs with a protrusion height of 0.6 mm were provided at a pitch of 9.8 mm. The thickness of the separator base, the protrusion height of the ribs, and the pitch of the ribs are values ​​obtained for the separator before the manufacture of the lead-acid battery, but they are almost the same as the values ​​measured by the procedure described above for the separator removed from the manufactured lead-acid battery.

[0081] (4) Manufacturing of lead-acid batteries Each unformed negative electrode plate was housed in a bag-shaped separator, and a plate group was formed by alternately stacking seven unformed negative electrode plates and six unformed positive electrode plates per cell. The tabs of the positive electrode plates and the tabs of the negative electrode plates were welded to the positive and negative electrode shelves, respectively, using the cast-on-strap (COS) method. The plate groups were inserted into a polypropylene battery case, electrolyte was poured in, and the plates were formed inside the case to assemble liquid-type lead-acid batteries E1-E49 and R1-R12 with a rated voltage of 12V and a rated capacity of 33Ah (20-hour rate capacity (capacity when discharged at a current (A) of 1 / 20 of the value stated in the rated capacity)). Six plate groups are connected in series inside the battery case.

[0082] The density of the electrolyte solution produced after the chemical conversion of the lead-acid battery at 20°C was adjusted to be in the range of 1.280 to 1.290.

[0083] [evaluation] The fabricated lead-acid batteries were fully charged using the procedure described above, and the IS life (number of cycles until the terminal voltage of the lead-acid battery reaches 7.2V) was determined. The results are shown in Tables 1-3. Each evaluation is shown as a percentage (%) with the result of lead-acid battery R4 set to 100%.

[0084] [Table 1]

[0085] [Table 2]

[0086] [Table 3]

[0087] As shown in Tables 1 and 2, lead-acid batteries E1 to E49, in which the negative electrode material contains 100 ppm or more of Bi element by mass and the integrated pore volume A of the separator (0.005 μm or more and 10 μm or less) is 0.93 mL / g or more, all showed good IS life. In particular, the improvement in IS life was significant when the integrated pore volume A was between 1.05 mL / g and 1.4 mL / g (E4 to E9, E11, E17 to E25, E40, E44 to E49).

[0088] Comparing E26 to E31, it can be seen that the oil content in the separator should ideally be between 12% and 20% by mass. If the oil content is excessively high, the resistance of the separator will increase, which is thought to reduce the improvement in IS life. Conversely, if the oil content is excessively low, the oxidative degradation of the separator will progress more easily, which is also thought to reduce the improvement in IS life.

[0089] Comparing E32 to E38, it can be seen that the minimum thickness of the separator (base thickness) should ideally be between 0.12 mm and 0.25 mm. Separators with a base thickness of less than 0.12 mm are considered superior from the perspective of IS life, but they are considered difficult to manufacture in mass production. On the other hand, if the base thickness exceeds 0.25 mm, the resistance of the separator increases, so the improvement in IS life of the separator decreases, as seen in E37 and E38.

[0090] Table 3 shows that even when the negative electrode material contains 100 ppm or more of Bi by mass, the IS lifetime cannot be improved if the cumulative pore volume A is insufficient, as in R1 to R6. Furthermore, even when the cumulative pore volume A is sufficiently large, as in R7 to R12, the IS lifetime decreases if the Bi content is too low, as in R7 and R8, or too high, as in R9 to R12. This is thought to be because if the Bi content is too low, gas generation at the negative electrode is reduced, thus diminishing the effect of suppressing stratification. Conversely, if the Bi content is too high, the hydrogen generation potential at the negative electrode shifts to the noble side, increasing the amount of hydrogen generated by the electrolysis of water on the surface of the negative electrode material, resulting in insufficient charging of the negative electrode material.

[0091] Furthermore, lead-acid batteries in which the Bi element content in the negative electrode material is 100 ppm or more and less than 350 ppm by mass, and the cumulative pore volume A of the separator (0.005 μm or more and 10 μm or less) is 0.93 mL / g or more, showed a significantly improved IS life compared to lead-acid batteries in which the Bi element content in the negative electrode material is less than 100 ppm or 350 ppm or more by mass, and the cumulative pore volume A of the separator (0.005 μm or more and 10 μm or less) is less than 0.93 mL / g. [Industrial applicability]

[0092] The lead-acid battery according to the present invention can be suitably used, for example, as a starting power source for IS-controlled vehicles (automobiles, motorcycles, etc.), industrial energy storage devices, and power sources for electric vehicles (forklifts, etc.). These applications are merely examples, and the applications of the lead-acid battery according to the present invention are not limited. [Explanation of symbols]

[0093] 1: Lead-acid battery, 2: Negative electrode plate, 3: Positive electrode plate, 4: Separator, 5: Positive electrode shelf, 6: Negative electrode shelf, 7: Positive electrode column, 8: Through connector, 9: Negative electrode column, 11: Electrode plate group, 12: Battery case, 13: Partition wall, 14: Cell chamber, 15: Cover, 16: Negative electrode terminal, 17: Positive electrode terminal, 18: Electrode cap

Claims

1. It comprises 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 aforementioned negative electrode plate includes a negative electrode material, The aforementioned negative electrode material contains the element Bi, The content of the element Bi in the negative electrode material is 100 ppm or more and less than 350 ppm by mass. The separator is porous, The minimum thickness of the separator is 0.20 mm or less. A lead-acid battery in which the separator has an integrated pore volume A of 0.005 μm or more and 10 μm or less, which is 0.93 mL / g or more.

2. The lead-acid battery according to claim 1, wherein the cumulative pore volume A is 1.05 mL / g or more and 1.4 mL / g or less.

3. The separator contains oil, The lead-acid battery according to claim 1 or 2, wherein the oil content in the separator is 12% by mass or more and 20% by mass or less.

4. The lead-acid battery according to claim 1 or 2, wherein the minimum thickness of the separator is 0.12 mm or more.

5. The lead-acid battery according to claim 1 or 2, wherein the ratio of the mass of the positive electrode material to the mass of the negative electrode material is 1.3 or more and 1.35 or less.

6. A lead-acid battery according to claim 1 or 2, for use in a vehicle with idle stop control.

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