lead-acid batteries

Abstract

SOLUTION: To provide a lead acid battery that includes a positive electrode plate, a negative electrode plate, a resin porous film interposed between the positive electrode plate and the negative electrode plate, and an electrolyte, in which the porous film includes a crystalline region and an amorphous region, and in the X-ray diffraction spectrum of the porous film, the crystallinity expressed as 100×Ic / (Ic+Ia) is 18% or more, Ic is the integrated intensity of the diffraction peak with the maximum peak height among the diffraction peaks corresponding to the crystalline region, Ia is the integrated intensity of the halo corresponding to the amorphous region, and the chemical oxygen demand in the electrolyte is equal to or less than 160 mg / L.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a lead-acid battery. [Background technology]

[0002] Lead-acid batteries are used in a variety of applications, including automotive and industrial use. A lead-acid battery consists of a positive electrode plate, a negative electrode plate, a separator between them, and an electrolyte. The separator in a lead-acid battery requires various performance characteristics. Generally, porous polyolefin films are used as separators.

[0003] Patent Document 1 proposes a separator for a lead-acid battery comprising a polyolefin microporous membrane, wherein the polyolefin microporous membrane comprises polyethylene, preferably ultra-high molecular weight polyethylene, a particulate filler, and a treatment plasticizer, wherein the particulate filler is present in an amount of 40% or more by weight, and the polyethylene comprises a shish-kebab forming polymer including a plurality of elongated chain crystals (shishi formation) and a plurality of folded chain crystals (kebab formation), wherein the average repetition or period of the kebab formation is from 1 nm to 150 nm, preferably less than 120 nm.

[0004] Patent document 2 proposes a lead-acid battery characterized by containing a reducing organic substance in an electrolyte solution of 0.5 mg / L to 3 mg / L.

[0005] Patent Document 3 proposes a ribbed separator for lead-acid batteries containing 5 to 30% by mass of oil, obtained by heating and melting a raw material composition consisting of a mixture of 20 to 60% by mass of polyolefin resin, 80 to 40% by mass of inorganic powder, and 40 to 240% by mass of mineral oil relative to these components, kneading it, forming it into a sheet having ribs, immersing it in an immersion tank of an organic solvent capable of dissolving the oil to extract and remove a portion of the oil, and then heating and drying it, characterized in that the difference in oil content between the rib portion and the base portion of the separator is 5% by mass or less. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2019-514173 [Patent Document 2] Japanese Patent Publication No. 2005-251394 [Patent Document 3] Japanese Patent Publication No. 2001-338631 [Overview of the project] [Problems that the invention aims to solve]

[0007] The inventors have found that reducing the chemical oxygen demand (COD), which is an indicator of the concentration of organic components in the electrolyte, improves charge acceptance.

[0008] However, the inventors have newly discovered that while reducing the amount of organic components in the electrolyte improves charge acceptance, this comes at the cost of a shorter lifespan in high-temperature overcharge tests. For example, in light-load life tests (e.g., 75°C JIS light-load life test (2-part method)), the test conditions are such that the amount of charge is greater than the amount of discharge. As a result, the lead-acid battery becomes overcharged during the test, generating hydrogen at the negative electrode and oxygen at the positive electrode due to electrolyte decomposition. Reducing the amount of organic components in light-load life tests improves charge acceptance, which tends to cause the lead-acid battery to become even more overcharged.

[0009] Oxygen generated on the positive electrode side attacks the separator's constituent materials, causing oxidative degradation of the separator. This leads to cracks or tears in the separator, causing the positive and negative electrode materials to come into contact at the damaged area of ​​the separator, resulting in a short circuit and ultimately ending the lifespan of the device. [Means for solving the problem]

[0010] One aspect of the present disclosure includes a positive electrode plate, a negative electrode plate, a porous resin film interposed between the positive electrode plate and the negative electrode plate, and an electrolytic solution. The porous film includes a crystalline region and an amorphous region. In the X-ray diffraction spectrum of the separator, the crystallinity represented by 100×I c / (I c +I a ) is 18% or more. I c is the integrated intensity of the diffraction peak with the maximum peak height among the diffraction peaks corresponding to the crystalline region, and I a is the integrated intensity of the halo corresponding to the amorphous region. The chemical oxygen demand in the electrolytic solution is 160 mg / L or less. This relates to a lead-acid battery.

Advantages of the Invention

[0011] According to the present disclosure, in a lead-acid battery, it is possible to improve the charge acceptance while improving the life in a high-temperature overcharge state test.

Brief Description of the Drawings

[0012] [Figure 1] It is a partially cutaway perspective view showing the appearance and internal structure of a lead-acid battery according to an embodiment of the present invention.

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials may be exemplified, but other numerical values and materials may be applied as long as the effects of the present disclosure can be obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less". In the following description, when the lower limit and the upper limit of a numerical value regarding a specific physical property or condition are exemplified, any combination of any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined as long as the lower limit is not more than the upper limit. When a plurality of materials are exemplified, one of them may be selected and used alone, or two or more of them may be used in combination.

[0014] Furthermore, this disclosure encompasses any combination of matters described in two or more claims arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims arbitrarily selected from the multiple claims set forth in the attached claims is possible, as long as it does not result in a technical inconsistency.

[0015] In this specification, the vertical direction of a lead-acid battery or its components (plates, case, separator, etc.) refers to the vertical direction of the lead-acid battery as it is positioned in its intended use. Each of the positive and negative plates is provided with tabs for connecting to external terminals. For example, in an electrolyte battery, the tabs are provided on the top of the plate so as to protrude upward.

[0016] The lead-acid battery relating to this disclosure may be a valve-regulated lead-acid battery (VRLA type battery), but an electrolytic lead-acid battery (vented type battery) is preferred because it can effectively utilize the effects of COD reduction.

[0017] A lead-acid battery comprises a positive electrode plate, a negative electrode plate, a separator interposed between the positive and negative electrode plates, and an electrolyte. The electrolyte contains sulfuric acid. Charging and discharging proceed through the movement of sulfate ions between the positive and negative electrode plates and the electrolyte. During discharge, sulfate ions move to the positive and negative electrode plates, causing the density of the electrolyte to decrease. During charging, sulfate ions move from the positive and negative electrode plates into the electrolyte, causing the density of the electrolyte to increase.

[0018] The separator includes a porous film made of resin. The porous film can be used as a separator on its own. Therefore, the porous film may also be referred to as a separator. In addition to the porous film, the separator may also include a nonwoven fabric.

[0019] The positive electrode plate, the negative electrode plate, and the separator constitute an electrode plate group. The electrode plate group and the electrolyte together constitute a cell. One electrode plate group constitutes one cell. A lead storage battery includes one or more electrode groups and thus includes one or more cells. There is no particular limitation on the number of positive electrode plates and negative electrode plates included in one electrode plate group. The electrode plate group included in the lead storage battery according to the present disclosure includes, for example, a total of 12 or more positive electrode plates and negative electrode plates. The plurality of electrode plate groups are usually accommodated in respective individual cell chambers and connected in series with each other.

[0020] The positive electrode plate includes a positive electrode material. The positive electrode material includes, as a positive electrode active material that exhibits capacitance through an oxidation-reduction reaction, at least lead dioxide during charging and at least lead sulfate during discharging.

[0021] The negative electrode plate includes a negative electrode material. The negative electrode material includes, as a negative electrode active material that exhibits capacitance through an oxidation-reduction reaction, at least lead during charging and at least lead sulfate during discharging.

[0022] (1) The lead storage battery according to an embodiment of the present disclosure includes a positive electrode plate, a negative electrode plate, a porous resin film interposed between the positive electrode plate and the negative electrode plate, and an electrolyte. The porous film includes a crystalline region and an amorphous region. In the X-ray diffraction spectrum of the separator, the crystallinity represented by 100×I c / (I c +I a ) is 18% or more. I c is the integrated intensity of the diffraction peak with the maximum peak height among the diffraction peaks corresponding to the crystalline region, and I a is the integrated intensity of the halo corresponding to the amorphous region. The chemical oxygen demand (COD) in the electrolyte is 160 mg / L or less.

[0023] COD (Chemical Oxygen Demand) is the amount of oxygen required to oxidize oxidizable substances in an electrolyte. The COD in an electrolyte can be considered an indicator of the concentration of organic components in the electrolyte. In this specification, COD refers to the COD in an electrolyte sample taken from a fully charged lead-acid battery in its initial state of use. An initial-use battery is one that has not been in use for very long and has shown little degradation.

[0024] The lead-acid battery described in (1) above has excellent charge acceptance and excellent lifespan performance in high-temperature overcharge tests.

[0025] (2) In the lead-acid battery described in (1) above, the chemical oxygen demand may be 100 mg / L or less.

[0026] The lead-acid battery described in (2) above has superior charge acceptance and its lifespan performance does not deteriorate easily in high-temperature overcharge tests.

[0027] (3) In the lead-acid battery described in (1) or (2) above, the chemical oxygen demand may be 15 mg / L or more.

[0028] The lead-acid batteries described in (3) above are less likely to experience further deterioration in lifespan performance during high-temperature overcharge tests.

[0029] (4) In the lead-acid battery described in any one of (1) to (3) above, the degree of crystallinity may be 40% or less.

[0030] The porous film provided in the lead-acid battery described in (4) above is not only highly flexible but also easy to manufacture.

[0031] (5) In the lead-acid battery described in any one of (1) to (4) above, the porous film may have a thickness of 0.1 mm or more and 0.3 mm or less.

[0032] In the lead-acid battery described in (5) above, the porous film is sufficiently thin and has high strength, thus providing higher charge acceptance and superior lifespan performance in high-temperature overcharge tests.

[0033] The porous film comprising the lead-acid battery according to this disclosure includes a crystalline region and an amorphous region. In the X-ray diffraction spectrum of the separator, 100 × I c / ( I c +I a The degree of crystallinity, as indicated by ), is 18% or higher. However, I c This is the integrated intensity of the diffraction peak with the maximum peak height among the diffraction peaks corresponding to the crystalline region. a This represents the integrated intensity of the halo corresponding to the amorphous region.

[0034] Reducing the COD in the electrolyte decreases side reactions such as oxidation of organic components, making it easier for the charging reactions of the positive and negative electrode active materials to proceed, thus improving charge acceptance. Reducing the COD in the electrolyte to 160 mg / L or less significantly improves charge acceptance.

[0035] On the other hand, as charge acceptance increases, the battery tends to have a shorter lifespan in high-temperature overcharge tests. The reason for this is presumed to be as follows: When lead-acid batteries are more prone to overcharging due to high charge acceptance, the amount of hydrogen and oxygen generated by the decomposition of the electrolyte increases. The large amount of oxygen generated on the positive electrode side attacks the porous film. As a result, the porous film oxidizes and deteriorates, causing cracks or tears, leading to an internal short circuit and ultimately the end of the battery's lifespan.

[0036] In contrast, when the crystallinity of the porous film is 18% or higher, even when the COD in the electrolyte is reduced to 160 mg / L or less to improve charge acceptance, the deterioration of lifespan performance in high-temperature overcharge conditions is significantly suppressed. This is because the oxidation resistance of the porous film improves significantly once the crystallinity reaches a certain level. As a result, the period until cracks or tears occur in the porous film is extended, improving lifespan performance.

[0037] Furthermore, increasing the crystallinity of the porous film to 23% or higher significantly improves its lifespan performance in high-temperature overcharge tests when the COD in the electrolyte is reduced to 160 mg / L or less. This is because the time until cracks or tears occur in the porous film becomes even longer, making it rare for the porous film to reach the end of its lifespan due to degradation.

[0038] 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") is, for example, 1.2 or higher, and may also be 1.3 or higher. The Mp / Mn ratio may also be 1.4 or lower. The preferred range for the Mp / Mn ratio is, for example, 1.2 or higher and 1.4 or lower, and may also be 1.3 or higher and 1.4 or lower. The mass of the positive electrode material is the mass of the positive electrode material contained in one positive electrode plate. The mass of the negative electrode material is the mass of the negative electrode material contained in one negative electrode plate. Increasing the Mp / Mn ratio to 1.2 or higher means reducing the amount of negative electrode material used. In other words, by increasing the Mp / Mn ratio to 1.2 or higher, lead-acid batteries can be made lighter and less expensive. Also, when the Mp / Mn ratio is 1.2 or higher, the load on the positive electrode plate can be reduced, making it easier to suppress softening and detachment of the positive electrode plate.

[0039] The lead-acid battery relating to this disclosure is also suitable for use in vehicles with idle stop-start (ISS) control.

[0040] In this specification, the fully charged state of a liquid lead-acid battery is defined according to the definition in JIS D 5301:2019. More specifically, the 20-hour rate current I is used until the terminal voltage (in volts) during charging, measured every 15 minutes in a 25°C ± 2°C water bath, or the electrolyte density converted to a temperature of 20°C, shows a constant value with three significant figures for three consecutive times. 20 Twice the current 2I 20 (Unit: A) The fully charged state of a lead-acid battery is defined as the state in which it has been charged. Note that the 20-hour rate current I 20This refers to a current (A) that is 1 / 20th of the Ah value listed for the rated capacity. The value listed for the rated capacity is a value with the unit Ah (ampere-hour). The unit of the current set based on the value listed for the rated capacity is A (ampere). In the case of a valve-regulated lead-acid battery, a fully charged state is defined as a 20-hour rate current of 1 in an air chamber at 25℃±2℃. 20 Five times the current 5I 20 (Unit: A) Constant current constant voltage charging is performed at 2.67V / cell (16.00V for a lead-acid battery with a rated voltage of 12V), and charging is terminated when the total charging time reaches 24 hours.

[0041] A fully charged lead-acid battery is a lead-acid battery that has been charged to its full capacity after chemical formation. The timing of charging a lead-acid battery to its full capacity can be immediately after chemical formation or after some time has passed since chemical formation. For example, a lead-acid battery that has been chemically formed and is in use (preferably in the early stages of use) may be charged.

[0042] In this specification, a "battery in its initial use" refers to a battery that has not been in use for very long and has shown little to no degradation.

[0043] The lead-acid battery according to the embodiments of the present invention will be described in more detail below with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0044] The following describes examples of components of a lead-acid battery.

[0045] (Positive plate) The positive electrode plate comprises a positive electrode current collector and a positive electrode material. The positive electrode material is held by the positive electrode current collector. The positive electrode material is the portion of the positive electrode plate excluding the positive electrode current collector. Note that adhesive members such as conductive layers, mats, and pasting paper may be attached to the positive electrode plate. Since the adhesive members are used integrally with the positive electrode plate, they are included as components of the electrode plate. When the positive electrode plate includes adhesive members, the positive electrode material is the portion of the positive electrode plate excluding the positive electrode current collector and the adhesive members.

[0046] The positive electrode current collector may be formed by casting lead (Pb) or a lead alloy, or by processing a lead or lead alloy sheet. The processing method may be, for example, expansion or punching. Using a grid-like current collector as the positive electrode current collector makes it easier to support the positive electrode material.

[0047] As the lead alloy used for the positive electrode current collector, Pb-Ca alloys and Pb-Ca-Sn alloys, which have excellent corrosion resistance and mechanical strength, are preferred. The positive electrode current collector may have metal layers of different compositions, and the metal layers may be one layer or multiple layers.

[0048] The positive electrode material includes a positive electrode active material that exhibits capacity through a redox reaction. The positive electrode active material includes lead dioxide, lead sulfate, etc. The positive electrode material may also include additives as needed. Additives may include reinforcing materials, antimony compounds, etc. Examples of reinforcing materials include inorganic fibers and organic fibers.

[0049] Unformed positive electrode plates are obtained by maturing and drying a positive electrode current collector and a positive electrode paste filled in the positive electrode current collector. The positive electrode paste is prepared by kneading a mixture containing lead powder, water, and sulfuric acid. The positive electrode paste may contain additives as needed. These additives may include reinforcing materials, antimony compounds, etc. Such positive electrode plates are also called paste-type positive electrode plates.

[0050] A positive electrode plate can be obtained by chemically treating an untreated positive electrode plate. Chemical treatment may be carried out by immersing the electrode plate group, including the untreated positive electrode plate, in an electrolyte containing sulfuric acid in the battery case of a lead-acid battery, and charging the electrode plate group. Chemical treatment may also be carried out before the assembly of the lead-acid battery or the electrode plate group.

[0051] (Negative electrode plate) The negative electrode plate comprises a negative electrode current collector and a negative electrode material. The negative electrode material is held by the negative electrode current collector. The negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector. Note that adhesive members such as conductive layers, mats, and pasting paper may be attached to the negative electrode plate. The adhesive members are included as components of the negative electrode plate. When the negative electrode plate includes adhesive members, the negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector and the adhesive members.

[0052] 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. The processing method may be expansion or punching. Using a grid-like current collector as the negative electrode current collector makes it easier to support the negative electrode material.

[0053] The lead alloy used for the negative electrode current collector may be any of the following: a Pb-Sb alloy, a Pb-Ca alloy, or a Pb-Ca-Sn alloy. The lead alloy used for 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. The negative electrode current collector may have metal layers of different compositions, and the metal layers may be one layer or multiple layers.

[0054] The negative electrode material contains a negative electrode active material that exhibits capacity through a redox reaction. The negative electrode active material includes lead, lead sulfate, etc. The negative electrode material may also contain Bi element in an amount of 100 ppm to 300 ppm by mass. The negative electrode material may contain other additives as needed. The additives may include organic shrinkage inhibitors, carbonaceous materials, barium sulfate, etc.

[0055] Examples of organic shrinkage inhibitors include lignin, lignin sulfonic acid, and synthetic organic shrinkage inhibitors. Synthetic organic shrinkage inhibitors may be, for example, formaldehyde condensates of phenolic compounds. Organic shrinkage inhibitors may be used individually or in combination of two or more. The content of organic shrinkage inhibitors in the negative electrode material is, for example, 0.01% by mass or more and 1% by mass or less.

[0056] As carbonaceous materials, carbon black, artificial graphite, natural graphite, hard carbon, soft carbon, etc., can be used. One type of carbonaceous material may be used alone, or two or more types may be used in combination. The carbonaceous material content in the negative electrode material is, for example, 0.1% by mass or more and 3% by mass or less.

[0057] The barium sulfate content in the negative electrode material is, for example, 0.1% by mass or more and 3% by mass or less.

[0058] Unformed negative electrode plates are obtained by aging and drying a negative electrode current collector and a negative electrode paste filled in the negative electrode current collector. Aging is preferably carried out in an atmosphere with a temperature higher than room temperature and high humidity. The negative electrode paste is prepared by kneading a mixture containing lead powder, water, and sulfuric acid. The negative electrode paste may contain additives as needed. Additives may include bismuth compounds (e.g., bismuth sulfate), organic shrinkage inhibitors, carbonaceous materials, barium sulfate, etc.

[0059] A negative electrode plate can be obtained by chemically treating an untreated negative electrode plate. Chemical treatment may be carried out by immersing a group of electrode plates, including the untreated negative electrode plate, in an electrolyte containing sulfuric acid in the battery case of a lead-acid battery, and charging the electrode plate group. Chemical treatment may also be carried out before the assembly of the lead-acid battery or the electrode plate group. The charged negative electrode active material contains spongy lead.

[0060] (electrolyte) The electrolyte is an aqueous solution containing sulfuric acid. The electrolyte may be gelled as needed. The electrolyte may further contain at least one metal ion selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions. The density of the electrolyte at 20°C is, for example, 1.10 or higher. The density of the electrolyte at 20°C may be 1.35 or lower. These densities are values ​​for the electrolyte of a fully charged lead-acid battery.

[0061] To ensure high power acceptance, the COD in the electrolyte should be 160 mg / L or less, but it may also be 130 mg / L or less, 100 mg / L or less, or 80 mg / L or less. Furthermore, the COD in the electrolyte may be 15 mg / L or more, 25 mg / L or more, 50 mg / L or more, or 80 mg / L or more. A preferred range for the COD in the electrolyte is, for example, 15 mg / L to 160 mg / L, but it may also be 25 mg / L to 130 mg / L, or 50 mg / L to 100 mg / L.

[0062] The amount of COD in the electrolyte can be controlled, for example, by the following methods. One of these methods may be used, or a combination of several may be used. (1) Adjust the concentration of organic additives in the electrolyte. (2) Adjust the content of organic components in components other than the electrolyte. "Components other than the electrolyte" include separators, current collectors for positive or negative electrode plates, and positive or negative electrode materials. In other words, the method in (2) can be broadly classified into the following three methods. (2-1) Control the content of relatively low molecular weight organic additives in the porous film. Examples of organic additives include penetrants and oils. (2-2) Remove at least a portion of the cutting oil adhering to the current collector of the positive or negative electrode plate, or to the metal plate before it is processed into a current collector, by washing or other means. (2-3) Control the content of at least one of the organic components and carbonaceous materials contained in the positive electrode material or the negative electrode material. The organic components contained in the electrode material also include organic shrinkage inhibitors.

[0063] Organic solvents may be used to clean current collectors or metal plates. Examples of organic solvents include at least one selected from alcohols, ketones, esters, ethers, amides, and sulfoxides. An example of an alcohol is ethanol. Examples of ketones are acetone and ethyl methyl ketone. An example of an ester is ethyl acetate. An example of an ether is tetrahydrofuran. Examples of amides are dimethylformamide and N-methyl-2-pyrrolidone. An example of a sulfoxide is dimethyl sulfoxide.

[0064] To prevent an excessive increase in COD in the electrolyte, it is desirable to use an organic solvent that is easily removed by washing with water, or an organic solvent that is miscible with water, as the organic solvent used to clean the current collector or metal plate. The cleaning time is preferably 3 seconds or more in an organic solvent that is miscible with water. There is no particular upper limit to the cleaning time, and it may be 60 seconds or less, for example.

[0065] The electrolyte used in the assembly of lead-acid batteries may contain organic additives. Examples of organic additives include surfactants. However, from the viewpoint of keeping the amount of COD in the electrolyte contained in lead-acid batteries low, it is preferable that the electrolyte used in the assembly of lead-acid batteries does not contain organic additives.

[0066] The COD of the electrolyte is measured in accordance with JIS K 0102-1:2021, "17.2 Oxygen consumption by acidic potassium permanganate (CODMn)". COD (CODMn) is calculated using the following formula. In this calculation, CODMn is calculated with 2 significant figures, 1 decimal place, and a lower limit of <0.5. CODMn=(titration value-BL)×F×1000 / V×0.2 Titration value: The volume (mL) of 5 mmol / L potassium permanganate aqueous solution required to titrate the sample prepared from the electrolyte. Blank (BL): The volume (mL) of 5 mmol / L potassium permanganate aqueous solution required for titration in a test using distilled water. F: Factor of potassium permanganate aqueous solution with a concentration of 5 mmol / L V: Volume (mL) of sample prepared from the electrolyte (sample used for titration) Oxygen equivalent (mg) in 1 mL of 0.2:5 mmol / L potassium permanganate aqueous solution

[0067] The titration sample is prepared using the following procedure: First, the electrolyte is taken from a fully charged lead-acid battery into a 300 mL Erlenmeyer flask. The amount of electrolyte taken should be a maximum of 100 mL, and adjusted so that the titration volume is in the range of 3.5 mL to 5.5 mL. If the amount taken is less than 100 mL, the amount is measured and distilled water is added until the diluted volume reaches 100 mL. In this way, the electrolyte sample is prepared. In addition, 100 mL of distilled water is prepared in a separate 300 mL Erlenmeyer flask as a sample for BL (Body Line). BL measurement is performed each time the sample prepared from the electrolyte is titrated.

[0068] Prepare titration samples from 100 mL of electrolyte solution and distilled water for BL using the following procedure. First, add 10 mL of 5 mmol / L potassium permanganate aqueous solution to the above sample using a volumetric pipette and stir. Next, heat each Erlenmeyer flask in a boiling water bath for 30 minutes. During this time, ensure that the water in the bath is always boiling and that the liquid level in the bath does not fall below the liquid level in the Erlenmeyer flask. After 30 minutes of heating, remove the Erlenmeyer flask and immediately add 10 mL of 12.5 mmol / L sodium oxalate aqueous solution to the liquid in the Erlenmeyer flask using a volumetric pipette. Prepare the titration sample by cooling the liquid to a temperature within the range of 50°C to 60°C. If the sample contains chloride ions, add 2 mL of 500 g / L silver nitrate aqueous solution using a volumetric pipette and stir the resulting mixture well until no precipitate remains and the liquid becomes clear. If the cloudiness persists, continue adding silver nitrate solution little by little while stirring until the cloudiness disappears. The amount of silver nitrate solution added should be such that the total amount of silver nitrate is 1g more than the equivalent amount of chloride ions contained in each sample. The silver nitrate solution is then added to the sample described above.

[0069] Each prepared sample for titration is titrated with a 5 mmol / L potassium permanganate aqueous solution. During titration, when the liquid in the Erlenmeyer flask turns slightly red, stop the titration and let it stand for about 30 seconds to check if the red color has disappeared. If the red color disappears, repeat the titration and standing process until the red color disappears. For samples prepared from the electrolyte and samples prepared from distilled water, use the amount of potassium permanganate aqueous solution (mL) required for titration as the titration value and BL in the above formula to determine the COD of the electrolyte. If the electrolyte is diluted with distilled water during sample preparation, calculate the COD of the electrolyte before dilution, taking the dilution into account.

[0070] (Porous film) A porous film is a resin film having pores. A porous film contains a polymer material. A porous film may optionally contain components such as oil, inorganic particles, penetrating agents, and pore-forming agents. The polymer material constituting the resin film (hereinafter also referred to as the base polymer) includes, for example, polyolefins. A polyolefin is a polymer containing at least olefin units (monomer units derived from olefins).

[0071] The base polymer typically includes crystalline polymers. Crystalline polymers include, for example, polyolefins. A polyolefin is a polymer that contains at least olefin units (i.e., a polymer that contains at least monomer units derived from olefins).

[0072] Polyolefins may be used in combination with other base polymers as the base polymer. The ratio of polyolefins to the total base polymer contained in the crystalline polymer is, for example, 50% by mass or more, may be 80% by mass or more, or may be 90% by mass or more. The ratio of polyolefins is, for example, 100% by mass or less. The base polymer may also be composed solely of polyolefins. When the ratio of polyolefins is this high, the oxidation resistance of the crystalline polymer tends to decrease, but even in such cases, high high-temperature overcharge life performance can be ensured by setting the degree of crystallinity within the above range.

[0073] Porous films contain crystalline regions where the base polymer molecules are relatively regularly arranged (i.e., highly aligned) and amorphous regions with low alignment. Therefore, in the XRD spectrum of a porous film, diffraction peaks from the crystalline regions are observed, as well as scattered light from the amorphous regions, which is observed as a halo. In the XRD spectrum of a porous film, 100×I c / ( I c +I a A crystallinity of 18% or higher, as expressed by the formula, results in excellent high-temperature overcharge lifespan even with low COD and high charge acceptance.

[0074] Here, I c This is the integrated intensity of the diffraction peak with the maximum peak height (first diffraction peak) among the diffraction peaks corresponding to the crystalline region, and I a This represents the integrated intensity of the halo corresponding to the amorphous region.

[0075] For example, in the XRD spectrum of a separator containing polyolefins with ethylene units, diffraction peaks corresponding to the (110) plane in the crystalline region are observed in the range where 2θ is between 20° and 22.5°, and diffraction peaks corresponding to the (200) plane in the crystalline region are observed in the range where 2θ is between 23° and 24.5°. In addition, a halo in the amorphous region is observed in the range where 2θ is between 17° and 27°. Among the diffraction peaks due to the crystalline region, the diffraction peak corresponding to the (110) plane has the largest peak height and corresponds to the first diffraction peak.

[0076] The degree of crystallinity should be 18% or higher, but from the viewpoint of ensuring higher high-temperature overcharge life performance, it may be 23% or higher or 25% or higher. The degree of crystallinity may be 40% or lower, or 37% or lower or 35% or lower. When the degree of crystallinity is within this range, it is easier to ensure the flexibility of the porous film and the manufacturing process is simpler.

[0077] The degree of crystallinity of the porous film may be 18% to 40%, 23% to 37%, 25% to 35%, 23% to 40%, or 23% to 35%.

[0078] The integrated intensities of diffraction peaks and halos are determined by fitting the diffraction peaks from the crystalline region and the halos from the amorphous region in the XRD spectrum of the separator. The resulting integrated intensity I of the first diffraction peak is... c and the integrated intensity of the halo I a Using this, the degree of crystallinity can be determined from the above formula.

[0079] Polyolefins include, for example, homopolymers of olefins, copolymers containing different olefin units, and copolymers containing olefin units and copolymerizable monomer units. Copolymers containing olefin units and copolymerizable monomer units may contain one or more types of olefin units. Copolymers containing olefin units and copolymerizable monomer units may also contain one or more types of copolymerizable monomer units. Copolymerizable monomer units are monomer units derived from polymerizable monomers other than olefins that are copolymerizable with olefins.

[0080] Examples of polyolefins include, for example, at least C 2-3 Examples include polymers containing olefins 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, it is preferable to use polyolefins containing at least ethylene units (e.g., polyethylene, ethylene-propylene copolymers). Polyolefins containing ethylene units (e.g., polyethylene, ethylene-propylene copolymers) may be used in combination with other polyolefins.

[0081] The porous film preferably contains oil. When the porous film contains oil, the effect of suppressing oxidative degradation of the porous film can be further enhanced, thereby ensuring higher high-temperature overcharge life performance. Oil refers to a hydrophobic substance that is liquid at room temperature (temperature between 20°C and 35°C) and separates from water. Oils include naturally derived oils, mineral oils, and synthetic oils. Mineral oils and synthetic oils are preferred as oils. Examples of oils include paraffin oil and silicone oil. The porous film may contain one type of oil, or a combination of two or more types.

[0082] The oil content in the porous film is preferably 11% by mass or more and 18% by mass or less. When the oil content is within this range, the effect of suppressing oxidative degradation of the porous film is further enhanced. In addition, the resistance of the porous film can be kept relatively low.

[0083] The porous film may be in sheet form. Alternatively, a sheet folded in an accordion shape may be used as the porous film. The porous film may also be formed into a bag shape. Either the positive electrode plate or the negative electrode plate may be wrapped in the bag-shaped porous film.

[0084] A porous film may or may not have ribs. A porous film with ribs, for example, comprises a base portion and ribs erected from the surface of the base portion. The ribs may be provided on only one surface of the porous film or each base portion, or on both surfaces. The base portion of a porous film refers to the part of the porous film that excludes protrusions such as ribs, and is the sheet-like portion that defines the outer shape of the porous film.

[0085] The thickness of the porous film is, for example, 0.09 mm or more. From the viewpoint of obtaining higher high-temperature overcharge life performance, 0.1 mm or more or 0.15 mm or more is preferable. The thickness of the porous film is, for example, 0.3 mm or less. From the viewpoint of keeping the resistance of the porous film low, the thickness of the porous film may be 0.25 mm or less or 0.2 mm or less. The thickness of the porous film means the average thickness of the portion of the porous film facing the electrode material. If the porous film comprises a base portion and ribs erected from at least one surface of the base portion, the thickness of the porous film is the average thickness of the base portion. If an adhesive member (mat, pasting paper, etc.) is attached to the porous film, the thickness of the adhesive member is not included in the thickness of the porous film.

[0086] The thickness of the porous film may be 0.09 mm or more and 0.3 mm or less (or 0.25 mm or less), 0.09 mm or more and 0.2 mm or less, 0.1 mm or more (or 0.15 mm or more) and 0.3 mm or less, 0.1 mm or more (or 0.15 mm or more) and 0.25 mm or less, or 0.1 mm or more (or 0.15 mm or more) and 0.2 mm or less.

[0087] If the porous film has ribs, the height of the ribs may be 0.05 mm or more. Alternatively, the height of the ribs may be 1.2 mm or less. The height of the ribs is the height of the portion that protrudes from the surface of the base (projection height).

[0088] The height of the ribs provided in the region of the porous film facing the positive electrode plate may be 0.4 mm or more. The height of the ribs provided in the region of the porous film facing the positive electrode plate may be 1.2 mm or less.

[0089] Porous films are obtained, for example, by extruding a resin composition containing a base polymer, a pore-forming agent, and a penetrating agent (surfactant) into a sheet, stretching it, and then removing at least a portion of 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. After the removal of the pore-forming agent, the sheet-like porous film is dried as needed. For example, the degree of crystallinity is adjusted by adjusting at least one selected from the group consisting of the cooling rate of the sheet during extrusion, the stretching ratio during stretching, and the temperature during drying. For example, rapidly cooling the sheet during extrusion, increasing the stretching ratio, or lowering the temperature during drying tends to increase the degree of crystallinity. Stretching may be performed by biaxial stretching, but is usually performed by uniaxial stretching. The sheet-like porous film may be folded into an accordion shape or processed into a bag shape as needed.

[0090] In a porous film having ribs, the ribs may be formed on the sheet during the extrusion molding of the resin composition. Alternatively, the ribs may be formed after the resin composition has been formed into a sheet or after the porosizing agent has been removed, by pressing the sheet with a roller having grooves corresponding to each rib.

[0091] Examples of pore-forming agents include liquid pore-forming agents and solid pore-forming agents. Preferably, the pore-forming agent contains at least oil. Using oil allows for the production of a porous film containing oil, further enhancing the effect of suppressing oxidative degradation. The pore-forming agent may be used alone or in combination of two or more types. Oil may be used in combination with other pore-forming agents. Liquid pore-forming agents and solid pore-forming agents may also be used in combination. Note that at room temperature (20°C to 35°C), liquid pore-forming agents are classified as liquid pore-forming agents, and solid pore-forming agents are classified as solid pore-forming agents.

[0092] As a liquid pore-forming agent, the oils mentioned above are preferred. As a solid pore-forming agent, polymer powders are an example.

[0093] The amount of pore-forming agent in a porous film may vary depending on the type. The amount of pore-forming agent in a porous film is, for example, 30 parts by mass or more per 100 parts by mass of base polymer. The amount of pore-forming agent is, for example, 60 parts by mass or less per 100 parts by mass of base polymer.

[0094] For example, a porous film containing oil is formed by extracting and removing some of the oil from a sheet formed using oil as a pore-forming agent, using a solvent. The solvent is selected, for example, depending on the type of oil. The oil content in the porous film can be adjusted by adjusting, for example, the type and composition of the solvent, the extraction conditions (extraction time, extraction temperature, solvent supply rate, etc.).

[0095] The surfactant used as a penetrating agent may be either an ionic surfactant or a nonionic surfactant. The surfactant may be used alone or in combination of two or more types.

[0096] The content of the penetrant in the porous film is, for example, 0.01% by mass or more, and may be 0.1% by mass or more. The content of the penetrant in the porous film may be 10% by mass or less. From the viewpoint of keeping the COD in the electrolyte low and improving charge acceptance, the content of the penetrant in the porous film may be 3% by mass or less, or 1% by mass or less, preferably 0.5% by mass or less, and more preferably 0.2% by mass or less.

[0097] The porous film (or the resin composition used to manufacture the porous film) may contain inorganic particles.

[0098] As inorganic particles, ceramic particles are preferred, for example. As ceramics constituting ceramic particles, at least one selected from the group consisting of silica, alumina, and titania can be cited.

[0099] The inorganic particle content in the porous film may be, for example, 40% by mass or more. The inorganic particle content may be, for example, 80% by mass or less, or 70% by mass or less.

[0100] The evaluation and measurement methods are described below. (1) Analysis or measurement of the size of porous film (Preparation of porous film) For the analysis or size measurement of porous films, porous films extracted from unused separators or from fully charged lead-acid batteries in their initial stages of use are used. The porous films extracted from lead-acid batteries are washed and dried prior to analysis or measurement.

[0101] The cleaning and drying of the porous film removed from the lead-acid battery is carried out in the following procedure: The porous film removed from the lead-acid battery is immersed in pure water for 1 hour to remove sulfuric acid from the porous film. Then the porous film is removed from the liquid in which it was immersed and allowed to stand at 25°C ± 5°C for 16 hours or more to dry.

[0102] (XRD spectrum) The XRD spectrum of a porous film is measured by irradiating the porous film surface with X-rays perpendicular to it. A sample for measurement is prepared by processing the portion of the porous film facing the electrode material into a strip. For porous films with ribs, the sample is prepared by processing the base portion into a strip, excluding the ribs. XRD spectrum measurement and fitting are performed under the following conditions.

[0103] (Measurement conditions) Measurement device: RINT-TTR2, manufactured by Rigaku Corporation. Fitting: FT (Step Scan) method Measurement angle range: 15-35° Step width: 0.02° Measurement speed: 5° / min XRD data processing: XRD pattern analysis software (PDXL2, manufactured by Rigaku) ​​was used.

[0104] (Thickness of the porous film and height of the ribs) The thickness of a porous film can be determined by measuring the thickness at five arbitrarily selected locations in a cross-sectional photograph of the porous film and averaging the results.

[0105] The height of the rib is determined by averaging the heights from one surface of the rib's base, measured at 10 arbitrarily selected locations on the rib in a cross-sectional photograph of the porous film.

[0106] (Oil content in porous film) A sample (hereinafter referred to as Sample A) is prepared by processing the portion of the porous film facing the electrode material into a strip shape. In the case of a porous film with ribs, Sample A is prepared by processing the base portion into a strip shape so as not to include the ribs.

[0107] Approximately 0.5 g of sample A is taken, accurately weighed, and the initial sample mass (m0) is determined. The weighed sample A is placed in a glass beaker of appropriate size, and 50 mL of n-hexane is added. Next, the beaker and sample are subjected to ultrasound for approximately 30 minutes to dissolve the oil contained in sample A into the n-hexane. Then, the sample is removed from the n-hexane, dried in the air at room temperature (temperature between 20°C and 35°C), and weighed to determine the mass of the sample after oil removal (m1). The oil content is then calculated using the following formula. The oil content is determined for 10 samples of sample A, and the average value is calculated. The resulting average value is taken as the oil content in the separator. Oil content (mass %) = (m0 - m1) / m0 × 100

[0108] (Content of inorganic particles in porous film) A portion of sample A, prepared in the same manner as described above, is taken, accurately weighed, placed in a platinum crucible, and heated with a Bunsen burner until no more white smoke is emitted. Next, the resulting sample is heated in an electric furnace (in an oxygen stream, 550°C ± 10°C) for approximately 1 hour to incinerate it, and the incinerated material is weighed. The ratio (percentage) of the mass of the incinerated material to the mass of sample A is calculated and used as the inorganic particle content (mass %). The inorganic particle content is determined for 10 samples of sample A, and the average value is calculated. The resulting average value is used as the inorganic particle content in the porous film.

[0109] (Percentage of penetrant in porous film) A portion of sample A, prepared in the same manner as described above, is taken, accurately weighed, and dried at room temperature (20°C to 35°C) under reduced pressure below atmospheric pressure for at least 12 hours. The dried material is placed in a platinum cell and set in a thermogravimetric analyzer, and the temperature is raised from room temperature to 800°C ± 1°C at a heating rate of 10 K / min. The weight loss when the temperature is raised from room temperature to 250°C ± 1°C is taken as the mass of the penetrant, and the ratio (percentage) of the mass of the penetrant to the mass of sample A is calculated and taken as the penetrant content (mass %). A Q5000IR manufactured by TA Instruments Inc. is used as the thermogravimetric analyzer. The penetrant content is determined for 10 samples of sample A and the average value is calculated. The obtained average value is taken as the penetrant content in the porous film.

[0110] (2) Evaluation of charge acceptance The charge acceptance of lead-acid batteries is determined in accordance with JIS D5301:2019, under the following conditions of discharge and charge, and the charging current I at 10 minutes after the start of charging is measured. ca2 We will evaluate based on the following. 1) After confirming that the electrolyte temperature of one cell near the center of the lead-acid battery is 25±2℃, set the 20-hour rate current I 20 It discharges at 3.42 times the current for 2.5 hours. 2) Immediately after the discharge described in 1) above, move the lead-acid battery to a cooling chamber at 0±1℃ and leave it there until the electrolyte temperature of one of the cells near the center reaches 0±1℃. 3) After confirming that the electrolyte temperature of any one cell near the center is 0±2℃, charge the lead-acid battery at the same temperature with a constant voltage of 2.4±0.015V / cell and a limiting current of 100A, and measure the charging current at 10 minutes after the start of charging. ca2 Measure.

[0111] (3) Light load life test Light load life is evaluated based on the number of cycles until life is reached in the following charge-discharge cycle test in accordance with JIS D5301:2019. However, for convenience, the ambient temperature of the test is changed from 40°C liquid phase to 75°C gas phase, and the 25A discharge time in the charge-discharge cycle is changed from 4 minutes to 2 minutes. (a) Discharge the test battery at a discharge current of 25A ± 0.1A for 2 minutes in a 75℃ environment. (b) Then, charge at a charging voltage of 14.80V (limiting current of 25.0A) for 10 minutes. (c) Repeat steps (a) and (b) above for 480 cycles, with each cycle consisting of 40 to 60 hours of rest, and then apply the rated cold cranking current I cc The battery is then discharged for 30 seconds. The number of cycles at which the voltage drops to 7.2V after 30 seconds is defined as the life cycle. Here, the cold cranking current I cc The current value shall be the value corresponding to the performance rank specified in JIS D 5301:2019.

[0112] Note that the rated cold cranking current I cc Since the discharge is performed every 480 cycles, the vertical axis is defined as I cc The voltage at 30 seconds during discharge is used as the voltage at the 30-second mark. From a graph with the number of cycles on the horizontal axis, the number of cycles at which the voltage at 30 seconds reaches 7.2V can be determined by linear interpolation, and this can be defined as the number of cycles for the lifespan.

[0113] The matters described herein can be combined in any way.

[0114] 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 battery case 12 is divided into multiple 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 vent plug 18 for each cell chamber. When replenishing with water, the vent plug 18 is removed and the water is supplied. The vent plug 18 may also have a function of venting gas generated in the cell chamber 14 to the outside of the battery.

[0115] Each electrode plate group 11 is constructed by stacking multiple negative electrode plates 2 and positive electrode plates 3 with separators 4 in between. In the cell chamber 14 located at one end of the battery case 12, a negative electrode shelf 6, which connects multiple negative electrode plates 2 in parallel, is connected to a through connector 8, and a positive electrode shelf 5, which 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, connecting the electrode plate groups 11 of adjacent cell chambers 14 in series.

[0116] [Examples] The present invention will be described in detail below based on examples and reference examples, but the present invention is not limited to the following examples.

[0117] 《Lead acid battery R1~R10》 Each lead-acid battery was manufactured using the following procedure. (1) Fabrication of separators A resin composition containing polyethylene, silica particles, paraffin-based oil as a pore-forming agent, and a penetrating agent was extruded into a sheet, stretched, and then a portion of the pore-forming agent was removed to produce a porous film having ribs on one side. The degree of crystallinity (%) of the porous film obtained by the procedure described above (100 × 1) c / ( I c +I a The cooling rate and stretching ratio of the extruded sheets were adjusted so that the ratio was as shown in Table 1 (13%).

[0118] The oil content of the porous film obtained by the procedure described above was 11-18% by mass, and the silica particle content was 60% by mass. The rib height obtained using the previously described procedure was 0.55 mm. The thickness of the porous film (base thickness) obtained using the previously described procedure was standardized to 0.2 mm.

[0119] Next, a sheet of porous film was folded in half so that ribs were positioned on the inner surface to form a bag, and the overlapping ends were pressed together to obtain a bag-shaped porous film (size when laid flat: 117 mm long x 152 mm wide). The pressed area was 3 mm wide and located 2 mm inward from the side edge of the porous film.

[0120] The crystallinity, oil content, silica particle content, base thickness, and rib height of the porous film were determined from the porous film before the lead-acid battery was manufactured, but they were almost the same as the values ​​measured using the previously described procedure for the porous film removed from the manufactured lead-acid battery.

[0121] (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 an antimony-free Pb-Ca-Sn alloy, and aged and dried to obtain an unformed positive electrode plate with a width of 137 mm, a height of 110 mm, and a thickness of 1.6 mm.

[0122] (3) Fabrication of the negative electrode plate A negative electrode paste was prepared by mixing lead oxide, carbon black, barium sulfate, lignin, reinforcing material (synthetic resin fiber), water, and sulfuric acid. The negative electrode paste was filled into the mesh of an expanded grid made of Pb-Ca-Sn alloy that did not contain antimony, and aged and dried to obtain an unformed negative electrode plate with a width of 137 mm, a height of 110 mm, and a thickness of 1.3 mm. The amounts of carbon black, barium sulfate, lignin, and synthetic resin fiber used were adjusted so that the content of each component was 0.3 mass%, 2.1 mass%, 0.1 mass%, and 0.1 mass%, respectively, for a negative electrode plate taken from a fully charged lead-acid battery.

[0123] (4) Manufacturing of lead-acid batteries Untreated negative electrode plates were placed in a porous film bag-like separator. The negative electrode plates and positive electrode plates were stacked with the separator in between. In this way, an electrode plate group was formed with seven untreated negative electrode plates and six untreated positive electrode plates.

[0124] The tabs of the positive electrode plate and the tabs of the negative electrode plate were welded to the positive and negative electrode trays, respectively, using a cast-on-strap method. The electrode plates were inserted into a polypropylene battery case, electrolyte was poured in, and a chemical conversion was performed inside the case to assemble a liquid-type lead-acid battery with a rated voltage of 12V and a 5-hour rate capacity of 30Ah. The 5-hour rate capacity refers to the capacity when discharged at a current (A) of 1 / 5 of the Ah value indicated in the rated capacity. Six electrode plate groups are connected in series inside the battery case.

[0125] A sulfuric acid aqueous solution was used as the electrolyte. The density of the electrolyte after chemical conversion at 20°C was 1.285. The COD of the electrolyte extracted from a fully charged lead-acid battery was adjusted to the values ​​shown in Table 1 on a mass basis. The COD was controlled by changing the amount of penetrant used when preparing the porous film.

[0126] 《Lead acid battery R11, E1~E9》 A lead-acid battery was fabricated in the same manner as in Comparative Examples 1 to 10, except that a porous film was used that was adjusted so that the degree of crystallinity (%) obtained by the procedure described above was the value shown in Table 2 (18%).

[0127] 《Lead acid battery E10~E16》 A lead-acid battery was fabricated in the same manner as in Comparative Examples 4-10, except that a porous film was used that was adjusted so that the degree of crystallinity (%) obtained by the procedure described above was the value shown in Table 2 (23%).

[0128] 《Lead acid battery E17~E23》 A lead-acid battery was fabricated in the same manner as in Comparative Examples 4-10, except that a porous film was used that was adjusted so that the degree of crystallinity (%) obtained by the procedure described above was the value shown in Table 2 (25%).

[0129] (5) Evaluation The charge acceptance and life performance of the lead-acid battery in a light-load life test at 75°C were evaluated using the procedure described above. Charge acceptance was evaluated using a relative value with the evaluation result of lead-acid battery R1 set to 100, and life performance in the light-load life test was evaluated using a relative value with the life cycle of lead-acid battery R1 set to 100.

[0130] The evaluation results are shown in Tables 1-4. E1-E23 are examples. R1-R11 are comparative examples.

[0131] [Table 1]

[0132] [Table 2]

[0133] [Table 3]

[0134] [Table 4]

[0135] Comparing batteries R1 and R11, when the COD is high at 170 mg / L, increasing the crystallinity from 13% to 18% improves the light-load life performance from 100% to 140%, a 40% improvement. In contrast, comparing batteries R10 and E9, when the COD is low at 15 mg / L, increasing the crystallinity from 13% to 18% improves the light-load life performance from 40% to 104%, a 64% improvement, and a 160% improvement compared to the base value at 13% crystallinity. In other words, the lower the COD, the greater the improvement in light-load life performance by increasing the crystallinity. Furthermore, battery E9 achieves a life performance of 104%, exceeding the 100% of battery R1. The same can be said when comparing Table 1 with Tables 3 and 4.

[0136] Furthermore, it can be understood that if the COD is 80 mg / L or higher when the crystallinity is 23% or higher, and if the COD is 50 mg / L or higher when the crystallinity is 25% or higher, even better lifespan performance can be stably obtained. This is presumed to be because the oxidative degradation of the porous film caused by the reduction of COD is suppressed by increasing the crystallinity of the porous film, thereby suppressing internal short circuits. [Industrial applicability]

[0137] The lead-acid battery disclosed herein is suitable for applications such as idle stop systems (e.g., lead-acid batteries for vehicles with idle stop systems) and as a starting power source for various vehicles (trucks, commercial vehicles such as taxis, motorcycles, etc.). Furthermore, the lead-acid battery is also suitable for use as a power source for industrial energy storage devices such as those for electric vehicles (e.g., forklifts). These applications are merely examples. The applications of the lead-acid battery disclosed herein are not limited to these. Idling stop (also called Idling Reduction) is sometimes referred to as IS. [Explanation of Symbols]

[0138] 1:Lead acid battery 2: Negative plate 3: Positive plate 4: Separator 5: Positive electrode shelf 6: Negative electrode shelf 7: Positive pole column 8: Through-connector 9: Negative pole column 11: Plate group 12:Battery container 13: Bulkhead 14: Cell Room 15: Lid 16: Negative terminal 17: Positive terminal 18: Liquid outlet stopper

Claims

1. Positive plate and The negative electrode plate and A porous resin film interposed between the positive electrode plate and the negative electrode plate, Electrolyte and Equipped with, The porous film includes a crystalline region and an amorphous region. In the X-ray diffraction spectrum of the porous film, 100 × I ｃ / (I ｃ +I ａ The degree of crystallinity, as indicated by ), is 18% or higher. I ｃ This is the integrated intensity of the diffraction peak with the maximum peak height among the diffraction peaks corresponding to the crystalline region. I ａ This is the integrated intensity of the halo corresponding to the amorphous region, A lead-acid battery in which the chemical oxygen demand in the electrolyte is 160 mg / L or less.

2. The lead-acid battery according to claim 1, wherein the chemical oxygen demand is 100 mg / L or less.

3. The lead-acid battery according to claim 1, wherein the chemical oxygen demand is 15 mg / L or more.

4. The lead-acid battery according to claim 1, wherein the degree of crystallinity is 40% or less.

5. The lead-acid battery according to claim 1, wherein the porous film has a thickness of 0.1 mm or more and 0.3 mm or less.

Images