Lead acid battery

Abstract

To provide a lead acid battery that can improve heavy load life performance.SOLUTION: A lead acid battery includes a positive electrode plate, a negative electrode plate, a porous film interposed between the positive electrode plate and the negative electrode plate, and an electrolyte, and the porous film contains a resin, in an X-ray diffraction spectrum of the porous film, a ratio expressed as I110 / (I110+I200) is 0.6 or more, where I110 is the integrated intensity of the diffraction peak corresponding to the (110) plane and I200 is the integrated intensity of the diffraction peak corresponding to the (200) plane, and the chemical oxygen demand of the electrolyte is less than 170 mg / L.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Lead-acid batteries are used in a variety of applications, including automotive and industrial applications. Lead-acid batteries include a positive electrode plate, a negative electrode plate, a separator interposed between them, and an electrolyte. Separators for lead-acid batteries are required to have various performance characteristics. Porous films containing polyolefins are generally used as separators.

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

[0004] Patent Document 2 proposes "a lead-acid battery characterized in that the electrolyte contains 0.5 mg / L or more and 3 mg / L or less of a reducing organic substance."

[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 the blend, while kneading the raw material composition and forming it into a sheet with ribs. The sheet is then immersed in an immersion bath of an organic solvent capable of dissolving the oil to extract and remove a portion of the oil, and then heated and dried. The ribbed separator for lead-acid batteries contains 5 to 30% by mass of the oil, and 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 Application Laid-Open No. 2005-251394 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-338631 Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors have discovered that changes in chemical oxygen demand (COD), which is an indicator of the concentration of organic components in the electrolyte, change the charge / discharge efficiency and significantly affect the deep discharge cycle performance (heavy load life performance).

[0008] The present inventors have newly discovered that even if the charging efficiency is increased by reducing the amount of organic components in the electrolyte, this does not necessarily result in an improvement in heavy-load life. For example, in heavy-load life tests (e.g., heavy-load life tests according to JIS D5301:2019), charging efficiency decreases when there is a large amount of organic components that inhibit charge-discharge reactions on the surfaces of the positive and negative electrodes due to a high level of COD. Therefore, in heavy-load life tests with a deep discharge depth, the lead-acid battery reaches the end of its life due to insufficient charging before the separator begins to deteriorate due to oxidation. On the other hand, when COD is low, charging efficiency improves. Therefore, it is expected that heavy-load life performance will improve.

[0009] However, contrary to expectations, low COD results in little improvement in heavy-load life. This is because improved charging efficiency makes the positive electrode material more susceptible to softening and shedding, increasing the contact area between the positive electrode material and the separator, leading to oxidative degradation of the separator. This can lead to cracks, breaks, holes, etc. in the separator, causing the positive electrode material and negative electrode material to come into contact at damaged points in the separator, resulting in a short circuit and the end of the lead-acid battery's life. [Means for solving the problem]

[0010] One aspect of the present disclosure provides a battery comprising: a positive electrode plate; a negative electrode plate; a porous film interposed between the positive electrode plate and the negative electrode plate; and an electrolyte solution, wherein the porous film contains a resin, and an X-ray diffraction spectrum of the porous film shows I 110 / (I 110 +I 200 ) is 0.6 or more, and I 110 is the integrated intensity of the diffraction peak corresponding to the (110) plane, and I 200 is the integrated intensity of the diffraction peak corresponding to the (200) plane, and the chemical oxygen demand in the electrolyte is less than 170 mg / L. [Effects of the Invention]

[0011] According to the present disclosure, the heavy load life performance of a lead-acid battery can be improved. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a partially cutaway perspective view showing the appearance and internal structure of a lead-acid battery according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes embodiments of the present disclosure using 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 are obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be interpreted as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits of numerical values related to specific physical properties or conditions are exemplified, 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 equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more of the materials may be used in combination.

[0014] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0015] In this specification, the up-down direction of a lead-acid battery or its components (electrode plates, battery case, separator, etc.) refers to the up-down direction in the vertical direction of the lead-acid battery when it is in use. Note that each of the positive and negative electrode plates has a lug for connecting to an external terminal. For example, in a flooded battery, the lug is provided on the top of the electrode plate so as to protrude upward.

[0016] The lead acid battery according to the present disclosure may be a valve regulated battery (VRLA battery), but is preferably a flooded battery (vented battery) in that it can effectively utilize the effects of reducing COD.

[0017] A lead-acid battery includes positive and negative electrode plates, a separator interposed between the positive and negative electrode plates, and an electrolyte. The electrolyte contains sulfuric acid. Charging and discharging proceeds as sulfate ions move between the positive and negative electrode plates and the electrolyte. During discharging, sulfate ions move to the positive and negative electrode plates, decreasing the density of the electrolyte. During charging, sulfate ions move from the positive and negative electrode plates into the electrolyte, increasing the density of the electrolyte.

[0018] The separator includes a porous film. The porous film can be used alone as a separator. Therefore, the porous film may also be referred to as a separator. The separator may include a nonwoven fabric in addition to the porous film.

[0019] The positive electrode plates, negative electrode plates, and separator constitute an electrode plate group. The electrode plate group, together with an electrolyte, constitutes a cell. One electrode plate group constitutes one cell. A lead-acid battery comprises one or more electrode groups, thereby comprising one or more cells. There is no particular limit to the number of positive electrode plates and negative electrode plates contained in one electrode plate group. The electrode plate group provided in the lead-acid battery according to the present disclosure includes, for example, a total of 12 or more positive electrode plates and negative electrode plates. Multiple electrode plate groups are usually housed in individual cell chambers and connected to each other in series.

[0020] The positive electrode plate contains a positive electrode material, which serves as a positive electrode active material that generates capacity through an oxidation-reduction reaction and contains at least lead dioxide during charging and at least lead sulfate during discharging.

[0021] The negative electrode plate contains a negative electrode material that contains at least lead as a negative electrode active material that develops capacity through an oxidation-reduction reaction during charging and at least lead sulfate during discharging.

[0022] (1) A lead-acid battery according to one embodiment of the present disclosure includes a positive electrode plate, a negative electrode plate, a porous film interposed between the positive electrode plate and the negative electrode plate, and an electrolyte solution, wherein the porous film contains a resin, and an X-ray diffraction spectrum of the porous film shows I 110 / (I 110 +I 200 ) is 0.6 or more, and I 110 is the integrated intensity of the diffraction peak corresponding to the (110) plane, and I 200 is the integrated intensity of the diffraction peak corresponding to the (200) plane, and the chemical oxygen demand (COD) in the electrolyte is less than 170 mg / L.

[0023] COD is the amount of oxygen required to oxidize oxidizable substances in the electrolyte. The COD in the electrolyte can be considered an index of the concentration of organic components contained in the electrolyte. In this specification, the COD is the COD in the electrolyte collected from a fully charged lead-acid battery in the early stages of use. An early-stage battery is a battery that has not been in use for very long and has hardly deteriorated.

[0024] The lead-acid battery described in (1) above has excellent heavy load life performance.

[0025] (2) In the lead-acid battery described in (1) above, the chemical oxygen demand may be 120 mg / L or less.

[0026] The lead-acid battery described in (2) above is further excellent in heavy load life performance.

[0027] (3) In the lead-acid battery according to any one of (1) and (2) above, the ratio R may be 0.7 or more.

[0028] The lead-acid battery described in (3) above is further excellent in heavy load life performance.

[0029] (4) In the lead-acid battery according to any one of the above (1) to (3), the porous film may have a thickness of 0.15 mm or more and 0.30 mm or less.

[0030] In the lead-acid battery described in (4) above, the porous film is sufficiently thin and has high strength, so that a higher heavy load life performance can be obtained.

[0031] In the X-ray diffraction spectrum of the porous film (specifically, the resin contained in the porous film) included in the lead-acid battery according to the present disclosure, I 110 / (I 110 +I 200 ) (hereinafter also referred to as "peak ratio R") is 0.6 or more. 110 is the integrated intensity of the diffraction peak corresponding to the (110) plane, and I 200is the integrated intensity of the diffraction peak corresponding to the (200) plane.

[0032] By reducing the COD in the electrolyte, side reactions such as oxidation of organic components are reduced, and the charging reaction between the positive and negative electrode active materials is facilitated, improving charging efficiency. Reducing the COD in the electrolyte to less than 170 mg / L significantly improves charging efficiency.

[0033] On the other hand, increasing the charging efficiency may not improve the battery life in heavy-load life tests. When charging efficiency is improved by reducing COD, the amount of charge electricity that would have been consumed in side reactions when COD was high is utilized in the charging reaction of the positive electrode material, increasing the utilization rate of the positive electrode material and making it more susceptible to softening and shedding. As a result, the contact area between the positive electrode material and the separator increases, causing oxidative degradation of the separator, resulting in cracks, breaks, and holes in the separator. The positive electrode material and the negative electrode material then come into contact at damaged areas of the separator, causing a short circuit and the end of the lead-acid battery's life. In other words, when the COD in the electrolyte is 170 mg / L or higher, the life degradation mode due to insufficient charging changes to a life degradation mode due to separator damage when the COD in the electrolyte is less than 170 mg / L. Furthermore, when the COD in the electrolyte is 170 mg / L or higher, the charging efficiency decreases, and in heavy-load life tests with deep discharge depths, the lead-acid battery reaches its end of life due to insufficient charging before the separator begins to oxidize and deteriorate.

[0034] In contrast, when the peak ratio R of the porous film is 0.6 or higher, it has been found that even if the COD in the electrolyte is reduced to less than 170 mg / L, the deterioration of the heavy-load life performance is significantly suppressed. This is because when the peak ratio R increases to a certain extent, the oxidation resistance of the porous film is significantly improved. As a result, the period until cracks or breakage occur in the porous film is extended, and the heavy-load life performance of the lead-acid battery is improved.

[0035] Furthermore, if the peak ratio R of the porous film is increased to 0.7 or more, the heavy-load life performance is significantly improved when the COD in the electrolyte is reduced to less than 170 mg / L. This is because the period until the porous film cracks or tears is further extended, and the lead-acid battery rarely reaches the end of its life due to deterioration of the porous film.

[0036] 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 more, and may be 1.3 or more. The Mp / Mn ratio may be 1.4 or less. A preferred range of the Mp / Mn ratio is, for example, 1.2 or more and 1.4 or less, and may be 1.3 or more and 1.4 or less. 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 more means reducing the amount of negative electrode material used. In other words, an Mp / Mn ratio of 1.2 or more can reduce the weight and cost of lead-acid batteries. Furthermore, an Mp / Mn ratio of 1.2 or more can reduce the load on the positive electrode plate, making it easier to suppress softening and detachment of the positive electrode material.

[0037] The lead-acid battery according to the present disclosure is also suitable for use in vehicles with start-stop control or idle stop-start (ISS) control.

[0038] In this specification, the fully charged state of a flooded lead-acid battery is defined by JIS D5301:2019. More specifically, the fully charged state is defined as a state in which a lead-acid battery is charged at a current 2I20 (unit: A), which is twice the 20-hour rate current I20, until the terminal voltage (unit: V) during charging or the electrolyte density converted to 20°C temperature, measured every 15 minutes in a water bath at 25°C ± 2°C, shows a constant value to three significant digits three times consecutively. Note that the 20-hour rate current I20 is a current (A) that is 1 / 20 of the value in Ah listed in the rated capacity. The value listed as the rated capacity is in Ah (ampere-hour). The unit of current set based on the value listed as the rated capacity is A (ampere).

[0039] A fully charged lead-acid battery is a lead-acid battery that has already been formed and charged to a fully charged state. The timing for charging a lead-acid battery to a fully charged state may be immediately after formation, or after a certain time (e.g., 720 hours or less) has passed since formation. For example, a lead-acid battery that has been formed and is in use (preferably in the early stages of use) may be charged.

[0040] In this specification, a battery in its early stages of use is a battery that has not been in use for a long time and has hardly deteriorated (for example, a battery that has been in use for only 720 hours or less since formation).

[0041] Hereinafter, lead-acid batteries according to embodiments of the present invention will be described in more detail with reference to the drawings, although the present invention is not limited to the following embodiments.

[0042] Examples of components of a lead-acid battery will be described below.

[0043] (positive electrode plate) The positive electrode plate includes a positive electrode collector and a positive electrode material. The positive electrode material is held by the positive electrode collector. The positive electrode material is the portion of the positive electrode plate excluding the positive electrode collector. An attachment member such as a conductive layer, mat, or pasting paper may be attached to the positive electrode plate. The attachment member is used integrally with the positive electrode plate, and is therefore included as a component of the positive electrode plate. When the positive electrode plate includes an attachment member, the positive electrode material is the portion of the positive electrode plate excluding the positive electrode collector and the attachment member.

[0044] 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, expanding or punching. When a grid-shaped current collector is used as the positive electrode current collector, it is easy to support the positive electrode material.

[0045] The lead alloy used for the positive electrode current collector is preferably a Pb-Ca alloy or a Pb-Ca-Sn alloy, which have excellent corrosion resistance and mechanical strength. The positive electrode current collector may have metal layers with different compositions, and the metal layer may be a single layer or multiple layers.

[0046] The positive electrode material includes a positive electrode active material that generates capacity through an oxidation-reduction reaction. Examples of the positive electrode active material include lead dioxide and lead sulfate. The positive electrode material may include additives as needed. The additives may include reinforcing materials, antimony compounds, and the like. Examples of reinforcing materials include inorganic fibers and organic fibers.

[0047] An unformed positive electrode plate is obtained by aging and drying a positive electrode paste filled on a 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. The additives may include reinforcing materials, antimony compounds, etc. Such positive electrode plates are also called paste-type positive electrode plates.

[0048] A positive electrode plate can be obtained by chemically forming an unformed positive electrode plate. Chemical formation may be performed by immersing an electrode plate assembly including the unformed positive electrode plate in an electrolyte containing sulfuric acid in a battery container of a lead-acid battery and charging the electrode plate assembly. Chemical formation may also be performed before assembling the lead-acid battery or the electrode plate assembly.

[0049] (negative plate) The negative electrode plate includes 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. An adhesive member such as a conductive layer, mat, or pasting paper may be attached to the negative electrode plate. The adhesive member is included as a component of the negative electrode plate. When the negative electrode plate includes an adhesive member, the negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector and the adhesive member.

[0050] 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 expanding or punching. If a grid-shaped current collector is used as the negative electrode current collector, it is easy to support the negative electrode material.

[0051] The lead alloy used for the negative electrode current collector may be any of a Pb-Sb alloy, a Pb-Ca alloy, and a Pb-Ca-Sn alloy. The lead alloy used for the negative electrode current collector may 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 with different compositions, and the metal layer may be a single layer or multiple layers.

[0052] The negative electrode material includes a negative electrode active material that exhibits capacity through an oxidation-reduction reaction. The negative electrode active material includes lead, lead sulfate, etc. The negative electrode material may include 100 ppm to 300 ppm of Bi element by mass. The negative electrode material may include other additives as needed. The additives may include an organic shrinkage inhibitor, a carbonaceous material, barium sulfate, etc.

[0053] Examples of the organic shrink-preventing agent include lignin, lignin sulfonic acid, and synthetic organic shrink-preventing agents. Examples of the synthetic organic shrink-preventing agent include formaldehyde condensates of phenolic compounds. One type of organic shrink-preventing agent may be used alone, or two or more types may be used in combination. The content of the organic shrink-preventing agent in the negative electrode material is, for example, 0.01% by mass or more and 1% by mass or less.

[0054] Examples of the carbonaceous material include carbon black, artificial graphite, natural graphite, hard carbon, and soft carbon. The carbonaceous material may be used alone or in combination of two or more. The content of the carbonaceous material in the negative electrode material is, for example, 0.1% by mass or more and 3% by mass or less.

[0055] The content of barium sulfate in the negative electrode material is, for example, 0.1% by mass or more and 3% by mass or less.

[0056] The unformed negative electrode plate is obtained by aging and drying the negative electrode current collector and the negative electrode paste filled in the negative electrode current collector. The aging is preferably performed in a high-humidity atmosphere at a temperature higher than room temperature. 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. The additives may include a bismuth compound (e.g., bismuth sulfate), an organic shrinkage inhibitor, a carbonaceous material, barium sulfate, etc.

[0057] A negative electrode plate can be obtained by chemically forming an unformed negative electrode plate. Chemical formation may be performed by immersing an electrode plate assembly including the unformed negative electrode plate in an electrolyte containing sulfuric acid in a battery container of a lead-acid battery and charging the electrode plate assembly. Chemical formation may be performed before assembling the lead-acid battery or the electrode plate assembly. The negative electrode active material in a charged state contains spongy lead.

[0058] (electrolyte) The electrolyte is an aqueous solution containing sulfuric acid. The electrolyte may be gelled as necessary. The electrolyte may further contain at least one metal ion selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions. The density of the electrolyte at 20°C is, for example, 1.10 or more. The density of the electrolyte at 20°C may be 1.35 or less. Note that these densities are values for the electrolyte of a fully charged lead-acid battery.

[0059] To ensure high charging efficiency and improve heavy-load life performance, the COD in the electrolyte should be less than 170 mg / L, but it may also be 160 mg / L or less, 120 mg / L or less, 100 mg / L or less, or 80 mg / L or less. The COD in the electrolyte may also be 15 mg / L or more, 20 mg / L or more, 25 mg / L or more, or 30 mg / L or more. A preferred range of the COD in the electrolyte is, for example, 15 mg / L or more but less than 170 mg / L, 20 mg / L or more but 160 mg / L or less, or 25 mg / L or more but 120 mg / L or less.

[0060] The COD amount in the electrolyte solution can be controlled, for example, by the following methods. The following methods may be adopted alone or in combination. (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 the separator, the positive or negative electrode current collector, and the positive or negative electrode material. In other words, method (2) can be broadly divided into the following three methods: (2-1) The content of relatively low molecular weight organic additives in the porous film is controlled. Examples of organic additives include penetrants and oils. (2-2) At least a part of the cutting oil adhering to the current collector of the positive or negative electrode plate or to the metal plate before being processed into the current collector is removed by washing or the like. (2-3) The content of at least one of the organic component and the carbonaceous material contained in the positive electrode material or the negative electrode material is controlled. The organic component contained in the electrode material also includes an organic shrinkage preventer.

[0061] An organic solvent can be used to clean the current collector or metal plate. Examples of the organic solvent include at least one selected from alcohols, ketones, esters, ethers, amides, and sulfoxides. Examples of the alcohol include ethanol. Examples of the ketone include acetone and ethyl methyl ketone. Examples of the ester include ethyl acetate. Examples of the ether include tetrahydrofuran. Examples of the amide include dimethylformamide and N-methyl-2-pyrrolidone. Examples of the sulfoxide include dimethyl sulfoxide.

[0062] To avoid excessive increase in COD in the electrolyte, it is desirable to use an organic solvent that is easily removed by washing with water or that is miscible with water as the organic solvent used to wash the current collector or metal plate. The washing time is preferably, for example, 3 seconds or more in a water-miscible organic solvent. The upper limit of the washing time is not particularly limited and may be, for example, 60 seconds or less.

[0063] The electrolyte used in the assembly of a lead-acid battery may contain an organic additive. Examples of the organic additive include a surfactant. However, from the viewpoint of keeping the COD amount in the electrolyte contained in the lead-acid battery low, it is preferable that the electrolyte used in the assembly of a lead-acid battery does not contain an organic additive.

[0064] 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: CODMn is calculated to two significant figures, one decimal place, and a lower limit of <0.5. CODMn=(titration value-BL)×F×1000 / V×0.2 Titration value: The amount (mL) of 5mmol / L potassium permanganate solution required to titrate the sample prepared from the electrolyte. Blank (BL): The amount (mL) of 5mmol / L potassium permanganate solution required for titration in a test using distilled water F: Factor of potassium permanganate solution with a concentration of 5mmol / L V: Volume (mL) of sample prepared from the electrolyte (sample used for titration) 0.2: The oxygen equivalent (mg) of 1 mL of 5 mmol / L potassium permanganate solution

[0065] The titration sample is prepared using the following procedure. First, electrolyte is collected from an initial, fully charged lead-acid battery into a 300 mL Erlenmeyer flask. The amount of electrolyte collected is limited to a maximum of 100 mL, and is adjusted so that the titration volume is in the range of 3.5 mL to 5.5 mL. If the amount collected is less than 100 mL, measure the collected volume and add distilled water 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 BL sample. BL measurement is performed each time a sample prepared from the electrolyte is titrated.

[0066] Prepare titration samples from 100 mL of electrolyte and BL distilled water samples using the following procedure. First, add 10 mL of 5 mmol / L potassium permanganate solution to the sample using a volumetric pipette and stir. Next, place each Erlenmeyer flask in a boiling water bath and heat for 30 minutes. Ensure that the water in the bath is always boiling and that the water level does not drop 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 solution using a volumetric pipette to the liquid in the Erlenmeyer flask. Cool the liquid to a temperature between 50°C and 60°C to prepare the titration sample. If the sample contains chloride ions, add 2 mL of 500 g / L silver nitrate solution using a volumetric pipette and stir the resulting mixture thoroughly until no precipitate remains and the liquid becomes clear. If the cloudiness does not disappear, add more silver nitrate solution little by little while stirring until the cloudiness disappears. Add the silver nitrate solution in such an amount that the total amount of silver nitrate is 1 g in excess of the equivalent amount of chloride ions contained in each sample. Add the silver nitrate solution to the above samples.

[0067] Each of the prepared titration samples is titrated with a 5 mmol / L potassium permanganate aqueous solution. When the liquid in the Erlenmeyer flask turns slightly red during titration, stop the titration and let it stand for about 30 seconds to check whether the red color has disappeared. If the red color has disappeared, repeat the titration and leaving process until the red color no longer disappears. For samples prepared from electrolyte and distilled water, use the amount of potassium permanganate aqueous solution (mL) required for titration as the titration value and BL in the above equation to calculate 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 into account the dilution amount.

[0068] (porous film) A porous film is a film having pores and containing a resin. The porous film contains a polymer material. The porous film contains optional components such as oil, inorganic particles, a penetrating agent, and a pore-forming agent, as needed. The polymer material (hereinafter also referred to as a base polymer) constituting the resin film includes, for example, a polyolefin. A polyolefin is a polymer containing at least an olefin unit (a monomer unit derived from an olefin).

[0069] The base polymer typically includes a crystalline polymer, such as a polyolefin. A polyolefin is a polymer that includes at least an olefin unit (i.e., a polymer that includes at least a monomer unit derived from an olefin).

[0070] The base polymer may be a combination of polyolefin and another base polymer. The ratio of polyolefin to the entire base polymer contained in the crystalline polymer is, for example, 50% by mass or more, 80% by mass or more, or even 90% by mass or more. The ratio of polyolefin is, for example, 100% by mass or less. The base polymer may be composed solely of polyolefin. When the ratio of polyolefin is this high, the oxidation resistance of the crystalline polymer tends to decrease. However, even in such cases, high heavy load life performance can be ensured by setting the peak ratio R within the above range.

[0071] The porous film may include a crystalline region where the molecules of the base polymer are arranged relatively regularly (i.e., highly ordered), and an amorphous region where the molecules are less ordered. In the XRD spectrum of the porous film, diffraction peaks due to the crystalline region may be observed, and scattered light due to the amorphous region may be observed as a halo. In the XRD spectrum of the porous film, I 110 / (I 110 +I 200 ) is 0.6 or more, excellent life performance can be obtained in a heavy load life test even when the COD is low and the charging efficiency is high.

[0072] where I 110 is the integrated intensity of the diffraction peak corresponding to the (110) plane, and I 200 is the integrated intensity of the diffraction peak corresponding to the (200) plane.

[0073] For example, in the XRD spectrum of a separator containing a polyolefin containing ethylene units, a diffraction peak corresponding to the (110) plane of the crystalline region is observed in the 2θ range of 20° to 22.5°, and a diffraction peak corresponding to the (200) plane of the crystalline region is observed in the 2θ range of 23° to 24.5°. Furthermore, a halo of the amorphous region is observed in the 2θ range of 17° to 27°. Of the diffraction peaks due to the crystalline region, the diffraction peak corresponding to the (110) plane has the greatest peak height.

[0074] The peak ratio R may be 0.6 or more, but may be 0.7 or more or 0.8 or more from the viewpoint of ensuring better life performance in a heavy load life test. The peak ratio R may be 1.0 or less, or may be 0.9 or less or 0.8 or less. When the peak ratio R is in such a range, it is easy to ensure the flexibility of the porous film and also easy to manufacture.

[0075] The peak ratio R of the porous film may be 0.6 or more and 1.0 or less, 0.7 or more and 0.9 or less, 0.6 or more and 0.9 or less, or 0.6 or more and 0.8 or less.

[0076] The integrated intensity of each diffraction peak (I 110 and I 200 ) is the intensity based on the area of each peak determined by fitting the diffraction peaks in the XRD spectrum of the separator. The integrated intensity I of the diffraction peak corresponding to the (110) plane is 110 and the integrated intensity of the diffraction peak corresponding to the (200) plane I 200 Using the formula: I 110 / (I 110 +I 200 ) the peak ratio R can be calculated.

[0077] Polyolefins include, for example, olefin homopolymers, copolymers containing different olefin units, and copolymers containing olefin units and copolymerizable monomer units. A copolymer containing olefin units and copolymerizable monomer units may contain one or more types of olefin units. Furthermore, a copolymer containing olefin units and copolymerizable monomer units may contain one or more types of copolymerizable monomer units. A copolymerizable monomer unit is a monomer unit derived from a polymerizable monomer other than an olefin that is copolymerizable with an olefin.

[0078] The polyolefin may, for example, be at least C 2-3 Polymers containing olefins as monomer units are also included. 2-3 The olefin may be at least one selected from the group consisting of ethylene and propylene. The polyolefin may be, for example, polyethylene, polypropylene, C 2-3 Copolymers containing olefins as monomer units (e.g., ethylene-propylene copolymers) are more preferred. Among polyolefins, polyolefins containing at least ethylene units (polyethylene, ethylene-propylene copolymers, etc.) are preferred. Polyolefins containing ethylene units (polyethylene, ethylene-propylene copolymers, etc.) may be used in combination with other polyolefins.

[0079] 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 life performance in a heavy load life test. Oil refers to a hydrophobic substance that is liquid at room temperature (a temperature of 20°C or higher and 35°C or lower) and separates from water. Oil includes naturally occurring oils, mineral oils, and synthetic oils. Preferred oils include mineral oils and synthetic 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 of oil.

[0080] The oil content in the porous film is preferably 13% by mass or more and 18% by mass or less. When the oil content is in 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.

[0081] The porous film may be in a sheet form. Alternatively, a sheet folded in an accordion shape may be used as the porous film. The porous film may be formed in a bag form. Either the positive electrode plate or the negative electrode plate may be wrapped in the bag-shaped porous film.

[0082] The porous film may or may not have ribs. A porous film having ribs, for example, comprises a base portion and ribs extending 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 may be provided on both surfaces. The base portion of the porous film refers to the constituent parts of the porous film excluding protrusions such as ribs, and refers to the sheet-like portion that defines the outer shape of the porous film.

[0083] The thickness of the porous film is, for example, 0.09 mm or more. From the viewpoint of obtaining higher heavy load life performance, 0.10 mm or more or 0.15 mm or more is preferable. The thickness of the porous film is, for example, 0.30 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 0.20 mm or less. The thickness of the porous film means the average thickness of the portion of the porous film facing the electrode material. When the porous film has a base portion and a rib erected from at least one surface of the base portion, the thickness of the porous film is the average thickness of the base portion. When an attachment member (such as a mat or pasting paper) is attached to the porous film, the thickness of the attachment member is not included in the thickness of the porous film.

[0084] The thickness of the porous film may be 0.09 mm or more and 0.30 mm or less (or 0.25 mm or less), 0.09 mm or more and 0.20 mm or less, 0.10 mm or more (or 0.15 mm or more) and 0.30 mm or less, 0.10 mm or more (or 0.15 mm or more) and 0.25 mm or less, or 0.10 mm or more (or 0.15 mm or more) and 0.20 mm or less.

[0085] When the porous film has ribs, the rib height may be 0.05 mm or more. Alternatively, the rib height may be 1.2 mm or less. The rib height is the height of the part that protrudes from the surface of the base part (protrusion height).

[0086] The height of the ribs provided in the region of the porous film facing the positive electrode plate may be 0.40 mm or more, or 1.2 mm or less.

[0087] A porous film can be obtained, for example, by extruding a resin composition containing a base polymer, a pore-forming agent, and a penetrating agent (surfactant) into a sheet, stretching the extrusion, 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 base polymer matrix. After removing the pore-forming agent, the sheet-shaped porous film is dried as needed. For example, the peak ratio R can be adjusted by adjusting at least one parameter 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, rapid cooling of the sheet during extrusion, increasing the stretching ratio, or decreasing the temperature during drying tends to increase the peak ratio R. The stretching process may be performed by biaxial stretching, but is usually performed by uniaxial stretching. The sheet-shaped porous film may be folded into an accordion shape or processed into a bag shape as needed.

[0088] In the case of a porous film having ribs, the ribs may be formed on the sheet when the resin composition is extruded, or may be formed by pressing the sheet with a roller having grooves corresponding to each rib after the resin composition is molded into a sheet or after the pore-forming agent is removed.

[0089] Examples of the pore-forming agent include liquid pore-forming agents and solid pore-forming agents. The pore-forming agent preferably contains at least oil. By using oil, a porous film containing oil is obtained, further enhancing the effect of suppressing oxidative degradation. One type of pore-forming agent may be used alone, or two or more types may be used in combination. Oil may be used in combination with another pore-forming agent. A liquid pore-forming agent may be used in combination with a solid pore-forming agent. At room temperature (a temperature of 20°C or higher and 35°C or lower), liquid pore-forming agents are classified as liquid pore-forming agents, and solid pore-forming agents are classified as solid pore-forming agents.

[0090] The liquid pore-forming agent is preferably the above-mentioned oil, and the solid pore-forming agent is, for example, a polymer powder.

[0091] The amount of pore-forming agent in the porous film may vary depending on the type. The amount of pore-forming agent in the porous film is, for example, 30 parts by mass or more per 100 parts by mass of the base polymer. The amount of pore-forming agent is, for example, 60 parts by mass or less per 100 parts by mass of the base polymer.

[0092] For example, a porous film containing oil can be formed by extracting and removing a portion 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. For example, the oil content in the porous film can be adjusted by adjusting the type and composition of the solvent, extraction conditions (extraction time, extraction temperature, solvent supply rate, etc.), etc.

[0093] The surfactant used as the penetrating agent may be, for example, either an ionic surfactant or a nonionic surfactant. The surfactant may be used alone or in combination of two or more.

[0094] 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 suppressing the COD in the electrolyte solution low and improving charge / discharge efficiency, 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.

[0095] The porous film (or the resin composition used to produce the porous film) may contain inorganic particles.

[0096] The inorganic particles are preferably, for example, ceramic particles, and examples of ceramics constituting the ceramic particles include at least one selected from the group consisting of silica, alumina, and titania.

[0097] The content of inorganic particles in the porous film may be, for example, 40% by mass or more, and may be, for example, 80% by mass or less, or 70% by mass or less.

[0098] The evaluation and measurement methods will be explained below. (1) Analysis or size measurement of porous films (Preparation of porous film) For the analysis or size measurement of the porous film, a porous film taken from an unused separator or a lead-acid battery in a fully charged state after initial use is used. The porous film taken from the lead-acid battery is washed and dried prior to the analysis or measurement.

[0099] The porous film removed from the lead-acid battery is washed and dried using the following procedure. The porous film is immersed in pure water for one hour to remove the sulfuric acid from the film. The porous film is then removed from the liquid and left to dry for at least 16 hours in an environment of 25°C ± 5°C.

[0100] (XRD spectrum) The XRD spectrum of a porous film is measured by irradiating the film with X-rays perpendicular to its surface. The measurement sample is prepared by cutting the portion of the porous film facing the electrode material into a strip. For porous films with ribs, the base portion is cut into a strip to avoid including the ribs. The measurement and fitting of the XRD spectrum are performed under the following conditions:

[0101] (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, Rigaku Corporation) was used.

[0102] (porous film thickness and rib height) The thickness of the porous film is determined by measuring the thickness at five arbitrarily selected points in a cross-sectional photograph of the porous film and averaging the measured values.

[0103] The height of the rib is determined by averaging the heights of the base portion of the rib from one surface measured at 10 arbitrarily selected points on the rib in a cross-sectional photograph of the porous film.

[0104] (Oil content in porous film) The portion of the porous film facing the electrode material is cut into a strip to prepare a sample (hereinafter referred to as Sample A). For porous films with ribs, Sample A is prepared by cutting the base portion into a strip so as not to include the ribs.

[0105] Approximately 0.5 g of sample A is taken and accurately weighed to determine the initial sample mass (m0). The weighed sample A is placed in an appropriately sized glass beaker and 50 mL of n-hexane is added. Next, ultrasonic waves are applied to the sample together with the beaker for approximately 30 minutes to dissolve the oil contained in sample A into n-hexane. Next, the sample is removed from the n-hexane and dried in the air at room temperature (a temperature between 20°C and 35°C), and then weighed to determine the mass (m1) of the sample after oil removal. The oil content is then calculated using the following formula. The oil content of 10 samples A is determined and the average value is calculated. The obtained average value is taken as the oil content in the porous film. Oil content (mass%) = (m0 - m1) / m0 x 100

[0106] (Content of inorganic particles in porous film) A portion of Sample A prepared in the same manner as above was taken, accurately weighed, and placed in a platinum crucible. It was then heated with a Bunsen burner until no white smoke was emitted. The resulting sample was then heated in an electric furnace (in an oxygen stream at 550°C ± 10°C) for approximately 1 hour to incinerate it, and the incinerated material was weighed. The percentage of the mass of the incinerated material relative to the mass of Sample A was calculated, and this was taken as the inorganic particle content (mass%). The inorganic particle content of 10 Samples A was determined, and the average value was calculated. The resulting average value was taken as the inorganic particle content in the porous film.

[0107] (Content of penetrant in porous film) A portion of Sample A prepared in the same manner as above was taken, accurately weighed, and dried for at least 12 hours at room temperature (20°C to 35°C) under reduced pressure below atmospheric pressure. The dried material was placed in a platinum cell and placed in a thermogravimetric analyzer. The temperature was raised from room temperature to 800°C ± 1°C at a rate of 10 K / min. The weight loss upon raising the temperature from room temperature to 250°C ± 1°C was taken as the mass of the penetrant, and the ratio (percentage) of the mass of the penetrant to the mass of Sample A was calculated, giving the penetrant content (mass%). A TA Instruments Q5000IR thermogravimetric analyzer was used. The penetrant content was determined for 10 Samples A and the average value was calculated. The average value obtained was taken as the penetrant content in the porous film.

[0108] (2) Heavy load life test Heavy-load life is evaluated based on the number of cycles required to reach the end of life in the following charge-discharge cycle test in accordance with JIS D5301:2019. A fully charged lead-acid battery with a rated voltage of 12 V is repeatedly discharged and charged under the following conditions. Here, (a) to (e) are performed in a water tank at 40°C ± 2°C.

[0109] In the heavy load life test, the 20-hour rate capacity C of the test battery 20 The discharge current and charge current are specified depending on the difference. The heavy load life test is carried out in the following steps (a) to (e). Here, the 20-hour rate capacity 20 This refers to the capacity when the battery is discharged to the end-of-discharge voltage at a current (A) that is 1 / 20 of the Ah value indicated on the rated capacity.

[0110] (a) Discharge: Discharge for 1 hour at a current of 20A or 40A. (b) Charging: Charging for 5 hours at a current of 5A or 10A. (c) Repetition: The above (a) and (b) constitute one cycle and are repeated 24 times. (d) Judgment discharge: After (c) above, continuous discharge is carried out at 20 A or 40 A down to 10.2 V, and the discharge duration is recorded. (e) Charging: Charge the battery at a current of 5A or 10A until the terminal voltage or electrolyte density (converted value at 25°C) of the lead-acid battery measured every 15 minutes shows a constant value for three consecutive times.

[0111] Here, the number of cycles until the battery reaches its end of life is determined by the 20-hour capacity C 20 This is the number of cycles at which the ATP concentration is 50% or less of the value obtained by dividing by 1.155.

[0112] The discharge and charge cycles (d) and (e) above are also included in the number of cycles.

[0113] 20 hour rate capacity C 20 When evaluating lead-acid batteries with a capacity of 55 Ah or more and 81 Ah or less, a discharge current of 20 A and a charge current of 5 A are used.

[0114] 20 hour rate capacity C 20 When evaluating lead-acid batteries with a capacity of over 81 Ah and up to 205 Ah, a discharge current of 40 A and a charge current of 10 A are used.

[0115] The items described in this specification can be combined in any manner.

[0116] FIG. 1 shows the appearance of an example of a lead-acid battery according to an embodiment of the present invention. The lead-acid battery 1 includes a battery case 12 that contains a plate group 11 and an electrolyte (not shown). The battery case 12 is divided into multiple cell chambers 14 by partition walls 13. Each cell chamber 14 contains one plate group 11. The opening of the battery case 12 is closed by a lid 15 that has a negative electrode terminal 16 and a positive electrode terminal 17. The lid 15 is provided with a vent plug 18 for each cell chamber. When rehydrating, the vent plug 18 is removed and rehydration liquid is added. The vent plug 18 may have the function of venting gas generated in the cell chambers 14 to the outside of the battery.

[0117] Each electrode plate group 11 is formed by stacking a plurality of negative electrode plates 2 and positive electrode plates 3 with separators 4 interposed therebetween. In a cell chamber 14 located at one end of the battery case 12, a negative electrode shelf 6 that connects a plurality of negative electrode plates 2 in parallel is connected to a feedthrough connector 8, and a positive electrode shelf 5 that connects a plurality of 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 outside the lid 15. In a 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 feedthrough connector 8 is connected to the positive electrode shelf 5. The negative electrode column 9 is connected to a negative electrode terminal 16 outside the lid 15. Each feedthrough 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.

[0118] [Example] The present invention will be specifically described below based on examples and reference examples, but the present invention is not limited to the following examples.

[0119] 《Lead acid battery R1~R11》 Each lead-acid battery was fabricated according to the following procedure. (1) Preparation of separator A resin composition containing polyethylene, silica particles, paraffinic oil as a pore-forming agent, and a penetrant was extruded into a sheet, stretched, and then partially removed to produce a porous film with ribs on one side. The cooling rate and stretching ratio of the extruded sheet were adjusted so that the peak ratio R of the porous film obtained by the above-mentioned procedure would be the value (0.58) shown in Table 1.

[0120] The oil content of the porous film determined by the above-mentioned procedure was 15% by mass, and the silica particle content was 60% by mass. The rib height obtained using the procedure described above was 0.55 mm. The thickness of the porous film (thickness of the base portion) obtained by the above-mentioned procedure was standardized to 0.2 mm.

[0121] Next, the sheet-like porous film was folded in half so that the ribs were located on the inner surface to form a bag, and the overlapping ends were crimped to obtain a bag-like porous film (size when laid flat: length 117 mm x width 152 mm). The crimped part was located 2 mm inside from the side edge of the porous film and had a width of 3 mm.

[0122] The peak ratio R, oil content, silica particle content, base thickness, and rib height of the porous film were values obtained for the porous film before the lead-acid battery was fabricated, but were almost the same as the values measured by the above-mentioned procedure for the porous film removed from the lead-acid battery after fabrication.

[0123] (2) Preparation 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 then aged and dried to obtain an unformed positive electrode plate measuring 137 mm wide, 110 mm high, and 1.6 mm thick.

[0124] (3) Preparation of negative electrode plate A negative electrode paste was prepared by mixing lead oxide, carbon black, barium sulfate, lignin, a reinforcing material (synthetic resin fiber), water, and sulfuric acid. The negative electrode paste was filled into the mesh of an expanded lattice made of an antimony-free Pb-Ca-Sn alloy, and then aged and dried to obtain an unformed negative electrode plate measuring 137 mm wide, 110 mm high, and 1.3 mm thick. The amounts of carbon black, barium sulfate, lignin, and synthetic resin fiber were adjusted so that the respective component contents of the negative electrode plate removed from a fully charged lead-acid battery were 0.3%, 2.1%, 0.1%, and 0.1% by mass, respectively.

[0125] (4) Preparation of lead-acid battery The unformed negative electrode plates were placed in a pouch-shaped porous film separator. The negative electrode plates and positive electrode plates were stacked with the separator interposed between them. In this way, an electrode plate assembly was formed with seven unformed negative electrode plates and six unformed positive electrode plates.

[0126] The positive and negative plate lugs were welded to the positive and negative shelf sections, respectively, using the cast-on-strap method. The plate assembly was inserted into a polypropylene battery case, electrolyte was poured in, and chemical formation was performed inside the battery case to assemble a flooded lead-acid battery with a rated voltage of 12V and a 5-hour rate capacity of 30Ah. The 5-hour rate capacity refers to the capacity when discharged at a current (A) equal to 1 / 5 of the Ah value listed in the rated capacity. Six plate groups were connected in series inside the battery case.

[0127] The electrolyte used was a sulfuric acid aqueous solution. The density of the electrolyte after formation at 20°C was 1.285. The electrolyte was removed from a fully charged lead-acid battery and adjusted to have a COD (COD by mass) shown in Table 1. The COD was controlled by changing the amount of penetrant used when preparing the porous film.

[0128] 《Lead acid battery R12, E1~E10》 Lead acid batteries were fabricated in the same manner as in Comparative Examples 1 to 11, except that a porous film adjusted so that the peak ratio R determined by the procedure described above would be the value (0.60) shown in Table 2 was used.

[0129] 《Lead acid battery R13, E11~E20》 Lead acid batteries were produced in the same manner as in Comparative Examples 1 to 11, except that a porous film adjusted so that the peak ratio R determined by the procedure described above would be the value (0.70) shown in Table 3 was used.

[0130] 《Lead acid battery R14, E21~E30》 Lead acid batteries were produced in the same manner as in Comparative Examples 1 to 11, except that a porous film adjusted so that the peak ratio R determined by the procedure described above would be the value (0.80) shown in Table 4 was used.

[0131] 《Lead acid battery R15, E31~E40》 Lead acid batteries were produced in the same manner as in Comparative Examples 1 to 11, except that a porous film adjusted so that the peak ratio R determined by the procedure described above would be the value (0.90) shown in Table 5 was used.

[0132] (5) Evaluation Using the procedure described above, the life performance of the lead-acid battery was evaluated in a heavy load life test at 40°C. The life performance was evaluated as a relative value when the number of cycles until the end of the life of the lead-acid battery R1 was set at 100.

[0133] The evaluation results are shown in Tables 1 to 5. E1 to E40 are examples, and R1 to R15 are comparative examples.

[0134] [Table 1]

[0135] [Table 2]

[0136] [Table 3]

[0137] [Table 4]

[0138] [Table 5]

[0139] For batteries R1, R12, R13, R14, and R15, the COD was as high as 170 mg / L, so even if the peak ratio R was increased from 0.58 to 0.90, the heavy-load life performance did not improve. This is because there were many organic components that inhibited the charging reaction on the surfaces of the positive and negative plates, reducing charging efficiency and causing the lead-acid battery to reach the end of its life due to insufficient charging before oxidation degradation of the separator began.

[0140] In batteries R2 to R11, the COD was less than 170 mg / L, improving the charging efficiency. However, there was little improvement in the heavy-load life performance. This is because the improved charging efficiency made the positive electrode material more susceptible to softening and shedding, increasing the contact area between the positive electrode material and the separator and causing oxidative degradation of the separator, which had a peak ratio R of less than 0.60 (0.58). Cracks, breaks, holes, etc. occurred in the separator, causing the positive electrode material and negative electrode material to come into contact at damaged areas of the separator, resulting in a short circuit and causing the lead-acid battery to reach the end of its life.

[0141] In batteries E1 to E10, the COD is less than 170 mg / L, which improves charging efficiency. Furthermore, the peak ratio R is 0.60, which improves heavy-load life performance. Compared with batteries E11 to E40, the improvement in heavy-load life performance is significant when the peak ratio R is 0.70 or higher, and even more significant when the COD is 120 mg / L or lower. [Industrial Applicability]

[0142] The lead-acid battery according to the present disclosure is suitable as a starting power source for various vehicles (commercial vehicles such as trucks and taxis, motorcycles, etc.), for example, a lead-acid battery employing start-stop control. The lead-acid battery can also be suitably used as a power source for industrial power storage devices such as electric vehicles (forklifts, etc.). Note that these uses are merely examples. The uses of the lead-acid battery according to the present disclosure are not limited to these. Start-stop control is sometimes referred to as idling stop-start (ISS). ISS control is also called idling reduction control. [Explanation of symbols]

[0143] 1:Lead acid battery 2: Negative electrode plate 3: Positive electrode plate 4: Separator 5: Positive electrode shelf 6: Negative electrode shelf 7: Positive pole 8: Through-connector 9: Negative pole 11: Plate group 12:Battery container 13: Bulkhead 14: Cell Room 15: Lid 16: Negative terminal 17: Positive terminal 18: Liquid vent plug

Claims

1. A positive electrode plate; A negative electrode plate; a porous film interposed between the positive electrode plate and the negative electrode plate; An electrolyte; Equipped with the porous film contains a resin, In the X-ray diffraction spectrum of the porous film, I １１０ / (I １１０ +I ２００ ) is 0.6 or more, I １１０ is the integrated intensity of the diffraction peak corresponding to the (110) plane, I ２００ is the integrated intensity of the diffraction peak corresponding to the (200) plane, A lead-acid battery, wherein the chemical oxygen demand in the electrolyte is less than 170 mg / L.

2. 2. The lead-acid battery of claim 1, wherein the chemical oxygen demand is 120 mg / L or less.

3. The lead-acid battery according to claim 1 , wherein the ratio R is 0.7 or greater.

4. 2. The lead-acid battery according to claim 1, wherein the porous film has a thickness of 0.15 mm or more and 0.30 mm or less.

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