Lead-acid battery separator and lead-acid battery

Abstract

To provide a separator for a lead-acid battery capable of having good bag-like workability and high battery safety, and a lead-acid battery including the same.SOLUTION: A separator for a liquid type lead-acid battery is provided having a porous base unit and a plurality of ribs provided on at least one surface of the porous base unit. The porous base unit has side end units arranged at both ends in a width direction and a center unit sandwiched between the side end units. Thickness of the side end unit is larger than that of the center unit. Relative element concentration of a nonmetallic element (S) is 0.01 atomic% or more and 0.5 atomic% or less when at least one surface of the base unit is measured by X-ray photoelectron spectroscopy.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a technology that provides good processability of a pouch-shaped separator and high battery safety. [Background technology]

[0002] When lead-acid batteries are repeatedly charged and discharged during use, their performance gradually deteriorates. As battery performance deteriorates, the internal pressure of the battery increases, which can exert a large amount of pressure between the positive and negative plates. When this occurs, the electrodes are prone to compression and deformation. This can cause the adhesive portion of the separator bag that houses the electrodes to open. This can cause the electrode plates to move and come into contact, resulting in a short circuit. To address this issue, a common method is to make the separator bag more difficult to open by strengthening its sealing (the force that seals the separator). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-245901 Summary of the Invention [Problem to be solved by the invention]

[0004] In contrast to common methods for making pouch-shaped separators difficult to open, Patent Document 1 adds a specific heat-sealing material to a separator for a sealed lead-acid battery to increase sealing strength. However, while the heat-sealing material described in Patent Document 1 is effective for separators made of fine glass fiber nonwoven fabric sheets, it is not suitable for separators for flooded lead-acid batteries that are primarily made of polyolefin.

[0005] The present invention was completed in light of the above circumstances, and an object of the present invention is to provide a pouch-shaped separator for a lead-acid battery that is easy to process and has high battery safety. [Means for solving the problem]

[0006] The technical means for solving the above problems disclosed in this specification are exemplified below. <1> The separator for a flooded lead-acid battery comprises a porous base portion and a plurality of ribs provided on at least one surface of the porous base; A separator for a flooded lead-acid battery, The porous base portion is Side end portions disposed on both ends in the width direction; a central portion sandwiched between the side edges; the thickness of the side edge is greater than the thickness of the central portion; and When at least one surface of the porous base portion is measured by X-ray photoelectron spectroscopy, the relative element concentration of a nonmetallic element (sulfur S) is 0.01 atomic % or more and 0.5 atomic % or less. Separator for flooded lead-acid batteries. <2> The ratio (S) / (C) of the relative element concentration of the nonmetallic element (S) to the relative element concentration of the nonmetallic element (carbon C) is 1.0 × 10 -4 That's it, 1.0 x 10 -2 Below is the item <1> The separator for a flooded lead-acid battery according to claim 1. <3> The difference in thickness between the side end portion and the central portion is 0.06 mm or more and 0.15 mm or less. item <1> or <2> The separator for a flooded lead-acid battery according to claim 1. <4> The side end has a resistance of 120 mΩ·cm 2 It has the following electrical resistance: item <1> ~ <3> The separator for a flooded lead-acid battery according to any one of claims 1 to 4. <5> The material may include any one or more of polyolefin resin, phenol resin, polyvinyl chloride resin, rubber, cellulose, and cellulose derivatives. item <1> ~ <4> The separator for a flooded lead-acid battery according to any one of claims 1 to 4. <6> The surface that satisfies the relative element concentration of the non-metallic element (S) being 0.01 atomic % or more and 0.5 atomic % or less is the inner surface of the porous base portion when processed into a bag shape that accommodates the electrodes. item <1> ~ <5> The separator for a flooded lead-acid battery according to any one of claims 1 to 4. <7> item <1> ~ <6> A flooded lead-acid battery comprising the flooded lead-acid battery separator according to any one of claims 1 to 4. [Effects of the Invention]

[0007] The lead-acid battery separator disclosed in this specification ensures the workability of the pouch-shaped separator and ensures the safety of a flooded lead-acid battery equipped with the lead-acid battery separator. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Outline of this embodiment) First, an outline of a lead-acid battery separator (hereinafter sometimes abbreviated as "separator") according to this embodiment will be described. The separator for a flooded lead-acid battery disclosed in this specification has a porous base portion and a plurality of ribs provided on at least one surface of the porous base portion, the porous base portion having side edges disposed at both ends in the width direction and a central portion sandwiched between the side edges, the side edges being thicker than the central portion, and the relative element concentration of a non-metallic element (S) when at least one surface of the porous base portion is measured by X-ray photoelectron spectroscopy is 0.01 atomic % or more and 0.5 atomic % or less.

[0009] The inventors attempted to identify the cause of improved adhesion at the adhesive bonded portion of a pouch-shaped separator and found that adhesive strength improves when the separator's base material, a thermoplastic resin (e.g., a polyolefin resin), is present in a larger and more uniform amount at the adhesive bonded portion. Specifically, separators contain thermoplastic resin, filler, and plasticizer as their primary ingredients. If the filler or plasticizer is present in large amounts or if clumps of filler or plasticizer are formed at the adhesive bonded portion, there will not be enough thermoplastic resin, resulting in a decrease in the solid adhesive bond between the thermoplastic resin layers. On the other hand, they found that a larger and more uniform amount of thermoplastic resin significantly increases the probability or area of ​​contact between the thermoplastic resin layers, leading to improved adhesive strength. This allows the creation of an electrode bag that is difficult to open while maintaining sealing to the separator, for example, in mechanical seals such as those used to pass gears. However, simply increasing the amount of thermoplastic resin worsens the separator's electrical resistance and gradually reduces its electrical capacity. As a feature of the present invention, the inventors discovered that the resistance of the entire battery does not deteriorate significantly by not changing the thickness of the central part of the separator, which led to the idea of ​​the present invention.

[0010] Based on the above, the inventors have found that by increasing the thickness of the thermoplastic resin in the adhesive zone, sufficient adhesion of the thermoplastic resin is achieved when molding the separator into a bag shape. Furthermore, by controlling the relative elemental concentration of nonmetallic elements (sulfur (S)) present in the separator, such as nonmetallic elements (S) derived from surfactants, the surfactant disperses the plasticizer so that it covers the entire thermoplastic resin, gradually resulting in a uniform distribution of the thermoplastic resin on the surface, thereby increasing the probability of adhesion between the thermoplastic resins. Possible methods for controlling the relative elemental concentration of nonmetallic elements (S) include (i) adjusting the amount of S added when mixing with the separator's main raw materials and / or (ii) adjusting the amount of S coated on the surface of the molded separator. It is preferable to use both control methods (i) and (ii). As a result, the separator obtained by the present invention not only significantly improved the peel strength, which evaluates the sealing ability of the adhesive zone, but also enhanced the mechanical strength of the side edges. Furthermore, according to the present invention, since the thickness of the central portion is maintained, good electrical resistance can be obtained while preventing tearing at the adhesive joints at the side edges, and the practical impact of breakage of the separator adhesive joints on battery life can be minimized.

[0011] (Detailed Description of the Present Embodiment) The separator for a flooded lead-acid battery according to this embodiment has a porous base portion and a plurality of ribs provided on at least one surface of the porous base portion, the porous base portion having side edges located at both ends in the width direction and a central portion sandwiched between the side edges, the side edges being thicker than the central portion, and the relative element concentration of non-metallic elements (sulfur S) measured on at least one surface of the porous base portion by X-ray photoelectron spectroscopy is 0.01 atomic % or more and 0.5 atomic % or less.

[0012] By setting the relative element concentration of the nonmetallic element (S) to 0.01 atomic % or more, the surfactant can disperse the plasticizer so that it covers the entire thermoplastic resin. As a result, the separator according to this embodiment has improved sealing properties at the adhesive layer. However, since excessive addition of the nonmetallic element (S) can cause side reactions within the battery, it is preferable that the relative element concentration of the nonmetallic element (S) be 0.5 atomic % or less. It is preferable that the relative element concentration of the nonmetallic element (S) be 0.015 atomic % or more and 0.45 atomic % or less. It is more preferable that the relative element concentration of the nonmetallic element (S) be 0.02 atomic % or more and 0.4 atomic % or less. It is even more preferable that the relative element concentration of the nonmetallic element (S) be 0.025 atomic % or more and 0.35 atomic % or less. It is most preferable that the relative element concentration of the nonmetallic element (S) be 0.03 atomic % or more and 0.3 atomic % or less.

[0013] The surface of the porous base portion where the relative element concentration of the nonmetallic element (S) in X-ray photoelectron spectroscopy measurement falls within the above numerical range is preferably the inner surface when the porous base portion is processed into a bag shape to accommodate the electrodes, in order to achieve both workability of the bag-shaped separator and safety of the flooded lead-acid battery.

[0014] In the separator, the ratio (S) / (C) of the relative element concentration of the nonmetallic element (S) to the relative element concentration of the nonmetallic element (C) is 1.0×10 -4 That's it, 1.0 x 10 -2 The ratio (S) / (C) of the relative element concentration of the nonmetallic element (S) to the relative element concentration of the nonmetallic element (C) is 1.0×10 or less. -4 On the other hand, if the nonmetallic element (S) is added in excess, there is a risk of side reactions occurring in the battery. Therefore, it is necessary to ensure that the ratio of the relative element concentrations (S) / (C) is 1.0 × 10 or more. -2 The relative element concentration ratio (S) / (C) is preferably 2.0×10 or less. -4 That's it, 7.0 x 10 -3It is preferable that the relative element concentration ratio (S) / (C) is 3.0×10 or less. -4 That's it, 5.0 x 10 -3 It is more preferable that the ratio is less than or equal to the above.

[0015] In this embodiment, the porous base portion of the separator has side ends located at both ends in the width direction and a central portion sandwiched between the side ends, and the side ends of the porous base portion are thicker than the central portion, thereby improving the sealing strength when the separator is made into a bag shape and ensuring excellent processability.

[0016] The difference in thickness between the side end portions and the central portion is preferably 0.06 mm or more and 0.15 mm or less. By making the difference in thickness between the side end portions and the central portion 0.06 mm or more, the separator for a flooded lead-acid battery of the present invention exhibits excellent processability when formed into a bag shape. On the other hand, if the difference in thickness is 0.16 mm or more, it tends to be difficult to transmit sufficient sealing force during sealing, so it is preferable that the difference in thickness be 0.15 mm or less. The difference in thickness between the side end portions and the central portion is more preferably 0.07 mm or more and 0.13 mm or less. The difference in thickness between the side end portions and the central portion is even more preferably 0.08 mm or more and 0.11 mm or less.

[0017] The side end is made of lead-acid battery with a CCA value of 120 mΩ cm to evaluate the starting performance of the battery. 2 It is preferable that the electrical resistance is 110 mΩ cm or less. 2 It is more preferable that the ratio is less than or equal to the above.

[0018] The separator according to this embodiment preferably contains a natural or synthetic material such as a polyolefin resin, a phenolic resin, a polyvinyl chloride (PVC) resin, rubber, synthetic wood pulp (SWP), glass fiber, a cellulosic material (e.g., composed of cellulose or a cellulose derivative, etc., in the form of fiber), or a combination thereof. This results in a microporous film having numerous uniform, fine, and intricately intertwined interconnected pores formed throughout the separator. From the viewpoint of forming uniform, fine interconnected pores throughout the separator, it is more preferable that the separator contain one or more of a polyolefin resin, a phenolic resin, a polyvinyl chloride resin, rubber, cellulose, and a cellulose derivative.

[0019] (Method for manufacturing lead-acid battery separator) An example of a specific method for producing the lead-acid battery separator according to this embodiment will be described below. The raw materials, consisting of a predetermined amount of polyolefin resin, filler, plasticizer, and various additives (surfactants, antioxidants, etc.), are stirred and mixed in a mixer to obtain a raw material mixture. Next, this mixture is extruded into a sheet using a twin-screw extruder while being heated, melted, and kneaded. This extruded sheet is passed between a pair of forming rolls, at least one of which has a predetermined groove engraved on it, to obtain a film-like product in which ribs of a predetermined shape are integrally formed on at least one side of the flat sheet. Next, this film-like product is immersed in an appropriate solvent to extract and remove a predetermined amount of plasticizer, and then dried. Finally, the desired microporous film is obtained by coating with additives.

[0020] The polyolefin resin may be a homopolymer or copolymer of polyethylene, polypropylene, polybutene, polymethylpentene, or the like, or a mixture thereof. Among these, polyethylene is preferred as the main component in terms of moldability and economy. Furthermore, ultra-high molecular weight polyethylene (UHMWPE) is more preferred. In some embodiments, one or more ultra-high molecular weight polyethylenes are used. Ultra-high molecular weight polyethylene (UHMWPE) has good compatibility with silica, and in microporous films, it maintains strength while bonding the skeleton of silica fine powder as an adhesive functional material, and is chemically stable and highly safe.

[0021] A preferred method for obtaining a separator involves melt-kneading a raw material composition primarily composed of a natural or synthetic material, such as the polyolefin resin, phenolic resin, PVC, rubber, synthetic wood pulp (SWP), glass fiber, cellulose fiber, or a combination thereof, to which a filler and a plasticizer have been added, followed by film formation and partial or complete removal of the plasticizer, thereby obtaining a microporous film with numerous uniform, fine, and intricately interwoven interconnected pores throughout the separator.

[0022] Examples of the filler that can be used include silica, mica, montmorillonite, kaolinite, asbestos, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, cement, calcium silicate, clay, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gel, glass particles, carbon black, activated carbon, carbon fiber, charcoal, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, lead oxide, tungsten, antimony oxide, zirconia, magnesia, alumina, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, magnesium carbonate, and combinations thereof. Among these, silica is preferred because it has a wide range of powder properties such as particle size and specific surface area, is relatively inexpensive and easily available, and contains few impurities.

[0023] Mineral oil is preferred as the plasticizer because it is easily recyclable. Plasticizers are the easiest component to remove from a mixture of polymer, filler, and plasticizer, and therefore contribute to imparting porosity to the separator. While the microporous film separator may contain zero plasticizer, adding an appropriate amount of a plasticizer such as mineral oil to a separator for flooded lead-acid batteries can contribute to improving oxidation resistance. In such cases, the plasticizer content in the separator is preferably 5 to 30 wt %. However, increasing the plasticizer content reduces the porosity of the microporous film and deteriorates the electrical resistance of the microporous film separator. From this perspective, the plasticizer content is more preferably 20 wt % or less.

[0024] As the solvent used to extract and remove the plasticizer, organic solvents such as organic chlorine compounds, hexane, heptane, octane, nonane, and decane, which are saturated hydrocarbons, can be used.

[0025] The raw material composition or the microporous film may contain or contain a surfactant (hydrophilizing agent), or, if necessary, additives such as an antioxidant, a lubricant, an antibacterial agent, a colorant, and the like.

[0026] The surfactants include alkyl sulfates, alkylaryl sulfonate salts, alkylphenol-alkylene oxide adducts, soaps, alkylnaphthalene sulfonates, dialkyl esters of sulfosuccinate, quaternary amines, block copolymers of ethylene oxide and propylene oxide, and salts of mono- and dialkyl phosphate esters.Additives that can be used include nonionic surfactants such as polyol fatty acid esters, polyethoxylated esters, polyethoxylated fatty alcohols, alkyl polysaccharides such as alkyl polyglycosides and blends thereof, amine ethoxylates, sorbitan fatty acid ester ethoxylates, organosilicone surfactants, ethylene vinyl acetate terpolymers, ethoxylated alkylaryl phosphate esters, and sucrose fatty acid esters.

[0027] (Separator shape and dimensions) The separator has an average pore size of less than 5 μm in diameter, preferably less than 1 μm. Preferably, more than 50% of the pores have a diameter of 0.5 μm or less. Preferably, at least 90% of the pores have a diameter of less than 0.9 μm. In some cases, the separator preferably has an average pore size in the range of 0.01 to 0.3 μm.

[0028] Pore ​​size is sometimes measured using the mercury intrusion method described by Ritter, HL, and Drake, LC, Industrial and Technical Chemical Analysis, 17th Edition, 787 (1945). According to this method, mercury is forced into pores of different sizes by varying the pressure applied to the mercury using a porosimeter (Porosimeter Model 2000, Carlo Erba). Pore size is measured by the mercury intrusion method using a porosimeter, while pore distribution may be determined by evaluation of raw data using MILESTONE 200 software.

[0029] The separator's total center thickness is preferably greater than 0.1 mm and less than or equal to 5.0 mm. The separator's total center thickness can be within the range of 0.15 to 2.5 mm, 0.25 to 2.25 mm, 0.5 to 2.0 mm, 0.5 to 1.5 mm, or 0.75 to 1.5 mm. The total center thickness includes not only the center base thickness but also the rib height, and is measured at the center where the center base thickness and rib height are greatest. In some cases, the separator can be approximately 0.8 mm or 1.1 mm thick.

[0030] The thickness of the central base of the separator is preferably about 0.05 mm to about 0.500 mm (for example, in a specific embodiment, about 0.20 mm).

[0031] The thickness of the side edge portion of the present invention can be determined according to the design of the forming roll.

[0032] The separator may have ribs on at least one surface, as desired, in the form of continuous or discontinuous vertical or horizontal straight ribs, serrated ribs, dimpled ribs, protrusions, or combinations thereof. Preferably, the ribs have a height of 0.008 mm to 1 mm and are spaced apart from each other by 0.001 mm to 20 mm. In some embodiments, the ribs are spaced apart from each other by 0 to 90 degrees.

[0033] On the other hand, there is a method of increasing mechanical strength by providing ribs (sometimes called back ribs or negative electrode ribs) on the negative electrode surface (e.g., the negative electrode contact surface or the negative electrode facing surface, etc.) of the separator. However, in some embodiments, providing negative electrode ribs reduces the adhesive area between thermoplastic resins, gradually reducing the peel strength. This can cause the adhesive area to tear after molding into a bag shape. The present inventors have discovered that, depending on the embodiment of the rib shape on the positive electrode surface (e.g., the positive electrode contact surface or the positive electrode facing surface of the separator), good battery performance can be obtained even without providing ribs on the negative electrode surface.

[0034] (liquid lead acid battery) The following configuration is preferred as an embodiment of a flooded lead-acid battery using the separator of the present invention: The separator is bag-shaped and houses the positive electrode plate or the negative electrode plate as required.

[0035] The positive and negative plates, electrolyte, lid, and battery case of the flooded lead-acid battery may have structures known in the art. For example, the flooded lead-acid battery separator according to the present embodiment may be incorporated into a vented lead-acid battery in which positive and negative plates are inserted into a battery case containing an electrolyte and the lid is closed.

[0036] The separator housing the positive electrode plate may be provided with positive electrode ribs, and in some embodiments, the separator housing the negative electrode plate may be provided with negative electrode ribs. [Example]

[0037] Next, examples of the present invention will be described in detail together with comparative examples.

[0038] Example 1 30% by weight of ultra-high molecular weight polyethylene resin powder with a weight-average molecular weight of 2.5 million as a polyolefin resin, 70% by weight of silica powder, and paraffinic mineral oil as a plasticizer were mixed in a mixer, and then 2% by weight of a surfactant was added. This raw material composition was extruded into a sheet using a twin-screw extruder equipped with a T-die at the tip while being heated, melted, and kneaded. The extruded sheet was passed through a pair of forming rolls, one of which had a groove engraved with a predetermined shape for the main rib for contacting the electrode plate, to obtain a film-like product in which the main rib for contacting the electrode plate of a predetermined shape was integrally formed on one side of the flat sheet. Next, this film-like product was immersed in trichloroethylene to extract and remove a predetermined amount of paraffinic mineral oil, dried, and then coated with a surfactant solution and dried to obtain a microporous film with a base thickness of 0.20 mm in the center. This was the separator for a flooded lead-acid battery of Example 1.

[0039] Example 2 A separator was produced in the same manner as in Example 1, except that the thickness of the side edge and the amount of the interfacial conversion agent were adjusted.

[0040] Example 3 A separator was produced in the same manner as in Example 1, except that the thickness of the side edge and the amount of the interfacial conversion agent were adjusted.

[0041] Example 4 A separator was produced in the same manner as in Example 1, except that the thickness of the side edge and the amount of the interfacial conversion agent were adjusted.

[0042] Example 5 A separator was produced in the same manner as in Example 1, except that the thickness of the side edge and the amount of the interfacial conversion agent were adjusted.

[0043] Example 6 A separator was produced in the same manner as in Example 1, except that the thickness of the side edge was adjusted.

[0044] (Comparative Example 1) A separator was produced in the same manner as in Example 1, except that the thickness of the side edge and the amount of the interfacial conversion agent were adjusted.

[0045] (Comparative Example 2) A separator was produced in the same manner as in Comparative Example 1, except that the thickness of the side edge portion was adjusted.

[0046] (Comparative Example 3) A separator was produced in the same manner as in Example 1, except that the thickness of the side edge and the proportions of the interfacial conversion agent, polyethylene resin, and mineral oil were adjusted.

[0047] Comparative Example 4 A separator was produced in the same manner as in Comparative Example 3, except that the thickness of the side edge and the amount of the interfacial conversion agent were adjusted.

[0048] (Comparative Example 5) A separator was produced in the same manner as in Example 1, except that the amount of the interfacial conversion agent added to the raw materials was adjusted and the surface of the separator was not coated with a surfactant.

[0049] (Comparative Example 6) A separator was produced in the same manner as in Example 1, except that the amount of the coated interfacial conversion agent was adjusted and no surfactant was added to the raw materials.

[0050] Next, various properties were evaluated by the following methods for each of the separators obtained above in Examples 1 to 6 and Comparative Examples 1 to 6. The results are shown in Table 1.

[0051] <Peel strength> The microporous film was cut into 80mm x 150mm rectangular pieces in the MD and CMD (Cross Machine Direction) directions to prepare test specimens. The test specimen was folded in half in the MD direction, and one side edge was sealed using a seal tester. Next, from the open side, the specimen was cut into 30mm x 150mm rectangular pieces in the MD and CMD directions to prepare tensile test specimens. Using an Instron tensile testing machine, set the distance between the grips of the testing machine to approximately 80 mm, attach both sides of the longitudinal direction of the two-layer test piece, conduct a tensile test at a tensile speed of 300 mm per minute, and read the tensile load (b) and distance (c) when the test piece is cut. The peel strength is calculated by dividing the tensile load (b) by the cross-sectional area of the test piece.

[0052] The peel strength was evaluated for the opening suppression effect when made into a bag shape, with ◎ for 17 N or more, ○ for 16 N or more, and × for less than 16 N. If it has a peel strength of 16 N or more, the suppression effect of bag breakage due to electrode deformation can be expected.

[0053] <X-ray Photoelectron Spectroscopy> A 5-mm small piece was cut out from the microporous film, covered with a 1-mm × 2-mm slot mask, and the measurement was carried out. The measurement conditions are shown below. Machine: Thermo Fisher ESCALAB250 Excitation source: mono.AlK α 15 kV × 10 mA Analysis size: approximately 1 mm (shape is ellipse) Photoelectron extraction angle: 0° (perpendicular to the sample surface)

[0054]

Table 1

Claims

1. a porous base portion; a plurality of ribs provided on at least one surface of the porous base; A separator for a flooded lead-acid battery, The composition contains a polyolefin resin, a filler, and a surfactant, the filler is at least one selected from the group consisting of silica, alumina, kaolinite, aluminum silicate, and calcium silicate; the surfactant is at least one selected from the group consisting of alkyl sulfates, alkylaryl sulfonates, alkylnaphthalene sulfonates, and dialkyl esters of sulfosuccinates; The porous base portion is Side end portions disposed on both ends in the width direction; a central portion sandwiched between the side edges; the thickness of the side edge is greater than the thickness of the central portion; and the relative element concentration of a nonmetallic element (sulfur S) when at least one surface of the porous base portion is measured by X-ray photoelectron spectroscopy is 0.01 atomic % or more and 0.5 atomic % or less; Separator for flooded lead-acid batteries.

2. The ratio (S) / (C) of the relative element concentration of the nonmetallic element (S) to the relative element concentration of the nonmetallic element (carbon C) is 1.0 × 10 -4 That's it, 1.0 x 10 -2 Below is the The separator for a flooded lead-acid battery according to claim 1.

3. The difference in thickness between the side end portion and the central portion is 0.06 mm or more and 0.15 mm or less.

3. The separator for a flooded lead-acid battery according to claim 1 or 2.

4. The side end has a resistance of 120 mΩ·cm 2 It has the following electrical resistance: The separator for a flooded lead-acid battery according to any one of claims 1 to 3.

5. A composition comprising any one or more of a phenolic resin, a polyvinyl chloride resin, a rubber, a cellulose, and a cellulose derivative. The separator for a flooded lead-acid battery according to any one of claims 1 to 4.

6. The surface where the relative element concentration of the non-metallic element (S) is 0.01 atomic % or more and 0.5 atomic % or less is the inner surface of the porous base portion when processed into a bag shape that accommodates the electrode. The separator for a flooded lead-acid battery according to any one of claims 1 to 5.

7. A flooded lead-acid battery comprising the separator for flooded lead-acid batteries according to any one of claims 1 to 6.

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