JP7789504B2 - Lead-acid battery separator and lead-acid battery - Google Patents

Description

The present invention relates to technology that provides excellent processability for pouch-shaped separators and high battery safety.

When a lead-acid battery is repeatedly charged and discharged during use, its performance gradually deteriorates. As battery performance deteriorates, the internal pressure of the battery increases, which can cause significant pressure to be applied between the positive and negative plates. When this happens, the electrodes are prone to compression and deformation. This can cause the adhesive portion of the bag-shaped separator 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, a common method is to make the bag-shaped separator more difficult to open by strengthening the sealing of the separator (the force that seals the separator).

Japanese Patent Application Laid-Open No. 2009-245901

In contrast to common methods for making pouch-shaped separators difficult to open, Patent Document 1 increases sealing strength by adding a specific heat-sealing material to separators for sealed lead-acid batteries. 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, which are primarily made of polyolefin.

The present invention was developed based on the above circumstances, and aims to provide a pouch-shaped separator for lead-acid batteries that is easy to process and has high battery safety.

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 portion,
The porous base portion is
Side end portions disposed on both ends in the width direction;
and a central portion sandwiched between the side end portions, wherein the thickness of the side end portions 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 or more and 1.0×10 ^or less;
Item <1> The separator for a flooded lead-acid battery.
<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.
The separator for a flooded lead-acid battery according to item <1> or <2>.
＜4＞
The side end has an electrical resistance of 120 mΩ ^cm2 or less.
The separator for a flooded lead-acid battery according to any one of items <1> to <3>.
<5>
The material may include any one or more of polyolefin resin, phenol resin, polyvinyl chloride resin, rubber, cellulose, and cellulose derivatives.
The separator for a flooded lead-acid battery according to any one of items <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 items <1> to <5>.
＜７＞
A flooded lead-acid battery comprising the separator for a flooded lead-acid battery according to any one of items <1> to <6>.

The lead-acid battery separator disclosed in this specification ensures the workability of the pouch-shaped separator and ensures the safety of flooded lead-acid batteries equipped with the lead-acid battery separator.

(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 comprises 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 a 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) 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.

The inventors attempted to identify the cause of improved adhesion in the adhesive bonded portion of a pouch-shaped separator and discovered that adhesive strength improves when the separator's base material, thermoplastic resin (e.g., polyolefin resin), is present in a larger, more uniform amount in 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 in the adhesive bonded portion, or if clumps of filler or plasticizer are formed, there is insufficient thermoplastic resin, resulting in less solid adhesion between the thermoplastic resin layers. On the other hand, they discovered that a larger, 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. A feature of the present invention is that the inventors discovered that by not changing the thickness of the central part of the separator, the resistance of the entire battery does not deteriorate significantly, which led to the idea for the present invention.

Based on the above, the inventors discovered that by increasing the thickness of the thermoplastic resin in the adhesive zone, sufficient adhesion of the thermoplastic resin was achieved for molding into a bag shape. Furthermore, by controlling the relative elemental concentration of non-metallic elements (sulfur S) present in the separator, such as non-metallic elements (S) derived from surfactants, the surfactant disperses the plasticizer to cover the entire thermoplastic resin, gradually creating 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 non-metallic elements (S) include (i) adjusting the amount added when mixing with the separator's main raw materials and/or (ii) adjusting the amount of coating when coating the surface of the molded separator. It is preferable to employ both control methods (i) and (ii). As a result, the separator obtained by this invention not only significantly improved 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, the thickness of the central portion is maintained, which makes it possible to prevent tearing at the adhesive joints on the side edges while obtaining good electrical resistance, thereby minimizing the impact on battery life caused by breakage of the separator adhesive joints in practical use.

(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 a non-metallic 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.

By ensuring that the relative element concentration of the nonmetallic element (S) is 0.01 atomic % or higher, the surfactant allows the plasticizer to be dispersed so as to cover the entire thermoplastic resin. As a result, the separator according to this embodiment has improved sealing properties at the adhesive layer. However, adding an excessive amount of nonmetallic element (S) can cause side reactions within the battery, so it is preferable that the relative element concentration of the nonmetallic element (S) is 0.5 atomic % or lower. It is preferable that the relative element concentration of the nonmetallic element (S) is 0.015 atomic % or higher and 0.45 atomic % or lower. It is more preferable that the relative element concentration of the nonmetallic element (S) is 0.02 atomic % or higher and 0.4 atomic % or lower. It is even more preferable that the relative element concentration of the nonmetallic element (S) is 0.025 atomic % or higher and 0.35 atomic % or lower. It is most preferable that the relative element concentration of the nonmetallic element (S) is 0.03 atomic % or higher and 0.3 atomic % or lower.

The porous base surface on which the relative element concentration of non-metallic elements (S) meets the above numerical range in X-ray photoelectron spectroscopy measurement is preferably the inner surface when the porous base is processed into a bag shape to house the electrodes, in order to achieve both workability of the bag-shaped separator and safety of the flooded lead-acid battery.

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 or more and 1.0× ^10-2 or less. It has been found that by ensuring that 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 or more, clumping of the filler or plasticizer is less likely to occur. On the other hand, since adding an excessive amount of nonmetallic element (S) may cause side reactions in the battery, it is preferable that the ratio (S)/(C) is 1.0× ^10-2 or less. It is preferable that the relative element concentration ratio (S)/(C) is 2.0× ^10-4 or more and 7.0× ^10-3 or less. It is more preferable that the relative element concentration ratio (S)/(C) is 3.0×10 ⁻⁴ or more and 5.0×10 ⁻³ or less.

In this embodiment, the porous base portion of the separator has side edges located at both ends in the width direction and a central portion sandwiched between the side edges. The side edges of the porous base portion are thicker than the central portion, improving the seal strength when the separator is formed into a bag, ensuring excellent processability.

The difference in thickness between the side end portion 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 portion 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 when sealing, so it is preferable that the difference in thickness be 0.15 mm or less. It is more preferable that the difference in thickness between the side end portion and the central portion be 0.07 mm or more and 0.13 mm or less. It is even more preferable that the difference in thickness between the side end portion and the central portion be 0.08 mm or more and 0.11 mm or less.

The side end portion preferably has an electrical resistance of 120 mΩ·cm ² or less, more preferably 110 mΩ·cm ² or less, in order to maintain the CCA value that evaluates the starting performance of a lead-acid battery.

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., which may be in the form of fiber), or a combination thereof. This results in a microporous film in which numerous interconnected pores are formed throughout the separator, with uniform, fine, and intricately intertwined pathways. From the perspective 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.

(Method for manufacturing a separator for a lead-acid battery)
An example of a specific method for producing the lead-acid battery separator according to this embodiment will be described below.
Raw materials consisting of predetermined amounts 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 through a pair of forming rolls, at least one of which has a predetermined groove, 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 a suitable solvent to extract and remove a predetermined amount of plasticizer, and then dried. Finally, the desired microporous film is obtained by coating with additives.

The polyolefin resin may be a homopolymer or copolymer of polyethylene, polypropylene, polybutene, polymethylpentene, 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 even more preferred. In some embodiments, one or more ultra-high molecular weight polyethylenes are used. Ultra-high molecular weight polyethylene (UHMWPE) has good miscibility with silica, and in microporous films, it maintains strength while bonding the skeleton of the silica powder as an adhesive functional material, and is chemically stable and highly safe.

Preferably, the method for obtaining the separator involves melting and 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 plasticizer have been added, and then forming a film, after which some or all of the plasticizer is removed. This results in a microporous film with countless interconnected pores that are uniform, fine, and have intricate, complex pathways throughout the separator.

The filler may be 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, or a combination thereof. Among these, silica is preferred, as it offers a wide range of powder properties, such as particle size and specific surface area, is readily available at low cost, and contains few impurities.

Mineral oil is preferred as the plasticizer because it is easily recyclable. Plasticizers are the component that is easiest to remove from a mixture of polymer, filler, and plasticizer, and therefore help impart porosity to the separator. Microporous film separators can contain zero plasticizer, but in separators for flooded lead-acid batteries, adding an appropriate amount of a plasticizer such as mineral oil can contribute to improved 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, it is more preferable that the plasticizer content be 20 wt. % or less.

The solvent used to extract and remove the plasticizer can be an organic chlorine compound or a saturated hydrocarbon organic solvent such as hexane, heptane, octane, nonane, or decane.

The raw material composition or the microporous film may contain or contain a surfactant (hydrophilizing agent), or, if necessary, additives such as antioxidants, lubricants, antibacterial agents, and colorants.

Such 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.

(Shape and dimensions of separator)
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 are 0.5 μm or less in diameter. 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.

Pore size is sometimes measured using the mercury intrusion method described in Ritter, H. L., and Drake, L. C., 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). While pore size is measured by the mercury intrusion method using the porosimeter, pore distribution may be determined by evaluation of raw data with MILESTONE 200 software.

The total thickness of the separator's central portion is preferably greater than 0.1 mm and less than or equal to 5.0 mm. The total thickness of the separator's central portion 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 thickness of the central portion includes not only the central base thickness but also the rib height, and is measured at the center where the central base thickness and rib height are greatest. In some cases, the separator can be approximately 0.8 mm or 1.1 mm thick.

The thickness of the central base of the separator is preferably about 0.05 mm to about 0.500 mm (e.g., about 0.20 mm in certain embodiments).

The thickness of the side end portion of the present invention can be determined in accordance with the design of the forming roll.

The separator's rib configuration may be provided on at least one surface, as needed, with continuous or discontinuous vertical or horizontal straight ribs, serrated ribs, dimpled ribs, protrusions, or combinations thereof. Preferably, the ribs are 0.008 mm to 1 mm high and spaced 0.001 mm to 20 mm apart. In some embodiments, the ribs are spaced 0 to 90 degrees apart from one another.

On the other hand, one method of increasing mechanical strength is to provide ribs (sometimes called back ribs or negative electrode ribs) on the negative electrode surface of the separator (e.g., the negative electrode contact surface or the negative electrode facing surface, etc.). However, in some embodiments, providing negative electrode ribs reduces the adhesive area between the thermoplastic resins, gradually reducing the peel strength. This can lead to tearing of the adhesive area after molding into a bag shape. The 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.

(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.

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

Positive electrode ribs may be provided on the separator housing the positive electrode plate, and in some embodiments, negative electrode ribs may be provided on the separator housing the negative electrode plate.

Next, examples of the present invention will be described in detail, along with comparative examples.

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. The extruded sheet was passed through a pair of forming rolls, one of which had a groove for a main rib for contacting the electrode plate, to obtain a film-like product in which a main rib of a predetermined shape was integrally formed on one side of the flat sheet. The film-like product was then immersed in trichloroethylene to extract and remove a predetermined amount of paraffinic mineral oil, dried, and coated with a surfactant solution and dried to obtain a microporous film with a base thickness of 0.20 mm at the center. This was used as the separator for a flooded lead-acid battery of Example 1.

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.

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.

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.

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.

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

(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.

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

(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 converting agent, polyethylene resin, and mineral oil were adjusted.

(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.

(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.

(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.

Next, various characteristics of the separators obtained above in Examples 1 to 6 and Comparative Examples 1 to 6 were evaluated using the following methods. The results are shown in Table 1.

<Peel strength>
The microporous film was cut into 80 mm x 150 mm 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, a 30 mm x 150 mm rectangular piece was cut in the MD and CMD directions to prepare a tensile test specimen.
Using an Instron tensile tester, the grip distance between the tester's grips was set to approximately 80 mm, and both longitudinal sides of the two-layered test piece were attached. The tensile test was performed at a pulling rate of 300 mm per minute, and the tensile load (b) and distance (c) at which the test piece broke were read. The peel strength was calculated by dividing the tensile load (b) by the cross-sectional area of the test piece.

The peel strength was evaluated based on whether the bag was shaped to prevent opening, with a ◎ being assigned for 17N or more, a ○ being assigned for 16N or more, and an × being assigned for less than 16N. A peel strength of 16N or more is expected to prevent bag breakage due to electrode deformation.

<X-ray photoelectron spectroscopy>
A small piece of 5 mm was cut out from the microporous film, and a 1 mm x 2 mm slot-type mask was placed over it to perform the measurement. The measurement conditions are shown below.
Machine: Thermo Fisher ESCALAB250
Excitation source: mono.AlK α 15kV × 10mA
Analysis size: Approximately 1 mm (circular shape)
Photoelectron take-off angle: 0° (perpendicular to the sample surface)

Claims (7)

a porous base portion;
a plurality of ribs provided on at least one surface of the porous base portion,
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;
and a central portion sandwiched between the side end portions, wherein the thickness of the side end portions 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. 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 or more and 1.0×10 ^or less;
The separator for a flooded lead-acid battery according to claim 1. 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. The side end has an electrical resistance of 120 mΩ ^cm2 or less.
The separator for a flooded lead-acid battery according to any one of claims 1 to 3. Contains any one or more of phenolic resin, polyvinyl chloride resin, rubber, cellulose, and cellulose derivatives,
The separator for a flooded lead-acid battery according to any one of claims 1 to 4. 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. A flooded lead-acid battery comprising the flooded lead-acid battery separator according to any one of claims 1 to 6.