lead-acid batteries

Abstract

SOLUTION: A lead acid battery comprises a positive electrode plate, a negative electrode plate, a separator interposed between the positive electrode plate and the negative electrode plate, and an electrolytic solution. Each of the positive electrode plate and the negative electrode plate includes a current collector and an electrode material. At least one of lower corners, which is a pair, of the positive electrode plate is chamfered. The separator includes a polyolefin. A thickness of a main part of the separator is 0.12 mm or more and less than 0.2 mm.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 positive and negative electrode plates, a separator interposed between them, and an electrolyte. Various performance characteristics are required of the components of a lead-acid battery.

[0003] Patent Document 1 proposes a lead-acid battery comprising plates, separators, and a battery case that houses the plates and separators, in which the plates and separators are alternately arranged in this order starting from the side closest to one inner wall surface of the battery case, the plate closest to the inner wall surface is exposed to the inner wall surface, and the separator has a base portion with a thickness of 0.25 mm or more.

[0004] Patent Document 2 proposes a lead-acid battery including positive and negative electrode plates in which expanded grids are used as positive and negative current collectors, the positive and negative current collectors being formed with positive and negative active materials, the expanded grid having an expanded expanded portion, a lug-forming cross rib portion consisting of a non-expanded portion formed on one end of the expanded portion in the expansion direction, and current collecting lugs formed on the cross rib portion, and the positive and negative current collectors being filled with positive and negative active materials, in which of the four corners of at least one of the positive and negative electrode plates, two corners located on the side opposite to the side on which the current collecting lug is provided are cut in a direction oblique to the longitudinal direction of the current collecting lug-forming cross rib portion, so that cut portions are formed in each of the two corners. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-133845 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-204639 Summary of the Invention [Problem to be solved by the invention]

[0006] Polyolefin-containing separators used in lead-acid batteries generally have a thickness of 0.2 mm or more at the main part. It is expected that the internal resistance can be reduced if a separator with a main part thickness of less than 0.2 mm can be used. However, if the main part thickness is less than 0.2 mm, oxidation degradation of the separator occurs due to contact with the positive electrode material, resulting in an internal short circuit, making it difficult to ensure excellent battery life.

[0007] On the other hand, when a current collector with a cut corner opposite the lug is used, as in Patent Document 2, gas generation during charging is unlikely because the cut corner does not contain electrode material. Because the gas does not sufficiently agitate the electrolyte, sulfate ions with a high specific gravity descend, resulting in significant stratification, which creates a difference in the specific gravity of the electrolyte (i.e., a difference in sulfuric acid concentration) between the upper and lower parts of the battery container. Significant stratification leads to deterioration of the positive electrode plate and reduced life performance. Stratification is particularly pronounced when lead-acid batteries are used in a partially charged state (PSOC). For example, in IS applications or charge-controlled applications such as idle start-stop (ISS) vehicles, lead-acid batteries are used in PSOC. Therefore, using a current collector with a cut corner significantly reduces life performance when used in PSOC (also known as IS life performance). [Means for solving the problem]

[0008] One aspect of the present invention is a lead-acid battery, The lead-acid battery includes a positive electrode plate, a negative electrode plate, a separator interposed between the positive electrode plate and the negative electrode plate, and an electrolyte; Each of the positive electrode plate and the negative electrode plate includes a current collector and an electrode material, At least one of a pair of lower corners of the positive electrode plate is chamfered, the separator comprises a polyolefin; The lead-acid battery is characterized in that the thickness of the main part of the separator is 0.12 mm or more and less than 0.2 mm. [Effects of the Invention]

[0009] In lead-acid batteries, excellent IS life performance can be ensured. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a plan view showing the appearance of an electrode plate used in a lead-acid battery according to an embodiment of the present invention. FIG. [Figure 2] 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

[0011] During discharge, lead-acid batteries produce lead sulfate on both the positive and negative plates, and water on the positive plate. During charging, metallic lead, lead dioxide, and sulfuric acid are produced from the lead sulfate and water. Because sulfate ions have a high specific gravity, they tend to sink to the bottom of the battery case. When electrolyte convection is difficult, a difference in sulfuric acid concentration occurs between the top and bottom of the battery case, resulting in stratification. In lead-acid batteries for general start-up use, gas is generated when the battery is overcharged or charged to a nearly fully charged state. The agitation effect of this gas causes electrolyte convection, suppressing stratification. In contrast, when lead-acid batteries are used in PSOC, gas generation during charging is low, resulting in insufficient agitation, which can lead to electrolyte stratification.

[0012] If a lead-acid battery is used in a stratified state, the low specific gravity of the electrolyte in the upper part of the battery case reduces charge / discharge efficiency and shortens its service life. Furthermore, the accumulation of lead sulfate in the negative plate becomes more pronounced in the lower part of the battery case, where the specific gravity of the electrolyte is higher, facilitating sulfation, which deactivates the lead sulfate. This causes charge / discharge reactions to concentrate at the top of the plate, facilitating the softening and deterioration of the positive electrode material. This can lead to the positive electrode material falling off the positive plate and eventually shortening the battery's service life. For example, if the fallen positive electrode material adheres to the negative plate while floating in the electrolyte and accumulates, it can cause a short circuit (known as a moss short circuit). If the fallen positive electrode material adheres to the positive plate and separator while floating in the electrolyte and accumulates, the separator's oxidation and deterioration progresses, leading to cracks or tears in the separator and potentially a short circuit. In addition, lead sulfate dissolves easily in the electrolyte at the top of the battery container, where the specific gravity of the electrolyte is low, and the lead ions produced by the dissolution are reduced on the negative electrode plate, causing lead crystals to precipitate in the form of dendrites that can penetrate the separator and cause a permeation short circuit, ultimately resulting in the end of the battery's life. In this way, the progression of stratification is likely to be a factor that determines the IS life performance of lead-acid batteries.

[0013] When using plates with chamfered bottom corners, the amount of gas generated during charging is small because there is no electrode material in the areas removed by the chamfering. Therefore, when a lead-acid battery with such plates is used in PSOC, electrolyte stratification becomes significant. When stratification becomes significant, the IS life performance decreases as described above.

[0014] On the other hand, separators containing polyolefins deteriorate due to oxidation of the polyolefins when in contact with the positive electrode material for a long period of time. In lead-acid batteries, oxidative degradation of the separator reduces the separator's flexibility, making it prone to cracking or tearing. Separators containing polyolefins with a thickness of less than 0.2 mm at the main part are even more prone to cracking or tearing, causing internal short circuits and shortening the life of the lead-acid battery. Even with such separators, it is difficult to ensure excellent life performance, so they are rarely used in conventional lead-acid batteries.

[0015] However, it has been discovered that in lead-acid batteries, when a separator containing polyolefin with a thickness of 0.12 mm or more but less than 0.2 mm at its main part is combined with a positive electrode plate with chamfered lower corners, the IS life performance is unexpectedly improved.

[0016] In view of this finding, a lead-acid battery according to one aspect of the present invention includes a positive electrode plate, a negative electrode plate, a separator interposed between the positive electrode plate and the negative electrode plate, and an electrolyte. Each of the positive electrode plate and the negative electrode plate includes a current collector and an electrode material. At least one of a pair of corners on the lower portion of at least the positive electrode plate is chamfered. The separator includes polyolefin. The thickness of a main portion of the separator is 0.12 mm or more and less than 0.2 mm.

[0017] A space is formed at the bottom of a lead-acid battery container in the area removed by the chamfering of the lower corner of the positive electrode plate. When a lead-acid battery is used in PSOC, even if positive electrode material falls off, the fallen positive electrode material collects in this space formed at the bottom of the container. Because charge / discharge reactions hardly occur in this space and the amount of gas generated is small, floating of the collected positive electrode material is reduced. This reduces the accumulation of the fallen positive electrode material on the electrode plate. Therefore, even when using a separator containing polyolefin with a thickness of 0.12 mm or more but less than 0.2 mm, Moss short circuits and short circuits due to oxidative degradation of the separator are suppressed. Separators with such small thicknesses have low resistance, which facilitates charge / discharge reactions and promotes gas generation even when used in PSOC. Therefore, even when using a positive electrode plate with chamfered lower corners, electrolyte convection can be achieved, suppressing stratification, thereby improving IS life performance.

[0018] Furthermore, even when the separator described above is used in combination with a positive electrode plate whose bottom corners are not chamfered, the IS life performance is reduced. This is thought to be due to the inability to suppress MOS short circuits or short circuits due to oxidative degradation of the separator. In other words, the effect of using the separator described above can only be obtained when combined with a positive electrode plate whose bottom corners are chamfered.

[0019] From the viewpoint of obtaining higher IS life performance, the thickness of the main part of the separator is preferably 0.18 mm or less, and from the same viewpoint, the thickness of the main part of the separator is preferably 0.125 mm or more.

[0020] Of the positive and negative electrode plates, at least one of a pair of corners at the lower part of the positive electrode plate may be chamfered. Furthermore, at least one of a pair of corners at the lower part of the negative electrode plate may be chamfered. It is particularly preferable that at least one of a pair of corners at the lower part of the positive electrode plate is chamfered, and that the pair of corners at the lower part of the negative electrode plate are not chamfered. By not chamfering both of the pair of corners at the lower part of the negative electrode plate in a lead-acid battery, the negative electrode plate has a portion at the lower corner that does not face the positive electrode plate (hereinafter referred to as the non-facing portion). This non-facing portion is unlikely to contribute to charge / discharge reactions, and reactions that generate hydrogen gas upon application of voltage are likely to occur. Therefore, by providing a non-facing portion on the negative electrode plate, hydrogen gas is generated, albeit in a small amount, even during PSOC, facilitating convection of the electrolyte. This further enhances the effect of suppressing stratification and further improves IS life performance. The amount of hydrogen gas generated at the non-facing portion is relatively small. Therefore, the positive electrode material falling off and contained in the space formed in the lower corner of the positive electrode plate where the positive electrode plate is missing is not sufficiently levitated. Therefore, even if the effect of convection of the electrolyte is slightly improved, the occurrence of a Moss short circuit can be suppressed.

[0021] The current collector of the positive electrode plate is preferably an expanded grid. During the manufacturing process of the positive electrode plate, the corners may be deformed due to interference with the manufacturing equipment. The expanded grid used for the positive electrode plate has a thick grid frame, so once the corners of the positive electrode plate using the expanded grid are deformed, they are difficult to return to their original shape. Therefore, when a lead-acid battery is manufactured using such a positive electrode plate, the corners of the positive electrode plate are likely to break through the separator in the early stages, causing a short circuit. Therefore, in the case of a positive electrode plate using an expanded grid, chamfering the corners of the positive electrode plate is advantageous because it can suppress the initial short circuit caused by deformation of the corners of the positive electrode plate.

[0022] The polyolefin contained in the separator preferably contains at least ethylene units. Polyolefins containing ethylene units as monomer units are prone to oxidative degradation. However, even when using a separator containing such a polyolefin prone to oxidative degradation and having a small thickness as described above, by combining it with a positive electrode plate with chamfered lower corners, oxidative degradation of the separator can be suppressed, ensuring excellent IS life performance.

[0023] The separator is preferably bag-shaped and accommodates the negative electrode plate, which can prevent the positive electrode plate and the negative electrode plate from shorting out through the positive electrode material that has settled near the corners of the positive electrode plate.

[0024] The total pore volume of the separator is 1.1 cm 3 / g or more 1.9cm 3 In this case, oxidation degradation of the separator is further suppressed, the diffusibility of the electrolyte is further increased, and the separator has a lower resistance, so that the IS life performance can be further improved.

[0025] The separator preferably contains oil, which further enhances the effect of suppressing oxidation degradation of the separator, thereby ensuring a higher IS life performance.

[0026] The oil content in the separator is preferably 12% by mass or more and 18% by mass or less. When the oil content is in this range, the effect of suppressing oxidative degradation is further enhanced, and the resistance of the separator can be further reduced, thereby ensuring a longer IS life.

[0027] The lead-acid battery may be a valve-regulated lead-acid battery (VRLA battery), but a flooded battery (vented battery) is preferred. In flooded batteries, stratification and the accumulation of shed positive electrode material on the electrode plate tend to become more pronounced. In such flooded batteries, combining a thin polyolefin-containing separator with a chamfered corner as described above significantly suppresses stratification and MOS short circuits.

[0028] (Terminology explanation) (Top and bottom directions of lead-acid batteries or components of lead-acid batteries) 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 the lead-acid battery is in use. The upper part of a lead-acid battery refers to the part above half of the height of the lead-acid battery when the lead-acid battery is in use. The lower part of a lead-acid battery refers to the part other than the upper part of the lead-acid battery. The upper part of each component of a lead-acid battery refers to the part above half of the height of each component when the lead-acid battery is in use. The lower part of each component refers to the part other than the upper part of each component. Each positive and negative electrode plate has a lug for connecting to an external terminal, and in a flooded battery, the lug is provided on the top of the electrode plate so as to protrude upward. The height of each electrode plate refers to the height of the part where the electrode material is present.

[0029] (Corner of the electrode plate) A typical electrode plate, when viewed from the front, has a substantially rectangular shape excluding the lugs and has four corners, including edges. When a lead-acid battery is in use, the four corners of the electrode plate are composed of a pair of corners located at the top and a pair of corners located at the bottom. In this specification, the corners of the electrode plate (or the parts corresponding to the corners if corners are missing) and the entire area surrounding them are referred to as corners. In each of the positive and negative electrode plates of the lead-acid battery according to the above aspects of the present invention, the chamfered corner is at least one of the pair of corners located at the bottom of the electrode plate. Note that the state in which the electrode plate is viewed from the front refers to the state in which each of the pair of main surfaces that occupy the majority of the surface of the electrode plate is viewed perpendicularly. Note that the main surfaces of the electrode plate refer to each of the pair of surfaces that occupy the majority of the surface of the electrode plate (i.e., the pair of surfaces excluding the end faces).

[0030] (Chamfering) In the lead-acid battery according to the above aspect of the present invention, at least one of a pair of lower corners of at least the positive electrode plate (and, if necessary, the negative electrode plate) is chamfered. A chamfered corner means that the corner and its surrounding area that would normally be present on the electrode plate are missing. In other words, the chamfered corner has a missing portion (hereinafter, sometimes referred to as a missing portion) in the electrode plate (more specifically, the corner and its surrounding area of ​​the electrode plate). This missing portion forms a space at the bottom of the battery case.

[0031] More specifically, a state in which each corner of the lower part is chamfered means that, when the areas of the missing parts at each corner of the lower part when viewed from the front of the electrode plate are S1 and S2, the proportion r (= S1 / (A+S) × 100(%) or S2 / (A+S) × 100(%)) of area S1 or S2 to the sum of area A of the electrode plate and total area S (= S1+S2) of the missing parts at the lower part is 0.1% or more. For one corner of the lower part, a state in which the corner is not chamfered includes a case in which proportion r is less than 0.1%.

[0032] The area A of the electrode plate is the projected area of ​​the portion of the electrode plate where the electrode material is present, projected in a direction perpendicular to one of the main surfaces of the electrode plate. The areas S1 and S2 of the missing portions at each corner of the lower part of the electrode plate are the area of ​​the missing portion of the electrode plate at each corner when compared to a rectangle (hereinafter also referred to as rectangle A) formed by two lines extending from the top and bottom edges of the portion where the electrode material is present in the respective directions (i.e., horizontally (also referred to as the first direction)) and two lines extending from the edges on both sides of the portion where the electrode material is present in the respective directions (i.e., vertically (also referred to as the second direction)). If there are areas where no electrode material is present near the top, bottom, or side edges of the portion where the electrode material is present, these areas where no electrode material is present are ignored when determining the bottom, top, and side edges.

[0033] The term "chamfered corners" does not necessarily mean that a process of removing the corners and their surrounding areas of the electrode plate is performed; rather, an electrode plate may be formed in a state where the corners and their surrounding areas are missing without removing the corners and their surrounding areas. When the corners are chamfered, the corners may have a surface formed by removing the corners and their surrounding areas, but this does not necessarily mean that a surface is formed. Examples of chamfered corners include a state where the corners and their surrounding areas are rounded, and a state where the corners and their surrounding areas are removed at an angle. The chamfering may be, for example, a C-chamfer or an R-chamfer.

[0034] (electrode material) In each of the positive and negative electrode plates, the electrode material is usually held by a current collector. The electrode material is the electrode plate excluding the current collector. A member such as a mat or pasting paper may be attached to the electrode plate. Such a member (also called an attachment member) is used integrally with the electrode plate and is therefore considered to be included in the electrode plate. When the electrode plate includes an attachment member, the electrode material is the electrode material excluding the current collector and the attachment member. In this specification, the electrode material of the positive electrode plate may be referred to as the positive electrode material, and the electrode material of the negative electrode plate may be referred to as the negative electrode material.

[0035] (Main part of the separator) When the separator is interposed between a positive electrode plate and a negative electrode plate, the main part of the separator refers to a portion of the separator that faces both the region of the positive electrode plate where the electrode material is disposed and the region of the negative electrode plate where the electrode material is disposed. In an electrode plate assembly including a positive electrode plate and a negative electrode plate, in a separator that faces only each electrode plate located at the end of the electrode plate assembly, the main part refers to a portion of the main surface of each electrode plate that faces the region of the electrode material disposed.

[0036] (Thickness of main part of separator) The thickness of the separator's main part means the average thickness of the main part. If the separator has a base portion and ribs erected from at least one surface of the base portion in the main part, the thickness of the separator's main part means the average thickness of the base portion. The base portion of the separator refers to the separator's constituent parts excluding protrusions such as ribs, and is the sheet-like portion that defines the separator's outer shape. If an attachment member (such as a mat or pasting paper) is attached to the separator, the thickness of the attachment member is not included in the separator's thickness.

[0037] (Polyolefin) Polyolefins are polymers containing at least olefin units (i.e., polymers containing at least monomer units derived from olefins). 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 and copolymerizable with an olefin.

[0038] (total pore volume of separator) The total pore volume of the separator is the sum of the volumes of all the pores in the separator determined by mercury intrusion porosimetry.

[0039] (oil) Oil refers to a hydrophobic substance that is liquid at room temperature (a temperature between 20°C and 35°C) and separates from water. Oil includes naturally occurring oils, mineral oils, and synthetic oils.

[0040] (fully charged) In this specification, the fully charged state of a lead-acid battery is defined by JIS D 5301:2019. More specifically, the fully charged state is defined as a state in which a lead-acid battery is charged in a water tank at 25°C ± 2°C at a current (A) that is 1 / 10 of the value listed as the rated capacity (Ah) until the terminal voltage during charging or the electrolyte density converted to a temperature of 20°C, measured every 15 minutes, shows a constant value to three significant digits three times in a row. Charging is performed with the electrolyte in the lead-acid battery filled to a specified liquid level. The value listed as the rated capacity is in Ah. The unit of current set based on the value listed as the rated capacity is A.

[0041] A fully charged lead-acid battery refers to a lead-acid battery that has already been chemically formed and is fully charged. A lead-acid battery may be fully charged immediately after chemical formation, or after a certain period of time has passed since chemical formation (for example, a lead-acid battery that has been chemically formed and is currently in use (preferably in the early stages of use) may be fully charged).

[0042] In this specification, a battery in its early stages of use refers to a battery that has not been in use for a long time and has not deteriorated much.

[0043] 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.

[0044] (separator) The thickness of the separator's main portion is 0.12 mm or more. From the viewpoint of ensuring higher IS life performance by further enhancing the effect of suppressing short circuits due to oxidative degradation, the thickness of the main portion is preferably 0.125 mm or more. From the viewpoint of improving the effect of suppressing early short circuits, the thickness of the main portion may be 0.14 mm or more or 0.15 mm or more. The thickness of the main portion is less than 0.2 mm. From the viewpoint of ensuring higher IS life performance by further enhancing the effect of promoting gas generation, the thickness of the main portion is preferably 0.18 mm or less, more preferably 0.175 mm or less, and may be 0.16 mm or less or 0.15 mm or less.

[0045] The thickness of a main portion of the separator may be 0.12 mm or more and less than 0.2 mm (or 0.18 mm or less), 0.125 mm or more and less than 0.2 mm (or 0.18 mm or less), 0.14 mm or more and less than 0.2 mm (or 0.18 mm or less), 0.15 mm or more and less than 0.2 mm (or 0.18 mm or less), 0.12 mm or more and less than 0.175 mm (or 0.16 mm or less), 0.125 mm or more and less than 0.175 mm (or 0.16 mm or less), 0.14 mm or more and less than 0.175 mm (or 0.16 mm or less), 0.15 mm or more and less than 0.175 mm (or 0.16 mm or less), 0.12 mm or more (or 0.125 mm or more) and 0.15 mm or less, or 0.14 mm or more and less than 0.15 mm.

[0046] The separator may be in the form of a sheet. Alternatively, a sheet folded in an accordion shape may be used as the separator. The separator may be formed in a bag shape, and either the positive electrode plate or the negative electrode plate may be wrapped in the bag-shaped separator. From the viewpoint of easily preventing a short circuit between the positive electrode plate and the negative electrode plate via the settled positive electrode material, it is preferable to house the negative electrode plate in a bag-shaped separator.

[0047] The separator may have ribs or may not have ribs. A separator with ribs, for example, has a base portion and ribs extending from the surface of the base portion. Ribs may be provided on only one surface of the separator or each base portion, or on both surfaces.

[0048] When the separator 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).

[0049] The height of the ribs provided in the region of the separator facing the positive electrode plate may be 0.4 mm or more, or 1.2 mm or less.

[0050] The total pore volume of the separator is, for example, 0.8 cm 3 / g or more, and 0.9cm 3 / g or more or 1.0cm 3 / g or more. From the viewpoint of further increasing the diffusibility of the electrolyte and further reducing the resistance of the separator to ensure a higher IS life performance, the total pore volume of the separator is 1.1 cm 3 The total pore volume of the separator is preferably 2.2 cm 3 / g or less, and 2.0 cm 3 / g or less. From the viewpoint of ensuring a higher IS life performance by enhancing the effect of suppressing oxidation degradation of the separator, the total pore volume of the separator should be 1.9 cm 3 / g or less is preferred.

[0051] The total pore volume of the separator is 0.8 cm 3 / g or more (or 0.9cm 3 / g or more)2.2cm 3 / g or less, 1.0cm 3 / g or more (or 1.1cm 3 / g or more)2.2cm 3 / g or less, 0.8cm 3 / g or more (or 0.9cm 3 / g or more)2.0cm 3 / g or less, 1.0cm 3 / g or more (or 1.1cm 3 / g or more)2.0cm 3 / g or less, 0.8cm 3 / g or more (or 0.9cm 3 / g or more) 1.9cm 3 / g or less, or 1.0cm 3 / g or more (or 1.1cm 3 / g or more) 1.9cm 3 / g or less.

[0052] The separator can be obtained, for example, by extruding a resin composition containing a polymer material (hereinafter also referred to as a base polymer), a pore-forming agent, and a penetrating agent (surfactant) into a sheet, and then removing the pore-forming agent. By removing at least a portion of the pore-forming agent, micropores are formed in the base polymer matrix. The resin composition may further contain inorganic particles. The sheet-shaped separator may be folded into an accordion shape or processed into a bag shape, as necessary.

[0053] In a separator having ribs, the ribs may be formed on the sheet when the resin composition is extrusion-molded, or may be formed by pressing the sheet with a roller having grooves corresponding to each rib after molding the resin composition into a sheet or after removing the pore-forming agent.

[0054] At least a polyolefin is used as the base polymer contained in the separator. As the base polymer, a polyolefin may be used in combination with another base polymer. The other base polymer is not particularly limited as long as it is one that is used in separators for lead-acid batteries. The ratio of polyolefin to the entire base polymer contained in the separator is, for example, 50% by mass or more, or may be 80% by mass or more, or may be 90% by mass or more. The ratio of polyolefin is, for example, 100% by mass or less. The base polymer may be composed of polyolefin alone.

[0055] 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 2-3Copolymers 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.

[0056] 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.

[0057] The content of inorganic particles in the separator is, for example, 40% by mass or more, or may be 50% by mass or more, and may be, for example, 80% by mass or less, 75% by mass or less, or 70% by mass or less.

[0058] The content of inorganic particles in the separator may be 40% by mass or more (or 50% by mass or more) and 80% by mass or less, 40% by mass or more (or 50% by mass or more) and 75% by mass or less, or 40% by mass or more (or 50% by mass or more) and 70% by mass or less.

[0059] Examples of the pore-forming agent include liquid pore-forming agents and solid pore-forming agents. From the viewpoint of further enhancing the effect of suppressing oxidative degradation of the separator and ensuring higher IS life performance, it is preferable to use at least oil as the pore-forming agent. 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.

[0060] The liquid pore-forming agent is preferably a mineral oil, a synthetic oil, etc. Examples of the liquid pore-forming agent include paraffin oil and silicone oil. Examples of the solid pore-forming agent include polymer powder.

[0061] The amount of pore-forming agent in the separator may vary depending on the type, so it is difficult to generalize, but it is, for example, 30 parts by mass or more per 100 parts by mass of the base polymer, and the amount of pore-forming agent is, for example, 60 parts by mass or less.

[0062] The oil content in the separator is, for example, 5% by mass or more. From the viewpoint of further enhancing the effect of suppressing oxidation degradation of the separator, the oil content in the separator is preferably 10% by mass or more, more preferably 12% by mass or more. The oil content in the separator is, for example, 20% by mass or less, preferably 18% by mass or less. In this case, it is easy to further reduce the resistance of the separator.

[0063] The oil content in the separator may be 5% by mass or more and 20% by mass or less (or 18% by mass or less), 10% by mass or more and 20% by mass or less (or 18% by mass or less), or 12% by mass or more and 20% by mass or less (or 18% by mass or less).

[0064] 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.

[0065] The amount of the penetrant in the separator is, for example, 0.1 parts by mass or more, and may be 0.5 parts by mass or more, per 100 parts by mass of the base polymer, and may be, for example, 10 parts by mass or less, and may be 5 parts by mass or less.

[0066] The amount of the penetrant in the separator may be 0.1 parts by mass or more (or 0.5 parts by mass or more) to 10 parts by mass or less, or 0.1 parts by mass or more (0.5 parts by mass or more) to 5 parts by mass or less, per 100 parts by mass of the base polymer.

[0067] The content of the penetrant in the separator is, for example, 0.01% by mass or more, and may be 0.1% by mass or more, and for example, 5% by mass or less, and may be 10% by mass or less.

[0068] The content of the penetrant in the separator may be 0.01% by mass or more (0.1 parts by mass or more) and 10% by mass or less, or 0.01% by mass or more (0.1 parts by mass or more) and 5% by mass or less.

[0069] (Separator analysis or size measurement) For separator analysis or size measurement, a separator taken from a lead-acid battery in its early stages of use is used.

[0070] The separator removed from the lead acid battery is washed and dried prior to analysis or measurement.

[0071] The separator removed from the lead-acid battery is washed and dried using the following procedure. The separator is immersed in pure water for one hour to remove the sulfuric acid from the separator. The separator is then removed from the liquid and left to dry for at least 16 hours in an environment of 25°C ± 5°C. When removing the separator from the lead-acid battery, it is removed from a fully charged lead-acid battery.

[0072] (Separator thickness and rib height) The thickness of the main part of the separator is determined by measuring the thickness at five arbitrarily selected points in a cross-sectional photograph of the separator and averaging the thicknesses.

[0073] 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 separator.

[0074] (total pore volume) First, a sample (hereinafter referred to as Sample A) is prepared by cutting the main part of the separator into a strip of 20 mm x 5 mm. For separators with ribs, Sample A is prepared by cutting the base part into a strip of 20 mm x 5 mm so as not to include the ribs.

[0075] The total pore volume of the separator is measured using sample A with a mercury porosimeter (Shimadzu Corporation, Autopore IV9510). The measurement pressure range is 4 psia (≒ 27.6 kPa) to 60,000 psia (≒ 414 MPa). The pore distribution uses a pore diameter range of 0.01 μm to 50 μm. The total pore volume is determined for 10 samples A, and the average value is calculated. The obtained average value is the total pore volume of the separator.

[0076] (oil content in separator) A sample (hereinafter referred to as Sample B) is prepared by cutting the main part of the separator into a strip shape. For separators with ribs, Sample B is prepared by cutting the base part into a strip shape so as not to include the ribs in the main part of the separator.

[0077] Approximately 0.5 g of sample B is taken and accurately weighed to determine the initial sample mass (m0). The weighed sample B is placed in an appropriately sized glass beaker and 50 mL of n-hexane is added. Next, ultrasonic waves are applied to the sample, including the beaker, for approximately 30 minutes to dissolve the oil contained in sample B into the 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 B is determined and the average value is calculated. The obtained average value is taken as the oil content in the separator. Oil content (mass%) = (m0 - m1) / m0 x 100

[0078] (Inorganic particle content in separator) A portion of Sample B 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, 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 B was calculated, and this was taken as the inorganic particle content (mass%). The inorganic particle content of 10 Samples B was determined, and the average value was calculated. The resulting average value was taken as the inorganic particle content in the separator.

[0079] (Content of penetrant in separator) A portion of Sample B 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 B was calculated, giving the penetrant content (mass%). A TA Instruments Q5000IR thermogravimetric analyzer was used. The penetrant content of 10 Sample Bs was determined and the average value was calculated. The average value obtained was taken as the penetrant content in the separator.

[0080] (positive electrode plate) The positive electrode plate is a paste-type positive electrode plate, which includes a positive electrode current collector and a positive electrode material. The positive electrode material is held by the positive electrode current collector.

[0081] 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. Examples of processing methods include expanding and punching. A grid-shaped current collector is preferred as the positive electrode current collector because it facilitates the support of the positive electrode material. When using a positive electrode current collector obtained by expanding (i.e., an expanded grid), deformation of the corners can easily cause short circuits in lead-acid batteries at the initial stage. However, by chamfering the lower corners of the positive electrode plate, it is possible to suppress initial short circuits while ensuring excellent IS life performance, even when using such an expanded grid.

[0082] The lead alloy used for the positive electrode current collector is preferably a Pb-Ca alloy or a Pb-Ca-Sn alloy in terms of corrosion resistance and mechanical strength. The positive electrode current collector may have lead alloy layers with different compositions, and the alloy layer may be a single layer or multiple layers.

[0083] At least one of a pair of corners at the bottom of the positive electrode plate is chamfered. As a result, a portion where the positive electrode plate is missing (missing portion) is formed at the corner. It is sufficient that at least one of the pair of corners at the bottom of the positive electrode plate is chamfered, and both may be chamfered.

[0084] When the positive electrode plate is viewed from the front, the ratio R1 of the total area S (= S1 + S2) of the missing portions at the lower corners to the sum of the area A of the positive electrode plate and the total area S of the missing portions is, for example, 0.1% or more or 0.5% or more. From the viewpoint of easily ensuring sufficient space to accommodate fallen positive electrode material even during repeated charge and discharge over a long period of time, the ratio R1 is preferably 1% or more, more preferably 2% or more. From the viewpoint of ensuring higher capacity, the ratio R1 of the missing portions is preferably 6% or less, more preferably 4% or less.

[0085] The proportion R1 of the missing portion may be 0.1% or more and 6% or less (or 4% or less), 0.5% or more and 6% or less (or 4% or less), 1% or more and 6% or less (or 4% or less), or 2% or more and 6% or less (or 4% or less).

[0086] The area A can be determined by binarizing the area where the electrode material is present and the other areas in a photograph of one of the main surfaces of the electrode plate, and calculating the area of ​​the area where the electrode material is present.

[0087] The areas S1 and S2 of the missing portions at the lower corners are determined by the following procedure, with reference to Fig. 1 (described later). In the example of Fig. 1, the missing portions are formed at both corners of the lower part of the electrode plate, and are indicated by X1 and X2. The electrode plate, excluding the lug portions, has a substantially rectangular (rectangular or square) shape when viewed from the front. The outline of the projected shape of the electrode plate has a straight line portion L1 extending parallel to a first direction (horizontal direction) that is the extension direction of the bottom side of the electrode plate, and a straight line portion L2 extending parallel to a second direction (vertical direction) that intersects with the first direction, and the straight line portions L1 and L2 are connected via a connecting portion C. The shape of the connecting portion C is not particularly limited, but may be, for example, at least one selected from the group consisting of a curve and a straight line inclined from the first direction and the second direction.

[0088] Consider an extension line E1, which is an extension of the straight line portion L1 toward the L2 side, and an extension line E2, which is an extension of the straight line portion L2 toward the L1 side. The areas of the missing portions S1 and S2 can be calculated by calculating the area of ​​the region surrounded by the extension line E1, the extension line E2, and the connecting portion C.

[0089] The ratio R1 of the total area S (=S1+S2) of the missing parts is calculated by the following formula (1). R1=S / (A+S) (1) The sum (=A+S) of the area A of the electrode plate and the total area S of the missing parts is the area of ​​the rectangle A mentioned above. The area of ​​rectangle A is the product of its height H and width W.

[0090] The total area S of the missing part at the bottom of the positive electrode plate is, for example, 1 cm 2 More than 2cm 2 The total area S may be, for example, 7 cm 2Less than or equal to 4.5cm 2 It may be the following:

[0091] The total area S is 1 cm 2 or more (or 2cm 2 over)7cm 2 Less than or equal to 1cm 2 or more (or 2cm 2 (more than)4.5cm 2 It may be the following:

[0092] When both of a pair of corners at the bottom of the positive electrode plate are chamfered, the areas S1 and S2 of the cutouts formed at each corner may be the same or different. Furthermore, the shapes of the cutouts formed at each corner when viewed from the front of the electrode plate may be the same or different.

[0093] A positive electrode plate with chamfered lower corners may be produced by fabricating an unformed or formed positive electrode plate and then removing the lower corners. Alternatively, a positive electrode plate with chamfered lower corners may be produced using a positive electrode current collector in which at least one of a pair of corners is chamfered at a portion of the positive electrode current collector corresponding to the lower part of the positive electrode plate. A positive electrode current collector with chamfered corners may be formed by chamfering the corners and their surrounding areas of a positive electrode current collector fabricated with corners at each corner. Alternatively, chamfered corners may be formed when the positive electrode current collector is fabricated. For example, when forming a positive electrode current collector by punching, the corners are punched into a shape with chamfered corners. When forming a positive electrode current collector by casting, a positive electrode current collector with chamfered corners is formed by casting using a mold with chamfered corners.

[0094] The positive electrode material contained in the positive electrode plate includes a positive electrode active material (lead dioxide or lead sulfate) that generates capacity through an oxidation-reduction reaction. The positive electrode material may also include other additives (such as reinforcing materials) as needed.

[0095] Examples of reinforcing additives include fibers (inorganic fibers, organic fibers, etc.). Examples of resins (or polymers) that constitute organic fibers include at least one selected from the group consisting of acrylic resins, polyolefin resins (polypropylene resins, polyethylene resins, etc.), polyester resins (including polyalkylene arylates (polyethylene terephthalate, etc.)), and celluloses (cellulose, cellulose derivatives (cellulose ether, cellulose ester, etc.)). Celluloses also include rayon.

[0096] The amount of the reinforcing material in the positive electrode material is, for example, 0.03 mass % or more, and the amount of the reinforcing material in the positive electrode material is, for example, 0.5 mass % or less.

[0097] The amount of reinforcing material in the positive electrode material can be determined by the following procedure: Analysis of the reinforcing material is carried out using positive electrode material sampled from a positive electrode plate removed from a fully charged lead-acid battery.

[0098] Positive electrode material is recovered from the positive electrode plate using the following procedure. First, a fully charged lead-acid battery is disassembled, and the obtained positive electrode plate is washed with water for 3 to 4 hours to remove the electrolyte from the positive electrode plate. The washed positive electrode plate is then dried in a thermostatic chamber at 60°C ± 5°C for at least 5 hours. After drying, if the positive electrode plate contains an adhesive material, the adhesive material is removed from the positive electrode plate by peeling. Positive electrode material for analysis (hereinafter referred to as sample C) is obtained by collecting the positive electrode material from near the center of the top, bottom, and left and right sides when viewed from the front. Sample C is crushed as necessary and used for analysis.

[0099] The crushed sample C is collected and accurately weighed. Next, sample C is added to a mixed solution of aqueous nitric acid (concentration: 25% by mass) and aqueous tartaric acid (concentration: 500 g / L) (mixing ratio (volume ratio) of aqueous nitric acid to aqueous tartaric acid = 7:2), and the soluble components are dissolved while stirring under heat. The resulting mixture is filtered using a membrane filter (average pore size: 0.45 μm or less). This leaves the reinforcing material contained in the positive electrode material as a solid on the filter paper. The resulting solid is washed with water and dried. The mass of the dried material is measured. The ratio (percentage) of the mass of the dried material to the mass of sample C is calculated. This ratio corresponds to the amount of reinforcing material in the positive electrode material.

[0100] Unformed paste-type positive electrode plates are obtained by filling a positive electrode current collector with a positive electrode paste, aging it, and drying it. The positive electrode paste is prepared by adding water and sulfuric acid to lead powder, an antimony compound, and optionally other additives (such as reinforcing materials), and kneading them.

[0101] A positive electrode plate can be obtained by chemically forming an unformed positive electrode plate. Chemical formation can 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 then charging the electrode plate assembly. However, chemical formation may also be performed before assembling the lead-acid battery or the electrode plate assembly.

[0102] (negative plate) The negative electrode plate of a lead-acid battery is composed of a negative electrode current collector and a negative electrode material. The negative electrode current collector can be formed in the same manner as the positive electrode current collector.

[0103] The lead alloy used in the negative electrode current collector may be any of a Pb-Sb alloy, a Pb-Ca alloy, and a Pb-Ca-Sn alloy. These lead or lead alloys may further contain at least one additive element selected from the group consisting of Ba, Ag, Al, Bi, As, Se, and Cu. The negative electrode current collector may have lead alloy layers with different compositions, and the alloy layer may be a single layer or multiple layers.

[0104] At least one of a pair of corners at the bottom of the negative electrode plate may be chamfered. When the corners are chamfered, a portion where the negative electrode plate is missing (missing portion) is formed at the corner. Both corners at the bottom of the negative electrode plate do not have to be chamfered.

[0105] When the corners of a negative electrode plate are chamfered, the ratio R1 of the total area S of the lower corners of the negative electrode plate, calculated in accordance with the case of a positive electrode plate, to the sum of the area A of the negative electrode plate and the total area S of the missing portion, may be selected from the range described for the positive electrode.

[0106] When both of the pair of corners at the bottom of the negative electrode plate are chamfered, the areas S1 and S2 of the cutouts formed at each corner may be the same or different. In addition, the shapes of the cutouts formed at each corner when viewed from the front of the electrode plate may be the same or different.

[0107] The areas S1 of the opposing cutout portions of the opposing positive and negative electrode plates may be the same or different. The areas S2 of the opposing cutout portions may be the same or different. The shapes of the opposing cutout portions may be the same or different.

[0108] If the negative electrode plate has no missing portion at the lower corner or if the area of ​​the missing portion is smaller than the area of ​​the missing portion at the corner of the opposing positive electrode plate, a non-facing portion is formed that does not face the positive electrode plate. If the negative electrode plate has such a non-facing portion at the lower corner, the amount of hydrogen gas generated increases, albeit slightly, and convection of the electrolyte is more likely to occur, which is more advantageous from the viewpoint of suppressing stratification.

[0109] When the positive electrode plate is stacked on the negative electrode plate and viewed from the front of the positive electrode plate, the ratio R2 of the total area S0 of the non-facing portions at the lower corners of the negative electrode plate to the sum of the area A of the negative electrode plate and the total area S (= S1 + S2) of the missing portions is, for example, 0.1% or more or 0.5% or more. From the viewpoint of further enhancing the electrolyte diffusion effect, the ratio R2 is preferably 1% or more, more preferably 2% or more. From the viewpoint of enhancing the effect of suppressing the floating of the settled positive electrode material, the ratio R2 of the non-facing portions is preferably 6% or less, more preferably 4% or less.

[0110] The proportion R2 of the non-facing portions may be 0.1% or more and 6% or less (or 4% or less), 0.5% or more and 6% or less (or 4% or less), 1% or more and 6% or less (or 4% or less), or 2% or more and 6% or less (or 4% or less).

[0111] The proportion R2 of the total area S0 of the non-facing portions is calculated by the following formula (2). R2=S0 / (A+S) (2) The area of ​​the rectangle A mentioned above is used as the sum (=A+S) of the area A of the electrode plate and the total area S of the missing parts. The area of ​​rectangle A is the product of the height H and width W of rectangle A. Area A and total area S can be calculated in the same way as for the positive electrode plate.

[0112] The total area S0 of the non-facing portions is the sum of the projected areas of the non-facing portions at each corner of the lower part of the negative plate when the state in which the positive plate is overlapped on the negative plate is viewed from the front of the positive plate. The total area S0 is calculated by binarizing the non-facing portions and other portions in a photograph taken from the front of the positive plate in which the positive plate is overlapped on the negative plate, and determining and summing the areas of the non-facing portions at each corner.

[0113] The total area S0 of the non-facing parts at the lower corners of the negative electrode plate is, for example, 1 cm 2 More than 2cm 2 The total area S0 may be, for example, 7 cm 2 Less than or equal to 4.5cm 2It may be the following:

[0114] The total area S0 is 1 cm 2 or more (or 2cm 2 over)7cm 2 Less than or equal to 1cm 2 or more (or 2cm 2 (more than)4.5cm 2 It may be the following:

[0115] A negative electrode plate with a chamfered lower corner can be produced in the same manner as the positive electrode plate.

[0116] The negative electrode material contained in the negative electrode plate contains a negative electrode active material (lead or lead sulfate) that generates capacity through an oxidation-reduction reaction, and may also contain an organic shrinkage inhibitor, a carbonaceous material (carbon black, etc.), barium sulfate, etc. The negative electrode material may also contain other additives (reinforcing materials, etc.) as needed.

[0117] Examples of the organic shrinkage inhibitor include lignin, lignin sulfonic acid or its salt, synthetic organic shrinkage inhibitor (such as a formaldehyde condensate of a phenol compound), etc. The negative electrode material may contain one type of organic shrinkage inhibitor or two or more types.

[0118] The content of the organic shrinkage inhibitor in the negative electrode material is, for example, 0.01% by mass or more, and 1% by mass or less.

[0119] Examples of the carbonaceous material include carbon black, graphite (artificial graphite, natural graphite, etc.), hard carbon, soft carbon, etc. The negative electrode material may contain one type of carbonaceous material or two or more types of carbonaceous materials.

[0120] The content of the carbonaceous material in the negative electrode material is, for example, 0.1 mass % or more, and may be, for example, 3 mass % or less.

[0121] 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.

[0122] Examples of the reinforcing material include fibers (inorganic fibers, organic fibers (such as organic fibers made of resin as described above for the reinforcing material of the positive electrode material)).

[0123] The amount of the reinforcing material in the negative electrode material is, for example, 0.03 mass % or more, and the amount of the reinforcing material in the negative electrode material is, for example, 0.5 mass % or less.

[0124] The negative electrode active material in the charged state is sponge lead, but the unformed negative electrode plate is usually made using lead powder.

[0125] The negative electrode plate can be formed by filling a negative electrode current collector with a negative electrode paste, aging and drying the paste to produce an unformed negative electrode plate, and then chemically forming the unformed negative electrode plate. The negative electrode paste is produced by adding water and sulfuric acid to lead powder, an organic shrinkage inhibitor, and various additives as needed, and kneading them. In the aging process, the unformed negative electrode plate is preferably aged at a temperature higher than room temperature and at a high humidity.

[0126] The formation can be carried out by immersing an electrode plate assembly including unformed negative plates in an electrolyte containing sulfuric acid in a battery jar of a lead-acid battery and then charging the electrode plate assembly. However, the formation can also be carried out before assembling the lead-acid battery or the electrode plate assembly. The formation produces spongy lead.

[0127] (Analysis of negative electrode materials or their constituents) The following describes the method for quantifying the organic shrinkage inhibitor, carbonaceous material, barium sulfate, and reinforcing material in the negative electrode material. Quantitative analysis of the components of the negative electrode material is performed using negative electrode material sampled from a negative electrode plate removed from a fully charged lead-acid battery.

[0128] Negative electrode material is recovered from the negative plate using the following procedure. First, a fully charged lead-acid battery is disassembled to obtain the negative plate to be analyzed. The obtained negative plate is washed with water to remove sulfuric acid from the negative plate. The washing is continued until a pH test paper is pressed against the washed surface of the negative plate and no color change is confirmed. However, the washing time should be within two hours. The washed negative plate is dried in a reduced pressure environment at 60±5°C for approximately six hours. After drying, if the negative plate contains an adhesive material, the adhesive material is removed from the negative plate by peeling. Next, the negative electrode material is separated from the negative plate to obtain a sample (hereinafter referred to as Sample D). Sample D is crushed as necessary and subjected to analysis.

[0129] Quantitative determination of organic shrinkage inhibitors The crushed sample D is immersed in a 1 mol / L NaOH aqueous solution to extract the organic shrinkage inhibitor. Insoluble components are removed by filtration from the NaOH aqueous solution containing the extracted organic shrinkage inhibitor, and the filtrate (hereinafter also referred to as filtrate E) is recovered.

[0130] A predetermined amount of filtrate E is measured, desalted, concentrated, and dried to obtain a powder of the organic shrinkage preventer (hereinafter also referred to as sample F). Desalting can be performed using a desalting column, by passing filtrate E through an ion exchange membrane, or by placing filtrate E in a dialysis tube and immersing it in distilled water.

[0131] The organic shrinkage inhibitor is identified by combining information obtained from the infrared spectrum of sample F, the ultraviolet-visible absorption spectrum of a solution obtained by dissolving sample F in distilled water or the like, the NMR spectrum of a solution obtained by dissolving sample F in a solvent such as heavy water, or information obtained from pyrolysis GC-MS, which can provide information on the individual compounds that make up the substance.

[0132] The ultraviolet-visible absorption spectrum of the filtrate E is measured. The content of the organic shrinkage inhibitor in the negative electrode material is quantified from the spectral intensity, the calibration curve prepared in advance, the measured amount of filtrate E, and the mass of sample D. If the structural formula of the organic shrinkage inhibitor to be analyzed cannot be precisely identified and a calibration curve for the same organic shrinkage inhibitor cannot be used, a calibration curve is prepared using an available organic shrinkage inhibitor that exhibits a similar ultraviolet-visible absorption spectrum, infrared spectrum, NMR spectrum, etc. to the organic shrinkage inhibitor to be analyzed.

[0133] Quantitative determination of carbonaceous materials, barium sulfate, and reinforcing materials 50 mL of 20% nitric acid was added to 10 g of the crushed sample D and heated for approximately 20 minutes to dissolve the lead components as lead ions. The resulting solution was then filtered to separate out the carbonaceous material, barium sulfate, and other solids.

[0134] The obtained solid content is dispersed in water to form a dispersion, and the reinforcing material is then recovered from the dispersion using a sieve. The reinforcing material is washed with water, dried, and its mass is measured. The ratio (percentage) of the mass of the dried material to the mass of sample D is calculated. This ratio corresponds to the amount of reinforcing material in the negative electrode material.

[0135] The dispersion liquid after removing the reinforcing material is subjected to suction filtration using a membrane filter whose mass has been measured in advance, and the membrane filter together with the filtered sample is dried in a dryer at 110°C ± 5°C. The resulting sample is a mixed sample of carbonaceous material and barium sulfate (hereinafter also referred to as Sample G). The mass of the membrane filter is subtracted from the total mass of Sample G and the membrane filter after drying to determine the mass of Sample G (M m ) is measured. After that, the dried sample G is placed in a crucible together with the membrane filter and burnt at 700°C or higher to be incinerated. The remaining residue is barium oxide. The mass of barium oxide is converted to the mass of barium sulfate to determine the mass of barium sulfate (M B ) to find the mass M m to mass M B The mass of the carbonaceous material is calculated by subtracting the above.

[0136] (electrode group) The electrode plate assembly includes at least one positive electrode plate, at least one negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate. When the electrode plate assembly includes two or more positive electrode plates, it is sufficient that at least one of the pair of lower corners of at least one positive electrode plate is chamfered. From the viewpoint of easily ensuring higher IS life performance, it is preferable that at least one of the pair of lower corners of 50% or more (preferably at least 80%) of the positive electrode plates included in the electrode plate assembly is chamfered. Of the positive electrode plates included in the electrode plate assembly, the proportion of positive electrode plates having at least one of the pair of lower corners chamfered is 100% or less. At least one of the pair of lower corners of all positive electrode plates included in the electrode plate assembly may be chamfered.

[0137] A lead-acid battery may include one electrode plate group, or two or more. When a lead-acid battery includes two or more electrode plate groups, at least one electrode plate group may include a positive electrode plate having at least one of a pair of lower corners chamfered. From the viewpoint of easily ensuring higher IS life performance, it is preferable that 50% or more (preferably 80% or more) of the electrode plate groups included in the lead-acid battery include positive electrode plates having at least one of a pair of lower corners chamfered. Of the electrode plate groups included in the lead-acid battery, the proportion of electrode plate groups including positive electrode plates having at least one of a pair of lower corners chamfered is 100% or less. It is preferable that all electrode plate groups included in the lead-acid battery include positive electrode plates having at least one of a pair of lower corners chamfered.

[0138] When the electrode plate assembly has two or more separators interposed between the positive and negative electrode plates, it is sufficient that the main portion of at least one of these separators has the thickness described above. From the viewpoint of easily ensuring higher IS life performance, it is preferable that the thickness of the main portion of 50% or more (preferably 80% or more) of the separators interposed between the positive and negative electrode plates included in the electrode plate assembly is within the above-mentioned range. Of the separators interposed between the positive and negative electrode plates included in the electrode plate assembly, the proportion of separators whose main portion has a thickness within the above-mentioned range is 100% or less. The main portion of all separators interposed between the positive and negative electrode plates included in the electrode plate assembly may have the above-mentioned thickness. In particular, it is preferable to configure the electrode plate assembly so that a separator whose main portion has a thickness within the above-mentioned range is interposed between the negative electrode plate and the positive electrode plate whose lower corner is chamfered.

[0139] When a lead-acid battery includes two or more electrode plate groups, it is sufficient that at least one electrode plate group includes a separator having a thickness within the above-mentioned range between the negative electrode plate and the positive electrode plate with a chamfered lower corner. From the viewpoint of easily ensuring higher IS life performance, it is preferable that 50% or more (preferably 80% or more) of the electrode plate groups included in the lead-acid battery include a separator having a thickness within the above-mentioned range between the negative electrode plate and the positive electrode plate with a chamfered lower corner. Of the electrode plate groups included in the lead-acid battery, the proportion of electrode plate groups having a separator having a thickness within the above-mentioned range between the negative electrode plate and the positive electrode plate with a chamfered lower corner is 100% or less. It is preferable that all of the electrode plate groups included in the lead-acid battery include a separator having a thickness within the above-mentioned range between the negative electrode plate and the positive electrode plate with a chamfered lower corner.

[0140] (electrolyte) The electrolyte is an aqueous solution containing sulfuric acid. The electrolyte may further contain at least one ion selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions. The electrolyte may be gelled as necessary.

[0141] The specific gravity of the electrolyte at 20° C. is, for example, 1.10 or more. The specific gravity of the electrolyte at 20° C. may be 1.35 or less. Note that these specific gravities are values ​​for the electrolyte of a pre-formed, fully charged lead-acid battery.

[0142] Fig. 1 is a plan view showing the appearance of an electrode plate 100 (positive electrode plate or negative electrode plate) used in a lead-acid battery according to one embodiment of the present invention. In the example of Fig. 1, the electrode plate 100 is a positive electrode plate, but it may also be a negative electrode plate. In Fig. 1, the electrode material is omitted from a portion of the electrode plate 100, so that the state of the current collector covered with the electrode material is also shown.

[0143] The electrode plate (positive electrode plate) 100 includes a current collector (positive electrode current collector) 101 and an electrode material (positive electrode material) 102 held by the current collector 101. In the example of FIG. 1, the current collector 101 is an expanded grid. The current collector 101 may be a stamped current collector or a cast current collector. The positive electrode current collector 101 includes a grid portion 103, a cross rib portion 104, and a tab portion 106. The cross rib portion 104 is provided at one end of the grid portion 103. The tab portion 106 is provided on the cross rib portion 104.

[0144] The general shape of the electrode plate 100 excluding the ear portions 106 is a rectangle with a width W and a height H, but a pair of corners at the bottom of the electrode plate 100 are chamfered, thereby forming missing portions X1 and X2 at each corner where the electrode plate 100 is missing.

[0145] The contour shape of the electrode plate 100 is the contour shape of the portion of the electrode plate 100 where the electrode material is present. When viewed from the front, the contour shape of the electrode plate 100 has a straight line portion L1 parallel to the horizontal direction of the electrode plate 100, which corresponds to the bottom side of the portion where the electrode material is present, two straight line portions L2 parallel to the vertical direction of the electrode plate 100, which correspond to the sides on both sides, a straight line portion L3 parallel to the straight line portion L1, which corresponds to the top side, and a connecting portion C at the lower corner that connects the straight line portion L1 and the straight line portion L2. In the illustrated example, the connecting portion C is configured as a straight line inclined with respect to the straight line portions L1 and L2, but the shape of the connecting portion C is not limited to this.

[0146] The extension line E1 is the extension line obtained by extending the straight portion L1 toward the L2 side, and the extension line E2 is the extension line obtained by extending the straight portion L2 toward the L1 side. In the electrode plate 100, the areas surrounded by the extension lines E1, E2, and the connection portion C at a pair of lower corners are the missing portions X1 and X2, where the electrode plate 100 is missing due to the chamfering of the corners. The area of ​​the missing portion X1 is S1, and the area of ​​the missing portion X2 is S2. The formation of these missing portions X1 and X2 creates a space at the bottom of the battery case, which can accommodate any fallen positive electrode material. This ensures high IS life performance even when using a separator containing polyolefin with a main portion thickness of 0.120 mm or more but less than 0.2 mm.

[0147] FIG. 2 shows an external view 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.

[0148] Each electrode plate group 11 is formed by stacking multiple negative electrode plates 2 and multiple positive electrode plates 3 with separators 4 interposed between them. Here, a pouch-shaped separator 4 is shown housing the negative electrode plates 2, but the shape of the separator is not particularly limited. In a cell chamber 14 located at one end of the battery case 12, a negative electrode shelf 6 that connects multiple negative electrode plates 2 in parallel is connected to a through-connector 8, and a positive electrode shelf 5 that connects multiple positive electrode plates 3 in parallel is connected to a positive electrode column 7. The positive electrode column 7 is connected to a positive electrode terminal 17 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 through-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 through-connector 8 passes through a through-hole provided in the partition wall 13 to connect the electrode plate groups 11 of adjacent cell chambers 14 in series.

[0149] The evaluation method for each characteristic will be explained below. (1)IS life performance Using the following procedure, the number of cycles until the terminal voltage of the lead-acid battery reaches 7.2V (1.2V / cell) is calculated and used as an index of IS life performance. (a) After fully charging, place the lead-acid battery in a cooling room at 0°C ± 1°C for at least 16 hours, and then confirm that the temperature of the electrolyte in one of the central cells is 0°C ± 1°C. (b) Discharge the lead-acid battery for 1.0 second at a current (A) 10 times the value in Ah listed as the rated capacity. (c) Discharge the lead-acid battery for 25 seconds at a current (A) that is 0.83 times the Ah value listed as the rated capacity. (d) Charge the lead-acid battery at a voltage of 14.0 V (2.33 V / cell) for 30 seconds. (e) The discharge and charge cycles (b) to (c) are repeated, with a minute current (20 mA) being discharged for 6 hours every 30 cycles. (f) In (b) above, find the number of cycles when the terminal voltage falls below 7.2V (1.2V / cell).

[0150] (2) Initial battery short circuit (a) Seven unformed negative plates and six unformed positive plates housed in a bag-shaped separator are alternately stacked to assemble an electrode plate assembly with unformed negative plates at both ends. At this time, visually check whether there are any holes in the separator due to bending of the current collector. (b) Six of the electrode plate groups in which no separator holes were found in (a) are placed in their respective cell compartments in the battery case, and lead-acid batteries are fabricated by injecting electrolyte and performing chemical conversion treatment. (c) After chemical formation, the lead-acid battery is discharged for 2.5 seconds at a current (A) that is 8.3 times the rated capacity (Ah). If the voltage after discharge is 9.5V (1.58V / cell) or less, it is considered to be a discharge failure. (d) The number of defective pouch-shaped separators n1 is calculated by adding together the number of pouch-shaped separators in which holes were confirmed in (a) and the number of pouch-shaped separators in which holes were confirmed in the electrode plate group that was determined to have a discharge failure in (c). (e) The percentage of defective pouch-shaped separators is calculated by dividing the number n1 of defective pouch-shaped separators by the total number N of pouch-shaped separators produced, and this percentage is designated as the initial battery short-circuit percentage (ppm). The total number N of produced pouch-shaped separators is the sum of the number of lead-acid batteries produced in (b) (= mass production quantity (e.g., 100,000)) multiplied by the number of all pouch-shaped separators included in one lead-acid battery (= 7 × 6 = 42), and the total number of pouch-shaped separators included in the electrode plate group including the separator in which holes were confirmed in (a).

[0151] [Example] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0152] Lead-acid batteries A1 to A12, B1 to B5, and C1 to C4 Each lead-acid battery was fabricated using separators and plates with the thicknesses shown in the table, according to the procedure below. The table also indicates whether the bottom corners of the plates used were chamfered. For some lead-acid batteries, the total pore volume of the separators used is also listed in the table.

[0153] (1) 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 amount of reinforcing material in the positive electrode material, measured using the procedure described above, was 0.15% by mass. The positive electrode paste was filled into the mesh portion of an expanded grid made of a Pb-Ca-Sn alloy containing no antimony, aged, and dried to obtain an unformed positive electrode plate measuring 100 mm wide, 110 mm high, and 1.6 mm thick.

[0154] (2) Preparation of the 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 grid made of a Pb-Ca-Sn alloy containing no antimony, aged, and dried to obtain an unformed negative electrode plate measuring 100 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 amounts of each component, measured using the previously described procedure on a negative electrode plate removed from a fully charged lead-acid battery, were 0.3 mass%, 2.1 mass%, 0.1 mass%, and 0.1 mass%, respectively.

[0155] (3) Chamfering the bottom corners of the electrode plates When a plate with chamfered lower corners was used in each lead-acid battery, such a plate was produced by chamfering the corners and their surroundings at both of the pair of lower corners of the positive plate produced in (1) above or the negative plate produced in (2) above. When the plate was viewed from the front, the shape of the part removed by chamfering (i.e., the missing part) was a right-angled isosceles triangle with a height of 17 mm, and the total area S of the missing part areas S1 and S2 was 289 mm 2 In this case, the proportion R1 of the total area S of the missing parts was 2.6%.

[0156] (4) Separator A resin composition containing 100 parts by mass of polyethylene, 160 parts by mass of silica particles, 80 parts by mass of paraffinic oil as a pore-forming agent, and 2 parts by mass of a penetrant was extruded into a sheet, and then a portion of the pore-forming agent was removed to produce a microporous membrane having a thickness of a main portion as determined by the procedure described above, as shown in the table, and a total pore volume as determined by the procedure described above. The oil content of the separator as determined by the procedure described was 12 to 18 mass%. The total pore volume of the separator in the lead-acid batteries shown in Tables 1 and 2 was 1.1 to 1.9 cm. 3 / g. Table 3 also shows the total pore volume of the separator.

[0157] Next, the sheet-like microporous membrane was folded in half to form a bag, and the overlapping ends were welded to obtain a bag-like separator. The bag-like separator had protruding ribs (external ribs) on its outer surface. The height of the external ribs was 0.6 mm, and the thickness of the base was 0.2 mm.

[0158] (5) Preparation of lead-acid batteries The unformed negative electrode plates were housed in a pouch-shaped separator and stacked with the positive electrode plates to form an electrode plate assembly consisting of seven unformed negative electrode plates and six unformed positive electrode plates.

[0159] The lugs of the positive and negative plates were welded to the positive and negative shelf sections, respectively, using the cast-on-strap (COS) 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 12 V and a rated capacity of 30 Ah (5-hour rate capacity (capacity when discharged at a current (A) of 1 / 5 the Ah value listed on the rated capacity)). Six plate groups were connected in series inside the battery case.

[0160] The electrolyte used was an aqueous sulfuric acid solution, and the specific gravity of the electrolyte after formation at 20°C was 1.285.

[0161] The results of evaluating the IS life performance and initial battery short-circuit rate for each lead-acid battery using the procedures described above are shown in the table. The initial battery short-circuit rate was calculated based on a mass production number of 100,000. In the table, the IS life performance is shown as a relative value, with the number of cycles for lead-acid battery B1 set at 100. It should be noted that A1 to A12 are working examples, B1 to B5 are comparative examples, and C1 to C4 are reference examples.

[0162] [Table 1]

[0163] As shown in Table 1, when a separator with a 0.2 mm thick core is used, IS life performance cannot be improved even when a positive electrode plate with chamfered lower corners is used (comparison between B1 and C1). Furthermore, when a positive electrode plate with unchamfered lower corners is used, IS life performance is reduced even when a separator with a 0.12 mm or greater but less than 0.2 mm thick core is used (comparison between B1 and B2 to B4). However, when a positive electrode plate with chamfered lower corners is combined with a separator with a 0.12 mm or greater but less than 0.2 mm thick core, IS life performance is significantly improved (comparison between C1 or B1 and A1 to A3). When a separator with a thickness less than 0.12 mm is used, whether or not the lower corners of the positive electrode plate are chamfered does not affect IS life performance (comparison between C2 and B5). Thus, the behavior of IS life performance when using a separator whose main part is 0.12 mm or more and less than 0.2 mm thick is completely different from when using a positive electrode plate with a chamfered lower corner and a positive electrode plate that is not chamfered. It can be said that the improvement in IS life performance shown in A1 to A3 can only be achieved by combining a separator whose main part is 0.12 mm or more and less than 0.2 mm thick with a positive electrode plate whose lower corner is chamfered.

[0164] Furthermore, as shown in Table 1, the occurrence of short circuits in the initial stage of the battery was significantly suppressed in A1 to A3 compared to the corresponding B2 to B4.

[0165] [Table 2]

[0166] As shown in Table 2, when a negative electrode plate with unchamfered lower corners is used, the IS life performance can be further improved compared to when a negative electrode plate with chamfered lower corners is used (comparison of A1 to A3 with A4 to A6).

[0167] [Table 3]

[0168] As shown in Table 3, in order to ensure even higher IS life performance, the total pore volume of the separator should be 1.1 cm 3 / g or more is preferable, and 1.9cm 3 / g or less is preferred. [Industrial Applicability]

[0169] The lead-acid battery according to the above aspect of the present invention is suitable for, for example, IS applications (such as lead-acid batteries for ISS vehicles) and as a starting power source for various vehicles (such as automobiles and motorcycles). The lead-acid battery may also be used as a power source for industrial power storage devices (such as electric vehicles). Note that these applications are merely examples, and the applications of the lead-acid battery according to the above aspect of the present invention are not limited to these. [Explanation of symbols]

[0170] 1: lead-acid battery, 2: negative electrode plate, 3: positive electrode plate, 4: separator, 5: positive electrode shelf, 6: negative electrode shelf, 7: positive electrode column, 8: through-connector, 9: negative electrode column, 11: electrode plate group, 12: battery case, 13: partition wall, 14: cell chamber, 15: lid, 16: negative electrode terminal, 17: positive electrode terminal, 18: liquid vent plug, 100: electrode plate, 101: current collector (positive electrode current collector), 102: electrode material (positive electrode material), 103: grid portion, 104: horizontal frame portion, 106: lug portion

Claims

1. A lead-acid battery, The lead-acid battery includes a positive electrode plate, a negative electrode plate, a separator interposed between the positive electrode plate and the negative electrode plate, and an electrolyte; Each of the positive electrode plate and the negative electrode plate includes a current collector and an electrode material, At least one of a pair of lower corners of the positive electrode plate is chamfered, The separator includes a base polymer in which polyolefin accounts for 50% by mass or more, The thickness of the main part of the separator is 0.12 mm or more and less than 0.2 mm, A lead-acid battery, wherein the separator has a total pore volume of 1.1 cm 3 / g or more and 1.9 cm 3 / g or less.

2. 2. The lead-acid battery according to claim 1, wherein the thickness of the main portion of the separator is 0.18 mm or less.

3. 3. The lead-acid battery according to claim 1, wherein the thickness of the main portion of the separator is 0.125 mm or more.

4. The lead-acid battery according to any one of claims 1 to 3, wherein the pair of corners of the negative electrode plate are not chamfered.

5. The lead acid battery according to any one of claims 1 to 4, wherein the current collector of the positive electrode plate is an expanded lattice.

6. The lead acid battery according to any one of claims 1 to 5, wherein the polyolefin contains at least an ethylene unit.

7. The lead acid battery according to any one of claims 1 to 6, wherein the separator is bag-shaped and accommodates the negative electrode plate.

8. The lead-acid battery according to any one of claims 1 to 7, wherein the separator contains oil.

9. The lead-acid battery according to claim 8 , wherein the content of the oil in the separator is 12 mass % or more and 18 mass % or less.

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