Lead acid battery

Abstract

To provide a lead acid battery capable of suppressing permeation short circuits during chemical conversion treatment.SOLUTION: A lead acid battery 100 includes a positive electrode 20, a negative electrode 30, a separator 40, and a porous membrane 50, and the porosity of the porous membrane 50 is 67.0% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a lead-acid battery.

Background Art

[0002] A lead-acid battery is one of the conventionally used secondary batteries and is widely used as an industrial or consumer secondary battery due to its reliability, low cost, etc. For example, a lead-acid battery can be used as an automotive lead-acid battery, a lead-acid battery for an electric vehicle, a lead-acid battery for a power supply device, etc.

[0003] There are cases where higher output is required for a lead-acid battery, and increasing the number of electrodes in the battery cell by reducing the thickness of the separator disposed between the positive electrode and the negative electrode has been considered. However, when the thickness of the separator is reduced, lead sulfate is likely to elute into the separator during the formation process in the battery manufacturing process, and penetration short-circuit may occur due to charge and discharge. On the other hand, techniques for solving penetration short-circuit and the like by improving the separator are known (for example, see Patent Document 1 below).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] From the viewpoint of adopting various configurations in a lead-acid battery, new techniques are required as techniques for solving penetration short-circuit.

[0006]

Means for Solving the Problems

[0007] The present disclosure relates to the following [1], [2], etc. in some aspects. [1] A lead-acid battery comprising a positive electrode, a negative electrode, a separator, and a porous membrane, wherein the porosity of the porous membrane is 67.0% or less. [2] The lead-acid battery according to [1], wherein the ratio of the porosity of the separator to the porosity of the porous membrane is 0.78 or less. [Advantages of the Invention]

[0008] According to one aspect of the present disclosure, a lead-acid battery capable of suppressing penetration short circuit during formation treatment can be provided. [Brief Description of the Drawings]

[0009]

Figure 1

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0011] In this specification, a numerical range indicated by "~" represents a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value of a numerical range at a certain step can be arbitrarily combined with the upper limit value or the lower limit value of a numerical range at another step. In the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples. "A or B" means that either one of A and B may be included, or both may be included. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances corresponding to each component in the composition when there are a plurality of substances corresponding to each component in the composition. The term "film" includes not only the structure formed over the entire surface but also the structure formed partially when observed as a plan view. The term "step" includes not only an independent step but also a step in which the intended action of the step is achieved even if it cannot be clearly distinguished from other steps. Since the specific gravity varies with temperature, in this specification, it is defined as the specific gravity converted at 25°C. "(Meth)acrylic" means at least one of acrylic and the corresponding methacrylic.

[0012] The lead-acid battery according to this embodiment includes a positive electrode, a negative electrode, a separator, and a porous film. In the lead-acid battery according to this embodiment, the porosity of the porous film is 67.0% or less.

[0013] According to the lead-acid battery of this embodiment, it is possible to suppress penetration short circuit during the formation process.

[0014] The lead-acid battery according to this embodiment can be used as a controlled valve type lead-acid battery. The lead-acid battery according to this embodiment can be used in automobiles, power supply devices, etc. Examples of the power supply device include UPS (Uninterruptible Power Supply), power supply for disaster prevention (emergency) radio, power supply for telephones, etc. The automobile, electric vehicle or power supply device according to this embodiment includes the lead-acid battery according to this embodiment.

[0015] The lead-acid battery according to this embodiment includes an electrode group according to this embodiment and a battery case that houses the electrode group. The electrode group according to this embodiment is an electrode group for a lead-acid battery and has the above-described positive electrode, negative electrode, separator, and porous film. As the lead-acid battery and electrode group according to this embodiment, a lead-acid battery and electrode group before formation can be used. The battery case is hollow and has an internal space for housing the electrode group. The lead-acid battery according to this embodiment may include a lid that seals the battery case. The lid may be provided with a control valve that controls the pressure inside the battery case, a positive electrode terminal that connects the positive electrode to the outside, and a negative electrode terminal that connects the negative electrode to the outside.

[0016] The lead-acid battery and the electrode group only need to have at least one positive electrode and may have a plurality of positive electrodes. The lead-acid battery and the electrode group only need to have at least one negative electrode and may have a plurality of negative electrodes. The number of positive and negative electrodes in the lead-acid battery and the electrode group may be the same or may not be the same. When the number of positive and negative electrodes is not the same, the number of negative electrodes may be more than the number of positive electrodes. The number of positive or negative electrodes may be 3 or more, or 4 or more. The number of positive or negative electrodes may be 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, or 3 or less. From these viewpoints, the number of positive or negative electrodes may be 3 to 10, 3 to 8, or 3 to 5. At least one (one or both) of the outermost electrodes in the electrode group may be a negative electrode.

[0017] The positive electrode has a positive electrode current collector and a positive electrode active material supported by the positive electrode current collector. The negative electrode has a negative electrode current collector and a negative electrode active material supported by the negative electrode current collector. The positive electrodes and negative electrodes may be arranged alternately with a separator and a porous membrane interposed therebetween. The member excluding the positive electrode current collector from the positive electrode is referred to as the "positive electrode active material", and the member excluding the negative electrode current collector from the negative electrode is referred to as the "negative electrode active material".

[0018] The positive electrode collector serves as a conductive path for current from the positive electrode active material and holds the positive electrode active material. The negative electrode collector serves as a conductive path for current from the negative electrode active material and holds the negative electrode active material. The negative electrode collector may be the same as the positive electrode collector, or may be different. Examples of the constituent material of the collector include lead alloys such as lead-calcium-tin alloys and lead-antimony-arsenic alloys. Depending on the application, selenium, silver, bismuth, etc. may be added to the collector. The collector has, for example, a lattice shape, and may be a cast lattice body, an expanded lattice body, etc. The collector can be obtained by forming a lead alloy into a lattice shape by gravity casting, expanding, punching, etc.

[0019] The plurality of positive electrodes may be electrically connected to each other by connecting the ears provided on the positive electrode current collector to each other via a strap. The strap of the positive electrode may be provided with a positive electrode pole for connecting the positive electrode to a positive electrode terminal. The plurality of negative electrodes may be electrically connected to each other by connecting the ears provided on the negative electrode current collector to each other via a strap. The strap of the negative electrode may be provided with a negative electrode pole for connecting the negative electrode to a negative electrode terminal.

[0020] The positive electrode active material is β-PbO 2 The positive electrode active material may include α-PbO. 2 and α-PbO 2 The positive electrode active material may contain PbO as necessary. 2 Pb components other than those listed above (e.g. PbSO 4 ), additives, etc.

[0021] Examples of additives that can be included in the positive electrode active material include carbon materials (excluding carbon fibers), short reinforcing fibers, etc. Examples of carbon materials include carbon black, graphite, etc. Examples of carbon black include furnace black, channel black, acetylene black, thermal black, ketjen black, etc. Examples of short reinforcing fibers include acrylic fibers, polyethylene fibers, polypropylene fibers, polyethylene terephthalate fibers, carbon fibers, etc.

[0022] The negative electrode active material can contain Pb as a Pb component. The negative electrode active material may contain porous spongy lead. The negative electrode active material can contain, if necessary, Pb components other than Pb (for example, PbSO 4 ), additives, etc.

[0023] Examples of additives that can be included in the negative electrode active material include resins having a sulfo group and / or a sulfonate group, barium sulfate, carbon materials (excluding carbon fibers), short reinforcing fibers, etc. Examples of resins having a sulfo group and / or a sulfonate group include lignin sulfonic acid, lignin sulfonates (for example, sodium lignin sulfonate), condensates of phenols, aminoaryl sulfonic acids, and formaldehyde (for example, condensates of bisphenol, aminobenzenesulfonic acid, and formaldehyde), etc. From the viewpoint of easily obtaining excellent charge acceptance, the negative electrode active material may contain at least one selected from the group consisting of lignin sulfonic acid, lignin sulfonates, and bisphenol-based resins, and from the viewpoint of particularly easily obtaining excellent charge acceptance, it may contain a bisphenol-based resin. Examples of carbon materials include carbon black, graphite, etc. Examples of carbon black include furnace black, channel black, acetylene black, thermal black, ketjen black, etc. Examples of short reinforcing fibers include acrylic fibers, polyethylene fibers, polypropylene fibers, polyethylene terephthalate fibers, carbon fibers, etc.

[0024] The positive electrode active material and the negative electrode active material can be obtained by aging and drying an active material paste containing raw materials of the active material to obtain an unformed active material and then forming the unformed active material. The positive electrode and the negative electrode can be obtained by aging and drying an active material paste supported by a current collector to obtain an unformed active material and then forming the unformed active material. The active material paste may contain a solvent and / or sulfuric acid. Examples of the solvent include water (e.g., ion-exchanged water), organic solvents, and the like. The unformed positive electrode active material may contain tribasic lead sulfate as a main component. Examples of the raw materials of the positive electrode active material include lead powder, lead dioxide (Pb 3 O 4 ), etc. The unformed negative electrode active material may contain tribasic lead sulfate as a main component. Examples of the raw materials of the negative electrode active material include lead powder, etc.

[0025] The lead storage battery according to the present embodiment includes a separator disposed between the positive electrode and the negative electrode. As the separator disposed between the positive electrode and the negative electrode, at least a part of the separator may be disposed between the positive electrode and the negative electrode.

[0026] The separator may be in contact with the positive electrode or may not be in contact with the positive electrode. The separator may cover at least a part of the active material region (the region where the positive electrode active material is disposed) of the positive electrode or may cover the entire active material region of the positive electrode. The separator may be in contact with the negative electrode or may not be in contact with the negative electrode. The separator may cover at least a part of the active material region (the region where the negative electrode active material is disposed) of the negative electrode or may cover the entire active material region of the negative electrode. The porosity of the separator may be 80.0% or more. The porosity of the separator may be 95.0% or less. The lead storage battery and the electrode group may have at least one separator or may have a plurality of separators. The separator may be in a bag shape or may be in a single-leaf form (not in a bag shape). The separator may be folded back so as to wrap the positive electrode or the negative electrode, and in the lead storage battery, the folded portion may be located below in the vertical direction.

[0027] The median pore diameter of the separator may preferably be 15.0 μm or less. The median pore diameter of the porous membrane can be measured by a mercury porosimeter (for example, manufactured by Quanta Chrome Co., trade name: Poro Master 60-GT).

[0028] In the separator, ribs may be arranged on at least one main surface selected from the group consisting of one surface and the other surface, and ribs may not be arranged on at least one main surface selected from the group consisting of one surface and the other surface. The separator can have at least one rib and may have a plurality of ribs.

[0029] The separator may contain glass fibers. The content rate of the glass fibers in the separator may be 80% or more. The separator may not contain an organic material (for example, an organic binder) or may contain an organic material. The separator may be a non-woven fabric.

[0030] Before being housed in the lead-acid battery or after being housed in the lead-acid battery, the thickness of the separator may be in the following range. From the viewpoint of easily achieving high output, the thickness of the separator may be 0.1 mm or more, 0.15 mm or more, 0.2 mm or more, more than 0.2 mm, 0.25 mm or more, 0.3 mm or more, more than 0.3 mm, 0.35 mm or more, or 0.4 mm or more. From the viewpoint of easily suppressing penetration short circuit, the thickness of the separator may be 5 mm or less, 4 mm or less, 3 mm or less, 2 mm or less, 1 mm or less, less than 1 mm, 0.9 mm or less, 0.8 mm or less, 0.7 mm or less, 0.65 mm or less, 0.6 mm or less, 0.55 mm or less, 0.5 mm or less, 0.45 mm or less, or 0.4 mm or less. From these viewpoints, the thickness of the separator may be 0.1 to 5 mm, 0.2 to 5 mm, more than 0.2 mm and 5 mm or less, 0.3 to 5 mm, more than 0.3 mm and 5 mm or less, 0.4 to 5 mm, 0.1 to 1 mm, 0.2 to 1 mm, more than 0.2 mm and 1 mm or less, 0.3 to 1 mm, more than 0.3 mm and 1 mm or less, or 0.4 to 1 mm. The thickness of the separator may be the average value (average thickness) of the measured values at 9 points in total (for example, 1 point at the center and 8 points around at equal intervals from each other).

[0031] The lead-acid battery according to this embodiment includes a porous membrane (porous membrane for lead-acid battery) disposed between the positive electrode and the negative electrode. As the porous membrane disposed between the positive electrode and the negative electrode, at least a part of the porous membrane may be disposed between the positive electrode and the negative electrode. Further, the porous membrane may be disposed at least on one of between the positive electrode and the separator and between the negative electrode and the separator. As the porous membrane disposed between the positive electrode and the separator, at least a part of the porous membrane may be disposed between the positive electrode and the separator. As the porous membrane disposed between the negative electrode and the separator, at least a part of the porous membrane may be disposed between the negative electrode and the separator.

[0032] The porous membrane may be in contact with the positive electrode or may not be in contact with the positive electrode. The porous membrane may cover at least a part of the active material region of the positive electrode or may cover the entire active material region of the positive electrode. The porous membrane may be in contact with the negative electrode or may not be in contact with the negative electrode. The porous membrane may cover at least a part of the active material region of the negative electrode or may cover the entire active material region of the negative electrode. From the viewpoint of easily suppressing penetration short circuit, the porous membrane of the lead-acid battery according to this embodiment may have a porous membrane disposed between the negative electrode and the separator and may not have a porous membrane disposed between the positive electrode and the separator. The lead-acid battery and the electrode group only need to have at least one porous membrane and may have a plurality of porous membranes. The porous membrane may be in a bag shape or may be a single sheet (not necessarily in a bag shape). The porous membrane may be folded back so as to wrap the positive electrode or the negative electrode, and in the lead-acid battery, the folded portion may be located below in the vertical direction.

[0033] The porous membrane contains glass fibers and may contain an organic material. Examples of the organic material include resin materials such as (meth)acrylic resins (e.g., (meth)acrylic binders), olefin resins, urethane resins, and styrene resins. Examples of the olefin resin include polyethylene and polypropylene. When a porous membrane containing a (meth)acrylic resin is used, the porous membrane adsorbs lead ions, suppressing an excessive increase in the lead ion content inside the separator and making it easier to suppress penetration short circuit. From the viewpoint of being easy to suppress penetration short circuit, the porous membrane may be a nonwoven fabric.

[0034] Before being housed in the lead-acid battery or after being housed in the lead-acid battery, the thickness of the porous film may be in the following range. From the viewpoint of easily achieving high output, the thickness of the porous film may be 0.05 mm or more, 0.08 mm or more, 0.10 mm or more, 0.12 mm or more, 0.15 mm or more, 0.18 mm or more, 0.20 mm or more, 0.22 mm or more, 0.25 mm or more, 0.28 mm or more, or 0.30 mm or more. From the viewpoint of easily suppressing penetration short circuit, the thickness of the porous film may be 0.50 mm or less, 0.45 mm or less, 0.40 mm or less, less than 0.40 mm, 0.35 mm or less, 0.30 mm or less, less than 0.30 mm, 0.28 mm or less, 0.25 mm or less, 0.22 mm or less, 0.20 mm or less, less than 0.20 mm, 0.18 mm or less, 0.15 mm or less, 0.12 mm or less, or 0.10 mm or less. From these viewpoints, the thickness of the porous film may be 0.05 to 0.50 mm, 0.05 to 0.40 mm, 0.05 mm or more and less than 0.40 mm, 0.05 to 0.30 mm, 0.05 mm or more and less than 0.30 mm, 0.05 to 0.20 mm, 0.05 mm or more and less than 0.20 mm, 0.05 to 0.10 mm, 0.10 to 0.50 mm, 0.10 to 0.40 mm, 0.10 mm or more and less than 0.40 mm, 0.10 to 0.30 mm, 0.10 mm or more and less than 0.30 mm, 0.10 to 0.20 mm, 0.10 mm or more and less than 0.20 mm, 0.20 to 0.50 mm, 0.20 to 0.40 mm, 0.20 mm or more and less than 0.40 mm, or 0.20 to 0.30 mm. The thickness of the porous film may be the average value (average thickness) of the measured values at a total of 9 points (for example, 1 point at the center and 8 points around at equal intervals). From the viewpoint of easily suppressing penetration short circuit, the thickness of the porous film may be smaller than the thickness of the separator.

[0035] Before being housed in a lead-acid battery or after being housed in a lead-acid battery, the ratio of the thickness of the porous membrane to the thickness of the separator (thickness of the porous membrane / thickness of the separator) may be in the following range. From the viewpoint of easily suppressing penetration short circuit, the thickness ratio may be 0.1 or more, 0.15 or more, 0.2 or more, 0.25 or more, 0.3 or more, 0.35 or more, 0.4 or more, 0.45 or more. From the viewpoint of easily suppressing penetration short circuit, the thickness ratio may be 0.5 or less, 0.45 or less, 0.4 or less, 0.35 or less, 0.3 or less, or 0.25 or less. From these viewpoints, the thickness ratio may be 0.1 to 0.5, more than 0.1 and less than 0.5, 0.1 to 0.3, 0.1 to 0.25, 0.2 to 0.5, more than 0.2 and less than 0.5, 0.2 to 0.3, 0.2 to 0.25, 0.25 to 0.5, more than 0.25 and less than 0.5, or 0.25 to 0.3.

[0036] From the viewpoint of suppressing penetration short circuit, the median pore diameter of the porous membrane may preferably be 48.1 μm or less. The median pore diameter of the porous membrane can be measured by a mercury porosimeter.

[0037] From the viewpoint of easily suppressing penetration short circuit, the ratio of the median pore diameter of the porous membrane to the median pore diameter of the separator (median pore diameter of the porous membrane / median pore diameter of the separator) is 4.0 or less, 3.0 or less, or 2.0 or less.

[0038] From the viewpoint of suppressing penetration short circuit, the porosity of the porous membrane is 67.0% or less. That is, it is sufficient that the porous membrane includes at least a part of the region having such a porosity, and the whole of the porous membrane may have such a porosity.

[0039] The porosity may be 67.0% or less, or 65.0% or less, 60.0% or less, 55.0% or less, 50.0% or less from the viewpoint of easily suppressing permeation short circuit. The porosity may be 40.0% or more from the viewpoint of improving discharge characteristics. From these viewpoints, the porosity may be 40.0% or more and 67.0% or less. The porosity of the porous membrane can be adjusted by the method for producing the porous membrane (wet method, dry method, spunbond method, meltblown method, thermal bonding method, chemical bonding method, needle punching method, hydroentangling method, etc.), the fiber diameter of the glass fiber used in producing the porous membrane, and the like.

[0040] The porosity of the porous membrane can be obtained by measuring the average pore diameter of the porous membrane with a mercury porosimeter. Specifically, it can be obtained by the following procedure.

[0041] Using a fully automatic pore size distribution measuring device (Poro Master 60 - GT, manufactured by Quanta Chrome Co.), 0.05 g of the separator was added to a small cell (diameter: 10 mm × 30 mm) for measurement. The mercury parameters were set to a mercury contact angle of 140 degrees and a mercury surface tension of 480 dyn / cm. Also, the measurement range of the pore diameter was set to 0.0036 to 1000 μm, and each value was calculated, and the median pore diameter was taken as the separator pore diameter.

[0042] The ratio of the porosity of the separator to the porosity of the porous membrane (porosity of the porous membrane / porosity of the separator) is 0.78 or less, or 0.60 or less from the viewpoint of easily suppressing permeation short circuit.

[0043] Before being housed in the lead - acid battery or after being housed in the lead - acid battery, the basis weight of the porous membrane may be in the following range. The basis weight of the porous membrane may be 40 g / cm 2 or more. The basis weight of the porous membrane may be 60 g / cm 2 or less. From these viewpoints, the basis weight of the porous membrane may be 40 to 60 g / cm 2

[0044] The bulk density of the porous membrane is 0.4 g / cm from the viewpoint of easily suppressing permeation short circuit.​3 or more, or 0.5 g / cm 3 It may be the above.

[0045] The lead-acid battery according to this embodiment may include an electrolyte. The electrolyte can be housed in an electrolyte tank. The electrolyte may contain sulfuric acid and may contain sulfate ions. The electrolyte may contain metal ions such as aluminum ions.

[0046] The specific gravity (before formation) of the electrolyte may be in the following range. From the viewpoint of easily suppressing penetration short circuit, the specific gravity of the electrolyte may be 1.30 or less, 1.25 or less, 1.24 or less, 1.23 or less, 1.22 or less, 1.21 or less, 1.20 or less, or 1.19 or less. From the viewpoint of easily suppressing penetration short circuit, the specific gravity of the electrolyte may be 1.10 or more, 1.12 or more, 1.14 or more, 1.15 or more, 1.16 or more, 1.18 or more, or 1.19 or more. From these viewpoints, the specific gravity of the electrolyte may be 1.10 to 1.30, 1.12 to 1.25, or 1.15 to 1.20.

[0047] An example of a lead-acid battery is shown using FIG. 1. FIG. 1 is an end view of the lead-acid battery when viewed from the vertical direction.

[0048] The lead-acid battery 100 shown in FIG. 1 includes an electrode group 10, an electrolyte (not shown), and an electrolyte tank (not shown) that houses the electrode group 10 and the electrolyte. The electrode group 10 has a plurality of positive electrodes 20, a plurality of negative electrodes 30, a plurality of separators 40 disposed between the positive electrode 20 and the negative electrode 30, and a plurality of porous membranes 50 disposed between the positive electrode 20 and the separator 40. The positive electrode 20 and the negative electrode 30 are alternately arranged via the separator 40 and the porous membrane 50, and the separator 40 and the porous membrane 50 are disposed between the positive electrode 20 and the negative electrode 30.

[0049] The separator 40 is formed by folding a sheet-like separator so as to wrap the positive electrode 20. One surface of the separator 40 (the inner surface when the separator 40 is folded) is in contact with the positive electrode 20, and the other surface of the separator 40 (the outer surface when the separator 40 is folded) is in contact with the porous film 50. The separator 40 covers the entire active material region of the positive electrode 20.

[0050] The porous film 50 is disposed between the positive electrode 20 and the separator 40. One surface of the porous film 50 is in contact with the positive electrode 20, and the other surface of the porous film 50 is in contact with the separator 40.

Example

[0051] Hereinafter, the present disclosure will be described more specifically with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0052] <Fabrication of Electrodes> As raw materials for the positive electrode active material, lead powder and lead dioxide (Pb 3 O 4 ) were used (lead powder: lead dioxide = 96:4 (mass ratio)). The raw materials for the positive electrode active material were mixed and kneaded with 0.07% by mass of reinforcing short fibers (acrylic fibers) and water based on the total mass of the raw materials for the positive electrode active material. Subsequently, while adding dilute sulfuric acid (specific gravity 1.280) little by little, kneading was performed to prepare a paste-like positive electrode active material.

[0053] Lead powder was used as the raw material for the negative electrode active material. A mixture containing 0.2% by mass (in terms of solid content) of a lignin-based resin (lignin sulfonate), 0.1% by mass of reinforcing short fibers (acrylic fibers), 1.0% by mass of barium sulfate, and 0.2% by mass of a carbon material (furnace black) was added to the lead powder and then dry-mixed (the above formulation amounts are the formulation amounts based on the total mass of the raw materials for the negative electrode active material). Next, water was added and then kneaded. Subsequently, while adding dilute sulfuric acid (specific gravity 1.280) little by little, kneading was performed to prepare a paste-like negative electrode active material.

[0054] The paste-like positive active material was filled into the electrode plate (positive current collector), and the paste-like negative active material was filled into the electrode plate (negative current collector) so that the ratio (N / P) of the total mass (N) of the negative active material to the total mass (P) of the positive active material in the control valve type lead-acid battery in the fully charged state was 0.86. As the electrode plate, a cast lattice made of lead alloy was used.

[0055] Using the electrode plate filled with the paste-like positive active material, an unformed positive electrode (length 140 mm, width 145 mm, thickness 3.2 mm (dimension of the active material region: length 140 mm, width 145 mm)) was produced through the aging process under the following aging conditions 1 to 3 and the drying process under the following drying conditions. Aging condition 1 "Temperature: 80 °C, Humidity: 98%, Time: 10 hours" Aging condition 2 "Temperature: 65 °C, Humidity: 75%, Time: 13 hours" Aging condition 3 "Temperature: 40 °C, Humidity: 65%, Time: 40 hours" Drying condition "Temperature: 60 °C, Time: 24 hours"

[0056] Using the electrode plate filled with the paste-like negative active material, an unformed negative electrode (length 116 mm, width 58 mm, thickness 2.5 mm (dimension of the active material region: length 116 mm, width 58 mm)) was produced through the aging process under the aging condition "Temperature: 40 °C, Humidity: 98%, Time: 40 hours" and the drying process under the drying condition "Temperature: 60 °C, Time: 24 hours".

[0057] <Preparation of porous membrane> The following non-woven fabric (length 250 mm, width 65 mm) was prepared as the porous membrane (porous membrane before being housed in the lead-acid battery). Porous membrane A: Median pore diameter 26.4 μm, porosity 48.1%, basis weight 50 g / cm 2 , thickness 0.10 mm, bulk density 0.54 g / cm 3 , porous membrane containing polypropylene and pulp Porous membrane B: Median pore diameter 42.5 μm, porosity 66.3%, basis weight 50 g / cm 2 , thickness 0.10 mm, bulk density 0.48 g / cm 3 , porous membrane containing polypropylene and pulp Porous membrane C: Median pore diameter 59.0 μm, porosity 76.8%, basis weight 28 g / cm 2 , thickness 0.10 mm, bulk density 0.20 g / cm 3 , porous membrane containing nylon and pulp Porous membrane D: Median pore diameter 57.3 μm, porosity 68.1%, basis weight 30 g / cm 2 , thickness 0.10 mm, bulk density 0.31 g / cm 3 , porous membrane containing polypropylene and pulp Porous membrane E: Median pore diameter 64.9 μm, porosity 71.2%, basis weight 20 g / cm 2 , thickness 0.10 mm, bulk density 0.29 g / cm 3 , porous membrane containing polypropylene and pulp

[0058] <Evaluation of porous membranes> (Porosity) Using a mercury porosimeter (manufactured by Quanta Chrome Co., product name: Poro Master 60-GT), the porosity of the above-mentioned porous membranes A to E was measured according to the following procedure. The results are shown in Table 1.

[0059] <Fabrication of separator> A separator (thickness: 0.80 mm) was prepared as a separator (manufactured by Nippon Sheet Glass Co., Ltd., product name: BMS-5) with a length of 434 mm and a width of 156 mm. When the porosity of the separator was measured in the same procedure as the above-mentioned porous membranes, the porosity of the separator was 86.1%.

[0060] <Fabrication of lead-acid battery> (Examples 1 to 2 and Comparative Examples 1 to 3) The above separator (thickness: 0.8 mm) was folded back in the longitudinal direction, and both main surfaces (active material regions of the positive electrode) of the unformed positive electrode were covered with the separator to obtain the positive electrode member A. Further, the above porous film was folded back in the longitudinal direction, and both main surfaces of the positive electrode member A were covered with the porous film to obtain the positive electrode member B. At this time, the longitudinal directions of the positive electrode, the separator, and the porous film were the same as each other, and the folded portions of the separator and the porous film were arranged so as to be located on one end side in the longitudinal direction of the positive electrode (the lower end side in the vertical direction of the positive electrode in the state where the positive electrode was housed in the lead-acid battery). Subsequently, an electrode group was produced by alternately laminating three positive electrode members B and four unformed negative electrodes. After inserting the electrode group and the spacer into the battery case, the positive electrode terminal and the negative electrode terminal were welded to the electrode group, and further, the battery case was sealed. At this time, by adjusting the thickness of the spacer, the distance between the positive electrode and the negative electrode was adjusted to 0.77 mm. Next, an electrolytic solution mainly composed of dilute sulfuric acid with a specific gravity of 1.22 was injected into the battery case from the exhaust plug port, and then a battery case forming cap was attached to produce the lead-acid batteries (battery capacity: 15 Ah) in each example and comparative example.

[0061] <Penetration short-circuit evaluation> As the penetration short-circuit evaluation, in a water tank at 40 °C, after leaving the above lead-acid battery standing for 3 hours, charge and discharge (battery case forming) were performed according to the following procedure. After charge and discharge, the separator was taken out, and the deposition state of lead on the surface of the separator was visually confirmed. When there was no deposition of lead on the surface of the separator and no penetration short-circuit occurred, it was evaluated as "A". When lead was deposited on the surface of the separator but no penetration short-circuit occurred, it was evaluated as "B". When lead was deposited on the surface of the separator and a penetration short-circuit occurred, it was evaluated as "C". Also, when the inter-terminal voltage (open-circuit voltage) after battery case forming was 2.0 V or more, it was determined as "No penetration short-circuit: A, B". The results are shown in Table 1. {Charge and discharge conditions} First charge: Current 19.5 A, 14.7 hours First discharge: Current 18.4 A, 1.8 hours Second charge: Current 19.0 A, 7.9 hours Third charge: Current 15.0 A, 11.8 hours Second Discharge: Current 24.3 A, 2.6 hours Third Charge: Current 19.4 A, 4.2 hours Fourth Charge: Current 12.5 A, 3.0 hours

[0062]

Table 1

Explanation of Symbols

[0063] 10…Electrode group, 20…Positive electrode, 30…Negative electrode, 40…Separator, 50…Porous membrane, 100…Lead-acid battery.

Claims

1. A lead-acid battery comprising a positive electrode, a negative electrode, a separator, and a porous membrane, wherein the porosity of the porous membrane is 67.0% or less.

2. The lead-acid battery according to claim 1, wherein the ratio of the porosity of the separator to the porosity of the porous membrane is 0.78 or less.

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