JP7694585B2 - Clad type positive electrode plate for lead-acid battery and lead-acid battery - Google Patents

Description

The present invention relates to a clad type positive electrode plate for a lead-acid battery and a lead-acid battery.

Lead-acid batteries are used in vehicles, industrial applications, and a variety of other applications. Lead-acid batteries contain a positive electrode plate, a negative electrode plate, and an electrolyte. Paste-type positive electrode plates and clad-type positive electrode plates are used as the positive electrode plate. Each electrode plate contains a current collector and an electrode material. In order to impart various functions, additives may be added to the components (e.g., electrode material) of the lead-acid battery.

Patent Document 1 proposes a lead-acid battery characterized in that, in a positive electrode material having a density of 3.1 g/ ^cm3 or more and containing an Sb element, an organic shrinkage preventer for a negative electrode material contains an S element at 3800 μmol/g or more.

Patent Document 2 proposes a lead-acid battery comprising a negative electrode plate whose negative electrode material contains an organic shrinkage inhibitor with an S element content of 3,500 μmol/g or more, and one or more electrolytes that are gelled, held in a separator, or held in granular silica.

Patent Document 3 proposes a positive plate for a lead-acid battery in which a positive electrode active material whose main component is lead powder is filled into a positive electrode grid, and which is characterized in that organic or glass short fibers and antimony are contained in the positive electrode active material.

Patent Document 4 proposes a lead-acid battery comprising a positive electrode plate, a negative electrode plate, and an electrolyte, the negative electrode material of the negative electrode plate containing graphite or carbon fiber and 1.1 mass% or more of barium element calculated as barium sulfate, and the positive electrode material of the positive electrode plate containing tin element.

It has also been proposed to adjust the density or specific surface area of the electrode material.

Patent Document 5 proposes a lead-acid battery comprising a positive electrode and a negative electrode, the positive electrode having a positive electrode current collector and a positive electrode material held by the positive electrode current collector, the negative electrode having a negative electrode current collector and a negative electrode material held by the negative electrode current collector, the specific surface area of the positive electrode material being 10 ^m2 /g or more, and the density of the positive electrode material being 3.8 g/ ^cm3 or more.

Patent Document 6 proposes a sealed lead-acid battery having a positive electrode in which a positive electrode active material having a density of 3.8 to 5.0 g/ ^cm3 is held in a lattice body formed of a lead alloy containing no antimony, and a sulfuric acid electrolyte having a density of 1.20 to 1.28 g/ ^cm3 .

JP 2016-225113 A JP 2016-189297 A JP 2010-277799 A International Publication No. 2018/025837 JP 2017-016970 A JP 2001-250589 A

In lead-acid batteries used in charge-discharge cycles including deep discharge, the temperature of the battery rises when the battery is repeatedly charged and discharged for a long period of time. It has become clear that in lead-acid batteries equipped with clad-type positive plates, if the density of the positive electrode material is relatively low, a sudden voltage rise may occur during charging if a charge-discharge cycle including deep discharge is performed at a high temperature (e.g., a temperature of 75°C or higher). For example, when a lead-acid battery is charged using a quasi-constant voltage method, if a sudden voltage rise occurs during charging, it may be recognized that the set charging voltage has been reached early, and charging may end, resulting in an insufficient charge state.

A first aspect of the present invention is a clad type positive electrode plate for a lead-acid battery,
The positive electrode plate includes a plurality of porous tubes, metal cores housed in the tubes, a positive electrode material filled in the tubes, and a current collecting portion connecting one end of the length direction of the plurality of metal cores arranged in a row,
The positive electrode material includes organic fibers,
The density of the positive electrode material is 3.75 g/ ^cm3 or less,
The present invention relates to a clad type positive electrode plate for a lead-acid battery, wherein the number of the organic fibers per unit volume (cm ³ ) of the positive electrode material is 400 or more and 15,000 or less.

A second aspect of the present invention is a clad type positive electrode plate for a lead-acid battery,
The positive electrode plate includes a plurality of porous tubes, metal cores housed in the tubes, a positive electrode material filled in the tubes, and a current collecting portion connecting one end of the length direction of the plurality of metal cores arranged in a row,
The positive electrode material includes organic fibers,
The density of the positive electrode material is 3.75 g/ ^cm3 or less,
The present invention relates to a clad type positive electrode plate for a lead-acid battery, wherein a ratio of the organic fibers to the positive electrode material is 0.013 volume % or more and 0.5 volume % or less.

A third aspect of the present invention is a lead-acid battery,
The lead-acid battery includes at least one electrode plate group and an electrolyte,
The plate group relates to a lead-acid battery comprising at least one of the above-mentioned clad type positive plate, at least one negative plate, and a separator interposed between the clad type positive plate and the negative plate.

It is possible to reduce the voltage rise during charging when a lead-acid battery equipped with a clad type positive plate is charged and discharged at high temperatures in a charge/discharge cycle that includes deep discharge.

FIG. 1 is a perspective view showing a schematic example of a lead-acid battery according to an embodiment of the present invention with the lid removed. FIG. 2 is a front view of the lead-acid battery of FIG. 1 . 1B is a schematic cross-sectional view of the cross section taken along line IIB-IIB in FIG. 1A, as viewed from the direction of the arrows. 1 is a graph showing the relationship between the voltage rise occurrence rate and the density of the positive electrode material in Table 1. 1 is a graph showing the relationship between the voltage rise occurrence rate and the number of organic fibers in Table 2. 1 is a graph showing the relationship between the voltage rise occurrence rate and the organic fiber ratio in Table 2. 13 is a graph showing the relationship between the voltage rise occurrence rate and the specific gravity of organic fibers in Table 3. 1 is a graph showing the relationship between the voltage rise occurrence rate and the oxygen element content of the organic fiber in Table 3. 1 is a graph showing the relationship between the initial capacity and the number of organic fibers in Table 4. 1 is a graph showing the relationship between the initial capacity and the organic fiber ratio in Table 4.

In lead-acid batteries used in charge-discharge cycles that include deep discharge, repeated charging and discharging over long periods of time can cause the battery temperature to rise (for example, to a temperature of 75°C or higher). This is because the battery is prone to becoming overcharged when charging, which generates heat, and also because the resistance increases with deep discharge, which generates more heat when discharging.

It has become clear that in a lead-acid battery equipped with a clad type positive plate, when the density of the positive electrode material is 3.75 g/cm3 or ^less , a sudden voltage rise occurs when charging and discharging, including deep discharging, at high temperatures. The problem of such a voltage rise is a new problem that has not been known until now. The clad type positive plate includes, for example, a plurality of porous tubes, a metal core housed in the tube, and a positive electrode material filled in the tube. When the density of the positive electrode material is low, sulfate ions are likely to penetrate into the inside of the positive electrode material. Although the details of the mechanism are unclear, it is thought that the above-mentioned voltage rise occurs when ions derived from the components contained in the metal core diffuse into the positive electrode material due to the action of the sulfate ions that have penetrated into the inside, forming some resistance component.

Lead-acid batteries are sometimes charged using a quasi-constant voltage method. In this method, charging is performed while the voltage (specifically, the terminal voltage) of the lead-acid battery is detected. More specifically, when the battery voltage is low at the beginning of charging, the charging current is large, and as charging progresses and the battery voltage rises, the charging current decreases, and charging ends when the battery voltage reaches a set value. In this type of charging method, if a sudden voltage rise occurs during charging as described above, the battery voltage may be mistakenly determined to have reached a set value even though charging has not actually progressed, and charging may end. A lead-acid battery that has finished charging is actually in an undercharged state, so it is difficult to operate the lead-acid battery for a long time even if it is installed in a device or equipment.

In view of the above, the lead-acid battery according to each of the first and second aspects of the present invention includes at least one electrode plate group and an electrolyte. The electrode plate group includes at least one clad type positive electrode plate, at least one negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a plurality of porous tubes, a core metal housed in the tube, a positive electrode material filled in the tube, and a current collector connecting one end of the longitudinal direction of the plurality of core metals arranged in a row. The positive electrode material includes organic fibers. The density of the positive electrode material is 3.75 g/ ^cm3 or less.

In the lead-acid battery according to the first aspect, (a) the number of organic fibers per unit volume (cm ³ ) of the positive electrode material is 400 or more and 15,000 or less.

In the lead-acid battery relating to the second aspect, (b) the ratio of organic fibers in the positive electrode material is 0.013 volume % or more and 0.5 volume % or less.

In the lead-acid battery according to the first and second aspects, even if the density of the positive electrode material is 3.75 g/cm ³ or less, the voltage rise during charging can be reduced when the positive electrode material is charged and discharged in a charge-discharge cycle including deep discharge at a high temperature (for example, 75° C.). Thus, the incidence of voltage rise in the lead-acid battery can be significantly reduced. Such an effect is obtained because the positive electrode material contains organic fibers so as to satisfy the above condition (a) or (b), and even if the density of the positive electrode material is small, the organic fibers prevent the movement of ions in the positive electrode material. More specifically, it is thought that the penetration of sulfate ions into the vicinity of the core metal is mitigated. Furthermore, even if sulfate ions reach the vicinity of the core metal and a component contained in the core metal is dissolved, the movement of ions derived from this component in the positive electrode material is prevented, and the diffusion to the entire positive electrode material is reduced. It is thought that the formation of resistance components in the positive electrode material is reduced, thereby reducing the above-mentioned voltage rise.

In this specification, the voltage increase during charging when charging and discharging in a charge-discharge cycle including deep discharge at a high temperature (e.g., 75°C) may be simply referred to as the "voltage increase during a high-temperature deep discharge cycle."

On the other hand, when the density of the positive electrode material in the clad type positive plate exceeds 3.75 g/cm ³ , the voltage rise during the high temperature deep discharge cycle is not a problem even if the positive electrode material does not contain organic fibers. In other words, it can be said that the voltage rise during the high temperature deep discharge cycle is a problem specific to the case where the density of the positive electrode material in the clad type positive plate is 3.75 g/cm ³ or less. In the first and second aspects of the present invention, such a specific problem can be solved by condition (a) or (b).

The present invention also includes a clad type positive electrode plate for a lead-acid battery that satisfies condition (a) or (b). Each of the clad type positive electrode plates for a lead-acid battery according to the third and fourth aspects of the present invention includes a plurality of porous tubes, a core metal housed in the tube, a positive electrode material filled in the tube, and a current collector that connects one end of the longitudinal direction of the plurality of core metals arranged in a row. The positive electrode material includes organic fibers. The density of the positive electrode material is 3.75 g/cm ³ or less. The clad type positive electrode plate for a lead-acid battery according to the third aspect satisfies the above condition (a). The clad type positive electrode plate for a lead-acid battery according to the fourth aspect satisfies the above condition (b). By using such a clad type positive electrode plate in a lead-acid battery, the above-mentioned effects described for the first or second aspect can be obtained.

Each of the first and third aspects may satisfy condition (b) in addition to condition (a). In this case, the voltage rise during high-temperature deep discharge cycles can be more effectively reduced.

The number of organic fibers per unit volume (cm ³ ) of the positive electrode material may be 800 or more. The ratio of the organic fibers in the positive electrode material may be 0.026 volume % or more. In these cases, the occurrence rate of voltage rise during high-temperature deep discharge cycles can be further reduced.

The number of organic fibers per unit volume (cm ³ ) of the positive electrode material may be 10,000 or less. The ratio of the organic fibers in the positive electrode material may be 0.32 volume % or less. In these cases, the positive electrode material is prevented from losing its binding strength and is less susceptible to cracking, making it easier to ensure a higher initial capacity.

It is preferable that the organic fibers contain fibers with a specific gravity of 1.2 or more. In this case, the occurrence rate of voltage rise during high-temperature deep discharge cycles can be further reduced. This is thought to be because the fibers are more easily dispersed more uniformly throughout the positive electrode material, further restricting the movement of ions within the positive electrode material.

The organic fibers contain oxygen elements, and the content of the oxygen elements in the organic fibers is preferably 10,000 μmol/g or more. In this case, the occurrence rate of voltage rise during high-temperature deep discharge cycles can be further reduced. When the organic fibers contain a large amount of oxygen elements, the organic fibers are more likely to form hydrogen bonds with water molecules. This makes it easier for the organic fibers to be more uniformly dispersed throughout the positive electrode material, and the movement of ions within the positive electrode material is further restricted by the organic fibers, which is thought to further reduce the occurrence rate of voltage rise during high-temperature deep discharge cycles.

The oxygen element content in the organic fiber may be 35,000 μmol/g or less. In this case, oxidative decomposition of the organic fiber is suppressed even when exposed to a positive electrode potential, so high durability can be ensured.

The organic fibers preferably include at least one selected from the group consisting of polyester fibers, acetalized polyvinyl alcohol fibers, polyurethane fibers, and cellulose fibers. These organic fibers have an appropriate specific gravity and are more easily dispersed uniformly throughout the positive electrode material. Therefore, it is believed that the movement of ions within the positive electrode material is further restricted by the organic fibers, thereby further reducing the incidence of voltage rise during high-temperature deep discharge cycles.

The density of the positive electrode material is preferably 3.7 g/cm ³ or less. In this case, the occurrence rate of voltage rise in the high-temperature deep discharge cycle becomes higher, but even in this range, the occurrence rate of voltage rise in the high-temperature deep discharge cycle can be reduced by including organic fibers in the positive electrode material so as to satisfy at least one of the above conditions (a) and (b).

From the viewpoint of easily securing a higher discharge capacity, the density of the positive electrode material is preferably 3.3 g/cm ³ or more.

The lead-acid battery may be either a valve regulated (sealed) lead-acid battery (VRLA type lead-acid battery) or a flooded (vented) lead-acid battery.

In this specification, the density of the positive electrode material, the number of organic fibers per unit volume, the ratio of organic fibers to the positive electrode material, the specific gravity of the organic fibers, and the oxygen element content in the organic fibers are determined for a positive electrode plate removed from a fully charged lead-acid battery.

(Explanation of terms)
(Positive electrode material)
The clad type positive plate includes a plurality of porous tubes, a metal core (spine) housed in each tube, a positive electrode material filled in the tube, and a current collector connecting one end of the longitudinal direction of the plurality of metal cores arranged in a row. The clad type positive plate may further include a linking seat (spine protector) connecting the plurality of tubes. In the clad type positive plate, the positive electrode material is the portion of the positive plate excluding the tube, the metal core, the current collector, and the linking seat. In the clad type positive plate, the metal core and the current collector may be collectively referred to as the positive electrode current collector. A member such as a mat may be attached to the positive plate. Such a member (also referred to as an attachment member) is used integrally with the positive plate, and is therefore included in the positive plate. In the case where the positive plate includes an attachment member (such as a mat), the positive electrode material is the portion of the positive plate excluding the tube, the positive electrode current collector, the linking seat, and the attachment member.

(Density of Positive Electrode Material)
The density of the positive electrode material is the density (g/cm ³ ) obtained by dividing the mass of the positive electrode material by the bulk volume of the positive electrode material obtained by mercury intrusion porosimetry. The density is obtained for a predetermined amount of unpulverized positive electrode material taken from a positive electrode plate removed from a lead-acid battery. The positive electrode material is taken from one tube located near the center of the positive electrode plate.

(Number of organic fibers per unit volume of positive electrode material)
The number of organic fibers per unit volume ( ^cm3 ) of the positive electrode material is a numerical value obtained by dividing the number of organic fibers contained in the positive electrode material by the bulk volume ( ^cm3 ) of the positive electrode material determined by mercury intrusion porosimetry. The number of organic fibers per unit volume ( ^cm3 ) of the positive electrode material is determined for a predetermined amount of unpulverized positive electrode material used to calculate the density.

(Proportion of organic fiber in the positive electrode material)
The ratio of organic fibers in the positive electrode material is the ratio (volume %) of the total volume of organic fibers contained in the positive electrode material to the bulk volume (cm ³ ) of the positive electrode material determined by mercury intrusion porosimetry. The ratio of organic fibers in the positive electrode material is determined for a predetermined amount of unpulverized positive electrode material used to calculate the density.

(fully charged)
The fully charged state of a flooded lead-acid battery is defined by JIS D 5301:2019. More specifically, the fully charged state is a state in which the lead-acid battery is charged in a water tank at 25°C ± 2°C with a current (A) 0.2 times the value (unit: Ah) listed as the rated capacity until the terminal voltage (V) during charging or the electrolyte density converted to a temperature of 20°C shows a constant value with three significant digits three consecutive times. In addition, in the case of a valve-regulated lead-acid battery, the fully charged state is a state in which constant current and constant voltage charging is performed at 2.23 V/cell in an air tank at 25°C ± 2°C with a current (A) 0.2 times the value (unit: Ah) listed as the rated capacity, and charging is terminated when the charging current during constant voltage charging becomes 0.005 times the value (A) listed as the rated capacity (unit: Ah).

A fully charged lead-acid battery is a lead-acid battery that has already been chemically prepared and is fully charged. A lead-acid battery can be fully charged immediately after chemical preparation, or after some time has passed since chemical preparation (for example, a lead-acid battery that is in use (preferably in the early stages of use) after chemical preparation can be fully charged). An early stage battery is a battery that has not been in use for very long and has hardly deteriorated at all.

(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 components of the lead-acid battery (such as 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. Each of the positive and negative plates has a lug for connecting to an external terminal. In some cases, such as a horizontal valve-regulated lead-acid battery, the lug is provided on the side of the plate so as to protrude laterally, but in most lead-acid batteries, the lug is usually provided on the top of the plate so as to protrude upward.

Below, the clad type positive electrode plate and lead acid battery according to an embodiment of the present invention will be described in terms of their main components, but the present invention is not limited to the following embodiments.

[Clad type positive electrode plate]
The clad type positive plate includes a plurality of porous tubes, a core metal housed in the tube, a positive electrode material filled in the tube, and a current collector that connects one end of the length direction of the plurality of core metals that are aligned in a row. Furthermore, the clad type positive plate usually includes a connecting seat that connects the plurality of tubes.

(Positive electrode material)
The positive electrode material includes organic fibers. The positive electrode material usually includes a positive electrode active material (specifically, at least one of lead dioxide and lead sulfate) that exhibits capacity through an oxidation-reduction reaction. The positive electrode material may include other additives as necessary.

The density of the positive electrode material is 3.75 g/cm ³ or less. In this case, the positive electrode material contains organic fibers, which causes a problem of voltage rise in the high-temperature deep discharge cycle, but by satisfying at least one of the above conditions (a) and (b), the voltage rise in the high-temperature deep discharge cycle can be reduced. The density of the positive electrode material may be 3.7 g/cm ³ or less. In this case, the occurrence rate of voltage rise in the high-temperature deep discharge cycle is further increased, but even in this case, by satisfying at least one of the above conditions (a) and (b), the voltage rise in the high-temperature deep discharge cycle can be reduced. From the viewpoint of easily securing a higher discharge capacity, the density of the positive electrode material is preferably 3.3 g/cm ³ or more.

The number of organic fibers per unit volume (cm ³ ) of the positive electrode material is 400 or more. From the viewpoint of further reducing the occurrence rate of voltage rise in high-temperature deep discharge cycles, the number of organic fibers per unit volume (cm ³ ) of the positive electrode material is preferably 800 or more. The number of organic fibers per unit volume (cm ³ ) of the positive electrode material is 15,000 or less, preferably 10,000 or less, and more preferably 7,500 or less or 7,200 or less. When the density of the positive electrode material is reduced, the binding force tends to decrease and cracks tend to occur easily. However, when the number of organic fibers is within such a range, a relatively high binding force can be secured in the positive electrode material, and cracks are reduced, so that a higher initial capacity can be secured. These lower and upper limits can be combined arbitrarily.

The ratio of organic fibers in the positive electrode material is 0.013% by volume or more. From the viewpoint of further reducing the occurrence rate of voltage rise in high-temperature deep discharge cycles, the ratio of organic fibers is preferably 0.026% by volume or more. The ratio of organic fibers is 0.5% by volume or less, preferably 0.32% by volume or less, and more preferably 0.25% by volume or less or 0.23% by volume or less. When the ratio of organic fibers is in such a range, a relatively high binding strength can be ensured in the positive electrode material, and cracking can be reduced, so that a higher initial capacity can be ensured. These lower and upper limits can be combined arbitrarily.

It is preferable that the organic fiber contains a fiber (hereinafter, sometimes referred to as the first fiber) having a specific gravity of 1.2 or more. In this case, since the first fiber has high dispersibility, the occurrence rate of voltage rise in the high-temperature deep discharge cycle can be further reduced. From the viewpoint of further reducing the occurrence rate of voltage rise in the high-temperature deep discharge cycle, the specific gravity of the first fiber is more preferably 1.25 or more or 1.26 or more. The specific gravity of the first fiber is, for example, 1.7 or less, and may be 1.6 or less or 1.5 or less. These lower and upper limits can be combined arbitrarily.

The organic fibers may contain fibers other than the first fibers (hereinafter, sometimes referred to as second fibers). However, from the viewpoint of ensuring high dispersibility of the organic fibers, it is preferable that the ratio of the first fibers to the total organic fibers contained in the positive electrode material is high. The ratio of the first fibers to the total organic fibers contained in the positive electrode material is preferably 60% by volume or more, more preferably 75% by volume or more, and even more preferably 90% by volume or more. The ratio of the first fibers to the total organic fibers is 100% by volume or less. The positive electrode material may contain only the first fibers as organic fibers. The second fibers are organic fibers having a specific gravity of less than 1.2 (for example, 0.8 to less than 1.2).

The organic fiber may contain oxygen elements. The content of oxygen elements in the organic fiber is, for example, 10,000 μmol/g or more, preferably 15,000 μmol/g or more, more preferably 17,000 μmol/g or more or 17,400 μmol/g or more, even more preferably 19,000 μmol/g or more or 20,000 μmol/g or more, and may be 20,800 μmol/g or more. When the content of oxygen elements is in such a range, the organic fiber is easily hydrogen-bonded with water molecules, so that the dispersibility of the organic fiber in the positive electrode material can be further increased, and the occurrence rate of voltage rise in high-temperature deep discharge cycles can be further reduced. The content of oxygen elements in the organic fiber is, for example, 50,000 μmol/g or less, and may be 40,000 μmol/g or less. From the viewpoint of ensuring higher durability of the organic fiber, the content of oxygen elements in the organic fiber is preferably 35,000 μmol/g or less. These lower and upper limits can be combined in any desired manner.

The average fiber diameter of the organic fibers is, for example, 1 μm or more, and may be 5 μm or more or 10 μm or more. When the average fiber diameter is in such a range, it is easy to ensure higher dispersibility of the organic fibers in the positive electrode material. The average fiber diameter of the organic fibers is, for example, 50 μm or less, and may be 30 μm or less or 20 μm or less. When the average fiber diameter is in such a range, it is easy to ensure higher conductivity of the positive electrode material. These lower and upper limits can be combined arbitrarily.

The average fiber length of the organic fibers is, for example, 0.1 mm or more, and may be 0.5 mm or more or 1 mm or more, or 1.5 mm or more or 2 mm or more. When the average fiber length is in such a range, it is easy to ensure higher dispersibility in the positive electrode material. The average fiber length of the organic fibers is, for example, 10 mm or less, and may be 6 mm or less. When the average fiber length is in such a range, it is easy to ensure higher dispersibility of the organic fibers and higher conductivity of the positive electrode material. These lower and upper limits can be combined arbitrarily.

The average fiber diameter of the organic fibers is the average value of the maximum diameters of 100 randomly selected organic fibers separated from the positive electrode material. The average fiber length of the organic fibers is the average value of the lengths of 100 randomly selected organic fibers separated from the positive electrode material.

Examples of organic fibers include polyester fibers, polyvinyl alcohol fibers (such as acetalized polyvinyl alcohol fibers), polyurethane fibers, acrylic fibers, polyacrylonitrile fibers, polyolefin fibers, polyvinyl chloride fibers, polystyrene fibers, polyamide fibers, and cellulose fibers. Cellulose fibers include not only fibers made of cellulose, but also fibers made of cellulose derivatives (e.g., cellulose ether, cellulose ester), rayon, and the like. The positive electrode material may contain one or more of these organic fibers. From the viewpoint of having a moderate specific gravity and being easy to ensure higher dispersibility in the positive electrode material, polyester fibers, acetalized polyvinyl alcohol fibers, polyurethane fibers, and cellulose fibers are preferred, and polyester fibers, acetalized polyvinyl alcohol fibers, and cellulose fibers are more preferred.

(others)
The core metal is made of, for example, a lead alloy. It is preferable to use a Pb-Sb based alloy for the core metal. The Pb-Sb based alloy may contain at least one of arsenic, selenium, bismuth, and tin, as necessary.

The current collecting section is made of, for example, a lead alloy. It is preferable to use a Pb-Sb alloy for the current collecting section. The Pb-Sb alloy may contain at least one of arsenic, selenium, bismuth, and tin, as necessary.

The porous tube is required only to accommodate the core metal inside and to hold the positive electrode material. The porous tube is usually a tubular fiber assembly. As the tubular fiber assembly, a fiber assembly in which fibers are woven into a tube shape may be used, or a tubular nonwoven or woven fabric may be used. Examples of fibers include inorganic fibers (such as glass fibers) and resin fibers. However, the fibers are not limited to these. The porous tube may be heat-treated as necessary. In addition, in the porous tube, the tubular fiber assembly may be impregnated with resin.

The length of the tube may be selected according to the length of the core. The outer diameter and thickness of the tube may be selected according to, for example, the shape of the core or the intended use of the lead-acid battery.

The linking seats are usually arranged at one end of the tube on the side of the current collector and the other end opposite the current collector. More specifically, in the longitudinal direction of the tube, one end of the tube on the side of the current collector is usually fixed to the current collector by an upper linking seat. The other end of the tube is sealed by a lower linking seat. The upper linking seat is usually formed by integrally molding resin so as to cover the upper part of the core and the current collector. The lower linking seat is usually made of resin, and is inserted into the opening at the other end of each tube. The current collector is usually formed with a lug for extracting electricity from the lead-acid battery.

The clad type positive plate is formed by accommodating multiple core metals, each of which has one end connected in the length direction by a current collector, in multiple tubes, and then filling the tubes with lead powder to form an unformed positive plate. The order of accommodating the core metals and filling the tubes with lead powder is not particularly limited. More specifically, the unformed positive plate is formed by accommodating multiple core metals in tubes, fixing one end of the multiple tubes to the current collector with an upper connecting member, filling the tubes with a mixture containing lead powder and organic fibers through the openings of the other ends of the tubes, and sealing the openings of the other ends of the multiple tubes with a lower connecting member. The lead powder contains at least lead monoxide. The lead powder may contain metallic lead. Also, lead powder and red lead may be used in combination.

The mixture may be filled into the tube by either a dry method or a wet method. For example, in the case of a dry method, the mixture in a dry state is filled into the tube as it is, and in the case of a wet method, a slurry-like mixture is filled. The mixture contains, for example, lead powder, organic fibers, and additives as necessary. For example, the slurry-like mixture is prepared by mixing lead powder, organic fibers, water, sulfuric acid, and additives as necessary. From the viewpoint of ensuring higher dispersibility of the organic fibers in the positive electrode material, it is preferable to use a slurry-like mixture. In particular, when the oxygen element content of the organic fibers is in the above-mentioned range, the organic fibers can be more uniformly dispersed in the slurry-like mixture by the action of moisture.

The unformed positive plate is then further formed. Lead dioxide is produced by the formation. Formation can be carried out, for example, by charging a plate group including unformed clad positive plates while they are immersed in an electrolyte containing sulfuric acid in a lead-acid battery container. This type of formation is called container formation. However, formation of the positive plate can also be carried out before assembling the plate group, and is not limited to container formation.

(Measurement of the density of the positive electrode material and analysis of the positive electrode material and its constituents)
The following describes a method for measuring the density of the positive electrode material, and a method for analyzing the positive electrode material or its components. Prior to measurement or analysis, a fully charged lead-acid battery is disassembled to obtain a positive electrode plate to be analyzed. The obtained positive electrode plate is washed with water and dried to remove the electrolyte in the positive electrode plate. The positive electrode material is then separated from the positive electrode plate to obtain an unpulverized sample (sample A). Sample A is pulverized into powder as necessary and subjected to analysis.

(1) Measurement of density of positive electrode material The density (bulk density) of unpulverized sample A is determined by mercury intrusion using a mercury porosimeter. More specifically, a predetermined amount of unpulverized sample A is first collected and its mass is measured. This sample A is placed in a measurement vessel of a mercury porosimeter, evacuated under reduced pressure, and then filled with mercury at a pressure of 0.5 psia to 0.55 psia (≒ 3.45 kPa to 3.79 kPa). The bulk volume of sample A is measured, and the measured mass of sample A is divided by the bulk volume to determine the density of the positive electrode material. The bulk volume is the volume of the measurement vessel minus the injected volume of mercury. An automatic porosimeter (Autopore IV9505) manufactured by Shimadzu Corporation is used as the mercury porosimeter.

(2) Analysis of Organic Fibers (2-1) Separation of Organic Fibers 5 g of sample A whose bulk volume was measured in (1) above was taken, and 50 mL of 20% by mass nitric acid and 20 mL of 300 g/L hydrogen peroxide solution were added to it. The resulting mixture was heated at 80°C ± 5°C until the lead components were completely dissolved. The resulting mixture was filtered to separate the solids. The resulting solids were dispersed in water to prepare a dispersion. Using a sieve, the organic fibers and components other than the organic fibers were separated from the dispersion.

(2-2) Number and ratio of organic fibers The number of all organic fibers separated in (2-1) above is counted and divided by the bulk volume (cm ³ ) of the positive electrode material measured in (1) to determine the number of organic fibers per unit volume of the positive electrode material.

(2-3) Specific Gravity of Organic Fiber A predetermined amount of the organic fiber separated in (2-1) above is collected, and the specific gravity of the fiber is determined by a density gradient tube method in accordance with JIS K7112-1999.

The total volume (cm 3 ) of the organic fibers contained in the collected sample A is calculated from the specific gravity of the fibers thus determined, the number of all the organic fibers calculated in ( ^2-2 ) above, and the mass of all the organic fibers. The volume-based ratio (volume %) of the total volume (cm 3 ) of the organic fibers to the bulk volume (cm ³ ) ^of the positive electrode material measured in (1) is determined. This ratio corresponds to the ratio (volume %) of the organic fibers in the positive electrode material.

(2-4) Content of oxygen element in organic fiber A predetermined amount of the organic fiber separated in (2-1) above is collected. The collected organic fiber is subjected to CHN/O elemental analysis using an organic microanalyzer to determine the amount of oxygen (μmol/g) per 1 g of organic fiber. As the organic microanalyzer, a CE-440 manufactured by Exeter Analytical, Inc. is used.

(2-5) Type of Organic Fiber The type (material) of the organic fiber is identified by combining information obtained from the pyrolysis GC-MS spectrum of the organic fiber separated in (2-1) above, and the infrared spectroscopy spectrum, ultraviolet-visible absorption spectrum, and NMR spectrum of the solution obtained by dissolving the organic fiber in a specific solvent.

(2-6) Average Fiber Diameter and Average Fiber Length of Organic Fibers From the organic fibers separated in (2-1) above, 100 fibers are randomly selected, and the maximum diameter of each fiber is measured and averaged to determine the average fiber diameter of the organic fibers.

Randomly select 100 fibers from the organic fibers separated in (2-1) above, and measure the length of each fiber. The fiber length is the length of the center line of the fiber. The average fiber length of the organic fibers is calculated by averaging the measured fiber lengths.

(Negative plate)
The negative electrode plate includes, for example, a negative electrode material and a current collector that holds the negative electrode material. The negative electrode material is the portion of the negative electrode plate excluding the current collector. A member such as a mat or pasting paper may be attached to the negative electrode plate. Such a member (also called an attachment member) is included in the negative electrode plate because it is used integrally with the negative electrode plate. When the negative electrode plate includes an attachment member (such as a mat or pasting paper), the negative electrode material is the portion of the negative electrode plate excluding the current collector and the attachment member.

Note that when a separator and mat are used together in the electrode plate assembly, and when a mat mainly made of nonwoven fabric is attached to the negative electrode plate, the thickness of the negative electrode plate includes the thickness of the mat. This is because the mat is used as one unit with the negative electrode plate. However, when a mat is attached to the separator, the thickness of the mat is included in the thickness of the separator.

The negative electrode current collector may be formed by casting lead (Pb) or a lead alloy, or by processing a lead sheet or a lead alloy sheet. Examples of processing methods include expanding and punching. It is preferable to use a lattice-shaped current collector as the negative electrode current collector because it is easy to support the negative electrode material.

The lead alloy used in the negative electrode current collector may be any of Pb-Sb alloy, Pb-Ca alloy, and Pb-Ca-Sn alloy. These lead or lead alloys may further contain at least one selected from the group consisting of Ba, Ag, Al, Bi, As, Se, Cu, etc. as an additive element. The negative electrode current collector may have a surface layer. The surface layer and the inner layer of the negative electrode current collector may have different compositions. The surface layer may be formed on a part of the negative electrode current collector. The surface layer may be formed on the ear portion of the negative electrode current collector. The surface layer of the ear portion may contain Sn or an Sn alloy.

The negative electrode material contains as an essential component a negative electrode active material (specifically, lead or lead sulfate) that develops capacity through an oxidation-reduction reaction, and may contain additives such as organic shrinkage inhibitors, carbonaceous materials, barium sulfate, and fibers (such as resin fibers). The additives are not limited to these. The negative electrode active material in a charged state is sponge-like lead, but an unformed negative electrode plate is usually made using lead powder. The lead powder preferably contains at least lead monoxide. The lead powder may further contain metallic lead.

An organic shrinkage inhibitor is an organic compound that has the function of suppressing the shrinkage of lead, which is the negative electrode active material, when a lead-acid battery is repeatedly charged and discharged. Organic shrinkage inhibitors are generally broadly classified into lignin compounds and synthetic organic shrinkage inhibitors. Synthetic organic shrinkage inhibitors can also be said to be organic shrinkage inhibitors other than lignin compounds. Examples of organic shrinkage inhibitors contained in the negative electrode material include lignin compounds and synthetic organic shrinkage inhibitors. The negative electrode material may contain one type of organic shrinkage inhibitor, or two or more types.

Lignin compounds include lignin and lignin derivatives. Lignin derivatives include lignin sulfonic acid or its salts (alkali metal salts (sodium salts, etc.)).

Synthetic organic shrink-proofing agents are organic polymers containing elemental sulfur. Examples of synthetic organic shrink-proofing agents include condensates of compounds having a sulfur-containing group and an aromatic ring with an aldehyde compound (aldehyde or its condensate (e.g., formaldehyde)). However, synthetic organic shrink-proofing agents are not limited to these. Among the sulfur-containing groups, sulfonic acid groups or sulfonyl groups, which are stable, are preferred. The sulfonic acid group may exist in an acid form or in a salt form such as a Na salt.

The content of the organic shrinkage inhibitor contained in the negative electrode material is, for example, 0.01% by mass or more, and may be 0.05% by mass or more. The content of the organic shrinkage inhibitor is, for example, 1.0% by mass or less, and may be 0.5% by mass or less. Here, the content of the organic shrinkage inhibitor contained in the negative electrode material is the content in the negative electrode material extracted from a fully charged lead-acid battery prepared using a method described below. These lower and upper limits can be combined in any combination.

Carbonaceous materials contained in the negative electrode material may include carbon black, graphite, hard carbon, soft carbon, etc. Examples of carbon black include acetylene black, furnace black, and lamp black. Furnace black also includes Ketjen Black (trade name). Graphite may be any carbonaceous material containing a graphite-type crystal structure, and may be either artificial graphite or natural graphite. The negative electrode material may contain one type of carbonaceous material, or two or more types.

The content of the carbonaceous material in the negative electrode material is, for example, 0.05% by mass or more, and may be 0.10% by mass or more. The content of the carbonaceous material is, for example, 5% by mass or less, and may be 3% by mass or less. These lower and upper limits can be combined in any manner.

(Barium Sulfate)
The content of barium sulfate in the negative electrode material is, for example, 0.05 mass% or more, and may be 0.10 mass% or more. The content of barium sulfate in the negative electrode material is, for example, 3 mass% or less, and may be 2 mass% or less. These lower and upper limits can be combined in any manner.

The negative electrode plate can be formed by applying or filling a negative electrode paste onto a negative electrode collector, maturing and drying the negative electrode paste to produce an unformed negative electrode plate, and then chemically forming the unformed negative electrode plate. The negative electrode paste is prepared, for example, by adding water and sulfuric acid (or an aqueous sulfuric acid solution) to lead powder and, if necessary, at least one selected from the group consisting of an organic shrinkage inhibitor, a carbonaceous material, barium sulfate, and other additives, and kneading the mixture. When maturing, it is preferable to mature the unformed negative electrode plate at a temperature higher than room temperature and at a high humidity.

Formation can be carried out by immersing a plate group including unformed negative plates in an electrolyte containing sulfuric acid in a lead-acid battery container and then charging the plate group. However, formation may also be carried out before assembling the lead-acid battery or the plate group. Formation produces spongy lead.

(Analysis of components of negative electrode material)
The method of analyzing the components of the negative electrode material will be described below. Prior to measurement or analysis, a fully charged lead-acid battery is disassembled to obtain a negative electrode plate to be analyzed. The obtained negative electrode plate is washed with water to remove sulfuric acid from the negative electrode plate. The washing is performed by pressing a pH test paper against the washed surface of the negative electrode plate until it is confirmed that the color of the test paper does not change. However, the washing time is within 2 hours. The washed negative electrode plate is dried at 60±5° C. for about 6 hours under a reduced pressure environment. If an attachment member is included in the negative electrode plate after drying, the attachment member is removed by peeling. Next, a sample (hereinafter referred to as sample B) is obtained by separating the negative electrode material from the negative electrode plate. Sample B is crushed as necessary and subjected to analysis.

(1) Analysis of organic shrink-preventing agent (1-1) Qualitative analysis of organic shrink-preventing agent in negative electrode material The ground sample B is immersed in a 1 mol/L aqueous sodium hydroxide solution to extract the organic shrink-preventing agent. Next, insoluble components are removed from the extract by filtration, and the resulting solution is desalted, concentrated, and dried. Desalting is performed using a desalting column, or by passing the solution through an ion exchange membrane, or by placing the solution in a dialysis tube and immersing it in distilled water. This is dried to obtain a powder sample of the organic shrink-preventing agent (hereinafter referred to as sample C).

The type of organic shrinkage inhibitor is identified by combining information obtained from the infrared spectrum measured using sample C of the organic shrinkage inhibitor obtained in this manner, the ultraviolet-visible absorption spectrum measured with an ultraviolet-visible spectrometer after diluting sample C with distilled water or the like, the NMR spectrum of the solution obtained by dissolving sample C in a specified solvent such as heavy water, or information obtained from pyrolysis GC-MS, which can obtain information on the individual compounds that make up the substance.

(1-2) Determination of the content of organic shrink-preventing agent in the negative electrode material As in (1-1) above, a solution is obtained by removing insoluble components from an extract containing the organic shrink-preventing agent by filtration. The ultraviolet-visible absorption spectrum of the obtained solution is measured. The content of the organic shrink-preventing agent in the negative electrode material is determined using the intensity of the peak characteristic of the organic shrink-preventing agent and a calibration curve prepared in advance.

When obtaining a lead-acid battery with an unknown content of organic shrink inhibitor and measuring the content of the organic shrink inhibitor, it may be impossible to use the same organic shrink inhibitor for the calibration curve because the structural formula of the organic shrink inhibitor cannot be precisely identified. In this case, a calibration curve is created using the organic shrink inhibitor extracted from the negative electrode of the battery and a separately available organic polymer whose ultraviolet-visible absorption spectrum, infrared spectrum, and NMR spectrum show similar shapes, and the content of the organic shrink inhibitor is measured using the ultraviolet-visible absorption spectrum.

(2) Quantitative Determination of Carbonaceous Material and Barium Sulfate 50 mL of 20% by mass nitric acid was added to 10 g of the crushed sample B, and the mixture was heated for about 20 minutes to dissolve the lead components as lead ions. The resulting solution was filtered to separate the carbonaceous material, barium sulfate, and other solids.

The obtained solid content is dispersed in water to obtain a dispersion, and then a sieve is used to remove components other than the carbonaceous material and barium sulfate (e.g., reinforcing material) from the dispersion. Next, the dispersion is subjected to suction filtration using a membrane filter whose mass has been measured in advance, and the membrane filter is dried together with the filtered sample in a dryer at 110°C ± 5°C. The filtered sample is a mixed sample of the carbonaceous material and barium sulfate. The mass of the membrane filter is subtracted from the total mass of the mixed sample after drying (hereinafter referred to as sample C) and the membrane filter to measure the mass (M _m ) of sample C. Then, sample C is placed in a crucible together with the membrane filter and incinerated at 1300°C or higher. The remaining residue is barium oxide. The mass of barium oxide is converted to the mass of barium sulfate to obtain the mass (M _B ) of barium sulfate. The mass of the carbonaceous material is calculated by subtracting the mass M _B from the mass M _m .

(Separator)
A separator may be disposed between the negative electrode plate and the positive electrode plate, and may be made of at least one material selected from a nonwoven fabric and a microporous membrane.

A nonwoven fabric is a mat of intertwined fibers without weaving them, and is mainly composed of fibers. For example, 60% or more by mass of the nonwoven fabric is made of fibers. Examples of fibers that can be used include glass fibers, polymer fibers (polyolefin fibers, acrylic fibers, polyester fibers (polyethylene terephthalate fibers, etc.)), and pulp fibers. Among these, glass fibers are preferred. The nonwoven fabric may contain components other than fibers (for example, acid-resistant inorganic powders, polymers as binders), etc.

On the other hand, a microporous membrane is a porous sheet mainly composed of components other than fiber components, and can be obtained, for example, by extruding a composition containing a pore-forming agent into a sheet, and then removing the pore-forming agent to form pores. The microporous membrane is preferably made of an acid-resistant material, and a microporous membrane mainly composed of a polymer component is preferable. The polymer component is preferably polyolefin (polyethylene, polypropylene, etc.). The pore-forming agent can be at least one selected from the group consisting of polymer powder and oil.

The separator may be made of, for example, only nonwoven fabric or only microporous membrane. If necessary, the separator may be a laminate of nonwoven fabric and microporous membrane, a laminate of different or the same materials, or a laminate of different or the same materials with recesses and protrusions interlocked.

The separator may be in the form of a sheet or a bag. A sheet-like separator may be sandwiched between the positive and negative plates. Alternatively, the electrode plates may be sandwiched between a folded sheet-like separator. In this case, the positive plate sandwiched between the folded sheet-like separator and the negative plate sandwiched between the folded sheet-like separator may be stacked, or one of the positive and negative plates may be sandwiched between the folded sheet-like separator and stacked with the other electrode plate. Alternatively, the sheet-like separator may be folded into a bellows shape, and the positive and negative plates may be sandwiched between the bellows-like separator so that the separator is interposed between them. When a separator folded like an accordion is used, the separator may be arranged so that the folded portion is along the horizontal direction of the lead-acid battery (for example, so that the folded portion is parallel to the horizontal direction), or so that the folded portion is along the vertical direction (for example, so that the folded portion is parallel to the vertical direction). In a separator folded like an accordion, recesses are formed alternately on both main surfaces of the separator. Since the upper portions of the positive and negative plates usually have lugs, when the separator is arranged so that the folded portion is along the horizontal direction of the lead-acid battery, the positive and negative plates are arranged only in the recesses on one main surface side of the separator (i.e., a double separator is interposed between the adjacent positive and negative plates). When the separator is arranged so that the folded portion is aligned with the vertical direction of the lead-acid battery, the positive electrode plate can be accommodated in the recess on one main surface side, and the negative electrode plate can be accommodated in the recess on the other main surface side (that is, a single layer of separator can be interposed between adjacent positive and negative electrode plates.) When a pouch-shaped separator is used, the pouch-shaped separator may accommodate either the positive or negative electrode plate.

(electrolyte)
The electrolyte is an aqueous solution containing sulfuric acid, which may be gelled as necessary.
The electrolyte may contain the above-mentioned polymer compound.

The electrolyte may contain cations (e.g., metal cations) and/or anions (e.g., anions other than sulfate anions (e.g., phosphate ions)) as necessary. Examples of metal cations include at least one selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions.

The specific gravity of the electrolyte in a fully charged lead-acid battery at 20°C is, for example, 1.20 or more, and may be 1.25 or more. The specific gravity of the electrolyte at 20°C is 1.35 or less, and may be 1.32 or less. These lower and upper limits can be combined in any manner.

(others)
The lead-acid battery can be obtained by a manufacturing method including a step of housing an electrode plate group and an electrolyte in a battery case. The electrode plate group is assembled by stacking a positive electrode plate, a negative electrode plate, and a separator so that the separator is interposed between the positive electrode plate and the negative electrode plate prior to housing in the battery case. The positive electrode plate, the negative electrode plate, the electrolyte, and the separator are each prepared prior to assembling the electrode plate group. The manufacturing method of the lead-acid battery may include a step of forming at least one of the positive electrode plate and the negative electrode plate, as necessary, after the step of housing the electrode plate group and the electrolyte in the battery case. One battery case usually houses one electrode plate group. Two or more electrode plate groups may be housed in one battery case as necessary. The lead-acid battery may include one battery case housing the electrode plate group and the electrolyte, or may include two or more battery cases. When two or more battery cases housing the electrode plate group and the electrolyte are provided, the electrode plate groups are usually connected in series.

Each plate in the plate group may be one or more. When the plate group has two or more positive plates, if the density of the positive electrode material for at least one positive plate is within the above-mentioned range and at least one of the above conditions (a) and (b) is satisfied, the generation of resistance components for this positive plate is reduced, and the effect of reducing the occurrence rate of voltage rise in the high-temperature deep discharge cycle in the lead-acid battery is obtained according to the number of such positive plates. From the viewpoint of further reducing the occurrence rate of voltage rise in the high-temperature deep discharge cycle, it is preferable that 50% or more (more preferably 80% or more or 90% or more) of the number of positive plates included in the plate group are positive plates that satisfy the above-mentioned conditions. Of the positive plates included in the plate group, the ratio of positive plates whose density of the positive electrode material is within the above-mentioned range and that satisfy the above-mentioned conditions is 100% or less. It is particularly preferable that all of the positive plates included in the plate group have a density of the positive electrode material within the above-mentioned range and satisfy the above-mentioned conditions.

When a lead-acid battery has two or more plate groups, at least some of the plate groups may have positive plates whose positive electrode material has a density in the above-mentioned range and satisfy the above-mentioned conditions. From the viewpoint of further reducing the occurrence rate of voltage rise in the high-temperature deep discharge cycle, it is preferable that 50% or more (more preferably 80% or more or 90% or more) of the plate groups included in the lead-acid battery have plate groups whose positive electrode material has a density in the above-mentioned range and satisfy the above-mentioned conditions. The ratio of the plate groups included in the lead-acid battery that have plate groups whose positive electrode material has a density in the above-mentioned range and satisfy the above-mentioned conditions is 100% or less. It is preferable that all of the plate groups included in the lead-acid battery have positive plates whose positive electrode material has a density in the above-mentioned range and satisfy the above-mentioned conditions.

Fig. 1 is a perspective view showing an example of a lead-acid battery according to an embodiment of the present invention with the cover removed. Fig. 2A is a front view of the lead-acid battery shown in Fig. 1, and Fig. 2B is a schematic cross-sectional view of the section taken along line IIB-IIB in Fig. 2A as viewed from the direction of the arrows.
The lead-acid battery 1 includes a battery case 10 that contains an electrode plate group 11 and an electrolyte 12. The electrode plate group 11 is formed by stacking a plurality of negative electrode plates 2 and clad type positive electrode plates 3 with a separator 4 interposed therebetween. Here, a state in which a sheet-like separator 4 is sandwiched between the negative electrode plates 2 and the clad type positive electrode plates 3 is shown, but the shape of the separator is not particularly limited.

The upper part of each of the multiple negative electrode plates 2 is provided with an upwardly protruding current collecting lug (not shown). The upper part of each of the multiple clad type positive electrode plates 3 is also provided with an upwardly protruding current collecting lug (not shown). The lugs of the negative electrode plates 2 are connected and integrated by a negative electrode strap 5a. Similarly, the lugs of the clad type positive electrode plates 3 are connected and integrated by a positive electrode strap 5b. The lower end of the negative electrode pole 6a is fixed to the upper part of the negative electrode strap 5a, and the lower end of the positive electrode pole 6b is fixed to the upper part of the positive electrode strap 5b.

The clad positive electrode plate for a lead-acid battery and the lead-acid battery according to one aspect of the present invention are summarized below.

(1) A clad type positive electrode plate for a lead-acid battery,
The positive electrode plate includes a plurality of porous tubes, metal cores housed in the tubes, a positive electrode material filled in the tubes, and a current collecting portion connecting one end of the length direction of the plurality of metal cores arranged in a row,
The positive electrode material includes organic fibers,
The density of the positive electrode material is 3.75 g/ ^cm3 or less,
The clad type positive electrode plate for a lead-acid battery, wherein the number of the organic fibers per unit volume (cm ³ ) of the positive electrode material is 400 or more and 15,000 or less.

(2) In the above (1), the number of the organic fibers per unit volume of the positive electrode material may be 800 or more.
(3) In the above (1) or (2), the number of the organic fibers per unit volume of the positive electrode material may be 10,000 or less, 7,500 or less, or 7,200 or less.

(4) In any one of (1) to (3) above, the ratio of the organic fibers to the positive electrode material may be 0.013 volume % or more and 0.5 volume % or less.

(5) A clad type positive electrode plate for a lead-acid battery,
The positive electrode plate includes a plurality of porous tubes, metal cores housed in the tubes, a positive electrode material filled in the tubes, and a current collecting portion connecting one end of the length direction of the plurality of metal cores arranged in a row,
The positive electrode material includes organic fibers,
The density of the positive electrode material is 3.75 g/ ^cm3 or less,
A clad type positive electrode plate for a lead-acid battery, wherein a ratio of the organic fibers to the positive electrode material is 0.013 volume % or more and 0.5 volume % or less.

(6) In any one of (1) to (5) above, the ratio of the organic fibers to the positive electrode material may be 0.026 volume percent or more.

(7) In any one of (1) to (6) above, the ratio of the organic fibers to the positive electrode material may be 0.32 vol.% or less, 0.25 vol.% or less, or 0.23 vol.% or less.

(8) In any one of (1) to (7) above, the organic fiber may include a fiber (first fiber) having a specific gravity of 1.2 or more.

(9) In (8) above, the specific gravity of the first fiber may be 1.25 or more or 1.26 or more.

(10) In (8) or (9) above, the specific gravity of the first fiber may be 1.7 or less, 1.6 or less, or 1.5 or less.

(11) In any one of (8) to (10) above, the ratio of the first fiber to the total organic fibers contained in the positive electrode material may be 60 volume% or more, 75 volume% or more, or 90 volume% or more.

(12) In (11) above, the ratio of the first fiber may be 100 volume % or less.

(13) In any one of (8) to (10) above, the positive electrode material may contain only the first fiber as the organic fiber.

(14) In any one of (1) to (13) above, the organic fiber may contain an oxygen element.

(15) In (14) above, the content of the oxygen element in the organic fiber may be 10,000 μmol/g or more, 15,000 μmol/g or more, 17,000 μmol/g or more, 17,400 μmol/g or more, 19,000 μmol/g or more, 20,000 μmol/g or more, or 20,800 μmol/g or more.

(16) In (14) or (15) above, the content of the oxygen element in the organic fiber may be 50,000 μmol/g or less, 40,000 μmol/g or less, or 35,000 μmol/g or less.

(17) In any one of (1) to (16) above, the average fiber diameter of the organic fibers may be 1 μm or more, 5 μm or more, or 10 μm or more.

(18) In any one of (1) to (17) above, the average fiber diameter of the organic fibers may be 50 μm or less, 30 μm or less, or 20 μm or less.

(19) In any one of (1) to (18) above, the average fiber length of the organic fibers may be 0.1 mm or more, 0.5 mm or more, 1 mm or more, 1.5 mm or more, or 2 mm or more.

(20) In any one of (1) to (19) above, the average fiber length of the organic fibers may be 10 mm or less, or 6 mm or less.

(21) In any one of (1) to (20) above, the organic fibers may include at least one selected from the group consisting of polyester fibers, acetalized polyvinyl alcohol fibers, polyurethane fibers, and cellulose fibers.

(22) In any one of the above (1) to (21), the density of the positive electrode material may be 3.7 g/ ^cm3 or less.

(23) In any one of the above (1) to (22), the density of the positive electrode material may be 3.3 g/ ^cm3 or more.

(24) A lead-acid battery,
The lead-acid battery includes at least one electrode plate group and an electrolyte,
The plate group includes at least one clad type positive plate according to any one of (1) to (23) above, at least one negative plate, and a separator interposed between the clad type positive plate and the negative plate. A lead-acid battery.

(25) In (24) above, the negative electrode plate may contain a negative electrode material.

(26) In the above (25), the negative electrode material may contain an organic shrinkage inhibitor.

(27) In the above (26), the content of the organic shrinkage inhibitor in the negative electrode material may be 0.01 mass% or more, or 0.05 mass% or more.

(28) In the above (26) or (27), the content of the organic shrinkage inhibitor in the negative electrode material may be 1.0 mass% or less, or 0.5 mass% or less.

(29) In any one of (25) to (28) above, the negative electrode material may contain a carbonaceous material.

(30) In the above (29), the content of the carbonaceous material in the negative electrode material may be 0.05 mass% or more, or 0.10 mass% or more.

(31) In the above (29) or (30), the content of the carbonaceous material in the negative electrode material may be 5 mass% or less, or 3 mass% or less.

(32) In any one of (25) to (31) above, the negative electrode material may contain barium sulfate.

(33) In the above (32), the content of the barium sulfate in the negative electrode material may be 0.05 mass% or more, or 0.10 mass% or more.

(34) In the above (32) or (33), the content of the barium sulfate in the negative electrode material may be 3% by mass or less, or 2% by mass or less.

(35) In any one of (25) to (34) above, the specific gravity of the electrolyte in the lead-acid battery in a fully charged state at 20°C may be 1.20 or more, or 1.25 or more.

(36) In any one of (25) to (35) above, the specific gravity of the electrolyte in the lead-acid battery in a fully charged state at 20°C may be 1.35 or less, or 1.32 or less.

[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.

Lead-acid batteries E1 to E19, R1 to R2, and C1 to C6
(1) Preparation of Positive Electrode Plate A clad type positive electrode plate is prepared by the following procedure.
First, 15 cores, each having one end in the length direction integrated with a current collector having an ear, are housed in each of 15 tubes. The current collector and one end in the length direction of the tube on the current collector side are covered with resin so that the ear is exposed, forming a resin upper link. The material of the cores and current collector is a Pb-Sb alloy, and each core is 295 mm long. A porous tube made of glass fiber, 310 mm long and 9.5 mm in outer diameter, is used as the tube.

A positive electrode slurry prepared by kneading lead powder (containing 80% by weight of lead oxide and 20% by weight of metallic lead), red lead, the organic fibers shown in the table, water, and dilute sulfuric acid is filled into the opening at the other end of the tube in the longitudinal direction. The opening at the other end of the tube is then sealed with a lower connecting member and dried. In this way, an unformed clad type positive electrode plate is produced. The width of the produced positive electrode plate is 143 mm.

The mass ratio of lead powder to red lead is 9:1. The amount of organic fiber added is adjusted so that the number of organic fibers per unit volume (cm ³ ) of the positive electrode material or the ratio of organic fibers to the positive electrode material determined by the above-mentioned procedure is the value shown in the table. The filling amount of the positive electrode slurry is adjusted so that the density of the positive electrode material determined by the above-mentioned procedure is the value shown in the table. The average fiber diameter of the organic fibers determined by the above-mentioned procedure is 14 μm, and the average fiber length is 2 mm.

(2) Preparation of negative electrode plate Lead powder (containing 80% by mass of lead oxide and 20% by mass of metallic lead), 0.3% by mass of carbon black, 0.1% by mass of organic shrinkage inhibitor (sodium lignin sulfonate), and 1.5% by mass of barium sulfate are mixed with water and dilute sulfuric acid to prepare a negative electrode paste. An unformed negative electrode plate (thickness 4.5 mm) is prepared by filling a cast grid (thickness 4.4 mm) made of Sb-based alloy as a negative electrode current collector with the negative electrode paste and drying it. The amount of the negative electrode paste filled is adjusted so that the mass of the negative electrode active material contained in the negative electrode material in one negative electrode plate after formation is 750±6 g in terms of Pb element. The length of the negative electrode plate is the same as the length of the tube of the positive electrode plate, and the width of the negative electrode plate is the same as the width of the positive electrode plate.

(3) Preparation of lead-acid battery Four unformed negative plates and three unformed clad positive plates having the same core shape are alternately stacked with a separator between them to form an electrode assembly as shown in Fig. 2B. A microporous polypropylene film having ribs on one surface is used as the separator. The separator is arranged so that the ribs are located on the positive plate side.

The plate group is placed in a polypropylene battery case, dilute sulfuric acid with a specific gravity of 1.280 at 20°C is poured into it, and a lid is glued to the opening of the battery case. Chemical formation is carried out while the battery case is kept in a water tank at 30°C ± 2°C. In this way, lead-acid batteries E1 to E19, C1 to C6, and R1 to R2 are obtained, each with a rated voltage of 2V and a rated capacity (5-hour rate) of 165 Ah. The lead-acid batteries are brought to a nearly fully charged state by chemical formation.

(4) Evaluation (a) Occurrence rate of voltage rise in high-temperature deep discharge cycle A high-temperature deep discharge cycle test is performed using a lead-acid battery after formation in a fully charged state. In the high-temperature deep discharge cycle test, the lead-acid battery is discharged for 3 hours at a current of 41.25 A while being held in a water tank at a temperature of 75°C ± 5°C, and is charged for 5.44 hours at a current of 29.7 A. This discharge and charge cycle is counted as one cycle, and the charge and discharge cycle is repeated 200 times.

Among 200 charge/discharge cycles, the percentage of cycles in which the time it takes for the lead-acid battery terminal voltage to reach 2.4 V during charging is less than 3.5 hours is determined. This percentage corresponds to the occurrence rate of voltage rise during charging in the high-temperature deep discharge cycle test, and serves as an index for evaluating voltage rise during high-temperature deep discharge cycles.

(b) Initial Capacity For the lead-acid batteries C1, E1, and E14 to E19, the initial capacity is measured by the following procedure.
First, the lead-acid battery after chemical formation in a fully charged state is discharged to 70 V at a current of 33 A while being held in a water tank at a temperature of 30° C.±2° C., and then is charged at a current of 33 A until the amount of electricity becomes 135% of the amount of electricity discharged. It is again discharged to 1.70 V at a current of 33 A, and the discharge capacity at this time is measured and regarded as the initial capacity. The initial capacity is evaluated as a ratio when the initial capacity of the lead-acid battery C1 is regarded as 100%.
The results are shown in Tables 1 to 4 and FIGS.

As shown in Table 1 and FIG. 3, in the positive electrode material of the clad type positive plate, when the density is 3.75 g/cm ³ or less, the occurrence rate of voltage rise in the high temperature deep discharge cycle increases (comparison between C1 to C4 and C5 to C6). In contrast, by including organic fibers in the positive electrode material, the occurrence rate of voltage rise in the high temperature deep discharge cycle when the density is 3.75 g/cm ³ or less can be significantly reduced (comparison between C1 to C4 and E1 to E4). This is thought to be because the presence of organic fibers in the positive electrode material hinders the movement of ions, making it difficult to generate resistance components. In addition, when the density of the positive electrode material exceeds 3.75 g/cm ³ , there is no difference in the occurrence rate of voltage rise in the high temperature deep discharge cycle depending on the presence or absence of organic fibers (comparison between C5 to C6 and R1 to R2). In other words, there is no problem of voltage rise in the high temperature deep discharge cycle.

As shown in Table 2, Figures 4 and 5, the effect of reducing voltage rise during high-temperature deep discharge cycles can be obtained when the number of organic fibers per unit volume ( ^cm3 ) of the positive electrode material is 400 or more and/or the ratio of organic fibers to the positive electrode material is 0.013 volume% or more. From the viewpoint of further reducing the occurrence rate of voltage rise during high-temperature deep discharge cycles, it is preferable that the number of organic fibers per unit volume ( ^cm3 ) of the positive electrode material is 800 or more and/or the ratio of organic fibers to the positive electrode material is 0.026 volume% or more.

As shown in Table 3 and Figure 6, when the specific gravity of the organic fiber is 1.2 or more (preferably 1.25 or more or 1.26 or more), the occurrence rate of voltage rise during high-temperature deep discharge cycles can be further reduced.

As shown in Table 3 and Figure 7, when the oxygen element content of the organic fiber is 15,000 μmol/g or more (preferably 17,000 μmol/g or more or 17,400 μmol/g or more), the occurrence rate of voltage rise during high-temperature deep discharge cycles can be further reduced.

These effects are thought to be due to the increased dispersion of organic fibers in the positive electrode material, which further restricts the movement of ions.

As shown in Table 4 and Figure 8, from the viewpoint of easily securing a higher initial capacity, the number of organic fibers per unit volume of the positive electrode material is preferably 7500 or less or 7200 or less. From the same viewpoint, the ratio of organic fibers in the positive electrode material is preferably 0.25 vol.% or less or 0.23 vol.% or less (Table 4 and Figure 9).

The clad positive plate according to one aspect of the present invention can be suitably used in long-life industrial lead-acid batteries or lead-acid batteries for electric vehicles (such as forklifts). The clad positive plate may also be used in lead-acid batteries for vehicles such as automobiles and motorcycles. However, these applications are merely examples, and the applications of the clad positive plate and the lead-acid battery including the same are not limited to these.

1: Lead-acid battery 2: Negative electrode plate 3: Positive electrode plate 4: Separator 5a: Negative electrode strap 5b: Positive electrode strap 6a: Negative electrode pole 6b: Positive electrode pole 10: Battery case 11: Plate group 12: Electrolyte

Claims (7)

A clad type positive electrode plate for a lead-acid battery,
The positive electrode plate includes a plurality of porous tubes, metal cores housed in the tubes, a positive electrode material filled in the tubes, and a current collecting portion connecting one end of the length direction of the plurality of metal cores arranged in a row,
The positive electrode material includes organic fibers,
The density of the positive electrode material is 3.75 g/ ^cm3 or less,
The number of the organic fibers per unit volume (cm ³ ) of the positive electrode material is 400 or more and 15,000 or less. 2. The clad type positive plate for a lead-acid battery according to claim 1, wherein a ratio of the organic fiber to the positive electrode material is 0.013 volume % or more and 0.5 volume % or less. A clad type positive electrode plate for a lead-acid battery,
The positive electrode plate includes a plurality of porous tubes, metal cores housed in the tubes, a positive electrode material filled in the tubes, and a current collecting portion connecting one end of the length direction of the plurality of metal cores arranged in a row,
The positive electrode material includes organic fibers,
The density of the positive electrode material is 3.75 g/cm ³ is as follows:
A clad type positive electrode plate for a lead-acid battery, wherein a ratio of the organic fiber to the positive electrode material is 0.013 volume % or more and 0.5 volume % or less. The clad type positive electrode plate for a lead-acid battery according to any one of claims 1 to 3, wherein the organic fibers include fibers having a specific gravity of 1.2 or more. The organic fiber contains an oxygen element,
The clad type positive electrode plate for a lead acid battery according to any one of claims 1 to 4, wherein the content of the oxygen element in the organic fiber is 10000 μmol/g or more. The clad type positive electrode plate for a lead-acid battery according to any one of claims 1 to 5, wherein the organic fiber includes at least one selected from the group consisting of polyester fiber, acetalized polyvinyl alcohol fiber, polyurethane fiber, and cellulose fiber. A lead-acid battery,
The lead-acid battery includes at least one electrode plate group and an electrolyte;
The plate group comprises at least one clad type positive plate according to any one of claims 1 to 6, at least one negative plate, and a separator interposed between the clad type positive plate and the negative plate. A lead-acid battery.

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