JP7651906B2 - Lead-acid battery - Google Patents

Description

The present invention relates to a lead-acid battery.

Lead-acid batteries are used in a variety of applications, including automotive and industrial use. Lead-acid batteries include positive and negative electrode plates and a separator disposed between them. Separators for lead-acid batteries are required to have a variety of performance characteristics. For this reason, lead-acid batteries using a variety of separators have been proposed.

Patent document 1 (JP Patent Publication 10-40896) discloses "a sealed lead-acid battery characterized by using, as a separator, a mat made of fine glass fibers and a synthetic fiber nonwoven fabric that has been hydrophilically treated."

Patent Document 2 (International Publication No. WO 2013/046498) discloses a "battery separator structure comprising a laminate of an acrylonitrile-based fiber nonwoven separator and a glass fiber mat separator, the acrylonitrile-based fiber nonwoven separator containing at least acrylonitrile-based fine fibers having a diameter of 0.5 μm to 2.0 μm."

Japanese Patent Application Publication No. 10-40896 International Publication No. 2013/046498

However, the conventional lead-acid batteries described above sometimes had insufficient cycle characteristics. In particular, the conventional lead-acid batteries showed a significant decrease in cycle life when they underwent charge-discharge cycles involving high-rate discharge.

One aspect of the present invention relates to a lead-acid battery. The lead-acid battery includes a plurality of positive and negative electrode plates arranged alternately, a separator, and an electrolyte, the separator including a first separator including a nonwoven fabric made of organic fibers and a second separator including a glass fiber mat, the nonwoven fabric and the glass fiber mat are arranged so as to be laminated between the positive electrode plate and the negative electrode plate adjacent to the positive electrode plate, and the pores Pf of the nonwoven fabric are filled with water. When measured by silver porosimetry, the ratio of the volume of the pores Pf with diameters in the range of 0.01 μm to 3.2 μm to the volume of all the pores Pf is Vf (%), and when the pores Pp of the positive electrode plate are measured by mercury porosimetry, the ratio of the volume of the pores Pp with diameters in the range of 0.01 μm to 3.2 μm to the volume of all the pores Pp is Vp (%), and the ratio Vf/Vp is in the range of 0.10 to 0.50.

The present invention provides a lead-acid battery with good, specified cycle characteristics.

1 is a cross-sectional view showing a schematic configuration of a lead-acid battery according to one embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of an example of an electrode plate group used in the lead-acid battery shown in FIG. 1 . 2 is a cross-sectional view showing a schematic configuration of another example of an electrode plate group used in the lead-acid battery shown in FIG. 1 . FIG. 1 is a graph showing characteristics of a lead-acid battery manufactured in an example.

The following describes an embodiment of the present invention using examples, but the present invention is not limited to the examples described below. In the following description, specific numerical values and materials may be exemplified, but other numerical values and materials may be applied as long as the effects of the present invention are obtained. In this specification, the range described as "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to A and less than or equal to B."

(Lead-acid battery)
The lead-acid battery according to this embodiment includes a plurality of positive and negative plates arranged alternately, a separator, and an electrolyte. The separator includes a first separator including a nonwoven fabric made of organic fibers, and a second separator including a glass fiber mat. The nonwoven fabric may be referred to as "nonwoven fabric (F)" below. The nonwoven fabric (F) and the glass fiber mat are arranged so as to be laminated between the positive plate and the negative plate adjacent to the positive plate. When the pores Pf of the nonwoven fabric are measured by mercury intrusion porosimetry, the ratio of the volume of the pores Pf having a diameter in the range of 0.01 μm to 3.2 μm to the volume of all the pores Pf is Vf (%). When the pores Pp of the positive plate are measured by mercury intrusion porosimetry, the ratio of the volume of the pores Pp having a diameter in the range of 0.01 μm to 3.2 μm to the volume of all the pores Pp is Vp (%). The ratio Vf/Vp is in the range of 0.10 to 0.50.

The "volume of all pores" is the volume measured by mercury intrusion porosimetry and corresponds to the sum of the individual volumes of all pores. The "volume of pores with diameters in the range of 0.01 μm to 3.2 μm" is the volume measured by mercury intrusion porosimetry and corresponds to the sum of the individual volumes of pores determined to have diameters in the range of 0.01 μm to 3.2 μm.

The positive electrode plate includes a positive electrode collector and a positive electrode material arranged around the positive electrode collector. When the pore distribution of the positive electrode plate is measured, the pores of the positive electrode material are measured. Therefore, the pores Pp of the positive electrode plate can be interpreted as the pores Pp of the positive electrode material contained in the positive electrode plate.

Nonwoven fabrics and glass fiber mats are formed by intertwining fine fibers. As a result, nonwoven fabrics and glass fiber mats contain many tiny voids. Such tiny voids can be considered as pores. In other words, nonwoven fabrics and glass fiber mats have a porous structure that contains many pores of different sizes. By performing pore distribution analysis on such nonwoven fabrics and glass fiber mats, information on the distribution of pore diameters can be obtained.

The glass fiber mat is a mat made of glass fibers. The glass fiber mat may be called an absorbent glass mat (AGM: Absorbed Glass Mat, or Absorbent Glass Mat). Therefore, in this specification, the glass fiber mat can be read as an absorbent glass mat.

Separators are required to prevent short circuits and retain the electrolyte. Glass fiber mats have a high porosity and are highly capable of retaining electrolyte. However, glass fiber mats alone are insufficient in preventing short circuits. For this reason, it has been proposed to use a combination of glass fiber mats and synthetic fiber nonwoven fabric.

In the lead-acid batteries described in Patent Documents 1 and 2, a synthetic fiber nonwoven fabric and a glass fiber mat are used as separators. Comparing synthetic fiber nonwoven fabric and glass fiber mat, the glass fiber mat generally has a higher affinity with the electrolyte. Therefore, when a synthetic fiber nonwoven fabric and a glass fiber mat are laminated and used, a large amount of electrolyte is held in the glass fiber mat, while the amount of electrolyte held in the synthetic fiber nonwoven fabric tends to be small. Such electrolyte imbalance causes various deteriorations in characteristics, such as an increase in the internal resistance of the lead-acid battery and a decrease in cycle life. In order to suppress the electrolyte imbalance, in the lead-acid batteries described in Patent Documents 1 and 2, an acrylonitrile fiber nonwoven fabric or a hydrophilically treated synthetic fiber nonwoven fabric is used as a synthetic fiber nonwoven fabric with a high affinity with the electrolyte.

The idea disclosed in Patent Documents 1 and 2 is to improve the hydrophilicity of a synthetic fiber nonwoven fabric by changing the material of the nonwoven fabric. However, such a method may not fully meet the current demands placed on lead-acid batteries. For example, a method of improving the hydrophilicity of a synthetic fiber nonwoven fabric by changing the material of the nonwoven fabric may not produce the expected effect when the electrolyte is reduced and an imbalance in the electrolyte occurs due to the use of the lead-acid battery. In such a situation, as a result of investigation, the inventors of the present application have discovered a technology for improving the characteristics of a lead-acid battery by an approach completely different from the conventional one. The present invention is based on this new knowledge.

When conventional separators containing synthetic fiber nonwoven fabric and glass fiber mats are used, the cycle characteristics are sometimes insufficient. During charge/discharge cycles, the expansion and contraction of the synthetic fiber nonwoven fabric and gas generation from the electrodes tend to reduce the electrolyte in the synthetic fiber nonwoven fabric. As a result of investigations, the inventors of the present application found that the reduction in electrolyte in the synthetic fiber nonwoven fabric is influenced by the structure of the positive electrode plate.

Furthermore, the inventors of the present application have focused on the proportion of fine pores, and have found that by making the ratio Vf/Vp of the proportion Vf of fine pores in the nonwoven fabric (F) to the proportion Vp of fine pores in the positive electrode plate higher than that of conventional lead-acid batteries, it is possible to improve the charge/discharge cycle characteristics. Specifically, they have found that by setting the ratio Vf/Vp in the range of 0.10 to 0.50, it is possible to significantly improve the characteristics (cycle life, etc.) of lead-acid batteries. The reason for this is currently unclear, but it can be considered as follows.

It is believed that the smaller the pores, the less fluid the electrolyte filled in the fine pores becomes. Therefore, the electrolyte filled in the fine pores is less likely to move from the filled area and is less likely to be absorbed into the pores in the positive plate. As a result, the amount of electrolyte in the nonwoven fabric (F) is maintained, and the deterioration of the performance of the lead-acid battery can be suppressed. For example, by maintaining the amount of electrolyte in the nonwoven fabric (F), the increase in internal resistance can be suppressed. By suppressing the increase in internal resistance, the increase in IR drop during high-rate discharge is suppressed, and the discharge capacity during high-rate discharge is maintained. Therefore, suppressing the increase in internal resistance is particularly effective in improving cycle characteristics accompanying high-rate discharge.

The ratio Vf/Vp is 0.10 or more, and may be 0.12 or more, 0.15 or more, 0.17 or more, or 0.20 or more. By increasing the ratio Vf/Vp, the cycle life with high rate discharge can be improved. The ratio Vf/Vp is 0.50 or less, and may be 0.33 or less, 0.27 or less, 0.20 or less, or 0.17 or less. By decreasing the ratio Vf/Vp, the first separator including the nonwoven fabric (F) can be easily manufactured, and the manufacturing cost can be reduced. These lower and upper limits can be arbitrarily combined as long as there is no contradiction. For example, the ratio Vf/Vp may be in the range of 0.10 to 0.50, the range of 0.12 to 0.50, the range of 0.15 to 0.50, the range of 0.17 to 0.50, or the range of 0.20 to 0.50. In these ranges, the upper limit may be replaced with 0.33, 0.27, 0.20, or 0.17, as long as the upper limit is not less than or equal to the lower limit.

The ratio Vf/Vp is preferably in the range of 0.12 to 0.33, and more preferably in the range of 0.17 to 0.33. These configurations can particularly improve the life characteristics in charge-discharge cycles involving high-rate discharge.

The ratio Vf/Vp can be changed by changing Vf and/or Vp. The ratio Vf may be changed by changing the diameter of the organic fibers constituting the nonwoven fabric (F) and/or the surface density (mass per unit area) of the nonwoven fabric (F). It is possible to increase Vf by decreasing the diameter of the organic fibers, and it is possible to decrease Vf by increasing the diameter of the organic fibers. It is also possible to increase Vf by increasing the surface density of the nonwoven fabric (F), and it is possible to decrease Vf by decreasing the surface density.

The proportion Vp can be changed by the manufacturing conditions of the positive electrode plate. For example, Vp can be changed by changing the manufacturing conditions of the positive electrode paste used in manufacturing the positive electrode plate, or the conditions for applying and drying the positive electrode paste. For example, the proportion of liquid in the positive electrode paste may be changed. The liquid in the positive electrode paste is removed when the positive electrode plate is formed. Therefore, Vp can be increased by increasing the proportion of liquid in the positive electrode paste. Alternatively, Vp can be changed by changing the particle size of the material (e.g., lead) used in the positive electrode paste. In general, Vp tends to decrease when the particle size of the material used in the positive electrode paste is increased.

The Vf (%) of the nonwoven fabric (F) may be 8.3% or more, 9.0% or more, 11.0% or more, 14.0% or more, or 16.0% or more. Vf may be 30.0% or less, 26.0% or less, or 22.0% or less. These lower and upper limits may be combined in any manner as long as there is no contradiction. For example, Vf may be in the range of 8.3 to 30.0%. The lower and/or upper limit of this range may be replaced with the lower and/or upper limit described above.

The Vp (%) of the positive plate may be 60.0% or more, or 70.0% or more. Vp may be 99.0% or less, or 92.0% or less. These lower and upper limits may be combined in any way as long as there is no contradiction. For example, Vp may be in the range of 60.0-99.0%, 60.0-92.0%, 70.0-99.0%, or 70.0-92.0%.

The average thickness of the nonwoven fabric (F) may be in the range of 0.05 mm to 0.5 mm (for example, in the range of 0.1 mm to 0.3 mm). By making the average thickness of the nonwoven fabric (F) 0.1 mm or more, the effect of preventing short circuits can be enhanced. By making the average thickness of the nonwoven fabric (F) 0.3 mm or less, the internal resistance can be reduced.

Each of the positive plates may include a positive electrode current collector including an expanded lattice portion (first expanded lattice portion), and each of the negative plates may include a negative electrode current collector including an expanded lattice portion (second expanded lattice portion). The first expanded lattice portion and the second expanded lattice portion may each be a lattice body without a frame around it. Since the expanded lattice portion is prone to bending, it is particularly important to prevent short circuits. In particular, a lattice body without a frame around it is prone to short circuits around the positive and negative plates due to the expansion of the electrode material. Therefore, when a current collector including an expanded lattice portion is used, it is preferable to house the positive and/or negative plates in a bag made of nonwoven fabric (F).

The organic fibers may include split fibers including acrylic fibers. By using split fibers, it becomes easier to increase the ratio Vf/Vp. By using acrylic fibers, it is possible to increase the liquid retention.

Acrylic fibers are fibers (acrylonitrile fibers) formed using a polymer (acrylonitrile polymer) containing acrylonitrile units. The acrylonitrile polymer may contain only acrylonitrile units as a constituent unit. Alternatively, the acrylonitrile polymer may be a copolymer containing acrylonitrile units and other monomer units. The other monomer units may be one type or two or more types. The proportion of acrylonitrile units in the polymer may be, for example, 50% by mass or more, 70% by mass or more, 80% by mass or more, or 85% by mass or more. Examples of other monomers that are copolymerized with acrylonitrile include acrylic acid, methacrylic acid, derivatives thereof, and olefin monomers (vinyl acetate, vinyl chloride, vinylidene chloride, etc.). Acrylic fibers include acrylic fibers.

The split fibers containing acrylic fibers may be commercially available split fibers or may be synthesized by a known method. The split fibers containing acrylic fibers may be formed, for example, by spinning composite fibers containing an acrylic fiber portion and another fiber portion. The polymer constituting the other fiber of the composite fiber may be a known polymer (polyethylene, polypropylene, other polymers). The nonwoven fabric (F) may be formed as follows. First, a sheet is obtained by papermaking fibers containing composite fibers. Next, a high-pressure water stream is sprayed onto the sheet to entangle the fibers and simultaneously split the composite fibers. In this way, a nonwoven fabric (F) containing split fibers (for example, split fibers of acrylic fibers) is obtained.

The organic fibers constituting the nonwoven fabric (F) may include organic fibers formed by the release of a component in the electrolyte from fibers containing the component in the electrolyte. By using such organic fibers, it becomes easier to increase the ratio Vf. The nonwoven fabric (F) used in the manufacture of a lead-acid battery may include organic fibers containing the component, or may be composed only of organic fibers containing the component. When a lead-acid battery is manufactured using such a nonwoven fabric (F), the component will release from the organic fibers over time. The release of the component makes it possible to increase the ratio of fine pores. The component released into the electrolyte may be a component that dissolves during electrolysis, or a component that decomposes in the electrolyte and releases from the organic fibers. Examples of such components include acetate. For the organic fibers containing such components, commercially available fibers may be used, or they may be synthesized by a known method.

The first separator may include multiple bags made of nonwoven fabric (F). In this case, each of the multiple positive electrode plates and the multiple negative electrode plates may be housed in the bag. The bag made of nonwoven fabric (F) is, for example, a bag with three sides closed and one side open. The bag may be formed, for example, by overlapping the nonwoven fabric (F) and heat welding at predetermined locations. The positive electrode plate and/or the negative electrode plate can be inserted from the open side of the bag.

The second separator may include a plurality of U-shaped cross-section mats made of glass fiber mats. The bags housing the first electrode plates may be disposed inside the U-shaped cross-section mats. Alternatively, the other electrode plates that are not the first electrode plates may be disposed inside the U-shaped cross-section mats. The U-shaped cross-section mats may be simply referred to as "U-shaped mats" below. From another perspective, the U-shaped cross-section mats are mats that are folded in half.

The nonwoven fabric (F) may be disposed adjacent to the positive electrode plate. For example, the positive electrode plate may be adjacent to the nonwoven fabric (F) by being contained in a bag made of the nonwoven fabric (F). When the nonwoven fabric (F) is adjacent to the positive electrode plate, the amount of electrolyte held in the nonwoven fabric (F) is particularly affected by the positive electrode plate. Therefore, when the nonwoven fabric (F) is adjacent to the positive electrode plate without a glass fiber mat, the configuration of the present invention is particularly advantageous.

The lead-acid battery of this embodiment may be a valve-regulated lead-acid battery or other lead-acid batteries (such as a flooded lead-acid battery). Valve-regulated batteries have the advantage of not requiring water replenishment. On the other hand, repeated charging and discharging can easily cause a problem in that the electrolyte gradually decreases and the internal resistance increases. In general, when a separator made of laminated synthetic fiber nonwoven fabric and glass fiber mat is used, the amount of electrolyte in the synthetic fiber nonwoven fabric tends to decrease significantly due to the decrease in electrolyte. Therefore, in the case of a valve-regulated lead-acid battery, the configuration of this embodiment is particularly preferable.

The positive electrode plates, the negative electrode plates, and the separator constitute an electrode plate group. The positive electrode plates and the negative electrode plates are alternately arranged in the order of negative electrode plate/positive electrode plate/negative electrode plate/positive electrode plate. That is, the positive electrode plates and the negative electrode plates are usually arranged one by one alternately. The number of positive electrode plates and the number of negative electrode plates may be different. Usually, the number of one of the positive electrode plates and the negative electrode plates is one more than the other. For example, the number of positive electrode plates may be one more than the number of negative electrode plates. Alternatively, the number of negative electrode plates may be one more than the number of positive electrode plates. In these cases, the more number of electrodes may be arranged at both ends of the electrode plate group. There is no limit to the number of positive electrode plates and negative electrode plates. The number of positive electrode plates and the number of negative electrode plates may each be independently in the range of 2 to 20 (for example, in the range of 3 to 16).

Between the positive electrode plate and the negative electrode plate adjacent to the positive electrode plate, a nonwoven fabric (F) and a glass fiber mat are arranged so as to be stacked. These may be arranged in the order of positive electrode plate/nonwoven fabric (F)/glass fiber mat/negative electrode plate. Alternatively, they may be arranged in the order of positive electrode plate/glass fiber mat/nonwoven fabric (F)/negative electrode plate.

In a preferred example, a first separator including a plurality of nonwoven fabric (F) bags and a second separator including a plurality of U-shaped mats are used. First to fourth examples of separator arrangement in this case are described below. In the first example, the positive electrode plate is housed in a nonwoven fabric (F) bag, and the bag is placed inside the U-shaped mat. The negative electrode plate is not placed inside the nonwoven fabric (F) bag or inside the U-shaped mat. In the second example, the negative electrode plate is housed in a nonwoven fabric (F) bag, and the bag is placed inside the U-shaped mat. The positive electrode plate is not placed inside the nonwoven fabric (F) bag or inside the U-shaped mat. In the third example, the positive electrode plate is housed in a nonwoven fabric (F) bag, and the negative electrode plate is placed inside the U-shaped mat. In the fourth example, the negative electrode plate is housed in a nonwoven fabric (F) bag, and the positive electrode plate is placed inside the U-shaped mat.

The configuration of the electrode plate group is not limited to the above configuration, so long as the nonwoven fabric (F) and the glass fiber mat are arranged so as to be stacked between the positive electrode plate and the negative electrode plate adjacent to the positive electrode plate. The form of the nonwoven fabric (F) and the form of the glass fiber mat may each independently be any of a sheet, a bag, and a U-shaped cross section.

(Evaluation of the ratio Vf/Vp)
The Vf (%) of the nonwoven fabric (F) and the Vp (%) of the positive plate are measured by porosimetry using mercury intrusion porosimetry. The ratio Vf/Vp can be calculated from the measured Vf and Vp. The volumes Vf and Vp may be measured using an unused first separator and positive plate. Alternatively, the volumes Vf and Vp may be measured using a first separator and positive plate taken out of a lead-acid battery.

When the separator and the positive plate are removed from the lead-acid battery for measurement, they are removed from the lead-acid battery in a fully charged state. The separator and the positive plate removed from the lead-acid battery are washed and dried prior to measurement. The separator is washed and dried in the following procedure. First, the separator removed from the lead-acid battery is immersed in pure water (cleaning solution) for one hour, thereby removing the sulfuric acid in the separator. Next, the separator is removed from the cleaning solution and left to stand in an environment at 25°C for 16 hours or more, thereby drying the separator. Measurements are performed on the separator obtained in this manner. The positive plate is washed in the same manner as the separator. Next, the washed positive plate is left to stand in an environment at 90°C for 6 hours or more, thereby drying it.

Specifically, the Vf of the nonwoven fabric (F) is measured as follows. First, a portion of the nonwoven fabric (F) constituting the first separator (for example, near the center where no welding has been performed) is cut to a size of 100 mm x 100 mm to obtain a sample. The pore distribution of the obtained sample is measured using a mercury porosimeter (Shimadzu Corporation, Autopore IV 9510). From the measured pore distribution, Vf is obtained. The measurement pressure range is 0.5 psia (3447 Pa) to approximately 60,000 psia (approximately 419 MPa). 0.5 psia (3447 Pa) corresponds to a pore with a diameter of 360 μm. Approximately 60,000 psia (approximately 419 MPa) corresponds to a pore with a diameter of 0.003 μm. Therefore, the above pressure range corresponds to a pore diameter range of 0.003 μm to 360 μm.

Specifically, the Vp of the positive plate is measured as follows. First, 1 g of positive electrode material is obtained as a sample from a portion of the positive plate (e.g., near the center of the positive plate). Except for using this sample, the pore distribution of the sample is measured under the same conditions as those for measuring the pore distribution of the nonwoven fabric (F). Vp is determined from the measured pore distribution.

(Average thickness of nonwoven fabric (F))
The average thickness of the nonwoven fabric (F) is the average value of thicknesses at 10 arbitrarily selected equally spaced points. The thickness at each point is measured, for example, using an outside micrometer (0 to 25 mm) as specified in JIS B7502:2016 (micrometer).

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/constant voltage charging of 2.23 V/cell is performed 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 reaches a value (A) 0.005 times the value (unit: Ah) listed as the rated capacity.

A fully charged lead-acid battery refers to a fully charged lead-acid battery that has already been chemically prepared. A lead-acid battery can be fully charged immediately after chemical preparation, or after a period of time has passed since chemical preparation (for example, a lead-acid battery that has been chemically prepared and is in use (preferably in the early stages of use) can be fully charged).

An example of the configuration of the lead-acid battery of the present invention is described below. The components described below may be the same as those described above. Publicly known components may be used for components other than those characteristic of the present invention.

(Separator)
The separator includes a first separator including a nonwoven fabric (F) made of organic fibers, and a second separator including a glass fiber mat. The first separator may be mostly (e.g., 80% by mass or more) made of the nonwoven fabric (F) or may be made only of the nonwoven fabric (F). The second separator may be mostly (e.g., 80% by mass or more) made of the glass fiber mat or may be made only of the glass fiber mat.

(Nonwoven fabric (F))
The nonwoven fabric (F) is made of organic fibers. 70% by mass or more (e.g., 80% by mass or more, 90% by mass or more, or 95% by mass or more) of the first separator is organic fibers. The first separator may be made of only organic fibers. Examples of organic fibers include synthetic fibers (polyolefin fibers, acrylic fibers, polyester fibers, etc.), fibers containing naturally derived components, etc. Examples of polyolefin fibers include polyethylene fibers and polypropylene fibers. Examples of polyester fibers include polyethylene terephthalate fibers, etc. Examples of fibers containing naturally derived components include pulp fibers (e.g., cellulose fibers). The first separator may contain components other than organic fibers, such as acid-resistant inorganic powders and polymers as binders.

In order to increase the permeability of the electrolyte into the fine pores and the retention of the electrolyte in the pores, it is preferable that the organic fibers have high hydrophilicity. From this perspective, it is preferable to use organic fibers that are more hydrophilic than polyolefin fibers that have not been hydrophilized. For example, a polymer (e.g., a copolymer) using a monomer containing a hydrophilic group (such as a hydroxyl group or a carboxyl group) may be used, or an organic fiber that has been hydrophilized may be used. A known hydrophilization treatment may be used for the hydrophilization treatment. Examples of organic fibers that are more hydrophilic than polyolefin fibers that have not been hydrophilized include acrylic fibers and polyethylene terephthalate fibers (PET fibers). One example of a preferred organic fiber is a copolymer synthesized using a monomer containing a hydrophilic group and acrylonitrile.

The organic fibers may be split fibers. By using split fibers, it becomes easier to increase the ratio Vf.

The average fiber diameter of the split fibers among the organic fibers constituting the nonwoven fabric (F) may be in the range of 0.01 μm to 1.0 μm (for example, in the range of 0.01 μm to 0.75 μm). The average fiber diameter of the organic fibers constituting the nonwoven fabric (F) may be in the range of 0.5 μm to 15 μm (for example, in the range of 0.5 μm to 10 μm). By setting the average fiber diameter to 9 μm or less, it becomes easier to increase the ratio Vf. The average fiber diameter of the organic fibers can be calculated by calculating the maximum diameter of any cross section perpendicular to the length direction for any 100 fibers, and averaging the 100 numerical values. Note that with regard to split fibers, each fiber after splitting is treated as one fiber. For example, a split fiber divided into 10 fibers is treated as 10 fibers.

The areal density of the nonwoven fabric (F) may be in the range of 40 g/m ² to 90 g/m ² (for example, in the range of 50 g/m ² to 80 g/m ² ). By setting the average fiber diameter of the organic fibers constituting the nonwoven fabric (F) in the range of 0.5 μm to 15 μm and setting the areal density of the nonwoven fabric (F) in the range of 40 g/m ² to 90 g/m ² , it becomes easier to increase the ratio Vf.

(fiberglass mat)
The glass fiber mat is, for example, a sheet (e.g., nonwoven fabric) formed using glass fibers. The entire glass fiber mat may be formed of glass fibers. Alternatively, the glass fiber mat may contain glass fibers as a main component. The glass fiber content in the second separator may be 90% by mass or more or 95% by mass or more. The second separator may contain components other than glass fibers, such as organic fibers, acid-resistant inorganic powder, and polymers as binders, and the content thereof is usually 20% by mass or less (e.g., 10% by mass or less or 5% by mass or less).

The average fiber diameter of the glass fibers may be in the range of 0.1 μm to 30 μm, or in the range of 0.5 μm to 15 μm. The average fiber diameter of the glass fibers can be calculated by determining the maximum diameter of any cross section perpendicular to the length direction of any 100 fibers, and averaging the 100 values.

The areal density of the glass fiber mat may be in the range of 100 g/m ² to 250 g/m ² (eg, in the range of 100 g/m ² to 200 g/m ² ).

(Positive electrode plate)
The positive electrode plate includes a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector. The positive electrode material is held by the positive electrode current collector. The positive electrode material is the positive electrode plate excluding the positive electrode current collector. The positive electrode current collector can be formed by casting lead or a lead alloy or processing a lead or lead alloy sheet. Examples of processing methods include expanding and punching.

In terms of corrosion resistance and mechanical strength, Pb-Ca alloys and Pb-Ca-Sn alloys are preferred as lead alloys for use in the positive electrode current collector. The positive electrode current collector may have lead alloy layers with different compositions, and may have multiple alloy layers. For the core metal, it is preferred to use a Pb-Ca alloy or a Pb-Sb alloy.

The positive electrode material contains a positive electrode active material (lead dioxide or lead sulfate) that develops capacity through an oxidation-reduction reaction. The positive electrode material may contain other additives as necessary.

The positive electrode plate may be prepared by the following method. First, a positive electrode collector is filled with a positive electrode paste, which is then aged and dried to prepare an unformed positive electrode plate. The unformed positive electrode plate is then formed to obtain a positive electrode plate. The positive electrode paste is prepared by mixing materials including lead powder, additives, water, and sulfuric acid.

The liquid content in the positive electrode paste may be in the range of 10 to 40% by mass (e.g., in the range of 10 to 30% by mass).

(Negative plate)
The negative plate of a lead-acid battery is composed of a negative current collector and a negative electrode material. The negative electrode material is the portion of the negative plate excluding the negative current collector.

The negative electrode current collector may be formed by casting lead or a lead alloy, or by processing a lead or lead alloy sheet. Examples of processing methods include expanding and punching.

The lead alloy used in the negative electrode current collector may be any of Pb-Sb alloys, Pb-Ca alloys, and Pb-Ca-Sn alloys. These lead or lead alloys may further contain other additive elements, and may contain at least one element selected from the group consisting of Ba, Ag, Al, Bi, As, Se, and Cu.

The negative electrode material includes a negative electrode active material (lead or lead sulfate) that develops capacity through an oxidation-reduction reaction. The negative electrode material may include a shrinkage inhibitor, a carbonaceous material (such as carbon black), barium sulfate, etc. The amount of the negative electrode material may include other additives as necessary.

The negative electrode active material in the charged state is spongy lead, but unformed negative plates are usually made from lead powder.

The negative electrode plate may be produced by the following method. First, a negative electrode current collector is filled with a negative electrode paste, which is then aged and dried to produce an unformed negative electrode plate. This unformed negative electrode plate is then chemically formed to obtain a negative electrode plate. The negative electrode paste can be produced, for example, by adding water and sulfuric acid to a material containing lead powder, an organic shrinkage inhibitor, and various additives as necessary, and kneading the mixture. In the aging process, it is preferable to age the unformed negative electrode plate in an environment that is higher than room temperature and has a high humidity.

The chemical formation may be carried out by immersing the plate group including the unformed negative plate in an electrolyte containing sulfuric acid in a lead-acid battery container and charging the plate group. The chemical formation may be carried out before assembling the lead-acid battery or before assembling the plate group. The chemical formation produces spongy lead.

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

The specific gravity of the electrolyte at 20° C. is, for example, 1.10 g/cm ³ or more. The specific gravity of the electrolyte at 20° C. may be 1.35 g/cm ³ or less. Note that these specific gravities are values for electrolyte in a preformed, fully charged lead-acid battery.

(Exterior body)
The lead-acid battery includes an exterior body. The exterior body may include a battery case that contains a plate group and an electrolyte, and a lid portion that covers an opening of the battery case. The battery case may include a plurality of cell chambers. One plate group may be arranged in one cell chamber. When the lead-acid battery is a valve-regulated lead-acid battery (VRLA battery), the exterior body includes a control valve. The control valve is usually arranged in the lid portion. The control valve opens when the internal pressure of the exterior body becomes high (for example, when it reaches or exceeds a predetermined value) to release gas inside the exterior body to the outside. The control valve may be a known control valve used in lead-acid batteries.

Examples of embodiments according to the present invention will be described below with reference to the drawings. The components described above can be applied to the components of the examples described below. The examples described below can be modified based on the above description. The matters described below may be applied to the above embodiments. In the embodiments described below, components that are not essential to the lead-acid battery of the present invention may be omitted.

Figure 1 is a cross-sectional view showing a schematic of part of the structure of an example of a valve-regulated lead-acid battery. The lead-acid battery 1 shown in Figure 1 includes a plate pack 30, an electrolyte (not shown), and an exterior body (a battery case 10 and a lid 12). The battery case 10 contains the plate pack 30 and the electrolyte. The upper opening of the battery case 10 is sealed by the lid 12.

The battery vessel 10 is divided into multiple (three in the example of FIG. 1) mutually independent cell chambers 10R. Each cell chamber 10R contains one electrode plate group 30. The lid 12 has an independent exhaust valve (control valve) 13 for each cell chamber 10R. When the internal pressure of the cell chamber 10R exceeds a predetermined upper limit, the exhaust valve 13 opens and releases some of the gas in the cell chamber 10R to the outside. When the internal pressure of the cell chamber 10R is equal to or lower than the upper limit, the exhaust valve 13 is closed, and oxygen generated in the positive electrode plate 31 is reduced by the negative electrode plate 32 in the same cell chamber 10R to produce water.

The structure of the valve-regulated lead-acid battery is not limited to the above. FIG. 1 shows an example in which an exhaust valve 13 is arranged in each cell chamber 10R. However, the valve-regulated lead-acid battery may have a structure in which the number of exhaust valves 13 is less than the number of cell chambers 10R. In that case, the lid of the valve-regulated lead-acid battery may have a collective exhaust chamber that communicates with each cell chamber. The collective exhaust chamber may have a smaller number of exhaust valves (e.g., one) than the number of cell chambers.

A cross-sectional view of an example of an electrode plate assembly 30 is shown in FIG. 2. Note that in the following figures, the positive electrode current collector and the negative electrode current collector are omitted. The electrode plate assembly 30 in FIG. 2 includes a positive electrode plate 31, a negative electrode plate 32, and a separator 40. The separator 40 includes a first separator 41 including a nonwoven fabric (F) and a second separator 42 including a glass fiber mat. The nonwoven fabric (F) constituting the first separator 41 has the characteristics described above.

The first separator 41 includes a number of bags 41a made of nonwoven fabric (F). Each bag 41a contains one positive electrode plate 31. The bags 41a may be formed by folding a nonwoven fabric (F) having a size approximately twice that of the positive electrode plate 31 in the middle and gluing the two overlapping sides. The two sides may be bonded, for example, by welding using heat.

The second separator 42 includes a number of U-shaped mats (U-shaped cross-section mats) 42a made of glass fiber mats. Inside each U-shaped mat 42a, a bag 41a and a positive electrode plate 31 housed therein are arranged.

The U-shaped mat 42a is formed by folding one mat at the folding portion 42b. The U-shaped mat 42a has a U-shaped cross section (the cross section shown in FIG. 1). The cross section is perpendicular to the direction in which the folding portion 42b extends. From another perspective, the U-shaped mat 42a is a mat that is folded at the folding portion 42b and then stacked. The inside of the U-shaped mat 42a means the space between the two sheet-like portions that are connected via the folding portion 42b.

The upper part of each of the negative electrode plates 32 is provided with an upwardly protruding current collecting ear (not shown). The upper part of each of the positive electrode plates 31 is also provided with an upwardly protruding current collecting ear (not shown). The ears of the negative electrode plates 32 are connected and integrated by a negative electrode strap (not shown). Similarly, the ears of the positive electrode plates 31 are connected and integrated by a positive electrode strap (not shown). The negative electrode strap is connected to a negative electrode pole (not shown) that serves as an external terminal. The positive electrode strap is connected to a positive electrode pole (not shown) that serves as an external terminal.

The plate group 30 is constructed by alternately arranging the positive electrode plates 31 and the negative electrode plates 32 housed in the bag 41a and the U-shaped mat 42a. As a result, the nonwoven fabric (F) and the glass fiber mat are arranged so as to be laminated between the positive electrode plate 31 and the negative electrode plate 32 adjacent to the positive electrode plate 31. FIG. 2 shows the plate group 30 including five positive electrode plates 31 and six negative electrode plates 32. The number of the negative electrode plates 32 is one more than the number of the positive electrode plates 31. The negative electrode plates 32 are arranged at both ends of the plate group 30. As described above, the number of the positive electrode plates 31 and the number of the negative electrode plates 32 can be changed. Furthermore, the positions of the positive electrode plates 31 and the negative electrode plates 32 may be interchanged. That is, the negative electrode plates 32 may be housed in the bag 41a and the U-shaped mat 42a.

A cross-sectional view of another example of the electrode plate group 30 is shown in FIG. 3. The electrode plate group 30 shown in FIG. 3 differs from the electrode plate group 30 shown in FIG. 2 only in the arrangement of the positive electrode plates 31, the negative electrode plates 32, and the separators 40, so a duplicated description will be omitted.

In the electrode plate group 30 shown in FIG. 3, the positive electrode plate 31 is disposed inside the U-shaped mat 42a, and the negative electrode plate 32 is housed in the bag 41a. The positive electrode plate 31 housed in the U-shaped mat 42a and the negative electrode plate 32 housed in the bag 41a are arranged alternately. The number of negative electrode plates 32 is one more than the number of positive electrode plates 31. The negative electrode plate 32 is disposed at both ends of the electrode plate group 30. As described above, the number of positive electrode plates 31 and the number of negative electrode plates 32 can be changed. The positive electrode plates 31 and the negative electrode plates 32 may also be interchanged. That is, the negative electrode plate 32 may be disposed inside the U-shaped mat 42a, and the positive electrode plate 31 may be housed in the bag 41a.

In the electrode plate group 30, a laminate of nonwoven fabric (F) and glass fiber mat is present on the straight line connecting the positive electrode material of any positive electrode plate 31 and the negative electrode material of the negative electrode plate 32 adjacent to that positive electrode plate 31.

The lead-acid battery according to the present invention is described below.

(1) a plurality of positive electrode plates and a plurality of negative electrode plates arranged alternately;
A separator;
An electrolyte.
the separator includes a first separator including a nonwoven fabric made of organic fibers and a second separator including a glass fiber mat;
the nonwoven fabric and the glass fiber mat are arranged so as to be laminated between the positive electrode plate and the negative electrode plate adjacent to the positive electrode plate,
When the pores Pf of the nonwoven fabric are measured by mercury intrusion porosimetry, the ratio of the volume of the pores Pf having a diameter in the range of 0.01 μm to 3.2 μm to the volume of all the pores Pf is Vf (%);
When the pores Pp of the positive electrode plate are measured by mercury intrusion porosimetry, the ratio of the volume of the pores Pp having a diameter in the range of 0.01 μm to 3.2 μm to the volume of all the pores Pp is Vp (%);
A lead-acid battery, the ratio Vf/Vp being in the range of 0.10 to 0.50.

(2) A lead-acid battery as described in (1) above, in which the ratio Vf/Vp is in the range of 0.12 to 0.33.

(3) A lead-acid battery as described in (1) above, in which the ratio Vf/Vp is in the range of 0.17 to 0.33.

(4) A lead-acid battery according to any one of (1) to (3) above, in which the average thickness of the nonwoven fabric is in the range of 0.1 mm to 0.3 mm.

(5) A lead-acid battery according to any one of (1) to (4) above, in which each of the plurality of positive electrode plates includes a positive electrode collector including a first expanded lattice portion, and each of the plurality of negative electrode plates includes a negative electrode collector including a second expanded lattice portion.

(6) A lead-acid battery according to any one of 1 to 5 above, wherein the organic fibers include split fibers containing acrylic fibers.

(7) A lead-acid battery according to any one of (1) to (6) above, in which the organic fibers include organic fibers formed by the release of a component from a fiber containing the component in the electrolyte solution in the electrolyte solution.

(8) A lead-acid battery according to any one of (1) to (7) above, in which the first separator includes a plurality of bags made of the nonwoven fabric, and each of the plurality of positive electrode plates and one of the plurality of negative electrode plates is housed in the bag.

(9) The lead-acid battery according to (8) above, in which the second separator includes a plurality of U-shaped cross-section mats made of the glass fiber mat, and the bags housing each of the one electrode plates are arranged inside the U-shaped cross-section mats.

(10) The lead-acid battery described in (8) above, in which the second separator includes a plurality of U-shaped mats made of the glass fiber mat, and each of the other electrode plates that is not one of the electrode plates is disposed inside the U-shaped mat.

(11) A lead-acid battery according to any one of (1) to (10) above, in which the nonwoven fabric is arranged adjacent to the positive electrode plate.

(12) A lead-acid battery according to any one of (1) to (11) above, which is a valve-regulated lead-acid battery.

[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.

(Preparation of lead-acid batteries A1 to A13 and C1 to C3)
Lead acid batteries A1 to A13 and C1 to C3 were produced by the following method.
(a) Preparation of negative electrode plate The raw material lead powder, lignin as an organic shrinkage inhibitor, barium sulfate, and carbon black were mixed with an appropriate amount of sulfuric acid aqueous solution to obtain a negative electrode paste. The materials were mixed so that the organic shrinkage inhibitor content was 0.1 mass%, the barium sulfate content was 0.4 mass%, and the carbon black content was 0.2 mass%. Next, the negative electrode paste was filled into the mesh part of an expanded lattice made of Pb-Ca-Sn alloy, and further aged and dried to obtain an unformed negative electrode plate.

(b) Preparation of Positive Electrode Plate A positive electrode paste was obtained by mixing raw lead powder and an aqueous sulfuric acid solution. The positive electrode paste was filled into the mesh of an expanded lattice made of a Pb-Ca-Sn alloy, and then aged and dried to obtain an unformed positive electrode plate. In this example, the value of the ratio Vp was changed by changing the content of the aqueous sulfuric acid solution in the positive electrode paste. Specifically, in the production of the lead-acid battery in Table 1, the content of the aqueous sulfuric acid solution in the positive electrode paste was changed in the range of 10 to 40 mass%. In order to increase Vp, the content of the aqueous sulfuric acid solution was increased.

(c) Preparation of separator As the separator, a bag-shaped separator (bag-shaped separator) formed by using a nonwoven fabric of organic fibers containing acrylic fibers and a U-shaped mat formed by using a glass fiber mat were prepared. In this example, the Vf of the nonwoven fabric was changed by changing the ratio and type of split fibers in the total fibers constituting the nonwoven fabric. Specifically, when increasing the Vf, the split fibers were increased compared to the single fibers, and/or the ratio of acetate contained in the split fibers was set to 3 mass% or more. In the production of the lead-acid battery in Table 1, the average fiber diameter of the organic fibers used in the nonwoven fabric was changed in the range of 0.5 to 15 μm. In addition, the surface density of the nonwoven fabric was changed in the range of 40 to 90 g/m ² .

(d) Preparation of lead-acid battery A lead-acid battery was prepared so that the rated voltage was 12 V and the rated 3-hour rate capacity was 60 Ah. One electrode plate group of the lead-acid battery includes 11 positive electrode plates and 12 negative electrode plates. Each positive electrode plate was housed in a bag-shaped separator, which was then placed inside a U-shaped mat. Next, the negative electrode plates and the positive electrode plates housed in the separator were alternately stacked to form an electrode plate group. The electrode plate group was housed in a polypropylene battery case together with an electrolyte (aqueous sulfuric acid solution), and chemical formation was performed in the battery case. In this way, valve-regulated lead-acid batteries (batteries A1 to A13 and C1 to C3) were prepared. The specific gravity of the electrolyte in the fully charged lead-acid battery at 20°C was 1.28.

(Evaluation of the ratio Vf/Vp of the produced lead-acid battery)
The separator and the positive electrode plate were removed from the fully charged lead-acid battery, and Vf and Vp were measured by the above-mentioned method. Then, the ratio Vf/Vp was calculated.

(Evaluation of cycle life of the produced lead-acid battery)
The lead acid battery thus produced was subjected to a charge-discharge cycle including a high-rate discharge to evaluate the cycle life at high-rate discharge. In the charge-discharge cycle, discharge was performed for 13 minutes at a discharge current of 150 A. Charging was performed using a five-stage constant current charging method. Specifically, charging was performed in the following manner. First, constant current charging was performed at 0.2 CA, and when the charging voltage reached the switching voltage, the charging current was reduced to 0.1 CA. The charging voltage was reduced by reducing the charging current, but when the charging voltage reached the switching voltage again, the charging current was reduced to 0.05 CA. When the charging voltage reached the switching voltage again, the charging current was reduced to 0.025 CA. When the charging voltage reached the switching voltage again, charging was continued for 2.5 hours while maintaining the charging current at 0.025 CA. In this manner, five stages of charging were performed. The switching voltage was set to 14.4 V. Note that 1C means the current (A) of the numerical value (Ah) listed as the rated capacity.

At the beginning of the above charge/discharge cycle and every 25 cycles, the discharge capacity was measured when the battery was discharged at a discharge current of 150 A until the battery voltage reached 8.4 V. The number of cycles when the discharge capacity reached 80% of the initial discharged capacity was taken as the life cycle number. The life cycle number of battery C3 was taken as 100%, and the life cycle numbers of the other batteries were evaluated in relative terms.

The evaluation results of the lead-acid batteries are shown in Table 1. Note that batteries C1 to C3 are conventional lead-acid batteries.

The data in Table 1 is shown in Figure 4. As shown in Table 1 and Figure 4, when the ratio Vf/Vp is in the range of 0.1 to 0.5 (e.g., in the range of 0.12 to 0.33), the cycle life is significantly improved. In terms of further improving the cycle life, the ratio Vf/Vp is preferably in the range of 0.12 to 0.33, and more preferably in the range of 0.17 to 0.33 (e.g., in the range of 0.20 to 0.33).

The present invention can be used in lead-acid batteries, for example, in valve-regulated lead-acid batteries. The valve-regulated lead-acid battery of the present invention may be used as a stationary valve-regulated lead-acid battery such as an uninterruptible power supply (UPS), but its use is not particularly limited.

1: Lead-acid battery 10: Battery case 10R: Cell chamber 12: Lid 13: Exhaust valve 30: Plate group 31: Positive electrode plate 32: Negative electrode plate 40: Separator 41: First separator 41a: Bag 42: Second separator 42a: U-shaped mat 42b: Folded portion

Claims (12)

A plurality of alternating positive and negative electrode plates;
A separator;
An electrolyte.
the separator includes a first separator including a nonwoven fabric made of organic fibers and a second separator including a glass fiber mat;
the nonwoven fabric and the glass fiber mat are arranged so as to be laminated between the positive electrode plate and the negative electrode plate adjacent to the positive electrode plate,
When the pores Pf of the nonwoven fabric are measured by mercury intrusion porosimetry, the ratio of the volume of the pores Pf having a diameter in the range of 0.01 μm to 3.2 μm to the volume of all the pores Pf is Vf (%);
When the pores Pp of the positive electrode plate are measured by mercury intrusion porosimetry, the ratio of the volume of the pores Pp having a diameter in the range of 0.01 μm to 3.2 μm to the volume of all the pores Pp is Vp (%);
The Vp(%) is in the range of 60.0 to 92.0%,
A lead-acid battery, the ratio Vf/Vp being in the range of 0.10 to 0.50. The lead-acid battery according to claim 1, wherein the ratio Vf/Vp is in the range of 0.12 to 0.33. The lead-acid battery according to claim 1, wherein the ratio Vf/Vp is in the range of 0.17 to 0.33. The lead-acid battery according to any one of claims 1 to 3, wherein the average thickness of the nonwoven fabric is in the range of 0.1 mm to 0.3 mm. Each of the plurality of positive electrode plates includes a positive electrode current collector including a first expanded lattice portion,
The lead-acid battery according to any one of claims 1 to 4, wherein each of the plurality of negative electrode plates includes a negative electrode current collector including a second expanded lattice portion. The lead acid battery according to any one of claims 1 to 5, wherein the organic fibers include split fibers containing acrylic fibers. The lead-acid battery according to any one of claims 1 to 6, wherein the organic fibers include organic fibers formed by dissociating a component that dissociates in the electrolyte from fibers that contain the component in the electrolyte. the first separator includes a plurality of bags made of the nonwoven fabric,
The lead-acid battery according to any one of claims 1 to 7, wherein each of the plurality of positive electrode plates and the plurality of negative electrode plates is housed in the bag. The second separator includes a plurality of U-shaped cross-section mats made of the glass fiber mat,
The lead-acid battery according to claim 8 , wherein the bag housing each of the one electrodes is disposed inside the U-shaped cross-section mat. The second separator includes a plurality of U-shaped cross-section mats made of the glass fiber mat,
The lead-acid battery according to claim 8 , wherein each of the other electrodes that is not the one electrode is disposed inside the U-shaped cross-section mat. The lead-acid battery according to any one of claims 1 to 10, wherein the nonwoven fabric is arranged adjacent to the positive electrode plate. The lead acid battery according to any one of claims 1 to 11, which is a valve-regulated lead acid battery.

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