JP6996264B2 - Lead-acid battery - Google Patents

Description

The present invention relates to a lead storage battery.

Lead-acid batteries are widely used in industry and are used, for example, in automobile batteries, backup power sources, and main power sources for electric vehicles. In particular, lead-acid batteries for automobiles are often placed in a high-temperature engine room, and it is particularly required to maintain the effect of suppressing the reduction of the electrolytic solution of the lead-acid battery (improvement of the liquid reduction performance).

By the way, a control valve type lead-acid battery provided with a valve mechanism or an open-type liquid-type lead-acid battery is used in an automobile. In the control valve type lead-acid battery, the oxygen gas generated from the positive electrode during charging is absorbed by the negative electrode. Therefore, the oxygen gas generated from the positive electrode at the end of charging reacts with the spongy lead of the negative electrode active material to form lead sulfate and Water is regenerated. As described above, in the control valve type lead-acid battery, the water lost due to the generation of oxygen gas at the positive electrode is regenerated, so that it is not necessary to replenish the electrolytic solution (for example, Patent Document 1). Against this background, control valve type lead-acid batteries are widely used, especially in Europe, but the control valve type lead-acid batteries have the disadvantage that they are more expensive than liquid-type lead-acid batteries.

On the other hand, the liquid-type lead-acid battery has a drawback that the liquid-reducing performance is inferior to that of the control valve type lead-acid battery because there is no mechanism for regenerating the electrolytic solution. Since the cost of a liquid-type lead-acid battery is lower than that of a control valve type lead-acid battery, it is considered that if the liquid-reducing performance of the liquid-type lead-acid battery can be improved, both the cost and the liquid-reducing performance can be achieved at the same time.

Japanese Unexamined Patent Publication No. 2007-250361

An object of the present invention is to provide a liquid lead-acid battery which is excellent in suppressing liquid reduction.

According to the study by the present inventors, a film body having pores having an average pore diameter of 20 μm or less and maintaining the tensile strength within a predetermined range is arranged between the positive electrode plate or the negative electrode plate and the separator. It was found that the liquid reduction can be suppressed. Such an effect can be obtained by using a membrane body having flexibility and elasticity and a small average pore diameter, while reducing convection, diffusion, etc. of the electrolytic solution to the extent that the battery performance is not impaired. It is considered that this is because it is possible to suppress the decrease of the electrolytic solution due to the evaporation of the liquid and the overcharging.

That is, in one embodiment, the present invention includes a positive electrode plate, a negative electrode plate, a separator arranged between the positive electrode plate and the negative electrode plate, and a positive electrode plate or a separator arranged between the negative electrode plate and the separator, and includes fibers. The membrane has pores having an average pore diameter of 20 μm or less, and the retention rate R of the tensile strength of the membrane defined by the following formula (1) is 0.60 or more. , A liquid lead-acid battery.
R = S ₁ / S ₀ ... (1)
In the formula, S ₀ represents the tensile strength (N / cm ² ) of the film body, and S ₁ places the liquid lead-acid battery in a hot water bath at 60 ° C. after fully charging the liquid lead-acid battery. In this state, it represents the tensile strength (N / cm ² ) of the film body after continuous constant voltage charging at a voltage of 14.4 V for 42 days.

In one embodiment, the ratio of fibers having a fiber diameter of less than 5 μm to the fibers is 25% or more. In one embodiment, the proportion of fibers having a fiber diameter of 5 μm or more and 20 μm or less in the fibers is 20% or more.

In one embodiment, the membrane body comprises a non-woven fabric containing organic fibers.

In one embodiment, the separator is a bag-shaped separator, and a positive electrode plate or a negative electrode plate and a film body are housed in the separator.

In one embodiment, the thickness of the membrane is 0.3 mm or less.

According to the present invention, it is possible to provide a liquid lead-acid battery which is excellent in suppressing liquid reduction.

It is a perspective view which shows the whole structure and the internal structure of the lead storage battery which concerns on one Embodiment. It is a perspective view which shows the electrode group of the lead storage battery which concerns on one Embodiment. It is a schematic cross-sectional view which shows the cross section seen by the arrow along the line III-III in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

FIG. 1 is a perspective view showing the overall configuration and internal structure of a liquid lead-acid battery (hereinafter, also simply referred to as “lead-acid battery”) according to an embodiment. As shown in FIG. 1, the lead-acid battery 1 according to the present embodiment includes an electric tank 2 having an open upper surface and a lid 3 for closing the opening of the electric tank 2. The battery case 2 and the lid 3 are made of polypropylene, for example. The lid 3 is provided with a negative electrode terminal 4, a positive electrode terminal 5, and a liquid port plug 6 for closing the liquid injection port provided in the lid 3.

Inside the battery case 2, an electrode group 7, a negative electrode column 8 connecting the electrode group 7 to the negative electrode terminal 4, a positive electrode column (not shown) connecting the electrode group 7 to the positive electrode terminal 5, dilute sulfuric acid, etc. Electrolyte and is stored.

FIG. 2 is a perspective view showing the electrode group 7. As shown in FIG. 2, the electrode group 7 includes a plate-shaped negative electrode plate 9, a plate-shaped positive electrode plate 10, and a separator 11 arranged between the negative electrode plate 9 and the positive electrode plate 10. The electrode group 7 has a structure in which a plurality of negative electrode plates 9 and positive electrode plates 10 are alternately laminated in a direction substantially parallel to the opening surface of the electric tank 2 via a separator 11. That is, the negative electrode plate 9 and the positive electrode plate 10 are arranged so that their main surfaces extend in the direction perpendicular to the opening surface of the battery case 2.

The negative electrode plate 9 has a negative electrode current collector 12 and a negative electrode material 13 held by the negative electrode current collector 12 and containing metallic lead (Pb) as an active material. The positive electrode plate 10 has a positive electrode current collector 14 and a positive electrode material 15 held on the positive electrode current collector 14 and containing lead dioxide (PbO ₂ ) as an active material. The selvage portions 12a of the negative electrode current collectors 12 in the plurality of negative electrode plates 9 are collectively welded by the negative electrode side strap 16. Similarly, the selvage portions 14a of the positive electrode current collectors 14 in the plurality of positive electrode plates 10 are collectively welded by the positive electrode side strap 17. The negative electrode side strap 16 and the positive electrode side strap 17 are connected to the negative electrode terminal 4 and the positive electrode terminal 5 via the negative electrode column 8 and the positive electrode column, respectively.

FIG. 3 is a schematic cross-sectional view showing a cross-sectional view taken along the line III-III in FIG. 2. As shown in FIG. 3, in one embodiment, a film body 18 is provided between the negative electrode plate 9 and the separator 11.

The separator 11 is formed in a bag shape, for example, and in one embodiment, the negative electrode plate 9 and the film body 18 are housed in the separator 11. Examples of the material forming the separator 11 include polyethylene (PE), polypropylene (PP) and the like. The separator 11 may be made by adhering inorganic particles such as SiO ₂ and Al ₂ O ₃ to a woven fabric, a non-woven fabric, a porous membrane or the like formed of these materials.

The thickness of the separator 11 is preferably 0.1 mm or more and 0.5 mm or less, and more preferably 0.2 mm or more and 0.3 mm or less. When the thickness of the separator 11 is 0.1 mm or more, the strength of the separator can be ensured. When the thickness of the separator 11 is 0.5 mm or less, an increase in the internal resistance of the battery can be suppressed.

The average pore diameter of the separator 11 is preferably 10 nm or more and 500 nm or less, and more preferably 30 nm or more and 200 nm or less. When the average pore diameter of the separator 11 is 10 nm or more, sulfate ions can be suitably passed through and the diffusion rate of sulfate ions can be ensured. When the average pore diameter of the separator 11 is 500 nm or less, the growth of lead dendrites is suppressed and short circuits are less likely to occur.

In one embodiment, the film body 18 is provided in close contact with the negative electrode plate 9 so as to cover the surface of the negative electrode plate 9. The film body 18 may be in the form of a sheet or a bag, for example. When the film body 18 is in the form of a sheet, the film body 18 covers the surface of the negative electrode plate 9 so as to be wound around the negative electrode plate 9. When the film body 18 has a bag shape, the negative electrode plate 9 is housed in the film body 18.

The membrane body 18 contains fibers. The film body 18 may include, for example, a woven fabric containing organic fibers (organic woven fabric), a non-woven fabric containing organic fibers (organic non-woven fabric), or a porous film other than that, preferably a non-woven fabric containing organic fibers. I have. Examples of the organic fiber include synthetic fibers such as polyethylene, polypropylene, polyester, nylon and aramid.

The film body 18 may be imparted with hydrophilicity by a dry hydrophilic treatment such as a sulfonate treatment or a fluorine treatment, or a wet hydrophilic treatment using a coating liquid containing a silica sol, an alumina sol or the like. The membrane body 18 preferably includes an organic woven fabric, an organic non-woven fabric, or a porous membrane that has been imparted with hydrophilicity by a dry or wet hydrophilic treatment.

The film body 18 may contain a plurality of types of fibers having different fiber diameters. Fine fibers having a fiber diameter of less than 5 μm (particularly about 1 μm or more and 2 μm or less) are considered to have an effect of suppressing the sedimentation of sulfuric acid by increasing the specific surface area of the membrane body 18. Thick fibers having a fiber diameter of 5 μm or more (particularly about 5 μm or more and 20 μm or less) have the effect of further improving the strength of the membrane body 18 and increasing the space of the membrane body 18 to increase the diffusion coefficient of sulfuric acid. It is thought that. The fiber diameter of the thick fiber is preferably 2.5 times or more the fiber diameter of the thin fiber.

The proportion of fibers having a fiber diameter of 5 μm or more in the total fibers contained in the membrane body 18 is preferably 20% or more, more preferably 30% or more, still more preferably 40% from the viewpoint of increasing the diffusion coefficient of sulfuric acid. The above is particularly preferably 50% or more, and from the viewpoint of suppressing the precipitation of sulfuric acid, it is preferably 90% or less, more preferably 85% or less, still more preferably 80% or less, and particularly preferably 75% or less. .. The proportion of fibers having a fiber diameter of 5 μm or more and 20 μm or less is preferably in the above range.

The proportion of fibers having a fiber diameter of less than 5 μm in the total fibers contained in the membrane body 18 is preferably 25% or more, more preferably 30% or more, still more preferably 35% or more from the viewpoint of suppressing the sedimentation of sulfuric acid. It is particularly preferably 40% or more, and from the viewpoint of increasing the diffusion coefficient of sulfuric acid, it is preferably 70% or less, more preferably 65% or less, still more preferably 60% or less, and particularly preferably 55% or less. .. The proportion of fibers having a fiber diameter of 1 μm or more and 2 μm or less is preferably in the above range.

The ratio of fibers having a predetermined fiber diameter to the fibers contained in the film body is measured based on an SEM image obtained by a scanning electron microscope (for example, manufactured by Hitachi High-Technologies Corporation). Specifically, the diameter of 100 fibers in the SEM image (the length (shortest distance) of the fibers in the lateral direction in the SEM image) is measured, and the distribution of the fiber diameters is obtained. Next, the ratio of the number of fibers having a predetermined fiber diameter to the total number of measured fibers is calculated.

The membrane body 18 has pores. The average pore diameter of the membrane body 18 is 20 μm or less, and from the viewpoint of further suppressing liquid reduction, preferably 19 μm or less, 18 μm or less, 17 μm or less, 16 μm or less, 15 μm or less, 14 μm or less, 13 μm or less, 12 μm or less, It is 11 μm or less or 10 μm or less. The average pore diameter of the film body 18 is preferably 1 μm or more, 2 μm or more, or 3 μm or more from the viewpoint of improving the output of the battery.

The average pore diameter of the membrane is X corresponding to the median value between the minimum value and the maximum value on the Y axis (pore volume or pore specific surface area) of the distribution curve in the integrated pore diameter distribution measured by the mercury intrusion method. It is calculated as the median diameter, which is the value of the axis (pore diameter). The average pore diameter of the membrane can be measured by, for example, Autopore IV 9500 manufactured by Shimadzu Corporation.

The porosity of the membrane body 18 is preferably 60% or more, more preferably 65% or more, still more preferably, from the viewpoint of facilitating the diffusion of sulfate ions and further increasing the space for retaining sulfate ions. It is 70% or more, particularly preferably 75% or more, and extremely preferably 80% or more. The porosity of the membrane body is calculated from the actual volume and the apparent volume according to the following formulas (I) to (III) for a sample cut into a rectangular parallelepiped shape of an appropriate size from the membrane body.
Porosity (%) = {1- (actual volume / apparent volume)} x 100 ... (I)
Actual volume (cm ³ ) = measured value of weight (g) / density (g / cm ³ ) ... (II)
Apparent volume (cm ³ ) = length (cm) x width (cm) x thickness (cm) ... (III)
The measured values are used for the length, width, and thickness of the sample when calculating the apparent volume.

The thickness of the film body 18 is preferably 0.3 mm or less, more preferably 0.25 mm or less, still more preferably 0.2 mm or less, and particularly preferably 0.15 mm or less, from the viewpoint of suppressing an increase in internal resistance. .. The thickness of the membrane body 18 is, for example, 0.03 mm or more or 0.1 mm or more from the viewpoint of the ability to prevent the sedimentation of sulfuric acid, the influence on the battery reaction, the strength and the like. When the film body 18 includes the non-woven fabric, the thickness of the film body 18 is determined according to the thickness of the fibers constituting the non-woven fabric and the like.

The film body 18 described above is a film body having a tensile strength maintenance rate R of 0.60 or more as defined by the following formula (1).
R = S ₁ / S ₀ ... (1)
In the formula, S ₀ represents the tensile strength of the film body 18 (unit: N / cm ² , also referred to as “pre-test tensile strength”), and S ₁ is 60 ° C. after the lead storage battery 1 is fully charged. With the lead-acid battery 1 placed in the hot water bath, the tensile strength of the film body 18 after continuous constant voltage charging at a voltage of 2.4 V for 42 days (N / cm ² , also referred to as "post-test tensile strength"). Represents.

The tensile strengths S ₀ and S ₁ of the film body 18 are values measured by a tensile tester. Specifically, a measurement sample of the film body 18 cut out to a size of 5 mm × 100 mm was installed in a tensile tester (for example, AGS-H 500N Autograph manufactured by Shimadzu Corporation), and a gauge point distance of 80 mm. Under the condition of the test speed of 50 mm / min, the maximum value of the tensile strength of the measurement sample when the measurement sample is pulled until it breaks is read. This test is performed on three measurement samples, and the average value of the maximum values of the obtained tensile strengths is defined as the tensile strength of the film body.

When actually calculating the retention rate R of the film body 18 in the lead storage battery 1, six equivalent lead storage batteries 1 (for example, lead storage batteries having the same model number) are used (lead storage battery 3 for measuring tensile strength S ₀ before the test). And 3 lead-acid batteries for measuring tensile strength S ₁ after the test) Prepare. The membrane body 18 is taken out from each of the three lead-acid batteries 1, washed with pure water, dried in a constant temperature bath at 60 ° C. for 24 hours to remove water, and then the pre-test tensile strength _S0 of the membrane body 18 is measured. do. The remaining three lead-acid batteries 1 are fully charged, and after the lead-acid batteries 1 are placed in a hot water bath at 60 ° C., constant voltage charging at a voltage of 14.4 V is continued for 42 days, and then the lead-acid batteries are used. The film body 18 is taken out from No. 1, and after washing and drying in the same manner as in the case of measuring the tensile strength S ₀ before the test, the tensile strength S ₁ after the test of the film body 18 is measured. Then, the maintenance rate R of the tensile strength is calculated from each of the measured tensile strengths S ₀ and S ₁ . At this time, the tensile strength of the film body 18 is measured for the three film bodies 18, and the average value thereof is used.

The retention rate R of the tensile strength of the film body 18 is 0.60 or more, and from the viewpoint of further suppressing liquid reduction, it is preferably 0.70 or more, more preferably 0.80 or more, still more preferably 0.85. As mentioned above, it is particularly preferably 0.90 or more.

The pre-test tensile strength S ₀ of the film body 18 is preferably 500 N / cm ² or more, more preferably 600 N / cm ² or more, and further preferably 700 N / cm ² or more.

In order to obtain the film body 18 having the maintenance rate R of the tensile strength or the tensile strength S ₀ before the test as described above, each property of the film body 18 as described above may be appropriately adjusted, and in particular, polypropylene and / Or use a film body containing polypropylene fibers, use a membrane body containing fibers having π bonds and / or hetero atoms (nitrogen atom, oxygen atom, etc.), do not have fiber orientation (fibers are isotropic) Use a thick (for example, 0.1 mm or more) membrane with a low proportion of fibers with a fiber diameter of less than 5 μm and a high proportion of fibers with a fiber diameter of 5 μm or more. Etc. are suitable.

In the above embodiment, the film body 18 covers all of the main surface (the surface facing the separator 11), the side surface, and the bottom surface of the negative electrode plate 9 and is provided so as to be in contact with the surfaces thereof (in close contact with each other). However, in another embodiment, the film body may be provided between the negative electrode plate 9 and the separator 11 so as to be separated from the negative electrode plate 9. In this case, the film body 18 may be provided, for example, on the surface of the separator 11 on the negative electrode side. From the viewpoint of further suppressing the liquid reduction, it is preferable that the film body 18 is provided so as to be in contact with (in close contact with) the surface of the negative electrode plate 9.

In the above embodiment, the film body 18 covers all of the main surface (the surface facing the separator 11), the side surface and the bottom surface of the negative electrode plate 9, but in other embodiments, the film body is the main surface of the negative electrode plate 9. It may be provided so as to cover only the surface (the surface facing the separator 11).

In the above embodiment, the film body 18 is provided between the negative electrode plate 9 and the separator 11, but in other embodiments, the film body is provided between the positive electrode plate 10 and the separator 11. good. That is, in the above description of the film body, the "negative electrode plate" may be read as "positive electrode plate".

<Example 1>
A paste-type plate was used in which a lead alloy lattice was filled with a paste prepared by kneading lead powder containing lead monoxide as a main component with dilute sulfuric acid. After that, an unmodified electrode plate was obtained through aging and drying steps. The unchemical positive electrode plate and the negative electrode plate are both composed of a mixture of divalent lead compounds such as lead monoxide (PbO) and tribasic lead sulfate ( _3PbO / PbSO4 / _H2O ). ing. Due to the chemical formation, the unchemical material of the positive electrode plate is oxidized to lead dioxide (PbO ₂ ), and the unchemical material of the negative electrode plate is reduced to spongy lead (Pb) to obtain an existing electrode plate (positive electrode plate, negative electrode plate). Was done.

As the film body, an organic non-woven fabric (main component: polypropylene, thickness: 0.2 mm) having an average pore diameter and tensile strength shown in Table 1 was used and arranged in the vicinity of the negative electrode plate. The fibers constituting the nonwoven fabric include two types, a fiber A: 40%, which is a fiber having a fiber diameter of 1 to 2 μm, and a fiber B: 60%, which is a fiber having a fiber diameter of 5 to 20 μm. As the separator, a bag-shaped polyethylene separator having a thickness of 0.25 mm and an average pore diameter of 30 nm to 200 nm was used, and the negative electrode plate and the film body were housed in the separator. Dilute sulfuric acid is used as the electrolytic solution, and the D size (JIS D5301; width: 173 mm, box height: 204 mm; negative electrode plate width: 145 mm, negative electrode plate height (including upper frame): 113 mm) is rated. A lead storage battery having a capacity of 60 Ah was produced.

<Examples 2 to 4>
A lead-acid battery was produced in the same manner as in Example 1 except that the average pore diameter and tensile strength of the membrane were changed as shown in Table 1.

<Example 5>
The size of the lead-acid battery is LN1 size, which is common in Europe (EN 50342-2. Width: 175 mm, box height: 190 mm. Negative electrode plate width: 143 mm, negative electrode plate height (including upper frame): 100 mm.) A lead-acid battery was produced in the same manner as in Example 1 except that it was changed to.

<Comparative Example 1>
A lead-acid battery was produced in the same manner as in Example 1 except that the film body was not provided on the negative electrode plate.

<Comparative Example 2>
A lead-acid battery was produced in the same manner as in Example 1 except that an organic nonwoven fabric having an average pore diameter and tensile strength as shown in Table 1 was used as the film body. The film body used in Comparative Example 2 contains two types, a fiber A: 90%, which is a fiber having a fiber diameter of 1 to 2 μm, and a fiber B: 10%, which is a fiber having a fiber diameter of 5 to 20 μm.

<Comparative Example 3>
A lead-acid battery was produced in the same manner as in Example 1 except that the average pore diameter and tensile strength of the membrane were changed as shown in Table 1.

(Calculation of average pore diameter)
The average pore diameter of the membrane was measured by Autopore IV 9500 manufactured by Shimadzu Corporation. The average pore diameter of the membrane is X corresponding to the median value between the minimum value and the maximum value on the Y axis (pore volume or pore specific surface area) of the distribution curve in the integrated pore diameter distribution measured by the mercury intrusion method. It was calculated as the median diameter, which is the value of the axis (pore diameter).

(Measurement of tensile strength and maintenance rate)
The tensile strength of the film body was measured by an AGS-H 500N autograph (tensile tester) manufactured by Shimadzu Corporation. A film body cut out to a size of 5 mm × 100 mm was installed in a testing machine, and was pulled until the film body was cut under the conditions of a gauge point distance of 80 mm and a test speed of 50 mm / min. The maximum value of the tensile strength of the test piece cut near the center of the membrane was read, and that value was taken as the tensile strength of the membrane. The tensile strength of the membrane was measured once before being applied to the battery (assembling the battery) (tensile strength before the test S ₀ ), and after the following liquid reduction test was completed, the membrane was taken out from the battery and measured again (after the test). Tensile strength S ₁ ). Table 1 shows these tensile strengths S ₀ and S ₁ , and the tensile strength maintenance rate R (= S ₁ / S ₀ ) calculated from these.

(Evaluation of liquid reduction suppression effect (liquid reduction test))
The liquid reduction performance (effect of suppressing liquid reduction) of the lead storage battery was measured as follows. First, a constant voltage charge at a voltage of 14.4 V was continued for 42 days in a state where the fully charged lead-acid battery was placed in a hot water bath in which the hot water bath temperature was set to 60 ° C. ± 2 ° C. During the test period, the hourly current value was recorded and the integrated charge capacity (Ah) was calculated. Further, the weight of the battery was recorded every week, and the amount of decrease in battery weight (g) from the initial stage was calculated. Since the cumulative charge electricity amount and the battery reduction amount are approximately proportional to each other, the cumulative charge electricity amount (g / Ah) is used as an index of the liquid reduction suppressing effect here. The liquid reduction suppressing effect in each Example and Comparative Example was evaluated based on the following criteria, assuming that the liquid reduction suppressing effect in the case where the membrane was not provided (Comparative Example 1) was 100. If the evaluation is A or B, it can be said that it is excellent in terms of suppressing liquid reduction.
A: less than 70 B: 70 or more and less than 75 C: 75 or more and less than 90 D: 90 or more and less than 100

From the above results, in the examples in which the average pore diameter of the film body was 20 μm or less and the maintenance rate R of the tensile strength was 0.60 or more, an excellent liquid reduction suppressing effect was obtained. On the other hand, in Comparative Example 1 in which the film body was not provided and Comparative Example 4 in which the average pore diameter of the film body was 40 μm, almost no difference in the liquid reduction suppressing effect was observed. Further, Comparative Example 2 and Comparative Example 3 using a film body having a tensile strength maintenance rate R of less than 0.60 were also inferior to the Examples in terms of the liquid reduction suppressing effect. It is considered that this is because the maintenance rate R of the tensile strength is low, so that the ability to follow the expansion and contraction of the electrode plate is inferior, and as a result, the liquid reduction cannot be sufficiently suppressed.

The present invention is not limited to the above examples, and includes various modifications. For example, the above-described embodiment has been described in detail in order to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to the embodiment including all the described configurations.

1 ... Lead-acid battery, 9 ... Negative electrode plate, 10 ... Positive electrode plate, 11 ... Separator, 18 ... Membrane.

Claims (6)

With a positive electrode plate
Negative electrode plate and
A separator arranged between the positive electrode plate and the negative electrode plate,
A film body arranged between the positive electrode plate or the negative electrode plate and the separator, and containing fibers,
Equipped with
The film body has pores having an average pore diameter of 20 μm or less, and has an average pore diameter of 20 μm or less.
A liquid lead-acid battery having a retention rate R of tensile strength of the film body defined by the following formula (1) of 0.60 or more.
R = S ₁ / S ₀ ... (1)
[In the formula, S ₀ represents the tensile strength (N / cm ² ) of the film body, and S ₁ is the liquid formula in a hot water bath at 60 ° C. after the liquid lead-acid battery is fully charged. It represents the tensile strength (N / cm ² ) of the film body after constant voltage charging at a voltage of 14.4 V was continued for 42 days with the lead storage battery arranged. ] The liquid lead-acid battery according to claim 1, wherein the ratio of fibers having a fiber diameter of less than 5 μm to the fibers is 25% or more. The liquid lead-acid battery according to claim 1 or 2, wherein the ratio of fibers having a fiber diameter of 5 μm or more and 20 μm or less to the fibers is 20% or more. The liquid lead-acid battery according to any one of claims 1 to 3, wherein the film body includes a nonwoven fabric containing organic fibers. The liquid lead-acid battery according to any one of claims 1 to 4, wherein the separator is a bag-shaped separator, and the positive electrode plate or the negative electrode plate and the film body are housed in the separator. The liquid lead-acid battery according to any one of claims 1 to 5, wherein the film body has a thickness of 0.3 mm or less.

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