JP2024062140A - Lead storage battery - Google Patents

Abstract

SOLUTION: To provide a lead storage battery which has a positive electrode plate, a negative electrode plate, a porous film which is interposed between the positive electrode plate and the negative electrode plate and is made of a resin, a non-woven fabric which is interposed between the positive electrode plate and the negative electrode plate and is brought into contact with the positive electrode plate, and an electrolyte, wherein a chemical oxygen request amount in the electrolyte is 160 mg/L or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a lead-acid battery.

Lead-acid batteries are used in vehicles, industrial applications, and a variety of other applications. Lead-acid batteries contain positive and negative electrode plates, a separator between them, and an electrolyte. Separators in lead-acid batteries are required to have a variety of performance characteristics. Porous films made of polyolefin are generally used as separators.

Patent Document 1 proposes a lead-acid battery comprising "positive and negative electrode plates, an electrolyte, and a separator, the separator being made of a porous sheet and a glass mat, and the electrolyte containing aluminum ions at 0.02 mol/L or more and 0.2 mol/L or less, and lithium ions at 0.02 mol/L or more and 0.2 mol/L or less."

Patent Document 2 proposes a flooded lead-acid battery comprising "a positive electrode plate, a negative electrode plate, a separator disposed between the positive electrode plate and the negative electrode plate, a membrane disposed between the negative electrode plate and the separator, an electrolyte, and a battery case that contains the positive electrode plate, the negative electrode plate, the separator, the membrane, and the electrolyte, the membrane having pores with an average pore diameter of 15 μm or less, and used so that the ratio of remaining capacity to full charge capacity is 90% or less."

Patent Document 3 proposes a method for manufacturing a flooded lead-acid battery, comprising the steps of: preparing a battery case divided into two or more regions by one or more partition walls; preparing two or more plate groups, each of which includes a plurality of positive plates, a plurality of polyolefin separators, a plurality of nonwoven fabrics, and a plurality of negative plates; housing the plate group in the region of the battery case; and supplying an electrolyte into the battery case, in which, when housing the plate group in the region of the battery case, the plate group is pressed into the region while a compressive force in the thickness direction of the plate group is applied to the plate group from the partition wall, where X and Y satisfy -1.1≦X-Y≦1.2, where the width of the region is X mm and the thickness of the plate group when removed from the battery after chemical formation is Y mm.

Patent document 4 proposes "a lead-acid battery characterized by containing 0.5 mg/L or more and 3 mg/L or less of reducing organic matter in the electrolyte."

JP 2013-84362 A International Publication No. 2018-105134 JP 2020-174058 A JP 2005-251394 A

Lead-acid batteries for vehicles are required to ensure excellent life performance (heavy-load life performance) in heavy-load life tests. In heavy-load life tests, the lead-acid battery is deeply discharged with a large current, and then charged with a charge of approximately the same amount of electricity as the discharged amount. Therefore, in order to obtain excellent heavy-load life performance, it is important to suppress side reactions. If part of the charged electricity is consumed in side reactions, the battery will become undercharged. In that case, the lead-acid battery will be discharged even deeper, so the positive electrode material will gradually soften and fall off the positive plate, reaching the end of its life. This tendency is particularly pronounced in commercial vehicles that are subject to relatively strong vibrations, such as trucks and taxis.

In response to this, by providing a nonwoven fabric that is interposed between the positive and negative electrode plates and that is in contact with the positive electrode plate, it is possible to reduce the shedding of the softened positive electrode material.

However, placing a nonwoven fabric between the positive and negative plates increases the physical barrier to ionic conduction in the electrolyte, increasing resistance and reducing cold cranking ampere (CCA) performance.

As described above, in a state where a certain degree of side reactions may occur, it is difficult to ensure excellent heavy-load life performance while maintaining high CCA performance. On the other hand, in recent years, there has been a demand for lead-acid batteries with better heavy-load life performance and CCA performance for use in vehicles equipped with idling stop functions and micro-hybrid vehicles.

One aspect of the present disclosure relates to a lead-acid battery comprising a positive electrode plate, a negative electrode plate, a resin porous film interposed between the positive electrode plate and the negative electrode plate, a nonwoven fabric interposed between the positive electrode plate and the negative electrode plate and in contact with the positive electrode plate, and an electrolyte, the chemical oxygen demand of the electrolyte being 160 mg/L or less.

In lead-acid batteries, it is possible to ensure excellent heavy-load life performance while maintaining high CCA performance.

1 is a partially cutaway perspective view showing the appearance and internal structure of a lead-acid battery according to one embodiment of the present invention; FIG. 2 is a schematic plan view of the separator of FIG. 1 .

In the following, the embodiment of the present disclosure will be described with examples, but the present disclosure 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 disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when a lower limit and an upper limit of a numerical value related to a specific physical property or condition are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of them may be selected and used alone, or two or more of them may be used in combination.

The present disclosure also encompasses combinations of features described in two or more claims arbitrarily selected from the multiple claims described in the accompanying claims. In other words, the features described in two or more claims arbitrarily selected from the multiple claims described in the accompanying claims may be combined as long as no technical contradiction arises.

In this specification, the up-down direction of a lead-acid battery or components of a lead-acid battery (electrode plates, battery case, separator, etc.) refers to the up-down direction in the vertical direction of the lead-acid battery arranged in a state of use. Each electrode plate, the positive electrode plate and the negative electrode plate, has a lug portion for connecting to an external terminal. For example, in a liquid battery, the lug portion is provided on the top of the electrode plate so as to protrude upward.

The lead-acid battery according to the present disclosure may be a valve-regulated battery (VRLA type battery), but a flooded battery (vented type battery) is preferred because it can effectively utilize the effect of reducing the chemical oxygen demand (COD) in the electrolyte.

A lead-acid battery comprises positive and negative plates, a separator interposed between the positive and negative plates, and an electrolyte. The electrolyte contains sulfuric acid. Charging and discharging proceeds as sulfate ions move between the positive and negative plates and the electrolyte. During discharging, sulfate ions move to the positive and negative plates, decreasing the density of the electrolyte. During charging, sulfate ions move from the positive and negative plates into the electrolyte, increasing the density of the electrolyte.

The positive and negative plates and the separator constitute an electrode plate group. The electrode plate group, together with the electrolyte, constitutes a cell. One electrode plate group constitutes one cell. A lead-acid battery comprises one or more electrode groups, and thus comprises one or more cells. There is no particular limit to the number of positive and negative plates contained in one electrode plate group. The electrode plate group of the lead-acid battery according to the present disclosure includes, for example, a total of 12 or more positive and negative plates. The multiple electrode plate groups are usually housed in individual cell chambers and connected to each other in series.

The positive electrode plate includes a positive electrode material. The positive electrode material contains at least lead dioxide during charging and at least lead sulfate during discharging as a positive electrode active material that develops capacity through an oxidation-reduction reaction.

The negative plate includes a negative electrode material. The negative electrode material contains at least lead during charging and at least lead sulfate during discharging as a negative electrode active material that develops capacity through an oxidation-reduction reaction.

(1) A lead-acid battery according to one embodiment of the present disclosure includes a positive electrode plate, a negative electrode plate, a resin porous film interposed between the positive electrode plate and the negative electrode plate, a nonwoven fabric interposed between the positive electrode plate and the negative electrode plate and in contact with the positive electrode plate, and an electrolyte, the chemical oxygen demand (COD) of the electrolyte being 160 mg/L or less.

The lead-acid battery according to one embodiment of the present invention has high CCA performance and excellent heavy load life performance. This is believed to be because, by adjusting the COD in the electrolyte, the decrease in the bonding strength between the positive electrode collector and the positive electrode material due to the progression of softening of the positive electrode material due to deep discharge is suppressed. When nonwoven fabric is used, the detachment of the positive electrode material can be reduced, but the softening of the positive electrode material due to deep discharge itself progresses. On the other hand, when the COD is set to 160 mg/L or less, the charge acceptance is improved, the discharge depth does not become excessively deep, the softening of the positive electrode material is less likely to progress, the increase in resistance due to the decrease in the bonding strength between the positive electrode collector and the positive electrode material is suppressed, and it is believed that the effect of the increase in resistance due to the nonwoven fabric is less likely to be reflected in the CCA performance.

In addition, organic matter in the electrolyte not only reduces the charge acceptance due to oxidative decomposition on the surface of the positive plate, but also affects both the charge and discharge reactions by inhibiting ionic conduction in the electrolyte. If the COD in the electrolyte exceeds 160 mg/L, the ionic conduction in the electrolyte is inhibited and the discharge reaction is inhibited, resulting in a decrease in CCA performance. In contrast, by reducing the COD in the electrolyte to 160 mg/L or less, ionic conduction is less likely to be inhibited, resulting in high CCA performance. The effect of improving CCA performance by reducing COD is also effectively exerted when a nonwoven fabric is interposed between the positive and negative plates in addition to the porous film. From the above, by interposing a porous film and a nonwoven fabric between the positive and negative plates and setting the COD in the electrolyte to a certain range or less, a lead-acid battery having both high CCA performance and heavy load life performance can be obtained.

(2) In the lead-acid battery described in (1) above, the nonwoven fabric may be a mat containing at least one type selected from the group consisting of glass fibers and organic fibers.

In the lead-acid battery described in (2) above, glass fibers have excellent oxidation resistance, and organic fibers have excellent flexibility and adhesion to the positive electrode material, so they are highly effective in preventing the softened positive electrode material from falling off.

(3) In the lead acid battery described in (1) or (2) above, the COD may be 100 mg/L or less.

The lead-acid battery described in (3) above has significantly improved discharge performance, resulting in higher CCA performance and better heavy-load life performance.

(4) In the lead acid battery described in any one of (1) to (3) above, the COD may be 1.0 mg/L or more.

The lead-acid battery described in (4) above has a COD that is not too small, making it easy to control the COD. This allows for a wider range of choices for the components of the lead-acid battery. In addition, when the COD is small, the battery has high charge acceptance and is charged to a full charge state in a heavy-load life test, but because the COD is not too small, oxidation degradation of the porous film facing the positive electrode is less likely to occur. This allows for better CCA performance and heavy-load life performance to be achieved.

(5) In the lead-acid battery described in any one of (1) to (4) above, the nonwoven fabric may be fixed to the surface of the positive electrode plate.

In the lead-acid battery described in (5) above, the positive electrode plate and the nonwoven fabric are integrated, which is effective in suppressing the softened positive electrode material from falling off. In addition, the surface area of the positive electrode plate covered by the nonwoven fabric is large, which significantly improves discharge performance by reducing COD.

(6) In the lead-acid battery described in any one of (1) to (5) above, the porous film may have a thickness of 100 μm or more and 300 μm or less.

In the lead-acid battery described in (6) above, the porous film is sufficiently thin and has high strength, so that higher CCA performance and better heavy load life performance can be obtained.

(7) In the lead-acid battery described in any one of (1) to (6) above, the nonwoven fabric may have a thickness of 30 μm or more and 800 μm or less.

In the lead-acid battery described in (7) above, the nonwoven fabric is sufficiently thin and has high strength, so that higher CCA performance and better heavy load life performance can be obtained.

(8) In the lead-acid battery described in any one of (1) to (7) above, the porous film may have an area at least partially at the end that is not covered by the nonwoven fabric.

According to the lead-acid battery described in (8) above, the size of the nonwoven fabric can be made large enough to suppress the fall-off of the softened positive electrode material while suppressing an increase in internal resistance.

The porous film can be used alone as a separator. Therefore, the porous film alone may be referred to as a separator. The nonwoven fabric also functions as a separator in cooperation with the porous film. Therefore, the porous film and the nonwoven fabric together may be referred to as a separator.

Interposing a porous film and nonwoven fabric between the positive and negative electrodes is effective in preventing the softened positive electrode material from falling off. However, the inventors have found that when the COD in the electrolyte exceeds a certain range, the degree of improvement in heavy load life performance achieved by using nonwoven fabric is limited.

Regardless of whether or not nonwoven fabric is used, if the chemical oxygen demand (COD) in the electrolyte exceeds a certain range, a side reaction occurs in which organic matter in the electrolyte is oxidized and decomposed on the surface of the positive plate, reducing the charge acceptance of the positive plate. On the other hand, in heavy-load life tests, the amount of discharged electricity is large during discharge (e.g., DOD 20-50%), so the positive electrode material softens due to deep discharge, the bonding strength between the positive electrode collector and the positive electrode material decreases, and resistance increases. Nonwoven fabric can reduce the shedding of the positive electrode material, but it cannot suppress the softening itself.

In contrast, when the COD in the electrolyte is controlled to 160 mg/L or less, the concentration of organic matter in the electrolyte is reduced. This reduces the proportion of side reactions to the charging reaction of the active material, making it difficult for the positive electrode material to soften due to insufficient charging.

The lower the COD in the electrolyte, the lower the concentration of organic matter in the electrolyte, and the less side reactions occur during charging. Therefore, it is assumed that the lower the COD in the electrolyte, the better the charging efficiency and the longer the life in heavy load life tests. However, in reality, as the charging amount increases, oxygen generated on the positive electrode side causes oxidation deterioration of the resin porous film, so the heavy load life does not necessarily improve and may even decrease. The oxidized and deteriorated porous film cracks or breaks, causing an internal short circuit between the positive and negative electrodes, and the lead-acid battery reaches the end of its life.

In response to this, by placing a nonwoven fabric between the positive and negative electrode plates and bringing the nonwoven fabric into contact with the positive electrode plate, it is possible to suppress oxidative deterioration of the porous film caused by oxygen generated near the positive electrode plate. In addition, by bringing the nonwoven fabric into contact with the positive electrode plate, it is also possible to prevent the positive electrode material from softening and falling off when it is in an overcharged or overdischarged state. This also contributes to improving the heavy load life performance.

In this specification, heavy load life performance refers to the life performance when the rated capacity (5-hour rate capacity) is taken as 100%, and discharge and charge are repeated to a region where the depth of discharge in one cycle is 20% or more (also called the heavy load region). Details of the test conditions for heavy load life performance are described later.

The nonwoven fabric may be in contact with the surface of the positive electrode plate, but may also be fixed to the surface of the positive electrode plate. By fixing the nonwoven fabric to the surface of the positive electrode plate and integrating the positive electrode plate and the nonwoven fabric, the effect of suppressing the fall-off of the softened positive electrode material is increased. In this case, the surface area of the positive electrode plate covered with the nonwoven fabric is increased, so that the heavy load life performance is more strongly affected by the value of COD. Therefore, the effect of improving the heavy load life performance by reducing COD is more pronounced. There are no particular limitations on the method of fixing the nonwoven fabric to the surface of the positive electrode plate, but examples include a method in which the nonwoven fabric is pressed and attached to the surface of the positive electrode plate in an unformed state, and then formed to fix it.

The ratio of the mass of the positive electrode material to the mass of the negative electrode material (hereinafter also referred to as the "Mp/Mn ratio") is, for example, 1.2 or more, and may be 1.3 or more. The Mp/Mn ratio may be 1.4 or less. The preferred range of the Mp/Mn ratio is, for example, 1.2 to 1.4, and may be 1.3 to 1.4. The mass of the positive electrode material is the mass of the positive electrode material contained in one positive plate. The mass of the negative electrode material is the mass of the negative electrode material contained in one negative plate. Increasing the Mp/Mn ratio to 1.2 or more means reducing the amount of negative electrode material used. In other words, by making the Mp/Mn ratio 1.2 or more, the lead-acid battery can be made lighter and less expensive. In addition, when the Mp/Mn ratio is 1.2 or more, the load on the positive plate can be reduced, making it easier to suppress the softening and falling off of the positive plate.

The lead-acid battery disclosed herein is suitable for use in vehicles that are controlled by idle stop-start (ISS). Lead-acid batteries installed in vehicles that are controlled by ISS are discharged to a deep DOD, so the effect of suppressing the detachment of the positive electrode material by using nonwoven fabric and the effect of improving CCA performance by controlling COD are more pronounced.

In this specification, the fully charged state of a flooded lead-acid battery is defined by the definition of JIS D 5301:2019. More specifically, the fully charged state is defined as a state in which a lead-acid battery is charged at a current 2I20, which is twice the 20-hour rate current I20, until the terminal voltage (unit: V) during charging measured every 15 minutes in a water tank at 25°C ± 2°C or the electrolyte density converted to a temperature of 20°C shows a constant value with three significant digits three consecutive times. The 20-hour rate current I20 is a current (A) that is 1/20 of the Ah value listed in the rated capacity. Hereinafter, the value in Ah listed as the rated capacity will be simply referred to as the "rated capacity". In addition, for valve-regulated lead-acid batteries, the fully charged state is the state in which charging is completed when the total charging time reaches 24 hours, at a constant current and constant voltage of 2.67 V/cell (16.00 V for lead-acid batteries with a rated voltage of 12 V) at a current 5I20, which is five times the 20-hour rate current I20, in an air tank at 25°C ± 2°C.

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

In this specification, a battery in its early stages of use is one that has not been in use for very long and has not deteriorated much.

The lead-acid battery according to the embodiment of the present invention will be described in more detail below with reference to the drawings. However, the present invention is not limited to the following embodiment.

Below, we explain some examples of the components of a lead-acid battery.

(Positive electrode plate)
The positive electrode plate includes a positive current collector and a positive electrode material. The positive electrode material is held by the positive current collector. The positive electrode material is the portion of the positive electrode plate excluding the positive current collector. An attachment member such as a conductive layer, a mat, or pasting paper may be attached to the positive electrode plate. The attachment member is used integrally with the positive electrode plate, and is therefore included in the components of the plate. When the positive electrode plate includes an attachment member, the positive electrode material is the portion of the positive electrode plate excluding the positive current collector and the attachment member.

The positive electrode collector may be formed by casting lead (Pb) or a lead alloy, or by processing a lead or lead alloy sheet. The processing method may be, for example, an expanding process or a punching process. If a lattice-shaped collector is used as the positive electrode collector, it is easy to support the positive electrode material.

The lead alloy used for the positive electrode current collector is preferably a Pb-Ca alloy or a Pb-Ca-Sn alloy, which has excellent corrosion resistance and mechanical strength. The positive electrode current collector may have metal layers with different compositions, and the metal layer may be a single layer or multiple layers.

The positive electrode material includes a positive electrode active material that exhibits capacity through an oxidation-reduction reaction. The positive electrode active material includes lead dioxide, lead sulfate, and the like. The positive electrode material may include additives as necessary. The additives may include reinforcing materials, antimony compounds, and the like. Examples of reinforcing materials include inorganic fibers and organic fibers.

An unformed positive electrode plate is obtained by aging and drying a positive electrode paste filled in a positive electrode current collector and a positive electrode current collector. The positive electrode paste is prepared by kneading a mixture containing lead powder, water, and sulfuric acid. The positive electrode paste may contain additives as necessary. The additives may include reinforcing materials, antimony compounds, etc. Such a positive electrode plate is also called a paste-type positive electrode plate.

A positive plate is obtained by chemically forming an unformed positive plate. Chemical formation may be performed by immersing a plate group including an unformed positive plate in an electrolyte containing sulfuric acid in a lead-acid battery container and charging the plate group. Chemical formation may be performed before assembling the lead-acid battery or the plate group.

(Negative plate)
The negative electrode plate includes a negative current collector and a negative electrode material. The negative electrode material is held by the negative current collector. The negative electrode material is the portion of the negative electrode plate excluding the negative current collector. An attachment member such as a conductive layer, a mat, or pasting paper may be attached to the negative electrode plate. The attachment member is included in the components of the negative electrode plate. When the negative electrode plate includes an attachment member, the negative electrode material is the portion of the negative electrode plate excluding the negative current collector and the attachment member.

The negative electrode current collector may be formed by casting lead (Pb) or a lead alloy, or by processing a lead or lead alloy sheet. The processing method may be an expanding process or a punching process. If a lattice-shaped current collector is used as the negative electrode current collector, 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. The lead alloy used in the negative electrode current collector may contain at least one element 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 metal layers with different compositions, and the metal layer may be one layer or multiple layers.

The negative electrode material includes a negative electrode active material that develops capacity through an oxidation-reduction reaction. The negative electrode active material includes lead, lead sulfate, and the like. The negative electrode material may include 100 ppm to 300 ppm of Bi element by mass. The negative electrode material may include other additives as necessary. The additives may include an organic shrinkage inhibitor, a carbonaceous material, barium sulfate, and the like.

Examples of organic shrinkage inhibitors include lignin, lignin sulfonic acid, and synthetic organic shrinkage inhibitors. The synthetic organic shrinkage inhibitor may be, for example, a formaldehyde condensate of a phenol compound. The organic shrinkage inhibitor may be used alone or in combination of two or more. The content of the organic shrinkage inhibitor in the negative electrode material is, for example, 0.01% by mass or more and 1% by mass or less.

Carbonaceous materials that can be used include carbon black, artificial graphite, natural graphite, hard carbon, and soft carbon. The carbonaceous materials may be used alone or in combination of two or more. The content of the carbonaceous material in the negative electrode material is, for example, 0.1% by mass or more and 3% by mass or less.

The barium sulfate content in the negative electrode material is, for example, 0.1% by mass or more and 3% by mass or less.

The unformed negative electrode plate is obtained by aging and drying the negative electrode current collector and the negative electrode paste filled in the negative electrode current collector. The aging is preferably performed in an atmosphere at a temperature higher than room temperature and with high humidity. The negative electrode paste is prepared by kneading a mixture containing lead powder, water, and sulfuric acid. The negative electrode paste may contain additives as necessary. The additives may include bismuth compounds (e.g., bismuth sulfate), organic shrinkage inhibitors, carbonaceous materials, barium sulfate, etc.

A negative plate is obtained by chemically forming an unformed negative plate. Chemical formation may be performed by immersing a plate assembly including the unformed negative plate in an electrolyte containing sulfuric acid in a lead-acid battery container and charging the plate assembly. Chemical formation may be performed before assembling the lead-acid battery or the plate assembly. The negative active material in the charged state contains spongy lead.

(Electrolyte)
The electrolyte is an aqueous solution containing sulfuric acid. The electrolyte may be gelled as necessary. The electrolyte may further contain at least one metal ion selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions. The density of the electrolyte at 20°C is, for example, 1.10 or more. The density of the electrolyte at 20°C may be 1.35 or less. These densities are values for the electrolyte of a lead-acid battery in a fully charged state.

The lower the COD in the electrolyte, the less the ion conduction in the electrolyte is inhibited, and the lower the battery resistance. Therefore, it is assumed that the lower the COD in the electrolyte, the better the CCA performance and heavy load life performance. However, it may not be easy to control the COD amount to less than 1 mg/L, which may narrow the range of choices for components of a lead-acid battery. In fact, if the COD in the electrolyte is too low, oxygen generated on the positive electrode side causes oxidation deterioration of the resin porous film, so the heavy load life does not necessarily improve, and may even decrease. In order to suppress such disadvantages and achieve better CCA performance and heavy load life performance, it is desirable to control the COD amount in the electrolyte to 1 mg/L or more.

The COD in the electrolyte may be 160 mg/L or less, but may also be 120 mg/L or less. In order to obtain higher CCA performance and better heavy load life performance, the COD in the electrolyte may be 100 mg/L or less, 50 mg/L or less, 30 mg/L or less, or 25 mg/L or less. The COD in the electrolyte may be 1 mg/L or more, 5 mg/L or more, or 8 mg/L or more. The preferred range of the COD in the electrolyte is, for example, 1 mg/L or more and 160 mg/L or less, 1 mg/L or more and 120 mg/L or less, 5 mg/L or more and 100 mg/L or less, or 5 mg/L or more and 50 mg/L or less.

The COD amount in the electrolytic solution can be controlled, for example, by the following methods. The following methods may be adopted alone or in combination.
(1) Adjusting the concentration of the organic additive in the electrolyte.
(2) Adjusting the content of organic components contained in components other than the electrolyte. Examples of "components other than the electrolyte" include a porous film, a current collector for a positive electrode plate or a negative electrode plate, and a positive electrode material or a negative electrode material. That is, the method of (2) can be broadly divided into the following three methods.
(2-1) The content of relatively low molecular weight organic additives contained in the porous film is controlled. Examples of the organic additives include penetrating agents and oils.
(2-2) At least a part of the cutting oil adhering to the positive or negative electrode collector or to the metal plate before being processed into a collector is removed by cleaning or the like.
(2-3) The content of at least one of the organic component and the carbonaceous material contained in the positive electrode material or the negative electrode material is controlled. The organic component contained in the electrode material also includes an organic shrinkage preventer.

An organic solvent may be used to clean the current collector or metal plate. Examples of the organic solvent include at least one selected from alcohols, ketones, esters, ethers, amides, and sulfoxides. Examples of the alcohol include ethanol. Examples of the ketone include acetone and ethyl methyl ketone. Examples of the ester include ethyl acetate. Examples of the ether include tetrahydrofuran. Examples of the amide include dimethylformamide and N-methyl-2-pyrrolidone. Examples of the sulfoxide include dimethyl sulfoxide.

In order not to excessively increase the COD in the electrolyte, it is desirable to use an organic solvent that is easily removed by washing with water, an organic solvent that is miscible with water, etc., as the organic solvent used to wash the current collector or metal plate. The washing time is preferably, for example, 3 seconds or more in an organic solvent that is miscible with water. There is no particular limit to the upper limit of the washing time, and it may be, for example, 60 seconds or less.

The electrolyte used in the assembly of the lead-acid battery may contain an organic additive. Examples of organic additives include surfactants. However, from the viewpoint of keeping the amount of COD in the electrolyte contained in the lead-acid battery low, it is preferable that the electrolyte used in the assembly of the lead-acid battery does not contain an organic additive.

The COD of the electrolyte is measured in accordance with JIS K 0102-1:2021 "17.2 Oxygen consumption by acidic potassium permanganate (CODMn)".
COD (CODMn) is calculated by the following formula: CODMn is calculated to two significant digits, one decimal place, and a lower limit of <0.5.
CODMn = (titer value - BL) x F x 1000/V x 0.2
Titration value: the amount (mL) of 5 mmol/L potassium permanganate aqueous solution required to titrate the sample prepared from the electrolyte
Blank (BL): Amount (mL) of 5 mmol/L potassium permanganate aqueous solution required for titration in a test using distilled water
F: Factor of 5 mmol/L potassium permanganate aqueous solution V: Amount (mL) of sample (sample used for titration) prepared from electrolyte
0.2: Oxygen equivalent (mg) of 1 mL of 5 mmol/L potassium permanganate aqueous solution

The titration sample is prepared in the following procedure. First, electrolyte is collected from an initial fully charged lead-acid battery into a 300 mL Erlenmeyer flask. The amount of electrolyte collected is adjusted to a maximum of 100 mL so that the titration amount is in the range of 3.5 mL to 5.5 mL. If the amount collected is less than 100 mL, the amount collected is measured and distilled water is added until the diluted amount is 100 mL. In this way, the electrolyte sample is prepared. In addition, 100 mL of distilled water is prepared in a separate 300 mL Erlenmeyer flask as a BL sample. The BL is measured every time a sample prepared from the electrolyte is titrated.

Prepare samples for titration from 100 mL of electrolyte sample and BL distilled water sample by the following procedure. First, add 10 mL of 5 mmol/L potassium permanganate solution to the above sample with a volumetric pipette and stir. Next, place each Erlenmeyer flask in a boiling water bath and heat for 30 minutes. At this time, the water in the water bath is always boiling, and the liquid level of the water bath should not be lower than the liquid level in the Erlenmeyer flask. After 30 minutes of heating, remove the Erlenmeyer flask and immediately add 10 mL of 12.5 mmol/L sodium oxalate solution to the liquid in the Erlenmeyer flask with a volumetric pipette. Prepare the sample for titration by cooling the liquid until the temperature is within the range of 50°C to 60°C. If the sample contains chloride ions, add 2 mL of 500 g/L silver nitrate solution with a graduated pipette and stir the resulting mixture until no precipitate remains and the liquid becomes transparent. If the cloudiness does not disappear, add more silver nitrate solution little by little and stir until the cloudiness disappears. The silver nitrate solution is added in such an amount that, overall, the silver nitrate is 1 g in excess of the equivalent amount of chloride ions contained in each sample. The silver nitrate solution is added to the above samples.

The prepared titration samples are titrated with a 5 mmol/L potassium permanganate aqueous solution. When the liquid in the Erlenmeyer flask turns slightly red during titration, stop the titration and leave it to stand for about 30 seconds to check whether the red color has disappeared. If the red color has disappeared, repeat titration and leaving it to stand until the red color does not disappear. For the sample prepared from the electrolyte and the sample prepared from distilled water, the amount (mL) of potassium permanganate aqueous solution required for titration is used as the titration value and BL in the above formula to determine the COD of the electrolyte. If the electrolyte is diluted with distilled water in the preparation of the sample, calculate the COD of the electrolyte before dilution taking into account the dilution amount.

(Porous film)
The porous film is a resin film having pores. The porous film includes a polymer material. The porous film includes optional components such as oil, inorganic particles, a penetrating agent, and a pore-forming agent, as necessary. The polymer material (hereinafter also referred to as a base polymer) constituting the resin film includes, for example, polyolefin. Polyolefin is a polymer that includes at least an olefin unit (a monomer unit derived from an olefin).

As the base polymer, polyolefin may be used in combination with other base polymers. The ratio of polyolefin to the total base polymer contained in the porous film is, for example, 50% by mass or more, or may be 80% by mass or more, or may be 90% by mass or more. The ratio of polyolefin is, for example, 100% by mass or less. The base polymer may be composed of polyolefin only.

Polyolefins include, for example, homopolymers of olefins, copolymers containing different olefin units, and copolymers containing olefin units and copolymerizable monomer units. A copolymer containing olefin units and copolymerizable monomer units may contain one or more types of olefin units. A copolymer containing olefin units and copolymerizable monomer units may contain one or more types of copolymerizable monomer units. A copolymerizable monomer unit is a monomer unit derived from a polymerizable monomer other than an olefin and copolymerizable with an olefin.

The polyolefin may, for example, be a polymer containing at least a C _2-3 olefin as a monomer unit. The C _2-3 olefin may be at least one selected from the group consisting of ethylene and propylene. The polyolefin may, for example, be polyethylene, polypropylene, an ethylene-propylene copolymer, or the like. Among these, polyolefins containing at least an ethylene unit, such as polyethylene and an ethylene-propylene copolymer, are preferred. A polyolefin containing an ethylene unit may be used in combination with another polyolefin.

The porous film may have at least a portion of the end portion that is not covered with the nonwoven fabric. This can prevent the softened positive electrode material from falling off while also preventing an increase in internal resistance.

The porous film is roughly rectangular, and usually has a total of four ends, including the top and bottom ends and both side ends. At one end, the width of the area of the porous film that is not covered with the nonwoven fabric (for example, w _p in FIG. 2 described later) may be, for example, 1 mm or more, and may be 2 mm or more. The width of this area may be, for example, 5 mm or less, 4.5 mm or less, or 4 mm or less. The porous film may have an area at the side end (preferably both side ends) that is not covered with the nonwoven fabric. When the porous film formed into a bag shape by crimping the end and the nonwoven fabric are laminated, a predetermined area of the side end including the crimped part is exposed outside the nonwoven fabric.

The width of the above region may be 1 mm or more (or 2 mm or more) and 5 mm or less, 1 mm or more (or 2 mm or more) and 4.5 mm or less, or 1 mm or more (or 2 mm or more) and 4 mm or less.

To increase the oxidation resistance of the porous film, it is desirable to provide ribs on the surface of the porous film facing the positive electrode plate. The ribs form a gap between the porous film and the positive electrode plate, reducing oxidation degradation of the porous film.

A porous film having ribs includes, for example, a base portion and ribs standing upright from the surface of the base portion. The ribs may be provided only on the surface of the base portion facing the positive electrode plate, or may be provided on both the positive electrode plate side and the negative electrode plate side. The base portion of the porous film refers to the constituent parts of the porous film excluding protrusions such as ribs, and refers to the sheet-like part that defines the outer shape of the porous film.

The height of the rib may be 0.05 mm or more. The height of the rib may be 1.2 mm or less. The height of the rib is the height of the part that protrudes from the surface of the base part (protrusion height).

The height of the ribs provided in the area of the porous film facing the positive electrode plate may be 0.4 mm or more. The height of the ribs provided in the area of the porous film facing the positive electrode plate may be 1.2 mm or less.

When ribs are provided on the positive electrode plate side of the porous film, they may be provided in an area not covered with nonwoven fabric. When ribs are provided on the portion facing the positive electrode material, nonwoven fabric may be placed between adjacent ribs. However, if ease of lamination with the nonwoven fabric is prioritized, ribs may not be provided on the positive electrode plate side of the porous film.

It is preferable that the porous film contains oil. Oil has the effect of suppressing oxidative deterioration of the porous film, so impregnating the porous film with oil results in a more significant improvement in heavy load life performance.

The oil content in the porous film is preferably 11% by mass or more, and may be 13% by mass or more. The oil content in the porous film is preferably 18% by mass or less. A preferred range for the oil content in the porous film may be, for example, 11% by mass or more and 18% by mass or less, or 13% by mass or more and 18% by mass or less. When the oil content is in such a range, the effect of suppressing oxidative deterioration of the porous film is further enhanced. In addition, the resistance of the porous film can be kept relatively low.

Oil refers to a hydrophobic substance that is liquid at room temperature (a temperature between 20°C and 35°C) and separates from water. Oils include naturally occurring oils, mineral oils, synthetic oils, etc., with mineral oils and synthetic oils being preferred. For example, paraffin oil, silicone oil, etc. can be preferably used. The porous film may contain one type of oil or a combination of two or more types of oil.

The porous film may contain inorganic particles. The inorganic particles are preferably ceramic particles. The ceramic particles may be made of at least one material selected from the group consisting of silica, alumina, and titania.

The content of inorganic particles in the porous film may be, for example, 40% by mass or more. The content of inorganic particles may be, for example, 80% by mass or less, or 70% by mass or less. A preferred range of the content of inorganic particles is, for example, 40% by mass or more and 80% by mass or less, or 40% by mass or more and 70% by mass or less.

The porous film may be in the form of a sheet, or a sheet folded in an accordion shape may be used as the porous film. The porous film may be formed in a bag shape. Either the positive electrode plate or the negative electrode plate may be wrapped in the bag-shaped porous film.

The porous film can be obtained, for example, by extruding a resin composition containing a base polymer and a pore-forming agent into a sheet, stretching the resin composition, and then removing at least a portion of the pore-forming agent. The resin composition may contain a penetrating agent (surfactant), etc. By removing at least a portion of the pore-forming agent, micropores are formed in the matrix of the base polymer. After removing the pore-forming agent, the sheet-shaped porous film is dried as necessary. The stretching may be performed by biaxial stretching, but is usually performed by uniaxial stretching. The sheet-shaped porous film may be processed into a bag shape as necessary.

In a porous film having ribs, the ribs may be formed when the resin composition is extruded into a sheet. The ribs may be formed by pressing the sheet with a roller having grooves corresponding to each rib after the resin composition is molded into a sheet or after the pore-forming agent is removed.

Examples of pore-forming agents include liquid pore-forming agents that are liquid at room temperature (temperatures of 20°C to 35°C) and solid pore-forming agents that are solid. Oil may be used as a liquid pore-forming agent. In this case, if a portion of the oil is left behind, a porous film containing oil is obtained. When extracting and removing the oil, the oil content in the porous film is adjusted by adjusting the type and composition of the solvent, the extraction conditions (extraction time, extraction temperature, solvent supply rate, etc.), etc. One type of pore-forming agent may be used alone, or two or more types may be used in combination. Oil may be used in combination with another pore-forming agent. A liquid pore-forming agent may be used in combination with a solid pore-forming agent. For example, a polymer powder may be used as a solid pore-forming agent.

The surfactant used as the penetrating agent may be, for example, either an ionic surfactant or a nonionic surfactant. The surfactant may be used alone or in combination of two or more kinds.

The content of the penetrant in the porous film is, for example, 0.01% by mass or more, and may be 0.1% by mass or more. The content of the penetrant in the porous film may be 10% by mass or less. From the viewpoint of keeping the COD in the electrolyte low and improving the charge acceptance, the content of the penetrant in the separator may be 3% by mass or less, or 1% by mass or less, preferably 0.5% by mass or less, and more preferably 0.2% by mass or less.

(Nonwoven fabric)
The nonwoven fabric is disposed between the porous film and the positive electrode plate so as to be in contact with the positive electrode plate. For example, when the porous film is bag-shaped and the negative electrode plate is housed in the bag, the nonwoven fabric may be disposed between both outer surfaces of the bag and the positive electrode plate. In this case, when the electrode plate at the end of the electrode plate group is a negative electrode plate, the nonwoven fabric may be disposed on one side of the bag-shaped porous film facing the positive electrode plate, and the nonwoven fabric may not be disposed on the other side not facing the positive electrode plate.

The nonwoven fabric may be a mat containing at least one type selected from the group consisting of glass fibers and organic fibers. Hereinafter, a mat containing glass fibers as the main component will be referred to as a glass fiber mat. A mat containing organic fibers as the main component will be referred to as an organic fiber mat. The main component refers to a component that accounts for 50% or more by mass of the mat.

The glass fiber mat is a nonwoven fabric made of glass fibers. The glass fiber mat may be a material called absorbent glass mat (AGM: Absorbed Glass Mat or Absorbent Glass Mat).

The glass fiber mat may be entirely made of glass fibers. The glass fiber content in the glass fiber mat may be 90% by mass or more, or 95% by mass or more. The glass fiber content in the glass fiber mat is 100% by mass or less. The glass fiber mat may contain components other than glass fibers, such as organic fibers, acid-resistant inorganic powders, and polymers as binders, but the content of these is usually 10% by mass or less, or 5% by mass or less.

The organic fiber mat may be formed entirely of organic fibers. The organic fiber content in the organic fiber mat may be 90% by mass or more, or 95% by mass or more. The organic fiber content in the organic fiber mat is 100% by mass or less. The organic fiber mat may contain components other than organic fibers, such as glass fibers, acid-resistant inorganic powders, and polymers as binders, but the content of these is usually 10% by mass or less, or 5% by mass or less.

The organic fibers may be polyolefin fibers, polyester fibers, acetalized polyvinyl alcohol fibers, polyurethane fibers, cellulose fibers, etc. These organic fibers have a high affinity with the positive electrode material and are easily attached to the positive electrode plate. Therefore, they are highly effective in preventing the softened positive electrode material from falling off.

The average fiber diameter of the glass fibers and organic fibers is, for example, 0.1 μm or more, and may be 0.5 μm or more. When the average fiber diameter is in this range, the effect of suppressing the falling off of the softened positive electrode material is enhanced. The average fiber diameter is, for example, 30 μm or less, and may be 10 μm or less. In this case, an excessive increase in the internal resistance of the battery can be suppressed. In addition, the nonwoven fabric can ensure a relatively high flexibility and can easily hold a relatively large amount of electrolyte.

The average fiber diameter of the nonwoven fabric may be 0.1 μm or more (or 0.5 μm or more) and 30 μm or less, or 0.1 μm or more (or 0.5 μm or more) and 10 μm or less.

The surface density of the nonwoven fabric is, for example, 10 g/m ² or more. The surface density of the nonwoven fabric may be 100 g/m ² or less, or 50 g/m ² or less.

The thickness of the nonwoven fabric is, for example, 30 μm or more, and may be 50 μm or more. The thickness of the nonwoven fabric is, for example, 800 μm or less, and may be 100 μm or less. When the thickness of the nonwoven fabric is within the above range, the nonwoven fabric is sufficiently thin and has high strength, so that higher CCA performance and better heavy load life performance can be obtained.

The porosity of the nonwoven fabric is, for example, 20% or more, and may be 40% or more. By having the porosity within the above range, the diffusibility of the electrolyte can be ensured and an increase in resistance can be suppressed. The porosity of the nonwoven fabric is, for example, 80% or less, and may be 70% or less.

The average pore diameter of the nonwoven fabric is, for example, 0.1 μm or more, and may be 0.5 μm or more. By having the average pore diameter within the above range, an increase in resistance due to the use of the nonwoven fabric can be suppressed. The average pore diameter is, for example, 100 μm or less, and may be 80 μm or less. By having the average pore diameter within the above range, falling off of the positive electrode material can be effectively suppressed.

The porous film and the nonwoven fabric may be laminated. The porous film and the nonwoven fabric may simply be stacked, or may be laminated or fixed using an adhesive. The porous film and the nonwoven fabric may also be laminated or fixed using welding or mechanical adhesion. For example, heat sealing may be used as a welding method. For example, gear sealing may be used as a mechanical adhesion method. For example, silicone adhesives, epoxy adhesives, and polyolefin adhesives may be used as adhesives. It is preferable to apply a small amount of adhesive so that the resistance of the laminate (separator) is not high. For example, it is preferable to apply the adhesive partially rather than to the entire surface of the porous film or nonwoven fabric to be bonded.

The evaluation and measurement methods will be described below.
(1) Analysis or size measurement of porous films and nonwovens (sample preparation)
For the analysis or size measurement of the porous film and nonwoven fabric, an unused porous film and nonwoven fabric or a porous film and nonwoven fabric removed from a lead-acid battery in a fully charged state at the beginning of use are used. The porous film and nonwoven fabric removed from the lead-acid battery are washed and dried prior to the analysis or measurement.

The porous film and nonwoven fabric removed from the lead-acid battery are washed and dried according to the following procedure. The porous film and nonwoven fabric removed from the lead-acid battery are immersed in pure water for one hour to remove the sulfuric acid in the separator. The porous film and nonwoven fabric are then removed from the liquid and left to stand for at least 16 hours in an environment of 25°C ± 5°C until they are dried.

(Thickness of porous film and nonwoven fabric and height of ribs)
The thickness of the porous film and nonwoven fabric is determined by measuring the thickness of the porous film portion or nonwoven fabric at five arbitrarily selected points in each cross-sectional photograph and averaging the measured values.

The rib height is determined by measuring the rib height from the base surface at 10 randomly selected points on a cross-sectional photograph of the porous film and averaging the measurements.

(Oil content in porous film)
If necessary, the nonwoven fabric is peeled off from the porous film, and the portion of the porous film facing the electrode material in the area where no adhesive is applied is processed into a rectangular shape to prepare a sample (hereinafter referred to as sample A). When the porous film has ribs, sample A is processed so as not to include the ribs.

Approximately 0.5 g of sample A is taken and accurately weighed to determine the initial mass of the sample (m0). The weighed sample A is placed in a glass beaker of appropriate size, and 50 mL of n-hexane is added. Next, ultrasonic waves are applied to the sample together with the beaker for approximately 30 minutes to dissolve the oil contained in sample A into n-hexane. Next, sample A is removed from n-hexane, dried in air at room temperature (temperature between 20°C and 35°C), and then weighed to determine the mass of the sample after the oil has been removed (m1). The oil content is then calculated using the following formula. The oil content is determined for 10 samples A, and the average value is calculated. The obtained average value is taken as the oil content in the porous film.

Oil content (mass%) = (m0 - m1)/m0 x 100

(Content of inorganic particles in porous film)
A portion of the sample A prepared in the same manner as above is taken, accurately weighed, and then placed in a platinum crucible and heated with a Bunsen burner until no white smoke is generated. The obtained sample is then heated in an electric furnace (in oxygen flow, 550°C ± 10°C) for about 1 hour to be incinerated, and the incinerated material is weighed. The ratio (percentage) of the mass of the incinerated material to the mass of sample A is calculated, and this is the content (mass%) of the inorganic particles. The content of the inorganic particles is determined for 10 samples A, and the average value is calculated. The obtained average value is the content of the inorganic particles in the porous film.

(Content of penetrant in porous film)
A part of sample A prepared in the same manner as above is taken, accurately weighed, and then dried for 12 hours or more at room temperature (temperature of 20°C to 35°C) in a reduced pressure environment lower than atmospheric pressure. The dried product is placed in a platinum cell and set in a thermogravimetric measuring device, and the temperature is raised from room temperature to 800°C ± 1°C at a heating rate of 10K/min. The weight loss amount when the temperature is raised from room temperature to 250°C ± 1°C is taken as the mass of the penetrant, and the ratio (percentage) of the mass of the penetrant to the mass of sample B is calculated, and the content (mass%) of the penetrant is taken as the above. As the thermogravimetric measuring device, a Q5000IR manufactured by T. A. Instruments is used. The content of the penetrant is determined for 10 samples A, and the average value is calculated. The obtained average value is taken as the content of the penetrant in the porous film.

(Average fiber diameter of nonwoven fabric)
The average fiber diameter of a nonwoven fabric can be determined by determining the maximum diameter of any 100 fibers taken out of the nonwoven fabric in any cross section perpendicular to the length direction, and averaging the maximum diameters.

(Area density of nonwoven fabric)
The portion of the nonwoven fabric facing the electrode material is cut, and the portion not coated with adhesive is sampled and weighed, and the length and width of the nonwoven fabric (in other words, the length and width of the cut portion) are measured. The area of the nonwoven fabric is calculated from the length and width, and the mass (g) of the nonwoven fabric per ¹ m2 is calculated as the areal density.

(Porosity of nonwoven fabric)
The porosity is determined by measuring the dimensions, weight and density of a sample cut into a rectangular parallelepiped of appropriate size, and calculating the ratio of apparent volume to true volume according to the following formula.
Porosity (%) = (apparent volume/true volume) x 100
Apparent volume (cm ³ )=length (cm)×width (cm)×thickness (cm)
True volume (cm ³ )=weight (g)/density (g/cm ³ )

(Average pore size of nonwoven fabric)
A portion of the nonwoven fabric facing the electrode material where no adhesive is applied is taken and cut to a size of 20 mm length x 5 mm width to prepare a measurement sample. The pore distribution of the measurement sample is measured by mercury intrusion using a Shimadzu Corporation mercury porosimeter "Autopore IV9510". The measurement pressure range is 4 psia (≒27.6 kPa) to 60,000 psia (≒414 MPa). The pore size range is 0.01 μm to 50 μm. The pore size at which the cumulative pore volume is 50% of the total pore volume is the average pore size.

The test method for lead-acid batteries will be described below.
(1) CCA Performance In accordance with JIS D 5301:2019, the starting ability of a lead-acid battery is evaluated by the terminal voltage 30 seconds after the start of discharge in the following procedure. A higher voltage value indicates higher starting ability and lower internal resistance.
(a) After fully charging the battery, place it in a cooling room at -18°C ± 1°C for a minimum of 16 hours.
(b) After confirming that the electrolyte temperature in one of the central cells is −18° C.±1° C., discharge the cell for 30 seconds at a cold cranking current of I _cc .
(c) Record the terminal voltage 30 seconds after the start of discharge.
Here, the cold cranking current _Icc is a current value according to the performance rank defined in JIS D 5301:2019.

(2) Heavy Load Life Performance The heavy load life performance is evaluated as follows.
JIS D 5301:2019 9.5.5 Life Test b) A heavy load test is performed in accordance with the heavy load life test. More specifically, a fully charged lead-acid battery is first discharged for 1 hour at the discharge current shown in Table 1, and then charged for 5 hours at the charge current shown in Table 1. This cycle of discharge and charge is defined as one cycle. The discharge current and discharge current are changed as shown in Table 1 according to the 20-hour rate capacity of the lead-acid battery. During the test, the lead-acid battery is placed in a water tank at 40°C ± 2°C. The water surface of the water tank is located 15 mm to 25 mm below the top surface of the battery. When several lead-acid batteries are placed in the water tank, the distance between adjacent lead-acid batteries and the distance between the lead-acid battery and the inner wall of the adjacent water tank are each at least 25 mm.

During the test, the battery is continuously discharged every 25 cycles at the discharge current shown in Table 1 until the terminal voltage of the lead-acid battery reaches 10.2 V, and the discharge duration is recorded. Next, the battery is charged every 15 minutes at the charge current shown in Table 1 until the terminal voltage of the lead-acid battery or the density of the electrolyte (converted value at 25°C) shows a constant value three times in a row. This discharge and charge are also counted in the number of cycles.

The test is terminated when it is confirmed that the capacity (Ah) calculated from the product of the discharge time and discharge current measured in the above test has fallen to 50% or less of the value calculated by dividing the 20-hour capacity by 1.155 and does not rise again. The number of cycles until the end of the test is used as an index of the life performance in the heavy load life test. The fact that the capacity does not rise again is confirmed by charging to a fully charged state after the capacity has fallen to 50% or less of the value calculated by dividing the 20-hour capacity by 1.155, and discharging again in the same manner as above, and the capacity calculated from the product of the discharge time and discharge current at this time is 50% or less of the value calculated by dividing the 20-hour capacity by 1.155. The number of cycles that constitutes the life can be calculated by approximating the number of cycles at which the 20-hour capacity is 50% or less of the value calculated by dividing the 20-hour capacity by 1.155 from a graph of the number of cycles vs. capacity plotted with the discharge capacity every 25 cycles.

Hydrate with purified water as needed, but do not hydrate immediately before continuous discharge.

The items described in this specification may be combined in any manner.

FIG. 1 shows an external appearance of an example of a lead-acid battery according to an embodiment of the present invention.
The lead-acid battery 1 includes a battery case 12 that contains a plate group 11 and an electrolyte (not shown). The battery case 12 is divided into a plurality of cell chambers 14 by partitions 13. Each cell chamber 14 contains one of the plate groups 11. The opening of the battery case 12 is closed by a lid 15 that includes a negative electrode terminal 16 and a positive electrode terminal 17. The lid 15 is provided with a vent plug 18 for each cell chamber. When rehydrating, the vent plug 18 is removed and rehydration liquid is replenished. The vent plug 18 may have a function of discharging gas generated in the cell chamber 14 to the outside of the battery.

Each electrode plate group 11 is formed by stacking a plurality of negative electrode plates 2 and positive electrode plates 3 with separators 4 between them. In the cell chamber 14 located at one end of the battery case 12, the negative electrode shelf 6 that connects the plurality of negative electrode plates 2 in parallel is connected to the through connector 8, and the positive electrode shelf 5 that connects the plurality of positive electrode plates 3 in parallel is connected to the positive electrode column 7. The positive electrode column 7 is connected to a positive electrode terminal 17 outside the lid 15. In the cell chamber 14 located at the other end of the battery case 12, the negative electrode column 9 is connected to the negative electrode shelf 6, and the through connector 8 is connected to the positive electrode shelf 5. The negative electrode column 9 is connected to a negative electrode terminal 16 outside the lid 15. Each through connector 8 passes through a through hole provided in the partition wall 13 to connect the electrode plate groups 11 of adjacent cell chambers 14 in series.

FIG. 2 is a schematic plan view of the separator 4. The separator 4 is a laminate of a bag-shaped porous film 4a and a nonwoven fabric 4b. The bag-shaped porous film 4a houses the negative electrode plate 2 of FIG. 1. The bag-shaped porous film 4a has a fold at the bottom end in FIG. 2 and an opening at the top end. At both side ends of the bag-shaped porous film 4a, a pressure-bonding portion 20 is provided linearly in the vertical direction so as to close the overlapped porous film 4a. At both side ends of the bag-shaped porous film 4a, a region 21 that is not covered with the glass fiber mat 4b is formed. The side end of the nonwoven fabric 4b is located inside the pressure-bonding portion 20. Therefore, the width w _p of the region 21 is larger than the width w a from the side end of the porous film _4a to the pressure-bonding portion 20 (more specifically, the outer position of the pressure-bonding portion 20).

In the lead-acid battery 1, the separator 4 is arranged so that the nonwoven fabric 4b is in contact with the positive electrode plate 3. In the separator 4 in FIG. 2, when the back side is in contact with the positive electrode plate 3, the nonwoven fabric 4b shown on the front side is also provided on the back side.

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

Lead-acid batteries E1 to E13
Each of the lead acid batteries of Examples 1 to 13 was produced according to the following procedure.
(1) Preparation of Separator A resin composition containing polyethylene, silica particles, paraffin-based oil as a pore-forming agent, and a penetrating agent was extruded into a sheet, stretched, and then a portion of the pore-forming agent was removed to prepare a porous film having ribs on one side.

The oil content of the porous film determined by the procedure described above was 11 to 18% by mass, and the silica particle content was 60% by mass.
The rib height determined by the procedure described above was 0.2 mm.
The thickness of the porous film (thickness of the base portion) determined by the above-mentioned procedure was standardized to 0.2 mm.

Next, the sheet-like porous film was folded in half so that the ribs were arranged on the inner surface to form a bag, and the overlapping ends were crimped to obtain a bag-like porous film (size when laid flat: length 117 mm x width 152 mm). The crimped part was 3 mm wide, located 2 mm inside from the side edge of the porous film.

A glass fiber mat (size under atmospheric pressure: length 117 mm × width 143 mm, thickness: 50 μm, average fiber diameter: 17 μm, surface density: 10 g/m ² , porosity: 80%, average pore diameter: 70 μm) was attached with an adhesive to both outer surfaces of the bag-shaped porous film as shown in Figure 2. The width of the porous film was larger than that of the glass fiber mat, and an area of 4.5 mm wide where the glass fiber mat was not overlapped was formed at both side ends of the porous film.

The porous film ratio R, oil content, silica particle content, base thickness, rib height, glass fiber mat size, average fiber diameter, and surface density are values determined for the porous film or glass fiber mat before the lead-acid battery was fabricated, but are approximately the same as the values measured by the procedure described above for the porous film or glass fiber mat removed from the lead-acid battery after fabrication.

(2) Preparation of Positive Electrode Plate A positive electrode paste was prepared by mixing lead oxide, reinforcing material (synthetic resin fiber), water and sulfuric acid. The positive electrode paste was filled into the mesh of an expanded lattice made of a Pb-Ca-Sn alloy not containing antimony, and aged and dried to obtain an unformed positive electrode plate having a width of 137 mm, a height of 110 mm and a thickness of 1.6 mm.

(3) Preparation of negative electrode plate Lead oxide, carbon black, barium sulfate, lignin, reinforcing material (synthetic resin fiber), water and sulfuric acid were mixed to prepare a negative electrode paste. The negative electrode paste was filled into the mesh of an expanded lattice made of an antimony-free Pb-Ca-Sn alloy, and aged and dried to obtain an unformed negative electrode plate with a width of 137 mm, a height of 110 mm and a thickness of 1.3 mm. The amounts of carbon black, barium sulfate, lignin and synthetic resin fiber used were adjusted so that the contents of each component in the negative electrode plate taken out of a fully charged lead-acid battery were 0.3 mass%, 2.1 mass%, 0.1 mass% and 0.1 mass%, respectively.

(4) Preparation of lead-acid battery An unformed negative plate was placed in a bag-shaped porous film of a separator. The negative plate and the positive plate were laminated through the separator so that the glass fiber mats attached to both outer surfaces of the bag were in contact with the positive plate. In this way, an electrode plate group was formed by seven unformed negative plates and six unformed positive plates.

The ears of the positive and negative plates were welded to the positive and negative shelf parts, respectively, using the cast-on-strap method. The plate group was inserted into a polypropylene battery case, electrolyte was poured in, and chemical formation was performed inside the battery case to assemble a flooded lead-acid battery with a rated voltage of 12 V and a 5-hour rate capacity of 30 Ah. The 5-hour rate capacity is the capacity when discharged at a current (A) that is 1/5 of the Ah value listed in the rated capacity. Six plate groups were connected in series inside the battery case.

An aqueous sulfuric acid solution was used as the electrolyte. The density of the electrolyte after formation at 20°C was 1.285. The electrolyte taken out of a fully charged lead-acid battery was adjusted so that its COD, by mass, was the value shown in Table 2. The COD was controlled by the amount of penetrant used when producing the porous film, the cleaning condition of the expanded grid of the positive and negative plates, etc.

Lead-acid batteries R1 to R15
A lead-acid battery was produced in the same manner as in Examples 1 to 13, except that in the preparation of the separator (1), no glass fiber mats were attached to either outer surface of the bag-shaped porous film.

(5) Evaluation The CCA performance and heavy load life performance of the lead-acid battery were evaluated according to the procedure described above. The heavy load life performance was evaluated according to the procedure described above for the lead-acid battery that was once fully charged. The CCA performance was evaluated as a relative value when the terminal voltage at 30 seconds of the lead-acid battery R15 was set to 100, and the heavy load life performance was evaluated as a relative value when the life cycle of the lead-acid battery R8 was set to 100.

The evaluation results are shown in Table 2. E1 to E13 are working examples. R1 to R15 are comparative examples.

As shown in Table 2, when nonwoven fabric was not used, the heavy load life performance was insufficient regardless of the COD. This was because the softening and falling off of the positive electrode material could not be suppressed regardless of the COD control. In particular, when the COD was 5 mg/L or less, especially 1 mg/L, oxygen was generated on the positive electrode side, and the porous film was damaged due to oxidative deterioration, further deteriorating the heavy load life performance.

On the other hand, when nonwoven fabric was used, the CCA performance and heavy load life performance were significantly improved by controlling the COD. That is, when the COD was 160 mg/L or less, the CCA performance and heavy load life performance were significantly improved. However, when the COD was 5 mg/L or less, especially 1 mg/L, the heavy load life performance decreased. This is thought to be because the porous film was damaged by oxygen generated on the positive electrode side due to too little COD in the electrolyte.

The lead-acid battery according to the present disclosure is suitable for use in idling stop applications (such as lead-acid batteries for vehicles with idling stop systems) and as a starting power source for various vehicles (such as trucks, commercial vehicles such as taxis, and motorcycles). Lead-acid batteries can also be suitably used as a power source for industrial power storage devices such as electric vehicles (such as forklifts). Note that these applications are merely examples. Applications of the lead-acid battery according to the present disclosure are not limited to these. Idling stop (also called idling reduction) is sometimes referred to as IS.

1: Lead-acid battery 2: Negative electrode plate 3: Positive electrode plate 4: Separator 4a: Porous film 4b: Glass fiber mat 5: Positive electrode shelf 6: Negative electrode shelf 7: Positive electrode column 8: Through connector 9: Negative electrode column 11: Electrode plate group 12: Battery case 13: Partition wall 14: Cell chamber 15: Lid 16: Negative electrode terminal 17: Positive electrode terminal 18: Vent plug 20: Crimping section 21: Area of porous film not covered with glass fiber mat

Claims (8)

A positive electrode plate;
A negative electrode plate;
a resin porous film interposed between the positive electrode plate and the negative electrode plate;
a nonwoven fabric interposed between the positive electrode plate and the negative electrode plate and in contact with the positive electrode plate;
An electrolyte;
Equipped with
A lead-acid battery, wherein the chemical oxygen demand in the electrolyte is 160 mg/L or less. The lead-acid battery according to claim 1, wherein the nonwoven fabric is a mat containing at least one type selected from the group consisting of glass fibers and organic fibers. The lead acid battery according to claim 1, wherein the chemical oxygen demand is 100 mg/L or less. The lead acid battery according to claim 1, wherein the chemical oxygen demand is 1.0 mg/L or more. The lead-acid battery according to claim 1, wherein the nonwoven fabric is fixed to the surface of the positive electrode plate. The lead-acid battery according to claim 1, wherein the porous film has a thickness of 100 μm or more and 300 μm or less. The lead-acid battery according to claim 1, wherein the nonwoven fabric has a thickness of 30 μm or more and 800 μm or less. The lead-acid battery according to claim 1 , wherein the porous film has an area not covered with the nonwoven fabric in at least a part of an end portion.