JP7757982B2 - lead acid battery - Google Patents

Description

The present invention relates to a lead-acid battery.

Lead-acid batteries are used in a variety of applications, including automotive and industrial use. Lead-acid batteries contain negative and positive plates, a separator (or mat), and an electrolyte. Each plate comprises a current collector and electrode material. The top of the current collector has a tab for connecting to an external terminal.

Lead-acid batteries are sometimes used in a state of insufficient charge known as partial state of charge (PSOC). For example, the lead-acid batteries installed in idle stop-start (ISS) vehicles are used in PSOC. When a lead-acid battery is repeatedly charged and discharged in PSOC, corrosion can reduce the thickness of the negative electrode plate's lug, resulting in reduced lifespan. To prevent this corrosion, the addition of a surface layer to the lug is being considered.

Patent Document 1 proposes a lead-acid battery comprising a positive electrode plate, a negative electrode plate, and an electrolyte, in which the negative electrode plate comprises a negative electrode current collector having a grid-shaped grid portion, an edge portion connected to the edge of the grid portion, and a current-collecting ear portion protruding from the edge portion, and a surface layer containing an alloy or metal selected from Pb-Sn alloys, Pb-Sb alloys, Pb-Sn-Sb alloys, and Sn is formed on the surface of at least one of the edge portion and the ear portion, and the electrolyte contains one or more selected from sodium ions, potassium ions, magnesium ions, aluminum ions, phosphoric acid, and boric acid.

In addition, additives are sometimes added to the components of lead-acid batteries in order to impart various functions.

Patent document 2 proposes a lead-acid battery in which a copolymer of propylene oxide and ethylene oxide is added to the negative electrode plate active material in combination with lignin sulfonic acid.

WO 2009/142220 Japanese Patent Application Publication No. 182662/1983

When a lead-acid battery is repeatedly charged and discharged at PSOC, the potential of the negative electrode plate lug reaches a range where corrosion is likely to progress. Corrosion of the lug causes thinning of the lug, which can lead to breakage, making charging and discharging impossible. As in Patent Document 1, providing a surface layer containing Sn on the lug reduces corrosion to some extent. However, to obtain the corrosion-inhibiting effect of the surface layer, the Sn concentration in the surface layer must be high, at 10% by mass or more.

One aspect of the present invention is a lead-acid battery,
The lead-acid battery includes at least one cell including a plate group and an electrolyte;
the electrode plate group includes a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate,
The negative electrode plate includes a current collector having a lug portion and a negative electrode material,
the ear portion has a surface layer containing Sn,
The Sn content in the surface layer is less than 10 mass %,
The negative electrode material relates to a lead-acid battery, and includes a polymer compound having a peak in the range of 3.2 ppm to 3.8 ppm in chemical shift of a ¹ H-NMR spectrum measured using deuterated chloroform as a solvent.

Another aspect of the present invention is a lead-acid battery,
The lead-acid battery includes at least one cell including a plate group and an electrolyte;
the electrode plate group includes a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate,
The negative electrode plate includes a current collector having a lug portion and a negative electrode material,
the ear portion has a surface layer containing Sn,
The Sn content in the surface layer is less than 10 mass %,
The negative electrode material relates to a lead-acid battery and comprises a polymer compound containing a repeating structure of oxyC _2-4 alkylene units.

1 is a partially cutaway exploded perspective view showing the appearance and internal structure of a lead-acid battery according to one aspect of the present invention. 10 is a graph showing changes in terminal voltage of lead-acid batteries E17 to E19 in PSOC cycles. 10 is a graph showing the change in potential of the lug of the negative electrode plate during the PSOC cycle of lead-acid batteries E17 to E19. 10 is a graph showing changes in the specific gravity of the electrolyte at the top of the electrode plate assembly during PSOC cycles of lead-acid batteries E17 to E19. 10 is a graph showing the relationship between the specific gravity of the electrolyte and the amount of thinning of the negative electrode plate in lead-acid batteries E20 to E23 and E24 to E27. FIG. 4 is an explanatory diagram of measurement points for the thickness of the electrode plate.

When lead-acid batteries are repeatedly charged and discharged in a PSOC cycle, corrosion can progress at the lug of the negative plate, causing thinning of the lug. During the PSOC cycle, the potential of the lug of the negative plate falls into a range in which lead sulfate is easily produced from lead during discharge, and the reduction of lead sulfate to lead is incomplete during charge. It is thought that this repeated cycle gradually progresses corrosion inside the lug, causing thinning of the lug.

At the potential of the negative electrode plate lug during the PSOC cycle, oxidation and reduction reactions of Sn are unlikely to occur. Therefore, if a Sn-containing surface layer is provided on the lug of the negative electrode plate, the shielding effect of Sn makes it difficult for oxidation and reduction reactions involving lead to occur at the lug. As a result, when a Sn-containing surface layer is provided on the lug of a negative electrode plate, edge thinning during the PSOC cycle is reduced compared to when no surface layer is provided. Therefore, edge thinning is reduced as the Sn content in the surface layer increases. On the other hand, a high Sn content is not only cost-inefficient, but also increases the amount of gas generated during overcharge, resulting in a greater loss of electrolyte. From the perspectives of reducing cost and reducing the amount of electrolyte lost during overcharge, it is advantageous to keep the Sn content of the surface layer low. However, when the Sn content is less than 10% by mass, it has been thought to be practically difficult to suppress edge thinning during the PSOC cycle using a Sn-containing surface layer.

However, it has been found that even when the Sn content in the surface layer of the ear of the negative plate is less than 10% by mass, adding a specific polymer compound to the negative electrode material of the negative plate significantly reduces ear thinning when the lead-acid battery is charged and discharged in PSOC.

In view of the above, a lead-acid battery according to one aspect of the present invention includes at least one cell including an electrode plate assembly and an electrolyte. The electrode plate assembly includes a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate. The negative electrode plate includes a current collector with a lug portion and a negative electrode material. The lug portion includes a surface layer containing Sn. The Sn content in the surface layer is less than 10 mass%. The negative electrode material includes a polymer compound having a peak in the chemical shift range of 3.2 ppm to 3.8 ppm in ^{a 1H} -NMR spectrum measured using deuterated chloroform as a solvent.
In the above ¹ H-NMR spectrum, the peak appearing in the chemical shift range of 3.2 ppm to 3.8 ppm is derived from an oxyC _2-4 alkylene unit.

A lead-acid battery according to another aspect of the present invention includes at least one cell including an electrode plate assembly and an electrolyte. The electrode plate assembly includes a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate. The negative electrode plate includes a current collector with a lug portion and a negative electrode material. The lug portion includes a surface layer containing Sn. The Sn content in the surface layer is less than 10 mass%. The negative electrode material includes a polymer compound including a repeating structure of oxy- _C2-4 alkylene units.

In lead-acid batteries according to one and other aspects of the present invention, the negative electrode material contains the polymer compound described above. Combining this negative electrode material with a negative electrode current collector having a surface layer containing Sn in the terminal area reduces edge thinning during PSOC cycles, even when the Sn content in the surface layer is less than 10% by mass. In addition to the lower Sn content in the surface layer compared to conventional methods, the inclusion of a polymer compound in the negative electrode material suppresses gas generation during overcharge, thereby reducing electrolyte loss (hereinafter sometimes simply referred to as "electrolyte loss"). In other words, this achieves both an excellent effect of reducing edge thinning during PSOC cycles and an excellent effect of reducing electrolyte loss during overcharge. Suppressing edge thinning prevents edge thinning from causing breakage of the terminal area, which can prevent charging and discharging. Therefore, even when the Sn content in the surface layer is less than 10% by mass, the lead-acid battery can be used in practice. This is advantageous in terms of extending the life of the lead-acid battery. Furthermore, the ability to reduce the Sn content in the surface layer is advantageous in terms of cost reduction.

The reason why the inclusion of the above-mentioned polymer compound in the negative electrode material reduces edge thinning in the negative electrode plate during the PSOC cycle is thought to be as follows: First, when the negative electrode material contains the above-mentioned polymer compound, the polymer compound is present in the vicinity of the lead, which is the negative electrode active material. This causes the potential of the negative electrode plate to shift in a more base direction during the PSOC cycle. The potential of the lug of the negative electrode plate also shifts in a more base direction, making it easier for the reduction reaction of lead sulfate to lead to proceed during charging. In addition to the shielding effect of Sn in the lug, lead sulfate is less likely to accumulate, making it possible to reduce edge thinning even though the Sn content in the surface layer is low at less than 10% by mass.

In addition, the low Sn content in the surface layer is thought to suppress the gas generation reaction involving Sn during overcharge. In addition, the potential of the negative electrode plate shifts in a more base direction, increasing the hydrogen overvoltage, thereby suppressing the generation of hydrogen gas in the negative electrode plate during overcharge. In this way, suppressing gas generation during overcharge can reduce loss of electrolyte.

The effect of suppressing edge thinning in the negative electrode plate during PSOC cycles and the effect of suppressing electrolyte loss during overcharge can be achieved even when the content of the polymer compound in the negative electrode material is very small (e.g., less than 0.01% by mass). From this, it is believed that the oxy- _C2-4 alkylene unit of the polymer compound contained in the negative electrode material exerts a high adsorption effect on lead. Furthermore, it is believed that the polymer compound spreading thinly on the lead surface facilitates a shift in the potential of the entire negative electrode plate, including the edge portion, toward a more noble direction. Furthermore, it is believed that the polymer compound spreading thinly on the lead surface increases the hydrogen overvoltage over a wide area of the lead surface of the negative electrode plate, inhibiting the side reaction of hydrogen generation due to proton reduction during overcharge. The fact that the polymer compound spreads thinly on the lead surface is consistent with the polymer compound's tendency to adopt a linear structure. Therefore, it is important that the polymer compound is included in the negative electrode material, regardless of whether it is included in components of the lead-acid battery other than the negative electrode material.

In a lead-acid battery according to one aspect of the present invention, the polymer compound may include an oxygen atom bonded to an end group and a —CH ₂ — group and/or a —CH< group bonded to the oxygen atom. In a ¹ H-NMR spectrum, the ratio of the integral of the peak between 3.2 ppm and 3.8 ppm to the total integral of the peak between 3.2 ppm and 3.8 ppm, the integral of the peak at hydrogen atoms of the _—CH 2 — group bonded to the oxygen atom, and the integral of the peak at hydrogen atoms of the —CH< group bonded to the oxygen atom is preferably 85% or more. Such a polymer compound contains many oxy-C _2-4 alkylene units in its molecule. This is thought to facilitate adsorption of the polymer compound to lead, and the linear structure facilitates thin coating of the lead surface. This further enhances the effect of reducing edge thinning of the negative electrode plate during PSOC cycles, and further improves the effect of suppressing loss of electrolyte during overcharge.

A polymer compound having a peak in the chemical shift range of 3.2 ppm to 3.8 ppm in a ¹ H-NMR spectrum preferably contains a repeating structure of oxy-C _{2-4 alkylene units. When a polymer compound containing a repeating structure of oxy-C 2-4 alkylene} units is used, it is thought that the polymer compound is more likely to adsorb to lead and to easily assume a linear structure, which makes it easier to thinly coat the lead surface. This is therefore advantageous in further enhancing the effect of suppressing edge thinning of the negative electrode plate during PSOC cycles and loss of electrolyte during overcharge.

The polymer compound may contain at least one selected from the group consisting of a hydroxy compound having a repeating structure of an oxy- _C2-4 alkylene unit, an etherified product of a hydroxy compound, and an esterified product of a hydroxy compound. Here, the hydroxy compound is at least one selected from the group consisting of a poly- _C2-4 alkylene glycol, a copolymer containing a repeating structure of an oxy- _C2-4 alkylene, and a poly- _C2-4 alkylene oxide adduct of a polyol. Use of such a polymer compound can further suppress edge thinning of the negative electrode plate during PSOC cycles and loss of electrolyte during overcharge.

The repeating structure of the oxy _C2-4 alkylene unit may contain at least a repeating structure of an oxypropylene unit (-O-CH( _-CH3 ) _-CH2- ). Such a polymer compound is thought to have an excellent balance of high adsorption to lead while easily spreading thinly on the lead surface. This makes it possible to more effectively reduce loss of electrolyte. It is also possible to further reduce thinning of the negative electrode plate.

As such, the polymer compound has high adsorption properties for lead while also being able to thinly coat the lead surface. Therefore, even if the polymer compound content in the negative electrode material is very small (more specifically, 400 ppm or less), it can reduce edge thinning of the negative electrode plate during PSOC cycles and electrolyte loss during overcharge. From the perspective of ensuring even greater effects in suppressing edge thinning and electrolyte loss, the polymer compound content in the negative electrode material is preferably 15 ppm or more.

The origin of the polymer compound contained in the negative electrode material is not particularly limited as long as the polymer compound can be contained in the negative electrode material. When producing a lead-acid battery, the polymer compound may be contained in any of the components of the lead-acid battery (e.g., the negative electrode plate, the positive electrode plate, the electrolyte, and the separator). The polymer compound may be contained in one component, or in two or more components (e.g., the negative electrode plate and the electrolyte).

The Sn content in the surface layer of the edge portion is preferably 7% by mass or less. Even with such a low Sn content, the polymer compound can reduce edge thinning and liquid loss.

The Sn content in the surface layer of the edge portion is preferably 0.01% by mass or more. In this case, it is possible to obtain the effect of suppressing edge thinning due to Sn. Furthermore, even with such a low Sn content, the action of the polymer compound can ensure a high effect in reducing edge thinning and liquid loss.

In at least one cell, the plate assembly includes multiple positive plates and multiple negative plates, with the positive plates and negative plates stacked alternately with separators interposed between them. Preferably, the plate assembly includes nine or more negative plates. Increasing the number of plates included in the plate assembly prevents a decrease in the specific gravity of the electrolyte above the plate assembly. This prevents lead dissolution, further enhancing the effect of preventing thinning of the negative plate edges.

It is preferable that the relationship between the distance between the positive and negative plates in the electrode plate assembly (electrode distance D) and the maximum separator thickness T be D-T≦0.15 mm or less. When the relationship between the electrode distance D and the separator maximum thickness T is in this range, the effect of suppressing the decrease in the specific gravity of the electrolyte in the upper part of the electrode plate assembly is further enhanced. Because the decrease in the specific gravity of the electrolyte around the ears is further suppressed, the effect of suppressing ear thinning of the negative plate is further enhanced.

The electrolyte preferably contains Al ions. In this case, the accumulation of lead sulfate during the PSOC cycle is suppressed, which further enhances the effect of suppressing the decrease in the specific gravity of the electrolyte around the ears, thereby further enhancing the effect of suppressing ear thinning of the negative plate.

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

In this specification, the Sn content in the surface layer of the ear portion of the negative electrode plate, the polymer compound content in the negative electrode material, the electrode distance D, and the maximum thickness T of the separator are determined for a negative electrode plate, electrode plate group, or separator removed from a fully charged lead-acid battery.

(Explanation of terms)
(Up and down direction of lead-acid battery or lead-acid battery components)
In this specification, the up-down direction of a lead-acid battery or its components (such as plates, a battery case, and a separator) refers to the up-down direction in the vertical direction of the lead-acid battery when the battery is in use. Each of the positive and negative plates has a lug for connecting to an external terminal. In some cases, such as horizontally placed valve-regulated lead-acid batteries, the lug is provided on the side of the plate so as to protrude laterally, but in most lead-acid batteries, the lug is usually provided on the top of the plate so as to protrude upward.

(surface layer of ear part)
When the cross section of the lug of the negative electrode plate or negative electrode current collector is observed with a metallurgical microscope, the outer layer having properties (color, state of metal particles, etc.) different from those of the inner layer is defined as the surface layer.

(Negative electrode material)
The negative electrode material is usually held by a current collector. The negative electrode material is the portion of the negative electrode plate excluding the current collector. A mat, pasting paper, or other member may be attached to the negative electrode plate. Such members (also referred to as attachment members) are used integrally with the negative electrode plate and are therefore included in the negative electrode plate. When the negative electrode plate includes an attachment member (such as a mat or pasting paper), the negative electrode material is the portion of the negative electrode plate excluding the current collector and attachment member.

(Polymer Compound)
The polymer compound satisfies at least one of the following conditions (i) and (ii):
Condition (i)
The polymer compound has a peak in the chemical shift range of 3.2 ppm to 3.8 ppm in the ¹ H-NMR spectrum measured using deuterated chloroform as a solvent.
Condition (ii)
The polymeric compound comprises a repeating structure of oxyC _2-4 alkylene units.

In condition (i), the peak in the range of 3.2 ppm or more and 3.8 ppm or less is derived from the oxy-C _2-4 alkylene unit. In other words, a polymer compound satisfying condition (ii) is also a polymer compound satisfying condition (i). A polymer compound satisfying condition (i) may contain a repeating structure of a monomer unit other than the oxy-C _2-4 alkylene unit, as long as it has a certain level of molecular weight. The number average molecular weight (Mn) of a polymer compound satisfying the above (i) or (ii) may be, for example, 300 or more.

(oxy _C2-4 alkylene unit)
The oxy C _2-4 alkylene unit is a unit represented by —O—R ¹ — (R ¹ represents a C _2-4 alkylene group).

(number average molecular weight)
In this specification, the number average molecular weight (Mn) is determined by gel permeation chromatography (GPC). The standard substance used in determining Mn is polyethylene glycol.

(distance between poles D)
The inter-electrode distance D is expressed by the following formula.
Distance between electrodes D = (pitch - thickness of positive electrode plate - thickness of negative electrode plate) / 2
Here, the pitch is the average value of the center-to-center distance between the lugs of a pair of adjacent positive plates. More specifically, the pitch is the average value of the center-to-center distance between the lugs of all pairs of adjacent positive plates included in the plate group. In a lead-acid battery having multiple series-connected plate groups, the pitch is the average value for one plate group (cell) located at the end and one plate group (cell) located near the center. Furthermore, the thickness of the positive plate is the average value of the thicknesses of all positive plates included in the plate group, and the thickness of the negative plate is the average value of the thicknesses of all negative plates included in the plate group.

(Maximum thickness T of separator)
The maximum thickness T of the separator is the average value of the maximum thicknesses t of all the separators included in the electrode plate group (cell). In a lead-acid battery having multiple electrode plate groups connected in series, the maximum thickness T of the separator is the average value of the thicknesses t of one electrode plate group (cell) located at the end and one electrode plate group (cell) located near the center.

If the thickness of the separator differs between the peripheral edge and the portion inside the peripheral edge, the maximum thickness t is measured for the portion inside the peripheral edge. If the separator has a base portion and ribs protruding from at least one main surface of the base portion, the thickness of the separator includes the thickness of the base portion and the ribs. For example, if ribs are formed on both sides of the separator, the thickness of the separator is the sum of the thickness of the base portion, the height of the ribs from the base portion on one main surface, and the height of the ribs from the base portion on the other main surface. The thickness of the separator where this sum is greatest is the maximum thickness t.

(fully charged)
The fully charged state of a flooded lead-acid battery is defined by JIS D 5301:2019. More specifically, a fully charged state is defined as a state in which a lead-acid battery is charged at a current (A) 0.2 times the value (unit: Ah) specified for the rated capacity, until the terminal voltage (V) during charging or the electrolyte density converted to a temperature of 20°C, measured every 15 minutes, shows a constant value to three significant digits three times in a row. For a valve-regulated lead-acid battery, the fully charged state is defined as a state in which the battery is charged in an air tank at 25°C at a constant current/constant voltage of 2.23 V/cell at a current (A) 0.2 times the value (unit: Ah) specified for the rated capacity, and charging is terminated when the charging current during constant voltage charging reaches a value (A) 0.005 times the value (unit: Ah) specified for the rated capacity.

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

Below, the lead-acid battery according to an embodiment of the present invention will be described in terms of its main components, but the present invention is not limited to the following embodiment.

[Lead acid battery]
(negative electrode plate)
The negative electrode plate includes a current collector (negative electrode current collector) with a lug portion and a negative electrode material.

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

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

The negative electrode current collector has a surface layer at least on the edge portion. The surface layer on the edge portion contains Sn. The surface layer contains, for example, a lead alloy containing Sn. Such a surface layer can suppress edge thinning during PSOC cycles.

The Sn content in the surface layer of the ear portion is less than 10% by mass, and may be 7% by mass or less, 6% by mass or less, or 5% by mass or less. The Sn content in the surface layer is, for example, 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more. Even with such a low Sn content in the surface layer, ear thinning can be reduced by combining it with a negative electrode material containing a polymer compound. Furthermore, the low Sn content also reduces the effect of reducing liquid loss.

The Sn content in the surface layer of the ear portion may be 0.01% by mass or more but less than 10% by mass (or 7% by mass or less), 0.05% by mass or more but less than 10% by mass (or 7% by mass or less), 0.1% by mass or more but less than 10% by mass (or 7% by mass or less), 0.01% by mass or more but less than 6% by mass (or 5% by mass or less), 0.05% by mass or more but less than 6% by mass (or 5% by mass or less), or 0.1% by mass or more but less than 6% by mass (or 5% by mass or less).

The thickness of the surface layer of the ear portion is, for example, 0.01 mm or more, and may be 0.015 mm or more, or 0.02 mm or more. The thickness of the surface layer is, for example, 0.1 mm or less, and may be 0.05 mm or less.

The thickness of the surface layer of the ear portion may be 0.01 mm or more and 0.1 mm or less (or 0.05 mm or less), 0.015 mm or more and 0.1 mm or less (or 0.05 mm or less), or 0.02 mm or more and 0.1 mm or less (or 0.05 mm or less).

(Surface layer analysis)
The method for measuring the Sn content in the surface layer and the thickness of the surface layer will be described below. The measurement is carried out on a negative electrode plate that has been removed from a lead-acid battery, washed with water, and dried under reduced pressure.

(1) Measurement of Sn content in the surface layer First, the edge of the negative electrode plate is cut along the thickness direction, and the cut surface is observed using a metallurgical microscope. The outer layer, which has different properties from the inner layer, is used as the surface layer, and a portion of it is scraped off to obtain a sample, and its mass is measured. The metallurgical microscope used is a GX53F manufactured by Olympus Corporation.

The Sn content in the surface layer is analyzed in accordance with lead separation inductively coupled plasma atomic emission spectroscopy as described in JIS H2105:1955. More specifically, the sample collected above is mixed with tartaric acid and dilute nitric acid to obtain an aqueous solution. Hydrochloric acid is added to the aqueous solution to precipitate lead chloride, which is then filtered and the filtrate is collected. The Sn concentration in the filtrate is analyzed using an ICP atomic emission spectrometer with a calibration curve method, and the Sn content in the surface layer of the ear is determined from this Sn concentration and the mass of the collected sample. The ICP atomic emission spectrometer used is an ICPS-8000 manufactured by Shimadzu Corporation.

(2) Thickness of the Surface Layer The ear portion of the negative electrode plate is impregnated with epoxy resin and cured. Next, the ear portion is cut along the thickness direction of the ear portion, and the cut surface is polished. The polished cut surface is observed with a metallurgical microscope, and the outer layer portion, which has different properties from the inner layer, is defined as the surface layer. The thickness is measured at any five points and averaged to determine the thickness of the surface layer. A GX53F manufactured by Olympus Corporation is used as the metallurgical microscope.

(Negative electrode material)
The negative electrode material includes the polymer compound. The negative electrode material further includes a negative electrode active material (specifically, lead or lead sulfate) that exhibits capacity through a redox reaction. The negative electrode material may include at least one selected from the group consisting of an organic shrinkage inhibitor, a carbonaceous material, and other additives. Examples of additives include, but are not limited to, barium sulfate and fibers (e.g., resin fibers). Note that the negative electrode active material in a charged state is sponge lead, but unformed negative plates are typically made using lead powder.

(Polymer Compound)
The polymer compound has a peak in the chemical shift range of 3.2 ppm to 3.8 ppm in ¹ H-NMR spectrum. Such a polymer compound has an oxy C _2-4 alkylene unit. Examples of the oxy C _2-4 alkylene unit include an oxyethylene unit, an oxypropylene unit, an oxytrimethylene unit, an oxy 2-methyl-1,3-propylene unit, an oxy 1,4-butylene unit, and an oxy 1,3-butylene unit. The polymer compound may have one type of such oxy C _2-4 alkylene unit, or two or more types.

The polymer compound preferably contains a repeating structure of an oxy _C2-4 alkylene unit. The repeating structure may contain one type of oxy _C2-4 alkylene unit, or two or more types of oxy _C2-4 alkylene units. The polymer compound may contain one type of the repeating structure, or two or more types of the repeating structure.

The polymer compounds having a repeating structure of oxy C _2-4 alkylene units also include polymer compounds classified as surfactants (more specifically, nonionic surfactants).

Examples of the polymer compound include hydroxy compounds having a repeating structure of oxy _C2-4 alkylene units (such as poly _C2-4 alkylene glycol, a copolymer containing a repeating structure of oxy _C2-4 alkylene, and a poly _C2-4 alkylene oxide adduct of a polyol), and ethers or esters of these hydroxy compounds.

Copolymers include copolymers containing different oxyC _2-4 alkylene units, etc. The copolymers may be block copolymers.

The polyol may be any of aliphatic polyols, alicyclic polyols, aromatic polyols, and heterocyclic polyols. From the viewpoint of facilitating thin spreading of the polymer compound on the lead surface, aliphatic polyols and alicyclic polyols (e.g., polyhydroxycyclohexane, polyhydroxynorbornane) are preferred, with aliphatic polyols being particularly preferred. Examples of aliphatic polyols include aliphatic diols, triols or higher polyols (e.g., glycerin, trimethylolpropane, pentaerythritol, sugars, or sugar alcohols). Examples of aliphatic diols include alkylene glycols having _{5 or} more carbon atoms. Examples of alkylene glycols include C5-14 alkylene glycols or _C5-10 alkylene glycols. Examples of sugars or sugar alcohols include sucrose, erythritol, xylitol, mannitol, and sorbitol. The sugars or sugar alcohols may have either a linear or cyclic structure. In the polyalkylene oxide adduct of polyol, the alkylene oxide corresponds to the oxy _C2-4 alkylene unit of the polymer compound and contains at least a _C2-4 alkylene oxide. From the viewpoint that the polymer compound is likely to have a linear structure, the polyol is preferably a diol.

The etherified product has an -OR2 group (wherein _R2 is an organic group) in which at least some of the terminal -OH groups (each consisting of a hydrogen atom at the terminal group and an oxygen atom bonded to that hydrogen ^atom ) of the hydroxy compound having a repeating structure of the above-mentioned oxy ^C2-4 alkylene unit have been etherified. Some or all of the terminals of the polymer compound may be etherified. For example, one terminal of the main chain of a linear polymer compound may be an -OH group and the other terminal may be an ^-OR2 group.

The esterified product has an —O—C( _═O) —R3 group (wherein R3 is an organic group) in which at least some of the terminal —OH groups (each consisting of a hydrogen atom at the terminal group and an oxygen atom bonded to that hydrogen atom) of the hydroxy compound having a repeating structure of the above-mentioned oxy ^{C2-4 alkylene} unit have been esterified. Some or all of the terminals of the polymer compound may be esterified. For example, one terminal of the main chain of a linear polymer compound may be an —OH group, and the other terminal may be an —O—C(═O) ^—R3 group.

Each of the organic groups ^R2 and ^R3 may be a hydrocarbon group. The hydrocarbon group may have a substituent (e.g., a hydroxy group, an alkoxy group, and/or a carboxy group). The hydrocarbon group may be any of aliphatic, alicyclic, and aromatic. The aromatic hydrocarbon group and the alicyclic hydrocarbon group may have an aliphatic hydrocarbon group (e.g., an alkyl group, an alkenyl group, an alkynyl group) as a substituent. The number of carbon atoms in the aliphatic hydrocarbon group as a substituent may be, for example, 1 to 30, 1 to 20, 1 to 10, 1 to 6, or 1 to 4.

Examples of aromatic hydrocarbon groups include aromatic hydrocarbon groups having 24 or less carbon atoms (e.g., 6 to 24). The number of carbon atoms in the aromatic hydrocarbon group may be 20 or less (e.g., 6 to 20), 14 or less (e.g., 6 to 14), or 12 or less (e.g., 6 to 12). Examples of aromatic hydrocarbon groups include aryl groups and bisaryl groups. Examples of aryl groups include phenyl groups and naphthyl groups. Examples of bisaryl groups include monovalent groups corresponding to bisarenes. Examples of bisarenes include biphenyl and bisarylalkanes (e.g., bisC _6-10 aryl C _1-4 alkane (2,2-bisphenylpropane, etc.)).

Examples of alicyclic hydrocarbon groups include alicyclic hydrocarbon groups having 16 or fewer carbon atoms. The alicyclic hydrocarbon group may be a bridged cyclic hydrocarbon group. The number of carbon atoms in the alicyclic hydrocarbon group may be 10 or fewer or 8 or fewer. The number of carbon atoms in the alicyclic hydrocarbon group may be, for example, 5 or more, or 6 or more.

The number of carbon atoms in the alicyclic hydrocarbon group may be 5 (or 6) or more and 16 (or less), 5 (or 6) or more and 10 (or less), or 5 (or 6) or more and 8 (or less).

Examples of alicyclic hydrocarbon groups include cycloalkyl groups (cyclopentyl, cyclohexyl, cyclooctyl, etc.) and cycloalkenyl groups (cyclohexenyl, cyclooctenyl, etc.). Alicyclic hydrocarbon groups also include hydrogenated versions of the above aromatic hydrocarbon groups.

Aliphatic hydrocarbon groups are preferred among hydrocarbon groups, as they facilitate the thin adhesion of the polymer compound to the lead surface. Aliphatic hydrocarbon groups may be saturated or unsaturated. Examples of aliphatic hydrocarbon groups include alkyl groups, alkenyl groups, alkynyl groups, dienyl groups with two carbon-carbon double bonds, and trienyl groups with three carbon-carbon double bonds. Aliphatic hydrocarbon groups may be either linear or branched.

The number of carbon atoms in the aliphatic hydrocarbon group is, for example, 30 or less, or may be 26 or 22 or less, 20 or 16 or less, 14 or 10 or less, or 8 or 6 or less. The lower limit for the number of carbon atoms depends on the type of aliphatic hydrocarbon group: 1 or more for alkyl groups, 2 or more for alkenyl and alkynyl groups, 3 or more for dienyl groups, and 4 or more for trienyl groups. Among these, alkyl and alkenyl groups are preferred from the viewpoint of facilitating a thin adhesion of the polymer compound to the lead surface.

Specific examples of alkyl groups include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, n-pentyl, neopentyl, i-pentyl, s-pentyl, 3-pentyl, t-pentyl, n-hexyl, 2-ethylhexyl, n-octyl, n-nonyl, n-decyl, i-decyl, undecyl, lauryl (dodecyl), tridecyl, myristyl, pentadecyl, cetyl, heptadecyl, stearyl, icosyl, heneicosyl, and behenyl.

Specific examples of the alkenyl group include vinyl, 1-propenyl, allyl, cis-9-heptadecen-1-yl, palmitoleyl, and oleyl. The alkenyl group may be, for example, a _C2-30 alkenyl group or a _C2-26 alkenyl group, a _C2-22 alkenyl group or a _C2-20 alkenyl group, or a _C10-20 alkenyl group.

Among the polymer compounds, the use of at least one selected from the group consisting of an etherified product of a hydroxy compound having a repeating structure of oxy-C _2-4 alkylene units and an esterified product of a hydroxy compound having a repeating structure of oxy _- C 2-4 alkylene units is preferred because it can further enhance the effect of reducing ear thinning of the negative electrode plate. Furthermore, even when these polymer compounds are used, a high effect of suppressing liquid loss can be ensured. Among these polymer compounds, a polymer compound having a repeating structure of oxypropylene units or a polymer compound having a repeating structure of oxyethylene units is preferred.

The polymer compound may have one or more hydrophobic groups. Examples of hydrophobic groups include the above-mentioned hydrocarbon groups, such as aromatic hydrocarbon groups, alicyclic hydrocarbon groups, and long-chain aliphatic hydrocarbon groups. Examples of long-chain aliphatic hydrocarbon groups include the above-mentioned aliphatic hydrocarbon groups (e.g., alkyl groups, alkenyl groups), and aliphatic hydrocarbon groups with 8 or more carbon atoms. The aliphatic hydrocarbon group preferably has 12 or more carbon atoms, and more preferably 16 or more carbon atoms. Among these, polymer compounds with long-chain aliphatic hydrocarbon groups are preferred because they are less likely to excessively adsorb lead and can further reduce ear thinning. The polymer compound may also be a polymer compound in which at least one of the hydrophobic groups is a long-chain aliphatic hydrocarbon group. The long-chain aliphatic hydrocarbon group may have 30 or fewer carbon atoms, 26 or fewer carbon atoms, or 22 or fewer carbon atoms.

The number of carbon atoms in the long-chain aliphatic hydrocarbon group may be 8 or more (or 12 or more) and 30 or less, 8 or more (or 12 or more) and 26 or less, 8 or more (or 12 or more) and 22 or less, 10 or more and 30 or less (or 26 or less), or 10 or more and 22 or less.

Among polymer compounds, polymer compounds having both hydrophilic and hydrophobic groups correspond to nonionic surfactants. The repeating structure of oxyethylene units exhibits high hydrophilicity and can serve as the hydrophilic group in nonionic surfactants. Therefore, it is preferable that the above-mentioned polymer compounds having hydrophobic groups contain repeating structures of oxyethylene units. Such polymer compounds selectively adsorb lead while preventing excessive coverage of the lead surface due to the balance between hydrophobicity and high hydrophilicity resulting from the repeating structure of oxyethylene units, thereby further reducing ear thinning while reducing solution loss. Such polymer compounds can ensure high adsorption of lead even with a relatively low molecular weight (e.g., Mn of 1000 or less).

Of the above polymer compounds, polyoxypropylene-polyoxyethylene block copolymers, etherified products of hydroxy compounds having a repeating structure of oxyethylene units, and esterified products of hydroxy compounds having a repeating structure of oxyethylene units are equivalent to nonionic surfactants.

In polyoxypropylene-polyoxyethylene block copolymers, the repeating structure of oxyethylene units corresponds to the hydrophilic group, and the repeating structure of oxypropylene units corresponds to the hydrophobic group. Such copolymers are also included in polymer compounds having hydrophobic groups.

Examples of polymer compounds having a hydrophobic group and a repeating oxyethylene unit structure include etherified polyethylene glycol (e.g., alkyl ethers), esterified polyethylene glycol (e.g., carboxylic acid esters), etherified polyethylene oxide adducts of the above polyols (e.g., alkyl ethers), and esterified polyethylene oxide adducts of the above polyols (e.g., triols or higher polyols) (e.g., carboxylic acid esters). Specific examples of such polymer compounds include polyethylene glycol oleate, polyethylene glycol dioleate, polyethylene glycol dilaurate, polyethylene glycol distearate, polyoxyethylene sorbitan cocoate, polyoxyethylene sorbitan oleate, polyoxyethylene sorbitan stearate, polyoxyethylene lauryl ether, polyoxyethylene tetradecyl ether, and polyoxyethylene cetyl ether. However, polymer compounds are not limited to these. Among these, esterified polyethylene glycol and esterified polyethylene oxide adducts of the above polyols are preferred, as they can further reduce ear thinning and significantly reduce fluid loss.

From the viewpoint of further enhancing the effect of reducing ear thinning of the negative electrode plate and further enhancing the effect of reducing liquid loss, it is also preferable that the repeating structure of oxy-C _2-4 alkylene contains at least a repeating structure of an oxypropylene unit. A polymer compound containing an oxypropylene unit has peaks derived from the -CH< and -CH ₂ - of the oxypropylene unit in the chemical shift range of 3.2 ppm to 3.8 ppm in the ¹ H-NMR spectrum. The electron densities around the hydrogen atom nuclei in these groups are different, resulting in split peaks. Such a polymer compound has peaks in the chemical shift range of ¹ H-NMR spectrum, for example, in the range of 3.2 ppm to 3.42 ppm and in the range of more than 3.42 ppm to 3.8 ppm. The peaks in the range of 3.2 ppm to 3.42 ppm are derived from —CH ₂ —, and the peaks in the range of more than 3.42 ppm to 3.8 ppm are derived from —CH< and —CH ₂ —.

Examples of polymer compounds containing at least a repeating structure of oxypropylene units include polypropylene glycol, copolymers containing a repeating structure of oxypropylene units, polypropylene oxide adducts of the above polyols, and etherified or esterified products thereof. Examples of copolymers include oxypropylene-oxyalkylene copolymers (wherein the oxyalkylene is a _C2-4 alkylene other than oxypropylene). Examples of oxypropylene-oxyalkylene copolymers include oxypropylene-oxyethylene copolymers and oxypropylene-oxytrimethylene copolymers. Oxypropylene-oxyalkylene copolymers are sometimes referred to as polyoxypropylene-polyoxyalkylene copolymers (e.g., polyoxypropylene-polyoxyethylene copolymers). Oxypropylene-oxyalkylene copolymers may also be block copolymers (e.g., polyoxypropylene-polyoxyethylene block copolymers). Examples of etherified products include polypropylene glycol alkyl ethers, alkyl ethers of oxypropylene-oxyalkylene copolymers (such as alkyl ethers of polyoxypropylene-polyoxyethylene copolymers), etc. Examples of esterified products include polypropylene glycol esters of carboxylic acids, carboxylic acid esters of oxypropylene-oxyalkylene copolymers (such as carboxylic acid esters of polyoxypropylene-polyoxyethylene copolymers), etc.

Examples of polymer compounds containing at least a repeating structure of oxypropylene units include polypropylene glycol, polyoxypropylene-polyoxyethylene copolymers (such as polyoxypropylene-polyoxyethylene block copolymers), polypropylene glycol alkyl ethers (such as alkyl ethers (methyl ether, ethyl ether, butyl ether) in which the above ^R2 is an alkyl having 10 or less carbon atoms (or 8 or less or 6 or less), which may have a substituent), polyoxyethylene-polyoxypropylene alkyl ethers (such as alkyl ethers (butyl ether, hydroxyhexyl ether) in which the above ^R2 is an alkyl having 10 or less carbon atoms (or 8 or less or 6 or less), which may have a substituent), polypropylene glycol carboxylates (such as polypropylene glycol acetates in which the above ^R3 is an alkyl having 10 or less carbon atoms (or 8 or less or 6 or less), and polypropylene oxide adducts of triol or higher polyols (such as polypropylene oxide adducts of glycerin). However, the polymer compounds are not limited to these.

In polymer compounds containing repeating oxypropylene units, the proportion of oxypropylene units is, for example, 5 mol% or more, and may be 10 mol% or more, or 20 mol% or more. The proportion of oxypropylene units is, for example, 100 mol% or less. In the above copolymers, the proportion of oxypropylene units may be 90 mol% or less, 75 mol% or less, 60 mol% or less, or 50 mol% or less, or 43 mol% or less.

In polymer compounds containing repeating oxypropylene units, the proportion of oxypropylene units may be 5 mol% or more and 100 mol% or less (or 90 mol% or less), 10 mol% or more and 100 mol% or less (or 90 mol% or less), 20 mol% or more and 100 mol% or less (or 90 mol% or less), 5 mol% or more and 75 mol% or less (or 60 mol% or less), 10 mol% or more and 75 mol% or less (or 60 mol% or less), 20 mol% or more and 75 mol% or less (or 60 mol% or less), 5 mol% or more and 50 mol% or less (or 43 mol% or less), 10 mol% or more and 50 mol% or less (or 43 mol% or less), or 20 mol% or more and 50 mol% or less (or 43 mol% or less).

From the viewpoints of increasing the adsorption ability of the polymer compound to lead and facilitating the polymer compound to assume a linear structure, it is preferable that the polymer compound contain a large number of oxy-C _2-4 alkylene units. Such a polymer compound contains, for example, an oxygen atom bonded to an end group and a —CH ₂ — group and/or a —CH< group bonded to the oxygen atom. In the ¹ H-NMR spectrum of the polymer compound, the integral of the peak between 3.2 ppm and 3.8 ppm accounts for a large proportion of the integral of this peak, the integral of the peak of the hydrogen atom of the —CH ₂ — group, and the integral of the peak of the hydrogen atom of the —CH< group. This proportion is, for example, 50% or more, and may be 80% or more. From the viewpoints of further enhancing the effect of reducing ear thinning of the negative electrode plate and further enhancing the effect of reducing liquid loss, the above proportion is preferably 85% or more, and more preferably 90% or more. For example, when a polymer compound has an —OH group at its terminal and a —CH ₂ — group and/or a —CH< group bonded to the oxygen atom of the —OH group, in the ¹ H-NMR spectrum, the peaks of the hydrogen atoms of the —CH ₂ — group and the —CH< group have chemical shifts in the range of more than 3.8 ppm to 4.0 ppm.

The negative electrode material may contain one type of polymer compound or two or more types.

The polymer compound may include a compound with an Mn of 300 or more, 400 or more, 500 or more, 600 or more, or 1,000 or more. The Mn of such a compound is, for example, 5 million or less, 1 million or less, 100,000 or less, 50,000 or less, 20,000 or less, or 15,000 or less, 10,000 or less. From the standpoint of facilitating retention of the compound in the negative electrode material and spreading it more thinly over the lead surface, the Mn of the above compound is preferably 5,000 or less, and may be 4,000 or less, or 3,000 or less. Two or more compounds with different Mn may be used as the polymer compound. In other words, the polymer compound may have multiple Mn peaks in its molecular weight distribution.

The Mn of the above compounds is 300 to 5 million (or 1 million or less), 400 to 5 million (or 1 million or less), 500 to 5 million (or 1 million or less), 600 to 5 million (or 1 million or less), 1,000 to 5 million (or 1 million or less), 300 to 100,000 (or 50,000 or less), 400 to 100,000 (or 50,000 or less), 500 to 100,000 (or 50,000 or less), 600 to 100,000 (or 50,000 or less), 1,000 to 100,000 (or 50,000 or less), 300 to 20,000 (or 15,000 or less), 300 to 10,000 (or 5,000 or less), 300 to 4,000 ( or 3000 or less), 400 or more and 20000 or less (or 15000 or less), 400 or more and 10000 or less (or 5000 or less), 400 or more and 4000 or less (or 3000 or less), 500 or more (or 600 or more) and 20000 or less, 500 or more (or 600 or more) and 15000 or less, 500 or more (or 600 or more) and 10000 or less, 500 or more (or 600 or more) and 5000 or less, 500 or more (or 600 or more) and 4000 or less, 500 or more (or 600 or more) and 3000 or less, 1000 or more and 20000 or less (or 15000 or less), 1000 or more and 10000 or less (or 5000 or less), or 1000 or more and 4000 or less (or 3000 or less).

The polymer compound preferably contains a compound with an Mn of at least 1,000. The Mn of such a compound may be 1,000 to 50,000, 1,000 to 20,000, 1,000 to 15,000, or 1,000 to 10,000. From the perspective of facilitating retention of the compound in the negative electrode material and spreading it more thinly over the lead surface, the Mn of the compound is preferably 1,000 to 5,000, 1,000 to 4,000, or 1,000 to 3,000. Using such a compound with Mn can further enhance the effect of reducing electrolyte loss. Furthermore, by reducing gas generation during overcharge, structural changes in the negative electrode material caused by collision of hydrogen gas with the negative electrode active material can be suppressed. Even when present in the electrolyte, such compounds with Mn easily migrate into the negative electrode material, allowing the compound to be replenished in the negative electrode material. This also facilitates retention of the compound in the negative electrode material. The polymer compound may be two or more compounds having different Mn values, that is, the polymer compound may have a plurality of Mn peaks in the molecular weight distribution.

The content of the polymer compound in the negative electrode material is, for example, 8 ppm or more by mass, and may be 10 ppm or more. From the perspective of further improving the effect of reducing ear thinning, the content of the polymer compound in the negative electrode material is preferably 15 ppm or more by mass. When the content of the polymer compound is within this range, it is easier to increase the hydrogen generation voltage and the effect of suppressing liquid loss can be further improved. The content of the polymer compound (by mass) in the negative electrode material may be, for example, 400 ppm or less, 380 ppm or less, or 370 ppm or less.

The polymer compound content (by mass) may be 8 ppm or more (or 10 ppm or more) and 400 ppm or less, 8 ppm or more (or 10 ppm or more) and 380 ppm or less, 8 ppm or more (or 10 ppm or more) and 370 ppm or less, 15 ppm or more and 400 ppm or less (or 380 ppm or less), or 15 ppm or more and 370 ppm or less.

(organic shrink-preventing agent)
The negative electrode material may contain an organic shrinkage inhibitor. The organic shrinkage inhibitor may be at least one selected from the group consisting of lignin compounds and synthetic organic shrinkage inhibitors. Examples of lignin compounds include lignin and lignin derivatives. Examples of lignin derivatives include lignin sulfonic acid or its salts (such as alkali metal salts (e.g., sodium salts)). Organic shrinkage inhibitors are generally broadly classified into lignin compounds and synthetic organic shrinkage inhibitors. Synthetic organic shrinkage inhibitors can also be considered organic shrinkage inhibitors other than lignin compounds. Synthetic organic shrinkage inhibitors are organic polymers containing sulfur and generally contain multiple aromatic rings in the molecule and sulfur as sulfur-containing groups. Among the sulfur-containing groups, sulfonic acid groups or sulfonyl groups, which are stable, are preferred. The sulfonic acid groups may exist in either an acid form or a salt form, such as a sodium salt. The negative electrode material may contain one or more organic shrinkage inhibitors.

As the organic shrink-preventing agent, it is preferable to use a condensation product containing at least an aromatic compound unit. Examples of such condensation products include condensation products of an aromatic compound with an aldehyde compound (at least one selected from the group consisting of aldehydes (e.g., formaldehyde) and condensates thereof). The organic shrink-preventing agent may contain one type of aromatic compound unit, or may contain two or more types of aromatic compound units.
The aromatic compound unit refers to a unit derived from an aromatic compound incorporated into the condensation product.

Examples of aromatic rings contained in aromatic compounds include benzene rings and naphthalene rings. When an aromatic compound contains multiple aromatic rings, the multiple aromatic rings may be linked by direct bonds or linking groups (e.g., alkylene groups (including alkylidene groups) or sulfone groups). Examples of such structures include bisarene structures (biphenyl, bisphenylalkane, bisphenylsulfone, etc.). Examples of aromatic compounds include compounds containing the above aromatic rings and at least one group selected from the group consisting of hydroxy groups and amino groups. The hydroxy or amino group may be directly bonded to the aromatic ring or may be bonded as an alkyl chain containing a hydroxy or amino group. The hydroxy group also includes salts of the hydroxy group (-OMe). The amino group also includes salts of the amino group (specifically, salts with anions). Examples of Me include alkali metals (e.g., Li, K, Na) and Group 2 metals of the periodic table (e.g., Ca, Mg).

Preferred aromatic compounds include bisarene compounds (bisphenol compounds, hydroxybiphenyl compounds, bisarene compounds having an amino group (such as bisarylalkane compounds having an amino group, bisarylsulfone compounds having an amino group, and biphenyl compounds having an amino group), hydroxyarene compounds (such as hydroxynaphthalene compounds and phenol compounds), and aminoarene compounds (such as aminonaphthalene compounds and aniline compounds (such as aminobenzenesulfonic acid and alkylaminobenzenesulfonic acid)). The aromatic compounds may further contain a substituent. The organic shrinkage inhibitor may contain one or more residues of these compounds. Preferred bisphenol compounds include bisphenol A, bisphenol S, and bisphenol F.

The condensate preferably contains at least a unit of an aromatic compound having a sulfur-containing group. In particular, using a condensate containing at least a unit of a bisphenol compound having a sulfur-containing group can further enhance the effect of suppressing ear thinning. From the perspective of enhancing the effect of suppressing fluid loss, it is preferable to use a condensate of an aldehyde compound with a naphthalene compound having a sulfur-containing group and at least one group selected from the group consisting of a hydroxyl group and an amino group.

The sulfur-containing group may be directly bonded to an aromatic ring contained in the compound, or may be bonded to the aromatic ring as an alkyl chain having a sulfur-containing group. The sulfur-containing group is not particularly limited, but examples include a sulfonyl group, a sulfonic acid group, or a salt thereof.

The organic shrinkage inhibitor may also include a condensate containing at least one selected from the group consisting of the above-mentioned bisarene compound units and monocyclic aromatic compound units (such as hydroxyarene compounds and/or aminoarene compounds). The organic shrinkage inhibitor may also include a condensate containing a bisarene compound unit and a monocyclic aromatic compound unit (especially a hydroxyarene compound). Examples of such condensates include condensates of a bisarene compound and a monocyclic aromatic compound with an aldehyde compound. Preferred hydroxyarene compounds are phenolsulfonic acid compounds (such as phenolsulfonic acid or its substituted derivatives). Preferred aminoarene compounds are aminobenzenesulfonic acid, alkylaminobenzenesulfonic acid, etc. Preferred monocyclic aromatic compounds are hydroxyarene compounds.

The content of the organic shrinkage inhibitor contained in the negative electrode material is, for example, 0.01% by mass or more, and may be 0.05% by mass or more. The content of the organic shrinkage inhibitor is, for example, 1.0% by mass or less, and may be 0.5% by mass or less.

The content of the organic shrinkage inhibitor contained in the negative electrode material may be 0.01% by mass or more and 1.0% by mass or less, 0.05% by mass or more and 1.0% by mass or less, 0.01% by mass or more and 0.5% by mass or less, or 0.05% by mass or more and 0.5% by mass or less.

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

The content of the carbonaceous material in the negative electrode material is, for example, 0.05% by mass or more, and may be 0.10% by mass or more. The content of the carbonaceous material is, for example, 5% by mass or less, and may be 3% by mass or less.

The content of the carbonaceous material in the negative electrode material may be 0.05% by mass or more and 5% by mass or less, 0.05% by mass or more and 3% by mass or less, 0.10% by mass or more and 5% by mass or less, or 0.10% by mass or more and 3% by mass or less.

(barium sulfate)
The content of barium sulfate in the negative electrode material is, for example, 0.05% by mass or more, and may be 0.10% by mass or more, and the content of barium sulfate in the negative electrode material is, for example, 3% by mass or less, and may be 2% by mass or less.

The content of barium sulfate in the negative electrode material may be 0.05% by mass or more and 3% by mass or less, 0.05% by mass or more and 2% by mass or less, 0.10% by mass or more and 3% by mass or less, or 0.10% by mass or more and 2% by mass or less.

(Analysis of the components of negative electrode materials)
The following describes a method for analyzing negative electrode materials or their constituent components. Prior to analysis, a fully charged lead-acid battery is disassembled to obtain a negative electrode plate to be analyzed. The obtained negative electrode plate is washed with water to remove sulfuric acid from the negative electrode plate. The washing is continued until a pH test paper is pressed against the washed surface of the negative electrode plate and no color change is confirmed. However, the washing time should be within two hours. The washed negative electrode plate is dried in a reduced pressure environment at 60±5°C for approximately six hours. If an adhesive material is included in the negative electrode plate after drying, the adhesive material is removed by peeling. Next, the negative electrode material is separated from the negative electrode plate and pulverized to obtain a sample (hereinafter referred to as Sample A).

(1) Analysis of Polymer Compounds (1-1) Qualitative Analysis of Polymer Compounds 150.0±0.1 mL of chloroform is added to 100.0±0.1 g of Sample A, and the mixture is stirred at 20±5°C for 16 hours to extract the polymer compound. The solid content is then removed by filtration. The polymer compound is identified by obtaining information from at least one of infrared spectroscopy, ultraviolet-visible absorption spectroscopy, NMR spectroscopy, LC-MS, and pyrolysis GC-MS for the chloroform solution containing the polymer compound obtained by extraction or the polymer compound obtained by drying the chloroform solution.

The chloroform-soluble fraction is recovered by distilling off the chloroform under reduced pressure from the chloroform solution containing the polymer compound obtained by extraction. The chloroform-soluble fraction is dissolved in deuterated chloroform, and ^{the 1H} -NMR spectrum is measured under the following conditions. From this ^1H -NMR spectrum, a peak in the chemical shift range of 3.2 ppm to 3.8 ppm is confirmed. Furthermore, the type of oxy- _C2-4 alkylene unit is identified from the peak in this range.

Apparatus: AL400 nuclear magnetic resonance spectrometer manufactured by JEOL Ltd. Observation frequency: 395.88 MHz
Pulse width: 6.30 μs
Pulse repetition time: 74.1411 seconds Number of integrations: 32
Measurement temperature: room temperature (20-35℃)
Standard: 7.24 ppm
Sample tube diameter: 5 mm

The integral value (V ₁ ) of the peaks present in the chemical shift range of 3.2 ppm to 3.8 ppm is determined from the ¹ H-NMR spectrum. Furthermore, the sum (V 2 ) of the integral values of the peaks in the ¹ H-NMR spectrum is determined for each of the hydrogen atoms of the —CH ₂ — groups and —CH< groups bonded to the oxygen atoms bonded to the end groups of the polymer compound. Then, from V ₁ and V ₂ , the proportion of V ₁ to the total of V ₁ and V ₂ (= V ₁ /( _{V 1} + V ₂ )×100(%)) is determined.

In qualitative analysis, when determining the integral value of a peak in a ¹ H-NMR spectrum, two points on the ¹ H-NMR spectrum where there is no significant signal are determined so as to sandwich the peak, and each integral value is calculated using the line connecting these two points as the baseline. For example, for a peak present in the chemical shift range of 3.2 ppm to 3.8 ppm, the line connecting the two points at 3.2 ppm and 3.8 ppm on the spectrum is used as the baseline. For example, for a peak present in the chemical shift range of more than 3.8 ppm but not more than 4.0 ppm, the line connecting the two points at 3.8 ppm and 4.0 ppm on the spectrum is used as the baseline.

(1-2) Quantitative Analysis of Polymer Compound: An appropriate amount of the chloroform-soluble matter is dissolved in deuterated chloroform together with tetrachloroethane (TCE) of _mr (g) measured with an accuracy of ±0.0001 g, and ^{the 1H} -NMR spectrum is measured. The integral value (S _a ) of the peak present in the chemical shift range of 3.2 to 3.8 ppm and the integral value (S _r ) of the peak derived from TCE are determined, and the mass-based content C _n (ppm) of the polymer compound in the negative electrode material is calculated using the following formula:

C _n =S _a /S _r ×N _r /N _a ×M _a /M _r ×m _r /m × 1000000
(In the formula, M _a is the molecular weight of the structure that exhibits a chemical shift peak in the range of 3.2 to 3.8 ppm (more specifically, the molecular weight of the repeating structure of oxyC _2-4 alkylene units), N _a is the number of hydrogen atoms bonded to carbon atoms in the main chain of the repeating structure, N _{r and} M _r are the number of hydrogen atoms contained in the molecule of the reference material and the molecular weight of the reference material, respectively, and m (g) is the mass of the negative electrode material used for extraction.)
In this analysis, the reference substance is TCE, so N _r =2 and M _r =168. Also, m=100.

For example, when the polymer compound is polypropylene glycol, M _a is 58 and N _a is 3. When the polymer compound is polyethylene glycol, M _a is 44 and N _a is 4. In the case of a copolymer, N _a and M _a are values obtained by averaging the N _a value and M _a value of each monomer unit using the molar ratio (mol %) of each monomer unit contained in the repeating structure.

In the quantitative analysis, the integral value of the peak in the ¹ H-NMR spectrum is determined using data processing software "ALICE" manufactured by JEOL Ltd.

(1-3) Measurement of Mn of Polymer Compound Using the above chloroform-soluble fraction, GPC measurement of the polymer compound is carried out using the following apparatus under the following conditions. Separately, a calibration curve (calibration curve) is created from a plot of Mn of a standard substance versus elution time. Based on this calibration curve and the GPC measurement results of the polymer compound, the Mn of the polymer compound is calculated. However, esterified products or etherified products may be in a decomposed state in the chloroform-soluble fraction.

Analysis system: 20A system (Shimadzu Corporation)
Column: GPC KF-805L (Shodex), two columns connected in series Column temperature: 30°C
Mobile phase: tetrahydrofuran Flow rate: 1 mL/min
Concentration: 0.20% by mass
Injection volume: 10μL
Standard substance: polyethylene glycol (Mn = 200,0000, 20,0000, 20,000, 2,000, 200)
Detector: Differential refractive index detector (Shodex RI-201H)

(2) Analysis of Organic Shrinkage Inhibitor (2-1) Qualitative Analysis of Organic Shrinkage Inhibitor in Negative Electrode Material Sample A is immersed in a 1 mol/L aqueous sodium hydroxide solution to extract the organic shrinkage inhibitor. Next, insoluble components are removed from the extract by filtration, and the resulting solution is desalted, concentrated, and dried. Desalting is performed using a desalting column, by passing the solution through an ion exchange membrane, or by placing the solution in a dialysis tube and immersing it in distilled water. This is dried to obtain a powder sample of the organic shrinkage inhibitor (hereinafter referred to as Sample B).

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

(2-2) Determination of the Content of Organic Shrinkage Inhibitor in the Negative Electrode Material As in (2-1) above, a solution is obtained after removing insoluble components from the extract by filtration. The ultraviolet-visible absorption spectrum of each obtained solution is measured. The content of the organic shrinkage inhibitor in the negative electrode material is determined using the intensity of the peak characteristic of the organic shrinkage inhibitor and a previously prepared calibration curve.

When obtaining a lead-acid battery with an unknown organic shrinkage inhibitor content and measuring the organic shrinkage inhibitor content, it may not be possible to precisely identify the structural formula of the organic shrinkage inhibitor, making it impossible to use the same organic shrinkage inhibitor for the calibration curve. In such cases, a calibration curve is created using a separately available organic polymer that exhibits similar shapes in UV-visible absorption spectrum, infrared spectrum, and NMR spectrum to the organic shrinkage inhibitor extracted from the battery's negative electrode, and the organic shrinkage inhibitor content is then measured using the UV-visible absorption spectrum.

(3) Quantitative Determination of Carbonaceous Material and Barium Sulfate 10 g of sample A was mixed with 50 ml of 20% by mass nitric acid and heated for approximately 20 minutes to dissolve the lead component as lead ions. The resulting solution was filtered to separate the carbonaceous material, barium sulfate, and other solids.

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

(others)
The negative electrode plate can be formed by applying or filling a negative electrode paste onto a negative electrode current collector, aging and drying the paste to produce an unformed negative electrode plate, and then chemically forming the unformed negative electrode plate. The negative electrode paste can be produced, for example, by adding water and sulfuric acid (or an aqueous sulfuric acid solution) to lead powder, a polymer compound, and, if necessary, at least one selected from the group consisting of an organic shrinkage inhibitor, a carbonaceous material, and other additives, and kneading the mixture. During aging, the unformed negative electrode plate is preferably aged at a temperature higher than room temperature and at a high humidity.

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

(positive electrode plate)
Positive electrode plates for lead-acid batteries can be classified into paste type, clad type, etc. Either paste type or clad type positive electrode plates may be used. A paste type positive electrode plate includes a positive electrode current collector and a positive electrode material. The positive electrode material is held by the positive electrode current collector. In a paste type positive electrode plate, the positive electrode material is the portion of the positive electrode plate excluding the positive electrode current collector. The positive electrode current collector may be formed by casting lead (Pb) or a lead alloy, or may be formed by processing a lead sheet or a lead alloy sheet. Examples of processing methods include expanding and punching. Using a lattice-shaped current collector as the positive electrode current collector is preferable because it makes it easier to support the positive electrode material. A clad positive electrode plate includes multiple porous tubes, a spine inserted into each tube, a current collector connecting the multiple spines, a positive electrode material filled into the tube with the spine inserted, and a spine protector connecting the multiple tubes. In a clad positive electrode plate, the positive electrode material is the portion of the positive electrode plate excluding the tube, spine, current collector, and spine protector. In a clad positive electrode plate, the spine and current collector together are sometimes referred to as a positive electrode collector.

Positive electrode plates may have mats, pasting paper, or other materials attached to them. Such materials (attaching materials) are used integrally with the positive electrode plate and are therefore included in the positive electrode plate. Also, when a positive electrode plate includes an attaching material (mat, pasting paper, etc.), the positive electrode material, in the case of a paste-type positive electrode plate, is the positive electrode plate excluding the positive electrode current collector and the attaching material.

In terms of corrosion resistance and mechanical strength, Pb-Sb alloys, Pb-Ca alloys, and Pb-Ca-Sn alloys are preferred as lead alloys for use in the positive electrode current collector. The positive electrode current collector may have a surface layer. The surface layer and the inner layer of the positive electrode current collector may have different compositions. The surface layer may be formed on only a portion of the positive electrode current collector. The surface layer may be formed only on the grid portion, the lug portion, or the frame portion of the positive electrode current collector.

The positive electrode material contained in the positive electrode plate contains a positive electrode active material (lead dioxide or lead sulfate) that generates capacity through an oxidation-reduction reaction. The positive electrode material may also contain other additives as needed.

Unformed paste-type positive electrode plates are obtained by filling a positive electrode current collector with positive electrode paste, aging it, and drying it. The positive electrode paste is prepared by kneading lead powder, additives, water, and sulfuric acid. Unformed clad-type positive electrode plates are formed by filling porous tubes with lead powder or lead powder slurry, into which spines connected by current collectors are inserted, and then joining multiple tubes with spine protectors. These unformed positive electrode plates are then chemically formed to obtain positive electrode plates.

Formation can be performed by immersing a group of electrodes, including unformed positive electrodes, in an electrolyte containing sulfuric acid in a lead-acid battery container and then charging the group of electrodes. However, formation can also be performed before assembling the lead-acid battery or the group of electrodes.

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

Nonwoven fabrics are mats made of intertwined fibers rather than woven together, and are primarily composed of fibers. For example, nonwoven fabrics are made up of fibers that account for 60% or more by mass. Fibers that can be used include glass fibers, polymer fibers (polyolefin fibers, acrylic fibers, polyester fibers (polyethylene terephthalate fibers, etc.)), pulp fibers, etc. Among these, glass fibers are preferred. Nonwoven fabrics may also contain components other than fibers (for example, acid-resistant inorganic powders, polymers as binders), etc.

On the other hand, a microporous membrane is a porous sheet primarily composed of components other than fiber components. For example, it can be obtained by extruding a composition containing a pore-forming agent into a sheet, and then removing the pore-forming agent to form pores. Microporous membranes are preferably made of acid-resistant materials, and microporous membranes primarily composed of polymer components are preferred. Preferred polymer components are polyolefins (polyethylene, polypropylene, etc.). Examples of pore-forming agents include at least one selected from the group consisting of polymer powders and oils.

The separator may be made of, for example, only nonwoven fabric or only microporous membrane. Furthermore, if necessary, the separator may be a laminate of nonwoven fabric and microporous membrane, a laminate of different or similar materials, or a laminate of different or similar materials with interlocking recesses and protrusions.

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

The maximum thickness T of the separator is, for example, 0.7 mm or more. The maximum thickness T of the separator is, for example, 0.95 mm or less.

The maximum separator thickness T is measured on a sample of a separator removed from a fully charged lead-acid battery, washed with water to remove sulfuric acid, and dried under atmospheric pressure. More specifically, a cross-sectional photograph is taken of each separator sample in the thickness direction, and the maximum thickness t is measured on this cross-sectional photograph. The maximum thickness T is determined by averaging the maximum thicknesses t of all separators included in the electrode plate group. In a lead-acid battery having multiple electrode plate groups connected in series, the maximum separator thickness T is the average value for one electrode plate group (cell) located at the end and one electrode plate group (cell) located near the center.

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

The electrolyte may optionally contain cations (e.g., metal cations) and/or anions (e.g., anions other than sulfate anions, such as phosphate ions). Examples of metal cations include at least one selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions. When the electrolyte contains Al ions, the decrease in specific gravity during PSOC cycling is suppressed, further reducing edge thinning of the negative electrode plate.

The specific gravity of the electrolyte in a fully charged lead-acid battery at 20°C is, for example, 1.20 or more, and may be 1.25 or more. The specific gravity of the electrolyte at 20°C is 1.35 or less, and preferably 1.32 or less.

The specific gravity of the electrolyte at 20°C may be 1.20 or more and 1.35 or less, 1.20 or more and 1.32 or less, 1.25 or more and 1.35 or less, or 1.25 or more and 1.32 or less.

(others)
A lead-acid battery can be obtained by a manufacturing method including a step of housing a plate assembly and an electrolyte in a cell chamber of a battery case. Each cell of the lead-acid battery includes a plate assembly and an electrolyte housed in each cell chamber. The plate assembly is assembled by stacking positive electrode plates, negative electrode plates, and a separator with the separator interposed between the positive electrode plates and the negative electrode plates prior to housing in the cell chamber. The positive electrode plates, negative electrode plates, electrolyte, and separator are each prepared prior to assembling the plate assembly. The manufacturing method of the lead-acid battery may include a step of chemically converting at least one of the positive electrode plates and the negative electrode plates, as necessary, after the step of housing the plate assembly and the electrolyte in the cell chamber.

The number of plates in the electrode plate group may be one or more. From the perspective of ensuring higher capacity, the number of negative plates included in the electrode plate group is preferably two or more, and may be four or more, or six or more. Furthermore, if the electrode plate group includes nine or more negative plates, the decrease in the specific gravity of the electrolyte in the upper part of the electrode plate group during the PSOC cycle is suppressed, making it difficult for lead to dissolve in the lug portion, further enhancing the effect of reducing thinning of the lug portion. Note that if the number of negative plates included in the electrode plate group is n, the number of positive plates is (n-1) or more and (n+1) or less when n≧2, and is 1 or 2 when n=1.

As described above, the inter-electrode distance D is determined from the pitch between adjacent pairs of positive plates and the thickness of each of the positive and negative plates in a plate group removed from a fully charged lead-acid battery. The pitch is measured at the bottom of the cross section of the shelf connecting the lugs of multiple positive plates in parallel. For example, if a plate group contains six positive plates and seven negative plates, the center-to-center distance between the lugs is measured at five locations and averaged to determine the pitch. Similarly, if a plate group contains seven positive plates and seven negative plates, the center-to-center distance between the lugs is measured at six locations and averaged to determine the pitch. For lead-acid batteries with multiple series-connected plate groups, the pitch is the average value determined for any two plate groups (cells). For example, in the case of a 12V lead-acid battery containing six plate groups, the pitch is determined by measuring the center-to-center distance between the lugs of the first and fourth plate groups counting from the positive terminal and averaging the measured values.

The thickness of each electrode plate is measured, for example, with a micrometer at three locations along the periphery of the electrode plate, near both ends and near the center of each side (a total of eight locations: positions indicated by numbers 1 to 8 in Figure 6), and then averaged. The thickness of the positive electrode plate is measured after rinsing with water to remove sulfuric acid and drying under atmospheric pressure, while the thickness of the negative electrode plate is measured after rinsing with water to remove sulfuric acid and vacuum drying (drying under a pressure lower than atmospheric pressure).

When a separator and mat are used together in a plate assembly, or when a mat made primarily of nonwoven fabric is attached to a plate, the thickness of the plate includes the thickness of the mat. This is because the mat is used as a single unit with the plate. However, when a mat is attached to the separator, the thickness of the mat is included in the thickness of the separator.

The difference between the inter-electrode distance D in the electrode plate assembly and the maximum separator thickness T (= D-T) is, for example, 0.20 mm or less, preferably 0.15 mm or less, and more preferably 0.10 mm or less. When D-T is within this range, the decrease in the specific gravity of the electrolyte in the upper part of the electrode plate assembly during PSOC cycles is suppressed, making it difficult for lead to dissolve in the edge portions, further enhancing the effect of reducing edge thinning. D-T is, for example, -1.5 mm or more.

FIG. 1 shows an external view 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 pack 11 and an electrolyte (not shown). The battery case 12 is divided into multiple cell chambers 14 by partition walls 13. Each cell chamber 14 contains one plate pack 11. The opening of the battery case 12 is closed with 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 solution is replenished. The vent plug 18 may have the function of venting gas generated in the cell chamber 14 to the outside of the battery.

Each electrode plate group 11 is constructed by stacking multiple negative electrode plates 2 and multiple positive electrode plates 3 with separators 4 interposed between them. Here, a pouch-shaped separator 4 is shown housing the negative electrode plates 2, but the separator shape is not particularly limited. In a cell chamber 14 located at one end of the battery case 12, a negative electrode shelf 6 that connects multiple negative electrode plates 2 in parallel is connected to a through-connector 8, and a positive electrode shelf 5 that connects multiple positive electrode plates 3 in parallel is connected to a positive electrode pole 7. The positive electrode pole 7 is connected to a positive electrode terminal 17 outside the lid 15. In a cell chamber 14 located at the other end of the battery case 12, a negative electrode pole 9 is connected to the negative electrode shelf 6, and a through-connector 8 is connected to the positive electrode shelf 5. The negative electrode pole 9 is connected to a negative electrode terminal 16 outside the lid 15. Each through-connector 8 passes through a through-hole in the partition wall 13, connecting the electrode plate groups 11 of adjacent cell chambers 14 in series.

The positive electrode shelf 5 is formed by welding the lugs on the top of each positive electrode plate 3 together using the cast-on-strap method or the burning method. The negative electrode shelf 6 is also formed by welding the lugs on the top of each negative electrode plate 2 together in the same manner as the positive electrode shelf 5.

Note that the lid 15 of the lead-acid battery has a single structure (single lid), but this is not limited to the illustrated example. The lid 15 may have a double structure, for example, comprising an inner lid and an outer lid (or top lid). A lid with a double structure may have a reflux structure between the inner lid and the outer lid for returning the electrolyte to the battery (inside the inner lid) from a reflux port provided in the inner lid.

In this specification, the amount of ear thinning, fluid loss performance, and PSOC life performance are evaluated using the following procedures. The test battery used for evaluation has a rated voltage of 12 V and a rated 5-hour rate capacity of 48 Ah.

(a) Evaluation 1: Thinning Amount of Edge The negative electrode plate was removed from the test battery, washed with water, dried, and the thickness of the edge (initial thickness: t ₀ ) was measured.
The test battery is charged and discharged according to the PSOC charge/discharge pattern (specifically, the pattern shown in Table 1) of the Battery Industry Association Standard SBA S 0101 (lead-acid batteries for idle-stop vehicles). After charging and discharging, the negative electrode plate is removed from the lead-acid battery, washed with water, and dried. Next, the negative electrode plate is impregnated with epoxy resin and allowed to harden. The edge portion is cut in the thickness direction, and the thickness _t1 of the edge portion is measured on the cut surface using a metallurgical microscope. The reduction in the edge thickness due to the charge/discharge cycle (= _t0 - _t1 (mm)) is then calculated as the edge thinning amount. An Olympus GX53F metallurgical microscope is used.
The thickness of the edge portion is determined by measuring the thickness at any five points on the edge portion with a vernier caliper and averaging the results.

(b) Evaluation 2: Liquid Loss Performance Using a test battery, the amount of electrolyte loss is determined from the change in mass of the test battery before and after a high-temperature durability test.
More specifically, the mass (M ₀ ) of the test battery is measured before the high-temperature durability test. The test battery is subjected to the following discharge and charge cycles 5,000 times in a water bath at 75°C ± 3°C, thereby conducting the high-temperature durability test. The mass (M ₁ ) of the test battery after the high-temperature durability test is measured. The amount of electrolyte loss is calculated by subtracting M ₁ from M ₀ .
Discharging: 25A, 2 minutes Charging: 14.8V, 25A, 10 minutes

(c) Evaluation 3: PSOC life performance
Using the test battery, steps 1 to 3 of the charge/discharge pattern shown in Table 1 are repeated until the terminal voltage reaches 7 V or until 120,000 times are reached. Otherwise, charge/discharge is performed according to the charge/discharge pattern in Table 1, and the change in the end-of-discharge voltage (V) is measured.

(d) Evaluation 4: Potential change at the lug of the negative electrode plate The test battery was charged and discharged under the same conditions as in Evaluation 3, and the change in potential at the lug of the negative electrode plate was measured. The potential at the lug of each negative electrode plate was measured using a lead reference electrode (Pb/PbSO ₄ ).

(e) Evaluation 5: Change in specific gravity of electrolyte at the top of the electrode plate assembly Using a test battery, charge and discharge were performed under the same conditions as in Evaluation 3 above, and a small amount of electrolyte was removed from the top of the electrode plate assembly at this time, and the change in specific gravity was measured using a hydrometer. The electrolyte was removed from a position 1 cm below the liquid surface of the electrolyte. The hydrometer used was a DMA35Ampere manufactured by Anton Paar.

The lead-acid battery according to one aspect of the present invention is summarized below.

(1) A lead-acid battery,
The lead-acid battery includes at least one cell including a plate group and an electrolyte;
the electrode plate group includes a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate,
The negative electrode plate includes a current collector having a lug portion and a negative electrode material,
the ear portion has a surface layer containing Sn,
The Sn content in the surface layer is less than 10 mass %,
The lead-acid battery, wherein the negative electrode material contains a polymer compound having a peak in the range of 3.2 ppm to 3.8 ppm in chemical shift of a ¹ H-NMR spectrum measured using deuterated chloroform as a solvent.

(2) In the above (1), the polymer compound contains an oxygen atom bonded to a terminal group and a —CH ₂ — group and/or a —CH< group bonded to the oxygen atom;
In the ¹ H-NMR spectrum, the ratio of the integral value of the peak to the total integral value of the peak, the integral value of the peak due to the hydrogen atom of the —CH ₂ — group, and the integral value of the peak due to the hydrogen atom of the —CH< group may be 85% or more.

(3) In the above (1) or (2), the polymer compound may contain a repeating structure of an oxyC _2-4 alkylene unit.

(4) A lead-acid battery,
The lead-acid battery includes at least one cell including a plate group and an electrolyte;
the electrode plate group includes a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate,
The negative electrode plate includes a current collector having a lug portion and a negative electrode material,
the ear portion has a surface layer containing Sn,
The Sn content in the surface layer is less than 10 mass %,
The negative electrode material of the lead-acid battery comprises a polymer compound containing a repeating structure of oxyC _2-4 alkylene units.

(5) In any one of (1) to (4) above, the Sn content in the surface layer may be 7% by mass or less, 6% by mass or less, or 5% by mass or less.

(6) In any one of (1) to (5) above, the Sn content in the surface layer may be 0.01 mass% or more, 0.05 mass% or more, or 0.1 mass% or more.

(7) In any one of (1) to (6) above, the thickness of the surface layer may be 0.01 mm or more, 0.015 mm or more, or 0.02 mm or more.

(8) In any one of (1) to (7) above, the thickness of the surface layer may be 0.1 mm or less, or 0.05 mm or less.

(9) In any one of (1) to (8) above, the polymer compound may include a compound having an Mn of 300 or more, 400 or more, 500 or more, 600 or more, or 1000 or more.

(10) In any one of (1) to (9) above, the polymer compound may include a compound having an Mn of 5 million or less, 1 million or less, 100,000 or less, 50,000 or less, 20,000 or less, 15,000 or less, 10,000 or less, 5,000 or less, 4,000 or less, or 3,000 or less.

(11) In any one of the above (1) to (10), the polymer compound contains at least one selected from the group consisting of a hydroxy compound having a repeating structure of an oxyC _2-4 alkylene unit, an etherified product of the hydroxy compound, and an esterified product of the hydroxy compound;
The hydroxy compound may be at least one selected from the group consisting of polyC _2-4 alkylene glycol, a copolymer containing a repeating structure of oxyC _2-4 alkylene, and a polyC _2-4 alkylene oxide adduct of a polyol.

(12) In any one of (1) to (11) above, the polymer compound may contain at least a repeating structure of an oxypropylene unit.

(13) In the above (12), the polymer compound may comprise at least one selected from the group consisting of polypropylene glycol, polyoxypropylene-polyoxyethylene copolymers (such as polyoxypropylene-polyoxyethylene block copolymers), polypropylene glycol alkyl ethers (such as alkyl ethers (methyl ether, ethyl ether, butyl ether) in which the above ^R2 is an alkyl having 10 or less carbon atoms (alternatively, 8 or less or 6 or less), polyoxyethylene-polyoxypropylene alkyl ethers (such as alkyl ethers (butyl ether, hydroxyhexyl ether) in which the above ^R2 is an alkyl having 10 or less carbon atoms (alternatively, 8 or less or 6 or less), polypropylene glycol carboxylates (such as polypropylene glycol acetates in which the above ^R3 is an alkyl having 10 or less carbon atoms (alternatively, 8 or less or 6 or less), and polypropylene oxide adducts of triol or higher polyols (such as polypropylene oxide adducts of glycerin).

(14) In (12) or (13) above, the proportion of the oxypropylene units in the polymer compound may be 5 mol% or more, 10 mol% or more, or 20 mol% or more.

(15) In any one of (12) to (14) above, the proportion of the oxypropylene units in the polymer compound may be 100 mol% or less, 90 mol% or less, 75 mol% or less, 60 mol% or less, 50 mol% or less, or 43 mol% or less.

(16) In any one of (1) to (15) above, the content of the polymer compound in the negative electrode material may be, by mass, 8 ppm or more, 10 ppm or more, or 15 ppm or more.

(17) In any one of (1) to (16) above, the content of the polymer compound in the negative electrode material may be, by mass, 400 ppm or less, 380 ppm or less, or 370 ppm or less.

(18) In any one of (1) to (17) above, the negative electrode material may further contain an organic shrinkage inhibitor.

(19) In (18) above, the content of the organic shrinkage inhibitor in the negative electrode material may be 0.01% by mass or more, or 0.05% by mass or more.

(20) In (18) or (19) above, the content of the organic shrinkage inhibitor in the negative electrode material may be 1.0 mass% or less, or 0.5 mass% or less.

(21) In any one of (1) to (20) above, the negative electrode material may further contain a carbonaceous material.

(22) In the above (21), the content of the carbonaceous material in the negative electrode material may be 0.05 mass% or more, or 0.10 mass% or more.

(23) In the above (21) or (22), the content of the carbonaceous material in the negative electrode material may be 5% by mass or less, or 3% by mass or less.

(24) In any one of (1) to (23) above, the negative electrode material may further contain barium sulfate.

(25) In (24) above, the content of barium sulfate in the negative electrode material may be 0.05% by mass or more, or 0.10% by mass or more.

(26) In (24) or (25) above, the content of barium sulfate in the negative electrode material may be 3% by mass or less, or 2% by mass or less.

(27) In any one of (1) to (26) above, the difference between the distance between the positive electrode plate and the negative electrode plate in the electrode plate group and the maximum thickness of the separator (= D-T) may be 0.20 mm or less, 0.15 mm or less, or 0.10 mm or less.

(28) In any one of (1) to (27) above, the difference (= D-T) between the distance between the positive electrode plate and the negative electrode plate in the electrode plate group and the maximum thickness of the separator may be -1.5 mm or more.

(29) In any one of (1) to (28) above, the maximum thickness T of the separator may be 0.7 mm or more.

(30) In any one of (1) to (29) above, the maximum thickness T of the separator may be 0.95 mm or less.

(31) In any one of (1) to (30) above, the number of negative electrode plates in the electrode plate group may be one or more, two or more, four or more, six or more, or nine or more.

(32) In any one of the above (1) to (30), in at least one of the cells, the electrode plate group includes two or more of the positive electrode plates and two or more of the negative electrode plates, and has a structure in which the positive electrode plates and the negative electrode plates are alternately stacked with the separator interposed therebetween;
The electrode plate group may include nine or more negative electrode plates.

(33) In (31) or (32) above, if the number of negative electrode plates included in the electrode plate group is n, the number of positive electrode plates is (n-1) or more and (n+1) or less when n≧2, and may be 1 or 2 when n=1.

(34) In any one of (1) to (33) above, the electrolyte may contain Al ions.

(35) In any one of (1) to (34) above, the specific gravity of the electrolyte in a fully charged lead-acid battery at 20°C may be 1.20 or more or 1.25 or more.

(36) In any one of (1) to (35) above, the specific gravity of the electrolyte in a fully charged lead-acid battery at 20°C may be 1.35 or less or 1.32 or less.

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

Lead-acid batteries E1 to E16 and C1 to C4
(1) Preparation of Negative Electrode Plate A Pb—Sn alloy sheet is stacked on a Pb—Ca—Sn alloy sheet, and the resulting sheet is rolled and then expanded. This results in a surface layer of a lead alloy containing Sn on the edge of the expanded grid made of a Pb—Ca—Sn alloy. The Pb—Sn alloy sheet used has a composition such that the Sn content of the surface layer determined by the procedure described above is the value shown in Tables 2 to 4. The thickness of the surface layer measured by the procedure described above is 0.02 mm. The grid having the surface layer formed in this way on its edge is used as a negative electrode current collector.
In the lead-acid battery C4, an expanded grid made of a Pb--Ca--Sn alloy with no surface layer provided on the edge portions is used.

A negative electrode paste is obtained by mixing lead powder, water, dilute sulfuric acid, carbon black, a polymer compound, sodium lignosulfonate as an organic shrinkage preventer, and barium sulfate. The components are mixed so that the contents of the organic shrinkage preventer, carbon black, and barium sulfate in the negative electrode material, all determined by the procedures previously described, are 0.1 mass%, 0.2 mass%, and 0.4 mass%, respectively. The polymer compounds shown in Tables 2 to 4 are mixed with the components so that the contents of the polymer compounds in the negative electrode material, determined by the procedures previously described, are the values shown in Tables 2 to 4. The negative electrode paste is filled into the mesh portion of the negative electrode current collector, aged, and dried to obtain an unformed negative electrode plate.

(2) Preparation of Positive Electrode Plate: Lead powder as raw material is mixed with sulfuric acid solution to obtain a positive electrode paste. The positive electrode paste is filled into the mesh portion of a Pb-Ca-Sn alloy expanded grid as a positive electrode current collector, and the mixture is aged and dried to obtain an unformed positive electrode plate.

(3) Preparation of lead-acid battery Unformed negative electrode plates were housed in a pouch-shaped separator made of a microporous polyethylene film, and eight unformed negative electrode plates and seven unformed positive electrode plates formed an electrode plate group.
The electrode plate group is inserted into a battery case, a predetermined amount of sulfuric acid aqueous solution is poured in as an electrolyte, and chemical formation is performed inside the battery case to produce a flooded lead-acid battery with a rated voltage of 12 V and a rated capacity of 48 Ah (5-hour rate). The specific gravity of the electrolyte in a fully charged lead-acid battery at 20°C is 1.28. The above chemical formation brings the lead-acid battery into a fully charged state.

When a polymer compound has a repeating structure of oxyethylene units, a peak derived from -CH 2 - of the oxyethylene units is observed in the chemical shift range of 3.2 ppm to 3.8 ppm in the ¹ H-NMR spectrum of the polymer compound measured by the above-mentioned procedure. When a polymer compound has a repeating structure of oxypropylene units, a peak derived from -CH ₂ - of the oxypropylene units is observed in the chemical shift range of 3.2 ppm to 3.42 ppm in the ¹ H-NMR spectrum of the polymer compound measured by the above- _mentioned procedure, and peaks derived from -CH< and -CH ₂ - of the oxypropylene units are observed in the chemical shift range of more than 3.42 ppm to 3.8 ppm. In addition, in the ¹ H-NMR spectrum, the proportion of the integral of the peak between 3.2 ppm and 3.8 ppm to the total integral of this peak, the integral of the peak of the hydrogen atom of the —CH ₂ — group bonded to the oxygen atom, and the integral of the peak of the hydrogen atom of the —CH< group bonded to the oxygen atom is 85 to 100%.

(4) Evaluation (a) Evaluation 1: Amount of Thinning at the Edge The negative electrode plate was removed from the lead-acid battery prepared above, and the amount of thinning at the edge was measured using the procedure described above. The amount of thinning at the edge of each lead-acid battery was evaluated as a relative ratio when the amount of thinning at the edge of lead-acid battery C1 was set to 1.

(b) Evaluation 2: Liquid Loss Performance Using the lead-acid battery, the amount of liquid loss was determined according to the procedure described above. The liquid loss performance was evaluated as a relative ratio when the amount of liquid loss of lead-acid battery C1 was set to 1.

The results are shown in Tables 2 to 4. Note that the Mn of the polymer compounds shown in Tables 2 to 4 is the Mn determined by the procedure already described. E1 to E16 are working examples, and C1 to C4 are comparative examples.

As shown in Table 2, when the negative electrode material does not contain a polymer compound, and the Sn content in the surface layer of the ear portion of the negative electrode plate is 10% by mass or 30% by mass, the amount of ear thinning can be significantly reduced from 10.5 to 1.2 or 1, compared to when no surface layer is provided (comparison of C4 with C2 and C1). In contrast, when the Sn content in the surface layer is less than 10% by mass, the effect of reducing ear thinning is low (comparison of C4 with C3, comparison of C3 with C2 and C1). However, even when the Sn content in the surface layer is less than 10% by mass, the amount of ear thinning can be reduced if the negative electrode material contains a polymer compound (comparison of C3 with E1 to E3). Furthermore, the amount of liquid loss is also reduced in E1 to E3.

As shown in Table 3, even when the Sn content in the surface layer is as low as 0.1% by mass, the amount of ear thinning can be significantly reduced by including a polymer compound in the negative electrode material (E4). From the results for the amount of ear thinning in E4, it can be inferred that the amount of ear thinning can be reduced by combining it with a polymer compound even when the Sn content in the surface layer is very small, such as 0.01% by mass or more or 0.05% by mass or more. The Sn content in the surface layer only needs to be less than 10% by mass, and even when it is 7% by mass or less or 5% by mass or less, the combination with a polymer compound can significantly reduce ear thinning.

As shown in Tables 2 and 3, to further enhance the effect of reducing ear thinning, the polymer content in the negative electrode material is preferably 15 ppm or more. There is no particular upper limit to the polymer content in the negative electrode material, but even at 400 ppm or less, an excellent effect of reducing ear thinning can be obtained.

Furthermore, as shown in Table 4, when an ether or ester of a hydroxy compound having a repeating structure of oxyC _2-4 alkylene units is used, it is possible to reduce thinning of the negative electrode plate edge and reduce the loss of liquid.

《Lead-acid batteries E17-E19》
(1) Preparation of Negative and Positive Electrode Plates Seven, eight, or nine unformed negative electrode plates are prepared per cell by adjusting the amount of lead per negative electrode plate and the thickness of the negative electrode plate so that the total amount of lead in the negative electrode material per cell is the same. Similarly, six, seven, or eight unformed positive electrode plates are prepared per cell by adjusting the amount of lead per positive electrode plate and the thickness of the positive electrode plate so that the total amount of lead in the positive electrode material per cell is the same. The preparation of the negative and positive electrode plates other than these is the same as for lead-acid battery E1.

(2) Preparation of Lead-Acid Battery: Unformed negative plates are housed in a pouch-shaped separator made of a polyethylene microporous film, and unformed negative plates and unformed positive plates are stacked to form a plate assembly. Lead-acid battery E17 uses seven unformed negative plates and six unformed positive plates. Lead-acid battery E18 uses eight unformed negative plates and seven unformed positive plates. Lead-acid battery E19 uses nine unformed negative plates and eight unformed positive plates. An aqueous sulfuric acid solution containing 17 g/L of Al ions is used as the electrolyte. The specific gravity of the electrolyte in a fully charged lead-acid battery at 20°C is 1.285. Other than these, lead-acid batteries E17 to E19 are prepared in the same manner as lead-acid battery E1. E17 to E19 are examples.

(3) Evaluation (c) Evaluation 3: PSOC life performance
The PSOC life performance of the obtained lead acid battery is evaluated according to the procedure described above.
The results are shown in Figure 2.

(d) Evaluation 4: Potential Change at the Lug of the Negative Electrode Plate Using the obtained lead-acid battery, the potential change at the lug of the negative electrode plate (voltage relative to the reference electrode) is measured according to the procedure described above.
The results are shown in Figure 3.

(e) Evaluation 5: Change in specific gravity of electrolyte above electrode plate assembly Using the obtained lead-acid battery, the change in specific gravity of the electrolyte above the electrode plate assembly is measured according to the procedure described above.
The results are shown in Figure 4.

As shown in Figure 2, when the plate group has seven or eight negative plates, the terminal voltage drops sharply once the PSOC cycles exceed 50,000 or 60,000. Along with this sudden drop in terminal voltage, the negative plate's edge thinning also becomes noticeable, leading to the end of its life. In contrast, when the plate group has nine negative plates, there is no sudden drop in terminal voltage, and edge thinning of the negative plate is suppressed, even when the PSOC cycles exceed 100,000.

As shown in Figure 3, the change in potential at the lug of the negative plate during PSOC cycling is almost the same regardless of the number of negative plates in the plate assembly. Meanwhile, when the number of negative plates in the plate assembly is seven or eight, the specific gravity of the electrolyte in the upper part of the plate assembly decreases around the cycle number at which a sudden drop in terminal voltage was observed in Figure 2 (Figure 4). In contrast, when the number of negative plates is nine, no sudden drop in the specific gravity of the electrolyte is observed (Figure 4). From Figures 3 and 4, it is believed that the suppression of edge thinning of the negative plate when there are nine negative plates in Figure 2 is due to the suppression of the decrease in the specific gravity of the electrolyte in the upper part of the plate assembly. Based on these results, it is believed that a plate assembly with more than nine negative plates can achieve the same effect as when there are nine negative plates. Therefore, from the perspective of further suppressing edge thinning, it is preferable for the plate assembly to have nine or more negative plates.

Lead-acid batteries E20 to E23 and E24 to E27
By adjusting the sulfuric acid concentration, electrolytes are prepared in which the specific gravities of fully charged lead-acid batteries at 20° C. are 1.20, 1.22, 1.24, and 1.28. Lead-acid batteries E20, E21, E22, and E23 are fabricated in the same manner as lead-acid battery E19, except for using the prepared electrolytes.

An aqueous sulfuric acid solution containing 7 g/L of Na ions instead of Al ions is used as the electrolyte. By adjusting the sulfuric acid concentration, an electrolyte is prepared in which the specific gravity of a fully charged lead-acid battery at 20°C is 1.20, 1.22, 1.24, or 1.28. Lead-acid batteries E24, E25, E26, and E27 are fabricated in the same manner as lead-acid battery E19, except for using the prepared electrolyte. E20 to E23 and E24 to E27 are examples.

Using each lead-acid battery, measure the amount of thinning at the edge of the negative electrode plate in the same manner as in Evaluation 1. The relationship between the specific gravity of the electrolyte and the amount of thinning at the edge is shown in Figure 5.

As shown in Figure 5, when the electrolyte contains Al ions, the amount of thinning of the negative electrode plate can be significantly reduced compared to when it contains Na ions.

The lead-acid batteries according to one and other aspects of the present invention are suitable for use in idle stop-start vehicles, for example, as lead-acid batteries for ISSs that are charged and discharged under PSOC conditions. Furthermore, lead-acid batteries can be suitably used, for example, as starting power sources for vehicles (cars, motorcycles, etc.) and industrial power storage devices (for example, power sources for electric vehicles (forklifts, etc.)). Note that these are merely examples, and the uses of lead-acid batteries are not limited to these.

1: Lead-acid battery 2: Negative electrode plate 3: Positive electrode plate 4: Separator 5: Positive electrode shelf 6: Negative electrode shelf 7: Positive electrode column 8: Through-connector 9: Negative electrode column 11: Plate group 12: Battery case 13: Partition wall 14: Cell chamber 15: Lid 16: Negative electrode terminal 17: Positive electrode terminal 18: Vent plug

Claims (12)

A lead-acid battery,
The lead-acid battery includes at least one cell including a plate group and an electrolyte;
the electrode plate group includes a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate,
The negative electrode plate includes a current collector having a lug portion and a negative electrode material,
the ear portion has a surface layer containing Sn,
The Sn content in the surface layer is less than 10 mass %,
the negative electrode material contains a polymer compound having a peak in the range of 3.2 ppm to 3.8 ppm in chemical shift of a ¹ H-NMR spectrum measured using deuterated chloroform as a solvent;
a content of the polymer compound in the negative electrode material of 400 ppm or less by mass ; the polymeric compound comprises an oxygen atom attached to a terminal group and a —CH ₂ — group and/or a —CH< group attached to the oxygen atom;
2. The lead acid battery according to claim ₁ , wherein in the ¹ H-NMR spectrum, the ratio of the integral value of the peak to the total integral value of the peak, the integral value of the peak of the hydrogen atom of the -CH 2 - group, and the integral value of the peak of the hydrogen atom of the -CH< group is 85% or more. 3. The lead acid battery according to claim 1, wherein the polymer compound contains a repeating structure of oxy-C _2-4 alkylene units. A lead-acid battery,
The lead-acid battery includes at least one cell including a plate group and an electrolyte;
the electrode plate group includes a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate,
The negative electrode plate includes a current collector having a lug portion and a negative electrode material,
the ear portion has a surface layer containing Sn,
The Sn content in the surface layer is less than 10 mass %,
the negative electrode material comprises a polymer compound containing a repeating structure of an oxyC _2-4 alkylene unit ,
a content of the polymer compound in the negative electrode material of 400 ppm or less by mass ; The lead-acid battery according to any one of claims 1 to 4, wherein the Sn content in the surface layer is 7 mass% or less. The lead-acid battery according to any one of claims 1 to 5, wherein the Sn content in the surface layer is 0.01 mass% or more. The lead-acid battery according to any one of claims 1 to 6, wherein the content of the polymer compound in the negative electrode material is 15 ppm or more by mass. In at least one of the cells, the electrode plate group includes two or more positive electrode plates and two or more negative electrode plates, and has a structure in which the positive electrode plates and the negative electrode plates are alternately stacked with the separator interposed therebetween,
The lead-acid battery according to any one of claims 1 to 7 , wherein the electrode plate group includes nine or more negative electrode plates. The lead-acid battery according to any one of claims 1 to 8 , wherein a difference between a distance between the positive electrode plate and the negative electrode plate in the electrode plate pack and a maximum thickness of the separator is 0.15 mm or less. The lead acid battery according to any one of claims 1 to 9 , wherein the electrolyte contains Al ions. the polymer compound contains at least one selected from the group consisting of a hydroxy compound having a repeating structure of an oxyC _2-4 alkylene unit, an etherified product of the hydroxy compound, and an esterified product of the hydroxy compound,
The lead acid battery according to any one of claims 1 to 10, wherein the hydroxy compound is at least one selected from the group consisting of polyC _2-4 alkylene glycol, a copolymer containing a repeating structure of oxyC _2-4 alkylene, and a polyC _2-4 alkylene oxide adduct of a polyol . The lead acid battery according to any one of claims 1 to 11 , wherein the polymer compound contains a repeating structure of oxypropylene units.