WO2024225273A1

WO2024225273A1 - Rolled lead alloy foil, electrode for lead acid battery, and lead acid battery

Info

Publication number: WO2024225273A1
Application number: PCT/JP2024/015926
Authority: WO
Inventors: 雅人長谷川; 章好荒木; 紳悟川田; 吉章荻原; 洋金子; 淳古川; 惠造山田; 明尋渡邉
Original assignee: 古河電気工業株式会社; 古河電池株式会社
Priority date: 2023-04-28
Filing date: 2024-04-23
Publication date: 2024-10-31

Abstract

Provided is a rolled lead alloy foil having excellent corrosion resistance. The rolled lead alloy foil is formed of a lead alloy containing 0.005 mass% to 0.1 mass% of calcium, 0.5 mass% to 2.0 mass% of tin, and at most 0.005 mass% of bismuth, with the balance consisting of lead and unavoidable impurities. When a plurality of measurement regions defined in a mesh shape are set on the cross section of the rolled lead alloy foil obtained by cutting the rolled lead alloy foil along a plane which is parallel to the rolling direction of the rolled lead alloy foil and which is perpendicular to the surface of the rolled lead alloy foil, and a local orientation difference of each measurement region is measured, the proportion of a measurement region, in which the local orientation difference is less than 1 degree, among all the measurement regions is at least 50 area%.

Description

Rolled lead alloy foil, electrode for lead-acid battery, and lead-acid battery

The present invention relates to rolled lead alloy foil, electrodes for lead-acid batteries, and lead-acid batteries.

The electrodes of lead-acid batteries are provided with an electrode lead layer made of lead alloy foil and an active material disposed on the surface of the electrode lead layer. For example, rolled lead alloy foil produced by rolling a lead alloy has been used as the lead alloy foil (see, for example, Patent Documents 1 and 2).

International Publication No. 2016/110907 WO 2015/145800

The rolled lead alloy foil used in the electrodes of lead-acid batteries is required to have corrosion resistance. If the corrosion resistance of the rolled lead alloy foil is insufficient, the rolled lead alloy foil corrodes and the mass of the lead alloy decreases, which may cause the lead-acid battery to deteriorate early. Therefore, the rolled lead alloy foil is required to have further improved corrosion resistance.
An object of the present invention is to provide a rolled lead alloy foil having excellent corrosion resistance. Another object of the present invention is to provide an electrode for a lead-acid battery and a lead-acid battery which are resistant to deterioration.

The rolled lead alloy foil according to one embodiment of the present invention is a rolled lead alloy foil formed of a lead alloy containing 0.005% to 0.1% by mass calcium, 0.5% to 2.0% by mass tin, and 0.005% by mass or less bismuth, with the remainder being lead and unavoidable impurities, and is characterized in that, when a cross section of the rolled lead alloy foil that appears when the rolled lead alloy foil is cut along a plane that is parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil, is set with a plurality of measurement areas defined in a mesh pattern, and the local orientation difference of each measurement area is measured, the proportion of all the measurement areas in which the local orientation difference is less than 1 degree is 50 area % or more.

In another embodiment of the present invention, the rolled lead alloy foil is formed of a lead alloy containing 0.005% to 0.1% by mass of calcium, 0.5% to 2.0% by mass of tin, 0.005% to 0.1% by mass of bismuth, and 0.1% to 0.1% by mass of silver, with the remainder being lead and unavoidable impurities. The gist of the present invention is that when the rolled lead alloy foil is cut along a plane parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil, a plurality of measurement areas defined in a mesh pattern are set on the cross section of the rolled lead alloy foil that appears when the rolled lead alloy foil is cut along a plane parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil, and the local orientation difference of each measurement area is measured, the proportion of the measurement areas in which the local orientation difference is less than 1 degree is 50% or more by area.

Furthermore, a lead acid battery electrode according to yet another aspect of the present invention comprises an electrode lead layer made of the rolled lead alloy foil according to the above-mentioned one aspect or the rolled lead alloy foil according to the above-mentioned other aspect, and an active material disposed on a surface of the electrode lead layer.
Furthermore, a lead-acid battery according to yet another aspect of the present invention includes the lead-acid battery electrode according to the above-mentioned yet another aspect.

The rolled lead alloy foil of the present invention has excellent corrosion resistance. Furthermore, the lead-acid battery electrode and the lead-acid battery of the present invention are less susceptible to deterioration.

1 is a cross-sectional view illustrating a structure of a bipolar lead-acid battery which is one embodiment of the lead-acid battery according to the present invention. FIG. 2 is a diagram illustrating a method for evaluating the corrosion resistance of a rolled lead alloy foil. 1 is a graph showing the relationship between the ratio of a measurement area having a KAM value of less than 1 degree and the corrosion rate of a rolled lead alloy foil. 1 is a graph showing the relationship between the percentage of grains less than 20 μm in size and the uniformity of corrosion. FIG. 1 is a diagram illustrating a method for measuring a KAM value. FIG. 13 is a diagram illustrating a method for calculating a KAM value of a measurement area.

One embodiment of the present invention will be described below. Note that the embodiment described below is merely one example of the present invention. In addition, various modifications and improvements can be made to this embodiment, and forms incorporating such modifications or improvements can also be included in the present invention.

The structure of a lead-acid battery 1 according to one embodiment of the present invention will be described with reference to Fig. 1. The lead-acid battery 1 shown in Fig. 1 is a bipolar type lead-acid battery, and includes a first plate unit in which a negative electrode 110 is fixed to a flat first plate 11, a second plate unit in which an electrolytic layer 105 is fixed to the inside of a frame-shaped second plate 12, a third plate unit in which a bipolar electrode 130 formed by forming a positive electrode 120 on one surface of a substrate 111 and a negative electrode 110 on the other surface of the substrate 111 is fixed to the inside of a frame-shaped third plate 13, and a fourth plate unit in which the positive electrode 120 is fixed to a flat fourth plate 14.
The second plate units and the third plate units are alternately stacked between the first plate unit and the fourth plate unit to form a substantially rectangular parallelepiped-shaped lead-acid battery 1. The respective numbers of the second plate units and the third plate units to be stacked are set so that the storage capacity of the lead-acid battery 1 becomes a desired value.

The first to

fourth plates

11, 12, 13, and 14 and the substrate 111 are formed of, for example, a known molding resin, and the first to

fourth plates

11, 12, 13, and 14 are fixed to each other by an appropriate method so that the inside is sealed and the electrolyte does not leak out.
A negative electrode terminal 107 is fixed to the first plate 11, and a negative electrode 110 fixed to the first plate 11 and the negative electrode terminal 107 are electrically connected.
A positive electrode terminal 108 is fixed to the fourth plate 14, and a positive electrode 120 fixed to the fourth plate 14 and the positive electrode terminal 108 are electrically connected.
The electrolytic layer 105 is formed, for example, from a glass fiber mat impregnated with an electrolyte solution containing sulfuric acid.

The negative electrode 110 includes a negative electrode lead layer 102 made of, for example, a well-known lead foil, and a negative electrode active material layer 104 disposed on the surface of the negative electrode lead layer 102 .
The positive electrode 120 comprises a positive electrode lead layer 101 (corresponding to the "electrode lead layer" which is a constituent element of the present invention) made of rolled lead alloy foil according to the present embodiment described later, and a positive electrode active material layer 103 arranged on the surface of the positive electrode lead layer 101.
The positive electrode 120 and the negative electrode 110 are fixed to the front and back surfaces of the substrate 111, respectively, and are electrically connected by an appropriate method. Alternatively, the positive electrode 120 and the negative electrode 110 may be fixed to one surface of each of the two substrates 111, and the other surfaces may be electrically connected and fixed to each other.

In the lead-acid battery 1 according to this embodiment having such a configuration, a bipolar electrode 130, which is an electrode for a lead-acid battery, is configured by the substrate 111, the positive electrode lead layer 101, the positive electrode active material layer 103, the negative electrode lead layer 102, and the negative electrode active material layer 104. A bipolar electrode is an electrode that functions as both a positive electrode and a negative electrode in one sheet.
The lead-acid battery 1 according to this embodiment has a battery configuration in which the cell members are connected in series by alternately stacking and assembling a plurality of cell members each including a positive electrode 120 having a positive electrode active material layer 103, a negative electrode 110 having a negative electrode active material layer 104, and an electrolytic layer 105 interposed between the cell members.
In this embodiment, a bipolar lead-acid battery having a bipolar electrode that has a single electrode functioning as both a positive electrode and a negative electrode has been shown as an example of a lead-acid battery, but the lead-acid battery according to this embodiment may also be a lead-acid battery that has an electrode that functions as a positive electrode and an electrode that functions as a negative electrode, and in which the separate positive and negative electrodes are arranged alternately.

<Regarding the rolled lead alloy foil constituting the positive electrode lead layer 101>
Next, the rolled lead alloy foil constituting the positive electrode lead layer 101 will be described. The rolled lead alloy foil according to this embodiment is a foil manufactured by rolling a lead alloy, and the lead alloy contains 0.005% by mass or more and 0.1% by mass or less of calcium (Ca), 0.5% by mass or more and 2.0% by mass or less of tin (Sn), and 0.005% by mass or less of bismuth, with the balance being lead (Pb) and unavoidable impurities (hereinafter, sometimes referred to as the "first lead alloy"). This lead alloy may be a lead alloy (hereinafter, sometimes referred to as the "second lead alloy") containing 0.005% by mass or more and 0.1% by mass or less of calcium, 0.5% by mass or more and 2.0% by mass or less of tin, 0.005% by mass or less of bismuth, and 0.1% by mass or less of silver, with the balance being lead and unavoidable impurities.

Furthermore, this rolled lead alloy foil is a foil in which, when a cross section of the rolled lead alloy foil is cut along a plane parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil, a number of measurement areas defined in a mesh pattern are set on the cross section of the rolled lead alloy foil, and the local orientation difference of each measurement area is measured, and the proportion of measurement areas in which the local orientation difference is less than 1 degree is 50 area % or more of all the measurement areas. Note that in this specification, "local orientation difference" is sometimes referred to as "KAM value." KAM is an abbreviation for Kernel Average Misorientation.

The rolled lead alloy foil according to this embodiment has a ratio of measurement areas with a KAM value of less than 1 degree to 50 area % or more of all measurement areas, i.e., there are many low strain areas and few high strain areas in the rolled lead alloy foil, so there is little residual strain in the rolled lead alloy foil. Therefore, this rolled lead alloy foil has excellent corrosion resistance. High strain areas with a KAM value of 1 degree or more have high internal elastic strain energy due to accumulated lattice strain and are susceptible to corrosion, but low strain areas with a KAM value of less than 1 degree have low internal elastic strain energy and are resistant to corrosion. An example of a method for manufacturing the rolled lead alloy foil according to this embodiment will be described in detail later.

Therefore, if a lead-acid battery electrode is formed by using the rolled lead alloy foil according to the present embodiment, which satisfies the above-mentioned conditions for the KAM value, as the lead layer for the electrode, the lead layer for the electrode has excellent corrosion resistance, so that the lead-acid battery electrode is not easily deteriorated. Also, a lead-acid battery such as a bipolar lead-acid battery including this lead-acid battery electrode is not easily deteriorated.
The method for measuring the KAM value is not particularly limited, but for example, it can be obtained by crystal orientation measurement using electron backscatter diffraction. That is, the rolled lead alloy foil according to this embodiment is cut, and a cross section parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil is exposed. Then, the KAM value can be obtained by analyzing the cross section by electron backscatter diffraction.

In this embodiment, a plurality of measurement regions defined in a mesh pattern are set on the cross section, the KAM value of each measurement region is measured, and the ratio of the area of the measurement regions having a KAM value of less than 1 degree is calculated. The shape of the measurement region is not particularly limited, and examples thereof include a triangle such as an equilateral triangle, a quadrangle such as a square, a rectangle, a parallelogram, or a rhombus, a hexagon such as a regular hexagon, or a circle such as a regular circle or an ellipse.
The proportion of measurement areas having a local orientation difference of less than 1 degree among all measurement areas must be 50 area % or more, preferably 75 area % or more, more preferably 85 area % or more, and most preferably 100 area %.
Furthermore, in order to improve the corrosion resistance of the rolled lead alloy foil, the ratio of the measurement areas in which the local orientation difference is less than 5 degrees to all the measurement areas is preferably 94 area % or more, more preferably 98 area % or more.

The rolled lead alloy foil according to this embodiment has rolled grains, which are crystal grains formed by rolling. In addition to the rolled grains, the foil may have recrystallized grains, which are crystal grains formed by heat treatment (i.e., the foil may have a mixed grain state having both rolled grains and recrystallized grains). In the rolled lead alloy foil according to this embodiment, the grain size of the grains is preferably sufficiently small in order to prevent the corroded portion from penetrating the rolled lead alloy foil in the thickness direction. Here, the grain size of the rolled grains is less than 1 μm, which is much smaller than the recrystallized grains, which have a grain size of several μm or more. Therefore, in order to ensure that the grain size of the grains of the rolled lead alloy foil is sufficiently small, it is preferable that the grain size of the recrystallized grains is sufficiently small. Specifically, when the diameter (grain size) of the grains observed in the cross section is measured, it is preferable that the proportion of the grains having a grain size of less than 20 μm among all the grains is 95 area % or more. This proportion can be calculated by dividing the total area of the grains having a grain size of less than 20 μm in the cross section by the total area of all the grains in the cross section.

By recrystallizing the material through heat treatment to form recrystallized grains, the local orientation difference is reduced, and the internal elastic strain energy is reduced and stabilized, improving the corrosion resistance of the rolled lead alloy foil. In addition, if there are many recrystallized grains with large grain sizes, the corroded portion may penetrate the rolled lead alloy foil in the thickness direction due to grain boundary corrosion that progresses along the grain boundaries, which may damage the lead-acid battery and make it unusable. For example, in a bipolar lead-acid battery, if a through hole is formed from the positive electrode side of the lead layer for the electrode, corrosion may progress further to other components, and the electrolytes on the positive and negative electrodes may circulate around each other, a phenomenon known as liquid junctions. As a result, the battery characteristics of the bipolar lead-acid battery may deteriorate, and in the worst case, the bipolar lead-acid battery may become unusable.

However, if there are many recrystallized grains with small grain sizes, corrosion progresses uniformly in the thickness direction, so that the corroded portion is less likely to penetrate through the rolled lead alloy foil in the thickness direction, and the lead-acid battery is less likely to become unusable.
In addition, when corrosion progresses uniformly in the thickness direction, the internal resistance increases, so the degree of deterioration due to corrosion can be detected based on the internal resistance. When corrosion penetrates the rolled lead alloy foil in the thickness direction, the lead-acid battery is damaged and becomes unusable, so the degree of deterioration due to corrosion cannot be detected.

Furthermore, the thickness of the rolled lead alloy foil according to the present embodiment is not particularly limited, but is preferably 0.02 mm to 1.5 mm, more preferably 0.02 mm to 1.0 mm, even more preferably 0.04 mm to 0.6 mm, and particularly preferably 0.05 mm to 0.3 mm. If the thickness of the rolled lead alloy foil is within the above range, the effect of reducing the weight of a lead-acid battery including a lead-acid battery electrode formed using the rolled lead alloy foil as an electrode lead layer is achieved.
If the thickness of the rolled lead alloy foil is 0.02 mm or more, the internal resistance of the lead-acid battery is likely to be low, so that a lead-acid battery with better performance is likely to be obtained. Also, if the thickness of the rolled lead alloy foil is 0.02 mm or more, the rolled lead alloy foil is unlikely to wrinkle or break during the manufacturing process, so that the reliability of the lead-acid battery is improved, and handling is easy, so that the tact time can be easily reduced.

On the other hand, if the thickness of the rolled lead alloy foil is 1.5 mm or less, the lead-acid battery can be made lighter, so that the weight energy density can be increased. Furthermore, if the thickness of the rolled lead alloy foil is 1.5 mm or less, the amount of the rolled lead alloy foil used can be reduced, so that the manufacturing cost can be reduced.
Therefore, if a lead-acid battery electrode is constructed using the rolled lead alloy foil according to this embodiment, which satisfies the above-mentioned conditions regarding the grain size, as an electrode lead layer, the corroded portion is unlikely to penetrate the rolled lead alloy foil in the thickness direction, and therefore the lead-acid battery electrode and the lead-acid battery including the lead-acid battery electrode are unlikely to be damaged and become unusable.

<About the composition of lead alloys>
Next, the alloy composition of the lead alloy forming the rolled lead alloy foil according to this embodiment will be described. This lead alloy is a lead alloy (first lead alloy) containing 0.005% by mass or more and 0.1% by mass or less of calcium, 0.5% by mass or more and 2.0% by mass or less of tin, 0.005% by mass or less of bismuth, and the balance being lead and unavoidable impurities. This lead alloy may also be a lead alloy (second lead alloy) containing 0.005% by mass or more and 0.1% by mass or less of calcium, 0.5% by mass or more and 2.0% by mass or less of tin, 0.005% by mass or less of bismuth, and 0.1% by mass or less of silver, and the balance being lead and unavoidable impurities.

When the lead alloy contains tin, the adhesion between the positive electrode lead layer 101, which is made of rolled lead alloy foil, and the positive electrode active material layer 103 is improved. However, when the lead alloy contains a large amount of tin, the susceptibility to intergranular corrosion increases, and the positive electrode lead layer 101 tends to deteriorate easily. Therefore, in both the first lead alloy and the second lead alloy, the tin content must be 0.5% by mass or more and 2.0% by mass or less, preferably 0.5% by mass or more and 1.8% by mass or less, and more preferably 0.5% by mass or more and 1.6% by mass or less.

In addition, when calcium is contained in a lead alloy, the grain boundary migration is inhibited, and the crystal grains of the lead alloy become fine. Therefore, when the lead alloy contains tin and calcium, the strength of the lead alloy is increased, and it becomes difficult to deform.
The calcium content in the lead alloy, in both the first lead alloy and the second lead alloy, must be 0.005% by mass or more and 0.1% by mass or less, preferably 0.005% by mass or more and 0.08% by mass or less, and more preferably 0.005% by mass or more and 0.06% by mass or less.
Silver (Ag) has the same additive effect as calcium, so it may be added to the lead alloy. When silver is contained in the lead alloy (second lead alloy), the silver content in the lead alloy must be 0.1 mass% or less, and is preferably 0.001 mass% or more and 0.1 mass% or less. However, even if silver is not actively added, it may be contained as an inevitable impurity due to contamination from the base metal.

On the other hand, when the lead alloy contains bismuth (Bi), the formability of the lead alloy by rolling or the like tends to decrease. That is, bismuth is one of the impurities that is preferably not contained as much as possible in the lead alloy forming the rolled lead alloy foil according to this embodiment. Therefore, the content of bismuth in the lead alloy must be 0.005 mass% or less in both the first lead alloy and the second lead alloy, and is preferably 0.001 mass% or more and 0.005 mass% or less, and is most preferably 0 mass%.
On the other hand, lead alloys may contain elements other than lead, tin, calcium, silver, and bismuth. These elements are impurities inevitably contained in lead alloys, and the total content of elements other than lead, tin, calcium, silver, and bismuth in the lead alloy is preferably 0.01% by mass or less, and most preferably 0% by mass.

<Manufacturing method of rolled lead alloy foil>
Next, an example of a method for producing the rolled lead alloy foil constituting the positive electrode lead layer 101 from a lead alloy will be described. The rolled lead alloy foil according to this embodiment can be produced by performing a combination of rolling and heat treatment.
By rolling the lead alloy at a high reduction rate to produce a rolled lead alloy foil, fine crystals (rolled grains) can be generated inside the foil. The reduction rate when rolling the lead alloy is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more.

By heat treating the rolled lead alloy foil at a temperature below the solution temperature after the above rolling, partial recrystallization occurs and recrystallized grains are generated. As a result, a mixed grain state having both rolled grains and recrystallized grains can be formed inside the foil. If heat treatment is performed at a high temperature above the solution temperature, the solution treatment causes grain boundary reaction type precipitation of coarse crystals, and corrosion easily occurs in which the corroded part penetrates the rolled lead alloy foil in the thickness direction.
The temperature of the heat treatment for generating recrystallized grains is preferably 100° C. or more and the solution temperature or less, more preferably 180° C. or more and the solution temperature or less, and even more preferably 200° C. or more and the solution temperature or less. The heat treatment time is not particularly limited and varies depending on the heat treatment temperature, but is preferably 30 minutes or more and 24 hours or less, more preferably 1 hour or more and 24 hours or less, and even more preferably 2 hours or more and 24 hours or less.

Three examples of the production of the rolled lead alloy foil according to this embodiment are shown below.
(Production Example 1)
A 5 mm thick alloy plate made of a lead alloy is rolled at a rolling reduction of 80% to obtain a 1 mm thick rolled plate. This rolling produces rolled grains. Next, the obtained rolled plate is heat treated (intermediate heat treatment) at 180°C for 2 hours. This intermediate heat treatment removes internal distortion of the rolled plate. The intermediate heat treated rolled plate is further rolled at a rolling reduction of 60% to obtain a 0.4 mm thick rolled lead alloy foil. Finally, the rolled lead alloy foil is heat treated at 100°C for 24 hours. This heat treatment produces recrystallized grains, forming a mixed grain state and removing internal distortion of the rolled lead alloy foil.

(Production Example 2)
A lead alloy slab with a thickness of 5 mm is manufactured, and left (heat treated) at 200°C for 1 hour without cooling to room temperature, and then slowly cooled to room temperature. This results in a slab with internal distortion removed. Next, this slab is rolled at a rolling reduction of 92% to produce a rolled lead alloy foil with a thickness of 0.4 mm. This rolling produces rolled grains. Finally, the rolled lead alloy foil is heat treated at 100°C for 24 hours. This heat treatment produces recrystallized grains, forming a mixed grain state and removing internal distortion in the rolled lead alloy foil.

(Production Example 3)
A 5 mm thick lead alloy slab is manufactured, left at 200°C for 1 hour (heat treatment) without cooling to room temperature, and then slowly cooled to room temperature. This results in a slab with no internal distortion. Next, this slab is rolled at a reduction rate of 80% to produce a rolled plate with a thickness of 1 mm. This rolling produces rolled grains.
Next, the obtained rolled plate is subjected to a heat treatment (intermediate heat treatment) at 180°C for 2 hours. This intermediate heat treatment removes the internal strain of the rolled plate. The intermediate heat-treated rolled plate is then rolled at a rolling reduction of 60% to obtain a rolled lead alloy foil with a thickness of 0.4 mm. Finally, the rolled lead alloy foil is subjected to a heat treatment at 100°C for 24 hours. This heat treatment produces recrystallized grains, forming a mixed grain state and removing the internal strain of the rolled lead alloy foil.

[Example]
The present invention will be described in more detail below with reference to examples and comparative examples.
Example 1
A 5.0 mm thick alloy plate was prepared, which was made of a lead alloy containing 0.06 mass % calcium, 1.6 mass % tin, 0.002 mass % or less bismuth, and the remainder being lead and unavoidable impurities. Using this alloy plate as a material, a rolled lead alloy foil was manufactured by the method shown in Manufacturing Example 1 above.
That is, an alloy plate having a thickness of 5.0 mm was rolled at a reduction rate of 80% to obtain a rolled plate having a thickness of 1.0 mm, and the rolled plate was subjected to an intermediate heat treatment (first stage heat treatment) at 180° C. for 2 hours. The rolled plate subjected to the intermediate heat treatment was then rolled at a reduction rate of 60% to obtain a rolled lead alloy foil having a thickness of 0.4 mm, and the rolled plate was subjected to a heat treatment (second stage heat treatment) at 100° C. for 24 hours.
The rolled lead alloy foil of Example 1 thus obtained was subjected to the following analyses and performance evaluations.

<Measurement of KAM value and calculation of area ratio>
First, the rolled lead alloy foil of Example 1 was cut to expose a cross section parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil. Then, of this cross section, an arbitrary location in the center part in the thickness direction, excluding the part near the surface of the rolled lead alloy foil where processing distortion is large, was set as the measurement target part, and the measurement target part was divided into a mesh-like shape to set a plurality of measurement areas defined in a mesh-like shape. In Example 1, as shown in Figure 5, the shape of the measurement target part was a square with a side of 20 μm, and the shape of each measurement area was a regular hexagon with a side of 0.3 μm.
The measurement target portion was analyzed by electron backscatter diffraction using a scanning electron microscope JSM-7001FA manufactured by JEOL Ltd. The analysis results were then analyzed using analysis software OIM Analysis (registered trademark) manufactured by TSL Solutions Co., Ltd., and the KAM value of each measurement region was calculated.

In this analysis, it was confirmed that the part with a large processing strain was excluded from the measurement object by taking the part with a CI value (Confidence Index), which is an index indicating the reliability when indexing to estimate the crystal orientation, of 0.1 or more as the measurement object part. In addition, in this analysis, the orientation difference of 15° or more was defined as a grain boundary. Therefore, according to this analysis, the calculation result of the KAM value of each measurement area is in the range of 0° or more and less than 15°.
The KAM value of a certain measurement area is calculated by averaging the orientation differences of the adjacent measurement areas. However, among the adjacent measurement areas, those with orientation differences of less than 0° or more than 15° are excluded from the calculation of the average value. Therefore, the KAM value is the average value of the orientation differences between adjacent measurement areas within the same crystal grain. Using FIG. 6 as an example, the KAM value of measurement area P is calculated by the calculation formula shown in FIG. 6. The numerical values written inside the six measurement areas adjacent to measurement area P are the orientation differences of that measurement area with respect to measurement area P.

Next, each measurement area was classified according to the KAM value. Classification was performed every 1°, and the measurement areas were classified into 15 types. That is, the measurement areas were classified into 15 types, namely, measurement areas with KAM values of 0° or more and less than 1°, measurement areas with KAM values of 1° or more and less than 2°, ..., measurement areas with KAM values of 14° or more and less than 15°. Then, the total area of each type of measurement area was calculated, and the total area was divided by the total area of all measurement areas to calculate the ratio (area ratio) of each type of measurement area.
Furthermore, using the results of the proportion of each type of measurement area, the proportion (area ratio) of the measurement area where the KAM value was 0° or more and less than 1°, the measurement area where the KAM value was 1° or more and less than 5°, and the measurement area where the KAM value was 5° or more and less than 15° was calculated.
This analysis was carried out at five arbitrary measurement points, and the average value was calculated. The results are shown in Table 1.

<Measurement of crystal grain diameter and calculation of area ratio>
The cross section was analyzed by electron backscatter diffraction in the same manner as in the measurement of the KAM value. The analysis results were then analyzed using analysis software OIM Analysis (registered trademark) manufactured by TSL Solutions Co., Ltd., and the diameters of the crystal grains observed in the cross section were measured. In this analysis, a grain boundary was defined as a boundary where the orientation difference was 15° or more, and the area of the crystal grain was calculated from the number of measurement regions present in the same crystal grain, and the diameter of the crystal grain was calculated by regarding the crystal grain as a perfect circle.
Next, each crystal grain was classified according to its diameter. The classification was performed in 0.1 μm increments, and the crystal grains were classified into multiple types. That is, the crystal grains were classified into crystal grains with diameters of more than 0 μm and less than 0.1 μm, crystal grains of 0.1 μm or more and less than 0.2 μm, crystal grains of 0.2 μm or more and less than 0.3 μm, and so on. The total area of each type of crystal grain was then calculated, and divided by the total area of all the measurement regions to calculate the proportion (area ratio) of each type of crystal grain. The results are shown in Table 1.

<Corrosion rate measurement>
A constant potential test was carried out to evaluate the corrosion resistance of the rolled lead alloy foil of Example 1. A positive electrode made using the rolled lead alloy foil of Example 1 and a negative electrode made using the lead foil were immersed in an electrolyte. The electrolyte was sulfuric acid with a specific gravity of 1.28 and a temperature of 60°C. A voltage with a potential difference of 1350 mV was applied between the positive electrode and the negative electrode, and a current was passed through the rolled lead alloy foil to oxidize (corrode). After the current had been applied for 7 days, the positive electrode was taken out and the corrosion rate of the rolled lead alloy foil was calculated.
The corrosion rate was calculated as follows. Oxides were removed from the rolled lead alloy foil taken out, and the mass of the removed oxides was taken as the amount of corrosion. The amount of corrosion was divided by the surface area of the rolled lead alloy foil before the constant potential test (amount of corrosion/surface area) to obtain the corrosion rate (mg/ ^cm2 ). The lower the corrosion rate, the higher the corrosion resistance of the rolled lead alloy foil. If the corrosion rate is less than 30 mg/ ^cm2 , it is determined that the corrosion resistance is excellent. The results are shown in Table 1.

<Evaluation of corrosion uniformity>
The rolled lead alloy foil after the constant potential test was cut to expose a cross section parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil. The cross section was then mirror-finished by electrolytic polishing and observed using an optical microscope. Then, the surface of the rolled lead alloy foil was found to be uniformly corroded (to approximately the same depth), and the thickness of the non-corroded part that was not corroded and remained as lead alloy was measured (see FIG. 2(a)). The same measurement was performed at five locations, and the average value was taken as the remaining thickness value. The thickness of the rolled lead alloy foil before the constant potential test minus the remaining thickness value was taken as the corrosion depth A (μm).

Next, the rolled lead alloy foil was observed under an optical microscope in the same manner as above, and the area where the corrosion progressed linearly or wedge-shaped from the surface to the inside of the foil was found, and the depth of the linear or wedge-shaped corrosion was measured (see FIG. 2(b)). The starting point for measuring the depth of the linear or wedge-shaped corrosion was not the surface of the rolled lead alloy foil before the constant potential test, but the surface of the rolled lead alloy foil where the surface was uniformly corroded after the constant potential test. The same measurement was performed at five locations, and the maximum value among them was taken as the corrosion depth B (μm).
The corrosion uniformity was evaluated by dividing the corrosion depth B by the corrosion depth A. When the rolled lead alloy foil is composed of fine crystals, the corrosion tends to progress uniformly, so the corrosion uniformity is small, whereas when the rolled lead alloy foil contains coarse crystals, the corrosion tends to progress linearly or wedge-shaped, so the corrosion uniformity is large. If the corrosion uniformity is 2 or less, it is judged that the corrosion is uniform and the corrosion resistance is excellent. The results are shown in Table 1.

<Evaluation of the Presence or Absence of Wrinkles or Folds>
The rolled lead alloy foil of Example 1 was fixed to a substrate. The rolled lead alloy foil fixed to the substrate was then visually observed to determine whether or not the rolled alloy foil had wrinkles or folds. The results are shown in Table 1.

Example 2
A rolled lead alloy foil of Example 2 was produced in exactly the same manner as in Example 1, except that the conditions of the second stage heat treatment were different as shown in Table 1. Then, analysis and performance evaluation were carried out in exactly the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

Example 3
A rolled lead alloy foil of Example 3 was produced in exactly the same manner as in Example 1, except that the conditions of the second stage heat treatment were different as shown in Table 1. Then, analysis and performance evaluation were carried out in exactly the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

Example 4
A rolled lead alloy foil of Example 4 was produced in exactly the same manner as in Example 1, except that the contents of tin and calcium in the lead alloy were different as shown in Table 1. Then, analysis and performance evaluation were carried out in exactly the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

Example 5
A rolled lead alloy foil of Example 5 was produced in exactly the same manner as in Example 1, except that the conditions of the second stage heat treatment were different as shown in Table 1. Then, analysis and performance evaluation were carried out in exactly the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

Example 6
The rolled lead alloy foil of Example 6 was produced in exactly the same manner as Example 1, except that the contents of tin and calcium in the lead alloy were different as shown in Table 1, and the conditions of the second stage heat treatment were different as shown in Table 1. Then, analysis and performance evaluation were carried out in exactly the same manner as Example 1. The results of the analysis and performance evaluation are shown in Table 1.

(Examples 7 to 15, 18 to 26)
The rolled lead alloy foils of Examples 7 to 15 and 18 to 26 were produced in exactly the same manner as in Example 1, except that the contents of tin, calcium, silver, and bismuth in the lead alloy were different as shown in Table 1. Then, analysis and performance evaluation were carried out in exactly the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

(Example 16)
A lead alloy having the same composition as that in Example 1 was prepared, and a rolled lead alloy foil was manufactured by the method shown in the above Manufacturing Example 2. That is, a lead alloy slab having a thickness of 5.0 mm was manufactured, and left at 200°C for 1 hour without cooling to room temperature (first stage heat treatment), and then slowly cooled to room temperature. Next, this slab was rolled at a rolling reduction of 92% to obtain a rolled lead alloy foil having a thickness of 0.4 mm. Finally, the rolled lead alloy foil was subjected to a heat treatment (second stage heat treatment) at 100°C for 24 hours.

(Example 17)
A lead alloy having the same composition as that in Example 1 was prepared, and a rolled lead alloy foil was produced by the method shown in the above-mentioned Production Example 3. That is, a lead alloy slab having a thickness of 5.0 mm was produced, and left at 200°C for 1 hour without cooling to room temperature (first stage heat treatment), and then slowly cooled to room temperature. Next, this slab was rolled at a rolling reduction of 80% to obtain a rolled plate having a thickness of 1.0 mm. Next, the obtained rolled plate was subjected to a heat treatment (intermediate heat treatment) at 180°C for 2 hours. Furthermore, the rolled plate subjected to the intermediate heat treatment was rolled at a rolling reduction of 60% to obtain a rolled lead alloy foil having a thickness of 0.4 mm. Finally, the rolled lead alloy foil was subjected to a heat treatment (second stage heat treatment) at 100°C for 24 hours.

(Comparative Example 1)
A rolled lead foil of Comparative Example 1 was manufactured in exactly the same manner as in Example 1, except that pure lead was used instead of the lead alloy and the second heat treatment was not performed. Then, analysis and performance evaluation were performed in exactly the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

(Comparative Example 2)
A rolled lead alloy foil of Comparative Example 2 was produced in the same manner as in Example 1, except that the second heat treatment was not performed. Then, analysis and performance evaluation were performed in the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

(Comparative Example 3)
A rolled lead alloy foil of Comparative Example 3 was produced in exactly the same manner as in Example 1, except that the conditions of the second stage heat treatment were different as shown in Table 1. Then, analysis and performance evaluation were carried out in exactly the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

(Comparative Example 4)
A rolled lead alloy foil of Comparative Example 4 was produced in exactly the same manner as in Example 1, except that the tin and calcium contents in the lead alloy were different as shown in Table 1, and that the second heat treatment was not performed. Then, analysis and performance evaluation were performed in exactly the same manner as in Example 1. The results of the analysis and performance evaluation are shown in Table 1.

As can be seen from the results shown in Table 1, in Examples 1 to 26, the proportion of the measurement area in which the KAM value was less than 1° was 50% or more by area, and therefore the corrosion rate was low and the corrosion resistance was excellent. In addition, in Examples 1, 2, 4, and 7 to 26, the proportion of crystal grains with a grain size of less than 20 μm was 95% or more by area, and therefore the corrosion uniformity was high and the corrosion resistance was excellent.
On the other hand, in Comparative Examples 2 to 4, the ratio of the measurement area where the KAM value was less than 1° was less than 50 area %, so that the corrosion rate was high and the corrosion resistance was insufficient.
The results of Examples 1 to 6 and Comparative Examples 2 to 4 are shown in the graphs of Figures 3 and 4. From the graph of Figure 3, it can be seen that when the ratio of the measurement area where the KAM value is less than 1° is 50 area % or more, the corrosion rate is less than 30 mg/ ^cm2 , and the corrosion resistance is excellent.
Furthermore, from the graph of FIG. 4, it can be seen that when the ratio of crystal grains having a grain size of less than 20 μm is 95 area % or more, the corrosion uniformity is 2 or less, and thus the corrosion uniformity is high.

1... Lead acid battery 101... Lead layer for positive electrode 102... Lead layer for negative electrode 103... Active material layer for positive electrode 104... Active material layer for negative electrode 105... Electrolytic layer 110... Negative electrode 111... Substrate 120... Positive electrode 130... Bipolar electrode

Claims

A rolled lead alloy foil containing 0.005% by mass or more and 0.1% by mass or less of calcium, 0.5% by mass or more and 2.0% by mass or less of tin, 0.005% by mass or less of bismuth, and the remainder being lead and unavoidable impurities,
A rolled lead alloy foil, comprising: a plurality of measurement areas defined in a mesh pattern on a cross section of the rolled lead alloy foil that appears when the rolled lead alloy foil is cut along a plane that is parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil; and when a local orientation difference is measured for each of the measurement areas, the proportion of the measurement areas having a local orientation difference of less than 1 degree among all the measurement areas is 50 area % or more.
A rolled lead alloy foil containing 0.005% by mass or more and 0.1% by mass or less of calcium, 0.5% by mass or more and 2.0% by mass or less of tin, 0.005% by mass or less of bismuth, 0.1% by mass or less of silver, and the remainder being lead and unavoidable impurities,
A rolled lead alloy foil, comprising: a plurality of measurement areas defined in a mesh pattern on a cross section of the rolled lead alloy foil that appears when the rolled lead alloy foil is cut along a plane that is parallel to the rolling direction of the rolled lead alloy foil and perpendicular to the surface of the rolled lead alloy foil; and when a local orientation difference is measured for each of the measurement areas, the proportion of the measurement areas having a local orientation difference of less than 1 degree among all the measurement areas is 50 area % or more.
The rolled lead alloy foil according to claim 1 or 2, in which, when the diameters of the crystal grains observed in the cross section are measured, the proportion of crystal grains having a grain size of less than 20 μm among all the crystal grains is 95% or more by area.
The rolled lead alloy foil according to claim 1 or 2, wherein the ratio of the measurement areas in which the local orientation difference is less than 5 degrees among all the measurement areas is 94 area % or more.
The rolled lead alloy foil according to claim 1 or 2, having a thickness of 0.02 mm or more and 1.5 mm or less.
An electrode for a lead-acid battery comprising an electrode lead layer made of the rolled lead alloy foil according to claim 1 or 2, and an active material disposed on the surface of the electrode lead layer.
The electrode for a lead acid battery according to claim 6, which is for a bipolar lead acid battery.
A lead-acid battery comprising the lead-acid battery electrode according to claim 6.