Aluminum alloy foil for battery current collectors and method for manufacturing the same

Abstract

To provide an aluminum alloy foil for a battery current collector which is excellent in both tensile strength and extension after foil rolling, and both tensile strength and extension after a low temperature heat treatment expected during a battery manufacturing process, particularly heat treatment at 120°C.SOLUTION: An aluminum alloy foil for a battery current collector is an aluminum alloy foil whose composition is 0.15 mass% or more and less than 0.3 mass% of Fe content, exceeding 0.8 mass% and less than 1.5 mass% of Si content, and the rest that is Al and inevitable impurity. An average circle-equivalent diameter of an intermetallic compound present in a surface of the aluminum alloy foil is 1.0 μm or less. A number density of an intermetallic compound, which is present in the surface of the aluminum alloy foil and has an average circle-equivalent diameter exceeding 3.0 μm, is 2.0×102 pieces / mm2 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to aluminum alloy foil for battery current collectors and a method for manufacturing the same. [Background technology]

[0002] Generally, aluminum foil is used as the positive electrode current collector in lithium-ion secondary batteries. In recent years, in order to increase the capacity of lithium-ion secondary batteries within a limited volume, it has become necessary to increase the volume and density of the active material layer, as well as to save space for the current collector and other components. For example, the thickness of the aluminum foil used in the positive electrode current collector is about 12 μm, but there is a possibility that further thinning of the foil will be required in the future.

[0003] The manufacturing method for this lithium-ion secondary battery generally involves the following steps. First, a slurry of active material, binder resin, and solvent is coated onto the surface of a metal foil, such as aluminum foil, which will serve as the current collector. At this time, the positive electrode active material is coated onto the metal foil that will become the positive electrode, and the slurry containing the negative electrode active material is coated onto the metal foil that will become the negative electrode. Next, the metal foil coated with the slurry is heated to, for example, 100-150°C to evaporate the solvent and dry it. Furthermore, in order to increase the density of the active material layer, the dried metal foil is pressed to obtain electrode material. During this pressing process, heating may be performed to increase the pressing efficiency. After that, further drying may be performed to, for example, 120-160°C. The electrode material manufactured in this way is cut or punched into the desired shape. Then, the positive electrode material, separator, and negative electrode material are laminated or wound together, connected to pull-out tab material, etc., and then housed in a case or laminate pack. Next, the lithium-ion secondary battery is manufactured by injecting electrolyte into a case or laminate pack, sealing it, and then performing initial charge-discharge cycles and aging processes. The manufacturing process described above is merely one example, but the aluminum foil used as a current collector undergoes various processing and thermal histories, including pressing and winding. As the thickness of the aluminum foil decreases, it becomes more prone to breakage during these manufacturing processes. Therefore, numerous techniques have been proposed to improve the mechanical properties of the aluminum foil, particularly its tensile strength and elongation, in order to manufacture it stably without breakage.

[0004] For example, Patent Document 1 specifies that the composition of aluminum foil for current collectors should have an Fe content of 0.3% to 3.0% by mass and a Si content of 0.8% to 1.5% by mass. Furthermore, by controlling the average diameter of large-diameter precipitates present in the aluminum alloy foil, its mechanical properties should be such that it has a tensile strength of 170 N / mm² at a foil thickness of 15 μm or less. 2 More than 280N / mm 2 The following technologies are disclosed to achieve growth rates of 4% to 10%. Furthermore, Patent Document 2 discloses an aluminum alloy foil for battery current collectors that contains an Fe content of 0.15% to 0.7% by mass, a Si content of 0.2% to 0.8% by mass, a Si content / Fe content ratio of 0.7 to 2.5, a tensile strength of 180 MPa or more after rolling, an elongation of 3.0% or more at a foil thickness of 12 μm, and maintains its elongation characteristics even after low-temperature heat treatment. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] WO2010 / 100924 Pamphlet [Patent Document 2] Japanese Patent Publication No. 2017-186629 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, Patent Document 1 does not describe the tensile strength and elongation after low-temperature heat treatment at 100-160°C, which is used in the battery manufacturing process. Furthermore, while the method for manufacturing aluminum foil for current collectors specifies that the cooling rate of the molten metal in the ingot-getting process should be between 100°C / sec and 500°C / sec, the maximum cooling rate in the examples is only 182°C / sec, and although the casting method is described as continuous casting, there is no specific description. Moreover, pure Al-based and Al-Fe-based aluminum foils are commonly used for positive electrode current collectors, and it is known that the elongation of these aluminum foils decreases significantly when subjected to low-temperature heat treatment at 100-160°C, which is used in the battery manufacturing process. The cause of this phenomenon has not yet been clarified, but it is suspected that the low heat treatment temperature makes recovery and recrystallization difficult, which contributes to the decrease in elongation. Furthermore, in the aforementioned Patent Document 2, the highest tensile strength value in the examples is 224 MPa, and further increases in strength are necessary to meet the recent demand for thinner foils.

[0007] Therefore, the present invention has been made in view of the above-mentioned problems, and aims to provide an aluminum alloy foil for battery current collectors that is excellent in both tensile strength and elongation after foil rolling, and in tensile strength and elongation after low-temperature heat treatment expected during the battery manufacturing process, particularly after heat treatment at 120°C. [Means for solving the problem]

[0008] In order to solve the aforementioned problems, the inventors conducted various studies and found that by controlling the Fe and Si content, as well as the size and number density of intermetallic compounds present on the surface of the aluminum alloy foil, high strength and high elongation can be obtained after foil rolling and after heat treatment at 120°C. In other words, the present invention has the following features.

[0009] [1] An aluminum alloy foil, wherein (1) the composition of the aluminum alloy foil is such that the iron (Fe) content is 0.15% by mass or more and less than 0.3% by mass, the silicon (Si) content is more than 0.8% by mass and less than 1.5% by mass, and the remainder is aluminum (Al) and unavoidable impurities, (2) the average equivalent circle diameter of the intermetallic compounds present on the surface of the aluminum alloy foil is 1.0 μm or less, and (3) the number density of intermetallic compounds present on the surface of the aluminum alloy foil with an equivalent circle diameter of 3.0 μm or more is 2.0 × 10 2 pieces / mm 2 An aluminum alloy foil for battery current collectors, characterized by the following:

[0010] [2] The aluminum alloy foil for battery current collector according to [1], wherein the decrease in electrical resistivity of the aluminum alloy foil after heat treatment at 120°C for 1 hour relative to the electrical resistivity after rolling is 0.03 μΩ·cm or more. [3] Tensile strength after rolling at a thickness of 12 μm is 235 N / mm 2 The aluminum alloy foil for battery current collectors described in [1] or [2], wherein the elongation is 3.0% or more. [4] Tensile strength of 225 N / mm after heat treatment at 120°C for 1 hour at a thickness of 12 μm. 2 The above is an aluminum alloy foil for battery current collectors as described in any of [1] to [3], having an elongation of 2.5% or more.

[0011] [5] A method for manufacturing aluminum alloy foil for battery current collectors, comprising a casting step of casting a molten metal having a composition of iron (Fe) content of 0.15 mass% or more and less than 0.3 mass%, silicon (Si) content of more than 0.8 mass% and less than 1.5 mass%, with the remainder being aluminum (Al) and unavoidable impurities, at a cooling rate of 250°C / sec or more to obtain a cast plate, and a rolling step of cold rolling the cast plate to obtain an aluminum alloy foil. [Effects of the Invention]

[0012] The aluminum alloy foil for battery current collectors according to the present invention exhibits excellent tensile strength and elongation even when thinned, after rolling and after low-temperature heat treatment at 120°C. Therefore, when used as a battery current collector, it is less likely to break during the battery manufacturing process and can improve the battery capacity per unit volume of the battery. [Modes for carrying out the invention]

[0013] The embodiments of the present invention will be described in detail below. The aluminum alloy foil for battery current collectors according to the present invention is a foil containing a predetermined amount of Fe and Si, with the remainder being Al and unavoidable impurities. As described later, this aluminum alloy foil for battery current collectors has a composition containing Fe and a larger amount of Si. Due to this composition, Si exists not only as an Al-Fe-Si intermetallic compound bonded with Al and Fe, but also as elemental Si not bonded to Al or Fe. This elemental Si is thought to exist in a solid solution state in the aluminum matrix or as crystal precipitates consisting only of Si. The behavior of this elemental Si is thought to have a significant influence on the elongation properties of the aluminum alloy foil after low-temperature heat treatment.

[0014] In the manufacturing method of the present invention, by employing a twin-roll casting method (TRC casting method) with a high molten metal cooling rate, elemental Si is obtained not only as a precipitate but also in a supersaturated solid solution state in the aluminum matrix. Since the Si dissolved in the aluminum matrix easily diffuses even during low-temperature heat treatment, the supersaturated solid solution of Si precipitates as a precipitate consisting only of Si. Normally, it is presumed that low-temperature heat treatment cannot sufficiently remove the strain introduced during rolling in the manufacturing process of aluminum foil, resulting in an uneven recovery state and causing a decrease in elongation. However, in the present invention, it is thought that a change occurs in the strain recovery state because recovery and Si precipitation occur simultaneously when low-temperature heat treatment is applied. Therefore, sufficient tensile elongation is maintained even after low-temperature heat treatment.

[0015] Furthermore, it has been found that by adopting TRC casting, despite the low Fe content, excellent tensile strength and elongation after rolling are obtained. This is considered to be because the high molten metal cooling rate in TRC casting refines crystallized products in the aluminum alloy foil and increases the amount of Fe solid-dissolved in the aluminum matrix phase. Furthermore, when the Si content in the aluminum alloy foil is increased, crystallized products are prone to coarsening, which may increase the occurrence of pinholes in the foil rolling process. This problem is also solved by the refinement of crystallized products achieved by TRC casting.

[0016] [Iron Content] Iron (Fe) contained in the aluminum alloy foil for battery current collectors of the present invention is an element that improves tensile strength, elongation and rollability through effects such as grain refinement, and is a component generally added to aluminum foils. The aforementioned effects are obtained more remarkably by TRC casting. The content of iron (Fe) in the aluminum alloy foil for battery current collectors is 0.15 mass% or more and less than 0.3 mass%, and more preferably 0.2 mass% or more and less than 0.27 mass%. When within the aforementioned range, the aluminum alloy foil for battery current collectors can exhibit excellent mechanical properties. If the iron (Fe) content is less than 0.15 mass%, the tensile strength tends to be insufficient. On the other hand, if the iron (Fe) content exceeds 0.3 mass%, it tends to adversely affect the elongation after low-temperature heat treatment.

[0017] [Silicon Content] For silicon (Si) contained in the aluminum alloy foil for battery current collectors of the present invention, TRC casting increases the solid solubility of silicon (Si) in the aluminum matrix phase and refines crystallized products consisting solely of silicon (Si), whereby improvements in strength and elongation after low-temperature heat treatment can be expected. The content of silicon (Si) in the aluminum alloy foil for battery current collectors is more than 0.8 mass% and less than 1.5 mass%, and more preferably 0.85 mass% or more and less than 1.2 mass%. If the content is 0.8 mass% or less, it is difficult to obtain sufficient elongation after low-temperature heat treatment. If the content is 1.5 mass% or more, coarse crystallized products, centerline segregation and the like occur during TRC casting, which may lead to frequent occurrence of pinholes and reduced elongation during foil rolling.

[0018] [Inevitable Impurities] The balance of the components constituting the aluminum alloy foil for battery current collectors according to the present invention consists of aluminum (Al) and inevitable impurities. The inevitable impurities refer to elements that are unavoidably mixed in during the production of the aluminum alloy foil. These inevitable impurities may be contained within a range that does not affect the properties of the aluminum alloy foil in the present invention. Examples of such inevitable impurities include transition elements such as manganese (Mn), copper (Cu), vanadium (V), titanium (Ti), zirconium (Zr), chromium (Cr) and nickel (Ni), as well as elements such as magnesium (Mg), zinc (Zn), boron (B), gallium (Ga) and bismuth (Bi). The content of each of these elements is preferably 0.05 mass% or less respectively in the aluminum alloy foil.

[0019] [Intermetallic Compounds] The average equivalent circle diameter of intermetallic compounds present on the surface of the aluminum alloy foil for battery current collectors according to the present invention is 1.0 µm or less, preferably 0.8 µm or less. Within the above range, high strength and high elongation are easily obtained, and excellent properties after low-temperature heat treatment are also achieved. Sufficient strength and elongation are difficult to obtain with coarse intermetallic compounds having an average equivalent circle diameter exceeding 1.0 µm. For the same reason, the number density of intermetallic compounds having an equivalent circle diameter exceeding 3.0 µm is 2.0×10 2 pieces / mm 2 or less, preferably 1.0×10 2 pieces / mm 2 or less. The intermetallic compounds referred to herein are particles having a contrast different from that of the aluminum matrix when the surface of the aluminum alloy foil is observed with, for example, a scanning electron microscope and imaged in a backscattered electron image (composition image). Intermetallic compounds refer to, but are not limited to, intermetallic compounds such as Al-Fe-based and Al-Fe-Si-based ones. However, particles consisting only of Si are not included herein, since their atomic number is close to that of aluminum, and no contrast difference from the aluminum matrix can be obtained by the above observation method.

[0020] [Production Method] Next, a method for manufacturing aluminum alloy foil for battery current collectors according to the present invention will be described. The present invention relates to a method for manufacturing aluminum alloy foil, which comprises a casting step of preparing an aluminum master alloy to be within the composition range, heating it to produce molten aluminum alloy, casting the molten aluminum alloy at a predetermined cooling rate to produce a cast plate, and a rolling step of cold rolling the cast plate to form foil.

[0021] [Casting Process] Aluminum ingots, various additive metal elements, or aluminum matrix alloys containing them are prepared such that the iron (Fe) content is 0.15% or more and less than 0.3% by mass, the silicon (Si) content is more than 0.8% by mass and less than 1.5% by mass, and the remainder consists of aluminum (Al) and unavoidable impurities. These are heated at 680 to 1000°C to produce molten aluminum alloy having the above composition. This molten metal is cast using the TRC casting method to produce cast plates. TRC casting allows for casting at a high molten metal cooling rate of 250°C / sec or more. The casting thickness is not particularly limited, but a thickness of 5 to 8 mm is preferred from the viewpoint of cooling rate and yield.

[0022] In this invention, TRC casting, which has a faster molten metal cooling rate during solidification than general DC casting (Direct Chill Casting), is preferred. While DC casting has a cooling rate of several degrees Celsius to tens of degrees Celsius / sec, TRC casting has a cooling rate of 250 degrees Celsius / sec or more. By using TRC casting, the intermetallic compounds contained in the aluminum alloy foil are refined, and a highly supersaturated solid solution state of Fe and Si is achieved. Therefore, it is possible to obtain aluminum alloy foil with high strength and high elongation while keeping the Fe content low. Furthermore, the fine dispersion of intermetallic compounds and the highly supersaturated solid solution state of Si are expected to be effective in suppressing the decrease in elongation after low-temperature heat treatment. On the other hand, there is no particular upper limit to the cooling rate in TRC casting, but from the viewpoint of the capacity of the TRC casting machine, 1000°C / sec or less is good, and 600°C / sec or less is preferable.

[0023] [Rolling process] [Cold rolling] The resulting cast sheet is cold-rolled according to a standard method to form an aluminum alloy foil of the desired thickness. Intermediate annealing may be performed one or more times during the cold-rolling process to improve rollability and control the solid solution and precipitation state.

[0024] [Intermediate annealing] In the method for manufacturing aluminum alloy foil for battery current collectors according to the present invention, an intermediate annealing step may or may not be included, but it may be performed for the purpose of improving rollability, to the extent that it does not affect the properties of the aluminum alloy foil. For optimal production efficiency, the intermediate annealing time is preferably 20 hours or less. Intermediate annealing may be performed using batch annealing or a continuous annealing line (CAL). Using a continuous annealing line is preferable because it allows for rapid heating and cooling, which suppresses the precipitation of supersaturated Fe and Si in the aluminum alloy while improving rollability.

[0025] [Homogeneous heat treatment] In the method for manufacturing aluminum alloy foil for battery current collectors according to the present invention, it is preferable not to include a homogenization heat treatment step. If a homogenization heat treatment step is performed, the supersaturated solid-solution additive elements due to the casting process, which has a high cooling rate, will precipitate, leading to coarsening of the microstructure, which may make it difficult to exhibit the features of this invention, such as sufficient high strength and elongation.

[0026] [Hot rolling] In the method for manufacturing aluminum alloy foil for battery current collectors according to the present invention, it is preferable that a hot rolling process is not included. If a hot rolling process is performed, the additive elements that have been supersaturated and dissolved in the casting process, which has a high cooling rate, may precipitate, leading to coarsening of the microstructure and making it difficult to exhibit the features of this invention, which are sufficient high strength and elongation.

[0027] [Properties of aluminum alloy foil] [Electrical resistivity] The aluminum alloy foil for battery current collectors according to the present invention has a decrease in electrical resistivity of 0.03 μΩ·cm or more, and more preferably 0.05 μΩ·cm or more, after heat treatment at 120°C for 1 hour relative to the electrical resistivity after rolling. The decrease in electrical resistivity refers to the difference between the electrical resistivity of the aluminum alloy foil after rolling and the electrical resistivity of the aluminum alloy foil after heat treatment at 120°C for 1 hour. Even if the aluminum alloy foil is subjected to low-temperature heat treatment at 120°C, it is thought that there is almost no effect on the electrical resistivity due to strain recovery, and the deposition of Al-Fe and Al-Fe-Si intermetallic compounds is also unlikely to occur. Therefore, the decrease in electrical resistivity here is presumed to be due to the deposition of elemental Si from the aluminum matrix. In other words, in this application, the decrease in electrical resistivity is positively correlated with the amount (concentration) of Si that was solid-dissolved in the aluminum matrix that precipitated due to the heat treatment. If the decrease in electrical resistivity is within the above range, the decrease in elongation after heat treatment at 120°C can be suppressed. In this context, "after rolling" refers to the period from when the aluminum alloy foil has been rolled and cooled to room temperature, until before the 120°C low-temperature heat treatment.

[0028] [Tensile strength, elongation] The aluminum alloy foil for battery current collectors according to the present invention has a tensile strength of 235 N / mm² after rolling at a thickness of 12 μm. 2 Preferably, the elongation is 3.0% or more, and more preferably, the tensile strength is 245 N / mm². 2 The elongation is 3.5% or more. Within this range, the breakage of the aluminum alloy foil can be suppressed during the battery manufacturing process.

[0029] [Tensile strength and elongation after heat treatment at 120°C] The aluminum alloy foil for battery current collectors according to the present invention has a thickness of 12 μm and a tensile strength of 225 N / mm² after heat treatment at 120°C for 1 hour. 2 Preferably, the elongation is 2.5% or more, and more preferably, the tensile strength is 240 N / mm². 2 The elongation is 3.0% or more. Within this range, the breakage of the aluminum alloy foil can be suppressed during the battery manufacturing process.

[0030] [Foil thickness] The aluminum alloy foil for battery current collectors according to the present invention is preferably 7 μm to 15 μm thick, and more preferably 9 μm to 12 μm thick. If it is less than 7 μm thick, problems arise with flatness control during rolling and the occurrence of pinholes, and it is also prone to breakage during the battery manufacturing process. If it is thicker than 15 μm, it is not possible to meet the requirements for thin foil. [Examples]

[0031] The present invention will be further clarified by providing examples and comparative examples below. First, the test method used in this example is shown below.

[0032] (Test method) [composition] The composition of each example and comparative example was measured by inductively coupled plasma atomic emission spectroscopy. Suitable measuring instruments include the iCAP6500DUO from Thermo Fisher Scientific K.K., or the ICPS-8100 from Shimadzu Corporation.

[0033] [Tensile test] A strip-shaped test specimen measuring 15 mm wide x 200 mm long was cut out so that the tensile direction was parallel to the rolling direction. The tensile testing machine used was a Strograph VES5D manufactured by Toyo Seiki Seisakusho Co., Ltd., at a tensile speed of 3 mm / min, with a gauge length of 100 mm between the chucks. The test was performed three times, and the average value was calculated. Tensile tests were performed after rolling and after heat treatment at 120°C.

[0034] [Intermetallic compounds] The surface of an aluminum alloy foil was observed at a magnification of 1000x using a field emission scanning electron microscope (JEOL Ltd. JSM-7200F). Backscattered electron images (composition images) were taken to make intermetallic compounds easier to see. The size of the intermetallic compounds was evaluated using image analysis and measurement software WinROOF2021 (Mitani Corporation, version 5.4.0). Contrast and brightness were adjusted in the image processing of the analysis software to clarify the intermetallic compounds. Subsequently, the image was binarized using a single threshold to extract data from the intermetallic compound portion of the aluminum alloy foil surface. The binarized data was processed to remove portions with an equivalent circle diameter of 0.3 μm or less, and the average particle size of the intermetallic compounds was calculated from the remaining portions with an equivalent circle diameter of 0.3 μm or more. The reason for removing portions smaller than 0.3 μm is that very small portions in the binarized data are likely to include minute surface irregularities and other elements besides intermetallic compounds. Furthermore, the number of intermetallic compounds with an equivalent circular diameter of 3.0 μm or more was measured, and the number per unit area was calculated. Images were taken in five random fields of view, and the average value was determined.

[0035] [Electrical resistivity] A strip of test material measuring 15 mm wide x 200 mm long was cut out with the rolling direction as the longitudinal side. The electrical resistance of the test material was measured using a HIOKI 3541 resistance meter, both after rolling and after heat treatment at 120°C. The terminal distance during measurement was 115 mm. The electrical resistivity ρ can be calculated using the formula ρ = R·A / L, where R is the electrical resistance, A is the cross-sectional area, and L is the length of current flow. The cross-sectional area A is the foil thickness × test piece width of 15 mm, and the length of current flow L is the distance between terminals, which is 115 mm.

[0036] (Examples 1-6, Comparative Examples 1-5) Aluminum alloys with the compositions shown in Table 1 were melted, and the molten metal was degassed and inclusion-removed before TRC casting produced 7 mm thick cast plates. These cast plates were then cold-rolled to produce 12 μm or 10 μm thick aluminum alloy foils. The aluminum alloy foils were then heat-treated by holding them at 120°C for 1 hour. The resulting aluminum alloy foils were subjected to the aforementioned tests. The results are shown in Table 1.

[0037] (Comparative Example 6) Ingots were prepared by DC casting with the compositions listed in Table 1. After surface machining, the ingots were subjected to homogenization heat treatment at the temperatures listed in Table 1, and then hot-rolled to a plate with a thickness of 7 mm. Subsequently, cold rolling and 120°C heat treatment were performed in the same manner as in the examples. The obtained aluminum alloy foils were subjected to the aforementioned tests. The results are shown in Table 1.

[0038] [Table 1]

[0039] [result] In Examples 1-6, the Fe and Si content was within the specified range, and the intermetallic compounds were fine due to TRC casting, resulting in excellent strength and elongation both after hardening and after 120°C heat treatment. On the other hand, Comparative Examples 1 and 2 had a Si content below the specified level, and sufficient elongation was not obtained after heat treatment at 120°C. Furthermore, Comparative Example 3 had a Si content exceeding the specified limit, resulting in an elongation of less than 3% after rolling. The surface appearance of the aluminum alloy foil was also streaky, negatively affecting the elongation. Furthermore, Comparative Example 4 had an Fe content below the specified level, resulting in insufficient strength both before and after heat treatment. Furthermore, Comparative Example 5 had an Fe content exceeding the specified limit, and therefore did not achieve sufficient elongation after heat treatment at 120°C. Furthermore, because Comparative Example 6 was not cast using TRC, the intermetallic compounds were coarse, and excellent values ​​for both strength and elongation were not obtained.

Claims

1. It is an aluminum alloy foil, (1) The composition of the aluminum alloy foil is such that the iron (Fe) content is 0.15% by mass or more and less than 0.3% by mass, the silicon (Si) content is more than 0.8% by mass and less than 1.5% by mass, and the remainder consists of aluminum (Al) and unavoidable impurities. (2) The average equivalent circle diameter of the intermetallic compounds present on the surface of the aluminum alloy foil is 1.0 μm or less. (3) The number density of intermetallic compounds with an equivalent circular diameter of 3.0 μm present on the surface of the aluminum alloy foil is 2.0 × 10 ２ pieces / mm ２ The following: (4) The tensile strength after heat treatment at 120°C for 1 hour at a thickness of 12 μm is 225 N / mm² or more, and the elongation is 2.5% or more. An aluminum alloy foil for battery current collectors, characterized by the following features.

2. The aluminum alloy foil for a battery current collector according to claim 1, wherein the decrease in electrical resistivity of the aluminum alloy foil after heat treatment at 120°C for 1 hour relative to the electrical resistivity after rolling is 0.03 μΩ·cm or more.

3. The tensile strength after rolling at a thickness of 12 μm is 235 N / mm². ２ The aluminum alloy foil for battery current collector according to claim 1 or 2, wherein the elongation is 3.0% or more.

4. The process comprises a casting step in which a molten metal having a composition of iron (Fe) content of 0.15% or more and less than 0.3% by mass, silicon (Si) content of more than 0.8% by mass and less than 1.5% by mass, with the remainder being aluminum (Al) and unavoidable impurities, is cast at a cooling rate of 250°C / sec or more to obtain a cast plate, and a rolling step in which the cast plate is cold-rolled to obtain an aluminum alloy foil. A method for manufacturing aluminum alloy foil for battery current collectors, wherein the tensile strength after heat treatment at 120°C for 1 hour at a thickness of 12 μm is 225 N / mm² or more, and the elongation is 2.5% or more.

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