Aluminum alloy sheet for lithium-ion battery and method for producing said sheet

Abstract

Provided is an aluminum alloy sheet for a high strength lithium-ion battery, the aluminum alloy sheet being applicable to a next generation high-capacity battery material. The present invention comprises, in terms of mass%, 0.1-0.4% of Si, 0.05-0.70% of Fe, 0.50-0.70% of Cu, 0.8-1.6% of Mn, and 0.50-0.90% of Mg, as well as 0.005-0.150% of Ti or 0.0001-0.150% of Ti and 0.0001-0.0500 mass% of B with the balance being Al and unavoidable impurities. The total content of Fe and Mn is 1.80 mass% or less, and the tensile strength is 230 MPa or more.

Description

Aluminum alloy plate for lithium-ion batteries and its manufacturing method

[0001] The present invention relates to a high-strength aluminum alloy plate used in lithium-ion batteries and a method for producing the same.

[0002] Electric vehicles, electric motorcycles, mobile phones, and personal computers powered by lithium-ion secondary batteries are widely used. Among these, demand for electric vehicles as environmentally friendly vehicles has been increasing in recent years. Aluminum alloy sheets are used as materials for lithium-ion secondary batteries, and are required to have formability, moderate strength, and the like.

[0003] For example, an aluminum alloy sheet is known in which a 3000 series aluminum alloy, or an aluminum alloy obtained by adding Mg to a 3000 series aluminum alloy, is co-containing with appropriate amounts of Zr, Ti and / or B (see Patent Document 1). This aluminum alloy sheet is said to have a high 45° earing ratio when deep-drawn into a cylindrical container even at a low rolling reduction, to have excellent product yield in rectangular draw and ironing, to have good rectangular draw and ironing formability for thin plates, and to have excellent productivity without cracking even when the pulse laser welding speed is increased.

[0004] Another aluminum alloy plate contains 1.05 to 1.50 mass% Fe, 0.30 to 0.70 mass% Mn, 0.002 to 0.15 mass% Ti, and less than 0.04 mass% B, with the balance being Al and impurities, the Fe / Mn ratio is regulated to 1.8 to 3.5, and the impurities are less than 0.20 mass% Si, less than 0.03 mass% Cu, less than 0.05 mass% Mg, and less than 0.03 mass% V. An aluminum alloy sheet for battery lids used in forming one-piece explosion-proof valves is known, which has a fully regulated chemical composition, an electrical conductivity of 53.0% IACS or higher, a 0.2% yield strength of 40 MPa or higher, an elongation of 40% or higher, a recrystallized structure, and an elongation of 5.0% or higher after cold rolling at a rolling reduction of 80% and after cold rolling at a rolling reduction of 90% (see Patent Document 2). This aluminum alloy sheet is said to have excellent heat dissipation properties, deformation resistance, and formability, little operating pressure variation, and excellent cyclic fatigue resistance.

[0005] JP 2004-197172 A International Publication No. 2019 / 111970

[0006] Aluminum alloy sheets used for the cases and lids of lithium-ion secondary batteries require basic performance such as formability, but for next-generation batteries, there is an increasing demand for higher strength and thinner walls.

[0007] The aluminum alloy sheet described in Patent Document 1 contains Zr, and in previous pulse laser welding, Zr refines crystal grains during solidification of the weld, making Zr essential for preventing weld cracking. However, with subsequent improvements in welding technology, Zr is no longer an essential element, as it is now possible to join welds using continuous welding. Furthermore, Zr can inhibit the refinement of crystal grains by Ti and B during slab casting, which can easily lead to slab cracking. Therefore, castability tends to be improved without the addition of Zr. For these reasons, the aluminum alloy described in Patent Document 1, which contains Zr, may not be able to ensure excellent castability.

[0008] On the other hand, the aluminum alloy sheet for battery lids described in Patent Document 2 contains Mn on the premise that it contains Fe. In this aluminum alloy sheet, the inclusion of Fe improves formability due to increased local elongation and realizes excellent work softening properties, and the addition of Mn realizes improved pressure resistance, improved softening resistance, and improved high-temperature creep properties. However, the aluminum alloy of Patent Document 2 has a base metal tensile strength of about 110 MPa, and in view of the recent demand for higher strength, there is room for further improvement in strength such as base metal tensile strength.

[0009] As described above, basic performance such as formability is still required for aluminum alloy sheets for lithium ion secondary batteries. However, for next-generation high-capacity battery materials, particularly, higher strength is increasingly required.

[0010] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an aluminum alloy sheet for high-strength lithium-ion batteries, which has excellent formability and is also applicable to next-generation high-capacity battery materials.

[0011] The aluminum alloy sheet for lithium-ion batteries according to the present invention is characterized by containing, in mass%, Si: 0.1 to 0.4%, Fe: 0.05 to 0.70%, Cu: 0.50 to 0.70%, Mn: 0.8 to 1.6%, and Mg: 0.50% to 0.90%, Ti: 0.005 to 0.150%, or Ti: 0.0001 to 0.150% and B: 0.0001 to 0.0500% by mass, with the balance consisting of Al and unavoidable impurities, the total content of Fe and Mn being 1.80% or less by mass, and a tensile strength of 230 MPa or more.

[0012] In the aluminum alloy sheet for lithium ion batteries according to the present invention, by suitably adjusting not only the contents of Fe and Mn in particular but also the total content of these elements (Fe, Mn), it is possible to provide an aluminum alloy sheet for lithium ion batteries with high strength that can also be used for next-generation high-capacity battery materials while ensuring formability.

[0013] <Aluminum Alloy Sheet for Lithium-Ion Batteries> An aluminum alloy sheet for lithium-ion batteries according to an embodiment of the present invention (hereinafter may be referred to as "the present embodiment") is characterized by containing, in mass%, Si: 0.1 to 0.4%, Fe: 0.05 to 0.70%, Cu: 0.50 to 0.70%, Mn: 0.8 to 1.6%, and Mg: 0.50% to 0.90%, Ti: 0.005 to 0.150%, or Ti: 0.0001 to 0.150% and B: 0.0001 to 0.0500 mass%, with the balance consisting of Al and unavoidable impurities, a total content of Fe and Mn being 1.80 mass% or less, and a tensile strength of 230 MPa or more.

[0014] Generally, when aluminum alloy sheets are strengthened, there is a problem that formability is reduced. That is, when Mn is contained in the aluminum alloy sheet, Mn is dissolved in the matrix to promote solid-solution strengthening, thereby achieving high strength (evaluated by tensile strength), but Al-Fe-Mn intermetallic compounds become coarse or the amount of such compounds increases. Thus, when high strength is achieved by solid-solution strengthening to an excessive degree, formability is reduced. Furthermore, when an aluminum alloy sheet is cold-rolled, high strength can be achieved by increasing the reduction rate and promoting work hardening, but when high strength is achieved by work hardening to an excessive degree, formability is reduced.

[0015] Therefore, the present inventors have found that, in order to obtain an aluminum alloy sheet with a tensile strength of 230 MPa or more, the Mn content should be 0.80 mass% or more and the rolling reduction should be 20% or more, while in order to suppress coarsening of Al-Fe-Mn intermetallic compounds with the aim of maintaining formability, the total content of Fe and Mn should be controlled to 1.80 mass% or less. An aluminum alloy sheet for lithium-ion batteries according to this embodiment, which is based on such findings, will be described in detail below.

[0016] The aluminum alloy plate for lithium ion batteries of this embodiment is not particularly limited in its use as long as it is used for lithium ion batteries, and can be used for, for example, battery lids, cases, and other battery components.

[0017] The constituent elements of the high-strength aluminum alloy sheet of this embodiment, Si, Fe, and Mn, impart strength to the aluminum alloy sheet and also refine the recrystallized structure and impart DI formability by finely dispersing and forming intermetallic compounds such as Al-Fe, Al-Mn, and Al-(Fe, Mn)-Si. Furthermore, if any of Si, Fe, and Mn is below the lower limit of the composition range described below, the above-mentioned effects are small and blister resistance is poor. On the other hand, if the content of Si, Fe, or Mn is above the upper limit of the composition range described below, coarse compounds are formed, which reduces DI formability and also results in poor weldability.

[0018] Si: 0.1 to 0.4 mass% Si is an essential element for imparting strength and formability to an aluminum alloy sheet. In this embodiment, the Si content is 0.1 to 0.4 mass%. If the Si content is less than 0.1 mass%, sufficient strength and formability cannot be obtained, and if the Si content exceeds 0.4 mass%, coarse intermetallic compounds such as Al-(Fe, Mn)-Si crystallize during ingot casting, resulting in reduced formability and weldability. The Si content is more preferably 0.15 to 0.35 mass%, and extremely preferably 0.2 to 0.3 mass%.

[0019] Fe: 0.05 to 0.70% by mass Fe is an essential element for imparting strength and formability to aluminum alloy sheets. To obtain sufficient strength and formability, the Fe content is set to 0.05% by mass or more. If the Fe content exceeds 0.7% by mass, the size and number of Fe-based intermetallic compounds increase, resulting in reduced formability and weldability. Therefore, the Fe content is set to 0.70% by mass or less. The Fe content is preferably 0.10 to 0.65% by mass, more preferably 0.12 to 0.60% by mass, and extremely preferably 0.15 to 0.50% by mass.

[0020] Mn: 0.8 to 1.6 mass% Mn is an essential element for imparting strength, softening resistance, and formability to aluminum alloy sheets. To obtain sufficient strength, softening resistance, and formability, the Mn content is set to 0.8 mass% or more. If the Mn content exceeds 1.6 mass%, the strength may become too high, resulting in a risk of reduced formability. The Mn content is preferably 0.9 to 1.5 mass%, more preferably 1.0 to 1.4 mass%, and most preferably 1.1 to 1.2 mass%.

[0021] Mg: 0.50 to 0.90 mass% Mg is an essential element for imparting strength to an aluminum alloy sheet. To obtain sufficient strength, the Mg content is set to 0.50 mass% or more. If the Mg content exceeds 0.90 mass%, the strength may become too high, resulting in a decrease in formability. The Mg content is preferably 0.55 to 0.85 mass%, more preferably 0.60 to 0.80 mass%, and extremely preferably 0.65 to 0.75 mass%.

[0022] Cu: 0.50 to 0.70 mass% Cu is an essential element for imparting strength to an aluminum alloy sheet. To obtain sufficient strength, the Cu content is set to 0.50 mass% or more. If the Cu content exceeds 0.70 mass%, the strength may become too high, resulting in a decrease in formability. The Cu content is preferably 0.51 to 0.65 mass%, more preferably 0.52 to 0.63 mass%, and most preferably 0.53 to 0.60 mass%.

[0023] Ti: 0.005 to 0.150 mass%, or Ti: 0.0001 to 0.150% and B: 0.0001 to 0.0500 mass% Ti and B generate various intermetallic compounds that become solidification nuclei, imparting strength and formability to the aluminum alloy sheet. In this embodiment, when only Ti is contained, Ti: 0.005 to 0.150 mass%, and when both Ti and B are contained, Ti: 0.0001 to 0.150 mass% and B: 0.0001 to 0.0500 mass% are used. When either Ti or B is below the respective lower limit values, sufficient strength and formability cannot be obtained. On the other hand, when Ti exceeds the upper limit value, TiAl ３ On the other hand, if B exceeds the upper limit, Ti-B compounds are stabilized and TiB ２ This reduces the grain refinement effect and also reduces the TiB ２ There is a risk that the Ti content will settle in the furnace and accumulate on the bottom of the furnace. In either case, the Ti content is preferably 0.010 to 0.140 mass%, more preferably 0.015 to 0.130 mass%, and extremely preferably 0.020 to 0.120 mass%. The B content is preferably 0.0010 to 0.0400 mass%, more preferably 0.0015 to 0.0300 mass%, and extremely preferably 0.0020 to 0.0200 mass%.

[0024] Total content of Fe and Mn: 1.80% by mass or less In the aluminum alloy sheet of this embodiment, if the total content of Fe and Mn exceeds 1.80% by mass, coarse crystals are generated in the alloy sheet, and formability deteriorates. Therefore, in order to maintain formability, the total content of Fe and Mn is controlled to 1.80% by mass or less. Note that the total content of Fe and Mn is preferably 1.75% by mass or less, more preferably 1.72% by mass or less, and extremely preferably 1.70% by mass or less.

[0025] Inevitable Impurities Inevitable impurities are uncontrolled elements that are inevitably mixed in from raw metals, returned materials, etc. Acceptable contents of these elements include, for example, V: less than 0.03 mass%, Cr: less than 0.20 mass%, Zn: less than 0.20 mass%, Ni: less than 0.10 mass%, Ga: less than 0.05 mass%, (each of Pb, Bi, Sn, Na, Ca, and Sr): less than 0.02%, and other elements, such as Co, Nb, Mo, and W: less than 0.05 mass%. Even if uncontrolled elements are contained within these ranges, none of the above-mentioned effects of the present invention are impaired.

[0026] No Zr Content The component composition of the aluminum alloy plate of this embodiment has been described above, but one of the features of the aluminum alloy plate of this embodiment is that it does not contain Zr, unlike the aluminum alloy plate described in Patent Document 1. In this embodiment, Zr is basically an uncontrolled element, but since the aluminum alloy plate does not contain Zr, there is no need to set the casting temperature, which will be described later, to a relatively high temperature, and therefore rapid cooling occurs during solidification, and Zr does not inhibit the effect of a refiner such as Ti, so that castability (evaluated by the presence or absence of casting cracks) is not deteriorated.

[0027] Tensile strength of 230 MPa or more: High strength is required for aluminum alloy sheets for next-generation high-capacity lithium-ion batteries. In the aluminum alloy sheet of this embodiment, the tensile strength (MPa) of the base material is used as an index for evaluating strength. The tensile strength is 230 MPa or more, preferably 260 MPa or more, more preferably 280 MPa or more, and extremely preferably 300 MPa or more.

[0028] It should be noted that this tensile strength (230 MPa or more) is not a performance that can be realized only by the composition of the above-mentioned elements, but is a performance that can be achieved by the composition and the manufacturing method described below (particularly, a cold rolling reduction of 20% or more). The manufacturing method will be described later.

[0029] <Method for manufacturing aluminum alloy sheet for lithium ion batteries> Hereinafter, a method for manufacturing the above-described "aluminum alloy sheet for lithium ion batteries" will be described in detail. Note that the method for manufacturing the aluminum alloy sheet for lithium ion batteries of the present embodiment described below is merely an example, and is not intended to be limited to the method described below.

[0030] The method for producing an aluminum alloy sheet for lithium-ion batteries according to this embodiment is characterized by comprising: a slab casting step of obtaining an ingot from a molten aluminum alloy having the above-described composition by a semi-continuous casting method; a homogenization treatment step of homogenizing the ingot at a holding temperature of 500 to 600°C for one hour or more; a hot rolling step of hot rolling the ingot after the homogenization treatment step to obtain a hot-rolled sheet; and a cold rolling step of cold-rolling the hot-rolled sheet at a rolling reduction of 20% or more. Each step will be described in detail below.

[0031] Slab Casting Process Ingots are produced by semi-continuous casting (DC casting). In the case of ordinary semi-continuous casting, the thickness of the ingot is generally about 400 mm to 600 mm, and therefore the solidification cooling rate at the center of the ingot is about 1°C / sec. Therefore, when semi-continuously casting a molten aluminum alloy with a particularly high content of Fe and Mn, relatively coarse intermetallic compounds such as Al(Fe·Mn) and α-Al-(Fe·Mn)-Si tend to crystallize from the molten aluminum alloy at the center of the ingot.

[0032] Although it depends on the width and thickness of the ingot, the casting speed in semi-continuous casting is usually 50 to 70 mm / min, taking productivity into consideration. Furthermore, when performing in-line degassing, depending on degassing conditions such as the flow rate of the inert gas, considering the actual residence time of the molten metal in the degassing treatment tank, the smaller the flow rate of the molten aluminum (the amount of molten metal supplied per unit time), the more efficient the degassing in the tank and the more likely it is that the amount of hydrogen gas in the ingot will be reduced. For these reasons, although it depends on factors such as the number of castings, it is preferable to limit the casting speed to 30 to 50 mm / min in order to reduce the amount of hydrogen gas in the ingot. A casting speed of less than 30 mm / min is undesirable because it reduces productivity. On the other hand, a casting speed of 50 mm / min or less reduces the slope of the sump (solid / liquid interface) in the ingot, preventing casting cracks. The casting speed is more preferably 35 to 48 mm / min, and most preferably 40 to 45 mm / min.

[0033] Homogenization treatment process: 500 to 600°C x 1 hour or more The homogenization treatment of the ingot obtained by casting using the semi-continuous casting method is a process for eliminating casting segregation by holding it at a high temperature to facilitate rolling, and it is necessary to hold it at 500 to 600°C for 1 hour or more. If the holding temperature is too low (less than 500°C) or the holding time is too short (less than 1 hour), the size of the precipitates becomes small, and the recrystallized grains during intermediate annealing described below become coarse, which ultimately leads to a decrease in the strength of the aluminum alloy sheet. On the other hand, if the heating temperature is too high (more than 600°C), there is a risk of the ingot partially melting, so-called burning.

[0034] The holding temperature in the homogenization treatment is preferably 520° C. or higher and 590° C. or lower, more preferably 525° C. or higher and 585° C. or lower, and extremely preferably 530° C. or higher and 580° C. The holding time in the homogenization treatment is preferably 1.5 hours or longer, more preferably 2 hours or longer, and extremely preferably 3 hours or longer.

[0035] Hot rolling step, cold rolling step before intermediate annealing, and intermediate annealing step In this embodiment, after the homogenization treatment step described above, the hot rolling step, the cold rolling step before intermediate annealing, and the intermediate annealing step are performed. However, the cold rolling step before intermediate annealing and the intermediate annealing step, which are performed for strength adjustment, may be omitted.

[0036] The cold rolling step before intermediate annealing and the intermediate annealing step can be omitted when the thickness of the aluminum alloy plate to be finally obtained is relatively large, for example, when an aluminum alloy plate having a thickness of about 2 mm is produced.

[0037] In contrast, when the cold rolling step before the intermediate annealing and the intermediate annealing step are performed without omitting them, the thickness of the aluminum alloy plate to be finally obtained is relatively small, for example, this applies to the case of producing an aluminum alloy plate with a plate thickness of about 0.6 mm.

[0038] In this embodiment, the detailed conditions of the above-mentioned three steps (hot rolling step, cold rolling step before intermediate annealing, and intermediate annealing step) are not specified, but they can be carried out, for example, as follows.

[0039] In the hot rolling process, although it depends on the model of the hot rolling mill, the ingot removed from the soaking furnace is usually hot rolled by several rolling passes to produce a hot-rolled sheet of a predetermined thickness (for example, about 4 to 8 mm) and wound into a coil.

[0040] In the cold rolling process before intermediate annealing, the coil wound in the hot rolling mill is passed through a cold rolling mill, and cold rolling is usually performed in multiple passes. Since work hardening occurs due to plastic strain introduced by cold rolling, an annealing treatment (intermediate annealing process) is performed as necessary.

[0041] Since the intermediate annealing step is also a softening treatment, the cold-rolled coil may be inserted into a batch furnace and held at a temperature of 300 to 400°C for one hour or more, depending on the material. If the holding temperature is less than 300°C, softening may not be promoted. The holding temperature may be 310°C or higher, 320°C or higher, or 330°C or higher. On the other hand, if the holding temperature exceeds 400°C, productivity may decrease. The holding temperature may be 390°C or lower, 380°C or lower, or 370°C or lower.

[0042] The cold-rolled sheet is thus subjected to intermediate annealing. The intermediate annealing step applied to the cold-rolled sheet described above may be continuous annealing or batch annealing.

[0043] Cold rolling step after hot rolling or cold rolling step after intermediate annealing In this embodiment, after the above-mentioned hot rolling (when the cold rolling step before intermediate annealing and the intermediate annealing step are not performed) or after the above-mentioned intermediate annealing step, a cold rolling step is further performed to adjust the strength of the base material (specifically, to improve the tensile strength).

[0044] In both the cold rolling process after hot rolling and the cold rolling process after intermediate annealing, the annealed sheet is cold rolled at a reduction rate of 20% or more to produce a base material with a tensile strength of 230 MPa or more. If the reduction rate is less than 20%, it is difficult to obtain a strength of 230 MPa, assuming the above-mentioned composition of the aluminum alloy sheet of this embodiment. Since the required strength and formability vary depending on the case, no upper limit for the reduction rate is specifically set, but a reduction rate of 80% or less can achieve both the desired strength and formability. When higher formability is required, the reduction rate is preferably 65% ​​or less. The reduction rate is preferably 25 to 65%, more preferably 30 to 60%, and most preferably 35 to 55%.

[0045] The effects of the present invention will be demonstrated by Examples 1 and 2 shown below, but the present invention is not limited to Examples 1 and 2 shown below. Examples 1 and 2 shown below are experimental examples in which the composition and the like of the high-strength aluminum alloy plate for lithium-ion batteries according to the present invention were specified by laboratory tests.

[0046] (Example 1: Evaluation of strength and formability depending on composition) Preparation of simulated materials 7.5 kg of ingots with eight levels of composition shown in Table 1 below were each placed in a #30 crucible, and the crucible was heated in a small electric furnace to melt the ingots. Next, a lance was inserted into the molten metal, and N ２Gas was blown in at a flow rate of 2.0 L / sec for 6 minutes to perform a degassing treatment. The mixture was then allowed to settle for 15 minutes, and any slag that had risen to the surface of the molten metal was removed with a stirring rod. The crucible was then removed from the small electric furnace, and the molten metal was poured into a mold with internal dimensions of 200 x 200 x 50 mm to produce an ingot. Test materials with compositions A to H (Invention Examples 1 to 6 and Comparative Examples 1 and 2) were obtained from the molten metal in each crucible. Disk samples of these test materials were then subjected to compositional analysis by optical emission spectroscopy. The results are shown in Table 1.

[0047]

[0048] Both sides of each ingot were machined by 5 mm to a thickness of 40 mm, and then homogenized at 590 ° C for 3 hours and 480 ° C for 2 hours. Then, hot rolling was performed to obtain hot-rolled plates with a thickness of 9.0 mm. Each hot-rolled plate was then cold-rolled to obtain cold-rolled plates A1 to H1 with a thickness of 1.5 mm and cold-rolled plates A2 to H2 with a thickness of 2.0 mm, respectively. Furthermore, these cold-rolled plates A1 to H1 and A2 to H2 were inserted into an annealer and subjected to an intermediate annealing treatment at 390 ° C for 1 hour, simulating batch annealing, to obtain annealed plates A1 to H1 and A2 to H2.

[0049] Next, the annealed sheet A1 having a thickness of 1.5 mm was cold rolled at a rolling reduction rate of 60% to obtain test material A160, and the annealed sheet A2 having a thickness of 2.0 mm was cold rolled at a rolling reduction rate of 70% to obtain test material A270.

[0050] Similarly, annealed sheets B1 to H1 and annealed sheets B2 to H2 were cold rolled at a reduction ratio of 60% or 70% to obtain test materials B160, B270, C160, C270, ..., H160, and H270.

[0051] Tensile Test JIS No. 5 test pieces were taken from each of the obtained test materials (A160, A270, B160, B270, C160, C270, D160, D270, E160, E270, F160, F270, G160, G270, H160, H270) so that the tensile direction was parallel to the rolling direction, and a tensile test was carried out in accordance with JIS Z2241 to determine the tensile strength (MPa), elongation (elongation at break) (%), and 0.2% yield strength (MPa).

[0052] Bending test: Test pieces were taken from each test material so that they were parallel to the rolling direction, and a 90° bending test was performed using the V-block method in accordance with JIS Z 2248 to check for cracks on the outside of the curved part of the test piece. The test was performed with an inner radius of 2 mm (R2). After visual inspection, those without cracks were marked with a ◯, and those with cracks were marked with an ×.

[0053] In evaluating formability, examples in which the bending test results were good at both the 60% and 70% reduction were evaluated as ◯, examples in which the bending test results were good at the 60% reduction but poor at the 70% reduction were evaluated as △, and examples in which the bending test results were poor at both the 60% and 70% reduction were evaluated as ×. The results are shown in Table 2.

[0054]

[0055] According to Table 2, in Examples 1 to 6, a tensile strength of 230 MPa was achieved with a predetermined composition range and a predetermined reduction ratio (20% or more), and the bending test results were also good when the reduction ratio was 60%.

[0056] On the other hand, the formability evaluation of Comparative Example 1 was poor because the Cu content was outside the predetermined composition range. Similarly, the formability evaluation of Comparative Example 2 was poor because the Mg content was outside the predetermined composition range.

[0057] Example 2: Evaluation of castability by composition Next, the castability of composition A (invention example 1) and composition I (comparison example 3) shown in Table 3 below was compared and evaluated.

[0058]

[0059] For both Composition A (Invention Example 1) and Composition I (Comparative Example 3), molten aluminum alloy was melted in a melting furnace and subjected to semi-continuous casting (DC casting) to obtain an ingot measuring 1070 mm in width, 560 mm in thickness, and 3250 mm in length. The casting temperature for Inventive Example 1 was 680 to 700°C, while the casting temperature for Comparative Example 3 was 700 to 720°C. The reason for the different casting temperatures in both examples is that Comparative Example 3, which contains Zr, crystallizes coarse crystals at low casting temperatures, making it necessary to increase the casting temperature.

[0060] Comparing Inventive Example 1 with Comparative Example 3, no casting cracks were observed in Inventive Example 1. Since Inventive Example 1 does not contain Zr, it is not necessary to raise the casting temperature so much, and so rapid cooling does not occur during solidification, which is thought to be why no casting cracks occurred. In addition, since Inventive Example 1 does not contain Zr, the effect of refiners such as Ti is not inhibited, which is also thought to be the reason why castability did not deteriorate.

[0061] In contrast, casting cracks occurred in Comparative Example 3, which contained Zr. This is thought to be because the casting temperature in Comparative Example 3 was high due to the inclusion of Zr, which resulted in rapid cooling during solidification, and Zr inhibited the effects of refiners such as Ti, resulting in poor castability.

Claims

1. An aluminum alloy sheet for lithium-ion batteries, characterized in that it contains, by mass%, Si: 0.1 to 0.4%, Fe: 0.05 to 0.70%, Cu: 0.50 to 0.70%, Mn: 0.8 to 1.6%, and Mg: 0.50% to 0.90%, Ti: 0.005 to 0.150%, or Ti: 0.0001 to 0.150% and B: 0.0001 to 0.0500% by mass, with the balance consisting of Al and unavoidable impurities, the total content of Fe and Mn being 1.80% or less by mass, and having a tensile strength of 230 MPa or more.

2. The aluminum alloy sheet for lithium ion batteries according to claim 1, containing, by mass%, Fe: 0.50% or less, Cu: 0.60% or less, and Mn: 1.2% or less.

3. A method for producing an aluminum alloy sheet for use in lithium-ion batteries according to claim 1 or 2, comprising: a slab casting step of obtaining an ingot from a molten aluminum alloy having the chemical composition according to claim 1 or 2 by semi-continuous casting; a homogenization treatment step of homogenizing the ingot at a holding temperature of 500 to 600°C for one hour or more; a hot rolling step of hot rolling the ingot after the homogenization treatment step to obtain a hot-rolled sheet; and a cold rolling step of cold rolling the hot-rolled sheet at a rolling reduction of 20% or more.

4. A method for producing an aluminum alloy sheet for use in lithium-ion batteries according to claim 1 or 2, comprising: a slab casting step of obtaining an ingot from a molten aluminum alloy having the chemical composition according to claim 1 or 2 by semi-continuous casting; a homogenization treatment step including homogenizing the ingot at a holding temperature of 500 to 600°C for one hour or more; a hot rolling step of hot rolling the ingot after the homogenization treatment step to obtain a hot-rolled sheet; a pre-intermediate annealing cold rolling step of cold rolling the hot-rolled sheet before intermediate annealing to obtain a cold-rolled sheet; an intermediate annealing step of annealing the cold-rolled sheet to obtain an annealed sheet; and a post-intermediate annealing cold rolling step of cold rolling the annealed sheet at a reduction of 20% or more.

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