JP6674826B2 - Aluminum alloy foil for battery current collector and method for producing the same - Google Patents

Description

  The present invention relates to an aluminum alloy foil for a battery current collector and a method for producing the same.

In recent years, for the purpose of increasing the capacity of a lithium ion battery, it is required to reduce the thickness of an aluminum foil or a copper foil serving as an electrode current collector and a separator. The aluminum foil used as the current collector of the positive electrode is thinned, so that the aluminum foil is easily broken in a battery production line. Therefore, when the thickness of the aluminum foil is reduced, high strength and high elongation are generally required to suppress breakage.
During the production of battery electrodes, there is a step in which heat is applied to the current collector. For example, in the production of lithium ion batteries, it is common to apply an electrode slurry to the current collector and then perform thermal drying at about 100 to 200 ° C. It is. Patent Literature 1 and Patent Literature 2 propose contents for securing the strength of the foil after the heat treatment in order to prevent the strength of the foil from decreasing during the low-temperature heat treatment and causing a problem during the battery manufacturing process.

Patent No. 5798128 JP 2014-114480 A JP 2014-47367 A JP 2012-224927 A

Asano et al., Light Metal, 64 (2014), 279p-284p.

However, we have found a phenomenon in which the elongation of aluminum foil is extremely reduced during low-temperature heat treatment, depending on the chemical composition and manufacturing process. Foil with extremely low elongation is brittle, and the risk of breakage during the electrode manufacturing process, for example, in a pressing step after heat drying, increases. Therefore, it is important that the electrode current collector has high elongation even after heat drying.
We have found that this phenomenon of elongation lowering due to low-temperature heat treatment in aluminum foil occurs remarkably when Fe is added as a chemical component to some extent. For example, as described in Patent Document 3 and Patent Document 4, in the documents conscious of high elongation, Fe is intentionally added as an additive element for refining crystal grains. There is a high possibility that it will decrease.

  A clear mechanism has not yet been elucidated with respect to the phenomenon of elongation reduction during low-temperature heat treatment of aluminum foil, which is the first phenomenon. It is known that in a material manufactured by high cold rolling such as a foil, not only Si but also Fe, which has a low diffusion rate in an Al matrix, undergoes diffusion and precipitation by low-temperature heat treatment. Non-Patent Document 1 reports that the segregation of Fe and Si at the grain boundary is a factor of the decrease in elongation, and it is presumed that Fe and Si have some influence on the microstructure after low-temperature heat treatment.

  In Non-Patent Document 1, although the positive addition of Fe or Si can be accepted as promoting the reduction in the elongation of the aluminum foil during the heat treatment, we add Fe to a certain amount or more to achieve high elongation. It has been found that a material to which is added can greatly suppress the decrease in elongation during low-temperature heat treatment. In addition, by performing a heat treatment that promotes the precipitation of Fe or Si, a decrease in elongation during low-temperature heat treatment can be particularly suppressed.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an aluminum alloy foil for a battery current collector having excellent strength and elongation characteristics.

The aluminum alloy foil for a battery current collector of the present invention contains Fe: 0.7% by mass or more and 1.5% by mass or less, and Si: 0.15% by mass or more and 0.5% by mass or less. Having a composition consisting of unavoidable impurities, wherein in the unavoidable impurities, Mn is 0.05% by mass or less, Cu is less than 0.001% by mass, the thickness is 5 to 20 μm, the tensile strength is 190 MPa or more, and the elongation is 4.2% or more, even when the heat treatment of 100 to 200 ° C. × 30 minutes to 10 hours, and wherein the elongation of 3.8% or more.

The invention of the second form of the aluminum alloy foil for a battery current collector is as follows: Fe: 0.7% to 1.5% by mass, Si: 0.15% to 0.5% by mass, Cu: 0 0.001% by mass or more and 0.05% by mass or less, with the balance having a composition consisting of Al and unavoidable impurities. In the unavoidable impurities, Mn is 0.05% by mass or less and the thickness is 5 to 5%. At 20 μm, the tensile strength is 190 MPa or more, the elongation is 4.2% or more, and the elongation is 3.8% or more even when heat treatment is performed at 100 to 200 ° C. for 30 minutes to 10 hours. And

The invention of the method for producing an aluminum alloy foil for a battery current collector of the present invention is characterized in that the aluminum alloy having the composition according to claim 1 or 2 is subjected to a homogenization treatment at 400 to 520 ° C. for 4 to 16 hours, In the subsequent cold rolling, intermediate annealing in the middle is not performed, or intermediate annealing is performed at 300 to 450 ° C. for 3 to 6 hours by a batch annealing method, and the final cold rolling reduction is 98.3% or more. What line cold rolling in the and a thickness of 5 to 20 [mu] m, a tensile strength of at least 190 MPa, and an elongation of 4.2% or more, a heat treatment was carried out 100 to 200 ° C. × 30 minutes to 10 hours Even in this case, an aluminum alloy foil for a battery current collector having an elongation of 3.8% or more is obtained .

Hereinafter, technical matters defined in the present invention will be described.
-Fe: 0.7 to 1.5%
Fe is an element that can refine crystal grains and improve the strength and elongation of the foil. Further, by adding together with Si, a decrease in elongation during low-temperature heat treatment can be suppressed. If the Fe content is less than 0.7%, the elongation value is low, and almost no improvement in elongation is observed even when added together with Si. If the Fe content exceeds 1.5%, Al-Fe-based and Al-Fe-Si-based crystallization become coarse, resulting in pinholes, breakage during rolling, and reduction in elongation. For this reason, the Fe content is determined within the above range. For the same reason, it is desirable to set the lower limit of the Fe content to 1.0% and the upper limit to 1.4%.

-Si: 0.15 to 0.5%
Si may be added to increase the strength of the foil, but its effect is smaller than that of Cu, Mn, and Mg, and if added too much, the risk of generating Al-Fe-Si-based coarse crystals increases. . Coarse crystallized substances are not usually added positively because they lead to pinholes in the foil or breakage during rolling. However, by adding Fe together with a certain amount or more, the elongation after rolling is improved, and the effect of suppressing the decrease in elongation during low-temperature heat treatment is also exerted. When the Si content is less than 0.15%, the effect on elongation described above is small. When the Si content is more than 0.5%, pinholes, breakage during rolling, and reduction in elongation due to coarse crystals formed during casting are reduced. Occurs. For this reason, the Si content is determined within the above range. For the same reason, it is desirable to set the lower limit of the Si content to 0.2% and the upper limit to 0.35%.

-Restriction of Mn content to 0.05% or less Mn has an effect of refining crystal grains similarly to Fe, and is an effective element for improving the elongation of the foil. However, Mn hinders dislocation movement during heat treatment and hinders recovery and recrystallization of the aluminum foil. It is not clear whether this is due to the effect of suppressing the recovery of the material, but the addition of Mn significantly reduces the elongation during low-temperature heat treatment. For this reason, when Mn is contained as an unavoidable impurity, it is desirable to control the content to 0.05% or less to suppress this decrease in elongation. More preferably, the upper limit is made 0.02%.

-Cu: 0.001% to 0.05%
Cu is an element that can improve the strength of the foil, and is contained as desired. If it is less than 0.001%, even if it is contained, it hardly contributes to improvement in strength. However, if the content exceeds 0.05%, the elongation after rolling is reduced, and the strength becomes too high, making rolling difficult. When Cu is contained as desired, the Cu content is set in the above range. When Cu is not positively contained, Cu may be contained as an unavoidable impurity at less than 0.001%.

Tensile strength 190MPa or more after rolling, elongation of 4.2% or more tensile strength of 190MPa or more, can be suppressed break in a cell manufacturing line by a growth of 4.2% or more. Since the value of the elongation changes depending on the thickness of the foil, the elongation becomes high even with the same alloy if the thickness is 12 μm or more.
It is desirable that the above characteristics be maintained even after the low-temperature heat treatment.
By suppressing the decrease in elongation during the battery manufacturing process including the low-temperature heat treatment, it is possible to make use of the high elongation characteristics of the foil with respect to the battery characteristics. Also By beauty value Shin at a minimum is maintained at more than 3.8%, it can suppress the break in the middle of the manufacturing process.
The low-temperature heat treatment can be performed on the basis of 100 to 200 ° C. × 10 hours. However, the condition of the low-temperature heat treatment is not limited to this, and for example, a treatment at 100 to 200 ° C. for 30 minutes to 10 hours can be shown. If the temperature is lower than 100 ° C., the desired effect such as drying is insufficient or too slow, so that it is not employed in a usual process. On the other hand, a treatment exceeding 200 ° C. cannot be employed because the softening of the foil occurs rapidly. Usually, in the low-temperature heat treatment line, a process for 30 minutes or more is performed to make the characteristics of the entire foil coil uniform. Note that a treatment exceeding 10 hours is uneconomical and unrealistic because a desired effect such as slurry drying saturates.

-Manufacturing method of aluminum alloy foil An aluminum alloy having the above composition is cast by a semi-continuous casting method or a continuous casting method, and the obtained ingot is homogenized at 400 to 520 ° C for 4 to 16 hours. If the temperature is kept lower than 400 ° C. or less than 4 hours, Fe, Si and the like are not sufficiently precipitated, and the reduction in the elongation of the foil during the low-temperature heat treatment becomes large. At a high temperature exceeding 520 ° C., the amount of solid solution of Fe or Si increases, which also causes a decrease in elongation during low-temperature heat treatment.

  This alloy has good rollability, and it is not necessary to perform intermediate annealing during cold rolling. However, when the rollability is reduced, for example, when a large amount of Cu is contained, intermediate annealing may be applied during cold rolling. There are two types of intermediate annealing: batch annealing (Batch Annealing) in which a coil is charged into a furnace and held for a certain period of time, and two types of methods in which a material is rapidly heated and quenched by a continuous annealing line (hereinafter referred to as CAL annealing). In the present invention, batch annealing is always adopted, and holding at 300 to 450 ° C. for 3 to 6 hours is performed. In the case of the CAL annealing, it has been confirmed that Fe, Si, and the like precipitated in the homogenization treatment re-dissolve, resulting in a decrease in foil elongation during low-temperature heat treatment.

  The final cold rolling reduction is 98.3% or more. It is known that crystal grains of an aluminum alloy are divided and refined only by rolling (grain subdivision). The higher the rolling reduction, the finer the crystal grains are. Therefore, by setting the final cold rolling reduction at the time of cold rolling to 98.3% or more, higher elongation characteristics can be obtained. The final cold rolling here refers to cold rolling from the thickness subjected to intermediate annealing during the rolling process to the final thickness, and when not performing intermediate annealing, from the sheet thickness after hot rolling to the final thickness. Cold rolling.

  According to the present invention, an aluminum foil for a battery current collector having excellent strength and excellent elongation characteristics can be obtained.

The aluminum alloy having the composition of the present invention can be produced by a conventional method, and a known semi-continuous casting method or continuous casting rolling method can be employed.
The ingot obtained by semi-continuous casting can be subjected to a homogenization treatment if desired. When performing the homogenization treatment, it is desirable to control the homogenization temperature to 400 to 520 ° C. and the holding time to 4 to 16 hours. As a result, segregation of alloy elements during casting can be eliminated, and the structure can be made uniform, whereby a thin foil can be rolled into a more suitable state.
If the homogenous temperature is lower than 400 ° C., local segregation may not be completely eliminated, and rolling becomes difficult due to uneven work hardening. On the other hand, if the homogenous temperature exceeds 520 ° C., local melting may occur. For this reason, the homogeneous temperature is desirably 400 to 520 ° C. If the homogenization time is less than 4 hours, the effect is not sufficient, and rolling becomes difficult due to uneven work hardening. On the other hand, when the time exceeds 16 hours, the precipitates are enlarged and easily broken during rolling. Therefore, the homogenization time is desirably 4 to 16 hours.

  Thereafter, hot rolling is performed to obtain an aluminum alloy material. Hot rolling can be performed by a conventional method, but the finishing temperature is desirably 200 to 290 ° C, more desirably 240 to 280 ° C.

The aluminum alloy material is subjected to cold rolling, subjected to intermediate annealing, cold rolled again, and finally cold rolled. Intermediate annealing can be performed by a conventional method using a batch annealing furnace or a continuous annealing furnace. In the present embodiment, the intermediate annealing may not be performed.
When performing intermediate annealing, it is performed by a batch annealing method, and is performed by holding at 300 to 450 ° C. for 3 to 6 hours.
The final cold rolling reduction is desirably 98.3% or more.
Through cold rolling and final cold rolling, an aluminum alloy foil having a thickness of 5 to 20 μm can be obtained. When Cu is not positively added, the aluminum alloy foil has a tensile strength of 190 MPa or more. Further, the elongation is 4.0% or more at a foil thickness of 12 μm.
The rolling reduction indicates the rolling reduction after the heat treatment. If intermediate annealing is performed during cold rolling, the thickness at the time of intermediate annealing starts. Material.

The obtained aluminum alloy foil is used for a battery current collector. In particular, it can be suitably used for a secondary battery such as a lithium ion battery. The current collector for a battery can be used for both the positive electrode and the negative electrode, but is mainly used for the positive electrode.
The battery current collector receives a heat history such as performing heat drying at 100 to 200 ° C. for about 30 minutes to 10 hours after applying the electrode slurry to the current collector. Even after this thermal history, the elongation at a foil thickness of 12 μm maintains the property of 3.5% or more.

Hereinafter, examples of the present invention will be described.
An ingot of an aluminum alloy having each composition shown in Table 1 (remainder Al and other unavoidable impurities) was homogenized under the conditions shown in Table 1, and then hot-rolled at a finishing temperature of 270 ° C. to 4.5 mm. Plate material. Thereafter, a sample of an aluminum alloy foil having a thickness of 12 μm and a width of 1200 mm was produced through cold rolling, intermediate annealing, and final cold rolling. Test material No. The intermediate annealing of No. 14 was batch annealing at 350 ° C. for 4 hours. In the intermediate annealing of No. 16, CAL annealing was performed at a temperature rise / cooling of about 100 ° C./sec and holding at 420 ° C. × 20 sec.

(Heat treatment)
During the electrode manufacturing process, the foil is subjected to a heat treatment at 100 to 200 ° C. At this time, there is a possibility that the elongation characteristics of the Al-Fe-based alloy foil having high elongation characteristics are sharply reduced. In the examples, changes in mechanical properties before heat treatment (after rolling) and when heat treatment was performed at 100, 150, and 200 ° C. for 10 hours were measured. The heat treatment time was set to the long time side (: 10 hours) which was most affected by the decrease in elongation within the assumed range.

(Tensile strength, elongation)
The tensile strength and the elongation were measured in accordance with JIS Z2241 by collecting a JIS No. 5 test piece from the sample and measuring the tensile strength at a tensile speed of 2 mm / s using a universal tensile tester (manufactured by Shimadzu Corporation).

(Rollability)
The rollability is as follows: in the case of rolling over a width of more than 1200 mm, a roll that could be rolled without breaking in the final pass (reduction rate) was evaluated as ○, and when the final pass broke less than 3 times per coil (about 10,000 m) △ indicates that it was determined that continuation of rolling was difficult due to, for example, breaking more than three times or being too hard. ○ is preferred, but if it is △ or more (within the last pass of about 10,000 m, the break is within 3 times), there is no problem in production.

  Table 2 shows the test results. As is clear from the table, in the examples of the present invention, the elongation characteristics were excellent even after the low-temperature heat treatment at 100 and 150 ° C. In the comparative examples, none of them had excellent elongation characteristics after the low-temperature heat treatment. In Comparative Example 21, the mechanical properties could not be measured because the homogenization temperature was too low to perform rolling to a 12 μm foil thickness without intermediate annealing.

Claims (3)

Fe: 0.7% by mass to 1.5% by mass, Si: 0.15% by mass to 0.5% by mass, and the balance is composed of Al and inevitable impurities. in the middle, Mn 0.05 mass% or less, Cu is less than 0.001 wt%, a thickness of 5 to 20 [mu] m, a tensile strength of at least 190 MPa, and a elongation of 4.2% or more, 100 An aluminum alloy foil for a battery current collector , wherein the elongation is 3.8% or more even when heat treatment is performed at a temperature of 200 ° C. for 30 minutes to 10 hours . Fe: 0.7% to 1.5% by mass, Si: 0.15% to 0.5% by mass, Cu: 0.001% to 0.05% by mass, with the balance being It has a composition consisting of Al and inevitable impurities. In the inevitable impurities, Mn is 0.05% by mass or less, thickness is 5 to 20 μm, tensile strength is 190 MPa or more, and elongation is 4.2% or more. And an elongation of 3.8% or more even when heat-treated at 100 to 200 ° C. for 30 minutes to 10 hours. The aluminum alloy having the composition according to claim 1 or 2, is subjected to a homogenization treatment of holding at 400 to 520 ° C for 4 to 16 hours, and in the subsequent cold rolling, no intermediate annealing is performed, or performing intermediate annealing for holding 3-6 hours at 300 to 450 ° C. in a batch annealing method, the final cold rolling rate I line cold rolling in the above 98.3%, a thickness of 5 to 20 [mu] m, Aluminum having a tensile strength of 190 MPa or more, an elongation of 4.2% or more, and an elongation of 3.8% or more even when subjected to heat treatment at 100 to 200 ° C. for 30 minutes to 10 hours. A method for producing an aluminum alloy foil such as a battery current collector, comprising obtaining an alloy foil .