JP6775335B2 - Manufacturing method of aluminum alloy foil for electrode current collector and aluminum alloy foil for electrode current collector - Google Patents

Description

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

Conventionally, an aluminum alloy foil having a thickness of about 15 μm has been used as an electrode current collector used in a lithium ion battery or the like. In recent years, the capacity of batteries has been increasing mainly for mobile devices, and it is required to thin the aluminum alloy foil used for the electrode current collector. In order to prevent defects in the battery manufacturing process that occur due to the thinning of the aluminum alloy foil, it is important for the aluminum alloy foil for the electrode current collector to have high strength and high elongation. Further, as the thickness of the aluminum alloy foil becomes thinner, it becomes difficult to roll the foil, and the risk of hole scratches and pinholes increases. Therefore, it is important to have excellent rollability.

For example, in Patent Document 1, Fe, Si, and Cu are added to an aluminum alloy, and the added elements are solid-dissolved to supersaturation by a continuous casting and rolling method or the like to achieve high strength of the aluminum alloy foil, and a crystallized product. The occurrence of pinholes is suppressed by miniaturizing.
In Patent Document 2, Fe, Si, and Cu are added to an aluminum alloy, and an appropriate heat treatment is performed in a homogenization treatment or the like to dissolve the added elements to achieve high strength of the aluminum alloy foil. ..
In Patent Document 3, Mn, Fe, and Cu are added to the aluminum alloy to increase the number of subgrains in the thickness direction of the foil to 30 or more, thereby achieving high strength and high elongation of the aluminum alloy foil. ..
In Patent Document 4, Fe and Cu are added to the aluminum alloy to reduce the size of the subgrain to 0.8 μm or less in the thickness direction and 45 μm or less in the rolling direction to achieve high strength and high elongation.

Patent No. 5791719 International Publication No. 2013-018162 Japanese Unexamined Patent Publication No. 2011-89196 Japanese Unexamined Patent Publication No. 2012-21205

Light metal Vol. 65 (2015) No. 4 p. 131-136

However, when each additive element is supersaturated and solid-solved by a continuous casting method as in Patent Document 1, foil rolling is extremely difficult, and it is difficult to manufacture a thin foil electrode current collector having a thickness of 15 μm or less. Is.
Further, in Patent Document 2, a special heat treatment is required to maintain a high solid solution amount of the additive element, and at that time, the implementation of intermediate annealing under general conditions is restricted. Therefore, it is extremely difficult to roll a thin foil.
In Patent Document 3, a relatively large amount of Mn is added in the addition of elements. Our research has shown that Al-Fe-Mn-based alloy foils are difficult to control in production because the strength increases and the elongation decreases at room temperature after rolling. In addition, the heat treatment performed in the electrode manufacturing process also causes an increase in strength and an extreme decrease in elongation, which may lead to fracture of the foil (anneal curing phenomenon, see Non-Patent Document 1).
In Patent Document 4, when the amount of Fe is small, the subgrain can be miniaturized, but it is difficult to miniaturize the crystal grains as described later, and it is difficult to actually obtain high elongation.

The present invention has been made in the context of the above circumstances, and is a method for producing an aluminum alloy foil for an electrode current collector and an aluminum alloy foil for an electrode current collector, which have achieved high strength and high elongation and are excellent in rollability. One of the purposes is to provide.

That is, the first aluminum alloy foil for an electrode current collector of the present invention has Fe: 0.56 % or more and 0.95 % or less, Cu: 0.12 % or more and 0.18 % or less, Si: 0.10% 0.01% or less, Mn: contains 0.10% or less, have a composition the balance of Al and unavoidable impurities, the crystal grain size in the thickness direction of the foil is on average 0. It is characterized by having a tensile strength of 261 MPa or more, an elongation of 2.5% or more immediately after the final cold rolling, and 2.5% or more even 60 days after the final cold rolling. To do.

Electrode current collector aluminum alloy foil of the second present invention, in the first invention, wherein the thickness of the foil is 15μm or less.

The third method for producing the aluminum alloy foil for the electrode current collector of the present invention is the first method for producing the aluminum alloy foil for the electrode current collector of the present invention, and the aluminum having the composition of the first invention. The alloy ingot is homogenized by holding it at 450 to 580 ° C. for 4 hours or more, and then cold rolling is performed so that the final cold rolling ratio in cold rolling is 98.3% or more. ..

The reasons for limiting the composition and the like specified in the present invention and the reasons for limiting the production conditions will be described below. The content of each component in the following is shown in mass%.

Fe: 0.5% or more and 1.0% or less Fe is an element that contributes to solid solution strengthening and finer crystal grains. If the Fe content is less than 0.5%, fine crystal grains cannot be obtained in the thickness direction, and if it exceeds 1.0%, the Al—Fe-based intermetallic compound becomes coarse and the foil rollability is improved. It reduces and increases the risk of pinholes.
Furthermore, we have found that when Fe is added in excess of 1.0%, the elongation tends to decrease at room temperature after rolling. For the same reason, it is desirable that the lower limit of the Fe content is 0.6% and the upper limit is 0.8%.

Cu: 0.05% or more and 0.25% or less Cu improves the strength of the foil by strengthening the solid solution. If it is less than 0.05%, the effect is not sufficient, and if it exceeds 0.20%, the strength of the foil is too high, so that the rollability is lowered and side cracks occur during rolling. Further, the addition of more than 0.25% significantly reduces the elongation of the foil. For the same reason, it is desirable that the lower limit of the Cu content is 0.10% and the upper limit is 0.20%.

Si: 0.01% or more and 0.10% or less Si promotes the precipitation of Fe if it is added in an appropriate amount, improves rollability, and also improves elongation characteristics. If it is less than 0.01%, the above action is not sufficient. If it exceeds 0.10%, the precipitation of Fe is promoted, and as a result, work softening in foil rolling occurs, and high strength cannot be obtained. In addition, Al-Fe-Si-based crystals become coarse and the elongation is lowered. For the same reason, it is desirable that the lower limit of the Si content is 0.03% and the upper limit is 0.08%.

Mn: 0.10% or less Mn is an element that contributes to solid solution strengthening and finer crystal grains. Crystal grains can be made finer by adding them together with Fe, but if the amount added is large, the mechanical properties change at room temperature after rolling, and heat treatment during the battery manufacturing process also causes an extreme decrease in elongation. The above problem can be avoided by limiting the Mn content to 0.10% or less. For the same reason, it is desirable to set the upper limit to 0.05%. It is not necessary to add it positively because it causes a decrease in elongation at room temperature, but by adding 0.01% or more, the elongation immediately after the final cold rolling can be slightly improved.

The average crystal grain size in the thickness direction of the foil is 0.8 μm or less. For example, a thin foil having a thickness of 15 μm or less breaks as soon as a constriction occurs due to local deformation. That is, high elongation can be obtained by making the grain diameter finer. In measuring the crystal grain size, it is necessary to define the grain boundaries, which are the boundaries between the crystal grains. The crystal grain boundaries referred to here refer to large tilt angle grain boundaries having an orientation difference of 15 ° or more between grains. Sub-crystal grains with an orientation difference of 0 ° to less than 15 ° also contribute to high elongation, but the degree is extremely small compared to the crystal grains. By setting the average crystal grain size in the thickness direction to 0.8 μm or less, high elongation of an aluminum alloy foil having a thickness of 15 μm or less is achieved.

Tensile strength of 250 MPa or more, elongation at a thickness of 12 μm is 2.5% or more immediately after the final cold rolling, and at least 60 days after the final cold rolling, the tensile strength is less than 250 MPa. However, the strength is insufficient, and it is difficult to thin the electrode current collector. Further, if the growth is less than 2.5%, there is a concern that a defect may occur in the production line. And the high elongation property of the foil needs to be possessed at the time when it is loaded on the electrode production line. Depending on the alloy component and the manufacturing process of the hard foil, the elongation may decrease sharply within 60 days after the final cold rolling. The thickness of 12 μm is for indicating a characteristic value and does not specify the thickness of the foil.
The tensile strength is more preferably 270 MPa or more, and the elongation at a thickness of 12 μm is more preferably 3.0% or more.

It is known that in an aluminum alloy having a final cold rolling ratio of 98.3% or more, crystal grains are divided and made finer just by rolling (grain subdivision). Since the higher the rolling ratio, the finer the crystal grains, the higher the elongation can be achieved by setting the final cold rolling ratio at the time of cold rolling to 98.3% or more.
Here, the final cold rolling means the rolling after the last intermediate annealing when the intermediate annealing is performed, and the rolling after the start of the cold rolling when the intermediate annealing is not performed.

That is, according to the present invention, it is possible to obtain a method for producing an aluminum alloy foil for an electrode current collector and an aluminum alloy foil for an electrode current collector, which have achieved high strength and high elongation and are excellent in rollability.

An embodiment of the present invention will be described below.
The aluminum alloy used as the material of the aluminum alloy foil has Fe: 0.5% or more and 1.0% or less, Cu: 0.05% or more and 0.25% or less, and Si: 0.01%, which are the component ranges of the present invention. It is melted so as to have a composition containing 0.10% or less and Mn: 0.10% or less and the balance being Al and unavoidable impurities. The melting method is not particularly limited, and a known semi-continuous casting method or the like can be used. The obtained ingot is subjected to a homogenization treatment of holding it at, for example, 450 to 580 ° C. for 4 hours or more, and then subjected to hot rolling.

After that, cold rolling is performed to obtain, for example, an aluminum alloy foil having a final thickness of 10 to 20 μm. During the cold rolling, intermediate annealing can be performed once or more than once. What is intermediate annealing? There are two types of methods: batch annealing, in which the coil is placed in a furnace and held for a certain period of time, and continuous annealing line (hereinafter referred to as CAL annealing), in which the material is rapidly heated and cooled. is there. In the present invention, any method may be used, but in CAL annealing, the strength of the foil as the final material is improved by making the crystal grains finer by rapid heating and quenching and increasing the solid solution amount of the solute element.

As a guideline for batch annealing, for example, at 350 to 450 ° C. for 3 hours or more. If the temperature is less than 350 ° C. or the time is less than 3 hours, recrystallization may not be completed, and if the temperature exceeds 450 ° C., there is a risk of coarsening of crystal grains due to secondary recrystallization. Examples of the CAL annealing include conditions of a temperature rise temperature of 10 to 250 ° C./sec, a heating temperature of 400 to 550 ° C., a holding time of none to 5 seconds, and a cooling rate of 20 to 200 ° C./sec.
Further, in the present invention, intermediate annealing may not be performed.
In cold rolling, the final cold rolling ratio is 98% or more. When intermediate annealing is performed, the final cold rolling ratio is indicated by the rolling ratio after the final intermediate annealing. When intermediate annealing is not performed, the rolling ratio after the start of cold rolling is shown.

The aluminum alloy foil of the present invention has characteristics such that the crystal grain size in the thickness direction is 1.0 μm or less on average, the tensile strength is 250 MPa or more, and the elongation at a thickness of 12 μm is 2.5% or more. Moreover, 2.5% or more is maintained even after at least 60 days have passed after the final cold rolling. Further, the aluminum alloy foil of the present invention can be used for a secondary battery electrode current collector, and can be particularly preferably used for a lithium ion secondary battery. The electrode current collector can be used for both the positive electrode and the negative electrode, but is mainly used for the positive electrode.

An ingot of an aluminum alloy having each composition (remaining Al and other unavoidable impurities) shown in Table 1 was homogenized at 520 ° C. for 10 hours and hot-rolled to a thickness of 4.5 mm. After that, cold rolling was performed to a thickness of 2.5 mm (1.0 mm for No. 9 and 0.6 mm for No. 10), and No. Intermediate annealing was carried out except for No. 12, and a sample of an aluminum alloy foil having a thickness of 12 μm was prepared through final cold rolling.
Intermediate annealing is No. Except for No. 11, a continuous annealing line (CAL annealing) was used. The conditions for CAL annealing were a heating temperature: 70 ° C./sec, a heating temperature: 500 ° C., a holding time: none, and a cooling rate: 50 ° C./sec. No. The intermediate annealing of No. 11 was carried out by batch annealing at 360 ° C. for 4 hours. The rolling ratio of each material is shown in Table 1.

(Measurement of crystal grain size in the thickness direction)
The RD-ND surface of the aluminum alloy foil was cut by CP (cross section polisher), and this cut surface was analyzed by the SEM-EBSD method. The entire thickness of the foil was observed at a magnification of × 2000 times, and when the particle size was actually measured, it was observed at × 5000 times. In the obtained orientation mapping image, the crystal grain size in the thickness direction of the foil was calculated by the line segment method from the grain map displaying the grain boundaries having an orientation difference of 15 ° or more. In addition, the observation of × 5000 times was carried out in three fields of view with one sample, and the crystal grain size was taken as the average value. The measurement results are shown in Table 1.

(mechanical nature)
The mechanical properties were measured by a tensile test. A JIS No. 5 shape test piece was prepared by punching in parallel with the rolling direction of the foil, and the test was carried out at an autograph (Shimadzu AGS-X 10 kN) at a test speed of 2 mm / min at n = 3.

(Rollability)
The rollability is as follows: In wide rolling with a width of more than 1200 mm, the one that can be rolled without breaking in the final pass (rolling ratio) is ○, and when the final pass breaks 3 times or less per coil (about 10000 m). Is marked with Δ, and marked with × for those judged to be difficult to continue rolling due to breakage exceeding 3 times or too hard. ◯ is preferable, but if it is Δ or more (breaking is within 3 times in the final pass of about 10000 m), there is no problem in manufacturing.

Claims (3)

By mass%, Fe: 0.56 % or more and 0.95 % or less, Cu: 0.12 % or more and 0.18 % or less, Si: 0.01% or more and 0.10% or less, Mn: 0.10% or less containing, possess the balance consisting of Al and unavoidable impurities, the crystal grain size in the thickness direction of the foil is 0.8μm or less in average, the tensile strength of 261MPa or more, immediately after elongation final cold rolling An aluminum alloy foil for an electrode current collector, which is 2.5% or more, and is 2.5% or more even after 60 days have passed after the final cold rolling . The aluminum alloy foil for an electrode current collector according to claim 1 , wherein the thickness of the foil is 15 μm or less. The method for producing an aluminum alloy foil for an electrode current collector according to claim 1 , wherein an aluminum alloy ingot having the composition according to claim 1 is homogenized at 450 to 580 ° C. for 4 hours or more. After that, a method for producing an aluminum alloy foil for an electrode current collector, which comprises performing cold rolling in which the final cold rolling ratio in cold rolling is 98.3% or more.