JP6545779B2 - Aluminum alloy foil for battery current collector - Google Patents

Description

  The present invention relates to an aluminum alloy foil for a battery current collector used as a positive electrode current collector or the like of a lithium ion battery.

  In recent years, for the purpose of increasing the capacity of a lithium ion battery, thinning of an aluminum foil or copper foil as an electrode current collector and a separator has been required. By thinning the aluminum foil used as the current collector of the positive electrode, breakage easily occurs in the battery production line. Therefore, when thinning an aluminum foil, in order to suppress breakage, it is generally required that high strength and high elongation be required.

  During the electrode manufacturing process of the battery, there is a process in which heat is applied to the aluminum foil which is a current collector. For example, in the production of a lithium ion battery, it is general to perform thermal drying at about 200 ° C. after applying an electrode slurry to a current collector. The aluminum foil changes its mechanical properties by heat treatment such as this thermal drying, but in many cases, a foil having high elongation before and after heat treatment is required. If the elongation is low before the heat treatment, the foil may break in the production line or wrinkles may occur even if the break does not occur. Also, high elongation is required for the foil after heat treatment. In order to prevent the aluminum foil from being broken or wrinkles due to expansion and contraction of the electrode mixture during charge and discharge of the battery, it is important that the foil has high elongation even after heat treatment.

  Patent Document 1 contains Fe: 0.8 to 2.0% (mass%, the same below), Ti: 0.02% or less (not including 0%, the same below), and contains Si as an impurity. An aluminum alloy foil containing 0.15% or less of Cu, 0.05% or less of Cu, and the balance of Al and other unavoidable impurities, having a tensile strength of 160 MPa or more and measured in liquid nitrogen by the double bridge method The electrical resistance is 0. An aluminum alloy foil for a lithium ion battery electrode current collector having a size of 55 μΩcm or less is disclosed. Also, in order to ensure strength and sufficient elongation after low temperature heat treatment (5 minutes at 170 ° C.), it is preferable to start hot rolling at 400 to 450 ° C. and finish at 200 to 250 ° C. It is described that the elongation after heat treatment is 3% or more.

  Patent Document 2 contains, by mass%, Fe: 0.8% or more and 2.0% or less, Si: 0.35% or less, Ti: 0.05% or less, and consists of the balance Al and unavoidable impurities. There are 800 or more Al-Fe-based compounds with equivalent circle diameter of 10 to 50 nm per cubic μm without generation of pinholes, and after oil bath heat treatment at 100 ° C for 1 minute with a tensile strength of 160 MPa or more An aluminum alloy foil for a lithium ion battery electrode current collector having a tensile strength of at least 150 MPa and a tensile strength of less than 150 MPa after oil bath heat treatment at 120 ° C. for one minute is disclosed.

JP, 2010-150637, A JP 2011-241410 A

  An object of the present invention is to provide an aluminum alloy foil for a battery current collector, which further improves the rollability and has high ductility before and after heat treatment.

Aluminum foil is manufactured by rolling, but its rollability decreases as the thickness of the foil decreases. Therefore, when producing a thin foil in general, polymerization rolling is performed in which two foils are stacked and rolled. In the case of polymerization rolling, rolling can be performed at twice the thickness during rolling with respect to a target foil thickness, and therefore, the rollability is better than single rolling, which is single-sheet rolling. In the aluminum foil obtained by polymerization rolling, the inner surface with which the foils are in contact during rolling is a matte surface without gloss, while the surface in contact with the rolling roll is a glossy surface with high gloss. The surface of this matte surface is not smooth and has irregularities as compared to the glossy surface. Due to the effect of the unevenness, the elongation property of the foil tends to be reduced as compared to the double-sided glossy foil obtained by single rolling. Therefore, polymerization rolling is not often used in products that often require high elongation characteristics such as current collectors of lithium ion batteries. In addition, since the unevenness of the surface causes a pinhole of the foil, it is considered that it is difficult to use in a product of severe quality.
In the present invention, in order to ensure high elongation even in such a polymerized rolled foil, the aluminum alloy foil for a battery final conductor of the following constitution was used.

That is, the aluminum alloy foil for a battery current collector of the present invention comprises: Fe: 1.0% by mass or more and 1.8% by mass or less, Si: 0.01% by mass or more and 0.06% by mass or less, Cu: 0.006 contains more mass% 0.015 mass% or less, have the balance consisting of Al and unavoidable impurities, the tensile strength of more than 180 MPa, elongation Ri der to 6.0%, in the thickness direction the grain Single-rolled foil with a gap of 1.0 μm or less, and the tensile strength after heat treatment at 200 ° C for 12 hours is 100 MPa or more, 0.2% proof stress is 60 MPa or more, elongation is 14% or more, average crystal particle size 6μm or less, Ru der and the ratio of the maximum crystal grain diameter / average crystal grain size of 3.0 or less.

In addition, the aluminum alloy foil for a battery current collector of the present invention comprises: Fe: 1.0% by mass or more and 1.8% by mass or less, Si: 0.01% by mass or more and 0.06% by mass or less, Cu: 0.006 It has a composition containing not less than mass% and not more than 0.015 mass%, with the balance being composed of Al and unavoidable impurities, having a tensile strength of 180 MPa or more, an elongation of 5.0% or more, and grain boundaries in the thickness direction interval following polymerization rolled foil der 1.0μm of Ri, 2 00 ° C. for 12 hours heat-treated after the tensile strength of more than 100 MPa, 0.2% proof stress than 60 MPa, and an elongation of 12% or more, average crystal grain size is 6μm or less, Ru der and the ratio of the maximum crystal grain diameter / average crystal grain size of 3.0 or less.

  The rollability is improved and the aluminum alloy foil for battery current collectors of the present invention has high ductility before and after heat treatment.

  Hereinafter, an embodiment of an aluminum alloy foil for a battery current collector according to the present invention will be described.

  The aluminum alloy foil for a battery current collector includes: Fe: 1.0% by mass or more and 1.8% by mass or less, Si: 0.01% by mass or more and 0.06% by mass or less, Cu: 0.006% by mass or more 0 It has a composition containing not more than 015% by mass and the balance being Al and unavoidable impurities. The reasons for adding these elements are as follows.

-Fe: 1.0% by mass or more and 1.8% by mass or less Fe is crystallized as an Al-Fe-based intermetallic compound at the time of casting and has an effect of becoming nuclei and refining crystal grains. If it is less than 1.0%, the effect of the refinement is scarce, and the grain size becomes large before and after heat treatment, making it difficult to obtain high elongation. When it exceeds 1.8%, a coarse intermetallic compound of Al-Fe system is easily formed, and the elongation and the rollability are reduced. In addition, this coarse intermetallic compound is also a cause of pinholes in one-side gloss foil obtained by polymerization rolling.

Si: 0.01% by mass or more and 0.06% by mass or less By regulating Si to 0.06% or less, the crystal grain size after heat treatment can be made uniform and refined, and high elongation characteristics can be obtained. Moreover, it leads to suppression of precipitation of Fe, and can suppress excessive work softening during cold rolling. In addition, the reduction of Si suppresses the formation of coarse intermetallic compounds of the Al-Fe-Si system, and the suppression of pinholes in thin foils can also be expected. Furthermore, the inventor has found an effect of suppressing the unevenness of the matte surface when polymerizing and rolling an Al-Fe alloy according to the regulation of Si, and the ductility improvement of one-side glossy foil manufactured by polymerization rolling and rolling It also leads to the suppression of breakage. When the content of Si exceeds 0.06% by mass, the Al-Fe-based intermetallic compound becomes coarse and the elongation decreases. Furthermore, since the coarse intermetallic compounds increase the surface roughness of the matte surface during polymerization rolling, the elongation of the polymerization rolled foil is particularly reduced. On the other hand, if the content of Si is less than 0.01% by mass, the precipitation of Fe is excessively suppressed, so that the work hardening is increased and the elongation and the rollability of the foil are reduced. In addition, the density of the intermetallic compound of a certain size that can be a nucleation site of recrystallization is reduced, and recrystallization inhibition causes coarse and uneven recrystallization grain size at the time of intermediate annealing, and the elongation of the final foil is It may cause a decline. In addition, in order to reduce Si to less than 0.01% by mass at the time of manufacture, it is necessary to use very pure Al base metal, and the manufacturing cost becomes extremely high. Therefore, it is desirable to add Si 0.01% by mass or more.

-Cu: 0.006 mass% or more and 0.015 mass% or less Cu is an element which increases the strength of a hard foil. If it is less than 0.006%, there is an increased possibility of causing excessive work-softening during cold rolling, and there is a risk that the tensile strength of the finally obtained foil may be significantly reduced. If excessive work softening occurs during rolling, the grain structure becomes uneven and coarse before and after heat treatment, and the elongation also decreases. By adding 0.006% or more of Cu, it is possible to suppress this excessive work softening in cold rolling and obtain stable mechanical properties. However, if it exceeds 0.015%, the elongation is greatly reduced due to the high strength of the foil. Further, the recrystallization temperature rises, and even if heat treatment is performed at 200 ° C. for 12 hours, recrystallization does not occur and it is difficult to obtain high ductility. In addition, Cu having a high content tends to cause side cracks at the time of rolling, and the rollability is lowered even in polymerization rolling.

  Among the aluminum alloy foils for battery current collectors having the above composition, the aluminum alloy foils for battery current collectors include single rolled foils manufactured by single rolling and polymerized rolled foils manufactured by polymerization rolling.

(Polymerized rolling foil)
In the polymerized rolled foil, the tensile strength at normal temperature (25 ° C.) is 175 MPa or more, the elongation is 5.0% or more, and the distance between crystal grain boundaries in the thickness direction is 1.0 μm or less. The tensile strength after heat treatment at 200 ° C. for 12 hours is 100 MPa or more, the 0.2% proof stress is 60 MPa or more, and the elongation is 12% or more.
The reason for this configuration is as follows.

-Tensile strength of 180 MPa or more, elongation of 5.0% or more In order to prevent the foil from breaking in the production line, the tensile strength of the foil after final cold rolling needs to be 180 MPa or more. The higher the elongation, the better. Even if it is a single-sided luster foil which is disadvantageous as an elongation characteristic manufactured by polymerization rolling, a fault can be prevented by having 5.0% or more of elongation.

-The distance between grain boundaries in the thickness direction of the rolled foil is 1.0 μm or less In the hard foil after rolling, the ductility tends to improve as the number of grain boundaries in the thickness direction of the foil increases. Have found. Elongation does not change extremely at boundaries of grain boundaries of 1.0 μm, but in the case of thin foils, the grain boundary spacing in the thickness direction is 1.0 μm or less, so it is stable and high You can get growth.

・ The tensile strength is 100MPa or more after heat treatment at 200 ° C for 12 hours, the 0.2% proof stress is 60MPa or more, the elongation is 12% or more After heat treatment assuming heat drying after applying the electrode slurry to the current collector If the tensile strength of the foil is less than 100MPa, 0.2% proof stress is less than 60MPa, and the elongation is less than 12%, the risk of causing breakage of the foil due to insufficient strength or wrinkles in the battery production line increases. It is desirable that the subsequent tensile strength and the like be in the above range. However, the conditions of the heat treatment of an actual current collector are not limited to the above.
As described above, by defining Si and Cu, it is possible to obtain a foil excellent in ductility and very excellent in elongation characteristics.

The average crystal grain size after heat treatment at 200 ° C. for 12 hours is 6 μm or less, and the ratio of the maximum crystal grain size / the average crystal grain size is 3.0 or less. Assumes thermal drying after applying the electrode slurry to the current collector. Even after the heat treatment, the material is easily deformed uniformly by refining the crystal grain size, and the elongation property is improved. However, when coarse crystal grains are mixed in fine crystal grains, stress concentration occurs at the time of deformation and constriction occurs at an early stage, leading to breakage. By forming a fine and uniform crystal grain structure in which the average crystal grain size is 6 μm or less and the ratio of the maximum crystal grain size / average crystal grain size is 3.0 or less, stable high ductility after heat treatment can be ensured.

(Single rolled foil)
The single-rolled foil can increase the elongation compared to the polymerized rolled foil, and can make the elongation 6.0% or more. That is, in a single-rolled foil, the tensile strength at normal temperature (25 ° C.) is 175 MPa or more, the elongation is 6.0% or more, and the distance between crystal grain boundaries in the thickness direction is 1.0 μm or less. The tensile strength after heat treatment at 200 ° C for 12 hours is 100 MPa or more, the 0.2% proof stress is 60 MPa or more, the elongation is 14% or more, the average grain size is 6 μm or less, and the maximum grain size / average grain size The ratio of crystal grain sizes is 3.0 or less.

  The thickness of the aluminum alloy foil for a battery current collector is not particularly limited, but is preferably in the range of 6 μm to 30 μm. If the thickness of the aluminum alloy foil is less than 6 μm, the electrical resistance may increase and the battery characteristics may be degraded. Also, it is difficult to produce an aluminum foil having a thickness of less than 6 μm by rolling, even if it is polymerization rolling, and there is a risk that additional steps will be required. When the thickness of the aluminum alloy foil exceeds 30 μm, the number of aluminum alloy foils that can be wound into the battery may be reduced, and the battery capacity may be reduced. The preferred range of thickness is 10 μm or more and 30 μm or less.

The aluminum alloy foil for battery current collectors having the above composition and characteristics is manufactured as follows.
First, the aluminum alloy having the predetermined composition range described above is melted and produced by a known method such as a semi-continuous casting method or a continuous casting and rolling method.
The ingot is homogenized at a temperature of 500 ° C. to 580 ° C. for 4 to 16 hours, and then hot rolled to form an aluminum alloy sheet. The finish temperature of this hot rolling is 280 ° C. or less. Next, intermediate annealing is performed as required, and cold rolling is performed to obtain an aluminum alloy foil having a desired thickness. The final cold rolling reduction in cold rolling is preferably 98.2% or more.
Hereinafter, these conditions will be described.

Homogenization: 4 to 16 hours at a temperature of 500 ° C. to 580 ° C. In the homogenization treatment at a temperature of less than 500 ° C., the precipitation of Fe is excessively promoted and the solid solution amount of Fe is reduced. Softening occurs to reduce tensile strength, and also causes softening at low temperature heat treatment. If the temperature exceeds 580 ° C., there is a possibility that the Al—Fe-based crystallized product may be coarsened, and there is a risk that the coarsening of crystal grains and the rolling property of the foil may be deteriorated. In addition, at high temperatures, precipitation of Fe is not sufficient, and even if the foil is heat treated at 200 ° C. for 12 hours after final rolling, recrystallization does not occur and it is difficult to obtain high ductility. In addition, holding for less than 4 hours is not sufficient as homogenization treatment, and treatment for more than 16 hours is not meaningful from the viewpoint of foil characteristics and manufacturing cost. Therefore, it is desirable to set the conditions of the homogenization treatment in the above range. The lower limit of the more desirable temperature is 540 ° C., and the upper limit is 580 ° C.

Hot Roll Finishing Temperature: 280 ° C. or Less The finish temperature of hot rolling is preferably 280 ° C. or less in order to suppress recrystallization after winding as much as possible. If the temperature exceeds 280 ° C. after winding and rolling, there is a risk that partial recrystallization will occur and grain structure mixed with the non-recrystallized region. In such a case, there is a concern that the grain structure may become nonuniform after intermediate annealing and eventually after final rolling, and the ductility may be reduced.

Intermediate Annealing Condition The aluminum alloy of the present embodiment has good rollability, and intermediate annealing during cold rolling is not necessary, but may be performed if desired. There are two types of intermediate annealing: batch annealing in which the coil is placed in a furnace and held for a fixed time, and rapid heating and quenching of the material by a continuous annealing line (hereinafter referred to as CAL annealing). . In the case of intermediate annealing, any method may be used in the present invention, but CAL annealing is preferred if strength and elongation after rolling are important, and batch annealing is preferred if elongation after heat treatment at 200 ° C. is important. When employing batch annealing, it is desirable to carry out holding at 300 to 450 ° C. for 3 to 6 hours.

-Final cold rolling ratio: 98.2% or more It is known that grain division and refinement of aluminum alloy occur only by rolling (grain subdivision). Since the finer the crystal grain proceeds as the rolling ratio becomes higher, by setting the final cold rolling ratio during cold rolling to at least 98.2%, the distance between the grain boundaries in the thickness direction of the foil becomes narrow, Higher elongation properties can be obtained. In addition, the final cold-rolling rate here is a cold-rolling rate from the thickness at the time of intermediate annealing to the final thickness when performing intermediate annealing in a rolling process, and when not performing intermediate annealing, It is a cold rolling rate from the plate thickness immediately before cold rolling to the final thickness, and can be calculated by [{(plate thickness before rolling−plate thickness after rolling) / plate thickness before rolling} × 100]. For both single rolling and polymerization rolling, the final cold rolling reduction is preferably 98.2% or more.
As the final cold rolling reduction ratio increases, the tensile strength and the elongation of the produced aluminum alloy foil tend to simultaneously increase.

The rolling reduction during polymerization rolling: 10% to 50% When the rolling reduction is less than 10%, a good matte surface can not be obtained, and when it exceeds 50%, the surface roughness of the matte surface becomes significantly large, It causes a decrease in growth. The rolling reduction is a rolling reduction in one rolling pass.

In this case, since this aluminum alloy has good elongation characteristics, either single rolling or polymerization rolling can be employed.
The thickness of the aluminum alloy foil after final cold rolling is not particularly limited, but as described above, the thickness is preferably in the range of 6 μm to 30 μm (more preferably 10 μm to 30 μm).
According to the above steps, an aluminum alloy foil for a current collector of a lithium ion battery can be manufactured. In the case of a single-rolled foil, a double-sided glossy surface is obtained, but in the case of a polymerized rolled foil, one side is a glossy surface and the opposite surface is a matte surface. As for the unevenness | corrugation in the matte side of this polymerization rolling foil, 0.20 micrometer or less is preferable by arithmetic mean roughness Ra.
The aluminum alloy foil for a battery current collector manufactured as described above has improved rollability and high ductility before and after heat treatment.

  As mentioned above, although embodiment of the aluminum alloy foil for battery collectors concerning this invention was described, the above-mentioned embodiment is an example, Comprising: It can change suitably in the range which does not deviate from the range of this invention.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  An ingot of an aluminum alloy having the composition shown in Table 1 (remainder Al and unavoidable impurities) was cast by semi-continuous casting. The obtained ingot was homogenized, hot rolled and cold rolled to obtain an aluminum alloy foil having a final foil thickness of 12 μm each. What was intermediately annealed after hot rolling was also produced. The conditions of the homogenization treatment, hot rolling, intermediate annealing, and cold rolling were as shown in Table 1. In the case of polymerization rolling, after being rolled to a thickness of 17.2 μm by single rolling, two sheets were stacked and rolled (total thickness 34.4 μm) and rolled to a thickness of 24 μm. One foil has a thickness of 12 μm. The rolling reduction is 30%.

The following items, such as tensile strength and elongation, were measured about the produced aluminum alloy foil.
(Tensile strength · 0.2% proof stress · Elongation)
Mechanical properties were measured in accordance with JIS Z2241 by collecting a JIS No. 5 test piece from the sample and using a universal tensile tester (manufactured by Shimadzu Corporation) at a tensile speed of 2 mm / sec.
(Surface roughness)
The surface shape of the matte surface of one-side gloss foil obtained by polymerization rolling is measured using a stylus type surface roughness measuring device (manufactured by Tokyo Seimitsu Co., Ltd.) based on JIS B0633: 2001, and the definition of JIS B0601: 2001 Arithmetic mean roughness Ra was determined based on.

(Measurement of crystal grain size in thickness direction)
The RD-ND side of the aluminum alloy foil was cut by CP (cross section polisher), and the cut surface was analyzed by SEM-EBSD method. The entire thickness of the foil was observed at a magnification of × 2000, and when actually measuring the particle size, observation was performed at × 3000. In the obtained orientation mapping image, the grain size in the thickness direction of the foil was calculated by the line segment method from the grain map in which the grain boundary having an orientation difference of 15 ° or more was displayed. In addition, observation of × 3000 was performed in three fields of view with one sample, and the crystal grain size was taken as the average value.

(Average grain size and ratio of maximum grain size / average grain size)
After electrolytic polishing of the foil surface, crystal orientation analysis is performed by SEM (Scanning Electron Microscope) -EBSD, and crystal grain boundaries between crystal grains of 15 ° or more are defined as HAGBs (high angle grain boundaries), The size of the grain surrounded by HAGBs was measured. The field size of 45 × 90 μm was measured in three fields of view at a magnification of × 1000, and the average crystal grain size and the maximum grain size / average grain size were calculated. The grain size of each crystal was calculated using the equivalent circle diameter, and the Area method (Average by Area Fraction Method) of EBSD was used to calculate the average grain size. For analysis, OIM Analysis from TSL Solutions was used.
Table 2 shows the evaluation results for the single-rolled foil and Table 3 for the polymerized rolled foil.

  The aluminum alloy foils of the examples were confirmed to have excellent tensile strength and elongation. In addition, in any of the examples, the rollability was also good without breaking during rolling.

Claims (2)

Fe: 1.0 mass% or more and 1.8 mass% or less, Si: 0.01 mass% or more and 0.06 mass% or less, Cu: 0.006 mass% or more and 0.015 mass% or less, and the balance is has a composition of Al and inevitable impurities, tensile strength more than 180 MPa, elongation is 6.0% or more, Ri single rolled foil der spacing of the crystal grain boundary following 1.0μm thickness direction,
Tensile strength after heat treatment at 200 ° C for 12 hours is 100MPa or more, 0.2% proof stress is 60MPa or more, elongation is 14% or more, average grain size is 6μm or less, and maximum grain size / average grain size Aluminum alloy foil for battery current collector characterized in that diameter ratio is 3.0 or less .   Fe: 1.0 mass% or more and 1.8 mass% or less, Si: 0.01 mass% or more and 0.06 mass% or less, Cu: 0.006 mass% or more and 0.015 mass% or less, and the balance is A polymerized rolled foil having a composition of Al and unavoidable impurities, having a tensile strength of 180 MPa or more, an elongation of 5.0% or more, and a distance between crystal grain boundaries in the thickness direction of 1.0 μm or less,
  Tensile strength after heat treatment at 200 ° C for 12 hours is 100MPa or more, 0.2% proof stress is 60MPa or more, elongation is 12% or more, average grain size is 6μm or less, and maximum grain size / average grain size Aluminum alloy foil for battery current collector characterized in that diameter ratio is 3.0 or less.