JP2010150637A - Aluminum alloy foil for lithium ion battery electrode charge collector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum foil for a lithium ion battery electrode charge collector which has sufficient tensile strength upon the application of an active material, drying and rolling upon electrode production, and, by performing heat treatment at a relatively low temperature of ≤200°C after that, has sufficient elongation upon coiling of a positive electrode and a negative electrode and when being assembled into a battery as an electrode, and can prevent deterioration and fracture of the positive electrode even upon repetition of charging-discharging as a battery. <P>SOLUTION: The aluminum alloy foil has a composition containing 0.8 to 2.0% Fe and ≤0.02% Ti, wherein, as impurities, the content of Si is regulated to ≤0.15% and the content of Cu is regulated to ≤0.05%, and the balance Al with the other inevitable impurities, wherein the tensile strength is ≥160 MPa, and the electric resistance measured in liquid nitrogen by a double bridge process is ≤0.55 μΩcm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an aluminum alloy foil for a lithium ion battery electrode current collector, more specifically, an aluminum foil for a non-aqueous electrolyte secondary battery electrode (positive electrode) current collector, more specifically, application of an electrode active material during electrode production. Non-aqueous electrolyte secondary battery electrode (positive electrode) that has excellent cycle characteristics, is resistant to breakage when wound, and has excellent cycle characteristics against electrode deterioration and breakage due to expansion and contraction of the electrode due to charge and discharge after the battery is formed The present invention relates to an aluminum foil for a current collector.

  There are two types of lithium ion secondary batteries: a cylindrical type and a square type, both of which consist of an electrode plate group in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. Injected and sealed structure.

  As the positive electrode active material, a lithium cobalt composite oxide, a lithium nickel composite oxide, a lithium manganese composite oxide, a lithium titanium composite oxide, or a mixed product obtained by combining several kinds of the positive electrode active materials is used. Carbon materials that can adsorb and desorb lithium ions such as coke and graphite are used.

  These positive electrode active materials or negative electrode active materials are prepared by adding a binder and, if necessary, a conductive agent and a solvent such as acetylene black and graphite, stirring and mixing them, and forming a kneaded material such as aluminum or copper. Lithium ion secondary battery is applied to a current collector made of foil, dried, rolled, heat treated during or before and after rolling to improve the binding force, and cut into a predetermined size to form a sheet. (Refer to Patent Document 1).

With respect to the aluminum foil for the positive electrode current collector, by using an aluminum foil having an elongation rate of 3% or more in the winding direction after being charged one or more times, the negative electrode active material is repeatedly expanded and contracted. It has been proposed to improve the cycle characteristics by preventing the positive electrode from being deteriorated or broken during the charge / discharge cycle (see Patent Document 2).
JP 2007-234277 A JP 2006-134762 A

  However, when an aluminum foil having an elongation of 3% or more is used, it is necessary to have a tensile strength that can withstand rolling after applying an active material and drying, and in order to ensure the elongation, the thickness of the foil is increased. There is a problem that the capacity of the battery is reduced.

  The present invention has been made to solve the above-mentioned problems, and its purpose is to have a sufficient tensile strength at the time of application, drying and rolling of an active material during electrode production, and thereafter a comparison of 200 ° C. or lower. When the positive electrode and the negative electrode are wound through the separator and further incorporated into the battery as an electrode, the positive electrode has a sufficient extension and is repeatedly charged and discharged as a battery. It is an object of the present invention to provide an aluminum foil for a lithium ion battery electrode current collector that can prevent deterioration and breakage of the battery and can make the cycle life of the battery sufficient.

  An aluminum alloy foil for a lithium ion battery electrode current collector according to claim 1 for achieving the above object contains Fe: 0.8 to 2.0%, Ti: 0.02% or less, It is an aluminum alloy foil comprising Si and 0.15% or less, Cu and 0.05% or less, the balance Al and other inevitable impurities, the tensile strength is 160 MPa or more, in liquid nitrogen by the double bridge method The measured electric resistance is 0.55 μΩcm or less.

  The aluminum alloy foil for a lithium ion battery electrode current collector according to claim 2 is characterized in that, in claim 1 or 2, the aluminum alloy foil further contains Mn: 0.05% or less.

  The aluminum alloy foil for a lithium ion battery electrode current collector according to claim 3 is characterized in that in any one of claims 1 to 3, the thickness is 10 to 30 μm.

  According to the present invention, it is excellent in the application property of the electrode active material at the time of electrode production, has sufficient tensile strength at the time of application, drying and rolling of electrode production, and then heat-treated at a relatively low temperature of 200 ° C. or less. Thus, when the positive electrode and the negative electrode are wound through the separator, and further assembled into the battery as an electrode, the electrode has sufficient extension, is not easily broken, and the electrode expands even when charging and discharging are repeated as the battery. Provided is an aluminum alloy foil for a lithium ion battery electrode current collector, which can prevent electrode deterioration and breakage due to shrinkage and can make the cycle life of the battery sufficient.

  By using the aluminum alloy foil for a lithium ion battery electrode current collector according to the present invention, the production yield is improved and a nonaqueous electrolyte secondary battery having a sufficient cycle life can be produced.

The significance and reasons for limitation of the alloy components in the aluminum alloy foil of the present invention will be described.
Fe functions to improve strength. The preferable content of Fe is in the range of 0.8 to 2.0%, and if it is less than 0.8%, sufficient tensile strength cannot be ensured. A local battery is formed between them, and the corrosion reaction proceeds and the corrosion resistance decreases. A more preferable content of Fe is 1.2 to 1.7%, and a more preferable content is 1.4 to 1.6%.

  Ti refines the crystal grains of the aluminum alloy foil. The preferable content of Ti is in the range of 0.02% or less, and if it exceeds 0.02%, it may cause pinholes in the aluminum alloy foil. B can be added together with Ti to obtain the same effect. For the same reason, the content of B in the aluminum alloy foil is preferably 0.01% by weight or less.

  Although Si is contained as an impurity, if the Si content is large, a compound containing Si or simple substance Si is precipitated and recrystallization is promoted too much, and the crystal grain size becomes coarse and the generation of pinholes increases. Since a local battery is formed with the Al component and the corrosion reaction proceeds and the corrosion resistance is lowered, the content is preferably regulated to 0.15% or less. More preferably, it is 0.08% or less.

  Cu is an element that improves the strength. However, when the Cu content is large, the amount of solid solution Cu increases, and the Al-Fe compound that cannot be solid solution precipitates rapidly in the cold rolling process. Since the average crystal grain size of the alloy foil is increased and the number of pinholes in the aluminum alloy foil is increased, it is preferably regulated to 0.05% or less. More preferably, the content is 0.01% or less.

  Mn functions to improve strength, but if it exceeds 0.05%, a coarse Al—Fe—Mn intermetallic compound is likely to be formed, and pinholes are likely to be generated. The content is 0.01% or less.

  In addition to Fe, Ti, B, Si, Cu, Mn, and Al, the aluminum alloy foil contains inevitable impurities such as Mg, Zn, Ga, Ni, Cr, Sn, Pb, and V. The contents of Zn, Ga, Ni, Cr, Sn, Pb, and V are each preferably 0.02% or less, and more preferably 0.01% or less. As for Mg, when the content increases, Mg concentrates at the interface between the aluminum base and the aluminum oxide film to form an MgO layer. This MgO layer becomes a weak boundary layer and adheres to the aluminum alloy foil. In order to reduce the property, the content is preferably limited to 0.005% or less. More preferably, it is 0.003% or less.

  The aluminum alloy foil of the present invention needs to have an electric resistance of 0.55 μΩcm or less. This is because a large number of fine Al—Fe intermetallic compounds are dispersed in the aluminum alloy foil to improve crystal grain refinement and strength, and at least 3% by heat treatment at a relatively low temperature of 200 ° C. or less. This is to obtain a large growth. In order to obtain a larger elongation, the electric resistance is more preferably 0.50 μΩcm or less.

  The electrical resistance is measured by forming a foil thickness x 3 mm width x 230 mm length, preparing a sample, measuring the thickness with a micrometer, spot welding the four terminals, and then using the double bridge method in liquid nitrogen After measuring the resistance, the specific resistance (electrical resistance) is calculated.

  The aluminum alloy foil of the present invention also needs to have a tensile strength of 160 MPa or more. This is because the active material is applied to the aluminum alloy foil and dried, and then the active material is peeled off by plastic deformation of the foil in a press-bonding process with a roll press for the purpose of improving the density of the active material and adhering to the current collector. This is to prevent the occurrence of.

  Moreover, in the said aluminum alloy foil, the thickness is 10-30 micrometers normally. For a lithium ion battery electrode current collector, the thickness is more preferably 10 to 15 μm.

  The surface roughness Ra of the aluminum alloy foil is preferably 0.08 to 0.30 μm. If the surface roughness Ra is large, pinholes are likely to occur in the aluminum alloy foil, and if the surface roughness Ra is small, the adhesion of the kneaded material such as the active material, binder, conductive agent and solvent decreases. To do. The surface roughness Ra of the aluminum alloy foil is more preferably 0.12 to 0.25 μm.

  The surface roughness Ra is measured in accordance with JIS B0601-2001. Specifically, the surface roughness Ra in the width direction of the aluminum alloy foil is arbitrary in the width direction on the surface of the aluminum alloy foil. The surface roughness Ra of 5 points is measured and the average value is referred to.

In addition, if the removal of oil such as rolling oil on the aluminum alloy foil surface is insufficient, not only the adhesion of the kneaded material is lowered, but also when the battery is repeatedly charged and discharged, the active material layer (electrode Since the adhesion between the mixture layer) and the final electrode is reduced, the residual oil content is preferably 140 μg / m ² or less.

  The aluminum alloy foil of the present invention is produced by subjecting an ingot of aluminum alloy having a predetermined composition to homogenization treatment, hot rolling, cold rolling, and final annealing as necessary. Rolling oil remains on the surface of the aluminum alloy foil after rolling, and rolling oil components such as mineral oil, fatty acid, and ester are detected. The remaining state of the rolling oil on the foil surface can be classified into adhering oil located in the outer layer portion of the aluminum surface and adsorbed oil located in the inner layer portion and having a very high bonding force with the aluminum substrate. Adhering oil is an oil component that dissolves in hexane, and adsorbed oil can be defined as oil that remains even if the oil on the foil surface is extracted with hexane.

The extraction method of adsorbed oil is performed as follows.
A surface area of about 400 cm ² of foil is immersed in 80 ml of hexane (5000-fold concentrated assay product) and subjected to ultrasonic cleaning for 20 minutes. Add 90 ml of distilled water, 30 ml of hexane and 30 ml of 6N hydrochloric acid (hexane-washed hydrochloric acid) to the foil after extraction with hexane, and let stand until the decomposition reaction of aluminum stops, and then add 10 ml of 6N hydrochloric acid until the foil surface is completely decomposed. put. Next, 40 ml of distilled water is added, and the hexane extract is transferred to a 100 ml beaker with a glass dropper, heated and evaporated until the extract reaches about 20 ml, and further evaporated to about 5 ml at room temperature. Then, it concentrate | evaporates under reduced pressure with a suction desiccator, hexane is evaporated completely, and foil surface adsorption | suction substance is obtained. This is dissolved in 100 μl of hexane, and 4 μl thereof is injected into a gas chromatograph. Gas chromatographic analysis conditions are as follows.
Equipment: GC-14B made by Shimadzu
Column: G column G-205 40m
Column temperature: 70 ° C. → 270 ° C. 10 ° C./min 10 min holding Detector: FID
Detector temperature: 320 ° C
Inlet temperature: 320 ° C
Carrier gas: N2 30ml / min
RANGE: 101 ATT5

Below, the manufacturing method of the aluminum alloy foil of this invention is demonstrated.
An aluminum alloy having the above composition is melted and ingot-formed by a known semi-continuous casting method. In order to set the electric resistance of the aluminum alloy foil to 0.55 μΩcm or less and ensure the strength, the obtained ingot is homogenized to finely precipitate the dissolved alloy elements. The homogenization treatment is preferably held at a temperature of 460 to 520 ° C. for 8 to 20 hours. If the temperature is lower than 460 ° C. or shorter than 8 hours, the homogenization treatment is insufficient, and if it exceeds 520 ° C., sufficient precipitation cannot be obtained. Moreover, the effect does not change even if the homogenization treatment is performed over 20 hours.

  Subsequently, hot rolling is performed. The hot rolling further promotes fine precipitation of Fe during hot working, makes the electric resistance of the aluminum alloy foil 0.55 μΩcm or less, and further ensures strength and sufficient elongation after low-temperature heat treatment. It is preferred to start at 450 ° C and end at 200-250 ° C. After hot rolling, it is wound up as a coil.

  In addition, after hot rolling, cold rolling at a working degree of 40 to 60% is performed to introduce a working strain that becomes a precipitation site, and then the first intermediate annealing is performed, and then cold rolling is performed and the second intermediate annealing is performed. The intermediate annealing conditions are preferably 300 to 400 ° C. for 1 to 5 hours in both the first and second rounds.

  In hot-rolled coils after hot rolling, both precipitation and structure are non-uniform. If cold rolling is performed as it is, non-uniform precipitation is likely to occur and it is difficult to obtain uniform structure. When this is continued, pinholes are likely to occur in the non-uniform tissue portion.

  In the present invention, after hot rolling, cold rolling with a work degree of 40 to 60% is performed, and then intermediate annealing is performed. It is preferable to cold-roll as soon as possible after hot rolling and to perform intermediate annealing. When cold rolling exceeding 60% is performed after hot rolling and intermediate annealing is performed, the formed non-uniform cold rolling structure is difficult to homogenize. After the hot rolling, cold rolling with a work degree of 40 to 60% is performed, then the first intermediate annealing is performed to perform cold rolling, the second intermediate annealing is performed, and further cold rolling and foil are performed. By rolling, the amount of precipitation is large, and dislocations are introduced uniformly by processing, so that the precipitation form becomes fine and uniform.

  The tensile strength of the aluminum alloy foil that has undergone the above steps is 160 MPa or more. Further, by performing a low-temperature heat treatment at 170 ° C. for 5 minutes, a large elongation of 3% or more is obtained even for a foil having a thickness of about 15 μm. be able to.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects of the present invention. These examples show one embodiment of the present invention, and the present invention is not limited thereto.

Example 1 and Comparative Example 1
Aluminum alloys having compositions A to K shown in Table 1 were melted, and a slab having a thickness of 500 mm was ingoted at a casting speed of 40 mm / min by a DC casting method. The obtained slab was homogenized at 480 ° C. for 12 hours, and then hot rolled at a start temperature of 400 ° C. and an end temperature of 250 ° C. to obtain a plate having a thickness of 4 mm.

  Subsequently, cold rolling was repeated a plurality of times on the hot rolled sheet to obtain an aluminum alloy foil having a thickness of 15 μm. During the cold rolling, when the plate thickness is 2 mm, the first intermediate annealing is performed at 300 ° C. for 2 hours, and when the plate thickness is 0.5 mm, the second annealing is performed at 300 ° C. for 2 hours. A second intermediate annealing was performed.

  The obtained aluminum alloy foil was measured for tensile strength and electrical resistance, and further subjected to low-temperature heat treatment at 170 ° C. for 5 minutes, and then measured for tensile strength and elongation. The measurement results are shown in Table 2. In Tables 1 and 2, those outside the conditions of the present invention are underlined.

  As shown in Table 2, each of the test materials 1 to 5 according to the present invention has an electrical resistance value of 0.55 μΩcm or less, a tensile strength of 160 MPa or more, and elongation after low-temperature heat treatment at 170 ° C. for 5 minutes. 3% or more, it had excellent characteristics as an aluminum alloy foil for lithium ion battery electrodes.

  On the other hand, the test material 6 had a low strength because the Fe content was small, and the test material 7 had a high Fe content, resulting in a decrease in foil rollability and an increase in pinholes. Since the test material 8 had a large amount of Si, the crystal grains were coarse and the occurrence of pinholes increased.

  Since the test material 9 had a large amount of Mn, the occurrence of pinholes increased. Since the test material 10 had a large amount of Cu, the crystal grains were coarse and many pinholes were generated, the electrical resistance value increased, and the elongation after the low-temperature heat treatment was insufficient.

Comparative Example 2
The aluminum alloy slab formed in Example 1 and having the composition of A in Table 1 was homogenized at 480 ° C. for 12 hours, and then hot-rolled at a start temperature of 480 ° C. and an end temperature of 280 ° C. to obtain a thickness A 4 mm plate was obtained.

  Subsequently, the hot rolling was repeatedly subjected to cold rolling a plurality of times to obtain an aluminum alloy foil having a thickness of 15 μm. In the middle of the cold rolling process, when the plate thickness is 2 mm, the first intermediate annealing is performed at 300 ° C. for 2 hours, and when the plate thickness is 0.5 mm, the first annealing is performed at 300 ° C. for 2 hours. A second intermediate annealing was performed.

  The obtained aluminum alloy foil was measured for tensile strength and electrical resistance in the same manner as in Example 1, and further measured for tensile strength and elongation after low-temperature heat treatment at 170 ° C. for 5 minutes. Table 3 shows the measurement results. In Table 3, those outside the conditions of the present invention are underlined.

  As shown in Table 3, since the test material 11 has a high hot rolling start temperature and end temperature, Fe fine precipitation is insufficient, electric resistance exceeds 0.55 μΩcm, strength and after low temperature heat treatment It was not possible to secure sufficient elongation.

Claims (3)

Fe: 0.8-2.0% (mass%, the same shall apply hereinafter), Ti: 0.02% or less (not including 0%, the same shall apply hereinafter), Si as an impurity being 0.15% or less, An aluminum alloy foil comprising Cu of 0.05% or less, the balance being Al and other inevitable impurities, having a tensile strength of 160 MPa or more and an electric resistance of 0.55 μΩcm measured in liquid nitrogen by the double bridge method An aluminum alloy foil for a lithium ion battery electrode current collector, characterized by: 3. The aluminum alloy foil for a lithium ion battery electrode current collector according to claim 1, wherein the aluminum alloy foil further contains Mn: 0.05% or less (excluding 0%, the same applies hereinafter). . The aluminum alloy foil for a lithium ion battery electrode current collector according to any one of claims 1 to 3, wherein the thickness is 10 to 30 µm.