Aluminium alloy foil

Abstract

The invention concerns a rolled battery electrode foil of an aluminium alloy comprising 0.06 – 0.16 wt% Si, 0.41-1.0 wt% Fe, ≤0.25 wt% Cu, ≤0.10 wt% Mn, ≤ 0.03 wt% Mg, ≤0.05 wt% Zn, 0.001-0.030 wt% Ti, ≤0.05 wt% each and ≤0.15 wt% in total of impurities, balance Al, having a thickness from 10 to 25 µm, and when measured after heat treatment of the aluminium foil at 120°C for 2 minutes having a tensile strength of at least 190 MPa and an elongation of at least 3%. The invention further concerns a process for the production of a battery electrode foil, an electrode for a secondary battery, and a secondary battery.

Description

[0001] ALUMINIUM ALLOY FOIL

[0002] The present invention relates to a battery electrode foil of an aluminium alloy having high strength and elongation, and having high thermal stability. The invention further relates to a process for the production of a battery electrode foil, an electrode for a secondary battery, and a secondary battery.

[0003] Secondary batteries with non-aqueous electrolyte, such as lithium ion batteries, are widely used in various applications, like in electronic equipment, power tools, electric vehicles, and grid storage. In lithium ion batteries the cathode is usually made of a thin aluminium alloy foil coated on both sides with active cathode material. The aluminium alloy foil acts as a current collector and is very thin, usually less then 25 pm thick. In other types of batteries also the current collector for the anode may be made of aluminium. The production of a cathode for a lithium ion battery involves coating of the aluminium alloy foil with active material, followed by drying at elevated temperature, e.g. 100-180°C, and finally calendering to compress the material. The cathode is then stacked together with an anode a separator and electrolyte, and wound or folded to form a battery cell that finally is packed, e.g. in a cylindrical or prismatic casing, or in a pouch.

[0004] To avoid breaking of the aluminium alloy foil during the production of the battery it must have high strength and high elongation. However, both strength and elongation usually decreases when the foil is exposed to elevated temperature during the drying step, which can cause problem with ruptures during the following calendering and winding or folding.

[0005] US9847530B2 discloses an aluminium foil for an electrode current collector having the composition of 0.03 to 1 .0% of Fe, 0.01 to 0.2% of Si, 0.0001 to 0.2% of Cu, 0.005 to 0.03% of Ti, with the rest being Al and unavoidable impurities. The foil is produced by continuous casting followed by cold rolling to final gauge without any heat treatment. The purpose is to obtain high strength, but the problem of elongation is not dealt with.

[0006] US9947917B2 discloses aluminium alloy foil for a current collector of an electrode, containing 1.0 to 2.0% of Fe, 0.01 to 0.2% of Si, 0.0001 to 0.2% of Cu, and 0.005 to 0.3% of Ti, the remainder being Al and inevitable impurities. The foil is produced by continuous casting followed by cold rolling to final gauge without any heat treatment. The purpose is to obtain high strength, but the problem of elongation is not dealt with.

[0007] US10916357B2 discloses an electrode current collector comprising an aluminium foil consisting of 0.03 to 1 .0% of Fe, 0.01 to 0.2% of Si, 0.0001 to 0.2% of Cu, Al, and unavoidable impurities. The foil is produced by continuous casting followed by cold rolling to a cold rolling reduction of 80% or lower, performing heat treatment at 550 to 620°C for 1 to 15 hours, and cold rolling to final gauge. The purpose is to obtain high strength and conductivity, but the problem of elongation is not dealt with. US10050257B2 discloses an electrode current collector formed by applying an active material on an aluminium alloy foil obtained by final cold rolling of an aluminium alloy obtained by subjecting an aluminium alloy ingot, comprising 0.1 to 1.0 mass% of Fe, 0.01 to 0.5 mass% of Si, and 0.01 to 0.2 mass % of Cu, with the rest consisting of Al and unavoidable impurities, to a homogenizing treatment at 550°C to 620°C for 3 to 6 hours, followed by a hot rolling with a starting temperature of 500°C to 550°C and an end-point temperature of 255°C to 300°C, and a cold rolling. The purpose is to obtain high strength and conductivity are obtained, but the problem of elongation is not dealt with.

[0008] DE112013005772T5 discloses an aluminium alloys foil comprising 0.1 to 0.6% wt% Si, 0.2 to 1.5 wt% Fe, and rest aluminium and unavoidable impurities, wherein the sum of Si content and Fe content is 0.48 wt% or more. The purpose is to obtain high strength, but the thermal stability is not dealt with. Further, production of the foil requires hot rolling of an ingot at a temperature of 350°C or lower, which is very difficult to do in practice without causing cracks in the material.

[0009] CN114277286A discloses an aluminium alloy foil for lithium batteries comprising 0.01-0.25% Si, 0.08 to 0.4% Fe; 0.01 to 0.05% Cu, <0.02% Mn, <0.04% Zn, <0.04% Ti, rest Al. The foil is produced by continuous casting and rolling at a speed of 950 mm / min to a thickness of 7 mm, followed by cold rolling. To obtain satisfactory mechanical properties, intermediate annealing for 27-35 hours is necessary.

[0010] W02012008567A1 discloses an aluminium foil for a battery current collector comprising 0.2 to 1.3 wt% Fe, 0.01 to 0.5 wt% Cu, 0.2 wt% or less Si, the balance being Al and unavoidable impurities. The foil is produced by casting an ingot followed by homogenisation, hot rolling and cold rolling, with intermediate continuous annealing. The purpose is to obtain a certain degree of strength, excellent elongation, and low electrical resistance, but the problem of thermal stability is not dealt with.

[0011] US4000009A discloses a process of producing a wrought sheet of aluminium alloy of the composition 0.085% Si, 0.365% Fe, 0.034% Cu, 0.02% Ti, 0.0050% B, and the remainder being aluminium. The production involves continuously casting molten alloy to form a sheet, heating the continuously cast sheet to a temperature in the range of approximately 480-620°C, cooling at a rate of not more than 333°C per hr, followed by cold reduction and annealing. Foils for battery electrodes are not dealt with.

[0012] CN104388766A discloses a production method of aluminium foil for lithium-ion batteries, wherein the weight percentage of the ingredients is Al >99.35%, Si 0.05-0.12%, Fe 0.35-0.45%, Cu 0.02-0.03%, Mn 0.005%, Mg 0.001%, Zn 0.023%, Cr 0.001%, T i0.015%, Mg, Mn, Zn, Cr and other trace elements are controlled according to the control standards of pure aluminium ingots. A strip is produced in a horizontal continuous casting and rolling machine at a speed of 1050-1100 mm / min and after three passes it is rolled to 6-7 mm. The strip is then cold rolled, followed by intermediate heat treatment for complete recrystallisation annealing (O temper). The annealed strip is then cold rolling and foil rolled. The mechanical properties are not disclosed and the problem of thermal stability is not dealt with. It has been found difficult to combine all mechanical requirements for a battery electrode foil, particularly for aluminium alloys having satisfactory electric conductivity and being possible to produce without coil breaks or other problems at rolling. Therefore, an object of the invention is to provide an AAlxxx or AA8xxx aluminium alloy foil combining high tensile strength and high elongation with thermal stability. It is a further object of the invention to provide an aluminium alloy foil that can be produced efficiently.

[0013] The invention concerns a rolled battery electrode foil of an aluminium alloy (hereinafter aluminium alloy foil) comprising 0.06 -0.16 wt% Si, 0.41-1.0 wt% Fe, <0.25 wt% Cu, <0.10 wt% Mn, < 0.03 wt% Mg, <0.05 wt% Zn, 0.001-0.030 wt% Ti, <0.05 wt% each and <0.15 wt% in total of impurities, balance Al. As rolled, the aluminium alloy foil has a thickness from 10 to 25 pm, preferably from 10 to 16 pm. When measured after heat treatment of the aluminium foil at 120°C for 2 minutes the tensile strength is at least 190 MPa and the elongation at least 3%.

[0014] The invention further concerns a process for the production of a battery electrode foil comprising continuous casting, preferably twin roll casting, an aluminium alloy with the above composition to obtain a sheet, preferably 0.5 -14 mm thick directly after casting, cold rolling the cast sheet to an intermediate thickness, preferably 0.05-3 mm thick, annealing the sheet at the intermediate thickness (also referred to as intermediate annealing) at a temperature of 150-320°C for 2-15 hours, cold rolling the annealed sheet to obtain a foil having final thickness of 10-25 pm, wherein no heat treatment leading to complete recrystallisation takes place after the continuous casting. Any such heat treatment preferably does not exceed 320°C.

[0015] Preferably, the tensile strength of the aluminium alloy foil when measured after heat treatment of the aluminium foil at 160°C for 2 minutes is at least 100% of the tensile strength as rolled.

[0016] As rolled the aluminium alloy foil preferably has a tensile strength of at least 190 MPa, most preferably at least 250 MPa, particularly most preferably at least 290 MPa. Preferably the tensile strength when measured after heat treatment of the aluminium foil at 120°C for 2 minutes is at least 100%, most preferably at least 110%, particularly most preferably at least 120% of the tensile strength as rolled. When measured after heat treatment of the aluminium foil at 160°C for 2 minutes the tensile strength is preferably at least at least 100%, most preferably at least 110%, of the tensile strength as rolled. Preferably, the tensile strength of the aluminium alloy foil as rolled and when measured after heat treatment of the aluminium foil at 120°C or 160°C does not exceed 350 MPa.

[0017] As rolled the aluminium alloy foil preferably has an elongation of at least 3%, most preferably at least 4%, particularly most preferably at least 4.5%. Preferably the elongation when measured after heat treatment of the aluminium foil at 120°C for 2 minutes is at least 3.5%, most preferably at least 4%. When measured after heat treatment of the aluminium foil at 160°C for 2 minutes the elongation is preferably at least 2%, most preferably at least 2.5%, particularly most preferably at least 3%. Preferably, the elongation of the foil as rolled and after heat treatment at 120°C or 160°C does not exceed 15%.

[0018] As rolled, the area weighted average equivalent circle diameter of the grains projected in the cross section transverse to the rolling direction of the aluminium foil, is not more than 2.4 pm, most preferably not more than 2.3 pm. In most cases the average equivalent circle diameter of the grains is at least 0.35 pm or at least 0.5 pm. The threshold for determining a grain boundary is a difference in orientation of at least 10°.

[0019] As rolled, the area weighted average equivalent circle diameter of the sub-grains projected in the cross section transverse to the rolling direction of the aluminium foil, is not more than 0.9 pm, most preferably not more than 0.8 pm. In most cases the average equivalent circle diameter of the grains is at least 0.1 pm or at least 0.2 pm. The threshold for determining a sub-grain boundary is a difference in orientation of at least 2°.

[0020] The average circle diameter is preferably measured using EBSD (electron backscatter diffraction) and any commercially available software suitable for the purpose.

[0021] It has been found that small grains and small sub-grains improves the mechanical properties of the aluminium foil.

[0022] As rolled the aluminium foil preferably has a volume fraction of Cu texture {112}< 111> of at least 20%, such as 20-50%, most preferably at least 22%, as measured by EBSD. A texture is identified as having a deviation of at most 11 ° from the ideal orientation.

[0023] The term “as rolled” as used herein refers to when the aluminium alloy foil has been rolled to its the final thickness but not undergone any further heat treatments, which in most cases is the condition of the foil when the process for coating the foil with active electrode material is started.

[0024] Unless otherwise specified all parts and percentages refer to parts and percent by weight.

[0025] The operator “<” as used herein refers to less than or equal to, and includes zero.

[0026] The texture and the grain size, as well as the mechanical properties like tensile strength and elongation, can be measured as described in the Examples herein.

[0027] The function of the various elements in the aluminium alloy are as follows: Si increases the strength of the aluminium alloy foil, while too high amounts of Si leads to large intermetallic particles and risk for pinholes. With too high content of Si it is also difficult to obtain high elongation. The content of Si in the aluminium alloy is preferably 0.06-0.13 wt%.

[0028] Fe increases the strength of the aluminium alloy foil, while to high amounts of Fe leads to coarse intermetallic particles and risk for pinholes. The content of Fe in the aluminium alloy is preferably 0.45-1.0 wt%, most preferably at least 0.460 wt% or at least 0.50 wt%, such as 0.460-1.0 wt% or 0.50-0.90 wt%, particularly most preferably 0.55-0.85 wt%.

[0029] Cu increases the strength of the aluminium alloy foil, while too high amounts of Cu leads to extensive work hardening at cold rolling and low elongation, at the same time as the risk for coil breaks increases. The content of Cu in the aluminium alloy is preferably 0.05-0.20 wt%, most preferably 0.10-0.19 wt%.

[0030] Zn increases the strength of the aluminium foil to some extent, but too high amounts of Zn lowers the corrosion potential, making the foil sensitive to corrosion and may also affect the operation of the battery. The content of Zn in the aluminium alloy is preferably 0.01-0.04 wt%, most preferably 0.02-0.04 wt%.

[0031] Ti is included as a grain refining agent, which reduces the risk for cracks. Too high amounts of Ti leads to coarse intermetallic particles and risk for pinholes. The content of Ti in the aluminium alloy is preferably 0.005-0.025 wt%, most preferably 0.010-0.020 wt%.

[0032] Small amounts of Mn increases the strength of the aluminium alloy foil, but too high amounts thereof lowers the electrical conductivity. The content of Mn in the aluminium alloy is preferably 0.001-0.07 wt%, most preferably 0.01-0.05 wt%.

[0033] Mg increases the hardness of the aluminium alloy foil and must not be included in too high amounts as it leads to low elongation and risk for coil breaks and other problems at rolling. The content of Mg in the aluminium alloy is preferably <0.02 wt%, most preferably <0.01 wt%.

[0034] Other elements may be included as impurities in an amount of <0.05 wt% each and <0.15 wt% in total. Preferably, the content of impurities in the aluminium alloy is <0.02 wt% each and <0.15 wt% in total.

[0035] One aspect of the invention relates to a foil of an AAlxxx aluminium alloy comprising 0.06 -0.16 wt% Si, 0.41-0.85 wt% Fe, 0.05-0.20 wt% Cu, 0.001-0.05 wt% Mn, < 0.03 wt% Mg, <0.05 wt% Zn, 0.005-0.030 wt% Ti, <0.05 wt% each and <0.15 wt% in total of impurities, balance Al.

[0036] Another aspect of the invention relates to a foil of an AA8xxx aluminium alloy comprising 0.06 - 0.16 wt% Si, 0.70-1.0 wt% Fe, <0.02 wt% Cu, 0.001-0.05 wt% Mn, < 0.01 wt% Mg, <0.03 wt% Zn, 0.001-0.030 wt% Ti, <0.05 wt% each and <0.15 wt% in total of impurities, balance Al. The aluminium alloy foil as rolled preferably has an electrical conductivity of at least 50% IACS, most preferably at least 55% IACS.

[0037] The aluminium alloy foil as rolled is preferably in a Hlx temper, such as H14, H16, H18, or H19, most preferably H18. This is achieved by not performing any heat treatment after completed cold rolling to its final thickness.

[0038] The aluminium alloy foil is preferably produced in a process involving continuous casting, most preferably twin roll continuous casting to a sheet. The thickness of the sheet directly after casting is preferably 1-10 mm, most preferably 3-5.8 mm. The casting speed is preferably 1200-2000 mm / min, most preferably 1400-1700 mm / min. Low thickness and high casting speed leads to high cooling rate, which is favourable in respect of maintaining high content of Fe in solid solution. The process preferably further comprises steps as described herein.

[0039] Compared to semi-continuous casting to an ingot, the cooling rate in continuous casting, particularly twin roll casting, is much higher. The cooling rate from 690°C to 120°C is preferably 350-700°C / s, most preferably 400-600°C / s. This affects the micro-structure, for example by increasing the number of intermetallic particles of an equivalent circle diameter within the range of 0.1-1 pm. Continuous casting with high cooling rate also facilitates higher amounts of Fe and Si in solid solution, which has been found to increase the thermal stability.

[0040] Intermediate annealing is most preferably performed at a thickness of 0.05-2 mm, particularly most preferably 0.2-2.4 mm. The cold rolling before the intermediate annealing is preferably done with a thickness reduction of 40-99%, most preferably 50-96%. The cold rolling after the intermediate annealing is preferably done with a thickness reduction of 75-99.8%, most preferably 88-99.7%.

[0041] The intermediate annealing temperature is preferably at 190-300°C, most preferably at 200- 290°C or 200-275°C. The time for the intermediate annealing is preferably 2-10 hours, most preferably 3-9 hours. It has been found that omission of intermediate annealing leads to coil breaks at rolling as well as poor thermal stability, i.e. insufficient tensile strength or elongation after heat treatment at 120°C and 160°C.

[0042] In contrast to high temperature annealing, the intermediate annealing is performed within a temperature range that does not result in recrystallisation of the aluminium alloy, but rather in stress relief.

[0043] To avoid recrystallisation after the continuous casting the aluminium alloy is preferably not subjected to any heat treatment exceeding 310°C, more preferably not exceeding 300°C, most preferably not exceeding 290°C, particularly most preferably not exceeding 275°C. It has been found that heat treatment at too high temperature leads to poor thermal stability in respect of tensile strength and elongation. Avoiding recrystallisation has been found to improve the thermal stability of the aluminium foil. High amount of Fe in solid solution, which is favoured by high cooling rate after casting, enables heat treatment at higher temperature without recrystallisation. A high degree of cold reduction before heat treatment lowers the temperature at which recrystallisation occurs.

[0044] An aluminium alloy foil according to the invention has been found to have a fine and uniform grain structure throughout the material, at the surface as well as in the centre of the foil. It has been found that a combination of high tensile strength and high elongation, as well as thermal stability then can be obtained.

[0045] The invention also concerns an electrode for a secondary battery comprising a current collector of an aluminium alloy foil as described herein and a coating on both sides of the foil with an active electrode material. The coating may, for example, be 5-150 pm thick on each side. The electrode is preferable a cathode in a secondary battery, such as a lithium ion battery or a sodium ion battery. The active electrode material, particularly cathode material, may include various materials, such as lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminium oxide (NCA), lithium iron phosphate (LFP), lithium titanate (LTO), and others known in the art, optionally in combination with an intermediate carbon coating.

[0046] The invention finally concerns a secondary battery, particularly lithium ion battery or sodium ion battery, comprising an anode, a cathode, a non-aqueous electrolyte, and a separator, wherein a least one of the anode or the cathode is an electrode as described herein. The anode, the cathode, the separator and the electrolyte are preferably stacked, folded or wound into a package that is placed into a hard casing like prismatic or cylindrical casing, or a soft casing like a pouch type packaging material.

[0047] Examples

[0048] Foils of aluminium alloys having compositions according to Table 1 were prepared from a melt of about 700°C by continuous twin roll casting at a speed of 1470-1600 mm / min to obtain sheets with a thickness of about 5.6 mm directly from the casting rolls, giving a cooling rate of approximately 450 °C / s down to around 120°C. The sheets were then cold rolled and processed as set out in Table 2, where “H” means temperature and time for homogenisation (if any), “IA” means temperature and time for intermediate annealing (if any), “IA Gauge” means the thickness in mm at which intermediate annealing (if any) took place, “Final Gauge” means the final thickness in mm after completed cold rolling, and “Coil Break” indicate whether there was one or more coil breaks during the cold rolling. When homogenisation was performed, this was done after cold rolling to a thickness of 2.4 mm, except for trial No. 6 where the homogenisation took place at a thickness of 3.05 mm. Samples from trials No. 6-12 and 14-25 were examined by EBSD (Electron Backscatter Diffraction) to determine the texture and grain size expressed as equivalent circle diameter (ECD). The samples were fixed by metal clamps and prepared by mechanical polishing at room temperature. The SEM was operated with a magnification of 1000x, a voltage of 10 kV and a step size 0.1 pm. The fraction of the texture components Cu {112}<111>, S {123}<634>, and Brass {011 }<211> were determined, applying a deviation from the ideal orientations of 11 °. The area weighted equivalent circle diameter (ECD) of the grains and the sub-grains projected in the cross section transverse to the rolling direction where determined, applying a threshold for grain boundaries of 10° difference in orientation and for sub-grain boundaries 2° difference in orientation. The results are shown in Table 3.

[0049] Samples of each foil were tested in respect of tensile strength (UTS) and elongation as rolled (“AR”), after heat treatment at 120°C for 2 minutes, and after heat treatment at 160°C for 2 minutes. The tensile and elongation tests were performed on 0.5” (12.7 mm) wide longitudinal parallel samples with a preload of 0.5 mm / min crosshead speed until 0.22 N and testing speed of 5 mm / min crosshead speed. The heat treatments at 120°C and 160°C, respectively, simulate a drying step in the production of an electrode and were performed in an oil bath where samples wrapped in a foil envelope were immersed for 2 minutes and then removed and quenched. The thickness was measured according to ASTM E 252 based on the weight of circular samples cut with precision die of known area. The results are shown in Table 4.

[0050] Table 1 : alloy compositions

[0051] Other elements: <0.05 wt% each and <0.15 wt% in total. Balance: aluminium.

[0052] Table 2:

[0053] In the trials 13-25 according to the invention the intermediate annealing was performed to obtain stress relief but not recrystallisation.

[0054] Table 3: texture and grain size Table 4: mechanical properties test results

[0055] It appears that in trials 13-21 according to the invention the targets for tensile strength and elongation after heat treatment at 120°C were reached, while in the comparative trials 1-12 at least one of tensile strength or elongation was below the target.

Claims

CLAIMS1. A rolled battery electrode foil of an aluminium alloy comprising 0.06 -0.16 wt% Si, 0.41- 1.0 wt% Fe, <0.25 wt% Cu, <0.10 wt% Mn, < 0.03 wt% Mg, <0.05 wt% Zn, 0.001-0.030 wt% Ti, <0.05 wt% each and <0.15 wt% in total of impurities, balance Al, having a thickness from 10 to 25 pm, and when measured after heat treatment of the aluminium foil at 120°C for 2 minutes having a tensile strength of at least 190 MPa and an elongation of at least 3%.

2. The battery electrode foil as claimed in claim 1 , wherein the tensile strength, when measured after heat treatment of the aluminium foil at 120°C for 2 minutes, is at least 100%, preferably at least 120% of the tensile strength as rolled.

3. The battery electrode foil as claimed in any one of the claims 1-2, wherein the tensile strength, when measured after heat treatment of the aluminium foil at 160°C for 2 minutes, is at least 100% of the tensile strength as rolled.

4. The battery electrode foil as claimed in any one of the claims 1-3, wherein the foil as rolled has a tensile strength of at least 190 MPa, preferably at least 250 MPa, most preferably at least 290 MPa..

5. The battery electrode foil as claimed in any one of the claims 1-4, wherein the foil as rolled has an elongation of at least 4%.

6. The battery electrode foil as claimed in any one of the claims 1-5, wherein the aluminium alloy comprises 0.45-1 .0 wt% Fe, preferably 0.460-1 .0 wt% Fe.

7. The battery electrode foil as claimed in any one of the claims 1-6, wherein the aluminium alloy comprises 0.05-0.20 wt% Cu, preferably 0.10-0.19 wt% Cu.

8. The battery electrode foil as claimed in any one of the claims 1-7, wherein the area weighted average equivalent circle diameter of the grains projected in the cross section transverse to the rolling direction of the aluminium foil and the threshold for grain boundaries being a difference in orientation of at least 10°, is not more than 2.4 pm, preferably not more than 2.3 pm.

9. The battery electrode foil as claimed in any one of the claims 1-8, wherein the area weighted average equivalent circle diameter of the sub-grains projected in the cross section transverse to the rolling direction of the aluminium foil and the threshold for subgrain boundaries being a difference in orientation of at least 2°, is not more than 0.9 pm, preferably not more than 0.8 pm.

10. The battery electrode foil as claimed in any one of the claims 1-9, wherein the volume fraction of Cu texture {112}<111> as measured by EBSD and applying a deviation of at most 11 ° from the ideal orientation, is at least 20%, preferably at least 22%.

11. The battery electrode foil as claimed in any one of the claims 1-9, wherein the foil has been produced in a process comprising continuous casting and cold rolling with intermediate annealing, wherein no heat treatment leading to complete recrystallisation has taken place after the continuous casting.

12. A process for the production of a battery electrode foil comprising continuous casting of an aluminium alloy comprising 0.06 -0.16 wt% Si, 0.41-1.0 wt% Fe, <0.25 wt% Cu, <0.10 wt% Mn, < 0.03 wt% Mg, <0.05 wt% Zn, 0.001-0.030 wt% Ti, <0.05 wt% each and <0.15 wt% in total of impurities, balance Al, to obtain a sheet, cold rolling the cast sheet to an intermediate thickness, annealing the sheet at the intermediate thickness at a temperature of 150-320°C for 2-15 hours, cold rolling the annealed sheet to obtain a foil having a final thickness of 10-25 pm, wherein no heat treatment leading to complete recrystallisation takes place after the continuous casting.

13. A process as claimed in claim 12, wherein the cold rolling after the intermediate annealing is done with a thickness reduction of 75-99.8%.

14. An electrode for a secondary battery comprising a current collector of a battery electrode foil according to any one of the claims 1-11.

15. A secondary battery comprising an anode, a cathode, a non-aqueous electrolyte, and a separator, wherein a least one of the anode or the cathode is an electrode according to claim 14.

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