Preparation method of battery aluminum foil and battery aluminum foil

Abstract

The invention discloses a preparation method of a battery aluminum foil and the battery aluminum foil. The preparation method comprises the following steps that S1, a raw material formula is prepared according to the following components in percentage by mass, and a casting process adopts a water-cooling semi-continuous casting method to prepare a cast ingot from the raw material formula; s2, the cast ingot is subjected to saw cutting and surface milling treatment; s3, the cast ingot subjected to saw cutting and surface milling treatment is put into a heating furnace to be subjected to homogenizing heat treatment; s4, the cast ingot is subjected to hot continuous rolling treatment; a hot-rolled coiled material is obtained; s5, the hot-rolled coiled material is subjected to cold rolling and intermediate annealing, and a cold-rolled blank is obtained; s6, the cold-rolled blank is cleaned, and a cold-rolled blank is obtained; and S7, the cold-rolled blank is subjected to foil rolling, and the battery aluminum foil with the thickness ranging from 0.01 mm to 0.015 mm is obtained. The prepared battery aluminum foil is excellent in comprehensive mechanical property, good in surface quality, low in pinhole density and low in belt breaking frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum processing, and in particular to a method for preparing a battery aluminum foil used for a positive electrode current collector of a power battery and the battery aluminum foil. Background Art

[0002] As a new generation of green and environmentally friendly energy storage devices, lithium-ion secondary batteries work on the principle of electron transfer and energy storage based on the embedding / de-embedding mechanism. The cathode material is an important factor in determining the specific capacity of lithium batteries. With the increasing demand for new energy vehicles, the energy density of lithium batteries for electric vehicles is also increasingly required. From the initial nickel-hydrogen battery to the later lithium iron phosphate battery and now the lithium manganese oxide battery and ternary lithium battery, the preparation of cathode materials is also constantly improving to meet the needs of market development.

[0003] Existing lithium batteries are mainly divided into two categories, one is the ordinary lithium primary battery composed of graphite negative electrode, and the other is the sandwich structure lithium ion battery composed of metal oxide electrolyte. The current lithium batteries all have the structural characteristics of multiple sheets wound and stacked. In order to meet the needs of fast charging and discharging, while taking into account good cycle life and safety, most of them now use highly conductive current collector materials as the connection carrier of the positive and negative electrode substrates, such as copper foil or aluminum foil. For aluminum foil, it generally has to go through the smelting stage to obtain an aluminum alloy flat ingot, and then the segregation and coarse grain layer on the surface of the ingot must be mechanically removed, and then the ingot must be homogenized, and then multiple reversible rolling and hot rolling are performed to obtain a hot-rolled coil. The hot-rolled coil is subjected to cold rough rolling to obtain a cold-rolled coil with the required dislocation density before annealing; then it is sent to an annealing furnace for annealing and heating to refine the grain structure and obtain an equiaxed grain structure; then it is subjected to multiple cold pressing to obtain an aluminum foil coil of the thickness required by the final customer; the aluminum foil coil is slit and finely cut to obtain a product of the width required by the customer.

[0004] However, the aluminum foil produced as described above is prone to frequent breaks, resulting in a high pinhole density and poor surface quality. Summary of the invention

[0005] The purpose of the embodiment of the present invention is to provide a method for preparing a battery aluminum foil, so as to solve the problem that the existing battery aluminum foil has high pinhole density and poor surface quality.

[0006] In order to solve the above technical problems, in a first aspect, an embodiment of the present invention provides a method for preparing a battery aluminum foil, the preparation method comprising the following steps:

[0007] Step S1, preparing a raw material formula according to the following components and mass percentages, and preparing an ingot by a water-cooled semi-continuous casting method in the melting and casting process: Si=0.02-0.10wt%, Fe=0.12-0.35wt%, Cu=0.03-0.10wt%, Mn=0.01-0.03wt%, Mg≤0.002wt%, Zn≤0.02wt%, Ti=0.01-0.03wt%, B≤0.003wt%, C≤0.003wt%, V=0.01-0.02wt%, and Al content greater than 99.45wt%;

[0008] Step S2, sawing and milling the ingot; wherein the ingot gate portion is sawed by 90-100 mm, the tail portion is sawed by 330-350 mm, the large surface is milled by 20-25 mm, the surface coarse grain layer is milled, the side is milled by 5 mm, the straightness after milling is less than or equal to 0.2 mm / m, and the surface roughness Ra is less than 5 μm;

[0009] Step S3, placing the ingot after sawing and milling into a heating furnace for homogenization heat treatment, wherein the temperature in the heating furnace during the homogenization heat treatment is 560-610° C., and the holding time is 6-15 hours, the furnace temperature is 460-500° C., and then hot rolling is performed;

[0010] Step S4, performing hot rolling on the ingot after homogenization heat treatment; wherein, the hot rolling is performed through multiple reversible rolling, and after the intermediate billet is rolled to a thickness of 20 to 35 mm, it enters a 3-stage hot rolling mill, and the hot rolling final rolling temperature is 300 to 350° C., to obtain a hot rolled coil with a thickness of 5.0 to 8.0 mm;

[0011] Step S5, cold rolling the hot rolled coil to a thickness of 1.6-4.0 mm and then performing intermediate annealing, the intermediate annealing temperature is 350-420° C., and the intermediate annealing holding time is 1-3 hours, wherein the intermediate annealing adopts nitrogen protection negative pressure degreasing annealing protection annealing; continue cold rolling to a thickness of 0.2-0.4 mm to obtain a cold rolled billet, the cold rolling process is maintained at a temperature of 20-50° C., and the temperature of the cold rolled billet after rolling is controlled within 30-80° C.;

[0012] Step S6, cleaning the cold-rolled blank to obtain a cold-rolled rough material;

[0013] Step S7, performing foil rolling on the cold rolled raw material to obtain a battery aluminum foil with a thickness of 0.01 to 0.015 mm.

[0014] Preferably, the step S1 specifically includes the following steps:

[0015] The components and mass percentages in the melt are adjusted according to the raw material formula, and a spray stirring smelting method is adopted to obtain a purified melt;

[0016] The melt temperature is controlled at 730-750°C, nitrogen or argon is introduced, the melt is refined for 12-30 minutes, and then the melt is allowed to stand for 15-30 minutes before slag removal. The melt is allowed to stand for 15-30 minutes after slag removal, and the furnace is poured, and the pouring temperature is controlled at 735-750°C, and degassing and filtering and purification treatment are performed. The ingot is obtained by grain refinement and semi-continuous water-cooled casting.

[0017] Preferably, in step S2, a modern CNC milling machine is used to mill the surface of the ingot to remove the defective layer on the surface of the ingot, and the upper and lower surfaces and both side surfaces of the ingot alloy are milled through a production line.

[0018] Preferably, step S2 further comprises: cleaning the surface of the ingot with an emulsion before entering the heating furnace.

[0019] Preferably, in step S3, when the ingot is heated in the heating furnace, the burners of the heating furnace are distributed along the width direction of the heating furnace, and the two large surfaces of the ingot are used as main heat exchange surfaces to heat the ingot;

[0020] During the heating process of the ingot in the heating furnace, the two large surfaces of the ingot do not contact any solid matter;

[0021] When the ingot is in and out of the heating furnace, the two large surfaces of the ingot do not slide relative to any solid matter.

[0022] Preferably, in step S4, the hot rolling is performed by using a 1+3 hot rolling mill.

[0023] Preferably, in step S5, in step S5, the cold rolling reduction passes are distributed as (5mm~8mm)-(1.6mm~4.0mm)-(1.0mm~2mm)-(0.5mm~1.0mm)-(0.3mm~0.5mm)-(0.2mm~0.3mm).

[0024] Preferably, the step S6 specifically comprises the steps of:

[0025] During cleaning, aluminum powder and foreign matter on the surface of the cold-rolled billet are removed by flowing water washing, high-pressure alkali solution spraying and rinsing in sequence. After cleaning, it is dried with hot air at 130-150℃ to obtain clean cold-rolled billet; the pressure during high-pressure alkali solution spraying is 4-6MPa, and the residual oil on the surface after cleaning is less than 1mg / m 2 , aluminum powder residue is less than 2mg / m 2 ; Add 1‰ sodium dodecyl sulfate and ethylenediaminetetraacetic acid to the cleaning solution.

[0026] Preferably, in step S7, the foil rolling passes are distributed as (0.2 mm to 0.3 mm) - (0.1 mm to 0.18 mm) - (0.05 mm to 0.07 mm) - (0.018 mm to 0.033 mm) - (0.013 mm to 0.0155 mm) - (0.010 mm to 0.012 mm).

[0027] In a second aspect, the present invention provides a battery aluminum foil, which is made by the above-mentioned method for preparing the battery aluminum foil, and the battery aluminum foil is used to manufacture a positive electrode collector of a power battery.

[0028] Compared with the prior art, the preparation method of battery aluminum foil in the present invention, through melting, casting, sawing and milling, heat preservation, hot rolling, cold rolling, cleaning and foil rolling according to the corresponding components and quality, the obtained battery aluminum foil has excellent comprehensive mechanical properties and good surface quality, which meets the requirements of battery positive electrode aluminum foil. At the same time, the hot rolling process technology is adopted to increase the thickness of the initial hot rolling blank and the thickness of the intermediate annealing, so as to obtain more grain layers, increase the interface (shear band) where the grains can rotate and slide, and improve the elongation of the final aluminum foil product; the whole production process prevents surface damage, and at the same time, the roller surface treatment technology is combined with the reasonable lubrication of the aluminum foil to reduce the surface microcrack defects of the aluminum foil and reduce the surface roughness of the aluminum foil, which can improve the elongation, reduce the pinhole density, reduce the break rate, reduce the downtime loss caused by the break and connection of the belt, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0030] Figure 1 A flow chart of a method for preparing a battery aluminum foil provided by an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of a method of unrolling and rolling up an aluminum foil provided in an embodiment of the present invention;

[0032] Figure 3 A schematic diagram of a method for unrolling and rolling up an aluminum foil provided in an embodiment of the present invention;

[0033] Figure 4 A schematic diagram of grain slip provided by an embodiment of the present invention;

[0034] Figure 5 A schematic diagram of grain rotation provided by an embodiment of the present invention;

[0035] Figure 6 A schematic diagram showing that surface defects of the aluminum foil caused by poor rolling lubrication of the aluminum foil provided in an embodiment of the present invention will be the source of stress concentration. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] First, please refer to the attached Figure 1 As shown, an embodiment of the present invention provides a method for preparing a battery aluminum foil, and the preparation method comprises the following steps:

[0038] Step S1, prepare a raw material formula according to the following components and mass percentages, and use a water-cooled semi-continuous casting method to prepare an ingot from the raw material formula in the melting and casting process: Si=0.02~0.10wt%, Fe=0.12~0.35wt%, Cu=0.03~0.10wt%, Mn=0.01~0.03wt%, Mg≤0.002wt%, Zn≤0.02wt%, Ti=0.01~0.03wt%, B≤0.003wt%, C≤0.003wt%, V=0.01~0.02wt%, and Al content is greater than 99.45wt%.

[0039] Specifically, by adjusting the components and mass percentages in the melt, adding fluoride, and adopting a spray stirring smelting method, heating and stirring are ensured while not destroying the surface oxide film, a purified melt is obtained, and the melt is treated to obtain an ingot.

[0040] Among them, in addition to the control of conventional elements, special control is also made on trace impurity elements V, B, and C, which is helpful to improve elongation and reduce pinholes. Adding V provides the core of grain refinement, thereby increasing the number of layers of aluminum foil grains and improving elongation. Controlling the B content can reduce the titanium attenuation and TiB2 agglomeration of the added aluminum titanium boron wire, refine the cast grains, and improve the elongation of aluminum foil. Fine grains provide a large number of grain boundaries, making it easier for the sliding and rotation of the grain boundaries to occur.

[0041] Specifically, as the content of Si contained in the aluminum alloy plain foil, the upper limit is preferably about 0.10wt%, and more preferably 0.06wt%. The lower limit can be 0.02wt%, and preferably 0.03wt%. Si forms an intermetallic compound together with Fe; however, when the amount of Si added is large, this will lead to coarsening of the compound size. When the content of Si is greater than the upper limit, the rolling ability and elongation performance are reduced due to the coarse crystallization product, and in addition, the uniformity of the recrystallized grain size distribution after the final annealing is reduced.

[0042] In order to improve the tensile strength of battery aluminum foil, a small amount of Cu is dissolved in the aluminum foil. Cu can usually significantly improve the tensile strength of the aluminum foil and has a work hardening effect. When the mass content of Cu is less than 0.005%, the work hardening effect is weak. Impurity Cu may cause hot cracks in high-grade industrial pure aluminum ingots, even though the Cu content in the alloy is very low. However, during continuous casting, due to the high cooling rate, when the Cu content is greater than 0.1%, an unbalanced low-melting eutectic will be formed during the condensation process, greatly increasing the tendency to hot cracks. Therefore, the Cu content is preferably 0.03-0.1wt%, and more preferably 0.03-0.08wt%.

[0043] In order to improve the elongation of battery aluminum foil, the upper limit of the Fe content contained in the aluminum foil is preferably about 0.35wt% or less, and more preferably about 0.30wt% or less. The lower limit is preferably about 0.12wt%, and more preferably about 0.15wt% or more. The maximum solid solubility of Fe in aluminum is 0.05%. Above this content, Fe crystallizes into Al3Fe compounds during the casting process, which can play a nucleation role during the dynamic recrystallization process of hot rolling; at the same time, the compound becomes a recrystallization nucleation point during the subsequent annealing process, and therefore has the effect of refining the recrystallized grains and has a PSN effect. Among them, the PSN effect refers to the particle stimulated nucleation effect (Particle Stimulated Nucleation), which is a physical phenomenon in which smaller particles have a stimulating effect on larger particles, promoting their nucleation and growth. Therefore, when the Fe content is less than the lower limit, the distribution density of coarse intermetallic compounds decreases, the refinement effect is weak, and the final grain size distribution becomes uneven. When the Fe content is greater than the upper limit, the grain refinement effect is saturated or even reduced. In addition, the size of the Al-Fe-based compound to be produced during casting is large, the elongation and rolling ability of the aluminum foil are reduced, and the compound size is too large to form pinholes. In addition, if the iron content is too low below 0.10% or during hot rolling, a coarse grain pattern will appear on the surface, and this defect will be inherited to the subsequent aluminum foil. Therefore, the Fe content is adjusted within the above range to make the battery aluminum foil have a higher elongation.

[0044] In order to improve the mechanical properties of aluminum foil, a small amount of Mn is dissolved in the aluminum matrix in pure aluminum to inhibit the recrystallization of aluminum. When Mn is in a very trace state, it can produce a work hardening effect similar to Cu, while increasing the recrystallization temperature and improving heat resistance; however, when the Mn content is large, it is easy to cause dendrite segregation, delay recrystallization during intermediate annealing and final annealing, and it is difficult to obtain uniform fine grains. Therefore, the Mn content is adjusted to 0.03wt% or less.

[0045] In order to further improve the ductility of the material, an element that refines the grains can be added. The upper limit of the V content in the aluminum alloy plain foil is preferably about 0.02wt%, and the lower limit can be 0.01wt%. When V forms an intermetallic compound with Al, the grains can be refined when a certain amount is added. However, when the amount of V added is large, a galvanic effect will be formed, accelerating corrosion. Therefore, it is necessary to limit the V content.

[0046] In order to improve the processing and forming properties of aluminum foil, a small amount of Mg in pure aluminum is solidified in the aluminum matrix, which can produce a work hardening effect similar to Cu; however, when the content of Mg is large, the difficulty of rolling processing is increased, and the elongation of the final product drops sharply. Mg precipitates on the grain boundary, Mg has a strong affinity with hydrogen atoms, the surface oxide film and Mg-H interact, and H2O infiltration is easily formed near the coarse second phase particles. If chloride ions are present, it is more easily corroded, the oxide film breaks, and microcracks are formed. Hydrogen is enriched at the crack tip, which promotes crack expansion. Therefore, the content of Mg is adjusted to 0.01wt% or less. Due to reasons similar to the above, the upper limit of the Mg content is more preferably set to 0.002% by mass.

[0047] In order to reduce the pinholes in the aluminum foil, the B element in the original aluminum ingot or the electrolytic aluminum water must be controlled. This element reacts with Al3Ti in the aluminum titanium boron refiner added during grain refinement to form coarse titanium aggregation, which weakens the grain refinement effect. Therefore, the B content is adjusted to less than 0.003wt% by mass or less, and more preferably less than 0.001wt%.

[0048] In order to further reduce the pinholes in aluminum foil, the C element in the original aluminum ingot or electrolytic aluminum water must be controlled. C and aluminum form a high-melting-point compound Al4C3, which is not conducive to subsequent rolling deformation, and gradually breaks into pinholes during the subsequent foil rolling process. Therefore, the C content is adjusted to less than 0.006wt%, and more preferably less than 0.003wt%.

[0049] Step S2, sawing and milling the ingot; wherein, the ingot gate part is sawed by 90-100 mm, the tail is sawed by 330-350 mm, the large surface is milled by 20-25 mm, the surface coarse grain layer is milled, the side is milled by 5 mm, the straightness after milling is less than or equal to 0.2 mm / m, and the surface roughness Ra is less than 5 μm.

[0050] Step S3, placing the ingot after sawing and milling into a heating furnace for homogenization heat treatment, wherein the temperature in the heating furnace during the homogenization heat treatment is 560-610°C, and the insulation time is 6-15 hours, the furnace outlet temperature is 460-500°C, and then hot rolling is performed.

[0051] Step S4, performing hot rolling treatment on the ingot that has undergone homogenization heat treatment; wherein, the hot rolling is carried out through multiple passes of reversible rolling, and after the intermediate billet is rolled to a thickness of 20 to 35 mm, it enters a 3-stage hot rolling mill train, and the hot rolling final rolling temperature is 300 to 350° C., to obtain a hot-rolled coil with a thickness of 5.0 to 8.0 mm.

[0052] During the hot rolling process, the large amount of pressure reduction in the ingot causes the large phase particles in the structure to be broken, reducing the impact of impurity elements on the plate. At the same time, the grain structure is elongated and flattened, and the elongated fiber structure will greatly reduce the plasticity of the alloy. The thickness of the finished product after hot finishing rolling is generally 4 to 8 mm, which is controlled by controlling the finishing rolling roll parameters, speed, final rolling temperature and other factors.

[0053] The key control of hot rolling surface quality includes the grinding of the rolls and the determination of the roll shape and roughness, which can obtain the appropriate plate shape, plate convexity and plate surface roughness, and ensure good bite and surface quality. For rough rolling, due to the large size of the ingot, the main thing is to ensure good bite, so the roughness Ra is between 1.8 and 2.5μm. For the continuous rolling unit, the main consideration is to control the surface quality, so the grinding roughness requirement is relatively high, generally between Ra0.8 and 1.8μm, and the grinding roughness requirements from the first rack at the entrance to the last rack at the exit are generally increased rack by rack. Hot rough rolling mills and hot finishing mills are generally equipped with brush roller devices, the purpose of which is to effectively control the thickness and uniformity of the aluminum layer on the surface of the rolls, so that the aluminum layer on the roll surface is in an ideal stable state. Correct use of brush rollers is conducive to obtaining good strip surface quality.

[0054] Step S5, cold rolling the hot-rolled coil to a thickness of 1.6-4.0 mm and then performing intermediate annealing, the intermediate annealing temperature is 350-420° C., and the intermediate annealing holding time is 1-3 hours, wherein the intermediate annealing adopts nitrogen protection negative pressure degreasing annealing protection annealing; continue cold rolling to a thickness of 0.2-0.4 mm to obtain a cold-rolled billet, the cold rolling process is maintained at a temperature of 20-50° C., and the temperature of the cold-rolled billet after rolling is controlled within 30-80° C.

[0055] In this embodiment, in step S5, the cold rolling reduction passes are distributed as (5mm~8mm)-(1.6mm~4.0mm)-(1.0mm~2mm)-(0.5mm~1.0mm)-(0.3mm~0.5mm)-(0.2mm~0.3mm).

[0056] Specifically, a four-roll irreversible cold rolling mill is used for rolling, which is divided into rough rolling and finish rolling. In order to obtain high-surface products, in addition to the control of rolling parameters and rolling oil parameters, nylon brush rollers are installed above and below the working rolls. During rolling, they rotate in the opposite direction to the rolls to remove foreign matter on the rolls. The rolling oil is used to wash away the debris adhering to the aluminum plate under high pressure, and finally a high-surface cold-rolled billet is obtained. The accumulated impurities are filtered out in the rolling oil filtration circulation system.

[0057] At the same time, if Figure 2 As shown, the upper unwinding and lower winding method can also be preferentially selected, and the aluminum foil is wound between the unwinding roller 5 and the winding roller 6, the unwinding roller 5 is the upper unwinding method, and the winding roller 6 is the lower unwinding method. A deflection roller 7 is arranged on one side of the unwinding roller 5, and a plate-shaped roller 8 is arranged on the inner side of the winding roller 6, and the aluminum foil is supported and arranged on the deflection roller 7 and the plate-shaped roller 8; an upper working roller 1 and a corresponding lower working roller 2 are arranged between the deflection roller 7 and the plate-shaped roller 8, an upper support roller 3 is arranged on the upper working roller 1, and a lower support roller 4 is arranged under the lower working roller 2, and the upper working roller 1 and the lower working roller 2 are supported by the upper support roller 3 and the lower support roller 4 respectively. During the cold rough rolling before intermediate annealing, the upper working roll 1 and the lower working roll 2 are set with a roll diameter difference of about 1%, and the rolling speeds of the upper and lower surfaces are different. During rolling and coiling, a "rolling zone" can be formed, forming a similar "twisting extrusion technology (TE)". This drastic plastic deformation refines the microstructure of the material to the micron scale, promotes the PSN effect, and thus obtains fine grains and more grain layers. This production method is only used in the cold rolling pass before annealing. If this method is used in the cold foil rolling after intermediate annealing, the surface microcrack defects will increase and the ductility of the final product will be reduced.

[0058] Optional, such as Figure 3 As shown, the method of opening and rolling up can also be preferred, and the aluminum foil is rolled between the unwinding roller 5 and the winding roller 6, the unwinding roller 5 is in the upper opening method, and the winding roller 6 is in the upper winding method. A deflection roller 7 is arranged on one side of the unwinding roller 5, and a plate-shaped roller 8 is arranged on the inner side of the winding roller 6, and the aluminum foil is supported and arranged on the deflection roller 7 and the plate-shaped roller 8; an upper working roller 1 and a corresponding lower working roller 2 are arranged between the deflection roller 7 and the plate-shaped roller 8, an upper support roller 3 is arranged on the upper working roller 1, and a lower support roller 4 is arranged under the lower working roller 2, and the upper working roller 1 and the lower working roller 2 are supported by the upper support roller 3 and the lower support roller 4 respectively.

[0059] Step S6, cleaning the cold-rolled blank to obtain a cold-rolled rough material.

[0060] Step S7, the cold rolled raw material is subjected to foil rolling to obtain battery aluminum foil with a thickness of 0.01 to 0.015 mm. The aluminum foil obtained by foil rolling is rolled to obtain a high surface product. The rollers in contact with the aluminum foil need to control the surface spiral lines, chatter lines, horizontal scratches and other defects that affect the surface quality of the aluminum foil due to poor roller grinding. The aluminum foil rolling parameters are controlled within a reasonable range to prevent slipping and dry friction. The oil film between the rollers is thin, the aluminum foil surface is closer to the roller surface, and the rolled aluminum foil has good brightness.

[0061] Step S8: Slitting and fine-cutting the finished battery aluminum foil to obtain aluminum coils of the width required by the customer, and then packaging.

[0062] In the specific embodiment, by melting, casting, sawing and milling, heat preservation, hot rolling, cold rolling, cleaning and foil rolling according to the corresponding components and qualities, the battery aluminum foil obtained has excellent comprehensive mechanical properties and good surface quality, which meets the requirements of being used as battery positive electrode aluminum foil. At the same time, the hot rolling process technology is adopted to increase the thickness of the initial hot rolling blank and the thickness of the intermediate annealing, so as to obtain more grain layers and increase the rotatable grains (such as Figure 5 as shown) and slip (as Figure 4 The interface (shear band) shown in Figure 2 can improve the elongation of the final aluminum foil product. Figure 6 As shown, the entire production process prevents surface damage, and the roller surface treatment technology is combined with reasonable lubrication of aluminum foil to reduce the surface microcrack defects of aluminum foil and reduce the surface roughness of aluminum foil, which can increase the elongation, reduce the pinhole density, reduce the belt break rate, reduce the downtime loss caused by belt breakage and belt splicing, and improve production efficiency. At the same time, this method can improve the elongation of 13-micron double-sided smooth aluminum foil from 3.5% to 4.5%, and the average pinhole density is less than 0.1 / m 2 It can greatly reduce the breakage of aluminum foil in subsequent processing, with the breakage rate of 0 to 1 time per 10,000 meters, which is more than 50% lower than other conventional methods.

[0063] In this embodiment, step S1 specifically includes the following steps:

[0064] The components and mass percentages in the melt are adjusted according to the raw material formula, and a spray stirring smelting method is adopted to obtain a purified melt;

[0065] The melt temperature is controlled at 730-750°C, nitrogen or argon is introduced, the melt is refined for 12-30 minutes, and then the melt is allowed to stand for 15-30 minutes before slag removal. The melt is allowed to stand for 15-30 minutes after slag removal, and the furnace is poured, and the pouring temperature is controlled at 735-750°C, and degassing and filtering and purification treatment are performed. The ingot is obtained by grain refinement and semi-continuous water-cooled casting.

[0066] In this embodiment, in step S2, a modern CNC milling machine is used to mill the surface of the ingot to remove the defective layer on the surface of the ingot, and the upper and lower surfaces and both side surfaces of the ingot alloy are milled through a production line.

[0067] In this embodiment, step S2 also includes: using an emulsion to clean the surface of the ingot before entering the heating furnace.

[0068] Specifically, a modern CNC milling machine is used to mill the surface (including the side) of the aluminum ingot to remove the defective layer on the surface of the ingot and ensure the structure and performance of the material. During milling, the upper and lower surfaces and both sides of the alloy are milled through the milling production line. After milling, the parallelism of the flat ingot is ≤0.2mm / m, and the surface roughness of the ingot is less than 5μm. The ingot is transported vertically from the milling machine to the hot rolling mill. This is to ensure the surface quality because the whole process does not contact the milled and to-be-rolled surfaces. Vertical placement not only saves space but also better protects the surface. The surface of the ingot needs to be cleaned with an emulsion before entering the heating furnace.

[0069] In this embodiment, in step S3, when the ingot is heated in the heating furnace, the burners of the heating furnace are distributed along the width direction of the heating furnace, and the two large surfaces of the ingot are used as main heat exchange surfaces to heat the ingot.

[0070] During the heating process of the ingot in the heating furnace, the two large surfaces of the ingot do not contact with any solid matter.

[0071] When the ingot is in and out of the heating furnace, the two large surfaces of the ingot do not slide relative to any solid matter. The surface damage of the ingot when it is in and out of the furnace is reduced, thereby ensuring the good surface quality of the ingot when it is on the rolling line roller. The chuck for lifting the ingot is specially designed. The clamping does not damage the surface quality of the workpiece and can clamp the ingot. The chuck is designed in the shape of a prism.

[0072] In this embodiment, in step S4, the hot rolling is performed by using a 1+3 hot rolling mill.

[0073] Specifically, the hot rolling process is rolled using a 1+3 hot rolling mill. Since most hot rolled strips are cold rolled billets with high surface requirements, the surface quality of the strip should be controlled by the following process without surface defects. The surface color is required to be uniform, without aluminum sticking, scratches and other surface defects, and is detected by anodizing method. From the perspective of controlling the surface quality of the strip, the first thing is how to overcome the possible scratches or aluminum sticking on the lower surface of the strip. Therefore, special attention should be paid to the material, surface, shape and operation of the roller, tension roller, guide roller and roller. The hot rolling roller is designed into a double cone with high sides and low in the middle. Therefore, only the edge of the lower surface contacts the roller, minimizing scratches. The surface defects at the edge are removed by process trimming; the second is to improve the cooling and lubrication performance of the emulsion to prevent aluminum sticking; the third is to improve the stability of the rolling process during rolling.

[0074] In this embodiment, step S6 specifically includes the following steps:

[0075] During cleaning, aluminum powder and foreign matter on the surface of the cold-rolled billet are removed by flowing water washing, high-pressure alkali solution spraying and rinsing in sequence. After cleaning, it is dried with hot air at 130-150℃ to obtain clean cold-rolled billet; the pressure during high-pressure alkali solution spraying is 4-6MPa, and the residual oil on the surface after cleaning is less than 1mg / m 2 , aluminum powder residue is less than 2mg / m 2 ; Add 1‰ sodium dodecyl sulfate and ethylenediaminetetraacetic acid to the cleaning solution.

[0076] In this embodiment, in step S7, the foil rolling passes are distributed as (0.2mm~0.3mm)-(0.1mm~0.18mm)-(0.05mm~0.07mm)-(0.018mm~0.033mm)-(0.013mm~0.0155mm)-(0.010mm~0.012mm).

[0077] In order to further understand the technical features of the present invention, a detailed description is given below in conjunction with specific implementation methods.

[0078] Embodiment 1 provides a method for preparing battery aluminum foil, and the specific steps are as follows: Step 1, ingredients: adjust the components and mass percentages in the melt, and adopt the blowing stirring melting technology to ensure heating and stirring while not destroying the surface oxide film to obtain a purified melt.

[0079] The chemical composition (wt%) is shown in Table 1 below;

[0080] Table 1. Chemical composition of each component (wt%)

[0081] element Si Fe Cu Mn Mg Zn C V B Ti Al Analytical Value 0.077 0.165 0.067 0.012 0.002 0.008 0.002 0.014 0.002 0.012 99.64

[0082] Step 2, casting: Control the fluidity of the melt, and cast an ingot with a thickness of 630mm through degassing, filtering, grain refinement and water curtain cooling. During the casting process, the aluminum liquid temperature in the degassing box is 709-713℃, the degassing rotor speed is 355r / min, the argon flow rate of the degassing box is 62L / min, the crystallizer liquid level is 80mm, the stable casting speed is 50mm / min, the water flow rate is 230m3 / h, the cooling water temperature is 31℃, the temperature at the end of the flow channel is 695-700℃, and the hydrogen content after degassing is 0.11ml / 100gAl. The ingot is cut and milled to obtain a smooth and straight ingot with a thickness of 590mm, a width of 1390mm, and a length of 4.9m.

[0083] Step 3: Homogenization: Push the ingot into the equalizing furnace with the inlet gas temperature at 620°C. It takes 21 hours from heating to cooling and 4 hours from cooling. It takes 25 hours from heating to leaving the furnace. Set the leaving furnace temperature at 500°C and 485°C.

[0084] Step 4, hot rolling: the ingot is sent to the hot rolling line for hot rolling, rough rolling 21 times to a thickness of 30mm, a width of 1374mm, and a length of 99m; finishing rolling 3 times to a thickness of 6mm, a width of 1350mm, and a length of 506m. The average final rolling temperature is 303.5℃.

[0085] Step 5: Rough cold rolling: cold rolling the hot rolled coil to a thickness of 2.0 mm by means of top opening and bottom winding.

[0086] Step 6: Intermediate annealing: heat the aluminum coil to 350°C and keep it warm for 2 hours.

[0087] Step 7: Cold finishing rolling: the aluminum coil is rolled to 0.3 mm by three passes of upper opening and lower rolling.

[0088] Step 8: Cleaning: Clean the finished aluminum coil.

[0089] Step 9: Foil rolling: The cleaned and qualified aluminum coil is foil rolled.

[0090] Step 10: Cut the aluminum coil into the width required by the customer.

[0091] Step 11: Packaging: Packing the finished foil products.

[0092] The mechanical properties of the aluminum coils of different thicknesses obtained by sampling from step 5 to step 9 are shown in Table 2 below;

[0093] Table 2 Mechanical properties data

[0094]

[0095]

[0096] The parameter table of steps 5 to 9 is shown in Table 3 below;

[0097] Table 3. Parameters of each step

[0098]

[0099] Embodiment 2 provides a method for preparing battery aluminum foil, and the specific steps are as follows: Step 1, ingredients: adjust the components and mass percentages in the melt, and adopt the blowing stirring melting technology to ensure heating and stirring while not destroying the surface oxide film, so as to obtain a purified melt.

[0100] The chemical composition (wt%) is shown in Table 4 below;

[0101] Table 4. Chemical composition of each component (wt%)

[0102] element Si Fe Cu Mn Mg Zn C V B Ti Al Analytical Value 0.067 0.204 0.031 0.014 0.002 0.007 0.002 0.015 0.002 0.012 99.63

[0103] Step 2: Casting: Control the fluidity of the melt, and cast an ingot with a thickness of 420 mm through degassing, filtration, grain refinement and water curtain cooling. The ingot is cut and milled to obtain a smooth ingot with a thickness of 380 mm.

[0104] Step 3: Homogenization: Push the ingot into the soaking furnace for homogenization treatment.

[0105] Step 4: Hot rolling: The ingot is sent to the hot rolling line for hot rolling, with 11 rough rolling passes to a thickness of 30 mm and 3 finish rolling passes to a thickness of 6 mm. The average final rolling temperature is 344°C.

[0106] Step 5: Rough cold rolling: cold rolling the hot rolled coil to a thickness of 4.0 mm by means of top opening and bottom winding.

[0107] Step 6: Intermediate annealing: heat the aluminum coil to 350°C and keep it warm for 2 hours.

[0108] Step 7: Cold finishing rolling: the aluminum coil is rolled to 0.25 mm through 3 passes of upper opening and lower rolling.

[0109] Step 8: Cleaning: Clean the finished aluminum coil.

[0110] Step 9: Foil rolling: The cleaned and qualified aluminum coil is foil rolled.

[0111] Step 10: Cut the aluminum coil into the width required by the customer.

[0112] Step 11: Packaging: Packing the finished foil rolls. The mechanical properties of the aluminum coils of different thicknesses obtained by sampling from step 5 to step 9 are shown in Table 5 below;

[0113] Table 5. Mechanical properties data

[0114] thickness Yield strength / MPa Tensile strength / MPa Elongation / % 4.0 62 134.78 17.5 2.23 66.3 138.32 12.8 1.18 103.9 153.83 12 0.63 126.6 167.33 8 0.41 137.3 175.64 7.7 0.25 144.5 186.35 5 0.19 154.3 187.85 5.4 0.13 161.8 193.95 4.4 0.054 166.7 199.5 4.8 0.03 172.3 207.7 5.3 0.019 184.6 217 5.1 0.013 193.7 221.6 4.7

[0115] The parameter table of steps 5 to 9 is shown in Table 6 below;

[0116] Table 6. Parameters of each step

[0117]

[0118] Specifically, Example 2 provides a method for preparing battery aluminum foil, and the specific steps are as follows: Step 1, ingredients: adjust the components and mass percentages in the melt, and adopt the blowing stirring melting technology to ensure heating and stirring while not destroying the surface oxide film, so as to obtain a purified melt.

[0119] The chemical composition (wt%) is shown in Table VII below;

[0120] Table 7. Chemical composition of each component (wt%)

[0121] element Si Fe Cu Mn Mg Zn C V B Ti Al Analytical Value 0.066 0.34 0.032 0.022 0.002 0.008 0.002 0.016 0.002 0.012 99.49

[0122] Step 2, casting: Control the fluidity of the melt, and cast an ingot with a thickness of 630mm through degassing, filtering, grain refinement and water curtain cooling. During the casting process, the spout temperature is 724℃, 711℃ before degassing, the degassing box temperature is 716℃, the degassing rotor is 297-301r / min, the nitrogen protection flow rate is 3.8m3 / h, and the degassing is 704℃. The H content before degassing is 0.4ml / 100g, and the H content after degassing is 0.11ml / 100g. The liquid level is 1538.05mm, the casting speed is 49.8mm / min, the cooling water flow rate is 221.3m3 / h, the water temperature is 34.5℃, and the flow plate end temperature is 683℃. The ingot is cut and milled to obtain a smooth and straight ingot with a thickness of 610mm, a width of 1150mm, and a length of 5.1m.

[0123] Step 3: Homogenization: Push the ingot into the soaking furnace for homogenization treatment, and the furnace temperature is 486℃.

[0124] Step 4: Hot rolling: The ingot is sent to the hot rolling line for hot rolling, with 21 rough rolling passes to an intermediate billet with a thickness of 32 mm, and 3 finish rolling passes to a thickness of 6 mm. The final rolling temperature is 331°C.

[0125] Step 5: Rough cold rolling: cold rolling the hot rolled coil to a thickness of 1.6 mm by means of top opening and bottom winding.

[0126] Step 6: Intermediate annealing: heat the aluminum coil to 350°C and keep it warm for 2 hours.

[0127] Step 7: Cold finishing rolling: the aluminum coil is rolled to 0.3 mm by three passes of upper opening and lower rolling.

[0128] Step 8: Cleaning: Clean the finished aluminum coil.

[0129] Step 9: Foil rolling: The cleaned and qualified aluminum coils are foil rolled.

[0130] Step 10: Cut the aluminum coil into the width required by the customer.

[0131] Step 11: Packaging: Packing the finished foil rolled products. The mechanical properties of the aluminum coils of different thicknesses obtained by sampling from step 5 to step 9 are shown in Table 8 below;

[0132] Table 8. Mechanical properties data

[0133]

[0134]

[0135] The parameter table of steps 5 to 9 is shown in Table 9 below;

[0136] Table 9. Parameters of each step

[0137]

[0138] In summary, the battery aluminum foil prepared by the preparation method of a battery aluminum foil of the present invention has excellent comprehensive mechanical properties and good surface quality, and meets the requirements of being used as a positive electrode aluminum foil of a battery. At the same time, the hot rolling process technology is adopted to increase the thickness of the initial hot-rolled blank and the thickness of the intermediate annealing, thereby obtaining more grain layers, increasing the interface (shear band) where the grains can rotate and slip, and improving the elongation of the final aluminum foil product. The entire production process prevents surface damage, and at the same time, the roller surface treatment technology is combined with the reasonable lubrication of the aluminum foil to reduce the surface microcrack defects of the aluminum foil and reduce the surface roughness of the aluminum foil, which can improve the elongation, reduce the pinhole density, reduce the break rate, reduce the downtime loss caused by the break and connection of the belt, and improve production efficiency.

[0139] In a second aspect, the present invention provides a battery aluminum foil, which is made by the preparation method of the battery aluminum foil of the above-mentioned embodiment 1, and the battery aluminum foil is used to manufacture a positive electrode collector of a power battery.

[0140] Compared with the related art, the preparation method of battery aluminum foil in the present invention, through melting, casting, sawing and milling, heat preservation, hot rolling, cold rolling, cleaning and foil rolling according to the corresponding components and quality, the obtained battery aluminum foil has excellent comprehensive mechanical properties and good surface quality, which meets the requirements of battery positive electrode aluminum foil. At the same time, the hot rolling process technology is adopted to increase the thickness of the initial hot rolling blank and the thickness of the intermediate annealing, so as to obtain more grain layers, increase the interface (shear band) where the grains can rotate and slip, and improve the elongation of the final aluminum foil product. The whole production process prevents surface damage, and at the same time, the roller surface treatment technology is combined with the reasonable lubrication of the aluminum foil to reduce the surface microcrack defects of the aluminum foil and reduce the surface roughness of the aluminum foil, which can improve the elongation, reduce the pinhole density, reduce the break rate, reduce the downtime loss caused by the break and connection, and improve production efficiency.

[0141] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0142] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a battery aluminum foil, characterized in that: The preparation method comprises the following steps: Step S1, preparing a raw material formula according to the following components and mass percentages, and preparing an ingot by a water-cooled semi-continuous casting method in the melting and casting process: Si=0.02-0.10wt%, Fe=0.12-0.35wt%, Cu=0.03-0.10wt%, Mn=0.01-0.03wt%, Mg≤0.002wt%, Zn≤0.02wt%, Ti=0.01-0.03wt%, B≤0.003wt%, C≤0.003wt%, V=0.01-0.02wt%, and Al content greater than 99.45wt%; Step S2, sawing and milling the ingot; wherein the ingot gate portion is sawed by 90-100 mm, the tail portion is sawed by 330-350 mm, the large surface is milled by 20-25 mm, the surface coarse grain layer is milled, the side is milled by 5 mm, the straightness after milling is less than or equal to 0.2 mm / m, and the surface roughness Ra is less than 5 μm; Step S3, placing the ingot after sawing and milling into a heating furnace for homogenization heat treatment, wherein the temperature in the heating furnace during the homogenization heat treatment is 560-610° C., and the holding time is 6-15 hours, the furnace temperature is 460-500° C., and then hot rolling is performed; Step S4, performing hot rolling on the ingot after homogenization heat treatment; wherein, the hot rolling is performed through multiple reversible rolling, and after the intermediate billet is rolled to a thickness of 20 to 35 mm, it enters a 3-stage hot rolling mill, and the hot rolling final rolling temperature is 300 to 350° C., to obtain a hot rolled coil with a thickness of 5.0 to 8.0 mm; Step S5, cold rolling the hot rolled coil to a thickness of 1.6-4.0 mm and then performing intermediate annealing, the intermediate annealing temperature is 350-420° C., and the intermediate annealing holding time is 1-3 hours, wherein the intermediate annealing adopts nitrogen protection negative pressure degreasing annealing protection annealing; continue cold rolling to a thickness of 0.2-0.4 mm to obtain a cold rolled billet, the cold rolling process is maintained at a temperature of 20-50° C., and the temperature of the cold rolled billet after rolling is controlled within 30-80° C.; Step S6, cleaning the cold-rolled blank to obtain a cold-rolled rough material; Step S7, performing foil rolling on the cold rolled raw material to obtain a battery aluminum foil with a thickness of 0.01 to 0.015 mm.

2. The method for preparing a battery aluminum foil according to claim 1, characterized in that: The step S1 specifically includes the following steps: The components and mass percentages in the melt are adjusted according to the raw material formula, and a spray stirring smelting method is adopted to obtain a purified melt; The melt temperature is controlled at 730-750°C, nitrogen or argon is introduced, the melt is refined for 12-30 minutes, and then the melt is allowed to stand for 15-30 minutes before slag removal. The melt is allowed to stand for 15-30 minutes after slag removal, and the furnace is poured, and the pouring temperature is controlled at 735-750°C, and degassing and filtering and purification treatment are performed. The ingot is obtained by grain refinement and semi-continuous water-cooled casting.

3. The method for preparing battery aluminum foil according to claim 1, characterized in that: In step S2, a modern CNC milling machine is used to mill the surface of the ingot to remove the defective layer on the surface of the ingot, and the upper and lower surfaces and both side surfaces of the ingot alloy are milled through a production line.

4. The method for preparing battery aluminum foil according to claim 3, characterized in that: Step S2 also includes: using an emulsion to clean the surface of the ingot before entering the heating furnace.

5. The method for preparing battery aluminum foil according to claim 1, characterized in that: In step S3, when the ingot is heated in the heating furnace, the burners of the heating furnace are distributed along the width direction of the heating furnace, and the two large surfaces of the ingot are used as main heat exchange surfaces to heat the ingot; During the heating process of the ingot in the heating furnace, the two large surfaces of the ingot do not contact any solid matter; When the ingot is in and out of the heating furnace, the two large surfaces of the ingot do not slide relative to any solid matter.

6. The method for preparing battery aluminum foil according to claim 1, characterized in that: In step S4, the hot rolling is performed by using a 1+3 hot rolling mill.

7. The method for preparing battery aluminum foil according to claim 1, characterized in that: In step S5, in step S5, the cold rolling reduction passes are distributed as (5mm~8mm)-(1.6mm~4.0mm)-(1.0mm~2mm)-(0.5mm~1.0mm)-(0.3mm~0.5mm)-(0.2mm~0.3mm).

8. The method for preparing battery aluminum foil according to claim 1, characterized in that: The step S6 specifically comprises the following steps: During cleaning, aluminum powder and foreign matter on the surface of the cold-rolled billet are removed by flowing water washing, high-pressure alkali solution spraying and rinsing in sequence. After cleaning, it is dried with hot air at 130-150℃ to obtain clean cold-rolled billet; the pressure during high-pressure alkali solution spraying is 4-6MPa, and the residual oil on the surface after cleaning is less than 1mg / m 2 , aluminum powder residue is less than 2mg / m 2 ; Add 1‰ sodium dodecyl sulfate and ethylenediaminetetraacetic acid to the cleaning solution.

9. The method for preparing battery aluminum foil according to claim 1, characterized in that: In step S7, the foil rolling passes are distributed as (0.2mm~0.3mm)-(0.1mm~0.18mm)-(0.05mm~0.07mm)-(0.018mm~0.033mm)-(0.013mm~0.0155mm)-(0.010mm~0.012mm).

10. A battery aluminum foil, characterized in that: The battery aluminum foil is made by the preparation method of the battery aluminum foil according to any one of claims 1 to 9, and the battery aluminum foil is used to manufacture the positive electrode current collector of the power battery.

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