Aluminum foil for lithium ion battery and cast-rolling production method thereof

Abstract

The application discloses an aluminum foil for lithium ion batteries and a cast-rolling production method thereof. The aluminum foil is composed of the following components in percentage by mass: Si 0.06-0.09%, Fe 0.09-0.12%, Cu 0.05-0.08%, Mg 0.06-0.09%, and the rest is Al and inevitable impurities. The cast-rolling production method comprises the following steps in sequence: smelting and preparing aluminum liquid, in-furnace refining and purifying, online degassing and filtering outside the furnace, ultrasonic-assisted casting and rolling, homogenizing annealing, cold rolling, longitudinal shearing, intermediate annealing, foil rolling, slitting and product annealing. The application improves the cleanliness of the aluminum liquid, refines the grains of the cast-rolled aluminum slab, and improves the uniformity of the structure and composition, thereby breaking the problem that strength and plasticity are difficult to be considered together, reducing the rolling passes, and shortening the process flow. The tensile strength of the 12 / 13 mu m aluminum foil is greater than 250 MPa, the elongation after fracture is greater than 6%, the surface wetting tension is greater than 40*10 ‑3 N / m, and the pinhole number is less than 0.01 / m 2 , which meets the development requirements of high-energy-density lithium ion batteries for new energy vehicles and large energy storage devices, and improves the safety and service life of the batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum foil preparation, and particularly relates to an aluminum foil for lithium ion batteries and a cast-rolling production method thereof. BACKGROUND

[0002] Lithium ion batteries have the advantages of high working voltage, large energy density, long cycle life, safety and environmental protection, and are widely used in power batteries and energy storage batteries. With the rapid development of new energy vehicles, photovoltaic power generation, wind power generation and 3C electronic industry in China, the development of power batteries and energy storage batteries is driven. The aluminum foil in the lithium ion battery is used as a positive electrode current collector material, which is not only a carrier of active substances but also a conductor for current collection, and is an important basic raw material for aluminum ion batteries, which has an important influence on the performance and quality of lithium ion batteries. With the development of power batteries and energy storage batteries towards higher and higher energy density, the requirements for aluminum foil are also higher and higher, firstly, the thickness of the aluminum foil is required to be thinner and thinner, secondly, the strength, plasticity and surface quality of the aluminum foil are required to be higher and higher, and finally, the production cost of the aluminum foil needs to be continuously reduced to improve the safety, energy density, cycle life of the battery and reduce the production cost of the battery.

[0003] The Chinese patent document with publication number CN119220861A discloses a method for preparing 1100 aluminum alloy new energy battery aluminum foil from electrolytic aluminum liquid, the aluminum foil is composed of the following components in mass percentage: Fe 0.55-0.6%, Si 0.1-0.13%, Cu 0.2-0.25%, Ti 0.01-0.02%, Mn≤0.01%, Zn 0.015-0.025%, Mg≤0.01%, Al≥99%. The preparation method includes casting, annealing, cold rolling, foil rolling and other processes, the tensile strength of the aluminum foil is 300-320 MPa, and the elongation is 3-4%, although the strength is high, the plasticity is poor.

[0004] The Chinese patent document with publication number CN111349825A discloses a preparation method for producing high-toughness battery aluminum foil by using a short-process cast-rolling blank, the aluminum foil is composed of the following components in mass percentage: Si 0.025-0.1%, Fe 1.25-1.65%, Cu 0.001-0.1%, Mn<0.05%, Mg<0.05%, Cr<0.05%, Zn<0.05%, Ti 0.01-0.04%, the rest is Al, the tensile strength of the aluminum foil is 85-125 MPa, and the elongation is 16-35%, although the plasticity is good, the strength is low.

[0005] The Chinese patent document with publication number CN119101831A discloses a high-strength, low-pinhole-rate, and heat-resistant power battery aluminum foil produced by a short process and a preparation method thereof. The aluminum foil comprises the following components: Fe 0.21-0.55%, Si 0.15-0.35%, Cu 0.02-0.08%, Ti 0.01-0.04%, Mn≤0.02%, Zn≤0.02%, Y 0.003-0.005%, Er 0.003-0.005%, Sc 0.003-0.005%, and the rest is Al. The method increases grain refinement by introducing composite spiral electromagnetic stirring and pulse current assisted rolling, but the technology is complex and difficult to realize large-scale production.

[0006] The Chinese patent document with publication number CN110484785A discloses a preparation process of an aluminum foil for high-performance power batteries. The aluminum foil is composed of the following components by mass percentage: Fe 0.4-0.55%, Si 0.1-0.20%, Cu 0.05-0.15%, Mn 0.05-0.15%, Mg≤0.05%, Ti 0.01-0.015%, Zn 0.05-0.1%, Al≥99.00%, and the balance is unavoidable impurities. The tensile strength of the aluminum foil reaches 245 MP, and the elongation rate reaches 3.5%, but the preparation process includes fourteen passes of cold rolling and four passes of foil rolling, which has the problems of multiple rolling processes and long process flow.

[0007] In summary, the existing technology still has one or more of the following problems: (1) By adjusting the alloy composition to improve the strength and plasticity of the aluminum foil, it is difficult to balance the strength and plasticity of the aluminum foil due to the mutual restraint between the strength and plasticity. (2) The current production of lithium-ion battery aluminum foil still has the problems of multiple rolling passes, long process flow, and low production efficiency. (3) The existing lithium-ion battery aluminum foil still has the problems of uneven microstructure and performance, high pinhole rate, insufficient surface cleanliness, and low darcy value, which leads to low yield of lithium-ion battery aluminum foil. Therefore, the existing lithium-ion battery aluminum foil and its preparation method still need to be improved and developed. SUMMARY

[0008] In view of the problems and deficiencies mentioned in the background art, the present application provides an aluminum foil for lithium ion batteries and a cast-rolling production method thereof. By improving the cleanliness of the molten aluminum, the strength and plasticity of the aluminum foil are improved, and the problem of difficult to balance strength and plasticity is solved. By ultrasonic-assisted casting and rolling, the grain of the cast-rolled aluminum slab is refined, the uniformity of the microstructure and the plasticity are improved, the cold rolling and foil rolling passes are reduced, the process flow is shortened, the production efficiency is improved, and the production cost is reduced. The aluminum foil with high strength, high plasticity and high quality is obtained, which meets the development needs of high energy density lithium ion batteries in new energy fields such as electric vehicles, photovoltaic power generation and wind power generation, improves the safety and cycle life of the battery, and reduces the production cost.

[0009] The technical scheme adopted by the present application to achieve the above-mentioned purposes is as follows:

[0010] The present application provides an aluminum foil for lithium ion batteries, which is characterized by: the aluminum foil is composed of the following components with mass percentage: Si 0.06-0.09%, Fe 0.09-0.12%, Cu 0.05-0.08%, Mg 0.06-0.09%, the rest being Al and unavoidable impurities, the single impurity ≤0.03%, and the total impurities ≤0.1%.

[0011] Among them, Si and Fe are inevitable elements in the aluminum foil, and a small amount of Si and Fe can enhance the strength of the aluminum foil. However, when the content of Si and Fe is too high, Si and Fe in the aluminum foil are easy to form coarse intermetallic compounds FeSiAl3 phase and Fe2SiAl8 phase, both of which are hard and brittle phases, which not only reduces the plasticity of the aluminum foil, but also causes the aluminum foil to be perforated during rolling and form pinhole defects. A small amount of Cu and Mg in the aluminum foil mainly enhances the strength of the aluminum foil, and a small amount of Cu and Mg can significantly enhance the strength of the aluminum foil through solid solution strengthening, but the content of Cu and Mg cannot be too high, otherwise it will cause the plasticity and corrosion resistance of the aluminum foil to decrease. Therefore, the content of Si, Fe, Cu and Mg needs to be strictly controlled. In addition, elements such as Mn, Cr, Zn and Ti are impurity elements in the aluminum foil, and too high content of impurity elements will not only reduce the plasticity and corrosion resistance of the aluminum foil, but also cause the aluminum foil to be perforated and form pinhole defects. Therefore, the impurity elements in the aluminum foil must be strictly limited.

[0012] The present application provides a cast-rolling production method of an aluminum foil for lithium ion batteries, which is characterized by sequentially comprising the following steps:

[0013] Step one: according to the component composition and mass percentage of the aluminum foil, the molten aluminum is prepared and the temperature of the molten aluminum is raised to 730-740℃;

[0014] Step two: the molten aluminum is subjected to in-furnace refining and purification treatment and out-of-furnace online degassing and filtration treatment;

[0015] Step three: continuously cast the molten aluminum into aluminum slab under the assistance of ultrasonic wave;

[0016] Step four: high-temperature homogenization annealing treatment is performed on the aluminum slab;

[0017] Step five: the aluminum slab after the homogenization annealing treatment is cold-rolled into aluminum foil blank;

[0018] Step six: longitudinal edge shearing and intermediate annealing treatment is performed on the aluminum foil blank;

[0019] Step seven: the aluminum foil blank after the intermediate annealing treatment is cold-rolled into aluminum foil;

[0020] Step eight: slitting and finished product annealing are performed on the aluminum foil to obtain the aluminum foil for lithium ion battery.

[0021] Preferably, the aluminum ingot with aluminum content greater than 99.85% and the aluminum-silicon alloy, aluminum-iron alloy, aluminum-copper alloy and magnesium ingot with impurity content lower than 0.03% are selected as the raw materials for smelting and preparing the molten aluminum in step one. In order to ensure that the impurity element content of the aluminum foil does not exceed the standard and ensure the purity of the aluminum foil, the aluminum ingot with high purity and the alloy are selected for smelting and preparing the molten aluminum.

[0022] Preferably, the inert gas for the in-furnace refining purification treatment in step two is nitrogen with purity ≥99.99%, the amount of the refining flux is 0.2-0.3% of the weight of the molten aluminum, the refining purification time is 24-26 minutes, and the flux is composed of the following components in mass percentage: AlCl3 36.12%, LiF 28.37%, CuCO3 21.69%, and Ce(NO3)3 13.82%.

[0023] The in-furnace refining purification is performed by using a powder spraying tank and spraying the powder solid flux into the molten aluminum by using the inert gas as the carrier, so that the flux contacts and reacts with the molten aluminum, captures and carries the aluminum oxide inclusions and hydrogen in the molten aluminum. The effect of the in-furnace refining purification is closely related to the component composition of the flux. The existing flux is mainly composed of chloride and fluoride of alkali metals such as Na, K and Ca. The smelting and refining purification treatment using such flux will cause the content of Na, K and Ca in the aluminum foil to be too high, which will eventually reduce the plasticity, electrical conductivity and corrosion resistance of the aluminum foil and reduce the service life of the battery.

[0024] In order to solve the problems of the existing flux, the application develops a high-efficiency flux without alkali metal, which is composed of AlCl3, LiF, CuCO3 and Ce(NO3)3 powder. The melting point and boiling point of AlCl3 are very low, and it sublimates into fine bubbles in the high-temperature aluminum liquid, which captures and removes the inclusions and hydrogen in the aluminum liquid. LiF forms a molten salt in the high-temperature aluminum liquid, which mainly dissolves and adsorbs the inclusions such as aluminum oxide, improves the surface tension of the aluminum liquid, promotes the separation of inclusions and aluminum liquid, and improves the effect of the flux on removing inclusions. CuCO3 decomposes CO2 bubbles in the aluminum liquid, which can adsorb and remove the inclusions and hydrogen in the aluminum liquid, and the decomposed Cu atoms can supplement the Cu content in the aluminum liquid to enhance the strength of the aluminum foil. Ce(NO3)3 acts as a heating agent, which mainly decomposes in the aluminum liquid and releases a large amount of heat, which can accelerate the melting of the flux in the aluminum liquid, improve the contact reaction between the flux and the aluminum liquid, and improve the flowability of the aluminum liquid, accelerate the floating and overflowing of inclusions and hydrogen, and improve the effect of removing inclusions and hydrogen. The decomposed NO and NO2 bubbles can also adsorb and remove inclusions and hydrogen, and the decomposed rare earth element Ce has strong affinity with hydrogen and oxygen, which can form stable rare earth hydride and oxide, and finally precipitate in the furnace bottom due to its high density and high melting point, which can play a role in hydrogen and oxygen fixation.

[0025] Preferably, the second step of the online degassing outside the furnace is to flow the aluminum liquid through the degassing box, and the purified gas introduced into the degassing box is a mixed gas composed of nitrogen gas with a purity of ≥99.99% and freon gas with a purity of ≥99.99%, and the volume percentage of freon gas in the mixed gas is 19-21%, and the flow rate of the mixed gas is 0.5-0.6L / kg of aluminum liquid.

[0026] In order to improve the cleanliness of the aluminum liquid, in addition to the in-furnace refining and purification, online degassing and filtration outside the furnace are also needed. In the existing online degassing technology of the degassing box, inert gas nitrogen or argon, or a mixed gas composed of inert gas and chlorine is usually introduced into the degassing box. Since the densities of nitrogen, argon and chlorine are small, the bubbles float quickly in the aluminum liquid, resulting in short contact time between the bubbles and the aluminum liquid, poor hydrogen removal effect. In addition, chlorine is a toxic and irritating gas, which can also corrode equipment and tools, and is relatively dangerous to use.

[0027] In order to improve the hydrogen removal effect of the degassing tank, the mixed gas composed of nitrogen and freon gas is creatively introduced into the degassing tank. Since the freon has large density, non-toxic and stable chemical property, the contact time of the bubbles and the aluminum liquid can be significantly increased. By using high-purity nitrogen and freon gas, the hydrogen removal effect of the degassing tank can be significantly improved. After the hydrogen removal by the degassing tank, the hydrogen content of the aluminum liquid can be reduced to 0.08 mL / 100 g Al or less, and the cleanliness of the aluminum liquid is greatly improved.

[0028] Preferably, the online filtering outside the furnace in step two is that the aluminum liquid flows through the ceramic filter plate with a porosity of 50 mesh and the electromagnetic filter in sequence. The electromagnetic filter has an electromagnetic field strength of 0.04-0.05 T and an electromagnetic field frequency of 15-17 kHz.

[0029] In order to realize the deep filtration of the aluminum liquid, the ceramic plate filtration and the electromagnetic filtration are creatively combined in the present application. The aluminum liquid is first filtered through the ceramic filter plate with a porosity of 50 mesh to remove the inclusions larger than 20 microns, and then the aluminum liquid is filtered through the electromagnetic filter for deep filtration. The filtering precision of the electromagnetic filtration is higher than that of the traditional ceramic tube filtration. The principle is that the aluminum liquid is conductive and the inclusions are not conductive. When the aluminum liquid flows through the ceramic tube separator, an alternating magnetic field is applied by an induction coil, so that the aluminum liquid is subjected to the electromagnetic force pointing to the center, and the inclusions are subjected to the electromagnetic repulsive force in the opposite direction, so that the inclusions gradually migrate and enrich to the inner surface of the ceramic tube separator, realizing the separation of the inclusions and the aluminum liquid. The principle and use method of the electromagnetic filter can be referred to relevant literature, which will not be described here. Through a large number of experimental explorations and researches, the electromagnetic field strength and frequency of the electromagnetic filter are optimized and designed. It is found that under the conditions of an electromagnetic field strength of 0.04-0.05 T and an electromagnetic field frequency of 15-17 kHz, the removal rate of the inclusions larger than 1 micron in the aluminum liquid can reach more than 98% after deep filtration by the electromagnetic filter, and the volume content of the inclusions is less than 0.02 mm 2 / kg Al, thereby greatly improving the cleanliness of the aluminum liquid.

[0030] Preferably, the ultrasonic frequency during the casting and rolling in step three is 10-12 kHz, the ultrasonic power is 5-7 kW, the temperature of the aluminum liquid in the forehearth is 690-700℃, the casting and rolling speed is 1200-1300 mm / min, the length of the casting and rolling zone is 70-75 mm, the cooling water pressure is 0.5-0.6 MPa, and the thickness of the aluminum slab is 6±0.1 mm.

[0031] Casting and rolling is through the front box nozzle to cast liquid aluminum continuously into the two casting and rolling mill roll gap, in the cooling and pressure of the casting and rolling roll cooling and solidification into aluminum slab. Because of the non-equilibrium solidification of aluminum liquid and the slow cooling and solidification, will cause the casting and rolling aluminum slab grain coarse and serious organization composition segregation, resulting in poor plasticity of aluminum slab, edge cracking is serious, and ultimately lead to the unevenness of aluminum foil organization composition. The prior art is usually adding refiner in the aluminum liquid to refine the grain of casting and rolling aluminum slab, but this method is first limited effect, casting and rolling aluminum slab plasticity is still poor, can not solve the edge cracking and serious organization composition segregation problem. In addition, adding aluminum titanium boron alloy and other refiners, due to the existence of a large number of TiB2 particle agglomeration, will lead to aluminum foil rolling perforation and increase the pinhole defect.

[0032] In view of the problems and deficiencies of the existing casting and rolling technology, the present application adopts ultrasonic assisted casting and rolling, the probe of the ultrasonic wave is set in the aluminum liquid of the front box of the casting and rolling mill, through the vibration and acoustic cavitation effect of the ultrasonic wave, the temperature uniformity of the aluminum liquid in the casting and rolling zone is improved, the number of grain heterogeneous nucleation is increased, the grain of the casting and rolling aluminum slab is refined, the composition segregation and edge cracking are eliminated, the uniformity and plasticity of the organization composition of the casting and rolling aluminum slab are improved, and the casting and rolling speed of the aluminum liquid and the yield of the aluminum slab are improved. The composition of the aluminum liquid is different, and the casting and rolling process is also different. In order to effectively play the function of ultrasonic assisted casting and rolling, it is necessary to reasonably match the frequency and power of ultrasonic wave and the process parameters such as aluminum liquid temperature and casting and rolling speed during casting and rolling, so as to obtain casting and rolling aluminum slab with fine and uniform grain and excellent plasticity.

[0033] As preferred, the high temperature homogenization annealing treatment of the aluminum slab in step four is to heat the aluminum slab to 300±3℃ for 1 hour, then continue to heat to 450±3℃ for 2 hours, then continue to heat to 585±3℃ for 5 hours, and finally cool to room temperature with the furnace.

[0034] The purpose of high-temperature homogenization annealing treatment of the cast-rolled aluminum slab is mainly to further eliminate the composition segregation of the aluminum slab, improve the composition uniformity and plasticity of the aluminum slab, and create favorable conditions for subsequent cold rolling. The high-temperature homogenization annealing of the cast-rolled aluminum slab first needs to strictly control the heating rate. Since the aluminum slab is usually in the form of a large coil for annealing in production, too fast heating rate will cause too large temperature difference between the inside and outside of the aluminum slab coil and result in uneven annealing effect. In order to solve this problem, the invention creatively adopts a stepwise heating mode, reduces the temperature difference between the inside and outside of the aluminum slab coil, and improves the temperature uniformity by maintaining the temperature at 300±3℃ for 1 hour and continuing to maintain the temperature at 450±3℃ for 2 hours. In addition, the heating temperature and holding time of the final annealing also need to be strictly controlled. The temperature is set at 585℃ for maintaining for 5 hours under the condition that the temperature fluctuation range is less than 3℃. If the final annealing temperature is low or the holding time is short, the composition segregation cannot be effectively eliminated and the plasticity of the aluminum slab cannot be improved. If the final annealing temperature is too high, the aluminum slab will be overburned, which will reduce the plasticity of the aluminum slab and the mechanical properties of the aluminum foil. The holding time of the final annealing should not be too long, otherwise the composition uniformity of the aluminum slab cannot be further improved, and a large amount of heat energy needs to be consumed due to high-temperature holding, which increases energy consumption and production cost.

[0035] As preferably, the process flow of cold rolling the aluminum slab into an aluminum foil blank in step five is: first pass rolling into 2±0.1mm, second pass rolling into 0.8±0.1mm, third pass rolling into 0.4±0.05mm, and fourth pass rolling into 0.2±0.05mm aluminum foil blank.

[0036] The conventional cast-rolled aluminum slab has coarse grains and serious composition segregation. In order to reduce the cold rolling deformation resistance and avoid cracking of the aluminum slab, it usually needs to be cold rolled for more than ten passes, and the deformation amount of each pass cannot exceed 50%. Due to the large number of cold rolling passes, the cold rolling process flow is long and the production efficiency is low. The invention adopts ultrasonic wave to assist the cast-rolled aluminum slab and high-temperature homogenization annealing treatment of the aluminum slab, refines the grain structure of the aluminum slab, eliminates the composition segregation, greatly improves the plasticity of the aluminum slab, creates favorable conditions for cold rolling of the aluminum slab, and the deformation amount of the cold rolling pass can be more than 50%, which effectively reduces the number of cold rolling passes, shortens the cold rolling process flow, and improves the cold rolling production efficiency.

[0037] As preferably, the intermediate annealing treatment of the aluminum foil blank in step six is heating the aluminum foil blank to 200±3℃ for 1 hour, then continuing to heat to 300±3℃ for 2 hours, continuing to heat to 380±3℃ for 3 hours, and finally cooling to room temperature with the furnace.

[0038] The aluminum slab will be work-hardened during the cold rolling process, which results in the increase of the strength and hardness of the aluminum slab, and the gradual decrease of the plasticity. With the increase of the cold rolling passes, the work-hardening of the aluminum slab becomes more and more serious, which is easy to cause the cracking of the aluminum foil blank. The purpose of the intermediate annealing of the aluminum foil blank is to eliminate the work-hardening and residual stress of the aluminum slab, to make the aluminum foil blank recrystallize, to obtain the fine and uniform grain structure, to reduce the hardness of the aluminum foil blank, and to improve the plasticity of the aluminum foil blank, so as to create favorable conditions for the subsequent foil rolling of the aluminum foil blank. The temperature rising speed, the annealing temperature and the annealing time also need to be strictly controlled during the intermediate annealing of the aluminum foil blank. By using the step temperature rising mode, the temperature difference between the inside and the outside of the aluminum foil blank roll can be reduced, and the temperature uniformity can be improved by keeping the temperature at 200±3℃ for 1 hour and keeping the temperature at 300±3℃ for 2 hours. The temperature rising to 380±3℃ for 3 hours means that the temperature is set at 380℃, and the temperature fluctuation range is less than 3℃ under the condition of keeping the temperature for 3 hours. If the final annealing temperature is too low or the time is too short, it is not enough to completely eliminate the work-hardening and residual stress of the aluminum foil blank, and it also cannot induce the recrystallization of the aluminum foil blank to obtain the fine and uniform grain structure. If the final annealing temperature is too high or the keeping time is too long, the recrystallized grains will grow and coarsen, which not only cannot improve the plasticity of the aluminum foil blank, but also will increase the energy consumption and the production cost.

[0039] Preferably, the process flow of the step seven is that the aluminum foil blank is cold-rolled into the aluminum foil with the thickness of 0.1±0.02mm by the first pass, 0.05±0.02mm by the second pass, 0.025±0.01mm by the third pass, and 0.012 or 0.013mm by the fourth pass.

[0040] The precision rolling mill set needs to be used to cold-roll the aluminum foil blank into the aluminum foil, so as to strictly control the deformation and the thickness of each pass. In the existing foil rolling stage of the aluminum foil, due to the coarse grain and the serious composition segregation of the aluminum foil blank, in order to reduce the cold rolling deformation resistance and avoid the cracking of the aluminum foil blank, the aluminum foil is usually obtained by passing through more than ten foil rolling passes. Since the foil rolling passes are many, the process flow is long, and the production efficiency is low. Since the aluminum foil blank of the present application is subjected to the intermediate annealing, the aluminum foil blank is completely recrystallized, the fine and uniform grain structure is obtained, and the plasticity of the aluminum foil blank is greatly improved. Therefore, the large deformation foil rolling can also be implemented, the foil rolling passes are significantly reduced, the foil rolling process flow is shortened, and the production efficiency is improved.

[0041] Preferably, the process flow of the step eight is that the aluminum foil is heated to 100±3℃ for 1 hour, then heated to 200±3℃ for 1 hour, then heated to 260±3℃ for 2 hours, and finally cooled to room temperature in the furnace.

[0042] The aluminum foil obtained by cold rolling has internal residual stress due to work hardening, unstable structure, and surface attached with lubricating oil, etc. The purpose of product annealing of the aluminum foil is mainly to eliminate the residual stress, unstable structure and oil removal of the aluminum foil, improve the use performance of the aluminum foil, and improve the surface quality of the aluminum foil. The product annealing of the aluminum foil also needs to control the heating speed to prevent the aluminum foil from having uneven performance due to too large temperature difference between the inside and outside of the aluminum foil roll. Meanwhile, the final annealing temperature and time need to be strictly controlled, and a stepwise heating mode is adopted, and the temperature difference between the inside and outside of the aluminum foil is reduced and the temperature uniformity is improved by keeping the temperature at 100 DEG C and 200 DEG C for 1 hour respectively. The temperature is set at 260 DEG C for keeping for 2 hours in the step of heating to 260 DEG C ± 3 DEG C, and the temperature fluctuation range is less than 3 DEG C. If the final annealing temperature is too low or the time is too short, the residual stress and unstable structure of the aluminum foil cannot be completely eliminated. If the final annealing temperature is too high or the keeping time is too long, the strength and hardness of the aluminum foil are reduced too much, and the high-strength and high-plasticity aluminum foil product cannot be obtained.

[0043] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0044] (1) The present application optimizes the component composition of the aluminum foil, strictly controls the content of impurity elements, adopts in-furnace refining purification and out-of-furnace online degassing filtration measures, greatly improves the purity of the aluminum foil, solves the problem of mutual restriction between strength and plasticity, greatly improves the strength and plasticity of the aluminum foil, and makes the aluminum foil have the advantages of high strength and high plasticity;

[0045] (2) The present application adopts ultrasonic assisted casting and rolling of aluminum plate blank, refines the grain structure of the aluminum plate blank, improves the uniformity of the structure and plasticity of the aluminum plate blank, and makes the aluminum plate blank can be deformed and cold rolled, greatly reduces the number of cold rolling passes, shortens the process flow, and is beneficial to improve the production efficiency of the aluminum foil and reduce the production cost;

[0046] (3) The tensile strength of the 12 μm / 13 μm aluminum foil of the present application is greater than 250 MPa, the elongation after fracture is greater than 6%, the surface wetting tension is greater than 40 × 10 -3 N / m, and the number of pinholes is less than 0.01 / m 2 The aluminum foil has excellent tensile mechanical properties and surface cleanliness, meets the development needs of high-energy density power batteries and large-scale energy storage batteries, and is beneficial to improve the safety and service life of the battery. DETAILED DESCRIPTION

[0047] Example 1:

[0048] The aluminum foil for lithium ion battery is composed of the following components in mass percentage: Si 0.08%, Fe 0.011%, Cu 0.06%, Mg 0.07%, the rest being Al and inevitable impurities, the impurities being ≤0.03% individually and ≤0.1% in total, and the cast-rolling production method comprises the following steps in sequence:

[0049] Step one: according to the component composition and mass percentage of the aluminum foil, aluminum ingots with aluminum content of 99.85% and aluminum silicon alloy, aluminum iron alloy, aluminum copper alloy and magnesium ingots with impurity content lower than 0.03% are selected as raw materials to smelt aluminum liquid and raise the temperature of the aluminum liquid to 735℃;

[0050] Step two: the aluminum liquid in the furnace is refined and purified for 25 minutes by using nitrogen gas with purity of 99.99% and flux with aluminum liquid weight of 0.25%, and then the aluminum liquid is subjected to on-line degassing and filtration by flowing through a degassing box, a ceramic filter plate and an electromagnetic filter arranged on the flow channel, the flux is composed of the following components in mass percentage: AlCl3 36.12%, LiF 28.37%, CuCO3 21.69%, Ce(NO3)3 13.82%, the degassing box is supplied with a mixed gas composed of nitrogen gas with purity of 99.99% and freon gas with purity of 99.99%, the volume percentage of the freon gas in the mixed gas is 20%, the flow rate of the mixed gas is 0.55L / kg of aluminum liquid, the porosity of the ceramic filter plate is 50 mesh, and the electromagnetic field strength of the electromagnetic filter is 0.045T and the electromagnetic field frequency is 16kHz;

[0051] Step three: the aluminum liquid is continuously cast-rolled into aluminum slab with thickness of 6±0.1mm under the conditions of ultrasonic frequency of 11kHz, ultrasonic power of 6kW, aluminum liquid temperature in the front box of 695℃, cast-rolling speed of 1250mm / min, cast-rolling zone length of 72mm and cooling water pressure of 0.55MPa;

[0052] Step four: the aluminum slab is heated to 300±3℃ and kept for 1 hour, then heated to 450±3℃ and kept for 2 hours, and then heated to 585±3℃ and kept for 5 hours for high-temperature homogenization annealing treatment of the aluminum slab;

[0053] Step five: the aluminum slab is cold-rolled into aluminum foil blank, the first pass is rolled to 2±0.1mm, the second pass is rolled to 0.8±0.1mm, the third pass is rolled to 0.4±0.05mm, and the fourth pass is rolled to 0.2±0.05mm of the aluminum foil blank;

[0054] Step six: the aluminum foil blank is subjected to longitudinal edge cutting, then heated to 200±3℃ and kept for 1 hour, then heated to 300±3℃ and kept for 2 hours, and then heated to 380±3℃ and kept for 3 hours for intermediate annealing treatment;

[0055] Step seven: cold rolling the aluminum foil blank into an aluminum foil, the first pass is 0.1±0.02mm, the second pass is 0.05±0.02mm, the third pass is 0.025±0.01mm, and the fourth pass is 0.012mm;

[0056] Step eight: slitting the aluminum foil, then heating the aluminum foil to 100±3℃ for 1 hour, then heating to 200±3℃ for 1 hour, and then heating to 260±3℃ for 2 hours for product annealing, and then cooling to obtain the aluminum foil for lithium ion batteries.

[0057] Example 2:

[0058] The aluminum foil for lithium ion batteries is composed of the following components by mass percentage: Si 0.07%, Fe 0.10%, Cu 0.07%, Mg 0.08%, the rest being Al and unavoidable impurities, individual impurities ≤0.03%, total impurities ≤0.1%, and the cast-rolling production method includes the following steps in order:

[0059] Step one: according to the composition and mass percentage of the aluminum foil, select aluminum ingots with an aluminum content of 99.85% and aluminum silicon alloy, aluminum iron alloy, aluminum copper alloy, and magnesium ingots with impurity contents below 0.03% as raw materials to smelt the aluminum liquid and raise the aluminum liquid temperature to 735℃;

[0060] Step two: purify the aluminum liquid in the furnace for 25 minutes using nitrogen gas with a purity of 99.99% and a flux of 0.25% of the weight of the aluminum liquid, then pass the aluminum liquid through a degassing box, a ceramic filter plate, and an electromagnetic filter arranged on the flow channel for online degassing and filtration, the flux is composed of the following components by mass percentage: AlCl3 36.12%, LiF 28.37%, CuCO3 21.69%, Ce(NO3)3 13.82%, a mixed gas composed of nitrogen gas with a purity of 99.99% and Freon gas with a purity of 99.99% is introduced into the degassing box, the volume percentage of Freon gas in the mixed gas is 20%, the flow rate of the mixed gas is 0.55L / kg of aluminum liquid, the porosity of the ceramic filter plate is 50 mesh, and the electromagnetic field strength of the electromagnetic filter is 0.045T and the electromagnetic field frequency is 16kHz;

[0061] Step three: continuously cast and roll the aluminum liquid into an aluminum slab with a thickness of 6±0.1mm under the following conditions: ultrasonic frequency of 11kHz, ultrasonic power of 6kW, aluminum liquid temperature in the front box of 695℃, casting and rolling speed of 1250mm / min, casting and rolling zone length of 72mm, and cooling water pressure of 0.55MPa;

[0062] Step four: the aluminum slab is heated to 300±3℃ for 1 hour, then heated to 450±3℃ for 2 hours, and then heated to 585±3℃ for 5 hours for high-temperature homogenization annealing treatment;

[0063] Step five: the aluminum slab is cold-rolled into an aluminum foil blank, the first pass is rolled to 2±0.1mm, the second pass is rolled to 0.8±0.1mm, the third pass is rolled to 0.4±0.05mm, and the fourth pass is rolled to 0.2±0.05mm of the aluminum foil blank;

[0064] Step six: the aluminum foil blank is subjected to longitudinal shearing edge, and then the aluminum foil blank is heated to 200±3℃ for 1 hour, then heated to 300±3℃ for 2 hours, and then heated to 380±3℃ for 3 hours for intermediate annealing treatment;

[0065] Step seven: the aluminum foil blank is cold-rolled into an aluminum foil, the first pass is rolled to 0.1±0.02mm, the second pass is rolled to 0.05±0.02mm, the third pass is rolled to 0.025±0.01mm, and the fourth pass is rolled to 0.013mm of the aluminum foil;

[0066] Step eight: the aluminum foil is slitting, and then the aluminum foil is heated to 100±3℃ for 1 hour, then heated to 200±3℃ for 1 hour, and then heated to 260±3℃ for 2 hours for product annealing, and the aluminum foil for lithium ion battery is obtained after cooling.

[0067] Example 3:

[0068] The aluminum foil for lithium ion battery is composed of the following components by mass percentage: Si 0.09%, Fe 0.12%, Cu 0.05%, Mg 0.09%, the rest is Al and unavoidable impurities, impurities ≤0.03% individually, impurities ≤0.1% in total, and the cast-rolling production method comprises the following steps in turn:

[0069] Step one: according to the component composition and mass percentage of the aluminum foil, aluminum ingots with an aluminum content of 99.85% and aluminum silicon alloy, aluminum iron alloy, aluminum copper alloy and magnesium ingots with an impurity content lower than 0.03% are selected as raw materials to smelt aluminum liquid and the temperature of the aluminum liquid is raised to 740℃;

[0070] Step two: purifying the aluminum liquid in the furnace for 26 minutes by using nitrogen gas with a purity of 99.99% and a flux with an aluminum liquid weight of 0.3%, and then performing online degassing and filtration on the aluminum liquid flowing through a degassing box, a ceramic filter plate and an electromagnetic filter arranged on the flow channel, the flux is composed of the following components in mass percentage: AlCl3 36.12%, LiF 28.37%, CuCO3 21.69%, Ce(NO3)3 13.82%, the degassing box is supplied with a mixed gas composed of nitrogen gas with a purity of 99.99% and Freon gas with a purity of 99.99%, the volume percentage of Freon gas in the mixed gas is 21%, the flow rate of the mixed gas is 0.5L / kg of aluminum liquid, the porosity of the ceramic filter plate is 50 mesh, the electromagnetic field strength of the electromagnetic filter is 0.05T, and the electromagnetic field frequency is 15kHz;

[0071] Step three: continuously casting and rolling the aluminum liquid into an aluminum slab with a thickness of 6±0.1mm under the conditions of an ultrasonic frequency of 12kHz, an ultrasonic power of 5kW, an aluminum liquid temperature in the front box of 700℃, a casting and rolling speed of 1200mm / min, a length of the casting and rolling area of 70mm, and a cooling water pressure of 0.6MPa;

[0072] Step four: heating the aluminum slab to 300±3℃ for 1 hour, then continuously heating to 450±3℃ for 2 hours, and then continuously heating to 585±3℃ for 5 hours for high-temperature homogenization annealing treatment of the aluminum slab;

[0073] Step five: cold rolling the aluminum slab into an aluminum foil blank, the first pass is 2±0.1mm, the second pass is 0.8±0.1mm, the third pass is 0.4±0.05mm, and the fourth pass is 0.2±0.05mm of the aluminum foil blank;

[0074] Step six: performing longitudinal edge cutting on the aluminum foil blank, then heating the aluminum foil blank to 200±3℃ for 1 hour, then continuously heating to 300±3℃ for 2 hours, and then continuously heating to 380±3℃ for 3 hours for intermediate annealing treatment;

[0075] Step seven: cold rolling the aluminum foil blank into an aluminum foil, the first pass is 0.1±0.02mm, the second pass is 0.05±0.02mm, the third pass is 0.025±0.01mm, and the fourth pass is 0.012mm of the aluminum foil;

[0076] Step eight: slitting the aluminum foil, then heating the aluminum foil to 100±3℃ for 1 hour, then continuously heating to 200±3℃ for 1 hour, and then continuously heating to 260±3℃ for 2 hours for product annealing, and obtaining the aluminum foil for lithium ion batteries after cooling.

[0077] Example 4:

[0078] The aluminum foil for lithium ion battery is composed of the following components in mass percentage: Si 0.06%, Fe 0.09%, Cu 0.08%, Mg 0.06%, the rest being Al and inevitable impurities, the impurities being ≤0.03% individually and ≤0.1% in total, and the cast-rolling production method comprising the following steps in sequence:

[0079] Step one: selecting aluminum ingot with aluminum content of 99.85% and aluminum silicon alloy, aluminum iron alloy, aluminum copper alloy and magnesium ingot with impurity content lower than 0.03% as raw materials to smelt aluminum liquid according to the component composition and mass percentage of the aluminum foil, and raising the temperature of the aluminum liquid to 730℃;

[0080] Step two: purifying the aluminum liquid in the furnace for 24 minutes by using nitrogen gas with purity of 99.99% and flux with aluminum liquid weight of 0.2%, and then performing online degassing and filtration of the aluminum liquid by flowing through a degassing box, a ceramic filter plate and an electromagnetic filter arranged on the flow channel, the flux being composed of the following components in mass percentage: AlCl3 36.12%, LiF 28.37%, CuCO3 21.69%, Ce(NO3)3 13.82%, the degassing box being supplied with mixed gas composed of nitrogen gas with purity of 99.99% and freon gas with purity of 99.99%, the volume percentage of the freon gas in the mixed gas being 19%, the flow rate of the mixed gas being 0.6L / kg of aluminum liquid, the porosity of the ceramic filter plate being 50 mesh, and the electromagnetic field strength of the electromagnetic filter being 0.04T and the electromagnetic field frequency being 17kHz;

[0081] Step three: continuously casting and rolling the aluminum liquid into aluminum slab with thickness of 6±0.1mm under the conditions of ultrasonic frequency of 10kHz, ultrasonic power of 7kW, aluminum liquid temperature in the front box of 690℃, casting and rolling speed of 1300mm / min, length of the casting and rolling zone of 75mm, and cooling water pressure of 0.5MPa;

[0082] Step four: heating the aluminum slab to 300±3℃ for 1 hour, then continuously heating to 450±3℃ for 2 hours, and then continuously heating to 585±3℃ for 5 hours to perform high-temperature homogenization annealing treatment on the aluminum slab;

[0083] Step five: cold rolling the aluminum slab into aluminum foil blank, the first pass being 2±0.1mm, the second pass being 0.8±0.1mm, the third pass being 0.4±0.05mm, and the fourth pass being 0.2±0.05mm;

[0084] Step six: performing longitudinal edge cutting on the aluminum foil blank, then heating the aluminum foil blank to 200±3℃ for 1 hour, then continuously heating to 300±3℃ for 2 hours, and then continuously heating to 380±3℃ for 3 hours to perform intermediate annealing treatment;

[0085] Step seven: cold rolling the aluminum foil blank into aluminum foil, the first pass is 0.1±0.02mm, the second pass is 0.05±0.02mm, the third pass is 0.025±0.01mm, and the fourth pass is 0.013mm aluminum foil;

[0086] Step eight: slitting the aluminum foil, then heating the aluminum foil to 100±3℃ for 1 hour, then heating to 200±3℃ for 1 hour, and then heating to 260±3℃ for 2 hours for product annealing, and then cooling to obtain the aluminum foil for lithium ion batteries.

[0087] Example 5:

[0088] The aluminum foil for lithium ion batteries is composed of the following components by mass percentage: Si 0.07%, Fe 0.09%, Cu 0.06%, Mg 0.09%, the rest being Al and unavoidable impurities, individual impurities ≤0.03%, total impurities ≤0.1%, and the cast-rolling production method comprises the following steps in sequence:

[0089] Step one: according to the component composition and mass percentage of the aluminum foil, aluminum ingots with an aluminum content of 99.85% and aluminum silicon alloy, aluminum iron alloy, aluminum copper alloy, and magnesium ingots with an impurity content of less than 0.03% are selected as raw materials to smelt the aluminum liquid and raise the temperature of the aluminum liquid to 735℃;

[0090] Step two: using nitrogen gas with a purity of 99.99% and a flux of 0.25% of the weight of the aluminum liquid to refine the aluminum liquid in the furnace for 25 minutes, and then flowing the aluminum liquid through a degassing box, a ceramic filter plate, and an electromagnetic filter arranged on the flow channel for online degassing and filtration, the flux is composed of the following components by mass percentage: AlCl3 36.12%, LiF 28.37%, CuCO3 21.69%, Ce(NO3)3 13.82%, a mixed gas composed of nitrogen gas with a purity of 99.99% and Freon gas with a purity of 99.99% is introduced into the degassing box, the volume percentage of Freon gas in the mixed gas is 20%, the flow rate of the mixed gas is 0.55L / kg of aluminum liquid, the porosity of the ceramic filter plate is 50 mesh, and the electromagnetic field strength of the electromagnetic filter is 0.045T and the electromagnetic field frequency is 16kHz;

[0091] Step three: continuously casting and rolling the aluminum liquid into an aluminum slab with a thickness of 6±0.1mm under the conditions of an ultrasonic frequency of 11kHz, an ultrasonic power of 6kW, an aluminum liquid temperature in the front box of 695℃, a casting and rolling speed of 1250mm / min, a casting and rolling zone length of 74mm, and a cooling water pressure of 0.55MPa;

[0092] Step four: the aluminum slab is heated to 300±3℃ for 1 hour, then heated to 450±3℃ for 2 hours, and then heated to 585±3℃ for 5 hours for high-temperature homogenization annealing treatment;

[0093] Step five: the aluminum slab is cold-rolled into an aluminum foil blank, the first pass is rolled to 2±0.1mm, the second pass is rolled to 0.8±0.1mm, the third pass is rolled to 0.4±0.05mm, and the fourth pass is rolled to 0.2±0.05mm of the aluminum foil blank;

[0094] Step six: the aluminum foil blank is subjected to longitudinal shearing edge, and then the aluminum foil blank is heated to 200±3℃ for 1 hour, then heated to 300±3℃ for 2 hours, and then heated to 380±3℃ for 3 hours for intermediate annealing treatment;

[0095] Step seven: the aluminum foil blank is cold-rolled into an aluminum foil, the first pass is rolled to 0.1±0.02mm, the second pass is rolled to 0.05±0.02mm, the third pass is rolled to 0.025±0.01mm, and the fourth pass is rolled to 0.012mm of the aluminum foil;

[0096] Step eight: the aluminum foil is slitting, and then the aluminum foil is heated to 100±3℃ for 1 hour, then heated to 200±3℃ for 1 hour, and then heated to 260±3℃ for 2 hours for product annealing, and the aluminum foil is obtained after cooling.

[0097] Comparative Example 1:

[0098] The cast-rolling production method of the aluminum foil of the present comparative example is the same as that of Example 1, except that the aluminum foil is composed of the following components in mass percentage: Si 0.08%, Fe 0.011%, Cu 0.03%, Mg 0.04%, the rest being Al and unavoidable impurities, impurities ≤0.03% individually, and impurities ≤0.1% in total.

[0099] Comparative Example 2:

[0100] The component composition and mass percentage of the aluminum foil of the present comparative example and the cast-rolling production method are the same as those of Example 1, except that the step two is to use the existing conventional flux to refine and purify the aluminum liquid in the furnace, and the flux is composed of the following components in mass percentage: NaCl 46.71%, KCl 30.62%, Na3AlF6 22.67%.

[0101] Comparative Example 3:

[0102] The component composition and mass percentage of the aluminum foil of the present comparative example and the casting and rolling production method are the same as those of Example 1, except that in Step three, the ultrasonic assisted casting and rolling is not adopted, but the molten aluminum is directly continuously cast and rolled into aluminum slab with thickness of 6±0.1 mm.

[0103] Comparative Example 4:

[0104] The component composition and mass percentage of the aluminum foil of the present comparative example and the casting and rolling production method are the same as those of Example 1, except that in Step six, the aluminum foil blank is heated to 200±3℃ for 1 hour, then continuously heated to 300±3℃ for 2 hours, and then continuously heated to 400±3℃ for 3 hours for intermediate annealing treatment.

[0105] Comparative Example 5:

[0106] The component composition and mass percentage of the aluminum foil of the present comparative example and the casting and rolling production method are the same as those of Example 1, except that in Step eight, the aluminum foil is heated to 100±3℃ for 1 hour, then continuously heated to 200±3℃ for 1 hour, and then continuously heated to 250±3℃ for 2 hours for final annealing.

[0107] Verification Example:

[0108] The aluminum foils obtained in Examples 1-5 and Comparative Examples 1-5 are sampled respectively, and the tensile test samples are processed according to the national standard GB / T16865 “Tensile Test Specimens and Methods for Wrought Aluminum and Magnesium and Their Alloys”, then the room temperature tensile test is carried out on the electronic tensile testing machine, the tensile strength and elongation at break of the aluminum foil are detected, the surface wetting tension of the aluminum foil is detected according to the national standard GB / T22638.4 “Test Methods for Aluminum Foil Part 4: Determination of Surface Wetting Tension”, and the number of pinholes per square meter of the aluminum foil is detected according to the national standard GB / T22638.2 “Test Methods for Aluminum Foil Part 2: Detection of Pinholes”, and the results are shown in Table 1. As can be seen from Table 1, the tensile strength of the aluminum foils of Examples 1-5 is greater than 250 MPa, the elongation at break is greater than 6%, the surface wetting tension is greater than 40×10 -3 N / m, and the number of pinholes is less than 0.01 / m 2 . The Cu and Mg contents of the aluminum foil of Comparative Example 1 are insufficient, resulting in low strength of the aluminum foil. In Comparative Example 2, the existing conventional flux is used to refine and purify the molten aluminum in the furnace, resulting in low strength, plasticity and surface wetting tension of the aluminum foil, and more pinholes. In Comparative Example 3, the ultrasonic assisted casting and rolling is not adopted to produce aluminum slab, resulting in coarse grains and composition segregation of the cast and rolled aluminum slab, which leads to low strength and plasticity of the aluminum foil, and more pinholes. In Comparative Example 4, the final annealing temperature of the aluminum foil blank is too high, resulting in grain growth and coarsening, which leads to low strength, plasticity and surface wetting tension of the aluminum foil, and more pinholes. In Comparative Example 5, the final annealing temperature of the aluminum foil is too low, although the strength of the aluminum foil is high, but the plasticity is low.

[0109] Table 1 Room temperature tensile mechanics, surface wetting tension and pinhole count of aluminum foils

[0110]

[0111] The application is described by way of example only, and the application is not limited to the embodiments disclosed. Other variations to the disclosed embodiments can be apparent to those skilled in the art, and such variations should be considered to be within the ambit of the present application as defined by the claims.

Claims

1. An aluminum foil for a lithium-ion battery, characterized by, The aluminum foil is composed of the following components in mass percentage: Si 0.06-0.09%, Fe 0.09-0.12%, Cu 0.05-0.08%, Mg 0.06-0.09%, the rest being Al and inevitable impurities, the impurities being ≤0.03% individually, ≤0.1% in total, the tensile strength of the aluminum foil being greater than 250 MPa, the elongation after breaking being greater than 6%, the surface wetting tension being greater than 40×10 -3 N / m, the number of pinholes being less than 0.01 / m 2 .

2. A cast-rolling production method of an aluminum foil for a lithium ion battery, the method being used for producing the aluminum foil for a lithium ion battery as claimed in claim 1, characterized by, Comprise the following steps in turn: Step one: according to the composition and mass percentage of aluminum foil, smelting and preparing aluminum liquid and increasing the temperature of aluminum liquid to 730-740℃; Step two: the furnace refining purification treatment and the furnace outside online degassing filtration treatment of aluminum liquid; Step three: under the auxiliary action of ultrasonic wave, continuously cast and roll aluminum liquid into aluminum slab; Step four: high temperature homogenization annealing treatment of aluminum slab; Step five: cold rolling aluminum slab after homogenization annealing treatment into aluminum foil blank; Step six: longitudinal cutting edge and intermediate annealing treatment of aluminum foil blank; Step seven: cold rolling aluminum foil blank after intermediate annealing treatment into aluminum foil; Step eight: slitting and finished product annealing of aluminum foil, obtaining the aluminum foil for lithium ion battery.

3. The cast-rolling production method of the aluminum foil for lithium-ion batteries according to claim 2, characterized by, The inert gas for the furnace refining purification treatment in step two is nitrogen with purity ≥99.99%, the amount of refining flux is 0.2-0.3% of the weight of aluminum liquid, the refining purification time is 24-26 minutes, and the flux is composed of the following components with mass percentage AlCl3 36.12%, LiF 28.37%, CuCO3 21.69%, Ce(NO3)3 13.82%.

4. The cast-rolling production method of the aluminum foil for lithium-ion batteries according to claim 2, characterized by, The furnace outside online degassing filtration treatment in step two is that aluminum liquid flows through degassing tank, ceramic filter plate with porosity of 50 mesh and electromagnetic filter in turn, the purification gas in the degassing tank is mixed gas composed of nitrogen with purity ≥99.99% and freon gas with purity ≥99.99%, the volume percentage of freon gas in the mixed gas is 19-21%, the flow of mixed gas is 0.5-0.6 L / kg of aluminum liquid, the electromagnetic field strength of electromagnetic filter is 0.04-0.05 T, and the electromagnetic field frequency is 15-17 kHz.

5. The cast-rolling production method of the aluminum foil for lithium-ion batteries according to claim 2, characterized by, The ultrasonic wave frequency during casting and rolling in step three is 10-12 kHz, the ultrasonic wave power is 5-7 kW, the temperature of aluminum liquid in front box is 690-700℃, the casting and rolling speed is 1200-1300 mm / min, the length of casting and rolling area is 70-75 mm, the cooling water pressure is 0.5-0.6 MPa, and the thickness of aluminum slab is 6±0.1 mm.

6. The cast-rolling production method of the aluminum foil for lithium-ion batteries according to claim 2, characterized by, The high temperature homogenization annealing treatment of aluminum slab in step four is that the aluminum slab is heated to 300±3℃ for 1 hour, then continuously heated to 450±3℃ for 2 hours, and then continuously heated to 585±3℃ for 5 hours.

7. The cast-rolling production method of the aluminum foil for lithium-ion batteries according to claim 2, characterized by, The process flow of cold rolling aluminum slab into aluminum foil blank in step five is: first pass rolling into 2±0.1 mm, second pass rolling into 0.8±0.1 mm, third pass rolling into 0.4±0.05 mm, and fourth pass rolling into 0.2±0.05 mm aluminum foil blank.

8. The cast-rolling production method of the aluminum foil for lithium-ion batteries according to claim 2, characterized by, The intermediate annealing treatment of aluminum foil blank in step six is that the aluminum foil blank is heated to 200±3℃ for 1 hour, then continuously heated to 300±3℃ for 2 hours, and then continuously heated to 380±3℃ for 3 hours.

9. The cast-rolling production method of the aluminum foil for lithium-ion batteries according to claim 2, characterized by, The process of cold rolling the aluminum foil blank into aluminum foil in step seven is as follows: the first pass is to roll into 0.1±0.02 mm, the second pass is to roll into 0.05±0.02 mm, the third pass is to roll into 0.025±0.01 mm, and the fourth pass is to roll into 0.012 or 0.013 mm aluminum foil.

10. The cast-rolling production method of the aluminum foil for lithium-ion batteries according to claim 2, characterized by, The process of product annealing of the aluminum foil in step eight is as follows: the aluminum foil is heated to 100±3℃ for 1 hour, then heated to 200±3℃ for 1 hour, then heated to 260±3℃ for 2 hours, and finally cooled to room temperature in the furnace.

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