Aluminum foil for lithium ion battery and cast rolling production method of aluminum foil

Abstract

The invention discloses an aluminum foil for a lithium ion battery and a cast rolling production method of the aluminum foil. The aluminum foil is prepared from the following components in percentage by mass: 0.06 to 0.09 percent of Si, 0.09 to 0.12 percent of Fe, 0.05 to 0.08 percent of Cu, 0.06 to 0.09 percent of Mg and the balance of Al and inevitable impurities. The cast rolling production method sequentially comprises the steps of smelting and preparing molten aluminum, refining and purifying in a furnace, online degassing and filtering outside the furnace, ultrasonic-assisted cast rolling, homogenizing annealing, cold rolling, longitudinal edge shearing, intermediate annealing, foil rolling, slitting and finished product annealing. By improving the cleanliness of molten aluminum, refining crystal grains of the cast-rolled aluminum plate blank and improving the uniformity of structural components, the problem that strength and plasticity are difficult to consider at the same time is solved, rolling passes are reduced, the technological process is shortened, the tensile strength of the aluminum foil with the thickness of 12 / 13 microns is larger than 250 MPa, the percentage elongation after fracture is larger than 6%, the surface wetting tension is larger than 40 * 10 <-3 > N / m, the number of pinholes is smaller than 0.01 / m < 2 >, and the service life of the aluminum foil is prolonged. The development requirements of high-energy-density lithium ion batteries for new energy automobiles and large energy storage equipment are met, the safety of the batteries is improved, and the service life of the batteries is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum foil preparation, and particularly relates to an aluminum foil for lithium ion batteries and a casting and rolling production method thereof. Background Art

[0002] Lithium-ion batteries, with their advantages of high operating voltage, high energy density, long cycle life, safety, and environmental protection, are widely used in power batteries and energy storage batteries. The rapid development of my country's new energy vehicles, photovoltaic power generation, wind power generation, and 3C electronics industries has driven the development of power batteries and energy storage batteries. Aluminum foil, as the positive electrode current collector material in lithium-ion batteries, serves as both a carrier of active substances and a conductor for current collection. It is an important basic raw material for aluminum-ion batteries and has a significant impact on their performance and quality. As power batteries and energy storage batteries develop towards ever-higher energy densities, the requirements for aluminum foil are also becoming increasingly stringent. First, the thickness of the aluminum foil must be reduced. Second, the strength, plasticity, and surface quality of the aluminum foil must be improved. Finally, the production cost of the aluminum foil must be continuously reduced to improve battery safety, energy density, cycle life, and reduce production costs.

[0003] Chinese patent publication CN119220861A discloses a method for producing 1100 aluminum alloy foil for new energy batteries from an electrolytic aluminum solution. The foil is composed of the following components by mass: 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%, and Al ≥ 99%. The production process includes casting, annealing, cold rolling, and foil rolling. The resulting foil has a tensile strength of 300-320 MPa and an elongation of 3-4%. While strong, it exhibits poor plasticity.

[0004] Chinese patent document CN111349825A discloses a method for producing high-toughness battery aluminum foil using a short-process cast-rolling process. The aluminum foil is composed of the following components by 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%, and the remainder is Al. The aluminum foil has a tensile strength of 85-125 MPa and an elongation of 16-35%. Although it has good plasticity, its strength is relatively low.

[0005] Chinese patent publication CN119101831A discloses a short-process, high-strength, low-pinporosity, heat-resistant aluminum foil for power batteries and its preparation method. The 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 remainder is Al. This method uses composite spiral electromagnetic stirring and pulsed current-assisted rolling to increase grain refinement, but the technology is complex and difficult to achieve large-scale production.

[0006] Chinese patent publication CN110484785A discloses a process for preparing high-performance aluminum foil for power batteries. The foil is composed of the following components by mass: 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%, with the remainder being unavoidable impurities. The foil achieves a tensile strength of 245 MPa and an elongation of 3.5%. However, the production process involves fourteen cold rolling passes and four foil rolling passes, resulting in multiple rolling steps and a lengthy process.

[0007] Based on the results of literature retrieval and production practice experience, the existing technology still has one or more of the following problems: (1) The strength and plasticity of aluminum foil are improved by adjusting the alloy composition. Due to the mutual restriction between strength and plasticity, it is difficult to achieve both strength and plasticity of aluminum foil. (2) The current production of aluminum foil for lithium-ion batteries still has problems such as many rolling passes, long process flow and low production efficiency. (3) The existing aluminum foil for lithium-ion batteries still has problems such as uneven microstructure and performance, high pinhole rate, insufficient surface cleanliness and low dyne value, resulting in a low yield of aluminum foil for lithium-ion batteries. Therefore, the existing aluminum foil for lithium-ion batteries and its preparation method still need to be improved and developed. Summary of the Invention

[0008] In response to the problems and deficiencies mentioned in the background technology, the present invention provides an aluminum foil for lithium-ion batteries and a casting and rolling production method thereof. By improving the cleanliness of the aluminum liquid, the strength and plasticity of the aluminum foil are improved, thereby solving the problem of finding a balance between strength and plasticity. Ultrasonic-assisted casting and rolling is used to refine the grains of the cast-rolled aluminum slab, improve the uniformity of the microstructure and plasticity, reduce the number of cold rolling and foil rolling passes, shorten the process flow, improve production efficiency, and reduce production costs. A high-strength, high-plasticity, high-quality aluminum foil is obtained to meet 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, improve battery safety and cycle life, and reduce production costs.

[0009] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are as follows:

[0010] The first aspect of the present invention provides an aluminum foil for lithium-ion batteries, which is characterized in that 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%, and the rest is Al and unavoidable impurities, with the impurity content of each individual being ≤0.03% and the total impurities being ≤0.1%.

[0011] Among them, Si and Fe are unavoidable elements in aluminum foil. Trace amounts of Si and Fe can enhance the foil's strength. However, when their content is too high, Si and Fe tend to form coarse intermetallic compounds, FeSiAl3 and Fe2SiAl8, in the foil. Both FeSiAl3 and Fe2SiAl8 are hard and brittle phases, which not only reduce the foil's plasticity but also cause perforation during the rolling process, forming pinhole defects. Trace amounts of Cu and Mg in aluminum foil primarily enhance its strength. These trace amounts can significantly enhance the foil's strength through solid solution strengthening. However, the Cu and Mg content should not be too high, otherwise the foil's plasticity and corrosion resistance will likely decline. Therefore, the content of Si, Fe, Cu, and Mg needs to be strictly controlled. Furthermore, elements such as Mn, Cr, Zn, and Ti are all impurity elements in aluminum foil. Excessive levels of these impurity elements not only reduce the foil's plasticity and corrosion resistance, but can also cause perforation, forming pinhole defects. Therefore, the impurity elements in aluminum foil must be strictly limited.

[0012] A second aspect of the present invention provides a casting and rolling production method for aluminum foil for lithium-ion batteries, which is characterized by sequentially comprising the following steps:

[0013] Step 1: According to the composition and mass percentage of the aluminum foil, smelt and prepare the aluminum liquid and raise the temperature of the aluminum liquid to 730-740℃;

[0014] Step 2: The aluminum liquid is subjected to in-furnace refining and purification treatment and out-furnace online degassing and filtration treatment;

[0015] Step 3: Continuously casting and rolling the molten aluminum into aluminum slabs under the assistance of ultrasonic waves;

[0016] Step 4: Perform high temperature homogenization annealing treatment on the aluminum slab;

[0017] Step 5: cold rolling the aluminum slab after homogenization annealing into aluminum foil;

[0018] Step 6: longitudinal shearing and intermediate annealing of the aluminum foil blank;

[0019] Step 7: cold rolling the intermediate annealed aluminum foil billet into aluminum foil;

[0020] Step eight: cutting and annealing the aluminum foil to obtain the aluminum foil for lithium-ion batteries.

[0021] Preferably, when smelting and preparing the molten aluminum in step 1, aluminum ingots with an aluminum content greater than 99.85% and aluminum-silicon alloys, aluminum-iron alloys, aluminum-copper alloys, and magnesium ingots with impurity contents less than 0.03% are preferably used as raw materials for smelting and preparing the molten aluminum. To ensure that the impurity element content of the aluminum foil does not exceed the standard and to ensure the purity of the aluminum foil, aluminum ingots and alloys with higher purity are preferably used for smelting and preparing the molten aluminum.

[0022] Preferably, the inert gas used for the refining and purification treatment in the furnace in step 2 is nitrogen with a purity of ≥99.99%, the amount of refining flux used is 0.2-0.3% of the weight of the aluminum liquid, the refining and purification time is 24-26 minutes, and the flux is composed of the following components in mass percentage: AlCl336.12%, LiF 28.37%, CuCO3 21.69%, and Ce(NO3)3 13.82%.

[0023] In-furnace refining and purification uses a powder spray canister, using an inert gas as a carrier, to spray powdered solid flux into molten aluminum. This allows the flux to react with the molten aluminum, capturing and carrying away inclusions such as aluminum oxide and hydrogen. The effectiveness of in-furnace refining and purification is closely related to the composition of the flux. Existing fluxes primarily consist of chloride and fluoride salts of alkali metals such as sodium, potassium, and calcium. Using this type of smelting, refining, and purification treatment can result in excessive levels of these metals in the aluminum foil, ultimately reducing the foil's plasticity, conductivity, and corrosion resistance, and shortening the battery life.

[0024] To address the problems of existing fluxes, the present invention has developed a high-efficiency, alkali-metal-free flux. The flux is composed of AlCl3, LiF, CuCO3, and Ce(NO3)3 powders. AlCl3 has very low melting and boiling points and rapidly sublimates into tiny bubbles in high-temperature molten aluminum. These bubbles capture and remove impurities and hydrogen from the molten aluminum during the upward buoyancy process, thereby removing impurities and hydrogen. LiF forms a molten salt in the high-temperature molten aluminum, primarily dissolving and adsorbing inclusions such as alumina, increasing the surface tension of the molten aluminum, promoting separation of the inclusions from the molten aluminum, and enhancing the flux's impurity-removing effectiveness. CuCO3 decomposes into CO2 bubbles in the molten aluminum. These CO2 bubbles absorb and remove impurities and hydrogen from the molten aluminum during the upward buoyancy process, enhancing the flux's impurity-removing and hydrogen-removing capabilities. The decomposed Cu atoms replenish the Cu content of the molten aluminum, strengthening the aluminum foil's strength. As a heating agent, Ce(NO3)3's main function is to decompose in the molten aluminum and release a large amount of heat. This firstly accelerates the dissolution of the flux in the molten aluminum and improves the contact reaction between the flux and the molten aluminum. Secondly, it can also increase the temperature of the local molten aluminum, improve the fluidity of the molten aluminum, accelerate the floating and overflow of inclusions and hydrogen, and improve the removal of impurities and hydrogen. The decomposed NO and NO2 bubbles can also absorb and carry away inclusions and hydrogen, enhancing the impurity removal and dehydrogenation of the flux. The decomposed rare earth element Ce has a strong affinity with hydrogen and oxygen, forming stable rare earth hydrides and oxides. Due to its high density and melting point, it finally precipitates at the bottom of the furnace, acting as a hydrogen and oxygen fixation.

[0025] Preferably, the online degassing outside the furnace in step 2 is to flow the molten aluminum through a degassing box, and the purified gas introduced into the degassing box is a mixed gas composed of nitrogen 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 19-21%, and the flow rate of the mixed gas is 0.5-0.6L / kg of aluminum liquid.

[0026] To improve the cleanliness of molten aluminum, in addition to in-furnace refining and purification, off-furnace online degassing and filtration are also required. Existing online degassing technologies typically introduce inert gases such as nitrogen or argon, or a mixture of inert gases and chlorine. Due to the low densities of nitrogen, argon, and chlorine, bubbles rise quickly in the molten aluminum, resulting in a short contact time between the bubbles and the molten aluminum, and poor hydrogen removal. Furthermore, chlorine is a toxic and irritating gas that corrodes equipment and tools, making its use hazardous.

[0027] In order to improve the dehydrogenation effect of the degassing box, the present invention creatively introduces a mixed gas composed of nitrogen and Freon gas into the degassing box. Since Freon has a high density, is non-toxic and has stable chemical properties, it can significantly increase the contact time between bubbles and molten aluminum. By using high-purity nitrogen and Freon gases, the dehydrogenation effect of the degassing box can be significantly improved. After dehydrogenation in the degassing box, the hydrogen content of the molten aluminum can be reduced to below 0.08mL / 100gAl, greatly improving the cleanliness of the molten aluminum.

[0028] Preferably, the off-furnace online filtration in step 2 is to allow the aluminum liquid to flow through a ceramic filter plate with a porosity of 50 mesh and an electromagnetic filter in sequence, wherein the electromagnetic field strength of the electromagnetic filter is 0.04-0.05T and the electromagnetic field frequency is 15-17kHz.

[0029] To achieve deep filtration of molten aluminum, this invention creatively combines ceramic plate filtration with electromagnetic filtration. The molten aluminum first flows through a 50-mesh ceramic filter plate for primary filtration, removing inclusions larger than 20μm. The molten aluminum then flows through an electromagnetic filter for deep filtration. Electromagnetic filtration achieves higher filtration precision than traditional ceramic tube filtration. This principle exploits the conductive nature of molten aluminum and the non-conductive properties of inclusions. As the molten aluminum flows through the ceramic tube separator, an alternating magnetic field is applied through an induction coil. This electromagnetic force acts on the molten aluminum, while the inclusions experience an opposing electromagnetic repulsive force. This forces the inclusions to migrate and accumulate on the inner surface of the ceramic tube separator, achieving separation between the inclusions and the molten aluminum. The principles and usage of electromagnetic filters can be found in relevant literature and will not be elaborated upon here. Through a large number of experimental explorations and studies, the present invention has optimized the electromagnetic field strength and frequency of the electromagnetic filter. It is found that under the conditions of electromagnetic field strength of 0.04-0.05T and electromagnetic field frequency of 15-17kHz, after deep filtration by the electromagnetic filter, the removal rate of inclusions larger than 1 micron in the aluminum liquid can reach more than 98%, and the volume content of inclusions is less than 0.02mm. 2 / kgAl, thereby greatly improving the cleanliness of the aluminum liquid.

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

[0031] Cast rolling is the process of continuously injecting molten aluminum into the gap between the two casting rolls of a casting and rolling mill through the front box casting nozzle. The aluminum slab is cooled and solidified into an aluminum slab under the cooling and pressure of the casting rolls. Due to the non-equilibrium solidification of the molten aluminum and the slow cooling and solidification, the cast aluminum slab will have coarse grains and severe structural segregation, resulting in poor plasticity of the aluminum slab, severe edge cracking, and ultimately uneven structural composition of the aluminum foil. The existing technology usually adds refiners to the molten aluminum to refine the grains of the cast aluminum slab, but this method has limited effectiveness. The plasticity of the cast aluminum slab is still poor, and it cannot solve the problems of edge cracking and severe structural segregation. In addition, the addition of refiners such as aluminum-titanium-boron alloys can cause perforation during the rolling of the aluminum foil due to the agglomeration of a large number of TiB2 particles, which increases pinhole defects.

[0032] In response to the problems and shortcomings of existing casting and rolling technologies, the present invention adopts ultrasonic-assisted casting and rolling. The ultrasonic probe is placed in the aluminum liquid in 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 heterogeneous nucleation of grains is increased, the grains of the cast-rolled aluminum slab are refined, component segregation and edge cracking are eliminated, the uniformity of the microstructure and plasticity of the cast-rolled aluminum slab is improved, and the casting and rolling speed of the aluminum liquid and the yield rate of the aluminum slab are increased. Different aluminum liquid compositions require different casting and rolling processes. In order to effectively utilize the function of ultrasonic-assisted casting and rolling, it is necessary to reasonably match the frequency and power of the ultrasonic wave as well as the process parameters such as the aluminum liquid temperature and casting and rolling speed during casting and rolling to obtain cast-rolled aluminum slabs with fine and uniform grains and excellent plasticity.

[0033] Preferably, the high-temperature homogenization annealing treatment of the aluminum slab in step 4 is to heat the aluminum slab to 300±3°C and keep it warm for 1 hour, then continue to heat it to 450±3°C and keep it warm for 2 hours, then continue to heat it to 585±3°C and keep it warm for 5 hours, and finally cool it to room temperature with the furnace.

[0034] The primary purpose of high-temperature homogenization annealing of cast aluminum slabs is to further eliminate compositional segregation, improve compositional uniformity and plasticity, and create favorable conditions for subsequent cold rolling. High-temperature homogenization annealing of cast aluminum slabs first requires strict control of the heating rate. Since aluminum slabs are typically annealed in large coils during production, a rapid heating rate can lead to significant temperature differences between the inside and outside of the coil, resulting in uneven annealing. To address this issue, the present invention innovatively employs a stepped heating pattern, maintaining the temperature at 300±3°C for one hour and then at 450±3°C for two hours. This reduces the temperature difference between the inside and outside of the coil and improves temperature uniformity. Furthermore, the heating temperature and holding time of the final annealing must be strictly controlled. The heating to 585±3°C and holding time for five hours involves setting the temperature at 585°C and maintaining the temperature within a range of less than 3°C for five hours. A low final annealing temperature or a short holding time, due to insufficient temperature or time, will not effectively eliminate compositional segregation and improve the plasticity of the aluminum slab. If the final annealing temperature is too high, the aluminum slab will be overheated, which will reduce the plasticity of the aluminum slab and the mechanical properties of the aluminum foil. The final annealing holding time should not be too long. Otherwise, it will not further improve the composition uniformity of the aluminum slab. Instead, the high temperature holding time will consume a lot of heat, increasing energy consumption and production costs.

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

[0036] Conventional cast-rolled aluminum slabs have coarse grains and severe component segregation. To reduce cold rolling deformation resistance and prevent cracking, they typically require more than a dozen cold rolling passes, with each pass causing no more than 50% deformation. This large number of cold rolling passes results in a long cold rolling process and low production efficiency. The present invention utilizes ultrasonic-assisted cast-rolling of aluminum slabs and performs high-temperature homogenization annealing on the aluminum slabs, thereby refining the grain structure of the aluminum slabs, eliminating component segregation, and significantly improving the plasticity of the aluminum slabs. This creates favorable conditions for cold rolling of the aluminum slabs, allowing the deformation per cold rolling pass to exceed 50%, effectively reducing the number of cold rolling passes, shortening the cold rolling process, and improving cold rolling production efficiency.

[0037] Preferably, the intermediate annealing treatment of the aluminum foil blank in step six is to heat the aluminum foil blank to 200±3°C and keep it warm for 1 hour, then continue to heat it to 300±3°C and keep it warm for 2 hours, then continue to heat it to 380±3°C and keep it warm for 3 hours, and finally cool it to room temperature with the furnace.

[0038] During the cold rolling process, aluminum slabs undergo work hardening, resulting in increased strength and hardness, while gradually decreasing plasticity. With increasing cold rolling passes, the work hardening of the aluminum slabs becomes more severe, which can easily cause cracking in the aluminum foil. The purpose of intermediate annealing of the aluminum foil is to eliminate the work hardening and residual stresses in the aluminum slabs, allowing recrystallization to occur, resulting in a fine and uniform grain structure, reducing the hardness, and improving the plasticity of the aluminum foil, thereby creating favorable conditions for subsequent foil rolling. Intermediate annealing of the aluminum foil also requires strict control of the heating rate, annealing temperature, and annealing time. Using a stepped heating mode, by maintaining the temperature at 200±3°C for 1 hour and 300±3°C for 2 hours, the temperature difference between the inside and outside of the aluminum foil coil can be reduced, improving temperature uniformity. The heating to 380±3°C and maintaining the temperature for 3 hours involves setting the temperature at 380°C with a temperature fluctuation range of less than 3°C for 3 hours. If the final annealing temperature is too low or the holding time is too short, it will not be enough to completely eliminate the work hardening and residual stress of the aluminum foil blank, nor will it induce recrystallization of the aluminum foil blank to obtain a fine and uniform grain structure. If the final annealing temperature is too high or the holding time is too long, the recrystallized grains will grow and coarsen, which will not only fail to improve the plasticity of the aluminum foil blank, but will increase energy consumption and production costs.

[0039] Preferably, the process flow of cold rolling the aluminum foil billet into aluminum foil in step seven is: the first pass is rolled into 0.1±0.02 mm, the second pass is rolled into 0.05±0.02 mm, the third pass is rolled into 0.025±0.01 mm, and the fourth pass is rolled into 0.012 or 0.013 mm aluminum foil.

[0040] Cold rolling of aluminum foil billets into aluminum foil requires the use of a finishing rolling unit so that the deformation and thickness of each pass can be strictly controlled. In the foil rolling stage of existing aluminum foil, due to the coarse grains and severe component segregation of the aluminum foil billets, in order to reduce the cold rolling deformation resistance and avoid cracking of the aluminum foil billets, more than a dozen foil rolling passes are usually required to obtain aluminum foil. Due to the large number of foil rolling passes, the process flow is long and the production efficiency is low. Since the aluminum foil billets of the present invention undergo complete recrystallization after intermediate annealing, a fine and uniform grain structure is obtained, and the plasticity of the aluminum foil billets is greatly improved, it is also possible to implement foil rolling with a large deformation amount, which significantly reduces the number of foil rolling passes, which is conducive to shortening the foil rolling process flow and improving production efficiency.

[0041] Preferably, the process flow of annealing the aluminum foil as a finished product in step eight is: heating the aluminum foil to 100±3°C and keeping it warm for 1 hour, then continuing to heat it to 200±3°C and keeping it warm for 1 hour, then continuing to heat it to 260±3°C and keeping it warm for 2 hours, and finally cooling it to room temperature with the furnace.

[0042] The aluminum foil obtained by cold rolling has residual stress inside due to work hardening, unstable structure, and lubricating oil on the surface. The purpose of annealing the aluminum foil is mainly to eliminate the residual stress, structural instability and degreasing of the aluminum foil, improve the performance of the aluminum foil, and enhance the surface quality of the aluminum foil. The finished annealing of the aluminum foil also requires controlling the heating rate to prevent the temperature difference between the inside and outside of the aluminum foil roll from being too large, resulting in uneven performance of the aluminum foil. At the same time, the final annealing temperature and time also need to be strictly controlled. By adopting a step-by-step heating mode, by keeping the temperature at 100°C and 200°C for 1 hour each, the temperature difference between the inside and outside of the aluminum foil can be reduced and the temperature uniformity can be improved. The heating to 260±3°C and keeping it warm for 2 hours means setting the temperature at 260°C and keeping it warm for 2 hours under the condition of ensuring that the temperature fluctuation range is less than 3°C. If the final annealing temperature is too low or the time is too short, it will not be enough to completely eliminate the residual stress and structural instability of the aluminum foil. The final annealing temperature cannot be too high or the holding time cannot be too long, otherwise the strength and hardness of the aluminum foil will drop too much, and it will be impossible to obtain a high-strength and high-plasticity aluminum foil product.

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

[0044] (1) The present invention optimizes the composition of aluminum foil, strictly controls the content of impurity elements, and adopts in-furnace refining and purification and out-of-furnace online degassing and filtration measures to significantly improve the purity of aluminum foil, solve the problem of mutual restriction between strength and plasticity, and significantly improve the strength and plasticity of aluminum foil, so that the aluminum foil has the advantages of both high strength and high plasticity;

[0045] (2) The present invention adopts ultrasonic wave to assist the casting and rolling of aluminum slabs, thereby refining the grain structure of the aluminum slabs, improving the uniformity of the organizational composition and the plasticity of the aluminum slabs, and enabling the aluminum slabs to be subjected to large deformation cold rolling, thereby significantly reducing the number of cold rolling passes and shortening the process flow, which is beneficial to improving the production efficiency of aluminum foil and reducing the production cost;

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

[0047] Example 1:

[0048] Aluminum foil for lithium-ion batteries is composed of the following components by mass percentage: Si 0.08%, Fe 0.011%, Cu 0.06%, Mg 0.07%, and the remainder is Al and unavoidable impurities, with the impurity content of each individual being ≤ 0.03% and the total impurities being ≤ 0.1%. The casting and rolling production method comprises the following steps in sequence:

[0049] Step 1: 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 content less than 0.03% as raw materials to smelt and prepare aluminum liquid and raise the aluminum liquid temperature to 735℃;

[0050] Step 2: Using 99.99% pure nitrogen and 0.25% flux by weight of the aluminum liquid to refine and purify the aluminum liquid in the furnace for 25 minutes, then the aluminum liquid flows through a degassing box, a ceramic filter plate and an electromagnetic filter arranged on a launder for online degassing and filtration, wherein 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%, and a mixed gas consisting of 99.99% pure nitrogen and 99.99% pure Freon gas 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 aluminum liquid, the porosity of the ceramic filter plate is 50 mesh, the electromagnetic field strength of the electromagnetic filter is 0.045T, and the electromagnetic field frequency is 16kHz;

[0051] Step 3: Continuously cast the aluminum liquid into an aluminum slab with a thickness of 6±0.1 mm under the conditions of an ultrasonic frequency of 11 kHz, an ultrasonic power of 6 kW, a front box aluminum liquid temperature of 695°C, a casting speed of 1250 mm / min, a casting zone length of 72 mm, and a cooling water pressure of 0.55 MPa;

[0052] Step 4: Heat the aluminum slab to 300±3°C and keep it for 1 hour, then continue to heat it to 450±3°C and keep it for 2 hours, and then continue to heat it to 585±3°C and keep it for 5 hours to perform high temperature homogenization annealing treatment on the aluminum slab;

[0053] Step 5: cold rolling the aluminum slab into aluminum foil billets, with the first pass rolling into 2±0.1mm, the second pass rolling into 0.8±0.1mm, the third pass rolling into 0.4±0.05mm, and the fourth pass rolling into 0.2±0.05mm aluminum foil billets;

[0054] Step 6: longitudinally shear the aluminum foil blank, then heat the aluminum foil blank to 200±3℃ and keep it for 1 hour, then continue to heat it to 300±3℃ and keep it for 2 hours, and then continue to heat it to 380±3℃ and keep it for 3 hours for intermediate annealing;

[0055] Step 7: cold rolling the aluminum foil billet into aluminum foil, with the first pass rolling into 0.1±0.02mm, the second pass rolling into 0.05±0.02mm, the third pass rolling into 0.025±0.01mm, and the fourth pass rolling into 0.012mm aluminum foil;

[0056] Step 8: Cut the aluminum foil, then heat the aluminum foil to 100±3°C and keep it warm for 1 hour, then continue to heat it to 200±3°C and keep it warm for 1 hour, then continue to heat it to 260±3°C and keep it warm for 2 hours to anneal the finished product, and after cooling, obtain the aluminum foil for lithium ion battery.

[0057] Example 2:

[0058] 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%, and the remainder is Al and unavoidable impurities, with the impurity content of each individual being ≤ 0.03% and the total impurities being ≤ 0.1%. The casting and rolling production method comprises the following steps in sequence:

[0059] Step 1: 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 content less than 0.03% as raw materials to smelt and prepare aluminum liquid and raise the aluminum liquid temperature to 735℃;

[0060] Step 2: Using 99.99% pure nitrogen and 0.25% flux by weight of the aluminum liquid to refine and purify the aluminum liquid in the furnace for 25 minutes, then the aluminum liquid flows through a degassing box, a ceramic filter plate and an electromagnetic filter arranged on a launder for online degassing and filtration, wherein 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%, and a mixed gas consisting of 99.99% pure nitrogen and 99.99% pure Freon gas 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 aluminum liquid, the porosity of the ceramic filter plate is 50 mesh, the electromagnetic field strength of the electromagnetic filter is 0.045T, and the electromagnetic field frequency is 16kHz;

[0061] Step 3: Continuously cast the aluminum liquid into an aluminum slab with a thickness of 6±0.1 mm under the conditions of an ultrasonic frequency of 11 kHz, an ultrasonic power of 6 kW, a front box aluminum liquid temperature of 695°C, a casting speed of 1250 mm / min, a casting zone length of 72 mm, and a cooling water pressure of 0.55 MPa;

[0062] Step 4: Heat the aluminum slab to 300±3°C and keep it for 1 hour, then continue to heat it to 450±3°C and keep it for 2 hours, and then continue to heat it to 585±3°C and keep it for 5 hours to perform high temperature homogenization annealing treatment on the aluminum slab;

[0063] Step 5: cold rolling the aluminum slab into aluminum foil billets, with the first pass rolling into 2±0.1mm, the second pass rolling into 0.8±0.1mm, the third pass rolling into 0.4±0.05mm, and the fourth pass rolling into 0.2±0.05mm aluminum foil billets;

[0064] Step 6: longitudinally shear the aluminum foil blank, then heat the aluminum foil blank to 200±3℃ and keep it for 1 hour, then continue to heat it to 300±3℃ and keep it for 2 hours, and then continue to heat it to 380±3℃ and keep it for 3 hours for intermediate annealing;

[0065] Step 7: cold rolling the aluminum foil billet into aluminum foil, with the first pass rolling into 0.1±0.02mm, the second pass rolling into 0.05±0.02mm, the third pass rolling into 0.025±0.01mm, and the fourth pass rolling into 0.013mm aluminum foil;

[0066] Step 8: Cut the aluminum foil, then heat the aluminum foil to 100±3°C and keep it warm for 1 hour, then continue to heat it to 200±3°C and keep it warm for 1 hour, then continue to heat it to 260±3°C and keep it warm for 2 hours to anneal the finished product, and after cooling, obtain the aluminum foil for lithium ion battery.

[0067] Example 3:

[0068] Aluminum foil for lithium-ion batteries is composed of the following components by mass percentage: Si 0.09%, Fe 0.12%, Cu 0.05%, Mg 0.09%, and the remainder is Al and unavoidable impurities, with the impurity content of each individual being ≤ 0.03% and the total impurities being ≤ 0.1%. The casting and rolling production method comprises the following steps in sequence:

[0069] Step 1: 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 content less than 0.03% as raw materials to smelt and prepare aluminum liquid and raise the aluminum liquid temperature to 740℃;

[0070] Step 2: Using 99.99% pure nitrogen and 0.3% of the weight of the aluminum liquid as a flux to refine and purify the aluminum liquid in the furnace for 26 minutes, the aluminum liquid is then passed through a degassing box, a ceramic filter plate and an electromagnetic filter arranged on a launder for online degassing and filtration. 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%. A mixed gas consisting of 99.99% pure nitrogen and 99.99% pure Freon gas is introduced into the degassing box. The volume percentage of Freon gas in the mixed gas is 21%. The flow rate of the mixed gas is 0.5 L / kg of aluminum liquid. The porosity of the ceramic filter plate is 50 mesh. The electromagnetic field strength of the electromagnetic filter is 0.05 T and the electromagnetic field frequency is 15 kHz.

[0071] Step 3: Continuously cast 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, a front box aluminum liquid temperature of 700℃, a casting speed of 1200mm / min, a casting zone length of 70mm, and a cooling water pressure of 0.6MPa;

[0072] Step 4: Heat the aluminum slab to 300±3°C and keep it for 1 hour, then continue to heat it to 450±3°C and keep it for 2 hours, and then continue to heat it to 585±3°C and keep it for 5 hours to perform high temperature homogenization annealing treatment on the aluminum slab;

[0073] Step 5: cold rolling the aluminum slab into aluminum foil billets, with the first pass rolling into 2±0.1mm, the second pass rolling into 0.8±0.1mm, the third pass rolling into 0.4±0.05mm, and the fourth pass rolling into 0.2±0.05mm aluminum foil billets;

[0074] Step 6: longitudinally shear the aluminum foil blank, then heat the aluminum foil blank to 200±3℃ and keep it for 1 hour, then continue to heat it to 300±3℃ and keep it for 2 hours, and then continue to heat it to 380±3℃ and keep it for 3 hours for intermediate annealing;

[0075] Step 7: cold rolling the aluminum foil billet into aluminum foil, with the first pass rolling into 0.1±0.02mm, the second pass rolling into 0.05±0.02mm, the third pass rolling into 0.025±0.01mm, and the fourth pass rolling into 0.012mm aluminum foil;

[0076] Step 8: Cut the aluminum foil, then heat the aluminum foil to 100±3°C and keep it warm for 1 hour, then continue to heat it to 200±3°C and keep it warm for 1 hour, then continue to heat it to 260±3°C and keep it warm for 2 hours to anneal the finished product, and after cooling, obtain the aluminum foil for lithium ion battery.

[0077] Example 4:

[0078] Aluminum foil for lithium-ion batteries is composed of the following components by mass percentage: Si 0.06%, Fe 0.09%, Cu 0.08%, Mg 0.06%, and the remainder is Al and unavoidable impurities, with the impurity content of each individual being ≤ 0.03% and the total impurities being ≤ 0.1%. The casting and rolling production method comprises the following steps in sequence:

[0079] Step 1: 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 content less than 0.03% as raw materials to smelt and prepare aluminum liquid and raise the aluminum liquid temperature to 730℃;

[0080] Step 2: Using 99.99% pure nitrogen and 0.2% by weight of the aluminum liquid as flux to refine and purify the aluminum liquid in the furnace for 24 minutes, the aluminum liquid is then passed through a degassing box, a ceramic filter plate, and an electromagnetic filter arranged on a launder 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%, and Ce(NO3)3 13.82%. A mixed gas consisting of 99.99% pure nitrogen and 99.99% pure Freon gas is introduced into the degassing box. The volume percentage of Freon gas in the mixed gas is 19%, and the flow rate of the mixed gas is 0.6 L / kg of aluminum liquid. The porosity of the ceramic filter plate is 50 mesh. The electromagnetic field strength of the electromagnetic filter is 0.04 T, and the electromagnetic field frequency is 17 kHz.

[0081] Step 3: Continuously cast the aluminum liquid into an aluminum slab with a thickness of 6±0.1mm under the conditions of an ultrasonic frequency of 10kHz, an ultrasonic power of 7kW, a front box aluminum liquid temperature of 690℃, a casting speed of 1300mm / min, a casting zone length of 75mm, and a cooling water pressure of 0.5MPa;

[0082] Step 4: Heat the aluminum slab to 300±3°C and keep it for 1 hour, then continue to heat it to 450±3°C and keep it for 2 hours, and then continue to heat it to 585±3°C and keep it for 5 hours to perform high temperature homogenization annealing treatment on the aluminum slab;

[0083] Step 5: cold rolling the aluminum slab into aluminum foil billets, with the first pass rolling into 2±0.1mm, the second pass rolling into 0.8±0.1mm, the third pass rolling into 0.4±0.05mm, and the fourth pass rolling into 0.2±0.05mm aluminum foil billets;

[0084] Step 6: longitudinally shear the aluminum foil blank, then heat the aluminum foil blank to 200±3℃ and keep it for 1 hour, then continue to heat it to 300±3℃ and keep it for 2 hours, and then continue to heat it to 380±3℃ and keep it for 3 hours for intermediate annealing;

[0085] Step 7: cold rolling the aluminum foil billet into aluminum foil, with the first pass rolling into 0.1±0.02mm, the second pass rolling into 0.05±0.02mm, the third pass rolling into 0.025±0.01mm, and the fourth pass rolling into 0.013mm aluminum foil;

[0086] Step 8: Cut the aluminum foil, then heat the aluminum foil to 100±3°C and keep it warm for 1 hour, then continue to heat it to 200±3°C and keep it warm for 1 hour, then continue to heat it to 260±3°C and keep it warm for 2 hours to anneal the finished product, and after cooling, obtain the aluminum foil for lithium ion battery.

[0087] Example 5:

[0088] 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%, and the remainder is Al and unavoidable impurities, with the impurity content of each individual being ≤ 0.03% and the total impurities being ≤ 0.1%. The casting and rolling production method comprises the following steps in sequence:

[0089] Step 1: 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 content less than 0.03% as raw materials to smelt and prepare aluminum liquid and raise the aluminum liquid temperature to 735℃;

[0090] Step 2: Using 99.99% pure nitrogen and 0.25% flux by weight of the aluminum liquid to refine and purify the aluminum liquid in the furnace for 25 minutes, then the aluminum liquid flows through a degassing box, a ceramic filter plate and an electromagnetic filter arranged on a launder for online degassing and filtration, wherein 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%, and a mixed gas consisting of 99.99% pure nitrogen and 99.99% pure Freon gas 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 aluminum liquid, the porosity of the ceramic filter plate is 50 mesh, the electromagnetic field strength of the electromagnetic filter is 0.045T, and the electromagnetic field frequency is 16kHz;

[0091] Step 3: Continuously cast the aluminum liquid into an aluminum slab with a thickness of 6±0.1 mm under the conditions of an ultrasonic frequency of 11 kHz, an ultrasonic power of 6 kW, a front box aluminum liquid temperature of 695°C, a casting speed of 1250 mm / min, a casting zone length of 74 mm, and a cooling water pressure of 0.55 MPa;

[0092] Step 4: Heat the aluminum slab to 300±3°C and keep it for 1 hour, then continue to heat it to 450±3°C and keep it for 2 hours, and then continue to heat it to 585±3°C and keep it for 5 hours to perform high temperature homogenization annealing treatment on the aluminum slab;

[0093] Step 5: cold rolling the aluminum slab into aluminum foil billets, with the first pass rolling into 2±0.1mm, the second pass rolling into 0.8±0.1mm, the third pass rolling into 0.4±0.05mm, and the fourth pass rolling into 0.2±0.05mm aluminum foil billets;

[0094] Step 6: longitudinally shear the aluminum foil blank, then heat the aluminum foil blank to 200±3℃ and keep it for 1 hour, then continue to heat it to 300±3℃ and keep it for 2 hours, and then continue to heat it to 380±3℃ and keep it for 3 hours for intermediate annealing;

[0095] Step 7: cold rolling the aluminum foil billet into aluminum foil, with the first pass rolling into 0.1±0.02mm, the second pass rolling into 0.05±0.02mm, the third pass rolling into 0.025±0.01mm, and the fourth pass rolling into 0.012mm aluminum foil;

[0096] Step 8: Cut the aluminum foil, then heat the aluminum foil to 100±3°C and keep it warm for 1 hour, then continue to heat it to 200±3°C and keep it warm for 1 hour, then continue to heat it to 260±3°C and keep it warm for 2 hours to anneal the finished product, and after cooling, obtain the aluminum foil for lithium ion battery.

[0097] Comparative Example 1:

[0098] The casting and rolling production method of the aluminum foil in this comparative example is the same as that in 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%, and the rest is Al and unavoidable impurities, with a single impurity ≤0.03% and a total impurity ≤0.1%.

[0099] Comparative Example 2:

[0100] The components, mass percentages, and casting and rolling production method of the aluminum foil in this comparative example are the same as those in Example 1, except that in step 2, the aluminum liquid in the furnace is refined and purified using an existing conventional flux. The flux is composed of the following components in mass percentages: NaCl 46.71%, KCl 30.62%, and Na3AlF6 22.67%.

[0101] Comparative Example 3:

[0102] The components, mass percentages and casting and rolling production method of the aluminum foil in this comparative example are the same as those in Example 1, except that ultrasonic-assisted casting and rolling is not used in step 3, but the aluminum liquid is directly and continuously cast and rolled into an aluminum slab with a thickness of 6±0.1 mm.

[0103] Comparative Example 4:

[0104] The components, mass percentages and casting and rolling production method of the aluminum foil in this comparative example are the same as those in Example 1, except that in step 6, the aluminum foil billet is heated to 200±3°C and kept warm for 1 hour, then further heated to 300±3°C and kept warm for 2 hours, and then further heated to 400±3°C and kept warm for 3 hours for intermediate annealing.

[0105] Comparative Example 5:

[0106] The components, mass percentages, and casting and rolling production method of the aluminum foil in this comparative example are the same as those in Example 1, except that in step eight, the aluminum foil is heated to 100±3°C and kept warm for 1 hour, then heated to 200±3°C and kept warm for 1 hour, and then heated to 250±3°C and kept warm for 2 hours for annealing the finished product.

[0107] Verification example:

[0108] Samples were taken from the aluminum foils obtained in Examples 1-5 and Comparative Examples 1-5, respectively. The tensile specimens were processed according to the national standard GB / T16865 "Test specimens and methods for tensile testing of deformed aluminum, magnesium and their alloy products". The specimens were then stretched at room temperature on an electronic tensile testing machine to test the tensile strength and elongation of the aluminum foils. The surface wetting tension of the aluminum foils was tested according to the national standard GB / T22638.4 "Test methods for aluminum foils - Part 4: Determination of surface wetting tension". The number of pinholes per square meter of the aluminum foils was tested according to the national standard GB / T22638.2 "Test methods for aluminum foils - Part 2: Detection of pinholes". 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 is greater than 6%, and the surface wetting tension is greater than 40×10 -3 N / m, the number of pinholes is less than 0.01 / m 2 . In Comparative Example 1, the strength of the aluminum foil is low due to the insufficient Cu and Mg content of the aluminum foil. In Comparative Example 2, the strength, plasticity and surface wetting tension of the aluminum foil are low due to the use of existing conventional flux to refine and purify the aluminum liquid in the furnace, and the number of pinholes is large. In Comparative Example 3, since ultrasonic assisted casting and rolling is not used to produce aluminum slabs, the grains of the cast and rolled aluminum slabs are coarse and the composition is segregated, resulting in low strength and plasticity of the aluminum foil, and a large number of pinholes. In Comparative Example 4, since the final annealing temperature of the aluminum foil billet is too high, the grains grow and coarsen, resulting in low strength, plasticity and surface wetting tension of the aluminum foil, and a large number of pinholes. In Comparative Example 5, since the final annealing temperature of the aluminum foil is too low, although the strength of the aluminum foil is high, the plasticity is low.

[0109] Table 1 Room temperature tensile strength, surface wetting tension and number of pinholes of aluminum foil

[0110]

[0111] The present invention is described through embodiments, but does not constitute a limitation of the present invention. With reference to the description of the present invention, other changes to the disclosed embodiments are easy for professionals in this field to think of, and such changes should fall within the scope defined by the claims of the present invention.

Claims

1. An aluminum foil for lithium-ion batteries, characterized in that 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%, and the rest is Al and unavoidable impurities, with a single impurity being ≤0.03% and a total of impurities being ≤0.1%.

2. A casting and rolling production method of aluminum foil for lithium ion batteries, the method being used to produce the aluminum foil for lithium ion batteries as claimed in claim 1, characterized in that: The following steps are included in sequence: Step 1: According to the composition and mass percentage of the aluminum foil, smelt and prepare the aluminum liquid and raise the temperature of the aluminum liquid to 730-740℃; Step 2: The aluminum liquid is subjected to in-furnace refining and purification treatment and out-furnace online degassing and filtration treatment; Step 3: Continuously casting and rolling the molten aluminum into aluminum slabs under the assistance of ultrasonic waves; Step 4: Perform high temperature homogenization annealing treatment on the aluminum slab; Step 5: cold rolling the aluminum slab after homogenization annealing into aluminum foil; Step 6: longitudinal shearing and intermediate annealing of the aluminum foil blank; Step 7: cold rolling the intermediate annealed aluminum foil billet into aluminum foil; Step eight: cutting and annealing the aluminum foil to obtain the aluminum foil for lithium-ion batteries.

3. The casting and rolling production method of aluminum foil for lithium ion batteries according to claim 2, characterized in that: The inert gas used for the refining and purification treatment in the furnace in step 2 is nitrogen with a purity of ≥99.99%. The amount of refining flux is 0.2-0.3% of the weight of the aluminum liquid. The refining and purification time is 24-26 minutes. The flux is composed of the following components in mass percentage: Composition: AlCl3 36.12%, LiF2 8.37%, CuCO3 21.69%, Ce(NO3)3 13.82%.

4. The casting and rolling production method of aluminum foil for lithium ion batteries according to claim 2, characterized in that: The online degassing and filtration treatment outside the furnace in step 2 is to pass the aluminum liquid through a degassing box, a ceramic filter plate with a porosity of 50 mesh, and an electromagnetic filter in sequence. The purified gas introduced into the degassing box is a mixed gas composed of nitrogen 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 19-21%, and the flow rate of the mixed gas is 0.5-0.6L / kg of aluminum liquid. The electromagnetic field strength of the electromagnetic filter is 0.04-0.05T, and the electromagnetic field frequency is 15-17kHz.

5. The casting and rolling production method of aluminum foil for lithium ion batteries according to claim 2, characterized in that: In step 3, the ultrasonic frequency during casting and rolling is 10-12kHz, the ultrasonic power is 5-7kW, the aluminum liquid temperature in the front box is 690-700℃, the casting and rolling speed is 1200-1300mm / min, the casting and rolling zone length is 70-75mm, the cooling water pressure is 0.5-0.6MPa, and the thickness of the aluminum slab is 6±0.1mm.

6. The casting and rolling production method of aluminum foil for lithium ion batteries according to claim 2, characterized in that: The high-temperature homogenization annealing treatment of the aluminum slab described in step 4 is to heat the aluminum slab to 300±3°C and keep it warm for 1 hour, then continue to heat it to 450±3°C and keep it warm for 2 hours, and then continue to heat it to 585±3°C and keep it warm for 5 hours.

7. The casting and rolling production method of aluminum foil for lithium ion batteries according to claim 2, characterized in that: The process flow of cold rolling the aluminum slab into aluminum foil billet in step 5 is as follows: the first pass is rolled into 2±0.1mm, the second pass is rolled into 0.8±0.1mm, the third pass is rolled into 0.4±0.05mm, and the fourth pass is rolled into 0.2±0.05mm aluminum foil billet.

8. The casting and rolling production method of aluminum foil for lithium ion batteries according to claim 2, characterized in that: In step 6, the intermediate annealing treatment of the aluminum foil blank is to heat the aluminum foil blank to 200±3°C and keep it warm for 1 hour, then continue to heat it to 300±3°C and keep it warm for 2 hours, and then continue to heat it to 380±3°C and keep it warm for 3 hours.

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

10. The casting and rolling production method of aluminum foil for lithium ion batteries according to claim 2, characterized in that: The process flow of annealing the aluminum foil as described in step eight is: heating the aluminum foil to 100±3°C and keeping it warm for 1 hour, then continuing to heat it to 200±3°C and keeping it warm for 1 hour, then continuing to heat it to 260±3°C and keeping it warm for 2 hours, and finally cooling it to room temperature with the furnace.

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