Fine-grain rolled copper foil for battery negative electrode current collector and method for producing the same

Abstract

The application discloses a fine-grain calendered copper foil for a battery negative electrode current collector and a preparation method thereof, and relates to the technical field of metal materials.The fine-grain calendered copper foil is prepared by accurately proportioning Sn, Ag, multielement rare earth and trace oxygen in a synergistic microalloying manner, can be stabilized and controlled at 1-10 mu m through solid solution strengthening, deformation coordination, grain boundary pinning and melt purification multiple coupling effects, effectively solves the problems of coarse grains of traditional copper foils, abnormal grain growth after annealing and insufficient organization stability, and through a differential synergistic organization regulation mechanism of Sn and Ag, supplemented by the grain boundary pinning effect of rare earth oxides, can avoid rolling edge cracks and belt breaks under super-large cold deformation, and can inhibit grain boundary migration during the annealing stage, so that the copper foil still maintains high bidirectional tensile strength after annealing, and the wrinkle resistance and fracture resistance during the coating, rolling and winding of the ultra-thin copper foil are improved.

Description

Technical Field

[0001] This invention relates to the field of metal materials technology, specifically to a fine-grained rolled copper foil for battery negative electrode current collectors and its preparation method. Background Technology

[0002] As the core energy storage device for power batteries, energy storage devices, and fast-charging consumer electronics, lithium-ion batteries are continuously iterating towards higher energy density, longer cycle life, and higher safety and stability. As a key substrate for carrying silicon-based / graphite negative electrode active materials, conducting electrons, and maintaining the stability of the electrode structure, the microstructure, mechanical properties, and dimensional stability of the negative electrode current collector copper foil directly determine the cell manufacturing yield and battery cycle life. As power batteries, energy storage batteries, and high-rate fast-charging batteries continue to develop towards higher energy density, longer cycle life, and higher safety, negative electrode current collector copper foil is gradually developing towards ultra-thinness, high strength, and high dimensional stability.

[0003] To reduce the proportion of inactive materials in battery cells and effectively improve the energy density of battery cells, the industry generally adopts the technical route of thinning copper foil. However, after the thickness of copper foil is reduced, its resistance to deformation and fracture is significantly degraded. In the entire process of negative electrode slurry coating, drying shrinkage, rolling densification, electrode slitting, and cell winding / stacking, processing defects such as wrinkling, wavy edges, broken strips, and dimensional deviations are easily generated. At the same time, silicon-based negative electrode materials will undergo repeated volume expansion and contraction of up to 300% during lithium insertion / extraction. During battery cycling, periodic alternating stress will be continuously applied to the current collector. If the tensile strength of copper foil is low, the thermal stability of grain structure is poor, and the mechanical anisotropy is prominent, it will cause irreversible plastic deformation of the current collector, active material shedding, and continuous increase in electrode interface contact resistance, ultimately resulting in rapid capacity decay and a significant reduction in cycle life.

[0004] Currently, copper foil used in the lithium battery industry is mainly divided into two systems: electrolytic copper foil and conventional rolled copper foil. Electrolytic copper foil is prepared by electrodeposition using copper sulfate electrolyte, resulting in low production costs and dominating the mainstream market for lithium battery copper foil. Its internal structure is mostly columnar crystals with a rough surface, which, while beneficial for the adhesion of negative electrode active materials, leads to insufficient tensile strength and poor deformation stability after ultra-thinning, making it unsuitable for high-stress conditions. Conventional rolled copper foil, formed through hot rolling of copper ingots and multi-pass cold rolling, has a dense and uniform matrix, and its conductivity and overall ductility are superior to electrolytic copper foil. However, this type of copper foil undergoes ultra-large deformation cold rolling and subsequent annealing... After processing, it is easy to form a strong preferred rolling texture and recrystallization texture. The highly concentrated grain orientation will cause a significant difference in mechanical properties between the rolling direction (RD) and transverse direction (TD) of the foil. Anisotropic deformation is prone to occur during electrode rolling, winding, and battery cycle service, making it difficult to maintain the flatness and long-term dimensional stability of the negative electrode. In addition, traditional rolled copper foil also has process shortcomings such as difficulty in shape control and limited yield in the large-width industrial mass production process. Based on this, a fine-grained rolled copper foil for battery negative electrode current collector and its preparation method are provided, which can eliminate the drawbacks of the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a fine-grained rolled copper foil for battery negative electrode current collectors and its preparation method, so as to solve the problems in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing fine-grained rolled copper foil for battery negative electrode current collectors includes the following steps: Step 1: Batching and Smelting: Grind all kinds of raw materials to remove surface oxide scale, prepare materials according to the mass percentage ratio of fine-grained rolled copper foil alloy components, add high-purity Cu, Sn, and Cu-Ag master alloy to the crucible in sequence, evacuate the furnace and control the power of the smelting furnace to preheat in stages, introduce argon gas to protect the smelting, add rare earth elements after the raw materials are fully melted, melt and stir and keep warm, and then quickly pour the molten metal into the mold to obtain alloy ingots; Step 2: Homogenization heat treatment: The alloy ingot is placed in a heat treatment furnace for homogenization treatment, and then cooled to room temperature to obtain the alloy ingot; Step 3: Hot rolling: The homogenized alloy ingot is milled, heated and held at the temperature, then hot rolled, and then cooled to room temperature to obtain alloy strip. Step 4: Multi-pass cold rolling: After removing the surface oxide scale from the hot-rolled alloy strip, it is subjected to multi-pass cold rolling at room temperature to finally obtain rolled copper foil. Step 5: Low-temperature annealing: The cold-rolled alloy foil is placed in a heat treatment furnace for annealing, and then cooled to room temperature to obtain fine-grained rolled copper foil for battery negative electrode current collector.

[0007] Based on the above technical solutions, the present invention also provides the following optional technical solutions: In one alternative, the mass percentage ratio in step one is: Sn: 0.01-0.1 wt.%, Ag: 0.008-0.015 wt.%, La: 0.005-0.015 wt.%, Ce: 0.001-0.01 wt.%, Y: 0.001-0.005 wt.%, Pr: 0.001-0.015 wt.%, O: 0.01-0.1 wt.%, with the balance being Cu and unavoidable impurities.

[0008] In one alternative: the purity of the high-purity Cu, Sn, and Cu-Ag master alloy in step one is 99.99 wt.%.

[0009] In one alternative: the vacuum degree of vacuum melting in step one is 0.5-10 Pa, the holding time is 10-15 min, the rare earth elements include one or more of La, Ce, Y, and Pr, the melting power is first preheated at 4.4 kW for 5 min, then increased to 6.2 kW for 5 min, then kept constant at 8.2 kW to 1100-1200 ℃, and after adding rare earth elements, the power is adjusted to 3-4 kW and held for 3-5 min.

[0010] In one alternative: the homogenization treatment in step two is carried out at a temperature of 900-950℃, with a holding time of 3-6 hours, and is cooled to room temperature in the furnace to obtain an alloy ingot with a thickness of 10-15 mm.

[0011] In one alternative: the heating temperature of hot rolling in step three is 900-930℃, the holding time is 40min, the total reduction rate of hot rolling is 50-70%, and after hot rolling, it is water-cooled to room temperature to obtain an alloy strip with a thickness of 3-5mm.

[0012] In one alternative: the cold rolling process in step four consists of 10-15 passes, with a total cold rolling reduction of 99.2-99.9%, ultimately yielding rolled copper foil with a thickness of 6-20 μm. The single-pass reduction rate for the first two passes is 20-30%, the single-pass reduction rate for subsequent passes is 35-40%, and the reduction rate for the final pass is 40-60%.

[0013] In one alternative: the annealing temperature in step five is 200-280℃, the holding time is 0.5-1h, and the cooling method is air cooling to room temperature.

[0014] A fine-grained rolled copper foil for use as a negative electrode current collector in a battery is prepared by the above method.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention achieves precise proportioning of Sn, Ag, multi-element rare earth elements and trace oxygen through synergistic microalloying. It can rely on the multiple coupling effects of solid solution strengthening, deformation coordination, grain boundary pinning and melt purification to stably control the annealed grains at 1-10μm, effectively solving the problems of coarse grains, abnormal grain growth after annealing and insufficient microstructure stability in traditional copper foil.

[0016] 2. This invention utilizes the differentiated synergistic organization control mechanism of Sn and Ag, supplemented by the grain boundary pinning effect of rare earth oxides, to avoid rolling edge cracks and strip breaks under ultra-large cold deformation. At the same time, it suppresses grain boundary migration during the annealing stage, so that the copper foil still maintains high bidirectional tensile strength after annealing, thereby improving the anti-wrinkle and anti-breakage capabilities of ultra-thin copper foil during coating, rolling, and winding processes.

[0017] 3. This invention uses a 0.01-0.1 wt.% trace low tin system combined with a 99.2%-99.9% ultra-high segmented cold rolling process to control the matrix stacking fault energy and uniformly construct cold rolling deformation bands and shear bands, weakening the single strong texture, dispersing grain orientation, significantly reducing the difference in mechanical properties between the rolling direction and the transverse direction of copper foil, and improving the anisotropic defects of the material.

[0018] 4. This invention, through the matching addition of composite rare earth elements and trace amounts of oxygen, can purify copper melt, optimize inclusion morphology, and reduce rolling crack sources. It simultaneously improves the strength and plasticity of copper foil with almost no loss of conductivity, making it suitable for the industrial production needs of 6-20μm ultra-thin battery negative electrode current collectors.

[0019] 5. This invention, through an integrated technical solution of component, ultra-high pressure rate segmented rolling, and low temperature annealing, differs from the single control approach of existing flexible circuit board copper foil and high tin phosphor bronze copper foil. It can adapt to the service conditions of silicon-based lithium battery anode, continuously constrain the volume expansion of active material during charging and discharging, slow down interface degradation, and extend battery cycle life and capacity retention. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow of the present invention.

[0021] Figure 2 This is a schematic diagram of the batching and smelting process structure of the present invention.

[0022] Figure 3 This is a schematic diagram of the homogenization heat treatment process structure of the present invention.

[0023] Figure 4 This is a schematic diagram of the hot rolling process structure of the present invention.

[0024] Figure 5 This is a schematic diagram of the multi-pass cold rolling process structure of the present invention.

[0025] Figure 6This is a schematic diagram of the low-temperature annealing process structure of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Example

[0027] like Figures 1-6 As shown, a method for preparing fine-grained rolled copper foil for battery negative electrode current collectors includes the following steps: Step 1: Batching and Smelting: Grind all raw materials to remove surface oxide scale, and prepare them according to the following mass percentages: Sn 0.05wt.%, Ag 0.008wt.%, La 0.008wt.%, Ce 0.005wt.%, Y 0.002wt.%, Pr 0.001wt.%, O 0.10wt.%, with the balance being Cu and unavoidable impurities. Combine high-purity Cu (99.99wt.%), Sn (99.99wt.%), and Cu-Ag master alloy (9... 9.99wt.%) were added sequentially to the crucible, and the vacuum was drawn to 5Pa. The power of the melting furnace was controlled to preheat at 4.4kW for 5min, then increased to 6.2kW for 5min, and then increased to 8.2kW and kept constant. The temperature was raised to 1100℃, and argon gas was introduced for protective melting. The temperature was held for 10min. After the raw materials were fully melted, rare earth elements La, Ce, Y and Pr were added. After melting, the mixture was stirred slightly. The power was adjusted to 3kW and the temperature was held for another 5min. Then the molten metal was quickly poured into the mold to obtain an alloy ingot. Step 2: Homogenization heat treatment: The alloy ingot is placed in a heat treatment furnace for homogenization treatment at a temperature of 950℃ and a holding time of 4 hours. Then it is cooled to room temperature in the furnace to obtain an alloy ingot with a thickness of 10mm. Step 3: Hot rolling treatment: The homogenized alloy ingot is milled, and the treated alloy ingot is heated to 900℃, held for 40 minutes and then hot rolled. The total reduction rate of hot rolling is 60%. After hot rolling, it is water cooled to room temperature to obtain an alloy strip with a thickness of 4mm. Step 4: Multi-pass cold rolling: After removing the surface oxide scale from the hot-rolled alloy strip, it is subjected to multi-pass cold rolling at room temperature. The process consists of 12 passes, with a total cold rolling reduction of 99.65%, ultimately obtaining a rolled copper foil with a thickness of 14μm. The single-pass reduction rate for the first two passes is 20%, the single-pass reduction rate for subsequent passes is 35-40%, and the reduction rate for the final pass is 40%. Step 5: Low-temperature annealing: The cold-rolled alloy foil is placed in a heat treatment furnace for annealing at a temperature of 265°C for 0.5 hours. Then it is air-cooled to room temperature to obtain fine-grained rolled copper foil for battery negative electrode current collector. Example

[0028] A method for preparing fine-grained rolled copper foil for battery negative electrode current collectors includes the following steps: The overall process steps are consistent with those in Example 1, except that: The component mass percentages in step one are: Sn 0.08wt.%, Ag 0.012wt.%, La 0.010wt.%, Ce 0.005wt.%, Y 0.003wt.%, Pr 0.005wt.%, O 0.08wt.%, with the balance being Cu and unavoidable impurities. The vacuum is evacuated to 0.5Pa, the temperature is raised to 1180℃ and held for 15min. After adding rare earth elements, the temperature is adjusted to 3kW and held for 3min. The homogenization temperature in step two is 930℃, and the holding time is 2h, resulting in an alloy ingot with a thickness of 10mm. In step three, the temperature is raised to 920°C, and the total hot rolling reduction is 60%, resulting in an alloy strip with a thickness of 4 mm. In step four, the total cold rolling reduction rate is 99.60%, with 12 processing passes. The single-pass reduction rate for the first two passes is 25%, the single-pass reduction rate for subsequent passes is 35-40%, and the reduction rate for the final pass is 45%, ultimately yielding a rolled copper foil with a thickness of 16μm. Example

[0029] A method for preparing fine-grained rolled copper foil for battery negative electrode current collectors includes the following steps: The overall process steps are consistent with those in Example 1, except that: The component mass percentages in step one are: Sn 0.10 wt.%, Ag 0.008 wt.%, La 0.008 wt.%, Ce 0.005 wt.%, Y 0.002 wt.%, Pr 0.001 wt.%, O 0.10 wt.%, with the balance being Cu and unavoidable impurities. The vacuum is evacuated to 3 Pa, the temperature is raised to 1180 °C, and held for 15 min. The homogenization temperature in step two is 950℃, and the holding time is 3 hours. In step three, the temperature is raised to 900°C and the total hot rolling reduction is 50%, resulting in an alloy strip with a thickness of 5 mm. In step four, the total cold rolling reduction rate is 99.80%, with 13 processing passes. The single-pass reduction rate for the first two passes is 30%, the single-pass reduction rate for subsequent passes is 35-40%, and the reduction rate for the final pass is 60%, ultimately obtaining a rolled copper foil with a thickness of 10μm. Example

[0030] A method for preparing fine-grained rolled copper foil for battery negative electrode current collectors includes the following steps: The overall process steps are consistent with those in Example 1, except that: The component mass percentages in step one are: Sn 0.05wt.%, Ag 0.010wt.%, La 0.008wt.%, Ce 0.008wt.%, Y 0.004wt.%, Pr 0.010wt.%, O 0.03wt.%, with the balance being Cu and unavoidable impurities, and the temperature is raised to 1130℃; The homogenization temperature in step two is 900℃, and the holding time is 6 hours. In step three, the temperature is raised to 930°C, and the total hot rolling reduction is 64%, resulting in an alloy strip with a thickness of 3.6 mm. In step four, the total cold rolling reduction rate is 99.69%, with 12 processing passes. The single-pass reduction rate for the first two passes is 30%, the single-pass reduction rate for subsequent passes is 35-40%, and the reduction rate for the final pass is 50%, ultimately obtaining a rolled copper foil with a thickness of 11μm. Example

[0031] A method for preparing fine-grained rolled copper foil for battery negative electrode current collectors includes the following steps: The overall process steps are consistent with those in Example 1, except that: The component mass percentages in step one are: Sn 0.08wt.%, Ag 0.010wt.%, La 0.008wt.%, Ce 0.005wt.%, Y 0.002wt.%, Pr 0.005wt.%, O 0.05wt.%, with the balance being Cu and unavoidable impurities. The vacuum is evacuated to 1 Pa, and the temperature is raised to 1180℃. The homogenization temperature in step two is 950℃, and the holding time is 5 hours. In step three, the temperature is raised to 900°C, and the total hot rolling reduction is 60%, resulting in an alloy strip with a thickness of 4 mm. In step four, the total cold rolling reduction rate is 99.70%, with 12 processing passes. The single-pass reduction rate for the first two passes is 20%, the single-pass reduction rate for subsequent passes is 35-40%, and the reduction rate for the final pass is 45%, ultimately obtaining a rolled copper foil with a thickness of 12μm. Example

[0032] A method for preparing fine-grained rolled copper foil for battery negative electrode current collectors includes the following steps: The overall process steps are consistent with those in Example 1, except that: The component mass percentages in step one are: Sn 0.10 wt.%, Ag 0.012 wt.%, La 0.015 wt.%, Ce 0.010 wt.%, Y 0.005 wt.%, Pr 0.015 wt.%, O 0.08 wt.%, with the balance being Cu and unavoidable impurities. The vacuum is drawn to 8 Pa and the temperature is raised to 1130 °C. The homogenization temperature in step two is 920℃, and the holding time is 3 hours. In step three, the temperature is raised to 900°C, and the total hot rolling reduction is 60%, resulting in an alloy strip with a thickness of 4 mm. In step four, the total cold rolling reduction rate is 99.70%, with 12 processing passes. The single-pass reduction rate for the first two passes is 25%, the single-pass reduction rate for subsequent passes is 35-40%, and the reduction rate for the final pass is 50%, ultimately obtaining a rolled copper foil with a thickness of 12μm.

[0033] Comparative Example The overall process steps are consistent with those in Example 1, except that: Sn is not added to the component mass percentage in step one. Specifically, it is: Ag 0.008 wt.%, La 0.008 wt.%, Ce 0.005 wt.%, Y 0.002 wt.%, Pr 0.001 wt.%, O 0.10 wt.%, with the balance being Cu and unavoidable impurities. Only high-purity Cu and Cu-Ag master alloy are added during smelting. In step four, a conventional cold rolling process is used, with the reduction rate of each pass being basically the same. The single-pass reduction rate is about 20%, and the total cold rolling reduction rate is 99.62%, ultimately obtaining a rolled copper foil with a thickness of 19μm.

[0034] Experimental Example The copper foil obtained in Example 1 has a tensile strength of 584.3 MPa along the rolling direction (RD) and a tensile strength of 604.3 MPa along the transverse direction (TD), with an average grain size of 5.21 μm. The copper foil obtained in Example 2 has a tensile strength of 594.5 MPa along the rolling direction (RD) and a tensile strength of 614.9 MPa along the transverse direction (TD), with an average grain size of 4.43 μm. The copper foil obtained in Example 3 has a tensile strength of 629.3 MPa along the rolling direction (RD) and a tensile strength of 643.9 MPa along the transverse direction (TD), with an average grain size of 3.18 μm. The copper foil obtained in Example 4 has a tensile strength of 605.8 MPa along the rolling direction (RD) and a tensile strength of 612.3 MPa along the transverse direction (TD), with an average grain size of 3.52 μm. The copper foil obtained in Example 5 has a tensile strength of 597.5 MPa along the rolling direction (RD), a tensile strength of 606.4 MPa along the transverse direction (TD), and an average grain size of 3.41 μm. The copper foil obtained in Example 6 has a tensile strength of 613.6 MPa along the rolling direction (RD), a tensile strength of 622.5 MPa along the transverse direction (TD), and an average grain size of 3.84 μm. The copper foil obtained in the comparative example has a tensile strength of 542.5 MPa along the rolling direction (RD) and a tensile strength of 586.3 MPa along the transverse direction (TD), with an average grain size of 22.39 μm.

[0035] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing fine-grained rolled copper foil for battery negative electrode current collectors, characterized in that, Includes the following steps: Step 1: Batching and Smelting: Grind all kinds of raw materials to remove surface oxide scale, prepare materials according to the mass percentage ratio of fine-grained rolled copper foil alloy components, add high-purity Cu, Sn, and Cu-Ag master alloy to the crucible in sequence, evacuate the furnace and control the power of the smelting furnace to preheat in stages, introduce argon gas to protect the smelting, add rare earth elements after the raw materials are fully melted, melt and stir and keep warm, and then quickly pour the molten metal into the mold to obtain alloy ingots; Step 2: Homogenization heat treatment: The alloy ingot is placed in a heat treatment furnace for homogenization treatment, and then cooled to room temperature to obtain the alloy ingot; Step 3: Hot rolling: The homogenized alloy ingot is milled, heated and held at the temperature, then hot rolled, and then cooled to room temperature to obtain alloy strip. Step 4: Multi-pass cold rolling: After removing the surface oxide scale from the hot-rolled alloy strip, it is subjected to multi-pass cold rolling at room temperature to finally obtain rolled copper foil. Step 5: Low-temperature annealing: The cold-rolled alloy foil is placed in a heat treatment furnace for annealing, and then cooled to room temperature to obtain fine-grained rolled copper foil for battery negative electrode current collector.

2. The method for preparing fine-grained rolled copper foil for battery negative electrode current collector according to claim 1, characterized in that, The mass percentage ratio in step one is as follows: Sn: 0.01-0.1 wt.%, Ag: 0.008-0.015 wt.%, La: 0.005-0.015 wt.%, Ce: 0.001-0.01 wt.%, Y: 0.001-0.005 wt.%, Pr: 0.001-0.015 wt.%, O: 0.01-0.1 wt.%, with the balance being Cu and unavoidable impurities.

3. The method for preparing fine-grained rolled copper foil for battery negative electrode current collector according to claim 1, characterized in that, The purity of the high-purity Cu, Sn, and Cu-Ag master alloy in step one is 99.99 wt.%.

4. The method for preparing fine-grained rolled copper foil for battery negative electrode current collector according to claim 1, characterized in that, The vacuum degree of vacuum melting in step one is 0.5-10 Pa, the holding time is 10-15 min, and the rare earth elements include one or more of La, Ce, Y, and Pr. The melting power is first preheated at 4.4 kW for 5 min, then increased to 6.2 kW for 5 min, and then kept constant at 8.2 kW to 1100-1200℃. After adding the rare earth elements, the power is adjusted to 3-4 kW and held for 3-5 min.

5. The method for preparing fine-grained rolled copper foil for battery negative electrode current collector according to claim 1, characterized in that, The homogenization treatment in step two is carried out at a temperature of 900-950℃ for 3-6 hours, and the cooling method is to cool the furnace to room temperature to obtain an alloy ingot with a thickness of 10-15mm.

6. The method for preparing fine-grained rolled copper foil for battery negative electrode current collector according to claim 1, characterized in that, In step three, the heating temperature for hot rolling is 900-930℃, the holding time is 40min, the total reduction rate for hot rolling is 50-70%, and after hot rolling, it is water-cooled to room temperature to obtain an alloy strip with a thickness of 3-5mm.

7. The method for preparing fine-grained rolled copper foil for battery negative electrode current collector according to claim 1, characterized in that, In step four, the cold rolling process consists of 10-15 passes, with a total cold rolling reduction of 99.2-99.9%, ultimately yielding rolled copper foil with a thickness of 6-20 μm. The single-pass reduction rate for the first two passes is 20-30%, the single-pass reduction rate for subsequent passes is 35-40%, and the reduction rate for the final pass is 40-60%.

8. The method for preparing fine-grained rolled copper foil for battery negative electrode current collector according to claim 1, characterized in that, The annealing process in step five is carried out at a temperature of 200-280℃, with a holding time of 0.5-1h, and is cooled to room temperature by air cooling.

9. A fine-grained rolled copper foil for use as a negative electrode current collector in a battery, characterized in that, Prepared by the method described in any one of claims 1-8.

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