Negative current collector and preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a negative electrode current collector and a preparation method and application thereof. The negative current collector comprises a first copper foil and a second copper foil arranged on at least one side surface of the first copper foil, the first copper foil is provided with a first pore, the second copper foil is provided with a second pore, and the tortuosity tau2 of the second copper foil is smaller than the tortuosity tau1 of the first copper foil. The negative electrode current collector can reduce the elongation percentage of the copper foil, and improve the energy density, the cycle performance and the rate capability of the battery at the same time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, in particular, relates to a negative electrode current collector and a preparation method and application thereof, more particularly, relates to a negative electrode current collector and a preparation method thereof, a negative electrode sheet, a battery and a power utilization device. BACKGROUND

[0002] Solid-state batteries have become a research hotspot in the field of new energy and have shown great application potential due to their significant advantages of high safety and high energy density. Although the medium-high silicon negative electrode system can help to improve the energy density of the battery by improving the negative electrode capacity, the volume expansion rate of the silicon-based material requires the design of a reserved expansion space, the introduction of a buffer layer and other structural designs to adapt, and such redundant designs occupy the internal space of the battery, leading to a decrease in the energy density, and the system still has safety hazards. In view of the above problems, the improvement of the negative electrode current collector has become an important breakthrough direction. However, the existing improvement measures are mostly adapted to traditional graphite negative electrodes, and the matching degree with the porous structure and high expansion characteristics of the high-silicon negative electrode is insufficient: the design of the current collector pores is not conducive to the transport of lithium ions, and the interface contact between the silicon negative electrode and the current collector is unstable. This not only leads to a low lithium ion transport efficiency, but also makes it difficult to balance the electrochemical performance and safety performance of the battery, and therefore the structure and performance of the negative electrode current collector still need to be further optimized. SUMMARY

[0003] The present application aims to at least partially solve one of the technical problems in the related art. To this end, the present application proposes a negative electrode current collector and a preparation method thereof, a negative electrode sheet, a battery and a power utilization device. The negative electrode current collector can reduce the elongation rate of the copper foil while improving the energy density, cycle performance and rate performance of the battery.

[0004] In a first aspect, the present application provides a negative electrode current collector, comprising a first copper foil and a second copper foil arranged on at least one side surface of the first copper foil, wherein the first copper foil has a first pore, the second copper foil has a second pore, and the tortuosity τ2 of the second copper foil is less than the tortuosity τ1 of the first copper foil. Thus, the negative electrode current collector can reduce the elongation rate of the copper foil while improving the energy density, cycle performance and rate performance of the battery.

[0005] According to an embodiment of the present application, at least one of the following conditions is met: The pore diameter φ2 of the second pore is greater than the pore diameter φ1 of the first pore. The porosity L2 of the second copper foil is greater than the porosity L1 of the first copper foil.

[0006] Thus, the above features can improve the tensile strength of the copper foil, reduce the elongation rate, improve the adhesion between the negative electrode active material and the copper foil, and improve the liquid retention amount of the battery, thereby improving the rate performance and cycle performance of the battery.

[0007] According to the embodiments of the present application, at least one of the following conditions is met: The porosity L1 of the first copper foil is 20% to 50%; The pore size φ1 of the first pore is 50 nm to 5 μm; The porosity L2 of the second copper foil is 70% to 95%; The pore size φ2 of the second pore is 10 μm to 500 μm; The tortuosity τ1 of the first copper foil satisfies: τ1>5; The tortuosity τ2 of the second copper foil is 1.5 to 3.

[0008] Therefore, the above features can reduce the electrolyte penetration resistance, the small inner pores, and improve the local current density distribution uniformity, thereby maximizing the ion transport efficiency; in addition, the second pores can disperse the lithium dendrite growth direction, and the first pores can form a local high-temperature isolation zone to improve the safety performance of the battery.

[0009] According to the embodiments of the present application, the first copper foil is provided with the second copper foil on both sides, and the negative current collector further comprises: A polymer base film is arranged on one side of the first copper foil and located between the first copper foil and the second copper foil; A third copper foil is arranged between the polymer base film and the second copper foil, and the third copper foil has a third pore; The tortuosity τ3 of the third copper foil is greater than the tortuosity τ2 of the second copper foil.

[0010] Therefore, the third copper foil is arranged between the polymer base film and the second copper foil, and the high tortuosity τ3 further enhances the mechanical properties of the negative current collector, provides additional structural support, ensures the mechanical stability during the charging and discharging process of the battery, and reduces the structural damage caused by expansion and contraction.

[0011] According to the embodiments of the present application, at least one of the following conditions is met: The pore size φ3 of the third pore is smaller than the pore size φ2 of the second pore; The porosity L3 of the third copper foil is smaller than the porosity L2 of the second copper foil; The material of the polymer base film includes at least one of polyethylene terephthalate, polypropylene, and polyimide.

[0012] Therefore, the above features can provide higher mechanical strength and structural stability, which helps to withstand the expansion and contraction of the active material during the charging and discharging process of the battery, reduces the structural damage, and the material of the above polymer base film has high chemical stability and thermal stability, which can effectively bond the negative active material and the negative current collector.

[0013] According to embodiments of the present application, at least one of the following conditions is met: The porosity L3 of the third copper foil is 20% to 50%; The pore size φ3 of the third pore is 50 nm to 5 μm; The tortuosity τ3 of the third copper foil satisfies: τ3 > 5.

[0014] Thus, the above features help to improve the tensile strength of the third copper foil, reduce its ductility, and enhance its structural stability, thereby better supporting the active material and improving the mechanical properties and cycle stability of the battery.

[0015] According to embodiments of the present application, at least one of the following conditions is met: The thickness of the first copper foil is 1 μm to 2 μm; The thickness of the second copper foil is 1 μm to 2 μm; The thickness of the third copper foil is 1 μm to 2 μm; The thickness of the polymer base film is 4.5 μm to 6 μm.

[0016] Thus, within the above ranges, it is helpful to provide sufficient mechanical strength to support the active material while maintaining a low resistance to improve the conductivity and cycle stability of the battery.

[0017] According to embodiments of the present application, the second copper foil is provided with a recess pattern on the surface away from the first copper foil. Thus, the above structure is conducive to directional release of expansion stress, reducing the risk of breaking of the negative electrode tab during the cycle to the end-of-life (EOL) stage of the battery, reducing local stress concentration, and reducing the electrode expansion rate.

[0018] According to embodiments of the present application, the recess pattern includes recess lines, and at least one of the following conditions is met: The width of the recess line is 1 μm to 10 μm; The depth of the recess line is 0.5 μm to 1 μm; The spacing between adjacent recess lines is 5 μm to 10 μm; The shape of the recess pattern includes at least one of a line, a circle.

[0019] Thus, by reasonably designing the width, depth, spacing, and shape of the recess pattern, a good balance can be achieved in stress dispersion and release for the negative electrode current collector, significantly reducing the risk of breaking of the negative electrode tab during the cycle to the EOL stage of the battery, reducing local stress concentration, and reducing the electrode expansion rate, thereby improving the overall performance and safety of the battery.

[0020] In a second aspect, the present application provides a method for preparing a negative electrode current collector, comprising: forming a thin copper film by a magnetron sputtering method; thickening the thin copper film by a water medium electroplating method to obtain a first copper foil; forming a second copper foil on at least one side surface of the first copper foil by a chemical vapor deposition method.

[0021] Therefore, the method is simple to operate and easy to implement, and is conducive to obtaining a copper foil with uniform thickness.

[0022] According to an embodiment of the present application, the above method comprises: forming the thin copper film on the opposite side surfaces of the polymer base film by the magnetron sputtering method; thickening the thin copper film by the water medium electroplating method to obtain a first copper foil and a third copper foil, respectively; forming the second copper foil on the surface of the first copper foil away from the polymer base film and the surface of the third copper foil away from the polymer base film by the chemical vapor deposition method.

[0023] Therefore, the method is simple to operate and easy to implement, and is conducive to obtaining a copper foil with uniform thickness.

[0024] According to an embodiment of the present application, before forming the thin copper film on the opposite side surfaces of the polymer base film, the method further comprises: surface treating and activating the surface of the polymer base film by the magnetron sputtering method.

[0025] Therefore, it is conducive to improving the adhesion and bonding strength of the copper foil and the polymer base film, and ensuring that the thin copper film can be uniformly and firmly deposited on the polymer base film.

[0026] According to an embodiment of the present application, the thickness of the thin copper film is 30 nm to 70 nm. Therefore, within the above range, the thin copper layer can optimize the ion transmission path, reduce local stress concentration, and enhance the cycle stability and safety of the battery.

[0027] In a third aspect, the present application provides a negative electrode sheet comprising the negative electrode current collector described above or prepared by the method described above. The negative electrode sheet comprises all the features and advantages of the negative electrode current collector described above or prepared by the method described above, and will not be repeated here.

[0028] In a fourth aspect of the present application, a battery is provided, comprising the negative current collector as described above, the negative current collector prepared by the method as described above, or the negative electrode tab as described above. The battery comprises all the features and advantages of the negative current collector as described above, the negative current collector prepared by the method as described above, or the negative electrode tab as described above, which will not be repeated here.

[0029] In a fifth aspect of the present application, an electric device is provided, comprising the negative current collector as described above, the negative current collector prepared by the method as described above, the negative electrode tab as described above, or the battery as described above. The electric device comprises all the features and advantages of the negative current collector as described above, the negative current collector prepared by the method as described above, the negative electrode tab as described above, or the battery as described above, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structural schematic diagram of the negative current collector of an embodiment of the present application; Figure 2 is a structural schematic diagram of the negative current collector of another embodiment of the present application; Figure 3 is a planar schematic diagram of the recess pattern of an embodiment of the present application.

[0031] Reference signs: 10: first copper foil; 20: second copper foil; 30: polymer base film; 40: third copper foil; 50: recess pattern. DETAILED DESCRIPTION

[0032] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0033] In the related art, the negative electrode current collector is mostly made of composite copper foil, but the application of the composite copper foil in the battery still has some significant shortcomings. First, the structure of the existing composite copper foil is usually a three-layer structure of a copper foil layer, a polymer substrate and a copper foil layer, wherein the copper foil layer is mainly prepared by electrodeposition method and does not have a porous structure. This makes the composite copper foil not only be able to transmit electrons and collect the current generated by the active material (such as negative electrode graphite / silicon) and conduct to the battery tab, but also be unable to transmit lithium ions, thereby limiting the overall performance of the battery. Second, the existing porous copper foil is mainly made by using copper sulfate solution to form pores, thereby obtaining a porous copper foil with a pore size within a certain range. Although this porous copper foil improves the energy density and liquid retention of the battery, thereby improving the rate performance and cycle stability of the battery, the pore structure is only controlled by the surface roughness, which shortens the transmission distance of lithium ions but does not consider the tortuosity of lithium ion transmission, so it cannot effectively shorten the transmission path of lithium ions. Finally, the existing electrolytic copper foil preparation technology mainly improves, iterates and upgrades the thickness, tensile strength and ductility of the copper foil to reduce the ductility of the copper foil, but the overall electrochemical performance of the battery is limited.

[0034] Based on the above research, the present application starts from the perspective of the pore structure and surface flatness of the copper foil layer, and constructs the relationship between the tortuosity of the copper foil layer and the pore size and porosity, as well as the correlation between these parameters and the ductility of the copper foil, thereby not only reducing the ductility of the copper foil, but also improving the overall performance of the battery.

[0035] In a first aspect of the present application, a negative electrode current collector is provided, referring to Figure 1 The negative electrode current collector includes a first copper foil 10 and a second copper foil 20 arranged on at least one side surface of the first copper foil, wherein the first copper foil 10 has a first pore, the second copper foil 20 has a second pore, and the tortuosity τ2 of the second copper foil 20 is less than the tortuosity τ1 of the first copper foil 10.

[0036] Therefore, the above structure design combines copper foils with different tortuosity to achieve the improvement of the performance of the battery in multiple aspects. On the one hand, the higher tortuosity τ1 of the first copper foil significantly improves the tensile strength of the copper foil, reduces the ductility of the copper foil, and enhances the structural stability thereof. On the other hand, the lower tortuosity τ2 effectively shortens the transmission path of electrons and lithium ions and enhances the adhesion between the negative electrode active material and the copper foil. The above two aspects work together to not only improve the liquid retention of the battery, but also significantly improve the rate performance, cycle stability and energy density of the battery.

[0037] In this paper, the tortuosity (τ) of the copper foil refers to the degree of curvature of the ion transport path, which directly affects the conductivity and energy transfer efficiency of the battery. When constructing the negative electrode current collector, the tortuosity (τ), porosity (L), and pore size (φ) of the copper foil are key parameters affecting battery performance. To optimize these parameters, the inventors derived the following general formula through fitting experimental data: τ = A((1-L) / L). B (φ0 / φ) C Where τ is the tortuosity of the copper foil, L is the porosity of the copper foil, φ is the actual pore diameter of the copper foil, φ0 is the pore diameter constant, and A, B, and C are fitting constants.

[0038] Furthermore, in order to describe the relationship between the tortuosity τ1 of the first copper foil and its porosity L1 and pore size φ1, the inventors obtained the following fitting formula for the tortuosity τ1 of the first copper foil based on experimental data: τ1=2.7((1-L1) / L1) 0.9 (1 / φ1) 0.5 ; The fitting formulas for the tortuosity τ2 of the second copper foil with its porosity L2 and pore size φ2 are as follows: τ2=2.5((1-L2) / L2) 0.7 (1 / φ2) 0.3 .

[0039] According to an embodiment of this application, the pore size φ2 of the second pore is larger than the pore size φ1 of the first pore. Therefore, the larger pore size of the second pore reduces the resistance to lithium ion transport, allowing lithium ions to be transported more quickly during charging and discharging, thereby significantly improving the rate performance of the battery; simultaneously, the smaller pore size of the first pore improves the uniformity of local current density distribution.

[0040] According to an embodiment of this application, the porosity L2 of the second copper foil 20 is greater than the porosity L1 of the first copper foil 10. Therefore, the high porosity L2 of the second copper foil can disperse the growth direction of lithium dendrites, while providing more space for the negative electrode active material, allowing it to be more uniformly distributed on the copper foil surface, thereby improving the utilization rate of the active material and increasing the energy density of the battery; simultaneously, the porosity L1 of the first copper foil can tightly anchor the active material (such as silicon particles), suppressing its shedding during cycling.

[0041] According to embodiments of this application, the porosity L1 of the first copper foil 10 is 20% to 50%, specifically within the range of 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any two of these ranges. Therefore, within the aforementioned porosity range, the first copper foil can tightly anchor the active material (such as silicon particles), suppressing its shedding during cycling, thereby improving the cycle stability of the battery. If the porosity L1 is too large, it may reduce the structural strength of the first copper foil, failing to effectively support the active material and affecting the mechanical properties of the battery; if the porosity L1 is too small, it may not provide sufficient space for the active material, limiting its distribution and utilization, thus affecting the battery's capacity and performance.

[0042] According to embodiments of this application, the pore size φ1 of the first pore is 50nm~5μm, specifically such as 50nm, 100nm, 300nm, 500nm, 700nm, 900nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or any two of these ranges. This helps improve the uniformity of local current density distribution and optimizes the electrochemical performance of the battery. If the pore size φ1 is too large, it may increase the permeation resistance of the electrolyte, reduce lithium-ion transport efficiency, and affect the rate performance of the battery; if the pore size φ1 is too small, it may lead to uneven current density distribution, excessively high local current density, and easily cause problems such as lithium dendrite growth, affecting the safety and cycle life of the battery.

[0043] According to embodiments of this application, the porosity L2 of the second copper foil 20 is 70%~95%, specifically 70%, 75%, 80%, 85%, 90%, 95%, or any two of these ranges. Therefore, the high porosity of the second copper foil can disperse the growth direction of lithium dendrites, providing more space for the negative electrode active material, allowing it to be more uniformly distributed on the copper foil surface, thereby improving the utilization rate of the active material and increasing the energy density of the battery. If the porosity L2 is too large, the structure of the second copper foil may be too loose, reducing its mechanical strength and stability, affecting the overall performance of the battery; if the porosity L2 is too small, it may not be able to fully utilize its advantage of providing space for the active material, limiting the improvement of the battery's energy density.

[0044] According to embodiments of this application, the pore size φ2 of the second pore is 10μm to 500μm, specifically within the range of 10μm, 30μm, 50μm, 70μm, 90μm, 100μm, 150μm, 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, 500μm, or any two of these ranges. Therefore, within the aforementioned pore size range, the transport resistance of lithium ions can be reduced, allowing lithium ions to be transported more quickly during charging and discharging, thereby significantly improving the rate performance of the battery. If the pore size φ2 is too large, it may lead to poor connectivity between pores, affecting the uniform distribution of the electrolyte and the uniformity of ion transport; if the pore size φ2 is too small, it cannot effectively reduce the transport resistance of lithium ions, making it difficult to fully realize its role in improving the rate performance of the battery.

[0045] According to an embodiment of this application, the tortuosity τ1 of the first copper foil 10 satisfies: τ1>5, specifically 5.1, 5.5, 6, 6.5, 7, 8, 9, 10. This helps to improve the tensile strength of the first copper foil, reduce its elongation, and enhance its structural stability, thereby better supporting the active material and improving the mechanical performance and cycle stability of the battery. If the tortuosity τ1 is too small, the tensile strength of the first copper foil will decrease, the elongation will increase, and it will be unable to effectively support the active material, easily leading to the active material detaching and affecting the cycle life of the battery.

[0046] According to embodiments of this application, the tortuosity τ2 of the second copper foil 20 is 1.5 to 3, specifically within the ranges of 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.7, 2.9, 3, or any two of these ranges. Within these ranges, it helps to shorten the transport path of electrons and lithium ions, improve the adhesion between the negative electrode active material and the copper foil, thereby increasing the battery's liquid retention capacity, rate capability, cycle performance, and energy density. If the tortuosity τ2 is too large, it may increase the length and complexity of the lithium ion transport path, reduce the lithium ion transport efficiency, and affect the battery's rate performance; if the tortuosity τ2 is too small, it may not be able to fully exert its effect of improving adhesion and liquid retention capacity, resulting in limited improvement in battery performance.

[0047] According to the embodiments of this application, referring to Figure 2The first copper foil 10 has second copper foils 20 disposed on both sides. The negative electrode current collector further includes: a polymer base film 30 disposed on one side of the first copper foil 10 and located between the first copper foil 10 and the second copper foil 20; and a third copper foil 40 disposed between the polymer base film 30 and the second copper foil 20, the third copper foil 40 having a third pore; wherein the tortuosity τ3 of the third copper foil 40 is greater than the tortuosity τ2 of the second copper foil 20. Thus, the third copper foil, disposed between the polymer base film and the second copper foil, with its higher tortuosity τ3, further enhances the mechanical properties of the negative electrode current collector, provides additional structural support, ensures mechanical stability during battery charging and discharging, and reduces structural damage caused by expansion and contraction.

[0048] According to an embodiment of this application, the pore size φ3 of the third pore is smaller than the pore size φ2 of the second pore. Therefore, the smaller pore size allows for better anchoring of active materials (such as silicon particles), reducing the shedding of active materials during battery cycling, thereby improving the battery's interface stability and cycle life.

[0049] According to an embodiment of this application, the porosity L3 of the third copper foil is less than the porosity L2 of the second copper foil. Therefore, the lower porosity of the third copper foil makes the copper foil structure more compact, providing higher mechanical strength and structural stability. This helps to withstand the expansion and contraction of the active material during battery charging and discharging, reducing structural damage.

[0050] According to embodiments of this application, the polymer base film is made of at least one of polyethylene terephthalate, polypropylene, and polyimide. Therefore, the above materials possess high chemical and thermal stability, and can effectively bond the negative electrode active material to the negative electrode current collector.

[0051] According to embodiments of this application, the porosity L3 of the third copper foil is 20% to 50%, specifically within the range of 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any two of these ranges. Therefore, within the aforementioned porosity range, the third copper foil can tightly anchor the active material (such as silicon particles), suppressing its shedding during cycling, thereby improving the cycle stability of the battery. If the porosity L3 is too large, it may reduce the structural strength of the third copper foil, failing to effectively support the active material and affecting the mechanical properties of the battery; if the porosity L3 is too small, it may not provide sufficient space for the active material, limiting its distribution and utilization, thus affecting the battery's capacity and performance.

[0052] According to embodiments of this application, the pore size φ3 of the third pore is 50nm~5μm, specifically such as 50nm, 100nm, 300nm, 500nm, 700nm, 900nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or any range between two of these. This helps improve the uniformity of local current density distribution and optimizes the electrochemical performance of the battery. If the pore size φ3 is too large, it may increase the permeation resistance of the electrolyte, reduce lithium-ion transport efficiency, and affect the rate performance of the battery; if the pore size φ3 is too small, it may lead to uneven current density distribution, excessively high local current density, and easily cause problems such as lithium dendrite growth, affecting the safety and cycle life of the battery.

[0053] According to embodiments of this application, the tortuosity τ3 of the third copper foil satisfies: τ3 > 5, specifically 5.1, 5.5, 6, 6.5, 7, 8, 9, 10. This helps to improve the tensile strength of the third copper foil, reduce its elongation, and enhance its structural stability, thereby better supporting the active material and improving the battery's mechanical performance and cycle stability. If the tortuosity τ3 is too small, the tensile strength of the third copper foil will decrease, the elongation will increase, it will be unable to effectively support the active material, and the active material will easily detach, affecting the battery's cycle life.

[0054] According to embodiments of this application, the thickness of the first copper foil 10 is 1µm to 2µm, specifically within the range of 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm, 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm, 2µm, or any two of these ranges. Within this range, sufficient mechanical strength is provided to support the active material while maintaining low resistance to improve the battery's conductivity and cycle stability. If the thickness of the first copper foil is too large, it may increase the overall weight of the battery, reduce energy density, and increase cost; if the thickness is too small, sufficient mechanical strength may not be provided, leading to structural instability and affecting the battery's cycle life and safety.

[0055] According to embodiments of this application, the thickness of the second copper foil 20 is 1µm to 2µm, specifically within the ranges of 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm, 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm, 2µm, or any two of these ranges. Within this range, it helps optimize the ion transport path, improve lithium-ion transport efficiency, maintain good contact with the electrolyte, and enhance the battery's rate performance and fast charge / discharge capability. If the thickness of the second copper foil is too large, it may increase the battery's internal resistance, reduce rate performance, and decrease the usable space for active materials, affecting the battery's energy density; if the thickness is too small, it may not effectively disperse the growth direction of lithium dendrites, reducing battery safety.

[0056] According to embodiments of this application, the thickness of the third copper foil 40 is 1µm to 2µm, specifically within the ranges of 1µm, 1.1µm, 1.2µm, 1.3µm, 1.4µm, 1.5µm, 1.6µm, 1.7µm, 1.8µm, 1.9µm, 2µm, or any two of these ranges. Within these ranges, it helps to further enhance mechanical properties, provide additional structural support, and improve the overall performance of the battery. If the thickness of the third copper foil is too large, it may lead to an increase in the overall thickness of the battery, reducing the energy density and increasing material costs; if the thickness is too small, it may not be able to fully exert its role in enhancing mechanical properties and optimizing ion transport, affecting the stability and performance of the battery.

[0057] According to embodiments of this application, the thickness of the polymer base film 30 is 4.5µm to 6µm, specifically 4.5µm, 4.6µm, 4.7µm, 4.8µm, 4.9µm, 5µm, 5.2µm, 5.4µm, 5.6µm, 5.8µm, 6µm, or any range between two of these. Within this range, it helps to provide good electrolyte wettability and electrolyte retention, ensuring uniform distribution of the electrolyte within the battery, while also acting as an isolation and buffer, improving battery safety and cycle stability. If the thickness of the polymer base film is too large, it may increase the battery's internal resistance, reduce the battery's rate performance, and reduce the usable space for active materials, affecting the battery's energy density; if the thickness is too small, it may not be able to effectively isolate the first copper foil and the second copper foil, reducing interface stability and affecting battery safety and cycle life.

[0058] According to an embodiment of this application, a recessed pattern 50 is provided on the surface of the second copper foil 20 away from the first copper foil 10. A planar schematic diagram of the recessed pattern 50 is shown below. Figure 3Therefore, the above structure is beneficial for the directional release of expansion stress, reducing the risk of electrode breakage during the end-of-life (EOL) stage of the battery, reducing local stress concentration, and reducing electrode expansion rate.

[0059] It is understandable that when the battery capacity decays to below 70%-80% of its initial capacity, it can be considered to have reached the EOL stage, which is manifested in problems such as increased battery charging frequency and extended charging time.

[0060] It is understandable that by rationally designing the width, depth, spacing, and shape of the recessed pattern, a good balance can be achieved in terms of stress dispersion and release in the negative electrode current collector, significantly reducing the risk of negative electrode breakage during the cycle-to-EOL stage, reducing local stress concentration, and lowering the electrode expansion rate, thereby improving the overall performance and safety of the battery.

[0061] According to embodiments of this application, the recessed pattern includes recessed lines with a width of 1µm to 10µm, specifically within the range of 1µm, 2µm, 3µm, 4µm, 5µm, 6µm, 7µm, 8µm, 9µm, 10µm, or any two of these ranges. Within this range, it helps optimize stress dispersion, ensuring uniform stress distribution on the copper foil surface, while reducing excessive material consumption and improving the overall battery performance. If the width of the recessed lines is too large, it may lead to excessive material consumption, increasing costs and potentially affecting the mechanical strength of the battery; if the width is too small, it may fail to effectively disperse stress, reducing the stress dispersion effect.

[0062] According to embodiments of this application, the depth of the recessed lines is 0.5µm to 1µm, specifically within the range of 0.5µm, 0.6µm, 0.7µm, 0.8µm, 0.9µm, 1µm, or any two thereof. Within this range, it helps to further enhance stress dispersion and release effects while ensuring the structural integrity of the copper foil. If the depth of the recessed lines is too large, it may damage the structural integrity of the copper foil, reduce its mechanical strength, and affect the stability of the battery; if the depth is too small, it may not be able to effectively release expansion stress, reducing the stress dispersion effect.

[0063] According to embodiments of this application, the spacing between adjacent recessed lines is 5µm to 10µm, specifically within the ranges of 5µm, 5.5µm, 6µm, 6.5µm, 7µm, 7.5µm, 8µm, 8.5µm, 9µm, 9.5µm, 10µm, or any two of these ranges. Within this range, it helps optimize the uniformity of stress dispersion and release, ensuring uniform stress distribution on the copper foil surface, while reducing local stress concentration and lowering the electrode expansion rate. If the spacing between adjacent recessed lines is too large, it may lead to uneven stress dispersion and local stress concentration, affecting the cycle life and safety of the battery; if the spacing is too small, it may increase the complexity and cost of the material, and may also affect the mechanical properties of the battery.

[0064] According to an embodiment of this application, the shape of the recessed pattern includes at least one of lines and circles. Thus, the shape can effectively guide stress release in a specific direction to provide a more uniform stress dispersion effect and reduce local stress concentration.

[0065] A second aspect of this application provides a method for preparing a negative electrode current collector, comprising: S10: A thin copper film is formed by magnetron sputtering.

[0066] According to embodiments of this application, the thin copper film is formed on opposite sides of a polymer base film using the magnetron sputtering method. Therefore, the above method can precisely control the thickness of the copper film, ensuring that the copper film formed on both sides of the polymer base film has a uniform thickness.

[0067] According to embodiments of this application, before forming the thin copper film on the opposite surfaces of the polymer base film, the method further includes: surface treatment and activation of the surface of the polymer base film using the magnetron sputtering method. Therefore, the above operation helps to improve the adhesion and bonding strength between the polymer base film and the copper film, ensuring that the thin copper film can be uniformly and firmly deposited on the polymer base film.

[0068] According to embodiments of this application, the surface treatment includes: fixing the polymer base film onto the sample stage of a sputtering device, then evacuating and introducing an inert gas (such as Ar) for pre-sputtering cleaning. This removes oil and oxidation from the surface of the polymer base film, providing a clean and ideal substrate surface for subsequent activation or electroplating.

[0069] According to embodiments of this application, activation includes: after pre-sputtering cleaning, switching the inert gas to the required gas (e.g., O2, N2) or using a mixed reactive gas (e.g., Ar and O2) according to activation requirements, followed by reactive plasma treatment. This introduces specific active chemical functional groups (e.g., carbonyl, carboxyl, amino groups) onto the surface of the surface-treated polymer base film, altering its surface chemical properties from inert and hydrophobic to active and hydrophilic, thereby significantly improving its surface energy and chemical affinity for subsequent copper foil.

[0070] According to embodiments of this application, the thickness of the thin copper film is 30nm to 70nm, specifically within the range of 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, or any two of these ranges. Therefore, within this range, the thin copper layer can optimize the ion transport path, reduce local stress concentration, and enhance the cycle stability and safety of the battery. If the thickness of the thin copper film is too thin, it may not be able to form sufficient adhesion with the polymer base film, making it prone to detachment during the expansion and contraction of the battery during charging and discharging, thus reducing the battery's mechanical stability and cycle life. If the thickness of the thin copper film is too thick, the excessively thick thin copper film may generate more stress in subsequent processing, making it more prone to cracking or detachment during subsequent use.

[0071] S20: The thin copper film is thickened by an aqueous electroplating method to obtain a first copper foil.

[0072] In this step, the thin copper film is thickened to make it more uniform, reducing the non-uniformity of the film layer and obtaining a first copper foil with uniform thickness, which can meet the conductivity requirements of the negative electrode current collector.

[0073] According to embodiments of this application, the thin copper film is thickened using the aqueous electroplating method to obtain a first copper foil and a third copper foil. This allows the first and third copper foils to achieve conductivity while exhibiting lower resistance, thus contributing to improved battery charging and discharging efficiency.

[0074] According to embodiments of this application, the thickness of the thickened copper film is 0.8µm-1.2µm, specifically within the range of 0.8µm, 0.9µm, 1µm, 1.1µm, 1.2µm, or any two thereof. Therefore, within the aforementioned thickness range, not only can the resistance of the copper foil be significantly reduced, but the uniformity and conductivity of the copper foil can also be improved.

[0075] S30: A second copper foil is formed on at least one side surface of the first copper foil by chemical vapor deposition.

[0076] According to embodiments of this application, a second copper foil is formed on the surface of the first copper foil away from the polymer base film and the surface of the third copper foil away from the polymer base film using the chemical vapor deposition method. Therefore, the above method enables good adhesion between the second copper foil and the first copper foil, and can form a second copper foil with high purity and uniform thickness.

[0077] According to an embodiment of this application, before forming the thin copper film, the method further includes: constructing a fitting formula between the tortuosity (τ) of the copper foil and its pore size (φ) and porosity (L). Using the fitting formula described above, the pore size and porosity of the first and second copper foils are adjusted so that the tortuosity τ2 of the second copper foil is less than the tortuosity τ1 of the first copper foil. The pore size and porosity can be adjusted according to the control parameters of chemical vapor deposition, such as temperature, pressure, gas flow rate, and deposition time.

[0078] According to an embodiment of this application, after forming the second copper foil, the method further includes forming a recessed pattern on the surface of the second copper foil. This allows for directional release of expansion stress, reduces localized stress concentration, and lowers the electrode expansion rate.

[0079] According to embodiments of this application, the specific method for forming the recessed pattern is not limited, and can be selected according to actual needs. In some embodiments, the recessed pattern can be formed by physical rolling with an embossing roller.

[0080] A third aspect of this application provides a negative electrode sheet comprising the negative electrode current collector described above or the negative electrode current collector prepared by the method described above. This negative electrode sheet includes all the features and advantages of the negative electrode current collector described above or the negative electrode current collector prepared by the method described above, which will not be repeated here.

[0081] A fourth aspect of this application provides a battery comprising the aforementioned negative electrode current collector, the negative electrode current collector prepared by the aforementioned method, or the aforementioned negative electrode sheet. This battery exhibits high rate performance, high cycle performance, and high energy density.

[0082] It is understood that there are no particular restrictions on the specific types and structures of the batteries mentioned above, as long as a negative electrode is required. For example, according to their application, batteries can include, but are not limited to, primary batteries, secondary batteries, and fuel cells. According to their shape, batteries can include, but are not limited to, prismatic batteries and cylindrical batteries; according to their active ion composition, batteries can include, but are not limited to, lithium-ion batteries and sodium-ion batteries; and according to their packaging, batteries can include, but are not limited to, pouch batteries and hard-shell batteries.

[0083] Typically, a battery may include a positive electrode, the aforementioned negative electrode, an electrolyte, and a separator.

[0084] In some embodiments, the electrolyte in the battery described above can be a liquid electrolyte (i.e., an electrolyte solution) or a solid electrolyte.

[0085] In some embodiments, the electrolyte is a liquid electrolyte. In this case, the positive electrode, negative electrode, and separator can be fabricated into a battery cell using a winding or stacking process, and the battery cell and electrolyte can be housed in an outer package. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0086] In other embodiments, the electrolyte is a solid electrolyte. In this case, the positive electrode, negative electrode, electrolyte, and separator can be fabricated into a battery cell using a winding or stacking process, and the battery cell can be housed in an outer package. The positive and negative electrodes are alternately stacked, and the electrolyte and separator are disposed between adjacent positive and negative electrodes.

[0087] In some embodiments, the separator may be a separator known in the art that can be used in batteries and is stable to the electrolyte used, such as a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene composite separator, etc.

[0088] In some embodiments, the positive electrode may include a current collector and a positive electrode active layer disposed on at least one side of the current collector.

[0089] In some embodiments, the positive current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, aluminum foil current collectors; composite current collectors may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. Composite current collectors can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] In some embodiments, the positive electrode active layer may include a positive electrode binder, a positive electrode conductive agent, and a positive electrode active material. Additives with specific functions and effects, such as thickeners, sodium supplements, film-forming additives, flame retardants, and high / low temperature stabilizers, may also be added as needed.

[0091] As an example, the positive electrode active material of the battery may include lithium nickel cobalt manganese oxide (including but not limited to NCM811, NCM613, NCM523, etc.), lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, or positive electrode active materials commonly used in the art.

[0092] As an example, the positive electrode binder in the positive electrode active layer may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0093] As an example, the positive electrode conductive agent in the positive electrode active layer may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] A fifth aspect of this application provides an electrical device comprising the aforementioned negative electrode current collector, the negative electrode current collector prepared by the aforementioned method, the aforementioned negative electrode sheet, or the aforementioned battery. This electrical device possesses all the features and advantages of the aforementioned negative electrode current collector, the negative electrode current collector prepared by the aforementioned method, the aforementioned negative electrode sheet, or the aforementioned battery, which will not be elaborated upon here.

[0095] According to embodiments of this application, the specific type of electrical device is not particularly limited and can be any device that uses a battery as a power source or energy storage unit. As examples, electrical devices include, but are not limited to, electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (e.g., mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, etc.

[0096] It is understandable that, in addition to the battery mentioned above, the electrical device also includes necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0097] The embodiments of this application are described in detail below.

[0098] Example 1 1. Preparation of negative electrode current collector (1) The first copper foil is constructed based on the fitting formula of its tortuosity τ1 and its porosity and pore size: τ1=2.7((1-L1) / L1) 0.9 (1 / φ1) 0.5 The porosity L1 of the first copper foil is 35%, and the pore diameter φ1 is 5µm, so the tortuosity τ1 is 6.

[0099] (2) Construct the second copper foil based on the fitting formula of its tortuosity τ2 and its porosity and pore size: τ2=2.5((1-L2) / L2) 0.7 (1 / φ2) 0.3 If the porosity L2 of the second copper foil is 85% and the pore diameter φ2 is 200µm, then the tortuosity τ2 is 2.

[0100] (3) Surface treatment and activation of polypropylene base film (PP base film): Fix the polymer base film on the sample stage of the sputtering equipment, then evacuate and introduce Ar for pre-sputtering cleaning; after the pre-sputtering cleaning is completed, close the Ar valve, introduce N2, and then perform reactive plasma treatment.

[0101] (4) A thin copper film with a thickness of 100 nm is deposited on both sides of the PP base film by magnetron sputtering, and then the thin copper film is thickened to 1 µm by water-medium electroplating to obtain the first copper foil.

[0102] (5) A second copper foil with a thickness of 1µm is formed on both sides of the first copper foil by chemical vapor deposition to obtain a negative current collector consisting of two layers of copper foil.

[0103] 2. Preparation of negative electrode sheet A negative electrode slurry is prepared by homogenizing graphite and 20% silicon carbide as the negative electrode active material, conductive carbon black and single-walled carbon nanotubes (SP & SWCNT) as conductive agents, carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber (CMC & PAA & SBR) as binders. The negative electrode slurry is then coated on both sides of the negative electrode current collector. After coating and baking, the coated electrode roll is obtained. After rolling, slitting and die cutting, the negative electrode sheet is obtained.

[0104] 3. Preparation of positive electrode sheet The positive electrode active material lithium nickel cobalt manganese oxide (NCM), conductive agent conductive carbon black and carbon nanotubes (SP&CNT), and binder PVDF (polyvinylidene fluoride) are prepared into a positive electrode slurry using a homogenizer. The positive electrode slurry is then coated on both sides of an aluminum foil, and after coating and baking, a coated electrode roll is obtained. After rolling, slitting, and die-cutting, a positive electrode sheet is obtained.

[0105] 4. Preparation of the diaphragm A 12µm thick (polyethylene) PE membrane is selected.

[0106] 5. Preparation of electrolyte The commercially available lithium salt used in the electrolyte is lithium hexafluorophosphate (LiPF6).

[0107] 6. Battery fabrication The negative electrode, separator, and positive electrode are stacked in sequence and then wound to obtain a 20Ah battery cell. Electrolyte is injected into the battery cell, and the battery is obtained through vacuum sealing, settling, formation, shaping, and sorting processes.

[0108] Example 2 Same as Example 1, except that: the porosity L1 of the first copper foil is 20%, the pore diameter φ1 is 5µm, and the tortuosity τ1 is 5.5; the porosity L2 of the second copper foil is 95%, the pore diameter φ2 is 500µm, and the tortuosity τ2 is 1.5.

[0109] Example 3 Same as Example 1, except that: the porosity L1 of the first copper foil is 50%, the pore size φ1 is 50nm, and the tortuosity τ1 is 7.5; the porosity L2 of the second copper foil is 70%, the pore size φ2 is 10µm, and the tortuosity τ2 is 3.

[0110] Example 4 Same as Example 1, except that: a third copper foil with a thickness of 1µm is deposited between the first copper foil and the second copper foil. The porosity L3 of the third copper foil is 40%, the pore size φ3 is 3µm, and the tortuosity τ3 is 6, thus obtaining a negative electrode current collector including three layers of copper foil.

[0111] Example 5 Same as Example 1, except that: embossing rollers are used to press out recessed lines with a width of 7µm and a depth of 0.8µm on the surface of the second copper foil, and the spacing between the recessed lines is 9µm.

[0112] Comparative Example 1 Same as Example 1, except that: the porosity L1 of the first copper foil is 35%, the pore diameter φ1 is 2µm, and the tortuosity τ1 is 6.5; the porosity L2 of the second copper foil is 85%, the pore diameter φ2 is 2µm, and the tortuosity τ2 is 8.

[0113] Comparative Example 2 Same as Example 1, except that: the porosity L1 of the first copper foil is 35%, the pore diameter φ1 is 5µm, and the tortuosity τ1 is 4; the porosity L2 of the second copper foil is 85%, the pore diameter φ2 is 200µm, and the tortuosity τ2 is 2.

[0114] Comparative Example 3 Same as Example 1, except that the negative electrode current collector only includes the first copper foil.

[0115] Comparative Example 4 Same as Example 1, except that the negative electrode current collector only includes the second copper foil.

[0116] Comparative Example 5 Same as Example 1, except that: the porosity L1 of the first copper foil is 35%, the pore diameter φ1 is 2µm, and the tortuosity τ1 is 6.5; the porosity L2 of the second copper foil is 85%, the pore diameter φ2 is 300µm, and the tortuosity τ2 is 1.

[0117] Comparative Example 6 Same as Example 1, except that: the porosity L1 of the first copper foil is 10%, the pore size φ1 is 20nm, and the tortuosity τ1 is 9.5; the porosity L2 of the second copper foil is 60%, the pore size φ2 is 600µm, and the tortuosity τ2 is 1.2.

[0118] Comparative Example 7 Similar to Example 1, except that: the porosity L1 of the first copper foil is 60%, the pore diameter φ1 is 7µm, and the tortuosity τ1 is 2.5; the porosity L2 of the second copper foil is 96%, the pore diameter φ2 is 5µm, and the tortuosity τ2 is 4.5.

[0119] Performance testing (1) Elongation of negative electrode sheet: The initial height and width of the negative electrode sheet before charging were measured with calipers. After the cell was de-capacitated, it was charged to the upper limit voltage of 4.35V with a constant current of 0.33C (4.4A) and a cutoff current of 0.05C (1A). Then the cell was disassembled and the height and width of the disassembled negative electrode sheet were measured with calipers. The elongation of the negative electrode sheet in the height and width directions was calculated using the following formulas:

[0120] (2) Energy density: The performance of the 20Ah cells after capacity testing was carried out. The 0.33C energy density of the cells was tested as capacity * platform voltage / mass, the rate charging (6.6A constant current and constant voltage charging to 4.35V, cut-off current 1A) and the cycle performance (20A constant current charging to 4.35V, cut-off current 1A, cut-off voltage 4.35V, and then 20A constant current discharging to 2.5V).

[0121] (3) 3C constant current charging ratio: Under an environment of 25±2℃, the capacity charged by the battery is the ratio of the capacity charged by the battery when it is charged to 4.35V with a constant current of 20A and the cutoff current is 1A, and then charged to 4.35V with a constant voltage.

[0122] (4) Cycle capacity retention rate: Discharge capacity at the 500th cycle / initial discharge capacity.

[0123]

[0124] Conclusion: As shown in Table 1, the tortuosity of the second copper foil in Examples 1-3 is less than that of the first copper foil, and the elongation of the negative electrode sheet in both the height and width directions is 0. This indicates that the negative electrode sheet prepared using the technical solution of this application has good structural stability and can improve the energy density and cycle performance of the battery. Example 4 adds a third copper foil, further enhancing the mechanical properties of the negative electrode current collector and ensuring mechanical stability during battery charging and discharging. Therefore, the energy density and cycle performance of the battery prepared in this example are superior to those in Examples 1-3. Example 5 adds recessed lines based on Example 1, further improving the overall performance and safety of the battery. Comparative Examples 1-7 show that the pore size, porosity, and tortuosity are outside the scope of this application, resulting in a decrease in various aspects of battery performance and poor structural stability of the negative electrode sheet.

[0125] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0126] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0127] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A negative electrode current collector, characterized in that, It includes a first copper foil and a second copper foil disposed on at least one side surface of the first copper foil, wherein the first copper foil has a first pore, the second copper foil has a second pore, and the tortuosity τ2 of the second copper foil is less than the tortuosity τ1 of the first copper foil.

2. The negative electrode current collector according to claim 1, characterized in that, At least one of the following conditions must be met: The diameter φ2 of the second pore is larger than the diameter φ1 of the first pore; The porosity L2 of the second copper foil is greater than the porosity L1 of the first copper foil.

3. The negative electrode current collector according to claim 1 or 2, characterized in that, At least one of the following conditions must be met: The porosity L1 of the first copper foil is 20%~50%; The pore size φ1 of the first pore is 50nm~5μm; The porosity L2 of the second copper foil is 70%~95%; The pore diameter φ2 of the second pore is 10μm~500μm; The tortuosity τ1 of the first copper foil satisfies: τ1>5; The tortuosity τ2 of the second copper foil is 1.5~3.

4. The negative electrode current collector according to claim 1, characterized in that, The first copper foil has a second copper foil on both sides, and the negative electrode current collector further includes: A polymer-based film is disposed on one side of the first copper foil and located between the first copper foil and the second copper foil; A third copper foil is disposed between the polymer base film and the second copper foil, and the third copper foil has a third pore. The tortuosity τ3 of the third copper foil is greater than the tortuosity τ2 of the second copper foil.

5. The negative electrode current collector according to claim 4, characterized in that, At least one of the following conditions must be met: The diameter φ3 of the third pore is smaller than the diameter φ2 of the second pore; The porosity L3 of the third copper foil is less than the porosity L2 of the second copper foil; The polymer base film is made of at least one of polyethylene terephthalate, polypropylene, and polyimide.

6. The negative electrode current collector according to claim 4 or 5, characterized in that, At least one of the following conditions must be met: The porosity L3 of the third copper foil is 20%~50%; The pore size φ3 of the third pore is 50nm~5μm; The tortuosity τ3 of the third copper foil satisfies: τ3>5.

7. The negative electrode current collector according to claim 4, characterized in that, At least one of the following conditions must be met: The thickness of the first copper foil is 1µm to 2µm; The thickness of the second copper foil is 1µm to 2µm; The thickness of the third copper foil is 1µm to 2µm; The thickness of the polymer-based film is 4.5µm to 6µm.

8. The negative electrode current collector according to claim 1, characterized in that, The second copper foil has a recessed pattern on its surface away from the first copper foil.

9. The negative electrode current collector according to claim 8, characterized in that, The recessed pattern includes recessed lines and satisfies at least one of the following conditions: The width of the recessed lines is 1µm to 10µm; The depth of the recessed lines is 0.5µm to 1µm; The spacing between adjacent recessed lines is 5µm to 10µm; The shape of the recessed pattern includes at least one of lines and circles.

10. A method for preparing the negative electrode current collector according to any one of claims 1 to 9, characterized in that, include: Thin copper films are formed by magnetron sputtering. The thin copper film is thickened by an aqueous electroplating method to obtain a first copper foil. A second copper foil is formed on at least one side of the surface of the first copper foil by chemical vapor deposition.

11. The method according to claim 10, characterized in that, include: The thin copper film is formed on opposite sides of the polymer base film by the magnetron sputtering method. The thin copper film is thickened by the aqueous electroplating method to obtain a first copper foil and a third copper foil, respectively. The second copper foil is formed on the surface of the first copper foil away from the polymer base film and the surface of the third copper foil away from the polymer base film by the chemical vapor deposition method.

12. The method according to claim 11, characterized in that, Before forming the thin copper film on opposite sides of the polymer base film, the process further includes: The surface of the polymer base film is treated and activated by the magnetron sputtering method.

13. The method according to any one of claims 10 to 12, characterized in that, The thickness of the thin copper film is 30nm~70nm.

14. A negative electrode sheet, characterized in that, The negative electrode current collector includes any one of claims 1 to 9 or the negative electrode current collector prepared by any one of claims 10 to 13.

15. A battery, characterized in that, It includes the negative electrode current collector according to any one of claims 1 to 9, the negative electrode current collector prepared by the method according to any one of claims 10 to 13, or the negative electrode sheet according to claim 14.

16. An electrical appliance, characterized in that, The negative electrode current collector includes any one of claims 1 to 9, the negative electrode current collector prepared by any one of claims 10 to 13, the negative electrode sheet of claim 14, or the battery of claim 15.

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