Functional current collector and secondary battery using same

Abstract

The invention provides a functional current collector which comprises a polymer base material and a metal layer, and the metal layer is arranged on at least one surface of the polymer base material; the metal layer comprises n sub-metal layers which are sequentially arranged in a stacked mode in the thickness direction of the metal layer, n is a positive integer larger than or equal to 6, the sub-metal layers contain elemental metal nanoparticles, and the grain size of the elemental metal nanoparticles does not exceed 500 nm; in the direction away from the surface of the polymer base material, the thickness gradient of the n sub-metal layers is gradually increased, and the average grain size gradient of the elemental metal nanoparticles contained in the n sub-metal layers is gradually increased. In the functional current collector provided by the invention, the metal layer is arranged into the sub-metal layers which are laminated in a layered manner, and the sub-metal layers are changed in a gradient manner according to the rule, so that the tensile strength and the ductility of the functional current collector can be remarkably improved. The elemental metal nanoparticles are utilized to construct the sub-metal layer in gradient change, so that the strength of the metal layer can be flexibly regulated and controlled in a large range, and the risk of copper foil fault and fracture caused by deformation of the functional current collector in battery circulation can be reduced; and the cycle life and the safety performance of the secondary battery using the functional current collector are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular, relates to a functional current collector and a secondary battery using the same. Background Art

[0002] With the rapid development of new energy and electronic technologies, battery cycle life, safety, and energy density have become paramount. The current collector, a crucial component of a battery, is used to collect the current generated by the battery's active materials to generate a larger current output. Its performance directly impacts the battery's cycle life, energy density, and safety.

[0003] At present, the positive and negative electrodes in lithium batteries and sodium batteries mostly use copper foil and aluminum foil as current collectors. This type of current collector has high cost and quality, which is not conducive to controlling battery costs and improving energy density. In this regard, functional current collectors have obvious advantages over traditional foils. Functional current collectors are usually a "sandwich" structure, with an inner layer of polymer high molecular layer and conductive metal layers on both sides. Since the metal layer on the surface of the functional current collector is thinner and the polymer layer inside is lighter, the functional current collector can maintain its lightness well, thereby increasing the energy density of the lithium-ion battery using it. On the other hand, the thinner metal layer on the surface of the functional current collector is easier to break than the current collector of traditional foil when the lithium-ion battery suffers thermal runaway, thereby isolating the connection between the active material and the current collector and preventing the thermal runaway of the lithium-ion battery from continuing.

[0004] While functional current collectors offer the advantages of low cost and light weight, their low tensile strength and elongation make them susceptible to foil breakage or copper foil separation during subsequent battery processing and use, severely reducing the battery's energy density and cycle life, and potentially posing safety risks. Furthermore, low tensile strength and elongation can lead to passive fracture during subsequent manufacturing or application, compromising performance. Summary of the Invention

[0005] The object of the present invention is to provide a functional current collector and a secondary battery using the same. The functional current collector has good tensile strength and elongation. Applying the functional current collector to the preparation of secondary batteries can improve the product performance of the secondary batteries.

[0006] According to a first aspect of the present invention, a functional current collector is provided. The functional current collector comprises a polymer substrate and a metal layer, the metal layer being disposed on at least one surface of the polymer substrate. The metal layer comprises n sub-metal layers stacked sequentially along its thickness, wherein n is a positive integer ≥ 6, the sub-metal layers containing elemental metal nanoparticles, and the grain size of the elemental metal nanoparticles does not exceed 500 nm. The thickness of the n sub-metal layers increases gradually away from the surface of the polymer substrate, and the average grain size of the elemental metal nanoparticles contained in the n sub-metal layers increases gradually. In the functional current collector provided by the present invention, by arranging the metal layer as a layered stack of sub-metal layers and causing the sub-metal layers to vary in a gradient according to the above-mentioned pattern, the tensile strength and elongation of the functional current collector can be significantly improved. By constructing the gradient-varying sub-metal layers using elemental metal nanoparticles, the strength of the metal layer can be flexibly controlled over a wide range, which helps reduce the risk of copper foil faulting and fracture caused by deformation of the functional current collector during battery cycling, thereby improving the cycle life and safety performance of secondary batteries using the functional current collector.

[0007] Preferably, the thickness of the sub-metal layer is represented by H, and any sub-metal layer satisfies 30 nm ≤ H ≤ 500 nm.

[0008] Preferably, D represents the grain size of the elemental metal nanoparticles, and any sub-metal layer satisfies the following: 20 nm ≤ D ≤ 250 nm.

[0009] Preferably, any two adjacent sub-metal layers satisfy the requirement that the difference in thickness between the two layers is 20 nm to 60 nm, and the difference in grain size of elemental metal nanoparticles contained therein is 20 nm to 40 nm.

[0010] Preferably, where H represents the thickness of the sub-metal layer and D represents the grain size of the elemental metal nanoparticles, any sub-metal layer satisfies 0.4 < D / H. Furthermore, the functional current collector possessing the aforementioned structural features can optimize the carrier mobility and concentration of the functional current collector during application, thereby improving its electrical conductivity.

[0011] Preferably, the thickness of the largest sub-metal layer is 280 nm to 300 nm.

[0012] Preferably, the grain size of the elemental metal nanoparticles contained in the thickest sub-metal layer does not exceed 250 nm.

[0013] Preferably, the number n of sub-metal layers provided on any surface of the polymer substrate satisfies 6≤n≤10.

[0014] Preferably, 6≤n≤8.

[0015] Preferably, the thickness of the metal layer is 1 μm to 3 μm.

[0016] Preferably, the thickness of the metal layer is 1 μm to 1.5 μm.

[0017] According to a second aspect of the present invention, a secondary battery is provided, comprising the functional current collector described above. The functional current collector has good tensile strength and elongation, which helps improve the structural stability of the secondary battery in which it is used. The secondary battery provided by this solution can achieve good cycle characteristics. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0019] In the following embodiments, a metal layer is formed by magnetron sputtering. During the forming process, the size of the metal grains can be accurately controlled by adjusting the target power and the gas source flow rate. The thickness of the metal layer can be controlled by adjusting the deposition time. In actual operation, the magnetron sputtering device used is equipped with a thickness measuring device, which can measure and control the thickness of the metal layer in real time. Example 1 This example uses magnetron sputtering to deposit elemental copper on the surface of a polymer substrate to form a copper metal layer. The polymer substrate used in this example is a 4.5μm-thick polypropylene film (PP film). Before use, the surface of the PP film must be free of impurities. The magnetron sputtering method used in this example is a high-vacuum roll-to-roll magnetron sputtering system, using argon as the gas source and a copper target as the target material, ensuring a smooth, impurity-free target surface.

[0020] The PP film was placed in a high vacuum roll-to-roll magnetron sputtering device, which was then started to perform magnetron sputtering. During the sputtering process, the film thickness was controlled by a film thickness detector using a quartz crystal as a sensor, and the metal material grain size was tested online non-destructively using laser ultrasonic technology. The materials and operating parameters involved in the sputtering process were set as follows: S1. Set the target power to 2.0 kW and the gas flow rate to 52.5 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 60 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 35 nm.

[0021] S2. Set the target power to 3.5 kW and the gas flow rate to 55.7 sccm, and magnetron sputter copper on the surface of the first sub-metal layer to form a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 100 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 65 nm.

[0022] S3. Set the target power to 4.5 kW and the gas flow rate to 63.3 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 140 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 95 nm.

[0023] S4. Set the target power to 5.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 180 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 125 nm.

[0024] S5. Set the target power to 6.0 kW and the gas flow rate to 77.5 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 220 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 155 nm.

[0025] S6. Set the target power to 7 kW and the gas flow rate to 79.3 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 260 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 185 nm.

[0026] S7. Set the target power to 8.0 kW and the gas flow rate to 80.6 sccm, and magnetron sputter copper on the surface of the sixth sub-metal layer, thereby forming a seventh sub-metal layer on the surface of the sixth sub-metal layer. The thickness of the seventh sub-metal layer is 300 nm, and the grain size of the elemental copper nanoparticles constituting the seventh sub-metal layer is 215 nm.

[0027] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, a sixth sub-metal layer, and a seventh sub-metal layer stacked sequentially along the thickness direction.

[0028] Example 2 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 2.0 kW and the gas flow rate to 45.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 50 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 30 nm.

[0029] S2. Set the target power to 3.5 kW and the gas flow rate to 51.4 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 90 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 60 nm.

[0030] S3. Set the target power to 4.0 kW and the gas flow rate to 67.5 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 130 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 90 nm.

[0031] S4. Set the target power to 5.0 kW and the gas flow rate to 72.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 170 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 120 nm.

[0032] S5. Set the target power to 6.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 210 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 150 nm.

[0033] S6. Set the target power to 7.0 kW and the gas flow rate to 77.1 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 250 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 180 nm.

[0034] S7. Set the target power to 8.0 kW and the gas flow rate to 78.8 sccm, and magnetron sputter copper on the surface of the sixth sub-metal layer, thereby forming a seventh sub-metal layer on the surface of the sixth sub-metal layer. The thickness of the seventh sub-metal layer is 290 nm, and the grain size of the elemental copper nanoparticles constituting the seventh sub-metal layer is 210 nm.

[0035] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0036] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, a sixth sub-metal layer, and a seventh sub-metal layer stacked sequentially along the thickness direction. Example 3 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 1.5 kW and the gas flow rate to 50.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 40 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 25 nm.

[0037] S2. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 55 nm.

[0038] S3. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 85 nm.

[0039] S4. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 115 nm.

[0040] S5. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 145 nm.

[0041] S6. Set the target power to 6.5 kW and the gas flow rate to 80.8 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 175 nm.

[0042] S7. Set the target power to 7.5 kW and the gas flow rate to 82.0 sccm, and magnetron sputter copper on the surface of the sixth sub-metal layer, thereby forming a seventh sub-metal layer on the surface of the sixth sub-metal layer. The thickness of the seventh sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the seventh sub-metal layer is 205 nm.

[0043] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0044] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, a sixth sub-metal layer, and a seventh sub-metal layer stacked sequentially along the thickness direction. Example 4 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 55 nm.

[0045] S2. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 85 nm.

[0046] S3. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 115 nm.

[0047] S4. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 145 nm.

[0048] S5. Set the target power to 6.5 kW and the gas flow rate to 80.8 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 175 nm.

[0049] S6. Set the target power to 7.5 kW and the gas flow rate to 82.0 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 205 nm.

[0050] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0051] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0052] Example 5 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 1.5 kW and the gas flow rate to 40.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 20 nm.

[0053] S2. Set the target power to 2.0 kW and the gas flow rate to 48.0 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 32 nm.

[0054] S3. Set the target power to 3.0 kW and the gas flow rate to 42.0 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 42 nm.

[0055] S4. Set the target power to 3.0 kW and the gas flow rate to 53.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 53 nm.

[0056] S5. Set the target power to 3.5 kW and the gas flow rate to 55.7 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 65 nm.

[0057] S6. Set the target power to 4.0 kW and the gas flow rate to 58.5 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 78 nm.

[0058] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0059] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0060] Example 6 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 55 nm.

[0061] S2. Set the target power to 4.5 kW and the gas flow rate to 63.3 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 95 nm.

[0062] S3. Set the target power to 5.5 kW and the gas flow rate to 73.6 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 135 nm.

[0063] S4. Set the target power to 7.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 175 nm.

[0064] S5. Set the target power to 8.0 kW and the gas flow rate to 80.6 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 215 nm.

[0065] S6. Set the target power to 9.0 kW and the gas flow rate to 81.7 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 245 nm.

[0066] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0067] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0068] Example 7 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 55 nm.

[0069] S2. Set the target power to 3.5 kW and the gas flow rate to 64.3 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 75 nm.

[0070] S3. Set the target power to 4.5 kW and the gas flow rate to 63.3 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 95 nm.

[0071] S4. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 115 nm.

[0072] S5. Set the target power to 5.5 kW and the gas flow rate to 73.6 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 135 nm.

[0073] S6. Set the target power to 6.0 kW and the gas flow rate to 77.5 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 155 nm.

[0074] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0075] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0076] Example 8 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 55 nm.

[0077] S2. Set the target power to 3.5 kW and the gas flow rate to 60.0 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 70 nm.

[0078] S3. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 85 nm.

[0079] S4. Set the target power to 4.5 kW and the gas flow rate to 66.7 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 100 nm.

[0080] S5. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 115 nm.

[0081] S6. Set the target power to 5.5 kW and the gas flow rate to 70.9 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 130 nm.

[0082] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0083] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0084] Example 9 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 55 nm.

[0085] S2. Set the target power to 4.5 kW and the gas flow rate to 66.7 sccm, and magnetron sputter copper on the surface of the first sub-metal layer to form a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 100 nm.

[0086] S3. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 145 nm.

[0087] S4. Set the target power to 7.0 kW and the gas flow rate to 81.4 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 190 nm.

[0088] S5. Set the target power to 8.0 kW and the gas flow rate to 82.5 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 220 nm.

[0089] S6. Set the target power to 9.0 kW and the gas flow rate to 81.7 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 245 nm.

[0090] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0091] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0092] Example 10 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 55 nm.

[0093] S2. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 95 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 85 nm.

[0094] S3. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 175 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 115 nm.

[0095] S4. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 180 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 145 nm.

[0096] S5. Set the target power to 7.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 270 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 175 nm.

[0097] S6. Set the target power to 7.5 kW and the gas flow rate to 82.0 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 205 nm.

[0098] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0099] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0100] Example 11 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 55 nm.

[0101] S2. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 85 nm.

[0102] S3. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 115 nm.

[0103] S4. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 145 nm.

[0104] S5. Set the target power to 7.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 175 nm.

[0105] S6. Set the target power to 7.5 kW and the gas flow rate to 82.0 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 205 nm.

[0106] S7. Set the target power to 8.5 kW and the gas flow rate to 82.9 sccm, and magnetron sputter copper on the surface of the sixth sub-metal layer, thereby forming a seventh sub-metal layer on the surface of the sixth sub-metal layer. The thickness of the seventh sub-metal layer is 320 nm, and the grain size of the elemental copper nanoparticles constituting the seventh sub-metal layer is 235 nm.

[0107] S8. Set the target power to 9.5 kW and the gas flow rate to 83.7 sccm, and magnetron sputter copper on the surface of the seventh sub-metal layer, thereby forming an eighth sub-metal layer on the surface of the seventh sub-metal layer. The thickness of the eighth sub-metal layer is 360 nm, and the grain size of the elemental copper nanoparticles constituting the eighth sub-metal layer is 265 nm.

[0108] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0109] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, a sixth sub-metal layer, a seventh metal layer, and an eighth metal layer stacked sequentially along the thickness direction.

[0110] Example 12 This embodiment refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this embodiment. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this embodiment are set as follows: S1. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 55 nm.

[0111] S2. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 85 nm.

[0112] S3. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 115 nm.

[0113] S4. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 145 nm.

[0114] S5. Set the target power to 7.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 175 nm.

[0115] S6. Set the target power to 7.5 kW and the gas flow rate to 82.0 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 205 nm.

[0116] S7. Set the target power to 8.5 kW and the gas flow rate to 82.9 sccm, and magnetron sputter copper on the surface of the sixth sub-metal layer, thereby forming a seventh sub-metal layer on the surface of the sixth sub-metal layer. The thickness of the seventh sub-metal layer is 320 nm, and the grain size of the elemental copper nanoparticles constituting the seventh sub-metal layer is 235 nm.

[0117] S8. Set the target power to 9.5 kW and the gas flow rate to 83.7 sccm, and magnetron sputter copper on the surface of the seventh sub-metal layer, thereby forming an eighth sub-metal layer on the surface of the seventh sub-metal layer. The thickness of the eighth sub-metal layer is 360 nm, and the grain size of the elemental copper nanoparticles constituting the eighth sub-metal layer is 265 nm.

[0118] S9. Set the target power to 10.5KW and the gas source flow rate to 84.3sccm, and magnetron sputter copper on the surface of the eighth sub-metal layer, thereby forming a ninth sub-metal layer on the surface of the eighth sub-metal layer. The thickness of the ninth sub-metal layer is 400nm, and the grain size of the elemental copper nanoparticles constituting the ninth sub-metal layer is 295nm.

[0119] S10. Set the target power to 11.0 KW and the gas source flow rate to 88.6 sccm, and magnetron sputter copper on the surface of the ninth sub-metal layer, thereby forming a tenth sub-metal layer on the surface of the ninth sub-metal layer. The thickness of the tenth sub-metal layer is 440 nm, and the grain size of the elemental copper nanoparticles constituting the tenth sub-metal layer is 325 nm.

[0120] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0121] Through the above operations, the functional current collector product of this embodiment is obtained. In the functional current collector product, copper metal layers are respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film is composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, a sixth sub-metal layer, a seventh metal layer, an eighth metal layer, a ninth metal layer, and a tenth metal layer stacked sequentially along the thickness direction.

[0122] Comparative Example 1 This comparative example refers to the method for preparing the functional current collector in Example 1, and uses magnetron sputtering to complete the production of the functional current collector in this example. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this comparative example are set as follows: The target power was set to 5.0 kW and the gas source flow rate was set to 69.0 sccm. Copper was magnetron sputtered on the surface of the PP film, thereby forming a copper metal layer on the surface of the PP film. The thickness of the copper metal layer was 1120 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer was 115 nm.

[0123] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this embodiment are strictly consistent with those in Example 1.

[0124] Through the above operations, a functional current collector product of this comparative example was prepared. In the functional current collector product, copper metal layers were respectively provided on two back-to-back surfaces of the PP film, and the grain size distribution of the elemental copper nanoparticles constituting the copper metal layer was uniform. Comparative Example 2 This comparative example uses the method for preparing the functional current collector in Example 1 and uses magnetron sputtering to complete the production of the functional current collector in this comparative example. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this comparative example are set as follows: S1. Set the target power to 1.5 kW and the gas flow rate to 50.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 40 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 25 nm.

[0125] S2. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 55 nm.

[0126] S3. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 85 nm.

[0127] S4. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 115 nm.

[0128] S5. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 145 nm.

[0129] S6. Set the target power to 6.5 kW and the gas flow rate to 80.8 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 175 nm.

[0130] S7. Set the target power to 7.5 kW and the gas flow rate to 82.0 sccm, and magnetron sputter copper on the surface of the sixth sub-metal layer, thereby forming a seventh sub-metal layer on the surface of the sixth sub-metal layer. The thickness of the seventh sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the seventh sub-metal layer is 205 nm.

[0131] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this comparative example are strictly consistent with those in Example 1.

[0132] Through the above operations, a functional current collector product of this comparative example was obtained. In the functional current collector product, copper metal layers were respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film was composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, a sixth sub-metal layer, and a seventh sub-metal layer stacked sequentially along the thickness direction.

[0133] Comparative Example 3 This comparative example uses the method for preparing the functional current collector in Example 1 and uses magnetron sputtering to complete the production of the functional current collector in this comparative example. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this comparative example are set as follows: S1. Set the target power to 1.5 kW and the gas flow rate to 50.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 40 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 25 nm.

[0134] S2. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 55 nm.

[0135] S3. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 115 nm.

[0136] S4. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 85 nm.

[0137] S5. Set the target power to 7.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 175 nm.

[0138] S6. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 145 nm.

[0139] S7. Set the target power to 7.5 kW and the gas flow rate to 82.0 sccm, and magnetron sputter copper on the surface of the sixth sub-metal layer, thereby forming a seventh sub-metal layer on the surface of the sixth sub-metal layer. The thickness of the seventh sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the seventh sub-metal layer is 205 nm.

[0140] Comparative Example 4 This comparative example uses the method for preparing the functional current collector in Example 1 and uses magnetron sputtering to complete the production of the functional current collector in this comparative example. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this comparative example are set as follows: S1. Set the target power to 7.5 kW and the gas flow rate to 82.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 205 nm.

[0141] S2. Set the target power to 7.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 175 nm.

[0142] S3. Set the target power to 6.0 kW and the gas flow rate to 72.5 sccm, and magnetron sputter copper on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 145 nm.

[0143] S4. Set the target power to 5.0 kW and the gas flow rate to 69.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 115 nm.

[0144] S5. Set the target power to 4.0 kW and the gas flow rate to 63.8 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 85 nm.

[0145] S6. Set the target power to 3.0 kW and the gas flow rate to 55.0 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 55 nm.

[0146] S7. Set the target power to 1.5 kW and the gas flow rate to 50 sccm, and magnetron sputter copper on the surface of the sixth sub-metal layer, thereby forming a seventh sub-metal layer on the surface of the sixth sub-metal layer. The thickness of the seventh sub-metal layer is 40 nm, and the grain size of the elemental copper nanoparticles constituting the seventh sub-metal layer is 25 nm.

[0147] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this comparative example are strictly consistent with those in Example 1.

[0148] Through the above operations, a functional current collector product of this comparative example was obtained. In the functional current collector product, copper metal layers were respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film was composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, a sixth sub-metal layer, and a seventh sub-metal layer stacked sequentially along the thickness direction. Comparative Example 5 This comparative example uses the method for preparing the functional current collector in Example 1 and uses magnetron sputtering to complete the production of the functional current collector in this comparative example. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this comparative example are set as follows: S1. Set the target power to 4.0 kW and the gas flow rate to 58.5 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 78 nm.

[0149] S2. Set the target power to 3.5 kW and the gas flow rate to 55.7 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 65 nm.

[0150] S3. Set the target power to 3.0 kW and the gas flow rate to 53.0 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 53 nm.

[0151] S4. Set the target power to 3.0 kW and the gas flow rate to 42.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 42 nm.

[0152] S5. Set the target power to 2.0 kW and the gas flow rate to 48.0 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 32 nm.

[0153] S6. Set the target power to 1.5 kW and the gas flow rate to 40 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 20 nm.

[0154] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this comparative example are strictly consistent with those in Example 1.

[0155] Through the above operations, a functional current collector product of this comparative example was obtained. In the functional current collector product, copper metal layers were respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film was composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0156] Comparative Example 6 This comparative example uses the method for preparing the functional current collector in Example 1 and uses magnetron sputtering to complete the production of the functional current collector in this comparative example. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this comparative example are set as follows: S1. Set the target power to 1.5 kW and the gas flow rate to 40.0 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 280 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 20 nm.

[0157] S2. Set the target power to 2.0 kW and the gas flow rate to 48.0 sccm, and magnetron sputter copper is plated on the surface of the first sub-metal layer, thereby forming a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 240 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 32 nm.

[0158] S3. Set the target power to 3.0 kW and the gas flow rate to 42.0 sccm, and magnetron sputter copper on the surface of the second sub-metal layer to form a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 200 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 42 nm.

[0159] S4. Set the target power to 3.0 kW and the gas flow rate to 42.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 160 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 53 nm.

[0160] S5. Set the target power to 3.5 kW and the gas flow rate to 55.7 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 120 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 65 nm.

[0161] S6. Set the target power to 4.0 kW and the gas flow rate to 58.5 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 80 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 78 nm.

[0162] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this comparative example are strictly consistent with those in Example 1.

[0163] Through the above operations, a functional current collector product of this comparative example was obtained. In the functional current collector product, copper metal layers were respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film was composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0164] Comparative Example 7 This comparative example uses the method for preparing the functional current collector in Example 1 and uses magnetron sputtering to complete the production of the functional current collector in this comparative example. The difference from Example 1 is that the operating parameters involved in the magnetron sputtering process in this comparative example are set as follows: S1. Set the target power to 2.0 kW and the gas flow rate to 52.5 sccm, and magnetron sputter copper onto the surface of the PP film, thereby forming a first sub-metal layer on the surface of the PP film. The thickness of the first sub-metal layer is 60 nm, and the grain size of the elemental copper nanoparticles constituting the first sub-metal layer is 35 nm.

[0165] S2. Set the target power to 3.5 kW and the gas flow rate to 55.7 sccm, and magnetron sputter copper on the surface of the first sub-metal layer to form a second sub-metal layer on the surface of the first sub-metal layer. The thickness of the second sub-metal layer is 100 nm, and the grain size of the elemental copper nanoparticles constituting the second sub-metal layer is 65 nm.

[0166] S3. Set the target power to 4.5 kW and the gas flow rate to 63.3 sccm, and magnetron sputter copper is plated on the surface of the second sub-metal layer, thereby forming a third sub-metal layer on the surface of the second sub-metal layer. The thickness of the third sub-metal layer is 140 nm, and the grain size of the elemental copper nanoparticles constituting the third sub-metal layer is 95 nm.

[0167] S4. Set the target power to 5.0 kW and the gas flow rate to 75.0 sccm, and magnetron sputter copper on the surface of the third sub-metal layer, thereby forming a fourth sub-metal layer on the surface of the third sub-metal layer. The thickness of the fourth sub-metal layer is 180 nm, and the grain size of the elemental copper nanoparticles constituting the fourth sub-metal layer is 125 nm.

[0168] S5. Set the target power to 6.0 kW and the gas flow rate to 77.5 sccm, and magnetron sputter copper on the surface of the fourth sub-metal layer, thereby forming a fifth sub-metal layer on the surface of the fourth sub-metal layer. The thickness of the fifth sub-metal layer is 220 nm, and the grain size of the elemental copper nanoparticles constituting the fifth sub-metal layer is 155 nm.

[0169] S6. Set the target power to 18.0 kW and the gas flow rate to 86.7 sccm, and magnetron sputter copper on the surface of the fifth sub-metal layer, thereby forming a sixth sub-metal layer on the surface of the fifth sub-metal layer. The thickness of the sixth sub-metal layer is 560 nm, and the grain size of the elemental copper nanoparticles constituting the sixth sub-metal layer is 520 nm.

[0170] Except for the above differences, the materials and other specific operations used in the process of preparing the functional current collector in this comparative example are strictly consistent with those in Example 1.

[0171] Through the above operations, a functional current collector product of this comparative example was obtained. In the functional current collector product, copper metal layers were respectively provided on the two back-to-back surfaces of the PP film, and the copper metal layer provided on any surface of the PP film was composed of a first sub-metal layer, a second sub-metal layer, a third sub-metal layer, a fourth sub-metal layer, a fifth sub-metal layer, and a sixth sub-metal layer stacked sequentially along the thickness direction.

[0172] Test Example 1 1. Test subjects The functional current collectors prepared in Examples 1 to 12 and Comparative Examples 1 to 7 were used as test objects.

[0173] 2. Test items (1) Tensile strength test: The tensile strength of the test object was measured using an MTS Criterion 42 tensile testing machine. The parameters of the MTS Criterion 42 tensile testing machine were set as follows: the clamp spacing on the tensile testing machine was 100 mm, the test speed was (250 ± 25) mm / min, and the tensile strength was obtained by the test.

[0174] (2) Elongation at break test: The elongation at break was measured using an MTS Criterion 42 tensile testing machine. The parameters of the MTS Criterion 42 tensile testing machine were set as follows: the clamp spacing on the tensile testing machine was 100 mm, the test speed was (250 ± 25) mm / min, and the elongation at break was obtained.

[0175] 3. Test results It can be seen from the test results that compared with the functional current collectors provided in Examples 1 to 12, the tensile strength and elongation at break of the functional current collectors provided in Comparative Examples 1 to 7 are significantly lower. The test objects in this test example are all functional current collectors with a metal layer covered on the surface of a polymer substrate. The polymer substrates used in the test objects are the same, but the thickness and grain size distribution of the metal layer included in each test object constitute different differences. The metal layer of the functional current collector prepared in Comparative Example 1 has no obvious layered arrangement, and the grain size of the copper elemental nanoparticles constituting its metal layer is basically consistent. The test objects provided in Examples 1 to 13 and Comparative Examples 2 to 7 respectively include multiple layers of sub-metal layers. In the functional current collector prepared in Comparative Example 2, the grain size of the elemental copper nanoparticles contained in the multiple layers of sub-metal layers located on the same side of the polymer substrate gradually increases along the direction away from the polymer substrate, but the thickness of the sub-metal layer does not constitute a regular gradient change. In the functional current collector prepared in Comparative Example 3, the thickness of the multilayer sub-metal layer located on the same side of the polymer substrate gradually increases along the direction away from the polymer substrate, but the grain size of the elemental copper nanoparticles constituting the sub-metal layer does not form a regular gradient change. In the functional current collector prepared in Comparative Example 4, the thickness of the multilayer sub-metal layer located on the same side of the polymer substrate and the average grain size of the elemental copper nanoparticles constituting the sub-metal layer both show a gradient decreasing trend along the direction away from the polymer substrate. In the functional current collector prepared in Comparative Example 5, the thickness of the multilayer sub-metal layer located on the same side of the polymer substrate gradually increases along the direction away from the polymer substrate, while the grain size of the elemental copper nanoparticles constituting the sub-metal layer gradually decreases. In the functional current collector prepared in Comparative Example 6, the thickness of the multilayer sub-metal layer located on the same side of the polymer substrate gradually decreases along the direction away from the polymer substrate, while the grain size of the elemental copper nanoparticles constituting the sub-metal layer gradually increases. In the functional current collector prepared in Comparative Example 7, the elemental copper nanoparticles constituting the metal layer include elemental copper particles with a particle size greater than 500nm, which is significantly larger than the grain size of the elemental copper nanoparticles included in the other test objects. The thickness of the sub-metal layer of the functional current collectors prepared in Comparative Examples 1 to 7 and the grain size distribution of the elemental copper nanoparticles constituting the sub-metal layer are different, and the tensile strength and elongation at break measured in these functional current collectors in this test example are all at a poor level. Different from Comparative Examples 1 to 7, the arrangement of the sub-metal layers included in the functional current collectors prepared in Examples 1 to 10 all meet the following distribution rules: the grain size of the elemental copper nanoparticles constituting the sub-metal layer does not exceed 500nm, and the thickness of the multiple sub-metal layers located on the same side of the polymer substrate and the average grain size of the elemental copper nanoparticles constituting the sub-metal layer both show a gradient increasing trend in the direction away from the polymer substrate.This shows that making the functional current collector provided with multiple sub-metal layers conform to the above-mentioned structural characteristics can significantly improve the tensile strength and elongation at break of the functional current collector.

[0176] In the functional current collectors prepared in Example 4 and Example 10, the total thickness of the metal layer located on the same side of the polymer substrate is the same, both 1080nm, and the gradient value of the grain size of the elemental copper nanoparticles contained in the adjacent sub-metal layers is 30nm. However, there is a difference in the degree of gradient change of the thickness of the adjacent sub-metal layers included in the two. In the functional current collector provided in Example 4, the thickness gradient of the adjacent sub-metal layers is 40nm, and in Example 10, the thickness gradient of the adjacent sub-metal layers ranges from 5nm to 90nm. The test results of this test example show that the mechanical properties of the functional current collector provided in Example 4 are better than those of the functional current collector provided in Example 10. By further setting up experiments on the degree of gradient change of the thickness of the adjacent sub-metal layers of the functional current collector, the experimental results show that for the functional current collector with multiple sub-metal layers stacked on the same side of the polymer substrate, the degree of gradient change of the thickness of the adjacent sub-metal layers is set between 20nm and 60nm, which is beneficial to optimizing the mechanical properties of the functional current collector.

[0177] Comparing the functional current collectors prepared in Example 4, Example 11, and Example 12, the functional current collector in Example 11 is equivalent to adding two sub-metal layers on the basis of the functional current collector prepared in Example 4, and the functional current collector in Example 12 is equivalent to adding two sub-metal layers on the basis of the functional current collector prepared in Example 11. As the number of sub-metal layers increases, the comprehensive mechanical properties of the functional current collector change to a certain extent. In this solution, controlling the number of sub-metal layers of the functional current collector to 6 to 10 layers can enable the functional current collector to have excellent mechanical properties.

[0178] In the functional current collectors prepared in Examples 4, 5, 6, 7, 8, and 9, the thickness gradient of the sub-metal layers on the same side of the polymer substrate showed the same trend and degree of variation, with the thickness difference between the two adjacent sub-metal layers being 40 nm. Comparing the functional current collectors provided in Examples 4, 6, 7, 8, and 9, the functional current collectors prepared in Examples 4, 6, and 7 achieved higher comprehensive mechanical performance evaluations. In the functional current collectors prepared in Examples 4, 6, and 7, the grain size gradient of the elemental copper nanoparticles contained in adjacent sub-metal layers ranged from 20 nm to 40 nm. In the functional current collector prepared in Example 8, the grain size gradient of the elemental copper nanoparticles contained in adjacent sub-metal layers was only 15 nm. In the functional current collector prepared in Example 5, the minimum grain size gradient of the elemental copper nanoparticles contained in adjacent sub-metal layers was only 10 nm. The grain size gradient of the elemental copper nanoparticles in the above two examples was relatively small. In the functional current collector prepared in Example 9, the gradient value of the elemental copper nanoparticles contained in some adjacent sub-metal layers reached 45 nm, which is relatively large. This shows that for a functional current collector comprising multiple sub-metal layers on the same side of a polymer substrate, optimizing the grain size gradient range of the elemental copper nanoparticles contained in the adjacent sub-metal layers to a range of 20 nm to 40 nm can further improve the mechanical properties of the functional current collector.

[0179] Table 1. Mechanical properties test results of functional fluid collectors

[0180] Test Example 2 1. Test Objects: The functional current collectors prepared in Examples 4, 5, 8, and 9 were used as test objects.

[0181] 2. Resistivity test (1) Test equipment: four-probe resistivity tester.

[0182] (2) Sample preparation: Cut out samples of appropriate size from the test piece, ensuring that the surface of the sample is flat and free of obvious oxidation and contamination.

[0183] (3) Testing steps: S1. Place the sample on the test platform of the four-probe resistivity tester and ensure that the probes are in good contact with the sample.

[0184] S2. Set the tester parameters.

[0185] S3. Start the tester. The instrument will apply current to the sample through the four probes and measure the corresponding voltage value.

[0186] S4. Based on the measured current and voltage values, as well as parameters such as the probe spacing, the instrument will automatically calculate the resistivity of the sample.

[0187] 3. Test results The test results of this test example are shown in Table 2. It can be seen that among the test objects in this test example, the functional current collector provided by Example 4 has the lowest measured resistivity, indicating that this functional current collector has the best conductivity. Based on the test results in Test Example 1, compared with Example 4, the resistivity of the functional current collectors provided by Examples 8 and 9 is higher. This shows that ensuring that the functional current collector prepared by this solution meets the gradient value of the grain size of the elemental copper nanoparticles contained in the adjacent sub-metal layers between 20nm and 40nm can further improve the conductivity of the functional current collector.

[0188] Similar to the functional current collector provided in Example 8, the functional current collector provided in Example 5 also has the problem of a relatively small gradient in the grain size of the elemental copper nanoparticles contained in the adjacent sub-metal layers. However, from the test results, it can be seen that the resistivity measured by the two constitutes a relatively obvious difference. Compared with the functional current collector provided in Example 5, the resistivity measured in Example 8 is significantly lower. Further comparing the structural features of the functional current collectors prepared in Example 5 and Example 8, the difference between the functional current collectors provided by the above two embodiments lies in the grain size of the elemental copper nanoparticles. Compared with the functional current collector provided in Example 8, the grain size of the elemental copper nanoparticles in the functional current collector provided in Example 5 is relatively small. Therefore, in the sub-metal layer of the same thickness, the functional current collector in Example 5 includes more elemental copper nanoparticles and more grain boundaries, resulting in an increased probability of electron scattering in the sub-metal layer, which is reflected in a decrease in the conductive performance of the functional current collector. In the functional current collector provided by this solution, by adjusting the ratio of the grain size of the elemental copper nanoparticles (represented by D) to the thickness of the sub-metal layer (represented by H), the grain boundaries of the elemental copper nanoparticles in the sub-metal layer can be better controlled. In the functional current collector provided by this solution, the sub-metal layer is set to meet 0.4 < D / H, which is conducive to achieving excellent conductive properties of the functional current collector.

[0189] Table 2. Resistivity test results of this test case

[0190] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents, but these modifications or replacements are all within the scope of protection of the present invention.

Claims

1. A functional current collector, characterized in that: The functional current collector includes a polymer substrate and a metal layer, wherein the metal layer is disposed on at least one surface of the polymer substrate; The metal layer comprises n sub-metal layers stacked in sequence along the thickness direction thereof, wherein n is a positive integer ≥ 6, and the sub-metal layers contain elemental metal nanoparticles, and the grain size of the elemental metal nanoparticles does not exceed 500 nm; Along a surface direction away from the polymer substrate, the thickness of the n sub-metal layers increases gradually, and the average grain size of the elemental metal nanoparticles contained in the n sub-metal layers increases gradually.

2. The functional fluid collector according to claim 1, wherein: H represents the thickness of the sub-metal layer, and any sub-metal layer satisfies 30 nm ≤ H ≤ 500 nm.

3. The functional current collector according to claim 1, wherein: D represents the grain size of the elemental metal nanoparticles, and any sub-metal layer satisfies the following: 20 nm ≤ D ≤ 250 nm.

4. The functional fluid collector according to claim 1, wherein: Any two adjacent sub-metal layers satisfy the requirement that the difference in thickness between the two layers is 20 nm to 60 nm, and the difference in grain size of the elemental metal nanoparticles contained in the two layers is 20 nm to 40 nm.

5. The functional current collector according to claim 4, wherein: H represents the thickness of the sub-metal layer, D represents the grain size of the elemental metal nanoparticles, and any sub-metal layer satisfies 0.4<D / H.

6. The functional current collector according to claim 4, wherein: The thickness of the largest sub-metal layer is 280 nm to 300 nm.

7. The functional current collector according to claim 4, wherein: The grain size of the elemental metal nanoparticles contained in the thickest sub-metal layer does not exceed 250 nm.

8. The functional fluid collector according to any one of claims 1 to 7, wherein: On any surface of the polymer substrate, the number n of the sub-metal layers provided satisfies 6≤n≤10.

9. The functional current collector according to claim 8, wherein: The thickness of the metal layer is 1 μm to 3 μm.

10. A secondary battery, characterized in that: The secondary battery includes the functional current collector according to any one of claims 1 to 9.

Images