Composite copper current collector and preparation method and application thereof

Abstract

The application provides a composite copper current collector and a preparation method and application thereof, the composite copper current collector comprises a base film, an interface modification layer and a gradient copper plating layer in sequence; the interface modification layer is formed with a Si-O-M covalent bond structure; M comprises at least one of Al, Si, Ti, Zr, Sn, Zn, Ce, Cu, Fe and W; the gradient copper layer comprises a fine-grained copper layer and a coarse-grained copper layer, and the fine-grained copper layer is located on one side of the interface modification layer; the average grain size of the fine-grained copper layer is 0.1-0.5 mu m, and the average grain size of the coarse-grained copper layer is 1-5 mu m. The composite copper current collector still has good mechanical properties and interface strength after long-term storage, that is, the interface separation and plating layer organization deterioration in the storage process of the composite copper current collector can be inhibited, and the mechanical properties and processing adaptability of the composite copper current collector after long-term storage can be ensured.

Description

Technical Field

[0001] This invention belongs to the field of current collectors and lithium battery technology, specifically relating to a composite copper current collector, its preparation method and application. Background Technology

[0002] As one of the core components of lithium-ion batteries, the current collector plays a crucial role in carrying active materials and conducting electrons. Its performance directly affects the battery's energy density, cycle life, and safety performance. Although traditional copper foil current collectors have excellent conductivity, they suffer from drawbacks such as high density, high cost, and susceptibility to corrosion, making it difficult to meet the development requirements of new energy vehicles for batteries that are "lightweight and cost-effective."

[0003] Composite copper foil for current collectors (such as PET / copper and PP / copper composite structures) have become a research hotspot in the current current collector field because their composite design of "polymer base film + metal coating" reduces copper usage and current collector weight while maintaining good conductivity. However, during long-term storage, composite copper foil is susceptible to environmental factors such as temperature, humidity, and oxygen. The interfacial bonding between the metal coating and the base film is prone to decrease, and grain growth, oxidation, and texture evolution can easily occur inside the copper coating. This leads to a significant decrease in the tensile strength, elongation, and other mechanical properties of the composite copper foil, which in turn affects the processing adaptability (such as electrode cutting and rolling) and the long-term reliability of the battery.

[0004] Existing technologies mostly focus on optimizing the preparation process of composite copper foils (such as magnetron sputtering power and electroplating parameter control) to improve initial performance, but neglect the performance degradation problem after long-term storage. For example, Chinese patent CN115274636A discloses a method for preparing a high-adhesion composite copper foil, which improves the adhesion of the coating by introducing a nano-pit structure on the surface of the base film, but does not address the control of the performance stability of the composite copper foil after storage; CN114824351A proposes a corrosion-resistant composite copper foil, which improves corrosion resistance by coating an anti-corrosion layer on the surface, but does not solve the problem of mechanical property degradation caused by coating microstructure evolution.

[0005] Therefore, addressing the technical challenges of mechanical property degradation and microstructure deterioration in composite copper foil after long-term storage, developing a composite copper foil structure and preparation method capable of regulating its post-storage performance is of great significance for promoting the industrial application of composite copper foil. Summary of the Invention

[0006] To address the problems and shortcomings of existing technologies, this invention provides a composite copper current collector, its preparation method, and its application. The composite copper current collector retains good mechanical properties and interfacial strength even after long-term storage, thus suppressing interfacial separation and coating deterioration during storage and ensuring the mechanical properties and processing adaptability of the composite copper current collector after long-term storage.

[0007] According to a first aspect of the present invention, a composite copper current collector is provided, comprising a base film, an interface modification layer, and a gradient copper plating layer in sequence; the interface modification layer has a Si-OM covalent bond structure formed therein; M includes at least one of Al, Si, Ti, Zr, Sn, Zn, Ce, Cu, Fe, and W; the gradient copper layer includes a fine-grained copper layer and a coarse-grained copper layer, the fine-grained copper layer being located on one side of the interface modification layer; the average grain size of the fine-grained copper layer is 0.1-0.5 μm, and the average grain size of the coarse-grained copper layer is 1-5 μm.

[0008] First, this invention introduces an interface modification layer with a Si-OM covalent bond network between the base film and the copper plating layer. M is selected from elements such as Al, Si, Ti, and Zr. The Si-OM covalent bonds are generated through the reaction of a silane coupling agent with inorganic oxide particles (the silanol groups (Si-OH) produced after the hydrolysis of the silane coupling agent undergo a "dehydration condensation" chemical reaction with the metal hydroxyl groups (M-OH) on the surface of the inorganic oxide particles), resulting in strong chemical bonds within the interface modification layer and high cohesive strength.

[0009] Compared to traditional physical adhesion or single coupling agent layers, this three-dimensional chemical cross-linked network exhibits extremely high stability under storage conditions such as humid heat and thermal cycling. Its chemical bonding (including Si-OM bonds and subsequent coordination with the copper plating layer) can effectively resist interfacial creep or peeling caused by environmental stress, significantly suppressing the phenomenon of interfacial separation in composite copper current collectors after long-term storage, and ensuring the initial integrity of the "base film-plating layer" structure. It should be noted here that the "subsequent coordination effect with the copper plating layer" mentioned above refers to the following: In the interface modification layer, if a silane coupling agent is used to form Si-OM covalent bonds with inorganic oxide particles, generally speaking, in addition to the siloxane bond, the other end of the silane coupling agent will have certain active groups. On the one hand, the silanol groups (Si-OH) generated by the hydrolysis of the siloxane bond can form stable chemical bonds (such as Si-OC bonds or hydrogen bonds) with active groups such as hydroxyl groups on the base film, and at the same time, they can form Si-O-Cu bonds with the copper plating layer. Therefore, it can effectively enhance the interfacial bonding force between the base film and the copper plating layer and improve the long-term storage stability of the composite copper current collector. On the other hand, the active groups on the other end of the silane coupling agent, such as amino (-NH2) and mercapto (-SH), can provide additional and stronger chemical bonding pathways (such as coordination bonds and chelation effects) for bonding with metals (copper), thereby significantly enhancing the interfacial bonding force, especially in situations where high stress or harsh environments are required. It should also be noted that even if the other end of the silane coupling agent does not contain an active group, it can still effectively enhance the interfacial bonding between the base film and the copper plating layer, and improve the long-term storage stability of the composite copper current collector. Its effect is still better than that of traditional physical adhesion or a single coupling agent layer.

[0010] It should be further explained here that the Si-OM covalent bonds formed in the interface modification layer can not only be formed by the reaction of the silane coupling agent and inorganic oxide particles mentioned above, but also by other methods that can form Si-OM covalent bonds in other embodiments.

[0011] Secondly, this invention designs a gradient copper coating consisting of an inner fine-grained copper layer and an outer coarse-grained copper layer. The fine-grained copper layer (fine-grained bottom layer) is adjacent to the interface modification layer, and its dense fine-grained structure acts as grain boundary pinning. During long-term storage, the small grains experience greater resistance to diffusion through grain boundaries, effectively inhibiting copper atom migration and recrystallization, thus preventing coarsening of the inner layer and maintaining a tight bond between the bottom layer and the interface layer. The coarse-grained copper layer (coarse-grained surface layer) has a lower grain boundary energy, resulting in higher structural stability during storage and reducing the likelihood of abnormal grain growth. This "fine at the bottom, coarse at the top" gradient structure ensures extremely low grain size change rate after long-term storage, effectively improving the problem of structural uniformity degradation and mechanical property decline caused by grain growth or stress release in existing single-grain-size coatings after storage.

[0012] Furthermore, controlling the grain size of the fine-grained copper layer (average grain size of 0.1-0.5 μm) and the coarse-grained copper layer (average grain size of 1-5 μm) within the aforementioned range can effectively balance the conductivity, mechanical stability, and subsequent processing performance of the composite copper current collector. Specifically, for the fine-grained copper layer, the finer the grain, the higher the yield strength of the material. However, when the grain size is too small, the grain boundary volume fraction increases sharply. Although the strength is extremely high, the internal stress of the coating also increases sharply, which can easily lead to spontaneous cracking or peeling from the interface modification layer. If the grain size is greater than 0.5 μm, the number of grain boundaries decreases significantly, and its function as a "stress buffer layer" is significantly weakened. For coarse-grained copper layers, if the grain size of the coarse-grained layer is less than 1μm, its conductivity will not be much different from that of the fine-grained layer, thus losing the original intention of gradient design; while excessively coarse grains (>5μm) have excellent conductivity, but the strengthening effect of grain boundaries is weakened. During the processing of battery electrode rolling, coarse grains may cause uneven deformation or slippage along specific crystal planes, resulting in orange peel or microcracks on the surface.

[0013] In summary, the composite copper current collector prepared by introducing specific interface modification layers and gradient coatings in this invention exhibits high interfacial strength and overall structural stability, forming a composite layered structure system with excellent mechanical properties and high structural stability. This results in a significantly lower degradation rate of key performance indicators such as peel strength, conductivity, tensile strength, elongation, and coating oxidation rate after long-term storage under vacuum packaging and temperature and humidity control compared to existing products. This effectively addresses the shortcomings of existing technologies, such as "mechanical property degradation and poor structural stability after long-term storage," providing reliable technical support for the production, storage, long-distance transportation, and further processing of composite current collectors.

[0014] Preferably, the thickness of the interface modification layer is 5-120 nm. Controlling the thickness of the interface modification layer to 5-120 nm ensures, on the one hand, that a sufficiently thick interface modification layer can effectively connect the base film and the copper plating layer, ensuring high interface strength of the double-layer interface; on the other hand, it also avoids introducing unnecessary interface impedance due to an excessively thick interface modification layer.

[0015] Preferably, the thickness of the interface modification layer is 10-100 nm; preferably, the thickness of the interface modification layer is 20-100 nm; preferably, the thickness of the interface modification layer is 30-100 nm. Preferably, the thickness of the fine-grained copper layer is 0.5-2 μm, and the thickness of the coarse-grained copper layer is 1-3 μm. The fine-grained layer thickness of 0.5-2 μm can effectively buffer stress and stabilize the interface; the coarse-grained layer thickness of 1-3 μm can ensure low resistance and high conductivity. The combination of the two achieves a synergistic effect of strong anchoring in the inner layer and high conductivity in the outer layer, and effectively releases the internal stress of the coating, preventing curling and peeling.

[0016] Preferably, in the interface modification layer, the Si-OM covalent bond structure is generated by the reaction of a silane coupling agent and inorganic oxide particles, where Si originates from the silane coupling agent and M originates from the inorganic oxide particles. The silane coupling agent includes at least one of γ-aminopropyltriethoxysilane (KH550), γ-aminopropyltrimethoxysilane (KH540), N-β-(aminoethyl)-γ-aminopropyldimethoxysilane (KH792), γ-glycidoxypropyltrimethoxysilane (KH560), and γ-mercaptopropyltrimethoxysilane (KH580). The inorganic oxide particles include at least one of alumina, silica, titanium dioxide, and zirconium oxide. In the interface modification layer, the silane coupling agent (such as KH550, KH560, etc.) and the inorganic oxide particles (such as alumina, silica, etc.) are chemically bonded through Si-OM covalent bonds to form a stable three-dimensional network structure. This design fully leverages the coordination enhancement effect of active functional groups (such as amino, epoxy, and mercapto groups) with the copper coating, as well as the rigid support advantage of different inorganic oxide particles, to achieve synergistic optimization of interfacial chemical anchoring and mechanical buffering, significantly improving the bonding strength and long-term storage stability of the composite copper current collector.

[0017] Preferably, the D50 of the inorganic oxide particles is 5-20 nm. Controlling the D50 of the inorganic oxide particles within this range allows for a balance between high activity and uniform dispersion within the silane coupling agent network. Particles that are too small are prone to agglomeration, while those that are too large reduce the specific surface area and weaken the bond density with the silane. This range ensures that the particles, as rigid crosslinking points, fully participate in Si-OM bond formation, constructing a dense and reinforced interfacial layer, maximizing interfacial bonding strength and stability.

[0018] Preferably, the surface roughness of the base film is 0.1-0.5 μm. This range provides sufficient specific surface area to enhance the mechanical interlocking of the interface modification layer, while avoiding excessive roughness that would prevent the interface modification layer from uniformly covering the surface. This ensures that the silane coupling agent and the base film are in full contact and form continuous chemical bonds, maximizing the interfacial bonding strength and stability.

[0019] Preferably, the base film is a polymer base film. Preferably, the material of the base film includes at least one of PET, PP, and PI.

[0020] Preferably, the thickness of the base film is 3-15 μm.

[0021] Preferably, the base film undergoes plasma treatment under the following conditions: an inert gas as the working gas, a treatment power of 50-150W, and a treatment time of 30-120s. Preferably, the inert gas is argon. Under the specific plasma treatment process described above, chemical activation and physical roughening can be simultaneously achieved on the base film surface. Specifically, firstly, active groups such as hydroxyl / carboxyl groups can be introduced to provide sufficient chemical bonding sites for the silane coupling agent; secondly, 0.1-0.5μm micro / nano structures can be formed simultaneously to enhance physical anchoring. The synergistic effect of these two processes maximizes the bonding strength and stability of the interface modification layer.

[0022] Preferably, the composite copper current collector further includes a surface protective layer, which is located on at least a portion of the surface of the gradient copper plating layer. The material of the surface protective layer includes at least one of Ni-Cu alloy, Ni-Co alloy, Cu-Zn alloy, Ni, Cu, Ti, Cr, Ni-P alloy, Cu-P alloy, and cuprous oxide. Further designing the surface protective layer to cover the surface of the gradient copper plating layer, using materials such as Ni-Cu alloy, can effectively inhibit the oxidation and electrochemical corrosion of the copper plating layer during storage and use, avoiding a decrease in conductivity or failure of interfacial bonding due to surface deterioration, thereby extending the service life of the composite current collector and maintaining its electrochemical stability.

[0023] Preferably, the thickness of the surface protective layer is 50-200 nm. This range ensures complete coverage of defects on the copper plating surface, effectively blocking oxygen and / or moisture corrosion, while avoiding increased internal stress or interfacial resistance due to excessive thickness, thus maximizing the synergy between protective efficiency and electrochemical stability.

[0024] Preferably, the surface protective layer material is a Ni-Cu alloy, wherein the Ni element content is 5-15 at%. Using a Ni-Cu alloy with a controlled Ni element content of 5-15 at% as the surface protective layer material is more conducive to the interfacial bonding between the surface protective layer and the copper plating layer. It can also more effectively inhibit the oxidation and corrosion of the copper layer, and avoid the decrease in conductivity or increase in internal stress due to excessive Ni content, thus balancing protective performance and electrochemical stability.

[0025] According to a second aspect of the present invention, a method for preparing any of the above-mentioned composite copper current collectors is provided, comprising the following steps: S1, preparing a mixed solution containing a silane coupling agent and inorganic oxide particles, completely immersing a base film in the mixed solution, and drying it to obtain a semi-finished product A, the semi-finished product A comprising a base film and an interface modification layer; S2, depositing a fine-grained copper layer on at least one side of the semi-finished product A by magnetron sputtering to obtain a semi-finished product B, wherein the magnetron sputtering process conditions are as follows: sputtering power of 250-350W, inert gas pressure of 0.35-0.65Pa, and deposition rate of 0.1-0.4nm / s; S3, depositing a coarse-grained copper layer on one side of the semi-finished product B by pulse electroplating, wherein the pulse electroplating process conditions are as follows: the electroplating solution used contains Cu 2+ 0.3~1 mol / L, H + 1.5~5 mol / L, pulse frequency 700-900Hz, duty cycle 40-60%, current density 1.5-3 A / dm³ 2 In the preparation method of the composite copper current collector provided by this invention, the immersion operation in S1 ensures that the silane coupling agent and inorganic oxide particles are uniformly composited on the surface of the base film, forming a hydroxyl-rich reaction interface, laying the foundation for subsequent chemical bonding. In S2, a fine-grained copper layer is deposited at a relatively low rate and moderate power to avoid damage to the underlying interface, while simultaneously forming a dense anchoring layer. In S3, by optimizing the pulse parameters and ion concentration, preferential grain growth is induced, achieving efficient deposition and stress release of the coarse-grained layer. Thus, the synergy of the above steps yields a composite copper current collector with high bonding strength, excellent conductivity, and long-term stability.

[0026] Preferably, the preparation method of the above-mentioned composite copper current collector further includes step S4, which is specifically operated as follows: S4, on one side of the coarse-grained copper layer of the product obtained in S3, a surface protective layer is deposited by magnetron sputtering. The magnetron sputtering process conditions are as follows: sputtering power of 100-400W, inert gas pressure of 0.3-1.5Pa, and deposition rate of 0.03-2nm / s. Furthermore, by depositing a protective layer on the surface of the coarse-grained copper layer through magnetron sputtering in S4, efficient encapsulation can be achieved without damaging the gradient plating structure as much as possible. A dense protective film is formed on its surface, effectively inhibiting copper layer oxidation and corrosion, and significantly extending the service life and storage stability of the composite current collector.

[0027] Preferably, in step S1, the soaking time is 10-50 min. Preferably, in step S1, the drying temperature is 90-110℃ and the drying time is 10-30 min.

[0028] According to a third aspect of the present invention, a battery is provided, comprising a negative electrode sheet, the negative electrode sheet comprising any of the aforementioned composite copper current collectors, or a composite copper current collector prepared by any of the aforementioned methods. The battery employing the composite copper current collector of the present invention has a negative electrode current collector that combines high interfacial bonding strength and low internal resistance, thus the prepared battery exhibits better cycle stability.

[0029] In summary, compared with the prior art, the present invention has the following technical effects: First, this invention introduces an interface modification layer with a Si-OM covalent bond network between the base film and the copper plating layer. Compared with traditional physical adhesion or single coupling agent layers, this three-dimensional chemical cross-linking network has extremely high stability under storage conditions such as humid heat and cold cycling. Its chemical bonding (including Si-OM bonds and subsequent coordination with the copper plating layer) can effectively resist interface creep or peeling caused by environmental stress, significantly suppressing the phenomenon of interface separation of the composite copper current collector after long-term storage, and ensuring the initial integrity of the "base film-plating layer" structure.

[0030] Secondly, this invention designs a gradient copper coating consisting of an inner fine-grained copper layer and an outer coarse-grained copper layer. This "fine at the bottom and coarse at the top" gradient structure results in extremely low grain size change rate after long-term storage, effectively improving the problem of microstructure uniformity destruction and mechanical property degradation caused by grain growth or stress release in single-grain-size coatings in the prior art after storage. Moreover, controlling the grain size of the fine-grained copper layer (average grain size of 0.1-0.5 μm) and the coarse-grained copper layer (average grain size of 1-5 μm) within the above-mentioned range can effectively balance the conductivity, mechanical stability, and subsequent processing performance of the composite copper current collector.

[0031] Therefore, by introducing a specific interface modification layer and gradient coating, the present invention enables the composite copper current collector to exhibit significantly lower degradation rates in key performance indicators such as peel strength, conductivity, tensile strength, elongation, and coating oxidation rate after long-term storage under vacuum packaging and temperature and humidity control compared to existing products. This effectively addresses the shortcomings of existing technologies, such as "mechanical property degradation and poor structural stability after long-term storage," and provides reliable technical support for the production, storage, long-distance transportation, and further processing of composite current collectors. Detailed Implementation

[0032] To enable those skilled in the art to better understand 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 some embodiments of the present invention, and not all embodiments.

[0033] Example 1 The composite copper current collector of this embodiment was prepared according to the following steps: S0, Pretreatment of polymer base film: Select a 6μm thick PET base film, place it in a plasma treatment device, use argon as the working gas, the treatment power is 100W, and the treatment time is 60s; after treatment, the surface Ra of the base film is 0.3μm. S1, Preparation of interface modification layer: The pretreated PET base film was immersed in an ethanol aqueous solution (ethanol:water = 3:1) containing nano alumina (8g / L, D50 is 10nm) and KH550 (3g / L) for 20min, and then dried at 100℃ for 15min. S2, Preparation of fine-grained copper layer in gradient copper plating: A fine-grained copper layer was prepared on the surface of the interface modified layer by magnetron sputtering with a sputtering power of 300W, an argon pressure of 0.5Pa, and a deposition rate of 0.2nm / s. S3, Preparation of the coarse-grained copper layer in the gradient copper plating: A coarse-grained copper layer is prepared on the surface of the fine-grained copper layer using pulse electroplating, wherein the electroplating solution contains 100 g / L copper sulfate (corresponding to Cu). 2+ 0.627 mol / L), sulfuric acid 120 g / L (corresponding to H₂) + 2.449 mol / L), pulse frequency 800 Hz, duty cycle 50%, current density 2 A / dm³ 2 ; S4, Surface protective layer preparation: A Ni-Cu alloy layer (Ni content 10 at%) was prepared on the surface of the coarse-grained copper layer by magnetron sputtering with a sputtering power of 200 W, an argon pressure of 0.8 Pa, and a deposition rate of 0.1 nm / s.

[0034] The composite copper current collector prepared above was vacuum dried at 70°C for 3 hours, vacuum-packed with aluminum-plastic composite film (vacuum degree 0.005MPa), and placed with silica gel desiccant (8% of the mass of the composite copper current collector) and stored in an environment of 20°C and 40%RH.

[0035] As mentioned above, the test methods for the thickness of the interface modification layer, the average grain size and thickness of the fine-grained copper layer and the coarse-grained copper layer in the gradient copper plating, and the thickness of the surface protective layer are as follows: The cross-section of the composite copper current collector is observed and its size is measured using a scanning electron microscope (SEM) combined with a transmission electron microscope (TEM). The grain size is statistically analyzed using the intercept method and the average value is taken. The thickness of each layer is the average value of multiple test points.

[0036] The test results showed that the thickness of the interface modification layer was 30 nm; the thickness of the fine-grained copper layer was 1 μm with an average grain size of 0.3 μm; the thickness of the coarse-grained copper layer was 2 μm with an average grain size of 3 μm; and the thickness of the surface protective layer was 100 nm.

[0037] The above-mentioned parameters obtained from other embodiments or comparative tests are also recorded in Table 1 below, referring to the above method.

[0038] Example 2 The difference between this embodiment and Example 1 is that, in S1, the silane coupling agent KH550 is changed to γ-aminopropyltrimethoxysilane (KH540). The rest is the same as in Example 1.

[0039] Example 3 The difference between this embodiment and Example 1 is that, in S1, the silane coupling agent KH550 is changed to γ-glycidoxypropyltrimethoxysilane (KH560). The rest is the same as in Example 1.

[0040] Example 4 The difference between this embodiment and Example 1 is that, in S1, the silane coupling agent KH550 is changed to γ-mercaptopropyltrimethoxysilane (KH580). The rest is the same as in Example 1.

[0041] Example 5 The difference between this embodiment and Embodiment 1 is that, in S1, the inorganic oxide particles (nano-alumina) are replaced with nano-silica. The rest is the same as in Embodiment 1.

[0042] Example 6 The difference between this embodiment and Embodiment 1 is that, in S1, the inorganic oxide particles (nano-alumina) are replaced with nano-titanium dioxide. The rest is the same as in Embodiment 1.

[0043] Example 7 The difference between this embodiment and Embodiment 1 is that, in S1, the inorganic oxide particles (nano-alumina) are replaced with nano-zirconia. The rest is the same as in Embodiment 1.

[0044] Example 8 The difference between this embodiment and Embodiment 1 is that, in S1, the D50 of the inorganic oxide nanoparticles (alumina nanoparticles) is adjusted to 30 nm. The rest is the same as in Embodiment 1.

[0045] Example 9 The difference between this embodiment and Embodiment 1 is that, in S1, the immersion time is controlled to adjust the final thickness of the interface modification layer to 5 nm. The rest is the same as in Embodiment 1.

[0046] Example 10 The difference between this embodiment and Embodiment 1 is that, in S1, the immersion time is controlled to adjust the final thickness of the interface modification layer to 50 nm. The rest is the same as in Embodiment 1.

[0047] Example 11 The difference between this embodiment and Embodiment 1 is that, in S1, the immersion time is controlled to adjust the final thickness of the interface modification layer to 80 nm. The rest is the same as in Embodiment 1.

[0048] Example 12 The difference between this embodiment and Embodiment 1 is that, in S1, the immersion time is controlled to adjust the final thickness of the interface modification layer to 100 nm. The rest is the same as in Embodiment 1.

[0049] Example 13 The difference between this embodiment and Embodiment 1 is that, in S1, the immersion time is controlled to adjust the final thickness of the interface modification layer to 120 nm. The rest is the same as in Embodiment 1.

[0050] Example 14 The difference between this embodiment and Embodiment 1 is that, in S2, the relevant parameters of the magnetron sputtering process are adjusted to adjust the final thickness of the fine-grained copper layer to 0.35 μm. The rest is the same as in Embodiment 1.

[0051] Example 15 The difference between this embodiment and Embodiment 1 is that, in S2, the relevant parameters of pulse electroplating are adjusted to adjust the final thickness of the coarse-grained copper layer to 4 μm. The rest is the same as in Embodiment 1.

[0052] Example 16 The difference between this embodiment and Embodiment 1 is that, in S0, the relevant parameters of the plasma treatment are adjusted to adjust the final roughness of the base film to 0.05 μm. The rest is the same as in Embodiment 1.

[0053] Example 17 The difference between this embodiment and Embodiment 1 is that, in S0, the relevant parameters of the plasma treatment are adjusted to adjust the final roughness of the base film to 0.65 μm. The rest is the same as in Embodiment 1.

[0054] Comparative Example 1 The difference between this comparative example and Example 1 is that the base film in the prepared composite copper current collector was not subjected to plasma treatment (i.e., step S0 was not performed), there was no interface modification layer (i.e., step S1 was not performed), and the copper layer was only a coarse-grained copper layer (the pulse electroplating process parameters were adjusted to make the average grain size of the coarse-grained copper layer 3 μm and the thickness 3 μm); the rest was the same as in Example 1.

[0055] Comparative Example 2 The difference between this comparative example and Example 1 is that the prepared composite copper current collector does not have an interface modification layer, i.e., step S1 is not performed; otherwise, it is the same as Example 1.

[0056] Comparative Example 3 The difference between this comparative example and Example 1 is that no silane coupling agent is added in S1, and the thickness of the final interface modification layer is also changed; otherwise, it is the same as Example 1.

[0057] Comparative Example 4 The difference between this comparative example and Example 1 is that no inorganic oxide particles are added in S1, and the thickness of the final interface modification layer is also changed; otherwise, it is the same as Example 1.

[0058] Comparative Example 5 The difference between this comparative example and Example 1 is that step S3 is omitted, meaning that the copper layer of the prepared composite copper current collector is only a fine-grained copper layer, and the magnetron sputtering process parameters are adjusted to make the thickness of the fine-grained copper layer 3μm; the rest is the same as Example 1.

[0059] Comparative Example 6 The difference between this comparative example and Example 1 is that step S2 is omitted, meaning that the copper layer of the prepared composite copper current collector is only a coarse-grained copper layer, and the pulse electroplating process parameters are adjusted so that the average grain size of the coarse-grained copper layer is 1 μm and the thickness is 3 μm; the rest is the same as Example 1.

[0060] Comparative Example 7 The difference between this comparative example and Example 1 is that in S2, the magnetron sputtering process parameters are adjusted so that the average grain size of the fine-grained copper layer is 0.05 μm and the thickness is 3 μm; the rest is the same as in Example 1.

[0061] Comparative Example 8 The difference between this comparative example and Example 1 is that in S2, the magnetron sputtering process parameters are adjusted so that the average grain size of the fine-grained copper layer is 0.8 μm and the thickness is 3 μm; the rest is the same as in Example 1.

[0062] Comparative Example 9 The difference between this comparative example and Example 1 is that in S3, the pulse electroplating process parameters are adjusted so that the average grain size of the coarse copper layer is 7μm and the thickness is 3μm; the rest is the same as in Example 1.

[0063] Test case 1. Experimental Construction Method The composite copper current collectors obtained in the above embodiments and comparative examples were subjected to the following performance tests: (1) Interface peel strength: According to GB / T2790-1995 standard, T-type peel test was carried out using an electronic universal testing machine at a test speed of 50 mm / min. Five parallel samples were tested for each group of samples, and the average value was taken. The peel strength was tested in the initial state and after 12 months of storage.

[0064] (2) Tensile strength: In accordance with GB / T1040.3-2006 standard, tensile test was performed using an electronic universal testing machine. The sample size was 15mm×100mm, the tensile speed was 50mm / min, and 5 parallel samples were tested for each group of samples. The average value was taken. The tensile strength in the initial state was tested respectively.

[0065] 2. Experimental Results The relevant performance test results of the composite copper current collectors obtained in the above embodiments and comparative examples are shown in Table 1.

[0066] Table 1. Performance test results of the composite copper current collectors obtained in the examples and comparative examples.

[0067] As can be seen from Table 1, the composite copper current collector provided by the present invention maintains good performance values ​​after long-term storage, which fully demonstrates that the composite structure of the present invention can effectively improve the storage stability of the composite copper current collector.

[0068] In Comparative Example 1, the prepared composite copper current collector had a base film that was not plasma treated and lacked an interface modification layer. The copper layer consisted only of coarse-grained copper, which resulted in a significant decrease in interface peel strength, tensile strength, and elongation after storage, a sharp increase in coating oxidation rate, and a significant degradation in battery cycle performance. The reason is that the base film without plasma treatment lacks active groups and micro / nano structures on its surface, and the absence of an interface modification layer means the lack of a Si-OM covalent bond network. The base film and copper layer are only physically adhered, resulting in extremely poor interfacial bonding. Furthermore, the single coarse-grained copper layer lacks grain boundary pinning effect, making it prone to grain growth and oxidation during storage, leading to rapid deterioration of mechanical and electrochemical properties.

[0069] In Comparative Example 2, the prepared composite copper current collector lacked an interface modification layer, resulting in a significant degradation of all performance characteristics after storage, which was far inferior to that of Example 1. The reason for this is the absence of an interface modification layer with a Si-OM covalent bond network. The interfacial bonding between the base film and the copper plating relies solely on the physical anchoring of plasma treatment and a small number of chemical bonds, which cannot resist the environmental stress during storage. The interface is prone to creep peeling, and the stress transmission between the plating and the base film is unbalanced, accelerating the deterioration of the plating structure.

[0070] In Comparative Example 3, in S1, no silane coupling agent was added, resulting in the interface modification layer failing to form a complete Si-OM covalent bond network. Only the inorganic oxide particles were physically filled, leading to insufficient interfacial bonding and significant performance degradation after storage. This is because the silane coupling agent is the core for forming Si-OM covalent bonds. Without the silane coupling agent, the inorganic oxide particles cannot form chemical bonds with the base film and copper plating, significantly weakening the cohesive strength and interfacial anchoring effect of the interface modification layer.

[0071] In Comparative Example 4, in S1, no inorganic oxide particles were added, resulting in an interface modification layer that was only a single coating of silane coupling agent without rigid cross-linking point support. The three-dimensional chemical network structure was incomplete, and the interfacial bonding strength decreased after storage, making the coating prone to stress deformation. The reason is that inorganic oxide particles provide rigid support for the Si-OM covalent bond network and increase the mechanical interlocking effect of the interface. Without particles, the silane coupling agent layer is prone to creep under environmental stress and cannot effectively transfer stress and inhibit interfacial separation.

[0072] In Comparative Examples 5-6, the copper layers of the prepared composite copper current collectors consisted only of fine-grained or coarse-grained copper layers. This resulted in a significant decrease in tensile strength and elongation after storage of a single fine-grained layer, and a significant decrease in interfacial peel strength and mechanical properties after storage of a single coarse-grained layer. The reason for this is that the single fine-grained layer has a high grain boundary volume fraction and high internal stress, making it prone to grain boundary migration and cracking during storage, leading to a sharp drop in elongation. The single coarse-grained layer lacks the grain boundary pinning effect of the fine-grained underlayer, making it easy for grains to grow. Voids easily appear at the interface with the interface modification layer, resulting in a rapid decrease in interfacial bonding strength.

[0073] In Comparative Examples 7-9, the average grain size of the fine-grained or coarse-grained copper layers was outside the preferred range, resulting in varying degrees of degradation in all properties after storage. The reasons are as follows: In Comparative Example 7, the grain size of the fine-grained layer was too small, leading to a sharp increase in internal stress. During storage, the coating was prone to cracking and peeling, resulting in a significant decrease in mechanical properties. In Comparative Example 8, the grain size of the fine-grained layer was too large, weakening the grain boundary pinning effect and failing to effectively suppress copper atom migration, leading to a decrease in interfacial bonding strength and mechanical properties. In Comparative Example 9, the grain size of the coarse-grained layer was too large, weakening the grain boundary strengthening effect, reducing processability and storage stability. Furthermore, the coarse grains were prone to uneven oxidation, resulting in deterioration of electrochemical performance.

[0074] Furthermore, observing Examples 1-4, it can be found that by adjusting the type of silane coupling agent used in S1, the various properties of the composite copper current collector remained at a high level with no significant differences. This is because the selected silane coupling agents all contain active functional groups, which can react with inorganic oxide particles to form Si-OM covalent bonds, and at the same time form effective bonds with the base film and copper plating, thus constructing a stable interface modification layer. Only slight performance fluctuations exist due to the different types of functional groups.

[0075] Observing Examples 1 and 5-7, it can be found that adjusting the types of inorganic oxide particles used in S1 did not significantly change the performance of the composite copper current collector, which remained excellent. The reason is that alumina, silicon dioxide, titanium dioxide, and zirconium oxide can all undergo dehydration condensation with silane coupling agents to form Si-OM covalent bonds, and all of them are nanoscale rigid particles, which can provide good support and cross-linking effect for the interface modification layer, achieving the synergy of interface chemical anchoring and mechanical buffering.

[0076] Observing Examples 1 and 8, the inorganic oxide nano-alumina particles in Example 8 have a larger D50, and their performance after storage is slightly worse than that in Example 1. The reason is that the particle D50 exceeds the preferred range of 5-20nm, the specific surface area is reduced, the bonding density with the silane coupling agent decreases, and the Si-OM covalent bond network cannot be fully formed. The compactness and anchoring effect of the interface modification layer are weakened. At the same time, large-diameter particles are prone to causing interface stress concentration, which accelerates the performance degradation during storage.

[0077] Observing Examples 1 and 9-13, it can be found that when the thickness of the interface modification layer is in the range of 5-120 nm, the composite copper current collector maintains excellent performance and low decay rate after storage. This is because this thickness range can ensure that the interface modification layer effectively connects the base film and the copper plating, forming a stable Si-OM covalent bond network, while avoiding the introduction of additional interface impedance, thus achieving a balance between interface strength and conductivity. It can also be found that the performance of Examples 9 and 13 is worse than that of Examples 1 and 10-12. This may be because the thickness of Example 9 is only 5 nm, the continuity of the interface modification layer is relatively poor, the integrity of the formed covalent bond network is reduced, and the interface anchoring effect is also reduced. The thickness of Example 13 is 120 nm, which is relatively thick. The relatively thick interface modification layer introduces higher interface impedance, and the internal stress of the layer will also increase, increasing the probability of interlayer delamination, resulting in performance that is worse than that of Examples 1 and 10-12.

[0078] Observing Examples 1 and 14-15, it can be found that when the fine-grained copper layer or the coarse-grained copper layer is not within the preferred range, the interfacial bonding force, mechanical properties and electrochemical properties all show a certain degree of attenuation after storage. The reason is that in Example 14, the thickness of the fine-grained layer is only 0.35μm, which cannot adequately buffer stress and stabilize the interface, and the interface is prone to separation during storage. In Example 15, the thickness of the coarse-grained layer reaches 4μm, the internal stress of the coating increases, and the excessively thick coarse-grained layer is prone to abnormal grain growth, resulting in a decrease in mechanical properties and oxidation resistance.

[0079] Observing Examples 1 and 16-17, it can be found that when the surface roughness of the base film is not within the preferred range, the performance of the composite copper current collector deteriorates after storage. The reason is that in Example 16, the roughness is only 0.05 μm, the specific surface area of ​​the base film is too small, the mechanical interlocking effect with the interface modification layer is insufficient, the chemical bonding sites are few, and the interfacial bonding force decreases. In Example 17, the roughness reaches 0.65 μm, the surface of the base film is too rough, the interface modification layer cannot be uniformly covered, and voids and defects are easily formed. During storage, the environmental medium is easily invaded, accelerating interface separation and coating oxidation.

[0080] 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 modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A composite copper current collector, characterized in that: The composite copper current collector comprises, in sequence, a base film, an interface modification layer, and a gradient copper plating layer; The interface modification layer contains a Si-OM covalent bond structure; M includes at least one of Al, Si, Ti, Zr, Sn, Zn, Ce, Cu, Fe, and W. The gradient copper layer includes a fine-grained copper layer and a coarse-grained copper layer, with the fine-grained copper layer located on one side of the interface modification layer; the average grain size of the fine-grained copper layer is 0.1-0.5 μm, and the average grain size of the coarse-grained copper layer is 1-5 μm.

2. The composite copper current collector as described in claim 1, characterized in that: The thickness of the interface modification layer is 5-120 nm; preferably, the thickness of the interface modification layer is 10-100 nm; preferably, the thickness of the interface modification layer is 20-100 nm; preferably, the thickness of the interface modification layer is 30-100 nm. And / or, the thickness of the fine-grained copper layer is 0.5-2 μm, and the thickness of the coarse-grained copper layer is 1-3 μm.

3. The composite copper current collector as described in claim 1, characterized in that: In the interface modification layer, the Si-OM covalent bond structure is generated by the reaction of silane coupling agent and inorganic oxide particles, wherein Si is derived from silane coupling agent and M is derived from inorganic oxide particles; The silane coupling agent includes at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane. The inorganic oxide particles include at least one of aluminum oxide, silicon dioxide, titanium dioxide, and zirconium oxide.

4. The composite copper current collector as described in claim 3, characterized in that: The D50 of the inorganic oxide particles is 5-20 nm.

5. The composite copper current collector as described in claim 1, characterized in that: The surface roughness of the base film is 0.1-0.5 μm.

6. The composite copper current collector as described in claim 1, characterized in that: The composite copper current collector further includes a surface protective layer, which is located on at least a portion of the surface of the gradient copper plating layer; The material of the surface protective layer includes at least one of Ni-Cu alloy, Ni-Co alloy, Cu-Zn alloy, Ni, Cu, Ti, Cr, Ni-P alloy, Cu-P alloy, and cuprous oxide.

7. The composite copper current collector as described in claim 6, characterized in that: The thickness of the surface protective layer is 50-200 nm.

8. The method for preparing the composite copper current collector according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1, prepare a mixed solution containing silane coupling agent and inorganic oxide particles, completely immerse the base film in the mixed solution, and dry it to obtain semi-finished product A, wherein semi-finished product A includes the base film and the interface modification layer; S2, deposit the fine-grained copper layer on at least one side of the semi-finished product A by magnetron sputtering to obtain semi-finished product B. The magnetron sputtering process conditions are as follows: sputtering power of 250-350W, inert gas pressure of 0.35-0.65Pa, and deposition rate of 0.1-0.4nm / s. S3, on one side of the semi-finished product B, a coarse-grained copper layer is deposited using pulse electroplating. The pulse electroplating process conditions are as follows: the electroplating solution used contains Cu. 2+ 0.3~1 mol / L, H + 1.5~5 mol / L, pulse frequency 700-900Hz, duty cycle 40-60%, current density 1.5-3 A / dm³ 2 .

9. The method for preparing the composite copper current collector as described in claim 8, characterized in that, It also includes step S4, the specific operation of which is as follows: S4, on one side of the coarse copper layer of the product obtained in S3, the surface protective layer is deposited by magnetron sputtering. The magnetron sputtering process conditions are as follows: sputtering power of 100-400W, inert gas pressure of 0.3-1.5Pa, and deposition rate of 0.03-2nm / s.

10. A battery, characterized in that, The battery includes a negative electrode, which includes a composite copper current collector as described in any one of claims 1 to 7, or a composite copper current collector prepared by the preparation method described in any one of claims 8 to 9.

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