Composite current collector and preparation method thereof

Abstract

The invention relates to a composite current collector and a preparation method thereof. The composite current collector comprises a base material layer and a conductive layer. The conductive layer at least comprises a first crystal grain layer and a second crystal grain layer, the first crystal grain layer is arranged between the second crystal grain layer and the base material layer and is connected with the base material layer, the average size of crystal grains of the first crystal grain layer is 150-1300 nm, and the ratio of the average size of the second crystal grain layer to the average size of crystal grains of the first crystal grain layer is (1.5-10): 1. Under the action of stress and heat of battery circulation, the structure can obviously inhibit the growth trend of crystal grains, especially the transmission of a coarsening phenomenon to an interface, so that the microscopic roughness and mechanical interlocking capability of the surface of the conductive layer are maintained for a long time, the reduction of peeling strength is delayed, and the service life of the conductive layer is prolonged. And the structural integrity and reliability of the current collector in long-term circulation are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a composite current collector and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, lithium batteries are placing increasingly higher demands on the performance of current collectors. Traditional copper foil current collectors suffer from problems such as heavy weight, high cost, and a tendency for adhesion to decrease during repeated charge and discharge cycles. In recent years, PET (polyethylene terephthalate) composite copper foil has attracted widespread attention due to its advantages such as light weight, low cost, and good flexibility.

[0003] However, in practical applications, it has been found that during the cyclic charging and discharging process of lithium batteries using PET composite copper foil, the stress changes caused by lithium-ion insertion / extraction and variations in battery operating temperature lead to copper foil grain growth. This results in a tendency for the copper foil surface to flatten, significantly reducing the peel strength between the copper foil and the PET substrate. In severe cases, localized or large-area copper foil detachment can occur, affecting the battery's cycle life and safety performance. Current conventional solutions mainly focus on improving adhesive properties or surface roughening treatments, but these methods are insufficient to fundamentally suppress the growth trend of copper foil grains under thermal stress, and their long-term effects are limited. Summary of the Invention

[0004] Therefore, it is necessary to provide a composite current collector for lithium batteries and its preparation method. By designing a special copper foil microstructure, the grain growth phenomenon caused by stress and temperature during battery cycle charging and discharging can be effectively suppressed, thereby maintaining the bonding strength between the copper foil and the PET substrate and improving the cycle life and safety of the battery.

[0005] The technical solution is as follows: A composite current collector, comprising: a substrate layer; a conductive layer, the conductive layer comprising at least a first grain layer and a second grain layer, the first grain layer being disposed between the second grain layer and the substrate layer and connected to the substrate layer, the average grain size of the first grain layer being 150~1300nm, and the ratio of the average size of the second grain layer to the average grain size of the first grain layer being (1.5~10):1.

[0006] In one embodiment, the thickness of the first grain layer accounts for 20% to 50% of the total thickness of the conductive layer, and the thickness of the second grain layer accounts for 50% to 80% of the total thickness of the conductive layer.

[0007] In one embodiment, the conductive layer is made of copper, and the conductive layer is also doped with doping elements in a total content of 0.01~2.0 at%, the doping elements including one or more of Ag, Zn, Sn, Cr, Zr, Ti, Mg, and Al.

[0008] In one embodiment, the local concentration of the dopant element at the grain boundary is higher than its average concentration inside the grain, and at least some of the grain boundaries are strengthening phase grain boundaries of intermetallic compounds containing the dopant element.

[0009] In one embodiment, the doping elements include Cr and Ag, wherein the Cr content is 0.05~0.5 at%, and the Ag content is 0.1~1.0 at%.

[0010] In one embodiment, the concentration of the dopant element decreases from the side closer to the substrate layer to the side farther away from the substrate layer, with a concentration gradient of 0.5~5 at% / μm.

[0011] In one embodiment, the area of ​​grains with {111} orientation in the first grain layer accounts for 40% to 70%.

[0012] In one embodiment, the area of ​​grains with {200} orientation in the second grain layer accounts for 50% to 80%.

[0013] In one embodiment, the composite current collector further includes a transition layer disposed between the first grain layer and the substrate layer. The transition layer comprises an organic-inorganic hybrid material containing carboxyl or hydroxyl functional groups, and the thickness of the transition layer is 10~100 nm.

[0014] In one embodiment, the conductive layer has a porous structure on the side away from the substrate layer, the porous structure having a pore size of 50~200 nm and a pore density of 10. 8 ~10 10 pcs / cm 2 .

[0015] A method for preparing a composite current collector, used to manufacture the composite current collector described in any one of the above, characterized by comprising the following steps:

[0016] Surface activation treatment is performed on the surface of the substrate layer;

[0017] Metallize the surface of the substrate layer and form a metal seed layer by vacuum sputtering;

[0018] A segmented electrodeposition process is used to deposit a conductive layer on a metallized PET substrate. The electrolyte used for electrodeposition contains copper ions and dopant elements, including one or more of Ag, Zn, Sn, Cr, Zr, Ti, Mg, and Al. In the first stage, the current density is 0.5~2 A / dm³. 2 The first grain layer is formed by deposition at temperatures of 20-35℃; in the second stage, the first grain layer is formed at a current density of 2-8 A / dm³. 2 A second grain layer is formed by deposition on the first grain layer under a temperature of 30~45℃.

[0019] The deposited conductive layer is subjected to segmented annealing heat treatment: first, it is held at 120~160℃ for 5~15 min, and then the temperature is raised to 180~230℃ and held for 3~10 min.

[0020] In one embodiment, the step of performing segmented annealing heat treatment on the deposited copper foil includes: first holding at 120~160℃ for 5~15 min, then raising the temperature to 180~230℃ and holding for 3~10 min, followed by the step of:

[0021] Micro-hole etching is performed on the surface of the conductive layer.

[0022] In one embodiment, the electrolyte further includes an organic carboxylate complexing agent, wherein the organic carboxylate is citrate, tartrate, or ethylenediaminetetraacetic acid.

[0023] The beneficial effects of the aforementioned composite current collector are as follows:

[0024] This composite current collector, through its gradient conductive layer structure consisting of a relatively fine-grained first grain layer and a relatively coarse-grained second grain layer, is beneficial for suppressing performance degradation during battery cycling when applied in lithium batteries. The high nanoscale grain boundary density of the first layer enhances interfacial bonding and stress buffering, while the significant grain size difference between the two layers creates a grain boundary migration barrier, jointly constraining the grain coarsening trend under thermal stress. This allows the surface microstructure of the conductive layer to be maintained over a long period, stabilizing the mechanical interlocking effect. Consequently, it reduces the peel strength decay rate of the composite current collector during long-term charge-discharge cycles in lithium batteries, effectively improving electrode structural integrity and battery cycle life.

[0025] The beneficial effects of the above-mentioned method for preparing composite current collectors are as follows:

[0026] This preparation method, through a segmented electroplating process, enables the controllable fabrication of a composite current collector with a gradient grain structure and interfacial properties. First, surface activation treatment enhances the substrate's bonding activity. Then, by precisely controlling the electrodeposition current density and temperature in stages, high-frequency nucleation of copper and dopant elements is induced under mild conditions, forming a first layer of nanocrystals with high grain boundary density. Next, under enhanced conditions, a second layer with significantly increased grain size is epitaxially grown on this first layer, thus constructing a grain size gradient in situ. Subsequent segmented annealing further drives the preferential segregation of dopant elements towards the grain boundaries, forming stable pinning points. This process ensures a high degree of controllability and consistency in the gradient structure, trace element distribution, and interfacial chemical bonding, thereby stably achieving composite current collector performance that suppresses grain coarsening and maintains high peel strength. Furthermore, the process parameters are well-defined and reproducible, facilitating industrialization. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the composite current collector described in one embodiment;

[0030] Figure 2 This is a schematic diagram of the composite current collector described in another embodiment;

[0031] Figure 3 This is a schematic diagram of the internal structure of the conductive layer described in one embodiment;

[0032] Figure 4 This is a flowchart of the preparation method of the composite current collector described in one embodiment.

[0033] Explanation of reference numerals in the attached figures:

[0034] 100. Composite current collector; 110. Substrate layer; 120. Conductive layer; 121. First grain layer; 122. Second grain layer; 130. Transition layer. Detailed Implementation

[0035] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0037] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0038] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0039] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0040] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0041] See Figure 1 , Figure 1 A schematic diagram of a composite current collector 100 according to an embodiment of the present invention is shown. The composite current collector 100 includes a substrate layer 110 and a conductive layer 120. The conductive layer 120 includes at least a first grain layer 121 and a second grain layer 122. The first grain layer 121 is disposed between the second grain layer 122 and the substrate layer 110 and is connected to the substrate layer 110. The average grain size of the first grain layer 121 is 150~1300 nm, and the ratio of the average size of the second grain layer 122 to the average grain size of the first grain layer 121 is (1.5~10):1. For example, the conductive layer 120 is a copper foil, and the substrate layer 110 is a PET layer.

[0042] The aforementioned composite current collector 100, by designing the conductive layer 120 as a layered structure comprising at least a first grain layer 121 and a second grain layer 122 with significantly different grain sizes, forms a material that combines buffering and load-bearing properties. The first grain layer 121, with its high-density grain boundaries provided by its nanoscale fine grains, facilitates increased effective contact and bonding points with the substrate layer 110, thereby strengthening the initial bonding force. Simultaneously, this fine-grained layer, acting as a buffer layer, effectively dissipates some of the stress from the upper layer and during battery cycling. The relatively larger grain size of the second grain layer 122 forms a size abrupt interface with the first layer; this discontinuity in the grain boundary structure constitutes an energy barrier for grain boundary migration. Under the stress and heat of battery cycling, this structure significantly suppresses the tendency for grain growth, especially the transmission of coarsening phenomena to the interface, thereby maintaining the microscopic roughness and mechanical interlocking capability of the conductive layer 120 surface for a long time. This, in turn, helps to delay the decline in peel strength and improves the structural integrity and reliability of the current collector during long-term cycling.

[0043] Furthermore, the conductive layer 120 has at least two layers, and the two conductive layers 120 are symmetrically disposed on both sides of the substrate layer 110.

[0044] It should be noted that the average grain size of the grain layer is measured and statistically analyzed using electron backscattering (EBSD). In a scanning electron microscope, the crystal orientation of each point is identified by detecting the Kikuchi diffraction pattern generated by the interaction of the electron beam with the sample. Grain boundaries are defined by the orientation difference between adjacent points, thereby reconstructing the grain morphology, size, and distribution.

[0045] Optionally, the ratio of the average size of the second grain layer 122 to the average size of the grains of the first grain layer 121 can be 1.5:1, 2:1, 2.6:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or any other ratio between these values.

[0046] In one embodiment, the thickness of the first grain layer 121 accounts for 20% to 50% of the total thickness of the conductive layer 120, and the thickness of the second grain layer 122 accounts for 50% to 80% of the total thickness of the conductive layer 120. The first grain layer 121 needs to be thick enough to form a continuous and effective nanocrystalline buffer and bonding interface, but excessive thickness will reduce the overall conductivity and ductility; the second grain layer 122, as the main body, needs to ensure the main conductive function and mechanical strength of the current collector. This ratio is conducive to ensuring that the interface strengthening effect of fine grains can be fully utilized, while the main structure of the coarse grain layer ensures excellent comprehensive performance. Therefore, without excessively sacrificing conductivity and material cost, it is beneficial to maximize the gain effect of interface stability, enabling the current collector to simultaneously possess high bonding force, low resistance, and good processing adaptability.

[0047] Optionally, the thickness percentage of the first grain layer 121 can be 20%, 30%, 40%, 50% or other values ​​within the range, and the thickness percentage of the second grain layer 122 can be 50%, 55%, 60%, 65%, 70%, 75%, 80% or any other value within the range.

[0048] In one embodiment, the conductive layer 120 is made of copper and is further doped with dopant elements in a total content of 0.01~2.0 at%, including one or more of Ag, Zn, Sn, Cr, Zr, Ti, Mg, and Al. Copper serves as a highly conductive substrate, and the addition of dopant elements primarily affects grain boundaries. These heteroatoms cause lattice distortion in the copper lattice and tend to segregate at grain boundaries during subsequent heat treatment. The grain boundary pinning effect generated by the dopant elements effectively hinders grain boundary migration under thermal activation, thereby synergistically enhancing the ability to suppress grain coarsening in conjunction with grain size gradient design. The trace addition avoids a significant loss of conductivity, achieving an excellent balance between stability and electrical performance.

[0049] It should be noted that the grain boundary pinning effect refers to the dragging force exerted by second-phase particles or solute atoms dispersed in a material on the migration of grain boundaries, which can fix the grain boundaries and is a classic mechanism for improving the thermal stability of materials.

[0050] Furthermore, the local concentration of dopant elements at grain boundaries is higher than their average concentration within the grains, and at least some grain boundaries are reinforced phase grain boundaries containing intermetallic compounds of the dopant elements. The high concentration of dopant elements at grain boundaries can form intermetallic compound reinforced phases. Through specific preparation and heat treatment processes, dopant atoms are driven to diffuse and accumulate at grain boundaries, even reacting with copper to form nanoscale intermetallic compounds, such as Cu-Cr and Cu-Zr phases. These enriched atoms or compound particles can lock the grain boundaries. Therefore, compared to solid-solution atoms, the compound reinforcement at grain boundaries has a stronger and more stable pinning effect on grain boundary migration, greatly increasing the activation energy of grain boundary migration and enhancing the resistance of conductive layer 120 to grain growth at battery operating temperatures.

[0051] In one embodiment, the doping elements include Cr and Ag, wherein the Cr content is 0.05~0.5 at%, and the Ag content is 0.1~1.0 at%. Cr has a significantly different atomic size from copper, exhibits a strong tendency to segregate, and readily forms stable precipitates, providing strong grain boundary pinning forces. Ag has high solid solubility in copper, which improves the material's ductility and conductivity. The combination of the two creates a synergistic effect. Thus, Cr enhances thermal stability, while Ag compensates for potential losses in plasticity and conductivity due to doping, enabling the current collector to simultaneously achieve extremely high structural stability and excellent overall electrical and mechanical properties.

[0052] In one embodiment, the dopant concentration decreases from the side closer to the substrate layer 110 to the side farther away from the substrate layer 110, with a concentration gradient of 0.5~5 at% / μm. This gradient design results in the highest dopant concentration and strongest grain boundary pinning effect in the interface region closer to the substrate layer 110, thus providing the most adequate protection for this critical bonding region. The decrease in concentration away from the substrate layer 110 reduces the impact of doping on overall conductivity. This arrangement further protects the performance of the composite current collector 100 material, concentrating limited dopant resources on the interface region where grain growth suppression is most needed and failure is most likely to occur, ensuring interface stability with higher efficiency, while also optimizing bulk conductivity.

[0053] In one embodiment, the area of ​​grains with a {111} orientation in the first grain layer 121 accounts for 40% to 70%. In face-centered cubic metals such as copper, the {111} plane has the densest atomic packing and the lowest surface energy. Grains with this orientation tend to grow parallel to the substrate surface during deposition, forming a denser and smoother initial film. The dense {111} texture in the conductive layer 120 helps to form a more uniform and less defective interfacial contact with the substrate or transition layer 130, improving the initial bonding strength; at the same time, this crystal orientation also has a positive effect on improving the corrosion resistance of the composite current collector 100.

[0054] Furthermore, in the second grain layer 122, the area of ​​grains with the {200} orientation accounts for 50% to 80%. Copper with the {200} orientation has a higher Young's modulus and a different coefficient of thermal expansion. It forms a texture gradient with the {111} orientation of the first layer. Therefore, this orientation difference can change the stress transmission path within the material, helping to disperse and buffer cyclic thermal stress and reduce stress concentration in a single direction. Simultaneously, the {200} orientation has a positive impact on improving conductivity, helping to reduce the current collector's resistance.

[0055] In one embodiment, the composite current collector 100 further includes a transition layer 130 disposed between the first grain layer 121 and the substrate layer 110. The transition layer 130 comprises an organic-inorganic hybrid material containing carboxyl or hydroxyl functional groups, and the thickness of the transition layer 130 is 10-100 nm. The organic components in the transition layer 130, such as polymer chains containing carboxyl or hydroxyl groups, can form strong hydrogen bonds or chemical bonds with the PET substrate; the inorganic components, such as SiO2 and Al2O3 networks, can interact strongly with the subsequently deposited copper. It bridges the organic substrate and the metal conductive layer 120 at the molecular scale, achieving a modulus transition from flexible polymer to rigid metal, greatly buffering interfacial stress; simultaneously, it elevates the interfacial bonding from physical adsorption or mechanical interlocking to chemical bonding, resulting in an order-of-magnitude increase in peel strength, fundamentally solving the risk of interfacial delamination.

[0056] It should be noted that organic-inorganic hybrid materials are composite materials at the nanoscale, in which the organic phase and inorganic components are connected by chemical bonds to form a homogeneous phase, possessing both the flexibility of organic materials and the high thermal stability and strength of inorganic materials.

[0057] In one embodiment, the conductive layer 120 has a pore structure on the side away from the substrate layer 110. The pore size of the pore structure is 50~200 nm and the pore density is 10. 8 ~10 10 pcs / cm 2These micropores significantly increase the specific surface area and surface roughness of the conductive layer 120. When electrode active materials, such as negative electrode graphite or silicon, are coated on it, a stronger bonding effect is generated, preventing the electrode from detaching from the current collector due to volume expansion and contraction during cycling. This helps to further improve the bonding force at the electrode-current collector interface, further ensuring the reliability of lithium-ion batteries.

[0058] Optionally, the hole structure can be a flat-bottomed hole or a through hole, and the hole shape can be circular, square, triangular, rhomboid or other shapes.

[0059] An embodiment of the present invention also provides a method for preparing a composite current collector 100, used to produce the composite current collector 100 of any one of the above, characterized by comprising the following steps:

[0060] S10: Perform surface activation treatment on the surface of the substrate layer 110;

[0061] S20: Metallize the surface of the substrate layer 110 by vacuum sputtering to form a metal seed layer;

[0062] S30: A conductive layer 120 is deposited on the activated PET substrate layer 110 using a segmented electrodeposition process. The electrolyte used for electrodeposition contains copper ions and doping elements, including one or more of Ag, Zn, Sn, Cr, Zr, Ti, Mg, and Al. In the first stage, the current density is 0.5~2 A / dm³. 2 The first grain layer 121 is formed by deposition at a temperature of 20~35℃; in the second stage, the first grain layer is formed by deposition at a current density of 2~8 A / dm³. 2 A second grain layer 122 is deposited on the first grain layer 121 under a temperature of 30~45℃.

[0063] S40: Perform segmented annealing heat treatment on the deposited conductive layer: first, hold at 120~160℃ for 5~15min, then raise the temperature to 180~230℃ and hold for 3~10min.

[0064] The above-described preparation method, through a segmented electroplating process, enables the controllable fabrication of the gradient grain structure and interfacial properties of the composite current collector 100. First, surface activation treatment enhances the substrate's bonding activity. Then, by precisely controlling the electrodeposition current density and temperature in stages, high-frequency nucleation of copper and dopant elements is induced under mild conditions, forming a first layer of nanocrystals with high grain boundary density. Next, under enhanced conditions, a second layer with significantly increased grain size is epitaxially grown on this first layer, thus constructing a grain size gradient in situ. Subsequent segmented annealing further drives the dopant elements to preferentially segregate towards the grain boundaries, forming stable pinning points. This process ensures a high degree of controllability and consistency in the gradient structure, trace element distribution, and interfacial chemical bonding, thereby stably achieving the performance of the composite current collector 100, which suppresses grain coarsening and maintains high peel strength. Furthermore, the process parameters are well-defined and reproducible, facilitating industrialization.

[0065] In other embodiments, the composite current collector can also be fabricated by separately fabricating a conductive layer 120 and a substrate layer 110, and then bonding the two together by a pressing and bonding method. The conductive layer 120 can be formed by calendering, electrolysis, or one or a combination of two other methods.

[0066] In one embodiment, step S40: performing segmented annealing heat treatment on the deposited conductive layer: first holding at 120~160℃ for 5~15 min, then raising the temperature to 180~230℃ and holding for 3~10 min, followed by the following step:

[0067] S50: Micro-hole etching is performed on the surface of the conductive layer.

[0068] Specifically, by using chemical or physical methods, such as chemical etching or plasma treatment, material is selectively removed from the surface of the conductive layer 120, which has formed a stable crystal structure, to form regularly distributed nanopores. This method can flexibly and controllably introduce surface microporous structures without damaging the properties of the conductive layer 120, such as grain structure and grain boundary state. Furthermore, the pore size and pore density are easy to adjust, providing a process means to optimize the adhesion of electrode paste.

[0069] In one embodiment, the electrolyte further includes an organic carboxylate complexing agent, wherein the organic carboxylate is citrate, tartrate, or ethylenediaminetetraacetic acid. Complexing agents such as citrate and tartrate can react with copper ions and doped metal ions (such as Cr). 3+ ,Zr 4 ⁺) Forming stable complexes and regulating their existence state and discharge potential in solution can promote more uniform and stable co-deposition of copper and dopant elements, preventing uneven composition or dendrite growth due to excessive differences in deposition rate; at the same time, the complexing agent can improve the dispersion ability of the plating solution, making the thickness and composition of the deposited layer more uniform, thereby ensuring the consistency of the structure and performance of each layer.

[0070] To verify the beneficial effects of the technical solution of the present invention, the following embodiments and comparative examples were designed, and their key performance was tested and compared.

[0071] Example 1

[0072] A composite current collector has a stacked structure comprising a conductive layer, a substrate layer, and another conductive layer. The substrate layer is a PET film with a thickness of 6 μm. The conductive layers have a total thickness of 2.0 μm. The first grain layer has a thickness of 0.6 μm and an average grain size of approximately 160 nm; the second grain layer has a thickness of 1.4 μm and an average grain size of approximately 800 nm, with a size ratio of 5:1.

[0073] Fabrication process: PET is activated by plasma, followed by magnetron sputtering metallization. Segmented electrodeposition: First stage, current density 1.0 A / dm³. 2 The first stage was carried out at a temperature of 25°C for a deposition time of 3 min; the second stage was conducted at a current density of 4.0 A / dm³. 2 The deposition time was 7 min at 40℃. The electrolyte was a conventional copper sulfate system. Annealing treatment: 160℃ for 10 min.

[0074] Test results: Initial peel strength: 3.8 N / cm. After holding at 85℃ and 1 MPa stress for 48 hours, simulating 500 cycles, the peel strength was 2.7 N / cm, with a retention rate of 71%. Post-cycle EBSD statistics showed that the average size of the first grain layer increased to 180 nm, and the average size of the second grain layer increased to 960 nm.

[0075] Example 2

[0076] A composite current collector, with the same structure as in Example 1, including the substrate layer (same as in Example 1), conductive layer (total thickness 2.4 μm), first grain layer (thickness 0.8 μm, average grain size approximately 350 nm), and second grain layer (thickness 1.6 μm, average grain size approximately 1750 nm, size ratio 5:1), dopant elements (0.3 at% Cr and 0.5 at% Ag added, with a gradient concentration), grain orientation (approximately 60% {111} orientation in the first layer and approximately 70% {200} orientation in the second layer), and no surface micropores.

[0077] Preparation process: Activation treatment is the same as in Example 1. Metallization treatment is the same as in Example 1. Segmented electrodeposition: The electrolyte is based on copper sulfate with the addition of citric acid complexing agent and Cr. 3+ Ag + Salt. First stage, current density 0.8 A / dm³ 2 The temperature was 28℃; in the second stage, the current density was 5.0 A / dm³. 2Temperature 42℃. Segmented annealing: first hold at 150℃ for 12 min, then raise the temperature to 220℃ and hold for 8 min.

[0078] Test results: Initial peel strength: 4.5 N / cm. Peel strength after 500 simulated cycles: 3.9 N / cm, retention rate 87%. Post-cycle EBSD statistics: The average size of the first grain layer increased to 405 nm, and the average size of the second grain layer increased to 1967 nm. TEM observation: Obvious nanoscale precipitates, Cu-Cr phase, are visible at the grain boundaries.

[0079] Example 3

[0080] A composite current collector includes a conductive layer, a transition layer, a substrate layer, and another conductive layer stacked sequentially. The substrate layer is the same as in Example 1. The transition layer contains an epoxy-silane hybrid material and has a thickness of approximately 30 nm. The conductive layer has a total thickness of 1.8 μm. The first grain layer has a thickness of 0.8 μm and an average grain size of approximately 1,289 nm; the second grain layer has a thickness of 1.0 μm and an average grain size of approximately 867 nm, with a size ratio of 3:1. The doping elements are the same as in Example 2. The grain orientation is the same as in Example 2. The surface micropores are formed by plasma etching, with an average pore diameter of approximately 100 nm and a pore density of approximately 5 × 10⁻⁶. 9 pcs / cm 2 .

[0081] Preparation process: A hybrid material precursor is spin-coated onto activated PET and cured to form a transition layer. The electrodeposition and annealing processes are the same as in Example 2. After annealing, plasma etching is performed to form surface micropores.

[0082] Test Results: Initial peel strength: 5.8 N / cm. Peel strength after 500 simulated cycles: 5.3 N / cm, capacity retention 91%. Post-cycle EBSD statistics: The average size of the first grain layer increased to 11.5 nm, and the second grain layer increased to 68 nm. Graphite-coated anodes were assembled for battery testing: After 1000 cycles at 1C, the battery capacity retention was 89.5%, and the increase in DC internal resistance was significantly lower than that of the comparative example.

[0083] Comparative Example 1

[0084] A composite current collector, with the same structure as in Example 1, wherein the substrate layer is the same as in Example 1. The conductive layer is a uniformly grained copper foil with a total thickness of 2.0 μm and an average grain size of approximately 780 nm. It has a gradient-free structure and is undoped.

[0085] Preparation process: After vacuum sputtering metallization of the PET pre-film, single-stage electrodeposition is performed: current density 3.0 A / dm³. 2 Deposit at 35℃ to the target thickness. Annealing: Hold at 160℃ for 10 min.

[0086] Test results: Initial peel strength: 3.5 N / cm. Peel strength after 500 simulated cycles: 1.4 N / cm, retention rate 40%. Post-cycle EBSD statistics: Average grain size increased to approximately 1790 nm, an increase of 129%.

[0087] Comparative Example 2

[0088] A composite current collector, with the same structure as in Example 1, and the same substrate layer as in Example 1. The conductive layer is a single-layer nanocrystalline copper foil with a total thickness of 1.0 μm and an average grain size of approximately 30 nm. It has no coarse-grained layer and is undoped.

[0089] Fabrication process: Single-stage high-frequency pulse electrodeposition to obtain nanocrystals. Annealing treatment: Same as comparative example 1.

[0090] Test results: Initial peel strength: 4.0 N / cm. Peel strength after 500 simulated cycles: 1.8 N / cm, retention rate 45%. Post-cycle EBSD statistics: Average grain size increased to approximately 85 nm, an increase of 183%. Grain coarsening was extremely significant. Initial resistance was slightly higher than the example, and resistance increased significantly after cycling.

[0091] The above data clearly demonstrates that the composite current collector structures provided in Examples 1-3 of this invention have significant advantages over traditional uniform structures or single-layer nanocrystalline structures in suppressing grain coarsening and maintaining peel strength. Among them, Example 3, which integrates gradient grains, trace element doping and segregation, grain orientation control, transition layer, and surface micropores, performs best, with a peel strength retention rate as high as 91%. Grain coarsening is effectively suppressed, ultimately translating into excellent battery cycle performance.

[0092] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite current collector, characterized in that, The composite current collector includes: Substrate layer; The conductive layer includes at least a first grain layer and a second grain layer. The first grain layer is disposed between the second grain layer and the substrate layer and is connected to the substrate layer. The average grain size of the first grain layer is 150~1300nm, and the ratio of the average grain size of the second grain layer to the average grain size of the first grain layer is (1.5~10):

1.

2. The composite current collector according to claim 1, characterized in that, The thickness of the first grain layer accounts for 20% to 50% of the total thickness of the conductive layer, and the thickness of the second grain layer accounts for 50% to 80% of the total thickness of the conductive layer.

3. The composite current collector according to claim 1, characterized in that, The conductive layer is made of copper and is also doped with doping elements in a total content of 0.01~2.0 at%, including one or more of Ag, Zn, Sn, Cr, Zr, Ti, Mg and Al.

4. The composite current collector according to claim 3, characterized in that, The local concentration of the dopant element at the grain boundary is higher than its average concentration within the grain, and at least some grain boundaries are reinforcing phase grain boundaries of intermetallic compounds containing the dopant element; and / or, The doping elements include Cr and Ag, wherein the Cr content is 0.05~0.5 at% and the Ag content is 0.1~1.0 at%.

5. The composite current collector according to claim 3, characterized in that, The concentration of the dopant element decreases from the side closer to the substrate layer to the side farther away from the substrate layer, with a concentration gradient of 0.5~5 at% / μm.

6. The composite current collector according to claim 1, characterized in that, In the first grain layer, the area of ​​grains with {111} orientation accounts for 40% to 70%; and / or, In the second grain layer, the area of ​​grains with {200} orientation accounts for 50% to 80%.

7. The composite current collector according to claim 1, characterized in that, The composite current collector further includes a transition layer disposed between the first grain layer and the substrate layer. The transition layer includes an organic-inorganic hybrid material containing carboxyl or hydroxyl functional groups, and the thickness of the transition layer is 10~100 nm.

8. The composite current collector according to claim 1, characterized in that, The conductive layer has a porous structure on the side away from the substrate layer, the pore size of which is 50~200 nm and the pore density is 10. 8 ~10 10 pcs / cm 2 .

9. A method for preparing a composite current collector, used to manufacture the composite current collector as described in any one of claims 1-8, characterized in that, Includes the following steps: Surface activation treatment is performed on the surface of the substrate layer; Metallize the surface of the substrate layer and form a metal seed layer by vacuum sputtering; A conductive layer is deposited on a metallized PET substrate using a segmented electrodeposition process. The electrolyte used for electrodeposition contains copper ions and dopant elements, with trace elements including one or more of Ag, Zn, Sn, Cr, Zr, Ti, Mg, and Al. In the first stage, the current density is 0.5~2 A / dm³. 2 The first grain layer is formed by deposition at temperatures of 20~35℃. In the second stage, the current density is 2~8 A / dm 2 A second grain layer is formed by deposition on the first grain layer under a temperature of 30~45℃. The deposited conductive layer is subjected to segmented annealing heat treatment: first, it is held at 120~160℃ for 5~15 min, and then the temperature is raised to 180~230℃ and held for 3~10 min.

10. The method for preparing the composite current collector as described in claim 9, characterized in that: Step 1: The deposited conductive layer undergoes segmented annealing heat treatment: first, it is held at 120~160℃ for 5~15 min, then heated to 180~230℃ and held for 3~10 min. The following steps are also included: Micro-etching is performed on the surface of the conductive layer; and / or, The electrolyte also includes an organic carboxylate complexing agent, wherein the organic carboxylate is citrate, tartrate, or ethylenediaminetetraacetic acid.

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