A functional current collector, a method for preparing the same and a lithium ion battery

Abstract

The application provides a functional current collector, a preparation method thereof and a lithium ion battery. The functional current collector comprises a current collector substrate, a metal plating layer on at least one side surface of the current collector substrate, the thickness of the metal plating layer is distributed in a stepped manner along a planar direction, the grain size of the metal plating layer is distributed in a gradient manner along the thickness direction of the metal plating layer, and the planar direction is perpendicular to the thickness direction of the metal plating layer. The application sets the metal plating layer with the thickness distributed in a stepped manner along the planar direction on the current collector substrate, and the grain size of the metal plating layer is distributed in a gradient manner along the thickness direction; the plating layer can not only realize the selective regulation of the thickness according to the differentiated needs of different regions of the current collector substrate, but also can optimize the internal stress distribution and the interface bonding strength, cooperatively improves the surface density, the elongation rate and the surface energy on the basis of maintaining the conductivity of the substrate, realizes the multidimensional comprehensive optimization of the corrosion resistance, the mechanical property and the surface property, and has good industrialization popularization value.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a functional current collector, its preparation method, and a lithium-ion battery. Background Technology

[0002] Copper foil, due to its excellent electrical and thermal conductivity and machinability, is widely used in key areas such as battery current collectors, electronic circuit boards, and electromagnetic shielding. To further optimize the performance of copper foil and meet the comprehensive performance requirements of high-end applications, the industry often modifies copper foil by surface aluminizing. The aluminum coating can give copper foil good corrosion resistance and oxidation resistance, while the synergistic effect of the aluminum-copper interface improves the mechanical properties and surface bonding ability of the copper foil.

[0003] Currently, aluminum plating processes for copper foil mainly include electroplating, sputtering coating, and vacuum evaporation. Among these, vacuum evaporation is increasingly widely used in large-scale production due to its advantages such as fast deposition rate, high coating purity, and tight adhesion to the substrate. However, existing vacuum evaporation aluminum plating processes have significant technical bottlenecks, making it difficult to meet the customized needs of high-end materials: 1. Uniform coating thickness and limited performance adjustment: Existing vacuum evaporation processes mostly use constant parameters to deposit aluminum layers, resulting in uniform coating thickness. This makes it impossible to customize differentiated thickness distributions according to the functional requirements of different areas of the copper foil. For example, battery current collector copper foil requires a thicker aluminum layer in the current collection area to improve corrosion resistance, while a thinner aluminum layer is needed in the bending area to ensure flexibility. Existing processes struggle to meet these differentiated requirements simultaneously. 2. Complex and inefficient gradient coating preparation: Some solutions attempt to prepare gradient aluminum layers through multiple vapor depositions and step-by-step parameter adjustments, but this requires repeated equipment start-ups and shutdowns and process parameter adjustments. This is not only cumbersome and inefficient, but also prone to problems such as insufficient interlayer adhesion and increased coating defects. Furthermore, fluctuations in the vacuum environment during multiple vapor depositions can affect the stability of coating quality. 3. Limited performance improvement and difficulty in meeting multi-dimensional needs: Existing aluminum-plated copper foils mostly focus on optimizing a single performance (such as corrosion resistance), with poor synergistic effects on mechanical properties (elongation, tensile strength) and surface properties (surface energy). Simultaneously, some processes suffer from poor interfacial compatibility between the coating and the substrate, leading to coating peeling and cracking, affecting the material's service life. 4. Poor equipment adaptability: Existing roll-to-roll vacuum vapor deposition equipment is mostly designed for uniform coatings, lacking the ability to precisely control gradient thickness coatings. This makes it difficult to achieve continuous and stable deposition across different gradient ranges, limiting the large-scale application of gradient aluminum-plated copper foils.

[0004] Therefore, how to take into account the differentiated functional requirements of different regions of copper foil and achieve multi-dimensional synergistic optimization of corrosion resistance, mechanical properties and surface properties is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a functional current collector, its preparation method, and a lithium-ion battery. The present invention involves depositing a metal coating with a stepped thickness along the planar direction on a current collector substrate, and further subdividing the grain size of the metal coating along its thickness direction. This structural design allows for selective control of the coating thickness based on the differentiated functional requirements of different regions of the current collector substrate. Simultaneously, the gradient grain size distribution effectively optimizes the internal stress distribution and interfacial bonding strength of the coating, thereby synergistically improving the areal density, elongation, and surface energy of the functional current collector while maintaining the original excellent conductivity of the substrate. This achieves multi-dimensional comprehensive optimization of corrosion resistance, mechanical properties, and surface properties. In summary, the present invention overcomes the limitations of existing technologies where the coating improvement effect is singular and it is difficult to simultaneously meet multi-dimensional performance requirements. It can meet the comprehensive performance requirements of current collectors in high-end application scenarios and has good industrial application value.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a functional current collector, the functional current collector comprising: Current collector matrix.

[0007] A metal coating is located on at least one side surface of the current collector substrate; the thickness of the metal coating is distributed in a stepped manner along the planar direction, and the grain size of the metal coating is distributed in a gradient manner along the thickness direction of the metal coating; wherein the planar direction is perpendicular to the thickness direction of the metal coating.

[0008] This invention features a metal coating with a stepped thickness along the planar direction on a current collector substrate, and the grain size of the metal coating is also gradient-distributed along its thickness. This structural design allows for selective control of the coating thickness based on the differentiated functional requirements of different regions of the current collector substrate. Simultaneously, the gradient grain size distribution effectively optimizes the internal stress distribution and interfacial bonding strength of the coating. Therefore, while maintaining the original excellent conductivity of the substrate, it synergistically improves the areal density, elongation, and surface energy of the functional current collector, achieving multi-dimensional comprehensive optimization of corrosion resistance, mechanical properties, and surface properties. In summary, this invention overcomes the limitations of existing technologies where the coating improvement effect is singular and it is difficult to simultaneously meet multi-dimensional performance requirements. It can meet the comprehensive performance requirements of current collectors in high-end application scenarios and has good industrial application value.

[0009] In this invention, a metallurgical bonding interface is formed between the metal coating and the current collector substrate, eliminating problems such as interlayer interface defects caused by multiple start-stop operations or step-by-step deposition. The internal grains of the metal coating are continuously penetrated without discontinuities or weak bonding interfaces.

[0010] Preferably, the grain size gradient of the metal coating increases along the thickness direction away from the current collector substrate.

[0011] In this invention, along the thickness direction away from the current collector substrate, the grain size gradient of the metal coating increases, which helps to alleviate the thermal stress and growth stress inside the coating, reduce the stress concentration at the interface between the coating and the substrate, and further improve the interfacial bonding strength. At the same time, the gradient grain structure can improve the toughness and fatigue resistance of the coating while maintaining the density of the coating surface, so that the functional current collector has excellent comprehensive mechanical stability.

[0012] Preferably, the grain size of the metal coating is 50~500nm, for example, it can be 50nm, 100nm, 150nm, etc.

[0013] Preferably, the grains inside the metal coating are in a continuous columnar shape along the planar direction.

[0014] In this invention, the grains inside the metal coating are continuous columnar along the planar direction, indicating that the metal coating is formed by a single continuous deposition process and there are no interlayer interface defects or weak bonding layers caused by multiple start-stop or step-by-step deposition. At the same time, the continuous columnar crystal structure is conducive to the rapid transport of electrons along the grain growth direction, which improves the conductivity of the coating and can effectively transfer and disperse stress, enhance the interfacial bonding strength and structural stability.

[0015] Preferably, the thickness difference between adjacent metal plating segments is 0.5~2μm, for example, it can be 0.5μm, 1μm, 1.5μm or 2μm.

[0016] This invention can precisely control the steepness of the metal coating gradient curve by controlling the thickness difference between adjacent metal coating segments, ensuring a smooth gradient transition and avoiding stress concentration or structural defects in the film layer caused by sudden changes in speed, thus meeting the requirements of different application scenarios for performance gradient rates.

[0017] Preferably, in the metal coating, there is a smooth transition between adjacent metal coating segments.

[0018] Preferably, the thickness of the metal coating is in the range of 0.5~4μm, for example, it can be 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm or 4μm, etc.

[0019] Preferably, the metal coating includes any one or a combination of at least two of the following: an aluminum layer, a copper layer, an aluminum alloy layer, or a copper alloy layer.

[0020] Preferably, the current collector substrate comprises copper foil.

[0021] In a second aspect, the present invention provides a method for preparing a functional current collector as described in the first aspect, the method comprising the following steps: Provide current collector substrate.

[0022] A metal coating with a stepped thickness along a planar direction is formed on at least one side surface of the current collector substrate by controlling the transport speed of the current collector substrate and the bias voltage applied to the current collector substrate; wherein the planar direction is perpendicular to the thickness direction of the current collector substrate.

[0023] This invention enables the one-time deposition of metal coatings with a stepped thickness distribution along the planar direction, eliminating the need for multiple equipment start-ups and shutdowns or step-by-step operations. It is simple to operate, highly efficient, free of interlayer defects, and significantly improves coating quality stability. It solves the problem of existing processes offering only single-dimensional performance improvements and failing to meet multi-dimensional requirements, thus satisfying the comprehensive performance demands of high-end applications. Notably, through the coordinated control of transmission speed and bias voltage, continuous columnar crystal growth and a gradient distribution of grain size are achieved within the metal coating. This unique microstructure effectively releases internal stress, further enhancing the coating's crack resistance and interfacial bonding strength, which is beneficial for improving the material's service stability under bending and stretching conditions. Furthermore, this process is flexible and controllable, allowing for the preparation of single-sided or double-sided metal coatings as needed. Gradient thickness and performance parameters can be flexibly adjusted, adapting to different specifications of current collectors and application scenarios. Moreover, it requires no modification to existing roll-to-roll vacuum deposition equipment, only adjustments to process parameters, demonstrating strong compatibility and ease of industrialization.

[0024] Preferably, the steps of the vapor deposition process include: The current collector substrate is placed in the vapor deposition chamber.

[0025] Under vacuum conditions, a metal coating is formed by controlling the transmission speed of the current collector substrate and the bias voltage applied to the current collector substrate.

[0026] It is cooled and shaped by cooling rollers.

[0027] Preferably, in the vapor deposition process, multiple independently controlled evaporation sources are arranged sequentially along the transport direction of the current collector substrate. Each evaporation source is equipped with an independent power adjustment module and a wire feeding control module, which are used to independently adjust the heating power of a single evaporation source and the amount of metal wire fed.

[0028] In this invention, each evaporation source is equipped with an independent power adjustment module and wire feeding control module, which can independently adjust the heating power and aluminum wire feeding amount of a single evaporation source. The process parameters of each evaporation source can be set individually and run synchronously, enabling precise control of the metal vapor concentration in different areas along the current collector substrate transport path. Furthermore, each group of evaporation sources shares the same vapor deposition chamber, eliminating the need for segmented vapor deposition and avoiding coating defects caused by vacuum environment fluctuations. This provides a vapor source basis for the one-time continuous deposition of metal coatings with stepped thickness distribution.

[0029] It should be noted that "multiple sets" refers to two or more sets, that is, at least two independently controlled evaporation sources are set along the transport direction of the current collector substrate. By setting the process parameters of each evaporation source differently, the metal vapor concentration along the substrate transport path in a single vapor deposition chamber can be controlled in segments, providing a structural basis for the continuous deposition of metal coatings with a stepped distribution along the planar direction.

[0030] Preferably, the transmission speed of the current collector substrate is 2~15 m / min, for example, it can be 2 m / min, 3 m / min, 4 m / min, 5 m / min, 6 m / min, 7 m / min, 8 m / min, 9 m / min, 10 m / min, 11 m / min, 12 m / min, 13 m / min, 14 m / min or 15 m / min, etc.

[0031] Preferably, the transmission speed of the current collector substrate changes continuously, and the rate of change between any two adjacent speeds is 20% to 60%, for example, it can be 20%, 30%, 40%, 50%, or 60%. For example, the transmission speed changes continuously from a first speed V1 to a second speed V2 at a rate of |V2-V1| / V1×100%; then it changes continuously from the second speed V2 to a third speed V3 at a rate of |V3-V2| / V2×100%, with all the above rates of change controlled within the range of 20% to 60%.

[0032] This invention can precisely control the steepness of the gradient curve by controlling the rate of change between any two adjacent velocities of adjacent aluminum layers, ensuring a smooth gradient transition and avoiding stress concentration or structural defects in the film layer caused by sudden velocity changes, thus meeting the requirements of different application scenarios for performance gradient rates.

[0033] Preferably, the bias voltage applied to the current collector substrate is 3250~600V, for example, it can be 250V, 300V, 400V, 450V, 500V, 550V or 600V.

[0034] In this invention, an appropriate bias voltage can effectively regulate the energy and migration ability of deposited particles, promote the full diffusion and dense accumulation of metal atoms on the surface of the current collector substrate, thereby forming a columnar crystal structure with continuous grains and tight interfacial bonding. At the same time, an appropriate bias voltage helps to reduce the internal stress of the coating, suppress the generation of microcracks, and further improve the structural stability and fatigue resistance of the functional current collector.

[0035] Preferably, the wire feeding rate is 200~400mm / min, for example, it can be 200mm / min, 250mm / min, 300mm / min, 350mm / min or 400mm / min, etc.

[0036] Preferably, the temperature of the cooling roller is -20 to -25°C, for example, it can be -20°C, -21°C, -22°C, -23°C, -24°C or -25°C.

[0037] Preferably, the current collector substrate is a pretreated current collector substrate, and the pretreatment steps include sequential cleaning and plasma activation.

[0038] This invention performs plasma activation on the current collector substrate, that is, it uses plasma bombardment to break the inert chemical bonds on the surface of the current collector substrate, thereby introducing active sites, which is beneficial to improving the interfacial bonding force between the metal coating and the current collector substrate.

[0039] Preferably, the preparation method includes the following steps: (1) Provide a current collector substrate; the thickness of the current collector substrate is 5~100μm (e.g., it can be 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, etc.), the width is 500~1600mm (e.g., it can be 500mm, 600mm, 700mm, 800mm, 900mm, 1000mm, 1100mm, 1200mm, 1300mm, 1400mm, 1500mm or 1600mm, etc.), and the surface roughness Ra≤0.2μm (e.g., it can be 0.01μm, 0.02μm, 0.05μm, 0.08μm, 0.10μm, 0.12μm, 0.15μm or 0.20μm, etc.).

[0040] The current collector substrate is ultrasonically cleaned with a cleaning power of 300-500W (e.g., 300W, 350W, 400W, 450W, or 500W) for 5-10 minutes (e.g., 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes). After cleaning, it is kept at 60-80℃ (e.g., 60℃, 65℃, 70℃, 75℃, or 80℃) with a vacuum degree <1×10⁻⁶. -2 Pa (for example, it could be 9 × 10) -3 Pa, 5×10 -3 Pa, 1×10 -3 Pa, 9×10 -4 Pa, 5×10 -4 Pa or 1×10 -4 Dry under conditions such as Pa for 15-20 minutes (e.g., 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes).

[0041] The dried current collector substrate is subjected to plasma activation for a processing time of 3-10 s (e.g., 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s, or 10 s, etc.) to obtain a pretreated current collector substrate. During the plasma activation process, the plasma includes argon plasma, with a plasma flow rate of 20-30 sccm (e.g., 20 sccm, 25 sccm, or 30 sccm, etc.), a plasma power of 300-600 W (e.g., 300 W, 400 W, 500 W, or 600 W, etc.), and a distance of 5-8 mm (e.g., 5 cm, 6 cm, 7 cm, or 8 cm, etc.) between the plasma source and the surface of the current collector substrate.

[0042] (2) Place the pretreated current collector substrate on the unwinding device of the vapor deposition machine and put the metal wire into the evaporation source of the vapor deposition machine.

[0043] The vapor deposition chamber was evacuated to a vacuum level of 5 × 10⁻⁶. -3 ~9.9×10 -3 Pa (for example, it could be 5 × 10) -3 Pa, 6×10 -3 Pa, 7×10 -3 Pa, 8×10 -3 Pa, 9×10 -3 Pa, 9.5 × 10 -3 Pa or 9.9 × 10 -3 Pa, etc.

[0044] Turn on the evaporation source and heat the metal wire until it vaporizes to form metal vapor. After the vapor deposition process parameters stabilize, turn on the unwinding device to deposit the metal vapor on at least one side of the current collector substrate. At the same time, control the transmission speed and bias value of the current collector substrate so that the thickness of the metal coating is distributed in a stepped manner along the plane to form a metal coating of a preset thickness.

[0045] The transmission speed of the current collector substrate is 2~15m / min, and the transmission speed varies continuously, with a change rate of 20~60% between any two adjacent speeds; the bias voltage is 250~600V; the heating power percentage of the evaporation source is 80%~95% (for example, it can be 80%, 85%, 90% or 95% etc.); and the wire feeding rate of the metal wire is 200~400mm / min.

[0046] The current collector is cooled to room temperature by a cooling roller at a temperature of -20~-25℃ and then cooled and shaped to obtain a functional current collector.

[0047] It should be noted that the heating power percentage of the evaporation source refers to the proportion of the heating power currently applied to the evaporation source to its rated maximum heating power.

[0048] Thirdly, the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes a functional current collector as described in the first aspect.

[0049] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0050] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention provides a metal coating with a stepped thickness along the planar direction on the current collector substrate, and the grain size of the metal coating is gradient-distributed along its thickness direction. This structural design can selectively control the coating thickness according to the differentiated functional requirements of different regions of the current collector substrate. At the same time, the gradient distribution of grain size effectively optimizes the stress distribution and interfacial bonding strength of the coating, thereby improving the areal density, elongation and surface energy of the functional current collector while maintaining the original excellent conductivity of the substrate. This achieves multi-dimensional comprehensive optimization of corrosion resistance, mechanical properties and surface properties. In summary, this invention overcomes the limitations of the prior art where the coating improvement effect is singular and it is difficult to meet the multi-dimensional performance requirements. It can meet the requirements of high-end application scenarios for the comprehensive performance of current collectors and has good industrial promotion value.

[0051] (2) This invention can achieve a metal coating with a stepped thickness distribution along the plane in a single vapor deposition process, without the need for multiple equipment start-ups and shutdowns or step-by-step operations. It is simple to operate, has high production efficiency, no interlayer defects, and significantly improves the stability of coating quality. It solves the problem of existing processes having only single performance improvement and difficulty in meeting multi-dimensional needs, and can meet the comprehensive performance requirements of high-end application scenarios. It is particularly noteworthy that by coordinating the control of transmission speed and bias voltage, continuous columnar crystal growth and gradient distribution of grain size are achieved inside the metal coating. This unique microstructure effectively releases the internal stress of the film layer, further enhancing the crack resistance and interfacial bonding strength of the coating, which is beneficial to improving the service stability of the material under bending, stretching and other working conditions. In addition, the process is flexible and controllable, and can realize the preparation of single-sided or double-sided metal coatings according to needs. The gradient thickness and performance parameters can be flexibly adjusted, which can be adapted to different specifications of current collectors and application scenarios. At the same time, it does not require modification of existing roll-to-roll vacuum vapor deposition equipment, only the process parameters need to be adjusted. It has strong compatibility and is easy to promote industrially. Detailed Implementation

[0052] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0053] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0054] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0055] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0056] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0057] Example 1 This embodiment provides a functional current collector, the functional current collector comprising: The current collector substrate is an electrolytic copper foil with a thickness of 5 μm and a width of 1400 mm.

[0058] An aluminum coating is located on one side surface of the current collector substrate; the thickness of the aluminum coating is distributed in a stepped manner along the planar direction, and the grain size of the aluminum coating is distributed in a gradient manner along the thickness direction of the aluminum coating; the grain size gradient of the aluminum coating increases along the thickness direction away from the current collector substrate; the grains inside the aluminum coating are continuous columnar along the planar direction; wherein, the planar direction is perpendicular to the thickness direction of the aluminum coating.

[0059] The grain size of the aluminum coating is 50~500nm; the thickness difference between adjacent aluminum coating segments is 0.5μm; the transition between adjacent aluminum coating segments is smooth; the thickness of the aluminum coating ranges from 0.5 to 2μm. This embodiment also provides a method for preparing the above-mentioned functional current collector, the method comprising the following steps: (1) Provide electrolytic copper foil as the current collector substrate; the surface roughness of the electrolytic copper foil is Ra=0.15μm.

[0060] The electrolytic copper foil was ultrasonically cleaned using anhydrous ethanol and deionized water at a power of 400 W for 8 minutes. After cleaning, it was subjected to an ultrasonic cleaning process at 70°C and a vacuum of 5 × 10⁻⁶. -3 Dry for 18 minutes under the condition of Pa.

[0061] The dried electrolytic copper foil was subjected to plasma activation for 4 seconds to obtain pretreated electrolytic copper foil. During the plasma activation process, the plasma was argon plasma with a flow rate of 25 sccm, a plasma power of 500 W, and a distance of 6 mm between the plasma source and the surface of the current collector substrate.

[0062] (2) Place the pretreated electrolytic copper foil on the unwinding device of the vapor deposition machine, and put the aluminum wire with a purity of 99.99% into the evaporation source of the vapor deposition machine; inside the vapor deposition machine, multiple sets of independently controlled evaporation sources are arranged in sequence along the transport direction of the electrolytic copper foil. Each set of evaporation sources is equipped with an independent power adjustment module and a wire feeding control module, which are used to independently adjust the heating power of a single evaporation source and the amount of gold and aluminum wire fed.

[0063] The vapor deposition chamber was closed and evacuated to a vacuum level of 9.9 × 10⁻⁶. -3 Pa.

[0064] The evaporation source is turned on to heat the aluminum wire until it vaporizes into aluminum vapor. After the evaporation process parameters stabilize, the unwinding device is turned on to deposit the aluminum vapor onto one side of the electrolytic copper foil. The conveying speed of the electrolytic copper foil is controlled at 13.4 m / min, the wire feed rate at 340 mm / min, the cooling roller temperature at -20°C, the bias voltage at 500 V, and the heating power percentage of the evaporation source at 80%. A first aluminum coating segment with a thickness of 0.5 μm is formed. After depositing 100 m, the conveying speed of the electrolytic copper foil is gradually changed to 8 m / min (the rate of change between adjacent speeds is 40%), and the bias voltage is 400 V. With all parameters unchanged, a second aluminum plating layer with a thickness of 1 μm is formed. After depositing 100 m, the transport speed of the electrolytic copper foil is gradually changed to 5.5 m / min (the rate of change between two adjacent speeds is 31%), the bias voltage is 370 V, and other parameters remain unchanged to form a third aluminum plating layer with a thickness of 1.5 μm. After depositing 100 m, the transport speed of the electrolytic copper foil is gradually changed to 4 m / min (the rate of change between two adjacent speeds is 27%), the bias voltage is 350 V, and other parameters remain unchanged to form a fourth aluminum plating layer with a thickness of 2 μm. Finally, an aluminum plating layer with a deposition length of 400 m is formed.

[0065] The sample is cooled to room temperature (25°C) by a cooling roller and then cooled and shaped to obtain a functional current collector.

[0066] The functional current collector provided in this embodiment was characterized, including the thickness, areal density, peel force, elongation, tensile strength, and surface energy of the aluminum coating. The thickness was measured using a Marl thickness gauge; the areal density was measured using a high-precision electronic analytical balance; the peel force was measured using a peel force tester, specifically, three points were selected on the aluminum coating surface to test and record the average peel force value; the elongation and tensile strength were both measured using an electronic universal testing machine, with 10 points each along the longitudinal (MD) and transverse (TD) directions of the aluminum coating, and the average value was taken; the surface energy was measured using a contact angle meter (water droplet method / ethylene glycol two-liquid method).

[0067] The test results are shown in Table 1.

[0068] Table 1 Example 2 This embodiment provides a functional current collector, the functional current collector comprising: The current collector substrate is a high-performance rolled copper foil with a thickness of 8μm and a width of 1200mm.

[0069] An aluminum coating is located on one side surface of the current collector substrate; the thickness of the aluminum coating is distributed in a stepped manner along the planar direction, and the grain size of the aluminum coating is distributed in a gradient manner along the thickness direction of the aluminum coating; the grain size gradient of the aluminum coating increases along the thickness direction away from the current collector substrate; the grains inside the aluminum coating are continuous columnar along the planar direction; wherein, the planar direction is perpendicular to the thickness direction of the aluminum coating.

[0070] The grain size of the aluminum coating is 50~500nm; the thickness difference between adjacent aluminum coating segments is 0.5μm; the transition between adjacent aluminum coating segments is smooth; the thickness of the aluminum coating ranges from 0.5 to 2μm. This embodiment also provides a method for preparing the above-mentioned functional current collector, the method comprising the following steps: (1) Provide high-performance rolled copper foil as current collector substrate; the high-performance rolled copper foil has a purity ≥99.98% and a surface roughness Ra≤0.08μm.

[0071] The high-performance rolled copper foil was ultrasonically cleaned using anhydrous ethanol and deionized water at a power of 500W for 6 minutes. After cleaning, it was subjected to an ultrasonic cleaning process at 70°C and a vacuum of 5×10⁻⁶. -3 Dry for 18 minutes under the condition of Pa.

[0072] The dried high-performance rolled copper foil was subjected to plasma activation for 10 seconds to obtain pretreated high-performance rolled copper foil. During the plasma activation process, the plasma was argon plasma with a flow rate of 20 sccm, a plasma power of 300 W, and a distance of 6 mm between the plasma source and the surface of the current collector substrate.

[0073] (2) Place the pretreated high-performance rolled copper foil on the unwinding device of the vapor deposition machine, and put the 99.99% pure aluminum wire into the evaporation source of the vapor deposition machine; inside the vapor deposition machine, multiple sets of independently controlled evaporation sources are arranged in sequence along the transport direction of the high-performance rolled copper foil. Each set of evaporation sources is equipped with an independent power adjustment module and a wire feeding control module, which are used to independently adjust the heating power of a single evaporation source and the amount of gold and aluminum wire fed.

[0074] The vapor deposition chamber was closed and evacuated to a vacuum level of 9.9 × 10⁻⁶. -3 Pa.

[0075] The evaporation source is turned on to heat the aluminum wire until it vaporizes into aluminum vapor. After the vapor deposition process parameters stabilize, the unwinding device is turned on to deposit the aluminum vapor onto one side surface of the high-performance rolled copper foil. The conveying speed of the high-performance rolled copper foil is controlled at 4 m / min, the wire feed rate at 340 mm / min, the cooling roller temperature at -25°C, the bias voltage at 550 V, and the heating power percentage of the evaporation source at 85%. A first aluminum coating segment with a thickness of 2 μm is formed. After depositing 100 m, the conveying speed of the high-performance rolled copper foil is gradually changed. With a speed of 2.5 m / min (the rate of change between two adjacent speeds is 37.5%), a bias voltage of 300 V, and other parameters remaining constant, a second aluminum coating segment with a thickness of 3 μm is formed. After depositing 100 m, the transport speed of the high-performance rolled copper foil is gradually changed to 2 m / min (the rate of change between two adjacent speeds is 20%), the bias voltage is 280 V, and other parameters remain constant, forming a third aluminum coating segment with a thickness of 4 μm. After depositing 100 m, an aluminum coating with a final deposition length of 300 m is formed.

[0076] The sample is cooled to room temperature (25°C) by a cooling roller and then cooled and shaped to obtain a functional current collector.

[0077] The functional current collector provided in this embodiment was characterized, including the thickness, areal density, peel force, elongation, tensile strength, and surface energy of the aluminum coating. The thickness was measured using a Marl thickness gauge; the areal density was measured using a high-precision electronic analytical balance; the peel force was measured using a peel force tester, specifically, three points were selected on the aluminum coating surface to test and record the average peel force value; the elongation and tensile strength were both measured using an electronic universal testing machine, with 10 points each along the longitudinal (MD) and transverse (TD) directions of the aluminum coating, and the average value was taken; the surface energy was measured using a contact angle meter (water droplet method / ethylene glycol two-liquid method).

[0078] The test results are shown in Table 2.

[0079] Table 2 Example 3 The difference between this embodiment and Embodiment 1 is that the transmission speed of the electrolytic copper foil is adjusted so that the thickness difference between adjacent metal plating segments is 0.2 μm.

[0080] The remaining preparation methods and parameters are consistent with those in Example 1.

[0081] Example 4 The difference between this embodiment and Embodiment 1 is that the transmission speed of the electrolytic copper foil is adjusted so that the thickness difference between adjacent metal plating segments is 2.5 μm.

[0082] The remaining preparation methods and parameters are consistent with those in Example 1.

[0083] Example 5 The difference between this embodiment and Embodiment 1 is that the transport speed of the electrolytic copper foil is adjusted so that the rate of change between the transport speed of the electrolytic copper foil in the first aluminum plating stage and the transport speed of the electrolytic copper foil in the second aluminum plating stage is 10%.

[0084] The remaining preparation methods and parameters are consistent with those in Example 1.

[0085] Example 6 The difference between this embodiment and Embodiment 1 is that the transport speed of the electrolytic copper foil is adjusted so that the rate of change between the transport speed of the electrolytic copper foil in the first aluminum plating stage and the transport speed of the electrolytic copper foil in the second aluminum plating stage is 70%.

[0086] The remaining preparation methods and parameters are consistent with those in Example 1.

[0087] Example 7 The difference between this embodiment and Embodiment 1 is that, throughout the entire process of aluminum vapor deposition on one side of the electrolytic copper foil, the bias voltage applied to the current collector substrate is 300V.

[0088] The remaining preparation methods and parameters are consistent with those in Example 1.

[0089] Example 8 The difference between this embodiment and Embodiment 1 is that, throughout the entire process of aluminum vapor deposition on one side of the electrolytic copper foil, the bias voltage applied to the current collector substrate is 700V.

[0090] The remaining preparation methods and parameters are consistent with those in Example 1.

[0091] Comparative Example 1 The difference between this comparative example and Example 1 is that the thickness of the aluminum coating is uniform, that is, during the evaporation process, the transport speed of the electrolytic copper foil is kept constant at 4m / min and the temperature of the cooling roller is kept constant at -25℃.

[0092] The remaining preparation methods and parameters are consistent with those in Example 1.

[0093] Comparative Example 2 The difference between this comparative example and Example 1 is that the first aluminum coating segment, the second aluminum coating segment, the third aluminum coating segment, and the fourth aluminum coating segment are deposited using different vapor deposition chambers.

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Performance testing The functional current collectors provided in Examples 1, 3-8, and Comparative Examples 1-2 were characterized, including the peel force, elongation, tensile strength, and surface energy of the aluminum coating. The areal density was measured using a high-precision electronic analytical balance; the peel force was measured using a peel force tester, specifically, three points were selected on the aluminum coating surface to measure and record the average peel force value; the elongation and tensile strength were both measured using an electronic universal testing machine, with 10 points each along the longitudinal (MD) and transverse (TD) directions of the aluminum coating for measurement, and the average value was taken; the surface energy was measured using a contact angle meter (water droplet method / ethylene glycol two-liquid method).

[0096] The test results are shown in Table 3.

[0097] Table 3 analyze: As shown in Tables 1, 2, and 3, the present invention provides a metal coating with a stepped thickness along the planar direction on the current collector substrate, and the grain size of the metal coating is gradient-distributed along its thickness direction. This structural design allows for selective control of the coating thickness according to the differentiated functional requirements of different regions of the current collector substrate. Simultaneously, the gradient distribution of grain size effectively optimizes the stress distribution and interfacial bonding strength within the coating, thereby synergistically improving the areal density, elongation, and surface energy of the functional current collector while maintaining the original excellent conductivity of the substrate, achieving improved corrosion resistance and mechanical properties. This invention achieves multi-dimensional comprehensive optimization of surface properties, enabling the deposition of metal coatings with a stepped thickness distribution along the planar direction in a single process. It eliminates the need for multiple equipment start-ups and shutdowns or step-by-step operations, simplifying operation, increasing production efficiency, eliminating interlayer defects, and significantly improving coating quality stability. Importantly, through the coordinated control of transmission speed and bias voltage, continuous columnar crystal growth and a gradient distribution of grain size are achieved within the metal coating. This microstructure effectively releases internal stress within the film, further enhancing the coating's crack resistance and interfacial bonding strength, and improving the material's service stability under bending, stretching, and other conditions.

[0098] A comparison of Examples 1 and 3-4 shows that if the thickness difference between adjacent metal plating segments is too small, the differential control effect of the gradient structure is weakened, and it cannot effectively match the functional requirements of different areas of the copper foil. At the same time, the stress release within the plating is insufficient, and the mechanical properties such as elongation and tensile strength decrease slightly compared to Example 1. The peel force and surface energy also decrease slightly. If the thickness difference between adjacent metal plating segments is too large, the sudden change in thickness between adjacent segments will lead to stress concentration. Microcracks are prone to occur in the plating transition area, the interfacial bonding force decreases, and the sheet resistance uniformity deteriorates. The mechanical properties (elongation, tensile strength, etc.) and peel force are significantly reduced, and the functionality of the gradient structure and the stability of the plating structure cannot be taken into account.

[0099] A comparison of Examples 1 and 5-6 shows that if the rate of change between the transport speed of the electrolytic copper foil in the first aluminum plating stage and the transport speed of the electrolytic copper foil in the second aluminum plating stage is too small, the change in the aluminum layer thickness gradient will be too gradual, making it impossible to achieve precise control of the stepped thickness distribution. The functionality of the gradient structure will be insufficient, and production efficiency will be reduced. The performance of each example will not show a significant advantage over Example 1. If the rate of change between the transport speed of the electrolytic copper foil in the first aluminum plating stage and the transport speed of the electrolytic copper foil in the second aluminum plating stage is too large, the sudden change in transport speed will cause drastic fluctuations in the aluminum vapor deposition state, resulting in an uneven coating grain structure, concentrated internal stress, and a significant decrease in mechanical properties (elongation, tensile strength, etc.) and peel force. The coating is prone to defects such as cracking and peeling, which cannot meet the requirements of large-scale production.

[0100] As can be seen from the comparison between Example 1 and Examples 7-8, if the bias voltage applied to the current collector substrate is constant and too small, the ion bombardment intensity is insufficient, the aluminum atom deposition density is poor, the coating grains are coarse, the interfacial bonding force is weak, and the core properties such as peel force, elongation, and tensile strength are significantly lower than those in Example 1, making it impossible to achieve precise control of the gradient grain structure. If the bias voltage applied to the current collector substrate is constant and too large, the ion bombardment is excessive, which will cause etching damage to the deposited aluminum layer, resulting in a decrease in coating density, excessive grain refinement, increased internal stress, and reduced elongation. At the same time, it will cause damage to the surface of the copper foil substrate, affecting the overall mechanical properties and service life of the current collector.

[0101] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, if the thickness of the aluminum coating is uniform, it is impossible to achieve a differentiated thickness distribution according to the functional requirements of different areas of the copper foil. Furthermore, due to the lack of gradient distribution of grain size, the internal stress of the coating is large, and the interfacial bonding strength and crack resistance are significantly worse. If the first, second, third, and fourth aluminum coating sections are deposited in different vapor deposition chambers, although a stepped thickness distribution is achieved, the operation is cumbersome and the production efficiency is low due to the repeated start-up and shutdown of the equipment and the repeated vacuum breaking and vacuuming. Moreover, there are obvious interlayer interface defects between each coating section, the grain structure is discontinuous, the coating bonding force is insufficient, interlayer cracking is prone to occur, and the overall performance is poor.

[0102] It should be noted that the technical solution of the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A functional current collector, characterized in that, The functional current collector includes: Current collector substrate; A metal coating is located on at least one side surface of the current collector substrate; the thickness of the metal coating is distributed in a stepped manner along the planar direction, and the grain size of the metal coating is distributed in a gradient manner along the thickness direction of the metal coating; wherein the planar direction is perpendicular to the thickness direction of the metal coating.

2. The functional current collector according to claim 1, characterized in that, Along the thickness direction away from the current collector substrate, the grain size gradient of the metal coating increases; And / or, the grain size of the metal coating is 50~500nm; And / or, the grains inside the metal coating are in a continuous columnar shape along the planar direction.

3. The functional current collector according to claim 1 or 2, characterized in that, In the metal coating, the thickness difference between adjacent metal coating segments is 0.5~2μm; And / or, in the metal coating, there is a smooth transition between adjacent metal coating segments; And / or, the thickness of the metal coating ranges from 0.5 to 4 μm; And / or, the metal coating includes any one or a combination of at least two of the following: an aluminum layer, a copper layer, a nickel layer, an aluminum alloy layer, or a copper alloy layer; And / or, the current collector substrate includes copper foil.

4. A method for preparing a functional current collector as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: Provide current collector substrate; A metal coating with a stepped thickness along a planar direction is formed on at least one side surface of the current collector substrate by controlling the transport speed of the current collector substrate and the bias voltage applied to the current collector substrate; wherein the planar direction is perpendicular to the thickness direction of the current collector substrate.

5. The preparation method according to claim 4, characterized in that, In the vapor deposition process, multiple independently controlled evaporation sources are arranged sequentially along the transport direction of the current collector substrate. Each evaporation source is equipped with an independent power adjustment module and a wire feeding control module, which are used to independently adjust the heating power of a single evaporation source and the amount of metal wire fed.

6. The preparation method according to claim 4 or 5, characterized in that, The transmission speed of the current collector substrate is 2~15m / min; And / or, the transmission speed of the current collector substrate varies continuously, and the rate of change between any two adjacent speeds is 20-60%.

7. The preparation method according to any one of claims 4-6, characterized in that, The bias voltage applied to the current collector substrate is 250~600V.

8. The preparation method according to any one of claims 4-7, characterized in that, The current collector substrate is a pretreated current collector substrate, and the pretreatment steps include sequential cleaning and plasma activation.

9. The preparation method according to any one of claims 4-8, characterized in that, The preparation method includes the following steps: (1) Provide a current collector substrate; the current collector substrate has a thickness of 5~100μm, a width of 500~1600mm, and a surface roughness Ra≤0.2μm; The current collector substrate is ultrasonically cleaned with a power of 300-500W for 5-10 minutes; after cleaning, it is kept at 60-80℃ and a vacuum degree <1×10⁻⁶. -2 Dry under Pa conditions for 15-20 minutes; The dried current collector substrate is subjected to plasma activation for 3-10 seconds to obtain a pretreated current collector substrate; wherein, during the plasma activation process, the plasma includes argon plasma, the plasma flow rate is 20-30 sccm, the plasma power is 300-600W, and the distance between the plasma source and the surface of the current collector substrate is 5-8mm. (2) Place the pretreated current collector substrate on the unwinding device of the vapor deposition machine and put the metal wire into the evaporation source of the vapor deposition machine; The vapor deposition chamber was evacuated to a vacuum level of 5 × 10⁻⁶. -3 ~9.9×10 -3 Pa; Turn on the evaporation source and heat the metal wire until it vaporizes to form metal vapor. After the vapor deposition process parameters stabilize, turn on the unwinding device to deposit the metal vapor on at least one side of the current collector substrate. At the same time, control the transmission speed and bias value of the current collector substrate so that the thickness of the metal coating is distributed in a stepped manner along the plane to form a metal coating of a preset thickness. The transmission speed of the current collector substrate is 2~15m / min, and the transmission speed is continuously varied, with a change rate of 20~60% between any two adjacent speeds; the bias voltage is 250~600V; the heating power percentage of the evaporation source is 80~95%; and the wire feeding rate of the metal wire is 200~400mm / min. The current collector is cooled to room temperature by a cooling roller at a temperature of -20~-25℃ and then cooled and shaped to obtain a functional current collector.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a functional current collector as described in any one of claims 1-3.

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