Anti-fatigue Cu-Zr composition gradient alloy film and preparation method and application thereof

Abstract

The present application relates to the technical field of battery current collector, in particular to an anti-fatigue Cu-Zr composition gradient alloy film and a preparation method and application thereof. The anti-fatigue Cu-Zr composition gradient alloy film is made of a substrate and two gradient films, the two gradient films are symmetrically deposited on two sides of the substrate, and any gradient film is sequentially stacked by a surface layer, an intermediate layer, a transition layer and a bottom layer from the surface to the substrate in the thickness direction. The anti-fatigue Cu-Zr composition gradient alloy film is prepared by a magnetron sputtering co-sputtering deposition process, the abnormal grain growth is controlled, the fatigue crack initiation is delayed and the fatigue crack propagation is inhibited, the fatigue performance of the nanocrystalline metal film is improved, the initiation and propagation of the fatigue crack are effectively inhibited, and thus the fatigue life of the Cu-Zr composition gradient alloy film is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of battery current collector technology, specifically to a fatigue-resistant Cu-Zr composition gradient alloy thin film, its preparation method, and its application. Background Technology

[0002] In recent years, composite current collectors employing a "metal / polymer film / metal" sandwich structure have been considered one of the key technological pathways to overcome the energy density bottleneck of lithium-ion and solid-state batteries. This composite structure combines the flexibility of polymer materials with the high conductivity of metal materials, while also offering cost-effectiveness and potential safety advantages. Studies have shown that composite current collectors can significantly reduce the mass of the current collector (by 50% to 80% compared to traditional metal foils), thereby increasing the specific energy density of the battery by 5% to 10%.

[0003] However, during battery charge-discharge cycles, the current collector is subjected to repeated mechanical loads. Due to the significant modulus difference between the metal film and the polymer matrix, this sandwich structure is prone to fatigue failure under cyclic loading. Fatigue failure of the current collector will severely impair the battery's electrochemical performance and cycle life, and may even pose safety hazards. Therefore, developing composite current collector metal films with excellent fatigue resistance is crucial.

[0004] Traditional nanocrystalline metal films typically exhibit poor fatigue performance due to their insufficient resistance to fatigue crack initiation and propagation caused by their microstructure. Cracks readily initiate in regions of abnormal grain growth and tend to propagate rapidly along grain boundaries, ultimately leading to the failure of the nanocrystalline metal film. Effectively suppressing abnormal grain growth, delaying crack initiation, and hindering crack propagation could significantly improve the fatigue resistance of nanocrystalline metal films, thereby enhancing the long-term service stability of composite current collectors.

[0005] Alloying is a common strategy for improving the fatigue resistance of metallic materials. By introducing alloying elements, the microstructural stability of nanocrystalline materials can be effectively enhanced, and grain growth under cyclic loading can be suppressed, thereby avoiding strain localization and improving resistance to fatigue crack initiation. However, alloying is usually accompanied by further refinement of nanocrystalline grain size, leading to a significant decrease in dislocation storage capacity within the grains and near loss of work hardening ability, thus reducing the ductility of alloyed nanocrystalline materials. This characteristic severely weakens the ability of alloyed nanocrystalline materials to resist fatigue crack propagation, making it extremely easy for cracks to propagate rapidly along grain boundaries once they initiate. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a fatigue-resistant Cu-Zr compositional gradient alloy thin film, its preparation method, and its applications. Based on a magnetron co-sputtering deposition process, this invention achieves gradient control of the thickness ratio and spatial concentration distribution of Zr in each layer (pure Cu, Cu-1Zr alloy, Cu-3Zr alloy, and Cu-7Zr alloy) by controlling the sputtering time and Zr target sputtering power. This successfully constructs a multilayer structure exhibiting microstructure and phase changes from the surface to the substrate. This multilayer structure effectively suppresses abnormal grain growth during fatigue, enhances resistance to fatigue crack initiation and propagation, significantly improves the fatigue performance of the thin film, and thus substantially extends the service life of the composite current collector.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first objective of this invention is to provide a fatigue-resistant Cu-Zr composition gradient alloy thin film. This film comprises a substrate and two gradient films, which are symmetrically deposited on both sides of the substrate. Each gradient film, along its thickness direction from the surface to the substrate, is composed of a surface layer, an intermediate layer, a transition layer, and a bottom layer, sequentially stacked. The surface layer is a Cu-7Zr alloy layer with a Zr content of 7 at.% to 7.5 at.% and a thickness of 50 nm to 80 nm. The intermediate layer is a Cu-3Zr alloy layer with a Zr content of 3 at.% to 3 at.% The first layer is a Cu-1Zr alloy layer with a Zr content of 1 at.% to 1.2 at.% and a thickness of 200 nm to 350 nm; the second layer is a pure copper layer with a thickness of 650 nm to 850 nm; the total thickness of any gradient film is 1200 nm to 1250 nm; the Cu-7Zr alloy layer, Cu-3Zr alloy layer and Cu-1Zr alloy layer are all composed of Cu-Zr grains, and the Cu-Zr grain size increases sequentially from the surface to the substrate, forming a grain size gradient.

[0009] Preferably, in any gradient film, the surface layer is a Cu-7Zr alloy layer with a Zr content of 7 at.% and a thickness of 50 nm or 80 nm; the intermediate layer is a Cu-3Zr alloy layer with a Zr content of 3 at.% and a thickness of 100 nm or 120 nm; and the transition layer is a Cu-1Zr alloy layer with a Zr content of 1 at.% and a thickness of 200 nm or 350 nm.

[0010] Preferably, in any gradient film, the thickness ratio of the pure Cu layer to the gradient film is 52~68:100; the thickness ratio of the Cu-1Zr alloy layer to the gradient film is 16~28:100; the thickness ratio of the Cu-3Zr alloy layer to the gradient film is 8~10:100; and the thickness ratio of the Cu-7Zr alloy layer to the gradient film is 4~6:100.

[0011] Preferably, in any gradient film, there is a change in structure and phase from the surface to the substrate:

[0012] The Cu-7Zr alloy layer exhibits an amorphous / crystalline dual-phase structure; the Cu-3Zr alloy layer and the Cu-1Zr alloy layer both have Zr distributed at the grain boundaries of Cu grains; the pure Cu layer consists of Cu grains.

[0013] Preferably, in any gradient film, from the surface to the substrate, the grain size of the Cu-7Zr alloy layer is 13.9nm~15.5nm, the grain size of the Cu-3Zr alloy layer is 25.5nm~26.7nm, and the grain size of the Cu-1Zr alloy layer is 34.1nm~35.5nm.

[0014] The second objective of this invention is to provide a method for preparing the aforementioned fatigue-resistant Cu-Zr composition gradient alloy thin film, wherein gradient films are symmetrically deposited on both sides of a substrate, and the deposition methods for the two gradient films are identical, comprising the following steps:

[0015] In a vacuum environment, a pure Cu layer is first deposited on the substrate using DC magnetron sputtering. Then, a transition layer, an intermediate layer, and a surface layer are sequentially co-sputtered onto the pure Cu layer according to the Zr content. After co-sputtering deposition, the substrate is cooled to room temperature to obtain a fatigue-resistant Cu-Zr composition gradient alloy thin film.

[0016] Preferably, the substrate rotation speed is 10 r / min to 15 r / min, the deposition gas pressure is 0.5 Pa, and the deposition temperature is room temperature. During sputtering, whether co-sputtering or sputtering alone, the gas pressure is kept constant; the rotation speed is kept constant during magnetron sputtering to ensure uniform deposition.

[0017] Preferably, during the deposition of a pure Cu layer, the Cu target sputtering power is 200W, the sputtering rate is 0.3nm / s, and the sputtering time is 2167s~2884s.

[0018] Preferably, during the deposition of the transition layer, intermediate layer, and surface layer, the sputtering power of the Cu target is 200W, and the sputtering conditions of the Zr target are as follows: for the Cu-7Zr alloy layer, the sputtering power is 84W, the sputtering rate is 0.14nm / s, and the sputtering time is 114s~182s; for the Cu-3Zr alloy layer, the sputtering power is 36W, the sputtering rate is 0.06nm / s, and the sputtering time is 278s~334s; and for the Cu-1Zr alloy layer, the sputtering power is 12W, the sputtering rate is 0.102nm / s, and the sputtering time is 625s~1094s.

[0019] Preferably, the substrate is selected from a flexible substrate, more preferably a polyimide film, polypropylene or polyethylene terephthalate.

[0020] A third objective of this invention is to provide the application of the fatigue-resistant Cu-Zr composition gradient alloy thin film in the preparation of composite current collectors.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention provides a fatigue-resistant Cu-Zr composition gradient alloy thin film, which is made of a substrate and two gradient films. The two gradient films are symmetrically deposited on both sides of the substrate. Each gradient film is formed by sequentially stacking a surface layer, an intermediate layer, a transition layer, and a bottom layer along the thickness direction from the surface to the substrate. The surface layer is a Cu-7Zr alloy layer with a Zr content of 7 at.% to 7.5 at.% and a thickness of 50 nm to 80 nm. The intermediate layer is a Cu-3Zr alloy layer with a Zr content of 3 at.% to 3.5 at.%. The first layer consists of a Cu-1Zr alloy layer with a Zr content of 1 at.% to 1.2 at.% and a thickness of 200 nm to 350 nm; the second layer is a pure copper layer with a thickness of 650 nm to 850 nm; the total thickness of any gradient film is 1200 nm to 1250 nm; the Cu-7Zr alloy layer, Cu-3Zr alloy layer, and Cu-1Zr alloy layer are all composed of Cu-Zr grains, and the Cu-Zr grain size increases sequentially from the surface to the substrate, forming a grain size gradient. This invention, through compositional and thickness gradient design, promotes the formation of grain size and phase gradient distributions in the fatigue-resistant Cu-Zr compositional gradient alloy film from the surface to the substrate. The unique grain size and phase gradient distributions result in a gradient distribution of plastic strain amplitude under cyclic loading, thereby avoiding strain localization, which is fundamentally different from homogeneous materials with randomly distributed strain. The crystalline / amorphous dual-phase layer on the surface enhances resistance to fatigue crack initiation, while the large-grained pure Cu layer at the bottom improves the fatigue crack propagation capability of the fatigue-resistant Cu-Zr composition gradient alloy film, resulting in excellent fatigue resistance. Compared to Cu films, the fatigue life of the fatigue-resistant Cu-Zr composition gradient alloy film of this invention is improved by more than 200%.

[0023] 2. This invention also provides a method for preparing fatigue-resistant Cu-Zr compositional gradient alloy thin films. The method employs magnetron sputtering dual-target co-sputtering deposition technology. By optimizing key parameters such as sputtering power, gas pressure, and substrate temperature, the composition of the thin film is precisely controllable, and the structure is dense and uniform. The substrate surface undergoes plasma cleaning and ion etching pretreatment to ensure the bonding strength at the film / substrate interface. During deposition, the substrate rotates at a constant speed of 10 r / min to achieve gradient distribution of elemental components and directional control of the microstructure. After deposition, the thin film is naturally cooled in a high-vacuum environment to minimize thermal stress and suppress structural defects. Attached Figure Description

[0024] Figure 1 The diagram shows the structure of the fatigue-resistant Cu-Zr composition gradient alloy thin film of Examples 1-2, the Cu thin film of Comparative Example 1, and the Cu-Zr alloy thin film of Comparative Example 2; wherein, (a) is Example 1, (b) is Example 2, (c) is Comparative Example 1, and (d) is Comparative Example 2.

[0025] Figure 2 The images show TEM cross-sectional photographs and grain size distribution diagrams of the fatigue-resistant Cu-Zr composition gradient alloy thin films of Examples 1 and 2; wherein, (a) is a TEM cross-sectional photograph of the fatigue-resistant Cu-Zr composition gradient alloy thin film of Example 1, (b) is a grain size distribution diagram of the fatigue-resistant Cu-Zr composition gradient alloy thin film of Example 1, (c) is a TEM cross-sectional photograph of the fatigue-resistant Cu-Zr composition gradient alloy thin film of Example 2, and (d) is a grain size distribution diagram of the fatigue-resistant Cu-Zr composition gradient alloy thin film of Example 2.

[0026] Figure 3 The images shown are STEM images, energy dispersive spectroscopy (EDS) images, HRTEM images of the surface Cu-7Zr layer, and graphs showing the change in hardness of the homogeneous fatigue-resistant Cu-Zr composition gradient alloy film with Zr content, as well as the changes in hardness of the film. In particular, (a) is a STEM image, (b) is an EDS image, (c) is an HRTEM image of the surface Cu-7Zr layer, the inset in (c) is a magnified view, and (d) is a graph showing the change in hardness of the homogeneous fatigue-resistant Cu-Zr composition gradient alloy film with Zr content.

[0027] Figure 4 The fatigue-resistance curves are for the fatigue-resistant Cu-Zr composition gradient alloy thin films of Examples 1-2, the Cu thin film of Comparative Example 1, and the Cu-Zr alloy thin film of Comparative Example 2. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be noted that the technical terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased on the market or prepared by existing methods.

[0029] A fatigue-resistant Cu-Zr composition gradient alloy thin film is made of a substrate and two gradient films, each with a total thickness of 1200 nm to 1250 nm. The gradient films include a surface layer, an intermediate layer, a transition layer, and a pure Cu layer, all with gradient Zr content. From the surface to the substrate, the microstructure and phase composition of the fatigue-resistant Cu-Zr composition gradient alloy thin film are, in sequence, an amorphous / crystalline dual-phase structure, Zr distributed at Cu grain boundaries, and Cu grains. Cu and Zr exhibit excellent amorphous formation capabilities, resulting in an amorphous-encapsulated crystalline dual-phase structure in the surface Cu-7Zr layer. As the Zr content decreases, Zr tends to segregate at grain boundaries, stabilizing and pinning these boundaries and inhibiting fatigue-induced grain growth.

[0030] In some embodiments, in any gradient film of the fatigue-resistant Cu-Zr composition gradient alloy thin film, the Zr element content from the substrate to the surface is 0 at.%, 1 at.%, 3 at.%, and 7 at.%, respectively, and the thicknesses are 850 nm, 200 nm, 100 nm, and 50 nm, respectively, with the out-of-plane grain size decreasing sequentially.

[0031] In some embodiments, in any gradient film of the fatigue-resistant Cu-Zr composition gradient alloy thin film, the Zr element content from the substrate to the surface is 0 at.%, 1 at.%, 3 at.%, and 7 at.%, respectively, and the thicknesses are 650 nm, 350 nm, 120 nm, and 80 nm, respectively, with the out-of-plane grain size decreasing sequentially.

[0032] The fatigue-resistant Cu-Zr composition gradient alloy thin film of this invention forms a grain size gradient and a phase distribution gradient from the surface to the substrate. Hardness and strength gradually decrease from the surface to the substrate. Under the same applied strain amplitude, the surface layer experiences a smaller plastic strain amplitude, inhibiting cyclic plastic accumulation and delaying surface crack initiation. Under cyclic loading, the gradient grain structure can suppress abnormal grain growth, reduce the inhomogeneity of plastic deformation, and improve crack initiation resistance. Furthermore, during the propagation of fatigue cracks initiated on the surface into the film, the gradient structure's lower layer, with its larger grain size and plastic deformation capacity, can effectively passivate crack tips and inhibit crack propagation. This unique Cu-Zr composition gradient design enables the alloy thin film to exhibit excellent fatigue resistance.

[0033] Compared to Cu thin films, the fatigue life of the fatigue-resistant Cu-Zr composition gradient alloy thin film of the present invention is improved by more than 200%.

[0034] Correspondingly, the present invention also provides a method for preparing fatigue-resistant Cu-Zr composition gradient alloy thin films, comprising the following steps:

[0035] In a vacuum environment, a gradient film is simultaneously co-sputtered on both sides of the substrate using a DC magnetron sputtering process. During the preparation of each layer of the gradient film, the deposition power of the Zr target is set according to the designed alloy composition, and the deposition time of each layer is also set differently according to the designed layer thickness, until the set number of layers is reached and cooled to room temperature to obtain a fatigue-resistant Cu-Zr composition gradient alloy thin film.

[0036] First, the substrate needs to be cleaned and dried. Then, the treated substrate is etched. Next, the target is pre-sputtered for a preset time to remove the adsorbed substances on the target surface. Finally, sputtering deposition is performed on the etched and cleaned substrate.

[0037] In some embodiments, the substrate etching and pre-sputtering methods are as follows:

[0038] The cleaned polyimide substrate was fixed on a base plate and placed into the coating chamber. A Cu target and a Zr target were placed on each side of the substrate inside the chamber, symmetrically positioned about the substrate. Then, the back vacuum of the chamber was evacuated to 4.0 × 10⁻⁶. -4 Pa, using Ar + Ion etching was used to remove impurities from the substrate surface. The etching power was 200W, the argon gas pressure was 0.5Pa, and the etching time was 5min.

[0039] Then, pre-sputtering is performed. Before pre-sputtering, argon gas is introduced for 30 seconds at a flow rate of 60 sccm. Then, pre-sputtering is performed for 30 seconds to remove adsorbed substances from the surface of the target material.

[0040] During the actual sputtering, the same process was used to deposit the same layer on both sides of the polyimide substrate simultaneously. The process used on one side is described below: a pure Cu layer was deposited by DC sputtering with a Cu target, followed by a Cu-Zr alloy layer deposited by co-sputtering with a DC Cu target and a Zr target. The sputtering power of the Cu target was 200W, the sputtering power of the Zr target was 12W~84W, the deposition pressure was 0.5Pa, the substrate rotation speed was fixed at 10r / min during the alternating sputtering deposition process, the sputtering rate of the Cu target was 0.3nm / s, the sputtering time of the pure Cu layer was 2167s~2884s, the sputtering rate of the Zr target was 0.02nm / s~0.14nm / s, and the sputtering time of the Cu-Zr alloy layer was 114s~1094s.

[0041] This invention prepares fatigue-resistant Cu-Zr composition gradient alloy thin films using a magnetron sputtering co-sputtering deposition process. This preparation method is simple, cost-effective, and easy to scale up, providing a high-performance metal thin film material solution for composite current collectors. It can effectively solve the fatigue problem of metal thin films in the prior art and promote the development and application of composite current collectors.

[0042] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will describe it in detail with reference to specific embodiments:

[0043] Example 1

[0044] A method for preparing a fatigue-resistant Cu-Zr composition gradient alloy thin film, wherein the target specifications, relative positions of the target and the substrate, and sputtering processes are completely identical on both sides of the polyimide substrate. The following describes only the process used on one side, including the following steps:

[0045] S1. Place the polyimide matrix in anhydrous ethanol and ultrasonically clean it for 15 minutes, then quickly dry it to ensure that the surface of the polyimide matrix is ​​clean and free of impurities.

[0046] S2. Fix the cleaned polyimide substrate onto the base plate and place it into the coating chamber. Then, evacuate the back vacuum to 4.0 × 10⁻⁶. -4 Etching begins below Pa to remove impurities from the surface of the polyimide substrate. The etching power is 200W, the etching pressure is 0.5Pa, and the time is 5min to obtain the pretreated substrate.

[0047] S3. Deposit gradient films using DC magnetron sputtering co-sputtering:

[0048] After argon gas is introduced into the coating chamber for 30 seconds to reach the working pressure, the Cu target and Zr target are pre-sputtered for 30 seconds at room temperature to remove adsorbed impurities on the surface of the Cu target and Zr target; wherein the argon gas flow rate is 60 sccm and the gas pressure is 0.5 Pa.

[0049] First, a pure Cu layer was deposited using a high-purity Cu target (99.999 wt.%) with a deposition power of 200 W, a sputtering rate of 0.3 nm / s, and a sputtering time of 2884 s, resulting in a pure Cu layer thickness of 850 nm. Subsequently, a transition layer, an intermediate layer, and a surface layer were sequentially co-sputtered onto the pure Cu layer using a high-purity Cu target and a high-purity Zr target (99.995 wt.%). The Zr content increased gradually from the substrate to the surface, with the Zr content in the transition layer, intermediate layer, and surface layer being 1 at.%, 3 at.%, and 7 at.%, respectively.

[0050] During the Cu-Zr alloy layer deposition process, the sputtering power of the Cu target was always maintained at 200W, and the sputtering power of the Zr target was set to 12W, 36W and 84W from the substrate to the surface, respectively. The sputtering rates were 0.02nm / s, 0.06nm / s and 0.14nm / s, respectively, and the sputtering times were 625s, 278s and 114s, respectively. The thickness of the Cu-1Zr alloy layer was 200nm, the thickness of the Cu-3Zr alloy layer was 100nm, the thickness of the Cu-7Zr alloy layer was 50nm, and the total sputtering time was 3901s.

[0051] After sputtering, the film was naturally cooled to room temperature in the vacuum coating chamber for 1 hour and then removed to obtain a gradient film with a total thickness of 1248 nm. The same process was used on the other side of the polyimide substrate to obtain the same gradient film, and finally, an anti-fatigue Cu-Zr composition gradient alloy thin film was obtained.

[0052] The microstructure of the prepared fatigue-resistant Cu-Zr composition gradient alloy thin film was characterized, specifically as follows: Figure 1 As shown in Figure (a), the fatigue-resistant Cu-Zr composition gradient alloy film exhibits a monotonically increasing grain size gradient from the surface to the substrate along the thickness direction, and its variation trend is completely consistent with the thickness distribution of each layer. Among them, in the Cu-7Zr alloy layer, the grains exhibit a fibrous morphology, and the grain boundaries have lost their sharp characteristics, instead showing a continuously distributed network amorphous phase; this network amorphous phase separates the grains from each other, forming a significant amorphous / crystalline dual-phase structure; as the Zr content decreases, the grains in the Cu-3Zr alloy layer, Cu-1Zr alloy layer, and pure Cu layer exhibit a typical columnar crystal structure. From the surface to the substrate, the microstructure and phases of the fatigue-resistant Cu-Zr composition gradient alloy film are, in order: amorphous / crystalline dual-phase structure, Zr distributed at Cu grain boundaries, and Cu grains.

[0053] Example 2

[0054] A method for preparing a fatigue-resistant Cu-Zr composition gradient alloy thin film, wherein the target specifications, relative positions of the target and the substrate, and sputtering processes are completely identical on both sides of the polyimide substrate. The following describes only the process used on one side, including the following steps:

[0055] Step 1: Place the polyimide matrix in anhydrous ethanol and ultrasonically clean it for 15 minutes, then quickly dry it to ensure that the surface of the polyimide matrix is ​​clean and free of impurities.

[0056] Step 2: Fix the cleaned polyimide substrate onto the base plate and place it into the coating chamber. Then, evacuate the back vacuum to 4.0 × 10⁻⁶. -4Etching begins below Pa to remove impurities from the surface of the polyimide substrate. The etching power is 200W, the etching pressure is 0.5Pa, and the time is 5min to obtain the pretreated substrate.

[0057] Step 3: Deposit gradient films using DC magnetron sputtering co-sputtering:

[0058] After argon gas is introduced into the coating chamber for 30 seconds to reach the working pressure, the Cu target and Zr target are pre-sputtered for 30 seconds at room temperature to remove adsorbed impurities on the surface of the Cu target and Zr target; wherein the argon gas flow rate is 60 sccm and the gas pressure is 0.5 Pa.

[0059] First, a pure Cu layer was deposited using a high-purity Cu target (99.999 wt.%) with a deposition power of 200 W, a sputtering rate of 0.3 nm / s, and a sputtering time of 2167 s, resulting in a pure Cu layer thickness of 650 nm. Subsequently, a transition layer, an intermediate layer, and a surface layer were sequentially co-sputtered onto the pure Cu layer using a high-purity Cu target and a high-purity Zr target (99.995 wt.%). The Zr content increased gradually from the substrate to the surface, with the Zr content in the transition layer, intermediate layer, and surface layer being 1 at.%, 3 at.%, and 7 at.%, respectively.

[0060] During the Cu-Zr alloy layer deposition process, the sputtering power of the Cu target was always maintained at 200W, and the sputtering power of the Zr target was set to 12W, 36W and 84W from the substrate to the surface, respectively. The sputtering rates were 0.02nm / s, 0.06nm / s and 0.14nm / s, respectively, and the sputtering times were 1094s, 334s and 182s, respectively. The thickness of the Cu-1Zr alloy layer was 350nm, the thickness of the Cu-3Zr alloy layer was 120nm, the thickness of the Cu-7Zr alloy layer was 80nm, and the total sputtering time was 3777s.

[0061] After sputtering, the film was naturally cooled to room temperature in the vacuum coating chamber for 1 hour and then removed to obtain a gradient film with a total thickness of 1202 nm. The same process was used on the other side of the polyimide substrate to obtain the same gradient film, and finally, an anti-fatigue Cu-Zr composition gradient alloy thin film was obtained.

[0062] The microstructure of the prepared fatigue-resistant Cu-Zr composition gradient alloy thin film was characterized, specifically as follows: Figure 1As shown in Figure (b), the fatigue-resistant Cu-Zr compositional gradient alloy thin film exhibits a gradually increasing grain size gradient and phase gradient along the thickness direction from the surface to the substrate. The grain size increases sequentially from the surface to the substrate, consistent with the layer thickness variation trend. The Cu-7Zr layer grains exhibit a fibrous structure, and the grain boundaries are no longer sharp. The grain boundary structure has been replaced by a network of amorphous phases that separate the grains, forming an amorphous / crystalline dual-phase structure. The Cu-3Zr layer, Cu-1Zr layer, and pure Cu layer grains exhibit a columnar crystal structure. From the surface to the substrate, the film structure and phases are, in sequence, an amorphous / crystalline dual-phase structure, Zr distributed at Cu grain boundaries, and Cu grains.

[0063] Example 3

[0064] A method for preparing a fatigue-resistant Cu-Zr composition gradient alloy thin film, wherein the target specifications, relative positions of the target and the substrate, and sputtering processes are completely identical on both sides of the polyimide substrate. The following describes only the process used on one side, including the following steps:

[0065] S1. Place the polyimide matrix in anhydrous ethanol and ultrasonically clean it for 15 minutes, then quickly dry it to ensure that the surface of the polyimide matrix is ​​clean and free of impurities.

[0066] S2. Fix the cleaned polyimide substrate onto the base plate and place it into the coating chamber. Then, evacuate the back vacuum to 4.0 × 10⁻⁶. -4 Etching begins below Pa to remove impurities from the surface of the polyimide substrate. The etching power is 200W, the etching pressure is 0.5Pa, and the time is 5min to obtain the pretreated substrate.

[0067] S3. Deposit gradient films using DC magnetron sputtering co-sputtering:

[0068] After argon gas is introduced into the coating chamber for 30 seconds to reach the working pressure, the Cu target and Zr target are pre-sputtered for 30 seconds at room temperature to remove adsorbed impurities on the surface of the Cu target and Zr target; wherein the argon gas flow rate is 60 sccm and the gas pressure is 0.5 Pa.

[0069] First, a pure Cu layer was deposited using a high-purity Cu target (purity 99.999 wt.%) with a deposition power of 200 W, a sputtering rate of 0.3 nm / s, and a sputtering time of 2884 s, resulting in a pure Cu layer thickness of 850 nm. Subsequently, a transition layer, an intermediate layer, and a surface layer were sequentially co-sputtered onto the pure Cu layer using a high-purity Cu target and a high-purity Zr target (purity 99.995 wt.%). The Zr content increased gradually from the substrate to the surface, with Zr contents of 1.2 at.%, 3.2 at.%, and 7.5 at.% in the transition layer, intermediate layer, and surface layer, respectively.

[0070] During the Cu-Zr alloy layer deposition process, the sputtering power of the Cu target was always maintained at 200W, and the sputtering power of the Zr target was set to 12W, 36W and 84W from the substrate to the surface, respectively. The sputtering rates were 0.02nm / s, 0.06nm / s and 0.14nm / s, respectively, and the sputtering times were 860s, 306s and 148s, respectively. The thickness of the Cu-1Zr alloy layer was 275nm, the thickness of the Cu-3Zr alloy layer was 110nm, the thickness of the Cu-7Zr alloy layer was 65nm, and the total sputtering time was 3901s.

[0071] After sputtering, the film was naturally cooled to room temperature in the vacuum coating chamber for 1 hour and then removed to obtain a gradient film with a total thickness of 1248 nm. The same process was used on the other side of the polyimide substrate to obtain the same gradient film, and finally, an anti-fatigue Cu-Zr composition gradient alloy thin film was obtained.

[0072] Comparative Example 1

[0073] A method for preparing a Cu thin film is the same as that in Example 1, except that Zr is not added. The same process is used to deposit the film on both sides of a polyimide substrate. The film deposition process is as follows: deposition rate of 0.3 nm / s, deposition time of 4000 s, and film thickness of 1207 nm, resulting in a Cu thin film. (Specific details are as follows...) Figure 1 As shown in Figure (c).

[0074] Comparative Example 2

[0075] A method for preparing a Cu-Zr alloy thin film is the same as that in Example 1, except that in step S3, the Zr element is kept constant at 1 at.%, with no gradient change. The same process is used to deposit the thin film on both sides of the polyimide substrate. The deposition process is as follows: the power of the Cu target and the Zr target are 200W and 12W, respectively; the deposition rates are 0.3 nm / s and 0.012 nm / s, respectively; the sputtering time is 3846 s; and the film thickness is 1200 nm, resulting in a Cu-Zr alloy thin film. Specifically, as shown below... Figure 1 As shown in Figure (d) of the document.

[0076] Depend on Figure 2 The results show that the fatigue-resistant Cu-Zr composition gradient alloy film exhibits significant differences in microstructure characteristics between layers in the thickness direction. Statistical analysis of the grain size of each layer reveals that the grain size of the film gradually decreases from the surface to the substrate.

[0077] Figure 3 Results (a) and (b) demonstrate the successful preparation of the fatigue-resistant Cu-Zr composition gradient alloy thin film of the present invention, and form a continuous grain size gradient and phase gradient; Figure 3Figure (c) shows the typical microstructure of the crystalline / amorphous dual-phase structure in the Cu-7Zr layer; Figure 3 Figure (d) shows the change in hardness of the fatigue-resistant Cu-Zr compositional gradient alloy film with Zr content, indicating a gradually decreasing hardness gradient from the surface to the substrate. In homogeneous materials, random hardness distribution often leads to stress concentration under cyclic loading, easily causing localized early fatigue failure. However, the gradually decreasing hardness gradient from the surface to the substrate results in a gradient distribution of stress under cyclic loading, thus avoiding premature strain localization. The hard layer on the surface can improve the film's resistance to crack initiation, while the soft layer inside can improve the film's resistance to crack propagation, thereby effectively improving the film's fatigue resistance.

[0078] Fatigue testing was conducted on a micro-force tensile tester (MTS Tytron 250) equipped with an in-situ resistance testing device, using a constant total strain control mode. Tension-tension fatigue loads were applied with a sinusoidal waveform at a frequency of 1 Hz. To ensure data reliability, each specimen was tested independently at least three times under the same conditions. The plastic strain amplitude was 0.8%, and the minimum strain was set to 0.2% to avoid buckling of the specimens. Figure 4 The results show that, under tensile fatigue loading conditions with a strain amplitude of 0.8%, the fatigue-resistant Cu-Zr composition gradient alloy film of the present invention exhibits excellent electrical stability and fatigue resistance under cyclic loading.

[0079] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

Claims

1. A fatigue-resistant Cu-Zr composition gradient alloy thin film, characterized in that, The fatigue-resistant Cu-Zr composition gradient alloy thin film is made of a substrate and two gradient films. The two gradient films are symmetrically deposited on both sides of the substrate. Each gradient film is formed by sequentially stacking a surface layer, an intermediate layer, a transition layer and a bottom layer along the thickness direction from the surface to the substrate. The surface layer is a Cu-7Zr alloy layer with a Zr content of 7 at.%~7.5 at.% and a thickness of 50nm~80nm; The intermediate layer is a Cu-3Zr alloy layer with a Zr content of 3 at.%~3.2 at.% and a thickness of 100nm~120nm; The transition layer is a Cu-1Zr alloy layer with a Zr content of 1 at.%~1.2 at.% and a thickness of 200 nm~350 nm; The bottom layer is a pure copper layer with a thickness of 650nm~850nm; The total thickness of any gradient film is 1200nm~1250nm; The Cu-7Zr alloy layer, Cu-3Zr alloy layer, and Cu-1Zr alloy layer are all composed of Cu-Zr grains, and the Cu-Zr grain size increases sequentially from the surface to the substrate, forming a grain size gradient. In any gradient film, the thickness ratio of the pure Cu layer to the gradient film is 52~68:100; The thickness ratio of the Cu-1Zr alloy layer to the gradient film is 16~28:100; The thickness ratio of the Cu-3Zr alloy layer to the gradient film is 8~10:100; The thickness ratio of the Cu-7Zr alloy layer to the gradient film is 4~6:100; In any gradient film, there are changes in structure and phase from the surface to the substrate: The Cu-7Zr alloy layer exhibits an amorphous / crystalline dual-phase structure; Both the Cu-3Zr alloy layer and the Cu-1Zr alloy layer have Zr distributed at the grain boundaries of Cu grains. The pure Cu layer consists of Cu grains.

2. The fatigue-resistant Cu-Zr composition gradient alloy thin film according to claim 1, characterized in that, In any gradient film, the surface layer is a Cu-7Zr alloy layer with a Zr content of 7 at.% and a thickness of 50 nm or 80 nm; The intermediate layer is a Cu-3Zr alloy layer with a Zr content of 3 at.% and a thickness of 100 nm or 120 nm. The transition layer is a Cu-1Zr alloy layer with a Zr content of 1 at.% and a thickness of 200 nm or 350 nm.

3. The fatigue-resistant Cu-Zr composition gradient alloy thin film according to claim 1, characterized in that, In any gradient film, from the surface to the substrate, the grain size of the Cu-7Zr alloy layer is 13.9 nm to 15.5 nm, the grain size of the Cu-3Zr alloy layer is 25.5 nm to 26.7 nm, and the grain size of the Cu-1Zr alloy layer is 34.1 nm to 35.5 nm.

4. A method for preparing an anti-fatigue Cu-Zr composition gradient alloy thin film according to any one of claims 1 to 3, characterized in that, A gradient film is symmetrically deposited on both sides of the substrate, and the deposition methods for the two gradient films are the same, including the following steps: In a vacuum environment, a pure Cu layer is first deposited on the substrate using DC magnetron sputtering. Then, a transition layer, an intermediate layer, and a surface layer are sequentially co-sputtered onto the pure Cu layer according to the Zr content. After co-sputtering deposition, the substrate is cooled to room temperature to obtain a fatigue-resistant Cu-Zr composition gradient alloy thin film.

5. The method for preparing fatigue-resistant Cu-Zr composition gradient alloy thin films according to claim 4, characterized in that, The substrate rotation rate was 10 r / min to 15 r / min, the deposition pressure was 0.5 Pa, and the deposition temperature was room temperature.

6. The method for preparing fatigue-resistant Cu-Zr composition gradient alloy thin films according to claim 4, characterized in that, During the deposition of the pure Cu layer, the Cu target sputtering power was 200W, the sputtering rate was 0.3nm / s, and the sputtering time was 2167s~2884s.

7. The method for preparing fatigue-resistant Cu-Zr composition gradient alloy thin films according to claim 4, characterized in that, During the deposition of the transition layer, intermediate layer, and surface layer, the sputtering power of the Cu target was 200 W, and the sputtering conditions of the Zr target were as follows: for the Cu-7Zr alloy layer, the sputtering power was 84 W, the sputtering rate was 0.14 nm / s, and the sputtering time was 114 s to 182 s; for the Cu-3Zr alloy layer, the sputtering power was 36 W, the sputtering rate was 0.06 nm / s, and the sputtering time was 278 s to 334 s; and for the Cu-1Zr alloy layer, the sputtering power was 12 W, the sputtering rate was 0.102 nm / s, and the sputtering time was 625 s to 1094 s.

8. The application of the fatigue-resistant Cu-Zr composition gradient alloy thin film of claim 1 in the preparation of composite current collectors.

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