Composite current collector, process for preparing the same and use thereof

Abstract

The application provides a composite current collector and a preparation process and application thereof. The composite current collector comprises a base film, a first metal layer arranged on at least one side surface of the base film, and a second metal layer arranged on the surface of the first metal layer away from the base film; the second metal layer comprises n layers of large-particle metal layers and m layers of small-particle metal layers, and the large-particle metal layers and the small-particle metal layers are alternately and laminatedly arranged; in adjacent large-particle metal layers and small-particle metal layers, the average particle size of the large-particle metal layers is denoted as x, the average particle size of the small-particle metal layers is denoted as y, the difference between the average particle sizes of the adjacent large-particle metal layers and small-particle metal layers is denoted as a, and the a satisfies the following condition: a=(x-y) / x and 10%≤a≤50%. The composite current collector provided by the application has excellent mechanical properties, corrosion resistance and wear resistance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a composite current collector, its preparation process, and its application. Background Technology

[0002] The rapid development of the new energy vehicle industry has further propelled the advancement of the lithium-ion battery field. As a fundamental material in lithium-ion batteries, the performance of current collectors directly impacts the battery's performance and lifespan. Currently, composite current collectors have become a research hotspot in the battery industry due to their advantages in both safety and cost-effectiveness.

[0003] Composite current collectors have a "sandwich" structure, consisting of a base film and conductive metal layers on both sides of the base film. Composite current collectors used as the negative electrode are typically fabricated by depositing two metal layers on each side of the base film using a magnetron sputtering + electroplating process, with the outermost metal layer being copper. However, the outermost copper metal layer has relatively low hardness and its surface is easily worn, making it unsuitable for use in batteries. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a composite current collector, its preparation process, and its applications. The composite current collector provided by the present invention improves the overall mechanical properties and optimizes corrosion resistance by sequentially depositing a first metal layer and a second metal layer on the surface of a base film, and alternately stacking large-particle metal layers and small-particle metal layers within the second metal layer. Simultaneously, it enhances the hardness and wear resistance of the second metal layer.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a composite current collector, the composite current collector comprising a base film, wherein a first metal layer is disposed on at least one surface of the base film, and a second metal layer is disposed on the surface of the first metal layer away from the base film.

[0007] The material of the second metal layer includes copper metal; the second metal layer includes n large-particle metal layers and m small-particle metal layers, the large-particle metal layers and the small-particle metal layers are alternately stacked, wherein 1≤n≤8 and n is an integer (e.g., 1, 2, 3, 4, 5, 6, 7 or 8, etc.), and m and n satisfy any one of the following conditions (i) to (iii): (i)m=n+1; (ii)m=n; (iii)m=n-1 and m is not equal to 0.

[0008] In adjacent large and small particle metal layers, the average particle size of the large particle metal layer is denoted as x, and the average particle size of the small particle metal layer is denoted as y. The difference in average particle size between the adjacent large and small particle metal layers is denoted as a. a satisfies the following condition: a = (xy) / x and 10% ≤ a ≤ 50%, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, etc.

[0009] This invention provides a composite current collector with the following advantages:

[0010] (1) A first metal layer and a second metal layer are sequentially disposed on the surface of the base film. The large-particle metal layer and the small-particle metal layer alternately stacked in the second metal layer can produce a synergistic effect:

[0011] ① Interface strengthening: The alternating particle size of each sub-metal layer forms an interface between different layers. This alternating structure is conducive to the interface strengthening effect. The different particle sizes of metal particles at the interface are interwoven, which can increase the structural strength of the second metal layer and improve the overall mechanical properties of the composite current collector.

[0012] ② Optimize corrosion resistance: When the particle size of each sub-metal layer changes alternately, more barrier layers can be formed at the interface between different layers to prevent corrosive media from penetrating into the metal layer;

[0013] ③ Improve wear resistance: The alternating particle size of each sub-metal layer can give the second metal layer higher hardness and wear resistance. This is because metal particles of different sizes will squeeze and intersect each other during the deposition process to form a dense metal layer structure, thereby enhancing the hardness and wear resistance of the second metal layer.

[0014] ④ Improve safety performance: Large particle metal layers are more resilient than small particle metal layers. When alternating large and small particle metal layers are punctured, the small particle metal layer breaks first and drives the large particle metal layer to break. This not only ensures safety performance, but also allows some battery cells to retain their function during the slow fracture process of the metal layers.

[0015] (2) The present invention limits the adjacent large-particle metal layers and small-particle metal layers to satisfy the condition a=(xy) / x and 10%≤a≤50%, which can better exert the synergistic effect between the large-particle metal layers and small-particle metal layers.

[0016] In this invention, when the number of large-particle metal layers exceeds 8, the production cost will increase, and the synergistic effect between the large-particle metal layers and the small-particle metal layers will not be further improved.

[0017] In this invention, when the average particle size difference 'a' between adjacent large and small metal particles is too small, the synergistic effect between the large and small metal particles cannot be achieved, or the synergistic effect is not obvious. When the average particle size difference 'a' between adjacent large and small metal particles is too large, it will lead to uneven stress distribution within the material, easily causing stress concentration in the smaller particle area, increasing the risk of material fatigue failure; it will also lead to insufficient interfacial bonding, making it easy for microcracks or peeling to occur at the interface; and it will affect the mechanical properties of the second metal layer.

[0018] Preferably, the base film is made of a polymer.

[0019] It should be noted that the base film may or may not be conductive.

[0020] Preferably, the material of the first metal layer includes copper.

[0021] Preferably, the thickness of the first metal layer is 50-100nm, for example, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm.

[0022] Preferably, in the n-layer large particle metal layer, the average particle size of a single large particle metal layer is 100-600nm, for example, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm or 600nm.

[0023] In this invention, when the average particle size of the large metal particles is too small, the surface tension of the large metal particles is low, which reduces the adhesion between the large and small metal particles, or makes the synergistic effect between the large and small metal particles not obvious. When the average particle size of the large metal particles is too large, it will not only affect the mechanical properties of the second metal layer, such as elongation at break and tensile strength, but also reduce the density of the metal layer.

[0024] Preferably, in the m-layer small particle metal layer, the average particle size of a single layer of small particle metal layer is 50-300nm, for example, 50nm, 100nm, 150nm, 200nm, 250nm or 300nm.

[0025] In this invention, when the average particle size of the small-particle metal layer is too small, the surface tension of the small-particle metal is low, which reduces the adhesion between the small-particle metal layer, the underlayer, or the base film. In addition, if the particles are too small, a higher current is required for preparation, which will increase the risk of the product being "burned". When the average particle size of the small-particle metal layer is too large, the density of the metal layer will be reduced.

[0026] Preferably, the thickness of the n-layer large particle metal layers increases layer by layer along the direction away from the base film.

[0027] In this invention, when the thickness of the n-layer large-particle metal layer increases layer by layer along the direction away from the polymer base film, the elongation at break of the composite current collector is effectively improved.

[0028] Preferably, the thickness of the m-layer small particle metal layer decreases layer by layer along the direction away from the base film.

[0029] In this invention, the overall toughness is improved when the thickness of the m-layer small particle metal layer decreases layer by layer along the direction away from the polymer base film.

[0030] Preferably, n satisfies the following condition: 3≤n≤4, for example, n is 3 or 4.

[0031] Preferably, a base layer is further provided between the base film and the first metal layer.

[0032] Preferably, the material of the substrate layer includes a nickel-niobium alloy; the thickness of the substrate layer is 5-50 nm, for example, 5 nm, 10 nm, 15 nm, 18 nm, 20 nm, 30 nm, 40 nm or 50 nm, and more preferably 10-20 nm.

[0033] Preferably, the total thickness of the substrate layer, the first metal layer, and the second metal layer is 0.8-1.2 μm, for example, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.05 μm, 1.1 μm, 1.15 μm, or 1.2 μm.

[0034] In this invention, when the total thickness of the base layer, the first metal layer and the second metal layer is too small, the conductivity of the composite current collector is poor; while when the total thickness is too large, on the one hand, it will increase the production cost of the composite current collector, and on the other hand, it will lead to a decrease in the mechanical properties of the composite current collector.

[0035] Preferably, a passivation layer is provided on the surface of the second metal layer away from the first metal layer.

[0036] Preferably, the base film is a conductive base film or a polymer base film.

[0037] Preferably, the conductive base film comprises a polymer material.

[0038] Secondly, the present invention provides a preparation process for the composite current collector described in the first aspect, the preparation process comprising:

[0039] (1) A first metal layer is magnetron sputtered onto the surface of a polymer base film;

[0040] (2) Containing Cu 2+ The solution is an electroplating solution, and a second metal layer is electroplated on the surface of the first metal layer to obtain the composite current collector.

[0041] The second metal layer comprises n large-particle metal layers and m small-particle metal layers, wherein the large-particle metal layers and the small-particle metal layers are alternately stacked, wherein 1≤n≤8 and n is an integer, and m and n satisfy any one of the following conditions (i) to (iii): (i)m=n+1; (ii)m=n; (iii)m=n-1 and m is not equal to 0.

[0042] When electroplating adjacent large-particle metal layers and small-particle metal layers, the ion current matching value of the large-particle metal layer is less than that of the small-particle metal layer, where the ion current matching value = electroplating current density / Cu during electroplating. 2+ The concentration.

[0043] The absolute value of the difference in ion current matching values ​​between adjacent large-particle metal layers and small-particle metal layers is denoted as b, where b satisfies the following condition: 0.1 A·L / (dm²). 2 ·mol)≤b≤3A·L / (dm 2 ·mol), for example, 0.1 A·L / (dm³). 2 ·mol), 0.5A·L / (dm 2 ·mol), 0.8A·L / (dm 2 ·mol), 1A·L / (dm 2 ·mol), 1.5A·L / (dm 2 ·mol), 1.8A·L / (dm 2 ·mol), 2A·L / (dm 2 ·mol), 2.5A·L / (dm 2 ·mol), 2.8A·L / (dm 2 ·mol), 2.9A·L / (dm 2 ·mol) or 3.0 A·L / (dm 2 ·mol), etc.

[0044] In this invention, a first metal layer and a second metal layer are prepared using magnetron sputtering and electroplating processes, respectively. By adjusting the ion current matching value, the particle size of the sub-metal layers in the second metal layer can be controlled, thereby producing alternating layers of large and small sub-metal particles. By limiting the absolute range of the difference in ion current matching values ​​between adjacent sub-metal layers, the average particle size difference between adjacent sub-metal layers can satisfy a = (xy) / x and 10% ≤ a ≤ 50%.

[0045] Preferably, the specific parameters of the magnetron sputtering in step (1) include: using a copper target as the target material, and a power density of 6.0-15 W / cm². 2 The argon flow rate is 50-70 mL / min, the coating vacuum degree is 0.06-0.08 Pa, the main roller temperature is 0-20℃, and the coating time is 5-8 s. The power density is, for example, 6.0 W / cm³. 2 7.0W / cm 2 8.0W / cm 2 9.0W / cm 2 10.0W / cm 2、 11.0W / cm 2 12.0W / cm 2 13.0W / cm 2 14.0W / cm 2 Or 15.0W / cm 2 Argon flow rate, for example, is 50 mL / min, 55 mL / min, 60 mL / min, or 65 mL / min; coating vacuum degree, for example, is 0.06 Pa, 0.067 Pa, or 0.08 Pa; main roller temperature, for example, is 0℃, 1℃, 5℃, 10℃, 15℃, or 20℃; coating time, for example, is 5s, 6s, 7s, or 8s.

[0046] Preferably, the electroplating method in step (2) specifically includes: using an insoluble iridium-plated electrode as the anode, using the thin film obtained in step (1) as the cathode, and using a Cu-containing electrode... 2+ The solution is used as an electroplating solution for electroplating.

[0047] Preferably, the Cu-containing 2+ Cu in solution 2+ The concentration is 30-65 g / L, for example, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L or 65 g / L, etc.

[0048] Preferably, the Cu-containing 2+ The solution is acidic, and the Cu-containing solution... 2+ H in the solution + The concentration is 2-2.5 mol / L, for example, 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L or 2.5 mol / L, etc.

[0049] Preferably, the Cu-containing 2+ The solution also contains electroplating additives.

[0050] Preferably, the electroplating additive includes at least one of a brightener, a wetting agent, and a leveling agent.

[0051] Preferably, the brightener comprises at least one of sodium polydithiopropane sulfonate, sodium phenyl dithiopropane sulfonate, sodium N,N-dimethyldithiopropane sulfonate, and sodium 3-mercapto-1-propane sulfonate.

[0052] Preferably, the wetting agent includes at least one of polyethylene glycol, polypropylene glycol, sodium dodecyl sulfate, and polyoxyethylene ether.

[0053] Preferably, the leveling agent comprises at least one of 2-mercaptobenzimidazole, ethylene thiourea, and tetrahydrothiazole copper sulfide.

[0054] Preferably, for electroplating n large-particle metal layers and m small-particle metal layers, the ion current matching value of each layer is denoted as c, where c satisfies the following condition: 0.1 A·L / (dm 2 ·mol)≤c≤6A·L / (dm 2 (·mol). The c is, for example, 0.1 A·L / (dm). 2 ·mol), 0.5A·L / (dm 2 ·mol), 0.8A·L / (dm 2 ·mol), 1A·L / (dm 2 ·mol), 1.5A·L / (dm 2 ·mol), 1.8A·L / (dm 2 ·mol), 2A·L / (dm 2 ·mol), 2.5A·L / (dm 2 ·mol), 2.8A·L / (dm 2 ·mol), 2.9A·L / (dm 2 ·mol), 3.0 A·L / (dm 2 ·mol), 3.1A·L / (dm 2 ·mol), 3.2A·L / (dm 2 ·mol), 3.5A·L / (dm 2 ·mol), 3.8A·L / (dm 2 ·mol), 4A·L / (dm 2 ·mol), 4.2A·L / (dm 2 ·mol), 4.5A·L / (dm 2 ·mol), 4.8A·L / (dm 2 ·mol), 5A·L / (dm 2 ·mol), 5.2A·L / (dm 2 ·mol), 5.5A·L / (dm 2·mol), 5.8A·L / (dm 2 ·mol), 5.9A·L / (dm 2 ·mol) or 6.0 A·L / (dm 2 ·mol), etc.

[0055] In this invention, if the current matching value c is too small during the electroplating process, it will reduce the dispersion ability of the plating solution and may cause copper sulfate to precipitate; if the current matching value c is too large, it will be difficult to control the electroplating process and increase the risk of "burning".

[0056] Preferably, for electroplating n large-particle metal layers and m small-particle metal layers, the electroplating time for each layer is denoted as t, where t satisfies the following condition: 5s ≤ t ≤ 2000s, for example, 5s, 8s, 11s, 12s, 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 79s, 100s, 200s, 500s, 1000s, 1500s, 1800s, or 2000s, etc.

[0057] Preferably, the electroplating temperature in step (2) is 20-40℃, for example, 20℃, 22℃, 25℃, 28℃, 30℃, 32℃, 35℃, 38℃ or 40℃.

[0058] Preferably, in step (1), a base layer is magnetron sputtered on the surface of the polymer base film before the first metal layer is magnetron sputtered.

[0059] Preferably, the specific parameters for magnetron sputtering of the substrate layer include: using a nickel-niobium target as the target material, and a power density of 2-5 W / cm². 2 The argon flow rate is 70-100 mL / min, the coating vacuum degree is 0.06-0.08 Pa, the main roller temperature is 0-20℃, and the coating time is 3-5 s. The power density is, for example, 2 W / cm³. 2 3W / cm 2 4W / cm 2 Or 5W / cm 2 Argon flow rate, for example, 70 mL / min, 80 mL / min, 90 mL / min or 100 mL / min; coating vacuum degree, for example, 0.06 Pa, 0.07 Pa or 0.08 Pa; main roller temperature, for example, 0℃, 1℃, 5℃, 10℃, 15℃ or 20℃; coating time, for example, 3s, 4s or 5s.

[0060] As a preferred embodiment of the present invention, the preparation process specifically includes the following steps:

[0061] (I) Perform surface cleaning treatment on the polymer film, and then apply 70-150 W·min / m 2 (e.g., 80 W·min / m) 2 90W·min / m 2 100W·min / m 2 Or 120W·min / m 2 The polymer film was subjected to corona treatment for 3-5 seconds at a discharge level of (etc.) to obtain the pretreated polymer film.

[0062] (II) Using a nickel-niobium target as the target material, a 5-50 nm thick base layer is magnetron sputtered onto the surface of the pretreated polymer base film.

[0063] The specific parameters for magnetron sputtering of the substrate include: a power density of 2-5 W / cm². 2 The argon flow rate is 70-100 mL / min, the coating vacuum degree is 0.06-0.08 Pa, the temperature of the main roller is 0-20℃, and the coating time is 3-5 s;

[0064] (III) Using a copper target as the target material, a first metal layer with a thickness of 50-100 nm is magnetron sputtered on the surface of the substrate layer;

[0065] The specific parameters for magnetron sputtering of the first metal layer include: a power density of 6.0-15 W / cm². 2 The argon flow rate is 50-70 mL / min, the coating vacuum degree is 0.06-0.08 Pa, the temperature of the main roller is 0-20℃, and the coating time is 5-8 s;

[0066] (IV) Using an insoluble iridium-plated electrode as the anode, and the thin film obtained in step (III) as the cathode, a Cu-containing electrode is used. 2+ The solution is an electroplating solution, and electroplating is carried out at 20-40℃ to form a second metal layer on the surface of the first metal layer.

[0067] Wherein, the Cu-containing 2+ The solution contains Cu 2+ H + And electroplating additives, Cu 2+ The concentration is 30-65 g / L, H +The concentration is 2-2.5 mol / L; the electroplating additive includes at least one of brightener, wetting agent and leveling agent; the second metal layer includes n large particle metal layers and m small particle metal layers, the large particle metal layers and the small particle metal layers are alternately stacked, wherein 1≤n≤8 and n is an integer, and m and n satisfy any one of the following conditions (i) to (iii): (i)m=n+1; (ii)m=n; (iii)m=n-1 and m is not equal to 0; for electroplating n large particle metal layers and m small particle metal layers, the ion current matching value of each layer is denoted as c, and c satisfies the following condition: 0.1A·L / (dm 2 ·mol)≤c≤6A·L / (dm 2 ·mol), where the ion current matching value = electroplating current density / Cu during electroplating 2+ The concentration; for electroplating n large-particle metal layers and m small-particle metal layers, the electroplating time for each layer is denoted as t, where t satisfies the following condition: 5s ≤ t ≤ 2000s; when electroplating adjacent large-particle metal layers and small-particle metal layers, the ion current matching value of the large-particle metal layer is < the ion current matching value of the small-particle metal layer; the absolute value of the difference between the ion current matching values ​​of adjacent large-particle metal layers and small-particle metal layers is denoted as b, where b satisfies the following condition: 0.1 A·L / (dm 2 ·mol)≤b≤3A·L / (dm 2 ·mol), such that in adjacent large and small metal layers, the average particle size of the large metal layer is denoted as x, the average particle size of the small metal layer is denoted as y, and the difference in average particle size between the adjacent large and small metal layers is denoted as a, wherein a satisfies the following condition: a=(xy) / x and 10%≤a≤50%.

[0068] (V) The film obtained in step (IV) is immersed in a passivating agent for 8-12 seconds (e.g., 8 seconds, 9 seconds, 10 seconds or 11 seconds), then washed with water, and then dried at 50-70°C (e.g., 55°C, 60°C or 65°C) to obtain the composite current collector.

[0069] The passivating agent includes a chromic anhydride solution with a concentration of 0.5-3 g / L, such as 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, or 2.5 g / L.

[0070] Secondly, the present invention provides a composite current collector, which is prepared by the preparation process described in the first aspect.

[0071] Thirdly, the present invention provides an electrode sheet, wherein the electrode sheet includes the composite current collector described in the first aspect or the composite current collector prepared by the preparation process described in the second aspect.

[0072] Fourthly, the present invention provides a secondary battery, wherein the secondary battery includes the electrode sheet described in the third aspect.

[0073] In this invention, the secondary battery includes, but is not limited to, lithium secondary batteries or sodium secondary batteries.

[0074] 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.

[0075] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0076] This invention provides a composite current collector with the following advantages:

[0077] (1) A first metal layer and a second metal layer are sequentially disposed on the surface of the base film. The large-particle metal layer and the small-particle metal layer alternately stacked in the second metal layer can produce a synergistic effect:

[0078] ① Interface strengthening: The alternating particle size of each sub-metal layer forms an interface between different layers. This alternating structure is conducive to the interface strengthening effect. The different particle sizes of metal particles at the interface are interwoven, which can increase the structural strength of the second metal layer and improve the overall mechanical properties of the composite current collector.

[0079] ② Optimize corrosion resistance: When the metal grain size of each sub-metal layer changes alternately, more barrier layers can be formed at the interface between different layers to prevent corrosive media from penetrating into the base metal;

[0080] ③ Improve wear resistance: The alternating particle size of each sub-metal layer can give the second metal layer higher hardness and wear resistance. This is because metal particles of different sizes will squeeze and intersect each other during the deposition process to form a dense metal layer structure, thereby enhancing the hardness and wear resistance of the second metal layer.

[0081] ④ Improve safety performance: Large particle metal layers are more resilient than small particle metal layers. When alternating large and small particle metal layers are punctured, the small particle metal layer breaks first and drives the large particle metal layer to break. This not only ensures safety performance, but also allows some battery cells to retain their function during the slow fracture process of the metal layers.

[0082] (2) The present invention limits the adjacent large-particle metal layers and small-particle metal layers to satisfy the condition a=(xy) / x and 10%≤a≤50%, which can better exert the synergistic effect between the large-particle metal layers and small-particle metal layers. Detailed Implementation

[0083] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0084] Example 1

[0085] This embodiment provides a composite current collector, which includes a base film and a composite layer disposed on both sides of the base film. Along the direction away from the base film, the composite layer includes a base layer, a first metal layer and a second metal layer stacked sequentially, and a passivation layer is disposed on the surface of the second metal layer away from the first metal layer.

[0086] The substrate is made of nickel-niobium alloy and has a thickness of 20 nm; the first metal layer is made of copper and has a thickness of 80 nm; the second metal layer is made of copper and has a thickness of 1072 nm, so that the total thickness of the substrate, the first metal layer and the second metal layer is 1172 nm.

[0087] The second metal layer consists of four large-particle metal layers and three small-particle metal layers, which are stacked alternately. The large-particle metal layers are in contact with the first metal layer and are furthest from the first metal layer. The average particle size of each large-particle metal layer is 150 nm and the thickness is 160 nm. The average particle size of each small-particle metal layer is 120 nm and the thickness is 144 nm.

[0088] The passivation layer is made of chromium anhydride and has a thickness of 50 nm.

[0089] This embodiment also provides a preparation process for the above-mentioned composite current collector, which includes the following steps:

[0090] (1) The surface-cleaned polyethylene terephthalate polymer film is placed in a roll-to-roll corona treatment device, and the discharge rate is controlled at 90 W·min / m. 2 The discharge time is 4 seconds;

[0091] (2) The pretreated polymer film was placed in a magnetron sputtering machine, using a nickel-niobium target with a purity of 99.99% as the target material, and a power density of 2 W / cm². 2 Argon flow rate is 80 mL / min, coating vacuum degree is 0.07 Pa, main roller temperature is 20℃, coating time is 3 s, thereby sputtering a base layer on the pretreated polymer film surface;

[0092] (3) The film after sputtering the substrate layer is placed back into the magnetron sputtering equipment, using a copper target with a purity of 99.99% as the target material, and a power density of 9.0 W / cm². 2 The argon flow rate is 60 mL / min, the coating vacuum degree is 0.07 Pa, the temperature of the main roller is 10℃, and the coating time is 7 s, thereby sputtering a first metal layer on the surface of the substrate.

[0093] (4) Dissolve copper sulfate and electroplating additives in deionized water, and add sulfuric acid to prepare an electroplating solution, wherein Cu 2+ The concentration was 45 g / L, H + The concentration of the plating agent was 2 mol / L. The electroplating additives were sodium phenyl dithiopropane sulfonate, sodium dodecyl sulfate, and 2-mercaptobenzimidazole. The concentration of sodium phenyl dithiopropane sulfonate was 0.0005 mg / L, the concentration of sodium dodecyl sulfate was 0.07 mg / L, and the concentration of 2-mercaptobenzimidazole was 0.06 mg / L. The film obtained in step (3) was placed in an electroplating apparatus. The prepared film was used as the cathode, and the insoluble iridium electrode was used as the anode. The film was electroplated at 25°C in the electroplating solution at a concentration of 1.42 A·L / (dm³). 2 ·mol), 1.76A·L / (dm 2 ·mol), 1.42A·L / (dm 2 ·mol), 1.76A·L / (dm 2 ·mol), 1.42A·L / (dm 2 ·mol), 1.76A·L / (dm 2 ·mol) and 1.42A·L / (dm 2 Electroplating was performed using a current matching value of 1.42 A·L / (dm³). 2 The electroplating time corresponding to the current matching value of 1.76 A·L / (dm) was 87 s. 2 The electroplating time corresponding to the current matching value of ·mol) is 63s, thereby electroplating a second metal layer on the surface of the first metal layer;

[0094] (5) The film obtained in step (4) is immersed in chromium anhydride passivating agent with a solution concentration of 2 g / L and a residence time of 8 s. After washing with water, it is dried in an oven at 60°C to finally obtain the composite current collector.

[0095] Example 2

[0096] The only difference between this embodiment and Embodiment 1 is that in step (4), the electroplating solution is first prepared with 0.35 A·L / (dm³). 2 Electroplating was performed for 1528 s at an ion current matching value of 0.71 A·L / (dm³).2 Electroplating with a current matching value of ·mol for 436s results in a second metal layer consisting of a stacked large-particle metal layer and a small-particle metal layer. The large-particle metal layer is closer to the base film, and its average particle size is adjusted to 600nm, and its thickness is adjusted to 700nm. The average particle size of the small-particle metal layer is adjusted to 300nm, and its thickness is adjusted to 400nm.

[0097] Example 3

[0098] The only difference between this embodiment and Embodiment 1 is that in step (4), the electroplating solution is prepared with 2.11 A·L / (dm³) 2 ·mol), 4.23A·L / (dm 2 ·mol), 2.11A·L / (dm 2 ·mol), 4.23A·L / (dm 2 ·mol), 2.11A·L / (dm 2 ·mol), 4.23A·L / (dm 2 ·mol), 2.11A·L / (dm 2 ·mol), 4.23A·L / (dm 2 ·mol), 2.11A·L / (dm 2 ·mol), 4.23A·L / (dm 2 ·mol), 2.11A·L / (dm 2 ·mol), 4.23A·L / (dm 2 ·mol), 2.11A·L / (dm 2 ·mol), 4.23A·L / (dm 2 ·mol) and 2.11A·L / (dm 2 Electroplating was performed using a current matching value of 2.11 A·L / (dm³). 2 The electroplating time corresponding to the current matching value of ·mol) is 36s, 4.23A·L / (dm). 2 The electroplating time corresponding to the current matching value of ·mol) is 7s, so that the second metal layer consists of 8 large particle metal layers and 7 small particle metal layers. The large particle metal layers are in contact with the first metal layer and the large particle metal layers are farthest from the first metal layer. The average particle size and thickness of each large particle metal layer are adjusted to 100nm; the average particle size and thickness of each small particle metal layer are adjusted to 50nm and 39nm.

[0099] Example 4

[0100] The only difference between this embodiment and Embodiment 1 is that in step (4), 1.42 A·L / (dm 2 The electroplating times corresponding to the current matching values ​​(·mol) were adjusted to 54s, 76s, 97s, and 120s respectively; 1.76A·L / (dm 2 The electroplating times corresponding to the current matching values ​​of ·mol were adjusted to 70s, 63s and 56s respectively, so that the thickness of the large particle metal layer increases layer by layer along the direction away from the base film, with thicknesses of 100nm, 140nm, 180nm and 220nm respectively; and the thickness of the small particle metal layer decreases layer by layer along the direction away from the base film, with thicknesses of 160nm, 144nm and 128nm respectively.

[0101] Comparative Example 1

[0102] The only difference between this comparative example and Example 1 is that in step (4), the electroplating solution is first prepared with 5.28 A·L / (dm³). 2 Electroplating was performed for 40 seconds at a current matching value of 0.32 A·L / (dm³). 2 Electroplating was performed for 1921 s at an ion current matching value of 5.28 A·L / (dm³). 2 Electroplating with a current matching value of ·mol for 40s results in a second metal layer consisting of one layer of large-particle metal and two layers of small-particle metal, which are alternately stacked. The large-particle metal layer is located between the two layers of small-particle metal. The average particle size of the large-particle metal layer is adjusted to 660nm and the thickness is adjusted to 800nm. The average particle size of each small-particle metal layer is adjusted to 40nm and the thickness is adjusted to 272nm.

[0103] Comparative Example 2

[0104] The only difference between this comparative example and Example 1 is that the ion current matching value is maintained at 1.76 A·L / (dm²) during the electroplating process. 2 The electroplating time was 469s, and the average particle size of the particles in the second metal layer was 120nm and the thickness was 1072nm.

[0105] Performance testing

[0106] The following tests were performed on the composite current collectors provided in the above embodiments and comparative examples:

[0107] ① Tensile strength and elongation at break tests:

[0108] The test data for the MD direction were obtained by referring to the national standard GB / T1040.3-2006 and are summarized in Table 1.

[0109] ② Corrosion resistance test:

[0110] The sample was placed in a corrosive medium (5 wt% NaCl aqueous solution) at room temperature for the experiment, and the rust formation time was recorded.

[0111] ③ Abrasion resistance test:

[0112] A CFT-I type friction and wear testing system was used for room temperature friction and wear tests. A linear reciprocating friction and wear method with spherical contact was employed. The sample size was 10mm × 10mm, and 6mm diameter Si3N4 balls were used as the grinding balls. The load was 5N, the reciprocating distance was 5mm, the reciprocating speed was 1m / min, and the test duration was 30min. During the friction and wear test, the profilometer was used to measure the surface profile curve of the wear track. Five locations were evenly selected on the 5mm long wear track for testing. The average cross-sectional area of ​​the wear track was calculated, and the wear volume was obtained by multiplying the average cross-sectional area by the wear track length. This volume was recorded as the wear amount. Finally, the average wear rate was obtained by dividing the wear amount by the product of the load and the sliding distance.

[0113] The test results are shown in Table 1.

[0114] Table 1

[0115]

[0116] analyze:

[0117] As shown in Examples 1-4, the present invention sequentially deposits a first metal layer and a second metal layer on the surface of the base film. The alternating large and small metal particles in the second metal layer create a synergistic effect, thereby improving the structural strength and hardness of the second metal layer. This results in the composite current collector possessing excellent mechanical properties, corrosion resistance, and wear resistance. Specifically, comparing Examples 1-3, it is evident that when the number of large metal particles (n) is preferably within the range of 3-4, the overall performance of the composite current collector is superior. Comparing Examples 1 and 4, it is clear that when the thickness of the large metal particles increases layer by layer away from the base film while the thickness of the small metal particles decreases layer by layer, the elongation at break and tensile strength of the composite current collector can be further improved, the rust formation time can be extended, and the average wear rate can be reduced, thus further enhancing the mechanical properties, corrosion resistance, and wear resistance.

[0118] As can be seen from Example 1 and Comparative Example 1, if the average particle size difference 'a' between adjacent large and small particle metal layers is too large, it will lead to a decrease in the tensile strength and elongation at break of the composite current collector, a shortening of the rusting time, and an increase in the average wear rate. In other words, the mechanical properties, corrosion resistance, and wear resistance of the composite current collector will all decrease.

[0119] As can be seen from Example 1 and Comparative Example 2, if the second metal layer consists only of small particle metal layers, the tensile strength and elongation at break of the composite current collector will be significantly reduced, the rusting time will be significantly shortened, and the average wear rate will be significantly increased. That is, the mechanical properties, corrosion resistance and wear resistance of the composite current collector will all be significantly reduced.

[0120] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite current collector, characterized in that, The composite current collector includes a base membrane, a first metal layer is disposed on at least one side surface of the base membrane, and a second metal layer is disposed on the surface of the first metal layer away from the base membrane. The material of the second metal layer includes copper metal; the second metal layer includes n large particle metal layers and m small particle metal layers, wherein the large particle metal layers and the small particle metal layers are alternately stacked, wherein 3≤n≤4 and n is an integer, and m and n satisfy any one of the following conditions (i) to (ii): (i) m=n+1; (ii) m=n-1; Along the direction away from the base film, the thickness of the n-layer large particle metal layer increases layer by layer; the thickness of the m-layer small particle metal layer decreases layer by layer. In adjacent large-particle metal layers and small-particle metal layers, the average particle size of the large-particle metal layer is denoted as x, and the average particle size of the small-particle metal layer is denoted as y. The difference in average particle size between the adjacent large-particle metal layers and small-particle metal layers is denoted as a. The a satisfies the following condition: a = (xy) / x and 10% ≤ a ≤ 50%. The average particle size of a single layer of small-particle metal is 100-300 nm; the average particle size of a single layer of large-particle metal is 100-600 nm. The second metal layer is prepared using an electroplating process; the ion current matching value of adjacent large-particle metal layers is less than the ion current matching value of small-particle metal layers, and the absolute value of the difference is denoted as b, wherein b satisfies the following condition: 0.1 A·L / (dm²). 2 ·mol)≤b≤3A·L / (dm 2 ·mol).

2. The composite current collector according to claim 1, characterized in that, The material of the first metal layer includes copper.

3. The composite current collector according to claim 1, characterized in that, The thickness of the first metal layer is 50-100 nm.

4. The composite current collector according to claim 1, characterized in that, A base layer is also disposed between the base film and the first metal layer.

5. The composite current collector according to claim 4, characterized in that, The substrate layer is made of a nickel-niobium alloy; the thickness of the substrate layer is 5-50 nm.

6. The composite current collector according to claim 5, characterized in that, The thickness of the substrate layer is 10-20 nm.

7. The composite current collector according to claim 4, characterized in that, The total thickness of the base layer, the first metal layer, and the second metal layer is 0.8-1.2 μm.

8. The composite current collector according to claim 1, characterized in that, A passivation layer is provided on the surface of the second metal layer away from the first metal layer.

9. The composite current collector according to claim 1, characterized in that, The base film is a conductive base film or a polymer base film.

10. A preparation process for the composite current collector according to any one of claims 1-9, characterized in that, The preparation process includes: (1) A first metal layer is magnetron sputtered onto the surface of a polymer base film; (2) With Cu 2+ The solution is an electroplating solution, and a second metal layer is electroplated on the surface of the first metal layer to obtain the composite current collector; The second metal layer includes n large-particle metal layers and m small-particle metal layers, wherein the large-particle metal layers and the small-particle metal layers are alternately stacked, wherein 3≤n≤4 and n is an integer, and m and n satisfy any one of the following conditions (i) to (ii): (i) m=n+1; (ii) m=n-1; When electroplating adjacent large-particle metal layers and small-particle metal layers, the ion current matching value of the large-particle metal layer is less than that of the small-particle metal layer, where the ion current matching value = electroplating current density / Cu during electroplating. 2+ The concentration; The absolute value of the difference in ion current matching values ​​between adjacent large-particle metal layers and small-particle metal layers is denoted as b, where b satisfies the following condition: 0.1 A·L / (dm²). 2 ·mol)≤b≤3A·L / (dm 2 ·mol).

11. The preparation process according to claim 10, characterized in that, The specific parameters for magnetron sputtering in step (1) include: using a copper target as the target material, and a power density of 6.0-15 W / cm². 2 The argon flow rate is 50-70 mL / min, the coating vacuum degree is 0.06-0.08 Pa, the temperature of the main roller is 0-20℃, and the coating time is 5-8 s.

12. The preparation process according to claim 10, characterized in that, The electroplating method described in step (2) specifically includes: using an insoluble iridium-plated electrode as the anode, using the thin film obtained in step (1) as the cathode, and using a Cu-containing electrode... 2+ The solution is used as an electroplating solution for electroplating.

13. The preparation process according to claim 10, characterized in that, The Cu-containing 2+ Cu in solution 2+ The concentration is 30-65 g / L.

14. The preparation process according to claim 10, characterized in that, The Cu-containing 2+ The solution is acidic, and the Cu-containing solution... 2+ H in the solution + The concentration is 2-2.5 mol / L.

15. The preparation process according to claim 10, characterized in that, The Cu-containing 2+ The solution also contains electroplating additives.

16. The preparation process according to claim 15, characterized in that, The electroplating additives include at least one of brighteners, wetting agents, and leveling agents.

17. The preparation process according to claim 16, characterized in that, The brightener includes at least one of sodium polydithiopropane sulfonate, sodium phenyl dithiopropane sulfonate, sodium N,N-dimethyldithiopropane sulfonate, and sodium 3-mercapto-1-propane sulfonate.

18. The preparation process according to claim 16, characterized in that, The wetting agent includes at least one of polyethylene glycol, polypropylene glycol, sodium dodecyl sulfate, and polyoxyethylene ether.

19. The preparation process according to claim 16, characterized in that, The leveling agent includes at least one of 2-mercaptobenzimidazole, ethylene thiourea, and tetrahydrothiazole copper sulfide.

20. The preparation process according to claim 10, characterized in that, For electroplating n large-particle metal layers and m small-particle metal layers, the ion current matching value of each layer is denoted as c, where c satisfies the following condition: 0.1 A·L / (dm 2 ·mol)≤c≤6A·L / (dm 2 ·mol).

21. The preparation process according to claim 10, characterized in that, For electroplating n large-particle metal layers and m small-particle metal layers, the electroplating time for each layer is denoted as t, where t satisfies the following condition: 5s≤t≤2000s.

22. The preparation process according to claim 10, characterized in that, The electroplating temperature in step (2) is 20-40℃.

23. The preparation process according to claim 10, characterized in that, In step (1), before magnetron sputtering the first metal layer, a base layer is magnetron sputtered on the surface of the polymer base film.

24. The preparation process according to claim 23, characterized in that, The specific parameters for the substrate layer sputtered by magnetron sputtering include: using a nickel-niobium target as the target material, and a power density of 2-5 W / cm². 2 The argon flow rate is 70-100 mL / min, the coating vacuum degree is 0.06-0.08 Pa, the temperature of the main roller is 0-20℃, and the coating time is 3-5 s.

25. The preparation process according to claim 10, characterized in that, The preparation process specifically includes the following steps: (I) Perform surface cleaning treatment on the polymer film, and then heat it at 70-150 W•min / m 2 The polymer film was pretreated by corona treatment for 3-5 seconds under a certain discharge level. (II) Using a nickel-niobium target as the target material, a 5-50 nm thick base layer is magnetron sputtered onto the surface of the pretreated polymer base film; The specific parameters for magnetron sputtering of the substrate include: a power density of 2-5 W / cm². 2 The argon flow rate is 70-100 mL / min, the coating vacuum degree is 0.06-0.08 Pa, the temperature of the main roller is 0-20℃, and the coating time is 3-5 s; (III) Using a copper target as the target material, a first metal layer with a thickness of 50-100 nm is magnetron sputtered on the surface of the substrate layer; The specific parameters for magnetron sputtering of the first metal layer include: a power density of 6.0-15 W / cm². 2 The argon flow rate is 50-70 mL / min, the coating vacuum degree is 0.06-0.08 Pa, the temperature of the main roller is 0-20℃, and the coating time is 5-8 s; (IV) Using an insoluble iridium-plated electrode as the anode, and the thin film obtained in step (III) as the cathode, a Cu-containing electrode is used. 2+ The solution is an electroplating solution, and electroplating is carried out at 20-40℃ to form a second metal layer on the surface of the first metal layer. Wherein, the Cu-containing 2+ The solution contains Cu 2+ H + And electroplating additives, Cu 2+ The concentration is 30-65 g / L, H + The concentration is 2-2.5 mol / L; the electroplating additive includes at least one of brightener, wetting agent and leveling agent; the second metal layer includes n large particle metal layers and m small particle metal layers, the large particle metal layers and the small particle metal layers are alternately stacked, wherein 3≤n≤4 and n is an integer, and m and n satisfy any one of the following conditions (i) to (ii): (i) m=n+1; (ii) m=n-1; for electroplating n large particle metal layers and m small particle metal layers, the ion current matching value of each layer is denoted as c, and c satisfies the following condition: 0.1 A·L / (dm 2 ·mol)≤c≤6A·L / (dm 2 ·mol), where the ion current matching value = electroplating current density / Cu during electroplating 2+ The concentration; for electroplating n large-particle metal layers and m small-particle metal layers, the electroplating time for each layer is denoted as t, where t satisfies the following condition: 5s ≤ t ≤ 2000s; when electroplating adjacent large-particle metal layers and small-particle metal layers, the ion current matching value of the large-particle metal layer is < the ion current matching value of the small-particle metal layer; the absolute value of the difference between the ion current matching values ​​of adjacent large-particle metal layers and small-particle metal layers is denoted as b, where b satisfies the following condition: 0.1 A·L / (dm 2 ·mol)≤b≤3A·L / (dm 2 ·mol), such that in adjacent large-particle metal layers and small-particle metal layers, the average particle size of the large-particle metal layer is denoted as x, the average particle size of the small-particle metal layer is denoted as y, and the difference in average particle size between the adjacent large-particle metal layers and small-particle metal layers is denoted as a, wherein a satisfies the following condition: a=(xy) / x and 10%≤a≤50%; (V) Immerse the film obtained in step (IV) in a passivating agent for 8-12 seconds, then wash with water, and then dry at 50-70°C to obtain the composite current collector; The passivating agent includes a chromic anhydride solution with a concentration of 0.5-3 g / L.

26. An electrode sheet, characterized in that, The electrode sheet includes the composite current collector as described in any one of claims 1-9 or the composite current collector prepared by the preparation process described in any one of claims 10-25.

27. A secondary battery, characterized in that, The secondary battery includes the electrode sheet as described in claim 26.

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