A current collector, its preparation method and application

Abstract

The application discloses a current collector and a preparation method and application thereof. The current collector comprises a conductive base film, a first conductive layer is arranged on the surface of the conductive base film, the first conductive layer has a porous structure on the side far from the current collector, the porous structure is a disordered porous structure, and the thickness of the conductive layer with the porous structure accounts for less than 50% of the total thickness of the first conductive layer. The current collector has good conductivity, low square resistance, and strong adhesion between the current collector and electrode material. Moreover, the current collector has good appearance and excellent mechanical properties.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a current collector and a preparation method and application thereof. BACKGROUND

[0002] The new energy automobile industry develops rapidly, which further promotes the development of the lithium ion battery field. As a basic material in the negative current collector of the lithium ion battery, the performance of the copper current collector directly affects the performance and service life of the lithium ion battery. At present, the main negative current collector is a copper metal foil, but the density of copper is large, which is not conducive to improving the energy density of the battery and the endurance of the battery. Compared with the traditional current collector, the composite current collector based on the polymer film has the characteristics of low cost, light weight and good internal insulation. These characteristics enable the composite current collector to reduce the cost of the battery and improve the energy density and safety of the battery when applied in the battery.

[0003] In addition, the negative electrode material of the battery is mostly a silicon-based material, but in the process of charging and discharging, the generation and decomposition of silicon lithium alloy are accompanied by a huge volume change. This volume change usually causes the silicon particles to break and powder, and the negative active material falls off from the electrode sheet, thereby reducing the service life of the battery.

[0004] Therefore, it is necessary to develop a new current collector to reduce the energy density of the current collector and improve the adhesion between the current collector and the electrode material. SUMMARY

[0005] In view of the above technical problems existing in the prior art, the purpose of the present application is to provide a current collector and a preparation method and application thereof. The current collector of the present application not only has good electrical conductivity, but also can effectively improve the adhesion between the current collector and the electrode material, solve the problem of easy falling off of the electrode material, and reduce the mass of the current collector, thereby improving the energy density of the battery prepared by using the same.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a current collector, which comprises a conductive base film, the surface of the conductive base film is provided with a first conductive layer, the first conductive layer has a porous structure on the side away from the current collector, the porous structure is a disordered porous structure, and the thickness of the conductive layer with the porous structure accounts for less than 50% of the total thickness of the first conductive layer.

[0008] In the present application, the thickness of the conductive layer with a porous structure accounts for 50% or less of the total thickness of the conductive layer, for example, 50%, 48%, 45%, 42%, 40%, 38%, 36%, 35%, 33%, 30%, 28%, 25%, 22%, 20%, 18%, 16%, 14%, 12%, 10%, 8%, 5%, or 3%, etc.

[0009] The present application uses a conductive base film as a substrate, sets a first conductive layer on the surface thereof, and regulates the morphology thereof to have a specific thickness of disordered porous structure on the side away from the current collector, so that the use amount of metal can be reduced while ensuring good conductivity of the current collector, and the adhesion between the current collector and the electrode material can be effectively improved.

[0010] The following is a preferred technical solution of the present application, but is not a limitation on the technical solutions provided by the present application. Through the following preferred technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0011] Preferably, the thickness of the conductive layer with a porous structure accounts for 10%-45% of the total thickness of the conductive layer.

[0012] Preferably, the conductive base film comprises a high molecular film and a second conductive layer arranged on the surface of the high molecular film, or the conductive base film comprises a high molecular film and conductive particles dispersed in the high molecular film. The present application does not specifically limit the type of conductive particles, for example, carbon nanotubes, carbon nanofibers, or carbon black, etc.

[0013] Preferably, the high molecular film comprises at least one of polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenyl ether (PPO), and polystyrene (PS).

[0014] Preferably, the first conductive layer and the second conductive layer are independently at least one of a copper layer, an aluminum layer, a copper alloy layer, or an aluminum alloy layer.

[0015] Preferably, the thickness of the second conductive layer is 50nm-100nm, for example, 50nm, 60nm, 70nm, 80nm, 90nm, or 100nm, etc. The thickness here refers to the single-sided thickness.

[0016] Preferably, the second conductive layer is prepared by a magnetron sputtering method.

[0017] The second conductive layer is prepared by the method of magnetron sputtering, which has the advantages of compact and uniform structure, controllable thickness, and compact, uniform and thin film layer.

[0018] Preferably, the high polymer film and the second conductive layer further comprise a substrate layer, which is a metal layer, a metal oxide layer or an alloy layer. The bonding force between the substrate layer and the second conductive layer is better than that between the high polymer film and the second conductive layer. Therefore, the bonding force of the second conductive layer is improved by providing the substrate layer.

[0019] Preferably, the substrate metal layer comprises at least one of a silicon-aluminum alloy layer, an aluminum oxide layer, a nickel-chromium alloy layer, a metal nickel layer or a metal chromium layer.

[0020] Preferably, the thickness of the substrate layer is 10 nm-50 nm, for example, 10 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 18 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, etc.

[0021] Preferably, the substrate layer is prepared by the method of magnetron sputtering. The method of magnetron sputtering has the advantages of compact and uniform structure, controllable thickness, and compact, uniform and thin film layer.

[0022] As a preferred technical solution of the current application, the average pore diameter of the pores in the conductive layer with a porous structure is 0.1 μm-10 μm, for example, 0.1 μm, 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, etc., preferably 0.5 μm-5 μm. If the average pore diameter is too small, the contact surface area of the electrode material and the current collector is small, and the bonding force is limitedly improved. If the average pore diameter is too large, the mechanical properties of the pole piece prepared by using the current collector will be reduced.

[0023] Preferably, the porosity of the conductive layer with a porous structure is 1%-50%, for example, 1%, 2%, 4%, 5%, 7%, 8%, 10%, 12.5%, 15%, 17%, 20%, 23%, 26%, 30%, 32.5%, 35%, 38%, 40%, 43%, 45%, 46%, 48% or 50%, etc., preferably 20%-40%. If the porosity is too low, the bonding force of the current collector and the electrode material is not good. If the porosity is too high, the conductive performance of the pole piece prepared by using the current collector will also be reduced.

[0024] Preferably, the first conductive layer comprises a first copper layer and a second copper layer, the first copper layer is close to the current collector, and the second copper layer is away from the current collector, and the second copper layer has a disordered porous structure.

[0025] Preferably, the thickness d1 of the first copper layer is 350 nm-1250 nm, for example, can be 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1050 nm, 1100 nm, 1150 nm, 1200 nm, or 1250 nm, etc. Preferably, the thickness d2 of the second copper layer is 0-625 nm and does not contain 0, for example, can be 0.5 nm, 1 nm, 3 nm, 6 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 60 nm, 70 nm, 80 nm, 100 nm, 125 nm, 150 nm, 165 nm, 180 nm, 200 nm, 225 nm, 240 nm, 260 nm, 280 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, or 625 nm, etc. Preferably, the first copper layer and the second copper layer are both prepared by water electroplating.

[0026] Preferably, on any side of the current collector, the total thickness of the first conductive layer, the second conductive layer, and the substrate layer is 500 nm-2000 nm, for example, can be 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1050 nm, 1100 nm, 1150 nm, 1200 nm, 1250 nm, or 1300 nm, etc., and the preferred total thickness is 800 nm-1300 nm. When the total thickness is small, the current collector has poor conductivity; when the total thickness is large, on the one hand, the production cost of the current collector is increased, and on the other hand, the mechanical properties of the current collector are reduced. It should be noted that the total thickness here refers to the thickness of the current collector on one side.

[0027] In a second aspect, the present application provides a preparation method of the current collector as described in the first aspect, comprising the following steps:

[0028] (1) preparing a second conductive layer on the surface of the polymer film to obtain a conductive base film;

[0029] (2) using the conductive base film as a cathode, performing first electroless plating on the surface of the second conductive layer of the conductive base film by using a plating solution containing metal ions, forming a first plated metal layer on the surface of the second conductive layer, and then continuing the electroless plating by increasing the current density to form a second plated metal layer on the surface of the first plated metal layer, thereby obtaining the current collector.

[0030] The method of the present application first prepares the second conductive layer on the surface of the polymer film, which on one hand improves the conductivity of the polymer film and on the other hand can be directly used as a cathode for electroless plating to form a metal plated layer on the surface thereof.

[0031] The purpose of preparing the first plated metal layer as a pre-plated layer and then depositing the second plated metal layer by increasing the current density is to improve the conductivity of the polymer film and prevent the pre-plated layer from being burned directly when electroless plating is performed by using a large current density. In addition, when the second plated metal layer is deposited by increasing the current density, a violent hydrogen evolution reaction occurs, which causes the formation of "small holes" and leaves holes in the second plated metal layer, thereby improving the adhesion between the current collector and the electrode material.

[0032] The method of the present application can reduce the amount of metal used in the current collector without additional equipment, improve the adhesion between the prepared current collector and the electrode material, and facilitate the industrialization of the current collector.

[0033] In the method of the present application, the thickness of the first plated copper layer and the second plated copper layer can be adjusted by adjusting the current density and the electroless plating time. In the same electroless plating time, a smaller current density can obtain a thinner plated layer.

[0034] In the method of the present application, the difference between the continued electroless plating in step (2) and the first electroless plating can only be that the current density is increased, or the current density is increased while other parameters are selected within the aforementioned limited range of the first electroless plating and the specific values are different from those of the first electroless plating.

[0035] Preferably, the polymer film is pretreated before magnetron sputtering in step (1).

[0036] Preferably, the pretreatment includes: after the polymer film is degreased, the polymer film is cleaned with alcohol and water, dried, and the pretreated polymer film is obtained. The alcohol can be ethanol and the water can be pure water.

[0037] In one embodiment, the polymer film is degreased by placing it in acetone.

[0038] As a preferred technical solution of the method for preparing the current collector, a base layer is prepared on the surface of the polymer film before the second conductive layer is prepared on the surface of the polymer film. Preferably, the base layer is prepared by magnetron sputtering, and in the preparation process, the material of the target is the base metal, the power density is 2 W / cm 2 -5 W / cm 2 (For example, it can be 2 W / cm 2 , 2.5 W / cm 2 , 3 W / cm 2 , 3.5 W / cm 2 , 4 W / cm 2 , 4.5 W / cm 2 , or 5 W / cm 2 , etc.), the flow rate of the protective gas is 80 mL / min-120 mL / min (for example, it can be 80 mL / min, 85 mL / min, 90 mL / min, 95 mL / min, 100 mL / min, 105 mL / min, 110 mL / min, 115 mL / min, or 120 mL / min, etc.), the vacuum degree of the film plating is 80 Pa-100 Pa (for example, it can be 80 Pa, 85 Pa, 90 Pa, 95 Pa, or 100 Pa, etc.), and the temperature of the main roller is -20°C to 30°C (for example, it can be -20°C, -10°C, 0°C, 10°C, 20°C, 22°C, 24°C, 26°C, 28°C, or 30°C, etc.).

[0039] Preferably, in step (1), the second conductive layer is prepared by magnetron sputtering, specifically including the following steps: placing the polymer film into a magnetron sputtering device, and performing magnetron sputtering with a target of conductive metal. The polymer film here can be an untreated polymer film, a pretreated polymer film, or a polymer film with a base metal layer formed on its surface.

[0040] Preferably, in the process of preparing the second conductive layer by magnetron sputtering, the power density is 7 W / cm 2 -12 W / cm 2 (For example, it can be 7 W / cm 2 , 8 W / cm 2 , 9 W / cm 2 , 9.5 W / cm 2 , 10 W / cm 2 , 10.5 W / cm 2 , 11 W / cm 2 , or 12 W / cm 2The flow rate of the protective gas is 50 mL / min-90 mL / min (for example, it can be 50 mL / min, 55 mL / min, 60 mL / min, 65 mL / min, 70 mL / min, 75 mL / min, 80 mL / min, 85 mL / min or 90 mL / min, etc.), the coating vacuum degree is 80 Pa-100 Pa (for example, it can be 80 Pa, 85 Pa, 90 Pa, 95 Pa or 100 Pa, etc.), and the temperature of the main roller is -20°C-30°C (for example, it can be -20°C, -10°C, 0°C, 10°C, 20°C, 22°C, 24°C, 26°C, 28°C or 30°C, etc.).

[0041] In the present application, the type of the protective gas is not specifically limited, and for example, it can be at least one of helium, argon or nitrogen.

[0042] In the method of water electroplating in step (2) of the preferred technical solution of the method for preparing the current collector according to the present application, the anode is an iridium plating electrode.

[0043] Preferably, the composition of the plating solution comprises 40 g / L-90 g / L of copper sulfate, 40 g / L-90 g / L of sulfuric acid and 40 mg / L-70 mg / L of chloride ions. For example, the concentration of copper sulfate can be 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L or 90 g / L, etc.; the concentration of sulfuric acid can be 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L or 90 g / L, etc.; and the concentration of chloride ions can be 40 mg / L, 42 mg / L, 45 mg / L, 47 mg / L, 50 mg / L, 53 mg / L, 56 mg / L, 58 mg / L, 60 mg / L, 62 mg / L, 65 mg / L, 68 mg / L or 70 mg / L, etc.

[0044] Preferably, the composition of the plating solution comprises 45 g / L-70 g / L of copper sulfate, 40 g / L-70 g / L of sulfuric acid and 50 mg / L-60 mg / L of chloride ions.

[0045] Preferably, the plating solution further comprises at least one of a brightener, a wetting agent and a leveling agent.

[0046] Preferably, the brightener comprises at least one of sodium poly(dithiopropyl sulfone), sodium 3-mercapto-1-propane sulfonate and sodium N,N-dimethyl dithiocarbamate propane sulfonate.

[0047] Preferably, the wetting agent comprises at least one of a fatty alcohol polyoxyethylene ether, a sunflower alkenediol polyoxyethylene ether, and sodium dodecyl sulfonate.

[0048] Preferably, the leveling agent comprises at least one of a benzotriazole, a 2-mercaptobenzimidazole, an ethylene thiourea, and a tetrahydrothiazole copper.

[0049] Preferably, in the plating solution, the concentration of the brightener is 3 mg / L-40 mg / L, for example, it can be 3 mg / L, 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 35 mg / L, or 40 mg / L, etc.; the concentration of the wetting agent is 5 mg / L-60 mg / L, for example, it can be 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, or 60 mg / L, etc.; the concentration of the leveling agent is 5 mg / L-60 mg / L, for example, it can be 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, or 60 mg / L, etc.

[0050] Preferably, the temperature of the first aqueous electroplating is 20℃-45℃, for example, it can be 20℃, 22℃, 23℃, 25℃, 28℃, 30℃, 33℃, 36℃, 38℃, 40℃, 43℃, or 45℃, etc.

[0051] Preferably, the current density of the first aqueous electroplating is J1, J1 is 0.1A / dm 2 -2A / dm 2 , for example, it can be 0.1A / dm 2 , 0.3A / dm 2 , 0.5A / dm 2 , 0.7A / dm 2 , 0.8A / dm 2 , 1A / dm 2 , 1.2A / dm 2 , 1.4A / dm 2 , 1.6A / dm 2 , 1.8A / dm 2 , or 2A / dm 2 , preferably 0.5A / dm 2 -1.5A / dm 2 .

[0052] In the present application, the unit A / dm 2 may be referred to as ASD.

[0053] By controlling the current density of the first aqueous electroplating, a first copper layer with higher compactness can be obtained.

[0054] Preferably, the current density of the second aqueous electroplating is J2, J2 is 0.1 A / dm 2 -5 A / dm 2 , for example, can be 0.1 A / dm 2 , 0.3 A / dm 2 , 0.5 A / dm 2 , 0.7 A / dm 2 , 0.8 A / dm 2 , 1 A / dm 2 , 1.2 A / dm 2 , 1.4 A / dm 2 , 1.6 A / dm 2 , 1.8 A / dm 2 , 2 A / dm 2 , 2.3 A / dm 2 , 2.6 A / dm 2 , 3 A / dm 2 , 3.2 A / dm 2 , 3.4 A / dm 2 , 3.6 A / dm 2 , 3.8 A / dm 2 , 4 A / dm 2 , 4.3 A / dm 2 , 4.6 A / dm 2 , 4.8 A / dm 2 , or 5 A / dm 2 , preferably 2 A / dm 2 -4 A / dm 2 . By controlling the current density of the second aqueous electroplating, the second plating layer can be ensured to have a suitable average pore size and porosity.

[0055] It should be noted that the current density of the second aqueous electroplating is not the larger the better, as the current density of the second aqueous electroplating increases, the number of pores increases, the sheet resistance of the prepared current collector is larger, and the fracture elongation and tensile strength of the current collector are reduced to a certain extent.

[0056] Preferably, the difference between J2 and J1 is 2 A / dm 2 -3.9 A / dm 2 , for example, can be 2 A / dm 2 , 2.2 A / dm 2 , 2.4 A / dm 2 , 2.6 A / dm 2 , 2.8 A / dm 2 , 3.0 A / dm2 3.2 A / dm 2 3.3 A / dm 2 3.4 A / dm 2 3.5 A / dm 2 3.7 A / dm 2 or 3.9 A / dm 2 etc.

[0057] The difference between the first current density and the second current density is within the above range, which can ensure the compactness of the first copper layer and meet the implementation of the porous structure of the second copper layer, and the bonding force between the current collector and the electrode material is improved.

[0058] As a preferred technical scheme of the method for preparing the current collector, the method further comprises, after step (2), immersing the prepared current collector in a silane coupling agent solution, washing and drying after immersion for a period of time, to obtain the surface-treated current collector.

[0059] Preferably, the concentration of the silane coupling agent solution is 0.5 g / L-3 g / L, for example, it can be 0.5 g / L, 0.8 g / L, 1 g / L, 1.3 g / L, 1.6 g / L, 2 g / L, 2.2 g / L, 2.4 g / L, 2.6 g / L, 2.8 g / L or 3 g / L, etc.

[0060] Preferably, the period of time is 10 s-30 s, for example, it can be 10 s, 12 s, 15 s, 18 s, 20 s, 22 s, 24 s, 26 s, 28 s or 30 s, etc.

[0061] Preferably, the temperature of the drying is 45℃-75℃, for example, 45℃, 47℃, 50℃, 52℃, 55℃, 58℃, 60℃, 65℃, 70℃ or 75℃, etc.

[0062] In one embodiment, the application provides a method for preparing a current collector, comprising the following steps:

[0063] Step 1: placing a high molecular film in acetone to remove oil, then washing with anhydrous ethanol and pure water, and finally drying to obtain a pretreated high molecular film;

[0064] Step 2: placing the pretreated high molecular film in a magnetron sputtering device, using a silicon-aluminum alloy target (purity: 99.99%) as a target material, a power density of 2 W / cm 2 -5 W / cm 2 , an argon flow rate of 80 mL / min-120 mL / min, a film plating vacuum degree of 80 Pa-100 Pa, a temperature of the main roller of 20℃-30℃, and a sputtering thickness of 10 nm-20 nm, to prepare a film with a sputtered base metal layer.

[0065] Step 3: The thin film with sputtered substrate metal layer is placed again in the magnetron sputtering device, a copper target (purity: 99.99%) is used as the target material, the power density is 7.0 W / cm 2 -12 W / cm 2 , the argon flow rate is 50 mL / min-90 mL / min, the film plating vacuum degree is 80 Pa-100 Pa, the temperature of the main roller during the film plating process is 20℃-30℃, the sputtering thickness is 50 nm-100 nm, and a thin film with sputtered conductive metal layer is prepared.

[0066] Step 4: A plating solution is prepared using deionized water as a solvent and copper sulfate as a copper salt, and the composition of the plating solution includes: 40 g / L-90 g / L of copper sulfate, 50 g / L-90 g / L of sulfuric acid, 40 mg / L-70 mg / L of chloride ions, 3 mg / L-40 mg / L of brightener, 5 mg / L-60 mg / L of wetting agent, and 5 mg / L-60 mg / L of leveling agent.

[0067] The thin film with sputtered conductive metal layer is placed in a water plating device, the thin film with sputtered conductive metal layer is used as a cathode, and an insoluble iridium plating electrode is used as an anode, and the thin film with sputtered conductive metal layer is subjected to first water plating (current density is 0.1 A / dm 2 -2 A / dm 2 ), and a first copper plating layer is obtained on the surface of the conductive metal layer.

[0068] Step 5: The thin film with the first copper plating layer prepared in step 4 is placed in a plating solution with the same composition, the current density of water plating is increased, the thin film is further subjected to water plating on the basis of the first plating layer, a second copper plating layer is formed on the surface of the first copper plating layer, and a final prepared current collector is obtained.

[0069] In a third aspect, the present application provides a negative electrode tab, which comprises the current collector of the first aspect and a negative material layer arranged on the surface of the current collector.

[0070] In an embodiment, the negative material layer comprises a negative material, a conductive agent, and a binder.

[0071] In an embodiment, the negative material comprises at least one of, but is not limited to, artificial graphite, natural graphite, and a silicon-based material.

[0072] In an embodiment, the conductive agent comprises at least one of conductive carbon black, graphene, and carbon nanotubes.

[0073] In an embodiment, the binder comprises at least one of styrene butadiene rubber and sodium carboxymethyl cellulose.

[0074] The preparation method of the negative electrode sheet is not limited in the present application, and those skilled in the art can refer to the methods disclosed in the prior art for preparation. Exemplarily, the preparation can be carried out according to the following method:

[0075] The negative electrode material, the conductive agent and the binder are added into N-methyl pyrrolidone, mixed uniformly, coated on the surface of the current collector of the first aspect, and dried to obtain the negative electrode sheet.

[0076] In a fourth aspect, the present application provides a battery comprising the negative electrode sheet of the third aspect.

[0077] The numerical range of the present application includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to the limited space and for the sake of simplicity, the present application does not exhaustively list the specific point values included in the range.

[0078] Compared with the prior art, the present application has the following beneficial effects:

[0079] (1) The present application uses a conductive base film as a substrate, sets a first conductive layer on the surface thereof, and controls the morphology to have a specific thickness of disordered porous structure on the side away from the current collector. This can ensure that the current collector has good conductivity, reduce the amount of metal used, and effectively improve the adhesion between the current collector and the electrode material.

[0080] (2) The tensile strength of the current collector of the present application is above 232 MPa, the elongation at break is above 17.8%, the square resistance is below 25 mΩ, and the adhesion between the current collector and the electrode material is above 167 N / m. DETAILED DESCRIPTION

[0081] The technical solutions of the present application will be further described below through specific embodiments.

[0082] The specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0083] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0084] In the embodiments of the present application, the thickness refers to the single-sided thickness.

[0085] Example 1

[0086] The embodiment provides a current collector, which comprises a conductive base film, the conductive base film comprises a polymer film and a base metal layer arranged on both sides of the polymer film, a surface of the base metal layer is provided with a second conductive metal layer, a surface of the second conductive metal layer is provided with a first conductive metal layer, the first conductive metal layer comprises a first copper layer and a second copper layer, the first copper layer is arranged on the second conductive metal layer, a surface of the first copper layer is provided with the second copper layer, the second copper layer has a disordered porous structure, a thickness d1 of the first copper layer is 500 nm, a thickness d2 of the second copper layer is 400 nm, an average pore size of the pores in the second copper layer is 6 microns, and a porosity of the second copper layer is 30%.

[0087] The polymer film is terephthalate glycol (PET), and the thickness is 4.5 microns.

[0088] The base metal layer is a silicon-aluminum alloy, and the thickness is 15 nm.

[0089] The second conductive metal layer is a copper layer, and the thickness is 75 nm.

[0090] The embodiment further provides a preparation method of the current collector, and the method comprises the following steps:

[0091] (1) a biaxially stretched PET film with a thickness of 4.5 microns is placed in 3M acetone for 10 minutes of oil removal, then cleaned with a pure water spray pipe for 5 minutes, and the cleaned film is placed in an oven for drying at 60 DEG C for 20 minutes, and after cooling, a pretreated PET film is obtained.

[0092] (2) the pretreated PET film is placed in a magnetron sputtering device, a silicon-aluminum alloy target (purity: 99.99%) is used as a target material, the power density is 4 W / cm 2 , the argon flow rate is 100 mL / min, the film plating vacuum degree is 90 Pa, and the temperature of the main roller is 20 DEG C, so that a film with a sputtered base metal layer is prepared.

[0093] (3) the film with the sputtered base metal layer is placed in the magnetron sputtering device again, a copper target (purity: 99.99%) is used as the target material, the power density is 8 W / cm 2 , the argon flow rate is 70 mL / min, the film plating vacuum degree is 80 Pa, the temperature of the main roller during the film plating process is 20 DEG C, and a film with a sputtered second conductive metal layer is prepared.

[0094] (4) a plating solution is prepared by using deionized water as a solvent, and the composition of the plating solution is: 45 g / L of copper sulfate, 70 g / L of sulfuric acid, 50 mg / L of chloride ions, 5 mg / L of sodium polydithiobispropane sulfonate, 10 mg / L of fatty alcohol polyoxyethylene ether and 10 mg / L of benzotriazole.

[0095] (5) The thin film with sputtered conductive metal layer is placed in the water plating equipment, taking the thin film with sputtered conductive metal layer as cathode and insoluble iridium plating electrode as anode, and the current density is controlled at 0.5 A / dm 2 The thin film with sputtered conductive metal layer is subjected to first water plating at 25℃, and the first copper layer is formed on the surface of the second conductive metal layer, thereby obtaining the thin film with plated first copper layer.

[0096] (6) The thin film with plated first copper layer is placed in the water plating equipment, and the current density is controlled at 4 A / dm 2 The thin film with plated first copper layer is subjected to second water plating at 25℃, and the second copper layer is formed on the basis of the first copper layer, and at the same time, holes are left in the second copper layer due to the large current density in the second water plating, thereby obtaining the current collector.

[0097] (7) The prepared current collector is immersed in the methanol solution of γ-methacryloxypropyltrimethoxysilane, the concentration of the silane coupling agent solution is 2 g / L, the residence time is 20 s, and after water washing, the current collector is dried in the oven at 60℃, thereby obtaining the final current collector.

[0098] Example 2

[0099] The current collector provided in the embodiment comprises a conductive base film, the conductive base film comprises a polymer film and a base metal layer arranged on both sides of the polymer film, the surface of the base metal layer is provided with a second conductive metal layer, the surface of the second conductive metal layer is provided with a first conductive metal layer, the first conductive metal layer comprises a first copper layer and a second copper layer, the first copper layer is arranged on the second conductive metal layer, the surface of the first copper layer is provided with the second copper layer, the second copper layer has a disordered porous structure, the thickness d1 of the first copper layer is 350 nm, the thickness d2 of the second copper layer is 220 nm, the average pore size of the holes in the second copper layer is 6 μm, and the porosity of the second copper layer is 40%.

[0100] The polymer film is polypropylene (PP) with a thickness of 5 μm.

[0101] The base metal layer is a nickel layer with a thickness of 25 nm.

[0102] The second conductive metal layer is a copper layer with a thickness of 50 nm.

[0103] The embodiment also provides a preparation method of the current collector, comprising the following steps:

[0104] (1) The PP film with a thickness of 5 μm was placed in 2M acetone for 20 min to remove oil, then cleaned with a pure water spray pipe for 5 min, and the cleaned film was dried in an oven at 70°C for 15 min. After cooling, the pretreated PP film was obtained.

[0105] (2) The pretreated PP film was placed in a magnetron sputtering device, a nickel target (purity: 99.99%) was used as the target material, the power density was 2 W / cm 2 , the argon flow rate was 120 mL / min, the vacuum degree of film plating was 100 Pa, and the temperature of the main roller was 25°C. The film with a sputtered base metal layer was prepared.

[0106] (3) The film with a sputtered base metal layer was placed again in a magnetron sputtering device, a copper target (purity: 99.99%) was used as the target material, the power density was 12 W / cm 2 , the argon flow rate was 50 mL / min, the vacuum degree of film plating was 90 Pa, and the temperature of the main roller was 30°C during the film plating process. The film with a sputtered second conductive metal layer was prepared.

[0107] (4) A plating solution was prepared using deionized water as the solvent, and the composition of the plating solution was: 60 g / L of copper sulfate, 80 g / L of sulfuric acid, 60 mg / L of chloride ion, 20 mg / L of 3-mercapto-1-propane sulfonic acid sodium, 30 mg / L of aloe glycol polyoxyethylene ether, and 60 mg / L of 2-mercaptobenzimidazole.

[0108] (5) The film with a sputtered conductive metal layer was placed in a water plating device, the film with a sputtered conductive metal layer was used as the cathode, and an insoluble iridium plating electrode was used as the anode. The current density was controlled at 1.5 A / dm 2 . The film with a sputtered conductive metal layer was subjected to first water plating at a temperature of 20°C, and a first copper layer was formed on the surface of the second conductive metal layer to obtain a film with a plated first copper layer.

[0109] (6) The film with a plated first copper layer was placed in a water plating device, and the current density was controlled at 4 A / dm 2 . Second water plating was performed at a temperature of 25°C, so that the film was further water-plated and thickened on the basis of the first copper layer to form a second copper layer on the basis of the first copper layer. At the same time, due to the larger current density during the second water plating, holes were left in the second copper layer to obtain a current collector.

[0110] (7) The prepared current collector was immersed in an ethylene glycol solution of vinyl trimethoxysilane, the concentration of the silane coupling agent solution was 3 g / L, the residence time was 15 s, and after water washing, the current collector was dried in an oven at 65°C. Finally, the current collector was obtained.

[0111] Example 3

[0112] The embodiment provides a current collector, which comprises a conductive base film, the conductive base film comprises a polymer film and a base metal layer arranged on both sides of the polymer film, a surface of the base metal layer is provided with a second conductive metal layer, a surface of the second conductive metal layer is provided with a first conductive metal layer, the first conductive metal layer comprises a first copper layer and a second copper layer, the first copper layer is arranged on the second conductive metal layer, a surface of the first copper layer is provided with the second copper layer, the second copper layer has a disordered porous structure, a thickness d1 of the first copper layer is 600 nm, a thickness d2 of the second copper layer is 375 nm, an average pore size of the pores in the second copper layer is 5.5 μm, and a porosity of the second copper layer is 36%.

[0113] The polymer film is terephthalic acid glycol ester (PET), and the thickness is 6 μm.

[0114] The base metal layer is a nickel-chromium alloy, and the thickness is 40 nm.

[0115] The second conductive metal layer is a copper layer, and the thickness of the conductive metal layer is 100 nm.

[0116] The embodiment further provides a preparation method of the current collector, and the method comprises the following steps:

[0117] (1) a biaxially stretched PET film with a thickness of 6 μm is placed in 3M acetone for 10 min for oil removal, then the film is cleaned by using a pure water spray pipe for 5 min, and the cleaned film is dried in an oven at 60 ℃ for 20 min; after cooling, a pretreated PET film is obtained.

[0118] (2) the pretreated PET film is placed in a magnetron sputtering device, a nickel-chromium alloy target (purity: 99.99%) is used as a target material, the power density is 5 W / cm 2 , the argon flow is 80 mL / min, the film plating vacuum degree is 80 Pa, and the temperature of a main roller is 25 ℃, so that a film with a sputtered base metal layer is prepared.

[0119] (3) the film with the sputtered base metal layer is placed in the magnetron sputtering device again, a copper target (purity: 99.99%) is used as the target material, the power density is 7 W / cm 2 , the argon flow is 90 mL / min, the film plating vacuum degree is 100 Pa, and the temperature of the main roller is 25 ℃ during the film plating process, so that a film with a sputtered second conductive metal layer is prepared.

[0120] (4) The plating solution is prepared with deionized water as solvent, and the composition of the plating solution is: 90 g / L of copper sulfate, 40 g / L of sulfuric acid, 70 mg / L of chloride ion, 40 mg / L of N, N-dimethyl dithioformamide propane sulfonic acid sodium, 50 mg / L of sodium dodecyl sulfonate and 30 mg / L of ethylene sulfourea.

[0121] (5) The thin film with sputtered conductive metal layer is placed in the water plating equipment, the thin film with sputtered conductive metal layer is used as cathode, and the insoluble iridium plating electrode is used as anode, and the current density is controlled to be 0.6 A / dm 2 The first water plating is performed on the thin film with sputtered conductive metal layer, the temperature is 25℃, the second conductive metal layer is formed on the surface of the first conductive metal layer, and the thin film with plated first copper layer is obtained.

[0122] (6) The thin film with plated first copper layer is placed in the water plating equipment, the current density is controlled to be 3.8 A / dm 2 The second water plating is performed, the temperature is 25℃, the thin film is further thickened on the basis of the first copper layer, the second copper layer is formed on the basis of the first copper layer, and the current density is large during the second water plating, so that holes are left in the second copper layer, and the current collector is obtained.

[0123] (7) The prepared current collector is immersed in the methanol solution of γ-methacryloxypropyl trimethoxysilane, the concentration of the silane coupling agent solution is 2 g / L, the residence time is 20 s, after water washing, the current collector is dried in the oven at 60℃, and finally the current collector is obtained.

[0124] Example 4

[0125] The current collector provided in the example is different from the example 1 in that the thickness of the first copper layer is 400 nm, and at this time, the thickness of the second copper layer accounts for 50% of the total thickness of the first copper layer and the second copper layer.

[0126] Example 5

[0127] The current collector provided in the example is different from the example 1 in that the thickness of the second copper layer is 300 nm, and at this time, the thickness of the second copper layer accounts for 37.5% of the total thickness of the first copper layer and the second copper layer.

[0128] Example 6

[0129] The current collector provided in the example is different from the example 1 in that the current density is controlled to be 5 A / dm 2 during the second water plating in the step (6), and the porosity of the second copper layer in the prepared current collector is 48%, and the average pore size of the holes in the second copper layer is 9 μm.

[0130] Example 7

[0131] This example is basically the same as Example 1, except that the thickness of the first copper layer is controlled to be 800 nm and the thickness of the second copper layer is controlled to be 100 nm, so that the thickness of the second copper layer accounts for 11.1% of the total thickness of the first copper layer and the second copper layer.

[0132] Example 8

[0133] This example is basically the same as Example 1, except that in step (6), the current density is controlled to be 3 A / dm 2 when the second electroless plating is performed, and the porosity of the second copper layer in the current collector prepared is 20%, and the average pore size of the pores in the second copper layer is 2.5 μm.

[0134] Example 9

[0135] This example is basically the same as Example 1, except that step (2) is not performed in the preparation method, and the current collector does not contain a base metal layer.

[0136] Comparative Example 1

[0137] This comparative example is basically the same as Example 1, except that in step (6), the current density is controlled to be 1.8 A / dm 2 when the second electroless plating is performed, and the porosity of the second copper layer in the current collector prepared is 10%, and the average pore size of the pores in the second copper layer is 1.2 μm.

[0138] Comparative Example 2

[0139] This comparative example is basically the same as Example 1, except that in step (6), the current density is controlled to be 6 A / dm 2 when the second electroless plating is performed, and the porosity of the second copper layer in the current collector prepared is 55%, and the average pore size of the pores in the second copper layer is 11 μm.

[0140] Comparative Example 3

[0141] This comparative example provides a current collector, which is different from Example 1 in that the thickness of the second copper layer is 600 nm, so that the thickness of the second copper layer accounts for 54.5% of the total thickness of the first copper layer and the second copper layer.

[0142] Comparative Example 4

[0143] This comparative example is basically the same as Example 1, except that the thickness of the first copper layer is 900 nm and the thickness of the second copper layer is 0.

[0144] Application Example

[0145] A negative electrode tab is prepared using the current collector prepared in Examples 1-8 and Comparative Examples 1-4, respectively, and the preparation method comprises the following steps:

[0146] The negative active material artificial graphite, conductive carbon black, CMC and SBR were added into N-methyl pyrrolidone, and the mass ratio of the artificial graphite, conductive carbon black, CMC and SBR was 94:2:2:2. After being mixed uniformly, the mixture was coated on the current collector, and after drying, the negative electrode sheet was obtained by cutting.

[0147] Test and evaluation of the current collector:

[0148] ①Tensile strength and elongation at break: the test was performed according to the national standard GB / T 1040.3-2006, and the test results of the present application were all the test data in the MD direction.

[0149] ②Adhesion test: a layer of 3M double-sided tape was adhered to a smooth stainless steel surface with a thickness of 3 mm, and after rolling, the negative electrode sheet was adhered on the double-sided tape, and then a layer of 3M double-sided tape was adhered on the negative electrode sheet, and after rolling again, a layer of small strips (150 mm x 15 mm) of ethylene acrylic acid copolymer film was covered on the 3M double-sided tape. Finally, the ethylene acrylic acid copolymer film of the sample strip was fixed to the upper clamp of the tensile testing machine, and the rest was fixed to the lower clamp. After fixing, the two were peeled off at an angle of 90° and a speed of 100 mm / min, and the peeling force, i.e. the adhesion between the electrode material and the current collector, was tested.

[0150] ③Appearance evaluation: appearance detection is the most basic and commonly used detection method. The appearance of the coating requires uniformity, smoothness, no oxidation discoloration, no grease, no corrosion, no burning, no dendritic and no spongy. The appearance of the current collector was detected by visual brightness empirical evaluation method. The grading reference standard of visual brightness empirical evaluation method is as follows:

[0151] a. First level (luminous) plated film surface is bright, without oil stains, no whitening, burning, etc., and the compactness is excellent;

[0152] b. Second level (semi-bright) plated film has a slight brightness, and the surface has slight whitening, burning, etc. which can be basically ignored, and the compactness is good;

[0153] c. Third level (non-bright) plated film surface is basically without luster, with serious burning, whitening, etc., and the compactness is poor.

[0154] ④The prepared flat current collector sample was placed on the sample stage, and the square resistance of the current collector was tested by using a four-probe square resistance meter.

[0155] The test results are shown in Table 1.

[0156] Table 1 Performance test of the current collector and adhesion test results of the current collector and the electrode material

[0157]

[0158] As shown in Table 1, the current collector has good conductivity, low sheet resistance, and strong adhesion between the current collector and the electrode material. Moreover, the current collector has good appearance and excellent mechanical properties.

[0159] As shown by the comparison between Examples 1, 4, 5, 7 and Comparative Examples 3 and 4, by controlling the thickness of the second copper layer with a disordered porous structure to account for 10% to 45% of the total thickness of the first copper layer and the second copper layer, the adhesion of the current collector can be improved while the mechanical properties of the current collector are ensured and the sheet resistance is reduced.

[0160] As shown by the comparison between Examples 1, 6, 8 and Comparative Example 2, during the second electroless plating in step (6), the current density should not be too large, which may result in a large porosity and a large average pore size, and is not conducive to improving the mechanical properties and adhesion of the current collector, and may also result in an increase in the sheet resistance, and even may cause the film to be scorched. In Example 1, a thin metal layer is prepared by magnetron sputtering, and then a first copper layer is prepared by using a small current density, and then the current density is increased to thicken the copper layer, which can improve the ability of the film to withstand a larger current density, and can achieve the purpose of creating pores and improving the adhesion between the current collector and the electrode material.

[0161] As shown by the comparison between Example 1 and Comparative Example 1, if the current density during the second electroless plating is small, the porosity will be reduced, and the adhesion between the current collector and the electrode material will be greatly reduced.

[0162] As shown by the comparison between Example 1 and Example 9, increasing the base metal layer is conducive to improving the mechanical properties and adhesion of the current collector.

[0163] As shown by the comparison between Example 1 and Comparative Example 3, when the thickness of the second copper layer accounts for a high proportion, the mechanical properties of the current collector will be reduced.

[0164] As shown by the comparison between Example 1 and Comparative Example 4, when the second copper layer is not provided, the adhesion between the current collector and the electrode material is poor.

[0165] The applicant declares that the detailed method of the present application is illustrated by the above examples, but the present application is not limited to the above detailed method, i.e. it does not mean that the present application must rely on the above detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A current collector characterized by comprising: The current collector comprises a conductive base film, a surface of the conductive base film is provided with a first conductive layer, the first conductive layer comprises a first copper layer and a second copper layer, the first copper layer is close to the current collector, the second copper layer is away from the current collector, and the second copper layer has a disordered porous structure; the thickness of the second copper layer accounts for 35%-45% of the total thickness of the first conductive layer; In the second copper layer, the average pore diameter of the pores is 2-6 μm, and the porosity is 20%-38%. The conductive base film comprises a high polymer film and a second conductive layer arranged on the surface of the high polymer film; and a substrate layer is further arranged between the high polymer film and the second conductive layer, wherein the substrate layer is a metal layer, a metal oxide layer or an alloy layer.

2. The current collector of claim 1, wherein The high polymer film comprises at least one of terephthalate glycol, polypropylene, polyimide, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenyl ether and polystyrene.

3. The current collector of claim 1, wherein The second conductive layer is at least one of a copper layer, an aluminum layer, a copper alloy layer or an aluminum alloy layer.

4. The current collector of claim 1, wherein The thickness of the second conductive layer is 50-100 nm.

5. The current collector of claim 1, wherein The second conductive layer is prepared by a magnetron sputtering method.

6. The current collector of claim 1, wherein The substrate layer comprises at least one of a silicon-aluminum alloy layer, an aluminum oxide layer, a nickel-chromium alloy layer, a metal nickel layer or a metal chromium layer.

7. The current collector of claim 1, wherein The thickness of the substrate layer is 10-50 nm.

8. The current collector of claim 1, wherein The substrate layer is prepared by a magnetron sputtering method.

9. The current collector of claim 1, wherein The thickness of the first copper layer d1 is 350-1250 nm.

10. The current collector of claim 1, wherein The thickness of the second copper layer d2 is 0-625 nm and does not contain 0.

11. The current collector of claim 1, wherein The first copper layer and the second copper layer are both prepared by a water electroplating method.

12. The current collector of claim 1, wherein On any side of the current collector, the total thickness of the first conductive layer, the second conductive layer and the substrate layer is 500-2000 nm.

13. The current collector of claim 12, wherein On any side of the current collector, the total thickness of the first conductive layer, the second conductive layer and the substrate layer is 800-1300 nm.

14. A method of making a current collector as claimed in any one of claims 1 to 13, characterised in that, The preparation method comprises the following steps: (1) preparing a second conductive layer on the surface of a high polymer film to obtain a conductive base film; (2) using the conductive base film as a cathode, using a plating solution containing metal ions to perform first water electroplating on the surface of the second conductive layer of the conductive base film, forming a first plated metal layer on the surface of the second conductive layer, then increasing the current density to perform second water electroplating, thereby forming a second plated metal layer on the surface of the first plated metal layer to obtain a current collector; Before step (1), a substrate layer is prepared on the surface of the high polymer film.

15. The method of claim 14, wherein, The substrate layer is prepared by magnetron sputtering, in which the material of the target is the base metal, the power density is 2 W / cm 2 -5 W / cm 2 , the flow rate of the protective gas is 80 mL / min-120 mL / min, the vacuum degree of the coating is 80 Pa-100 Pa, and the temperature of the main roller is -20℃ to 30℃.

16. The method of claim 14, wherein, In step (1), the second conductive layer is prepared by magnetron sputtering, specifically including the following steps: placing the high polymer film into a magnetron sputtering device and performing magnetron sputtering on a conductive metal target.

17. The preparation method according to claim 14, characterized in that, The power density is 7 W / cm 2 -12 W / cm 2 during the process of preparing the second conductive layer by magnetron sputtering, the flow rate of protective gas is 50 mL / min-90 mL / min, the vacuum degree of coating is 80 Pa-100 Pa, and the temperature of the main roller is -20℃ to 30℃.

18. The method of claim 14, wherein, In step (2), the anode is an iridium plating electrode.

19. The method of claim 14, wherein, In step (2), the composition of the plating solution comprises 40-90 g / L of copper sulfate, 40-90 g / L of sulfuric acid and 40-70 mg / L of chloride ions.

20. The method of claim 19, wherein, The composition of the plating solution in step (2) includes 45 g / L-70 g / L of copper sulfate, 40 g / L-70 g / L of sulfuric acid, and 50 mg / L-60 mg / L of chloride ions.

21. The method of claim 19, wherein, The plating solution in step (2) further includes at least one of a brightener, a wetting agent, and a leveling agent.

22. The method of claim 21, wherein, The brightener includes at least one of sodium polydithiopropyl sulfone, sodium 3-mercapto-1-propane sulfonate, and N,N-dimethyl dithiocarbamic acid propane sulfonate.

23. The preparation method according to claim 21, characterized in that, The wetting agent includes at least one of a fatty alcohol polyoxyethylene ether, a sunflower alkynediol polyoxyethylene ether, and sodium dodecyl sulfonate.

24. The method of claim 21, wherein, The leveling agent includes at least one of benzotriazole, 2-mercaptobenzimidazole, ethylene thiourea, and tetrahydrothiazole copper sulfide.

25. The method of claim 21, wherein, In the plating solution in step (2), the concentration of the brightener is 3 mg / L-40 mg / L, the concentration of the wetting agent is 5 mg / L-60 mg / L, and the concentration of the leveling agent is 5 mg / L-60 mg / L.

26. The method of claim 14, wherein, The temperature of the first aqueous electroplating in step (2) is 20°C-45°C.

27. The method of claim 14, wherein, The current density of the first electroplating in step (2) is J1, J1 is 0.1 A / dm 2 -2 A / dm 2 .

28. The preparation method according to claim 27, characterized in that, The current density of the first electroplating in step (2) is J1, J1 is 0.5 A / dm 2 -1.5 A / dm 2 .

29. The method of claim 14, wherein, The current density of the second electroplating in step (2) is J2, J2 is 0.1 A / dm 2 -5 A / dm 2 .

30. The method of claim 29, wherein, The current density of the second electroplating in step (2) is J2, J2 is 2 A / dm 2 -4 A / dm 2 .

31. The method of any one of claims 27-30, wherein the method further comprises, The difference between J2 and J1 is 2A / dm 2 -3.9 A / dm 2 .

32. A negative electrode sheet characterized by comprising: The negative electrode sheet includes the current collector according to any one of claims 1-13 and a negative electrode material layer disposed on the surface of the current collector.

33. A battery, characterized by The battery includes the negative electrode sheet according to claim 32.

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