A negative electrode current collector, a preparation method thereof, and an application thereof

Abstract

The present invention provides a negative electrode current collector, a preparation method and an application thereof. The negative electrode current collector includes a polymer layer and a bonding layer provided on at least one surface of the polymer layer. On the surface of the bonding layer away from the current collector, a conductive layer and a reinforcing layer are sequentially provided. The bonding layer includes a metal photothermal material, and both the conductive layer and the reinforcing layer independently include a metal. By providing a bonding layer containing a metal photothermal material between the polymer layer and the conductive layer, and further providing a reinforcing layer on the surface of the conductive layer, the present invention can not only improve the bonding force between the metal of the conductive layer and the polymer layer carrier, but also prevent the swelling of the polymer layer caused by the direct contact between the electrolyte and the polymer layer, preventing the influence on the bonding force. In addition, the negative electrode current collector prepared by the present invention not only reduces the weight of the traditional copper foil current collector, but also can effectively increase the toughness and strength of the copper foil, improving the safety performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and relates to a negative electrode current collector, a preparation method thereof, and an application thereof. Background Art

[0002] As an energy storage battery for new energy at present, lithium batteries have extensive applications in electric vehicles, energy storage, etc. The structure of a lithium-ion battery mainly consists of four parts: a positive electrode, a negative electrode, an electrolyte, and a separator. Among them, the copper foil acts as the carrier of the negative electrode in the lithium-ion battery, also called the negative electrode current collector. Utilizing the advantages of good electron transmission performance and low resistivity of copper, the current generated by the battery active material can be converged to form a larger current output. With the increasing requirements for higher energy density of lithium-ion batteries, various materials are developing towards the characteristics of being thinner and lighter, and the copper foil is no exception.

[0003] The existing copper foils are mainly divided into rolled copper foils and electrolytic copper foils. The rolled copper foil is thinned by mechanical means from a thick copper foil. For example, in patent CN103579578B, a rolled copper foil with a thickness of 4 - 20 μm and a film are used to prepare a negative electrode sheet, and by improving the tensile strength of the copper foil and the bonding strength of the binder in the film, the extension of the negative electrode sheet during charge and discharge is inhibited. The electrolytic copper foil is formed by electrolytic deposition of copper on the cathode and then peeled off. For example, in patent CN108930050A, a preparation method of an ultra-thin electronic copper foil for a lithium-ion battery negative electrode current collector is provided. In this patent, a copper sulfate electrolyte is deposited on the cathode surface by electrolysis to form an electrolytic copper foil with a thickness of 8 - 15 μm, and then this electrolytic copper foil is peeled off from the cathode surface and rolled to obtain a copper foil with a thickness of 6 μm. After applying an anti-adhesive agent on the surface of the copper foil, annealing, surface treatment, cleaning, and drying, an ultra-thin electronic copper foil for a lithium-ion battery negative electrode current collector is obtained.

[0004] The existing lithium-ion batteries mainly select rolled copper foils or electrolytic copper foils with a thickness of less than 12 μm as the negative electrode current collector, and in order to improve the energy density of the battery, the copper foil is developing towards being thinner and lighter. Currently, the copper foils used in the market are mainly 8 μm and 6 μm in thickness. However, as the copper foil becomes thinner and thinner, the requirement for the overall uniformity of the battery is getting higher and higher, and the production process and cost will also increase accordingly; moreover, the toughness of the ultra-thin copper foil becomes worse, and it is more likely to break and cause a short circuit, reducing the safety performance of the battery. Therefore, providing a negative electrode current collector with a thin thickness, light weight, and good toughness is of great significance for improving the safety performance and electrochemical performance of lithium-ion batteries. Summary of the Invention

[0005] In view of the problems in the prior art, the purpose of the present invention is to provide a negative electrode current collector, a preparation method thereof and an application. By providing a bonding layer containing a metal photothermal material between the polymer layer and the conductive layer, and further providing a reinforcing layer on the surface of the conductive layer, the present invention can not only improve the bonding force between the metal of the conductive layer and the polymer layer carrier, but also prevent the swelling of the polymer layer caused by the direct contact between the electrolyte and the polymer layer, thus preventing the influence on the bonding force. In addition, the negative electrode current collector prepared by the present invention not only reduces the weight of the traditional copper foil current collector, but also effectively increases the toughness and strength of the copper foil, improving the safety performance of the battery.

[0006] To achieve the purpose of this invention, the following technical solutions are adopted:

[0007] In a first aspect, the present invention provides a negative electrode current collector, which includes a polymer layer and a bonding layer provided on at least one surface of the polymer layer. On the surface of the bonding layer away from the current collector, a conductive layer and a reinforcing layer are sequentially provided. The bonding layer includes a metal photothermal material, and both the conductive layer and the reinforcing layer independently include a metal.

[0008] In the present invention, the negative electrode current collector includes a polymer layer, and a bonding layer, a conductive layer and a reinforcing layer sequentially provided on at least one surface of the polymer layer. This structure of the negative electrode current collector can not only improve the bonding force between the metal of the conductive layer and the polymer layer carrier, but also prevent the swelling of the polymer layer caused by the direct contact between the electrolyte and the polymer layer, thus preventing the influence on the bonding force. In addition, the negative electrode current collector prepared by the present invention not only reduces the weight of the traditional copper foil current collector, but also effectively increases the toughness and strength of the copper foil, improving the safety performance of the battery. The specific technical principle is as follows:

[0009] First, in the prior art copper foil / polymer / copper foil three-layer composite current collector, after being made into a battery, it has to go through repeated charge and discharge processes. During the charge and discharge process, due to the large difference in the thermal expansion coefficients of the polymer and the copper foil, repeated charge and discharge are particularly likely to cause the separation of the copper foil from the polymer substrate. In the present invention, a bonding layer containing a specific metal photothermal material is provided between the polymer layer and the conductive layer. The metal photothermal material can generate heat under light irradiation to melt the polymer, thereby being nailed into the polymer layer. At the same time, the metal photothermal material can be melted with the metal of the conductive layer. The bonding force between this metal-metal is relatively strong, which can enhance the interaction force between the bonding layer and the conductive layer, so that the conductive layer is tightly bonded to the polymer layer through the bonding layer, equivalent to the conductive layer with a large number of "nails (metal photothermal materials)" being nailed into the polymer layer, effectively improving the bonding force between the copper foil and the polymer substrate and reducing the risk of their separation.

[0010] Second, a reinforcing layer is provided on the surface of the conductive layer of the present invention to further thicken the conductive layer, enabling the finally prepared negative electrode current collector to meet the use requirements.

[0011] Thirdly, through the synergistic cooperation among the polymer layer, the specific bonding layer, the conductive layer and the reinforcing layer, the negative electrode current collector of the present invention not only reduces the mass of the traditional negative electrode current collector and is applicable to the preparation of ultra-thin current collectors, but also can effectively increase the toughness and strength of the current collector and improve the safety performance of the battery.

[0012] It should be noted that the metal photothermal material in the present invention refers to a metal material that has a photothermal effect after absorbing light.

[0013] It should be noted that "independently" in the present invention means that the selection of the two does not interfere with each other. For example, "both the conductive layer and the reinforcing layer independently include metals", which means that the conductive layer includes metals and the reinforcing layer also includes metals, but the metals in the conductive layer and the metals in the reinforcing layer can be the same or different.

[0014] Preferably, the metal photothermal material includes silver nanoparticles. The silver nanoparticles generate a large amount of heat after being irradiated with light, which is beneficial to the tight bonding between the bonding layer and the polymer layer. At the same time, silver and the metal in the conductive layer can be melted when heated. The bonding force between such metals nails the conductive layer to the polymer layer. Even if the polymer layer undergoes thermal expansion, the force between the polymer and the bonding layer will become tighter under the action of the "nails", realizing a strong bonding between the polymer layer, the bonding layer and the conductive layer, effectively preventing the detachment problem caused by different coefficients of thermal expansion between the base material and the copper foil, significantly enhancing the toughness and strength of the negative electrode current collector, and improving the safety performance of the battery.

[0015] Preferably, the diameter of the silver nanoparticles is 10 - 100 nm, and can be, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc.

[0016] Preferably, the areal density of the metal photothermal material in the bonding layer is 1 - 2 mg / m 2 , and can be, for example, 1 mg / m 2 , 1.1 mg / m 2 , 1.2 mg / m 2 , 1.3 mg / m 2 , 1.4 mg / m 2 , 1.5 mg / m 2 , 1.6 mg / m 2 , 1.7 mg / m 2 , 1.8 mg / m 2 , 1.9 mg / m 2 or 2 mg / m 2etc. Within this range, while the bonding strength can be taken into account, there will be no accumulation between the nanoparticles, which will affect the surface flatness of the material. When the areal density is on the high side, the nanoparticles are likely to accumulate on the surface of the substrate, resulting in a decrease in the flatness of the substrate before entering the next process. When the areal density is on the low side, since the distance between the nanoparticles is relatively large, the bonding strength will also decrease.

[0017] It should be noted that although the bonding layer of the present invention is expressed as a "layer", it does not need to be a complete and dense film layer structure. It can be formed by uniformly dispersing the metal photothermal material on the polymer layer. Further, it can be composed of particles of the metal photothermal material located on the surface of the polymer layer. When the areal density of the metal photothermal material is 1-2 mg / m 2 the comprehensive performance of the negative electrode current collector is better.

[0018] Preferably, the polymer layer includes polyethylene terephthalate (PET).

[0019] Preferably, the thickness of the polymer layer is 2-10 μm, for example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.

[0020] As a preferred technical solution of the negative electrode current collector of the present invention, the conductive layer includes a first copper layer.

[0021] Preferably, the thickness of the first copper layer is 20-90 nm, for example, it can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm or 90 nm, etc.

[0022] Preferably, the conductive layer further includes a titanium layer. The titanium layer is disposed between the first copper layer and the bonding layer, which can further improve the bonding strength between the bonding layer and copper.

[0023] Preferably, the thickness of the titanium layer is 1-10 nm, for example, it can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, etc.

[0024] As a preferred technical solution of the negative electrode current collector of the present invention, the reinforcing layer includes a second copper layer. By further thickening the conductive layer with the copper layer, the electrochemical performance of the current collector is improved.

[0025] Preferably, the thickness of the reinforcing layer is 1-2 μm, for example, it can be 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm or 2.0 μm, etc.

[0026] Preferably, the total thickness of the negative electrode current collector is 1.0 - 2.1 μm, for example, it can be 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.1 μm, etc.

[0027] In a second aspect, the present invention provides a method for preparing the negative electrode current collector according to the first aspect, and the preparation method includes:

[0028] (1) Coating a metal photothermal material on at least one surface of the polymer layer and drying it by infrared to obtain a first substrate, where the first substrate includes a polymer layer and a bonding layer provided on at least one surface of the polymer layer;

[0029] (2) Physically vapor depositing a first metal on the surface of the bonding layer of the first substrate obtained in step (1) to form a conductive layer, thereby obtaining a second substrate;

[0030] (3) Electrochemically depositing a second metal on the surface of the conductive layer of the second substrate obtained in step (2) to form a reinforcing layer, thereby obtaining the negative electrode current collector.

[0031] In the present invention, first, a metal photothermal material is coated on the surface of the polymer layer, and then through infrared drying, by utilizing the characteristic that the metal photothermal material absorbs light and generates heat, the metal photothermal material absorbs infrared light to generate a large amount of heat, thereby promoting the melting of the polymer layer, enabling the metal photothermal material to bond and penetrate into the polymer layer, and forming a bonding layer on at least one surface of the polymer layer. Then, a conductive layer is deposited on the surface of the bonding layer by physical vapor deposition (PVD), and then the conductive layer is thickened by electrochemical deposition (ECP) to form a reinforcing layer to meet the usage requirements, and the negative electrode current collector is prepared.

[0032] In the present invention, PVD is first used to prepare the conductive layer, and then ECP is used to prepare the reinforcing layer. On the one hand, the reason is that the ECP technology requires the deposited substrate to be conductive, and it is difficult for the first substrate to meet the requirements of ECP deposition. If the ECP technology is first used to deposit a conductive layer on the bonding layer, the deposition effect is poor. Therefore, a conductive layer is deposited in advance by PVD, and then the conductive layer is thickened by the ECP technology to form a reinforcing layer. On the other hand, heat is generated during the deposition process of PVD, and the polymer layer will undergo thermal swelling and deformation under the influence of a large amount of heat. Before the preparation of the negative electrode current collector is completed, the "nail" effect of the metal photothermal material cannot be effectively exerted, and it is difficult to effectively inhibit the deformation of the polymer layer; while ECP is carried out in a solution, and its temperature is relatively low, generally only 25 °C, and it will not generate a large amount of heat to cause deformation of the polymer layer. A conductive layer is deposited in advance by PVD, and then ECP is used to thicken the conductive layer, which can not only thicken the current collector to meet the usage requirements, but also prevent the influence of the whole process of PVD on the performance of the current collector, and a negative electrode current collector with better safety performance can be prepared.

[0033] The preparation method of the present invention can not only improve the bonding strength between the metal and the polymer layer, but also prevent the heat generated during the charge and discharge process from causing thermal expansion of the substrate, thereby affecting the bonding strength. In addition, the negative electrode current collector prepared by the present invention not only reduces the weight of the traditional copper foil current collector, but also effectively increases the toughness and strength of the copper foil, improving the safety performance of the battery.

[0034] Preferably, before coating the metal photothermal material on at least one surface of the polymer layer in step (1), the surface of the polymer layer is also cleaned to remove the oil stain on the surface.

[0035] As a preferred technical solution of the preparation method of the present invention, the coating of the metal photothermal material on at least one surface of the polymer layer in step (1) is carried out as follows:

[0036] The atomized nanoparticle solution is sprayed on at least one surface of the polymer layer by a spraying method, and the nanoparticle solution includes a silver nanoparticle solution.

[0037] Preferably, the diameter of the silver nanoparticles in the silver nanoparticle solution is 10-100 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc.

[0038] Preferably, the concentration of the nanoparticle solution is 0.1-1 mg / L, for example, it can be 0.1 mg / L, 0.2 mg / L, 0.3 mg / L, 0.4 mg / L, 0.5 mg / L, 0.6 mg / L, 0.7 mg / L, 0.8 mg / L, 0.9 mg / L or 1 mg / L, etc.

[0039] Preferably, the spraying amount of the nanoparticle solution is 1-2 L / m 2 , for example, it can be 1 L / m 2 , 1.1 L / m 2 , 1.2 L / m 2 , 1.3 L / m 2 , 1.4 L / m 2 , 1.5 L / m 2 , 1.6 L / m 2 , 1.7 L / m 2 , 1.8 L / m 2 , 1.9 L / m 2 or 2 L / m 2 etc.

[0040] The present invention sprays a misty silver nanoparticle solution in a spraying manner, and further regulates the concentration and spraying amount of the nanoparticle solution. Only a small amount of silver nanoparticles is required to achieve the binding effect, improving the dispersibility of the metal photothermal material. By adjusting the content of the binding layer and the surface density of the metal photothermal material to 1-2 mg / m 2 , the comprehensive performance of the negative current collector is improved.

[0041] Preferably, the wavelength of the light for infrared drying in step (1) is 400-450 nm, for example, it can be 400 nm, 405 nm, 410 nm, 415 nm, 420 nm, 425 nm, 430 nm, 435 nm, 440 nm, 445 nm or 450 nm, etc. The silver nanoparticle solution is dried by light of a specific wavelength, and the silver nanoparticles exert a photothermal effect, improving the binding force between the polymer layer, the binding layer and the conductive layer.

[0042] As a preferred technical solution of the preparation method of the present invention, before physically vapor depositing the first metal in step (2), titanium with a thickness of 1-10 nm is also deposited on the surface of the binding layer by physical vapor deposition, for example, it can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, etc. Through the deposition of titanium, the binding force between the first metal and the binding layer is further enhanced.

[0043] Preferably, the first metal in step (2) includes copper, and the deposition thickness of the first metal is 20-90 nm, for example, it can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm or 90 nm, etc.

[0044] In the present invention, depositing a relatively thin titanium and copper by PVD in advance can prevent excessive heat generated by PVD from causing thermal swelling and deformation of the polymer layer, and is also beneficial to the subsequent ECP.

[0045] Preferably, the physical vapor deposition method in step (2) includes magnetron sputtering.

[0046] Preferably, the sheet resistance of the second substrate in step (2) is 0.1-2.0 Ω / square, for example, it can be 0.1 Ω / square, 0.5 Ω / square, 1.0 Ω / square, 1.5 Ω / square, 0.18 Ω / square or 0.2 Ω / square, etc.

[0047] As a preferred technical solution of the preparation method of the present invention, the solution for electrochemical deposition in step (3) includes sulfuric acid, copper sulfate, chloride ions and copper plating additives.

[0048] Preferably, the concentration of sulfuric acid in the electrochemically deposited solution is 15 - 30 g / L, for example, it can be 15 g / L, 18 g / L, 21 g / L, 24 g / L, 27 g / L, 30 g / L, etc.

[0049] Preferably, the concentration of copper sulfate in the electrochemically deposited solution is 180 - 220 g / L, for example, it can be 180 g / L, 185 g / L, 190 g / L, 195 g / L, 200 g / L, 205 g / L, 210 g / L, 215 g / L, 220 g / L, etc.

[0050] Preferably, the concentration of chloride ions in the electrochemically deposited solution is 50 - 100 ppm, for example, it can be 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, etc.

[0051] Preferably, the concentration of copper plating additive in the electrochemically deposited solution is 40 - 50 mL / L, for example, it can be 40 mL / L, 42 mL / L, 44 mL / L, 46 mL / L, 48 mL / L, 50 mL / L, etc.

[0052] It should be noted that the concentration unit "mL / L" refers to the proportion of the volume of the active ingredient in the total volume. For example, when the concentration of the copper plating additive in the electrochemically deposited solution is 40 - 50 mL / L, it means that in 1 L of the electrochemically deposited solution, there are 40 - 50 mL of copper plating additive.

[0053] Preferably, the current density of the electrochemically deposition is 5 - 10 ASD, for example, it can be 5 ASD, 6 ASD, 7 ASD, 8 ASD, 9 ASD, 10 ASD, etc.

[0054] Preferably, the time of the electrochemically deposition is 1 - 2 min, for example, it can be 1 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min, 2 min, etc.

[0055] In the present invention, by adjusting the deposition conditions such as the current density and deposition time of the electrochemically deposition, a Cu layer with good compactness and a thickness within the required range can be obtained. If the current density is increased, the obtained coating has poor compactness and a large film resistance; if the current density is decreased, the electrochemically deposition time needs to be extended to obtain the required thickness, which will result in low productivity of the equipment.

[0056] As a preferred technical solution of the preparation method of the present invention, the preparation method includes:

[0057] (1) Spray a misty nanoparticle solution on at least one surface of the polymer layer. The nanoparticle solution includes a silver nanoparticle solution. The concentration of the nanoparticle solution is 0.1 - 1 mg / L, and the spraying amount is 1 - 2 L / m 2 . After spraying, perform infrared drying by irradiating with light having a wavelength of 400 - 450 nm to obtain a first substrate. The first substrate includes a polymer layer and a bonding layer provided on at least one surface of the polymer layer;

[0058] (2) Deposit titanium with a thickness of 1 - 10 nm on the surface of the bonding layer of the first substrate in step (1) by magnetron sputtering, and then magnetron sputter copper with a thickness of 20 - 90 nm on the surface of the titanium, that is, form a conductive layer on the surface of the bonding layer away from the polymer layer to obtain a second substrate. The sheet resistance of the second substrate is 0.1 - 2.0 Ω / □;

[0059] (3) Electrochemically deposit copper with a thickness of 1 - 2 μm on the surface of the conductive layer of the second substrate in step (2) to form a reinforcing layer, thereby obtaining a negative electrode current collector;

[0060] Among them, the electrochemically depositing solution includes 15 - 30 g / L of sulfuric acid, 180 - 220 g / L of copper sulfate, 50 - 100 ppm of chloride ions, and 40 - 50 mL / L of copper plating additive. The current density of the electrochemically deposition is 5 - 10 ASD, and the time is 1 - 2 min.

[0061] In a third aspect, the present invention provides an application of the above-mentioned negative electrode current collector, and the negative electrode current collector is applied to the negative electrode of a lithium-ion battery.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] In the present invention, the negative electrode current collector includes a polymer layer and a bonding layer, a conductive layer, and a reinforcing layer sequentially provided on at least one surface of the polymer layer. This structure of the negative electrode current collector can not only improve the bonding force between the metal of the conductive layer and the polymer layer carrier, but also prevent the problem of poor bonding force caused by thermal expansion of the substrate during charge and discharge; in addition, the negative electrode current collector prepared by the present invention not only reduces the weight of the traditional copper foil current collector, but also can effectively increase the toughness and strength of the copper foil, and improve the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 is a side view of the negative electrode current collector in a specific embodiment of the present invention.

[0065] Figure 2 is a top view of the first substrate in a specific embodiment of the present invention.

[0066] Figure 3It is a side view of the second substrate in a specific embodiment of the present invention.

[0067] Among them, 1 - polymer layer; 2 - bonding layer; 3 - conductive layer; 4 - reinforcing layer. Specific embodiment

[0068] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0069] The embodiment part of the present invention provides a negative electrode current collector, and its structural schematic diagram is as Figure 1 shown. The negative electrode current collector includes a polymer layer 1 and a bonding layer 2 provided on at least one surface of the polymer layer 1. The bonding layer 2 is sequentially provided with a conductive layer 3 and a reinforcing layer 4 on the surface away from the current collector. The bonding layer 2 includes a metal photothermal material, and the conductive layer 3 and the reinforcing layer 4 both independently include a metal.

[0070] In some embodiments, the metal photothermal material includes silver nanoparticles.

[0071] In some embodiments, the diameter of the silver nanoparticles is 10 - 100 nm.

[0072] In some embodiments, the areal density of the metal photothermal material in the bonding layer 2 is 1 - 2 mg / m 2 .

[0073] In some embodiments, the conductive layer 3 includes a first copper layer.

[0074] In some embodiments, the thickness of the first copper layer is 20 - 90 nm.

[0075] In some embodiments, the conductive layer 3 further includes a titanium layer, and the titanium layer is disposed between the first copper layer and the bonding layer 2.

[0076] In some embodiments, the thickness of the titanium layer is 1 - 10 nm.

[0077] In some embodiments, the reinforcing layer 4 includes a second copper layer.

[0078] In some embodiments, the thickness of the reinforcing layer 4 is 1 - 2 μm.

[0079] In some embodiments, the total thickness of the negative electrode current collector is 1.0 - 2.1 μm.

[0080] The embodiment part of the present invention also provides a preparation method of the above-mentioned negative electrode current collector, and the preparation method includes:

[0081] (1) Coat a metal photothermal material on at least one surface of the polymer layer 1 and perform infrared drying to obtain a first substrate. The top view of the first substrate is as shown in Figure 2 . The first substrate includes a polymer layer 1 and a bonding layer 2 provided on at least one surface of the polymer layer 1;

[0082] (2) Physically vapor deposit a first metal on the surface of the bonding layer 2 of the first substrate in step (1) to form a conductive layer 3, and obtain a second substrate. The side view of the second substrate is as shown in Figure 3 ;

[0083] (3) Electrochemically deposit a second metal on the surface of the conductive layer 3 of the second substrate in step (2) to form a reinforcing layer 4, and obtain a negative current collector. The side view of the negative current collector is as shown in Figure 1 .

[0084] In some embodiments, the coating of the metal photothermal material on at least one surface of the polymer layer 1 in step (1) is carried out as follows:

[0085] In some embodiments, a misty nanoparticle solution is sprayed on at least one surface of the polymer layer 1 by a spraying method. The nanoparticle solution includes a silver nanoparticle solution.

[0086] In some embodiments, the diameter of the silver nanoparticles in the silver nanoparticle solution is 10 - 100 nm.

[0087] In some embodiments, the concentration of the nanoparticle solution is 0.1 - 1 mg / L.

[0088] In some embodiments, the spraying amount of the nanoparticle solution is 1 - 2 L / m 2 , and by controlling the concentration and spraying amount of the nanoparticle solution, the performance of the bonding layer 2 is regulated, and at the same time, the metal photothermal material is uniformly dispersed on the polymer layer 1, presenting a uniform dot-like distribution, as shown in Figure 2 .

[0089] In some embodiments, the wavelength of the light for infrared drying in step (1) is 400 - 450 nm.

[0090] In some embodiments, before physically vapor depositing the first metal in step (2), titanium with a thickness of 1 - 10 nm is also deposited on the surface of the bonding layer 2 by physical vapor deposition.

[0091] In some embodiments, the first metal in step (2) includes copper, and the deposited thickness of the first metal is 20 - 90 nm.

[0092] In some embodiments, the physical vapor deposition method in step (2) includes magnetron sputtering.

[0093] In some embodiments, the sheet resistance of the second substrate in step (2) is 0.1 - 2 Ω / sq.

[0094] In some embodiments, the solution for electrochemical deposition in step (3) includes sulfuric acid, copper sulfate, chloride ions, and a copper plating additive.

[0095] In some embodiments, the concentration of sulfuric acid in the solution for electrochemical deposition is 15 - 30 g / L.

[0096] In some embodiments, the concentration of copper sulfate in the solution for electrochemical deposition is 180 - 220 g / L.

[0097] In some embodiments, the concentration of chloride ions in the solution for electrochemical deposition is 50 - 100 ppm.

[0098] In some embodiments, the concentration of the copper plating additive in the solution for electrochemical deposition is 40 - 50 mL / L.

[0099] In some embodiments, the current density for electrochemical deposition is 5 - 20 ASD.

[0100] In some embodiments, the time for electrochemical deposition is 1 - 2 min.

[0101] In some embodiments, the preparation method includes:

[0102] (1) Spraying a misty nanoparticle solution on at least one surface of the polymer layer 1 in a spray manner. The nanoparticle solution includes a silver nanoparticle solution. The concentration of the nanoparticle solution is 0.1 - 1 mg / L, and the spraying amount is 1 - 2 L / m 2 , and after spraying, infrared drying is performed by irradiating with light having a wavelength of 400 - 450 nm to obtain a first substrate. The first substrate includes the polymer layer 1 and a bonding layer 2 provided on at least one surface of the polymer layer 1;

[0103] (2) Depositing titanium with a thickness of 1 - 10 nm on the surface of the bonding layer 2 of the first substrate in step (1) by magnetron sputtering, and then magnetron sputtering copper with a thickness of 20 - 90 nm on the surface of the titanium, that is, forming a conductive layer 3 on the surface of the bonding layer 2 away from the polymer layer 1 to obtain a second substrate. The sheet resistance of the second substrate is 0.1 - 2 Ω / sq;

[0104] (3) Electrochemically depositing copper with a thickness of 1 - 2 μm on the surface of the conductive layer 3 of the second substrate in step (2) to form a reinforcing layer 4 to obtain a negative current collector;

[0105] Among them, the solution for electrochemical deposition includes 15 - 30 g / L of sulfuric acid, 180 - 220 g / L of copper sulfate, 50 - 100 ppm of chloride ions, and 40 - 50 mL / L of copper plating additive. The current density of the electrochemical deposition is 5 - 10 ASD, and the time is 1 - 2 min.

[0106] Example 1

[0107] This example provides a negative electrode current collector, and its structural schematic diagram is as Figure 1 shown. The negative electrode current collector includes a polymer layer 1 and binding layers 2 provided on both side surfaces of the polymer layer 1. On the side surface of the binding layer 2 away from the polymer layer 1, a conductive layer 3 and a reinforcing layer 4 are sequentially provided;

[0108] The polymer layer 1 is a PET film with a thickness of 10 μm; the binding layer 2 includes silver nanoparticles with a diameter of 50 nm, and the areal density of the silver nanoparticles is 1.5 mg / m 2 ; the conductive layer 3 is a copper layer with a thickness of 60 nm and a titanium layer with a thickness of 5 nm, and the titanium layer is located between the copper layer and the binding layer 2; the reinforcing layer 4 is a copper layer with a thickness of 1.5 μm; the total thickness of the negative electrode current collector is 11.6 μm.

[0109] This example also provides a preparation method for the above negative electrode current collector, including:

[0110] (1) Clean the surface of the PET film to remove surface oil stains, and then spray a misty silver nanoparticle solution on both side surfaces of the PET film by a spraying method. The concentration of the silver nanoparticle solution is 1.0 mg / L, and the spraying amount is 1.5 L / m 2 , and after spraying, perform infrared drying by irradiating with light having a wavelength of 430 nm to obtain a first substrate, as Figure 2 shown. The first substrate includes a polymer layer 1 and binding layers 2 provided on both side surfaces of the polymer layer 1;

[0111] (2) Deposit a titanium layer with a thickness of 5 nm on the surface of the binding layer 2 of the first substrate in step (1) by magnetron sputtering, and then magnetron sputter a copper layer with a thickness of 60 nm on the surface of the titanium, that is, form a conductive layer 3 on the side surface of the binding layer 2 away from the polymer layer 1 to obtain a second substrate, as Figure 3 shown. The resistivity of the second substrate is 0.5 Ω / square;

[0112] (3) Electrochemically deposit copper with a thickness of 1.5 μm on the surface of the conductive layer 3 of the second substrate in step (2) to form a reinforcing layer 4, and obtain the negative electrode current collector;

[0113] Among them, the electrochemically deposited solution includes 20 g / L of sulfuric acid, 200 g / L of copper sulfate, 75 ppm of chloride ions, and 45 mL / L of copper plating additive. The current density of the electrochemically deposition is 7.5 ASD, and the time is 1.5 min.

[0114] Example 2

[0115] This example provides a negative current collector, and its structural schematic diagram is as Figure 1 shown. The negative current collector includes a polymer layer 1 and binding layers 2 provided on both side surfaces of the polymer layer 1. On the side surface of the binding layer 2 away from the polymer layer 1, a conductive layer 3 and a reinforcing layer 4 are sequentially provided;

[0116] The polymer layer 1 is a PET film with a thickness of 5 μm; the binding layer 2 includes silver nanoparticles with a diameter of 20 nm, and the areal density of the silver nanoparticles is 1 mg / m 2 ; the conductive layer 3 is a copper layer with a thickness of 90 nm and a titanium layer with a thickness of 10 nm, and the titanium layer is located between the copper layer and the binding layer 2; the reinforcing layer 4 is a copper layer with a thickness of 2 μm; the total thickness of the negative current collector is 7.1 μm.

[0117] This example also provides a preparation method of the above negative current collector, including:

[0118] (1) Clean the surface of the PET film to remove surface oil stains, and then spray a misty silver nanoparticle solution on both side surfaces of the PET film by spraying. The concentration of the silver nanoparticle solution is 1 mg / L, and the spraying amount is 1 L / m 2 , and after spraying, perform infrared drying by irradiating with light with a wavelength of 400 nm to obtain a first substrate, as Figure 2 shown. The first substrate includes a polymer layer 1 and binding layers 2 provided on both side surfaces of the polymer layer 1;

[0119] (2) Deposit a 10-nm-thick titanium layer on the surface of the binding layer 2 of the first substrate in step (1) by magnetron sputtering, and then magnetron sputter a 90-nm-thick copper layer on the surface of the titanium, that is, form a conductive layer 3 on the side surface of the binding layer 2 away from the polymer layer 1 to obtain a second substrate, as Figure 3 shown. The resistivity of the second substrate is 0.1 Ω / square;

[0120] (3) Electrochemically deposit a 2-μm-thick copper layer on the surface of the conductive layer 3 of the second substrate in step (2) to form a reinforcing layer 4 to obtain a negative current collector;

[0121] Among them, the electrochemically deposited solution includes 30 g / L of copper pyrophosphate, 220 g / L of potassium pyrophosphate, 100 ppm of chloride ions, and 50 mL / L of copper plating additive. The current density of the electrochemically deposition is 10 ASD, and the time is 2 min.

[0122] Example 3

[0123] This example provides a negative electrode current collector, the structural schematic diagram of which is as Figure 1 shown. The negative electrode current collector includes a polymer layer 1 and binding layers 2 provided on both surface sides of the polymer layer 1. On the surface side of the binding layer 2 away from the polymer layer 1, a conductive layer 3 and a reinforcing layer 4 are sequentially provided;

[0124] The polymer layer 1 is a PET film with a thickness of 6 μm; the binding layer 2 includes silver nanoparticles with a diameter of 80 nm, and the areal density of the silver nanoparticles is 2 mg / m 2 ; the conductive layer 3 is a copper layer with a thickness of 20 nm and a titanium layer with a thickness of 3 nm, and the titanium layer is located between the copper layer and the binding layer 2; the reinforcing layer 4 is a copper layer with a thickness of 1 μm; the total thickness of the negative electrode current collector is 7.0 μm.

[0125] This example also provides a preparation method for the above-mentioned negative electrode current collector, including:

[0126] (1) Clean the surface of the PET film to remove surface oil stains, and then spray a misty silver nanoparticle solution on both surface sides of the PET film by a spraying method. The concentration of the silver nanoparticle solution is 1.0 mg / L, and the spraying amount is 2 L / m 2 , and after spraying, perform infrared drying by irradiating with light having a wavelength of 450 nm to obtain a first substrate, as Figure 2 shown. The first substrate includes a polymer layer 1 and binding layers 2 provided on both surface sides of the polymer layer 1;

[0127] (2) Deposit a titanium layer with a thickness of 3 nm on the surface of the binding layer 2 of the first substrate in step (1) by magnetron sputtering, and then magnetron sputter a copper layer with a thickness of 20 nm on the surface of the titanium, that is, form a conductive layer 3 on the surface side of the binding layer 2 away from the polymer layer 1 to obtain a second substrate, as Figure 3 shown. The resistivity of the second substrate is 2 Ω / □;

[0128] (3) Electrochemically deposit copper with a thickness of 1 μm on the surface of the conductive layer 3 of the second substrate in step (2) to form a reinforcing layer 4 to obtain the negative electrode current collector;

[0129] Among them, the electrochemically deposited solution includes 15 g / L of sulfuric acid, 180 g / L of copper sulfate, 50 ppm of chloride ions, and 40 mL / L of copper plating additive, and the current density of the electrochemistry deposition is 5 ASD and the time is 2 min.

[0130] Example 4

[0131] Except that in step (1), the concentration of the silver nanoparticle solution is 1.5 mg / L and the spraying amount is 2.5 L / m2 , so that the surface density of silver nanoparticles is 3.75 mg / m 2 Except for the above, the others are the same as those in Example 1.

[0132] Example 5

[0133] Except that the thickness of the copper layer in the conductive layer 3 is 200 nm and the thickness of the copper layer in the reinforcing layer 4 is 1.36 μm, the others are the same as those in Example 1.

[0134] Example 6

[0135] Except that the thickness of the copper layer in the conductive layer 3 is 10 nm and the thickness of the copper layer in the reinforcing layer 4 is 1.55 μm, the others are the same as those in Example 1.

[0136] Comparative Example 1

[0137] Except for not performing the operation in step (1), that is, not setting the bonding layer 2, the others are the same as those in Example 1.

[0138] Comparative Example 2

[0139] Except for replacing the silver nanoparticle solution in step (1) with a Ni nanoparticle solution, the others are the same as those in Example 1.

[0140] Comparative Example 3

[0141] Except for replacing the infrared drying in step (1) with drying in a vacuum oven at 80 °C, the others are the same as those in Example 1.

[0142] Comparative Example 4

[0143] Except for not performing the operation in step (2), that is, not setting the conductive layer 3 in the negative electrode current collector, the others are the same as those in Example 1.

[0144] Comparative Example 5

[0145] Except for not performing the operation in step (3), and directly sputtering the thickness of copper to 1.56 μm when magnetron sputtering copper on the surface of titanium in step (2), that is, not setting the reinforcing layer 4, the others are the same as those in Example 1.

[0146] Performance test of the negative electrode current collector

[0147] Adhesion test: Take the test sample and soak it in the electrolyte for 48 h, and then perform the test by the cross-cut method (GB / T 9286) after taking it out. The electrolyte is a compound of lithium hexafluorophosphate and ethylene carbonate. The test results are shown in Table 1;

[0148] Tensile strength test: The tensile strength is tested according to the standard of GB / T 5230-1995.

[0149] Resistivity test: The test was carried out using a four-probe resistance tester.

[0150] Table 1

[0151]

[0152]

[0153] In summary, from Examples 1-6, it can be seen that in the present invention, by providing a bonding layer 2 containing a metal photothermal material between the polymer layer 1 and the conductive layer 3, and further providing a reinforcing layer 4 on the surface of the conductive layer 3, not only can the bonding force between the metal of the conductive layer 3 and the carrier of the polymer layer 1 be improved, but also the swelling of the polymer layer 1 caused by the direct contact between the electrolyte and the polymer layer 1 can be prevented, thus preventing the influence on the bonding force. In addition, the negative electrode current collector prepared by the present invention not only reduces the weight of the traditional copper foil current collector, but also can effectively increase the toughness and strength of the copper foil, and improve the safety performance of the battery.

[0154] By comparing Example 1 with Example 4, it can be seen that in the present invention, the metal photothermal material does not need to form a relatively thick bonding layer 2, and its uniform dispersion on the polymer layer 1 can achieve the problem of enhancing the bonding force between the metal and the polymer and preventing the swelling of the polymer layer 1 caused by the direct contact between the electrolyte and the polymer layer 1. In Example 4, the concentration of the silver nanoparticle solution is too high and the spraying amount is too much, resulting in a relatively large areal density of silver nanoparticles in the finally formed bonding layer 2, leading to local accumulation, which will affect the flatness of the surface, and thus tip discharge will occur during electrochemical deposition, resulting in a decrease in uniformity and a decrease in the resultant force at the accumulated place. Therefore, the bonding force performance of Example 1 is better.

[0155] By comparing Example 1 with Examples 5-6, it can be seen that in the present invention, by first physically vapor depositing a certain thickness of titanium layer and copper layer, and then electrochemically depositing the copper layer to thicken it, it is possible to prevent excessive heat generated by sputtering a too thick conductive layer 3 and prevent the thermal swelling of the polymer layer 1. While meeting the usage requirements of the current collector, the toughness and strength of the negative electrode current collector are improved. In Example 5, the total thickness between the copper layer of the conductive layer 3 and the copper layer of the reinforcing layer 4 remains unchanged, but the copper deposited by magnetron sputtering is too thick, which is likely to generate more heat, resulting in phenomena such as wrinkles in the substrate film. The too thick copper layer deposited by magnetron sputtering will also cause an increase in the stress of the copper layer, thus affecting the polymer layer 1 and the bonding layer 2. Therefore, the bonding force performance of Example 1 is higher than that of Example 5. In Example 6, the total thickness between the copper layer of the conductive layer 3 and the copper layer of the reinforcing layer 4 remains unchanged, but the electrochemically deposited copper is too much and the magnetron sputtered copper is too little. The sheet resistance of the substrate when it enters the electrochemical deposition is relatively large, so that a large amount of electrical energy will be converted into heat during the electrochemical deposition process, affecting the bonding force between the electrochemically deposited copper layer and the substrate. Therefore, the bonding force of Example 1 is better than that of Example 6.

[0156] From the comparison between Example 1 and Comparative Examples 1-2, it can be seen that in the present invention, without providing the bonding layer 2 or using a nickel layer in the bonding layer 2, the technical effects of the present invention cannot be achieved. In Comparative Example 1, without the bonding layer 2, the bonding force between the polymer layer 1 and the conductive layer 3 cannot be effectively enhanced. After being soaked in the electrolyte solution, the surface of the polymer layer 1 is prone to swelling, and the conductive layer 3 and the reinforcing layer 4 are prone to peeling off, affecting the toughness and strength of the negative electrode current collector. In Comparative Example 2, although the bonding layer 2 is provided, the sputtered nickel scheme is adopted, which does not have the effect of absorbing light and releasing heat of the metal photothermal material in the present invention and does not have the effect of enhancing the bonding force. Therefore, the bonding force performance of Comparative Examples 1-2 is significantly worse than that of Example 1.

[0157] From the comparison between Example 1 and Comparative Example 3, it can be seen that the metal photothermal material in the present invention can exert its photothermal effect when dried under infrared irradiation, and the temperature generated on the surface of the material is relatively high, which can be nailed in the polymer layer 1 to enhance the bonding force between the polymer layer 1 and the conductive layer 3. In Comparative Example 3, the conventional vacuum heating drying method is adopted, and there is no strong bonding force between the bonding force and the polymer layer 1, which affects the tight bonding between the layers of the negative electrode current collector. Therefore, the bonding force performance of Comparative Example 3 is significantly worse than that of Example 1.

[0158] From the comparison between Example 1 and Comparative Examples 4-5, it can be seen that the setting of the conductive layer 3 and the reinforcing layer 4 in the present invention is beneficial to maintaining the preparation of the negative electrode current collector and improving the toughness, strength and safety performance of the negative electrode current collector. In Comparative Example 4, without the conductive layer 3, copper is directly deposited on the surface of the bonding layer 2 by electrochemical deposition technology. The conductivity of the substrate is poor, and electrochemical deposition is difficult to carry out. The surface of the prepared negative electrode current collector is uneven, and the toughness and strength are both poor. In Comparative Example 5, without the reinforcing layer 4, the copper layer of the conductive layer 3 is thickened by magnetron sputtering to replace the reinforcing layer 4. A large amount of heat is generated during magnetron sputtering, causing thermal swelling of the polymer layer 1. At this time, the negative electrode current collector has not been prepared yet, and the bonding layer 2 cannot effectively play the role of a "nail" to fix the polymer layer 1, resulting in deformation of both the polymer layer 1 and the bonding layer 2, affecting the overall toughness, strength and safety performance of the negative electrode current collector.

[0159] The above is only the specific implementation manner 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 thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A negative electrode current collector, characterized in that, The negative current collector includes a polymer layer and a bonding layer provided on at least one surface of the polymer layer. On the surface of the bonding layer away from the current collector, a conductive layer and a reinforcing layer are sequentially provided. The bonding layer includes a metal photothermal material, and the metal photothermal material includes silver nanoparticles. Both the conductive layer and the reinforcing layer independently include a metal; The negative current collector is prepared by the following method, and the preparation method includes the following steps: (1) Coating a metal photothermal material on at least one surface of the polymer layer and drying with infrared light to obtain a first substrate, which includes a polymer layer and a bonding layer provided on at least one surface of the polymer layer; (2) Physically vapor depositing a first metal on the surface of the bonding layer of the first substrate in step (1) to form a conductive layer, obtaining a second substrate; (3) Electrochemically depositing a second metal on the surface of the conductive layer of the second substrate in step (2) to form a reinforcing layer, obtaining the negative current collector.

2. The negative electrode current collector according to claim 1, wherein The diameter of the silver nanoparticles is 10 - 100 nm; The areal density of the metal photothermal material in the bonding layer is 1-2 mg / m 2 .

3. The negative electrode current collector according to claim 1 or 2, characterized in that, The conductive layer includes a first copper layer; The thickness of the first copper layer is 20 - 90 nm; The conductive layer further includes a titanium layer, and the titanium layer is provided between the first copper layer and the bonding layer; The thickness of the titanium layer is 1 - 10 nm.

4. The negative electrode current collector according to claim 1 or 2, wherein The reinforcing layer includes a second copper layer; The thickness of the reinforcing layer is 1 - 2 μm; The total thickness of the negative current collector is 1.0 - 2.1 μm.

5. A method for preparing the negative electrode current collector according to any one of claims 1-4, characterized in that, The preparation method includes: (1) Coating a metal photothermal material on at least one surface of the polymer layer and drying with infrared light to obtain a first substrate, which includes a polymer layer and a bonding layer provided on at least one surface of the polymer layer; (2) Physically vapor depositing a first metal on the surface of the bonding layer of the first substrate in step (1) to form a conductive layer, obtaining a second substrate; (3) Electrochemically depositing a second metal on the surface of the conductive layer of the second substrate in step (2) to form a reinforcing layer, obtaining the negative current collector.

6. The preparation method according to claim 5, characterized in that, The coating of the metal photothermal material on at least one surface of the polymer layer in step (1) is carried out as follows: Spraying a misty nanoparticle solution on at least one surface of the polymer layer in a spray manner, and the nanoparticle solution includes a silver nanoparticle solution; The diameter of the silver nanoparticles in the silver nanoparticle solution is 10 - 100 nm; The concentration of the nanoparticle solution is 0.1 - 1 mg / L; The spraying amount of the nanoparticle solution is 1 to 2 L / m 2 ; The wavelength of the light for drying with infrared light in step (1) is 400 - 450 nm.

7. The preparation method according to claim 5 or 6, characterized in that, Before physically vapor depositing the first metal in step (2), titanium with a thickness of 1 - 10 nm is also deposited on the surface of the bonding layer by physical vapor deposition; The first metal in step (2) includes copper, and the deposited thickness of the first metal is 20 - 90 nm; The physical vapor deposition method in step (2) includes magnetron sputtering; The sheet resistance of the second substrate in step (2) is 0.1 - 2.0 Ω / □.

8. The preparation method according to claim 5 or 6, characterized in that, The solution for electrochemical deposition in step (3) includes sulfuric acid, copper sulfate, chloride ions, and a copper plating additive; The concentration of sulfuric acid in the solution for electrochemical deposition is 15 - 30 g / L; The concentration of copper sulfate in the solution for electrochemcial deposition is 180 - 220 g / L; The concentration of chloride ions in the solution for electrochemcial deposition is 50 - 100 ppm; The concentration of copper plating additive in the solution for electrochemcial deposition is 40 - 50 mL / L; The current density for electrochemcial deposition is 5 - 10 ASD; The time for electrochemcial deposition is 1 - 2 min.

9. The preparation method according to claim 5 or 6, characterized in that, The preparation method includes: (1) Spraying a mist-like nanoparticle solution on at least one surface of the polymer layer, the nanoparticle solution including a silver nanoparticle solution, the concentration of the nanoparticle solution being 0.1 to 1.0 mg / L, and the spraying amount being 1 to 2 L / m 2 , after spraying, infrared drying is carried out by irradiating with light having a wavelength of 400 to 450 nm to obtain a first substrate, the first substrate including a polymer layer and a bonding layer provided on at least one surface of the polymer layer; (2) Depositing titanium with a thickness of 1 - 10 nm on the surface of the bonding layer of the first substrate in step (1) by magnetron sputtering, and then magnetron sputtering copper with a thickness of 20 - 90 nm on the surface of the titanium, so as to form a conductive layer on the surface of the bonding layer away from the polymer layer, and obtaining a second substrate, the sheet resistance of the second substrate being 0.1 - 2.0 Ω / □; (3) Electrochemically depositing copper with a thickness of 1 - 2 μm on the surface of the conductive layer of the second substrate in step (2) to form a reinforcing layer, and obtaining a negative current collector; Wherein, the solution for electrochemcial deposition includes 15 - 30 g / L of sulfuric acid, 180 - 220 g / L of copper sulfate, 50 - 100 ppm of chloride ions and 40 - 50 mL / L of copper plating additive, the current density for electrochemcial deposition being 5 - 10 ASD and the time being 1 - 2 min.

10. An application of the negative electrode current collector according to any one of claims 1-4, characterized in that, The negative current collector is applied to the negative electrode of a lithium ion battery.

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