Method for producing a functional current collector containing a tin-cadmium alloy, functional current collector containing a tin-cadmium alloy, secondary battery

Abstract

The application provides a preparation method of a functional current collector containing a tin-cadmium alloy, and the preparation method comprises a conductive layer forming process of forming a conductive layer on the surface of a base film, the base film comprising a polymer substrate and a first metal layer arranged in a laminated mode, and the first metal layer comprising at least one of copper, a copper alloy, aluminum and an aluminum alloy; and the conductive layer forming process comprises the following operations: S1. taking the base film as a processing object, plating a tin-cadmium alloy layer on the surface of the first metal layer, and the tin-cadmium alloy layer comprises a tin-cadmium alloy; and S2. plating a second metal layer on the surface of the tin-cadmium alloy layer, and the second metal layer comprises copper, a copper alloy, aluminum and an aluminum alloy. In the above method, the forming of the second metal layer is to thicken the conductive layer so that the functional current collector has sufficient conductive performance, and the application is characterized in that the tin-cadmium alloy layer is formed on the surface of the base film before the second metal layer is formed, based on which, the processing efficiency, the qualified rate of finished products, the compactness of the conductive layer and the elongation rate of the functional current collector are all improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional current collector, and particularly relates to a preparation method of a functional current collector containing a tin-cadmium alloy, the functional current collector containing the tin-cadmium alloy, and a secondary battery. BACKGROUND

[0002] The current collector is an important component in a lithium ion battery, which can collect and output the current generated by active materials, and input the electric current to the active materials. With the development of lithium battery technology, the thickness, weight and safety of the traditional current collector have gradually failed to meet the demand for high energy density and high safety. In this background, the functional current collector with a "sandwich" structure (metal-polymer substrate-metal) emerges as the times require. Compared with the traditional aluminum foil or copper foil, the functional current collector has a thinner thickness and can effectively reduce the thermal runaway of the battery in the event of a short circuit. Based on the advantages of high energy density, low cost and high safety, the functional current collector is expected to be widely used in the production and manufacturing of lithium ion batteries in the future.

[0003] At present, the industrialized mass production of functional current collectors generally involves the following steps: first, depositing a thin metal conductive layer on a polymer substrate by magnetron sputtering to make the thin film substrate conductive; and then thickening the metal conductive layer by water plating. The functional current collector prepared by this process usually has a loose surface structure of the metal conductive layer, which is prone to have the problem of unqualified compactness. In addition, during the processing of magnetron sputtering and water plating thickening, the changes in environmental temperature, the impact of magnetron sputtering, and the corrosion of the electroplating solution will all cause the elongation of the thin film substrate to decrease, thereby causing the functional current collector to have the problem of insufficient elongation. SUMMARY

[0004] In order to improve the compactness of the conductive layer of the functional current collector and the elongation of the functional current collector, the present application provides a preparation method of a functional current collector containing a tin-cadmium alloy, the functional current collector containing the tin-cadmium alloy, and a secondary battery.

[0005] According to a first aspect of the present application, there is provided a method for manufacturing a functional current collector containing a tin-cadmium alloy, the method comprising a conductive layer forming process for forming a conductive layer on a surface of a base film, the base film comprising a polymer substrate and a first metal layer arranged in a stack, the first metal layer comprising at least one of copper, a copper alloy, aluminum, and an aluminum alloy; the conductive layer forming process comprising the following operations: S1. plating a tin-cadmium alloy layer on a surface of the first metal layer with the base film as a processing object, the tin-cadmium alloy layer containing a metal comprising a tin-cadmium alloy; and S2. plating a second metal layer on a surface of the tin-cadmium alloy layer, the second metal layer containing a metal comprising copper, a copper alloy, aluminum, and an aluminum alloy. In the above method, the second metal layer is formed by thickening the conductive layer to provide the functional current collector with sufficient conductivity. The present application is characterized in that the tin-cadmium alloy layer is formed on the surface of the base film before the second metal layer is formed. In the process of manufacturing the functional current collector, the tin-cadmium alloy layer can protect the base film from corrosion during the formation of the second metal layer. The film composed of the base film and the tin-cadmium alloy layer is used as a forming carrier for the second metal layer. The tin-cadmium alloy layer can improve the surface defects of the first metal layer and reduce the sheet resistance of the forming carrier for the second metal layer, thereby improving the forming quality of the second metal layer. Since the tin-cadmium alloy layer can improve the forming quality of the second metal layer, the thickness and the sheet resistance of the base film do not need to be strictly controlled within a very low range, which can reduce the production difficulty of the base film, the probability of perforation of the base film due to too thin thickness, and the production energy consumption and cost of the base film.

[0006] Preferably, in S1 of the conductive layer forming process, the plating solution for plating the tin-cadmium alloy is a first plating solution, the first plating solution comprising a main salt component and a complexing agent component, the main salt component comprising a cadmium salt and a tin salt, and the complexing agent component comprising nitrilotriacetic acid, disodium ethylenediaminetetraacetate, and an ammonium salt, the ammonium salt comprising at least one of ammonium chloride and ammonium fluoride. Based on the types of main salts, the specific complexing agent component can comprehensively control the composition, brightness, and uniformity of the tin-cadmium alloy layer.

[0007] Preferably, the cadmium salt comprises cadmium sulfate, the tin salt comprises stannous chloride; when the ammonium salt comprises ammonium chloride, the components of the first plating solution satisfy, in terms of mass ratio, cadmium sulfate:stannous chloride:ammoniotriacetic acid:ethylenediaminetetraacetic acid disodium salt:ammonium chloride = 30-50:8-15:30-60:30-60:200-300; when the ammonium salt comprises ammonium fluoride, the components of the first plating solution satisfy, in terms of mass ratio, cadmium sulfate:stannous chloride:ammoniotriacetic acid:ethylenediaminetetraacetic acid disodium salt:ammonium fluoride = 30-50:8-15:30-60:30-60:80-100. Further limiting the component ratio of the main salt component and the complexing agent component to the above range can control the tin content of the tin-cadmium alloy formed based on the plating solution through electroplating to be 20-40 wt.%, which is conducive to maintaining the cathode current at a high efficiency level in the subsequent process of plating the second metal layer, and can improve the flatness and compactness of the second metal layer. The ammonium salt in the first plating solution mainly functions to complex tin ions, and if the amount of the ammonium salt contained in the first plating solution is higher than the above range, the tin content of the tin-cadmium alloy is lower than the preferred range, and if the amount of the ammonium salt contained in the first plating solution is lower than the above range, the tin content of the tin-cadmium alloy is higher than the preferred range, which can cause the uniformity of the tin-cadmium alloy layer to deteriorate. The ethylenediaminetetraacetic acid disodium salt functions as a complexing agent in the first plating solution, and the amount of the ethylenediaminetetraacetic acid disodium salt in the electroplating solution is in the above preferred ratio range, which is conducive to improving the electroplating efficiency of the formed tin-cadmium alloy layer, and when the amount of the ethylenediaminetetraacetic acid disodium salt is lower than the above ratio range, the tin-cadmium alloy crystallinity decreases, and the brightness of the tin-cadmium alloy layer decreases, and when the amount of the ethylenediaminetetraacetic acid disodium salt is higher than the above ratio range, white precipitates are likely to appear in the first plating solution.

[0008] Preferably, the first plating solution further comprises a leveling agent component and / or a brightener component, the leveling agent component comprises at least one of peregalon, polyethylene glycol, and the brightener component comprises at least one of heliotropin, gum arabic, and dextrin. In the leveling agent component, both peregalon and polyethylene glycol can function to prevent the tin-cadmium alloy layer from having burrs, and in addition, polyethylene glycol can also function to eliminate pinholes in the process of forming the tin-cadmium alloy layer, and the combination of peregalon and polyethylene glycol can further promote the tin-cadmium alloy crystallinity. In the brightener component, the combination of heliotropin and gum arabic can effectively improve the gloss of the tin-cadmium alloy layer.

[0009] Preferably, the weight average molecular weight of the polyethylene glycol is 6000-12000.

[0010] Preferably, the first plating solution comprises cadmium sulfate, stannous chloride, disodium ethylenediaminetetraacetate, nitrilotriacetic acid, ammonium chloride, polyethylene glycol, heliotropin, gum arabic, and the components of the first plating solution satisfy the following conditions: cadmium sulfate 30 g / L to 50 g / L, stannous chloride 8 g / L to 15 g / L, disodium ethylenediaminetetraacetate 30 g / L to 60 g / L, nitrilotriacetic acid 30 g / L to 60 g / L, ammonium chloride 200 g / L to 300 g / L, polyethylene glycol 2 g / L to 5 g / L, heliotropin 1 g / L to 2 g / L, and gum arabic 2 g / L to 5 g / L; or ammonium fluoride is used to replace the ammonium chloride in the above formula, and the content of ammonium fluoride in the first plating solution is 80 g / L to 100 g / L; or dextrin is used to replace the gum arabic in the above formula, and the content of dextrin in the first plating solution is 2 g / L to 3 g / L.

[0011] Preferably, the first plating solution further comprises paraformaldehyde, and the content of paraformaldehyde in the first plating solution is 3 g / L to 5 g / L.

[0012] Preferably, the pH value of the first plating solution is 4 to 6. By controlling the pH value of the first plating solution within the above range, the co-deposition of tin and cadmium is facilitated, thereby further improving the plating quality of the tin-cadmium alloy layer.

[0013] Preferably, the pH value of the first plating solution is 4.5 to 5.

[0014] Preferably, the preparation of the first plating solution comprises the following steps: step A. separately dissolving disodium ethylenediaminetetraacetate and cadmium salt with water to obtain a disodium ethylenediaminetetraacetate aqueous solution and a cadmium salt aqueous solution, and mixing the disodium ethylenediaminetetraacetate aqueous solution and the cadmium salt aqueous solution to obtain a first raw material solution; step B. dissolving an ammonium salt in water to obtain an ammonium salt aqueous solution, dissolving nitrilotriacetic acid in water to obtain a nitrilotriacetic acid solution, and then adding a tin salt to the nitrilotriacetic acid solution to obtain an acidified tin salt solution, and mixing the ammonium salt aqueous solution and the acidified tin salt solution to obtain a second raw material solution; and step C. mixing the first raw material solution and the second raw material solution. It should be noted that, in the preparation of the first plating solution, the preparation of the first raw material solution (step A) and the preparation of the second raw material solution (step B) do not need to strictly follow a specific order, and the first raw material solution can be prepared first and then the second raw material solution, or the second raw material solution can be prepared first and then the first raw material solution, or the first raw material solution and the second raw material solution can be prepared simultaneously. By preparing the first plating solution in the above manner, the corrosion of the first plating solution to the magnetron film as the base film is reduced, and the co-deposition state of tin and cadmium is further optimized, thereby improving the plating quality of the tin-cadmium alloy layer.

[0015] Preferably, when the first electroplating solution further comprises a leveler component and a brightener component, during the preparation of the first electroplating solution, a step D is further provided after the step C, the step D comprising: dissolving the leveler component in water to prepare a leveler solution, dissolving the brightener component in an alcohol solvent to prepare a brightener solution, and then adding the leveler solution and the brightener solution into the mixed solution prepared in the step C.

[0016] Preferably, during the preparation of the first electroplating solution, a pH adjusting operation is further provided, so that the pH of the first electroplating solution reaches 4-6 before the first electroplating solution is used for electroplating.

[0017] Preferably, in the S1 of the conductive layer forming process, the tin-cadmium alloy layer is formed by electroplating using the first electroplating solution, the cathode current density is 0.5 A*dm -2 -1 A*dm -2 , and the electroplating temperature is 10-30°C.

[0018] Optionally, in the S1 of the conductive layer forming process, the anode used for electroplating the tin-cadmium alloy layer is selected from a tin-cadmium alloy anode, a tin metal anode, and a cadmium metal anode.

[0019] According to a second aspect of the present application, a functional current collector containing a tin-cadmium alloy is provided, the functional current collector comprising a base film and a conductive layer; the base film comprises a polymer substrate and a first metal layer which are arranged in a stack, and the first metal layer comprises at least one of copper, a copper alloy, aluminum, and an aluminum alloy; the conductive layer comprises a tin-cadmium alloy layer and a second metal layer which are arranged in a stack, the tin-cadmium alloy layer contains a tin-cadmium alloy, and the second metal layer contains at least one of copper, a copper alloy, aluminum, and an aluminum alloy; the first metal layer, the tin-cadmium alloy layer, and the second metal layer are arranged in a stack in the thickness direction of the functional current collector. In the functional current collector provided by the present application, the tin-cadmium alloy layer is arranged to effectively improve the adhesion between the base film and the conductive layer, and to improve the compactness of the second metal layer, thereby improving the structural stability and the electrical conductivity of the functional current collector, and further improving the ductility of the functional current collector, which is beneficial to improving the mechanical strength of the functional current collector.

[0020] Preferably, in the tin-cadmium alloy, the tin content is 20-40 wt.%, and the cadmium content is 60-80 wt.%.

[0021] Preferably, in the tin-cadmium alloy, the tin content is 30 wt.%, and the cadmium content is 70 wt.%.

[0022] Preferably, the thickness of the tin-cadmium alloy layer is 100-500 nm. The thickness of the tin-cadmium alloy layer reaching the above range is beneficial to reducing the difficulty of forming the subsequent second metal layer.

[0023] Preferably, the thickness of the first metal layer is 20-100 nm.

[0024] Preferably, the thickness of the second metal layer is 100-500 nm.

[0025] Preferably, the sheet resistance of the functional current collector is ≤ 23 mΩ.

[0026] According to a third aspect of the present application, there is provided a secondary battery comprising the functional current collector comprising the tin-cadmium alloy as described above. DETAILED DESCRIPTION

[0027] In order to make the person skilled in the art better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0028] Embodiment 1

[0029] In this embodiment, a magnetron film with a sheet resistance of 1.5 Ω is used as a base film for preparing the functional current collector. The magnetron film used in this embodiment is composed of a polymer substrate and copper metal layers arranged on both sides of the polymer substrate. The polymer substrate is made of polypropylene (PP) and has a thickness of 4.5 μm. The copper metal layer directly combined with the surface of the polymer substrate is marked as the first metal layer, and the thickness of each first metal layer is 40 nm.

[0030] In the process of preparing the functional current collector in this embodiment, two electroplating treatments are involved. The electroplating solution used includes a first electroplating solution and a second electroplating solution. The components and preparation method of the first electroplating solution and the second electroplating solution are described as follows.

[0031] The components of the first electroplating solution used in this embodiment are as follows: cadmium sulfate 40 g / L, stannous chloride 12 g / L, disodium ethylenediaminetetraacetate 50 g / L, nitrilotriacetic acid 40 g / L, ammonium chloride 250 g / L, polyethylene glycol (weight average molecular weight 8000) 5 g / L, peregal 5 g / L, heliotropin 2 g / L, and gum arabic 5 g / L. The first electroplating solution is prepared according to the above components by the following steps:

[0032] Step A. Dissolve disodium ethylenediaminetetraacetate in pure water at 70 °C until the disodium ethylenediaminetetraacetate is completely dissolved to obtain a disodium ethylenediaminetetraacetate aqueous solution. Dissolve cadmium sulfate in a small amount of pure water to obtain a cadmium sulfate aqueous solution. Add the cadmium sulfate aqueous solution to the disodium ethylenediaminetetraacetate aqueous solution and stir uniformly to obtain a first raw material solution.

[0033] Step B. A small amount of warm pure water is added to ammonium chloride until the ammonium chloride is dissolved to obtain an ammonium chloride aqueous solution; nitrilotriacetic acid is dissolved in a small amount of warm pure water to obtain a nitrilotriacetic acid solution, then stannous chloride is added to the nitrilotriacetic acid solution, and after being fully dissolved, an acidified stannous chloride solution is obtained; then the acidified stannous chloride solution is added to the ammonium chloride aqueous solution, and stirred uniformly to obtain a second raw material solution.

[0034] Step C. The first raw material solution and the second raw material solution are mixed to obtain a plating solution mother liquor.

[0035] Step D. Nerolidol and gum arabic are dissolved in an ethanol solution to obtain a brightener solution; the brightener solution is used to dissolve polyethylene glycol and peregal in a small amount of hot pure water to obtain a leveling agent solution, then the leveling agent solution is added to the plating solution mother liquor, then the brightener solution is added thereto, and after being fully stirred, a first plating solution semi-product is obtained.

[0036] Step E. The first plating solution semi-product is diluted to a preset total volume according to the component composition of the first plating solution, stirred uniformly, and the pH value of the solution is adjusted to pH = 5 using ammonia water, thereby obtaining the first plating solution.

[0037] The component composition of the second plating solution used in this embodiment is specifically as follows: 1,4-cyclohexanedione monomethyl glycol ketal 0.1 g / L, potassium phthalimide 0.2 g / L, 3-amino-1,2-propanediol 0.3 g / L, copper sulfate 120 g / L, sulfuric acid 70 g / L, chloride ion 70 mg / L, ethylene thiourea 0.0005 mg / L, sodium dodecyl sulfonate 0.08 mg / L, and polyethylene glycol 0.07 g / L. The preparation of the second plating solution is completed according to the above component composition and the following steps:

[0038] Step A. 10 g of 1,4-cyclohexanedione monomethyl glycol ketal is added to 200 mL of pure water, and stirred until the 1,4-cyclohexanedione monomethyl glycol ketal is completely dissolved to obtain a clear solution, thereby completing the preparation of the 1,4-cyclohexanedione monomethyl glycol ketal solution.

[0039] Step B. 30 g of 3-amino-1,2-propanediol is added to 500 mL of pure water, and stirred until the 3-amino-1,2-propanediol is completely dissolved to obtain a clear solution, thereby completing the preparation of the 3-amino-1,2-propanediol solution.

[0040] Step C. Potassium phthalimide is slowly added to the 1,4-cyclohexanedione monomethyl glycol ketal solution, and stirred until the mixture is completely dissolved, then the 3-amino-1,2-propanediol solution is slowly added to the mixture, and then pure water is added to make up to 1 L, and the mixture is continuously stirred until it is uniformly mixed, thereby obtaining a copper plating additive.

[0041] Step D. Copper sulfate, sulfuric acid, chloride ion (chloride ion is provided by commercially available hydrochloric acid, concentration 10 ml / L, grade analytical pure), ethylenethiourea, sodium dodecyl sulfonate and polyethylene glycol are mixed in pure water, and then 10 mL of copper plating additive is added thereto, and mixed thoroughly to obtain a second electroplating solution.

[0042] The base film is loaded into an electroplating device loaded with the first electroplating solution and the second electroplating solution prepared in this example, and the conductive layer forming process is completed according to the following operation:

[0043] S1. The base film is unwound by using the electroplating device, washed with water, and the film line speed is controlled at 3 m / min. The base film is allowed to enter the electroplating tank loaded with the first electroplating solution, the temperature of the plating solution is controlled at 20°C, a tin-cadmium alloy plate (mass ratio Cd / Sn = 6:4) is used as the anode, and the cathode current density is set at 1 A*dm -2 , thereby plating a tin-cadmium alloy layer on the surface of the first metal layer of the base film.

[0044] S2. The base film with the tin-cadmium alloy layer on the surface is allowed to enter the brush plating tank loaded with the second electroplating solution, the temperature of the plating solution is controlled at 40°C, and the brush plating voltage is set at 2V. The surface of the tin-cadmium alloy layer is subjected to electro-brush copper plating treatment, thereby plating a copper metal layer on the surface of the tin-cadmium alloy layer as a second metal layer, to obtain a semi-finished film.

[0045] S3. The semi-finished film is sequentially subjected to double reverse flow water washing treatment, anti-oxidation treatment, drying treatment and winding treatment, wherein the winding treatment includes slitting. Thus, the functional current collector of this example is prepared.

[0046] In the functional current collector prepared in this example, the surface of the base film is sequentially covered with a tin-cadmium alloy layer and a second metal layer. On any surface of the base film, the thickness of the tin-cadmium alloy layer is 500 nm, and the thickness of the second metal layer is 460 nm. The tin-cadmium alloy layer and the second metal layer together serve as the conductive layer of the functional current collector.

[0047] Example 2

[0048] The base film used to prepare the functional current collector in this example is consistent with the base film used in Example 1.

[0049] In the process of preparing the functional current collector in this example, two electroplating treatments are involved, and the electroplating solution used includes a first electroplating solution and a second electroplating solution. The composition and preparation method of the second electroplating solution are consistent with those of the second electroplating solution used in Example 1. The composition and preparation method of the first electroplating solution are as follows.

[0050] The component composition of the first electroplating solution used in the embodiment is specifically as follows: cadmium sulfate 40 g / L, stannous chloride 12 g / L, disodium ethylenediaminetetraacetate 50 g / L, nitrilotriacetic acid 40 g / L, ammonium chloride 250 g / L, polyethylene glycol (weight average molecular weight 8000) 5 g / L, heliotropin 2 g / L, and gum arabic 5 g / L. The preparation of the first electroplating solution is completed according to the above component composition and the following steps:

[0051] Step A. Dissolve disodium ethylenediaminetetraacetate in pure water at 70°C until the disodium ethylenediaminetetraacetate is completely dissolved to obtain a disodium ethylenediaminetetraacetate aqueous solution; dissolve cadmium sulfate in a small amount of pure water to obtain a cadmium sulfate aqueous solution; add the cadmium sulfate aqueous solution to the disodium ethylenediaminetetraacetate aqueous solution and stir uniformly to obtain a first raw material solution.

[0052] Step B. Add a small amount of warm pure water to ammonium chloride to obtain an ammonium chloride aqueous solution after the ammonium chloride is dissolved; dissolve nitrilotriacetic acid in a small amount of warm pure water to obtain a nitrilotriacetic acid solution, then add stannous chloride to the nitrilotriacetic acid solution, and fully dissolve to obtain an acidified stannous chloride solution; then add the acidified stannous chloride solution to the ammonium chloride aqueous solution and stir uniformly to obtain a second raw material solution.

[0053] Step C. Mix the first raw material solution and the second raw material solution to obtain an electroplating solution mother liquor.

[0054] Step D. Dissolve heliotropin and dextrin in an ethanol solution to obtain a brightener solution; dissolve polyethylene glycol in a small amount of hot pure water to obtain a leveling agent solution, then add the leveling agent solution to the electroplating solution mother liquor, then add the brightener solution thereto, and fully stir to obtain a first electroplating solution semi-product.

[0055] Step E. Dilute the first electroplating solution semi-product to a preset total volume according to the component composition of the first electroplating solution, stir uniformly, and adjust the pH value of the solution with ammonia water until the solution pH = 5, thereby obtaining the first electroplating solution.

[0056] The base film is loaded into an electroplating device loaded with the first electroplating solution and the second electroplating solution prepared in the embodiment to complete the conductive layer forming process. In the conductive layer forming process of the embodiment, the full-line film drawing speed is 5 m / min. Except that the first electroplating solution used in the embodiment is different from that in Embodiment 1, the other materials involved in the conductive layer forming process of the embodiment and the corresponding operations are consistent with those in the conductive layer forming process of Embodiment 1.

[0057] In the functional current collector prepared in the embodiment, the surface of the base film is sequentially covered with a tin-cadmium alloy layer and a second metal layer. On either surface of the base film, the tin-cadmium alloy layer has a thickness of 500 nm, and the second metal layer has a thickness of 460 nm. The tin-cadmium alloy layer and the second metal layer together serve as the conductive layer of the functional current collector.

[0058] Embodiment 3

[0059] The base film used for preparing the functional current collector in the embodiment is identical to the base film used in Embodiment 1.

[0060] In the process of preparing the functional current collector in the embodiment, two electroplating processes are involved. The electroplating solution used includes a first electroplating solution and a second electroplating solution. The second electroplating solution has the same composition and preparation method as the second electroplating solution used in Embodiment 1. The first electroplating solution has the following composition and preparation method.

[0061] The first electroplating solution used in the embodiment has the following composition: cadmium sulfate 40 g / L, stannous chloride 12 g / L, disodium ethylenediaminetetraacetate 50 g / L, nitrilotriacetic acid 40 g / L, ammonium fluoride 90 g / L, polyethylene glycol (weight average molecular weight 8000) 5 g / L, peregal 5 g / L, heliotropin 2 g / L, and dextrin 4 g / L. The first electroplating solution is prepared according to the above composition by the following steps:

[0062] Step A. Dissolve disodium ethylenediaminetetraacetate in pure water at 70°C until the disodium ethylenediaminetetraacetate is completely dissolved to obtain a disodium ethylenediaminetetraacetate aqueous solution. Dissolve cadmium sulfate in a small amount of pure water to obtain a cadmium sulfate aqueous solution. Add the cadmium sulfate aqueous solution to the disodium ethylenediaminetetraacetate aqueous solution and stir until uniform to obtain a first raw material solution.

[0063] Step B. Add a small amount of warm pure water to ammonium fluoride to dissolve the ammonium fluoride and obtain an ammonium fluoride aqueous solution. Dissolve nitrilotriacetic acid in a small amount of warm pure water to obtain a nitrilotriacetic acid solution. Then add stannous chloride to the nitrilotriacetic acid solution and fully dissolve to obtain an acidified stannous chloride solution. Then add the acidified stannous chloride solution to the ammonium fluoride aqueous solution and stir until uniform to obtain a second raw material solution.

[0064] Step C. Mix the first raw material solution and the second raw material solution to obtain an electroplating solution mother liquor.

[0065] Step D. Dissolve heliotropin and dextrin in an ethanol solution to obtain a brightener solution. Dissolve polyethylene glycol and peregal in a small amount of hot pure water to obtain a leveling agent solution. Then add the leveling agent solution to the electroplating solution mother liquor. Then add the brightener solution to the mixture and fully stir to obtain a first electroplating solution semi-finished product.

[0066] Step E. Dilute the first electroplating solution semi-finished product to a preset total volume according to the component composition of the first electroplating solution, stir uniformly, and adjust the pH value of the solution to pH = 5 by using ammonia water, thereby obtaining the first electroplating solution.

[0067] The base film is loaded into the electroplating equipment loaded with the first electroplating solution and the second electroplating solution prepared in this example, and the conductive layer forming process is completed. During the conductive layer forming process of this example, the full-line film drawing speed is 7 m / min. Except that the film drawing speed and the first electroplating solution used constitute the difference from Example 1, the other materials involved in the conductive layer forming process of this example and the corresponding operations are consistent with the conductive layer forming process in Example 1.

[0068] In the functional current collector prepared in this example, the surface of the base film is sequentially covered with a tin-cadmium alloy layer and a second metal layer. On any surface of the base film, the thickness of the tin-cadmium alloy layer is 500 nm, and the thickness of the second metal layer is 460 nm. The tin-cadmium alloy layer and the second metal layer together serve as the conductive layer of the functional current collector.

[0069] Comparative Example 1

[0070] The base film used to prepare the functional current collector in this comparative example is consistent with the base film used in Example 1.

[0071] During the preparation of the functional current collector in this comparative example, the electroplating solution used in the electroplating process is the second electroplating solution prepared in Example 1.

[0072] The base film is loaded into the electroplating equipment loaded with the second electroplating solution prepared in Example 1, and the conductive layer forming process is completed according to the following operations:

[0073] S1. The base film is unwound using the electroplating equipment, washed with water, and the full-line film drawing speed is 3 m / min. The base film is allowed to enter the brush plating tank containing the second electroplating solution, the plating solution temperature is controlled at 40°C, and the brush plating voltage is set at 2V. Thus, a copper metal layer is plated on the surface of the first metal layer of the base film as a second metal layer, and a semi-finished film is obtained.

[0074] S2. The semi-finished film is sequentially subjected to double reverse flow water washing treatment, oxidation resistance treatment, drying treatment, and winding treatment. The related operations involved in this step are consistent with S3 in the conductive layer forming process of Example 1. Thus, the functional current collector of this comparative example is prepared.

[0075] In the functional current collector prepared in this comparative example, the surface of the base film is covered with a second metal layer. On any surface of the base film, the thickness of the second metal layer is 960 nm. The second metal layer serves as the conductive layer of the functional current collector.

[0076] Comparative Example 2

[0077] The base film for preparing the functional current collector of the present comparative example is identical to that employed in Example 2.

[0078] In the process of preparing the functional current collector of the present comparative example, the plating solution employed in the plating treatment involved is the second plating solution employed in Example 2, i.e., identical to the second plating solution prepared in Example 1.

[0079] The base film is loaded into the plating apparatus loaded with the above-mentioned second plating solution, and the conductive layer forming process is completed according to the following operations:

[0080] S1. The base film is unwound using the plating apparatus, washed with water, and drawn at a line speed of 5 m / min, so that the base film enters the brush plating tank loaded with the second plating solution, the plating solution temperature is controlled at 40°C, and the brush plating voltage is set at 2 V, so as to plate a copper metal layer as the second metal layer on the surface of the first metal layer of the base film, thereby obtaining a semi-finished film.

[0081] S2. The semi-finished film is sequentially subjected to double reverse flow washing treatment, oxidation resistance treatment, drying treatment, and winding treatment, and the related operations involved in this step are identical to S3 in the conductive layer forming process of Example 2, thereby preparing the functional current collector of the present comparative example.

[0082] In the functional current collector prepared in the present comparative example, the surface of the base film is covered with the second metal layer, and the thickness of the second metal layer on any surface of the base film is 960 nm, and the second metal layer serves as the conductive layer of the functional current collector.

[0083] Comparative Example 3

[0084] The base film for preparing the functional current collector of the present comparative example is identical to that employed in Example 3.

[0085] In the process of preparing the functional current collector of the present comparative example, the plating solution employed in the plating treatment involved is the second plating solution employed in Example 3, i.e., identical to the second plating solution prepared in Example 1.

[0086] The base film is loaded into the plating apparatus loaded with the above-mentioned second plating solution, and the conductive layer forming process is completed according to the following operations:

[0087] S1. The base film is unwound using the plating apparatus, washed with water, and drawn at a line speed of 7 m / min, so that the base film enters the brush plating tank loaded with the second plating solution, the plating solution temperature is controlled at 40°C, and the brush plating voltage is set at 2 V, so as to plate a copper metal layer as the second metal layer on the surface of the first metal layer of the base film, thereby obtaining a semi-finished film.

[0088] S2. The semi-finished film is sequentially subjected to double reverse-flow water washing treatment, anti-oxidation treatment, drying treatment and winding treatment. The related operations involved in this step are consistent with S3 in the conductive layer forming process of Example 3. Thus, the functional current collector of this comparative example is prepared.

[0089] In the functional current collector prepared in this comparative example, the surface of the base film is covered with the second metal layer, and the thickness of the second metal layer on either surface of the base film is 960 nm. The second metal layer is used as the conductive layer of the functional current collector.

[0090] Comparative Example 4

[0091] The base film used to prepare the functional current collector in this comparative example is consistent with that used in Example 1.

[0092] In the process of preparing the functional current collector in this comparative example, two electroplating treatments are involved. The electroplating solution used includes a first electroplating solution and a second electroplating solution. The composition and preparation method of the second electroplating solution are consistent with those of the second electroplating solution used in Example 1. The composition and preparation method of the first electroplating solution are as follows.

[0093] The first electroplating solution used in this comparative example is different from the first electroplating solution used in Example 1 in that the first electroplating solution used in this comparative example does not contain cadmium sulfate. Specifically, the composition of the first electroplating solution used in this comparative example is as follows: stannous chloride 12 g / L, disodium ethylenediaminetetraacetate 50 g / L, nitrilotriacetic acid 40 g / L, ammonium chloride 250 g / L, polyethylene glycol (weight average molecular weight 8000) 5 g / L, peregal 5 g / L, heliotropin 2 g / L, and gum arabic 5 g / L.

[0094] Based on the difference between the composition of the first electroplating solution used in this comparative example and that used in Example 1, the raw materials used to prepare the first electroplating solution in this comparative example do not include cadmium sulfate. Accordingly, the steps for preparing the first electroplating solution in this comparative example are completed by referring to Example 1. The difference between this comparative example and Example 1 is that the operation involving cadmium sulfate is omitted in the process of preparing the first electroplating solution in this comparative example. Except for this difference, the other operations for preparing the first electroplating solution in this comparative example are consistent with those in Example 1.

[0095] The base film is loaded into the electroplating equipment loaded with the first electroplating solution and the second electroplating solution prepared in this comparative example, and the conductive layer forming process is completed. In the conductive layer forming process of this comparative example, the full-line film line speed is 3 m / min. Except for the difference between the first electroplating solution used and that used in Example 1, the other materials and corresponding operations involved in the conductive layer forming process of this comparative example are consistent with those in Example 1.

[0096] In the functional current collector prepared in the present comparative example, the surface of the base film is sequentially covered with a tin metal layer and a second metal layer, and on either surface of the base film, the thickness of the tin metal layer is 500 nm and the thickness of the second metal layer is 460 nm, so that the tin metal layer and the second metal layer together serve as the conductive layer of the functional current collector.

[0097] Comparative Example 5

[0098] The base film used for preparing the functional current collector in the present comparative example is identical to the base film used in Example 1.

[0099] In the process of preparing the functional current collector in the present comparative example, two plating processes are involved, and the plating solutions used include a first plating solution and a second plating solution, wherein the composition and preparation of the second plating solution are identical to those of the second plating solution used in Example 1. The composition and preparation of the first plating solution are as follows.

[0100] The first plating solution used in the present comparative example differs from the first plating solution used in Example 1 in that the first plating solution used in the present comparative example does not contain stannous chloride. Specifically, the composition of the first plating solution used in the present comparative example is as follows: cadmium sulfate 40 g / L, disodium ethylenediaminetetraacetate 50 g / L, nitrilotriacetic acid 40 g / L, ammonium chloride 250 g / L, polyethylene glycol (weight average molecular weight 8000) 5 g / L, peregal 5 g / L, heliotropin 2 g / L, and gum arabic 5 g / L.

[0101] Based on the difference between the composition of the first plating solution used in the present comparative example and that used in Example 1, the raw materials used for preparing the first plating solution in the present comparative example do not include stannous chloride. Accordingly, the steps for preparing the first plating solution in the present comparative example are completed by referring to the steps for preparing the first plating solution in Example 1, and the difference between the present comparative example and Example 1 is that the present comparative example omits the operation involving stannous chloride in the process of preparing the first plating solution, and other operations for preparing the first plating solution in the present comparative example are identical to those in Example 1.

[0102] The base film is loaded into the plating equipment loaded with the first plating solution and the second plating solution prepared in the present comparative example, and the conductive layer forming process is completed. In the conductive layer forming process of the present comparative example, the line speed of the full-drawing film is 3 m / min, and except for the difference between the first plating solution used in the present comparative example and that used in Example 1, other materials and corresponding operations involved in the conductive layer forming process of the present comparative example are identical to those in Example 1.

[0103] In the functional current collector prepared in the present comparative example, the surface of the base film is sequentially covered with a cadmium metal layer and a second metal layer, and on either surface of the base film, the thickness of the cadmium metal layer is 500 nm and the thickness of the second metal layer is 460 nm, with the cadmium metal layer and the second metal layer together serving as the conductive layer of the functional current collector.

[0104] Test Example 1

[0105] 1. Test Object

[0106] The functional current collectors prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were used as test objects in the present test example, with 50 replicates for each test object and 1 replicate for each sample.

[0107] 2. Test Items and Test Methods Thereof

[0108] (1) Compactness Test: The compactness test was performed in a dark room, with the test object being tightly attached to and fully covering the backlight plate (light-emitting surface) of a flat backlight, the flat backlight being turned on, and a camera being used to take a picture of the projection of the light-emitting surface along the light propagation direction at an angle perpendicular to the backlight plate, the light spot area (light-transmitting area) in the picture representing the non-compact area of the test object and the dark area in the picture representing the compact area of the test object, the compactness of the test object being characterized in the following manner:

[0109] Compactness = Compact Area / Backlight Plate Area.

[0110] A compactness of ≥ 90% was taken as the pass standard.

[0111] (2) Elongation Test: The test object was baked at 150°C for 3 minutes, and the test object was cut into 15-mm-wide strip samples along MD (machine direction) and TD (transverse direction) respectively, the edges of the strip samples were checked to ensure that there were no notches or burrs and that the film surface of the strip samples was not damaged, and the qualified strip samples were used for testing. The strip samples were placed in the upper and lower clamps of a tensile testing machine, the strip samples were clamped and tensioned by the clamps, the running speed of the tensile testing machine was set to 50 mm / min, and the tensile distance was set to 50 mm, and the strip samples were stretched for testing. An elongation of ≥ 3% was taken as the pass standard.

[0112] (3) Adhesion Test: The functional current collector was baked at a temperature of 150°C for 3 minutes, and then cooled to room temperature, 3M tape was adhered to the surface of the functional current collector, and then a 2-kg standard pressure roller was used to roll on the surface of the 3M tape (the side facing away from the functional current collector) once, and then the 3M tape was peeled off from the surface of the functional current collector at an angle of 180° and a speed of 100 mm / min. After the 3M tape was completely peeled off, the proportion of the area of the second metal layer that was peeled off by the 3M tape to the total area of the second metal layer was calculated.

[0113] 3. Test results

[0114] In the test objects, the functional set fluid provided by Example 1 and Comparative Example 1 were mutually controlled, the functional set fluid provided by Example 2 and Comparative Example 2 were mutually controlled, and the functional set fluid provided by Example 3 and Comparative Example 3 were mutually controlled. In the above mutually controlled groups, the difference was whether the electroplating process of applying the first electroplating solution containing cadmium salt and tin salt was included in the process of preparing the functional set fluid. Based on the above difference, the functional set fluid of Examples 1-3 were all provided with a tin-cadmium alloy layer, while the functional set fluid of Comparative Examples 1-3 were all not provided with a tin-cadmium alloy layer. From the test data, it can be seen that in the above mutually controlled groups, the functional set fluid provided with a tin-cadmium alloy layer achieved higher compactness of the conductive layer and higher ductility, and in the adhesion test, the functional set fluid provided with a tin-cadmium alloy layer did not have the second metal layer fall off, while the second metal layer of the functional set fluid not provided with a tin-cadmium alloy layer had about 2%-5% fall off to different degrees. In the process of preparing the functional set fluid of Examples 1-3, the tin-cadmium alloy layer was made on the surface of the first metal layer before the second metal layer was formed, and after the tin-cadmium alloy layer was formed, the film composed of the base film and the tin-cadmium alloy layer was used as the forming carrier of the second metal layer. The provision of the tin-cadmium alloy layer can improve the surface defects of the first metal layer and reduce the sheet resistance of the second metal layer forming carrier, thereby improving the forming quality of the second metal layer. As the second metal layer formed on the surface of the tin-cadmium alloy layer in the process of preparing the functional set fluid of Examples 1-3 did not fall off in the adhesion test, it shows that the second metal layer of these functional set fluids has higher cohesion. In summary, based on the provision of the tin-cadmium alloy layer, the functional set fluid prepared by Examples 1-3 respectively achieved high compactness, high ductility, and excellent structural stability. The sheet resistance of the functional set fluid prepared by the three examples was not more than 23 mΩ.

[0115] In Comparative Examples 4 and 5, the electroplating film-drawing speed was the same as in Example 1 during the preparation of the functional current collectors. The difference in the conductive layer configuration of the functional current collectors obtained from the three examples was that a tin-cadmium alloy layer was placed between the first and second metal layers of the functional current collector in Example 1, a tin metal layer was placed between the first and second metal layers of the functional current collector in Comparative Example 4, and a cadmium metal layer was placed between the first and second metal layers of the functional current collector in Comparative Example 5. Using the functional current collector obtained in Example 1 as a comparison, the elongation of the functional current collectors obtained in Comparative Examples 4 and 5 was also relatively low. This indicates that, compared to tin metal and cadmium metal, a tin-cadmium alloy is more beneficial for improving the elongation of functional current collectors. Furthermore, the functional current collector with a tin metal layer (Comparative Example 4) exhibited a second metal layer detachment during the adhesion test, demonstrating that the quality of the second metal layer in the functional current collector was poor. While the functional current collector with a cadmium metal layer (Comparative Example 5) remained detached during the adhesion test, the addition of the cadmium metal layer significantly increased the cost of the functional current collector compared to the tin-cadmium alloy layer.

[0116] Table 1. Statistical results of test case 1

[0117]

[0118] Example 4

[0119] This embodiment refers to Example 1 for preparing a functional current collector. The preparation of the functional current collector in this embodiment also involves two electroplating processes. The electroplating solutions used include a first electroplating solution and a second electroplating solution. The composition and preparation method of the second electroplating solution are consistent with those used in Example 1. This embodiment follows the process of preparing the first electroplating solution in Example 1. In this embodiment, the specific operations, material types, and amounts in steps A, B, C, and D are consistent with those in Example 1. However, in step E of preparing the first electroplating solution, the pH value of the semi-finished first electroplating solution is adjusted to 4, thus obtaining the first electroplating solution of this embodiment. Therefore, the only difference between the first electroplating solutions prepared in this embodiment and those prepared in Example 1 is the pH value. The pH value of the first electroplating solution prepared in this embodiment is 4, while the pH value of the first electroplating solution prepared in Example 1 is 5.

[0120] The base film is loaded into the electroplating equipment loaded with the first electroplating solution and the second electroplating solution prepared in the present example to complete the conductive layer forming process. During the conductive layer forming process of the present example, the full-line film drawing speed is 3 m / min. Except that the first electroplating solution used in the present example is different from that in Example 1, the other materials and corresponding operations involved in the conductive layer forming process of the present example are consistent with those in the conductive layer forming process of Example 1.

[0121] In the functional current collector prepared in the present example, the surface of the base film is sequentially covered with a tin-cadmium alloy layer and a second metal layer. On either surface of the base film, the thickness of the tin-cadmium alloy layer is 500 nm, and the thickness of the second metal layer is 460 nm. The tin-cadmium alloy layer and the second metal layer together serve as the conductive layer of the functional current collector.

[0122] Example 5

[0123] The functional current collector is prepared in the present example with reference to Example 1. During the preparation of the functional current collector in the present example, two electroplating processes are involved. The electroplating solutions used include a first electroplating solution and a second electroplating solution. The composition and preparation method of the second electroplating solution are consistent with those of the second electroplating solution used in Example 1. The preparation of the first electroplating solution in the present example is completed with reference to the preparation of the first electroplating solution in Example 1. During the preparation of the first electroplating solution in the present example, the specific operations, types and amounts of materials involved in steps A, B, C and D are consistent with those in Example 1. However, in step E of preparing the first electroplating solution in the present example, the pH value of the first electroplating solution semi-product is adjusted to 6. Thus, the first electroplating solution in the present example is obtained. Therefore, the only difference between the first electroplating solutions prepared in the present example and in Example 1 is the pH value. The pH value of the first electroplating solution prepared in the present example is 6, while the pH value of the first electroplating solution prepared in Example 1 is 5.

[0124] The base film is loaded into the electroplating equipment loaded with the first electroplating solution and the second electroplating solution prepared in the present example to complete the conductive layer forming process. During the conductive layer forming process of the present example, the full-line film drawing speed is 3 m / min. Except that the first electroplating solution used in the present example is different from that in Example 1, the other materials and corresponding operations involved in the conductive layer forming process of the present example are consistent with those in the conductive layer forming process of Example 1.

[0125] In the functional current collector prepared in the present example, the surface of the base film is sequentially covered with a tin-cadmium alloy layer and a second metal layer. On either surface of the base film, the thickness of the tin-cadmium alloy layer is 500 nm, and the thickness of the second metal layer is 460 nm. The tin-cadmium alloy layer and the second metal layer together serve as the conductive layer of the functional current collector.

[0126] Example 6

[0127] The functional current collector of the present example is prepared according to the process of Example 1. In the process of preparing the functional current collector of the present example, two plating processes are involved, and the plating solutions used include a first plating solution and a second plating solution. The second plating solution used in the present example is identical to the second plating solution used in Example 1 in terms of the composition and preparation. The first plating solution of the present example is prepared according to the process of preparing the first plating solution of Example 1. In the process of preparing the first plating solution of the present example, the specific operations, types and amounts of materials involved in Step A, Step B, Step C and Step D are identical to those of Example 1. However, in Step E of preparing the first plating solution of the present example, the pH value of the first plating solution semi-product is adjusted to 3.8, thereby obtaining the first plating solution of the present example. Thus, the only difference between the first plating solutions prepared in the present example and Example 1 is the pH value. The pH value of the first plating solution prepared in the present example is 3.8, while the pH value of the first plating solution prepared in Example 1 is 5.

[0128] The base film is loaded into the plating equipment loaded with the first plating solution and the second plating solution prepared in the present example, and the conductive layer forming process is completed. In the conductive layer forming process of the present example, the line speed of the film drawing is 3 m / min. Except for the first plating solution used, the other materials and corresponding operations involved in the conductive layer forming process of the present example are identical to those of Example 1.

[0129] In the functional current collector prepared in the present example, the surface of the base film is sequentially covered with a tin-cadmium alloy layer and a second metal layer. On either surface of the base film, the thickness of the tin-cadmium alloy layer is 500 nm, and the thickness of the second metal layer is 460 nm. The tin-cadmium alloy layer and the second metal layer together serve as the conductive layer of the functional current collector.

[0130] Example 7

[0131] The functional current collector of the present example is prepared according to the method of Example 1. In the process of preparing the functional current collector of the present example, two electroplating processes are involved, and the electroplating solutions used include a first electroplating solution and a second electroplating solution. The composition and preparation of the second electroplating solution used in the present example are consistent with those of the second electroplating solution used in Example 1. The first electroplating solution of the present example is prepared according to the method of preparing the first electroplating solution of Example 1. In the process of preparing the first electroplating solution of the present example, the specific operations, types and amounts of materials involved in steps A, B, C and D are consistent with those of Example 1. However, in step E of preparing the first electroplating solution of the present example, the pH value of the first electroplating solution semi-product is adjusted to 6.2, thereby obtaining the first electroplating solution of the present example. Thus, the only difference between the first electroplating solutions prepared in the present example and Example 1 is the pH value. The pH value of the first electroplating solution prepared in the present example is 6.2, while the pH value of the first electroplating solution prepared in Example 1 is 5.

[0132] The base film is loaded into the electroplating equipment loaded with the first electroplating solution and the second electroplating solution prepared in the present example, and the conductive layer forming process is completed. In the conductive layer forming process of the present example, the full-line film line speed is 3 m / min. Except for the difference in the first electroplating solution used, the other materials and corresponding operations involved in the conductive layer forming process of the present example are consistent with those of the conductive layer forming process of Example 1.

[0133] In the functional current collector prepared in the present example, the surface of the base film is sequentially covered with a tin-cadmium alloy layer and a second metal layer. On either surface of the base film, the thickness of the tin-cadmium alloy layer is 500 nm, and the thickness of the second metal layer is 460 nm. The tin-cadmium alloy layer and the second metal layer together serve as the conductive layer of the functional current collector.

[0134] Test Example 2

[0135] 1. Test object

[0136] The functional current collectors prepared in Examples 4 to 7 are used as test objects in the present test example, with 50 repetitions for each test object and 1 repetition for each sample.

[0137] 2. Test items and test methods

[0138] (1) Compactness test: the relevant test method is consistent with that of Test Example 1.

[0139] (2) Ductility test: the relevant test method is consistent with that of Test Example 1.

[0140] (3) Adhesion test: the relevant test method is consistent with that of Test Example 1.

[0141] 3. Test results

[0142] The test results are shown in Table 2. The functional set fluid densification test, ductility test, and adhesion test results shown in Table 2 for Example 1 are carried over from the test results in Test Example 1. The test results of this test example show that the pH of the first plating solution can affect the product performance of the functional set fluid. When the pH of the first plating solution is 4-6, the comprehensive performance of the functional set fluid is better. When the pH of the first plating solution used to form the tin-cadmium alloy layer reaches 4-6, the co-deposition of tin and cadmium is facilitated, the plating layer quality of the tin-cadmium alloy layer is improved, and thus the plating layer quality of the second metal layer is also improved.

[0143] Table 2. Test result statistics of Test Example 2

[0144]

[0145]

[0146] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents, and these modifications or replacements are within the protection scope of the present application.

Claims

1. A method for preparing a functional current collector containing a tin-cadmium alloy, characterized in that: The preparation method includes a conductive layer forming step of forming a conductive layer on the surface of a base film. The base film includes a polymer substrate and a first metal layer stacked together. The first metal layer includes at least one of copper, copper alloy, aluminum, and aluminum alloy. The conductive layer forming process includes the following operations: S1. Using the base film as the processing object, a tin-cadmium alloy layer is plated on the surface of the first metal layer, wherein the metal contained in the tin-cadmium alloy layer includes tin-cadmium alloy. S2. A second metal layer is plated on the surface of the tin-cadmium alloy layer, wherein the metal contained in the second metal layer includes copper, copper alloy, aluminum, and aluminum alloy.

2. The preparation method according to claim 1, characterized in that: In step S1 of the conductive layer forming process, the plating solution used to plate the tin-cadmium alloy is a first electroplating solution. The first electroplating solution includes a main salt component and a complexing agent component. The main salt component includes cadmium salt and tin salt. The complexing agent component includes aminotriacetic acid, disodium ethylenediaminetetraacetate, and ammonium salt. The ammonium salt includes at least one of ammonium chloride and ammonium fluoride.

3. The preparation method according to claim 2, characterized in that: The cadmium salt includes cadmium sulfate, and the tin salt includes stannous chloride; When the ammonium salt includes ammonium chloride, the composition of the first electroplating solution, calculated by mass ratio, satisfies the following: cadmium sulfate: stannous chloride: aminotriacetic acid: disodium ethylenediaminetetraacetate: ammonium chloride = 30-50: 8-15: 30-60: 30-60: 200-300; When the ammonium salt includes ammonium fluoride, the composition of the first electroplating solution, calculated by mass ratio, satisfies the following: cadmium sulfate: stannous chloride: aminotriacetic acid: disodium ethylenediaminetetraacetate: ammonium fluoride = 30-50: 8-15: 30-60: 30-60: 80-100.

4. The preparation method according to claim 2, characterized in that: The first electroplating solution further includes a leveling agent component and / or a brightening agent component. The leveling agent component includes at least one of sizing agent and polyethylene glycol, and the brightening agent component includes at least one of jasmine aldehyde, gum arabic, and dextrin.

5. The preparation method according to claim 2, characterized in that: The pH value of the first electroplating solution is 4 to 6.

6. The preparation method according to claim 2, characterized in that, The preparation of the first electroplating solution includes the following operations: Step A. Dissolve disodium ethylenediaminetetraacetate and cadmium salt separately in water to prepare aqueous solutions of disodium ethylenediaminetetraacetate and cadmium salt. Mix the aqueous solutions of disodium ethylenediaminetetraacetate and cadmium salt to obtain the first raw material solution. Step B. Dissolve the ammonium salt in water to obtain an ammonium salt aqueous solution. Dissolve nitric acid in water to obtain a nitric acid solution. Then add tin salt to the solution to obtain an acidified tin salt solution. Mix the ammonium salt aqueous solution and the acidified tin salt solution to obtain a second raw material solution. Step C. Mix the first raw material liquid and the second raw material liquid.

7. A functional current collector containing a tin-cadmium alloy, characterized in that: The functional current collector includes a base film and a conductive layer; The base film includes a polymer substrate and a first metal layer stacked together, wherein the first metal layer includes at least one of copper, copper alloy, aluminum, and aluminum alloy. The conductive layer includes a tin-cadmium alloy layer and a second metal layer stacked together. The tin-cadmium alloy layer contains a tin-cadmium alloy, and the second metal layer contains at least one of copper, copper alloy, aluminum, and aluminum alloy. In the thickness direction of the functional current collector, the first metal layer, the tin-cadmium alloy layer, and the second metal layer are stacked sequentially. The functional current collector is prepared using the method for preparing a tin-cadmium alloy functional current collector as described in any one of claims 1 to 6.

8. The functional current collector containing tin-cadmium alloy as described in claim 7, characterized in that: In the tin-cadmium alloy, the tin content is 20 wt.% to 40 wt.%, and the cadmium content is 60 wt.% to 80 wt.%.

9. The functional current collector containing tin-cadmium alloy as described in claim 7, characterized in that: The thickness of the tin-cadmium alloy layer is 100 nm to 500 nm.

10. A secondary battery, characterized in that: The secondary battery includes a tin-cadmium alloy current collector as described in any one of claims 7 to 9.

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