Composite metal foil and method of making and using same

Abstract

The present application provides a kind of composite metal foil and its preparation method and application.The composite metal foil is embedded with suitable amount of metal in base layer, is combined more closely with the metal layer covering the surface of base layer, and supplements the strength of base film and improves the bending resistance of base film, so that the composite metal foil has better peel strength.The composite metal foil, especially copper foil, can be used as negative current collector, achieving the lightweight of battery product, not only improving the peel strength of copper foil, but also improving the conductivity of copper foil in local area;At the same time, the copper metal embedded structure also provides a fast thermal response interface, improves the safety of battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of composite metal foil, and particularly relates to a composite metal foil and a preparation method and application thereof. BACKGROUND

[0002] Conventional lithium-ion batteries (LIBs) are continuously developing to improve their electrochemical performance and safety. In the past decade, the research on electrode and electrolyte materials has significantly contributed to the development of conventional batteries. However, the current collector in conventional LIBs has not been given enough attention. As an important unit to collect and disperse electrons from the electrode and conduct current, the performance of the current collector significantly affects the performance of LIBs. The current collector has necessary properties such as electrochemical stability, electrical conductivity, mechanical strength, density, sustainability, and cost.

[0003] The current collector wettability and surface performance affect the electrochemical performance of LIBs, the surface cleanliness and cutting quality affect the safety of LIBs, and the thickness seriously affects the energy density of LIBs. Reducing the thickness of the current collector helps to increase the mass ratio and volume energy density of the battery. Therefore, with the development of LIBs, the thickness of copper foil is reduced to 4-8 μm, and the mass ratio in the battery is reduced from 19.3% to about 6%, although the thickness of the current collector can be further reduced, but the ultra-thin current collector with weak mechanical properties is prone to wrinkles and breakage during the coating process, in addition, the manufacturing cost will also increase continuously.

[0004] In order to meet the growing demand for high energy and safety of batteries, especially the demand for commercialization of electric vehicles, further progress is needed. The metalized plastic current collector (MPCC) with a metal-polymer-metal multi-layer composite structure is an innovative solution. This method has several advantages. First, it effectively reduces the weight and thickness of the lithium-ion battery, thereby improving its energy density. Second, the polymer with electrical insulation and high elongation performance in the MPCC significantly improves the safety performance of the lithium-ion battery by preventing thermal runaway.

[0005] There have been reports on a new current collector structure with a polymer-based film layer carrying a metal layer, and the metal layer is used to carry an electrode active material layer. The main disadvantage of the existing composite current collector technology is that the copper foil is easy to peel off, fall off, and has poor adhesion. The reasons leading to this disadvantage are mainly the chemical structure difference, physical property difference and improper surface treatment between the polymer-based film layer and the metal layer.

[0006] The existing technology usually adds an adhesive or multiple conductive layers to make up for this defect, but this will increase the process. How to more effectively and conveniently improve the adhesion between the polymer-based film layer and the metal layer of the composite current collector is a problem worthy of study in the field. SUMMARY

[0007] The present application aims to solve the problem of insufficient bonding force between the polymer base film layer and the metal layer in the prior art, and provides a composite metal foil with higher peeling strength.

[0008] Another object of the present application is to provide a preparation method of the composite metal foil.

[0009] Still another object of the present application is to provide an application of the composite metal foil.

[0010] The above objects of the present application are achieved by the following technical solutions.

[0011] A composite metal foil comprises a base layer and a metal layer on the surface of the base layer, wherein the base layer comprises a porous polymer base film and metal embedded in the pores of the porous polymer base film; and the content of the metal in the base layer is 8-25 wt%.

[0012] The metal in the base layer and the metal layer on the surface of the base layer are formed in the same process.

[0013] In the prior art, especially in the field of batteries, the base film for preparing the composite metal foil is generally a polymer base film without pores. The inventors have found that using a porous polymer as the base film, part of the metal will enter the pores of the porous polymer during the metal plating process, thereby forming a porous polymer base film embedded with metal. This kind of base film is more firmly combined with the metal layer, and can make the composite metal foil have higher peeling strength.

[0014] Preferably, the porosity of the porous polymer base film is 15-40%. The appropriate porosity can make the composite metal foil have good mechanical strength and thermal shrinkage performance. More preferably, the porosity of the porous polymer base film is 20-35%.

[0015] The preparation method of the porous polymer base film in the present application can be prepared by referring to the known preparation technology of the porous polymer base film. For example, when the polymer is polyolefin, the method described in CN118772479A can be referred to for preparation.

[0016] Preferably, the polymer of the porous polymer base film is selected from polyethylene, polytetrafluoroethylene, polyvinylidene fluoride, polyimide, polyethylene terephthalate, polypropylene, polysulfone, polydimethylsiloxane, polyamide, polystyrene, polyvinyl chloride, aramid, polyoxadiazole, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, polyoxadiazole, polypropylene, polyamide-based urea, polyformaldehyde, epoxy resin, phenolic resin, silicone rubber, polycarbonate, polyvinyl alcohol, polyethylene glycol, or any combination thereof.

[0017] Preferably, the metal accounts for 0.04-0.12 g / cm3 of the mass volume of the substrate layer. 3 .

[0018] More preferably, the metal accounts for 0.055-0.09 g / cm3 of the mass volume of the substrate layer. 3 In the present application, the mass of the metal in the substrate layer can be obtained by subtracting the mass of the metal layer from the mass of the composite metal foil, and then subtracting the mass of the porous polymer base film. The mass of the metal layer can be obtained by physical methods or a calculation method using a scanning electron microscope. The physical method is to peel off the metal layer with adhesive tape and then weigh it.

[0019] The calculation method is to determine the thickness of the metal layer by a scanning electron microscope, and then obtain the mass according to the thickness of the metal layer × the area of the metal layer × the density of the metal.

[0020] Preferably, the peeling strength of the composite metal foil is greater than 400 N / m.

[0021] More preferably, the peeling strength of the composite metal foil is greater than 500 N / m.

[0022] In the present application, the test method for the peeling strength of the composite metal foil is as follows:

[0023] The prepared flat metal foil sample is cut into a test sample with a width of 24 mm and a length of 300 mm. One end of the cut test sample is folded against the adhesive surface to form a folded layer with a length of about 12 mm. The other end of the test sample is pasted to one end of a steel plate, and then rolled twice with an adhesive tape pressure roller at a speed of 600 mm / min. Then, the test sample is placed in an electronic peeling tester, and the test speed is set to 250 mm / min. The force value during the peeling process is automatically recorded by the equipment, and the peeling strength of the test sample is reported accordingly.

[0024] Preferably, the thickness of the substrate layer is 2-8 μm.

[0025] Preferably, the thickness of the metal layer is 0.1-1.0 μm.

[0026] Preferably, the metal layer is formed by chemical plating.

[0027] The preparation method of the composite metal foil comprises the following steps:

[0028] S1: roughening treatment of the porous polymer base film;

[0029] S2: sensitization treatment of the roughened base film;

[0030] S3: water washing treatment of the sensitized base film;

[0031] S4: activation treatment of the water-washed base film;

[0032] S5 carries out a chemical plating treatment on the base film after the activation treatment, to cover the surface of the base layer with a metal layer.

[0033] More preferably, the roughening treatment of S1 is achieved by plasma treatment.

[0034] The number of plasma treatments can be one or more.

[0035] More preferably, the power of each plasma treatment is 50-150 W, and the time of each plasma treatment is 30-180 seconds.

[0036] More preferably, the sensitization treatment of S2 is to immerse the roughened base film in a stannous salt solution, and the immersion time is preferably 1-2 minutes.

[0037] The stannous salt solution is preferably a stannous chloride solution, and the concentration thereof is preferably 30-40 g / L.

[0038] The purpose of the water washing treatment of S3 is to form a gel film on the base film after the sensitization treatment, to facilitate the activation treatment of S4. The water washing treatment can specifically be to wash the sensitized base film in deionized water at a temperature of 20-50°C.

[0039] Preferably, the washing time can be 10-20 seconds.

[0040] The purpose of the activation treatment of S4 is to prepare for chemical copper plating.

[0041] More specifically, the activation is achieved by immersing the water-washed base film in an activation liquid.

[0042] The immersion time is 1-2 minutes. The activation liquid can be a palladium chloride solution, and the concentration thereof can be 0.5-1.0 g / L.

[0043] The chemical plating metal of S5 can refer to the existing method of plating metal on the surface of a base film.

[0044] More specifically, taking copper plating as an example, the main components of the copper plating solution for the chemical plating metal include 10.0 g / L of copper sulfate, 15.0 g / L of sodium hydroxide, 36.0 g / L of tetrahydrate potassium sodium tartrate, 10.0 g / L of ethylenediaminetetraacetic acid disodium, 10.0 mL / L of formaldehyde, 5.0 ml / L of 2’2 dipyridyl, and 5.0 g / L of nickel sulfate mixed solution.

[0045] The time of the chemical copper plating is 3-5 minutes.

[0046] Preferably, before S1, a step of cleaning the base film is further included. The purpose of the cleaning is to remove oil stains or impurities on the base film.

[0047] Preferably, after the end of S5, a step of performing an antioxidation treatment is further included.

[0048] More preferably, in the present application, the metal layer is a metal layer formed of copper, nickel and / or aluminum or a carbide layer of copper, nickel and / or aluminum. More preferably, the metal layer is a metal layer formed of copper.

[0049] Application of the composite metal foil as a negative electrode current collector.

[0050] Compared with the prior art, the present application has the following beneficial effects:

[0051] The present application provides a composite metal foil, which has a suitable amount of metal embedded in the base layer, is more closely combined with the metal layer located on the surface of the base layer, and the metal also supplements the strength of the base film and improves the bending resistance of the base film, so that the composite metal foil has better peel strength. The composite metal foil, especially the copper foil, can be used as a negative electrode current collector, achieving the lightweight of the battery product, not only improving the peel strength of the copper foil, but also improving the electrical conductivity of the copper foil in the local area; at the same time, the copper metal embedded structure also provides a fast thermal response interface, improving the safety of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0052] Fig. 1 SEM diagram of the composite metal foil prepared for Example 4.

[0053] Fig. 2 SEM diagram of the composite metal foil embedded layer structure prepared for Example 5.

[0054] Fig. 3 SEM diagram of the composite metal foil prepared for Comparative Example 3;

[0055] Wherein, 1 is the metal layer, 2 is the base layer, 3 is the metal embedded in the pores of the base layer, and 4 is the pores of the base layer. DETAILED DESCRIPTION

[0056] The present application will be further described below in conjunction with examples. These examples are only used to illustrate the present application and are not used to limit the scope of the present application. The experimental methods not specified in the following example are usually carried out according to the conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, if not specifically stated, are all raw materials and reagents that can be obtained commercially through conventional market channels. Any non-essential changes and substitutions made by those skilled in the art on the basis of the present application shall fall within the scope of the present application.

[0057] Examples 1-5 and Comparative Examples 1 and 2

[0058] Referring to Table 1, PE-based films with different porosities (porosity) were selected, and composite copper foils were prepared according to the following process.

[0059] The PE-based film was self-made, and the method was specifically prepared according to the method recorded in the embodiment of CN118772479A by adjusting the parameters.

[0060] The porosity of the base film P = [1-(base film mass / skeleton density) / base film apparent volume] x 100%

[0061] The mass of the base film: the actual mass of the PE-based film, which can be measured by a balance.

[0062] The skeleton density: the density of the raw material used for the PE-based film, that is, the density of the raw material when the porous structure is not made.

[0063] The apparent volume of the base film: the volume of the PE-based film in the natural state (the porous structure has been made), which can be measured physically.

[0064] Preparation of composite copper foil:

[0065] S1 base film roughening treatment is plasma treatment:

[0066] Put the decontaminated base film into the vacuum plasma cavity, close the valve, turn on the power, and vacuum to 5x10 -2 Pa, and the working gas is one of nitrogen, argon, oxygen or a mixture gas, the working gas pressure is controlled at 1 Pa, the working power is set between 150 W, the temperature is 25℃, and the time is 90 seconds. Get the roughened base film after plasma treatment.

[0067] S2 base film sensitization:

[0068] Completely immerse the roughened base film in the sensitization liquid and soak for 1-2 minutes at a temperature of 30℃.

[0069] The sensitization solvent is a self-made stannous chloride solution with a concentration of 30g / L.

[0070] S3 base film washing treatment:

[0071] Take out the sensitized base film from the sensitization liquid and wash it in deionized water at a temperature of 45℃ to form a gel film on the surface of the base film, and the washing time is 10-15 seconds.

[0072] S4 base film activation:

[0073] Completely immerse the cleaned base film in the activation liquid and soak for 1-2 minutes at a temperature of 25℃.

[0074] The activation solvent is a self-made palladium chloride solution with a concentration of 1.0g / L.

[0075] S5 electroless copper plating

[0076] The surface of the base film after S4 treatment is subjected to electroless copper plating.

[0077] The composition of the electroless copper plating solution is 10.0 g / L of copper sulfate, 15.0 g / L of sodium hydroxide, 36.0 g / L of potassium sodium tartrate tetrahydrate, 10.0 g / L of disodium ethylenediaminetetraacetate, 10.0 mL / L of formaldehyde, 5.0 ml / L of 2’2dipyridyl, and 5.0 g / L of nickel sulfate mixed solution. After the above solution components are configured, they are thoroughly mixed and stirred to be uniform. The treated base film is horizontally placed in the electroless copper plating solution, and the electroless plating time is 3-5 min at a temperature of 40°C. The solution is made more uniform by using ultrasonic vibration to assist the plating. After the copper plating is completed, the base film is taken out, washed with deionized water, and subjected to an oxidation resistance treatment, and then dried in a drying oven.

[0078] Comparative Examples 3 and 4

[0079] PE base films having porosities of 0 and 30%, respectively, are treated by a magnetron sputtering method, and then subjected to electroless copper plating under the same conditions as S5 above to produce composite copper films as Comparative Example 3 and Comparative Example 4. The magnetron sputtering method is specifically operated as follows:

[0080] The vacuum chamber cavity shape front door is closed, and then the cavity is vacuumed to 8.0 x 10 -4 Pa. Different flow rates of argon gas are introduced and the position of the gate valve is adjusted to adjust the working gas pressure to the desired range. After the working gas pressure is stabilized, the plating roller speed is set to 10 m / min, the required radio frequency sputtering power is set to 350 W, the working gas pressure is set to 0.02 Pa, and the glow is started to deposit the thin film for 5 mins.

[0081] The test method for the peel strength is as follows:

[0082] The prepared flat metal foil sample is cut into a sample having a width of 24 mm and a length of 300 mm. One end of the cut sample is folded with the adhesive surface facing inward to form a folded layer having a length of about 12 mm. The other end of the sample is adhered to one end of a steel plate, and then rolled twice with an adhesive tape rolling machine at a speed of 600 mm / min. Then, the sample is placed in an electronic peel tester, and the test speed is set to 250 mm / min. The force value during the peeling process is recorded automatically by the equipment, and the peel strength of the sample is reported based on the force value.

[0083] Copper content in the base layer = mass of copper in the base layer (g) / mass of the base film (g)

[0084] Mass of copper in the base layer = mass of the composite copper foil (g) - mass of the base film (g) - mass of the copper layer (g)

[0085] In addition, whether the copper is embedded in the base layer is observed by a scanning electron microscope and an EDS method on a cross section.

[0086] The mass of the copper layer can be obtained by a physical method or a calculation method by a scanning electron microscope. The physical method is to peel off the copper layer with adhesive tape and then weigh it.

[0087] The calculation method is to determine the thickness of the copper layer by a scanning electron microscope, and then obtain it according to the thickness of the copper layer x the area of the copper layer x the density of copper. In the examples, the mass of the copper layer is obtained by the calculation method.

[0088] The mass-volume content of the copper particles in the base layer = the mass of the copper in the base film (g) / the apparent volume of the base film (cm 3 )

[0089] Bending resistance test: using a cutting device, different samples are prepared into the same size of 15 mm x 100 mm, a bending resistance tester or manual bending is used for tens of times, the copper foil surface peeling and copper powder falling are observed, and the surface wrinkles and cracks at the bending part are observed by an optical microscope to comprehensively determine.

[0090] The copper foil is not peeled off, no copper powder is fallen off, and there is a small crack on the surface, which is determined to be excellent. The copper foil is not peeled off, a small amount of copper powder is fallen off, and there is a small crack on the surface, which is determined to be better. The copper foil is peeled off, a small amount of copper powder is fallen off, and there is a crack on the surface, which is determined to be general.

[0091] Safety performance test: the composite copper foil of examples 1-5 is prepared into a battery, and no fire and smoke phenomenon occurs in the small capacity soft package battery needle test.

[0092] Table 1 test data of the composite copper foil prepared by examples 1-5 and comparative examples 1-4

[0093]

[0094]

[0095] From examples 1-5 and comparative examples 1 and 3, and Figs. 1-3 It can be seen that the composite metal foil prepared by the porous polymer base film of the application has higher metal peeling strength. As can be seen from comparative example 2, if the porosity of the polymer base film is low, it is difficult to make a sufficient amount of copper enter the polymer base film, so it is difficult to achieve the ideal effect of improving the peeling strength. As can be seen from comparative example 4, other processing methods cannot make copper more effectively enter the polymer base film, resulting in no obvious improvement in peeling strength.

[0096] Finally, it should be noted that the above examples are merely intended 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 preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A composite metal foil, comprising a substrate layer and a metal layer located on the surface of the substrate layer, characterized in that, The substrate layer comprises a porous polymer base membrane and a metal embedded in the pores of the porous polymer base membrane; the metal content in the substrate layer is 8-25 wt%. The porosity of the porous polymer-based membrane is 15-40%.

2. The composite metal foil according to claim 1, characterized in that, The porosity of the porous polymer-based membrane is 20-35%.

3. The composite metal foil according to claim 1, characterized in that, The polymer of the porous polymer-based membrane is selected from polyethylene, polytetrafluoroethylene, polyvinylidene fluoride, polyimide, polyethylene terephthalate, polypropylene, polysulfone, polydimethylsiloxane, polyamide, polystyrene, polyvinyl chloride, aramid, polydiphenylene dicarboxylate, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalate), polypropylene, polyamide urea, polyoxymethylene, epoxy resin, phenolic resin, silicone rubber, polycarbonate, polyvinyl alcohol, polyethylene glycol, or any combination thereof.

4. The composite metal foil according to claim 1, characterized in that, In the substrate layer, the metal content by mass volume is 0.04–0.12 g / cm³. 3 .

5. The composite metal foil according to claim 1, characterized in that, The peel strength of the composite metal foil is greater than 400 N / m.

6. The composite metal foil according to claim 1, characterized in that, The thickness of the substrate layer is 2–8 μm.

7. The composite metal foil according to claim 1, characterized in that, The metal layer is a metal layer formed of copper, nickel and / or aluminum, or a carbide layer of copper, nickel and / or aluminum.

8. The method for preparing the composite metal foil according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Roughening treatment is applied to the porous polymer-based membrane; S2. Sensitize the roughened base film; S3. The sensitized base film is washed with water. S4. Activate the base film after water washing; S5. Perform chemical plating on the activated base film to cover the surface of the substrate layer with a metal layer.

9. The application of the composite metal foil according to any one of claims 1 to 7 as a negative electrode current collector.

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