Primer coating solution containing multiple binders and metal foil containing primer coating layer

Abstract

The present invention relates to a metal foil comprising a primer coating solution containing multiple binders and a primer coating layer, and in particular to a metal foil comprising a primer coating solution containing multiple binders capable of improving bonding strength and a primer coating layer. According to one embodiment of the present invention, as a primer coating solution for forming a primer coating layer on a metal foil for a secondary battery, a primer coating solution comprising multiple binders comprising 0.01 to 10.00 wt% of a carbon material, 0.01 to 20.00 wt% of a multiple binder, and 70.00 to 99.98 wt% of a solvent, based on 100 wt% of the primer coating solution, may be provided.

Description

Technology Field

[0001] The present invention relates to a metal foil comprising a primer coating solution containing multiple binders and a primer coating layer, and in particular to a metal foil comprising a primer coating solution containing multiple binders capable of improving bonding strength and a primer coating layer. Background Technology

[0003] The matters described in this background technology section are written to enhance understanding of the background of the invention and may include matters that are not prior art already known to those skilled in the art to which this technology belongs.

[0005] Energy storage devices such as lithium-ion batteries, supercapacitors, fuel cells, and aqueous zinc batteries play an important role in modern society and are mainly composed of a positive electrode, a negative electrode, and an electrolyte. The positive and negative electrodes each consist of a composite layer made of an active material, a conductive material, and a binder, and a metal current collector layer for electron transfer between this composite layer and an external circuit. Generally, aluminum foil is used as the positive electrode current collector, and copper foil is used as the negative electrode current collector.

[0006] Recently, active research has been conducted to improve the energy density of energy storage devices, and as part of this effort, thick film technology, which increases the thickness of the composite layer, is attracting attention. While thickened composite layers can contain more active material to increase energy density, this can simultaneously lead to a degradation of electrochemical performance and mechanical stability issues. In particular, the conduction paths of ions and electrons in thick composite layers become longer, increasing internal resistance; consequently, this can result in heat generation and non-uniformity in electrochemical reactions.

[0007] Furthermore, the safety of energy storage devices is emerging as a critical issue. The generation and diffusion of flammable gases at the interface between the composite layer and the current collector can lead to thermal runaway and explosion accidents in batteries. Such gas generation is primarily caused by the decomposition of the electrolyte or interfacial reactions, and countermeasures are required to effectively control it.

[0008] To address these issues, the strategy of applying a primer coating to the surface of the current collector is gaining attention. Primer coatings can improve electrochemical performance by enhancing the adhesion between the current collector and the composite layer, and reduce adverse reactions at the interface. Conventionally, primer coatings utilizing carbon-based materials such as carbon black have been primarily used. While carbon black provides excellent electrical conductivity, it is difficult to form a uniform coating layer due to particle aggregation, and there are issues with insufficient bonding strength between the current collector and the composite layer. Furthermore, performance degradation may occur during long-term use due to the chemical instability of carbon black. Prior art literature

[0010] Korean Published Patent Application No. 10-2023-0088113 The problem to be solved

[0011] The present invention aims to provide a primer coating solution comprising multiple binders capable of improving the bonding strength of a coating layer, and a metal foil comprising a primer coating layer. means of solving the problem

[0013] According to one embodiment of the present invention, as a primer coating solution for forming a primer coating layer on a metal foil for a secondary battery, a primer coating solution comprising a multi-binder comprising 0.01 to 10.00 wt% of a carbon material, 0.01 to 20.00 wt% of a multi-binder, and 70.00 to 99.98 wt% of a solvent, based on 100 wt% of the primer coating solution, may be provided.

[0014] In addition, the above carbon material may be provided as a primer coating solution comprising a multi-binder which is any one of a zero-dimensional carbon material, a one-dimensional carbon material, a two-dimensional carbon material, or a combination thereof.

[0015] In addition, the above carbon material may be provided as a primer coating solution comprising a multi-binder, which is a carbon nanofiber (CNF).

[0016] In addition, a primer coating solution may be provided comprising a multi-binder including a combination of two or more of PAA (Polyacrylic acid), PVA (Polyvinyl Alcohol), PVDF (Polyvinylidene fluoride), CMC (Carboxymethyl Cellulose), SBR (Styrene-Butadiene Rubber), GA (Gum Arabic), SA (Sodium Alginate), PI (Polyimid), PFTE (Polytetrafluoroethylene), and PAN (Polyacrylonitrile).

[0017] In addition, a primer coating solution may be provided that includes a multi-binder, wherein the multi-binder is a dual binder comprising PAA and PVA.

[0018] In addition, a primer coating solution may be provided comprising a multi-binder in which PAA and PVA are each 65 to 55 weight% and 35 to 45 weight%, respectively, with respect to 100% weight of the multi-binder.

[0019] In addition, a primer coating solution may be provided comprising a multi-binder in which PAA and PVA are each 60% by weight and 40% by weight, respectively, of the 100% by weight of the multi-binder.

[0020] In addition, the above solvent may be provided as a primer coating solution comprising a multi-binder which is one of water, deionized water, NMP, ethanol, dihydroterpinol, and dihydroterpinol acetate.

[0021] In addition, the carbon material is carbon nanofiber, the multi-binder is a dual binder mixed with PAA and PAV, and the solvent is deionized water. A primer coating solution may be provided that includes the carbon material, the multi-binder, and the solvent in a ratio of 3.1 to 3.3 wt% carbon material, 1.5 to 1.7 wt% multi-binder, and 95.0 to 95.4 wt% solvent relative to 100 wt% of the coating solution.

[0022] According to one embodiment of the present invention, a metal foil may be provided comprising: a metal layer; and a primer coating layer formed by applying a primer coating solution according to any one of claims 1 to 9 to the metal layer.

[0023] In addition, a metal foil formed by coating the metal layer, which is the primer coating solution, by ultrasonic spray coating may be provided. Effects of the invention

[0025] According to the present invention, there is an effect of providing a metal foil comprising a primer coating solution containing multiple binders capable of improving bonding strength and a primer coating layer. Brief explanation of the drawing

[0027] Figure 1 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 1. Figure 2 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 2. Figure 3 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 3. Figure 4 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 4. FIG. 5 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Example 1 of the present invention. Figure 6 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Example 2 of the present invention. Figure 7 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Example 3 of the present invention. Figure 8 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 5. Figure 9 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 6. Figure 10 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 7. Figure 11 is a drawing showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 8. FIG. 12 is a drawing showing the peeling test results of a metal foil coated with a primer coating solution according to Example 4 of the present invention. FIG. 13 is a drawing showing the peeling test results of a metal foil coated with a primer coating solution according to Example 5 of the present invention. FIG. 14 is a drawing showing the peeling test results of a metal foil coated with a primer coating solution according to Example 6 of the present invention. FIG. 15 is a drawing showing the peeling test results of a metal foil coated with a primer coating solution according to Example 7 of the present invention. Figure 16 is a diagram showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 9. Figure 17 is a drawing showing the peeling test results of a metal foil coated with a primer coating solution according to Comparative Example 10. FIG. 18 is a cross-sectional view showing a state in which platinum is coated on a metal foil coated with a primer coating solution according to Example 2 of the present invention. Specific details for implementing the invention

[0028] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. The embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0030] A primer coating solution comprising multiple binders according to one embodiment of the present invention may include a carbon material, multiple binders, and a solvent.

[0031] In one embodiment of the present invention, the carbon material may be understood as any one of "0-dimensional carbon material," "1-dimensional carbon material," "2-dimensional carbon material," or a combination thereof.

[0032] In one embodiment of the present invention, the "zero-dimensional carbon material" is a carbon material considered as a point form without specific directionality, and may be, for example, spherical or polyhedral. Such a zero-dimensional carbon material can be understood as having a size at the nanometer level in all directions. Specifically, the zero-dimensional carbon material may be any one of carbon black, fullerene, pine lead, lead, lamp black, channel black, Farness black, acetylene black super py, and Ketjen black, or a combination thereof.

[0033] In addition, in one embodiment of the present invention, the "one-dimensional carbon material" is a carbon material having a structure that is elongated in one direction and relatively short in the other direction, for example, at the nanometer level, and may be in the form of a tube, for example. Specifically, the one-dimensional carbon material may be any one of carbon nanotubes (single-walled carbon nanotubes, double-walled carbon nanotubes, thin-walled carbon nanotubes, multi-walled carbon nanotubes), carbon nanofibers, carbon nanorods, or a combination thereof.

[0034] In addition, in one embodiment of the present invention, the "two-dimensional carbon material" can be understood as a material in the form of a thin layer that is widely extended in two directions. In this case, the two-dimensional carbon material may have a thickness of about a few atomic layers. Specifically, the two-dimensional carbon material may be any one of graphene, single-layer graphene, multilayer graphene, graphene oxide (GO), and reduced-oxidized graphene (rGO), or a combination thereof.

[0035] In the following examples, carbon nanofiber (CNF) is used as the carbon material, but the concept of the present invention is not limited thereto.

[0037] In one embodiment of the present invention, the multi-binder may be understood to include two or more materials that can be used as binders. For example, the multi-binder may be composed of a combination of two or more of PAA (Polyacrylic acid), PVA (Polyvinyl Alcohol), PVDF (Polyvinylidene fluoride), CMC (Carboxymethyl Cellulose), SBR (Styrene-Butadiene Rubber), GA (Gum Arabic), SA (Sodium Alginate), PI (Polyimid), PFTE (Polytetrafluoroethylene), and PAN (Polyacrylonitrile).

[0038] In the following examples, the multi-binder is described as a double binder using PAA and PVA, but the concept of the present invention is not limited thereto. For example, the multi-binder may be a triple binder in which three or more binder materials are mixed, or it may be formed by mixing other materials other than PAA or PVA.

[0040] In one embodiment of the present invention, the solvent may be understood as a known liquid material capable of dissolving a carbon material and a multi-binder, and may be, for example, water, deionized water, NMP, ethanol, dihydroterpinol, or dihydroterpinol acetate. Hereinafter, deionized water (Di-water) is used as an example of a solvent, but the concept of the present invention is not limited thereto.

[0042] A primer coating solution according to one embodiment of the present invention having the above-described composition may comprise, with respect to 100 weight% of the coating solution, 0.01 to 10.00 weight% of a carbon material, 0.01 to 20.00 weight% of a multi-binder, and 70.00 to 99.98 weight% of a solvent. In the following description, the expression "range 1 to range 2" means range 1 or greater and range 2 or less.

[0043] The content of carbon material and multi-binder can be adjusted according to the application in which the primer coating solution is used, and in order to achieve the desired effect of improving bonding strength through the embodiments of the present invention, at least 0.01 weight% of each must be included in the primer coating solution.

[0044] At this time, if the carbon material content exceeds 10.00 wt%, it may be difficult to disperse carbon when preparing the primer coating solution, the coating process may be poor due to high viscosity, and problems such as excessive aggregation of carbon within the coating layer may occur. If the multi-binder content exceeds 20.00 wt%, the conductivity of the primer coating layer decreases and the resistance between the current collector and the electrode increases, which may cause a problem where the role of the current collector in moving electrons to the external circuit is reduced. Therefore, it is desirable to limit the carbon material and multi-binder content to 10.00 wt% and 20.00 wt%, respectively.

[0045] Meanwhile, according to the embodiments, the primer coating solution may further include various additives such as conductive additives, interface stabilizing additives, ion conductive additives, reinforcing additives, viscosity modifiers, dispersants, and functional additives.

[0046] For example, in the case of a primer coating solution used to form a primer coating layer for a secondary battery current collector, particularly for a current collector used in LFP and LFMP electrodes, it may contain 3.1 to 3.3 wt% of a carbon material, 1.5 to 1.7 wt% of a multi-binder, and 95.0 to 95.4 wt% of a solvent, based on 100 wt% of the coating solution. In the following comparative examples and embodiments, the coating solution is described as being composed of 3.2 wt% of a carbon material, 1.6 wt% of a multi-binder, and 95.2 wt% of a solvent.

[0047] Here, when the multi-binder is a dual binder composed of PAA and PVA, the content of PAA and PVA may be 65 to 55 wt% and 35 to 45 wt%, respectively, with respect to 100 wt% of the multi-binder. When the dual binder is composed within such a range, the bonding strength of the primer coating layer is maintained excellently, thereby improving the stability of the secondary battery. Specific experimental results regarding this will be described later.

[0048] In this case, PAA possesses a high glass transition temperature, giving it rigidity, and is characterized by high bonding strength with metals due to carboxyl groups. In contrast, PVA has a low glass transition temperature, making it relatively flexible and effective in suppressing volume expansion. When these two materials are used as a dual binder, one can leverage both the binding strength-enhancing properties of PAA and the volume expansion-suppressing properties of PVA. Consequently, the bonding strength of the primer coating layer is enhanced, while the problem of volume expansion caused by various factors can be effectively suppressed. In particular, when PAA or a rigid binder is used as a single binder, problems such as structural breakage of the primer coating layer may occur during volume expansion; however, by using PVA and PAA together, it is possible to achieve the effect of suppressing large volume changes while allowing for a certain level of volume variation.

[0050] Meanwhile, a primer coating solution according to one embodiment of the present invention having the above composition can form a primer coating layer by being applied to a metal foil and dried. At this time, the application of the primer coating solution can be carried out by known application methods such as ultrasonic spray, gravure, slot die, spray, and dip coating. In the following description, the primer coating solution is described using ultrasonic spray as an example, but the concept of the present invention is not limited thereto.

[0051] The primer coating solution applied to the metal foil can be adhered to the metal foil by undergoing a drying process. According to one embodiment of the present invention, the drying process may be carried out at a temperature of 90 degrees or higher and 110 degrees or lower. When drying is performed within this range, the adhesion of the primer coating layer is maintained excellently, thereby improving the stability of the secondary battery. Specific experimental results regarding this will be described later.

[0053] Hereinafter, specific experimental examples that can confirm the effects of the embodiments of the present invention will be described with reference to the drawings.

[0054] The experimental examples described below were tested in the following common environment, except for conditions specifically mentioned in each example.

[0055] - Metal foil: Aluminum foil, thickness 15nm

[0056] - Carbon material: CNF, 3.2 wt% (0.8 g)

[0057] - Multi-binder: Sigma's PAA, Alpha Eisa's PVA, total 1.6 wt% (total 0.4 g)

[0058] - Solvent: Deionized water, 95.2 wt% (23.8 g)

[0059] - Method for preparing coating solution: Dissolve the carbon material and multi-binder in a certain amount of solvent, then add additional solvent 1 to 2 times and mix.

[0060] - Coating method: After placing the metal foil on a hot plate set to 100 degrees Celsius, ultrasonic spray coating is performed using an ultrasonic generator with a rated power of 4.9W at a height of 27 cm at a set spray speed.

[0061] - Release medium: Scotch tape

[0062] - Peeling Test Method: After performing the operation of attaching and detaching the peeling medium from the metal foil formed on the primer coating layer once and twice, the tester relatively evaluates the amount of peeling material attached to each peeling medium.

[0064] Table 1 shows the results of a peel test performed after applying a primer coating solution according to each example or comparative example to a metal foil and allowing it to be completely dried, with different types of binders and composition ratios. Here, the adhesion strength was evaluated based on the relative degree to which the peeled material adheres to the peeling medium as perceived by the experimenter visually; the result is a relative evaluation where the value is closer to 100 when the amount of peeled material is small and closer to 0 when the amount is large, and is the average value of measurements taken with different ultrasonic spray speeds and spray times.

[0065] division Corresponding drawings Binder composition Drying temperature Bonding strength evaluation Comparative Example 1 Fig. 1 PAA single 100℃ 85 Comparative Example 2 Fig. 2 PVA single 85 Comparative Example 3 Fig. 3 PAA 75 wt%, PVA 25 wt% 50 Comparative Example 4 Fig. 4 PAA 70 wt%, PVA 30 wt% 60 Example 1 Fig. 5 PAA 65 wt%, PVA 35 wt% 90 Example 2 Fig. 6 PAA 60 wt%, PVA 40 wt% 95 Example 3 Fig. 7 PAA 55 wt%, PVA 45 wt% 90 Comparative Example 5 Fig. 8 PAA 50 wt%, PVA 50 wt% 65 Comparative Example 6 Fig. 9 PAA 45 wt%, PVA 55 wt% 55

[0066] FIG. 1 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 1, FIG. 2 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 2, FIG. 3 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 3, FIG. 4 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 4, FIG. 5 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Example 1 of the present invention, FIG. 6 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Example 2 of the present invention, FIG. 7 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Example 3 of the present invention, FIG. 8 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 5, and FIG. 9 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 6.

[0067] Here, each drawing includes a drawing showing the state in which a primer coating solution is applied to a metal foil when the ultrasonic spray speed of the comparative example or example corresponding to each drawing is 5 ml / h and the spraying time is adjusted to 10 minutes, 5 minutes, and 3 minutes, and when the ultrasonic spray speed is 1 ml / h and spraying is performed for 25 minutes, an enlarged view of the location where peeling is performed using a peeling medium, and a drawing showing the state of the peeling medium when peeling is performed once and when peeling is performed twice.

[0068] Specifically, Comparative Example 1 (Fig. 1) is a case where PAA is included as a single binder in the primer coating solution, Comparative Example 2 (Fig. 2) is a case where PVA is included as a single binder in the primer coating solution, Comparative Example 3 (Fig. 3) is a case where 75 wt% (1.2 g) of PAA and 25 wt% (0.4 g) of PVA are included in the primer coating solution based on 100 wt% of multiple binders, Comparative Example 4 (Fig. 4) is a case where 70 wt% (1.12 g) of PAA and 30 wt% (0.48 g) of PVA are included in the primer coating solution based on 100 wt% of multiple binders, Comparative Example 5 (Fig. 8) is a case where 50 wt% (0.8 g) of PAA and 50 wt% (0.8 g) of PVA are included in the primer coating solution based on 100 wt% of multiple binders, and Comparative Example 6 (Fig. 9) is a multiple This is the case where 45 wt% (0.72 g) of PAA and 55 wt% (0.88 g) of PVA are included in the primer coating solution for every 100 wt% of binder.

[0069] Meanwhile, Example 1 (Fig. 5) is a case where 65 wt% (1.04 g) of PAA and 35 wt% (0.56 g) of PVA are included in the primer coating solution for 100 wt% of the multi-binder, and Example 2 (Fig. 6) is a case where 60 wt% (0.96 g) of PAA and 40 wt% (0.64 g) of PVA are included in the primer coating solution for 100 wt% of the multi-binder.

[0070] Referring to FIGS. 1 to 9 and Table 1 above, when PAA or PVA is used as a single binder, as in Comparative Examples 1 and 2, a certain level of binding strength is shown. However, when the content of PAA as a multi-binder is 70 wt% or more (Comparative Examples 3 and 4) or 50 wt% or less (Comparative Examples 5 and 6), it was confirmed that it has a lower level of binding strength than a single binder. However, when the content of PAA as a multi-binder is 65 wt% or less and 55 wt% or more, and the content of PVA is 35 wt% or more and 45 wt% or less, as in Examples 1 to 3, it was confirmed that it shows superior binding strength compared to when it is used as a single binder. Furthermore, in this case, as described above, the effect of preventing problems caused by volume expansion of the secondary battery due to PVA can be obtained.

[0071] In particular, it was confirmed that the best binding strength was shown when the content of PAA and PVA was 60:40, as in Example 2.

[0073] Meanwhile, Table 2 shows the results of a peel test performed when a primer coating solution according to each example or comparative example was applied to a metal foil and completely dried at different drying temperatures, based on the multi-binder composition ratio of Example 2, which showed the best bonding strength as described above. Here, the bonding strength was evaluated based on the relative degree to which the peeled material adhered to the peeling medium as perceived by the experimenter visually; the result was evaluated as a relative value where the less peeled material there was, the closer it was to 100, and the more peeled material there was, the closer it was to 0, and it is the average value of measurements taken with different ultrasonic spray speeds and spray times.

[0075] division Corresponding drawings Binder composition Drying temperature Bonding strength evaluation Example 2 Fig. 6 PAA 60 wt%, PVA 40 wt% 100℃ 95 Comparative Example 7 Fig. 10 PAA 60 wt%, PVA 40 wt% 70℃ 40 Comparative Example 8 Fig. 11 PAA 60 wt%, PVA 40 wt% 80℃ 50 Example 4 Fig. 12 PAA 60 wt%, PVA 40 wt% 90℃ 92.5 Example 5 Fig. 13 PAA 60 wt%, PVA 40 wt% 95℃ 92.5 Example 6 Fig. 14 PAA 60 wt%, PVA 40 wt% 105℃ 92.5 Example 7 Fig. 15 PAA 60 wt%, PVA 40 wt% 110℃ 92.5 Comparative Example 9 Fig. 16 PAA 60 wt%, PVA 40 wt% 120℃ 45 Comparative Example 10 Fig. 17 PAA 60 wt%, PVA 40 wt% 140℃ 55

[0076] FIG. 10 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 7, FIG. 11 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 8, FIG. 12 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Example 4 of the present invention, FIG. 13 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Example 5 of the present invention, FIG. 14 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Example 6 of the present invention, FIG. 15 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Example 7 of the present invention, FIG. 16 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 9, and FIG. 17 is a drawing showing the peel test results of a metal foil coated with a primer coating solution according to Comparative Example 10.

[0077] Specifically, Example 2 (Fig. 6) is the experimental result when the drying temperature is set to 100 degrees Celsius, Comparative Example 7 (Fig. 10) is the case when the drying temperature is set to 50 degrees Celsius, Comparative Example 8 (Fig. 11) is the case when the drying temperature is set to 70 degrees Celsius, Comparative Example 9 (Fig. 16) is the case when the drying temperature is set to 120 degrees Celsius, and Comparative Example 10 (Fig. 17) is the case when the drying temperature is set to 140 degrees Celsius.

[0078] Meanwhile, Example 4 (Fig. 12) is a case where the drying temperature is set to 90 degrees Celsius, Example 5 (Fig. 13) is a case where the drying temperature is set to 95 degrees Celsius, Example 6 (Fig. 14) is a case where the drying temperature is set to 105 degrees Celsius, and Example 7 (Fig. 15) is a case where the drying temperature is set to 95 degrees Celsius.

[0080] Referring to Figures 6, 10 to 17, and Table 2 above, the best binding strength was observed when the drying temperature was set to 100 degrees Celsius, and superior binding strength was also observed at 90 degrees Celsius and 110 degrees Celsius compared to when a single binder was used. It was confirmed that when the drying temperature was 70 degrees Celsius or lower or 120 degrees Celsius or higher, the binding strength was lower than that of a single binder.

[0082] A metal foil comprising a primer coating layer according to one embodiment of the present invention may include a metal layer and a primer coating layer formed by applying a primer coating solution according to any one of the embodiments described above. Such a metal foil may be used as a current collector or electrode for a secondary battery, and specifically may be a current collector for an LFP / LMFP / dry electrode.

[0083] As confirmed by the above description and the experimental results of Examples 1 to 7, the metal foil with the primer coating layer formed thereon can have excellent bonding strength.

[0084] FIG. 18 is a cross-sectional view showing a state in which platinum is coated on a metal foil formed by applying a primer coating solution according to Example 2 of the present invention. Referring to FIG. 18, it can be seen that a platinum layer is hermetically deposited on an aluminum metal foil formed on a primer coating layer by applying a primer coating solution having the conditions according to Example 2 described above.

[0086] The embodiments of the present invention described above have been explained with reference to the embodiments illustrated in the drawings for the sake of understanding, but this is merely illustrative and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the appended claims.

Claims

Claim 1 A primer coating solution for forming a primer coating layer on a metal foil for a secondary battery comprises, based on 100 wt% of the primer coating solution, 0.01 to 10.00 wt% of a carbon material, 0.01 to 20.00 wt% of a multi-binder, and 70.00 to 99.98 wt% of a solvent, wherein the multi-binder is a dual binder comprising PAA and PVA, and PAA and PVA are, respectively, 55 to 65 wt% and 35 to 45 wt% based on 100 wt% of the multi-binder, and the solvent is one of NMP, dihydroterpinol, and dihydroterpinol acetate, and the carbon material is a carbon nanofiber, wherein the carbon material, the multi-binder, and the solvent comprise, based on 100 wt% of the coating solution, 3.1 to 3.3 wt% of the carbon material, 1.5 to 1.7 wt% of the multi-binder, and 95.0 to 99.98 wt% of the solvent. A primer coating solution containing multiple binders, included in a ratio of 95.4 weight%. Claim 2 In claim 1, the primer coating liquid comprising a multi-binder in which the carbon material is any one of a zero-dimensional carbon material, a one-dimensional carbon material, a two-dimensional carbon material, or a combination thereof. Claim 3 In claim 2, the carbon material is a primer coating solution comprising a multi-binder that is carbon nanofiber (CNF). Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 A primer coating solution comprising a multi-binder, wherein PAA and PVA are each 60% by weight and 40% by weight, respectively, of the multi-binder 100% by weight. Claim 8 delete Claim 9 delete Claim 10 A metal foil comprising: a metal layer; and a primer coating layer formed by applying a primer coating solution according to any one of claims 1 to 3 and 7 to the metal layer. Claim 11 In claim 10, a metal foil formed by coating the metal layer, which is the primer coating solution, by ultrasonic spray coating. Claim 12 In claim 10, the primer coating layer is a metal foil formed by drying the primer coating solution at a temperature of 90 to 110 degrees Celsius after it is applied to the metal layer. Claim 13 In claim 12, the primer coating layer is a metal foil formed by drying the primer coating solution at a temperature of 100 degrees Celsius after it is applied to the metal layer.

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