Water-resistant carbon-coated foil as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of conductive paste, and particularly relates to a water-resistant carbon-coated foil as well as a preparation method and application thereof. According to the water-resistant carbon-coated foil, the surface of the base material is coated with the conductive slurry; the conductive slurry comprises a conductive agent, a water-resistant material, a binder and a dispersing aid, the waterproof material comprises a shell component and an inner core component, the shell component is a hydrophilic polymer, and the core component is a hydrophobic polymer. When the surface of the base material of the water-resistant carbon-coated foil is coated with the conductive paste, a high-density and high-molecular-weight carbon-coated layer with an interpenetrating network structure is obtained through the crosslinking effect, water is difficult to permeate into the bonding position of the coating and the base material due to improvement of the compactness of the coating, the water resistance of the coating is further improved, and the water-resistant carbon-coated foil can be applied to an electrochemical device.

Description

Technical Field

[0001] This invention relates to the field of conductive paste technology, and in particular to a water-resistant carbon foil, its preparation method, and its application. Background Technology

[0002] With the accelerating pace of carbon emission reduction, efficient, environmentally friendly, and low-carbon energy storage has become a key concern in the energy storage industry. Using deionized water as a solvent system to replace oil-based slurries is a development trend, as seen in aqueous cathodes in lithium batteries, and aqueous positive / negative electrodes in sodium batteries and supercapacitors. However, due to poor interfacial adhesion between the active material and the current collector, problems such as high resistance and low peel strength exist, necessitating the introduction of water-resistant carbon foil to address these issues.

[0003] In existing technologies, conductive pastes for carbon-coated foils can be categorized into water-based and oil-based systems based on the binder. In oil-based systems, due to the water-insoluble nature of oil-based binders, the carbon coating achieves extremely high water resistance. However, this coating exhibits poor stability in the oily electrolyte environment of the aforementioned batteries, hindering long-cycle performance. Water-based binders, on the other hand, have a simpler preparation process and less environmental pollution, making them the mainstream choice in the industry. However, the water-soluble polymer binder results in poor water resistance of the carbon coating, making it easily dissolved and damaged by water-based electrode active material pastes, thus rendering it ineffective. Furthermore, as the precision of carbon-coated current collectors increases, the coating thickness decreases, further reducing the coating's water resistance. This leads to the carbon coating being soaked and peeling off in water-based application environments, ultimately resulting in coating failure. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a water-resistant carbon foil, its preparation method and application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a water-resistant carbon foil, wherein a conductive paste is coated on the surface of the substrate; the conductive paste includes a water-resistant material, the water-resistant material comprising a core component formed by a hydrophobic polymer and an outer shell component formed by a hydrophilic polymer.

[0006] When the conductive paste is coated on the surface of the substrate of the water-resistant carbon foil of the present invention, the water-resistant material and the binder in the paste form a high-density, high-molecular-weight interpenetrating network structure through cross-linking in the coating, thereby constructing a continuous hydrophobic barrier. This structure effectively prevents water from penetrating to the bonding interface between the coating and the substrate, thereby improving the water resistance of the coating.

[0007] In a preferred embodiment of the water-resistant carbon foil of the present invention, the molecular weight of the outer shell component is 10,000 to 200,000; the outer shell component is at least one of polyacrylic acid, polyacrylate, carboxymethyl cellulose, alginate, and chitosan.

[0008] In a preferred embodiment of the water-resistant carbon foil of the present invention, the molecular weight of the core component is 200,000 to 3,000,000; the hydrophobic polymer contains carboxyl, hydroxyl or amino groups, and is at least one of polyacrylic acid, polyacrylate, carboxymethyl cellulose, alginate and chitosan.

[0009] In a preferred embodiment of the water-resistant carbon-coated foil of the present invention, the substrate is a conductive film; preferably, it includes at least one of aluminum foil, copper foil, stainless steel foil, and composite current collector foil; the thickness of the substrate is 3.5μm-20μm; preferably, the thickness of the aluminum foil is 5μm-10μm; and the thickness of the copper foil is 3.5μm-16μm.

[0010] Preferably, the thickness of the aluminum foil is any one or a combination of 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, and 10μm. Preferably, the thickness of the copper foil is any one or a combination of 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, and 16μm.

[0011] In a second aspect, the present invention provides a method for preparing the water-resistant carbon foil, wherein the conductive paste is coated on the surface of a substrate; The coating refers to applying a conductive paste to the surface of a substrate. The coating method described herein employs any one of the following methods: roller coating, blade coating, spray coating, dip coating, or printing.

[0012] Preferably, the coating is performed using any one of gravure roller coating, micro-gravure roller coating, comma doctor blade coating, or transfer coating; the coating speed is 10 m / min - 250 m / min; and the coating thickness is 0.1 μm - 100 μm.

[0013] Thirdly, the present invention provides a method for preparing the water-resistant material in the water-resistant carbon foil, comprising the following steps: (1) Dissolve the polymer in water to prepare an aqueous polymer solution; dissolve the crosslinking agent in an oil solvent to obtain an oil solution; (2) First, take a portion of the oil phase solution and the aqueous phase solution, heat and mix them to obtain a seed emulsion; then add the remaining oil phase solution, continue heating and mixing to obtain a nucleus emulsion; (3) Add an organic solution to the core emulsion to obtain a hydrophobic polymer as the core component; (4) The hydrophobic polymer is added to an organic solution, and then a hydrophilic polymer is added. The solution is heated to dissolve the solution and the water-resistant material is obtained. The organic solution is demulsified and dried to obtain the water-resistant material.

[0014] In a preferred embodiment of the method for preparing the water-resistant material of the present invention, in step (1), the polymer contains carboxyl, hydroxyl or amino groups; preferably, the polymer is at least one of polyacrylic acid, polyacrylate, carboxymethyl cellulose, alginate and chitosan; The molecular weight of the polymer is 2000-100000; Preferably, the molecular weight of the polymer is any one or a combination of 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, and 10000.

[0015] In step (1), the ratio of the polymer to water by weight is 0.5-3:10; Preferably, the ratio of the polymer to water is any one or a combination of 0.5:10, 1:10, 1.5:10, 2:10, 2.5:10, and 3:10. In step (1), a pH buffer, preferably ammonia or sodium bicarbonate, may be added when the polymer is dissolved in water; the ratio of the pH buffer to water by weight is 0.03-0.07:10. Preferably, the ratio of the pH buffer to water is any one or both of the following: 0.03:10, 0.04:10, 0.05:10, 0.06:10, and 0.07:10.

[0016] In step (1), the crosslinking agent is at least one of polycarbodiimide, melamine-formaldehyde resin, urea-formaldehyde resin, epoxy resin, modified phenolic resin, alkali metal hydroxide, multifunctional aziridine, zinc and zirconium complex, and polyethyleneimine.

[0017] In step (1), the oil phase solvent is at least one of isopropanol, n-butanol, isononol, isononol isononyl ester, cyclic siloxane, toluene, ethyl acetate, tetrahydrofuran, N-methylpyrrolidone, and N,N-dimethylformamide; wherein, by weight, the ratio of the crosslinking agent to the oil phase solvent is 0.1-3:10; Preferably, the ratio of the crosslinking agent to the oil phase solvent is any one or a combination of 0.1:10, 0.5:10, 1:10, 1.5:10, 2:10, 2.5:10, and 3:10.

[0018] In step (2), the oil phase solution accounts for 5%-10% of the oil phase solution obtained in step (1) by mass percentage; Preferably, the portion of the oil phase solution accounts for any one or both of the following values ​​of the oil phase solution obtained in step (1): 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%.

[0019] In step (2), the heating temperature is 50℃-100℃ and the time is 10min~30min; Preferably, the heating temperature is any one or a range of two of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, and 100°C; and the heating time is any one or a range of two of 10 min, 15 min, 20 min, 25 min, and 30 min.

[0020] Preferably, in step (2), the remaining oil phase solution is added by dropwise addition, and the dropwise addition time is 90-120 min; Preferably, the dripping time is any one or a range of two of 90 min, 100 min, 110 min, and 120 min.

[0021] In step (3), the organic solution is at least one of ethanol, methanol, n-butanol, n-pentanol, ethylene glycol methyl ether, tetrahydrofuran, toluene, ethyl acetate, and cyclohexane; the concentration of the organic solution is 70%-100%; preferably ethanol; and the ratio of the organic solution to the core emulsion by weight is 0.1-2:10. Preferably, the concentration of the organic solution is any one or a combination of 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%; and the ratio of the organic solution to the nucleoside emulsion is any one or a combination of 0.1:10, 0.5:10, 1:10, 1.5:10, and 2:10.

[0022] In step (3), the molecular weight of the hydrophobic polymer is 200,000 to 3,000,000; Preferably, the molecular weight of the hydrophobic polymer is any one or a combination of 200,000, 500,000, 1,000,000, 1,500,000, 2,000,000, 2,500,000, and 3,000,000.

[0023] In step (4), the hydrophilic polymer is at least one of polyacrylic acid, polyacrylate, carboxymethyl cellulose, alginate, and chitosan, with a molecular weight of 2000-10000. Preferably, the molecular weight of the hydrophilic polymer is any one or a combination of 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, and 10000.

[0024] In step (4), the organic solution is at least one of ethanol, methanol, n-butanol, n-pentanol, ethylene glycol methyl ether, tetrahydrofuran, toluene, ethyl acetate, and cyclohexane; the concentration of the organic solution is 10%-20%; preferably ethanol; and the ratio of the organic solution to the hydrophobic polymer by weight is 10:0.5-3.

[0025] In step (4), the amount of the hydrophilic polymer added is 3-5 times the mass of the polymer in step (1).

[0026] In step (4), the heating temperature is 50℃-100℃ and the time is 10min-30min; Preferably, the heating temperature is any one or a range of two of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, and 100°C; and the heating time is any one or a range of two of 10 min, 15 min, 20 min, 25 min, and 30 min.

[0027] In step (4), after adding an organic solution to break the emulsion, the mixture is filtered using a 300-1000 mesh sieve. Preferably, the filtration uses a screen with a mesh size of 300 mesh, 400 mesh, 500 mesh, 600 mesh, 700 mesh, 800 mesh, 900 mesh, or 1000 mesh, or a range of two of these mesh sizes.

[0028] In step (4), the water-resistant material is a polymer core-shell structure, with the outer shell component being a hydrophilic polymer and the inner core component being a hydrophobic polymer; The outer shell component has a molecular weight of 10,000 to 200,000; the core component has a molecular weight of 200,000 to 3,000,000.

[0029] Fourthly, the present invention provides a conductive paste, comprising the following components by weight: 10-70 parts of conductive agent, 20-35 parts of water-resistant material prepared by the preparation method, 10-20 parts of binder, and 0.5-3 parts of dispersant. The mass ratio of the conductive agent to the water-resistant material is (1.5-3):1.

[0030] Preferably, the mass ratio of the conductive agent to the water-resistant material is any one or a combination of 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, and 3:1.

[0031] In the conductive paste of the present invention, the water-resistant material can be stably present in the conductive paste. Even if the core is a hydrophobic polymer with poor water solubility, it can still be uniformly dispersed in the aqueous paste system by conventional dispersion methods. During the coating and baking process of the conductive paste, as the solvent evaporates, the shell is subjected to surface tension and will spread out or decompose / evaporate under heat, so that the hydrophobic polymer of the core comes into contact with the binder and undergoes cross-linking, resulting in a highly dense, high molecular weight carbon coating layer with an interpenetrating network structure.

[0032] In a preferred embodiment of the conductive paste of the present invention, the conductive agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene; and / or, the binder is at least one of carboxymethyl cellulose, alginate, chitosan, and guar gum; and / or, the dispersing agent is at least one of polyvinylpyrrolidone, polyacrylate, and polyvinyl alcohol.

[0033] Fifthly, the present invention applies the water-resistant carbon foil to an electrochemical device.

[0034] In a preferred embodiment of the conductive paste described in this invention, the electrochemical device is a lithium-ion battery, a sodium-ion battery, a supercapacitor, or the like.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: The water-resistant material of this invention has a shell made of a low molecular weight hydrophilic compound and a core made of a hydrophobic polymer. During the baking process of coating the current collector substrate foil, the conductive paste prepared by the invention will spread out or decompose / evaporate due to surface tension as the solvent evaporates. This allows the hydrophobic polymer in the core to come into contact with the binder and undergo cross-linking, resulting in a highly dense, high molecular weight carbon coating layer with an interpenetrating network structure. The increased density of the coating makes it difficult for water to penetrate to the bonding area between the coating and the aluminum foil substrate, thereby improving the water resistance of the coating. Detailed Implementation

[0036] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0037] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified. In the following examples, "parts" refers to parts by weight.

[0038] Example 1: A water-resistant material The preparation method of this water-resistant material is as follows: (1) Take 100 parts of pure water, add 0.5 parts of sodium bicarbonate, then add 10 parts of polyacrylic acid (molecular weight 2000-5000), stir until completely dissolved to obtain an aqueous solution; take 10 parts of isopropanol, add 1 part of polycarbodiimide, stir to obtain an oil solution; (2) Take 5% (mass percentage) of the oil phase solution obtained in step (1) and mix it with the aqueous phase solution obtained in step (1). Disperse the mixture evenly under stirring at 200 rpm, heat it in an 80℃ water bath for 25 min, and obtain a seed emulsion with a bluish surface. Add the remaining oil phase solution dropwise into the obtained seed emulsion and disperse it evenly under stirring at 200 rpm. Heating in an 80℃ water bath for 90 minutes followed by a reaction time of 25 minutes yielded a milky white, uniform microsphere emulsion. (3) Add 20 parts of anhydrous ethanol to the obtained 100 parts of microsphere emulsion to demulsify, filter and dry to obtain core high molecular weight polyacrylic acid microspheres with a molecular weight Mw of 1358029 and some unreacted carbodiimide reactive groups on its surface. (4) Take 50 parts of pure water and 10 parts of anhydrous ethanol and mix them evenly. Add 10 parts of the obtained core high molecular weight polyacrylic acid microspheres and disperse them evenly to obtain a turbid solution. Take 40 parts of polyacrylic acid (molecular weight of 2000-5000) and add it to the obtained turbid solution. Stir at 200 rpm to dissolve and heat in an 80°C water bath for 30 min to obtain a semi-transparent solution. Filter the obtained semi-transparent solution through an 800-mesh sieve to obtain a lower semi-transparent emulsion. Add 12 parts of anhydrous ethanol to break the emulsion, filter and dry to obtain a water-resistant material.

[0039] The above-mentioned water-resistant material, with a solid content of 20%, was dissolved in a system of pure water and anhydrous ethanol in a ratio of 5:1 to obtain its emulsion, which appeared translucent. This is because the core of the water-resistant material is a high-molecular-weight polymer that is insoluble in water or has extremely poor water solubility, while the shell is a substance that is highly water-soluble. When the core-shell structure is formed, the system changes from a water-insoluble core to a core-shell structure that is partially soluble and slightly soluble in water, thus changing its appearance from turbid to translucent.

[0040] Example 2: A water-resistant material The difference from Example 1 is as follows: In step (4), take 50 parts of polyacrylic acid.

[0041] Example 3: A water-resistant material The difference from Example 1 is as follows: In step (4), 30 parts of polyacrylic acid were taken, stirred at 200 rpm to dissolve, and then heated in a 50°C water bath for 30 min.

[0042] Example 4: A water-resistant material The difference from Example 1 is as follows: In step (4), 50 parts of polyacrylic acid were taken, stirred at 200 rpm to dissolve, and then heated in a 90°C water bath for 30 min.

[0043] Example 5: A water-resistant material The difference from Example 1 is as follows: In step (1), take 0.5 parts of polycarbodiimide. In step (2), 10% (mass percentage) of the obtained oil phase solution is mixed with the obtained aqueous phase solution; the mixture is heated in a 60°C water bath for 30 minutes to obtain a seed emulsion.

[0044] Example 6: A water-resistant material The difference from Example 1 is as follows: In step (1), the molecular weight of polyacrylic acid is 5000-10000, and 1.5 parts of polycarbodiimide are taken; In step (2), a seed emulsion is obtained by heating in a 90°C water bath for 15 minutes.

[0045] Comparative Example 1: A water-resistant material The difference from Example 1 is as follows: In step (4), take 15 parts of polyacrylic acid.

[0046] Comparative Example 2: A water-resistant material The difference from Example 1 is as follows: In step (4), take 65 parts of polyacrylic acid.

[0047] Comparative Example 3: A water-resistant material The difference from Example 1 is as follows: In step (1), the molecular weight of polyacrylic acid is 1000-2000.

[0048] Example 7: A conductive paste The conductive paste comprises, by weight percentage: conductive agent, water-resistant material, binder, and dispersant.

[0049] The method for preparing the conductive paste is as follows: (1) Take pure water, add dispersant, and stir at low speed of 200 rpm for 5 min; (2) Add sodium alginate and stir at 500 rpm for 30 min; (3) Add conductive agent, stir at low speed of 200 rpm for 10 min until the conductive agent is fully wetted, scrape the wall, evacuate to a vacuum degree of 0.08 MPa, and stir at 1800 rpm for 160 min. (4) Transfer to a wet grinding machine and grind at 800 rpm for 30 min; (5) Transfer to a mixing tank, add water-resistant material, add pure water according to the system solid content of 10%, evacuate to a vacuum degree of 0.08Mpa, stir at 500rpm for 100min, and sieve through a 200-mesh sieve to obtain conductive slurry.

[0050] The following conductive pastes were prepared according to the above method, and their composition is shown in Table 1: Table 1 Experimental example: 1. The stability of the conductive paste is tested using the following method: The conductive paste prepared in Example 3 was left to stand for one month, and its state was observed to see if it could flow normally. If it could flow normally, its stability was good; if it could not flow normally, its stability was poor and it had deteriorated.

[0051] 2. Take the conductive paste from Example 3 that has been left to stand for one month to prepare carbon foil. The preparation method is as follows: The conductive pastes of experimental groups 1-4 and control groups 1-5 were uniformly coated onto the surface of 10μm aluminum foil after degreasing treatment using a micro-gravure roller coating method. After drying, aluminum foil with a conductive coating thickness of 1μm on one side was obtained, with three parallel coatings per group.

[0052] The water resistance of the coating on the coated aluminum foil was tested using the following method: (1) Soak a cotton ball in pure water until fully saturated; (2) Lay one sample of the aluminum foil-coated sample to be tested flat on a glass surface; (3) Use tweezers to pick up the soaked cotton ball and squeeze it until no water flows out in a stream and there are no obvious water droplets; (4) Hold the cotton ball with tweezers and wipe it back and forth on the surface of the sample to be tested with even force for a length of 5cm; (5) Observe the wiped area of ​​the sample (the 5cm area wiped). If the aluminum foil substrate is exposed, it is determined that the pure water wiping test of the sample has been completed. (6) Replace the other two samples in the same group and repeat steps 4 and 5 above with different cotton balls; (7) To judge the water resistance, the judgment criteria are: a. <10 times, poor water resistance; b. 10~30 times, average water resistance; c. >31 times, good water resistance.

[0053] The test results are shown in Table 2: Table 2 As shown in the table, the aluminum foil coated with the conductive paste containing the water-resistant materials of Examples 1-6 can be wiped more than 30 times, indicating a high water resistance level. During the drying process of the carbon coating layer, the low molecular weight polyacrylic acid of the water-resistant material structure shell in the conductive paste will spread and open due to surface tension, exposing the high molecular weight polyacrylic acid core. Some of the crosslinking groups on its surface bond with the binder, resulting in a highly dense, high molecular weight carbon coating layer with an interpenetrating network structure through crosslinking. The increased density of the coating makes it difficult for water to penetrate to the bonding area between the coating and the aluminum foil substrate, thereby improving the water resistance of the coating.

[0054] Compared with experimental group 1, the aluminum foil coated with conductive paste in control group 1 had less polyacrylic acid added in step (4) during the preparation of water-resistant material, resulting in uneven growth of the shell on the surface of some microspheres. This led to insufficient water solubility of the microspheres, which could not be stably present in the preparation of conductive paste. Most of the microspheres were filtered out during sieving, resulting in only 8-15 wiping times for the carbon-coated foil and a low water resistance level. The conductive paste in control group 2 had excessive polyacrylic acid added in step (4) during the preparation of water-resistant material, resulting in an excessively thick shell of water-resistant material. In addition, a large amount of low molecular weight polyacrylic acid was precipitated with the water-resistant material during the demulsification, filtration, and drying steps. The water-resistant material shell and the low molecular weight polyacrylic acid in the slurry drastically increased the viscosity of the slurry. After standing for a month, the two were very likely to undergo a cross-linking reaction, which further reduced the fluidity of the conductive slurry. Finally, the conductive slurry became jelly-like and deteriorated, and could not be properly coated onto the aluminum foil substrate. The aluminum foil coated with the conductive slurry of control group 3 had a low molecular weight of polyacrylic acid in step (1) of the preparation of the water-resistant material. As a result, the core structure of the core-shell microspheres was loose and unstable during growth, and the molecular weight was low. The core had no water resistance, so the foil could only be wiped twice, resulting in a low water resistance level.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A water-resistant coated carbon foil, characterized in that, The substrate surface is coated with a conductive paste; the conductive paste includes a water-resistant material, which includes a core component formed by a hydrophobic polymer and an outer shell component formed by a hydrophilic polymer.

2. The water-resistant carbon foil according to claim 1, characterized in that, The outer shell component is at least one of polyacrylic acid, polyacrylate, carboxymethyl cellulose, alginate, and chitosan.

3. The water-resistant carbon foil according to claim 1, characterized in that, The hydrophobic polymer contains carboxyl, hydroxyl, or amino groups, and is at least one of polyacrylic acid, polyacrylate, carboxymethyl cellulose, alginate, and chitosan.

4. A method for preparing the water-resistant carbon foil according to any one of claims 1-3, characterized in that, The conductive paste is coated onto the surface of the substrate.

5. A method for preparing the water-resistant material in the water-resistant carbon foil according to claim 1, characterized in that, Includes the following steps: (1) Dissolve the polymer in water to prepare an aqueous polymer solution; dissolve the crosslinking agent in an oil solvent to obtain an oil solution; (2) First, take a portion of the oil phase solution and the aqueous phase solution, heat and mix them to obtain a seed emulsion; then add the remaining oil phase solution, continue heating and mixing to obtain a nucleus emulsion; (3) Add an organic solution to the core emulsion to obtain a hydrophobic polymer as the core component; (4) Add the hydrophobic polymer to an organic solution, then add the hydrophilic polymer as the shell component, heat to dissolve and obtain a water-resistant material solution, add an organic solution to demulsify and dry to obtain a water-resistant material.

6. The method for preparing the water-resistant material according to claim 5, characterized in that, In step (1), the polymer contains carboxyl, hydroxyl or amino functional groups, and is at least one of acrylic acid, polyacrylate, carboxymethyl cellulose, alginate and chitosan.

7. The method for preparing the water-resistant material according to claim 5, characterized in that, The hydrophilic polymer is at least one of polyacrylic acid, polyacrylate, carboxymethyl cellulose, alginate, and chitosan.

8. A conductive paste, characterized in that, The product comprises, by weight, the following components: 10-70 parts of conductive agent, 20-35 parts of water-resistant material prepared by any of the preparation methods described in claims 5-7, 10-20 parts of binder, and 0.5-3 parts of dispersant.

9. The conductive paste according to claim 8, characterized in that, The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene.

10. The application of the water-resistant carbon foil according to any one of claims 1-4 in an electrochemical device.

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