Carbon material and preparation method therefor, water-based conductive coating, and carbon-coated aluminum foil

Abstract

In order to solve the problem that existing water-based conductive coatings have a poor adhesion force on the surface of an oil-stain-containing aluminum foil, the present application provides a carbon material and a preparation method, a water-based conductive coating, and a carbon-coated aluminum foil. The preparation method comprises the following steps: uniformly mixing water, an alcoholization agent, and a carbon material, and performing alcoholization treatment; and using a surface modifier to modify the alcoholized carbon material, wherein the surface modifier comprises one or more of hydroxyalkanoate or phosphate esters, so as to obtain the modified carbon material. In the present application, the carbon material is subjected to alcoholization treatment, so that hydroxyl groups allowing for grafting are increased on the surface of the carbon material; and then the surface modifier is used to modify the carbon material. The modified carbon material has certain affinity for rolling oil, and is applied to the water-based conductive coating, which synergizes with the high oil absorption value characteristic of the carbon material, so as to break the "barrier" of an oil film to enable polar groups in a coating resin to come into contact with a substrate to generate an acting force, thereby improving the adhesion force. In addition, in the water-based conductive coating, the filling amount of the carbon material can further be increased so as to reduce the resistance of a coating.

Description

Carbon material and preparation method, water-based conductive coating and carbon-coated aluminum foil

[0001] This application is based on the Chinese invention application with application number 202311692987.3 filed on December 11, 2023, entitled "A carbon material and preparation method, water-based conductive coating and carbon-coated aluminum foil", and claims its priority. Technical Field

[0002] The present application relates to the technical field of lithium-ion batteries, and in particular to a carbon material and a preparation method thereof, a water-based conductive coating and a carbon-coated aluminum foil. Background Art

[0003] Waterborne conductive coatings are adhesive and conductive coatings. The carbon coating formed after film formation is applied to the surface of the positive electrode current collector of lithium-ion batteries to reduce the battery's internal resistance, prevent the positive electrode active material from falling off, and protect the current collector. Therefore, the core properties of waterborne conductive coatings are adhesion to the current collector aluminum foil, peel strength to the positive electrode active material, conductivity after film formation, and resistance to electrolyte.

[0004] As shown in Figure 1, in terms of adhesion performance, the polar groups such as carboxyl groups in the resin component of the water-based conductive coating easily interact with the hydroxyl groups on the surface of the current collector aluminum foil, which theoretically has good adhesion performance. However, due to the cold rolling process of the current collector aluminum foil, a large amount of rolling oil easily remains on the surface. This rolling oil has very low polarity and forms a molecular-level isolation oil film between the carbon coating and the current collector aluminum foil, which blocks the contact between the polar groups of the coating and the aluminum foil, seriously affecting the adhesion performance. The commonly used method currently is to improve the adhesion of the carbon coating by temporarily changing the polarity of the residual rolling oil or reducing the residual amount through corona or baking treatment of the substrate, but the effect is limited and is not effective for heavily oil-contaminated aluminum foil or current collector aluminum foil with oil spots.

[0005] Furthermore, carbon material, the source of electrical conductivity in water-based conductive coatings, has a critical parameter: its loading. Since carbon material lacks adhesion to aluminum foil, a higher loading yields better conductivity but poorer adhesion. This limits further improvements in the carbon coating's electrical properties. Therefore, overcoming these technical issues and drawbacks has become a key challenge.

[0006] Application Contents

[0007] To address the problem that existing water-based conductive coatings have poor adhesion on the surface of aluminum foil, the present application provides a carbon material and a preparation method, a water-based conductive coating, and a carbon-coated aluminum foil.

[0008] The technical solutions adopted by this application to solve the above technical problems are as follows:

[0009] The first aspect of the present application provides a method for preparing a carbon material, comprising the following steps:

[0010] Alcoholization treatment of the carbon material: uniformly mix water, an alcoholizing agent, and the carbon material, and perform alcoholization treatment at 150° C. to 180° C. for 3 to 5 hours to obtain an alcoholized carbon material;

[0011] Surface modification of carbon materials: The alcoholized carbon material is modified using a surface modifier, wherein the surface modifier includes one or more of hydroxyalkanoates or phosphates to obtain a modified carbon material.

[0012] Optionally, the operation of "uniformly mixing water, alcoholizing agent and carbon material" includes: uniformly mixing 50 to 75 parts of water, 26 to 47 parts of alcoholizing agent and 1 to 3 parts of carbon material in parts by weight.

[0013] Optionally, in the operation of "alcoholization treatment of carbon materials", it is included that: the carbon material includes one or more of carbon black, graphite, graphene, and carbon nanotubes; the alcoholizing agent includes one or more of nitric acid, phosphoric acid, perchloric acid, and sulfuric acid.

[0014] Optionally, the "carbon material surface modification" operation includes: dissolving 0.3 to 0.8 parts of the surface modifier in a first solvent, adding 4.5 to 7 parts of the alcoholized carbon material, stirring and ultrasonically treating for 5 to 20 minutes, transferring to a reactor, and reacting at 120°C to 160°C for 8 to 12 hours.

[0015] Optionally, in the operation of "carbon material surface modification", the first solvent includes one or more of carbon tetrachloride, toluene, xylene, butyl ester, ethylene glycol monobutyl ether, propylene glycol methyl ether, propylene glycol butyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether and dipropylene glycol methyl ether acetate.

[0016] Optionally, the hydroxyalkanoate substances include one or more of 16-hydroxy-hexadecanoic acid methyl ester, 16-hydroxy-hexadecanoic acid butyl ester, 12-hydroxy-dodecanoic acid ethyl ester, 3-hydroxyhexadecanoic acid methyl ester, hydroxytetradecanoic acid methyl ester, and hydroxytetradecanoic acid butyl ester; the phosphates include one or more of diphenyl phosphate, ditolyl phosphate, dipentyl phosphate, dibutyl phosphate, dimethyl phosphate, diethyl phosphate, and dipropyl phosphate.

[0017] In a second aspect, the present application provides a carbon material prepared by the above-mentioned method for preparing the carbon material.

[0018] In a third aspect, the present application provides a water-based conductive coating, which comprises, by weight, 35 to 75 parts of water, 15 to 20 parts of a second solvent, 15 to 30 parts of a resin, and 4.5 to 8 parts of the above-mentioned carbon material.

[0019] Optionally, the second solvent includes one or more of ethanol, ethylene glycol monobutyl ether, and ethylene glycol; and the resin includes one or more of acrylic resin, epoxy resin, polyester resin, and polyurethane resin.

[0020] In a fourth aspect, the present application provides a carbon-coated aluminum foil comprising a current collector and a coating layer, wherein the coating layer is coated on at least one surface of the current collector, and the coating layer is formed by coating the above-mentioned aqueous conductive coating on at least one surface of the current collector.

[0021] According to the preparation method of the carbon material provided in the present application, the present application first performs an alcoholization treatment on the carbon material to increase the hydroxyl groups on the surface of the carbon material available for grafting; then the alcoholized carbon material is surface-modified; the specific method is: in a solvent phase, the carbon material is modified using a surface modifier under high temperature and high pressure conditions; the surface modifier is a low-polarity small molecule substance, and since the main component of the residual rolling oil is a low-polarity substance such as an alkanoate, the modified carbon material has a certain affinity for rolling oil, and its application in water-based conductive coatings can cooperate with the high oil absorption value of the carbon material, open the "blockade" of the oil film, and allow polar groups such as carboxyl groups in the coating resin to contact the substrate to generate a force, thereby achieving improved adhesion; based on the improvement in adhesion, in the formulation design process of the water-based conductive coating, the filling amount of the carbon material can be increased to achieve improved conductive performance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a diagram showing the effect of the carbon material of the present application before treatment;

[0023] FIG2 is a diagram showing the effect of the carbon material after treatment in this application;

[0024] FIG3 is a comparison of the adhesion of the carbon coating prepared by carbon material modification and the untreated carbon coating on the surface of the heavy oil-contaminated current collector aluminum foil;

[0025] The reference numerals in the drawings of the specification are as follows: 1-carbon coating; 11-active groups in the resin; 12-groups grafted onto the surface of the carbon material; 2-positive electrode current collector; 21-active groups in the substrate; 3-residual rolling oil. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects solved by this application more clear, the application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0028] In one embodiment, the first aspect of the present application provides a method for preparing a carbon material, comprising the following steps:

[0029] Alcoholization treatment of the carbon material: uniformly mix water, an alcoholizing agent, and the carbon material, and perform alcoholization treatment at 150° C. to 180° C. for 3 to 5 hours to obtain an alcoholized carbon material;

[0030] Surface modification of carbon materials: The alcoholized carbon material is modified using a surface modifier, wherein the surface modifier includes one or more of hydroxyalkanoates or phosphates to obtain a modified carbon material.

[0031] Specifically, the alcoholization treatment of the carbon material includes the pretreatment of the carbon material, and the pretreatment of the carbon material includes the following steps: ultrasonically cleaning the carbon material in a cleaning agent to remove impurities on the surface of the carbon material, filtering, washing, and drying to obtain a clean carbon material; the mass ratio of the carbon material to the cleaning agent is 1 to 10:90 to 99.

[0032] In a preferred embodiment, the mass ratio of the carbon material to the cleaning agent is 3-8:92-97; for example, any mass ratio among 1:99; 2:98; 3:97; 4:96; 5:95; 6:94; 7:93; 8:92; 9:91 or 10:90.

[0033] Specifically, 5 parts of carbon material were placed in an ultrasonic cleaning device, and 95 parts of a cleaning agent were added and cleaned for 10 minutes to remove impurities on the surface of the carbon material. Then, an appropriate filter cloth was selected for suction filtration, washed with water, and dried in a vacuum drying oven at 50°C.

[0034] In one embodiment, the cleaning agent is one or more of butanone, acetone, ethyl acetate, ethanol and butyl acetate.

[0035] The cleaning agent can remove impurities on the surface of the carbon material, and a clean carbon material can be obtained through filtering, washing and drying.

[0036] Specifically, in the alcoholization process of the carbon material, the water is deionized water or distilled water; the specific process is: water, alcoholizing agent and carbon material are mixed evenly and then transferred to a reactor, alcoholization treatment is carried out at 150℃-180℃ for 3-5h, the carbon material after alcoholization treatment is taken out, centrifuged and washed, and vacuum dried in an environment of 40℃-60℃ to obtain the alcoholized carbon material.

[0037] In a preferred embodiment, the reactor is a high-pressure reactor. Furthermore, the high-pressure reactor is a high-pressure reactor lined with polytetrafluoroethylene.

[0038] In a preferred embodiment, the temperature for the alcoholization treatment of water, alcoholizing agent and carbon material is 160° C., and the alcoholization treatment time is 4 hours.

[0039] In a preferred embodiment, the alcoholized carbon material is vacuum-dried at 50°C. In one embodiment, the surface modifier comprises one or more hydroxyalkanoates or phosphates. The carbon material is modified using low-polarity, small-molecule substances such as hydroxyl long-chain alkanoates and phosphates. Since the residual rolling oil is primarily composed of low-polarity substances such as alkanoates, the modified carbon material exhibits a certain affinity for rolling oil. Application of this in water-based conductive coatings can synergize with the carbon material's high oil absorption properties, unlocking the oil film and allowing polar groups such as carboxyl groups in the coating resin to contact the substrate, generating forces and improving adhesion. Based on this improved adhesion, the carbon material loading can be increased during the formulation design of the water-based conductive coating, thereby enhancing the coating's conductivity.

[0040] As shown in Figure 1, the polar groups such as carboxyl groups in the resin component of the water-based conductive coating easily interact with the hydroxyl groups on the surface of the current collector aluminum foil, and theoretically have good adhesion performance. However, due to the cold rolling process of the current collector aluminum foil, a large amount of rolling oil is easily left on the surface. These rolling oils have very low polarity and form a molecular-level isolation oil film between the carbon coating and the current collector aluminum foil, which blocks the contact between the polar groups of the coating and the aluminum foil, seriously affecting the adhesion performance.

[0041] Figure 2 is a diagram showing the effect of the water-based conductive coating of the present application forming a film on the surface of the current collector; the present application first performs an alcoholization treatment on the carbon material to increase the hydroxyl groups grafted on the surface of the carbon material; then the surface of the alcoholized carbon material is modified; the specific method is: in a solvent phase, the carbon material is modified using a surface modifier under high temperature and high pressure conditions; the surface modifier is a low-polarity small molecule substance, and since the main component of the residual rolling oil is a low-polarity substance such as an alkanoate, the modified carbon material has a certain affinity for rolling oil, and its application in water-based conductive coatings can cooperate with the high oil absorption value characteristics of the carbon material, open the "blockade" of the oil film, and allow polar groups such as carboxyl groups in the coating resin to contact the substrate to generate a force, thereby achieving improved adhesion.

[0042] In one embodiment, the operation of "uniformly mixing water, alcoholizing agent and carbon material" includes: uniformly mixing 50-75 parts of water, 26-47 parts of alcoholizing agent and 1-3 parts of carbon material in parts by weight.

[0043] In a preferred embodiment, the water is 60-65 parts, for example, any one of 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts, 70 parts, 71 parts, 72 parts, 73 parts, 74 parts or 75 parts, or a range value consisting of any two parts.

[0044] In a preferred embodiment, the alcoholizing agent is 30 to 40 parts, for example, any one of 26 parts, 27 parts, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts or 47 parts, or a range consisting of any two of the values.

[0045] In a preferred embodiment, the carbon material is 1.5 to 2.5 parts, for example, any one of 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, 2.0 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.7 parts, 2.8 parts, 2.9 parts or 3.0 parts, or a range consisting of any two of the values.

[0046] The type and amount of alcohol used for the activation treatment of carbon materials, as well as the temperature and time conditions of the treatment process, must be matched experimentally, because a strong alcoholization process will cause the structural degree of the carbon material to decrease and affect the conductivity, while an overly mild alcoholization process cannot produce enough active sites for reaction; within the range of 50 to 75 parts of water, 26 to 47 parts of the alcoholizing agent, and 1 to 3 parts of the carbon material and the alcoholization temperature at 150°C to 180°C for 3 to 5 hours, it will not affect the conductive properties of the carbon material, but will also increase the hydroxyl groups available for grafting on the surface of the carbon material, thereby facilitating the subsequent modification of the carbon material.

[0047] In one embodiment, the operation of "alcoholization treatment of carbon materials" includes: the carbon material includes one or more of carbon black, graphite, graphene, and carbon nanotubes; and the alcoholizing agent includes one or more of nitric acid, phosphoric acid, perchloric acid, and sulfuric acid.

[0048] Specifically, the carbon black includes conductive carbon black, and the conductive carbon black includes acetylene black and furnace black.

[0049] The graphite includes, but is not limited to, one or more of natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. The natural graphite may be scaly graphite, flaky graphite, soil graphite, and / or graphite particles obtained by subjecting these graphites as raw materials to spheroidization, densification, and the like. The artificial graphite may be obtained by graphitizing organic substances such as coal tar pitch, coal-based heavy crude oil, atmospheric residue, petroleum-based heavy crude oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin at high temperatures.

[0050] Specifically, nitric acid, phosphoric acid, perchloric acid, and sulfuric acid can all provide graftable hydroxyl groups on the surface of the carbon material, facilitating subsequent modification of the carbon material.

[0051] In one embodiment, the "carbon material surface modification" operation includes: dissolving 0.3 to 0.8 parts of the surface modifier in a first solvent, adding 4.5 to 7 parts of the alcoholized carbon material, stirring and ultrasonically treating for 5 to 20 minutes, transferring to a reactor, and reacting at 120° C. to 160° C. for 8 to 12 hours.

[0052] In a preferred embodiment, the surface modifier is 0.4 to 0.7 parts, for example, any one of 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts or 0.8 parts, or a range consisting of any two of the values.

[0053] In a preferred embodiment, the alcoholized carbon material is 5 to 6 parts, for example, any one of 4.5 parts, 4.6 parts, 4.7 parts, 4.8 parts, 4.9 parts, 5.0 parts, 5.1 parts, 5.2 parts, 5.3 parts, 5.4 parts, 5.5 parts, 5.6 parts, 5.7 parts, 5.8 parts, 5.9 parts, 6.0 parts, 6.1 parts, 6.2 parts, 6.3 parts, 6.4 parts, 6.5 parts, 6.6 parts, 6.7 parts, 6.8 parts, 6.9 parts or 7.0 parts, or a range value consisting of any two points.

[0054] Specifically, the process of modifying the alcoholized carbon material with the surface modifier is as follows: dissolving the surface modifier in a first solvent, then adding the alcoholized carbon material, stirring at 600 rpm and ultrasonically treating for 10 minutes, transferring it to a reactor, reacting at 120°C to 160°C for 8 to 12 hours, taking it out, filtering it, washing it with chloroform, and drying it in a vacuum drying oven at 80°C to obtain a modified carbon material.

[0055] In a preferred embodiment, the heating temperature is 130°C to 150°C, for example, any one of 120°C, 121°C, 122°C, 123°C, 124°C, 125°C, 126°C, 127°C, 128°C, 129°C, 130°C, 131°C, 132°C, 133°C, 134°C, 135°C, 136°C, 137°C, 138°C, 139°C, 140°C, 141°C, 142°C, 143°C, 144°C, 145°C, 146°C, 147°C, 148°C, 149°C, 150°C, 151°C, 152°C, 153°C, 154°C, 155°C, 156°C, 157°C, 158°C, 159°C or 160°C, or a range consisting of any two of the values.

[0056] In a preferred embodiment, the reaction time is 9-11 h; for example, any one of 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h or 12 h, or a range consisting of any two of the values.

[0057] In one embodiment, in the operation of "carbon material surface modification", the first solvent includes one or more of carbon tetrachloride, toluene, xylene, butyl ester, ethylene glycol monobutyl ether, propylene glycol methyl ether, propylene glycol butyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether and dipropylene glycol methyl ether acetate.

[0058] In one embodiment, the hydroxyalkanoate substances include one or more of 16-hydroxy-hexadecanoic acid methyl ester, 16-hydroxy-hexadecanoic acid butyl ester, 12-hydroxy-dodecanoic acid ethyl ester, 3-hydroxyhexadecanoic acid methyl ester, hydroxytetradecanoic acid methyl ester, and hydroxytetradecanoic acid butyl ester; the phosphate esters include one or more of diphenyl phosphate, ditolyl phosphate, dipentyl phosphate, dibutyl phosphate, dimethyl phosphate, diethyl phosphate, and dipropyl phosphate.

[0059] Specifically, 16-hydroxy-hexadecanoic acid methyl ester, 16-hydroxy-hexadecanoic acid butyl ester, 12-hydroxy-dodecanoic acid ethyl ester, 3-hydroxyhexadecanoic acid methyl ester, hydroxytetradecanoic acid methyl ester, and hydroxytetradecanoic acid butyl ester are hydroxy long-chain alkanoic acid esters; diphenyl phosphate, ditolyl phosphate, dipentyl phosphate, dibutyl phosphate, dimethyl phosphate, diethyl phosphate, and dipropyl phosphate are low-polarity small molecular substances of the phosphate ester class; the carbon material is modified by using hydroxy long-chain alkanoic acid esters and low-polarity small molecular substances of the phosphate ester class; since the main components of the residual rolling oil are low-polarity substances such as alkanoic acid esters, the modified carbon material has a certain affinity for rolling oil, and its application in water-based conductive coatings can synergize with the high oil absorption value of the carbon material, open the "blockade" of the oil film, and allow polar groups such as carboxyl groups in the coating resin to contact the substrate to generate a force, thereby achieving improved adhesion; based on the improvement in adhesion, in the formulation design process of the water-based conductive coating, the filling amount of the carbon material can be increased to achieve improved conductive properties of the coating.

[0060] In a second aspect, the present application provides a carbon material prepared by the above-mentioned method for preparing the carbon material.

[0061] The modified carbon material in this application has a certain affinity for rolling oil. When used in water-based conductive coatings, it can cooperate with the high oil absorption characteristics of the carbon material to open the "blockade" of the oil film, allowing polar groups such as carboxyl groups in the coating resin to contact the substrate to generate a force, thereby achieving improved adhesion.

[0062] The third aspect of the present application provides a water-based conductive coating, which includes, by weight, 35 to 75 parts of water, 15 to 20 parts of a second solvent, 15 to 30 parts of a resin, and 4.5 to 8 parts of the above-mentioned carbon material. After mixing evenly, a sand mill is used to disperse the mixed materials to a fineness of 10 to 25 to obtain a water-based conductive coating.

[0063] Preferably, the fineness of the coating is 10-25; the viscosity is 30-1000 mPa·s; and the solid content of the coating is 5-15%.

[0064] In a preferred embodiment, the water is 40 to 70 parts, for example, any one of 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts, 70 parts, 71 parts, 72 parts, 73 parts, 74 parts or 75 parts, or a range consisting of any two parts.

[0065] In a preferred embodiment, the second solvent is 16 to 18 parts, for example, any one of 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, or a range consisting of any two of the values.

[0066] In a preferred embodiment, the resin is 20 to 25 parts, for example, any one of 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts or 30 parts, or a range consisting of any two of the values.

[0067] In a preferred embodiment, the carbon material is 5 to 8 parts, for example, any one of 4.5 parts, 5.0 parts, 5.5 parts, 6.0 parts, 6.5 parts, 7.0 parts, 7.5 parts or 8.0 parts, or a range consisting of any two of the values.

[0068] This application applies the modified carbon material to water-based conductive coatings. Based on the principle of like dissolves like, the high oil absorption value of the carbon material is used to destroy the oil film, allowing groups such as carboxyl groups in the coating resin to contact the substrate to achieve improved adhesion.

[0069] To improve adhesion, the carbon material loading can be increased during the formulation design of water-based conductive coatings to enhance the coating's conductivity. For example, increasing the carbon material loading from 55% to 70% can reduce resistance by nearly 50%.

[0070] In one embodiment, the second solvent includes one or more of ethanol, ethylene glycol monobutyl ether, and ethylene glycol; and the resin includes one or more of acrylic resin, epoxy resin, polyester resin, and polyurethane resin.

[0071] In a fourth aspect, the present application provides a carbon-coated aluminum foil comprising a current collector and a coating layer, wherein the coating layer is coated on at least one surface of the current collector, and the coating layer is formed by coating the above-mentioned aqueous conductive coating on at least one surface of the current collector.

[0072] The coating layer on the surface of the carbon-coated aluminum foil of the present application is formed by applying a water-based conductive coating to at least one surface of the current collector. The water-based conductive coating of the present application uses a modified carbon material. The modified carbon material is applied to the water-based conductive coating. According to the principle of like dissolves like, the carbon material's high oil absorption value is synergistically used to destroy the oil film, allowing groups such as carboxyl groups in the coating resin to contact the substrate, thereby improving adhesion. Based on the improved adhesion, the carbon material filling amount can be increased during the formulation design of the water-based conductive coating to achieve improved coating conductivity. For example, increasing the carbon material filling amount from 55% to 70% reduces the resistance by nearly 50%. This not only reduces substrate processing costs, but also improves the construction adaptability of the water-based conductive coating. Further increasing the carbon material filling amount reduces the resistance, which is very meaningful for improving the overall performance of lithium-ion batteries.

[0073] In one embodiment, the coating layer of the carbon-coated aluminum foil has a thickness of 0.3 to 2 μm.

[0074] In a preferred embodiment, the coating layer thickness of the carbon-coated aluminum foil is 0.5 to 1.5 μm, for example, any value among 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, and 2.0 μm, or a range value consisting of any two value points.

[0075] The present application is further described below through examples.

[0076] Example 1:

[0077] 1. Alcoholization treatment of carbon materials:

[0078] 1) Ultrasonic cleaning of 5 parts of carbon material in 95 parts of butanone for 10 minutes to remove impurities on the surface of the carbon material, then filtering with appropriate filter cloth, washing with deionized water and drying in a vacuum drying oven at 50°C;

[0079] 2) 57 parts deionized water, 40 parts dilute nitric acid, 1 part phosphoric acid, and 2 parts acetylene black were mixed in sequence, stirred evenly, and transferred to a polytetrafluoroethylene-lined autoclave for alcoholization at 160°C for 4 hours. The mixture was centrifuged, washed with deionized water, and dried under vacuum at 50°C to obtain an alcoholized carbon material.

[0080] 2. Surface modification of carbon materials

[0081] First, 0.78 parts of 12-hydroxy-dodecanoic acid ethyl ester was dissolved in toluene, and then 7 parts of alcoholized carbon material was added. After stirring at 600 rpm and ultrasonic treatment for 10 minutes, it was transferred to a reactor and reacted at 120°C for 10 hours. The mixture was taken out, filtered, washed with chloroform, and dried in a vacuum drying oven at 80°C to obtain an alkanoate-modified carbon material.

[0082] 3. Preparation of positive electrode water-based carbon-coated aluminum foil:

[0083] 48.89 parts of deionized water, 20 parts of solvent, 25 parts of resin, and 6.11 parts of alkanoate-modified carbon material were mixed in this order and then dispersed to a fineness of 15 μm using a sand mill to obtain a water-based conductive coating with a carbon material loading of 55%. The coating was applied to both sides of the current collector aluminum foil and baked in a hot air oven at 125°C for 30 seconds to obtain a carbon-coated aluminum foil with a single-side coating thickness of 0.5 μm, designated S1.

[0084] Example 2

[0085] Example 2 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application. It includes most of the operating steps in Example 1, except that:

[0086] Preparation of positive electrode water-based carbon-coated aluminum foil:

[0087] 51.12 parts of deionized water, 20 parts of solvent, 22.22 parts of resin, and 6.66 parts of alkanoate-modified carbon material were mixed in this order and then dispersed to a fineness of 15 μm using a sand mill to obtain a water-based conductive coating with a 60% carbon material loading. The coating was applied to both sides of the current collector aluminum foil and baked in a hot air oven at 125°C for 30 seconds to obtain a carbon-coated aluminum foil with a single-side coating thickness of 0.5 μm, designated S2.

[0088] Example 3

[0089] Example 3 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application. It includes most of the steps in Example 1, except that:

[0090] Preparation of positive electrode water-based carbon-coated aluminum foil:

[0091] 53.34 parts of deionized water, 20 parts of solvent, 19.44 parts of resin, and 7.22 parts of alkanoate-modified carbon material were mixed in this order and then dispersed to a fineness of 15 μm using a sand mill to obtain a water-based conductive coating with a carbon material loading of 65%. The coating was applied to both sides of the current collector aluminum foil and baked in a hot air oven at 125°C for 30 seconds to obtain a carbon-coated aluminum foil with a single-side coating thickness of 0.5 μm, designated S3.

[0092] Example 4

[0093] Example 4 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application. It includes most of the operating steps in Example 1, except that:

[0094] Preparation of positive electrode water-based carbon-coated aluminum foil:

[0095] 55.55 parts of deionized water, 20 parts of solvent, 16.67 parts of resin, and 7.78 parts of alkanoate-modified carbon material were mixed in this order and then dispersed to a fineness of 15 μm using a sand mill to obtain a water-based conductive coating with a 70% carbon material loading. The coating was applied to both sides of the current collector aluminum foil and baked in a hot air oven at 125°C for 30 seconds to obtain a carbon-coated aluminum foil with a single-side coating thickness of 0.5 μm, designated S4.

[0096] Comparative Example 1

[0097] Comparative Example 1 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application, and includes most of the operating steps in Example 1, except that:

[0098] Without alcoholization treatment of the carbon material, a water-based conductive coating with a carbon material filling amount of 55% was prepared, and after baking, a carbon-coated aluminum foil was obtained, which was marked as X1.

[0099] Comparative Example 2

[0100] Comparative Example 2 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application, and includes most of the operating steps in Example 1, except that:

[0101] Without alcoholization treatment of the carbon material, a water-based conductive coating with a carbon material filling amount of 70% was prepared, and after baking, a carbon-coated aluminum foil was obtained, which was marked as X2.

[0102] Comparative Example 3

[0103] Comparative Example 3 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application, and includes most of the operating steps in Example 1, except that:

[0104] Without performing surface modification on the carbon material, a water-based conductive coating with a carbon material filling amount of 55% was prepared, and after baking, a carbon-coated aluminum foil was obtained, which was marked as X3.

[0105] Comparative Example 4

[0106] Comparative Example 4 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application, and includes most of the steps in Example 1, except that:

[0107] Without performing surface modification on the carbon material, a water-based conductive coating with a carbon material filling amount of 70% was prepared, and after baking, a carbon-coated aluminum foil was obtained, which was marked as X4.

[0108] Comparative Example 5

[0109] Comparative Example 5 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application, and includes most of the operating steps in Example 1, except that:

[0110] Without performing carbon material treatment, a water-based conductive coating with a carbon material filling amount of 55% was prepared, and after baking, a carbon-coated aluminum foil was obtained, which was marked as X5.

[0111] Comparative Example 6

[0112] Comparative Example 6 is used to illustrate a carbon material and preparation method, a water-based conductive coating, and a carbon-coated aluminum foil disclosed in this application, and includes most of the operating steps in Example 1, except that:

[0113] Without performing carbon material treatment, a water-based conductive coating with a carbon material filling amount of 70% was prepared, and after baking, a carbon-coated aluminum foil was obtained, which was marked as X6.

[0114] Performance testing:

[0115] (1) Adhesion test:

[0116] The carbon-coated aluminum foils prepared in Examples 1-4 and Comparative Examples 1-6 were peeled off using 3M tape to evaluate the degree of peeling;

[0117] Test method: Place the carbon-coated aluminum foil with the coating facing up and adhere it to the coating with 3M tape. Use your fingers to flatten the 3M tape on the coating to dislodge any bubbles between the 3M tape and the coating, ensuring maximum adhesion between the 3M tape and the coating. Pull the 3M tape vertically upward from the bottom end and record the degree of coating shedding.

[0118] (2) Conductivity test:

[0119] The resistance of the carbon-coated aluminum foils prepared in Examples 1-4 and Comparative Examples 1-6 was tested respectively;

[0120] The test equipment used was a diaphragm resistance test system, Chuanyuan Technology TT-ACCF-G2A. The test pressure was 23 MPa, and the hold time was 5 seconds. Three values ​​were measured for each carbon-coated aluminum foil, and the results were averaged.

[0121] The test results obtained in Examples 1 to 4 and Comparative Examples 1 to 6 are shown in Table 1.

[0122] Table 1

[0123] Some adhesion test results are shown in Figure 3; from left to right they are X5, X6, and S4;

[0124] As can be seen from the test results in Table 1, Examples 1-4 of the present application use long-chain alkanoate or phosphate ester small molecule materials with a structure similar to the residual rolling oil on the substrate as grafts, and achieve surface modification of the carbon material through a high-pressure solvent thermal reaction. The modified carbon material is applied to a water-based conductive coating. According to the principle of like-compatibility, the high oil absorption value of the carbon material is synergistically used to destroy the oil film, allowing groups such as carboxyl groups in the coating resin to contact the substrate, thereby improving adhesion. Figures 1 and 2 show the adhesion improvement mechanism analysis, and Figure 3 shows the adhesion of the coating before (X6) and after (S4) carbon material treatment, showing a significant improvement in adhesion.

[0125] To improve adhesion, the carbon material loading can be increased during the formulation design of water-based conductive coatings to enhance the coating's conductivity. For example, increasing the carbon material loading from 55% to 70% can reduce resistance by nearly 50%.

[0126] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a carbon material, wherein: The following steps are involved: Alcoholization treatment of carbon material: water, alcoholization agent and carbon material are mixed evenly, and alcoholization treatment is performed at 150° C.-180° C. for 3-5 hours to obtain alcoholized carbon material; Surface modification of carbon material: using a surface modifier to modify the alcoholized carbon material, wherein the surface modifier includes one or more of hydroxyalkanoates or phosphates to obtain a modified carbon material.

2. The method for preparing a carbon material according to claim 1, wherein: The operation of "mixing water, alcoholizing agent and carbon material uniformly" includes: mixing 50-75 parts of water, 26-47 parts of alcoholizing agent and 1-3 parts of carbon material uniformly by weight.

3. The method for preparing a carbon material according to claim 1, wherein: In the operation of "alcoholization treatment of carbon materials", it includes: the carbon material includes one or more of carbon black, graphite, graphene, and carbon nanotubes; the alcoholization agent includes one or more of nitric acid, phosphoric acid, perchloric acid, and sulfuric acid.

4. The method for preparing a carbon material according to claim 1, wherein: The "carbon material surface modification" operation includes: dissolving 0.3 to 0.8 parts of the surface modifier in a first solvent by weight, then adding 4.5 to 7 parts of the alcoholized carbon material, stirring and ultrasonically treating for 5 to 20 minutes, transferring to a reactor, and reacting at 120° C. to 160° C. for 8 to 12 hours.

5. The method for preparing a carbon material according to claim 4, wherein: In the operation of "carbon material surface modification", the first solvent includes one or more of carbon tetrachloride, toluene, xylene, butyl ester, ethylene glycol monobutyl ether, propylene glycol methyl ether, propylene glycol butyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether and dipropylene glycol methyl ether acetate.

6. The method for preparing a carbon material according to claim 1, wherein: The hydroxyalkanoic acid ester substances include one or more of 16-hydroxy-hexadecanoic acid methyl ester, 16-hydroxy-hexadecanoic acid butyl ester, 12-hydroxy-dodecanoic acid ethyl ester, 3-hydroxyhexadecanoic acid methyl ester, hydroxytetradecanoic acid methyl ester, and hydroxytetradecanoic acid butyl ester; the phosphate esters include one or more of diphenyl phosphate, ditolyl phosphate, dipentyl phosphate, dibutyl phosphate, dimethyl phosphate, diethyl phosphate, and dipropyl phosphate.

7. A carbon material, wherein: The carbon material is prepared by the method for preparing the carbon material according to any one of claims 1 to 6.

8. A water-based conductive coating, wherein: By weight, it comprises 35 to 75 parts of water, 15 to 20 parts of a second solvent, 15 to 30 parts of a resin and 4.5 to 8 parts of the carbon material according to claim 7.

9. The water-based conductive coating according to claim 8, wherein: The second solvent includes one or more of ethanol, ethylene glycol monobutyl ether, and ethylene glycol; the resin includes one or more of acrylic resin, epoxy resin, polyester resin, and polyurethane resin.

10. A carbon-coated aluminum foil, wherein: The invention comprises a current collector and a coating layer, wherein the coating layer is coated on at least one surface of the current collector, and the coating layer is formed by coating the aqueous conductive coating according to any one of claims 8 to 9 on at least one surface of the current collector.

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