Open hollow carbon material, preparation method thereof, and carbon-coated aluminum foil

Abstract

The present invention relates to the technical field of lithium-ion batteries, and discloses an open hollow carbon material, a preparation method thereof, and a carbon-coated aluminum foil. The interior of the open hollow carbon material is hollow to form a cavity, and at least one opening is distributed on the outer surface. The opening connects the cavity of the open hollow carbon material and the outside, and the area of the opening accounts for 20% to 40% of the outer surface area of the open hollow carbon material. When the positive electrode active material contacts the hollow carbon material with an opening on the surface, the opening increases the contact area between the carbon coating layer and the positive electrode active material on the one hand, and can also serve as a "cage" to trap the active material on the other hand, greatly improving the wettability and peeling strength between the carbon-coated aluminum foil current collector and the positive electrode active material layer. In addition, the use of ionic small molecules as a modifying component to modify the open hollow carbon material improves the stability of the carbon-coated aluminum foil coating without having a negative effect on other properties. The carbon-coated aluminum foil using the open hollow carbon material improves the overall performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an open hollow carbon material and a preparation method thereof, and a carbon-coated aluminum foil. Background Art

[0002] The aluminum foil current collector is an indispensable component of lithium-ion batteries. It contacts the positive electrode active material and carries the positive electrode active material and collects the output current. The substrate of carbon-coated aluminum foil is aluminum foil, which is coated with a dispersed conductive carbon material. Using carbon-coated aluminum foil as the positive electrode current collector for lithium-ion batteries can reduce the contact resistance between the positive electrode active material and the current collector. Because the particles of the positive electrode active material are large, they are in point-to-surface contact with the aluminum foil current collector, resulting in poor peel strength. Carbon-coated aluminum foil can improve the peel strength of the positive electrode active material, preventing expansion and separation between the positive electrode active material and the current collector during the continuous charge and discharge process of lithium-ion batteries.

[0003] Carbon-coated aluminum foil coatings are composed of three materials: a binder, a conductive carbon material, and a solvent. To further improve the peel strength between carbon-coated aluminum foil and the positive electrode active material, various binder structures have emerged in the prior art. However, achieving higher peel strength carbon-coated aluminum foil by simply developing binders has become increasingly difficult. As another major component of carbon-coated aluminum foil coatings, existing conductive carbon materials are all in the form of solid particles. The differences in particle morphology and aggregation of conductive carbon materials significantly affect the roughness of the carbon-coated aluminum foil surface, which in turn affects the wettability and peel strength of the positive electrode active material. Therefore, improving the peel strength of carbon-coated aluminum foil coatings by selecting and modifying the morphology and aggregation of conductive carbon materials should be considered. Furthermore, conductive carbon materials are difficult to disperse in carbon-coated aluminum foil coatings and are prone to sedimentation, resulting in reduced construction efficiency. In particular, agglomeration during the sedimentation process can affect the performance stability and consistency of lithium-ion batteries. Currently, grafting the conductive carbon material surface with polyvinylpyrrolidone (PVP) can improve the stability of carbon-coated aluminum foil coatings, but this has a negative effect on the conductivity of lithium-ion batteries.

[0004] Therefore, improving the peel strength of carbon-coated aluminum foil coating by selecting the morphology and aggregation state of conductive carbon materials is a new path. At the same time, it is very necessary to improve the stability of carbon-coated aluminum foil coating by modifying conductive carbon materials without affecting the conductive properties, thereby improving the overall performance of lithium-ion batteries. Summary of the Invention

[0005] In view of the problems in the prior art that the particle morphology and aggregation state of the conductive carbon material affect the roughness of the carbon-coated aluminum foil surface and the peeling strength to the positive electrode active material, as well as the poor stability of the carbon-coated aluminum foil coating, the present invention provides an open hollow carbon material and a preparation method thereof, and a carbon-coated aluminum foil.

[0006] In a first aspect, the present invention provides an open hollow carbon material, wherein the interior of the open hollow carbon material is hollow to form a cavity, and at least one opening is distributed on the outer surface of the open hollow carbon material, wherein the opening connects the cavity of the open hollow carbon material and the outside of the open hollow carbon material, and the area of the opening accounts for 20% to 40% of the outer surface area of the open hollow carbon material.

[0007] In a second aspect, the present invention provides a method for preparing the open hollow carbon material of the first aspect, comprising:

[0008] 1 to 6 parts of a matrix material and 94 to 99 parts of an acid solution are mixed and then subjected to acid etching treatment under high pressure conditions to obtain an open hollow carbon material; the reaction temperature of the acid etching treatment is 120 to 180° C., the reaction pressure is 0.3 to 1.2 MPa, and the reaction time is 6 to 12 hours.

[0009] In a third aspect, the present invention provides a modified open hollow carbon material, which is obtained by grafting the open hollow carbon material of the first aspect and a modifying component.

[0010] In a fourth aspect, the present invention provides a carbon-coated aluminum foil, which is prepared by the following method:

[0011] 5 to 15 parts of water, 10 to 30 parts of a second solvent, 10 to 25 parts of a binder, and 40 to 60 parts of a modified open hollow carbon material are mixed and ground to obtain a carbon-coated aluminum foil coating; the second solvent comprises one or more of ethanol, n-butanol, tert-butanol, isobutanol, n-propanol, isopropanol, and ethylene glycol monobutyl ether; and the binder is an acrylic resin;

[0012] The carbon-coated aluminum foil coating is coated on the current collector aluminum foil by gravure or micro-gravure and then dried to obtain the carbon-coated aluminum foil; the drying temperature is 80-200° C. and the drying time is 5-120 seconds.

[0013] The present invention uses a hollow carbon material as a matrix material. After pre-treating the hollow carbon material, it is mixed with an acid solution and acid-etched under high pressure conditions to create holes on the outer surface of the hollow carbon material to obtain a hollow carbon material with an open surface. The opening connects the cavity of the open hollow carbon material with the exterior of the open hollow carbon material. When the positive electrode active material contacts the hollow carbon material with an open surface, the opening increases the contact area between the carbon coating layer and the positive electrode active material. On the other hand, it can also act as a "cage" to trap the active material, greatly improving the wettability and peel strength between the carbon-coated aluminum foil current collector and the positive electrode active material layer, thereby avoiding expansion and separation between the positive electrode active material and the carbon-coated aluminum foil current collector during continuous charge and discharge. The present invention modifies an open hollow carbon material by using a water-soluble small molecule modifying component to obtain a modified open hollow carbon material. The modifying component has two sulfonic acid groups and one phenolic hydroxyl group, wherein the phenolic hydroxyl group acts as a grafting group to react with the carboxyl group on the surface of the open hollow carbon material after acid etching, thereby improving the stability of the conductive carbon material in the carbon-coated aluminum foil coating. At the same time, since the modifying component is an ionic small molecule, it has little effect on the conductive performance of the lithium-ion battery. The carbon-coated aluminum foil using the open hollow carbon material improves the overall performance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of hollow aggregated carbon and open hollow carbon materials in an embodiment of the present invention;

[0015] Figure 2 Schematic diagram of the mechanism by which the carbon-coated aluminum foil improves the peel strength through the open hollow carbon material in an embodiment of the present invention;

[0016] Figure 3 This is a physical picture of the carbon-coated aluminum foil in Example 1 of the present invention. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] In a first aspect, an embodiment of the present invention discloses an open hollow carbon material, wherein the interior of the open hollow carbon material is hollow to form a cavity, and at least one opening is distributed on the outer surface of the open hollow carbon material, wherein the opening connects the cavity of the open hollow carbon material and the outside of the open hollow carbon material, and the area of the opening accounts for 20% to 40% of the outer surface area of the open hollow carbon material.

[0019] Furthermore, unlike existing solid structure conductive carbon materials such as conductive carbon black SP, acetylene black, furnace black, and graphite, the interior of the open hollow carbon material is a cavity formed by a hollow structure, and part of the outer surface is distributed with irregular holes, i.e., openings. These openings connect the internal cavity and the outside, forming an open hollow carbon material with an open surface, which increases the roughness of the conductive carbon material and improves the contact area between the carbon-coated aluminum foil current collector and the positive electrode active material.

[0020] Optionally, the matrix material of the open hollow carbon material includes one or both of hollow aggregated carbon and hollow carbon nanofibers, the hollow aggregated carbon is a single-particle hollow carbon sphere aggregate, and the hollow carbon nanofiber is a hollow through-the-hole carbon nanofiber.

[0021] Furthermore, the hollow carbon material of this embodiment is selected from carbon aggregates (hollow aggregated carbon) with single particles having a hollow structure and fused into a "grape bunch" shape, hollow carbon nanofibers, and other carbon materials with hollow structures, or a combination of the two, preferably hollow aggregated carbon.

[0022] Optionally, the particle size of the hollow carbon spheres of the hollow aggregated carbon is 80 to 200 nm, and the outer diameter of the hollow carbon nanofibers is 100 to 300 nm.

[0023] Optionally, the cavity volume of the hollow aggregated carbon accounts for 80% to 90%; the cavity volume of the hollow carbon nanofiber accounts for 70% to 80%.

[0024] Furthermore, when the matrix material of the open hollow carbon material is hollow aggregated carbon, the cavity accounts for 60% to 90% of the volume of the hollow aggregated carbon, and the preferred cavity volume ratio is 80% to 90%; when the matrix material of the open hollow carbon material is hollow carbon nanofiber, the cavity accounts for 50% to 80% of the volume of the hollow carbon nanofiber, and the preferred cavity volume ratio is 70% to 80%.

[0025] In a second aspect, an embodiment of the present invention discloses a method for preparing the open hollow carbon material of the first aspect, comprising:

[0026] 1 to 6 parts of a matrix material and 94 to 99 parts of an acid solution are mixed and then subjected to acid etching treatment under high pressure conditions to obtain an open hollow carbon material; the reaction temperature of the acid etching treatment is 120 to 180° C., the reaction pressure is 0.3 to 1.2 MPa, and the reaction time is 6 to 12 hours.

[0027] Optionally, the acid solution includes one or more of dilute nitric acid, dilute hydrochloric acid, perchloric acid, and dilute sulfuric acid.

[0028] Furthermore, under normal pressure conditions, carbon materials are difficult to react with acids and can usually only react with strong oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid. However, the violent reaction of strong oxidizing acids will cause the structure of the hollow carbon material to be completely destroyed, the operation is complicated and the waste liquid treatment is difficult, which poses safety risks and environmental problems. Figure 1 As shown, the hollow aggregated carbon of this embodiment is an aggregate of multiple hollow carbon spheres, the surface of the hollow carbon sphere is a closed spherical shell, and the interior is a cavity. The hollow aggregated carbon is subjected to acid etching treatment with an acid solution under high pressure conditions, and part of the surface of the hollow aggregated carbon is destroyed. One or more holes, i.e., openings, appear on the surface of the closed spherical shell, and the openings connect the inside of the cavity with the outside of the spherical shell, thereby obtaining an open hollow carbon material after acid etching. After acid etching, the surface of the hollow carbon material becomes rough and openings appear on part of the surface. At the same time, part of the surface is carboxylated to produce carboxyl groups, which can serve as reactive sites. The type and amount of acid used for acid etching, as well as the temperature, pressure, and time conditions of the acid etching process, have been experimentally matched to prevent strong acid etching from causing structural dissociation of the hollow carbon material, and overly mild acid etching will not produce openings.

[0029] In a third aspect, an embodiment of the present invention discloses a modified open hollow carbon material, which is obtained by grafting the open hollow carbon material of the first aspect and a modifying component.

[0030] Furthermore, grafting refers to the reaction of chemically bonding appropriate side chains or functional side groups. Grafting can impart new properties to the grafted material, forming a grafted, modified material with desired properties. After acid etching, a portion of the hollow carbon material's surface becomes carboxylated, creating carboxyl groups, which increase the number of active sites for modification reactions. In this example, a modified component was used to modify an open-ended hollow carbon material containing carboxyl groups to obtain a modified open-ended hollow carbon material.

[0031] Optionally, the modifying component is a water-soluble small molecule having a disulfonic acid group and a monophenolic hydroxyl group.

[0032] Furthermore, the modified component contains two sulfonic acid groups and one phenolic hydroxyl group, which acts as a grafting group to react with the carboxyl groups on the surface of the acid-etched open-core hollow carbon material to produce a modified open-core hollow carbon material. One end of the modified component binds to the surface of the conductive carbon material, while the other end is immersed in water, providing resistance and electrostatic repulsion, allowing the conductive carbon material to be suspended in the carbon-coated aluminum foil coating. This improves the stability of the conductive carbon material in the carbon-coated aluminum foil coating. Furthermore, because the modified component is an ionic small molecule, it has minimal impact on the conductivity of lithium-ion batteries.

[0033] Optionally, the preparation method of the modified open hollow carbon material includes:

[0034] 4-anilinesulfonic acid, 4-chlorobenzenesulfonic acid and toluene are mixed and then a palladium catalyst is added to carry out a first reaction to obtain a first intermediate product; the reaction temperature of the first reaction is 60-90° C. and the reaction time is 4-5 hours;

[0035] Add p-hydroxybenzoic acid and benzene to a flask, and add silicon tetrachloride dropwise to carry out a second reaction to obtain a second intermediate product; the reaction temperature of the second reaction is 40-70°C, and the reaction time is 3-5h;

[0036] The first intermediate product, the second intermediate product, tetrahydrofuran and pyridine are added to the flask for a third reaction to obtain a modified component; the reaction temperature of the third reaction is -10 to 10°C, and the reaction time is 3 to 6 hours;

[0037] 60 to 80 parts of water, 10 to 30 parts of a first solvent, 1 to 10 parts of a modifying component and 5 to 15 parts of an open hollow carbon material are mixed and subjected to a modification reaction to obtain a modified open hollow carbon material; the reaction temperature of the modification reaction is 150 to 180° C., the reaction pressure is 0.7 to 1.4 MPa, and the reaction time is 6 to 12 hours.

[0038] Further, 0.1 mol of 4-anilinesulfonic acid, 0.1 mol of 4-chlorobenzenesulfonic acid and 100 mL of toluene were added to the flask, nitrogen was introduced, 0.01 g of palladium catalyst was added, and the first reaction was carried out by stirring. The temperature of the first reaction was 60° C. to 90° C., and the time was 4 to 5 h. After the reaction, a first intermediate product was obtained. The first reaction was:

[0039]

[0040] 1 mol of p-hydroxybenzoic acid and 500 mL of benzene were added to a flask, heated to 40-70°C, and 0.6 mol of silicon tetrachloride was added dropwise to carry out a second reaction. The second reaction time was 3-5 hours. After the reaction was completed, a second intermediate product was obtained. The second reaction was:

[0041]

[0042] 0.1 mol of the first intermediate product, 0.1 mol of the second intermediate product, 50 mL of tetrahydrofuran and 0.1 mol of pyridine were added to a flask, nitrogen was introduced, and the flask was stirred at a temperature of -10 to 10° C. for 3 to 6 hours to obtain a modified component. The modified component was separated and dissolved in deionized water to obtain a 50% concentration aqueous solution of the modified component. The third reaction was as follows:

[0043]

[0044] 60 to 80 parts of deionized water, 10 to 30 parts of solvent, 1 to 10 parts of modified component aqueous solution and 5 to 15 parts of open hollow carbon material are mixed evenly and ground using a sand mill to a fineness of 15 to 30 μm. The mixture is then transferred to a high-pressure reactor for modification reaction. The modification reaction temperature is 150 to 180°C, the pressure is 0.7 to 1.4 MPa, and the time is 6 to 12 hours to obtain a modified open hollow carbon material with an open hollow conductive carbon material mass concentration of 5 to 15 wt%.

[0045] Optionally, the first solvent includes one or more of ethanol, n-butanol, tert-butanol, isobutanol, n-propanol, isopropanol, 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.

[0046] Furthermore, the first solvent is used as a cosolvent, and alcohol and ether solvents are used as cosolvents during the preparation of the coating to improve the dispersion performance. In this embodiment, the first solvent is also used to adjust the modification reaction speed of the open hollow carbon material, which is beneficial to the formation of the modified open hollow carbon material.

[0047] In a fourth aspect, an embodiment of the present invention discloses a carbon-coated aluminum foil, which is prepared by the following method:

[0048] 5 to 15 parts of water, 10 to 30 parts of a second solvent, 10 to 25 parts of a binder, and 40 to 60 parts of a modified open hollow carbon material are mixed and ground to obtain a carbon-coated aluminum foil coating; the second solvent comprises one or more of ethanol, n-butanol, tert-butanol, isobutanol, n-propanol, isopropanol, and ethylene glycol monobutyl ether; and the binder is an acrylic resin;

[0049] The carbon-coated aluminum foil coating is coated on the current collector aluminum foil by gravure or micro-gravure and then dried to obtain the carbon-coated aluminum foil; the drying temperature is 80-200° C. and the drying time is 5-120 seconds.

[0050] Furthermore, the second solvent, using alcohol or ether as a cosolvent, is used to adjust the drying speed of the coating and promote film formation, so that the carbon-coated aluminum foil has good adhesion, gloss, and water and chemical resistance. The binder is a commercially available acrylic resin specifically for carbon-coated aluminum foil coating. The carbon-coated aluminum foil coating has a fineness of less than or equal to 15 μm, a viscosity of 30 to 1000 mPa·s, and a solid content of 5 to 25 wt%. The carbon coating layer of the carbon-coated aluminum foil has a film weight of 0.2 to 2 g / m 2 .like Figure 2In the carbon-coated aluminum foil of the present embodiment shown, the positive electrode active material is coated on the surface of the carbon coating layer of the carbon-coated aluminum foil, and part of the polyvinylidene fluoride (PVDF) in the positive electrode active material is embedded in the opening of the open hollow carbon material. After the positive electrode active material is dried, the PVDF is stably present in the hollow "cage" of the open hollow carbon material, thereby achieving the effect of improving the wettability and peel strength.

[0051] The specific embodiment of carbon-coated aluminum foil is as follows:

[0052] Example 1

[0053] Preparation of open hollow carbon materials:

[0054] 5 parts of hollow aggregated carbon were used as a matrix material and ultrasonically cleaned in 95 parts of anhydrous ethanol for 10 minutes to remove surface impurities. The product was then centrifuged and washed with deionized water and then dried in a vacuum drying oven at 80° C. to obtain pretreated hollow aggregated carbon.

[0055] Mix 2 parts of pretreated hollow aggregated carbon, 20 parts of dilute sulfuric acid, 20 parts of dilute nitric acid and 58 parts of deionized water, transfer the mixture into a high-pressure reactor and seal it for high-pressure acid etching treatment. The acid etching temperature is 130°C, the pressure is 0.4 MPa, and the time is 10 h. After the acid etching treatment, centrifuge and wash with deionized water until neutral, and vacuum dry at 60°C to obtain an open hollow carbon material.

[0056] Preparation of modified components:

[0057] 0.1 mol of 4-anilinesulfonic acid, 0.1 mol of 4-chlorobenzenesulfonic acid and 100 mL of toluene were added to a flask, nitrogen was introduced, 0.01 g of palladium catalyst was added, and the first reaction was carried out by stirring at a temperature of 80° C. for 4.5 h. After the reaction, a first intermediate product was obtained;

[0058] 1 mol of p-hydroxybenzoic acid and 500 mL of benzene were added to a flask, heated to 50°C, and 0.6 mol of silicon tetrachloride was added dropwise. After keeping the temperature for 4 hours, the reaction mixture was fractionated to obtain the second intermediate product.

[0059] 0.1 mol of the first intermediate product, 0.1 mol of the second intermediate product, 50 mL of tetrahydrofuran and 0.1 mol of pyridine were added to a flask, and nitrogen was introduced with stirring to carry out a third reaction. The temperature of the third reaction was 0-5°C and the time was 3 h to obtain a modified component. The modified component was separated and dissolved in deionized water to obtain a 50% concentration aqueous solution of the modified component.

[0060] Preparation of modified open hollow carbon materials:

[0061] 75 parts of deionized water, 10 parts of ethanol, 5 parts of aqueous solution of the modified component and 10 parts of the open hollow carbon material were mixed evenly and ground into a fineness of 20 μm using a sand mill. The mixture was then transferred to a high-pressure reactor for modification reaction. The temperature of the modification reaction was 160°C, the pressure was 0.85 MPa, and the time was 8 hours to obtain a modified open hollow carbon material with a mass concentration of 10 wt% of the open hollow conductive carbon material.

[0062] Preparation of carbon-coated aluminum foil:

[0063] 10 parts of deionized water, 20 parts of ethanol, 20 parts of acrylic resin binder, and 50 parts of modified open hollow carbon material were mixed in order, and then ground and dispersed using a sand mill to obtain a carbon-coated aluminum foil coating. The fineness of the carbon-coated aluminum foil coating was 10 μm.

[0064] The carbon-coated aluminum foil coating is coated on the current collector aluminum foil by gravure or micro-gravure coating, and baked in a hot air oven at 120°C for 30s to obtain the carbon-coated aluminum foil. Figure 3 The carbon coating layer in the carbon-coated aluminum foil shown has a film weight of 0.5 g / m 2 , marked as S1.

[0065] Example 2

[0066] Compared with Example 1, Example 2 is different in that the high-pressure acid etching temperature for the preparation of the open hollow carbon material is 150° C., the pressure is 0.7 MPa, and the time is 8 h. Other preparation methods are the same and are marked as S2.

[0067] Example 3

[0068] Compared with Example 1, Example 3 has different high-pressure acid etching temperatures of 180° C., pressures of 1.2 MPa, and time of 6 h for the preparation of open hollow carbon materials. Other preparation methods are the same and are marked as S3.

[0069] Example 4

[0070] Compared with Example 3, Example 4 is a method in which the base material for preparing the open hollow carbon material is hollow carbon nanofiber, and other preparation methods are the same, which is marked as S4.

[0071] Comparative Example 1

[0072] Compared with Example 2, in Comparative Example 1, the base material for preparing the open hollow carbon material is solid aggregated carbon (conductive carbon black SP), and the other preparation methods are the same, which is marked as X1.

[0073] Comparative Example 2

[0074] Comparative Example 2 is compared with Example 2, in which the open hollow carbon material is prepared under normal pressure conditions of high pressure acid etching, and other preparation methods are the same, and is marked as X2.

[0075] Comparative Example 3

[0076] Comparative Example 3 Compared with Example 2, the hollow carbon material prepared by the open hollow carbon material is not subjected to acid etching treatment, and other preparation methods are the same, which is marked as X3.

[0077] Comparative Example 4

[0078] Compared with Example 2, Comparative Example 4 uses PVP as the modifying component for preparing the modified open hollow carbon material, and other preparation methods are the same, which is marked as X4.

[0079] Comparative Example 5

[0080] Compared with Example 2, in Comparative Example 5, the modified open hollow carbon material was prepared without modification, and other preparation methods were the same, and it was marked as X5.

[0081] Comparative Example 6

[0082] Compared with Example 2, Comparative Example 6 replaces the base material for preparing the open hollow carbon material with nano hollow carbon spheres instead of aggregates. Other preparation methods are the same and are marked as X6.

[0083] The carbon-coated aluminum foils S1 to S4 and X1 to X6 obtained in the examples and comparative examples were tested for adhesion, solvent resistance, surface contact resistance, and peel strength. The slurry stability of the carbon-coated aluminum foil coating was also tested. The test results are shown in Table 1.

[0084] (1) Adhesion test: Place the coating side of the carbon-coated aluminum foil upwards and stick it to the coating with 3M tape. Then pull the 3M tape vertically upwards from the bottom to observe the degree of coating shedding.

[0085] (2) Solvent resistance test: NMP resistance: Dip a cotton swab in N-methylpyrrolidone (NMP) and wipe the same position of the carbon-coated aluminum foil back and forth with even force. The wiping distance is about 6 cm. One round trip is counted as one time. The number of wiping times when the aluminum foil substrate leaks out is recorded. Electrolyte resistance: The test method is the same as that of NMP resistance, except that the test solvent is replaced with electrolyte.

[0086] (3) Surface contact resistance test: The surface contact resistance of the carbon-coated aluminum foil coating was tested using an ST-2258C four-probe tester.

[0087] (4) Peel strength test: Lithium iron phosphate slurry (battery positive electrode active material) was coated on the surface of carbon-coated aluminum foil. After drying, the test was performed using a tensile tester according to the method shown in GB2792-2014 and converted into N / m.

[0088] (5) Slurry stability test: Place the carbon-coated aluminum foil paint at room temperature for 60 days to observe whether there is precipitation, and place the carbon-coated aluminum foil paint at 50°C for 30 days to observe whether there is precipitation.

[0089] Table 1 Performance test results of carbon-coated aluminum foil and carbon-coated aluminum foil coating

[0090]

[0091] From the test results in Table 1, it can be seen that, on the one hand, the peel strength of the embodiment of the open hollow carbon material is significantly improved compared with the comparative example of the solid carbon material, the comparative example of the hollow carbon material subjected to normal pressure acid etching, and the comparative example of the hollow carbon material without acid etching. When the open hollow carbon material is in contact with the positive electrode active material, the opening increases the contact area between the carbon-coated layer of the carbon-coated aluminum foil and the positive electrode active material, and can also serve as a "cage" to trap the active material, resulting in higher peel strength, greatly improving the wettability and peel strength between the carbon-coated aluminum foil current collector and the positive electrode active material layer. At the same time, the open hollow carbon material after acid etching provides more active sites for modification reactions, and the slurry stability is better. On the other hand, the slurry stability of the unmodified comparative example is poor; the comparative example modified with PVP can improve the slurry stability, but has a significant negative effect on adhesion, solvent resistance and surface contact resistance; unlike the carbon-coated aluminum foil modified with PVP and the unmodified carbon-coated aluminum foil, the embodiment greatly improves the stability of the carbon-coated coating by modifying the modifying component. At the same time, since the modifying component is an ionic small molecule, it has little effect on the surface contact resistance of the lithium-ion battery. The carbon-coated aluminum foil using open hollow carbon materials improves the overall performance of the lithium-ion battery. The slurry stability of the carbon-coated aluminum foil comparative example using nano hollow carbon balls is improved to a certain extent. This is because the nano hollow carbon balls exist independently, the particles are smaller, and the stability is better after modification. However, the nano hollow carbon balls do not have the longitudinal anchoring effect and natural conductive path of aggregated carbon or hollow carbon fibers, so the peel strength is limited, the surface contact resistance is higher, and the conductivity is affected. At the same time, it is explained from the side that high-pressure acid etching forms openings on the surface of hollow aggregated carbon but does not destroy the aggregation state of hollow aggregated carbon.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An open hollow carbon material, characterized in that: The interior of the open hollow carbon material is hollow to form a cavity, and at least one opening is distributed on the outer surface of the open hollow carbon material, wherein the opening connects the cavity of the open hollow carbon material and the exterior of the open hollow carbon material, and the area of the opening accounts for 20% to 40% of the outer surface area of the open hollow carbon material; the matrix material of the open hollow carbon material comprises one or both of hollow aggregated carbon and hollow carbon nanofibers, wherein the hollow aggregated carbon is a single-particle hollow carbon sphere aggregate, and the hollow carbon nanofiber is a hollow and penetrating carbon nanofiber; The open hollow carbon material is obtained by mixing 1 to 6 parts of a matrix material with 94 to 99 parts of an acid solution and then performing an acid etching treatment under high pressure conditions; the acid solution includes one or more of dilute nitric acid, dilute hydrochloric acid, perchloric acid, and dilute sulfuric acid; the reaction temperature of the acid etching treatment is 120 to 180°C, the reaction pressure is 0.3 to 1.2 MPa, and the reaction time is 6 to 12 hours.

2. The open hollow carbon material according to claim 1, characterized in that: The particle size of the hollow carbon spheres of the hollow aggregated carbon is 80-200 nm, and the outer diameter of the hollow carbon nanofibers is 100-300 nm.

3. The open hollow carbon material according to claim 1, characterized in that: The hollow aggregated carbon has a cavity volume ratio of 80% to 90%; the hollow carbon nanofiber has a cavity volume ratio of 70% to 80%.

4. A method for preparing an open hollow carbon material according to any one of claims 1 to 3, characterized in that: include: 1-6 parts of a matrix material and 94-99 parts of an acid solution are mixed and then subjected to acid etching treatment under high pressure conditions to obtain an open hollow carbon material.

5. A modified open hollow carbon material, characterized in that: The modified open hollow carbon material is obtained by grafting the open hollow carbon material according to any one of claims 1 to 3 with a modifying component, wherein the modifying component is a water-soluble small molecule having a disulfonic acid group and a monophenolic hydroxyl group.

6. The modified open hollow carbon material according to claim 5, characterized in that: The preparation method of the modified open hollow carbon material comprises: 4-anilinesulfonic acid, 4-chlorobenzenesulfonic acid and toluene are mixed and then a palladium catalyst is added to perform a first reaction to obtain a first intermediate product; the reaction temperature of the first reaction is 60-90° C. and the reaction time is 4-5 hours; Add p-hydroxybenzoic acid and benzene to a flask, and add silicon tetrachloride dropwise to carry out a second reaction to obtain a second intermediate product; the reaction temperature of the second reaction is 40-70°C, and the reaction time is 3-5 hours; The first intermediate product, the second intermediate product, tetrahydrofuran and pyridine are added to the flask for a third reaction to obtain a modified component; the reaction temperature of the third reaction is -10 to 10°C, and the reaction time is 3 to 6 hours; 60-80 parts of water, 10-30 parts of a first solvent, 1-10 parts of a modifying component, and 5-15 parts of an open hollow carbon material are mixed and subjected to a modification reaction to obtain a modified open hollow carbon material; the reaction temperature of the modification reaction is 150-180° C., the reaction pressure is 0.7-1.4 MPa, and the reaction time is 6-12 h.

7. The modified open hollow carbon material according to claim 6, characterized in that: The first solvent includes one or more of ethanol, n-butanol, tert-butanol, isobutanol, n-propanol, isopropanol, 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.

8. A carbon-coated aluminum foil, characterized in that: The carbon-coated aluminum foil is prepared by the following method: 5-15 parts of water, 10-30 parts of a second solvent, 10-25 parts of a binder, and 40-60 parts of the modified open hollow carbon material according to any one of claims 5 to 7 are mixed and ground to obtain a carbon-coated aluminum foil coating; the second solvent comprises one or more of ethanol, n-butanol, tert-butanol, isobutanol, n-propanol, isopropanol, and ethylene glycol monobutyl ether; and the binder is an acrylic resin; The carbon-coated aluminum foil coating is coated on the current collector aluminum foil by gravure or micro-gravure and then dried to obtain the carbon-coated aluminum foil; the drying temperature is 80-200° C. and the drying time is 5-120 seconds.

Images