Composite flake graphite and preparation method thereof, current collector and preparation method thereof, battery monomer, battery and electric equipment

Abstract

The invention provides composite flake graphite and a preparation method thereof, a current collector and a preparation method thereof, a battery monomer, a battery and electric equipment, and belongs to the technical field of batteries. The preparation method of the composite flake graphite comprises the following steps: mixing and crushing raw materials containing flake graphite, an MXene material and a solvent to prepare graphite slurry, and then filtering and drying the graphite slurry in sequence to prepare the composite flake graphite, the particle size of the crushed flake graphite in the graphite slurry is 3-10 [mu] m, and the particle size of the crushed MXene material in the graphite slurry is 0.5-1 [mu] m. The flake graphite and the MXene material are mixed and crushed to prepare the composite flake graphite, the composite flake graphite can be used as a raw material to prepare the conductive slurry, the conductive slurry is used for coating the surface of the current collector to form the carbon-containing composite coating, and compared with an existing graphite coating, the carbon-containing composite coating has better conductivity, high voltage resistance and electrolyte corrosion resistance; therefore, the consistency and the long-cycle reliability of the battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular, to composite flaky graphite and its preparation method, current collector and its preparation method, battery monomer, battery and electrical equipment. Background Art

[0002] In recent years, the shipment volume of chemical energy storage batteries has increased rapidly. Among them, lithium iron phosphate batteries have become the first choice for energy storage batteries due to their low cost, high safety and long cycle life. However, the lithium iron phosphate material itself has poor ionic conductivity and electronic conductivity. In the traditional lithium battery electrode manufacturing process, the active material slurry is directly coated on the surface of the aluminum foil current collector, and after drying, the active material is fixed on the surface of the aluminum foil current collector through a binder. However, the contact area between the rigid metal current collector and the active material particles is limited, and the interface resistance is large, which causes an increase in the internal resistance of the battery and has a negative impact on the battery performance, especially under high-current charge and discharge conditions. In addition, the bonding strength of the binder is limited. During continuous charge and discharge, it is easy for the active material to expand and detach from the current collector, resulting in a further increase in the internal resistance of the battery, affecting the cycle life and safety performance of the battery.

[0003] To apply it to high-power or long-life scenarios, reasonable design and optimization are required for the lithium iron phosphate material and the electrode. Carbon-coated aluminum foil is a current collector that can well improve the contact interface between the positive electrode active material and the foil material, can greatly reduce the contact resistance between the active material and the current collector, increase the wettability and adhesion of the active material, improve the battery consistency, and enhance the cycle life and rate performance of the battery.

[0004] However, traditional carbon-coated aluminum foil mainly uses carbon black as a conductive agent, and its dispersion in the conductive slurry is poor, resulting in uneven distribution on the surface of the aluminum foil substrate, so that the conductivity, adhesion and consistency between the aluminum foil substrate and the lithium iron phosphate active coating are not ideal. At the same time, the carbon-coated aluminum foil produced has poor corrosion resistance to the electrolyte under high voltage and high temperature conditions, and the corrosion of the current collector causes battery performance failure, thus unable to meet the long-life requirements of the battery. Summary of the Invention

[0005] The present application provides composite flaky graphite and its preparation method, current collector and its preparation method, battery monomer, battery and electrical equipment, which can improve the cycle performance of the battery.

[0006] The embodiments of the present application are implemented as follows:

[0007] In a first aspect, an example of the present application provides a method for preparing composite flaky graphite, which includes: mixing and pulverizing a raw material containing flaky graphite, MXene material and a solvent to obtain a graphite slurry, and then subjecting the graphite slurry to filtration and drying treatments in sequence to obtain composite flaky graphite; the particle size of the pulverized flaky graphite in the graphite slurry is 3 μm to 10 μm, and the particle size of the pulverized MXene material in the graphite slurry is 0.5 μm to 1 μm.

[0008] In the above technical solution, the method for preparing the composite flaky graphite of the present application obtains the composite flaky graphite by mixing and pulverizing the flaky graphite and the MXene material. The composite flaky graphite can be used as a raw material to make a conductive slurry, and the conductive slurry is used to coat the surface of the substrate of the current collector to form a carbon-containing composite coating. The MXene material in the carbon-containing composite coating is in a flaky shape and can block ion transport, making it difficult for ions to transport, which is beneficial to hindering the further reaction of the ions in the electrolyte with the substrate of the current collector, thereby reducing the corrosion of the substrate of the current collector. Compared with the existing graphite coating, it has better high-voltage resistance and electrolyte corrosion resistance, and further achieves the purpose of extending the cycle life of the battery cell. At the same time, because the flaky graphite has good electrical conductivity, a reasonable specific surface area, and good hydrophilicity, the conductive slurry prepared therefrom has better dispersibility and stability and can be evenly coated on the surface of the current collector, further improving the electrical conductivity and adhesion performance of the electrode sheet, thereby improving the consistency and long-cycle reliability of the battery. And because the MXene material has excellent electrical conductivity, the conductive slurry including the MXene material can improve the problems of high internal resistance and poor electrical conductivity of lithium iron phosphate and other positive electrodes, thereby improving the rate, low-temperature, cycle and storage performance of the battery cell, and further extending the service life of the battery cell.

[0009] Combined with the first aspect, in the first possible example of the first aspect of the present application, the chemical formula of the above MXene material is Ti 3 C 2 T x , where T is -OH, -H, -F or -Cl.

[0010] In the above example, by selecting the above MXene material, the MXene material can be compounded on the surface of the flaky graphite, improving the electrical conductivity and high-voltage resistance of the prepared battery.

[0011] Combined with the first aspect, in the second possible example of the first aspect of the present application, the mass ratio of the above flaky graphite to the MXene material is 1 to 2:1.

[0012] In the above example, by making the mass ratio of the flaky graphite and the MXene material within the above range, not only can the flaky graphite and the MXene material be evenly mixed, with the MXene material being compounded on the surface of the flaky graphite, but also the agglomeration of the MXene material can be reduced, avoiding the decline in the overall performance of the battery caused by the agglomeration of the MXene material hindering the transmission of electrons.

[0013] Combined with the first aspect, in the third possible example of the first aspect of the present application, the mass percentage of the flaky graphite in the above graphite slurry is 0.1 wt% to 1 wt%.

[0014] In the above example, by making the mass percentage of the flaky graphite in the graphite slurry within the above range, it is beneficial to evenly mix the flaky graphite and the MXene material.

[0015] Combined with the first aspect, in the fourth possible example of the first aspect of the present application, the mass percentage of the MXene material in the above graphite slurry is 0.1 wt% to 0.5 wt%.

[0016] In the above example, by making the mass percentage of the MXene material in the graphite slurry within the above range, it is beneficial to evenly mix the flaky graphite and the MXene material.

[0017] Combined with the first aspect, in the fifth possible example of the first aspect of the present application, the above solvent includes ethanol and water, and the volume fraction of ethanol in the solvent is 5% to 95%.

[0018] In the above example, by selecting a mixture of ethanol and water as the solvent, ethanol and water can be separated from the system after drying, thus avoiding the introduction of impurities and ensuring the normal cycling of the battery.

[0019] Combined with the first aspect, in the sixth possible example of the first aspect of the present application, the method of mixing and pulverizing the above raw materials includes ball milling, grinding, magnetic stirring or dispersion disk mixing.

[0020] Combined with the first aspect, in the seventh possible example of the first aspect of the present application, the method of mixing and pulverizing the above raw materials includes ball milling at a rotation speed of 300 rpm to 3500 rpm for at least 3 h.

[0021] In the above example, by ball milling the raw materials at the above rotation speed, the particle size of the pulverized flaky graphite in the graphite slurry can be 3 μm to 10 μm, and the particle size of the pulverized MXene material in the graphite slurry can be 0.5 μm to 1 μm, and the MXene material can be evenly compounded on the surface of the flaky graphite.

[0022] In the second aspect, the example of the present application provides a composite flaky graphite, which is prepared according to the preparation method of the composite flaky graphite in the above embodiment.

[0023] In the above technical solution, the composite flaky graphite of the present application can be used as a raw material to make a conductive paste, and the conductive paste is used to coat the surface of the current collector to form a carbon-containing composite coating. The MXene material in the carbon-containing composite coating is flaky and can block ion transport, making ion transport difficult, which is beneficial to hindering the further reaction between the ions in the electrolyte and the matrix of the current collector, thereby reducing the corrosion of the matrix of the current collector. Compared with the existing graphite coating, it has better high-voltage resistance and electrolyte corrosion resistance, and further achieves the purpose of extending the cycle life of the battery cell. At the same time, because the flaky graphite has good electrical conductivity, a reasonable specific surface area, and good hydrophilicity, the conductive paste prepared therefrom has better dispersibility and stability, can be evenly coated on the surface of the current collector, and further improves the electrical conductivity and adhesion performance of the electrode sheet, thereby improving the consistency and long-cycle reliability of the battery. Moreover, because the MXene material has excellent electrical conductivity, the conductive paste including the MXene material can improve the problems of high internal resistance and poor electrical conductivity of lithium iron phosphate and other positive electrodes, thereby improving the rate, low-temperature, cycle, and storage performance of the battery cell, and further extending the service life of the battery cell.

[0024] In a third aspect, an example of the present application provides a current collector, which includes a matrix and a carbon-containing composite coating. The carbon-containing composite coating is disposed on at least one surface of the matrix, and the carbon-containing composite coating includes the composite flaky graphite in the above embodiments.

[0025] In the above technical solution, the current collector of the present application improves the high-voltage resistance, electrolyte corrosion resistance of the current collector, and the adhesion between the active material layer and the current collector by disposing a carbon-containing composite coating on at least one surface of the matrix, thereby reducing the internal resistance of the prepared lithium-ion battery or sodium-ion battery, and improving the cycle life, high-voltage resistance, and corrosion resistance of the lithium-ion battery or sodium-ion battery.

[0026] Combined with the third aspect, in the first possible example of the third aspect of the present application, the above carbon-containing composite coating includes a conductive agent, the conductive agent includes composite flaky graphite and a conductive material, the conductive material includes conductive carbon black, and the mass ratio of the composite flaky graphite to the conductive material is 50:50 to 70:30.

[0027] In the above example, by making the mass ratio of the composite flaky graphite to the conductive material in the conductive material within the above range, it is beneficial to improve the high-voltage resistance, electrolyte corrosion resistance of the current collector, and the adhesion between the active material layer and the current collector, thereby reducing the internal resistance of the prepared lithium-ion battery or sodium-ion battery, and improving the cycle life, high-voltage resistance, and corrosion resistance of the lithium-ion battery or sodium-ion battery.

[0028] Combined with the third aspect, in the second possible example of the third aspect of the present application, the above conductive material further includes flake graphite, and the mass ratio of flake graphite to conductive carbon black is 0.1:99.9 to 20:80.

[0029] In the fourth aspect, an example of the present application provides a method for preparing the current collector in the above embodiment, which includes disposing a conductive paste on one side of a substrate, the conductive paste includes composite flake graphite, and drying to obtain the current collector.

[0030] In the above technical solution, the method for preparing the current collector of the present application is simple, the obtained current collector has a stable structure, and has the characteristics of high voltage resistance and electrolyte corrosion resistance, thereby reducing the internal resistance of the obtained lithium-ion battery or sodium-ion battery, and improving the cycle life, high voltage resistance and corrosion resistance of the lithium-ion battery or sodium-ion battery.

[0031] Combined with the fourth aspect, in the first possible example of the fourth aspect of the present application, the above conductive paste includes 6 to 15 parts by weight of a conductive agent, 18 to 20 parts by weight of a binder, 1 to 3 parts by weight of a film-forming agent, 1 to 3 parts by weight of an auxiliary agent, and 65 to 75 parts by weight of a solvent. The conductive agent includes composite flake graphite and a conductive material, and the mass ratio of composite flake graphite to the conductive material is 50:50 to 70:30; optionally, the binder includes polyvinylidene fluoride and / or polyacrylic acid; optionally, the film-forming agent includes any one or more of ammonium persulfate, tert-butyl perpivalate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-p-tert-butylcyclohexyl peroxydicarbonate, and diethyl peroxydicarbonate; optionally, the auxiliary agent is prepared by dissolving an alkali and a strong base weak acid salt in water, the alkali includes sodium hydroxide, and the strong base weak acid salt includes a carbonate and a bicarbonate; optionally, the solvent includes water and an organic solvent, and the mass ratio of water to the organic solvent is 4 to 5:1, and the organic solvent includes any one or more of isopropanol, methanol, and ethanol.

[0032] Combined with the fourth aspect, in the second possible example of the fourth aspect of the present application, the method for disposing the conductive paste on at least one side of the substrate includes knife coating, spraying, or gravure printing;

[0033] Optionally, the method for disposing the conductive paste on at least one side of the substrate is knife coating.

[0034] In the above technical solution, the doctor blade coating method can make the flaky MXene material in the conductive paste parallel or nearly parallel to the contact surface between the substrate and the conductive paste, further improving the performance of the flaky MXene material in blocking ion transport, which is beneficial to hindering the further reaction between the ions in the electrolyte and the substrate of the current collector, thereby reducing the corrosion of the substrate of the current collector. Compared with the existing graphite coating, it has better high-voltage resistance and electrolyte corrosion resistance, and thus achieves the purpose of extending the cycle life of the battery cell.

[0035] In a fifth aspect, an example of the present application provides a battery cell, which includes the current collector in the above embodiments.

[0036] In a sixth aspect, an example of the present application provides a battery, which includes the battery cell in the above embodiments.

[0037] In a seventh aspect, an example of the present application provides an electrical device, which includes the battery cell or the battery in the above embodiments, and the battery cell or the battery is used to provide electrical energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0039] Figure 1 It is a schematic structural diagram of the battery and the current collector of the embodiment of the present application.

[0040] Figure 2 It is an electron microscope image of the carbon-containing composite coating of Embodiment 1 of the present application.

[0041] Figure 3 It is an electron microscope image of the carbon-containing composite coating of Embodiment 2 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The following will describe the implementation solutions of the present application in detail with reference to the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. Those conditions not specified in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0043] The inventors found that ordinary carbon-coated aluminum foils use carbon materials such as carbon black and conductive graphite as the main components of the carbon coating slurry, and the coating uniformity on the aluminum foil substrate is poor. Moreover, the carbon black particles are connected to the foil by an adhesive, but the adhesive is not conductive. If the carbon black coating is too thick, many carbon black particles will block between the lithium iron phosphate particles and the aluminum foil, which will have a negative impact on the conductivity. If the carbon black coating is too thin, the carbon black cannot fully fill the triangular area between the lithium iron phosphate particles and the foil, and the conductivity will be lower than that of the electrode sheet with carbon black incorporated. In addition, carbon black and conductive graphite cannot prevent the aluminum foil substrate from being corroded and oxidized under long-term high voltage and electrolyte immersion, resulting in poor adhesion and conductivity between the substrate and the active material, and further leading to battery failure.

[0044] Based on this, the present application provides a composite flaky graphite, a preparation method thereof, a current collector, a preparation method thereof, a battery cell, a battery and an electrical device, which can improve the electrical performance of the battery.

[0045] The following specifically describes a composite flaky graphite, a preparation method thereof, a current collector, a preparation method thereof, a battery cell, a battery and an electrical device according to an embodiment of the present application:

[0046] The present application provides a preparation method of a composite flaky graphite, which includes the following steps:

[0047] S1. Prepare a graphite slurry

[0048] Mix and pulverize raw materials including flaky graphite, MXene material and a solvent to obtain a graphite slurry. The particle size of the pulverized flaky graphite in the graphite slurry is 3 μm to 10 μm, and the particle size of the pulverized MXene material in the graphite slurry is 0.5 μm to 1 μm.

[0049] Among them, the particle size of the flaky graphite is 5 μm to 25 μm.

[0050] The chemical formula of the MXene material is Ti 3 C 2 T x , where T is -OH, -H, -F or -Cl. For example, the chemical formula of the MXene material can be Ti 3 C 2 F 2 , Ti 3 C 2 (OH) 2 or Ti 3 C 2 O.

[0051] By selecting the above MXene material, the MXene material can be compounded on the surface of the flaky graphite, improving the conductivity and high-voltage resistance performance of the prepared battery.

[0052] Optionally, the mass ratio of flaky graphite to MXene material is 1-2:1.

[0053] As an example, the mass ratio of flaky graphite to MXene material can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1.

[0054] By making the mass ratio of flaky graphite to MXene material within the above range, not only can the flaky graphite and MXene material be mixed evenly, with the MXene material being compounded on the surface of the flaky graphite, but also the agglomeration of the MXene material can be reduced, avoiding the decline in the overall performance of the battery caused by the agglomeration of the MXene material hindering the electron transport.

[0055] Optionally, the solvent includes ethanol and water, and the volume fraction of ethanol in the solvent is 5%-95%.

[0056] As an example, the volume fraction of ethanol in the solvent can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95%.

[0057] By selecting a mixture of ethanol and water as the solvent, ethanol and water can be separated from the system after drying, thus avoiding the introduction of impurities and ensuring the normal cycling of the battery.

[0058] Optionally, the mass percentage of flaky graphite in the graphite slurry is 0.1wt%-1wt%.

[0059] As an example, the mass percentage of flaky graphite in the graphite slurry can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1wt%.

[0060] By making the mass percentage of flaky graphite in the graphite slurry within the above range, it is beneficial to the uniform mixing of flaky graphite and MXene material.

[0061] Optionally, the mass percentage of MXene material in the graphite slurry is 0.1wt%-0.5wt%.

[0062] As an example, the mass percentage of MXene material in the graphite slurry can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt% or 0.5wt%.

[0063] By making the mass percentage of MXene material in the graphite slurry within the above range, it is beneficial to the uniform mixing of flaky graphite and MXene material.

[0064] The method of mixing and pulverizing raw materials includes ball milling, grinding, magnetic stirring or dispersion disk mixing.

[0065] An embodiment of the present application provides a method for mixing and pulverizing raw materials, which includes first mixing and stirring the raw materials at a temperature of 15°C to 30°C for 0.5 h to 3 h to obtain a mixture, then dispersing the mixed liquid under ultrasonic action for 0.5 h to 3 h, and then adding the mixed liquid after ultrasonic treatment into a ball milling tank, adding grinding balls according to a mass ratio of grinding balls to solid components in the mixed liquid of 5 to 20:1, wherein the material of the grinding balls can be agate or zirconia, the diameters of the grinding balls are 1.5 mm and 0.8 mm respectively, and the grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to a mass ratio of 0.8 to 1.2:1, and ball milling at a speed of 300 rpm to 3500 rpm for at least 3 h.

[0066] S2. Prepare composite flake graphite

[0067] Sieve the graphite slurry and let it stand for 2 h to 24 h. After the solid and liquid in the graphite slurry are fully stratified, remove the upper liquid in the graphite slurry, place the lower liquid in the graphite slurry in a dryer, and dry it at a temperature of 40°C to 100°C for 8 h to 48 h to obtain composite flake graphite.

[0068] The preparation method of the composite flake graphite of the present application prepares the composite flake graphite by mixing and pulverizing flake graphite and MXene materials. The composite flake graphite can be used as a raw material to make a conductive paste, and the conductive paste is used to coat the surface of the substrate of the current collector to form a carbon-containing composite coating. The MXene material in the carbon-containing composite coating is in the form of flakes, which can block ion transport, making ion transport difficult, and is conducive to hindering the further reaction of ions in the electrolyte with the substrate of the current collector, thereby reducing the corrosion of the substrate of the current collector. Compared with the existing graphite coating, it has better high-voltage resistance and electrolyte corrosion resistance, and further achieves the purpose of extending the cycle life of the battery monomer. At the same time, because flake graphite has good electrical conductivity, a reasonable specific surface area, and good hydrophilicity, the conductive paste prepared therefrom has better dispersibility and stability, and can be evenly coated on the surface of the current collector, further improving the conductivity and adhesion performance of the electrode sheet, thereby improving the consistency and long-cycle reliability of the battery. And because the MXene material has excellent electrical conductivity, the conductive paste including the MXene material can improve the problems of high internal resistance and poor conductivity of lithium iron phosphate and other positive electrodes, thereby improving the rate, low temperature, cycle and storage performance of the battery monomer, and further extending the service life of the battery monomer.

[0069] The present application also provides a composite flake graphite, which is prepared according to the preparation method of the composite flake graphite in the above embodiment.

[0070] The composite flaky graphite of the present application can be used as a raw material to make a conductive paste, which is used to coat the surface of a current collector to form a carbon-containing composite coating. The MXene material in the carbon-containing composite coating is flaky and can block ion transport, making ion transport difficult. This is beneficial to preventing further reaction between the ions in the electrolyte and the matrix of the current collector, thereby reducing the corrosion of the matrix of the current collector. Compared with the existing graphite coating, it has better high-voltage resistance and electrolyte corrosion resistance, and thus achieves the purpose of extending the cycle life of the battery cell. At the same time, due to the good electrical conductivity, reasonable specific surface area, and good hydrophilicity of the flaky graphite, the conductive paste prepared therefrom has better dispersibility and stability and can be evenly coated on the surface of the current collector, further improving the electrical conductivity and adhesion performance of the electrode sheet, thereby improving the consistency and long-cycle reliability of the battery. Moreover, due to the excellent electrical conductivity of the MXene material, the conductive paste including the MXene material can improve the problems of high internal resistance and poor electrical conductivity of lithium iron phosphate and other positive electrodes, thereby enhancing the rate performance, low-temperature performance, cycle performance, and storage performance of the battery cell, and further extending the service life of the battery cell.

[0071] The present application also provides a current collector, which includes a matrix and a carbon-containing composite coating. The carbon-containing composite coating is provided on at least one side of the matrix, and the carbon-containing composite coating includes the composite flaky graphite in the above embodiments.

[0072] Among them, the matrix includes aluminum foil.

[0073] The thickness of the aluminum foil is 6 μm to 20 μm, the thickness of the carbon-containing composite coating before drying is 3 μm to 18 μm, and the thickness of the carbon-containing composite coating after drying is 0.5 μm to 3 μm.

[0074] The carbon-containing composite coating includes a conductive agent. The conductive agent includes composite flaky graphite and a conductive material. The conductive material includes conductive carbon black. The mass ratio of the composite flaky graphite to the conductive material is 50:50 to 70:30.

[0075] As an example, the mass ratio of the composite flaky graphite to the conductive material can be 50:50, 55:45, 60:40, 65:35, or 70:30.

[0076] By making the mass ratio of the composite flaky graphite to the conductive material in the above range in the conductive material, it is beneficial to improve the high-voltage resistance, electrolyte corrosion resistance of the current collector, and the adhesion between the active material layer and the current collector, thereby reducing the internal resistance of the prepared lithium-ion battery or sodium-ion battery and improving the cycle life, high-voltage resistance, and corrosion resistance of the lithium-ion battery or sodium-ion battery.

[0077] Optionally, the conductive material further includes flaky graphite, and the mass ratio of the flaky graphite to the conductive carbon black is 0.1:99.9 to 20:80.

[0078] For example, the mass ratio of flake graphite to conductive carbon black can be 0.1:99.9, 0.5:99.5, 1:99, 5:95, 10:90, 15:85 or 20:80.

[0079] By providing a carbon-containing composite coating on at least one surface of the substrate, the current collector of the present application improves the high-voltage resistance, electrolyte corrosion resistance of the current collector, and the adhesion between the active material layer and the current collector, thereby reducing the internal resistance of the prepared lithium-ion battery or sodium-ion battery and improving the cycle life, high-voltage resistance and corrosion resistance of the lithium-ion battery or sodium-ion battery.

[0080] The present application also provides a method for preparing the current collector in the above embodiments, which includes the following steps:

[0081] S1. Treat the substrate

[0082] Treat the surface of the substrate to wash away the residual oil and impurity on the surface of the substrate.

[0083] S2. Prepare the conductive paste

[0084] Mix 6 to 15 parts by weight of a conductive agent, 18 to 20 parts by weight of a binder, 1 to 3 parts by weight of a film-forming agent, 1 to 3 parts by weight of an auxiliary agent, and 65 to 75 parts by weight of a solvent evenly to obtain the conductive paste.

[0085] Among them, the binder includes polyvinylidene fluoride and / or polyacrylic acid.

[0086] The film-forming agent includes any one or more of ammonium persulfate, tert-butyl perpivalate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-p-tert-butylcyclohexyl peroxydicarbonate, and diethyl peroxydicarbonate.

[0087] The auxiliary agent is prepared by dissolving an alkali and a strong base weak acid salt in water. The alkali includes sodium hydroxide, and the strong base weak acid salt includes carbonate and bicarbonate.

[0088] The solvent includes water and an organic solvent, and the mass ratio of water to the organic solvent is 4 to 5:1. The organic solvent includes any one or more of isopropanol, methanol, and ethanol.

[0089] S3. Prepare the current collector

[0090] Coat the prepared conductive paste on the surface of the substrate, and the coating width does not exceed the width of the substrate. Then place the substrate coated with the conductive paste in a dryer and dry it at a temperature of 100°C to 200°C for 2 minutes to 60 minutes to form a carbon-containing composite coating on the surface of the substrate.

[0091] Optionally, the method of applying the conductive paste on the surface of the substrate includes knife coating, spraying or gravure printing, and the application method of the conductive paste includes gap coating or continuous coating.

[0092] Optionally, the method of applying the conductive paste on the surface of the substrate is knife coating.

[0093] The knife coating method can make the flaky MXene material in the conductive paste parallel or nearly parallel to the contact surface between the substrate and the conductive paste, further improving the performance of the flaky MXene material in blocking ion transport, facilitating the hindrance of the reaction between the ions in the electrolyte and the substrate of the current collector, thereby reducing the corrosion of the substrate of the current collector, and having better high-voltage resistance and electrolyte corrosion resistance compared with the existing graphite coating, and further achieving the purpose of prolonging the cycle life of the battery cell.

[0094] Optionally, the included angle between at least 50% of the flaky MXene material and the contact surface between the substrate and the carbon-containing composite coating is -30° to 30°.

[0095] Optionally, the included angle between at least 60% of the flaky MXene material and the contact surface between the substrate and the carbon-containing composite coating is -30° to 30°.

[0096] Optionally, the included angle between at least 60% of the flaky MXene material and the contact surface between the substrate and the carbon-containing composite coating is -20° to 20°.

[0097] Optionally, the included angle between at least 70% of the flaky MXene material and the contact surface between the substrate and the carbon-containing composite coating is -20° to 20°.

[0098] Optionally, the included angle between at least 80% of the flaky MXene material and the contact surface between the substrate and the carbon-containing composite coating is -20° to 20°.

[0099] The preparation method of the current collector of the present application is simple, the obtained current collector has a stable structure, and has the characteristics of high-voltage resistance and electrolyte corrosion resistance, thereby reducing the internal resistance of the prepared lithium-ion battery or sodium-ion battery, and improving the cycle life, high-voltage resistance and corrosion resistance of the lithium-ion battery or sodium-ion battery.

[0100] Please refer to Figure 1 , the present application also provides a battery cell, which includes the current collector in the above embodiments.

[0101] The present application also provides a battery, which includes the battery cell in the above embodiments.

[0102] The present application also provides an electrical device, which includes the battery cell or the battery in the above embodiments, and the battery cell or the battery is used to provide electrical energy.

[0103] The following further describes in detail a composite flake graphite of the present application, its preparation method, a current collector, its preparation method, a battery monomer, a battery and an electrical device in conjunction with embodiments.

[0104] Example 1

[0105] The embodiment of the present application provides a composite flake graphite, its preparation method, a current collector and its preparation method, including the following steps:

[0106] 1. Preparation of composite flake graphite

[0107] S1. Preparation of graphite slurry

[0108] The flake graphite and the MXene material are simultaneously added to a solvent to obtain a raw material. First, the raw material is mixed and stirred at a temperature of 25 °C for 2 h to obtain a mixture, and then the mixed solution is dispersed under ultrasonic action for 1 h. Then, the mixed solution after ultrasonic treatment is added to a ball mill tank, and grinding balls are added according to a mass ratio of 10:1 of the grinding balls to the solid components in the mixed solution. The material of the grinding balls is zirconia, and the diameters of the grinding balls are 1.5 mm and 0.8 mm respectively, and the grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to a mass ratio of 1:1, and ball milled at a speed of 360 rpm for 16 h to obtain a graphite slurry. The mass percentage of the flake graphite in the graphite slurry is 0.4 wt%, the mass percentage of the MXene material is 0.2 wt%, the particle size of the crushed flake graphite in the graphite slurry is 10 μm, and the particle size of the crushed MXene material in the graphite slurry is 1 μm.

[0109] Among them, the MXene material is Ti 3 C 2 O, the solvent is a mixture of ethanol and water, the volume fraction of ethanol in the solvent is 50%, and the mass ratio of the flake graphite to the MXene material is 2:1.

[0110] S2. Preparation of composite flake graphite

[0111] The graphite slurry is sieved (100 mesh), and after removing the grinding balls, it is left standing for 5 h. After the solid and liquid in the graphite slurry are fully layered, the upper liquid in the graphite slurry is removed, and the lower liquid in the graphite slurry is placed in a dryer and dried at a temperature of 60 °C for 12 h to obtain the composite flake graphite.

[0112] 2. Preparation of current collector

[0113] S1. Treatment of substrate

[0114] The surface of the aluminum foil is treated to wash away the residual oil and impurity on the surface of the aluminum foil.

[0115] S2. Preparation of conductive slurry

[0116] 10 parts by weight of a conductive agent, 18 parts by weight of a binder, 1 part by weight of a film-forming agent, 1 part by weight of an auxiliary agent, and 65 parts by weight of a solvent are mixed evenly to obtain a conductive paste.

[0117] Among them, the conductive agent includes composite flaky graphite and conductive carbon black, and the mass ratio of the composite flaky graphite to the conductive carbon black is 67:33; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, and the auxiliary agent is prepared by dissolving an alkali and a strong base weak acid salt in water. The alkali is sodium hydroxide, and the strong base weak acid salt is a carbonate; the solvent is a mixture of water and ethanol in a mass ratio of 4:1.

[0118] S3. Prepare a current collector

[0119] The prepared conductive paste is coated on the surface of the substrate by a doctor blade method, and the coating width does not exceed the width of the substrate. Then, the substrate coated with the conductive paste is placed in a dryer and dried at a temperature of 45°C for 16 h to form a carbon-containing composite coating on the surface of the substrate.

[0120] Please refer to Figure 2 , Figure 2 which is an electron micrograph of the carbon-containing composite coating.

[0121] Example 2

[0122] An embodiment of the present application provides a composite flaky graphite and a preparation method thereof, a current collector and a preparation method thereof, including the following steps:

[0123] 1. Prepare composite flaky graphite

[0124] S1. Prepare a graphite paste

[0125] Flaky graphite and MXene material are simultaneously added to a solvent to obtain a raw material. First, the raw material is mixed and stirred at a temperature of 25°C for 2 h to obtain a mixture. Then, the mixed solution is dispersed under ultrasonic action for 1 h. Then, the mixed solution after ultrasonic treatment is added to a ball mill tank, and grinding balls are added according to a mass ratio of 10:1 of the grinding balls to the solid components in the mixed solution. The material of the grinding balls is zirconia, and the diameters of the grinding balls are 1.5 mm and 0.8 mm respectively, and the grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to a mass ratio of 1:1, and ball milled at a rotation speed of 360 rpm for 16 h to obtain a graphite paste. The mass percentage of flaky graphite in the graphite paste is 0.2 wt%, the mass percentage of MXene material is 0.2 wt%, the particle size of the crushed flaky graphite in the graphite paste is 10 μm, and the particle size of the crushed MXene material in the graphite paste is 1 μm.

[0126] Among them, the MXene material is Ti 3 C 2O, the solvent is a mixture of ethanol and water, the volume fraction of ethanol in the solvent is 50%, and the mass ratio of flake graphite to MXene material is 1:1.

[0127] S2. Preparation of composite flake graphite

[0128] Sieve the graphite slurry (100 mesh), remove the grinding balls, let it stand for 5 h. After the solid and liquid in the graphite slurry are fully stratified, remove the upper liquid in the graphite slurry. Place the lower liquid in the graphite slurry in a dryer and dry it at 60 °C for 12 h to obtain composite flake graphite.

[0129] 2. Preparation of current collector

[0130] S1. Treatment of substrate

[0131] Treat the surface of the aluminum foil to wash away the residual oil and impurity on the surface of the aluminum foil.

[0132] S2. Preparation of conductive paste

[0133] Mix 10 parts by weight of conductive agent, 18 parts by weight of binder, 1 part by weight of film-forming agent, 1 part by weight of auxiliary agent and 65 parts by weight of solvent evenly to obtain conductive paste.

[0134] Among them, the conductive agent includes composite flake graphite and conductive carbon black, and the mass ratio of composite flake graphite to conductive carbon black is 67:33; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, and the auxiliary agent is prepared by dissolving alkali and strong base weak salt in water. The alkali is sodium hydroxide and the strong base weak salt is carbonate; the solvent is a mixture of water and ethanol with a mass ratio of 4:1.

[0135] S3. Preparation of current collector

[0136] Coat the prepared conductive paste on the surface of the substrate by the doctor blade method, and the coating width does not exceed the width of the substrate. Then place the substrate coated with the conductive paste in a dryer and dry it at 45 °C for 16 h to form a carbon-containing composite coating on the surface of the substrate.

[0137] Please refer to Figure 3 , Figure 3 which is the electron micrograph of the carbon-containing composite coating.

[0138] Example 3

[0139] The embodiment of the present application provides a composite flake graphite and its preparation method, a current collector and its preparation method, including the following steps:

[0140] 1. Preparation of composite flake graphite

[0141] S1. Preparation of graphite slurry

[0142] Flake graphite and MXene materials are simultaneously added to a solvent to obtain a raw material. First, the raw material is mixed and stirred at a temperature of 25 °C for 2 h to obtain a mixture. Then, the mixture is dispersed under ultrasonic action for 1 h. Subsequently, the ultrasonic-treated mixture is added to a ball mill jar, and grinding balls are added according to a mass ratio of 10:1 of the grinding balls to the solid components in the mixture. The material of the grinding balls is zirconia, and the diameters of the grinding balls are 1.5 mm and 0.8 mm, respectively. The grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to a mass ratio of 1:1. Ball milling is carried out at a rotational speed of 360 rpm for 16 h to obtain a graphite slurry. The mass percentage of flake graphite in the graphite slurry is 0.4 wt%, and the mass percentage of MXene material is 0.2 wt%. The particle size of the crushed flake graphite in the graphite slurry is 10 μm, and the particle size of the crushed MXene material in the graphite slurry is 1 μm.

[0143] Among them, the MXene material is Ti 3 C 2 (OH) 2 , the solvent is a mixture of ethanol and water, the volume fraction of ethanol in the solvent is 50%, and the mass ratio of flake graphite to MXene material is 2:1.

[0144] S2. Preparation of composite flake graphite

[0145] The graphite slurry is sieved (100 mesh). After removing the grinding balls, it is left standing for 5 h. After the solid and liquid in the graphite slurry are fully separated, the upper liquid in the graphite slurry is removed. The lower liquid in the graphite slurry is placed in a dryer and dried at a temperature of 60 °C for 12 h to obtain composite flake graphite.

[0146] 2. Preparation of current collector

[0147] S1. Treatment of substrate

[0148] The surface of the aluminum foil is treated to wash away the residual oil and impurity on the surface of the aluminum foil.

[0149] S2. Preparation of conductive paste

[0150] 10 parts by weight of conductive agent, 18 parts by weight of binder, 1 part by weight of film-forming agent, 1 part by weight of auxiliary agent and 65 parts by weight of solvent are mixed evenly to obtain a conductive paste.

[0151] Among them, the conductive agent includes composite flake graphite and conductive carbon black, and the mass ratio of composite flake graphite to conductive carbon black is 67:33; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, and the auxiliary agent is prepared by dissolving an alkali and a strong base weak acid salt in water. The alkali is sodium hydroxide, and the strong base weak acid salt is carbonate; the solvent is a mixture of water and ethanol according to a mass ratio of 4:1.

[0152] S3. Preparation of current collector

[0153] The prepared conductive paste is coated on the surface of the substrate by means of blade coating, and the coating width does not exceed the width of the substrate. Then, the substrate coated with the conductive paste is placed in a dryer and dried at a temperature of 45°C for 16 h to form a carbon-containing composite coating on the surface of the substrate.

[0154] Example 4

[0155] An embodiment of the present application provides a composite flaky graphite, a preparation method thereof, a current collector and a preparation method thereof, including the following steps:

[0156] 1. Preparation of composite flaky graphite

[0157] S1. Preparation of graphite paste

[0158] The flaky graphite and the MXene material are simultaneously added to a solvent to obtain a raw material. First, the raw material is mixed and stirred at a temperature of 25°C for 2 h to obtain a mixture. Then, the mixture is dispersed under ultrasonic action for 1 h. Then, the mixture after ultrasonic treatment is added to a ball milling tank, and grinding balls are added according to a mass ratio of 10:1 of the grinding balls to the solid components in the mixture. The material of the grinding balls is zirconia, and the diameters of the grinding balls are 1.5 mm and 0.8 mm respectively, and the grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to a mass ratio of 1:1. Ball milling is carried out at a rotation speed of 360 rpm for 16 h to obtain a graphite paste. The mass percentage of the flaky graphite in the graphite paste is 0.4 wt%, the mass percentage of the MXene material is 0.2 wt%, the particle size of the crushed flaky graphite in the graphite paste is 6 μm, and the particle size of the crushed MXene material in the graphite paste is 0.8 μm.

[0159] Among them, the MXene material is Ti 3 C 2 O, the solvent is a mixture of ethanol and water, the volume fraction of ethanol in the solvent is 50%, and the mass ratio of the flaky graphite to the MXene material is 2:1.

[0160] S2. Preparation of composite flaky graphite

[0161] The graphite paste is sieved (100 mesh), and after removing the grinding balls, it is left standing for 5 h. After the solid and liquid in the graphite paste are fully layered, the upper liquid in the graphite paste is removed. The lower liquid in the graphite paste is placed in a dryer and dried at a temperature of 60°C for 12 h to obtain the composite flaky graphite.

[0162] 2. Preparation of current collector

[0163] S1. Treatment of substrate

[0164] The surface of the aluminum foil is treated to wash away the residual oil and impurity on the surface of the aluminum foil.

[0165] S2. Preparation of Conductive Paste

[0166] Mix 10 parts by weight of conductive agent, 18 parts by weight of binder, 1 part by weight of film-forming agent, 1 part by weight of auxiliary agent and 65 parts by weight of solvent evenly to obtain the conductive paste.

[0167] Among them, the conductive agent includes composite flaky graphite and conductive carbon black, and the mass ratio of composite flaky graphite to conductive carbon black is 67:33; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, and the auxiliary agent is prepared by dissolving alkali and strong base weak acid salt in water. The alkali is sodium hydroxide, and the strong base weak acid salt is carbonate; the solvent is a mixture of water and ethanol with a mass ratio of 4:1.

[0168] S3. Preparation of Current Collector

[0169] Coat the prepared conductive paste on the surface of the substrate by the doctor blade method, and the coating width does not exceed the width of the substrate. Then place the substrate coated with the conductive paste in a dryer and dry it at 45 °C for 16 h to form a carbon-containing composite coating on the surface of the substrate.

[0170] Example 5

[0171] This application example provides a composite flaky graphite and its preparation method, a current collector and its preparation method, including the following steps:

[0172] 1. Preparation of Composite Flaky Graphite

[0173] S1. Preparation of Graphite Slurry

[0174] Add flaky graphite and MXene material into the solvent simultaneously to obtain the raw material. First, mix and stir the raw material at 25 °C for 2 h to obtain a mixture, then disperse the mixed solution under ultrasonic action for 1 h. Then add the mixed solution after ultrasonic treatment into the ball mill tank, and add grinding balls according to the mass ratio of grinding balls to solid components in the mixed solution of 10:1. The material of the grinding balls is zirconia, the diameters of the grinding balls are 1.5 mm and 0.8 mm respectively, and the grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to the mass ratio of 1:1. Ball mill at a speed of 360 rpm for 16 h to obtain the graphite slurry. The mass percentage of flaky graphite in the graphite slurry is 0.4 wt%, the mass percentage of MXene material is 0.2 wt%, the particle size of the crushed flaky graphite in the graphite slurry is 3 μm, and the particle size of the crushed MXene material in the graphite slurry is 0.5 μm.

[0175] Among them, the MXene material is Ti 3 C 2 O, the solvent is a mixture of ethanol and water, the volume fraction of ethanol in the solvent is 50%, and the mass ratio of flaky graphite to MXene material is 2:1.

[0176] S2. Prepare composite flaky graphite

[0177] Screen the graphite slurry (100 mesh), remove the grinding balls, let it stand for 5 h, until the solid and liquid in the graphite slurry are fully stratified, remove the upper liquid in the graphite slurry, put the lower liquid in the graphite slurry into a dryer, and dry it at 60 °C for 12 h to obtain composite flaky graphite.

[0178] 2. Prepare the current collector

[0179] S1. Treat the substrate

[0180] Treat the surface of the aluminum foil and wash away the residual oil and impurity on the surface of the aluminum foil.

[0181] S2. Prepare the conductive paste

[0182] Mix 10 parts by weight of conductive agent, 18 parts by weight of binder, 1 part by weight of film-forming agent, 1 part by weight of auxiliary agent and 65 parts by weight of solvent evenly to obtain the conductive paste.

[0183] Among them, the conductive agent includes composite flaky graphite and conductive carbon black, and the mass ratio of composite flaky graphite to conductive carbon black is 67:33; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, and the auxiliary agent is prepared by dissolving alkali and strong base weak acid salt in water. The alkali is sodium hydroxide, and the strong base weak acid salt is carbonate; the solvent is a mixture of water and ethanol with a mass ratio of 4:1.

[0184] S3. Prepare the current collector

[0185] Coat the prepared conductive paste on the surface of the substrate by the doctor blade method, and the coating width does not exceed the width of the substrate. Then put the substrate coated with the conductive paste into a dryer and dry it at 45 °C for 16 h to form a carbon-containing composite coating on the surface of the substrate.

[0186] Example 6

[0187] The embodiment of the present application provides a composite flaky graphite and its preparation method, a current collector and its preparation method, including the following steps:

[0188] 1. Prepare composite flaky graphite

[0189] S1. Prepare the graphite slurry

[0190] Flake graphite and MXene materials are simultaneously added to a solvent to obtain a raw material. First, the raw material is mixed and stirred at a temperature of 25 °C for 2 h to obtain a mixture. Then, the mixture is dispersed under ultrasonic action for 1 h. Next, the ultrasonic-completed mixture is added to a ball milling tank, and grinding balls are added according to a mass ratio of 10:1 of the grinding balls to the solid components in the mixture. The material of the grinding balls is zirconia, and the diameters of the grinding balls are 1.5 mm and 0.8 mm, respectively. The grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to a mass ratio of 1:1, and ball milling is carried out at a rotation speed of 360 rpm for 16 h to obtain a graphite slurry. The mass percentage of flake graphite in the graphite slurry is 0.4 wt%, the mass percentage of MXene material is 0.2 wt%, the particle size of the crushed flake graphite in the graphite slurry is 10 μm, and the particle size of the crushed MXene material in the graphite slurry is 1 μm.

[0191] Among them, the MXene material is Ti 3 C 2 O. The solvent is a mixture of ethanol and water, and the volume fraction of ethanol in the solvent is 50%. The mass ratio of flake graphite to MXene material is 2:1.

[0192] S2. Preparation of composite flake graphite

[0193] The graphite slurry is sieved (100 mesh). After removing the grinding balls, it is left standing for 5 h. After the solid and liquid in the graphite slurry are fully stratified, the upper liquid in the graphite slurry is removed. The lower liquid in the graphite slurry is placed in a dryer and dried at a temperature of 60 °C for 12 h to obtain composite flake graphite.

[0194] 2. Preparation of current collector

[0195] S1. Treatment of substrate

[0196] The surface of the aluminum foil is treated to wash away the residual oil and impurity on the surface of the aluminum foil.

[0197] S2. Preparation of conductive paste

[0198] 10 parts by weight of conductive agent, 18 parts by weight of binder, 1 part by weight of film-forming agent, 1 part by weight of auxiliary agent and 65 parts by weight of solvent are mixed evenly to obtain a conductive paste.

[0199] Among them, the conductive agent includes composite flake graphite and conductive carbon black, and the mass ratio of composite flake graphite to conductive carbon black is 50:50; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, and the auxiliary agent is prepared by dissolving an alkali and a strong base weak acid salt in water. The alkali is sodium hydroxide, and the strong base weak acid salt is carbonate; the solvent is a mixture of water and ethanol according to a mass ratio of 4:1.

[0200] S3. Preparation of current collector

[0201] The prepared conductive paste is coated on the surface of the substrate by a doctor blade method, and the coating width does not exceed the width of the substrate. Then, the substrate coated with the conductive paste is placed in a dryer and dried at a temperature of 45 °C for 16 h to form a carbon-containing composite coating on the surface of the substrate.

[0202] Example 7

[0203] An embodiment of the present application provides a composite flake graphite, a preparation method thereof, a current collector, and a preparation method thereof, including the following steps:

[0204] 1. Preparation of composite flake graphite

[0205] S1. Preparation of graphite slurry

[0206] Flake graphite and MXene material are simultaneously added to a solvent to obtain a raw material. First, the raw material is mixed and stirred at a temperature of 25 °C for 2 h to obtain a mixture. Then, the mixture is dispersed under ultrasonic action for 1 h. Then, the ultrasonic-completed mixture is added to a ball mill jar, and grinding balls are added according to a mass ratio of 10:1 of the grinding balls to the solid components in the mixture. The material of the grinding balls is zirconia, and the diameters of the grinding balls are 1.5 mm and 0.8 mm respectively, and the grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to a mass ratio of 1:1, and ball milled at a rotation speed of 360 rpm for 16 h to obtain a graphite slurry. The mass percentage of flake graphite in the graphite slurry is 0.4 wt%, the mass percentage of MXene material is 0.2 wt%, the particle size of the crushed flake graphite in the graphite slurry is 10 μm, and the particle size of the crushed MXene material in the graphite slurry is 1 μm.

[0207] Among them, the MXene material is Ti 3 C 2 O, the solvent is a mixture of ethanol and water, the volume fraction of ethanol in the solvent is 50%, and the mass ratio of flake graphite to MXene material is 2:1.

[0208] S2. Preparation of composite flake graphite

[0209] The graphite slurry is sieved (100 mesh), and after removing the grinding balls, it is left standing for 5 h. After the solid and liquid in the graphite slurry are fully layered, the upper liquid in the graphite slurry is removed. The lower liquid in the graphite slurry is placed in a dryer and dried at a temperature of 60 °C for 12 h to obtain composite flake graphite.

[0210] 2. Preparation of current collector

[0211] S1. Treatment of substrate

[0212] The surface of the aluminum foil is treated to wash away the residual oil and impurity on the surface of the aluminum foil.

[0213] S2. Preparation of conductive paste

[0214] Mix 10 parts by weight of a conductive agent, 18 parts by weight of a binder, 1 part by weight of a film-forming agent, 1 part by weight of an auxiliary agent, and 65 parts by weight of a solvent evenly to obtain a conductive paste.

[0215] Among them, the conductive agent includes composite flaky graphite and conductive carbon black, and the mass ratio of the composite flaky graphite to the conductive carbon black is 70:30; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, and the auxiliary agent is prepared by dissolving an alkali and a strong base weak acid salt in water. The alkali is sodium hydroxide, and the strong base weak acid salt is a carbonate; the solvent is a mixture of water and ethanol with a mass ratio of 4:1.

[0216] S3. Prepare a current collector

[0217] Coat the prepared conductive paste on the surface of the substrate by means of knife coating, and the coating width does not exceed the width of the substrate. Then, place the substrate coated with the conductive paste in a dryer and dry it at a temperature of 45 °C for 16 h to form a carbon-containing composite coating on the surface of the substrate.

[0218] Example 8

[0219] The embodiment of the present application provides a composite flaky graphite and its preparation method, a current collector and its preparation method, including the following steps:

[0220] 1. Prepare composite flaky graphite

[0221] S1. Prepare a graphite paste

[0222] Add flaky graphite and MXene material to a solvent simultaneously to obtain a raw material. First, mix and stir the raw material at a temperature of 25 °C for 2 h to obtain a mixture, then disperse the mixed solution under ultrasonic action for 1 h, and then add the mixed solution after ultrasonic treatment to a ball mill tank. Add grinding balls according to a mass ratio of 10:1 of the grinding balls to the solid components in the mixed solution. The material of the grinding balls is zirconia, the diameters of the grinding balls are 1.5 mm and 0.8 mm respectively, and the grinding balls with diameters of 1.5 mm and 0.8 mm are mixed according to a mass ratio of 1:1. Ball mill at a rotation speed of 360 rpm for 16 h to obtain a graphite paste. The mass percentage of flaky graphite in the graphite paste is 0.4 wt%, the mass percentage of MXene material is 0.2 wt%, the particle size of the crushed flaky graphite in the graphite paste is 10 μm, and the particle size of the crushed MXene material in the graphite paste is 1 μm.

[0223] Among them, the MXene material is Ti 3 C 2 O, the solvent is a mixture of ethanol and water, the volume fraction of ethanol in the solvent is 50%, and the mass ratio of flaky graphite to MXene material is 2:1.

[0224] S2. Preparation of Composite Flaky Graphite

[0225] Sieve the graphite slurry (100 mesh), remove the grinding balls, let it stand for 5 h. After the solid and liquid in the graphite slurry are fully stratified, remove the upper liquid in the graphite slurry. Place the lower liquid in the graphite slurry in a dryer and dry it at 60 °C for 12 h to obtain composite flaky graphite.

[0226] 2. Preparation of Current Collector

[0227] S1. Treatment of Substrate

[0228] Treat the surface of the aluminum foil to wash away the residual oil and impurity on the surface of the aluminum foil.

[0229] S2. Preparation of Conductive Paste

[0230] Mix 10 parts by weight of conductive agent, 18 parts by weight of binder, 1 part by weight of film-forming agent, 1 part by weight of auxiliary agent and 65 parts by weight of solvent evenly to obtain conductive paste.

[0231] Among them, the conductive agent includes composite flaky graphite, conductive carbon black and flaky graphite, and the mass ratio of composite flaky graphite, conductive carbon black and flaky graphite is 20:70:10; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, the auxiliary agent is prepared by dissolving alkali and strong base weak acid salt in water, the alkali is sodium hydroxide, and the strong base weak acid salt is carbonate; the solvent is a mixture of water and ethanol with a mass ratio of 4:1.

[0232] S3. Preparation of Current Collector

[0233] Coat the prepared conductive paste on the surface of the substrate by the doctor blade method, and the coating width does not exceed the width of the substrate. Then place the substrate coated with the conductive paste in a dryer and dry it at 45 °C for 16 h to form a carbon-containing composite coating on the surface of the substrate.

[0234] Comparative Example 1

[0235] The comparative example of this application provides a current collector and its preparation method, including the following steps:

[0236] S1. Treatment of Substrate

[0237] Treat the surface of the aluminum foil to wash away the residual oil and impurity on the surface of the aluminum foil.

[0238] S2. Preparation of Conductive Paste

[0239] Mix 10 parts by weight of conductive agent, 18 parts by weight of binder, 1 part by weight of film-forming agent, 1 part by weight of auxiliary agent and 65 parts by weight of solvent evenly to obtain conductive paste.

[0240] Among them, the conductive agent includes conductive carbon black, the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, the auxiliary agent is prepared by dissolving an alkali and a strong base-weak acid salt in water, the alkali is sodium hydroxide, and the strong base-weak acid salt is a carbonate; the solvent is a mixture of water and ethanol in a mass ratio of 4:1.

[0241] S3. Prepare the current collector

[0242] The prepared conductive paste is coated on the surface of the substrate by a doctor blade method, and the coating width does not exceed the width of the substrate. Then, the substrate coated with the conductive paste is placed in a dryer and dried at a temperature of 45°C for 16 h to form a carbon-containing coating on the surface of the substrate.

[0243] Comparative Example 2

[0244] The comparative example of the present application provides a current collector and a preparation method thereof, including the following steps:

[0245] S1. Treat the substrate

[0246] Treat the surface of the aluminum foil to wash away the residual oil and impurity on the surface of the aluminum foil.

[0247] S2. Prepare the conductive paste

[0248] 10 parts by weight of a conductive agent, 18 parts by weight of a binder, 1 part by weight of a film-forming agent, 1 part by weight of an auxiliary agent and 65 parts by weight of a solvent are mixed uniformly to obtain a conductive paste.

[0249] Among them, the conductive agent includes flake graphite, MXene material and conductive carbon black, and the mass ratio of flake graphite, MXene material and conductive carbon black is 47.5:47.5:5; the binder is polyvinylidene fluoride, the film-forming agent is diethyl peroxydicarbonate, the auxiliary agent is prepared by dissolving an alkali and a strong base-weak acid salt in water, the alkali is sodium hydroxide, and the strong base-weak acid salt is a carbonate; the solvent is a mixture of water and ethanol in a mass ratio of 4:1.

[0250] Among them, the MXene material is Ti 3 C 2 O.

[0251] S3. Prepare the current collector

[0252] The prepared conductive paste is coated on the surface of the substrate by a doctor blade method, and the coating width does not exceed the width of the substrate. Then, the substrate coated with the conductive paste is placed in a dryer and dried at a temperature of 45°C for 16 h to form a carbon-containing coating on the surface of the substrate.

[0253] Test Example 1

[0254] Take the current collectors prepared in Examples 1 to 8 and Comparative Examples 1 to 2, make them into button cells, and measure their CV first-cycle oxidation potential and cycle life. The results are shown in Table 1.

[0255] The test method is as follows:

[0256] 1. Prepare the lithium cobalt oxide positive electrode sheet

[0257] Prepare the PVDF adhesive solution, add PVDF and NMP, disperse for 1 h, the solid content of the adhesive solution is 3.3%, add LCO and superp, ball mill for 1 h, where LCO:superp:PVDF:NMP = 8:1:1:30. The slurry has a solid content of 25%. Coat the slurry on the carbon-coated aluminum current collector and dry it in a vacuum oven for 16 h.

[0258] 2. Prepare the button cell

[0259] Cut the dried electrode sheet (12 mm), put the electrode sheet into the glove box, and the assembly order from bottom to top is: negative electrode shell, spring piece, gasket, lithium sheet (19 mm), separator, LCO electrode sheet (12 mm), positive electrode shell. The lithium-ion secondary electrolyte is used. After assembly, let it stand for 4 h. Perform formation, discharge at 0.1C and charge at 0.1C, and repeat three times to activate the button cell. Test the CV curve.

[0260] 3. Test methods and data

[0261] Discharge the button cell at 0.1C until it is fully discharged, and then charge it at 0.1C until it is fully charged, and repeat three times to activate the button cell.

[0262] Test the CV curve of the battery, set the upper limit potential to 4.6V, the lower limit potential to 3V, the number of scanning cycles to 5, and the sampling interval to 0.2 mv / s. Since the relatively stable oxidation potential of the aluminum current collector is about 4.5V, it is required that the peak value of the first cycle is greater than or equal to 4.5V. Test the cycle performance of the battery, set the cut-off voltage to 4.45V, charge and discharge at 1C, let it stand for 3 min in the middle of each charge and discharge step, and measure the capacity retention rate of the battery after 500 cycles.

[0263] Table 1 Battery performance obtained from current collectors of Examples 1-8 and Comparative Examples 1-2

[0264]

[0265]

[0266] As can be seen from Examples 1-8, the battery monomers prepared from the composite flake graphite of the embodiments of the present application have a cycle retention rate ≥ 79.8% after 500 cycles, and the CV first-cycle oxidation potential ≥ 4.87V, indicating that the battery monomers prepared from the composite flake graphite of the embodiments of the present application have good high-voltage resistance and long cycle life.

[0267] It can be seen from the comparison between Comparative Example 1 and Examples 1-8 that the conductive agent in the carbon-containing coating in Comparative Example 1 only includes conductive carbon black and no composite flake graphite, which results in the CV first-cycle oxidation potential of the prepared battery monomer being only 4.36 V and the cycle retention rate after 500 cycles being only 69.2%, far lower than the CV first-cycle oxidation potential of the battery monomers prepared in Examples 1-8 and the cycle retention rate after 500 cycles.

[0268] It can be seen from the comparison between Comparative Example 2 and Examples 1-8 that the conductive agent in the carbon-containing coating in Comparative Example 2 is a mixture of flake graphite, MXene material and conductive carbon black, and it does not prepare composite flake graphite by compounding flake graphite and MXene material, which results in the CV first-cycle oxidation potential of the prepared battery monomer being only 4.38 V and the cycle retention rate after 500 cycles being only 72.5%, far lower than the CV first-cycle oxidation potential of the battery monomers prepared in Examples 1-8 and the cycle retention rate after 500 cycles.

[0269] The above are only specific embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing composite flake graphite, characterized in that: The preparation method of the composite flake graphite comprises: mixing and crushing raw materials including flake graphite, MXene material and solvent to obtain graphite slurry, and then filtering and drying the graphite slurry in sequence to obtain composite flake graphite; The particle size of the flaky graphite after being crushed in the graphite slurry is 3 μm to 10 μm, and the particle size of the MXene material after being crushed in the graphite slurry is 0.5 μm to 1 μm.

2. The method for preparing composite flake graphite according to claim 1, characterized in that: The chemical formula of the MXene material is Ti3C2T x , T is -OH, -H, -F or -Cl.

3. The method for preparing composite flake graphite according to claim 1, characterized in that: The mass ratio of the flake graphite to the MXene material is 1 to 2:

1.

4. The method for preparing composite flake graphite according to claim 1, characterized in that: The mass percentage of the flake graphite in the graphite slurry is 0.1wt% to 1wt%.

5. The method for preparing composite flake graphite according to claim 1, characterized in that: The mass percentage of the MXene material in the graphite slurry is 0.1 wt % to 0.5 wt %.

6. The method for preparing composite flake graphite according to any one of claims 1 to 5, characterized in that: The solvent includes ethanol and water, and the volume fraction of the ethanol in the solvent is 5% to 95%.

7. The method for preparing composite flake graphite according to any one of claims 1 to 5, characterized in that: Methods for mixing and pulverizing the raw materials include ball milling, grinding, magnetic stirring or dispersing disk mixing.

8. The method for preparing composite flake graphite according to any one of claims 1 to 5, characterized in that: The method of mixing and pulverizing the raw materials comprises ball milling at a rotation speed of 300 rpm to 3500 rpm for at least 3 hours.

9. A composite flake graphite, characterized in that: The composite flake graphite is prepared according to the method for preparing composite flake graphite according to any one of claims 1 to 8.

10. A current collector, characterized in that: The current collector comprises a substrate and a carbon-containing composite coating, wherein the carbon-containing composite coating is disposed on at least one side of the substrate, and the carbon-containing composite coating comprises the composite flake graphite according to claim 9.

11. The current collector according to claim 10, characterized in that: The carbon-containing composite coating comprises a conductive agent, the conductive agent comprises the composite flake graphite and a conductive material, the conductive material comprises conductive carbon black, and the mass ratio of the composite flake graphite to the conductive material is 50:50 to 70:

30.

12. The current collector according to claim 11, characterized in that: The conductive material further comprises flake graphite, and the mass ratio of the flake graphite to the conductive carbon black is 0.1:99.9 to 20:

80.

13. A method for preparing the current collector according to claim 10, characterized in that: The preparation method of the current collector comprises: placing a conductive paste on one side of the substrate, wherein the conductive paste comprises composite flake graphite, and drying the paste to obtain the current collector.

14. The method for preparing a current collector according to claim 13, characterized in that: The conductive paste comprises 6 to 15 parts by weight of a conductive agent, 18 to 20 parts by weight of a binder, 1 to 3 parts by weight of a film-forming agent, 1 to 3 parts by weight of an auxiliary agent, and 65 to 75 parts by weight of a solvent, wherein the conductive agent comprises the composite flake graphite and a conductive material, and the mass ratio of the composite flake graphite to the conductive material is 50:50 to 70:30; Optionally, the binder includes polyvinylidene fluoride and / or polyacrylic acid; Optionally, the film-forming agent includes any one or more of ammonium persulfate, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-p-tert-butylcyclohexyl peroxydicarbonate and diethyl peroxydicarbonate; Optionally, the auxiliary agent is prepared by dissolving a base and a strong base weak acid salt in water, the base includes sodium hydroxide, and the strong base weak acid salt includes carbonate and bicarbonate; Optionally, the solvent includes water and an organic solvent, the mass ratio of the water to the organic solvent is 4 to 5:1, and the organic solvent includes any one or more of isopropanol, methanol and ethanol.

15. The method for preparing a current collector according to claim 13, characterized in that: The method of disposing the conductive paste on at least one side of the substrate includes doctor blade coating, spray coating or gravure printing; Optionally, the conductive paste is disposed on at least one side of the substrate by scraping.

16. A battery cell, characterized in that: The battery cell comprises the current collector according to any one of claims 10 to 12.

17. A battery, characterized in that: The battery comprises the battery cell according to claim 16.

18. An electrical equipment, characterized in that: The electrical equipment comprises the battery cell according to claim 16 or the battery according to claim 17, and the battery cell or the battery is used to provide electrical energy.

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