A positive electrode current collector surface water-based conductive coating and a preparation method and application thereof

Abstract

This invention discloses an aqueous conductive coating on the surface of a positive electrode current collector, its preparation method, and its application. The preparation method includes: step S1, weighing raw materials according to mass parts and mixing them evenly to obtain a mixed slurry; step S2, placing the mixed slurry in a high-speed disperser for high-speed mechanical dispersion to obtain a first slurry; step S3, placing the first slurry in a vacuum degassing machine for high-speed emulsification dispersion to obtain a second slurry; step S4, placing the second slurry in a sand mill for sand milling dispersion to obtain a final slurry; step S5, coating the final slurry onto the positive electrode current collector and drying it to obtain an aqueous conductive coating on the surface of the positive electrode current collector. Using this aqueous conductive slurry to prepare a positive electrode sheet and applying it to a lithium-ion secondary battery can significantly reduce the battery's internal impedance, improve the battery's long-cycle performance, effectively increase the battery's low-temperature discharge capacity, and ultimately improve the overall performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to an aqueous conductive coating on the surface of a positive electrode current collector, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are a type of chemical battery that relies on lithium ions shuttling between the positive and negative electrodes to achieve discharge. Due to their advantages such as high energy density, high operating voltage, long cycle life, and high charge / discharge rate, they are widely used in new energy vehicles, 3C products, and energy storage batteries. The main materials of a lithium-ion battery include positive electrode materials, negative electrode materials, electrolyte, and separator. However, in addition to these four main components, the current collector used to store the positive and negative electrode materials is also an important part of a lithium-ion battery. For lithium-ion batteries, aluminum foil is typically used as the positive electrode current collector, and copper foil as the negative electrode current collector.

[0003] In the lithium battery field, aluminum foil is used as a current collector in lithium-ion batteries. Typically, the lithium-ion battery industry uses rolled aluminum foil as the positive electrode current collector, and the current collector plays a crucial role in improving the charge and discharge efficiency of lithium batteries. However, the rigid aluminum foil has a limited contact area with the active material, resulting in high interfacial resistance between the active material and the current collector. Furthermore, the limited bonding strength between the current collector and the binder and active material leads to continuous changes in electrode volume during long charge-discharge cycles, resulting in loose bonding between particles and easy powder shedding, causing rapid degradation of battery capacity and cycle life. Additionally, the oxidative decomposition products of the electrolyte undergo electrochemical reactions on the current collector surface, which also leads to and accelerates corrosion of the current collector.

[0004] To address the aforementioned issues, Chinese invention patent CN109037692B discloses a conductive coated aluminum foil for lithium-ion batteries and its preparation method. The invention includes an aluminum foil body and a conductive coating, with the conductive coating uniformly coated on both surfaces of the aluminum foil. The conductive coating comprises the following components by weight: 85-95 parts of environmentally friendly adhesive, 5-15 parts of conductive filler, and 1-3 parts of surfactant. The preparation method includes the following steps: 1. Preparing the conductive coating; 2. Surface treatment of the aluminum foil; 3. Applying the conductive coating; 4. Coating molding. This invention, through a reasonable conductive paste formulation design and effective coating process, ensures that the conductive coating adheres firmly to the aluminum foil surface. Furthermore, the coating exhibits significant conductivity, and the bonding system is safe and environmentally friendly, without polluting the environment. The resulting aluminum foil, when used in lithium-ion batteries, can significantly reduce the battery's internal resistance, increase the lithium-ion diffusion rate, improve the battery's cycle performance and low-temperature resistance, and extend its service life. However, due to the lack of significant improvement in the adhesion between the carbon coating layer and the positive electrode active material, the mechanical properties of the coated conductive coating are poor, and the battery's internal impedance has not been significantly improved, ultimately resulting in insufficient improvement in battery performance.

[0005] In conclusion, developing a conductive paste for coating the surface of positive electrode current collector aluminum foil for lithium batteries, which has good conductivity, high heat dissipation performance, low internal impedance, and good adhesion, and can effectively improve the low-temperature discharge capability and extend the cycle life of lithium batteries, has broad market application value and prospects, and can effectively promote the further development of the lithium battery industry. Summary of the Invention

[0006] This invention provides an aqueous conductive coating for the surface of a positive electrode current collector, its preparation method, and its application. An aqueous conductive slurry is prepared from raw materials containing two-dimensional Mxene material through a three-step dispersion process: high-speed mechanical dispersion, high-speed emulsification dispersion, and sand milling dispersion. This slurry is then coated onto an aluminum foil positive electrode current collector to form an aqueous conductive coating on the current collector surface. This coating features a small contact angle, good hydrophilicity, high peel strength, and low sheet resistance. When this aqueous conductive slurry is used to prepare a positive electrode sheet and applied to lithium-ion secondary batteries, it can significantly reduce the battery's internal impedance, improve its long-cycle performance, effectively increase its low-temperature discharge capacity, and ultimately enhance the overall performance of the battery, thus having positive practical significance for the development of lithium batteries.

[0007] In a first aspect, embodiments of the present invention provide a method for preparing an aqueous conductive coating on the surface of a positive electrode current collector, the method comprising:

[0008] Step S1: Weigh the raw materials according to the mass parts and mix them evenly to obtain a mixed slurry. The raw materials include: 69-84 parts water, 8-12 parts polyelectrolyte, 8-12 parts conductive agent, and 0.1-5 parts two-dimensional Mxene material.

[0009] Step S2: Place the mixed slurry in a high-speed disperser for high-speed mechanical dispersion to obtain a first slurry;

[0010] Step S3: Place the first slurry in a vacuum degassing machine for high-speed emulsification and dispersion to obtain the second slurry;

[0011] Step S4: Place the second slurry in a sand mill for sand milling and dispersion to obtain the final slurry;

[0012] Step S5: The final slurry is coated onto the positive electrode current collector and dried to obtain an aqueous conductive coating on the surface of the positive electrode current collector.

[0013] Preferably, the polyelectrolyte comprises one or more of the following: polyacrylate, polymethacrylate, polystyrene sulfonate, polyethylene sulfonate, and polyethylene phosphate;

[0014] The conductive agent includes one or more of conductive carbon black, graphene, and carbon nanotubes; the particle size D50 of the conductive agent is between 30nm and 60nm.

[0015] The two-dimensional Mxenes include: transition metal carbides and / or transition metal nitrides;

[0016] The transition metal carbides include: Ti3C2, Ti3AlC2, Ti2C, Ti2AlC, Nb2C, Nb2AlC, Nb4C3, Nb4AlC3, and Ta4C3T. x Ta4AlC3, V4C3T x One or more of the following: V4AlC3, V2AlC, TiVAlC, TiNbAlC, TiTaAlC, VNbAlC, Ti2VAlC2, Ti2TaAlC2, Mo2TiAlC2, Ti3AlCN, and Mo2Ti2AlC3;

[0017] The transition metal nitrides include Ti2AlN and / or Ti4AlN3.

[0018] Preferably, the raw materials further include: 0.1-0.5 parts of pH adjuster, 0.1-0.2 parts of surfactant, 0.05-0.2 parts of thickener, and 0.1-1 parts of silane coupling agent.

[0019] More preferably, the pH adjuster includes one or more of the following: ammonia, sodium hydroxide, calcium hydroxide, and alkanolamine;

[0020] The surfactants include one or more of the following: sulfonates, sulfate esters, stearic acid, polyethylene glycol, and polyols;

[0021] The thickener includes one or more of the following: methylcellulose, hydroxyethylcellulose, methylhydroxypropylcellulose, guar gum, polyvinyl alcohol, and polyethylene wax;

[0022] Silane coupling agents include one or more of the following: A-150, A-151, A-171, A-172, A-187, A-174, A-1891, A-189, A-1100, A-1120, KH-550, KH-560, KH-570, KH-580, KH-590, KH-902, KH-792, and KH-903.

[0023] Preferably, the linear velocity of the high-speed disperser is between 7 m / s and 15 m / s; the high-speed mechanical dispersion time is between 15 min and 60 min.

[0024] The high-speed emulsification dispersion has a rotational speed between 100 r / min and 500 r / min and a revolution speed between 500 r / min and 1200 r / min; the high-speed emulsification dispersion time is 30 min to 150 min.

[0025] The diameter of the zirconium beads used in the sand milling dispersion is between 0.1 mm and 0.6 mm; the sand milling dispersion time is between 10 min and 60 min.

[0026] Preferably, the slurry coating method includes any one of the following: gravure coating, blade coating, spin coating, and slot coating.

[0027] Secondly, embodiments of the present invention provide an aqueous conductive coating on the surface of a positive current collector prepared by the preparation method described in the first aspect above.

[0028] Preferably, the thickness of the aqueous conductive coating on the surface of the positive electrode current collector is between 0.5 μm and 2 μm.

[0029] Thirdly, embodiments of the present invention provide a positive electrode sheet, the positive electrode sheet comprising the aqueous conductive coating on the surface of the positive current collector as described in the second aspect above.

[0030] Fourthly, embodiments of the present invention provide a lithium-ion secondary battery, wherein the lithium-ion secondary battery includes the positive electrode sheet described in the third aspect above.

[0031] This invention provides a method for preparing an aqueous conductive coating on the surface of a positive electrode current collector. The method involves a three-step dispersion process using raw materials containing two-dimensional Mxene material: high-speed mechanical dispersion, high-speed emulsification dispersion, and sand milling dispersion. This aqueous conductive slurry is then coated onto an aluminum foil positive electrode current collector to form an aqueous conductive coating on the current collector surface. This coating exhibits characteristics such as a small contact angle, good hydrophilicity, high peel strength, and low sheet resistance. The aqueous conductive slurry is used to prepare a positive electrode sheet and applied in lithium-ion secondary batteries. The use of two-dimensional Mxene material provides excellent surface properties, which enhances the adhesion and mechanical properties of the conductive coating. Yes, and the high conductivity of this two-dimensional Mxene material can reduce the overall internal resistance of the battery when used in power batteries. On the other hand, the conductive slurry provided in this embodiment of the invention adopts a three-step dispersion process during preparation, which makes the particle size of the material in the conductive slurry smaller, the specific surface area larger, and the dispersion stability better, which is more conducive to the coating process. This effectively reduces the sheet resistance after the conductive slurry is coated. Through the synergistic effect of the above two aspects, the overall performance of the battery can be improved, so that the power battery using the aqueous conductive coating on the surface of the positive electrode current collector provided in this embodiment of the invention has the characteristics of lower internal resistance, higher low-temperature discharge capacity, and longer cycle life. Attached Figure Description

[0032] The technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0033] Figure 1This is a flowchart of the preparation method of the aqueous conductive coating on the surface of the positive electrode current collector provided in the embodiments of the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, not intended to limit the scope of protection of the present invention.

[0035] This invention provides a method for preparing an aqueous conductive coating on the surface of a positive electrode current collector, such as... Figure 1 As shown, the specific steps include:

[0036] Step S1: Weigh the raw materials according to the mass fraction and mix them evenly to obtain a mixed slurry;

[0037] The main raw materials include: 69-84 parts water, 8-12 parts polyelectrolyte, 8-12 parts conductive agent, and 0.1-5 parts two-dimensional Mxene material;

[0038] Specifically, the polyelectrolyte is a high-performance polyelectrolyte, including one or more of the following: polyacrylate, polymethacrylate, polystyrene sulfonate, polyethylene sulfonate, and polyethylene phosphate;

[0039] The conductive agent includes one or more of conductive carbon black, graphene, and carbon nanotubes; the particle size D50 of the conductive agent is between 30nm and 60nm.

[0040] Two-dimensional Mxenes include: transition metal carbides and / or transition metal nitrides; transition metal carbides include: Ti3C2, Ti3AlC2, Ti2C, Ti2AlC, Nb2C, Nb2AlC, Nb4C3, Nb4AlC3, Ta4C3T x Ta4AlC3, V4C3T x One or more of V4AlC3, V2AlC, TiVAlC, TiNbAlC, TiTaAlC, VNbAlC, Ti2VAlC2, Ti2TaAlC2, Mo2TiAlC2, Ti3AlCN, and Mo2Ti2AlC3; transition metal nitrides include Ti2AlN and / or Ti4AlN3.

[0041] In addition, the raw materials also contain: 0.1-0.5 parts pH adjuster, 0.1-0.2 parts surfactant, 0.05-0.2 parts thickener, and 0.1-1 parts silane coupling agent;

[0042] Specifically, pH adjusters include one or more of the following: ammonia, sodium hydroxide, calcium hydroxide, and alkanolamines;

[0043] Surfactants include one or more of the following: sulfonates, sulfate esters, stearic acid, polyethylene glycol, and polyols; wherein, sulfonates are specifically sodium dodecylbenzene sulfonate.

[0044] Thickeners include one or more of the following: methylcellulose, hydroxyethylcellulose, methylhydroxypropylcellulose, guar gum, polyvinyl alcohol, and polyethylene wax;

[0045] The types of silane coupling agents include one or more of the following: A-150, A-151, A-171, A-172, A-187, A-174, A-1891, A-189, A-1100, A-1120, KH-550, KH-560, KH-570, KH-580, KH-590, KH-902, KH-792, and KH-903.

[0046] Step S2: Place the mixed slurry in a high-speed disperser for high-speed mechanical dispersion to obtain the first slurry;

[0047] The linear velocity of the high-speed disperser is between 7m / s and 15m / s.

[0048] Step S3: Place the first slurry in a vacuum degassing machine for high-speed emulsification and dispersion to obtain the second slurry;

[0049] Among them, the rotation speed of the high-speed emulsification dispersion is between 100 r / min and 500 r / min, and the revolution speed is between 500 r / min and 1200 r / min.

[0050] Step S4: Place the second slurry in a sand mill for sand milling and dispersion to obtain the final slurry;

[0051] The diameter of the zirconium beads used in the sand milling dispersion is between 0.1mm and 0.6mm.

[0052] Step S5: The final slurry is coated onto the positive current collector and dried to obtain an aqueous conductive coating on the surface of the positive current collector.

[0053] The slurry coating method includes any one of the following: gravure coating, blade coating, spin coating, and slot coating; the dry film thickness is between 0.5μm and 2μm.

[0054] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, aluminum foil.

[0055] The aqueous conductive coating on the surface of the positive current collector prepared by the above preparation method in this embodiment of the invention has a dry film thickness between 0.5 μm and 2 μm. The positive electrode sheet with the aqueous conductive coating on the surface of the positive current collector can be applied to lithium-ion secondary batteries. The lithium-ion secondary battery can be a storage battery that provides power for electric vehicles, electric trains, electric bicycles, etc.

[0056] To better understand the technical solution provided by the present invention, the following specific examples illustrate the preparation method and characteristics of the aqueous conductive coating on the surface of the positive electrode current collector of the present invention.

[0057] Example 1

[0058] This embodiment provides a method for preparing an aqueous conductive coating on the surface of a positive electrode current collector, the specific steps of which are as follows:

[0059] (1) Weigh the raw materials according to the following mass parts: 73.2 parts water, 12 parts high-performance polyelectrolyte, 12 parts conductive agent, 2 parts two-dimensional Mxenes material, 0.1 parts pH adjuster, 0.1 parts surfactant, 0.1 parts thickener, and 0.5 parts silane coupling agent, and mix them evenly to obtain a mixed slurry.

[0060] The specific raw materials used are as follows: high-performance polyelectrolyte is grafted modified sodium polyacrylate, conductive agent is conductive carbon black with a particle size D50 of 30nm, two-dimensional Mxenes material is Ti3AlC2, pH adjuster is sodium hydroxide, surfactant is sodium dodecylbenzenesulfonate, thickener is guar gum, and silane coupling agent is KH560.

[0061] (2) The mixed slurry is placed in a high-speed disperser and mechanically dispersed at high speed. The dispersion linear velocity is 12 m / s and the dispersion time is 30 min to obtain the first slurry.

[0062] (3) The first slurry is placed in a vacuum degassing machine for high-speed emulsification and dispersion. The rotation speed of the vacuum degassing machine is 300 r / min, the revolution speed is 800 r / min, and the dispersion time is 60 min to obtain the second slurry.

[0063] (4) Place the second slurry in a sand mill for sand milling and dispersion. The zircon beads selected have a particle size of 0.3 mm and the sand milling time is 20 min to obtain the final slurry.

[0064] (5) The final slurry is coated onto the aluminum foil positive electrode current collector by micro-grooving roller coating. After drying in a vacuum drying oven, a water-based conductive coating with a thickness of 1 μm is obtained on the surface of the positive electrode current collector.

[0065] The final slurry and the aqueous conductive coating on the surface of the positive electrode current collector prepared in this embodiment were tested:

[0066] (1) Contact angle test: The hydrophilic properties of the aqueous conductive coating on the surface of the positive current collector prepared in this embodiment were tested using a contact angle tester, and the contact angle test data were obtained. The test results are detailed in Table 1.

[0067] (2) Peel strength test: The water-based conductive coating on the surface of the positive current collector prepared in this embodiment was subjected to a conventional peel strength test. A 5cm long and 1.5cm wide tape was adhered to the coating surface and the peel strength was tested using a tensile testing machine. The test results are detailed in Table 1.

[0068] (3) Sheet resistance test: The final slurry prepared in this embodiment was coated on an insulating polyethylene terephthalate (PET) film and its sheet resistance was tested. The test results are detailed in Table 1.

[0069] (4) Cycle capacity retention test: The final slurry was coated onto aluminum foil, and then lithium iron phosphate positive electrode slurry was coated onto the surface to form a positive electrode sheet. A lithium sheet was used as the negative electrode to form a CR2032 coin cell. The positive electrode active material was lithium iron phosphate, the negative electrode was a lithium metal sheet, and the separator was a polypropylene membrane (PP membrane). One mole of electrolyte was injected; the electrolyte was a mixed solution of LiPF6 and ethylene carbonate EC / dimethyl carbonate DMC (volume ratio 1:1). The electrical performance of the coin cell was tested: the cycle retention rate after 1000 cycles at 1C was tested. The test results are detailed in Table 1.

[0070] Example 2

[0071] This embodiment provides a method for preparing an aqueous conductive coating on the surface of a positive electrode current collector, the specific steps of which are as follows:

[0072] (1) Weigh the raw materials according to the following mass parts: 78.5 parts water, 10 parts high-performance polyelectrolyte, 8 parts conductive agent, 3 parts two-dimensional Mxenes material, 0.1 parts pH adjuster, 0.1 parts surfactant, 0.1 parts thickener, and 0.2 parts silane coupling agent, and mix them evenly to obtain a mixed slurry;

[0073] The specific raw materials used are: high-performance polyelectrolyte sodium polystyrene sulfonate, conductive agent graphene with a particle size D50 of 50nm, two-dimensional Mxenes material Ti3C2, pH adjuster ammonia water, surfactant sulfate salt type surfactant, thickener methyl hydroxypropyl cellulose, and silane coupling agent A-150.

[0074] (2) The mixed slurry is placed in a high-speed disperser and mechanically dispersed at high speed. The dispersion linear velocity is 12 m / s and the dispersion time is 30 min to obtain the first slurry.

[0075] (3) The first slurry is placed in a vacuum degassing machine for high-speed emulsification and dispersion. The rotation speed of the vacuum degassing machine is 300 r / min, the revolution speed is 800 r / min, and the dispersion time is 90 min to obtain the second slurry.

[0076] (4) Place the second slurry in a sand mill for sand milling and dispersion. The zircon beads selected have a particle size of 0.3 mm and the sand milling time is 30 min to obtain the final slurry.

[0077] (5) The final slurry is coated onto the aluminum foil positive electrode current collector by micro-grooving roller coating. After drying in a vacuum drying oven, a water-based conductive coating with a thickness of 1 μm is obtained on the surface of the positive electrode current collector.

[0078] The aqueous conductive coating on the surface of the positive electrode current collector prepared in this embodiment was tested: the peel strength of the aqueous conductive coating was tested; the sheet resistance of the final slurry was tested; it was assembled into a lithium iron phosphate CR2032 coin cell and cycle performance was tested; the hydrophilicity of the aqueous conductive coating was tested and the contact angle was tested; the test methods were the same as in Example 1, and the test results are detailed in Table 1.

[0079] Example 3

[0080] This embodiment provides a method for preparing an aqueous conductive coating on the surface of a positive electrode current collector, the specific steps of which are as follows:

[0081] (1) Weigh the raw materials according to the following mass parts: 77.2 parts water, 12 parts high-performance polyelectrolyte, 8 parts conductive agent, 2 parts two-dimensional Mxenes material, 0.1 parts pH adjuster, 0.1 parts surfactant, 0.1 parts thickener, and 0.5 parts silane coupling agent, and mix them evenly to obtain a mixed slurry.

[0082] The specific raw materials used are as follows: high-performance polyelectrolyte is grafted modified sodium polymethacrylate, conductive agent is conductive carbon black with a particle size D50 of 40nm, two-dimensional Mxenes material is Ti3AlCN, pH adjuster is calcium hydroxide, surfactant is polyethylene glycol, thickener is hydroxyethyl cellulose, and silane coupling agent is A-1100.

[0083] (2) The mixed slurry was placed in a high-speed disperser and mechanically dispersed at a high speed of 12 m / s for 20 min to obtain the first slurry.

[0084] (3) The first slurry was placed in a vacuum degassing machine for high-speed emulsification and dispersion. The rotation speed of the vacuum degassing machine was 300 r / min, the revolution speed was 800 r / min, and the dispersion time was 120 min to obtain the second slurry.

[0085] (4) Place the second slurry in a sand mill for sand milling and dispersion. The zircon beads selected have a particle size of 0.3 mm and the sand milling time is 20 min to obtain the final slurry.

[0086] (5) The final slurry is coated onto the aluminum foil positive electrode current collector by micro-grooving roller coating. After drying in a vacuum drying oven, a water-based conductive coating with a thickness of 2 μm is obtained on the surface of the positive electrode current collector.

[0087] The aqueous conductive coating on the surface of the positive electrode current collector prepared in this embodiment was tested: the peel strength of the aqueous conductive coating was tested; the sheet resistance of the final slurry was tested; it was assembled into a lithium iron phosphate CR2032 coin cell and cycle performance was tested; the hydrophilicity of the aqueous conductive coating was tested and the contact angle was tested; the test methods were the same as in Example 1, and the test results are detailed in Table 1.

[0088] Example 4

[0089] This embodiment provides a method for preparing an aqueous conductive coating on the surface of a positive electrode current collector, the specific steps of which are as follows:

[0090] (1) Weigh the raw materials according to the following mass parts: 76.2 parts water, 10 parts high-performance polyelectrolyte, 10 parts conductive agent, 3 parts two-dimensional Mxenes material, 0.1 parts pH adjuster, 0.1 parts surfactant, 0.1 parts thickener, and 0.5 parts silane coupling agent, and mix them evenly to obtain a mixed slurry.

[0091] The specific raw materials used are as follows: high-performance polyelectrolyte is grafted modified sodium polyacrylate, conductive agent is conductive carbon black with a particle size D50 of 40nm, two-dimensional Mxenes material is a mixture of Nb4C3 and Nb2C, pH adjuster is sodium hydroxide, surfactant is sodium dodecylbenzenesulfonate, thickener is polyvinyl alcohol, and silane coupling agent is KH-590.

[0092] (2) The mixed slurry was placed in a high-speed disperser and mechanically dispersed at a speed of 12 m / s for 60 min to obtain the first slurry.

[0093] (3) The first slurry is placed in a vacuum degassing machine for high-speed emulsification and dispersion. The rotation speed of the vacuum degassing machine is 300 r / min, the revolution speed is 800 r / min, and the dispersion time is 90 min to obtain the second slurry.

[0094] (4) Place the second slurry in a sand mill for sand milling and dispersion. The zircon beads selected have a particle size of 0.3 mm and the sand milling time is 40 min to obtain the final slurry.

[0095] (5) The final slurry is coated onto the aluminum foil positive electrode current collector by micro-grooving roller coating. After drying in a vacuum drying oven, a water-based conductive coating with a thickness of 1 μm is obtained on the surface of the positive electrode current collector.

[0096] The aqueous conductive coating on the surface of the positive electrode current collector prepared in this embodiment was tested: the peel strength of the aqueous conductive coating was tested; the sheet resistance of the final slurry was tested; it was assembled into a lithium iron phosphate CR2032 coin cell and cycle performance was tested; the hydrophilicity of the aqueous conductive coating was tested and the contact angle was tested; the test methods were the same as in Example 1, and the test results are detailed in Table 1.

[0097] To better illustrate the effects of the embodiments of the present invention, a comparative example is provided to be made with the embodiments described above.

[0098] Comparative Example 1

[0099] This comparative example uses blank aluminum foil as the positive current collector and does not have a conductive coating.

[0100] A slurry prepared using lithium iron phosphate as the positive electrode active material, carbon black as the conductive agent, and a binder was coated onto aluminum foil to form a positive electrode sheet, which was then assembled into a lithium iron phosphate CR2032 coin cell and subjected to cycle performance testing. The contact angle of the blank aluminum foil was tested for its hydrophilic properties. The test results are detailed in Table 1.

[0101] Comparative Example 2

[0102] The steps for preparing the conductive coating in this comparative example are basically the same as those in Example 1. The difference is that no two-dimensional Mxenes material was added in this comparative example.

[0103] The conductive coating prepared in this comparative example was tested as follows: the peel strength of the conductive coating was tested; the sheet resistance of the final slurry without two-dimensional Mxenes material was tested; it was assembled into a lithium iron phosphate CR2032 coin cell and its cycle performance was tested; the hydrophilicity of the conductive coating was tested and the contact angle was tested; the test methods were the same as in Example 1, and the test results are detailed in Table 1.

[0104] Comparative Example 3

[0105] The steps for preparing the conductive coating in this comparative example are basically the same as those in Example 1. The difference is that in this comparative example, only conventional high-speed dispersion is used in the slurry preparation process.

[0106] The conductive coating prepared in this comparative example was tested as follows: the peel strength of the conductive coating was tested; the sheet resistance of the final slurry after conventional high-speed dispersion was tested; it was assembled into a lithium iron phosphate CR2032 coin cell and its cycle performance was tested; the hydrophilicity of the conductive coating was tested and the contact angle was tested; the test methods were the same as in Example 1, and the test results are detailed in Table 1.

[0107] Table 1 summarizes the test data for Examples 1-4 and Comparative Examples 1-3:

[0108]

[0109] Table 1

[0110] The test data comparison in Table 1 shows that:

[0111] The contact angles of the aluminum foil coated with the water-based conductive coating in Examples 1-4 of the present invention are much smaller than those of the blank aluminum foil in Comparative Example 1 and the aluminum foil coated with the conductive coating in Comparative Examples 2-3. This indicates that the water-based conductive coating of Examples 1-4 of the present invention effectively reduces the contact angle of the aluminum foil surface, improves the hydrophilic properties, and is beneficial to the coating and adhesion of the positive electrode slurry prepared later.

[0112] The aqueous conductive coating on the surface of the positive electrode current collector in Examples 1-4 of this invention has a higher peel strength than that in Comparative Examples 2-3. This is because the two-dimensional Mxene material used in Examples 1-4 can provide the coating with a stronger bonding force, preventing the coating from falling off or peeling during subsequent use, thus reducing the performance of the battery.

[0113] The aqueous conductive coatings on the positive electrode current collector surface of Examples 1-4 and Comparative Example 3 have very low sheet resistance compared to Comparative Example 2. This is because two-dimensional Mxene material was used in the slurries of Examples 1-4 and Comparative Example 3. The high conductivity of this material can reduce the overall internal resistance of the battery when used in power batteries. The lower sheet resistance of Examples 1-4 compared to Comparative Example 3 is because the preparation process of the conductive slurry of Examples 1-4 adopted high-speed mechanical dispersion, high-speed emulsification dispersion, and sand milling dispersion. Compared to Comparative Example 3, which only used a conventional high-speed dispersion process, the three-step dispersion process of Examples 1-4 resulted in smaller particle size and larger specific surface area of ​​the material in the conductive slurry, effectively improving and ensuring the uniformity and stability of the slurry system, which is more conducive to coating processing and reduces the sheet resistance of the conductive coating after coating to a certain extent.

[0114] The positive electrode sheets prepared from the final slurry of Examples 1-4 of this invention, when assembled into lithium iron phosphate CR2032 coin cells, exhibit better cycle capacity retention rates at both room temperature and -20°C than the batteries assembled in Comparative Examples 1-3. This is because the conductive slurry of Examples 1-4 of this invention, on the one hand, uses a two-dimensional Mxene material, which has excellent surface properties, enhancing the adhesion of the conductive coating and improving mechanical properties. Furthermore, the high conductivity of this material can reduce the overall internal resistance of the battery when used in power batteries. On the other hand, the conductive slurry preparation process of this invention employs a three-step dispersion treatment process, effectively reducing the sheet resistance after the conductive slurry coating. Through the synergistic effect of these two aspects, the overall performance of the battery can be improved. As a result, the power battery using the aqueous conductive coating on the surface of the positive electrode current collector provided by this invention has characteristics of lower internal impedance, higher low-temperature discharge capacity, and longer cycle life.

[0115] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an aqueous conductive coating on the surface of a positive electrode current collector, characterized in that, The preparation method includes: Step S1: Weigh the raw materials according to their mass percentages and mix them evenly to obtain a mixed slurry. The raw materials include: 69-84 parts water, 8-12 parts polyelectrolyte, 8-12 parts conductive agent, and 0.1-5 parts two-dimensional Mxene material. The polyelectrolyte includes one or more of polyacrylate, polymethacrylate, polystyrene sulfonate, polyethylene sulfonate, and polyethylene phosphate. The conductive agent includes one or more of conductive carbon black, graphene, and carbon nanotubes. The two-dimensional Mxene material includes transition metal carbides and / or transition metal nitrides. Step S2: The mixed slurry is placed in a high-speed disperser for high-speed mechanical dispersion to obtain a first slurry; the linear velocity of the high-speed disperser is between 7 m / s and 15 m / s; the high-speed mechanical dispersion time is between 15 min and 60 min. Step S3: The first slurry is placed in a vacuum degassing machine and subjected to high-speed emulsification and dispersion to obtain a second slurry; the rotation speed of the high-speed emulsification and dispersion is between 100 r / min and 500 r / min, and the revolution speed is between 500 r / min and 1200 r / min; the high-speed emulsification and dispersion time is between 30 min and 150 min. Step S4: The second slurry is placed in a sand mill for sand milling and dispersion to obtain the final slurry; the diameter of the zirconium beads used in the sand milling and dispersion is between 0.1 mm and 0.6 mm; the sand milling and dispersion time is 10 min to 60 min. Step S5: The final slurry is coated onto the positive electrode current collector and dried to obtain an aqueous conductive coating on the surface of the positive electrode current collector.

2. The production method according to claim 1, characterized by, The particle size D50 of the conductive agent is between 30nm and 60nm; The transition metal carbides include one or more of the following: Ti3C2, Ti3AlC2, Ti2C, Ti2AlC, Nb2C, Nb2AlC, Nb4C3, Nb4AlC3, Ta4AlC3, V4AlC3, V2AlC, TiVAlC, TiNbAlC, TiTaAlC, VNbAlC, Ti2VAlC2, Ti2TaAlC2, Mo2TiAlC2, Ti3AlCN, and Mo2Ti2AlC3; The transition metal nitrides include Ti2AlN and / or Ti4AlN3.

3. The production method according to claim 1, characterized by, The raw materials also include: 0.1-0.5 parts of pH adjuster, 0.1-0.2 parts of surfactant, 0.05-0.2 parts of thickener, and 0.1-1 parts of silane coupling agent.

4. The production method according to claim 3, characterized by, The pH adjuster includes one or more of the following: ammonia, sodium hydroxide, calcium hydroxide, and alkanolamine; The surfactants include one or more of the following: sulfonates, sulfate esters, stearic acid, polyethylene glycol, and polyols; The thickener includes one or more of the following: methylcellulose, hydroxyethylcellulose, methylhydroxypropylcellulose, guar gum, polyvinyl alcohol, and polyethylene wax; Silane coupling agents include one or more of the following: A-150, A-151, A-171, A-172, A-187, A-174, A-1891, A-189, A-1100, A-1120, KH-550, KH-560, KH-570, KH-580, KH-590, KH-902, KH-792, and KH-903.

5. The preparation method according to claim 1, characterized in that, The slurry coating method includes any one of the following: gravure coating, scraping coating, spin coating, and slot coating.

6. An aqueous conductive coating on the surface of a positive current collector prepared by the preparation method according to any one of claims 1-5.

7. The positive electrode current collector surface aqueous conductive coating of claim 6, wherein, The thickness of the aqueous conductive coating on the surface of the positive electrode current collector is between 0.5 μm and 2 μm.

8. A positive electrode sheet, characterized in that, The positive electrode sheet comprises the aqueous conductive coating on the surface of the positive current collector as described in claim 6.

9. A lithium-ion secondary battery characterized by comprising: The lithium-ion secondary battery comprises the positive electrode sheet as described in claim 8.

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