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

Abstract

The invention provides a water-resistant carbon-coated current collector as well as a preparation method and application thereof, and relates to the technical field of batteries. Specifically, the method comprises the following steps: preparing a core-shell type composite binder; the core layer is obtained by polymerizing raw materials including a first monomer, a second monomer and a cross-linking monomer, and the shell layer is obtained by polymerizing raw materials including a third monomer, a fourth monomer and a functional monomer; preparing conductive slurry containing a conductive material and a dispersing agent, fully mixing the conductive slurry with the core-shell type composite binder, and adjusting the pH value to obtain pre-coating slurry; and coating the surface of a metal foil with the carbon-coated current collector, and carrying out heat treatment to obtain the carbon-coated current collector. The binder disclosed by the invention has high water resistance, can effectively prevent a carbon-coated coating from falling off when an active coating is coated, and improves the stripping force of the active coating, meanwhile, the core-shell structure of the binder prevents the surface of a conductive agent from being excessively wrapped, and specific functional groups form strong interface bonding, so that the carbon-coated coating and an interface are compounded more tightly, and the service life of the conductive agent is prolonged. And the coating resistance of the carbon coating layer and the diaphragm resistance of the coated pole piece can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a water-resistant carbon-coated current collector and a preparation method and application thereof. Background Art

[0002] As a key power supply component for new energy vehicles and modern electronic devices, the performance of batteries has a significant impact on the energy density, charge and discharge rate, and cycle life of the overall product. Current battery electrodes usually use metal foil as a current collector, and a mixed slurry containing active materials, binders, and conductive agents is coated on the surface of the foil for preparation. However, traditional metal foils have many shortcomings as current collectors; specifically, the surface of the metal foil is relatively smooth and has low chemical activity, making it difficult for the active material to form a strong bond with it. The stress generated during the battery charge and discharge cycle can easily cause the active material to fall off the foil surface, resulting in the destruction of the internal conductive network of the battery, which in turn affects the battery's capacity retention and cycle life. On the other hand, the interface resistance between the metal foil and the active material is relatively large, and the transmission of electrons at the interface is not smooth enough, which limits the performance of the battery at high-rate charge and discharge, such as long charging time, insufficient discharge power, and other problems, and cannot meet some application scenarios with high requirements for charge and discharge speed.

[0003] Existing methods for improving adhesion mostly focus on optimizing the binder formulation. However, relying solely on binder improvements has limited effectiveness. Significant stress is generated between the solid particles and the metal foil during cycling, making it difficult to fundamentally address the issue of active material shedding. Furthermore, the high cost of some high-performance binders makes large-scale applications unfavorable. While higher doses of conductive agents can be added to improve electronic conductivity, this can affect the active material ratio, reducing the battery's energy density, and further improvement in electronic conduction at the interface remains to be seen.

[0004] In order to improve the conductivity and cycle stability of the metal foil current collector, a specific carbon coating process can be used to form a conductive carbon coating layer on the surface of the foil; the carbon coating layer can not only increase the effective surface area of the metal foil and improve the conductivity, but also enhance the adhesion between the active material and the current collector, alleviate the impact of volume change on battery performance, and thus improve the overall electrochemical performance and cycle stability of the lithium-ion battery.

[0005] There are already studies on carbon-coated current collectors. For example, CN114843447A discloses a carbon-coated negative electrode current collector, comprising a conductive layer and a carbon-coated layer. The carbon-coated layer and the negative electrode active material layer are cross-embedded in a mutually riveted structure, which can significantly reduce the interface resistance of the electrode plate and slow down the plate pulverization phenomenon during the cycle of lithium-ion batteries. However, this patent still has the problem of improving the roughening treatment method. Although the bonding strength and conductivity of the carbon-coated layer and the negative electrode plate are improved, it produces regular or irregular holes or cracks on the surface or inside of the carbon-coated layer through the infiltration and volatilization of the solvent. While effectively enhancing the peeling strength and adhesion of the plate, it has the disadvantage of poor batch consistency and is not suitable for large-scale industrial applications. In addition, due to the uneven distribution of the active material, the electrode may peel off or break during the charge and discharge process.

[0006] For example, CN105870400A discloses a negative electrode sheet for a lithium-ion battery, which is composed of a carbon-coated current collector and an active layer coated on the surface of the carbon-coated current collector. The carbon-coated current collector is composed of a copper foil and a carbon layer coated on the surface of the copper foil. Both the active layer and the carbon layer contain a binder and a conductive agent. The binders interact with each other, and the conductive agents bond with each other to enhance the adhesion of the active material, thereby improving the overall adhesion of the negative electrode sheet for the lithium-ion battery. This patent still has a series of defects. Conventional emulsion-type binders, including SBR emulsions, will have a phenomenon of latex particles floating in the slurry, resulting in a decrease in the adhesion between the coating and the current collector; and in actual use, the water resistance of the primer coating prepared based on the emulsion-type binder is poor, and there is a risk that the primer coating will easily fall off during the coating of the negative electrode coating.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] The first object of the present invention is to provide a method for preparing a water-resistant carbon-coated current collector.

[0009] The second purpose of the present invention is to provide a water-resistant carbon-coated current collector prepared by the preparation method of the water-resistant carbon-coated current collector.

[0010] The third object of the present invention is to provide a use of the water-resistant carbon-coated current collector in secondary batteries.

[0011] For carbon-coated current collectors in the battery field, whether for lithium or sodium batteries, when the primer adhesive used is an emulsion-type adhesive, there is a defect of poor dispersibility; and because it is point-to-point bonding, the bonding force is relatively poor, and the uneven distribution or insufficient number of bonding points may cause the electrode to peel or break during the charge and discharge process. In addition, the emulsion-type adhesive will have the phenomenon of latex particles floating up, resulting in a decrease in the bonding force between the coating and the current collector. Correspondingly, when the primer adhesive used is a solution-type adhesive, its bonding force is relatively high, but it is easy to over-wrap the surface of the conductive agent, resulting in a large interface resistance, which will hinder the transmission of electrons to a certain extent, resulting in an increase in the contact impedance between the particles and an increase in the polarization of the battery charge and discharge; at the same time, due to the large specific surface area of the conductive agent, when achieving a better bonding effect, the dosage of the solution-type adhesive is higher than that of the emulsion-type adhesive.

[0012] Moreover, the carbon-coated current collector prepared based on the two existing types of primer-coated carbon binders has insufficient water resistance, and there is a risk of the primer coating falling off during the coating of the electrode coating during the processing of the battery, and the expected effect cannot be achieved.

[0013] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted: A method for preparing a water-resistant carbon-coated current collector comprises the following steps: (1) Preparing a core-shell composite adhesive; wherein the core layer is obtained by polymerizing a first monomer, a second monomer, and a crosslinking monomer as raw materials, and the shell layer is obtained by polymerizing a third monomer, a fourth monomer, a functional monomer, and as raw materials; (2) preparing a conductive slurry containing a conductive material and a dispersant, fully mixing the conductive slurry with the core-shell composite binder, and adjusting the pH to 4.5-7.5 to obtain a pre-coating slurry; (3) The pre-coating slurry is applied to the surface of the metal foil, and a carbon-coated current collector is obtained after heat treatment.

[0014] A water-resistant carbon-coated current collector is prepared based on the preparation method of the water-resistant carbon-coated current collector.

[0015] And the use of the water-resistant carbon-coated current collector in secondary batteries.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a highly water-resistant core-shell composite binder for secondary battery electrode collectors. By preparing a composite structure latex particle having a latex-type core and a water-soluble shell after neutralization, the defects of the current primer binder can be effectively overcome.

[0017] The binder of the present invention takes a core-shell structure as its core and provides structural support for the entire coating. Specifically, the spherical structure of the core layer provides macroscopic stability, and the specific functional groups of the water-soluble shell after neutralization provide bonding force. Its flexible chain segments can release local stress through molecular movement, and the combination of the core layer and shell layer molecular chains can effectively inhibit the migration of the binder, thereby ensuring the integrity and stability of the binder in the carbon coating layer.

[0018] (2) The functional groups in the shell layer of the binder in the present invention are directionally distributed on the surface of the emulsion particles. After drying and forming a film, it preferentially contacts the current collector substrate, forming a strong interfacial bond, which effectively improves the bonding performance. On the other hand, by optimizing the functional groups of the shell layer, the shell layer has better wettability, adhesion and stretchability of the molecular chain segments, which can more effectively form chemical bonds or physical adsorption with the surface of the metal foil and conductive carbon material; this strong bonding force ensures a close fit between the carbon coating layer and the current collector substrate, thereby improving the bonding performance and adhesion effect of the carbon-coated current collector foil, and effectively solving the problem of easy detachment of the carbon coating layer of the traditional carbon-coated current collector.

[0019] (3) The present invention, through the monomer formula used in the core-shell composite binder, can achieve the compositional and structural design of the core and shell layers, and customize and optimize them according to actual needs. The present invention can further achieve precise control of the properties of the carbon coating layer by adjusting parameters such as the component ratio, particle size, and distribution. This flexibility enables the new core-shell structure binder emulsion to adapt to the performance requirements of different application scenarios.

[0020] (4) The present invention mixes the conductive paste with a specific composite binder first, and then adjusts the pH to a specific range to obtain a pre-coating paste with a suitable viscosity; specifically, in the present invention, the acidic environment with a low pH is first neutralized with an alkaline substance to weaken the intermolecular hydrogen bond force of the shell polymer chain, thereby allowing the molecular chain to stretch and dissolve; further, based on the difference in the adjusted pH value, the degree of neutralization is different, and the degree of stretching of the molecular chain is different, thereby achieving a good coating effect for conductive agents or conductive agent combinations with different specific surface areas, and realizing precise control of the performance of the carbon coating layer.

[0021] Correspondingly, in the process of preparing the carbon coating slurry, the acidic environment with a low pH has a low viscosity, which is conducive to the dispersion of the binder and conductive agent particles. After the alkaline substance is neutralized, the shell carboxyl groups are gradually ionized and the molecular chains stretch, achieving "network coverage" of the conductive agent.

[0022] When the conductive material used has a small average specific surface area (such as conductive graphite), its particle size is relatively large, making it suitable for adjusting the pH to a lower level. In this case, the molecular chains are less stretched, forming a dense coating. When the conductive material used has a larger average specific surface area (such as conductive carbon black), its particle size is relatively small, making it suitable for adjusting the pH to a higher level. In this case, the molecular chains are more stretched, forming a porous network structure. When using a combination of several conductive agents (such as a combination of conductive carbon black, conductive graphite, and graphene), the pH and binder emulsion formula need to be adjusted according to the composition of the conductive agent to achieve precise control of the conductive agent's "network coverage." DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments, but those skilled in the art will understand that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially. In addition, the terms "first", "1", "2" etc. are only used for descriptive purposes and should not be interpreted as indicating or suggesting relative importance.

[0024] The first aspect of the present invention is to provide a method for preparing a water-resistant carbon-coated current collector, which mainly includes the following steps (1) to (3).

[0025] (1) Preparing a core-shell composite adhesive; wherein the core layer is obtained by polymerizing a first monomer, a second monomer, and a cross-linking monomer as raw materials, and the shell layer is obtained by polymerizing a third monomer, a fourth monomer, and a functional monomer as raw materials.

[0026] In this step, a new binder emulsion with a core-shell structure is prepared by using olefin monomers and cross-linking monomers as main raw materials, water as solvent or dispersion medium, and a specific synthesis process.

[0027] As a preferred embodiment, the first monomer includes a soft monomer containing an olefinic compound composed of 5 to 100 carbon atoms and other heteroatoms, and Tg < 50°C. Specifically, the first monomer includes an acrylate compound. As a more preferred embodiment, the first monomer includes a combination of one or more of ethyl acrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl methacrylate, isodecyl methylpropional, amyl acrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isooctyl acrylate, isooctyl methacrylate, lauryl acrylate, lauryl methacrylate, octadecyl acrylate, octadecyl methacrylate, ethoxy nonylphenol acrylate, diethylene glycol monoethyl ether acrylate, and methoxy polyethylene glycol methacrylate.

[0028] As a preferred embodiment, the second monomer comprises a hard monomer containing an olefinic compound composed of 5 to 100 carbon atoms and other heteroatoms, with a Tg greater than 50°C. As a more preferred embodiment, the second monomer comprises a combination of one or more of methyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, tetrahydrofurfuryl methacrylate, ethoxyphenol acrylate, acrylonitrile, methacrylonitrile, styrene, vinyl pyrrolidone, and acrylamide.

[0029] As a preferred embodiment, the third monomer includes a soft monomer of an olefinic compound composed of 5 to 100 carbon atoms and other heteroatoms. Specifically, the third monomer includes an acrylate compound, and the third monomer has the same selection range as the first monomer. However, the third monomer and the first monomer are independently selected as components, and the same or different compounds can be used.

[0030] As a preferred embodiment, the fourth monomer includes one or more of acrylic acid, methacrylic acid, β-acryloxypropionic acid, maleic anhydride, itaconic acid, crotonic acid, and 4-vinylbenzoic acid.

[0031] As a preferred embodiment, the functional monomer includes an epoxy-containing compound to enhance the bonding performance with the current collector. As a more preferred embodiment, the functional monomer includes a combination of one or more of glycidyl methacrylate, glycidyl acrylate, p-vinylphenyl glycidyl ether, and tetrahydrofuran acrylate.

[0032] As a preferred embodiment, the crosslinking monomer comprises an olefinic compound containing multiple carbon-carbon double bonds, and the number of carbon-carbon double bonds of any crosslinking monomer is ≥ 2. As a more preferred embodiment, the crosslinking monomer comprises a combination of one or more of 1,6-hexanediol diacrylate, ethylene oxide diacrylate, ethoxylated bisphenol A diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, and propoxylated glycerol triacrylate.

[0033] As a preferred embodiment, the usage ratio of the first monomer, the second monomer and the cross-linking monomer is (25-75): (25-75): (0.5-5) by mass.

[0034] As a preferred embodiment, the usage ratio of the third monomer, the fourth monomer and the functional monomer is (25-50): (5-20): (25-50) by mass.

[0035] As a preferred embodiment, the mass ratio of the monomer raw materials of the core layer to the shell layer is 1:(0.5-2).

[0036] As a preferred embodiment, the preparation method of the core-shell composite binder comprises the following steps: S1, preparing a solution comprising an emulsifier and deionized water, adding the first monomer, the second monomer, and the cross-linking monomer, performing a pre-emulsification treatment, and then adding an initiator and performing a polymerization reaction to obtain a core emulsion; S2. preparing a mixed solution comprising the third monomer, the fourth monomer, and the functional monomer; dropping the mixed solution into the core emulsion, and then adding an initiator and performing a polymerization reaction to obtain the core-shell composite adhesive.

[0037] As a more preferred embodiment, in steps S1 and S2, the emulsifier independently includes at least one of calcium dodecylbenzoate, sodium dodecylsulfonate, sodium dodecyl sulfate, SR-10, SE-10, SN-10 or OP-10, and the initiator independently includes a combination of one or more of sodium persulfate, potassium persulfate, ammonium persulfate, and azobisisobutylamidine hydrochloride.

[0038] As a more preferred embodiment, the pH of the core-shell composite binder is 2.5-3.5.

[0039] As a more preferred embodiment, in step S1, the amount of the emulsifier is 0.5 wt.% to 2.5 wt.% of the total monomer amount, the amount of the initiator is 0.5 wt.% to 2 wt.% of the total monomer amount, and the mass ratio of the sum of the mass of the monomers and the emulsifier to the mass of the deionized water is 1:1.5 to 9. It is worth noting that the monomers described in step S1 refer to the first monomer, the second monomer, and the cross-linking monomer involved in this step.

[0040] As a more preferred embodiment, in step S1, the pre-emulsification treatment includes: continuously stirring at 200 rpm to 300 rpm for 30 min to 50 min.

[0041] As a more preferred embodiment, in step S1, the temperature of the polymerization reaction is 55°C~85°C, and the time of the polymerization reaction is 2h~6h; in some optional embodiments, the temperature of the polymerization reaction includes but is not limited to any one of 55, 60, 65, 70, 75, 80, 85 (°C) or a numerical range consisting of any two of them, and the time of the polymerization reaction includes but is not limited to any one of 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 (h) or a numerical range consisting of any two of them.

[0042] As a more preferred embodiment, in step S1, the particle size D50 in the core emulsion is 20 nm to 500 nm, including but not limited to any one of 20, 30, 40, 50, 80, 100, 150, 200, 250, 300, 350, 400, 450, 500 (nm) or a numerical range consisting of any two of them.

[0043] As a more preferred embodiment, in step S2, when the oily monomer is introduced into S2, an emulsifier is also added during the preparation of the mixed solution; the type and amount of the emulsifier can refer to the preferred method in step S1.

[0044] As a more preferred embodiment, the amount of the initiator is 0.5 wt.% to 2 wt.% of the cross-linking monomer.

[0045] As a more preferred embodiment, in step S2, the duration of the dripping is 0.5h~2h.

[0046] As a more preferred embodiment, in step S2, the temperature of the polymerization reaction is 55°C~85°C, and the time of the polymerization reaction is 2h~8h; in some optional embodiments, the temperature of the polymerization reaction includes but is not limited to any one of 55, 60, 65, 70, 75, 80, 85 (°C) or a numerical range consisting of any two of them, and the time of the polymerization reaction includes but is not limited to any one of 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 (h) or a numerical range consisting of any two of them.

[0047] As a more preferred embodiment, the particle size D50 of the core-shell composite binder is 20 nm~1 μm, including but not limited to any one of 20, 50, 80, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 (nm) or a numerical range consisting of any two of them.

[0048] (2) preparing a conductive paste containing a conductive material and a dispersant, fully mixing the conductive paste with the core-shell composite binder, and adjusting the pH to 4.5-7.5 to obtain a pre-coating paste.

[0049] As a preferred embodiment, the conductive material includes at least one of conductive carbon black, conductive graphite or graphene.

[0050] As a preferred embodiment, the dispersant includes at least one of dodecylbenzenesulfonic acid, naphthalenesulfonic acid formaldehyde condensate, sodium dodecylsulfonate, sodium hexadecylsulfonate, phosphonic acid and its salts, polyacrylic acid, polymethacrylic acid, polymaleic acid, polystyrene sodium maleate, polystyrene lithium maleate, polystyrenesulfonic acid, polyethylenesulfonic acid, polyphosphonic acid, polyphosphonate, polyvinylpyrrolidone, polyethyleneimine, sodium carboxymethylcellulose, lithium carboxymethylcellulose, sodium carboxyethylcellulose, lithium carboxyethylcellulose, polyvinyl alcohol, and cellulose ether derivatives.

[0051] As a preferred embodiment, the mass ratio of the dispersant to the conductive material is 0.5%~30%; as a more preferred embodiment, the conductive paste also includes a solvent deionized water, and the mass ratio of the conductive material to the dispersant and to the deionized water is 1:(4~20).

[0052] As a preferred embodiment, the pH is adjusted to any one of 4.5, 5, 5.5, 6, 6.5, 7, 7.5, or a numerical range consisting of any two thereof. In some more preferred embodiments, the pH is adjusted to 5.5-7.5.

[0053] As a preferred embodiment, the alkaline reagent for adjusting the pH includes but is not limited to lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, ammonia water, ethylenediamine, m-phenylenediamine, etc., and more preferably, lithium hydroxide solution is used for adjustment, and the solution concentration is 5wt.%~20wt.%.

[0054] As a preferred embodiment, the pH is adjusted after the thorough mixing, and the thorough mixing includes but is not limited to one or more means such as stirring, oscillation, centrifugation, shaking, ultrasound, and heat treatment.

[0055] (3) The pre-coating slurry is applied to the surface of the metal foil, and a carbon-coated current collector is obtained after heat treatment.

[0056] As a preferred embodiment, the coating method includes but is not limited to slot extrusion coating, transfer coating, gravure coating, micro gravure coating, etc.

[0057] As a preferred embodiment, the coating thickness is 1 μm to 1.5 μm.

[0058] It is understandable that those skilled in the art can adjust process parameters such as coating speed, coating amount and coating temperature to obtain a carbon coating layer with high uniformity and high firmness.

[0059] As a preferred embodiment, the heat treatment temperature is 80°C to 130°C, and the heat treatment time is 2 minutes to 5 minutes. The heat treatment is used to remove the water solvent in the carbon coating layer, so that the carbon coating layer is tightly combined with the metal foil material to form a composite foil with excellent performance.

[0060] As a preferred embodiment, the metal foil is copper foil.

[0061] The second aspect of the present invention is to provide a water-resistant carbon-coated current collector, which is prepared based on the preparation method of the water-resistant carbon-coated current collector as described in the first aspect.

[0062] The third aspect of the present invention is the use of the water-resistant carbon-coated current collector as described in the second aspect in secondary batteries.

[0063] Example 1 S1. After stirring and dissolving 0.51 g of emulsifier and 500 mL of deionized water, add 50 g of the first monomer, 50 g of the second monomer, and 0.5 g of the cross-linking monomer, and continue stirring at 400 rpm for 40 min for pre-emulsification. Then, heat to 70°C while stirring at 200 rpm, then add 0.5 g of initiator, and react for 4.5 h to obtain a core emulsion.

[0064] S2. 30 g of the third monomer, 10 g of the fourth monomer, and 10 g of the functional monomer are mixed to obtain a shell solution.

[0065] S3. After step S1 is completed, continue stirring at a constant temperature and add the shell solution obtained in step S2 dropwise to the core emulsion obtained in step S1. The addition is completed within 1.5 hours, and then 0.2 g of initiator is added. Continue stirring at 70°C for 5 hours to obtain a binder emulsion with a solid content of 23.0% and a pH of 3.5.

[0066] S4. Disperse the conductive carbon black, conductive graphite, graphene, dispersant (lithium carboxymethyl cellulose), and deionized water evenly using a high-speed disperser. The mass ratio of the solids is conductive carbon black: conductive graphite: graphene: dispersant lithium carboxymethyl cellulose = 43.65:43.65:9.70:3.00, to obtain a conductive slurry with a solid content of 10%.

[0067] S5. Mix 600 g of the conductive paste with 174 g of the binder emulsion, and stir at 1000 rpm for 0.5 h; then adjust the pH to 5.5±0.1 with 10 wt.% lithium hydroxide aqueous solution while stirring to obtain a pre-coating slurry.

[0068] S6. The pre-coating slurry is uniformly coated on the surface of the copper foil by a gravure coating method; the coating is performed at a coating temperature of 90° C. until the coating thickness reaches 1.5 μm to obtain a composite current collector precursor.

[0069] S7. Dry the composite current collector precursor at 100° C. for 3 minutes to remove the water solvent, thereby obtaining the carbon-coated copper foil current collector of this embodiment.

[0070] Example 2 S1. After stirring and dissolving 0.51 g of emulsifier and 500 mL of deionized water, 50 g of the first monomer, 50 g of the second monomer, and 0.5 g of the cross-linking monomer were added and stirred at 400 rpm for 40 min for pre-emulsification. The temperature was then raised to 80°C while stirring at 200 rpm. Then, 0.5 g of initiator was added and the reaction was carried out for 3 h to obtain a core emulsion.

[0071] S2. 120 g of the third monomer, 40 g of the fourth monomer, and 40 g of the functional monomer are mixed to obtain a shell solution.

[0072] S3. After step S1 is completed, continue stirring at a constant temperature and add the shell solution obtained in step S2 dropwise to the core emulsion obtained in step S1. The addition is completed within 2 hours, and then 1 g of initiator is added. Continue stirring and keep warm at 80°C for 3 hours to obtain a binder emulsion with a solid content of 37% and a pH of 3.0.

[0073] S4. Conductive carbon black, conductive graphite, graphene, dispersant lithium carboxymethyl cellulose, and deionized water are uniformly dispersed by a high-speed disperser. The mass ratio of solids is conductive carbon black: conductive graphite: graphene: dispersant lithium carboxymethyl cellulose = 43.65:43.65:9.70:3.00, and a conductive slurry with a solid content of 10% is obtained.

[0074] S5. Mix 600 g of the conductive paste with 108 g of the binder emulsion, and stir at 1000 rpm for 0.5 h; then adjust the pH to 5.5±0.1 with 10 wt.% lithium hydroxide aqueous solution while stirring to obtain a pre-coating slurry.

[0075] S6. The pre-coating slurry is uniformly coated on the surface of the copper foil by a gravure coating method; the coating is performed at a coating temperature of 90° C. until the coating thickness reaches 1.5 μm to obtain a composite current collector precursor.

[0076] S7. Dry the composite current collector precursor at 100° C. for 3 minutes to remove the water solvent, thereby obtaining the carbon-coated copper foil current collector of this embodiment.

[0077] Example 3 S1. After stirring and dissolving 1.5 g of emulsifier and 1375 mL of deionized water, add 25 g of the first monomer, 70 g of the second monomer, and 5 g of the cross-linking monomer, and continue stirring at 200 rpm for 30 min for pre-emulsification. Then, heat to 70°C while stirring at 200 rpm, then add 1 g of initiator, and react for 4.5 h to obtain a core emulsion.

[0078] S2. 30 g of the third monomer, 10 g of the fourth monomer, and 10 g of the functional monomer are mixed to obtain a shell solution.

[0079] S3. After step S1 is completed, continue stirring at a constant temperature and add the shell solution obtained in step S2 dropwise to the core emulsion obtained in step S1. The addition is completed within 1 hour, and then 0.2 g of initiator is added. Continue stirring and keep warm at 70°C for 5 hours to obtain a binder emulsion with a solid content of 10.0% and a pH of 4.0.

[0080] S4. Conductive carbon black, conductive graphite, graphene, dispersant lithium carboxymethyl cellulose, and deionized water are uniformly dispersed by a high-speed disperser. The mass ratio of solids is conductive carbon black: conductive graphite: graphene: dispersant lithium carboxymethyl cellulose = 43.65:43.65:9.70:3.00, and a conductive slurry with a solid content of 10% is obtained.

[0081] S5. Mix 600 g of the conductive paste with 400 g of the binder emulsion, and stir at 1000 rpm for 0.5 h; then adjust the pH to 5.5±0.1 with 10 wt.% lithium hydroxide aqueous solution while stirring to obtain a pre-coating slurry.

[0082] S6. The pre-coating slurry is uniformly coated on the surface of the copper foil by a gravure coating method; the coating is performed at a coating temperature of 90° C. until the coating thickness reaches 1.5 μm to obtain a composite current collector precursor.

[0083] S7. Dry the composite current collector precursor at 100° C. for 3 minutes to remove the water solvent, thereby obtaining the carbon-coated copper foil current collector of this embodiment.

[0084] Example 4 S1. After stirring and dissolving 1.5 g of emulsifier and 500 mL of deionized water, add 75 g of the first monomer, 25 g of the second monomer, and 5 g of the cross-linking monomer, and continue stirring at 300 rpm for 40 min for pre-emulsification. Then, heat to 85°C while stirring at 200 rpm, then add 0.5 g of initiator, and react for 2.5 h to obtain a core emulsion.

[0085] S2. 50 g of the third monomer, 25 g of the fourth monomer, and 25 g of the functional monomer are mixed to obtain a shell solution.

[0086] S3. After step S1 is completed, continue stirring at a constant temperature and add the shell solution obtained in step S2 dropwise to the core emulsion obtained in step S1. The addition is completed within 2 hours, and then 1 g of initiator is added. Continue stirring and keep warm at 85°C for 3 hours to obtain a binder emulsion with a solid content of 29% and a pH of 3.2.

[0087] S4. Conductive carbon black, conductive graphite, graphene, dispersant lithium carboxymethyl cellulose, and deionized water are uniformly dispersed by a high-speed disperser. The mass ratio of solids is conductive carbon black: conductive graphite: graphene: dispersant lithium carboxymethyl cellulose = 43.65:43.65:9.70:3.00, and a conductive slurry with a solid content of 10% is obtained.

[0088] S5. Mix 600 g of the conductive paste with 138 g of the binder emulsion, and stir at 1000 rpm for 0.5 h; then adjust the pH to 5.5±0.1 with 10 wt.% lithium hydroxide aqueous solution while stirring to obtain a pre-coating slurry.

[0089] S6. The pre-coating slurry is uniformly coated on the surface of the copper foil by a gravure coating method; the coating is performed at a coating temperature of 90° C. until the coating thickness reaches 1.5 μm to obtain a composite current collector precursor.

[0090] S7. Dry the composite current collector precursor at 100° C. for 3 minutes to remove the water solvent, thereby obtaining the carbon-coated copper foil current collector of this embodiment.

[0091] Table 1 below provides the weight ratios of the ingredients used in Examples 1 to 4; wherein, the unit of measurement of water in Table 1 is mL, and the unit of measurement of raw materials other than water is g; Initiator 1 corresponds to the initiator added in step S1, and Initiator 2 corresponds to the initiator added in step S3.

[0092] Table 1

[0093] Example 5 It is basically the same as Example 1, except that: In S4, conductive carbon black, conductive graphite, graphene, dispersant polyvinyl pyrrolidone, and deionized water are uniformly dispersed in a high-speed disperser. The mass ratio of solids is conductive carbon black: conductive graphite: graphene: dispersant lithium carboxymethyl cellulose = 43.65:43.65:9.70:3.00, to obtain a conductive slurry with a solid content of 10%; and the pH is adjusted to 4.8±0.1 in S5.

[0094] Example 6 It is basically the same as Example 1, except that: In S4, conductive carbon black, conductive graphite, graphene, dispersant polystyrene lithium maleate, and deionized water are uniformly dispersed in a high-speed disperser. The mass ratio of solids is conductive carbon black: conductive graphite: graphene: dispersant lithium carboxymethyl cellulose = 43.65:43.65:9.70:3.00, to obtain a conductive slurry with a solid content of 10%; and the pH is adjusted to 6.7±0.1 in S5.

[0095] Examples 7-8 The process is basically the same as Example 1, except that the types of the emulsifier, the first monomer, the second monomer, the cross-linking monomer, the initiator, the third monomer, the fourth monomer, and the functional monomer are different.

[0096] Table 2 below provides the specific types of reactant raw materials used in each example.

[0097] Table 2

[0098] Comparative Example 1 The method is basically the same as Example 1, except that steps S1 to S3 are omitted, and the binder emulsion in step S5 is replaced by a mixture of SBR and CMC in an amount equal to the actual solid content, with a mass ratio of SBR:CMC=1.8:1.

[0099] Comparative Example 2 The method is basically the same as Example 1, except that steps S1 to S3 are omitted, and the binder emulsion in step S5 is replaced with PAA in an amount equal to the actual solid content.

[0100] Comparative Example 3 The method is basically the same as Example 1, except that the step of adjusting the pH in step S5 is omitted.

[0101] Test example The negative electrode active material graphite, silicon-carbon negative electrode, conductive agent Super-Li, binder SBR, binder PAA, and dispersant CMC were added to deionized water solvent in a mass ratio of 76.8:19.2:0.5:1.3:2.0:0.2, adjusted to 50% solid content, and stirred thoroughly to obtain a mixed slurry. The mixed slurry was then filtered through a 200-mesh screen and evenly coated on the above-mentioned carbon-coated copper foil material. After drying and roller pressing, the negative electrode sheets corresponding to the respective embodiments and comparative examples were obtained. The surface density of each negative electrode sheet was 12.0 mg / cm 2 , compacted density is 1.5g / cm 3 .

[0102] (1) Adhesion performance test First, 3M special peelable double-sided tape was bonded to a stainless steel plate. Then, each current collector was cut into 2cm×20cm strips and the primer-coated side was bonded to the tape. The tensile testing machine clamped the current collector and performed a 180° peeling at a stroke speed of 100mm / min. The test data was judged based on the average value of the stable period. This was repeated 5 times and the average value was taken to obtain the coating peel strength.

[0103] (2) Coating resistance test Each current collector was cut into five discs with a radius of 16 mm, and tested using a two-probe method. The average value was taken to obtain the resistance of the current collector surface coating.

[0104] (3) Electrode resistance test The negative electrode sheets corresponding to the embodiments and comparative examples were cut into five discs with a radius of 16 mm, and tested using a two-probe method. The average value was taken to obtain the resistance of the electrode sheet.

[0105] (IV) Electrolyte resistance test Fix each current collector on the bottom plate of the scratch resistance tester, and install a cotton swab soaked in the above electrolyte on the scraper head. Scrape back and forth with a load of 40g and a stroke speed of 100mm / min until the foil is exposed. Record the number of scratches, repeat 5 times, take the average value, and use the number of scratches to evaluate the coating's electrolyte resistance.

[0106] (5) Water resistance test Fix each current collector on the bottom plate of the scratch resistance tester, and install a cotton swab soaked in deionized water on the scraper head. Scrape back and forth with a load of 40g and a stroke speed of 100mm / min until the foil is exposed. Record the number of scratches, repeat 5 times, take the average value, and use the number of scratches to evaluate the water resistance of the coating.

[0107] (6) Peeling performance test A tensile tester was used to test the bonding strength between the negative electrode active coating and the carbon-coated current collector; the negative electrode sheet obtained above was cut into 20mm×200mm strips: the sheet was then bonded to the tape, and the tensile testing machine clamped the sheet for 180° peeling, with a stroke speed of 100mm / min. The test data was judged based on the average value of the stable period.

[0108] Table 3

[0109] Based on Table 3, we can see that: (1) Adhesion test experiments show that compared with traditional binders, the adhesion strength (N / m) of the carbon coating layer of the present invention to the current collector is improved by more than 100%, and the adhesion between the active coating and the current collector is improved by about 50%.

[0110] (2) One end of the binder's shell molecular chain stretches in the solvent, providing the binder with good adhesion and cohesive force. Simultaneously, the core's restraining effect prevents the polymer from completely encapsulating the conductive agent, reducing contact impedance between particles and ensuring battery performance. Furthermore, since no additional conductive agent is added, the battery's energy density is not affected, optimizing the electronic conductivity of the primer coating. Sheet resistance meter testing shows that the coating resistance is approximately 24% lower than that of conventional binders, and due to the closer composite of the active coating and the interface, the sheet resistance is reduced by approximately 40%.

[0111] (3) Solvent resistance is significantly improved, and the viscosity and ratio can be rationally controlled based on the conductive paste ratio and process conditions. The addition of alkaline substances precisely adjusts the pH and viscosity of the final product (5.5-7.0), allowing the shell molecular chains to stretch and form a well-coated structure. This results in a water wipe resistance of >200 times and an electrolyte wipe resistance of >100 times.

[0112] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a water-resistant carbon-coated current collector, characterized in that: The steps include: (1) Preparing a core-shell composite adhesive; wherein the core layer is obtained by polymerizing a first monomer, a second monomer, and a crosslinking monomer as raw materials, and the shell layer is obtained by polymerizing a third monomer, a fourth monomer, and a functional monomer as raw materials; (2) preparing a conductive slurry containing a conductive material and a dispersant, fully mixing the conductive slurry with the core-shell composite binder, and adjusting the pH to 4.5-7.5 to obtain a pre-coating slurry; (3) applying the pre-coating slurry to the surface of the metal foil, and obtaining a carbon-coated current collector after heat treatment; Wherein, the first monomer and / or the third monomer include an acrylic ester compound, the second monomer includes an alkenyl-containing hard monomer, and the fourth monomer includes an alkenyl-containing organic acid compound.

2. The method for preparing a water-resistant carbon-coated current collector according to claim 1, wherein: Satisfy at least one of the following characteristics (A) to (B): (A) The functional monomer includes an epoxy group; (B) The crosslinking monomer includes at least two carbon-carbon double bonds.

3. The method for preparing a water-resistant carbon-coated current collector according to claim 2, wherein: Satisfy at least one of the following characteristics (a) to (e): (a) the first monomer and the third monomer independently include at least one of ethyl acrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl methacrylate, isodecyl methylpropional, amyl acrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isooctyl acrylate, isooctyl methacrylate, lauryl acrylate, lauryl methacrylate, octadecyl acrylate, octadecyl methacrylate, ethoxy nonylphenol acrylate, diethylene glycol monoethyl ether acrylate, and methoxy polyethylene glycol methacrylate; (b) the second monomer comprises at least one of methyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, tetrahydrofurfuryl methacrylate, ethoxyphenol acrylate, acrylonitrile, methacrylonitrile, styrene, vinyl pyrrolidone, and acrylamide; (c) the fourth monomer comprises at least one of acrylic acid, methacrylic acid, β-acryloxypropionic acid, itaconic acid, maleic anhydride, crotonic acid, and 4-vinylbenzoic acid; (d) the functional monomer comprises at least one of glycidyl methacrylate, glycidyl acrylate, p-vinylphenyl glycidyl ether, and tetrahydrofuran acrylate; (e) The crosslinking monomer includes at least one of 1,6-hexanediol diacrylate, ethylene oxide diacrylate, ethoxylated bisphenol A diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, and propoxylated glycerol triacrylate.

4. The method for preparing a water-resistant carbon-coated current collector according to claim 1, wherein: By mass, the usage ratio of the first monomer, the second monomer and the cross-linking monomer is (25-75): (25-75): (0.5-5); And / or, based on mass, the usage ratio of the third monomer, the fourth monomer and the functional monomer is (25-50): (5-20): (25-50).

5. The method for preparing a water-resistant carbon-coated current collector according to claim 1, wherein: The preparation method of the core-shell composite adhesive comprises the following steps: S1, preparing a solution comprising an emulsifier and deionized water, adding the first monomer, the second monomer, and the cross-linking monomer, performing a pre-emulsification treatment, and then adding an initiator and performing a polymerization reaction to obtain a core emulsion; S2. preparing a mixed solution comprising the third monomer, the fourth monomer, and the functional monomer; dropping the mixed solution into the core emulsion, and then adding an initiator and performing a polymerization reaction to obtain the core-shell composite adhesive.

6. The method for preparing a water-resistant carbon-coated current collector according to claim 5, characterized in that: In step S1, the pre-emulsification treatment includes: continuously stirring at 200 rpm to 300 rpm for 30 min to 50 min.

7. The method for preparing a water-resistant carbon-coated current collector according to claim 5, characterized in that: In step S1, the polymerization reaction temperature is 55° C. to 85° C., and the polymerization reaction time is 2 h to 6 h; And / or, in step S2, the polymerization reaction temperature is 55° C. to 85° C., and the polymerization reaction time is 2 h to 8 h.

8. The method for preparing a water-resistant carbon-coated current collector according to claim 1, wherein: The conductive material includes at least one of conductive carbon black, conductive graphite or graphene; and / or the dispersant comprises at least one of dodecylbenzenesulfonic acid, naphthalenesulfonic acid formaldehyde condensate, sodium dodecylsulfonate, sodium hexadecylsulfonate, phosphonic acid and its salts, polyacrylic acid, polymethacrylic acid, polymaleic acid, polystyrene sodium maleate, polystyrene lithium maleate, polystyrenesulfonic acid, polyethylenesulfonic acid, polyphosphonic acid, polyphosphonate, polyvinylpyrrolidone, polyethyleneimine, sodium carboxymethylcellulose, lithium carboxymethylcellulose, sodium carboxyethylcellulose, lithium carboxyethylcellulose, polyvinyl alcohol, and cellulose ether derivatives; And / or, the metal foil includes copper foil or aluminum foil.

9. A water-resistant carbon-coated current collector prepared by the method for preparing a water-resistant carbon-coated current collector according to any one of claims 1 to 8.

10. Use of the water-resistant carbon-coated current collector according to claim 9 in secondary batteries.

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