Current collector prime coat slurry for dry-method electrode, electrode plate and preparation method of electrode plate

Abstract

The invention relates to the technical field of dry-method electrode materials, and particularly discloses current collector prime coat slurry for a dry-method electrode, an electrode plate and a preparation method of the electrode plate. The preparation method of the current collector prime coat slurry for the dry-method electrode comprises the following steps: S1, dispersing a conductive agent in polydopamine to obtain a composite material; s2, grafting an epoxy group on the polydopamine in the composite material to obtain a reaction type micro-crosslinking conductive agent; and S3, mixing the hydroxyl polyurethane dispersion, polyamide acid and the reactive micro-crosslinking conductive agent, and carrying out a ring-opening reaction to obtain the prime coat slurry. The prime coat slurry is not a simple mixture of a single adhesive and a conductive agent, but a three-dimensional network which is rigid and flexible, highly crosslinked and firm in interface is constructed on a molecular level through a reaction, so that the prime coat slurry has relatively high adhesive force and relatively high conductivity.

Description

Technical Field

[0001] This application relates to the field of dry electrode materials technology, and in particular to a current collector primer slurry, electrode sheet and preparation method thereof for dry electrodes. Background Technology

[0002] Dry electrode technology, as a key process for manufacturing next-generation high-performance batteries, has attracted widespread attention due to its advantages such as no need for solvents or only a small amount of solvents, low energy consumption, and high energy density. Currently, some dry processes directly heat-press the active material layer (such as a mixture of dry powders like lithium iron phosphate or ternary materials, conductive particles, and binder particles) onto a metal current collector (such as copper foil or aluminum foil). However, the interfacial bonding between the two is weak, and the contact resistance is high.

[0003] To address the weak interfacial adhesion between the active material layer and the metal current collector in dry electrode processes, some improved dry electrode processes typically involve pre-coating the current collector with a primer slurry. However, current primer slurries often consist of a simple mixture of a single binder (such as polyacrylic acid) and a conductive agent (such as carbon black). While this helps improve the interfacial adhesion between the active material layer and the metal current collector to some extent, it still suffers from the following drawbacks: poor interfacial compatibility, insufficient interfacial wettability and chemical bonding between the binder and the dry powder layer and current collector, and easy peeling of the primer slurry layer during rolling, leading to interfacial failure.

[0004] Increasing the binder content typically improves the adhesion of primer slurries, but this reduces electronic conductivity. Improving the conductivity of primer slurries usually requires increasing the conductive agent content, but this reduces mechanical bond strength. Therefore, developing a primer slurry that simultaneously provides strong adhesion and high electronic conductivity is crucial for advancing the commercial application of dry electrode technology. Summary of the Invention

[0005] This application aims to overcome the shortcomings of related dry electrode technologies and provide a current collector primer slurry for dry electrodes, which significantly enhances the interfacial bonding and conductivity between the dry electrode layer and the current collector. This application also provides a method for preparing the aforementioned primer slurry, and its application in the preparation of dry electrodes.

[0006] In the first aspect, this application proposes a method for preparing a current collector undercoating slurry for dry electrodes, and adopts the following technical solution.

[0007] A method for preparing a current collector primer slurry for dry electrode fabrication, comprising: S1, Disperse the conductive agent in polydopamine to obtain a composite material; S2, grafting epoxy groups onto polydopamine in the composite material to obtain a reactive micro-crosslinked conductive agent; S3, take the hydroxyl polyurethane dispersion, polyamic acid and the reactive micro-crosslinking conductive agent, mix them, and carry out a ring-opening reaction to obtain the primer slurry.

[0008] By adopting the above technical solution, the primer slurry forms a viscous conductive whole through physical dispersion and chemical cross-linking, thus laying the foundation for obtaining excellent interfacial performance. This primer slurry is not a simple mixture of adhesive and conductive agent, but rather constructs a rigid-flexible, highly cross-linked, and strongly interfacial three-dimensional network at the molecular level through reaction, giving it high adhesion and high conductivity.

[0009] A preferred embodiment of the preparation method of the current collector primer slurry for dry electrode is as follows: step S1 includes: dispersing a conductive agent in a Tris-HCl buffer solution with a pH of 8.0-9.0, wherein the concentration of the conductive agent in the Tris-HCl buffer solution is 2-4 mg / mL; adding dopamine hydrochloride, wherein the concentration of dopamine hydrochloride in the Tris-HCl buffer solution is 1-2 mg / mL; stirring until the reaction is complete to obtain a composite material of polydopamine composite conductive agent.

[0010] By adopting the above technical solution, in a pH environment (8.0~9.0), dopamine hydrochloride undergoes self-oxidative polymerization with a moderate and controllable reaction rate, forming a uniform, dense, and firm polydopamine film on the conductive agent surface, thus preventing polydopamine from agglomerating due to excessively rapid reaction. Step S1 can be carried out at room temperature, and the stirring reaction time can be 12~24 hours.

[0011] A preferred embodiment of the preparation method of the current collector primer slurry for dry electrode is as follows: step S2 includes: adding an epoxy-containing silane coupling agent to the Tris-HCl buffer solution after the reaction in step S1, wherein the mass ratio of the added epoxy-containing silane coupling agent to the dopamine hydrochloride is (0.5~1.5):1; then continuously stirring the reaction at a temperature of 40~60°C, so that the epoxy groups of the silane coupling agent are grafted onto the polydopamine in the composite material, and a reactive micro-crosslinked conductive agent is obtained.

[0012] By employing the above technical solution, the epoxy groups of the epoxy-containing silane coupling agent are firmly bonded to the surface of polydopamine, creating sites for reaction with the hydroxyl groups of the hydroxyl polyurethane dispersion. The stirring reaction time in step S2 can be 6-12 hours. The reactive micro-crosslinked conductive agent is obtained by centrifugation, washing (using a 1:1 volume ratio of ethanol and water), and drying.

[0013] A preferred embodiment of the preparation method of the current collector primer slurry for dry electrode is that the epoxy-containing silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0014] By employing the above technical solution, the two coupling agents are hydrolyzed in Tris-HCl buffer, transforming methoxy groups into hydroxyl groups and the coupling agents into silanols. The resulting silanols undergo dehydration condensation with catechol hydroxyl groups or other hydroxyl groups on the polydopamine surface, forming strong Si-OC covalent bonds, thus grafting epoxy functional groups onto the polydopamine surface. Simultaneously, the silanols also condense with each other to form a stable siloxane network, firmly anchored to the polydopamine surface. γ-(2,3-epoxypropoxy)propyltrimethoxysilane or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane both exhibit high reactivity and thermal stability, reacting with polydopamine to form a durable cross-linked network.

[0015] A preferred embodiment of the preparation method of the current collector primer slurry for dry electrode is as follows: Step S3 includes: mixing hydroxyl polyurethane dispersion, polyamic acid and the reactive micro-crosslinking conductive agent according to a mass ratio of (1~2):(0.2~0.5):(4~6), first heating to 80~100℃ to evaporate the solvent and carry out a pre-curing reaction, so that the epoxy groups on polydopamine and the hydroxyl groups of hydroxyl polyurethane dispersion undergo preliminary crosslinking, and then reacting at 150~180℃, imidizing the polyamic acid and releasing water molecules to further promote the ring-opening reaction of unreacted epoxy groups, forming a micro-crosslinking network, and obtaining the primer slurry.

[0016] By adopting the above technical solution, the first step, at a temperature of 80~100℃ for 10~20 minutes, first evaporates the solvent, and then the epoxy groups react with the hydroxyl groups of polyurethane to form a basic network framework with a certain degree of flexibility. If the second step is carried out at a high temperature in this stage, the reaction will be too fast, resulting in excessive internal stress in the slurry or poor leveling. The second step is carried out at a high temperature of 150~180℃ for 10~20 minutes. This step has two simultaneous and mutually promoting effects: imidization of polyamic acid, that is, the intramolecular dehydration condensation reaction of adjacent amide and carboxyl groups on the polyamic acid molecular chain to form a five-membered ring as an imide ring, generating a rigid polyimide network, which provides the coating with a skeleton-like high strength, high modulus and heat resistance. The imidization process of polyamic acid releases water molecules, which act as chemical switches at high temperatures to promote the ring-opening reaction of residual epoxy groups, further increasing the crosslinking density and ultimately forming a rigid-flexible interpenetrating network. Polyimide provides rigidity and polyurethane provides flexibility. The two work together through covalent bonds and physical entanglement to make the base coating both strong and tough.

[0017] A preferred embodiment of the preparation method of the current collector primer slurry for dry electrode is as follows: In step S3, the mixing of the hydroxyl polyurethane dispersion, polyamic acid, and the reactive micro-crosslinking conductive agent includes: first mixing the reactive micro-crosslinking conductive agent and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in a solvent, applying ultrasound for in-situ activation and dispersion, so that the functional groups on the surface of the conductive agent are fully exposed to obtain a dispersion; then mixing the dispersion with the hydroxyl polyurethane dispersion, polyamic acid, and solvent.

[0018] By adopting the above technical solution, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is an ionic liquid. By introducing the ionic liquid and combining it with ultrasonic treatment, the ionic liquid acts as a highly efficient dispersant, effectively isolating and stabilizing the reactive micro-crosslinked conductive agent. Ultrasound provides high energy, dispersing the reactive micro-crosslinked conductive agent bundles and fully exposing the epoxy functional groups on its surface. This ensures that the reaction sites of the reactive micro-crosslinked conductive agent are uniformly distributed in the slurry, thereby forming a uniform conductive crosslinked network after reaction and curing with the hydroxyl polyurethane dispersion and polyamic acid. The solvent in step S3 can be water and ethanol in a 1:1 volume ratio.

[0019] Secondly, this application proposes a current collector primer slurry for dry electrode and adopts the following technical solution.

[0020] A current collector primer slurry for dry electrode is prepared according to the above-described method for preparing a current collector primer slurry for dry electrode.

[0021] By adopting the above technical solution, the primer slurry prepared by this method has strong adhesion and high conductivity to the current collector and active material layer.

[0022] Thirdly, this application proposes an electrode sheet and adopts the following technical solution.

[0023] An electrode sheet comprising the above-described current collector primer slurry for dry electrodes, the electrode sheet being obtained by the following preparation method.

[0024] Prepare reactive micro-crosslinked conductive agents.

[0025] A hydroxyl polyurethane dispersion, polyamic acid, and the reactive micro-crosslinking conductive agent are mixed and then coated onto a current collector. The mixture is heated to carry out a ring-opening reaction and an imidization reaction, resulting in a primer slurry layer attached to the current collector.

[0026] The active material, conductive agent, and polytetrafluoroethylene powder are dry-mixed in a mass ratio of (94~98):(1~3):(1~3). The polytetrafluoroethylene powder is then fiberized to obtain a fiberized mixture. The mixture is then rolled at 70~90℃ and 50~80MPa to form a self-supporting electrode membrane.

[0027] The electrode film is stacked on the primer slurry layer and hot-pressed at a temperature of 100~150℃ and a pressure of 100~200MPa to obtain the electrode sheet.

[0028] By employing the above technical solution, the thickness of the primer slurry layer can be 1~5μm. Applying high shear force to the mixed dry powder, such as stirring at 4000~8000 rpm for 8~12 minutes with a high-speed mixer, can fibrillate the polytetrafluoroethylene powder, forming a three-dimensional network and initially binding other particles. Rolling allows the particles to rearrange, remove air, and achieve the required compaction density, softening the surface of the polytetrafluoroethylene fibers, promoting their fusion with the active material, and improving the strength and flexibility of the electrode film. The rolling speed can be 0.5~2m / min. The thickness of the electrode film can be 80~120μm. Hot pressing softens the primer slurry layer, allowing it to come into close contact with the electrode film and penetrate and intercalate. The hot pressing time can be 0.5~5min. The electrode sheet can be a positive electrode; for example, the current collector can be an aluminum foil with a thickness of 10~16μm, the active material can be lithium iron phosphate, ternary materials, etc., and the conductive agent can be carbon black, graphite, carbon nanotubes, and graphene, etc. The electrode sheet can also be a negative electrode. For example, the current collector is a copper foil with a thickness of 4~8μm, the active material is lithium titanate, and the conductive agent is a composite system of carbon nanotubes (CNTs) and graphene in a mass ratio of (1~5):(1~5). By utilizing the two-dimensional planar conductivity of graphene and the one-dimensional linear conductivity of CNTs to interlock, a highly efficient three-dimensional conductive network is constructed, which greatly reduces the interfacial contact resistance.

[0029] In summary, the current collector primer slurry, electrode sheet, and preparation method of this application for dry electrode have the following beneficial effects: The primer slurry is obtained by dispersing a conductive agent in polydopamine to obtain a composite material, then grafting epoxy groups onto the polydopamine, and then performing a ring-opening crosslinking reaction with a hydroxyl polyurethane dispersion and polyamic acid, thus constructing a rigid-flexible, highly crosslinked, and interfacially robust three-dimensional network, giving the primer slurry high adhesion and high conductivity. The electrode sheet prepared using this primer slurry exhibits significantly improved peel strength between the primer slurry and the electrode film and current collector, significantly reduced interfacial contact resistance, and extremely high interfacial stability during long-term battery cycling. Attached Figure Description

[0030] Figure 1 This is a flowchart of the implementation steps of Example 1. Detailed Implementation

[0031] The technical solutions in the embodiments are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the following embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] The following is information on the sources of some of the raw materials used in each embodiment and comparative example.

[0033] The hydroxyl polyurethane dispersion, supplied by Guangdong Dongdun New Material Technology Co., Ltd., model number SEAPUR51P21, is a hydroxyl-containing waterborne polycarbonate polyurethane dispersion, a slightly white liquid.

[0034] The following are the mass parts of each substance described in the various embodiments and comparative examples. Example 1

[0035] A method for preparing a current collector primer slurry for dry electrode fabrication, see reference. Figure 1 This includes the following steps.

[0036] S1, using carbon nanotubes and graphene in a mass ratio of 1:1 as conductive agents, the conductive agents were dispersed in a Tris-HCl buffer solution with a pH of 8.5 and a concentration of 2 mg / mL in the Tris-HCl buffer solution. Dopamine hydrochloride was added, and the concentration of dopamine hydrochloride in the Tris-HCl buffer solution was 2 mg / mL. The mixture was stirred at room temperature (25~30℃) for 18 hours to obtain a composite material of polydopamine composite conductive agent present in the buffer solution.

[0037] S2. In the Tris-HCl buffer solution after the reaction in step S1, an epoxy-containing silane coupling agent is added. The silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane. The mass ratio of the added epoxy-containing silane coupling agent to dopamine hydrochloride is 0.5:1. Then, the mixture is heated to 40°C and stirred continuously for 12 hours to graft the epoxy groups of the silane coupling agent onto the polydopamine in the composite material. The product is then centrifuged, washed with a 1:1 volume ratio of ethanol and water, and dried to obtain a reactive micro-crosslinked conductive agent.

[0038] S3. First, the reactive micro-crosslinking conductive agent and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ionic liquid) are mixed in half of the solvent, which is water and ethanol in a volume ratio of 1:1. Ultrasonic treatment (300W power, 20 minutes) is applied to activate and disperse the agent in situ, so that the functional groups on the surface of the conductive agent are fully exposed to obtain a dispersion. Then, the dispersion is mixed with the hydroxyl polyurethane dispersion, polyamic acid and the other half of the solvent, which is water and ethanol in a volume ratio of 1:1. After all the mixture is mixed, the mass ratio of the hydroxyl polyurethane dispersion, polyamic acid, reactive micro-crosslinking conductive agent, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and the solvent is 1:0.5:4:0.5:100. After mixing all the ingredients, the mixture is heated in two steps. In the first step, the mixture is heated to 80°C and held for 20 minutes to evaporate the solvent. Then, the epoxy groups on the polydopamine and the hydroxyl groups of the hydroxyl polyurethane dispersion undergo preliminary cross-linking. In the second step, the mixture is heated to 150°C and held for 20 minutes to imidize the polyamic acid and release water molecules to further promote the ring-opening reaction of the unreacted epoxy groups. The mixture is then completely cured to form a micro-crosslinked network, resulting in the primer slurry. Example 2

[0039] A method for preparing a current collector primer slurry for dry electrode includes the following steps.

[0040] S1, using carbon nanotubes and graphene in a mass ratio of 1:1 as conductive agents, the conductive agents were dispersed in a Tris-HCl buffer solution with a pH of 8.5 and a concentration of 4 mg / mL in the Tris-HCl buffer solution. Dopamine hydrochloride was added and the concentration of dopamine hydrochloride in the Tris-HCl buffer solution was 1 mg / mL. The mixture was stirred at room temperature (25~30℃) for 18 hours to obtain a composite material of polydopamine composite conductive agent present in the buffer solution.

[0041] S2. In the Tris-HCl buffer solution after the reaction in step S1, an epoxy-containing silane coupling agent is added. The silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane. The mass ratio of the added epoxy-containing silane coupling agent to dopamine hydrochloride is 1.5:1. Then, the mixture is heated to 60°C and stirred continuously for 6 hours to graft the epoxy groups of the silane coupling agent onto the polydopamine in the composite material. After centrifugation, washing with a 1:1 volume ratio of ethanol and water, and drying, a reactive micro-crosslinked conductive agent is obtained.

[0042] S3. First, the reactive micro-crosslinking conductive agent and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ionic liquid) are mixed in half of the solvent, which is water and ethanol in a volume ratio of 1:1. Ultrasonic treatment (300W power, 20 minutes) is applied to activate and disperse the agent in situ, so that the functional groups on the surface of the conductive agent are fully exposed to obtain a dispersion. Then, the dispersion is mixed with the hydroxyl polyurethane dispersion, polyamic acid and the other half of the solvent, which is water and ethanol in a volume ratio of 1:1. After all the mixture is mixed, the mass ratio of the hydroxyl polyurethane dispersion, polyamic acid, reactive micro-crosslinking conductive agent, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and the solvent is 2:0.2:6:0.2:100. After mixing all the ingredients, the mixture is heated in two steps. In the first step, the mixture is heated to 100°C and held for 10 minutes to evaporate the solvent. Then, the epoxy groups on the polydopamine and the hydroxyl groups of the hydroxyl polyurethane dispersion undergo preliminary cross-linking. In the second step, the mixture is heated to 180°C and held for 10 minutes to imidize the polyamic acid and release water molecules to further promote the ring-opening reaction of the unreacted epoxy groups, forming a micro-crosslinked network to obtain the primer slurry. Example 3

[0043] A method for preparing a current collector primer slurry for dry electrode includes the following steps.

[0044] S1, using carbon nanotubes and graphene in a mass ratio of 1:1 as conductive agents, the conductive agents were dispersed in a Tris-HCl buffer solution with a pH of 8.5 and a concentration of 3 mg / mL in the Tris-HCl buffer solution. Dopamine hydrochloride was added, and the concentration of dopamine hydrochloride in the Tris-HCl buffer solution was 1.5 mg / mL. The mixture was stirred at room temperature (25~30℃) for 18 hours to obtain a composite material of polydopamine composite conductive agent present in the buffer solution.

[0045] S2, In the Tris-HCl buffer solution after the reaction in step S1, an epoxy-containing silane coupling agent is added. The silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane. The mass ratio of the added epoxy-containing silane coupling agent to dopamine hydrochloride is 1:1. Then, the mixture is heated to 50°C and stirred continuously for 9 hours to graft the epoxy groups of the silane coupling agent onto the polydopamine in the composite material. After centrifugation, washing with a 1:1 volume ratio of ethanol and water, and drying, a reactive micro-crosslinked conductive agent is obtained.

[0046] S3. First, the reactive micro-crosslinking conductive agent and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ionic liquid) are mixed in half of the solvent, which is water and ethanol in a volume ratio of 1:1. Ultrasonic treatment (300W power, 20 minutes) is applied to activate and disperse the agent in situ, so that the functional groups on the surface of the conductive agent are fully exposed to obtain a dispersion. Then, the dispersion is mixed with the hydroxyl polyurethane dispersion, polyamic acid and the other half of the solvent, which is water and ethanol in a volume ratio of 1:1. After all the mixture is mixed, the mass ratio of the hydroxyl polyurethane dispersion, polyamic acid, reactive micro-crosslinking conductive agent, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and the solvent is 1.5:0.3:5:0.3:100. After mixing all the ingredients, the mixture is heated in two steps. In the first step, the mixture is heated to 90°C and held for 15 minutes to evaporate the solvent. Then, the epoxy groups on the polydopamine and the hydroxyl groups of the hydroxyl polyurethane dispersion undergo preliminary cross-linking. In the second step, the mixture is heated to 165°C and held for 15 minutes to imidize the polyamic acid and release water molecules to further promote the ring-opening reaction of the unreacted epoxy groups, forming a micro-crosslinked network to obtain the primer slurry. Example 4

[0047] A method for preparing a current collector primer slurry for dry electrodes, compared to Example 3, only the silane coupling agent is replaced by γ-(2,3-epoxypropoxy)propyltrimethoxysilane with an equal mass of β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, while other conditions remain the same, and the primer slurry is finally obtained.

[0048] Application Example 1 The process of preparing the primer slurry in Example 1 was incorporated into the process of preparing the electrode sheet, and an electrode sheet was prepared. The preparation steps are as follows.

[0049] First, a reactive micro-crosslinked conductive agent is prepared, which is equivalent to steps S1 and S2 in Example 1.

[0050] Secondly, a base coating slurry layer is prepared to adhere to the current collector. The preparation method is to mix the raw materials in step S3 of Example 1, coat them onto the current collector, and then heat them to react, as follows.

[0051] S3. First, the reactive micro-crosslinking conductive agent and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ionic liquid) are mixed in half of the solvent, which is water and ethanol in a volume ratio of 1:1. Ultrasonic treatment (300W power, 20 minutes) is applied to activate and disperse the agent in situ, so that the functional groups on the surface of the conductive agent are fully exposed to obtain a dispersion. Then, the dispersion is mixed with the hydroxyl polyurethane dispersion, polyamic acid and the other half of the solvent, which is water and ethanol in a volume ratio of 1:1. After all the mixture is mixed, the mass ratio of the hydroxyl polyurethane dispersion, polyamic acid, reactive micro-crosslinking conductive agent, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and the solvent is 1:0.5:4:0.5:100. After mixing, the mixture is coated onto an aluminum foil current collector with a thickness of 13 μm. Then, the reaction is carried out in two steps. In the first step, the mixture is heated to 80°C and held for 20 minutes to evaporate the solvent. Then, the epoxy groups on the polydopamine and the hydroxyl groups of the hydroxyl polyurethane dispersion undergo preliminary cross-linking. In the second step, the mixture is heated to 150°C and held for 20 minutes to imidize the polyamic acid and release water molecules to further promote the ring-opening reaction of the unreacted epoxy groups, forming a micro-cross-linked network. The solvent evaporates, and a primer slurry layer with a thickness of 3 μm is obtained and adhered to the current collector.

[0052] Finally, step S4 is added to prepare the electrode film, and step S5 is added to heat-press the primer slurry layer attached to the current collector and the electrode film.

[0053] S4 uses lithium iron phosphate as the active material and carbon nanotubes and graphene in a mass ratio of 1:1 as conductive agents. The active material, conductive agents, and polytetrafluoroethylene powder are dry-mixed in a mass ratio of 94:3:3. High shear force is applied to the mixed dry powder, specifically by stirring at 6000 rpm for 10 minutes in a high-speed mixer to fibrillate the polytetrafluoroethylene powder, resulting in a fibrillated mixture. This mixture is then rolled at 70°C, 80 MPa, and 1 m / min to form a self-supporting electrode film with a thickness of 100 μm.

[0054] S5. The self-supporting electrode film is stacked on the base coating slurry layer and hot-pressed at 100℃ and 200MPa for 2 minutes to obtain the electrode sheet, which is used as the positive electrode.

[0055] Application Example 2 The process of preparing the primer slurry in Example 2 was incorporated into the process of preparing the electrode sheet, and an electrode sheet was prepared. The preparation steps are as follows.

[0056] First, a reactive micro-crosslinked conductive agent is prepared, which is equivalent to steps S1 and S2 in Example 2.

[0057] Secondly, a base coating slurry layer is prepared to adhere to the current collector. The preparation method is to mix the raw materials in step S3 of Example 2, coat them onto the current collector, and then heat them to react, as follows.

[0058] S3. First, the reactive micro-crosslinking conductive agent and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ionic liquid) are mixed in half of the solvent, which is water and ethanol in a volume ratio of 1:1. Ultrasonic treatment (300W power, 20 minutes) is applied to activate and disperse the agent in situ, so that the functional groups on the surface of the conductive agent are fully exposed to obtain a dispersion. Then, the dispersion is mixed with the hydroxyl polyurethane dispersion, polyamic acid and the other half of the solvent, which is water and ethanol in a volume ratio of 1:1. After all the mixture is mixed, the mass ratio of the hydroxyl polyurethane dispersion, polyamic acid, reactive micro-crosslinking conductive agent, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and the solvent is 2:0.2:6:0.2:100. After mixing, the mixture is coated onto an aluminum foil current collector with a thickness of 13 μm. Then, the reaction is carried out in two steps. In the first step, the mixture is heated to 100°C and held for 10 minutes to evaporate the solvent. Then, the epoxy groups on the polydopamine and the hydroxyl groups of the hydroxyl polyurethane dispersion undergo preliminary cross-linking. In the second step, the mixture is heated to 180°C and held for 10 minutes to imidize the polyamic acid and release water molecules to further promote the ring-opening reaction of the unreacted epoxy groups, forming a micro-cross-linked network. The solvent evaporates, and a primer slurry layer with a thickness of 3 μm is obtained on the current collector.

[0059] Finally, step S4 is added to prepare the electrode film, and step S5 is added to heat-press the primer slurry layer attached to the current collector and the electrode film.

[0060] S4 uses lithium iron phosphate as the active material and carbon nanotubes and graphene in a 1:1 mass ratio as conductive agents. The active material, conductive agents, and polytetrafluoroethylene powder are dry-mixed in a mass ratio of 98:1:1. High shear force is applied to the mixed dry powder, specifically by stirring at 6000 rpm for 10 minutes in a high-speed mixer to fibrillate the polytetrafluoroethylene powder, resulting in a fibrillated mixture. This mixture is then rolled at 90°C, 50 MPa, and 1 m / min to form a self-supporting electrode film with a thickness of 100 μm.

[0061] S5. The self-supporting electrode film is stacked on the base coating slurry layer and hot-pressed at 150℃ and 100MPa for 2 minutes to obtain the electrode sheet, which is used as the positive electrode.

[0062] Application Example 3 The process of preparing the primer slurry in Example 3 was incorporated into the process of preparing the electrode sheet, and an electrode sheet was prepared. The preparation steps are as follows.

[0063] First, a reactive micro-crosslinked conductive agent is prepared, which is equivalent to steps S1 and S2 in Example 3.

[0064] Secondly, a base coating slurry layer is prepared to adhere to the current collector. The preparation method is to mix the raw materials in step S3 of Example 3, coat them onto the current collector, and then heat them to react, as follows.

[0065] S3. First, the reactive micro-crosslinking conductive agent and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (ionic liquid) are mixed in half of the solvent, which is water and ethanol in a volume ratio of 1:1. Ultrasonic treatment (300W power, 20 minutes) is applied to activate and disperse the agent in situ, so that the functional groups on the surface of the conductive agent are fully exposed to obtain a dispersion. Then, the dispersion is mixed with the hydroxyl polyurethane dispersion, polyamic acid and the other half of the solvent, which is water and ethanol in a volume ratio of 1:1. After all the mixture is mixed, the mass ratio of the hydroxyl polyurethane dispersion, polyamic acid, reactive micro-crosslinking conductive agent, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and the solvent is 1.5:0.3:5:0.3:100. After mixing, the mixture is coated onto an aluminum foil current collector with a thickness of 13 μm. Then, the mixture is heated in two steps. In the first step, the mixture is heated to 90°C and held for 15 minutes to allow the epoxy groups on the polydopamine to undergo initial cross-linking with the hydroxyl groups of the hydroxyl polyurethane dispersion. In the second step, the mixture is heated to 165°C and held for 15 minutes to imidize the polyamic acid and release water molecules to further promote the ring-opening of unreacted epoxy groups, forming a micro-cross-linked network. The solvent evaporates, resulting in a primer slurry layer attached to the current collector with a thickness of 3 μm.

[0066] Finally, step S4 is added to prepare the electrode film, and step S5 is added to heat-press the primer slurry layer attached to the current collector and the electrode film.

[0067] S4 uses lithium iron phosphate as the active material and carbon nanotubes and graphene in a 1:1 mass ratio as conductive agents. The active material, conductive agents, and polytetrafluoroethylene powder are dry-mixed in a mass ratio of 96:2:2. High shear force is applied to the mixed dry powder, specifically by stirring at 6000 rpm for 10 minutes in a high-speed mixer to fibrillate the polytetrafluoroethylene powder, resulting in a fibrillated mixture. This mixture is then rolled at 80°C, 65 MPa, and 1 m / min to form a self-supporting electrode film with a thickness of 100 μm.

[0068] S5. The self-supporting electrode film is stacked on the base coating slurry layer and hot-pressed at 125℃ and 150MPa for 2 minutes to obtain the electrode sheet, which is used as the positive electrode.

[0069] Application Example 4 The process of preparing the primer slurry in Example 4 was incorporated into the process of preparing the electrode sheet, resulting in an electrode sheet. In this application example, compared to Application Example 3, the only difference was that the silane coupling agent was replaced by an equal mass of β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane instead of γ-(2,3-epoxypropoxy)propyltrimethoxysilane; all other conditions remained the same. The resulting electrode sheet was then used as the positive electrode.

[0070] Comparative Example 1 A method for preparing a current collector primer slurry for dry electrodes, the only difference from Application Example 1 is that in this application example, polyamic acid is replaced with an equal mass of hydroxyl polyurethane dispersion, all other aspects are the same, and an electrode sheet is finally prepared for use as a positive electrode.

[0071] Comparative Example 2 A method for preparing a current collector primer slurry for dry electrode is described. Compared with Application Example 2, the only difference is that the silane coupling agent in this application example is replaced by an equal mass of γ-(2,3-epoxypropoxy)propyltrimethoxysilane. All other aspects are the same, and an electrode sheet is finally prepared for use as a positive electrode.

[0072] Comparative Example 3 Using polyacrylic acid as a binder, carbon nanotubes and graphene in a 1:1 mass ratio as conductive agents, polyvinylpyrrolidone as a dispersant, γ-aminopropyltriethoxysilane as a coupling agent, and N-methylpyrrolidone as a solvent, the binder, conductive agent, dispersant, and coupling agent were added to the solvent, stirred evenly, and degassed to obtain a slurry. The mass fractions of each component in the slurry were: binder 6%, conductive agent 4%, dispersant 0.5%, and coupling agent 1%. The slurry was coated onto an aluminum foil current collector with a thickness of 13 μm and dried at 80 °C to form a 3 μm thick base coat slurry layer attached to the current collector.

[0073] A self-supporting electrode film with a thickness of 100 μm was prepared in the same manner as in Application Example 3.

[0074] The self-supporting electrode film is stacked on the base coating slurry layer and hot-pressed at 125℃ and 150MPa for 2 minutes to obtain the electrode sheet, which is used as the positive electrode.

[0075] Comparative Example 4 The only difference between this comparative example and Comparative Example 3 is that the mass fractions of each component in the slurry are: binder 10%, conductive agent 1%, dispersant 0.5%, and coupling agent 1%. The resulting electrode sheet is used as the positive electrode.

[0076] Comparative Example 5 The only difference between this comparative example and Comparative Example 3 is that the mass fractions of each component in the slurry are: binder 1%, conductive agent 10%, dispersant 0.5%, and coupling agent 1%. The resulting electrode sheet is used as the positive electrode.

[0077] Experimental Example 1 The electrode sheets prepared for use cases 1-4 and comparative examples 1-5 were subjected to quantitative tests on interfacial conductivity and bonding strength. The test methods and reference standards are as follows.

[0078] Conductivity testing was performed using the four-probe method to measure the sheet resistance of the electrode.

[0079] The interfacial adhesion strength test employs a 180° peel strength test to quantify the adhesion force between the electrode active layer and the current collector. The test standard refers to GB / T 2790~1995 "Adhesives - 180° Peel Strength Test Method - Flexible Materials vs. Rigid Materials". Specifically, the electrode sheet is cut into strips 25mm wide and 300mm long. The electrode film is separated from the starting end of the current collector and fixed separately on the upper and lower clamps of a universal testing machine. A 180° peel is performed at a constant rate of 100mm / min. The peel force during the peeling process is recorded, the average force value is obtained, and the peel strength is calculated.

[0080] The test results are shown in Table 1 below.

[0081] Table 1 Electrode resistance and peel strength test

[0082] As can be seen from Table 1, compared with the electrode sheets of Comparative Examples 1 to 5, the electrode sheets of Application Examples 1 to 4 have lower electrode resistivity. Since the current collector and electrode film are the same in Comparative Examples 1 to 5 and Application Examples 1 to 4, it can be concluded that the sum of the resistance of the primer slurry layer and the contact resistance between the primer slurry layer and the current collector and electrode film in Application Examples 1 to 4 is less than that in Comparative Examples 1 to 5. Therefore, the primer slurry layer of the embodiments not only enhances the bonding force between the current collector and the electrode film, but also enhances the conductivity between the current collector and the electrode film.

[0083] Compared to Application Example 1, Comparative Example 1 eliminated the use of polyamic acid, resulting in decreased adhesion, reduced peel strength, and increased resistivity of the primer slurry layer. This is because the polyamic acid can be imidized during the curing process of the epoxy groups and hydroxyl groups on the polyurethane dispersion grafted onto polydopamine, generating a rigid polyimide network. This network provides the coating with a skeleton-like structure of high strength, high modulus, and heat resistance. The imidization process of polyamic acid releases water molecules, promoting the ring-opening reaction of residual epoxy groups, further increasing the crosslinking density, and ultimately forming a rigid-flexible interpenetrating network. Polyimide provides rigidity and polyurethane provides flexibility. Through covalent bonds and physical entanglement, the two work synergistically to resist rolling shear forces and buffer the volume change stress of the electrodes during cycling.

[0084] Compared to Application Example 2, in Comparative Example 2, replacing the silane coupling agent with an epoxy-containing silane coupling agent and using an equal mass of epoxy-free γ-aminopropyltriethoxysilane resulted in decreased adhesion, reduced peel strength, and increased resistivity of the primer slurry layer. This is because the absence of epoxy groups to connect polydopamine and polyurethane prevents the formation of a strong cross-linked network, thus reducing conductivity.

[0085] Comparative Examples 3-5 use simple compounding of binders and conductive agents, which lack cross-linking effect. The resulting primer slurry layer cannot achieve a balance between strong adhesion and conductivity. Increasing the binder content significantly reduces conductivity, while increasing the conductive agent content significantly reduces adhesion, failing to meet increasingly demanding market requirements.

[0086] Electrode sheets using the primer slurry of this application exhibit low primer slurry layer and interfacial contact resistance, resulting in superior electron transport capability. Furthermore, the primer slurry layer has strong adhesion to the current collector and electrode film, making it difficult to peel off and providing a long cycle life.

[0087] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a current collector primer slurry for dry electrode fabrication, characterized in that, include: S1, Disperse the conductive agent in polydopamine to obtain a composite material; S2, grafting epoxy groups onto polydopamine in the composite material to obtain a reactive micro-crosslinked conductive agent; S3, take the hydroxyl polyurethane dispersion, polyamic acid and the reactive micro-crosslinking conductive agent, mix them, and carry out a ring-opening reaction to obtain the primer slurry.

2. The method for preparing the current collector primer slurry for dry electrode according to claim 1, characterized in that, Step S1 includes: dispersing the conductive agent in a Tris-HCl buffer solution with a pH of 8.0-9.0, wherein the concentration of the conductive agent in the Tris-HCl buffer solution is 2-4 mg / mL; adding dopamine hydrochloride, wherein the concentration of dopamine hydrochloride in the Tris-HCl buffer solution is 1-2 mg / mL; stirring until the reaction is complete to obtain a composite material of polydopamine composite conductive agent.

3. The method for preparing the current collector primer slurry for dry electrode according to claim 2, characterized in that, Step S2 includes: adding an epoxy-containing silane coupling agent to the Tris-HCl buffer solution after the reaction in step S1, wherein the mass ratio of the added epoxy-containing silane coupling agent to the dopamine hydrochloride is (0.5~1.5):1, and then continuously stirring the reaction at a temperature of 40~60°C, so that the epoxy groups of the silane coupling agent are grafted onto the polydopamine in the composite material, and a reactive micro-crosslinked conductive agent is obtained.

4. The method for preparing the current collector primer slurry for dry electrode according to claim 3, characterized in that, The epoxy-containing silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

5. The method for preparing the current collector primer slurry for dry electrode according to claim 1, characterized in that, Step S3 includes: mixing hydroxyl polyurethane dispersion, polyamic acid and the reactive micro-crosslinking conductive agent according to a mass ratio of (1~2):(0.2~0.5):(4~6), first heating to 80~100℃ to evaporate the solvent and carry out a pre-curing reaction, so that the epoxy groups on polydopamine and the hydroxyl groups of hydroxyl polyurethane dispersion undergo preliminary crosslinking, and then reacting at 150~180℃, imidizing the polyamic acid and releasing water molecules to further promote the ring-opening reaction of unreacted epoxy groups, forming a micro-crosslinking network, and obtaining the primer slurry.

6. The method for preparing the current collector primer slurry for dry electrode according to claim 5, characterized in that, In step S3, the mixing of the hydroxyl polyurethane dispersion, polyamic acid, and the reactive micro-crosslinking conductive agent includes: first mixing the reactive micro-crosslinking conductive agent and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in a solvent, applying ultrasound for in-situ activation and dispersion, so that the functional groups on the surface of the conductive agent are fully exposed to obtain a dispersion; then mixing the dispersion with the hydroxyl polyurethane dispersion, polyamic acid, and solvent.

7. A current collector primer slurry for dry electrode fabrication, characterized in that, The current collector primer slurry for dry electrode preparation method according to any one of claims 1 to 6 is prepared.

8. An electrode sheet, characterized in that, Includes the current collector primer slurry for dry electrode as described in claim 7; the electrode sheet is obtained by the following preparation method: Preparation of reactive micro-crosslinked conductive agents; A hydroxyl polyurethane dispersion, polyamic acid, and the reactive micro-crosslinking conductive agent are mixed and then coated onto a current collector. The mixture is heated to carry out a ring-opening reaction and an imidization reaction to obtain a primer slurry layer attached to the current collector. The active material, conductive agent, and polytetrafluoroethylene powder are dry-mixed in a mass ratio of (94~98):(1~3):(1~3). The polytetrafluoroethylene powder is then fiberized to obtain a fiberized mixture. The mixture is then rolled at 70~90℃ and 50~80MPa to form a self-supporting electrode film. The electrode film is stacked on the primer slurry layer and hot-pressed at a temperature of 100~150℃ and a pressure of 100~200MPa to obtain the electrode sheet.

Images