Current collector prime coat formula and preparation method thereof

Abstract

The invention provides a current collector prime coat formula and a preparation method thereof, and relates to the technical field of lithium ion battery positive electrode current collector processing. The formula of the current collector prime coat comprises a main binder, a composite conductive agent, a coupling agent and a solvent, and the composite conductive agent is composed of carbon black and a carbon tube. Due to the three-dimensional structure of the composite conductive agent and the chemical bonding effect of the silane coupling agent, the coating can be better attached to the surface of an aluminum foil current collector in the charging and discharging process of the battery, the coating is prevented from falling off or stripping, and by combining the chemical bonding effect of the coupling agent, the coating can be effectively prevented from falling off. And the conductivity, electrolyte corrosion resistance, interface bonding force with an active material and the mechanical property of the foil material of the coating are remarkably improved. Due to the structural advantages of the composite conductive agent, electron transmission is more efficient, and the coating is more stable.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion battery positive electrode current collector processing, and in particular to a current collector primer formulation and a preparation method thereof. Background Art

[0002] In the manufacturing process of lithium-ion batteries, the current collector, a key component of the battery, plays an important role in collecting and conducting current. Aluminum foil is widely used as a current collector material due to its excellent conductivity and lightweight properties. However, to further improve battery performance, the aluminum foil current collector is usually subjected to surface pretreatment. This involves applying a primer layer to the surface to improve its bonding with the positive electrode active material and reduce interfacial resistance, thereby improving the battery's charge and discharge efficiency and stability.

[0003] The aluminum foil current collector primer formula in the prior art mainly adopts solvent-based adhesives (such as polyacrylate, PAA) or single carbon materials (such as conductive carbon black). These traditional formulas have many defects in practical applications. On the one hand, insufficient conductivity is a prominent problem. The solvent-based adhesive itself has poor conductivity, and although the single carbon material has a certain conductivity, its uneven dispersion leads to the presence of areas with poor conductivity in the coating, which makes the coating resistance higher and affects the charge and discharge performance of the battery. On the other hand, poor electrolyte resistance is also a problem that needs to be solved urgently. During the operation of the battery, the electrolyte will come into contact with the coating. The coating with traditional formula has poor resistance to electrolyte corrosion, and the electrolyte can easily penetrate into the interior of the coating, causing the coating to swell or peel off. The instability of this coating will destroy the internal structure of the battery and reduce the stability and service life of the battery.

[0004] With the continuous development of lithium-ion battery technology, especially the increasing demand for high-energy-density power batteries and energy storage batteries, higher requirements are being placed on the performance of current collector primers. To meet these demands, there is an urgent need to develop a current collector primer formulation and preparation method that can significantly improve the coating's conductivity and interfacial bonding with the active material, while also increasing the foil's tensile strength and elongation to meet the manufacturing requirements of high-energy-density batteries. Summary of the Invention

[0005] The present application provides a current collector primer formulation and a preparation method thereof to solve the problems of poor conductivity, tensile strength and elongation in the current current collector primer layer.

[0006] In a first aspect, the present application provides a current collector primer formulation comprising: a main binder, a composite conductive agent, a silane coupling agent, and deionized water.

[0007] Through the above scheme, the composite conductive agent in the formulation is composed of carbon black and carbon nanotubes. The carbon black particles are spherical, with a high specific surface area and good conductivity. The spherical structure enables the carbon black particles to form multiple contact points in the coating, providing multiple paths for electron transport. The carbon nanotubes are tubular, with excellent conductivity and a high aspect ratio. The tubular structure enables the carbon nanotubes to form continuous conductive pathways in the coating, allowing electrons to be efficiently transported along the long axis of the carbon nanotubes. The combination of spherical carbon black and tubular carbon nanotubes forms a three-dimensional conductive network. The carbon nanotubes "bridge" the gaps between the carbon black particles, while the carbon black particles fill the voids between the carbon nanotubes. This structure is similar to a combination of a "skeleton" (carbon nanotubes) and a "filler" (carbon black), allowing electrons to be efficiently transported throughout the coating. The three-dimensional conductive network formed by the composite conductive agent not only improves conductivity but also enhances the structural stability of the coating. This stable structure allows the coating to better maintain contact with the active material during battery charging and discharging. Moreover, the silane coupling agent can form chemical bonds with the surface of the aluminum foil current collector and the organic materials in the coating (such as binders and conductive agents), further enhancing the bonding force between the coating and the current collector. The three-dimensional structure of the composite conductive agent and the chemical bonding of the silane coupling agent enable the coating to better adhere to the surface of the aluminum foil current collector during the battery charge and discharge process, preventing the coating from falling off or peeling off, thereby improving the stability and service life of the battery. The current collector primer formula of the present application significantly improves the conductivity, electrolyte corrosion resistance, interfacial bonding with active materials, and mechanical properties of the foil by rationally matching the composite conductive agent of spherical carbon black and tubular carbon tubes, combined with the chemical bonding of the silane coupling agent. The structural advantages of this composite conductive agent make electron transmission more efficient and the coating more stable.

[0008] In a possible design, by mass percentage, the main binder accounts for 40% to 60%; the composite conductive agent accounts for 20% to 40%; the silane coupling agent accounts for 2% to 5%, and deionized water is the balance.

[0009] Through the above scheme, the main binder is the key component in the primer formula, which is mainly responsible for firmly combining other ingredients (such as conductive agent, silane coupling agent, etc.) and attaching them to the surface of the aluminum foil current collector. Ensure that the binder is in sufficient quantity to maintain the integrity and adhesion of the coating. If it is less than 40%, the coating structure may become loose and unable to effectively adhere to the aluminum foil surface, affecting the stability and service life of the coating. Avoid excessive binder content, which will reduce the flexibility and conductivity of the coating. Too much binder may make the coating too rigid and prone to cracking due to volume changes during battery charging and discharging. It will also reduce the effective content of the conductive agent and affect the conductive performance. The ratio range of 40% to 60% can balance the adhesion, flexibility and conductivity of the coating, ensuring that the coating remains stable during battery use without affecting the performance of other ingredients.

[0010] Composite conductive agents (including carbon black and carbon tubes) are key components for improving the conductivity of the coating, and they reduce the resistance of the coating by building a conductive network. Make sure that the coating has enough conductive agent to build an effective conductive network. If it is less than 20%, the conductive network may be discontinuous, resulting in excessively high coating resistance, affecting the charge and discharge efficiency of the battery. Avoid excessive conductive agent content, which reduces the mechanical properties and adhesion of the coating. Too much conductive agent may make the coating too fragile and easy to fall off due to volume changes during battery charging and discharging. It will also increase the thickness of the coating and affect the overall design of the battery. A ratio range of 20% to 40% can ensure that the coating has good conductivity without affecting the adhesion and mechanical properties of the coating, effectively reducing the coating resistance and improving battery performance.

[0011] Silane coupling agents are primarily used to enhance the interfacial adhesion between the coating and the aluminum foil current collector and provide a certain degree of resistance to electrolyte corrosion. Ensure that the silane coupling agent content is sufficient to form an effective chemical bond and enhance the adhesion between the coating and the aluminum foil. If the content is less than 2%, sufficient chemical bonds may not form, resulting in insufficient coating adhesion. Avoid excessive silane coupling agent content, as this can reduce the coating's flexibility and conductivity. Excessive silane coupling agent content can make the coating too brittle, affecting its stability during battery charge and discharge, while also increasing the coating's thickness and cost. A ratio of 2% to 5% effectively enhances the coating's adhesion to the aluminum foil and improves the coating's resistance to electrolyte corrosion, while maintaining its flexibility and conductivity.

[0012] Deionized water is used as a solvent to dissolve and disperse the other ingredients so that the formulation can be evenly coated on the surface of the aluminum foil.

[0013] In a possible design, the composite conductive agent is composed of carbon black and carbon tubes, the carbon tubes include single-walled carbon tubes and multi-walled carbon tubes, and the ratio of carbon black, single-walled carbon tubes and multi-walled carbon tubes is (50-1000):(1-20):(0.5-2).

[0014] In the above scheme, carbon black serves as the base conductive material, providing numerous conductive contact points and forming the basic framework of the conductive network. Ensure sufficient carbon black content to build the basic conductive network. If the content is less than 50 parts per million, the conductive network may be too sparse and ineffective in reducing the coating's resistance. Avoid excessive carbon black content, as this can reduce the coating's flexibility and adhesion. Excessive carbon black content, exceeding 1000 parts per million, can make the coating too rigid and prone to cracking due to volume changes during battery charging and discharging. Single-walled carbon nanotubes (SWNTs), with their excellent conductivity and high aspect ratio, can form efficient conductive pathways in the coating. Ensure sufficient SWNTs to build continuous conductive pathways. If the content is less than 1 part per million, the SWNTs' contribution may be limited, failing to effectively enhance conductivity. Avoid excessive SWNT content, exceeding 20 parts per million, to reduce the coating's cost and complexity. Excessive SWNT content can increase coating thickness and cost, and may also affect coating uniformity. Multi-walled carbon nanotubes (MWNTs), with their high mechanical strength and good conductivity, can provide additional structural support and conductive pathways in the coating. Ensure sufficient MWCNTs to enhance the coating's mechanical properties and electrical conductivity. If less than 0.5 phr, the MWCNTs' effect may be insignificant. Avoid excessive MWCNT content, which can reduce the coating's flexibility and adhesion. Excessive MWCNTs may make the coating too rigid, and above 2 phr, affecting its stability during battery charge and discharge.

[0015] In a possible design, nano-titanium dioxide modified epoxy resin is also included, and the proportion of nano-titanium dioxide modified epoxy resin is 10% to 20% by mass.

[0016] Through the above solution, nano-titanium dioxide exhibits high hardness and excellent dispersibility, allowing it to be evenly distributed in epoxy resin to form a nanocomposite. This nanocomposite significantly enhances the mechanical strength and toughness of the epoxy resin. Nano-titanium dioxide improves the epoxy resin's heat and chemical resistance, making it more stable in high-temperature and electrolyte environments. The addition of nano-titanium dioxide improves the epoxy resin's conductivity. Although its inherent conductivity is not as good as that of carbon materials, it can synergize with the conductive agent to further optimize the coating's conductive network. A 10% nano-titanium dioxide-modified epoxy resin provides sufficient nano-titanium dioxide to enhance the epoxy resin's mechanical properties, heat resistance, and corrosion resistance. A content below 10% may not fully demonstrate the nano-titanium dioxide's modifying effect. A 20% content avoids excessive epoxy resin content, thereby reducing the coating's thickness and weight, maintaining its lightweight and flexibility. Epoxy resin modified with 10% to 20% nano-titanium dioxide achieves an optimal balance between mechanical properties, corrosion resistance, and conductivity, ensuring the coating's stability and efficiency during battery operation.

[0017] In a possible design, an aqueous defoamer is also included, and the proportion of the aqueous defoamer is 0.05% to 0.5% by mass.

[0018] With the above solution, bubbles are easily generated during the coating preparation process, especially during the stirring and mixing stages. The presence of bubbles can affect the uniformity and adhesion of the coating, leading to coating defects such as pinholes and surface unevenness. A water-based defoamer can effectively eliminate these bubbles, ensuring coating uniformity and integrity. By eliminating bubbles, the water-based defoamer can improve the quality of the coating, making it smoother and more uniform, reducing surface defects, and thus enhancing the overall performance and reliability of the battery. During the coating process, bubbles can cause uneven coating thickness, affecting the conductivity and adhesion of the coating. The water-based defoamer can improve application performance and ensure that the coating is evenly applied to the aluminum foil current collector surface. A 0.05% water-based defoamer provides sufficient defoaming capacity to effectively eliminate bubbles generated during the coating preparation and coating process. A concentration below 0.05% may not completely eliminate bubbles, affecting coating quality. A 0.5% concentration ensures that the defoamer dosage is not excessive, thereby avoiding negative impacts on other coating properties (such as conductivity and adhesion). Excessive defoamer may form impurities in the coating, affecting coating uniformity and adhesion.

[0019] In one possible design, the main binder is a water-based polyurethane-acrylic composite emulsion or PAA, the silane coupling agent is KH-570, and the water-based defoaming agent is polyether-modified siloxane.

[0020] Through the above scheme, polyurethane has good flexibility and mechanical strength, while acrylic resin provides excellent adhesion and weather resistance. The combination of the two can combine the advantages of both, so that the coating can achieve the best balance between flexibility, adhesion and mechanical strength. The polyurethane-acrylic composite emulsion has good chemical corrosion resistance, can effectively resist the erosion of the electrolyte, and extend the service life of the coating. PAA (polyacrylic acid) has excellent adhesion and can firmly adhere to the surface of the aluminum foil current collector. PAA can form a uniform film to ensure the uniformity and consistency of the coating, and is suitable for battery application scenarios that are cost-sensitive and have high adhesion requirements.

[0021] KH-570 (γ-methacryloxypropyltrimethoxysilane) is an aminosilane coupling agent that can form strong chemical bonds between organic materials (such as binders and conductive agents) and inorganic materials (such as aluminum foil), significantly enhancing the interfacial bonding between the coating and the current collector (enhancing the chemical bonding with the metal foil).

[0022] Polyether-modified siloxane is a highly effective defoamer that quickly eliminates bubbles during coating preparation and application, ensuring coating uniformity and integrity. This defoamer exhibits excellent compatibility with water-based systems and does not adversely react with other coating components, ensuring coating stability and performance. This current collector primer formulation further optimizes the coating's adhesion, chemical resistance, flexibility, and application performance.

[0023] In the second aspect, the present application provides a method for preparing a current collector primer formulation, comprising the following steps: a premixing stage: mixing the main binder, the first part of carbon black and deionized water, and controlling the solid content of the mixed system to be 15% to 25%; shear stirring at a speed of 1000rpm to 1500rpm for 10 to 20 minutes to obtain a primary dispersion slurry; a carbon black enhanced dispersion stage: adding the second part of carbon black to the primary dispersion slurry, and stirring at a high speed of 2000rpm to 2500rpm for 120 to 160 minutes; adding deionized water and continuing to disperse for 20 to 40 minutes; a carbon nanotube dispersion stage: adding multi-walled carbon nanotubes and single-walled carbon nanotubes in turn, and stirring at a high speed of 2000rpm to 2500rpm for 100 to 150 minutes; a post-processing stage: adding a silane coupling agent and dispersing for 15 to 30 minutes; filtering after stirring to obtain a uniform primer slurry.

[0024] Through the above scheme, during the premixing stage, by controlling the solid content and applying appropriate shear agitation, the primary binder and carbon black can be initially dispersed in deionized water, forming a relatively uniform primary dispersion slurry. This lays the foundation for the subsequent dispersion process. A low solid content and appropriate stirring speed prevent carbon black particles from agglomerating early on, thereby improving the efficiency and effectiveness of subsequent dispersion. High-speed agitation further breaks up carbon black particle agglomerations, allowing for a uniform distribution within the slurry. Prolonged stirring (120-160 minutes) ensures sufficient dispersion of the carbon black, thereby improving the conductivity of the coating. By adding carbon black in stages, the dispersion state can be better controlled, optimizing the construction of the conductive network and reducing coating resistance. Continuing the dispersion process after adding deionized water further optimizes the slurry's fluidity, making it more suitable for subsequent coating processes. Carbon nanotubes (especially single-walled carbon nanotubes) have a high aspect ratio and excellent conductivity, but are prone to agglomeration. High-speed agitation allows for a uniform dispersion of carbon nanotubes within the slurry, preventing agglomeration and fully utilizing their conductive properties. The addition of carbon nanotubes can further optimize the conductive network, work synergistically with carbon black to build a more efficient and continuous conductive path, and significantly reduce the resistance of the coating. The high strength and toughness of carbon nanotubes can enhance the mechanical properties of the coating, making the coating tougher and able to withstand greater mechanical stress. Silane coupling agents can form chemical bonds with the surface of the aluminum foil current collector and the organic materials in the coating (such as binders and conductive agents), significantly enhancing the interfacial bonding between the coating and the current collector, and preventing the coating from falling off or peeling off. Silane coupling agents can improve the chemical corrosion resistance of the coating, making the coating more stable in the electrolyte environment and extending the service life of the battery. The preparation method of the current collector primer formula provided in this scheme ensures the uniform distribution and full dispersion of each component through a staged mixing and dispersion process, thereby significantly improving the conductivity, mechanical properties, interfacial bonding and construction performance of the primer formula. This preparation method not only solves the problems of uneven dispersion and agglomeration that may occur in traditional processes, but also provides an efficient and stable solution for high-performance lithium-ion battery current collector primers.

[0025] In a possible design, the premixing stage further includes: adding nano-titanium dioxide modified epoxy resin; the post-processing stage further includes: adding a water-based defoaming agent, with the addition amount being 0.05% to 0.5% of the total mass of the slurry.

[0026] According to the above scheme, in the premixing stage, the main binder, the first part of carbon black, nano-titanium dioxide modified epoxy resin and deionized water are mixed, and the solid content of the mixed system is controlled to be 15% to 25%; shear stirring is carried out at a speed of 1000rpm to 1500rpm for 10 to 20 minutes to obtain a primary dispersion slurry. Nano-titanium dioxide modified epoxy resin can significantly improve the mechanical strength and toughness of the coating. The high hardness and good dispersibility of nano-titanium dioxide make the coating more stable under mechanical stress and able to withstand greater tensile and bending stress. Nano-titanium dioxide modified epoxy resin can synergistically work with conductive agents (such as carbon black and carbon nanotubes) to further optimize the conductive network and reduce the coating resistance. Adding nano-titanium dioxide modified epoxy resin in the premixing stage can ensure that it is fully mixed with other ingredients to form a uniform primary dispersion slurry, laying the foundation for the subsequent dispersion process.

[0027] During the post-processing stage, after adding the silane coupling agent, a water-based defoamer is added at a rate of 0.05% to 0.5% of the total slurry mass. After stirring, the mixture is filtered to obtain a uniform primer slurry. The water-based defoamer effectively eliminates bubbles generated during the stirring and mixing process, ensuring the uniformity and integrity of the slurry. The presence of bubbles can cause defects such as pinholes and surface unevenness in the coating, affecting its conductivity and adhesion. By eliminating bubbles, the water-based defoamer improves the quality of the coating, making it smoother and more uniform, reducing surface defects, and thus enhancing the overall performance and reliability of the battery. The addition of the defoamer improves application performance, ensuring that the coating is evenly applied to the aluminum foil current collector surface and reducing uneven coating thickness caused by bubbles.

[0028] By adding nano-titanium dioxide-modified epoxy resin during the premixing stage and a water-based defoamer during the post-processing stage, this method for preparing the current collector primer further optimizes the coating's mechanical properties, heat resistance, chemical resistance, and conductivity, while also improving the coating's quality and workability. This design not only solves the uneven dispersion and air bubble issues that can occur in traditional processes, but also provides a more comprehensive, efficient, and environmentally friendly solution for current collector primers in high-performance lithium-ion batteries.

[0029] In one possible design, the main binder is a water-based polyurethane-acrylic composite emulsion or PAA; the silane coupling agent is at least one silane selected from methacryloxy, epoxy, amino or mercapto groups; and the water-based defoaming agent is at least one selected from polyethers, silicone emulsions, and mineral oil-based groups.

[0030] Polyurethane offers good flexibility and mechanical strength, while acrylic resin provides excellent adhesion and weather resistance. Combining the two combines the advantages of both, creating a coating that achieves an optimal balance between flexibility, adhesion, and mechanical strength. PAA exhibits excellent adhesion, allowing it to firmly adhere to the aluminum foil current collector surface. PAA is a common binder with a relatively low cost, making it suitable for large-scale production.

[0031] Methacryloxysilanes (such as KH-570) can form strong chemical bonds with organic materials (such as binders and conductive agents) and inorganic materials (such as aluminum foil), significantly enhancing the interfacial bonding between the coating and the current collector. Epoxysilanes can improve the chemical resistance of the coating, making it more stable in the electrolyte environment. Aminosilanes can improve the flexibility of the coating, allowing it to better adapt to volume changes during battery charging and discharging. Mercaptosilanes can form strong bonds with a variety of materials, further improving the adhesion of the coating.

[0032] Polyether defoamers, silicone emulsion defoamers, and mineral oil-based defoamers can all quickly eliminate bubbles, ensuring the uniformity and integrity of the slurry. The addition of a water-based defoamer improves application performance, ensuring the coating is evenly applied to the aluminum foil current collector surface and reducing uneven coating thickness caused by bubbles.

[0033] In a possible design, the mass ratio of the first portion of carbon black to the second portion of carbon black is 1:1; and the mass ratio of the multi-walled carbon nanotubes to the single-walled carbon nanotubes is (5-10):1.

[0034] Using this approach, equal amounts of the first and second carbon black are added during the premixing and dispersion stages, respectively. By adding equal amounts of carbon black in separate steps, the dispersion of the carbon black can be better controlled, agglomeration can be avoided, and uniform distribution of the carbon black within the slurry can be ensured. Adding equal amounts of carbon black in two steps helps to build a more uniform and continuous conductive network, reducing coating resistance and improving battery charge and discharge efficiency. Evenly dispersed carbon black improves coating stability and mitigates the degradation of conductivity and mechanical properties caused by carbon black agglomeration.

[0035] During the carbon nanotube dispersion stage, multi-walled carbon nanotubes and single-walled carbon nanotubes are added sequentially, maintaining a controlled mass ratio of (5-10):1. Single-walled carbon nanotubes have higher conductivity and superior conductive network building capabilities, while multi-walled carbon nanotubes have higher mechanical strength. By controlling the mass ratio, the conductive properties of single-walled carbon nanotubes and the mechanical properties of multi-walled carbon nanotubes can be fully utilized. By controlling the mass ratio of multi-walled carbon nanotubes to single-walled carbon nanotubes, a more efficient and continuous conductive path can be constructed, significantly reducing the coating resistance and improving the battery's charge and discharge efficiency.

[0036] The above description is only an overview of the technical solutions of the embodiments of the present application. In order to more clearly understand the technical means of the embodiments of the present application, they can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiments of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application, a brief introduction will be given below to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians, other drawings can be obtained based on these drawings without any creative work.

[0038] Figure 1 This is a flow chart of a method for preparing a current collector primer formulation provided in one embodiment of the present application.

[0039] Figure 2 This is a photo of carbon tube agglomeration distribution in a current collector bottom coating provided in one embodiment of the present application.

[0040] Figure 3 This is a photograph of carbon tube agglomeration distribution in a current collector bottom coating provided in another embodiment of the present application. DETAILED DESCRIPTION

[0041] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification, claims and drawings of this application are intended to cover non-exclusive inclusions.

[0043] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0044] The term "and / or" in this document simply describes a relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists, A and B exist, and B exists. Additionally, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0045] The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order, and may explicitly or implicitly include one or more such features.

[0046] In the description of this application, unless otherwise specified, "plurality" means more than two (including two), and similarly, "multiple groups" means more than two (including two).

[0047] As can be seen from the background technology, the current aluminum foil current collector primer formula has insufficient conductivity, and after being coated on the current collector surface, the tensile strength and elongation performance are poor, resulting in a poor internal structure of the battery, reducing the stability and service life of the battery.

[0048] In view of this, the embodiment of the present application provides a current collector primer formulation and preparation method thereof, wherein the primer formulation includes: a main binder, a composite conductive agent, a coupling agent, and a solvent. Among them, the composite conductive agent is composed of carbon black and carbon tubes. By rationally matching the composite conductive agent of spherical carbon black and tubular carbon tubes, combined with the chemical bonding effect of the silane coupling agent, the conductivity of the coating, the resistance to electrolyte corrosion, the interfacial bonding force with the active material, and the mechanical properties of the foil are significantly improved. The structural advantages of this composite conductive agent make electron transmission more efficient and the coating more stable.

[0049] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0050] In this embodiment, a current collector primer formulation is provided, comprising a primary binder, a composite conductive agent, a silane coupling agent, and deionized water. The composite conductive agent in the formulation is composed of carbon black and carbon tubes (including single-walled carbon tubes and multi-walled carbon tubes). It can be seen that the carbon black particles are spherical, have a high specific surface area and good conductivity. The spherical structure enables the carbon black particles to form multiple contact points in the coating, providing multiple paths for electron transmission. The carbon tubes (including single-walled carbon tubes and multi-walled carbon tubes) are tubular structures with excellent conductivity and a high aspect ratio. The tubular structure enables the carbon tubes to form continuous conductive channels in the coating, and electrons can be efficiently transmitted along the long axis direction of the carbon tubes. The combination of spherical carbon black and tubular carbon tubes can form a three-dimensional conductive network. The carbon tubes can "bridge" the gaps between the carbon black particles, while the carbon black particles can fill the gaps between the carbon tubes. This structure is similar to a combination of a "skeleton" (carbon tube) and a "filler" (carbon black), allowing electrons to be efficiently transmitted throughout the coating. The three-dimensional conductive network formed by the composite conductive agent not only improves the conductivity, but also enhances the structural stability of the coating. This stable structure enables the coating to better maintain contact with the active material during the battery charging and discharging process. In addition, the silane coupling agent can form chemical bonds with the surface of the aluminum foil current collector and the organic materials in the coating (such as binders and conductive agents), further enhancing the bonding force between the coating and the current collector. The three-dimensional structure of the composite conductive agent and the chemical bonding of the silane coupling agent enable the coating to better adhere to the surface of the aluminum foil current collector during the battery charging and discharging process, preventing the coating from falling off or peeling off, thereby improving the stability and service life of the battery. The current collector primer formula of the present application significantly improves the conductivity, electrolyte corrosion resistance, interfacial bonding with active materials, and mechanical properties of the foil by rationally matching the composite conductive agent of spherical carbon black and tubular carbon tubes, combined with the chemical bonding of the silane coupling agent. The structural advantages of this composite conductive agent make electron transmission more efficient and the coating more stable.

[0051] In some embodiments, by mass percentage, the main binder accounts for 40% to 60%; the composite conductive agent accounts for 20% to 40%; the silane coupling agent accounts for 2% to 5%, and deionized water is the balance.

[0052] The main binder is a key component in the primer formula, which is mainly responsible for firmly combining other ingredients (such as conductive agents, silane coupling agents, etc.) and attaching them to the surface of the aluminum foil current collector. Make sure that the binder is in sufficient quantity to maintain the integrity and adhesion of the coating. If it is less than 40%, the coating structure may become loose and unable to effectively adhere to the aluminum foil surface, affecting the stability and service life of the coating. Avoid excessive binder content, which will reduce the flexibility and conductivity of the coating. Too much binder may make the coating too rigid and prone to cracking due to volume changes during battery charging and discharging. It will also reduce the effective content of the conductive agent and affect the conductive performance. The ratio range of 40% to 60% can balance the adhesion, flexibility and conductivity of the coating, ensuring that the coating remains stable during battery use without affecting the performance of other ingredients.

[0053] Composite conductive agents (including carbon black and carbon tubes) are key components for improving the conductivity of the coating, and they reduce the resistance of the coating by building a conductive network. Make sure that the coating has enough conductive agent to build an effective conductive network. If it is less than 20%, the conductive network may be discontinuous, resulting in excessively high coating resistance, affecting the charge and discharge efficiency of the battery. Avoid excessive conductive agent content, which reduces the mechanical properties and adhesion of the coating. Too much conductive agent may make the coating too fragile and easy to fall off due to volume changes during battery charging and discharging. It will also increase the thickness of the coating and affect the overall design of the battery. A ratio range of 20% to 40% can ensure that the coating has good conductivity without affecting the adhesion and mechanical properties of the coating, effectively reducing the coating resistance and improving battery performance.

[0054] Silane coupling agents are primarily used to enhance the interfacial adhesion between the coating and the aluminum foil current collector and provide a certain degree of resistance to electrolyte corrosion. Ensure that the silane coupling agent content is sufficient to form an effective chemical bond and enhance the adhesion between the coating and the aluminum foil. If the content is less than 2%, sufficient chemical bonds may not form, resulting in insufficient coating adhesion. Avoid excessive silane coupling agent content, as this can reduce the coating's flexibility and conductivity. Excessive silane coupling agent content can make the coating too brittle, affecting its stability during battery charge and discharge, while also increasing the coating's thickness and cost. A ratio of 2% to 5% effectively enhances the coating's adhesion to the aluminum foil and improves the coating's resistance to electrolyte corrosion, while maintaining its flexibility and conductivity.

[0055] Deionized water is used as a solvent to dissolve and disperse the other ingredients so that the formulation can be evenly coated on the surface of the aluminum foil.

[0056] In some embodiments, the ratio of carbon black, single-walled carbon nanotubes, and multi-walled carbon nanotubes is (50-1000):(1-20):(0.5-2).

[0057] As a basic conductive material, carbon black provides numerous conductive contact points, forming the basic framework of the conductive network. Ensure sufficient carbon black to build the basic conductive network. If the carbon black content is less than 50 parts per million, the conductive network may be too sparse and ineffective in reducing the coating's resistance. Avoid excessive carbon black content, as this can reduce the coating's flexibility and adhesion. Excessive carbon black content, exceeding 1000 parts per million, can make the coating too rigid and prone to cracking due to volume changes during battery charging and discharging. Single-walled carbon nanotubes (SWNTs), with their excellent conductivity and high aspect ratio, can form efficient conductive pathways in the coating. Ensure sufficient SWNTs to build continuous conductive pathways. If the SWNT content is less than 1 part per million, their contribution may be limited and ineffective in improving conductivity. Avoid excessive SWNT content, exceeding 20 parts per million, to reduce the coating's cost and complexity. Excessive SWNTs may increase coating thickness and cost, and may also affect coating uniformity. Multi-walled carbon nanotubes (MWNTs), with their high mechanical strength and good conductivity, can provide additional structural support and conductive pathways in the coating. Ensure sufficient MWCNTs to enhance the coating's mechanical properties and electrical conductivity. If less than 0.5 phr, the MWCNTs' effect may be insignificant. Avoid excessive MWCNT content, which can reduce the coating's flexibility and adhesion. Excessive MWCNTs may make the coating too rigid, and above 2 phr, affecting its stability during battery charge and discharge.

[0058] In some embodiments, the current collector primer formulation may further include nano-titanium dioxide modified epoxy resin. When the nano-titanium dioxide modified epoxy resin is added, the amount of the nano-titanium dioxide modified epoxy resin added may be 10% to 20% of the total mass in terms of mass percentage.

[0059] Nano-titanium dioxide has high hardness and excellent dispersibility, allowing it to be evenly distributed in epoxy resin to form a nanocomposite. This nanocomposite significantly improves the mechanical strength and toughness of epoxy resin. Nano-titanium dioxide also enhances the heat and chemical resistance of epoxy resin, making it more stable in high-temperature and electrolyte environments. The addition of nano-titanium dioxide improves the conductivity of epoxy resin. Although its inherent conductivity is not as good as that of carbon materials, it can synergize with conductive agents to further optimize the conductive network of the coating. A 10% nano-titanium dioxide-modified epoxy resin provides sufficient nano-titanium dioxide to enhance the mechanical properties, heat resistance, and corrosion resistance of the epoxy resin. A content below 10% may not fully demonstrate the modifying effect of the nano-titanium dioxide. A 20% content avoids excessive epoxy resin content, thereby reducing the thickness and weight of the coating and maintaining its lightweight and flexibility. Epoxy resin modified with 10% to 20% nano-titanium dioxide achieves an optimal balance between mechanical properties, corrosion resistance, and conductivity, ensuring the coating is stable and efficient during battery operation.

[0060] In some embodiments, the current collector primer formulation may further include an aqueous defoamer. When the aqueous defoamer is added, the amount of the aqueous defoamer added may be 0.05% to 0.5% of the total mass, in terms of mass percentage.

[0061] During the coating preparation process, especially during the stirring and mixing stages, bubbles are easily generated. The presence of bubbles can affect coating uniformity and adhesion, leading to coating defects such as pinholes and surface unevenness. Aqueous defoamers can effectively eliminate these bubbles, ensuring coating uniformity and integrity. By eliminating bubbles, aqueous defoamers can improve the quality of the coating, making it smoother and more uniform, reducing surface defects, and thus enhancing overall battery performance and reliability. During the coating process, bubbles can cause uneven coating thickness, affecting conductivity and adhesion. Aqueous defoamers can improve application performance and ensure uniform coating application on the aluminum foil current collector surface. A 0.05% aqueous defoamer provides sufficient defoaming capacity to effectively eliminate bubbles generated during coating preparation and coating. A concentration below 0.05% may not completely eliminate bubbles, affecting coating quality. A 0.5% concentration ensures that the defoamer dosage is moderate, thus avoiding negative impacts on other coating properties (such as conductivity and adhesion). Excessive defoamer may form impurities in the coating, affecting uniformity and adhesion.

[0062] In some embodiments, the primary binder may be selected from aqueous polyurethane-acrylic composite emulsion or PAA (polyacrylic acid).

[0063] Polyurethane offers excellent flexibility and mechanical strength, while acrylic resin provides excellent adhesion and weather resistance. The combination of the two combines the advantages of both, resulting in a coating that achieves an optimal balance between flexibility, adhesion, and mechanical strength. Polyurethane-acrylic composite emulsions exhibit excellent chemical resistance, effectively resisting electrolyte erosion and extending the coating's service life. PAA exhibits excellent adhesion and can firmly adhere to the surface of the aluminum foil current collector. PAA forms a uniform film, ensuring coating uniformity and consistency, making it suitable for cost-sensitive battery applications with high adhesion requirements.

[0064] In some embodiments, the silane coupling agent is KH-570. KH-570 (γ-methacryloxypropyltrimethoxysilane) is an aminosilane coupling agent that can form strong chemical bonds between organic materials (such as binders and conductive agents) and inorganic materials (such as aluminum foil), significantly enhancing the interfacial bonding between the coating and the current collector (enhancing the chemical bonding with the metal foil).

[0065] In some embodiments, the aqueous defoamer is a polyether-modified siloxane. Polyether-modified siloxane is a highly effective defoamer that rapidly eliminates bubbles during coating preparation and application, ensuring coating uniformity and integrity. This defoamer exhibits excellent compatibility with aqueous systems and does not adversely react with other coating components, ensuring coating stability and performance. This current collector primer formulation can further optimize the coating's adhesion, chemical resistance, flexibility, and application performance.

[0066] Based on the above embodiments, a method for preparing a current collector primer formulation is provided in this embodiment. Figure 1 This is a flow chart of the preparation method of a current collector primer provided in this embodiment. Please refer to Figure 1 , the preparation method comprises:

[0067] Step 1, premixing stage: mix the main binder, the first part of carbon black and deionized water, and control the solid content of the mixed system to be 15% to 25%; shear and stir at a speed of 1000rpm to 1500rpm for 10 to 20 minutes to obtain a primary dispersed slurry.

[0068] During the premixing stage, controlling the solids content and applying appropriate shear agitation can initially disperse the primary binder and carbon black in deionized water, forming a relatively uniform primary dispersion slurry. This lays the foundation for the subsequent dispersion process. Controlling the solids content of the mixed system to 15% to 25% and shear agitation at 1000 to 1500 rpm for 10 to 20 minutes can prevent carbon black particle agglomeration in the early stages, thereby improving the efficiency and effectiveness of subsequent dispersion.

[0069] Step 2, carbon black enhanced dispersion stage: add the second part of carbon black to the primary dispersion slurry, stir at a high speed of 2000rpm to 2500rpm for 120 to 160 minutes; add deionized water and continue to disperse for 20 to 40 minutes.

[0070] Add the second portion of carbon black and stir at high speed at 2000rpm~2500rpm for 120~160 minutes. High-speed stirring can further break up the agglomeration of carbon black particles and make them evenly distributed in the slurry. Long-term stirring (120~160 minutes) ensures the full dispersion of carbon black, thereby improving the conductivity of the coating. By adding carbon black in steps, the dispersion state of carbon black can be better controlled, the construction of the conductive network can be optimized, and the coating resistance can be reduced. Continuing to disperse after adding deionized water can further optimize the fluidity of the slurry, making it more suitable for subsequent coating processes.

[0071] Step 3, carbon nanotube dispersion stage: add multi-walled carbon nanotubes and single-walled carbon nanotubes in sequence, and stir at a high speed of 2000 rpm to 2500 rpm for 100 to 150 minutes.

[0072] Carbon nanotubes (especially single-walled carbon nanotubes) have a high aspect ratio and excellent conductivity, but are prone to agglomeration. Through high-speed stirring, carbon nanotubes can be evenly dispersed in the slurry, avoiding agglomeration and giving full play to their conductive properties. The addition of carbon nanotubes can further optimize the conductive network, synergizing with carbon black to build a more efficient and continuous conductive path, significantly reducing the resistance of the coating. The high strength and toughness of carbon nanotubes can enhance the mechanical properties of the coating, making the coating tougher and able to withstand greater mechanical stress.

[0073] Step 4, post-processing stage: add silane coupling agent and disperse for 15 to 30 minutes; stir and filter to obtain a uniform primer slurry.

[0074] In some embodiments, lithium fluoride can be added along with a silane coupling agent. The silane coupling agent strengthens the SEI film through chemical bonding, while lithium fluoride further stabilizes the SEI film by reducing interfacial impedance and inhibiting side reactions. The synergistic effect of the two can significantly improve the overall performance of the SEI film.

[0075] Silane coupling agents can form chemical bonds with the surface of the aluminum foil current collector and the organic materials in the coating (such as binders and conductive agents), significantly enhancing the interfacial bonding between the coating and the current collector and preventing the coating from falling off or peeling. Silane coupling agents can also improve the coating's chemical resistance, making it more stable in the electrolyte environment and extending the battery's service life.

[0076] The preparation method for the current collector primer provided in this proposal ensures uniform distribution and full dispersion of the ingredients through a staged mixing and dispersion process, significantly improving the primer's conductivity, mechanical properties, interfacial adhesion, and workability. This preparation method not only solves the uneven dispersion and agglomeration issues that can occur in traditional processes, but also provides an efficient and stable solution for high-performance lithium-ion battery current collector primers.

[0077] In some embodiments, the premixing stage further includes: adding nano-titanium dioxide modified epoxy resin; the post-processing stage further includes: adding a water-based defoaming agent, with the addition amount being 0.05% to 0.5% of the total mass of the slurry.

[0078] That is to say, in some embodiments, the premixing stage is to mix the main binder, the first part of carbon black, nano-titanium dioxide modified epoxy resin and deionized water, and control the solid content of the mixed system to be 15% to 25%; shear stirring is carried out at a speed of 1000rpm to 1500rpm for 10 to 20 minutes to obtain a primary dispersion slurry. Nano-titanium dioxide modified epoxy resin can significantly improve the mechanical strength and toughness of the coating. The high hardness and good dispersibility of nano-titanium dioxide make the coating more stable under mechanical stress and able to withstand greater tensile and bending stresses. Nano-titanium dioxide modified epoxy resin can synergistically act with conductive agents (such as carbon black and carbon nanotubes) to further optimize the conductive network and reduce the coating resistance. Adding nano-titanium dioxide modified epoxy resin in the premixing stage can ensure that it is fully mixed with other ingredients to form a uniform primary dispersion slurry, laying the foundation for the subsequent dispersion process.

[0079] In the post-processing stage of some embodiments, after adding the silane coupling agent, an aqueous defoamer may be added, and the amount of the aqueous defoamer added is 0.05% to 0.5% of the total mass of the slurry; after stirring, the mixture is filtered to obtain a uniform primer slurry. The aqueous defoamer can effectively eliminate bubbles generated during the stirring and mixing process to ensure the uniformity and integrity of the slurry. The presence of bubbles may cause defects such as pinholes and uneven surfaces in the coating, affecting the conductivity and adhesion of the coating. By eliminating bubbles, the aqueous defoamer can improve the quality of the coating, making it smoother and more uniform, reducing surface defects, and thus improving the overall performance and reliability of the battery. The addition of the defoamer can improve the construction performance, ensure that the coating can be evenly coated on the surface of the aluminum foil current collector, and reduce the problem of uneven coating thickness caused by bubbles.

[0080] By adding nano-titanium dioxide-modified epoxy resin during the premixing stage and a water-based defoamer during the post-processing stage, this method for preparing the current collector primer further optimizes the coating's mechanical properties, heat resistance, chemical resistance, and conductivity, while also improving the coating's quality and workability. This design not only solves the uneven dispersion and air bubble issues that can occur in traditional processes, but also provides a more comprehensive, efficient, and environmentally friendly solution for current collector primers in high-performance lithium-ion batteries.

[0081] In some embodiments, the primary binder is a water-based polyurethane-acrylic composite emulsion or PAA. Polyurethane has good flexibility and mechanical strength, while acrylic resin provides excellent adhesion and weather resistance. The combination of the two can combine the advantages of both, so that the coating achieves an optimal balance between flexibility, adhesion, and mechanical strength. PAA has excellent adhesion and can firmly adhere to the surface of the aluminum foil current collector. PAA is a common binder with relatively low cost and is suitable for large-scale production. The appropriate material can be selected as the primary binder according to the specific situation.

[0082] In some embodiments, the silane coupling agent is at least one silane selected from methacryloxy, epoxy, amino, or mercapto groups.

[0083] Methacryloxysilane (such as KH-570) can form strong chemical bonds with organic materials (such as binders and conductive agents) and inorganic materials (such as aluminum foil), significantly enhancing the interfacial bonding between the coating and the current collector. Epoxysilane can improve the chemical corrosion resistance of the coating, making it more stable in the electrolyte environment. Aminosilane can improve the flexibility of the coating, allowing it to better adapt to volume changes during battery charging and discharging. Mercaptosilane can form strong bonds with a variety of materials, further improving the adhesion of the coating. Suitable materials can be selected as silane coupling agents according to specific circumstances.

[0084] In some embodiments, the aqueous defoaming agent is selected from at least one of polyethers, silicone emulsions, and mineral oil-based defoamers.

[0085] The addition of a water-based defoamer improves construction performance, ensuring that the coating can be evenly applied to the surface of the aluminum foil current collector and reducing the problem of uneven coating thickness caused by bubbles. Polyether defoamers, silicone emulsion defoamers, and mineral oil-based defoamers can all quickly eliminate bubbles and ensure the uniformity and integrity of the slurry. Among them, polyether defoamers have good compatibility with water-based systems and will not react adversely with other components in the slurry. Silicone emulsion defoamers have good stability in high temperature and electrolyte environments and will not decompose or become ineffective. Mineral oil-based defoamers are relatively low in cost and suitable for large-scale production. You can choose the appropriate water-based defoamer according to the specific situation.

[0086] In some embodiments, the mass ratio of the first portion of carbon black to the second portion of carbon black is 1:1; the mass ratio of the multi-walled carbon nanotubes to the single-walled carbon nanotubes is (5-10):1.

[0087] During the premixing stage and the carbon black intensive dispersion stage, equal weights of the first and second carbon blacks are added. By adding equal weights of carbon black in separate steps, the dispersion of the carbon black can be better controlled, agglomeration can be avoided, and uniform distribution of the carbon black in the slurry can be ensured. Adding equal weights of carbon black in two steps helps to build a more uniform and continuous conductive network, reducing coating resistance and improving battery charge and discharge efficiency. Evenly dispersed carbon black improves coating stability and reduces the reduction in conductivity and mechanical properties caused by carbon black agglomeration.

[0088] During the carbon nanotube dispersion stage, multi-walled carbon nanotubes and single-walled carbon nanotubes are added sequentially, maintaining a controlled mass ratio of (5-10):1. Single-walled carbon nanotubes have higher conductivity and superior conductive network building capabilities, while multi-walled carbon nanotubes have higher mechanical strength. By controlling the mass ratio, the conductive properties of single-walled carbon nanotubes and the mechanical properties of multi-walled carbon nanotubes can be fully utilized. By controlling the mass ratio of multi-walled carbon nanotubes to single-walled carbon nanotubes, a more efficient and continuous conductive path can be constructed, significantly reducing the coating resistance and improving the battery's charge and discharge efficiency.

[0089] The current collector primer formulation obtained in the above examples can significantly improve the conductivity, interfacial bonding strength and mechanical properties of the coating to meet the requirements of high-performance batteries.

[0090] Example 1

[0091] Based on the above embodiment, this embodiment provides a current collector primer slurry comprising: a primary binder of a waterborne polyurethane-acrylic emulsion; a composite conductive agent comprising carbon black, multi-walled carbon nanotubes (MWCNTs), and single-walled carbon nanotubes (SWCNTs), with the ratio of carbon black, MWCNTs, and SWCNTs being 800:10:1; a silane coupling agent of KH-570; and a water-based defoaming agent of polyether-modified siloxane. The slurry comprises, by mass, 50% of the waterborne polyurethane-acrylic emulsion; 30% of the composite conductive agent; 3% of the KH-570; 15% of the nano-titanium dioxide-modified epoxy resin; and 0.2% of the polyether-modified siloxane. Deionized water accounts for the remainder.

[0092] The preparation method of the current collector primer slurry in this embodiment is:

[0093] Mixing the aqueous polyurethane-acrylic emulsion, the nano-titanium dioxide modified epoxy resin, the first portion of carbon black, and deionized water, controlling the solid content of the mixed system to be 15% to 25%; shear stirring at a speed of 1000 rpm to 1500 rpm for 10 to 20 minutes to obtain a primary dispersed slurry;

[0094] Add the remaining (second part) carbon black to the primary dispersion slurry and stir at a high speed of 2000 rpm to 2500 rpm for 120 to 160 minutes; add deionized water and continue to disperse for 20 to 40 minutes;

[0095] Add multi-walled carbon nanotubes and single-walled carbon nanotubes in sequence, and stir at a high speed of 2000 rpm to 2500 rpm for 100 to 150 minutes;

[0096] Post-processing stage: add silane coupling agent and disperse for 15 to 30 minutes; then add polyether modified siloxane, stir and filter to obtain a uniform primer slurry.

[0097] The obtained current collector primer slurry was subjected to performance testing, and the test results are shown in Table 1.

[0098] Performance testing:

[0099] To verify the performance of the current collector primer slurry prepared in this example, we designed a series of performance tests, including conductivity testing (testing penetration resistance), interfacial adhesion testing, electrolyte resistance testing (immersion for 7 days), mechanical properties testing (tensile strength and elongation), and battery performance. The following is a detailed analysis of the test methods and results:

[0100] Conductivity test: The prepared primer slurry is evenly coated on the surface of the aluminum foil current collector and dried to form a coating.

[0101] Test equipment: A four-probe tester was used to measure the resistivity of the coating.

[0102] Test steps:

[0103] The aluminum foil sample coated with the primer slurry was fixed on a testing platform.

[0104] Use a four-probe tester to measure the penetration resistance of the coating and record the data.

[0105] In this embodiment, the measurement was repeated three times and the average value was taken as the final result data.

[0106] The test results show that the through-line resistance value of the primer slurry of this embodiment is 4.21, which indicates that the primer slurry of this embodiment has better conductivity, can effectively reduce the coating resistance, and improve the charge and discharge efficiency of the battery.

[0107] Interface bonding strength test:

[0108] Test purpose: To evaluate the interfacial bonding strength between the primer slurry and the aluminum foil current collector.

[0109] Test method:

[0110] Sample preparation: The prepared primer slurry is evenly coated on the surface of the aluminum foil current collector and dried to form a coating.

[0111] Test equipment: Use a peel tester to perform a 180° peel test.

[0112] Test steps:

[0113] The aluminum foil sample coated with the primer slurry was fixed on a peel tester. A 180° peel test was performed at a peel speed of 100 mm / min, and the peel force was recorded.

[0114] Repeat the measurement three times and take the average value as the final result.

[0115] Result analysis:

[0116] Expected results: The primer slurry of this embodiment should have higher interfacial bonding strength, and the peeling force should be 1.5 times higher than that of the traditional formula.

[0117] Actual Results: Test results show that the peel force of this example is 1.2 N / cm. This indicates that the bonding force between the primer slurry and the aluminum foil current collector is strong, which can effectively prevent the coating from falling off or peeling off during the battery charging and discharging process.

[0118] Electrolyte resistance test

[0119] Test purpose: To evaluate the corrosion resistance of the primer slurry to electrolyte.

[0120] Test method:

[0121] Sample preparation: The prepared primer slurry is evenly coated on the surface of the aluminum foil current collector and dried to form a coating.

[0122] Test equipment: Use a constant temperature and humidity chamber and an electrochemical workstation.

[0123] Test steps:

[0124] The aluminum foil sample coated with the primer slurry was immersed in the electrolyte and placed in a constant temperature and humidity chamber with the temperature set at 45°C for 7 days.

[0125] After immersion, the samples were taken out, rinsed with deionized water, and dried to observe the appearance and adhesion of the coating.

[0126] Electrochemical impedance spectroscopy (EIS) tests were performed using an electrochemical workstation to record the impedance changes of the coating.

[0127] Actual results: The test results show that the coating of this embodiment has no obvious swelling or peeling phenomenon after immersion for 7 days, which indicates that the primer slurry of this embodiment has excellent resistance to electrolyte corrosion and can effectively prevent coating damage caused by electrolyte penetration.

[0128] Mechanical properties testing

[0129] Test purpose: To evaluate the mechanical properties of the primer slurry, especially tensile strength and elongation.

[0130] Test method:

[0131] Sample preparation: The prepared primer slurry is evenly coated on the surface of the aluminum foil current collector and dried to form a coating.

[0132] Testing equipment: Use universal material testing machine.

[0133] Test steps:

[0134] The aluminum foil sample coated with the primer slurry was fixed on a universal material testing machine.

[0135] The tensile test was carried out at a tensile speed of 10 mm / min, and the tensile strength and elongation were recorded.

[0136] Repeat the measurement three times and take the average value as the final result.

[0137] Result analysis:

[0138] The test results show that the tensile strength of this embodiment is 270 MPa and the elongation is 4.5%.

[0139] Battery performance test

[0140] Test purpose: To evaluate the performance of the primer slurry in actual batteries, especially the cycle stability.

[0141] Test method:

[0142] Sample preparation: The prepared primer slurry is evenly coated on the surface of the aluminum foil current collector and used to assemble the battery after drying.

[0143] Test equipment: Use battery test system.

[0144] Test steps:

[0145] The aluminum foil current collector coated with the primer slurry was used to assemble the battery.

[0146] Charge and discharge tests were carried out at room temperature to record the charge and discharge efficiency and cycle stability of the battery.

[0147] Repeat the measurement three times and take the average value as the final result.

[0148] The test results show that in the cycle test, the capacity retention rate of the battery of this embodiment is 93.5% after 500 cycles of charge and discharge at 45°C, which shows that the primer slurry of this embodiment can significantly improve the performance of the battery and extend the service life of the battery.

[0149] Example 2

[0150] This embodiment provides a current collector primer slurry, which differs from embodiment 1 in that the ratio of carbon black, multi-walled carbon nanotubes, and single-walled carbon nanotubes in the composite conductive agent of this embodiment is 80:5:1. Other materials and steps are the same.

[0151] The performance of the primer obtained in Example 2 was tested, and the test results are shown in Table 1.

[0152] Example 3

[0153] This embodiment provides a current collector primer slurry, which differs from embodiment 1 in that the silane coupling agent KH-570 is not added in this embodiment. The other materials and steps are the same.

[0154] The performance of the primer obtained in Example 3 was tested, and the test results are shown in Table 1.

[0155] Example 4

[0156] This embodiment provides a current collector primer slurry, which differs from embodiment 1 in that nano-titanium dioxide-modified epoxy resin is not added in this embodiment. Other materials and steps are the same.

[0157] The performance of the primer obtained in Example 4 was tested, and the test results are shown in Table 1.

[0158] Example 5

[0159] This embodiment provides a current collector primer slurry, which differs from embodiment 1 in that the main binder in this embodiment is replaced with PAA. Other materials and steps are the same.

[0160] The performance of the primer obtained in Example 5 was tested, and the test results are shown in Table 1.

[0161] Comparative Example 1

[0162] This embodiment provides a current collector primer slurry. This embodiment differs from Example 1 in that the primary binder is replaced with PAA. The composite conductive agent comprises only carbon black. In this slurry, by mass, PAA accounts for 50%; carbon black accounts for 30%; KH-570 accounts for 0%; nano-titanium dioxide-modified epoxy resin accounts for 0%; and polyether-modified siloxane accounts for 0%. The balance is deionized water.

[0163] The performance of the primer obtained in Comparative Example 1 was tested, and the test results are shown in Table 1.

[0164] Table 1:

[0165]

[0166] As can be seen from Table 1:

[0167] According to the comparison of the results of Examples 1 to 5 and the results of Comparative Example 1, the conductivity test (test penetration resistance value), interface bonding test, electrolyte resistance test (immersion for 7 days), mechanical property test (tensile strength and elongation) of the primer slurry obtained by the current collector primer slurry formula and preparation method provided in the present application, as well as the battery performance are compared with Comparative Example 1. The use of the formula and method in the examples of the present application can significantly improve the conductivity, interface bonding and mechanical properties of the coating to meet the needs of high-performance batteries.

[0168] Figure 2 This is a photo of the carbon tube distribution in Example 1. Figure 3 This is a photo of the carbon tube distribution in Example 2. Please refer to Figure 2 and Figure 3 Among them, the spherical ones are carbon black and the tubular ones are carbon tubes. Figure 2 The carbon black and carbon tubes are evenly distributed. Figure 3 The carbon tubes and carbon black are agglomerated and unevenly distributed. Therefore, the comparison between Example 1 and Example 2 shows that the conductive agent with a ratio of carbon black, multi-walled carbon tubes and single-walled carbon tubes of 80:5:1 has a lower through-line resistance than the conductive agent with a ratio of carbon black, multi-walled carbon tubes and single-walled carbon tubes of 800:10:1. However, due to the high content of carbon tubes, the carbon tubes will be agglomerated and unevenly distributed (such as Figure 2 ), which slightly reduces the overall performance.

[0169] Comparison between Example 1 and Example 3 shows that the silane coupling agent KH-570 can improve the chemical bonding of the metal foil of the primer layer, thereby improving the electrical conductivity and interface bonding strength.

[0170] Comparison between Example 1 and Example 4 shows that the nano-titanium dioxide-modified epoxy resin improves the electrolyte corrosion resistance and hardness, thereby increasing the tensile strength and elongation.

[0171] Comparison between Example 1 and Example 5 shows that both the aqueous polyurethane-acrylic acid composite emulsion and PAA can achieve good bonding effects.

[0172] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A current collector primer formulation for lithium-ion batteries, characterized in that: include: A main binder, a composite conductive agent, a coupling agent and a solvent, wherein the composite conductive agent is composed of carbon black and carbon tubes.

2. The current collector primer formulation according to claim 1, characterized in that: In terms of mass percentage, the main binder accounts for 40% to 60%; the composite conductive agent accounts for 20% to 40%; the coupling agent accounts for 2% to 5%, and the solvent is the balance.

3. The current collector primer formulation according to claim 1, characterized in that: The carbon tubes include single-walled carbon tubes and multi-walled carbon tubes, and the ratio of the carbon black, the single-walled carbon tubes and the multi-walled carbon tubes is (50-1000): (1-20): (0.5-2).

4. The current collector primer formulation according to claim 1, characterized in that: Also includes nano-titanium dioxide modified epoxy resin, the nano-titanium dioxide modified epoxy resin accounts for 10% to 20% by mass; and / or The coupling agent is a silane coupling agent.

5. The current collector primer formulation according to any one of claims 1 to 4, characterized in that: The invention also includes a defoaming agent, which is an aqueous defoaming agent; in terms of mass percentage, the aqueous defoaming agent accounts for 0.05% to 0.5%.

6. The current collector primer formulation according to claim 5, characterized in that: The aqueous defoamer is polyether-modified siloxane.

7. A method for preparing a current collector primer slurry for lithium-ion batteries, characterized in that: Including steps: Premixing stage: Mix the main binder, the first part of carbon black and deionized water, and control the solid content of the mixed system to 15% to 25%; shear and stir at a speed of 1000 rpm to 1500 rpm for 10 to 20 minutes to obtain a primary dispersed slurry; Carbon black enhanced dispersion stage: add the second portion of carbon black to the primary dispersion slurry, stir at a high speed of 2000 rpm to 2500 rpm for 120 to 160 minutes; add deionized water and continue to disperse for 20 to 40 minutes; Carbon nanotube dispersion stage: add multi-walled carbon nanotubes and single-walled carbon nanotubes in sequence, and stir at a high speed of 2000 rpm to 2500 rpm for 100 to 150 minutes; Post-processing stage: add silane coupling agent and disperse for 15 to 30 minutes; stir and filter to obtain a uniform primer slurry.

8. The preparation method according to claim 7, characterized in that The premixing stage also includes: adding nano-titanium dioxide modified epoxy resin; The post-processing stage further includes: adding an aqueous defoamer in an amount of 0.05% to 0.5% of the total mass of the slurry.

9. The preparation method according to claim 8, characterized in that The main binder is water-based polyurethane-acrylic acid composite emulsion or PAA; The silane coupling agent is at least one silane selected from methacryloxy, epoxy, amino or mercapto groups; The aqueous defoamer is selected from at least one of polyethers, silicone emulsions, and mineral oil-based defoamers.

10. The preparation method according to claim 7, characterized in that The ratio of the carbon black, the single-walled carbon tubes and the multi-walled carbon tubes is (50-1000):(1-20):(0.5-2); wherein the mass ratio of the first part of carbon black to the second part of carbon black is 1:1.

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