A high-rate carbon-coated foil material and its preparation method

Abstract

The present invention relates to the technical field of batteries, and specifically to a high-rate carbon-coated foil and a preparation method thereof. The present invention prepares a high-rate carbon-coated foil, which includes a light foil, a second carbon-based conductive layer formed on the surface of the light foil, and a first carbon-based conductive layer formed on the surface of the second carbon-based conductive layer. The specific steps are as follows: mixing and stirring a first carbon-based conductive agent, a second carbon-based conductive agent, a binder, and a solvent to prepare a first conductive paste; mixing and stirring a third carbon-based conductive agent, a fourth carbon-based conductive agent, a binder, and a solvent to prepare a second conductive paste; coating the second conductive paste on the light foil and drying to obtain an intermediate foil; and then coating the first conductive paste on the intermediate foil and drying to obtain the finished product. The finished foil prepared by the present invention has good electrical conductivity and rate performance, and can significantly improve the rate performance and service life of the battery, so it has broad application prospects in the technical field of batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and specifically to a high-rate carbon-coated foil and a preparation method thereof. Background Art

[0002] With the rapid development of electronic products, the requirements for materials are increasing day by day. In particular, materials are required to have characteristics such as electrical conductivity, high temperature resistance, and corrosion resistance. In this context, carbon-coated foils, as materials with good electrical conductivity, high temperature resistance, and corrosion resistance, are widely used in key parts such as heat dissipation components and connection circuits of electronic products, effectively improving the performance and stability of electronic products. The carbon-coated foil improves the electrical conductivity between the foil and the subsequently coated electrode material by uniformly and finely coating the dispersed conductive agent on the light foil, thereby improving the rate performance of the battery. During the preparation process of the carbon-coated foil, the conductivity efficiency and bonding force of the conductive layer are crucial. However, there are still some technical problems to be solved. First, the existing conductive agents have low conductivity efficiency, resulting in the fact that the conductivity of the prepared carbon-coated foil cannot significantly improve the rate performance of the electrode, and at the same time, the production cost is increased. Second, the bonding force between the conductive layer and the electrode material layer is insufficient, resulting in a large interfacial resistance and failing to achieve the design expectation of improving the electrical conductivity between the foil and the electrode material. In addition, due to the weak bonding force, the carbon-coated layer and the electrode material layer may fall off from the foil together during the entire life cycle of the battery, thus shortening the life of the battery.

[0003] In order to overcome the defects of the prior art, the present invention provides a high-rate carbon-coated foil and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-rate carbon-coated foil and a preparation method thereof to solve the problems in the prior art.

[0005] To solve the above technical problems, the present invention provides the following technical solutions:

[0006] A high-rate carbon-coated foil includes a light foil and a conductive layer formed on the surface of the light foil; the conductive layer includes a second carbon-based conductive layer formed on the surface of the light foil and a first carbon-based conductive layer formed on the surface of the second carbon-based conductive layer;

[0007] Mix the first carbon-based conductive agent, the second carbon-based conductive agent, a solvent, and an adhesive to obtain a first conductive paste, and mix the third carbon-based conductive agent, the fourth carbon-based conductive agent, a solvent, and an adhesive to obtain a second conductive paste;

[0008] Coat the second conductive paste on the surface of the light foil, and obtain the second carbon-based conductive layer after drying; coat the first conductive paste on the surface of the second carbon-based conductive layer, and obtain the first carbon-based conductive layer after drying.

[0009] Preferably, the mass ratio of the third carbon-based conductive agent to the fourth carbon-based conductive agent in the second conductive paste is b, and the mass ratio of the first carbon-based conductive agent to the second carbon-based conductive agent in the first conductive paste is a; a and b satisfy the relationship a > b, and a / b ≤ 100.

[0010] Preferably, the range of a is 0.1 - 10, and the range of b is 0.1 - 10.

[0011] Preferably, the thickness of the first carbon-based conductive layer is greater than that of the second carbon-based conductive layer.

[0012] Preferably, the dimension refers to the dimension of the three-dimensional structure of the conductive agent particles; a point (without length, width, and height) is zero-dimensional; a straight line (only with length) is one-dimensional; a plane (with length and width) is two-dimensional; a solid (with length, width, and height) is three-dimensional.

[0013] Preferably, the zero-dimensional conductive agent refers to a dot-like particle conductive agent without internal pores, such as Super P, carbon black, and Ketjenblack; the one-dimensional conductive agent refers to a linear conductive agent, such as carbon nanotubes; the two-dimensional conductive agent refers to a conductive agent with a planar structure, such as graphene; the three-dimensional conductive agent refers to a conductive agent with a rich internal pore structure or a regular three-dimensional framework structure, such as activated carbon.

[0014] Preferably, the first carbon-based conductive agent and the third carbon-based conductive agent are one-dimensional, two-dimensional, or three-dimensional conductive agents, specifically any one of activated carbon, carbon nanotubes, and graphene; the second carbon-based conductive agent and the fourth carbon-based conductive agent are zero-dimensional, one-dimensional, or two-dimensional conductive agents, specifically any one of Super P, Ketjenblack, carbon black, carbon nanotubes, and graphene; the dimension of the third carbon-based conductive agent is greater than that of the fourth carbon-based conductive agent; the dimension of the first carbon-based conductive agent is greater than that of the second carbon-based conductive agent.

[0015] Preferably, the types of the first conductive agent and the third conductive agent are the same; the types of the second conductive agent and the fourth conductive agent are the same.

[0016] Preferably, the binder is any one or more of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polyethylene oxide, and water-based epoxy resin; the solvent is any one of ethanol, acetone, methanol, and deionized water; a dispersant can also be added to the first conductive paste and the second conductive paste, and the dispersant is any one or more of water-based sodium polyacrylate and polymethacrylate.

[0017] Preferably, since the function of the second carbon-based conductive layer is to establish a connection between the optical foil and the first carbon-based conductive layer, taking into account both the bonding strength and the consistency of the conductive network, its own conductivity is weaker than that of the first carbon-based conductive layer. Therefore, the thinner its thickness, the more beneficial it is to improve the overall conductivity of the conductive layer. However, it cannot be too thin, otherwise the bonding strength cannot be guaranteed.

[0018] Preferably, using the same conductive agent for the first carbon-based conductive layer and the second carbon-based conductive layer is more conducive to improving the compatibility during the double-layer coating process, enhancing the conductivity consistency in the thickness direction of the conductive layer, and also facilitating the reduction of the types of raw materials and the production costs of raw material and production line management.

[0019] A preparation method of a high-rate carbon-coated foil material includes the following steps:

[0020] Step 1: Mix a first carbon-based conductive agent, a second carbon-based conductive agent, a solvent, and an adhesive to obtain a first conductive paste, wherein the mass ratio of the first carbon-based conductive agent to the second carbon-based conductive agent in the first conductive paste is a; mix a third carbon-based conductive agent, a fourth carbon-based conductive agent, a solvent, and an adhesive to obtain a second conductive paste, wherein the mass ratio of the third carbon-based conductive agent to the fourth carbon-based conductive agent in the second conductive paste is b; a and b satisfy the relationship a > b and a / b ≤ 100;

[0021] Step 2: Coat the second conductive paste on the optical foil and dry it to obtain an intermediate foil material;

[0022] Step 3: Coat the first conductive paste on the intermediate foil material and dry it to obtain the finished product.

[0023] Preferably, in Step 1, the mass ratio of the first carbon-based conductive agent, the second carbon-based conductive agent, and the adhesive in the first conductive paste is (3 - 8):(1 - 4):(4 - 10), and the mass ratio of the third carbon-based conductive agent, the fourth carbon-based conductive agent, and the adhesive in the second conductive paste is (3 - 8):(1 - 4):(4 - 10).

[0024] Preferably, in step one, the mixing step of the first conductive paste is as follows: mix the first carbon-based conductive agent and the second carbon-based conductive agent according to a mass ratio of a, add 20 wt% of a solvent and perform low-speed kneading and stirring, stirring at a revolution speed of 20 - 40 r / min and a rotation speed of 1000 - 1800 r / min for 90 min - 150 min; then add a binder and 40 wt% of a solvent and perform low-speed kneading and stirring, stirring at a revolution speed of 20 - 40 r / min and a rotation speed of 1000 - 1800 r / min for 60 min - 90 min; then add 40 wt% of a solvent and perform high-speed dispersion stirring, stirring at a revolution speed of 35 - 50 r / min and a rotation speed of 2000 - 3500 r / min for 60 min - 90 min; the mixing step of the second conductive paste is as follows: mix the third carbon-based conductive agent and the fourth carbon-based conductive agent according to a mass ratio of b, add 20 wt% of a solvent and perform low-speed kneading and stirring, stirring at a revolution speed of 20 - 40 r / min and a rotation speed of 1000 - 1800 r / min for 90 min - 150 min; then add a binder and 40 wt% of a solvent and perform low-speed kneading and stirring, stirring at a revolution speed of 20 - 40 r / min and a rotation speed of 1000 - 1800 r / min for 60 min - 90 min; then add 40 wt% of a solvent and perform high-speed dispersion stirring, stirring at a revolution speed of 35 - 50 r / min and a rotation speed of 2000 - 3500 r / min for 60 min - 90 min.

[0025] Advantages of the present invention:

[0026] The present invention prepares a high-rate carbon-coated foil, which includes a light foil, a second carbon-based conductive layer formed on the surface of the light foil, and a first carbon-based conductive layer formed on the surface of the second carbon-based conductive layer. The specific steps are as follows: mix and stir the first carbon-based conductive agent, the second carbon-based conductive agent, an adhesive, and a solvent to prepare the first conductive paste; mix and stir the third carbon-based conductive agent, the fourth carbon-based conductive agent, an adhesive, and a solvent to prepare the second conductive paste; coat the second conductive paste on the light foil and dry it to obtain an intermediate foil; then coat the first conductive paste on the intermediate foil and dry it to obtain the finished product.

[0027] The characteristics of the present invention are that conventional carbon-coated foils usually select a single one-dimensional conductive agent to prepare conductive paste for coating. For example, when using carbon black alone, the conductivity of the prepared carbon-coated aluminum foil and the bonding strength with the electrode material cannot meet the requirements of high-rate fast-charging batteries. However, the carbon-coated foil prepared by this solution includes two conductive agents of different dimensions. After the two conductive agents of different dimensions are blended, a three-dimensional conductive network can be formed, and its conduction path is shorter, and the electron transport ability is significantly improved. On this basis, this solution sets the conductive layer as a double-layer structure, including a second carbon-based conductive layer formed on the surface of the light foil and a first carbon-based conductive layer formed on the surface of the second carbon-based conductive layer.

[0028] In the first carbon-based conductive layer, the proportion of the carbon-based conductive agent with a higher dimension is higher, making the porosity of the upper conductive layer higher and the surface roughness higher. During the process of coating the electrode material on its surface, the leveling performance and wetting performance of the electrode paste are both excellent, and the bonding strength between the conductive layer and the electrode material layer is higher than that of the conventional carbon-coated foil. At the same time, due to the good wetting effect of the electrode material during the coating process, the electrode material particles and the electrode conductive material after coating can be interlocked with the three-dimensional pores in the conductive layer, and the electrode conductive material can establish a conductive channel with the three-dimensional conductive network in the conductive layer, shortening the conduction path and having excellent rate performance.

[0029] The proportion of the carbon-based conductive agent with a higher dimension in the second carbon-based conductive layer should not be too high because the carbon-based conductive agents with a higher dimension are prone to agglomeration due to the existence of van der Waals forces. The agglomeration causes them to be unable to form a uniform bonding network with the adhesive particles, and the adhesive particles themselves cluster together and cannot exert their original bonding effect. Since the bare foil itself has no adhesiveness, it will lead to insufficient bonding force between the lower conductive agent and the bare foil, and it is easy for the entire conductive layer to fall off from the bare foil. Therefore, in this solution, a lower conductive layer with a lower content of the carbon-based conductive agent with a higher dimension is first coated on the bare foil to ensure the bonding force between the lower conductive layer and the bare foil. Since the lower conductive layer contains a binder, when the upper conductive layer is coated on the surface of the lower conductive layer, it can maintain sufficient bonding strength with the upper conductive layer with a higher content of the carbon-based conductive agent with a higher dimension. Therefore, a and b satisfy the relationship a > b.

[0030] Secondly, since two conductive agents with different dimensions are selected in both the upper and lower conductive layers to construct the conductive network, the conductivity consistency of the conductive layer in the thickness direction can be better, and more electron transfer channels can be established from the bare foil to the electrode material layer. Therefore, on this basis, the difference between a and b of the first carbon-based conductive layer and the second carbon-based conductive layer should not be too large. If the difference is too large, it will lead to poor conductivity consistency between the upper and lower layers, resulting in a decrease in compatibility when coating the second carbon-based conductive layer, resulting in too large an interfacial impedance between the upper and lower conductive layers and affecting the performance of the foil. Therefore, a / b ≤ 100.

[0031] In addition, the slurry preparation methods for both the first carbon-based conductive layer and the second carbon-based conductive layer are selected as the step-by-step kneading preparation method. Since the particle size of the carbon-based conductive agent is usually very small and prone to agglomeration, kneading is carried out under a high solid content to make the conductive agents fully uniform and interlocked and wound with each other. Then, a binder and a dispersant are introduced for homogenization, which can improve the uniformity of the slurry. This is not only beneficial to improving the slurry stability and avoiding sedimentation during the use of the slurry, but also more conducive to establishing a more uniform and highly consistent three-dimensional conductive network of the conductive layer, reducing the risk of local lithium plating in the manufactured battery.

[0032] In summary, on the basis of ensuring the peel strength between the conductive layer and the optical foil, the present solution effectively improves the bonding force between the conductive layer of the carbon-coated foil and the electrode material layer, increases the conductive path between the conductive layer and the electrode material layer, and obtains a carbon-coated foil with high rate performance. The battery made of this foil has good rate performance and service life. Detailed implementation mode

[0033] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] Source of raw materials:

[0035] The foil material selects 12μm aluminum foil; carbon nanotubes with a diameter of 20nm and a length of 10μm; Super P with a particle size of 40nm; graphene with a particle size of 40nm; water-based epoxy resin provided by Foshan Juntu New Materials Co., Ltd., model JT-801; water-based sodium polyacrylate provided by Dutch Solpro Solewend Company, model AD20.

[0036] Example 1: Step 1: Mix the first carbon-based conductive agent carbon nanotubes and the second carbon-based conductive agent Super P according to a mass ratio of a, add 20wt% deionized water and perform low-speed kneading and stirring, and stir at a speed of 40r / min for revolution and 1800r / min for rotation for 150min; then add the binder water-based epoxy resin and 40wt% solvent deionized water and perform low-speed kneading and stirring, and stir at a speed of 40r / min for revolution and 1800r / min for rotation for 90min; then add 40wt% solvent deionized water and perform high-speed dispersion stirring, and stir at a speed of 50r / min for revolution and 3500r / min for rotation for 90min to obtain the first conductive paste, and the solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent carbon nanotubes, the second carbon-based conductive agent Super P and the adhesive water-based epoxy resin is 3:2:5, and a = 1.5;

[0037] Mix the third carbon-based conductive agent, carbon nanotubes, and the fourth carbon-based conductive agent, SuperP, in a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the second conductive paste, and the solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, SuperP, and the water-based epoxy resin binder is 2:3:5, and b = 0.67;

[0038] Step 2: Coat the second conductive paste on the light foil and dry it to obtain the intermediate foil;

[0039] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thicknesses of the first and second carbon-based conductive layers in any one conductive layer are both 0.25 μm.

[0040] Example 2: Change the thickness of the first carbon-based conductive layer to 0.4 μm and the thickness of the second carbon-based conductive layer to 0.1 μm, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Mix the first carbon-based conductive agent, carbon nanotubes, and the second carbon-based conductive agent, Super P, in a mass ratio of a, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the first conductive paste, and the solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 3:2:5, and a = 1.5;

[0041] Mix the third carbon-based conductive agent, carbon nanotubes, and the fourth carbon-based conductive agent, Super P, in a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the second conductive paste, and the solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 2:3:5, and b = 0.67;

[0042] Step 2: Coat the second conductive paste on the light foil and dry it to obtain the intermediate foil;

[0043] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thickness of the first carbon-based conductive layer in any one conductive layer is 0.4 μm, and the thickness of the second carbon-based conductive layer is 0.1 μm.

[0044] Example 3: Replace the two conductive agents in the first conductive paste with graphene and carbon nanotubes, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Mix the first carbon-based conductive agent, graphene, and the second carbon-based conductive agent, carbon nanotubes, in a mass ratio of a, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the first conductive paste, and the solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 3:2:5, and a = 1.5;

[0045] Mix the third carbon-based conductive agent, carbon nanotubes, and the fourth carbon-based conductive agent, Super P, in a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a revolution speed of 40 r / min and a rotation speed of 1800 r / min for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a revolution speed of 40 r / min and a rotation speed of 1800 r / min for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a revolution speed of 50 r / min and a rotation speed of 3500 r / min for 90 min to obtain the second conductive paste, and the solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 2:3:5, and b = 0.67;

[0046] Step 2: Coat the second conductive paste on the light foil and dry it to obtain an intermediate foil;

[0047] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thicknesses of the first and second carbon-based conductive layers in any one conductive layer are both 0.25 μm.

[0048] Example 4: Add the dispersant, water-based sodium polyacrylate, to the first conductive paste and the second conductive paste, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Mix the first carbon-based conductive agent, carbon nanotubes, and the second carbon-based conductive agent, Super P, in a mass ratio of a, add 20 wt% deionized water, and perform low-speed kneading and stirring at a revolution speed of 40 r / min and a rotation speed of 1800 r / min for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a revolution speed of 40 r / min and a rotation speed of 1800 r / min for 90 min; then add 40 wt% solvent deionized water and the dispersant, water-based sodium polyacrylate, and perform high-speed dispersion stirring at a revolution speed of 50 r / min and a rotation speed of 3500 r / min for 90 min to obtain the first conductive paste, and the solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, the water-based epoxy resin binder, and the dispersant, water-based sodium polyacrylate, is 3:2:4.5:0.5, and a = 1.5;

[0049] Mix the third carbon-based conductive agent, carbon nanotubes, and the fourth carbon-based conductive agent, Super P, in a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent, deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and the dispersant, water-based sodium polyacrylate, and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the second conductive paste. The solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, the water-based epoxy resin as the binder, and the water-based sodium polyacrylate as the dispersant is 2:3:4.5:0.5, and b = 0.67;

[0050] Step 2: Coat the second conductive paste on the light foil and dry it to obtain an intermediate foil;

[0051] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thickness of the first and second carbon-based conductive layers in any one conductive layer is 0.25 μm.

[0052] Example 5: Change the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin as the binder in the first conductive paste to 4:1:5; change the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin as the binder in the second conductive paste to 1:4:5, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Mix the first carbon-based conductive agent, carbon nanotubes, and the second carbon-based conductive agent, Super P, in a mass ratio of a, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent, deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the first conductive paste. The solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin as the binder is 4:1:5, and a = 4;

[0053] Mix the third carbon-based conductive agent, carbon nanotubes, and the fourth carbon-based conductive agent, Super P, in a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% of the solvent, deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% of the solvent, deionized water, and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the second conductive paste, and the solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 1:4:5, and b = 0.25;

[0054] Step 2: Coat the second conductive paste on the light foil and dry it to obtain the intermediate foil;

[0055] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thickness of the first and second carbon-based conductive layers in any one conductive layer is 0.25 μm.

[0056] Example 6: Change the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin binder in the first conductive paste to 10:1:10; change the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder in the second conductive paste to 1:10:10, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Mix the first carbon-based conductive agent, carbon nanotubes, and the second carbon-based conductive agent, Super P, in a mass ratio of a, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% of the solvent, deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% of the solvent, deionized water, and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the first conductive paste, and the solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 10:1:10, and a = 10;

[0057] Mix the third carbon-based conductive agent, carbon nanotubes, and the fourth carbon-based conductive agent, Super P, in a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the second conductive paste. The solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 1:10:10, and b = 0.1;

[0058] Step 2: Coat the second conductive paste on the light foil and dry it to obtain the intermediate foil;

[0059] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thickness of the first and second carbon-based conductive layers in any one conductive layer is 0.25 μm.

[0060] Comparative Example 1: Change the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin binder in the first conductive paste to 2:3:5; change the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder in the second conductive paste to 3:2:5, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Mix the first carbon-based conductive agent, carbon nanotubes, and the second carbon-based conductive agent, Super P, in a mass ratio of a, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the first conductive paste. The solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 2:3:5, and a = 0.67;

[0061] Mix the third carbon-based conductive agent, carbon nanotubes, and the fourth carbon-based conductive agent, Super P, in a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the second conductive paste. The solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 3:2:5, and b = 1.5;

[0062] Step 2: Coat the second conductive paste on the light foil and dry it to obtain an intermediate foil;

[0063] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thickness of the first and second carbon-based conductive layers in any one conductive layer is 0.25 μm.

[0064] Comparative Example 2: Change the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin binder in the first conductive paste to 3:2:5; change the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder in the second conductive paste to 3:2:5, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Mix the first carbon-based conductive agent, carbon nanotubes, and the second carbon-based conductive agent, Super P, in a mass ratio of a, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the first conductive paste. The solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent, carbon nanotubes, the second carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 3:2:5, and a = 1.5;

[0065] Mix the third carbon-based conductive agent, carbon nanotubes, and the fourth carbon-based conductive agent, Super P, in a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the second conductive paste, and the solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent, carbon nanotubes, the fourth carbon-based conductive agent, Super P, and the water-based epoxy resin binder is 3:2:5, and b = 1.5;

[0066] Step 2: Coat the second conductive paste on the light foil and dry it to obtain the intermediate foil;

[0067] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thickness of the first and second carbon-based conductive layers in any one conductive layer is 0.25 μm.

[0068] Comparative Example 3: Replace the double-layer conductive layer with a single-layer conductive layer, and only one type of conductive agent is used in the single-layer conductive layer, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Perform low-speed kneading and stirring on the conductive agent Super P and 20 wt% deionized water at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder, water-based epoxy resin, and 40 wt% solvent deionized water and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the conductive paste, and the solid content of the conductive paste is 10%; in this step, the mass ratio of the conductive agent Super P and the water-based epoxy resin binder is 1:1;

[0069] Step 2: Coat the conductive paste on the light foil and dry it to obtain the finished product; both sides of the light foil are coated with a conductive layer, and the thickness of the conductive layer in any one conductive layer is 0.25 μm.

[0070] Comparative Example 4: The mass ratio of the first carbon-based conductive agent carbon nanotubes, the second carbon-based conductive agent Super P, and the binder aqueous epoxy resin in the first conductive paste was changed to 15:1:15; the mass ratio of the third carbon-based conductive agent carbon nanotubes, the fourth carbon-based conductive agent Super P, and the binder aqueous epoxy resin in the second conductive paste was changed to 1:15:15, and the rest was the same as in Example 1. The specific steps are as follows: Step 1: Mix the first carbon-based conductive agent carbon nanotubes and the second carbon-based conductive agent Super P according to a mass ratio of a, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder aqueous epoxy resin and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the first conductive paste, and the solid content of the first conductive paste is 10%; in this step, the mass ratio of the first carbon-based conductive agent carbon nanotubes, the second carbon-based conductive agent Super P, and the binder aqueous epoxy resin is 15:1:15, and a = 15;

[0071] Mix the third carbon-based conductive agent carbon nanotubes and the fourth carbon-based conductive agent Super P according to a mass ratio of b, add 20 wt% deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 150 min; then add the binder aqueous epoxy resin and 40 wt% solvent deionized water, and perform low-speed kneading and stirring at a speed of 40 r / min for revolution and 1800 r / min for rotation for 90 min; then add 40 wt% solvent deionized water and perform high-speed dispersion stirring at a speed of 50 r / min for revolution and 3500 r / min for rotation for 90 min to obtain the second conductive paste, and the solid content of the second conductive paste is 10%; in this step, the mass ratio of the third carbon-based conductive agent carbon nanotubes, the fourth carbon-based conductive agent Super P, and the binder aqueous epoxy resin is 1:15:15, and b = 0.07;

[0072] Step 2: Coat the second conductive paste on the light foil and dry it to obtain an intermediate foil;

[0073] Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain a finished product; both sides of the light foil are coated with a conductive layer, and the thickness of the first and second carbon-based conductive layers on either side of the conductive layer is 0.25 μm.

[0074] Detection test:

[0075] Peeling force test: Place the supporting steel plate on the sample foil, and use a utility knife to cut out a sample piece of 125 mm * 50 mm; Take a 3M double-sided tape with a width of 20 mm and a length of 125 mm, and paste it on the steel plate; Paste the sample piece on the steel plate through the 3M tape, and roll it back and forth with a pressure roller 2 times; Use a paper cutter to cut out a strip of paper with a length of 180 mm and a width of 15 mm. Take a 3M tape with a length of 110 mm and a width of 20 mm, paste the tape on the sample piece, and let one end of it stick to the strip of paper, and roll it back and forth with a pressure roller 2 times; Bend the strip of paper 180°, fix the test sample piece on the test fixture of the BLD-200H electronic peeling tester, fix the unfixed end of the strip of paper on the chuck, and conduct peeling; After the peeling is completed, the test results are obtained.

[0076] Battery preparation method: Preparation of the positive electrode: Double-sidedly coat the surface of the carbon-coated foil material prepared in the specific embodiment of the present invention with the positive electrode paste. The content of each component of the positive electrode paste is as follows: by mass fraction, 92 parts of lithium iron phosphate, 3 parts of carbon nanotubes, 2 parts of Super P, 3 parts of PVDF, and the solvent is NMP; The solid content of the positive electrode paste is 60%. Preparation of the negative electrode: Use a conventional pure copper foil with a thickness of 18 μm, and double-sidedly coat the surface of the copper foil with the negative electrode paste. The content of each component of the negative electrode paste is as follows: by mass fraction, 95 parts of graphite, 1 part of Super P, 2 parts of SBR, 2 parts of CMC, and the solvent is deionized water; The solid content of the negative electrode paste is 48%. The separator is a ceramic separator with a thickness of 9 μm. The electrolyte consists of 88 wt% of the solvent EC and 12 wt% of the solute LiFP. Both the positive and negative electrodes are coated, dried, die-cut, then laminated with the separator, and the electrolyte is injected to make a laminated soft-pack small battery.

[0077] Cycling performance test: At 25 °C, perform a cycling test on the battery to be tested according to the following procedure: Charge the sample battery after formation at a rate of 1C to full charge (i.e., constant current charge until 3.65V and then constant voltage charge until the current reaches 0.05C and then stop), and discharge to full (i.e., constant current discharge until 2.5V and then constant voltage discharge until the current reaches 0.05C and then stop). One charge-discharge cycle is one cycle. After 500 cycles, record its full charge capacity, divide it by its first full charge capacity, and the capacity retention rate after 500 cycles is obtained.

[0078] DC impedance test: At 25 °C, charge the battery to be tested to 50% SOC, discharge it at a current of 1C for 18 seconds, record the battery voltage U2, current I before the discharge stops, and the battery voltage U1 after the battery voltage stabilizes. Calculate according to the formula R = (U2 - U1) / I to obtain the DC internal resistance R. The results are shown in the following table:

[0079]

[0080]

[0081] Conclusion: Compared with Example 1:

[0082] In Example 2, the thickness ratio of the conductive layer is better, the peel strength is close, the internal resistance is lower, and the rate performance is better;

[0083] In Example 3, the dimension of the upper conductive agent is higher, the peel strength is close, the internal resistance is lower, and the rate performance is better;

[0084] In Example 4, a dispersant is added, the peel strength is better, the internal resistance is lower, and the rate performance and cycle performance are better;

[0085] In Examples 5 and 6, the a / b value gradually increases, the consistency between the upper and lower layers becomes worse, and the bonding at the interface between the upper and lower layers becomes worse, manifested as both the peel strength and the internal resistance becoming worse;

[0086] In Comparative Example 1, the a / b is too small, and both the peel strength and the internal resistance are very poor;

[0087] In Comparative Example 2, a / b is 1, and the peel strength and the internal resistance are not good;

[0088] Comparative Example 3 is a single-layer carbon-coated layer, with a large internal resistance and poor rate performance;

[0089] In Comparative Example 4, the a / b is too large, and both the peel strength and the internal resistance are very poor.

[0090] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0091] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention 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 perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high magnification carbon-coated foil, characterized in that: It includes a light foil and a conductive layer formed on the surface of the light foil; the conductive layer includes a second carbon-based conductive layer formed on the surface of the light foil and a first carbon-based conductive layer formed on the surface of the second carbon-based conductive layer; Mix the first carbon-based conductive agent, the second carbon-based conductive agent, a solvent, and an adhesive to obtain a first conductive paste, and mix the third carbon-based conductive agent, the fourth carbon-based conductive agent, a solvent, and an adhesive to obtain a second conductive paste; the mass ratio of the third carbon-based conductive agent to the fourth carbon-based conductive agent in the second conductive paste is b, and the mass ratio of the first carbon-based conductive agent to the second carbon-based conductive agent in the first conductive paste is a; a and b satisfy the relationship a > b and a / b ≤ 100; the first carbon-based conductive agent and the third carbon-based conductive agent are one-dimensional, two-dimensional, or three-dimensional conductive agents, specifically any one of activated carbon, carbon nanotubes, and graphene; the second carbon-based conductive agent and the fourth carbon-based conductive agent are zero-dimensional, one-dimensional, or two-dimensional conductive agents, specifically any one of Ketjen black, carbon black, carbon nanotubes, and graphene; the dimension of the third carbon-based conductive agent is greater than the dimension of the fourth carbon-based conductive agent; the dimension of the first carbon-based conductive agent is greater than the dimension of the second carbon-based conductive agent; the range of a is 0.1 - 10, and the range of b is 0.1 - 10; Coat the second conductive paste on the surface of the light foil and dry it to obtain a second carbon-based conductive layer; coat the first conductive paste on the surface of the second carbon-based conductive layer and dry it to obtain a first carbon-based conductive layer.

2. The high-rate carbon-coated foil according to claim 1, characterized in that: The thickness of the first carbon-based conductive layer is greater than that of the second carbon-based conductive layer.

3. The high-rate carbon-coated foil according to claim 1, characterized in that: The adhesive is any one or more of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polyethylene oxide, and water-based epoxy resin; the solvent is any one of ethanol, acetone, methanol, and deionized water; a dispersant is added to the first conductive paste and the second conductive paste, and the dispersant is any one or more of water-based sodium polyacrylate and polymethacrylate.

4. A preparation method of a high magnification carbon-coated foil, characterized in that: It includes the following steps: Step 1: Mix the first carbon-based conductive agent, the second carbon-based conductive agent, a solvent, and an adhesive to obtain a first conductive paste, where the mass ratio of the first carbon-based conductive agent to the second carbon-based conductive agent in the first conductive paste is a; mix the third carbon-based conductive agent, the fourth carbon-based conductive agent, a solvent, and an adhesive to obtain a second conductive paste, where the mass ratio of the third carbon-based conductive agent to the fourth carbon-based conductive agent in the second conductive paste is b; a and b satisfy the relationship a > b and a / b ≤ 100; The first carbon-based conductive agent and the third carbon-based conductive agent are one-dimensional, two-dimensional, or three-dimensional conductive agents, specifically any one of activated carbon, carbon nanotubes, and graphene; the second carbon-based conductive agent and the fourth carbon-based conductive agent are zero-dimensional, one-dimensional, or two-dimensional conductive agents, specifically any one of Ketjen black, carbon black, carbon nanotubes, and graphene; the dimension of the third carbon-based conductive agent is greater than the dimension of the fourth carbon-based conductive agent; the dimension of the first carbon-based conductive agent is greater than the dimension of the second carbon-based conductive agent; the range of a is 0.1 - 10, and the range of b is 0.1 - 10; Step 2: Coat the second conductive paste on the light foil and dry it to obtain an intermediate foil; Step 3: Coat the first conductive paste on the intermediate foil and dry it to obtain the finished product.

5. The preparation method of a high magnification carbon-coated foil according to claim 4, characterized in that: In Step 1, the mass ratio of the first carbon-based conductive agent, the second carbon-based conductive agent, and the binder in the first conductive paste is (3-8):(1-4):(4-10), and the mass ratio of the third carbon-based conductive agent, the fourth carbon-based conductive agent, and the binder in the second conductive paste is (3-8):(1-4):(4-10).

6. The preparation method of a high magnification carbon-coated foil according to claim 4, characterized in that: In Step 1, the mixing procedure of the first conductive paste is as follows: Mix the first carbon-based conductive agent and the second carbon-based conductive agent according to the mass ratio a, add 20 wt% of the solvent and conduct low-speed kneading and stirring at a speed of 20-40 r / min for revolution and 1000-1800 r / min for rotation for 90-150 min; then add the binder and 40 wt% of the solvent and conduct low-speed kneading and stirring at a speed of 20-40 r / min for revolution and 1000-1800 r / min for rotation for 60-90 min; then add 40 wt% of the solvent and conduct high-speed dispersion stirring at a speed of 35-50 r / min for revolution and 2000-3500 r / min for rotation for 60-90 min. The mixing procedure of the second conductive paste is as follows: Mix the third carbon-based conductive agent and the fourth carbon-based conductive agent according to the mass ratio b, add 20 wt% of the solvent and conduct low-speed kneading and stirring at a speed of 20-40 r / min for revolution and 1000-1800 r / min for rotation for 90-150 min; then add the binder and 40 wt% of the solvent and conduct low-speed kneading and stirring at a speed of 20-40 r / min for revolution and 1000-1800 r / min for rotation for 60-90 min; then add 40 wt% of the solvent and conduct high-speed dispersion stirring at a speed of 35-50 r / min for revolution and 2000-3500 r / min for rotation for 60-90 min.

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