Negative electrode edge coating emulsion, preparation method, negative electrode ceramic slurry, and negative electrode sheet

Abstract

The present invention belongs to the field of new energy materials. Disclosed is a negative electrode edge coating emulsion. The negative electrode edge coating emulsion is obtained by a free radical emulsion polymerization reaction of a soft monomer, a hard monomer and a functional monomer as reaction monomers in the presence of an emulsifier and an initiator, the weight of the emulsifier being equal to or less than 0.4 wt% of the total weight of the reaction monomers, and the weight of the functional monomer being equivalent to 5 wt%-15 wt% of the total weight of the reaction monomers. Compared with traditional emulsions, the present negative electrode edge coating emulsion has higher surface tension, and can be matched with negative electrode slurry having high surface tension when ceramic slurry is prepared from same according to a ratio, so as to achieve the purposes of no material blending and no interpenetration between the two materials, and an excellent overlapping performance. Moreover, the edge coating emulsion can provide good peeling force and achieve good bonding with separators. Further disclosed in the present invention are the use of the negative electrode edge coating emulsion, a negative electrode ceramic slurry, and a negative electrode sheet.

Description

A negative electrode edge-coated emulsion, its preparation method, a negative electrode ceramic slurry, and a negative electrode sheet.

[0001] This application claims priority to Chinese Patent Application No. 2024117319287, filed on November 29, 2024, entitled "A negative electrode edge-coated emulsion, preparation method, negative electrode ceramic slurry, and negative electrode sheet", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of new energy technology, and in particular to a negative electrode edge-coated emulsion and its preparation method, as well as a negative electrode ceramic slurry and a negative electrode sheet containing the edge-coated emulsion. Background Technology

[0003] With the increasing demand for lithium-ion batteries, people are paying more and more attention to their safety. Lithium crystals can form in lithium-ion batteries during repeated cycles, which may puncture the separator. This can lead to problems ranging from large voltage differences to short circuits. Therefore, it is necessary to introduce edge coating adhesive during the coating process in battery manufacturing.

[0004] Traditional electrode fabrication processes lack edge coating and involve direct cutting on copper foil, which can lead to misalignment or damage to the negative electrode material area. By introducing an edge coating agent blended with boehmite to create a negative electrode ceramic slurry, which is then coated onto the sides of the electrode, the equipment can automatically identify and cut the electrode during the cutting process.

[0005] Generally, negative electrode slurries have high surface tension, requiring matching edge coaters with high surface tension. If an edge coater with low surface tension is used, the negative electrode ceramic slurry will migrate towards the negative electrode slurry; this phenomenon is known as the Marangoni effect. However, the increase in surface tension and peel strength have opposite trends, creating a contradiction between the surface tension and peel strength of the edge coater. Peel strength is a crucial performance indicator for achieving adhesion between the edge coater and the separator, and the high surface tension of the edge coater is essential to ensure that the negative electrode ceramic slurry does not negatively impact the performance of the main material. Therefore, balancing the high surface tension and peel strength of the edge coater becomes a pressing technical problem to be solved. Summary of the Invention

[0006] The purpose of this application is to provide a negative electrode edge-coated emulsion, which has a higher surface tension than traditional emulsions. After preparing ceramic slurry according to the specified ratio, it can be matched with the high surface tension negative electrode slurry to achieve the purpose of preventing material flow and interpenetration between the two, and has excellent bonding performance. At the same time, the edge coating can provide good peel force and achieve good adhesion with the separator.

[0007] Meanwhile, the present invention also discloses the preparation method of the negative electrode edge-coated emulsion, the negative electrode ceramic slurry, and the negative electrode sheet.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A negative electrode edge-coated emulsion, wherein the negative electrode edge-coated emulsion is obtained by free radical emulsion polymerization in the presence of a soft monomer, a hard monomer, and a functional monomer as reactive monomers, under the condition of an emulsifier and an initiator;

[0010] The weight of the emulsifier is equal to or less than 0.4 wt% of the total weight of the reactive monomers;

[0011] The weight of the functional monomer is equivalent to 5 wt% to 15 wt% of the total weight of the reactive monomer;

[0012] The weight of the soft monomer is equivalent to 52 wt% to 72 wt% of the total weight of the reactive monomers;

[0013] The weight of the hard monomer is equivalent to 18 wt% to 36 wt% of the total weight of the reactive monomers;

[0014] The functional monomer contains at least one functional group selected from carboxyl, hydroxyl, and amide groups;

[0015] In this invention, some functional monomers are hard monomers or soft monomers. Unless otherwise specified, the aforementioned hard monomers and soft monomers do not contain functional monomers. Generally, both hard and soft monomers are preferably acrylate / methacrylate monomers, but other non-ester monomers such as styrene, acrylonitrile, and other oil-soluble monomers containing olefin bonds may also be included. In this invention, the reactive monomers may also include other monomers, such as crosslinking monomers.

[0016] In some embodiments of the present invention, the functional monomer is more preferably 10wt% to 15wt% or 5wt% to 10wt%.

[0017] This invention improves the surface tension of traditional edge-coating emulsions from 32 mN / m to about 40 mN / m through the following two core methods, so as to adapt to the surface tension of the negative electrode slurry while maintaining excellent peel strength.

[0018] 1. Reduce the amount of emulsifier. Studies have found that the less emulsifier used, the greater the surface tension. At the same time, reducing the amount of emulsifier will increase the instability of the emulsion, thereby reducing the peel force of the edge coating.

[0019] 2. To address the weakening of the peel strength of the edge coating due to the reduction in emulsifier dosage, a certain amount of functional monomers is used to improve this weakening trend.

[0020] Functional monomers contain amino, carboxyl, hydroxyl, and amide groups, which are polar groups. They increase the intermolecular interaction forces at the adhesive interface, improve interfacial adhesion conditions, and thus enhance interfacial adhesion. They also change the mechanical and rheological properties of the adhesive layer, such as increasing cohesive strength and elastic modulus, and raising the glass transition temperature and bulk viscosity. Therefore, under the premise of controlling the amount of emulsifier, using functional monomers is an effective means to improve the problem of weakened peel force caused by the reduction of surfactant.

[0021] Meanwhile, during the verification process of adjusting the dosage of functional monomers, it was further discovered that increasing the dosage of functional monomers leads to a slight increase in surface tension. Although the effect on surface tension is not as significant as that of emulsifiers, the appropriate dosage of functional monomers can effectively improve surface tension, although the mechanism is not yet clear.

[0022] In this invention, most of the functional monomers are water-soluble monomers, and a small portion are oil-soluble monomers.

[0023] In summary, this invention increases surface tension by reducing the amount of emulsifier and overcomes the weakening of peel force caused by the reduction in emulsifier dosage by using functional monomers. Ultimately, the negative electrode edge coating emulsion of this invention exhibits improved surface tension and good peel force when applied to negative electrode ceramic slurry.

[0024] In the above-mentioned negative electrode edge coating emulsion, the soft monomer is one or more of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, isooctyl acrylate, and lauryl acrylate.

[0025] The hard monomer is one or more of ethyl methacrylate, vinyl acetate, methyl methacrylate, styrene, and acrylonitrile;

[0026] The functional monomer is one or more of acrylic acid, acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N,N-dimethylacrylamide.

[0027] Regarding soft monomers and hard monomers, there is no strict definition in this field of the glass transition temperature boundary of linear polymers. Generally speaking, linear polymers obtained by polymerizing hard monomers have a higher glass transition temperature, while linear polymers obtained by polymerizing soft monomers have a lower glass transition temperature. Here, glass transition temperature generally refers to the glass transition temperature of simple linear polymers. Soft monomers are used in the coating field to provide adhesion, while hard monomers provide bonding force. In this invention, excessive soft monomers cause edge coating peeling and stringing, while excessive hard monomers cause the coating to become too hard. Excess of either type of monomer will lead to impaired peel force.

[0028] Preferably, the polymer content in the negative electrode edge coating emulsion is 20wt% to 24wt%; preferably, the weight ratio of the soft monomer to the hard monomer is 6:4 to 7:3.

[0029] In some embodiments of the present invention, the monomers used to prepare the polymer negative electrode edge-coating emulsion further include crosslinking monomers. The amount of crosslinking monomers used is equivalent to 0-0.4 wt% of the total weight of the soft monomer, the hard monomer, the functional monomer, and the crosslinking monomers; the polymer is a crosslinked polymer. Commonly used crosslinking monomers in the art are applicable in this invention, generally compounds with multiple double bonds, such as N,N-methylenebisacrylamide, divinylbenzene, dipropylene glycol diacrylate, etc. That is, in the above-mentioned negative electrode edge-coating emulsion, the polymer is a linear polymer or a crosslinked polymer; if it is a linear polymer, then a crosslinking monomer is not required; if it is a crosslinked polymer, then a crosslinking monomer is required.

[0030] In the above-mentioned negative electrode edge coating emulsion, the emulsifier is one or a combination of two of anionic surfactants and nonionic surfactants;

[0031] The anionic surfactant is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, and esterified polyoxyethylene alkyl ether.

[0032] The nonionic surfactant is one or more combinations of dodecylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and condensates of alkylphenol and ethylene oxide.

[0033] The emulsifier is present in an amount equivalent to 0.25 wt% to 0.4 wt% of the total weight of the reactants.

[0034] Generally, when most emulsifiers are controlled at 0.25wt% or higher, the stability of the emulsion system can be guaranteed. If the concentration is lower than this value, only a portion of the emulsifiers can maintain the stability of the emulsion, and most of the system is at risk of demulsification.

[0035] During the experiment, a high-performance emulsifier was screened out. This emulsifier is sodium dodecyl sulfate, and the weight of the emulsifier can be 0.1 wt% to 0.4 wt% of the total weight of the reactants.

[0036] Meanwhile, the present invention also discloses a method for preparing the above-mentioned negative electrode edge-coated emulsion, wherein the negative electrode edge-coated emulsion is obtained by free radical emulsion polymerization.

[0037] The method for free radical emulsion polymerization is as follows:

[0038] Step 1: Weigh water, a portion of emulsifier, and a portion of reactant monomers into a flask, stir, purge with nitrogen, and heat to 75-80°C. After the temperature stabilizes, begin adding a portion of the initiator solution, with a concentration of 1wt%-3wt%.

[0039] Step 2: Add the remaining emulsifier and remaining reactive monomers to water and stir to obtain a homogeneous pre-emulsion;

[0040] Step 3: After the reaction stabilizes, begin adding the pre-emulsion and part of the initiator solution dropwise;

[0041] Step 4: After the addition is complete, keep the reaction at a certain temperature for a period of time, raise the temperature to 80-90℃, and add the remaining initiator solution to eliminate residue;

[0042] Step 5: Neutralize the product with alkali to adjust the pH to 7-9, then filter to obtain the edge coating emulsion.

[0043] The monomer distribution ratio in steps 1 and 2 is 0.5:2.5 to 1:1; the initiator distribution ratio in steps 1 and 3 is 1:1 to 1:2.5; the amount of initiator in the initiator solution in step 4 is 5% to 15% of the total mass of the initiator; the emulsifier ratio in steps 1 and 2 is 0.5:2.5 to 1:1; a water-soluble initiator is selected, and its amount is controlled at 0.3% to 1% of the total weight of the reacting monomers; the dropping time in step 3 is 1 to 2 hours; the pre-emulsion and part of the initiator solution are added dropwise in step 3 0.5 to 1.5 hours after the reaction stabilizes.

[0044] In addition, the present invention also discloses a negative electrode ceramic slurry, comprising the negative electrode edge coating emulsion and boehmite as described above; the solid content of the negative electrode ceramic slurry is 35-45 wt%.

[0045] Finally, the present invention also discloses a negative electrode sheet, comprising a current collector, a negative electrode slurry coated on the center of one side surface of the current collector, and a negative electrode ceramic slurry as described above coated on the edge of one side surface of the current collector; there is an interface between the negative electrode slurry and the negative electrode ceramic slurry.

[0046] In embodiments of the present invention, relevant verifications were conducted using a negative electrode slurry with a surface tension of 40±2mN / m and the negative electrode ceramic slurry of the present invention. When the surface tension difference between the two is small, good interface clarity can be maintained. In several cases of the present invention, it is verified that the surface tension difference between the negative electrode ceramic slurry and the negative electrode slurry should not be greater than 6mN / m. More specifically, when the surface tension is lower than that of the negative electrode slurry, the difference should not be greater than 4mN / m, and when the surface tension is higher than that of the negative electrode slurry, the difference should not be greater than 6mN / m.

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] 1. This invention uses a suitable ratio of soft and hard monomers to ensure basic peel performance and the softness or hardness of the adhesive;

[0049] 2. By reducing the amount of emulsifier, the surface tension is increased to make the interface between the negative electrode ceramic slurry and the negative electrode slurry more clearly defined;

[0050] 3. By using a certain amount of functional monomers, the trend of decreased peel strength caused by reduced emulsifier dosage was reversed. Simultaneously, increasing the amount of functional monomers leads to an increase in surface tension. While its impact on surface tension is not as significant as that of surfactants, the appropriate use of functional monomers can effectively improve surface tension.

[0051] Through the above optimizations, the negative electrode edge-coating emulsion of the present invention, after being prepared into a negative electrode ceramic slurry, can maintain a clear interface with the negative electrode slurry, without problems such as cross-contamination, which is conducive to machine vision recognition for automated cutting, while ensuring the basic mechanical properties of the negative electrode ceramic slurry, such as peel strength. Attached Figure Description

[0052] Figure 1 shows a photograph of the overlap between the emulsion prepared in Comparative Example 1 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0053] Figure 2 shows a photograph of the overlap between the emulsion prepared in Comparative Example 2 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0054] Figure 3 is a photograph showing the overlap between the emulsion prepared in Example 1 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0055] Figure 4 is a photograph showing the overlap between the emulsion prepared in Example 2 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0056] Figure 5 shows a photograph of the overlap between the emulsion prepared in Comparative Example 3 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0057] Figure 6 shows a photograph of the overlap between the emulsion prepared in Comparative Example 4 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0058] Figure 7 is a photograph showing the overlap between the emulsion prepared in Example 3 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0059] Figure 8 is a photograph showing the overlap between the emulsion prepared in Example 4 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0060] Figure 9 is a photograph showing the overlap between the emulsion prepared in Example 5 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0061] Figure 10 shows a photograph of the overlap between the emulsion prepared in Comparative Example 5 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0062] Figure 11 is a photograph showing the overlap between the emulsion prepared in Comparative Example 6 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0063] Figure 12 is a photograph showing the overlap between the emulsion prepared in Example 6 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0064] Figure 13 is a photograph showing the overlap between the emulsion prepared in Example 7 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0065] Figure 14 is a photograph showing the overlap between the emulsion prepared in Example 8 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0066] Figure 15 is a photograph showing the overlap between the emulsion prepared in Example 9 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0067] Figure 16 is a photograph showing the overlap between the emulsion prepared in Example 10 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0068] Figure 17 is a photograph showing the overlap between the emulsion prepared in Example 11 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0069] Figure 18 is a photograph showing the overlap between the emulsion prepared in Example 12 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0070] Figure 19 is a photograph showing the overlap between the emulsion prepared in Example 13 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0071] Figure 20 is a photograph showing the overlap between the emulsion prepared in Example 14 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0072] Figure 21 is a photograph showing the overlap between the emulsion prepared in Example 15 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0073] Figure 22 is a photograph showing the overlap between the emulsion prepared in Example 16 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0074] Figure 23 shows a photograph of the overlap between the emulsion prepared in Comparative Example 7 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0075] Figure 24 shows a photograph of the overlap between the emulsion prepared in Comparative Example 8 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0076] Figure 25 is a photograph showing the overlap between the emulsion prepared in Example 17 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0077] Figure 26 is a photograph showing the overlap between the emulsion prepared in Example 18 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0078] Figure 27 is a photograph showing the overlap between the emulsion prepared in Example 19 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0079] Figure 28 shows a photograph of the overlap between the emulsion prepared in Comparative Example 9 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0080] Figure 29 is a photograph showing the overlap between the emulsion prepared in Example 20 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0081] Figure 30 is a photograph showing the overlap between the emulsion prepared in Example 21 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0082] Figure 31 is a photograph showing the overlap between the emulsion prepared in Example 22 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0083] Figure 32 is a photograph showing the overlap between the emulsion prepared in Example 23 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0084] Figure 33 is a photograph showing the overlap between the emulsion prepared in Example 24 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0085] Figure 34 is a photograph showing the overlap between the emulsion prepared in Example 25 and the negative electrode slurry after the emulsion was prepared into a negative electrode ceramic slurry.

[0086] Figure 35 is a schematic diagram of the negative electrode ceramic slurry and the negative electrode slurry layer in the background technology.

[0087] In Figure 35, 1. negative electrode sheet, 2. negative electrode slurry, 3. negative electrode ceramic slurry. Detailed Implementation

[0088] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0089] Part One explores the effects of emulsifier ratio and functional monomers on peel strength, surface tension, and overlap.

[0090] The preparation method of the negative electrode edge-coated emulsion of the present invention is as follows:

[0091] Step 1: Weigh deionized water, a portion of emulsifier, and a portion of monomer into a flask, stir, purge with nitrogen, and heat to approximately 80°C. After the temperature stabilizes, begin adding a portion of the initiator solution, with a concentration of 1.5 wt%.

[0092] Step 2: Add the remaining emulsifier and monomer to deionized water and stir thoroughly to obtain a uniform pre-emulsion;

[0093] Step 3: After the reaction has stabilized for 1 hour, start adding the pre-emulsion and part of the initiator solution dropwise, and complete the addition within 1.5 hours;

[0094] Step 4: After the addition is complete, keep the reaction at this temperature for 2 hours, then raise the temperature to 85°C and add the remaining initiator solution, which contains 0.1% of the total monomer mass, to eliminate residues; stop the reaction after 2 hours of residue elimination.

[0095] Step 5: Neutralize the product with sodium hydroxide to adjust the pH to 8, then filter to obtain the edge coating emulsion.

[0096] The types of emulsifiers and monomers used in the above methods are shown in Table 1 below;

[0097] In Examples 1 and 2 and Comparative Examples 1 and 2, the weight of deionized water in steps 1 and 2 was 315 g, and the deionized water ratio in steps 1 and 2 was 4:1; the total weight of all monomers was 100 g; the initiator was ammonium persulfate, with a weight of 1 g, and its ratio in steps 1 and 3 was 1:2.5; the amount of initiator in the initiator solution in step 4 was 10% of the total mass of the initiator; the emulsifier ratio in steps 1 and 2 was 0.5:2.5; and the monomer ratio in steps 1 and 2 was 0.5:2.5.

[0098] In Examples 3 to 5 and Comparative Examples 3 to 4, the weight of deionized water in steps 1 and 2 was 350g, and the ratio of deionized water in steps 1 and 2 was 4:1; the total weight of all monomers was 100g; the initiator was ammonium persulfate, and the weight of the initiator was 0.5g, with a ratio of 1:1 in steps 1 and 3; the ratio of emulsifier 1 in step 2 to emulsifier 1 was 1:2; and the ratio of monomers in steps 1 and 2 was 1:2.

[0099] In Examples 6 to 8 and Comparative Examples 5 to 6, the weight of deionized water in steps 1 and 2 was 400g, and the ratio of deionized water in steps 1 and 2 was 4:1; the total weight of all monomers was 100g; the initiator was ammonium persulfate, and the weight of the initiator was 0.3g, and its ratio in steps 1 and 3 was 1:1.5; the ratio of emulsifier 1 in steps 2 to emulsifier 1 was 1:1; and the ratio of monomers in steps 1 and 2 was 1:1.

[0100] In Table 1 below, the weight ratio of SR-10 to OP10 in the compound emulsifier SR-10 / OP10 is 2:1; emulsifier OP-10: condensate of alkylphenol and ethylene oxide; SR-10: esterified polyoxyethylene alkyl ether.

[0101] Table 1 Formula Table (Unit: g)

[0102] Part Two explores the effects of soft and hard monomers on peel force, surface tension, and overlap.

[0103] The preparation method is the same as in Part 1. In this part, the functional monomers are acrylamide and acrylic acid, and the total amount of the two is 10 wt% of the total monomers. In this part, the parameters such as the proportion of functional monomers, the type and amount of initiator, and the amount of water are the same as in Example 4. The types and amounts of soft monomers and hard monomers are changed in this part, and can be found in Table 2.

[0104] Table 2 Formula Table Unit: g

[0105] Part Three explores the influence of the ratio of soft to hard monomers on peel force, surface tension, and overlap.

[0106] The process in this section is the same as in the first section, and the formulation is largely the same as in Example 4, except that the ratio of butyl acrylate to methyl methacrylate is different. Refer to Table 3 for the formulation; the total amount of butyl acrylate and methyl methacrylate is 90 wt% of the total monomers.

[0107] Table 3 Formula Table (Unit: g)

[0108] Part IV explores the effects of the proportion of functional monomers on peel force, surface tension, and overlap.

[0109] The process in this section is the same as in the first section; the amount and type of emulsifier and water remain unchanged; the remaining variables are detailed in Table 4 below.

[0110] Table 4 Formula Table (Unit: g)

[0111] Part 5 explores the effects of the ratio of crosslinking monomers on peel force, surface tension, and overlap.

[0112] The process in this part is the same as in the first part, and the formula is generally the same as in Example 4. The difference is that this part adds crosslinking monomers based on Example 4. The specific selection of the type and amount of crosslinking monomers (equivalent to the percentage of soft monomers, hard monomers, functional monomers, and the total weight of crosslinking monomers) is shown in Table 5 below.

[0113] Table 5 Formula Table (Unit: g)

[0114] Performance testing

[0115] The preparation method and peel strength performance test of the negative electrode ceramic slurry are as follows:

[0116] The negative electrode edge coating emulsion is mixed with boehmite to form a negative electrode ceramic slurry with a solid content of 45 wt%; the solid content mentioned here refers to the content of boehmite, polymer and other substances.

[0117] The negative electrode ceramic slurry was coated onto copper foil and baked in an oven at 110°C for 20 minutes. It was then hot-pressed with a diaphragm at 100°C and 2MPa for 1 minute, and the peel strength was tested.

[0118] Preparation of negative electrode slurry: Graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black (Super P) were mixed in a mass ratio of 96:1.2:1.8:1, deionized water was added as a solvent, and the mixture was prepared into a slurry with a solid content of 50wt%. The negative electrode slurry was obtained by stirring it evenly in a vacuum mixer.

[0119] The negative electrode slurry (surface tension approximately 40±1 mN / m) and the negative electrode ceramic slurry are overlapped according to the following method:

[0120] A drop of the negative electrode slurry the size of a one-yuan coin is placed in the container. A drop of the same size of negative electrode ceramic slurry is then placed 0.5 cm from the edge of the negative electrode slurry. The timer is set for 3 minutes once the edges of the two slurries begin to contact. Observe whether there is any boundary shifting or spreading when the two slurries come into contact. If either problem occurs, it indicates material cross-contamination; if no problem occurs, it indicates excellent bonding performance. Refer to Figure 35 and Figures 1 to 34. In Figure 35, the negative electrode sheet is labeled 1, the negative electrode slurry (black in production) is 2, and the negative electrode ceramic slurry (white in production) is 3. Figure 30 shows the arrangement relationship between the negative electrode slurry and the negative electrode ceramic slurry. By visually identifying the intersection of the two, the equipment can perform automated cutting. Correspondingly, in Figures 1 to 34, the background is the copper electrode sheet, the white slurry is the negative electrode ceramic slurry, and the black slurry is the negative electrode slurry layer.

[0121] The bonding performance between the negative electrode slurry and the negative electrode ceramic slurry was observed.

[0122] The test results for Parts 1 to 5 above are shown in Table 6 below;

[0123] Table 6 Test Results

[0124] Results analysis:

[0125] 1. Referring to Examples 1 to 8 and Comparative Examples 1 to 6, it can be seen that the amount of emulsifier is the core factor affecting surface tension; when the amount of emulsifier is less than 0.4%, the surface tension is greater than 38 mN / m; in a few cases, when the amount of emulsifier reaches 0.5%, a large surface tension can still be maintained, such as in Comparative Example 6.

[0126] The effect of preventing penetration and cross-contamination is shown in Figures 1 to 14. From the results in Figures 1 to 14, it can be seen that as the amount of emulsifier decreases, the interface becomes clearer. Meanwhile, as can be seen from the above examples and comparative examples, as the amount of emulsifier decreases, the peel strength shows a significant decreasing trend. 2. As can be seen from Examples 9 to 13, by using appropriate proportions of soft and hard monomers, various selectable soft and hard monomers, under suitable formulation conditions, can achieve generally good peel strength and surface tension.

[0127] As can be seen from Figures 15 to 19, the interfaces of each sample are very clear, demonstrating excellent prevention of seepage and cross-contamination.

[0128] 3. As can be seen from Examples 14 to 16 and Example 4, the ratio of soft to hard monomers has a significant impact on peel strength, but little impact on surface tension, which can generally be maintained above 39 mN / m. In this invention, soft monomers provide adhesion, and hard monomers provide bonding strength. Excessive soft monomers lead to stringing during edge coating peeling, while excessive hard monomers result in overly hard coating. An excess of either monomer will impair peel strength.

[0129] As can be seen from Figures 20 to 22, the interfaces of each sample are very clear, demonstrating excellent prevention of seepage and cross-contamination.

[0130] 4. As can be seen from Examples 17 to 19, Example 4, and Comparative Examples 7 to 9, when the weight ratio of soft monomer to hard monomer is fixed, when the amount of functional monomer is reduced to 0, the peel force and surface tension are significantly reduced. When the amount of functional monomer is increased to 2.5 wt%, the surface tension is significantly improved and the interface is clear, but the improvement in peel force is still not obvious. When the amount of functional monomer is increased to 5 wt%, the peel force is improved to a certain extent, reaching 0.199 N / cm.

[0131] In Figures 23 to 31, Figure 23 shows a clear blurring of the interface, which further proves that the reduction of surface tension is the core reason for penetration and material cross-contamination.

[0132] In this invention, the functional monomers have the following functions: 1. They compensate for the decrease in peel strength caused by the reduction of emulsifier; 2. There is a correlation between the presence or absence of functional monomers and the surface tension. Changes in the amount of functional monomers have a significant impact on surface tension, but the impact is not enough to affect the clarity of the interface. As seen in Comparative Examples 7 to 9 and Examples 17 to 19, when the amount of functional monomers changes from 0 to 20, the peel strength undergoes a process of increase and decrease, with the optimal amount of functional monomers for peel strength being 10%. As seen in Examples 17, 20, and 21, the choice of functional monomer type has a significant impact on peel strength. From Comparative Examples 7 to 9 and Examples 17 to 19, the amount of functional monomers has little impact on the clarity of the interface.

[0133] 5. As can be seen from Examples 23 to 25 and Example 4, the use of crosslinking monomers can further improve the peeling force, without affecting the surface tension. The interface clarity of each sample is very good, and it has excellent effects in preventing penetration and cross-contamination.

[0134] Using Examples 1 and 2, and Comparative Examples 1 and 2 as a set of data, Figures 1 to 4 are explained. In Figure 1, the area of ​​white negative electrode ceramic slurry on the left side that cross-links and interpenetrates into the black negative electrode slurry on the right side accounts for approximately 3 / 4 of the area of ​​the black negative electrode slurry. In Figure 2, the area of ​​white negative electrode ceramic slurry on the left side that cross-links and interpenetrates into the black negative electrode slurry on the right side accounts for approximately 2 / 3 of the area of ​​the black negative electrode slurry. In Figure 3, the white negative electrode ceramic slurry on the left side slightly cross-links and interpenetrates into the black negative electrode slurry on the right side, but a relatively clear black-and-white boundary can be seen. In Figure 4, the white negative electrode ceramic slurry on the left side does not cross-link or interpenetrate into the black negative electrode slurry on the right side, and a clear black-and-white boundary exists between the two. The experimental phenomena in Figures 5 to 34 are basically consistent with those in Figures 1 to 4, all reflecting the degree of cross-linking and interpenetration and the black-and-white boundary of different groups of slurries. Specific details will not be elaborated further.

[0135] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A negative electrode edge-coated emulsion, characterized in that, The negative electrode edge-coated emulsion is obtained by free radical emulsion polymerization in the presence of emulsifiers and initiators, using soft monomers, hard monomers, and functional monomers as reactive monomers. The weight of the emulsifier is equal to or less than 0.4 wt% of the total weight of the reactive monomers; The weight of the functional monomer is equivalent to 5 wt% to 15 wt% of the total weight of the reactive monomer; The weight of the soft monomer is equivalent to 52 wt% to 72 wt% of the total weight of the reactive monomers; The weight of the hard monomer is equivalent to 18 wt% to 36 wt% of the total weight of the reactive monomers; The functional monomer contains at least one functional group selected from carboxyl, hydroxyl, and amide groups; the soft monomer is one or more selected from ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, isooctyl acrylate, and lauryl acrylate; the hard monomer is one or more selected from ethyl methacrylate, vinyl acetate, methyl methacrylate, styrene, and acrylonitrile.

2. The negative electrode edge-coated emulsion according to claim 1, characterized in that, The functional monomer is one or more of acrylic acid, acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N,N-dimethylacrylamide.

3. The negative electrode edge-coated emulsion according to claim 1, characterized in that, The polymer content in the negative electrode edge coating emulsion is 20wt% to 24wt%. The weight ratio of the soft monomer to the hard monomer is 6:4 to 7:

3.

4. The negative electrode edge-coated emulsion according to claim 1, characterized in that, The reactive monomer used to prepare the negative electrode edge-coated emulsion further includes a crosslinking monomer, and the amount of the crosslinking monomer is equivalent to 0 to 0.4 wt% of the total weight of the soft monomer, the hard monomer, the functional monomer, and the crosslinking monomer. The emulsifier is one or a combination of two of anionic surfactants and nonionic surfactants; The anionic surfactant is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, and esterified polyoxyethylene alkyl ether. The nonionic surfactant is one or more combinations of dodecylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and condensates of alkylphenol and ethylene oxide. The emulsifier is present in an amount equivalent to 0.25 wt% to 0.4 wt% of the total weight of the reactants.

5. The negative electrode edge-coated emulsion according to claim 1, characterized in that, The emulsifier is sodium dodecyl sulfate, and the weight of the emulsifier is equivalent to 0.1 wt% to 0.4 wt% of the total weight of the reactants.

6. A method for preparing a negative electrode edge-coated emulsion as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Weigh water, a portion of the emulsifier, and a portion of the reactant monomer into a flask, stir, purge with nitrogen, and heat to 75-80°C. After the temperature stabilizes, begin adding a portion of the initiator solution, the concentration of which is 1wt%-3wt%. Step 2: Add the remaining emulsifier and the remaining reactive monomer to water and stir to obtain a uniform pre-emulsion; Step 3: After the reaction stabilizes, begin adding the pre-emulsion and a portion of the initiator solution dropwise; Step 4: After the addition is complete, keep the reaction at a certain temperature for a period of time, raise the temperature to 80-90°C, and add the remaining initiator solution to eliminate residue; Step 5: Neutralize the product with alkali to adjust the pH to 7-9, then filter to obtain the edge coating emulsion.

7. The method for preparing the negative electrode edge-coated emulsion according to claim 6, characterized in that, The monomer distribution ratio in steps 1 and 2 is 0.5:2.5 to 1:1; the initiator solution distribution ratio in steps 1 and 3 is 1:1 to 1:2.5; the amount of initiator in the initiator solution in step 4 is 5% to 15% of the total mass of the initiator; the emulsifier distribution ratio in steps 1 and 2 is 0.5:2.5 to 1:1; the initiator is selected as a water-soluble initiator, and its amount is controlled at 0.3% to 1% of the total weight of the monomers; the dropping time in step 3 is 1 to 2 hours; the pre-emulsion and part of the initiator solution are added dropwise in step 3 0.5 to 1.5 hours after the reaction stabilizes.

8. A negative electrode ceramic slurry, characterized in that, It includes the negative electrode edge coating emulsion as described in any one of claims 1 to 5, and boehmite; the solid content of the negative electrode ceramic slurry is 35wt% to 45wt%.

9. A negative electrode sheet, characterized in that, It includes a current collector, a negative electrode slurry coated on the center of one side surface of the current collector, and a negative electrode ceramic slurry as described in claim 8 coated on the edge of one side surface of the current collector; there is an interface between the negative electrode slurry and the negative electrode ceramic slurry.

10. The negative electrode sheet according to claim 9, characterized in that, The surface tension of the negative electrode slurry is 38–42 mN / m, and the surface tension of the negative electrode ceramic slurry is 38–46 mN / m.

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