Aqueous binder for secondary battery electrode and use thereof

Abstract

The present invention relates to an aqueous binder for a secondary battery electrode and the use thereof, and belongs to the technical field of battery binders. The technical problem to be solved by the present invention is to provide an aqueous binder for a secondary battery electrode having both flexibility and adhesion performance. The binder comprises a graft polymer, having an acrylonitrile polymer as a main chain, which is grafted with acrylate latex particles, wherein the polymerization monomer of the acrylonitrile polymer comprises an acrylonitrile monomer and an acrylic monomer; and the polymerization monomer of the acrylate latex particles comprises a crosslinking monomer and a non-crosslinking monomer. The aqueous binder of the present invention has good flexibility and high adhesion performance to positive and negative electrodes. Therefore, it can be used in a positive electrode sheet or a negative electrode sheet of a secondary battery, effectively reducing the thickness rebound rate of the electrode sheet after being rolled and leaving to stand for 24 h, and improving the performance of the battery. Furthermore, the aqueous binder is environmentally friendly and has a simple preparation process. Therefore, large-scale and continuous production can be achieved, further reducing production costs and improving production efficiency.

Description

Water-based adhesives for secondary battery electrodes and their applications

[0001] Cross-references to related applications

[0002] This invention claims the benefit and priority of Chinese Patent Application CN2024107907066, filed on June 19, 2024, which is incorporated herein by reference in its entirety and for all other purposes. Technical Field

[0003] This invention relates to water-based adhesives for secondary battery electrodes and their applications, belonging to the field of battery adhesive technology. Background Technology

[0004] With the continuous development and widespread application of lithium battery technology, the requirements for electrode materials are becoming increasingly stringent. Traditional organic solvent-based electrode slurries pose safety hazards such as flammability, explosiveness, and toxicity, and their production process generates large amounts of waste gas, wastewater, and waste residue, causing serious environmental pollution. Therefore, developing an environmentally friendly, safe, and efficient aqueous electrode slurry preparation technology has become an urgent task.

[0005] One of the essential raw materials for aqueous electrode slurries is the aqueous binder. Using aqueous binders to prepare electrode slurries offers advantages such as environmental friendliness, safety, and high efficiency. Aqueous binders can influence the dispersibility and suspension of positive and / or negative electrode materials, as well as the adhesion of the active coating to the foil, thereby affecting the cell's expansion, internal resistance, and cycle life. Furthermore, aqueous binder technology can significantly reduce production costs, improve production efficiency, and further enhance the market competitiveness of lithium batteries.

[0006] Currently, commonly used water-based adhesives include sodium carboxymethyl cellulose (CMC), sodium polyacrylate (PAA), styrene-butadiene rubber (SBR), and styrene-acrylic rubber (SBR). Each polymer has its own application characteristics and shortcomings, and different types of water-based adhesives are often mixed and matched based on their performance. For example, when CMC and SBR are used together, the electrode is flexible and has excellent processing performance, but the coating has low adhesion to the foil and low cohesion between active materials, resulting in poor suppression of electrode volume changes and affecting cycle performance. When CMC and PAA are used together, the adhesion is high, the cell expansion is reduced, the internal resistance is low, and the cycle performance is even better, but the electrode is hard and brittle, leading to material loss and cracking during processing, ultimately affecting the cell manufacturing process. Although CMC, PAA, and SBR can meet the requirements of each process stage, they cannot fully utilize the advantages of PAA material, such as high adhesion, low internal resistance, and long cycle life. To address the issue that water-based adhesives cannot fully leverage the advantages of PAA materials when mixed, there is an urgent need to develop water-based PAA adhesives that combine flexibility and adhesion. Summary of the Invention

[0007] To address the above deficiencies, the technical problem solved by this invention is to provide a water-based adhesive for secondary battery electrodes that combines flexibility and adhesion.

[0008] The present invention relates to a water-based adhesive for secondary battery electrodes, comprising a grafted polymer, wherein the grafted polymer has an acrylonitrile polymer as the main chain and is grafted with acrylate latex particles; wherein the monomers of the acrylonitrile polymer include acrylonitrile monomers and acrylic monomers; the monomers of the acrylate latex particles include crosslinking monomers and non-crosslinking monomers, wherein the non-crosslinking monomers include acrylate monomers.

[0009] Acrylic latex particles account for 20-60% of the weight of the grafted polymer.

[0010] In some specific embodiments, the acrylonitrile monomers include at least one of acrylonitrile and methacrylonitrile; the acrylic monomers include at least one of acrylic acid, methacrylic acid, allyloxyhydroxypropyl sulfonic acid, vinyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, propylene sulfonic acid, methpropylene sulfonic acid, itaconic acid, maleic acid, β-acryloyloxypropionic acid, and 2-fluoroacrylic acid; the crosslinking monomers are substances with at least two double bonds, preferably including at least one of ethylene glycol dimethacrylate, ethylene glycol diacrylate, allyl methacrylate, allyl acrylate, N,N-methylenebisacrylamide, dicarboxylic acid dimethacrylate, glycerol dimethacrylate, glycidyl methacrylate, glycidyl methacrylate, glycidyl methacrylate, glycidyl methacrylate, ethylene glycol diacetoacetate diester of methacrylate, and divinylbenzene; the acrylate monomers include methyl acrylate and methacrylic acid. The following are at least one of the following: methyl methacrylate, ethyl acrylate, ethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, butyl acrylate, butyl methacrylate, n-octyl acrylate, isooctyl acrylate, isooctyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, octadecyl acrylate, octadecyl methacrylate, isobornyl acrylate, isobornyl methacrylate, propyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl methacrylate, hexadecyl acrylate, sulfonyl acrylate, sulfonyl methacrylate, glycidyl methacrylate, tert-butylaminoethyl methacrylate, dimethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, vinyl methacrylate, benzyl methacrylate, phenyl methacrylate, and hexadecyl methacrylate.

[0011] In one embodiment of the invention, the weight ratio of acrylonitrile monomers to acrylic monomers is 40–80:10–60. In a specific embodiment, the weight ratio of acrylonitrile monomers to acrylic monomers is 50:30.

[0012] In some embodiments of the present invention, the polymer monomers of the acrylonitrile polymer also include acrylamide monomers.

[0013] In some embodiments of the present invention, the acrylamide monomer is a substance containing a double bond and an amide group, including but not limited to at least one of acrylamide, methacrylamide, N-ethylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N-hydroxypropylacrylamide.

[0014] In some embodiments of the present invention, the weight ratio of acrylonitrile monomers, acrylic monomers and acrylamide monomers is 40-80:10-60:0-30.

[0015] In some embodiments of the present invention, the non-crosslinked monomer further includes at least one of acrylonitrile monomers and styrene monomers.

[0016] In some embodiments of the present invention, the styrene monomer includes at least one of styrene, p-fluorostyrene, methylstyrene, m-fluorostyrene, o-fluorostyrene, sodium styrene sulfonate, p-methoxystyrene, o-methylstyrene, and p-methylstyrene.

[0017] In some embodiments of the present invention, the secondary battery electrode uses an aqueous binder and also includes a solvent, wherein the solvent is water.

[0018] In one specific embodiment of the present invention, the secondary battery electrode uses an aqueous adhesive with a solid content of 12%, and its viscosity is 2000-200000 mPa·s when measured at 25°C.

[0019] The present invention also provides the application of the water-based adhesive described in the present invention in the preparation of positive or negative electrode sheets for secondary batteries.

[0020] The present invention provides a water-based adhesive for secondary battery electrodes, which has excellent flexibility and adhesion, and can be used in the preparation of positive or negative electrode sheets for secondary batteries.

[0021] The present invention also provides a positive electrode sheet for a secondary battery.

[0022] The positive electrode of the secondary battery of the present invention includes a current collector, a positive electrode active material coated on the current collector, and an adhesive, wherein the adhesive is an aqueous adhesive for the secondary battery electrode of the present invention.

[0023] In one embodiment of the present invention, the amount of adhesive is 1 to 3% of the weight of the coating layer. The coating layer referred to in the present invention refers to all substances coated on the surface of the current collector, calculated in terms of solid content.

[0024] In one specific embodiment, the amount of adhesive is 2% of the weight of the coating layer.

[0025] The present invention also provides a negative electrode sheet for a secondary battery.

[0026] The negative electrode sheet of the secondary battery of the present invention includes a current collector, a negative electrode active material coated on the current collector, and an adhesive, wherein the adhesive is the water-based adhesive for the secondary battery electrode of the present invention.

[0027] In one embodiment of the invention, the amount of adhesive is 1 to 3% of the weight of the coating layer. In a specific embodiment, the amount of adhesive is 2% of the weight of the coating layer.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention provides a water-based adhesive for secondary battery electrodes. It has good flexibility and high adhesion performance to both positive and negative electrodes. It can be used in the positive or negative electrode sheets of secondary batteries, effectively reducing the thickness rebound rate after the electrode sheets are rolled and left to stand for 24 hours, thereby improving the performance of the battery.

[0030] The present invention provides a water-based adhesive for the secondary battery electrode. This water-based adhesive is environmentally friendly and its preparation method is simple, enabling large-scale, continuous production, thereby further reducing production costs and improving production efficiency. Detailed Implementation

[0031] The present invention relates to a water-based adhesive for secondary battery electrodes, comprising a grafted polymer, wherein the grafted polymer has an acrylonitrile polymer as the main chain and is grafted with acrylate latex particles; wherein the monomers of the acrylonitrile polymer include acrylonitrile monomers and acrylic monomers; the monomers of the acrylate latex particles include crosslinking monomers and non-crosslinking monomers, wherein the non-crosslinking monomers include acrylate monomers.

[0032] Acrylic latex particles account for 20-60% of the weight of the grafted polymer.

[0033] The present invention provides a water-based adhesive for the secondary battery electrode, with a grafted polymer as the main component. The grafted polymer has an acrylonitrile polymer as the main chain and is grafted with acrylate latex particles, which can improve the flexibility of the adhesive and its adhesion to the positive and negative electrodes.

[0034] The grafted polymer of the present invention has an acrylonitrile polymer as the main chain, and the polymer monomers of the acrylonitrile polymer include acrylonitrile monomers and acrylic monomers.

[0035] Acrylonitrile monomers are substances containing double bonds and nitrile groups, including but not limited to at least one of acrylonitrile and methacrylonitrile.

[0036] Acrylic monomers include at least one of acrylic acid, methacrylic acid, allyloxyhydroxypropyl sulfonic acid, vinyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, propene sulfonic acid, methpropylene sulfonic acid, itaconic acid, maleic acid, β-acryloyloxypropionic acid, and 2-fluoroacrylic acid.

[0037] The ratio of acrylonitrile monomers to acrylic monomers can be conventional in the art. In one embodiment of the invention, the weight ratio of acrylonitrile monomers to acrylic monomers is 40–80:10–60. In a specific embodiment, the weight ratio of acrylonitrile monomers to acrylic monomers is 50:30.

[0038] In some embodiments of the present invention, the polymer monomers of the acrylonitrile polymer also include acrylamide monomers.

[0039] In some embodiments of the present invention, the acrylamide monomer is a substance containing a double bond and an amide group, including but not limited to at least one of acrylamide, methacrylamide, N-ethylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N-hydroxypropylacrylamide.

[0040] In some embodiments of the present invention, the weight ratio of acrylonitrile monomers, acrylic monomers and acrylamide monomers is 40-80:10-60:0-30.

[0041] Acrylic ester latex particles are tiny particles formed during emulsion polymerization. These particles are formed from monomers through free radical polymerization or ionic polymerization. In one embodiment of the present invention, the monomers for the acrylic ester latex particles include crosslinked monomers and non-crosslinked monomers, wherein the non-crosslinked monomers include acrylate monomers.

[0042] The crosslinking monomer is a substance with at least two double bonds, including but not limited to at least one of the following: ethylene glycol dimethacrylate, ethylene glycol diacrylate, allyl methacrylate, allyl acrylate, N,N-methylenebisacrylamide, dicarboxylic acid dimethacrylate, glycerol dimethacrylate, propylene oxide methacrylate, propylene oxide methacrylate, propylene oxide methacrylate, propylene oxide methacrylate, ethylene glycol diacetoacetate methacrylate, and divinylbenzene.

[0043] Acrylate monomers include at least one of the following: methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, butyl acrylate, butyl methacrylate, n-octyl acrylate, isooctyl acrylate, isooctyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, octadecyl acrylate, octadecyl methacrylate, isobornyl acrylate, isobornyl methacrylate, propyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl methacrylate, hexadecyl acrylate, sulfonyl acrylate, sulfonyl methacrylate, glycidyl methacrylate, tert-butylaminoethyl methacrylate, dimethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, vinyl methacrylate, benzyl methacrylate, phenyl methacrylate, and hexadecyl methacrylate.

[0044] In some embodiments of the present invention, the non-crosslinked monomer further includes at least one of acrylonitrile monomers and styrene monomers.

[0045] Styrene monomers include, but are not limited to, at least one of styrene, p-fluorostyrene, methylstyrene, m-fluorostyrene, o-fluorostyrene, sodium styrene sulfonate, p-methoxystyrene, o-methylstyrene, and p-methylstyrene.

[0046] The present invention provides a water-based adhesive for the secondary battery electrode, and also includes a solvent, wherein the solvent is water.

[0047] The water-based binder for the secondary battery electrode of the present invention may also include additives such as dispersants, leveling agents, and thickeners.

[0048] In one specific embodiment of the present invention, the secondary battery electrode uses an aqueous adhesive with a solid content of 12%, and its viscosity is 2000-200000 mPa·s when measured at 25°C.

[0049] The viscosity described in this invention was measured using a Brookfield DV2T viscometer at 25°C. Rotor type 64# was used, with speeds of 60 rpm (range 1000 mPa·s), 30 rpm (range 20000 mPa·s), 12 rpm (range 50000 mPa·s), 6 rpm (range 100000 mPa·s), and 3 rpm (range 200000 mPa·s). Suitable ranges were selected to ensure the test values ​​were between 10% and 100% of the range. Comparative Example 5 used a 61# rotor at 60 rpm (range 100 rpm). The secondary battery electrode of this invention uses a water-based binder, which can be prepared using conventional methods.

[0050] The water-based adhesive for the secondary battery electrode of this invention can be prepared using conventional methods. In some embodiments, the preparation method of the water-based adhesive for the secondary battery electrode of this invention includes the following steps:

[0051] The monomers of acrylonitrile polymers are thoroughly mixed with a solvent, and an initiator is added to initiate the reaction. After reacting for 5 to 15 hours, the monomers of acrylate latex particles and an emulsifier are added to continue the reaction until it ends. After neutralization, an aqueous adhesive for the secondary battery electrode is obtained.

[0052] In this method, the initiator can be a conventional initiator in the art, and the reaction temperature is related to the type of monomer, which can be obtained through conventional experiments. In one embodiment of the invention, the initiator is a peroxide, such as ammonium persulfate, and the reaction temperature is 60–80°C.

[0053] In the polymerization of polymer latex particles, an emulsifier needs to be added. Commonly used emulsifiers in the art are all suitable for this invention. In some embodiments of this invention, sodium dodecyl sulfate is selected as the emulsifier.

[0054] The present invention also provides the application of the water-based adhesive described in the present invention in the preparation of positive or negative electrode sheets for secondary batteries.

[0055] The present invention provides a water-based adhesive for secondary battery electrodes, which has excellent flexibility and adhesion, and can be used in the preparation of positive or negative electrode sheets for secondary batteries.

[0056] In one embodiment of the present invention, the positive electrode sheet is prepared by coating a positive electrode slurry onto a current collector. The positive electrode slurry is prepared by a positive electrode active material, a conductive agent, the binder of the present invention, and water. Commonly used positive electrode active materials are applicable to the present invention, including but not limited to lithium iron phosphate positive electrodes and lithium cobalt oxide positive electrodes.

[0057] In one embodiment of the present invention, the negative electrode sheet is prepared by coating a negative electrode slurry onto a current collector. The negative electrode slurry is prepared by a negative electrode active material, a conductive agent, CMC, the binder of the present invention, and water. Commonly used negative electrode active materials are applicable to the present invention, including but not limited to graphite negative electrodes, silicon-carbon negative electrodes, silicon-oxygen negative electrodes, and hard carbon negative electrodes.

[0058] The present invention also provides a positive electrode sheet for a secondary battery.

[0059] The positive electrode of the secondary battery of the present invention includes a current collector, a positive electrode active material coated on the current collector, and an adhesive, wherein the adhesive is an aqueous adhesive for the secondary battery electrode of the present invention.

[0060] The current collector can be a commonly used positive electrode current collector in the art, such as aluminum foil or carbon-coated aluminum foil. The positive electrode active material can also be a commonly used positive electrode active material in the art, including but not limited to lithium iron phosphate, lithium manganese iron phosphate, and ternary positive electrode materials.

[0061] The adhesive of this invention has excellent adhesion; therefore, a small amount can achieve a good bonding effect. In one embodiment of this invention, the amount of adhesive is 1-3% of the weight of the coating layer. The coating layer referred to in this invention refers to all substances coated on the surface of the current collector, calculated based on solid content.

[0062] In one specific embodiment, the amount of adhesive is 2% of the weight of the coating layer.

[0063] The present invention also provides a negative electrode sheet for a secondary battery.

[0064] The negative electrode sheet of the secondary battery of the present invention includes a current collector, a negative electrode active material coated on the current collector, and an adhesive, wherein the adhesive is the water-based adhesive for the secondary battery electrode of the present invention.

[0065] Commonly used negative electrode current collectors in this field are applicable to this invention, such as copper foil and carbon-coated copper foil. The negative electrode active material can also be commonly used in this field, including but not limited to graphite, hard carbon, and silicon-based materials.

[0066] In one embodiment of the invention, the amount of adhesive is 1 to 3% of the weight of the coating layer. In a specific embodiment, the amount of adhesive is 2% of the weight of the coating layer.

[0067] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0068] Example

[0069] 1) Add a measured amount of distilled water to a 5000mL four-necked flask, then add the acrylonitrile polymer monomers and mix thoroughly.

[0070] 2) Raise the temperature to the reaction temperature, add the initiator, and after reacting for 10 hours, add more initiator; and start adding the pre-emulsified mixture of the monomers of acrylate latex particles and the emulsifier dropwise.

[0071] 3) After the addition is complete, add the initiator, keep warm for 12 hours, discharge the material, neutralize it, and adjust the pH value to 6.5-9.0; filter the material to obtain the final product.

[0072] The monomers used and the polymerization conditions are shown in Table 1. The total amount of distilled water used was 2250 mL.

[0073] Table 1

[0074] Comparative Example 1

[0075] 1) Add a measured amount of distilled water to a 5000mL four-necked flask, then add the acrylonitrile polymer monomers and mix thoroughly.

[0076] 2) Raise the temperature to the reaction temperature, add the initiator, react for 10 hours, discharge the material, neutralize, and adjust the pH value to 6.5-9.0; filter and discharge the material to obtain the final product.

[0077] Comparative Example 2

[0078] 1) Add a measured amount of distilled water to a 5000mL four-necked flask, then add the acrylonitrile polymer monomers and mix thoroughly.

[0079] 2) Raise the temperature to the reaction temperature, add the initiator, and after reacting for 10 hours, add the initiator again; and start adding the pre-emulsified mixture of the monomers of acrylate latex particles and the emulsifier dropwise.

[0080] 3) After the addition is complete, add the initiator, keep warm for 12 hours, discharge the material, neutralize it, and adjust the pH value to 6.5-9.0; filter the material to obtain the final product.

[0081] Comparative Example 3

[0082] 1) Add a measured amount of distilled water to a 5000mL four-necked flask, then add the acrylonitrile polymer monomers and mix thoroughly.

[0083] 2) Raise the temperature to the reaction temperature, add the initiator, and after reacting for 10 hours, add the initiator again; and start adding the pre-emulsified mixture of the monomers of acrylate latex particles and the emulsifier dropwise.

[0084] 3) After the addition is complete, add the initiator, keep warm for 12 hours, discharge the material, neutralize it, and adjust the pH value to 6.5-9.0; filter the material to obtain the final product.

[0085] Comparative Example 4

[0086] 1) Add a measured amount of distilled water to a 5000mL four-necked flask, then add the acrylonitrile polymer monomers and mix thoroughly.

[0087] 2) Raise the temperature to the reaction temperature, add the initiator, and after reacting for 10 hours, add the initiator again; and start adding the pre-emulsified mixture of the monomers of acrylate latex particles and the emulsifier dropwise.

[0088] 3) After the addition is complete, add the initiator, keep warm for 12 hours, discharge the material, neutralize it, and adjust the pH value to 6.5-9.0; filter the material to obtain the final product.

[0089] Comparative Example 5

[0090] 1) Add a measured amount of distilled water to a 5000mL four-necked flask;

[0091] 2) Raise the temperature to the reaction temperature, add the initiator, and begin dropping in the pre-emulsified mixture of the monomers of the acrylate latex particles and the emulsifier;

[0092] 3) After the addition is complete, add the initiator, keep warm for 12 hours, discharge the material, neutralize it, and adjust the pH value to 6.5-9.0; filter the material to obtain the final product.

[0093] Comparative Example 6

[0094] The adhesive composition is 1.5% PAA + 0.5% SBR. (PAA brand: Meishan Indira LA136D, SBR brand: Japan Zeon BM-451B)

[0095] Comparative Example 7

[0096] The adhesives obtained from Comparative Example 1 and Comparative Example 5 were mixed at a solid mass ratio of 50.96%:49.04% to obtain a blended adhesive.

[0097] The performance of the adhesives in the above examples and comparative examples was measured, and the results are shown in Table 2.

[0098] Table 2

[0099] Solid content testing: The moisture content was measured using a moisture analyzer (LHS16-A, accuracy: 0.1 g, Shanghai Tianmei Balance Instrument Co., Ltd.). The moisture analyzer was set to a heating temperature of 115℃; the heating method was standard; and the termination method was automatic stop after 70 seconds.

[0100] Viscosity testing: A Brookfield DV2T viscometer was used at a temperature of 25℃. The rotor model was 64#. The speed ranges were 60 rpm (range 1000 mPa·s), 30 rpm (range 20000 mPa·s), 12 rpm (range 50000 mPa·s), 6 rpm (range 100000 mPa·s), and 3 rpm (range 200000). A suitable range was selected so that the test value was between 10% and 100% of the range. For comparative example 5, a 61# rotor was used at 60 rpm (range 100 rpm).

[0101] The flexibility of the adhesive film prepared in the examples was measured.

[0102] Film preparation: Lay the PET film flat on a clean glass plate, and drop an appropriate amount of ethanol between the PET film and the glass plate to facilitate tight adhesion. Use a disposable dropper to take 20 mL of the adhesive to be tested (i.e., the adhesive solution) after centrifugation and defoaming, and drop it onto the flat PET film. Adjust the thickness of the adjustable scraper according to the solid content of the adhesive solution to control the thickness of the adhesive solution after drying to 0.03±0.005 mm. Scrape the adhesive solution onto the PET film to form a uniform thickness. Then transfer the sample to a forced-air oven at 110℃ and bake for 60 min (the glass plate must be placed horizontally, otherwise the adhesive solution will flow during baking, causing uneven sample thickness). Peel the adhesive film off the PET film and place it in a 30% RH drying environment for equilibration for 30 min.

[0103] Mechanical performance testing: After drying, take a piece of film with uniform thickness and accurately cut it into strips 100mm long and 10mm wide using a double-edged blade; conduct the test according to standard GB / T528-2009, controlling the ambient temperature at 10~38℃ and the humidity at 20~30%RH; the power supply voltage fluctuation should not exceed ±10% of the rated voltage. The test results are shown in Table 3.

[0104] Table 3

[0105] It is evident that the greater the elongation at break of the adhesive film, the better the flexibility of the adhesive film. By comparing the data of the examples and comparative examples in the table above, it can be seen that Comparative Example 6 is the combination commonly used at present, indicating that the present invention can effectively increase the flexibility of PAA without the need to add SBR.

[0106] The adhesives of the examples and comparative examples were applied to the positive or negative electrode sheets of the battery, and the adhesion force of the adhesives of the examples and comparative examples to the positive and negative electrode sheets was measured.

[0107] Negative electrode slurry preparation: CMC, graphite, and conductive agent are added sequentially and dry-mixed with a double planetary mixer for 30 minutes. Water is added and kneaded for 1 hour. Then, binder is added and stirred for 6 hours. The viscosity is adjusted to a suitable slurry viscosity for coating. The slurry formula is as follows: by weight of solid content, graphite 96.5 parts, conductive agent sp 1.0 parts, binder 2.0 parts, and CMC 0.5 parts.

[0108] Preparation of positive electrode slurry: Lithium iron phosphate, conductive agent, binder, and water are added sequentially to control the solid content of the slurry to 60%, and stirred for 4 hours with a double planetary stirrer. The viscosity is adjusted to a suitable viscosity for coating. The slurry formula is: 96 parts lithium iron phosphate, 2 parts conductive agent (sp), and 2 parts binder by weight of solid content.

[0109] Electrode preparation: A small coating machine is used to coat the negative electrode slurry onto copper foil and the positive electrode slurry onto aluminum foil. After drying in an oven tunnel, the electrodes are cut using a cutting tool, weighed, and their areal density is calculated. Then, the electrodes are rolled to the compacted density using a roller press to obtain positive and negative electrode sheets. Specifically, the positive electrode sheet is obtained by scraping the positive electrode slurry, and the negative electrode sheet is obtained by scraping the negative electrode slurry.

[0110] Adhesion strength test method: Cut the electrode sheet into 40mm*100mm sizes, and firmly attach the coated side of the electrode sheet to a stainless steel plate with double-sided tape. Peel the electrode sheet 20-30mm off the stainless steel plate and fix it with tape, with the other end of the tape fixed between the upper and lower clamps and the steel plate. First, calibrate and zero the plate, set the test width, electrode sheet peeling length of 50mm, peeling speed of 20mm / min, and then start the test. The peel strength curve and average value can be obtained. When processing the data, delete the start and end segments of the test to obtain the standard curve. The adhesion strength is calculated using the formula: Adhesion strength = FN / 0.04, where FN is the average peel strength in N, and 0.04 is the average width of the electrode sheet in m.

[0111] Method for testing electrode thickness change rate after 24 hours of static storage: Use a 32×22mm sampler to take a sample and weigh it. Calculate the theoretical thickness under specified compaction using a formula. Turn on the roller press and feed the electrode into it for pressing. Measure the thickness of the pressed electrode and compare it with the theoretical thickness from the previous step. Adjust the roller gap of the roller press according to the actual situation based on the comparison results. Repeat the pressing and comparison process until the theoretical thickness is reached. Quickly use a micrometer to measure 6 points on the electrode where the error from the theoretical thickness is within ±3μm and mark them. Then, quickly place the electrode in the required environment. Measure the thickness after rebound and calculate the rebound rate at the electrode storage location within the specified time period. (Check that the micrometer is zeroed after each measurement to prevent measurement errors.)

[0112] Control the negative electrode surface density: 80-100 g / m³ 2 The compacted density is 1.65 g / cm³. 3 The surface density of the positive electrode is 230-240 g / m³. 2 The compacted density is 2.4 g / cm³. 3 The test results are shown in Table 4.

[0113] Table 4

[0114] By comparing the data of the above examples and comparative examples, Example 3 shows that the adhesion is at its highest value regardless of whether it is a positive or negative electrode, the rebound rate of the electrode sheet after rolling is low, and it also has flexibility. This example is the preferred example.

Claims

1. A water-based adhesive for secondary battery electrodes, characterized in that: Includes grafted polymers, wherein the grafted polymers are mainly composed of acrylonitrile polymers and grafted with acrylate latex particles; The monomers for the acrylonitrile polymers include acrylonitrile monomers and acrylic monomers; the monomers for the acrylate latex particles include crosslinking monomers and non-crosslinking monomers, wherein the non-crosslinking monomers include acrylate monomers. Acrylic latex particles account for 20-60% of the weight of the grafted polymer.

2. The aqueous adhesive for secondary battery electrodes according to claim 1, characterized in that: Acrylonitrile monomers include at least one of acrylonitrile and methacrylonitrile; Acrylic monomers include at least one of acrylic acid, methacrylic acid, allyloxyhydroxypropyl sulfonic acid, vinyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, propylene sulfonic acid, methpropylene sulfonic acid, itaconic acid, maleic acid, β-acryloyloxypropionic acid, and 2-fluoroacrylic acid. Crosslinking monomers are substances with at least two double bonds; Acrylate monomers include at least one of the following: methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, butyl acrylate, butyl methacrylate, n-octyl acrylate, isooctyl acrylate, isooctyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, octadecyl acrylate, octadecyl methacrylate, isobornyl acrylate, isobornyl methacrylate, propyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl methacrylate, hexadecyl acrylate, sulfonyl acrylate, sulfonyl methacrylate, glycidyl methacrylate, tert-butylaminoethyl methacrylate, dimethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, vinyl methacrylate, benzyl methacrylate, phenyl methacrylate, and hexadecyl methacrylate.

3. The aqueous adhesive for secondary battery electrodes according to claim 2, characterized in that: The crosslinking monomers include at least one of the following: ethylene glycol dimethacrylate, ethylene glycol diacrylate, allyl methacrylate, allyl acrylate, N,N-methylenebisacrylamide, dicarboxylic acid dimethacrylate, glycerol dimethacrylate, propylene oxide methacrylate, propylene oxide methacrylate, propylene oxide methacrylate, ethylene glycol diacetoacetate methacrylate, and divinylbenzene.

4. The aqueous adhesive for secondary battery electrodes according to claim 1, characterized in that: The weight ratio of acrylonitrile monomers to acrylic monomers is 40–80:10–60.

5. The aqueous adhesive for the secondary battery electrode according to claim 4, characterized in that: The weight ratio of acrylonitrile monomers to acrylic monomers is 50:

30.

6. The aqueous adhesive for secondary battery electrodes according to claim 1, characterized in that: The monomers for the polymerization of acrylonitrile polymers also include acrylamide monomers; The acrylamide monomers include at least one of acrylamide, methacrylamide, N-ethylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N-hydroxypropylacrylamide.

7. The aqueous adhesive for secondary battery electrodes according to claim 6, characterized in that: The weight ratio of acrylonitrile monomers, acrylic monomers, and acrylamide monomers is 40–80:10–60:0–30.

8. The aqueous adhesive for secondary battery electrodes according to claim 1, characterized in that: The non-crosslinked monomers also include at least one of acrylonitrile monomers and styrene monomers; The styrene monomers include at least one of styrene, p-fluorostyrene, methylstyrene, m-fluorostyrene, o-fluorostyrene, sodium styrene sulfonate, p-methoxystyrene, o-methylstyrene, and p-methylstyrene.

9. The aqueous adhesive for secondary battery electrodes according to claim 1, characterized in that: It also includes a solvent, wherein the solvent is water.

10. The aqueous adhesive for the secondary battery electrode according to claim 9, characterized in that: With a solid content of 12%, its viscosity is 2000~200000mPa·s when measured at 25℃.

11. The use of the water-based binder of any one of claims 1 to 10 in the preparation of positive or negative electrode sheets for secondary batteries.

12. A positive electrode sheet for a secondary battery, characterized in that: It includes a current collector, a positive electrode active material coated on the current collector, and an adhesive, wherein the adhesive is an aqueous adhesive for secondary battery electrodes as described in any one of claims 1 to 10.

13. The positive electrode of the secondary battery according to claim 12, characterized in that: The amount of adhesive is 1 to 3% of the weight of the coating layer.

14. The positive electrode of the secondary battery according to claim 13, characterized in that: The amount of adhesive is 2% of the weight of the coating layer.

15. A negative electrode sheet for a secondary battery, characterized in that: It includes a current collector, a negative electrode active material coated on the current collector, and an adhesive, wherein the adhesive is an aqueous adhesive for secondary battery electrodes as described in any one of claims 1 to 10.

16. The negative electrode sheet of the secondary battery according to claim 15, characterized in that: The amount of adhesive is 1 to 3% of the weight of the coating layer.

17. The negative electrode sheet of the secondary battery according to claim 16, characterized in that: The amount of adhesive is 2% of the weight of the coating layer.

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