Positive electrode edge coating protection hot-press adhesive, preparation therefor and use thereof

Abstract

The present application relates to the technical field of lithium battery materials and binders, and discloses a positive electrode edge coating protection hot-press adhesive, preparation therefor and a use thereof. The hot-press adhesive is obtained copolymerizing an acrylic monomer, an acrylate monomer, an oil-soluble monomer and a modified monomer in a solvent NMP, and the mass percentage content of each monomer is as follows: 5-12% of the acrylic monomer, 45-80% of the acrylate monomer, 10-40% of the oil-soluble monomer, and 1-10% of the modified monomer. The hot-press adhesive of the present application is an oil-based polymer binder, which is mainly applied to bonding for positive electrode sheet edge coating, and can achieve effective bonding between a positive electrode and a separator; the electrolyte resistance of the hot-press adhesive is significantly improved, and the problem of unintended mixing with positive electrode slurry is solved.

Description

A positive electrode edge coating protective hot pressing adhesive and its preparation and application

[0001] This application requests the priority of the Chinese patent application submitted to the China Patent Office on November 29, 2023, with application number 202311607080.2 and application name "A positive electrode edge coating protective hot pressing adhesive and its preparation and application", all of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of lithium battery materials and adhesives, and specifically relates to a positive electrode edge coating protective hot pressing adhesive and its preparation and application. Background Art

[0003] During the multiple cycles of lithium-ion batteries, lithium crystals may appear, which may pierce the diaphragm and cause direct contact between the positive and negative electrodes, thus causing a short circuit. Therefore, a side coating (edge ​​coating glue) coating is needed to protect it. At the same time, during the cutting process, the equipment needs to identify and cut the edges of the electrode. The traditional process of direct cutting may cause misalignment or damage to the positive electrode material area, so the presence of side coating glue can ensure its normal cutting process. The bonding between the side coating glue and the diaphragm can ensure the stable combination of the electrode and the diaphragm, avoiding the risk of misalignment. The application process of edge coating glue in the positive electrode edge coating protection is mainly to mix it with boehmite, then apply it to form a film, and then use the diaphragm for hot pressing to ensure its effective bonding with the diaphragm.

[0004] Polyacrylates have adhesive properties and can be used as pressure-sensitive and heat-sensitive adhesives. They are widely used in the packaging or encapsulation of daily necessities and electronic products. However, when ordinary polyacrylate adhesives are used for positive electrode edge coating protection, they have the following problems: 1. Poor wettability with PP (polypropylene) separators and large surface energy differences result in weak adhesion; 2. There will be serious crosstalk problems with the positive electrode slurry (crosstalk refers to when the edge coating slurry and the positive electrode slurry come into contact at the same time, due to the difference in surface tension and properties between the two, the two will penetrate each other, rather than being two clearly defined streams of material. This can also lead to coating anomalies. Therefore, the edge coating slurry has high crosstalk performance requirements and is required to prevent crosstalk during processing); 3. The electrolyte resistance is generally low.

[0005] Therefore, the development of a polyacrylate binder that can be directly polymerized in NMP (N-methylpyrrolidone) solvent, can be suitable for positive electrode edge coating protection, and can improve the anti-channeling performance with the positive electrode slurry has broad market prospects. Summary of the Invention

[0006] In view of the shortcomings and deficiencies of the above-mentioned prior art, the primary purpose of this application is to provide a positive electrode edge coating protective hot pressing adhesive.

[0007] Another object of the present application is to provide a method for preparing the above-mentioned positive electrode edge coating protective hot pressing adhesive.

[0008] Another object of the present application is to provide an application of the above-mentioned positive electrode edge coating protective hot pressing adhesive in bonding the positive electrode plate and the diaphragm.

[0009] The purpose of this application is achieved through the following technical solutions:

[0010] A positive electrode edge coating protective hot-press adhesive is obtained by copolymerizing acrylic monomers, acrylic ester monomers, oil-soluble monomers and modified monomers in NMP (N-methylpyrrolidone) solvent. The weight percentage of each monomer is as follows: acrylic monomer 5% to 12%, acrylic ester monomer 45% to 80%, oil-soluble monomer 10% to 40%, and modified monomer 1% to 10%.

[0011] Furthermore, the acrylic monomer is acrylic acid or methacrylic acid.

[0012] More preferably, the acrylic monomer is a partially neutralized acrylic monomer, and the neutralization degree of the partially neutralized acrylic monomer is 10% to 100%, and more preferably the neutralization degree is 40% to 90%.

[0013] Furthermore, the acrylic acid ester monomer is at least one of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, C13-C16 (meth)acrylate, octadecyl (meth)acrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

[0014] Further preferably, the acrylic acid ester monomer is a mixture of at least one short-chain acrylic acid ester monomer selected from methyl (meth)acrylate and ethyl (meth)acrylate and at least one long-chain acrylic acid ester monomer selected from butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, C13-C16 (meth)acrylate, and octadecyl (meth)acrylate; wherein the mass ratio of the short-chain acrylic acid ester monomer to the long-chain acrylic acid ester monomer is 2:1 to 0:1.

[0015] Furthermore, the oil-soluble monomer is at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and styrene; and the modified monomer is at least one of acrylamide, methacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, itaconic acid, hydroxyethyl acrylate, and hydroxyethyl methacrylate.

[0016] Furthermore, the hot pressing adhesive also contains 0 to 1% of a cross-linking monomer; the cross-linking monomer is at least one of divinylbenzene, polyethylene glycol (200 to 600) diacrylate, polyethylene glycol (200 to 600) dimethacrylate, N,N-methylenebisacrylamide, pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, trimethylolpropane tri(3-aziridinyl propionate), polyurethane acrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, and ethoxylated (30) bisphenol A diacrylate.

[0017] The method for preparing the positive electrode edge coating protective hot pressing adhesive comprises the following steps:

[0018] (1) stirring and mixing acrylic monomer, acrylic ester monomer, oil-soluble monomer and modified monomer to obtain a mixed monomer solution;

[0019] (2) taking a portion of the mixed monomer solution and stirring with the solvent NMP to dissolve uniformly, heating to the initiation temperature, and adding the initiator dropwise to carry out the first stage reaction;

[0020] (3) adding the remaining mixed monomer solution and initiator dropwise to carry out the second stage reaction, cooling after the reaction is completed, neutralizing, cooling and filtering to obtain a positive electrode edge coating protective hot pressing adhesive.

[0021] Furthermore, the amount of the solvent NMP added is 0.5 to 5 times the total mass of the mixed monomer solution.

[0022] Furthermore, the partial mixed monomer solution in step (2) refers to a mixed monomer solution that accounts for 20% to 50% of the total mass of the mixed monomer solution.

[0023] Furthermore, the initiator is at least one of benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptanenitrile; the amount of the initiator added is 0.1% to 2% of the total mass of the mixed monomer solution; and the initiation temperature is 30 to 100°C.

[0024] Furthermore, the reaction time of the first stage reaction is 0.5 to 2 hours; the reaction time of the second stage reaction is 2 to 24 hours.

[0025] The application of the above-mentioned positive electrode edge coating protective hot pressing adhesive in bonding the positive electrode plate and the diaphragm.

[0026] Furthermore, the application method is: coating the positive electrode edge with protective hot pressing adhesive and boehmite, mixing and homogenizing the mixture, coating and drying the obtained slurry to form a film, and then hot pressing and bonding the film with the separator at 80-100°C.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) The monomers and polymers of the hot-pressed adhesive of the present application can be directly polymerized in NMP. The product does not need to separate the solvent and does not need to be added to NMP for dissolution in subsequent applications, thereby ensuring the stability of the product and effectively reducing costs.

[0029] (2) The hot pressing adhesive obtained in the present application is an oily polymer adhesive, which is mainly used for bonding the edge coating of the positive electrode. The Tg (glass transition temperature) of the material is adjusted by different monomer ratios to achieve effective softening of the sample. It has a low softening point and can be bonded to the diaphragm base film by hot pressing at a certain temperature (80-100°C), thereby achieving stable bonding between the positive electrode and the diaphragm; avoiding dislocation during rapid coating; and having stable electrolyte tolerance and electrical insulation, which can effectively avoid the occurrence of dangers such as short circuits when lithium crystals pierce the diaphragm.

[0030] (3) The hot-pressed adhesive of the present application adjusts the type of material monomers and controls the addition amount range of acrylic ester monomers, oil-soluble monomers and modified monomers, as well as the neutralization degree of acrylic monomers, thereby regulating the softening point, cohesive force, surface tension and electrolyte swelling resistance of the polymer hot-pressed adhesive, so that the polymer hot-pressed adhesive binder has good hot-pressed bonding performance, anti-channeling performance and electrolyte resistance. The obtained hot-pressed adhesive product can be coated with a small amount of adhesive at the edge of the positive electrode plate and achieve effective bonding, which can effectively reduce costs and improve product performance.

[0031] (4) The present application further introduces long-chain acrylic ester monomers and controls the proportion range of long-chain acrylic ester monomers to effectively improve the adhesion to the PP base film and improve its resistance to material leakage and electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a diagram showing the state of the hot pressing adhesive obtained in Example 1 mixed with boehmite, coated and dried to form a film, and then hot pressed and bonded to a PP separator.

[0033] FIG2 is a graph showing the test results of the positive electrode slurry cross-contamination resistance performance of the hot pressing adhesive obtained in Example 1 at room temperature for 5 minutes. DETAILED DESCRIPTION

[0034] The present application is further described in detail below with reference to examples, but the implementation methods of the present application are not limited thereto.

[0035] The product properties in the following examples are tested as follows:

[0036] (1) Softening point test:

[0037] After the hot-pressed adhesive is coated and dried, the softening point of the pure adhesive film is tested using differential scanning calorimetry (DSC). Specifically, a thermogravimetric instrument is used for testing with a heating rate of 10°C / min. When the softening point is reached, an obvious inflection point will appear on the test curve, which is the softening point temperature.

[0038] (2) Peel strength test:

[0039] A hot-press adhesive and boehmite were mixed in a mass ratio of 1:5 to form a slurry. The resulting slurry was coated and dried to form a film with a thickness of 50 to 70 μm. The film was then hot-pressed onto a 13 to 16 μm thick PP separator. The hot-pressing conditions were: 3 MPa pressure, 90°C temperature, and 8 minutes. The peel strength was tested using a universal mechanical tensile tester with a 180-degree upward peel angle. The sample width was 2 cm, the length was 10 cm, and the tensile speed was 50 cm / min.

[0040] (3) Resistance to positive electrode slurry leakage:

[0041] The hot-press adhesive binder and boehmite were mixed in a mass ratio of 1:5 to obtain a uniform slurry, which was then filtered to obtain the positive electrode side coating slurry. PVDF was added to the NMP and dissolved uniformly. Conductive carbon was added and dispersed for 2 hours. The ternary positive electrode material (NCM811) was added and dispersed at high speed for 2 hours. The positive electrode slurry was filtered to obtain the positive electrode slurry. The mass ratio of the ternary positive electrode material, conductive carbon, and PVDF in the positive electrode slurry was 96.8:2:1.2, and the solid content of the positive electrode slurry was 75%. A certain amount of positive electrode side coating slurry and positive electrode slurry were drawn with a pipette, and the two slurries were brought into contact. The cross-linking and penetration phenomena were observed, and the time it took for the two materials to show significant penetration was observed.

[0042] (4) Electrolyte resistance:

[0043] The hot pressing adhesive and boehmite were mixed in a mass ratio of 1:5 and filtered to obtain the positive electrode side coating slurry. The positive electrode side coating slurry was applied to aluminum foil, dried to form a film, and then hot pressed and bonded to the PP separator to obtain the positive electrode plate. The hot pressing conditions were: pressure of 3MPa, temperature of 90°C, and hot pressing time of 8min. The positive electrode plate was immersed in the electrolyte and its mass swelling rate (swelling rate = (mass after swelling of the film - initial mass of the film) / initial mass of the film × 100%) and the appearance of the plate (observe whether the film and separator on the plate are cracked or detached) after immersion in the electrolyte at 60°C for 7 days were tested.

[0044] Example 1

[0045] A positive electrode edge coating protective hot pressing adhesive of this embodiment is prepared by the following method:

[0046] (1) 5 g of acrylic acid (neutralization degree 80%), 20 g of oil-soluble monomer units, 10 g of methyl methacrylate, 40 g of butyl acrylate, and 5 g of acrylamide were added to a beaker and stirred to obtain a uniform phase A; 30 wt% of the solution was taken from phase A as phase B.

[0047] (2) Add 200 g of NMP and phase B into a beaker and stir evenly. Heat to 80°C and dropwise add a solution containing 0.2 g of initiator benzoyl peroxide to react for 1 hour.

[0048] (3) The remaining phase A and a solution containing 0.4 g of initiator benzoyl peroxide are added dropwise at the same time. The addition time is 2 h. After the addition is completed, the reaction is continued for 4 h. The temperature is raised to 90 ° C., and a solution containing 0.1 g of initiator benzoyl peroxide is added. The reaction is continued for 2 h. The temperature is lowered to 40 ° C., and then triethylamine is added for amine neutralization. The molar ratio of triethylamine to acrylic monomer is 0.7:1. After cooling and filtration, the positive electrode edge coating protective hot pressing adhesive can be obtained.

[0049] Different oil-soluble monomer polymerization units were selected according to Table 1, and the product properties were tested. The results are shown below:

[0050] Table 1 Properties of hot-press adhesives obtained from different oil-soluble monomers

[0051] It can be seen from the results in Table 1 that the hot pressing adhesives obtained by using different oil-soluble monomers in this application all have good hot pressing bonding performance, anti-channeling performance and electrolyte resistance performance.

[0052] FIG1 shows a state in which the hot-press adhesive obtained in this embodiment is mixed with boehmite, coated and dried to form a film, and then hot-pressed bonded with a PP separator (the oil-soluble monomer of the test sample is acrylonitrile).

[0053] The test results of the hot-pressed adhesive obtained in this embodiment for the resistance to positive electrode slurry leakage at room temperature for 5 minutes are shown in Figure 2 (the oil-soluble monomer of the test sample is selected as acrylonitrile). It can be seen from the figure that the positive electrode edge coating slurry and the positive electrode slurry of this embodiment did not show any leakage within 5 minutes at room temperature.

[0054] Example 2

[0055] A positive electrode edge coating protective hot pressing adhesive of this embodiment is prepared by the following method:

[0056] (1) Add 5 g of acrylic acid (neutralization degree 90%), 20 g of acrylonitrile, 10 g of methyl methacrylate, 40 g of isobornyl acrylate, and 5 g of modified monomer into a beaker and stir to obtain a uniform phase A; take out 40 wt% of the solution from phase A as phase B.

[0057] (2) Add 300 g of NMP and phase B into a beaker and stir evenly. Heat to 80°C and dropwise add a solution containing 0.2 g of initiator azobisisobutyronitrile to react for 1 hour.

[0058] (3) The remaining phase A and a solution containing 0.4 g of initiator azobisisobutyronitrile were added dropwise at the same time. The addition time was 2 h. After the addition was completed, the reaction was continued for 4 h. The temperature was raised to 90 ° C., and a solution containing 0.1 g of initiator azobisisobutyronitrile was added. The reaction was continued for 2 h. The temperature was lowered to 40 ° C., and then triethylamine was added for amine neutralization. The molar ratio of triethylamine to acrylic monomer was 0.7:1. After cooling and filtration, the positive electrode edge coating protective hot pressing adhesive was obtained.

[0059] Different modified monomers were selected according to Table 2, and the product performance was tested. The results are shown below:

[0060] Table 2 Properties of hot-press adhesives obtained with different modified monomers

[0061] It can be seen from the results in Table 2 that the hot pressing adhesives obtained by using different modified monomers in this application all have good hot pressing bonding performance, anti-channeling performance and electrolyte resistance.

[0062] Example 3

[0063] A positive electrode edge coating protective hot pressing adhesive of this embodiment is prepared by the following method:

[0064] (1) 5 g of acrylic acid with different neutralization degrees, 20 g of acrylonitrile, 10 g of methyl methacrylate, 40 g of butyl acrylate, 5 g of acrylamide, and 0.3 g of trimethylolpropane triacrylate were added to a beaker and stirred to obtain a uniform phase A; 20 wt% of the solution was taken from phase A as phase B.

[0065] (2) Add 200 g of NMP and phase B into a beaker and stir evenly. Heat to 80°C and dropwise add a solution containing 0.2 g of initiator benzoyl peroxide to react for 1 hour.

[0066] (3) The remaining phase A and a solution containing 0.4 g of initiator benzoyl peroxide are added dropwise at the same time. The addition time is 2 h. After the addition is completed, the reaction is continued for 4 h. The temperature is raised to 90 ° C., and a solution containing 0.1 g of initiator benzoyl peroxide is added. The reaction is continued for 2 h. The temperature is lowered to 40 ° C., and then triethylamine is added for amine neutralization. The molar ratio of triethylamine to acrylic monomer is 0.7:1. After cooling and filtration, the positive electrode edge coating protective hot pressing adhesive can be obtained.

[0067] According to Table 3, acrylic acid with different neutralization degrees was selected and the product performance was tested. The results are shown below:

[0068] Table 3 Properties of hot press adhesives obtained from acrylic acid with different neutralization degrees

[0069] From the results in Table 3, it can be seen that with the increase of the neutralization degree of acrylic acid, the bonding performance, anti-channeling performance and electrolyte resistance of the obtained hot pressing adhesive show an improving trend. Good hot pressing bonding performance, anti-channeling performance and electrolyte resistance can be achieved in the neutralization degree range of 10% to 100%. However, after the neutralization degree reaches 100%, the corresponding performance decreases. The optimal comprehensive performance can be achieved when the neutralization degree is 40% to 90%.

[0070] Example 4

[0071] A positive electrode edge coating protective hot pressing adhesive of this embodiment is prepared by the following method:

[0072] (1) Different masses of acrylic acid (neutralization degree 50%), 10 g acrylonitrile, 20 g methyl methacrylate, 40 g isooctyl acrylate, 5 g isobornyl acrylate, 5 g acrylamide, 3 g hydroxyethyl acrylate, and 0.45 g trimethylolpropane triacrylate were added to a beaker and stirred to obtain a uniform phase A; 50 wt% of the solution from phase A was taken out as phase B.

[0073] (2) Add 200 g of NMP and phase B into a beaker and stir evenly. Heat to 80°C and dropwise add a solution containing 0.2 g of initiator benzoyl peroxide to react for 1 hour.

[0074] (3) The remaining phase A and a solution containing 0.4 g of initiator benzoyl peroxide are added dropwise at the same time. The addition time is 2 h. After the addition is completed, the reaction is continued for 4 h. The temperature is raised to 90 ° C., and a solution containing 0.1 g of initiator benzoyl peroxide is added. The reaction is continued for 2 h. The temperature is lowered to 40 ° C., and then triethylamine is added for amine neutralization. The molar ratio of triethylamine to acrylic monomer is 0.7:1. After cooling and filtration, the positive electrode edge coating protective hot pressing adhesive can be obtained.

[0075] According to Table 4, acrylic acid of different qualities was selected and the product performance was tested. The results are shown below:

[0076] Table 4 Properties of hot press adhesives obtained with different acrylic acid addition amounts

[0077] The results in Table 4 show that without the addition of acrylic acid monomer, the resulting hot press adhesive exhibits significantly reduced bonding performance, resistance to cross-contamination, and electrolyte resistance, failing to meet performance requirements. With increasing levels of acrylic acid monomer, the softening point of the resulting hot press adhesive increases, the peel strength initially increases and then decreases, and both resistance to cross-contamination and electrolyte resistance improve. Acrylic acid monomer additions in the 5% to 12% range exhibit superior hot press adhesive performance, resistance to cross-contamination, and electrolyte resistance.

[0078] Example 5

[0079] A positive electrode edge coating protective hot pressing adhesive of this embodiment is prepared by the following method:

[0080] (1) 5 g of acrylic acid (neutralization degree 50%), 10 g of acrylonitrile, acrylic ester monomers of different weights and compositions, 2.5 g of acrylamide, 2.5 g of hydroxyethyl acrylate, and 0.45 g of polyethylene glycol diacrylate were added to a beaker and stirred to obtain a uniform phase A; 30 wt% of the solution from phase A was taken as phase B.

[0081] (2) Add NMP (2 times the total mass of the mixed monomer solution) and phase B into a beaker and stir evenly. Heat to 80°C and dropwise add a solution containing 0.2g of initiator azobisisobutyronitrile to react for 1 hour.

[0082] (3) The remaining phase A and a solution containing 0.4 g of initiator azobisisobutyronitrile were added dropwise at the same time. The addition time was 2 h. After the addition was completed, the reaction was continued for 4 h. The temperature was raised to 90 ° C., and a solution containing 0.1 g of initiator azobisisobutyronitrile was added. The reaction was continued for 2 h. The temperature was lowered to 40 ° C., and then triethylamine was added for amine neutralization. The molar ratio of triethylamine to acrylic monomer was 0.7:1. After cooling and filtration, the positive electrode edge coating protective hot pressing adhesive was obtained.

[0083] According to Table 5, acrylic acid ester monomers of different masses and compositions were selected and the product properties were tested. The results are shown below:

[0084] Table 5 Properties of hot-press adhesives obtained from acrylic acid ester monomers of different mass and composition

[0085] From the results in Table 5, it can be seen that when no acrylic acid ester monomers are added, the bonding performance, resistance to material leakage and electrolyte resistance of the obtained hot-press adhesive are significantly reduced, which does not meet the use requirements. With the increase of the amount of acrylic acid ester monomer added, the softening point of the obtained hot-press adhesive shows a downward trend, and the peel strength shows a trend of first increasing and then decreasing. Acrylic acid ester monomers have better hot-pressing adhesion, resistance to material leakage and electrolyte resistance when the addition amount ranges from 45% to 80%. It was also found that when no long-chain acrylic acid ester monomers were added, the bonding performance and electrolyte resistance of the obtained hot-press adhesive were significantly reduced. The hot-press adhesive obtained when the mass ratio of short-chain acrylic acid ester monomers (methyl (meth)acrylate, ethyl (meth)acrylate) to long-chain acrylic acid ester monomers is in the range of 2:1 to 0:1 has good hot-pressing adhesion, resistance to material leakage and electrolyte resistance.

[0086] Example 6

[0087] A positive electrode edge coating protective hot pressing adhesive of this embodiment is prepared by the following method:

[0088] (1) 7 g of acrylic acid (neutralization degree 50%), different amounts of oil-soluble monomers, 15 g of methyl methacrylate, 30 g of isooctyl acrylate, 15 g of butyl acrylate, 5 g of acrylamide, 5 g of hydroxyethyl acrylate, 5 g of isobornyl acrylate, and 0.3 g of polyethylene glycol diacrylate were added to a beaker and stirred to obtain a uniform phase A; 30 wt% of the solution was taken out from phase A as phase B.

[0089] (2) Add NMP (3 times the total mass of the mixed monomer solution) and phase B into a beaker and stir evenly. Heat to 80°C and dropwise add a solution containing 0.2g of initiator azobisisobutyronitrile to react for 1 hour.

[0090] (3) The remaining phase A and a solution containing 0.4 g of initiator azobisisobutyronitrile were added dropwise at the same time. The addition time was 2 h. After the addition was completed, the reaction was continued for 4 h. The temperature was raised to 90 ° C., and a solution containing 0.1 g of initiator azobisisobutyronitrile was added. The reaction was continued for 2 h. The temperature was lowered to 40 ° C., and then triethylamine was added for amine neutralization. The molar ratio of triethylamine to acrylic monomer was 0.7:1. After cooling and filtration, the positive electrode edge coating protective hot pressing adhesive was obtained.

[0091] According to Table 6, different addition amounts of oil-soluble monomers were selected and the product properties were tested. The results are shown below:

[0092] Table 6 Properties of hot press adhesives obtained with different addition amounts of oil-soluble monomers

[0093] The results in Table 6 show that without the addition of oil-soluble monomers, the resulting hot-press adhesive exhibits significantly reduced bonding performance, resistance to cross-contamination, and electrolyte resistance, failing to meet usage requirements. As the amount of oil-soluble monomer added increases, the softening point of the resulting hot-press adhesive increases, while the peel strength, resistance to cross-contamination, and electrolyte resistance first increase and then decrease. The addition of oil-soluble monomers, which have strong polar bonds, can improve bonding performance; however, excessive amounts of oil-soluble monomers, due to their high Tg, can lead to excessive cohesion and hardening of the film, resulting in decreased bonding performance. Furthermore, due to the high surface tension of oil-soluble monomers, increasing their surface tension with increasing dosage can lead to decreased resistance to cross-contamination. Oil-soluble monomers exhibit superior hot-press adhesive performance, resistance to cross-contamination, and electrolyte resistance when added in an amount ranging from 10% to 40%.

[0094] Example 7

[0095] A positive electrode edge coating protective hot pressing adhesive of this embodiment is prepared by the following method:

[0096] (1) 5 g of acrylic acid (neutralization degree 80%), 20 g of acrylonitrile, 10 g of methyl methacrylate, 40 g of butyl acrylate, different amounts of modified monomers, and 0.4 g of N,N-methylenebisacrylamide were added to a beaker and stirred to obtain a uniform phase A; 30 wt% of the solution was taken from phase A as phase B.

[0097] (2) Add NMP (4 times the total mass of the mixed monomer solution) and phase B into a beaker and stir evenly. Heat to 80°C and dropwise add a solution containing 0.2g of initiator benzoyl peroxide to react for 1 hour.

[0098] (3) The remaining phase A and a solution containing 0.4 g of initiator benzoyl peroxide are added dropwise at the same time. The addition time is 2 h. After the addition is completed, the reaction is continued for 4 h. The temperature is raised to 90 ° C., and a solution containing 0.1 g of initiator benzoyl peroxide is added. The reaction is continued for 2 h. The temperature is lowered to 40 ° C., and then triethylamine is added for amine neutralization. The molar ratio of triethylamine to acrylic monomer is 0.7:1. After cooling and filtration, the positive electrode edge coating protective hot pressing adhesive can be obtained.

[0099] Different addition amounts of modified monomers were selected according to Table 7, and the product properties were tested. The results are shown below:

[0100] Table 7 Properties of hot press adhesives obtained with different addition amounts of modified monomers

[0101] The results in Table 7 show that a certain amount of modified monomer can improve the bonding performance and solvent resistance of the hot press adhesive. However, adding too much modified monomer will increase the softening point and reduce the bonding performance. The modified monomer has a thermal cross-linking effect, which can strengthen the network structure of the polymer and improve the material's resistance to electrolyte swelling. The modified monomer also has strong polar bonds, which can improve its bonding performance. However, too much modified monomer can lead to excessive cohesion of the film and harden the film due to its high Tg, which in turn leads to a decrease in bonding performance. The modified monomer has better hot press adhesion, material resistance, and electrolyte resistance when added in an amount ranging from 1% to 10%.

[0102] The above embodiments are preferred implementation modes of the present application, but the implementation modes of the present application are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present application should be considered as equivalent replacement methods and are included in the scope of protection of the present application.

Claims

1. A positive electrode edge coating protective hot pressing adhesive, characterized in that: The polyol is obtained by copolymerization of acrylic acid monomer, acrylic acid ester monomer, oil-soluble monomer and modified monomer in solvent N-methylpyrrolidone, wherein the mass percentage of each monomer is: acrylic acid monomer 5%-12%, acrylic acid ester monomer 45%-80%, oil-soluble monomer 10%-40%, and modified monomer 1%-10%.

2. The positive electrode edge coating protective hot pressing adhesive according to claim 1, characterized in that: The acrylic monomer is acrylic acid or methacrylic acid; the acrylic ester monomer is at least one of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, C13-C16 (meth)acrylate, octadecyl (meth)acrylate, alkoxyphenol acrylate, and glycidyl (meth)acrylate.

3. The positive electrode edge coating protective hot pressing adhesive according to claim 2, characterized in that: The acrylic acid ester monomer is a mixture of at least one short-chain acrylic acid ester monomer selected from methyl (meth)acrylate and ethyl (meth)acrylate and at least one long-chain acrylic acid ester monomer selected from butyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, C13-C16 (meth)acrylate, and octadecyl (meth)acrylate; wherein the mass ratio of the short-chain acrylic acid ester monomer to the long-chain acrylic acid ester monomer is 2:1 to 0:

1.

4. The positive electrode edge coating protective hot pressing adhesive according to claim 1, characterized in that: The acrylic monomer is a partially neutralized acrylic monomer, and the neutralization degree of the partially neutralized acrylic monomer is 10% to 100%; preferably, the neutralization degree of the partially neutralized acrylic monomer is 40% to 90%.

5. A positive electrode edge coating protective hot pressing adhesive according to any one of claims 1 to 4, characterized in that: The oil-soluble monomer is at least one of acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and styrene; the modified monomer is at least one of acrylamide, methacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, itaconic acid, hydroxyethyl acrylate and hydroxyethyl methacrylate.

6. The positive electrode edge coating protective hot pressing adhesive according to claim 1, characterized in that: The hot pressing adhesive also contains 0 to 1% of a cross-linking monomer; the cross-linking monomer is at least one of divinylbenzene, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, N,N-methylenebisacrylamide, pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, trimethylolpropane tri(3-aziridinyl propionate), polyurethane acrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, and ethoxylated bisphenol A diacrylate.

7. A method for preparing a positive electrode edge coating protective hot pressing adhesive according to any one of claims 1 to 6, characterized in that: The method comprises the following preparation steps: (1) stirring and mixing acrylic monomers, acrylic ester monomers, oil-soluble monomers and modified monomers to obtain a mixed monomer solution; (2) taking part of the mixed monomer solution and the solvent N-methylpyrrolidone, stirring and dissolving them uniformly, heating them to the initiation temperature, and adding the initiator dropwise to carry out the first stage reaction; (3) adding the remaining mixed monomer solution and initiator dropwise to carry out the second stage reaction, cooling after the reaction is completed, neutralizing, cooling and filtering, and obtaining a positive electrode edge coating protective hot pressing adhesive.

8. The method for preparing a positive electrode edge coating protective hot pressing adhesive according to claim 7, characterized in that: The added amount of the solvent NMP is 0.5 to 5 times the total mass of the mixed monomer solution; the partial mixed monomer solution refers to a mixed monomer solution that accounts for 20% to 50% of the total mass of the mixed monomer solution.

9. The method for preparing a positive electrode edge coating protective hot pressing adhesive according to claim 7, characterized in that: The initiator is at least one of benzoyl peroxide, azobisisobutyronitrile and azobisisoheptylnitrile; the added amount of the initiator is 0.1% to 2% of the total mass of the mixed monomer solution; and the initiation temperature is 30 to 100°C.

10. The method for preparing a positive electrode edge coating protective hot pressing adhesive according to claim 7, characterized in that: The reaction time of the first stage reaction is 0.5 to 2 hours; the reaction time of the second stage reaction is 2 to 24 hours.

11. Application of a positive electrode edge coating protective hot pressing adhesive according to any one of claims 1 to 6 in bonding a positive electrode plate to a separator, characterized in that: The application method is: coating the positive electrode edge with protective hot pressing glue and mixing with boehmite to form a slurry, coating and drying the obtained slurry to form a film, and then hot pressing and bonding with the separator at 80-100°C.

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