A special post-crosslinking water-based adhesive for lithium batteries and a preparation method and application thereof

Abstract

The present application relates to the technical field of water-based adhesive, and discloses a special post-crosslinking water-based adhesive for lithium battery and a preparation method and application thereof, which comprises the following raw materials in parts by mass: soft monomer 10-80 parts, hard monomer 10-90 parts, functional monomer 0.02-10 parts, emulsifier 0.2-4 parts, special crosslinking agent 0.02-4 parts, initiator 0.1-5 parts, pH regulator 1-30 parts, and water 200-900 parts. The synthesis and crosslinking of the adhesive are divided into two steps, the special post-crosslinking water-based adhesive for lithium battery is first synthesized to make the battery cell, and then the special crosslinking agent is added, so that the special post-crosslinking water-based adhesive for lithium battery and the special crosslinking agent are further crosslinked in the later battery formation process, and the adhesive in the pole piece is crosslinked into a whole in the form of chemical bond. Before crosslinking, the adhesive has excellent flexibility and wettability to the adherend, and after crosslinking, the strength is greatly improved, the pole piece is more firm, the processing of the pole piece is not affected, and the adhesive force is improved.

Description

Technical Field

[0001] This invention relates to the field of waterborne adhesives technology, specifically to a post-crosslinking waterborne adhesive for lithium batteries, its preparation method, and its application. Background Technology

[0002] The rapid development of the new energy vehicle and energy storage industries has placed higher demands on the energy density and safety of lithium batteries. This has spurred the emergence and promotion of ternary materials and silicon-based anode materials, and these new materials have also placed higher performance requirements on their supporting auxiliary materials and adhesives. Currently, aqueous adhesives for lithium batteries are mainly classified into two types: emulsion-type (styrene-butadiene emulsion, styrene-acrylic emulsion) and solution-type (PAA). SBR is a representative emulsion-type product, while LA133 / LA136D is a representative solution-type product. Although SBR has good flexibility, which is beneficial for secondary processing of the electrode, its adhesive strength is relatively low, especially when used in silicon-based anode materials, where severe material delamination from the current collector can occur. PAA solution-type products have higher adhesive strength, but the hard and brittle nature of their adhesive film results in poor electrode processing performance, limiting the amount of adhesive used.

[0003] Currently, although some companies combine PAA and SBR adhesives for silicon-carbon anode materials, their performance is only suitable for materials with low silicon content (<10%), and cannot meet the requirements for high-silicon materials. Chinese patent CN110396154A discloses a crosslinked aqueous adhesive for silicon-based anodes and its preparation method. This method involves adding crosslinking functional monomers during adhesive synthesis to achieve crosslinking between molecular chains; however, its degree of crosslinking is limited, and it affects the spreading performance of molecular chains on the adhered material, which to some extent affects the peel strength. Summary of the Invention

[0004] The present invention aims to provide a post-crosslinking aqueous adhesive for lithium batteries, its preparation method and application, in order to solve the problems in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a lithium battery-specific post-crosslinking aqueous adhesive, the molecular chain containing 5-30 wt% amino and hydroxyl groups, which can undergo an addition reaction with a special crosslinking agent during the battery formation stage, and undergo secondary crosslinking in the battery.

[0006] Preferably, as an improvement, a post-crosslinking aqueous adhesive for lithium batteries comprises, by weight, the following raw materials: 10-80 parts of soft monomer, 10-90 parts of hard monomer, 0.02-10 parts of functional monomer, 0.2-4 parts of emulsifier, 0.1-5 parts of initiator, 1-30 parts of pH adjuster, and 200-900 parts of water.

[0007] Preferably, as an improvement, the soft monomer is at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, isooctyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, isopentyl acrylate, isooctyl acrylate, isononyl acrylate, isodecanyl acrylate, tridecyl acrylate, lauryl (meth)acrylate, polyethylene glycol (meth)acrylate, methoxy polyethylene glycol monoacrylate, and octadecyl methacrylate.

[0008] Preferably, as an improvement, the hard monomer is at least one selected from (meth)acrylic acid, acrylonitrile, styrene, methyl methacrylate, (meth)acrylamide, tert-butyl methacrylate, phenyl methacrylate, isobornyl methacrylate, N,N-dimethylacrylamide, cyclohexyl methacrylate, ethyl methacrylate, N-vinylpyrrolidone, and N-vinylcaprolactam.

[0009] Preferably, as an improvement, the functional monomer is at least one of 1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trihydroxypropane trimethacrylate, N,N-methylenediacrylamide, allyl methacrylate, hydroxyethylacrylamide, glycidyl methacrylate, and divinylbenzene.

[0010] Preferably, as an improvement, the emulsifier is at least one selected from sodium dodecyl sulfate, sodium dodecyl sulfonate, dodecyl octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, decylphenol polyoxyethylene ether, dodecylphenol polyoxyethylene ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, fatty alcohol polyoxyethylene ether, sodium vinyl sulfonate, sodium p-styrene sulfonate, sodium allyl hydroxypropyl sulfonate, sodium 2-acrylamido-2-methylpropanesulfonate, and allyloxy fatty alcohol oxyethylene ether ammonium sulfate.

[0011] Preferably, as an improvement, the special crosslinking agent is at least one of 2,6-toluene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, 2,2,4-trimethylhexane diisocyanate, dicyclohexylmethylene diisocyanate, isophorone diisocyanate, furan diisocyanate, or other small molecules and polymers containing multiple isocyanate groups; the initiator is at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; and the pH adjuster is at least one of ammonia, ethylenediamine, sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, lithium carbonate, and lithium bicarbonate.

[0012] Preferably, as an improvement, a method for preparing a post-crosslinking aqueous adhesive specifically for lithium batteries is characterized by comprising the following steps:

[0013] Step 1: Add solvent, emulsifier, and some water-soluble monomer to the reaction apparatus, and stir at 40-60°C until completely dissolved;

[0014] Step 2: Add the soft monomer and some functional monomers to the reaction apparatus and stir at 40-60°C until the materials are evenly mixed.

[0015] Step 3: Introduce nitrogen gas and heat the system to 60–85°C;

[0016] Step 4: Dissolve the initiator in pure water and stir thoroughly to prepare an aqueous solution with a mass fraction of 1% to 30%; then add the initiator aqueous solution into the reaction apparatus and keep the temperature constant while stirring, and react for 5 to 120 minutes.

[0017] Step 5: Add hard monomers and some functional monomers dropwise, and continue the reaction for 1 to 8 hours. After the dropwise addition begins, add the initiator every 1 to 4 hours. After the dropwise addition is completed, continue the reaction for 3 to 12 hours.

[0018] Step 6: After cooling, filter the material through a filter screen, add a pH adjuster, and adjust the pH to 7-8 to obtain the final product.

[0019] Preferably, as an improvement, the application of a lithium battery-specific post-crosslinking aqueous adhesive in the preparation of lithium-ion battery adhesives.

[0020] Preferably, as an improvement, a special crosslinking agent is added during the lithium-ion battery electrolyte filling process. The ratio of the amount of special crosslinking agent to the battery capacity is 0.006g / 1000mAh to 0.03g / 1000mAh. The special crosslinking agent undergoes an addition reaction with the lithium battery-specific post-crosslinking aqueous adhesive to form a network structure.

[0021] The principle and advantages of this solution are as follows: In practical applications, the synthesis and crosslinking of the adhesive in this technical solution are divided into two steps. First, a lithium battery-specific post-crosslinking aqueous adhesive is synthesized to make the battery cell. Then, a special crosslinking agent is added, which further crosslinks with the special crosslinking agent during the later battery formation and use process. This allows the adhesive in the electrode to be crosslinked into a whole through chemical bonds. Before crosslinking, the adhesive has excellent flexibility and wettability to the adhered materials. After crosslinking, the strength is greatly improved, and the electrode is more firmly bonded. This does not affect the processing of the electrode and can improve the adhesion. In the process of technical research and development, optimizing the crosslinking method of the adhesive and the content of related functional groups is a major challenge of this technical solution. Through screening, the isocyanate groups in the special isocyanate crosslinking agent are used to react with the amino and hydroxyl groups in the lithium battery-specific post-crosslinking aqueous adhesive to achieve a further crosslinking effect. Therefore, this technical solution has the following advantages compared with the existing technology:

[0022] 1. This technical solution can improve the flexibility of lithium battery negative electrode sheets, enhance their processing performance, and solve problems such as winding cracking and debonding.

[0023] 2. After hot pressing formation, the adhesive particles cross-link to form a network structure, which fixes the adhered material, making the entire electrode structure more stable and improving the peel force and cohesion between the lithium battery negative electrode material and the copper foil.

[0024] 3. This technical solution solves the problem of silicon-carbon anode material expanding and detaching from copper foil during application. It provides a certain degree of protection for the anode material during repeated lithium-ion insertion and extraction, improves structural damage, extends battery life, and enhances battery performance.

[0025] 4. In this technical solution, after the binder is cross-linked, the swelling degree of the electrolyte is greatly reduced, which will reduce the impact on the porosity of the electrode, facilitate the migration of lithium ions, and significantly reduce the internal resistance of the battery. Detailed Implementation

[0026] The following detailed description provides further details on specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials and reagents used are all commercially available.

[0027] Overview of the plan:

[0028] A post-crosslinking aqueous adhesive for lithium batteries contains 5-30 wt% amino and hydroxyl groups in its molecular chain. During the battery formation stage, it can undergo an addition reaction with a special crosslinking agent to achieve secondary crosslinking in the battery. By weight, it comprises the following raw materials: 10-80 parts soft monomer, 10-90 parts hard monomer, 0.02-10 parts functional monomer, 0.2-4 parts emulsifier, 0.1-5 parts initiator, 1-30 parts pH adjuster, and 200-900 parts water. The solid content of the adhesive is 10-30%.

[0029] The soft monomer is at least one of the following: methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, isooctyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, isopentyl acrylate, isooctyl acrylate, isononyl acrylate, isodecanyl acrylate, tridecyl acrylate, lauryl (meth)acrylate, polyethylene glycol (meth)acrylate, methoxy polyethylene glycol monoacrylate, and octadecyl methacrylate.

[0030] The hard monomer is at least one of (meth)acrylic acid, acrylonitrile, styrene, methyl methacrylate, (meth)acrylamide, tert-butyl methacrylate, phenyl methacrylate, isobornyl methacrylate, N,N-dimethylacrylamide, cyclohexyl methacrylate, ethyl methacrylate, N-vinylpyrrolidone, and N-vinylcaprolactam.

[0031] The functional monomer is at least one of 1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trihydroxypropane trimethacrylate, N,N-methylenediacrylamide, allyl methacrylate, hydroxyethylacrylamide, glycidyl methacrylate, and divinylbenzene.

[0032] The emulsifier is at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, dodecyl octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, decylphenol polyoxyethylene ether, dodecylphenol polyoxyethylene ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, fatty alcohol polyoxyethylene ether, sodium vinyl sulfonate, sodium p-styrene sulfonate, sodium allyl hydroxypropyl sulfonate, sodium 2-acrylamido-2-methylpropanesulfonate, and allyloxy fatty alcohol oxyethylene ether ammonium sulfate.

[0033] The specific crosslinking agent is at least one of 2,6-toluene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, 2,2,4-trimethylhexane diisocyanate, dicyclohexylmethylene diisocyanate, isophorone diisocyanate, furan diisocyanate, or other small molecules and polymers containing multiple isocyanate groups.

[0034] The initiator is at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0035] The pH adjuster is at least one of ammonia, ethylenediamine, sodium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, lithium carbonate, and lithium bicarbonate.

[0036] A method for preparing a post-crosslinking aqueous adhesive specifically for lithium batteries includes the following steps:

[0037] Step 1: Add 200-900 parts water and 0.2-4 parts emulsifier to the reaction apparatus, and stir at 40-60°C until completely dissolved;

[0038] Step 2: Add 10-80 parts of soft monomer and 0.02-10 parts of functional monomer to the reaction device, and stir at 40-60°C until the materials are evenly mixed.

[0039] Step 3: Simultaneously introduce high-purity nitrogen gas for 0.5–1.5 hours and raise the system temperature to 60–85°C;

[0040] Step 4: Dissolve the initiator in deionized water and stir thoroughly to prepare an aqueous solution with a mass fraction of 1% to 30%; then add 1 to 10 parts of the initiator aqueous solution to the reaction apparatus, and keep the temperature constant while stirring, and react for 5 to 120 minutes.

[0041] Step 5: Add 10-90 parts of hard monomer dropwise, and continue the reaction for 1-8 hours. After the dropwise addition begins, add 1-10 parts of initiator aqueous solution every 1-4 hours. After the dropwise addition is completed, continue the reaction for 3-12 hours.

[0042] Step 6: After cooling, filter the material through a filter screen, add a pH adjuster, and adjust the pH to 7-8 to obtain a lithium battery-specific post-crosslinking aqueous adhesive.

[0043] Step 7: During the electrolyte filling process of the lithium-ion battery made of lithium battery-specific post-crosslinking aqueous adhesive, a special crosslinking agent is added. The ratio of the amount of special crosslinking agent to the battery capacity is 0.006g / 1000mAh to 0.03g / 1000mAh. The special crosslinking agent is immersed in the lithium battery-specific post-crosslinking aqueous adhesive along with the electrolyte and is captured by hydroxyl and amino groups to undergo an addition reaction. The molecular chains of the lithium battery-specific post-crosslinking aqueous adhesive crosslink to form a network structure.

[0044] Example 1

[0045] A method for preparing a post-crosslinking aqueous adhesive specifically for lithium batteries includes the following steps:

[0046] Step 1: Add 400 parts of pure water, 2 parts of sodium dodecyl sulfate, and 2.5 parts of acrylic acid to the reaction apparatus, heat to 40°C and stir until completely dissolved.

[0047] Step 2: Add 37 parts of n-butyl acrylate, 10 parts of hydroxypropyl acrylate, and 0.5 parts of divinylbenzene to the reaction apparatus; continue stirring until the materials are mixed evenly.

[0048] Step 3: Simultaneously introduce high-purity nitrogen gas for 1 hour and raise the system temperature to 75°C.

[0049] Step 4: Dissolve 2 parts of ammonium persulfate in 8 parts of pure water to obtain an ammonium persulfate solution. Add 2 parts of the ammonium persulfate solution to the reaction apparatus and keep the temperature constant while stirring. React for 120 minutes.

[0050] Step 5: Add 2g of ammonium persulfate solution. Mix 10 parts hydroxyethyl acrylamide, 20 parts acrylonitrile, 10 parts acrylic acid, and 10 parts methyl methacrylate thoroughly. Add this mixture dropwise to the reaction apparatus over 6 hours. After the dropwise addition begins, add 2 parts of the ammonium persulfate solution to the reaction system every 2 hours until the addition is complete. After the dropwise addition is complete, continue the reaction for another 8 hours.

[0051] Step 6: After the reaction is complete, cool the system to room temperature, add sodium hydroxide solution, and adjust the pH to 7 to obtain a post-crosslinking aqueous adhesive for lithium batteries.

[0052] Example 2

[0053] The difference between this embodiment and Example 1 is that, in this embodiment, the proportions of n-butyl acrylate are reduced to 27 parts and hydroxypropyl acrylate is increased to 20 parts, while the remaining monomers and processes are the same.

[0054] Example 3

[0055] The difference between this embodiment and Example 1 is that, in this embodiment, based on the formulation of Example 1, n-butyl acrylate is replaced with isooctyl acrylate, while the remaining monomers and processes are the same.

[0056] Example 4

[0057] The difference between this embodiment and Example 1 is that, in this embodiment, the functional monomer hydroxyethyl acrylamide is increased to 15 parts and the hard monomer methyl methacrylate is reduced to 5 parts, while the remaining monomers and processes are the same, based on the proportions in Example 1.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 1 is that the functional monomer divinylbenzene is increased to 2.5 parts based on the ratio in Example 1, while the remaining monomers and processes are the same.

[0060] Comparative Example 2

[0061] This comparative example uses SBR-3001 as the adhesive.

[0062] Comparative Example 3

[0063] This comparative example uses PAA-LA136D as the adhesive.

[0064] Experimental Example

[0065] The adhesives of the above embodiments and comparative examples were subjected to performance tests. Specifically, the lithium-ion battery adhesives prepared in each embodiment and the lithium-ion battery adhesives described in the comparative examples were poured into Teflon molds, baked at 40 degrees Celsius for 8 hours, and then dried at 85 degrees Celsius. The resulting adhesive film thickness was 500–2000 μm, and the film was cut into 1*3 cm samples for testing. The samples were then immersed in electrolyte (a special crosslinking agent was added in the examples). The test indicators included swelling degree, strength, and elongation. The test methods for each indicator are as follows:

[0066] 1. The test method for swelling degree is as follows:

[0067] The original mass of the sample was recorded using an analytical balance. The sample was then immersed in 20–30 ml of electrolyte (2 g of a special crosslinking agent was added in this example) and sealed in a 70°C oven. The electrolyte composition was ethylene carbonate: methyl ethyl carbonate: diethyl carbonate in a mass ratio of 3:5:2. Samples were removed after immersion for 24 h, 72 h, 120 h, and 240 h, respectively. The surface electrolyte was wiped off with lint-free paper, and the weight of the sample after immersion in the electrolyte was recorded using an analytical balance. The degree of swelling is equal to the increase in mass of the sample after immersion in the electrolyte divided by the original mass of the sample.

[0068] 2. The test methods for strength and elongation are as follows:

[0069] The original sample and the sample immersed in the electrolyte (2g of special crosslinking agent was added in the example) were stretched at a speed of 50mm / min using a tensile testing machine until the sample broke. The displacement and force were recorded simultaneously. The elongation of the film is equal to the displacement at break divided by the sample length, and the film strength is equal to the force at break divided by the cross-sectional area.

[0070] Each group was tested three times in a row, and the average value was taken. The test results are shown in Table 1.

[0071] Table 1

[0072]

[0073]

[0074] As shown in the table above, the lithium-ion battery adhesive prepared using the formulation and method of this invention exhibits flexibility comparable to or better than SBR, and has better electrolyte affinity. After electrolyte injection and crosslinking, the adhesive film has higher strength than PAA, and some electrolyte is released, resulting in improved conductivity. Comparing Examples 2 and 4 with Example 1, it is evident that increasing the amount of monomers containing hydroxyl and amino groups can, to some extent, improve the strength of the pure adhesive film and reduce the elongation at break and electrolyte swelling. Comparing Example 3 with Example 1, it is evident that reducing the adhesive's Tg can, to some extent, increase flexibility, but at the cost of some strength. Comparing Comparative Example 1 with Example 1, it is evident that increasing the degree of crosslinking during synthesis increases the film strength, but significantly reduces flexibility.

[0075] Application examples

[0076] The lithium-ion battery adhesives prepared in Examples 1-4 and the lithium-ion battery adhesives described in Comparative Examples 1-3 were combined with the same mass fraction of the same silicon-based negative electrode material and other auxiliary materials (adhesive dosage 2.0%) to prepare negative electrode sheets, and their flexibility, cohesion, and peel strength were compared. The negative electrode sheets prepared above were then combined with the same positive electrode sheets and separator to prepare a lithium battery (capacity 1000mAh); wherein the lithium battery prepared with the adhesives in the examples also had a special crosslinking agent (0.006g / 1000mAh) added. The lithium battery was subjected to high-temperature (60-80℃) formation and charge-discharge tests, the specific methods of which are as follows, and the specific results are shown in Table 2.

[0077] 1. Fabrication of the negative electrode sheet

[0078] The lithium-ion battery adhesives prepared in Examples 1-4 and the lithium-ion battery adhesives described in Comparative Examples 1-3 were mixed with conductive carbon black, silicon-based anode material, and CMC at a mass ratio of 3:10:86:1, respectively. A certain amount of deionized water was added, and the mixture was dispersed for 3 hours using a shear disperser to prepare an anode material with a solid content of 45 wt%. The dispersed anode material was uniformly coated onto copper foil using a coating machine and dried in an oven to obtain a single-sided anode sheet with a thickness of 100-150 μm. Then, the second side was coated using the same method to obtain a double-sided anode sheet. The sheet was then rolled using a roller press and finally placed in a vacuum drying oven and dried at 80°C for 10 hours.

[0079] 2. The flexibility test uses the needle coiling method:

[0080] After cold pressing, the negative electrode sheet is wound around a 1.2mm winding needle. The part around the winding needle is then aligned with force, and then a microscope is used to magnify the bent tip 100 times to observe the number of cracks.

[0081] 3. Peel force test:

[0082] The above-mentioned single-sided negative electrode sheet was cut into 20*100mm samples and tested using a 90-degree peel strength tester.

[0083] A 20mm wide double-sided adhesive tape is attached to the corresponding substrate on the 90° peel strength tester. The copper foil side of the sample is then attached to the double-sided adhesive tape, ensuring the edges are completely aligned. A 20mm wide transparent test tape is attached to the surface of the negative electrode material of the electrode sheet, extending 100mm beyond the sample. Finally, it is compacted with a pressure roller. The excess transparent tape is then fixed to the fixture of the 90° peel strength tester, forming a 90° angle with the sample. The 90° peel strength tester is started, and the sample is stretched at a speed of 50mm / min. The average tensile force after stabilization is recorded, which yields the electrode sheet cohesion.

[0084] A 20mm wide double-sided adhesive tape is attached to the corresponding substrate on the 90-degree peel strength tester. The negative electrode material side of the sample is then attached to the double-sided adhesive tape, ensuring the edges are completely aligned. A 20mm wide transparent test tape is attached to the copper foil side of the electrode, extending 100mm beyond the sample, and finally compacted with a pressure roller. The excess transparent tape is then fixed to the fixture of the 90-degree peel strength tester, forming a 90° angle with the sample. The 90-degree peel strength tester is started, and the sample is stretched at a speed of 50mm / min. The average tensile force after stabilization is recorded, which yields the electrode adhesion.

[0085] 4. Manufacturing of Lithium-ion Batteries

[0086] Five parts of positive electrode binder (PVDF) and 95 parts of LiCoO2 and conductive agent are thoroughly mixed into a slurry. The slurry is then coated onto a clean aluminum foil in the same manner as the negative electrode sheet. After drying and compaction, the positive electrode sheet is obtained.

[0087] Cut the positive electrode sheet and the aforementioned negative electrode sheet, weld on the tabs, and dry under vacuum at 100°C for 24 hours. Place the positive and negative electrodes in the battery container through the battery separator as needed, and then roll, fold, or otherwise place them into the battery container. Inject electrolyte into the battery container. In the example, the lithium battery made with the adhesive is also made with a special crosslinking agent (0.006g / 1000mAh). After sealing, a lithium-ion battery is obtained.

[0088] 5. Battery internal resistance and charge / discharge cycle test

[0089] The manufactured lithium-ion batteries were left to stand at 25°C for 24 hours, and then subjected to high-temperature (80°C) formation and aging using a hot-pressing fixture formation cabinet. Subsequently, the following charge and discharge operations were performed at 25°C: charging at a 1C rate using constant voltage and constant current (CC-CV) mode to 4.2V (current interruption condition: 0.02C), and discharging at a 1C rate using constant current (CC) mode to 3.0V. The initial capacity C0 and battery internal resistance were measured.

[0090] Then, the same charge-discharge operation was repeated at 25°C, and the capacity C1 after 500 cycles was measured. The capacity retention rate ΔC = (C1 / C0) × 100 (%) was then calculated. A higher capacity retention rate indicates less capacity loss and better cycle characteristics.

[0091] The battery was disassembled after 500 cycles to observe the adhesion and peeling of active materials on the negative electrode.

[0092] Table 2

[0093]

[0094] As shown in the table above, the silicon-based negative electrode sheet made from the binder for lithium-ion batteries prepared using the formulation and method of this invention has better flexibility and adhesion, and is less prone to cracking and powder shedding during winding. The lithium-ion batteries produced by the binders in Examples 1-4 have lower internal resistance, the negative electrode material is less prone to expansion and detachment, and the cycle life is longer.

[0095] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. The application of a lithium battery-specific post-crosslinking aqueous adhesive in the preparation of lithium-ion battery adhesives, characterized in that: This lithium-ion battery-specific post-crosslinking aqueous adhesive can undergo an addition reaction with a dedicated crosslinking agent during the battery formation stage, enabling secondary crosslinking within the battery. The dedicated crosslinking agent is added during the lithium-ion battery electrolyte filling process. This dedicated crosslinking agent is at least one of 2,6-toluene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, 2,2,4-trimethylhexane diisocyanate, dicyclohexylmethylene diisocyanate, isophorone diisocyanate, furan diisocyanate, or other small molecules and polymers containing isocyanate groups. The preparation method of this lithium-ion battery-specific post-crosslinking aqueous adhesive includes the following steps: Step 1: Add 400 parts of pure water, 2 parts of sodium dodecyl sulfate, and 2.5 parts of acrylic acid to the reaction apparatus, heat to 40°C and stir until completely dissolved; Step 2: Add 37 parts of n-butyl acrylate, 10 parts of hydroxypropyl acrylate, and 0.5 parts of divinylbenzene to the reaction apparatus; continue stirring until the materials are mixed evenly. Step 3: Simultaneously introduce high-purity nitrogen gas for 1 hour and raise the system temperature to 75°C; Step 4: Dissolve 2 parts of ammonium persulfate in 8 parts of pure water to obtain an ammonium persulfate solution. Take 2 parts of the ammonium persulfate solution and add it to the reaction apparatus. Keep the temperature constant and stir for 120 minutes. Step 5: Add 2g of ammonium persulfate solution, mix 10 parts of hydroxyethyl acrylamide, 20 parts of acrylonitrile, 10 parts of acrylic acid, and 10 parts of methyl methacrylate completely, and add the mixture dropwise to the reaction apparatus for 6 hours. After the dropwise addition begins, add 2 parts of the above ammonium persulfate solution to the reaction system every 2 hours until the dropwise addition is complete. After the dropwise addition is complete, continue the reaction for 8 hours. Step 6: After the reaction is complete, cool the system to room temperature, add sodium hydroxide solution, and adjust the pH to 7 to obtain a post-crosslinking aqueous adhesive for lithium batteries.

2. The application of a lithium battery-specific post-crosslinking aqueous adhesive in the preparation of lithium-ion battery adhesives, characterized in that: This lithium-ion battery-specific post-crosslinking aqueous adhesive can undergo an addition reaction with a dedicated crosslinking agent during the battery formation stage, enabling secondary crosslinking within the battery. The dedicated crosslinking agent is added during the lithium-ion battery electrolyte filling process. This dedicated crosslinking agent is at least one of 2,6-toluene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, 2,2,4-trimethylhexane diisocyanate, dicyclohexylmethylene diisocyanate, isophorone diisocyanate, furan diisocyanate, or other small molecules and polymers containing isocyanate groups. The preparation method of this lithium-ion battery-specific post-crosslinking aqueous adhesive includes the following steps: Step 1: Add 400 parts of pure water, 2 parts of sodium dodecyl sulfate, and 2.5 parts of acrylic acid to the reaction apparatus, heat to 40°C and stir until completely dissolved; Step 2: Add 27 parts of n-butyl acrylate, 20 parts of hydroxypropyl acrylate, and 0.5 parts of divinylbenzene to the reaction apparatus; continue stirring until the materials are mixed evenly. Step 3: Simultaneously introduce high-purity nitrogen gas for 1 hour and raise the system temperature to 75°C; Step 4: Dissolve 2 parts of ammonium persulfate in 8 parts of pure water to obtain an ammonium persulfate solution. Take 2 parts of the ammonium persulfate solution and add it to the reaction apparatus. Keep the temperature constant and stir for 120 minutes. Step 5: Add 2g of ammonium persulfate solution, mix 10 parts of hydroxyethyl acrylamide, 20 parts of acrylonitrile, 10 parts of acrylic acid, and 10 parts of methyl methacrylate completely, and add the mixture dropwise to the reaction apparatus for 6 hours. After the dropwise addition begins, add 2 parts of the above ammonium persulfate solution to the reaction system every 2 hours until the dropwise addition is complete. After the dropwise addition is complete, continue the reaction for 8 hours. Step 6: After the reaction is complete, cool the system to room temperature, add sodium hydroxide solution, and adjust the pH to 7 to obtain a post-crosslinking aqueous adhesive for lithium batteries.

3. The application of a lithium battery-specific post-crosslinking aqueous adhesive in the preparation of lithium-ion battery adhesives, characterized in that: This lithium-ion battery-specific post-crosslinking aqueous adhesive can undergo an addition reaction with a dedicated crosslinking agent during the battery formation stage, enabling secondary crosslinking within the battery. The dedicated crosslinking agent is added during the lithium-ion battery electrolyte filling process. This dedicated crosslinking agent is at least one of 2,6-toluene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, 2,2,4-trimethylhexane diisocyanate, dicyclohexylmethylene diisocyanate, isophorone diisocyanate, furan diisocyanate, or other small molecules and polymers containing isocyanate groups. The preparation method of this lithium-ion battery-specific post-crosslinking aqueous adhesive includes the following steps: Step 1: Add 400 parts of pure water, 2 parts of sodium dodecyl sulfate, and 2.5 parts of acrylic acid to the reaction apparatus, heat to 40°C and stir until completely dissolved; Step 2: Add 37 parts isooctyl acrylate, 10 parts hydroxypropyl acrylate, and 0.5 parts divinylbenzene to the reaction apparatus; continue stirring until the materials are evenly mixed. Step 3: Simultaneously introduce high-purity nitrogen gas for 1 hour and raise the system temperature to 75°C; Step 4: Dissolve 2 parts of ammonium persulfate in 8 parts of pure water to obtain an ammonium persulfate solution. Take 2 parts of the ammonium persulfate solution and add it to the reaction apparatus. Keep the temperature constant and stir for 120 minutes. Step 5: Add 2g of ammonium persulfate solution, mix 10 parts of hydroxyethyl acrylamide, 20 parts of acrylonitrile, 10 parts of acrylic acid, and 10 parts of methyl methacrylate completely, and add the mixture dropwise to the reaction apparatus for 6 hours. After the dropwise addition begins, add 2 parts of the above ammonium persulfate solution to the reaction system every 2 hours until the dropwise addition is complete. After the dropwise addition is complete, continue the reaction for 8 hours. Step 6: After the reaction is complete, cool the system to room temperature, add sodium hydroxide solution, and adjust the pH to 7 to obtain a post-crosslinking aqueous adhesive for lithium batteries.

4. The application of a lithium battery-specific post-crosslinking aqueous adhesive in the preparation of lithium-ion battery adhesives, characterized in that: This lithium-ion battery-specific post-crosslinking aqueous adhesive can undergo an addition reaction with a dedicated crosslinking agent during the battery formation stage, enabling secondary crosslinking within the battery. The dedicated crosslinking agent is added during the lithium-ion battery electrolyte filling process. This dedicated crosslinking agent is at least one of 2,6-toluene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, 2,2,4-trimethylhexane diisocyanate, dicyclohexylmethylene diisocyanate, isophorone diisocyanate, furan diisocyanate, or other small molecules and polymers containing isocyanate groups. The preparation method of this lithium-ion battery-specific post-crosslinking aqueous adhesive includes the following steps: Step 1: Add 400 parts of pure water, 2 parts of sodium dodecyl sulfate, and 2.5 parts of acrylic acid to the reaction apparatus, heat to 40°C and stir until completely dissolved; Step 2: Add 37 parts of n-butyl acrylate, 10 parts of hydroxypropyl acrylate, and 0.5 parts of divinylbenzene to the reaction apparatus; continue stirring until the materials are mixed evenly. Step 3: Simultaneously introduce high-purity nitrogen gas for 1 hour and raise the system temperature to 75°C; Step 4: Dissolve 2 parts of ammonium persulfate in 8 parts of pure water to obtain an ammonium persulfate solution. Take 2 parts of the ammonium persulfate solution and add it to the reaction apparatus. Keep the temperature constant and stir for 120 minutes. Step 5: Add 2g of ammonium persulfate solution, mix 15 parts of hydroxyethyl acrylamide, 20 parts of acrylonitrile, 10 parts of acrylic acid, and 5 parts of methyl methacrylate completely, and add the mixture dropwise to the reaction apparatus for 6 hours. After the dropwise addition begins, add 2 parts of the above ammonium persulfate solution to the reaction system every 2 hours until the dropwise addition is complete. After the dropwise addition is complete, continue the reaction for 8 hours. Step 6: After the reaction is complete, cool the system to room temperature, add sodium hydroxide solution, and adjust the pH to 7 to obtain a post-crosslinking aqueous adhesive for lithium batteries.

Images