Waterborne polyurethane as well as preparation method and application thereof

Abstract

The invention discloses waterborne polyurethane as well as a preparation method and application thereof. The waterborne polyurethane is prepared from the following raw materials: first polyol resin, second polyol resin, a polyisocyanate curing agent, a chain extender, a cross-linking agent, a neutralizer, a catalyst and a solvent. The second polyhydric alcohol resin is polyhydric alcohol resin containing a benzene ring. The hydroxyl-terminated polybutadiene styrene is used as the second polyol resin, so that the adhesive strength can be remarkably improved. And moreover, the balance between the main chain elasticity and the anchoring capability of side phenyl is ensured, and good dispersity and film-forming property are kept while the bonding force is improved. The waterborne polyurethane is synthesized by adopting a three-step polymerization process, benzene rings are ensured to be distributed on two sides of a polymer chain instead of the middle part of a main chain, an effective connection structure of graphite / conductive agent-benzene ring-main chain-benzene ring-graphite / conductive agent is formed, and the problems that the main chain and dispersed particles are too high in affinity and cannot be effectively stretched due to the fact that the benzene rings are too close to the main chain are solved.

Description

Technical Field

[0001] This invention relates to the field of polymeric compound compositions, and more specifically to an aqueous polyurethane, its preparation method, and its applications. Background Technology

[0002] Lithium-ion rechargeable batteries undergo volume expansion during charge and discharge. Traditional binders struggle to accommodate this volume change, leading to electrode structure damage and capacity decay. Existing waterborne polyurethane binders suffer from insufficient adhesion to the negative electrode material, and their main chain rigidity is too high to withstand the high expansion rate during charge and discharge. Furthermore, waterborne polyurethane exhibits poor dispersibility and coating properties, failing to meet the technical requirements for stable battery charge and discharge structures. Therefore, developing a waterborne polyurethane with strong adhesion that can solve the volume expansion problem during battery charge and discharge is crucial.

[0003] Chinese invention patent application CN120209766A discloses a high-adhesion polyurethane adhesive for lithium-ion batteries and its preparation method. The cyano group can be introduced by using acrylonitrile-modified polyolefin polyols, or diols or diamines containing cyano groups, which can improve the adhesion of the polyurethane adhesive and facilitate the adhesion of active materials to the current collector. However, the influence of cohesive force is ignored, and the improvement in adhesion is not significant. Chinese invention patent CN119219889B discloses an aqueous polyurethane dispersion, its preparation method, and its application. It uses polybutadiene polyols with specific structures and molecular weights as soft segments. Through component design and mutual compounding, the aqueous polyurethane dispersion has lower polarity and surface energy, exhibiting excellent solvent resistance, low-temperature resistance, hydrolysis resistance, and mechanical properties. However, its effect on solving the volume expansion problem during battery charging and discharging is not significant. Summary of the Invention

[0004] In order to develop a waterborne polyurethane with strong adhesion that can solve the problem of volume expansion during battery charging and discharging, the first aspect of the present invention provides a waterborne polyurethane, the raw materials for which include a first polyol resin, a second polyol resin, a polyisocyanate curing agent, a chain extender, a crosslinking agent, a neutralizing agent, a catalyst and a solvent; the second polyol resin is a polyol resin containing benzene rings.

[0005] Existing waterborne polyurethanes used in battery anode bonding suffer from insufficient adhesion. This application introduces a polyol resin containing benzene rings. Utilizing the affinity between benzene rings and graphite anodes, the benzene rings polymerize on both sides of the main chain of the waterborne polyurethane, and the side benzene rings are inserted into the graphite anode, forming a graphite / conductive agent-side benzene ring-polyurethane main chain-side benzene ring-another graphite / conductive agent system. This enhances the connection between particles, thereby increasing the adhesion between the waterborne polyurethane and the graphite anode.

[0006] In one embodiment, the raw materials prepared by weight include 30-50 parts of a first polyol resin, 1-20 parts of a second polyol resin, 5-20 parts of a polyisocyanate curing agent, 1-5 parts of a chain extender, 10-20 parts of a crosslinking agent, 10-20 parts of a neutralizing agent, 0.01-0.1 parts of a catalyst, and 70-90 parts of a solvent.

[0007] In one embodiment, the raw materials prepared by weight include 35-45 parts of a first polyol resin, 5-15 parts of a second polyol resin, 10-15 parts of a polyisocyanate curing agent, 1-3 parts of a chain extender, 10-15 parts of a crosslinking agent, 10-15 parts of a neutralizing agent, 0.03-0.08 parts of a catalyst, and 70-90 parts of a solvent.

[0008] The amount of the second polyol resin added is between 5 and 13 parts by weight. When the amount of the second polyol resin added exceeds the preferred range, the benzene ring will gradually approach the main chain of the polyurethane. The affinity between the main chain and the dispersed particles increases sharply, resulting in ineffective expansion and failure to form an effective connection of graphite-benzene ring-main chain-benzene ring-another graphite / conductive agent. The adhesive strength decreases as the amount of the second polyol resin used increases.

[0009] In one embodiment, the second polyol resin is hydroxyl-terminated polybutadiene styrene.

[0010] In one embodiment, the hydroxyl-terminated polybutadiene styrene has a number-average molecular weight > 2000, a hydroxyl value of 0.7-0.8 mmol / g, and a benzene content of 15-20 wt%.

[0011] In one embodiment, the curing agent includes at least one of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, or dicyclohexylmethane diisocyanate.

[0012] In one embodiment, the first polyol resin includes at least one of hydroxyl-terminated polybutadiene, hydrogenated hydroxyl-terminated polybutadiene, or hydroxyl-terminated polybutadiene acrylonitrile.

[0013] In one embodiment, the first polyol resin is hydrogenated hydroxyl-terminated polybutadiene.

[0014] In one embodiment, the chain extender is a hydrophilic chain extender, which includes at least one of D-glyceric acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolacetic acid, trihydroxysulfonic acid, or dihydroxysuccinic acid.

[0015] In one embodiment, the hydrophilic chain extender includes at least one of dimethylolpropionic acid or dimethylolbutyric acid.

[0016] In one embodiment, the hydrophilic chain extender is 2,2-dihydroxymethylpropionic acid.

[0017] In one embodiment, the raw materials for preparation further include deionized water, the neutralizing agent is an aqueous solution containing an alkaline substance, and the mass ratio of the alkaline substance to water in the aqueous solution containing the alkaline substance is 1:(10-30); the crosslinking agent is an aqueous solution containing a polyamine, and the mass ratio of the polyamine to water in the aqueous solution containing the polyamine is 1:(10-30).

[0018] In one embodiment, the polyamine includes at least one of diethylenetriamine or di(hexamethylene)triamine.

[0019] In one embodiment, the polyamine is diethylenetriamine.

[0020] In one embodiment, the alkaline substance includes at least one of triethylamine, sodium hydroxide, potassium hydroxide, or lithium hydroxide.

[0021] In one embodiment, the alkaline substance includes at least one of sodium hydroxide or lithium hydroxide.

[0022] In one embodiment, the alkaline substance is sodium hydroxide.

[0023] In one embodiment, the catalyst includes at least one of dimethyltin dinedecanoate, dibutyltin dilaurate, or dioctyltin dilaurate.

[0024] In one embodiment, the catalyst is dimethyltin dinedecanoate.

[0025] In one embodiment, the solvent includes at least one of acetone, butanone, ethyl acetate, propyl propionate, or propyl acetate.

[0026] In one embodiment, the solvent is butanone.

[0027] A second aspect of the present invention provides a method for preparing waterborne polyurethane, comprising the following steps: The first polyol resin, polyisocyanate curing agent, and catalyst are reacted in an inert gas to obtain the first prepolymer; After cooling, a chain extender and solvent are added to the first prepolymer to continue the reaction, yielding the second prepolymer; A second polyol resin is added to the second prepolymer to continue the reaction, resulting in a polymer solution; The polymer solution was cooled, a neutralizing agent was added and stirred to disperse it, then deionized water was added to dilute and stir, then a crosslinking agent was added and stirred to disperse it, and the solvent was distilled off under reduced pressure to obtain waterborne polyurethane.

[0028] This application employs a three-step method for synthesizing polyurethane polymers, which can anchor benzene rings to the side chains of polyurethane, thereby forming an aqueous polyurethane with benzene rings in the side chains. This achieves the technical effect of inserting benzene rings into graphite and improves adhesion.

[0029] In one embodiment, the reaction temperature of the first prepolymer is 80-90°C; the reaction temperature of the second prepolymer is 65-75°C; and the reaction temperature of the polymer solution is 68-75°C.

[0030] In one embodiment, the reaction temperature of the first prepolymer is 85°C; the reaction temperature of the second prepolymer is 70°C; and the reaction temperature of the polymer solution is 70°C.

[0031] In one embodiment, the reaction time of the first prepolymer is 2-4 hours; the reaction temperature of the second prepolymer is 4-6 hours; and the reaction temperature of the polymer solution is 12-14 hours.

[0032] In one embodiment, the reaction time of the first prepolymer is 3 hours; the reaction temperature of the second prepolymer is 5 hours; and the reaction temperature of the polymer solution is 13 hours.

[0033] As one embodiment, the addition of the neutralizing agent involves stirring and dispersing for 5-10 minutes, the addition of deionized water involves dilution and stirring for 10-20 minutes, and the addition of the crosslinking agent involves stirring and dispersing for 20-40 minutes.

[0034] As one embodiment, the addition of the neutralizing agent involves stirring and dispersing for 5 minutes, the addition of deionized water involves dilution and stirring for 15 minutes, and the addition of the crosslinking agent involves stirring and dispersing for 30 minutes.

[0035] In one embodiment, the addition of deionized water is used to dilute the polymer to a solid content of 25-35 wt%.

[0036] In one embodiment, deionized water is added to dilute the polymer to a solid content of 30 wt%.

[0037] In one embodiment, the inert gas is nitrogen.

[0038] A third aspect of the present invention provides an application of aqueous polyurethane in the negative electrode of a lithium-ion secondary battery.

[0039] Compared with the prior art, the present invention has the following beneficial effects: (1) The waterborne polyurethane of the present invention uses hydroxyl-terminated polybutadiene styrene with a number average molecular weight >2500, a hydroxyl value of 0.6-0.7 mmol / g, and a benzene content of 5-15 wt% as the second polyol resin, which can significantly improve cohesion, enhance the connection between particles, increase the connection between graphite active materials, and make it less prone to powdering and cracking; during battery charging and discharging, it can reduce the situation of active material shedding and capacity reduction due to low cohesion.

[0040] (2) The waterborne polyurethane of the present invention uses 5-13 parts by weight of hydroxyl-terminated polybutadiene styrene, which ensures the balance between the elasticity of the main chain and the "anchoring" ability of the side phenyl groups, and maintains good dispersibility and film-forming properties while improving adhesion.

[0041] (3) The method for preparing waterborne polyurethane described in this invention uses a three-step polymerization process to synthesize waterborne polyurethane, ensuring that the benzene rings are distributed on both sides of the polymer chain rather than in the middle of the main chain, forming an effective connection structure of "graphite / conductive agent-benzene ring-main chain-benzene ring-graphite / conductive agent", avoiding the problem that the main chain and dispersed particles have too high affinity due to the benzene rings being too close to the main chain, and thus cannot be effectively spread.

[0042] (4) The waterborne polyurethane of the present invention uses dicyclohexylmethane diisocyanate as a curing agent. The resulting high-elasticity carbon chain structure can adapt very well to the high expansion rate of the main material during the charging process, thereby improving the cycle stability of the battery.

[0043] (5) The waterborne polyurethane of the present invention is applied to graphite anode and silicon-carbon anode to improve adhesion to the battery anode, and the high elastic carbon chain in the middle of the main chain can adapt well to the high expansion rate of the main material during the charging process. Detailed Implementation

[0044] Example 1 A waterborne polyurethane, the raw materials for preparation include 45g of a first polyol resin, 5g of a second polyol resin, 13.33g of a polyisocyanate curing agent, 2.66g of a chain extender, 10.5g of a crosslinking agent, 14.71g of a neutralizing agent, 0.05g of a catalyst, 81g of a solvent, and deionized water.

[0045] The first polyol resin is hydrogenated hydroxyl-terminated polybutadiene, purchased from Clayville, with the brand name HLBH-P2000.

[0046] The second polyol resin is hydroxyl-terminated polybutadiene styrene with a number-average molecular weight >2000, a hydroxyl value of 0.7-0.8 mmol / g, and a benzene content of 18 wt%. It was purchased from Zibo Qilong Chemical Co., Ltd. and is classified as Type II.

[0047] The polyisocyanate curing agent is dicyclohexylmethane diisocyanate, purchased from Wanhua Chemical Group Co., Ltd.

[0048] The chain extender is 2,2-dihydroxymethylpropionic acid.

[0049] The crosslinking agent is an aqueous solution of diethylenetriamine, wherein the mass ratio of diethylenetriamine to water in the aqueous solution of diethylenetriamine is 0.5:10.

[0050] The neutralizing agent is an aqueous solution of sodium hydroxide, wherein the mass ratio of sodium hydroxide to water in the aqueous solution is 0.71:14.

[0051] The catalyst is dimethyltin dinedecanoate.

[0052] The solvent is butanone.

[0053] A method for preparing waterborne polyurethane includes the following steps: The first polyol resin, polyisocyanate curing agent and catalyst were placed in nitrogen and reacted at 85°C for 3 hours to obtain the first prepolymer. After cooling to 70°C, a chain extender and solvent were added to the first prepolymer and the reaction continued for 5 hours to obtain the second prepolymer. Add the second polyol resin to the second prepolymer and continue the reaction for 13 hours to obtain a polymer solution; The polymer solution was cooled to 30°C, a neutralizing agent was added and stirred for 5 minutes, then deionized water was added and stirred for 15 minutes. The crosslinking agent was then added and stirred for 30 minutes. The solvent was distilled off under reduced pressure to obtain waterborne polyurethane.

[0054] The polymer is diluted with deionized water until the solid content is 30 wt%.

[0055] Example 2 A waterborne polyurethane and its preparation method are disclosed. The raw materials include 40g of a first polyol resin, 10g of a second polyol resin, 13.33g of a polyisocyanate curing agent, 2.66g of a chain extender, 10.5g of a crosslinking agent, 14.71g of a neutralizing agent, 0.05g of a catalyst, 81g of a solvent, and deionized water.

[0056] The remaining implementation methods are the same as in Example 1.

[0057] Example 3 A waterborne polyurethane and its preparation method are disclosed. The raw materials include 37g of a first polyol resin, 13g of a second polyol resin, 13.33g of a polyisocyanate curing agent, 2.66g of a chain extender, 10.5g of a crosslinking agent, 14.71g of a neutralizing agent, 0.05g of a catalyst, 81g of a solvent, and deionized water.

[0058] The remaining implementation methods are the same as in Example 1.

[0059] Comparative Example 1 A waterborne polyurethane and its preparation method are described. The specific implementation method is the same as in Example 1, except that 5g of hydroxyl-terminated polybutadiene styrene is replaced with 0.52g of bisphenol A.

[0060] Note: The 5g hydroxyl-terminated polybutadiene styrene in Example 1 and the 0.52g bisphenol A in Comparative Example 1 have the same molar amount of hydroxyl groups.

[0061] Comparative Example 2 A waterborne polyurethane and its preparation method are described. The specific implementation method is the same as in Example 1, except that 5g of hydroxyl-terminated polybutadiene styrene is replaced with 0.31g of p-hydroxyphenylethanol.

[0062] Note: The 5g hydroxyl-terminated polybutadiene styrene in Example 1 and the 0.31g p-hydroxyphenylethanol in Comparative Example 2 have the same molar amount of hydroxyl groups.

[0063] Comparative Example 3 A waterborne polyurethane, the raw materials for preparation include 50g of a first polyol resin, 13.33g of a polyisocyanate curing agent, 2.66g of a chain extender, 10.5g of a crosslinking agent, 14.71g of a neutralizing agent, 0.05g of a catalyst, 81g of a solvent, and deionized water.

[0064] The first polyol resin is hydrogenated hydroxyl-terminated polybutadiene, purchased from Clayville, with the brand name HLBH-P2000.

[0065] The polyisocyanate curing agent is 4,4'-methylenebis(phenyl isocyanate), purchased from Wanhua Chemical Group Co., Ltd.

[0066] The chain extender is 2,2-dihydroxymethylpropionic acid.

[0067] The crosslinking agent is an aqueous solution of diethylenetriamine, wherein the mass ratio of diethylenetriamine to water in the aqueous solution of diethylenetriamine is 0.5:10.

[0068] The neutralizing agent is an aqueous solution of sodium hydroxide, wherein the mass ratio of sodium hydroxide to water in the aqueous solution is 0.71:14.

[0069] The catalyst is dimethyltin dinedecanoate.

[0070] The solvent is butanone.

[0071] A method for preparing waterborne polyurethane includes the following steps: The first polyol resin, polyisocyanate curing agent and catalyst were placed in nitrogen and reacted at 85°C for 3 hours to obtain the first prepolymer. After cooling to 70°C, a chain extender and solvent were added to the first prepolymer and the reaction continued for 16 hours to obtain a polymer solution. The polymer solution was cooled to 30°C, a neutralizing agent was added and stirred for 5 minutes, then deionized water was added and stirred for 15 minutes. The crosslinking agent was then added and stirred for 30 minutes. The solvent was distilled off under reduced pressure to obtain waterborne polyurethane.

[0072] The polymer is diluted with deionized water until the solid content is 30 wt%.

[0073] Comparative Example 4 A waterborne polyurethane, with the same specific implementation as Example 1, differs in that a method for preparing the waterborne polyurethane includes the following steps: The first polyol resin, polyisocyanate curing agent and catalyst were placed in nitrogen and reacted at 85°C for 3 hours to obtain the first prepolymer. After cooling to 70°C, a chain extender, solvent, and second polyol resin were added to the first prepolymer and the reaction continued for 15 hours to obtain a polymer solution. The polymer solution was cooled to 30°C, a neutralizing agent was added and stirred for 5 minutes, then deionized water was added and stirred for 15 minutes. The crosslinking agent was then added and stirred for 30 minutes. The solvent was distilled off under reduced pressure to obtain waterborne polyurethane.

[0074] The polymer is diluted with deionized water until the solid content is 30 wt%.

[0075] Comparative Example 5 A waterborne polyurethane, with the same specific implementation as Example 1, differs in that a method for preparing the waterborne polyurethane includes the following steps: The first polyol resin, polyisocyanate curing agent, catalyst, chain extender, solvent, and second polyol resin were placed in nitrogen and reacted at 70°C for 18 hours to obtain a polymer solution. The polymer solution was cooled to 30°C, a neutralizing agent was added and stirred for 5 minutes, then deionized water was added and stirred for 15 minutes. The crosslinking agent was then added and stirred for 30 minutes. The solvent was distilled off under reduced pressure to obtain waterborne polyurethane.

[0076] The polymer is diluted with deionized water until the solid content is 30 wt%.

[0077] Comparative Example 6 A waterborne polyurethane and its preparation method are described. The specific implementation method is the same as in Example 1, except that the second polyol resin is hydroxyl-terminated polybutadiene styrene with a number-average molecular weight > 2500, a hydroxyl value of 0.6-0.7 mmol / g, and a benzene content of 10 wt%. It was purchased from Zibo Qilong Chemical Co., Ltd. and is designated as Type I.

[0078] Comparative Example 7 A waterborne polyurethane and its preparation method are described. The specific implementation method is the same as in Example 1, except that the amount of the second polyol resin added is 0.

[0079] A method for preparing waterborne polyurethane includes the following steps: The first polyol resin, polyisocyanate curing agent and catalyst were placed in nitrogen and reacted at 85°C for 3 hours to obtain the first prepolymer. After cooling to 70°C, a chain extender and solvent were added to the first prepolymer and the reaction continued for 16 hours to obtain a polymer solution. The polymer solution was cooled to 30°C, a neutralizing agent was added and stirred for 5 minutes, then deionized water was added and stirred for 15 minutes. The crosslinking agent was then added and stirred for 30 minutes. The solvent was distilled off under reduced pressure to obtain waterborne polyurethane.

[0080] The polymer is diluted with deionized water until the solid content is 30 wt%.

[0081] Performance testing 1. Adhesion test: Graphite, conductive carbon black, aqueous polyurethane (based on solid content) prepared in the examples and comparative examples, and sodium carboxymethyl cellulose were mixed in a mass ratio of 94:2:3:1. An equal mass of deionized water was added and the mixture was uniformly coated onto the surface of a 6 μm double-sided copper foil. The coating was then baked in an oven at 120°C for 5 min to obtain an electrode sheet with a coating thickness of 150±20 μm for later use.

[0082] Cut the electrode sheet into strips of varying lengths, each 20 mm wide, for later use; Use double-sided tape to adhere an irregularly shaped strip of coating to the surface, and attach a 210 mm × 50 mm × 1.5 mm (length × width × thickness) steel sheet to the other side.

[0083] A 180° peel test was performed on a tensile testing machine to test the peel force. The tensile speed was 20 mm / min. The effective length of the average peel force was calculated by removing the first 5 mm and the last 10 mm.

[0084] 2. Cohesion test: Graphite, conductive carbon black, aqueous polyurethane (based on solid content) prepared in the examples and comparative examples, and sodium carboxymethyl cellulose were mixed in a mass ratio of 94:2:3:1. An equal mass of deionized water was added and the mixture was uniformly coated onto the surface of a 6 μm double-sided copper foil. The coating was then baked in an oven at 120°C for 5 min to obtain an electrode sheet with a coating thickness of 150±20 μm for later use.

[0085] Cut the electrode sheet into strips of varying lengths, each 20 mm wide, for later use; Use double-sided tape to adhere to the surface of an irregularly shaped copper foil strip, and attach a 210 mm × 50 mm × 1.5 mm (length × width × thickness) steel sheet to the other side.

[0086] Use low-tack tape to adhere to the surface of irregularly long strips of coating, leaving a portion as a clamping point; On a tensile testing machine, a 180° peel test was performed to test the peel force. The tensile speed was 20 mm / min. The fracture surface was taken as the middle coating layer as the effective strip (the effective strip means that the fracture surface occurs between the active materials, that is, part of the active material is taken off the coating surface by the tape). The effective length was calculated by removing the first 5 mm and the last 10 mm after the average cohesive force.

[0087] The test results are shown in Table 1.

[0088] Table 1

[0089] Example 1, compared with Comparative Example 7, demonstrates that the introduction of a second polyol resin with a benzene ring helps to improve peel strength and cohesive strength.

[0090] Examples 1, 2, and 3 show that adding a second polyol resin helps improve adhesion, but the increase is not unlimited. This is because excessive use of the second polyol resin makes it impossible to obtain the target polymer with benzene rings on both sides of the main chain through stepwise polymerization. The closer the benzene rings are to the main chain, the more drastically the affinity between the main chain and the dispersed particles increases, preventing effective expansion and the formation of an effective connection between graphite-benzene ring-main chain-benzene ring-another graphite / conductive agent. Consequently, adhesion and cohesion decrease with increasing use of the second polyol resin.

[0091] Compared with Example 1, Comparative Examples 1 and 2 showed that using other small-molecule benzene ring polyols with non-side phenyl groups did not significantly improve the adhesion. This is because the non-side phenyl groups cannot be inserted into the graphite layer, and the polarity of the functional groups on both sides affects the affinity between the non-side phenyl groups and the graphite layer.

[0092] Comparisons 4 and 5 with Example 1 show that the desired target polymer was not synthesized according to the specific steps, resulting in poor improvement in adhesive strength and cohesive strength.

[0093] A comparison of Comparative Example 6 and Example 1 shows that the second polyol resin, using the same type but with different parameters, did not significantly improve adhesion compared to the first. This is because the second polyol resin used in Comparative Example 6 has an excessively large molecular weight and low functionality, resulting in some resin failing to react and becoming "anchored" segments on both sides of the main chain. Furthermore, the benzene content of the second polyol resin used in Comparative Example 6 is lower than that used in Example 1, leading to insufficient density of side phenyl groups, insufficient affinity between the main chain and graphite, and insufficient intercalation of side phenyl groups in the graphite. This results in decreased "anchoring" ability and reduced adhesion and cohesion.

Claims

1. A waterborne polyurethane, characterized in that, The raw materials for preparation include a first polyol resin, a second polyol resin, a polyisocyanate curing agent, a chain extender, a crosslinking agent, a neutralizing agent, a catalyst, and a solvent; the second polyol resin is a polyol resin containing benzene rings.

2. The waterborne polyurethane according to claim 1, characterized in that, The raw materials prepared by weight include 30-50 parts of first polyol resin, 1-20 parts of second polyol resin, 5-20 parts of polyisocyanate curing agent, 1-5 parts of chain extender, 10-20 parts of crosslinking agent, 10-20 parts of neutralizer, 0.01-0.1 parts of catalyst and 70-90 parts of solvent.

3. The waterborne polyurethane according to claim 1, characterized in that, The second polyol resin is hydroxyl-terminated polybutadiene styrene.

4. The waterborne polyurethane according to claim 3, characterized in that, The hydroxyl-terminated polybutadiene styrene has a number-average molecular weight >2000, a hydroxyl value of 0.7-0.8 mmol / g, and a benzene content of 15-20 wt%.

5. The waterborne polyurethane according to claim 1, characterized in that, The curing agent includes at least one of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, or dicyclohexylmethane diisocyanate.

6. The waterborne polyurethane according to claim 1, characterized in that, The raw materials for preparation also include deionized water, the neutralizing agent is an aqueous solution containing an alkaline substance, and the mass ratio of the alkaline substance to water in the aqueous solution containing the alkaline substance is 1:(10-30); the crosslinking agent is an aqueous solution containing a polyamine, and the mass ratio of the polyamine to water in the aqueous solution containing the polyamine is 1:(10-30).

7. A method for preparing waterborne polyurethane according to claim 6, characterized in that, Includes the following steps: The first polyol resin, polyisocyanate curing agent, and catalyst are reacted in an inert gas to obtain the first prepolymer; After cooling, a chain extender and solvent are added to the first prepolymer to continue the reaction, yielding the second prepolymer; A second polyol resin is added to the second prepolymer to continue the reaction, resulting in a polymer solution; The polymer solution was cooled, a neutralizing agent was added and stirred to disperse it, then deionized water was added to dilute and stir, then a crosslinking agent was added and stirred to disperse it, and the solvent was distilled off under reduced pressure to obtain waterborne polyurethane.

8. The method for preparing waterborne polyurethane according to claim 7, characterized in that, The reaction temperature of the first prepolymer is 80-90℃; the reaction temperature of the second prepolymer is 65-75℃; and the reaction temperature of the polymer solution is 68-75℃.

9. The method for preparing waterborne polyurethane according to claim 7, characterized in that, The polymer is diluted with deionized water until the solid content is 25-35 wt%.

10. An application of the waterborne polyurethane according to any one of claims 1-6, characterized in that, It is used in the negative electrode of lithium-ion secondary batteries.

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