Waterborne polyurethane as well as preparation method and application thereof

Abstract

The invention provides waterborne polyurethane as well as a preparation method and application thereof, and belongs to the field of lithium ion batteries. The aqueous amino acid molecular chains contain anionic polyurethane chain segments and zwitterionic chain segments, so that the binder has good ion conduction performance, and meanwhile, due to the acting force between the molecular chains and the two chain segments are not dissolved in electrolyte, the binding force of the binder is greatly improved; the prepared polyurethane binder has good solvent resistance in an electrolyte, that is, the polyurethane binder has low swelling degree; the anion chain segment, the zwitterionic chain segment and the acrylic acid (ester) chain segment have strong polarity, so that the prepared binder has good adhesion performance; a polyurethane chain segment is used as a soft segment part of a molecular chain, has high elasticity, and well meets the volume change of an active substance in a circulation process; and a molecular chain contains an anionic polyurethane chain segment and a zwitterionic chain segment, so that the binder has good water solubility.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to an aqueous polyurethane, its preparation method, and its application. Background Technology

[0002] With its advantages of safety, high energy density, and long cycle life, lithium-ion batteries are currently widely used in electric vehicles and smart electronic products. Lithium-ion batteries can be divided into several key components based on their composition and function, including the positive electrode, electrolyte, and negative electrode. In the positive and negative electrodes of a lithium-ion battery, a binder is needed to bond the positive or negative active material to the conductive agent on the current collector, thereby forming a stable positive and negative electrode. Although the amount of binder used in battery materials is relatively small in industrial applications, it has a significant impact on the battery's capacity, rate performance, and cycle life.

[0003] PVDF is commonly used as a binder for the positive and negative electrodes of lithium-ion batteries due to its good chemical and electrochemical stability. However, PVDF relies solely on van der Waals forces to bind with conductive agents and active components, resulting in insufficient bonding ability. This can lead to electrode structure instability and affect cycle life. Furthermore, PVDF itself lacks good ionic conductivity, which may affect lithium-ion transport within the electrode. Traditional solvent-based aqueous polyurethanes, as binders, exhibit good bonding performance, excellent mechanical properties, and flexibility. However, their solvent resistance in electrolytes is poor, resulting in high swelling, which severely degrades mechanical properties and may affect the battery's long-term cycle life at high voltages. Moreover, the main chain of aqueous polyurethanes is primarily linked by covalent bonds, lacking groups for free electron or ion transport, thus resulting in low electronic and ionic conductivity. Summary of the Invention

[0004] This invention provides an aqueous polyurethane, its preparation method, and its application. The aqueous polyurethane of this invention has good flexibility and can effectively buffer the expansion and contraction of electrode materials. At the same time, the electrode prepared by the aqueous polyurethane has lower electrolyte swelling, better ion transport capability, higher specific capacity, and higher battery long-cycle capacity retention rate.

[0005] This invention provides an aqueous polyurethane having the structural formula shown in Formula 1:

[0006]

[0007] In Formula 1: n is a natural number from 1 to 100, and R1 includes a first alkylene group, a first cycloalkylene group, or a first arylalkylene group;

[0008] R2 has the structural formula shown in Equation 2:

[0009]

[0010] In Equation 2, x > 0, y > 0, z > 0, R 10 Including the first alkyl group, R 11 It includes triethylamine, triethanolamine or lithium; R3 includes a second alkylene, a second cycloalkylene or a second arylalkylene; R4, R8 and R9 independently include hydrogen or a second alkylene; R5 includes oxygen or nitrogen; R6 includes a third alkylene; R7 is hydrogen, a fourth alkylene or fluorine; Z is an anion.

[0011] Preferably, the first alkyl group, the second alkyl group, the third alkyl group, and the fourth alkyl group independently include methyl, ethyl, or propyl.

[0012] Preferably, the number of carbon atoms in the first alkylene group and the second alkylene group is independently 1 to 6;

[0013] The number of carbon atoms in the first and second cycloalkyl groups is independently 5 to 10;

[0014] The number of carbon atoms in the first and second arylene alkyl groups is independently 6 to 10;

[0015] The anions include sulfonate, carboxylate, or phosphate.

[0016] The present invention also provides a method for preparing the waterborne polyurethane described in the above technical solution, comprising the following steps:

[0017] Polydiol, diisocyanate, dimethylolcarboxylic acid and organometallic catalyst are mixed to carry out a first polymerization reaction. Then, the resulting polymerization product is mixed with hydroxy acrylate or hydroxyacrylamide and a polymerization inhibitor to carry out a second polymerization reaction to obtain an aqueous polyurethane prepolymer solution.

[0018] The aqueous polyurethane prepolymer solution is mixed with a neutralizing agent to carry out a neutralization reaction, thereby obtaining a neutralization reaction product;

[0019] The neutralization reaction product is mixed with the first water and then mixed with an aqueous solution of an amine chain extender to carry out a chain extension reaction, thereby obtaining an aqueous polyurethane solution.

[0020] The acrylic monomer or acrylate monomer is mixed with the aqueous polyurethane solution, zwitterionic monomer, and second water, and then mixed with an aqueous solution of ammonium persulfate to carry out a third polymerization reaction to obtain the aqueous polyurethane.

[0021] Preferably, the ratio of the amount of hydroxyl groups in the polydiol to the amount of hydroxyl groups in the hydroxyacrylate or hydroxyacrylamide is 0.05 to 0.4:1.

[0022] The hydroxy acrylates include one or more of the following: hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, pentaerythritol triacrylate, pentaerythritol diacrylate, glycerol 1,3-diglyceryl alcohol diacrylate, and glycerol diacrylate.

[0023] The hydroxyacrylamide includes one or more of N-hydroxyethylacrylamide, N-(3-hydroxypropyl)acrylamide, and N-(4-hydroxybutyl)acrylamide.

[0024] The polymerization inhibitor includes one or more of hydroquinone, tert-butylcatechol, and p-hydroxyanisole, and the mass of the polymerization inhibitor is 0.1 to 1.5% of the mass of hydroxyacrylate or hydroxyacrylamide.

[0025] Preferably, the neutralizing agent includes one or more of triethylamine, triethanolamine, and lithium hydroxide, and the amount of the neutralizing agent is 50 to 100% of the amount of dihydroxymethylcarboxylic acid.

[0026] The amine chain extender includes one or more of ethylenediamine, propylenediamine, butanediamine, 2-methylpentanediamine, hexamethylenediamine, isophoronediamine, and sodium ethylenediaminoethanesulfonate.

[0027] Preferably, the zwitterionic monomer comprises one of methacryloylethyl sulfobetaine, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propionic acid)ammonium hydroxide, 2-methacryloyloxyethyl phosphoric acid choline, 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate, and 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt.

[0028] The acrylate monomer includes any one of methyl acrylate, ethyl acrylate, and dodecyl acrylate.

[0029] Preferably, the ratio of the amount of hydroxyl group in the dihydroxymethylcarboxylic acid to the amount of hydroxyl group in the hydroxyacrylate or hydroxyacrylamide is 0.05 to 0.4:1.

[0030] The ratio of the amount of isocyanate in the diisocyanate to the amount of hydroxyl group in the hydroxy acrylate or hydroxyacrylamide is 0.05 to 0.4:1.

[0031] The diisocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 2,4-ethylphenyl diisocyanate, methylcyclohexyl diisocyanate, and 2,2,4-trimethylhexane diisocyanate.

[0032] Preferably, the first polymerization reaction temperature is 70–85°C and the time is 1–4 hours;

[0033] The second polymerization reaction is carried out at a temperature of 70–85°C for 2–4 hours.

[0034] The third polymerization reaction is carried out at a temperature of 65–80°C for 2–6 hours.

[0035] The present invention also provides the application of the aqueous polyurethane described in the above technical solution or the aqueous polyurethane prepared by the preparation method described in the above technical solution as an adhesive in the positive and negative electrode sheets of lithium-ion batteries.

[0036] The aqueous amino acid molecular chain of this invention is composed of polyurethane segments containing anions and polyacrylate (ester) segments containing zwitterionic segments. The introduction of the anionic polyurethane segments and zwitterionic segments gives the binder excellent ion-conducting properties. Simultaneously, due to the intermolecular forces and the insolubility of both segments in the electrolyte, the prepared polyurethane binder exhibits good solvent resistance in the electrolyte, i.e., low swelling degree. Furthermore, the anionic, zwitterionic, and acrylate (ester) segments all possess strong polarity, resulting in excellent adhesion properties in the prepared binder. The polyurethane segments, as the soft segments of the molecular chain, possess high elasticity, effectively accommodating volume changes of the active material during cycling. And the presence of both anionic and zwitterionic segments in the molecular chain gives the binder good water solubility.

[0037] Furthermore, the quaternary ammonium salt and sulfonate groups in the zwitterionic segments have strong polarity and can enhance the bonding strength between the active material and the current collector through electrostatic interaction. The polydiol chain in the main chain provides flexibility, enabling the prepared battery electrode to have good mechanical properties and flexibility. Thus, the electrode coated with polyurethane binder can better adapt to the volume changes of the electrode material during charge and discharge cycles. Moreover, polydiol has good lithium-ion transport capabilities, enhancing the ion transport capacity at the electrode electrode-electrolyte interface, thereby improving the cycle life and electrochemical performance of the battery. Lithium-ion batteries assembled using motor electrodes prepared from this aqueous polyurethane have high specific capacity and high long-cycle capacity retention.

[0038] The preparation method of this invention is convenient, safe and environmentally friendly, and reduces production costs compared with organic oil-based polyurethanes; it introduces zwitterionic monomers that facilitate lithium-ion transport into the structure, thereby enhancing the lithium-ion diffusion capability of the final waterborne polyurethane adhesive.

[0039] The results of the examples show that the molecular weight of the waterborne polyurethane adhesive provided by the present invention is 4.3 × 10⁻⁶. 4 ~5.3×10 4Da has a thermal decomposition temperature of 295–310℃; when used in the positive electrode of lithium-ion batteries, its peel strength is 89–101 N·m. -1 The initial interfacial impedance is 98.2–105.3 Ω, and the capacity retention is 85.8–89.1%. When used in lithium-ion battery anodes, the peel strength is 74–80 N·m. -1 It has an initial interface impedance of 101.5–107.2 Ω and a capacity retention rate of 79.3–84.6%. It has high adhesion, strong lithium-ion transport capability and high capacity retention rate, and is suitable for positive and negative electrodes of lithium-ion batteries. Attached Figure Description

[0040] Figure 1 The swelling degree of the thoroughly dried films of Examples 5, 1 and 2 of the present invention after immersion in electrolyte at 25°C and 60°C for 24 hours is shown.

[0041] Figure 2 The peeling curves of the positive electrode sheets of lithium-ion batteries prepared in Application Example 5 and Comparative Application Example 1 of the present invention are shown.

[0042] Figure 3 Electrochemical impedance spectroscopy at 25°C for lithium iron phosphate / lithium metal batteries assembled from lithium-ion battery positive electrode sheets prepared in Application Example 5 and Comparative Application Example 1 of the present invention.

[0043] Figure 4 The lithium-ion diffusion coefficient of the lithium iron phosphate / lithium metal battery assembled from the lithium-ion battery positive electrode prepared in Application Example 5 and Comparative Application Example 1 of the present invention at 25°C;

[0044] Figure 5 The graph shows the long-cycle charge-discharge performance of a lithium iron phosphate / lithium metal battery assembled from the positive electrode sheet of a lithium-ion battery prepared for Application Example 5 of the present invention at 25°C and 1C rate.

[0045] Figure 6 The lithium iron phosphate / lithium metal batteries prepared for Application Example 5 and Comparative Application Example 1 of the present invention exhibit cycle charge-discharge performance at 25°C and different rates. Detailed Implementation

[0046] This invention provides an aqueous polyurethane having the structural formula shown in Formula 1:

[0047]

[0048] In Formula 1: n is a natural number from 1 to 100, R1 includes a first alkylene group, a first cycloalkylene group, or a first arylalkylene group, and R2 has the structural formula shown in Formula 2:

[0049]

[0050] In Equation 2, x > 0, y > 0, z > 0, R 10 Including the first alkyl group, R 11 It includes triethylamine, triethanolamine or lithium; R3 includes a second alkylene, a second cycloalkylene or a second arylalkylene; R4, R8 and R9 independently include hydrogen or a second alkylene; R5 includes oxygen or nitrogen; R6 includes a third alkylene; R7 is hydrogen, a fourth alkylene or fluorine; Z is an anion.

[0051] In this invention, n, x, y, and z can independently be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100.

[0052] In this invention, the first alkyl group, the second alkyl group, the third alkyl group, and the fourth alkyl group preferably independently include methyl, ethyl, or propyl.

[0053] In this invention, the number of carbon atoms in the first alkylene and the second alkylene is preferably 1 to 6 independently. In specific embodiments of this invention, the number of carbon atoms in the first alkylene and the second alkylene can be 2, 3, 4 or 5 independently.

[0054] In this invention, the number of carbon atoms in the first cycloalkyl group and the second cycloalkyl group is preferably 5 to 10 independently. In specific embodiments of this invention, the number of carbon atoms in the first cycloalkyl group and the second cycloalkyl group can be 6, 7, 8 or 9 independently.

[0055] In this invention, the number of carbon atoms in the first arylene alkyl group and the second arylene alkyl group is preferably 6 to 10. In specific embodiments of this invention, the number of carbon atoms in the first arylene alkyl group and the second arylene alkyl group can be 6, 7, 8 or 9.

[0056] In this invention, the anion preferably includes sulfonate, carboxylate, or phosphate.

[0057] The present invention limits the types and ranges of R1, R2, R3, R4, R5, R6, R7, R8, R9, x, y and z to the ranges mentioned above, which can ensure that the waterborne polyurethane acrylate adhesive has good bonding strength and ion transport capability.

[0058] This invention utilizes anionic aqueous polyurethane segments and zwitterionic polyacrylate segments to achieve good solubility in water. The quaternary ammonium salt and sulfonate groups in the zwitterionic segments can enhance the adhesion strength between the active material and the current collector through electrostatic interaction. The polydiol chain in the molecular chain has good mechanical properties and flexibility, and also has a good ability to transport lithium ions, thus enhancing the ion transport capability at the electrode electrode-electrolyte interface.

[0059] The present invention also provides a method for preparing the waterborne polyurethane described in the above technical solution, comprising the following steps:

[0060] Polydiol, diisocyanate, dimethylolcarboxylic acid and organometallic catalyst are mixed to carry out a first polymerization reaction. Then, the resulting polymerization product is mixed with hydroxy acrylate or hydroxyacrylamide and a polymerization inhibitor to carry out a second polymerization reaction to obtain an aqueous polyurethane prepolymer solution.

[0061] The aqueous polyurethane prepolymer solution is mixed with a neutralizing agent to carry out a neutralization reaction, thereby obtaining a neutralization reaction product;

[0062] The neutralization reaction product is mixed with the first water and then mixed with an aqueous solution of an amine chain extender to carry out a chain extension reaction, thereby obtaining an aqueous polyurethane solution.

[0063] The waterborne polyurethane is obtained by mixing acrylic monomer or acrylate monomer with the aqueous polyurethane solution, zwitterionic monomer, and second water, and then mixing with an aqueous solution of ammonium persulfate.

[0064] In this invention, a first polymerization reaction is carried out by mixing polydiol, diisocyanate, dihydroxymethylcarboxylic acid and organometallic catalyst, and then the resulting polymerization product is mixed with hydroxyacrylate or hydroxyacrylamide and a polymerization inhibitor to carry out a second polymerization reaction to obtain an aqueous polyurethane prepolymer solution.

[0065] In this invention, the ratio of the amount of hydroxyl groups in the polydiol to the amount of hydroxyl groups in the hydroxyacrylate or hydroxyacrylamide is 0.05 to 0.4:1. In specific embodiments of this invention, the ratio of the amount of hydroxyl groups in the polydiol to the amount of hydroxyl groups in the hydroxyacrylate or hydroxyacrylamide can be 0.1:1, 0.2:1, or 0.3:1. The polydiol preferably includes one or more of polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, polyethylene glycol-propylene glycol, poly(1,6-hexanediol adipate), polypentyl adipate diol, and poly(1,4-butanediol adipate). Multiple types; the molecular weight of the polydiol is preferably 500-3000 Da. In specific embodiments of the present invention, the molecular weight of the polydiol can be 1000 Da, 1500 Da, 2000 Da, or 2500 Da; the hydroxy acrylate preferably includes one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, pentaerythritol triacrylate, pentaerythritol diacrylate, glycerol 1,3-diglyceryl alcohol diacrylate, and glycerol diacrylate; the hydroxyacrylamide preferably includes one or more of N-hydroxyethylacrylamide, N-(3-hydroxypropyl)acrylamide, and N-(4-hydroxybutyl)acrylamide.

[0066] In this invention, the ratio of the amount of hydroxyl group in the dimethylolcarboxylic acid to the amount of hydroxyl group in the hydroxyacrylate or hydroxyacrylamide is 0.05 to 0.4:1. In specific embodiments of this invention, the ratio of the amount of hydroxyl group in the dimethylolcarboxylic acid to the amount of hydroxyl group in the hydroxyacrylate or hydroxyacrylamide can be 0.1:1, 0.2:1, or 0.3:1. The dimethylolcarboxylic acid preferably includes one or both of dimethylolpropionic acid and dimethylolbutyric acid.

[0067] In this invention, the ratio of the amount of isocyanate in the diisocyanate to the amount of hydroxyl group in the hydroxy acrylate or hydroxyacrylamide is 0.05 to 0.4:1. In specific embodiments of this invention, the ratio of the amount of isocyanate in the diisocyanate to the amount of hydroxyl group in the hydroxy acrylate or hydroxyacrylamide can be 0.1:1, 0.2:1, or 0.3:1. The diisocyanate preferably includes one or more of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 2,4-ethylphenyl diisocyanate, methylcyclohexyl diisocyanate, and 2,2,4-trimethylhexane diisocyanate.

[0068] In this invention, the catalyst preferably comprises a tin-containing organometallic catalyst and / or a bismuth-containing organometallic catalyst, wherein the bismuth-containing organometallic catalyst preferably comprises MC-710 produced by Beijing Baiyuan Chemical Co., Ltd.; the mass of the catalyst is preferably 0.001 to 0.1% of the mass of the diisocyanate. In specific embodiments of this invention, the mass of the catalyst can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, or 0.09% of the mass of the diisocyanate.

[0069] In this invention, the preferred temperature for the first polymerization reaction is 70–85°C, and the preferred time is 1–4 hours.

[0070] In this invention, the mass of the polymerization inhibitor is preferably 0.1-1.5% of the mass of hydroxyacrylate or hydroxyacrylamide. In specific embodiments of this invention, the mass of the polymerization inhibitor can be 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, or 1.4% of the mass of hydroxyacrylate or hydroxyacrylamide. The polymerization inhibitor preferably includes one or more of hydroquinone, tert-butylcatechol, and p-hydroxyanisole.

[0071] In this invention, the temperature of the second polymerization reaction is preferably 70-85°C, and the time is preferably 2-4 hours.

[0072] After obtaining the aqueous polyurethane prepolymer solution, the present invention mixes the aqueous polyurethane prepolymer solution with a neutralizing agent to carry out a neutralization reaction to obtain a neutralization reaction product.

[0073] In this invention, the amount of the neutralizing agent is preferably 50-100% of the amount of dimethylolcarboxylic acid. In specific embodiments of this invention, the amount of the neutralizing agent can be 60%, 70%, 80%, or 90% of the amount of dimethylolcarboxylic acid. The neutralizing agent preferably includes one or more of triethylamine, triethanolamine, and lithium hydroxide.

[0074] In this invention, the temperature of the neutralization reaction is preferably 70-85°C, and the time is preferably 1-10 min. In specific embodiments of this invention, the temperature of the neutralization reaction can be 75°C, 80°C, or 90°C, and the time can be 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, or 9 min.

[0075] The purpose of the neutralization reaction is to adjust the pH, prevent side reactions, and stabilize the polyurethane dispersion.

[0076] After obtaining the neutralization reaction product, the present invention mixes the neutralization reaction product with first water and then mixes it with an aqueous solution of amine chain extender to carry out a chain extension reaction, thereby obtaining an aqueous polyurethane solution.

[0077] In this invention, the temperature of the first water is preferably 2 to 10°C. In a specific embodiment of this invention, the temperature of the first water can be 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, or 9°C. The mixing time with the first water is preferably 1 to 5 minutes. In a specific embodiment of this invention, the mixing time with the first water can be 2 minutes, 3 minutes, or 4 minutes.

[0078] In this invention, the first water serves to adjust the viscosity and solid content of the system.

[0079] In this invention, the solid content of polyurethane in the neutralization reaction product is preferably 30-40%.

[0080] In this invention, the amine chain extender preferably includes one or more of ethylenediamine, propylenediamine, butanediamine, 2-methylpentanediamine, hexamethylenediamine, isophoronediamine, and sodium ethylenediaminoethanesulfonate.

[0081] In this invention, the amount of the amine chain extender is preferably 2 to 4 times the amount of the diisocyanate.

[0082] In this invention, the preferred temperature for the chain extension reaction is 70–85°C, and the preferred time is 0.5–2 h.

[0083] After obtaining the aqueous polyurethane solution, the present invention mixes the acrylic monomer or acrylate monomer with the aqueous polyurethane solution, the zwitterionic monomer, and the second water, and then mixes it with the aqueous solution of ammonium persulfate to carry out a second polymerization reaction to obtain the aqueous polyurethane.

[0084] In this invention, the amount of the zwitterionic monomer is preferably 4 to 8 times the amount of the diisocyanate, and the zwitterionic monomer preferably includes one of methacryloylethyl sulfobetaine, 2-methacryloyloxyethyl phosphoric acid choline, propionate betaine, and 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate 2-methacryloyloxyethyl phosphoric acid choline.

[0085] The amount of acrylic monomer or acrylate monomer is preferably 4 to 8 times the amount of diisocyanate, and the acrylate monomer preferably includes any one of methyl acrylate, ethyl acrylate and dodecyl acrylate.

[0086] In this invention, the total solid content of acrylic monomers or acrylate monomers and zwitterionic monomers in the mixture obtained by mixing the acrylic monomer or acrylate monomer with the aqueous polyurethane solution, zwitterionic monomer, and second water, and then mixing with an aqueous solution of ammonium persulfate, is preferably 20-50%.

[0087] In this invention, the mass of the ammonium persulfate is preferably 1 to 2% of the total mass of the zwitterionic monomer, acrylic acid or acrylate monomer, more preferably 1.5%, and the mass concentration of the aqueous solution of the ammonium persulfate is preferably 20 to 30%.

[0088] In this invention, the temperature of the third polymerization reaction is preferably 65-80°C and the time is preferably 2-6 hours. In a specific embodiment of this invention, the temperature of the third polymerization reaction can be 70°C or 75°C and the time can be 3 hours, 4 hours or 5 hours.

[0089] In this invention, the third polymerization reaction preferably includes a third' polymerization reaction and a third" polymerization reaction;

[0090] After the third polymerization reaction, the present invention preferably dilutes the resulting system with water before carrying out the third polymerization reaction. The present invention does not have a specific limitation on the amount of water used; it can be added according to the solid content of the target waterborne polyurethane emulsion.

[0091] After the third polymerization reaction is completed, the present invention preferably cools the obtained system to 25-45°C and filters it with a 100-200 mesh filter cloth to obtain an aqueous polyurethane emulsion, which is applied to the positive and negative electrode sheets of lithium-ion batteries.

[0092] The present invention also provides the application of the aqueous polyurethane described in the above technical solution or the aqueous polyurethane prepared by the preparation method described in the above technical solution as an adhesive in the positive and negative electrode sheets of lithium-ion batteries.

[0093] In this invention, the method for preparing the positive or negative electrode sheet of a lithium-ion battery preferably includes the following steps:

[0094] (1) Mix the positive electrode active material or the negative electrode active material with the conductive agent to obtain a mixed powder;

[0095] (2) The mixed powder obtained in step (1) is mixed with the emulsion of waterborne polyurethane and then water is added to adjust the viscosity to obtain a slurry.

[0096] (3) The slurry obtained in step (2) is coated onto the current collector with a scraper, then dried, rolled, and cut into pieces.

[0097] This invention involves mixing a positive or negative active material with a conductive agent to obtain a mixed powder.

[0098] The preferred positive electrode active material is lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO4), or ternary nickel-cobalt-manganese 811 (LiNi). 0.8 Co 0.1 Mn 0.1 O2), ternary nickel-cobalt-manganese 523 (LiNi) 0.5 Co0.2 Mn 0.3 O2), ternary nickel-cobalt-aluminum 811 (LiNi) 0.8 Co 0.1 Al 0.1 O2) and ternary nickel-cobalt-manganese 622 (LiNi 0.6 Co 0.2 Mn 0.2 One or more of the following (O2); the negative electrode active material is preferably one or more of artificial graphite, natural graphite, hard carbon, and silicon-carbon negative electrode.

[0099] In this invention, the conductive agent is preferably one or more of superconducting carbon black, carbon nanotubes, acetylene black, and Ketjen black.

[0100] By limiting the types of positive electrode active material, negative electrode active material, and conductive agent to the above-mentioned range, this invention ensures that the positive and negative electrode sheets have good performance.

[0101] In this invention, the mixing in step (1) is preferably carried out in a ball mill, the ball mill speed is preferably 600-1200 rpm, and the time is preferably 1-3 h. Limiting the ball mill speed and time to the above range ensures uniform mixing of the materials.

[0102] In this invention, the preferred mass ratio of the positive electrode active material, the conductive agent, and the aqueous polyurethane emulsion is (75-95):(2-15):(3-10), more preferably 80:10:5. Limiting the mass ratio of the positive electrode active material, the conductive agent, and the aqueous polyurethane emulsion to the above range ensures good electrochemical performance of the positive electrode sheet.

[0103] After obtaining the mixed powder, the present invention mixes the mixed powder obtained in step (1) with the emulsion of waterborne polyurethane and then adds water to adjust the viscosity to obtain a slurry.

[0104] In this invention, the mixing in step (2) is preferably carried out in a ball mill, with the ball mill speed preferably being 600–1200 rpm and the time preferably being 1–4 h. Limiting the ball mill speed and time to the above range ensures uniform mixing of the materials.

[0105] In this invention, the resistivity of the water in step (2) is preferably greater than 0.1 MΩ·cm. This invention does not have specific limitations on the viscosity adjustment operation; the viscosity of the slurry can be adjusted to 1–25 Pa·s.

[0106] After adding water, the present invention preferably performs a secondary ball milling on the resulting slurry; the preferred rotation speed of the secondary ball milling is 700-1200 rpm; the preferred time of the secondary ball milling is 1-4 hours.

[0107] After obtaining the slurry, the present invention applies the slurry obtained in step (2) to the current collector with a scraper, and then dries, rolls, and cuts the slurry into pieces.

[0108] In this invention, the current collector is preferably aluminum foil or copper foil.

[0109] In this invention, the drying is preferably performed sequentially as atmospheric pressure drying and vacuum drying.

[0110] In this invention, the temperature for atmospheric pressure drying is preferably 40–70°C, and the drying time is preferably 6–12 hours. In this invention, the temperature for vacuum drying is preferably 90–120°C, and the drying time is preferably 10–24 hours. This invention, through sequential atmospheric pressure drying and vacuum drying, ensures thorough drying of the electrode, which is beneficial to the electrode's electrical performance.

[0111] The present invention does not impose any special limitations on the operation of the rolling and cutting process; any operation known to those skilled in the art can be used.

[0112] The aqueous polymer binder provided by this invention can improve the stability of the electrode and the lithium-ion transport capacity when used in the positive and negative electrodes of lithium-ion batteries, thereby improving the rate performance and cycle stability of lithium-ion batteries.

[0113] The following detailed description of the waterborne polyurethane, its preparation method, and its application provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0114] Example 1

[0115] The structure of the waterborne polyurethane in the prepared waterborne polyurethane acrylate adhesive is shown in Formula 1:

[0116]

[0117] In Formula 1, n is 16; R1 is methylene;

[0118] R2 has the structure shown in Equation 2:

[0119]

[0120] In Equation 2, R 10 For methyl, R 11 R3 is triethylamine, R4 is methylene, R5 is oxygen, R6 is methyl, R7 is hydrogen, R8 is hydrogen, R9 is methyl, and Z is sulfonate.

[0121] The preparation method of the waterborne polyurethane acrylate adhesive comprises the following steps:

[0122] (1) 250g of polytetramethylene ether glycol (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) with a molecular weight of 2000 Da, 16.77g of dimethylolpropionic acid (Shanghai Bid Pharmaceutical Technology Co., Ltd.), and 0.02g of bismuth organometallic catalyst (MC-710, Beijing Baiyuan Chemical Co., Ltd.) were added to the reactor, heated to 70°C, stirred for 10 min, and then 21.02g of hexamethylene diisocyanate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) were added dropwise to the reactor within 1 h. The polymerization reaction was carried out at 70°C for 4 h to obtain the first prepolymer solution.

[0123] (2) Add 145.15g of hydroxyethyl acrylate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) and 2.18g of p-hydroxyanisole (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) to the first prepolymer solution obtained in step (1), and carry out the polymerization reaction at 70°C for 2 hours. After cooling, an aqueous polyurethane prepolymer solution is obtained.

[0124] (3) At 70°C, 6.33g of triethylamine (Annegi (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added to the aqueous polyurethane prepolymer solution obtained in step (2); after stirring for 5 min, 658.91g of water at 5°C was added to adjust the solid content to 40%; after stirring for 3 min, 200.02g of ethylenediamine aqueous solution with a solid content of 7.5% (Annegi (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added, and the mixture was reacted for 2 h to obtain an aqueous polyurethane solution with a solid content of 35%.

[0125] (4) In the aqueous polyurethane solution of step (3), add 297.35g of methacryloyl ethyl sulfobetaine (Kmart (Tianjin) Chemical Technology Co., Ltd.) and 86.09g of methyl acrylate (Shanghai Bide Pharmaceutical Technology Co., Ltd.), stir for 3 minutes, add 1533.76g of water within 3 minutes to make the monomer solid content 20%, add 22.83g of aqueous solution of ammonium persulfate with a solid content of 24% (Annaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.), and carry out polymerization reaction at 70°C for 4 hours; then add 1286.33g of water and continue polymerization reaction for 2 hours. After cooling to 30°C, filter with 200-mesh filter cloth to finally obtain an aqueous polyurethane acrylate (ester) binder emulsion with a solid content of 20%, denoted as A1.

[0126] Example 2

[0127] The structure of the waterborne polyurethane in the prepared waterborne polyurethane acrylate adhesive is shown in Formula 1:

[0128]

[0129] In Formula 1, n is 12; R1 is methylene;

[0130] R2 has the structure shown in Equation 2:

[0131]

[0132] In Equation 2, R 10 For methyl, R 11 R3 is triethylamine, R4 is methylene, R5 is oxygen, R6 is methyl, R7 is hydrogen, R8 is hydrogen, and R9 is methyl. Z is sulfonate.

[0133] The preparation method of the waterborne polyurethane acrylate adhesive comprises the following steps:

[0134] (1) 200g of polytetramethylene ether glycol (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) with a molecular weight of 2000 Da, 26.83g of dimethylolpropionic acid (Shanghai Bid Pharmaceutical Technology Co., Ltd.), and 0.03g of bismuth organometallic catalyst (MC-710, Beijing Baiyuan Chemical Co., Ltd.) were added to the reactor, heated to 70°C, stirred for 10 min, and then 33.64g of hexamethylene diisocyanate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) were added dropwise to the reactor within 1 h. The polymerization reaction was carried out at 70°C for 4 h to obtain the first prepolymer solution.

[0135] (2) Add 116.12g of hydroxyethyl acrylate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) and 1.74g of p-hydroxyanisole (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) to the first prepolymer solution obtained in step (1), and carry out the polymerization reaction at 70°C for 2 hours. After cooling, an aqueous polyurethane prepolymer solution is obtained.

[0136] (3) At 70°C, 10.12g of triethylamine (Annegi (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added to the aqueous polyurethane prepolymer solution obtained in step (2); after stirring for 5 min, 580.07g of water at 5°C was added to adjust the solid content to 40%; after stirring for 3 min, 200.33g of ethylenediamine aqueous solution with a solid content of 6% (Shanghai Anegi) was added, and the mixture was reacted for 2 h to obtain an aqueous polyurethane solution with a solid content of 35%.

[0137] (4) In the aqueous polyurethane solution of step (3), add 223.48g of methacryloyl ethyl sulfobetaine (Kmart (Tianjin) Chemical Technology Co., Ltd.) and 68.87g of methyl acrylate (Shanghai Bide Pharmaceutical Technology Co., Ltd.), stir for 3 min, add 1209.4g of water within 3 min to make the monomer solid content 20%, add 18.90g of aqueous solution of ammonium persulfate with a solid content of 24% (Annaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.), and carry out polymerization reaction at 70℃ for 4 h; then add 767.08g of water and continue polymerization reaction for 2 h. After cooling to 30℃, filter with 200 mesh filter cloth to finally obtain aqueous polyurethane acrylate (ester) adhesive emulsion with a solid content of 20%, denoted as A2.

[0138] Example 3

[0139] The structure of the waterborne polyurethane in the prepared waterborne polyurethane acrylate adhesive is shown in Formula 1:

[0140]

[0141] In Formula 1, n is 17; R1 is methylene;

[0142] R2 has the structure shown in Equation 2:

[0143]

[0144] In Equation 2, R 10 For methyl, R 11 R3 is triethylamine, R4 is methylene, R5 is oxygen, R6 is methyl, R7 is hydrogen, R8 is hydrogen, R9 is methyl, and Z is sulfonate.

[0145] The preparation method of the waterborne polyurethane acrylate adhesive comprises the following steps:

[0146] (1) 400g of polytetramethylene ether glycol (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) with a molecular weight of 2000 Da, 13.41g of dimethylolpropionic acid (Shanghai Bid Pharmaceutical Technology Co., Ltd.), and 0.03g of bismuth organometallic catalyst (MC-710, Beijing Baiyuan Chemical Co., Ltd.) were added to the reactor, heated to 70°C, stirred for 10 min, and then 33.64g of hexamethylene diisocyanate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) were added dropwise to the reactor within 1 h. The polymerization reaction was carried out at 70°C for 4 h to obtain the first prepolymer solution.

[0147] (2) Add 116.12g of hydroxyethyl acrylate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) and 1.74g of p-hydroxyanisole (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) to the first prepolymer solution obtained in step (1), and carry out the polymerization reaction at 70°C for 2 hours. After cooling, an aqueous polyurethane prepolymer solution is obtained.

[0148] (3) At 70°C, 5.06 g of triethylamine (Annegi (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added to the aqueous polyurethane prepolymer solution obtained in step (2); after stirring for 5 min, 852.36 g of water at 5°C was added to adjust the solid content to 40%; after stirring for 3 min, 237.21 g of ethylenediamine aqueous solution with a solid content of 5% (Annegi (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added, and the mixture was reacted for 2 h to obtain an aqueous polyurethane solution with a solid content of 35%.

[0149] (4) In the aqueous polyurethane solution of step (3), add 223.48g of methacryloyl ethyl sulfobetaine (Kmart (Tianjin) Chemical Technology Co., Ltd.) and 68.87g of methyl acrylate (Shanghai Bide Pharmaceutical Technology Co., Ltd.), stir for 3 min, add 1209.40g of water within 3 min to make the monomer solid content 20%, add 18.90g of aqueous solution of ammonium persulfate with a solid content of 24% (Annaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.), and carry out polymerization reaction at 70℃ for 4 h; then add 1228.96g of water and continue polymerization reaction for 2 h. After cooling to 30℃, filter with 200 mesh filter cloth to finally obtain aqueous polyurethane acrylate (ester) adhesive emulsion with a solid content of 20%, denoted as A3.

[0150] Example 4

[0151] The structure of the waterborne polyurethane in the prepared waterborne polyurethane acrylate adhesive is shown in Formula 1:

[0152]

[0153] In Formula 1, n is 16; R1 is methylene;

[0154] R2 has the structure shown in Equation 2:

[0155]

[0156] In Equation 2, R 10 For methyl, R 11 R3 is triethylamine, R4 is methylene, R5 is nitrogen, R6 is methyl, R7 is hydrogen, R8 is hydrogen, R9 is hydrogen, and Z is sulfonate.

[0157] The preparation method of the waterborne polyurethane acrylate adhesive comprises the following steps:

[0158] (1) 250g of polytetramethylene ether glycol (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) with a molecular weight of 2000Da, 16.77g of dimethylolpropionic acid (Shanghai Bid Pharmaceutical Technology Co., Ltd.), and 0.02g of bismuth organometallic catalyst (MC-710, Beijing Baiyuan Chemical Co., Ltd.) were added to the reactor, heated to 70℃ and stirred for 10min. Then, 21.02g of hexamethylene diisocyanate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) were added dropwise to the reactor within 1h. The polymerization reaction was carried out at 70℃ for 4h to obtain the first prepolymer solution.

[0159] (2) Add 126.38g of hydroxyl acrylate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) and 1.89g of hydroquinone (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) to the first prepolymer solution obtained in step (1), and carry out the polymerization reaction at 70°C for 2 hours. After cooling, an aqueous polyurethane prepolymer solution is obtained.

[0160] (3) At 70°C, 6.33g of triethylamine (Shanghai Anaiji Anaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added to the aqueous polyurethane prepolymer solution obtained in step (2). After stirring for 5 minutes, 630.75g of water at 5°C was added to adjust the solid content to 40%. After stirring for 3 minutes, 193.04g of ethylenediamine aqueous solution with a solid content of 8% (Shanghai Anaiji Anaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added, and the mixture was reacted for 2 hours to obtain an aqueous polyurethane solution with a solid content of 35%.

[0161] (4) In the aqueous polyurethane solution of step (3), add 297.35g of methacryloyl ethyl sulfobetaine (Kmart (Tianjin) Chemical Technology Co., Ltd.) and 72.06g of acrylic acid (Shanghai Bide Pharmaceutical Technology Co., Ltd.), stir for 3 min, add 1478.84g of water within 3 min to make the monomer solid content 20%, add 23.09g of aqueous solution of ammonium persulfate with a solid content of 24% (Annaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.), and carry out polymerization reaction at 70℃ for 4 h; then add 926.47g of water, continue polymerization reaction for 2 h, cool down to 30℃, filter with 200 mesh filter cloth, and finally obtain aqueous polyurethane acrylate (ester) binder emulsion with a solid content of 20%, denoted as A4.

[0162] Example 5

[0163] The structure of the waterborne polyurethane in the prepared waterborne polyurethane acrylate adhesive is shown in Formula 1:

[0164]

[0165] In Formula 1, n is 15; R1 is methylene;

[0166] R2 has the structure shown in Equation 2:

[0167]

[0168] In Equation 2, R 10 For methyl, R 11 R3 is triethylamine, R4 is methylene, R5 is nitrogen, R6 is methyl, R7 is hydrogen, R8 is hydrogen, R9 is hydrogen, and Z is sulfonate.

[0169] The preparation method of the waterborne polyurethane acrylate adhesive comprises the following steps:

[0170] (1) 200g of polytetramethylene ether glycol (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) with a molecular weight of 2000 Da, 26.83g of dimethylolpropionic acid (Shanghai Bid Pharmaceutical Technology Co., Ltd.), and 0.03g of bismuth organometallic catalyst (MC-710, Beijing Baiyuan Chemical Co., Ltd.) were added to the reactor, heated to 70°C, stirred for 10 min, and then 33.64g of hexamethylene diisocyanate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) were added dropwise to the reactor within 1 h. The polymerization reaction was carried out at 70°C for 4 h to obtain the first prepolymer solution.

[0171] (2) Add 101.10g of hydroxyl acrylate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) and 1.51g of p-hydroxyanisole (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) to the first prepolymer solution obtained in step (1), and carry out the polymerization reaction at 70°C for 2 hours. After cooling, an aqueous polyurethane prepolymer solution is obtained.

[0172] (3) At 70°C, 10.12g of triethylamine (Shanghai Anaiji Anaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added to the aqueous polyurethane prepolymer solution obtained in step (2); after stirring for 5 min, 557.56g of water at 5°C was added to adjust the solid content to 40%; after stirring for 3 min, 182.41g of ethylenediamine aqueous solution with a solid content of 6.5% (Anaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added, and the mixture was reacted for 2 h to obtain an aqueous polyurethane solution with a solid content of 35%.

[0173] (4) In the aqueous polyurethane solution of step (3), add 223.48g of methacryloyl ethyl sulfobetaine (Kmart (Tianjin) Chemical Technology Co., Ltd.) and 57.65g of acrylic acid (Shanghai Bide Pharmaceutical Technology Co., Ltd.), stir for 3 min, add 1164.52g of water within 3 min to make the monomer solid content 20%, add 18.20g of aqueous solution of ammonium persulfate with a solid content of 24% (Annaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.), and carry out polymerization reaction at 70℃ for 4 h; then add 762.42g of water, react for 2 h, cool down to 30℃, filter with 200 mesh filter cloth, and finally obtain aqueous polyurethane acrylate (ester) adhesive emulsion with a solid content of 20%, denoted as A5.

[0174] Example 6

[0175] The structure of the waterborne polyurethane in the prepared waterborne polyurethane acrylate adhesive is shown in Formula 1:

[0176]

[0177] In Formula 1, n is 12; R1 is methylene;

[0178] R2 has the structure shown in Equation 2:

[0179]

[0180] In Equation 2, R 10 For methyl, R 11 R3 is triethylamine, R4 is methylene, R5 is oxygen, R6 is methyl, R7 is hydrogen, R8 is hydrogen, R9 is hydrogen, and Z is sulfonate.

[0181] The preparation method of the waterborne polyurethane acrylate adhesive comprises the following steps:

[0182] (1) 400g of polytetramethylene ether glycol (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) with a molecular weight of 2000 Da, 13.41g of dimethylolpropionic acid (Shanghai Bid Pharmaceutical Technology Co., Ltd.), and 0.03g of bismuth organometallic catalyst (MC-710, Beijing Baiyuan Chemical Co., Ltd.) were added to the reactor, heated to 70°C, stirred for 10 min, and then 33.64g of hexamethylene diisocyanate (Shanghai Bid Pharmaceutical Technology Co., Ltd.) were added dropwise to the reactor within 1 h. The polymerization reaction was carried out at 70°C for 4 h to obtain the first prepolymer solution.

[0183] (2) Add 116.12g of hydroxyethyl acrylate (Shanghai Bide) and 1.74g of p-hydroxyanisole (Sigma-Aldrich (Shanghai) Trading Co., Ltd.) to the first prepolymer solution obtained in step (1), and carry out the polymerization reaction at 70°C for 2 hours. After cooling, an aqueous polyurethane prepolymer solution is obtained.

[0184] (3) At 70°C, 5.06g of triethylamine (Shanghai Anaiji) was added to the aqueous polyurethane prepolymer solution obtained in step (2); after stirring for 5 min, 852.36g of water at 5°C was added to adjust the solid content to 40%; after stirring for 3 min, 237.21g of ethylenediamine aqueous solution with a solid content of 5% (Anaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.) was added, and the mixture was reacted for 2 h to obtain an aqueous polyurethane solution with a solid content of 35%.

[0185] (4) In the aqueous polyurethane solution of step (3), add 223.48g of methacryloyl ethyl sulfobetaine (Kmart (Tianjin) Chemical Technology Co., Ltd.) and 57.65g of acrylic acid (Shanghai Bide Pharmaceutical Technology Co., Ltd.), stir for 3 min, add 1124.52g of water within 3 min to make the monomer solid content 20%, add 18.38g of aqueous solution of ammonium persulfate with a solid content of 24% (Annaiji (Shanghai) Pharmaceutical Chemical Co., Ltd.), and carry out polymerization reaction at 70℃ for 4 h; then add 1238.94g of water and continue polymerization reaction for 2 h. After cooling to 30℃, filter with 200 mesh filter cloth to finally obtain aqueous polyurethane acrylate (ester) binder emulsion with a solid content of 20%, which is denoted as A6.

[0186] Comparative Example 1

[0187] 200g of dry PVDF HSV900 powder and 1800g of N-methylpyrrolidone were added to a reaction vessel and stirred at 800rpm for 12h at 25℃ to obtain PVDF binder B1.

[0188] Comparative Example 2

[0189] 100g of sodium carboxymethyl cellulose powder (Shenzhen Kejing, MAC500LC) and 1900g of purified water were added to a reaction vessel and stirred at 800rpm for 4 hours at 25°C. Then, 430g of styrene-butadiene rubber latex with a solid content of 35% (Shenzhen Kejing, S2919) and 2750g of purified water were added to the vessel and stirred at 800rpm for 4 hours at 25°C to obtain water-based adhesive B2.

[0190] Application Examples 1-6

[0191] The aqueous polyurethane acrylate binders A1-A6 from Examples 1-6 were used to prepare lithium iron phosphate positive electrode sheets C1-C6 for lithium-ion batteries. The preparation method is as follows:

[0192] 1) 80g of lithium iron phosphate and 10g of superconducting carbon black were ball-milled at 1080rpm for 1h to obtain a mixed powder;

[0193] 2) Add 50g of waterborne polyurethane acrylate binder emulsion with a solid content of 20% to the mixed powder obtained in step 1), then add 190g of pure water, and continue ball milling at 1080rpm for 3h to obtain positive electrode slurry.

[0194] 3) The positive electrode slurry obtained in step 2) is coated onto aluminum foil using a scraper, dried at 60°C under normal pressure for 12 hours, and then dried under vacuum at 120°C for 24 hours. The foil is then rolled, cut into sheets, and lithium-ion battery positive electrode sheets C1 to C6 are obtained.

[0195] Application Examples 7-12

[0196] The aqueous polyurethane acrylate binders A1-A6 from Examples 1-6 were used to prepare artificial graphite negative electrode sheets C7-C12 for lithium-ion batteries. The preparation method is as follows:

[0197] 1) 80g of artificial graphite and 10g of superconducting carbon black were ball-milled at 1080rpm for 1h to obtain a mixed powder;

[0198] 2) Add 50g of waterborne polyurethane acrylate binder emulsion with a solid content of 20% to the mixed powder obtained in step 1), then add 190g of pure water, and continue ball milling at 1080rpm for 3h to obtain positive electrode slurry.

[0199] 3) The negative electrode slurry obtained in step 2) is coated onto copper foil using a scraper, dried at 60°C under normal pressure for 12 hours, and then dried under vacuum at 120°C for 24 hours. The foil is then rolled, cut into sheets, and lithium-ion battery negative electrode sheets C7 to C12 are obtained.

[0200] Comparative Application Example 1

[0201] The lithium iron phosphate positive electrode sheet D1 for lithium-ion batteries was prepared using binder B1 from Comparative Example 1. The preparation method is as follows:

[0202] 1) 80g of lithium iron phosphate and 10g of superconducting carbon black were ball-milled at 1080rpm for 1h to obtain a mixed powder;

[0203] 2) Ball mill 200g of binder B1 with the mixed powder obtained in step 1) at 1080 rpm for 2 hours, then add 120g of N-methylpyrrolidone and continue ball milling at 1080 rpm for 3 hours to obtain the positive electrode slurry.

[0204] 3) The positive electrode slurry obtained in step 2) is coated onto aluminum foil using a scraper, dried at 60°C under normal pressure for 12 hours, and then dried under vacuum at 120°C for 24 hours. The foil is then rolled, cut into sheets, and lithium-ion battery positive electrode sheet D1 is obtained.

[0205] Comparative Application Example 2

[0206] Artificial graphite negative electrode sheet D2 for lithium-ion batteries was prepared using binder B2 from Comparative Example 2. The preparation method is as follows:

[0207] 1) 80g of artificial graphite and 10g of superconducting carbon black were ball-milled at 1080rpm for 1h to obtain a mixed powder;

[0208] 2) Ball mill 120g of binder B2 with the mixed powder obtained in step 1) at 1080 rpm for 2 hours, then add 100g of pure water and continue ball milling at 1080 rpm for 3 hours to obtain the negative electrode slurry.

[0209] 3) The negative electrode slurry obtained in step 2) is coated onto aluminum foil using a scraper, dried at 60°C under normal pressure for 12 hours, and then dried under vacuum at 120°C for 24 hours. The foil is then rolled, cut into sheets, and lithium-ion battery negative electrode sheet D2 is obtained.

[0210] The properties of the waterborne polyurethane adhesives prepared in Examples 1 to 6 were tested. The test method was as follows: the waterborne polyurethane adhesives were dried in a 60°C forced-air drying oven for 12 hours, and then vacuum dried at 80°C for 24 hours to obtain solvent-free waterborne polyurethane films.

[0211] The weight-average molecular weight and molecular weight dispersibility index of waterborne polyurethane acrylate in waterborne polyurethane acrylate adhesives were determined by gel permeation chromatography (Waters 600E), with the reference sample being narrowly dispersed polystyrene of different molecular weights and the mobile phase being dimethylformamide.

[0212] The tensile strength and elongation at break of the waterborne polyurethane acrylate in the waterborne polyurethane acrylate adhesive were determined using a tensile testing machine (Shanghai Songdun, WDW-5). The test conditions were: under a nitrogen atmosphere, the temperature was increased from 25℃ to 600℃ at a heating rate of 10℃ / min. -1 .

[0213] The thermal decomposition temperature of the waterborne polyurethane acrylate in the waterborne polyurethane acrylate adhesive was determined by thermogravimetric analysis (NETZSCH TG209, Germany). The results are shown in Table 1.

[0214] Table 1. Performance of the waterborne polyurethane adhesives prepared in Examples 1-6

[0215]

[0216]

[0217] Based on the test results in Table 1, the molecular weight of the waterborne polymer binder is 3.9 × 10⁻⁶. 4 -5.3×10 4 Da, is far lower than the molecular weight of commercially available PVDF adhesives (PVDF HSV900 has a molecular weight of 5 × 10⁻⁶). 5 Therefore, the battery slurry prepared using the waterborne polyurethane acrylate binder of the present invention has a lower viscosity, which helps to achieve uniform coating of the slurry; the waterborne polymer binder of the present invention has a high thermal decomposition temperature, exhibiting excellent heat resistance, which can meet the operating requirements of the battery in a high-temperature environment. The waterborne polyurethane in the waterborne polyurethane acrylate binder has good tensile strength modulus and elongation at break, which makes the prepared electrode sheet have good mechanical properties and flexibility.

[0218] The swelling degree of the films formed after thorough drying in Examples 1-6 and Comparative Example 1 was tested.

[0219] Weigh the samples after soaking in the electrolyte (1M LiPF6 in DMC:EC:EMC=1:1:1 (volume ratio)) at 25℃ and 60℃ for 12h and 24h respectively. The degree of swelling was calculated.

[0220] The swelling degrees obtained from the tests are shown in Table 2. Figure 1 The swelling degree of the thoroughly dried films of Examples 5, 1 and 2 of the present invention after immersion in electrolyte at 25°C and 60°C for 24 hours is shown.

[0221] Table 2. Swelling properties of the films prepared in Examples 1-6 and Comparative Examples 1-2

[0222]

[0223] The test results in Table 2 show that the swelling degree of aqueous polyurethane after immersion in electrolyte for 24 hours at 25°C is 20.44%-26.55%, which is lower than the swelling degree of films formed by commercial PVDF (32.66%) and CMC-SBR (26.61%). At 60°C, the swelling degree of aqueous polyurethane after immersion in electrolyte for 24 hours is 30.03%-33.82%, which is also lower than the swelling degree of films formed by commercial PVDF (38.65%) and CMC-SBR (40.10%). This indicates that the aqueous polyurethane acrylate binder of the present invention has a lower swelling degree. Therefore, the electrode prepared using the aqueous polyurethane acrylate binder of the present invention reduces the harm of active material shedding during long cycles, helping to maintain the stability of the battery under high voltage long-term cycling.

[0224] The peel strength and areal density of the lithium-ion battery positive electrode sheets C1-C6 and D1 prepared in corresponding use cases 1-6 and Comparative Example 1 were tested.

[0225] The areal density of the electrode active material is the mass of lithium iron phosphate per unit area, which is calculated.

[0226] The peel strength between the dried coating of the slurry on the surface of the current collector in the electrode and the current collector was determined according to the test method of GB / T 2791-1995.

[0227] The peel strength and areal density data obtained from the test are shown in Table 3.

[0228] The method for assembling lithium-ion batteries using C1-C6 and D1 lithium-ion battery positive electrode sheets is as follows:

[0229] A solution of lithium hexafluorophosphate dissolved in ethylene carbonate, dimethyl carbonate, and diethyl carbonate (1M LiPF6 in DMC:EC:EMC = 1:1:1 (volume ratio)) was used as the electrolyte. A polypropylene microporous membrane (Celgard 2325) was used as the separator. The lithium metal, electrolyte, separator, electrolyte, lithium-ion battery positive electrode (lithium iron phosphate positive electrode), stainless steel gasket, and stainless steel spring were placed in the CR2032 type negative electrode shell in the following order, with the lithium metal, electrolyte, separator, electrolyte, lithium-ion battery positive electrode sheet (lithium iron phosphate positive electrode sheet), stainless steel gasket, and stainless steel spring sheet at the center of the negative electrode shell. The CR2032 type positive electrode shell was placed on top. The entire assembly was then placed in an MSK 110 type battery packaging machine. Under the locked state, the pressure was increased to 50 psi for sealing. After unlocking, the lithium iron phosphate / lithium metal battery was obtained. The electrolyte volume for each lithium iron phosphate / lithium metal battery was 40 μL, which was required to be dropped equally onto both sides of the separator to ensure that the separator was fully wetted.

[0230] The initial interfacial impedance of the assembled lithium iron phosphate / lithium metal battery was tested using an electrochemical workstation (VersaSTAT3, Princeton, USA). The test parameters were as follows: test temperature 25℃, frequency 1,000,000 Hz, and amplitude 5 mV.

[0231] The assembled battery was subjected to battery cycle testing in a battery cycle tester (Wuhan Landian, CT3002A). The test parameters of the assembled battery are as follows: test temperature is 25℃, cutoff voltage is 2.5-4.2V, charge / discharge rate is 1C, and the standard specific capacity of active material is 170mAh / g.

[0232] The results of testing and calculation of the initial interface impedance, lithium-ion diffusion coefficient, initial discharge specific capacity, discharge specific capacity at 800 cycles, and capacity retention (the ratio of discharge specific capacity to initial discharge specific capacity) of lithium iron phosphate / lithium metal batteries are shown in Table 3.

[0233] Figure 1 The swelling degree of the thoroughly dried films of Examples 5, 1 and 2 of the present invention after immersion in electrolyte at 25°C and 60°C for 24 hours is shown.

[0234] Figure 2 The peeling curves of the positive electrode sheets of lithium-ion batteries prepared in Application Example 5 and Comparative Application Example 1 of the present invention are shown.

[0235] Figure 3 Electrochemical impedance spectroscopy at 25°C for lithium iron phosphate / lithium metal batteries assembled from lithium-ion battery positive electrode sheets prepared in Application Example 5 and Comparative Application Example 1 of the present invention.

[0236] Figure 4 The lithium-ion diffusion coefficient of the lithium iron phosphate / lithium metal battery assembled from the lithium-ion battery positive electrode prepared in Application Example 5 and Comparative Application Example 1 of the present invention at 25°C;

[0237] Figure 5 The graph shows the long-cycle charge-discharge performance of a lithium iron phosphate / lithium metal battery assembled from the positive electrode sheet of a lithium-ion battery prepared for Application Example 5 of the present invention at 25°C and 1C rate.

[0238] Depend on Figure 5 It can be seen that under a high current C of 1, the capacity retention rate can still be maintained at 85.9% after 800 cycles, which proves that the lithium iron phosphate / lithium metal battery assembled with the positive electrode sheet of the lithium-ion battery prepared by this binder has excellent cycle stability.

[0239] Figure 6 The lithium iron phosphate / lithium metal batteries prepared for Application Example 5 and Comparative Application Example 1 of the present invention exhibit cycle charge-discharge performance at 25°C and different rates.

[0240] Depend on Figure 6 It can be seen that, under different current densities, the lithium iron phosphate / lithium metal batteries assembled from the lithium-ion battery positive electrode prepared with this binder consistently exhibit higher discharge capacity than comparative application example 1 in Application Example 5. This advantage is particularly significant at higher rates, indicating that the lithium iron phosphate / lithium metal batteries assembled from the lithium-ion battery positive electrode prepared with this binder have superior electrochemical performance under high rate conditions.

[0241] Table 3 Performance test data of lithium iron phosphate / lithium metal batteries

[0242]

[0243] Table 3 shows that, under similar areal density conditions, the peel strength of the positive electrode sheets C1 to C6 prepared using the aqueous polyurethane acrylate binder of this invention is higher than that of the positive electrode sheet D1 prepared using the PVDF binder, indicating that the aqueous polyurethane acrylate binder has superior bonding performance. Furthermore, the lithium iron phosphate / lithium metal batteries assembled using the positive electrode sheets C1 to C6 prepared based on this aqueous polyurethane acrylate binder have lower initial interfacial impedance than the D1 battery assembled using the PVDF binder. The calculated lithium-ion diffusion coefficient also demonstrates that the aqueous polyurethane acrylate binder has superior performance in lithium-ion transport. Although the C1 to C6 batteries using the aqueous polymer binder and the D1 battery using the PVDF binder have comparable initial discharge specific capacities, after 800 cycles, the C1 to C6 batteries exhibit higher capacity retention, demonstrating superior cycle stability.

[0244] The peel strength and areal density of the lithium-ion battery negative electrode sheets C7-C12 and D2 prepared in corresponding use cases 7-12 and comparative example 2 were tested.

[0245] The areal density of the active material in the electrode is the mass of artificial graphite per unit area, which is calculated.

[0246] The peel strength between the dried coating of the slurry on the surface of the current collector in the electrode and the current collector was determined according to the test method of GB / T 2791-1995.

[0247] The peel strength and areal density test data obtained are shown in Table 4.

[0248] The method for assembling lithium-ion batteries using C7-C12 and D2 lithium-ion battery negative electrode sheets is as follows:

[0249] A solution of lithium hexafluorophosphate dissolved in ethylene carbonate, dimethyl carbonate, and diethyl carbonate (1M LiPF6 in DMC:EC:EMC = 1:1:1 (volume ratio)) was used as the electrolyte. A polypropylene microporous membrane (Celgard 2325) was used as the separator. The lithium metal, electrolyte, separator, lithium-ion battery positive electrode (artificial graphite negative electrode), stainless steel gasket, and stainless steel spring were placed in the CR2032 type negative electrode shell in the following order, with the lithium metal, electrolyte, separator, electrolyte, lithium-ion battery positive electrode sheet (artificial graphite negative electrode sheet), stainless steel gasket, and stainless steel spring sheet at the center of the negative electrode shell. The CR2032 type positive electrode shell was placed on top. The entire assembly was then placed in an MSK 110 type battery packaging machine. Under the locked state, the pressure was increased to 50 psi for sealing. After unlocking, the artificial graphite / lithium metal battery was obtained. The electrolyte volume for each artificial graphite / lithium metal battery was 40 μL, which was required to be dropped equally onto both sides of the separator to ensure that the separator was fully wetted.

[0250] The initial interfacial impedance of the assembled artificial graphite / lithium metal battery was tested using an electrochemical workstation (VersaSTAT3, Princeton, USA). The test parameters were as follows: test temperature 25℃, frequency 1,000,000 Hz, and amplitude 5 mV.

[0251] The assembled artificial graphite / lithium metal battery was subjected to battery cycle testing in a battery cycle tester (Wuhan Landian, CT3002A). The test parameters were as follows: test temperature 25℃, cutoff voltage 0.005~1.5V, charge / discharge rate 1C, and standard specific capacity of active material 374mAh / g. The initial interfacial impedance, lithium-ion diffusion coefficient, initial discharge specific capacity, discharge specific capacity at 800 cycles, and capacity retention (ratio of discharge specific capacity to initial discharge specific capacity) of the artificial graphite / lithium metal battery were obtained through testing and calculation, and are shown in Table 4.

[0252] Table 4 Performance test data of artificial graphite / lithium metal batteries

[0253]

[0254] The data in Table 4 show that, under similar areal density conditions, the peel strength of the negative electrode sheets C7-C12 prepared using the aqueous polymer binder of this invention is higher than that of the negative electrode sheet D2 prepared using the SBR / CMC binder, indicating that the aqueous polymer binder has superior bonding performance. Furthermore, the artificial graphite / lithium metal batteries assembled using negative electrode sheets C7-C12 prepared based on this aqueous polyurethane acrylate binder have lower initial interfacial impedance than the D2 battery using the SBR / CMC binder, indicating that the aqueous polymer binder has superior lithium-ion transport capabilities. The calculated lithium-ion diffusion coefficient also indicates that the artificial graphite / lithium metal batteries prepared using the aqueous polyurethane acrylate binder have better lithium-ion transport performance. Compared to batteries assembled using negative electrode sheet D2 prepared with SBR / CMC binder, artificial graphite / lithium metal batteries assembled using negative electrode sheets C7-C12 prepared with aqueous polymer binder not only exhibit higher initial discharge specific capacity but also maintain a high capacity retention rate after 800 cycles. This indicates that the aqueous polymer binder with optimized monomer ratio in this invention can produce artificial graphite negative electrode sheets with superior or comparable performance.

[0255] Four types of full cells were assembled using lithium iron phosphate positive electrode sheets C3 and D1 prepared with the aqueous polymer binder and PVDF binder of the present invention, and artificial graphite negative electrode sheets C9 and D2 prepared with the aqueous polymer binder and SBR / CMC binder of the present invention. The method is as follows:

[0256] A solution of lithium hexafluorophosphate dissolved in ethylene carbonate, dimethyl carbonate, and diethyl carbonate (1M LiPF6 in DMC:EC:EMC = 1:1:1 (volume ratio)) was used as the electrolyte. A polypropylene microporous membrane (Celgard 2325) was used as the separator. C5 or D1 was used as the positive electrode, and C9 or D2 was used as the negative electrode. The positive electrode, electrolyte, separator, negative electrode, stainless steel gasket, and stainless steel spring were placed in the CR2032 type negative electrode shell in the following order, with the positive electrode, electrolyte, separator, electrolyte, negative electrode, stainless steel gasket, and stainless steel spring in the center of the negative electrode shell. The CR2032 type positive electrode shell was placed on top. The entire assembly was then placed in an MSK 110 type battery packaging machine. Under the locked state, the pressure was increased to 50 psi for sealing. After unlocking, the full cells E1 to E4 were obtained. The electrolyte volume for each cell was 40 μL, which was required to be dropped equally onto both sides of the separator to ensure that the separator was fully wetted.

[0257] The assembled batteries E1 to E4 were subjected to battery cycle testing in a battery cycle tester (Wuhan Landian, CT3002A). The test conditions for the assembled full batteries were as follows: test temperature 25℃, cutoff voltage 2.5–4.2 V, charge / discharge rate 1C, and standard specific capacity of active material 170 mAh / g. The results of the full battery tests, including the initial discharge specific capacity, the discharge specific capacity after 2000 cycles, and the capacity retention rate (the ratio of discharge specific capacity to initial discharge specific capacity), are shown in Table 5.

[0258] Table 5 Performance test data of full batteries E1 to E4

[0259]

[0260] Table 5 further shows that the lithium iron phosphate / artificial graphite battery E1, assembled from the lithium iron phosphate positive electrode C5 prepared using the aqueous polyurethane acrylate binder of the present invention and the artificial graphite negative electrode C9, exhibits a slightly higher initial specific capacity and better long-cycle stability compared to battery E4, which is assembled from the positive electrode prepared using PVDF binder and the negative electrode prepared using SBR / CMC binder. Furthermore, even when the aqueous polyurethane acrylate binder of the present invention is used interchangeably with commercial PVDF or SBR / CMC binders to prepare electrode sheets, the assembled batteries E1 and E3 still exhibit good electrochemical performance.

[0261] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A waterborne polyurethane, characterized in that, It has the structural formula shown in Equation 1: In Formula 1: n is a natural number from 1 to 100, and R1 includes a first alkylene group, a first cycloalkylene group, or a first arylalkylene group; R2 has the structural formula shown in Equation 2: In Equation 2, x > 0, y > 0, z > 0, R 10 Including the first alkyl group, R 11 It includes triethylamine, triethanolamine or lithium; R3 includes a second alkylene, a second cycloalkylene or a second arylalkylene; R4, R8 and R9 independently include hydrogen or a second alkylene; R5 includes oxygen or nitrogen; R6 includes a third alkylene; R7 is hydrogen, a fourth alkylene or fluorine; Z is an anion.

2. The waterborne polyurethane according to claim 1, characterized in that, The first alkyl group, the second alkyl group, the third alkyl group, and the fourth alkyl group independently include methyl, ethyl, or propyl.

3. The waterborne polyurethane according to claim 1, characterized in that, The number of carbon atoms in the first and second alkylene groups is independently 1 to 6; The number of carbon atoms in the first and second cycloalkyl groups is independently 5 to 10; The number of carbon atoms in the first and second arylene alkyl groups is independently 6 to 10; The anions include sulfonate, carboxylate, or phosphate.

4. The method for preparing the waterborne polyurethane according to any one of claims 1 to 3, characterized in that, Includes the following steps: Polydiol, diisocyanate, dimethylolcarboxylic acid and organometallic catalyst are mixed to carry out a first polymerization reaction. Then, the resulting polymerization product is mixed with hydroxy acrylate or hydroxyacrylamide and a polymerization inhibitor to carry out a second polymerization reaction to obtain an aqueous polyurethane prepolymer solution. The aqueous polyurethane prepolymer solution is mixed with a neutralizing agent to carry out a neutralization reaction, thereby obtaining a neutralization reaction product; The neutralization reaction product is mixed with the first water and then mixed with an aqueous solution of an amine chain extender to carry out a chain extension reaction, thereby obtaining an aqueous polyurethane solution. The aqueous polyurethane is obtained by mixing acrylic monomer or acrylate monomer with the aqueous polyurethane solution, zwitterionic monomer, and second water, and then mixing with an aqueous solution of ammonium persulfate.

5. The preparation method according to claim 4, characterized in that, The ratio of the amount of hydroxyl groups in the polydiol to the amount of hydroxyl groups in the hydroxyacrylate or hydroxyacrylamide is 0.05 to 0.4:

1. The hydroxy acrylates include one or more of the following: hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, pentaerythritol triacrylate, pentaerythritol diacrylate, glycerol 1,3-diglyceryl alcohol diacrylate, and glycerol diacrylate. The hydroxyacrylamide includes one or more of N-hydroxyethylacrylamide, N-(3-hydroxypropyl)acrylamide, and N-(4-hydroxybutyl)acrylamide. The polymerization inhibitor includes one or more of hydroquinone, tert-butylcatechol, and p-hydroxyanisole, and the mass of the polymerization inhibitor is 0.1 to 1.5% of the mass of hydroxyacrylate or hydroxyacrylamide.

6. The preparation method according to claim 4, characterized in that, The neutralizing agent includes one or more of triethylamine, triethanolamine, and lithium hydroxide, and the amount of the neutralizing agent is 50 to 100% of the amount of dihydroxymethylcarboxylic acid. The amine chain extender includes one or more of ethylenediamine, propylenediamine, butanediamine, 2-methylpentanediamine, hexamethylenediamine, isophoronediamine, and sodium ethylenediaminoethanesulfonate.

7. The preparation method according to claim 4, characterized in that, The zwitterionic monomers include one of the following: methacryloylethyl sulfobetaine, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propionic acid)ammonium hydroxide, 2-methacryloyloxyethyl phosphoric acid choline, 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate, and 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt. The acrylate monomer includes any one of methyl acrylate, ethyl acrylate, and dodecyl acrylate.

8. The preparation method according to claim 4, characterized in that, The ratio of the amount of hydroxyl group in the dihydroxymethylcarboxylic acid to the amount of hydroxyl group in the hydroxyacrylate or hydroxyacrylamide is 0.05 to 0.4:

1. The ratio of the amount of isocyanate in the diisocyanate to the amount of hydroxyl group in the hydroxy acrylate or hydroxyacrylamide is 0.05 to 0.4:

1. The diisocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 2,4-ethylphenyl diisocyanate, methylcyclohexyl diisocyanate, and 2,2,4-trimethylhexane diisocyanate.

9. The preparation method according to claim 4, characterized in that, The first polymerization reaction is carried out at a temperature of 70–85°C for 1–4 hours. The second polymerization reaction is carried out at a temperature of 70–85°C for 2–4 hours. The third polymerization reaction is carried out at a temperature of 65–80°C for 2–6 hours.

10. The application of the aqueous polyurethane according to any one of claims 1 to 3 or the aqueous polyurethane prepared by the preparation method according to any one of claims 4 to 9 as an adhesive in the positive and negative electrode sheets of lithium-ion batteries.

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