A low-polarity crosslinking type waterborne polyurethane binder suitable for silicon-carbon negative electrodes and a preparation method thereof

Abstract

This invention belongs to the field of lithium battery material technology, specifically disclosing a low-polarity cross-linked aqueous polyurethane binder suitable for silicon-carbon anodes and its preparation method. The invention uses low-polarity hydrophobic polyols as the main soft segments and medium-to-low polarity polyols as auxiliary modified soft segments. Aliphatic and aromatic polyisocyanates are used to construct hard segments. Multifunctional cross-linking monomers are introduced to build a three-dimensional cross-linked network. Hydrophilic chain extenders and neutralizing agents are added to impart water dispersibility. A low-polarity cross-linked aqueous polyurethane dispersion is obtained through prepolymer synthesis, neutralization, phase inversion emulsification, post-chain extension, and solvent removal. The resulting binder exhibits low swelling, high toughness, strong adhesion, electrochemical stability, and environmental friendliness. It can effectively buffer the volume expansion of silicon-carbon anodes during charge and discharge, making it suitable for silicon-carbon anodes with high volume expansion and significantly improving the long-cycle stability of lithium batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery material technology, specifically relating to a low-polarity cross-linked aqueous polyurethane binder suitable for silicon-carbon anodes and its preparation method, especially suitable for high-volume-expansion silicon-carbon anodes, which can significantly improve the long-cycle stability of lithium batteries. Background Technology

[0002] Lithium-ion batteries, as a representative of rechargeable batteries, are widely used in portable electronic devices, power tools, electric vehicles, and energy storage due to their high energy density and long cycle life. Silicon-carbon anodes, with their extremely high theoretical specific capacity (4200 mAh / g), are the core anode material for next-generation high-energy-density lithium batteries. However, they experience volume expansion exceeding 300% during charge and discharge, leading to electrode pulverization, active material shedding, and interface failure, severely shortening the cycle life of lithium batteries. As a key component of silicon-carbon anodes, binders must simultaneously possess excellent adhesion, high elasticity (to buffer volume expansion), resistance to electrolyte swelling (to prevent softening during long-term cycling), and environmentally friendly processability.

[0003] Currently, commonly used binders for silicon-carbon anodes mainly include polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC) composite systems. Among them, although PAA has good electrolyte resistance, the film is hard and brittle, and cannot effectively buffer the volume expansion of silicon-carbon, resulting in a sharp capacity decay in the later stages of cycling. The SBR / CMC system has good elasticity, but poor resistance to electrolyte swelling, and is prone to softening and debinding after long-term immersion, and there is also a risk of organic residue.

[0004] To address the inherent shortcomings of the two types of binders mentioned above, researchers have focused on waterborne polyurethane systems. These systems, with their advantages of highly designable molecular structures, combining elasticity and adhesion, and being environmentally friendly with no solvent residue, have become a research hotspot for silicon-carbon anode binders. However, existing waterborne polyurethane binders still have many drawbacks. For example, patents CN104115316B, CN105324873B, CN105378988B, CN109075290B, CN115702510B, CN115917793B, CN113711383A, CN120283313A, and CN121548885A, filed by Daiichi Kogyo Pharmaceutical Co., Ltd. of Japan, mainly use polyolefin polyols such as polybutadiene polyol, polyisoprene polyol, polyisobutylene polyol, hydrogenated polybutadiene polyol, hydrogenated isoprene polyol, and polychloroprene polyol. The main chain of this type of polyolefin polyol is a pure hydrocarbon structure with almost no polar functional groups. It has very weak interaction with silicon-carbon anode materials and current collectors, resulting in weak interfacial adhesion. The polyolefin binder has insufficient toughness and ductility (elongation at break <300%), making it unable to adapt to the 300% volume expansion of silicon-carbon. After long cycles, the electrode is prone to cracking and capacity drops.

[0005] Therefore, it is of great significance to develop a novel waterborne polyurethane adhesive that can simultaneously solve problems such as volume expansion of silicon-based anode materials, electrolyte swelling, weak adhesion, and insufficient toughness and ductility. Summary of the Invention

[0006] This invention provides a low-polarity hydrophobic crosslinked waterborne polyurethane adhesive and its preparation method. By regulating molecular polarity, constructing a crosslinked network, and designing soft and hard segments in a coordinated manner, a low-swelling, high-toughness, strong-adhesion, and environmentally friendly adhesive for silicon-carbon anodes is prepared, fundamentally solving the problem of cyclic degradation of silicon-carbon anodes.

[0007] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a low-polarity hydrophobic crosslinking waterborne polyurethane adhesive, comprising the following components: low-polarity hydrophobic polyol, medium-low polarity polyol, polyisocyanate, multifunctional crosslinking monomer, hydrophilic chain extender, neutralizer, post-chain extender, solvent, and water.

[0009] This binder uses low-polarity hydrophobic polyols as the main soft segments and medium- and low-polarity polyols as auxiliary modified soft segments to construct a gradient polarity soft segment system. Aliphatic polyisocyanates and aromatic polyisocyanates are compounded to construct hard segments. A three-dimensional cross-linking network is further constructed through multifunctional cross-linking monomers. Hydrophilic chain extenders are introduced to give the polyurethane prepolymer water dispersibility. Finally, the molecular weight is increased by post-chain extenders to enhance toughness and solvent resistance, forming a polyurethane molecular structure that is "hydrophobic and resistant to swelling, highly elastic and resistant to deformation, cross-linked and stable structure, water-based, environmentally friendly and easy to process".

[0010] The specific types of each component are selected as follows:

[0011] Low-polarity hydrophobic polyols: selected from one or more of long-chain aliphatic polyester polyols, bio-based hydrogenated polyols, and fully saturated hydrocarbon diols. Long-chain aliphatic polyester polyols refer to aliphatic polyester polyols with a carbon number ≥16, which can be synthesized from long-chain dicarboxylic acids (≥C8) or long-chain diols (≥C8). Specific examples include poly(1,8-octanoic acid diol), poly(1,10-decanoic acid diol), poly(1,12-dodecanediol diol), poly(1,14-tetradecanediol diol), poly(1,16-hexadecanediol diol), poly(1,10-decanoic acid diol), poly(1,12-dodecanediol diol), and poly(1,12-tetradecanediol diol). Bio-based hydrogenated polyols are selected from one or more of hydrogenated dimerols and hydrogenated dimer acid polyester polyols. Commercially available hydrogenated dimerols (C36) and hydrogenated dimer acid polyester polyols (C36 dimerol and long-chain diol condensation) include Cargill Pripol™ 2033 / 2043 / 2050 / 2051, Cargill Priplast™ 1838 / 3238 / 3187 / 3196 / 3294, Nisshin Oliodiol™ 36H / 36HB, Oleon RADIANOL 1990, Oleon RADIA 7280 / 7282 / 7285 / 7287 / 7288, BASF Empol™ 1064, and Beijing Baiyuan: HDM-D2033 / 2043, etc. Fully saturated hydrocarbon diols can be selected from one or more of ethylene-α-olefin copolydiols and poly-α-olefin (PAO) diols. Examples of ethylene-α-olefin copolydiols include ethylene-octene copolydiol, ethylene-decene copolydiol, and ethylene-dodecene copolydiol. Examples of poly-α-olefin diols include poly(1-hexene) diol and poly(1-octene) diol.

[0012] Medium to low polarity polyols: preferred polytetrahydrofuran ether diol, oleic acid-based (castor oil) polyols, polycarbonate polyols, polycaprolactone polyols, polysiloxane polyols, and fluorinated polyols, etc. These polyols can be used alone or in combination. Polytetrahydrofuran ether diol, such as PTMEG1000 / 2000; castor oil polyol, such as BASF SOVERMOL® 750 / 805 / 815, Vertellus Polycins D280; polycarbonate polyol (PCDL), such as Asahi Kasei G3450J / G3452 / T5652, Ube PH200, Mitsubishi BENEBiOL 3000; polycaprolactone polyol (PCL), such as Daicel PLACACCEL 220EB / 220N, BASF PD1-20; polysiloxane polyol, such as Dow XIAMETER OFS-0930 hydroxyl silicone oil polyol, Wacker POLYSILOXANE OH series; fluorinated polyol, such as Daikin Fluon PFPE perfluoropolyether diol, 3MDyneon fluorinated polyol, etc.

[0013] Polyisocyanates: Preferred polyisocyanates are those commonly used in the art, including aliphatic (ester-cyclic) polyisocyanates and aromatic isocyanates. Aliphatic (alicyclic) polyisocyanates: Options include hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), isophthalic diisocyanate (XDI), α,α,α,α-tetramethylphenyl diisocyanate (TMXDI), etc. Aromatic isocyanates: Options include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene 1,5-diisocyanate (NDI), and polymethylene polyphenyl polyisocyanate (PAPI).

[0014] Multifunctional crosslinking monomer: preferably one or more of trimethylolpropane (TMP), trimethylolethane, glycerol, diethanolamine, triethanolamine, triisopropanolamine, and tributanolamine.

[0015] Hydrophilic chain extender: Introduces hydrophilic groups into the molecular chain, enabling the polyurethane prepolymer to be uniformly dispersed in aqueous solvents, suitable for the preparation process of water-based negative electrode slurries. Preferably, it is a carboxylic acid and its salt, sulfonic acid and its sulfonate containing two or more active hydrogen groups. Specifically, it can be selected from one or more of the following: 2,2-dimethylolpropionic acid (DMPA), 2,2-dimethylolbutyric acid (DMBA), dimethylolvalerate (DMVA), diaminobenzoic acid, tartaric acid (TA), 1,3-phenylenediamine-4,6-disulfonic acid, 2,4-diaminotoluene-5-sulfonic acid, sodium 1,2-propanediol-3-sulfonate, sodium 1,4-butanediol-2-sulfonate, sodium N,N-di(2-hydroxyethyl)-2-aminoethanesulfonate, sodium N,N-di(2-hydroxyethyl)-2-aminopropanesulfonate, sodium ethylenediaminoethanesulfonate, and sodium 2,4-diaminobenzenesulfonate.

[0016] Neutralizing agent: selected from one or more volatile bases such as ammonia, trimethylamine, triethylamine, N,N-dimethylethanolamine, N-methyldiethanolamine, and triethanolamine.

[0017] Post-chain extender: Preferably, a small molecule polyol or polyamine containing two or more active hydrogen groups is used, or an amino alcohol. Specifically, one or more of the following can be selected: ethylenediamine, propylenediamine, butyldiamine, hexamethylenediamine, piperazine, isophorone diamine, hydrazine hydrate, adipic dihydrazide, ethylene glycol, 1,4-butanediol, 1,6-hexanediol, N-methyldiethanolamine, diethanolamine, diisopropanolamine, 1,3-diaminopropanol, 2-amino-2-methyl-1-propanol, and aminosilane coupling agent KH550.

[0018] Solvents: One or more organic solvents such as acetone, butanone, N-methyl-2-pyrrolidone, tetrahydrofuran, dioxane, ethyl acetate, butyl acetate, and toluene can be used.

[0019] Furthermore, the low-polarity hydrophobic polyol accounts for 60-90% of the total mass of the polyol, and the medium-low polarity polyol accounts for 10-40% of the total mass of the polyol; the ratio (mass ratio) of the aliphatic polyisocyanate and the aromatic polyisocyanate is 5:1-1:5, and the amount of polyisocyanate is calculated based on the molar ratio of NCO functional groups and OH functional groups in the reaction system, and the ratio is 1.05-1.50;

[0020] Secondly, the present invention provides a method for preparing the above-mentioned low-polarity hydrophobic crosslinking waterborne polyurethane adhesive, comprising the following steps:

[0021] (1) Synthesis of prepolymer: Low polarity hydrophobic polyol and medium-low polarity polyol are added to the reaction vessel and dehydrated under vacuum conditions; after cooling, polyisocyanate is added, followed by solvent dilution, gas replacement is carried out by inert gas, and the reaction is kept at a constant temperature; after cooling, crosslinking agent and hydrophilic chain extender are added, and the reaction is continued after stirring evenly to prepare NCO-terminated prepolymer;

[0022] (2) Neutralization reaction: Cool the NCO prepolymer prepared in step (1), dilute it with the reaction solvent, slowly add the neutralizing agent, and stir the reaction.

[0023] (3) Phase inversion emulsification: The prepolymer from step (2) is transferred to a dispersion vessel. Under high-speed stirring, deionized water is slowly added dropwise to the neutralized prepolymer and stirred continuously to form a uniform polyurethane prepolymer aqueous dispersion.

[0024] (4) Post-chain extension: While maintaining stirring, add the post-chain extender to the aqueous dispersion obtained in step (3) to carry out the reaction;

[0025] (5) Solvent removal and finished product preparation: The system after the reaction in step (4) is subjected to vacuum distillation to remove the reaction solvent, cooled and filtered to obtain the final aqueous dispersion of waterborne polyurethane adhesive.

[0026] More specifically, the preparation method of the low-polarity hydrophobic crosslinking waterborne polyurethane adhesive includes the following steps:

[0027] (1) Synthesis of prepolymer: Low polarity hydrophobic polyol and medium-low polarity polyol were added to a four-necked flask and dehydrated for 1-2 h at 115℃ and vacuum degree ≤ -0.08 MPa to remove water from the raw materials; the temperature was lowered to below 50 ℃, polyisocyanate was added, followed by solvent dilution, and the solid content of the system was controlled at 40-60%. Nitrogen gas was purged for 15 min for gas replacement, and the reaction temperature was controlled at 60-80 ℃ for 3-4 h. The reaction temperature was lowered to 60 ℃, crosslinking agent and hydrophilic chain extender were added, and after stirring evenly, the reaction was continued at a constant temperature for 1-2 h to prepare NCO-terminated prepolymer.

[0028] (2) Neutralization reaction: Cool the NCO prepolymer prepared in step (1) to 30 °C, add reaction solvent to dilute to 30-40% solid content, slowly add neutralizing agent, and stir reaction for 10-20 min;

[0029] (3) Phase inversion emulsification: Transfer the prepolymer from step (2) to a dispersion vessel, and slowly add deionized water to the neutralized prepolymer under a high-speed stirring speed of 2000-3000 rpm, and continue stirring for 15-30 min to form a uniform polyurethane prepolymer aqueous dispersion.

[0030] (4) Post-chain extension: While keeping the mixture stirred, add the post-chain extender to the aqueous dispersion obtained in step (3), control the reaction temperature at 35-50 ℃, and react for 1-2 h;

[0031] (5) Solvent removal and finished product preparation: The system after the reaction in step (4) is placed under negative pressure with a vacuum degree ≤ -0.09 MPa, heated to 45-55℃, and distilled under reduced pressure for 0.5-1 h to completely remove the reaction solvent in the synthesis process. The pH is adjusted to 7-9, cooled to room temperature, filtered, and the final waterborne polyurethane adhesive aqueous dispersion is obtained.

[0032] Compared with the prior art, the present invention has the following innovations and advantages:

[0033] 1. Innovative Structural Design

[0034] 1) The first gradient polarity composite soft segment is used to separate the microphase by polarity control. Low polarity hydrophobic polyol is used as the main soft segment to provide electrolyte resistance and mechanical flexibility, which is the basis for the anti-expansion of silicon carbon. Medium and low polarity polyol is used as an auxiliary monomer to connect the low polarity hydrophobic main body with the hard segment / hydrophilic group. The appropriate polarity improves compatibility, ensures stable water dispersion and uniform particle size, and improves the wettability of polyurethane interface. The dual synergistic adaptation to the volume expansion and contraction of silicon carbon, and the reinforcement of mechanical strength and electrode interface adhesion ability.

[0035] 2) The hard segments of aliphatic and aromatic polyisocyanates are stacked and entangled through hydrogen bonds, van der Waals forces and hydrophobic association to build a reversible physical cross-linking network, balancing the rigidity and flexibility of the bonding, ensuring the bonding strength between the powder and the current collector, and avoiding the brittleness of the electrode.

[0036] 3) Abandoning linear molecular structures, multifunctional cross-linked monomers construct a three-dimensional cross-linked network, which improves strength and modulus, disperses expansion stress, significantly enhances the anchoring force on current collectors (copper foil) and active particles, improves the overall structural stability of the electrode, and makes it less likely to loosen and fall off during charging and discharging.

[0037] 4) A dual process of prepolymer hydrophilic modification and subsequent molecular chain extension is used. After emulsification and dispersion, secondary chain extension is performed to increase the molecular weight of the polymer and improve the mechanical toughness, electrolyte resistance and solvent resistance of the binder.

[0038] 2. Innovation by circumventing raw material barriers

[0039] It offers a comprehensive multi-category polyol raw material system, abandoning the industry's conventional limitations on polyolefin polyol raw materials. It selects various types of monomers such as long-chain hydrophobic polyester diols, hydrogenated dimer diols, and special modified diols, which can be flexibly combined.

[0040] 3. Product application performance advantages

[0041] 1) Hydrophobic and swelling resistant: The hydrophobic molecular framework + multi-crosslinked network framework blocks electrolyte erosion, the binder is not easy to fail, and the long-term cycle stability of the battery is significantly improved.

[0042] 2) High elasticity and deformation resistance: Excellent elasticity can buffer the huge volume expansion of silicon carbon, eliminating the problems of electrode cracking and powder shedding;

[0043] 3) Excellent overall electrochemical performance: The molecular structure is rich in urethane bonds, ether bonds and urea bonds, which helps to form a stable passivation layer on the silicon surface, inhibits electrolyte decomposition, and makes the battery with higher initial efficiency, discharge specific capacity, excellent rate charge and discharge performance, and significantly reduced cycle decay rate.

[0044] 4) Excellent processing performance: Water-based dispersible system, environmentally friendly and safe production, the product does not contain toxic organic solvents, and the slurry has good fluidity and coating uniformity. Detailed Implementation

[0045] The present invention will be further described below with reference to specific embodiments.

[0046] A general preparation process for polyurethane aqueous dispersions includes the following steps (applicable uniformly to all examples):

[0047] 1. Prepolymer Synthesis: Low-polarity hydrophobic polyols and medium-low-polarity polyols were added to a four-necked flask and dehydrated at 115℃ and vacuum degree ≤ -0.08 MPa for 1-2 h to remove moisture from the raw materials; the temperature was lowered to below 50℃, polyisocyanate was added, followed by solvent dilution, and the solid content of the system was controlled at 40-60%. Nitrogen gas was purged for 15 min for gas replacement, and the reaction temperature was controlled at 60-80℃ for 3-4 h; the reaction temperature was lowered to 60℃, crosslinking agent and hydrophilic chain extender were added, and after stirring evenly, the reaction was continued at a constant temperature for 1-2 h to prepare the NCO-terminated prepolymer;

[0048] 2. Neutralization reaction: Cool the NCO-terminated prepolymer prepared in step 1 to 30 °C, add reaction solvent to dilute to a solid content of 30-40%, slowly add neutralizing agent, stir reaction for 10-20 min to neutralize the carboxyl groups in the prepolymer;

[0049] 3. Phase inversion emulsification: Transfer the prepolymer from step 2 to a dispersion vessel. Under high-speed stirring (2000-3000 rpm), slowly add deionized water dropwise to the neutralized prepolymer and continue stirring for 15-30 min.

[0050] 4. Post-chain extension: While maintaining stirring, add the post-chain extender to the aqueous dispersion obtained in step 3, control the reaction temperature at 35-50 ℃, and react for 1-2 h. The residual NCO groups in the prepolymer react with the post-chain extender to increase the molecular weight and crosslinking density of the polyurethane.

[0051] 5. Solvent removal and finished product preparation: Place the system after the reaction in step 4 under negative pressure (vacuum degree ≤ -0.09MPa), heat to 45-55 ℃, distill under reduced pressure for 0.5-1 h to completely remove the reaction solvent in the synthesis process, adjust the pH to 7-9, cool to room temperature, filter and discharge to obtain the final aqueous dispersion of waterborne polyurethane adhesive.

[0052] Example 1

[0053] In a four-necked flask, 82 parts of poly(1,10-decanediol sebacate) (hydroxyl value ≈ 30 mg KOH / g), 13 parts of PTMEG1000, and 5 parts of castor oil polyol (BASF SOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under vacuum. After cooling, 10.58 parts of isophorone diisocyanate, 4.53 parts of diphenylmethane diisocyanate, and 120 parts of butanone were added. The mixture was reacted at 75°C for 3 hours, then cooled to 60°C, and 2.0 parts of trimethylolpropane and 5.0 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60°C for 1 hour. Then, the mixture was cooled to 30°C, and butanone was added to dilute the mixture to a solid content of approximately 30%. 3.66 parts of triethylamine were added, and the mixture was stirred to carry out the reaction. Finally, 250 parts by weight of water were slowly added, and the mixture was emulsified and dispersed under high-speed stirring. An aqueous solution obtained by diluting 1.52 parts by mass of ethylenediamine with 40 parts by mass of water was added to the dispersion, and the chain extension reaction was carried out at 50 °C for 1 hour. The solvent was removed by vacuum distillation, and the pH was adjusted to 7-9 with triethylamine to obtain a polyurethane aqueous dispersion 1 with a solid content of about 30%.

[0054] Example 2

[0055] In a four-necked flask, 78 parts of poly(1,10-decanediol sebacate) (hydroxyl value ≈ 30 mg KOH / g), 17 parts of polycarbonate polyol (Asahi Kasei T5652, hydroxyl value ≈ 56 mg KOH / g), and 5 parts of castor oil polyol (BASF SOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under heating and vacuum. After cooling, 7.92 parts of diphenylmethane diisocyanate, 7.42 parts of dicyclohexylmethane diisocyanate, and 120 parts of butanone were added. The mixture was reacted at 75 °C for 3 hours, then cooled to 60 °C, and 3 parts of trimethylolpropane and 6.0 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60 °C for 1 hour. Then, the mixture was cooled to 30 °C, and butanone was added to dilute the mixture to a solid content of approximately 30%. 4.39 parts of triethylamine were added, and the mixture was stirred to carry out the reaction. Then, slowly add 250 parts by weight of water and emulsify and disperse under high-speed stirring. Add an aqueous solution obtained by diluting 2.46 parts by weight of ethylenediamine with 40 parts by weight of water to the dispersion, and carry out a chain extension reaction at 50 °C for 1 hour. Remove the solvent by vacuum distillation, adjust the pH to 7-9 with triethylamine, and obtain a polyurethane aqueous dispersion 2 with a solid content of about 30%.

[0056] Example 3

[0057] In a four-necked flask, 68 parts of poly(1,10-decanediol sebacate) (hydroxyl value ≈ 30 mg KOH / g), 27 parts of PTMEG1000, and 5 parts of castor oil polyol (BASF SOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under vacuum. After cooling, 10.85 parts of diphenylmethane diisocyanate, 8.26 parts of dicyclohexylmethane diisocyanate, and 120 parts of butanone were added. The mixture was reacted at 75 °C for 3 hours, then cooled to 60 °C, and 2.0 parts of trimethylolpropane and 5.0 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60 °C for 1 hour. Then, the mixture was cooled to 30 °C, and butanone was added to dilute the mixture to a solid content of approximately 30%. 3.66 parts of triethylamine were added, and the mixture was stirred to carry out the reaction. Finally, 250 parts by weight of water were slowly added, and the mixture was emulsified and dispersed under high-speed stirring. An aqueous solution of 3.12 parts by mass of ethylenediamine diluted with 40 parts by mass of water was added to the dispersion, and the chain extension reaction was carried out at 50 °C for 1 hour. The solvent was removed by vacuum distillation, and the pH was adjusted to 7-9 with triethylamine to obtain a polyurethane aqueous dispersion 3 with a solid content of about 30%.

[0058] Example 4

[0059] In a four-necked flask, 63 parts of poly(1,10-decanediol sebacate) (hydroxyl value ≈ 30 mg KOH / g), 32 parts of polycarbonate polyol (Asahi Kasei T5652, hydroxyl value ≈ 56 mg KOH / g), and 5 parts of castor oil polyol (BASF SOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under heating and vacuum conditions. After cooling, 7.96 parts of dicyclohexylmethane diisocyanate, 12.85 parts of diphenylmethane diisocyanate, and 120 parts of butanone were added. The mixture was reacted at 75°C for 3 hours, then cooled to 60°C, and 3.5 parts of trimethylolpropane and 7.0 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60°C for 1 hour. Then, the mixture was cooled to 30°C, and butanone was added to dilute the mixture to a solid content of approximately 30%. Finally, 5.12 parts of triethylamine were added, and the mixture was stirred to carry out the reaction. Then slowly add 250 parts by weight of water and emulsify and disperse under high-speed stirring. Add an aqueous solution obtained by diluting 3.96 parts by weight of ethylenediamine with 40 parts by weight of water to the dispersion, and carry out chain extension reaction at 50 °C for 1 hour. Remove the solvent by vacuum distillation, adjust the pH to 7-9 with triethylamine, and obtain a polyurethane aqueous dispersion 4 with a solid content of about 30%.

[0060] Example 5

[0061] In a four-necked flask, 75 parts of poly(1,10-decanediol sebacate) (hydroxyl value ≈ 30 mg KOH / g), 20 parts of PTMEG1000, and 5 parts of castor oil polyol (BASF SOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under vacuum. After cooling, 7.82 parts of dicyclohexylmethane diisocyanate, 9.96 parts of diphenylmethane diisocyanate, and 120 parts of butanone were added. The mixture was reacted at 75 °C for 3 hours, then cooled to 60 °C, and 3.0 parts of trimethylolpropane and 5.5 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60 °C for 1 hour. Then, the mixture was cooled to 30 °C, and butanone was added to dilute to a solid content of approximately 30%. 4.02 parts of triethylamine were added for neutralization, and the mixture was stirred to continue the reaction. Finally, 250 parts by weight of water were slowly added, and the mixture was emulsified and dispersed under high-speed stirring. An aqueous solution of 2.92 parts by mass of ethylenediamine diluted with 40 parts by mass of water was added to the dispersion, and the chain extension reaction was carried out at 50 °C for 1 hour. The solvent was removed by vacuum distillation, and the pH was adjusted to 7-9 with triethylamine to obtain a polyurethane aqueous dispersion 5 with a solid content of about 30%.

[0062] Example 6

[0063] In a four-necked flask, 70 parts of hydrogenated diol (Cargill Pripol™ 2033, hydroxyl value ≈ 207 mg KOH / g), 25 parts of polycarbonate polyol (Asahi Kasei T5652, hydroxyl value ≈ 56 mg KOH / g), and 5 parts of castor oil polyol (BASFSOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under heating and vacuum conditions. After cooling, 16.85 parts of dicyclohexylmethane diisocyanate, 22.68 parts of diphenylmethane diisocyanate, and 150 parts of butanone were added. The mixture was reacted at 75 °C for 3 hours, then cooled to 60 °C, and 2.5 parts of trimethylolpropane and 6 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60 °C for 1 hour. Then, the mixture was cooled to 30 °C, and butanone was added to dilute to a solid content of approximately 30%. 4.39 parts of triethylamine were added for neutralization, and the mixture was stirred to continue the reaction. Then slowly add 250 parts by weight of water and emulsify and disperse under high-speed stirring. Add an aqueous solution obtained by diluting 5.21 parts by weight of ethylenediamine with 40 parts by weight of water to the dispersion, and carry out chain extension reaction at 50 °C for 1 hour. Remove the solvent by vacuum distillation, adjust the pH to 7-9 with triethylamine, and obtain a polyurethane aqueous dispersion 6 with a solid content of about 30%.

[0064] Example 7

[0065] In a four-necked flask, 70 parts of hydrogenated diol (Cargill Pripol™ 2033, hydroxyl value ≈ 207 mg KOH / g), 20 parts of PTMEG1000, and 5 parts of castor oil polyol (BASF SOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under heating and vacuum. After cooling, 18.62 parts of dicyclohexylmethane diisocyanate, 24.82 parts of diphenylmethane diisocyanate, and 150 parts of butanone were added. The mixture was reacted at 75 °C for 3 hours, then cooled to 60 °C, and 3.5 parts of trimethylolpropane and 7 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60 °C for 1 hour. Then, the mixture was cooled to 30 °C, and butanone was added to dilute to a solid content of approximately 30%. 5.12 parts of triethylamine were added for neutralization, and the mixture was stirred to carry out the reaction. Finally, 250 parts by weight of water were slowly added, and the mixture was emulsified and dispersed under high-speed stirring. An aqueous solution of 7.86 parts by mass of ethylenediamine diluted with 40 parts by mass of water was added to the dispersion, and the chain extension reaction was carried out at 50 °C for 1 hour. The solvent was removed by vacuum distillation, and the pH was adjusted to 7-9 with triethylamine to obtain a polyurethane aqueous dispersion 7 with a solid content of about 30%.

[0066] Example 8

[0067] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen purge tube, 85 parts of hydrogenated diol (Cargill Pripol™ 2033, hydroxyl value ≈ 207 mg KOH / g), 10 parts of polycarbonate polyol (Asahi Kasei T5652, hydroxyl value ≈ 56 mg KOH / g), and 5 parts of castor oil polyol (BASF SOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under heating and vacuum conditions. After cooling, 22.36 parts of dicyclohexylmethane diisocyanate, 18.95 parts of diphenylmethane diisocyanate, and 150 parts of butanone were added. After reacting at 75°C for 3 hours, the temperature was lowered to 60°C, and 2.5 parts of trimethylolpropane and 4.5 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60°C for 1 hour. The temperature was then lowered to 30 °C, and methyl ethyl ketone was added to dilute the mixture to a solid content of approximately 30%. 3.29 parts of triethylamine were added for neutralization, and the mixture was stirred to allow the reaction to proceed. Then, 250 parts by weight of water were slowly added, and emulsification and dispersion were carried out under high-speed stirring. An aqueous solution obtained by diluting 4.82 parts by weight of ethylenediamine with 40 parts by weight of water was added to the dispersion, and the chain extension reaction was carried out at 50 °C for 1 hour. The solvent was removed by vacuum distillation, and the pH was adjusted to 7-9 with triethylamine to obtain a polyurethane aqueous dispersion with a solid content of approximately 30%.

[0068] Example 9

[0069] In a four-necked flask, 68 parts of hydrogenated diol (Cargill Pripol™ 2033, hydroxyl value ≈ 207 mg KOH / g), 27 parts of PTMEG1000, and 5 parts of castor oil polyol (BASF SOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under heating and vacuum. After cooling, 15.92 parts of dicyclohexylmethane diisocyanate, 21.35 parts of diphenylmethane diisocyanate, and 150 parts of butanone were added. The mixture was reacted at 75 °C for 3 hours, then cooled to 60 °C, and 2.0 parts of trimethylolpropane and 6.5 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60 °C for 1 hour. Then, the mixture was cooled to 30 °C, and butanone was added to dilute to a solid content of approximately 30%. 4.76 parts of triethylamine were added for neutralization, and the mixture was stirred to continue the reaction. Finally, 250 parts by weight of water were slowly added, and the mixture was emulsified and dispersed under high-speed stirring. An aqueous solution of 5.36 parts by mass of ethylenediamine diluted with 40 parts by mass of water was added to the dispersion, and the chain extension reaction was carried out at 50 °C for 1 hour. The solvent was removed by vacuum distillation, and the pH was adjusted to 7-9 with triethylamine to obtain a polyurethane aqueous dispersion with a solid content of about 30%.

[0070] Example 10

[0071] In a four-necked flask, 62 parts of hydrogenated diol (Cargill Pripol™ 2033, hydroxyl value ≈ 207 mg KOH / g), 27 parts of polycarbonate polyol (Asahi Kasei T5652, hydroxyl value ≈ 56 mg KOH / g), and 5 parts of castor oil polyol (BASFSOVERMOL® 805, hydroxyl value ≈ 170 mg KOH / g) were added, and the mixture was dehydrated under heating and vacuum. After cooling, 15.88 parts of dicyclohexylmethane diisocyanate, 23.92 parts of diphenylmethane diisocyanate, and 150 parts of butanone were added. The mixture was reacted at 75 °C for 3 hours, then cooled to 60 °C, and 3.5 parts of trimethylolpropane and 7.0 parts of 2,2-dimethylolpropionic acid were added. The reaction was continued at 60 °C for 1 hour. Then, the mixture was cooled to 30 °C, and butanone was added to dilute to a solid content of approximately 30%. 5.12 parts of triethylamine were added for neutralization, and the mixture was stirred to continue the reaction. Then slowly add 250 parts by weight of water and emulsify and disperse under high-speed stirring. Add an aqueous solution obtained by diluting 9.05 parts by weight of ethylenediamine with 40 parts by weight of water to the dispersion, and carry out chain extension reaction at 50 °C for 1 hour. Remove the solvent by vacuum distillation, adjust the pH to 7-9 with triethylamine, and obtain a polyurethane aqueous dispersion 10 with a solid content of about 30%.

[0072] Performance testing:

[0073] The performance of the polyurethane dispersions prepared in the examples was tested, as follows:

[0074] Particle size: Take a small amount of polyurethane adhesive emulsion, dilute it with deionized water, and test it with a Malvern particle size analyzer.

[0075] Swelling rate: Pour the polyurethane aqueous dispersion into a film and allow it to evaporate at room temperature for 8-12 hours. After film formation, place it in a forced-air drying oven at 60-80℃ for 2-4 hours. Cut the film into 3×1 cm pieces and weigh them as W0. Immerse the film in the electrolyte and place it in a forced-air drying oven at 60℃ for 72 hours. After removing the film, allow it to dry on the surface and weigh it as W1. Swelling rate = (W1-W0) / W0.

[0076] Tensile strength / elongation at break: The dried polyurethane adhesive film (approximately 0.5-1 mm thick) was cut into 60 mm × 115 mm dumbbell-shaped specimens and tested using a universal testing machine at 25°C and 50% RH, with a loading speed of 100 mm / min. Tensile strength: σ = F max / A(F max (where A is the initial cross-sectional area of ​​the specimen, representing the maximum tensile force); Elongation at break: ε = (L... t -L0) / L0×100%(L t L0 is the gauge length at the time of breakage, and L0 is the initial gauge length.

[0077] The test results are shown in Table 1 below. It can be seen that the polyurethane aqueous dispersion prepared according to the method of the present invention has good stability. By rationally designing and constructing the crosslinking network, the polyurethane film has excellent electrolyte resistance, high tensile strength and elongation at break. It can effectively avoid the problems of electrode cracking and powder shedding by using the stretching of polyurethane chain segments to buffer the volume expansion stress of silicon material during charging and discharging. At the same time, the peel force of the silicon-carbon negative electrode prepared by the polyurethane aqueous dispersion as a binder in the embodiments of the present invention is increased by 30-50% compared with the traditional SBR binder, and the adhesion ability is significantly enhanced, further ensuring the structural integrity of silicon-based electrode under cyclic conditions.

[0078] Table 1. Particle size of polyurethane dispersions and swelling ratio and mechanical properties of films in commercial electrolytes for each example.

[0079]

[0080] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims of the present invention, will be protected by patent law.

Claims

1. A low-polarity crosslinking waterborne polyurethane adhesive, characterized in that, It includes the following components: low-polarity hydrophobic polyol, medium-low polarity polyol, polyisocyanate, multifunctional crosslinking monomer, hydrophilic chain extender, neutralizer, post-chain extender, solvent and water; The low-polarity hydrophobic polyol is selected from one or more of long-chain aliphatic polyester polyols, bio-based hydrogenated polyols, and fully saturated hydrocarbon diols. The medium-low polarity polyols are selected from one or more of polytetrahydrofuran ether diol, castor oil polyol, polycarbonate polyol, polycaprolactone polyol, polysiloxane polyol, and fluorinated polyols. The polyisocyanates include aliphatic polyisocyanates and aromatic polyisocyanates; The multifunctional crosslinking monomer is selected from one or more of trimethylolpropane, trimethylolethane, glycerol, diethanolamine, triethanolamine, triisopropanolamine, and tributanolamine; The hydrophilic chain extender is selected from one or more of carboxylic acids and carboxylates containing two or more active hydrogen groups, sulfonic acids and sulfonates; The neutralizing agent is a volatile alkali; The chain extender is selected from one or more small molecule polyols, polyamines, and amino alcohols containing two or more active hydrogen groups; The solvent is an organic solvent.

2. The low-polarity crosslinking waterborne polyurethane adhesive according to claim 1, characterized in that, The long-chain aliphatic polyester polyol is selected from one or more of the following: poly(1,8-octanediol octanoate), poly(1,10-decanediol sebacic acid), poly(1,12-dodecanediol sebacic acid), poly(1,14-tetradecanediol sebacic acid), poly(1,16-hexadecanediol sebacic acid), poly(1,10-decanediol sebacic acid), poly(1,12-dodecanediol sebacic acid), and poly(1,12-dodecanediol sebacic acid). The bio-based hydrogenated polyol is selected from one or more of hydrogenated dimerols and hydrogenated dimer acid polyester polyols; The fully saturated hydrocarbon diol is selected from one or more of ethylene-α-olefin copolydiol and polyα-olefin diol.

3. The low-polarity crosslinking waterborne polyurethane adhesive according to claim 1, characterized in that, The aliphatic polyisocyanate is selected from one or more of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, isophthalimethylene diisocyanate, and α,α,α,α-tetramethylphthalimethylene diisocyanate. The aromatic polyisocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, naphthalene 1,5-diisocyanate, and polymethylene polyphenyl polyisocyanate.

4. The low-polarity crosslinking waterborne polyurethane adhesive according to claim 1, characterized in that, The hydrophilic chain extender is selected from one or more of the following: 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, dimethylolvalerate, diaminobenzoic acid, tartaric acid, 1,3-phenylenediamine-4,6-disulfonic acid, 2,4-diaminotoluene-5-sulfonic acid, sodium 1,2-propanediol-3-sulfonate, sodium 1,4-butanediol-2-sulfonate, sodium N,N-di(2-hydroxyethyl)-2-aminoethanesulfonate, sodium N,N-di(2-hydroxyethyl)-2-aminopropanesulfonate, sodium ethylenediaminoethanesulfonate, and sodium 2,4-diaminobenzenesulfonate.

5. The low-polarity crosslinking waterborne polyurethane adhesive according to claim 1, characterized in that, The neutralizing agent is selected from one or more of ammonia, trimethylamine, triethylamine, N,N-dimethylethanolamine, N-methyldiethanolamine, and triethanolamine.

6. The low-polarity crosslinking waterborne polyurethane adhesive according to claim 1, characterized in that, The chain extender is selected from one or more of the following: ethylenediamine, propylenediamine, butanediamine, hexamethylenediamine, piperazine, isophorone diamine, hydrazine hydrate, adipic dihydrazide, ethylene glycol, 1,4-butanediol, 1,6-hexanediol, N-methyldiethanolamine, diethanolamine, diisopropanolamine, 1,3-diaminopropanol, 2-amino-2-methyl-1-propanol, and aminosilane coupling agent KH550.

7. The low-polarity crosslinking waterborne polyurethane adhesive according to claim 1, characterized in that, The solvent is selected from one or more of acetone, butanone, N-methyl-2-pyrrolidone, tetrahydrofuran, dioxane, ethyl acetate, butyl acetate, and toluene.

8. The low-polarity crosslinking waterborne polyurethane adhesive according to claim 1, characterized in that, The low-polarity hydrophobic polyol accounts for 60-90% of the total mass of the polyol, and the medium-low polarity polyol accounts for 10-40% of the total mass of the polyol; the ratio of aliphatic polyisocyanate to aromatic polyisocyanate is 5:1-1:5, and the amount of polyisocyanate is calculated based on the molar ratio of NCO functional groups to OH functional groups in the reaction system, and the ratio is 1.05-1.

50.

9. A method for preparing the low-polarity crosslinking waterborne polyurethane adhesive according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Synthesis of prepolymer: Low polarity hydrophobic polyol and medium-low polarity polyol are added to the reaction vessel and dehydrated under vacuum conditions; after cooling, polyisocyanate is added, followed by solvent dilution, gas replacement is carried out by inert gas, and the reaction is kept at a constant temperature; after cooling, crosslinking agent and hydrophilic chain extender are added, and the reaction is continued after stirring evenly to prepare NCO-terminated prepolymer; (2) Neutralization reaction: Cool the NCO prepolymer prepared in step (1), dilute it with the reaction solvent, slowly add the neutralizing agent, and stir the reaction. (3) Phase inversion emulsification: The prepolymer from step (2) is transferred to a dispersion vessel. Under high-speed stirring, deionized water is slowly added dropwise to the neutralized prepolymer and stirred continuously to form a uniform polyurethane prepolymer aqueous dispersion. (4) Post-chain extension: While maintaining stirring, add the post-chain extender to the aqueous dispersion obtained in step (3) to carry out the reaction; (5) Solvent removal and finished product preparation: The system after the reaction in step (4) is subjected to vacuum distillation to remove the reaction solvent, cooled and filtered to obtain the final aqueous dispersion of waterborne polyurethane adhesive.

10. The preparation method according to claim 9, characterized in that, Includes the following steps: (1) Synthesis of prepolymer: Low polarity hydrophobic polyol and medium-low polarity polyol were added to a four-necked flask and dehydrated for 1-2 h at 115 ℃ and vacuum degree ≤ -0.08 MPa to remove water from the raw materials; the temperature was lowered to below 50 ℃, polyisocyanate was added, followed by solvent dilution, and the solid content of the system was controlled at 40-60%. Nitrogen gas was purged for 15 min for gas replacement, and the reaction temperature was controlled at 60-80 ℃. The reaction was kept at a constant temperature for 3-4 h; the reaction temperature was lowered to 60 ℃, crosslinking agent and hydrophilic chain extender were added, and after stirring evenly, the reaction was kept at a constant temperature for 1-2 h to prepare NCO-terminated prepolymer; (2) Neutralization reaction: Cool the NCO prepolymer prepared in step (1) to 30 °C, add reaction solvent to dilute to 30-40% solid content, slowly add neutralizing agent, and stir reaction for 10-20 min; (3) Phase inversion emulsification: Transfer the prepolymer from step (2) to a dispersion vessel, and slowly add deionized water to the neutralized prepolymer under high-speed stirring at a speed of 2000-3000 rpm, and continue stirring for 15-30 min to form a uniform polyurethane prepolymer aqueous dispersion. (4) Post-chain extension: While keeping the mixture stirred, add the post-chain extender to the aqueous dispersion obtained in step (3), control the reaction temperature at 35-50 ℃, and react for 1-2 h; (5) Solvent removal and finished product preparation: The system after the reaction in step (4) is placed under negative pressure with a vacuum degree ≤ -0.09MPa, heated to 45-55 ℃, and distilled under reduced pressure for 0.5-1 h to completely remove the reaction solvent in the synthesis process. The pH is adjusted to 7-9, cooled to room temperature, filtered, and the final waterborne polyurethane adhesive aqueous dispersion is obtained.

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