Multi-walled carbon nanotube in-situ composite polyurethane and preparation method thereof

Abstract

The present application relates to multi-walled carbon nanotube in-situ composite polyurethane and its preparation method, and belongs to the technical field of lithium ion battery materials. The present application solves the technical problem of providing a multi-walled carbon nanotube in-situ composite polyurethane, which facilitates the dispersion of carbon nanotubes. The polyurethane is formed by polymerization of polyurethane prepolymer and multi-walled carbon nanotubes, the end group of the polyurethane prepolymer is isocyanate group, and the multi-walled carbon nanotubes contain active groups that react with the end group of the polyurethane prepolymer. The polyurethane of the present application is grafted with carbon tubes in-situ, combined in the form of covalent bond, avoids the aggregation of carbon tubes, and improves the stability of the slurry. During the emulsification process, the carbon tubes penetrate through the entire latex particle, which is beneficial to the electron transport of the system. The polyurethane of the present application can be used as a negative electrode adhesive after being blended with PAA, which can avoid the negative influence on the peeling force and electrical performance caused by the introduction of small molecules. The adhesive can not only increase flexibility, but also reduce the DCR of the battery, and improve the charge-discharge performance.

Description

Technical Field

[0001] This invention relates to in-situ composite polyurethane with multi-walled carbon nanotubes and its preparation method, belonging to the field of lithium-ion battery material technology. Background Technology

[0002] In silicon-carbon anode materials, Si particles act as the active material, responsible for providing lithium storage capacity; while C plays a crucial role in buffering, effectively mitigating the volume changes of the silicon anode during charge and discharge. Furthermore, C improves the conductivity of Si materials and prevents Si particles from agglomerating during charge-discharge cycles. Therefore, silicon-carbon composite materials combine the advantages of both Si and C, exhibiting high specific capacity and long cycle life, and are expected to replace graphite as the leading anode material for next-generation lithium-ion batteries.

[0003] Currently, silicon-carbon anodes mostly use high-molecular-weight PAA-based binders to blend with carbon nanotube conductive paste to improve cell conductivity, electrode rebound, cycle life, and other properties. This physical blending method has two drawbacks: first, carbon nanotubes aggregate during dispersion, leading to uneven dispersion; second, the use of small-molecule dispersants results in electrode peeling and impaired electrical properties. Furthermore, because PAA is relatively hard and brittle, SBR emulsions are usually added for toughening to meet processing requirements. Therefore, a new binder that facilitates carbon nanotube dispersion is needed. Summary of the Invention

[0004] To address the above deficiencies, the technical problem solved by this invention is to provide an in-situ composite polyurethane with multi-walled carbon nanotubes, which facilitates the dispersion of carbon nanotubes.

[0005] This invention relates to an in-situ composite polyurethane using multi-walled carbon nanotubes, which is polymerized from a polyurethane prepolymer and multi-walled carbon nanotubes. The end groups of the polyurethane prepolymer are isocyanate groups, and the multi-walled carbon nanotubes contain active groups that react with the end groups of the polyurethane prepolymer.

[0006] In one embodiment of the present invention, the multi-walled carbon nanotubes contain at least one of hydroxyl and amino groups.

[0007] In one embodiment of the present invention, the molar ratio of isocyanate in the polyurethane prepolymer to active groups in the multi-walled carbon nanotubes is greater than or equal to 1:1. In some specific embodiments, the molar ratio of isocyanate in the polyurethane prepolymer to active groups in the multi-walled carbon nanotubes is 1 to 50:1. Further, in some preferred embodiments, the molar ratio of isocyanate in the polyurethane prepolymer to active groups in the multi-walled carbon nanotubes is 1 to 10:1.

[0008] In one embodiment of the present invention, the molecular weight of the polyurethane prepolymer is 10,000 to 150,000 Mn.

[0009] The present invention also provides a method for preparing the in-situ composite polyurethane of multi-walled carbon nanotubes as described in the present invention.

[0010] The present invention discloses a method for preparing in-situ composite polyurethane using multi-walled carbon nanotubes, comprising the following steps:

[0011] (1) Preparation of polyurethane prepolymer: Macromolecular polyol, diisocyanate and catalyst are subjected to prepolymerization reaction, followed by the addition of organic solvent to reduce viscosity, then the addition of hydrophilic chain extender to extend chain, and then the addition of small molecule chain extender to extend chain, to obtain polyurethane prepolymer.

[0012] (2) Preparation of in-situ composite polyurethane of multi-walled carbon nanotubes: Mix multi-walled carbon nanotubes and isocyanate-terminated polyurethane prepolymer prepared in step (1) and react them. Control the reaction temperature to 50-60℃ and the reaction time to 1-5h. Then add a neutralizing agent to obtain in-situ composite polyurethane of multi-walled carbon nanotubes.

[0013] In some embodiments of the present invention, the macromolecular polyol is at least one of polyether diol, polyester diol, polycarbonate diol and hydroxyl-terminated polybutadiene diol, and the weight-average molecular weight of the macromolecular polyol is 500 to 3000.

[0014] The diisocyanate is at least one selected from hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate, diphenylmethane diisocyanate, methylcyclohexane diisocyanate, terephthalic diisocyanate, 1,4-cyclohexane diisocyanate, phenylenediamine diisocyanate, and tetramethyl-m-phenylenediamine diisocyanate.

[0015] The catalyst is at least one of organotin, organobismuth, and organic amine;

[0016] The organic solvent is at least one of acetone, butanone, tetrahydrofuran, ethyl acetate, and toluene;

[0017] The hydrophilic chain extender is at least one of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, sodium ethylenediaminoethanesulfonate, sodium 1,4-butanediol sulfonate, sodium 2,4-diaminobenzenesulfonate, and 2,3-dihydroxypropane-1-sulfonic acid.

[0018] The small molecule chain extender is at least one of 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-butanediamine, 1,6-hexanediamine, ethylenediamine, and isophoronediamine;

[0019] The neutralizing agent is at least one of triethylamine, triethanolamine, sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0020] In some embodiments of the present invention, in step (1), the reaction temperature of the prepolymerization reaction is 50-95°C and the reaction time is 1-6h.

[0021] The present invention also provides a silicon-based anode adhesive.

[0022] The silicon-based anode adhesive of the present invention includes a polyacrylic adhesive and the multi-walled carbon nanotube in-situ composite polyurethane described in the present invention, wherein the weight of the multi-walled carbon nanotube in-situ composite polyurethane accounts for 5% to 50% of the total weight of the polyacrylic adhesive and the multi-walled carbon nanotube in-situ composite polyurethane.

[0023] The present invention also provides a silicon-based anode sheet.

[0024] The silicon-based anode sheet of the present invention includes an anode active material and an adhesive, wherein the adhesive is the silicon-based anode adhesive described in the present invention.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention utilizes in-situ grafted carbon nanotubes (CNTs) to bind the polyurethane particles together via covalent bonds, preventing CNT aggregation and improving slurry stability. During emulsification, the CNTs penetrate the entire latex particle, facilitating electron transport within the system. When blended with PAA (polyaluminum acetate), this polyurethane can be used as a negative electrode binder, avoiding the negative impacts on peel strength and electrical properties caused by the introduction of small molecules. This binder not only increases flexibility but also reduces cell DCR (discharge rate reduction) and improves charge-discharge performance. Attached Figure Description

[0027] Figure 1 This is a schematic diagram illustrating the preparation of in-situ composite polyurethane using multi-walled carbon nanotubes in an embodiment of the present invention. Detailed Implementation

[0028] This invention relates to an in-situ composite polyurethane using multi-walled carbon nanotubes, which is polymerized from a polyurethane prepolymer and multi-walled carbon nanotubes. The end groups of the polyurethane prepolymer are isocyanate groups, and the multi-walled carbon nanotubes contain active groups that react with the end groups of the polyurethane prepolymer.

[0029] This invention utilizes in-situ grafted carbon nanotubes, which are covalently bonded to the polyurethane, preventing carbon nanotube aggregation and improving slurry stability. In one embodiment of this invention, the diameter of the multi-walled carbon nanotubes is 1–30 μm.

[0030] In one embodiment of the present invention, the polyurethane prepolymer is end-capped with isocyanate, wherein the multi-walled carbon nanotubes contain at least one of hydroxyl and amino groups.

[0031] In one embodiment of the present invention, the molar ratio of isocyanate in the polyurethane prepolymer to active groups in the multi-walled carbon nanotubes is greater than or equal to 1:1. In some specific embodiments, the molar ratio of isocyanate in the polyurethane prepolymer to active groups in the multi-walled carbon nanotubes is 1 to 50:1. Further, in some preferred embodiments, the molar ratio of isocyanate in the polyurethane prepolymer to active groups in the multi-walled carbon nanotubes is 1 to 10:1.

[0032] In one embodiment of the present invention, the molecular weight of the polyurethane prepolymer is 10,000 to 150,000 Mn.

[0033] The present invention discloses a method for preparing in-situ composite polyurethane using multi-walled carbon nanotubes, comprising the following steps:

[0034] (1) Preparation of polyurethane prepolymer: Macromolecular polyol, diisocyanate and catalyst are subjected to prepolymerization reaction, followed by the addition of organic solvent to reduce viscosity, then the addition of hydrophilic chain extender to extend chain, and then the addition of small molecule chain extender to extend chain, to obtain polyurethane prepolymer.

[0035] (2) Preparation of in-situ composite polyurethane of multi-walled carbon nanotubes: Mix multi-walled carbon nanotubes and isocyanate-terminated polyurethane prepolymer prepared in step (1) and react them. Control the reaction temperature to 50-60℃ and the reaction time to 1-5h. Then add a neutralizing agent to obtain in-situ composite polyurethane of multi-walled carbon nanotubes.

[0036] Step (1) involves preparing a polyurethane prepolymer by prepolymerizing a macromolecular polyol, diisocyanate and catalyst, followed by adding an organic solvent to reduce viscosity, then adding a hydrophilic chain extender to extend the chain, and finally adding a small molecule chain extender to extend the chain, thus obtaining the polyurethane prepolymer.

[0037] Commonly used macromolecular diols in this field are applicable to this invention. In some embodiments of this invention, the macromolecular polyol is at least one selected from polyether diol, polyester diol, polycarbonate diol, and hydroxyl-terminated polybutadiene diol, and the weight-average molecular weight of the macromolecular polyol is 500 to 3000.

[0038] The diisocyanate can be a commonly used diisocyanate in the synthesis of polyurethanes. In some embodiments of the present invention, the diisocyanate is at least one selected from hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate, diphenylmethane diisocyanate, methylcyclohexane diisocyanate, terephthalic diisocyanate, 1,4-cyclohexane diisocyanate, phenylenediamine diisocyanate, and tetramethylisophthalic diisocyanate.

[0039] The ratio of diol to diisocyanate is a conventional ratio in the art. In some embodiments of the present invention, the molar ratio of hydroxyl groups in the diol to isocyanates in the diisocyanate is 0.1 to 0.5:1, and the preferred ratio is 0.3:1.

[0040] Catalysts commonly used in the art are all suitable for this invention. In some embodiments of this invention, the catalyst is at least one selected from organotin, organobismuth, and organic amine.

[0041] After prepolymerization of macromolecular diols and diisocyanates, organic solvents are added to reduce the viscosity of the system. The organic solvents are added in proportions of 1 to 5 times the total mass of solids, so that the prepolymer can be well emulsified and dispersed during neutralization and salt formation.

[0042] The organic solvent used here can be a commonly used organic solvent in the art. In some embodiments of the present invention, the organic solvent is at least one selected from acetone, butanone, tetrahydrofuran, ethyl acetate, and toluene.

[0043] Chain extension is performed by adding a hydrophilic chain extender. The hydrophilic chain extender used is commonly used in the art. In some embodiments of the present invention, the hydrophilic chain extender is at least one of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, sodium ethylenediamine ethanesulfonate, sodium 1,4-butanediol sulfonate, sodium 2,4-diaminobenzenesulfonate, and 2,3-dihydroxypropane-1-sulfonic acid.

[0044] The proportion of hydrophilic chain extender added is 1 wt% to 10 wt% of the total mass of the reactants.

[0045] Commonly used small molecule chain extenders in this field are applicable to this invention. In some embodiments of this invention, the small molecule chain extender is at least one selected from 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-butanediamine, 1,6-hexanediamine, ethylenediamine, and isophoronediamine.

[0046] The proportion of small molecule chain extenders added is 1 wt% to 10 wt% of the total mass of the reactants.

[0047] In some embodiments of the present invention, in step (1), the reaction temperature of the prepolymerization reaction is 50-95°C and the reaction time is 1-6h.

[0048] Step (2) is to prepare in-situ composite polyurethane with multi-walled carbon nanotubes. Multi-walled carbon nanotubes and polyurethane prepolymer prepared in step (1) are mixed and reacted. The reaction temperature is controlled at 50-60℃ and the reaction time is 1-5h. Then a neutralizing agent is added to obtain in-situ composite polyurethane with multi-walled carbon nanotubes.

[0049] In some embodiments of the present invention, the neutralizing agent is at least one selected from triethylamine, triethanolamine, sodium hydroxide, lithium hydroxide, and potassium hydroxide. The amount of neutralizing agent used is conventionally selected in the art; in some specific embodiments, the hydrophilic groups are neutralized equimolarly with the neutralizing agent.

[0050] The silicon-based anode adhesive of the present invention includes a polyacrylic adhesive and the multi-walled carbon nanotube in-situ composite polyurethane described in the present invention, wherein the weight of the multi-walled carbon nanotube in-situ composite polyurethane accounts for 5% to 50% of the total weight of the polyacrylic adhesive and the multi-walled carbon nanotube in-situ composite polyurethane.

[0051] The polyacrylic adhesive described in this invention can be a commonly used PAA adhesive in the art, which will not be elaborated here.

[0052] The silicon-based anode sheet of the present invention includes an anode active material and an adhesive, wherein the adhesive is the silicon-based anode adhesive described in the present invention.

[0053] The specific embodiments of the present invention are further described below with reference to examples, but the present invention is not limited to the scope of the examples described. In the examples, the polyester polyol has a weight-average molecular weight Mw = 2000, is poly(1,4-butanediol adipate) diol, abbreviated as PBA2000, and was purchased from Asahikawa Chemical.

[0054] The multi-walled carbon nanotubes with hydroxyl groups were purchased from Siasun Nanotech, model XFM05; the multi-walled carbon nanotubes with amino groups were purchased from Siasun Nanotech, model XFM62; and the multi-walled carbon nanotubes without active functional groups were purchased from Siasun Nanotech, model XFQ043.

[0055] Polyacrylic adhesives mainly employ precipitation polymerization, which polymerizes acrylic acid and acrylate monomers in an aqueous phase and then precipitates them.

[0056] Example 1

[0057] like Figure 1 As shown, the in-situ composite polyurethane of multi-walled carbon nanotubes was prepared using the following method:

[0058] 100g of polyester polyol (Mw=2000) was dehydrated at 100℃ under vacuum for 2h, then 57g of isophorone diisocyanate was added, and prepolymerization was carried out at 85℃ for 2h. Then, under reflux, 200mL of acetone and 12.5g of dimethicone were added, and the reaction was carried out at 55℃ for 3h. Then, 2.5g of 1,4-butanediol was added, and the reaction continued for 1h. Hydroxyl-containing multi-walled carbon nanotubes were added to the polyurethane prepolymer solution, controlling the molar ratio of isocyanate in the polyurethane prepolymer to hydroxyl groups in the multi-walled carbon nanotubes to be 4:1. After reacting for 3h, triethylamine was added for neutralization for 0.5h, and the mixture was dispersed in deionized water under high-speed stirring to form an in-situ composite polyurethane emulsion of multi-walled carbon nanotubes. The organic solvent was then removed. GPC analysis showed that its number-average molecular weight was Mn=65458.

[0059] Example 2

[0060] Multi-walled carbon nanotube in-situ composite polyurethane was prepared according to the method of Example 1. The only difference was that the molar ratio of isocyanate in the polyurethane prepolymer to hydroxyl groups in the multi-walled carbon nanotube was changed to 1:1, and the molar amount of 1,4-butanediol was reduced accordingly.

[0061] Example 3

[0062] In-situ composite polyurethane with multi-walled carbon nanotubes was prepared according to the method of Example 1. The only difference was that the molar ratio of isocyanate in the polyurethane prepolymer to hydroxyl groups in the multi-walled carbon nanotubes was changed to 20:1, and the molar amount of 1,4-butanediol was increased accordingly.

[0063] Example 4

[0064] Multi-walled carbon nanotube in-situ composite polyurethane was prepared according to the method of Example 1. The only difference was that the molar ratio of isocyanate in the polyurethane prepolymer to hydroxyl groups in the multi-walled carbon nanotube was changed to 50:1, and the molar amount of 1,4-butanediol was increased accordingly.

[0065] Comparative Example 1

[0066] The method is the same as in Example 1, except that the multi-walled carbon nanotubes with hydroxyl groups in Example 1 are replaced with multi-walled carbon nanotubes without active functional groups, resulting in a polyurethane emulsion blended with polyurethane and multi-walled carbon nanotubes.

[0067] Comparative Example 2

[0068] The method is the same as in Example 1, except that the multi-walled carbon nanotubes with hydroxyl groups in Example 1 are replaced with multi-walled carbon nanotubes without active functional groups, and the multi-walled carbon nanotubes are added to the polyurethane emulsion after the solvent has been removed, and the mixture is stirred repeatedly until homogeneous.

[0069] Comparative Example 3

[0070] The method was the same as in Example 1, except that the multi-walled carbon nanotubes with hydroxyl groups in Example 1 were replaced with equimolar amounts of 1,4-butanediol to obtain a polyurethane emulsion.

[0071] Film Production:

[0072] The polyurethane (PU) emulsions in Examples 1-4 and Comparative Examples 1-3 were respectively compounded with polyacrylic acid (PAA) solution at a mass ratio of PAA:PU = 8:2 to obtain composite adhesive, which was used to make electrode sheets.

[0073] The electrode was prepared by mixing graphite (AGP): conductive carbon black (SP): carboxymethyl cellulose (CMC): composite adhesive in a ratio of 96:1:0.5:2.5, and then the prepared electrode was baked at 70°C for 0.5 hours.

[0074] In Comparative Example 3, when preparing the electrode, multi-walled carbon nanotubes without active groups were added in an equal mass ratio to those in Example 1.

[0075] The preparation method of polyacrylic acid solution (PAA solution) is as follows: 900g of deionized water is deoxygenated for 1 hour, then 50g of acrylic acid and 50g of acrylonitrile are added, and the mixture is reacted at 65-70℃ for 10 hours under the initiation of ammonium persulfate to obtain polyacrylic acid particle precipitate. Then lithium hydroxide and a small amount of pure water are added to neutralize it to obtain a viscous polyacrylic acid solution.

[0076] Performance testing:

[0077] Electrode peel strength characterization: A 100×20mm copper foil electrode is cut and laid flat on a glass plate. Double-sided tape is used to fix the sample along its length to the test stage, and 3M tape is applied to the sample surface. Ensure a smooth, flat, and bubble-free bond between the sample and the tape. Then, a roller is used to roll back and forth three times under its own weight to achieve uniform contact. One end of the sample (the end furthest from the testing machine) is pulled 180° horizontally in the opposite direction of the electrode using transparent tape and fixed to the traction belt of the testing machine. The testing machine speed is then set to 20mm / min, and the start button is pressed. The peel strength value is recorded after the displayed value stabilizes. Data should only be recorded after the peel strength value has stabilized for the same sample. The same batch of samples should be tested at least three times. If the test error exceeds 2%, the test must be repeated. After the test, the testing machine is turned off, and the test data is processed.

[0078] Electrode cohesive strength characterization: Clean the surface of a glass plate, cut a 100×20mm copper foil electrode, lay it flat on the glass plate, and fix the sample to the test stage along its length using double-sided tape. Gently cut off the blank ends of the sample with a blade and bond them to the electrode coating surface with 3M tape. Ensure a smooth, flat, and bubble-free adhesion between the sample and the tape. Then, roll the sample surface back and forth three times under its own weight to achieve uniform contact. Adhere the sample horizontally at 180° along the length of the electrode with transparent tape, ensuring the transparent tape completely covers the electrode surface. Then, fix the transparent tape to the traction belt of the testing machine, set the testing machine speed to 20mm / min, and click run. The testing machine will start running. Record the cohesive strength value after the value displayed on the testing machine stabilizes. For the same sample, data should only be recorded after the cohesive strength value has stabilized. The same batch of samples should be tested at least three times. If the sample test error exceeds 2%, it needs to be retested. After the test, turn off the testing machine and compile the test data.

[0079] Electrode surface resistivity measurement: Place the sample in an oven and bake at 85°C for 24 hours. Record the sample thickness after baking using a micrometer. Turn on the four-probe detector, place the sample on the probe stage, input the thickness, diameter, and probe distance, select an appropriate current range, and begin the measurement.

[0080] 1mm Needle Winding Test Method: Using a QTX type coating tester (shaft diameter: 1mm; 2mm; 3mm; 4mm; 5mm; 10mm; 15mm), wind the electrode sheet around the shaft, making 3 turns, then pull firmly on the tail end of the electrode sheet. Control the ambient temperature at 10–38℃ and the humidity at 30–40% RH. Lay the bent electrode sheet flat and observe for cracking.

[0081] DCR measurement at 0℃: Take 3 packs of soft-pack battery cells and charge them with constant current for 10 seconds. Record the voltage before and after charging. Then DCR = (voltage after 10 seconds of charging - voltage before charging) / current.

[0082] The results are shown in Table 1.

[0083] Table 1

[0084]

[0085] Note: In Comparative Example 2, the addition of multi-walled carbon nanotubes to the polyurethane emulsion caused the emulsion to become unstable and break down, so the various properties were not tested and are replaced with " / ".

[0086] The PAA solution is used directly as an adhesive to prepare the electrode without adding PU solution, and multi-walled carbon nanotubes without active groups are added to it in the same mass ratio as in Example 1.

[0087] As can be seen, compared to Example 5, Examples 1-4 show increased flexibility and correspondingly decreased sheet resistance and DCR. When Example 1 and Example 5 are combined, compared to Example 5, flexibility is improved, sheet resistance and DCR are correspondingly decreased, but peel strength and cohesive strength are also correspondingly reduced. In Comparative Example 1, since there is no chemical grafting between multi-walled carbon nanotubes and polyurethane, sheet resistance and DCR are correspondingly increased compared to Example 1. In Comparative Example 2, because multi-walled carbon nanotubes are added to the polyurethane emulsion, the emulsion breaks down shortly after addition, indicating that simple blending cannot guarantee the dispersion of multi-walled carbon nanotubes. In Comparative Example 3, adding multi-walled carbon nanotubes during electrode fabrication results in a relatively smaller reduction in sheet resistance and DCR compared to introducing multi-walled carbon nanotubes through chemical grafting of polyurethane. Therefore, the above demonstrates that in-situ grafting of multi-walled carbon nanotubes into polyurethane has the most significant advantage in improving the electrical properties of polyacrylic acid and polyurethane composite electrodes.

[0088] Centrifugation stability test: The polyurethane emulsions prepared in the examples and comparative examples were centrifuged at different speeds for 15 min, and the layering and precipitation were observed. When the upper layer of the emulsion was clear and the lower layer was precipitate after centrifugation, the emulsion was considered to have separated into layers. After separation, due to the conical or hemispherical bottom of the centrifuge tube, if the amount of precipitate was less than half the bottom volume after centrifugation, it was considered slight precipitation. If the amount of precipitate was half or more the bottom volume, it was considered substantial precipitation. The results are shown in Table 2.

[0089] Table 2

[0090] Example 2000r / min 3000r / min 4000r / min Example 1 No emulsion separation or precipitation No emulsion separation or precipitation Large amount of sediment Example 2 No emulsion separation or precipitation Large amount of sediment / Example 3 No emulsion separation or precipitation No emulsion separation or precipitation Large amount of sediment Example 4 No emulsion separation or precipitation No emulsion separation or precipitation Large amount of sediment Comparative Example 1 No emulsion separation or precipitation Slight sedimentation Large amount of sediment Comparative Example 2 Precipitation and demulsification / /

[0091] Note: Since increasing the rotation speed after a large amount of sedimentation is meaningless, the experimental results are marked with " / " to indicate that no detection was performed.

[0092] It is evident that the emulsion stability decreases with increasing multi-walled carbon nanotube content. Introducing multi-walled carbon nanotubes via in-situ polymerization also leads to a decrease in emulsion stability. Furthermore, directly adding multi-walled carbon nanotubes to polyurethane emulsions directly disrupts the stability of the polyurethane emulsion, resulting in emulsion demulsification.

Claims

1. In-situ composite polyurethane with multi-walled carbon nanotubes, characterized in that: It is formed by polymerizing polyurethane prepolymer and multi-walled carbon nanotubes, wherein the end groups of the polyurethane prepolymer are isocyanate groups, and the multi-walled carbon nanotubes contain active groups that react with the end groups of the polyurethane prepolymer.

2. The in-situ composite polyurethane with multi-walled carbon nanotubes according to claim 1, characterized in that: Multi-walled carbon nanotubes contain at least one of hydroxyl and amino groups.

3. The in-situ composite polyurethane with multi-walled carbon nanotubes according to claim 1, characterized in that: The molar ratio of isocyanate in the polyurethane prepolymer to active groups in the multi-walled carbon nanotubes is greater than or equal to 1:1, preferably 1 to 50:1, and more preferably 1 to 10:

1.

4. The in-situ composite polyurethane with multi-walled carbon nanotubes according to claim 1, characterized in that: The molecular weight of the polyurethane prepolymer is 10,000 to 150,000 Mn.

5. The method for preparing multi-walled carbon nanotube in-situ composite polyurethane according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Preparation of polyurethane prepolymer: Macromolecular polyol, diisocyanate and catalyst are subjected to prepolymerization reaction, followed by the addition of organic solvent to reduce viscosity, then the addition of hydrophilic chain extender to extend chain, and then the addition of small molecule chain extender to extend chain, to obtain polyurethane prepolymer. (2) Preparation of in-situ composite polyurethane with multi-walled carbon nanotubes: Mix multi-walled carbon nanotubes and polyurethane prepolymer prepared in step (1) and react them. Control the reaction temperature to 50-60℃ and the reaction time to 1-5h. Then add a neutralizing agent to obtain in-situ composite polyurethane with multi-walled carbon nanotubes.

6. The method for preparing in-situ composite polyurethane using multi-walled carbon nanotubes according to claim 5, characterized in that: The macromolecular polyol is at least one of polyether diol, polyester diol, polycarbonate diol and hydroxyl-terminated polybutadiene diol, and the weight-average molecular weight of the macromolecular polyol is 500 to 3000. The diisocyanate is at least one selected from hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate, diphenylmethane diisocyanate, methylcyclohexane diisocyanate, terephthalic diisocyanate, 1,4-cyclohexane diisocyanate, phenylenediamine diisocyanate, and tetramethyl-m-phenylenediamine diisocyanate. The catalyst is at least one of organotin, organobismuth, and organic amine; The organic solvent is at least one of acetone, butanone, tetrahydrofuran, ethyl acetate, and toluene; The hydrophilic chain extender is at least one of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid, sodium ethylenediaminoethanesulfonate, sodium 1,4-butanediol sulfonate, sodium 2,4-diaminobenzenesulfonate, and 2,3-dihydroxypropane-1-sulfonic acid. The small molecule chain extender is at least one of 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-butanediamine, 1,6-hexanediamine, ethylenediamine, and isophoronediamine; The neutralizing agent is at least one of triethylamine, triethanolamine, sodium hydroxide, lithium hydroxide, and potassium hydroxide.

7. The method for preparing in-situ composite polyurethane with multi-walled carbon nanotubes according to claim 5, characterized in that: In step (1), the reaction temperature of the prepolymerization reaction is 50-95℃ and the reaction time is 1-6h.

8. A silicon-carbon anode binder, characterized in that: It includes polyacrylic adhesives and the multi-walled carbon nanotube in-situ composite polyurethane as described in any one of claims 1 to 4, wherein the weight of the multi-walled carbon nanotube in-situ composite polyurethane accounts for 5% to 50% of the total weight of the polyacrylic adhesive and the multi-walled carbon nanotube in-situ composite polyurethane.

9. A silicon-carbon anode sheet, comprising an anode active material and a binder, characterized in that: The adhesive is the silicon-carbon anode adhesive as described in claim 8.

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