Highly dispersed binder based on polysaccharide-acrylic acid copolymer and carbon-coated aluminum foil

Abstract

The invention discloses a highly dispersed binder and carbon-coated aluminum foil based on a polysaccharide-acrylic acid copolymer, belonging to the technical field of lithium-ion battery current collectors. Chitosan is modified by sulfonation, and perfluorooctylethanol and epichlorohydrin are used to generate perfluoroalkyl glycidyl ether under the action of a catalyst. The epoxy groups on the perfluoroalkyl glycidyl ether are then subjected to a ring-opening esterification reaction by an acid anhydride, thereby obtaining a double-group modified acrylate having hydroxyl and fluorine groups. The structural formula contains a large number of hydroxyl and fluorine groups, and can be polymerized into a double-crosslinked interpenetrating polymer powder. The hydroxyl group, as a polar group, can form hydrogen bonds or other chemical bonds with a variety of substrates, thereby enhancing the adhesion between the polymer and the substrate; the fluorination modification can further improve the film-forming properties of the polymer, making the carbon-coated aluminum foil smoother and flatter. At the same time, the fluorination modification can significantly improve the corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery current collectors, and particularly relates to a highly dispersed binder based on a polysaccharide-acrylic acid copolymer and a carbon-coated aluminum foil. Background Art

[0002] Aluminum foil is the most commonly used positive electrode current collector and has an important impact on battery performance. The internal resistance of lithium-ion batteries directly affects the reliability and cycle life of the battery. The current collector is both a carrier of active substances and a conductor for collecting current generated during operation. It can form a larger current and improve the charging and discharging efficiency of lithium batteries. Conventional aluminum foil has a certain rigidity and a limited area of ​​contact with the positive electrode material in the electrode sheet, which affects the internal resistance of the positive electrode sheet. Therefore, the aluminum foil is subjected to a certain surface treatment and then coated with carbon, which can not only prevent corrosion, but also reduce internal resistance, enhance conductivity and increase adhesion to PVDF.

[0003] The molecular weight of the polyacrylic acid binder prepared in the prior art is between 150,000 and 250,000. Theoretically, under the premise of ensuring the dispersion performance of the binder in the carbon conductive material, the higher the molecular weight of the polyacrylic acid resin, the better the comprehensive performance of the coating film obtained. Therefore, a smaller molecular weight is also one of the factors that lead to the poor corrosion resistance of the binder.

[0004] Chinese patent publication number CN116462800B discloses a method for preparing a polyacrylic acid binder for aluminum foil carbon coating slurry and a binder thereof. By adding an appropriate amount of acrylic acid monomer, a larger number of polar groups are introduced to generate an acrylic resin with a larger molecular weight, so that the paint film has good chemical resistance. However, in this solution, the larger the molecular weight of the polyacrylic acid binder, the longer its molecular chains, and the higher the degree of entanglement between them, which will lead to a decrease in the solubility of the binder in the solvent, thereby affecting the fluidity of the binder, making it difficult to evenly apply or penetrate during application, thereby affecting the bonding effect. Summary of the Invention

[0005] The present invention aims to provide a highly dispersed binder based on a polysaccharide-acrylic acid copolymer. The binder comprises chitosan, which is modified by sulfonation, and perfluorooctylethanol and epichlorohydrin are used as catalysts to generate perfluoroalkyl glycidyl ether. The epoxy groups on the perfluoroalkyl glycidyl ether are then subjected to a ring-opening esterification reaction by an acid anhydride, thereby obtaining a double-group modified acrylate having hydroxyl and fluorine groups. The binder has a large number of hydroxyl and fluorine groups in its structural formula and can be polymerized into a double-crosslinked interpenetrating polymer powder. The hydroxyl group, as a polar group, can form hydrogen bonds or other chemical bonds with various substrates, thereby enhancing the adhesion between the polymer and the substrate.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A highly dispersed binder based on a polysaccharide-acrylic acid copolymer is prepared by the following steps:

[0008] Step 1: Add sulfonated modified chitosan and 50-60% sodium hydroxide solution into the reactor, stir at 20-25℃ and 500-600r / min for 30-40min, add digroup modified acrylate and isocyanate into the reactor, continue stirring for 40-60min, add 10-12mL of 0.3-0.4% dibutyltin dilaurate solution into the reactor, continue stirring for 30-40min, then add acrylic acid and polyether polyol. The mixture was stirred at 95-100°C and 500-600 r / min for 1-2 hours, cooled to 55-65°C, and sodium sulfite as an initiator and hydroxymethyl acrylamide as a cross-linking agent were added to the reactor. The mixture was heated to 70-80°C and stirred at 500-600 r / min for 3-4 hours. The mixture was filtered, and the filter cake was washed with deionized water and anhydrous ethanol for 2-3 times respectively. The mixture was vacuum dried at 60-80°C for 1-2 hours and ground to obtain a double-crosslinked interpenetrating polymer powder.

[0009] Step 2: Add graphene oxide and deionized water into a reactor, stir for 5-6 minutes at 20-25°C and 500-600r / min, then add the double-crosslinked interpenetrating polymer powder, continue stirring and reacting for 1-2 hours, filter, wash the filter cake with deionized water and anhydrous ethanol 2-3 times respectively, dry in a vacuum at 60-80°C for 1-2 hours, grind and crush to obtain a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0010] Furthermore, in step 1, the usage ratio of sulfonated modified chitosan, sodium hydroxide solution, digroup modified acrylate, isocyanate, dibutyltin dilaurate solution, acrylic acid, polyether polyol, sodium sulfite and hydroxymethyl acrylamide is 20-30 g: 200-300 mL: 40-50 mL: 50-60 mL: 30-40 mL: 35-45 mL: 2-3 g: 3-4 g.

[0011] Furthermore, in step 2, the usage ratio of graphene oxide, deionized water and double-crosslinked interpenetrating polymer powder is 10-15 g: 100-200 mL: 20-30 g.

[0012] Furthermore, the digroup-modified acrylate in step 1 is prepared by the following steps:

[0013] Maleic anhydride and hydroxypropyl methacrylate are added to a reactor, stirred at 20-25°C and 500-600 r / min for 30-40 minutes, and then hydroquinone is added as a polymerization inhibitor, and stirring is continued for 1-2 hours to obtain a maleic anhydride mixed solution; perfluorooctylethanol and epichlorohydrin are added to a reactor, and sodium ethoxide catalyst is added, and stirring is carried out at 20-25°C and 500-600 r / min for 22-24 hours, and then the maleic anhydride mixed solution and tetraethylammonium bromide catalyst are added, and the mixture is heated to 120-130°C, and stirring is continued for 14-16 hours, and reduced pressure distillation is performed, condensation is performed, and an intermediate fraction is selected to obtain a digroup-modified acrylate.

[0014] Furthermore, the usage ratio of maleic anhydride, hydroxypropyl methacrylate and hydroquinone is 20-30 g:100-120 mL:0.1-0.2 g.

[0015] Further, a mixed solution of perfluorooctylethanol, epichlorohydrin, sodium ethoxide, maleic anhydride and tetraethylammonium bromide 50-60 mL: 65-68 mL: 0.1-0.2 g: 70-75 mL: 0.25-0.3 g.

[0016] Furthermore, the sulfonated modified chitosan in step 1 is prepared by the following steps:

[0017] Chitosan, 3-mercaptopropyltrimethoxysilane and ethanol are added to a reactor, stirred at 60-70°C and 500-600 r / min for 1-2 hours, filtered, and the filter cake is washed with deionized water 2-3 times, and vacuum dried at 60-80°C for 1-2 hours to obtain thiol-modified chitosan; thiol-modified chitosan and a hydrogen peroxide solution with a mass fraction of 20-30wt% are added to a reactor, stirred and reacted at 20-25°C and 500-600 r / min for 1-2 hours, and then a 0.5-0.6M sodium hydroxide solution is added to adjust the pH value to 9, filtered, and the filter cake is washed with deionized water and ethanol 2-3 times, and vacuum dried at 60-80°C for 1-2 hours to obtain sulfonated modified chitosan.

[0018] Furthermore, the usage ratio of chitosan, 3-mercaptopropyltrimethoxysilane and ethanol is 40-50 g: 100-120 mL: 200-300 mL.

[0019] Furthermore, the usage ratio of the thiol-modified chitosan and the hydrogen peroxide solution is 20-30 g: 200-300 mL.

[0020] Furthermore, in step 2, graphene oxide is prepared by the following steps:

[0021] Adding graphene and a concentrated nitric acid solution with a mass fraction of 60-65% into a reactor, stirring at 95-100°C and 500-600 r / min for 3-4 hours, filtering, washing the filter cake with deionized water and anhydrous ethanol 2-3 times respectively, and vacuum drying at 60-80°C for 1-2 hours to obtain graphene oxide;

[0022] Furthermore, the usage ratio of graphene and concentrated nitric acid solution is 10-12 g: 100-200 mL.

[0023] A method for preparing carbon-coated aluminum foil comprises the following steps:

[0024] Calcium hydroxide powder with a particle size of 2-3 mm and deionized water are added to a reactor, pre-cured at 120-125°C for 30-40 minutes, a highly dispersed binder is added, and the curing is continued for 2-3 hours to obtain a carbon-coated aluminum foil slurry. Finally, the carbon-coated aluminum foil slurry is coated on an aluminum foil substrate and dried at 97-100°C to obtain a carbon-coated aluminum foil.

[0025] Furthermore, the usage ratio of calcium hydroxide powder, deionized water and highly dispersed binder is 10-12 g: 200-300 mL: 10-12 g.

[0026] Beneficial effects of the present invention:

[0027] 1. The highly dispersed binder prepared by the present invention has excellent bonding properties and good dispersibility for carbon conductive materials. By sulfonating chitosan, hydroxylating acrylic acid monomers, and introducing fluorine into the structural formula, a double-group modified acrylate is obtained. The hydroxyl group, as a polar group, can form hydrogen bonds or other chemical bonds with a variety of substrates, thereby enhancing the adhesion between the polymer and the substrate. After polymerization with the polyurethane monomer, a double-crosslinked interpenetrating polymer powder is obtained, and graphene is interspersed in the polymer network of the double-crosslinked interpenetrating polymer powder to improve the dispersibility of the graphene. Graphene has excellent electrical and thermal conductivity, which can increase the electrical conductivity and heat dissipation capabilities of the binder.

[0028] 2. The sulfonated modified chitosan of the present invention is obtained by grafting the hydroxyl groups on the chitosan surface with a silane coupling agent containing a mercapto group. The mercapto group is oxidized to a sulfonic acid group under the action of hydrogen peroxide. In addition, the double-crosslinked interpenetrating polymer powder is copolymerized by acrylic acid monomers and polyurethane monomers. The structural formula also contains a large number of sulfonic acid groups. The intermediate product (polysulfide) of the sulfur-lithium battery is easily dissolved in the electrolyte and then shuttled to the negative electrode, resulting in a decrease in electrochemical performance. The sulfonic acid groups in the double-crosslinked polysaccharide network capture the polysulfide, reduce the shuttle effect, promote the migration of lithium ions inside the lithium-sulfur battery, reduce the internal resistance of the battery, and improve the cycle performance of the lithium battery.

[0029] 3. The double-crosslinked interpenetrating polymer powder of the present invention is prepared by reacting perfluorooctylethanol and epichlorohydrin in the presence of a catalyst to generate perfluoroalkyl glycidyl ether, and then using maleic anhydride to perform a ring-opening esterification reaction on the epoxy groups on the perfluoroalkyl glycidyl ether, thereby obtaining a double-group modified acrylate having hydroxyl and fluorine groups. The structural formula contains a large number of hydroxyl groups, fluorine groups, and flexible chain segments. When polymerized into the double-crosslinked interpenetrating polymer powder, the hydroxyl groups, as a polar group, can form hydrogen bonds or other chemical bonds with a variety of substrates, thereby enhancing the adhesion between the polymer and the substrate. The fluorination modification can further improve the film-forming properties of the polymer, making the carbon-coated aluminum foil smoother and flatter, while increasing the hardness and scratch resistance of the carbon-coated aluminum foil, and the fluorination modification can significantly enhance the corrosion resistance. The large number of long carbon chain flexible chain segments can still maintain a certain degree of flexibility at low temperatures, can absorb and disperse stress when subjected to external forces, and reduce shedding from the carbon-coated aluminum foil due to stress concentration.

[0030] 4. Excessive polysaccharides may swell in the organic electrolyte, causing the binder network to relax and reducing the stability of the electrode structure. The existence of the interpenetrating polymer network can reduce the swelling in the organic electrolyte caused by excessive addition of polysaccharide substances without affecting the three-dimensional network, thereby improving the stability of the electrode structure; the polymer chains in the interpenetrating network form a tight network structure through chemical or physical cross-linking. This structure can limit the movement and swelling behavior of the polysaccharide molecular chains, thereby reducing the swelling phenomenon to a certain extent; the polymer chains and fluorine groups in the interpenetrating network form a barrier to prevent or slow down the direct contact between the solvent molecules in the organic electrolyte and the polysaccharide molecules. This shielding effect can further reduce the adsorption and swelling effects of the solvent molecules on the polysaccharide. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] Example 1: A highly dispersed binder based on a polysaccharide-acrylic acid copolymer was prepared by the following steps:

[0033] S1: 40 g of chitosan, 100 mL of 3-mercaptopropyltrimethoxysilane and 200 mL of ethanol were added to a reactor, stirred at 60°C and 500 r / min for 1 h, filtered, and the filter cake was washed twice with deionized water and dried in vacuum at 60°C for 1 h to obtain thiol-modified chitosan; 20 g of thiol-modified chitosan and 200 mL of 20 wt% hydrogen peroxide solution were added to a reactor, stirred at 20°C and 500 r / min for 1 h, and then a 0.5 M sodium hydroxide solution was added to a pH value of 9, filtered, and the filter cake was washed twice with deionized water and ethanol, and dried in vacuum at 60°C for 1 h to obtain sulfonated modified chitosan.

[0034] The hydroxyl groups on the surface of chitosan are grafted with a silane coupling agent containing a mercapto group. The mercapto group is oxidized into a sulfonic acid group under the action of hydrogen peroxide. The sulfonate group can promote the migration of lithium ions inside the lithium-sulfur battery, reduce the internal resistance of the battery, and improve the cycle performance of the lithium battery.

[0035] S2: Add 20g of maleic anhydride and 100mL of hydroxypropyl methacrylate into a reactor, stir for 30min at 20°C and 500r / min, then add 0.1g of hydroquinone as a polymerization inhibitor, and continue stirring for 1h to obtain a maleic anhydride mixed solution; add 50mL of perfluorooctylethanol and 65mL of epichlorohydrin into a reactor, add 0.1g of sodium ethoxide catalyst, stir and react at 20°C and 500r / min for 22h, then add 70mL of maleic anhydride mixed solution and 0.25g of tetraethylammonium bromide catalyst, heat to 120°C, continue stirring and react for 14h, transfer to a distillation kettle after the reaction is completed, distill under reduced pressure, condense, select the intermediate fraction, and obtain a digroup modified acrylate.

[0036] Perfluorooctylethanol and epichlorohydrin will generate perfluoroalkyl glycidyl ether under the action of catalyst. The epoxy group on the perfluoroalkyl glycidyl ether is subjected to ring-opening esterification reaction using acid anhydride to obtain a double-group modified acrylate with hydroxyl and fluorine groups. Maleic anhydride has a flexible chain segment, which can avoid the problem of high brittleness of the adhesive at low temperatures, thereby preventing it from falling off.

[0037] S3: 20 g of sulfonated modified chitosan and 200 mL of 50% sodium hydroxide solution were added to the reactor, stirred at 20 ° C and 500 r / min for 30 min, 40 mL of double-group modified acrylate and 50 mL of isocyanate were added to the reactor, and the stirring reaction continued for 40 min. 10 mL of 0.3% dibutyltin dilaurate solution was added to the reactor and the stirring reaction continued for 30 min. Then 30 mL of acrylic acid and 35 mL of polyether polyol were added, and nitrogen was introduced. The reaction was stirred at 95 ° C and 500 r / min for 1 h, cooled to 55 ° C, and 2 g of sodium sulfite as an initiator and 3 g of hydroxymethyl acrylamide as a cross-linking agent were added to the reactor. The reaction was heated to 70 ° C and stirred at 500 r / min for 3 h. Filtered, the filter cake was washed twice with deionized water and anhydrous ethanol respectively, dried in a vacuum at 60 ° C for 1 h, and ground to obtain a double-crosslinked interpenetrating polymer powder.

[0038] S4: Add 10g of graphene and 100mL of concentrated nitric acid solution with a mass fraction of 60% into a reactor, stir at 95℃ and 500r / min for 3h, filter, wash the filter cake with deionized water and anhydrous ethanol twice respectively, and vacuum dry at 60℃ for 1h to obtain graphene oxide; add 10g of graphene oxide and 100mL of deionized water into a reactor, stir at 20℃ and 500r / min for 5min, then add 20g of double-crosslinked interpenetrating polymer powder, continue stirring and reacting for 1h, filter, wash the filter cake with deionized water and anhydrous ethanol twice respectively, vacuum dry at 60℃ for 1h, grind and crush to obtain a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0039] Graphene is acidified to give it a carboxyl group on its surface. Functional groups such as hydroxyl groups in chitosan and polyurethane molecules can form hydrogen bonds and other interactions with other materials in the battery, thereby enhancing the bonding force between the binder and the electrode material. The intermediate product (polysulfide) of the sulfur-lithium battery is easily dissolved in the electrolyte and then shuttles to the negative electrode, resulting in a decrease in electrochemical performance. The sulfonic acid groups in the double-cross-linked interpenetrating network can capture polysulfide, reduce the shuttle effect, and improve the electrochemical performance of the battery.

[0040] Example 2: A highly dispersed binder based on a polysaccharide-acrylic acid copolymer was prepared by the following steps:

[0041] S1: 45 g of chitosan, 110 mL of 3-mercaptopropyltrimethoxysilane and 250 mL of ethanol were added to a reactor, stirred at 65 ° C and 550 r / min for 1.2 h, filtered, and the filter cake was washed with deionized water twice, and vacuum dried at 70 ° C for 1.2 h to obtain thiol-modified chitosan; 25 g of thiol-modified chitosan and 250 mL of 25 wt% hydrogen peroxide solution were added to a reactor, stirred at 23 ° C and 550 r / min for 1.2 h, and then a 0.55 M sodium hydroxide solution was added to a pH value of 9, filtered, and the filter cake was washed with deionized water and ethanol twice, and vacuum dried at 70 ° C for 1.2 h to obtain sulfonated modified chitosan.

[0042] S2: 25 g of maleic anhydride and 110 mL of hydroxypropyl methacrylate were added to a reactor, stirred at 23°C and 550 r / min for 35 min, then 0.15 g of hydroquinone as an inhibitor was added, and stirring was continued for 1.2 h to obtain a maleic anhydride mixed solution; 55 mL of perfluorooctylethanol and 66 mL of epichlorohydrin were added to a reactor, 0.15 g of sodium ethoxide catalyst was added, and the reaction was stirred at 23°C and 550 r / min for 23 h, then 73 mL of maleic anhydride mixed solution and 0.28 g of tetraethylammonium bromide catalyst were added, heated to 125°C, and the reaction was continued with stirring for 15 h. After the reaction was completed, the mixture was transferred to a distillation kettle, distilled under reduced pressure, condensed, and the intermediate fraction was selected to obtain a digroup-modified acrylate.

[0043] S3: 25g of sulfonated chitosan and 250mL of 55% sodium hydroxide solution were added to the reactor, stirred at 22.5℃ and 550r / min for 35min, 45mL of digroup modified acrylate and 55mL of isocyanate were added to the reactor, and the stirring reaction continued for 50min, 11mL of 0.35% dibutyltin dilaurate solution was added to the reactor, and the stirring reaction continued for 35min, 35mL of acrylic acid and 40mL of polyol were added to the reactor, and the reaction mixture was stirred for 1 minute. Ether polyol was protected by nitrogen and stirred at 97.5°C and 550r / min for 1.5h. The mixture was cooled to 60°C, 2.5g of sodium sulfite as an initiator and 3.5g of hydroxymethyl acrylamide as a cross-linking agent were added to the reactor, heated to 75°C, stirred at 550r / min for 3.5h, filtered, and the filter cake was washed twice with deionized water and then with anhydrous ethanol, and vacuum dried at 70°C for 1.5h. The powder was ground to obtain a double-crosslinked interpenetrating polymer powder.

[0044] S4: 11 g of graphene and 150 mL of concentrated nitric acid solution with a mass fraction of 63% were added to a reactor, stirred at 98°C and 550 r / min for 3.4 h, filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol respectively, and vacuum dried at 70°C for 1.2 h to obtain graphene oxide; 13 g of graphene oxide and 150 mL of deionized water were added to a reactor, stirred at 23°C and 550 r / min for 5 min, and then 25 g of double-crosslinked interpenetrating polymer powder was added, and the stirring reaction was continued for 1.2 h, filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol respectively, and vacuum dried at 70°C for 1.2 h, and ground to obtain a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0045] Example 3: A highly dispersed binder based on a polysaccharide-acrylic acid copolymer was prepared by the following steps:

[0046] S1: 50 g of chitosan, 120 mL of 3-mercaptopropyltrimethoxysilane and 300 mL of ethanol were added to a reactor, stirred at 70 ° C and 600 r / min for 2 h, filtered, and the filter cake was washed with deionized water three times and vacuum dried at 80 ° C for 2 h to obtain thiol-modified chitosan; 30 g of thiol-modified chitosan and 300 mL of 30 wt% hydrogen peroxide solution were added to a reactor, stirred at 25 ° C and 600 r / min for 2 h, and then a 0.6 M sodium hydroxide solution was added to a pH value of 9, filtered, and the filter cake was washed with deionized water and ethanol three times, and vacuum dried at 80 ° C for 2 h to obtain sulfonated modified chitosan.

[0047] S2: 30 g of maleic anhydride and 120 mL of hydroxypropyl methacrylate were added to a reactor, stirred at 25°C and 600 r / min for 40 min, then 0.2 g of hydroquinone as a polymerization inhibitor was added, and stirring was continued for 2 h to obtain a maleic anhydride mixed solution; 60 mL of perfluorooctylethanol and 68 mL of epichlorohydrin were added to a reactor, 0.2 g of sodium ethoxide catalyst was added, and the reaction was stirred at 25°C and 600 r / min for 24 h, then 75 mL of maleic anhydride mixed solution and 0.3 g of tetraethylammonium bromide catalyst were added, heated to 130°C, and the reaction was continued with stirring for 16 h. After the reaction was completed, the mixture was transferred to a distillation kettle, distilled under reduced pressure, condensed, and the intermediate fraction was selected to obtain a digroup-modified acrylate.

[0048] S3: 30 g of sulfonated modified chitosan and 300 mL of 60% sodium hydroxide solution were added to the reactor, stirred at 25 ° C and 600 r / min for 40 min, 50 mL of double-group modified acrylate and 60 mL of isocyanate were added to the reactor, and the stirring reaction continued for 60 min. 12 mL of 0.4% dibutyltin dilaurate solution was added to the reactor and the stirring was continued for 40 min. Then 40 mL of acrylic acid and 45 mL of polyether polyol were added, and nitrogen was introduced. Stirring reaction was carried out at 100 ° C and 600 r / min for 2 h, cooled to 65 ° C, 3 g of sodium sulfite as an initiator and 4 g of hydroxymethyl acrylamide as a cross-linking agent were added to the reactor, heated to 80 ° C, stirred at 600 r / min for 4 h, filtered, and the filter cake was washed three times with deionized water and then with anhydrous ethanol, and vacuum dried at 80 ° C for 2 h, ground and crushed to obtain a double-crosslinked interpenetrating polymer powder.

[0049] S4: Add 12 g of graphene and 200 mL of concentrated nitric acid solution with a mass fraction of 65% into a reactor, stir at 100 ° C and 600 r / min for 4 hours, filter, wash the filter cake with deionized water and anhydrous ethanol three times respectively, and vacuum dry at 80 ° C for 2 hours to obtain graphene oxide; add 15 g of graphene oxide and 200 mL of deionized water into a reactor, stir at 25 ° C and 600 r / min for 6 minutes, then add 30 g of double-crosslinked interpenetrating polymer powder, continue stirring and reacting for 2 hours, filter, wash the filter cake with deionized water and anhydrous ethanol three times respectively, vacuum dry at 80 ° C for 2 hours, grind and crush to obtain a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0050] Example 4: A method for preparing a carbon-coated aluminum foil, comprising the following steps:

[0051] 10 g of calcium hydroxide powder with a particle size of 2-3 mm and 200 mL of deionized water were added to a reactor, pre-cured at 120° C. for 30 min, 10 g of the highly dispersed binder obtained in Example 1 was added, and the curing was continued for 2 h to obtain a carbon-coated aluminum foil slurry. Finally, the carbon-coated aluminum foil slurry was coated on an aluminum foil substrate and dried at 97° C. to obtain a carbon-coated aluminum foil.

[0052] Example 5: A method for preparing a carbon-coated aluminum foil, comprising the following steps:

[0053] 11 g of calcium hydroxide powder with a particle size of 2-3 mm and 250 mL of deionized water were added to a reactor, pre-cured at 123° C. for 35 min, 11 g of the highly dispersed binder obtained in Example 2 was added, and the curing was continued for 2.3 h to obtain a carbon-coated aluminum foil slurry. Finally, the carbon-coated aluminum foil slurry was coated on an aluminum foil substrate and dried at 98° C. to obtain a carbon-coated aluminum foil.

[0054] Example 6: A method for preparing a carbon-coated aluminum foil, comprising the following steps:

[0055] 12 g of calcium hydroxide powder with a particle size of 2-3 mm and 300 mL of deionized water were added to a reactor, pre-cured at 125° C. for 40 min, 12 g of the highly dispersed binder obtained in Example 3 was added, and the curing was continued for 3 h to obtain a carbon-coated aluminum foil slurry. Finally, the carbon-coated aluminum foil slurry was coated on an aluminum foil substrate and dried at 100° C. to obtain a carbon-coated aluminum foil.

[0056] Comparative Example 1: Based on Example 3, the sulfonated modified chitosan in step S3 was replaced by the chitosan in step S1, and the other steps remained unchanged to prepare a highly dispersed binder based on a polysaccharide-acrylic acid copolymer.

[0057] Comparative Example 2: Based on Example 3, maleic anhydride in step S2 was omitted, and the remaining steps remained unchanged to prepare a highly dispersed binder based on a polysaccharide-acrylic acid copolymer.

[0058] Comparative Example 3: Based on Example 3, the polyether polyol in step S3 was omitted, and the other steps remained unchanged to prepare a highly dispersed binder based on a polysaccharide-acrylic acid copolymer.

[0059] In the Examples and Comparative Examples:

[0060] Chitosan, hydroxypropyl methacrylate, maleic anhydride, perfluorooctylethanol, and epichlorohydrin were purchased from Sigma-Aldrich.

[0061] The highly dispersed binders based on polysaccharide-acrylic acid copolymers obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were prepared into carbon-coated aluminum foils according to the method of Example 6 and the performance was tested. The results are shown in Table 1:

[0062] 1. Viscosity test: Refer to the national standard GB / T22235-2008 and use the rotational viscosity method on the NDJ-7 rotational viscometer of Shanghai Yulong Instrument Co., Ltd.

[0063] 2. Mechanical properties test: Referring to the standard of GB / T2567-2008, the bending strength and shear strength were tested on a Shenzhen Xinsansi CMT-6503 microcomputer-controlled electronic universal tensile testing machine with a loading speed of 2mm / min;

[0064] 3. Volume resistivity test: refer to QJ1523-1988 standard, and conduct the test on GEST-123 volume resistivity tester of Beijing Guance Precision Instrument Equipment Co., Ltd. The test requirements are: sample size is 50mm×5mm×0.5mm;

[0065] 4. Thermal coefficient determination: Refer to GB / T10297-2015 standard, carried out on the TC-3000 universal thermal conductivity tester of Xi'an Xiaxi Electronic Technology Co., Ltd., with a sample size of 25mm×3mm.

[0066] 5. Peel strength: The adhesion performance of carbon-coated aluminum foil was tested by 180° peeling using an AG-Xplus universal tensile testing machine from Shimadzu Corporation of Japan.

[0067] Table 1 Carbon-coated aluminum foil performance test table

[0068]

[0069] As can be seen from Table 1, the viscosity, shear strength, thermal conductivity, and peel strength of the carbon-coated aluminum foil prepared with the high-dispersion binder based on polysaccharide-acrylic acid copolymer in Examples 1 to 3 are significantly higher than those of the comparative example, and the volume resistivity is significantly lower than that of the comparative example, indicating that the carbon-coated aluminum foil prepared by the present invention has excellent viscosity, good heat dissipation capacity, high conductivity, and high peel strength.

[0070] In Comparative Example 1, the sulfonated modified chitosan is replaced with chitosan, and the hydroxyl groups on the surface of the chitosan are grafted with a thiol-containing silane coupling agent. The thiol groups are oxidized into sulfonic acid groups under the action of hydrogen peroxide. The sulfonate groups can promote the migration of lithium ions inside the lithium-sulfur battery, reduce the internal resistance of the battery, and improve the cycle performance of the lithium battery.

[0071] In Comparative Example 2, maleic anhydride is omitted. Maleic anhydride has a flexible chain segment, which can avoid the problem of brittleness of the adhesive at low temperatures, thereby preventing it from falling off. Maleic anhydride can undergo a ring-opening esterification reaction on the epoxy groups on the perfluoroalkyl glycidyl ether, thereby obtaining a double-group modified acrylate having a hydroxyl group and a fluorine group. The double-group modification can improve the bonding ability of the adhesive and improve the corrosion resistance of the adhesive.

[0072] In Comparative Example 3, the polyether polyol is discarded. The polyether polyol can be copolymerized with acrylic acid to form an interpenetrating network. The interpenetrating network can effectively load graphene, improve the dispersibility of graphene in the battery electrolyte, and prevent the agglomeration and precipitation of graphene. Functional groups such as hydroxyl groups in chitosan and polyurethane molecules can form hydrogen bonds and other interactions with other materials in the battery, thereby enhancing the bonding force between the binder and the electrode material. The intermediate product (polysulfide) of the sulfur-lithium battery is easily dissolved in the electrolyte and then shuttled to the negative electrode, resulting in a decrease in electrochemical performance. The sulfonic acid groups in the interpenetrating network can capture polysulfide, reduce the shuttle effect, and improve the electrochemical performance of the battery.

[0073] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0074] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A highly dispersed binder based on a polysaccharide-acrylic acid copolymer, characterized in that: Prepared by the following steps: Step 1: adding sulfonated modified chitosan and 50-60wt% sodium hydroxide solution to a reactor, stirring at 20-25°C and 500-600r / min for 30-40min, adding digroup modified acrylate and isocyanate to the reactor, continuing to stir and react for 40-60min, adding 0.3-0.4wt% dibutyltin dilaurate solution to the reactor, continuing to stir for 30-40min, then adding acrylic acid and polyether polyol, passing nitrogen protection, stirring at 95-100°C and 500-600r / min for 1-2h, cooling to 55-65°C, adding sodium sulfite and hydroxymethyl acrylamide to the reactor, heating to 70-80°C, stirring at 500-600r / min for 3-4h, filtering, washing the filter cake with deionized water and anhydrous ethanol for 2-3 times respectively, vacuum drying, grinding and crushing to obtain a double-crosslinked interpenetrating polymer powder; Step 2: Add graphene oxide and deionized water to a reactor, stir at 20-25°C and 500-600 rpm for 5-6 minutes, then add the double-crosslinked interpenetrating polymer powder, continue stirring and reacting for 1-2 hours, filter, wash the filter cake with deionized water and anhydrous ethanol 2-3 times respectively, dry in a vacuum at 60-80°C for 1-2 hours, and grind to obtain a highly dispersed binder based on a polysaccharide-acrylic acid copolymer; The digroup-modified acrylate in step 1 is prepared by the following steps: Maleic anhydride and hydroxypropyl methacrylate are added to a reaction kettle, stirred at 20-25°C and 500-600 r / min for 30-40 minutes, then hydroquinone is added, and stirring is continued for 1-2 hours to obtain a maleic anhydride mixed solution; perfluorooctylethanol and epichlorohydrin are added to a reaction kettle, sodium ethoxide is added, and stirring is carried out at 20-25°C and 500-600 r / min for 22-24 hours, then the maleic anhydride mixed solution and tetraethylammonium bromide are added, heated to 120-130°C, and stirring is continued for 14-16 hours, and vacuum distillation is performed, condensation is performed, and the middle fraction is selected to obtain a digroup modified acrylate.

2. The highly dispersed binder based on polysaccharide-acrylic acid copolymer according to claim 1, characterized in that: The amount ratio of the sulfonated modified chitosan, sodium hydroxide solution, digroup modified acrylate, isocyanate, dibutyltin dilaurate solution, acrylic acid, polyether polyol, sodium sulfite and hydroxymethyl acrylamide described in step 1 is 20-30g: 200-300mL: 40-50mL: 50-60mL: 30-40mL: 35-45mL: 2-3g: 3-4g.

3. The highly dispersed binder based on polysaccharide-acrylic acid copolymer according to claim 1, characterized in that: The usage ratio of the graphene oxide, deionized water and double-crosslinked interpenetrating polymer powder in step 2 is 10-15 g: 100-200 mL: 20-30 g.

4. The highly dispersed binder based on polysaccharide-acrylic acid copolymer according to claim 1, characterized in that: The usage ratio of maleic anhydride, hydroxypropyl methacrylate and hydroquinone is 20-30 g:100-120 mL:0.1-0.2 g.

5. The highly dispersed binder based on polysaccharide-acrylic acid copolymer according to claim 1, characterized in that: The perfluorooctylethanol, epichlorohydrin, sodium ethoxide, maleic anhydride mixed solution and tetraethylammonium bromide 50-60mL: 65-68mL: 0.1-0.2g: 70-75mL: 0.25-0.3g.

6. The highly dispersed binder based on polysaccharide-acrylic acid copolymer according to claim 1, characterized in that: The sulfonated modified chitosan described in step 1 is prepared by the following steps: Chitosan, 3-mercaptopropyltrimethoxysilane and ethanol are added to a reactor in a ratio of 40-50 g: 100-120 mL: 200-300 mL, stirred at 60-70° C. and 500-600 r / min for 1-2 hours, filtered, and the filter cake is washed with deionized water 2-3 times and vacuum dried to obtain thiol-modified chitosan; thiol-modified chitosan and 20-30 wt% hydrogen peroxide solution are added to a reactor in a ratio of 20-30 g: 200-300 mL, stirred at 20-25° C. and 500-600 r / min for 1-2 hours, and then a 0.5-0.6 M sodium hydroxide solution is added to a pH value of 9, filtered, and the filter cake is washed with deionized water and ethanol 2-3 times and vacuum dried to obtain sulfonated modified chitosan.

7. The highly dispersed binder based on polysaccharide-acrylic acid copolymer according to claim 1, characterized in that: In step 2, graphene oxide is prepared by the following steps: Graphene and 60-65wt% concentrated nitric acid solution were added to a reactor, stirred at 95-100°C and 500-600r / min for 3-4h, filtered, and the filter cake was washed with deionized water and anhydrous ethanol 2-3 times respectively, and vacuum dried to obtain graphene oxide.

8. The highly dispersed binder based on polysaccharide-acrylic acid copolymer according to claim 7, characterized in that: The usage ratio of the graphene and the concentrated nitric acid solution is 10-12 g: 100-200 mL.

9. A carbon-coated aluminum foil, characterized in that: The raw materials include the highly dispersed binder described in claim 1, and the carbon-coated aluminum foil is prepared by the following steps: Calcium hydroxide powder with a particle size of 2-3 mm and deionized water are added to a reactor, pre-cured at 120-125°C for 30-40 minutes, a highly dispersed binder is added, and the curing is continued for 2-3 hours to obtain a carbon-coated aluminum foil slurry. Finally, the carbon-coated aluminum foil slurry is coated on an aluminum foil substrate and dried at 97-100°C to obtain a carbon-coated aluminum foil. The usage ratio of the calcium hydroxide powder, deionized water and highly dispersed binder is 10-12 g: 200-300 mL: 10-12 g.

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