High-dispersion binder based on polysaccharide-acrylic acid copolymer and carbon-coated aluminum foil

Abstract

The invention discloses a high-dispersion binder based on a polysaccharide-acrylic acid copolymer and a carbon-coated aluminum foil, and belongs to the technical field of lithium ion battery current collectors. Chitosan is subjected to sulfonation modification, perfluoroalkyl glycidyl ether is generated from perfluorooctyl ethanol and epichlorohydrin under the action of a catalyst, and the carbon-coated aluminum foil is prepared. The preparation method comprises the following steps: performing a ring-opening esterification reaction on an epoxy group on perfluoroalkyl glycidyl ether through acid anhydride to obtain double-group modified acrylate with hydroxyl and fluorine, the structural formula contains a large amount of hydroxyl and fluorine groups, the double-group modified acrylate can be polymerized into double-crosslinking interpenetrating polymer powder, the hydroxyl is a polar group, and the fluorine group is a fluorine group. The polymer can form hydrogen bonds or other chemical bonds with various base materials, so that the adhesive force between the polymer and the base materials is enhanced; fluorination modification can further improve the film-forming property of the polymer, so that the carbon-coated aluminum foil is smoother and smoother, and meanwhile, fluorination modification can significantly improve the corrosion resistance.

Description

Technical Field

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

[0002] Aluminum foil is the most commonly used positive current collector and has an important impact on battery performance. The internal resistance of a lithium-ion battery directly affects the reliability and cycle life of the battery. The current collector is both a carrier for active materials and a conductor for collecting the current generated during operation, capable of forming a large current and improving the charge and discharge efficiency of a lithium battery. Conventional aluminum foil has a certain rigidity, and the contact area with the positive electrode material in the electrode sheet is limited, affecting the internal resistance of the positive electrode sheet. Therefore, after performing a certain surface treatment on the aluminum foil and then coating it with carbon, corrosion can be prevented, the internal resistance can be reduced, the electrical conductivity can be enhanced, and the adhesion to PVDF can be increased.

[0003] In the prior art, the molecular weight of the polyacrylic acid binder prepared is between 150,000 and 250,000. Theoretically speaking, on 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 more excellent the comprehensive performance of the prepared coating film. Therefore, the relatively small molecular weight is also one of the factors leading to the poor corrosion resistance of the binder.

[0004] Chinese Patent Publication No. CN116462800B discloses a preparation method and a binder for a polyacrylic acid binder for aluminum foil carbon coating slurry. By adding an appropriate amount of acrylic acid monomer and introducing more polar groups, a polyacrylic acid resin with a larger molecular weight is generated, making the paint film have good chemical resistance. However, in this solution, the larger the molecular weight of the polyacrylic acid binder, the longer its molecular chain and the higher the entanglement degree among them, which will lead to a decrease in the solubility of the binder in the solvent, thereby affecting the fluidity of the binder and making it difficult to uniformly apply or penetrate during the application process, thus affecting the bonding effect. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly dispersed binder based on a polysaccharide-acrylic acid copolymer. By sulfonating and modifying chitosan, perfluoroalkyl glycidyl ether is generated under the action of a catalyst by perfluorooctyl ethanol and epichlorohydrin, and then the epoxy group on the perfluoroalkyl glycidyl ether is subjected to ring-opening esterification reaction by an acid anhydride, thereby obtaining a double-group modified acrylate with hydroxyl and fluorine groups. The structural formula contains a large number of hydroxyl and fluorine groups, which can polymerize 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: A highly dispersed binder based on a polysaccharide-acrylic acid copolymer is prepared by the following steps: Step 1: Add sulfonated modified chitosan and a sodium hydroxide solution with a mass fraction of 50 - 60% into a reaction kettle, stir at 20 - 25 °C and 500 - 600 r / min for 30 - 40 min, add a double-group modified acrylate and isocyanate into the reaction kettle, continue stirring and reacting for 40 - 60 min, add 10 - 12 mL of a dibutyltin dilaurate solution with a mass fraction of 0.3 - 0.4% into the reaction kettle, continue stirring for 30 - 40 min, then add acrylic acid and polyether polyol, introduce nitrogen for protection, stir and react at 95 - 100 °C and 500 - 600 r / min for 1 - 2 h, cool to 55 - 65 °C, add sodium sulfite as an initiator and methylolacrylamide as a cross-linking agent into the reaction kettle, heat to 70 - 80 °C, stir at 500 - 600 r / min for 3 - 4 h, filter, wash the filter cake with deionized water and absolute ethanol respectively for 2 - 3 times, vacuum dry at 60 - 80 °C for 1 - 2 h, grind and pulverize to obtain a double-crosslinked interpenetrating polymer powder.

[0007] Step 2: Add graphene oxide and deionized water into a reaction kettle, stir at 20 - 25 °C and 500 - 600 r / min for 5 - 6 min, then add the double-crosslinked interpenetrating polymer powder, continue stirring and reacting for 1 - 2 h, filter, wash the filter cake with deionized water and absolute ethanol respectively for 2 - 3 times, vacuum dry at 60 - 80 °C for 1 - 2 h, grind and pulverize to obtain a highly dispersed binder based on a polysaccharide-acrylic acid copolymer.

[0008] Further, the dosage ratio of sulfonated modified chitosan, sodium hydroxide solution, double-group modified acrylate, isocyanate, dibutyltin dilaurate solution, acrylic acid, polyether polyol, sodium sulfite and methylolacrylamide in Step 1 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.

[0009] Further, the dosage ratio of graphene oxide, deionized water and double-crosslinked interpenetrating polymer powder in Step 2 is 10 - 15 g : 100 - 200 mL : 20 - 30 g.

[0010] Further, the double-group modified acrylate in Step 1 is prepared by the following steps: Maleic anhydride and hydroxypropyl methacrylate were added to a reaction kettle, stirred for 30 - 40 min under the conditions of 20 - 25 °C and 500 - 600 r / min, then hydroquinone as an inhibitor was added, and stirring was continued for 1 - 2 h to obtain a maleic anhydride mixed solution; Perfluorooctyl ethanol and epichlorohydrin were added to the reaction kettle, sodium ethoxide catalyst was added, and stirring reaction was carried out for 22 - 24 h under the conditions of 20 - 25 °C and 500 - 600 r / min, then the maleic anhydride mixed solution and tetraethylammonium bromide catalyst were added, heated to 120 - 130 °C, and stirring reaction was continued for 14 - 16 h, followed by reduced pressure distillation and condensation, and the middle fraction was selected to obtain the double-group modified acrylate.

[0011] Furthermore, the dosage ratio of maleic anhydride, hydroxypropyl methacrylate and hydroquinone is 20 - 30 g : 100 - 120 mL : 0.1 - 0.2 g.

[0012] Furthermore, the dosage of perfluorooctyl ethanol, epichlorohydrin, sodium ethoxide, maleic anhydride mixed solution and tetraethylammonium bromide is 50 - 60 mL : 65 - 68 mL : 0.1 - 0.2 g : 70 - 75 mL : 0.25 - 0.3 g.

[0013] Furthermore, the sulfonated modified chitosan described in step one is prepared through the following steps: Chitosan, 3-mercaptopropyltrimethoxysilane and ethanol were added to a reaction kettle, stirred for 1 - 2 h under the conditions of 60 - 70 °C and 500 - 600 r / min, filtered, the filter cake was washed with deionized water 2 - 3 times, and vacuum dried at 60 - 80 °C for 1 - 2 h to obtain mercapto-modified chitosan; Mercapto-modified chitosan and a hydrogen peroxide solution with a mass fraction of 20 - 30 wt% were added to the reaction kettle, stirred and reacted for 1 - 2 h under the conditions of 20 - 25 °C and 500 - 600 r / min, then a sodium hydroxide solution with a concentration of 0.5 - 0.6 M was added to adjust the pH value to 9, filtered, the filter cake was washed with deionized water and ethanol 2 - 3 times, and vacuum dried at 60 - 80 °C for 1 - 2 h to obtain sulfonated modified chitosan.

[0014] Furthermore, the dosage ratio of chitosan, 3-mercaptopropyltrimethoxysilane and ethanol is 40 - 50 g : 100 - 120 mL : 200 - 300 mL.

[0015] Furthermore, the dosage ratio of mercapto-modified chitosan and hydrogen peroxide solution is 20 - 30 g : 200 - 300 mL.

[0016] Furthermore, the graphene oxide in step two is prepared through the following steps: Add graphene and a concentrated nitric acid solution with a mass fraction of 60 - 65% into a reaction kettle, stir at 95 - 100 °C and 500 - 600 r / min for 3 - 4 h, filter, wash the filter cake with deionized water and absolute ethanol 2 - 3 times respectively, and dry it in vacuum at 60 - 80 °C for 1 - 2 h to obtain graphene oxide; Furthermore, the dosage ratio of graphene to the concentrated nitric acid solution is 10 - 12 g : 100 - 200 mL.

[0017] A preparation method of carbon - coated aluminum foil includes the following steps: Add calcium hydroxide powder with a particle size of 2 - 3 mm and deionized water into a reaction kettle, pre - cure at 120 - 125 °C for 30 - 40 min, add a highly - dispersed binder, and continue to cure for 2 - 3 h to obtain a carbon - coated aluminum foil slurry. Finally, coat the carbon - coated aluminum foil slurry on an aluminum foil substrate and dry it at 97 - 100 °C to obtain the carbon - coated aluminum foil.

[0018] Furthermore, the dosage ratio of calcium hydroxide powder, deionized water and the highly - dispersed binder is 10 - 12 g : 200 - 300 mL : 10 - 12 g.

[0019] The beneficial effects of the present invention are as follows: 1. The highly - dispersed binder prepared by the present invention has excellent adhesion and good dispersibility for carbon conductive materials. By sulfonating and modifying chitosan and hydroxylating acrylic monomers, and introducing fluorine elements into the structural formula, a double - group - modified acrylate is obtained. As a polar group, the hydroxyl group can form hydrogen bonds or other chemical bonds with various substrates, thereby enhancing the adhesion between the polymer and the substrate. After polymerization with polyurethane monomers, a double - crosslinked interpenetrating polymer powder is obtained, and graphene is interspersed in the polymerization network of the double - crosslinked interpenetrating polymer powder to improve the dispersibility of graphene. Graphene has excellent electrical and thermal conductivity coefficients, which can increase the electrical conductivity and heat dissipation capacity of the binder.

[0020] 2. The sulfonated modified chitosan of the present invention is grafted with a thiol - containing silane coupling agent through the hydroxyl groups on the surface of chitosan, and the thiol group is oxidized to a sulfonic acid group under the action of hydrogen peroxide. And the double - crosslinked interpenetrating polymer powder is copolymerized from acrylic monomers and polyurethane monomers, and its structural formula also contains a large number of sulfonic acid groups. The intermediate product (polysulfide) of lithium - sulfur batteries is easily dissolved in the electrolyte and then shuttles to the negative electrode, resulting in a decrease in electrochemical performance. Through the sulfonic acid groups in the double - crosslinked polysaccharide network, polysulfides are captured, the shuttle effect is reduced, the migration of lithium ions inside the lithium - sulfur battery is promoted, the internal resistance of the battery is reduced, and the cycle performance of the lithium battery is improved.

[0021] 3. The double-crosslinked interpenetrating polymer powder of the present invention. Perfluoroalkyl glycidyl ether is formed by perfluorooctyl ethanol and epichlorohydrin under the action of a catalyst. The epoxy group on the perfluoroalkyl glycidyl ether is subjected to ring-opening esterification reaction with maleic anhydride, thereby obtaining a double-group modified acrylate with hydroxyl and fluorine groups. The structural formula contains a large number of hydroxyl groups, fluorine groups and flexible chain segments. When polymerizing into the 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; fluorination modification can further improve the film-forming performance of the polymer, making the carbon-coated aluminum foil smoother and flatter, while improving the hardness and scratch resistance of the carbon-coated aluminum foil, and fluorination modification can significantly improve the anti-corrosion ability; a large number of long carbon chain flexible chain segments can still maintain a certain flexibility at low temperatures, and can absorb and disperse stress when subjected to external forces, reducing the detachment from the carbon-coated aluminum foil due to stress concentration; 4. Excessive polysaccharides may swell in the organic electrolyte, resulting in the relaxation of the binder network and reducing the electrode structure stability. 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, and improve the electrode structure stability; the polymer chains in the interpenetrating network form a tight network structure through chemical crosslinking or physical crosslinking. 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 effect of the solvent molecules on the polysaccharides. Detailed implementation mode

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0023] Example 1: A highly dispersed binder based on a polysaccharide-acrylic copolymer is prepared by the following steps: S1: Add 40 g of chitosan, 100 mL of 3-mercaptopropyltrimethoxysilane, and 200 mL of ethanol into a reaction kettle, stir for 1 h at 60 °C and 500 r / min, filter, wash the filter cake with deionized water twice, and dry it in vacuum at 60 °C for 1 h to obtain mercapto-modified chitosan; Add 20 g of mercapto-modified chitosan and 200 mL of hydrogen peroxide solution with a mass fraction of 20 wt% into the reaction kettle, stir and react for 1 h at 20 °C and 500 r / min, then add sodium hydroxide solution with a concentration of 0.5 M until the pH value reaches 9, filter, wash the filter cake with deionized water and ethanol twice, and dry it in vacuum at 60 °C for 1 h to obtain sulfonated-modified chitosan.

[0024] The hydroxyl groups on the surface of chitosan are grafted with a mercapto-containing silane coupling agent, and the mercapto groups are oxidized to sulfonic acid groups under the action of hydrogen peroxide. The sulfonic acid groups can promote the migration of lithium ions inside the lithium-sulfur battery, reduce the internal resistance of the battery, and improve the cycling performance of the lithium battery.

[0025] S2: Add 20 g of maleic anhydride and 100 mL of hydroxypropyl methacrylate into a reaction kettle, stir for 30 min at 20 °C and 500 r / min, then add 0.1 g of hydroquinone as an inhibitor, and continue to stir for 1 h to obtain a maleic anhydride mixed solution; Add 50 mL of perfluorooctyl ethanol and 65 mL of epichlorohydrin into the reaction kettle, add 0.1 g of sodium ethoxide catalyst, stir and react for 22 h at 20 °C and 500 r / min, then add 70 mL of the maleic anhydride mixed solution and 0.25 g of tetraethylammonium bromide catalyst, heat to 120 °C, and continue to stir and react for 14 h. After the reaction is completed, transfer it to a distillation kettle, carry out vacuum distillation, condensation, and select the middle fraction to obtain a double-group modified acrylate.

[0026] Perfluorooctyl ethanol and epichlorohydrin will generate perfluoroalkyl glycidyl ether under the action of a catalyst. The epoxy groups on the perfluoroalkyl glycidyl ether are subjected to ring-opening esterification reaction with maleic anhydride, so as 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 binder at low temperature, thus avoiding shedding.

[0027] S3: Add 20 g of sulfonated modified chitosan and 200 mL of 50% sodium hydroxide solution by mass to the reaction kettle, stir for 30 min at 20 °C and 500 r / min, add 40 mL of double-group modified acrylate and 50 mL of isocyanate to the reaction kettle, continue stirring and reacting for 40 min, add 10 mL of 0.3% dibutyltin dilaurate solution by mass to the reaction kettle, continue stirring for 30 min, then add 30 mL of acrylic acid and 35 mL of polyether polyol, introduce nitrogen protection, stir and react for 1 h at 95 °C and 500 r / min, cool to 55 °C, add 2 g of sodium sulfite as an initiator and 3 g of methylolacrylamide as a crosslinking agent to the reaction kettle, heat to 70 °C, stir at 500 r / min for 3 h, filter, wash the filter cake with ionized water and absolute ethanol twice respectively, vacuum dry at 60 °C for 1 h, grind and pulverize to obtain double-crosslinked interpenetrating polymer powder.

[0028] S4: Add 10 g of graphene and 100 mL of 60% concentrated nitric acid solution by mass to the reaction kettle, stir for 3 h at 95 °C and 500 r / min, filter, wash the filter cake with ionized water and absolute ethanol twice respectively, vacuum dry at 60 °C for 1 h to obtain graphene oxide; add 10 g of graphene oxide and 100 mL of deionized water to the reaction kettle, stir for 5 min at 20 °C and 500 r / min, then add 20 g of double-crosslinked interpenetrating polymer powder, continue stirring and reacting for 1 h, filter, wash the filter cake with ionized water and absolute ethanol twice respectively, vacuum dry at 60 °C for 1 h, grind and pulverize to obtain a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0029] The graphene is acidified so that its surface has carboxyl groups, and functional groups such as hydroxyl groups in chitosan and polyurethane molecules can form hydrogen bonds and other interactions with other materials in the battery, enhancing the adhesion between the binder and the electrode material; the intermediate product (polysulfide) of the lithium-sulfur 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-crosslinked interpenetrating network can capture polysulfides, reduce the shuttle effect, and improve the electrochemical performance of the battery.

[0030] Example 2: A highly dispersed binder based on polysaccharide-acrylic acid copolymer is prepared by the following steps: S1: Add 45 g of chitosan, 110 mL of 3-mercaptopropyltrimethoxysilane, and 250 mL of ethanol into a reaction kettle, stir for 1.2 h under the conditions of 65 °C and 550 r / min, filter, wash the filter cake twice with deionized water, and dry it in vacuum at 70 °C for 1.2 h to obtain mercapto-modified chitosan; Add 25 g of mercapto-modified chitosan and 250 mL of hydrogen peroxide solution with a mass fraction of 25 wt% into the reaction kettle, stir and react for 1.2 h under the conditions of 23 °C and 550 r / min, then add sodium hydroxide solution with a concentration of 0.55 M until the pH value reaches 9, filter, wash the filter cake twice with deionized water and ethanol, and dry it in vacuum at 70 °C for 1.2 h to obtain sulfonated modified chitosan.

[0031] S2: Add 25 g of maleic anhydride and 110 mL of hydroxypropyl methacrylate into a reaction kettle, stir for 35 min under the conditions of 23 °C and 550 r / min, then add 0.15 g of hydroquinone as an inhibitor, and continue to stir for 1.2 h to obtain a maleic anhydride mixed solution; Add 55 mL of perfluorooctyl ethanol and 66 mL of epichlorohydrin into the reaction kettle, add 0.15 g of sodium ethoxide catalyst, stir and react for 23 h under the conditions of 23 °C and 550 r / min, then add 73 mL of the maleic anhydride mixed solution and 0.28 g of tetraethylammonium bromide catalyst, heat to 125 °C, and continue to stir and react for 15 h. After the reaction is completed, transfer it to a distillation kettle, carry out vacuum distillation, condensation, and select the middle fraction to obtain a double-group modified acrylate.

[0032] S3: Add 25 g of sulfonated modified chitosan and 250 mL of sodium hydroxide solution with a mass fraction of 55% into a reaction kettle, stir for 35 min under the conditions of 22.5 °C and 550 r / min, add 45 mL of double-group modified acrylate and 55 mL of isocyanate into the reaction kettle, continue to stir and react for 50 min, add 11 mL of dibutyltin dilaurate solution with a mass fraction of 0.35% into the reaction kettle, continue to stir for 35 min, add 35 mL of acrylic acid and 40 mL of polyether polyol, introduce nitrogen protection, stir and react for 1.5 h under the conditions of 97.5 °C and 550 r / min, cool to 60 °C, add 2.5 g of sodium sulfite as an initiator and 3.5 g of methylolacrylamide as a crosslinking agent into the reaction kettle, heat to 75 °C, and stir at a speed of 550 r / min for 3.5 h, filter, wash the filter cake twice with ionic water and then with absolute ethanol respectively, and carry out vacuum drying at 70 °C for 1.5 h, grind and crush to obtain double-crosslinked interpenetrating polymer powder.

[0033] S4: Add 11 g of graphene and 150 mL of concentrated nitric acid solution with a mass fraction of 63% into a reaction kettle, stir for 3.4 h under the conditions of 98 °C and 550 r / min, filter, wash the filter cake twice with deionized water and absolute ethanol respectively, and dry it in vacuum at 70 °C for 1.2 h to obtain graphene oxide; Add 13 g of graphene oxide and 150 mL of deionized water into a reaction kettle, stir for 5 min under the conditions of 23 °C and 550 r / min, then add 25 g of double-crosslinked interpenetrating polymer powder, continue to stir and react for 1.2 h, filter, wash the filter cake twice with deionized water and absolute ethanol respectively, dry it in vacuum at 70 °C for 1.2 h, grind and crush it to obtain a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0034] Example 3: A highly dispersed binder based on polysaccharide-acrylic acid copolymer is prepared by the following steps: S1: Add 50 g of chitosan, 120 mL of 3-mercaptopropyltrimethoxysilane and 300 mL of ethanol into a reaction kettle, stir for 2 h under the conditions of 70 °C and 600 r / min, filter, wash the filter cake three times with deionized water, and dry it in vacuum at 80 °C for 2 h to obtain mercapto-modified chitosan; Add 30 g of mercapto-modified chitosan and 300 mL of hydrogen peroxide solution with a mass fraction of 30 wt% into a reaction kettle, stir and react for 2 h under the conditions of 25 °C and 600 r / min, then add sodium hydroxide solution with a concentration of 0.6 M until the pH value reaches 9, filter, wash the filter cake three times with deionized water and ethanol, and dry it in vacuum at 80 °C for 2 h to obtain sulfonated modified chitosan.

[0035] S2: Add 30 g of maleic anhydride and 120 mL of hydroxypropyl methacrylate into a reaction kettle, stir for 40 min under the conditions of 25 °C and 600 r / min, then add 0.2 g of hydroquinone as a polymerization inhibitor, continue to stir for 2 h to obtain a maleic anhydride mixed solution; Add 60 mL of perfluorooctyl ethanol and 68 mL of epichlorohydrin into a reaction kettle, add 0.2 g of sodium ethoxide catalyst, stir and react for 24 h under the conditions of 25 °C and 600 r / min, then add 75 mL of the maleic anhydride mixed solution and 0.3 g of tetraethylammonium bromide catalyst, heat to 130 °C, continue to stir and react for 16 h, transfer to a distillation kettle after the reaction is completed, carry out vacuum distillation, condensation, and select the middle fraction to obtain a double-group modified acrylate.

[0036] S3: Add 30 g of sulfonated modified chitosan and 300 mL of sodium hydroxide solution with a mass fraction of 60% into the reaction kettle, stir for 40 min under the conditions of 25 °C and 600 r / min, add 50 mL of double-group modified acrylate and 60 mL of isocyanate into the reaction kettle, continue to stir and react for 60 min, add 12 mL of dibutyltin dilaurate solution with a mass fraction of 0.4% into the reaction kettle, continue to stir for 40 min, then add 40 mL of acrylic acid and 45 mL of polyether polyol, introduce nitrogen for protection, stir and react for 2 h under the conditions of 100 °C and 600 r / min, cool to 65 °C, add 3 g of sodium sulfite as an initiator and 4 g of hydroxymethylacrylamide as a crosslinking agent into the reaction kettle, heat to 80 °C, stir at a speed of 600 r / min for 4 h, filter, wash the filter cake with deionized water and then with absolute ethanol three times respectively, and conduct vacuum drying at 80 °C for 2 h, grind and pulverize to obtain the double-crosslinked interpenetrating polymer powder.

[0037] S4: Add 12 g of graphene and 200 mL of concentrated nitric acid solution with a mass fraction of 65% into the reaction kettle, stir for 4 h under the conditions of 100 °C and 600 r / min, filter, wash the filter cake with deionized water and absolute ethanol three times respectively, conduct vacuum drying at 80 °C for 2 h to obtain graphene oxide; add 15 g of graphene oxide and 200 mL of deionized water into the reaction kettle, stir for 6 min under the conditions of 25 °C and 600 r / min, then add 30 g of the double-crosslinked interpenetrating polymer powder, continue to stir and react for 2 h, filter, wash the filter cake with deionized water and absolute ethanol three times respectively, conduct vacuum drying at 80 °C for 2 h, grind and pulverize to obtain the highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0038] Example 4: A preparation method of carbon-coated aluminum foil, comprising the following steps: Add 10 g of calcium hydroxide powder with a particle size of 2 - 3 mm and 200 mL of deionized water into the reaction kettle, pre-cure at 120 °C for 30 min, add 10 g of the highly dispersed binder obtained in Example 1, continue to cure for 2 h to obtain the carbon-coated aluminum foil slurry, and finally coat the carbon-coated aluminum foil slurry on the aluminum foil substrate and dry at 97 °C to obtain the carbon-coated aluminum foil.

[0039] Example 5: A preparation method of carbon-coated aluminum foil, comprising the following steps: Add 11 g of calcium hydroxide powder with a particle size of 2 - 3 mm and 250 mL of deionized water into the reaction kettle, pre-cure at 123 °C for 35 min, add 11 g of the highly dispersed binder obtained in Example 2, continue to cure for 2.3 h to obtain the carbon-coated aluminum foil slurry, and finally coat the carbon-coated aluminum foil slurry on the aluminum foil substrate and dry at 98 °C to obtain the carbon-coated aluminum foil.

[0040] Embodiment 6: A method for preparing a carbon-coated aluminum foil, comprising the following steps: 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.

[0041] Comparative Example 1: Based on Example 3, the sulfonated modified chitosan in step S3 is replaced by the chitosan in step S1, and the other steps remain unchanged to prepare a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0042] Comparative Example 2: Based on Example 3, maleic anhydride in step S2 was omitted, and the other steps remained unchanged to prepare a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

[0043] 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 polysaccharide-acrylic acid copolymer.

[0044] In the embodiments and comparative examples: Chitosan, hydroxypropyl methacrylate, maleic anhydride, perfluorooctylethanol and epichlorohydrin were purchased from Sigma-Aldrich.

[0045] The highly dispersed binders based on polysaccharide-acrylic acid copolymer obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were respectively prepared into carbon-coated aluminum foils according to the method of Example 6 for performance testing. The results are shown in Table 1: 1. Viscosity test: refer to the national standard GB / T22235-2008, use the rotational viscosity method on the NDJ-7 rotational viscometer of Shanghai Yulong Instrument Co., Ltd.; 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; 3. Volume resistivity test: refer to QJ1523-1988 standard, and carry out on GEST-123 volume resistivity tester of Beijing Guance Precision Instrument Equipment Co., Ltd. Test requirements: sample size is 50mm×5mm×0.5mm; 4. Thermal coefficient determination: Referring to the standard of GB / T10297-2015, it was carried out on the TC-3000 universal thermal conductivity tester of Xi'an Xiaxi Electronic Technology Co., Ltd., and the sample size was 25mm×3mm.

[0046] 5. Peeling strength: The AG-Xplus universal tensile testing machine of Shimadzu Corporation, Japan was used to conduct a 180° peeling test on the adhesion performance of the carbon-coated aluminum foil.

[0047] Table 1 Performance test table of carbon-coated aluminum foil As can be seen from Table 1, for the carbon-coated aluminum foils prepared from the highly dispersed binders based on polysaccharide-acrylic acid copolymer in Examples 1 - 3, the viscosity, shear strength, thermal conductivity, and peeling strength are significantly higher than those of the comparative examples, and the volume resistivity is significantly smaller than that of the comparative examples, indicating that the carbon-coated aluminum foil prepared by the present invention has excellent viscosity, good heat dissipation ability, high conductivity, and high peeling strength.

[0048] In Comparative Example 1, sulfonated modified chitosan was replaced with chitosan. The hydroxyl groups on the surface of chitosan were grafted with a thiol-containing silane coupling agent, and the thiol groups were oxidized to sulfonic acid groups under the action of hydrogen peroxide. The sulfonic acid groups can promote the migration of lithium ions inside the lithium-sulfur battery, reduce the internal resistance of the battery, and improve the cycling performance of the lithium battery.

[0049] In Comparative Example 2, maleic anhydride was omitted. Maleic anhydride has a flexible chain segment, which can avoid the problem of high brittleness of the binder at low temperatures, thus avoiding shedding. Maleic anhydride can carry out a ring-opening esterification reaction on the epoxy group of perfluoroalkyl glycidyl ether to obtain a double-group modified acrylate with hydroxyl and fluorine groups. The double-group modification can improve the binding ability of the binder and enhance the anti-corrosion ability of the binder.

[0050] In Comparative Example 3, polyether polyol was omitted. Polyether polyol can copolymerize with acrylic acid to form an interpenetrating network. The interpenetrating network can effectively load graphene, improve the dispersion of graphene in the battery electrolyte, and prevent the agglomeration and precipitation of graphene. The hydroxyl and other functional groups in chitosan and polyurethane molecules can form hydrogen bonds and other interactions with other materials in the battery, enhancing the adhesion between the binder and the electrode material; the intermediate product (polysulfide) of the lithium-sulfur battery is easily soluble in the electrolyte and then shuttles to the negative electrode, resulting in a decrease in electrochemical performance. The sulfonic acid groups in the interpenetrating network can capture polysulfides, reduce the shuttle effect, and improve the electrochemical performance of the battery.

[0051] It should be noted that in this document, relational terms such as first and second are only used 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 "comprising", "including" or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0052] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present 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, introducing nitrogen protection, stirring and reacting 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 ionized water and anhydrous ethanol for 2-3 times respectively, vacuum drying, grinding and crushing to obtain a double cross-linked interpenetrating polymer powder; 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 cross-linked interpenetrating polymer powder, continue stirring and reacting for 1-2 hours, filter, wash the filter cake with deionized water and anhydrous ethanol for 2-3 times respectively, dry in vacuum at 60-80°C for 1-2 hours, grind and crush to obtain a highly dispersed binder based on polysaccharide-acrylic acid copolymer.

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 graphene oxide, deionized water and double cross-linked 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 digroup-modified acrylate in step 1 is prepared by the following steps: Add maleic anhydride and hydroxypropyl methacrylate into a reaction kettle, stir at 20-25°C and 500-600r / min for 30-40min, then add hydroquinone, continue stirring for 1-2h to obtain a maleic anhydride mixed solution; add perfluorooctylethanol and epichlorohydrin into a reaction kettle, add sodium ethoxide, stir at 20-25°C and 500-600r / min for 22-24h, then add the maleic anhydride mixed solution and tetraethylammonium bromide, heat to 120-130°C, continue stirring for 14-16h, distill under reduced pressure, condense, select the middle fraction, and obtain a digroup modified acrylate.

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

6. The highly dispersed binder based on polysaccharide-acrylic acid copolymer according to claim 4, 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.

7. 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 dosage 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, the filter cake is washed with deionized water for 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 dosage ratio of 20-30 g: 200-300 mL, stirred at 20-25° C. and 500-600 r / min for 1-2 hours, then a 0.5-0.6 M sodium hydroxide solution is added to a pH value of 9, filtered, the filter cake is washed with deionized water and ethanol for 2-3 times, and vacuum dried to obtain sulfonated modified chitosan.

8. 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 are added into a reactor, stirred at 95-100°C and 500-600r / min for 3-4h, filtered, the filter cake is washed with deionized water and anhydrous ethanol for 2-3 times respectively, and vacuum dried to obtain graphene oxide.

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

10. 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 reaction kettle, 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, and 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 10-12g:200-300mL:10-12g.

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