Water-based binder for carbon-coated aluminum foil of lithium ion battery and preparation method of water-based binder

Abstract

The invention discloses a water-based binder for a carbon-coated aluminum foil of a lithium ion battery and a preparation method of the water-based binder, and relates to the technical field of lithium ion battery binders. The aqueous binder comprises the following components: modified glucose, conductive composite particles, glutaraldehyde, sodium carboxymethyl cellulose, sodium polyacrylate and deionized water. The preparation method comprises the following steps: sequentially adding the sodium polyacrylate and the conductive composite particles into the deionized water, and uniformly stirring; then adding modified glucose and sodium carboxymethyl cellulose, and continuously stirring uniformly; and finally, adding glutaraldehyde, and stirring for reaction to obtain the water-based adhesive for the carbon-coated aluminum foil of the lithium ion battery. According to the invention, renewable biomass glucose is used as a main raw material, water is matched as a solvent, an organic solvent is abandoned, the production process is pollution-free, and the raw material is degradable and environment-friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery binders, and specifically to an aqueous binder for carbon-coated aluminum foil of lithium-ion batteries and a preparation method thereof. Background Art

[0002] With the rapid development of the lithium-ion battery industry, carbon-coated aluminum foil, as a key material to improve the energy density and cycle stability of batteries, its performance plays a decisive role in the overall performance of the battery. And the binder, as the core component of carbon-coated aluminum foil, its performance directly affects the bonding effect between the electrode material and the current collector.

[0003] Currently, the binders applied to carbon-coated aluminum foil of lithium-ion batteries in the market are mostly solvent-based binders, such as polyvinylidene fluoride (PVDF). Such binders usually need to be dissolved and dispersed with organic solvents such as N-methylpyrrolidone (NMP). NMP not only has certain toxicity and poses a potential threat to the health of operators, but also has a high boiling point and is difficult to recycle, resulting in high energy consumption and increased costs in the production process. At the same time, the volatilization of organic solvents will also cause serious environmental pollution, which does not conform to the development trend of green environmental protection. In addition, solvent-based binders have potential safety hazards of flammability and explosion during use, increasing the difficulty of risk control in the production process.

[0004] In recent years, the in-depth development of the environmental protection concept has promoted the industry to gradually increase the research on aqueous binders, but there are still many problems with existing aqueous binders. Some aqueous binders, in order to pursue bonding performance, use a large amount of non-degradable high molecular polymers, which are difficult to decompose naturally after the battery is scrapped and will also cause environmental pollution; there are also some aqueous binders that use degradable components, but their comprehensive performance is poor and cannot meet the performance requirements of the binder for carbon-coated aluminum foil of lithium-ion batteries.

[0005] Glucose, as a biomass material with a wide range of sources, has environmental protection advantages such as being renewable, degradable, and having good biocompatibility. Applying it to the field of binders for carbon-coated aluminum foil of lithium-ion batteries can solve the environmental protection problems of traditional binders. However, glucose itself has extremely poor conductivity and cannot effectively promote the electron transfer between the electrode material and the current collector, and it is difficult to meet the requirement that the binder for carbon-coated aluminum foil must have good conductivity to reduce the interface resistance and improve the charge and discharge performance of the battery. Summary of the Invention

[0006] The purpose of the present invention is to provide an aqueous binder for carbon-coated aluminum foil of lithium-ion batteries and a preparation method thereof, so as to solve the technical problems of the existing binders being not environmentally friendly and the poor conductivity of the glucose binder proposed in the above background art.

[0007] To achieve the above purpose, the present invention provides the following technical solutions: An aqueous binder for carbon-coated aluminum foil of a lithium-ion battery, comprising the following components by weight: 40 - 60 parts of modified glucose, 10 - 20 parts of conductive composite particles, 3 - 6 parts of glutaraldehyde, 1 - 3 parts of sodium carboxymethylcellulose, 0.5 - 1 part of sodium polyacrylate, and 50 - 80 parts of water.

[0008] In the technical solution of the present invention, glucose is selected as the main component of the binder. As a biomass material with a wide range of sources, glucose has environmental protection advantages such as being renewable, biodegradable, and having good biocompatibility, and the solvent is water, which is green and environmentally friendly. The conductive composite particles can improve the conductivity of the binder and reduce the electrode interface impedance. Glutaraldehyde is used as a cross-linking agent, and the two aldehyde groups in its molecule can undergo a cross-linking reaction with active groups such as hydroxyl groups in the modified glucose molecule to form a three-dimensional network structure within the binder system. This cross-linked structure enhances the cohesion and mechanical strength of the binder. Sodium carboxymethylcellulose is used as a thickening agent. It is easily soluble in water, can effectively adjust the viscosity of the binder, improve the rheological properties, and enable the binder to have good workability during the coating process, be evenly coated on the surface of the aluminum foil, and avoid phenomena such as sagging and accumulation. It can also stabilize the dispersion state of the conductive composite particles in the binder and prevent their sedimentation. Sodium polyacrylate is used as a dispersant, adsorbing on the surface of the conductive composite particles. Through electrostatic repulsion and steric hindrance effects, it effectively prevents the aggregation of the conductive composite particles. The uniformly dispersed conductive composite particles not only facilitate the construction of a continuous and efficient conductive network but also ensure the uniform performance of each part of the binder, avoiding a decrease in local conductivity or coating defects caused by particle aggregation.

[0009] Preferably, the preparation method of the modified glucose comprises the following steps: (1) Prepare a glucose solution, then add aniline to the glucose solution, and carry out a stirring reaction under heating conditions to obtain an aniline-modified glucose solution; (2) Add melamine to the aniline-modified glucose solution, heat and stir the reaction. After the reaction is completed, carry out vacuum distillation on the solution to remove excess water and small molecule impurities to obtain the modified glucose.

[0010] In the technical solution of the present invention, as described above, water-based glucose which is green and environmentally friendly is used as the binder. However, glucose itself has extremely poor conductivity and cannot effectively promote the electron transfer between the electrode material and the current collector. Therefore, the present invention modifies glucose. The aniline molecule contains an amino group, and there are multiple hydroxyl groups in the glucose molecule. Under certain conditions, aniline and glucose undergo a nucleophilic substitution reaction. The amino group of aniline acts as a nucleophile and attacks the carbon atom connected to the hydroxyl group in the glucose molecule. The hydroxyl group is removed in the form of water, and the amino group replaces the position of the hydroxyl group, thereby introducing the conjugated structure of aniline into the glucose molecule. Since the π electrons in the conjugated structure can be delocalized within the entire conjugated system and have good electron mobility, this enables the modified glucose molecule to have a certain electron transfer ability, creating conditions for improving the conductivity of the binder. The melamine molecule contains multiple amino groups. In addition to the retained hydroxyl groups in the aniline-modified glucose molecule, the newly introduced conjugated structure also has certain reactivity. The amino group of melamine and the hydroxyl group or the active sites on the conjugated structure in the aniline-modified glucose molecule undergo a condensation reaction under heating conditions. During the reaction process, a water molecule is removed between the amino group and the hydroxyl group to form a new chemical bond, connecting melamine to the aniline-modified glucose molecule. The introduction of melamine not only increases the molecular weight and the complexity of the spatial structure of the glucose molecule, but also its nitrogen-containing functional groups can combine with the functional groups on the surface of the subsequent added conductive composite particles through hydrogen bonds or other intermolecular forces, enhancing the binding force between the binder matrix and the conductive particles, further optimizing the electron transfer path, and synergistically improving the conductivity of the binder.

[0011] Preferably, in the step (1), glucose is dissolved in water to prepare a glucose solution, and the addition amount of aniline is 10-15% of the mass of glucose.

[0012] Preferably, in the step (2), the addition amount of melamine is 3-8% of the mass of glucose.

[0013] Preferably, the preparation method of the conductive composite particles includes the following steps: (a) Mix carbon nanotubes and graphene to obtain mixed particles; (b) Acidify the mixed particles to introduce carboxyl functional groups on the surface of the mixed particles. After the acidification treatment is completed, wash the conductive particles repeatedly with water until neutral, and then dry them to obtain pretreated conductive particles; (c) Add polyaniline to N-methylpyrrolidone and stir to dissolve it to prepare a polyaniline solution. Add the pretreated conductive particles to the polyaniline solution, heat and stir to react, so that polyaniline is coated on the surface of the pretreated conductive particles to obtain conductive composite particles.

[0014] In the technical solution of the present invention, the electrical conductivity of the binder is improved from two aspects. On the one hand, as described above, the glucose itself is conductively modified to preliminarily improve the electrical conductivity of the binder. On the other hand, the present invention further improves the electrical conductivity of the binder by adding conductive composite particles thereto. Through the synergistic effect of the two aspects, the binder has excellent electrical conductivity. The specific preparation method of the conductive composite particles is as follows: First, carbon nanotubes and graphene are selected and mixed as conductive particles, and acid treatment is carried out through a nitric acid solution to introduce functional groups such as carboxyl groups on their surfaces, increasing the surface activity of the conductive particles. Then, polyaniline is used to coat them. Polyaniline itself is a conductive polymer material with good electrical conductivity. The coated polyaniline not only can conduct electricity by itself, but also builds an additional conductive bridge between the conductive particles, increasing the number of conductive paths between the conductive particles, enabling electrons to be transmitted more efficiently between the conductive particles. At the same time, the polyaniline coating layer can also improve the compatibility and bonding force between the conductive particles and the binder matrix (modified glucose), enabling the conductive particles to be better dispersed in the binder, avoiding the aggregation of the conductive particles, thereby maintaining a stable and efficient conductive network and significantly improving the electrical conductivity of the binder.

[0015] Preferably, in the step (a), the mass ratio of carbon nanotubes to graphene is 3:0.5 - 2.

[0016] Preferably, in the step (b), the acid treatment refers to adding the mixed particles to a nitric acid solution for acid treatment, and the mass concentration of the nitric acid solution is 5 - 10%.

[0017] Preferably, in the step (c), the heating reaction temperature is 70 °C and the reaction time is 6 h.

[0018] Preferably, the mass ratio of the pretreated conductive particles to polyaniline is 10:1 - 3.

[0019] In the technical solution of the present invention, as described above, by coating the conductive particles with polyaniline, the number of conductive paths between the conductive particles is increased, enabling electrons to be transmitted more efficiently between the conductive particles, thereby enhancing the improvement of the electrical conductivity of the binder. To achieve the above technical effects, it is necessary to coat a sufficient amount of polyaniline on the surface of the conductive particles. Therefore, the present invention controls the mass ratio of the pretreated conductive particles to polyaniline to be less than 10 / 1. However, the research team of the present invention unexpectedly found that as the amount of polyaniline continues to increase, when the mass ratio of the pretreated conductive particles to polyaniline is less than 10 / 3, the flexibility of the binder suddenly drops significantly after curing and drying. During the charge and discharge process of a lithium-ion battery, the electrode material will experience volume expansion and contraction, and the binder needs to have good flexibility to adapt to this change. Otherwise, the binder is prone to cracking, affecting the service life of the electrode material. The above phenomenon may be because the polyaniline molecular chain has a certain rigid structure. When an excessive amount of polyaniline coats the surface of the conductive particles, a large number of rigid polyaniline molecules will form a thick and rigid coating layer around the conductive particles. This rigid coating layer restricts the relative movement and deformation ability between the conductive particles and between the conductive particles and the binder matrix, resulting in poor flexibility of the binder. Therefore, in order to balance the electrical conductivity and flexibility of the binder, the present invention controls the mass ratio of the pretreated conductive particles to polyaniline within the range of 10:1 - 3.

[0020] A preparation method of an aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery comprises the following steps: Sodium polyacrylate and conductive composite particles are sequentially added into water and stirred evenly; then modified glucose and sodium carboxymethylcellulose are added, and stirring is continued until evenly mixed; finally, glutaraldehyde is added and stirred for reaction to obtain the aqueous binder for the carbon-coated aluminum foil of the lithium-ion battery.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Using renewable biomass glucose as the main raw material and water as the solvent, abandoning organic solvents, the production process is pollution-free, and the raw materials are degradable, which is green and environmentally friendly; 2. Through the synergistic effect of modified glucose and conductive composite particles, the electrical conductivity of the binder is greatly improved, and each additive optimizes the construction and dispersibility, ensuring the stable performance of the battery; 3. Controlling the coating amount of polyaniline on the surface of the conductive particles, avoiding the decrease in flexibility caused by excessive polyaniline, and achieving the balance of the electrical conductivity and flexibility of the binder. Specific embodiments

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the implementation rules 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 creative work are within the scope of protection of the present invention.

[0023] The main raw material specifications and related suppliers used in the specific examples are as follows: Glucose: analytical grade (≥99.5%), Shandong Lukang; Aniline: analytical grade (≥99.5%), Sinopharm Chemical Reagent; Melamine: industrial grade (≥99%), white powder (C3H6N6), Sichuan Meifeng; Carbon nanotubes: diameter 10-20 nm, length 10-30μm, purity >95%, Jiangsu Tiannai; Graphene: sheet size 0.5-5μm, thickness 1-5nm, Ningbo Moxi; Sodium carboxymethyl cellulose: high viscosity type (degree of substitution 0.6), battery grade (no metal impurities), Ashland Chemical; Sodium polyacrylate: low molecular weight (2000-5000), Jiangsu Fumiao Technology.

[0024] Example 1 A water-based binder for a lithium-ion battery carbon-coated aluminum foil, comprising the following components in parts by weight: 55 parts of modified glucose, 18 parts of conductive composite particles, 5 parts of glutaraldehyde, 2.5 parts of sodium carboxymethyl cellulose, 0.9 parts of sodium polyacrylate, and 75 parts of deionized water.

[0025] Preparation of modified glucose: (1) Weigh 50g of glucose and place it in a 500mL beaker. Add 400mL of deionized water and stir with a magnetic stirrer until it is completely dissolved to prepare a glucose solution. Weigh 7g of aniline and slowly add it to the glucose solution. Place the beaker in a digital constant temperature water bath, heat it to 80℃, stir at 300r / min for 3 hours to obtain an aniline-modified glucose solution.

[0026] (2) Weigh 3.5 g of melamine and add it to the above aniline-modified glucose solution. Raise the water bath temperature to 90°C and continue stirring at 300 r / min for 4 hours. After the reaction is completed, transfer the solution to a rotary evaporator and perform reduced pressure distillation at -0.09 MPa vacuum and 60°C to remove excess water and small molecular impurities to obtain modified glucose.

[0027] Preparation of conductive composite particles: (a) Weigh 30 g of carbon nanotubes and 18 g of graphene, place them in a clean and dry mortar, and grind and mix them thoroughly for 10 minutes to obtain mixed particles; (b)Prepare a 7% (mass concentration) nitric acid solution of 500 mL. Add the mixed particles to the nitric acid solution, place it in a water bath at 60 °C, and stir for acidification treatment at a rotation speed of 250 r / min for 2 hours. After the acidification is completed, use a Buchner funnel and a suction filtration device, and repeatedly wash the particles with deionized water until the pH value of the washing solution is about 7. Transfer the washed particles to a vacuum drying oven and dry them at 80 °C for 12 hours to obtain pretreated conductive particles.

[0028] (c)Weigh 10 g of pretreated conductive particles and 2.5 g of polyaniline. Add the polyaniline to 200 mL of N-methylpyrrolidone, and use an electric stirrer to stir at a rotation speed of 400 r / min until it is completely dissolved to prepare a polyaniline solution. Add the pretreated conductive particles to the polyaniline solution, place it in a water bath at 70 °C, and stir and react at a rotation speed of 350 r / min for 6 hours. After the reaction is completed, perform centrifugal separation (4000 r / min, 10 minutes), and wash it successively with an appropriate amount of N-methylpyrrolidone and deionized water, and finally dry it in a vacuum drying oven at 60 °C for 8 hours to obtain conductive composite particles.

[0029] A preparation method of an aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery, comprising the following steps: Add deionized water to a beaker, and successively add sodium polyacrylate and conductive composite particles, and use an electric stirrer to stir at a rotation speed of 350 r / min for 15 minutes until uniformly dispersed. Then add modified glucose and sodium carboxymethylcellulose, and continue to stir for 20 minutes. Finally, add glutaraldehyde and stir and react for 1 hour to obtain an aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery.

[0030] Example 2 An aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery, comprising the following components by weight: 45 parts of modified glucose, 12 parts of conductive composite particles, 4 parts of glutaraldehyde, 1.5 parts of sodium carboxymethylcellulose, 0.7 part of sodium polyacrylate, and 60 parts of deionized water.

[0031] Preparation of modified glucose: (1)Weigh 50 g of glucose and place it in a 500 mL beaker, add 400 mL of deionized water, and use a magnetic stirrer to stir until it is completely dissolved to prepare a glucose solution. Weigh 5.5 g of aniline and slowly add it to the glucose solution. Place the beaker in a digital display constant temperature water bath, heat it to 80 °C, and stir and react at a rotation speed of 300 r / min for 3 hours to obtain an aniline-modified glucose solution.

[0032] (2) Weigh 2 g of melamine and add it to the above-mentioned aniline-modified glucose solution. Raise the water bath temperature to 90 °C and continue to stir and react at a speed of 300 r / min for 4 hours. After the reaction is completed, transfer the solution to a rotary evaporator and perform vacuum distillation under a vacuum of -0.09 MPa and at 60 °C to remove excess water and small molecule impurities, obtaining modified glucose.

[0033] Preparation of conductive composite particles: (a) Weigh 30 g of carbon nanotubes and 10 g of graphene, place them in a clean and dry mortar, and grind and mix them thoroughly for 10 minutes to obtain mixed particles; (b) Prepare a 7% (mass concentration), 500 mL nitric acid solution, add the mixed particles to the nitric acid solution, place it in a water bath at 60 °C, and stir and acidify for 2 hours at a speed of 250 r / min. After acidification is completed, use a Buchner funnel and a suction filtration device to wash the particles repeatedly with deionized water until the pH value of the washing solution is about 7. Transfer the washed particles to a vacuum drying oven and dry them at 80 °C for 12 hours to obtain pretreated conductive particles.

[0034] (c) Weigh 10 g of pretreated conductive particles and 1.5 g of polyaniline. Add polyaniline to 200 mL of N-methylpyrrolidone and use an electric stirrer to stir at a speed of 400 r / min until completely dissolved to prepare a polyaniline solution. Add the pretreated conductive particles to the polyaniline solution, place it in a water bath at 70 °C, and stir and react at a speed of 350 r / min for 6 hours. After the reaction is completed, perform centrifugal separation (4000 r / min, 10 minutes), wash with an appropriate amount of N-methylpyrrolidone and deionized water in sequence, and finally dry in a vacuum drying oven at 60 °C for 8 hours to obtain conductive composite particles.

[0035] A preparation method of an aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery, comprising the following steps: Add deionized water to a beaker, add sodium polyacrylate and conductive composite particles in sequence, and use an electric stirrer to stir at a speed of 350 r / min for 15 minutes until evenly dispersed. Then add modified glucose and sodium carboxymethylcellulose, and continue to stir for 20 minutes. Finally, add glutaraldehyde and stir and react for 1 hour to obtain an aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery.

[0036] Example 3 An aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery, comprising the following components by weight: 50 parts of modified glucose, 15 parts of conductive composite particles, 4.5 parts of glutaraldehyde, 2 parts of sodium carboxymethylcellulose, 0.8 part of sodium polyacrylate, and 65 parts of deionized water.

[0037] Preparation of modified glucose: (1) Weigh 50g of glucose and place it in a 500mL beaker. Add 400mL of deionized water and stir with a magnetic stirrer until it is completely dissolved to prepare a glucose solution. Weigh 6g of aniline and slowly add it to the glucose solution. Place the beaker in a digital constant temperature water bath, heat it to 80℃, and stir at 300r / min for 3 hours to obtain an aniline-modified glucose solution.

[0038] (2) Weigh 2.5 g of melamine and add it to the above aniline-modified glucose solution. Raise the water bath temperature to 90°C and continue stirring at 300 r / min for 4 hours. After the reaction is completed, transfer the solution to a rotary evaporator and perform reduced pressure distillation at -0.09 MPa vacuum and 60°C to remove excess water and small molecular impurities to obtain modified glucose.

[0039] Preparation of conductive composite particles: (a) Weigh 30 g of carbon nanotubes and 10 g of graphene, place them in a clean and dry mortar, and grind and mix them thoroughly for 10 minutes to obtain mixed particles; (b) Prepare 500 mL of nitric acid solution with a mass concentration of 7%, add the mixed particles to the nitric acid solution, put them into a 60°C water bath, and stir at 250 r / min for acidification for 2 hours. After the acidification is completed, use a Buchner funnel and a suction filtration device to repeatedly wash the particles with deionized water until the pH value of the washing solution is about 7, transfer the washed particles to a vacuum drying oven, and dry them at 80°C for 12 hours to obtain pretreated conductive particles.

[0040] (c) Weigh 10 g of pretreated conductive particles and 2 g of polyaniline. Add polyaniline to 200 mL of N-methylpyrrolidone and stir at 400 r / min with an electric stirrer until completely dissolved to prepare a polyaniline solution. Add the pretreated conductive particles to the polyaniline solution, place in a 70°C water bath, and stir at 350 r / min for 6 hours. After the reaction is completed, centrifuge (4000 r / min, 10 minutes), wash with appropriate amounts of N-methylpyrrolidone and deionized water in turn, and finally dry in a 60°C vacuum drying oven for 8 hours to obtain conductive composite particles.

[0041] A method for preparing an aqueous binder for a lithium ion battery carbon-coated aluminum foil comprises the following steps: Add deionized water to a beaker, add sodium polyacrylate and conductive composite particles in sequence, and stir with an electric stirrer at 350r / min for 15 minutes until uniformly dispersed. Then add modified glucose and sodium carboxymethyl cellulose, and continue stirring for 20 minutes. Finally, add glutaraldehyde and stir for 1 hour to obtain a water-based binder for carbon-coated aluminum foil for lithium-ion batteries.

[0042] Example 4 A water-based binder for a lithium-ion battery carbon-coated aluminum foil, comprising the following components in parts by weight: 60 parts of modified glucose, 20 parts of conductive composite particles, 6 parts of glutaraldehyde, 3 parts of sodium carboxymethyl cellulose, 1 part of sodium polyacrylate, and 80 parts of deionized water.

[0043] Preparation of modified glucose: (1) Weigh 50g of glucose and place it in a 500mL beaker. Add 400mL of deionized water and stir with a magnetic stirrer until it is completely dissolved to prepare a glucose solution. Weigh 7.5g of aniline and slowly add it to the glucose solution. Place the beaker in a digital constant temperature water bath, heat it to 80℃, stir at 300r / min for 3 hours to obtain an aniline-modified glucose solution.

[0044] (2) Weigh 4 g of melamine and add it to the above aniline-modified glucose solution. Raise the water bath temperature to 90°C and continue stirring at 300 r / min for 4 hours. After the reaction is completed, transfer the solution to a rotary evaporator and perform reduced pressure distillation at -0.09 MPa vacuum and 60°C to remove excess water and small molecular impurities to obtain modified glucose.

[0045] Preparation of conductive composite particles: (a) Weigh 30 g of carbon nanotubes and 20 g of graphene, place them in a clean and dry mortar, and grind and mix them thoroughly for 10 minutes to obtain mixed particles; (b) Prepare 500 mL of nitric acid solution with a mass concentration of 10%, add the mixed particles to the nitric acid solution, put them into a 60°C water bath, and stir at 250 r / min for acidification for 2 hours. After the acidification is completed, use a Buchner funnel and a suction filtration device to repeatedly wash the particles with deionized water until the pH value of the washing solution is about 7, transfer the washed particles to a vacuum drying oven, and dry them at 80°C for 12 hours to obtain pretreated conductive particles.

[0046] (c) Weigh 10g of pretreated conductive particles and 3g of polyaniline. Add polyaniline to 200mL of N-methylpyrrolidone and stir at 400r / min with an electric stirrer until completely dissolved to prepare a polyaniline solution. Add the pretreated conductive particles to the polyaniline solution, place in a 70°C water bath, and stir at 350r / min for 6 hours. After the reaction is completed, centrifuge (4000r / min, 10 minutes), wash with appropriate amounts of N-methylpyrrolidone and deionized water in turn, and finally dry in a 60°C vacuum drying oven for 8 hours to obtain conductive composite particles.

[0047] A method for preparing an aqueous binder for a lithium ion battery carbon-coated aluminum foil comprises the following steps: Add deionized water to a beaker, and sequentially add sodium polyacrylate and conductive composite particles. Use an electric stirrer to stir at a speed of 350 r / min for 15 minutes until evenly dispersed. Then add modified glucose and sodium carboxymethylcellulose, and continue to stir for 20 minutes. Finally, add glutaraldehyde and stir and react for 1 hour to obtain an aqueous binder for a lithium-ion battery carbon-coated aluminum foil.

[0048] Example 5 An aqueous binder for a lithium-ion battery carbon-coated aluminum foil, comprising the following components by weight: 40 parts of modified glucose, 10 parts of conductive composite particles, 3 parts of glutaraldehyde, 1 part of sodium carboxymethylcellulose, 0.5 part of sodium polyacrylate, and 50 parts of deionized water.

[0049] Preparation of modified glucose: (1) Weigh 50 g of glucose and place it in a 500 mL beaker. Add 400 mL of deionized water and use a magnetic stirrer to stir until completely dissolved to prepare a glucose solution. Weigh 5 g of aniline and slowly add it to the glucose solution. Place the beaker in a digital display constant temperature water bath and heat it to 80 °C, and stir and react at a speed of 300 r / min for 3 hours to obtain an aniline-modified glucose solution.

[0050] (2) Weigh 1.5 g of melamine and add it to the above aniline-modified glucose solution. Raise the water bath temperature to 90 °C and continue to stir and react at a speed of 300 r / min for 4 hours. After the reaction is completed, transfer the solution to a rotary evaporator and perform vacuum distillation at a vacuum degree of -0.09 MPa and a temperature of 60 °C to remove excess water and small molecule impurities to obtain modified glucose.

[0051] Preparation of conductive composite particles: (a) Weigh 30 g of carbon nanotubes and 5 g of graphene and place them in a clean and dry mortar, and thoroughly grind and mix for 10 minutes to obtain mixed particles; (b) Prepare a 500 mL nitric acid solution with a mass concentration of 5%. Add the mixed particles to the nitric acid solution, place it in a 60 °C water bath, and stir and acidify at a speed of 250 r / min for 2 hours. After the acidification is completed, use a Buchner funnel and a suction filtration device to repeatedly wash the particles with deionized water until the pH value of the washing solution is about 7. Transfer the washed particles to a vacuum drying oven and dry them at 80 °C for 12 hours to obtain pretreated conductive particles.

[0052] (c) Weigh 10 g of pretreated conductive particles and 1 g of polyaniline. Add the polyaniline into 200 mL of N-methylpyrrolidone, and use an electric stirrer to stir at a speed of 400 r / min until it is completely dissolved to prepare a polyaniline solution. Add the pretreated conductive particles into the polyaniline solution, put it into a water bath at 70 °C, and stir and react at a speed of 350 r / min for 6 hours. After the reaction, centrifuge (4000 r / min, 10 minutes), and wash it successively with an appropriate amount of N-methylpyrrolidone and deionized water. Finally, dry it in a vacuum drying oven at 60 °C for 8 hours to obtain conductive composite particles.

[0053] A preparation method of an aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery, comprising the following steps: Add deionized water into a beaker, add sodium polyacrylate and conductive composite particles in sequence, and use an electric stirrer to stir at a speed of 350 r / min for 15 minutes until uniformly dispersed. Then add modified glucose and sodium carboxymethylcellulose, and continue to stir for 20 minutes. Finally, add glutaraldehyde and stir and react for 1 hour to obtain an aqueous binder for a carbon-coated aluminum foil of a lithium-ion battery.

[0054] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the modified glucose is replaced with ordinary glucose, and the remaining steps are the same.

[0055] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no conductive composite particles are added to the binder components, and the remaining steps are the same.

[0056] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the conductive composite particles are not treated with polyaniline coating, and the remaining steps are the same.

[0057] Comparative Example 4 The difference between Comparative Example 4 and Example 4 is that in the preparation process of the conductive composite particles, the mass ratio of the pretreated conductive particles to polyaniline is 10:4, and the remaining steps are the same.

[0058] Comparative Example 5 The difference between Comparative Example 5 and Example 4 is that in the preparation process of the conductive composite particles, the mass ratio of the pretreated conductive particles to polyaniline is 10:5, and the remaining steps are the same.

[0059] Performance test: 1. Conductivity test: The test was carried out by the four-probe method. The carbon-coated aluminum foil of the lithium-ion battery was evenly coated on the surface of the clean aluminum foil with an aqueous binder to form a coating with a thickness of about 0.1 mm, and dried in a vacuum drying oven at 80 °C for 12 hours to completely cure the binder. The aluminum foil with the cured coating was placed on the test bench of the four-probe tester, and the four probes were adjusted to be in close contact with the coating surface and perpendicular. The test current was set to 10 mA, and the resistance value displayed by the tester was read. The resistivity of the coating was calculated according to the formula, and the test area was fixed at 1 cm 2 , and each sample was tested 3 times, and the average value was taken as the final result. The smaller the resistivity, the better the conductive performance of the binder. The test results are shown in Table 1.

[0060] 2. Flexibility test: The flexibility of the binder was evaluated by a bending test. The aluminum foil coated with the aqueous binder and cured was cut into strips of 20 mm × 100 mm and tested using a flexibility tester. One end of the aluminum foil was fixed on the fixture of the tester, and the other end was pressed by a robotic arm to bend the aluminum foil around a cylinder with a diameter of 3 mm at a bending speed of 1 time per second. During the bending process, the state of the surface of the binder coating was observed in real time using a high-definition camera, and the number of bends when the coating first showed cracking or peeling was recorded. If no obvious defects appeared in the coating after 200 bends, it was determined that the flexibility was good. Each sample was tested 3 times, and the minimum value was taken as the result. The test results are shown in Table 1.

[0061] 3. Bonding strength test: The bonding strength test was carried out using a universal tensile testing machine. The aluminum foil coated with the aqueous binder was cut into strips of 25 mm × 50 mm and bonded to another aluminum foil of the same size in a 25 mm × 25 mm area with the binder and cured at room temperature for 48 hours. The bonded sample was clamped on the fixture of the tensile testing machine to ensure that the sample was clamped correctly and the force was evenly distributed. The tensile speed was set to 5 mm / min, the tensile testing machine was started, and the sample was continuously stretched until the bonding interface was damaged, and the maximum tensile force value at the time of damage was recorded. The bonding strength was calculated according to the formula, and each sample was tested 3 times, and the average value was taken. The test results are shown in Table 1.

[0062] Table 1: Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An aqueous binder for carbon-coated aluminum foil of a lithium-ion battery, characterized in that, It comprises the following components by weight parts: 40 - 60 parts of modified glucose, 10 - 20 parts of conductive composite particles, 3 - 6 parts of glutaraldehyde, 1 - 3 parts of sodium carboxymethyl cellulose, 0.5 - 1 part of sodium polyacrylate, and 50 - 80 parts of water.

2. The aqueous binder for carbon-coated aluminum foil of a lithium-ion battery according to claim 1, characterized in that, The preparation method of the modified glucose comprises the following steps: (1) Prepare a glucose solution, then add aniline to the glucose solution, and carry out a stirring reaction under heating conditions to obtain an aniline - modified glucose solution; (2) Add melamine to the aniline - modified glucose solution, carry out a heating and stirring reaction. After the reaction is completed, carry out vacuum distillation on the solution to remove excess water and small - molecule impurities to obtain modified glucose.

3. The aqueous binder for carbon-coated aluminum foil of a lithium-ion battery according to claim 2, characterized in that, In the step (1), dissolve glucose in water to prepare a glucose solution, and the addition amount of aniline is 10 - 15% of the mass of glucose.

4. The aqueous binder for carbon-coated aluminum foil of a lithium-ion battery according to claim 2, characterized in that, In the step (2), the addition amount of melamine is 3 - 8% of the mass of glucose.

5. The aqueous binder for carbon-coated aluminum foil of a lithium-ion battery according to claim 1, characterized in that, The preparation method of the conductive composite particles comprises the following steps: (a) Mix carbon nanotubes and graphene to obtain mixed particles; (b) Carry out acidification treatment on the mixed particles to introduce carboxyl functional groups on the surface of the mixed particles. After the acidification treatment is completed, wash the conductive particles repeatedly with water until neutral, and then carry out drying to obtain pretreated conductive particles; (c) Add polyaniline to N - methylpyrrolidone and stir to dissolve it to prepare a polyaniline solution. Add the pretreated conductive particles to the polyaniline solution, and carry out a heating and stirring reaction to make polyaniline coat on the surface of the pretreated conductive particles to obtain conductive composite particles.

6. The aqueous binder for carbon-coated aluminum foil of a lithium-ion battery according to claim 5, wherein, In the step (a), the mass ratio of carbon nanotubes to graphene is 3:0.5 - 2.

7. The aqueous binder for carbon-coated aluminum foil of a lithium-ion battery according to claim 5, characterized in that, In the step (b), the acidification treatment refers to adding the mixed particles to a nitric acid solution for acidification treatment, and the mass concentration of the nitric acid solution is 5 - 10%.

8. The aqueous binder for carbon-coated aluminum foil of a lithium-ion battery according to claim 5, characterized in that, In the step (c), the heating reaction temperature is 70 °C and the reaction time is 6 h.

9. The aqueous binder for carbon-coated aluminum foil of a lithium-ion battery according to claim 8, characterized in that, The mass ratio of the pretreated conductive particles to polyaniline is 10:1 - 3.

10. A preparation method of an aqueous binder for carbon-coated aluminum foil of a lithium-ion battery, characterized in that, It comprises the following steps: Sequentially add sodium polyacrylate and conductive composite particles to water and stir evenly; then add modified glucose and sodium carboxymethyl cellulose and continue to stir evenly; finally add glutaraldehyde and carry out a stirring reaction to obtain an aqueous binder for lithium - ion battery carbon - coated aluminum foil.

Images