Graphene conductive paste based on core-shell structure dispersing agent and preparation method of graphene conductive paste

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to graphene conductive paste based on a core-shell structure dispersant and a preparation method thereof.The graphene conductive paste based on the core-shell structure dispersant comprises, by weight, 0.5-5 parts of graphene, 5-10 parts of a conductive agent, 0.2-2.5 parts of the core-shell structure dispersant, 15-20 parts of a PVDF binder and 0.1-1.5 parts of a plasticizer, and 61-79.2 parts by weight of a diluent. The core-shell structure dispersing agent is introduced into the graphene conductive slurry, so that the dispersity and the stability of graphene in the conductive slurry are effectively improved, and meanwhile, the coating performance of the conductive slurry is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a graphene conductive slurry based on a core-shell structure dispersant and its preparation method. Background Technology

[0002] In the field of lithium-ion battery manufacturing, graphene has become a highly promising conductive agent material due to its ultra-high electrical conductivity, ultra-large specific surface area, excellent mechanical strength, and good chemical stability. However, due to the high surface energy and strong van der Waals forces between graphene sheets, it is prone to stacking and agglomerating in conductive slurries. This not only disrupts the continuity of the conductive network, leading to increased local resistance, but also clogs the pores between active material particles, resulting in a decrease in battery rate performance. Furthermore, uneven dispersion of graphene in conductive slurries can also lead to decreased stability of the slurry, affecting coating performance. In cathode slurry systems composed of high-nickel ternary materials and polyvinylidene fluoride (PVDF) binders, graphene also suffers from poor interfacial compatibility with PVDF and high-nickel ternary materials.

[0003] Existing technologies generally improve the dispersibility of graphene in conductive slurries by optimizing dispersants. Some studies use single small-molecule dispersants to improve the dispersibility of graphene in conductive slurries; however, the interaction between small-molecule dispersants and graphene is weak, and they are prone to agglomeration after long-term storage, leading to increased viscosity and decreased fluidity of the conductive slurry. Other studies use polymeric dispersants to improve the dispersibility of graphene in conductive slurries. Although polymeric dispersants can enhance the dispersion effect of graphene to a certain extent, the molecular chains of polymeric dispersants are prone to entanglement, which reduces the conductivity and coating performance of the conductive slurry. In addition, existing methods of optimizing dispersants cannot effectively improve the interfacial compatibility between graphene and PVDF binders or high-nickel ternary materials (such as NCM811), resulting in problems such as conductive network breakage and increased interfacial impedance during charge and discharge. This leads to drawbacks such as rapid battery capacity decay and short cycle life (capacity retention is often less than 75% after 500 cycles), making it difficult to meet the industrial production requirements of high-energy-density lithium-ion batteries. Summary of the Invention

[0004] To address the technical problem that graphene in a cathode slurry system composed of high-nickel ternary materials and PVDF binder is prone to poor stability, conductivity, and coating performance due to uneven dispersion and poor interfacial compatibility, this invention provides a graphene conductive slurry based on a core-shell structured dispersant and its preparation method. By introducing a core-shell structured dispersant into the graphene conductive slurry, the dispersibility and stability of graphene in the conductive slurry are effectively improved, while the coating performance of the conductive slurry is also improved.

[0005] The technical solution of this invention is as follows: In a first aspect, the present invention provides a graphene conductive slurry based on a core-shell structure dispersant, comprising the following components: 0.5-5 parts by weight of graphene, 5-10 parts by weight of conductive agent, 0.2-2.5 parts by weight of core-shell structure dispersant, 15-20 parts by weight of PVDF binder, 0.1-1.5 parts by weight of plasticizer, and 61-79.2 parts by weight of diluent.

[0006] Furthermore, the core-shell structured dispersant comprises a hyperbranched polyester core and a fluorinated acrylate copolymer shell, which are chemically bonded to form the core-shell structure. The hyperbranched polyester core has a three-dimensional spherical structure, its molecular chains are not easily entangled, and its viscosity does not change significantly with increasing molecular weight. This provides significant steric hindrance for graphene sheets in conductive slurries, preventing graphene sheet aggregation. The fluorinated acrylate copolymer shell has an extremely low surface energy significantly lower than that of graphene, reducing the total surface energy of the slurry system and inhibiting graphene sheet aggregation. The fluorinated acrylate copolymer shell also exhibits good compatibility with PVDF. The core-shell structured dispersant used in this invention has a transitional structure from a polar core to a non-polar shell, which can buffer the polarity difference between the high-nickel surface of the high-nickel ternary material and the PVDF surface, reduce interfacial tension, and allow PVDF to spread more smoothly on the surface of the high-nickel ternary material particles to form a continuous bonding network. At the same time, the hyperbranched polyester is rich in polar groups such as hydroxyl (-OH) and carboxyl (-COOH), which can interact with the residual alkali on the surface of the high-nickel ternary material, reducing the direct reaction between the residual alkali and PVDF.

[0007] Furthermore, the molecular weight of hyperbranched polyester is 20,000-100,000 g / mol, and the molecular weight of fluorinated acrylate copolymer is 30,000-70,000 g / mol.

[0008] Furthermore, the conductive agent is at least one of carbon black or carbon nanotubes, with carbon black being preferred; the plasticizer is dibutyl phthalate; and the diluent is N-methylpyrrolidone.

[0009] Furthermore, the viscosity of the graphene conductive paste is 3000-5000 mPa·s. This invention, by controlling the viscosity of the graphene conductive paste, ensures that the uniformity error of the graphene conductive paste during coating is ≤ ±5 μm.

[0010] Furthermore, the core-shell structured dispersant is prepared by reacting hyperbranched polyester with a fluorinated acrylate copolymer under the action of an initiator.

[0011] Furthermore, the preparation method of the core-shell structured dispersant is as follows: Step (1): Double bond modification is performed on the hyperbranched polyester to obtain double bond modified hyperbranched polyester; Step (2): Add the double bond modified hyperbranched polyester and fluorinated acrylate copolymer to tetrahydrofuran and stir until homogeneous to form a reactant solution; Step (3): Add an initiator to the reactant solution and heat it to 60-80℃ under nitrogen protection to obtain a reaction solution containing a core-shell structured dispersant. Purify the reaction solution containing the core-shell structured dispersant by precipitation to obtain the core-shell structured dispersant.

[0012] Hyperbranched polyester is prepared by reacting AB2-type monomers with polyols in the presence of a catalyst. The molar ratio of AB2-type monomers to polyols is controlled at 5-10:1, the mass of the catalyst is 0.5%-2% of the sum of the masses of AB2-type monomers and polyols, the reaction temperature is 120-160℃, and the reaction time is typically 6-12 hours. The AB2-type monomer is 2,2-dimethylolpropionic acid, the polyol is pentaerythritol, and the catalyst is p-toluenesulfonic acid.

[0013] The fluorinated acrylate copolymer is prepared by reacting pentaerythritol dodecylfluoroheptyl methacrylate and butyl acrylate in the presence of azobisisobutyronitrile (AIBN). The molar ratio of dodecylfluoroheptyl methacrylate to butyl acrylate is 1-3:7-9. The mass of the second initiator is 0.5%-1.5% of the sum of the masses of dodecylfluoroheptyl methacrylate and butyl acrylate. The reaction temperature is 60-80℃ and the reaction time is 4-8 hours.

[0014] Furthermore, in step (2), the mass ratio of the double-bond modified hyperbranched polyester to the fluorinated acrylate copolymer is 1-3:7-9; in step (3), the initiator is benzoyl peroxide, the mass of the initiator is 0.5%-1.5% of the total mass of the double-bond modified hyperbranched polyester and the fluorinated acrylate copolymer, and the reaction time is 6-12 hours.

[0015] Secondly, the present invention provides a method for preparing the graphene conductive paste as described above, comprising the following steps: Step 1: Prepare the mixture by adding plasticizer and PVDF binder to the diluent in sequence, heating to 65±2℃ and stirring to obtain a uniform mixture; Step 2: Base material mixing. Graphene and conductive agent are added to the mixture and stirred at a constant temperature of 65±2℃ to obtain a conductive mixture. Step 3: After the conductive mixture cools to room temperature, add a core-shell structured dispersant to it, and then perform ultrasonic dispersion to obtain a dispersion. Step 4: Homogenization control. The dispersion is homogenized and then the viscosity of the homogenized dispersion is adjusted to 3000-5000 mPa·s to obtain graphene conductive slurry.

[0016] The dispersion stability of the graphene conductive slurry prepared by the above method is significantly improved. After being stored at 25°C for 48 hours, the graphene agglomerate particle size change rate is ≤15%, the viscosity change rate of the graphene conductive slurry after 48 hours is ≤20%, the viscosity change rate after 7 days is ≤30%, and the electrical conductivity of the graphene conductive slurry is greater than 1200 S / cm.

[0017] Furthermore, in step one, the stirring speed is 500-600 rpm, and the stirring time is 20-40 min; in step two, the constant temperature stirring speed is 500-600 rpm, and the constant temperature stirring time is 20-40 min. In step three, the ultrasonic dispersion power is 200W, and the ultrasonic dispersion time is 30 minutes; in step four, the homogenization is performed using a high shear homogenizer at a speed of 10000-12000 rpm for 10 minutes.

[0018] The beneficial effects of this invention are as follows: This invention provides a graphene conductive paste based on a core-shell structured dispersant and its preparation method. Adding only 0.2-2.5 parts by weight of the core-shell structured dispersant to the graphene conductive paste significantly reduces the particle size change rate of graphene agglomerates after 48 hours of storage at room temperature, and keeps the viscosity change rate of the graphene conductive paste at a low level during storage. This fundamentally inhibits graphene agglomeration and ensures the long-term stability of the graphene conductive paste. Furthermore, this invention precisely controls the coating viscosity of the graphene conductive paste to 3000-5000 mPa·s by adjusting the composition and ratio of the graphene conductive paste, reducing the surface roughness of the coating, minimizing coating thickness uniformity errors, significantly improving coating accuracy, reducing equipment blockage, and increasing production efficiency. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0020] The preparation methods of the hyperbranched polyester and fluorinated acrylate copolymer used in the embodiments of the present invention are as follows: (I) Preparation of hyperbranched polyesters Step 1-1: Polymerization reaction. AB2 type monomer, polyol, and catalyst are added to a three-necked flask equipped with a stirrer, thermometer, and condenser. Under nitrogen protection, the temperature is gradually raised to 140℃ to carry out the polycondensation reaction. During the reaction, water generated in the reaction is continuously evaporated. The reaction progress is judged by measuring the acid value of the system. When the acid value drops to 10%-20% of the initial value, the reaction is considered to be basically complete, yielding the hyperbranched crude polyester product. The reaction time is usually 6-12 hours. The AB2 type monomer is 2,2-dimethylolpropionic acid, the polyol is pentaerythritol, and the catalyst is p-toluenesulfonic acid. The molar ratio of 2,2-dimethylolpropionic acid to pentaerythritol is 6:1, and the mass of p-toluenesulfonic acid is 1.2% of the sum of the masses of 2,2-dimethylolpropionic acid and pentaerythritol. Steps 1-2: Treatment of crude hyperbranched polyester product. After the polymerization reaction is complete, wait for the system temperature to cool to room temperature, dissolve the crude hyperbranched polyester product in tetrahydrofuran at 5-10 times its mass, and then purify it by precipitation. Add excess petroleum ether to the tetrahydrofuran solution containing the dissolved crude hyperbranched polyester product to precipitate the hyperbranched polyester. After filtration, vacuum dry the hyperbranched polyester precipitate at 40-60℃ for 8-12 hours to obtain hyperbranched polyester.

[0021] (II) Preparation of Fluorinated Acrylate Copolymers Step 2-1: Monomer mixing. Add dodecyl fluoroheptyl methacrylate, butyl acrylate, and azobisisobutyronitrile (AIBN) to a reaction vessel equipped with a stirrer, thermometer, and condenser. Add an appropriate amount of toluene as a solvent. The molar ratio of dodecyl fluoroheptyl methacrylate to butyl acrylate is 1-3:7-9, and the mass of AIBN is 0.5%-1.5% of the combined mass of dodecyl fluoroheptyl methacrylate and butyl acrylate. The amount of solvent used is 1-2 times the combined mass of dodecyl fluoroheptyl methacrylate and butyl acrylate.

[0022] Step 2-2: Polymerization reaction. Under nitrogen protection, the reaction system from Step 2-1 is gradually heated to 60-80℃. AIBN decomposes to generate free radicals, which initiate the free radical polymerization of dodecafluoroheptyl methacrylate and butyl acrylate. During the reaction, stirring is continuous, and the reaction time is 4-8 hours to obtain the reaction solution. The molecular weight and molecular weight distribution of the polymer in the reaction solution are monitored by gel permeation chromatography (GPC) to ensure that the expected parameters are met.

[0023] Step 2-3: Reaction solution treatment. After the polymerization reaction is completed, the reaction solution obtained in Step 2-2 is cooled to room temperature, and toluene is removed by vacuum distillation to obtain the crude product of the fluorinated acrylate copolymer. Then, the crude product is dissolved in chloroform and dialyzed through a dialysis bag (molecular weight cutoff of 5000-10000) for 24-48 hours to remove unreacted monomers and small molecule impurities such as AIBN. Finally, the dialyzed solution is vacuum dried at 40-60℃ to obtain the fluorinated acrylate copolymer.

[0024] Example 1 A graphene conductive paste based on a core-shell structured dispersant comprises the following components: 2.45 parts by weight of graphene, 5 parts by weight of carbon black, 1.25 parts by weight of a core-shell structured dispersant, 17 parts by weight of PVDF binder, 1.25 parts by weight of dibutyl phthalate, and 73.05 parts by weight of N-methylpyrrolidone. The core-shell structured dispersant comprises a hyperbranched polyester core and a fluorinated acrylate copolymer shell, the hyperbranched polyester and the fluorinated acrylate copolymer forming a core-shell structure through chemical bonding. The molecular weight of the hyperbranched polyester is 20,000-100,000 g / mol, and the molecular weight of the fluorinated acrylate copolymer is 30,000-70,000 g / mol. The viscosity of the graphene conductive paste is 3,000-5,000 mPa·s. The preparation method of the core-shell structured dispersant is as follows: Step (1): Double bond modification of hyperbranched polyester was carried out by dissolving hyperbranched polyester in dichloromethane at a mass of 5 times its mass, adding methacryloyl chloride and triethylamine, and controlling the mass ratio of hyperbranched polyester, methacryloyl chloride and triethylamine at 1:2:1.5. The reaction was carried out at room temperature for 12 hours. After the reaction was completed, triethylamine hydrochloride was removed by washing with water and separation, and dichloromethane was removed by vacuum distillation to obtain double bond modified hyperbranched polyester.

[0025] Step (2): Add the double-bond modified hyperbranched polyester and the fluorinated acrylate copolymer to tetrahydrofuran and stir until homogeneous to form a reactant solution. The mass ratio of the double-bond modified hyperbranched polyester to the fluorinated acrylate copolymer is 3:7, and the mass of tetrahydrofuran is 5 times the sum of the masses of the double-bond modified hyperbranched polyester and the fluorinated acrylate copolymer.

[0026] Step (3): Benzoyl peroxide was added to the reactant solution, and the mixture was heated to 80 °C and reacted for 12 hours under nitrogen protection to obtain a reaction solution containing a core-shell structured dispersant. The reaction solution containing the core-shell structured dispersant was cooled to room temperature and purified by precipitation. Excess methanol was added to the reaction solution containing the core-shell structured dispersant to precipitate the dispersant. After filtration, the precipitate was vacuum dried at 60 °C for 12 hours to obtain the core-shell structured dispersant. The mass of benzoyl peroxide was 1.0% of the combined mass of the double-bond modified hyperbranched polyester and the fluorinated acrylate copolymer.

[0027] A method for preparing graphene conductive paste based on a core-shell structured dispersant includes the following steps: Step 1: Prepare the mixture. First, add 73.05 parts by weight of N-methylpyrrolidone to the reactor. Then, add 1.25 parts by weight of dibutyl phthalate and 17 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the dibutyl phthalate and PVDF binder are completely dissolved to obtain a homogeneous mixture.

[0028] Step 2: Base material mixing. Add 2.45 parts by weight of graphene and 2.5 parts by weight of carbon black to the mixture, and stir at 600 rpm for 20 minutes at 65°C to obtain a conductive mixture. The graphene sheets have a diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0029] Step 3: After the conductive mixture cools to 25°C, add 1.25 parts by weight of core-shell structure dispersant, and then disperse it using 200W ultrasonic waves for 30 minutes at an ultrasonic frequency of 40kHz to obtain the dispersion.

[0030] Step 4: Homogenization and Adjustment. Homogenize the dispersion for 10 minutes using a high-shear homogenizer at 11,000 rpm, monitoring the viscosity of the dispersion in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized dispersion to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 ), to obtain graphene conductive paste.

[0031] The stability of the graphene conductive paste was tested using the following methods: the graphene conductive paste was sealed and stored at 25°C, and the conductivity was measured to be 1480 S / cm using the four-probe method. The particle size change rate of the agglomerates in the graphene conductive paste after 48 hours of sealed storage was determined to be 8% using a laser particle size analyzer. The viscosity change rates of the graphene conductive paste after 48 hours and 7 days of sealed storage were measured to be 12% and 25% respectively using a rotational rheometer.

[0032] Example 2 A graphene conductive paste based on a core-shell structured dispersant comprises the following components: 2.45 parts by weight of graphene, 2.5 parts by weight of carbon black, 0.2 parts by weight of a core-shell structured dispersant, 17 parts by weight of PVDF binder, 1.25 parts by weight of dibutyl phthalate, and 76.6 parts by weight of N-methylpyrrolidone. The core-shell structured dispersant comprises a hyperbranched polyester core and a fluorinated acrylate copolymer shell, the hyperbranched polyester and the fluorinated acrylate copolymer forming a core-shell structure through chemical bonding. The molecular weight of the hyperbranched polyester is 20,000-100,000 g / mol, and the molecular weight of the fluorinated acrylate copolymer is 30,000-70,000 g / mol. The viscosity of the graphene conductive paste is 3,000-5,000 mPa·s. The preparation method of the core-shell structured dispersant is the same as in Example 1.

[0033] A method for preparing graphene conductive paste based on a core-shell structured dispersant includes the following steps: Step 1: Prepare the mixture. First, add 76.6 parts by weight of N-methylpyrrolidone to the reactor. Then, add 1.25 parts by weight of dibutyl phthalate and 17 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the dibutyl phthalate and PVDF binder are completely dissolved to obtain a homogeneous mixture.

[0034] Step 2: Base material mixing. Add 2.45 parts by weight of graphene and 2.5 parts by weight of carbon black to the mixture, and stir at 600 rpm for 20 minutes at 65°C to obtain a conductive mixture. The graphene sheets have a diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0035] Step 3: After the conductive mixture cools to 25°C, add 0.2 parts by weight of core-shell structure dispersant, and then disperse it using 200W ultrasound for 30 minutes at an ultrasound frequency of 40kHz to obtain the dispersion.

[0036] Step 4: Homogenization and Adjustment. Homogenize the dispersion for 10 minutes using a high-shear homogenizer at 11,000 rpm, monitoring the viscosity of the dispersion in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized dispersion to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 ), to obtain graphene conductive paste.

[0037] The stability of the graphene conductive paste was tested using the following methods: the graphene conductive paste was sealed and stored at 25°C. The conductivity was measured to be 1220 S / cm using the four-probe method. The particle size change rate of the agglomerates in the graphene conductive paste after 48 hours of sealed storage was determined to be 13% using a laser particle size analyzer. The viscosity change rates of the graphene conductive paste after 48 hours and 7 days of sealed storage were measured to be 19% and 29%, respectively, using a rotational rheometer.

[0038] Example 3 A graphene conductive paste based on a core-shell structured dispersant comprises the following components: 2.45 parts by weight of graphene, 2.5 parts by weight of carbon black, 2.5 parts by weight of a core-shell structured dispersant, 17 parts by weight of PVDF binder, 1.25 parts by weight of dibutyl phthalate, and 74.3 parts by weight of N-methylpyrrolidone. The core-shell structured dispersant comprises a hyperbranched polyester core and a fluorinated acrylate copolymer shell, the hyperbranched polyester and the fluorinated acrylate copolymer forming a core-shell structure through chemical bonding. The molecular weight of the hyperbranched polyester is 20,000-100,000 g / mol, and the molecular weight of the fluorinated acrylate copolymer is 30,000-70,000 g / mol. The viscosity of the graphene conductive paste is 3,000-5,000 mPa·s. The preparation method of the core-shell structured dispersant is the same as in Example 1.

[0039] A method for preparing graphene conductive paste based on a core-shell structured dispersant includes the following steps: Step 1: Prepare the mixture. First, add 74.3 parts by weight of N-methylpyrrolidone to the reactor. Then, add 1.25 parts by weight of dibutyl phthalate and 17 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the dibutyl phthalate and PVDF binder are completely dissolved to obtain a homogeneous mixture.

[0040] Step 2: Base material mixing. Add 2.45 parts by weight of graphene and 2.5 parts by weight of carbon black to the mixture, and stir at 600 rpm for 20 minutes at 65°C to obtain a conductive mixture. The graphene sheets have a diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0041] Step 3: After the conductive mixture cools to 25°C, add 2.5 parts by weight of core-shell structure dispersant, and then disperse it using 200W ultrasonic waves for 30 minutes at an ultrasonic frequency of 40kHz to obtain the dispersion.

[0042] Step 4: Homogenization and Adjustment. Homogenize the dispersion for 10 minutes using a high-shear homogenizer at 11,000 rpm, monitoring the viscosity of the dispersion in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized dispersion to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 ), to obtain graphene conductive paste.

[0043] The stability of the graphene conductive paste was tested using the following methods: the graphene conductive paste was sealed and stored at 25°C, and the conductivity was measured to be 1350 S / cm using the four-probe method. The particle size change rate of the agglomerates in the graphene conductive paste after 48 hours of sealed storage was determined to be 10% using a laser particle size analyzer. The viscosity change rates of the graphene conductive paste after 48 hours and 7 days of sealed storage were measured to be 14% and 28%, respectively, using a rotational rheometer.

[0044] Comparative Example 1 Comparative Example 1 provides a graphene conductive paste comprising the following components: 2.45 parts by weight of graphene, 5 parts by weight of carbon black, 1.25 parts by weight of polyvinylpyrrolidone (polyvinylpyrrolidone K30 purchased from Shandong Xinxiong Biotechnology Co., Ltd.), 17 parts by weight of PVDF binder, 1.25 parts by weight of dibutyl phthalate, and 73.05 parts by weight of N-methylpyrrolidone.

[0045] The preparation method of the graphene conductive paste in Comparative Example 1 is basically the same as that in Example 1, the main difference being the addition of polyvinylpyrrolidone as a dispersant in step three. The preparation method of the graphene conductive paste in Comparative Example 1 is as follows: Step 1: Prepare the mixture. First, add 73.05 parts by weight of N-methylpyrrolidone to the reactor. Then, add 1.25 parts by weight of dibutyl phthalate and 17 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the dibutyl phthalate and PVDF binder are completely dissolved to obtain a homogeneous mixture.

[0046] Step 2: Base material mixing. Add 2.45 parts by weight of graphene and 2.5 parts by weight of carbon black to the mixture, and stir at 600 rpm for 20 minutes at 65°C to obtain a conductive mixture. The graphene sheets have a diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0047] Step 3: After the conductive mixture cools to 25°C, add 1.25 parts by weight of polyvinylpyrrolidone, and then disperse it using 200W ultrasonic waves for 30 minutes at an ultrasonic frequency of 40kHz to obtain a dispersion.

[0048] Step 4: Homogenization and Adjustment. Homogenize the dispersion for 10 minutes using a high-shear homogenizer at 11,000 rpm, monitoring the viscosity of the dispersion in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized dispersion to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 ), to obtain graphene conductive paste.

[0049] The stability of the graphene conductive paste was tested using the following methods: the graphene conductive paste was sealed and stored at 25°C, and the conductivity was measured to be 1080 S / cm using the four-probe method. The particle size change rate of the agglomerates in the graphene conductive paste after 48 hours of sealed storage was determined to be 21% using a laser particle size analyzer. The viscosity change rates of the graphene conductive paste after 48 hours and 7 days of sealed storage were measured to be 26% and 48%, respectively, using a rotational rheometer.

[0050] Comparative Example 2 Comparative Example 2 provides a graphene conductive paste, which, by weight parts, comprises the following components: 2.45 parts by weight of graphene, 5 parts by weight of carbon black, 1.25 parts by weight of hyperbranched polyester, 17 parts by weight of PVDF binder, 1.25 parts by weight of dibutyl phthalate, and 73.05 parts by weight of N-methylpyrrolidone.

[0051] The preparation method of the graphene conductive paste in Comparative Example 2 is basically the same as that in Example 1, the main difference being the addition of hyperbranched polyester as a dispersant in step three. The preparation method of the graphene conductive paste in Comparative Example 2 is as follows: Step 1: Prepare the mixture. First, add 73.05 parts by weight of N-methylpyrrolidone to the reactor. Then, add 1.25 parts by weight of dibutyl phthalate and 17 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the dibutyl phthalate and PVDF binder are completely dissolved to obtain a homogeneous mixture.

[0052] Step 2: Base material mixing. Add 2.45 parts by weight of graphene and 2.5 parts by weight of carbon black to the mixture, and stir at 600 rpm for 20 minutes at 65°C to obtain a conductive mixture. The graphene sheets have a diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0053] Step 3: After the conductive mixture cools to 25°C, add 1.25 parts by weight of hyperbranched polyester, and then disperse it using 200W ultrasonic waves for 30 minutes at an ultrasonic frequency of 40kHz to obtain a dispersion.

[0054] Step 4: Homogenization and Adjustment. Homogenize the dispersion for 10 minutes using a high-shear homogenizer at 11,000 rpm, monitoring the viscosity of the dispersion in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized dispersion to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 ), to obtain graphene conductive paste.

[0055] The stability of the graphene conductive paste was tested using the following methods: the graphene conductive paste was sealed and stored at 25°C. The conductivity was measured to be 1250 S / cm using the four-probe method. The particle size change rate of the agglomerates in the graphene conductive paste after 48 hours of sealed storage was determined to be 14% using a laser particle size analyzer. The viscosity change rates of the graphene conductive paste after 48 hours and 7 days of sealed storage were measured to be 22% and 39%, respectively, using a rotational rheometer.

[0056] Comparative Example 3 Comparative Example 3 provides a graphene conductive paste comprising the following components: 2.45 parts by weight of graphene, 5 parts by weight of carbon black, 17 parts by weight of PVDF binder, 1.25 parts by weight of dibutyl phthalate, and 74.3 parts by weight of N-methylpyrrolidone.

[0057] The preparation method of the graphene conductive paste in Comparative Example 3 is basically the same as that in Example 1, the main difference being that a dispersant is not added in step three. The preparation method of the graphene conductive paste in Comparative Example 3 is as follows: Step 1: Prepare the mixture. First, add 73.05 parts by weight of N-methylpyrrolidone to the reactor. Then, add 1.25 parts by weight of dibutyl phthalate and 17 parts by weight of PVDF binder to the N-methylpyrrolidone in the reactor. After heating to 65°C, stir at 600 rpm for 30 minutes until the dibutyl phthalate and PVDF binder are completely dissolved to obtain a homogeneous mixture.

[0058] Step 2: Base material mixing. Add 2.45 parts by weight of graphene and 2.5 parts by weight of carbon black to the mixture, and stir at 600 rpm for 20 minutes at 65°C to obtain a conductive mixture. The graphene sheets have a diameter of 5-10 μm and a thickness ≤10 nm; the carbon black is Super P with a specific surface area of ​​62 m². 2 / g.

[0059] Step 3: Homogenization and Adjustment. Homogenize the dispersion for 10 minutes using a high-shear homogenizer at 11,000 rpm, monitoring the viscosity of the dispersion in real time using a Brookfield viscometer. Then, adjust the viscosity of the homogenized dispersion to 4200 mPa·s (at 25°C and a shear rate of 100 s⁻¹). -1 ), to obtain graphene conductive paste.

[0060] The stability of the graphene conductive slurry was tested using the following methods: the graphene conductive slurry was sealed and stored at 25°C. The conductivity was measured to be 1025 S / cm using the four-probe method. The particle size change rate of the agglomerates in the graphene conductive slurry after 48 hours of sealed storage was determined to be 24% using a laser particle size analyzer. The viscosity change rates of the graphene conductive slurry after 48 hours and 7 days of sealed storage were measured to be 32% and 75% respectively using a rotational rheometer.

[0061] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A graphene conductive paste based on a core-shell structured dispersant, characterized in that, It includes the following components: 0.5-5 parts by weight of graphene, 5-10 parts by weight of conductive agent, 0.2-2.5 parts by weight of core-shell structure dispersant, 15-20 parts by weight of PVDF binder, 0.1-1.5 parts by weight of plasticizer, and 61-79.2 parts by weight of diluent.

2. The graphene conductive paste based on a core-shell structured dispersant as described in claim 1, characterized in that, The core-shell structured dispersant comprises a hyperbranched polyester core and a fluorinated acrylate copolymer shell, which are chemically bonded to form the core-shell structure.

3. The graphene conductive paste based on a core-shell structure dispersant as described in claim 2, characterized in that, The molecular weight of hyperbranched polyester is 20,000-100,000 g / mol, and the molecular weight of fluorinated acrylate copolymer is 30,000-70,000 g / mol.

4. The graphene conductive paste based on a core-shell structure dispersant as described in claim 2, characterized in that, The conductive agent is at least one of carbon black or carbon nanotubes; the plasticizer is dibutyl phthalate; and the diluent is N-methylpyrrolidone.

5. A graphene conductive paste based on a core-shell structured dispersant as described in claim 2, characterized in that, The viscosity of the graphene conductive paste is 3000-5000 mPa·s.

6. The graphene conductive paste based on a core-shell structure dispersant as described in claim 3, characterized in that, The core-shell structured dispersant is prepared by reacting hyperbranched polyester with fluorinated acrylate copolymer under the action of an initiator.

7. The graphene conductive paste based on a core-shell structured dispersant as described in claim 6, characterized in that, The preparation method of core-shell structured dispersants is as follows: Step (1): Double bond modification is performed on the hyperbranched polyester to obtain double bond modified hyperbranched polyester; Step (2): Add the double bond modified hyperbranched polyester and fluorinated acrylate copolymer to tetrahydrofuran and stir until homogeneous to form a reactant solution; Step (3): Add an initiator to the reactant solution and heat it to 60-80℃ under nitrogen protection to obtain a reaction solution containing a core-shell structured dispersant. Purify the reaction solution containing the core-shell structured dispersant by precipitation to obtain the core-shell structured dispersant.

8. The graphene conductive paste based on a core-shell structure dispersant as described in claim 7, characterized in that, In step (2), the mass ratio of double bond modified hyperbranched polyester to fluorinated acrylate copolymer is 1-3:7-9; in step (3), the initiator is benzoyl peroxide, the mass of the initiator is 0.5%-1.5% of the total mass of double bond modified hyperbranched polyester and fluorinated acrylate copolymer, and the reaction time is 6-12 hours.

9. A method for preparing a graphene conductive paste as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Prepare the mixture by adding plasticizer and PVDF binder to the diluent in sequence, heating to 65±2℃ and stirring to obtain a uniform mixture; Step 2: Base material mixing. Graphene and conductive agent are added to the mixture and stirred at a constant temperature of 65±2℃ to obtain a conductive mixture. Step 3: Add core-shell structured dispersant. After the conductive mixture cools to room temperature, add the core-shell structured dispersant and then perform ultrasonic dispersion to obtain a dispersion. Step 4: Homogenization control. The dispersion is homogenized and then the viscosity of the homogenized dispersion is adjusted to 3000-5000 mPa·s to obtain graphene conductive slurry.

10. A graphene conductive paste based on a core-shell structured dispersant as described in claim 9, characterized in that, In step one, the stirring speed is 500-600 rpm and the stirring time is 20-40 min; in step two, the stirring speed is 500-600 rpm and the stirring time is 20-40 min; in step three, the ultrasonic dispersion power is 200W and the ultrasonic dispersion time is 30 min; in step four, the homogenizer is used to homogenize at a speed of 10000-12000 rpm for 10 min.