Preparation method of negative electrode plate made of graphene composite negative electrode material

Abstract

The invention discloses a preparation method of a graphene composite negative electrode material negative electrode plate. The preparation method comprises the following steps: preparing a glue solution: mixing CMC (Carboxymethyl Cellulose) with deionized water; high-viscosity kneading and stirring: adding the graphene active material, the conductive agent and the glue solution in batches, and performing high-viscosity kneading and stirring; high-speed dispersion: stirring at a high speed to make the slurry fully uniform; a coating process: coating a copper foil with the slurry through an extrusion type coating machine; and pole piece forming: carrying out rolling, slitting and die cutting on the coated pole piece to obtain a negative pole piece with stable performance, by the preparation method of the graphene composite negative pole material negative pole piece, the slurry dispersion uniformity of the graphene composite negative pole material is improved, the discharge performance of a battery is improved, the cycle life of the battery is prolonged, and through a semi-dry stirring process, the graphene composite negative pole material negative pole piece is obtained. The glue solution is added in batches, and a high-kneading and high-viscosity stirring technology is adopted, so that friction and relative movement are generated among materials, the material agglomeration phenomenon is effectively reduced, and uniform dispersion of the slurry is ensured.

Description

Technical Field

[0001] The present invention relates to a method for preparing a negative electrode sheet of a graphene composite negative electrode material, belonging to the technical field of negative electrode sheet preparation. Background Art

[0002] With the rapid development of lithium-ion battery technology, as one of the core components of the battery, the performance of the negative electrode material directly affects key indicators such as the specific capacity, rate performance, and cycle life of the battery. Among the existing negative electrode materials, traditional carbon-based materials such as graphite have good electrical conductivity and stability, but their theoretical specific capacity is only 372 mAh / g, which is difficult to meet the development needs of high-energy-density batteries. Therefore, the research and development of graphene composite negative electrode materials with high specific capacity and good cycle stability has become one of the current research hotspots.

[0003] Currently, the preparation process of the negative electrode material slurry mainly includes two parts: wet stirring and coating process. In the traditional wet stirring process, the materials are mixed under low viscosity conditions. Due to insufficient shear force, it is easy to cause insufficient dispersion of graphene and conductive agents, and the particles are prone to agglomeration. At the same time, the stability of the slurry is poor, and sedimentation and stratification may occur over time. In addition, the existing coating process has limitations in terms of coating speed, baking temperature, and surface density control, resulting in uneven thickness and rough surface of the negative electrode sheet, which cannot meet the production requirements of high-performance batteries.

[0004] Regarding the preparation of graphene composite negative electrode materials, the following main problems currently exist: 1. Uneven slurry dispersion: The high specific surface area and agglomeration tendency of graphene materials in the slurry lead to difficult dispersion, and the traditional low-shear stirring process cannot fully achieve uniform mixing.

[0005] 2. Agglomeration phenomenon of conductive agents: The conductive agent particles are fine and prone to agglomeration during the stirring process, unable to form a uniform conductive network, affecting the electrical conductivity and energy density of the electrode.

[0006] 3. Unstable coating: The slurry viscosity is unstable, resulting in defects such as stripes, particles, or uneven thickness during the coating process, and it is difficult to control the surface density of the negative electrode sheet.

[0007] 4. Poor baking process: The existing coating baking temperature range is narrow, unable to quickly dry the slurry, and at the same time, it is easy to cause cracking or incomplete drying of the negative electrode sheet, affecting subsequent battery assembly and performance.

[0008] 5. Limited battery performance: Due to the above problems, the prepared negative electrode battery has a low specific capacity under high-rate discharge and poor cycle stability, unable to meet the application requirements of high-energy-density batteries.

[0009] Therefore, there is an urgent need for a method for preparing a negative electrode sheet of a graphene composite negative electrode material. Summary of the Invention

[0010] The object of the present invention is to provide a method for preparing a negative electrode sheet of a graphene composite negative electrode material to solve the problems raised in the above-mentioned background technology.

[0011] To achieve the above object, the present invention provides the following technical solution: A method for preparing a negative electrode sheet of a graphene composite negative electrode material, the method for preparing the negative electrode sheet of the graphene composite negative electrode material includes the following steps: Step 1: Mix sodium carboxymethyl cellulose (CMC) and deionized water in a certain proportion and stir for 3 h to make a colloidal solution.

[0012] Step 2: After taking 50% of the required colloidal solution, add the active material (94% - 96%) of the graphene composite negative electrode material, the conductive agent (1% - 3%), and an appropriate amount of deionized water into the stirring tank according to the weight ratio, control the stirring speed at 10 - 20 RPM and the dispersion speed at 500 - 1000 RPM, and perform high-viscosity kneading and stirring for 1.5 - 2 h; Step 3: Then add 50% of the colloidal solution, control the stirring speed at 10 - 20 RPM and the dispersion speed at 1500 - 2000 RPM, and perform high-speed fractionation for 2 - 2.5 h. The slurry temperature is 25 - 50 °C. Perform high-solid-content and high-viscosity kneading and stirring to cause friction and relative movement between the materials, reduce material agglomeration, study an efficient pulping process, and achieve the purpose of uniformly stirring the slurry. Finally, add SBR and stir and mix, control the stirring speed at 15 - 25 RPM and the dispersion speed at 500 - 800 RPM, stir for 0.5 h, measure and adjust the viscosity, the solid content is between 45% - 49%, the viscosity is between 1800 - 3500 mpas, and the slurry passes through a 150-mesh sieve; Step 4: Coat the slurry prepared in Step 3 on a clean and dry copper foil at room temperature with an extrusion coater; the coating speed of the coater is 10 - 30 m / min, and the coating baking temperature can be adjusted at 65 - 120 °C in the front, middle, and rear sections to ensure that the electrode sheet is dry, and the surface density is within the process range of 158 - 164 g / ㎡; Step 5: Place the electrode sheet coated in Step 4 for rolling, slitting, and die-cutting to obtain a negative electrode sheet.

[0013] As a preferred technical solution of the present invention, the conductive agent is conductive carbon black SP.

[0014] As a preferred technical solution of the present invention, the binder is styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC).

[0015] As a preferred technical solution of the present invention, the colloidal solution in Step 1 is added separately.

[0016] As a preferred technical solution of the present invention, the dosage of the adhesion enhancer is 2% to 4% of the total weight of the graphene composite anode material, the conductive agent and the binder.

[0017] As a preferred technical solution of the present invention, the thickness of the copper foil is 6 - 8 μm, the coating speed of the coater is 10 - 30 m / min, and the coating baking temperature can be adjusted between 65 - 120 °C in the front, middle and back sections to ensure the dryness of the electrode sheet. The coating areal density is: 158 - 164 g / ㎡ on both sides.

[0018] As a preferred technical solution of the present invention, the rolling speed of the electrode sheet is 10 - 50 m / min.

[0019] As a preferred technical solution of the present invention, for the anode electrode sheet prepared in step five, the electrode sheet film is cut into square electrode sheets to be used as the anode sheet of the full cell.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of the anode sheet of the graphene composite anode material of the present invention, including the preparation methods of the anode sheet such as ingredient homogenization, coating, and sheet making, improves the slurry dispersion uniformity of the graphene composite anode material, enhances the discharge performance and cycle life of the battery. Through the semi-dry mixing process, the adhesive solution is added in batches, and the high kneading and high viscosity stirring technologies are adopted to generate friction and relative movement between the materials, effectively reducing the material agglomeration phenomenon and ensuring the uniform dispersion of the slurry. At the same time, the high shear force during the high viscosity kneading and stirring process can fully disperse the fine particles, prevent the agglomeration of the conductive agent, form a uniform conductive network, and improve the conductive performance of the anode material. In addition, by optimizing the coating process, controlling the coating speed and baking temperature, it is ensured that the anode sheet is evenly coated, has a smooth surface, is fully dried, and the areal density is stable. Finally, the graphene composite anode material prepared by the present invention has the characteristics of good slurry stability, high coating quality, large specific capacity, long cycle life, excellent rate performance, etc., meeting the requirements of high energy density lithium-ion batteries for anode materials. Description of the Drawings

[0021] Figure 1 Schematic diagram of the anode sheet prepared by the present invention. Detailed Embodiments

[0022] The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0023] Please refer to Figure 1 The present invention provides a method for preparing an anode sheet of a graphene composite anode material: Raw material preparation and batching: The raw materials used include: Graphene material: Graphene with a high specific surface area, good electrical conductivity, and stable structure; Negative electrode active material: Such as artificial graphite, natural graphite, or other carbon materials; Conductive agent: Such as carbon black, conductive carbon nanotubes, etc., which have good electrical conductivity and are easy to disperse; Binder: Select binders such as PVDF (polyvinylidene fluoride) to ensure the adhesion and stability of the materials; Solvent: Such as NMP (N-methylpyrrolidone), etc., as the solvent for the binder to ensure uniform dispersion of the materials; Additive: Auxiliary materials such as dispersants can be added as needed to further improve the stability and dispersibility of the slurry.

[0024] Batching steps: (1) Weigh graphene, active material, conductive agent, binder, and solvent according to the formula ratio; (2) Add part of the solvent into the stirring container to provide a good flow environment for subsequent stirring; (3) Mix the binder and the solvent in proportion to prepare a binder solution; (4) Gradually add graphene and the conductive agent into the stirring container and start stirring and dispersing.

[0025] Semi-dry process high-viscosity stirring and homogenization: In order to reduce material agglomeration and ensure full mixing and dispersion of each component, the present invention uses a semi-dry process and high-viscosity stirring equipment for homogenization.

[0026] Specific steps: (1) Add the binder solution in batches: During the stirring process, add the binder solution to graphene, active material, and conductive agent step by step in a divided manner; (2) Use high-viscosity kneading and stirring: Utilize a stirring equipment with high shear force to cause friction and relative movement between the materials to achieve the effect of uniform dispersion; (3) Disperse the conductive agent with high shear force: The conductive agent particles are small and easy to agglomerate. Through high-shear stirring force, it is fully dispersed to ensure the uniformity of the conductive network; (4) Continuously stir: The homogenization process lasts for a certain period of time until the slurry reaches a uniform and stable state with good fluidity and dispersibility.

[0027] Coating process: (1) Coating equipment: Select a coater and adjust the coating speed to achieve a stable coating effect; (2) Coating process: Pour the prepared slurry into the slurry tank of the coater; uniformly coat the slurry on the current collector (such as copper foil) by means of blade coating or roll coating; control the coating speed within an appropriate range to ensure coating uniformity and surface smoothness.

[0028] (3) Areal density control: Ensure that the areal density of the negative electrode sheet is within the designed range by adjusting the blade gap, coating speed, and slurry concentration.

[0029] Coating and baking: The baking process is used to dry the coated negative electrode sheet, remove the solvent in the slurry, and ensure the drying uniformity of the electrode sheet.

[0030] (1) Baking equipment: Use a multi-stage baking furnace with adjustable temperature; (2) Temperature control: Set the temperatures at the front, middle, and rear sections of the baking furnace between 65°C and 120°C respectively, and ensure stable solvent evaporation and prevent cracks on the surface of the slurry by gradually increasing the temperature; (3) Baking time: Control the baking time according to the coating thickness and baking temperature to ensure that the coating is thoroughly dried; (4) Inspection of drying effect: The surface of the dried negative electrode sheet is smooth and free of particulate matter, meeting the process requirements.

[0031] Sheet making and post-treatment: (1) Roll pressing treatment: Conduct roll pressing treatment on the dried negative electrode sheet to increase the density of the material and optimize the mechanical strength and electrochemical performance of the negative electrode sheet; The roll pressing parameters (such as pressure, speed) need to be adjusted according to the thickness of the negative electrode sheet and the design requirements.

[0032] (2) Cutting and assembly: Cut the roll-pressed negative electrode sheet into electrode sheets that meet the battery design dimensions; assemble the negative electrode sheet with other battery components (such as separator, electrolyte, positive electrode sheet, etc.) into a battery.

[0033] Performance testing and effect verification: Conduct performance testing on the prepared battery, mainly including: (1) Battery discharge performance testing: Test the discharge specific capacity of the battery at different rates to ensure that it has a high specific capacity and excellent rate performance; (2) Cycle life testing: Conduct multiple charge-discharge cycle tests on the battery to evaluate its capacity retention rate and cycle life; (3) Inspection of the surface quality of the negative electrode sheet: Use a microscope or other detection equipment to check the coating uniformity and particle-free condition on the surface of the negative electrode sheet; (4) Areal density stability testing: Verify the stability within the process range by detecting the areal density of the negative electrode sheet at multiple points.

[0034] The preparation method of the negative electrode sheet of the graphene composite negative electrode material, such as ingredient homogenization, coating, and sheet making, improves the homogenization of the graphene composite negative electrode material slurry and enhances the battery discharge performance and cycle life. The graphene composite negative electrode material prepared by the present invention is evenly coated, with a smooth surface and no particles. It has good slurry stability and areal density stability. The battery prepared has a discharge specific capacity greater than 360 mAh / g at a 0.5C rate and greater than 355 mAh / g at a 1C rate. The present invention mainly adds the sizing agent in batches through semi-dry stirring, and uses high kneading and high-viscosity stirring homogenization to generate friction and relative movement between various materials, reducing material agglomeration. It studies an efficient pulping process to achieve the purpose of evenly stirring the slurry. During ultra-high viscosity kneading and stirring, the high shear force can more fully disperse the conductive agent with fine particles that are prone to agglomeration. The coating speed of the coater is 10 - 30 m / min. The coating baking temperature can be adjusted from 65 to 120 °C in the front, middle, and rear sections to ensure the drying of the electrode sheet and the areal density within the process range of 158 - 164 g / m2. The graphene composite negative electrode material has the characteristics of high specific capacity, long cycle life, and good rate performance.

[0035] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art 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 method for preparing a graphene composite negative electrode material negative electrode sheet, characterized in that: The method for preparing a negative electrode sheet of a graphene composite negative electrode material comprises the following steps: Step 1: Mix sodium carboxymethyl cellulose (CMC) and deionized water in proportion and stir for 3 hours to prepare a glue solution; Step 2: After taking 50% of the required glue solution, add the graphene composite negative electrode material active material (94%-96%), conductive agent (1%-3%), and an appropriate amount of deionized water into the stirring tank according to the weight ratio, control the stirring speed to 10-20RPM and the dispersion speed to 500-1000RPM for high viscosity kneading and stirring for 1.5-2h; Step 3: Add 50% of the glue solution and control the stirring speed to 10-20RPM and the dispersion speed to 1500-2000RPM for high-speed fractionation for 2-2.5h. The slurry temperature is 25-50℃. The high solid content and high viscosity are kneaded and stirred to generate friction and relative movement between the materials, reduce material agglomeration, and study the efficient pulping process to achieve the purpose of uniformly stirring the slurry. Finally, add SBR and stir and mix to control the stirring speed to 15-25RPM and the dispersion speed to 500-800RPM. Stir for 0.5h, measure the viscosity and adjust the viscosity. The solid content is between 45% and 49%, the viscosity is between 1800-3500mpas, and the slurry passes through a 150-mesh sieve. Step 4: Apply the slurry prepared in step 3 to the clean and dry copper foil with an extrusion coater at room temperature; the coating speed of the coater is 10-30m / min, and the coating baking temperature is adjustable at 65-120℃ before, during and after the coating to ensure that the electrode is dry and the surface density is within the process range of 158-164g / ㎡; Step 5: Place the electrode sheet coated in step 4 for rolling, slitting and die-cutting to obtain the negative electrode sheet.

2. The method for preparing a graphene composite negative electrode material negative electrode sheet according to claim 1, characterized in that: The conductive agent is conductive carbon black SP.

3. The method for preparing a graphene composite negative electrode material negative electrode sheet according to claim 1, characterized in that: The binder is styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC).

4. The method for preparing a graphene composite negative electrode material negative electrode sheet according to claim 1, characterized in that: The glue solution in step 1 is added separately.

5. The method for preparing a negative electrode sheet of a graphene composite negative electrode material according to claim 1, characterized in that: The amount of the adhesion enhancer is 2% to 4% of the total weight of the graphene composite negative electrode material, the conductive agent and the binder.

6. The method for preparing a graphene composite negative electrode material negative electrode sheet according to claim 1, characterized in that: The copper foil thickness is 6-8um, the coating speed of the coating machine is 10-30 m / min, the coating baking temperature is adjustable at 65-120°C in the front, middle and rear stages to ensure the electrode is dry, and the coating surface density is: 158-164g / ㎡ on both sides.

7. The method for preparing a graphene composite negative electrode material negative electrode sheet according to claim 1, characterized in that: The pole piece rolling speed is 10-50 m / min.

8. The method for preparing a graphene composite negative electrode material negative electrode sheet according to claim 1, characterized in that: The negative electrode sheet prepared in step 5 is cut into square electrode sheets to serve as the negative electrode sheet of the full battery.

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