Negative electrode paste capable of inhibiting viscosity rebound, preparation method of negative electrode paste and lithium ion battery negative electrode

Abstract

The invention belongs to the technical field of preparation of lithium ion battery negative electrode slurry, and particularly relates to negative electrode slurry for inhibiting viscosity rebound, a preparation method of the negative electrode slurry and a lithium ion battery negative electrode. According to the negative electrode slurry provided by the invention, graphite, silicon carbon, conductive carbon black, single-walled carbon nanotubes, polyacrylic acid and butadiene styrene rubber are taken as main raw materials, a step-by-step preparation process of dry mixing, infiltration, kneading, high-speed dispersion and slow stirring is adopted, and the solid content in the kneading stage is accurately controlled at 68-70%; by optimizing the stress history of a slurry system and the rheological property of a multi-phase suspension system, the viscosity rebound is remarkably inhibited. Test results show that the prepared negative electrode slurry shows excellent viscosity rebound inhibition characteristics under the working conditions of static standing and dynamic stirring, the problem of coating instability easily caused by viscosity rebound of the negative electrode slurry can be effectively solved, and technical support is provided for improving the preparation yield and performance stability of the lithium ion battery negative electrode plate.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode slurry preparation technology, specifically relating to an anode slurry that suppresses viscosity rebound, its preparation method, and a lithium-ion battery anode. Background Technology

[0002] As the core component for energy storage and release in lithium-ion batteries, the performance of the anode directly determines the battery's cycle life, rate performance, and energy density. Therefore, related preparation technologies have always been a key research focus in this field. Lithium-ion battery anode sheets are generally prepared using a wet coating process. This process requires uniformly mixing the anode material, conductive agent, binder, and other components to form a stable and homogeneous slurry system. The slurry is then uniformly coated onto the surface of copper foil using coating equipment to obtain anode sheets with consistent areal density. The viscosity stability of the slurry system is a crucial prerequisite for ensuring the smooth implementation of the coating process and the uniformity of the anode sheet performance. Abnormal fluctuations in slurry viscosity will directly affect the stability of the coating, and in severe cases, may even lead to the scrapping of a large number of electrode sheets.

[0003] To improve the dispersion of components in negative electrode slurry and avoid performance degradation caused by particle agglomeration, the industry currently employs a dry kneading process for slurry preparation. The core principle of this process is to utilize high shear forces to achieve sufficient dissociation and uniform dispersion of the negative electrode material (such as graphite) and conductive agent particles, thereby significantly optimizing the slurry dispersion quality. Therefore, it has been widely used in the field of negative electrode slurry preparation.

[0004] However, negative electrode slurry is essentially a multiphase suspension system and exhibits typical non-Newtonian fluid characteristics. During the static storage after homogenization or in subsequent processing steps, the slurry inevitably experiences a viscosity rebound, known in the industry as viscosity bounce. Viscosity bounce can be categorized into static and dynamic viscosity bounce, with the static viscosity bounce being particularly significant. This viscosity bounce problem greatly increases the difficulty of controlling the coating process, easily causing process defects such as coating die clogging and coating thickness deviations. It also leads to a significant decrease in the uniformity of the final negative electrode sheet density, severely restricting the large-scale production and product performance stability of lithium-ion batteries.

[0005] In recent years, with the deepening research on the rheological properties of negative electrode slurry systems, the industry has gradually recognized that viscoelastic fluids such as negative electrode slurries possess certain memory characteristics. Their viscosity rebound is, to some extent, a mapping of the stress history and is closely related to the composition and preparation process of the slurry. However, to date, a complete theoretical system regarding the mechanism of viscosity rebound has not yet been formed, and exploring technical solutions to effectively suppress viscosity rebound in negative electrode slurries remains an important research topic in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a negative electrode slurry that suppresses viscosity rebound, its preparation method, and a lithium-ion battery negative electrode. The purpose of this invention is to improve the viscosity stability of the negative electrode slurry, thereby better ensuring the smooth implementation of the coating process and the stable performance of the negative electrode sheet.

[0007] The first aspect of this invention provides a method for preparing a negative electrode slurry that suppresses viscosity rebound, comprising the following steps: (1) Dry mixing stage: Graphite, silicon carbide and conductive agent are dry mixed; (2) Impregnation stage: Add the first part of the polyacrylic acid (PAA) aqueous solution to the dry-mixed powder for impregnation; (3) High solids kneading stage: Continue to add the second part of the polyacrylic acid aqueous solution and deionized water to the system for kneading. By adjusting the amount of deionized water added, the solids content of the kneading system is controlled at 68%~70%; (4) High-speed dispersion stage: Add the remaining amount of polyacrylic acid aqueous solution and single-walled carbon nanotubes (SWCNTs) for high-speed shear dispersion; (5) Slow stirring stage: Add styrene-butadiene rubber (SBR) and stir at low speed until uniform to obtain negative electrode slurry.

[0008] As a further optimization of the above-mentioned negative electrode slurry preparation method, the raw materials of the negative electrode slurry, by mass parts, include: Graphite: 80-90 parts; Silicon-carbon: 8-15 parts; Conductive agent: 0.3~0.8 parts; Aqueous solution of polyacrylic acid (PAA) with a mass fraction of 4%~8%: 1.5~3 parts; Single-walled carbon nanotubes (SWCNTs): 0.1~0.5 parts; Styrene-butadiene rubber (SBR): 1.0~2.0 parts.

[0009] As a further optimization of the above-mentioned negative electrode slurry preparation method, the conductive agent is superconducting carbon black (SuperP).

[0010] As a further optimization of the above-mentioned negative electrode slurry preparation method, the dry mixing time in step (1) is 10~25 min.

[0011] As a further optimization of the above-mentioned negative electrode slurry preparation method, in step (2), the mass percentage of the first part of the polyacrylic acid aqueous solution is 15%~25% of its total amount; the wetting time is 15~30 min.

[0012] As a further optimization of the above-mentioned negative electrode slurry preparation method, in step (3), the mass percentage of the polyacrylic acid aqueous solution in the second part is 30%~40% of the total amount used; the kneading time is 40~80 min.

[0013] As a further optimization of the above-mentioned negative electrode slurry preparation method, in step (4), the high-speed shear dispersion time is 90~150min; the high-speed dispersion linear velocity is controlled at 12-15m / s.

[0014] As a further optimization of the above-mentioned negative electrode slurry preparation method, in step (5), the low-speed stirring time is 20~60min; the low-speed stirring linear speed does not exceed 2m / s.

[0015] The second aspect of the present invention is to provide a negative electrode slurry, which is prepared by any of the above preparation methods; the negative electrode slurry is a multiphase suspension system and has low viscosity rebound characteristics, wherein the viscosity rebound change does not exceed 18000 mPa·s under the condition of standing at room temperature for 24 h; and the viscosity rebound change does not exceed 1000 mPa·s under the condition of dynamic stirring at 10 r / min for 24 h.

[0016] A third aspect of the present invention is to provide a negative electrode for a lithium-ion battery, comprising a negative electrode current collector and a negative electrode film layer coated on at least one side of the negative electrode current collector, wherein the negative electrode film layer is formed by coating and drying the aforementioned negative electrode slurry; the negative electrode current collector is a copper foil.

[0017] Beneficial effects The negative electrode slurry provided by this invention uses graphite, silicon carbide, conductive carbon black, single-walled carbon nanotubes, polyacrylic acid, and styrene-butadiene rubber as main raw materials. It is prepared using a process of "dry mixing-impregnation-kneading-high-speed dispersion-slow stirring." By precisely controlling the solid-liquid ratio during the kneading stage, the kneading solid content is controlled at 68%~70%, improving the stress history of the slurry system and the rheological properties of the multiphase suspension system. This significantly suppresses the viscosity rebound phenomenon of the negative electrode slurry during storage and subsequent processing. Whether under static storage conditions or dynamic stirring production conditions, this negative electrode slurry exhibits excellent viscosity rebound suppression characteristics, effectively avoiding a sharp increase or runaway rebound in viscosity. This effectively reduces the risk of coating failure caused by unstable slurry viscosity, providing technical support for the stable preparation of lithium-ion battery negative electrode sheets and possessing good industrial application value. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of the present invention.

[0019] Figure 2 The graphs show the static viscosity changes of Example 1 and Comparative Example 1.

[0020] Figure 3This is a graph showing the static viscosity change in Example 2.

[0021] Figure 4 This is a graph showing the static viscosity change in Example 3.

[0022] Figure 5 This is a graph showing the static viscosity change of Comparative Example 1.

[0023] Figure 6 The graphs show the dynamic viscosity changes of Example 1 and Comparative Example 1. Detailed Implementation

[0024] This invention provides a lithium-ion battery anode slurry and its preparation method. The lithium-ion battery anode slurry of this invention, by weight, comprises the following raw materials: 80-90 parts graphite, 8-15 parts silicon-carbon, 0.3-0.8 parts superconducting carbon black (Super P), 1.5-3 parts a 4%-8% (w / w) aqueous solution of polyacrylic acid (PAA), 0.1-0.5 parts single-walled carbon nanotubes (SWCNTs), 1.0-2.0 parts styrene-butadiene rubber (SBR), and deionized water for controlling the solid content during the kneading stage.

[0025] The specific preparation process of the negative electrode slurry of the present invention is as follows: Figure 1 As shown, it includes the following steps: (1) Dry mixing stage The weighed graphite, silicon carbide, and superconducting carbon black are dry-mixed for 10-25 minutes. This step ensures that the powder materials achieve a microscopically uniform distribution in a dry state.

[0026] (2) Immersion stage Add 15%-25% of the total amount of polyacrylic acid aqueous solution to the dry-mixed powder and impregnate for 15-30 minutes. This stage aims to initially wet the surface of the active material with the polymer binder, preparing it for subsequent kneading and shearing.

[0027] (3) High solids content kneading stage Add 30%-40% of the total volume of polyacrylic acid aqueous solution to the system, followed by an appropriate amount of deionized water, and knead for 40-80 minutes. During this stage, the solid content of the system must be strictly controlled between 68% and 70% by adjusting the amount of water added. Experiments show that this material system is sensitive to kneading solid content; a specific range of kneading solid content is a crucial factor in forming a stable rheological network within the slurry and is also key to suppressing subsequent viscosity rebound.

[0028] (4) High-speed dispersion stage Add the remaining amount of polyacrylic acid aqueous solution, then add single-walled carbon nanotubes, and turn on the high-speed dispersion disk for high-speed shearing, with a dispersion time of 90-150 minutes. This stage utilizes long-chain single-walled carbon nanotubes to construct a conductive network and further reduce the slurry particle size.

[0029] (5) Slow stirring stage Finally, add styrene-butadiene rubber (SBR) and stir slowly at low speed for 20-60 minutes to obtain the final negative electrode slurry.

[0030] The present invention is further illustrated below with specific embodiments. These embodiments are exemplary and intended to illustrate the problem and explain the present invention, and are not intended to be limiting.

[0031] Example 1 95.75 parts of the main material and 0.5 parts of SP were dry-mixed. The main material included 85 parts of graphite and 10.75 parts of silicon carbide (SO310 type silicon carbide composite material produced by Lanxi Zhide New Energy Materials Co., Ltd., hereinafter the same). The mixing time was 15 min. 20% of the PAA aqueous solution was added and soaked for 20 min. Then, 30% of the PAA aqueous solution was added and kneaded. During kneading, an appropriate amount of water was added to make the solid content 69.7%. Kneading was carried out for 50 min. Then, the remaining PAA aqueous solution and 0.25 parts of SWCNT were added and dispersed at high speed for 120 min. Finally, 1.5 parts of SBR were added and slowly stirred to obtain a negative electrode slurry. In this embodiment, the mass fraction of PAA in the PAA aqueous solution was 6%, and the total amount of PAA aqueous solution was 2 parts.

[0032] Example 2 95.75 parts of the main material and 0.5 parts of SP were dry-mixed. The main material included 85 parts of graphite and 10.75 parts of silicon carbide. The mixing time was 15 min. A 20% PAA aqueous solution was added and the mixture was soaked for 20 min. Then, a 35% PAA aqueous solution was added and kneaded, adding an appropriate amount of water during kneading to achieve a solid content of 68.5%. Kneading was continued for 50 min. The remaining PAA aqueous solution and 0.25 parts of SWCNT were then added and dispersed at high speed for 120 min. Finally, 1.5 parts of SBR were added and the mixture was slowly stirred to obtain a negative electrode slurry. In this embodiment, the mass fraction of PAA in the PAA aqueous solution was 6%, and the total amount of PAA aqueous solution used was 2 parts.

[0033] Example 3 95.75 parts of the main material and 0.5 parts of SP were dry-mixed. The main material included 85 parts of graphite and 10.75 parts of silicon carbide. The mixing time was 15 min. A 20% PAA aqueous solution was added and the mixture was soaked for 20 min. Then, a 38% PAA aqueous solution was added and kneaded, adding an appropriate amount of water during kneading to achieve a solid content of 68%. Kneading was continued for 50 min. The remaining PAA aqueous solution and 0.25 parts of SWCNT were then added and dispersed at high speed for 120 min. Finally, 1.5 parts of SBR were added and the mixture was slowly stirred to obtain a negative electrode slurry. In this embodiment, the mass fraction of PAA in the PAA aqueous solution was 6%, and the total amount of PAA aqueous solution used was 2 parts.

[0034] Comparative Example 1 95.75 parts of the main material and 0.5 parts of SP were dry-mixed. The main material included 85 parts of graphite and 10.75 parts of silicon carbide. The mixing time was 15 min. 20% of the PAA aqueous solution was added and the mixture was soaked for 20 min. Then, 40% of the PAA aqueous solution was added and kneaded, adding an appropriate amount of water during kneading to achieve a solid content of 67.7%. Kneading was continued for 50 min. The remaining PAA aqueous solution and 0.25 parts of SWCNT were then added and dispersed at high speed for 120 min. Finally, 1.5 parts of SBR were added and the mixture was slowly stirred to obtain a negative electrode slurry. In this comparative example, the mass fraction of PAA in the PAA aqueous solution was 6%, and the total amount of PAA aqueous solution used was 2 parts.

[0035] Comparative Example 2 95.75 parts of the main material and 0.5 parts of SP were dry-mixed. The main material included 85 parts of graphite and 10.75 parts of silicon carbide. The mixing time was 15 min. A 20% PAA aqueous solution was added and the mixture was soaked for 20 min. Then, a 25% PAA aqueous solution was added and kneaded, adding an appropriate amount of water during kneading to achieve a solid content of 70.7%. Kneading was continued for 50 min. The remaining PAA aqueous solution and 0.25 parts of SWCNT were then added and dispersed at high speed for 120 min. Finally, 1.5 parts of SBR were added and the mixture was slowly stirred to obtain a negative electrode slurry. In this comparative example, the mass fraction of PAA in the PAA aqueous solution was 6%, and the total amount of PAA aqueous solution used was 2 parts.

[0036] Test case The static viscosity test method is as follows: After homogenization, take 500 mL of slurry and place it in a clean beaker. Let it stand at room temperature and use a digital viscometer to test the viscosity every 2 hours. Continue testing for 24 hours and record the viscosity change data.

[0037] The 24-hour static viscosity data for Example 1 and Comparative Example 1 are as follows: Figure 2 As shown, the 24-hour static viscosity data for Example 2 are as follows: Figure 3 As shown, the 24-hour static viscosity data for Example 3 are as follows: Figure 3 As shown, the 24-hour static viscosity data for Comparative Example 2 are as follows: Figure 4 As shown in the figure, the standing viscosity of Comparative Example 1 (kneading solids content 67.7%) increased sharply from an initial 5410 mPa·s to 46565 mPa·s after 24 hours, with a viscosity rebound change of 41155 mPa·s. The curve shows a steep upward trend, indicating that the viscosity rebound rate of the slurry is fast and the stability is extremely poor at low kneading solids content. The standing viscosity rebound of Comparative Example 2 (kneading solids content 70.7%) was the most drastic, rising sharply from an initial 5350 mPa·s to 127745 mPa·s after 24 hours, with a viscosity rebound change as high as 122395 mPa·s. The slope of the curve was significantly higher than that of other groups, indicating that excessively high kneading solids content will lead to uncontrolled viscosity rebound of the slurry, seriously affecting storage and coating stability. The standing viscosity of Example 1 (kneaded solids content 69.7%) gradually increased from an initial 5159 mPa·s to 14989 mPa·s, with a viscosity rebound change of only 9830 mPa·s, which is only 23.9% of that of Comparative Example 1 and 8.0% of that of Comparative Example 2. The viscosity remained low and increased slowly with minimal fluctuations, making it the group with the best viscosity stability. The standing viscosity of Examples 2 (kneaded solids content 68.5%) and 3 (kneaded solids content 68%) increased from an initial 5691 mPa·s and 5544 mPa·s to 21550 mPa·s and 23350 mPa·s, respectively, with viscosity rebound changes of 15859 mPa·s and 17806 mPa·s, which are only 38.5%~43.3% of that of Comparative Example 1 and 12.9%~14.5% of that of Comparative Example 2. The viscosity showed a moderate upward trend, and the stability was significantly better than that of the comparative examples.

[0038] Analysis of the kneading solids content range shows that the slurry system of the present invention is highly sensitive to solids content. When the kneading solids content is controlled within the range of 68% to 70%, the viscosity rebound rate of the negative electrode slurry can be effectively reduced. If the solids content is lower than 68% (as in Comparative Example 1) or higher than 70% (as in Comparative Example 2), the viscosity rebound of the slurry will be abruptly aggravated. This indicates that the present invention can significantly optimize the stress history of the slurry by designing the system composition and kneading solids content, thereby significantly suppressing viscosity rebound.

[0039] Example 1 and Comparative Example 1 were selected for dynamic viscosity testing. The testing method was as follows: After homogenization, the slurry was placed in a homogenizing tank for vacuum preservation, and the slurry was continuously stirred at a speed of 10 r / min. Every 2 hours, 500 mL of slurry was taken and transferred to a beaker, and the viscosity was tested using a digital viscometer. The test was continued for 24 hours, and the viscosity change trend was recorded.

[0040] The dynamic viscosity of Comparative Example 1 showed a fluctuating upward trend, with a change of 2681 mPa·s over 24 hours. The curve showed a significant increase in the later stages, indicating that the viscosity rebound was still prominent in dynamic scenarios with low kneading solids content. The dynamic viscosity of Example 1 showed a smooth and fluctuating upward trend, with small fluctuations and overall stability. The change over 24 hours was only 931 mPa·s, which was only 34.7% of that of Comparative Example 1. This proves that the process of the present invention can also effectively maintain viscosity stability in dynamic stirring production scenarios, significantly suppressing viscosity increase and thus reducing the risk of coating failure.

[0041] In summary, the negative electrode slurry prepared by this invention uses graphite, silicon carbide, conductive carbon black, single-walled carbon nanotubes, polyacrylic acid, and styrene-butadiene rubber as main raw materials. By precisely controlling the solid-liquid ratio during the kneading stage, the kneading solid content is controlled at 68%~70%. Combined with a step-by-step preparation process of "dry mixing-wetting-kneading-high-speed dispersion-slow stirring," effective suppression of viscosity rebound in the negative electrode slurry is achieved. Test results show that the negative electrode slurry prepared using the technical solution of this invention exhibits significantly suppressed viscosity rebound under both static and dynamic stirring conditions. Example 1 demonstrates the best viscosity stability, with its 24-hour static viscosity rebound change being only 23.9% of Comparative Example 1 and 8.0% of Comparative Example 2, and its dynamic viscosity rebound change being only 34.7% of Comparative Example 1. This invention, by optimizing the stress history of the slurry system, improves the rheological properties of the multiphase suspension system, effectively solving the problem of viscosity rebound in negative electrode slurry leading to coating instability, and providing technical support for improving the preparation yield and performance stability of lithium-ion battery negative electrode sheets.

[0042] The above embodiments are exemplary and are intended to illustrate the technical concept and features of the present invention, so that those skilled in the art can understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a negative electrode slurry that suppresses viscosity rebound, characterized in that, Includes the following steps: (1) Dry mixing stage: Graphite, silicon carbide and conductive agent are dry mixed; (2) Impregnation stage: Add the first part of the polyacrylic acid (PAA) aqueous solution to the dry-mixed powder for impregnation; (3) High solids kneading stage: Continue to add the second part of the polyacrylic acid aqueous solution and deionized water to the system for kneading. By adjusting the amount of deionized water added, the solids content of the kneading system is controlled at 68%~70%; (4) High-speed dispersion stage: Add the remaining amount of polyacrylic acid aqueous solution and single-walled carbon nanotubes for high-speed shear dispersion; (5) Slow stirring stage: Add styrene-butadiene rubber and stir at low speed until uniform to obtain negative electrode slurry.

2. The preparation method according to claim 1, characterized in that, The raw materials of the negative electrode slurry, by mass, include: Graphite: 80-90 parts; Silicon-carbon: 8-15 parts; Conductive agent: 0.3~0.8 parts; A 4%~8% (w / w) aqueous solution of polyacrylic acid: 1.5~3 parts; Single-walled carbon nanotubes: 0.1~0.5 parts; Styrene-butadiene rubber: 1.0~2.0 parts.

3. The preparation method according to claim 2, characterized in that, The conductive agent is superconducting carbon black.

4. The preparation method according to claim 1, characterized in that, The dry mixing time in step (1) is 10~25 min.

5. The preparation method according to claim 1, characterized in that, In step (2), the mass percentage of the first part of the polyacrylic acid aqueous solution is 15% to 25% of its total amount; the soaking time is 15 to 30 minutes.

6. The preparation method according to claim 1, characterized in that, In step (3), the polyacrylic acid aqueous solution in the second part accounts for 30% to 40% of the total mass of the product; the kneading time is 40 to 80 minutes.

7. The preparation method according to claim 1, characterized in that, In step (4), the high-speed shear dispersion time is 90~150min; the high-speed dispersion linear velocity is 12-15m / s.

8. The preparation method according to claim 1, characterized in that, In step (5), the low-speed stirring time is 20~60min; the low-speed stirring linear speed does not exceed 2m / s.

9. A negative electrode slurry, characterized in that, The negative electrode slurry is prepared by any one of the preparation methods described in claims 1-8; the negative electrode slurry is a multiphase suspension system and has low viscosity rebound characteristics. Under the condition of standing at room temperature for 24 hours, the viscosity rebound change does not exceed 18000 mPa·s; under the condition of dynamic stirring at 10 r / min for 24 hours, the viscosity rebound change does not exceed 1000 mPa·s.

10. A lithium-ion battery negative, characterized in that, It includes a negative electrode current collector and a negative electrode film layer coated on at least one side of the negative electrode current collector, wherein the negative electrode film layer is made by coating and drying the negative electrode slurry according to claim 9; the negative electrode current collector is a copper foil.

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