A method for preparing negative electrode slurry and negative electrode slurry

Abstract

The present invention relates to the field of lithium battery technology, and more particularly to a method for preparing a negative electrode slurry and the negative electrode slurry. The method comprises dry-mixing a negative electrode active material, a conductive agent, and a portion of CMC in proportion, stirring and dispersing the mixture; adding deionized water, kneading, and scraping the mixture; adding the remaining CMC, kneading, and scraping the mixture; adding deionized water, stirring and dispersing the mixture to obtain a mixture; defoaming the mixture; and adding SBR in proportion and mixing uniformly to obtain the negative electrode slurry. The preparation method provided by the present invention has the advantage of reducing the coexistence time of mutually exclusive SBR and CMC. The negative electrode slurry prepared by the preparation method has improved blue bleaching, thereby having better uniformity and stronger adhesion.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a preparation method of a negative electrode slurry and the negative electrode slurry. Background Art

[0002] In the lithium battery industry, lithium-ion battery electrode slurry usually includes electrode active materials, conductive agents and binders. Among them, the use of binders can significantly enhance the adhesion between the electrode material and the current collector and improve the processing performance of the slurry. The most commonly used binder choices are CMC (carboxymethyl cellulose) and SBR (polystyrene butadiene copolymer).

[0003] Since the overall performance of lithium batteries is directly and profoundly affected by the characteristics of the slurry, optimizing the slurry preparation process is crucial to improving various battery performances. Currently, many patents have been reported for the preparation of negative electrode slurries using CMC and SBR as binders.

[0004] For example, patent publication number CN117317222A reports a lithium battery negative electrode slurry and its preparation method. The preparation method comprises mixing graphite, a conductive agent, and a first binder (including CMC), adding deionized water to prepare a first slurry; adding a second binder (including CMC) and deionized water to the first slurry to prepare a second slurry; then, under stirring, adding an organic solvent and SBR in sequence, stirring evenly, cooling and defoaming, to obtain the lithium battery negative electrode slurry. For another example, patent publication number CN118039904A reports a lithium ion battery negative electrode slurry and its homogenization process. The homogenization process uses an aqueous system combined with a wet process, including a negative electrode slurry (including CMC) and a dry mix. The negative electrode slurry and the dry mix are then mixed and dispersed in steps, SBR is added to the mixed slurry, stirred and dispersed at a low speed, and vacuumed to remove bubbles to obtain the target slurry.

[0005] Since SBR contains negatively charged carboxyl groups and is mutually exclusive with the carboxyl groups on the surface of CMC, when the two coexist for a long time, the SBR particles float up, causing the slurry to "bleach blue", that is, the solid components in the slurry are unevenly distributed, resulting in inconsistent color of the coating layer. In the above-mentioned slurry preparation process, the process flow is to first add SBR and disperse it at a low speed, and then prepare the required negative electrode slurry through defoaming treatment. Taking into account the slurry parameter test time, the coexistence time of SBR and CMC is about 1.5h, which is very prone to blue bleaching. This blue bleaching slurry will cause uneven concentration distribution of SBR and reduced adhesion after coating, and then stick to the roller during rolling, affecting battery performance. Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for preparing a negative electrode slurry and a negative electrode slurry. The preparation method has the advantage of reducing the coexistence time of mutually exclusive SBR and CMC. The negative electrode slurry prepared by the preparation method has improved blue bleaching phenomenon, thereby having better uniformity and stronger adhesion.

[0007] To achieve the above-mentioned purpose, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a negative electrode slurry, comprising the following steps:

[0009] S1. The negative electrode active material, conductive agent, and part of the CMC are dry mixed in proportion and stirred and dispersed;

[0010] S2. Add deionized water, knead and scrape;

[0011] S3. Add the remaining CMC, knead and scrape;

[0012] S4. Add deionized water, stir and disperse to obtain a mixture;

[0013] S5. Defoaming the mixture;

[0014] S6. Add SBR in proportion and mix evenly to obtain the negative electrode slurry.

[0015] In conventional negative electrode slurry preparation methods, the prolonged coexistence of SBR and CMC can easily cause the slurry to bluish. The present invention improves the bluish bleaching of the slurry by adjusting the production process to reduce the coexistence time of these two mutually exclusive substances, SBR and CMC. Secondly, the present invention adds CMC in batches. Initially, a portion of the CMC is added to initially form a stable colloidal system, which initially wets and disperses the graphite particles. The remaining CMC is then added. This allows for more effective encapsulation and stabilization of the individual particles, building on the already well-dispersed structure and preventing agglomeration.

[0016] Preferably, in step S1, part of the negative electrode active material, the conductive agent, part of the CMC, and the remaining negative electrode active material are added in sequence according to proportion and dry mixed.

[0017] By adding graphite in batches, the distribution of particles during the mixing process can be better controlled to ensure the uniformity of the slurry.

[0018] Preferably, in order to construct a preliminary colloidal system, a smaller amount of CMC is preferably added. Specifically, in step S1, 25% to 35% of the total amount by mass of CMC is added.

[0019] Preferably, in step S1, the revolution speed is 5-15 rpm and the rotation speed is 750-950 rpm.

[0020] Preferably, in step S2, the material is scraped after kneading at a revolution speed of 5-15 rpm for 8-15 minutes.

[0021] Preferably, in step S3, the material is scraped after kneading at a revolution speed of 5-15 rpm for 45-75 minutes.

[0022] Preferably, the step S4 further includes the following steps:

[0023] S4.1. Add deionized water and disperse at a speed of 5-15 rpm and 1200-1400 rpm for 60-80 min.

[0024] S4.2 Add deionized water and disperse at a speed of 5-15 rpm and 800-1000 rpm for 20-40 minutes;

[0025] The mass of the deionized water added in step S4.1 is greater than the mass of the deionized water added in step S4.2.

[0026] By adding water in stages, the slurry can achieve the ideal fluidity and stability. First, add a large amount of deionized water to achieve the initial dispersion of the slurry and form a relatively uniform slurry base. After the initial dispersion of the slurry is completed, adjust the stirring speed to avoid excessive shear force that may damage the material.

[0027] Preferably, in step S5, the defoaming treatment includes stirring defoaming and / or vacuum defoaming.

[0028] Preferably, in step S5, the stirring and defoaming conditions are stirring and defoaming at a speed of 5-15 rpm and 400-600 rpm for 30 minutes.

[0029] Preferably, in step S6, SBR is added to the defoaming mixture under static mixing conditions.

[0030] Since SBR is a polymer material, when using traditional stirring methods, too high a shear speed will cause the SBR to be broken up, resulting in low slurry viscosity, poor stability, and a reduced slurry storage period; too low a stirring speed will cause SBR to be unevenly dispersed in the slurry system, the slurry will be severely bluish, and then cause the roller to stick during the coating, roller pressing and slitting processes.

[0031] The static mixing does not rely on dynamic stirring blades, but promotes material mixing through static elements. Preferably, in step S6, SBR is added to the defoamed mixture through a pipeline mixer.

[0032] Inline mixers utilize static components (such as spiral blades and baffles) fixed within the pipeline to alter the fluid's flow path, achieving mixing through the fluid's own kinetic energy. This method achieves mixing with lower shear forces, reducing the risk of excessive shearing of polymers like SBR, thereby maintaining the appropriate viscosity and stability of the slurry. Furthermore, while traditional stirring and mixing methods require 15 to 30 minutes to disperse SBR, the rapid mixing capabilities of inline mixers allow for quicker dispersion, shortening preparation time while minimizing the risk of prolonged contact between SBR and other components in the slurry.

[0033] Preferably, during the preparation of the negative electrode slurry, the reaction temperature is maintained at no higher than 80°C.

[0034] Preferably, the negative electrode slurry comprises the following components in parts by mass:

[0035] 90~98 parts of negative electrode active material, 0.5~1 parts of conductive agent, 0.3~0.7 parts of CMC, 1.2~2.4 parts of SBR.

[0036] Preferably, the negative electrode active material includes graphite.

[0037] Preferably, the conductive agent includes SP.

[0038] In a second aspect, the present invention further provides a negative electrode slurry prepared according to the above preparation method.

[0039] The beneficial effects of the present invention are:

[0040] 1. In this application, by adjusting the production process, the coexistence time of SBR and CMC, two mutually exclusive substances, is reduced, the blue bleaching of the slurry is improved, and the uniformity and adhesion of the negative electrode slurry are improved.

[0041] 2. In this application, a static mixing method is adopted, which can provide a uniform dispersion environment under low shear force conditions, further improve the blue bleaching phenomenon of the slurry, and save about 15 to 30 minutes in the preparation of each can of slurry, which helps to improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the slurry state of an embodiment of the present invention;

[0043] Figure 2 Schematic diagram of the slurry state of the comparative example of the present invention;

[0044] Figure 3 It is a box plot of the bonding force of the examples of the present invention and the comparative examples. DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0046] The raw materials used in the following examples are all conventional chemicals purchased from the market. Example

[0047] The method for preparing the negative electrode slurry of the present invention comprises the following steps:

[0048] S1. Weigh the materials in a ratio of 97:0.7:0.5:1.8 for artificial graphite: SP: CMC: SBR. Add 50% by weight of graphite, SP, 30% by weight of CMC, and 50% by weight of graphite to a blender. Disperse at a speed of 14 rpm and 850 rpm for 30 minutes, maintaining the temperature below 80°C.

[0049] S2. Add 40% of the total mass ratio of deionized water, control the temperature not higher than 80 ℃, the revolution speed is 14rpm and knead the scraper for 10min;

[0050] S3 was added to the total amount of mass ratio of 70% of CMC, the revolution speed of 14rpm after kneading 60min scraping;

[0051] S4. Add 40% of the total amount by mass of deionized water, disperse at a speed of 14 rpm and 1300 rpm for 70 min, and control the temperature not higher than 80 ° C and the vacuum not higher than -90 Kpa;

[0052] S5. Add 20% of the total amount by mass of deionized water, disperse at a speed of 14 rpm and 900 rpm for 30 min, and control the temperature not higher than 80 ° C and the vacuum not higher than -90Kpa;

[0053] S6. Stir and defoam at a speed of 14 rpm and 500 rpm for 30 min;

[0054] S7. Set the SBR flow rate according to the slurry transfer flow rate and add SBR through the pipeline mixer.

[0055] Comparative Example

[0056] S1. Weigh the materials in a ratio of 97:0.7:0.5:1.8 for artificial graphite: SP: CMC: SBR. Add 50% by weight of graphite, SP, 30% by weight of CMC, and 50% by weight of graphite to a blender. Disperse at a speed of 14 rpm and 850 rpm for 30 minutes, maintaining the temperature below 80°C.

[0057] S2. Add 40% of the total mass ratio of deionized water, control the temperature not higher than 80 ℃, the revolution speed is 14rpm and knead the scraper for 10min;

[0058] S3 was added to the total amount of mass ratio of 70% of CMC, the revolution speed of 14rpm after kneading 60min scraping;

[0059] S4. Add 40% of the total amount by mass of deionized water, disperse at a speed of 14 rpm and 1300 rpm for 70 min, and control the temperature not higher than 80 ° C and the vacuum not higher than -90 Kpa;

[0060] S5. Add 20% of the total amount by mass of deionized water, disperse at a speed of 14 rpm and 900 rpm for 30 min, and control the temperature not higher than 80 ° C and the vacuum not higher than -90Kpa;

[0061] S6. After adding SBR, disperse at a speed of 14 rpm and 900 rpm for 25 minutes, and control the temperature not higher than 80 ° C and the vacuum degree not higher than -90 Kpa;

[0062] S7. Stir and defoam at a speed of 14 rpm and 500 rpm for 30 min.

[0063] Depend on Figure 1 and Figure 2 It can be seen that the blue bleaching area of ​​the embodiment is about 1.5cm 2 The blue bleaching area of ​​the comparative example is about 3.2cm 2 Compared with the comparative example, the blue bleaching area of ​​the negative electrode slurry in the embodiment is significantly reduced, and the blue bleaching phenomenon is significantly improved, which directly reflects that the dispersion of SBR in the slurry is more uniform.

[0064] The slurries obtained in the examples and comparative examples were made into pole pieces and rolled, and 62 groups of samples were taken respectively and their bonding strength was tested to obtain the following: Figure 3 Box plot of the bonding force shown. Figure 3 It can be seen that the bonding strength of the embodiment is significantly improved compared to the comparative example, with the improvement being about 25%.

Claims

1. A method for preparing a negative electrode slurry, characterized in that: The steps include: S1. The negative electrode active material, conductive agent, and part of the CMC are dry mixed in proportion and stirred and dispersed; S2. Add deionized water, knead and scrape; S3. Add the remaining CMC, knead and scrape; S4. Add deionized water, stir and disperse to obtain a mixture; S5. Defoaming the mixture; S6. Under static mixing conditions, add SBR to the defoaming mixture and mix evenly to obtain the negative electrode slurry.

2. The method for preparing the negative electrode slurry according to claim 1, wherein: In the step S1, part of the negative electrode active material, the conductive agent, part of the CMC, and the remaining negative electrode active material are added in sequence according to proportion and dry mixed.

3. The method for preparing the negative electrode slurry according to claim 1, wherein: In the step S1, CMC is added in an amount of 25% to 35% by mass.

4. The method for preparing the negative electrode slurry according to claim 1, wherein: The step S4 further includes the following steps: S4.

1. adding deionized water and dispersing at a speed of 5 to 15 rpm and 1200 to 1400 rpm for 60 to 80 minutes; S4.2 Add deionized water and disperse at a speed of 5-15 rpm and 800-1000 rpm for 20-40 minutes; The mass of the deionized water added in step S4.1 is greater than the mass of the deionized water added in step S4.

2.

5. The method for preparing the negative electrode slurry according to claim 1, wherein: In step S5, the defoaming treatment includes stirring defoaming and / or vacuum defoaming.

6. The method for preparing the negative electrode slurry according to claim 1, wherein: The negative electrode slurry includes the following components in parts by mass: 90-98 parts of negative electrode active material, 0.5-1 parts of conductive agent, 0.3-0.7 parts of CMC, 1.2-2.4 parts of SBR.

7. The method for preparing the negative electrode slurry according to claim 1, wherein: The negative electrode active material includes graphite.

8. The method for preparing negative electrode slurry according to claim 1, wherein: The conductive agent includes SP.

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