Preparation method and application of lithium ion battery positive electrode slurry dispersing agent

Abstract

The invention discloses a preparation method and application of a lithium ion battery positive electrode slurry dispersant, and belongs to the technical field of lithium ion batteries. The method comprises the following steps: adding N-ethyl pyrrolidone, olefine acid ester, an initiator and a solvent into a container for polymerization reaction; cooling to room temperature to further promote complete precipitation of the polymer; separating the mixed solution from a reaction mixture in a direct filtering manner; a proper amount of pure solvent is used for repeated washing and precipitation; placing the washed polymer precipitate in a vacuum drying box; and carrying out vacuum drying treatment at a proper temperature to obtain the dispersing agent. The preparation method is simple, the polymer block copolymer dispersing agent is added into positive electrode slurry, the dispersity and stability of the slurry can be improved, the solid content ratio of the slurry can be remarkably increased, the amplification is between 2.5% and 4%, the stability of the slurry within 24 hours is enhanced, and the long-time uniformity and dispersity of the slurry are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a preparation method and application of a dispersant for a positive electrode slurry of a lithium-ion battery. Background Art

[0002] In the modern lithium-ion battery manufacturing process, the preparation of the positive electrode slurry is crucial. The positive electrode slurry is composed of various materials such as positive electrode active materials, conductive agents, binders, and solvents. These materials need to be fully mixed and dispersed to ensure the uniformity and stability of the slurry. The performance of lithium-ion batteries depends to a large extent on the uniformity and stability of the electrode materials. Therefore, the dispersant plays a key role in this process. There are various types of slurry dispersants, mainly including ionic dispersants, non-ionic dispersants, and polymer dispersants, etc. Among them, polymer dispersants, due to their long molecular chains and complex structures, can effectively wrap the particle surface to form a protective layer, achieving a more stable dispersion effect. Polymer dispersants can also further prevent particle agglomeration through steric hindrance effects and electrostatic repulsion, improving the fluidity and coating properties of the slurry. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem of uneven dispersion of the positive electrode slurry, and to provide a preparation method and application of a dispersant for a positive electrode slurry of a lithium-ion battery. This dispersant not only has excellent dispersion ability for the positive electrode slurry, but also the lithium battery prepared with its positive electrode slurry exhibits higher specific capacity and cycle performance. The preparation method of the present invention has simple steps and convenient operation, and the prepared polymer has high purity and stable performance. At the same time, the prepared positive electrode slurry has good dispersion stability.

[0004] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0005] A preparation method of a dispersant for a positive electrode slurry of a lithium-ion battery, the method is as follows:

[0006] Step 1: Preparation of polymer: Add N-ethyl pyrrolidine (NVP), acrylate, initiator, and solvent into a container for polymerization reaction;

[0007] Step 2: Separation, washing, and drying of the polymer: By cooling to room temperature, further promote the complete precipitation of the polymer; Separate it from the reaction mixture by direct filtration; Use an appropriate amount of pure solvent to wash the precipitate repeatedly; Place the washed polymer precipitate in a vacuum drying oven; Perform vacuum drying treatment at an appropriate temperature to obtain the dispersant.

[0008] Further, in step one, the acrylic ester is one or more of methyl methacrylate, 2-hydroxyethyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate; the initiator is azobisisobutyronitrile or benzoyl peroxide; the solvent is one or more of methanol, ethanol, acetonitrile or a mixed solvent.

[0009] Further, in step one, the mixed solvent is a methanol-water system or an ethanol-deionized water system.

[0010] Further, in step one, the molar percentages of NVP, acrylic ester, and initiator are 19.5% - 90%: 0.5%: 9.5% - 80%, and the solvent is 1 - 3 times the total volume of N-ethylpyrrolidine (NVP), acrylic ester, and initiator.

[0011] Further, in step one, the temperature of the polymerization reaction is 50 - 85°C, and the time is 80 - 360 min.

[0012] Further, in step one, a catalyst ferric bromide (FeBr3) with a mass of 0.05% of the total mass of the monomers is added, and its catalytic effect in a specific solvent system is utilized to promote the polymerization chain growth reaction.

[0013] Further, in step two, the drying is vacuum drying or freeze drying to ensure the dryness and stability of the sample.

[0014] An application of the positive electrode slurry dispersant prepared by the above preparation method, in which the dispersant, conductive agent, binder, and lithium iron phosphate are formulated into a positive electrode slurry in a certain proportion, the viscosity of the positive electrode slurry is adjusted for coating, a button cell is prepared, and its electrochemical performance is tested.

[0015] Further, the mass ratio of the dispersant, conductive agent, binder, and lithium iron phosphate is 0.001 - 0.005: 0.03: 0.02 - 0.024: 0.945.

[0016] The beneficial effects of the present invention compared with the prior art are as follows:

[0017] 1. The preparation method is simple. Adding the block copolymer dispersant to the positive electrode slurry can improve the dispersibility and stability of the slurry, significantly increase the solid content ratio of the slurry, with an increase range between 2.5% and 4%, and also enhance the stability of the slurry within 24 hours, ensuring its long-term uniformity and dispersibility.

[0018] 2. The lithium-ion battery prepared with the positive electrode slurry added with the block copolymer dispersant of the present invention exhibits higher specific capacity and cycling performance. Description of the Drawings

[0019] Figure 1 Coating state diagrams of the positive electrode slurry for Example 1 (left) and Comparative Example 1 (right);

[0020] Figure 2 Graph of the change in the static viscosity of the positive electrode slurry for 24 hours in Example 1 and Comparative Example 1;

[0021] Figure 3 Cycling curves of Example 1 and Comparative Example 1; Detailed implementation manners

[0022] The technical solutions in the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention. For those conditions not specified in the embodiments, they shall be carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0023] The present invention proposes an innovative method, that is, N-vinylpyrrolidone (NVP) and acrylic ester are copolymerized to synthesize a polymer block copolymer as an efficient dispersant for the positive electrode slurry of lithium-ion batteries. Due to the unique molecular structure and properties of this dispersant, it can effectively coat the surface of the positive electrode active material particles to form a protective layer, preventing particle agglomeration and sedimentation. At the same time, this dispersant can further improve the fluidity and coating property of the slurry through steric hindrance effect and electrostatic repulsion, ensuring the uniform distribution and close arrangement of the positive electrode material. Therefore, adding this polymer block copolymer dispersant to the positive electrode slurry can significantly improve the dispersibility and stability of the slurry.

[0024] Experimental results show that the positive electrode slurry using this polymer block copolymer dispersant can significantly increase the solid content ratio of the slurry, with an increase range between 2.5% and 4%, and greatly enhance the stability of the slurry within 24 hours, ensuring its long-term uniformity and dispersibility. Further, the lithium-ion battery prepared with the positive electrode slurry added with the polymer block copolymer dispersant of the present invention has significantly improved specific capacity and cycling performance. Therefore, the polymer block copolymer dispersant proposed by the present invention has broad application prospects and important economic value in the field of lithium-ion battery manufacturing.

[0025] Example 1

[0026] 1. Preparation of polymer: Accurately weigh N-ethyl pyrrolidine, methyl methacrylate and initiator azobisisobutyronitrile according to the established molar ratio (NVP:MA:initiator = 7.95:2:0.05) and add them to the ethanol-deionized water system in sequence, ensuring that the volume of the solvent is sufficient to dissolve all reactants. Then add the prepared reactants to the three-necked flask one by one, ensuring that each substance is evenly dispersed in the solvent. Use a stirrer to stir the reaction mixture to ensure that the reactants are fully mixed. Place the three-necked flask under a temperature controller, set the temperature of the polymerization reaction within the range of 50 - 85 °C, and start timing. The reaction time is 120 minutes. During the reaction, continuously observe the state of the reaction mixture to ensure the smooth progress of the reaction.

[0027] 2. Separation, washing and drying of the polymer: After the reaction is completed, lower the temperature to room temperature, stop stirring, and let the polymer precipitate fully. Use a filter and filter paper to separate the polymer from the reaction mixture and collect the polymer precipitate. Wash the collected polymer precipitate with an appropriate amount of deionized water to remove unreacted monomers, impurities and residual solvents. The washing process should be repeated multiple times until the washing liquid becomes clear to ensure the washing effect. Place the washed sample in a vacuum drying oven and perform vacuum drying at an appropriate temperature until the sample is completely dry. Collect the dried polymer sample, weigh it and record.

[0028] 3. Preparation of the positive electrode slurry: Dissolve the sample dispersant, conductive agent, binder, and lithium iron phosphate in the solvent NMP according to the ratio of 0.003:0.03:0.022:0.945, and use a stirrer to fully stir the mixture to ensure that the solid powder is evenly dispersed in NMP.

[0029] Finally, adjust the viscosity of the slurry for coating, prepare a button cell, and test its electrochemical performance.

[0030] Example 2

[0031] Preparation of the positive electrode slurry: Dissolve the dispersant, conductive agent, binder, and lithium iron phosphate provided in Example 1 in the solvent NMP according to the ratio of 0.002:0.03:0.023:0.945, and use a stirrer to fully stir the mixture to ensure that the solid powder is evenly dispersed in NMP.

[0032] Finally, adjust the viscosity of the slurry for coating, prepare a button cell, and test its electrochemical performance.

[0033] Comparative Example 1

[0034] Dissolve the conductive agent, binder, and lithium iron phosphate in NMP solvent at a ratio of 0.03:0.025:0.945, and use a stirrer to fully stir the mixture to ensure that the solid powder is evenly dispersed in NMP.

[0035] Finally, adjust the viscosity of the slurry for coating, prepare a button cell, and test its electrochemical performance.

[0036] Comparative Example 2

[0037] Other conditions are the same as in Example 2. The main difference from Example 1 is that the dispersant is selected as the common dispersant PVP.

[0038] Comparative Example 3

[0039] Other conditions are the same as in Example 2. The main difference from Example 1 is that the dispersant is selected as the common dispersant PAA.

[0040] Table 1 Viscosity and Coating State of the Positive Electrode Slurry Prepared in Examples and Comparative Examples

[0041] Serial number Sample Solid content of slurry Viscosity of slurry Coating state 1 Example 1 53％ 11000 Good 2 Example 2 51.5％ 12400 Good 3 Control sample 1 49％ 14000 Slightly granular 4 Control sample 2 51％ 13300 Slightly granular 5 Control sample 3 50.7％ 15600 Good

[0042] Table 2 Specific Capacities of Lithium-Ion Button Cells Prepared in Example 1 and Comparative Example 1 at 0.1C and 1C

[0043]

[0044] According to the data in Table 1 and Figure 1 It can be seen that Examples 1 and 2 have a significantly improved solid content effect compared with Comparative Example 1, and can improve the coating effect to a certain extent. In addition, compared with Example 1, the effects shown by Comparative Sample 2 and Comparative Sample 3 in improving the solid content rate and coating state are inferior to the former, further highlighting the superiority of Example 1 in these two aspects.

[0045] Figure 2 The viscosity change curves of the positive electrode slurries in Example 1 and Comparative Example 1 under the condition of standing for 24 hours are presented. The comparative analysis results show that the viscosity change of Example 1 shows higher stability compared with Comparative Example 1. This proves that by adding the dispersant prepared by the present invention to the positive electrode slurry, the dispersibility problem of the slurry can be effectively solved, thereby significantly improving the stability of the slurry.

[0046] According to the data analysis results in Table 2, it can be clearly observed that Examples 1 and 2 have higher specific capacity values under the discharge conditions of 0.1C and 1C compared with the comparative examples. This result indicates that by introducing the dispersant prepared by the present invention into the positive electrode slurry, the specific capacity performance of the battery can be significantly improved, and its effect is better than that of Comparative Example 2 and Comparative Example 3.

[0047] Furthermore, Figure 3 intuitively shows the cycling performance curves of Example 1 and Comparative Example 1 at room temperature. It can be clearly seen from the figure that the capacity retention rate of Example 1 is significantly improved compared with that of Comparative Example 1. This finding further corroborates the positive effect of adding the dispersant prepared by the present invention on improving the battery cycling performance, thereby optimizing the overall performance of the battery to some extent.

Claims

1. A method for preparing a lithium ion battery positive electrode slurry dispersant, characterized in that: The method is: Step 1: Preparation of high molecular weight polymer: N-ethylpyrrolidine (NVP), acrylate, initiator and solvent are added into a container for polymerization reaction; Step 2: Cool down to room temperature, filter, wash the precipitate repeatedly with a solvent, and dry to obtain a dispersant.

2. The method for preparing a lithium ion battery positive electrode slurry dispersant according to claim 1, characterized in that: In step 1, the acrylate is one or more of methyl methacrylate, hydroxyethyl methacrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; the initiator is azobisisobutyronitrile or benzoyl peroxide; and the solvent is one or more of methanol, ethanol, acetonitrile, or a mixed solvent.

3. The method for preparing a lithium ion battery positive electrode slurry dispersant according to claim 2, characterized in that: In step 1, the mixed solvent is a methanol-water system or an ethanol-deionized water system.

4. The method for preparing a lithium ion battery positive electrode slurry dispersant according to claim 1, characterized in that: In step 1, the molar percentages of the NVP, olefinic acid ester and initiator are 19.5% to 90%: 0.5%: 9.5% to 80%, and the solvent is 1 to 3 times the total volume of N-ethylpyrrolidine, olefinic acid ester and initiator.

5. The method for preparing a lithium ion battery positive electrode slurry dispersant according to claim 1, characterized in that: In step 1, the polymerization reaction temperature is 50-85° C. and the reaction time is 80-360 min.

6. The method for preparing a lithium ion battery positive electrode slurry dispersant according to any one of claims 1 to 5, characterized in that: In step 1, 0.05% of the total weight of the monomers is added as a catalyst, ferric bromide.

7. The method for preparing a lithium ion battery positive electrode slurry dispersant according to claim 1, characterized in that: In step 2, the drying is vacuum drying or freeze drying to ensure the dryness and stability of the sample.

8. An application of a positive electrode slurry dispersant prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The dispersant, conductive agent, adhesive and lithium iron phosphate are prepared into positive electrode slurry in a certain proportion, the viscosity of the positive electrode slurry is adjusted and coated to prepare a button battery, and its electrochemical performance is tested.

9. The use of a lithium-ion battery positive electrode slurry dispersant according to claim 8, characterized in that: The mass ratio of the dispersant, the conductive agent, the adhesive and the lithium iron phosphate is 0.001-0.005:0.03:0.02-0.024:0.945.

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