A method for preparing negative electrode slurry capable of scalably improving the mechanical strength of silicon-carbon materials

Abstract

The present application relates to the technical field of lithium battery materials, and in particular to a method for preparing negative electrode slurry that can improve the mechanical strength of silicon-carbon materials on a large scale. A method for preparing negative electrode slurry that can improve the mechanical strength of silicon-carbon materials on a large scale, under the initiation of a catalyst, uses an epoxy resin crosslinking agent to react with the carboxyl or hydroxyl group in PAA to form a crosslinked structure, thereby improving the mechanical strength of PAA, achieving a better volume expansion inhibition effect on silicon-carbon materials, and obtaining better cycle life and pole piece stability. At the same time, it has the advantages of simple process, easy operation, and large-scale production. In addition, this method does not change the formula and slurry process of silicon-carbon materials, has high process adaptability, and has important promotion and application value in the field of lithium-ion batteries.

Description

Technical Field

[0001] The present application relates to the technical field of lithium battery materials, and in particular to a method for preparing a negative electrode slurry that can scalably improve the mechanical strength of silicon-carbon materials. Background Art

[0002] As one of the current mainstream energy storage devices, lithium-ion batteries have important applications in the fields of new energy and electric vehicles. However, the traditional graphite anode has certain limitations in terms of energy density, so people have begun to study higher-capacity silicon-carbon composites as alternative materials. Silicon and carbon are widely available resources on the earth, and their synthesis costs are relatively low, which helps to reduce the manufacturing cost of lithium-ion batteries and improve the commercial feasibility of batteries. Silicon-carbon composites have higher lithium storage capacity than traditional graphite anodes. This is because silicon has more active sites that can be embedded in lithium ions, thereby increasing the energy density of the battery. However, silicon will undergo significant volume expansion and contraction during the charging and discharging process, which may cause problems such as fatigue, peeling and fracture of the electrode structure, affecting the cycle life and stability of the battery. Since the volume change of silicon-carbon materials may cause the decomposition of the electrolyte and thermal runaway of the battery, there are certain safety hazards, and it is necessary to strengthen the safety design and monitoring of the battery. After long-term cyclic use, the cycle performance of silicon-carbon materials will decay, resulting in problems such as reduced battery capacity and decreased voltage platform, so further research and solutions are needed. In summary, silicon-carbon negative electrode materials for lithium-ion batteries have many advantages such as high capacity, abundant resources, and excellent electrochemical properties, but they still face challenges in terms of volume expansion, safety, and cycle performance degradation. Further in-depth research and technological improvements are needed to achieve their widespread application in the battery field.

[0003] In recent years, researchers have made some progress in solving the volume expansion problem of silicon-carbon materials in lithium-ion batteries. One of the main methods is to use binders to improve the volume expansion problem of silicon-carbon materials. Binders play the role of fixing silicon particles in silicon-carbon materials to prevent them from undergoing large volume expansion and contraction during charging and discharging. By forming strong chemical bonds or physical adsorption with silicon particles or carbon materials, binders can effectively maintain the stability of the electrode structure. Studies have shown that the use of suitable binders can significantly improve the cycle stability of silicon-carbon materials. These binders can slow down the volume change rate of silicon particles and reduce the expansion of electrodes during the cycle, thereby extending the life of the battery. Researchers have optimized the interaction between binders and silicon-carbon materials by adjusting parameters such as the type, content and structure of the binder to achieve better volume expansion inhibition. For example, some high molecular polymers, nano-scale particles or silicon-containing compounds have been used in the design of binders.

[0004] As a high molecular polymer, polyacrylic acid (PAA) can form a stable bond with silicon-carbon materials, effectively fix silicon particles and carbon materials, and slow down their volume expansion and contraction during the charge and discharge process. Studies have shown that the use of PAA binder can significantly improve the cycle stability of silicon-carbon materials. PAA can effectively inhibit the agglomeration and peeling of silicon particles, reduce damage to the electrode structure, and extend the cycle life of the battery. The current common method is to optimize the interaction between PAA and silicon-carbon materials by adjusting parameters such as the molecular structure, content, and degree of cross-linking of PAA to achieve a better volume expansion inhibition effect. For example, controlling the molecular weight and cross-linking density of PAA can affect its adhesion and stability with silicon-carbon materials. Improving the volume expansion problem of silicon-carbon materials by using PAA binder does have a positive effect, but there are also some potential disadvantages. Although PAA can effectively fix silicon particles and carbon materials, its own low mechanical strength makes it difficult to cope with the large volume changes of silicon-carbon materials during charging and discharging, resulting in loose electrode structure and delamination. Adding excessive PAA content during the preparation of silicon-carbon electrodes will affect the electron transport and ion diffusion properties of the electrode, increase the thickness and mass of the electrode, and thus reduce the energy density and power density of the battery. Therefore, improving the wear resistance and mechanical strength of PAA is a key technical problem in improving the cycle life of silicon-carbon materials in lithium-ion batteries. Summary of the invention

[0005] In order to solve the above technical problems, the present application provides a method for preparing a negative electrode slurry that can scalably improve the mechanical strength of silicon-carbon materials. Under the initiation of a catalyst, an epoxy resin crosslinker is used to undergo an epoxidation reaction with the carboxyl or hydroxyl group in PAA to form a crosslinked structure, thereby improving the mechanical strength of PAA, achieving a better volume expansion inhibition effect on the silicon-carbon material, and obtaining better cycle life and electrode stability. In addition, the method does not change the formula and slurry process of the silicon-carbon material, has high process adaptability, and is easy to promote and apply on a large scale.

[0006] The present application provides a method for preparing a negative electrode slurry that can scalably improve the mechanical strength of silicon-carbon materials, using the following technical solutions:

[0007] A method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of a silicon-carbon material comprises the following steps:

[0008] S1, the thickener and the dispersing solvent are stirred evenly, and vacuum degassing is performed to obtain a glue solution;

[0009] S2, adding part of the conductive agent to the glue solution in batches, stirring evenly, and vacuuming and degassing to obtain a conductive slurry;

[0010] S3, adding part of the conductive agent to the negative electrode active material in batches and stirring evenly to obtain a premix;

[0011] S4, adding the conductive paste to the premix and kneading, then adding the binder and stirring and mixing, stirring at 25-60 rpm, 500-1500 rpm, stirring time of 0.5-1h, vacuum degassing, and obtaining a mixed solution;

[0012] S5, adding the crosslinking agent and the catalyst to the initiator and stirring and mixing them to obtain a modified mixed solution;

[0013] S6. Add the modified mixed solution into the mixed solution and stir to obtain a negative electrode slurry that can improve the mechanical strength of the silicon-carbon material on a large scale.

[0014] By adopting the above technical scheme, in step S1, the thickener and the dispersing solvent are stirred evenly and vacuumed for degassing to make the glue more dense and uniform, providing a good foundation for the subsequent steps. In step S2, the conductive agent is added to the glue in batches, stirred evenly and vacuumed for degassing to obtain a conductive slurry, which provides a conductive support for the subsequent improvement of the mechanical strength of the silicon-carbon material. In step S3, the premix of the conductive agent and the negative electrode active material is prepared, which provides a stable negative electrode material basis for the subsequent steps. In step S4, by kneading the conductive slurry with the premix, adding the binder and stirring and mixing to form a mixed solution, and vacuuming and degassing, the uniformity and stability of the mixed solution can be ensured. In steps S5 and S6, by stirring and mixing the initiator, crosslinking agent and catalyst and adding the modified mixed solution, the epoxy resin crosslinker and the carboxyl or hydroxyl group in PAA undergo an epoxidation reaction to form a crosslinked structure, thereby improving the mechanical strength of PAA and achieving a better volume expansion inhibition effect on the silicon-carbon material. Through the organic synergistic effect of the above steps, a method for preparing negative electrode slurry that can scalably improve the mechanical strength of silicon-carbon materials is realized, which provides a significant improvement in the electrochemical performance, cell internal resistance and cycle performance of lithium-ion batteries.

[0015] Preferably, the mass ratio of the negative electrode active material, conductive agent, binder, thickener, cross-linking agent, catalyst and initiator is (90-96): (1-5): (0.7-2): (0.7-2): (0.3-1): (0.015-0.05): (0.75-1.5); the solid content of the negative electrode slurry is 35%-55%.

[0016] Preferably, the mass ratio of the negative electrode active material, conductive agent, binder, thickener, cross-linking agent, catalyst and initiator is (93-95): (2.5-4): (0.9-1.5): (0.9-1.5): (0.4-0.7): (0.02-0.03): (0.9-1.1); the solid content of the negative electrode slurry is 40%-50%.

[0017] Preferably, the negative electrode active material is any one of silicon-carbon material, silicon-oxygen material, pre-lithiation silicon-oxygen material, and pre-magnesiation silicon-carbon material; the conductive agent is at least one of acetylene black, Ketjen black, carbon nanotubes, graphene and conductive carbon black.

[0018] Preferably, the binder is polyacrylic acid (PAA), the thickener is sodium carboxymethyl cellulose (CMC), the dispersing solvent is at least one of pure water, ethanol and acetone, the catalyst is at least one of copper sulfate and aluminum sulfate, and the initiator is acetone.

[0019] Preferably, the cross-linking agent is epoxy resin.

[0020] By adopting the above technical solution, the role of the epoxy resin in this application is to form a cross-linked structure by undergoing an epoxidation reaction with the carboxyl or hydroxyl groups in PAA. Such a cross-linked structure can enhance the mechanical strength of PAA, improve the overall mechanical strength of the silicon-carbon material, and effectively inhibit the volume expansion of the silicon-carbon material, thereby improving the cycle life and pole piece stability of the battery. The role of the cross-linking agent is to initiate and form a cross-linked structure during the preparation process. This cross-linked structure can provide better support and stability during the battery's cyclic charge and discharge process, reduce the expansion and contraction of the silicon-carbon material, thereby extending the battery's service life and improving performance. Therefore, by introducing epoxy resin as a cross-linking agent, the mechanical strength and stability of the silicon-carbon material can be significantly improved, while the original formula and process flow of the silicon-carbon material are not changed, making this method easier to promote and apply on a large scale.

[0021] Preferably, in step S1, the stirring is performed by using a double planetary stirring kettle for mixing, with a stirring revolution of 40-60rpm, a rotation of 2000-4000rpm, a stirring time of 1-3h, and a material temperature of 25-35°C in the stirring kettle; the process conditions for vacuum degassing are: the degassing vacuum is 0.08-0.1MPa, and the degassing time is 0.5-1h.

[0022] Preferably, in step S2, the stirring is carried out by using a double planetary stirring kettle for mixing, with a stirring revolution of 40-60rpm, a rotation of 2000-4000rpm, a stirring time of 1-3h, and a conductive slurry temperature in the stirring kettle of 25-35°C; the process conditions for vacuum degassing are: the degassing vacuum is 0.08-0.1MPa, and the degassing time is 0.5-1h.

[0023] Preferably, in step S3, the stirring is performed by using a double planetary stirring kettle for mixing, with a revolution of 25-60 rpm and a rotation of 100-1000 rpm, and a stirring time of 1-2 h.

[0024] Preferably, in step S4, the stirring during kneading is performed by using a double planetary stirring kettle for mixing, with a stirring revolution of 40-60rpm, a rotation of 2000-4000rpm, a stirring time of 1-3h, and a material temperature of 30-50°C in the stirring kettle; the process conditions for vacuum degassing are: the degassing vacuum is 0.08-0.1MPa, and the degassing time is 0.5-1h.

[0025] Preferably, in step S5, the stirring and mixing is performed by using a double planetary stirring kettle for mixing, with a stirring speed of 25-60 rpm, a rotation speed of 500-1500 rpm, a stirring time of 0.5-1 h, and a material temperature of 30-50° C. in the stirring kettle.

[0026] Preferably, in step S6, the stirring and mixing is performed by using a double planetary stirring kettle for mixing, with a stirring revolution of 25-60 rpm, a rotation of 500-1500 rpm, a stirring time of 0.5-3 h, and a material temperature of 30-50° C. in the stirring kettle.

[0027] By adopting the above technical solution, the double planetary stirring kettle provides a more effective mixing method, which can ensure that the various components are fully mixed and uniform, avoid local unevenness causing differences in the performance of the negative electrode slurry, and thus improve the efficiency and quality of the reaction. By setting the stirring revolution and rotation speed and stirring time, it can be ensured that the cross-linking agent, catalyst and other components are fully mixed, and it is conducive to promoting the chemical reaction. Appropriate stirring speed and time can improve the efficiency of cross-linking structure formation. Stirring and mixing within a temperature range of 30-50°C can promote the reaction, facilitate dissolution and diffusion, and ensure the sufficiency and uniformity of cross-linking. By using a double planetary stirring kettle for mixing in step S6, and according to the set parameters such as stirring speed, time and temperature, it is ensured that the cross-linking agent and other components are mixed uniformly and react fully, thereby improving the performance of the negative electrode slurry, and the mechanical strength of the silicon-carbon material can be improved.

[0028] In summary, the beneficial technical effects of this application are:

[0029] 1. Improve mechanical strength: By introducing epoxy resin cross-linking agent, the mechanical strength of PAA material is effectively improved, the overall structural stability of silicon-carbon material is strengthened, and the negative electrode slurry is more durable.

[0030] 2. Improve the volume expansion inhibition effect: The formation of a cross-linked structure can effectively inhibit the volume expansion of silicon-carbon materials during the charging and discharging process, reduce damage to the battery, and thus improve the cycle life and electrode stability.

[0031] 3. No change in formula and process: This method improves the mechanical strength of silicon-carbon materials without changing the formula and slurry process of silicon-carbon materials. The process has high adaptability and is easy to scale up and promote.

[0032] 4. Improve battery performance: After the prepared negative electrode slurry is applied to lithium-ion batteries, the electrochemical performance of the battery can be significantly improved, the internal resistance of the battery cell can be reduced, and the cycle performance of the battery can be improved, which greatly improves the service life and performance of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following is a brief introduction to the drawings used in the embodiments:

[0034] Figure 1 The cycle curves of Example 1, Example 5 and Comparative Example 1 at 1C / 1C room temperature are shown;

[0035] in, Figure 1 A2 is the lithium ion battery obtained in Example 1; Figure 1 A1 is the lithium ion battery obtained in Example 5; Figure 1 A3 is the lithium ion battery obtained in Comparative Example 1. DETAILED DESCRIPTION

[0036] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0037] Example 1

[0038] A method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of a silicon-carbon material comprises the following steps:

[0039] S0. Material preparation: The materials are prepared according to the mass ratio of silicon-carbon material, acetylene black, polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), epoxy resin, copper sulfate and acetone of 90:5:0.7:0.7:0.3:0.015:0.75, and the solid content of the negative electrode slurry is 35%;

[0040] S1. Glue preparation: sodium carboxymethyl cellulose (CMC) and pure water are mixed in a double planetary stirring kettle, the stirring speed is 40 rpm, the rotation speed is 2000 rpm, the stirring time is 3 h, the temperature of the conductive slurry in the stirring kettle is 35° C., the degassing is performed under vacuum, the degassing vacuum is 0.08 MPa, and the degassing time is 0.5 h to obtain a glue solution;

[0041] S2. Preparation of conductive paste: 50% of acetylene black was added to the glue in batches and mixed in a double planetary stirring kettle. The stirring time was 1 hour and the material temperature in the stirring kettle was 25°C. The degassing was performed by vacuuming, the degassing vacuum was 0.08MPa, and the degassing time was 0.5h to obtain the conductive paste.

[0042] S3, premix: 50% of acetylene black is added to the silicon-carbon material in batches, and a double planetary stirring kettle is used for mixing, with a stirring speed of 25 rpm, a rotation speed of 100 rpm, and a stirring time of 2 h to obtain a premix;

[0043] S4, slurry preparation: add the conductive slurry to the premix and knead, use a double planetary stirring kettle to mix, stir at 40 rpm, rotate at 2000 rpm, stir for 3 hours, and the material temperature in the stirring kettle is 50°C; then add the binder and stir and mix, stir at 25 rpm, rotate at 500 rpm, stir for 1 hour, vacuum degassing, the degassing vacuum is 0.08 MPa, and the degassing time is 0.5 hour to obtain a mixed solution;

[0044] S5. Preparation of modified mixed solution: Add epoxy resin and copper sulfate to acetone, use double planetary stirring kettle to mix, stir at 25 rpm, 500 rpm, stirring time for 1 hour, the material temperature in the stirring kettle is 50°C, to obtain a modified mixed solution; S6. Cross-linking polymerization: Add the modified mixed solution to the mixed solution, use double planetary stirring kettle to mix, stir at 25 rpm, 500 rpm, stirring time for 3 hours, the material temperature in the stirring kettle is 50°C, to obtain a negative electrode slurry that can scalably improve the mechanical strength of silicon-carbon materials.

[0045] Example 2

[0046] A method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of a silicon-carbon material comprises the following steps:

[0047] S0. Material preparation: The materials are prepared according to the mass ratio of silicon oxide material, graphene, polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), epoxy resin, aluminum sulfate and acetone of 96:1:2:2:2:0.05:1.5, and the solid content of the negative electrode slurry is 55%;

[0048] S1. Glue preparation: sodium carboxymethyl cellulose (CMC) and ethanol are mixed in a double planetary stirring kettle, the stirring speed is 60 rpm, the rotation speed is 4000 rpm, the stirring time is 1 hour, the temperature of the conductive slurry in the stirring kettle is 25° C., the degassing is performed under vacuum, the degassing vacuum is 0.1 MPa, and the degassing time is 1 hour to obtain a glue solution;

[0049] S2. Preparation of conductive slurry: 50% of graphene is added to the glue in batches and mixed in a double planetary stirring kettle. The stirring is performed at 60 rpm, 4000 rpm, and the stirring time is 1 hour. The material temperature in the stirring kettle is 25°C. The conductive slurry is obtained by vacuum degassing with a degassing vacuum of 0.1 MPa and a degassing time of 1 hour.

[0050] S3, premix: 50% of graphene is added to the silicon-oxygen material in batches, and a double planetary stirring kettle is used for mixing, with a revolution of 60 rpm and a rotation of 1000 rpm for 1 hour to obtain a premix;

[0051] S4, slurry preparation: add the conductive slurry to the premix and knead it, use a double planetary stirring kettle to mix the materials, stir the revolution of 60rpm, rotate at 4000rpm, stir for 1h, and the material temperature in the stirring kettle is 30°C; then add the binder and stir and mix, stir the revolution of 60rpm, rotate at 1500rpm, stir for 0.5h, vacuum degassing, the degassing vacuum is 0.1MPa, and the degassing time is 1h to obtain a mixed solution;

[0052] S5. Preparation of modified mixed solution: adding epoxy resin and aluminum sulfate to acetone, mixing in a double planetary stirring kettle, stirring at 60 rpm, 1500 rpm, stirring time of 1 h, and material temperature of 50° C. in the stirring kettle, to obtain a modified mixed solution;

[0053] S6. Cross-linking polymerization: add the modified mixed solution to the mixed solution, use a double planetary stirring kettle to mix the materials, stir at 60 rpm, 1500 rpm, stirring time of 0.5 h, and the material temperature in the stirring kettle of 50°C to obtain a negative electrode slurry that can scalably improve the mechanical strength of silicon-carbon materials.

[0054] Example 3

[0055] A method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of a silicon-carbon material comprises the following steps:

[0056] S0. Material preparation: The material is prepared according to the mass ratio of pre-magnesiumized silicon-carbon material, graphene, polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), epoxy resin, aluminum sulfate and acetone of 93:2.5:0.9:0.9:0.4:0.02:0.9, and the negative electrode slurry is prepared with a solid content of 50%;

[0057] S1. Glue preparation: sodium carboxymethyl cellulose (CMC) and acetone are mixed in a double planetary stirring kettle, the stirring revolution is 50 rpm, the rotation is 3000 rpm, the stirring time is 2 h, the temperature of the conductive slurry in the stirring kettle is 30° C., the degassing is performed under vacuum, the degassing vacuum is 0.09 MPa, and the degassing time is 0.8 h to obtain a glue solution;

[0058] S2. Preparation of conductive slurry: 50% of graphene was added to the glue in batches and mixed in a double planetary stirring kettle. The stirring revolution was 50 rpm and the rotation was 3000 rpm. The stirring time was 2 h. The material temperature in the stirring kettle was 31° C. The degassing was performed under vacuum at a vacuum of 0.09 MPa for a degassing time of 0.7 h to obtain a conductive slurry.

[0059] S3, premix: 50% of graphene is added to the pre-magnesiumized silicon-carbon material in batches, and a double planetary stirring kettle is used for mixing, with a stirring speed of 40 rpm, a rotation speed of 500 rpm, and a stirring time of 1.5 h to obtain a premix;

[0060] S4, slurry preparation: add the conductive slurry to the premix and knead it, use a double planetary stirring kettle to mix the materials, stir the revolution of 50rpm, rotate at 3000rpm, stir for 2h, and the material temperature in the stirring kettle is 40°C; then add polyacrylic acid (PAA) and stir and mix, stir the revolution of 40rpm, rotate at 900rpm, stir for 0.8h, vacuum degassing, the degassing vacuum is 0.09MPa, and the degassing time is 0.7h to obtain a mixed solution;

[0061] S5. Preparation of modified mixed solution: adding epoxy resin and aluminum sulfate to acetone, mixing in a double planetary stirring kettle, stirring at an orbital speed of 40 rpm, an autorotation speed of 900 rpm, a stirring time of 0.7 h, and a material temperature of 40° C. in the stirring kettle to obtain a modified mixed solution;

[0062] S6. Cross-linking polymerization: add the modified mixed solution to the mixed solution, use a double planetary stirring kettle to mix the materials, stir at 40 rpm, 900 rpm, stir for 1.5 h, and set the material temperature in the stirring kettle at 40°C to obtain a negative electrode slurry that can scalably improve the mechanical strength of silicon-carbon materials.

[0063] Example 4

[0064] S0. Material preparation: The negative electrode active material, conductive carbon black, polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), epoxy resin, aluminum sulfate and acetone are prepared in a mass ratio of 95:4:1.5:1.5:0.7:0.03:1.1, and the negative electrode slurry is prepared with a solid content of 40%. The negative electrode active material is a pre-lithiation silicon oxide material: SiO / C (425 mAh / g);

[0065] S1. Glue preparation: sodium carboxymethyl cellulose (CMC) and acetone are mixed in a double planetary stirring kettle, the stirring revolution is 50 rpm, the rotation is 3000 rpm, the stirring time is 2 h, the temperature of the conductive slurry in the stirring kettle is 30° C., the degassing is performed under vacuum, the degassing vacuum is 0.09 MPa, and the degassing time is 0.8 h to obtain a glue solution;

[0066] S2. Preparation of conductive slurry: 50% of conductive carbon black was added to the glue in batches and mixed in a double planetary stirring kettle. The stirring was performed at a revolution of 50 rpm and a rotation of 3000 rpm for 2 h. The material temperature in the stirring kettle was 31° C. The conductive slurry was prepared by vacuum degassing at a vacuum of 0.09 MPa for 0.7 h.

[0067] S3, premix: 50% of the conductive carbon black is added to the negative electrode active material in batches, and a double planetary stirring kettle is used for mixing, with a stirring speed of 40 rpm, a rotation speed of 500 rpm, and a stirring time of 1.5 h to obtain a premix;

[0068] S4, slurry preparation: add the conductive slurry to the premix and knead it, use a double planetary stirring kettle to mix the materials, stir the revolution of 50rpm, rotate at 3000rpm, stir for 2h, and the material temperature in the stirring kettle is 40°C; then add polyacrylic acid (PAA) and stir and mix, stir the revolution of 40rpm, rotate at 900rpm, stir for 0.8h, vacuum degassing, the degassing vacuum is 0.09MPa, and the degassing time is 0.7h to obtain a mixed solution;

[0069] S5. Preparation of modified mixed solution: adding epoxy resin and aluminum sulfate to acetone, mixing in a double planetary stirring kettle, stirring at an orbital speed of 40 rpm, an autorotation speed of 900 rpm, a stirring time of 0.7 h, and a material temperature of 40° C. in the stirring kettle to obtain a modified mixed solution;

[0070] S6. Cross-linking polymerization: add the modified mixed solution to the mixed solution, use a double planetary stirring kettle to mix the materials, stir at 40 rpm, 900 rpm, stir for 1.5 h, and set the material temperature in the stirring kettle at 40°C to obtain a negative electrode slurry that can scalably improve the mechanical strength of silicon-carbon materials.

[0071] Example 5

[0072] The same as Example 4, except that: S0, preparation: the mass ratio of the negative electrode active material, conductive carbon black, polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), epoxy resin, aluminum sulfate and acetone is 93:3.5:1:1:0.5:0.025:1, the negative electrode slurry is prepared with a solid content of 40%, and the negative electrode active material is a pre-lithiation silicon oxide material: SiO / C (425mAh / g).

[0073] Comparative Example 1

[0074] S0. Material preparation: The negative electrode active material, conductive carbon black, polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC) are prepared in a mass ratio of 93:3.5:1:1, and the negative electrode slurry is prepared with a solid content of 40%. The negative electrode active material is a pre-lithiation silicon oxide material: SiO / C (425 mAh / g).

[0075] S1. Glue preparation: sodium carboxymethyl cellulose (CMC) and acetone are mixed in a double planetary stirring kettle, the stirring revolution is 50 rpm, the rotation is 3000 rpm, the stirring time is 2 h, the temperature of the conductive slurry in the stirring kettle is 30° C., the degassing is performed under vacuum, the degassing vacuum is 0.09 MPa, and the degassing time is 0.8 h to obtain a glue solution;

[0076] S2. Preparation of conductive slurry: 50% conductive carbon black was added to the glue in batches and mixed in a double planetary stirring kettle. The stirring time was 2 hours and the material temperature in the stirring kettle was 31°C. The degassing was performed by vacuuming. The degassing vacuum was 0.09 MPa and the degassing time was 0.7 hours to obtain the conductive slurry.

[0077] S3, premix: 50% of conductive carbon black is added to the pre-lithiated silicon-oxygen material in batches, and mixed in a double planetary stirring kettle, with a stirring speed of 40 rpm and a rotation speed of 500 rpm for 1.5 h to obtain a premix;

[0078] S4. Preparation of slurry: Add conductive slurry to premix and knead, use double planetary stirring kettle for mixing, stirring revolution of 50 rpm, rotation of 3000 rpm, stirring time of 2 h, material temperature in stirring kettle 40°C; then add binder and stir and mix, stirring revolution of 40 rpm, rotation of 900 rpm, stirring time of 0.8 h, vacuum degassing, degassing vacuum of 0.09 MPa, degassing time of 0.7 h, obtain mixed solution, obtain negative electrode slurry.

[0079] Performance Testing

[0080] The negative electrode slurries prepared in Examples 1 to 5 and Comparative Example 1 were respectively made into lithium-ion batteries in the following manner and subjected to electrochemical tests; wherein the lithium-ion batteries obtained in Example 1, Example 5 and Comparative Example 1 were labeled A2, A1 and A3, respectively.

[0081] (1) Preparation of positive electrode sheet: The prepared positive electrode slurry is evenly coated on the front and back sides of the aluminum foil, dried, rolled, and die-cut to form a positive electrode sheet. The coating double-sided surface density is 50 mg / cm 2 ;

[0082] (2) Prepare the negative electrode sheet. Evenly coat the prepared negative electrode slurry on the front and back of the copper foil, dry, roll and die-cut to make the negative electrode sheet. The coating double-sided surface density is 22 mg / cm 2 .

[0083] (3) Preparation of high energy density lithium-ion batteries: The aforementioned positive electrode sheets, negative electrode sheets and separators are stacked to form bare cells. After short-circuit testing, they are welded to the tabs, sealed on the top and sides, baked, injected, formed, sealed and divided into two parts to form soft-pack lithium-ion batteries.

[0084] Electrochemical testing

[0085] 1. DC internal resistance test: At room temperature 25±1℃, charge to 4.25V with 1C constant current, then charge with constant voltage, with the cut-off current at 0.05C and stand for 3H, record the voltage V0; discharge with 5C constant current for 3s, record the voltage after 3s as V1, DC internal resistance DCR = (V0-V1) / 5C;

[0086] 2. Cycle life test: At room temperature 25±1℃, charge at 1C constant current to 4.25V, then charge at constant voltage, let stand for 10min at a cut-off current of 0.05C, discharge at 1C constant current to 2.75V, cycle 500 times, with an interval of 10min between each charge and discharge, record the capacity and calculate the capacity retention rate (discharge capacity after cycle / discharge capacity in the first cycle).

[0087] The test results are shown in Table 1. The cycle curves of the lithium ion batteries obtained in Example 1, Example 5 and Comparative Example 1 at room temperature are shown in Table 1. Figure 1 shown.

[0088] Table 1 Electrochemical performance test results

[0089]

[0090]

[0091] As can be seen from Table 1, the negative electrode slurry obtained in the present application that can scalably improve the mechanical strength of silicon-carbon materials is used to make lithium-ion batteries, and its electrochemical performance, battery cell internal resistance, cycle performance, etc. are greatly improved.

[0092] The above embodiments are only used to explain the technical solution of the present application rather than to limit it. Although the above embodiments provide a specific description of the present application, relevant technical personnel should understand that the specific implementation methods of the present application can still be modified or replaced by equivalents, and any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of silicon-carbon materials, characterized in that: The following steps are involved: S1, the thickener and the dispersing solvent are stirred evenly, and vacuum degassing is performed to obtain a glue solution; S2, adding part of the conductive agent to the glue solution in batches, stirring evenly, and vacuuming and degassing to obtain a conductive slurry; S3, adding part of the conductive agent to the negative electrode active material in batches and stirring evenly to obtain a premix; S4, adding the conductive paste to the premix and kneading, then adding the binder and stirring and mixing, stirring at 25-60 rpm, 500-1500 rpm, stirring time of 0.5-1h, vacuum degassing, and obtaining a mixed solution; S5, adding the crosslinking agent and the catalyst to the initiator and stirring and mixing them to obtain a modified mixed solution; S6, adding the modified mixed solution to the mixed solution and stirring and mixing, to obtain a negative electrode slurry that can scalably improve the mechanical strength of the silicon-carbon material; The mass ratio of the negative electrode active material, conductive agent, binder, thickener, cross-linking agent, catalyst and initiator is (93-95): (2.5-4): (0.9-1.5): (0.9-1.5): (0.4-0.7): (0.02-0.03): (0.9-1.1); the solid content of the negative electrode slurry is 40%-50%; The negative electrode active material is any one of silicon-carbon material, silicon-oxygen material, pre-lithiation silicon-oxygen material, and pre-magnesiation silicon-carbon material; the conductive agent is at least one of acetylene black, Ketjen black, carbon nanotubes, graphene, and conductive carbon black; The binder is polyacrylic acid (PAA), the thickener is sodium carboxymethyl cellulose (CMC), the dispersing solvent is at least one of pure water, ethanol and acetone, the cross-linking agent is epoxy resin; the catalyst is at least one of copper sulfate and aluminum sulfate, and the initiator is acetone.

2. A method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of silicon-carbon materials according to claim 1, characterized in that: In step S1, the stirring is carried out by using a double planetary stirring kettle for mixing, the stirring revolution is 40-60rpm, the rotation is 2000-4000rpm, the stirring time is 1-3h, and the material temperature in the stirring kettle is 25-35°C; the process conditions for vacuum degassing are: the degassing vacuum is 0.08-0.1MPa, and the degassing time is 0.5-1h.

3. The method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of silicon-carbon materials according to claim 1, characterized in that: In step S2, the stirring is carried out by using a double planetary stirring kettle for mixing, with a stirring revolution of 40-60rpm, a rotation of 2000-4000rpm, a stirring time of 1-3h, and a conductive slurry temperature of 25-35°C in the stirring kettle; the process conditions for vacuum degassing are: the degassing vacuum is 0.08-0.1MPa, and the degassing time is 0.5-1h.

4. The method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of silicon-carbon materials according to claim 1, characterized in that: In step S3, the stirring is performed by using a double planetary stirring kettle to mix the materials, with a revolution of 25-60 rpm and a rotation of 100-1000 rpm, and a stirring time of 1-2 h.

5. The method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of silicon-carbon materials according to claim 1, characterized in that: In step S4, the stirring during kneading is performed by using a double planetary stirring kettle for mixing, with a stirring revolution of 40-60rpm, a rotation of 2000-4000rpm, a stirring time of 1-3h, and a material temperature of 30-50°C in the stirring kettle; the process conditions for vacuum degassing are: the degassing vacuum is 0.08-0.1MPa, and the degassing time is 0.5-1h.

6. The method for preparing a negative electrode slurry capable of scalably improving the mechanical strength of silicon-carbon materials according to claim 1, characterized in that: In step S5, the stirring and mixing is carried out by using a double planetary stirring kettle, the stirring revolution is 25-60rpm, the rotation is 500-1500rpm, the stirring time is 0.5-1h, and the material temperature in the stirring kettle is 30-50°C. In step S6, the stirring and mixing is carried out by using a double planetary stirring kettle, the stirring revolution is 25-60rpm, the rotation is 500-1500rpm, the stirring time is 0.5-3h, and the material temperature in the stirring kettle is 30-50°C.

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