Silicon-carbon negative electrode slurry, preparation method and application thereof

Abstract

The application provides a silicon-carbon negative electrode slurry, a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing sodium carboxymethyl cellulose powder and a solvent to obtain a sodium carboxymethyl cellulose solution; (2) mixing a negative electrode active material and a conductive agent to obtain an active material powder; (3) adding part of the sodium carboxymethyl cellulose solution, a first part of a polyacrylic acid binder and a solvent to the active material powder to obtain an intermediate slurry; and (4) adding a second part of the polyacrylic acid binder to the intermediate slurry, and then adding the remaining sodium carboxymethyl cellulose solution, a third part of the polyacrylic acid binder and a solvent. The negative electrode active material comprises CVD silicon-carbon. The method provided by the application effectively reduces the slurry viscosity and the requirement for stirring equipment, inhibits the volume expansion of the CVD silicon-carbon during use, and is simple in preparation method and suitable for large-scale application.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a silicon-carbon negative electrode slurry and a preparation method and application thereof. Background Art

[0002] The manufacturing process of lithium-ion battery electrodes is a crucial step in the entire lithium-ion battery manufacturing process, significantly impacting the battery's performance. Anode slurry is a non-Newtonian, high-viscosity fluid formed by uniformly mixing the anode active material, binder, solvent, thickener, and other powders and liquids. This fluid must possess a certain viscosity, good flowability, and a sufficiently small particle size.

[0003] In the traditional negative electrode slurry preparation process, negative electrode active material, conductive carbon, binder, and dispersant are often added together and stirred and mixed. However, this not only places high demands on the stirring equipment, but also accelerates the wear and aging of the equipment. Moreover, the prepared slurry cannot guarantee good dispersion and uniformity, and large particles will remain. At the same time, the viscosity and solid content of the slurry cannot meet the expected standards.

[0004] Especially when CVD silicon carbon is used as the negative electrode active material, since it is often accompanied by large volume changes during the charge and discharge process, a binder with stronger adhesion is required. However, the molecular weight and viscosity of such binders are usually large. It is difficult to obtain a negative electrode slurry with good dispersion and uniformity using traditional methods, and it will cause serious wear and tear on the stirring equipment.

[0005] Therefore, how to develop a negative electrode slurry preparation method that can effectively reduce the slurry viscosity during the stirring process, reduce the requirements for stirring equipment, and at the same time ensure that the negative electrode slurry has good dispersion and uniformity, so that CVD silicon carbon will not produce large volume expansion during use, is an urgent problem to be solved. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention aims to provide a silicon-carbon negative electrode slurry, its preparation method, and its application. The preparation method provided by the present invention, through a specific order of adding sodium carboxymethylcellulose solution and polyacrylic acid binder, effectively reduces the viscosity during the preparation of the silicon-carbon negative electrode slurry, alleviates wear on equipment, and significantly reduces the requirements for stirring equipment. It can ensure that the viscosity, solids content, and fineness of the slurry are all within the standard range, suppressing the volume expansion of CVD silicon-carbon during use. Furthermore, the preparation method is simple and suitable for large-scale application.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a silicon-carbon negative electrode slurry, the preparation method comprising:

[0009] (1) mixing sodium carboxymethyl cellulose powder and a solvent to obtain a sodium carboxymethyl cellulose solution;

[0010] (2) performing a second mixing of the negative electrode active material and the conductive agent to obtain active material powder;

[0011] (3) adding a portion of the sodium carboxymethyl cellulose solution, the first portion of the polyacrylic acid binder, and the solvent to the active material powder for a third mixing step to obtain an intermediate slurry;

[0012] (4) adding the second portion of the polyacrylic acid binder to the intermediate slurry for a fourth mixing, and then adding the remaining sodium carboxymethyl cellulose solution, the third portion of the polyacrylic acid binder, and the solvent for a fifth mixing;

[0013] The negative electrode active material includes CVD silicon carbon.

[0014] It is understood that CVD silicon carbon refers to a silicon-carbon composite material prepared by chemical vapor deposition (CVD).

[0015] In the present invention, by adjusting the order of adding the sodium carboxymethyl cellulose solution and the polyacrylic acid binder during the preparation of the silicon-carbon negative electrode slurry, the viscosity of the silicon-carbon negative electrode slurry during the preparation process is effectively reduced, the wear of the slurry mixing on the equipment is reduced, and the viscosity, solid content and fineness of the slurry can be ensured to be within the standard range; at the same time, thanks to the synergistic effect of the sodium carboxymethyl cellulose solution and the polyacrylic acid binder, the volume expansion phenomenon of the CVD silicon-carbon during use is effectively suppressed, and the preparation method is simple and suitable for large-scale application.

[0016] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0017] Preferably, based on the total mass of the solid components in the silicon-carbon negative electrode slurry as 100%, in step (1), the mass proportion of the sodium carboxymethyl cellulose powder is 0.5-2%, for example, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8% or 2.0%, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0018] In the present invention, by regulating the amount of sodium carboxymethyl cellulose added in the preparation of the negative electrode slurry, the mixing effect of the silicon-carbon negative electrode slurry can be further optimized, which is more conducive to improving the comprehensive performance of the slurry.

[0019] Preferably, in step (1), the mass ratio of the sodium carboxymethyl cellulose powder to the solvent is (1-2%):(98-99%), for example, 1.0%:99.0%, 1.2%:98.8%, 1.4%:98.6%, 1.6%:98.4%, 1.8%:98.2%, 2.0%:98.0%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0020] Preferably, the solvent comprises deionized water.

[0021] Preferably, the first mixing process is: a first stirring for 30 to 60 minutes at a revolution speed of 15 to 18 rpm and a dispersion speed of 500 to 1000 rpm, and then a second stirring for 300 to 500 minutes at a revolution speed of 20 to 30 rpm and a dispersion speed of 1000 to 2000 rpm.

[0022] For example, during the first stirring process of the first mixing, the revolution speed may be 15 rpm, 16 rpm, 17 rpm or 18 rpm, the dispersion speed may be 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm, and the stirring time may be 30 min, 40 min, 50 min or 60 min; during the second stirring process of the first mixing, the revolution speed may be 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, 31 rpm, 32 rpm, 33 rpm, 34 rpm, 35 rpm, 36 rpm, 37 rpm, 38 rpm, 39 rpm, 40 rpm, 41 rpm, 42 rpm, 43 rpm, 44 rpm, 45 rpm, 46 rpm, 47 rpm, 48 rpm, 49 rpm, 50 rpm, 51 rpm, 52 rpm, 53 rpm, 54 rpm, 55 rpm, 56 rpm, 57 rpm, 58 rpm, 59 rpm, 60 rpm, 61 rpm, 62 rpm, 63 rpm, 64 rpm, 65 rpm, 66 rpm, 67 rpm, 68 rpm, 69 rpm, 70 The dispersion speed can be 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm or 2000 rpm, etc. The stirring time can be 300 min, 350 min, 400 min, 450 min or 500 min, etc., but are not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0023] In the present invention, whether to adopt the second stirring can be selected according to the quality requirements of the slurry. After the first stirring, a relatively uniformly mixed sodium carboxymethyl cellulose solution can be obtained. By adding the second stirring, the mixing effect of the sodium carboxymethyl cellulose solution can be further improved.

[0024] Preferably, the viscosity of the sodium carboxymethyl cellulose solution is 10,000 to 20,000 mPa·s, for example, 10,000 mPa·s, 12,000 mPa·s, 14,000 mPa·s, 16,000 mPa·s, 18,000 mPa·s or 20,000 mPa·s, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, after the first stirring is completed, the pot wall and the stirring paddle are scraped, the vacuum is turned on, and the circulating water is turned on.

[0026] Preferably, the negative electrode active material further includes graphite.

[0027] Preferably, the mass ratio of the graphite, CVD silicon carbon and conductive agent is (88-96%):(3-10%):(1-2%), for example, 88%:10%:2%, 90%:8%:2%, 92%:6%:2%, 94%:4%:2%, 96%:3%:1%, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0028] Preferably, the second mixing process is: performing a third stirring for 30 to 60 minutes at a revolution speed of 15 to 25 rpm and a dispersion speed of 200 to 1000 rpm.

[0029] For example, during the second mixing process, the revolution speed may be 15 rpm, 16 rpm, 17 rpm, 18 rpm, 19 rpm, 20 rpm, 21 rpm, 22 rpm, 23 rpm, 24 rpm or 25 rpm, etc., the dispersion speed may be 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm, etc., and the stirring time may be 30 min, 40 min, 50 min or 60 min, etc., but are not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0030] Preferably, based on the total mass of the solid components in the silicon-carbon negative electrode slurry as 100%, the total mass of the first part, the second part and the third part of the polyacrylic acid binder accounts for 2 to 4%, for example, 2.0%, 2.5%, 3.0%, 3.5% or 4.0%, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0031] In the present invention, the amount of polyacrylic acid binder added can be selected according to the amount of CVD silicon carbon added. By regulating the total amount of polyacrylic acid binder added during the preparation of silicon-carbon negative electrode slurry, a better balance can be achieved between reducing slurry viscosity and inhibiting CVD silicon volume expansion.

[0032] Preferably, taking the total mass of the first part, the second part and the third part of the polyacrylic acid adhesive as 100%, the mass proportion of the first part of the polyacrylic acid adhesive in step (3) is 20% to 40%, for example, 20%, 25%, 30%, 35% or 40%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0033] Preferably, based on the mass of the sodium carboxymethyl cellulose solution in step (1) being 100%, the mass proportion of the partial sodium carboxymethyl cellulose solution in step (3) is 20% to 50%, for example, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0034] In the present invention, by regulating the amount of the polyacrylic acid binder and the sodium carboxymethyl cellulose solution added in step (3), the mixing effect of the silicon-carbon negative electrode slurry can be further optimized, which is more conducive to the uniform dispersion of the slurry.

[0035] Preferably, the third mixing process is: performing a fourth stirring for 10 to 30 minutes at a revolution speed of 10 to 15 rpm, and then performing a fifth stirring for 60 to 90 minutes at a revolution speed of 25 to 35 rpm and a dispersion speed of 2000 to 3500 rpm.

[0036] For example, during the fourth stirring process of the third mixing, the revolution speed may be 10 rpm, 11 rpm, 12 rpm, 13 rpm, 14 rpm or 15 rpm, and the stirring time may be 10 min, 15 min, 20 min, 25 min or 30 min, etc.; during the fifth stirring process of the third mixing, the revolution speed may be 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, 31 rpm, 32 rpm, 33 rpm, 34 rpm or 35 rpm, etc., the dispersion speed may be 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm, 3000 rpm, 3200 rpm or 3500 rpm, etc., and the stirring time may be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min, etc., but are not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0037] Preferably, taking the total mass of the first part, the second part and the third part of the polyacrylic acid binder as 100%, in the fourth mixing of step (4), the mass proportion of the second part of the polyacrylic acid binder is 20% to 40%, for example, 20%, 25%, 30%, 35% or 40%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0038] In the present invention, the amount of the second part of the polyacrylic acid binder added can be adjusted according to the amount of the first part of the polyacrylic acid binder added to better reduce the viscosity of the slurry during stirring, reduce wear on equipment, and achieve better slurry mixing effect.

[0039] Preferably, the fourth mixing process is: a sixth stirring for 10 to 30 minutes at a revolution speed of 10 to 15 rpm and a dispersion speed of 200 to 500 rpm, and then a seventh stirring for 60 to 120 minutes at a revolution speed of 25 to 35 rpm and a dispersion speed of 2000 to 3500 rpm.

[0040] For example, during the sixth stirring process of the fourth mixing, the revolution speed may be 10 rpm, 11 rpm, 12 rpm, 13 rpm, 14 rpm or 15 rpm, the dispersion speed may be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, and the stirring time may be 10 min, 15 min, 20 min, 25 min or 30 min, etc.; during the seventh stirring process of the fourth mixing, the revolution speed may be 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, 31 rpm, 32 rpm, 33 rpm, 34 rpm, 35 rpm, 36 rpm, 37 rpm, 38 rpm, 39 rpm, 40 rpm, 41 rpm, 42 rpm, 43 rpm, 44 rpm, 45 rpm, 46 rpm, 47 rpm, 48 rpm, 49 rpm, 50 rpm, 51 rpm, 52 rpm, 53 rpm, 54 rpm, 55 rpm, 56 rpm, 57 rpm, 58 rpm, 59 rpm, 60 rpm, 61 rpm, 62 rpm, 63 rpm, 64 rpm, 65 rpm, 66 rpm, 67 rpm, 68 rpm, 69 rpm, 70 rpm, 71 rpm, 72 rpm, 73 rpm, 74 rpm, 75 rpm, 76 rpm, 77 rpm, 78 rpm, 79 rpm, 80 rpm, 81 rpm, 82 rpm, 83 rpm, The dispersion speed may be 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm, 3000 rpm, 3200 rpm or 3500 rpm, etc. The stirring time may be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] Preferably, the fifth mixing process of step (4) is: an eighth stirring for 10 to 30 minutes at a revolution speed of 10 to 15 rpm and a dispersion speed of 400 to 1000 rpm, and then a ninth stirring for 90 to 120 minutes at a revolution speed of 25 to 35 rpm and a dispersion speed of 2000 to 3500 rpm.

[0042] For example, during the eighth stirring process of the fifth mixing, the revolution speed may be 10 rpm, 11 rpm, 12 rpm, 13 rpm, 14 rpm or 15 rpm, the dispersion speed may be 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm or 1000 rpm, and the stirring time may be 10 min, 15 min, 20 min, 25 min or 30 min, etc.; during the ninth stirring process of the fifth mixing, the revolution speed may be 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, 30 rpm, etc. The dispersion speed may be 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm, 3000 rpm, 3200 rpm or 3500 rpm, etc. The stirring time may be 90 min, 95 min, 100 min, 105 min, 110 min, 115 min or 120 min, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0043] Preferably, the viscosity of the silicon-carbon negative electrode slurry is 3000-6000 mPa·s, for example, 3000 mPa·s, 3500 mPa·s, 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, 5500 mPa·s or 6000 mPa·s, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0044] In the present invention, two stirring speeds are used in each mixing process of step (3) and step (4), which can further reduce the wear of the equipment by the solid particles in the slurry during the stirring process.

[0045] As a preferred technical solution, the preparation method comprises the following steps:

[0046] (1) Taking the total mass of the solid components of the silicon-carbon negative electrode slurry as 100%, weigh 0.5-2% of sodium carboxymethyl cellulose powder by mass, and prepare a sodium carboxymethyl cellulose solution according to the mass ratio of sodium carboxymethyl cellulose powder to solvent of (1-2%): (98-99%), and perform a first stirring for 30-60 minutes at a revolution speed of 15-18 rpm and a dispersion speed of 500-1000 rpm. After the first stirring is completed, scrape the pot wall and the stirring paddle, turn on the vacuum, turn on the circulating water, and perform a second stirring for 300-500 minutes at a revolution speed of 20-30 rpm and a dispersion speed of 1000-2000 rpm, so as to obtain a sodium carboxymethyl cellulose solution with a viscosity of 10000-20000 mPa·s;

[0047] (2) performing a third stirring for 30 to 60 minutes at a revolution speed of 15 to 25 rpm and a dispersion speed of 200 to 1000 rpm according to a mass ratio of graphite, CVD silicon carbon powder, and conductive agent (88 to 96%): (3 to 10%): (1 to 2%) to obtain an active material powder;

[0048] (3) Based on the total mass of the solid components in the silicon-carbon negative electrode slurry being 100%, a polyacrylic acid binder accounting for 2-4% by mass is weighed and set aside; then, 20-40% of the standby polyacrylic acid binder, 20-50% of the sodium carboxymethyl cellulose solution in step (1) and a solvent are added to the active material powder, and a fourth stirring is performed for 10-30 minutes at a revolution speed of 10-15 rpm, and then a fifth stirring is performed for 60-90 minutes at a revolution speed of 25-35 rpm and a dispersion speed of 2000-3500 rpm to obtain an intermediate slurry;

[0049] (4) Add 20-40% of the standby polyacrylic acid binder described in step (3) to the intermediate slurry, and perform a sixth stirring for 10-30 minutes at a revolution speed of 10-15 rpm and a dispersion speed of 200-500 rpm, and then perform a seventh stirring for 60-120 minutes at a revolution speed of 25-35 rpm and a dispersion speed of 2000-3500 rpm; then add the remaining sodium carboxymethyl cellulose solution, polyacrylic acid binder and solvent, and perform an eighth stirring for 10-30 minutes at a revolution speed of 10-15 rpm and a dispersion speed of 400-1000 rpm, and then perform a ninth stirring for 90-120 minutes at a revolution speed of 25-35 rpm and a dispersion speed of 2000-3500 rpm, to obtain a silicon-carbon negative electrode slurry with a viscosity of 3000-6000 mPa·s.

[0050] In a second aspect, the present invention provides a silicon-carbon negative electrode slurry, which is prepared by the preparation method described in the first aspect.

[0051] In a third aspect, the present invention provides a silicon-carbon negative electrode sheet, which is obtained by coating the silicon-carbon negative electrode slurry described in the second aspect on the surface of the negative electrode current collector.

[0052] In a fourth aspect, the present invention further provides a lithium-ion battery, comprising the silicon-carbon negative electrode sheet as described in the third aspect.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] The preparation method of the silicon-carbon negative electrode slurry provided by the present invention effectively reduces the viscosity of the silicon-carbon negative electrode slurry during preparation by a specific order of adding the sodium carboxymethyl cellulose solution and the polyacrylic acid binder, reduces wear on equipment, ensures that the viscosity, solid content and fineness of the slurry are all within the standard range, and suppresses the volume expansion phenomenon of CVD silicon-carbon during use. When applied to lithium-ion batteries, it exhibits excellent battery performance, and the preparation method is simple and suitable for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a flow chart of the preparation method of the silicon-carbon negative electrode slurry in Example 1. DETAILED DESCRIPTION

[0056] The technical solutions of the present invention are further illustrated by specific examples below. Those skilled in the art should understand that the examples are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusions.

[0058] Example 1

[0059] This embodiment provides a lithium ion battery negative electrode slurry, such as Figure 1 As shown, it is obtained by the following preparation method:

[0060] (1) Preparation of sodium carboxymethyl cellulose solution (CMC solution)

[0061] Taking the total mass of the solid components of the silicon-carbon negative electrode slurry as 100%, weigh 1.5% of sodium carboxymethyl cellulose powder (CMC) by mass, and mix the sodium carboxymethyl cellulose powder with water in a double planetary mixer at a mass ratio of 1.5%:98.5%. Then, perform the first stirring for 50 minutes at a revolution speed of 17 rpm and a dispersion speed of 800 rpm. After the first stirring is completed, scrape the pot wall and the stirring paddle, then turn on the vacuum, start the circulating water, and perform the second stirring for 400 minutes at a revolution speed of 25 rpm and a dispersion speed of 1500 rpm. After the second stirring is completed, test its viscosity and control it at 10,000 to 20,000 mPa·s.

[0062] (2) Mixed negative electrode active materials

[0063] The prepared negative electrode active material graphite, CVD silicon carbon powder and conductive carbon black (SP) were added to a double planetary mixer in a mass ratio of 92%:6%:2% and mixed. The mixture was stirred for 50 minutes at a revolution speed of 20 rpm and a dispersion speed of 700 rpm to obtain a uniformly mixed active material powder.

[0064] (3) Kneading of negative electrode active materials

[0065] Based on the total mass of the solid components in the silicon-carbon negative electrode slurry as 100%, a polyacrylic acid binder (PAA) with a mass ratio of 3% was weighed and set aside; 30% of the prepared sodium carboxymethyl cellulose solution, 30% of the total polyacrylic acid binder and water were added to the uniformly mixed active material powder obtained above, and the mixture was first stirred for 20 minutes at a revolution speed of 12 rpm, followed by a fifth stirring for 80 minutes at a revolution speed of 30 rpm and a dispersion speed of 3000 rpm;

[0066] (4) Forming silicon-carbon negative electrode slurry

[0067] 30% of the total polyacrylic acid binder and water were added to the intermediate slurry. The slurry was then stirred for 20 minutes at a revolution speed of 13 rpm and a dispersion speed of 300 rpm. The slurry was then stirred for 90 minutes at a revolution speed of 30 rpm and a dispersion speed of 3000 rpm. After the seventh stirring, the remaining polyacrylic acid binder, the remaining sodium carboxymethylcellulose solvent, and water were added. The slurry was then stirred for 20 minutes at a revolution speed of 13 rpm and a dispersion speed of 700 rpm. The slurry was then stirred for 100 minutes at a revolution speed of 30 rpm and a dispersion speed of 3000 rpm. The viscosity of the slurry was measured to be approximately 3000 to 6000 mPa·s.

[0068] Example 2

[0069] This embodiment provides a lithium ion battery negative electrode slurry, which is prepared by the following preparation method:

[0070] (1) Preparation of sodium carboxymethyl cellulose solution

[0071] Taking the total mass of the solid components of the silicon-carbon negative electrode slurry as 100%, weigh 0.5% of sodium carboxymethyl cellulose powder and mix it with water in a double planetary mixer at a mass ratio of 2%:98%. Then, perform the first stirring for 30 minutes at a revolution speed of 15 rpm and a dispersion speed of 500 rpm. After the stirring is completed, scrape the pot wall and stirring paddle, then turn on the vacuum, start the circulating water, and perform the second stirring for 300 minutes at a revolution speed of 20 rpm and a dispersion speed of 1000 rpm. After the stirring is completed, test its viscosity and control it within 10,000 to 20,000 mPa·s.

[0072] (2) Mixed negative electrode active materials

[0073] The prepared negative electrode active material graphite, CVD silicon carbon powder and SP were added to a double planetary mixer in a mass ratio of 90%:9%:1% and mixed. The third stirring was performed at a revolution speed of 15 rpm and a dispersion speed of 200 rpm for 30 minutes to obtain a uniformly mixed active material powder.

[0074] (3) Kneading of negative electrode active materials

[0075] Based on the total mass of the solid components in the silicon-carbon negative electrode slurry being 100%, a polyacrylic acid binder accounting for 2% by mass was weighed and set aside; 20% of the sodium carboxymethyl cellulose solution prepared in step (1), 20% of the total polyacrylic acid binder, and water were added to the uniformly mixed active material powder obtained above, and a fourth stirring was performed at a revolution speed of 10 rpm for 10 minutes, followed by a fifth stirring at a revolution speed of 25 rpm and a dispersion speed of 2000 rpm for 60 minutes;

[0076] (4) Forming silicon-carbon negative electrode slurry

[0077] 40% of the total polyacrylic acid binder and water were added to the intermediate slurry. The slurry was then stirred for 30 minutes at a revolution speed of 15 rpm and a dispersion speed of 500 rpm. The slurry was then stirred for 120 minutes at a revolution speed of 35 rpm and a dispersion speed of 3500 rpm. After the seventh stirring, the remaining polyacrylic acid binder, the remaining sodium carboxymethylcellulose solvent, and water were added. The slurry was then stirred for 30 minutes at a revolution speed of 15 rpm and a dispersion speed of 1000 rpm. The slurry was then stirred for 120 minutes at a revolution speed of 35 rpm and a dispersion speed of 3500 rpm. The viscosity of the slurry was measured to be approximately 3000 to 6000 mPa·s.

[0078] Example 3

[0079] This embodiment provides a lithium ion battery negative electrode slurry, which is prepared by the following preparation method:

[0080] (1) Preparation of sodium carboxymethyl cellulose solution

[0081] Taking the total mass of the solid components of the silicon-carbon negative electrode slurry as 100%, weigh 2% of sodium carboxymethyl cellulose powder and mix it with water in a double planetary mixer at a mass ratio of 1%:99%. Then, perform the first stirring for 60 minutes at a revolution speed of 18 rpm and a dispersion speed of 1000 rpm. After the stirring is completed, scrape the pot wall and stirring paddle, then turn on the vacuum, start the circulating water, and perform the second stirring for 500 minutes at a revolution speed of 30 rpm and a dispersion speed of 2000 rpm. After the stirring is completed, test its viscosity and control it within 10,000 to 20,000 mPa·s.

[0082] (2) Mixed negative electrode active materials

[0083] The prepared negative electrode active material graphite, CVD silicon carbon powder and SP were added to a double planetary mixer in a mass ratio of 96%:3%:1% and mixed. The third stirring was performed at a revolution speed of 25 rpm and a dispersion speed of 1000 rpm for 60 minutes to obtain a uniformly mixed active material powder.

[0084] (3) Kneading of negative electrode active materials

[0085] Based on the total mass of the solid components in the silicon-carbon negative electrode slurry being 100%, a polyacrylic acid binder having a mass fraction of 4% was weighed and set aside; a sodium carboxymethyl cellulose solution having a mass fraction of 50%, 40% of the total polyacrylic acid binder, and water were added to the uniformly mixed active material powder obtained above, and a fourth stirring was performed at a revolution speed of 15 rpm for 30 minutes, followed by a fifth stirring at a revolution speed of 35 rpm and a dispersion speed of 3500 rpm for 90 minutes;

[0086] (4) Forming silicon-carbon negative electrode slurry

[0087] 20% of the total polyacrylic acid binder and water were added to the intermediate slurry. The mixture was then stirred for 10 minutes at a revolution speed of 10 rpm and a dispersion speed of 200 rpm, followed by a seventh stirring period of 60 minutes at a revolution speed of 25 rpm and a dispersion speed of 2000 rpm. After the stirring was completed, the remaining polyacrylic acid binder, the remaining sodium carboxymethylcellulose solvent, and water were added. The mixture was then stirred for 10 minutes at a revolution speed of 10 rpm and a dispersion speed of 400 rpm, followed by a ninth stirring period of 90 minutes at a revolution speed of 25 rpm and a dispersion speed of 2000 rpm. The viscosity of the mixture was measured to be approximately 3000 to 6000 mPa·s.

[0088] Example 4

[0089] The difference between this embodiment and embodiment 1 is that in step (1), 0.3% by weight of sodium carboxymethyl cellulose powder is weighed.

[0090] The rest of the preparation methods and parameters were the same as those in Example 1.

[0091] Example 5

[0092] The difference between this embodiment and embodiment 1 is that in step (1), 3% by weight of sodium carboxymethyl cellulose powder is weighed.

[0093] The rest of the preparation methods and parameters were the same as those in Example 1.

[0094] Example 6

[0095] The difference between this embodiment and embodiment 1 is that in step (3), 1% by weight of polyacrylic acid binder is weighed and set aside.

[0096] The rest of the preparation methods and parameters were the same as those in Example 1.

[0097] Example 7

[0098] The difference between this embodiment and embodiment 1 is that in step (3), 6% by weight of polyacrylic acid adhesive is weighed and set aside.

[0099] The rest of the preparation methods and parameters were the same as those in Example 1.

[0100] Example 8

[0101] The difference between this embodiment and embodiment 1 is that in step (3), 10% of the sodium carboxymethyl cellulose solution is added to the obtained uniformly mixed active substance powder.

[0102] The rest of the preparation methods and parameters were the same as those in Example 1.

[0103] Example 9

[0104] The difference between this embodiment and embodiment 1 is that in step (3), 60% of the sodium carboxymethyl cellulose solution is added to the obtained uniformly mixed active substance powder.

[0105] The rest of the preparation methods and parameters were the same as those in Example 1.

[0106] Example 10

[0107] The difference between this embodiment and embodiment 1 is that in step (3), 10% of the total polyacrylic acid binder is added to the obtained uniformly mixed active material powder.

[0108] The rest of the preparation methods and parameters were the same as those in Example 1.

[0109] Example 11

[0110] The difference between this embodiment and embodiment 1 is that in step (3), 50% of the total polyacrylic acid binder is added to the obtained uniformly mixed active material powder.

[0111] The rest of the preparation methods and parameters were the same as those in Example 1.

[0112] Example 12

[0113] The difference between this embodiment and embodiment 1 is that in step (4), 10% of the total polyacrylic acid binder is added to the slurry obtained in step (3).

[0114] The rest of the preparation methods and parameters were the same as those in Example 1.

[0115] Example 13

[0116] The difference between this embodiment and embodiment 1 is that in step (4), 50% of the total polyacrylic acid binder is added to the slurry obtained in step (3).

[0117] The rest of the preparation methods and parameters were the same as those in Example 1.

[0118] Example 14

[0119] The difference between this embodiment and embodiment 1 is that in step (1), stirring is performed at an orbital speed of 18 rpm and a dispersion speed of 1000 rpm for 60 min, and no subsequent stirring is performed.

[0120] The rest of the preparation methods and parameters were the same as those in Example 1.

[0121] Comparative Example 1

[0122] The difference between this comparative example and Example 1 is that all the prepared sodium carboxymethyl cellulose solution, all the polyacrylic acid binder and water are added to the intermediate slurry obtained in step (2) at one time, and the mixture is first stirred at an orbital speed of 12 rpm for 60 min, and then stirred at an orbital speed of 30 rpm and a dispersion speed of 3000 rpm for 270 min.

[0123] The rest of the preparation methods and parameters were the same as those in Example 1.

[0124] Comparative Example 2

[0125] The difference between this comparative example and Example 1 is that the polyacrylic acid binder is not added in step (3), the sixth and seventh stirrings are not performed in step (4), and all the polyacrylic acid binder is added in the eighth stirring.

[0126] Other preparation methods and parameters remained the same as in Example 1.

[0127] Comparative Example 3

[0128] The difference between this comparative example and Example 1 is that the sixth stirring and the seventh stirring are not performed in step (4).

[0129] Other preparation methods and parameters remained the same as in Example 1.

[0130] Performance Testing

[0131] The silicon-carbon negative electrode slurry prepared in Examples 1 to 14 and Comparative Examples 1 to 3 was coated on the surface of a copper foil to obtain a silicon-carbon negative electrode sheet, and then its powder loss rate and peeling force were tested; the above-mentioned silicon-carbon negative electrode sheet and the positive electrode sheet were prepared into a lithium-ion battery equipped with a silicon-carbon negative electrode by winding, packaging, liquid injection, formation, capacity separation, aging, and sorting. The prepared lithium-ion battery was then tested for initial discharge specific capacity, first-week coulomb efficiency, and cycle capacity retention rate using a Xinwei test cabinet at 20°C. The test results are shown in Table 1:

[0132] Table 1

[0133]

[0134]

[0135] From the comparison of the data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1, it can be seen that the silicon-carbon negative electrode prepared by the preparation method of the silicon-carbon negative electrode slurry provided by the present invention has a significantly reduced powder loss rate; when applied to lithium-ion batteries, it shows a higher first-week efficiency and a higher capacity retention rate after 100 cycles. This shows that the preparation method of the silicon-carbon negative electrode slurry provided by the present invention, through the specific order of adding sodium carboxymethyl cellulose solution and polyacrylic acid binder, can not only ensure that the viscosity, solid content and fineness of the slurry are within the standard range, reducing wear on the equipment, but also effectively suppressing the volume expansion phenomenon of CVD silicon-carbon during use, thereby improving the capacity retention rate of the lithium-ion battery and improving the overall performance of the battery.

[0136] Comparing the data of Examples 4-7 with Example 1 in Table 1, it can be seen that varying the amount of sodium carboxymethyl cellulose and polyacrylic acid binder added to the entire silicon-carbon anode slurry preparation affects the powder shedding rate and peeling force of the anode sheet, the volume expansion of the CVD silicon-carbon during use, and, consequently, the overall performance of the battery. In practical applications, different mass fractions of sodium carboxymethyl cellulose and polyacrylic acid binder can be selected based on the powder shedding rate, peeling force, and electrochemical performance of the anode slurry. Taking the total mass of the solid components of the silicon-carbon anode slurry as 100%, a mass fraction of 0.5-2% sodium carboxymethyl cellulose and a mass fraction of 2-4% polyacrylic acid binder are more conducive to obtaining anode slurries with excellent overall performance.

[0137] Comparing the data of Examples 8 to 13 with Example 1 in Table 1, it can be seen that changing the amount of polyacrylic acid binder and / or sodium carboxymethyl cellulose added in different mixing stages will also affect the physical and chemical properties of the silicon-carbon negative electrode sheet and battery performance. Taking the total mass of all polyacrylic acid binder and all sodium carboxymethyl cellulose solution as 100%, when the mass proportion of the first part of polyacrylic acid binder is 20-40%, the mass proportion of the first part of sodium carboxymethyl cellulose solution is 20-50%, and the mass proportion of the second part of polyacrylic acid binder is 20-40%, it is more conducive to the uniform dispersion of the silicon-carbon negative electrode slurry, thereby more conducive to improving the overall performance of the negative electrode slurry.

[0138] From the comparison of the data of Example 14 and Example 1 in Table 1, it can be seen that during the mixing process of the sodium carboxymethyl cellulose solution, by adding a second stirring, the mixing effect of the sodium carboxymethyl cellulose solution can be further improved, thereby obtaining a silicon-carbon negative electrode slurry with better comprehensive performance.

[0139] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode slurry, characterized in that: The preparation method comprises: (1) mixing sodium carboxymethyl cellulose powder and a solvent to obtain a sodium carboxymethyl cellulose solution; (2) performing a second mixing of the negative electrode active material and the conductive agent to obtain active material powder; (3) adding a portion of the sodium carboxymethyl cellulose solution, the first portion of the polyacrylic acid binder, and the solvent to the active substance powder for a third mixing step to obtain an intermediate slurry; (4) adding the second portion of the polyacrylic acid binder to the intermediate slurry for a fourth mixing process, and then adding the remaining sodium carboxymethyl cellulose solution, the third portion of the polyacrylic acid binder, and the solvent for a fifth mixing process; The negative electrode active material includes CVD silicon carbon; The first mixing process in step (1) is as follows: a first stirring for 30 to 60 minutes at a revolution speed of 15 to 18 rpm and a dispersion speed of 500 to 1000 rpm, and then a second stirring for 300 to 500 minutes at a revolution speed of 20 to 30 rpm and a dispersion speed of 1000 to 2000 rpm; The second mixing process in step (2) is as follows: performing a third stirring for 30 to 60 minutes at a revolution speed of 15 to 25 rpm and a dispersion speed of 200 to 1000 rpm; The third mixing process of step (3) is as follows: a fourth stirring for 10 to 30 minutes at a revolution speed of 10 to 15 rpm, and then a fifth stirring for 60 to 90 minutes at a revolution speed of 25 to 35 rpm and a dispersion speed of 2000 to 3500 rpm; based on the total mass of the first part, the second part and the third part of the polyacrylic acid binder being 100%, the mass proportion of the first part of the polyacrylic acid binder in step (3) is 20 to 40%; based on the mass of the sodium carboxymethyl cellulose solution in step (1) being 100%, the mass proportion of the sodium carboxymethyl cellulose solution in step (3) is 20 to 50%; The fourth mixing process of step (4) is as follows: a sixth stirring for 10 to 30 minutes at a revolution speed of 10 to 15 rpm and a dispersion speed of 200 to 500 rpm, and then a seventh stirring for 60 to 120 minutes at a revolution speed of 25 to 35 rpm and a dispersion speed of 2000 to 3500 rpm; in the fourth mixing of step (4), the mass proportion of the second part of the polyacrylic acid binder is 20 to 40%; The fifth mixing process of step (4) is as follows: an eighth stirring for 10 to 30 minutes at a revolution speed of 10 to 15 rpm and a dispersion speed of 400 to 1000 rpm, and then a ninth stirring for 90 to 120 minutes at a revolution speed of 25 to 35 rpm and a dispersion speed of 2000 to 3500 rpm; The viscosity of the silicon-carbon negative electrode slurry is 3000-6000 mPa·s.

2. The method for preparing the silicon-carbon negative electrode slurry according to claim 1, wherein: Taking the total mass of the solid components in the silicon-carbon negative electrode slurry as 100%, in step (1), the mass proportion of the sodium carboxymethyl cellulose powder is 0.5-2%.

3. The method for preparing the silicon-carbon negative electrode slurry according to claim 1, wherein: In step (1), the mass ratio of the sodium carboxymethyl cellulose powder to the solvent is (1-2%):(98-99%).

4. The method for preparing the silicon-carbon negative electrode slurry according to claim 1, wherein: The viscosity of the sodium carboxymethyl cellulose solution is 10000-20000 mPa·s.

5. The method for preparing the silicon-carbon negative electrode slurry according to claim 1, wherein: After the first stirring is completed, the pot wall and the stirring paddle are scraped, the vacuum is turned on, and the circulating water is turned on.

6. The method for preparing the silicon-carbon negative electrode slurry according to claim 1, wherein: The negative electrode active material further includes graphite.

7. The method for preparing the silicon-carbon negative electrode slurry according to claim 6, wherein: The mass ratio of the graphite, CVD silicon-carbon powder and conductive agent is (88-96%): (3-10%): (1-2%).

8. The method for preparing the silicon-carbon negative electrode slurry according to claim 1, wherein: Taking the total mass of the solid components in the silicon-carbon negative electrode slurry as 100%, the total mass of the first part, the second part and the third part of the polyacrylic acid binder accounts for 2-4%.

9. The method for preparing the silicon-carbon negative electrode slurry according to claim 1, wherein: The preparation method comprises: (1) Based on the total mass of the solid components of the silicon-carbon negative electrode slurry being 100%, 0.5-2% of sodium carboxymethyl cellulose powder is weighed, and a sodium carboxymethyl cellulose solution is prepared according to the mass ratio of sodium carboxymethyl cellulose powder to solvent of (1-2%):(98-99%), and the first stirring is performed. After the first stirring is completed, the pot wall and the stirring paddle are scraped, the vacuum is turned on, the circulating water is turned on, and the second stirring is performed to obtain a sodium carboxymethyl cellulose solution with a viscosity of 10,000-20,000 mPa·s; (2) performing the second mixing according to the mass ratio of graphite, CVD silicon carbon powder and conductive agent (88-96%): (3-10%): (1-2%) to obtain active material powder; (3) Based on the total mass of the solid components in the silicon-carbon negative electrode slurry being 100%, a polyacrylic acid binder accounting for 2-4% by mass is weighed and set aside; then, the first portion of the polyacrylic acid binder, the portion of the sodium carboxymethyl cellulose solution and the solvent are added to the active material powder to perform the third mixing to obtain an intermediate slurry; (4) adding the second part of the polyacrylic acid binder to the intermediate slurry and performing the fourth mixing; then adding the remaining sodium carboxymethyl cellulose solution, the third part of the polyacrylic acid binder and the solvent, and performing the fifth mixing to obtain the silicon-carbon negative electrode slurry.

10. A silicon-carbon negative electrode slurry, characterized in that: The silicon-carbon negative electrode slurry is prepared by the preparation method according to any one of claims 1 to 9.

11. A silicon-carbon negative electrode sheet, characterized in that: The silicon-carbon negative electrode sheet is obtained by coating the silicon-carbon negative electrode slurry according to claim 10 on the surface of the negative electrode current collector.

12. A lithium ion battery, characterized in that: The lithium-ion battery includes the silicon-carbon negative electrode sheet as claimed in claim 11.

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