A silicon-based negative electrode slurry and its preparation method, negative electrode sheet and battery

Abstract

This invention provides a silicon-based negative electrode slurry, its preparation method, a negative electrode sheet, and a battery. The preparation method includes: first mixing silicon-based materials, graphite materials, a zero-dimensional conductive agent, and a dispersant to obtain a first mixture; second mixing the first mixture, a first portion of a one-dimensional conductive agent, and a first portion of a first binder to obtain a second mixture; third mixing the second mixture with a solvent to obtain a third mixture; fourth mixing the third mixture, a second portion of the one-dimensional conductive agent, a second portion of the first binder, and a solvent to obtain a fourth mixture; and fifth mixing the fourth mixture, a third portion of the one-dimensional conductive agent, and a third portion of the first binder to obtain the silicon-based negative electrode slurry. This invention, by adding the one-dimensional conductive agent and the first binder in three stages, ensures material dispersion, promotes the formation of a stable three-dimensional network structure, improves the peeling force of the negative electrode sheet, and resolves the contradiction between homogenization and low damage.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a silicon-based negative electrode slurry and its preparation method, a negative electrode sheet and a battery. Background Technology

[0002] With the rapid growth in demand for high-energy-density lithium-ion batteries from new energy vehicles and energy storage systems, silicon-based anode materials are considered key anode materials for next-generation lithium-ion batteries due to their theoretical specific capacity (approximately 4200 mAh / g) being far higher than that of traditional graphite anodes (372 mAh / g). However, silicon materials exhibit a volume expansion effect of approximately 300% during charge and discharge, which can easily lead to problems such as active material pulverization and continuous growth of solid electrolyte interfacial films, severely restricting their commercial application.

[0003] To alleviate the aforementioned problems, the mainstream technical approach has been to combine nano-silicon with conductive carbon matrices (such as graphite, carbon nanotubes, and graphene) to form silicon-carbon anodes. In this approach, slurry mixing is the first critical step in electrode manufacturing, and its quality directly determines the distribution of active materials, conductive agents, and binders in three-dimensional space, thus having a decisive impact on the integrity of the electrode's conductive network, mechanical stability, and electrochemical performance.

[0004] Currently, existing technologies for preparing silicon-carbon anode slurries mainly follow the traditional stirring process used for graphite anodes, which generally suffers from the following problems:

[0005] ① Homogenization and low damage are difficult to achieve simultaneously: In silicon-carbon composite materials, nano-silicon particles have high surface energy and are extremely prone to agglomeration. To break up the agglomeration, high shear force is often required. However, excessive mechanical force can lead to the breakage of brittle nano-silicon particles, damage to the carbon skeleton structure, and may cause the conductive agent (such as carbon nanotubes) to break due to excessive shearing, which is not conducive to the establishment of a stable conductive network.

[0006] ② Strong dependence on dispersion medium and sequence: The interaction between binders (such as CMC, SBR, polyacrylic acid) and silicon and carbon surfaces is complex. Traditional single-step or simple two-step feeding and stirring methods are difficult to achieve ideal adsorption and coating of binder molecules on the surface of active materials, which easily leads to poor slurry stability, rapid sedimentation, and the appearance of a "jelly-like" texture.

[0007] Therefore, developing a method for preparing silicon-based anode slurry that can achieve uniform dispersion at the nanoscale, maximize the protection of material structural integrity, and possess high process stability and repeatability has become an urgent need to break through the bottleneck of silicon-based anode applications and improve the overall performance of high-energy-density batteries. Summary of the Invention

[0008] The purpose of this invention is to provide a silicon-based negative electrode slurry and its preparation method, a negative electrode sheet and a battery. The preparation method involves adding a one-dimensional conductive agent and a first binder in three stages, which not only ensures material dispersion and enhances the conductivity of the electrode sheet, but also promotes the uniform and firm coating of the first binder molecules on the surface of the active material, forming a stable three-dimensional network structure and improving the peeling force of the negative electrode sheet, thereby solving the contradiction between homogenization and low damage.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a silicon-based anode paste, the method comprising the following steps:

[0011] (1) A first mixture is obtained by mixing silicon-based material, graphite material, zero-dimensional conductive agent and dispersant;

[0012] (2) The first mixture from step (1), the first part of the one-dimensional conductive agent, and the first part of the first adhesive are mixed a second time to obtain a second mixture;

[0013] (3) The second mixture from step (2) and the solvent are mixed for a third time to obtain a third mixture;

[0014] (4) Mix the third mixture described in step (3), the second part of the one-dimensional conductive agent, the second part of the first binder, and the solvent in a fourth mixture to obtain a fourth mixture;

[0015] (5) The fourth mixture, the third part of the one-dimensional conductive agent and the third part of the first binder described in step (4) are mixed for the fifth time to obtain the silicon-based negative electrode slurry.

[0016] The preparation method of this invention involves first mixing silicon-based materials, graphite materials, zero-dimensional conductive agents, and dispersants without adding solvent. Then, a one-dimensional conductive agent and a first binder are added for the first time to prevent the above materials from agglomerating in the solvent and to promote the uniform and firm coating of the first binder molecules on the surface of the active material. Solvent is then added again for dispersion. Subsequently, the one-dimensional conductive agent and the first binder are added in two more separate additions for dispersion. Therefore, this invention, by adding the one-dimensional conductive agent in three separate additions, helps to disperse the one-dimensional conductive agent and enhances the conductivity of the electrode. At the same time, this invention, by adding the first binder in three separate additions, promotes the uniform and firm coating of the first binder molecules on the surface of the active material, forming a stable three-dimensional network structure, which helps to improve the peeling force of the negative electrode, thereby resolving the contradiction between homogenization and low damage.

[0017] The first part, the second part, and the third part of the one-dimensional conductive agent in this invention refer to the fact that, during the preparation process, all one-dimensional conductive agents are divided into three parts for addition in three stages; the same applies to the first part, the first binder, the second part, and the third part.

[0018] Preferably, in step (1), the stirring time of the first mixing is 30 min to 60 min, for example, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min; the revolution speed is 25 rpm to 30 rpm, for example, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm or 30 rpm; the rotation speed is 1500 rpm to 2000 rpm, for example, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm or 2000 rpm; and the stirring temperature is below 45℃, for example, 25℃, 35℃ or 44℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the silicon-based material in step (1) includes silicon-carbon material.

[0020] Preferably, the zero-dimensional conductive agent in step (1) includes conductive carbon black.

[0021] Preferably, the dispersant in step (1) comprises sodium carboxymethyl cellulose.

[0022] Preferably, in step (2), the first part of the one-dimensional conductive agent accounts for 25wt%-30wt% of the total amount of one-dimensional conductive agent added. For example, it can be 25wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, in step (2), the first part of the first adhesive accounts for 20wt%-30wt% of the total amount of the first adhesive added. For example, it can be 20wt%, 22wt%, 24wt%, 26wt%, 28wt% or 30wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the mixing time in step (2) is 10 min to 30 min, for example, 10 min, 15 min, 20 min, 25 min or 30 min; the revolution speed is 25 rpm to 30 rpm, for example, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm or 30 rpm; the rotation speed is 1500 rpm to 2000 rpm, for example, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm or 2000 rpm; and the stirring temperature is below 45℃, for example, 25℃, 35℃ or 44℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the one-dimensional conductive agent in step (2), the one-dimensional conductive agent in step (4), and the one-dimensional conductive agent in step (5) are all carbon nanotubes (single-arm carbon nanotubes).

[0026] Preferably, the first adhesive in step (2), the first adhesive in step (4), and the first adhesive in step (5) are all polyacrylic adhesives (such as polyacrylic acid and / or lithium polyacrylate).

[0027] Preferably, the third mixing time in step (3) is 10 min to 30 min, for example, 10 min, 15 min, 20 min, 25 min or 30 min, the revolution speed is 25 rpm to 30 rpm, for example, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm or 30 rpm, and the stirring temperature is below 45℃, for example, 25℃, 35℃ or 44℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the solid content of the third mixture in step (3) is 69wt%-73wt%, for example, it can be 69wt%, 70wt%, 71wt%, 72wt% or 73wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, in step (4), the second part of the one-dimensional conductive agent accounts for 25wt%-30wt% of the total amount of one-dimensional conductive agent added. For example, it can be 25wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, in step (4), the second part of the first adhesive accounts for 20wt%-30wt% of the total amount of the first adhesive added. For example, it can be 20wt%, 22wt%, 24wt%, 26wt%, 28wt% or 30wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the time for the fourth mixing in step (4) is greater than the time for the second mixing in step (2).

[0032] Preferably, the rotation speed of the fourth mixture in step (4) is greater than the rotation speed of the second mixture in step (2).

[0033] Preferably, the temperature of the fourth mixture in step (4) is lower than the temperature of the second mixture in step (2).

[0034] In this invention, a second mixing is performed when the one-dimensional conductive agent and the first binder are added for the first time, and a fourth mixing is performed when the one-dimensional conductive agent and the first binder are added for the second time. In order to cooperate with the three-time addition method, the time and rotation speed of the fourth mixing must be greater than those of the second mixing, and the temperature of the fourth mixing must be lower than that of the second mixing, so as to maximize the uniformity of dispersion and reduce damage to the material.

[0035] Preferably, the fourth mixing time in step (4) is 60 min-100 min, for example, 60 min, 70 min, 80 min, 90 min or 100 min; the revolution speed is 25 rpm-30 rpm, for example, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm or 30 rpm; the rotation speed is 3000 rpm-4500 rpm, for example, 3000 rpm, 3500 rpm, 3800 rpm, 4000 rpm or 4500 rpm; the stirring temperature is below 25℃, for example, 5℃, 10℃, 15℃, 20℃ or 24℃; and the vacuum degree is <-80 kPa, for example, -85 kPa, -88 kPa, -90 kPa, -92 kPa or -95 kPa, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the solid content of the fourth mixture in step (4) is 40wt%-50wt%, for example, it can be 40wt%, 42wt%, 44wt%, 46wt%, 48wt% or 50wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, an auxiliary agent is added during the fifth mixing in step (5).

[0038] In this invention, an additive is added during the final addition of the one-dimensional conductive agent and the first binder to complement the large amount of one-dimensional conductive agent and the first binder in the system, promote the uniform dispersion of all one-dimensional conductive agents and the first binder, and at the same time, the addition of the additive can further match the mixing conditions during the fifth mixing.

[0039] Preferably, the additives include butanediol and / or ethyl cellulose.

[0040] Preferably, the third part of the one-dimensional conductive agent in step (5) accounts for 40wt%-50wt% of the total amount of one-dimensional conductive agent added. For example, it can be 40wt%, 42wt%, 44wt%, 46wt%, 48wt% or 50wt%, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the third part of the first adhesive in step (5) accounts for 40wt%-60wt% of the total amount of the first adhesive added. For example, it can be 40wt%, 45wt%, 50wt%, 55wt% or 60wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the time for the fifth mixing in step (5) is greater than the time for the second mixing in step (2).

[0043] Preferably, the rotation speed of the fifth mixture in step (5) is greater than the rotation speed of the second mixture in step (2).

[0044] Preferably, the temperature of the fifth mixture in step (5) is lower than the temperature of the second mixture in step (2).

[0045] Similarly, when adding the one-dimensional conductive agent and the first binder for the last time, a greater rotation speed, a longer time, and a lower temperature are required. However, there is no need to further improve the fourth mixture. Since an additive is added during the last addition, the conditions for the fifth mixture can be improved based on the second mixture to avoid the problem of material damage caused by blindly increasing the stirring speed and time.

[0046] Preferably, the fifth mixing time in step (5) is 60 min to 100 min, for example, 60 min, 70 min, 80 min, 90 min or 100 min; the revolution speed is 25 rpm to 30 rpm, for example, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm or 30 rpm; the rotation speed is 3000 rpm to 4500 rpm, for example, 3000 rpm, 3500 rpm, 3800 rpm, 4000 rpm or 4500 rpm; the stirring temperature is below 25℃, for example, 10℃, 15℃, 20℃ or 24℃; and the vacuum degree is < -80 kPa, for example, -85 kPa, -88 kPa, -90 kPa, -92 kPa or -95 kPa, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, after the fifth mixing in step (5) is completed, a second binder is added to the resulting mixture to continue the sixth mixing.

[0048] Preferably, the second adhesive comprises styrene-butadiene rubber.

[0049] Preferably, the sixth mixing time is 20-40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes; the revolution speed is 25-30 rpm, for example, 25 rpm, 26 rpm, 27 rpm, 28 rpm, 29 rpm, or 30 rpm; the rotation speed is 1500-2000 rpm, for example, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, or 2000 rpm; the stirring temperature is below 25°C, for example, 10°C, 15°C, 20°C, or 24°C; and the vacuum degree is <-80 kPa, for example, -85 kPa, -88 kPa, -90 kPa, -92 kPa, or -95 kPa, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, after the sixth mixing is completed, defoaming and filtration are also performed;

[0051] Preferably, the defoaming time is 10-30 minutes, for example, 10, 15, 20, 25, or 30 minutes; the revolution speed is 25-30 rpm, for example, 25, 26, 27, 28, 29, or 30 rpm; the stirring temperature is below 25°C, for example, 0°C, 5°C, 10°C, 15°C, 20°C, or 25°C; and the vacuum degree is <-80 kPa, for example, -85 kPa, -88 kPa, -90 kPa, -92 kPa, or -95 kPa, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, by mass, the silicon-based negative electrode slurry in step (5) comprises 15-20 parts of silicon-based material, such as 15, 16, 17, 18, 19, or 20 parts; 80-85 parts of graphite material, such as 80, 81, 82, 83, 84, or 85 parts; 0.2-0.7 parts of zero-dimensional conductive agent, such as 0.2, 0.3, 0.4, 0.5, 0.6, or 0.7 parts; and 0.1-0.2 parts of one-dimensional conductive agent, such as 0.1, 0.12, or 0.14 parts. 0.16 parts, 0.18 parts, or 0.2 parts; 2.5 parts to 4 parts of a first binder, such as 2.5 parts, 2.8 parts, 3 parts, 3.5 parts, 3.8 parts, or 4 parts; 0.25 parts to 0.5 parts of a dispersant, such as 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, or 0.5 parts; 0 parts to 0.8 parts of a second binder, such as 0 parts, 0.2 parts, 0.4 parts, 0.6 parts, or 0.8 parts; 1 part to 5 parts of an additive, such as 1 part, 2 parts, 3 parts, 4 parts, or 5 parts; and a solvent (deionized water).

[0053] Preferably, the solid content of the silicon-based negative electrode slurry in step (5) is 40wt%-50wt%, for example, it can be 40wt%, 42wt%, 44wt%, 46wt%, 48wt% or 50wt%, and the viscosity is 3000mPa·s-5000mPa·s, for example, it can be 3000mPa·s, 3500mPa·s, 4000mPa·s, 4500mPa·s or 5000mPa·s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] In a second aspect, the present invention provides a silicon-based anode slurry, which is prepared by the preparation method described in the first aspect.

[0055] Thirdly, the present invention provides a negative electrode sheet, wherein the slurry for preparing the negative electrode sheet comprises the silicon-based negative electrode slurry as described in the second aspect.

[0056] Fourthly, the present invention provides a battery comprising a negative electrode as described in the third aspect.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The preparation method of this invention involves first mixing silicon-based materials, graphite materials, zero-dimensional conductive agents, and dispersants without adding solvent. Then, a one-dimensional conductive agent and a first binder are added for the first time to prevent the materials from agglomerating in the solvent and to promote uniform and firm coating of the first binder molecules on the surface of the active material. Solvent is then added again for dispersion, followed by two more additions of the one-dimensional conductive agent and the first binder for dispersion. Therefore, this invention, by adding the one-dimensional conductive agent in three stages, facilitates its dispersion and enhances the conductivity of the electrode. Simultaneously, the three-stage addition of the first binder promotes uniform and firm coating of the first binder molecules on the surface of the active material, forming a stable three-dimensional network structure, which helps improve the peel strength of the negative electrode, thus resolving the contradiction between homogenization and low damage. Furthermore, this invention clarifies the optimal matching relationship of key process parameters (such as rotation speed, time, temperature, and vacuum degree at each stage), establishes a standardized operating procedure, significantly reduces batch variations, and improves the consistency of the slurry and the electrode. Attached Figure Description

[0059] Figure 1 This is a schematic diagram illustrating the flowability of the silicon-based anode slurry described in Embodiment 1 of the present invention.

[0060] Figure 2 This is a schematic diagram illustrating the flowability of the silicon-based anode slurry described in Comparative Example 1 of the present invention.

[0061] Figure 3 This is a schematic diagram illustrating the flowability of the silicon-based anode slurry described in Comparative Example 2 of the present invention. Detailed Implementation

[0062] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0063] Example 1

[0064] This embodiment provides a silicon-based anode slurry and its preparation method. By weight, the silicon-based anode slurry includes 18 parts of silicon-carbon material, 82 parts of graphite material, 0.5 parts of conductive carbon black, 0.15 parts of single-arm carbon nanotubes, 3 parts of polyacrylic acid, 0.3 parts of sodium carboxymethyl cellulose, 0.5 parts of styrene-butadiene rubber, 2 parts of additives (specifically butanediol), and deionized water. The silicon-based anode slurry is prepared according to this formula.

[0065] The preparation method of the silicon-based anode slurry includes the following steps:

[0066] (1) Silicon carbon material, graphite material, conductive carbon black and sodium carboxymethyl cellulose are added to a mixing tank for the first mixing. The stirring time of the first mixing is 40 min, the revolution speed is set to 25 rpm, the rotation speed is set to 1800 rpm, and the stirring temperature is 35℃ to obtain the first mixture.

[0067] (2) Add 30wt% of single-arm carbon nanotubes and 30wt% of polyacrylic acid to a mixing tank for a second mixing. The mixing time for the second mixing is 20min, the revolution speed is set to 30rpm, the rotation speed is set to 1800rpm, and the mixing temperature is 40℃ to obtain the second mixture.

[0068] (3) Based on the kneading solid content of silicon carbide and graphite, deionized water is added to the mixing tank for a third mixing. The third mixing time is 20 min, the revolution speed is set to 30 rpm, and the stirring temperature is 40 ℃, to obtain a third mixture with a solid content of 70 wt%.

[0069] (4) Add 25wt% of single-arm carbon nanotubes, 20wt% of polyacrylic acid and deionized water to a mixing tank for a fourth mixing. The fourth mixing time is 80min, the revolution speed is set to 25rpm, the rotation speed is set to 4000rpm, the stirring temperature is 20℃, and the vacuum degree is -90kpa to obtain a fourth mixture with a solid content of 45wt%.

[0070] (5) Add 45wt% of single-arm carbon nanotubes, 50wt% of polyacrylic acid binder and additives to a mixing tank for a fifth mixing. The fifth mixing time is 80min, the revolution speed is set to 30rpm, the rotation speed is set to 4000rpm, the stirring temperature is 20℃, and the vacuum degree is -90kpa to obtain the fifth mixture.

[0071] (6) Add styrene-butadiene rubber to a mixing tank and disperse for 30 min. The dispersion revolution speed is set to 25 rpm, the rotation speed is set to 2000 rpm, the stirring temperature is 23℃, and the vacuum degree is -85 kPa to obtain the sixth mixture.

[0072] (7) The sixth mixture was slowly stirred in a mixing tank for 20 minutes to defoam. The defoaming revolution speed was set to 30 rpm, the stirring temperature was 20℃, and the vacuum degree was -85 kPa.

[0073] (8) After defoaming, the slurry is filtered with a sieve to obtain the silicon-based negative electrode slurry with a solid content of 45wt% and a viscosity of 4000mPa·s.

[0074] Example 2

[0075] This embodiment provides a silicon-based anode slurry and its preparation method. By weight, the silicon-based anode slurry includes 20 parts of silicon-carbon material, 80 parts of graphite material, 0.7 parts of conductive carbon black, 0.1 parts of single-arm carbon nanotubes, 4 parts of polyacrylic acid, 0.5 parts of sodium carboxymethyl cellulose, 0.8 parts of styrene-butadiene rubber, 5 parts of additives (specifically ethyl cellulose), and deionized water. The silicon-based anode slurry is prepared according to this formula.

[0076] The preparation method of the silicon-based anode slurry includes the following steps:

[0077] (1) Silicon carbon material, graphite material, conductive carbon black and sodium carboxymethyl cellulose are added to a mixing tank for the first mixing. The stirring time of the first mixing is 60 min, the revolution speed is set to 25 rpm, the rotation speed is set to 1500 rpm, and the stirring temperature is 35℃ to obtain the first mixture.

[0078] (2) Add 25wt% of single-arm carbon nanotubes and 30wt% of polyacrylic acid to a mixing tank for a second mixing. The mixing time for the second mixing is 30min, the revolution speed is set to 25rpm, the rotation speed is set to 1500rpm, and the mixing temperature is 40℃ to obtain the second mixture.

[0079] (3) Based on the kneading solid content of silicon carbide and graphite, deionized water is added to the mixing tank for a third mixing. The third mixing time is 10 min, the revolution speed is set to 30 rpm, and the stirring temperature is 40℃, to obtain a third mixture with a solid content of 73 wt%.

[0080] (4) Add 25wt% of single-arm carbon nanotubes, 30wt% of polyacrylic acid and deionized water to a mixing tank for a fourth mixing. The fourth mixing time is 100min, the revolution speed is set to 25rpm, the rotation speed is set to 3000rpm, the stirring temperature is 23℃, and the vacuum degree is -85kpa ​​to obtain a fourth mixture with a solid content of 50wt%.

[0081] (5) Add 50wt% of single-arm carbon nanotubes, 40wt% of polyacrylic acid binder and additives to a mixing tank for a fifth mixing. The fifth mixing time is 60min, the revolution speed is set to 30rpm, the rotation speed is set to 4500rpm, the stirring temperature is 20℃, and the vacuum degree is -90kpa to obtain the fifth mixture.

[0082] (6) Add styrene-butadiene rubber to a mixing tank and disperse for 40 min. The dispersion revolution speed is set to 30 rpm, the rotation speed is set to 1500 rpm, the stirring temperature is 20℃, and the vacuum degree is -90 kPa to obtain the sixth mixture.

[0083] (7) The sixth mixture was slowly stirred in a mixing tank for 30 minutes to defoam. The defoaming revolution speed was set to 25 rpm, the stirring temperature was 20℃, and the vacuum degree was -85 kPa.

[0084] (8) After defoaming, the slurry is filtered with a sieve to obtain the silicon-based negative electrode slurry with a solid content of 50 wt% and a viscosity of 5000 mPa·s.

[0085] Example 3

[0086] This embodiment provides a silicon-based anode slurry and its preparation method. By weight, the silicon-based anode slurry comprises 15 parts of silicon-carbon material, 85 parts of graphite material, 0.2 parts of conductive carbon black, 0.2 parts of single-arm carbon nanotubes, 2.5 parts of polyacrylic acid, 0.25 parts of sodium carboxymethyl cellulose, 0.1 parts of styrene-butadiene rubber, 1 part of additives (specifically butanediol), and deionized water. The silicon-based anode slurry is prepared according to this formula.

[0087] The preparation method of the silicon-based anode slurry includes the following steps:

[0088] (1) Silicon carbon material, graphite material, conductive carbon black and sodium carboxymethyl cellulose are added to a mixing tank for the first mixing. The mixing time of the first mixing is 30 min, the revolution speed is set to 30 rpm, the rotation speed is set to 2000 rpm, and the mixing temperature is 40℃ to obtain the first mixture.

[0089] (2) Add 30wt% of single-arm carbon nanotubes and 20wt% of polyacrylic acid to a mixing tank for a second mixing. The mixing time for the second mixing is 10min, the revolution speed is set to 30rpm, the rotation speed is set to 2000rpm, and the mixing temperature is 40℃ to obtain the second mixture.

[0090] (3) Based on the kneading solid content of silicon carbide and graphite, deionized water is added to the mixing tank for a third mixing. The third mixing time is 30 min, the revolution speed is set to 25 rpm, and the stirring temperature is 35℃, to obtain a third mixture with a solid content of 69 wt%.

[0091] (4) Add 30wt% of single-arm carbon nanotubes, 20wt% of polyacrylic acid and deionized water to a mixing tank for a fourth mixing. The fourth mixing time is 100min, the revolution speed is set to 25rpm, the rotation speed is set to 3000rpm, the stirring temperature is 15℃, and the vacuum degree is -85kpa ​​to obtain a fourth mixture with a solid content of 40wt%.

[0092] (5) Add 40wt% of single-arm carbon nanotubes, 60wt% of polyacrylic acid binder and additives to a mixing tank for a fifth mixing. The fifth mixing time is 100min, the revolution speed is set to 25rpm, the rotation speed is set to 3000rpm, the stirring temperature is 15℃, and the vacuum degree is -85kpa ​​to obtain the fifth mixture.

[0093] (6) Add styrene-butadiene rubber to a mixing tank and disperse for 20 minutes. The dispersion revolution speed is set to 25 rpm, the rotation speed is set to 2000 rpm, the stirring temperature is 20℃, and the vacuum degree is -85 kPa to obtain the sixth mixture.

[0094] (7) The sixth mixture was slowly stirred in a mixing tank for 10 minutes to defoam. The defoaming revolution speed was set to 30 rpm, the stirring temperature was 20℃, and the vacuum degree was -90 kPa.

[0095] (8) After defoaming, the slurry is filtered with a sieve to obtain the silicon-based negative electrode slurry with a solid content of 40wt% and a viscosity of 3000mPa·s.

[0096] Example 4

[0097] This embodiment provides a silicon-based negative electrode slurry and its preparation method. The preparation method is the same as that in Example 1 except that the time, rotation speed and temperature of the fourth mixing in step (4) are the same as those of the second mixing in step (2) (the fourth mixing time is 20 min, the rotation speed is set to 1800 rpm and the stirring temperature is 40℃).

[0098] Example 5

[0099] This embodiment provides a silicon-based negative electrode slurry and its preparation method. The preparation method is the same as that in Example 1 except that the time, rotation speed and temperature of the fifth mixing in step (5) are the same as those of the second mixing in step (2) (the time of the fifth mixing is 20 min, the rotation speed is set to 1800 rpm and the stirring temperature is 40℃).

[0100] Example 6

[0101] This embodiment provides a silicon-based negative electrode slurry and its preparation method. The preparation method is the same as that in Example 1, except that the additives in step (5) are added in step (4).

[0102] Example 7

[0103] This embodiment provides a silicon-based negative electrode slurry and its preparation method. The preparation method is the same as that in Example 1, except that the additives mentioned in step (5) are added in step (2).

[0104] Comparative Example 1

[0105] This comparative example provides a silicon-based anode slurry and its preparation method. By mass, the silicon-based anode slurry comprises 18 parts of silicon-carbon material, 82 parts of graphite material, 0.5 parts of conductive carbon black, 0.15 parts of single-arm carbon nanotubes, 3 parts of polyacrylic acid, 0.3 parts of sodium carboxymethyl cellulose, 0.5 parts of styrene-butadiene rubber, 2 parts of additives (specifically butanediol), and deionized water. The silicon-based anode slurry is prepared according to this formula.

[0106] The preparation method of the silicon-based anode slurry includes the following steps:

[0107] (1) Silicon carbon material, graphite material, conductive carbon black and sodium carboxymethyl cellulose are added to a mixing tank for the first mixing. The stirring time of the first mixing is 40 min, the revolution speed is set to 25 rpm, the rotation speed is set to 1800 rpm, and the stirring temperature is 35℃ to obtain the first mixture.

[0108] (2) All single-arm carbon nanotubes, 50 wt% polyacrylic acid, additives and deionized water were added to a mixing tank for a second mixing. The mixing time for the second mixing was 70 min, the revolution speed was set to 30 rpm, the rotation speed was set to 1800 rpm, and the mixing temperature was 40 °C, to obtain a second mixture with a solid content of 70 wt%.

[0109] (3) The remaining polyacrylic acid and deionized water are added to the mixing tank for a third mixing. The third mixing time is 150 min, the revolution speed is set to 25 rpm, the rotation speed is set to 4000 rpm, the stirring temperature is 20℃, and the vacuum degree is -90 kPa.

[0110] (4) Add styrene-butadiene rubber to a mixing tank and disperse for 30 min. The dispersion revolution speed is set to 25 rpm, the rotation speed is set to 2000 rpm, the stirring temperature is 23℃, and the vacuum degree is -85 kPa to obtain the fourth mixture.

[0111] (5) The fourth mixture was slowly stirred in a mixing tank for 20 minutes to defoam. The defoaming revolution speed was set to 30 rpm, the stirring temperature was 20℃, and the vacuum degree was -85 kPa.

[0112] (6) After defoaming, the slurry is filtered with a sieve to obtain the silicon-based negative electrode slurry with a solid content of 45wt% and a viscosity of 4000mPa·s.

[0113] Comparative Example 2

[0114] This comparative example provides a silicon-based anode slurry and its preparation method. By mass, the silicon-based anode slurry comprises 18 parts of silicon-carbon material, 82 parts of graphite material, 0.5 parts of conductive carbon black, 0.15 parts of single-arm carbon nanotubes, 3 parts of polyacrylic acid, 0.3 parts of sodium carboxymethyl cellulose, 0.5 parts of styrene-butadiene rubber, 2 parts of additives (specifically butanediol), and deionized water. The silicon-based anode slurry is prepared according to this formula.

[0115] The preparation method of the silicon-based anode slurry includes the following steps:

[0116] (1) Silicon carbon material, graphite material, conductive carbon black and sodium carboxymethyl cellulose are added to a mixing tank for the first mixing. The stirring time of the first mixing is 40 min, the revolution speed is set to 25 rpm, the rotation speed is set to 1800 rpm, and the stirring temperature is 35℃ to obtain the first mixture.

[0117] (2) Add 50wt% of single-arm carbon nanotubes, 50wt% of polyacrylic acid, additives and deionized water to a mixing tank for a second mixing. The mixing time for the second mixing is 70min, the revolution speed is set to 30rpm, the rotation speed is set to 1800rpm, and the mixing temperature is 40℃ to obtain a second mixture with a solid content of 70wt%.

[0118] (3) The remaining polyacrylic acid, the remaining single-arm carbon nanotubes and deionized water are added to the mixing tank for a third mixing. The third mixing time is 150 min, the revolution speed is set to 25 rpm, the rotation speed is set to 4000 rpm, the stirring temperature is 20℃, and the vacuum degree is -90 kPa.

[0119] (4) Add styrene-butadiene rubber to a mixing tank and disperse for 30 min. The dispersion revolution speed is set to 25 rpm, the rotation speed is set to 2000 rpm, the stirring temperature is 23℃, and the vacuum degree is -85 kPa to obtain the fourth mixture.

[0120] (5) The fourth mixture was slowly stirred in a mixing tank for 20 minutes to defoam. The defoaming revolution speed was set to 30 rpm, the stirring temperature was 20℃, and the vacuum degree was -85 kPa.

[0121] (6) After defoaming, the slurry is filtered with a sieve to obtain the silicon-based negative electrode slurry with a solid content of 45wt% and a viscosity of 4000mPa·s.

[0122] A schematic diagram of the flowability of the silicon-based anode slurry obtained in Example 1 above is shown below. Figure 1 As shown in the diagram, the flowability of the silicon-based anode slurry obtained in Comparative Example 1 is illustrated in the figure below. Figure 2 As shown in the diagram, the flowability of the silicon-based anode slurry obtained in Comparative Example 2 is illustrated in the figure below. Figure 3 As shown, by Figures 1-3 The comparison shows that the silicon-based anode slurry obtained in Example 1 has better fluidity, while the silicon-based anode slurries obtained in Comparative Examples 1 and 2 are jelly-like and have poor fluidity.

[0123] The silicon-based negative electrode slurries obtained in the above examples and comparative examples were used to prepare negative electrode sheets under the same conditions. The film resistance, peel force, and cohesive force of the negative electrode sheets were tested. The film resistance was tested using a film resistance tester, specifically using the four-probe method. The peel force and cohesive force were tested using a high-speed rail peel tester. The specific method was to peel the sample at a 180° angle and measure the average peel force and cohesive force per unit width. The peel force was assessed by directly attaching tape to the electrode sheet to evaluate the force between the electrode sheet and the current collector, while the cohesive force was assessed by attaching tape to both sides of the electrode sheet to evaluate the force between the electrodes.

[0124] The test results are shown in Table 1 below:

[0125] Table 1

[0126]

[0127] As can be seen from Table 1 above:

[0128] As can be seen from Example 1 and Comparative Examples 1-2, in Comparative Example 1, the one-dimensional conductive agent was added all at once, while the first binder was added in two separate additions. In Comparative Example 2, the one-dimensional conductive agent was added in two separate additions, and the first binder was also added in two separate additions. This resulted in decreased material dispersibility, which is not conducive to the formation of a stable three-dimensional network structure. Therefore, the slurry obtained in Comparative Examples 1-2 had lower fluidity than that of Example 1, and the performance of the prepared electrode decreased. As can be seen from Example 1 and Examples 4-5, the mixing conditions for the second or third addition of the one-dimensional conductive agent and the first binder were the same as those for the first addition, resulting in decreased slurry performance. Preferably, the mixing time and rotation speed of the fourth and fifth mixing were greater than those of the second mixing, and the mixing temperature of the fourth and fifth mixing were lower than that of the second mixing. As can be seen from Example 1 and Examples 6-7, the present invention preferably adds an additive when the one-dimensional conductive agent and the first binder are added for the last time, which can further improve the performance of the electrode.

[0129] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a silicon-based negative electrode paste, characterized in that, The preparation method includes the following steps: (1) A first mixture is obtained by mixing silicon-based material, graphite material, zero-dimensional conductive agent and dispersant; (2) The first mixture from step (1), the first part of the one-dimensional conductive agent, and the first part of the first adhesive are mixed a second time to obtain a second mixture; (3) The second mixture from step (2) and the solvent are mixed for a third time to obtain a third mixture; (4) Mix the third mixture described in step (3), the second part of the one-dimensional conductive agent, the second part of the first binder, and the solvent in a fourth mixture to obtain a fourth mixture; (5) The fourth mixture, the third part of the one-dimensional conductive agent and the third part of the first binder described in step (4) are mixed for the fifth time to obtain the silicon-based negative electrode slurry.

2. The preparation method according to claim 1, characterized in that, Step (1) The stirring time of the first mixture is 30min-60min, the revolution speed is 25rpm-30rpm, the rotation speed is 1500rpm-2000rpm, and the stirring temperature is below 45℃; Preferably, the silicon-based material in step (1) includes silicon-carbon material; Preferably, the zero-dimensional conductive agent in step (1) includes conductive carbon black; Preferably, the dispersant in step (1) comprises sodium carboxymethyl cellulose.

3. The preparation method according to claim 1 or 2, characterized in that, Step (2) The first part of the one-dimensional conductive agent accounts for 25wt%-30wt% of the total amount of one-dimensional conductive agent added; Preferably, in step (2), the first portion of the first adhesive accounts for 20wt%-30wt% of the total amount of the first adhesive added; Preferably, in step (2), the second mixing time is 10 min-30 min, the revolution speed is 25 rpm-30 rpm, the rotation speed is 1500 rpm-2000 rpm, and the stirring temperature is below 45℃; Preferably, the one-dimensional conductive agent in step (2), the one-dimensional conductive agent in step (4), and the one-dimensional conductive agent in step (5) are all carbon nanotubes; Preferably, the first adhesive in step (2), the first adhesive in step (4), and the first adhesive in step (5) are all polyacrylic adhesives.

4. The preparation method according to claim 1 or 2, characterized in that, The third mixing time in step (3) is 10 min-30 min, the revolution speed is 25 rpm-30 rpm, and the stirring temperature is below 45℃; Preferably, the solid content of the third mixture in step (3) is 69wt%-73wt%.

5. The preparation method according to claim 1 or 2, characterized in that, Step (4) The second part of the one-dimensional conductive agent accounts for 25wt%-30wt% of the total amount of one-dimensional conductive agent added; Preferably, in step (4), the second part of the first adhesive accounts for 20wt%-30wt% of the total amount of the first adhesive added; Preferably, the time for the fourth mixing in step (4) is greater than the time for the second mixing in step (2); Preferably, the rotational speed of the fourth mixture in step (4) is greater than the rotational speed of the second mixture in step (2); Preferably, the temperature of the fourth mixture in step (4) is lower than the temperature of the second mixture in step (2); Preferably, the fourth mixing time in step (4) is 60 min-100 min, the revolution speed is 25 rpm-30 rpm, the rotation speed is 3000 rpm-4500 rpm, the stirring temperature is below 25℃, and the vacuum degree is <-80 kPa. Preferably, the solid content of the fourth mixture in step (4) is 40wt%-50wt%.

6. The preparation method according to claim 1 or 2, characterized in that, In step (5), an auxiliary agent was also added during the fifth mixing process; Preferably, the adjuvants include butanediol and / or ethyl cellulose; Preferably, the third part of the one-dimensional conductive agent in step (5) accounts for 40wt%-50wt% of the total amount of one-dimensional conductive agent added; Preferably, the third part of the first adhesive in step (5) accounts for 40wt%-60wt% of the total amount of the first adhesive added; Preferably, the time for the fifth mixing in step (5) is greater than the time for the second mixing in step (2); Preferably, the rotational speed of the fifth mixture in step (5) is greater than the rotational speed of the second mixture in step (2); Preferably, the temperature of the fifth mixture in step (5) is lower than the temperature of the second mixture in step (2); Preferably, the fifth mixing time in step (5) is 60 min-100 min, the revolution speed is 25 rpm-30 rpm, the rotation speed is 3000 rpm-4500 rpm, the stirring temperature is below 25℃, and the vacuum degree is <-80 kPa.

7. The preparation method according to claim 1 or 2, characterized in that, After the fifth mixing in step (5) is completed, a second binder is added to the resulting mixture to continue the sixth mixing; Preferably, the second adhesive comprises styrene-butadiene rubber; Preferably, the sixth mixing time is 20-40 minutes, the revolution speed is 25-30 rpm, the rotation speed is 1500-2000 rpm, the stirring temperature is below 25°C, and the vacuum degree is <-80 kPa. Preferably, after the sixth mixing is completed, defoaming and filtration are also performed; Preferably, the defoaming time is 10-30 minutes, the revolution speed is 25-30 rpm, the stirring temperature is below 25°C, and the vacuum degree is <-80 kPa. Preferably, by mass, the silicon-based negative electrode slurry in step (5) comprises 15-20 parts of silicon-based material, 80-85 parts of graphite material, 0.2-0.7 parts of zero-dimensional conductive agent, 0.1-0.2 parts of one-dimensional conductive agent, 2.5-4 parts of first binder, 0.25-0.5 parts of dispersant, 0-0.8 parts of second binder, 1-5 parts of additives and solvent; Preferably, the solid content of the silicon-based negative electrode slurry in step (5) is 40wt%-50wt%, and the viscosity is 3000mPa·s-5000mPa·s.

8. A silicon-based anode paste, characterized in that, The silicon-based anode slurry is prepared by the preparation method according to any one of claims 1-7.

9. A negative electrode sheet, characterized in that, The slurry for preparing the negative electrode sheet includes the silicon-based negative electrode slurry as described in claim 8.

10. A battery, characterized in that, The battery includes the negative electrode as described in claim 9.

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