Silicon-based graphite mixed slurry, preparation method thereof, negative plate and battery

Abstract

The invention provides silicon-based graphite mixed slurry and a preparation method thereof, a negative plate and a battery. The preparation method comprises the following steps: S1, performing first mixing on raw materials including a silicon-based active material, polyacrylic acid and water to obtain first slurry; s2, performing second mixing on raw materials comprising a dispersing agent and water to obtain second slurry; s3, performing third mixing on the second slurry, graphite and a first conductive agent to obtain third slurry; s4, performing fourth mixing on the first slurry and the third slurry to obtain fourth slurry; and S5, carrying out fifth mixing on the fourth slurry, a second conductive agent, butadiene styrene rubber and water to obtain the silicon-based graphite mixed slurry. The silicon-based graphite mixed slurry prepared by the preparation method is applied to the negative electrode plate, so that the negative electrode plate has relatively high specific capacity and cycling stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a silicon-based graphite mixed slurry, a preparation method thereof, a negative electrode sheet and a battery. BACKGROUND

[0002] With the continuous development of lithium ion battery technology, people have higher demands on the energy density of lithium ion batteries. From the perspective of negative electrode materials, the specific capacity of existing graphite materials is close to the theoretical value. In order to further improve the energy density of the battery, one of the main development directions at present is to add silicon materials with higher specific capacity to graphite. Silicon materials have extremely high lithium storage capacity and abundant resources. The theoretical specific capacity of pure silicon material is 4200mAh / g, and the specific capacity of silicon monoxide can also reach a high capacity of 1400-1500mAh / g. Silicon material is the most promising alternative to graphite to become the next generation of lithium ion battery negative electrode material. However, due to the high expansion / contraction coefficient of silicon negative electrode, it constantly pulverizes during the cycle process, the overall structure of the material is destroyed, the consumption of active lithium is significantly higher than that of graphite negative electrode, and finally leads to faster cycle performance decay. At the same time, the expansion of silicon particles produces additional compressive stress on graphite particles, inhibits the insertion of lithium ions, and reduces the capacity of graphite.

[0003] In order to alleviate the expansion effect of silicon materials and further improve the performance of the battery, a certain amount of polyacrylic acid is usually added to the silicon-doped formula. The content of carboxyl groups in polyacrylic acid is high, which can form a strong hydrogen bond with silicon particles containing hydroxyl groups on the surface. After drying, the ester group is coated on the surface of the silicon particles, which is equivalent to an artificial SEI film, effectively protecting the silicon particles, inhibiting the expansion of the silicon particles and reducing the consumption of electrolyte, thereby enhancing the integrity of the electrode. For graphite particles, the expansion / contraction coefficient is small, the structural stability is high, and the conductivity is excellent, so there is no need for protection by polyacrylic acid. Conventional butadiene rubber can meet the integrity of the graphite negative electrode. If too much polyacrylic acid acts on the surface of the graphite particles, it will affect the normal deintercalation of lithium ions on the surface of the graphite particles.

[0004] The negative electrode slurry process is mainly divided into dry process and wet process. The wet process is to mix the dispersant and binder uniformly, then add the negative electrode main material, conductive agent, solvent and the like for stirring and dispersion. When using this process, the conductive agent with a large specific surface area is easy to absorb the solvent, and the main material added later is prone to powder agglomeration, resulting in increased slurry viscosity and uneven dispersion. The dry process is to first mix the dry powder, then wet the powder, and finally dilute and disperse. The dry process has a large friction force during the material wetting stage, which can achieve good dispersion of various materials. The ideal slurry state is that the active material particles are small, uniformly dispersed, and there is no agglomeration, the conductive agent forms a thin layer and disperses into a conductive network, and a large amount of active material particles are interconnected on the current collector.

[0005] No matter the dry homogenization process or the wet homogenization process, the purpose is to disperse the liquid mixture uniformly and form a stable slurry, which cannot provide conditions favorable to the formation of hydrogen bonds for the silicon material and the polyacrylic acid, and the polyacrylic acid is uniformly distributed on the surfaces of the silicon particles and the graphite particles, which weakens the protection of the silicon material and simultaneously affects the lithium deintercalation performance of the graphite material. Therefore, it is necessary to develop a new homogenization process suitable for the silicon-doped negative electrode system. SUMMARY

[0006] The main purpose of the present application is to provide a silicon-based graphite mixed slurry, a preparation method thereof, a negative electrode sheet and a battery, so as to solve the problem that the silicon-based negative electrode material in the prior art is prone to expansion during the cycle process, resulting in poor cycle stability of the battery.

[0007] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a preparation method of a silicon-based graphite mixed slurry is provided, which comprises the following steps: step S1, first mixing raw materials including a silicon-based active material, polyacrylic acid and water to obtain a first slurry; step S2, second mixing raw materials including a dispersant and water to obtain a second slurry; step S3, third mixing the second slurry, graphite and a first conductive agent to obtain a third slurry; step S4, fourth mixing the first slurry and the third slurry to obtain a fourth slurry; and step S5, fifth mixing the fourth slurry, a second conductive agent, a butadiene styrene rubber and water to obtain the silicon-based graphite mixed slurry.

[0008] Further, the mass ratio of the above-mentioned graphite to the silicon-based active material is (94-96):5; and / or, the mass ratio of the polyacrylic acid to the butadiene styrene rubber is (10-27):1.

[0009] Further, the mass ratio of the above-mentioned first conductive agent to the second conductive agent is 1:(2-5).

[0010] Further, the mass ratio of the total mass of the above-mentioned silicon-based active material and graphite, the total mass of the first conductive agent and the second conductive agent, the total mass of the polyacrylic acid and the butadiene styrene rubber, and the mass of the dispersant is (87-96):(1-3):(2-10):(0.1-1).

[0011] Further, the above-mentioned first conductive agent is selected from any one or more of super conductive carbon black, vapor phase grown carbon fiber and ketjen black; and / or, the second conductive agent is carbon nanotube; and / or, the silicon-based active material is selected from any one or more of silicon monoxide, silicon nanoparticles, silicon nanowires and silicon-carbon composite; and / or, the dispersant is selected from sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

[0012] Further, the solid content of the first slurry is 15-20%; and / or, the solid content of the third slurry is 65-70%; and / or, the solid content of the silicon-based graphite mixed slurry is 45-50%.

[0013] Further, the first mixing, the second mixing, the third mixing, the fourth mixing and the fifth mixing are all stirring mixing; preferably, the revolution speed of the first mixing is 15-30 rpm, and the rotation speed is 100-500 rpm; and / or, the time of the first mixing is 1-2 h; and / or, the revolution speed of the second mixing is 15-30 rpm, and the rotation speed is 1500-2000 rpm; and / or, the time of the second mixing is 3-5 h; and / or, the revolution speed of the third mixing is 15-30 rpm, and the rotation speed is 500-1500 rpm; and / or, the time of the third mixing is 1-2 h; and / or, the revolution speed of the fourth mixing is 15-30 rpm, and the rotation speed is 300-500 rpm; and / or, the time of the fourth mixing is 1.5-2.5 h; and / or, the revolution speed of the fifth mixing is 15-30 rpm, and the rotation speed is 300-500 rpm; and / or, the time of the fifth mixing is 0.5-1.5 h.

[0014] According to another aspect of the present application, there is provided a silicon-based graphite mixed slurry prepared by the aforementioned preparation method.

[0015] According to still another aspect of the present application, there is provided a negative electrode sheet comprising a current collector and a negative electrode active layer formed by sequentially coating and drying the aforementioned silicon-based graphite mixed slurry.

[0016] According to still another aspect of the present application, there is provided a battery comprising a positive electrode sheet, an electrolyte and a negative electrode sheet, wherein the negative electrode sheet is the aforementioned negative electrode sheet.

[0017] The silicon-based active material and the polyacrylic acid are mixed in step S1, which enables the polyacrylic acid to more fully and uniformly coat the surface of the silicon-based active material. The carboxyl groups in the polyacrylic acid are connected to the hydroxyl groups on the surface of the silicon-based active material through hydrogen bonding, and a stable ester chemical bond is formed after baking, which is equivalent to providing a layer of artificial SEI film for the silicon-based active material, helping to inhibit the expansion of the silicon-based active material during charging and discharging, reducing the consumption of electrolyte, and thus helping to improve the stability and cycle performance of the electrode. In step S3, the graphite and the conductive agent are mixed first, which helps to reduce the excessive effect of the polyacrylic acid on the graphite, helps to maintain the normal deintercalation of lithium ions on the surface of the graphite particles, and thus helps to improve the capacity of the silicon-based graphite mixed slurry. In step S5, the addition of the second conductive agent and the styrene-butadiene rubber helps to further enhance the flexibility and structural stability of the electrode. The styrene-butadiene rubber can improve the bonding force between the graphite and the silicon particles while ensuring the flexibility of the electrode sheet, and the second conductive agent can form a more efficient and stable long-range conductive network, reducing the risk of fracture of the electrode sheet during manufacturing and use, and thus helping to improve the overall performance of the battery. The silicon-based graphite mixed slurry prepared by the preparation method of the present application applied to the negative electrode sheet helps to make the negative electrode sheet have higher specific capacity and cycle stability. DETAILED DESCRIPTION

[0018] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0019] As analyzed in the background art of the present application, the silicon-based negative electrode material in the prior art has the problem of easy expansion during the cycle process, resulting in poor cycle stability of the battery. In order to solve this problem, the present application provides a silicon-based graphite mixed slurry, a preparation method thereof, a negative electrode sheet and a battery.

[0020] In a typical embodiment of the present application, a preparation method of a silicon-based graphite mixed slurry is provided, which includes the following steps: step S1, first mixing raw materials including a silicon-based active material, polyacrylic acid and water to obtain a first slurry; step S2, second mixing raw materials including a dispersing agent and water to obtain a second slurry; step S3, third mixing the second slurry, graphite and a first conductive agent to obtain a third slurry; step S4, fourth mixing the first slurry and the third slurry to obtain a fourth slurry; and step S5, fifth mixing the fourth slurry, a second conductive agent, a styrene-butadiene rubber and water to obtain a silicon-based graphite mixed slurry.

[0021] In step S1, the silicon-based active material is mixed with the polyacrylic acid, which allows the polyacrylic acid to coat the surface of the silicon-based active material more fully and uniformly. The carboxyl groups in the polyacrylic acid are connected to the hydroxyl groups on the surface of the silicon-based active material through hydrogen bonding, and after baking, a stable ester chemical bond is formed, which is equivalent to providing the silicon-based active material with an artificial SEI film, which helps to inhibit the expansion of the silicon-based active material during charging and discharging, reduces the consumption of electrolyte, and thus helps to improve the stability and cycle performance of the electrode. In step S3, by first mixing the graphite with the conductive agent, it helps to reduce the excessive effect of the polyacrylic acid on the graphite, and helps to maintain the normal deintercalation of lithium ions on the surface of the graphite particles, and thus helps to improve the capacity of the silicon-based graphite mixed slurry. In step S5, by adding a second conductive agent and a butadiene-styrene rubber, it helps to further enhance the flexibility and structural stability of the electrode. The butadiene-styrene rubber can improve the bonding force between the graphite and the silicon particles, while ensuring the flexibility of the electrode sheet, and the second conductive agent can form a more efficient and stable long-range conductive network, reducing the risk of fracture of the electrode sheet during manufacturing and use, thereby helping to improve the overall performance of the battery. The silicon-based graphite mixed slurry prepared by the preparation method of the present application applied to the negative electrode sheet helps to make the negative electrode sheet have higher specific capacity and cycle stability.

[0022] To further reduce the expansion rate of the silicon-based negative electrode material during the cycle process and improve the cycle stability of the battery, in an embodiment of the present application, the number average molecular weight of the above-mentioned polyacrylic acid is 600000-1500000 g / mol; and / or, the mass fraction of the styrene segment in the butadiene-styrene rubber is 18-22%; and / or, the number average molecular weight of the butadiene-styrene rubber is 100000-1000000 g / mol.

[0023] In an embodiment of the present application, the mass ratio of the above-mentioned graphite to the silicon-based active material is (94-96):5; and / or, the mass ratio of the polyacrylic acid to the butadiene-styrene rubber is (10-27):1, which can be specifically 10:1, 15:1, 20:1, 25:1, 27:1 and any range value between any two ratios.

[0024] The incorporation of silicon-based active material into the negative electrode material can significantly improve the energy density of the battery, as the theoretical specific capacity of silicon is much higher than that of graphite. However, the high expansion coefficient of silicon material can lead to rapid degradation of the cycle performance of the battery. Controlling the mass ratio of graphite to silicon-based active material within the above-mentioned range helps to balance the capacity and cycle stability of the negative electrode sheet. Controlling the mass ratio of polyacrylic acid to butadiene-styrene rubber within the above-mentioned range helps to improve the stability of the structure and conductive network of the negative electrode sheet using such a formulation, thereby further improving the specific capacity and cycle stability of the negative electrode material.

[0025] In an embodiment of the present application, the mass ratio of the first conductive agent to the second conductive agent is 1:(2-5), specifically, 1:2, 1:3, 1:4, 1:5, and any range between any two ratios.

[0026] The first conductive agent and the second conductive agent each have unique conductive mechanisms and properties. The first conductive agent, as a traditional conductive agent, can provide point-to-point conductive connections, while the second conductive agent can form longer, through conductive paths. Controlling the mass ratio of the first conductive agent to the second conductive agent within the above range helps to build a composite, complete conductive network, which not only helps to improve the conductivity of the electrode, but also helps to enhance the transmission efficiency of electrons between active materials, thereby helping to improve the overall electrochemical performance of the battery. And the use of the first conductive agent and the second conductive agent helps to optimize the flowability and viscosity of the slurry.

[0027] In order to further improve the specific capacity and cycle stability of the negative active material, in an embodiment of the present application, the mass ratio of the total mass of the silicon-based active material and graphite, the total mass of the first conductive agent and the second conductive agent, the total mass of polyacrylic acid and styrene butadiene rubber, and the mass of the dispersant is (87-96):(1-3):(2-10):(0.1-1).

[0028] In an embodiment of the present application, the first conductive agent is selected from one or more of super conductive carbon black, vapor grown carbon fiber, and ketjen black; and / or, the second conductive agent is carbon nanotube; and / or, the silicon-based active material is selected from any one or more of silicon monoxide, silicon nanoparticles, silicon nanowires, and silicon-carbon composite; and / or, the dispersant is selected from sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

[0029] In order to improve the uniformity of dispersion between components and reduce the agglomeration and delamination of the slurry, in an embodiment of the present application, the solid content of the first slurry is preferably 15-20%; and / or, the solid content of the third slurry is 65-70%; and / or, the solid content of the silicon-based graphite mixed slurry is 45-50%.

[0030] In an embodiment of the present application, the first mixing, the second mixing, the third mixing, the fourth mixing and the fifth mixing are all stirring mixing; preferably, the first mixing has an orbital rotation speed of 15-30 rpm and a rotary rotation speed of 100-500 rpm; and / or, the first mixing has a time of 1-2 h; and / or, the second mixing has an orbital rotation speed of 15-30 rpm and a rotary rotation speed of 1500-2000 rpm; and / or, the second mixing has a time of 3-5 h; and / or, the third mixing has an orbital rotation speed of 15-30 rpm and a rotary rotation speed of 500-1500 rpm; and / or, the third mixing has a time of 1-2 h; and / or, the fourth mixing has an orbital rotation speed of 15-30 rpm and a rotary rotation speed of 300-500 rpm; and / or, the fourth mixing has a time of 1.5-2.5 h; and / or, the fifth mixing has an orbital rotation speed of 15-30 rpm and a rotary rotation speed of 300-500 rpm; and / or, the fifth mixing has a time of 0.5-1.5 h.

[0031] Controlling the orbital rotation speed, the rotary rotation speed and the time of the first mixing within the above ranges helps to promote the sufficient contact and strong mixing of the silicon-based active material and the polyacrylic acid in the liquid-phase slurry, thereby helping to promote the formation of hydrogen bonds, enhancing the coating effect of the silicon-based active material after coating and baking, and further helping to reduce the expansion rate of the silicon-based active material during charging and discharging. Controlling the orbital rotation speed, the rotary rotation speed and the time of the second mixing within the above ranges helps to refine the slurry particles, reduce the agglomeration between the particles, and make the slurry more uniform, thereby helping to improve the overall dispersibility and rheology of the slurry. Controlling the orbital rotation speed, the rotary rotation speed and the time of the third mixing within the above ranges helps to uniformly disperse the graphite and the first conductive agent in water, forming a stable conductive network, thereby helping to improve the conductivity and charging / discharging efficiency of the electrode. Controlling the orbital rotation speed, the rotary rotation speed and the time of the fourth mixing and the fifth mixing within the above ranges helps to improve the uniformity of the dispersion between the components, thereby helping to further improve the specific capacity and cycle stability of the battery.

[0032] In an embodiment of the present application, the time for the slurry to stand after the first mixing is completed is not more than 6 h.

[0033] In an embodiment of the present application, in the step S5, the fourth slurry is sequentially mixed with the second conductive agent, the styrene-butadiene rubber and water to obtain a silicon-based graphite mixed slurry, wherein the fifth mixing is completed under vacuum stirring, and the orbital rotation speed of each step of mixing is 15-30 rpm, and the rotary rotation speed of each step of mixing is 300-500 rpm.

[0034] In another typical embodiment of the present application, a silicon-based graphite mixed slurry is provided, which is prepared by the above-mentioned preparation method.

[0035] Since the silicon-based graphite mixed slurry is prepared by the preparation method of the present application, the silicon-based active material in the silicon-based graphite mixed slurry is uniformly wrapped by polyacrylic acid, which helps to inhibit the expansion of the silicon-based active material during the charging and discharging process, reduces the consumption of electrolyte, and thus helps to improve the stability and cycle performance of the electrode.

[0036] In another typical embodiment of the present application, a negative electrode sheet is provided, which comprises a current collector and a negative electrode active layer formed by coating and drying the aforementioned silicon-based graphite mixed slurry in sequence.

[0037] Since the negative electrode sheet contains the negative electrode active layer formed by coating and drying the silicon-based graphite mixed slurry of the present application in sequence, the negative electrode sheet has high specific capacity and cycle stability.

[0038] In another typical embodiment of the present application, a battery is provided, which comprises a positive electrode sheet, an electrolyte, and a negative electrode sheet, wherein the negative electrode sheet is the aforementioned negative electrode sheet.

[0039] Since the negative electrode sheet of the battery contains the negative electrode active layer formed by coating and drying the silicon-based graphite mixed slurry of the present application in sequence, the battery has high specific capacity and cycle stability.

[0040] The beneficial effects of the present application will be further illustrated in conjunction with the examples below.

[0041] Example 1

[0042] Step S1, the silicon nanoparticles, polyacrylic acid (number average molecular weight is 1000000 g / mol) and water are first mixed, the first mixing is carried out under vacuum stirring, the revolution speed of the first mixing is 15 rpm, the rotation speed is 500 rpm, the time of the first mixing is 2 h, to obtain a first slurry, the solid content is 15%; Step S2, the sodium carboxymethyl cellulose and water are second mixed, the second mixing is carried out under vacuum stirring, the revolution speed of the second mixing is 15 rpm, the rotation speed is 1500 rpm, the time of the second mixing is 5 h, to obtain a second slurry; Step S3, the second slurry, graphite and super conductive carbon black are third mixed, the third mixing is carried out under vacuum stirring, the revolution speed of the third mixing is 15 rpm, the rotation speed is 500 rpm, the time of the third mixing is 1 h, to obtain a third slurry, the solid content is 65%; Step S4, the first slurry and the third slurry are fourth mixed, the fourth mixing is carried out under vacuum stirring, the revolution speed of the fourth mixing is 15 rpm, the rotation speed is 500 rpm, the time of the fourth mixing is 2 h, to obtain a fourth slurry; Step S5, the fourth slurry is sequentially mixed with carbon nanotubes, butadiene styrene rubber (the mass ratio of styrene segment is 20%, the number average molecular weight of butadiene styrene rubber is 500000 g / mol) and water, the fifth mixing is carried out under vacuum stirring, the revolution speed of the mixing is 15 rpm, the rotation speed is 500 rpm, the stirring time is 0.75 h, to obtain a silicon-based graphite mixed slurry, the solid content is 45%. Wherein, the mass ratio of graphite to silicon nanoparticles is 95:5, the mass ratio of polyacrylic acid to butadiene styrene rubber is 10:1, the mass ratio of the total mass of silicon nanoparticles and graphite, the total mass of super conductive carbon black and carbon nanotubes, the total mass of polyacrylic acid and butadiene styrene rubber to the mass of sodium carboxymethyl cellulose is 95.9:1:2.5:0.6, the mass ratio of super conductive carbon black to carbon nanotubes is 1:3.

[0043] Example 2

[0044] The difference from example 1 is that the mass ratio of graphite to silicon nanoparticles is 94:5, and finally a silicon-based graphite mixed slurry is obtained.

[0045] Example 3

[0046] The difference from example 1 is that the mass ratio of graphite to silicon nanoparticles is 96:5, and finally a silicon-based graphite mixed slurry is obtained.

[0047] Example 4

[0048] The difference from example 1 is that the mass ratio of graphite to silicon nanoparticles is 93:5, and finally a silicon-based graphite mixed slurry is obtained.

[0049] Example 5

[0050] The difference from Example 1 is that the mass ratio of polyacrylic acid to styrene butadiene rubber is 14.2:1, and finally a silicon-based graphite mixed slurry is obtained.

[0051] Example 6

[0052] The difference from Example 1 is that the mass ratio of polyacrylic acid to styrene butadiene rubber is 26.7:1, and finally a silicon-based graphite mixed slurry is obtained.

[0053] Example 7

[0054] The difference from Example 1 is that the mass ratio of polyacrylic acid to styrene butadiene rubber is 35:1, and finally a silicon-based graphite mixed slurry is obtained.

[0055] Example 8

[0056] The difference from Example 1 is that the mass ratio of the total mass of silicon nanoparticles and graphite, the total mass of super-conductive carbon black and carbon nanotubes, the total mass of polyacrylic acid and styrene butadiene rubber, and the mass of sodium carboxymethyl cellulose is 96.5:0.8:2.2:0.5, and finally a silicon-based graphite mixed slurry is obtained.

[0057] Example 9

[0058] The difference from example 1 is that, in step S1, the silicon nanoparticles, polyacrylic acid (number average molecular weight 600000 g / mol) and water are first mixed, the first mixing is carried out under vacuum stirring, the first mixing has a revolution speed of 20 rpm and a rotation speed of 300 rpm, the first mixing time is 1.5 h, and a first slurry is obtained, with a solid content of 17%; in step S2, the lithium carboxymethyl cellulose and water are second mixed, the second mixing is carried out under vacuum stirring, the second mixing has a revolution speed of 20 rpm and a rotation speed of 1700 rpm, the second mixing time is 4 h, and a second slurry is obtained; in step S3, the second slurry, graphite and super-conductive carbon black are third mixed, the third mixing is carried out under vacuum stirring, the third mixing has a revolution speed of 20 rpm and a rotation speed of 1000 rpm, the third mixing time is 2 h, and a third slurry is obtained, with a solid content of 67%; in step S4, the first slurry and the third slurry are fourth mixed, the fourth mixing is carried out under vacuum stirring, the fourth mixing has a revolution speed of 30 rpm and a rotation speed of 400 rpm, the fourth mixing time is 2.5 h, and a fourth slurry is obtained; in step S5, the fourth slurry is sequentially fifth mixed with carbon nanotubes, butadiene styrene rubber (the mass ratio of styrene segments is 18%, and the number average molecular weight of butadiene styrene rubber is 1000000 g / mol) and water, the fifth mixing is carried out under vacuum stirring, the mixing has a revolution speed of 30 rpm and a rotation speed of 400 rpm, and the stirring time is 1.5 h, and a silicon-based graphite mixed slurry is obtained, with a solid content of 47%. The mass ratio of graphite to silicon nanoparticles is 95:5, the mass ratio of polyacrylic acid to butadiene styrene rubber is 10:1, and the mass ratio of the total mass of silicon nanoparticles and graphite, the total mass of super-conductive carbon black and carbon nanotubes, the total mass of polyacrylic acid and butadiene styrene rubber to the mass of lithium carboxymethyl cellulose is 95.9:1:2.5:0.6, and the mass ratio of super-conductive carbon black to carbon nanotubes is 1:5.

[0059] Example 10

[0060] The difference from Example 1 is that, in step S1, the silicon nanoparticles, polyacrylic acid (number average molecular weight 1500000 g / mol) and water are first mixed, the first mixing is carried out under vacuum stirring, the first mixing has a revolution speed of 30 rpm and a rotation speed of 100 rpm, the first mixing time is 1 h, and a first slurry is obtained, with a solid content of 20%; in step S2, the sodium carboxymethyl cellulose and water are second mixed, the second mixing is carried out under vacuum stirring, the second mixing has a revolution speed of 30 rpm and a rotation speed of 2000 rpm, the second mixing time is 3 h, and a second slurry is obtained; in step S3, the second slurry, graphite and super-conductive carbon black are third mixed, the third mixing is carried out under vacuum stirring, the third mixing has a revolution speed of 30 rpm and a rotation speed of 1500 rpm, the third mixing time is 1.5 h, and a third slurry is obtained, with a solid content of 70%; in step S4, the first slurry and the third slurry are fourth mixed, the fourth mixing is carried out under vacuum stirring, the fourth mixing has a revolution speed of 20 rpm and a rotation speed of 300 rpm, the fourth mixing time is 1.5 h, and a fourth slurry is obtained; in step S5, the fourth slurry is sequentially fifth mixed with carbon nanotubes, butadiene styrene rubber (the mass ratio of styrene segments is 22%, and the number average molecular weight of butadiene styrene rubber is 100000 g / mol) and water, the fifth mixing is carried out under vacuum stirring, the mixing has a revolution speed of 20 rpm and a rotation speed of 300 rpm, and the stirring time is 0.5 h, and a silicon-based graphite mixed slurry is obtained, with a solid content of 50%. The mass ratio of graphite to silicon nanoparticles is 95:5, the mass ratio of polyacrylic acid to butadiene styrene rubber is 10:1, and the mass ratio of the total mass of silicon nanoparticles and graphite, the total mass of super-conductive carbon black and carbon nanotubes, the total mass of polyacrylic acid and butadiene styrene rubber to the mass of sodium carboxymethyl cellulose is 95.9:1:2.5:0.6, and the mass ratio of super-conductive carbon black to carbon nanotubes is 1:2.

[0061] Comparative Example 1

[0062] The difference from example 1 is that, in step S1, the sodium carboxymethyl cellulose, polyacrylic acid and water are first mixed, the first mixing is carried out under vacuum stirring, the revolution speed of the first mixing is 15 rpm, the rotation speed is 1500 rpm, the time of the first mixing is 5 h, and the first slurry is obtained; in step S2, 50% of the first slurry, graphite and silicon nanoparticles are second mixed, the second mixing is carried out under vacuum stirring, the revolution speed of the second mixing is 15 rpm, the rotation speed is 500 rpm, the time of the second mixing is 2 h, and the second slurry is obtained; in step S3, the second slurry and super conductive carbon black are third mixed, the third mixing is carried out under vacuum stirring, the revolution speed of the third mixing is 15 rpm, the rotation speed is 500 rpm, the time of the third mixing is 1 h, and the third slurry is obtained; in step S4, the third slurry and the remaining first slurry are fourth mixed, the fourth mixing is carried out under vacuum stirring, the revolution speed of the fourth mixing is 15 rpm, the rotation speed is 1500 rpm, the time of the fourth mixing is 1 h; in step S5, the fourth slurry, carbon nanotubes, butadiene styrene rubber and water are fifth mixed, the fifth mixing is carried out under vacuum stirring, the revolution speed is 15 rpm, the rotation speed is 500 rpm, the stirring time is 0.75 h, and the silicon-based graphite mixed slurry is obtained, and the solid content is 45%. The mass ratio of the graphite and the silicon nanoparticles is 95:5, the mass ratio of the polyacrylic acid and the butadiene styrene rubber is 10:1, the mass ratio of the total mass of the silicon nanoparticles and the graphite, the total mass of the super conductive carbon black and the carbon nanotubes, the total mass of the polyacrylic acid and the butadiene styrene rubber and the mass of the sodium carboxymethyl cellulose is 95.9:1:2.5:0.6, and the mass ratio of the super conductive carbon black and the carbon nanotubes is 1:3.

[0063] Battery preparation

[0064] The negative electrode slurry prepared by the examples and the comparative examples is coated on a copper foil, and after drying, a negative electrode sheet is prepared, and the negative electrode sheet is assembled into a battery for performance test.

[0065] Performance test

[0066] The batteries prepared by the examples and the comparative examples are tested for the first discharge specific capacity and the capacity retention rate at 0.33C under the voltage range of 0-2.0V in a 25℃ constant temperature oven, and the test results are shown in Table 1.

[0067] Table 1

[0068]

[0069]

[0070] From the above description, it can be seen that the above examples of the present application achieve the following technical effects:

[0071] In step S1, the silicon-based active material is mixed with the polyacrylic acid, which allows the polyacrylic acid to coat the surface of the silicon-based active material more fully and uniformly. The carboxyl groups in the polyacrylic acid are connected to the hydroxyl groups on the surface of the silicon-based active material through hydrogen bonding, and after baking, a stable ester chemical bond is formed, which is equivalent to providing the silicon-based active material with an artificial SEI film, which helps to inhibit the expansion of the silicon-based active material during charging and discharging, reduces the consumption of electrolyte, and thus helps to improve the stability and cycle performance of the electrode. In step S3, by first mixing the graphite with the conductive agent, it helps to reduce the excessive effect of the polyacrylic acid on the graphite, and helps to maintain the normal deintercalation of lithium ions on the surface of the graphite particles, and thus helps to improve the capacity of the silicon-based graphite mixed slurry. In step S5, by adding the second conductive agent and the butadiene styrene rubber, it helps to further enhance the flexibility and structural stability of the electrode. The butadiene styrene rubber can improve the bonding force between the graphite and the silicon particles, while ensuring the flexibility of the electrode sheet, and the second conductive agent can form a more efficient and stable long-range conductive network, reducing the risk of breakage of the electrode sheet during manufacturing and use, and thus helping to improve the overall performance of the battery. The silicon-based graphite mixed slurry prepared by the preparation method of the present application applied to the negative electrode sheet helps to make the negative electrode sheet have higher specific capacity and cycle stability.

[0072] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a silicon-based graphite mixed slurry, characterized in that, The preparation method includes the following steps: Step S1: The raw materials including silicon-based active materials, polyacrylic acid and water are mixed for the first time to obtain a first slurry; Step S2 involves a second mixing of the raw materials, including the dispersant and water, to obtain a second slurry; Step S3: The second slurry, graphite and the first conductive agent are mixed in a third way to obtain a third slurry; Step S4: Mix the first slurry and the third slurry in a fourth mixing process to obtain a fourth slurry; Step S5: The fourth slurry, the second conductive agent, styrene-butadiene rubber and water are mixed for the fifth time to obtain the silicon-based graphite mixed slurry.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the graphite to the silicon-based active material is (94-96):5; and / or the mass ratio of the polyacrylic acid to the styrene-butadiene rubber is (10-27):

1.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the first conductive agent to the second conductive agent is 1:(2-5).

4. The preparation method according to any one of claims 1 to 3, characterized in that, The mass ratio of the total mass of the silicon-based active material and the graphite, the total mass of the first conductive agent and the second conductive agent, the total mass of the polyacrylic acid and the styrene-butadiene rubber, and the mass of the dispersant is (87-96):(1-3):(2-10):(0.1-1).

5. The preparation method according to any one of claims 1 to 4, characterized in that, The first conductive agent is selected from any one or more of superconducting carbon black, vapor-grown carbon fiber, and Ketjen black; and / or, the second conductive agent is carbon nanotubes; and / or, the silicon-based active material is selected from any one or more of silicon suboxide, silicon nanoparticles, silicon nanowires, and silicon-carbon composites; and / or, the dispersant is selected from sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The first slurry has a solid content of 15-20%; and / or, the third slurry has a solid content of 65-70%; and / or, the silicon-based graphite mixed slurry has a solid content of 45-50%.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The first mixture, the second mixture, the third mixture, the fourth mixture, and the fifth mixture are all stirred mixtures; Preferably, the revolution speed of the first mixture is 15-30 rpm, and the rotation speed is 100-500 rpm; and / or, the mixing time of the first mixture is 1-2 hours. And / or, the second mixture has an orbital speed of 15-30 rpm and a rotational speed of 1500-2000 rpm; and / or, the second mixture has a mixing time of 3-5 hours; And / or, the revolution speed of the third mixture is 15-30 rpm, and the rotation speed is 500-1500 rpm; and / or, the time of the third mixture is 1-2 hours; And / or, the revolution speed of the fourth mixture is 15-30 rpm, and the rotation speed is 300-500 rpm; and / or, the time of the fourth mixture is 1.5-2.5 h; And / or, the revolution speed of the fifth mixture is 15-30 rpm and the rotation speed is 300-500 rpm; and / or, the time of the fifth mixture is 0.5-1.5 h.

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

9. A negative electrode sheet, comprising a current collector and a negative electrode active layer, characterized in that, The negative electrode active layer is formed by coating and drying the silicon-based graphite mixed slurry as described in claim 8.

10. A battery comprising a positive electrode, an electrolyte, and a negative electrode, characterized in that, The negative electrode is the negative electrode as described in claim 9.

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