Method for controlling fibrillation degree of negative pole piece prepared by dry method

Abstract

According to the method for controlling the fibrillation degree of the negative pole piece prepared by the dry method, the parameter when the negative pole piece is prepared by the dry method meets # imgabs0 # 65% < = C0 < = 130%, so that the fibrillation degree is controlled when the negative pole piece is prepared by the dry method; therefore, a reliable method is provided for controlling the quality of the negative pole piece prepared by a dry method in large-scale production, and the consistency and reliability of the quality of the negative pole piece in the production process are improved.

Description

Technical Field

[0001] The invention relates to the technical field of dry-process electrodes and secondary batteries, in particular to a method for controlling the fibrillation degree of a negative electrode sheet prepared by a dry process. Technical Background

[0002] Lithium-ion batteries are widely used in various electronic devices and electric vehicles and are one of the most mainstream battery technologies. For example, mobile phones, portable computers, camcorders, cameras, electric vehicles, energy storage systems and other fields. Although lithium-ion batteries have been widely used in various industries, their safety, cycle life and cost still face huge challenges. For example, the existing lithium-ion battery preparation process mostly adopts wet method, which has problems such as solvent residue and environmental pollution. The dry electrode preparation process has become a research hotspot due to its advantages such as solvent-free, environmentally friendly and easy large-scale production.

[0003] Compared with the traditional wet coating technology, the dry electrode process has many significant advantages: first, its manufacturing process is simple, with fewer process steps. After mass production, the overall cost of battery cell manufacturing can be reduced by 18%, and there is no need to use solvent NMP, which reduces environmental pollution, and the equipment occupies a smaller area, which is more suitable for large-scale production. Secondly, since there is no gap after solvent evaporation, the dry electrode has a closer contact between particles, a higher compaction density, an energy density that can be increased by 20%, and a greater electrode thickness limit, which can further increase the surface capacity. Finally, the fiber mesh is coated with the active material under the dry process, and the formed mesh structure remains intact after long-term charging and discharging, inhibiting the volume expansion of the active material and preventing the particles from falling off, thereby improving the electrical performance. In addition, the dry process can also form a more continuous ion conduction channel and a good electron conduction network in the electrode, optimizing the ion and electron conduction performance. Finally, the dry electrode process has a wide range of applications, not only for lithium-ion batteries and solid-state batteries, but also for a variety of electrode materials such as positive and negative electrode materials.

[0004] In the dry process, adhesives such as polytetrafluoroethylene undergo fibrillation under the action of mechanical shear force, encapsulating components such as active materials and conductive agents. Therefore, the degree of fibrillation of the adhesive is crucial to the performance of the electrode. However, in actual production, the degree of fibrillation is often affected by a combination of factors, including the amount of main materials, temperature, time, shear rate, etc. The complexity of these factors makes it difficult for testers to accurately control the degree of fibrillation through conventional means, which in turn leads to the inability to effectively optimize the performance of the electrode. This may not only cause the production personnel to be unable to accurately judge the battery performance, but also in large-scale production, it may cause differences in the performance of different batches of batteries, thereby affecting the consistency and reliability of the product. Therefore, when preparing electrodes through a dry process, how to accurately control their degree of fibrillation has become a difficult problem in current research. Summary of the invention

[0005] The present invention aims at the problems in the prior art and provides a method for controlling the degree of fibrillation of negative electrode sheets prepared by a dry process, thereby solving the quality problem of negative electrode sheets caused by the difficulty in controlling the degree of fibrillation when preparing negative electrode sheets by a dry process, and improving the consistency and reliability of negative electrode sheets in large-scale production.

[0006] In a first aspect, the present invention provides a method for controlling the fibrillation degree of a negative electrode sheet prepared by a dry process, wherein a negative electrode raw material containing a negative electrode active material, a binder, and a conductive agent is subjected to dry mixing and high-speed shearing in sequence to achieve fibrillation to form a negative electrode dry powder, the negative electrode dry powder is prepared into a negative electrode film using a film forming device, and then the negative electrode film and a negative electrode foil are thermally composited by roller pressing to obtain a dry process negative electrode sheet;

[0007] In the above steps, by regulating 65%≤C0≤130%, which can realize the regulation of the fibrillation degree, wherein C0 is the fibrillation degree, M is the mass of the negative electrode active material, in kg, and LD is the bulk density of the negative electrode active material, in g / cm 3 , L is the volume of the dry mixing tank, unit L, T 1 is the material temperature during fibrillation, unit is °C, Δt is the fibrillation dispersion time, unit is min, K 1 is the empirical coefficient, K 1 =0.65, γ is the fibrillation shear rate, n is the rotation speed during fibrillation, unit is rpm, r is the radius of the fibrillation dispersion rotor, unit is m, and h is the stator-rotor distance of the mixer motor, unit is mm.

[0008] As some preferred solutions, 75%≤C0≤105%.

[0009] As a further solution, the negative electrode active material is not limited in principle, and technicians can select corresponding negative electrode active materials according to needs, such as one or more of carbon materials, silicon-carbon materials, and silicon-oxygen materials.

[0010] As a further solution, the carbon material is selected from any one of natural graphite, artificial graphite, micro carbon spheres, hard carbon, and soft carbon.

[0011] As a further solution, the binder is selected from any one or more of polymers, rubbers, and cellulose derivatives.

[0012] As a further embodiment, the conductive agent is selected from any one or more of carbon black, Super P, activated carbon, graphite, graphene, multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon fibers, conductive carbon black, carbon nanospheres, ellipsoidal carbon, hard carbon, amorphous carbon, silicon carbide, acetylene black, Ketjen black, and vapor grown carbon fiber (VGCF).

[0013] As a further solution, the mass proportion of the negative electrode active material in the negative electrode dry powder is selected from 85%-99.3%.

[0014] As a further solution, the mass proportion of the binder in the negative electrode dry powder is selected from 0.3%-10%.

[0015] As a further solution, the mass proportion of the conductive agent in the negative electrode dry powder is selected from 0.4%-5%.

[0016] As a further solution, the dry mixing speed is selected from 1000rpm-3000rpm, and the mixing time is selected from 5-20min.

[0017] As a further solution, the rotation speed for achieving fibrillation by high-speed shearing is selected from 4000 rpm to 8000 rpm, and the time is selected from 3 to 30 min.

[0018] As a further solution, the stator-rotor spacing h of the mixer motor is selected from 0.2-0.4 mm.

[0019] As a further solution, after high-speed shearing, the process also includes obtaining negative electrode dry powder by refining the material.

[0020] As a further solution, when the negative electrode dry powder is formed into a film, the film thinning is carried out at a temperature of 70-250°C.

[0021] As a further solution, the roller pressure of the roller hot compounding can be set to 2-50t, and the temperature can be set to 70-250°C.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects: on the basis of considering the conventional factors affecting the degree of fibrillation, the present invention further combines the properties of the negative electrode active material, and takes the factors affecting the collision dynamics into consideration at the same time, thereby obtaining a formula and method for regulating the degree of fibrillation. By selecting appropriate parameters through the formula, the present invention can obtain dry-process negative electrode sheets with good fibrillation degree, and at the same time achieve precise control of the performance of different batches of batteries, thereby improving the reliability and consistency of product production, and providing favorable guarantees for large-scale production. The dry-process negative electrode sheets prepared by this scheme have good compaction density and excellent peel strength, and have better resistance than the electrode sheets prepared by the wet method, and are expected to provide guarantees for the large-scale production of dry-process negative electrode sheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a SEM image of the dry-process negative electrode sheet prepared in Example 1;

[0025] Figure 2 This is a comparison chart of the compaction density, resistivity and peel strength of the negative electrode sheets prepared in Example 1 and Comparative Example 3;

[0026] Figure 3 This is a physical picture of the dry-process negative electrode sheet prepared in Example 1 after being rolled. DETAILED DESCRIPTION

[0027] For ease of understanding, the present invention will be described in more detail below and examples of the present invention are given, but the scope of the present invention is not limited thereby.

[0028] The following is a description of terms or words, and unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0029] In a first aspect, the present invention provides a method for controlling the fibrillation degree of a negative electrode sheet prepared by a dry process, wherein a negative electrode raw material containing a negative electrode active material, a binder, and a conductive agent is subjected to dry mixing and high-speed shearing in sequence to achieve fibrillation to form a negative electrode dry powder, the negative electrode dry powder is prepared into a negative electrode film using a film forming device, and then the negative electrode film and a negative electrode foil are thermally composited by roller pressing to obtain a dry process negative electrode sheet;

[0030] In the above steps, by regulating 65%≤C0≤130%, which can realize the regulation of the fibrillation degree, wherein C0 is the fibrillation degree, M is the mass of the negative electrode active material, in kg, and LD is the bulk density of the negative electrode active material, in g / cm 3 , L is the volume of the dry mixing tank, unit L, T 1 is the material temperature during fibrillation, unit is °C, Δt is the fibrillation dispersion time, unit is min, K 1 is the empirical coefficient, K 1 =0.65, γ is the fibrillation shear rate, n is the rotation speed during fibrillation, unit is rpm, r is the radius of the fibrillation dispersion rotor, unit is m, and h is the stator-rotor distance of the mixer motor, unit is mm.

[0031] Binders represented by polytetrafluoroethylene will undergo fibrillation under the action of mechanical shear force to form a fibrous structure. Therefore, the principle of dry preparation of negative electrode sheets is to subject the mixed negative electrode active materials, binders, and conductive agents to high-speed shear to achieve binder fibrillation, thereby tightly bonding the negative electrode active materials and conductive agents together to form a self-supporting film. Therefore, for dry electrode preparation, the degree of fibrillation is crucial; in current research, faced with many factors affecting the degree of fibrillation, the main material dosage, temperature, time, rotation speed, empirical coefficient, etc. during fibrillation are usually taken into consideration as the main indicators, while the influence of the radius of the fibrillation dispersion rotor and the stator-rotor spacing of the mixer motor on the shear rate, as well as the effect of the shear rate combined with the volume of the stirring tank and the bulk density of the main material on the collision dynamics between particles are not considered; and for negative electrode active materials, there is often a strong agglomeration effect, which makes the collision and speed between the materials during fibrillation Rate, temperature, time and empirical coefficient will together constitute the key indicators affecting the degree of fibrillation. In the formula, the material mass per unit volume is first considered, which is the basis of fibrillation. The mass of the negative electrode active material and the volume and bulk density of the mixing tank jointly determine the difficulty of mixing and the collision results between the materials during mixing. Secondly, the fibrillation degree formula proposed by the inventor also considers the effect of material temperature on fibrillation. Temperature control helps to adjust the fluidity and adhesion of the material, which helps to achieve good fibrillation more easily. At the same time, in this scheme, the effect of the shear rate and dispersion time of fibrillation on fibrillation is further considered. By multiplying the shear rate of fibrillation by the dispersion time, and combining the effect of fibrillation temperature and mixing degree, as well as the empirical coefficient obtained based on a large number of experiments, the control of the degree of fibrillation is achieved, and a negative electrode sheet with an ideal degree of fibrillation is obtained. This formula not only focuses on the effects of main material dosage, temperature, time, rotation speed, test coefficient and other conditions on fibrillation, but also combines the effects of factors such as stirring tank volume, main material bulk density and shear rate on collision dynamics, thus providing a reliable control method for controlling fibrillation during dry preparation of negative electrode sheets.

[0032] As some examples, 75%≤C0≤105%. The degree of fibrillation will affect the structure and performance of the electrode material. Excessive fibrillation may lead to a decrease in the adhesion between the material and the substrate, while too little fibrillation may lead to insufficient bonding between the binder and the active material. Therefore, it is necessary to control the degree of fibrillation. When the degree of fibrillation meets 75%≤C0≤105%, it can effectively improve the dispersibility of components such as negative electrode active materials, binders, and conductive agents, ensure good contact between conductive agents and active materials, improve the conductivity of negative electrode sheets, and reduce the resistance of negative electrode sheets. In addition, when the degree of fibrillation meets 75%-105%, it also helps to enhance the adhesion between active materials and current collectors, avoid the shedding of active materials during the cycle, and thus optimize the cycle performance.

[0033] As some examples, the negative electrode active material is not limited in principle, and technicians can select corresponding negative electrode active materials according to needs, such as one or more of carbon materials, silicon-carbon materials, and silicon-oxygen materials.

[0034] As some examples, the carbon material is selected from any one of natural graphite, artificial graphite, micro carbon beads, hard carbon, and soft carbon.

[0035] As some examples, the binder is selected from any one or more of polymers, rubbers, and cellulose derivatives.

[0036] As some examples, the polymer is selected from any one or more of polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinylidene fluoride, polyvinyl pyrrolidone, polyethylene, polypropylene, polyimide, polyacrylic acid, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, polyamide, and copolymers of tetrafluoroethylene and ethylene or hexafluoropropylene.

[0037] As some examples, the rubber is selected from any one or more of styrene-butadiene rubber, EPDM rubber, and fluororubber.

[0038] As some examples, the cellulose derivatives are selected from any one or more of carboxymethyl cellulose, hydroxypropyl cellulose, and diacetyl cellulose.

[0039] As some examples, the conductive agent is selected from any one or more of carbon black, Super P, activated carbon, graphite, graphene, multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon fibers, conductive carbon black, carbon nanospheres, ellipsoidal carbon, hard carbon, amorphous carbon, silicon carbide, acetylene black, Ketjen black, and vapor grown carbon fiber (VGCF).

[0040] As some examples, the mass proportion of negative electrode active material in the negative electrode dry powder is selected from 85%-99.3%.

[0041] As some examples, the mass proportion of the binder in the negative electrode dry powder is selected from 0.3%-10%.

[0042] As some examples, the mass proportion of the conductive agent in the negative electrode dry powder is selected from 0.4% to 5%.

[0043] As some examples, the dry mixing speed is selected from 1000 rpm to 3000 rpm, and the mixing time is selected from 5 to 20 min.

[0044] As some examples, the rotation speed for achieving fibrillation by high-speed shearing is selected from 4000 rpm to 8000 rpm, and the time is selected from 3 to 30 min.

[0045] As some examples, the stator-rotor spacing h of the mixer motor is selected from 0.2-0.4 mm.

[0046] As some examples, after high-speed shearing, the process of obtaining negative electrode dry powder by refining the material is also included. Refining is conducive to obtaining fine and uniform dry powder material.

[0047] As some examples, when the negative electrode dry powder is formed into a film, the film thinning is carried out at a temperature of 70-250°C.

[0048] As some examples, the roll pressure of the roll hot compounding may be set to 2-50 tons, and the temperature may be set to 70-250°C.

[0049] Suitable film thinning and roller pressing thermal composite conditions are conducive to improving the film forming efficiency, obtaining positive electrode sheets with the designed target thickness, surface density and porosity, and improving the overall mechanical properties of the sheets.

[0050] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application and do not represent all possible embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0051] The chemical raw materials involved in the following examples and comparative examples are all prior art and are commercially available. The experimental devices, test devices, etc. involved in the following examples and comparative examples are all conventional devices in the art, without special requirements and limitations.

[0052] Example 1

[0053] Natural graphite, carbon black, Super P, activated carbon, and carboxymethyl cellulose were weighed in a mass ratio of 95:2:0.5:0.3:2.2 and loaded into a 10L dry mixing tank. The bulk density of natural graphite was 0.35 g / cm3 , the mass of natural graphite is 3 kg. It is stirred for 5 min at 2000 rpm using a dry mixing blender, and then fibrillated by high-speed shearing for 10 min at 95 °C and 4500 rpm to obtain the negative electrode dry powder. Among them, the radius of the fibrillated dispersion rotor is 0.0764 m, and the stator-rotor spacing of the mixer motor is 0.4 mm. Through the film-forming thinning equipment, a precursor of the negative electrode sheet of the secondary battery with a surface density of 9 mg / cm 2 is prepared under the condition that the temperature of the film-forming opposing rollers is 120 °C. Subsequently, under the conditions of a thermal composite opposing roller temperature of 100 °C and a pressure of 5 T, the precursor of the negative electrode sheet of the secondary battery is roll-pressed onto both sides of the carbon-coated copper foil. Among them, the thickness of the carbon-coated copper foil is 10 μm to obtain the negative electrode sheet of the secondary battery. Among them, the fibrillation degree C0 is 86.6%.

[0054] Example 2

[0055] The preparation method and synthesis steps are the same as those in Example 1, except that the volume of the dry mixing tank is selected from 11 L, and the loose bulk density of natural graphite is 0.25 g / cm 3 , and the fibrillation degree C0 is 110.2%.

[0056] Example 3

[0057] The preparation method and synthesis steps are the same as those in Example 1, except that the amount of natural graphite used is 4 kg, and the loose bulk density of natural graphite is 0.45 g / cm 3 , and the fibrillation degree C0 is 90%.

[0058] Example 4

[0059] The preparation method and synthesis steps are the same as those in Example 1, except that the loose bulk density of natural graphite is 0.48 g / cm 3 , the high-speed shearing fibrillation temperature is 100 °C, and the fibrillation degree C0 is 66.5%.

[0060] Comparative Example 1

[0061] The preparation method and synthesis steps are the same as those in Example 1, except that the amount of natural graphite used is 1 kg, and the fibrillation degree C0 of natural graphite is 28.87%.

[0062] Comparative Example 2

[0063] The preparation method and synthesis steps are the same as those in Example 1, except that the high-speed shearing fibrillation temperature is 60 °C, and the fibrillation degree C0 is 54.71%.

[0064] Comparative Example 3

[0065] Natural graphite, carbon black, Super P, activated carbon, and carboxymethyl cellulose were weighed in a ratio of 95:2:0.5:0.3:2.2 and dissolved in deionized water, stirred evenly, to obtain a negative electrode slurry, which was then coated on the surface of a 10 μm carbon-coated copper foil by wet coating, wherein the double-sided surface density was 18 mg / cm 2 After coating, the graphite negative electrode sheet was rolled and compacted to a density of 1.6 g / cm 3 ; Die-cut the qualified negative electrode sheet after rolling to obtain the negative electrode sheet of the secondary battery.

[0066] Test Method

[0067] Pole sheet resistivity: tested using Yuanneng Technology BER2500 pole sheet resistance meter, the sample is a rolled pole sheet, the sample contact area is 154mm 2 , pressure 10N, holding time 5s, test 3 parallel samples and take the average value of the results.

[0068] Pole peel strength: Use Shanghai Yuhan Machinery YC-125B universal testing tensile machine to test, the steps are as follows

[0069] (1) Cutting the electrode: Take the rolled electrode and cut it with a die cutter to a length and width of 200 mm*15 mm.

[0070] (2) Fix the electrode: Take a flat thin steel plate, about 170mm long and 50mm wide, wipe the surface of the stainless steel plate with alcohol 3 times, and let it dry for 10 minutes. Stick a 3M double-sided tape in the center of the steel plate (the length should be greater than the sample test length and the same width as the electrode), smooth it, and ensure that the double-sided tape is tightly attached to the center of the steel plate. Remove the double-sided tape, attach the electrode to the tape, and use a 2.5Kg pressure roller to roll back and forth 6 times to ensure that the electrode and the tape are completely attached.

[0071] (3) The unadhesive end of the specimen is peeled off from the steel plate by about 20 mm. Insert the steel plate with the fixed electrode into the lower clamp of the tensile machine and fix it; insert the unadhesive electrode into the upper clamp of the tensile machine and fix it, so that the electrode attached to the adhesive tape is at 90 degrees to the electrode fixed by the upper clamp.

[0072] (4) Set the test speed (400 mm / min), sample width (15 mm), peeling length 50 mm and other parameter information, click the test option, the test starts, and the equipment automatically records the force value during the peeling process and reports the peel strength of the sample accordingly.

[0073] (5) Repeat the sample cutting, preparation, and testing procedures (1) to (4) to test the peel strength values ​​of the three samples and take the average value of the results.

[0074] The test results are shown in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] From Examples 1-4 and Comparative Examples 1-3, it can be observed that Examples 1-4, in which the fibrillation degree C0 satisfies 65%-130%, exhibit better compaction density, resistivity, and peel strength than Comparative Examples 1-2, in which the fibrillation degree C0 does not satisfy 65%-130%, or Comparative Example 3 prepared by a wet method. At the same time, compared with Examples 1-4, Comparative Example 1-2 cannot form a film, indicating that the regulation proposed in this scheme 65%≤C0≤130%, which can effectively control the fibrillation degree of the negative electrode sheet prepared by the dry method, thereby optimizing the performance of the negative electrode sheet.

[0079] First, it can be observed from Example 1 and Comparative Examples 1-2 that the degree of fibrillation is affected by many factors, such as the mass of the negative electrode active material, the loose density of the negative electrode active material, the volume of the dry stirring tank, the material temperature during fibrillation, the fibrillation dispersion time, and the fibrillation shear rate. When the parameters for preparing the negative electrode sheet cannot meet 65%≤C0≤130%, Comparative Examples 1 and 2 cannot successfully form a film due to their low degree of fibrillation, resulting in failure in the preparation of the negative electrode sheet.

[0080] In addition, the proposed scheme satisfies the 65%≤C0≤130%, the method for adjusting the degree of fibrillation is applicable to the dry process for preparing negative electrode sheets, according to Example 1, Comparative Example 3, and Figure 2 It can be observed that on the basis of the same raw materials, the method proposed in this scheme can effectively regulate the degree of fibrillation, thereby optimizing the performance of the negative electrode sheet, especially Figure 2 It can be observed that the resistivity and peel strength of Comparative Example 3 are weaker than those of Example 1, which further proves that the negative electrode sheet prepared by the method proposed in this scheme can effectively optimize the performance of the negative electrode sheet.

[0081] Based on the control of the degree of fibrillation, we further discussed the effect of the degree of fibrillation on the performance of the negative electrode.

[0082] First, from Examples 1-4, Figure 1 It can be observed that based on different preparation parameters, Examples 1-4 all exhibit good compaction density, resistivity and peel strength, and Figure 1It shows a layered morphology. Such results once again prove the effectiveness of the control parameters in this scheme. Furthermore, compared with Examples 2 and 4, Examples 1 and 3 show better compaction density, resistivity and peel strength. This may be because when the degree of fibrillation meets 75%≤C0≤105%, the negative electrode active material, adhesive and conductive agent can better contact each other, thereby optimizing the negative electrode sheet resistance. At the same time, the degree of fibrillation that meets 75%≤C0≤105% can further enhance the adhesion between the active material, adhesive, conductive agent and negative electrode current collector. Therefore, Examples 1 and 3 show better resistance and peel strength.

[0083] The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. Although the embodiments of the present invention have been shown and described above, it can be understood that the above-described embodiments are exemplary and cannot be understood as limitations of the present invention. Those of ordinary skill in the art can change, modify, replace and deform the above-described embodiments within the scope of the present invention. In addition, those of ordinary skill in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples without contradiction.

Claims

1. A method for controlling the fibrillation degree of a negative electrode sheet prepared by a dry process, characterized in that: The negative electrode raw materials containing negative electrode active materials, binders and conductive agents are sequentially subjected to dry mixing and high-speed shearing to achieve fibrillation to form negative electrode dry powder, the negative electrode dry powder is prepared into a negative electrode film using a film forming device, and the negative electrode film and negative electrode foil are then hot-compounded by roller pressing to obtain a dry-process negative electrode sheet; In the above steps, the process parameters meet 65%≤C0≤130%, where C0 is the fibrillation degree, M is the mass of the negative electrode active material, in kg, and LD is the bulk density of the negative electrode active material, in g / cm 3 , L is the volume of the dry mixing tank, unit L, T1 is the material temperature during fibrillation, unit ℃, Δt is the fibrillation dispersion time, unit min, K1 is the empirical coefficient, K1 = 0.65, γ is the fibrillation shear rate, n is the rotation speed during fibrillation, unit is rpm, r is the radius of the fibrillation dispersion rotor, unit is m, and h is the stator-rotor distance of the mixer motor, unit is mm.

2. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: Process parameters meet 75%≤C0≤105%.

3. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: The negative electrode active material is selected from one or more of carbon materials, silicon-carbon materials, and silicon-oxygen materials.

4. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: The binder is selected from any one or more of polymers, rubbers, and cellulose derivatives.

5. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: The conductive agent is selected from any one or more of carbon black, SuperP, activated carbon, graphite, graphene, multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon fibers, conductive carbon black, carbon nanospheres, ellipsoidal carbon, hard carbon, amorphous carbon, silicon carbide, acetylene black, Ketjen black, and vapor-grown carbon fibers.

6. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: The mass proportion of the negative electrode active material in the negative electrode dry powder is selected from 85% to 99.3%; Preferably, the mass proportion of the binder in the negative electrode dry powder is selected from 0.3%-10%; Preferably, the mass proportion of the conductive agent in the negative electrode dry powder is selected from 0.4%-5%.

7. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: The dry mixing speed is selected from 1000rpm-3000rpm, and the mixing time is selected from 5-20min; Preferably, the speed of achieving fibrillation by high-speed shearing is selected from 4000rpm-8000rpm, and the time is selected from 3-30min; Preferably, the stator-rotor spacing h of the mixer motor is selected from 0.2-0.4 mm.

8. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: After high-speed shearing, the process also includes obtaining negative electrode dry powder by refining the material.

9. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: When the negative electrode dry powder is formed into a film, the film thinning is carried out at a temperature of 70-250°C.

10. The method for controlling the fibrillation degree of the negative electrode sheet prepared by dry process according to claim 1, characterized in that: The roller pressure of roller hot compounding can be set to 2-50t, and the temperature can be set to 70-250℃.

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