A method for regulating dry electrode fibrosis

Abstract

The present invention discloses a method for regulating dry electrode fiberization, which adopts the countercurrent or constant current principle to realize a high-speed difference in phase-reversed mixture flow, namely a volume stretching flow field. By controlling the parameter characteristics of the binder, the materials are mixed according to a certain method, and the micro-nano binder particles are efficiently intercalated, and the mesh-like fiberized network structure formed after exfoliation and fiberization "coats" the active particles, thereby achieving sufficient and uniform mixing and dispersion of the active particles in the binder. The present invention solves the problems of high cost, difficult recycling, toxicity, high pollution and high energy consumption of solvents used in traditional lithium battery production; significantly and stably improves the uniformity of the mixed materials; minimizes the destructiveness to the microstructure of the active material during the mixing process; greatly shortens the pulping time, compressing it to minutes; and reduces the process difficulty of dry preparation of electrode sheets.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for regulating dry electrode fiberization. Background Art

[0002] With the growing lithium battery market and increasingly widespread applications, manufacturing costs and environmental impacts are among the challenges facing lithium batteries. Traditional lithium batteries are manufactured using a solvent-based process, where a suspended liquid slurry is coated onto a foil current collector. This process typically uses toxic and expensive organic solvents such as N,N-dimethylpyrrolidone (NMP). During the manufacturing process, NMP can contain excessive moisture, leading to swelling and rapid performance degradation during battery cycling. Furthermore, solvent evaporation and recovery during the manufacturing process consume significant energy.

[0003] Based on the above problems, solvent-free manufacturing methods are of great research significance in developing cost-effective and environmentally friendly lithium batteries. Many researchers have used dry processes to prepare electrode sheets and batteries. They mix powders such as active materials, conductive materials, and binders, and use various methods such as jet grinding, extrusion, and air flow crushing to form a continuous self-supporting dry film. The film is composited with the current collector to form an electrode sheet. The production advantages of this dry electrode preparation process are: ① It saves the stirring energy of the solvent, and the energy and equipment are reduced during the stirring process; ② It eliminates the need for solvent drying, recovery, and loss processing; ③ Stirring, coating, and rolling are achieved on the same equipment, reducing the equipment ratio; ④ It saves time and labor costs. Therefore, it not only reduces product energy consumption and production costs, but also improves the life of lithium batteries.

[0004] However, in dry electrode preparation methods, since the binder exists in a fiberized form, fiberization of the binder is extremely important. In existing processes, the binder is dry-fiberized using methods such as airflow milling and jet milling. This fiberization is difficult, and the high shear forces within the equipment can lead to a decrease in the binder's bonding properties. The most direct and serious consequence is partial inactivation of the positive and negative active particles and surface cracking. Furthermore, high shear forces place high demands on equipment, resulting in high production costs and hindering large-scale production. If the shear forces are reduced, the binder's fiberization level is low, insufficient to bond the active particles and conductive agent, leading to problems such as powder shedding and difficulty in hot pressing the electrodes. Patent CN112420986 A uses a variety of machines, including high-shear mixers, airflow mills, and screw extruders, to dry-prepare electrodes. Patent CN 112289976 A employs a stirring speed of 17,000-25,000 rpm for 10 to 30 minutes for fiberization. These solutions place high demands on equipment, and the extremely high shear forces can adversely affect the structure of the active particles.

[0005] Therefore, how to dry-process a dry electrode fiberization and regulation method with a high degree of fiberization, little damage to the microstructure of the active material, and low equipment requirements has become an urgent problem that technicians in this field need to solve. Summary of the Invention

[0006] In response to the problems existing in the prior art, the present invention provides a method for regulating the fiberization of dry-process electrodes. The fiberization method provided by the present invention adopts a volume stretching flow field mixing method and principle, which has the significant advantage of not only greatly reducing the difficulty of fiberization of the binder, but also achieving a higher degree of fiberization of the network structure, which is most conducive to overlapping a complete three-dimensional mesh structure and improving the firmness of the bond between material components; greatly reducing the damage to the microstructure of the active particles, and stably improving the optimal uniformity of the mixed materials; shortening the pulping and mixing time, and compressing it to minutes; the present invention can also improve the degree of fiberization of the adhesive, making the binder more fully fiberized and the dispersion uniformity between the components better, reducing the amount of binder used and improving the calendering effect, and can prepare thick electrodes, which will be beneficial to improving the energy density of the battery. This method can quickly reduce costs and realize large-scale production by enterprises by significantly reducing the process difficulty of dry-process preparation of electrode sheets.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A method for regulating dry electrode fibrosis, comprising the following steps:

[0009] (1) Powder premixing: premix the electrode active material, conductive agent, and fiberizable binder at a constant temperature of less than 30°C for 10 to 60 minutes;

[0010] (2) Pre-fiberization-in situ cross-linking reaction: the powder pre-mixed in step (1) is heated at a temperature of 50-150°C, and the in situ cross-linking reaction time is 10 min-60 min;

[0011] (3) Uniform fiberization: The material in step (2) is placed in a mixing and dispersing device having a uniformly distributed star-shaped rotor and an eccentrically and / or angled agitator. The linear velocity is maintained at 35-50 m / s, the uniform fiberization dispersion time is 5-10 min, and the number of cycles is not more than 3 times. The fiberization method is to place the mixed material containing the binder under the action of a reverse mixture flow, also known as a volume stretching flow field, to promote the orderly arrangement of the binder and in-situ fiberization. Because the shearing effect of the volume stretching flow field is relatively weak, the destructive effect on the active material is small. The flow field is more conducive to improving the efficient intercalation of the binder coarse fibers and the peeling to form fine fibers to solidify the active material.

[0012] (4) Dry film: The material after uniform fiberization in step (3) is rolled into a dry film by horizontal and vertical rolling, with the temperature controlled at 60-150°C;

[0013] (5) Dry electrode sheet: The dry film is laminated to both sides of the current collector by hot roller pressing to obtain a dry electrode sheet.

[0014] Furthermore, the fiberizable binder in step (1) includes but is not limited to at least one of polytetrafluoroethylene, styrene-butadiene rubber, polyvinylidene fluoride, polyethylene oxide, poly(vinylidene fluoride-hexafluoropropylene), polyacrylonitrile, (methyl)polyacrylonitrile, polyvinyl alcohol, polyacrylic acid, polymethyl methacrylate, modified polymethyl methacrylate, polyvinylidene fluoride copolymer, and polystyrene, that is, the binder may be a mixture of two or more thereof;

[0015] The fiberizable binder is of dispersed type, not suspended type;

[0016] The particle size D50 of the fiberizable binder material is 100nm-50μm, the aspect ratio is greater than 5, and the purity is 99.9%. 5 -10 8 Since the physical properties of the binder have a great influence on the fiber network structure, the properties and specifications of the binder are specified.

[0017] The fiberizable adhesive is a low melting point adhesive with a temperature of 50-150°C.

[0018] The fibrillizable binder polymer is subjected to a volumetric stretching flow field, which causes the binder to be arranged in an orderly manner and fibrillated in situ. The shearing effect of the volumetric stretching flow field is relatively weak, causing minimal damage to the active material. The flow field allows the binder to be coarsely fibrillated, and the coarse fibers to be efficiently intercalated and exfoliated to form fine fibers.

[0019] Furthermore, the powder premixing in step (1) is carried out at a constant temperature of less than 30°C (in any form of mixing method) in order to avoid uneven fiberization of the binder in advance, which would affect the microstructure of the hot-pressed film.

[0020] Furthermore, the in-situ cross-linking reaction in step (2) needs to control the reaction temperature and time to achieve the expansion of the adhesive.

[0021] Furthermore, the heating method of the heating treatment in step (2) is resistance heating or infrared heating.

[0022] Furthermore, the rotor of the mixing and dispersing equipment for achieving uniform fiberization in step (3) is a star-shaped rotor with a uniform layout.

[0023] Furthermore, the stirring blade of the mixing and dispersing equipment for achieving uniform fiberization in step (3) has an inclination angle of 0-30°.

[0024] Furthermore, the stirring paddle of the mixing and dispersing equipment for achieving uniform fiberization in step (3) is eccentrically mounted, and the rotation direction and speed of the stirring paddle can be optimally adapted to the application site;

[0025] Furthermore, the mixing and dispersing equipment for achieving uniform fiberization in step (3) is provided with bottom / wall scrapers to provide additional stirring. This can prevent agglomeration on the pot wall and bottom, and achieve uniformity of the slurry during the circulating dispersion process.

[0026] Furthermore, the homogenizing, mixing and dispersing equipment in step (3) can be a drum mixer, a conical screw mixer, an intensive mixer, etc.

[0027] Furthermore, the purpose of uniform fiberization in step (3) is to obtain a uniform mixed powder and to further uniformly fiberize the pre-fiberized and expanded binder to obtain a better mesh fiber network structure; the mesh structure after fiberization is used to "coat" the active particles.

[0028] Furthermore, the hot pressing temperature is controlled during the rolling process in step (4), otherwise the membrane will not be easily formed and will be difficult to transfer to the current collector.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] 1. The present invention utilizes countercurrent or constant flow mixing methods and principles to achieve a high-speed differential, inverse volume stretching flow field. This significantly enhances the efficient intercalation and exfoliation of micro-nano adhesive particles, which, after fiberization, form a reticulated, fibrous network structure that "coats" the active particles. The eccentric and angled stirring of the stirring paddles creates a high-speed differential, inverse volume stretching flow field for the mixed material, forming a strong vertical component of the mixture flow. This not only significantly reduces the difficulty of binder fiberization, but also results in a more highly fiberized network structure that facilitates the formation of a complete three-dimensional network structure, enhancing the bond strength between material components.

[0031] 2. The fiberization control method of the present invention significantly shortens the mixing time of the powder, reduces the degree of damage to the microstructure of the active material, reduces the inactivation ratio of the active material due to high shear force, and achieves the optimization of the material mixing of the active material in the binder.

[0032] 3. The fiberization control method of the present invention avoids uneven fiberization in advance, which affects the forming of the membrane during the rolling process; it can also avoid incomplete fiberization, which causes the membrane to be crushed and unable to be formed during the rolling process.

[0033] 4. The fiberization method of the present invention can greatly reduce the process difficulty of dry-process preparation of electrode sheets, which is conducive to the preparation of thick electrodes, quickly reduces costs, and realizes large-scale production in enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a visual photo of fibrosis in Example 1.

[0035] Figure 2 This is the scanning electron microscope after roller pressing of Example 1.

[0036] Figure 3 This is a visual photo of fibrosis in Example 2.

[0037] Figure 4 This is a photo of Example 2 after roller pressing.

[0038] Figure 5 This is a photo of Comparative Example 1 after roller pressing.

[0039] Figure 6 This is a photo of comparative example 2 after roller pressing.

[0040] Figure 7 This is a photo of comparative example 3 after roller pressing.

[0041] Figure 8 This is a photo of comparative example 4 after roller pressing.

[0042] Figure 9 Schematic diagram of the volume extension flow field principle of inversely mixed materials. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to specific examples. It should be understood that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention, and that those skilled in the art may make non-essential improvements and adjustments based on the contents of the above invention.

[0044] Example 1

[0045] The control method of dry electrode fibrosis in this embodiment is as follows:

[0046] (1) Powder premixing: premix the electrode active material small particle size ternary material (NCM622), the conductive agent Ketjen black (KB), and the fiberizable binder dispersed polytetrafluoroethylene (powder). The premixing method is any mixing method such as double planetary stirring. The premixing time is 30 min. The small particle size ternary material (NCM622): dispersed polytetrafluoroethylene (powder): Ketjen black (KB) = 80:10:10. The total mass is controlled at 200 g. The polytetrafluoroethylene binder particle size D50 is 5.5±2 μm, the aspect ratio is greater than 5, the purity is 99.9%, and the molecular weight is 10 5 -10 8g / mol;

[0047] (2) In-situ cross-linking reaction-prefiberization: The powder after mixing in step (1) is heated by resistance heating at a temperature of 60±3°C and an in-situ cross-linking reaction time of 30 min;

[0048] (3) Homogeneous fiberization: the material after the in-situ cross-linking reaction in step (2) is placed in an intensive mixer, the stirring paddle of the intensive mixer is tilted at an angle of 0°, the stirring paddle of the intensive mixer is eccentrically installed, the rotation direction and speed of the stirring paddle can be optimally adapted to the application site, the dispersion speed is maintained at 35-40 m / s, the step time is 5 min, the total number of cycles is 1, and the intensive mixer is equipped with bottom / wall scrapers to provide additional stirring, which can prevent agglomeration on the pot wall and bottom, and achieve homogenization of the slurry during the cyclic dispersion process;

[0049] (4) Dry film: The fiberized material in step (3) is rolled into a dry film by horizontal and vertical rolling, the temperature is controlled at 80°C, and the film is rolled into a roll;

[0050] (5) Dry electrode: The dry film is bonded to both sides of the current collector by hot roller pressing to obtain a dry electrode.

[0051] Example 2

[0052] The difference between Example 2 and Example 1 is that the ratio of graphite: dispersed polytetrafluoroethylene (emulsion): Ketjen black (KB) is 80:10:10.

[0053] Example 3

[0054] The difference between Example 3 and Example 2 is that step (3) is a fiberization step, the stirring blade of the intensive mixer has an inclination angle of 30°, and the dispersion speed is maintained at 35-40 m / s.

[0055] Comparative Example 1

[0056] The difference between Comparative Example 1 and Example 2 is that the molecular weight of the binder is 4000-20000 g / mol.

[0057] Comparative Example 2

[0058] The difference between Comparative Example 2 and Example 2 is that the dispersion speed of the uniform fiberization in step (3) is maintained at 20-30 m / s.

[0059] Comparative Example 3

[0060] The difference between Comparative Example 3 and Example 2 is that the dispersion speed of the uniform fiberization in step (3) is maintained at 35-40 m / s, the step time is 5 min, and the total number of cycles is 4 times.

[0061] Comparative Example 4

[0062] The difference between Comparative Example 4 and Example 2 is that the uniform fiberization mixing and dispersing equipment in step (3) is not eccentric or tilted, the dispersion speed is maintained at 35-40 m / s, the step time is 5 min, and the total number of cycles is 1.

[0063] The scanning electron microscope and photographs of the fiberized powders or the pole pieces after rolling prepared in Examples 1 to 3 and Comparative Examples 1 to 4 are as follows: Figure 1-8 shown. Figure 1 This is a visual fiberization photo of the powder after uniform fiberization in Example 1. Figure 1 It can be clearly seen from the photo that there are already fibrous filaments in the material; Figure 2 This is a photo of the material after fiberization in Example 2, where the material portion has been completely integrated; Figure 3 Scanning electron microscopy of Example 3 after roller pressing shows that the material particles are of similar size and uniform, and the surface of the electrode is relatively uniform with obvious filaments and fibrosis; Figure 4 The photo of Example 3 after rolling shows that the rolling discharge is uniform, the electrode film has no holes, and the edges are neat, which affects the quality of the electrode film; Figure 5-8 This is the film-out situation after roller pressing in comparative example 1-4. Figure 5 The molecular weight of the binder is relatively small, the surface of the electrode after rolling is relatively rough, and the edges of the electrode and diaphragm are uneven; Figure 6 This is a picture of comparative example 2 after roller pressing. The dispersion speed is low and the degree of fiberization is low. After roller pressing, the surface of the pole piece is relatively smooth and delicate, and the edge of the pole piece is not neat. Figure 7 This is a picture of the powder after roller pressing in Example 3. It can be seen from the picture that the edge regularity of the pole piece is seriously reduced due to excessive fiberization, resulting in a decrease in the quality of the pole piece; Figure 8 In comparative example 4, the equipment operating parameters are normal, but because the equipment is not eccentric and tilted, the powder fiberization degree is insufficient. After rolling, the surface of the pole piece is relatively rough and the edge neatness is seriously insufficient, resulting in pole piece waste. Figure 5-8 From the comparative photos after rolling, it is not difficult to see that insufficient or excessive fiberization will cause uneven edges of the electrode film, affecting the forming quality of the electrode film.

[0064] In summary, after the mixed material uses the fiberization control method of the present invention, it can be clearly seen that fibrous filaments exist in the material. The surface of the electrode after rolling is relatively uniform, with obvious filamentous and fibrous states. The rolled film is more neat, with almost no edge defects, which improves material utilization.

[0065] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling dry electrode fiberization, characterized in that The following steps are involved: (1) Powder premixing: premix the electrode active material, conductive agent, and fiberizable binder at a constant temperature of less than 30°C for 10 to 60 minutes; (2) Pre-fiberization-in situ cross-linking reaction: the powder pre-mixed in step (1) is heated at a temperature of 50-150°C, and the in situ cross-linking reaction time is 10 min-60 min; (3) Uniform fiberization: The material in step (2) is placed in a mixing and dispersing device having a uniformly distributed star-shaped rotor and an eccentrically installed stirring paddle, maintaining a linear speed of 35-50 m / s, a uniform fiberization and dispersion time of 5-10 min, and a cycle number of not more than 3 times; (4) Dry film: The material after uniform fiberization in step (3) is rolled into a dry film by horizontal and vertical rolling, with the temperature controlled at 60-150°C; (5) Dry electrode sheet: The dry film is laminated to both sides of the current collector by hot roller pressing to obtain a dry electrode sheet; The molecular weight of the fiberizable binder is 10 5 -10 8 g / mol.

2. The method for controlling dry electrode fiberization according to claim 1, characterized in that: The premixing method in step (1) is ball milling, double planetary mixing, sand milling, cone milling or high-speed grinding.

3. The method for controlling dry electrode fiberization according to claim 1, characterized in that: The fiberizable binder includes at least one of polytetrafluoroethylene, styrene-butadiene rubber, polyvinylidene fluoride, polyethylene oxide, poly(vinylidene fluoride-hexafluoropropylene), polyacrylonitrile, polyvinyl alcohol, polyacrylic acid, polymethyl methacrylate, modified polymethyl methacrylate, and polystyrene.

4. The method for controlling dry electrode fiberization according to claim 1 or 3, characterized in that: The fiberizable binder is a dispersed type, with a particle size D50 of 100 nm-50 μm and a purity of 99.9%. The fiberizable binder has a low melting point of 50-150° C.

5. The method for controlling dry electrode fiberization according to claim 1, characterized in that: The heating method of the heating treatment in step (2) is resistance heating or infrared heating.

6. The method for controlling dry electrode fiberization according to claim 1, characterized in that: The mixing and dispersing equipment in step (3) is a drum mixer, a conical screw mixer or an intensive mixer.

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