CN115881888A - Regulation and control method for dry-method electrode fibrosis - Google Patents

Abstract

The invention discloses a regulating method for dry electrode fibrosis, which adopts a countercurrent or constant flow principle to realize a high-speed difference phase-reversal mixture flow, namely a volume stretching flow field. The materials are mixed according to a certain method by controlling the parameter characteristics of the binder, and the active particles are coated by a reticular fibrosis network structure formed by efficiently intercalating and exfoliating the micro-nano binder particles, so that the active particles are fully and uniformly mixed and dispersed in the binder. The invention solves the problems of high solvent cost, difficult recovery, toxicity, large pollution and high energy consumption in the traditional lithium battery production; obviously and stably improving the uniformity of the mixed materials; the destructiveness of the microstructure of the active substance in the mixing process is reduced to the maximum extent; greatly shortening the pulping time, and compressing the pulp to be measured in minutes; the process difficulty of preparing the electrode plate by a dry method is reduced.

Description

Regulation and control method for dry-method electrode fibrosis

Technical Field

The invention relates to the technical field of lithium batteries, in particular to a regulating and controlling method for dry electrode fibrosis.

Background

With the increasing expansion of the lithium battery market and the immobilization of applications, the manufacturing cost and environmental impact thereof are one of the challenges facing lithium batteries. The traditional lithium battery adopts a solvent method manufacturing process, namely, the suspension liquid slurry is coated on a foil current collector. The disadvantage of this process is that it usually uses toxic and expensive organic solvent such as N, N-dimethyl pyrrolidone (NMP), etc., and NMP causes problems such as swelling and too fast performance decay during the cycling process of the battery due to too high moisture content during the manufacturing process. In addition, solvent evaporation and recovery during the manufacturing process cause significant energy consumption.

Based on the above problems, the solvent-free manufacturing method has important research significance in developing a lithium battery which is cost-effective and environmentally friendly. Many researchers have used dry processes to prepare electrode plates and batteries, which mix powders such as active materials, conductive materials, binders, etc., and roll them by various methods such as jet milling, extrusion, air flow pulverization, etc. to form continuous self-supporting dry films, which are then combined with current collectors to form electrode plates. The dry electrode preparation process has the production advantages that: (1) the stirring energy of the solvent is saved, the energy is reduced in the stirring process, and the equipment is also reduced; (2) the treatment of solvent drying, recovery and loss is omitted; (3) stirring, coating and rolling are realized on the same equipment, and the equipment proportion is reduced; (4) time and labor cost are saved. Therefore, the energy consumption of the product is reduced, the production cost is reduced, and the service life of the lithium battery can be prolonged.

However, in the dry electrode production method, the binder exists in a fibrous form, and therefore, the fibrous form of the binder is very important. Because the binder is subjected to dry fiberization by methods such as jet milling and jet grinding in the preparation process of the prior art, the fiberization difficulty is high, the bonding performance of the binder is reduced due to high shearing force in equipment, and the most direct serious consequences are partial inactivation, surface cracking and the like of the positive and negative active particles. In addition, the requirement of high shearing force on equipment is high, so that the production cost is high, and the large-scale production is not facilitated; if the shearing force is reduced, the fiberization degree of the binder is low, the binder is not enough to adhere active particles and a conductive agent, the problems of powder falling and the like are easily caused, and the electrode is difficult to be hot-pressed and molded. The patent CN 112420986A uses various machines such as a high-shearing force stirrer, a jet mill and a screw extruder to prepare the electrode in a dry method, and the patent CN 112289976A uses a speed of 17000-25000rpm to stir for 10-30 min to carry out fiberization, so that the requirements on equipment are high, and the extremely high shearing force can generate adverse effects on the structure of the active particles.

Therefore, how to prepare a dry electrode fibrosis and regulation method with high fibrosis degree, small damage to the microstructure of an active substance and low equipment requirement by a dry method becomes a problem which needs to be solved by the technical personnel in the field urgently.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a regulating and controlling method for dry-method electrode fibrosis. The fiberization method provided by the invention adopts a volume stretching flow field mixing method and principle, and has the remarkable advantages that the fiberization difficulty of the binder is greatly reduced, the fiberization degree of the network structure is higher, the complete three-dimensional network structure can be lapped, and the bonding firmness of the material components is improved; the damage of the microstructure of the active particles is greatly reduced, and the optimal uniformity of the mixed material is stably improved; the pulping mixing time is shortened, and the pulping mixing time is reduced to be measured in minutes; the invention can improve the fiberization degree of the adhesive, so that the fiberization of the adhesive is more sufficient, the dispersion uniformity among the components is better, the use amount of the adhesive is reduced, the calendering effect is improved, and the thick electrode can be prepared, which is beneficial to improving the energy density of the battery. The method can rapidly reduce the cost due to greatly reducing the process difficulty of preparing the electrode plate by the dry method, and realize large-scale production of enterprises.

In order to solve the technical problems, the invention adopts the following technical scheme:

a method for regulating and controlling dry-method electrode fibrosis comprises the following steps:

(1) Pre-mixing powder: premixing an electrode active substance, a conductive agent and a fiberizable binder at a constant temperature of less than 30 ℃ for 10min to 60min;

(2) Prefibration-in situ crosslinking reaction: heating the powder premixed in the step (1) at the temperature of 50-150 ℃, wherein the in-situ crosslinking reaction time is 10-60min;

(3) Homogenizing and fiberizing: putting the material in the step (2) into mixing and dispersing equipment, wherein the mixing and dispersing equipment is provided with a star-shaped rotor which is uniformly distributed, stirring paddles are arranged eccentrically and/or angularly, the linear speed of 35-50m/s is kept, the uniform fiberization dispersion time is 5-10min, and the cycle number is not more than 3; the fiberization method is that the mixed material containing the binder is acted by a reversed mixture flow which can also be called a volume stretching flow field to promote the ordered arrangement and in-situ fiberization of the binder. The shearing action of the volume stretching flow field is relatively weak, so that the damage effect on the active material is small, and the flow field is more favorable for improving the solidification effect of the active material caused by the fine fiber formed by the efficient intercalation and stripping of the coarse fiber of the binder;

(4) Dry-process membrane: carrying out horizontal rolling and vertical rolling on the material subjected to the uniform fiberization in the step (3), controlling the temperature to be 60-150 ℃, and rolling into a dry-process membrane;

(5) Dry electrode sheet: and compounding the dry-process membrane to the two sides of the current collector through hot rolling to obtain the dry-process electrode pole piece.

Further, 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, (meth) polyacrylonitrile, polyvinyl alcohol, polyacrylic acid, polymethyl methacrylate, modified polymethyl methacrylate, polyvinylidene fluoride-based copolymer, polystyrene, that is, the binder may be a mixture of two or more thereof;

wherein the fiberizable binder is a dispersed, non-suspended type;

the particle size D50 of the fiberizable binder material is 100nm-50 μm, the length-diameter ratio is more than 5, and the purity is 99.9%. Has a molecular weight of 10 ⁵ -10 ⁸ g/mol. The physical parameters of the binder have a large influence on the fiberized network structure, and thus the binder properties and specification parameters are specified.

The fiberizable binder is a low melting point bond at 50-150 ℃.

The fiberizable binder polymer orders and fiberizes the binder in situ under the action of a volumetric tensile flow field. The shearing action of the volume stretching flow field is relatively weak, the damage action to the active material is small, and the flow field leads the binder to be coarse-fibered and the coarse fiber to be efficiently intercalated and stripped to form fine fiber.

Further, the powder premixing in the step (1) is carried out in an environment with a constant temperature of less than 30 ℃ (in any form of mixing mode), so that the problem that the adhesive is subjected to nonuniform fibrosis in advance to influence the microstructure of a hot-pressing membrane is solved.

Further, the in-situ crosslinking reaction in the step (2) needs to control the reaction temperature and time to realize the expansion of the binder.

Further, the heating method of the heating treatment in the step (2) is resistance heating or infrared heating.

Further, the rotor of the mixing and dispersing equipment for realizing the uniform fiberization in the step (3) is a star-shaped rotor and is uniformly distributed.

Further, the inclination angle of the stirring paddle of the mixing and dispersing equipment for realizing the uniform fiberization in the step (3) is 0-30 degrees.

Further, the stirring paddle of the mixing and dispersing equipment for realizing the uniform fibrosis in the step (3) is in an eccentric installation stirring mode, and the rotating direction and the speed of the stirring paddle can be optimally adapted to application places;

further, the mixing and dispersing device for realizing the step (3) of homogenizing is provided with a bottom/wall scraper to provide additional stirring. It can prevent the agglomeration of the pot wall and the pot bottom and realize the homogenization of the slurry in the circulating dispersion process.

Further, the homogenizing, mixing and dispersing device of the step (3) can be a drum mixer, a conical screw type mixer, a dense mixer and the like.

Further, the step (3) is carried out uniformly, wherein the aim of uniform fiberization is to obtain uniform mixed powder, and the pre-fiberized expanded binder is further uniformly fiberized to obtain a better reticular fiber network structure; the reticular structure after the fibrosis is realized to carry out 'coating' on the active particles.

Further, the rolling process in the step (4) controls the hot-pressing temperature, otherwise, the diaphragm is not easy to form and is difficult to transfer to the current collector.

Compared with the prior art, the invention at least comprises the following beneficial effects:

1. the invention adopts a counter-current or constant-current mixing method and principle to realize a high-speed-difference phase-reversal volume stretching flow field, and has the remarkable advantages that micro-nano adhesive particles are efficiently intercalated and stripped, and a reticular fibrosis network structure is formed after fibrosis to coat active particles. The decentralization and the angled stirring of the stirring paddle generate a reversed volume stretching mixed material flow field with high speed difference, and a strong vertical component of the mixed material flow is formed, so that the fiberization difficulty of the binder is greatly reduced, the fiberization degree of the network structure is higher, the complete three-dimensional network structure is more favorable for lap joint, and the firmness of the bonding between the material components is improved.

2. The fibrosis regulation and control method obviously shortens the mixing time of the powder, reduces the damage degree of the microstructure of the active material, reduces the inactivation proportion of the active material caused by high shear force, and realizes the optimization of the material mixing of the active material in the binder.

3. The fibrosis regulation and control method disclosed by the invention avoids the influence on the forming of the diaphragm in the rolling process due to uneven fibrosis carried out in advance; and the phenomenon that the diaphragm is crushed and cannot be formed in the rolling process due to incomplete fiberization can be avoided.

4. The fiberization method can greatly reduce the process difficulty of preparing the electrode slice by a dry method, is beneficial to preparing a thick electrode, quickly reduces the cost and realizes the large-scale production of enterprises.

Drawings

FIG. 1 is an image of the fiberization of example 1.

FIG. 2 is a scanning electron microscope after rolling in example 1.

FIG. 3 is a photograph of an observed fibrosis in example 2.

FIG. 4 is a photograph of example 2 after rolling.

Fig. 5 is a photograph of comparative example 1 after rolling.

Fig. 6 is a photograph of comparative example 2 after rolling.

Fig. 7 is a photograph after rolling of comparative example 3.

Fig. 8 is a photograph of comparative example 4 after rolling.

FIG. 9 is a schematic diagram of the principle of the volume stretching flow field of the inverse mixture.

Detailed Description

The present invention will be further described with reference to the following examples. It is to be understood that the following examples are illustrative only and are not intended to limit the scope of the invention, which is to be given numerous insubstantial modifications and adaptations by those skilled in the art based on the teachings set forth above.

Example 1

The method for regulating and controlling the dry electrode fibrosis comprises the following steps:

(1) Pre-mixing powder: premixing an electrode active substance small-particle-size ternary material (NCM 622), a conductive agent Keqin Black (KB) and fiberizable binder dispersion type polytetrafluoroethylene (powder), wherein the premixing mode is any one of a double-planet stirring mode and the like, and the premixing time is 30min; wherein the ternary material with small particle size (NCM 622), the dispersed polytetrafluoroethylene (powder), the Ketjen Black (KB) =80, the total mass is controlled to be 200g, the particle size D50 of the polytetrafluoroethylene binder is 5.5 +/-2 mu m, the length-diameter ratio is more than 5, the purity is 99.9 percent, and the molecular weight is 10 ⁵ -10 ⁸ g/mol；

(2) In situ crosslinking reaction-prefibration: heating the powder mixed in the step (1) in a resistance heating mode at 60 +/-3 ℃ for 30min;

(3) Homogenization: putting the material subjected to the in-situ crosslinking reaction in the step (2) into a dense mixer, wherein the inclination angle of a stirring paddle of the dense mixer is 0 degree, the stirring paddle of the dense mixer is in an eccentric installation stirring mode, the rotation direction and the speed of the stirring paddle can be optimally adapted to an application place, the dispersion speed is kept at 35-40m/s, the step time is 5min, the total cycle time is 1 time, a bottom/wall scraper is arranged on the dense mixer to provide additional stirring, the agglomeration of a pot wall and the pot bottom can be prevented, and the homogenization of the slurry is realized in the circulating dispersion process;

(4) Dry-process membrane: rolling the material uniformly fibrillated in the step (3) into a dry-process membrane by horizontal rolling and vertical rolling, controlling the temperature to be 80 ℃, and coiling and uncoiling the dry-process membrane;

(5) Dry-process electrode: and (3) laminating the dry-process membrane to the two surfaces of the current collector through hot rolling to obtain the dry-process electrode pole piece.

Example 2

Example 2 differs from example 1 in that graphite, dispersed polytetrafluoroethylene (in emulsion state), ketjen Black (KB) = 80.

Example 3

Example 3 differs from example 2 in that the fiberization step was carried out in step (3), the angle of inclination of the blades of the intensive mixer was 30 °, and the dispersion speed was maintained at 35-40m/s.

Comparative example 1

Comparative example 1 differs from example 2 in that the binder has a molecular weight of 4000 to 20000g/mol.

Comparative example 2

Comparative example 2 is different from example 2 in that the dispersion speed of step (3) fiberization is maintained at 20-30m/s.

Comparative example 3

The comparative example 3 is different from the example 2 in that the dispersion speed of the step (3) is maintained at 35 to 40m/s for the fibrillation, the step time is 5min, and the total number of cycles is 4.

Comparative example 4

The comparative example 4 is different from the example 2 in that the mixing and dispersing apparatus fiberized in the step (3) has no eccentricity and no inclination, the dispersing speed is kept at 35-40m/s, the step time is 5min, and the total number of cycles is 1.

Scanning electron micrographs of the fiberized powder prepared in examples 1 to 3 and comparative examples 1 to 4 or the rolled pole pieces are shown in FIGS. 1 to 8. FIG. 1 is a photograph showing the uniform fiberization of the powder of example 1, and it is apparent from the photograph of FIG. 1 that the fiberized filaments are present in the material; FIG. 2 is a photograph of the fiberized material of example 2, with the material portions fully integrated; FIG. 3 example 3 scanning electron microscope after rolling, material particle size is similar and uniform, pole piece surface is relatively uniform, and obvious filamentous, fibrous state is present; FIG. 4 shows that the rolled photos in example 3 have uniform material discharge, no holes in the pole piece film, and regular edges, which affect the quality of the pole piece film; FIGS. 5-8 show the film forming conditions of comparative examples 1-4 after rolling, wherein the molecular weight of the binder in FIG. 5 is small, the surface of the rolled pole piece is rough, and the edges of the pole piece films are uneven; FIG. 6 is a rolled picture of comparative example 2, which shows a low dispersion rate and a low degree of fiberization, and the rolled pole piece has a smooth and fine surface and irregular edge; FIG. 7 is a picture of the rolled sheet after the powder fiberization in comparative example 3, and it is seen from the picture that the pole piece has a seriously reduced edge uniformity due to the transition fiberization, resulting in a reduced quality of the pole piece; FIG. 8 shows a comparative example 4, in which the operating parameters of the apparatus are normal, but the degree of fiberization of powder is insufficient because the apparatus is not eccentric and inclined, and the surface of the rolled pole piece is rough, and the edge uniformity is seriously insufficient, which results in the waste of the pole piece. It can be seen from the photographs after rolling of the comparative examples in fig. 5 to 8 that insufficient or excessive degree of fibrillation causes uneven edges of the pole piece film, which affects the forming quality of the pole piece film.

In conclusion, after the fibrosis regulation and control method disclosed by the invention is used for mixed materials, the situation that fibrosis filaments exist in the materials can be obviously seen, the surfaces of rolled pole pieces are relatively uniform, the obvious filament and fibrosis states exist, rolled films are more neat, and the utilization rate of the materials is improved almost without the problem of edge defects.

The foregoing shows and describes the general principles and features of the present invention, together with the advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (7)

1. A regulating and controlling method for dry electrode fibrosis is characterized by comprising the following steps:

(1) Pre-mixing powder: premixing an electrode active substance, a conductive agent and a fiberizable binder at a constant temperature of less than 30 ℃ for 10min to 60min;

(2) Prefibration-in situ crosslinking reaction: heating the powder premixed in the step (1) at the temperature of 50-150 ℃, wherein the in-situ crosslinking reaction time is 10-60min;

(3) Homogenizing and fiberizing: putting the materials in the step (2) into mixing and dispersing equipment, wherein the mixing and dispersing equipment is provided with a star-shaped rotor which is uniformly distributed, stirring paddles are arranged in an eccentric and/or angled mode, the linear speed of 35-50m/s is kept, the uniform fibrosis dispersion time is 5-10min, and the cycle number is not more than 3 times;

(4) Dry-process membrane: carrying out horizontal rolling and vertical rolling on the material subjected to the uniform fiberization in the step (3), controlling the temperature to be 60-150 ℃, and rolling into a dry-process membrane;

(5) Dry electrode sheet: and compounding the dry-process membrane to the two sides of the current collector through hot rolling to obtain the dry-process electrode pole piece.

2. The method for regulating dry electrode fibrosis according to claim 1, wherein the method comprises the following steps: the premixing mode in the step (1) is ball milling, double-planet stirring, sand milling, cone milling or high-speed grinding.

3. The method for regulating dry electrode fibrosis according to claim 1, wherein the method comprises the following steps: the fiberizable binder comprises at least one of polytetrafluoroethylene, styrene-butadiene rubber, polyvinylidene fluoride, polyethylene oxide, poly (vinylidene fluoride-hexafluoropropylene), polyacrylonitrile, (meth) polyacrylonitrile, polyvinyl alcohol, polyacrylic acid, polymethyl methacrylate, modified polymethyl methacrylate, polyvinylidene fluoride copolymer and polystyrene.

4. The method for regulating dry electrode fibrosis according to claim 1 or 3, wherein: the fiberizable binder is dispersed, the grain diameter D50 is 100nm-50 mu m, the purity is 99.9 percent, and the molecular weight is 10 ⁵ -10 ⁸ g/mol, fiberizable binder is a low melting point bond at 50-150 ℃.

5. The method for regulating dry electrode fibrosis according to claim 1, wherein the method comprises the following steps: the heating mode of the heating treatment in the step (2) is resistance heating or infrared heating.

6. The method for regulating dry electrode fibrosis according to claim 1, wherein the method comprises the following steps: and (3) adopting a rotary drum mixer, a conical screw type mixer or a dense mixer as mixing and dispersing equipment.

7. The method for regulating dry electrode fibrosis according to claim 1, wherein the method comprises the following steps: in the step (3), the installation angle of the stirring paddle is 0-30 degrees.

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