Slot die coating system and coating method using electrostatic self-assembly dry electrode powder

Abstract

The present invention aims to provide a slot die coating system using an electrostatic self-assembled dry electrode powder that can manufacture a high-density dry electrode having excellent dispersibility and bonding strength by preventing powder aggregation and forming a real-time core-shell electrostatic self-assembled powder in which electrode active materials charged with heterogeneous polarity and binders / conductive materials are uniformly adsorbed by electrostatic attraction by utilizing the heterogeneous charging characteristics of atmospheric pressure oxygen plasma and atmospheric pressure nitrogen plasma.

Description

Technology Field

[0001] The present invention relates to a dry coating technology for a secondary battery electrode process, and more specifically, to a slot die coating system and coating method using an electrostatic self-assembled dry electrode powder, wherein an electrode active material, a binder, and a conductive material are charged with different polarities using atmospheric pressure plasma to form a core-shell structured dry electrode powder through self-assembly by electrostatic attraction, and the powder is quantitatively ejected using a slot die method to coat an electrode substrate while controlling the edges to be smooth in a non-contact manner. Background Technology

[0003] As the demand for electric vehicles and energy storage systems (ESS) increases rapidly, interest in dry electrode process technology is growing in order to simultaneously improve the energy density of secondary batteries used in these applications and reduce manufacturing costs. Conventional wet electrode processes involve applying a slurry, in which electrode active materials, conductive materials, and binders are dispersed in a solvent, onto a current collector and then drying it. However, many problems have been pointed out, such as high costs associated with drying and solvent recovery equipment, reduced production speed due to the drying process, and reduced safety caused by residual solvent. Consequently, various dry electrode process technologies are being proposed that form and coat raw materials in a dried powder state directly onto an electrode substrate without using a solvent.

[0005] For example, Patent Registration No. 2465331, "Coating apparatus and coating method for secondary battery electrode process," discloses a method in which polar surface treatment using plasma is performed on each of the electrode active material, conductive material, and binder, or a core-shell structure in which a binder is coated on the outer surface of the active material is formed in advance, and then a carrier gas is used to spray onto the electrode substrate through a spray nozzle, and the non-adherent powder that does not adhere to the substrate is recovered and reused through a suction nozzle. However, this method makes it difficult to precisely control discharge uniformity due to pressure variations caused by the carrier gas, requires a separate suction device for spraying and recovery of non-adherent powder, and has persistent issues regarding dust management due to the scattering of non-adherent powder.

[0007] In addition, Patent Registration No. 2923021, "Self-standing Electrode Film Forming Machine with Improved Edge Smoothness," discloses a method in which dried mixed powder is fed into the lower part of a hopper and formed into a film using a pair of rolling rolls attached to the lower part of the hopper, and the edge smoothness of the film is improved by the action of rubbing the edges and surfaces of the dry electrode film formed by rotating disc-shaped wings (disks) formed at both ends of one rolling roll at least three times faster than the other rolling roll. However, this method has the problem that there is a concern for particle accumulation and contamination or damage to the roll surface due to fine mechanical friction between the disc-shaped wings at the end of the roll and the rolling roll axis and between the barrier wall when used for a long period of time, there is a maintenance burden such as the need to remove slitting debris, and it is difficult to actively control the distribution of the powder in the width direction at an earlier stage because the edge shape is determined only when it reaches the rolling roll stage.

[0009] Conventional dry electrode process technologies that have appeared to date, including the aforementioned patent, have the following problems.

[0010] First, there is a problem in that spontaneous micro-aggregation occurs between the active material, conductive material, and binder in powder form, causing the binder to clump locally and induce electrode defects.

[0011] Second, since it relies on the nozzle spraying method, there is a problem where thickness non-uniformity occurs during large-area / wide coating due to variations in spray particles between the center and the edges caused by the non-uniformity of the nozzle spray.

[0012] Third, since non-stick powder is forcibly sucked up and recovered, not only is the suction recovery inefficient, but the electrostatic induction state on the substrate is also disrupted, and there is a problem that it is difficult to control the continuous coating thickness in real time.

[0013] Fourth, there is a problem in that the smoothness of the edges of the electrode substrate is poor and powder leakage occurs, so a separate slitting and cutting process is essential.

[0014] Fifth, since the hopper discharging the core shell relies on a simple gravity-feed hopper structure, powder stagnation occurs inside the hopper, resulting in irregular powder flow on the inner wall and making continuous quantitative feeding impossible.

[0015] Therefore, there is an urgent need for the emergence of a dry electrode process technology that can solve the above-mentioned problems, maximize the dispersibility of the electrode powder, and ultra-precisely control the smoothness of the edges of the coating layer. The problem to be solved

[0017] The present invention has been devised to solve the aforementioned problems. The objective of the present invention is to provide a slot die coating system and a coating method using an electrostatic self-assembled dry electrode powder, which can prevent powder aggregation and manufacture a high-density dry electrode having excellent dispersibility and bonding strength by forming a real-time core-shell electrostatic self-assembled powder in which electrode active materials charged with heterogeneous polarity and binders / conductive materials are uniformly adsorbed by electrostatic attraction using the heterogeneous charging characteristics of atmospheric pressure oxygen plasma and atmospheric pressure nitrogen plasma.

[0018] Another objective of the present invention is to provide a slot die coating system and a coating method using electrostatic self-assembling dry electrode powder, which prevents charge discharge of charged powder by applying a ceramic insulating coating to the inner wall of the slot die and enables quantitative discharge by uniformizing the slip speed of the powder by installing an ultrasonic fluidization injector.

[0019] Another objective of the present invention is to provide a slot die coating system and a coating method using electrostatic self-assembling dry electrode powder, which can manufacture a high-density dry electrode with smooth edges by fundamentally blocking leakage and lateral diffusion of the powder through non-contact electromagnetic field control by placing electric field generating units at both ends of the slot die lip. means of solving the problem

[0021] A slot die coating system using an electrostatic self-assembling dry electrode powder according to the present invention comprises: a first plasma treatment unit that treats an active material with atmospheric pressure oxygen plasma to induce a negative (-) charge on the surface of the active material; a second plasma treatment unit that treats a binder and a conductive material with atmospheric pressure nitrogen plasma to induce a positive (+) charge on the surface of the binder and the conductive material; an electrostatic mixing chamber that forms a dry electrode powder by self-assembling in real time into a core-shell structure in which the binder and the conductive material are attached by electrostatic attraction to the surface of the active material supplied from the first and second plasma treatment units, respectively; and a slot die unit that quantitatively discharges the dry electrode powder supplied from the core-shell synthesis unit toward a moving electrode substrate. The device is characterized by comprising an electric field generating unit that is positioned on each side of the lip end of the slot die unit to generate a local electric field, thereby suppressing the diffusion or leakage of the discharged dry electrode powder into the side in the slot width direction through a non-contact electromagnetic repulsion force.

[0023] Preferably, the slot die unit comprises a die body having an internal manifold through which dry electrode powder flows, and a ceramic coating layer is formed on the manifold wall to prevent the charge of the charged dry electrode powder from being discharged.

[0025] Preferably, the ceramic coating layer is formed of a hybrid ceramic comprising aluminum oxide (Al2O3) and silicon carbide (SiC).

[0027] Preferably, the slot die unit is equipped with an ultrasonic fluidization injector at a position adjacent to the lip of the slot die and applies ultrasonic vibration so that the discharged dry electrode powder is extruded with a uniform flow rate in the slot width direction.

[0029] Preferably, the electric field generating unit generates an electric field of the same polarity as the charge charged on the dry electrode powder, thereby suppressing the dry electrode powder from spreading to the side of the lip end due to the repulsive force between the charges.

[0031] Preferably, it is configured to further include a compression unit for compressing a dry powder layer discharged onto an electrode substrate.

[0033] A slot die coating method using an electrostatic self-assembling dry electrode powder according to the present invention comprises: a heterogeneous charging step (S1) in which an electrode active material is treated with atmospheric pressure oxygen plasma to induce a negative (-) charge, and a binder and a conductive material are treated with atmospheric pressure nitrogen plasma to induce a positive (+) charge; a core-shell synthesis step (S2) in which the charged electrode active material, the binder, and the conductive material are self-assembled by electrostatic attraction within an electrostatic mixing chamber to form a dry electrode powder with a core-shell structure in which the binder and the conductive material are attached to the surface of the electrode active material; and a slot die discharge step (S3) in which the dry electrode powder is discharged in a measured amount toward an electrode substrate moving through a slot die. It is characterized by including an edge electric field control and compression step (S4) that generates a local electric field on both sides of the lip end of the slot die to suppress lateral diffusion or leakage of the discharged dry electrode powder in a non-contact manner while compressing the dry electrode powder adhered to the electrode substrate. Effects of the invention

[0035] The slot die coating system using dry electrode powder according to the present invention charges the electrode active material, binder, and conductive material with atmospheric pressure plasma of different polarities, and self-assembles the core-shell structured powder in real time using only electrostatic attraction, thereby significantly improving the bonding strength and dispersibility between the active material and the binder, and accordingly, can obtain a uniformly dispersed electrode powder while minimizing the binder content.

[0036] In addition, by forming a high-insulating ceramic coating layer inside the slot die to prevent the charged powder from coming into contact with the metal manifold and prematurely discharging the charge, and by placing an ultrasonic fluidization injector adjacent to the lip to discharge the powder with a uniform flow rate across the entire width of the slot, large-area ultra-precision quantitative discharge is possible, thereby resolving the problem of thickness variation and enabling the realization of ultra-precision electrodes.

[0037] In addition, by forming a local electric field of the same polarity as the charged powder through electric field generating units placed at both ends of the slot die lip, leakage and lateral diffusion at the edges can be fundamentally blocked in a non-contact manner due to electrostatic repulsion, thereby enabling the production of a high-density dry electrode with smooth edges. Brief explanation of the drawing

[0039] FIG. 1 is a schematic diagram illustrating a slot die coating system using a dry electrode powder according to the present invention. Figure 2 is a drawing showing a slot die with electric field generating units mounted on both sides as illustrated in Figure 1. Figure 3 is an enlarged view of the lip end of the slot die discharge unit illustrated in Figure 1. Specific details for implementing the invention

[0040] The technical features of the slot die coating system using dry electrode powder according to the present invention are: ① that the active material, binder, and conductive material are each charged with atmospheric pressure plasma of different polarities to enable real-time self-assembly of a core-shell structured powder solely through electrostatic attraction; ② that a ceramic coating layer is formed on the inner wall of the slot die and an ultrasonic fluidization injector is mounted adjacent to the lip to enable large-area ultra-precision quantitative dispensing; and ③ that electric field generating units are placed at both ends of the slot die lip to enable the formation of smooth edges in a non-contact manner through electrostatic repulsion.

[0042] The slot die coating system using electrostatic self-assembly type dry electrode powder according to the present invention comprises, as a basic configuration, a core-shell synthesis unit (10) that can simultaneously secure inter-particle bonding force and dispersibility without using mechanical stirring or solvent, a slot die unit (20) that discharges dry electrode powder onto an electrode substrate, and an electric field generating unit (25) mounted on both ends of the slot die lip.

[0044] A core-shell is a composite particle consisting of a core and a shell surrounding it. The active material is located in the core, which is the center of the particle, and the shell, which is a thin layer surrounding the core, is composed of a binder and a conductive material or a surface modification layer. In wet electrodes, the binder dissolves in a solvent and naturally coats the surface of the active material. However, in dry processes, since there is no solvent, the binder may not adhere uniformly to the surface of the active material, leading to problems such as the active material easily detaching, reduced coating layer strength, poor dispersion of the conductive material, and reduced electrode density. To solve these problems, a binder or conductive material is applied to the surface of the active material in advance to form a core-shell structure.

[0045] There are various methods for forming core-shells. Generally, plasma treatment is performed in a vacuum, whereas atmospheric pressure plasma is performed at atmospheric pressure. Atmospheric pressure plasma treatment offers several advantages, including the elimination of the need for a vacuum chamber, the ability to enable continuous production, the applicability of roll-to-roll processes, and very high productivity. In this invention, core-shells are formed using atmospheric pressure plasma treatment. The use of atmospheric pressure plasma activates the surface of the active material, which facilitates the attachment of binders and conductive materials. Since this atmospheric pressure plasma treatment itself is not a characteristic technology unique to this invention and is already being implemented in various fields, specific details will not be described.

[0047] The core-shell synthesis unit (10) is configured to include a first plasma processing unit (11), a second plasma processing unit (13), and an electrostatic mixing chamber (15).

[0048] The first plasma treatment unit (11) exposes an electrode active material (111) forming a positive or negative electrode of a secondary battery to an atmospheric pressure oxygen plasma to charge the surface of the active material with a negative (-) charge, thereby enabling the suppression of aggregation of the active material and conductive material, improvement of the thickness uniformity of the electrode coating layer, improvement of adhesion between the binder and the active material, uniformization of the internal conductive network of the electrode, and improvement of the energy density and charge / discharge characteristics of the electrode.

[0049] In the second plasma treatment unit (13), the binder and conductive material (131) are exposed to atmospheric pressure nitrogen plasma to charge the surface of the binder and conductive material with positive (+) charges.

[0050] The electrostatic mixing chamber (15) is connected to the first plasma processing unit (11) and the second plasma processing unit (13) through pipes equipped with pumps (17, 17'), and when an electrode active material (111) with a negative (-) charge and a binder and conductive material (131) with a positive (+) charge are supplied, the binder and conductive material (131) are uniformly adsorbed onto the surface of the electrode active material (111) by electrostatic attraction between opposite polarities, thereby forming a dry electrode powder (151) in real time through a core-shell structure.

[0051] The types of plasma gases used in the first plasma processing unit (11) and the second plasma processing unit (13) are not limited to oxygen and nitrogen, and various atmospheric pressure plasma gases such as argon and helium can be selectively used depending on the polarity to be charged and the surface characteristics of the material.

[0053] The slot die unit (20) is connected to the lower part of the electrostatic mixing chamber (15) to quantitatively discharge dry electrode powder (151) toward an electrode substrate (30) moving through the slot die lip (23). The slot die unit (20) is provided with a die body (21) having an internal manifold through which the dry electrode powder flows. The die body (21) is formed with a manifold structure in which the upper part is connected to the lower part of the electrostatic mixing chamber (15) and the width narrows toward the lower part, thereby guiding the dry electrode powder (151) toward the lip (23).

[0054] A high-insulation ceramic coating layer (211) is formed on the inner wall of the inner manifold of the die body (21), and the ceramic coating layer (211) is made of a hybrid ceramic containing aluminum oxide (Al2O3) and silicon carbide (SiC) and has high insulation properties.

[0055] Since the dry electrode powder (151) carries a surface charge due to plasma charging, if it comes into direct contact with the inner wall of a metal manifold, the charged charge may be discharged prematurely, and there is a risk that the core-shell structure will collapse. The high-insulating ceramic coating layer (211) blocks this ground discharge, thereby stably maintaining the self-assembled core-shell structure and the charged state even while the dry electrode powder (151) passes through the inside of the slot die.

[0057] The ultrasonic fluidization injector (27) is positioned adjacent to the lip (23) of the slot die and applies ultrasonic vibration. Since the dry electrode powder is a mixture of active material, conductive material, and binder, the particles may clump together or aggregate. The ultrasonic fluidization injector (27) applies ultrasonic vibration to the powder to alleviate the aggregation of the particles and create a state where the particles can flow. That is, the ultrasonic fluidization injector (27) contributes to the resolution of aggregation and improvement of fluidity by reducing the bonding and friction between powder particles to loosen clumping, the uniformization of the powder supply amount so that the powder moves uniformly across the entire width of the lip slot, and the improvement of coating thickness uniformity and edge shape uniformity by reducing the variation in the powder supply amount in the slot width direction.

[0058] Unlike liquid slurry, dry electrode powder (151) moves while suspended or dispersed in a gas, so variations in flow resistance are likely to occur in the slot width direction. The ultrasonic fluidization injector (27) maintains the fluidity of the powder uniformly through local ultrasonic vibrations, thereby controlling the extrusion of the same amount of dry electrode powder (151) over the entire width of the lip (23). This allows for the formation of an electrode layer with uniform thickness and density in the slot width direction without variations in nozzle injection pressure caused by the carrier gas or uneven downward behavior due to gravity-fed supply.

[0060] The electric field generating unit (25) is assembled on each side of the end of the lip (23) of the slot die. The electric field generating unit (25) generates a local electric field of the same polarity as the charge charged on the dry electrode powder (151). When the dry electrode powder (151) discharged through the lip (23) shows a tendency to spread to the side in the slot width direction or to leak out to the outer edge of the lip (23), the repulsive force between the electric field formed by the electric field generating unit (25) and the charge of the charged powder pushes it out in a non-contact manner, thereby suppressing the dry electrode powder (151) from spreading to the side of the end of the lip (23) and precisely limiting the discharge width without physical contact or friction members.

[0061] The non-contact electric field control method using such an electric field generating unit (25) has a superior process advantage in that, compared to the conventional slitting method, there is no physical friction drive part, so there is no burden of tolerance management and wear, and the distribution of the powder in the width direction can be determined in advance at the slot die discharge stage.

[0062] The dry electrode powder (151), whose width direction shape is determined by passing through the electric field generating unit (25), is adhered to the moving electrode substrate (30). In this case, the adhesion force due to electrostatic attraction can be maximized by applying a charge opposite to the charging polarity of the dry electrode powder (151) to the electrode substrate (30).

[0064] The slot die coating system of the present invention may further include a compression unit for rolling a dry electrode powder (151) attached to an electrode substrate (30). The compression unit is composed of a pair of heating rollers and passes the electrode substrate attached to the dry electrode powder (151) through the electrode substrate heated to 100°C or higher and compresses it to a desired thickness and density, thereby improving the adhesion and bonding between the electrode active material contained in the electrode substrate (30) and the dry electrode powder (151).

[0066] A coating method using a slot die coating system utilizing an electrostatic self-assembling type dry electrode powder according to the present invention comprises: a heterogeneous charging step (S1) in which an electrode active material is treated with atmospheric pressure oxygen plasma to induce a negative (-) charge, and a binder and a conductive material are treated with atmospheric pressure nitrogen plasma to induce a positive (+) charge; a core-shell synthesis step (S2) in which the charged electrode active material, the binder, and the conductive material are self-assembled by electrostatic attraction within an electrostatic mixing chamber to form a dry electrode powder having a core-shell structure in which the binder and the conductive material are attached to the surface of the electrode active material; and a slot die discharge step (S3) in which the dry electrode powder is discharged in a measured amount toward an electrode substrate moving through a slot die. The process includes an edge electric field control and compression step (S4) that generates a local electric field on both sides of the lip end of the slot die to suppress lateral diffusion or leakage of the discharged dry electrode powder in a non-contact manner while compressing the dry electrode powder attached to the electrode substrate.

[0068] In step S1, the electrode active material (111) is treated with atmospheric pressure oxygen plasma to induce a negative charge, and separately, the binder and conductive material (131) are treated with atmospheric pressure nitrogen plasma to induce a positive charge. At this time, since the active material and the binder and conductive material are independently charged in different plasma treatment sections, a stable surface charge can be secured without mutual reaction or aggregation.

[0070] In step S2, the charge-induced electrode active material (111) and the binder and conductive material (131) are supplied into the electrostatic mixing chamber (15), and a dry electrode powder (151) with a core-shell structure in which the binder and conductive material (131) are attached to the surface of the electrode active material (111) by electrostatic attraction is self-assembled in real time.

[0072] In step S3, the dry electrode powder (151) formed in step S2 is moved through a manifold having a ceramic coating layer (21) formed inside the die body of the slot die, and ultrasonic vibration is applied by an ultrasonic fluidization injector (27) positioned adjacent to the lip (23) to extrude it with a uniform flow rate in the slot width direction.

[0074] In step S4, a local electric field of the same polarity as the charge polarity of the dry electrode powder is formed through electric field generating units (25) placed on both sides of the lip (23) end of the slot die to suppress lateral diffusion and leakage of the powder in a non-contact manner, and after the discharged dry electrode powder is adhered to a moving electrode substrate (30), the final dry electrode is completed by rolling it using a compression unit as needed.

[0076] The above description is an illustrative description of the present invention, and the embodiments disclosed in the specification are intended to explain, not limit, the technical concept of the present invention. Therefore, those skilled in the art to which the present invention pertains may make various modifications and variations within the scope of the technical concept of the present invention without departing from it. Accordingly, the scope of protection of the present invention shall be interpreted by the matters described in the claims, and technical matters within the equivalent scope thereof shall also be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0078] 10 : Core-Shell Synthesis Unit 11: 1st Plasma Processing Unit 111: Active Material 13: Second Plasma Treatment Unit 131: Binder and Conductive Material 15: Electrostatic mixing chamber 151: Dry electrode powder 17, 17' : Pump 20: Slot die unit 21: Die body 211: Ceramic coating layer 23 : Lip 25 : Electric field generating unit 27 : Ultrasonic fluidization injector 30: Electrode substrate

Claims

Claim 1 A slot die coating system using electrostatic self-assembled dry electrode powder, characterized by comprising: a core-shell synthesis unit including a first plasma treatment unit that induces a negative (-) charge on the surface of an active material by treating the active material with atmospheric pressure oxygen plasma; a second plasma treatment unit that induces a positive (+) charge on the surface of a binder and a conductive material by treating the binder and a conductive material with atmospheric pressure nitrogen plasma; and an electrostatic mixing chamber in which the binder and the conductive material are attached to the surface of the active material supplied from the first and second plasma treatment units, respectively, in real-time self-assembled into a core-shell structure by electrostatic attraction to form a dry electrode powder; a slot die unit that quantitatively discharges the dry electrode powder supplied from the core-shell synthesis unit toward a moving electrode substrate; and an electric field generation unit disposed on both sides of the lip end of the slot die unit to generate a local electric field and suppress the discharged dry electrode powder from spreading or leaking to the side in the slot width direction through a non-contact electromagnetic repulsion force. Claim 2 A slot die coating system using electrostatic self-assembling dry electrode powder, characterized in that, in claim 1, the slot die unit comprises a die body having an internal manifold through which dry electrode powder flows, and a ceramic coating layer is formed on the manifold wall to prevent the discharge of the charge of the charged dry electrode powder. Claim 3 A slot die coating system using an electrostatic self-assembly type dry electrode powder, characterized in that, in paragraph 2, the ceramic coating layer is formed from a hybrid ceramic comprising aluminum oxide (Al2O3) and silicon carbide (SiC). Claim 4 A slot die coating system using electrostatic self-assembling dry electrode powder, characterized in that, in claim 1, the slot die unit further includes an ultrasonic fluidization injector mounted adjacent to the lip of the slot die to apply ultrasonic vibration, thereby causing the discharged dry electrode powder to be extruded with a uniform flow rate in the slot width direction. Claim 5 A slot die coating system using an electrostatic self-assembling dry electrode powder, characterized in that, in claim 1, the electric field generating unit generates an electric field of the same polarity as the charge charged on the dry electrode powder, thereby suppressing the dry electrode powder from spreading to the side of the lip end due to the repulsive force between the charges. Claim 6 A slot die coating system using an electrostatic self-assembly type dry electrode powder, characterized in that, in claim 1, it further includes a compression unit for compressing a dry powder layer discharged onto the electrode substrate. Claim 7 A slot die coating method using electrostatic self-assembled dry electrode powder, characterized by comprising: a heterogeneous charging step in which an electrode active material is treated with atmospheric pressure oxygen plasma to induce a negative (-) charge, and a binder and a conductive material are treated with atmospheric pressure nitrogen plasma to induce a positive (+) charge; a core-shell synthesis step in which the charged electrode active material, the binder, and the conductive material are self-assembled by electrostatic attraction within an electrostatic mixing chamber to form a dry electrode powder with a core-shell structure in which the binder and the conductive material are attached to the surface of the electrode active material; a slot die discharge step in which the dry electrode powder is discharged in a measured amount toward an electrode substrate moving through a slot die; and an edge electric field control and compression step in which a local electric field is generated on both sides of the lip end of the slot die to suppress lateral diffusion or leakage of the discharged dry electrode powder in a non-contact manner while compressing the dry electrode powder adhered to the electrode substrate.

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