Slit extrusion coating machine with improved coating solution flow

Abstract

A slot extrusion coating machine is provided that enables uniform flow of coating solution without stagnation. The slot extrusion coating machine includes: at least two die assemblies; a pad disposed between the two die assemblies to form a slot; and a manifold disposed in the die assemblies, the manifold being connected in communication with the slot as a recessed chamber for receiving the coating solution, wherein the coating solution is discharged through a discharge port connected in communication with the slot and coated onto the surface of a continuously moving substrate, and in a cross-section along the direction of travel of the substrate, the ratio B / S of the manifold length B (mm) to the manifold cross-sectional area S (cm²) is within the range of 1.9 to 9.8.

Description

Technical Field

[0001] This disclosure relates to a slot extrusion coating machine, and more particularly to a slot extrusion coating machine that improves the flow of coating solution inside the slot extrusion coating machine.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0159175, filed in Korea on November 24, 2020, the disclosure of which is incorporated herein by reference. Background Technology

[0003] With technological advancements and the growing demand for mobile devices, the need for secondary batteries as an energy source is also rapidly increasing. These secondary batteries essentially consist of electrode assemblies that function as power generation elements. The electrode assemblies are formed by stacking a positive electrode, a separator, and a negative electrode at least once. The positive and negative electrodes are prepared by coating and drying positive and negative active material slurries, respectively, onto current collectors made of aluminum and copper foil. To balance the charge / discharge characteristics of the secondary battery, the positive and negative active material slurries should be uniformly coated onto the current collector, typically using a slot extrusion coating machine.

[0004] Figure 1 An example of a coating method using a conventional slot extrusion coating machine is shown. Figure 2 Along the machining direction (MD) (the direction of travel of the current collector) Figure 1 A cross-sectional view of a slot extrusion coating machine taken from section II-II'.

[0005] refer to Figure 1 and Figure 2 In the electrode manufacturing method using a slot extrusion coating machine 30, an electrode active material slurry discharged from the slot extrusion coating machine 30 is applied as a coating solution to a current collector 20 conveyed by a coating roller 10. The electrode active material slurry discharged from the slot extrusion coating machine 30 is widely coated on one surface of the current collector 20 to form an electrode active material layer. The slot extrusion coating machine 30 includes two die assemblies 31 and 32, and a slot 35 is formed by inserting a pad 34 between the two die assemblies 31 and 32. The electrode active material slurry can be discharged via a discharge port 37 connected in communication with the slot 35, thereby forming the electrode active material layer.

[0006] refer to Figure 2The internal shape of the slot extrusion coating machine 30 can be seen. Reference numeral 26 indicates a manifold containing electrode active material slurry (coating solution). Manifold 26 is connected via a supply pipe to an externally mounted electrode active material slurry supply chamber (not shown) to receive the electrode active material slurry. When manifold 26 is filled with electrode active material slurry, the slurry is guided to flow along the slot 35 and discharged to the outside through discharge port 37.

[0007] The shape of the die blocks 31 and 32, especially the internal design including the manifold 26, is a major factor determining the flow uniformity in the width direction. High flow uniformity means small flow velocity deviation. Electrode active material slurries are non-Newtonian fluids with viscosities ranging from several thousand centipoises (cps) to tens of thousands of centipoises, and during coating, there is a large flow velocity deviation in the width direction. Flow velocity deviation leads to loading deviation. With the development of the secondary battery industry, some projects are necessary. In these projects, large coating widths are required to improve productivity, which inevitably comes with large loading deviations. Furthermore, the rheological properties of the electrode active material slurries developed to meet the required characteristics (e.g., high capacity, high output, and low cost) gradually increase the flow velocity deviation in the width direction, making the design of this part very important.

[0008] Currently, the slot extrusion coating machine 30 is designed with the concept of minimizing flow rate deviation. However, inside the slot extrusion coating machine 30, especially in the manifold 26, flow rate distribution occurs in the flow of the electrode active material slurry. Furthermore, the electrode active material slurry, after experiencing a long residence time, deforms under pressures of tens to hundreds of kilopascals (kPa), easily forming aggregates. The formation of these aggregates not only deforms the flow path inside the die assemblies 31 and 32, increasing the flow rate deviation, but also blocks the discharge port 37, or the aggregates are discharged onto the current collector 20, resulting in coating defects such as uneven and non-uniform coating surfaces.

[0009] Therefore, improvements to these parts should be reflected in the interior of die assemblies 31 and 32. However, in the current field of slot extrusion coating machines, such designs have not been evaluated and reflected at a high level, and problems such as agglomeration are addressed by increasing the number of washes. Increased washes lead to reduced production utilization, and in particular, with the recent expansion of demand for secondary batteries into those used in vehicles, stable long-term production has become crucial, thus creating a fundamental solution that minimizes the relative retention of electrode active material slurry within the slot extrusion coating machine. Summary of the Invention

[0010] Technical issues

[0011] This disclosure is designed to solve problems in related technologies, thereby providing a slot extrusion coating machine that enables the coating solution to flow uniformly without stagnation.

[0012] These and other objects and advantages of this disclosure will become apparent from the following detailed description, and will be further appreciated from the exemplary embodiments thereof. Furthermore, it will be readily understood that the objects and advantages of this disclosure may be achieved by the means shown in the appended claims and combinations thereof.

[0013] Technical solution

[0014] In one aspect of this disclosure, a slot extrusion coating machine is provided, comprising: at least two die assemblies; a pad disposed between the two die assemblies to form a slot; and a manifold disposed in the die assemblies, the manifold being connected in communication with the slot as a recessed chamber for receiving a coating solution, wherein the coating solution is discharged and coated onto the surface of a continuously traveling substrate through an outlet connected in communication with the slot, and wherein, in a cross section along the travel direction of the substrate, the ratio B / S of the manifold length B (mm) to the manifold cross-sectional area S (cm²) is in the range of 1.9 to 9.8.

[0015] The die head assembly size is the length from the die lip, which serves as the front end of the die head assembly, to the rear surface of the die head assembly. The die head assembly size can be equal to or less than 350 mm.

[0016] The ratio B / S of the manifold length B (mm) to the manifold cross-sectional area S (cm²) can be determined to result in a flow rate deviation of less than 20% and an average residence time equal to or less than 200 seconds, wherein the flow rate deviation is the difference between the maximum and minimum values ​​of the flow rate measured along the width direction of the slot extrusion coater.

[0017] In another aspect of this disclosure, a slot extrusion coating machine is provided, comprising: a lower die assembly; an intermediate die assembly disposed above the lower die assembly to form a lower slot between the lower die assembly and the intermediate die assembly; and an upper die assembly disposed above the intermediate die assembly to form an upper slot between the intermediate die assembly and the upper die assembly; a first manifold disposed in the lower die assembly, the first manifold being connected in communication with the lower slot as a recessed chamber for receiving a first coating solution; and a second manifold disposed in the intermediate die assembly, the second manifold being connected in communication with the upper slot as a recessed chamber for receiving a second coating solution. The first coating solution is discharged and applied to the surface of a continuously traveling substrate through a lower discharge port connected in communication with the lower slit, and the second coating solution is discharged and applied to the surface of the continuously traveling substrate through an upper discharge port connected in communication with the upper slit. Furthermore, in a cross-section perpendicular to the width direction of the slit extrusion coating machine, the ratio B' (mm) of the first manifold length to the first manifold cross-sectional area S' (cm²) is within the range of 1.9 to 9.8, or the ratio B” / S” of the second manifold length B” (mm) to the second manifold cross-sectional area S” (cm²) is within the range of 1.9 to 9.8.

[0018] The ratio B' (mm) of the first manifold length to the first manifold cross-sectional area S' (cm²) (B' / S') or the ratio B” / S” of the second manifold length to the second manifold cross-sectional area S” (cm²) (B” / S”) can be determined to cause a flow rate deviation of less than 20% and an average residence time equal to or less than 200 seconds, wherein the flow rate deviation is the difference between the maximum and minimum values ​​of the flow rate measured along the width direction of the slot extrusion coating machine.

[0019] The slot extrusion coating machine can be configured to discharge and coat an electrode active material slurry onto the surface of a continuously moving substrate through at least one of a lower slot and an upper slot, with the direction of discharge of the electrode active material slurry being almost horizontal. The slot extrusion coating machine is thus installed, and the surfaces of the lower die assembly, the intermediate die assembly, and the upper die assembly opposite to the direction of discharge of the electrode active material slurry can be almost perpendicular.

[0020] The contact surface between the intermediate mold head block and the upper mold head block can be parallel to the horizontal plane.

[0021] The lower slit and the upper slit can form an angle of 30 to 60 degrees.

[0022] The slot extrusion coating machine may be configured to discharge and coat an electrode active material slurry onto the surface of a continuously moving substrate through at least one of a lower slot and an upper slot, and may further include a lower pad configured to define the lower slot and an upper pad configured to define the upper slot.

[0023] Each of the lower and upper pads includes an opening by cutting a region thereof, thereby determining the coating width of the electrode active material layer formed on the substrate, and the lower and upper pads are aligned with each other in the vertical direction.

[0024] The intermediate mold head assembly may include a first intermediate mold head assembly and a second intermediate mold head assembly, and the first intermediate mold head assembly and the second intermediate mold head assembly can make face-to-face contact with each other and slide along the contact surface, thereby being able to move relative to each other.

[0025] The first intermediate die head assembly can be fixedly coupled to the lower die head assembly by bolt coupling, and the second intermediate die head assembly can be fixedly coupled to the upper die head assembly by bolt coupling, thereby the first intermediate die head assembly and the lower die head assembly can move as a whole, and the second intermediate die head assembly and the upper die head assembly can move as a whole.

[0026] A step can be formed between the lower discharge port and the upper discharge port.

[0027] According to other examples, a slot extrusion coating machine can be configured to discharge and coat an electrode active material slurry onto the surface of a continuously moving substrate through at least one of a lower slot and an upper slot, and the direction of discharge of the electrode active material slurry can be opposite to the direction of gravity.

[0028] Beneficial effects

[0029] According to this disclosure, the flow of the electrode active material slurry (coating solution) within the slot extrusion coating machine is uniform. The residence time of the electrode active material slurry in any part of the manifold and slot can be reduced, thereby preventing slurry aggregation. As a result, there is no problem of flow velocity deviation in the width direction due to flow deformation, or of aggregated electrode active material slurry clogging the discharge port.

[0030] Therefore, when using the slot extrusion coating machine of this disclosure to coat electrode active material slurry, the slurry flows uniformly without stagnation, thus facilitating long-term coating processes and achieving high production efficiency. The electrode active material slurry does not aggregate, thereby preventing defects on the coated surface. Consequently, the coating quality of the product can be improved.

[0031] According to this disclosure, the ratio of manifold length to manifold cross-sectional area is within a predetermined range, thereby providing a die assembly with reduced flow rate deviation. Unlike prior art methods that eliminate agglomerates by increasing the number of cleaning cycles, this method fundamentally prevents agglomeration, allowing the slot extrusion coating machine to easily perform long-term coating processes with excellent productivity.

[0032] Because of the reduced flow rate deviation, the slot extrusion coating machine according to this disclosure can uniformly form a coating layer of desired thickness, especially an electrode active material layer, with a uniform loading. Preferably, it can also be manufactured as a dual-slot extrusion coating machine capable of simultaneously coating two electrode active material slurries, thus exhibiting excellent performance and productivity. When using the slot extrusion coating machine of this disclosure to apply electrode active material slurry to the current collector while driving it, thereby manufacturing electrodes for secondary batteries, it has the advantage of uniform coating even under high-speed travel or long-width coating conditions. Attached Figure Description

[0033] The accompanying drawings illustrate preferred embodiments of the present disclosure and, together with the foregoing disclosure, are intended to provide a further understanding of the technical features of the present disclosure. Therefore, the present disclosure should not be construed as being limited to the drawings.

[0034] Figure 1 A schematic diagram showing an example of using a slot extrusion coating machine according to conventional technology is shown.

[0035] Figure 2 It is along Figure 1 The sectional view taken from section II-II'.

[0036] Figure 3 This is a cross-sectional view of a slot extrusion coating machine according to one embodiment of the present disclosure.

[0037] Figure 4 This is a schematic exploded perspective view of a slot extrusion coating machine according to one embodiment of the present disclosure.

[0038] Figure 5 This is a schematic cross-sectional view of a slot extrusion coating machine according to another embodiment of the present disclosure.

[0039] Figure 6 This is a schematic exploded perspective view of a slot extrusion coating machine according to another embodiment of the present disclosure. Detailed Implementation

[0040] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Before the description, it should be understood that the terminology used in the specification and appended claims should not be construed as limited to its generic or dictionary meanings. Rather, it is interpreted based on the meanings and concepts corresponding to the technical aspects of the present disclosure, based on the principle of allowing the inventors to properly define the terms for best explanation. Therefore, the description presented herein is merely a preferred example, intended only to illustrate the point and not to limit the scope of the disclosure. Consequently, it should be understood that other equivalents and modifications are possible without departing from the scope of the disclosure.

[0041] The slot extrusion coating machine of this disclosure may include one or more slots. When the slot extrusion coating machine includes two slots, these two slots may include a lower slot and an upper slot, and a double layer of coating solution is applied to the substrate. The “substrate” described below refers to a current collector, and the coating solution is an “electrode active material slurry.” All coating solutions discharged through the slots are electrode active material slurries, and electrode active material slurries having the same or different composition (type of active material, conductive material, binder), content (amount of each of the active material, conductive material, and binder), or physical properties can be discharged through each slot. In particular, the dual-slot extrusion coating machine of this disclosure, including two slots, is optimized for electrodes manufactured by simultaneously coating at least two electrode active material slurries or by alternately coating at least two electrode active material slurries to perform patterned coating. However, the scope of this disclosure is not necessarily limited thereto. For example, the substrate may be a porous support constituting a diaphragm, and the coating solution may be organic. That is, any substrate and any coating solution are possible when thin film coating is required.

[0042] Figure 3 This is a cross-sectional view of a slot extrusion coating machine according to one embodiment of the present disclosure. Figure 4 This is a schematic exploded perspective view of a slot extrusion coating machine according to one embodiment of the present disclosure.

[0043] refer to Figure 3 and Figure 4 The slot extrusion coating machine 100 includes two die assemblies 110 and 130. A pad 113 for forming a slot 101 is disposed between the die assemblies 110 and 130. The die assemblies 110 and 130 are assembled to each other by fastening members (not shown) such as bolts. The illustrated example has two die assemblies. There may also be two or more die assemblies.

[0044] exist Figure 3In this design, the slit extrusion coating machine 100 is mounted in a direction (X direction) that discharges the electrode active material slurry (coating solution) at a substantially horizontal level (approximately ±5 degrees). However, the slit extrusion coating machine 100 is not limited to the example form described here. For example, the slit extrusion coating machine 100 may be configured with a vertical die that discharges the electrode active material slurry in the opposite direction to gravity, discharging the electrode active material slurry in an upward direction (Y direction).

[0045] A slit 101 is formed between die head assemblies 110 and 130 at positions where they face each other. A spacer 113 is provided between die head assemblies 110 and 130 to provide a gap between them, thereby forming a slit 101 corresponding to a channel through which the coating solution 150 can flow. The thickness of the spacer 113 determines the vertical width of the slit 101 (the slit gap in the Y direction).

[0046] The pad 113 can include an opening 113a by cutting a region, and can be inserted into the remaining portion of the edge region of the opposing surfaces of the die head assemblies 110 and 130, excluding one side. Accordingly, a discharge port 101a is formed between die lips 111 and 131, the front ends of die head assemblies 110 and 130, respectively, to discharge the coating solution 150 to the outside. The discharge port 101a can be formed when the die lips 111 and 131 are spaced apart from each other.

[0047] The gasket 113 acts as a gasket to prevent the coating solution 150 from leaking into the gap between the die assembly blocks 110 and 130, except for the area forming the discharge port 101a. The gasket 113 is preferably made of a material with sealing properties.

[0048] Either of the die head assemblies 110 and 130 includes a manifold 112 having a predetermined depth and communicating with slit 101. In this embodiment, an example is shown where the manifold 112 is provided by recessing inward from the upper surface of the bottom die head assembly 110. The manifold 112 is a recessed chamber that receives coating solution 150. The area of ​​the die head assembly 110 from the tip of the manifold 112 to the die lip 111 is the overflow area (land) 114. The manifold 112 is connected via a supply pipe to an externally mounted coating solution supply chamber (not shown) to receive the coating solution 150. When the manifold 112 is filled with coating solution 150, the coating solution 150 flows along slit 101 and is discharged to the outside through discharge port 101a.

[0049] According to the slit extrusion coating machine 100 with this structure, a coating roller 180 provided in a rotatable manner is provided in front of the slit extrusion coating machine 100. The substrate 190 to be coated is driven by rotating the coating roller 180. By discharging the coating solution 150 and continuously contacting the coating solution 150 with the surface of the substrate 190, the coating solution 150 can be applied to the substrate 190. Alternatively, the supply and interruption of the coating solution 150 can be alternated, thereby allowing pattern coating processing to be performed intermittently on the substrate 190.

[0050] The coating solution 150 needs to have a uniform flow in the manifold 112 to achieve good coating quality. If there are areas in the manifold 112 where the electrode active material slurry (coating solution 150) is stagnant or moving slowly, prolonged use can cause the slurry to accumulate inside the manifold 112, leading to flow deformation. This can result in flow rate deviations in the width direction, or the coating surface may become uneven due to clogging of the discharge port 101a by accumulated electrode active material slurry clumps, resulting in surface defects. Even if the clumps are discharged and coated onto the substrate 190, the coating is still defective. The flow rate deviation is the difference between the maximum and minimum values ​​of the flow rate measured along the width direction of the slot extrusion coater 100.

[0051] To ensure uniform flow within the slot extrusion coater 100 (i.e., flow in the flow path including manifold 112), it is preferable that the ratio B / S of the manifold length B (mm) to the manifold cross-sectional area S (cm²) is within the range of 1.9 to 9.8. The manifold 112 can be configured to extend in the width direction of the slot extrusion coater 100, and its length or cross-sectional area along the width direction can be constant or not. In any case, it is sufficient as long as a predetermined range is met at any cross-section (i.e., any point) along the travel direction of the substrate 190. The die assembly dimensions, i.e., the length from the die lips 111 and 131 to the rear surfaces 110c and 130c of the die assemblies 110 and 130, can be equal to or less than 350 mm.

[0052] The manifold length B corresponds to the distance from the front end to the rear end of the manifold 112 as seen from the upper surface of the die assembly 110 (that is, the opening length of the uppermost section of the manifold 112). Since the depth of the manifold 112 is determined taking into account the thickness of the die assembly 110 and has a lower limit, the manifold length B is a factor that greatly affects the manifold volume.

[0053] The inventors have proposed a new parameter, B / S, relating the ratio of manifold length B to manifold cross-sectional area S, and have discovered that adjusting this new parameter can improve the flow of the coating solution within a slot extrusion coater 100. Prior to this disclosure, there was no technique that considered the influence of the ratio of manifold length to manifold cross-sectional area on average residence time and flow rate deviation, nor was there a technique to improve flow rate deviation based on this fact. Therefore, this disclosure does not involve simple dimensional changes or optimizations. Furthermore, the improvement in flow rate deviation is very significant for a range of the ratio B / S of manifold length B to manifold cross-sectional area S, which presents a challenge in this invention.

[0054] The inventors have confirmed that the average residence time (stagnation time) gradually decreases as the ratio of manifold length B to manifold cross-sectional area S, B / S, increases. In terms of flow uniformity, a shorter average residence time is better. From the perspective of average residence time, to increase the ratio of manifold length B to manifold cross-sectional area S, B / S, the value of the manifold cross-sectional area S can be fixed, and the manifold length B can be increased. Alternatively, the manifold length B can be fixed, and the manifold cross-sectional area S can be decreased. Furthermore, while increasing the manifold length B, the manifold cross-sectional area S can be further decreased relative to the manifold length B.

[0055] However, to meet the required production and coating quality standards, the ratio B / S of the manifold length B to the manifold cross-sectional area S cannot be reduced. The inventors have discovered that when the ratio B / S of the manifold length B to the manifold cross-sectional area S is set within an appropriate range, the flow velocity deviation in the width direction can be reduced to a desired level while decreasing the average residence time. This satisfies the required production and coating quality standards and simultaneously balances the flow of the coating solution.

[0056] The overflow zone length A represents the distance from the die lip 111 to the front end of the manifold 112. The inventors have confirmed that, when the manifold length B is fixed and the overflow zone length A is varied, the flow rate deviation tends to decrease as the overflow zone length A increases. Furthermore, the inventors have confirmed that, when the manifold length B is further increased, the flow rate deviation decreases even if the overflow zone length A remains the same. The inventors have also confirmed that, when the manifold length B is fixed and the overflow zone length A is increased, the average residence time decreases.

[0057] The inventors have confirmed that when the overflow zone length A is fixed and the manifold length B changes, the flow rate deviation tends to decrease as the manifold length B increases. Furthermore, the inventors have confirmed that when the overflow zone length A is further increased, the flow rate deviation will decrease even if the manifold length B remains the same. Finally, the inventors have confirmed that when the overflow zone length A is fixed and the manifold length B increases, the average residence time will increase.

[0058] Considering the above results, the longer the overflow zone length A and manifold length B, the more advantageous it is in terms of flow rate deviation. However, since the slot extrusion coating machine 100 needs to be implemented within a limited space, the overflow zone length A and manifold length B cannot be increased indefinitely. The inventors have discovered that, in different die blocks with the same overflow zone length A, in order to obtain an average residence time and flow rate deviation that indicate the uniform flow of the coating solution, the ratio B / S of the manifold length B to the manifold cross-sectional area S is used as a parameter, and this parameter is controlled to meet a predetermined value. A shorter average residence time is ideal; however, it is preferable that the average residence time is equal to or less than 200 seconds, taking into account the coating solution viscosity and coating speed in current secondary battery electrode processes. Similarly, a smaller flow rate deviation is also ideal; however, as long as the flow rate deviation is less than 20%, this flow rate deviation is considered acceptable and managed as the desired flow rate deviation. The inventors have confirmed that if the ratio B / S of the manifold length B to the manifold cross-sectional area S is within the range of 1.9 to 9.8, then the average residence time can be equal to or less than 200 seconds, and the flow rate deviation can be less than 20%. Therefore, this disclosure also provides a slot extrusion coating machine, wherein the die assembly has a manifold length B to manifold cross-sectional area S ratio B / S that results in an average residence time equal to or less than 200 seconds and a flow rate deviation of less than 20%.

[0059] According to this disclosure, the flow of the electrode active material slurry, which is the coating solution 150, is uniform inside the slot extrusion coating machine 100. Because the dwell time of the electrode active material slurry in any part of the manifold 112 and the slot 101 is shortened, agglomeration of the electrode active material slurry is prevented. As a result, there are no problems of flow deformation leading to flow rate deviation in the width direction and the resulting loading deviation, nor are there problems of coating defects caused by agglomerated electrode active material slurry lumps clogging the discharge port 101a or being discharged onto the substrate 190.

[0060] Therefore, when using the slot extrusion coating machine 100 of this disclosure to coat the electrode active material slurry, the slurry flows uniformly without stagnation, making the slot extrusion coating machine easy to use for long-term coating and providing excellent productivity. The electrode active material slurry does not aggregate, thus preventing defects from appearing on the coated surface. Therefore, the coating quality of the product can be improved.

[0061] According to this disclosure, the ratio B / S of the manifold length B to the manifold cross-sectional area S is within a predetermined range, thereby providing die assemblies 110 and 130 that improve the flow of the coating solution. Unlike the prior art, which eliminates agglomerates by increasing the number of cleaning cycles, the formation of agglomerates can be fundamentally prevented, thus allowing the slot extrusion coater 100 to easily perform long-term coating with excellent productivity.

[0062] Figure 5 This is a schematic cross-sectional view of a slot extrusion coating machine according to another embodiment of the present disclosure. Figure 6 This is a schematic exploded perspective view of a slit extrusion coating machine according to another embodiment of the present disclosure. The slit extrusion coating machine according to another embodiment of the present disclosure is a double-slit extrusion coating machine having two slits.

[0063] The dual-slit extrusion coating machine 200 according to this disclosure includes a lower slit 201 and an upper slit 202, and a coating solution (preferably an electrode active material slurry) can be extruded through at least one of the lower slit 201 and the upper slit 202, and the coating solution is applied to the surface of a continuously moving substrate 290. When the lower slit 201 and the upper slit 202 are used simultaneously, two identical or different electrode active material slurries can be coated simultaneously or alternately on the substrate 290.

[0064] To manufacture high-energy-density rechargeable batteries, the thickness of the electrode active material layer, initially approximately 130 micrometers, is gradually increased to 300 micrometers. When forming such a thick electrode active material layer using a conventional slot extrusion coating machine, the final electrode is manufactured unevenly due to the increased migration of binders and conductive materials in the active material slurry during drying. To address this issue, performing two coating processes, such as thin coating and drying of the electrode active material layer followed by another coating and drying, is time-consuming. To simultaneously improve electrode performance and productivity, a dual-slot extrusion coating machine 200 can be used to coat two types of electrode active material slurries simultaneously. Thus, the dual-slot extrusion coating machine 200 is optimized for the process of coating electrode active material slurries to manufacture rechargeable batteries.

[0065] refer to Figure 5 and Figure 6 The double-slit extrusion coating machine 200 includes a lower die head assembly 210, an intermediate die head assembly 220 disposed on the upper part of the lower die head assembly 210, and an upper die head assembly 230 disposed on the upper part of the intermediate die head assembly 220.

[0066] exist Figure 5In the middle, the double slit extrusion coating machine 200 is installed in the direction (X direction) of the basic horizontal (approximately ±5 degrees) of the discharge electrode active material slurry (coating solution).

[0067] The intermediate die block 220 is a block located in the middle of the blocks constituting the double-slit extrusion coating machine 200, and is disposed between the lower die block 210 and the upper die block 230 to form a double slit. In this embodiment, the intermediate die block 220 has a right-angled triangle cross-section, but is not limited to this shape. As an example, the cross-section can be set as an isosceles triangle.

[0068] The first surface 220a of the intermediate die assembly 220 facing the upper die assembly 230 is almost horizontal, and the surface 230d of the upper die assembly 230 opposite to the surface 230b facing the first surface 220a (i.e., the upper surface forming the outer peripheral surface of the double-slit extrusion coating machine 200) is also almost horizontal. Thus, the first surface 220a and the opposing surface 230d are almost parallel to each other. The surface 210d of the lower die assembly 210 opposite to the surface 210b facing the intermediate die assembly 220 (i.e., the lower surface forming the outer peripheral surface of the double-slit extrusion coating machine 200) is also almost horizontal, and this surface is the bottom surface 210d (XZ plane).

[0069] The surfaces of the lower die head assembly 210, the middle die head assembly 220, and the upper die head assembly 230 that are opposite to the direction of the discharge electrode active material slurry, namely the rear surfaces 210c, 220c, and 230c, are almost perpendicular (in the Y direction).

[0070] In the lower die assembly 210 and upper die assembly 230, which are the outermost die assembly blocks, the bottom surface 210d of the lower die assembly 210 and the upper surface 230d of the upper die assembly 230, which are manufactured to be almost perpendicular to the rear surfaces 210c and 230c, can be used in the surfaces forming the outer peripheral surfaces of the double-slit extrusion coating machine 200. Furthermore, the first surface 220a of the intermediate die assembly 220, which is manufactured to be almost perpendicular to the rear surface 220c, can be used. In such die assemblies 210, 220, and 230, since the corners formed by the surfaces are formed as right angles, right-angled portions exist in the cross-section. And since vertical or horizontal surfaces can be used as reference surfaces, it is easy to manufacture or process the die assemblies 210, 220, and 230 and ensure their accuracy. Furthermore, the combined lower die assembly 210, intermediate die assembly 220, and upper die assembly 230 have a generally rectangular shape, with only the front portion discharging the coating solution inclined towards the substrate 290. This is highly advantageous because the assembled shape is similar to that of a slit extrusion coating machine containing a single slit (e.g., Figure 3The shapes of the 100 in the middle are roughly similar, so they can share the same slot extrusion coating machine bracket, etc.

[0071] The dual-slit extrusion coating machine 200 may further include two or more fixing units 240 disposed on its rear surfaces 210c, 220c, and 230c. The fixing units 240 are configured to secure between the lower die assembly 210 and the intermediate die assembly 220, and between the intermediate die assembly 220 and the upper die assembly 230. Multiple fixing units 240 may be disposed in the width direction of the dual-slit extrusion coating machine 200. Bolts are fastened to the fixing units 240, thereby assembling the lower die assembly 210, the intermediate die assembly 220, and the upper die assembly 230 together.

[0072] The lower die head assembly 210, the middle die head assembly 220 and the upper die head assembly 230 are not limited to the shapes of the above examples, and as an example, they can be constructed as vertical dies, wherein the direction of discharging the electrode active material slurry is upward, and the rear surfaces 210c, 220c and 230c are bottom surfaces.

[0073] The lower die assembly 210 is the lowest die assembly in the die assembly that constitutes the double slit extrusion coating machine 200, and its surface 210b facing the middle die assembly 220 has an inclined shape, thereby forming an angle of about 30 to 60 degrees relative to the bottom surface.

[0074] A lower slit 201 can be formed at a position where the lower die head assembly 210 and the intermediate die head assembly 220 face each other. For example, a lower backing plate 213 can be inserted between the lower die head assembly 210 and the intermediate die head assembly 220 to provide a gap therebetween, thereby forming a lower slit 201 corresponding to a channel through which the first coating solution 250 can flow. That is, the lower backing plate 213 defines the lower slit 201, and in this case, the thickness of the lower backing plate 213 determines the vertical width of the lower slit 201 (the slit gap in the Y-axis direction).

[0075] The lower pad 213 includes a first opening 213a by cutting a region, thereby determining the coating width of the electrode active material layer formed on the substrate 290, and the lower pad 213 can be inserted into the remaining portion of the edge region of the opposing surfaces of the lower die assembly 210 and the intermediate die assembly 220, except for one side. Accordingly, a lower discharge port 201a is formed only between the lower die lip 211 (the front end portion of the lower die assembly 210) and the intermediate die lip 221 (the front end portion of the intermediate die assembly 220) to discharge the first coating solution 250 to the outside. The lower discharge port 201a can be formed by spacing the lower die lip 211 and the intermediate die lip 221 apart from each other.

[0076] For reference, the lower pad 213 serves as a gasket to prevent the first coating solution 250 from leaking into the gap between the lower die assembly 210 and the intermediate die assembly 220, except for the area forming the lower discharge port 201a. Thus, the lower pad 213 is preferably made of a material with sealing properties.

[0077] The lower die assembly 210 includes a first manifold 212 having a predetermined depth on a surface 210b facing the intermediate die assembly 220 and communicatively connected to the lower slit 201. The first manifold 212 is a recessed chamber. Although not shown in the figure, the first manifold 212 is connected via a supply pipe to a supply chamber (not shown) of a first coating solution 250 mounted externally to receive the first coating solution 250. When the first manifold 212 is filled with the first coating solution 250, the first coating solution 250 flows along the lower slit 201 and is discharged to the outside through the lower discharge port 201a.

[0078] Here, the ratio B' (mm) of the first manifold length to the first manifold cross-sectional area S' (cm²) is preferably in the range of 1.9 to 9.8. The reason for this preferred value is the same as that described in the previous embodiments.

[0079] The upper die head assembly 230 is positioned to face the first surface 220a, that is, the upper surface of the intermediate die head assembly 220 which is horizontal to the bottom surface. Thus, the upper slit 202 is formed at the position where the intermediate die head assembly 220 and the upper die head assembly 230 face each other.

[0080] Similar to the lower slit 201 described above, an upper pad 233 can be inserted between the intermediate die assembly 220 and the upper die assembly 230 to provide a gap therebetween. Accordingly, an upper slit 202 is formed corresponding to a channel through which the second coating solution 260 can flow. In this case, the upper pad 233 determines the vertical width of the upper slit 202 (the slit gap in the Y-axis direction).

[0081] Furthermore, the upper pad 233 also has a structure similar to the lower pad 213 described above. The upper pad 233 includes a second opening portion 233a by cutting a region, and can be inserted into the remaining portion of the edge region of the opposing surfaces of the intermediate die assembly 220 and the upper die assembly 230, except for one side. Similarly, except for the front portion of the upper slit 202, the peripheral direction of the upper pad 233 is blocked, and the upper discharge port 202a is formed only between the front end portion of the intermediate die assembly 220 and the front end portion of the upper die assembly 230. The front end portion of the upper die assembly 230 is defined as the upper die lip 231. In other words, the upper discharge port 202a can be formed by spacing the intermediate die lip 221 and the upper die lip 231 apart from each other. In this way, the upper pad 233 defines the upper slit 202. The lower pad 213 and the upper pad 233 determine the coating width of the electrode active material layer applied on the substrate 290 and are aligned with each other in the vertical direction.

[0082] Furthermore, the intermediate die assembly 220 includes a second manifold 232, which has a predetermined depth on its surface 220a facing the upper die assembly 230 and is communicatively connected to the upper slit 202. The second manifold 232 is a recessed chamber. Although not shown in the figures, the second manifold 232 is connected via a supply pipe to a supply chamber of an externally mounted second coating solution 260 to receive the second coating solution 260. When the second coating solution 260 is supplied from the outside along the pipe-shaped supply pipe and the second manifold 232 is filled with the second coating solution 260, the second coating solution 260 flows along the upper slit 202, which is communicatively connected to the second manifold 232, and is discharged to the outside through the upper discharge port 202a.

[0083] Here, the ratio B” / S” of the second manifold length B”” to the second manifold cross-sectional area S””” is preferably in the range of 1.9 to 9.8. The reason for this preferred value is the same as that described in the foregoing embodiments.

[0084] The upper slit 202 and the lower slit 201 can form an angle of approximately 30 to 60 degrees. The upper slit 202 and the lower slit 201 can intersect at a single point, and the upper discharge port 202a and the lower discharge port 201a can be located near the intersection point. Accordingly, the discharge points of the first coating solution 250 and the second coating solution 260 can be roughly concentrated at one point. When the angle is approximately 30 to 60 degrees, the electrode active material slurry discharged from the upper discharge port 202a and the electrode active material slurry discharged from the lower discharge port 201a will not immediately form a vortex after being discharged simultaneously. When a vortex forms, mixing occurs, making it difficult to form a double layer.

[0085] In the coating method using a dual-slit extrusion coating machine 200, a rotatable coating roller 280 is provided in front of the machine. The substrate 290 to be coated is driven by rotating the coating roller 280, and a coating solution, such as an electrode active material slurry, is extruded through at least one of the upper slit 202 and the lower slit 201 to form an electrode active material layer on the substrate 290. A first coating solution 250 and a second coating solution 260 continuously contact the surface of the substrate 290, thereby allowing the substrate 290 to be coated in a two-layer manner. Alternatively, the supply and interruption of the first coating solution 250 and the second coating solution 260 are alternately performed, thereby allowing pattern coating to be performed intermittently on the substrate 290.

[0086] The dual-slit extrusion coating machine 200 of this disclosure can uniformly form a coating layer of desired thickness, especially an electrode active material layer. Preferably, it can also be manufactured as a dual-slit extrusion coating machine capable of simultaneously coating two types of electrode active material slurries, thus exhibiting excellent performance and productivity. When using the dual-slit extrusion coating machine 200 of this disclosure, electrode active material slurry is coated on the current collector serving as the substrate 290 while driving the current collector, thereby manufacturing electrodes for secondary batteries. Even under conditions of high-speed travel or long-width coating, it has the advantage of achieving uniform coating.

[0087] Meanwhile, this embodiment has described, by way of example, the application of two layers of coating solution or the alternating supply of coating solution to perform pattern coating process. However, it is understood that, unless otherwise stated, the embodiment is also applicable to the application of three or more layers simultaneously by providing three or more slits.

[0088] Furthermore, the following modified example is also possible: the intermediate mold assembly 220 includes a first intermediate mold assembly and a second intermediate mold assembly, the first and second intermediate mold assemblies being in face-to-face contact with each other and configured to slide along the contact surface, thereby being movable relative to each other. In such a modified example, a total of four mold assemblies are included.

[0089] The first intermediate die head assembly is fixedly coupled to the lower die head assembly 210 by bolts or the like, and the second intermediate die head assembly is fixedly coupled to the upper die head assembly 230 by bolts or the like. Accordingly, the first intermediate die head assembly and the lower die head assembly 210 can move as a whole, and the second intermediate die head assembly and the upper die head assembly 230 can move as a whole.

[0090] According to this modified example, the upper discharge port 202a and the lower discharge port 201a can be spaced apart from each other in the horizontal direction, thus being arranged front and back. A separate device can be used, or the operator can manually move the lower die assembly 210 relative to the upper die assembly 230. For example, with the lower die assembly 210 stationary, a step can be formed between the lower discharge port 201a and the upper discharge port 202a by moving the upper die assembly 230 backward (opposite to the direction of coating solution discharge) or forward (in the discharge direction) along the sliding surface. Here, the sliding surface refers to the opposing surfaces of the first intermediate die assembly and the second intermediate die assembly.

[0091] The width of the step formed in the above manner can be determined to be within the range of approximately several hundred micrometers to several millimeters, and can be determined according to the physical properties and viscosity of the first coating solution 250 and the second coating solution 260 formed on the substrate, or the desired thickness of each layer on the substrate 290. For example, as the thickness of the coating formed on the substrate 290 increases, the value of the step width can also increase.

[0092] Furthermore, since the lower discharge port 201a and the upper discharge port 202a are arranged at mutually spaced positions in the horizontal direction, there is no need to worry about the second coating solution 260 discharged from the upper discharge port 202a flowing into the lower discharge port 201a or the first coating solution 250 discharged from the lower discharge port 201a flowing into the upper discharge port 202a.

[0093] In other words, there is no need to worry that the coating solution discharged through the lower discharge port 201a or the upper discharge port 202a will be blocked by the surface of the step formed between the lower discharge port 201a and the upper discharge port 202a and flow into another discharge port, thereby enabling a smoother multilayer active material coating process.

[0094] If it is necessary to change the relative position between the lower discharge port 201a and the upper discharge port 202a, the dual-slit extrusion coating machine according to the modified example of this disclosure as described above can be easily adjusted by sliding the lower die assembly 210 and / or the upper die assembly 230, without having to disassemble and reassemble each die assembly 210, 220 and 230, thereby greatly improving the throughput.

[0095] The changes will be described in detail below. Figure 2 The results for the overflow zone length A, manifold length B, and manifold cross-sectional area S in the slit extrusion coating machine 100 shown, as well as the residence time and flow rate deviation confirmed by simulation.

[0096] This analysis assumes the following scenario for the negative electrode active material slurry: where the ratio of artificial graphite: natural graphite: conductive material: thickener (CMC): binder (SBR) is 85.1:9.5:1:1.5:3. The density of the negative electrode active material slurry is 1.35 kg / m³. 3 The solids content is 48%. As for coating conditions, the loading after drying is 10.6 mg / cm³. 2 The coating speed is 80 m / min, the backing plate thickness is 1 mm, and the coating width is 1040 mm.

[0097] Simulations were performed for overflow zone lengths of 38, 45, 50, and 88 mm (in 1 mm increments). Simulations were also performed for manifold lengths of 49, 49.6, 50.3, 50.9, 51, 51.5, 52, 52.1, 52.8, 53.1, 53.4, 54, 54.8, 54.9, 56.8, 57.4, 57.7, and 58.6 mm. The manifold width was fixed at 1080 mm. The manifold cross-sectional area was determined to be within the range of 4 to 54 square centimeters.

[0098] As simulation results show, when the manifold length is fixed and the overflow zone length changes, the velocity deviation tends to decrease as the overflow zone length increases. When the manifold length is fixed and the overflow zone length increases, the mean residence time tends to decrease. When the overflow zone length is fixed and the manifold length changes, the velocity deviation tends to decrease as the manifold length increases. It has been confirmed that when the overflow zone length is fixed and the manifold length increases, the mean residence time increases. It has been found that the ratio of manifold length to manifold cross-sectional area is controlled as a parameter to achieve the desired level of mean residence time and velocity deviation.

[0099] As a result of examining the ratio B / S of manifold length B to manifold cross-sectional area S relative to all simulation conditions, it has been confirmed that the mean residence time gradually decreases as this ratio increases. A shorter mean residence time is better; however, since there is no critical point for minimizing the mean residence time, if the mean residence time is equal to or less than 200 seconds, the flow velocity deviation at this point should be further considered.

[0100] Tables 1 and 2 below summarize the average residence time and velocity deviation, depending on the ratio of manifold length to manifold cross-sectional area, in the simulation results above, with the overflow zone length fixed at 50 mm and the manifold length fixed at 54 mm. The average residence time and velocity deviation are arranged in descending order of B / S ratio.

[0101] Table 1

[0102]

[0103] Table 2

[0104]

[0105]

[0106] Referring to Tables 1 and 2, the average residence time decreases as the ratio of manifold length B to manifold cross-sectional area S, B / S, increases, provided that the flow rate deviation is less than 20% when the ratio of manifold length B to manifold cross-sectional area S, B / S, is within a predetermined range. Tables 1 and 2 show the case where the overflow zone length + manifold length is 104 mm, where the flow rate deviation is less than 20% and the average residence time is equal to or less than 200 seconds when B / S is between 1.9 and 9.8.

[0107] These simulations demonstrate that when the flow rate ratio (B / S) is between 1.9 and 9.8 as proposed in this disclosure, the flow rate deviation can be less than 20%, and the average residence time can be equal to or less than 200 seconds. Within the size range of slot extrusion coating machines that consider the dimensions of current collectors currently used in the manufacture of secondary batteries, if the B / S meets the range of 1.9 to 9.8, then die blocks with a flow rate deviation typically less than 20% and an average residence time equal to or less than 200 seconds can be designed. The flow rate deviation and average residence time given here are, for example, under the processing conditions of the characteristics and coating speed of electrode active material slurries currently used in the manufacture of secondary batteries, and, for example, within the size range of slot extrusion coating machines, represent appropriate conditions for nearly uniform coating solution flow. In the simulation conditions, if other conditions change, such as a change in the overflow zone length, then the flow rate deviation and average residence time may change; however, as long as the B / S is within the range of 1.9 to 9.8, the current problem of improving flowability in the coating process for the manufacture of secondary batteries can be adequately solved.

[0108] As proposed in this disclosure, it has been confirmed that when the ratio of manifold length to manifold cross-sectional area meets a predetermined range, the average residence time and flow velocity deviation can be controlled at an appropriate value, thereby significantly improving flowability compared to the prior art.

[0109] This disclosure has been described in detail. However, it should be understood that while the detailed description and specific examples indicate preferred embodiments of this disclosure, they are given by way of example only, as various variations and modifications within the scope of this disclosure will be clearly understood by those skilled in the art from the detailed description.

Claims

1. A slot extrusion coating machine, comprising: At least two mold head blocks; A pad is placed between the two mold head blocks to form a slit; as well as A manifold disposed in the die assembly, the manifold being connected in communication with the slit as a recessed chamber for receiving the coating solution. The coating solution is discharged through a discharge port connected in communication with the slit and applied to the surface of the substrate. In a cross-section along the traveling direction of the substrate, the ratio B / S of the manifold length B to the manifold cross-sectional area S is within the range of 1.9 to 9.8, where the unit of manifold length B is millimeters and the unit of manifold cross-sectional area S is square centimeters. The ratio B / S of the manifold length B to the manifold cross-sectional area S is determined to cause the flow deviation to be less than 20% and the average residence time to be equal to or less than 200 seconds. The flow deviation is the difference between the maximum and minimum flow values ​​measured along the width direction of the slot extrusion coating machine.

2. The slot extrusion coating machine as claimed in claim 1, wherein the die assembly size is the length from the die lip serving as the front end of the die assembly to the rear surface of the die assembly, and the die assembly size is equal to or less than 350 mm.

3. A slot extrusion coating machine, comprising: Lower die head assembly; An intermediate die head assembly is disposed above the lower die head assembly to form a lower slit between the lower die head assembly and the intermediate die head assembly; An upper die head assembly is disposed above the intermediate die head assembly to form an upper slit between the intermediate die head assembly and the upper die head assembly; A first manifold is provided in the lower die assembly, and the first manifold is connected in communication with the lower slit as a recessed chamber for receiving the first coating solution. as well as A second manifold, disposed within the intermediate die assembly, is connected in communication with the upper slit as a recessed chamber for receiving the second coating solution. The first coating solution is discharged and applied to the surface of the continuously moving substrate through a lower discharge port connected in communication with the lower slit. The second coating solution is discharged and applied to the surface of the continuously moving substrate through an upper discharge port connected in communication with the upper slit. In a cross-section perpendicular to the width direction of the slot extrusion coating machine, the ratio B' / S' of the first manifold length B' to the first manifold cross-sectional area S' is within the range of 1.9 to 9.8, where the unit of the first manifold length B' is millimeters and the unit of the manifold cross-sectional area S' is square centimeters; or the ratio B" / S" of the second manifold length B"" to the second manifold cross-sectional area S"" is within the range of 1.9 to 9.8, where the unit of the second manifold length B"" is millimeters and the unit of the second manifold cross-sectional area S"" is square centimeters. The ratio B' / S' of the first manifold length B' to the first manifold cross-sectional area S' or the ratio B” / S” of the second manifold length B” to the second manifold cross-sectional area S” is determined to cause the flow deviation to be less than 20% and the average residence time to be equal to or less than 200 seconds, wherein the flow deviation is the difference between the maximum and minimum flow values ​​measured along the width direction of the slot extrusion coating machine.

4. The slit extrusion coating machine of claim 3, wherein the slit extrusion coating machine is configured to extrude and coat an electrode active material slurry onto the surface of a continuously traveling substrate through at least one of the lower slit and the upper slit, the slit extrusion coating machine being mounted such that the direction of discharge of the electrode active material slurry is nearly horizontal, and the surfaces of the lower die assembly, the intermediate die assembly, and the upper die assembly opposite to the direction of discharge of the electrode active material slurry are nearly vertical.

5. The slot extrusion coating machine as claimed in claim 3, wherein the contact surface between the intermediate die assembly and the upper die assembly is parallel to the horizontal plane.

6. The slot extrusion coating machine as claimed in claim 3, wherein the lower slot and the upper slot form an angle of 30 to 60 degrees.

7. The slit extrusion coating machine of claim 3, wherein the slit extrusion coating machine is configured to extrude and coat an electrode active material slurry onto the surface of a continuously traveling substrate through at least one of the lower slit and the upper slit. The slot extrusion coating machine further includes: A lower pad configured to define the lower slit; as well as The upper pad is configured to define the upper slit. Each of the lower and upper pads includes an opening by cutting a region therein, thereby determining the coating width of the electrode active material layer formed on the substrate. The lower pad and the upper pad are aligned with each other in the vertical direction.

8. The slot extrusion coating machine as described in claim 3, wherein the intermediate die assembly comprises a first intermediate die assembly and a second intermediate die assembly. The first intermediate mold head block and the second intermediate mold head block are in face-to-face contact with each other and slide along the contact surface, thereby allowing them to move relative to each other.

9. The slot extrusion coating machine as claimed in claim 8, wherein the first intermediate die assembly is fixedly coupled to the lower die assembly by bolt coupling, and the second intermediate die assembly is fixedly coupled to the upper die assembly by bolt coupling, thereby the first intermediate die assembly and the lower die assembly move as a whole, and the second intermediate die assembly and the upper die assembly move as a whole.

10. The slot extrusion coating machine of claim 8, wherein a step is formed between the lower discharge port and the upper discharge port.

11. The slit extrusion coating machine of claim 3, wherein the slit extrusion coating machine is configured to extrude and coat an electrode active material slurry onto the surface of a continuously traveling substrate through at least one of the lower slit and the upper slit, and the direction of discharge of the electrode active material slurry is opposite to the direction of gravity.

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