Apparatus for forming self-standing film using differential speed rolling

Abstract

The present invention relates to a self-standing film forming apparatus by two-speed rolling, comprising: a hopper for supplying powder to the lower portion; a first rolling roll that rotates in close contact with the lower portion of the hopper; a second rolling roll that rotates in close contact with the lower portion of the hopper and the first rolling roll; and two disc blades attached to both ends of the second rolling roll; wherein both ends of the first rolling roll are in close contact with the inner surface of the two disc blades, and the surface roughness Rz of the inner surface of the disc blade is 1 to 200 μm, and the first rolling roll and the second rolling roll rotate in opposite directions and at different speeds to form and discharge a self-standing film.

Description

Technology Field

[0001] The present invention relates to a self-standing film forming apparatus by two-speed rolling, wherein disc wings are attached to both sides of one of a pair of rolls for forming a self-standing film, and a roughness pattern is formed on the inner surface of the disc wings and on at least one of the pair of rolls to form the thickness of the self-standing film uniformly and to produce an electrode with high smoothness of the edges of the self-standing film. Background Technology

[0003] In the fabrication of conventional electrochemical devices, various devices are being developed to mix oxide powder, which is an active material, with carbon powder or solid electrolyte powder, which is a conductive material, and then form them into a film.

[0004] Generally, organic binders added to bind and mold each mixed powder particle can degrade electrical properties, so to minimize their amount, a so-called wet electrode coating method is used in which a large amount of organic solvent is used to coat the substrate foil.

[0005] However, these wet electrode coating methods require a large amount of energy input and massive facilities for solvent evaporation, as well as facilities for solvent recovery, resulting in high production costs. Therefore, to lower the production cost of batteries and reduce investment costs and environmental burdens, a solvent-free dry electrode coating method is being developed.

[0006] The most important and difficult part of the dry electrode coating process is the coating of the cathode material. The cathode material is a metal oxide, which is an electrochemically active material with a diameter of 1 to 20 μm. Since it is an inorganic material with no plastic deformation force, it is not easy to form.

[0007] Generally, the weight percent range of the cathode material composition can be said to be 70 to 98% cathode active material, 1 to 10% binder, and 1 to 20% conductive material. Typical cathode compositions used in production limit the amount of binder to a smaller amount because it has a significant effect on the characteristics of the electrode, and the binder content of commercially available electrode compositions is 5% or less.

[0008] The process of manufacturing a material coated with such an anode material can be simply divided into the following three steps: first, a homogeneous mixed powder is prepared by mixing the electrode active material powder, carbon powder which is a conductive material, and a binder; second, an electrode film is formed using the mixed powder; and third, the formed electrode film is adhered to a foil, such as a metal which is a current collector and a conductive material, to complete the electrode.

[0009] Among the methods developed to date, the process of forming electrode films using dry powder via roll pressing is primarily used and is known to be one of the most economical methods. Molding and adhesion are possible thanks to a small amount of organic binder added to the blended powder, and minimizing this content improves the electrochemical properties of the electrode. However, if the organic binder content is too low, moldability, inter-particle bonding, adhesion to the substrate foil, and lifespan decrease, so there is a limit to how much the organic binder content can be reduced.

[0010] Various binders that can be used in dry coating are known, and fibrous binders are used or attempts are made to fiberize the binder to increase the effect of binding particles while minimizing the binder content. Representative binders that are most widely used include PTFE (Polytetrafluoroethylene), nanocellulose fibers, and sericin, which are being studied, and PVDF (polyvinylidene fluoride), TPU (thermoplastic polyurethane), and binders of various other components are being attempted.

[0012] [Film Forming via PTFE Fiberization]

[0013] First, considering PTFE as a representative binder, it is used as a fiber to bind inorganic crystal particles because it is a material that can be easily fiberized by external force.

[0014] US Patent Publication US 4,976,904 A provides a mechanism in which an extruder barrel is provided with an electrode material that is advanced axially while mixing and kneading the material to fibrillate (fiberize) a polymer binder, and a forming means at the end of the barrel receives the resulting mixture to continuously form a film composed of a fibrillated polymer binder and an active material while another electrode material continues to advance and be processed within the barrel.

[0015] U.S. Patent Publication US 5,316,556 A presents a method for making an electrode by extruding a homogeneously mixed cathode material under shear stress to thin the cathode material, rolling it several times to make it thin, and then moving it onto a conductive substrate material and bonding it.

[0016] U.S. Patent Publication US 10,062,900 B2 discloses a method for manufacturing a self-standing film (or free-standing film) by undergoing a fibrillable fluoropolymer process. This method involves providing a dry, solvent-free composition comprising polytetrafluoroethylene, an electrically conductive, electrochemically inert carbon material, and an electrochemically active anode material, and then applying a shear force to the dry, solvent-free composition to produce a composition that is at least partially PTFE fibrillated to produce an anode film.

[0017] When forming a self-standing film, fiberization can proceed instantaneously due to a high speed ratio and be formed into a film simultaneously. Since additional steps for fiberization, such as separate kneaders and extruders, are not required or can be simplified, there is an advantage in simplifying the film manufacturing process. However, conventional methods have the problem that it is difficult to form the self-standing film with a uniform thickness and difficult to produce an electrode with high smoothness at the edges of the self-standing film, thus requiring additional processes.

[0019] [Method to improve film homogeneity]

[0020] When performing dry coating, additional kneading is required to homogenize or level the film thickness and to further binder fiberize it, and multi-stage rolling may be necessary for this purpose. Since controlling the spacing and force between each roll requires precision, there are attempts to perform kneading using as few rolls as possible.

[0021] In Registered Patent Publication No. 10-2772671, a separate shear roll is used to supplement the lack of kneading in the direct calendering method, thereby further trimming the formed film as it moves along the roll.

[0022] In Korean Patent Publication No. 10-2023-0033001, there is a case where a buffer roll is rotated in the opposite direction of the film's movement to make contact and homogenize the surface.

[0023] In Korean Patent Publication No. 10-2025-0085472, there is a method in which a rolling roll vibrates axially and performs multiple rubbing motions in a short moment to compensate for the lack of kneading in the direct calendering method. This requires the provision of a device or function capable of applying axial motion.

[0024] Published Patent Application No. 10-2025-0006811 may be a method to increase the effect of kneading, that is, the effect of strengthening shear force, by performing rolling at a position deviating from the direction of the force acting between rolls.

[0025] Surface finishing techniques used as a means for such homogenization have problems such as applying additional force to films formed by strong stress, which can cause them to break or significantly increase defects, and reducing productivity due to damage to the rolls, difficulty in adjusting the gap between rolls, and complexity of roll control when multiple rolls are used.

[0027] [Removal of film edges]

[0028] Generally, in order to cut off the non-uniform edges of a formed film, the formed film is removed by cutting it while it is being transported in contact with the roll surface. Since the non-uniform interface at the boundary between the part covered by the coating layer and the part not covered in the coating part of the electrode is a problem, the problem can be solved by cutting off the edge part of the coating part, that is, the edge part. However, the cut coating part must be cleanly removed from the roller system, and for this purpose, additional devices including a suction device are required.

[0029] Published Patent Application No. 10-2024-0099044 describes cutting the edges of the coating using a laser, while Published Patent Application No. 10-2021-0133365, Published Patent Application No. 10-2023-0097790, Registered Patent Application No. 10-2772671, Registered Patent Application No. 10-2663774, and US Patent Application Publishing US 2020 / 0227722 A1 introduce methods of mechanically cutting using a stripper, and Chinese Patent Application CN 115621408 A also introduces the concept of cutting the molded film and storing it separately.

[0030] Published Patent Application No. 10-2021-0104170 introduces a method in which a polymer layer is formed together with the electrode layer at both ends adjacent to it during rolling, and then the polymer layer is removed separately later. However, the boundary between the electrode layer and the polymer layer is not clear, and it requires the inconvenient task of removing the polymer layer separately after forming.

[0031] Problems arise during the process of trimming the edges of the coating portion of the self-supporting film or electrode, requiring the clean removal of the cut portion, and cleaning and replacement are necessary during the calendering stage using multiple rolls due to contamination and damage to the roll surfaces.

[0032] In addition, when the edges of the formed film are cut, the binder fibers binding the crystal particles are disassembled, causing the particles inside to be released; these particles can contaminate the device, damage the surface of the roll, and adversely affect the properties of the electrode.

[0033] Registered Patent Publication No. 10-2887374 relates to a dry electrode coating system, in which a hopper and a pair of rolls for producing a self-supporting film are integrated, and the accumulation of powder on a blocking plate vibrating with ultrasound is prevented so that a film with high edge smoothness can be produced from the hopper, but some powder still accumulates inside, so it is necessary to further increase the edge smoothness.

[0034] There are common problems that significantly affect the productivity of these self-supporting film forming methods, one of which is the non-uniformity of the edges of the electrode coating.

[0035] In Registered Patent Publication No. 10-2923021, the powder is supplied between two rolling rolls attached to the lower part of a hopper and formed into a film shape, and the smoothness of the edges of the self-supporting dry electrode film formed by the rotation of a disc-shaped blade attached to one of the rolling rolls is improved. This method is effective and allows for obtaining clean, straight edges without cutting the edges. It also prevents the accumulation of powder in the corners at the ends of both rolls due to the rotating disc. Prior art literature

[0037] US Patent Publication US 4,976,904 A US Patent Publication US 5,316,556 A US Patent Publication US 10,062,900 B2 Registered Patent Publication No. 10-2772671 Published Patent Publication No. 10-2023-0033001 Published Patent Publication No. 10-2025-0085472 Published Patent Publication No. 10-2025-0006811 Published Patent Publication No. 10-2024-0099044 Published Patent Publication No. 10-2021-0133365 Published Patent Publication No. 10-2023-0097790 Registered Patent Publication No. 10-2663774 US Patent Application Publication US 2020 / 0227722 A1 China Patent Application Publication CN 115621408 A Published Patent Publication No. 10-2021-0104170 Registered Patent Publication No. 10-2887374 Registered Patent Publication No. 10-2923021 The problem to be solved

[0038] The objective of the present invention is to improve the homogeneity, smoothness of the edges, and meandering progression of the self-standing film when the powder, which is a dried mixed powder comprising a battery electrode powder, a conductive material, and a small amount of polymer binder without containing a liquid solvent, is formed into a self-standing film and discharged between two rolls rotating in opposite directions at different speeds.

[0039] In addition, the present invention aims to increase the production speed by simplifying the electrode production process through the elimination or reduction of multiple calendering and rolling steps.

[0040] In addition, the present invention aims to omit the process of using a multi-stage calendering roll and cutting off the magnetic edge, i.e., the edge, of the primary formed electrode, and to enable immediate compression, i.e., lamination, onto a metal aluminum foil after forming.

[0041] In addition, the present invention improves the homogeneity, smoothness of the edges, and meandering progression of the self-standing film when a solid electrolyte powder is formed into a self-standing film and discharged between two rolls rotating in opposite directions at different speeds without containing a liquid solvent.

[0042] The problems that the present invention aims to solve are not limited to the above purposes, and other technical problems not explicitly stated above will be easily understood by those skilled in the art through the structure and operation of the present invention below. means of solving the problem

[0044] In order to solve the above problem, the present invention includes the following configuration.

[0045] The present invention relates to a self-standing film forming apparatus by two-speed rolling, comprising: a hopper for supplying powder to the lower portion; a first rolling roll that rotates in close contact with the lower portion of the hopper; a second rolling roll that rotates in close contact with the lower portion of the hopper and the first rolling roll; and two disc blades attached to both ends of the second rolling roll; wherein both ends of the first rolling roll are in close contact with the inner surface of the two disc blades, and the surface roughness Rz of the inner surface of the disc blade is 1 to 200 μm, and the first rolling roll and the second rolling roll rotate in opposite directions and at different speeds to form and discharge a self-standing film.

[0046] The present invention is characterized in that the surface roughness Rz of at least one of the first rolling roll or the second rolling roll is 1 to 20 μm.

[0047] The surface roughness of the inner surface of the disc wing of the present invention has a roughness pattern, and the roughness pattern is characterized by being radial, in which grooves are formed extending outward from the center of the roll.

[0048] The surface roughness of the inner surface of the disc wing of the present invention has a roughness pattern, and the roughness pattern is characterized in that a groove extending outward from the center of the roll is inclined in a direction opposite to the rotational direction of the roll.

[0049] The surface roughness of the inner surface of the disc wing of the present invention has a roughness pattern, and the roughness pattern is characterized in that a groove extending outward from the center of the roll is formed to be inclined in the direction of rotation of the roll.

[0050] The first rolling roll of the present invention is characterized by rotating at a faster speed than the second rolling roll.

[0051] The second rolling roll of the present invention is characterized by rotating at a faster speed than the first rolling roll.

[0052] The surface roughness of the inner surface of the disc wing of the present invention has a roughness pattern, and the roughness pattern is characterized by a portion formed such that a groove extending outward from the center of the roll is inclined in a direction opposite to the rotational direction of the roll, and a portion formed such that a groove extending outward from the center of the roll is inclined in the rotational direction of the roll intersects with each other.

[0053] The portion of the inner surface of the disc wing of the present invention that comes into contact with the first rolling roll or the second rolling roll is formed concavely so that a portion of both ends of the first rolling roll or the second rolling roll is inserted therein.

[0054] The portion of the inner surface of the disc wing of the present invention that comes into contact with the first rolling roll or the second rolling roll is formed concavely so that a portion of both ends of the first rolling roll or the second rolling roll is inserted 1 mm to 10 mm.

[0055] The present invention relates to a self-standing film forming apparatus by two-speed rolling, comprising: a hopper for supplying powder to the lower portion; a first rolling roll that rotates in close contact with the lower portion of the hopper; a second rolling roll that rotates in close contact with the lower portion of the hopper and in close contact with the first rolling roll; and two disc blades attached to both ends of the second rolling roll; wherein both ends of the first rolling roll are in close contact with the inner surface of the two disc blades, and the surface roughness Rz of at least one of the first rolling roll or the second rolling roll is 1 to 20 μm, and the first rolling roll and the second rolling roll rotate in opposite directions and at different speeds to form and discharge a self-standing film.

[0056] At least one of the first rolling roll or the second rolling roll of the present invention has a surface roughness pattern, and the roughness pattern is characterized by grooves forming on the roll surface in the circumferential direction.

[0057] At least one of the first rolling roll or the second rolling roll of the present invention has a surface roughness pattern, and the roughness pattern is characterized by having zigzag-shaped grooves formed on the roll surface in the circumferential direction.

[0058] At least one of the first rolling roll or the second rolling roll of the present invention has a surface roughness pattern, and the roughness pattern is characterized by having wave-shaped grooves formed on the roll surface in the circumferential direction.

[0059] The present invention is characterized in that the depth of the groove is 20% or less of the thickness of the self-supporting film. Effects of the invention

[0061] The effect of the present invention is to improve the homogeneity, smoothness of the edges, and meandering progression of the self-standing film when the powder, which is a dried mixed powder comprising a battery electrode powder, a conductive material, and a small amount of polymer binder without containing a liquid solvent, is formed into a self-standing film and discharged between two rolls rotating in opposite directions at different speeds.

[0062] In addition, the effect of the present invention is to simplify the electrode production process by eliminating or reducing multiple calendering and rolling steps.

[0063] In addition, the effect of the present invention is to omit the process of using a multi-stage calendering roll and cutting off the magnetic edge, or edge, of the primary formed electrode, and to enable lamination, or compression, onto a metal aluminum foil immediately after forming.

[0064] In addition, the effect of the present invention is to improve the homogeneity, smoothness of the edges, and meandering progression of the self-standing film when solid electrolyte powder is formed into a self-standing film and discharged between two rolls rotating in opposite directions at different speeds without containing a liquid solvent.

[0065] The effects of the present invention are not limited to the effects mentioned above, and other effects not explicitly stated above will be easily understood by those skilled in the art through the structure and operation of the present invention below. Brief explanation of the drawing

[0067] FIG. 1 illustrates a schematic flowchart for explaining the operation of a self-supporting film forming device by two-speed rolling according to the present invention. FIG. 2 illustrates a self-supporting film forming device by two-speed rolling according to the present invention. FIG. 3 illustrates a graph to explain the stability of the process using the self-standing film forming device by two-speed rolling according to the present invention. FIG. 4 illustrates a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention, together with a comparative example. FIG. 5 illustrates a conceptual diagram explaining the roughness and surface condition of a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention. FIG. 6 illustrates an example of the roughness and pattern of the roll surface of a self-supporting film forming device by two-speed rolling according to the present invention. FIG. 7 illustrates a self-standing film with smooth edges formed by the self-standing film forming device by two-speed rolling according to the present invention, together with a comparative example. FIG. 8 illustrates the connection relationship of the rolls of the self-supporting film forming device by two-speed rolling according to the present invention. FIGS. 9 and 10 illustrate various embodiments of the inner surface roughness pattern of the disc wing of the self-supporting film forming device by two-speed rolling according to the present invention. FIG. 11 illustrates another embodiment of the connection relationship of the rolls of a self-supporting film forming device by two-speed rolling according to the present invention. FIG. 12 illustrates various embodiments of the roll surface roughness of a self-supporting film forming device by two-speed rolling according to the present invention. FIG. 13 illustrates the change in surface roughness of a self-standing film according to the speed ratio of the rolling rolls of R 401 of the self-standing film forming device by two-speed rolling according to the present invention. FIG. 14(a) illustrates the surface condition of a self-standing film formed by the rolling roll of R 601 of the self-standing film forming device by two-speed rolling according to the present invention, and FIG. 14(b) illustrates the surface condition of a self-standing film formed by the rolling roll of R 601 of the self-standing film forming device by two-speed rolling according to the present invention after compression. FIGS. 15 and 16 illustrate a self-standing film with smooth edges formed by the self-standing film forming device by two-speed rolling according to the present invention, together with a comparative example. Figure 17 shows the edge roughness measured by standing a self-standing film vertically and then photographing its edge. FIG. 18 shows an electron microscope image showing the magnetic edge of a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention. Figure 19 shows a photograph showing the edge roughness after lamination of a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention. FIG. 20 shows a graph representing the characteristics of an electrode measured after lamination of a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention. Specific details for implementing the invention

[0068] The overall structure and operation according to a preferred embodiment of the present invention will be described below. These embodiments are exemplary and do not limit the structure and operation of the present invention. Other structures and operations not explicitly shown in the embodiments may also be considered as part of the technical concept of the present invention if they are easily understood by a person skilled in the art through the embodiments described below.

[0070] When forming using two rolls, the forming is performed using shear force rather than compressive force. To increase the shear force, a differential speed rolling (DSR) method is used, in which the rotational speeds of the two rolls are different.

[0071] The positive aspects of the forming method utilizing this two-speed rolling method can be summarized as follows.

[0072] When powder forming under dual-speed rolling or asymmetric rolling conditions where two rolls are driven at different rotational speeds, the rotational speed ratio has a decisive influence on the stress distribution and size within the molded body.

[0073] If the speeds of the two rolls differ, strong shear deformation occurs within the powder layer due to the speed difference; this introduces shear stress to the normal compressive stress generated in conventional constant-speed rolling, thereby promoting rearrangement and plastic deformation among powder particles.

[0074] Generally, as the speed ratio increases—that is, as the speed difference between the two rolls increases—the rolling load required under the same compression conditions tends to decrease. This is because shear stress increases the fluidity of the powder, making it possible to achieve high densification with less force.

[0075] Stress distribution in the thickness direction of the molded body can be controlled by adjusting the speed ratio; an appropriate speed ratio helps alleviate residual stress within the molded body and suppress crack formation by reducing the stress difference between the surface and the center, thereby increasing the uniformity of the stress distribution.

[0076] As the velocity ratio increases, shear deformation is maximized, allowing for the production of a green body with a higher density than the conventional rolling method, because it more effectively fills the voids between powder particles.

[0077] The present invention aims to have a homogeneous film having a sufficient kneading effect by forming a film between shear rolls having a high rotation ratio, wherein the high rotation ratio is at least 3 or more, and a more preferable rotation ratio can be obtained in the range of 5 to 50.

[0078] In addition to the configuration of the disc wings attached to both ends of the roll and the roll disclosed in Registered Patent Publication No. 10-2923021, the present invention can have a decisive influence on the forming of a self-standing film by defining the surface roughness and roughness pattern of the roll and the disc wings.

[0080] FIG. 1 illustrates a schematic flowchart for explaining the operation of a self-supporting film forming device by two-speed rolling according to the present invention.

[0081] Referring to FIG. 1, the self-standing film forming device by two-speed rolling according to the present invention can utilize the self-standing film discharged through the steps of preparing a mixed powder (S100), granulating the prepared mixed powder (S200), and forming a self-standing film (S300) directly as an electrode or solid electrolyte of a secondary battery.

[0082] Conventionally, the self-standing film discharged through the step of forming the self-standing film (S300) must be subjected to a step (S400) of using a multi-stage calendering roll to increase the homogeneity of the self-standing film through multiple kneading steps, and then the edges of the self-standing film with low smoothness must be cut off through the step (S500) of cutting the edges, and then a lamination step (S600) must be performed.

[0083] However, in order to perform the step (S400) using multi-stage calendering rolls, adjusting the spacing and force between each roll is complex, and as the number of rolls used increases, the complexity of adjustment, roll damage, and roll contamination also increase, leading to a decrease in productivity.

[0084] In addition, even when performing the edge cutting step (S500), productivity is reduced because the edge must be cut while the self-supporting film is moving in contact with the roll surface and the cut edge must be cleanly removed so that contamination of the rolls does not occur.

[0085] However, the self-standing film forming device by two-speed rolling of the present invention can increase the homogeneity and edge smoothness of the self-standing film so that the self-standing film can be used directly as an electrode or solid electrolyte of a secondary battery without going through the step of using a multi-stage calendering roll (S400) and the step of cutting the edges (S500) for the self-standing film discharged through the step of forming the self-standing film (S300).

[0087] FIG. 2 illustrates a self-supporting film forming device by two-speed rolling according to the present invention.

[0088] Referring to FIG. 2, the self-supporting film forming device by two-speed rolling according to the present invention may include a powder supply unit (100), a hopper (200), and a rolling roll assembly (300).

[0089] The powder supply unit (100) conveys the mixed powder (10) to the top of the hopper (200) and evenly sprays the mixed powder (10) at the top of the hopper (200), and the hopper (200) temporarily stores the mixed powder (10), and the rolling roll assembly (300) is attached to the bottom of the hopper (200) and operates.

[0090] The above powder supply unit (100) includes a scatterer (110), a distance sensor (120), a scatterer drive motor (130), a scatterer drive controller (140), a conveying device controller (150), a powder conveying device (160), and a powder storage silo (170), and the powder (10) filled into the hopper (200) is stacked to a height within a set range and to a height that is evenly distributed on both sides, so that the thickness of the molded product is constant and the meandering phenomenon is prevented.

[0091] The powder (10) stored in the powder storage silo (170) moves through the powder transfer device (160) and falls onto the scatterer (110), and the distance sensor (120) measures the cumulative level of the powder (10) accumulating on the scatterer (110) and maintains a constant height at which the powder (10) accumulates by adjusting the supply amount through the powder transfer device (160) with the transfer device controller (150).

[0092] The scatter drive motor (130) that rotates the scatter (110) can adjust the rotation speed by the scatter drive controller (140).

[0093] The above hopper (200) includes a side plate (210), a distance sensor (220), a blocking plate (230), and a side plate heating rod (240), and the side plate (210) and the blocking plate (230) are formed to be similar in size to the roll attached to the bottom by limiting the internal size of the hopper (200).

[0094] The distance sensor (220) measures the accumulated height of the powder (10) accumulating in the hopper (200) and maintains the height at a constant level through the scatter drive controller (140), which can adjust the speed of the scatter drive motor (130).

[0095] At least one distance sensor (220) can be installed on the side plate (210) or blocking plate (230), and each distance sensor (220) is installed at a different height so as to measure the accumulated height of the powder (10) accumulated in the hopper (200).

[0096] The above-mentioned side plate heating rod (240) allows the inside of the hopper (200) to maintain an appropriate temperature, thereby allowing the powder (10) stored inside the hopper (200) to maintain a constant temperature and maintain an optimal condition for rolling and molding.

[0097] The above distance sensor (120, 220) may use at least one of a capacitive sensor, an inductive current sensor, an infrared laser sensor, etc.

[0098] The scatter (110) is positioned in the upper part connected to the inside of the hopper (200) in the same direction as the first and second rolling rolls (310, 320), and the scatter rotor, which has a length equal to the length of the rolling section of the first and second rolling rolls (310, 320), blocks the entire passage through which the powder (10) goes down, so that the powder (10) between the blades attached to the outside of the rotor goes down only when the rotor rotates.

[0099] The powder (10) goes down into the hopper (200) below the scatter (110) and then reaches the first and second rolling rolls (310, 320). When the condition is completed that the powder (10) is supplied at a uniform height, it is formed into a self-supporting film (20) by the first and second rolling rolls (310, 320), and the thickness of the formed self-supporting film (20) is approximately 40 to 300 μm in the case of an electrode or solid electrolyte.

[0100] The above rolling roll assembly (300) includes a first rolling roll (310), a second rolling roll (320), a roll penetration heating rod (312), a disc wing (323), a slide (342), and a driving motor (350). The first rolling roll (310) and the second rolling roll (320) are in close contact with each other and are in close contact with the lower part of the hopper (200), and rotate in opposite directions and at different speeds to form and discharge a self-standing film (20).

[0101] The first rolling roll (310) and the second rolling roll (320) are connected to the drive motor (350) by a chain (390) and can be rotated, and can be adjusted to rotate in opposite directions and at different speeds.

[0102] The above drive motor (350) can be connected to a drive element such as a T-shaped through-type worm gear, a worm gear through-shaft, a helical gear, or a chain (390) to rotate the first rolling roll (310) and the second rolling roll (320).

[0103] The first rolling roll (310) and the second rolling roll (320) can be heated by a heating means, and preferably heated by a roll penetration heating rod (312) installed within at least one roll penetration axis (311, 312) to maintain an optimal temperature for forming a self-supporting film (20).

[0104] A disc wing (320) is attached to each end of the second rolling roll (320), and both ends of the first rolling roll (310) are in close contact with the inner surface of the two disc wings (320). The first rolling roll (310) and the second rolling roll (320) rotate in opposite directions and at different speeds to form and discharge a self-standing film (20).

[0106] FIG. 3 illustrates a graph to explain the stability of the process using the self-standing film forming device by two-speed rolling according to the present invention.

[0107] Referring to Fig. 3, the process map illustrating the relationship between the velocity ratio (λ) and the shear force (τ) is divided into three regions.

[0108] Region 1 is a case where the shear force (τ) is too low and forming is not done well. When manufacturing a cathode, a graphite-based composition generally falls into this region, but this can be resolved by using a rolling roll with a surface having a high coefficient of friction to move it to Region 2.

[0109] In Region 2, the shear force (τ) is appropriately high so that it does not fail or generate a large number of defects during deformation, and when the velocity ratio increases, the shear force (τ) actually decreases due to the shear softening phenomenon.

[0110] If the shear force (τ) is large, the surface roughness of the electrode film increases accordingly, and at a high velocity ratio (λ) where the shear force (τ) decreases, the surface roughness also decreases.

[0111] In the present invention, when forming an NMC-based anode, the film obtained by rolling up to a speed ratio (λ) of 40 obtained homogeneous and good characteristics at a high rotation ratio.

[0112] When the speed ratio (λ) is 40 or higher, the experiment is meaningless because there is little change in characteristics even at higher speed ratios (λ), and there are problems with the operation of the machine device, so the speed ratio was limited to a maximum of 40.

[0113] When considering the measured electrode characteristics, the case with a velocity ratio of 40 was the most superior; thus, sufficiently superior characteristics can occur even at velocity ratios higher than that, so a velocity ratio of up to 100 can be expected, and based on the results of Figure 13 measured using NMC532, the desirable velocity ratio appears to be 10 or higher. Generally, at a velocity ratio of 10 or higher, it can be seen as a region where shear softening is dominant, moving beyond the stage of rising due to friction.

[0114] In Region 3, the shear force (τ) is high due to large friction, but the molding process is not successful and fracture occurs. In particular, in the case of electrode materials with a main component of very small crystals, such as LFP with a diameter of about 1 μm, the friction, or shear force (τ), is excessive, making it difficult to obtain a homogeneous film, but molding may be partially possible at a low speed ratio (λ).

[0115] In addition, at high speed ratios (λ), crushing and cutting of the molded product can be observed, which can be attributed to excessive shearing. The appropriate speed ratio or the range where material forming does not fail can vary depending on various factors such as the type of material, the condition of the roll surface, and the temperature of the roll. It can be moved to a stable region 2 (Region 2) by adding additives that can reduce friction or by changing the composition.

[0116] In particular, when forming an electrode film, the gap size between the rolls, the shear force (τ) applied to the powder material during forming, and the temperature are important. The gap size is similar to the desired film thickness, and since the thickness of the electrode produced is related not only to the gap size but also to the material properties, the rotation speed of the rolls, and the speed ratio (λ), it can be quantified by verifying it experimentally or empirically.

[0117] The appropriate roll size is a diameter of 30 to 120 mm. If the roll diameter exceeds 120 mm, friction is excessive, resulting in poor formability and making it difficult to obtain a continuous film. If the roll diameter is too small, the nip zone is reduced, and the pelletized powder may not be caught between the rolls.

[0118] Among a pair of rolling rolls, a first rolling roll (310) and a second rolling roll (320), disc wings (323) are attached to both ends of the second rolling roll (320), and the first rolling roll (310) is inserted between the two disc wings (323) so as to be in close contact with the second rolling roll (320).

[0119] A self-standing film is formed by inserting the first rolling roll (310) between the disc wings (323) of the second rolling roll (320) to which the disc wings (323) are attached, such that the rotational speed ratio (λ) of one of the first rolling roll (310) and the second rolling roll (320) is 3 or more.

[0120] The appropriate velocity ratio (λ) varies depending on the target thickness and the state of the powder, but theoretically, as long as it is not in the region of excessive shear, the higher the velocity ratio (λ), the higher the homogeneity can be increased due to the kneading effect and the fiberization of the binder can proceed further.

[0121] Generally, films formed in a region with a high velocity ratio (λ) can have higher tensile strength due to the tendency of fibers to align in one direction.

[0123] FIG. 4 illustrates a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention, together with a comparative example.

[0124] Referring to FIG. 4, the phenomena observed when forming a film from a powder (10) are as follows: Film A shows ideal forming, Film B shows a defect where cracking occurs due to a lack of material at the edge, and Film C shows a situation where wrinkles form because more material accumulates at the edge.

[0125] Of these three, only film A is normal and the others are defective, and these defects can be prevented by modifying the pattern and roughness of the roll and the roughness and pattern of the inner surface of the disc wings (323) at both ends of the roll.

[0127] FIG. 5 illustrates a conceptual diagram explaining the roughness and surface condition of a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention.

[0128] Referring to Fig. 5(a), the active particle size (D) used in the anode is from a minimum of 1 to a maximum of 20 μm, so the groove depth (Rz) of the roughness formed on the roll surface is also appropriate in this range, and sufficient results can be obtained even with a roll surface having random roughness without directionality.

[0129] Furthermore, an appropriate pattern can reduce friction during rolling and increase the formability and strength of the film, and this can vary depending on the shape and direction of the pattern, namely whether it is circumferential or axial.

[0130] In addition, the shear force (τ) acting between rolls with different rotational speed ratios (λ) increases, which can lead to significant PTFE fiberization within the powder during the molding process.

[0131] Means for quantitatively evaluating surface roughness include Ra, a one-dimensional linear evaluation value, or Sa, a two-dimensional evaluation value of a specific area; however, in powder molding, Rz or Sz, which represent the average maximum height of the surface roughness curvature, are more important, so these values ​​are used.

[0132] Additionally, W represents the waviness spacing, which is the curvature formed when grinding or carving the roll surface.

[0133] The magnitude of surface roughness is closely related to the average size of large particles among the powder particles, and particles tend to move along the grooves of the rough surface, which can cause additional binder fiberization and homogenization of the particle distribution.

[0134] These values ​​can be measured using an optical microscope capable of quantifying surface roughness, and various methods can be utilized to produce a surface suitable for the state of the powder and molding conditions.

[0135] Although conditions vary depending on the material and temperature, generally, as the speed ratio increases, there are additional factors to consider regarding the roughness of the molded film, namely kurtosis (Rku, Sku) and asymmetry (Rsk, Ssk).

[0136] If the kurtosis (Rku, Sku) value is 3 or higher, it shows a shape with sharp peaks, and if it is 3 or lower, it shows a blunt shape. This value also changes with changes in the speed ratio of the forming rolls, and if this value decreases, it means that the sharp parts become blunted.

[0137] 5.

[0138] Referring to Fig. 5(b), if the skewness (Rsk, Ssk) is positive, sharp peaks develop outward on the surface, and referring to Fig. 5(c), if it is negative, the surface becomes blunted outward and the valleys in between form sharp valleys. Likewise, if this value is positive, the likelihood of crystal grains in the sharp peaks falling off increases.

[0139] Therefore, for stable production, it is desirable to work under conditions where the kurtosis (Rku, Sku) and asymmetry (Rsk, Ssk) of the molded self-standing film of Fig. 5(c) are low.

[0140] There are various methods for roughening the surface or creating patterns, and among them, the methods selected in the present invention include polishing using abrasive paper or abrasive stone, creating a certain curvature on equipment such as a lathe using a tool, engraving using a laser, chemically etching using a corrosive chemical, or plasma etching.

[0142] FIG. 6 illustrates an example of the roughness and pattern of the roll surface of a self-supporting film forming device by two-speed rolling according to the present invention.

[0143] If the surface of the roll is too smooth, the powder slides off the surface of the roll and is difficult to get caught between the rolls, so molding is not done well, because the actual leaf area becomes very small.

[0144] Therefore, it is necessary to perform roughening operations and pattern formation to roughen the roll surface so that particles can be trapped between the rolls.

[0145] If surface roughness is high, friction increases; if friction is excessively high, increasing the speed ratio may cause the formed film to break or result in many defects, and the roughness of the formed electrode film also increases, leading to a greater loss of crystal grains.

[0146] On the other hand, if friction is too small, not only will the powder not get caught between the rolls, but the fiberization of the binder within the electrode material may also be insufficient, and the forming of the film is highly likely to be non-homogeneous.

[0147] The characteristics of friction can vary depending not only on the physicochemical properties of the powder material but also on the temperature of the forming rolls and the powder, electrode surface roughness, roughness pattern, gap between rolls, speed ratio, roll diameter, etc.

[0148] Referring to Fig. 6, examples of the surface roughness and roughness patterns of the roll are illustrated.

[0149] Roughness patterns can be created through methods such as grinding with abrasive stones or abrasive paper, grinding with mechanical tools, chemical or electrochemical etching, plasma etching, and laser engraving.

[0150] The groove shape formed on the surface of the first rolling roll (310) and the second rolling roll (320) of the present invention is a non-directional pattern 310-P1, which can have various frictional forces, but is a shape that is difficult to produce through general processing or grinding.

[0151] 310-P2 is a form that can be obtained using abrasive paper or abrasive stone used for cylindrical grinding, and 310-P3, 310-P4, and 310-P5 can be obtained through lathe machining, laser engraving, chemical etching, and plasma etching.

[0152] When roughening the surface of a roll, specific patterns can be used to reduce friction and improve formability. An example of this is a roll made of a narrow spiral with a small pitch in the circumferential direction, such as the 310-P3. This roughening pattern is created by using a lathe to rotate the roll and making grooves at regular intervals with a small pitch, resulting in a spiral shape where the grooves are almost straight.

[0153] Although lathe machining is the easiest method, chemical etching or laser engraving may be more suitable for obtaining more precise patterns, and these patterns allow the size of the nip zone to be sufficiently large while keeping the shear stress due to frictional resistance low.

[0154] The depth of the grooves should not be too deep, because if the depth of the grooves is too deep, a film cannot be formed and a crushed powder may be obtained. Also, when forming not only electrodes but also solid electrolytes, if the depth of the grooves is too deep relative to the thickness, it may be produced in the form of a powder rather than a film.

[0155] Generally, as confirmed through experiments, a continuous film form can be obtained when the Rz value is 20% or less of the desired thickness.

[0156] In order to maximize the fiberization of a binder such as PTFE using shear force and kneading effect when forming an electrode film and to ensure that the film is formed safely without being destroyed, it is desirable to have a groove of 20% or less of the desired film thickness. Therefore, when the film thickness is 100 μm, it is desirable to maintain the depth of the groove at 20 μm or less.

[0157] Meanwhile, 310-P3 allows for easy stretching and polishing of the film due to the grooves formed in the circumferential direction during roll rolling, but it exhibits anisotropy in which the binder fibers are arranged only in the direction of travel, so the strength increases in the direction of travel while the strength decreases in the direction perpendicular to it or in the direction of the roll axis, which can also be disadvantageous in terms of the homogeneity of the film.

[0158] In cases where it is necessary to allow the particles to move in the axial direction, since there is insufficient opportunity for the rolled particles to spread evenly in 310-P3, it is more desirable to form grooves in a wave or zigzag shape to allow for slight lateral movement, even if grooves are formed in the circumferential direction as in 310-P4.

[0159] In other words, it is more desirable to create curved grooves instead of straight grooves, which allows for two-dimensional elongation of the binder and even distribution of particles as it moves in the axial direction, and the roughness pattern of the rolling roll can be formed on only one roll, but if necessary, a roughness pattern can be formed by mixing it on both rolls.

[0160] In addition, as mentioned above, the 310-P5 pattern can be used when it is necessary to increase friction and shear force while moving particles in the axial direction.

[0161] Since rolling rolls used in mass production facilities rotate at high speeds for a long time, wear problems may occur, so materials with high hardness must be used. Suitable materials include sintered bodies or thermal spray coating materials with tungsten carbide (WC) as the main component.

[0163] FIG. 7 illustrates a self-standing film with smooth edges formed by the self-standing film forming device by two-speed rolling according to the present invention, together with a comparative example.

[0164] Referring to Fig. 7(a), the self-supporting film contains powder particles and a fibrous binder fibril.

[0165] In the second rolling roll (320), which is either the first rolling roll (310) or the second rolling roll (320) that forms the self-supporting film, disc wings (323) larger than the roll diameter are attached to both ends. This prevents the powder from escaping when the powder fed between the two rolls is rolled while rotating, and ensures that the powder flowing into the leaf zone is continuously supplied without stagnation.

[0166] These characteristics are similar to those disclosed in Registered Patent Publication No. 10-2923021, but in addition to this, the effect may vary significantly depending on the surface roughness and roughness pattern formed on the roll surface.

[0167] While using mirror-polished rolls and disc blades without surface roughness makes film forming impossible and continuous production impossible, roll surfaces and inner surfaces of disc blades with non-directional, random surface roughness basically helps in homogeneous film forming.

[0168] However, since not only surface roughness but also roughness patterns can be formed in various forms and formability can be significantly affected depending on the shape of the roughness pattern, the present invention sets conditions for artificial roughness patterns after setting a basic roughness range.

[0169] By using the disc wing (323) of the present invention, the smoothness of the edges of the self-supporting film being formed is increased, so that additional trimming work is not required.

[0170] Referring to FIG. 7(c), when using the disc wing (323) of the present invention, the binder fibers at the edge of the molded film become a whipstitched edge as if stitching the edge with thread, whereas, as shown in FIG. 7(b), when the edge of the film is cut by a trimming operation, there is a problem that the loss particles inside the film are more likely to escape.

[0172] FIG. 8 illustrates the connection relationship of the rolls of the self-supporting film forming device by two-speed rolling according to the present invention.

[0173] Referring to FIG. 8(a) and FIG. 8(b), the roughness pattern of the rolling rolls (310, 320) may be formed on only one roll, but may also be formed by mixing the roughness pattern on both rolls (310, 320) as needed, and may also be formed on the inner surface of the disc wing (323).

[0174] There are various factors that can affect the smoothness of the film edges. In the case of materials containing a large amount of adhesive components such as PTFE, the smoothness is lowered because the powder tends to adhere to the surface of the well-polished roll when molding and clumps easily. On the other hand, the smoothness is improved because the adhesive strength is reduced on the inner surface of the disc wing with a rough surface, which reduces the stretching effect of the edges.

[0175] The phenomena shown in Figures 4A, B, and C are the result of competition between material transfer in the roll and material transfer on the inner surface of the disc wing at both ends of the roll. Film A is the desirable result, but if the material does not sufficiently move to the edge of the film, it is formed like Film B, and conversely, if the material moves excessively to the edge of the film, it is formed like Film C.

[0176] The surface roughness and roughness pattern of the inner surface of the disc wing also have an effect; a certain degree of roughness is required to reduce the adhesion of the electrode material on the inner surface of the disc wing, and fine protruding areas on the inner surface of the disc wing serve to cut off the edges of the electrode film.

[0177] The inner surface of the disc wing has a rough surface with a surface roughness Rz value of 1 to 200 μm, but the inner surface of the disc wing may have a rougher surface depending on the adhesive force of the powder (10) which is the electrode material, or to cut off the edge of the electrode film being molded.

[0178] Referring to FIG. 8(c), the disc wing can be detached separately and polished, etched, or engraved. Since the disc wing requires special surface processing, it can be separated from the roll, and when attached to both ends of the roll, it can be fixed to the side of the roll using embedded countersunk bolts.

[0180] FIGS. 9 and 10 illustrate various embodiments of the inner surface roughness pattern of the disc wing of the self-supporting film forming device by two-speed rolling according to the present invention.

[0181] FIG. 9(a) illustrates a case where a groove of a roughness pattern is formed in a circumferential direction on the inner surface of the disc wing (323) (323-P1), and FIG. 9(b) illustrates a case where a groove of a roughness pattern is formed radially on the inner surface of the disc wing (323) so as to face outward from the center of the second rolling roll (320) (323-P2).

[0182] In the case of 323-P1, the second rolling roll (320) is stretched in the direction of rotation, so the smoothness is lowered, whereas in the case of 323-P2, the powder has a cutting effect, so a relatively high smoothness can be obtained, so 323-P2 is a more preferred pattern for powders used in the scope to which the present invention is applied.

[0183] Referring to FIG. 10(c) and FIG. 10(d), one of two inclined radial patterns can be selected and used by considering the case where material is abundant and the case where material is scarce at both ends of the rolling rolls (310, 320) during film forming, and referring to FIG. 10(e), an example with a more complex pattern is presented.

[0184] The roughness pattern of 323-P3 shown in FIG. 10(c) is formed such that the grooves extending outward from the center of the rolling roll (320) are inclined in the opposite direction to the rotation direction of the roll, and the roughness pattern of 323-P4 shown in FIG. 10(d) is formed such that the grooves extending outward from the center of the rolling roll (320) are inclined in the rotation direction of the roll.

[0185] The roughness pattern of 323-P3 is a shape that pushes out surrounding powder, and it is desirable to use it when the material becomes abundant at both ends of the rolling rolls (310, 320) during film forming.

[0186] The roughness pattern of 323-P4 is a shape that attracts more surrounding powder, and it is desirable to use it when there is a shortage of material at both ends of the rolling rolls (310, 320) during film forming.

[0187] It is preferable that the second rolling roll (320) to which the disc wing (323) is attached rotates at a faster speed than the first rolling roll (310) and has a roughness pattern of 323-P3 that pushes out surrounding powder when material becomes excessive at the edge of the electrode film.

[0188] It is preferable that the first rolling roll (310) rotates at a faster speed than the second rolling roll (320) to which the disc wing (323) is attached, and has a roughness pattern of 323-P4 that attracts surrounding powder when material is lacking at the edge of the electrode film.

[0189] The roughness pattern formed on the inner surface of the disc wing (323) can be appropriately selected according to the operation method of the rolling roll (310, 320), but when two disc wings (323) are attached to both ends of one rolling roll, the roughness pattern formed on the inner surface of each disc wing (323) is combined so as to be mirror-symmetric to each other.

[0190] In the case of 323-P5 in Fig. 10 (e), it is a mixture of 323-P3 and 323-P4, and using the roughness pattern of 323-P5, satisfactory results such as film A in Fig. 4 can be obtained under various experimental conditions, which is a form that exhibits appropriate stirring and cutting effects.

[0191] These various patterns must be appropriately selected depending on the characteristics of the electrode material.

[0193] FIG. 11 illustrates another embodiment of the connection relationship of the rolls of a self-supporting film forming device by two-speed rolling according to the present invention.

[0194] Referring to FIG. 11(a) and FIG. 11(c), a structure is illustrated in which a circular concave portion is formed in the disc wing (323-1) so that the end of the rolling roll (320-1) can be inserted.

[0195] This is a case where a disc wing (323-1) having a circular concave portion is used so that the end portion of the rolling roll (320-1) can be partially inserted.

[0196] Referring to FIG. 11(b), the electrode material is formed at the gap d1 between the first rolling roll (310) and the second rolling roll (320), but since the gap d2 between the first rolling roll (310) and the disc wing (323) is very small, when the first rolling roll (310) and the second rolling roll (320) rotate relative to each other to perform a rolling operation, a strong pressure is applied at P1, the point where the disc wing (323) and the second rolling roll (320) meet, causing the disc wing (323) and the second rolling roll (320) to spread apart and a gap to form.

[0197] Due to this tendency, fibers such as PTFE and CNT may get caught in P1, frequently resulting in the edges of the electrode film not being smooth.

[0198] As illustrated in FIG. 11(a) and FIG. 11(c), if a disc wing (323-1) having a circular concave portion is used so that the end portion of the rolling roll (320-1) can be partially inserted, the tendency for the disc wing (323) and the second rolling roll (320) to separate and create a gap can be prevented, so that the powder compressed between the rolls is not concentrated at the point (P1) where the disc wing (323-1) and the rolling roll (320-1) meet, and can be formed uniformly.

[0199] However, the second rolling roll (320) is characterized by being longer than the first rolling roll (310) by the depth into which it is inserted into the disc wing (323-1).

[0200] The depth at which the end of the second rolling roll (320) is inserted into the disc wing (323-1) is set to 2 mm in the present invention, but generally, in almost all cases, it is preferable to insert it to a depth in the range of 1 to 10 mm.

[0202] FIG. 12 illustrates various embodiments of the roll surface roughness of a self-supporting film forming device by two-speed rolling according to the present invention.

[0203] Referring to Fig. 12, three different surface roughness Rz rolls are shown to verify the surface roughness effect of the rolling rolls.

[0204] [Example 1]

[0205] To verify the effect of surface roughness on rolling rolls, rolls with three different surface roughness Rz are shown.

[0206] The rolling roll has a diameter of 60 mm and a rolling area length of 100 mm, and is rotary polished to have surface roughness, so that circumferential grooves are formed on the surface.

[0207] The surface roughness characteristics of the three rolls are as shown in Table 1 below. The machining method is such that R601 is ground using an abrasive stone, while R602 and R603 are machined on a lathe to have different surface roughness.

[0208] The data in Table 1 were measured using a Keyence (Japan) VHX-X1F digital microscope, and the samples were from standard rolls R2 with a diameter of 60 mm. These rolls were used to form the anode film. The composition of the powder for manufacturing the anode film was, by weight, 95% NMC532 (Umicore, Belgium), 3% PTFE (China), 1.5% multi-wall CNT (JEIO CNT, Korea), and 0.5% Ketjen Black (Ketjen Black 600JD). After the mixed powder was properly mixed in a blender with applied shear force, it became a powder in the form of pellets with fiberization, and this powder was fed into the molding machine of Fig. 1.

[0209] A self-standing film can be obtained by rotating R2 of Table 1 and R1 having a disc-shaped blade, respectively, and introducing the above-mentioned mixed powder between them. The diameter of the rolls used at this time is 60 mm and the length is 100 mm.

[0210] Powder introduced through a device such as that shown in FIG. 1 enters between a pair of forming rolls, namely a disc attachment roll (310) and a general roll (320), which rotate in opposite directions at different speeds through a hopper, and is discharged in the form of a film. The temperature of the self-standing film forming machine was selected and maintained at either 90°C or 120°C.

[0211] As a result of the basic experiments of the present invention, it was found that the moldability was poor in rolls with roughness (Rz, Sz) of 1.0 μm or less. This is because the contact angle is lowered due to the smooth surface, preventing the powder from being sufficiently placed between the rolls and causing it to slip, making homogeneous molding impossible. On the other hand, when using rolls with an appropriately rough surface, the self-standing film surface showed smoother and more homogeneous molding results. On well-polished surfaces with low roughness, molding did not occur and the material tended to break. Therefore, in the present invention, experiments were basically conducted using rolls with roughness Rz, Sz of 1.0 μm or more. The surface of the roll used for two-speed rolling is shown in FIG. 12.

[0212] Characteristics of self-standing film according to R601 rotation speed ratio (Gap: 200 μm) R601 Measurement characteristics Surface roughness characteristics of R601 Surface roughness and physical properties of self-supporting films Rotation speed ratio λ (Gap: 200 μm), molding temperature 120℃ 5 10 20 40 Roughness characteristics Sa (μm) 0.36 0.52 0.53 0.48 0.63 Sz (μm) 2.92 6.97 6.2 4.81 5.86 Ssk 1.1 1.23 0.93 0.42 0.11 Sku 1.82 7.82 5.95 3.77 3.26 W (μm) 75.88 501 400 453 467 Density (g / cm³) 2.43 2.43 2.43 2.38 Thickness (μm) 252 248 251 248

[0213] The gap between the rolls (gap 1) was 200 μm, and the surface roughness of the roll (R601) in Table 1 was Sa 0.36 and Sz 2.92 μm. The thickness of the self-standing film obtained after forming was approximately 250 μm, and the density was approximately 2.4 g / cm³. One of the characteristics of the R601 roll is that although the roll roughness exhibits low values, the formed self-standing film has Sz, Ssk, and Sku values ​​that tend to decrease with increasing rotational speed ratio. This is because as the speed ratio increases, the shear softening phenomenon becomes dominant, causing the values ​​to actually decrease. The phenomenon where Rku and Rsk decrease with higher speed ratios appears as the opposite in R602 and R603, which have high Rz values ​​on the roll surface.

[0214] Characteristics of self-standing film according to R602 rotation speed ratio (Gap 1: 200 μm) R602 Measurement characteristics Surface roughness of R602 Surface roughness and physical properties of self-supporting films Rotation speed ratio λ (Gap: 200 μm), molding temperature 90℃ 5 7 10 Roughness characteristics Sa (μm) 1.8 0.82 0.93 0.98 Sz (μm) 7.81 8.39 9.33 11.66 Ssk 4.3 0.39 0.49 0.56 Sku 3.51 3.9 3.92 4.7 W (μm) 216 739 740 774 Density (g / cm³) 2.36 2.28 2.10 Thickness (μm) 278 270 273

[0215] Characteristics of self-standing film according to R603 rotation speed ratio (Gap 1: 200 μm) R603 Measurement characteristics Surface roughness characteristics of R603 Surface roughness and physical properties of self-supporting films Rotation speed ratio (Gap: 200 μm), molding temperature 90℃ 1:5 1:7 1:10 Roughness characteristics Sa (μm) 2.52 0.74 0.83 0.9 Sz (μm) 10.54 7.21 10.26 14.7 Ssk 5.55 0.16 1.27 1.77 Sku 4.99 2.96 7.27 12.8 W (μm) 269 630 706 700 Density (g / cm³) 2.23 2.11 2.12 Thickness (μm) 279 285 278

[0216] Tables 2 and 3 show that for rolls with very high surface roughness, the Sz, Ssk, and Sku values ​​tend to increase as the rotational speed ratio increases. Therefore, for self-standing films obtained using rolls with high surface roughness, the detachment of crystal grains and increased inhomogeneity can be expected.

[0217] The change in W value according to the rotational speed ratio increases slightly as the speed ratio increases, so this value appears to be unrelated to the W value of the forming roll surface.

[0218] The thickness after compression with aluminum foil, i.e., lamination, decreases by 25–35% to a range of 185–202 μm, and the density increases to 3.2–3.4 g / cm³. The values ​​of surface roughness after compression with the self-standing film are shown in Table 4.

[0219] Surface roughness of self-supporting film formed with R601 after compression Roll 601, speed ratio 1:5 (200 rpm), forming temperature 90 ℃ Surface roughness of self-supporting film Fig. 14(a) Surface roughness after compression Fig. 14(b) Sa μm 0.97 0.15 Sz μm 14.23 2.03 Ssk 0.96 0.22 Sku 5.92 4.27 W μm 525 316

[0221] FIG. 13 illustrates the change in surface roughness of a self-standing film according to the speed ratio of the rolling rolls of R 401 of the self-standing film forming device by two-speed rolling according to the present invention.

[0222] Referring to FIG. 13, a graph is shown of the change in surface roughness of a self-standing film according to the rotational speed ratio (λ) (d1: 100 μm) of the rolling roll of R 401 of the self-standing film forming device by two-speed rolling according to the present invention.

[0223] As the rotational speed ratio (λ) increases, the surface roughness also increases, and when the rotational speed ratio (λ) is 10, the surface roughness reaches a maximum and then shows a decreasing trend.

[0224] This phenomenon is identical to Region 2 in Fig. 3. It can be seen that the surface roughness value increases up to a rotational speed ratio (λ) of 10 and then decreases above that, and a desirable rotational speed ratio (λ) is observed at a value of 10 or higher, and it is expected that there will be less loss of crystal grains due to the lowered Ssk, Sku, and Sz.

[0225] These results are obtained at a temperature of 80°C, but if the forming operation is performed at 120°C, a surface with much higher smoothness can be obtained, and if the experiment is conducted at a higher temperature, the surface roughness decreases and the applied torque is measured to be lower.

[0226] Furthermore, since these results may vary when using different binder materials or different anode crystals, the present invention exhibits a general trend: at low speed ratios, frictional force acts predominantly, resulting in a region where torque and surface roughness increase, whereas at high speed ratios, a region where torque and surface roughness decrease due to shear softening appears.

[0227] We will examine this in more detail in Example 2.

[0228] [Example 2]

[0229] The rolling roll has a diameter of 40 mm and a rolling area width of 100 mm, and is rotary polished to have a uniform surface roughness, so that circumferential grooves are formed on the surface.

[0230] The rotational speed ratio, the high-speed rotating roll R401 among the forming rolls, and the thickness, density, and roughness of the formed film are shown in Table 2. The gap between the rolls (d1) is 100 μm, and the surface of the R401 is polished using an abrasive stone. The temperature of the self-supporting film forming machine is maintained at 80℃.

[0231] Surface roughness of self-standing film according to rolling roll speed ratio (d1: 100 μm) of R401 R401 Measurement characteristics Surface roughness characteristics of R401 Surface roughness and physical properties of self-standing films Rotation speed ratio (Gap: 100 μm) Molding temperature 90℃ 1:5 1:10 1:20 1:40 Roughness characteristics Sa (μm) 0.22 0.51 0.46 0.53 0.33 Sz (μm) 2.33 6.57 8.8 7.09 3.01 Ssk 1.88 1.58 3.5 1.26 -0.07 Sku 7.38 10.1 25.76 8.39 3.4 W (μm) 26.08 330 333 323 318 Density (g / cm³) 2.4 2.39 2.25 2.41 Thickness (μm) 132 133 135 130

[0232] Looking at the results in Table 5, it can be seen that the roughness of the self-standing film increased significantly at a rotational speed ratio of 1:10 compared to 1:5, and then gradually decreased again at higher rotational ratios of 1:20 and 1:40. This phenomenon varies depending on the type, composition, and condition of the molding material. Generally, a more improved effect is observed at higher rotational ratios, and in this case, a very smooth film with low roughness can be obtained at a high rotational ratio of 1:40.

[0233] Thickness and density of self-standing film after compression according to rolling roll speed ratio (d1: 100 μm) of R401 Roll 401 Molding temperature 90℃ Thickness and density according to rolling roll speed ratio (Gap: 100 μm) (1:5) (1:10) (1:20) (1:40) self-standing electrode film Average thickness (㎛) 132 133 137 130 Average density (g / cm³) 2.40 2.39 2.28 2.41 Self-standing film portion after compression Average thickness (㎛) 99 92 96 86 Average density (g / cm³) 3.32 3.38 3.36 3.28 Thickness reduction rate (%) 25% 30.8% 32.1% 33.8%

[0234] When the above self-standing film and aluminum foil are compressed and bonded in a lamination roller, the thickness of the anode excluding the aluminum foil shows a decrease in thickness compared to the self-standing film state before compression, with a thickness reduction rate of about 25 to 34%, and the thickness of the anode film after compression also tends to decrease depending on the speed ratio.

[0236] FIG. 14(a) illustrates the surface condition of a self-standing film formed by the rolling roll of R 601 of the self-standing film forming device by two-speed rolling according to the present invention, and FIG. 14(b) illustrates the surface condition of a self-standing film formed by the rolling roll of R 601 of the self-standing film forming device by two-speed rolling according to the present invention after compression.

[0237] FIG. 14(a) shows that there are cases where a wavy pattern appears on the surface of a self-standing film by the rolling roll of R 601 of the self-standing film forming device by two-speed rolling according to the present invention.

[0238] FIG. 14(b) shows the surface condition of the self-supporting film after it has been pressed onto a metal aluminum foil through a lamination step.

[0239] According to the flowchart of the operation according to the present invention in FIG. 1, it is shown that the wavy pattern of the self-standing film caused by the difference in density that may be formed after such strong two-speed rolling can be significantly mitigated through the subsequent lamination step.

[0240] Ultimately, it shows that a homogeneous coating layer can be created without the need for separate grinding rolls, and these wavy patterns can always appear when rolling dry powder, and are caused by the so-called stick and slip phenomenon where particles stick to and slide off the roll surface when rolling between two rolls.

[0241] Since these wavy patterns sometimes provide loose passages that help the penetration of the electrolyte, they have the effect of reducing the tortuosity of ion movement among the electrode characteristics or lowering the curvature limit at which the electrode can be bent, so they are not always negative to the characteristics of the electrode. However, as described in FIG. 1, a complete electrode can be manufactured by only the lamination step (S600) of bonding with a metal aluminum foil after forming a self-supporting film, without going through the step of using a multi-stage calendering roll (S400) and the step of cutting the edges (S500).

[0243] FIGS. 15 and 16 illustrate a self-standing film with smooth edges formed by the self-standing film forming device by two-speed rolling according to the present invention, together with a comparative example.

[0244] Figures 15 and 16 show photographs of the edge patterns of the self-supporting films of the examples and comparative examples.

[0245] [Example 3]

[0246] The rolling roll has a diameter of 40 mm and a rolling area width of 100 mm. Experiments were conducted on the surface roughness and roughness pattern on the surface of the disc blade, and the results can be seen due to the difference between using a disc blade with a well-polished surface and using a disc blade with a rough surface.

[0247] FIG. 15(a) first shows the case where a disc blade polished with 2000 grit abrasive paper is used, and FIG. 15(b) shows the case where a disc blade polished with 120 grit abrasive paper is used.

[0248] Figure 15(a) shows the case where a disc with a better polished surface is used under the same conditions, and the wrinkles at the edges become larger, which may be the result of being stretched further by the adhesive force of the PTFE binder.

[0249] In contrast, FIG. 15(b) shows the case where a disc wing with a rough surface is used, creating a straighter edge.

[0250] Just like the surface of the grinding roll, it is desirable that the inner surface of the disc blade also has an appropriate roughness, that is, an Rz value of 1 to 20 μm.

[0251] FIG. 16(a) shows that the grooves of the roughness pattern of the disc wing are formed in the circumferential direction, and FIG. 16(b) shows that the grooves of the roughness pattern of the disc wing are formed radially.

[0252] You can see the difference between a pattern formed in a concentric circle by rotating it in a circumferential direction using Grit 120 abrasive paper and a pattern formed in a radial direction by grinding.

[0253] In the case of Fig. 16(a), the roll is stretched in the direction of rotation, and the smoothness is reduced, which can be said to be a result similar to using the disc wing with a well-polished surface of Fig. 15(a).

[0254] In contrast, since Fig. 16 (b) has the effect of cutting the powder and can obtain a relatively high smoothness, Fig. 16 (b) is a more preferred pattern for powders used in the scope to which the present invention is applied.

[0256] Figure 17 shows the edge roughness measured by standing a self-standing film vertically and then photographing its edge.

[0257] The edges of the film formed at a temperature of 120°C using a rolling roll Roll 601 were measured.

[0258] This shows the results of measuring the curvature or roughness of the edges using an optical microscope.

[0259] Edge roughness results of the self-supporting film. Roughness values ​​and density thickness according to the velocity ratio (λ). Roll 601, forming temperature 120℃ Edge roughness Speed ​​ratio λ 5 10 20 40 Ra(㎛) 1.04 2.09 1.95 1.55 Rz(㎛) 6.29 13.33 13.65 10.17 Rp(㎛) 2.46 4.24 7.05 3.73 Rv(㎛) 3.82 9.09 6.59 6.43 Rsk -0.66 -0.86 0.14 -0.55 Rku 3.56 4.61 3.48 3.79 Average thickness (㎛) 252 248 251 248 Density (g / cm³) 2.43 2.43 2.43 2.38

[0260] Figure 17 shows the edge of a self-standing film showing the results of Table 1 after it was set up vertically, and Table 7 shows the edge roughness values ​​measured in this way.

[0261] Looking at the Rz value, it is 14 μm or less, the Rsk value is lower than 0, indicating a smoother surface, and the Rku value is slightly higher than 3, showing slightly sharper edge curvature. Since the roughness is generally low, it can be said that the conditions are relatively suitable for production.

[0263] FIG. 18 shows an electron microscope image showing the magnetic edge of a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention.

[0264] Referring to Fig. 18, it can be seen that the smoothness of the magnetic edge of the molded self-supporting film is high, and that PTFE fibers surround the edge region, so that the phenomenon of crystal particles escaping from the edge during the film molding process can be prevented.

[0266] Figure 19 shows a photograph showing the edge roughness after lamination of a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention.

[0267] Figure 19(a) is a photograph of an anode pressed onto aluminum foil, and Figure 19(b) shows a magnified photograph of its edge.

[0268] From the enlarged photograph in Fig. 19(b), it can be seen that the curvature value is up to 60 μm, and generally, the curvature at the edge of the self-supporting film appears small, but it appears that the curvature increases after compression.

[0270] FIG. 20 shows a graph representing the characteristics of an electrode measured after lamination of a self-standing film formed by the self-standing film forming device by two-speed rolling according to the present invention.

[0271] A 2032 coin-type battery was fabricated to analyze the electrochemical characteristics of the electrode measured after lamination of the molded self-supporting film, and a battery with lithium metal as the counter electrode was fabricated to eliminate the negative electrode effect.

[0272] The electrolyte used is 1M LiPF6(EC / DEC. 1 / 1)+FEC 5 wt%, and the separator used is an Al2O3 coated PP separator with a thickness of 29 μm and a porosity of 43%.

[0273] Charging was performed in CCCV mode from 3.0 V to 4.2 V with a cut-off of 0.05 C, and discharging was performed in CC mode from 4.2 V to 3.0 V with a cut-off. The charging and discharging C-rates were 0.1 C, 0.5 C, 1.0 C, 2.0 C, and 0.1 C in sequence, and 5 cycles were performed at each C-rate condition.

[0274] The results do not show a significant difference depending on the velocity ratio, but the sample with a higher velocity ratio exhibits slightly higher discharge characteristics. In other words, this experiment proves that the sample formed with a high velocity ratio is internally more homogeneous and can have superior characteristics.

[0275] Through additional experiments manufacturing anodes with different materials, it can be seen that the rate ratio range with process stability varies.

[0276] The conclusions obtained from this experiment can generally be applied to almost all cases, including electrode materials, that is, when molding incompressible powders mixed with a small amount of binder material.

[0278] The present invention solves conventional problems by forming a self-standing film using a two-speed rolling method, and increases the homogeneity of the material by setting the rotational speed ratio (λ) high.

[0279] Conventionally, in order to increase the homogeneity of the material, it is necessary to gradually roll using several additional rolls, but the present invention can achieve the effect of increasing the homogeneity of the material simply by setting the rotational speed ratio (λ) of a pair of rolling rolls high.

[0280] In addition, conventional methods have problems with internal defects that may occur due to additional rolling after the powder is primarily formed into a plate when passing through multiple rolling rolls, but the present invention can avoid this.

[0281] In addition, since the cumulative height of the powder inside the hopper is also important in terms of the moldability and homogeneity of the material, in the present invention, a scatterer, which is a means to maintain a constant and uniform cumulative height of the powder, is inserted into the interior of the top of the hopper.

[0282] In addition, the present invention can apply a large number of shear deformations in a short period of time using a high-speed rotation ratio to obtain a sufficient kneading or polishing effect to improve the homogeneity of the self-standing film, and particularly enhance the effect by using a rolling roll having a unique roughness pattern and surface roughness.

[0283] As shown in Fig. 3, in order to improve formability, two-speed rolling must be performed under conditions with an appropriate range of shear force, so by selecting an appropriate surface roughness and roughness pattern of the rolling roll, it is possible to handle various materials. Explanation of the symbols

[0285] 10: Powder 20: Self-standing electrode film 100: Powder supply unit 110: Scatter 120: Distance sensor 130: Scatter drive motor 140 Scatter Drive Controller 150: Transfer device regulator 160: Powder conveying device 170: Powder storage silo 200: Hopper 210: Side panel 220: Distance sensor 230: Block 240: Side plate heating rod 300: Rolled Roll Assembly 310: 1st rolling roll 311: Roll Penetration Axis 312: Roll-through heating rod 320: Second rolling roll 322: Roll Penetration Axis 323: Disc wing 330: Bearing 331: Grooved bearing 340: Bearing block 341: Spacing adjustment spacer 342: Slide 350: Drive motor 360: T-shaped through-type worm gear 370: Worm gear through shaft 390: Chain 323-1: Disc wing with a cylindrical pattern 323-2: Disc wings with a radial pattern 323-3: Disc wings with a helical pattern 323-4: Disc wing with helical pattern (2) 323-5: Disc wings with a composite pattern

Claims

Claim 1 A self-standing film forming apparatus by two-speed rolling comprises: a hopper for supplying powder downward; a first rolling roll that rotates in close contact with the lower part of the hopper; a second rolling roll that rotates in close contact with the lower part of the hopper and the first rolling roll; and two disc blades attached to both ends of the second rolling roll; wherein both ends of the first rolling roll are in close contact with the inner surface of the two disc blades, and the surface roughness Rz of the inner surface of the disc blades is 1 to 200 μm, and the protruding area of ​​the inner surface of the disc blades cuts off the edge of the self-standing film, and the first rolling roll and the second rolling roll rotate in opposite directions and at different speeds to form and discharge the self-standing film, and the speed ratio of the first rolling roll and the second rolling roll is a region where the shear force decreases due to a shear softening phenomenon as the speed ratio increases. Device. Claim 2 A self-supporting film forming apparatus by two-speed rolling, characterized in that, in claim 1, the surface roughness Rz of at least one of the first rolling roll or the second rolling roll is 1 to 20 μm. Claim 3 A self-supporting film forming apparatus by two-speed rolling, characterized in that, in claim 1, the inner surface roughness of the disc wing has a roughness pattern, and the roughness pattern is radial, with grooves formed outward from the center of the roll. Claim 4 A self-supporting film forming apparatus by two-speed rolling, characterized in that, in claim 1, the inner surface roughness of the disc wing has a roughness pattern, and the roughness pattern is formed such that a groove extending outward from the center of the roll is inclined in a direction opposite to the rotational direction of the roll. Claim 5 A self-supporting film forming apparatus by two-speed rolling, characterized in that, in claim 1, the inner surface roughness of the disc wing has a roughness pattern, and the roughness pattern is formed such that a groove extending outward from the center of the roll is inclined in the direction of rotation of the roll. Claim 6 A self-supporting film forming device by two-speed rolling according to claim 4, characterized in that the first rolling roll rotates at a faster speed than the second rolling roll. Claim 7 A self-supporting film forming device by two-speed rolling according to claim 5, characterized in that the second rolling roll rotates at a faster speed than the first rolling roll. Claim 8 A self-standing film forming apparatus by two-speed rolling, wherein, in claim 1, the inner surface roughness of the disc wing has a roughness pattern, and the roughness pattern is characterized by a portion formed such that a groove extending outward from the center of the roll is inclined in the opposite direction to the rotation direction of the roll, and a portion formed such that a groove extending outward from the center of the roll is inclined in the rotation direction of the roll intersects with each other. Claim 9 A self-standing film forming apparatus by two-speed rolling according to claim 1, characterized in that the portion of the inner surface of the disc wing that comes into contact with the first rolling roll or the second rolling roll is formed concavely so that a portion of both ends of the first rolling roll or the second rolling roll is inserted therein. Claim 10 A self-standing film forming device by two-speed rolling according to claim 9, characterized in that the portion of the inner surface of the disc wing that comes into contact with the first rolling roll or the second rolling roll is formed concavely so that a portion of both ends of the first rolling roll or the second rolling roll is inserted 1 mm to 10 mm. Claim 11 The present invention relates to a self-standing film forming apparatus by two-speed rolling, comprising: a hopper for supplying powder downward; a first rolling roll that rotates in close contact with the lower part of the hopper; a second rolling roll that rotates in close contact with the lower part of the hopper and the first rolling roll; and two disc blades attached to both ends of the second rolling roll; wherein both ends of the first rolling roll are in close contact with the inner surface of the two disc blades, and the surface roughness Rz of at least one of the first rolling roll or the second rolling roll is 1 to 20 μm, and the protruding area of ​​the inner surface of the disc blade cuts off the edge of the self-standing film, and the first rolling roll and the second rolling roll rotate in opposite directions and at different speeds to form and discharge the self-standing film, and the speed ratio of the first rolling roll and the second rolling roll is characterized in that the shear force decreases due to a shear softening phenomenon when the speed ratio increases. Self-supporting film forming device by rolling at this speed. Claim 12 A self-supporting film forming apparatus by two-speed rolling, wherein, in claim 11, the surface roughness of at least one of the first rolling roll or the second rolling roll has a roughness pattern, and said roughness pattern is characterized by grooves being formed on the roll surface in the circumferential direction. Claim 13 A self-supporting film forming apparatus by two-speed rolling, wherein, in claim 11, the surface roughness of at least one of the first rolling roll or the second rolling roll has a roughness pattern, and the roughness pattern is characterized by zigzag-shaped grooves being formed on the roll surface in the circumferential direction. Claim 14 A self-supporting film forming apparatus by two-speed rolling, wherein, in claim 11, the surface roughness of at least one of the first rolling roll or the second rolling roll has a roughness pattern, and the roughness pattern is characterized by a wave-shaped groove being formed on the roll surface in the circumferential direction. Claim 15 A self-supporting film forming apparatus by two-speed rolling, characterized in that, in any one of claims 12 to 14, the depth of the groove is 20% or less of the thickness of the self-supporting film.

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