Plasma treatment method for improving insulation defects in battery cells and method for manufacturing a secondary battery including the same

Abstract

The present invention relates to a method for manufacturing pouch-type secondary batteries, and more specifically, to a plasma treatment method, a method for manufacturing secondary batteries, and a manufacturing apparatus that can improve the insulating performance of the pouch sealing. According to one embodiment of the present invention, a pouch-type secondary battery is provided, comprising a metal layer having a polypropylene coating layer formed on its lower surface, the polypropylene coating layer comprising an upper pouch case having a metal layer and a polypropylene coating layer formed on its upper surface, the polypropylene coating layer comprising a lower pouch case having a metal layer and a polypropylene coating layer formed on its upper and lower surfaces, and a battery cell having leads whose upper and lower surfaces are heat-fused together between the upper and lower pouch cases when the upper and lower pouch cases are sealed by heat fusion, wherein the pouch sheet is subjected to the plasma surface treatment up to the sealing region and the temporary bonding region near the sealing region.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a pouch-type secondary battery, and more specifically, to a plasma treatment method, a secondary battery manufacturing method, and a manufacturing apparatus capable of improving the insulation performance of the sealing of a pouch.

Background Art

[0002] A secondary battery is a battery that can be repeatedly used through a discharging process of converting chemical energy into electrical energy and a charging process of converting electrical energy into chemical energy.

[0003] The secondary battery may include a nickel-cadmium (Ni-Cd) battery, a nickel-metal hydride (Ni-MH) battery, a lithium-metal battery, a lithium-ion (Li-Ion) battery, and a lithium-ion polymer battery (hereinafter referred to as "LIPB").

[0004] The lithium secondary battery has a cycle life of about 500 cycles or more and a short charging time of about 1 hour to 2 hours, and is about 30% to 40% lighter than a nickel-metal hydride battery, so weight reduction is possible. Among existing secondary batteries, the voltage per unit battery (30 to 37V) is the highest, it has excellent energy density, and can have characteristics optimized for mobile devices.

[0005] The lithium secondary battery may be manufactured as a pouch-type secondary battery in which the battery cell is sealed with a pouch made of an aluminum sealing material.

[0006] A pouch-type secondary battery may include a battery cell housed in a pouch that acts as a sealing material, lead tabs electrically connected to electrode tabs of electrodes provided on the battery cell and extended to the outside of the pouch, and an insulating film that electrically insulates the lead tabs. In particular, the pouch can function to seal the battery cell housed inside by heat-sealing the inner surface of the pouch together with the insulating film formed on the lead tabs of the battery cell, or by directly heat-sealing the inner surfaces of the pouch to each other. The insulating film is generally made of polypropylene (PP) film.

[0007] Pouch sealing serves to seal a specific space within the pouch that contains the electrolyte. As battery cells are repeatedly charged and discharged, gas is generated, increasing the pressure inside the pouch. For this reason, high strength is required for pouch sealing.

[0008] On the other hand, during heat sealing of the pouch, the polypropylene (PP) film melts and diffuses to adhere. The polypropylene film not only adheres to the pouch, but also separates the metal layer of the pouch, such as aluminum, from the electrolyte, thereby preventing corrosion of the metal layer and preventing current from flowing through the pouch and increasing its resistance.

[0009] Korean Published Patent No. 10-2022-0154638 (hereinafter referred to as the "prior patent") discloses a method for manufacturing a pouch-type secondary battery to ensure uniform sealing of the pouch. In particular, it discloses a method of plasma-treating the pouch before sealing, in order to maintain uniformity of the sealing surface even over a wide temperature or pressure range.

[0010] However, prior patents only consider aspects such as plasma surface treatment and uniformity of the sealing surface, and do not consider aspects such as sealing strength, and in particular do not disclose the conditions, timing, and thermal fusion conditions for the plasma surface treatment. Therefore, there is a need to present a specific plasma surface treatment apparatus and process that can improve the sealing strength of the pouch.

[0011] Furthermore, the sealing surface of the pouch is formed not only between opposing pouches, but also between opposing pouches and leads. Therefore, the sealing strength between the pouch and the lead is also very important and must be taken into consideration.

[0012] Furthermore, during heat sealing of the pouch, a temporary bonding region is formed near the sealing area. That is, the opposing upper and lower polypropylene (PP) layers are melted and pressurized during the sealing process, causing them to detach from the sealing area, and the molten polypropylene moves into the inner area of ​​the pouch. At this time, a region is created where the molten upper and lower polypropylene layers that have detached from the sealing area bond to each other, and this can be called a temporary bonding region.

[0013] Unlike the heat-sealed sealing area, the temporary bonding area is not a pressurized area, and therefore the polypropylene bond thickness is relatively large, making it less resistant to high temperatures and potentially causing insulation problems. This is because if the bond in the temporary bonding area breaks due to an increase in the pouch's pressure resistance, the aluminum core may be exposed to the electrolyte. This is because the polypropylene coating layer, which provides insulation, may peel off and be removed.

[0014] Temporary adhesion zones and related problems can occur not only between pouches but also between pouches and leads. Therefore, resolving problems caused by temporary adhesion zones is an essential issue that must be addressed in pouch sealing.

[0015] The manufacturing of pouch-type secondary batteries is primarily focused on mass production rather than small-scale production, and since all processes are carried out sequentially, process efficiency, i.e., increasing the number of good products that can be produced per unit time, is extremely important. Therefore, there is a need to provide a plasma surface treatment apparatus and process, as well as pouch-type secondary battery manufacturing apparatus and process, that can be organically and easily integrated with conventional pouch-type secondary battery manufacturing processes and equipment, while also being easy to configure and control. [Overview of the Initiative] [Problems that the invention aims to solve]

[0016] The present invention aims to solve the problems of conventional pouch-type rechargeable batteries.

[0017] Through one embodiment of the present invention, a pouch-type secondary battery, a manufacturing apparatus therefor, and a manufacturing method therefor are provided that enhance the sealing strength of the pouch in the sealing region, prevent the occurrence of temporary bonding regions, and significantly reduce insulation defects in the pouch.

[0018] Through one embodiment of the present invention, a manufacturing apparatus and method for pouch-type secondary batteries are provided that can be easily integrated with conventional manufacturing apparatus and methods for pouch-type secondary batteries.

[0019] Through one embodiment of the present invention, a manufacturing apparatus and method for a pouch-type secondary battery are provided that enable continuous and organic plasma treatment of the surface of the pouch.

[0020] Through one embodiment of the present invention, a plasma surface treatment method is provided that can prevent the occurrence of temporary adhesion regions not only between pouches but especially between pouches and leads, or reduce the sealing strength in temporary adhesion regions, and a method for manufacturing a pouch-type secondary battery including the same. [Means for solving the problem]

[0021] To achieve the aforementioned objectives, according to one embodiment of the present invention, a pouch-type secondary battery manufacturing apparatus can be provided, which includes a moving stage on which a pouch before sealing is placed and which linearly moves the pouch in a first direction to form a first plasma electrode, a plasma head that forms a second plasma electrode and irradiates the surface of the pouch with a gas to generate plasma gas in order to improve the sealing strength of the pouch after sealing, and an AC power supply device that discharges the gas and applies an AC power supply between the first electrode and the second electrode so that the plasma gas is irradiated onto the surface of the pouch.

[0022] In this embodiment, plasma discharge can be continuously performed, and plasma treatment of the surface of the pouch can be carried out.

[0023] The plasma head is preferably provided so as to be separated in a second direction perpendicular to the first direction.

[0024] The plasma head may be fixed and provided so as to irradiate a gas downward vertically onto the surface of the pouch. Therefore, an efficient plasma treatment may be performed because the supply direction of the gas for discharge and the moving direction of the plasma gas are the same as the gravitational direction.

[0025] The moving stage is preferably provided so as to move the pouch at a constant speed. The moving stage is provided so as to move the pouch at a constant speed, and the plasma head may be supported by the moving stage and irradiate a gas for generating the plasma gas onto the surface of the moving pouch.

[0026] The plasma head preferably continuously supplies a gas for plasma discharge at a constant flow rate.

[0027] The gas discharged during plasma generation may contain argon (Ar). The argon is preferably continuously injected at a flow rate of 6 LPM.

[0028] The gas discharged during plasma generation may contain nitrogen (N2) or oxygen (O2). The nitrogen or oxygen may be continuously injected at a flow rate of 40 to 60 sccm.

[0029] The linear moving speed of the pouch before sealing is preferably 10 mm / s to 120 mm / s. A decrease in the linear moving speed under the same plasma conditions means an increase in the plasma treatment intensity.

[0030] The AC power supply device may be provided so as to discharge a gas with a power of 180 W to 200 W. ​ It is preferable to seal the pouch by heat-sealing the surface-treated pouch through the aforementioned plasma gas. That is, it is preferable to plasma-surface-treat the sealing region of the pouch, and then, after the sealing regions overlap, seal it by heat-sealing. By performing plasma surface treatment on the sealing region, the sealing strength can be improved.

[0032] Furthermore, it is preferable to perform plasma surface treatment on the area near the sealing region, i.e., the temporary bonding region into which the molten PP layer in the sealing region flows. The upper and lower temporary bonding regions are regions that do not overlap with each other and are regions where thermal fusion does not occur. By performing plasma surface treatment on the temporary bonding region, the sealing strength can be significantly reduced.

[0033] On the other hand, it is preferable that the surface of the pouch is plasma-treated in the lead region where the lead penetrates and sealing takes place, while the lead itself is not plasma-treated. This allows for increased sealing strength in the sealing region between the pouch and the lead, while significantly reducing sealing strength in the temporary bonding region between the pouch and the lead.

[0034] The heat fusion may be performed at 210 degrees Celsius and under a pressure of 0.3 MPa for 1.2 seconds.

[0035] To achieve the aforementioned objectives, according to one embodiment of the present invention, a method for manufacturing a pouch-type secondary battery is provided, comprising: a pouch supply step of continuously moving a pouch sheet having a metal layer coated with a polypropylene layer on a moving stage; a plasma surface treatment step of applying an AC power supply between the moving stage and a plasma head and discharging a gas irradiated from the plasma head to irradiate the surface of the polypropylene layer of the pouch sheet with plasma gas; a casing step of forming a pouch case together with a battery cell having leads having a metal layer coated with a polypropylene layer by molding the plasma surface-treated pouch sheet; and a pouch sealing step of sealing the pouch case by forming a sealing region through thermal fusion, wherein the plasma surface treatment is performed on the pouch sheet up to the sealing region and the temporary bonding region near the sealing region.

[0036] The plasma surface treatment may be omitted from the leads that penetrate the sealing region. Furthermore, the plasma surface treatment may be omitted from the leads that penetrate the temporary bonding region. Therefore, it is preferable that no separate plasma surface treatment is performed on the fluoropropylene layer of the leads.

[0037] Preferably, the sealing strength in the sealing region between the pouch sheet and the lead is three times greater than the sealing strength in the temporary bonding region between the pouch sheet and the lead. In other words, it is preferable that the sealing strength in the temporary bonding region is less than one-third of the sealing strength in the sealing region, or even lower.

[0038] If the sealing strength is high in the temporary bonding area, when the sealing in the temporary bonding area is damaged, the conventional polypropylene layer of the pouch and / or lead may be damaged, exposing the metal layer to the electrolyte. On the other hand, if the sealing strength is low in the temporary bonding area, when the sealing in the temporary bonding area is damaged, it does not affect the conventional polypropylene layer of the pouch and / or lead. Therefore, since the metal layer is still protected by the polypropylene layer, damage to the insulating performance can be prevented.

[0039] The sealing strength in the temporary bonding region between the pouch sheet and the lead is preferably less than 40 N / 15 mm. Such a sealing strength is significantly lower than the sealing strength when plasma surface treatment is not performed.

[0040] It is preferable that adhesion does not occur between opposing polypropylene layers in the temporary bonding region between the pouch sheet and the lead. That is, the temporary bonding region itself may be formed, but adhesion of the PP layers in the temporary bonding region may be intentionally excluded.

[0041] To achieve the aforementioned objectives, a pouch-type secondary battery may be provided, comprising: an upper pouch case having a metal layer and a polypropylene coating layer formed on its lower surface, the polypropylene coating layer comprising an upper pouch case having a metal layer and a polypropylene coating layer formed on its upper surface, the polypropylene coating layer comprising a lower pouch case having a metal layer and polypropylene coating layers formed on its upper and lower surfaces, and a battery cell having leads whose upper and lower surfaces are heat-fused together between the upper and lower pouch cases when the upper and lower pouch cases are sealed by heat fusion, wherein the upper or lower pouch case is subjected to the plasma surface treatment up to the sealing region and the temporary bonding region near the sealing region.

[0042] Preferably, the sealing strength in the sealing region between the upper or lower pouch case and the lead is three times or more greater than the sealing strength in the temporary bonding region between the upper or lower pouch case and the lead.

[0043] It is preferable to eliminate plasma surface treatment of the polypropylene coating layer of the lead.

[0044] The sealing strength in the temporary bonding area between the upper or lower pouch case and the lead may be less than 40 N / 15 mm.

[0045] In the upper or lower pouch case, the carbon atom ratio on the plasma-treated surface may be lower than the carbon atom ratio on the surface that has not been plasma-treated. [Effects of the Invention]

[0046] Through one embodiment of the present invention, it is possible to provide a pouch-type secondary battery, a manufacturing apparatus therefor, and a manufacturing method therefor, which enhances the sealing strength of the pouch in the sealing region, prevents the occurrence of temporary bonding regions, and significantly reduces insulation defects in the pouch.

[0047] Through one embodiment of the present invention, it is possible to provide a manufacturing apparatus and method for pouch-type secondary batteries that can be easily integrated with conventional manufacturing apparatus and methods for pouch-type secondary batteries.

[0048] Through one embodiment of the present invention, a manufacturing apparatus and method for pouch-type secondary batteries can be provided that enable continuous and organic plasma treatment of the surface of the pouch.

[0049] Through one embodiment of the present invention, a plasma surface treatment method and a method for manufacturing a pouch-type secondary battery including the same can be provided, which can prevent the occurrence of temporary adhesion regions not only between pouches but especially between pouches and leads, or reduce the sealing strength in temporary adhesion regions. [Brief explanation of the drawing]

[0050] [Figure 1] This is a conceptual diagram of a pouch-type secondary battery manufacturing apparatus according to one embodiment of the present invention. [Figure 2] This is a diagram of the unfolded unit pouch. [Figure 3] This is a disassembled perspective view of a pouch-type rechargeable battery before casing. [Figure 4] This is a perspective view of a pouch-type rechargeable battery after casing. [Figure 5] This is a manufacturing flow for a pouch-type secondary battery according to one embodiment of the present invention. [Figure 6] This is a schematic diagram showing the cross-sectional changes between the sealing area and the temporary adhesion area during pouch sealing. [Figure 7] This is a schematic diagram of a pouch-type secondary battery manufacturing apparatus according to one embodiment of the invention. [Figure 8] This is a table of plasma treatment and sealing process variables and sampling methods. [Figure 9] This is a cross-sectional image of the sealing area and temporary bonding area in the pouch and lead portion. [Figure 10] This is a cross-sectional image of the pouch portion, the sealing area within the pouch portion, and the temporary bonding area. [Figure 11] This graph shows the change in sealing strength from the temporary bonding area to the sealing area. [Figure 12] This is a graph comparing the strength in the temporary bonding area and the sealing area. [Modes for carrying out the invention]

[0051] A pouch-type secondary battery manufacturing apparatus according to one embodiment of the present invention will be described in detail below with reference to the attached drawings.

[0052] First, with reference to Figure 1, the apparatus and method for plasma surface treatment of pouches will be described.

[0053] The pouch 10 is placed on a moving stage 20, which may be configured to move the pouch linearly in a first direction.

[0054] The pouch 10 may be moved linearly together with the moving stage 20, or the pouch 10 may be moved linearly on the moving stage 20 alone. Here, it is preferable that the pouch 10 is moved horizontally. For example, it is preferable that the pouch is moved in the longitudinal direction (pouch supply direction) while the upper surface facing the plasma head remains horizontal.

[0055] A plasma head 30 may be provided at a position separated from the moving stage 20. The plasma head 30 may be configured to supply plasma gas 40 to the surface of the pouch 10. The plasma head 20 may have a width corresponding to the length of the width of the pouch 10. Therefore, it may be configured to supply plasma gas 40 corresponding to the entire width of the pouch 10.

[0056] The plasma head may be fixed in a position perpendicular to the first direction. Therefore, plasma gas 40 is continuously supplied to the fixed plasma head, and the pouch 10 can continuously pass through the plasma section or region to which the plasma gas 40 is supplied. At this time, plasma surface treatment is performed on the pouch 10.

[0057] The pouch 10 forms a bag that houses the battery cells inside. Specifically, a sheet-like pouch 10 is cut and molded, and the frame surfaces of opposing pouches are heat-fused together to seal the battery cells inside.

[0058] According to this embodiment, plasma surface treatment may be performed not only on the frame surface of the pouch that is heat-sealed, but also on the inner surface of the pouch that is in close contact with the battery cell. In other words, according to this embodiment, the pouch that undergoes plasma surface treatment may be a pouch before sealing, but also a pouch sheet before cutting and molding for bag formation.

[0059] When plasma surface treatment is performed on a pouch sheet, it may be possible to perform the plasma surface treatment continuously and automatically. In particular, since only a part of the pouch, especially the sealing part, is not plasma surface treated, the subsequent process is very simple. For example, when plasma surface treatment is performed on four frame surfaces of a rectangular pouch, continuous plasma surface treatment is not easy.

[0060] As shown in Figure 2, the single pouch 10 forming the single pouch-type secondary battery may be cut from the pouch sheet and formed as a thin rectangular sheet.

[0061] The pouch sheet may be formed by providing polypropylene layers on the outer and inner surfaces of an aluminum sheet. That is, when a sealing material is formed with a pouch sheet, the outer surface of the polypropylene forms the outer surface of the pouch, the inner surface of the fluoropropylene forms the outer surface of the pouch, and the aluminum sheet is not exposed to the outside air and the internal electrolyte.

[0062] As shown in the diagram, the frame surfaces 13, 14, 15, and 16 of the single pouch 10 may form a sealing region 11. The inner region of the sealing region 12 may form a cell region 12 in which a battery cell is in close contact and filled with electrolyte.

[0063] A folding portion 17 may be formed in the middle of the cell region 12, and after battery cells are placed in either of the cell regions 12 on either side of the folding portion, the left and right cell regions 12 and the sealing region 10 may overlap with the folding portion as the center. After that, pouch sealing is performed by heat fusion of the sealing region 11.

[0064] If there is no folding section, the unit pouch sheet 10 shown in Figure 2 may be the upper and lower casings of the pouch casing. Since the upper and lower casings are positioned facing each other and then sealed, the sealing area 11 appears in the same manner. However, if there is a folding section, sealing is unnecessary due to the folding section, so sealing may be performed with three line segments, and if there is no folding section, sealing may be performed with four line segments.

[0065] As can be seen, if only the sealing region 11 shown in Figure 2 is to be plasma surface treated, the plasma surface treatment process becomes very complex. First, the left and right frame surfaces 13 and 14 must be plasma treated intermittently, and then, after rotating the pouch 10 by 90 degrees, the upper and lower frame surfaces 15 and 16 must be plasma treated intermittently. Therefore, at least two plasma heads are required, and the widths of the plasma heads may differ from each other.

[0066] Ultimately, when only the sealing region 11 is plasma surface-treated, plasma control is not easy, and the equipment becomes complex. In particular, the plasma surface treatment must be performed uniformly across the entire sealing region 11, but uneven plasma treatment areas can occur on the frame surface at the edges. This is because rotation of the pouch 10 is necessary when plasma treating the entire sealing region 11. In this case, some areas may not be plasma surface-treated, while other areas may be treated overlappingly.

[0067] Furthermore, when performing plasma surface treatment only on the sealing region 11, this must be done after cutting the sheet-like pouch. This is because the direction of travel of the pouch relative to the plasma processing device must be changed. Therefore, it is not easy to perform plasma surface treatment while transporting the pouch sheet in a roll-to-roll (RtoR) configuration.

[0068] On the other hand, according to one embodiment of the present invention, plasma surface treatment may be performed only on one surface of the pouch corresponding to the inner surface before sealing, and plasma surface treatment may not be necessary on the other surface of the pouch corresponding to the outer surface.

[0069] According to one embodiment of the present invention, it is not necessary to change the position of the pouch, and in particular, the number of plasma heads can be reduced. For example, a sheet-like pouch can be passed continuously through a single plasma head. In particular, as shown in Figure 2, plasma treatment may be performed on the entire region of the pouch without dividing it into a sealing region 11 and a cell region 12. That is, plasma surface treatment can be performed very easily on the entire polypropylene coating layer corresponding to the inner surface of the pouch.

[0070] In short, according to this embodiment, plasma treatment is performed on the entire surface of one side of the pouch sheet before cutting it into a single pouch and before sealing, enabling a highly effective and simple device configuration and control logic.

[0071] On the other hand, when pouch sealing is performed in the unit pouch 10 shown in Figure 2, a temporary bonding region 19 may be formed between the sealing region 11 and the cell region 12. The temporary bonding region 19 can also be described as a temporary bonding region that is generated when the molten polypropylene sealing region 11 moves to the cell region 12 when the opposing polypropylene layers are heat-fused.

[0072] The temporary bonding region 19 is an area where adhesion occurs in an unintended location during the heat fusion process. Cracks occurring in the temporary bonding region 19 can expose the internal metal layer of the pouch or lead, shortening the lifespan of the secondary battery and causing insulation failure, leading to performance degradation. Such cracks in the temporary bonding region 19 are more likely to occur between the pouch and the lead than between the pouches themselves.

[0073] The battery cell leads penetrate the sealing area 11 in the cell area 12 and are located outside the pouch. The upper surface of the leads is heat-sealed to the upper pouch case, and the lower surface of the leads is heat-sealed to the lower pouch case. The thickness of the leads complicates the cross-section of the sealing, increasing the risk of stress concentration when the internal pressure of the pouch rises. Therefore, crack formation problems may occur more frequently in the temporary bonding area between the pouch and the leads than in the temporary bonding area between the pouches.

[0074] According to one embodiment of the present invention, by intentionally reducing the sealing strength in the temporary bonding area, adhesion at unintended locations can be prevented, thereby resolving the problem of insulation failure. In particular, by significantly reducing the sealing strength in the temporary bonding area between the pouch and the lead, or by eliminating adhesion in the temporary bonding area, it is possible to provide a pouch-type secondary battery that enhances durability and prevents performance degradation.

[0075] Figures 3 and 4 show an example of a pouch-type secondary battery in which the unit pouches are formed separately at the top and bottom and then sealed together.

[0076] The upper pouch 10a and the lower pouch 10b may each be referred to as a unit pouch, and all of them may be plasma surface treated as described above.

[0077] The upper pouch 10a and the lower pouch 10b each have a sealing area 11 and a cell area 12, respectively, into which the battery cell 50 is inserted. The battery cell 50 has leads 51 and 52, and the leads may be divided into an anode lead 51 and a cathode lead 52.

[0078] The leads 51 and 52 penetrate from the cell region 12 through the sealing region 11 during pouch sealing and are exposed to the outside of the pouch-type secondary battery as shown in Figure 4.

[0079] Figure 4 shows the AA' and BB' cross-sections. The AA' cross-section is a cross-section where a lead is interposed between two pouches for sealing, and the BB' cross-section is a cross-section where two pouches are sealed together. A detailed explanation of these cross-sectional images will be provided later with reference to Figures 9 and 10.

[0080] A method for manufacturing a secondary battery according to one embodiment of the present invention will be described in detail below with reference to Figure 5.

[0081] The manufacturing process for pouch-type secondary batteries includes electrode processes, assembly processes, and chemical processes, and this embodiment may particularly relate to the assembly process.

[0082] First, a pouch that forms a bag, or case, for a pouch-type secondary battery may be provided (S10). That is, a pouch supply step may be performed. The pouch here is preferably a sheet-shaped pouch. Therefore, the pouch may be moved continuously on a moving stage using a roll-to-roll mechanism. Here, the moving stage may be a horizontal stage or a roll-shaped stage.

[0083] If the moving stage is a horizontal stage, the moving stage may move linearly together with the sheet-like pouch, and the plasma surface treatment of the pouch may be performed while the stage is moving linearly.

[0084] If the moving stage is roll-shaped, the sheet-like pouch can move linearly while the roll rotates. Of course, the roll may only rotate in a fixed position without moving linearly. In this case, the pouch sheet may be supported by the roll, and the plasma surface treatment may be performed while it is supported by the roll.

[0085] In this case, it is preferable that the pouch sheet is a roll of pouch sheets before cutting, rather than pouches that have been cut for the production of a single pouch-type battery.

[0086] Plasma surface treatment is performed on the supplied pouch sheet (S20). That is, a plasma surface treatment step may be performed. Plasma surface treatment may be performed by continuously irradiating the surface of the pouch sheet with plasma gas from a plasma head, as described above. In this case, it is preferable that the plasma head irradiates the plasma gas substantially corresponding to the entire width of the pouch sheet. Therefore, by the pouch sheet passing through the plasma head at a constant speed, plasma treatment may be performed substantially on the entire surface of the pouch sheet. Of course, here, the surface refers to the surface that will form the inner surface in the subsequent pouch case, so plasma treatment on the surface that will form the outer surface of the subsequent pouch case would be meaningless.

[0087] After the plasma treatment of the pouch sheet is completed, the pouch sheet is molded to form a pouch case together with the battery cells (S30). That is, a casing step may be performed. Specifically, the roll of pouch sheet may be cut into unit pouches. After the battery cells are tightly attached to the cut unit pouches, a pouch case can be formed. At this time, the pouch may be formed to create a space into which the battery cells are inserted. The unit pouch may be in a form in which the upper case and lower case of the pouch case are connected through a folding part, and each of the upper case and lower case, which are separated from each other, is also called a unit pouch.

[0088] After a pouch case containing the battery cells is formed, the pouch case may be sealed by heat fusion (S40). That is, a pouch sealing step may be performed. Here, the pouch sealing may be performed except for a path through which the electrolyte can be injected into the pouch case. After the electrolyte has been injected, the injection port may be further sealed.

[0089] The sealing process will be explained in more detail through Figure 6.

[0090] The pouch 10 may include a pouch layer 110 having an internal core, i.e., a metal layer. The outer surface of the pouch layer 110 may be coated with a polyethylene (PET) layer. The inner surface of the pouch layer 110 may be coated with a polypropylene (PP) layer. As described above, it may also include a surface layer 130 modified through polypropylene plasma surface treatment and an unmodified core layer 120.

[0091] The sealing blocks move above and below the frames of the opposing pouches 10 to seal the pouches. At this time, not only compressive force but also heat is applied. As shown in Figure 6(a), during heat fusion, the opposing modified surface layers 130 melt and adhere to each other to form a single bonded PP layer 140.

[0092] As the heat fusion progresses, the polypropylene layer moves to the cell region, as shown in Figure 6(b), and a temporary bonding region is formed. At this time, only the surface layer 130, not the core layer 120 of the PP layer, may move to the temporary bonding region. In other words, the plasma-surface-treated PP, rather than the unmodified PP that has not undergone plasma surface treatment, will move to the temporary bonding region.

[0093] As shown in Figure 6(c), the PP of the surface layer 130 moves to the temporary bonding region, but the upper PP surface layer and the lower PP surface layer do not bond in the temporary bonding region. In other words, in the temporary bonding region, the upper PP surface layer and the lower PP surface layer only make vertical contact with respect to the interface and do not bond to each other.

[0094] The plasma surface treatment method and configuration according to this embodiment will be described in detail below.

[0095] In this embodiment, the plasma treatment technique refers to direct plasma. In direct plasma, radicals, ions, and electrons within the plasma all act on the sample, and their high energy makes it easy to break molecular bonds and form new ones. When this is applied to the plasma surface treatment of a pouch, it means that the pouch is placed in the plasma generation space. That is, as shown in Figure 1, the plasma head 30 and the stage 20 function as the anode and cathode, respectively. An AC voltage is applied between the plasma head 30 and the stage 20, and a gas is discharged to generate plasma gas, which then affects the surface of the pouch.

[0096] As shown in Figure 7, the plasma generator 50 includes a moving stage 20 and a plasma head 30, where the moving stage 20 functions as the first electrode and the plasma head 30 functions as the second electrode. The first electrode may be a cathode, in which case the second electrode becomes the anode. The anode and cathode are connected to an AC power supply 54, which can provide power for plasma generation. That is, the space between the moving stage 20 and the plasma head 30 becomes the plasma generation space, and plasma gas generated by the discharge of gas may act on the surface of the pouch 20 to perform plasma surface treatment.

[0097] The plasma head 30 is equipped with a nozzle 31. A gas to be discharged is irradiated toward the pouch 10 through the nozzle 31. The irradiated gas is discharged by a strong electric field formed between the plasma head 20 and the moving stage 30 and converted into plasma gas.

[0098] Surface treatment may be performed by continuously irradiating the pouch with pressure, causing the plasma gas to collide with the pouch surface and modify the polypropylene layer on the pouch surface.

[0099] When using direct plasma, the active gas, such as nitrogen or oxygen, may discharge and directly act on the sample. However, gases such as nitrogen and oxygen are relatively difficult to generate into plasma at low power. Therefore, it is preferable to use argon gas, which can be generated into plasma through relatively low power.

[0100] In other words, an argon atmosphere may be formed in the space between the plasma head 30 and the moving stage 20, and small amounts of nitrogen or oxygen may be irradiated. The high-energy argon plasma transfers energy to the nitrogen and oxygen gases, causing them to be converted into plasma. Therefore, the argon gas in this case can be considered a carrier gas that supplies nitrogen and oxygen plasma gas to the surface of the pouch.

[0101] In conclusion, it was found that after plasma treatment, radicals and other substances react with the surface of the polypropylene pouch, increasing its surface energy. Subsequently, during melting at high temperatures, cohesive forces are generated between the different surfaces, making sealing easier.

[0102] To verify the effect of using indirect plasma to improve the sealing strength of pouches, the following examples and comparative examples were conducted.

[0103] -Example 1- A plasma was formed by continuously injecting 40 sccm of nitrogen (N2) gas and 6 LPM of argon (Ar) gas, and discharging the gas with 200 W of power. The plasma was generated as it was ejected through the plasma head 30 according to the gas flow rate. The pouch 10 passed through the injection section at a linear velocity of 120 mm / s. Subsequently, the plasma-treated pouch was heat-pressed for 1.2 seconds at a temperature of 210 degrees Celsius and a pressure of 0.3 MPa, and pouch sealing was performed by thermal fusion. Since the surface treatment effect of the plasma changes over time, the heat-pressure after plasma surface treatment was performed within 5 minutes.

[0104] -Example 2 The pouch line speed was set to 60 mm / s. All other conditions were the same as in Example 1.

[0105] -Example 3 The pouch line speed was set to 10 mm / s. All other conditions were the same as in Example 1.

[0106] - Comparative Example 1 No plasma treatment was performed, and the same thermal fusion sealing conditions as in Example 1 were used.

[0107] Figure 8 is a table showing the sealing process variables and sampling methods.

[0108] The sealing strength of the sealed pouches was measured using the tensile strength measurement function of a universal testing machine (UTM), measuring the force from sampling until the seal broke. The UTM was operated at a constant speed of 5 mm / min to break the seal, and the average force measured from 4.5 kgf up to 8 mm was recorded.

[0109] As shown in the diagram, cross-sectional image capture and sealing strength measurement were performed using a cross-section parallel to the longitudinal direction of the lead.

[0110] Examples 1 to 3 show that the plasma intensity can be changed by altering the linear velocity of the pouch. It can be seen that the slower the pouch linear velocity, the higher the plasma surface treatment intensity. In addition, the plasma surface treatment intensity can be increased by increasing the discharge power or increasing the flow rate of the discharge material.

[0111] The following describes the cross-sectional changes in the sealing region and the temporary bonding region with reference to Figures 9 and 10.

[0112] In Figures 9 and 10, the upper region of the PET layer in the upper pouch and the lower region of the PET layer in the lower pouch are noise generated during cross-sectional imaging and can therefore be ignored. Similarly, the region to the right of the interface 150 is also noise generated during cross-sectional imaging and can therefore be ignored.

[0113] Figure 9(a) shows the sealing cross-section of the lead portion in Comparative Example 1, i.e., when plasma surface treatment is not performed, and in this case, plasma surface treatment is not performed on the PP layers of both the pouch and the lead.

[0114] Figure 9(b) shows the sealing cross-section of the lead portion in Comparative Example 3, i.e., when plasma surface treatment was performed with a relatively weak intensity. This is the case where plasma treatment was performed on the pouch PP layer, but not on the lead PP layer.

[0115] Comparing Figure 9(a) and Figure 9(b), it can be seen that there is a significant difference in the position and shape of the interface 150. The interface 150 can be described as the surface that separates the PP adhesive portion 160 from the empty space 170.

[0116] In the case where plasma surface treatment is not performed, the interface 150 is formed at a position further away from the boundary between the sealing region and the temporary bonding region, and it can be seen that an adhesive portion 160 is formed in the temporary bonding region without distinction between the pouch PP layer and the lead PP layer.

[0117] This is thought to be because the molten PP in the sealing region was pushed out into the temporary bonding region, where it adhered to the pouch PP layer and lead PP layer to form a single adhesive portion 160. In other words, it is thought that the molten PP flowed along the pouch PP layer and lead PP layer, forming the adhesive portion 160.

[0118] When plasma surface treatment is performed, the interface 150 is generated near the boundary between the sealing region and the temporary bonding region, and it can be seen that the pouch PP layer and the lead PP layer do not form an adhesive area with respect to the interface 150. It can be seen that such an interface 150 appears in the form of an upper and lower straight line, and then forms a boundary with the empty space 170 as it moves away from the temporary bonding region.

[0119] This suggests that the molten PP in the sealing region is pushed into the temporary bonding region and tends to adhere to the surface-modified pouch PP layer, but does not adhere to the unmodified lead PP layer. In other words, the molten PP flows along the pouch PP layer, while it does not flow along the lead PP layer, thus preventing the formation of an adhesive area. Therefore, in the temporary bonding region, the pouch PP layer and the lead PP layer are discontinuous with respect to the interface 150, resulting in significantly lower strength in the temporary bonding region. Consequently, there is no risk of de-adhesion of the pouch PP layer or lead PPc layer in the temporary bonding region, thus preventing insulation failure due to de-adhesion.

[0120] Figure 10(a) shows the sealing cross-section of the pouch in Comparative Example 1, i.e., when plasma surface treatment was not performed. It can be seen that a temporary bonding region was formed, and adhesion occurred between the pouch PP film and the pouch PP film in the temporary bonding region. It can be seen that the sealing strength in such a temporary bonding region is lower than the sealing strength in the sealing region, but it becomes stronger than the unintended strength value, which can cause insulation failure.

[0121] This is because the PP layer of the upper pouch and the PP layer of the lower pouch in the temporary bonding region have not undergone surface modification. Therefore, the molten PP tends not to adhere to the upper and lower PP layers. However, it is thought that the molten PP flows along the upper and lower pouch PP layers, forming the adhesive portion 160. Then, the molten PP in the temporary bonding region adheres to both the upper and lower PP layers, forming the adhesive portion 160, and finally, it is thought to be continuously adhered to the upper and lower PP layers. Consequently, if the adhesive portion 160 breaks, it pulls the upper and lower PP layers apart, causing the PP layers to debond, which can lead to insulation failure.

[0122] Figure 10(b) shows the sealing cross-section of the pouch in Comparative Example 3, i.e., when plasma surface treatment was performed with a relatively weak intensity. As shown in the figure, it can be seen that adhesion has not occurred between the PP films of the pouch in the temporary bonding region.

[0123] This is thought to be because surface modification was performed on the PP layer of the upper pouch and the PP layer of the lower pouch in the temporary bonding region, causing the molten PP to tend to adhere to the upper and lower PP layers. In other words, the molten PP flows along the PP layer of the upper pouch and the PP layer of the lower pouch, but because the tendency to adhere to the PP layer is even greater, a discontinuous interface 160 may be formed between them.

[0124] Because the upper PP layer and the lower PP layer are discontinuous with respect to the interface 160, the adhesive portion is eliminated in the temporary bonding region, and therefore the sealing strength converges to zero. Consequently, there is no risk of debonding in the temporary bonding region, and therefore insulation failure due to debonding can be prevented.

[0125] On the other hand, pouch sealing defects can occur more frequently due to sealing between the pouch and the lead than between the pouches themselves. Therefore, by comparing the changes in pouch sealing strength and the difference in strength at the lead, the difference in effectiveness with and without plasma treatment can be observed more clearly.

[0126] Figure 11 shows the change in sealing strength as the material moves from the temporary bonding region to the sealing region. It can be seen that in the examples where plasma surface treatment was performed, the sealing strength in the temporary bonding region is relatively low. In particular, the strength is even lower in the examples where the plasma surface treatment strength is low. On the other hand, it can be seen that the sealing strength is relatively very high when plasma surface treatment is not performed.

[0127] On the other hand, Figure 11 also confirms that the sealing strength in the sealing region is even higher in the plasma surface treatment.

[0128] Figure 12 shows the main strength and temporary bonding strength in the comparative example and the example. Main strength refers to the sealing strength in the sealing area.

[0129] When plasma surface treatment is not performed, the temporary adhesion strength is at half the level of the main strength, whereas when plasma surface treatment is performed, the temporary adhesion strength is at less than one-third of the main strength. In particular, when the plasma surface treatment strength is relatively small, the temporary adhesion strength becomes significantly lower than the main strength, and can even approach zero.

[0130] On the other hand, the inventors were able to confirm through XPS analysis that the PP layer was modified through plasma surface treatment. X-ray photoelectron spectroscopy (XPS) is also known as an electron spectroscopic analysis method for chemical analysis (ESCA), and is a technique for analyzing the surface chemical properties of a material. XPS can measure not only the elemental composition but also the chemical and electronic states of atoms within a material.

[0131] When plasma surface treatment was performed compared to when it was not, it was confirmed that the carbon (C) ratio decreased from the atomic ratio on the surface of the PP layer of the pouch. In other words, it was confirmed that the carbon ratio decreased and the surface of the PP layer was modified.

[0132] This means that by performing XPS analysis on the surface of the PP layer after the fact, it is possible to determine whether or not plasma surface treatment was performed, and to distinguish between areas where plasma surface treatment was performed and areas where it was not.

[0133] When thermal fusion is performed in the sealing region of a PP layer whose surface has been modified by plasma surface treatment, it can be seen that the sealing strength is improved through an increase in the adhesive force between the molten PP and the PP layer.

[0134] On the other hand, no pressure is applied in the temporary bonding region near the sealing region. A difference in adhesive strength can be artificially created between the molten PP extruded into the temporary bonding region and the PP layer of the pouch or lead. The molten PP will have greater adhesive strength between plasma-treated PP layers, while the molten PP will have less adhesive strength between untreated PP layers. In other words, the molten PP layer tends to flow along the plasma-treated PP layer. This difference can be used to prevent the formation of continuous adhesive areas in the temporary bonding region, significantly reducing the sealing strength in that region. [Industrial applicability]

[0135] This is described in the detailed description of the invention.

Claims

1. A moving stage that supports the pouch before sealing and moves the pouch linearly in a first direction to form a first plasma electrode, A plasma head is used to irradiate the surface of the pouch with a gas for plasma gas generation in order to form a second plasma electrode and improve the pouch sealing strength after sealing, A pouch-type secondary battery manufacturing apparatus, including an AC power supply device that applies an AC power supply between the first plasma electrode and the second plasma electrode so that the gas is discharged and plasma gas is irradiated onto the surface of the pouch.

2. The pouch-type secondary battery manufacturing apparatus according to claim 1, wherein the plasma head is provided spaced apart in a second direction perpendicular to the first direction.

3. The pouch-type secondary battery manufacturing apparatus according to claim 2, wherein the plasma head is fixed and positioned to irradiate the surface of the pouch with gas vertically downward.

4. The pouch-type secondary battery manufacturing apparatus according to claim 3, wherein the moving stage is provided to move the pouch at a constant speed, and the plasma head irradiates the surface of the pouch, which is supported and moved by the moving stage, with the gas for plasma gas generation.

5. The pouch-type secondary battery manufacturing apparatus according to any one of claims 1 to 4, wherein the plasma head continuously supplies a gas for plasma discharge at a constant flow rate.

6. The pouch-type secondary battery manufacturing apparatus according to claim 5, wherein the gas discharged when plasma is generated contains argon (Ar).

7. The pouch-type secondary battery manufacturing apparatus according to claim 6, wherein the argon is continuously injected at a flow rate of 6 LPM.

8. The gas discharged during plasma generation is nitrogen (N ２ ) or oxygen (O ２ A pouch-type secondary battery manufacturing apparatus according to claim 7, including ).

9. The pouch-type secondary battery manufacturing apparatus according to claim 8, wherein the nitrogen or oxygen is continuously injected at a flow rate of 40 sccm.

10. The pouch-type secondary battery manufacturing apparatus according to claim 5, wherein the linear movement speed of the pouch before sealing is 10 mm / s to 120 mm / s.

11. The pouch-type secondary battery manufacturing apparatus according to claim 5, wherein the AC power supply is provided to discharge the gas with a power of 200W.

12. A pouch supply stage in which a pouch sheet, in which a metal layer is coated with a polypropylene layer, is continuously moved on a moving stage, A plasma surface treatment step is performed in which an AC power supply is applied between the moving stage and the plasma head, and the gas irradiated from the plasma head is discharged to irradiate the surface of the polypropylene layer of the pouch sheet with plasma gas, A casing step in which the plasma-surface-treated pouch sheet is molded to form a pouch case together with a battery cell having a metal layer coated with a polypropylene layer, The process includes a pouch sealing step of sealing the pouch case by forming a sealing region through heat fusion, A method for manufacturing a pouch-type secondary battery, wherein the pouch sheet is subjected to the plasma surface treatment up to the sealing region and the temporary adhesion region near the sealing region.

13. The method for manufacturing a pouch-type secondary battery according to claim 12, wherein the plasma surface treatment is excluded from the leads that penetrate the sealing region.

14. The method for manufacturing a pouch-type secondary battery according to claim 13, wherein the sealing strength for the sealing region between the pouch sheet and the lead is three times or more greater than the sealing strength for the temporary bonding region between the pouch sheet and the lead.

15. The method for manufacturing a pouch-type secondary battery according to claim 14, wherein the sealing strength in the temporary bonding region between the pouch sheet and the lead is less than 40 N / 15 mm.

16. It has a metal layer, and a polypropylene coating layer is formed on the lower surface, and the polypropylene coating layer is plasma surface treated upper pouch case, It has a metal layer, and a polypropylene coating layer is formed on the upper surface, and the polypropylene coating layer is plasma surface treated lower pouch case, A battery cell having a metal layer, with polypropylene coating layers formed on its upper and lower surfaces, and when the upper pouch case and the lower pouch case are sealed by heat fusion, the upper and lower surfaces of the leads are heat-fused together between the upper pouch case and the lower pouch case, A pouch-type secondary battery, wherein the upper or lower pouch case is subjected to the plasma surface treatment up to the sealing region and the temporary adhesion region near the sealing region.

17. The pouch-type secondary battery according to claim 16, wherein the plasma surface treatment of the polypropylene coating layer of the lead is eliminated.

18. The pouch-type secondary battery according to claim 17, wherein the sealing strength for the sealing region between the upper or lower pouch case and the lead is three times or more greater than the sealing strength for the temporary bonding region between the upper or lower pouch case and the lead.

19. The pouch-type secondary battery according to claim 17, wherein the sealing strength in the temporary bonding area between the upper or lower pouch case and the lead is less than 40 N / 15 mm.

20. The pouch-type secondary battery according to any one of claims 16 to 19, wherein the carbon atom ratio on the plasma-treated surface in the upper or lower pouch case is lower than the carbon atom ratio on the surface that is not plasma-treated.

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