Electrode assembly three-dimensional

Abstract

To provide an electrode assembly with a structure that improves bending durability and safety.SOLUTION: In an electrode assembly including at least one unit cell having a pair of electrode plates having different polarities with a separation membrane therebetween, electrode lead connection tabs are formed on at least two of the plurality of electrode plates included in the electrode assembly, the width of at least one of the electrode lead connection tabs is designed to be at least 1 / 2 the width of the electrode plate. A tab-lead coupling portion where the electrode lead connection tab and an electrode lead are coupled to each other is located inside the separation membrane.SELECTED DRAWING: Figure 13a

Description

[Technical Field]

[0001] The present invention relates to an electrode assembly having a structure that prevents damage to electrodes and electrode terminals, which is a mechanical problem of batteries that can occur due to repeated external forces such as bending and twisting in a flexible environment, and that improves workability while minimizing loss of energy density by disposing the outermost electrode of the electrode assembly as a cathode, thereby improving bending durability and safety. [Background technology]

[0002] Unlike primary batteries, which cannot be recharged, secondary batteries are batteries that can be charged and discharged, and are widely used in cutting-edge electronic devices such as cellular phones, laptops, and camcorders. Due to the trend toward lighter and more sophisticated portable electronic devices and the development of the Internet of Things (IoT), much research has been conducted into secondary batteries used as their driving power sources.

[0003] In particular, lithium secondary batteries have the advantages of higher voltage and higher energy density per unit weight than nickel-cadmium batteries and nickel-metal hydride batteries, which are widely used as power sources for portable electronic devices, and demand for them is on the rise.

[0004] A secondary battery is a battery that utilizes an electrochemical reaction that occurs between an electrolyte and electrodes when an anode and a cathode are inserted into the electrolyte and the electrodes are connected together. Unlike existing primary batteries, secondary batteries are rechargeable and dischargeable, meaning that the energy consumed by electrical and electronic products can be recharged using a charger and used repeatedly. Therefore, secondary batteries are becoming more widespread along with the popularization of wireless electrical and electronic products.

[0005] Typically, lithium secondary batteries use a jelly-roll-like wound electrode assembly, in which a separator is inserted between a positive electrode plate and a negative electrode plate and then wound up into a spiral, or a stacked electrode assembly, in which multiple positive and negative electrode plates are stacked with separators sandwiched between them. For example, a cylindrical battery is formed by placing a wound electrode assembly in a cylindrical can, injecting an electrolyte, and then sealing it. A prismatic battery is formed by compressing a wound electrode assembly or a stacked electrode assembly to make it flat and then placing it in a prismatic can. A pouch-type battery is formed by packaging a wound electrode assembly or a stacked electrode assembly together with an electrolyte in a pouch-shaped outer casing. In such electrode assemblies, a positive electrode tab and a negative electrode tab, respectively, can be extended to the outside of the electrode assembly and connected to the positive and negative electrodes of the secondary battery.

[0006] Meanwhile, the electrode tabs on the multiple anode and cathode plates stacked vertically are connected to the electrode leads. However, in the conventional connection structure between the electrode tabs and the electrode leads, the connection strength is somewhat weakened during the direct welding process, and problems can occur in the connection between the electrode tabs and the electrode leads due to deformation of the battery during use, such as bending.

[0007] When existing lithium secondary batteries, which have an electrode assembly and a housing material encasing the electrode assembly, undergo bending tests, the housing material can be damaged, and short circuits can occur due to misalignment and misalignment of the components within the electrode assembly, such as the anode, cathode, electrode lead, and separator. As described above, in the case of existing lithium ion secondary batteries, external impact or force can easily cause the terminals to break, resulting in a rapid decrease in capacity and often preventing the battery from functioning properly.

[0008] Korean Patent Publication No. 10-2013-0063709, for example, discloses a pouch-type secondary battery in which two electrodes, a separator, and an electrolyte are placed in a pouch and sealed. The pouch comprises an inner resin layer, a metal foil layer, and an outer resin layer, and a buffer layer less reactive than the metal foil layer is formed on the surface where the inner resin layer and the metal foil layer abut. The formation of a buffer layer less reactive than the metal foil layer has the advantage of preventing corrosion of the battery exterior by suppressing oxidation of the metal foil layer even if the inner resin layer is damaged, such as by microcracks. However, metal foil is fundamentally vulnerable to deformation, such as wrinkling, during bending, which can degrade the performance of flexible batteries.

[0009] In the prior art, when a typical battery assembly is bent, compressive stress is applied to the inside of the bent portion and tensile stress is applied to the battery on the opposite side, causing the exterior material encasing the battery's electrode assembly to expand and contract, resulting in localized mechanical damage. Therefore, there is a need for a new flexible battery assembly that improves not only the exterior material of the flexible battery but also the structure between the electrode plates, electrode tabs, and electrode leads that constitute the internal electrode assembly. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent Publication No. 10-2013-0063709 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, the object of the present invention is to prevent damage to electrodes and electrode terminals when bending a flexible battery by disposing the outermost electrode as a cathode in an electrode assembly having multiple electrodes stacked one above the other with a separator interposed therebetween, thereby improving workability, minimizing loss of energy density, and improving bending durability and safety. [Means for solving the problem]

[0012] In an electrode assembly including at least one unit cell having a pair of electrode plates with opposite polarities sandwiching a separator, at least two of the electrode plates included in the electrode assembly are formed with electrode lead connection tabs, and at least one of the electrode lead connection tabs has a width designed to be at least half the width of the electrode plate.

[0013] The electrode lead connecting tab and the tab-lead joint portion to which the electrode lead is joined are located inside the separator.

[0014] The pair of electrode plates included in the unit cell are stacked such that electrode lead connection tabs formed on the pair of electrode plates overlap each other.

[0015] The pair of electrode plates, arranged such that the electrode lead connecting tabs overlap, are insulated by separating the tab-lead coupling portions from each other by the separation film.

[0016] The width of the electrode lead connection tab is designed to be the same as the width of the electrode plate.

[0017] A flexible material is formed on the electrode lead connecting tab in a region where the electrode lead is connected.

[0018] The electrode lead connection tabs formed on the pair of electrode plates are arranged in the same direction at one end of the electrode assembly.

[0019] The electrode lead connection tabs formed on the pair of electrode plates determine a thickness difference within the electrode assembly.

[0020] The electrode assembly is formed by stacking three or more electrodes, each having a mixture layer with a different area.

[0021] In the electrode assembly, a cathode is disposed on the outermost electrode plate.

[0022] The area of ​​the mixture layer of the anode plate, which is located opposite the outermost electrode plate on which the cathode is disposed across the separator membrane, of the electrode assembly is smallest.

[0023] The area of ​​the cathode mixture applied to the cathode plate of the pair of electrode plates is set to be larger than the area of ​​the anode mixture applied to the anode plate. [Effects of the Invention]

[0024] According to the present invention, in an electrode assembly having multiple electrodes stacked one above the other with a separator interposed therebetween, at least one electrode is configured to include a tab for connecting electrodes in parallel and a tab for connecting an electrode lead, and the outermost electrode is configured as a cathode, thereby preventing damage to the electrodes and electrode terminals, which is a mechanical problem of batteries that can occur due to repeated external bending or twisting in a flexible environment. In addition, by configuring the outermost electrodes of the top and bottom rows as cathodes, workability is improved, energy density loss is minimized, and bending durability and safety are improved. [Brief explanation of the drawings]

[0025] [Figure 1] 1 illustrates an exemplary configuration of an electrode assembly that constitutes a flexible battery according to the present invention. [Figure 2] 1 is an exploded view of an electrode assembly in a state where the outermost electrode of the electrode assembly is arranged as a cathode according to an embodiment of the present invention. [Figure 3]1 shows the arrangement of a plurality of electrodes constituting an electrode assembly and a separator disposed between the plurality of electrodes. [Figure 4] 1 shows the arrangement of a plurality of electrodes constituting an electrode assembly and a separator disposed between the plurality of electrodes. [Figure 5a] 1A and 1B show exploded views of various electrode assemblies in which the outermost electrode of the electrode assembly is positioned as an anode and a cathode. [Figure 5b] 1A and 1B show exploded views of various electrode assemblies in which the outermost electrode of the electrode assembly is positioned as an anode and a cathode. [Figure 5c] 1A and 1B show exploded views of various electrode assemblies in which the outermost electrode of the electrode assembly is positioned as an anode and a cathode. [Figure 5d] 1A and 1B show exploded views of various electrode assemblies in which the outermost electrode of the electrode assembly is positioned as an anode and a cathode. [Figure 5e] 1A and 1B show exploded views of various electrode assemblies in which the outermost electrode of the electrode assembly is positioned as an anode and a cathode. [Figure 5f] 1A and 1B show exploded views of various electrode assemblies in which the outermost electrode of the electrode assembly is positioned as an anode and a cathode. [Figure 6] With the outermost electrode of the electrode assembly positioned as the anode, lithium metal is deposited on the anode during charging and discharging due to the area of ​​the inner cathode and anode mixture. [Figure 7] 1 shows the areas of the cathode mix and the anode mix applied to a pair of electrode plates having different polarities, including only tabs for connecting electrodes in parallel, according to the present invention. [Figure 8] The areas of the cathode mixture and the anode mixture on the cathode plate including only the tab for connecting electrodes in parallel and the anode plate including both the tab for connecting electrodes in parallel and the tab for connecting leads are shown. [Figure 9] 1 shows a flexible battery having an electrode assembly and an exterior material portion encasing the electrode assembly. [Figure 10] 1 shows a state in which patterns such as an upper imprint portion and a lower imprint portion are formed in a direction parallel to the width of an exterior material portion constituting a flexible battery. [Figure 11] The specific configurations of the upper and lower stamped portions formed on the exterior material portion will be described. [Figure 12] 10 is a graph showing bending cycles during charge and discharge in a case where the outermost electrode of an electrode assembly is arranged as a cathode according to an embodiment of the present invention, a case where the outermost electrode is arranged as an anode, and a case where a general battery is combined; [Figure 13a] 10A and 10B are diagrams illustrating an embodiment of the present invention based on the electrode width and the width of the lead connection tab. [Figure 13b] 10A and 10B are diagrams illustrating an embodiment of the present invention based on the electrode width and the width of the lead connection tab. [Figure 13c] 10A and 10B are diagrams illustrating an embodiment of the present invention based on the electrode width and the width of the lead connection tab. [Figure 14] 1A to 1C are diagrams illustrating a method for improving the flexibility of a battery by stacking electrodes according to one embodiment of the present invention. [Figure 15] 10 is a graph showing bending evaluation results of batteries including electrode assemblies in which the outermost electrode of an electrode assembly is divided into a positive electrode and a negative electrode, and the widths of electrode lead connection tabs are configured to be different from each other, according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, a flexible battery according to the present invention will be described with reference to the accompanying drawings.

[0027] The following examples are provided to aid in understanding the present invention, and are not intended to limit the scope of the present invention. Therefore, equivalent inventions that perform the same functions as the present invention are also within the scope of the present invention.

[0028] In addition, when adding reference numerals to components in each drawing, it should be noted that the same components are denoted by the same numerals as much as possible even if they are displayed in different drawings. Furthermore, in describing the present invention, if it is determined that a detailed description of related known structures or functions may confuse the gist of the present invention, the detailed description thereof will be omitted.

[0029] An embodiment of an electrode assembly according to the present invention in which the outermost electrode of the electrode assembly is arranged as a cathode will be described with reference to FIGS.

[0030] The electrode assembly includes a cathode plate 10, an anode plate 20, an electrolyte that serves as an ion transfer medium between the cathode and anode plates, and electrode tabs located on the edges of the electrode plates and separated into those for connecting electrodes in parallel and those for connecting electrode leads depending on the application. At least one of the electrode plates, including the cathode plate 10 and the anode plate 20, may have a tab for connecting electrodes in parallel and a tab for connecting electrode leads spaced apart on both sides. For example, any cathode plate 10 located at the top or bottom of the electrode assembly 100 may have a tab 12 for connecting cathodes in parallel and a tab 14 for connecting cathode leads, and any anode plate 20 located opposite any cathode plate 10 and separated by a separator may have a tab 22 for connecting anodes in parallel and a tab 24 for connecting anode leads.

[0031] Here, the electrode plate is in a form in which an electrode mixture is applied to the cross section or both surfaces of an electrode current collector, and the electrode parallel connection tab and the electrode lead connection tab are in a form in which the electrode current collector is exposed without being coated with an electrode mixture.

[0032] The plurality of electrode plates are connected to each other with the same polarity via electrode tabs for parallel electrode connection. That is, the plurality of cathode plates 10 and the plurality of anode plates 20 are electrically connected in parallel by tab-to-tab connectors that connect the electrode tabs.

[0033] Meanwhile, an electrical connection between the electrode lead connecting tab of the electrode assembly and the electrode lead provides a path for electrons to move from the electrode assembly to the outside of the exterior. A separator may be disposed between electrode plates of opposite polarity, and functions to block the flow of electrons but allow ions contained in the electrolyte to pass through.

[0034] Electrode parallel connection tabs 12, 22 formed on the edge of the cathode plate 10 or anode plate 20 electrically connect electrode plates of the same polarity in parallel to each other. The parallel-connected tab-to-tab joints are positioned on a separator film enclosing the outer surface of the outermost electrode plate forming the top or bottom layer of the electrode assembly and are then finished by taping.

[0035] In the present invention, the tab-to-tab joint where the electrode parallel connection tabs 12, 22 formed on the electrode plate are joined to each other, and the tab-to-lead joint where the electrode lead connection tabs 14, 24 are joined to the electrode leads are electrically connected by any one of joining methods including spot electric welding, ultrasonic welding, laser welding, and bonding with a conductive adhesive.

[0036] Referring to Figure 3, cathode plate 10 and anode plate 20 are stacked consecutively with separator 30 sandwiched between them, and the separator may be stacked in a zigzag pattern, completely enveloping the outer periphery of the electrode assembly. Conventional methods of simply stacking cathode and anode plates can result in problems such as lithium deposition and internal short circuits due to misalignment and misalignment between the electrodes and separator within the electrode assembly caused by external bending or twisting, resulting in reduced safety. However, the present invention utilizes a zigzag stacking method and a tab-to-tab connector electrically connected to the parallel connection tabs, which grips the electrodes within the electrode assembly, minimizing misalignment and misalignment even in a flexible environment.

[0037] 4, the zigzag-stacked electrodes are shown unfolded to facilitate comparison of the area and understanding of the structure. A separate reinforcing tab 70 can be added to the electrode lead connection tabs 14, 24 located on one side of the electrode assembly for reinforcement. By connecting the electrode lead 60 to the reinforcing tab 70, the electrode lead connection tabs 14, 24 and the electrode lead 60 are joined together to form a tab-lead joint 50 having an overlapping structure using the reinforcing tab 70. The reinforcing joint method for connecting the electrode lead connection tabs 14, 24 and the electrode lead 60 using the reinforcing tab 70 corresponds to at least one of an anode tab and a cathode tab.

[0038] The reinforcing tab 70 physically reinforces the connection between the electrode lead connecting tabs 14, 24 and the electrode lead 60 by reinforcing the strength of the connection portion. For example, a reinforcing tab 70 made of the same or different metal and 1 to 5 times thicker than the electrode lead connecting tab is superimposed on the upper part of the electrode lead connecting tab extending from the electrode plate of the electrode assembly, and then welded for reinforcement. The reinforcing tab 70 and the electrode lead connecting tab reinforced by superimposing them may have the same or different widths. The width of the reinforced reinforcing tab 70 may be 3 mm to 5 mm, and the length may be 2 mm to 4 mm, but this is merely an example and is not limited to this.

[0039] The electrode lead, which is joined to the electrode lead connecting tab by being bonded onto the reinforcing tab 70 reinforced by overlapping, may have a width of 2 mm to 3 mm and a length of 0.5 mm to 1 mm, but this is merely an example and is not limited thereto. In the present invention, the current collector of the electrode plate may be made of any one of a group including aluminum, stainless steel, and copper, and the electrode lead may be made of any one of a group including aluminum, nickel, and nickel-coated copper. The reinforcing tab, which is overlapped on the electrode lead connecting tab and the tab-lead joint portion of the electrode lead for reinforcement, is formed in any one of a group including a circle, an oval, and a polygon.

[0040] In addition, the electrode lead coupled to one of the electrode lead connecting tabs constituting the electrode assembly may be bent 180 degrees in the opposite direction while still bonded toward the electrode assembly, forming a bent tab 80 structure facing outward from the electrode assembly. This minimizes local mechanical stress in a flexible environment and provides a reinforced bond between the electrode tab and the electrode lead. The bonding method between the electrode lead connecting tab and the electrode lead 60 by bending corresponds to at least one of the anode tab and the cathode tab. The electrode lead 60 coupled to the electrode lead connecting tab may have a width of 2 mm to 3 mm and a length of 1 mm to 3 mm, but this is merely an example and is not limited thereto.

[0041] Meanwhile, the tab-lead coupling part 50, which combines the electrode lead connecting tabs 14, 24 and the electrode lead 60 using the reinforcing tab 70, and the tab-lead coupling part 50, which combines the electrode lead connecting tab and the electrode lead 60 having a bent tab 80 structure, are inserted / aligned inside the separator, i.e., arranged inside. This prevents the terminal part, which is the weakest point of a flexible battery, from being exposed to the outside, thereby protecting it.

[0042] In FIG. 4, electrodes B and B', which are provided with both an electrode lead connection tab and a parallel connection tab, have a smaller area of ​​the mixture layer applied than electrode C, which is provided with only a parallel electrode connection tab.

[0043] Furthermore, the area of ​​the mixture layer of electrode B, which is located on the outer side, is larger than the area of ​​the mixture layer of electrode B', which is located on the inner side, thereby reducing the deposition of metallic lithium near the corners of the cathode.

[0044] In the present invention, electrode B corresponds to the outermost electrode serving as a cathode, and electrode B' corresponds to an anode electrode plate facing the outermost electrode across a separator. That is, electrode B serving as a cathode is disposed at the bottom of the electrode assembly, and electrode B' serving as an anode is disposed immediately above electrode B. Electrode C, serving as a cathode and having only a tab for connecting electrodes in parallel, is disposed above electrode B'. A general electrode having only a tab for connecting electrodes in parallel may be further disposed between electrode B' and electrode C.

[0045] 5a to 5f show exploded views of various electrode assemblies in which the outermost electrode of the electrode assembly is positioned as an anode and a cathode.

[0046] FIG. 6 shows how lithium metal is deposited on the cathode during charging and discharging depending on the area of ​​the cathode and anode mixture in the electrode assembly, with the outermost electrode being the anode.

[0047] In order to prevent damage to the electrode tab / lead connection portion, which is the most susceptible to breakage during the bending process of a flexible battery, the electrode tab / lead connection portion is positioned inside the electrode without being exposed to the outside. The most effective way to achieve this is to reduce the area of ​​the mixture layer applied to an electrode that has both a tab for connecting electrodes in parallel and a tab for connecting electrode leads, compared to an electrode that has only a tab for connecting electrodes in parallel.

[0048] When the outermost electrode is disposed as the anode, as shown in Figures 5a, 5b, and 6, the area of ​​the anode mixture layer facing the cathode on which the electrode lead connection tab is formed must also be correspondingly smaller. The reason for this is that if this is not the case, lithium that escapes from the anode during charging will deposit near the corners of the cathode, reducing capacity and efficiency and increasing resistance. At the same time, the deposited lithium will grow into needle-like shapes, damaging the separator and causing an internal short circuit within the battery.

[0049] Referring to FIG. 5a, when the outermost electrode of the electrode assembly is an anode, the outermost anode must be coated on its cross section. When the anode is located in the middle layer, the anode must have an uncoated area so that the coated layer of anode mix containing anode active material faces the coated layer of cathode mix containing cathode active material over the entire area.

[0050] 5b, in another solution, the outermost anode must be coated on its cross section and positioned between a cathode having both a tab for connecting electrodes in parallel and a tab for connecting an electrode lead and a cathode having only a tab for connecting electrodes in parallel. The anode without a tab for connecting an electrode lead must be smaller in size than the other anodes having only a tab for connecting electrodes in parallel. This means that the area where the anode mixture layer should be located (501) cannot be utilized, resulting in a lower energy density. Furthermore, a large difference in thickness occurs around the cathode lead / tab connection point in the thickness direction of the electrode assembly, where the electrodes are stacked, which can lead to damage to the connection point and reduce the quality of the flexible battery during bending.

[0051] Furthermore, referring to FIG. 5c, a flexible member 502 such as adhesive tape, pressure sensitive adhesive, resin, or the like made of an acrylic or urethane-based material that is an inactive material that does not react with the electrolyte but blocks the flow of ions must be added to the portion 502 where the cathode and anode do not face each other.

[0052] However, the above-mentioned solutions require the manufacture of electrodes in various sizes and types, such as electrodes having only tabs for parallel connection between the anode and cathode, and electrodes having all the necessary tabs for lead connection. Furthermore, the design and management must be carried out taking into consideration all the surfaces where the anode and cathode contact each other, and additional materials must be used. This results in a rather low processability, high manufacturing costs, and low energy density.

[0053] Also, referring to Figures 5d and 5e, if an electrode having a tab-lead coupling portion, i.e., both a lead connection tab and a parallel connection tab, is not biased toward either of the outermost electrodes of the electrode assembly, even if the outermost electrode is positioned as a cathode, the tab-lead coupling portion positioned inside the electrode assembly must be configured to have a stepped portion 503 by making the sizes of the anodes having only parallel connection tabs different from each other, as shown in Figure 5d, or a portion 504 where the composite layer is not applied must be formed to prevent reaction of the anode active material, as shown in Figure 5e.

[0054] However, this requires the manufacture of electrodes in various sizes and types, such as electrodes with only tabs for parallel connection between the anode and cathode, and electrodes with all the necessary tabs for connecting the electrode leads, and the design and management must take into consideration all the surfaces where the anode and cathode contact, resulting in significantly reduced processability and higher manufacturing costs.

[0055] Also, referring to FIG. 5f, if the electrode lead connection tab is disposed between the electrodes of the electrode assembly rather than on one of the outermost electrodes in the thickness direction of the electrodes of the electrode assembly, there is a problem that electrodes of various sizes must be manufactured and managed separately to prevent dendrites from forming when the battery is charged.

[0056] Furthermore, when the electrode lead is disposed in the middle of the electrode assembly, the step (e.g., 505) in the thickness of the internal electrode further weakens the durability in the battery's operating environment, such as bending and twisting. Therefore, unless the step 505 is supplemented by filling it with a flexible inert material, cracks and breaks occur in the weak parts in terms of mechanical rigidity and flexibility, causing performance degradation or the inability to operate.

[0057] In other words, considering the above problems, it is preferable that the electrode and electrode lead provided with the lead connection tab are designed to be biased toward the outermost edge of the electrode of the electrode assembly.

[0058] 6, when the outermost electrode of the electrode assembly is an anode, if the internal anode and cathode do not face each other, i.e., if the anode mixture layer extends beyond the cathode mixture layer (601), performance degradation due to lithium deposition in certain areas and safety issues due to dendrites may occur. Also, if the outermost electrode of the electrode assembly is a double-sided anode, lithium ions in the outer anode mixture layer may migrate toward the cathode and react, causing safety issues.

[0059] 7 and 8 show a method for designing an appropriate area of ​​the electrode mixture layer to solve the above-mentioned problems.

[0060] Furthermore, if the area of ​​the anode mixture layer that contributes to capacity development is reduced in order to suppress the above-mentioned phenomenon, the energy density will also decrease accordingly, which is not preferable.

[0061] On the other hand, when the anode mixture layer is applied to both sides, the areas to which it is applied must be different, which can cause a problem of reduced process capacity in the manufacturing process. Therefore, according to the present invention, it is preferable that the outermost electrode of the electrode assembly be configured as a cathode.

[0062] Figure 7 shows a pair of electrode plates with different polarities, including only the electrode parallel connection tabs, in which the area of ​​the cathode mix applied to the cathode plate is set larger than the area of ​​the anode mix applied to the anode plate. The difference d between the corner of the anode mix and the cathode mix is ​​designed to be within 5 mm of the corner of the anode mix. In this case, the cathode capacity per unit area is 1 to 1.2 times the anode capacity per unit area.

[0063] FIG. 8 shows a cathode plate including only a tab for connecting electrodes in parallel facing a separator, and an anode plate including both a tab for connecting electrodes in parallel and a tab for connecting leads. The area of ​​the cathode mixture applied to the cathode plate including only the tab for connecting electrodes in parallel is set larger than the area of ​​the anode plate including both the tab for connecting electrodes in parallel and the tab for connecting leads. The difference d between the corner of the cathode mixture and the corner of the anode mixture is designed to be within 5 mm of the outward deviation. Furthermore, the connection between the electrode tab and the electrode terminal, i.e., the tab-lead coupling part 50 formed on the anode plate, which is the physically most vulnerable part of a flexible battery, is located within the separator of the electrode assembly to prevent cracking or breaking at the vulnerable part. To this end, the cathode plate including only the tab for connecting electrodes in parallel can be designed larger by the length D of the electrode tab formed on the edge of the anode plate including the tab-lead coupling part 50 and not coated with the anode mixture. For ease of understanding, a cathode plate including only a tab for connecting electrodes in parallel is preferably configured to cover an anode plate including both a tab for connecting electrodes in parallel and a tab for connecting leads. This structure can improve the bending durability of the electrode tab-terminal connection portion of the flexible battery.

[0064] Referring to FIG. 9, the electrode assembly according to the present invention includes an exterior material part 200 having a structure in which an upper stamped part and a lower stamped part are repeatedly stamped to enclose the exterior of the electrode assembly.

[0065] Referring to FIG. 10, the multiple upper and lower imprinted portions repeatedly imprinted on the exterior material portion have a repeated pattern and shape that allows compression and tension of the flexible battery having the electrode assembly during bending, twisting, or creasing.

[0066] The plurality of upper and lower imprint portions may be continuously formed in a direction parallel to the width of the electrode assembly and the exterior material portion.

[0067] The plurality of upper and lower stamping portions may be stamped by upper and lower molds, respectively.

[0068] The exterior material portion that encases the outside of the electrode assembly may have an upper exterior material portion 210 and a lower exterior material portion 220 on the electrode assembly based on the red dotted line of the sealing portion 230. In other words, the multiple upper stamping portions 212, 222 and lower stamping portions 214, 224 repeated on the exterior material portion are formed in a symmetrical structure based on the sealing portion and are stamped symmetrically on the upper exterior material portion 210 and the lower exterior material portion 220. In the above state, the sealing portion is folded symmetrically up and down, and then the electrode assembly is placed inside the exterior material portion.

[0069] The width of the sealing portion, which is the criterion for separating the upper exterior material portion 210 and the lower exterior material portion 220, is 3mm to 5mm, and the actual sealing width may be 1mm to 2mm, but this is only an example and is not limited to this.

[0070] Referring to FIG. 11, the height h of the upper imprint portions and the height h' of the lower imprint portions repeated on the exterior material portion may be the same (h=h').

[0071] The height h of the multiple upper stamping portions and the height h' of the lower stamping portions repeated on the exterior material portion are 0.5 mm to 1 mm, with the optimal value being 0.75 mm, but this is only one example and is not limited to this.

[0072] Meanwhile, the width a between the highest points of the plurality of adjacent upper imprint portions on the exterior material portion and the width b between the lowest points of the plurality of lower imprint portions are the same (a=b), forming a wavy pattern.

[0073] In the present invention, the outermost electrode of an electrode assembly having a plurality of electrodes stacked one above the other with a separator interposed therebetween is disposed as a cathode, thereby preventing damage to the electrode terminals when the flexible battery is bent.

[0074] 12 is a graph showing the change in battery voltage as a function of the number of bending cycles performed simultaneously with charging and discharging for a battery in which the outermost electrode is arranged as a cathode according to an embodiment of the present invention, a battery in which the outermost electrode is arranged as an anode, and a general battery in which the tabs for connecting electrodes in parallel and the tabs for connecting electrode leads are not separately configured. The test conditions were a curvature radius of 25 mm and a bending speed of 20 cycles per minute, and the battery was charged and discharged in real time while repeatedly bending. The voltage was monitored.

[0075] Referring to Figure 12, the results of a bending evaluation of batteries with a cathode and an anode applied to the outermost electrode are shown. In the case of the general battery described above, the electrode lead-tab connection was damaged before exceeding 30 bending cycles. When the outermost electrode was configured as the anode, voltage noise occurred around 3,800 bending cycles, followed by a sudden voltage drop during charging. In contrast, when the outermost electrode was configured as the cathode according to the present invention, the electrode terminal and electrode were not damaged even after bending more than 6,000 times, demonstrating normal electrochemical operation.

[0076] That is, the electrode assembly according to the present invention includes a separator and an anode and a cathode having opposite polarities stacked in order, and the outermost electrodes of the top and bottom layers are cathodes, thereby improving processability, minimizing loss of energy density, and improving bending durability and safety.

[0077] 13a to 13c are diagrams for explaining embodiments of the present invention based on the electrode width and the width of the lead connection tab.

[0078] Referring to FIG. 13a, the electrode width and lead connection tab width of the first electrode (Electrode 1) are Wn1 and Wn2, respectively, and the electrode width and lead connection tab width of the second electrode (Electrode 2) are Wp1 and Wp2, respectively.

[0079] 13a is a diagram illustrating a case where Wn2 is at least half of Wn1 and Wp2 is at least half of Wp1. According to this embodiment, when the electrode widths Wn1 and Wp1 of adjacent electrodes are the same, the widths Wn2 and Wp2 of the lead connection tabs of adjacent electrodes are designed to be at least half of the electrode widths Wn1 and Wp1, and the electrodes can be formed and arranged so that a predetermined area overlaps each other.

[0080] In conventional flexible batteries, the tab-lead joint where the electrode tab and electrode lead are joined is formed outside the separator of the electrode assembly and exposed to the outside, which reduces durability in flexible environments such as bending, and frequently results in the electrode lead being separated or the electrode tab not coated with a composite being damaged or cut.

[0081] To solve this problem, the present invention addresses the issue by positioning the tab-lead coupling, where the electrode tab and electrode lead are coupled, inside the separator of the electrode assembly. However, even here, if external force is repeatedly applied more frequently, the electrode tab can be damaged or broken even inside the separator. This is a phenomenon caused by material deformation along the step when bending due to the difference in thickness between the electrode tab and tab-lead coupling, which are positioned inside the separator, and the electrodes, which are stacked with different sizes. Therefore, the present invention proposes the following method for manufacturing a flexible battery to solve the above problem by minimizing the difference in thickness within the electrode assembly.

[0082] If the electrode tabs of the electrodes having different polarities and connected to the (+) electrode lead and the (-) electrode lead, respectively, are arranged outside the separator so that they are aligned in the same direction and on the same line, an internal short circuit may occur, resulting in a safety issue. To prevent this issue from occurring, the electrode tabs of the electrodes having different polarities are separated or spaced apart in opposite directions so as not to overlap, and the width of the electrode tabs of each electrode is determined according to the relative positions of the electrode tabs of each electrode.

[0083] However, in the present invention, the electrode tabs are positioned inside the separator of the electrode assembly, and a tab-lead coupling portion where the electrode tab and the electrode lead are coupled can be formed inside the separator, so the electrode tabs of each electrode of opposite polarity can be insulated by the separator. That is, the electrode tabs of each electrode of the present invention can have greater design freedom for the width of the electrode tabs formed on each electrode. For example, as shown in FIG. 13a, if the electrode widths of each electrode of opposite polarity are Wn1 and Wp1, respectively, the widths of the lead connection tabs Wn2 and Wp2 can be fabricated to be at least half of the electrode widths Wn1 and Wp1 (red lines), respectively. That is, even if the widths Wn2 and Wp2 of the lead connection tabs of each electrode appear to overlap visually / physically, the lead connection tabs and tab-lead coupling portion of each electrode can be separated by the separator and thus be electronically insulated. Therefore, in the present invention, the widths Wn2 and Wp2 of the lead connection tabs of each electrode are set to be at least half of the electrode widths Wn1 and Wp1 of each electrode, thereby preventing cracks and breaks at the electrode tab-lead joints due to thickness differences within the electrode assembly.

[0084] In another example, Figure 13b illustrates a case where the width (e.g., Wn2) of the lead connection tab and the width (e.g., Wn1) of the electrode are the same. Referring to Figure 13b, the width 1301 of the lead connection tab of the first electrode and the width 1302 of the lead connection tab of the second electrode can be formed to be the same as the electrode width of each electrode. In this case, as in the embodiment of Figure 13a, the tab-lead coupling portion and the electrode tab can be disposed inside the separator of the electrode assembly, thereby eliminating the risk of short-circuiting between the electrodes.

[0085] FIG. 13c is a view illustrating a method for reducing thickness differences due to uncoated composite material in an electrode tab-lead coupling portion according to an embodiment of the present invention.

[0086] 13c, in order to minimize thickness differences due to uncoated composite at the electrode tab-lead joint, a flexible material that does not react with the anode, anode, or electrolyte (e.g., acrylic or urethane resins, or films, tapes, or adhesives made of a mixture thereof) may be inserted or attached to the electrode tab region 1303 connected to the electrode lead. The flexible material may have flexibility similar to or greater than that of each of the electrode composite layers that make up the electrode assembly.

[0087] FIG. 14 is a diagram illustrating a method for improving battery flexibility by stacking multiple electrodes according to an embodiment of the present invention. Referring to FIG. 14, flexible batteries with various electrode stacking structures and stacking numbers can be manufactured using the present invention to improve battery flexibility. In this case, the tab-lead coupling portion formed by connecting the electrode lead and the electrode tab is positioned within the separator of the electrode assembly. Furthermore, the present invention effectively reduces thickness differences formed in the electrode tab-lead coupling portion of each electrode, thereby enabling improved flexibility and stable operation compared to conventional batteries in operating environments where battery bending characteristics are required, while also providing safety from risks such as internal short circuits. Furthermore, as described above, the present invention designs the electrode lead connecting tab, which is coupled to the electrode lead, to have a larger width than conventional flexible batteries, thereby ensuring a stable current path and minimizing the increase in internal resistance of the battery. This minimizes heat generation due to resistance, thereby ensuring safety.

[0088] FIG. 15 is a graph showing the bending evaluation results of batteries formed with electrode assemblies in which the outermost electrode is divided into anode and cathode, and the widths of the electrode lead connection tabs are configured to be different from each other, according to one embodiment of the present invention.

[0089] Here, a total of four types of evaluation samples were prepared (outermost electrode arranged as a cathode + conventional electrode tab, outermost electrode arranged as a cathode + developed electrode tab, outermost electrode arranged as an anode + conventional electrode tab, outermost electrode arranged as an anode + developed electrode tab). The developed electrode tab refers to an electrode tab positioned inside the separator of the electrode assembly as described above, and configured such that the lead connection tab regions overlap each other based on the projection area in the positional relationship of the electrode lead connection tab portions respectively configured between electrodes of different polarities facing each other across the separator.

[0090] Referring to FIG. 15, the voltage was monitored while repeatedly evaluating bending using each sample at a state of charge of 50%.

[0091] The test conditions were a 20 mm radius of curvature and a bending speed of 25 times per minute. The voltage was monitored in real time while repeatedly bending. The results showed that the battery with the outermost electrode of the electrode assembly as the anode exhibited voltage noise before 2,000 bending cycles, and the electrode lead connection tab broke, causing a sudden drop in voltage. However, the battery with the outermost electrode of the electrode assembly as the cathode exhibited greater durability than the battery with the outermost electrode as the anode, and the battery constructed with the developed electrode tab exhibited greater durability than conventional electrode tabs. Therefore, it can be said that the flexible battery constructed with the developed electrode tab structure and with the outermost electrode of the electrode assembly as the cathode according to the present invention is superior in durability against external forces such as repeated bending to conventional flexible batteries.

Claims

1. An electrode assembly including at least one unit cell having a pair of electrode plates with different polarities sandwiching a separator, two electrode plates among the plurality of electrode plates included in the electrode assembly are formed with electrode lead connection tabs arranged in the same direction at one end of the electrode assembly; At least one of the electrode lead connection tabs has a width that is equal to or greater than half the width of the electrode plate; a parallel connection tab for connecting the same poles of the plurality of electrode plates is formed at the other end opposite to the one end of the electrode assembly, The electrode lead connecting tab and the tab-lead connecting portion to which the electrode lead is connected are located in an internal space of a separator located between the pair of electrode plates and are not exposed to the outside of the separator.

2. 2. The electrode assembly of claim 1, wherein the pair of electrode plates included in the unit cell are stacked such that the separator is positioned between the pair of electrode plates, and electrode lead connection tabs formed on the pair of electrode plates are insulated by the separator, and the pair of electrode plates overlap each other in the stacking direction.

3. The electrode assembly of claim 1 , wherein the width of the electrode lead connection tab is designed to be the same as the width of the electrode plate.

4. The electrode assembly of claim 1 , wherein a flexible material is formed on a region of the electrode lead connection tab that is connected to the electrode lead.

5. The electrode assembly according to claim 1 , wherein the electrode assembly is formed by stacking three or more electrodes, each electrode having a mixture layer with a different area.

6. The electrode assembly according to claim 5 , wherein a cathode is disposed on the outermost electrode plate of the electrode assembly.

7. The electrode assembly according to claim 6 , wherein the area of ​​the mixture layer of the anode plate facing the outermost electrode plate on which the cathode is disposed across the separator is smallest.

8. 2. The electrode assembly according to claim 1, wherein an area of ​​the cathode mixture applied to the cathode plate of the pair of electrode plates is set larger than an area of ​​the anode mixture applied to the anode plate.

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