End electrode for secondary battery, manufacturing method thereof, electrode assembly including same, and secondary battery

Abstract

According to one embodiment of the present invention, there is provided an end electrode for a secondary battery, the end electrode including a current collector and an active material layer formed on one side of the current collector, the active material layer including a flat portion where the thickness of the active material layer is constant and an inclined portion where the thickness of the active material layer is reduced compared to the flat portion, and a tape attached to a portion of the other side of the current collector corresponding to the inclined portion. There is also provided an end electrode, a manufacturing method thereof, an electrode assembly including the end electrode, and a secondary battery.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0119928 filed on September 8, 2023, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an end electrode for a secondary battery, a method for manufacturing the same, and an electrode assembly and a secondary battery including the same. [Background technology]

[0003] As technological development and demand for mobile devices increases, the demand for secondary batteries as an energy source is rapidly increasing. In particular, secondary batteries are attracting much attention as an energy source for mobile devices such as mobile phones, digital cameras, laptops, and wearable devices, as well as for power devices such as electric bicycles, electric vehicles, and hybrid electric vehicles.

[0004] Depending on the shape of the battery case, secondary batteries are classified into cylindrical batteries in which the electrode assembly is housed in a cylindrical metal can, prismatic batteries in which the electrode assembly is housed in a prismatic metal can, and pouch batteries in which the electrode assembly is housed in a pouch-shaped case made of an aluminum laminate sheet.

[0005] Meanwhile, the electrode assembly housed in the battery case is a chargeable / dischargeable power generating element consisting of a stack structure of a positive electrode, a separator, and a negative electrode, and is classified into a jelly roll type, a stack type, and a stack / fold type. The jelly roll type is a long sheet-type positive electrode and negative electrode coated with an active material, with a separator interposed between them, and then rolled up. The stack type is a type in which multiple positive electrodes and negative electrodes of a predetermined size are stacked in order with a separator interposed between them. The stack-and-fold type is a hybrid structure of the jelly roll type and the stack type, in which unit cells are placed on a separator film and then rolled up.

[0006] Among these, the electrode assembly including a stack includes a laminated form of unit electrodes including tabs, except for the jelly roll type.

[0007] In this case, the positive and negative electrodes used are manufactured by mixing materials such as active materials, conductive agents, and binders with a solvent to prepare a slurry, which is then applied to a current collector sheet, dried, rolled, and then slit into unit electrodes. In this case, since the slurry is a viscous liquid material, the slurry flows on the current collector sheet at the boundary between the coated and uncoated areas, causing a sliding phenomenon in which the thickness of the flowing area becomes thinner.

[0008] This sliding phenomenon occurs between the uncoated area, i.e., the uncoated portion, formed to secure the tab area, and the coated portion of the coated area, and is therefore generally located at the top end of the electrode assembly.

[0009] However, due to the sliding phenomenon, the adhesive strength between the electrode and the separator at the top of the thin electrode assembly is weakened or not bonded at all, which increases the distance between the positive electrode, separator, and negative electrode, thereby increasing resistance, promoting side reactions, and causing local swelling, ultimately resulting in a decrease in battery performance.

[0010] In recent years, various methods have been developed to solve the above problems, including the roller tilt method, which twists the rolling roller to roll the entire cell, the sub-roller method, which presses the top end again using an additional roller, and the JF taping method, which applies tape to the liner during the jig formation stage so that the top end of the cell receives the same pressure as the center of the cell.

[0011] However, the roller tilt method can improve adhesion at the top end, but has the problem of weakening adhesion at the bottom end or increasing the possibility of non-adhesion. The sub-roller method is difficult to fine-tune, has no guide for optimal conditions, and can have side effects from overpressure. The JF taping method has the problem that if tolerances occur in the cell position within the jig forming equipment, pressure differences can occur, which can lead to performance deviations between cells.

[0012] Therefore, there is a need to develop a secondary battery technology that can solve the problem of the upper end of the electrode assembly sliding without causing additional problems. Summary of the Invention [Problem to be solved by the invention]

[0013] An object of the present invention is to provide an electrode, an electrode assembly, and a secondary battery that can reduce gaps between components by supplementing the thickness of slopes where the thickness of an active material layer is thin due to sliding that occurs during the electrode manufacturing process, thereby preventing an increase in resistance and side reactions associated with the slopes, improving swelling, and improving life characteristics.

[0014] Another object of the present invention is to provide a manufacturing method that enables the thickness compensation to be covered in the pre-sliding area in order to achieve the above-mentioned effect.

[0015] The problems to be solved by the embodiments of the present invention are not limited to those described above, and problems not mentioned will be clearly understood by a person having ordinary skill in the art to which the present invention pertains from this specification and the accompanying drawings. [Means for solving the problem]

[0016] An end surface electrode for a secondary battery according to one embodiment of the present invention, the end electrode includes a current collector and an active material layer formed on one surface of the current collector; the active material layer includes a flat portion where the thickness of the active material layer is constant and an inclined portion where the thickness of the active material layer decreases compared to the flat portion, The end electrode has a current collector on the other surface thereof, and a tape attached to a portion corresponding to the inclined portion.

[0017] Here, the current collector may have a tab formed thereon, and the tab may be positioned in a direction in which the inclined portion is formed.

[0018] In this case, the tape formed on the other surface of the edge electrode may be formed to have the same length as the width of the edge electrode in a direction perpendicular to the direction in which the tab of the edge electrode protrudes.

[0019] The tape may be cast polypropylene (CPP).

[0020] The formed thickness of the tape may be 30% to 100% of the thickness of the flat portion.

[0021] Furthermore, according to another embodiment of the present invention, there is provided a method for manufacturing an end electrode, comprising the steps of: The present invention provides a method for manufacturing an end electrode, which comprises applying an electrode slurry containing an active material to one side of a current collector sheet, drying the applied slurry, and rolling the applied slurry to form an active material layer having a flat portion with a constant thickness and an inclined portion whose thickness decreases compared to the flat portion, and then attaching tape to the other side of the current collector sheet corresponding to the inclined portion before a slitting process for cutting the active material layer into unit electrodes.

[0022] The inclined portion formed by applying the electrode slurry may be formed on a non-coated portion of the current collector sheet on which the electrode slurry is not applied and on which a tab is subsequently formed.

[0023] Alternatively, the tabs may be formed by a notching process, which may be performed simultaneously with or after the slitting process.

[0024] According to another embodiment of the present invention, there is provided an electrode assembly for a secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the end electrode is located on one or both sides of the outermost edge of the electrode assembly.

[0025] Here, the end electrode may be an end positive electrode.

[0026] In this case, the active material layer of the end electrode may be formed in a direction facing the negative electrode located inside the electrode assembly.

[0027] The electrode assembly may be in the form of stacked unit electrodes, for example, a stack-and-fold type electrode assembly in which a unit cell including an electrode and a separator is wound in one direction by a separator film, a laminate-and-stack type electrode assembly in which the unit cell and the separator are stacked and laminated, or a zigzag stack type electrode assembly in which the unit cell or unit electrode is folded in a zigzag shape by the separator film.

[0028] According to another embodiment of the present invention, there is provided a secondary battery including such an electrode assembly and an electrolyte. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 2 is a cross-sectional view of an end electrode according to an embodiment of the present invention. [Figure 2] FIG. 4 is a plan view of the other surface of the current collector of the end electrode according to the embodiment of the present invention. [Figure 3] 5A to 5C are schematic diagrams showing some steps of a method for manufacturing an end electrode according to another embodiment of the present invention. [Figure 4] FIG. 10 is a cross-sectional view of an electrode assembly according to another embodiment of the present invention. [Figure 5] 5A to 5C are schematic diagrams showing various types of electrode assemblies according to other embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a semiconductor device according to an embodiment of the present invention;

[0031] In order to clearly describe the present invention, portions not necessary for the description will be omitted and the same reference numerals will be used throughout the specification to refer to the same or similar components.

[0032] Furthermore, the size and thickness of each component shown in the drawings are arbitrarily shown for the convenience of explanation, and the present invention is not necessarily limited to those shown. In the drawings, the thicknesses of some layers and regions are exaggerated to clearly show them. In the drawings, the thicknesses of some layers and regions are exaggerated for the convenience of explanation.

[0033] Furthermore, throughout the specification, when a part is said to "comprise" a certain element, this does not mean that it may further include other elements, unless otherwise specified.

[0034] Also, throughout the specification, "on a plane" means a view of the subject part from above, and "on a cross section" means a view of the subject part cut vertically from the side.

[0035] As used throughout this specification, terms indicating degrees, such as "about," "substantially," and the like, when presented with tolerances for manufacturing and materials inherent in the meaning referred to, are used to mean a numerical value or approximation thereof, and are used to prevent malicious infringers from unfairly using precise or absolute numerical values ​​disclosed to facilitate understanding of this specification.

[0036] As used herein, "width," "length," and "width" refer to those defined in the specification.

[0037] FIG. 1 shows a cross-sectional view of an end electrode according to one embodiment of the present invention, and FIG. 2 shows a plan view of the other surface of the current collector of the end electrode.

[0038] 1 and 2, an end electrode 100 according to an embodiment of the present invention includes a current collector 111 and an active material layer 120 formed on one surface of the current collector 111, the active material layer 120 having a flat portion 121 where the active material layer 120 has a constant thickness and an inclined portion 122 where the thickness of the active material layer 120 is reduced compared to the flat portion 121. In addition, a tab 112 is formed on the current collector 111, and the tab 112 is located in the direction in which the inclined portion 122 is formed.

[0039] Not only the end electrode 100, but also the double-sided electrode that is subsequently stacked together with the end electrode 100 is naturally formed by coating with active material slurry, and therefore has a flat portion and an inclined portion in the direction of the uncoated portion where the tab is formed, as described above.Since the electrode assembly is manufactured in the direction in which the stacking and winding are performed so that the inclined portions are aligned, gaps are inevitably formed between the components of the electrode assembly at the locations of the inclined portions.

[0040] However, the occurrence of such gaps reduces the adhesion between the electrodes and the separator, forming spaces between the electrodes, which can subsequently lead to the active formation of lithium dendrites and side reactions with the electrolyte. In addition, the accelerated side reactions can also lead to localized swelling due to gas generation, which can significantly threaten the safety of the secondary battery.

[0041] Therefore, active research has been conducted into methods for solving this problem, and the present invention solves this problem by attaching tape to the outermost end electrodes.

[0042] Referring again to Figures 1 and 2, the end electrode 100 according to one embodiment of the present invention has a structure in which a tape 130 is attached to the other side of the current collector 111 on which the active material layer 120 is not formed, at a position corresponding to the inclined portion 122.

[0043] By attaching the tape 130 in this manner, the thickness difference occurring at the inclined portion 122 can be reduced, and accordingly, the pressure variation can be reduced, thereby ensuring the safety of the secondary battery and improving its performance.

[0044] In this case, in order to effectively cover the inclined portion 122, the tape 130 may be formed to a length (l) corresponding to the inclined portion 122, or may be formed to a length equal to the width (w) of the end electrode 100, which is a direction perpendicular to the direction in which the tab 112 of the end electrode 100 protrudes.

[0045] Furthermore, the thickness (T1) of the tape 130 must be thick enough to offset the difference in thickness between the flat portion 121 and the inclined portion 122. At this time, the thickness (T1) varies depending on the number of electrodes to be stacked, and is not limited to the following, but specifically may be 30% to 100% of the thickness (T0) of the flat portion, more specifically may be 50% to 100%, and even more specifically may be 70% to 90%.

[0046] If the thickness of the tape 130 exceeds this range, it is not preferable because it is too thin and cannot adequately cover the thickness difference as the electrodes are stacked in the electrode assembly, and if it is too thick, it is not preferable because it will increase the volume of the electrode assembly.

[0047] The type of such tape is not limited as long as it is made of a material that does not cause side reactions in the operation of the secondary battery, and insulating tapes used in conventionally known batteries can be used, and more specifically, cast polypropylene (CPP) may be used.

[0048] 3 shows a schematic diagram of several steps for manufacturing such an end electrode 100. Specifically, the tape attachment step is shown, with (a) showing the surface on which the active material layer is formed and (b) showing the surface to which the tape is attached.

[0049] Referring to Figures 1 and 2 together with Figure 3, to manufacture the end electrode 100, first, an electrode slurry containing an active material is applied to one side of the current collecting sheet 210, dried, and rolled to form an active material layer 220 including a flat portion 221 having a constant thickness and an inclined portion 222 whose thickness decreases compared to the flat portion 221.

[0050] Thereafter, a slitting 240 process is performed to cut the current collecting sheet 210 into unit electrodes. Prior to this slitting 240 process, a tape 230 is attached to the other side of the current collecting sheet 210, i.e., the side on which the active material layer 220 is not formed (see (b)), so that the tape 230 covers the area corresponding to the inclined portion 222.

[0051] At this time, the inclined portion 222 occurs at the interface between the uncoated portion where the electrode slurry is not applied and the coated portion where the electrode slurry is applied, and is therefore formed on the uncoated portion side of the active material layer 220 where the tab 112 is to be formed, and therefore the tape 230 is attached adjacent to the tab 112.

[0052] After the attachment of the tape 230 is completed, a process of slitting 240 the current collecting sheet 210 having the active material layer 220 formed on one side into unit electrodes is performed, and a notching process for forming the tabs 112 is also performed simultaneously with or after the slitting 240 process, thereby manufacturing the end electrode 100.

[0053] As described above, according to the present invention, the tape 230 is attached before the slitting 240 process into the unit electrodes, so that the width (w) of the end electrode 100 and the length of the tape 230 match, as described above. This eliminates process-related variations in the attachment position and size of the tape 130 compared to when the tape is attached after the unit electrodes or electrode assemblies are manufactured, and therefore electrode assemblies of similar quality can be manufactured.

[0054] Furthermore, the entire area of ​​the inclined portion 122 of the end electrode 100 can be covered, and an uncovered portion that may occur at the width end of the end electrode 100 is not formed, which is more preferable.

[0055] Meanwhile, according to another embodiment of the present invention, there is provided an electrode assembly for a secondary battery including the unit electrode, a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0056] Such an electrode assembly is illustrated in FIG. 4, which shows a cross-sectional view of an electrode assembly 300 according to another embodiment of the present invention.

[0057] 4, an electrode assembly 300 according to another embodiment of the present invention has a structure in which end electrodes are formed on both sides of the outermost periphery and a double-sided electrode is formed therebetween. In this case, the end electrode located at the outermost periphery may be an end positive electrode 310, and the inner double-sided electrodes may be stacked so that the electrodes facing each other have opposite polarities.

[0058] For convenience of explanation, FIG. 4 shows only the negative electrode 320 facing the end face positive electrode 310, and the illustration and description of the other electrodes positioned therebetween are omitted.

[0059] If the end electrode located at the outermost periphery is a negative electrode, a negative electrode active material layer unnecessary for capacity expression will be added, which may reduce the energy density compared to the volume, and therefore is not preferable. Therefore, the end electrode may be an end positive electrode 310.

[0060] Furthermore, even if the electrode located at the outermost periphery is a double-sided positive electrode including active material layers on both sides of a current collector, there is no negative electrode to accept Li ions released from the outermost active material layer facing the battery case, which may cause problems such as corrosion of the battery case and lithium plating. Therefore, it is preferable to position the end positive electrode 310 at the outermost periphery. Therefore, in this case, the active material layer 312 of the end positive electrode 310 may be stacked so as to be formed in a direction facing the negative electrode 320 located inside the electrode assembly 300.

[0061] Furthermore, as described above, the active material layer 312 of the end surface positive electrode 310 has a flat portion 312a where the thickness of the active material layer 312 is constant and an inclined portion 312b where the thickness decreases from the flat portion 312a, and therefore, a gap occurs in the direction of forming the tab 313 where the inclined portion 312b is formed, widening the distance between the components of the electrode assembly 300.

[0062] The occurrence of such gaps can cause many problems within the secondary battery. According to one embodiment of the present invention, each of the outermost end surface positive electrodes 310 has tape 314 attached to the other side of the current collector 311 where the active material layer 312 is not formed, at a location corresponding to the inclined portion 312b.

[0063] Additional configurations such as the specific attachment position and size of the tape are the same as those described with reference to FIGS.

[0064] As described above, in the electrode assembly 300 according to the present invention, the tape 314 is attached to the other surface of the current collector 311 of the outermost end surface positive electrode 310 in a manner corresponding to the inclined portion 312b. Therefore, the tape 314 serves to offset the difference in thickness between the flat portion 312a and the inclined portion 312b, and uniform pressure can be applied to the flat portion 312a and the inclined portion 312b. This solves the problems of the prior art, such as a decrease in adhesive strength between the electrode and the separator, an increase in side reactions, and swelling.

[0065] Meanwhile, the electrode assemblies to which this configuration can be applied are not limited as long as they have a structure including unit electrodes, and to illustrate these examples, Fig. 5 shows schematic diagrams illustrating various types of electrode assemblies 410, 420, and 430 to which the edge electrodes of the present invention can be applied. Here, the electrode assemblies in Fig. 5 are shown as cross-sectional views in a direction perpendicular to the direction in which the tabs are formed, rather than in the direction in which the tabs are formed, and therefore the portions where the tapes are formed are not shown.

[0066] Referring to FIG. 5, (a) shows a stack-and-fold type electrode assembly 410, (b) shows a laminate-and-stack type electrode assembly 420, and (c) shows a zigzag-stack type electrode assembly 430.

[0067] Specifically, the stack-and-fold type electrode assembly 410 has a structure in which a unit cell 411 including an electrode and a separator is wound in one direction by a separator film 412 .

[0068] Here, the unit cell 411 may be a monocell including one electrode and a separator; a full cell having a structure in which electrodes of opposite polarities are located at the outermost periphery, for example, a positive electrode / separator / negative electrode structure; a bicell having a structure in which electrodes of the same polarity are located at the outermost periphery, for example, a positive electrode / separator / negative electrode / separator / positive electrode structure or a negative electrode / separator / positive electrode / separator / negative electrode structure; or a combination thereof.

[0069] Similarly, the laminate-and-stack type electrode assembly 420 may have a structure in which the unit cells 421 are stacked and laminated with the separator 422 .

[0070] Here, the stack of unit cells 421 and separation membranes 422 is a concept including a structure in which the separation membranes 422 are included around the outer periphery of the unit cells 421, and the unit cells 421 are the same as those described for the unit cells 411.

[0071] Finally, the zigzag stack electrode assembly 430 may have a structure in which a unit cell or unit electrode 431 is folded in a zigzag shape by a separating film 432 .

[0072] At this time, the unit cell 431 is the same as that described above.

[0073] Meanwhile, the composition and structure of the positive electrode, negative electrode, and separator that constitute the electrode assembly are known in the art, and therefore will not be described in detail herein.

[0074] According to another embodiment of the present invention, there is provided a secondary battery including the electrode assembly and an electrolyte.

[0075] Such secondary batteries are also known in the art, and detailed description thereof will be omitted in this specification, except for the above-mentioned configuration.

[0076] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the claims below also fall within the scope of the present invention. [Industrial Applicability]

[0077] According to the present invention, the end electrode and the electrode assembly including the end electrode of the present invention compensate for the inclined portion where the thickness of the active material layer is thinned due to sliding that occurs during the electrode manufacturing process, thereby reducing the gap between components and preventing the associated increase in resistance and side reactions, thereby improving swelling and improving life characteristics.

[0078] In addition, the thickness can be supplemented by attaching tape to the other side of the outermost electrode of the electrode assembly, i.e., the other side on which the active material layer is not formed, which does not reduce the reaction area of ​​the active material layer and reduces capacity loss, which is advantageous for ensuring high capacity.

[0079] Furthermore, according to the end electrode manufacturing method of the present invention, the above effect can be achieved with a very simple taping method. Before the slitting process for the unit electrode, the tape is attached to the entire surface, and then the slitting process is performed. Since the tape conforms to the shape of the end electrode to which it is applied and can cover the entire width of the end electrode, there is no process variation in the tape attachment position, size, etc., compared to when the tape is attached after stacking, and this is even more effective. [Explanation of symbols]

[0080] 100 Edge electrode 120, 220, 312 active material layer 130, 230, 314 tape 210 Current collecting sheet 240 Slitting 250 Notching 300, 410, 420, 430 Electrode Assembly 310 End face positive electrode 320 negative electrode 330 Separation membrane 411, 421, 431 Unit electrode or unit cell 412, 422, 432 Separation membrane or separation film 1200, 2200 separation film 1300 double-sided tape 1310 First double-sided tape 1320 Second double-sided tape

Claims

1. An end electrode for a secondary battery, The end electrode for a secondary battery includes a current collector and an active material layer formed on one surface of the current collector, the active material layer includes a flat portion where the thickness of the active material layer is constant and an inclined portion where the thickness of the active material layer is reduced compared to the flat portion, The end electrode for a secondary battery has a tape attached to the other surface of the current collector at a position corresponding to the inclined portion.

2. 2. The end electrode for a secondary battery according to claim 1, wherein the current collector has a tab formed thereon, the tab being positioned in a direction in which the inclined portion is formed.

3. 2. The end electrode for a secondary battery according to claim 1, wherein the tape is formed to have a length equal to the width of the end electrode for a secondary battery in a direction perpendicular to the direction in which the tab of the end electrode for a secondary battery protrudes.

4. 2. The end electrode for a secondary battery according to claim 1, wherein the tape is made of cast polypropylene (CPP).

5. 2. The end electrode for a secondary battery according to claim 1, wherein the thickness of the tape is 30% to 100% of the thickness of the flat portion.

6. A method for manufacturing the end electrode for a secondary battery according to claim 1, comprising: A method for manufacturing an end electrode for a secondary battery, comprising: applying an electrode slurry containing an active material to one surface of a current collector sheet, drying the applied electrode slurry, and rolling the applied electrode slurry to form the active material layer including the flat portion having a constant thickness and the inclined portion having a thickness that is reduced compared to the flat portion; and attaching the tape to the other surface of the current collector sheet corresponding to the inclined portion before a slitting process in which the active material layer is cut into unit electrodes.

7. 7. The method for manufacturing an end electrode for a secondary battery according to claim 6, wherein the inclined portion formed by applying the electrode slurry is formed on an uncoated portion side of the current collecting sheet on which the electrode slurry is not applied and on which a tab is subsequently formed.

8. 8. The method of manufacturing an end electrode for a secondary battery according to claim 7, wherein the tab is formed by a notching process, and the notching process is performed simultaneously with or after the slitting process.

9. 10. An electrode assembly for a secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the end electrode for the secondary battery according to claim 1 is located on one or both sides of the outermost edge of the electrode assembly for the secondary battery.

10. The electrode assembly for a secondary battery according to claim 9 , wherein the end electrode for the secondary battery is an end positive electrode.

11. The electrode assembly for a secondary battery according to claim 10 , wherein the active material layer of the end surface positive electrode is formed in a direction facing the negative electrode located inside the electrode assembly for a secondary battery.

12. 10. The electrode assembly for a secondary battery according to claim 9, wherein the electrode assembly for a secondary battery is a stack-and-fold type electrode assembly in which a unit cell including an electrode and the separator is wound in one direction by a separator film, a laminate-and-stack type electrode assembly in which the unit cell and the separator are stacked and laminated, or a zigzag stack type electrode assembly in which the unit cell or the unit electrode is folded in a zigzag shape by the separator film.

13. A secondary battery comprising the electrode assembly for a secondary battery according to any one of claims 9 to 12 and an electrolyte.

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