Electrode assembly, manufacturing method thereof, and lithium secondary battery including the same

Abstract

The present invention relates to an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode and the negative electrode each have a flat portion where an active material layer has a constant thickness and a sloping portion where the thickness of the active material layer decreases from the flat portion, and the sloping portion of the positive electrode and the sloping portion of the negative electrode are each bonded to a separator interposed therebetween, a manufacturing method thereof, and a lithium secondary battery including the electrode assembly.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0172864, filed December 6, 2021, and Korean Patent Application No. 10-2022-0165534, filed December 1, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

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

[0003] With technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and working potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Recently, the design of electronic devices has become a very important factor in consumer product selection, and electronic devices are becoming smaller and thinner according to consumer preferences. As a result, there is a demand for smaller and thinner lithium secondary batteries to minimize the internal space of electronic devices, and the demand for such batteries is increasing.

[0005] Such a lithium secondary battery is manufactured by manufacturing a positive electrode and a negative electrode, stacking them together with a separator to form an electrode assembly, and then incorporating the electrode assembly into a secondary battery case together with an electrolyte.

[0006] The electrodes of the secondary battery are manufactured by applying electrode active material slurry to a current collector. The electrode is divided into a holding portion where the slurry is applied and a non-coating portion where the slurry is not applied. Due to the coating of the electrode active material slurry, a sliding phenomenon occurs at both ends of the boundary between the holding portion and the non-coating portion, where the coating is not physically perpendicular but is inclined depending on the concentration of the slurry.

[0007] However, when this sliding phenomenon occurs, electrons move in the current collector due to the charging current in the inclined area, causing lithium ions to move from the positive electrode to the negative electrode. However, there is a difference in the speed at which these electrons move, making it more likely that lithium will precipitate. In addition, the distance between the positive and negative electrode active materials is greater than in other areas, increasing resistance and reducing cell performance.

[0008] This problem is particularly serious in the case of rapid charging, where the effect of resistance becomes greater.

[0009] Therefore, there is a pressing need to develop secondary battery technology that can solve these problems. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide a secondary battery that can control the concentration gradient phenomenon due to distance when lithium is absorbed and released by adhering the portions corresponding to the inclined portions of the active material layer in the same manner as the flat portions, thereby eliminating resistance non-uniformity and preventing problems such as lithium precipitation, thereby improving the overall performance of the secondary battery and ensuring safety. [Means for solving the problem]

[0011] An electrode assembly according to an embodiment of the present invention comprises: An electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the positive electrode and the negative electrode each have 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 from the flat portion, The inclined portion of the positive electrode and the inclined portion of the negative electrode are each bonded to a separator interposed therebetween.

[0012] Here, the electrode assemblies are Guo The bicell has the same polarity as the positive electrode. Guo The cell may be a full cell in which the electrodes have different polarities, or a mono cell containing one electrode and one or two separators.

[0013] The inclined portion may include a first section in which the thickness of the active material layer gradually decreases from the flat section in a region close to the tab in the extension direction of the tab, or a second section in which the thickness of the active material layer gradually decreases from the flat section in the first section and a region far from the tab.

[0014] The difference between the distance between the positive electrode and the negative electrode at the inclined portion and the distance between the positive electrode and the negative electrode at the flat portion may be 0.4 mm or less.

[0015] The adhesive strength between the positive electrode and the separator at the inclined portion may be 30 gf / 20 mm to 100 gf / 20 mm, and the adhesive strength between the negative electrode and the separator at the inclined portion may be 10 gf / 20 mm to 50 gf / 20 mm.

[0016] On the other hand, according to another embodiment of the present invention, A method for manufacturing an electrode assembly, comprising: (a) preparing an electrode assembly including the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode; (b) laminating the electrode assembly with a pair of first rollers; (c) additionally laminating the electrode assembly with a pair of second rollers at positions corresponding to the inclined portion of the positive electrode and the inclined portion of the negative electrode, thereby bonding the inclined portion of the positive electrode and the inclined portion of the negative electrode to the separator interposed therebetween, respectively.

[0017] The pair of first rollers may laminate the electrode assembly in consideration of the thickness of the electrode assembly.

[0018] In addition, the pair of second rollers may additionally laminate the electrode assembly at positions corresponding to the inclined portions of the positive electrode and negative electrode so that the adhesive strength between the positive electrode and the separator at the inclined portions is 30 gf / 20 mm to 100 gf / 20 mm, and the adhesive strength between the negative electrode and the separator at the inclined portions is 10 gf / 20 mm to 50 gf / 20 mm.

[0019] Furthermore, the second roller of the pair may include a heating device, and the first roller of the pair may also include a heating device.

[0020] Here, the heating device may apply heat of 40 to 120° C. to the electrode assembly.

[0021] The present invention also provides a lithium secondary battery in which the electrode assembly according to one embodiment of the present invention and an electrolyte are housed in a battery case.

[0022] Here, the number of the electrode assemblies is two or more, and an additional separator is disposed between the two or more electrode assemblies.

[0023] In this case, the additional separator may be a unit separator, and the two or more electrode assemblies may be stacked with the additional separator sandwiched therebetween to form a stacked assembly.

[0024] Alternatively, the additional separator may be a separator film, and the two or more electrode assemblies may be wound around the separator film to form a wound-up assembly. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a diagram schematically illustrating an electrode assembly according to an embodiment of the present invention. [Figure 2] 10A and 10B are diagrams schematically illustrating an electrode assembly according to another embodiment of the present invention. [Figure 3] 3A to 3C are diagrams schematically illustrating a part of a method for manufacturing an electrode assembly according to an embodiment of the present invention. [Figure 4] 10 is a photograph of Comparative Examples 1 and 2 according to Experimental Example 2 of the present invention. [Figure 5] 10 is a photograph relating to Examples 1 and 2 according to Experimental Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The terms and words used in this specification and claims should not be construed in their ordinary or dictionary sense, but should be construed in a meaning and concept that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and various equivalents and modifications that can replace them may exist at the time of filing this application, and the scope of the present invention is not limited to the embodiments described below.

[0027] The present invention will be described in detail below with reference to the drawings and embodiments. The terms and phrases used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, in accordance with the principle that the inventor can appropriately define the concepts of terms in order to best describe his or her invention.

[0028] Furthermore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0029] According to one embodiment of the present invention, there is provided an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the positive electrode and the negative electrode each have 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 from the flat portion, The sloped portion of the positive electrode and the sloped portion of the negative electrode are bonded to a separator interposed therebetween to provide an electrode assembly.

[0030] At this time, the electrode assemblies are unit electrode assemblies, and the outermost Guo The electrodes may be bi-cells having the same polarity, and may be unit electrode assemblies having a structure of positive electrode / separator / negative electrode / separator / positive electrode or negative electrode / separator / positive electrode / separator / negative electrode. Guo The full cell may be, for example, a unit electrode assembly having a positive electrode / separator / negative electrode structure, or may be a mono-cell including one electrode and one or two separators, but is not limited thereto. In particular, the outermost electrodes on both sides may be Guo The electrodes may have the same polarity.

[0031] The inclined portion may include a first section in which the thickness of the active material layer gradually decreases from the flat section in a region close to the tab in the extension direction of the tab, or a second section in which the thickness of the active material layer gradually decreases from the flat section in the first section and a region far from the tab.

[0032] That is, the inclined portion may be formed at one end where the tab is formed, or at both the one end and the other end.

[0033] To more clearly illustrate this structure, FIG. 1 shows a schematic diagram of an electrode assembly 100 having a tab at one end and a slope at the other end according to an embodiment of the present invention.

[0034] Referring to FIG. 1, an electrode assembly 100 includes two positive electrodes 110, one negative electrode 120, and two separators 130 interposed between the positive electrode 110 and the negative electrode 120.

[0035] In this case, two positive electrodes 110 are present on either side of one negative electrode 120 .

[0036] The positive electrode 110 and the negative electrode 120 have flat portions 100a where the active material layers 112, 122 formed on the current collectors 111, 121 have a constant thickness, and inclined portions 100b where the thickness of the active material layers decreases from the flat portions 100a.

[0037] In this case, the inclined portions 100b are located in regions close to and far from the tabs 113 and 123 in the extension direction of the tabs 113 and 123 from both sides of the flat portion 100a based on the flat portion 100a.

[0038] However, conventionally, the inclined portions of the positive and negative electrodes cannot contact the separator interposed therebetween through a typical lamination process due to the difference in thickness between the positive and negative electrodes and the flat portions. As a result, the separation distance between the positive and negative electrodes increases, resulting in high resistance at the inclined portions.

[0039] However, in the electrode assembly 100 according to the present invention, the inclined portions 100b of the positive electrode 110 and the negative electrode 120 are mostly attached to the separator 130.

[0040] Similarly, FIG. 2 schematically illustrates an electrode assembly 200 having a tab at one end and an inclined portion at the other end according to another embodiment of the present invention.

[0041] Referring to FIG. 2, the electrode assembly 200 includes one positive electrode 210, two negative electrodes 220, and two separators 230 interposed between the positive electrode 210 and the negative electrode 220.

[0042] In this case, two negative electrodes 220 are present on either side of one positive electrode 210 .

[0043] The positive electrode 210 and the negative electrode 220 have flat portions 200a where the active material layers 212, 222 formed on the current collectors 211, 221, respectively, have a constant thickness, and inclined portions 200b where the thickness of the active material layers decreases from the flat portions 200a.

[0044] In this case, the inclined portions 200b are located in regions close to and far from the tabs 213 and 223 in the extension direction of the tabs 213 and 223 from both sides of the flat portion 200a based on the flat portion 200a.

[0045] In the electrode assembly 200 of FIG. 2, similarly to the electrode assembly 100 of FIG. 1, the inclined portions 200b of the positive electrode 210 and the negative electrode 220 of the present invention are mostly adhered to the separator 230. In the electrode assembly 200 of FIG.

[0046] As shown in FIGS. 1 and 2, the separation film is attached to the inclined portion because a separate lamination process is additionally performed on the inclined portion, as will be described later.

[0047] In this way, when the positive electrode and the negative electrode are attached to the separator at the inclined portion to narrow the gap between them, the lithium supply rate is similar to that at the flat portion, and therefore the lithium ion concentration gradient is not large, which can solve the problems of increased resistance and lithium deposition.

[0048] In such a structure of the present invention, the difference between the distance between the positive electrode and the negative electrode in the inclined portion and the distance between the positive electrode and the negative electrode in the flat portion may be 0.4 mm or less, specifically 0.2 mm, and more specifically 50 μm to 100 μm.

[0049] That is, according to the present invention, the positive electrode and the negative electrode in the inclined portion are respectively adhered to the separator, and the distance therebetween is approximately similar to the distance between the positive electrode and the negative electrode in the flat portion.

[0050] In addition, the adhesive strength between the positive electrode and the separation membrane adhered to the separation membrane at the inclined portion may be 30 gf / 20 mm to 100 gf / 20 mm, and the adhesive strength between the negative electrode and the separation membrane adhered to the separation membrane at the inclined portion may be 10 gf / 20 mm to 50 gf / 20 mm.

[0051] That is, the positive electrode and the separator, and the negative electrode and the separator can have adhesive strength of a certain magnitude or more even at the inclined portion.

[0052] Here, the adhesive strength is measured by measuring the adhesive strength between the positive electrode and the separator when the positive electrode is located in the middle of the manufactured electrode assembly, and the adhesive strength between the negative electrode and the separator when the negative electrode is located in the middle of the manufactured electrode assembly.

[0053] The electrode assembly is mounted on a UTM (Universal Testing Machine) (LLOYD Instrument LF Plus) and a force is applied at 180 degrees at a measurement speed of 10 mm / min to measure the force required to peel the electrode assembly from the inclined portion.

[0054] If the adhesive strength between the positive electrode and the separator or the adhesive strength between the negative electrode and the separator is too low outside the above range, the gap between the positive electrode and the negative electrode at the inclined portion gradually increases during charging and discharging of the secondary battery, thereby preventing the intended effects of the present invention from being fully achieved. On the other hand, if the gap is too large, it may damage the positive electrode or the negative electrode and the separator, which is undesirable.

[0055] Meanwhile, according to the present invention, there is provided a method for manufacturing an electrode assembly, comprising: (a) preparing an electrode assembly including the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode; (b) laminating the electrode assembly with a pair of first rollers; (c) additionally laminating the electrode assembly with a pair of second rollers at positions corresponding to the inclined portion of the positive electrode and the inclined portion of the negative electrode, thereby bonding the inclined portion of the positive electrode and the inclined portion of the negative electrode to the separator interposed therebetween, respectively.

[0056] That is, the method for manufacturing an electrode assembly according to the present invention begins with manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0057] Here, the positive electrode and the negative electrode have a flat portion where the thickness of the active material layer is constant and a sloped portion where the thickness decreases from the flat portion, due to the wet process of coating the slurry on the current collector.

[0058] The manufactured positive and negative electrodes are then stacked with a separator interposed therebetween.

[0059] Here, the materials contained in the positive and negative electrodes, the manufacturing method thereof, and the structure of the separator are well known in the art, and therefore, detailed description thereof will be omitted herein.

[0060] Here, the electrode assembly may be a unit electrode assembly, which is referred to in the art as a bi-cell or a full cell, as described above. After manufacturing the electrode assembly, the electrode assembly is laminated using a pair of first rollers. Furthermore, the present invention further performs a step of additionally laminating the electrode assembly using a pair of second rollers at positions corresponding to the inclined portions of the positive electrode and the negative electrode, thereby adhering the inclined portions of the positive electrode and the inclined portions of the negative electrode to the separator interposed therebetween.

[0061] That is, the present invention is different from the prior art in that, in addition to the lamination for the existing electrode assembly, additional lamination is performed at the portion corresponding to the inclined portion.

[0062] To explain the lamination step of the manufacturing method, FIG. 2 is a schematic diagram showing a part of the manufacturing method of the electrode assembly of the present invention.

[0063] Referring to FIG. 2, the electrode assembly 100' undergoes primary lamination using a pair of first rollers 300.

[0064] At this time, the pair of first rollers 300 may laminate the electrode assembly in consideration of the thickness of the electrode assembly.

[0065] That is, a lamination process is carried out to firmly bond these together with the separator to form a single unit.

[0066] At this time, the lamination is performed by a pair of first rollers 300, and the lamination strength can be set in consideration of the overall thickness of the electrode assembly and the distance between the pair of first rollers 300.

[0067] Specifically, the lamination is carried out at a pressure of 5 MPa to 12 MPa.

[0068] If the pressure is too low and outside of this range, the components of the electrode assembly may not be bonded sufficiently, and if the pressure is too high, the components may be damaged, which is undesirable.

[0069] In addition, after the lamination, the present invention may additionally laminate the electrode assembly 100′ using a pair of second rollers 400 so that the inclined portions of the positive and negative electrodes are adhered to the separator at positions corresponding to the inclined portions of the positive and negative electrodes.

[0070] The lamination performed first by the pair of first rollers 300 is performed taking into consideration the thickness of the entire electrode assembly 100′. Therefore, the thickness of the active material layer in the sloped portions of the positive and negative electrodes is smaller than the thickness of the active material layer in the flat portions, and therefore sufficient adhesion with the separator interposed therebetween is not achieved.

[0071] As a result, as described above, the gap between the positive electrode and the negative electrode increases, and lithium ions move from the positive electrode to the negative electrode at different speeds. This increases the possibility of lithium precipitation, which increases resistance and reduces cell performance.

[0072] Therefore, in the present invention, by performing additional lamination at the position corresponding to the inclined portion, the gap between the positive electrode and the negative electrode can be reduced to a level similar to that of the flat portion.

[0073] At this time, the additional lamination is performed so that the adhesive strength between the positive electrode and the separator at the inclined portion is 30 gf / 20 mm to 100 gf / 20 mm, and the adhesive strength between the negative electrode and the separator at the inclined portion is 10 gf / 20 mm to 50 gf / 20 mm.

[0074] The additional lamination for this purpose is carried out at a pressure of 0.01 MPa to 8 MPa.

[0075] If the pressure is too low, i.e., outside the above range, the positive and negative electrodes in the inclined portion are not adhered to the separator and the gap between them is still large. If the pressure is too high, the components may be damaged, which is undesirable.

[0076] On the other hand, as explained above, the additional lamination is performed to bond components that are spaced apart from one another, and therefore requires a relatively high level of pressure.

[0077] However, when additional lamination is performed with high pressure, the possibility of damaging the components, such as detachment of the active material, tearing or perforation of the separator, etc., increases significantly.

[0078] Therefore, in order to reduce such damage while bonding the positive electrode and negative electrode to the separator even at the inclined portion, the pair of second rollers may include a heating device.

[0079] When lamination is performed while applying heat using the heating device, sufficient lamination can be achieved even with weaker pressure, thereby reducing physical damage caused by increased pressure and achieving sufficient adhesive strength between the electrode and the separator.

[0080] Therefore, similarly from this point of view, the first roller of the pair may also include a heating device.

[0081] At this time, the heating device may apply heat of 40 to 120° C. to the electrode assembly.

[0082] If the temperature is too low and outside the above range, the effect of the heat application cannot be obtained, and if the temperature is too high, problems such as shrinkage or leaching of the separator or changes in the structure or physical state of the active material layer may occur, which is not preferable.

[0083] Meanwhile, according to another embodiment of the present invention, there is provided a lithium secondary battery in which the electrode assembly and an electrolyte are housed in a battery case.

[0084] Here, the lithium secondary battery may have a structure including two or more electrode assemblies and an additional separator between the two or more electrode assemblies.

[0085] Specifically, the additional separator may be a unit separator, and the two or more electrode assemblies may be stacked with the additional separator sandwiched between them to form a stacked assembly, or the additional separator may be a separator film, and the two or more electrode assemblies may be wound around the separator film to form a wound assembly.

[0086] That is, the lithium secondary battery according to the present invention may include a stacked type or stack-and-folded type assembly in which the electrode assembly prepared above is used as a unit electrode assembly.

[0087] Other components of the lithium secondary battery are well known in the art, and therefore, a description thereof will be omitted here.

[0088] <Comparative Example 1> LiCoO2 as a positive electrode active material, carbon black as a conductive agent, and PVDF (polyvinylidene fluoride) as a binder were mixed in a weight ratio of 97.6:1.1:1.3 in N-methylpyrrolidone solvent to prepare a slurry for a positive electrode active material layer. The slurry for the positive electrode active material layer was then coated on both sides of a 10 μm-thick aluminum (Al) thin film serving as a positive electrode current collector using a slot die.

[0089] Thereafter, the mixture was dried under vacuum at 130°C for 2.5 hours to form an active material layer. The active material layer thus formed was rolled using a roll pressing method so that the porosity of the flat portion of the active material layer became 17%, thereby preparing a positive electrode having an active material layer.

[0090] A slurry for the negative electrode active material layer was prepared by mixing a mixture of artificial graphite as the negative electrode active material, a binder (a mixture of SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose) in a weight ratio of 2:1), and carbon black as a conductive agent in a weight ratio of 96.4:0.5:3.1 with water as the dispersion medium in a weight ratio of 1:2. The slurry for the negative electrode active material layer was coated on both sides of an 8 μm-thick copper (Cu) thin film serving as a negative electrode current collector using a slot die.

[0091] Thereafter, the mixture was dried under vacuum at 130°C for 12 hours to form an active material layer. The active material layer thus formed was rolled using a roll pressing method so that the porosity of the flat portion of the active material layer became 28%, thereby preparing a negative electrode having an active material layer.

[0092] The prepared cathode and anode and porous polyethylene separator were used to fabricate an A-type bi-cell with a cathode / separator / anode / separator / cathode structure, which was then laminated using a flat press at 100°C and 9.5 MPa.

[0093] <Comparative Example 2> A C-type bicell with a negative electrode / separator / positive electrode / separator / negative electrode structure was fabricated using the positive and negative electrodes and porous polyethylene separator fabricated in Comparative Example 1, and then laminated using a flat press at 100°C and 9.5 MPa.

[0094] Example 1 The type A bicell manufactured in Comparative Example 1 was additionally laminated at a position corresponding to the inclined portion using a flat press under the conditions of 100° C. and 5 MPa.

[0095] <Example 2> The C-type bicell manufactured in Comparative Example 2 was additionally laminated at a position corresponding to the inclined portion using a flat press under the conditions of 100° C. and 5 MPa.

[0096] <Experimental Example 1> The adhesive strength of the bicelle in the inclined portion of each of the comparative examples 1 and 2 and the examples 1 and 2 was measured.

[0097] The adhesive strength was measured between the positive electrode and the separator for type C bicells, which have a positive electrode located in the middle, and between the negative electrode and the separator for type A bicells, which have a negative electrode located in the middle.

[0098] The bicell was placed in a UTM device (LLOYD Instrument LF Plus) and a force was applied at a 180° angle at a measurement speed of 10 mm / min to measure the force required to peel the separator and electrode from the inclined portion. The results are shown in Table 1 below.

[0099] [Table 1] Adhesive strength (gf / 20mm) Comparative Example 1 Not glued Comparative Example 2 Not glued Example 1 20 Example 2 40

[0100] <Experimental Example 2> The positive electrodes were separated from the bicells prepared in Comparative Examples 1 and 2 and Examples 1 and 2, and photographs thereof were taken and shown in FIGS. 4 and 5 below.

[0101] 4 and 5, it can be seen that the positive electrode separated in the comparative example of Fig. 4 was not adhered to the separator, and the separator was not transferred at the upper end. In contrast, Fig. 5 shows that the positive electrode separated in the example was transferred over the entire surface.

[0102] Those skilled in the art will appreciate that various applications and modifications within the scope of the present invention will be possible based on the above content. [Industrial Applicability]

[0103] In the electrode assembly according to the present invention, the sloped portion where the thickness of the active material layer decreases in an electrode assembly including a positive electrode, a negative electrode, and a separator is separately laminated, and the portion of the active material layer corresponding to the sloped portion is adhered to the separator interposed therebetween, similar to the flat portion. This reduces the distance between the positive electrode and the negative electrode in the sloped portion to a similar extent to the flat portion, thereby controlling the concentration gradient phenomenon due to the distance during lithium absorption and desorption and eliminating resistance non-uniformity, thereby improving the overall performance of a secondary battery including the same.

[0104] Furthermore, problems such as lithium deposition that mainly occur in the inclined portions can be prevented, thereby ensuring safety.

Claims

1. An electrode assembly for a lithium secondary battery, The battery includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; the positive electrode and the negative electrode each have 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 from the flat portion, The inclined portion of the positive electrode and the inclined portion of the negative electrode are bonded to a separator interposed between the inclined portion of the positive electrode and the inclined portion of the negative electrode.

2. 2. The electrode assembly of claim 1, wherein the inclined portion includes a first section in which the thickness of the active material layer gradually decreases from a flat section in a region closer to the tab in an extension direction of the tab, or a second section in which the thickness of the active material layer gradually decreases from a flat section in a region farther from the tab.

3. 3. The electrode assembly according to claim 1, wherein a difference between a distance between the positive electrode and the negative electrode at the inclined portion and a distance between the positive electrode and the negative electrode at the flat portion is 0.4 mm or less.

4. 3. The electrode assembly of claim 1, wherein an adhesive strength between the positive electrode and the separator at the inclined portion is 30 gf / 20 mm to 100 gf / 20 mm, and an adhesive strength between the negative electrode and the separator at the inclined portion is 10 gf / 20 mm to 50 gf / 20 mm.

5. 2. The method for manufacturing an electrode assembly according to claim 1, (a) preparing an electrode assembly including the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode; (b) laminating the electrode assembly with a pair of first rollers; (c) additionally laminating the electrode assembly with a pair of second rollers at positions corresponding to the inclined portions of the positive electrode and the negative electrode, thereby adhering the inclined portions of the positive electrode and the inclined portions of the negative electrode to a separator interposed between the inclined portions of the positive electrode and the inclined portions of the negative electrode.

6. The method of manufacturing an electrode assembly according to claim 5 , wherein the pair of first rollers laminate the electrode assembly in consideration of a thickness of the electrode assembly.

7. 6. The method for manufacturing an electrode assembly of claim 5, wherein the pair of second rollers additionally laminate the electrode assembly at positions corresponding to the inclined portions of the positive electrode and the negative electrode so that an adhesive strength between the positive electrode and the separator at the inclined portions is 30 gf / 20 mm to 100 gf / 20 mm and an adhesive strength between the negative electrode and the separator at the inclined portions is 10 gf / 20 mm to 50 gf / 20 mm.

8. The method for manufacturing an electrode assembly according to claim 5 , wherein the pair of second rollers includes a heating device.

9. The method for manufacturing an electrode assembly according to claim 5 , wherein the pair of first rollers includes a heating device.

10. The method of claim 8 or 9, wherein the heating device applies heat of 40 to 120° C. to the electrode assembly.

11. A lithium secondary battery comprising the electrode assembly according to claim 1 and an electrolyte solution housed in a battery case.

12. The lithium secondary battery of claim 11 , wherein the battery includes two or more electrode assemblies, and an additional separator is disposed between the two or more electrode assemblies.

13. The lithium secondary battery of claim 12 , wherein the additional separator is a unit separator, and the two or more electrode assemblies are stacked with the additional separator sandwiched between them to form a stacked assembly.

14. The lithium secondary battery of claim 12 , wherein the additional separator is a separator film, and the two or more electrode assemblies are wound around the separator film to form a wound assembly.

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