Electrode assembly, manufacturing method thereof, and lithium secondary battery including 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 dated December 6, 2021 and Korean Patent Application No. 10-2022-0165534 dated 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 manufacturing method thereof, and a lithium secondary battery including the same. [Background technology]

[0003] Along 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 itself has become a very important factor in consumers' product selection, and electronic devices are gradually becoming smaller and thinner according to consumer preferences. As a result, in order to minimize the waste of internal space in electronic devices, lithium secondary batteries are also required to be smaller and thinner, and the demand for them is increasing.

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

[0006] The electrodes of the secondary battery are formed by applying an electrode active material slurry to a current collector. The electrodes are divided into a holding portion where the slurry is applied and a non-coated portion where the slurry is not applied. When the electrode active material slurry is applied, a sliding phenomenon occurs at both ends of the boundary between the holding portion and the non-coated portion, where the electrode active material slurry is not coated at a right angle but is coated at an angle depending on the concentration of the slurry.

[0007] However, when this sliding phenomenon occurs, there is a problem that in the inclined portion, the charging current causes electrons to move in the current collector and lithium ions to move from the positive electrode to the negative electrode, but the speed at which they move varies, making it highly likely that lithium will be precipitated. In addition, the distance between the positive and negative electrode active materials is greater than in other portions, increasing resistance and degrading cell performance.

[0008] This problem is particularly serious during rapid charging, since 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 controls the concentration gradient phenomenon due to distance when lithium is absorbed and released, thereby eliminating resistance non-uniformity and preventing problems such as lithium precipitation, thereby improving the overall performance of the secondary battery and ensuring safety, by adhering the portions corresponding to the inclined portions of the active material layer in the same manner as the flat portions. [Means for solving the problem]

[0011] According to an embodiment of the present invention, an electrode assembly includes: An electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, each of the positive electrode and the negative electrode has 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 assembly may be a bicell in which the electrodes at the outermost corners on both sides have the same polarity, a full cell in which the electrodes at the outermost corners of the positive electrode have different polarities, or a monocell including one electrode and one or two separators.

[0013] In addition, the inclined portion may include a first section in which the thickness of the active material layer gradually decreases from the flat portion 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 portion in the first section and in a region far from the tab.

[0014] 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 may be 0.4 mm or less.

[0015] The adhesive strength between the positive electrode and 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 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 the steps of: (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; and (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.

[0017] The pair of first rollers may laminate the electrode assembly in consideration of a 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 such 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] Additionally, 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 electrode assembly may include two or more electrode assemblies, and an additional separator may be provided 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 interposed 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 description of the drawings]

[0025] [Figure 1] 1 is a schematic diagram illustrating an electrode assembly according to an embodiment of the present invention; [Diagram 2]FIG. 4 is a schematic diagram illustrating an electrode assembly according to another embodiment of the present invention. [Diagram 3] 5A to 5C are diagrams illustrating a part of a method for manufacturing an electrode assembly according to an embodiment of the present invention. [Figure 4] Photographs relating to Comparative Examples 1 and 2 according to Experimental Example 2 of the present invention. [Diagram 5] 6 is a photograph relating to Examples 1 and 2 according to Experimental Example 2 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The terms and words used in the present specification and claims should not be interpreted in their ordinary or dictionary sense, but should be interpreted in the sense and concept consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concept of the term to best describe their invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely preferred embodiments of the present invention, and do not fully represent the technical idea of ​​the present invention, and therefore there may be various equivalents and modifications that can replace them at the time of filing, 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 words used in the 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 correspond to the technical ideas of the present invention, in accordance with the principle that the inventor can appropriately define the concepts of the terms in order to best describe his / her invention.

[0028] Furthermore, it should be understood that the embodiment described in this specification and the configurations shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and therefore there may be various equivalents and modified examples 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, each of the positive electrode and the negative electrode has 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; An electrode assembly is provided in which the positive electrode slope and the negative electrode slope are bonded to each other with a separator interposed therebetween.

[0030] In this case, the electrode assembly may be a unit electrode assembly having a positive electrode / separator / negative electrode / separator / positive electrode or negative electrode / separator / positive electrode / separator / negative electrode structure as a bicell in which electrodes at the outermost corners of both sides have the same polarity; a unit electrode assembly having a positive electrode / separator / negative electrode structure as a full cell in which electrodes at the outermost corners of both sides have different polarities; or a monocell including one electrode and one or two separators, or, in particular, a bicell in which electrodes at the outermost corners of both sides have the same polarity, but is not limited thereto.

[0031] In addition, the inclined portion may include a first section in which the thickness of the active material layer gradually decreases from the flat portion 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 portion in the first section and in a region far from the tab.

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

[0033] In order to more clearly show this structure, FIG. 1 shows a schematic diagram of an electrode assembly 100 having a tab at one end and an inclined portion 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] Positive electrode 110 and negative electrode 120 have active material layers 112, 122 formed on current collectors 111, 121, respectively, which have flat portions 100a with a constant thickness and inclined portions 100b where the thickness of the active material layer decreases from flat portion 100a.

[0037] At this time, the inclined portions 100b are located in regions close to and far from the tabs 113, 123 in the extension direction of the tabs 113, 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 between them by a general lamination process due to the thickness difference between the inclined portions and the flat portions, and as a result, the distance between the positive and negative electrodes becomes large, resulting in high resistance at the inclined portions.

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

[0040] Similarly, FIG. 2 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] At this time, two negative electrodes 220 are present on either side of one positive electrode 210 .

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

[0044] At this time, the inclined portions 200b are located in regions close to and far from the tabs 213, 223 in the extension direction of the tabs 213, 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 almost entirely attached 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 further performed on the inclined portion, as will be described later.

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

[0048] In such a structure of the present invention, 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, specifically 0.2 mm, and more specifically 50 μm to 100 μm.

[0049] That is, according to the present invention, the positive and negative electrodes in the inclined portion are respectively attached to the separator, and the distance therebetween is approximately similar to the distance between the positive and negative electrodes 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 may have an adhesive strength of at least a certain level even at the inclined portion.

[0052] Here, the adhesive strength is measured by measuring the adhesive strength between a positive electrode and a separator when a positive electrode is located in the middle of a manufactured electrode assembly, and the adhesive strength between a negative electrode and a separator when a negative electrode is located in the middle of a 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 them off 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 including the positive electrode and the negative electrode, and therefore the intended effect of the present invention cannot be fully achieved. On the other hand, if the gap is made too large, it is not preferable because it may damage the positive electrode or the negative electrode and the separator.

[0055] Meanwhile, according to the present invention, there is provided a method for manufacturing an electrode assembly, comprising the steps of: (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; and (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.

[0056] That is, the method for manufacturing an electrode assembly according to the present invention begins with the preparation of 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 active material layer has a constant thickness and a sloping portion where the thickness decreases from the flat portion by a wet process of applying a slurry onto a 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 will not be described in detail herein.

[0060] Here, the electrode assembly may be a unit electrode assembly, which is called a bi-cell or a full cell in the art, as described above. After manufacturing the electrode assembly, a step of laminating the electrode assembly with a pair of first rollers is performed. Furthermore, the present invention further performs a step of 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, and bonding the inclined portion of the positive electrode and the inclined portion of the negative electrode with the separator interposed therebetween.

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

[0062] In order to explain the lamination step of the manufacturing method, FIG. 2 is a schematic diagram of 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 by 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 total 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 outside this range, the components of the electrode assembly may not be bonded sufficiently, whereas if the pressure is too high, the components may be damaged, which are 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 overall thickness of the electrode assembly 100′, so that the thickness of the active material layer in the positive and negative electrode portions having inclined portions 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 distance between the positive electrode and the negative electrode increases, and lithium ions move from the positive electrode to the negative electrode, but because there is a difference in the speed at which they move, there is a high possibility that lithium precipitation will occur, which increases resistance and reduces cell performance.

[0072] Therefore, in the present invention, by performing additional lamination at a position corresponding to the inclined portion, the distance 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 and outside of this range, the positive and negative electrodes in the inclined portions are not bonded to the separator and the gap between them is still large, whereas 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 degree of pressure.

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

[0078] Therefore, in order to reduce such damage while bonding the positive electrode and the 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 a weaker pressure, so that sufficient adhesive strength between the electrodes and the separator can be obtained while reducing physical damage caused by increased pressure.

[0080] Accordingly, similarly in this respect, 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, whereas if the heat is applied at an excessively high temperature, problems such as shrinkage or elution of the separator or changes in the structure or physical state of the active material layer may occur, which is undesirable.

[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 contained 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 therebetween to form a stacked assembly, or the additional separator may be a separation film, and the two or more electrode assemblies may be wound around the separation film to form a winding assembly.

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

[0087] Other components of the lithium secondary battery are well known in the art, so the description thereof is omitted in this specification.

[0088] <Comparative Example 1> A slurry for a positive electrode active material layer was prepared by mixing LiCoO2 as a positive electrode active material, carbon black as a conductive agent, and PVDF (polyvinylidene fluoride) as a binder in a weight ratio of 97.6:1.1:1.3 in N-methylpyrrolidone solvent, and the slurry for a positive electrode active material layer was coated on both sides of an aluminum (Al) thin film, which was a positive electrode current collector having a thickness of 10 μm, using a slot die.

[0089] Thereafter, the active material layer was formed by drying for 2.5 hours under vacuum at 130° C. The active material layer thus formed was rolled by roll pressing so that the porosity of the flat part of the active material layer was 17%, thereby preparing a positive electrode having an active material layer.

[0090] A mixture of artificial graphite as the negative electrode active material, 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 was mixed with water as a dispersion medium in a weight ratio of 1:2 to prepare a slurry for the negative electrode active material layer. Using a slot die, the slurry for the negative electrode active material layer was coated on both sides of a copper (Cu) thin film, which was an 8 μm-thick negative electrode current collector.

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

[0092] The prepared positive and negative electrodes and a porous polyethylene separator were used to prepare an A-type bicell with a positive electrode / separator / negative electrode / separator / positive electrode structure, which was then laminated using a flat press at 100°C under 9.5 MPa.

[0093] <Comparative Example 2> A C-type bicell having a negative electrode / separator / positive electrode / separator / negative electrode structure was manufactured using the positive electrode and negative electrode manufactured in Comparative Example 1 and a porous polyethylene separator, and then laminated using a flat press. The lamination was performed under the conditions of 100° C. and 9.5 MPa.

[0094] <Example 1> The A-type bicell manufactured in Comparative Example 1 was subjected to additional lamination at a position corresponding to the inclined portion again at 100° C. and 5 MPa using a flat plate press.

[0095] <Example 2> The C-type bicell manufactured in Comparative Example 2 was subjected to additional lamination at a position corresponding to the inclined portion again at 100° C. and 5 MPa using a flat plate press.

[0096] <Experimental Example 1> For the bicells of Comparative Examples 1 and 2 and Examples 1 and 2, the adhesive strength at the inclined portion was measured.

[0097] The adhesive strength was measured using a C-type bicell, which has a positive electrode located in the middle, as the adhesive strength between the positive electrode and the separation membrane, and an A-type bicell, which has a negative electrode located in the middle, as the adhesive strength between the negative electrode and the separation membrane.

[0098] The bicell was placed in a UTM device (LLOYD Instrument LF Plus) and a force was applied at 180 degrees 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 are 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 is not attached to the separator, and the separator is not transferred to the upper end portion, whereas Fig. 5 shows that the positive electrode separated in the example is entirely transferred.

[0102] Those skilled in the art will appreciate that the present invention can be applied in a variety of ways and modified within the scope of the present invention based on the above content. [Industrial Applicability]

[0103] In the electrode assembly according to the present invention, the thickness of the active material layer in the electrode assembly including the positive electrode, the negative electrode, and the separator is reduced by laminating the sloped portion separately, and the portion of the active material layer corresponding to the sloped portion is bonded to the separator interposed therebetween in the same manner as the flat portion, thereby reducing the distance between the positive electrode and the negative electrode in the sloped portion similar to the flat portion, thereby controlling the concentration gradient phenomenon due to the distance during the absorption and desorption of lithium, and eliminating the resistance non-uniformity, thereby improving the overall performance of the secondary battery including the same.

[0104] Furthermore, problems such as lithium deposition that mainly occurred in the inclined portions can be prevented, and safety can be ensured.

Claims

1. An electrode assembly for a lithium secondary battery, comprising: 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 with a constant thickness of the active material layer and an inclined portion where the thickness of the active material layer decreases from the flat portion, and the inclined portion of the positive electrode and the inclined portion of the negative electrode are adhered to a separator interposed between the inclined portion of the positive electrode and the inclined portion of the negative electrode.

2. The electrode assembly according to claim 1, wherein the inclined portion includes a first section where the thickness of the active material layer gradually decreases from the flat portion in a region close to the tab in the extending direction of the tab, or a second section where the thickness of the active material layer gradually decreases from the flat portion in a region far from the tab.

3. The electrode assembly according to claim 1 or 2, wherein 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 is 0.4 mm or less.

4. The electrode assembly according to claim 1 or 2, wherein the adhesive strength between the positive electrode and the separator in the inclined portion is 30 gf / 20 mm to 100 gf / 20 mm, and the adhesive strength between the negative electrode and the separator in the inclined portion is 10 gf / 20 mm to 50 gf / 20 mm.

5. A method for manufacturing the electrode assembly according to claim 1, comprising: (a) manufacturing 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; and (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 to adhere the inclined portion of the positive electrode and the inclined portion of the negative electrode to a separator interposed between the inclined portion of the positive electrode and the inclined portion of the negative electrode.

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

7. The method for manufacturing an electrode assembly according to claim 5, wherein the pair of second rollers are configured such that the adhesive strength between the positive electrode and the separator in the inclined portion is 30 gf / 20 mm to 100 gf / 20 mm, and the adhesive strength between the negative electrode and the separator in the inclined portion is 10 gf / 20 mm to 50 gf / 20 mm at positions corresponding to the inclined portion of the positive electrode and the inclined portion of the negative electrode, and the electrode assembly is additionally laminated.

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 for manufacturing an electrode assembly according to claim 8 or 9, wherein the heating device applies heat of 40 to 120°C to the electrode assembly.

11. A lithium secondary battery in which the electrode assembly according to claim 1 and an electrolytic solution are incorporated in a battery case.

12. The lithium secondary battery according to claim 11, wherein two or more of the electrode assemblies are included, and an additional separator is included between the two or more electrode assemblies.

13. The lithium secondary battery according to claim 12, wherein the additional separator is a unit separator, and the two or more electrode assemblies are laminated with the additional separator interposed therebetween to form a laminated assembly.

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

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