Jelly roll type electrode assembly, battery cell including the same, and cylindrical battery

Abstract

A jelly roll type electrode assembly according to one embodiment of the present invention includes a positive electrode sheet, a negative electrode sheet, and a separator sheet interposed between the positive electrode sheet and the negative electrode sheet, wherein a portion of the separator sheet facing one end of the positive electrode sheet located inside the jelly roll type electrode assembly includes a first separator sheet portion facing the negative electrode sheet and a second separator sheet portion facing the positive electrode sheet, and a friction coefficient between the first separator sheet portion and the negative electrode sheet is smaller than a friction coefficient between the second separator sheet portion and the positive electrode sheet.

Description

[Technical field]

[0001] Cross-references to related applications This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0032953 filed on March 16, 2022 and Korean Patent Application No. 10-2023-0032949 filed on March 14, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a jelly-roll type electrode assembly, a battery cell including the same, and a cylindrical battery, and more particularly to a jelly-roll type electrode assembly that prevents internal short circuits, a battery cell including the same, and a cylindrical battery. [Background technology]

[0003] In modern society, as the use of portable devices such as mobile phones, laptops, camcorders, and digital cameras has become commonplace, there has been active development of technology related to such mobile devices. In addition, rechargeable secondary batteries are used as the power source for electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (P-HEVs), etc., as a solution to air pollution caused by existing gasoline-powered vehicles that use fossil fuels, so there is an increasing need for the development of secondary batteries.

[0004] Currently commercialized secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Of these, lithium secondary batteries are attracting attention due to their advantages of being able to be charged and discharged freely, having a low self-discharge rate, and having a high energy density.

[0005] Lithium secondary batteries are classified into cylindrical, square, and pouch types according to the shape of the exterior material in which the electrode assembly is housed, and are largely classified into jelly roll types in which a separator is interposed between long sheet-type positive and negative electrodes coated with active materials and then wound up, stack types in which a number of positive and negative electrodes of a given size are stacked in sequence with a separator interposed between them, and stack / folding types in which stack-type unit cells are wound up on a long separator film. Among these, the jelly roll type electrode assembly has the advantage of being the easiest to manufacture and having a high energy density per weight.

[0006] Such a jelly roll type electrode assembly is manufactured by interposing a separator between a positive electrode and a negative electrode and then winding the electrode into a cylindrical shape. The winding process is carried out by winding the separator and the electrodes around a winding core separated into two parts, and then removing the winding core from the electrode assembly.

[0007] Fig. 1 is a perspective view of a conventional jelly-roll type electrode assembly. Fig. 2 is an enlarged view of the "U" portion of Fig. 1. Fig. 3 is a diagram for explaining the change in electrode length in a conventional electrode assembly. Here, the enlarged partial view of Fig. 2 shows that the center portion C is deformed after charging and discharging the electrode assembly.

[0008] 1 to 3, a conventional jelly roll type electrode assembly may be formed by winding a positive electrode 10 and a negative electrode 20. A positive electrode tab 11 attached to the positive electrode 10 and a negative electrode tab 21 attached to the negative electrode 20 may protrude in directions opposite to each other in the jelly roll type electrode assembly. A separator is interposed between the positive electrode 10 and the negative electrode 20 in the jelly roll type electrode assembly.

[0009] The positive electrode 10 may have a free edge. When the positive electrode tab 11 is not located at the end of the positive electrode sheet, one end of the positive electrode 10 may be provided with a coating layer on which an active material is applied, which may be referred to as a free edge portion 10A. A step may be formed around the center C of the electrode assembly due to the free edge portion 10A, and the electrode assembly may expand or contract during the charge and discharge process of the battery cell, causing the periphery of the center C of the electrode assembly to be deformed as shown in the partially enlarged view of FIG. 2.

[0010] More specifically, referring to Fig. 3, the electrode length may change as the electrode assembly expands or contracts during charging and discharging of the battery cell. During this process, friction between the electrodes 10, 20 and the separator 30 may restrict sliding, and the negative electrode 20 facing the free edge portion 10A may bend due to a step or other impingement. If this phenomenon is repeated, the separator 30 between the positive electrode 10 and the negative electrode 20 may be damaged, causing cracks or internal disconnection of the electrode assembly, which may significantly impair the safety of the battery cell. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide an electrode assembly that solves the problem of internal disconnection of the electrode assembly caused by a change in electrode length during charging of a battery cell, a battery cell including the same, and a cylindrical battery.

[0012] However, the problems to be solved by the embodiments of the present invention are not limited to the above problems, and may be variously expanded within the scope of the technical ideas included in the present invention. [Means for solving the problem]

[0013] A jelly roll type electrode assembly according to one embodiment of the present invention includes a positive electrode sheet, a negative electrode sheet, and a separator sheet interposed between the positive electrode sheet and the negative electrode sheet, wherein a portion of the separator sheet facing one end of the positive electrode sheet located inside the jelly roll type electrode assembly includes a first separator sheet portion facing the negative electrode sheet and a second separator sheet portion facing the positive electrode sheet, and a friction coefficient between the first separator sheet portion and the negative electrode sheet is smaller than a friction coefficient between the second separator sheet portion and the positive electrode sheet.

[0014] One end of the positive electrode sheet may be formed as a free edge portion including an active material.

[0015] The free edge portion may include a portion of one end of the positive electrode sheet where the positive electrode active material is coated on an electrode collector.

[0016] One end of the negative electrode sheet may be located more inward of the jelly-roll type electrode assembly than one end of the positive electrode sheet.

[0017] The jelly roll type electrode assembly may further include a slip layer located between the first separator sheet portion and the negative electrode sheet, and a friction coefficient between the slip layer and the first separator sheet portion or a friction coefficient between the slip layer and the negative electrode sheet may be smaller than a friction coefficient between the second separator sheet portion and the positive electrode sheet.

[0018] One end portion of the positive electrode sheet may be formed as a free edge portion including an active material, and the slip layer may be located on the first separator sheet portion covering the free edge portion.

[0019] Based on a cross section of the jelly roll type electrode assembly, the free edge portion may be located between both ends of the slip layer.

[0020] The length of the slip layer may be from 10mm to 30mm.

[0021] The slip layer may be made of a porous material.

[0022] The jelly-roll type electrode assembly may further include a barrier layer located between the separator sheet and the positive electrode sheet to face the free edge portion.

[0023] The barrier layer may be located on the second separator sheet portion covering the free-edge portion.

[0024] The coefficient of friction between the barrier layer and the second separator sheet portion or the coefficient of friction between the barrier layer and the positive electrode sheet may be greater than the coefficient of friction between the first separator sheet portion and the negative electrode sheet.

[0025] The jelly roll type electrode assembly may further include a separator overlapping portion formed at a portion of the separator sheet overlapping one end of the positive electrode sheet in a direction from the outside to the inside of the jelly roll type electrode assembly.

[0026] The separator membrane overlapping portion may be formed between one end portion of the positive electrode sheet and the negative electrode sheet, and a thickness of the separator membrane overlapping portion may be formed to be thicker than a thickness of a portion of the separator membrane sheet that does not face the one end portion of the positive electrode sheet.

[0027] The separation membrane sheet may include a first separation membrane sheet located on one side of the positive electrode sheet and a second separation membrane sheet located on the other side of the positive electrode sheet, and the separation membrane overlapping portion may include one end portion of the first separation membrane sheet formed by bending the first separation membrane sheet at least twice in the same direction to cover a cutting surface of one end portion of the positive electrode sheet, and one end portion of the second separation membrane sheet overlapping with the one end portion of the first separation membrane sheet.

[0028] One end portion of the second separation membrane sheet may be bent at least twice at its end portion to include a double layer.

[0029] A battery cell according to another embodiment of the present invention includes the above-described jelly-roll type electrode assembly and a battery case that houses the jelly-roll type electrode assembly.

[0030] A cylindrical battery according to another embodiment of the present invention includes the above-described battery cell. Effect of the Invention

[0031] According to the embodiment, the electrode assembly of the present invention can prevent internal disconnection of the jelly-roll type electrode assembly by minimizing friction between the electrodes and the separator, thereby improving the safety of the battery cell.

[0032] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a perspective view of a conventional jelly-roll type electrode assembly. [Diagram 2] FIG. 2 is an enlarged view of the "U" portion of FIG. [Diagram 3] FIG. 3 is a diagram for explaining a change in length of an electrode in a conventional electrode assembly. [Figure 4] FIG. 4 is a perspective view of an electrode assembly according to an embodiment of the present invention. [Diagram 5] FIG. 5 is an exploded perspective view showing the electrode assembly of FIG. 4 before being wound up. [Figure 6] FIG. 6 is a diagram showing the electrodes and the separator located around the free edge portion. [Figure 7] FIG. 7 is a diagram showing a modification of the electrode assembly of FIG. [Figure 8] FIG. 8 is a diagram showing still another modified example of the electrode assembly of FIG. [Figure 9] FIG. 9 is a diagram showing an electrode assembly according to another embodiment of the present invention. [Figure 10]FIG. 10 is a diagram showing an electrode assembly according to still another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] In the following, various embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the embodiments of the present invention. The present invention may be embodied in various forms other than those described below, and the scope of the present invention is not limited to the embodiments described herein.

[0035] In order to clearly describe the present invention, parts that are not relevant to the description will be omitted, and the same reference numerals will be used throughout the specification to refer to the same or similar components.

[0036] In addition, the size and thickness of each component shown in the drawings are arbitrarily enlarged or reduced for the convenience of explanation, and it is obvious that the contents of the present invention are not limited to those shown in the drawings. In the following drawings, the thickness of each layer is enlarged to clearly express various layers and regions. And in the following drawings, the thickness of some layers and regions is exaggerated for the convenience of explanation.

[0037] In addition, when a layer, film, region, plate, or other part is described as being "on" or "above" another part, this should be understood to include not only the case where the layer, film, region, plate, or other part is "directly on" the other part, but also the case where there is another part between them. Conversely, when a layer, film, region, plate, or other part is described as being "directly on" the other part, it means that there is no other part between them. In addition, being "on" or "above" a reference part means being located above or below the reference part, and does not necessarily mean being located "on" or "above" the opposite direction of gravity. On the other hand, being described as being "on" or "above" another part, as well as being described as being "on" or "above" another part, should also be understood by referring to the above content.

[0038] Furthermore, throughout the specification, when a part "comprises" a certain element, this does not mean to exclude other elements, but means that the part may further include other elements, unless specifically stated to the contrary.

[0039] Furthermore, throughout the specification, the term "on a plane" means when the part in question is viewed from above, and the term "on a cross section" means when the part in question is cut vertically and viewed from the side.

[0040] Hereinafter, an electrode assembly according to an embodiment of the present invention will be described.

[0041] Fig. 4 is a perspective view of an electrode assembly according to an embodiment of the present invention, and Fig. 5 is an exploded perspective view showing the electrode assembly of Fig. 4 before being wound up.

[0042] 4 and 5, the jelly roll type electrode assembly 50 of this embodiment may include a positive electrode sheet 100, a negative electrode sheet 200, and a separator sheet 300 interposed between the positive electrode sheet 100 and the negative electrode sheet 200. The positive electrode sheet 100, the negative electrode sheet 200, and the separator sheet 300 may be alternately stacked to form a sheet type laminate. The sheet type laminate may be wound around a long rod-shaped winding core. Here, the positive electrode sheet 100 and the negative electrode sheet 200 may be collectively referred to as electrode sheets (positive electrode sheet 100, negative electrode sheet 200).

[0043] Meanwhile, at the center C of the jelly roll type electrode assembly 50, the negative electrode sheet 200 may be extended from the positive electrode sheet 100 and wound. That is, the negative electrode sheet 200 and the separator sheet 300 may be wound around a core first, and then the positive electrode sheet 100 may be additionally provided and wound together. Considering the chemical reaction of a lithium ion battery, since the negative electrode receives lithium ions from the positive electrode, it is preferable that the length and width of the negative electrode sheet 200 are larger than those of the positive electrode sheet 100 for smooth charging and discharging. Therefore, when winding the sheet-type laminate, it is preferable that the negative electrode sheet 200 is wound before the positive electrode sheet 100, so that the negative electrode sheet 200 is located at the innermost part of the center C, and one end of the positive electrode sheet 100 may be located outside the negative electrode sheet 200 (left side in FIG. 6). In other words, one end of the negative electrode sheet 200 may be located closer to the center C of the electrode assembly 50 than one end of the positive electrode sheet 100. The center portion C of the electrode assembly 50 may be the inside as shown in FIG.

[0044] One end of the negative electrode sheet 200 may be located more inwardly of the center C of the electrode assembly 50 than one end of the positive electrode sheet 100. In addition, the other end of the negative electrode sheet 200 located on the outer circumferential surface of the electrode assembly 50 may also be located so as to extend to cover the other end of the positive electrode sheet 100. Here, the center C of the electrode assembly 50 may refer to a radial central portion based on a cross section of the jelly roll type electrode assembly.

[0045] The electrode sheets 100 and 200 may be formed by applying a slurry containing an electrode active material onto a current collector. The positive electrode sheet 100 may include a coating portion 130 to which the slurry is applied and an uncoated portion 120 to which the slurry is not applied, and the negative electrode sheet 200 may include a coating portion 230 to which the slurry is applied and an uncoated portion 220 to which the slurry is not applied. In addition, a positive electrode tab 110 may be located in the uncoated portion 120 of the positive electrode sheet 100, and a negative electrode tab 210 may be located in the uncoated portion 220 of the negative electrode sheet 200. The positive electrode tab 110 and the negative electrode tab 210 may protrude in a direction opposite to each other in the height direction of the electrode assembly (x-axis direction in FIG. 5). However, they may be formed differently depending on the design.

[0046] Here, the electrode slurry may typically include an electrode active material, a conductive material, a binder, and a solvent, but is not limited thereto. In addition, the current collector may be stainless steel, aluminum, copper, nickel, titanium, calcined carbon, etc., and may be provided in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. Examples of the current collector used in the positive electrode sheet 100 include aluminum or an alloy thereof, and examples of the current collector used in the negative electrode sheet 200 include copper, nickel, stainless steel, or an alloy of any one of these.

[0047] The separator sheet 300 separates the positive electrode sheet 100 and the negative electrode sheet 200, and can provide a passage for ions to move between the positive electrode sheet 100 and the negative electrode sheet 200. The separator sheet 300 is a major component that determines the performance of a secondary battery, and in order for the separator sheet 300 to have properties suitable for a secondary battery, it must satisfy physical properties such as minimizing the thickness to reduce electrical resistance and maximizing the porosity and pore size. It must also satisfy electrochemical properties such as wetting with the electrolyte.

[0048] A coating material may be applied to one or both sides of the separator sheet 300 to form a coating layer, which may improve the heat resistance and safety of the separator sheet 300. For example, one or both sides of the substrate of the separator sheet 300 may be coated with a coating material containing alumina (Al2O3) and a binder. When the substrate is coated with alumina, which has high heat resistance, the separator sheet 300 can prevent an internal short circuit in the battery cell by physically and continuously blocking contact between the positive and negative electrodes even in high temperature conditions inside the battery cell, such as thermal runaway.

[0049] The coating layer of the separation membrane sheet 300 may include ceramic particles and a polymer binder. An example of the ceramic particles is alumina, and the properties of the separation membrane sheet 300 may vary depending on the diameter of the alumina. For example, the smaller the diameter of the alumina, the lower the friction coefficient of the coating layer. The smaller the diameter of the alumina, the greater the surface area of ​​the particles, and a relatively large number of particles can come into contact with the fabric of the separation membrane sheet 300, improving the adhesion of the particles and suppressing deformation of the separation membrane sheet 300. In addition, even when a coating material is repeatedly applied to the fabric of the separation membrane sheet 300, if the diameter of the particles is small, the thickness of the coating layer may become thin, and the air permeability of the coating layer may increase and the ion conduction resistance of the separation membrane sheet 300 may decrease compared to when the diameter of the particles is large.

[0050] The coating layer may vary depending on the coating material used to form the coating layer. When the coating layer is formed using a coating material having a high coefficient of friction with respect to the separator material, the coating layer may be formed on one side of the separator sheet 300 facing the positive electrode sheet 100. Alternatively, a coating layer may be formed on each side of the separator sheet 300, and the coefficient of friction of the first coating layer formed on one side of the separator sheet 300 facing the negative electrode sheet 200 may be designed to be smaller than the coefficient of friction of the second coating layer formed on the other side of the separator sheet 300 facing the positive electrode sheet 100. In order to make the coefficients of friction of the first coating layer and the second coating layer different from each other, the diameter of the ceramic particles may be adjusted as described above.

[0051] Meanwhile, one end of the positive electrode sheet 100 may have a free edge portion 100A. One end of the positive electrode sheet 100 may be formed with a coated portion 130 instead of an uncoated portion 120, and such an end portion may be referred to as a free edge portion or a coated edge portion. As shown in FIG. 5, according to this embodiment, the positive electrode tab 110 may be located in the center of the positive electrode sheet 100 instead of at one end thereof. Therefore, it may be referred to as a free edge portion 100A in the sense that the positive electrode tab 110 is not located at one end of the positive electrode sheet 100, or that the uncoated portion 120 for the positive electrode tab 110 to be located is not formed. Alternatively, since one end of the positive electrode sheet 100 is formed with a coated portion 130 and the coating layer is cut, it may be referred to as a coated edge portion. Here, the one end of the positive electrode sheet 100 where the free edge portion or the coated edge portion is formed may be the core of a jelly roll type electrode assembly. This means that the positive electrode tab 110 does not need to be located around the center C of the electrode assembly.

[0052] As a result of the free edge portion 100A being formed at one end of the positive electrode sheet 100, a phenomenon occurs in which a portion of the negative electrode sheet 200 facing the free edge portion 100A is bent during volumetric expansion of the electrode assembly, which may cause a problem in that the separator sheet 300 is damaged. However, in the electrode assembly of this embodiment, the friction level between the separator sheet 300 and the electrode sheets (positive electrode sheet 100, negative electrode sheet 200) is changed to solve the above problem.

[0053] Fig. 6 is a view showing an electrode and a separator located around the free edge portion described above. Fig. 7 is a view showing a modified example of the electrode assembly of Fig. 6. Fig. 8 is a view showing yet another modified example of the electrode assembly of Fig. 6.

[0054] In the electrode assembly of this embodiment shown in Fig. 6, the electrode sheets (positive electrode sheet 100, negative electrode sheet 200) and separator sheet 300 around the free edge portion 100A are in a wound state, but for convenience of explanation in Fig. 6, they are shown flat and the electrode sheets (positive electrode sheet 100, negative electrode sheet 200) and separator sheet 300 are not in close contact with each other. In Fig. 6, the negative electrode sheets 200 disposed above and below the positive electrode sheet 100 may be wound before or after the positive electrode sheet 100 when the electrode assembly is wound.

[0055] 6, in the electrode assembly of this embodiment, the separator sheet 300 may have a portion of the separator sheet facing the free edge portion 100A corresponding to one end of the positive electrode sheet 100 located inside the jelly roll type electrode assembly. Here, facing the free edge portion 100A means overlapping each other in a direction toward the center C of the jelly roll type electrode assembly 50 in FIG. 4. In other words, in FIGS. 5 and 6, the portion of the separator sheet overlapping the free edge portion 100A in the z-axis direction may include a first separator sheet portion facing the negative electrode sheet 200 and a second separator sheet portion facing the positive electrode sheet 100.

[0056] The positive electrode tab (positive electrode tab 110 shown in FIG. 5) according to this embodiment is formed at a position away from the center C of the electrode assembly 50 shown in FIG. 4 (see FIG. 5). The center C of the electrode assembly may be located on one side in the y-axis direction where the free edge portion 100A is located in FIGS. 5 and 6. Therefore, the coating portion 130 in FIG. 5 is formed on the current collector of the positive electrode sheet 100 up to one end of the positive electrode sheet 100 adjacent to the center C of the electrode assembly, and the free edge portion 100A may refer to a portion where the coating portion 130 is formed on the current collector of the positive electrode sheet 100 at one end of the positive electrode sheet 100. In other words, one end of the free edge portion 100A may have a shape in which the coating portion 130 is cut.

[0057] A portion of the separator sheet corresponding to the free edge portion 100A may have a width of a first range T1 based on one end peripheral edge of the positive electrode sheet 100. The separator sheet 300 may include a first surface 300A facing the negative electrode sheet 200 and a second surface 300B facing the positive electrode sheet 100. The portion of the separator sheet 300 may include a first separator sheet portion facing the negative electrode sheet 200 and a second separator sheet portion facing the positive electrode sheet 100. The first separator sheet portion may include the first surface 300A, and the second separator sheet portion may include the second surface 300B.

[0058] In this embodiment, the coefficient of friction between the first surface 300A of the first separator sheet part and the negative electrode sheet 200 may be different from the coefficient of friction between the second surface 300B of the second separator sheet part and the positive electrode sheet 100. Specifically, the coefficient of friction between the first surface 300A of the first separator sheet part and the negative electrode sheet 200 may be smaller than the coefficient of friction between the second surface 300B of the second separator sheet part and the positive electrode sheet 100. In this way, by forming the coefficient of friction between the first separator sheet part having the first surface 300A of the separator sheet 300 located around the free edge part 100A and the negative electrode sheet 200 to be relatively small, the separator sheet 300 and the negative electrode sheet 200 can slide between each other, and the bending phenomenon of the negative electrode sheet 200 and the internal disconnection of the electrode assembly caused thereby can be prevented. In other words, the negative electrode sheet 200 can slide better than the positive electrode sheet 100 when the electrode assembly expands. Therefore, when the electrode assembly expands as the battery cell is charged, the length of the electrode sheet increases, and thus the end of the negative electrode sheet 200 can be prevented from bending.

[0059] In this embodiment, the relative friction coefficients are adjusted to be different, so that it is possible to compare the magnitudes of the above-mentioned friction coefficients using a conventional friction coefficient measuring method and equipment.

[0060] The separator sheet 300 may be provided in various ways.

[0061] As described above, the surface roughness may be adjusted to relatively reduce the coefficient of friction between the first separator sheet portion 300A of the separator sheet 300 located around the free edge portion 100A and the negative electrode sheet 200. As an example, a coating layer may be formed on each side of the separator sheet 300. The surface roughness of the first side 300A and the second side 300B may be different depending on the coating layer formed on each side. When the coating layer includes ceramic particles, the diameters of the ceramic particles in the coating layer formed on the first side 300A and the ceramic particles in the coating layer formed on the second side 300B may be different from each other. The diameter of the ceramic particles in the coating layer formed on the first side 300A may be smaller than the diameter of the ceramic particles in the coating layer formed on the second side 300B.

[0062] As another example, a coating layer may be formed on only one side of the separator membrane sheet 300, so that the surface roughness of the first side 300A and the second side 300B are different. When the surface roughness of the coating layer is smaller than that of the substrate of the separator membrane sheet 300, the coating layer may be formed on the first side 300A. When the surface roughness of the coating layer is larger than that of the substrate of the separator membrane sheet 300, the coating layer may be formed on the second side 300B.

[0063] As another example, a coating layer may not be formed on the separation membrane sheet 300. The surface roughness of the first side 300A and the second side 300B of the separation membrane sheet 300 may be different depending on the characteristics of the separation membrane fabric. In this case, the first side 300A may be a side of the separation membrane fabric that has a relatively low surface roughness, and the second side 300B may be a side of the separation membrane fabric that has a relatively high surface roughness.

[0064] In this embodiment, the relative surface roughness is adjusted to be different, so that the magnitude of the surface roughness can be compared using a conventional surface roughness measuring method and surface roughness measuring equipment.

[0065] Referring to FIG. 7, a slip layer 400 may be provided in an electrode assembly according to another embodiment of the present invention.

[0066] The slip layer 400 may be provided between the first separator sheet portion, which is the separator sheet 300 around the free edge portion 100A, and the negative electrode sheet 200 to induce slippage between the separator sheet 300 and the negative electrode sheet 200. The slip layer 400 may have a lower friction coefficient than the separator sheet 300. Specifically, the friction coefficient between the slip layer 400 and the first separator sheet portion or the friction coefficient between the slip layer 400 and the negative electrode sheet 200 may be lower than the friction coefficient between the second separator sheet portion and the positive electrode sheet 100. The slip layer 400 may be attached to the negative electrode sheet 200 or the first separator sheet portion using a material that is adhesive at room temperature. When the slip layer 400 is attached to the negative electrode sheet 200, the coefficient of friction between the slip layer 400 and the first separator sheet portion may be smaller than the coefficient of friction between the second separator sheet portion and the positive electrode sheet 100, and when the slip layer 400 is attached to the first separator sheet portion, the coefficient of friction between the slip layer 400 and the negative electrode sheet 200 may be smaller than the coefficient of friction between the second separator sheet portion and the positive electrode sheet 100.

[0067] The slip layer 400 may be made of a porous material. The slip layer 400 may contain a large number of pores, so that the movement of lithium ions or charges between the positive electrode sheet 100 and the negative electrode sheet 200 is not hindered. If the slip layer 400 is not made of a porous material, it may cause a short circuit problem due to lithium precipitation. Examples of materials used for the slip layer 400 include polyethylene (PE) and polypropylene (PP), and the material used for the substrate of the separator sheet 300 may also be applied to the slip layer 400. Alternatively, the slip layer 400 may be used so as to have a form in which the substrate surface of the separator sheet 300 is ceramic-coated.

[0068] The slip layer 400 may be provided around the free-edge portion 100A. The slip layer 400 may be located to correspond to the free-edge portion 100A. Here, corresponding to the free-edge portion 100A means that the slip layer 400 overlaps with the free-edge portion 100A in a direction toward the center C of the jelly roll type electrode assembly.

[0069] The slip layer 400 may be located on the first surface 300A of the separator sheet 300 that covers the free-edge portion 100A and does not contact the free-edge portion 100A.

[0070] Since the positive electrode sheet 100 repeatedly expands and contracts due to the charge and discharge of a battery cell including an electrode assembly, the slip layer 400 may be provided in consideration of the fluctuating position of the free edge portion 100A. Specifically, as shown in FIG. 7, the position of the free edge portion 100A may fluctuate within a first range T1 due to the expansion or contraction of the positive electrode sheet 100. In this case, the first length L1, which is the length of the slip layer 400, is set to be greater than the length of the first range T1, so that the slip layer 400 and the free edge portion 100A may correspond to each other. When the portion wound first in the extension direction of the positive electrode sheet 100, the negative electrode sheet 200, or the separator sheet 300 is defined as the inner side, and the portion wound later as the outer side, one end of the slip layer 400 may be located inside the free edge portion 100A, and the other end of the slip layer 400 may be located outside the free edge portion 100A. In the direction in which the positive electrode sheet 100, the negative electrode sheet 200, or the separator sheet 300 extends, the slip layer 400 may be disposed such that the free edge portion 100A is located between both ends of the slip layer 400. Based on the cross section of the wound electrode assembly, the slip layer 400 may be disposed such that the free edge portion 100A is located between both ends of the slip layer 400. In this case, the cross section of the wound electrode assembly refers to the plane shown in FIG. 7 and may be a plane perpendicular to the central axis of the electrode assembly being wound. Here, both ends of the slip layer 400 may be ends in the length direction, and the length direction may be the direction in which the positive electrode sheet 100, the negative electrode sheet 200, or the separator sheet 300 extends.

[0071] As a specific example, the first length L1 of the slip layer 400 may range from 10 mm to 30 mm or from 15 mm to 25 mm, or the first length L1 of the slip layer 400 may be about 20 mm. Here, the first length L1 may be calculated based on the direction in which the positive electrode sheet 100, the negative electrode sheet 200, or the separator sheet 300 extends. Here, the first length L1 may be calculated based on the direction perpendicular to the height direction of the electrode assembly.

[0072] Referring to FIG. 8, the barrier layer 400' according to this embodiment may be provided between the positive electrode sheet 100 and the separator sheet 300, unlike the barrier layer 400' provided between the separator sheet 300 and the negative electrode sheet 200 in the embodiment of FIG. 7. The barrier layer 400' may be located on the second separator sheet part 300 covering the free edge part 100A, so as to correspond to the free edge part 100A. In this case, the barrier layer 400' not only induces slippage between the separator sheet 300 and the positive electrode sheet 100, but also physically prevents internal short circuiting by doubling the separator sheet 300 and the barrier layer 400' between the negative electrode sheet 200 and the positive electrode sheet 100. In this case, the friction coefficient between the barrier layer 400' and the second separator sheet part or the friction coefficient between the barrier layer 400' and the positive electrode sheet 100 is preferably greater than the friction coefficient between the first separator sheet part and the negative electrode sheet 200. This is because the barrier layer 400' can prevent an internal short circuit between the negative electrode sheet 200 and the positive electrode sheet 100, and also prevents bending of the negative electrode sheet 200, thereby significantly enhancing the effect of preventing an internal short circuit.

[0073] FIG. 8 only shows that a barrier layer 400′ is provided between the positive electrode sheet 100 and the separator sheet 300. However, as a modified embodiment, as described in FIG. 7, a barrier layer 400′ may be provided between the positive electrode sheet 100 and the separator sheet 300, in addition to the slip layer 400 between the negative electrode sheet 200 and the separator sheet 300.

[0074] FIG. 9 is a diagram showing an electrode assembly according to another embodiment of the present invention.

[0075] 9, at least one of the two slip layers 400 described in FIG. 7 may be omitted, and a separation membrane overlapping portion 305P may be formed at the position where the slip layer 400 is omitted. The separation membrane overlapping portion 305P may be formed in a portion of the separation membrane sheet 300 that overlaps with one end portion of the positive electrode sheet 100 in a direction from the outside toward the inside (center) of the jelly roll type electrode assembly. The separation membrane overlapping portion 305P according to this embodiment is formed between one end portion of the positive electrode sheet 100 and the negative electrode sheet 200, and at this time, the thickness of the separation membrane overlapping portion 305P may be formed to be thicker than the thickness of a portion of the separation membrane sheet that does not face one end portion of the positive electrode sheet 100.

[0076] The separator sheet 305 according to this embodiment may include a first separator sheet 305a located on one side of the positive electrode sheet 100 and a second separator sheet 305b located on the other side of the positive electrode sheet 100. The separator overlapping portion 305P may include one end portion of the first separator sheet 305a formed by bending the first separator sheet 305a at least twice in the same direction so as to cover the cutting surface 100C of one end portion of the positive electrode sheet 100, and one end portion of the second separator sheet 305b overlapping one end portion of the first separator sheet 305a. Here, one end portion of the first separator sheet 305a may be formed by bending to cover the free edge portion 100A. One end portion of the first separator sheet 305a may be bent twice to cover the upper surface, side surface and lower surface of the free edge portion 100A.

[0077] One end portion of the second separator sheet 305b may be bent at least twice to include a double layer. Specifically, the second separator sheet 305b may be bent in a direction toward the first separator sheet 305a and bent again to overlap the bent portion of the first separator sheet 305a. One end portion of the second separator sheet 305b may include a double layer. According to this embodiment, a triple-layered separator overlap portion 305P is formed between the positive electrode sheet 100 and the negative electrode sheet 200, so that an internal short circuit between the negative electrode sheet 200 and the positive electrode sheet 100 can be physically prevented.

[0078] In addition, the slip layer 400 according to this embodiment may include a separator substrate layer 400a and an adhesive layer 400b formed on one side of the separator substrate layer 400a. The adhesive layer 400b may serve to attach the slip layer 400 to the negative electrode sheet 200. The slip layer 400 may further include a back coating layer 400c located on the back side of the separator substrate layer 400a where the adhesive layer 400b is located. The back coating layer 400c may serve to prevent the adhesive layers 400b from adhering to each other when the slip layer 400 is wound in the form of a tape in a preparation process for attaching the slip layer 400 to the negative electrode sheet 200.

[0079] The description of slip layer 400 described herein is applicable to the slip layer 400 previously described in FIGS.

[0080] FIG. 10 is a diagram showing an electrode assembly according to still another embodiment of the present invention.

[0081] The embodiment of FIG. 10 is almost identical to the embodiment described in FIG. 9, but the differences will be described below.

[0082] 10, the second separation membrane sheet 305c may not be bent, unlike the second separation membrane sheet 305b described in FIG. 9. In other words, one end of the second separation membrane sheet 305c according to this embodiment may not be bent and may overlap the first separation membrane sheet 305a in FIG. 9. Therefore, the separation membrane overlapping part 305P according to this embodiment is formed between the positive electrode sheet 100 and the negative electrode sheet 200 in a double-overlapped state, so that an internal short circuit between the negative electrode sheet 200 and the positive electrode sheet 100 can be physically prevented.

[0083] In addition to the differences described above, all of the contents described in FIG. 9 are applicable to this embodiment.

[0084] Meanwhile, the jelly roll type electrode assembly according to the present embodiment may be housed in a battery case to form a battery cell. Specifically, the jelly roll type electrode assembly may be inserted into a cylindrical or prismatic metal container, which may then be filled with an electrolyte and sealed to form a battery cell. The battery cell including the jelly roll type electrode assembly may be a cylindrical or prismatic battery, but the shape of the battery cell including the jelly roll type electrode assembly is not limited to the above examples.

[0085] 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 following claims also belong to the scope of the present invention. [Explanation of symbols]

[0086] 100: Positive electrode sheet 100A: Free edge section 110: Positive tap 120: Uncoated section 130: Coating section 200: Negative electrode sheet 300: Separation membrane sheet 305: Separation membrane overlapping section 400: Slip layer 400': Barrier layer

Claims

1. A jelly roll type electrode assembly including a positive electrode sheet, a negative electrode sheet, and a separator sheet interposed between the positive electrode sheet and the negative electrode sheet, a portion of the separator sheet facing one end of the positive electrode sheet located inside the jelly-roll type electrode assembly includes a first separator sheet portion facing the negative electrode sheet and a second separator sheet portion facing the positive electrode sheet, a coefficient of friction between the first separator sheet portion and the negative electrode sheet is smaller than a coefficient of friction between the second separator sheet portion and the positive electrode sheet.

2. 2. The jelly-roll type electrode assembly of claim 1, wherein one end of the positive electrode sheet is formed as a free edge portion containing an active material.

3. 3. The jelly-roll type electrode assembly of claim 2, wherein the free edge portion includes a portion of one end of the positive electrode sheet where a positive electrode active material is coated on an electrode collector.

4. The jelly roll type electrode assembly of claim 1 , wherein one end of the negative electrode sheet is located more inward than one end of the positive electrode sheet in the jelly roll type electrode assembly.

5. The negative electrode sheet further includes a slip layer located between the first separator sheet portion and the negative electrode sheet, 2. The jelly roll type electrode assembly of claim 1, wherein a friction coefficient between the slip layer and the first separator sheet portion or a friction coefficient between the slip layer and the negative electrode sheet is smaller than a friction coefficient between the second separator sheet portion and the positive electrode sheet.

6. One end of the positive electrode sheet is formed as a free edge portion including an active material, 6. The jelly roll type electrode assembly of claim 5, wherein the slip layer is positioned on the first separator sheet portion covering the free edge portion.

7. 7. The jelly roll type electrode assembly of claim 6, wherein the free edge portion is located between both ends of the slip layer based on a cross section of the jelly roll type electrode assembly.

8. 6. The jelly roll electrode assembly of claim 5, wherein the length of the slip layer is between 10 mm and 30 mm.

9. 6. The jelly roll type electrode assembly of claim 5, wherein the slip layer is made of a porous material.

10. 3. The jelly roll type electrode assembly of claim 2, further comprising a barrier layer positioned between the separator sheet and the positive electrode sheet so as to face the free edge portion.

11. 11. The jelly roll type electrode assembly of claim 10, wherein the barrier layer is located on the second separator sheet portion covering the free edge portion.

12. 12. The jelly roll type electrode assembly of claim 11, wherein a friction coefficient between the barrier layer and the second separator sheet portion or a friction coefficient between the barrier layer and the positive electrode sheet is greater than a friction coefficient between the first separator sheet portion and the negative electrode sheet.

13. 2. The jelly roll type electrode assembly of claim 1, further comprising a separator overlapping portion formed at a portion of the separator sheet overlapping one end of the positive electrode sheet in a direction from the outside to the inside of the jelly roll type electrode assembly.

14. 14. The jelly roll type electrode assembly of claim 13, wherein the separator overlap portion is formed between one end of the positive electrode sheet and the negative electrode sheet, and the thickness of the separator overlap portion is greater than a thickness of a portion of the separator sheet that does not face the one end of the positive electrode sheet.

15. The separator sheet includes a first separator sheet located on one side of the positive electrode sheet and a second separator sheet located on the other side of the positive electrode sheet, 15. The jelly-roll type electrode assembly of claim 14, wherein the separator overlapping portion includes one end portion of the first separator sheet formed by bending the first separator sheet at least twice in the same direction to cover a cutting surface of one end portion of the positive electrode sheet, and one end portion of the second separator sheet overlapping with the one end portion of the first separator sheet.

16. 16. The jelly roll type electrode assembly of claim 15, wherein one end of the second separator sheet is bent at least twice at its end to include a double layer.

17. A jelly roll type electrode assembly according to any one of claims 1 to 16, and a battery case that houses the jelly roll type electrode assembly.

18. A cylindrical battery comprising the battery cell of claim 17.

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