Jelly roll type electrode assembly, and secondary battery including the same

Abstract

The present invention relates to a jelly-roll type electrode assembly and a secondary battery including the same.

Description

Technical Field

[0001] The present invention relates to a jelly roll type electrode assembly and a secondary battery including the same, and more specifically, to a jelly roll type electrode assembly having an outer peripheral tab structure and a cylindrical secondary battery including the same. This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0090108, filed with the Korean Intellectual Property Office on July 21, 2022, and all of its content is incorporated herein by reference.

Background Art

[0002] In the case of a cylindrical battery, a long electrode with a determined width is wound in a roll shape to manufacture a jelly roll type electrode assembly. A cylindrical battery manufactured by inserting such a jelly roll type electrode assembly into a battery case repeatedly contracts / expands the electrode during charge and discharge, and stress due to a step is formed by the jelly roll structure.

[0003] Particularly, in the case of a jelly roll type electrode assembly having a negative electrode outermost structure, the outermost negative electrode covers the end of the positive electrode, and the space adjacent to the free edge of the positive electrode is empty due to the thickness of the positive electrode. At this time, the step due to the positive electrode thickness forms stress on the negative electrode, and such stress is concentrated on the opposite surface of the surface facing the positive electrode during charge and discharge, inducing a negative electrode outer shell crack.

[0004] In order to prevent the occurrence of such negative electrode outer shell cracks, it is necessary to develop a technology capable of improving the concentration of negative electrode stress in the region.

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a jelly roll type electrode assembly with a modified design of the jelly roll type electrode assembly and a secondary battery including the same.

[0006] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned should be clearly understood by those skilled in the art from the following description.

Means for Solving the Problems

[0007] One embodiment of the present invention is a jelly roll type electrode assembly in which a first electrode, a first separator, a second electrode, and a second separator are sequentially laminated and wound, and the first electrode, the first separator, the second electrode, and the second separator each include a first end portion where winding starts and a second end portion where winding ends along the length direction, and the second end portion of the first separator or the second separator extends longer than the second end portion of the second electrode, and includes a step relaxation portion bent or rolled on the second end portion side of the second electrode, and provides a jelly roll type electrode assembly.

[0008] Another embodiment of the present invention provides a secondary battery including the jelly roll type electrode assembly; and a battery case for accommodating the electrode assembly.

Advantages of the Invention

[0009] The jelly roll type electrode assembly according to one embodiment of the present invention, and the secondary battery including the same can improve the stress concentration concentrated on the outermost negative electrode by relaxing the step due to the positive electrode thickness, and can prevent cracks and deformation of the electrode assembly.

[0010] Also, the jelly roll type electrode assembly according to one embodiment of the present invention, and the secondary battery including the same utilize a step relaxation portion in which the design of the jelly roll type electrode assembly is changed, so that while being economical, local problems such as lithium precipitation in the region can be prevented.

[0011] The advantages of the present invention are not limited to the advantages mentioned above, and the advantages not mentioned should be clearly understood by those skilled in the art from the specification of the present application and the attached drawings.

Brief Description of the Drawings

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Description of Reference Numerals

[0013] 1000 ··· Jelly roll type electrode assembly 100, 100' ··· First electrode 101 ··· First electrode current collector 102, 103 ··· First electrode active material layer 120 ··· Second end portion of the first electrode 20 ··· First separator 21 ··· First end portion of the first separator 22 ··· Second end portion of the first separator 300 ··· Second electrode 301 ··· Second electrode current collector 302, 303 ··· Second electrode active material layer 320 ··· Second end portion of the second electrode 40 ··· Second separator 41 ··· First end portion of the second separator 42 ··· Second end portion of the second separator 50 ··· Step relaxation portion 60 ··· Step portion 70 ··· Tape for preventing disconnection H1 ··· First step H2 ··· Second step T1, T1' ··· Thickness of the step relaxation portion T2 ··· Thickness of the second end portion of the second electrode L1 ··· Length in the winding axis direction of the step relaxation portion L2 ··· Length in the longitudinal direction of the step relaxation portion

Mode for Carrying Out the Invention

[0014] Throughout the specification of the present application, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but can further include other components.

[0015] Throughout the specification of the present application, when a certain member is located "on" another member, this includes not only the case where a certain member is in contact with another member, but also the case where there is another member between the two members.

[0016] Hereinafter, the present invention will be described in detail with reference to the drawings. However, the drawings are for illustrative purposes only, and the scope of the present invention is not limited by the drawings.

[0017] One embodiment of the present invention is a jelly roll-type electrode assembly in which a first electrode, a first separator, a second electrode, and a second separator are sequentially laminated and wound, and the first electrode, the first separator, the second electrode, and the second separator each include a first end portion where winding starts along the length direction and a second end portion where winding ends. The second end portion of the first separator or the second separator extends longer than the second end portion of the second electrode and includes a step relaxation portion bent or rolled on the second end portion side of the second electrode. The jelly roll-type electrode assembly according to the present invention can form a predetermined step according to the thickness of the step relaxation portion to relax the step formed by the thickness of the second end portion of the second electrode, improve the stress concentration concentrated on the opposite surface of the surface facing the second end portion of the first electrode, and prevent cracks and deformations generated on the outer contour of the electrode assembly.

[0018] FIG. 1 shows a jelly roll-type electrode assembly including a step relaxation portion in which a first separator is rolled according to one embodiment of the present invention, and FIG. 2 shows a jelly roll-type electrode assembly including a step relaxation portion in which a second separator is rolled according to one embodiment of the present invention.

[0019] Referring to FIG. 1, in the jelly roll-type electrode assembly according to one embodiment of the present invention, the first electrode 100, the first separator 20, the second electrode 300, and the second separator 40 each include a first end portion where winding starts along the length direction and a second end portion where winding ends. The second end portion 22 of the first separator 20 may extend longer than the second end portion of the second electrode 300 and include a step relaxation portion 50 bent or rolled on the second end portion 320 side of the second electrode 300.

[0020] Referring to FIG. 2, in a jelly roll type electrode assembly according to an embodiment of the present invention, the first electrode 100, the first separator 20, the second electrode 300, and the second separator 40 each include a first end where winding starts along the length direction and a second end where winding ends. The second end 42 of the second separator 40 may extend longer than the second end 320 of the second electrode 300 and may include a step relaxation portion 50 that is bent or rolled on the side of the second end 320 of the second electrode 300.

[0021] Here, the bending may be to bend the first separator or the second separator two or more times at a predetermined interval so that the second end of the first separator or the second separator is located at the center of the step relaxation portion, thereby forming a multi-layered sheet form. The rolling may be to wind the first separator or the second separator two or more times at a predetermined interval so that the second end is located at the center of the step relaxation portion, thereby forming a roll form having an oval cross-section. The bending or rolling form may vary depending on the flexibility of the material of the first separator or the second separator.

[0022] FIG. 3 is an image embodying a jelly roll type electrode assembly according to an embodiment of the present invention.

[0023] Referring to FIG. 3, in a jelly roll type electrode assembly 1000 according to an embodiment of the present invention, the second end of the first separator 20 may extend longer than the second end of the second electrode 300 and may be rolled on the side of the second end of the second electrode to form a step relaxation portion 50. It may have a predetermined thickness and may form a roll form having an oval cross-section.

[0024] According to an embodiment of the present invention, the winding axis direction length L1 of the step relaxation portion may be 50% or more and 100% or less based on the winding axis direction length of the first electrode being 100%. Specifically, the winding axis direction length of the step relaxation portion may be 55% or more, 60% or more, or 65% or more based on the winding axis direction length of the first electrode being 100%, and the winding axis direction length of the step relaxation portion may be 95% or less, 90% or less, or 85% or less based on the winding axis direction length of the first electrode being 100%. When the winding axis direction length range of the step relaxation portion within the above range is satisfied, the stress concentrated on the opposite surface of the surface of the first electrode facing the second step due to the step formed by the second end portion of the second electrode can be effectively dispersed, and problems such as crack generation can be effectively reduced, thereby ensuring the stability of the battery.

[0025] According to an embodiment of the present invention, the step relaxation portion may be formed by bending or rolling the second end portion of the first separator or the second separator 3 or more times and 16 or less times on the second end portion side of the second electrode. Specifically, the step relaxation portion may be formed by bending or rolling the second end portion of the first separator or the second separator 4 or more times, 6 or more times, or 8 or more times on the second end portion side of the second electrode, and the step relaxation portion may be formed by bending or rolling the second end portion of the first separator or the second separator 14 or less times, 12 or less times, or 10 or less times on the second end portion side of the second electrode. For example, when the step due to the thickness of the second electrode is 170 μm, a first separator or a second separator having a thickness of 13 μm may be bent or rolled 4 or more times and 10 or less times to form a step relaxation portion having a thickness range of 55 μm or more and 130 μm or less. When the step due to the thickness of the second electrode is 130 μm, a first separator or a second separator having a thickness of 12.5 μm may be bent or rolled 4 or more times and 10 or less times to form a step relaxation portion having a thickness range of 50 μm or more and 100 μm or less, thereby adjusting the thickness range to a predetermined ratio. When the number of bending or rolling times within the above range is satisfied, the thickness of the step relaxation portion satisfies a predetermined ratio with respect to the thickness of the second end portion of the second electrode, so that the step relaxation effect becomes excellent, and additional step formation problems and process non-economic problems that may occur due to excessive bending or rolling can be prevented.

[0026] FIG. 4 is a diagram schematically showing a stepped portion of a jelly roll type electrode assembly according to an embodiment of the present invention.

[0027] Referring to FIG. 4, the jelly roll type electrode assembly according to an embodiment of the present invention includes a stepped portion 60 which is an empty space formed in a region where the first electrode 100 covers the second end portion 320 of the second electrode 300, and the stepped portion relaxation portion 50 may be provided in the stepped portion 60. Specifically, in the electrode assembly according to an embodiment of the present invention, the first electrode 100 located at the outermost periphery may be extended longer than the second end portion 320 of the second electrode 300 and additionally wound around the outer periphery of the electrode assembly, and a step due to the thickness of the second electrode may be formed adjacent to the second end portion 320 of the second electrode 300. That is, the jelly roll type electrode assembly according to an embodiment of the present invention may form a laminated structure of the first electrode / the first separator / the second electrode / the second separator / the first electrode in a wound state, but the length of the second electrode may be shorter than that of the remaining layers, and there may be a region where a laminated structure of the first electrode / the first separator / the empty space / the second separator / the first electrode is formed at the outermost periphery. In other words, a stepped portion 60 which is an empty space surrounded by the first separator (not shown) in contact with the inner peripheral surface of the first electrode 100 / the second end portion 320 of the second electrode 300 / the first electrode 100' or the second separator (not shown) may be formed. Specifically, the stepped portion relaxation portion 50 may be provided in the stepped portion 60 and may be provided on the opposite surface of the surface of the first electrode 100' located inside the electrode assembly facing the winding axis. Further, the stepped portion relaxation portion can disperse the stress concentrated in the region where the second end portion 320 of the second electrode 300 contacts the inner peripheral surface of the first electrode 100 by forming a region additionally in contact with the inner peripheral surface of the first electrode 100 located at the outermost periphery.

[0028] According to an embodiment of the present invention, the step relaxation portion may be provided in direct contact with or separated from the second end portion of the second electrode. Specifically, when the step relaxation portion is provided separated from the second end portion of the second electrode, the separation distance between the step relaxation portion and the second end portion of the second electrode may be 1 mm or more and 2 mm or less. More specifically, the separation distance between the step relaxation portion and the second end portion of the second electrode may be 1 mm or more and 1.5 mm or less, or 1.5 mm or more and 2 mm or less. When the separation distance within the above range is satisfied, in order to effectively disperse the stress concentrated in the region where the first electrode and the second end portion of the second electrode are in contact, the first separator or the second separator is bent or rolled to form a step relaxation portion having an appropriate thickness, which facilitates the process, prevents unnecessary material loss, and ensures economic efficiency.

[0029] According to an embodiment of the present invention, the step portion may include a first step formed by the thickness of the step relaxation portion; and a second step formed by the difference between the thickness of the second electrode and the thickness of the step relaxation portion.

[0030] Referring to FIG. 4, the first step H1 may be the same as the thickness T1 of the step relaxation portion, and the second step H2 may be the same as the difference between the thickness T2 of the second electrode and the thickness T1 of the step relaxation portion. Specifically, the first step H1 may be the same as the thickness T1 of the step relaxation portion measured at the position where the step relaxation portion and the inner peripheral surface of the first electrode are in contact, and the second step H2 may be the same as the difference between the thickness T2 of the second electrode measured at the position where the second end portion of the second electrode and the inner peripheral surface of the first electrode are in contact and the thickness T1 of the step relaxation portion measured at the position where the step relaxation portion and the inner peripheral surface of the first electrode are in contact.

[0031] More specifically, referring to FIG. 1, the step relaxation portion may be formed by bending or rolling the first separator 20, and the first step H1 may mean the thickness T1 of the step relaxation portion, which is the linear distance between the first electrode 100 and the second separator 40 measured in a direction perpendicular to the winding axis at the position where the inner peripheral surface of the step relaxation portion 50 and the first electrode 100 are in contact. On the other hand, referring to FIG. 2, the step relaxation portion 50 may be formed by bending or rolling the second separator 40, and the first step H1 may mean the thickness T1' of the step relaxation portion, which is the linear distance between the first separator and the first electrode measured in a direction perpendicular to the winding axis at the position where the first separator in contact with the inner peripheral surface of the step relaxation portion and the first electrode are in contact. However, due to the flexibility of the materials forming the step relaxation portion and the first electrode, and the differences in bending or rolling forms, the position in contact with the inner peripheral surface of the first electrode may be different, and the thicknesses T1 and T1' of the step relaxation portion can be approximated to the value obtained by subtracting the thickness of one layer of the first separator or the second separator from the thickness of the center portion of the step relaxation portion.

[0032] According to an embodiment of the present invention, the first step may be 20% or more and 95% or less of the second end thickness of the second electrode. Specifically, referring to FIG. 4, the first step H1 may be 25% or more, 30% or more, 35% or more, or 40% or more of the second end thickness T2 of the second electrode, and the first step H1 may be 90% or less, 85% or less, 80% or less, or 75% or less of the second end thickness T2 of the second electrode. When the numerical range of the above range is satisfied, it is possible to form a two-step step in a stepped manner, and the stress concentrated on the opposite surface of the surface of the first electrode facing the second step can be effectively dispersed by the first step and the second step, thereby effectively reducing problems such as crack generation and ensuring the stability of the battery.

[0033] According to one embodiment of the present invention, the volume of the step relaxation portion may be 5% or more and 95% or less of the volume of the step portion. Specifically, the volume of the step relaxation portion may be 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more of the volume of the step portion, and the volume of the step relaxation portion may be 90% or less, 85% or less, 80% or less, or 75% or less of the volume of the step portion. Referring to FIGS. 3 and 4, when the second end portion of the first separator or the second separator is bent or rolled toward the second end portion side of the second electrode, the step relaxation portion is in a form approximating a rectangular parallelepiped. Therefore, the volume of the step relaxation portion may be approximately calculated by the rectangular parallelepiped volume formula. Specifically, it may be approximately calculated using the winding axis direction length L1, the length direction length L2, and the thickness T1 of the step relaxation portion. In addition, since the volume of the step portion may vary depending on the tension of the manufacturing apparatus, the charge and discharge state, the outer diameter of the jelly roll, etc. during the manufacturing process of the cell, the volume of the step portion may be approximately calculated through a trigonometric function. Specifically, a virtual triangle may be drawn with the second end portion thickness T2 of the second electrode as the height and the length of the first electrode or the second separator surrounding the step portion as the base, and it may be approximately calculated. In some cases, the volume of the step portion may be confirmed by a Computed Tomography (CT) technique. When the volume range of the step relaxation portion within the above range is satisfied, the stress concentrated on the opposite surface of the surface of the first electrode facing the second step due to the first step can be effectively dispersed, and since the volume of the step relaxation portion does not exceed the volume of the step portion even when the electrode assembly is impregnated with the electrolyte, it is possible to prevent a problem of damage to the electrode assembly that may additionally occur when the volume of the electrode assembly changes due to the charge and discharge cycle of the secondary battery.

[0034] According to an embodiment of the present invention, the thickness of the step relaxation portion may be 20 μm or more and 150 μm or less. Specifically, the thickness of the step relaxation portion may be 30 μm or more, 40 μm or more, 50 μm or more, or 60 μm or more, and the thickness of the step relaxation portion may be 140 μm or less, 130 μm or less, 120 μm or less, 110 μm or less, or 100 μm or less. The thickness of the step relaxation portion may have the largest value at the center of the step relaxation portion where the second end of the first separator or the second separator is located, and may have the smallest value at the end of the step relaxation portion where the first separator or the second separator is bent or rolled. When the thickness range of the step relaxation portion within the above range is satisfied, the step due to the thickness of the second electrode can be effectively relaxed, and thereby the stress concentrated thereon can be effectively dispersed. For example, when the step due to the thickness of the second electrode is 170 μm, a step relaxation portion having a thickness range of 55 μm or more and 130 μm or less may be formed. When the step due to the thickness of the second electrode is 130 μm, the thickness range of the step relaxation portion may be adjusted so as to relax the step due to the thickness of the second electrode with a predetermined ratio of the first step and the second step by forming a step relaxation portion having a thickness range of 50 μm or more and 100 μm or less.

[0035] Referring to FIG. 3, the length L2 in the length direction of the step relaxation portion included in the jelly roll type electrode assembly according to an embodiment of the present invention may be 8 mm or more and 30 mm or less. Specifically, the length L2 in the length direction of the step relaxation portion may be 10 mm or more, 12 mm or more, 14 mm or more, or 16 mm or more, and the length L2 in the length direction of the step relaxation portion may be 28 mm or less, 26 mm or less, 24 mm or less, 22 mm or less, or 20 mm or less. The length in the length direction of the step relaxation portion may mean the length measured from one end to the other end of the step relaxation portion where the first separator or the second separator is bent or rolled. When the length range of the step relaxation portion within the above range is satisfied, the step due to the thickness of the second electrode can be effectively relaxed, and the first electrode located on the outermost contour of the wound jelly roll type electrode assembly and surrounding the step portion has an appropriate inclination and bending, so that damage to the region in contact with the second end portion of the second electrode or damage due to the pressure acting on the opposite surface of the empty space can be minimized.

[0036] According to an embodiment of the present invention, the second end portion of the first electrode may be extended longer than the second end portion of the second electrode and additionally wound around the outer contour of the electrode assembly. Further, according to an embodiment of the present invention, the first electrode may be a negative electrode and the second electrode may be a positive electrode. Specifically, the first electrode, which is the outermost layer of the electrode assembly, may be a negative electrode, and the electrode assembly may have a negative electrode outermost structure in which a negative electrode / separator / positive electrode / separator is wound. In other words, it may have an outer peripheral tab structure in which the negative electrode is exposed on the outermost contour of the jelly roll type electrode assembly.

[0037] According to an embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector and containing a negative electrode active material. In other words, the negative electrode active material layer may be formed on the negative electrode active material portion of the negative electrode current collector, and the surface without the negative electrode active material layer may be represented as a negative electrode plain portion.

[0038] According to one embodiment of the present invention, the negative electrode current collector may include a negative electrode active material portion on which a negative electrode active material layer is formed and a negative electrode blank portion on which no negative electrode active material layer is formed, and may include a tab on the negative electrode blank portion. Specifically, the negative electrode current collector may include a negative electrode blank portion and may include a negative electrode tab formed on the negative electrode blank portion. Thereby, the manufactured electrode assembly may include one or more negative electrode tabs.

[0039] According to one embodiment of the present invention, the negative electrode active material layer may include a negative electrode active material including one or more selected from the group consisting of silicon-based materials and carbon-based materials. Specifically, the negative electrode active material layer may include a silicon-based material in a content of more than 0% and 20% or less. Further, the negative electrode active material layer may further include a negative electrode conductive material and a negative electrode binder, and the negative electrode active material; negative electrode conductive material; and negative electrode binder may be used without limitation substances used in the art.

[0040] According to one embodiment of the present invention, the negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. For example, as the negative electrode current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the negative electrode current collector.

[0041] The thickness of the negative electrode current collector may be 70 μm or more and 180 μm or less, but the thickness of the negative electrode current collector is not limited thereto.

[0042] According to one embodiment of the present invention, the negative electrode binder may include at least any one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include these various copolymers.

[0043] According to one embodiment of the present invention, the negative electrode conductive material is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0044] According to an embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector. Specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on one or both surfaces of the positive electrode current collector and containing a positive electrode active material. In other words, the positive electrode active material layer may be formed on the positive electrode active material portion of the positive electrode current collector, and the surface without the positive electrode active material layer may be represented as a positive electrode plain portion.

[0045] According to an embodiment of the present invention, the positive electrode current collector may include a positive electrode active material portion where a positive electrode active material is formed and a positive electrode plain portion where no positive electrode active material is formed, and may include a tab on the positive electrode plain portion. Specifically, the positive electrode current collector may include a positive electrode plain portion and may include a positive electrode tab formed on the positive electrode plain portion. As a result, the manufactured electrode assembly may include one or more positive electrode tabs.

[0046] According to an embodiment of the present invention, the positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. Specifically, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used.

[0047] Further, the positive electrode current collector may usually have a thickness of 80 to 190 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0048] According to an embodiment of the present invention, the positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; the chemical formula Li 1+x Mn 2-xLithium manganese oxides such as O4 (0 ≦ x ≦ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-y M y O2 (where M is at least any one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ y ≦ 0.3), Ni-site type lithium nickel oxide represented by; chemical formula LiMn 2-z M z O2 (where M is at least any one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ z ≦ 0.1), or lithium manganese composite oxide represented by Li2Mn3MO8 (where M is at least any one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include, but are not limited to, LiMn2O4 in which a part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li-metal.

[0049] According to one embodiment of the present invention, the positive electrode active material layer may further include a positive electrode conductive material and a positive electrode binder. The positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without particular limitation as long as it does not induce a chemical change and has electronic conductivity. Specifically, the positive electrode conductive material includes graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more thereof may be used.

[0050] In addition, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesion force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used.

[0051] According to an embodiment of the present invention, the second end portion of the second electrode may be in the form of a free edge. Here, the free edge form may mean a form in which the end portion of the second electrode active material layer of the electrode coincides with the end portion of the electrode current collector. That is, the jelly roll type electrode assembly according to an embodiment of the present invention may have a structure in which the first electrode, which is the outermost layer, covers the second end portion of the second electrode in the free edge form, and may include a step portion that is an empty space formed in the region where the first electrode covers the second end portion of the second electrode, and may include a step relaxation portion provided in direct contact with or separated from one side of the second end portion of the second electrode in the free edge form within the step portion.

[0052] FIG. 5 schematically shows the laminated structure of a jelly roll type electrode assembly according to an embodiment of the present invention.

[0053] Referring to FIG. 5, in the first electrodes 100, 100', the first electrode 100 exists at the outermost periphery of the electrode assembly 1000. The first electrode 100 includes first electrode active material layers 102 and 103 on both sides of a first electrode current collector 101, and may include a non - coating area. On the other hand, the second electrode 300 exists at the outermost periphery of the electrode assembly 1000. The second electrode 300 includes positive electrode active material layers 302 and 303 on both sides of a second electrode current collector 301, but may not include a non - coating area. In other words, it may be in the form of a free edge where the ends of the second electrode current collector and the second electrode active material layer coincide. That is, the second end 320 of the second electrode 300 may include the ends of the second electrode active material layers 302 and 303 having the same length in the longitudinal direction and the end of the second electrode current collector 301, and the second end 320 of the second electrode 300 may have the ends of the second electrode active material layers 302 and 303 and the end of the second electrode current collector 301 coincide. On the other hand, according to an embodiment of the present invention, the non - coating area existing on the opposite surface of the surface of the first electrode 100 facing the end of the second end 320 of the second electrode 300 may further include a disconnection prevention tape 70 attached to reduce the possibility of short - circuit or crack due to stress concentration in the area.

[0054] According to an embodiment of the present invention, the jelly roll type electrode assembly may further include a plurality of separators. For example, the jelly roll type electrode assembly may have a structure in which a first electrode / a first separator / a second electrode / a second separator are laminated in this order. The separator separates the first electrode and the second electrode and provides a movement path for lithium ions. Usually, any separator that can be used in a secondary battery can be used without particular limitation. In particular, a separator that has a low resistance to the ion movement of the electrolyte and has excellent electrolyte moisture retention ability is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, the separator may usually have a thickness of 10 μm or more and 20 μm or less, and a coated separator containing a ceramic component or a polymer substance may be used to ensure heat resistance or mechanical strength. Optionally, it may be used in a single-layer or multi-layer structure.

[0055] An embodiment of the present invention provides a secondary battery including the jelly roll type electrode assembly; and a battery case for housing the electrode assembly; the content included in the jelly roll type electrode assembly being the same as described above.

[0056] According to an embodiment of the present invention, the secondary battery may include a cap assembly coupled to the opening of the battery case, and the cap assembly may include a top cap, a safety vent, a current interruption element, etc.

[0057] According to an embodiment of the present invention, the first electrode may be in direct contact with the inner surface of the battery case, and the battery case may serve as a first electrode terminal.

[0058] According to one embodiment of the present invention, the interior of the battery case may contain an electrolyte. Specifically, examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0059] According to one embodiment of the present invention, examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triethyl phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc.

[0060] According to one embodiment of the present invention, the metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte solution. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN) 2- , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 -, (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0061] According to one embodiment of the present invention, in addition to the constituent components of the electrolyte, for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, improving the discharge capacity of the battery, etc., for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or additives such as aluminum trichloride may be further included in one or more.

[0062] According to one embodiment of the present invention, the battery case may be cylindrical. That is, the jelly roll type electrode assembly according to the present invention can be housed in a cylindrical battery case, and the assembly including a positive electrode, a negative electrode, and a separator; a cap assembly; and the battery case containing an electrolyte has a cylindrical shape, so the form of the manufactured secondary battery itself may be cylindrical.

[0063] Hereinafter, examples will be given to specifically describe the present invention in detail. However, the examples according to the present invention may be deformed into various forms, and it should not be construed that the scope of the present invention is limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those with average knowledge in the industry.

[0064] Example Example 1 Manufacture of Electrode Assembly An Al foil was prepared as a positive current collector, and a positive electrode active material layer was formed by applying and drying a positive electrode active material slurry on the positive current collector to manufacture a positive electrode as a second electrode.

[0065] Next, a pure copper (Pure Cu) foil with a thickness of 8 μm was prepared as a negative current collector, and a negative electrode active material layer was formed by applying and drying a negative electrode active material slurry on the negative current collector to manufacture a negative electrode as a first electrode.

[0066] On the other hand, two separators each having a coating layer formed on one surface of a sheet-like polyethylene base material layer were prepared as a first separator and a second separator, respectively.

[0067] Thereafter, winding was started from one end in the length direction of the first separator and the second separator, and the first electrode and the second electrode were sequentially inserted to manufacture a jelly roll type electrode assembly.

[0068] At this time, at the outermost part of the jelly roll type electrode assembly, the first separator was provided so as to extend longer than the second end of the second electrode, and the second end of the first separator was rolled 15 times toward the second end side of the second electrode, so that a step relaxation portion was provided in a step portion which is an empty space formed in a region where the first electrode covers the second end of the second electrode, so as to have the structure according to FIG. 1. At this time, the thickness of the second end of the second electrode was 130 μm, the thickness of the step relaxation portion was 117 μm, the length in the length direction of the step relaxation portion was 11 mm, and the step relaxation portion was provided at a distance of 1 mm from the second end of the second electrode.

[0069] Manufacture of secondary battery After inserting the jelly roll type electrode assembly into a cylindrical battery case, an electrolytic solution was injected, and the cylindrical battery can was sealed to manufacture a secondary battery.

[0070] Example 2 By rolling the second end portion of the first separator 7 times toward the second end portion side of the second electrode, except that the thickness of the step relaxation portion is 58.5 μm and the lengthwise length of the step relaxation portion is 10 mm, a jelly roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1.

[0071] Comparative Example 1 Except for not providing a step relaxation portion, a jelly roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1.

[0072] Experimental Example Experimental Example 1 - Evaluation of Electrode Crack Improvement (SEM) Secondary batteries according to Example 1, Example 2, and Comparative Example 1 were prepared. Thereafter, charge and discharge were performed 50 cycles (Cycle) under the conditions of 23°C and in the range of SOC 0% to 100%.

[0073] After the cycles, the secondary batteries according to Example 1, Example 2, and Comparative Example 1 were each disassembled, and the first electrode at the position corresponding to the second end portion of the second electrode was ion milled with an Ar ion beam, and the thickness of the first electrode after the cycles was measured using a scanning electron microscope (SEM).

[0074] Thereafter, the degree of improvement in electrode cracks was evaluated by comparing the thickness ratio of the step relaxation portion according to the following formula 1 and the deformation rate of the first electrode according to the following formula 2. At this time, the evaluation conditions and evaluation results are shown in Table 1 and FIGS. 6 to 8 below.

[0075] [Formula 1] Thickness ratio (%) of the step relaxation portion = {Thickness (T1, μm) of the step relaxation portion / Thickness (T2, μm) of the second end portion of the second electrode} × 100

[0076] [Equation 2] Deformation rate (%) of the first electrode = { (Thickness of the first electrode (μm)- Thickness (μm) of the first electrode after 50 cycles ) / Thickness (μm) of the first electrode} × 100

[0077]

Table 1

[0078] FIG. 6 is an SEM image showing the crack improvement evaluation result of the secondary battery according to Example 1, FIG. 7 is an SEM image showing the crack improvement evaluation result of the secondary battery according to Example 2, and FIG. 8 is an SEM image showing the crack improvement evaluation result of the secondary battery according to Comparative Example 1. Referring to Table 1 and FIGS. 6 to 8, it was confirmed that the deformation rate of the first electrode of the secondary batteries according to Example 1 and Example 2 decreased by 8.12% to 14.75% compared to the secondary battery according to Comparative Example 1. In particular, it was confirmed that the deformation rate of the first electrode of the secondary battery according to Example 1, in which the thickness ratio of the step relaxation portion is 90%, is the lowest at 0.75%.

[0079] When comparing Example 1 and Example 2 with Comparative Example 1, when the contraction / expansion of the electrode is repeated during cycling, stress may be concentrated on the first electrode by the second end portion of the second electrode, and cracks and deformation may occur. However, by providing a step relaxation portion in the step portion, which is an empty space formed adjacent to the second end portion of the second electrode, and relaxing the step due to the thickness of the second electrode, it can be seen that the stress concentration of the first electrode can be improved and the possibility of crack generation can be reduced.

[0080] Also, when adjusting the thickness T1 (μm) of the step relaxation portion and the thickness ratio (T1 / T2, %) of the step relaxation portion within a specific range, it can be seen that the effect of reducing the possibility of crack generation in the first electrode by the second end portion of the second electrode is more excellent.

[0081] That is, in the jelly roll type electrode assembly according to one embodiment of the present invention and the secondary battery including the same, by alleviating the step due to the positive electrode thickness, it can be seen that the stress concentration concentrated on the outermost negative electrode is improved, and cracks and deformation of the electrode assembly can be prevented.

[0082] Experimental Example 2 - Evaluation of Electrode Crack Improvement (Simulation) For the secondary batteries according to Example 1, Example 2, and Comparative Example 1, the degree of improvement in electrode cracks at the first electrode facing the second end portion of the second electrode was evaluated by simulation. Specifically, by simulating the volume change of the step relaxation portion provided in the step portion, the maximum deformation rate of the first electrode during the expansion of the jelly roll type electrode assembly was measured, and the results are shown in FIGS. 9 to 11 below. At this time, the second electrode has a free edge having the same position of the second electrode current collector and the second electrode active material layer at the longitudinal end, and the first electrode was set under the same conditions as copper foil (Cu Foil).

[0083] FIG. 9 is a simulation image showing the evaluation result of crack improvement of the secondary battery according to Example 1, FIG. 10 is a simulation image showing the evaluation result of crack improvement of the secondary battery according to Example 2, and FIG. 11 is a simulation image showing the evaluation result of crack improvement of the secondary battery according to Comparative Example 1.

[0084] Referring to FIGS. 10 and 11, in the case of Example 2 including a step relaxation portion having a thickness of 45% compared to the thickness of the second end portion of the second electrode, it was confirmed that the maximum deformation rate occurred on the opposite surface of the first electrode facing the second end portion of the second electrode.

[0085] Specifically, the maximum deformation rate of the first electrode of the secondary battery according to Comparative Example 1 was 0.0651, and the maximum deformation rate of the first electrode of the secondary battery according to Example 2 was 0.0468. It was confirmed that the maximum deformation rate of the outermost first electrode in Example 2 decreased by 28.1% compared to Comparative Example 1.

[0086] Thus, when the stepped portion is provided with a step relaxation portion, it can be seen that the bending of the first electrode is relaxed at the second end portion of the second electrode, the maximum deformation rate is decreased, and thus the possibility of crack generation in the first electrode is decreased.

[0087] Referring to FIGS. 9 and 11, it was confirmed that in the secondary battery according to Example 1, while the bending of the first electrode hardly occurs at the second end portion of the second electrode, the bending of the first electrode occurs at the longitudinal end portion of the step relaxation portion, and thereby the maximum deformation rate of the first electrode is measured. The maximum deformation rate of the first electrode of the secondary battery according to Example 1 was 0.0259, and it was confirmed that this was decreased by 60.2% compared to the maximum deformation rate of the first electrode of the secondary battery according to Comparative Example 1.

[0088] Thus, when the stepped portion is provided with a step relaxation portion, the bending of the first electrode at the second end portion of the second electrode is relaxed, the maximum deformation rate of the first electrode is decreased, and thereby the possibility of crack generation in the first electrode is decreased. When the step relaxation portion is provided with a thickness similar to that of the second end portion of the second electrode, that is, in the case of Example 1, it can be seen that the possibility of crack generation in the first electrode is the lowest.

[0089] That is, it can be seen that the jelly roll type electrode assembly according to an embodiment of the present invention, and the secondary battery including the same, can improve the concentration of stress concentrated on the outermost negative electrode by relaxing the step due to the positive electrode thickness, and can prevent cracks and deformation of the electrode assembly.

[0090] Further, the jelly roll type electrode assembly according to an embodiment of the present invention, and the secondary battery including the same, utilize a step relaxation portion in which the design of the jelly roll type electrode assembly is changed, and thus it can be seen that while being economical, it is possible to prevent the occurrence of local problems such as lithium precipitation in the region.

[0091] The preferred embodiments have been presented above to assist in the understanding of the present invention. However, it is obvious to those skilled in the art that the above embodiments are merely illustrative of the description, and various changes and modifications are possible within the scope of the description and the scope of the technical idea. Naturally, such variations and modifications belong to the scope of the claims.

Claims

1. A jelly roll type electrode assembly in which a first electrode, a first separator, a second electrode, and a second separator are sequentially laminated and wound, the first electrode, the first separator, the second electrode, and the second separator each include a first end portion where winding starts and a second end portion where winding ends along the length direction, the second end portion of the first separator or the second separator extends longer than the second end portion of the second electrode, and is provided with a step relaxation portion that relaxes the step due to the thickness of the second electrode within a step portion that is an empty space formed adjacent to the second end portion of the second electrode. The step relaxation portion is formed by rolling the second end portion of the first separator or the second separator that extends longer toward the second end portion side of the second electrode. The first electrode is a negative electrode and the second electrode is a positive electrode. A jelly roll type electrode assembly.

2. The jelly roll type electrode assembly according to claim 1, wherein the step relaxation portion is formed by rolling the second end portion of the first separator or the second separator 3 or more times and 16 or less times toward the second end portion side of the second electrode.

3. The jelly roll type electrode assembly according to claim 1, wherein the step relaxation portion is provided within the step portion.

4. The step portion includes a first step formed by the thickness of the step relaxation portion; and a second step formed by the difference between the thickness of the second electrode and the thickness of the step relaxation portion; The jelly roll type electrode assembly according to claim 3, including.

5. The jelly roll type electrode assembly according to claim 4, wherein the first step is 20% or more and 95% or less of the thickness of the second end portion of the second electrode.

6. The jelly roll type electrode assembly according to claim 3, wherein the volume of the step relaxation portion is 5% or more and 95% or less of the volume of the step portion.

7. The jelly roll type electrode assembly according to claim 1, wherein the thickness of the step relaxation portion is 20 μm or more and 150 μm or less.

8. The jelly roll type electrode assembly according to claim 1, wherein the length in the length direction of the step relaxation portion is 8 mm or more and 30 mm or less.

9. The jelly roll type electrode assembly according to claim 1, wherein the second end portion of the first electrode extends longer than the second end portion of the second electrode and is further wound around the outer contour of the jelly roll type electrode assembly.

10. The jelly roll type electrode assembly according to any one of claims 1 to 9; and A battery case for housing the jelly roll type electrode assembly; A secondary battery including the same.

11. The secondary battery according to claim 10, wherein the battery case is cylindrical.

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