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 including a separator overlapping portion and a cylindrical secondary battery including the same. This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0165808, filed with the Korean Intellectual Property Office on December 1, 2022, and all of its contents are incorporated herein by reference.

Background Art

[0002] In the case of a cylindrical battery, a long electrode with a fixed 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 repeats contraction / expansion of the electrodes during charging and discharging. In particular, when an in tab is located at the core of the jelly roll type electrode assembly or a silicon-based active material is added to the negative electrode, the degree of contraction / expansion of the electrode assembly increases, and thus the pressure acting on the core portion of the electrode assembly increases significantly.

[0003] In recent years, as low resistance / high capacity designs have increased, the jelly roll type electrode assembly has increasingly included multiple tabs or a silicon-based active material has been added, thereby increasing the deformability of the electrode assembly located in the core portion due to contraction / expansion of the electrode assembly. In particular, when the separator located between the negative electrode and the positive electrode is damaged, there has been a problem that the negative electrode and the positive electrode come into direct contact, resulting in heat generation and ignition due to an internal short circuit.

[0004] In order to solve the problems of damage to the separator and occurrence of an internal short circuit due to such deformation of the electrode assembly, there is a need for the development of a technology that can protect the negative electrode and the separator in this area and suppress the occurrence of an internal short circuit.

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 above-described problems, and other problems not mentioned can 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 separator, a negative electrode, a second separator, and a positive electrode are sequentially laminated and wound, wherein the positive electrode includes a first surface that is the winding axis direction of the jelly roll type electrode assembly, and a second surface that is the opposite surface of the first surface, and a core portion of the electrode assembly includes a separator overlapping portion between the positive electrode and the negative electrode facing the first surface of the positive electrode, and the separator overlapping portion provides a jelly roll type electrode assembly in which three or more separators are overlapped and arranged.

[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 includes a bent structure of a core portion separator and a separator overlapping portion in which the friction coefficient between interfaces is adjusted, thereby suppressing the sliding of the electrode during charging and discharging of the battery and preventing damage to the negative electrode and the separator due to deformation of the electrode assembly caused by contraction / expansion of the electrode. Even when damage to the separator occurs, an internal short circuit between the positive electrode and the negative electrode is prevented by the separator overlapping portion, and the stability and life characteristics of the battery can be improved.

[0010] The effects of the present invention are not limited to the above-described effects, and effects not mentioned can be clearly understood by those skilled in the art from the present specification and the accompanying drawings.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0012] Throughout the present specification, when a certain part "includes" a certain component, this means that, unless otherwise stated, it does not exclude other components, but may further include other components.

[0013] Throughout the present specification, when a member is located "above" another member, this includes not only the case where a member is in contact with another member, but also the case where there is another member between the two members.

[0014] One embodiment of the present invention is a jelly roll type electrode assembly in which a first separator; a negative electrode; a second separator; and a positive electrode are sequentially laminated and wound, wherein the positive electrode includes a first surface that is the winding axis direction of the jelly roll type electrode assembly, and a second surface that is the opposite surface of the first surface, and the core portion of the electrode assembly includes a separator overlapping portion between the positive electrode and the negative electrode facing the first surface of the positive electrode, and the separator overlapping portion provides a jelly roll type electrode assembly in which three or more separators are overlapped and arranged.

[0015] The jelly roll type electrode assembly according to one embodiment of the present invention includes a separator overlapping portion, thereby suppressing the sliding of the electrodes during charging and discharging of the battery, preventing damage to the negative electrode and the separator from deformation of the electrode assembly due to contraction / expansion of the electrodes, and even when damage to the separator occurs, preventing an internal short circuit between the positive electrode and the negative electrode by the separator overlapping portion, and improving the stability and life characteristics of the battery. Here, the "core portion" is a hollow located on the winding axis of the electrode assembly; and a region including a part of the laminated structure of the wound first separator / negative electrode / second separator / positive electrode, and may mean a region within two turns (Turns) of the positive electrode from one end in the length direction of the positive electrode located on the innermost side of the electrode assembly. Further, the "one turn (Turn)" means the length required for winding 360° of the electrode or separator included in the electrode assembly from a reference point, and the length can be determined according to the outer diameter of the winding core used for winding the electrode assembly, the thickness of the electrode or separator, and the number of windings of the electrode or separator located inside. For example, one turn of the positive electrode may mean the length required to wind the positive electrode 360° in the winding direction of the jelly roll type electrode assembly from one end in the length direction of the positive electrode.

[0016] Figures 1 and 2 show a jelly roll type electrode assembly including a separator overlapping portion according to an embodiment of the present invention. Specifically, Figure 1 shows a jelly roll type electrode assembly including a separator overlapping portion according to an embodiment of the present invention, and Figure 2 is an enlarged view of part A in Figure 1.

[0017] According to an embodiment of the present invention, in the core portion of the electrode assembly, the first separator, the negative electrode, and the second separator may extend longer than the lengthwise end portion of the positive electrode and may be further wound. Specifically, referring to Figures 1 and 2, the first separator 200, the negative electrode 100, and the second separator 400 may extend longer than the lengthwise end portion 310 of the positive electrode and may be further wound. That is, after the winding of the first separator, the negative electrode, and the second separator is performed, the winding may be performed together with the positive electrode. For example, after the first separator, the negative electrode, and the second separator are wound around the winding core one or more turns (turn), the winding may be performed together with the positive electrode. That is, in the core portion of the jelly roll type electrode assembly, the lengthwise end portions 210, 110, 410 of the first separator, the negative electrode, and the second separator may be located inside the lengthwise end portion 310 of the positive electrode. In other words, the length and width of the negative electrode may be larger than those of the positive electrode, and the length and width of the first separator and the second separator located on one side and the opposite side of the negative electrode may also be larger than those of the positive electrode. When the first separator, the negative electrode, and the second separator extend longer than the lengthwise end portion of the positive electrode and are further wound, the transfer of lithium ions in the positive electrode to the negative electrode in the chemical reaction of the lithium ion battery can be made easier. When the length and width of the negative electrode are formed wider, the area of the negative electrode that receives lithium ions increases, preventing a decrease in charge / discharge efficiency, and the battery can be excellent in stability and life characteristics.

[0018] Figure 3 schematically shows the separator overlapping portion of the jelly roll type electrode assembly according to an embodiment of the present invention.

[0019] According to an embodiment of the present invention, the core portion of the electrode assembly includes a separator overlapping portion between the positive electrode and the negative electrode facing the first surface of the positive electrode, and the separator overlapping portion may have three or more separators arranged in an overlapping manner. Specifically, referring to FIGS. 1 to 3, the core portion of the electrode assembly includes a separator overlapping portion (S) between the positive electrode 300 and the negative electrode 100 facing the first surface of the positive electrode, and the separator overlapping portion (S) may mean a part of a region where three or more separators arranged in an overlapping manner are centered on the longitudinal end portion 310 of the positive electrode. Here, the separator overlapping portion (S) may mean a region up to the end portion of a region where three or more separators arranged in an overlapping manner are centered on the longitudinal end portion 310 of the positive electrode, that is, the longitudinal end portion of the separator overlapping portion, and a region having the same length in the core portion direction of the electrode assembly. Specifically, the separator overlapping portion (S) may mean a region from the longitudinal end portion of the separator overlapping portion (S) centered on the longitudinal end portion 310 of the positive electrode to the same length (L') as the isolation distance (L) between the longitudinal end portion of the separator overlapping portion and the longitudinal end portion of the positive electrode in the core portion direction of the electrode assembly, and may mean a region having a length of L + L' = L + L = 2L from the longitudinal end portion of the separator overlapping portion (S).

[0020] According to one embodiment of the present invention, the separator overlapping portion may be arranged such that the first separator and the second separator, which extend from the longitudinal end of the negative electrode in the core portion of the electrode assembly, overlap each other. Specifically, referring to FIGS. 1 to 3, the separator overlapping portion (S) may be arranged such that the first separator 200' and the second separator 400', which extend from the longitudinal end 110 of the negative electrode in the core portion of the electrode assembly, overlap each other, and the first separator 200 and the second separator 400 may include a region extending from the longitudinal end 110 of the negative electrode. That is, the first separator 200 and the second separator 400 may extend longer than the longitudinal end 110 of the negative electrode and may be further wound. In other words, after the winding of the first separator 200 and the second separator 400 is performed by a predetermined length, the winding may be performed together with the negative electrode 100. That is, the first separator 200' and the second separator 400' extending from the longitudinal end 110 of the negative electrode may be a part of the first separator 200 and the second separator 400 that have been wound before the negative electrode 100, and may be bent and overlapped to form the separator overlapping portion (S). That is, without providing another auxiliary separator or the like, the separator overlapping portion can be formed by a bent structure integrally extending from the first separator and the second separator. Thereby, with a simpler structure, the number of separators constituting the separator overlapping portion can be adjusted to three or more. Further, when the separator overlapping portion is formed by arranging the first separator and the second separator, which extend from the longitudinal end of the negative electrode, to overlap each other, damage to the negative electrode and the separator can be prevented from deformation of the electrode assembly due to contraction / expansion of the electrode, and even when damage to the separator occurs, an internal short circuit between the positive electrode and the negative electrode can be prevented by the separator overlapping portion, and the stability and life characteristics of the battery can be improved.

[0021] According to an embodiment of the present invention, the first separator and the second separator extend from a longitudinal end of the negative electrode in a core portion of the electrode assembly, and are both bent in a direction opposite to a direction facing the winding axis of the negative electrode, and may be disposed to overlap between the positive electrode and the second separator facing the first surface of the positive electrode. Specifically, referring to FIGS. 1 and 2, the first separator 200' and the second separator 400' extending from the longitudinal end 110 of the negative electrode may be both bent in a direction opposite to the direction facing the winding axis of the negative electrode, that is, toward the longitudinal end 310 side of the positive electrode, and may be disposed to overlap between the positive electrode 300 and the negative electrode 100 facing the first surface of the positive electrode to form a separator overlapping portion (S). Thereby, with a simpler bending structure, the number of separators constituting the separator overlapping portion can be three or more, and the adjustment of the facing direction of the separators constituting the separator overlapping portion can be made easier.

[0022] According to an embodiment of the present invention, the separator overlapping portion may include a first interface where the second separator and the second separator are in direct contact; and a second interface where the second separator and the first separator are in direct contact. Specifically, referring to FIG. 3, the separator overlapping portion (S) may have three or more separators disposed to overlap, and may include one or more of the first separators 200, 200' and the second separators 400, 400', and may include a first interface (S1) where the second separator 400 and the second separator 400' are in direct contact; and a second interface (S2) where the second separator 400' and the first separator 200' are in direct contact. In other words, the separator overlapping portion includes an overlapping structure of a plurality of separators, namely the first separator and the second separator, rather than a single separator overlapping structure, and may include interfaces where these are in contact with each other. By including a plurality of interfaces in the separator overlapping portion, the adjustment of the facing direction of the separators and the adjustment of the friction coefficient of each interface can be facilitated with a simpler bending structure.

[0023] According to an embodiment of the present invention, the friction coefficients of the first interface and the second interface may each be 0.4 or more. Specifically, referring to FIG. 3, the friction coefficients of the first interface (S1) and the second interface (S2) may each be 0.42 or more, 0.44 or more, or 0.46 or more. In other words, the separator overlapping portion includes a stacked structure of a first separator and a second separator, which are a plurality of separators, rather than a stacked structure of a single separator, and includes a plurality of interfaces where these are in contact with each other. At this time, the friction coefficients of the plurality of interfaces may each be adjusted to be within a specific range or more. When the friction coefficients of the first interface and the second interface satisfy the above-described range, it is possible to suppress the sliding of the positive electrode by the first separator and the second separator formed integrally with the separator overlapping portion during charging and discharging of the battery, and to prevent damage to the negative electrode and the separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes. Here, the friction coefficient (μ) means the static friction coefficient measured according to the ASTM D1894 standard, and the friction coefficient can be measured by a dry method, and can have a larger value when the test piece is impregnated with distilled water or an electrolytic solution and measured by a wet method.

[0024] According to an embodiment of the present invention, the friction coefficient of the first interface may be 0.6 or more, and the friction coefficient of the second interface may be 0.4 or more. Specifically, referring to FIG. 3, the friction coefficients of the first interface (S1) and the second interface (S2) may be different from each other according to the types and facing directions of the facing first separators 200, 200' and the second separators 400, 400'. More specifically, the friction coefficient of the first interface (S1) may be 0.62 or more, 0.64 or more, or 0.66 or more, and the friction coefficient of the second interface (S2) may be 0.42 or more, 0.44 or more, or 0.46 or more. When adjusting the friction coefficient between the interfaces of the separators included in the separator overlapping portion to the above-described range, sliding of the electrodes is suppressed during charging and discharging of the battery, and damage to the negative electrode and the separator is prevented from deformation of the electrode assembly due to contraction / expansion of the electrodes. Even when damage to the separator occurs, an internal short circuit between the positive electrode and the negative electrode is prevented by the separator overlapping portion, and the stability and life characteristics of the battery can be improved.

[0025] According to one embodiment of the present invention, the jelly roll type electrode assembly may include a plurality of separators. For example, the jelly roll type electrode assembly may have a structure in which a first separator / negative electrode / second separator / positive electrode are sequentially laminated. The separators 200 and 400 separate the negative electrode 100 and the positive electrode 300 and provide a migration path for lithium ions, and can be used without particular limitation as long as they are usually used as separators in secondary batteries. In particular, it is preferably low resistance to the ion migration of the electrolyte and excellent in electrolyte moisture retention ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a homopolymer of ethylene, a homopolymer of propylene, 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 non-woven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. Further, the separator may usually have a thickness of 10 μm or more and 20 μm or less, and a separator in which a slurry containing a ceramic component or a polymer substance is coated on a base material layer made of the above-described separator material to ensure heat resistance or mechanical strength may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0026] FIG. 5 schematically shows a separator overlapping portion of a jelly roll type electrode assembly according to one embodiment of the present invention. Specifically, FIG. 5(a) schematically shows a separator overlapping portion of a jelly roll type electrode assembly including a first separator and a second separator each provided with a coating layer on both surfaces, and FIG. 5(b) schematically shows a separator overlapping portion of a jelly roll type electrode assembly including a first separator and a second separator without a coating layer.

[0027] According to an embodiment of the present invention, the first separator and the second separator may each include a coating layer provided on at least one surface. Specifically, referring to FIGS. 3 and 5(a), the first separators 200, 200' and the second separators 400, 400' each include the coating layers 202, 202', 402, 402' provided on at least one surface and the base material layers 201, 201', 401, 401'. By adjusting the components, content, and particle size of the coating layer, a specific range of friction coefficients can be achieved. Specifically, the friction coefficient between the coating layers of the separators and the friction coefficient between the base material layers may be greater than the friction coefficient between the coating layer and the base material layer. Further, the friction coefficient can be measured in a dry method, but there can be a more significant difference when measured in a wet method, i.e., when impregnated in distilled water or electrolyte solution.

[0028] When including the coating layers provided on at least one surface of the first separator and the second separator, by adjusting the facing direction of the coating layers provided on at least one surface of the first separator and the second separator, the friction coefficient between the interfaces of the separators included in the separator overlapping portion is adjusted to a specific range, suppressing the sliding of the electrodes during charging and discharging of the battery, and preventing damage to the negative electrode and the separator from deformation of the electrode assembly due to contraction / expansion of the electrodes.

[0029] According to an embodiment of the present invention, the first separator and the second separator may each include a coating layer provided on at least one surface, and the coating layer may include an inorganic component, a binder component, and a lithium salt. By the separator including the above-described components, although it includes a binder for improving the adhesive force with the electrode and an inorganic component for improving the mechanical strength of the separator, an increase in internal resistance due to the elution of the lithium salt contained in the coating layer is not caused, so excellent cell stability can be achieved.

[0030] In addition, since the electrolyte impregnation level of the electrode facing the separator can be increased, it is possible to have advantageous performance in terms of long-term life. Specifically, the coating layer may contain the inorganic component, and the coating layer containing the inorganic component is advantageous in terms of thermal shrinkage rate compared to a separator made of a simple polymer material. Therefore, the separator containing this can have further excellent high-temperature stability.

[0031] Specifically, the lithium salt may be substantially the same as those contained in the electrolyte of a lithium secondary battery. For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2) 2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, and lithium tetraphenylborate, and may be one or more selected from the group consisting of them.

[0032] The inorganic component is not particularly limited as long as it does not cause an oxidation and / or reduction reaction, that is, an electrochemical reaction, with the positive or negative electrode current collector within the operating voltage range of the battery (for example, 0 to 5V based on Li / Li + reference), and does not inhibit electrical conductivity. For example, BaTiO3, Pb(Zr, Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT), Pb(Mg3Nb 2 / 3 )O3 - PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, and TiO2, and may be one or more selected from the group consisting of them.

[0033] The binder is not particularly limited as long as it exhibits the binding force with the electrode laminated on the separator and the binding force between the inorganic component and the lithium salt in the mixed coating layer, and is not easily dissolved by the electrolytic solution. For example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide may be one or a mixture of two or more selected from the group consisting of, preferably, PVdF or PVdF-CTFE.

[0034] According to an embodiment of the present invention, the first separator and the second separator may each include a coating layer provided on at least one surface, and the surface of the first separator and the second separator on which the coating layer is provided may have a larger coefficient of friction than the surface of the first separator and the second separator on which the coating layer is not provided. Specifically, referring to FIG. 3, the first separators 200, 200' and the second separators 400, 400' each include a coating layer 202, 202', 402, 402' provided on one surface, and the surface of the first separator and the second separator on which the coating layer is provided may have a larger coefficient of friction than the surface of the first separator and the second separator on which the coating layer is not provided. That is, the coating layer can increase the coefficient of friction at the interface when provided on the separator. By adjusting the facing direction of the coating layer provided on one surface of the first separator and the second separator, the coefficient of friction between the interfaces of the separators included in the separator overlapping portion is adjusted to a specific range, suppressing the sliding of the electrodes during charging and discharging of the battery, and preventing damage to the negative electrode and the separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes.

[0035] According to an embodiment of the present invention, the first separator and the second separator may each include a coating layer provided on one surface. Specifically, referring to FIG. 3, the first separators 200, 200' and the second separators 400, 400' each include the coating layers 202, 202', 402, 402' provided on one surface and base material layers 201, 201', 401, 401', and can have a coefficient of friction within a specific range by adjusting the components, content, and particle size of the coating layer.

[0036] When including a coating layer provided on one side of the first separator and the second separator, by adjusting the facing direction of the coating layers provided on one side of the first separator and the second separator, the friction coefficient between the interfaces of the separators included in the separator overlapping portion is adjusted to a specific range, suppressing the sliding of the electrodes during charging and discharging of the battery, and preventing damage to the negative electrode and the separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes.

[0037] According to an embodiment of the present invention, the first separator and the second separator each include a coating layer provided on one side, and the first interface may be such that the coating layer of the second separator and the coating layer of the second separator are in direct contact. Specifically, referring to FIG. 3, the first separators 200, 200' and the second separators 400, 400' each include coating layers 202, 202', 402, 402' provided on one side, and the first interface (S1) may be such that the coating layer 402 of the second separator and the coating layer 402' of the second separator are in direct contact. When the coating layer of the second separator and the coating layer of the second separator are in direct contact, that is, the friction coefficient between the coating layers of the separators may be greater than the friction coefficient between the base material layers or the friction coefficient between the coating layer and the base material layer, and the friction coefficient of the first interface may have an even larger value. When the coating layer of the second separator and the coating layer of the second separator are in direct contact at the first interface, the friction coefficient between the interfaces of the separators included in the separator overlapping portion increases, and by suppressing the sliding of the electrodes during charging and discharging of the battery, damage to the negative electrode and the separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes can be prevented.

[0038] According to an embodiment of the present invention, the first separator and the second separator each include a coating layer provided on one surface, and the second interface may be such that the surface of the second separator where the coating layer is not provided is in direct contact with the surface of the first separator where the coating layer is not provided. Specifically, referring to FIG. 3, the first separators 200, 200' and the second separators 400, 400' each include coating layers 202, 202', 402, 402' provided on one surface, and the second interface (S2) may be such that the surface of the second separator where the coating layer is not provided, i.e., the second separator base material layer 401', is in direct contact with the surface of the first separator where the coating layer is not provided, i.e., the first separator base material layer 201'. When the surface of the second separator where the coating layer is not provided is in direct contact with the surface of the second separator where the coating layer is not provided, i.e., the friction coefficient between the base material layers of the separator may be greater than the friction coefficient between the coating layer and the base material layer, and the friction coefficient of the second interface may have an even larger value. When the surface of the second separator where the coating layer is not provided is in direct contact with the surface of the first separator where the coating layer is not provided at the second interface, the friction coefficient between the interfaces of the separators included in the separator overlapping portion increases, and by suppressing the sliding of the electrodes during charging and discharging of the battery, damage to the negative electrode and the separator can be prevented due to deformation of the electrode assembly caused by contraction / expansion of the electrodes.

[0039] According to an embodiment of the present invention, the first interface may be such that the second separator facing the first surface of the positive electrode and the second separator extending from the lengthwise end of the negative electrode in the core portion of the electrode assembly are in direct contact. Specifically, referring to FIGS. 1 to 3, the second separator 400' extending from the lengthwise end 110 of the negative electrode may be superimposed between the positive electrode 300 and the negative electrode 100 facing the first surface of the positive electrode to form a separator superimposed portion (S). At this time, since the second separator 400 is located between the positive electrode 300 and the negative electrode 100 facing the first surface of the positive electrode, the extended second separator 400' may be in direct contact with the second separator 400 located between the positive electrode 300 and the negative electrode 100. That is, a first interface (S1) may be formed in which the second separator 400 and the second separator 400' extending from the lengthwise end 110 of the negative electrode in the core portion of the electrode assembly are in direct contact. Thereby, with a simpler bending structure, the number of separators constituting the separator superimposed portion can be made three or more, and the adjustment of the facing direction of the separators constituting the separator superimposed portion and the adjustment of the frictional force at the interface can be made easier.

[0040] According to an embodiment of the present invention, the second interface may be such that the first separator extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly and the second separator extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly are in direct contact. Specifically, referring to FIGS. 1 to 3, the first separator 200' extending from the longitudinal end 110 of the negative electrode; and the second separator 400' extending from the longitudinal end of the negative electrode may be superimposed between the positive electrode 300 and the negative electrode 100 facing the first surface of the positive electrode to form a separator superimposed portion (S). At this time, a second interface (S2) may be formed in which the first separator 200' extending from the longitudinal end 110 of the negative electrode and the second separator 400' extending from the longitudinal end 110 of the negative electrode are in direct contact. Thereby, with a simpler bending structure, the number of separators constituting the separator superimposed portion can be three or more, and the adjustment of the facing direction of the separators constituting the separator superimposed portion and the adjustment of the frictional force at the interface can be made easier.

[0041] According to an embodiment of the present invention, the length in the longitudinal direction of the separator superimposed portion may be 30% or more based on 100% of the periphery of the electrode assembly. Specifically, the length in the longitudinal direction of the separator superimposed portion may be 40% or more or 50% or more based on 100% of the periphery of the electrode assembly, and may be 1 / 3 turn or more or 1 / 2 turn or more of the inner peripheral surface of the core portion of the electrode assembly.

[0042] Here, the periphery of the electrode assembly means the periphery of the inner peripheral surface of the electrode assembly, and the "periphery of the inner peripheral surface" may mean a virtual circumference having a radius equal to the largest value among the distances to the innermost layer in contact with the hollow of the electrode assembly centered on the winding axis of the electrode assembly. For example, the periphery of the inner peripheral surface of the electrode assembly may be about 10 mm, but is not limited thereto.

[0043] Also, referring to FIG. 3, the length in the longitudinal direction of the separator overlapping portion may mean a length of L+L’=L+L=2L. That is, the first separator extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly; and the second separator extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly may be arranged between the positive electrode and the negative electrode facing the first surface of the positive electrode, at least 1 / 6 turn or at least 1 / 4 turn from the longitudinal end of the positive electrode. In this case, the length in the longitudinal direction of the separator overlapping portion may be at least 1 / 3 turn or at least 1 / 2 turn. When the length range in the longitudinal direction of the separator overlapping portion described above is satisfied, the frictional force between the interfaces of the separators included in the separator overlapping portion suppresses the sliding of the electrodes during charge and discharge of the battery, which is sufficient to prevent damage to the negative electrode and the separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes.

[0044] According to an embodiment of the present invention, the isolation distance between the longitudinal end of the separator overlapping portion and the longitudinal end of the positive electrode may be 3 mm or more. Specifically, referring to FIG. 3, the isolation distance (L) between the longitudinal end of the separator overlapping portion and the longitudinal end of the positive electrode may be 4 mm or more, 5 mm or more, or 6 mm or more.

[0045] That is, the first separator 200’ extending from the longitudinal end 110 of the negative electrode in the core portion of the electrode assembly; and the second separator 400’ extending from the longitudinal end 110 of the negative electrode in the core portion of the electrode assembly may be arranged at least 3 mm from the longitudinal end 310 of the positive electrode between the positive electrode 300 and the negative electrode 100 facing the first surface of the positive electrode.

[0046] When the length range in the length direction of the separator overlapping portion described above is satisfied, even when there are process errors during the loading of the first separator and the second separator, the separator overlapping portion can be disposed between the positive electrode and the negative electrode facing the first surface of the positive electrode. Further, the frictional force between the interfaces of the separators included in the separator overlapping portion is sufficient to prevent damage to the negative electrode and the separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes by suppressing the sliding of the electrodes during charging and discharging of the battery.

[0047] 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, referring to FIG. 3, the positive electrode 300 may include a positive electrode current collector 301 and positive electrode active material layers 302 and 303 formed on one or both surfaces of the positive electrode current collector 301 and containing a positive electrode active material. In other words, the positive electrode active material layer is formed on the positive electrode active material coating portion of the positive electrode current collector, and the surface where the positive electrode active material layer is not provided can be referred to as a positive electrode plain portion.

[0048] According to an embodiment of the present invention, the positive electrode current collector may include a positive electrode active material coating portion where the positive electrode active material is coated and a positive electrode plain portion where the positive electrode active material is not coated, 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 provided on the positive electrode plain portion.

[0049] According to one embodiment of the present invention, the electrode assembly is formed by laminating and winding a positive electrode, a separator, and a negative electrode. The positive electrode may include a positive electrode current collector; and a positive electrode active material layer provided on at least one surface of the positive electrode current collector and having a longitudinal end portion at the same position as the positive electrode current collector. Specifically, referring to FIG. 3, the electrode assembly is formed by laminating and winding a positive electrode 300, separators 200 and 400, and a negative electrode 100. The positive electrode 300 may include a positive electrode current collector 301; and positive electrode active material layers 302 and 303 provided on at least one surface of the positive electrode current collector 301 and having a longitudinal end portion 310 at the same position as the positive electrode current collector 301. In other words, one longitudinal end portion 310 of the positive electrode may be in the form of a free-edge. Thereby, the area of the plain part of the unnecessary positive electrode current collector can be reduced to ensure economy, and since a slitting process can be performed after forming the active material layer on the electrode, a roll-to-roll process including the slitting process and the winding process can be performed more efficiently. Here, "the same position" means that the longitudinal end portions are the same, and may include a case where the end portions are formed at substantially the same position due to process errors that may occur in a slitting process or the like.

[0050] According to one embodiment of the present invention, the positive electrode current collector is not particularly limited as long as it does not cause 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-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. That is, the positive electrode current collector may be provided in the form of surface-treated stainless steel, aluminum foil, or the like.

[0051] Further, the positive electrode current collector may usually have a thickness of 3 to 50 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion 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.

[0052] According to one embodiment of the present invention, the positive electrode active material may be a commonly used positive electrode active material. Specifically, examples of the positive electrode active material include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; the chemical formula Li 1+x Mn 2-x O4 (0 ≦ x ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; the chemical formula LiNi 1-y M y O2 (where M is at least 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; the chemical formula LiMn 2-z M z O2 (where M is at least 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 one selected from the group consisting of Fe, Co, Ni, Cu, and Zn). Examples include, but are not limited to, LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li-metal.

[0053] 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 has electron conductivity without causing chemical changes. Specifically, examples of the positive electrode conductive material include 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, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0054] Also, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesive 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 monomer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used.

[0055] According to one 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, referring to FIG. 3, the negative electrode 100 may include a negative electrode current collector 101 and negative electrode active material layers 102 and 103 formed on one or both sides of the negative electrode current collector 101 and containing a negative electrode active material. In other words, the negative electrode active material layer is formed on the negative electrode active material coating portion of the negative electrode current collector, and the surface where the negative electrode active material layer is not provided can be referred to as a negative electrode plain portion.

[0056] According to one embodiment of the present invention, the negative electrode current collector may include a negative electrode active material coating portion where a negative electrode active material layer is formed and a negative electrode plain portion where no negative electrode active material layer is formed, and may include a tab on the negative electrode plain portion. Specifically, the negative electrode current collector may include a negative electrode plain portion and may include a negative electrode tab provided on the negative electrode plain portion. Thereby, the manufactured electrode assembly may include one or more negative electrode tabs.

[0057] According to one embodiment of the present invention, the negative electrode active material layer may include a negative electrode active material containing one or more selected from the group consisting of a silicon-based material and a carbon-based material. 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 can be used without limitation as long as they are materials used in the art.

[0058] According to one embodiment of the present invention, the negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has 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. The thickness of the negative electrode current collector may be 6 μm or more and 80 μm or less, but the thickness of the negative electrode current collector is not limited thereto.

[0059] 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 various copolymers thereof.

[0060] According to one embodiment of the present invention, the negative electrode conductive material is not particularly limited as long as it does not cause 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.

[0061] One 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. Specifically, the secondary battery may include the electrode assembly according to the above-described one embodiment and a battery case for accommodating the electrode assembly.

[0062] The secondary battery according to the present invention includes a bent structure of a core part separator and a separator overlapping part with an adjusted friction coefficient between interfaces, thereby preventing internal short circuits between the positive electrode and the negative electrode even when the electrode assembly is deformed due to contraction / expansion of the electrodes during charging and discharging of the battery, and improving the stability and life characteristics of the battery.

[0063] According to an embodiment of the present invention, the battery case may be cylindrical. Specifically, the battery case may be cylindrical, rectangular, or pouch-shaped according to the application, but when the battery case is cylindrical, it is more suitable for accommodating a jelly roll type electrode assembly. When the battery case is cylindrical, the shape of the secondary battery including the jelly roll type electrode assembly and the battery case for accommodating the electrode assembly may be cylindrical.

[0064] According to an embodiment of the present invention, the inside 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.

[0065] According to an 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, and ethyl propionate.

[0066] 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. 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 one or more selected from the group consisting of (CF3CF2SO2)2N - may be used.

[0067] 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 decrease in battery capacity, improving the discharge capacity of the battery, etc., for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or additives such as aluminum trichloride may be further included in one or more kinds.

Examples

[0068] 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 different forms, and it should not be construed that the scope of the present invention is limited to the examples described later. The examples in this specification are provided to more fully explain the present invention to those with average knowledge in the industry.

[0069] <Examples> <Example 1> (Manufacture of electrode assembly) An Al foil with a thickness of 15 μm and a length in the width direction of 63.9 mm was prepared as a positive electrode current collector, and a positive electrode active material layer was formed by applying and drying a positive electrode active material slurry containing an NMCA (Ni-Mn-Co-Al) composite with a Ni content of 92% or more as a positive electrode active material and CNT as a conductive material on the positive electrode current collector, and a positive electrode having a thickness of 154 μm was manufactured.

[0070] Next, a Cu foil with a thickness of 8 μm and a length in the width direction of 65.1 mm was prepared as a negative electrode current collector, and a negative electrode active material layer was formed by applying and drying a negative electrode active material slurry containing 50 parts by weight of artificial graphite and natural graphite respectively as a negative electrode active material on the negative electrode current collector, and a negative electrode having a thickness of 187 μm was manufactured.

[0071] On one hand, as the first separator and the second separator, two separators were each prepared, on one side of a sheet-like polyethylene base material layer of which a coating layer containing Al2O3 as an inorganic component, a PVdF-based binder as a binder component, and a lithium salt was formed.

[0072] Before winding the jelly roll type electrode assembly, the base material layers of the first separator and the second separator were overlapped so as to face each other, and an extension part was provided for the first separator and the second separator in the direction opposite to the winding direction by a length corresponding to about 3 turns of the winding core. At this time, as the winding core, one having a peripheral edge of the outer peripheral surface of about 10 mm was used.

[0073] Thereafter, starting from the longitudinal ends of the first separator and the second separator, the points corresponding to 3 turns of the winding core were folded back in the winding direction to start winding, and the negative electrode and the positive electrode were sequentially inserted to manufacture a jelly roll type electrode assembly. At this time, in the core part of the jelly roll type electrode assembly, a separator overlapping part was provided by interposing the extension parts of the first separator and the second separator between one side in the winding axis direction of the positive electrode and the second separator located on one side of the negative electrode, so as to have the structure according to FIGS. 1 and 2. At this time, the isolation distance (L) between the longitudinal end of the separator overlapping part and the longitudinal end of the positive electrode was 3 mm, and the longitudinal length (L + L' = 2L) of the separator overlapping part was adjusted to be 6 mm. The peripheral edge of the inner peripheral surface of the manufactured jelly roll type electrode assembly was about 10 mm.

[0074] (Manufacture of secondary battery) After inserting the jelly roll type electrode assembly into a cylindrical battery case, an electrolytic solution in which ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) were mixed at a weight ratio of 4:9:3 and LiPF6 was dissolved at 15 wt% was injected, and the cylindrical battery can was sealed with a cap assembly to manufacture a secondary battery.

[0075] <Example 2> Except that two separators, each having a coating layer containing Al2O3 as an inorganic component, a PVdF-based binder as a binder component, and a lithium salt formed on both sides of a sheet-like polyethylene base material layer, were used as the first separator and the second separator, a jelly roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1.

[0076] <Example 3> Except that two separators without a coating layer formed on both sides of a sheet-like polyethylene base material layer were used as the first separator and the second separator, a jelly roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1.

[0077] <Example 4> Except that the isolation distance (L) between the lengthwise end of the separator overlapping portion and the lengthwise end of the positive electrode was 1.5 mm and the length (L + L' = 2L) in the lengthwise direction of the separator overlapping portion was adjusted to 3 mm, a jelly roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1.

[0078] <Comparative Example 1> Except that no separator overlapping portion was provided, a jelly roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1.

[0079] <Experimental Example> <Experimental Example 1 - Evaluation of Coefficient of Friction> The coefficient of friction (μ) between the coating layers of the first separator and the second separator, between the coating layer and the base material layer, and between the base material layers was measured according to the ASTM D1894 standard. At this time, the coefficient of friction was measured by the dry method, and after impregnating the same test piece in the electrolytic solution for 60 minutes, it was re-measured by the wet method and is shown in Table 1 below.

[0080]

Table 1

[0081] Referring to Table 1 above, it was confirmed that the friction coefficient between the coating layers of the first separator and the second separator has a higher value compared to the friction coefficient between the base material layers or between the coating layer and the base material layer. Also, it was confirmed that the friction coefficient measured in the wet state has a higher value than the friction coefficient measured in the dry state. Specifically, the friction coefficient between the base material layers has a relatively lower value compared to the friction coefficient between the coating layer and the base material layer. However, in the wet state, which is the internal environment of the secondary battery to be manufactured, it was confirmed that the friction coefficient between the base material layers has an even higher value. Thereby, when impregnated with distilled water or electrolyte, it can be seen that the friction coefficient between the coating layers of the separator of the first separator and the second separator and the friction coefficient between the base material layers have larger values than the friction coefficient between the coating layer and the base material layer. Also, it can be seen that by adjusting the facing direction of the coating layer provided on one side of the first separator and the second separator, the friction coefficient between the interfaces of the separators included in the separator overlapping portion is adjusted to a specific range.

[0082] <Experimental Example 2 - Core Impingement Evaluation> (Evaluation of Short - Term Cycle Stability) The secondary batteries manufactured in Examples 1 to 4 and Comparative Example 1 above were prepared. After each of the secondary batteries was activated by proceeding 2 cycles with charging at 4.2V - 2.5V, 0.2C and discharging at 0.2C, secondary batteries after proceeding 20 cycles under the conditions of 4.3V - 2.5V, 1C / 1C @25℃ were prepared respectively. The core part was subjected to computed tomography (CT) to confirm the presence or absence of Core Impingement, thereby evaluating the short - term cycle stability. The images are shown in Figures 4 and 6 respectively.

[0083] (Evaluation of Long - Term Cycle Stability) The secondary batteries manufactured in Example 1 and Comparative Example 1 were each activated by proceeding for 2 cycles at 4.2V - 2.5V, 0.2C charge, and 0.2C discharge, and then secondary batteries were prepared. After that, the activated secondary batteries were each advanced for 200 cycles under the conditions of 4.25V (0.3C) - 2.85V (0.5C) and @55°C, and the core part was subjected to computed tomography (CT) to check for the presence or absence of Core Impingement to evaluate the long-term cycle stability, and the images are shown in Figure 7 respectively. Also, the energy density, capacity retention rate, and Coulomb efficiency due to cycle progression were measured and are shown in Table 2 and Figure 8 below.

[0084]

Table 2

[0085] (Evaluation of Core Impingement) The presence or absence of Core Impingement in the secondary batteries of Example 1 and Comparative Example 1 was evaluated by the following method.

[0086] Figure 9 schematically shows the evaluation method for the presence or absence of Core Impingement. Specifically, (a) in Figure 9 schematically shows the evaluation method for the presence or absence of Core Impingement when deformation occurs in the negative electrode, and (b) in Figure 9 schematically shows the evaluation method for the presence or absence of Core Impingement when no deformation occurs in the negative electrode.

[0087] 1) On the first surface of the positive electrode 300, extend a straight line connecting the end portion 310 in the length direction of the positive electrode and a point where the isolation distance from the end is 5 mm, and draw a first extension line (E1).

[0088] 2-1) When deformation occurs in the negative electrode, In the core part of the jelly roll type electrode assembly, on the surface of the negative electrode 100 facing the first surface of the positive electrode, extend a straight line connecting two points where the bending direction changes within a separation distance of 5 mm from the longitudinal end 310 of the positive electrode, and draw a second extension line (E2).

[0089] 2-2) When no deformation has occurred in the negative electrode, In the core part of the jelly roll type electrode assembly, on the surface of the negative electrode 100 facing the first surface of the positive electrode, extend a straight line connecting two points with a separation distance of 5 mm from the longitudinal end 310 of the positive electrode, and draw a second extension line (E2).

[0090] 3) When the angle from the first extension line (E1) to the second extension line (E2) exceeds 25° in the counterclockwise direction around the intersection of the first extension line (E1) and the second extension line (E2), it was evaluated that Core Impingement occurred.

[0091] On the other hand, as for the evaluation method of the occurrence of Core Impingement, when obtaining an unknown secondary battery (Unknown Cell), evaluate the occurrence of Core Impingement at the initial acquisition time point, re-evaluate the occurrence of Core Impingement every 250 cycles, and compare and analyze with the conditions of Core Impingement of the secondary battery of the embodiment according to the present invention, and it can be applied in this way.

[0092] FIG. 4 is a CT image showing the evaluation results of the short-term cycle stability of the secondary batteries according to Example 1 and Comparative Example 1, and FIG. 7 is a CT image showing the evaluation results of the long-term cycle stability of the secondary batteries according to Example 1 and Comparative Example 1.

[0093] Referring to FIGS. 4 and 7, it was confirmed that Core Impingement did not occur in the secondary battery manufactured in Example 1 in both the short-term cycle stability evaluation and the long-term cycle stability evaluation. However, it was confirmed that Core Impingement occurred in the secondary battery manufactured in Comparative Example 1 in both the short-term cycle stability evaluation and the long-term cycle stability evaluation. Specifically, it was confirmed that Core Impingement did not occur in the secondary battery manufactured in Comparative Example 1 before activation, but Core Impingement occurred in some of the secondary batteries after activation. Furthermore, after 20 cycles corresponding to the short-term cycle and after 200 cycles corresponding to the long-term cycle, it was confirmed that the frequency and degree of Core Impingement due to damage to the negative electrode and separator by the longitudinal end portion of the positive electrode, that is, contraction / expansion of the electrode assembly, increased significantly.

[0094] FIG. 6 is a CT image showing the evaluation results of the short-term cycle stability of the secondary batteries according to Examples 1 to 4.

[0095] Referring to FIG. 6, it was confirmed that Core Impingement did not occur in any of the secondary batteries manufactured in Examples 1 to 4 after activation. However, in the case of Example 3 including the first separator and the second separator without the coating layer, it was confirmed that a slight warping phenomenon of the negative electrode facing the first surface of the positive electrode occurred after the accelerated cycle. In the case of Example 4 in which the separator overlapping portion was provided to be less than 6 mm, it was confirmed that a slight warping phenomenon of the negative electrode facing the first surface of the positive electrode occurred after activation, and Core Impingement occurred after the accelerated cycle.

[0096] Accordingly, when including the coating layer provided on at least one surface of the first separator and the second separator, if the separator overlapping portion does not include the coating layer, that is, when both the first interface and the second interface are in contact with the base material layer and the base material layer, a higher friction coefficient can be realized compared to the case where the coating layer is not present. It can be seen that the sliding of the electrode is suppressed, and the effect of preventing damage to the negative electrode and the separator is excellent even during the contraction / expansion of the electrode. Furthermore, when adjusting the length of the separator overlapping portion to be equal to or greater than a specific range, it can be seen that the effect of preventing damage to the negative electrode and the separator described above is further excellent.

[0097] FIG. 8 is a graph showing the evaluation results of the long-term cycle stability of the secondary battery according to Example 1 and Comparative Example 1. Specifically, FIG. 8(a) is a graph showing the capacity retention rate of the secondary battery according to Example 1 and Comparative Example 1 as the cycle progresses, and FIG. 8(b) is a graph showing the Coulomb efficiency of the secondary battery according to Example 1 and Comparative Example 1 as the cycle progresses.

[0098] Referring to Table 2 and FIG. 8, it was confirmed that the secondary battery according to Example 1 showed an initial energy density and a capacity retention rate at a similar level to those of the comparative example without the separator overlapping portion, despite the separator overlapping portion being provided for the improvement of Core Impingement. In contrast, it was confirmed that the secondary battery according to Comparative Example 1 showed a decrease in the capacity retention rate after the initial 50 cycles, that is, when the long-term cycle progressed. Specifically, after 50 cycles, a reversal of the Coulomb efficiency occurred with the secondary battery according to Example 1, and since it had a large fluctuation range, it was confirmed that a decrease in life due to internal short circuit occurred.

[0099] Accordingly, it can be seen that the secondary battery according to Example 1 is excellent in battery stability and life characteristics compared to the secondary battery according to Comparative Example 1 without the separator overlapping portion, even when the separator overlapping portion is provided, and there is no significant decrease in the initial energy density and the capacity retention rate.

[0100] That is, the jelly roll type electrode assembly according to one embodiment of the present invention includes a separator overlapping portion where three or more separators are stacked and arranged at a specific position, so that it is possible to suppress the sliding of the electrodes during charging and discharging of the battery and prevent damage to the negative electrode and the separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes. Also, even when damage to the separator occurs, it can be seen that the internal short circuit between the positive electrode and the negative electrode is prevented by the separator overlapping portion, and the stability and life characteristics of the battery can be improved. Furthermore, when adjusting the bending structure of the core part separator, the friction coefficient between the interfaces, and the length range of the separator overlapping portion, it can be seen that the above-described effects are even more excellent.

[0101] The above detailed description illustrates and describes the present invention. Also, the foregoing content only shows and describes preferred embodiments of the present invention. As described above, the present invention can be used in various other combinations, modifications, and environments, and can be changed or modified within the scope of the concept of the invention disclosed in this specification, the scope equivalent to the foregoing disclosure, and / or the scope of the technology or knowledge in the industry. Therefore, the above detailed description of the invention is not intended to limit the present invention to the disclosed embodiments. Also, the appended claims should be construed to include other embodiments.

Explanation of Reference Numerals

[0102] 100 ··· Negative electrode 101 ··· Negative electrode current collector 102, 103 ··· Negative electrode active material layers 110 ··· Longitudinal end portion of the negative electrode 200, 200’ ··· First separator 210 ··· Longitudinal end portion of the first separator 201, 201’ ··· First separator base material layer 202, 202’ ··· First separator coating layer 300 ··· Positive electrode 301 ··· Positive electrode current collector 302, 303 ··· Positive electrode active material layers 310 ··· Lengthwise end of the positive electrode 400, 400’ ··· Second separator 410 ··· Lengthwise end of the second separator 401, 401’ ··· Second separator base material layer 402, 402’ ··· Second separator coating layer S ··· Separator overlapping part S1 ··· First interface S2 ··· Second interface L, L’ ··· Isolation distance between the lengthwise end of the separator overlapping part and the lengthwise end of the positive electrode E1 ··· First extension line E2 ··· Second extension line

Claims

1. A jelly roll type electrode assembly in which a first separator, a negative electrode, a second separator, and a positive electrode are sequentially laminated and wound, The positive electrode includes a first surface that is the winding axis direction of the jelly roll type electrode assembly, and a second surface that is the opposite surface of the first surface, The core portion of the electrode assembly includes a separator overlapping portion between the positive electrode and the negative electrode facing the first surface of the positive electrode, In the separator overlapping portion, there are three or more separators arranged in an overlapping manner, The separator overlapping portion is It includes a first interface where the second separator and the second separator are in direct contact; and a second interface where the second separator and the first separator are in direct contact, The friction coefficients of the first interface and the second interface are each 0.4 or more, A jelly roll type electrode assembly.

2. In the core portion of the electrode assembly, The first separator, the negative electrode, and the second separator extend longer than the length direction ends of the positive electrode and are further wound, The jelly roll type electrode assembly according to Claim 1.

3. The separator overlapping portion is In the core portion of the electrode assembly, the first separator and the second separator, which extend from the length direction ends of the negative electrode, are arranged in an overlapping manner, The jelly roll type electrode assembly according to Claim 1 or 2.

4. The first separator and the second separator are Extending from the length direction ends of the negative electrode in the core portion of the electrode assembly, Bent together in the opposite direction to the direction facing the winding axis of the negative electrode, Arranged in an overlapping manner between the positive electrode and the second separator facing the first surface of the positive electrode, The jelly roll type electrode assembly according to claim 1 or 2.

5. The friction coefficient of the first interface is 0.6 or more, and the friction coefficient of the second interface is 0.4 or more. The jelly roll type electrode assembly according to claim 1.

6. The first separator and the second separator each include a coating layer provided on at least one surface, and the surfaces of the first separator and the second separator on which the coating layers are provided have a larger friction coefficient than the surfaces of the first separator and the second separator on which the coating layers are not provided. The jelly roll type electrode assembly according to claim 1.

7. The first separator and the second separator each include a coating layer provided on at least one surface, and the coating layer includes an inorganic component, a binder component, and a lithium salt. The jelly roll type electrode assembly according to claim 1.

8. The first separator and the second separator each include a coating layer provided on one surface, and the first interface is where the coating layer of the second separator and the coating layer of the second separator are in direct contact. The jelly roll type electrode assembly according to claim 1.

9. The first separator and the second separator each include a coating layer provided on one surface, and the second interface is where the surface of the second separator on which the coating layer is not provided and the surface of the first separator on which the coating layer is not provided are in direct contact. The jelly roll type electrode assembly according to claim 1.

10. The first interface is such that the second separator facing the first surface of the positive electrode and the second separator extending from the lengthwise end of the negative electrode in the core part of the electrode assembly are in direct contact. The jelly roll type electrode assembly according to claim 1.

11. The second interface is such that the first separator extending from the lengthwise end of the negative electrode in the core part of the electrode assembly and the second separator extending from the lengthwise end of the negative electrode in the core part of the electrode assembly are in direct contact. The jelly roll type electrode assembly according to claim 1.

12. The length in the lengthwise direction of the separator overlapping part is 30% or more with the length of the periphery of the electrode assembly being 100%. The jelly roll type electrode assembly according to claim 1 or 2.

13. The isolation distance between the lengthwise end of the separator overlapping part and the lengthwise end of the positive electrode is 3 mm or more. The jelly roll type electrode assembly according to claim 1 or 2.

14. The jelly roll type electrode assembly according to claim 1 or 2; and A secondary battery including a battery case for housing the electrode assembly.

15. The secondary battery according to claim 14, wherein the battery case is cylindrical.

Images