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, more particularly 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 in the Korean Intellectual Property Office on December 1, 2022, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] In the case of cylindrical batteries, a jelly roll type electrode assembly is manufactured by winding a long electrode with a fixed width into a roll. A cylindrical battery manufactured by inserting such a jelly roll type electrode assembly into a battery case undergoes repeated contraction / expansion of the electrodes during charging / discharging. In particular, if an in tab is located in the core of the jelly roll type electrode assembly or a silicon-based active material is added to the negative electrode, which increases the degree of contraction / expansion of the electrode assembly, the pressure acting on the core of the electrode assembly increases significantly.

[0003] In recent years, as low resistance / high capacity designs have become more common, jelly roll type electrode assemblies have come to include multiple tabs or have silicon-based active materials added thereto. This increases the possibility of deformation of the electrode assembly located in the core portion due to contraction / expansion of the electrode assembly. In particular, if a separator located between the negative and positive electrodes is damaged, the negative and positive electrodes may come into direct contact with each other, resulting in an internal short circuit, which may cause heat generation and fire.

[0004] In order to solve the problems of separator damage and internal short circuit caused by deformation of the electrode assembly, there is a need to develop technology that can protect the negative electrode and separator in the corresponding area and suppress the occurrence of internal short circuit. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a jelly-roll type electrode assembly having 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 those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0007] One embodiment of the present invention provides a jelly roll type electrode assembly in which a first separator, a negative electrode, a second separator, and a positive electrode are sequentially stacked and wound up, in which the positive electrode has a first surface which is in the winding axis direction of the jelly roll type electrode assembly, and a second surface which is the opposite surface to the first surface, a core portion of the electrode assembly includes a separator overlap portion between the positive electrode and the negative electrode which faces the first surface of the positive electrode, and the separator overlap portion has three or more layers of separators arranged in an overlapping manner.

[0008] Another embodiment of the present invention provides a secondary battery comprising the jelly-roll type electrode assembly; and a battery case for housing the electrode assembly. Effect of the Invention

[0009] A jelly roll type electrode assembly according to an embodiment of the present invention includes a separator overlapping part having a folded structure of a core separator and an adjusted friction coefficient between the interfaces, thereby suppressing sliding of the electrodes during charging and discharging of the battery, thereby preventing damage to the negative electrode and separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes. Even if the separator is damaged, the separator overlapping part prevents internal short circuits between the positive and negative electrodes, thereby improving the stability and life characteristics of the battery.

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

[0011] [Figure 1] 1 illustrates a jelly roll type electrode assembly including a separator overlapping portion according to an embodiment of the present invention. [Diagram 2] 1 illustrates a jelly roll type electrode assembly including a separator overlapping portion according to an embodiment of the present invention. [Diagram 3] 1 is a schematic diagram illustrating a separator overlapping portion of a jelly roll type electrode assembly according to an embodiment of the present invention. [Figure 4] 1 is a CT image showing an evaluation result of short-term cycle stability of secondary batteries according to Example 1 and Comparative Example 1. [Diagram 5] 1 is a schematic diagram illustrating a separator overlapping portion of a jelly roll type electrode assembly according to an embodiment of the present invention. [Figure 6] 1 is a CT image showing the evaluation results of short-term cycle stability of secondary batteries according to Examples 1 to 4. [Figure 7] 1 is a CT image showing an evaluation result of long-term cycle stability of secondary batteries according to Example 1 and Comparative Example 1. [Figure 8] 1 is a graph showing the evaluation results of the long-term cycle stability of secondary batteries according to Example 1 and Comparative Example 1. [Figure 9] 1 illustrates a method for evaluating whether or not a core separator of a jelly-roll type electrode assembly according to an embodiment of the present invention is damaged. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Throughout this specification, when a part is said to "comprise" a certain element, this means that it may further include other elements, but not to the exclusion of other elements, unless specifically stated to the contrary.

[0013] Throughout this specification, when a member is said to be "on" another member, this includes not only when the member is in contact with the other member, but also when there is another member between the two members.

[0014] One embodiment of the present invention provides a jelly roll type electrode assembly in which a first separator, a negative electrode, a second separator, and a positive electrode are sequentially stacked and wound up, in which the positive electrode has a first surface which is in the winding axis direction of the jelly roll type electrode assembly, and a second surface which is the opposite surface to the first surface, a core portion of the electrode assembly includes a separator overlap portion between the positive electrode and the negative electrode which faces the first surface of the positive electrode, and the separator overlap portion has three or more layers of separators arranged in an overlapping manner.

[0015] According to an embodiment of the present invention, a jelly roll type electrode assembly includes a separator overlapping portion, which prevents the electrode from sliding during charging and discharging of the battery, thereby preventing damage to the negative electrode and separator due to deformation of the electrode assembly caused by contraction / expansion of the electrode, and even if the separator is damaged, the separator overlapping portion prevents an internal short circuit between the positive electrode and the negative electrode, thereby improving the stability and life characteristics of the battery. Here, the "core portion" may refer to a hollow portion located on the winding shaft of the electrode assembly and a region including a part of a laminated structure of a first separator / negative electrode / second separator / positive electrode that is wound up, and may refer to a region within two turns of the positive electrode from one end of the positive electrode in the length direction located at the innermost side of the electrode assembly. In addition, the "one turn" refers to a length required for winding an electrode or separator included in the electrode assembly 360° from a reference point, and the length may be determined according to the outer diameter of a 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 refer to a length required to wind the positive electrode 360° from a longitudinal end of the positive electrode in a direction in which the jelly-roll type electrode assembly is wound.

[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 of the electrode assembly, the first separator, the negative electrode, and the second separator may extend longer than the longitudinal end of the positive electrode and be further wound. Specifically, referring to FIG. 1 and FIG. 2, the first separator 200, the negative electrode 100, and the second separator 400 may extend longer than the longitudinal end 310 of the positive electrode and be further wound. That is, the first separator, the negative electrode, and the second separator may be wound together with the positive electrode after being wound. For example, the first separator, the negative electrode, and the second separator may be wound together around a winding core for one or more turns, and then be wound together with the positive electrode. That is, in the core of the jelly roll type electrode assembly, the longitudinal ends 210, 110, and 410 of the first separator, the negative electrode, and the second separator may be located inside the longitudinal end 310 of the positive electrode. In other words, the length and width of the negative electrode may be greater than that 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 greater than that of the positive electrode. When the first separator, the negative electrode, and the second separator extend longer than the longitudinal end of the positive electrode and are further wound up, the transfer of lithium ions from the positive electrode to the negative electrode in the chemical reaction of the lithium ion battery can be further facilitated. When the length or width of the negative electrode is formed wider, the area of ​​the negative electrode that receives lithium ions increases, preventing a decrease in charge / discharge efficiency and providing excellent stability and life characteristics of the battery.

[0018] FIG. 3 is a schematic diagram showing a separator overlapping portion of a jelly roll type electrode assembly according to an embodiment of the present invention.

[0019] According to one embodiment of the present invention, the core part of the electrode assembly includes a separator overlap part between the positive electrode and the negative electrode facing the first surface of the positive electrode, and the separator overlap part may have three or more overlapping separators. Specifically, referring to Figs. 1 to 3, the core part of the electrode assembly includes a separator overlap part (S) between the positive electrode 300 and the negative electrode 100 facing the first surface of the positive electrode, and the separator overlap part (S) may refer to a part of a region in which three or more separators are overlapped around a longitudinal end 310 of the positive electrode. Here, the separator overlap part (S) may refer to an end of a region in which three or more separators are overlapped around a longitudinal end 310 of the positive electrode, i.e., a region having the same length in the direction of the core part of the electrode assembly as the region up to the longitudinal end of the separator overlap part. Specifically, the separator overlapping portion (S) refers to a region from the longitudinal end of the separator overlapping portion (S) to a length (L') in the core portion direction of the electrode assembly that is the same as the separation distance (L) between the longitudinal end of the separator overlapping portion and the longitudinal end of the positive electrode, centered on the longitudinal end 310 of the positive electrode, and may refer to a region having a length of L+L'=L+L=2L from the longitudinal end 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 extend from the longitudinal end of the negative electrode in the core of the electrode assembly and are overlapped. 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' extend from the longitudinal end 110 of the negative electrode in the core of the electrode assembly and are overlapped, and the first separator 200 and the second separator 400 may include an area 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 be further wound up. In other words, the first separator 200 and the second separator 400 may be wound up together with the negative electrode 100 after being wound up to a predetermined length. 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 were wound before the negative electrode 100, and may be folded and overlapped to form a separator overlapping portion (S). That is, the separator overlapping portion can be formed by a folded structure that extends integrally from the first separator and the second separator without providing a separate auxiliary separator or the like. This allows the separators constituting the separator overlapping portion to be adjusted to three or more layers with a simpler structure. In addition, when the first separator and the second separator extending from the longitudinal end of the negative electrode are arranged in an overlapping manner to form a separator overlapping portion, 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. Even if damage to the separator occurs, the separator overlapping portion can prevent an internal short circuit between the positive electrode and the negative electrode, thereby improving the stability and life characteristics of the battery.

[0021] According to one embodiment of the present invention, the first separator and the second separator may extend from the longitudinal end of the negative electrode in the core of the electrode assembly, be folded in the opposite direction to the direction facing the winding shaft of the negative electrode, and be arranged overlapping 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 folded in the opposite direction to the direction facing the winding shaft of the negative electrode, i.e., toward the longitudinal end 310 of the positive electrode, and may be arranged overlapping 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). This allows the separators constituting the separator overlapping portion to be three or more times stacked with a simpler folding structure, and makes it easier to adjust the facing direction of the separators constituting the separator overlapping portion.

[0022] According to one 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 with each other, and a second interface where the second separator and the first separator are in direct contact with each other. Specifically, referring to Fig. 3, the separator overlapping portion (S) may include three or more separators arranged in an overlapping manner, 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 with each other, and a second interface (S2) where the second separator 400' and the first separator 200' are in direct contact with each other. In other words, the separator overlapping portion may include a structure in which a first separator and a second separator are overlapped, rather than a structure in which a single separator is overlapped, and may include interfaces where the first and second separators are in contact with each other. By including multiple interfaces in the separator overlapping portion, it is possible to easily adjust the facing direction of the separators and the friction coefficient of each interface by a simpler folding structure.

[0023] According to an embodiment of the present invention, the first interface and the second interface may each have a coefficient of friction of 0.4 or more. Specifically, referring to FIG. 3, the first interface (S1) and the second interface (S2) may each have a coefficient of friction of 0.42 or more, 0.44 or more, or 0.46 or more. In other words, the separator overlapping portion does not have a single separator overlapping structure, but includes a first separator and a second separator overlapping structure, which are multiple separators, and includes multiple interfaces where the first separator and the second separator are in contact with each other, and in this case, the coefficients of friction of the multiple interfaces may each be adjusted to be greater than or equal to a specific range. When the coefficients of friction of the first interface and the second interface satisfy the above-mentioned range, the first separator and the second separator formed integrally with the separator overlapping portion can suppress sliding of the positive electrode during charging and discharging of the battery, and 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. Here, the friction coefficient (μ) refers to the static friction coefficient measured according to ASTM D1894. The friction coefficient may be measured in a dry manner, and may have a larger value when measured in a wet manner by immersing a test piece in distilled water or an electrolyte.

[0024] According to one embodiment of the present invention, the first interface may have a friction coefficient of 0.6 or more, and the second interface may have a friction coefficient of 0.4 or more. Specifically, referring to Fig. 3, the friction coefficients of the first interface (S1) and the second interface (S2) may differ from each other depending on the types and facing directions of the first separator 200, 200' and the second separator 400, 400' that face each other. 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 the friction coefficient between the interfaces of the separators included in the separator overlap portion is adjusted to the above-mentioned range, sliding of the electrodes during charging and discharging of the battery is suppressed, thereby preventing damage to the negative electrode and separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes. Even if damage to the separator occurs, the separator overlap portion prevents internal short circuits between the positive and negative electrodes, thereby improving the stability and life characteristics of the battery.

[0025] According to an 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 / anode / second separator / cathode are sequentially laminated. The separators 200 and 400 separate the anode 100 and the cathode 300 and provide a path for lithium ions to move. Any separators that are generally used as separators in secondary batteries may be used without particular limitation. In particular, it is preferable that the separators have low resistance to ion movement of the electrolyte and have excellent electrolyte moisture absorption ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene 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. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting point glass fiber, a polyethylene terephthalate fiber, or the like, may be used. The separator may generally have a thickness of 10 μm or more and 20 μm or less, and may be a separator in which the above-mentioned separator material is used as a substrate layer and a slurry containing a ceramic component or a polymeric substance is coated on the substrate layer in order to ensure heat resistance or mechanical strength, or may be selectively used as a single layer or multilayer structure.

[0026] Fig. 5 is a schematic diagram of a separator overlapping portion of a jelly roll type electrode assembly according to an embodiment of the present invention. Specifically, Fig. 5(a) is a schematic diagram of a separator overlapping portion of a jelly roll type electrode assembly including a first separator and a second separator each having a coating layer on both sides, and Fig. 5(b) is a schematic diagram of a separator overlapping portion of a jelly roll type electrode assembly including a first separator and a second separator each not having 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 side. Specifically, referring to FIG. 3 and FIG. 5 (a), the first separator 200, 200' and the second separator 400, 400' each include the coating layer 202, 202', 402, 402' and the substrate layer 201, 201', 401, 401' provided on at least one side, and the coating layer may have a friction coefficient in a specific range by adjusting the components, content, and particle size. Specifically, the friction coefficient between the coating layers and between the substrate layers of the separator may be greater than the friction coefficient between the coating layers and the substrate layers. In addition, the friction coefficient may be measured in a dry manner, but may have a more significant difference when measured in a wet manner, i.e., when immersed in distilled water or an electrolyte.

[0028] In the case where a coating layer is provided on at least 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 can be adjusted to a specific range by adjusting the facing direction of the coating layer provided on at least one side of the first separator and the second separator, thereby suppressing sliding of the electrodes during charging and discharging of the battery, and preventing damage to the negative electrode and separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes.

[0029] According to one embodiment of the present invention, the first separator and the second separator may each include a coating layer provided on at least one surface thereof, and the coating layer may include an inorganic component, a binder component, and a lithium salt. By including the above-mentioned components in the separator, the binder for improving adhesion to the electrode and the inorganic component for improving the mechanical strength of the separator are included, and yet an increase in internal resistance due to the elution of the lithium salt included in the coating layer is not brought about, and thus the cell stability can be excellent.

[0030] In addition, the electrolyte impregnation level of the electrode facing the separator can be increased, which can provide advantageous performance in terms of long life. Specifically, the coating layer may include the inorganic component, and since the coating layer including the inorganic component has an advantageous thermal shrinkage rate compared to a separator made of a simple polymer material, the separator including the coating layer may have better high temperature stability.

[0031] Specifically, the lithium salt may be substantially the same as that 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.

[0032] The inorganic component is a volatile organic compound that can be used in a range of operating voltages (e.g., Li / Li + There are no particular limitations on the material as long as it does not undergo an oxidation and / or reduction reaction, i.e., an electrochemical reaction, with the positive or negative electrode current collector at a voltage of 0 to 5 V relative to the reference voltage, 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 - It may be one or more selected from the group consisting of PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, and TiO2.

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

[0034] According to one embodiment of the present invention, the first separator and the second separator may each include a coating layer provided on at least one side, and the surface of the first separator and the second separator on which the coating layer is provided may have a higher friction coefficient 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 separator 200, 200' and the second separator 400, 400' may each include a coating layer 202, 202', 402, 402' provided on one side, and the surface of the first separator and the second separator on which the coating layer is provided may have a higher friction coefficient than the surface of the first separator and the second separator on which the coating layer is not provided. That is, when the coating layer is provided on the separator, it can increase the friction coefficient of the interface. 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 can be adjusted within a specific range, thereby suppressing sliding of the electrodes during charging and discharging of the battery, and preventing damage to the negative electrode and 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 side. Specifically, referring to Fig. 3, the first separator 200, 200' and the second separator 400, 400' each include the coating layer 202, 202', 402, 402' and the base layer 201, 201', 401, 401' provided on one side, and the friction coefficient can be within a specific range by adjusting the components, contents, and particle size of the coating layer.

[0036] In the case where a coating layer is 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 can be adjusted to a specific range by adjusting the facing direction of the coating layer provided on one side of the first separator and the second separator, thereby suppressing sliding of the electrodes during charging and discharging of the battery, and preventing damage to the negative electrode and separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes.

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

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

[0039] According to one embodiment of the present invention, the first interface may be in direct contact with the second separator facing the first surface of the positive electrode and the second separator extending from the longitudinal end of the negative electrode in the core of the electrode assembly. Specifically, referring to Figs. 1 to 3, the second separator 400' extending from the longitudinal end 110 of the negative electrode may be overlapped 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). In this case, 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 longitudinal end 110 of the negative electrode in the core portion of the electrode assembly are in direct contact with each other. This allows the separators constituting the separator overlapping portion to be stacked in three or more layers with a simpler folding structure, and makes it easier to adjust the facing direction of the separators constituting the separator overlapping portion and to adjust the frictional force at the interface.

[0040] According to one embodiment of the present invention, the second interface may be formed by direct contact between the first separator extending from the longitudinal end of the negative electrode in the core of the electrode assembly and the second separator extending from the longitudinal end of the negative electrode in the core of the electrode assembly. 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 overlapped 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). In this case, 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 may be directly in contact with each other to form a second interface (S2). This makes it possible to have three or more separators constituting the separator overlapping portion with an even simpler folding structure, and makes it even easier to adjust the facing direction of the separators constituting the separator overlapping portion and the frictional force at the interface.

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

[0042] Here, the periphery of the electrode assembly refers to the periphery of the inner periphery of the electrode assembly, and the "periphery of the inner periphery" may refer to a virtual circumference having a radius that is the maximum value among the distances from the winding shaft of the electrode assembly to the innermost layer that contacts the hollow of the electrode assembly. For example, the periphery of the inner periphery of the electrode assembly may be about 10 mm, but is not limited to this.

[0043] Also, referring to FIG. 3, the length of the separator overlapping portion in the longitudinal direction may be L+L'=L+L=2L. That is, the first separator extending from the longitudinal end of the negative electrode in the core of the electrode assembly; and the second separator extending from the longitudinal end of the negative electrode in the core of the electrode assembly may be disposed 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, and in this case, the length of the separator overlapping portion in the longitudinal direction may be at least 1 / 3 turn or at least 1 / 2 turn. When the separator overlapping portion satisfies the above-mentioned longitudinal length range, the frictional force between the interfaces of the separators included in the separator overlapping portion suppresses the sliding of the electrodes during charging and discharging of the battery, and 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 one embodiment of the present invention, the separation 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 separation 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 disposed 3 mm or more 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 of the separator overlapping part in the length direction is satisfied, even if a process error exists when the first separator and the second separator are inserted, the separator overlapping part can be disposed between the positive electrode and the negative electrode facing the first surface of the positive electrode. In addition, frictional force between the interfaces of the separators included in the separator overlapping part suppresses sliding of the electrodes during charging and discharging of the battery, and 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.

[0047] According to one 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, 303 formed on one or both sides of the positive electrode current collector 301 and including a positive electrode active material. In other words, the positive electrode active material layer is formed on the positive electrode active material-coated portion of the positive electrode current collector, and the surface on which the positive electrode active material layer is not provided may be referred to as a positive electrode uncoated portion.

[0048] According to an embodiment of the present invention, the positive electrode current collector may include a positive electrode active material-coated portion on which a positive electrode active material is coated, and a positive electrode uncoated portion on which a positive electrode active material is not coated, and may include a tab on the positive electrode uncoated portion. Specifically, the positive electrode current collector may include a positive electrode uncoated portion, and may include a positive electrode tab provided on the positive electrode uncoated portion.

[0049] According to one embodiment of the present invention, the electrode assembly may include a positive electrode, a separator, and a negative electrode that are stacked and wound, and the positive electrode may include a positive electrode current collector and a positive electrode active material layer that is provided on at least one side of the positive electrode current collector and has a longitudinal end at the same position as the positive electrode current collector. Specifically, referring to FIG. 3, the electrode assembly may include a positive electrode 300, a separator 200, 400, and a negative electrode 100 that are stacked and wound, and the positive electrode 300 may include a positive electrode current collector 301 and positive electrode active material layers 302, 303 that are provided on at least one side of the positive electrode current collector 301 and have a longitudinal end 310 at the same position as the positive electrode current collector 301. In other words, one longitudinal end 310 of the positive electrode may be in the form of a free edge. As a result, the area of ​​the unnecessary uncoated portion of the positive electrode current collector can be reduced to ensure economy, and since the slitting process can be performed after the active material layer is formed on the electrode, the roll-to-roll process including the slitting process and the winding process can be performed more efficiently. Here, "the same position" means that the end portions in the length direction are the same, and may include the case where the end portions are formed at substantially the same position due to process errors that may occur in the slitting process, etc.

[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, and specifically, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. That is, the positive electrode current collector may be provided in the form of surface-treated stainless steel, aluminum foil, etc.

[0051] The positive electrode current collector may have a thickness of 3 to 50 μm, and may have fine irregularities formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, 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, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2) or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+x Mn 2-x O4 (0≦x≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-y M y Lithium nickel oxide with Ni site represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦y≦0.3 is satisfied); 2-z M z Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxide represented by Li2Mn3MO8 (wherein 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 Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4 in which part of the Li in the chemical formula is replaced 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 electrical conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without causing a chemical change in the battery that is constructed. Specifically, the positive electrode conductive material may be graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; 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, and the like, and one or more of these may be used alone or in mixture.

[0054] The positive electrode binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength 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, and various copolymers thereof, and one or more of these may be used alone or in combination.

[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 a negative electrode active material layer 102, 103 formed on one or both sides of the negative electrode current collector 101 and including a negative electrode active material. In other words, the negative electrode active material layer is formed on a negative electrode active material coated portion of the negative electrode current collector, and a surface on which the negative electrode active material layer is not provided may be referred to as a negative electrode uncoated portion.

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

[0057] According to an embodiment of the present invention, the negative electrode active material layer may include a negative electrode active material including at least one selected from the group consisting of a silicon-based material and a carbon-based material. 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, the negative electrode conductive material, and the negative electrode binder may be any material used in the art without limitation.

[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 electrical conductivity. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, 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 is not limited thereto.

[0059] According to one embodiment of the present invention, the negative electrode binder may include at least 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, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may 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, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

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

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

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

[0064] According to one embodiment of the present invention, the inside of the battery case may contain an electrolyte. Specifically, the electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in manufacturing a lithium secondary battery. Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0065] According to one embodiment of the present invention, the non-aqueous organic solvent may be, for example, an aprotic organic solvent 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, or 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 dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt is 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.

[0067] According to one embodiment of the present invention, in addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery. EXAMPLES

[0068] Hereinafter, the present invention will be described in detail with reference to examples in order to specifically explain the present invention. However, the examples according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples in the present specification are provided to more completely explain the present invention to those having average knowledge in the art.

[0069] <Example> <Example 1> (Manufacturing of electrode assemblies) An Al foil having a thickness of 15 μm and a width of 63.9 mm was prepared as a positive electrode current collector. 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 was applied onto the positive electrode current collector and dried to form a positive electrode active material layer, thereby producing a positive electrode having a thickness of 154 μm.

[0070] Next, a Cu foil having a thickness of 8 μm and a length of 65.1 mm in the width direction was prepared as a negative electrode current collector, and a negative electrode active material slurry containing 50 parts by weight each of artificial graphite and natural graphite as negative electrode active materials was applied onto the negative electrode current collector and dried to form a negative electrode active material layer, thereby producing a negative electrode having a thickness of 187 μm.

[0071] On the other hand, two separators were prepared as the first and second 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 one side of a sheet-like polyethylene base layer.

[0072] Before winding the jelly roll type electrode assembly, the first separator and the second separator were stacked so that their base layers faced each other, and the first separator and the second separator were provided with extensions in the opposite direction to the winding direction by a length corresponding to about 3 turns of the winding core. In this case, the winding core had a periphery of about 10 mm.

[0073] Then, the first and second separators were folded back in the winding direction at points corresponding to three turns of the winding core from the longitudinal ends thereof to start winding, and the negative and positive electrodes were sequentially inserted to manufacture a jelly roll type electrode assembly. In this case, the core part of the jelly roll type electrode assembly had a separator overlapping part provided between one side of the positive electrode in the winding axis direction and the second separator located on one side of the negative electrode by interposing the extension parts of the first and second separators, so as to have a structure as shown in Figs. 1 and 2. In this case, the separation distance (L) between the longitudinal end of the separator overlapping part and the longitudinal end of the positive electrode was adjusted to be 3 mm, and the longitudinal length of the separator overlapping part (L+L'=2L) was adjusted to be 6 mm. The periphery of the inner peripheral surface of the manufactured jelly roll type electrode assembly was about 10 mm.

[0074] (Secondary battery manufacturing) The jelly-roll type electrode assembly was inserted into a cylindrical battery case, and an electrolyte solution prepared by mixing ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) in a weight ratio of 4:9:3 and dissolving LiPF6 to contain 15 wt% was poured into the cylindrical battery case, and the cylindrical battery case was sealed with a cap assembly to manufacture a secondary battery.

[0075] <Example 2> A jelly-roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1, except that the first and second separators were 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 substrate layer.

[0076] <Example 3> A jelly-roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1, except that two separators each having no coating layer formed on both sides of a sheet-shaped polyethylene substrate layer were used as the first separator and the second separator.

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

[0078] <Comparative Example 1> A jelly-roll type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1, except that a separator overlapping portion was not provided.

[0079] <Experimental Example> <Experimental Example 1 - Evaluation of friction coefficient> The coefficients of friction (μ) between the coating layers of the first separator and the second separator, between the coating layers and the substrate layers, and between the substrate layers of the first separator and the second separator were measured according to ASTM D 1894. In this case, the coefficients of friction were measured in a dry manner, and then the same test pieces were immersed in the electrolyte for 60 minutes and then remeasured in a wet manner. The results are shown in Table 1 below.

[0080] [Table 1]

[0081] Referring to Table 1, it was confirmed that the coefficient of friction between coating layers of the first separator and the second separator is higher than the coefficient of friction between substrate layers or between coating layers and substrate layers. In addition, it was confirmed that the coefficient of friction measured in a wet state is higher than the coefficient of friction measured in a dry state. Specifically, it was confirmed that the coefficient of friction between substrate layers is relatively lower than the coefficient of friction between coating layers and substrate layers, but the coefficient of friction between substrate layers is higher in a wet state, which is the internal environment of a secondary battery to be manufactured. As a result, it can be seen that the coefficient of friction between coating layers and between substrate layers of the first separator and the second separator is higher than the coefficient of friction between coating layers and substrate layers when immersed in distilled water or electrolyte. In addition, it can be seen that the friction coefficient between the interfaces of the separators included in the separator overlapping portion can be adjusted to a specific range by adjusting the facing direction of the coating layers provided on one side of the first separator and the second separator.

[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 were activated by performing 2 cycles of 4.2V-2.5V, 0.2C charge, and 0.2C discharge to prepare secondary batteries. Then, the activated secondary batteries were each subjected to 20 cycles of 4.3V-2.5V, 1C / 1C @25°C to prepare secondary batteries, and the short-term cycle stability was evaluated by checking the presence or absence of core impingement by performing computed tomography (CT) of the core part, and the images are shown in FIG. 4 and FIG. 6, respectively.

[0083] (Evaluation of long-term cycle stability) The secondary batteries manufactured in Example 1 and Comparative Example 1 were activated by performing two cycles of 4.2V-2.5V, 0.2C charge, and 0.2C discharge, respectively, to prepare secondary batteries. Then, the activated secondary batteries were each subjected to 200 cycles under the conditions of 4.25V (0.3C)-2.85V (0.5C) @55°C, and the core part was subjected to computed tomography (CT) to confirm the presence or absence of core impingement, thereby evaluating the long-term cycle stability, and the images are shown in FIG. 7. In addition, the energy density, capacity retention rate, and coulombic efficiency according to the cycle progression were measured, and are shown in Table 2 and FIG. 8 below.

[0084] [Table 2]

[0085] (Core Impingement Evaluation) The secondary batteries of Example 1 and Comparative Example 1 were evaluated for the occurrence of core impingement by the following method.

[0086] Fig. 9 is a schematic diagram showing a method for evaluating the occurrence of core impingement. Specifically, Fig. 9(a) is a schematic diagram showing a method for evaluating the occurrence of core impingement when deformation occurs in the negative electrode, and Fig. 9(b) is a schematic diagram showing a method for evaluating the occurrence of core impingement when deformation does not occur in the negative electrode.

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

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

[0089] 2-2) If there is no deformation in the negative electrode, In the core portion of the jelly roll type electrode assembly, a second extension line (E2) is drawn by extending a straight line connecting two points on the surface of the negative electrode 100 facing the first surface of the positive electrode, the two points being spaced 5 mm apart from the longitudinal end 310 of the positive electrode.

[0090] 3) It was determined that a core impingement occurred when the angle from the first extension line (E1) to the second extension line (E2) in a counterclockwise direction exceeds 25° centered on the intersection point of the first extension line (E1) and the second extension line (E2).

[0091] Meanwhile, the method of evaluating the occurrence of core impingement can be applied in the following manner: when an unknown secondary battery is obtained, the occurrence of core impingement is evaluated at the time of initial acquisition, and the occurrence of core impingement is re-evaluated every 250 cycles, and the result is compared and analyzed with the core impingement conditions of the secondary battery of the embodiment of the present invention.

[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] 4 and 7, it was confirmed that the secondary battery manufactured in Example 1 did not have core impingement in both the short cycle stability evaluation and the long cycle stability evaluation, but the secondary battery manufactured in Comparative Example 1 had core impingement in both the short cycle stability evaluation and the long cycle stability evaluation. Specifically, it was confirmed that the secondary battery manufactured in Comparative Example 1 did not have core impingement before activation, but some secondary batteries after activation had core impingement. Furthermore, it was confirmed that the frequency and degree of damage to the negative electrode and separator due to the longitudinal end of the positive electrode, i.e., core impingement due to contraction / expansion of the electrode assembly, significantly increased after 20 cycles corresponding to the short cycle and after 200 cycles corresponding to the long cycle.

[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] 6, it was confirmed that no core impingement occurred in any of the secondary batteries manufactured in Examples 1 to 4 after activation, but in the case of Example 3 including the first and second separators without a coating layer, it was confirmed that a slight warping phenomenon occurred in the negative electrode facing the first surface of the positive electrode after the accelerated cycle.In the case of Example 4 in which the separator overlapping portion was set to less than 6 mm, it was confirmed that a slight warping phenomenon occurred in the negative electrode facing the first surface of the positive electrode after activation, and a core impingement occurred after the accelerated cycle.

[0096] As a result, when the first separator and the second separator include a coating layer on at least one side thereof, a higher friction coefficient can be achieved than when the separator overlap portion does not include a coating layer, i.e., when both the first interface and the second interface are in contact with the base material layer, and it can be seen that the sliding of the electrodes is suppressed, thereby providing an excellent effect of preventing damage to the negative electrode and the separator even when the electrodes contract / expand. Furthermore, it can be seen that when the length of the separator overlap portion is adjusted to a specific range or more, the above-mentioned effect of preventing damage to the negative electrode and the separator is even more excellent.

[0097] Fig. 8 is a graph showing the evaluation results of the long-term cycle stability of the secondary batteries according to Example 1 and Comparative Example 1. Specifically, (a) of Fig. 8 is a graph showing the capacity retention rate over the course of cycles of the secondary batteries according to Example 1 and Comparative Example 1, and (b) of Fig. 8 is a graph showing the coulombic efficiency over the course of cycles of the secondary batteries according to Example 1 and Comparative Example 1.

[0098] 8, it was confirmed that the secondary battery according to Example 1, which has a separator overlapping portion for improving the core impingement, exhibits an initial energy density and a capacity retention rate at similar levels to the comparative example in which the separator overlapping portion is not provided. In contrast, it was confirmed that the secondary battery according to Comparative Example 1 experiences a decrease in the capacity retention rate after the initial 50 cycles, i.e., when long-term cycles are performed. Specifically, it was confirmed that the coulombic efficiency of the secondary battery according to Example 1 is reversed after 50 cycles, and has a large fluctuation range, resulting in a decrease in lifespan due to an internal short circuit.

[0099] This shows that the secondary battery according to Example 1 does not experience a significant decrease in initial energy density and capacity retention rate even when a separator overlapping portion is provided, whereas the secondary battery according to Comparative Example 1, which does not have a separator overlapping portion, has superior battery stability and life characteristics.

[0100] That is, the jelly roll type electrode assembly according to an embodiment of the present invention includes a separator overlapping part in which three or more separators are overlapped at a specific position, thereby suppressing sliding of the electrodes during charging and discharging of the battery, thereby preventing damage to the negative electrode and separator due to deformation of the electrode assembly caused by contraction / expansion of the electrodes. In addition, even if the separator is damaged, the separator overlapping part prevents internal shorts between the positive and negative electrodes, thereby improving the stability and life characteristics of the battery. Furthermore, it is found that the above-mentioned effects are even more excellent when the folding structure of the core separator, the friction coefficient between the interfaces, and the length range of the separator overlapping part are adjusted.

[0101] The above detailed description is illustrative and explanatory of the present invention. Moreover, the above-mentioned contents are merely illustrative and explanatory of preferred embodiments of the present invention. As mentioned above, the present invention can be used in various other combinations, modifications, and environments, and changes or modifications can be made within the scope of the inventive concept disclosed herein, the scope of the above-mentioned disclosure, and / or the skill or knowledge of the art. Therefore, the above detailed description of the invention is not intended to limit the present invention to the disclosed embodiments. Moreover, the appended claims should be construed to include other embodiments. [Explanation of symbols]

[0102] 100...Negative electrode 101...Negative electrode current collector 102, 103...Negative electrode active material layer 110: End portion in the longitudinal direction of the negative electrode 200, 200' First separator 210 Lengthwise end portion of first separator 201, 201' First separator substrate layer 202, 202' First separator coating layer 300...Positive electrode 301...Positive electrode current collector 302, 303...Cathode active material layer 310: Positive electrode end in longitudinal direction 400, 400' Second separator 410 Lengthwise end of second separator 401, 401' Second separator substrate layer 402, 402'...Second separator coating layer S: Separator overlapping section S1...1st interface S2...Second interface L, L': Distance between the longitudinal end of the separator overlapping part and the longitudinal end of the positive electrode E1...1st 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 stacked and wound, the positive electrode includes a first surface in a winding axis direction of the jelly roll type electrode assembly, and a second surface opposite to the first surface, the core portion of the electrode assembly includes a separator overlap portion between the positive electrode and the negative electrode facing a first surface of the positive electrode, The separator overlapping portion of the jelly roll type electrode assembly has three or more overlapping separators.

2. In the core portion of the electrode assembly, 2. The jelly roll type electrode assembly of claim 1, wherein the first separator, the negative electrode, and the second separator extend beyond the longitudinal ends of the positive electrode and are further wound up.

3. The separator overlapping portion is 3. The jelly roll type electrode assembly according to claim 1, wherein the first separator and the second separator extending from a longitudinal end of the negative electrode in a core portion of the electrode assembly are arranged to overlap each other.

4. The first separator and the second separator are a core portion of the electrode assembly, the core portion extending from a longitudinal end of the negative electrode; The negative electrode is bent in a direction opposite to the direction facing the winding shaft, The jelly roll type electrode assembly according to claim 1 , wherein the positive electrode and the second separator facing the first surface of the positive electrode are overlapped with each other.

5. The separator overlapping portion is a first interface where the second separator and the first separator are in direct contact with each other; and a second interface where the second separator and the first separator are in direct contact with each other; 3. The jelly roll type electrode assembly of claim 1, wherein the first interface and the second interface each have a coefficient of friction of 0.4 or more.

6. The friction coefficient of the first interface is 0.6 or more; 6. The jelly roll type electrode assembly of claim 5, wherein the second interface has a coefficient of friction of 0.4 or more.

7. the first separator and the second separator each include a coating layer provided on at least one surface thereof; 6. The jelly roll type electrode assembly of claim 5, wherein the surfaces of the first separator and the second separator on which the coating layer is provided have a higher coefficient of friction than the surfaces of the first separator and the second separator on which the coating layer is not provided.

8. the first separator and the second separator each include a coating layer provided on at least one surface thereof; 6. The jelly roll type electrode assembly of claim 5, wherein the coating layer comprises an inorganic component, a binder component, and a lithium salt.

9. the first separator and the second separator each include a coating layer provided on one surface thereof, 6. The jelly roll type electrode assembly of claim 5, wherein the first interface is a direct interface between the coating layer of the first separator and the coating layer of the second separator.

10. the first separator and the second separator each include a coating layer provided on one surface thereof, 6. The jelly roll type electrode assembly of claim 5, wherein the second interface is formed by a surface of the second separator not having a coating layer directly contacting a surface of the first separator not having a coating layer.

11. 6. The jelly roll type electrode assembly according to claim 5, wherein the first interface is formed by direct contact between the second separator facing the first surface of the positive electrode and the second separator extending from a longitudinal end of the negative electrode in a core portion of the electrode assembly.

12. 6. The jelly roll type electrode assembly according to claim 5, wherein the second interface is formed by direct contact between the first separator extending from the longitudinal end of the negative electrode in a core portion of the electrode assembly and the second separator extending from the longitudinal end of the negative electrode in a core portion of the electrode assembly.

13. The length of the separator overlapping portion in the longitudinal direction is 3. The jelly-roll type electrode assembly according to claim 1, wherein the peripheral length of the electrode assembly is 30% or more, assuming that the peripheral length of the electrode assembly is 100%.

14. 3. The jelly-roll type electrode assembly according to claim 1, wherein a separation distance between a longitudinal end of the separator overlapping portion and a longitudinal end of the positive electrode is 3 mm or more.

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

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

Images