Winding type electrode assembly, manufacturing method for winding type electrode assembly, and secondary battery including winding type electrode assembly

Abstract

The invention relates to a wound electrode assembly, a manufacturing method for the wound electrode assembly, and a secondary battery including the wound electrode assembly.

Description

Technical Field

[0001] The present invention relates to a wound electrode assembly, a method for manufacturing a wound electrode assembly, and a secondary battery including the wound electrode assembly, and particularly to a wound electrode assembly including a flexible film heated by a heating element inserted into a hollow section of a core portion of the wound electrode assembly, a method for manufacturing a wound electrode assembly, and a cylindrical secondary battery including the wound electrode assembly. Background Art

[0002] For cylindrical batteries, a wound electrode assembly is manufactured by winding a long electrode of a predetermined width into a roll. Cylindrical batteries manufactured by inserting such a wound electrode assembly into a battery case experience repeated contraction and expansion of the electrodes during charging and discharging. In particular, when the degree of contraction and expansion of the electrode assembly is increased by tabs located in the core of the wound electrode assembly or silicon-based active materials added to the negative electrode, the pressure acting on the core portion of the electrode assembly is greatly increased.

[0003] At the same time, the core portion of the cylindrical battery has a space for the core axis of the wound electrode assembly, wherein the space is an empty space used when assembling the cylindrical battery, such as the insertion process and welding process of the wound electrode assembly into the battery box, that is, the hollow section of the core portion.

[0004] With the recent increase in low-resistance / high-capacity designs, wound-type electrode assemblies are increasingly including multiple tabs or adding silicon-based active materials. This increases the likelihood of deformation of the core portion of the electrode assembly due to contraction / expansion of the electrode assembly. Specifically, core deformation, i.e., collapse of the hollow section of the core portion and its inability to maintain a circular shape, leads to a decrease in battery life and also causes rupture of the separator located between the negative and positive electrodes, resulting in internal short circuits caused by direct contact between the negative and positive electrodes, leading to heat generation and fire.

[0005] In order to solve the problems of deterioration of battery life, separator rupture and internal short circuit occurrence caused by deformation of the electrode assembly, it is necessary to develop a technology that can support the hollow section of the core part in the corresponding area to maintain its circular shape and suppress internal short circuit. Summary of the Invention

[0006] Technical issues

[0007] An aspect of the present invention is to provide a wound-type electrode assembly having an improved design, a method for manufacturing the wound-type electrode assembly, and a secondary battery including the wound-type electrode assembly.

[0008] However, technical aspects of the present invention are not limited to the above-mentioned aspects, and other technical aspects not mentioned will be clearly understood by those skilled in the art from the following description.

[0009] Technical Solution

[0010] According to one aspect of the present invention, there is provided a wound-type electrode assembly comprising a first separator, a negative electrode, a second separator, and a positive electrode, which are sequentially laminated and wound, wherein: a core portion of the wound-type electrode assembly comprises a flexible film disposed between the first separator and the second separator; a length of the flexible film in a longitudinal direction is 100% to 150% of a circumference based on 100% of an inner circumference of the wound-type electrode assembly; the flexible film is heated by a heating element inserted into a hollow section of the core portion of the wound-type electrode assembly; and a tensile strength of the flexible film after heating is 18 kgf / mm 2 Up to 25kgf / mm 2 .

[0011] According to another aspect of the present invention, there is provided a method for manufacturing a wound electrode assembly, the wound electrode assembly including a first separator, a negative electrode, a second separator, and a positive electrode that are sequentially laminated and wound, the method comprising: (a) winding the first separator and the second separator; (b) introducing a flexible film between the first separator and the second separator; (c) introducing the negative electrode; (d) introducing the positive electrode; and (e) performing heating by inserting a heating element into a hollow section of a core portion of the wound electrode assembly, wherein: a length of the flexible film in a longitudinal direction is 100% to 150% of a 100% inner circumference of the wound electrode assembly; and a tensile strength of the flexible film after heating is 18 kgf / mm 2 Up to 25kgf / mm 2 .

[0012] According to still another aspect of the present invention, there is provided a secondary battery including: a wound-type electrode assembly; and a battery case for accommodating the electrode assembly.

[0013] Beneficial effects

[0014] The wound electrode assembly according to an embodiment of the present invention includes a flexible film that has a certain rigidity after being heated by a heating element inserted into the hollow section of the core portion, so that the hollow section of the core portion is supported to resist deformation of the electrode assembly caused by contraction / expansion of the electrodes during battery charging / discharging and maintain its circular shape, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive electrode and the negative electrode, thereby improving battery stability and service life characteristics.

[0015] The method for manufacturing a wound electrode assembly according to an embodiment of the present invention can produce a wound electrode assembly including a flexible film having a predetermined degree of rigidity after heating in a simpler manner, and ensure productivity and economic efficiency due to the rigidity of the flexible film before heating, which is suitable for a continuous process using existing roll-to-roll processing equipment.

[0016] In addition, in the secondary battery according to the present invention, the hollow section of the core portion is supported to maintain its circular shape even when the electrode assembly is deformed due to contraction / expansion of the electrodes during battery charge / discharge, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive electrode and the negative electrode, thereby improving battery stability and service life characteristics.

[0017] The beneficial effects of the present invention are not limited to the above-mentioned beneficial effects, and those skilled in the art will clearly understand unstated beneficial effects from the description and drawings of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A wound-type electrode assembly including a flexible film according to an embodiment of the present invention is illustrated.

[0019] Figure 2 A method for manufacturing a wound-type electrode assembly including a flexible film according to an embodiment of the present invention is schematically illustrated.

[0020] Figure 3 and Figure 4 CT images showing the long-term cycle evaluation results of the wound-type electrode assemblies of Examples 1 and 2.

[0021] Figures 5 to 7 CT images showing the long-term cycle evaluation results of the wound-type electrode assemblies of Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0022] Throughout this specification, unless explicitly described to the contrary, the words “comprise,” “include,” or “contain,” and variations such as “comprises,” “comprising,” or “having,” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

[0023] Throughout this specification, when a member is disposed “on” another member, this includes not only a case where one member is in contact with another member but also a case where another member exists between the two members.

[0024] Throughout this specification, the term "flexible film" refers to a film having a predetermined degree of rigidity required for easy winding of a wound electrode assembly, i.e., a rigidity of a specific value or less, and may refer to a film having a rigidity of 16 kgf / mm2 or less tensile strength of the film.

[0025] According to an embodiment of the present invention, there is provided a wound-type electrode assembly including a first separator, a negative electrode, a second separator, and a positive electrode that are sequentially laminated and wound, wherein: a core portion of the wound-type electrode assembly includes a flexible film disposed between the first separator and the second separator; a length of the flexible film in a longitudinal direction is 100% to 150% of a circumference based on 100% of an inner circumference of the wound-type electrode assembly; the flexible film is heated by a heating element inserted into a hollow section of the core portion of the wound-type electrode assembly; and a tensile strength of the flexible film after heating is 18 kgf / mm 2 Up to 25kgf / mm 2 .

[0026] A wound-type electrode assembly according to an embodiment of the present invention includes a flexible film having a predetermined degree of rigidity after being heated by a heating element inserted into a hollow section of a core portion, so that the hollow section of the core portion is supported to maintain its circular shape against deformation of the electrode assembly due to contraction / expansion of the electrodes during battery charge / discharge, thereby preventing damage to the positive electrode and separator and suppressing internal short circuits between the positive electrode and the negative electrode, thereby improving battery stability and service life characteristics.

[0027] According to an embodiment of the present invention, the core portion of a wound electrode assembly may include a flexible film disposed between a first separator and a second separator. As used herein, the term "core portion" refers to a region including: a hollow section located at the winding axis of the electrode assembly; and a portion of the laminated structure of the wound electrode assembly, and may refer to the region from one end portion of the negative electrode in the longitudinal direction, located at the innermost portion of the electrode assembly, to the end portions of the first and second separators. The core portion may refer to the region within three turns of one end portion of the negative electrode in the longitudinal direction.

[0028] According to an embodiment of the present invention, the core portion of the wound-type electrode assembly may not include the positive electrode and the negative electrode. In other words, the core portion of the wound-type electrode assembly may be composed of the first separator, the flexible film, and the second separator.

[0029] In an embodiment of the present invention, one surface and the other surface of the flexible film may not be in direct contact with the negative electrode or the positive electrode. In other words, one surface and the other surface of the flexible film may be in direct contact with the separator, wherein the separator may include a first separator and a second separator.

[0030] This configuration can minimize a decrease in charge / discharge capacity due to a reduction in a negative electrode area receiving lithium ions, hindrance of electrolyte impregnation, or other problems even when a flexible film is included in the core portion of a wound-type electrode assembly.

[0031] According to an embodiment of the present invention, the core portion of the wound electrode assembly may include a flexible film arranged between a first separator and a second separator, and may include: a first region having a laminated structure of the first separator and the second separator; and a second region having a laminated structure of the first separator, the flexible film and the second separator.

[0032] Figure 1 A wound-type electrode assembly including a flexible film according to an embodiment of the present invention is shown, and Figure 2 A method for manufacturing a wound-type electrode assembly including a flexible film according to an embodiment of the present invention is schematically illustrated.

[0033] Reference Figure 1 and Figure 2 , the core portion of the wound electrode assembly may include: a first region having a laminate structure of a first separator and a second separator; and a second region having a laminate structure of a first separator, a flexible film, and a second separator. Specifically, the core portion of the wound electrode assembly may include a flexible film disposed between the first separator and the second separator, and therefore may include: a first region having a laminate structure of a first separator and a second separator; and a second region having a laminate structure of a first separator, a flexible film, and a second separator. More specifically, the length of the first region in the longitudinal direction may be L1, and the length of the second region in the longitudinal direction may be L2. The core portion (C) may refer to a region having the sum of the length L1 of the first region in the longitudinal direction and the length L2 of the second region in the longitudinal direction, that is, a length in the longitudinal direction of L1+L2, where L3=0.

[0034] In this case, one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction can contact each other, and as described below, the step difference can be minimized by adjusting the thickness range of the flexible film. In other words, local problems such as the step difference formed due to the thickness difference between the flexible film and the negative electrode and the precipitation of lithium in the step difference formation area can be minimized.

[0035] According to an embodiment of the present invention, the length of the first region in the longitudinal direction may be 1 to 1.7 turns. Specifically, the length L1 of the first region in the longitudinal direction may be 1.1 turns or more, 1.2 turns or more, or 1.3 turns or more, and may be 1.6 turns or less, 1.5 turns or less, or 1.4 turns or less.

[0036] In particular, the term "one turn" may refer to the length required to wind a separator included in an electrode assembly 360° from a reference point, and this length may be determined based on the outer diameter of a mandrel used to wind the electrode assembly, the thicknesses of the first separator, the flexible film, and the second separator, and the number of times the first separator, the flexible film, and the second separator located inside are wound. For example, the term "one turn" may refer to the length required to wind the first separator 360° along the direction in which the wound electrode assembly is wound from the end portion of the first separator in the longitudinal direction.

[0037] If the length of the first region in the longitudinal direction meets the aforementioned range, winding of the electrode assembly can be more easily achieved by adjusting the distance between one end portion of the separator in the longitudinal direction and one end portion of the flexible film in the longitudinal direction. If the length of the first region in the longitudinal direction is less than one turn, the tension for continuous winding may be insufficient when winding using a mandrel.

[0038] According to an embodiment of the present invention, the core portion of the wound electrode assembly may further include a third region having a laminated structure of a first separator and a second separator. Specifically, the core portion of the wound electrode assembly may include: a first region having a laminated structure of a first separator and a second separator; a second region having a laminated structure of a first separator, a flexible film, and a second separator; and a third region having a laminated structure of a first separator and a second separator. More specifically, the length of the first region in the longitudinal direction may be L1, the length of the second region in the longitudinal direction may be L2, and the length of the third region in the longitudinal direction may be L3. The core portion (C) may refer to a region having the sum of the length L1 of the first region in the longitudinal direction, the length L2 of the second region in the longitudinal direction, and the length L3 of the third region in the longitudinal direction, that is, a length in the longitudinal direction of L1+L2+L3, wherein L3>0.

[0039] In this case, one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may not contact each other, and as described below, the distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction can be adjusted to minimize damage to the separator caused by the end portion of the electrode or the flexible film even during contraction / expansion of the electrode assembly.

[0040] According to an embodiment of the present invention, the length of the flexible film in the longitudinal direction may be 100% to 150% of the 100% inner circumference of the wound electrode assembly. Specifically, the length of the flexible film in the longitudinal direction may be 105% or more, 110% or more, 115% or more, or 120% or more, and 145% or less, 140% or less, 135% or less, or 130% or less, based on 100% of the inner circumference of the wound electrode assembly.

[0041] In particular, the term "inner circumference" may refer to the circumference of an imaginary circle whose radius is the maximum value of the distance from the winding axis of the electrode assembly to the innermost layer in contact with the hollow portion of the electrode assembly, and the length may be determined based on the outer diameter of the mandrel used to wind the electrode assembly. For example, the inner circumference may have a value of approximately 10 mm.

[0042] According to an embodiment of the present invention, the length of the flexible film in the longitudinal direction may be 0.9 to 1.4 turns. Specifically, the distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may be 1 turn or more, or 1.1 turns or more, and 1.3 turns or less, or 1.2 turns or less. Figure 2 , the length of the flexible film in the longitudinal direction may be the same as the length L2 of the second region in the longitudinal direction.

[0043] If the length of the flexible film in the longitudinal direction satisfies the aforementioned range, the core support effect by the heated flexible film can be further enhanced, and a decrease in battery capacity and energy density can be minimized, thereby preventing degradation of electrochemical characteristics.

[0044] According to an embodiment of the present invention, the distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may be 0.5 turns or less. Specifically, the distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may be 0.4 turns or less, or 0.3 turns or less. Figure 2 , a distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may be the same as a length L3 of the third region in the longitudinal direction.

[0045] In this case, one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction can contact each other, and the thickness of the flexible film and the negative electrode can be adjusted to minimize the step difference caused by the thickness difference between the electrode and the flexible film.

[0046] According to an embodiment of the present invention, the distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may be 0.3 to 0.7 turns. Specifically, the distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may be 0.4 turns or more, or 0.5 turns or more, and 0.6 turns or less, or 0.5 turns or less. Figure 2 , a distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may be the same as a length L3 of the third region in the longitudinal direction.

[0047] In this case, one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may not contact each other, and the distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction can be adjusted to minimize damage to the separator caused by the end portion of the electrode or the flexible film even during contraction / expansion of the electrode assembly.

[0048] According to an embodiment of the present invention, the flexible membrane may further include a fixing member located on at least one surface thereof. Specifically, the fixing member is used to minimize sliding of the flexible membrane, and an adhesive or adhesive tape may be used for this purpose. The addition of a fixing member can minimize damage to the separator caused by the end portions of the electrode or flexible membrane even during contraction / expansion of the electrode assembly or sliding of the flexible membrane.

[0049] According to an embodiment of the present invention, the flexible film may be heated by a heating element inserted into a hollow section of a core portion of a wound-type electrode assembly.

[0050] According to an embodiment of the present invention, the tensile strength of the flexible film before heating may be 9 kgf / mm 2 Up to 16kgf / mm 2 Specifically, the tensile strength of the flexible film before heating may be 10 kgf / mm 2 or greater, 11kgf / mm 2 or larger, or 12kgf / mm 2 or greater, and 15kgf / mm 2 or less, 14kgf / mm 2 or smaller, or 13kgf / mm 2 or smaller.

[0051] According to an embodiment of the present invention, the tensile strength of the flexible film can be increased after heating. Specifically, the tensile strength of the flexible film can be increased according to the deformation of the flexible film after one or both surfaces of the flexible film are heated, and the increase rate of the tensile strength can vary depending on the degree of heating of the flexible film, that is, the heating area, heating temperature, and heating time.

[0052] According to an embodiment of the present invention, the tensile strength of the heated flexible film may be 150% to 200% of the 100% tensile strength before heating. Specifically, the tensile strength of the heated flexible film may be 160% or more, 170% or more, or 180% or more, and 190% or less, 180% or less, or 170% or less, based on the 100% tensile strength before heating.

[0053] According to an embodiment of the present invention, the tensile strength of the heated flexible film may be 18 kgf / mm 2 Up to 25kgf / mm 2 Specifically, the tensile strength of the heated flexible film can be 19 kgf / mm 2 or greater, 20kgf / mm 2 or greater, or 21kgf / mm 2 or greater, and 24kgf / mm 2 or less, 23kgf / mm 2 or smaller, or 22kgf / mm 2 or smaller.

[0054] Specifically, the tensile strength of the flexible film can be measured by preparing a sample having a size of 20 mm×100 mm and a thickness of 10 μm from a heated film specimen and testing the sample using a universal testing machine (UTM) at room temperature at a speed of 2 cm / min.

[0055] If the rigidity of the flexible film before heating satisfies the aforementioned range, the rigidity of a wound-type electrode assembly including the flexible film may be more suitable for a roll-to-roll process, thereby improving productivity and economic efficiency of the wound-type electrode assembly.

[0056] If the tensile strength of the heated flexible film satisfies the aforementioned range, the core support effect generated by the heated flexible film can be further enhanced, and continuous production of electrode assemblies can be achieved using existing roll-to-roll processing equipment, thereby ensuring productivity and economic efficiency.

[0057] According to an embodiment of the present invention, the heating element may be a reformer pin. Figure 2In c, the heating element may be a reforming pin 200 that pushes a separator (not shown) located in the hollow section (H) of the core portion of the wound electrode assembly 100 toward the inner circumferential surface of the core portion of the wound electrode assembly 100, so that the wound electrode assembly 100 is molded into a hollow section having a cylindrical shape.

[0058] A pair of mandrels can be used during the winding process of a jellyroll-type electrode assembly. The mandrels can be used to wind the electrode assembly into a jellyroll-type electrode assembly, and then the electrode assembly can be separated from the mandrels. Specifically, within the hollow section of the core portion of the jellyroll-type electrode assembly, a separator is present that crosses the hollow section in a manner corresponding to the gap between the pair of mandrels used for winding. In order to remove the separator that crosses the hollow section and restore the central portion of the electrode assembly to a circular shape, it is necessary to arrange the central portion using a reforming pin through a separate reforming process after the electrode assembly is wound.

[0059] The use of reforming pins as heating elements facilitates subsequent removal of separators from the hollow section of the core portion of the wound electrode assembly after winding, thereby improving electrode assembly productivity. Furthermore, the degree of heating of the flexible film, i.e., the heating area, heating temperature, and heating time, can be adjusted within a specific range, thereby ensuring a predetermined degree of rigidity of the heated flexible film.

[0060] According to an embodiment of the present invention, heating can be performed on one surface of the flexible film. Specifically, heating can be performed on the entire area of ​​one surface of the flexible film.

[0061] According to an embodiment of the present invention, the heating may be performed at a temperature of 50° C. to 80° C. for 5 to 15 seconds.

[0062] A wound-type electrode assembly including a flexible film having a predetermined degree of rigidity may be manufactured by adjusting the degree of heating of the flexible film, ie, a heating area, a heating temperature, and a heating time, to within specific ranges.

[0063] According to an embodiment of the present invention, heating may be performed at 55° C. or higher, 60° C. or higher, or 65° C. or higher, and 75° C. or lower, 70° C. or lower, or 65° C. or lower. For example, heating may be performed at 60° C.

[0064] According to an embodiment of the present invention, heating can be performed for 5 seconds to 15 seconds. Specifically, heating can be performed for 6 seconds or longer, 7 seconds or longer, 8 seconds or longer, or 9 seconds or longer, and can be performed for 14 seconds or shorter, 13 seconds or shorter, 12 seconds or shorter, or 11 seconds or shorter. For example, heating can be performed for 10 seconds.

[0065] If the aforementioned heating time conditions and heating temperature conditions are satisfied, a wound electrode assembly including a flexible film having a predetermined degree of rigidity can be more easily manufactured, and the core support effect by the heated flexible film can be further enhanced.

[0066] However, excessive heating may shrink the separator, while insufficient heating may result in an unsatisfactory increase in the rigidity of the heated flexible film, leading to poor core portion support.

[0067] According to an embodiment of the present invention, the length of the core portion of the wound electrode assembly in the longitudinal direction may be 2 to 3 turns. Specifically, the length of the core portion of the wound electrode assembly in the longitudinal direction may be 2.1 turns or more, 2.2 turns or more, 2.3 turns or more, 2.4 turns or more, or 2.5 turns or more, and the length in the longitudinal direction may be 2.9 turns or less, 2.8 turns or less, 2.7 turns or less, 2.6 turns or less, or 2.5 turns or less.

[0068] Reference Figure 2 The length of the core part in the longitudinal direction can be the same as the sum of the length L1 of the first region in the longitudinal direction and the length L2 of the second region in the longitudinal direction, or can be the same as the sum of the length L1 of the first region in the longitudinal direction, the length L2 of the second region in the longitudinal direction and the length L3 of the third region in the longitudinal direction.

[0069] In particular, the term "1 turn" may refer to the length required to wind a separator included in an electrode assembly 360° from a reference point, and this length may be determined based on the outer diameter of a mandrel used to wind the electrode assembly, the thickness of the first separator, the flexible film, and the second separator, and the number of times the first separator, the flexible film, and the second separator located inside are wound. For example, the term "1 turn" may refer to the length required to wind the first separator 360° along the direction in which the wound electrode assembly is wound from the end portion of the first separator in the longitudinal direction.

[0070] If the length of the core portion in the longitudinal direction satisfies the aforementioned range, a space sufficient for arranging the flexible film can be ensured, and the core supporting effect by the heated flexible film can be further enhanced.

[0071] According to an embodiment of the present invention, the length of the flexible film in the width direction may be 95% to 105% based on 100% of the length of the wound electrode assembly in the width direction. Specifically, the length of the flexible film in the width direction may be 96% or more, 97% or more, 98% or more, 99% or more, or 100% or more, and 104% or less, 103% or less, 102% or less, 101% or less, or 100% or less based on 100% of the length of the wound electrode assembly in the width direction.

[0072] If the length of the flexible film in the width direction satisfies the aforementioned range, the length of the flexible film can correspond to the length of the wound electrode assembly in the width direction, and this condition is conducive to supporting the core part of the wound electrode assembly and can obtain an excellent effect of preventing core deformation.

[0073] If the flexible film is too short in the width direction, the effect of preventing core deformation may be reduced. If the flexible film is excessively exposed in the width direction of the wound electrode assembly, it may cause more defects and local problems during the insertion process into the battery case, such as lithium precipitation due to step formation.

[0074] According to an embodiment of the present invention, the flexible film may include at least one selected from polypropylene, polyethylene, polyester, and polyamide. Specifically, the flexible film may include at least one selected from polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), and polyamide (PA). For example, the flexible film may include polypropylene (PP).

[0075] When the flexible film is formed from the aforementioned type of material, the rigidity of the heated flexible film may be sufficient to support the core portion of the wound electrode assembly, and the rigidity of the flexible film before heating may be more suitable for roll-to-roll processing, thereby improving the productivity and economic efficiency of the wound electrode assembly.

[0076] According to an embodiment of the present invention, the thickness of the flexible film may be 5% to 20% based on 100% thickness of the negative electrode. Specifically, the thickness of the flexible film may be 6% or more, 7% or more, 8% or more, 9% or more, or 10% or more, and 19% or less, 18% or less, 17% or less, 16% or less, or 15% or less based on 100% thickness of the negative electrode.

[0077] If the thickness of the flexible film satisfies the aforementioned range, the step difference can be minimized by adjusting the thickness range of the flexible film. In other words, local problems such as the step difference formed due to the thickness difference between the flexible film and the negative electrode and the precipitation of lithium in the step difference formation area can be minimized.

[0078] According to an embodiment of the present invention, the thickness of the flexible film may be 10 μm to 50 μm. Specifically, the thickness of the flexible film may be 15 μm or more, 20 μm or more, or 25 μm or more, and 45 μm or less, 40 μm or less, or 35 μm or less.

[0079] If the thickness of the flexible film satisfies the aforementioned range, the rigidity of the heated flexible film may be sufficient to support the core portion of the wound electrode assembly, and the rigidity of the flexible film before heating may be more suitable for roll-to-roll processing, thereby improving the productivity and economic efficiency of the wound electrode assembly.

[0080] According to an embodiment of the present invention, a 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, wherein the ends of the positive electrode current collector and the positive electrode active material layer in the longitudinal direction may be located at the same position. In other words, one end of the positive electrode in the longitudinal direction may have a free edge.

[0081] Thus, the area of ​​unnecessary uncoated portions of the positive electrode current collector can be reduced to ensure economic efficiency, and the slitting process can be performed after forming an active material layer on the electrode, thereby more efficiently performing a roll-to-roll process including the slitting process and the winding process.

[0082] The term “same position” means that the lengths of the end portions in the longitudinal direction are the same as each other, and may include that the end portions are formed substantially at the same position due to process errors that may occur in a slitting process or the like.

[0083] According to an embodiment of the present invention, the positive electrode current collector may include a positive electrode coated portion coated with a positive electrode active material and a positive electrode uncoated portion not coated with the positive electrode active material. A tab may be included 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 formed on the positive electrode uncoated portion.

[0084] According to an embodiment of the present invention, the positive electrode current collector is not particularly limited as long as the positive electrode current collector has conductivity and does not cause chemical changes in the battery. Specifically, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used as the positive electrode current collector. That is, the positive electrode current collector can be provided in the form of surface-treated stainless steel, aluminum foil, etc.

[0085] In addition, the positive electrode current collector may generally have a thickness of 5 μm to 30 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion 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, mesh, porous body, foam body, and non-woven fabric body.

[0086] According to an 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 may include: layered compounds, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted by one or more transition metals; lithium iron oxide, such as LiFe3O4; lithium manganese oxide, such as Li 1+x Mn 2-x O4 (0≤x≤0.33), LiMnO3, LiMn2O3 and LiMnO2 compounds; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5 and Cu2V2O7; 1-y M y Ni-type lithiated nickel oxide represented by O2 (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); 2-z M z A lithium manganese composite oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and 0.01≤z≤0.1) or LiMnO4 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMnO4, wherein some of the Li in the chemical formula is replaced by an alkaline earth metal ion or the like, but is not limited thereto. The positive electrode may be Li metal.

[0087] According to an 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 positive electrode, and any conductive material that does not cause chemical changes in the constructed battery while having electronic conductivity may be used without particular limitation. Specifically, examples of positive electrode conductive materials may include: graphite, such as natural graphite, artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, etc., and one of the above materials may be used alone or a mixture of two or more of the above materials may be used.

[0088] The positive electrode binder is used to enhance the adhesion strength between the positive electrode active material particles and the adhesion strength between the positive electrode active material and the positive electrode current collector. Specific examples of the binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and one of the above may be used alone, or a mixture of two or more of the above may be used.

[0089] According to an embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector and containing a negative electrode active material. In other words, the negative electrode active material layer may be formed on the negative electrode coating portion of the negative electrode current collector, and the surface on which the negative electrode active material layer is not provided may be referred to as a negative electrode uncoated portion.

[0090] According to an embodiment of the present invention, the negative electrode current collector may include a negative electrode coated portion having a negative electrode active material layer formed thereon and a negative electrode uncoated portion having no negative electrode active material layer formed thereon, and may include a tab located on the negative electrode uncoated portion. Specifically, the negative electrode current collector may include the negative electrode uncoated portion and may include a negative electrode tab formed on the negative electrode uncoated portion. Thus, the manufactured electrode assembly may include at least one negative electrode tab.

[0091] 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 formed of materials used in the art without limitation.

[0092] According to embodiments of the present invention, the negative electrode current collector is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like can be used as the negative electrode current collector. Specifically, transition metals with good carbon adsorption, such as copper and nickel, can be used as the negative electrode current collector. The thickness of the negative electrode current collector can be 5 μm to 30 μm, but the thickness of the negative electrode current collector is not limited thereto.

[0093] According to an 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, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen of the above materials is replaced by Li, Na, Ca, etc., and may also include various copolymers of these substances.

[0094] According to an embodiment of the present invention, the negative electrode conductive material is not particularly limited, as long as it has conductivity and does not cause chemical changes in the corresponding battery. Examples of negative electrode conductive materials may include: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as carbon fluoride powder, aluminum powder, 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.

[0095] According to an embodiment of the present invention, a wound electrode assembly may include a plurality of separators. For example, the wound electrode assembly may have a structure in which separator / negative electrode / separator / positive electrode are laminated in sequence. The separator is used to separate the negative electrode and the positive electrode, and to provide a channel for the migration of lithium ions. The material used for the separator is not particularly limited as long as it is a material commonly used as a separator for secondary batteries, and in particular, a material that has low resistance to electrolyte ion migration and is well impregnated in the electrolyte is preferred. Specifically, a porous polymer film can be used, for example, a porous polymer film formed of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer; or a laminate structure having two or more layers formed of these polymers can be used. Alternatively, a typical porous non-woven fabric can be used, such as a non-woven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like. In addition, to ensure heat resistance or mechanical strength, the separator may include a coating formed by coating a slurry containing a ceramic component or a polymer component on a base layer formed of the aforementioned separator material, and may selectively have a single-layer structure or a multi-layer structure. The thickness of the separator may be 10 μm to 20 μm, but is not limited thereto.

[0096] According to another embodiment of the present invention, there is provided a method for manufacturing a wound electrode assembly, the wound electrode assembly including a first separator, a negative electrode, a second separator, and a positive electrode that are sequentially laminated and wound, the method comprising: (a) winding the first separator and the second separator; (b) introducing a flexible film between the first separator and the second separator; (c) introducing the negative electrode; (d) introducing the positive electrode; and (e) performing heating by inserting a heating element into a hollow section of a core portion of the wound electrode assembly, wherein: a length of the flexible film in a longitudinal direction is 100% to 150% of a circumference based on 100% of an inner circumference of the wound electrode assembly; and a tensile strength of the flexible film after heating is 18 kgf / mm 2 Up to 25kgf / mm 2 .

[0097] The method for manufacturing a wound electrode assembly according to an embodiment of the present invention can produce a wound electrode assembly including a flexible film having a predetermined degree of rigidity after heating in a simpler manner, and ensure productivity and economic efficiency due to the rigidity of the flexible film before heating, which is suitable for a continuous process using existing roll-to-roll processing equipment.

[0098] In addition, the wound electrode assembly obtained by the manufacturing method includes a flexible film in the core portion, which has a predetermined degree of rigidity after heating, so that the hollow section of the core portion is supported to resist deformation of the electrode assembly caused by contraction / expansion of the electrodes during battery charging / discharging and maintain its circular shape, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive electrode and the negative electrode, thereby improving battery stability and service life characteristics.

[0099] According to an embodiment of the present invention, the length of the flexible film in the longitudinal direction may be 100% to 150% of the 100% inner circumference of the wound electrode assembly. Specifically, the length of the flexible film in the longitudinal direction may be 105% or more, 110% or more, 115% or more, or 120% or more, and 145% or less, 140% or less, 135% or less, or 130% or less, based on 100% of the inner circumference of the wound electrode assembly.

[0100] If the length of the flexible film in the longitudinal direction satisfies the aforementioned range, the core support effect by the heated flexible film can be further enhanced, and a decrease in battery capacity and energy density can be minimized, thereby preventing degradation of electrochemical characteristics.

[0101] According to an embodiment of the present invention, the tensile strength of the heated flexible film may be 18 kgf / mm 2 Up to 25kgf / mm 2Specifically, the tensile strength of the heated flexible film can be 19 kgf / mm 2 or greater, 20kgf / mm 2 or greater, or 21kgf / mm 2 or greater, and 24kgf / mm 2 or less, 23kgf / mm 2 or smaller, or 22kgf / mm 2 or smaller.

[0102] If the tensile strength of the heated flexible film satisfies the aforementioned range, the core support effect generated by the heated flexible film can be further enhanced, and continuous production of electrode assemblies can be achieved using existing roll-to-roll processing equipment, thereby ensuring productivity and economic efficiency.

[0103] In particular, the core portion and the inner circumference, the properties of the flexible film, namely, the tensile strength and rate of increase of the tensile strength before heating, and the method for measuring the tensile strength of the flexible film may be as described for the wound electrode assembly. Furthermore, the first to third regions included in the core portion, the length (L1) of the first region, the length (L2) of the second region, the length (L3) of the third region, and the longitudinal length (L1+L2+L3) of the core portion may be as described for the wound electrode assembly.

[0104] According to an embodiment of the present invention, the method for manufacturing a wound electrode assembly can be performed by a roll-to-roll process. Specifically, steps (a) to (d) can be performed by a roll-to-roll process in which a plurality of flexible metal foils, etc., are processed while traveling between rollers.

[0105] In particular, the roll-to-roll process may refer to a method in which a flexible and thin metal sheet-shaped electrode current collector wound around a roll is unwound to provide an electrode current collector, an electrode slurry containing an electrode active material is coated on at least one surface of the electrode current collector and dried to form an electrode mixture layer, and then the treated electrode current collector is wound again around another roll to be recovered.

[0106] The term "introduction" may refer to a series of introduction and winding steps performed during the manufacture of an electrode assembly by a roll-to-roll process, that is, the term may refer to a part of the winding process. Specifically, the term may refer to a process of introducing a film or electrode to be additionally wound between a plurality of separators, each of the plurality of separators being wound around a mandrel to a portion of the length in the longitudinal direction starting from one end portion in the longitudinal direction, or a process of introducing a film or electrode to be additionally wound on one surface of a plurality of separators partially wound around a mandrel. Alternatively, the term may refer to a process of manufacturing an electrode assembly by continuously winding the introduced film or electrode together with a plurality of partially wound separators, and may involve a slitting process of cutting a portion of the length in the longitudinal direction as needed.

[0107] The method for manufacturing a wound electrode assembly according to an embodiment of the present invention can continuously produce a wound electrode assembly including a heated flexible film by using existing roll-to-roll processing equipment. In other words, in the method for manufacturing a wound electrode assembly, step (b) can be performed after step (a) and before step (c), and thus the entire process can be performed by a roll-to-roll process used in the art.

[0108] That is, the method for manufacturing a wound electrode assembly according to an embodiment of the present invention can continuously produce a wound electrode assembly including a flexible film having a predetermined degree of rigidity after heating by using existing roll-to-roll processing equipment, thereby ensuring productivity and economic efficiency.

[0109] According to one embodiment of the present invention, a method for manufacturing a wound electrode assembly may include heating a heating element inserted into a hollow section of a core portion of the wound electrode assembly. Specifically, the heating element may be a reforming pin, and the reforming pin may be as described with respect to the wound electrode assembly.

[0110] According to an embodiment of the present invention, a reforming pin can be inserted into the hollow section of the electrode assembly, and then the reforming pin is allowed to repeatedly advance and retreat, thereby pushing the separator across the hollow section of the core portion to the innermost layer in contact with the hollow section of the electrode assembly, and removing the separator.

[0111] According to an embodiment of the present invention, the diameter of the reforming pin may be 70% to 90% of the 100% diameter of the hollow section of the core portion. Specifically, the diameter of the reforming pin may be 75% or more, 80% or more, or 85% or more, and 85% or less, 80% or less, or 75% or less of the 100% diameter of the hollow section of the core portion.

[0112] If the diameter of the reforming pin satisfies the aforementioned range, the degree of heating of the flexible film, i.e., the heating area, heating temperature and heating time are adjusted to a specific range, thereby ensuring a predetermined degree of rigidity of the heated flexible film and preventing the separator from protruding during removal of the reforming pin.

[0113] According to an embodiment of the present invention, the length of the reforming pin may be 100% or more based on 100% of the length of the wound-type electrode assembly in the width direction.

[0114] If the length of the reforming pin satisfies the aforementioned range, the length of the reforming pin can correspond to the length of the wound electrode assembly in the width direction, and the process of removing the separator of the hollow section across the core portion of the electrode assembly and heating can be performed more uniformly over the entire length of the electrode assembly in the width direction.

[0115] According to an embodiment of the present invention, the heating may be performed at a temperature of 50° C. to 80° C. for 5 to 15 seconds.

[0116] According to an embodiment of the present invention, heating may be performed at 55° C. or higher, 60° C. or higher, or 65° C. or higher and 75° C. or lower, 70° C. or lower, or 65° C. or lower. For example, heating may be performed at 60° C.

[0117] According to an embodiment of the present invention, heating can be performed for 5 seconds to 15 seconds. Specifically, heating can be performed for 6 seconds or longer, 7 seconds or longer, 8 seconds or longer, or 9 seconds or longer, and can be performed for 14 seconds or shorter, 13 seconds or shorter, 12 seconds or shorter, or 11 seconds or shorter. For example, heating can be performed for 10 seconds.

[0118] If the aforementioned heating time conditions and heating temperature conditions are satisfied, a wound electrode assembly including a flexible film having a predetermined degree of rigidity can be more easily manufactured, and the core support effect by the heated flexible film can be further enhanced.

[0119] However, excessive heating may shrink the separator, while insufficient heating may result in an unsatisfactory increase in the rigidity of the heated flexible film, leading to a decrease in the core portion supporting effect.

[0120] Figure 2 A method for manufacturing a wound-type electrode assembly including a flexible film according to an embodiment of the present invention is schematically illustrated.

[0121] Reference Figure 2 , step (a) may be to wind the first separator and the second separator. Step (b) may be performed after the first separator and the second separator are wound to a predetermined length using a mandrel.

[0122] That is, a flexible film can be introduced between a first separator and a second separator that are wound to a predetermined length. Thus, the core portion of the wound electrode assembly may not include a positive electrode and a negative electrode, and one surface and the other surface of the flexible film may not be in direct contact with the negative electrode or the positive electrode. Specifically, the widthwise length, material, and thickness of the introduced flexible film may be as described with respect to the wound electrode assembly.

[0123] Through step (b), the flexible film may have a predetermined length, and the core portion of the wound-type electrode assembly including the flexible film may also have a predetermined length.

[0124] Then, step (c) and step (d) may be performed in sequence.

[0125] According to an embodiment of the present invention, step (c) may be introducing the negative electrode, and specifically, introducing the negative electrode between the first separator and the second separator.

[0126] In particular, one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may not contact each other, and the distance between one end portion of the flexible film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction can be adjusted to minimize damage to the separator caused by the end portion of the electrode or the flexible film even during contraction / expansion of the electrode assembly.

[0127] On the other hand, when one end portion of the flexible film in the longitudinal direction contacts one end portion of the negative electrode in the longitudinal direction, the thickness range of the flexible film can be adjusted to minimize the step difference, thereby minimizing local problems such as lithium precipitation in the step difference formation area.

[0128] Then, step (e) can be performed after steps (a) to (d). Specifically, heating can be performed by inserting a heating element into the hollow section of the core portion after the wound electrode assembly is wound. More specifically, using a reforming pin as a heating element can simultaneously achieve the process of removing the separator that crosses the hollow section of the core portion of the electrode assembly and the heating process.

[0129] The method for manufacturing a wound electrode assembly according to an embodiment of the present invention can produce a wound electrode assembly including a flexible film having a predetermined degree of rigidity after heating in a simpler manner, and ensure productivity and economic efficiency due to the rigidity of the flexible film before heating, which is suitable for a continuous process using existing roll-to-roll processing equipment.

[0130] An embodiment of the present invention provides a wound-type electrode assembly produced by the above-described wound-type electrode assembly manufacturing method.

[0131] The wound-type electrode assembly according to an embodiment of the present invention includes a flexible film having a predetermined degree of rigidity after heating, so that the hollow section of the core portion is supported to maintain its circular shape against deformation of the electrode assembly due to contraction / expansion of the electrodes during battery charge / discharge, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive electrode and the negative electrode, thereby improving battery stability and service life characteristics.

[0132] Embodiments of the present invention provide a secondary battery including: a wound electrode assembly; and a battery case for accommodating the electrode assembly. Specifically, the secondary battery may include the electrode assembly according to the aforementioned embodiment and a battery case for accommodating the electrode assembly.

[0133] In the secondary battery according to the present invention, the hollow section of the core portion is supported to maintain its circular shape even when the electrode assembly is deformed due to contraction / expansion of the electrodes during battery charge / discharge, thereby preventing damage to the positive electrode and the separator and suppressing an internal short circuit between the positive electrode and the negative electrode, thereby improving battery stability and service life characteristics.

[0134] According to an embodiment of the present invention, the battery case may have a cylindrical shape. Specifically, the battery case may have a cylindrical, square, or pouch shape according to its use, but is not limited thereto.

[0135] According to an embodiment of the present invention, an electrolyte may be included in the battery case. Specifically, examples of the electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used to manufacture lithium secondary batteries, but are not limited thereto. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0136] According to an embodiment of the present invention, examples of non-aqueous organic solvents may include aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate and ethyl propionate.

[0137] According to an embodiment of the present invention, the metal salt may be a lithium salt, and a material having good solubility in a non-aqueous electrolyte may be used as the lithium salt. For example, at least one selected from the group consisting of the following may be used as the anion of the lithium salt: - 、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 - .

[0138] According to an embodiment of the present invention, for the purpose of improving the service life characteristics of the battery, preventing the battery capacity from decreasing, and increasing the discharge capacity of the battery, in addition to the electrolyte components, the electrolyte may further include at least one additive, for example, a halogenated alkylene carbonate-based compound, such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme dimethyl ether, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum chloride.

[0139] Embodiments of the present invention provide a battery module including a secondary battery as a unit cell and a battery pack including the battery module. The battery module and the battery pack include a secondary battery having improved high capacity and excellent battery stability and service life characteristics, and thus can be used as a power source for medium-sized and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0140] Modes for Carrying Out the Invention

[0141] Hereinafter, in order to better understand the present invention, exemplary embodiments will be described. However, exemplary embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be interpreted as being limited to the exemplary embodiments described below. Exemplary embodiments of the present invention are provided to more fully illustrate the present invention to those skilled in the art.

[0142] Examples

[0143] Example 1

[0144] Manufacturing of electrode assemblies

[0145] By using Li(Ni 0.93 Co 0.01 Mn 0.03 Al 0.03 )O2, CNT as a positive electrode conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 98.2:0.8:1.0 to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated on an aluminum current collector having a thickness of 15 μm and a length of 64 mm in the width direction, followed by drying and then roll-pressing to form a positive electrode active material layer, thereby preparing a positive electrode with a thickness of 175 μm.

[0146] Then, a mixture of natural graphite (C, average particle size of 10 μm, POSCO Chemical Co., Ltd.) and SiO (average particle size (D)) with a weight ratio of 95:5 was prepared. 50) is 5μm) (5wt% SiO) as a negative electrode active material. The negative electrode active material, carbon black as a conductive material, and a mixture of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as a first binder are mixed in a weight ratio of 98:1:1 to prepare a negative electrode active material composition. Thereafter, 7.8g of distilled water is introduced into 5g of the negative electrode active material composition, followed by stirring to prepare a negative electrode active material slurry. The negative electrode active material slurry is coated on a copper (Cu) metal film having a thickness of 10μm and a length of 65mm in the width direction as a negative electrode current collector, and then dried (drying temperature of 120°C for 1 minute) to form a negative electrode having an average thickness of 185μm. In particular, the temperature of the circulating air is 60°C.

[0147] Thereafter, a flexible film of polypropylene (PP) material having a length of 65 mm in the width direction, a length of 15 mm in the longitudinal direction, and a thickness of 50 μm, and two separators including a first separator and a second separator made of polyethylene (PE) material having a thickness of 13 μm were prepared. Specifically, a sample having a size of 20 mm × 100 mm and a thickness of 10 μm was prepared from the flexible film, and then the tensile strength was tested using a universal testing machine (UTM) at room temperature at a speed of 2 cm / min. The measured tensile strength was 11 kgf / mm 2 .

[0148] After that, the first separator and the second separator are arranged in sequence and wound using a mandrel with a diameter of 3.4 mm, and then the flexible film is additionally introduced between the first separator and the second separator, followed by further winding. After the flexible film is completely wound, the negative electrode and the positive electrode are introduced in sequence at a distance of 6 μm from the flexible film, followed by winding. A sealing tape made of PET material is attached and completed at the end portion where the winding is completed, while wrapping the outer peripheral surface of the top end and the bottom end of the winding, thereby manufacturing a wound electrode assembly. In particular, the inner circumference of the wound electrode assembly is about 12 mm, and the length from the end portion of the negative electrode in the longitudinal direction to the end portion of the first separator in the longitudinal direction is about 15 mm.

[0149] Afterwards, a reforming pin with a heater and a diameter of 2.5 mm is inserted into the hollow section of the core portion of the electrode assembly, and the reforming pin is then allowed to repeatedly advance and retreat, thereby pushing the separator across the hollow section of the core portion to the innermost layer in contact with the hollow section of the electrode assembly, and removing the separator. In particular, the heater provided in the reforming pin can be adjusted to 60°C, and the reforming is performed for 10 seconds. In particular, a sample having a size of 20 mm × 100 mm and a thickness of 10 μm is prepared from a heated flexible film, and then the tensile strength is tested at room temperature under a speed condition of 2 cm / min by using a universal testing machine (UTM). The measured tensile strength is 18 kgf / mm 2 .

[0150] Manufacturing of secondary batteries

[0151] The wound electrode assembly is inserted into a cylindrical battery case. Afterwards, an electrolyte solution obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:50:30 and dissolving LiPF6 in the mixture to 1.3M is injected into the battery case, and the cylindrical battery can then be sealed with a cap assembly, thereby manufacturing a secondary battery.

[0152] Example 2

[0153] A wound-type electrode assembly and a secondary battery were manufactured by the same method as in Example 1, except that a film made of a polyethylene (PE) material was used as the flexible film.

[0154] Specifically, a sample with a size of 20 mm × 100 mm and a thickness of 10 μm was prepared from a flexible film, and then the tensile strength was tested by using a universal testing machine (UTM) at room temperature at a speed of 2 cm / min. The measured tensile strength was 15 kgf / mm 2 , and the tensile strength of the heated flexible film is 25kgf / mm 2 .

[0155] Comparative Example 1

[0156] A wound-type electrode assembly and a secondary battery were manufactured by the same method as Example 1, except that the flexible film was not introduced.

[0157] Comparative Example 2

[0158] A wound electrode assembly and a secondary battery were manufactured by the same method as in Example 1, except that a film made of a polyimide (PI) material was used as the flexible film. Specifically, a sample with a size of 20 mm × 100 mm and a thickness of 10 μm was prepared from the PI film, and then the tensile strength was tested using a universal testing machine (UTM) at room temperature at a speed of 2 cm / min. The measured tensile strength was 5 kgf / mm 2 , and the tensile strength of the heated flexible film is 10kgf / mm 2 .

[0159] Comparative Example 3

[0160] A wound-type electrode assembly and a secondary battery were manufactured by the same method as in Example 1, except that a film having a length of 30 mm in the longitudinal direction was used as the flexible film.

[0161] Experimental examples

[0162] Experimental Example 1: Evaluation of Cyclic Stability

[0163] The secondary batteries manufactured in the examples and comparative examples were subjected to a cycle test using an electrochemical charger / discharger at 25°C at 4.2V to 2.85V and 0.5C / 0.5C. After 50 cycles, the core deformation of the core portion was examined by computed tomography (CT) to evaluate the cycle stability, and the core deformation was observed at 4.2V to 2.85V and 0.5C / 0.5C, respectively. Figures 3 to 7 An image of the core portion is shown in .

[0164] Experimental Example 2: Evaluation of Service Life

[0165] The service life of the secondary batteries manufactured in the examples and comparative examples was tested using an electrochemical charger / discharger, and the capacity retention was evaluated. The secondary batteries were cycled at 4.2V to 2.85V, 1C / 1C, and the capacity retention was measured by charging / discharging the secondary batteries at 0.2C / 0.2C (4.2V to 2.85V) every 100 cycles during the test. The results are shown in Table 1.

[0166] Lifespan retention rate (%) = {(nth cycle discharge capacity) / (first cycle discharge capacity)} × 100

[0167] Experimental Example 3: Evaluation of Resistance Increase Rate

[0168] After measuring the capacity retention rate by charging / discharging at 0.2C / 0.2C (4.2V to 2.85V) every 100 cycles during the test of Experimental Example 2, the resistance was measured by 0.5C pulse discharge at an SOC of 50, thereby comparing and analyzing the resistance increase rate. The results are shown in Table 1.

[0169] Table 1

[0170]

[0171] Refer to Table 1 and Figures 3 to 7 , the secondary battery according to the embodiment of the present invention includes a flexible film in the core portion, and at the same time increases the rigidity of the flexible film by heating using a reforming pin during the manufacture of the wound electrode assembly, thereby reducing the deformation of the core. In addition, the secondary batteries according to Examples 1 and 2 can exhibit the designed capacity and have improved service life and resistance characteristics. However, as in Comparative Examples 1 to 3, when the flexible film is not included, or when the tensile strength of the flexible film is 18 kgf / mm even after heating 2 When the length of the flexible film is too small or smaller, in other words, when a film with poor rigidity is used, the core deforms, resulting in increased battery resistance and deterioration of service life characteristics. In addition, excessive increase in the length of the flexible film in the longitudinal direction leads to a decrease in the length of the electrode in the longitudinal direction, thereby reducing the designed capacity and the actual discharge capacity that can be achieved.

[0172] Therefore, a wound electrode assembly and a secondary battery including the wound electrode assembly according to an embodiment of the present invention include a flexible film having a predetermined degree of rigidity after being heated by a heating element inserted into a hollow section of a core portion, so that the hollow section of the core portion is supported to maintain its circular shape against deformation of the electrode assembly due to contraction / expansion of the electrodes during battery charge / discharge, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive electrode and the negative electrode, thereby improving battery stability and service life characteristics.

[0173] The foregoing detailed description is intended to illustrate and explain the present invention. Furthermore, the foregoing description is intended only to illustrate and describe preferred embodiments of the present invention, and as described above, the present invention may be used in various other combinations, variations, and environments, and may be altered and modified within the scope of the inventive concept disclosed in this specification, within the scope equivalent to the above disclosure, and / or within the skill or knowledge in the art. Therefore, the foregoing detailed description of the present invention is not intended to limit the present invention to the disclosed embodiments. Furthermore, the appended claims should be interpreted to encompass other embodiments as well.

[0174] Industrial Applicability

[0175] A wound electrode assembly and a secondary battery including the wound electrode assembly according to an embodiment of the present invention include a flexible film having a predetermined degree of rigidity after being heated by a heating element inserted into a hollow section of a core portion, so that the hollow section of the core portion is supported to maintain its circular shape against deformation of the electrode assembly due to contraction / expansion of the electrodes during battery charge / discharge, thereby preventing damage to the positive electrode and separator and suppressing internal short circuits between the positive electrode and the negative electrode, thereby improving battery stability and life characteristics.

[0176] [Explanation of Reference Numerals]

[0177] 10: First separator

[0178] 20: Negative electrode

[0179] 30: Second separator

[0180] 40: Positive electrode

[0181] 50: Flexible membrane

[0182] 100: Wound electrode assembly

[0183] 200: Reorganization sales

[0184] L1: length of the first region in the longitudinal direction

[0185] L2: length of the second region in the longitudinal direction

[0186] L3: length of the third region in the longitudinal direction

[0187] C: core part

[0188] H: Hollow section of the core

Claims

1. A wound-type electrode assembly comprising a first separator, a negative electrode, a second separator, and a positive electrode, which are sequentially layered and wound, in, The core portion of the wound-type electrode assembly includes a flexible film disposed between the first separator and the second separator, The length of the flexible film in the longitudinal direction is 100% to 150% based on 100% of the inner circumference of the wound electrode assembly. The flexible film is heated by a heating element inserted into a hollow section of the core portion of the wound electrode assembly, and The tensile strength of the flexible film after heating is 18 kgf / mm 2 Up to 25kgf / mm 2 .

2. The wound electrode assembly according to claim 1, wherein: The heating element is a reformer pin.

3. The wound electrode assembly according to claim 1, wherein: The heating is performed at a temperature of 50° C. to 80° C. for 5 seconds to 15 seconds.

4. The wound electrode assembly according to claim 1, wherein: The length of the core portion of the wound electrode assembly in the longitudinal direction is 2 to 3 turns.

5. The wound electrode assembly according to claim 1, wherein Neither the negative electrode nor the positive electrode is included in the core portion of the wound-type electrode assembly.

6. The wound electrode assembly according to claim 1, wherein One surface and the other surface of the flexible film are not in direct contact with the negative electrode or the positive electrode.

7. The wound electrode assembly according to claim 1, wherein: The length of the flexible film in the width direction is 95% to 105% based on 100% of the length of the wound-type electrode assembly in the width direction.

8. The wound electrode assembly according to claim 1, wherein The flexible film has a thickness of 5% to 20% based on 100% of the thickness of the negative electrode.

9. The wound electrode assembly according to claim 1, wherein: The flexible film has a thickness of 10 μm to 50 μm.

10. The wound electrode assembly according to claim 1, wherein The positive electrode includes 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 The positive electrode current collector and the positive electrode active material layer respectively have end portions in the longitudinal direction at the same position.

11. A method for manufacturing a wound-type electrode assembly, the wound-type electrode assembly comprising a first separator, a negative electrode, a second separator, and a positive electrode layered and wound in sequence, the method comprising: (a) winding the first separator and the second separator; (b) introducing a flexible film between the first separator and the second separator; (c) introducing a negative electrode; (d) introducing a positive electrode, and (e) performing heating by a heating element inserted into a hollow section of a core portion of the wound-type electrode assembly, wherein the length of the flexible film in the longitudinal direction is 100% to 150% based on 100% of the inner circumference of the wound electrode assembly, and The tensile strength of the flexible film after heating is 18 kgf / mm 2 Up to 25kgf / mm 2 .

12. The method for manufacturing a wound-type electrode assembly according to claim 11, wherein: The heating element is a reformer pin.

13. The method for manufacturing a wound-type electrode assembly according to claim 12, wherein: The diameter of the reforming pin is 70% to 90% based on 100% of the diameter of the hollow section of the core portion.

14. The method for manufacturing a wound-type electrode assembly according to claim 11, wherein The heating is performed at a temperature of 50° C. to 80° C. for 5 seconds to 15 seconds. 15 . A wound electrode assembly manufactured by the method according to claim 11 .

16. A secondary battery comprising: The wound electrode assembly according to any one of claims 1 to 10 and 15; as well as A battery box for accommodating the electrode assembly.

17. The secondary battery according to claim 16, wherein The battery box is cylindrical in shape.

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