Wound-type electrode assembly, method for manufacturing wound-type electrode assembly, and secondary battery including same

Abstract

The present invention relates to a wound electrode assembly in which a first separator, a negative electrode, a second separator, and a positive electrode are laminated and wound in this order, in which a core portion of the wound electrode assembly includes a rigid film provided between the first separator and the second separator, the rigid film having a thickness of 5-10 [mu] m based on 100% of a perimeter of an inner circumferential surface of the wound electrode assembly. The rigid film has a longitudinal length of 100% to 150% and a tensile strength of 18 kgf / mm2 to 25 kgf / mm2.

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 in particular, to a wound electrode assembly including a rigid film, 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 having a predetermined width into a roll shape. A cylindrical battery manufactured by inserting such a wound electrode assembly into a battery case undergoes repeated contraction / expansion of the electrode during charging and discharging. In particular, when the degree of contraction / expansion of the electrode assembly increases due to a tab (in tab) located in the core of the wound electrode assembly or a silicon-based active material 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 winding core axis of the wound electrode assembly, wherein the space is an empty space used when assembling the cylindrical battery, such as during 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 electrode assemblies are increasingly incorporating multiple tabs or undergoing addition of silicon-based active materials. This increases the likelihood of deformation in the core portion of the electrode assembly due to shrinkage / expansion of the electrode assembly, and specifically, core deformation, i.e., collapse of the hollow section of the core portion and its inability to maintain a circular shape, leads to deterioration of battery life, and also causes rupture of the separator located between the negative electrode and the positive electrode, thereby causing heat generation and fire due to internal short circuits caused by direct contact between the negative electrode and the positive electrode.

[0005] In order to solve the problems of battery life deterioration, separator rupture and internal short circuit occurrence caused by deformation of the electrode assembly, it is necessary to develop a technology capable of supporting 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 electrode assembly, the wound 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 electrode assembly comprises a rigid film disposed between the first separator and the second separator; a length of the rigid film in a longitudinal direction is 100% to 150% based on 100% of a circumference of an inner peripheral surface of the wound electrode assembly; and a tensile strength of the rigid film 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 comprising a first separator, a negative electrode, a second separator and a positive electrode which are laminated and wound in sequence, the method comprising: (a) winding the first separator and the second separator; (b) introducing a rigid film between the first separator and the second separator; (c) introducing the negative electrode; and (d) introducing the positive electrode, wherein: based on 100% of the circumference of the inner circumferential surface of the wound electrode assembly, the length of the rigid film in the longitudinal direction is 100% to 150%; and the tensile strength of the rigid film 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] A wound electrode assembly according to an embodiment of the present invention includes a rigid film having a predetermined degree of rigidity in a core portion, so that a hollow section of the core portion is supported to resist deformation of the electrode assembly due to contraction / expansion of the electrode during battery charge / discharge to maintain its circular shape, 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.

[0015] The method for manufacturing a wound type electrode assembly according to an embodiment of the present invention may produce a wound type electrode assembly including a rigid film having a predetermined degree of rigidity through a continuous process using an existing roll-to-roll processing device, thereby ensuring productivity and economic efficiency.

[0016] In addition, in the secondary battery according to the present invention, the hollow section of the core portion is supported so as to maintain its circular shape even when the electrode assembly is deformed due to contraction / expansion of the electrode during battery charging / discharging, 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.

[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 specification and drawings of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0021] Figures 5 to 7 are 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 the specification, unless explicitly described to the contrary, the words “comprise,” “include,” or “contain,” and variations such as “comprising,” “including,” or “having,” will be understood to imply the further 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 "rigid film" refers to a film having a predetermined degree of rigidity required for supporting the core portion of a wound-type electrode assembly, that is, a rigidity of a specific value or more, and may refer to a film having a rigidity of 18 kgf / mm 2 or greater tensile strength of the film.

[0025] According to an embodiment of the present invention, there is provided a wound electrode assembly, the wound 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 electrode assembly comprises a rigid film disposed between the first separator and the second separator; a length of the rigid film in a longitudinal direction is 100% to 150% based on 100% of a circumference of an inner peripheral surface of the wound electrode assembly; and a tensile strength of the rigid film is 18 kgf / mm 2 Up to 25kgf / mm 2 .

[0026] The wound electrode assembly according to an embodiment of the present invention includes a rigid film having a predetermined degree of rigidity in the core portion, so that the hollow section of the core portion is supported to resist deformation of the electrode assembly due to contraction / expansion of the electrode during battery charging / discharging to maintain its circular shape, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive and negative electrodes, thereby improving battery stability and service life characteristics.

[0027] According to an embodiment of the present invention, the core portion of the wound electrode assembly may include a rigid film disposed between the first separator and the second separator. As used herein, the term "core portion" refers to an area including the following parts: 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 an area from one end portion of the negative electrode located at the innermost part of the electrode assembly in the longitudinal direction to the end portion of the first separator and the second separator. The core portion may refer to an area within 3 turns from 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 rigid film, and the second separator.

[0029] In an embodiment of the present invention, one surface and the other surface of the rigid 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 rigid 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 problems such as a decrease in charge / discharge capacity or hindrance of electrolyte impregnation due to a decrease in the negative electrode area receiving lithium ions even when a rigid 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 rigid 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 rigid film and the second separator.

[0032] Figure 1 A wound electrode assembly including a rigid 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 rigid 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 laminated structure of a first separator and a second separator; and a second region having a laminated structure of a first separator, a rigid film, and a second separator. Specifically, the core portion (C) of the wound electrode assembly may include a rigid film disposed between the first separator and the second separator, and therefore may include: a first region having a laminated structure of a first separator and a second separator; and a second region having a laminated structure of a first separator, a rigid 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, the length L1+L2 in the longitudinal direction, wherein L3=0.

[0034] In this case, one end portion of the rigid film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may contact each other, and as described below, the step difference may be minimized by adjusting the thickness range of the rigid film. In other words, local problems such as the step difference formed due to the thickness difference between the rigid film and the negative electrode and the precipitation of lithium in the step difference formation region may 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 "1 turn" may refer to a length required to wind a separator included in an electrode assembly 360° from a reference point, and the 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 rigid film, and the second separator, and the number of windings of the first separator, the rigid film, and the second separator located inside. For example, the term "1 turn" may refer to a length required to wind the first separator 360° in a direction in which the wound electrode assembly is wound from an end portion of the first separator in the longitudinal direction.

[0037] If the length of the first region in the longitudinal direction satisfies 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 rigid film in the longitudinal direction. If the length of the first region in the longitudinal direction is less than 1 turn, in winding using a mandrel, the tension for continuous winding may be insufficient.

[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 rigid 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, the length L1+L2+L3 in the longitudinal direction, wherein L3>0.

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

[0040] According to an embodiment of the present invention, based on 100% of the circumference of the inner circumferential surface of the wound electrode assembly, the length of the rigid film in the longitudinal direction may be 100% to 150%. Specifically, based on 100% of the circumference of the inner circumferential surface of the wound electrode assembly, the length of the rigid 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.

[0041] In particular, the term "inner circumference" may refer to the circumference of an imaginary circle whose radius has the maximum value among the distances 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 according to the outer diameter of the mandrel for winding the electrode assembly. For example, the inner circumference may have a value of about 10 mm.

[0042] According to an embodiment of the present invention, the length of the rigid film in the longitudinal direction may be 0.9 to 1.4 turns. Specifically, the distance between one end portion of the rigid film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction may be 1 turn or more, 1.1 turns or more, 1.3 turns or less, or 1.2 turns or less. Figure 2 , the length of the rigid 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 rigid film in the longitudinal direction satisfies the aforementioned range, the core supporting effect of the rigid film can be further enhanced, and the reduction in battery capacity and energy density can be minimized, thereby preventing the degradation of electrochemical characteristics.

[0044] According to an embodiment of the present invention, the tensile strength of the rigid film may be 18 kgf / mm 2 Up to 25kgf / mm 2 Specifically, the tensile strength of the rigid film can be 19kgf / mm 2 or larger, 20kgf / mm 2 or larger, or 21kgf / mm 2 or greater and 24kgf / mm 2 or less, 23kgf / mm 2 or less, or 22kgf / mm 2 or smaller.

[0045] Specifically, the tensile strength of the rigid film may be measured by preparing a sample having a size of 20 mm×100 mm and a thickness of 10 μm from a film specimen and testing the rigid film sample using a universal testing machine (UTM) at room temperature under a speed condition of 2 cm / min.

[0046] If the tensile strength of the rigid film satisfies the aforementioned range, the core supporting effect of the rigid film can be further enhanced, and continuous production of the electrode assembly can be achieved using existing roll-to-roll processing equipment, thereby ensuring productivity and economic efficiency.

[0047] 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.

[0048] 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.

[0049] If the length of the core portion in the longitudinal direction satisfies the aforementioned range, a sufficient space for arranging the rigid film can be ensured, and the core supporting effect of the rigid film can be further enhanced.

[0050] According to an embodiment of the present invention, the distance between one end portion of the rigid 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 rigid 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 rigid 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.

[0051] In this case, one end portion of the rigid 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 rigid film and the negative electrode can be adjusted to minimize the step difference caused by the thickness difference between the electrode and the rigid film.

[0052] According to an embodiment of the present invention, the distance between one end portion of the rigid 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 rigid 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 rigid 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.

[0053] In this case, an end portion of the rigid film in the longitudinal direction and an end portion of the negative electrode in the longitudinal direction may not contact each other, and the distance between an end portion of the rigid film in the longitudinal direction and an end portion of the negative electrode in the longitudinal direction may be adjusted to minimize damage to the separator caused by the end portion of the electrode or the rigid film even during contraction / expansion of the electrode assembly.

[0054] According to an embodiment of the present invention, the rigid film may further include a fixing member located on at least one surface thereof. Specifically, the fixing member is used to minimize the sliding of the rigid film, and an adhesive or adhesive tape may be used for this purpose. Further including a fixing member can minimize the damage caused to the separator by the end portion of the electrode or rigid film even during the contraction / expansion of the electrode assembly or the sliding of the rigid film.

[0055] According to an embodiment of the present invention, based on 100% of the length in the lateral direction of the wound electrode assembly, the length of the rigid film in the lateral direction may be 95% to 105%. Specifically, based on 100% of the length in the lateral direction of the wound electrode assembly, the length of the rigid film in the lateral 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.

[0056] If the length of the rigid film in the lateral direction satisfies the aforementioned range, the length of the rigid film can correspond to the length of the wound electrode assembly in the lateral direction, and this condition is conducive to supporting the wound electrode assembly and can obtain an excellent effect of preventing core deformation.

[0057] If the length of the rigid film in the lateral direction is too short, the effect of preventing the core from deforming may be reduced. If the rigid film is excessively exposed in the lateral direction of the wound electrode assembly, more defects and local problems such as lithium precipitation due to step formation may be caused during the insertion process into the battery case.

[0058] According to an embodiment of the present invention, the rigid film may include at least one selected from polypropylene, polyethylene, polyester and polyamide. Specifically, the rigid film may include at least one selected from polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET) and polyamide (PAs). For example, the rigid film may include polypropylene (PP).

[0059] When the rigid film is formed of the aforementioned type of material, the rigidity of the rigid film may be sufficient to support the core portion of the wound electrode assembly and the rigidity of the rigid film may be more suitable for roll-to-roll processing, thereby improving productivity and economic efficiency of the wound electrode assembly.

[0060] According to an embodiment of the present invention, the thickness of the rigid film may be 5% to 20% based on 100% of the thickness of the negative electrode. Specifically, the thickness of the rigid 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% of the thickness of the negative electrode.

[0061] If the thickness of the rigid film satisfies the aforementioned range, the step difference can be minimized by adjusting the thickness range of the rigid film. In other words, local problems such as the step difference formed due to the thickness difference between the rigid film and the negative electrode and the precipitation of lithium in the step difference formation area can be minimized.

[0062] According to an embodiment of the present invention, the thickness of the rigid film may be 10 to 50 μm. Specifically, the thickness of the rigid 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.

[0063] If the thickness of the rigid film satisfies the aforementioned range, the rigidity of the rigid film may be sufficient to support the core portion of the wound electrode assembly and the rigidity of the rigid film may be more suitable for roll-to-roll processing, thereby improving productivity and economic efficiency of the wound electrode assembly.

[0064] According to an embodiment of the present invention, the positive electrode may include: a positive electrode current collector; and a positive electrode active material layer, the positive electrode active material layer being disposed on at least one surface of the positive electrode current collector, wherein the positive electrode current collector and the positive electrode active material layer may have ends at the same position in the longitudinal direction. In other words, one end in the longitudinal direction of the positive electrode may have a free edge form.

[0065] 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.

[0066] 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 a process error that may occur in a slitting process or the like.

[0067] 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.

[0068] 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 does not cause chemical changes in the battery while having conductivity, and 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.

[0069] In addition, the positive electrode current collector may generally have a thickness of 5 μm to 30 μm, and fine concavoconvex portions 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, a sheet, a foil, a net, a porous body, a foam body, and a nonwoven body.

[0070] 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 (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); represented by the chemical formula LiMn2-z M z O2 (M is at least one selected from the group including Co, Ni, Fe, Cr, Zn and Ta, and 0.01≤z≤0.1) or a lithium manganese composite oxide represented by the chemical formula Li2Mn3MO8 (M is at least one selected from the group including Fe, Co, Ni, Cu and Zn); LiMn2O4, wherein some Li is replaced by alkaline earth metal ions, etc., but is not limited thereto. The positive electrode may be Li metal.

[0071] According to an embodiment of the present invention, the positive electrode active material may also include a positive electrode conductive material and a positive electrode binder. The positive electrode conductive material is used to impart 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, and one of the above materials may be used alone or a mixture of two or more of the above materials may be used.

[0072] 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 binders 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 its various copolymers, etc., and one of the above can be used alone, or a mixture of two or more of the above can be used.

[0073] 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 disposed 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 disposed may be represented as a negative electrode uncoated portion.

[0074] According to an embodiment of the present invention, the negative electrode current collector may include a negative electrode coating portion formed with a negative electrode active material layer and a negative electrode uncoated portion where the negative electrode active material layer is not formed, and may include a tab located 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 formed on the negative electrode uncoated portion. Therefore, the manufactured electrode assembly may include at least one negative electrode tab.

[0075] According to an embodiment of the present invention, the negative electrode active material layer may include a negative electrode active material, the negative electrode active material including at least one selected from the group consisting of silicon-based materials and carbon-based materials. The negative electrode active material layer may also 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.

[0076] According to an embodiment of the present invention, the negative electrode current collector is not particularly limited as long as the negative electrode current collector does not cause chemical changes in the battery while having conductivity. For example, copper, 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 negative electrode current collector. Specifically, transition metals that adsorb carbon well, such as copper and nickel, can be used as the negative electrode current collector. The thickness of the negative electrode current collector may be 5 μm to 30 μm, but the thickness of the negative electrode current collector is not limited thereto.

[0077] 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 substances in which the hydrogen of the above materials is replaced by Li, Na, Ca, etc., and the negative electrode binder may also include various copolymers of these materials.

[0078] 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 thereof 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 powders, aluminum powders and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives.

[0079] According to an embodiment of the present invention, a wound electrode assembly may include a plurality of separators. For example, a 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 path 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 a secondary battery, and in particular, it is preferred that the material has low resistance to electrolyte ion migration and is well immersed in the electrolyte. Specifically, a porous polymer film can be used, for example, a porous polymer film formed by 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 laminated structure having two or more layers formed by these polymers can be used. Alternatively, a typical porous non-woven fabric can be used, such as a non-woven fabric composed of high melting point glass fibers, polyethylene terephthalate fibers, and the like. In addition, in order to ensure heat resistance or mechanical strength, the separator may include a coating layer 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.

[0080] According to another embodiment of the present invention, there is provided a method for manufacturing a wound electrode assembly, the wound electrode assembly comprising a first separator, a negative electrode, a second separator and a positive electrode which are laminated and wound in sequence, the method comprising: (a) winding the first separator and the second separator; (b) introducing a rigid film between the first separator and the second separator; (c) introducing the negative electrode; and (d) introducing the positive electrode, wherein: based on 100% of the circumference of the inner circumferential surface of the wound electrode assembly, the length of the rigid film in the longitudinal direction is 100% to 150%; and the tensile strength of the rigid film is 18 kgf / mm 2 Up to 25kgf / mm 2 .

[0081] The method for manufacturing a wound type electrode assembly according to an embodiment of the present invention may produce a wound type electrode assembly including a rigid film through a continuous process using an existing roll-to-roll processing apparatus, thereby ensuring productivity and economic efficiency.

[0082] In addition, the wound electrode assembly obtained by the manufacturing method includes a rigid film having a predetermined degree of rigidity, so that the hollow section of the core portion is supported to resist deformation of the electrode assembly caused by contraction / expansion of the electrode during battery charging / discharging to maintain its circular shape, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive and negative electrodes, thereby improving battery stability and service life characteristics.

[0083] According to an embodiment of the present invention, based on 100% of the circumference of the inner circumferential surface of the wound electrode assembly, the length of the rigid film in the longitudinal direction may be 100% to 150%. Specifically, based on 100% of the circumference of the inner circumferential surface of the wound electrode assembly, the length of the rigid 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.

[0084] If the length of the rigid film in the longitudinal direction satisfies the aforementioned range, the core supporting effect of the rigid film can be further enhanced, and the reduction in battery capacity and energy density can be minimized, thereby preventing the degradation of electrochemical characteristics.

[0085] According to an embodiment of the present invention, the tensile strength of the rigid film may be 18 kgf / mm 2 Up to 25kgf / mm 2 Specifically, the tensile strength of the rigid film can be 19kgf / mm 2 or larger, 20kgf / mm 2 or larger, or 21kgf / mm 2 or greater and 24kgf / mm 2 or less, 23kgf / mm 2 or less, or 22kgf / mm 2 or smaller.

[0086] If the tensile strength of the rigid film satisfies the aforementioned range, the core supporting effect of the rigid film can be further enhanced, and continuous production of the electrode assembly can be achieved using existing roll-to-roll processing equipment, thereby ensuring productivity and economic efficiency.

[0087] In particular, the meanings of the core portion and the circumference of the inner circumferential surface and the method for measuring the tensile strength of the rigid film may be as described with respect to the wound electrode assembly. In addition, the meanings of 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 length (L1+L2+L3) of the core portion in the longitudinal direction are as described with respect to the wound electrode assembly.

[0088] 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, wherein a plurality of flexible metal foils or the like are processed while traveling between rollers.

[0089] In particular, the roll-to-roll process may refer to a method in which a flexible and thin metal sheet-like electrode current collector wound around a roll is unrolled 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 the treated electrode current collector is then wound around another roll again for recovery.

[0090] 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 further wound between a plurality of separators, wherein a plurality of separators are wound around a mandrel for a portion of the length in the longitudinal direction starting from an end portion in the longitudinal direction; or a process of introducing a film or electrode to be further wound on one surface of a plurality of separators that have been partially wound around a mandrel. Alternatively, the term may refer to a process of manufacturing an electrode assembly by continuously winding a portion of a film or electrode that has been introduced together with a plurality of wound separators, and may involve a slitting process of cutting a portion of the length in the longitudinal direction as required.

[0091] 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 rigid film by using an existing roll-to-roll processing device. 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.

[0092] That is, the method for manufacturing a wound type electrode assembly according to an embodiment of the present invention may continuously produce a wound type electrode assembly including a rigid film having a predetermined degree of rigidity by using an existing roll-to-roll processing apparatus, thereby ensuring productivity and economic efficiency.

[0093] Figure 2 A method for manufacturing a wound type electrode assembly including a rigid film according to an embodiment of the present invention is schematically illustrated.

[0094] 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.

[0095] That is, the rigid film may be introduced between the first separator and the second separator wound to a predetermined length. Thus, the core portion of the wound electrode assembly may not include the positive electrode and the negative electrode, and one surface and the other surface of the rigid film may not directly contact the negative electrode or the positive electrode.

[0096] Through step (b), the rigid film may have a predetermined length, and the core portion of the wound type electrode assembly including the rigid film may also have a predetermined length.

[0097] Then, steps (c) and (d) may be performed sequentially.

[0098] 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.

[0099] In particular, an end portion of the rigid film in the longitudinal direction and an end portion of the negative electrode in the longitudinal direction may not contact each other, and the distance between an end portion of the rigid film in the longitudinal direction and an end portion of the negative electrode in the longitudinal direction may be adjusted to minimize damage to the separator caused by the end portion of the electrode or the rigid film even during contraction / expansion of the electrode assembly.

[0100] On the other hand, when one end portion of the rigid film in the longitudinal direction contacts one end portion of the negative electrode in the longitudinal direction, the thickness range of the rigid film can be adjusted to minimize the step difference, thereby minimizing local problems such as lithium precipitation in the step difference formation area.

[0101] According to an embodiment of the present invention, based on 100% of the length of the wound electrode assembly in the transverse direction, the length of the rigid film in the transverse direction may be 95% to 105%. Specifically, based on 100% of the length of the wound electrode assembly in the transverse direction, the length of the rigid film in the transverse 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.

[0102] If the length of the rigid film in the transverse direction satisfies the aforementioned range, the length of the rigid film can correspond to the length of the wound electrode assembly in the transverse 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.

[0103] According to an embodiment of the present invention, the rigid film may include at least one selected from polypropylene, polyethylene, polyester and polyamide. Specifically, the rigid film may include at least one selected from polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET) and polyamide (PAs). For example, the rigid film may be polypropylene (PP).

[0104] When the rigid film is formed of the aforementioned type of material, the rigidity of the rigid film may be sufficient to support the core portion of the wound electrode assembly and the rigidity of the rigid film may be more suitable for roll-to-roll processing, thereby improving productivity and economic efficiency of the wound electrode assembly.

[0105] According to an embodiment of the present invention, the thickness of the rigid film may be 5% to 20% based on 100% of the thickness of the negative electrode. Specifically, the thickness of the rigid 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% of the thickness of the negative electrode.

[0106] If the thickness of the rigid film satisfies the aforementioned range, the step difference can be minimized by adjusting the thickness range of the rigid film. In other words, local problems such as the step difference formed due to the thickness difference between the rigid film and the negative electrode and the precipitation of lithium in the step difference formation area can be minimized.

[0107] According to an embodiment of the present invention, the thickness of the rigid film may be 10 to 50 μm. Specifically, the thickness of the rigid 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.

[0108] If the thickness of the rigid film satisfies the aforementioned range, the rigidity of the rigid film may be sufficient to support the core portion of the wound electrode assembly and the rigidity of the rigid film may be more suitable for roll-to-roll processing, thereby improving productivity and economic efficiency of the wound electrode assembly.

[0109] An embodiment of the present invention provides a wound-type electrode assembly produced by the above-mentioned wound-type electrode assembly manufacturing method.

[0110] The wound electrode assembly according to an embodiment of the present invention includes a rigid film having a predetermined degree of rigidity, so that the hollow section of the core portion is supported to resist deformation of the electrode assembly due to contraction / expansion of the electrode during battery charge / discharge to maintain its circular shape, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive and negative electrodes, thereby improving battery stability and service life characteristics.

[0111] An embodiment of the present invention provides 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 foregoing embodiment and a battery case for accommodating the electrode assembly.

[0112] In the secondary battery according to the present invention, the hollow section of the core portion is supported so as to maintain its circular shape even when the electrode assembly is deformed due to contraction / expansion of the electrode 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.

[0113] According to an embodiment of the present invention, the battery box may have a cylindrical shape. Specifically, the battery box may have a cylindrical shape, a square shape, or a pouch shape according to its use, but is not limited thereto.

[0114] According to an embodiment of the present invention, an electrolyte may be included in the battery box. Specifically, examples of electrolytes 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.

[0115] 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, tetrahydrofuran, 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.

[0116] According to an embodiment of the present invention, the metal salt may be a lithium salt, and a material that dissolves well 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 - .

[0117] 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 compound, such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glycol dimethyl ether, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinones, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum chloride.

[0118] 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 and large devices selected from the group including electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0119] Mode for Carrying Out the Invention

[0120] 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 in order to more completely illustrate the present invention to those skilled in the art.

[0121] Examples

[0122] Example 1

[0123] Manufacturing of electrode assemblies

[0124] By using Li(Ni 0.93 Co0.01 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 lateral direction, followed by drying, and then rolling to form a positive electrode active material layer, thereby preparing a positive electrode having a thickness of 175 μm.

[0125] Then, 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 were 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 lateral direction as a negative electrode current collector, and then dried (drying temperature of 120°C, 1 minute) to form a negative electrode having an average thickness of 185μm. At this time, the temperature of the circulating air is 60°C.

[0126] Thereafter, a rigid film of a polypropylene (PP) material having a length of 65 mm in the transverse 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 of a polyethylene (PE) material having a thickness of 13 μm were prepared respectively. At this time, a sample having a size of 20 mm×100 mm and a thickness of 10 μm was prepared from the rigid film, and then the tensile strength was tested at a speed of 2 cm / min at room temperature by using a universal testing machine (UTM). The measured tensile strength was 25 kgf / mm 2 .

[0127] Thereafter, the first separator and the second separator are arranged and wound in sequence using a mandrel having a diameter of 3.4 mm, and then the rigid film is introduced between the first separator and the second separator, followed by further winding. After the rigid film is completely wound, the negative electrode and the positive electrode are introduced in sequence at a distance of 6 mm from the rigid film, followed by winding. The sealing tape of the PET material is attached to and finally ends 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. At this time, the circumference of the inner peripheral surface 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.

[0128] Manufacturing of secondary batteries

[0129] The wound electrode assembly is inserted into a cylindrical battery case. Thereafter, 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 to 1.3M in the mixture is injected into the battery case, and then the cylindrical battery can can be sealed with a cap assembly, thereby manufacturing a secondary battery.

[0130] Example 2

[0131] A wound type electrode assembly and a secondary battery were manufactured by the same method as in Example 1, except that a film of polyethylene (PE) material was used as the rigid film.

[0132] At this time, a sample with a size of 20 mm×100 mm and a thickness of 10 μm was prepared from a polyethylene (PE) film, and then the tensile strength was tested by using a universal testing machine (UTM) at room temperature under a speed condition of 2 cm / min. The measured tensile strength was 18 kgf / mm 2 .

[0133] Comparative Example 1

[0134] A wound-type electrode assembly and a secondary battery were manufactured by the same method as in Example 1, except that the rigid film was not introduced.

[0135] Comparative Example 2

[0136] A wound electrode assembly and a secondary battery were manufactured by the same method as in Example 1, except that a film of polyimide (PI) material was used as a rigid film. At this time, 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 at room temperature at a speed of 2 cm / min using a universal testing machine (UTM). The measured tensile strength was 10 kgf / mm 2 .

[0137] Comparative Example 3

[0138] 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 rigid film.

[0139] Experimental Example

[0140] Experimental Example 1: Evaluation of Cyclic Stability

[0141] The secondary batteries manufactured in the examples and comparative examples were subjected to a cycle test at 25°C, 4.2V to 2.85V, 0.5C / 0.5C by using an electrochemical charger / discharger. After 50 cycles, the core deformation of the core portion was examined by computer tomography (CT) to evaluate the cycle stability, and the core deformation was measured at 25°C, 4.2V to 2.85V, 0.5C / 0.5C, respectively. Figures 3 to 7 An image thereof is shown in FIG.

[0142] Experimental Example 2: Evaluation of Service Life

[0143] 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 battery was subjected to a cycle test at 4.2V to 2.85V, 1C / 1C, and the capacity retention was measured by charging / discharging the secondary battery at 0.2C / 0.2C (4.2V to 2.85V) every 100 cycles during the test. The results are shown in Table 1.

[0144] Life retention rate (%) = {(discharge capacity in the Nth cycle) / (discharge capacity in the first cycle)}×100

[0145] Experimental Example 3: Evaluation of resistance increase rate

[0146] 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 in Experimental Example 2, the resistance was measured by 0.5C pulse discharge in SOC 50, and the resistance increase rate was compared and analyzed. The results are shown in Table 1.

[0147] Table 1

[0148]

[0149] Refer to Table 1 and Figures 3 to 7 , the secondary battery according to the embodiment of the present invention includes a rigid film in the core portion, so that the core deformation is reduced, thereby showing the designed capacity and ensuring improved service life and resistance characteristics. However, as in Comparative Examples 1 to 3, when the rigid film is not included or the use of 18kgf / mm2 When the tensile strength is below and the film has a weak rigidity, the core is deformed, resulting in an increase in resistance and deterioration in the service life characteristics of the battery. In addition, an excessive increase in the length of the rigid film in the longitudinal direction leads to a decrease in the length of the electrode in the longitudinal direction, thereby reducing the design capacity and the discharge capacity that can actually be performed.

[0150] It can therefore be observed that the wound electrode assembly and the secondary battery including the wound electrode assembly according to an embodiment of the present invention include a rigid film having a predetermined degree of rigidity in the core portion, so that the hollow section of the core portion is supported to resist deformation of the electrode assembly due to contraction / expansion of the electrodes during battery charging / discharging to maintain its circular shape, thereby preventing damage to the positive electrode and the separator and suppressing internal short circuits between the positive and negative electrodes, thereby improving battery stability and service life characteristics.

[0151] The foregoing detailed description is intended to illustrate and explain the present invention. In addition, the foregoing description is only for the purpose of illustrating and describing the preferred embodiments of the present invention, and as described above, the present invention may be used in various other combinations, variations, and in various other environments, and may be changed and modified within the scope of the concept of the present invention disclosed in this specification, within the scope equivalent to the above disclosure, and / or within the scope of the technology 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. In addition, the appended claims should be interpreted as also including other embodiments.

[0152] Industrial Applicability

[0153] A wound electrode assembly and a secondary battery including the wound electrode assembly according to an embodiment of the present invention include a rigid film having a predetermined degree of rigidity, so that the hollow section of the core portion is supported to resist deformation of the electrode assembly due to contraction / expansion of the electrode during battery charge / discharge to maintain its circular shape, 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 life characteristics.

[0154] [Description of Reference Numerals]

[0155] 10: First separator

[0156] 20: Negative electrode

[0157] 30: Second separator

[0158] 40: Positive electrode

[0159] 50: Rigid membrane

[0160] L1: length of the first area in the longitudinal direction

[0161] L2: length of the second area in the longitudinal direction

[0162] L3: length of the third region in the longitudinal direction

[0163] C: Core part

Claims

1. A wound 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 electrode assembly includes a rigid film disposed between the first separator and the second separator, The length of the rigid film in the longitudinal direction is 100% to 150% based on 100% of the circumference of the inner peripheral surface of the wound electrode assembly, and The tensile strength of the rigid film is 18 kgf / mm 2 Up to 25kgf / mm 2 .

2. 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.

3. 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.

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

5. The wound electrode assembly according to claim 1, wherein: A distance between one end portion of the rigid film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction is 0.3 to 0.7 turns.

6. The wound electrode assembly according to claim 1, wherein: The length of the rigid film in the transverse direction is 95% to 105% based on 100% of the length of the wound electrode assembly in the transverse direction.

7. The wound electrode assembly according to claim 1, wherein: The rigid film includes at least one selected from the group consisting of polypropylene, polyethylene, polyester, and polyamide.

8. The wound electrode assembly according to claim 1, wherein: The thickness of the rigid film is 5% to 20% based on 100% of the thickness of the negative electrode.

9. The wound electrode assembly according to claim 1, wherein: The rigid 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 disposed on at least one surface of the positive electrode current collector, and The positive electrode current collector and the positive electrode active material layer have end portions at the same position in the longitudinal direction, respectively.

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 which are sequentially layered and wound, the method comprising: (a) winding the first separator and the second separator; (b) introducing a rigid film between the first separator and the second separator; (c) introducing a negative electrode; and (d) introducing the positive electrode, wherein the length of the rigid film in the longitudinal direction is 100% to 150% based on 100% of the circumference of the inner peripheral surface of the wound electrode assembly, and The tensile strength of the rigid film is 18 kgf / mm 2 Up to 25kgf / mm 2 .

12. The method according to claim 11, wherein: A distance between one end portion of the rigid film in the longitudinal direction and one end portion of the negative electrode in the longitudinal direction is 0.3 to 0.7 turns.

13. The method according to claim 11, wherein: The rigid film includes any one selected from polypropylene, polyethylene, polyester and polyamide.

14. The method according to claim 11, wherein: The thickness of the rigid film is 5% to 20% based on 100% of the thickness of the negative electrode.

15. The method according to claim 11, wherein: The rigid film has a thickness of 10 μm to 50 μm. 16 . A wound type electrode assembly manufactured by the method according to claim 11 .

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

18. The secondary battery according to claim 17, wherein The battery case has a cylindrical shape.

Images