Electrode assembly and secondary battery including the same

Abstract

Disclosed is an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, in which a dry adhesive force of the separator to the negative electrode is greater than a dry adhesive force of the separator to the positive electrode.

Description

Technical Field

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0140906, filed on October 20, 2023, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly and a secondary battery including the electrode assembly. Background Art

[0003] Secondary batteries are categorized into button-type, cylindrical, prismatic, and pouch-type batteries based on the shape of their housings. Unlike primary batteries, secondary batteries can be recharged and can be manufactured in small sizes with large capacities. Consequently, significant research and development efforts are underway on secondary batteries.

[0004] Recently, with the increasing popularity of electric vehicles (EVs), the technological development and demand for large-capacity secondary batteries used in EVs have also increased. In order to manufacture large-capacity secondary batteries, the size of the electrode assembly installed in the battery case has also increased.

[0005] The electrode assembly is a rechargeable / dischargeable power generation device having a stacked structure of electrodes and separators. The separator includes an organic / inorganic composite porous coating to provide adhesion between the electrodes and the separator.

[0006] After being installed in a battery case (packaging), the electrode assembly is manufactured into a secondary battery through an encapsulation process and / or an activation process. However, after the activation process, a bending phenomenon occurs in which the electrode assembly bends or twists due to uneven adhesion between the separator and the electrodes. This is because the expansion rate of the negative electrode is greater than the expansion rate of the positive electrode before and after the activation process, resulting in deformation of the shape of the secondary battery itself including the electrode assembly.

[0007] Therefore, there is a need to develop a technology to prevent a bending phenomenon of an electrode assembly or a secondary battery including the electrode assembly. Summary of the Invention

[0008] Technical issues

[0009] The present invention has been made in an effort to provide an electrode assembly and a secondary battery capable of preventing a bending phenomenon of the electrode assembly or the secondary battery including the same.

[0010] Technical Solution

[0011] An exemplary embodiment of the present invention provides an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator has a dry adhesive force to the negative electrode greater than a dry adhesive force to the positive electrode.

[0012] Another exemplary embodiment of the present invention provides a secondary battery including a sealed battery case and an electrode assembly according to an exemplary embodiment of the present invention within the battery case.

[0013] Beneficial effects

[0014] The electrode assembly according to the exemplary embodiment of the present invention has an effect of preventing a bending phenomenon that may occur after activation of a secondary battery including the electrode assembly.

[0015] The electrode assembly according to the exemplary embodiment of the present invention can prevent a bending phenomenon, thereby aligning and fixing electrodes so that the electrodes are not misaligned, thereby improving energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : is a graph showing the measurement results of the dry adhesive force of the separator to the positive electrode, the dry adhesive force of the separator to the negative electrode, the wet adhesive force of the separator to the positive electrode, and the wet adhesive force of the separator to the negative electrode according to Example 1 and Comparative Example 1.

[0017] Figure 2 1 is a photograph showing the interface of the negative electrode, the positive electrode, and the separator after activation of the secondary battery of each of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0018] Hereinafter, exemplary embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be embodied in various forms and is not limited to the configurations described herein.

[0019] When a part “includes,” “contains,” or “has” a constituent element in the present specification, unless otherwise specifically stated, this does not mean that another constituent element is excluded but means that another constituent element may be further included.

[0020] In this specification, "dry adhesion" refers to the adhesion of the separator measured when the electrode assembly including the separator is not immersed in an electrolyte solution. In other words, dry adhesion refers to the adhesion of the separator measured before the electrode assembly is activated. In this specification, dry adhesion is also referred to as the adhesion of the separator in a dry state.

[0021] In this specification, "wet adhesion" refers to the adhesion of the separator measured when the electrode assembly including the separator is immersed in an electrolyte solution. In other words, wet adhesion refers to the adhesion of the separator measured after the electrode assembly is activated. In this specification, wet adhesion is also referred to as the adhesion of the separator when immersed in an electrolyte solution.

[0022] In this specification, the dry adhesion and wet adhesion can be measured by cutting the electrode assembly into a size of 55 mm wide and 20 mm long to prepare a sample in which a positive electrode, a separator, and a negative electrode are stacked, and then using a tensile testing machine (UTM equipment) to peel the separator of the sample from one side of the separator at a speed of 100 mm / min in a 90° peeling mode. That is, the method for measuring the dry adhesion and wet adhesion is the same except whether the electrode assembly is immersed in the electrolyte solution. In addition, the absolute value of the difference in the measured adhesion can be defined as the deviation of the adhesion.

[0023] In this specification, "activation" or "activation process" of a secondary battery refers to a process (or step) of activating the secondary battery and removing gas after a charging process of the secondary battery.

[0024] <Electrode Assembly>

[0025] After the activation process, the negative electrode and the positive electrode each expand. In this case, the expansion rates of the negative electrode and the positive electrode differ after the activation process. This difference in expansion rate between the negative electrode and the positive electrode causes uneven adhesion between the separator and the electrodes, resulting in a bending phenomenon where the electrode assembly bends or twists.

[0026] Therefore, exemplary embodiments of the present invention provide an electrode assembly in which the dry adhesion of the separator to the negative electrode is greater than the dry adhesion of the separator to the positive electrode. This can prevent the occurrence of a bending phenomenon after the activation process of a secondary battery including the electrode assembly. In addition, it can also prevent the occurrence of a dog bone shape at the interface between the separator and the electrode after the activation process of the secondary battery.

[0027] Thus, a secondary battery including an electrode assembly having excellent performance may be provided.

[0028] In an exemplary embodiment of the present invention, the dry adhesion of the separator to the negative electrode may be 0.5 gf / 20 mm to 30 gf / 20 mm, preferably 3 gf / 20 mm or more and 25 gf / 20 mm or less, and more preferably 5 gf / 20 mm or more and 15 gf / 20 mm or less.

[0029] In exemplary embodiments of the present invention, the dry adhesion of the separator to the positive electrode may be 0.2 gf / 20 mm to 20 gf / 20 mm, preferably 1 gf / 20 mm or more and 15 gf / 20 mm or less, and more preferably 1.5 gf / 20 mm or more and 10 gf / 20 mm or less.

[0030] In an exemplary embodiment of the present invention, the dry adhesive force of the separator to the negative electrode may be 1.5 to 5 times, preferably 1.5 to 2 times or 2.5 to 5 times, the dry adhesive force of the separator to the positive electrode.

[0031] In an exemplary embodiment of the present invention, the magnitude deviation between the dry adhesive force of the separator to the negative electrode and the dry adhesive force of the separator to the positive electrode may be 10 gf / 20 mm or less, preferably 8 gf / 20 mm or less, and more preferably 5 gf / 20 mm or less. Deviation refers to the absolute value of the difference in adhesive force.

[0032] When the dry adhesion of the separator to the positive and negative electrodes satisfies the above range, not only can the bending phenomenon after the activation process be prevented, but the electrode assembly can also be more easily transported while maintaining the stacking structure of the electrode assembly manufactured during the stacking process. In other words, since the deterioration of the electrode assembly performance caused by the misalignment of the electrode positions during the transport process can be prevented, the resulting manufactured electrode assembly exhibits excellent performance.

[0033] In an exemplary embodiment of the present invention, the separator may have a greater wet adhesive force to the positive electrode than to the negative electrode. That is, in a state immersed in an electrolyte solution, the separator may have a greater adhesive force to the positive electrode than to the negative electrode.

[0034] In exemplary embodiments of the present invention, the separator may have a wet adhesive force to the positive electrode of 10 gf / 20 mm or more and 30 gf / 20 mm or less, preferably 10 gf / 20 mm or more and 20 gf / 20 mm or less.

[0035] In exemplary embodiments of the present invention, the separator may have a wet adhesive force to the negative electrode of 3 gf / 20 mm or more and 15 gf / 20 mm or less, preferably 5 gf / 20 mm or more and 10 gf / 20 mm or less.

[0036] In exemplary embodiments of the present invention, the separator may have a wet adhesive force to the negative electrode of 2 gf / 20 mm or more and 15 gf / 20 mm or less, more preferably 2.5 gf / 20 mm or more and 8 gf / 20 mm or less.

[0037] In exemplary embodiments of the present invention, the wet adhesive force of the separator to the positive electrode may be 1.5 to 3 times, preferably 1.5 to 2.5 times, the wet adhesive force of the separator to the negative electrode.

[0038] In an exemplary embodiment of the present invention, the deviation between the wet adhesive force of the separator to the positive electrode and the wet adhesive force of the separator to the negative electrode may be 8 gf / 20 mm or less, preferably 5 gf / 20 mm or less. The deviation refers to the absolute value of the difference in adhesive force.

[0039] When the wet adhesive force satisfies the above range, it is easy to prevent the secondary battery from bending during activation of the secondary battery including the electrode assembly, that is, the performance of the secondary battery can be improved.

[0040] That is, the electrode assembly according to the exemplary embodiment of the present invention has a feature in which the separator has a certain amount of adhesive force to the negative electrode before and after immersion in the electrolyte solution, and the relative magnitudes of the adhesive force of the separator to the positive electrode and the negative electrode are different before and after immersion in the electrolyte solution. This can prevent the secondary battery from bending after the activation process.

[0041] In an exemplary embodiment of the present invention, the separator may include a porous polymer substrate, a first organic / inorganic composite porous coating layer formed on one surface of the polymer substrate, and a second organic / inorganic composite porous coating layer formed on the other surface of the polymer substrate. In other words, the separator may include different organic / inorganic composite porous coating layers on both surfaces.

[0042] In an exemplary embodiment of the present invention, the first organic / inorganic composite porous coating layer and the second organic / inorganic composite porous coating layer may each include one or more types of particulate binder resins and one or more types of inorganic particles.

[0043] In an exemplary embodiment of the present invention, the first organic / inorganic composite porous coating layer refers to a layer in contact with the negative electrode, and the second organic / inorganic porous coating layer refers to a layer in contact with the positive electrode.

[0044] In an exemplary embodiment of the present invention, the first organic / inorganic composite porous coating may be a cured product of a first composition including a particulate binder resin and inorganic particles, and may include 50 to 80 parts by weight, preferably 60 to 70 parts by weight, of the particulate binder resin based on 100 parts by weight of the first composition.

[0045] In an exemplary embodiment of the present invention, the second organic / inorganic composite porous coating may be a cured product of a second composition including a particulate binder resin and inorganic particles, and may include 10 to 40 parts by weight, preferably 15 to 35 parts by weight, of the particulate binder resin based on 100 parts by weight of the second composition.

[0046] In an exemplary embodiment of the present invention, the particulate binder resin may include one or more selected from the group consisting of acrylic acid-based polymer particles, fluorine-based polymer particles, and mixed polymer particles of fluorine-based polymers and acrylic acid-based polymers. Specifically, the mixed polymer particles of fluorine-based polymers and acrylic acid-based polymers may include the fluorine-based polymer and the acrylic acid-based polymer in a weight ratio of 50:50 to 80:20.

[0047] The binder resin includes mixed polymer particles of a fluorine-based polymer and an acrylic-based polymer, which allows the separator to maintain a certain level of adhesion or higher before and after immersion in an electrolyte solution. This means that the shape stability of the electrode assembly can be improved, making it easier to provide an electrode assembly with uniform performance.

[0048] In exemplary embodiments of the present invention, the fluorine-based polymer may be a homopolymer of vinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and another polymerizable monomer, or a mixture of two or more thereof.

[0049] More specifically, another polymerizable monomer that can be polymerized with vinylidene fluoride can include but is not limited to one or more selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene and fluorinated vinyl. In particular, the fluorine-based polymer can be a copolymer of vinylidene fluoride and hexafluoropropylene (HFP). The content of vinylidene fluoride and another polymerizable monomer can be, but is not limited to, 1% to 20% by weight of the copolymer, preferably 1% to 5% by weight. The above-mentioned another polymerizable monomer is intended to increase wet adhesion. If its content is less than 1% by weight, it may be difficult to achieve wet adhesion, and if the content exceeds the above range, the resistance of the separator may become too high, which may deteriorate the performance of the electrode assembly.

[0050] In the present invention, the comonomer content in the PVDF-based polymer can be measured by using a Varian 500 MHz 1H-NMR method. For detailed measurement methods, please refer to Journal of Materials Chemistry, 2012, 22, 341 or AMT-3412-0k. To confirm the NMR spectrum, appropriate equipment such as, for example, a Bruker Avance III HD 700 MHz NMR or a Varian 500 MHz NMR can be used.

[0051] In the present invention, the acrylic acid-based polymer may be preferably (meth)acrylate or acrylic acid-styrene copolymer. Specific examples of such (meth)acrylate include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, and vinyl di(meth)acrylate, and may be one or more selected from these. Among them, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, and methyl (meth)acrylate is particularly preferred.

[0052] More specifically, the acrylic-styrene copolymer may include an acrylic-based adhesive, and the acrylic-based adhesive may be a polyacrylate-based adhesive. For example, the adhesive may be one or more selected from the group consisting of styrene-butadiene rubber, nitril-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and acrylate-based polymers, and specifically, may be a copolymer including acrylate.

[0053] In an exemplary embodiment of the present invention, the first organic / inorganic composite porous coating layer and the second organic / inorganic porous coating layer may each include a first binder resin including acrylic acid-based polymer particles and a second binder resin including mixed polymer particles of a fluorine-based polymer and an acrylic acid-based polymer.

[0054] In exemplary embodiments of the present invention, the acrylic-based polymer particles may have a glass transition temperature (Tg) of 40°C to 90°C, preferably 40°C to 60°C.

[0055] In an exemplary embodiment of the present invention, the inorganic particles may have a non-rectangular structure. When the inorganic particles satisfying the above structure are used, the separator has appropriate air permeability without interfering with the formation of the adhesive force of the separator.

[0056] Specifically, in an exemplary embodiment of the present invention, the inorganic particles may be Al 2 O 3 .

[0057] In an exemplary embodiment of the present invention, the separators may be folded and stacked in a zigzag form. That is, the electrode assemblies according to an exemplary embodiment of the present invention may be stacked in a zigzag form.

[0058] In this specification, the stacking form in which the first electrode and the second electrode are alternately arranged between the folds of the folded separator is referred to as zigzag stacking.

[0059] In this case, more specifically describing a form in which the first electrode and the second electrode are alternately arranged between the folds of the folded separator, the folded separator may refer to separators that are stacked while overlapping in a zigzag manner. More specifically, the separators are stacked in a zigzag manner while being folded in a form that alternates back and forth between the left side of the stacking axis and the right side of the stacking axis based on the stacking axis. Further, the stacking is performed so that the first electrode and the second electrode are alternately arranged between the folds of the stacked separators. Here, the stacking axis refers to a virtual axis that is parallel to the direction in which the first electrode, the separator, and the second electrode are stacked and passes through the center of the stack in which the electrodes and the separator are stacked.

[0060] That is, the configuration in which the first electrode and the second electrode are alternately arranged between the folds of the partition means that the partitions are stacked in the direction of the stacking axis while overlapping in a zigzag shape, and the first electrode and the second electrode are each alternately inserted one after another into the space generated as the partitions overlap (between the partitions, i.e., between the folds of the partitions).

[0061] Common techniques or devices in the art can be used to perform zigzag stacking.

[0062] In an exemplary embodiment of the present invention, the negative electrode may include one or more of graphite and a silicon-based compound. The silicon-based compound may be referred to as a silicon-based active material. The silicon-based compound may include, but is not limited to, SiO2, and silicon-based compounds commonly used in the art may be used.

[0063] More specifically, in an exemplary embodiment of the present invention, the negative electrode may include a negative electrode collector and a negative electrode active material layer located on at least one surface of the negative electrode collector and including a negative electrode active material, a binder polymer and a conductive material, wherein the negative electrode active material layer may include a lower region in contact with the surface of the negative electrode collector and an upper region in contact with the surface of the lower region and extending to the surface of the negative electrode active material layer, and the lower region and the upper region may each independently include one or more of graphite and a silicon-based compound as the negative electrode active material.

[0064] In the exemplary embodiment of the present invention, the silicon-based compound may have a form in which the content thereof increases as the negative electrode active material layer becomes farther from the surface of the negative electrode current collector.

[0065] <Secondary Battery>

[0066] An exemplary embodiment of the present invention provides a secondary battery including a sealed battery case and an electrode assembly according to an exemplary embodiment of the present invention within the battery case. The secondary battery according to the exemplary embodiment of the present invention has a feature of not causing a bending phenomenon after an activation process.

[0067] Specifically, a flat ruler (hereinafter referred to as ruler "a") is placed at one end of the secondary battery, and a separate flat ruler (hereinafter referred to as ruler "b") is used to measure the maximum distance to the surface of the secondary battery facing the flat surface on which the secondary battery is placed. In this case, when the distance between the concave portion of the secondary battery measured using ruler "b" and one surface of ruler "a" is less than 3 mm, it is defined as having no bending.

[0068] A secondary battery according to an exemplary embodiment of the present invention may include a battery case into which an electrolyte solution is injected.

[0069] The secondary battery according to the exemplary embodiment of the present invention may undergo an activation process. The secondary battery according to the exemplary embodiment of the present invention may not be bent after the activation process. In this case, after the activation process, the electrode assembly removed by opening the battery case may also not be bent.

[0070] In an exemplary embodiment of the present invention, the activation process of the secondary battery may be carried out under a temperature condition of 45° C. to 55° C. and a temperature of 0.5 kgf / cm 2 Up to 1.5kgf / cm 2 The secondary battery is charged one or more times at 0.3C to 0.8C under pressure conditions.

[0071] Although exemplary embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited thereto and that various modifications and changes may be made without departing from the technical spirit of the present invention defined in the claims.

[0072] Embodiments of the invention

[0073] 1) Example 1

[0074] <Manufacturing of Electrode Assembly>

[0075] In order to prepare the negative electrode, artificial graphite as a carbon-based active material, a binder polymer (SBR (styrene-butadiene rubber) and CMC (carboxymethyl cellulose)) and carbon black as a conductive material are mixed in a weight ratio of 95.5:3:1.5 with water as a dispersion medium in a weight ratio of 1:2 to prepare a slurry for the first active material layer. The slurry for the second active material layer is prepared, which is the same as the first active material layer except that SiO2 (silicon dioxide) with a Coulombic efficiency of 80% or more when charged and discharged at 0.1C is prepared as a silicon-based active material, and the carbon-based active material and the silicon-based active material are mixed in a weight ratio of 9:1. That is, the weight ratio of the active material, the binder polymer, the carbon black and the carbon nanotubes (CNTs) is 95.5:3:1.0:0.5, and the weight ratio of the carbon-based active material and the silicon-based active material in the active material is 9:1.

[0076] The specific surface area of ​​carbon nanotubes (CNTs) is 550 m 2 / g. Carbon nanotubes (CNTs) are multi-walled carbon nanotubes.

[0077] The first active material layer and the second active material layer were formed by coating the slurry for the first active material layer on one surface of a copper (Cu) thin film (which was a negative electrode current collector having a thickness of 10 μm) using a double slot die, then coating the slurry for the second active material layer on the slurry for the first active material layer, and then drying the coated slurry at 130° C. under vacuum for 1 hour.

[0078] The first active material layer and the second active material layer formed in this manner were simultaneously rolled using a roll pressing method to prepare a negative electrode including an active material layer having a double-layer structure with a thickness of 80 μm. In this case, the thickness ratio of the first active material layer (rollpressing) and the second active material layer was 1:1. The loading amount based on the dry weight of the negative electrode active material layer was 512 mg / 25 cm 2 (Dry standard: 292 μm).

[0079] Next, in order to prepare the positive electrode, Li(Ni0.3 Mn 0.5 Co 0.2 )O2 (NCM-352), carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 96:2:2 to prepare a slurry for the positive electrode active material. The slurry was coated on one surface of an aluminum current collector having a thickness of 15 μm, and then dried and rolled under the same conditions as the negative electrode layer electrode to prepare the positive electrode. In this case, the loading amount based on the dry weight of the positive electrode active material layer was 988 mg / cm 2 (Dry standard: 242 μm).

[0080] Finally, to prepare a separator, a polyethylene film (PE, thickness 9 μm), which is a porous polymer substrate, was prepared.

[0081] Then, a first composition obtained by adding a first binder, inorganic particles, and a dispersant to distilled water at room temperature and a second composition obtained by adding a second binder, inorganic particles, and a dispersant were prepared, respectively.

[0082] In this case, as the first binder, a copolymer of styrene and butyl acrylate was used, the weight ratio of the two monomers (styrene and butyl acrylate) was adjusted to 80:20, and the glass transition temperature (Tg) was 45°C.

[0083] As the second binder, a PVDF-HFP binder having an HFP-derived repeat unit content of 5 wt % was used.

[0084] In addition, Al2O3 is used as inorganic particles.

[0085] Thereafter, the same amount of 0.7 μm zirconia beads as the inorganic particles were added to distilled water, and the mixture was bead milled for 2 hours using a paint shaker to prepare an inorganic dispersion.

[0086] Then, a surfactant was additionally added to the inorganic dispersion, and the inorganic dispersion was stirred at 10 rpm for 10 minutes to prepare first and second slurries in which first and second binder particles and inorganic particles were dispersed, respectively.

[0087] In this case, the content of the first binder was 60 parts by weight based on 100 parts by weight of the first slurry, and the content of the second binder was 20 parts by weight based on 100 parts by weight of the second slurry.

[0088] Thereafter, the first slurry and the second slurry were each coated on both surfaces of a polyethylene film (PE, thickness 9 μm) using a doctor blade and dried using a hot air blower to form porous coating layers, each having a thickness of 2.5 μm, to obtain a separator of Example 1 having a total thickness of 14 μm.

[0089] While the prepared positive electrode, negative electrode and separator are supplied to the stacking station, the separator is folded and the positive electrode, negative electrode and separator are stacked. Specifically, a stack of 39 electrode sheets was prepared by stacking the positive electrode, negative electrode and separator on the stacking station in the form of alternating positive and negative electrodes between the folds of the separator. Then, the electrode assembly of Example 1 was prepared by heating and pressing the stack for 15 seconds (time condition) under a temperature condition of 60°C and a pressure condition of 2MPa.

[0090] The dry adhesion of the electrode assembly of Example 1 to the negative electrode and the dry adhesion to the positive electrode were measured. Figure 1 shown.

[0091] Specifically, the dry adhesion of the electrode assembly of Example 1 to the negative electrode and the dry adhesion to the positive electrode were measured by cutting a portion of the electrode assembly into a size of 20 mm × 70 mm, immersing the electrode assembly in an electrolyte solution to prepare a specimen in which the positive electrode, the separator, and the negative electrode were stacked, and then peeling the separator of the specimen from one side of the separator at a speed of 100 mm / min in a 90° peeling mode using a tensile tester (UTM equipment).

[0092] <Preparation of Secondary Battery>

[0093] The electrode assembly of Example 1 was placed in a bag exterior material (battery case) of a laminate of CPP / aluminum / nylon, an ethyl methyl carbonate electrolyte solution containing LiPF6 was injected, and the bag exterior material was heat-sealed to complete the assembly of the secondary battery.

[0094] Thereafter, the secondary battery was subjected to a secondary battery activation process in which the secondary battery was activated under the temperature conditions of 50° C. and 1.0 kgf / cm 2 Under the pressure condition of , the secondary battery is charged at 0.5C.

[0095] Comparative Example 1

[0096] An electrode assembly and a secondary battery were prepared in the same manner as in Example 1, except that the binder contained in the slurry coated on both surfaces of the polyethylene film (PE, thickness 9 μm) D was a PVdF-based binder, and the content of the PVdF-based binder was 50 parts by weight based on 100 parts by weight of the slurry.

[0097] Experimental Example 1 - Dry Adhesion Evaluation

[0098] Each electrode assembly of Example 1 and Comparative Example 1 was cut into a size of 55 mm in width and 20 mm in length to prepare a sample in which a positive electrode, a separator, and a negative electrode were stacked. After affixing a double-sided tape on a glass slide, the positive or negative electrode of the sample was attached to the double-sided tape, and the sample was pressed with a constant pressure to adhere the sample to the double-sided tape. Then, the dry adhesion of the separator to the positive electrode and the dry adhesion of the separator to the negative electrode were measured using a 90° peel test method.

[0099] Specifically, dry adhesion of the separator to the positive electrode and dry adhesion of the separator to the negative electrode were measured by pulling the separator at a speed of 100 mm / min using a tensile tester (UTM equipment) to measure the force of peeling the separator from each of the positive and negative electrodes.

[0100] Experimental Example 2 - Wet Adhesion Evaluation

[0101] After activating each electrode assembly of Example 1 and Comparative Example 1, the electrode assembly was cut into a size of 55 mm in width and 20 mm in length to prepare a sample in which a positive electrode, a separator, and a negative electrode were stacked. After affixing a double-sided tape on a glass slide, the positive or negative electrode of the sample was attached to the double-sided tape, and the sample was pressed with a constant pressure to adhere the sample to the double-sided tape. Then, the wet adhesion of the separator to the positive electrode and the wet adhesion of the separator to the negative electrode were measured using a 90° peel test method.

[0102] Specifically, the wet adhesion of the separator to the positive electrode and the wet adhesion of the separator to the negative electrode were measured by pulling the separator at a speed of 100 mm / min using a tensile tester (UTM equipment) to measure the force of the separator peeling from each of the positive and negative electrodes.

[0103] Reference Figure 1 , Example 1 shows that the dry adhesion of the separator to the positive electrode before activation was 0.5 gf / 20 mm, and the dry adhesion of the separator to the negative electrode was 9.3 gf / 20 mm. In other words, it can be seen that the dry adhesion of the separator to the negative electrode is greater than the dry adhesion of the separator to the positive electrode. After the secondary battery is activated under a high temperature and high pressure environment, in Example 1, the wet adhesion of the separator to the positive electrode increased to 10.1 gf / 20 mm, and the wet adhesion of the separator to the negative electrode decreased to 5.8 gf / 20 mm. In other words, it can be seen that the wet adhesion of the separator to the positive electrode and the wet adhesion of the separator to the negative electrode are balanced.

[0104] In contrast, Comparative Example 1 shows that the dry adhesion of the separator to the positive electrode before activation is 11.3 gf / 20 mm, and the dry adhesion of the separator to the negative electrode is 0.5 gf / 20 mm. In other words, it can be seen that the dry adhesion of the separator to the positive electrode is greater. After the secondary battery is activated under a high temperature and high pressure environment, in Comparative Example 1, the wet adhesion of the separator to the positive electrode is reduced to 9.1 gf / 20 mm, and the wet adhesion of the separator to the negative electrode is increased to 0.9 gf / 20 mm. However, it can be seen that there is a large deviation between the wet adhesion of the separator to the positive electrode and the wet adhesion of the separator to the negative electrode, and they are not balanced.

[0105] Reference Figure 2 , it can be seen that in Example 1 in which the wet adhesive force is uniform, the dog bone phenomenon and the bending phenomenon are not observed, while in the electrode assembly of Comparative Example 1 in which the wet adhesive force is uneven, the dog bone phenomenon and the bending phenomenon occur.

[0106] This indicates that when the dry adhesion of the separator to the negative electrode is greater than the dry adhesion of the separator to the positive electrode, the wetting of the electrolyte solution is better.

[0107] While the present invention has been described with reference to preferred exemplary embodiments, it will be understood by those skilled in the art that various modifications and variations can be made to the present invention without departing from the technical spirit and scope of the present invention.

Claims

1. An electrode assembly comprising: positive electrode; negative electrode; and A separator is provided between the positive electrode and the negative electrode, The dry adhesive force of the separator to the negative electrode is greater than the dry adhesive force of the separator to the positive electrode. 2 . The electrode assembly according to claim 1 , wherein the separator has a dry adhesive force to the negative electrode of 0.5 gf / 20 mm to 30 gf / 20 mm. 3 . The electrode assembly according to claim 1 , wherein the separator has a dry adhesion of 0.2 gf / 20 mm to 20 gf / 20 mm to the positive electrode. 4 . The electrode assembly according to claim 1 , wherein a dry adhesive force of the separator to the negative electrode is 1.5 to 5 times greater than a dry adhesive force of the separator to the positive electrode.

5. The electrode assembly according to claim 1, wherein the separator comprises: porous polymer substrate; forming a first organic / inorganic composite porous coating layer on one surface of the polymer substrate; and A second organic / inorganic composite porous coating layer is formed on the other surface of the polymer substrate.

6. The electrode assembly according to claim 5, wherein the first organic / inorganic composite porous coating layer and the second organic / inorganic composite porous coating layer each comprise a particulate binder resin and inorganic particles, and The particulate binder resin includes one or more selected from the group consisting of acrylic-based polymer particles, fluorine-based polymer particles, and mixed polymer particles of fluorine-based polymer and acrylic-based polymer.

7. The electrode assembly according to claim 5, wherein the first organic / inorganic composite porous coating layer is a cured product of a first composition comprising a particulate binder resin and inorganic particles, and comprises 50 parts by weight to 80 parts by weight of the particulate binder resin based on 100 parts by weight of the first composition.

8. The electrode assembly according to claim 5, wherein the second organic / inorganic composite porous coating layer is a cured product of a second composition comprising a particulate binder resin and inorganic particles, and comprises 10 parts by weight to 40 parts by weight of the particulate binder resin based on 100 parts by weight of the second composition. 9 . The electrode assembly according to claim 1 , wherein the separators are folded and stacked in a zigzag shape.

10. A secondary battery comprising: Sealed battery housing; and An electrode assembly according to any one of claims 1 to 9 within the battery housing.

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