Electrode assembly and secondary battery including the same

Abstract

This invention relates to an electrode assembly with excellent insulation properties and a secondary battery including the electrode assembly. The electrode assembly according to the invention comprises a positive electrode, a negative electrode, and a separator inserted between the positive and negative electrodes, satisfying the following expression (1), and having a thickness greater than or equal to 10 mm. Expression (1): (A × B) + 6B ≥ 90. In expression (1), A is the ratio of the total length to the total width of the electrode assembly, and B is the thickness of the separator measured in μm.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2024-0044979, filed on April 2, 2024, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates to an electrode assembly having excellent insulation properties and a secondary battery including the electrode assembly. Background Technology

[0003] Typically, secondary batteries are prepared by applying an electrode active material slurry to a positive current collector and a negative current collector to prepare a positive electrode and a negative electrode, respectively; stacking the electrodes on the corresponding sides of a separator to form an electrode assembly of a specific shape; and then housing the electrode assembly in a battery case and injecting an electrolyte solution into the battery case.

[0004] When the electrode assembly becomes thicker—that is, when multiple electrodes are stacked to a thickness equal to the total thickness—more active material can be incorporated, and the battery capacity can be increased. However, because stacking connects a large number of electrodes in parallel, this reduces the resistance of the electrode assembly, leading to insulation degradation.

[0005] Therefore, for secondary batteries that include electrode assemblies with a thickness exceeding a certain level, ensuring proper insulation is an important task. Summary of the Invention

[0006] Technical issues

[0007] The present invention seeks to solve the problem of insulation degradation, which becomes more severe as the thickness of the electrode assembly increases, and therefore provides an electrode assembly configured such that its dimensions and the thickness of its separators satisfy a specific expression, and provides a secondary battery including the electrode assembly.

[0008] Technical solution

[0009] 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 electrode assembly satisfies the following expression (1) and has a thickness of 10 mm or more.

[0010] Expression (1): (A × B) + 6B ≥ 90

[0011] In the above expression (1),

[0012] A is the ratio of the total length to the total width of the electrode assembly.

[0013] B is the thickness value of the separator measured in μm.

[0014] The present invention provides a secondary battery comprising: an electrode assembly; an electrolyte; and a battery case for housing the electrode assembly and the electrolyte.

[0015] Beneficial effects

[0016] The electrode assembly according to the invention is configured to have a thickness of 10 mm or more, and its aspect ratio and the thickness value of the spacers satisfy a specific expression, and therefore has the insulating effect of properly formed spacers, the electrode resistance effect, and the effect of high initial capacity.

[0017] In other words, because the secondary battery including this electrode assembly exhibits high capacity and excellent insulation, it has the advantages of a lower risk of explosion caused by internal short circuits and physical / electrical shocks, as well as a lower risk of battery performance degradation due to voltage drop. Attached Figure Description

[0018] Figure 1 This is an exploded perspective view of a secondary battery according to an embodiment of the present invention.

[0019] Figure 2 This is a diagram illustrating the configuration of a bag according to an embodiment. Detailed Implementation

[0020] The invention will be described in more detail below.

[0021] As demand for high-capacity batteries, such as those used in electric vehicles, increases, the rated capacity of secondary battery cells is also increasing, leading to a trend towards larger electrode assemblies in terms of size and thickness. This means that the increased resistance of the electrode assemblies due to the large number of electrodes stacked in parallel for larger capacity results in insulation degradation. In particular, because pouch-type secondary batteries are less durable than can-type secondary batteries, they are more prone to safety incidents such as overheating and explosions when internal short circuits occur due to insulation degradation.

[0022] As a result of repeated research in order to develop secondary batteries with excellent insulation and high capacity, the inventors discovered that when the ratio of the total length to the total width of the electrode assembly (hereinafter referred to as the aspect ratio) and the thickness of the separators included in the electrode assembly meet certain conditions, the insulation characteristics can be excellent even in medium and large battery cells with a thickness of 10 mm or more, and thus the present invention was completed.

[0023] Insulation properties have a significant impact on the safety of secondary batteries, and increasing the aspect ratio of the electrode assembly is often used to achieve excellent insulation characteristics. When the thickness of the electrode assembly is less than 10 mm, excellent insulation can be maintained simply by adjusting the aspect ratio of the electrode assembly. However, when the thickness of the electrode assembly is greater than 10 mm, the insulation may decrease rapidly due to the parallel connection of the electrodes. Therefore, it can be seen that it is necessary to control the thickness of the separator and the aspect ratio of the electrode assembly.

[0024] In this specification, total length refers to the length measured in the longitudinal direction, and total width refers to the length measured in the width direction. Here, the description of the longitudinal direction assumes that the electrode assembly has a rectangular shape, the direction in which the long side is measured is the longitudinal direction, and the direction perpendicular to the longitudinal direction, i.e., the direction in which the short side is measured, is the width direction. The positive electrode layer, negative electrode layer, and spacers constituting the electrode assembly can be stacked in the thickness direction perpendicular to both the longitudinal and width directions.

[0025] The electrode assembly according to the present invention is characterized by comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, and satisfies the following expression (1), and has a thickness of 10 mm or more.

[0026] Expression (1): (A × B) + 6B ≥ 90

[0027] In the above expression (1),

[0028] A is the ratio of the total length to the total width of the electrode assembly.

[0029] B is the thickness value of the separator measured in µm.

[0030] Meanwhile, in the above expression (1), (A × B) + 6B can be greater than or equal to 90, preferably greater than or equal to 95, and more preferably greater than or equal to 100. However, given the energy density of the battery cell, less than or equal to 400 is preferred. When (A × B) + 6B is greater than or equal to 90, given the component resistance determined by the length of the electrodes constituting the electrode assembly, the thickness of the separator is appropriately formed, so that excellent insulation characteristics can be achieved without additional degradation of battery performance.

[0031] According to an embodiment of the present invention, in the above expression (1), A can be 1 to 10.5, and B can be 8 to 50.

[0032] In a particular embodiment, when A in the above expression (1) is greater than or equal to 5, and particularly 6 to 10.5, the above B can be 8 to 40, preferably 9 to 30, and more preferably 9 to 20.

[0033] In another embodiment, when A in the above expression (1) is greater than or equal to 2.5 and less than 5, and particularly 2.5 to 3.5, the above B can be 10 to 45, preferably 11 to 35, and more preferably 11 to 25.

[0034] In another embodiment, when A in the above expression (1) is greater than or equal to 1 and less than 2.5, and especially 1 to 2, the above B can be 12 to 50, preferably 13 to 40, and more preferably 13 to 30.

[0035] If the value of A increases, i.e., the aspect ratio of the electrode assembly increases, the length of the electrode increases, and therefore the assembly resistance increases, resulting in relatively excellent insulation. Thus, sufficient insulation properties can be ensured even with a relatively small thickness of the spacer. Conversely, if the value of A decreases, i.e., the aspect ratio of the electrode assembly decreases, the length of the electrode decreases, causing the assembly resistance to decrease, thereby relatively reducing the insulation properties. Therefore, it is desirable to ensure sufficient insulation by increasing the thickness of the spacer as described above.

[0036] Meanwhile, the total length of the electrode assembly can be from 20 mm to 1000 mm, particularly from 50 mm to 800 mm, and even more particularly from 100 mm to 600 mm, and the total width can be from 20 mm to 1000 mm, particularly from 40 mm to 400 mm, and even more particularly from 50 mm to 200 mm.

[0037] In an embodiment of the invention, the leakage current measured after applying a voltage of 50 V to the electrode assembly for 10 seconds can be less than or equal to 0.5 mA. As previously stated, since the electrode assembly satisfying the above expression (1) has excellent insulation, the leakage current can be very low, as described above. In particular, the leakage current is a value measured when a voltage is applied under DC conditions using a high-voltage tester.

[0038] Furthermore, the thickness of the electrode assembly can be greater than or equal to 10 mm, particularly greater than or equal to 13 mm, and even more particularly greater than or equal to 15 mm, less than or equal to 200 mm, or less than or equal to 100 mm. As mentioned above, insulation decreases with increasing thickness, thus the present invention can be applied more effectively. However, when the thickness of the electrode assembly is less than 10 mm, it is inappropriate to predict the insulation using expression (1) because the insulation degradation is not obvious.

[0039] Stacked electrode assemblies are preferred for electrode assemblies, having a structure in which positive and negative electrodes are sequentially stacked with spacers between them. Since the present invention compensates for insulation degradation while utilizing the effect of increased capacity obtained by stacking electrodes in parallel, stacked electrode assemblies are preferred for electrode assemblies.

[0040] Meanwhile, the secondary battery according to the present invention includes: an electrode assembly; an electrolyte; and a battery case for housing the electrode assembly and the electrolyte.

[0041] The battery case may include a barrier layer, a base layer formed on one surface of the barrier layer, and a sealant layer formed on the other surface of the barrier layer. The battery case may be a bag including at least one cup-shaped portion that is bent in one direction, and the electrode assembly and electrolyte may be housed in at least one cup-shaped portion.

[0042] Figure 1 This illustration shows an exploded perspective view of a pouch-type secondary battery according to an embodiment of the secondary battery of the present invention, and Figure 2 This is a cross-sectional view illustrating the bag film laminate. In the following description, a secondary battery according to an embodiment of the present invention will be described in more detail with reference to the accompanying drawings.

[0043] bag

[0044] Bag 100 can be prepared by inserting a bag film laminate having a flexible base layer 10, a barrier layer 20 and a sealant layer 30 in sequence into a compression molding apparatus, and applying pressure to a portion of the bag film laminate by a punch to stretch it, thereby forming a cup-shaped portion (accommodating portion) that is bent in one direction.

[0045] basal layer

[0046] The base layer 10 is disposed on the outermost layer of the bag to protect the electrode assembly from external impacts and to electrically insulate the electrode assembly.

[0047] The substrate 10 may be made of a polymer material, which may be one or more polymer materials selected from the group consisting of: for example, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylate-based polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, poly(p-phenylenebenzobisoxazole), polyarylate, and Teflon.

[0048] The base layer 10 can be a single-layer structure, and as... Figure 2As shown, the substrate 10 can also be a multilayer structure in which different polymer films 12 and 14 are laminated. In the case that the substrate 10 is a multilayer structure, an adhesive layer 16a can be provided between the polymer films.

[0049] Meanwhile, the substrate layer 10 can have a total thickness of 10 μm to 60 μm, preferably 20 μm to 50 μm, and more preferably 30 μm to 50 μm. When the substrate layer is a multilayer structure, the thickness includes the thickness of the adhesive layer. When the substrate layer 10 falls within the above range, it exhibits excellent durability, insulation, and formability. When the thickness of the substrate layer is too small, durability may decrease, and the substrate layer may be damaged during molding. When the thickness is too large, formability may decrease, and the total thickness of the bag may increase, thereby reducing the space available to house the battery and lowering the energy density.

[0050] According to an embodiment, the base layer 10 can be a stacked structure of polyethylene terephthalate (PET) film and nylon film. In this case, it is preferable that the nylon film is disposed on the side of the barrier layer 20, i.e., the inner side, while the polyethylene terephthalate film is disposed on the surface side of the bag.

[0051] Polyethylene terephthalate (PET) exhibits excellent durability and electrical insulation, and therefore, when a PET film is placed on the surface side, it displays excellent durability and insulation. However, because the PET film has weak adhesion to the aluminum alloy film constituting the barrier layer 20 and different stretching behavior, separation between the base layer and the barrier layer may occur during the molding process when the PET film is placed on the barrier layer side, and the barrier layer cannot be stretched uniformly, resulting in reduced formability. In contrast, since nylon film has similar stretching behavior to the aluminum alloy film constituting the barrier layer 20, placing a nylon film between the polyethylene terephthalate and the barrier layer can improve formability.

[0052] The polyethylene terephthalate (PET) film can have a thickness of 5 μm to 20 μm, preferably 5 μm to 15 μm, and more preferably 7 μm to 15 μm, while the nylon film can have a thickness of 2010 μm to 40 μm, preferably 2010 μm to 35 μm, and more preferably 2515 μm to 25 μm. When the thicknesses of the PET film and the nylon film fall within the above-mentioned ranges, they exhibit excellent formability and rigidity after molding.

[0053] Barrier layer

[0054] The barrier layer 20 is used to ensure the mechanical strength of the bag 100, prevent gas, moisture, etc. from entering from the outside of the secondary battery, and prevent electrolyte leakage.

[0055] The barrier layer 20 may have a thickness of 4 μm to 100 μm, more preferably 50 μm to 80 μm, and even more preferably 60 μm to 80 μm. When the thickness of the barrier layer falls within the above range, formability is improved, increasing the forming depth of the cup-shaped portion even when forming two cups, or reducing the occurrence of cracks and / or pinholes, thereby improving the resistance to external stress after forming.

[0056] Meanwhile, the barrier layer 20 can be made of metallic materials, and in particular of aluminum alloy film.

[0057] Aluminum alloy films may include aluminum and other metallic elements, such as those selected from one, two or more of the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si) and zinc (Zn).

[0058] Preferably, the aluminum alloy film may include iron (Fe) in an amount of 1.2% to 1.7% by weight, preferably 1.3% to 1.7% by weight, and more preferably 1.3% to 1.45% by weight. When the amount of iron (Fe) in the aluminum alloy film falls within the above range, the occurrence of cracks or pinholes can be minimized even if the cup-shaped portion is formed very deeply.

[0059] sealant layer

[0060] The sealant layer 30 is heat-pressed to seal the bag and is positioned on the innermost layer of the bag film laminate 1.

[0061] Since the sealant layer 30 is the surface that will come into contact with the electrolyte and electrode assembly after the bag is formed, the sealant layer is required to be insulating and corrosion resistant, and high sealing performance is required because it is necessary to prevent the movement of substances between the inside and outside by completely sealing the interior.

[0062] The sealant layer 30 may be made of a polymer material, which may be selected from one or more of the following: for example, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylate polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aromatic polyamide, nylon, polyester, poly(p-phenylenebenzobisazole), polyaryl compounds and Teflon, and among these materials, polypropylene (PP) is particularly preferred, as it has excellent mechanical properties such as tensile strength, rigidity, surface hardness, abrasion resistance and heat resistance, as well as chemical properties such as corrosion resistance.

[0063] More specifically, the sealant layer 30 may include polypropylene, cast polypropylene (CPP), acid-modified polypropylene, polypropylene-butene-ethylene copolymer, or a combination thereof.

[0064] The sealant layer 30 can have a single-layer structure or a multi-layer structure comprising two or more layers of different polymer materials.

[0065] The sealant layer can have a total thickness of 60 μm to 100 μm, preferably 60 μm to 90 μm, and more preferably 70 μm to 90 μm. When the thickness of the sealant layer is too small, the sealing durability and insulation may be reduced, and when the thickness is too large, the flexibility may be reduced, and the total thickness of the bag film laminate may increase, resulting in a decrease in energy density per unit volume.

[0066] The bag film laminate 1 can be prepared using methods widely known in the relevant art for preparing bag film laminates. For example, the bag film laminate can be prepared by bonding the base layer 10 to the upper surface of the barrier layer 20 with an adhesive, and forming the sealant layer 30 on the lower surface of the barrier layer 20 by co-extrusion or adhesive, but the method is not limited to this.

[0067] Bag 100 is prepared by inserting the aforementioned bag film laminate into a forming apparatus and applying pressure to a portion of the bag film laminate using a punch to form a cup-shaped portion. The pressure can be approximately 0.3 MPa to 1 MPa, preferably approximately 0.3 MPa to 0.8 MPa, and more preferably approximately 0.4 MPa to 0.6 MPa. During the forming of the cup-shaped portion, if the pressure is too low, wrinkles may occur due to over-drawing; if the pressure is too high, the forming depth may be reduced due to insufficient drawing.

[0068] Meanwhile, the punch's moving speed can be from 20 mm / min to 80 mm / min, preferably from 30 mm / min to 70 mm / min, and more preferably from 40 mm / min to 60 mm / min. If the pressure is too low or the punch's moving speed is too high during forming, wrinkles may occur due to buckling. Conversely, if the pressure is too high or the punch's moving speed is too low during forming, the stress concentrated at the corners of the cup-shaped portion during forming may increase, potentially increasing the formation of pinholes or cracks.

[0069] The bag 100 of the present invention prepared by the above method includes a lower box 101, an upper box 102 and a folded portion 130 connecting the upper box and the lower box, and the upper box and / or the lower box includes a cup-shaped portion 110 that is recessed in one direction.

[0070] In particular, the bag 100 according to the invention can be as follows: Figure 1 The cup-shaped portion 110 shown is a single cup shape formed in the lower box 101, but the embodiment is not limited to this, and the bag 100 can also be a double cup shape in both the upper and lower boxes, where the cup-shaped portion is formed. A double-cup bag can accommodate a thicker electrode assembly than a single-cup bag because after accommodating the electrode assembly and electrolyte, the upper box is folded so that the cup-shaped portions of the upper box and the lower box face each other, and therefore, it is advantageous in achieving high energy density.

[0071] The cup-shaped portion 110 has a receiving space for accommodating the electrode assembly 200. Meanwhile, the bag 100 may include a platform 120 surrounding the cup-shaped portion 110. The platform 120 refers to the unformed portion of the bag film laminate, i.e., the remaining area other than the cup-shaped portion 110. The platform 120 is the portion that is sealed by heat bonding during the sealing process after the electrode assembly 200 is accommodated in the cup-shaped portion 110 and the electrolyte solution is injected.

[0072] The cup-shaped portion 110 may include a bottom surface and a peripheral surface. The peripheral surface may connect the bottom surface and the platform 120. Multiple peripheral surfaces may be included, and more specifically, four peripheral surfaces may be included. The bottom surface may cover one side of the electrode assembly 200, and the peripheral surfaces may surround the periphery of the electrode assembly 200.

[0073] Simultaneously, after connecting the lower box 101 to the upper box 102, housing the electrode assembly 200 in the cup-shaped portion 110, and injecting the electrolyte solution, the folding portion 130 is folded so that the upper box 102 seals the cup-shaped portion 110 of the lower box 101. With the folding portion 130 included, since the lower box 101 and the upper box 102 are integrally connected, the number of sides to be sealed during the subsequent sealing process is reduced, which improves manufacturability.

[0074] The folded portion 130 can be spaced apart from the cup-shaped portion 110, and the distance between the folded portion 130 and the cup-shaped portion 110 can be about 0.5 mm to 3 mm, and preferably about 0.5 mm to 2 mm. If the folded portion 130 is too close to the cup-shaped portion 110, folding cannot be performed smoothly, and if the folded portion 130 is too far from the cup-shaped portion 110, the total volume of the secondary battery may increase, and therefore, the energy density per unit volume may decrease. In the case of two cups, the folded portion can be formed to satisfy the above-mentioned distance for each cup-shaped portion.

[0075] Electrode assembly

[0076] Electrode assembly 200 may include a plurality of electrodes stacked alternately and a plurality of spacers. The plurality of electrodes may be stacked alternately with spacers between them, and may include positive and negative electrodes with opposite polarities.

[0077] Additionally, multiple electrode tabs 230 welded together may be provided in the electrode assembly 200. These electrode tabs 230 can be connected to multiple electrodes 210 and protrude from the electrode assembly 200 to the outside to serve as a path for electron movement between the inside and outside of the electrode assembly 200. The multiple electrode tabs 230 may be positioned inside the bag 100.

[0078] The electrode contact 230 connected to the positive electrode and the electrode contact 230 connected to the negative electrode may protrude in different directions with respect to the electrode assembly 200. However, the implementation is not limited to this, and the electrode contact 230 connected to the positive electrode and the electrode contact 230 connected to the negative electrode may also protrude side by side in the same direction.

[0079] Leads 240 that supply power to the outside of the secondary battery can be connected to multiple electrode contacts 230 by spot welding or the like. One end of the lead 240 can be connected to the multiple electrode contacts 230, and the other end can protrude to the outside of the bag 100.

[0080] A portion of the lead 240 may be surrounded by an insulating portion 250. For example, the insulating portion 250 may include an insulating tape. The insulating portion 250 may be positioned between the platform 120 of the first box 101 and the second box 102, and in this state, the platform 120 and the second box 102 may be thermally bonded to each other. In this case, a portion of the platform 120 and the second box 102 may be thermally bonded to the insulating portion 250. Therefore, the insulating portion 250 can prevent the power generated from the electrode assembly 200 from flowing through the lead 240 to the bag 100 and maintain the seal of the bag 100.

[0081] Furthermore, the secondary battery according to the present invention may, as needed, include at least one fixing member on the outer surface of the electrode assembly. In the case of an electrode assembly having a rectangular shape with a total length that is longer than its total width (for convenience, referred to as a long battery cell), a fixing member that is wound around the electrode assembly in the total width direction to fix it can be used to avoid misalignment of the constituent elements of the electrode assembly, namely the positive electrode, the negative electrode, and the separator.

[0082] The fixing member can have a porous structure. When the fixing member has a porous structure, the electrolyte can penetrate the fixing member to wet the electrode assembly, thereby preventing a reduction in electrolyte wetting in the electrode assembly due to the fixing member. In particular, the fixing member can be a terminating tape with an adhesive layer formed on one surface of a substrate layer in a polymer material with a porous structure, but is not limited to this. The polymer material can be, for example, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), etc., but is not limited to this.

[0083] As a fixing member, a fixing member having a width of approximately 10 mm to 50 mm or approximately 20 mm to 40 mm along the total width direction of the electrode assembly is preferred. When the width of the fixing member is too large, the outer surface area of ​​the electrode assembly covered by the fixing member may increase, and thus the contact area with the electrolyte may decrease, resulting in reduced electrolyte wetting and potentially reduced friction between the electrode assembly and the battery case, leading to decreased impact resistance. Conversely, when the width of the fixing member is too small, the fixing effect on the electrode assembly may be reduced.

[0084] The secondary battery may include 2 to 10, preferably 2 to 8, and more preferably 3 to 7 fixing members. In this case, the fixing members can be arranged at symmetrical positions along the total length, and preferably, the fixing members can be arranged to be equally spaced apart from each other. When multiple fixing members are provided and arranged as described above, the electrode assembly of the long battery cell structure with a relatively long total length can be securely fixed.

[0085] Meanwhile, the contact area between the fixing member and the electrode assembly can be 30% or less, 25% or less, or 20% or less of the total surface area of ​​the electrode assembly. In particular, the contact area between the fixing member and the electrode assembly can be 0% to 30%, 1% to 30%, 5% to 30%, 5% to 25%, or 5% to 20% of the total surface area of ​​the electrode assembly.

[0086] The contact area between the fixing members and the electrode assembly can be adjusted by controlling the width or number of fixing members used. Since the fixing members are typically made of a material with a lower coefficient of friction compared to the separators on the outermost surface of the electrode assembly, an increased area of ​​the fixing members surrounding the electrode assembly can lead to reduced friction between the electrode assembly and the inner surface of the battery compartment. Therefore, when using fixing members, it is desirable to suppress this reduction in friction by adjusting the contact area with the electrode assembly to 30% or less.

[0087] Meanwhile, any positive electrode, negative electrode, separator, and electrolyte can be used in the present invention without limitation, as long as they are commonly used in secondary batteries, but the following description can be considered as preferred examples.

[0088] The positive electrode can be a sheet-type positive electrode, which may include a thin metal plate with excellent conductivity, such as a positive electrode current collector formed of aluminum foil, and a layer of positive electrode active material applied to one side or one and the other side of the positive electrode current collector. The negative electrode can be a sheet-type negative electrode, which may include a thin metal plate with excellent conductivity, such as a negative electrode current collector formed of copper (Cu) or nickel (Ni) foil, and a layer of negative electrode active material applied to one side or one and the other side of the negative electrode current collector.

[0089] The positive electrode active material layer 22 may include lithium metal oxides containing transition metals such as lithium and cobalt, manganese and / or nickel as the positive electrode active material, and may also include conductive materials and / or binders as needed. Various materials commonly used in the preparation of secondary batteries can be used, and there are no limitations on the positive electrode active material, conductive material, and binder.

[0090] Specifically, the positive electrode may include one or more of the following as the positive electrode active material: lithium nickel-based composite oxide, lithium manganese-based composite oxide and lithium iron phosphate-based composite oxide, and preferably includes lithium nickel-based composite oxide, which may be represented by the following chemical formula 1.

[0091] [Chemical Formula 1]

[0092] Li 1+x (Ni a Co b Mn c M d O2

[0093] In the above chemical formula 1,

[0094] M is selected from one or more of the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0095] -0.4≤x≤0.4, 0.30≤a≤1, 0≤b≤0.70, 0≤c≤0.70, 0≤d≤0.10, and a+b+c+d=1.

[0096] The above 1 + x refers to the molar ratio of lithium in the lithium nickel-based composite oxide, where -0.1 ≤ x ≤ 0.2 or 0 ≤ x ≤ 0.2 can be satisfied. When the molar ratio of lithium falls within the above range, the crystal structure of the lithium nickel-based composite oxide can be stably formed.

[0097] The above a refers to the molar ratio of nickel in all metals other than lithium in the lithium nickel-based composite oxide, where 0.70 ≤ a < 1, 0.80 ≤ a < 1 or 0.90 ≤ a < 1 can be satisfied. When the molar ratio of nickel falls within the above range, high energy density can be achieved, and thus, high capacity is possible.

[0098] The above b refers to the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based composite oxide, where 0 < b ≤ 0.25, 0 < b ≤ 0.15 or 0 < b ≤ 0.05 can be satisfied. When the molar ratio of cobalt falls within the above range, good resistance characteristics and output characteristics can be achieved.

[0099] The above c refers to the molar ratio of manganese in all metals other than lithium in the lithium nickel-based composite oxide, where 0 < c ≤ 0.25, 0 < c ≤ 0.15 or 0 < c ≤ 0.05 can be satisfied. When the molar ratio of manganese falls within the above range, the positive electrode active material has excellent structural stability.

[0100] The above d refers to the molar ratio of element M in all metals other than lithium in the lithium nickel-based composite oxide, where 0 ≤ d ≤ 0.08, 0 ≤ d ≤ 0.05 or 0 ≤ d ≤ 0.03 can be satisfied.

[0101] In particular, a, b, c, and d in Chemical Formula 1 above can respectively satisfy 0.80 ≤ a < 1, 0 < b ≤ 0.15, 0 < c ≤ 0.15, and 0 ≤ d ≤ 0.05.

[0102] When the lithium-nickel-based composite oxide is an NCM oxide containing all of nickel, cobalt, and manganese, the resistivity of the positive electrode may be low, and thus, the phenomenon of insulation deterioration caused by the increase in the thickness of the aforementioned electrode assembly may become more obvious, indicating that the effect according to the composition satisfying the above Expression (1) may be maximized.

[0103] Meanwhile, the lithium manganese-based composite oxide can be one or more selected from the group containing the following: Li p Mn 1- q M a q A2, Li p Mn2O 4-r X r 、Li p Mn 2-q M a q Mb r A4, Li p Co 1-q M a q A2, Li p Co 1-q M a q O 2-r X r Li p Ni 1-q M a q O 2-r X r Li p Ni 1-q Co q O 2-r X r Li p Ni 1-q-r Co q M a r A w Li p Ni 1-q-r Co q M a r O 2-w X w Li p Ni 1-q-r Mn q M a r A w and Li p Ni 1-q- r Mn q M a r O 2-w X w And at this point, p, q, r, and w can satisfy 0.9≤p≤1.6, 0≤q≤1, 0≤r≤1, and 0≤w≤2, respectively, M a and M b X are elements that are the same or different from each other, each of which is one or more elements selected from the group consisting of: Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth elements, A is one or more elements selected from O, F, S and P, and X is one or more elements selected from the group consisting of F, S and P.

[0104] In addition, lithium iron phosphate-based composite oxides can be represented by the following chemical formula 2.

[0105] [Chemical Formula 2]

[0106] LiFe 1-k M c k PO4

[0107] In the above chemical formula 2,

[0108] M C It is selected from one or more of the following: Ni, Co, Mn, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir, and V, and

[0109] 0≤k<1.

[0110] The negative electrode active material layer 12 may include: carbon-based materials, such as graphite; metals or alloys including metals; metal oxides; and composite materials of metals and carbon as the negative electrode active material, and may also include conductive materials and / or binders as needed. Various materials commonly used in the fabrication of secondary batteries can be used, and there are no limitations on the negative electrode active material, conductive material, and binder.

[0111] In particular, the negative electrode may include graphite as the negative electrode active material. When the negative electrode active material is graphite, the resistivity of the negative electrode may be low, and therefore, the insulation degradation caused by the increased thickness of the aforementioned electrode assembly may become more pronounced, indicating that the effect of the composition satisfying the above expression (1) may be maximized.

[0112] The separator can be a porous polymer membrane commonly used as a conventional separator, and is, for example, a polyolefin-based porous polymer membrane, such as ethylene homopolymer, propylene homopolymer, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-methacrylate copolymer, etc., which can be used alone or in stacks. Alternatively, a polyolefin-based porous polymer membrane with inorganic particles (e.g., Al2O3) applied or a common porous nonwoven fabric, such as a nonwoven fabric formed from high-melting-point glass fiber, polyethylene terephthalate fiber, etc., can be used, but the material is not limited to these.

[0113] Meanwhile, any electrolyte capable of moving lithium ions generated by the electrochemical reaction of the electrodes during charging and discharging can be used without restriction, and for example, a non-aqueous organic solvent in which lithium salts are dissolved can be used.

[0114] Any compound capable of providing lithium ions used in lithium secondary batteries can be used as a lithium salt without particular limitation. Specifically, for lithium salts, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc., can be used. The concentration of the lithium salt can be appropriately varied within a generally available range, but this range can be from 0.1 M to 5.0 M, preferably from 0.1 M to 3.0 M.

[0115] Any non-aqueous organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. For example, solvents based on cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate, organic solvents based on linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and ethyl methyl carbonate (EMC), or mixtures thereof, can be used.

[0116] Secondary batteries can be used in a variety of devices. For example, they can be used in electric vehicles, including electric bicycles, electric vehicles, and hybrid electric vehicles (HEVs).

[0117] Therefore, according to another embodiment of the present invention, a battery module including a secondary battery as a unit battery and a battery pack including the battery module are provided.

[0118] Battery modules or battery packs can be used as a power source for one or more medium and large-sized devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or systems for energy storage.

[0119] The invention will be described in more detail below with reference to specific examples.

[0120] Methods of implementing the present invention

[0121] [Example and Comparative Example: Fabrication of Electrode Components]

[0122] Example 1

[0123] Will include Li[Ni 0.8 Co 0.1 Mn 0.1A stacked electrode assembly with a total length of 600 mm, a total width of 100 mm, and a thickness of 13.7 mm was prepared by alternately stacking an electrode with O2 as the positive electrode active material and a negative electrode including graphite as the negative electrode active material, with a safety reinforcement spacer (SRS) with a thickness of 17 µm between them.

[0124] Examples 2 through 5 and comparison example 1

[0125] Except that the 17 μm thick safety reinforcement spacer is replaced with a safety reinforcement spacer with a thickness of 15 μm, 13 μm, 11 μm, 9 μm and 7 μm respectively, the stacked electrode assemblies according to Examples 2 to 5 and Comparative Example 1 are prepared using the same process as in Example 1 above.

[0126] Example 6

[0127] Except that the total length of the electrode assembly becomes 350 mm, the stacked electrode assembly is prepared using the same process as in Example 1 above.

[0128] Examples 7 through 9 and comparison examples 2 through 3

[0129] Except that the 17 μm thick safety reinforcement spacer was replaced with a safety reinforcement spacer with thicknesses of 15 μm, 13 μm, 11 μm, 9 μm and 7 μm respectively, the stacked electrode assemblies according to Examples 7 to 9 and Comparative Examples 2 to 3 were prepared using the same process as in Example 6 above.

[0130] Example 10

[0131] Except that the total length of the electrode assembly becomes 250 mm, the stacked electrode assembly is prepared using the same process as in Example 1 above.

[0132] Examples 11 to 13 and Comparison Examples 4 to 5

[0133] Except that the 17 μm thick safety reinforcement spacer is replaced with a safety reinforcement spacer with a thickness of 15 μm, 13 μm, 11 μm, 9 μm and 7 μm respectively, the stacked electrode assemblies according to Examples 11 to 13 and Comparative Examples 4 to 5 are prepared using the same process as in Example 10 above.

[0134] Example 14

[0135] Except that the total length of the electrode assembly becomes 200 mm, the stacked electrode assembly is prepared using the same process as in Example 1 above.

[0136] Examples 15 to 16 and comparison examples 6 to 8

[0137] Except that the 17 μm thick safety reinforcement spacer is replaced with a safety reinforcement spacer with thicknesses of 15 μm, 13 μm, 11 μm, 9 μm and 7 μm respectively, the stacked electrode assemblies according to Examples 15 to 16 and Comparative Examples 6 to 8 are prepared using the same process as in Example 14 above.

[0138] Example 17

[0139] Except that the total length of the electrode assembly becomes 100 mm, the stacked electrode assembly is prepared using the same process as in Example 1 above.

[0140] Examples 18 to 19 and comparison examples 9 to 11

[0141] Except that the 17 μm thick safety reinforcement spacer is replaced with a safety reinforcement spacer with thicknesses of 15 μm, 13 μm, 11 μm, 9 μm and 7 μm respectively, the stacked electrode assemblies according to Examples 18 to 19 and Comparative Examples 9 to 11 are prepared using the same process as in Example 17 above.

[0142] Compare Example 12

[0143] Will include Li[Ni 0.8 Co 0.1 Mn 0.1 A stacked electrode assembly with a total length of 250 mm, a total width of 100 mm, and a thickness of 5.7 mm was prepared by alternately stacking an electrode with O2 as the positive electrode active material and an electrode with graphite as the negative electrode active material, with a safety reinforcement spacer (SRS) of 17 µm thickness between them.

[0144] Compare Examples 13 to 17

[0145] Except that the 17 μm thick safety reinforcement spacer was replaced with a safety reinforcement spacer with thicknesses of 15 μm, 13 μm, 11 μm, 9 μm and 7 μm respectively, the stacked electrode assemblies according to Comparative Examples 13 to 17 were prepared using the same process as in Comparative Example 12 above.

[0146] Compare Example 18

[0147] Will include Li[Ni 0.8 Co 0.1 Mn 0.1A stacked electrode assembly with a total length of 100 mm, a total width of 100 mm, and a thickness of 5.7 mm was prepared by alternately stacking an electrode with O2 as the positive electrode active material and a negative electrode including graphite as the negative electrode active material, with a safety reinforcement spacer (SRS) with a thickness of 17 µm between them.

[0148] Compare Examples 19 to 23

[0149] Except that the 17 μm thick safety reinforcement spacer was replaced with a safety reinforcement spacer with thicknesses of 15 μm, 13 μm, 11 μm, 9 μm and 7 μm respectively, the stacked electrode assemblies according to Comparative Examples 19 to 23 were prepared using the same process as in Comparative Example 18 above.

[0150] [Experimental Example]

[0151] Experimental Example 1: Insulation Assessment

[0152] For the electrode assemblies prepared according to Examples 1 to 19 and Comparative Examples 1 to 17, insulation was evaluated using an AC / DC / IR high-voltage tester (Model 19052, Chroma). Specifically, a voltage of 50 V was applied for 10 seconds under DC conditions, and then the leakage current was measured, and values ​​less than or equal to 0.5 mA were listed in Table 1 below as passing and values ​​greater than 0.5 mA as failing.

[0153] [Table 1]

[0154]

[0155] From the results listed in Table 1 above, it can be seen that, in the case of a thick battery cell with a thickness of 13.7 mm, the electrode assemblies according to Examples 1 to 19 that satisfy the above expression (1) have better insulation properties than the electrode assemblies according to Comparative Examples 1 to 11 that do not satisfy expression (1).

[0156] Meanwhile, in the case of thin battery cells with a thickness of 5.7 mm prepared according to Comparative Examples 12 to 23, it can be seen that whether or not the above expression (1) is satisfied does not indicate insulation properties.

[0157] In other words, it can be seen that expression (1) is only effective as an indicator for predicting insulation for thick battery cells with a thickness of 10 mm or more.

[0158] Meanwhile, comparing the insulation evaluation results between Comparative Example 17 and Comparative Example 23, it can be seen that in the case of thin battery cells with a thickness of less than 10 mm, the insulation characteristics can be improved simply by increasing the aspect ratio without adjusting the thickness of the separator.

[0159] Experiment Example 2: Performance Evaluation

[0160] A bag was prepared in which nylon / polyethylene terephthalate / Al alloy film / polypropylene were sequentially stacked to form a cup-shaped portion. Electrode assemblies prepared according to each of Examples 10 to 13 and Comparative Examples 12 to 17 were housed in the cup-shaped portion, and then an electrolyte solution prepared by dissolving 1.0 M LiPF6 in an organic solvent of ethylene carbonate (EC): ethyl carbonate (EMC) mixed in a volume ratio of 30:70 was injected. The bag was then sealed, and an activation process was performed to prepare a bag-type secondary battery. The final thickness of the secondary battery including the electrode assemblies according to each of Examples 10 to 13 was 14.2 mm, and the final thickness of the secondary battery including the electrode assemblies according to each of Comparative Examples 12 to 17 was 6.1 mm.

[0161] The prepared secondary battery was charged to 4.2 V at a constant current of 0.33 C at room temperature, then discharged to 2.5 V at a constant current of 0.33 C to check the initial capacity, and then charged again to 30% SOC at a constant current of 0.33 C, and then the AC resistance was measured. The results are listed in Table 2 below.

[0162] [Table 2]

[0163]

[0164] The results listed in Table 2 above show that the battery cell including a thick electrode assembly with a thickness of 13.7 mm has a higher capacity and lower resistance than the battery cell including a thin electrode assembly with a thickness of 5.7 mm.

Claims

1. An electrode assembly comprising: Positive electrode, negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode assembly has a thickness of 10 mm or more and satisfies the following expression (1): (A × B) + 6B ≥ 90, In the expression (1), A is the ratio of the total length to the total width of the electrode assembly, and B is the thickness value of the separator measured in μm.

2. The electrode assembly of claim 1, wherein, In the expression (1), A is greater than or equal to 5, and B is between 8 and 40.

3. The electrode assembly of claim 1, wherein, In the expression (1), A is greater than or equal to 2.5 and less than 5, and B is between 10 and 45.

4. The electrode assembly of claim 1, wherein, In the expression (1), A is greater than or equal to 1 and less than 2.5, and B is between 12 and 50.

5. The electrode assembly of claim 1, wherein, The leakage current measured after applying a voltage of 50 V to the electrode assembly for 10 seconds was less than or equal to 0.5 mA.

6. The electrode assembly of claim 1, wherein, The positive electrode includes one or more of the following as the positive electrode active material: lithium nickel-based composite oxide, lithium manganese-based composite oxide, and lithium iron phosphate-based composite oxide.

7. The electrode assembly according to claim 1, wherein The positive electrode comprises a lithium-nickel-based composite oxide as the positive electrode active material, and The lithium-nickel-based composite oxide is represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x (Ni a Co b Mn c M d )O2 Wherein, in the chemical formula 1, M is selected from one or more of the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and -0.4≤x≤0.4, 0.30≤a≤1, 0≤b≤0.70, 0≤c≤0.70, 0≤d≤0.10, and a+b+c+d=1.

8. The electrode assembly of claim 1, wherein, The electrode assembly is a stacked electrode assembly.

9. A secondary battery, comprising: The electrode assembly according to claim 1; Electrolytes; as well as A battery case that houses the electrode assembly and the electrolyte.

10. The secondary battery according to claim 9, wherein The battery box includes a barrier layer, a base layer formed on one surface of the barrier layer, and a sealant layer formed on the other surface of the barrier layer. The battery compartment is a bag comprising at least one cup-shaped portion bent in one direction, and The electrode assembly and the electrolyte are housed in at least one cup-shaped portion.

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