Electrode assembly and secondary battery comprising same

Abstract

The present invention relates to an electrode assembly having excellent insulation and a secondary battery comprising same. The electrode assembly according to the present invention comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, satisfies expression (1), and has a thickness of 10 mm or more. Expression (1): (A x 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 value of the separator measured in units of µm.

Description

Electrode assembly and secondary battery including the same

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

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

[0003] Secondary batteries are generally manufactured by applying electrode active material slurry to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, laminating them on both sides of a separator to form an electrode assembly of a predetermined shape, then housing the electrode assembly in a battery case and injecting an electrolyte.

[0004] As the thickness of the electrode assembly increases, i.e., as a greater number of electrodes are stacked, more active material can be contained, thereby increasing the capacity of the battery. However, as a greater number of electrodes are connected in parallel through the stacking, the resistance of the electrode assembly may decrease, which may lead to a problem of deterioration in insulation.

[0005] Therefore, it is an important task to secure appropriate insulation in a secondary battery including an electrode assembly having a thickness greater than a certain level.

[0006] The present invention aims to solve the problem that the insulation deterioration becomes more severe as the thickness of the electrode assembly increases, and accordingly provides an electrode assembly configured such that the size and thickness of the separator satisfy a specific formula, and a secondary battery including the same.

[0007] The present invention provides an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, satisfying the following equation (1), and having a thickness of 10 mm or more.

[0008] Equation (1): (A × B) + 6B ≥ 90

[0009] In the above equation (1),

[0010] A is the ratio of the electric field to the overall width of the electrode assembly,

[0011] B is the thickness value of the above membrane measured in μm.

[0012]

[0013] The present invention provides a secondary battery including the electrode assembly; an electrolyte; and a battery case that accommodates the electrode assembly and the electrolyte.

[0014] The electrode assembly according to the present invention has a thickness of 10 mm or more, and is configured such that the aspect ratio and the thickness value of the separator satisfy a specific formula, thereby providing an effect in which the initial capacity is high while at the same time the resistivity of the electrode and the insulating effect by the separator are appropriately formed.

[0015] That is, the secondary battery including the above electrode assembly exhibits high capacity and has excellent insulation properties, so there is a low risk of explosion due to internal short circuit and physical / electrical shock, and there is also a low risk of battery performance deterioration due to voltage drop.

[0016] Figure 1 is an exploded perspective view of a secondary battery according to one embodiment of the present invention.

[0017] Figure 2 is a drawing for explaining the configuration of a pouch according to an embodiment.

[0018] Hereinafter, the present invention will be described in more detail.

[0019]

[0020] Recently, with the increasing demand for high-capacity batteries, such as those for electric vehicles, the rated capacity of secondary battery cells has increased, leading to a corresponding increase in the size and thickness of electrode assemblies. This trend has led to a rise in the size and thickness of electrode assemblies. As more electrodes are stacked in parallel to achieve higher capacities, this decreases the resistance of the electrode assembly, leading to a decline in insulation. In particular, pouch-type secondary batteries are less durable than can-type secondary batteries, making them more vulnerable to safety hazards such as overheating and explosion if an internal short circuit occurs due to reduced insulation.

[0021] The inventors of the present invention have conducted repeated research to develop a secondary battery with high capacity and excellent insulation properties, and as a result, have 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 separator included in the electrode assembly satisfy specific conditions, excellent insulation properties can be implemented even in medium- to large-sized cells having a thickness of 10 mm or more, thereby completing the present invention.

[0022] The safety of secondary batteries depends significantly on their insulating properties, and to achieve excellent insulating properties, a method of significantly adjusting the aspect ratio of the electrode assembly is generally used. However, when the electrode assembly thickness is less than 10 mm, excellent insulating properties can be maintained simply by adjusting the aspect ratio of the electrode assembly. However, when the electrode assembly thickness is 10 mm or more, the parallel connection of the electrodes rapidly deteriorates insulating properties, and therefore, it was confirmed that both the aspect ratio of the electrode assembly and the thickness of the separator must be controlled.

[0023] In this specification, the total length refers to the length measured in the longitudinal direction, and the total width refers to the length measured in the width direction. Here, to explain the longitudinal direction, if the electrode assembly is assumed to be rectangular, the direction in which the long side is measured is called the longitudinal direction, and the direction perpendicular to the longitudinal direction, that is, the direction in which the short side is measured, is called the width direction. The positive electrode layers, the negative electrode layers, and the separator forming the electrode assembly can be laminated in a thickness direction perpendicular to both the longitudinal direction and the width direction.

[0024]

[0025] An electrode assembly according to the present invention comprises an anode, a cathode, and a separator interposed between the anode and the cathode, and is characterized in that it satisfies the following equation (1) and has a thickness of 10 mm or more.

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

[0027] In the above equation (1),

[0028] A is the ratio of the electric field to the overall width of the electrode assembly,

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

[0030]

[0031] Meanwhile, (A × B) + 6B in the above formula (1) may be 90 or more, preferably 95 or more, and more preferably 100 or more. However, considering the energy density of the cell, it is preferably 400 or less. When (A × B) + 6B is 90 or more, the thickness of the separator is appropriately formed considering the assembly resistance determined by the length of the electrodes constituting the electrode assembly, so that excellent insulation characteristics can be implemented without deterioration of other battery performances.

[0032] According to one embodiment of the present invention, A in the above formula (1) may be 1 to 10.5, and B may be 8 to 50.

[0033] In a specific embodiment, when A in the above formula (1) is 5 or more, specifically 6 to 10.5, B may be 8 to 40, preferably 9 to 30, and more preferably 9 to 20.

[0034] In another embodiment, when A in the above formula (1) is 2.5 or more and less than 5, specifically 2.5 to 3.5, B may be 10 to 45, preferably 11 to 35, and more preferably 11 to 25.

[0035] In another embodiment, when A in the above formula (1) is 1 or more and less than 2.5, specifically 1 to 2, B may be 12 to 50, preferably 13 to 40, and more preferably 13 to 30.

[0036] As the A value increases, that is, as the aspect ratio of the electrode assembly increases, the length of the electrode increases, so the assembly resistance increases, resulting in relatively excellent insulation properties. Therefore, even when a separator of relatively low thickness is used, sufficient insulation properties can be secured. Conversely, as the A value decreases, that is, as the aspect ratio of the electrode assembly decreases, the length of the electrode shortens, so the assembly resistance decreases, resulting in relatively poor insulation properties. Therefore, it is desirable to increase the thickness of the separator as described above to sufficiently secure insulation properties.

[0037] Meanwhile, the overall length of the electrode assembly may be 20 mm to 1,000 mm, specifically 50 mm to 800 mm, more specifically 100 mm to 600 mm, and the overall width may be 20 mm to 1,000 mm, specifically 40 mm to 400 mm, more specifically 50 mm to 200 mm.

[0038] In one embodiment of the present invention, the leakage current measured after applying a voltage of 50 V to the electrode assembly for 10 seconds may be 0.5 mA or less. As described above, the electrode assembly satisfying the above formula (1) has excellent insulation properties, so the leakage current can be implemented as low as described above. Specifically, the leakage current is a value measured when a voltage is applied under DC conditions using a Hipot tester.

[0039] In addition, the thickness of the electrode assembly may be 10 mm or more, specifically 13 mm or more, more specifically 15 mm or more, and may be 200 mm or less, or 100 mm or less. As described above, as the thickness increases, the insulation decreases, so the present invention can be applied more usefully. However, when the thickness of the electrode assembly is less than 10 mm, the insulation decrease phenomenon is minimal, so it is not suitable for predicting the insulation through equation (1).

[0040] The above electrode assembly is preferably a stacked electrode assembly having a structure in which a positive electrode and a negative electrode are sequentially stacked with a separator between them. Since the present invention is an invention for utilizing the capacity improvement effect that can be obtained by stacking electrodes in parallel while simultaneously compensating for the problem of reduced insulation, it is suitable that the electrode assembly be a stacked electrode assembly.

[0041]

[0042] Meanwhile, a secondary battery according to the present invention includes the electrode assembly; an electrolyte; and a battery case that accommodates the electrode assembly and the electrolyte.

[0043] The battery case is a pouch including a barrier layer, a substrate layer formed on one surface of the barrier layer, and a sealant layer formed on the other surface of the barrier layer, and including at least one cup portion curved in one direction, and an electrode assembly and an electrolyte can be accommodated in the at least one cup portion.

[0044] Fig. 1 is an exploded perspective view of a pouch-type secondary battery, which is one embodiment of a secondary battery according to the present invention, and Fig. 2 is a cross-sectional view of a pouch film laminate. Hereinafter, with reference to the drawings, a secondary battery according to one embodiment of the present invention will be described in more detail.

[0045]

[0046] pouch

[0047] The above pouch (100) has flexibility and can be manufactured by inserting a pouch film laminate in which a substrate layer (10), a barrier layer (20), and a sealant layer (30) are sequentially laminated into a press molding device, and applying pressure with a punch to a portion of the pouch film laminate to stretch it, thereby forming a cup portion (receiving portion) having a shape curved in one direction.

[0048]

[0049] Substrate layer

[0050] The substrate layer (10) is placed on the outermost layer of the pouch to protect the electrode assembly from external impact and electrically insulate it.

[0051] The above-mentioned substrate layer (10) may be made of a polymer material, and for example, may be made of one or more polymer materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon.

[0052] The above substrate layer (10) may have a single-layer structure, or may have a multi-layer structure in which different polymer films (12, 14) are laminated, as illustrated in Fig. 2. When the substrate layer (10) has a multi-layer structure, an adhesive layer (16a) may be interposed between the polymer films.

[0053] Meanwhile, the substrate layer (10) may 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 has a multilayer structure, the thickness includes the adhesive layer. When the substrate layer (10) satisfies the above range, durability, insulation, and formability are excellent. If the substrate layer thickness is too thin, durability is reduced, and the substrate layer may be damaged during the forming process, and if it is too thick, formability may be reduced, the overall thickness of the pouch may increase, and the battery accommodation space may be reduced, which may lower the energy density.

[0054] According to one embodiment, the substrate layer (10) may be a laminated structure of a polyethylene terephthalate (PET) film and a nylon film. In this case, it is preferable that the nylon film is disposed on the barrier layer (20) side, i.e., on the inside, and the polyethylene terephthalate film is disposed on the surface side of the pouch.

[0055] Polyethylene terephthalate (PET) has excellent durability and electrical insulation properties, and when a PET film is placed on the surface side, it exhibits excellent durability and insulation properties. However, in the case of the PET film, the adhesion to the aluminum alloy thin film constituting the barrier layer (20) is weak, and the stretching behavior is also different. Therefore, when the PET film is placed on the barrier layer side, the substrate layer and the barrier layer may be peeled off during the forming process, and the barrier layer may not be stretched uniformly, which may cause a problem of reduced formability. In contrast, since the stretching behavior of a nylon film is similar to that of an aluminum alloy thin film constituting the barrier layer (20), when a nylon film is placed between the polyethylene terephthalate and the barrier layer, an effect of improving formability can be obtained.

[0056] The above polyethylene terephthalate film may have a thickness of 5 µm to 20 µm, preferably 5 µm to 15 µm, and more preferably 7 µm to 15 µm, and the above nylon film may 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 polyethylene terephthalate film and the nylon film satisfy the above ranges, excellent formability and post-formed rigidity are exhibited.

[0057]

[0058] barrier layer

[0059] The barrier layer (20) is intended to secure the mechanical strength of the pouch (100), block the ingress of gas or moisture from outside the secondary battery, and prevent leakage of electrolyte.

[0060] The barrier layer (20) may have a thickness of 40 µm to 100 µm, more preferably 50 µm to 80 µm, and even more preferably 60 µm to 80 µm. When the barrier layer thickness satisfies the above range, the formability is improved, thereby increasing the cup portion forming depth, or reducing the occurrence of cracks and / or pinholes even during two-cup forming, thereby improving resistance to external stress after forming.

[0061] Meanwhile, the barrier layer (20) may be made of a metal material, and specifically, may be made of an aluminum alloy thin film.

[0062] The above aluminum alloy thin film may include one or more kinds selected from the group consisting of aluminum and metal elements other than aluminum, for example, iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0063] Preferably, the aluminum alloy thin film may have an iron (Fe) content of 1.2 wt% to 1.7 wt%, preferably 1.3 wt% to 1.7 wt%, and more preferably 1.3 wt% to 1.45 wt%. When the iron (Fe) content in the aluminum alloy thin film satisfies the above range, even when the cup portion is formed deeply, the occurrence of cracks or pinholes can be minimized.

[0064]

[0065] sealant layer

[0066] The sealant layer (30) is bonded through heat compression to seal the pouch, and is located on the innermost layer of the pouch film laminate (1).

[0067] The sealant layer (30) must have insulating and corrosion resistance properties because it is the surface that comes into contact with the electrolyte and electrode assembly after the pouch is formed, and must completely seal the inside to block material movement between the inside and the outside, so it must have high sealing properties.

[0068] The above sealant layer (30) may be made of a polymer material, and may be made of at least one selected from the group consisting of, for example, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon. Among these, it is particularly preferable to include polypropylene (PP), which has excellent mechanical properties such as tensile strength, rigidity, surface hardness, wear resistance, and heat resistance, and chemical properties such as corrosion resistance.

[0069] More specifically, the sealant layer (30) may include polypropylene, cast polypropylene (CPP), acid modified polypropylene, polypropylene-butylene-ethylene copolymer, or a combination thereof.

[0070] The above sealant layer (30) may have a single-layer structure or may have a multi-layer structure including two or more layers made of different polymer materials.

[0071] The sealant layer may have a total thickness of 60 µm to 100 µm, preferably 60 µm to 90 µm, and more preferably 70 µm to 90 µm. If the thickness of the sealant layer is too thin, the sealing durability and insulation may be reduced, and if it is too thick, the flexibility may be reduced and the total thickness of the pouch film laminate may increase, which may lower the energy density per volume.

[0072]

[0073] The above pouch film laminate (1) can be manufactured through a method for manufacturing a pouch film laminate known in the art. For example, the pouch film laminate can be manufactured through a method of attaching a substrate layer (10) to the upper surface of a barrier layer (20) using an adhesive, and forming a sealant layer (30) on the lower surface of the barrier layer (20) using co-extrusion or an adhesive, but is not limited thereto.

[0074]

[0075] A pouch (100) is manufactured by inserting the above-described pouch film laminate into a molding device and applying pressure to a portion of the pouch film laminate with a punch to form a cup portion. At this time, the pressure may be approximately 0.3 MPa to 1 MPa, preferably 0.3 MPa to 0.8 MPa, and more preferably 0.4 MPa to 0.6 MPa. If the pressure is too low during molding of the cup portion, excessive drawing may occur, resulting in wrinkles, and if it is too high, drawing may not occur properly, resulting in a low molding depth.

[0076] Meanwhile, the movement speed of the punch may be 20 mm / min to 80 mm / min, preferably 30 mm / min to 70 mm / min, and more preferably 40 mm / min to 60 mm / min. If the pressure during forming is too low or the movement speed of the punch is too fast, wrinkles due to buckling may occur, and if the pressure during forming is too high or the movement speed of the punch is too slow, the stress concentrated at the corner of the cup portion during forming may increase, which may increase the occurrence of pinholes or cracks.

[0077]

[0078] The pouch (100) of the present invention manufactured through the above method includes a lower case (101), an upper case (102), and a folding part (130) connecting the lower case and the lower case, and the upper case and / or the lower case includes a cup part (110) having a shape that is indented in one direction.

[0079] Specifically, the pouch (100) according to the present invention may be a single-cup shape in which the cup portion (110) is formed only in the lower case (101), as illustrated in FIG. 1, but is not limited thereto, and may be a double-cup shape in which cup portions are formed in both the upper case and the lower case. In the case of a double-cup shape pouch, since the upper case is folded so that the cup portions of the upper case and the cup portions of the lower case face each other after accommodating the electrode assembly and the electrolyte, it is possible to accommodate an electrode assembly having a thicker thickness than a single-cup shape pouch, and thus has the advantage of being advantageous in implementing high energy density.

[0080] The cup portion (110) has a receiving space for receiving the electrode assembly (200). Meanwhile, the pouch (100) may include a terrace (120) around the cup portion (110). The terrace (120) refers to a non-molded portion of the pouch film laminate, i.e., the remaining area excluding the cup portion (110). The terrace (129) is a portion that is sealed through thermal bonding in the process of receiving the electrode assembly (200) in the cup portion (110), injecting an electrolyte, and then sealing.

[0081] The cup portion (110) may include a bottom surface and a peripheral surface. The peripheral surface may connect the bottom surface and the terrace (120). A plurality of peripheral surfaces, more specifically four, may be provided. The bottom surface may cover one side of the electrode assembly (200), and the peripheral surface may surround the perimeter of the electrode assembly (200).

[0082] Meanwhile, the folding portion (130) connects the lower case (101) and the upper case (102), accommodates the electrode assembly (200) in the cup portion (110), and, after injecting the electrolyte, folds to allow the upper case (102) to seal the cup portion (110) of the lower case (101). When the folding portion (130) is included, the lower case (101) and the upper case (102) are connected as one piece, so that when performing the sealing process later, the number of sides to be sealed is reduced, thereby improving the processability.

[0083] The above folding portion (130) is formed to be spaced apart from the cup portion (110), and the distance between the folding portion (130) and the cup portion (110) may be about 0.5 mm to 3 mm, preferably about 0.5 mm to 2 mm. If the folding portion (130) is formed too close to the cup portion (110), folding may not be performed smoothly, and if the folding portion (130) is formed too far from the cup portion (110), the overall volume of the secondary battery may increase, thereby decreasing the energy density per volume. In the case of a two-cup case, the folding portion may be formed to satisfy the above distance for each cup portion.

[0084]

[0085] electrode assembly

[0086] The electrode assembly (200) may include a plurality of electrodes and a plurality of separators that are alternately stacked. The plurality of electrodes may be alternately stacked with the separator in between and include positive and negative electrodes having opposite polarities.

[0087] Additionally, the electrode assembly (200) may be provided with a plurality of electrode tabs (230) welded to each other. The plurality of electrode tabs (230) may be connected to the plurality of electrodes (210) and may protrude outwardly from the electrode assembly (200) to act as a passage through which electrons may move between the inside and the outside of the electrode assembly (200). The plurality of electrode tabs (230) may be located within the pouch (100).

[0088] The electrode tab (230) connected to the positive electrode and the electrode tab (230) connected to the negative electrode may protrude in different directions with respect to the electrode assembly (200). However, this is not limited to the present invention, and the electrode tab (230) connected to the positive electrode and the electrode tab (230) connected to the negative electrode may also protrude in the same direction while being parallel to each other.

[0089] A lead (240) for supplying electricity to the outside of the secondary battery may be connected to a plurality of electrode tabs (230) by spot welding or the like. One end of the lead (240) may be connected to the plurality of electrode tabs (230) and the other end may protrude to the outside of the pouch (100).

[0090] 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 terrace (120) of the first case (101) and the second case (102), and in this state, the terrace (120) and the second case (102) may be thermally fused to each other. In this case, portions of the terrace (120) and the second case (102) may be thermally fused to the insulating portion (250). Accordingly, the insulating portion (250) may prevent electricity generated from the electrode assembly (200) from flowing to the pouch (100) through the lead (240) and maintain the sealing of the pouch (100).

[0091]

[0092] Meanwhile, the secondary battery according to the present invention may further include at least one fixing member on the outer surface of the electrode assembly, if necessary. In the case of an electrode assembly having a rectangular shape with a length longer than its full width (for convenience, referred to as a "long-cell"), a fixing member that wraps and fixes the electrode assembly in the full width direction may be used to prevent the alignment of the components of the electrode assembly, i.e., the positive electrode, the negative electrode, and the separator, from being disturbed.

[0093] The above-mentioned fixing member may include a porous structure. When the fixing member includes a porous structure, the electrolyte can pass through the fixing member and be impregnated into the electrode assembly, thereby preventing the electrolyte impregnation property of the electrode assembly from being reduced due to the fixing member. Specifically, the fixing member may be a finishing tape having an adhesive layer formed on one surface of a polymer material substrate layer having a porous structure, but is not limited thereto. The polymer material may be, for example, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), etc., but is not limited thereto.

[0094] The above-mentioned fixing member preferably has a width of about 10 to 50 mm or 20 to 40 mm in the direction of the full width of the electrode assembly. If the width of the fixing member is too wide, the outer surface area of ​​the electrode assembly covered by the fixing member increases, thereby reducing the contact area with the electrolyte, which may result in reduced electrolyte impregnation, and reduced friction between the electrode assembly and the battery case, which may result in reduced impact resistance. On the other hand, if the width of the fixing member is too thin, the effect of fixing the electrode assembly may be reduced.

[0095] The secondary battery may include 2 to 10, preferably 2 to 8, and more preferably 3 to 7, fixing members. At this time, the fixing members may be arranged at positions symmetrical left and right along the electric field direction, and preferably, the fixing members may be arranged at equal intervals. When a plurality of fixing members are provided and arranged as described above, an electrode assembly having a long-cell structure with a long electric field length can be firmly fixed.

[0096] Meanwhile, the contact area between the fixing member and the electrode assembly may be 30% or less, 25% or less, or 20% or less of the total surface area of ​​the electrode assembly. Specifically, the contact area between the fixing member and the electrode assembly may 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.

[0097] The contact area between the fixing member and the electrode assembly can be adjusted by adjusting the width of the fixing member used or the number of fixing members used. Since the fixing member generally used is made of a material having a lower coefficient of friction than the separator arranged on the outermost surface of the electrode assembly, if the area of ​​the fixing member surrounding the electrode assembly increases, the frictional force between the electrode assembly and the inner surface of the battery case may decrease. Therefore, when using the fixing member, it is preferable to suppress the decrease in frictional force by limiting the contact area between the electrode assemblies to 30% or less.

[0098]

[0099] Meanwhile, the positive electrode, negative electrode, separator, and electrolyte may be used in the present invention without limitation if they are commonly used in secondary batteries, but the following description may be referred to as a preferred example.

[0100] The positive electrode is a sheet-shaped positive electrode, and may include a positive electrode current collector made of a metal thin plate with excellent conductivity, such as aluminum foil, and a positive electrode active material layer coated on one or both surfaces thereof. The negative electrode is a sheet-shaped negative electrode, and may include a negative electrode current collector made of a metal thin plate with excellent conductivity, such as copper (Cu) or nickel (Ni) foil, and a negative electrode active material layer coated on one or both surfaces thereof.

[0101] The above-mentioned positive electrode active material layer (22) may include a lithium metal oxide containing lithium and a transition metal such as cobalt, manganese, and / or nickel as a positive electrode active material, and may further include a conductive material and / or a binder as needed. The positive electrode active material, conductive material, and binder may be any of a variety of materials commonly used in the manufacture of secondary batteries without limitation.

[0102] Specifically, the positive electrode may include at least one selected from the group consisting of a lithium nickel-based composite oxide, a lithium manganese-based composite oxide, and a lithium iron phosphate-based composite oxide as a positive electrode active material, and preferably may include a lithium nickel-based composite oxide, and the lithium nickel-based composite oxide may be represented by the following chemical formula 1.

[0103] [Chemical Formula 1]

[0104] Li 1+x (Ni a Co b Mn c M d )O2

[0105] In the above chemical formula 1,

[0106] M is at least one selected from 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,

[0107] -0.4≤x≤0.4, 0.30≤a≤1, 0≤b≤0.70, 0≤c≤0.70, 0≤d≤0.10, a+b+c+d=1.

[0108] The above 1+x represents the molar ratio of lithium in the lithium nickel-based composite oxide, and may be -0.1≤x≤0.2, or 0≤x≤0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based composite oxide can be stably formed.

[0109] The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based composite oxide, and may be 0.70≤a<1, 0.80≤a<1, or 0.90≤a<1. When the molar ratio of nickel satisfies the above range, a high energy density is exhibited, enabling high capacity implementation.

[0110] The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel composite oxide, and is 0. <b≤0.25, 0<b≤0.15, 또는 0<b≤0.05일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0111] The above c represents the molar ratio of manganese among all metals excluding lithium in the lithium nickel composite oxide, and is 0. <c≤0.25, 0<c≤0.15, 또는 0<c≤0.05일 수 있다. 망간의 몰비가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타난다.

[0112] The above d represents the molar ratio of the M element among the total metal excluding lithium in the lithium nickel-based composite oxide, and the above d may be 0≤d≤0.08, 0≤d≤0.05, or 0≤d≤0.03.

[0113] Specifically, a, b, c and d of the above chemical formula 1 are 0.80≤a<1, 0, respectively. <b≤0.15, 0<c≤0.15, 0≤d≤0.05를 만족할 수 있다.

[0114] When the lithium nickel composite oxide is an NCM oxide containing all of nickel, cobalt, and manganese, the resistivity of the positive electrode is formed low, so the phenomenon of insulation deterioration due to an increase in the thickness of the electrode assembly described above becomes more evident, and thus the effect of configuring it to satisfy the above formula (1) can be maximized.

[0115] Meanwhile, the lithium manganese composite oxide is Li p Mn 1-qM a q A2, Li p Mn2O 4-r X r , Li p Mn 2-q M a q M b 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 It may be one or more selected from the group consisting of, wherein p, q, r and w are 0.9≤p≤1.6, 0≤q≤1, 0≤r≤1, 0≤w≤2, respectively, and M a Wow M bare the same or different and are at least one element 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 at least one element selected from the group consisting of O, F, S and P, and X is at least one element selected from the group consisting of F, S and P.

[0116] In addition, the lithium iron phosphate composite oxide can be represented by the following chemical formula 2.

[0117] [Chemical Formula 2]

[0118] LiFe 1-k M c k PO4

[0119] In the above chemical formula 2,

[0120] M c is at least one selected from Ni, Co, Mn, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir and V,

[0121] 0≤k<1.

[0122]

[0123] The above-described negative electrode active material layer (12) may include a negative electrode active material such as a carbonaceous material such as graphite; a metal or an alloy composed of the metal; an oxide of the metal; and a composite of the metal and carbon, and may further include a conductive material and / or a binder as needed. The negative electrode active material, conductive material, and binder may be various materials commonly used in the manufacture of secondary batteries without limitation.

[0124] Specifically, the negative electrode may include graphite as a negative electrode active material. When the negative electrode active material is graphite, the resistivity of the negative electrode is formed low, so the phenomenon of insulation deterioration due to an increase in the thickness of the electrode assembly described above becomes more evident, and thus the effect of configuring it to satisfy the above formula (1) can be maximized.

[0125]

[0126] The above separator may be a conventional porous polymer film used as a separator in the past, for example, a polyolefin-based porous polymer film such as an ethylene homopolymer, a propylene homopolymer, a copolymer of ethylene and butene, a copolymer of ethylene and hexene, and a copolymer of ethylene and methacrylate, etc., used alone or in a laminated manner. In addition, a polyolefin-based porous polymer film coated with inorganic particles (e.g., Al2O3) or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

[0127]

[0128] Meanwhile, as the electrolyte, any electrolyte capable of moving lithium ions generated by an electrochemical reaction at the electrode during charge and discharge can be used without limitation, and for example, a lithium salt dissolved in a non-aqueous organic solvent can be used.

[0129] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt may be appropriately changed within a generally usable range, but is preferably used within a range of 0.1 M to 5.0 M, and preferably 0.1 M to 3.0 M.

[0130] The above non-aqueous organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. For example, cyclic carbonate-based solvents such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate; linear carbonate-based organic solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and ethyl methyl carbonate (EMC); or mixed organic solvents thereof may be used.

[0131]

[0132] The above secondary battery can be applied to various devices. For example, it can be applied to electric vehicles such as electric bicycles, electric cars, and hybrid electric vehicles (HEVs).

[0133] Accordingly, according to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided.

[0134] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0135]

[0136] Hereinafter, the present invention will be described in more detail through specific examples.

[0137] [Examples and Comparative Examples: Manufacturing of Electrode Assemblies]

[0138] Example 1

[0139] Li[Ni as a cathode active material 0.8 Co 0.1 Mn 0.1 ]The anode containing O2 and A stacked electrode assembly having a total length of 600 mm, a total width of 100 mm, and a thickness of 13.7 mm was manufactured by alternately stacking negative electrodes containing graphite as a negative active material with a 17 μm thick safety reinforced separator (SRS) interposed therebetween.

[0140]

[0141] Examples 2 to 5 and Comparative Example 1

[0142] Stacked electrode assemblies of Examples 2 to 5 and Comparative Example 1 were manufactured using the same process as Example 1, except that stability-enhancing separators having thicknesses of 15 µm, 13 µm, 11 µm, 9 µm, and 7 µm were used instead of the 17 µm-thick stability-enhancing separator.

[0143]

[0144] Example 6

[0145] A stacked electrode assembly was manufactured using the same process as Example 1, except that the total length of the electrode assembly was changed to 350 mm.

[0146]

[0147] Examples 7 to 9 and Comparative Examples 2 to 3

[0148] Stacked electrode assemblies of Examples 7 to 9 and Comparative Examples 2 to 3 were manufactured using the same process as Example 6, except that stability-enhancing separators having thicknesses of 15 μm, 13 μm, 11 μm, 9 μm, and 7 μm were used instead of the stability-enhancing separator having a thickness of 17 μm.

[0149]

[0150] Example 10

[0151] A stacked electrode assembly was manufactured using the same process as Example 1, except that the total length of the electrode assembly was changed to 250 mm.

[0152]

[0153] Examples 11 to 13 and Comparative Examples 4 to 5

[0154] Stacked electrode assemblies of Examples 11 to 13 and Comparative Examples 4 to 5 were manufactured using the same process as Example 10, except that stability-enhancing separators having thicknesses of 15 µm, 13 µm, 11 µm, 9 µm, and 7 µm were used instead of the 17 µm-thick stability-enhancing separator.

[0155]

[0156] Example 14

[0157] A stacked electrode assembly was manufactured using the same process as Example 1, except that the total length of the electrode assembly was changed to 200 mm.

[0158]

[0159] Examples 15 to 16 and Comparative Examples 6 to 8

[0160] Stacked electrode assemblies of Examples 15 to 16 and Comparative Examples 6 to 8 were manufactured using the same process as Example 14, except that stability-enhancing separators having thicknesses of 15 μm, 13 μm, 11 μm, 9 μm, and 7 μm were used instead of the stability-enhancing separator having a thickness of 17 μm.

[0161]

[0162] Example 17

[0163] A stacked electrode assembly was manufactured using the same process as Example 1, except that the total length of the electrode assembly was changed to 100 mm.

[0164]

[0165] Examples 18 to 19 and Comparative Examples 9 to 11

[0166] Stacked electrode assemblies of Examples 18 to 19 and Comparative Examples 9 to 11 were manufactured using the same process as Example 17, except that stability-enhancing separators having thicknesses of 15 μm, 13 μm, 11 μm, 9 μm, and 7 μm were used instead of the stability-enhancing separator having a thickness of 17 μm.

[0167]

[0168] Comparative Example 12

[0169] Li[Ni as a cathode active material 0.8 Co 0.1 Mn 0.1 ]The anode containing O2 and A stacked electrode assembly having a total length of 250 mm, a total width of 100 mm, and a thickness of 5.7 mm was manufactured by alternately stacking negative electrodes containing graphite as a negative active material with a 17 μm thick safety reinforced separator (SRS) interposed therebetween.

[0170]

[0171] Comparative examples 13 to 17

[0172] Stacked electrode assemblies of Comparative Examples 13 to 17 were manufactured using the same process as Comparative Example 12, except that stability-enhancing separators having thicknesses of 15 µm, 13 µm, 11 µm, 9 µm, and 7 µm were used instead of the 17 µm-thick stability-enhancing separator.

[0173]

[0174] Comparative Example 18

[0175] Li[Ni as a cathode active material 0.8 Co 0.1 Mn 0.1 ]The anode containing O2 and A stacked electrode assembly having a total length of 100 mm, a total width of 100 mm, and a thickness of 5.7 mm was manufactured by alternately stacking negative electrodes containing graphite as a negative active material with a 17 ㎛ thick safety reinforced separator (SRS) in between.

[0176]

[0177] Comparative examples 19 to 23

[0178] Stacked electrode assemblies of Comparative Examples 19 to 23 were manufactured using the same process as Comparative Example 18, except that stability-enhancing separators having thicknesses of 15 µm, 13 µm, 11 µm, 9 µm, and 7 µm were used instead of the 17 µm-thick stability-enhancing separator.

[0179]

[0180] [Experimental Example]

[0181] Experimental Example 1: Insulation Evaluation

[0182] The electrode assemblies manufactured in Examples 1 to 19 and Comparative Examples 1 to 17 were evaluated for insulation properties using an AC / DC / IR Hipot tester (Model 19052, Chroma). Specifically, when a voltage of 50 V was applied for 10 seconds under DC conditions and the leakage current was measured, a value of 0.5 mA or less was PASS, and a value exceeding 0.5 mA was FAIL, as shown in Table 1 below.

[0183] Electrode assembly thickness (mm) Overall length (mm) Overall width (mm) Aspect ratio (A) Thickness of separator (㎛) (B) (A × B) + 6B Insulation evaluation Example 1 13.76 00 100 6 17 20 4 PASS Example 2 15 180 PASS Example 3 13 15 6 PASS Example 4 11 13 2 PASS Example 5 9 108 PASS Comparative Example 1 78 4 FAIL Example 6 13.73 50 100 3.5 17 16 1.5 PASS Example 7 15 14 2.5 PASS Example 8 13 12 3.5 PASS Example 9 11 10 4.5 PASS Comparative Example 2 98 5.5 FAIL Comparative Example 3 76 6.5 FAIL Example 1013.72501002.517144.5PASS Example 1115127.5PASS Example 1213110.5PASS Example 131193.5PASS Comparative Example 4976.5FAIL Comparative Example 5759.5FAIL Example 1413.7200100217136PASS Example 1515120PASS Example 1613104PASS Comparative Example 61188FAIL Comparative Example 7972FAIL Comparative Example 8756FAIL Example 1713.7100100117119PASS Example 1815105PASS Example 191391PASS Comparative Example 91177FAIL Comparative Example 10963FAILComparison Example 11749FAILComparison Example 125.72501002.517144.5PASSComparison Example 1315127.5PASSComparison Example 1413110.5PASSComparison Example 151193.5PASSComparison Example 16976.5PASSComparison Example 17759.5PASSComparison Example 185.7100100117119PASSComparison Example 1915105PASSComparison Example 201391PASSComparison Example 211177PASSComparison Example 22963PASSComparison Example 23749FAIL

[0184]

[0185] Through the results in Table 1 above, it can be confirmed that, for a thick cell having a thickness of 13.7 mm, the electrode assemblies of Examples 1 to 19 that satisfy Equation (1) have superior insulation properties compared to the electrode assemblies of Comparative Examples 1 to 11 that do not satisfy Equation (1).

[0186] Meanwhile, in the case of thin cells having a thickness of 5.7 mm manufactured in Comparative Examples 12 to 23, it can be confirmed that whether or not the above equation (1) is satisfied does not represent the insulation.

[0187] That is, it can be confirmed that the above equation (1) is valid as an indicator for predicting insulation only in thick cells having a thickness of 10 mm or more.

[0188] Meanwhile, by comparing the insulation evaluation results of Comparative Example 17 and Comparative Example 23, it can be confirmed that, in the case of a thin cell with a thickness of less than 10 mm, the insulation properties can be improved simply by increasing the aspect ratio without adjusting the thickness of the separator.

[0189]

[0190] Experimental Example 2: Performance Evaluation

[0191] A pouch was prepared by sequentially laminating nylon / polyethylene terephthalate / Al alloy thin film / polypropylene and molding a cup portion. After the electrode assemblies manufactured in Examples 10 to 13 and Comparative Examples 12 to 17 were accommodated in the cup portion, an electrolyte solution manufactured by dissolving 1.0 M LiPF6 in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 was injected, followed by sealing and performing an activation process to manufacture a pouch-type secondary battery. The final thickness of the secondary batteries with the electrode assemblies of Examples 10 to 13 embedded therein was 14.2 mm, and the final thickness of the secondary batteries with the electrode assemblies of Comparative Examples 12 to 17 embedded therein was 6.1 mm.

[0192] The manufactured secondary battery was charged to 4.2 V at room temperature with a constant current of 0.33 C, then discharged to 2.5 V with a constant current of 0.33 C to check the initial capacity. Then, it was charged again with a constant current of 0.33 C to 30% of the SOC, and the AC resistance was measured. The results are shown in Table 2 below.

[0193] Cell thickness (mm) Total length (mm) Total width (mm) Aspect ratio Thickness of membrane (㎛) Initial capacity (0.33C, mAh) AC resistance (1KHz, mOhm) Example 10 14.2 250 100 2.5 17.5 8.5 0.77 Example 11 15 59.5 0.75 Example 12 13 60.5 0.73 Example 13 116 1.5 0.71 Comparative example 126.1 250 100 2.5 17.24 51.87 Comparative example 13 15 25.5 1.85 Comparative example 14 13 26.5 1.83 Comparative example 15 1127.5 1.81 Comparative example 16 9 28.5 1.79 Comparative example 17 7 29.5 1.77

[0194]

[0195] Through the results in Table 2 above, it can be confirmed that a cell including a thick electrode assembly having a thickness of 13.7 mm has a higher capacity and lower resistance than a cell including a thin electrode assembly having a thickness of 5.7 mm.

Claims

1. It includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, Satisfies the following equation (1), Electrode assembly with a thickness of 10 mm or more: Equation (1): (A × B) + 6B ≥ 90 In the above equation (1), A is the ratio of the electric field to the overall width of the electrode assembly, B is the thickness value of the above membrane measured in μm.

2. In claim 1, An electrode assembly, wherein A in the above formula (1) is 5 or more and B is 8 to 40.

3. In claim 1, An electrode assembly wherein A in the above formula (1) is 2.5 or more and less than 5, and B is 10 to 45.

4. In claim 1, An electrode assembly, wherein A in the above formula (1) is 1 or more and less than 2.5, and B is 12 to 50.

5. In claim 1, An electrode assembly, wherein a leakage current measured after applying a voltage of 50 V to the electrode assembly for 10 seconds is 0.5 mA or less.

6. In claim 1, An electrode assembly, wherein the positive electrode comprises at least one selected from the group consisting of a lithium nickel-based composite oxide, a lithium manganese-based composite oxide, and a lithium iron phosphate-based composite oxide as a positive electrode active material.

7. In claim 1, The above positive electrode includes a lithium nickel-based composite oxide as a positive electrode active material, The above lithium nickel-based composite oxide is an electrode assembly represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x (Ni a Co b Mr c M d )O2 In the above chemical formula 1, M is at least one selected from 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, -0.4≤x≤0.4, 0.30≤a≤1, 0≤b≤0.70, 0≤c≤0.70, 0≤d≤0.10, a+b+c+d=1.

8. In claim 1, The electrode assembly is a stacked electrode assembly.

9. Electrode assembly according to claim 1; electrolyte; and A secondary battery comprising a battery case that accommodates the electrode assembly and electrolyte.

10. In claim 9, the battery case includes a barrier layer, a substrate layer formed on one surface of the barrier layer, and a sealant layer formed on the other surface of the barrier layer. A pouch comprising at least one cup portion that is curved in one direction, A secondary battery, wherein an electrode assembly and an electrolyte are accommodated in at least one of the cup portions.

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