Secondary battery

Abstract

To provide a secondary battery capable of suppressing separation of an electrode assembly and / or leakage of an electrolyte even when subjected to external impact or mechanical stress.SOLUTION: A secondary battery having excellent impact resistance is provided. The secondary battery includes a battery case comprising: an electrode assembly; an electrolyte; and an accommodation to accommodate the electrode assembly and the electrolyte. The secondary battery satisfies the formula (1): W / S≤42(g / Ah) m-2. In the formula (1), W is an amount of electrolyte per unit capacity of the secondary battery [unit: g / Ah], and S is a product of a total length [unit: m] and a full width [unit: m] of the electrode assembly.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, and more particularly to a secondary battery having excellent impact resistance. [Background technology]

[0002] In general, secondary batteries are manufactured by coating a positive electrode active material slurry on a positive electrode current collector and a negative electrode current collector to form a positive electrode and a negative electrode, laminating them on both sides of a separator to form an electrode assembly of a predetermined shape, and then placing the electrode assembly in a pouch and injecting an electrolyte solution.

[0003] Secondary batteries are classified into pouch-type and can-type batteries depending on the material of the case that houses the electrode assembly. Pouch-type secondary batteries are manufactured by pressing a flexible pouch film laminate to form a cup, placing an electrode assembly in the cup, injecting electrolyte, and then sealing the seal. Can-type secondary batteries are manufactured by placing an electrode assembly in a metal can, injecting electrolyte, and then assembling a top cap to seal the can.

[0004] Pouch-type secondary batteries have the advantages of being light in weight, having excellent space utilization, and being able to achieve high energy density using a stacked electrode assembly, but have the disadvantage of being more vulnerable to external impacts than can-type secondary batteries.

[0005] In recent years, as the environments in which secondary batteries are used have become more diverse, there has been a demand for secondary batteries to have excellent durability and safety even in harsh environments, and this has led to a demand for improved impact resistance of secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention is made to solve the above-mentioned problems, and relates to a secondary battery in which the size of the electrode assembly and the amount of electrolyte per unit capacity satisfy specific conditions, thereby increasing the frictional force between the electrode assembly and the battery case (e.g., pouch), thereby preventing detachment of the electrode assembly and / or leakage of electrolyte even when subjected to external impact or mechanical stress. [Means for solving the problem]

[0007] According to one embodiment, the present invention provides a secondary battery including an electrode assembly, an electrolyte, and a battery case including a storage portion for storing the electrode assembly and the electrolyte, wherein the secondary battery satisfies the following formula (1):

[0008] Formula (1): W / S≦42 In the formula (1), W is the weight of the electrolyte per unit capacity of the secondary battery [unit: g / Ah], and S is the product of the total length [unit: m] and the total width [unit: m] of the electrode assembly.

[0009] The secondary battery disclosed herein may include any, some, or all of the features described below. The secondary battery may be a pouch-type battery, a cylindrical battery, a prismatic battery, or the like. As a specific example, the secondary battery may be a pouch-type battery.

[0010] Unless otherwise specified, the capacity of a secondary battery refers to the rated capacity of the secondary battery. The secondary battery can have a rated capacity of 50 Ah to 200 Ah, preferably 50 Ah to 150 Ah, and more preferably 60 Ah to 140 Ah. The "rated capacity of a secondary battery" refers to the electrical capacity exhibited when a fully charged battery is continuously discharged at 0.33 C and reaches the discharge cut-off voltage. In this case, the full charge voltage (charge cut-off voltage) and discharge cut-off voltage can be appropriately selected depending on the type of secondary battery. For example, if the secondary battery is an NCM cell, the rated capacity may be the discharge capacity when the secondary battery is charged to 4.25 V and then discharged to 2.5 V at 0.33 C. The "unit capacity" refers to 1 Ah. The W has a unit of g / Ah, and the S has a unit of m 2 and W / S is (g / Ah) m -2 It can have units of

[0011] The W may be 2.2 g / Ah or less, preferably 1.5 to 2.2 g / Ah, more preferably 1.7 to 2.2 g / Ah, and the S may be 0.01 m 2 ~0.2m 2 , 0.02m 2 ~0.09m 2 , preferably 0.03 m 2 ~0.08m 2 , more preferably 0.03 m 2 ~0.75m 2 may be.

[0012] Here, the weight of the electrolyte in the secondary battery refers to the amount of electrolyte remaining in the secondary battery after the activation process, and therefore the total weight of the electrolyte may refer to the total weight of the electrolyte present after the secondary battery is manufactured or during operation.

[0013] W / S (unit: (g / Ah) m -2 ) is, for example, 0.1(g / Ah) m -2 ~42(g / Ah)·m -2 , 1(g / Ah)·m -2 ~42(g / Ah)·m -2 , 5(g / Ah)·m -2 ~42(g / Ah)·m -2 , 10(g / Ah)·m -2 ~42(g / Ah)·m -2 , or 20(g / Ah)·m -2 ~42(g / Ah)·m -2 However, the W / S (unit: (g / Ah) m -2 ) is preferably 30 (g / Ah) m -2 ~42(g / Ah)·m -2 , more preferably 35(g / Ah)·m -2 ~42(g / Ah)·m -2 may be.

[0014] The secondary battery can be manufactured by preparing an electrode active material slurry, applying it to a positive electrode current collector and a negative electrode current collector to obtain a positive electrode and a negative electrode, stacking at least one layer of the positive electrode and at least one layer of the negative electrode with a separator interposed between the positive electrode layer and the negative electrode layer to obtain an electrode assembly, and then placing the electrode assembly in a battery case such as a pouch, a cylindrical can, or a prismatic can, and adding an electrolyte to the electrode assembly.

[0015] A pouch-type secondary battery can be manufactured by pressing a pouch film laminate to form a cup portion having a shape and dimensions suitable for accommodating an electrode assembly, placing the electrode assembly in the cup portion, adding an electrolyte solution, and sealing the pouch film laminate along the seal portion. A can-type secondary battery can be manufactured by accommodating an electrode assembly in a metal can, injecting an electrolyte solution into the can, and sealing the can by fitting a cap over the opening of the can. As described above, the can can have a cylindrical shape or a polygonal shape such as a rectangle, a rectangular parallelepiped, or a diamond.

[0016] The electrolyte of the secondary battery will be described later. The electrode assembly of the secondary battery will be described later. The battery case of the secondary battery may be a pouch, and the pouch may be used as a concept commonly understood in the field of secondary battery design and manufacturing. Alternatively, the battery case of the secondary battery may be a can as described herein. At least a portion of the electrolyte may be provided between the electrode assembly and the inner surface of the battery case facing the electrode assembly.

[0017] In particular, in a pouch-type secondary battery, the electrode assembly may have a rectangular shape extending in the length direction when viewed in a plan view. In this specification, the term "total length" refers to the length measured in the length direction unless otherwise specified. The width direction of the electrode assembly refers to a direction perpendicular to the length direction and is disposed on the plane of at least one layer of the positive electrode, negative electrode, and separator. In this specification, the term "total width" refers to a value measured in the width direction unless otherwise specified. In the electrode assembly, the positive electrode layer, negative electrode layer, and separator may be stacked in a thickness direction perpendicular to both the length direction and the width direction. Here, a plan view may refer to a viewing direction parallel to the thickness direction of the electrode assembly.

[0018] In the case of a can-type secondary battery, the electrode assembly may be wound around a winding axis parallel to the length or width direction. Therefore, the other direction, either the length or width direction, that is not parallel to the winding axis may be parallel to the circumferential direction of the electrode assembly. In the case of a can-type secondary battery, the total length refers to the length of the electrode assembly in the direction of the winding axis when wound, and the total width refers to the length of the electrode assembly in the direction perpendicular to the winding axis when wound.

[0019] The battery case may be a pouch that can be provided in any manner disclosed herein. Specifically, the pouch may be formed by pressing at least one cup portion into a pouch film laminate. As a result, the cup portion may be formed as a flat portion protruding outward from the remainder of the pouch film laminate. The cup portion may have a tray-like shape. The cup portion may include a flat main surface surrounded by one or more side walls that are integral with the remainder of the pouch film laminate. The flat main surface of the cup portion may have a basic planar rectangular shape, but the corners may be rounded depending on processing requirements and design. The pouch may have any, some, or all of the features of the pouches described herein, unless otherwise specified or technically inappropriate.

[0020] According to one embodiment, the battery case may be a pouch made of a pouch film laminate. The pouch, specifically the pouch film laminate, may include a barrier layer, a substrate layer, and a sealant layer. The substrate layer may be disposed on one side of the barrier layer, and the sealant layer may be disposed on the other side of the barrier layer (i.e., the opposite side of the substrate layer). In some examples, the substrate layer, the barrier layer, and the sealant layer may form a pouch film laminate, specifically a laminated structure. The pouch, specifically the pouch film laminate, may be press-formed (e.g., stretch-formed and / or drawn) to form at least one cup portion protruding outward from the remainder of the pouch or the remainder of the pouch film laminate. The electrode assembly may be accommodated in the one or more cup portions. The at least one cup portion may have a shape and dimensions for accommodating the electrode assembly. Unless otherwise specified or technically inappropriate, the components of the pouch may implement any, some, or all of the features disclosed herein. Specifically, any one of the substrate layer, barrier layer, and sealant layer may be implemented as specifically described below.

[0021] The secondary battery may have a rated capacity of 50 Ah to 200 Ah, preferably 50 Ah to 150 Ah, and more preferably 60 Ah to 140 Ah. The electrode assembly may have a substantially rectangular shape in plan view, and the ratio of the total length to the total width of the electrode assembly may be 2.5 to 20, 3 to 15, 5 to 10, or 5 to 8. When the ratio of the total length to the total width of the electrode assembly satisfies the above specific range, it can further contribute to increasing the frictional force without increasing the amount of electrolyte.

[0022] Specifically, the electrode assembly may have a total length of 200 mm to 800 mm and a total width of 40 mm to 200 mm. The electrode assembly may preferably have a total length of 400 mm to 600 mm and a total width of 50 to 150 mm, and more preferably have a total length of 500 mm to 600 mm and a total width of 50 to 100 mm. When the total width and total length of the electrode assembly satisfy the above specific ranges, this can further contribute to increasing the frictional force without increasing the amount of electrolyte. Here, the total length and total width may refer to the maximum lengths of the electrode assembly in the lengthwise and widthwise directions, respectively, on a plane.

[0023] Meanwhile, the weight of the electrode assembly may be 500 g to 1500 g, preferably 550 g to 1450 g, and more preferably 600 g to 1400 g. When the weight of the electrode assembly satisfies the above range, a high capacity can be achieved, and the frictional force between the electrode assembly and the inner surface of the battery case is increased, resulting in excellent impact resistance.

[0024] Meanwhile, the secondary battery according to the present invention may further include at least one fixing member that wraps around the outer surface of the electrode assembly in a width direction to fix the electrode assembly. In this case, the contact area between the fixing member and the electrode assembly may be 30% or less, 0-30%, 1-30%, 5-30%, 5-25%, or 5-20% of the total surface area of ​​the electrode assembly. Because the fixing member is generally made of a material with a low friction coefficient, increasing the area of ​​the fixing member may reduce the frictional force between the electrode assembly and the inner surface of the battery case. Therefore, when using a fixing member, it is preferable to limit the contact area between the electrode assemblies to 30% or less to prevent a decrease in frictional force. Meanwhile, the battery case may be a pouch-type case. The pouch-type case may include a barrier layer, a substrate layer formed on one side of the barrier layer, and a sealant layer formed on the other side of the barrier layer, and may include at least one cup-shaped portion recessed in one direction. The electrode assembly and the electrolyte may be accommodated in the cup-shaped portion of the pouch.

[0025] On the other hand, the friction force between the electrode assembly and the inner surface of the battery case may be 15 kgf or more, preferably 15 kgf to 40 kgf, and more preferably 17 kgf to 35 kgf.

[0026] The frictional force between the electrode assembly and the inner surface of the battery case can be measured as follows: A portion of the battery case is cut open, the positive electrode tab is held with a jig connected to a wire, and the wire is connected to a universal testing machine (UTM). The force applied while pulling at a constant speed, for example, 100 mm / min, is measured and evaluated as the frictional force between the electrode assembly and the inner surface of the battery case.

[0027] The secondary battery may have zero electrolyte leakage when subjected to a crash shock test under crash conditions of 133.7 G x 15.8 ms. The crash shock test is performed under crash conditions of 133.7 G x 15.8 ms, and after the crash shock test, the weight of electrolyte leaked to the outside of the battery case and the degree of play of the electrode assembly inside and outside the battery case are inspected.

[0028] According to one embodiment, the electrode assembly may have a total length of 0.2 m to 0.8 m, a total width of 0.05 m to 0.15 m, and a weight of electrolyte per unit capacity of 1.0 to 2.8 g / Ah. In this case, W / S is 30 (g / Ah) m -2 ~42(g / Ah)·m -2 According to another embodiment, the electrode assembly may have a total length of 0.3 m to 0.8 m, a total width of 0.06 m to 0.12 m, and a weight of electrolyte per unit capacity of 1.2 to 2.5 g / Ah. In this case, W / S is 30 (g / Ah) m -2 ~42(g / Ah)·m -2 may be.

[0029] According to another embodiment, the electrode assembly may have a total length of 0.4 m to 0.6 m, a total width of 0.07 m to 0.11 m, and a weight of electrolyte per unit capacity of 1.5 to 2.4 g / Ah. In this case, W / S is 30 (g / Ah) m -2~42(g / Ah)·m -2 may be.

[0030] In another aspect, the present invention provides a secondary battery including an electrode assembly, an electrolyte, and a battery case. 2 The battery case may have a surface area of ​​1000 μm or less, and a total weight of the electrolyte may be 440 g or less. The battery case may contain an electrode assembly and an electrolyte. The electrode assembly, the electrolyte, and the battery case may be configured so that the friction force between the electrode assembly and the inner surface of the battery case is 15 kgf or more.

[0031] Specifically, when the electrode assembly has a rectangular shape, the surface area of ​​the electrode assembly may be the product of the total length and the total width. 2 ~0.08m 2 , 0.03m 2 ~0.07m 2 , or 0.04m 2 ~0.06m 2 may be. [Effects of the Invention]

[0032] When the size of the electrode assembly and the amount of electrolyte per unit capacity meet certain conditions, as in the case of the secondary battery according to the present invention, the frictional force between the electrode assembly and the battery case is significantly increased compared to conventional batteries, thereby suppressing detachment of the electrode assembly and / or leakage of electrolyte upon external impact, thereby achieving excellent impact resistance. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram illustrating the configuration of a pouch according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0034] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0035] The present invention will be described in more detail below. In recent years, 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 trend toward an increase in the size and weight of electrode assemblies. However, as the size and weight of electrode assemblies increase, the electrode assemblies are more likely to move and damage or puncture the battery case when subjected to external impact. This problem is particularly severe in pouch-type batteries, which have battery cases with low rigidity. Damage to the battery case can lead to electrolyte leakage or deformation of the electrode assembly, resulting in serious problems with the performance and safety of the battery.

[0036] Meanwhile, residual electrolyte remaining after impregnation in the electrode assembly may remain on the surface of the electrode assembly and the inner surface of the battery case. However, due to the wettability of the electrolyte, if the electrolyte is present on the inner surface of the battery case and the surface of the electrode assembly, the frictional force between the electrode assembly and the inner surface of the battery case is reduced, thereby exacerbating the movement of the electrode assembly upon external impact. If the total amount of electrolyte in the secondary battery increases, the amount of electrolyte remaining on the electrode assembly and the inner surface of the battery case also increases, further reducing the frictional force. Therefore, while a smaller amount of electrolyte in the secondary battery is preferable in terms of impact resistance, an excessively small amount of electrolyte can adversely affect the capacity of the secondary battery and reduce the operability and lifespan of the secondary battery.

[0037] The inventors conducted extensive research to develop a secondary battery that has excellent electrochemical performance and impact resistance. As a result, they discovered that when the cross-sectional area of ​​the electrode assembly, the content of the electrolyte, and the capacity of the secondary battery meet certain conditions, the frictional force between the electrode assembly and the battery case is significantly increased compared to conventional methods. As a result, damage to the battery case due to separation of the electrode assembly upon external impact is suppressed, achieving excellent impact resistance and minimizing deterioration of electrochemical properties, which led to the completion of the present invention.

[0038] The secondary battery according to the present invention includes an electrode assembly, an electrolyte, and a battery case including a storage portion for storing the electrode assembly and the electrolyte, and is characterized by satisfying the following formula (1):

[0039] Formula (1): W / S≦42 The unit of W / S in the above formula (1) is (g / Ah) m -2 The W (unit: g / Ah) is the weight of the electrolyte per unit capacity of the secondary battery, and can be measured by dividing the total weight (unit: g) of the electrolyte in the secondary battery by the rated capacity (unit: Ah) of the secondary battery. Meanwhile, the total weight of the electrolyte in the secondary battery refers to the total weight of the electrolyte remaining in the secondary battery after the activation process.

[0040] Preferably, the W / S (unit: (g / Ah) m -2 ) is 42(g / Ah)·m -2 Below, 0.1(g / Ah) m -2 ~42(g / Ah)·m -2 , 1(g / Ah)·m -2 ~42(g / Ah)·m -2 , 5(g / Ah)·m -2 ~42(g / Ah)·m -2 , 10(g / Ah)·m -2 ~42(g / Ah)·m -2 , or 20(g / Ah)·m -2 ~42(g / Ah)·m -2 However, it is not limited to this. Preferably, the W / S (unit: (g / Ah) m -2 ) is 30(g / Ah)·m-2 ~42(g / Ah)·m -2 , more preferably 35(g / Ah)·m -2 ~42(g / Ah)·m -2 W / S may be 42(g / Ah) m -2 If the frictional force between the electrode assembly and the inner surface of the battery case (e.g., the bottom surface of the cup part of the pouch) that contacts the electrode assembly is significantly increased, thereby minimizing detachment of the electrode assembly when an external impact is applied, and minimizing electrolyte leakage due to damage to the battery case.

[0041] Meanwhile, W may vary depending on the size of the electrode assembly, but may be, for example, 2.2 g / Ah or less, preferably 1.5 g / Ah to 2.2 g / Ah, and more preferably 1.7 g / Ah to 2.2 g / Ah. If W is too large, the effect of increasing the frictional force between the electrode assembly and the inner surface of the battery case may be negligible, and if it is too small, there may be insufficient electrolyte during battery operation, resulting in reduced battery performance.

[0042] Meanwhile, S is the cross-sectional area of ​​the electrode assembly, which is the product of the total length and the total width of the electrode assembly, where the total length and the total width are measured in meters.

[0043] The S is, for example, 0.02 to 0.09 m 2 , preferably 0.03 to 0.08 m 2 , more preferably 0.03 to 0.75 m 2 If S is too small, the battery capacity decreases and the effect of increasing the frictional force between the electrode assembly and the battery case is negligible, whereas if S is too large, there is a problem that the risk of an accident occurring when a stability problem occurs is greater.

[0044] The secondary battery may have a rated capacity of 50 Ah to 200 Ah, preferably 50 Ah to 150 Ah, and more preferably 60 Ah to 140 Ah. When the rated capacity of the secondary battery satisfies the above range, a high-capacity secondary battery can be realized.

[0045] Meanwhile, the secondary battery according to the present invention may be a pouch-type secondary battery. In this case, the battery case may be a pouch including, for example, a barrier layer, a substrate layer formed on one side of the barrier layer, and a sealant layer formed on the other side of the barrier layer, and including at least one cup-shaped portion concave in one direction, and the electrode assembly and the electrolyte may be accommodated in the cup-shaped portion of the pouch.

[0046] On the other hand, when the condition of the formula (1) is satisfied, the frictional force between the electrode assembly and the inner surface of the battery case (e.g., the bottom surface of the cup portion of the pouch) is high, such as 15 kgf or more, preferably 15 kgf to 40 kgf, and more preferably 17 kgf to 35 kgf, and the electrode assembly is less likely to come off due to an external impact, minimizing damage to the pouch, thereby exhibiting excellent impact resistance.

[0047] At this time, the frictional force between the electrode assembly and the inner surface of the battery case can be measured by the following method. First, a portion of the battery case is cut open, the positive electrode tab is held with a jig connected to a wire, and the wire is connected to a universal testing machine (UTM). The wire is then pulled at a constant speed, for example, 100 mm / min, and the applied force is measured, which can be evaluated as the friction force between the electrode assembly and the inner surface of the battery case.

[0048] Meanwhile, the secondary battery according to the present invention has excellent impact resistance because the high friction between the electrode assembly and the battery case minimizes separation of the electrode assembly upon external impact. For example, the secondary battery according to the present invention does not leak electrolyte when subjected to a crash shock test under crash conditions of 133.7G x 15.8ms. That is, the secondary battery according to the present invention exhibits zero electrolyte leakage after a crash shock test under crash conditions of 133.7G x 15.8ms.

[0049] The crash shock test can be performed by attaching a test battery to a jig of a drop shock device, allowing the battery to free-fall from a specific height, and then determining whether the battery is damaged. The free-fall height is determined by taking into account the crash conditions to be measured (acceleration x duration). Specifically, the impact energy under the crash conditions to be measured is converted into potential energy, and the height at which the converted potential energy can be achieved is calculated, taking into account the weight of the test battery, to determine the free-fall height. Meanwhile, whether the battery is damaged can be evaluated by checking whether electrolyte leakage is present.

[0050] Fig. 1 is an exploded perspective view of a pouch-type secondary battery which is one embodiment of the secondary battery according to the present invention, and Fig. 2 is a view showing a cross section of a pouch film laminate. Hereinafter, a secondary battery according to one embodiment of the present invention will be described in more detail with reference to the drawings.

[0051] Pouch The pouch 100 is a battery case for accommodating an electrode assembly and an electrolyte, and includes a barrier layer 20, a substrate layer 10 formed on one side of the barrier layer, and a sealant layer 30 formed on the other side of the barrier layer, and includes at least one cup portion (accommodation portion) that is concave in one direction.

[0052] Specifically, the pouch 100 can be manufactured by inserting a flexible pouch film laminate, in which a base 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 that is concave in one direction.

[0053] Base material layer The base layer 10 is disposed on the outermost layer of the pouch, and serves to protect the electrode assembly from external impacts and to provide electrical insulation.

[0054] The substrate layer 10 may be made of a polymer material, for example, 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 (registered trademark).

[0055] The base layer 10 may have a single layer structure, or may have a multilayer structure in which different polymer films 12 and 14 are laminated as shown in Figure 2. When the base layer 10 has a multilayer structure, an adhesive layer 16a may be interposed between the polymer films.

[0056] 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 thickness of the adhesive layer. When the substrate layer 10 satisfies the above range, it exhibits excellent durability, insulating properties, and formability. If the thickness of the substrate layer is too thin, durability may be poor and the substrate layer may be damaged during the forming process. If the thickness of the substrate layer is too thick, formability may be reduced, the total thickness of the pouch may increase, the battery storage space may be reduced, and the energy density may be reduced.

[0057] According to one embodiment, the base layer 10 may have 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., the inner side, and the polyethylene terephthalate film is disposed on the outer surface side of the pouch.

[0058] 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. Because PET film has weak adhesion to the aluminum alloy thin film that constitutes the barrier layer 20 and has a different stretching behavior, placing a PET film on the barrier layer side can cause peeling between the substrate layer and the barrier layer during the molding process, resulting in uneven stretching of the barrier layer and reduced formability. In contrast, because nylon film has a similar stretching behavior to the aluminum alloy thin film that constitutes the barrier layer 20, placing a nylon film between the polyethylene terephthalate and the barrier layer can improve formability.

[0059] The 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 nylon film may have a thickness of 10 μm to 40 μm, preferably 10 μm to 35 μm, and more preferably 15 μm to 25 μm. When the thicknesses of the polyethylene terephthalate film and the nylon film satisfy the above ranges, they exhibit excellent formability and rigidity after forming.

[0060] Barrier layer The barrier layer 20 is intended to ensure the mechanical strength of the pouch 100, to block the entry and exit of gas or moisture outside the secondary battery, and to prevent leakage of the electrolyte.

[0061] 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 thickness of the barrier layer satisfies the above range, moldability is improved, the molding depth of the cup portion is increased, or cracks and / or pinholes are reduced during two-cup molding, and resistance to external stress after molding is improved.

[0062] On the other hand, the barrier layer 20 may be made of a metal material, specifically, an aluminum alloy thin film. The aluminum alloy thin film may contain aluminum and one or more metal elements other than aluminum, such as iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0063] Preferably, the aluminum alloy thin film has an iron (Fe) content of 1.2 wt% to 1.7 wt%, preferably 1.3 wt% to 1.7 wt%, more preferably 1.3 wt% to 1.45 wt%. When the iron (Fe) content in the aluminum alloy thin film satisfies the above range, it is possible to minimize the occurrence of cracks and pinholes even when the cup portion is formed deep.

[0064] Sealant layer The sealant layer 30 is bonded by thermocompression to seal the pouch, and is located as the innermost layer of the pouch film laminate.

[0065] The sealant layer 30 is the surface that comes into contact with the electrolyte and the electrode assembly after the pouch is formed, so it must have insulating and corrosion resistance. It must also have high sealing properties because it must completely seal the interior and prevent material transfer between the inside and outside.

[0066] The sealant layer 30 may be made of a polymer material, for example, one or more 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 (registered trademark). Among these, it is particularly preferable to use polypropylene (PP), which has excellent mechanical properties such as tensile strength, rigidity, surface hardness, abrasion resistance, and heat resistance, and excellent chemical properties such as corrosion resistance.

[0067] More specifically, the sealant layer 30 may include polypropylene, cast polypropylene (CPP), acid modified polypropylene, polypropylene-butylene-ethylene copolymer, or a combination thereof.

[0068] The sealant layer 30 may be a single layer structure or a multi-layer structure including two or more layers made of different polymeric materials. 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 sealant layer is too thin, the seal durability and insulation properties may be poor, and if it is too thick, the bendability may be poor, the total thickness of the pouch film laminate may increase, and the energy density per volume may decrease.

[0069] The pouch film laminate can be manufactured by a method known in the art for manufacturing a pouch film laminate, for example, by attaching 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 with coextrusion or an adhesive, but is not limited thereto.

[0070] The pouch film laminate described above is inserted into a molding device, and pressure is applied to a portion of the pouch film laminate with a punch to form a cup portion, thereby producing a pouch 100. In this case, the pressure may be about 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 the formation of the cup portion, excessive drawing may occur, resulting in wrinkles, whereas if the pressure is too high, insufficient drawing may occur, resulting in a reduced molding depth.

[0071] Meanwhile, the moving 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 molding is too low or the moving speed of the punch is too fast, wrinkles may occur due to buckling, and if the pressure during molding is too high or the moving speed of the punch is too slow, stress may concentrate on the corners of the cup portion during molding, which may increase the occurrence of pinholes and cracks.

[0072] The pouch 100 of the present invention manufactured by the above-mentioned method includes a lower case 101, an upper case 102, and a folding portion 130 connecting the lower case and the upper case and / or the lower case includes a cup portion 110 that is concave in one direction.

[0073] Specifically, the pouch 100 according to the present invention may be a one-cup type in which a cup portion 110 is formed only in the lower case 101, as shown in Fig. 1, but is not limited thereto and may be a two-cup type in which cup portions are formed in both the upper and lower cases. In the case of a two-cup type pouch, after accommodating the electrode assembly and electrolyte, the upper case is folded so that the cup portion of the upper case and the cup portion of the lower case face each other, so that a thicker electrode assembly can be accommodated than in a one-cup type pouch, which is advantageous in achieving a high energy density.

[0074] The cup part 110 has an accommodating space for accommodating the electrode assembly 200. Meanwhile, the pouch 100 may include a terrace 120 around the periphery of the cup part 110. The terrace 120 refers to an unformed portion of the pouch film laminate, i.e., the remaining area excluding the cup part 110. The terrace 120 is a portion that is sealed by thermal bonding in a sealing process after the electrode assembly 200 is accommodated in the cup part 110 and an electrolyte is injected.

[0075] The cup portion 110 may include a bottom surface and a peripheral surface. The peripheral surface may connect the bottom surface to the terrace 120. A plurality of peripheral surfaces, more specifically, four peripheral surfaces, may be provided. The bottom surface may cover one side of the electrode assembly 200, and the peripheral surface may surround the electrode assembly 200.

[0076] Meanwhile, the folding unit 130 connects the lower case 101 and the upper case 102, stores the electrode assembly 200 in the cup unit 110, and is folded after the electrolyte is injected, thereby allowing the upper case 102 to seal the cup unit 110 of the lower case 101. When the folding unit 130 is included, the lower case 101 and the upper case 102 are connected integrally, which reduces the number of sides to be sealed in a subsequent sealing process, thereby improving processability.

[0077] The 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, and 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 total volume of the secondary battery may increase and the energy density per volume may decrease. In the case of a two-cup case, the folding portion may be formed to satisfy the above-mentioned distance from each cup portion.

[0078] electrode assembly The electrode assembly 200 may include a plurality of electrodes and a plurality of separators stacked alternately. The plurality of electrodes may include positive and negative electrodes having opposite polarities, stacked alternately with separators interposed therebetween.

[0079] In addition, 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 a plurality of electrodes, protrude from the electrode assembly 200 to the outside, and act as a path through which electrons can move between the inside and outside of the electrode assembly 200. The plurality of electrode tabs 230 may be located inside the pouch 100.

[0080] The electrode tab 230 connected to the positive electrode and the electrode tab 230 connected to the negative electrode may protrude in different directions from each other with respect to the electrode assembly 200. However, without being limited thereto, the electrode tab 230 connected to the positive electrode and the electrode tab 230 connected to the negative electrode may be arranged side by side and protrude in the same direction.

[0081] A lead 240 for supplying electricity to the outside of the secondary battery may be connected to the plurality of electrode tabs 230 by spot welding, etc. One end of the lead 240 may be connected to the plurality of electrode tabs 230, and the other end may protrude outside the pouch 100.

[0082] A portion of the lead 240 may be surrounded by the insulating portion 250. For example, the insulating portion 250 may include 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 heat-sealed to each other. In this case, portions of the terrace 120 and the second case 102 may be heat-sealed to the insulating portion 250. Therefore, the insulating portion 250 prevents electricity generated from the electrode assembly 200 from flowing to the pouch 100 via the lead 240, thereby maintaining the seal of the pouch 100.

[0083] Meanwhile, in the present invention, the electrode assembly 200 may have a ratio of the total length to the total width of 5 to 10, preferably 5 to 8. When the ratio of the total length to the total width satisfies the above range, a high energy density can be achieved in a limited space.

[0084] For example, the electrode assembly may have a total length of 400 mm to 600 mm and a total width of 50 to 150 mm, and preferably a total length of 500 mm to 600 mm and a total width of 50 to 100 mm.

[0085] Meanwhile, although not limited thereto, the weight of the electrode assembly may be 500 g to 1500 g, preferably 550 g to 1450 g, and more preferably 600 g to 1400 g. When the weight of the electrode assembly satisfies the above range, a high capacity can be achieved, and the frictional force between the electrode assembly and the inner surface of the battery case is increased, resulting in excellent impact resistance.

[0086] 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 a rectangular electrode assembly whose overall length is longer than its overall width (for convenience, referred to as a "long cell"), a fixing member may be used to wrap and fix the electrode assembly in the overall width direction to prevent misalignment of the components of the electrode assembly, i.e., the positive electrode, the negative electrode, and the separator.

[0087] The fixing member may have a porous structure. When the fixing member has a porous structure, the electrolyte can pass through the fixing member and penetrate into the electrode assembly, thereby preventing the fixing member from impregnating the electrode assembly with the electrolyte. Specifically, the fixing member may be, but is not limited to, a finishing tape having a base layer made of a porous polymer material and an adhesive layer formed on one side of the base layer. The polymer material may be, but is not limited to, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), etc.

[0088] The fixing member preferably has a width of about 10 to 50 mm or 20 to 40 mm along the entire width direction of the electrode assembly. If the fixing member is too wide, the area of ​​the outer surface of the electrode assembly covered by the fixing member increases, reducing the contact area with the electrolyte, reducing the impregnation of the electrolyte and the frictional force between the electrode assembly and the battery case, which may reduce impact resistance. On the other hand, if the fixing member is too thin, the fixing effect of the electrode assembly may be reduced.

[0089] 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 may be arranged symmetrically along the entire length, 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 overall length can be firmly fixed.

[0090] 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.

[0091] The contact area between the fixing member and the electrode assembly can be adjusted by adjusting the width or number of fixing members used. Since fixing members typically have a lower coefficient of friction than the separator disposed on the outermost surface of the electrode assembly, increasing the area of ​​the fixing member surrounding the electrode assembly can reduce the frictional force between the electrode assembly and the inner surface of the battery case. Therefore, when using fixing members, it is preferable to reduce the contact area between the electrode assemblies by 30% or less to prevent a decrease in frictional force.

[0092] electrolyte The electrolyte is used to transfer lithium ions generated by electrochemical reactions at the electrodes during charging and discharging of the secondary battery, and may contain an organic solvent and a lithium salt.

[0093] The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0094] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, or LiB(C, O) . The lithium salt concentration is preferably within the range of 0.1 to 5.0 M, and more preferably 0.1 to 3.0 M. When the lithium salt concentration is within the above range, the electrolyte has suitable conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0095] In addition to the components of the electrolyte, the electrolyte may further contain additives for improving the life characteristics of the battery, suppressing a decrease in the battery capacity, and improving the discharge capacity of the battery. [Example]

[0096] The present invention will be described in more detail below with reference to specific examples.

[0097] Example 1 A pouch was prepared by sequentially laminating nylon, polyethylene terephthalate, an aluminum alloy thin film, and polypropylene to form a cup. A stacked electrode assembly measuring 548 mm in length, 99 mm in width, and 1380 g in weight was placed in the cup, and an electrolyte was poured into the pouch, which was then sealed and activated to produce a pouch-type secondary battery. The electrolyte was poured so that the remaining amount of electrolyte per unit capacity after the activation process was 2.2 g / Ah.

[0098] Example 2 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte was injected so that the amount of remaining electrolyte per unit capacity after the activation process was 2.15 g / Ah.

[0099] Example 3 A pouch-type secondary battery was fabricated in the same manner as in Example 1, except that a stacked electrode assembly having a total length of 548 mm, a total width of 78 mm, and a weight of 641 g was used, and the electrolyte was injected so that the amount of remaining electrolyte per unit capacity after the activation process was 1.7 g / Ah.

[0100] Comparative Example 1 A pouch-type secondary battery was fabricated in the same manner as in Example 1, except that a stack-type electrode assembly having a total length of 548 mm, a total width of 78 mm, and a weight of 641 g was used, and the electrolyte was injected so that the amount of remaining electrolyte per unit capacity after the activation process was 2.2 g / Ah.

[0101] Comparative Example 2 A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte was injected so that the amount of remaining electrolyte per unit capacity after the activation process was 2.3 g / Ah.

[0102] Experimental example 1: Friction force evaluation For the pouch-type secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2, the frictional force between the inner surface of the cup portion of the pouch and the electrode assembly was measured by the following method.

[0103] A portion of the pouch of the secondary battery was cut open, and the positive electrode tab was held with a jig connected to a wire. The wire was then connected to a universal testing machine (UTM), and the force applied was measured while pulling at a speed of 100 mm / min. The force was evaluated as the friction force between the electrode assembly and the bottom surface of the cup portion. The measurement results are shown in Table 1 below.

[0104] Experimental example 2: Collision impact test A crash shock test was conducted on the pouch-type secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 under the impact conditions of 133.7 G x 15.8 ms. The measurement results are shown in Table 1 below. After the test, if no electrolyte leakage or electrode assembly separation occurred, it was indicated as Pass, and if electrolyte leakage and / or electrode assembly separation occurred, it was indicated as Fail.

[0105] [Table 1]

[0106] As shown in Table 1 above, W / S is 42 (g / Ah) m -2 In the case of the batteries of Examples 1 to 3 where the W / S was less than 42 (g / Ah) m, the frictional force between the electrode assembly and the inner surface of the pouch was as high as 15 kgf or more, which prevented the electrode assembly from coming off due to external impact, and demonstrated excellent impact resistance. -2 In the case of Comparative Examples 1 and 2, where the amount was excessive, the frictional force was significantly reduced, resulting in electrolyte leakage during the impact test. [Explanation of symbols]

[0107] 10 Base material layer 12, 14 Polymer film 16a Adhesive layer 20 Barrier Layer 30 Sealant Layer 100 pouches 101 Lower case 102 Upper case 110 Cup section 120 Terrace 130 Folding section 200 electrode assembly 230 Electrode Tab 240 leads 250 Insulation

Claims

1. an electrode assembly; An electrolyte; a battery case including a housing portion for housing the electrode assembly and the electrolyte; A lithium secondary battery comprising: The electrode assembly has a ratio of overall length to overall width of 5 to 10; The weight of the electrolyte per unit capacity of the lithium secondary battery is 1.0 to 2.8 g / Ah; the battery case is a pouch or a rectangular can, a frictional force between the electrode assembly and the inner surface of the battery case being 15 kgf or more;

2. The electrode assembly has a cross-sectional area of ​​0.01 to 0.2 m ２ 2. The lithium secondary battery according to claim 1, wherein

3. 2. The lithium secondary battery according to claim 1, wherein the weight of the electrolyte per unit capacity of the lithium secondary battery is 1.5 g / Ah to 2.4 g / Ah.

4. 2. The lithium secondary battery of claim 1, wherein the electrode assembly has a total length of 200 mm to 800 mm and a total width of 40 mm to 200 mm.

5. 10. The lithium secondary battery of claim 1, wherein the lithium secondary battery exhibits zero electrolyte leakage when subjected to a crash shock test under crash conditions of 133.7 G x 15.8 ms.

6. 2. The lithium secondary battery according to claim 1, wherein the rated capacity of the lithium secondary battery is 50 Ah to 200 Ah.

7. The lithium secondary battery of claim 1 , further comprising at least one fixing member that is wound around the outer surface of the electrode assembly in a width direction and fixes the electrode assembly.

8. 8. The lithium secondary battery according to claim 7, wherein the contact area between the fixing member and the electrode assembly is 30% or less of the total surface area of ​​the electrode assembly.

9. 2. The lithium secondary battery according to claim 1, wherein the electrode assembly has a weight of 500 g to 1500 g.

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