Secondary battery

Abstract

The present invention relates to a secondary battery having improved impact resistance. A secondary battery of the present invention includes an electrode assembly, an electrolyte, and a battery case including a housing portion in which the electrode assembly and the electrolyte are housed. The secondary battery satisfies the following equation (1): W / S < = 42 (g / Ah) m-2. In equation (1), W is the electrolyte amount [unit: g / Ah] per unit capacity of the secondary battery, and S is the product of the total length [unit: m] and the total width [unit: m] of the electrode assembly.

Description

Technical Field

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

[0002] Lithium secondary batteries are generally prepared by the following process: electrode active material slurry is coated on the positive electrode collector and the negative electrode collector to make the positive electrode and the negative electrode. Then, the positive electrode and the negative electrode are stacked on both sides of the separator to form an electrode assembly. Next, the electrode assembly is housed in a bag and the electrolyte is injected into the case.

[0003] According to the material of the shell that contains the electrode assembly, the secondary battery is divided into a pouch-type secondary battery and a can-type secondary battery. Among them, the pouch-type secondary battery is manufactured by pressing the flexible bag film stack to form a cup portion, accommodating the electrode assembly in the cup portion, then injecting the electrolyte, and sealing the sealing portion. The can-type secondary battery is manufactured by accommodating the electrode assembly in a can made of a metal material, injecting the electrolyte, and assembling the top cover with the upper part of the can to seal it.

[0004] Pouch-type secondary batteries have advantages such as light weight, excellent space utilization, and high energy density due to the use of stacked electrode assemblies, but have the disadvantage of being easily affected by external impacts compared to can-type secondary batteries. Recently, as the use environment of secondary batteries has become more diverse, secondary batteries are required to have excellent durability and safety even in harsh environments, and therefore, it is necessary to improve the impact resistance of pouch-type secondary batteries. Summary of the invention

[0005] Technical issues

[0006] One aspect of the present invention provides a secondary battery in which the size of an electrode assembly and the amount of electrolyte per unit capacity meet specific conditions to increase the friction between the electrode assembly and a battery case (e.g., a bag), thereby suppressing separation of the electrode assembly and / or leakage of the electrolyte when subjected to external impact.

[0007] Technical Solution

[0008] According to one aspect of the present invention, there is provided a secondary battery comprising an electrode assembly, an electrolyte and a battery case, wherein the battery case comprises a receiving portion for receiving the electrode assembly and the electrolyte therein. The secondary battery satisfies the following equation (1):

[0009] Equation (1): W / S ≤ 42 (g / Ah) m -2

[0010] Wherein, in equation (1), W is the electrolyte weight 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.

[0011] The secondary battery as disclosed herein may also include any, some or all of the features as described below. It is contemplated that the secondary battery may be provided as a pouch-type battery, a cylindrical battery or a prismatic battery. In a specific example, the secondary battery may be provided as a pouch-type battery.

[0012] Unless otherwise specified, the capacity of a secondary battery can be defined by the rated capacity of the secondary battery. The rated capacity of a secondary battery can be 50Ah to 200Ah, preferably 50Ah to 150Ah, and more preferably 60Ah to 140Ah. The expression of the rated capacity of a secondary battery refers to the capacity generated when a fully charged battery is continuously discharged at 0.33C to the discharge termination voltage. At this time, the full charge voltage (charge termination voltage) and the discharge termination voltage can be appropriately selected according to the type of the secondary battery. For example, when the secondary battery is an NCM battery, the rated capacity can be the discharge capacity when the secondary battery is charged to 4.25V and discharged to 2.5V at 0.33C. The expression "unit capacity" refers to 1Ah.

[0013] The unit of parameter W can be g / Ah (gram / ampere hour). The unit of parameter S can be m 2 (square meters). The unit of the quotient W / S can be (g / Ah)·m -2 .

[0014] W may be about 2.2 g / Ah or less, preferably about 1.5 g / Ah to about 2.2 g / Ah, more preferably about 1.7 g / Ah to about 2.2 g / Ah, and S may be 0.01 m 2 Up to 0.2m 2 、0.02m 2 Up to 0.09m 2 , preferably 0.03m 2 Up to 0.08m 2 , more preferably 0.03m 2 Up to 0.75m 2 .

[0015] Here, the total weight of the electrolyte in the secondary battery refers to the amount of electrolyte remaining in the secondary battery after the activation process. Therefore, the total weight of the electrolyte can represent the weight of the electrolyte present in the secondary battery after manufacturing is completed or during operation.

[0016] W / S can be 0.1 (g / Ah)·m -2 To 42 (g / Ah) m -2 、1(g / Ah)·m-2 To 42 (g / Ah) m -2 、5(g / Ah)·m -2 To 42 (g / Ah) m -2 、10(g / Ah)·m -2 To 42 (g / Ah) m - 2, or 20 (g / Ah) m - 2 to 42 (g / Ah) m - 2, but not limited thereto. In a specific example, W / S may be 30 (g / Ah)·m - 2 to 42 (g / Ah) m - 2, preferably 35 (g / Ah)·m - 2 to 42 (g / Ah) m - 2.

[0017] The secondary battery can be manufactured by preparing respective electrode active material slurries and coating them on the positive electrode collector and the negative electrode collector to obtain the positive electrode and the negative electrode. One or more layers of positive electrodes and one or more layers of separators are stacked on each other in a manner that the separators are interposed between the positive electrode layer and the negative electrode layer to obtain an electrode assembly. The electrode assembly is housed in a battery case, and an electrolyte is injected into the battery case, which can be a bag, a cylindrical can or a polyhedral can.

[0018] A pouch-type secondary battery can be manufactured by a process in which a bag film stack is pressed to form a cup portion having a shape and size to accommodate an electrode assembly. After the electrode assembly is arranged in the cup portion, an electrolyte can be added and it can be sealed along a sealing portion of the bag film stack. A can-type secondary battery can be manufactured by a process in which the electrode assembly is housed in a can made of a metal material, an electrolyte is injected into the can, and the can is sealed by installing a lid on the opening of the can. As described above, the can can have a cylindrical shape or a polyhedral shape, such as a (rectangular) cuboid or a rhombus.

[0019] The electrolyte of the secondary battery can be provided as described in detail below. The electrode assembly of the secondary battery can be provided as described in detail below. The battery housing of the secondary battery can be a bag, which can be used herein according to the understanding of the secondary battery design and manufacturing field. As an alternative, the battery housing of the secondary battery can be a can as described herein. In particular, the electrolyte can be at least partially disposed between the electrode assembly and the inner surface of the battery housing facing the electrode assembly.

[0020] In particular, in a pouch-type secondary battery, the electrode assembly may have a rectangular shape elongated in the longitudinal direction in a plan view, which may be referred to as the length direction herein. The full length as used herein may be 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 located in a plane of at least one of the (multiple) positive electrode layers, (multiple) negative electrode layers, and (multiple) separators. The full width as used herein may be measured in the width direction, unless otherwise specified. In the electrode assembly, (multiple) positive electrode layers, (multiple) negative electrode layers, and (multiple) separators may be stacked in a thickness direction perpendicular to both the length direction and the width direction. Here, the plan view may refer to a viewing direction parallel to the thickness direction of the electrode assembly.

[0021] In the case of a can type secondary battery, the electrode assembly as described above may be wound along a winding axis parallel to the length direction or the width direction. Therefore, the other direction in the length direction and the 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 full length may refer to the length in the winding axis direction in the wound state, and the full width refers to the length in the direction perpendicular to the winding axis in the wound state.

[0022] The battery housing may be a bag, which may be provided in any manner disclosed herein. In particular, the bag may be formed by pressing at least one cup portion into a bag film stack. Thus, the cup portion may be formed as a planar portion protruding outwardly from the remainder of the bag film stack. The cup portion may have a tray-like shape. The cup portion may have a flat main surface surrounded by one or more side walls that are integrated with the rest of the bag film stack. The flat main surface of the cup portion may have a rectangular basic shape in a plan view, wherein the corners may be rounded due to processing requirements or design. The bag may implement any, some or all of the features of the bag as disclosed herein, unless otherwise stated or technically inappropriate.

[0023] According to one aspect of the present invention, the battery housing can be a bag made of a bag film stack. The bag, in particular the bag film stack, can include a barrier layer, a substrate layer and a sealant layer. The substrate layer can be arranged on one surface of the barrier layer, and the sealant layer can be arranged on another surface of the barrier layer (i.e., the opposite surface of the substrate layer). In some examples, the substrate layer, the barrier layer and the sealant layer can form a bag film stack, in particular a laminated structure. The bag, in particular the bag film stack, can be press-formed (in particular stretch-formed and / or stretched) so as to have more than one cup protruding outward (from the rest of the bag or the rest of the bag film stack). The electrode assembly can be accommodated in more than one cup. The shape and size of more than one cup can be designed to accommodate the electrode assembly. The components of the bag can each realize any, some or all of the corresponding features disclosed herein, unless otherwise stated or technically inappropriate. In particular, any one of the substrate layer, the barrier layer and the sealant layer can be realized as described in detail below.

[0024] The rated capacity of the secondary battery may be about 50 Ah to about 200 Ah, preferably about 50 Ah to about 150 Ah, and more preferably about 60 Ah to about 140 Ah.

[0025] The electrode assembly may have a substantially rectangular shape in plan view, such that the ratio of the overall length to the overall width of the electrode assembly is 2.5 to 20, or 3 to 15, or 5 to 10, or 5 to 8. The specific aspect ratio of the electrode assembly may further contribute to increasing the aforementioned frictional forces without increasing the demand for electrolyte.

[0026] 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 have a total length of 400 mm to 600 mm, and a total width of 50 mm to 150 mm. Preferably, the electrode assembly may have a total length of 500 mm to 600 mm, and a total width of 50 mm to 100 mm. Specific combinations of the total length and total width of the electrode assembly may further contribute to increasing the friction as described above without increasing the demand for electrolyte. The total length and total width may refer to the maximum extension of the electrode assembly in the length direction and the width direction in a plan view, respectively.

[0027] Meanwhile, the weight of the electrode assembly may be 500 g to 1500 g, preferably 550 g to 1450 g, more preferably 600 g to 1400 g. When the weight of the electrode assembly satisfies the above range, high capacity can be achieved, and the friction between the electrode assembly and the inner surface of the battery case is increased, thereby having excellent impact resistance.

[0028] At the same time, the secondary battery may further include at least one fixing component that is fixed on the outer surface of the electrode assembly by wrapping the electrode assembly in the width direction. In this case, the contact area between the fixing component and the electrode assembly may be less than 30%, 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. Since the fixing component is usually made of a material with a low friction coefficient, the friction between the electrode assembly and the inner surface of the battery housing may decrease when the area of ​​the fixing component increases. Therefore, when using a fixing component, it is expected to suppress the reduction of friction by setting the contact area between the electrode assemblies to less than 30%. At the same time, the battery housing may be a bag-type housing. The bag-type housing may be a bag, which includes a barrier layer, a substrate layer disposed on one surface of the barrier layer, and a sealant layer disposed on another surface of the barrier layer, and includes at least one cup portion recessed in one direction, and the electrode assembly and the electrolyte can be accommodated in the cup portion of the bag.

[0029] 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.

[0030] The friction force between the inner surface of the battery case of the secondary battery and the electrode assembly can be determined as follows: a portion of the battery case is cut open; the positive electrode tab is clamped with a zig connected with a wire; the wire is connected to a universal material testing machine (UTM); and the force applied when the wire is stretched at a constant speed (e.g., 100 mm / min) is measured to determine the friction force between the electrode assembly and the inner surface of the battery case.

[0031] When the secondary battery is subjected to a collision impact test under the collision condition of 133.7G x15.8m·s, the leakage of the electrolyte can be zero. The collision impact test is performed under the collision condition of 133.7G x 15.8m·s. After the collision impact test, the battery case is checked for electrolyte weight loss due to leakage to the outside of the battery case, and displacement of the electrode assembly inside and outside the battery case.

[0032] In a specific example, the total length of the electrode assembly can be 0.2m to 0.8m, the total width can be 0.05m to 0.15m, and the electrolyte weight per unit volume can be 1.0 to 2.8g / Ah. This example can achieve 30 (g / Ah)·m - 2 to 42 (g / Ah) m - 2's quotations w / s.

[0033] In a further specific example, the total length of the electrode assembly can be 0.3m to 0.8m, the total width can be 0.06m to 0.12m, and the electrolyte weight per unit volume can be 1.2 to 2.5g / Ah. This example can achieve 30 (g / Ah)·m - 2 to 42 (g / Ah) m - 2's quotations w / s.

[0034] In a further specific example, the total length of the electrode assembly can be 0.4m to 0.6m, the total width can be 0.07m to 0.11m, and the electrolyte weight per unit capacity can be 1.5 to 2.4g / Ah. This example can achieve 30 (g / Ah)·m - 2 to 42 (g / Ah) m - 2's quotations w / s.

[0035] According to another aspect, a secondary battery may be provided, which includes an electrode assembly, an electrolyte, and a battery case. The surface area of ​​the electrode assembly may be 0.01 to 0.2 m 2 The total weight of the electrolyte may be 440 g or less. The battery case may contain the electrode assembly and the electrolyte. The electrode assembly, the electrolyte, and the battery case may be configured such that the friction between the electrode assembly and the inner surface of the battery case is 15 kgf or more.

[0036] In particular, the surface area of ​​the electrode assembly may be the product of its full length and full width, provided that the electrode assembly has a rectangular shape as described above. The surface area of ​​the electrode assembly may be 0.02 m 2 Up to 0.08m 2 , or 0.03m 2 Up to 0.07m 2 , or 0.04m 2 Up to 0.06m 2 .

[0037] Beneficial Effects

[0038] When the size of the electrode assembly and the weight of the electrolyte per unit capacity meet specific conditions as in the secondary battery of the present invention, the friction between the electrode assembly and the battery case can be increased compared to the prior art, so that when subjected to external impact, the separation of the electrode assembly and / or the leakage of the electrolyte can be suppressed, thereby achieving excellent impact resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The above and other aspects, features and other advantages of the present invention will be more clearly understood through the following detailed description in conjunction with the accompanying drawings, in which:

[0040] Figure 1 It is an exploded perspective view of a secondary battery according to an embodiment of the present invention.

[0041] Figure 2 It is a figure for demonstrating the structure of a bag. DETAILED DESCRIPTION

[0042] The terms or words used in the specification and claims should not be construed as limited to the dictionary meanings, but should be understood as appropriate concepts by the inventor based on his / her ability to define the terms in order to best describe his / her invention for others to see.

[0043] Hereinafter, the present invention will be described in more detail.

[0044] Recently, as the demand for high-capacity batteries such as batteries for electric vehicles increases, the rated capacity of each secondary battery cell is increasing, so the size and weight of the electrode assembly tend to increase. However, as the size and weight of the electrode assembly increase, the phenomenon of the battery case being damaged or the electrode assembly penetrating the battery case while the electrode assembly moves when subjected to external impact is intensifying. In particular, this limitation is particularly severe in pouch-type batteries with low rigidity of the battery case. If the battery case is damaged, the electrolyte may leak, or the electrode assembly may deform, resulting in serious limitations on battery performance and safety.

[0045] At the same time, the electrolyte remaining after impregnation in the electrode assembly may remain on the surface of the electrode assembly and inside the battery case. Since the electrolyte has wettability, when the electrolyte is present on the inner surface of the battery case and on the surface of the electrode assembly, the friction between the electrode assembly and the inner surface of the battery case is reduced, and as a result, the movement of the electrode assembly is further aggravated during external impact. When the total amount of electrolyte solution in the secondary battery increases, the amount of electrolyte remaining inside the electrode assembly and the battery case increases, and as a result, the friction is further reduced. Therefore, in terms of impact resistance, the less the amount of electrolyte in the secondary battery, the better, but if the amount of electrolyte is too little, it may have an adverse effect on the capacity of the secondary battery and may reduce the operation and life of the secondary battery.

[0046] After repeated research, a secondary battery was developed that can achieve both excellent electrochemical performance and impact resistance. It was found that when the cross-sectional area of ​​the electrode assembly, the content of the electrolyte and the capacity of the secondary battery meet specific conditions, the friction between the electrode assembly and the battery case is increased compared with the prior art. Therefore, when subjected to external impact, the damage to the battery case caused by the separation of the electrode assembly is suppressed while minimizing the decline in electrochemical performance, thereby achieving excellent impact resistance. As a result, the present invention was completed.

[0047] The secondary battery of the present invention is characterized by comprising: an electrode assembly, an electrolyte, and a battery case including a housing portion for housing the electrode assembly and the electrolyte therein, and satisfying the following equation (1).

[0048] Equation (1): W / S ≤ 42 (g / Ah) m - 2

[0049] Wherein, the unit of W / S in equation 1 may be (g / Ah)·m - 2.

[0050] W may represent the electrolyte weight per unit capacity of the secondary battery and may be measured by dividing the total electrolyte weight (unit: g) in the secondary battery by the rated capacity (unit: Ah) of the secondary battery. The total electrolyte weight in the secondary battery may refer to the total weight of the electrolyte remaining in the secondary battery after the activation process.

[0051] W / S can be 42 (g / Ah)·m - 2 or less, 0.1(g / Ah)·m - 2 to 42 (g / Ah) m - 2. 1(g / Ah)·m - 2 to 42 (g / Ah) m - 2.5 (g / Ah) m - 2 to 42 (g / Ah) m - 2.10(g / Ah)·m - 2 to 42 (g / Ah) m - 2, or 20 (g / Ah) m - 2 to 42 (g / Ah) m - 2, but not limited thereto. W / S may preferably be 30 (g / Ah)·m - 2 to 42 (g / Ah) m - 2, more preferably about 35 (g / Ah)·m - 2 to about 42 (g / Ah)·m - 2. When W / S is about 42 (g / Ah)·m - 2 or less, the friction between the electrode assembly and the inner surface of the battery case in contact with the electrode assembly (e.g., the bottom surface of the cup portion of the bag) can be greatly increased. As a result, when subjected to external impact, the separation of the electrode assembly can be minimized, thereby minimizing the leakage of the electrolyte due to damage to the battery case.

[0052] 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 friction between the electrode assembly and the inner surface of the battery case may not be significant, and if W is too small, the battery performance may be deteriorated due to insufficient electrolyte when the battery is driven.

[0053] S may be a cross-sectional area of ​​the electrode assembly, and may be a value obtained by multiplying the full length and the full width of the electrode assembly. Here, the full length and the full width may use values ​​measured in m.

[0054] S can be, for example, 0.02 m 2 Up to 0.09m 2 , preferably 0.03m 2 Up to 0.08m 2 , more preferably 0.03m 2 Up to 0.75m 2 If S is too small, the battery capacity may decrease and the effect of increasing friction may not be significant, while if S is too large, there is a limitation that the risk of an accident increases when a stability problem occurs.

[0055] The rated capacity of the secondary battery may be 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.

[0056] The secondary battery of the present invention may be a pouch-type secondary battery. In this case, the battery case may be a pouch, which includes, for example, a barrier layer, a substrate layer disposed on one surface of the barrier layer, and a sealant layer disposed on another surface of the barrier layer, and further includes at least one cup portion recessed in one direction, and the electrode assembly and the electrolyte may be contained in the cup portion of the pouch.

[0057] When the condition of equation (1) is met, the friction force between the electrode assembly and the inner surface of the battery case (e.g., the bottom surface of the cup portion of the bag) can be greater than about 15 kgf, preferably about 15 kgf to about 40 kgf, and more preferably about 17 kgf to about 35 kgf, so as to minimize the displacement of the electrode assembly during external impact, thereby minimizing damage to the bag, and thus the impact resistance can be very excellent.

[0058] Here, the friction force between the electrode assembly and the inner surface of the battery case may be measured by the following method.

[0059] First, a portion of the secondary battery case can be cut open, the positive electrode tab can be clamped with a zigzag connected to a wire, the wire can be connected to a universal material testing machine (UTM), and then the force applied when the wire is stretched at a constant speed (e.g., 100 mm / min) can be measured to evaluate the friction between the electrode assembly and the inner surface of the battery case.

[0060] The secondary battery of the present invention may have a high friction between the electrode assembly and the battery case so as to minimize the separation of the electrode assembly when subjected to external impact, thereby having excellent impact resistance. For example, in the secondary battery of the present invention, when a collision impact test is performed under a collision condition of about 133.7G x 15.8ms, electrolyte leakage may not occur. In other words, when the secondary battery of the present invention is subjected to a collision impact test under a collision condition of 133.7G×15.8m·s, the leakage of the electrolyte is zero. The collision impact test can be performed by the following process: the battery to be tested is mounted on a fixture of a drop impact device, and then the battery is allowed to fall freely at a specific height to determine whether the battery is damaged. Here, the free fall height is set in consideration of the collision condition to be tested (acceleration×duration). Specifically, the free fall height can be set by the following process: the impact energy under the collision condition to be tested is converted into potential energy, and then the height of the converted potential energy is calculated in consideration of the weight of the battery to be tested. Whether the battery is damaged can be evaluated by whether there is electrolyte leakage.

[0061] Figure 1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention, Figure 2 is a cross-sectional view of a bag film stack. Hereinafter, a secondary battery according to an embodiment of the present invention will be described in more detail.

[0062] bag

[0063] The bag 100 may be a battery case for accommodating an electrode assembly and an electrolyte, and may include a barrier layer 20, a substrate layer 10 disposed on one surface of the barrier layer, and a sealant layer 30 disposed on another surface of the barrier layer, and may also include at least one cup portion (accommodating portion) recessed in one direction.

[0064] Specifically, the bag 100 can be flexible and can be manufactured by the following method: inserting a bag film stack having a substrate layer 10, a barrier layer 20 and a sealant layer 30 stacked in sequence into a press-forming device, and applying pressure to a partial area of ​​the bag film stack using a punch so that the bag film stack is stretched to form a cup portion recessed in one direction.

[0065] Base material layer

[0066] The base material layer 10 may be disposed on the outermost layer of the pouch, and may be configured to protect and electrically insulate the electrode assembly when subjected to external impact.

[0067] The substrate layer 10 may be made of a polymer material, for example, at least one polymer material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, poly(p-phenylene benzobisoxazole), polyarylate and Teflon.

[0068] The substrate layer 10 may have a single layer structure, or Figure 2 As shown, it may have a multi-layer structure in which different polymer films 12 and 14 are stacked. When the base material layer 10 has a multi-layer structure, an adhesive layer 16a may be provided between the polymer films.

[0069] The total thickness of the substrate layer 10 may be from about 10 μm to about 60 μm, preferably from about 20 μm to about 50 μm, and more preferably from about 30 μm to about 50 μm. When the substrate layer has a multilayer structure, the thickness refers to the cumulative thickness including the adhesive layer. When the substrate layer 10 satisfies the above range, durability, insulation and formability may be excellent. When the thickness of the substrate layer is too thin, durability may be reduced, and the substrate layer is easily damaged during the molding process. When the thickness of the substrate layer is too thick, formability may deteriorate, the overall thickness of the bag may increase, and the battery accommodating space may be reduced, resulting in a reduction in energy density.

[0070] According to one embodiment, the base material layer 10 may have a stacked structure of a polyethylene terephthalate (PET) film and a nylon film. Here, the nylon film may be disposed on one side of the barrier layer 20, that is, inside the barrier layer 20, and the polyethylene terephthalate film may be disposed on the surface side of the bag.

[0071] Polyethylene terephthalate (PET) may have excellent durability and electrical insulation, so when the PET film is placed on the surface side, the durability and insulation may be excellent. However, for the PET film, since the adhesion with the aluminum alloy film constituting the barrier layer 20 is weak and the tensile behavior is different, when the PET film is placed on one side of the barrier layer, the base layer and the barrier layer may be peeled off during the molding process, and the barrier layer may not be stretched uniformly, resulting in deterioration of the moldability. In contrast, since the nylon film has a similar tensile behavior to the aluminum alloy film constituting the barrier layer 20, when the nylon film is placed between the polyethylene terephthalate and the barrier layer, the effect of improving the moldability can be obtained.

[0072] The thickness of the polyethylene terephthalate film may be about 5 μm to about 20 μm, preferably about 5 μm to about 15 μm, and more preferably about 7 μm to about 15 μm. The thickness of the nylon film may be about 10 μm to about 40 μm, preferably about 10 μm to about 35 μm, and more preferably about 15 μm to about 25 μm. When the thickness of the polyethylene terephthalate film and the nylon film satisfies the above range, the moldability and rigidity after molding may be excellent.

[0073] Barrier layer

[0074] The barrier layer 20 may be configured to ensure mechanical strength of the pouch 100 , block entry and discharge of gas or moisture outside the secondary battery, and prevent leakage of the electrolyte.

[0075] The thickness of the barrier layer 20 may be about 40 μm to about 100 μm, more preferably about 50 μm to about 80 μm, more preferably about 60 μm to about 80 μm. When the thickness of the barrier layer satisfies the above range, the moldability may be improved to increase the cup molding depth, or the resistance to external stress after molding may be improved because cracks and / or pinholes are less likely to be generated even when two cups are molded.

[0076] The barrier layer 20 may be made of a metal material, and specifically may be made of an aluminum alloy film.

[0077] The aluminum alloy film may include aluminum and metal elements other than aluminum, for example, at least one or more metal elements selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg) and zinc (Zn).

[0078] Preferably, the iron (Fe) content of the aluminum alloy film may be about 1.2 wt % to about 1.7 wt %, preferably about 1.3 wt % to about 1.7 wt %, more preferably about 1.3 wt % to about 1.45 wt %. When the iron (Fe) content in the aluminum alloy film satisfies the above range, even if the cup portion is formed deeper, the occurrence of cracks or pinholes can be minimized.

[0079] Sealant layer

[0080] The sealant layer 30 may be configured to seal the bag by thermal compression bonding, and is disposed at the innermost layer of the bag film stack 1 .

[0081] Since the sealant layer 30 is the surface in contact with the electrolyte and the electrode assembly after the bag is formed, the sealant layer 30 must have insulation and corrosion resistance. In addition, since the inside of the sealant layer 30 must be completely sealed to prevent the movement of materials between the inside and the outside, the sealant layer 30 must have excellent sealing properties.

[0082] The sealant layer 30 may be made of a polymer material, for example, at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyphenylene benzobisoxazole, polyarylate and Teflon, and particularly preferably includes polypropylene (PP). These materials are examples of materials that exhibit excellent mechanical properties (e.g., tensile strength, rigidity, surface hardness, wear resistance and heat resistance) and chemical properties (e.g., corrosion resistance).

[0083] More specifically, the sealant layer 30 may include polypropylene, cast polypropylene (CPP), acid-modified polypropylene, polypropylene-butylene-ethylene copolymer, or a combination thereof.

[0084] The sealant layer 30 may have a single-layer structure or a multi-layer structure including two or more layers made of different polymer materials.

[0085] The total cumulative thickness of the sealant layer may be about 60 μm to about 100 μm, preferably about 60 μm to about 90 μm, and more preferably about 70 μm to about 90 μm. If the thickness of the sealant layer is too thin, the sealing durability and insulation may be deteriorated, and if the sealant layer is too thick, the flexibility may be deteriorated and the total thickness of the bag film stack may increase, resulting in a decrease in energy density relative to volume.

[0086] The bag film stack can be manufactured by a manufacturing method of the bag film stack known in the art. For example, the bag film stack can be manufactured by attaching the base material layer 10 to the upper surface of the barrier layer 20 by an adhesive, and forming the sealant layer 30 on the lower surface of the barrier layer 20 by coextrusion or an adhesive, but is not limited thereto.

[0087] The bag 100 can be manufactured by inserting the bag film stack as described above into a molding device and applying pressure to a partial area of ​​the bag film stack using a punch to form a cup portion. Here, the pressure may be about 0.3 MPa to about 1 MPa, preferably about 0.3 MPa to about 0.8 MPa, and more preferably about 0.4 MPa to about 0.6 MPa. If the pressure is too low when the cup portion is molded, overstretching may occur and wrinkles may be generated. If the pressure is too high, stretching may not be performed well, so the molding depth may be reduced.

[0088] The moving speed of the punch may be about 20 mm / min to about 80 mm / min, preferably about 30 mm / min to about 70 mm / min, and more preferably about 40 mm / min to about 60 mm / min. If the pressure during molding is too small or the moving speed of the punch is too fast, wrinkles may be generated due to buckling, and if the pressure during molding is too large or the moving speed of the punch is too slow, the stress concentrated at the corner of the cup during molding may increase, thereby increasing the occurrence of pinholes or cracks.

[0089] The bag 100 of the present invention manufactured by the above method may include a lower shell 101, an upper shell 102, and a folding portion 130 connecting the upper shell and the lower shell, and the upper shell and / or the lower shell may include a cup portion 110 recessed in one direction.

[0090] Specifically, Figure 1 As shown, the bag 100 of the present invention may have a cup shape in which the cup portion 110 is formed only in the lower shell 101, but is not limited thereto. For example, the bag 100 may have a double cup shape in which cup portions are formed on both the upper shell and the lower shell. For a double cup-shaped bag, after accommodating the electrode assembly and the electrolyte, the upper shell may be folded so that the cup portion of the upper shell and the cup portion of the lower shell face each other, and thus a thicker electrode assembly may be accommodated than a bag having a single cup shape, thereby achieving high energy density.

[0091] The cup portion 110 may have an accommodation space for accommodating the electrode assembly 200. The bag 100 may include a platform 120 surrounding the cup portion 110. The platform 120 may refer to an unformed portion of the bag film stack, that is, a remaining area other than the cup portion 110. The platform 129 may be a portion sealed by thermal bonding in the process of accommodating the electrode assembly 200 in the cup portion 110 and injecting an electrolyte for sealing.

[0092] The cup portion 110 may include a bottom surface and a peripheral surface. The peripheral surface may connect the bottom surface to the platform 120. The peripheral surface may be provided in a plurality, more specifically four. The bottom surface may cover one surface of the electrode assembly 200, and the peripheral surface may surround the electrode assembly 200.

[0093] The folding portion 130 may connect the lower case 101 to the upper case 102, accommodate the electrode assembly 200 in the cup portion 110, inject the electrolyte, and then may be folded so that the upper case 102 seals the cup portion 110 of the lower case 101. When the folding portion 130 is provided, since the lower case 101 and the upper case 102 are integrally connected to each other, when a sealing process is performed later, the number of sides to be sealed may be reduced, improving processability.

[0094] The folding portion 130 is disposed to be spaced apart from the cup portion 110, and the spacing distance between the folding portion 130 and the cup portion 110 may be about 0.5 mm to about 3 mm, preferably about 0.5 mm to about 2 mm. If the folding portion 130 is disposed too close to the cup portion 110, folding may not be performed smoothly, and if the folding portion 130 is disposed too far from the cup portion 110, the total volume of the secondary battery may increase, and the energy density relative to the volume may decrease. For a double cup-shaped housing, a folding portion may be provided to meet the spacing distance of each cup portion.

[0095] Electrode assembly

[0096] The electrode assembly 200 may include a plurality of electrodes and a plurality of separators that are alternately stacked. The plurality of electrodes include positive electrodes and negative electrodes that are alternately stacked with separators therebetween and have opposite polarities.

[0097] In addition, the electrode assembly 200 may include 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 protrude from the electrode assembly 200 to the outside to serve as a passage for electrons to move between the inside and outside of the electrode assembly 200. The plurality of electrode tabs 230 may be disposed inside the bag 100.

[0098] The electrode tab 230 connected to the positive electrode and the electrode tab 230 connected to the negative electrode may protrude in different directions relative to the electrode assembly 200. However, the present invention is not limited thereto, and the electrode tab 230 connected to the positive electrode and the electrode tab 230 connected to the negative electrode may protrude in the same direction in parallel with each other.

[0099] A lead 240 supplying power to the outside of the secondary battery may be connected to the plurality of electrode tabs 230 by spot welding, etc. The lead 240 may have one end connected to the plurality of electrode tabs 230 and the other end protruding to the outside of the pouch 100 .

[0100] 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 disposed between the platform 120 and the second shell 102 of the first shell 101, in which state the platform 120 and the second shell 102 may be thermally fused to each other. In this case, a portion of each of the platform 120 and the second shell 102 may be thermally fused to the insulating portion 250. Therefore, the insulating portion 250 may prevent the current generated from the electrode assembly 200 from flowing into the bag 100 through the lead 240, and may keep the bag 100 in a sealed state.

[0101] In the present invention, the ratio of the total length to the total width of the electrode assembly 200 may be about 5 to about 10, preferably about 5 to about 8. When the ratio of the total length to the total width satisfies the above range, high energy density can be achieved in a limited space.

[0102] For example, the electrode assembly may have an overall length of about 400 mm to about 600 mm, an overall width of about 50 mm to about 150 mm, preferably an overall length of about 500 mm to about 600 mm and an overall width of about 50 mm to about 100 mm.

[0103] The weight of the electrode assembly may be 500 g to 1500 g, preferably 550 g to 1450 g, more preferably 600 g to 1400 g, but is not limited thereto. When the weight of the electrode assembly satisfies the above range, high capacity can be achieved, and the friction between the electrode assembly and the inner surface of the battery case is increased, thereby having excellent impact resistance.

[0104] If necessary, the secondary battery may also include at least one fixing component on the outer surface of the electrode assembly. For a rectangular electrode assembly (referred to as a "long battery cell" for convenience) whose total length is greater than the total width, a fixing component is used to prevent the components of the electrode assembly (such as the negative electrode, the positive electrode, and the separator) from being misaligned. The fixing component wraps the electrode assembly in the width direction and fixes it.

[0105] The fixing component may include a porous structure. When the fixing component includes a porous structure, the electrolyte may pass through the fixing component and be impregnated into the electrode assembly, thereby preventing the electrolyte wettability of the electrode assembly from being reduced due to the fixing component. Specifically, the fixing component may be a finishing tape having an adhesive layer formed on one side of a polymer base 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.

[0106] The width of the fixing member along the full width direction of the electrode assembly is preferably about 10 to 50 mm or 20 to 40 mm. If the width of the fixing member is too wide, the outer surface area of ​​the electrode assembly covered by the fixing member increases, so that the electrolyte wettability may be reduced due to the reduced contact area with the electrolyte, and the impact resistance may be reduced due to the reduced friction between the electrode assembly and the battery case. On the other hand, if the width of the fixing member is too thin, the effect of fixing the electrode assembly may be reduced.

[0107] The secondary battery may include 2 to 10 fixing parts, preferably 2 to 8 fixing parts, and more preferably 3 to 7 fixing parts. At this time, the fixing parts may be arranged at left-right symmetrical positions along the length direction, and preferably, the fixing parts may be spaced at equal intervals. When a plurality of fixing parts are provided and arranged as described above, an electrode assembly having a long cell structure with a long length may be firmly fixed.

[0108] At the same time, the contact area between the fixing component and the electrode assembly may be less than 30%, less than 25%, or less than 20% of the total surface area of ​​the electrode assembly. Specifically, the contact area between the fixing component 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.

[0109] The contact area between the fixing part and the electrode assembly can be adjusted by adjusting the width or number of the fixing parts used. Since the fixing parts commonly used are made of a material having a friction coefficient smaller than that of the diaphragm provided on the outermost surface of the electrode assembly. Therefore, as the area of ​​the fixing parts surrounding the electrode assembly increases, the friction between the electrode assembly and the inner surface of the battery case will decrease. Therefore, when using the fixing parts, it is desirable to suppress the reduction of the friction by setting the contact area between the electrode assemblies to 30% or less.

[0110] Electrolyte

[0111] The electrolyte may be configured to move lithium ions generated by an electrochemical reaction of an electrode during charge and discharge of the secondary battery, and may include an organic solvent and a lithium salt.

[0112] The organic solvent can be used without particular limitation, as long as it is used as a medium for the ions involved in the electrochemical reaction of the battery to move through. Specifically, examples of the organic solvent may include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (R is a linear, branched or cyclic hydrocarbon group of C2 to C20, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. In the above examples, carbonate solvents are preferred, and a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) which can improve the charging and discharging performance of the battery is preferred.

[0113] The lithium salt may be a compound capable of providing lithium ions used in a lithium secondary battery, but is not limited thereto. Specifically, the lithium salt may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2, etc. The concentration of the lithium salt may preferably be used in the range of about 0.1M to about 5.0M, preferably about 0.1M to about 3.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, and thus can exhibit excellent electrolyte performance, allowing lithium ions to move effectively.

[0114] In addition to the above-mentioned components of the electrolyte, the electrolyte may further include additives to improve the life characteristics of the battery, suppress the reduction of the battery capacity, and increase the discharge capacity of the battery.

[0115] Example

[0116] Hereinafter, the present invention will be described in detail with reference to specific examples.

[0117] Example 1

[0118] A bag in which nylon / polyethylene terephthalate / Al alloy film / polypropylene is stacked in sequence and formed with a cup portion is prepared. A stacked electrode assembly having a total length of about 548 mm, a total width of about 99 mm, and a weight of 1380 g is accommodated in the cup portion. Next, an electrolyte is injected, the bag is sealed, and then an activation process is performed to manufacture a pouch-type secondary battery. Here, the electrolyte is injected so that the residual amount of electrolyte per unit capacity after the activation process is about 2.2 g / Ah.

[0119] Example 2

[0120] A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte was injected so that the residual amount of the electrolyte per unit capacity after the activation process was about 2.15 g / Ah.

[0121] Example 3

[0122] A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that a stacked electrode assembly having a total length of approximately 548 mm, a total width of approximately 78 mm, and a weight of 641 g was used, and the electrolyte was injected so that the residual electrolyte per unit capacity after the activation process was approximately 1.7 g / Ah.

[0123] Comparative Example 1

[0124] A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that a stacked electrode assembly having a total length of approximately 548 mm, a total width of approximately 78 mm, and a weight of 641 g was used, and the electrolyte was injected so that the residual electrolyte per unit capacity after the activation process was approximately 2.2 g / Ah.

[0125] Comparative Example 2

[0126] A pouch-type secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte was injected so that the residual amount of the electrolyte per unit capacity after the activation process was about 2.3 g / Ah.

[0127] Experimental Example 1: Friction Evaluation

[0128] For each of the pouch-type secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 and 2, the friction force between the inner surface of the pouch cup and the electrode assembly 200 was measured using the following method.

[0129] A portion of the secondary battery bag was cut, the positive electrode tab was clamped with a zig wire, and the wire was connected to a universal testing machine (UTM). Next, a tensile force was applied to the wire at a speed of about 100 mm / min to measure and evaluate the friction between the electrode assembly and the bottom surface of the cup.

[0130] The measurement results are shown in Table 1 below.

[0131] Experimental Example 2: Collision Impact Test

[0132] The pouch-type secondary batteries prepared in Examples 1-3 and Comparative Examples 1 and 2 were subjected to a collision impact test under a collision impact condition of 133.7G x 15.8ms. The measurement results are shown in Table 1 below. After the collision impact test, if no electrolyte leakage and electrode assembly separation occurred, the result was reported as "passed", and if electrolyte leakage and / or electrode assembly separation occurred, the result was reported as "failed".

[0133] [Table 1]

[0134]

[0135] As shown in [Table 1], for W / S less than 42 (g / Ah)·m - 2, the friction between the electrode assembly and the inner surface of the bag is as high as about 15 kgf or more, thereby suppressing the separation of the electrode assembly due to external impact, thereby showing excellent impact resistance. On the other hand, for W / S exceeding about 42 (g / Ah)·m - In Comparative Examples 1 and 2 of 2, the friction force was significantly reduced, and as a result, electrolyte leakage occurred during the impact test.

Claims

1. A secondary battery comprising: Electrode assembly; Electrolyte; a battery case accommodating the electrode assembly and the electrolyte, Wherein, the secondary battery is configured to satisfy the following equation 1: Equation (1): W / S ≤ 42 (g / Ah) m - 2 Wherein, in equation (1), W is the electrolyte weight per unit capacity of the secondary battery, in units of g / Ah; S is the product of the full length and full width of the electrode assembly, in units of m.

2. The secondary battery according to claim 1, wherein The battery case is a bag including a barrier layer, a base material layer disposed on one surface of the barrier layer, and a sealant layer disposed on another surface of the barrier layer, and including at least one cup portion recessed in one direction, and The electrode assembly and the electrolyte are accommodated in the at least one cup portion.

3. The secondary battery according to claim 1 or 2, wherein: The W / S is 30 (g / Ah)·m - 2 to 42 (g / Ah) m - Within the range of 2.

4. The secondary battery according to claim 1 or 2, wherein: W in equation (1) is 2.2 g / Ah or less.

5. The secondary battery according to claim 1 or 2, wherein: W in equation (1) is in the range of 1.5 g / Ah to 2.2 g / Ah.

6. The secondary battery according to claim 1 or 2, wherein: S in equation (1) is 0.02 m 2 Up to 0.09m 2 within the range.

7. The secondary battery according to claim 1 or 2, wherein: The ratio of the total length to the total width of the electrode assembly is in the range of 5 to 10.

8. The secondary battery according to claim 1 or 2, wherein: The overall length of the electrode assembly is 400 mm to 600 mm, and the overall width of the electrode assembly is 50 mm to 150 mm.

9. The secondary battery according to claim 1, wherein The friction force between the electrode assembly and the inner surface of the battery case is greater than 15 kgf.

10. The secondary battery according to claim 1 or 2, wherein: The rated capacity of the secondary battery is in the range of 50 Ah to 200 Ah.

11. The secondary battery according to claim 1 or 2, wherein: When a collision impact test is performed on the secondary battery under a collision condition of 133.7G×15.8ms, a leakage amount of an electrolyte of the secondary battery is zero. 12 . The secondary battery according to claim 1 , further comprising at least one fixing member fixed to an outer surface of the electrode assembly by wrapping the electrode assembly in a full width direction.

13. The secondary battery according to claim 12, wherein: A contact area between the fixing member and the electrode assembly is less than 30% of a total surface area of ​​the electrode assembly.

14. The secondary battery according to claim 1, wherein The weight of the electrode assembly is in the range of 500 g to 1500 g.

15. A secondary battery comprising an electrode assembly, an electrolyte, and a battery case accommodating the electrode assembly and the electrolyte, in, The surface area of ​​the electrode assembly is 0.01 m 2 Up to 0.2m 2 ; The total weight of the electrolyte is less than 440 g; and The electrode assembly, the electrolyte, and the battery case are configured so that a friction force between the electrode assembly and an inner surface of the battery case is 15 kgf or more.

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