Pouch-type battery case and pouch-type secondary battery

Abstract

The present invention relates to a pouch-type battery case and a pouch-type secondary battery, the pouch-type battery case for accommodating an electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode and comprising a pouch film laminate including: a sealing layer formed as an innermost layer from a first polymer, a gas barrier layer formed as an innermost layer from a second polymer, and a surface protection layer formed as an innermost layer from a third polymer; the surface protection layer is formed by a second polymer as an outermost layer; the gas barrier layer is laminated between the surface protection layer and the sealing layer and is formed of an aluminum alloy thin film having a thickness of 60 [mu] m to 100 [mu] m and a grain size of 10 [mu] m to 13 [mu] m.

Description

[0001] This application is a divisional application of the application filed on April 14, 2021, with application number 202180018391.8 and invention title "Pouch-type Battery Housing and Pouch-type Secondary Battery" (PCT / KR2021 / 004686, national phase entry date August 31, 2022). Technical Field

[0002] This application claims priority to Korean Patent Application 10-2020-0045542, filed on April 14, 2020, which is incorporated herein by reference in its entirety.

[0003] This invention relates to pouch-type battery housings and pouch-type secondary batteries, and more specifically, to pouch-type battery housings and pouch-type secondary batteries in which moldability is improved by increasing tensile strength and elongation. Background Technology

[0004] Generally speaking, rechargeable batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, and lithium-ion polymer batteries. These rechargeable batteries are used not only in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable game devices, power tools, and e-bikes, but also in large products requiring high output, such as electric vehicles and hybrid vehicles, and energy storage devices and backup energy storage devices for storing surplus power or renewable energy.

[0005] To manufacture this secondary battery, firstly, positive and negative current collectors are coated with electrode active material slurry to create positive and negative electrodes, respectively. Then, the positive and negative electrodes are laminated onto both sides of a separator to form an electrode assembly with a predetermined shape. After housing the electrode assembly in a battery casing and injecting electrolyte, the battery casing is sealed.

[0006] Based on the material of the casing housing the electrode components, secondary batteries are classified into pouch-type, can-type, and similar types. Pouch-type batteries house the electrode components in a pouch made of a flexible polymer material. Can-type batteries, on the other hand, house the electrode components in a casing made of materials such as metal or plastic.

[0007] The bag, which serves as the casing of the pouch-type secondary battery, is prepared by pressing a flexible bag film laminate to form a cup-shaped portion. Then, when the cup-shaped portion is formed, the electrode assembly is housed in the receiving space of the cup-shaped portion, and the sealing portion is sealed to manufacture the secondary battery.

[0008] Drawing in the pressing process is performed by inserting the bag film laminate into a pressing device and applying pressure to the bag film laminate using a stamping press to elongate it. The bag film laminate consists of multiple layers, and the gas barrier layer therein is made of metal. However, conventional bag film laminates are limited by forming a deeper cup-shaped portion, and also by reducing the fillet radius when applying filleting to the bottom edge and the edge of the opening of the cup-shaped portion. In addition, conventional bag film laminates are limited by forming a near-vertical outer wall of the cup-shaped portion. Accordingly, the problems are: the dead space of the secondary battery increases, and the size of the electrode assembly may decrease, resulting in a decrease in energy efficiency relative to volume. Summary of the Invention

[0009] Technical issues

[0010] One aspect of the present invention provides a pouch-type battery casing in which formability is improved by increasing tensile strength and elongation, and a pouch-type secondary battery.

[0011] The purpose of this invention is not limited to the above-described purposes, and other purposes not described herein will be clearly understood by those skilled in the art based on the following description.

[0012] Technical solution

[0013] According to one aspect of the invention, a pouch-type battery housing is provided for housing an electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode. The pouch-type battery housing includes a pouch film laminate comprising: a sealing layer formed of a first polymer as the innermost layer; a surface protective layer formed of a second polymer as the outermost layer; and a gas barrier layer laminated between the surface protective layer and the sealing layer and formed of an aluminum alloy film having a thickness of 60 μm to 100 μm and a grain size of 10 μm to 13 μm. Furthermore, the aluminum alloy film may contain 1.2% to 1.7% by weight of iron.

[0014] In addition, the aluminum alloy film may contain 1.3% to 1.7% by weight of iron.

[0015] In addition, the aluminum alloy film may contain 0.2% by weight or less of silicon.

[0016] Furthermore, the aluminum alloy film may have a grain size of 10.5 μm to 12.5 μm.

[0017] In addition, the alloy number of the aluminum alloy film can be AA8021.

[0018] Furthermore, the gas barrier layer may have a thickness of 70 μm to 90 μm.

[0019] Furthermore, the thickness of the sealing layer can be 0.6 to 1.2 times the thickness of the gas barrier layer, for example, in the range of 30 μm to 90 μm.

[0020] In addition, the first polymer may include polypropylene (PP).

[0021] In addition, the surface protective layer may have a thickness of 6 μm to 25 μm.

[0022] In addition, the second polymer may include polyethylene terephthalate (PET).

[0023] Furthermore, the pouch-type battery housing may further include a stretching aid layer made of a third polymer and laminated between the surface protective layer and the gas barrier layer.

[0024] In addition, the stretching aid layer may have a thickness of 20 μm to 50 μm.

[0025] In addition, the third polymer may include nylon.

[0026] In addition, the bag film laminate has a total thickness of 180 μm or greater, for example, 180 μm to 210 μm.

[0027] In addition, the bag film laminate may have a tensile strength of 200 N / 15 mm to 300 N / 15 mm and an elongation of 105% to 150%, wherein the tensile strength is measured while the bag film laminate is being stretched at a stretching speed of 50 mm / min after being cut into 15 mm × 80 mm dimensions.

[0028] According to another aspect of the present invention, a pouch-type secondary battery is provided, comprising: an electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode; and a pouch-type battery housing housing the electrode assembly, wherein the pouch-type battery housing comprises a pouch film laminate, the pouch film laminate comprising: a sealing layer formed of a first polymer as an innermost layer; a surface protection layer formed of a second polymer as an outermost layer; and a gas barrier layer laminated between the surface protection layer and the sealing layer and formed of an aluminum alloy film having a thickness of 60 μm to 100 μm and a grain size of 10 μm to 13 μm.

[0029] Other specific details of the invention are included in the detailed description and drawings.

[0030] Beneficial effects

[0031] According to embodiments of the present invention, at least the following effects can be achieved:

[0032] The pouch-type battery casing according to the present invention improves the tensile strength, elongation, and toughness of the pouch film laminate by using a pouch film laminate comprising an aluminum alloy film having a specific thickness and grain size as a gas barrier layer. Using this pouch film laminate, the molding depth can be increased without pinholes or cracks during the molding of the cup-shaped portion, and the radius of curvature of the cup-shaped portion edge can be reduced, thereby increasing the housing volume of the battery assembly.

[0033] Furthermore, since the bag film laminate according to the present invention has excellent puncture strength, it can more effectively protect the internal electrode assembly even if it is subjected to greater external pressure or damaged by being punctured by a sharp object.

[0034] The effects of the invention are not limited to those exemplified above, but many more different effects are included in this specification. Attached Figure Description

[0035] Figure 1 This is an assembly diagram of a secondary battery according to an embodiment of the present invention.

[0036] Figure 2 This is a cross-sectional view of a bag film laminate according to an embodiment of the present invention.

[0037] Figure 3 This is a graph showing the iron and silicon content of aluminum alloys with alloy number AA8079 and AA8021.

[0038] Figure 4 This is a graph showing the tensile strength, elongation, and grain size of aluminum alloys AA8079 and AA8021.

[0039] Figure 5 These are magnified SEM images of the grains of the aluminum alloy film with alloy number AA8021 used in Example 1 and the aluminum alloy film with alloy number AA8079 used in Comparative Example 3.

[0040] Figure 6 The graph shows the test results of tensile strength and elongation of the bag film laminates prepared according to the present invention, Comparative Example 1, and Comparative Example 2.

[0041] Figure 7 The graph shows the test results of the puncture strength of the bag film laminates prepared according to the present invention, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0042] The advantages and features of the invention, and its implementation methods, will be illustrated by the following embodiments described with reference to the accompanying drawings. However, the invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Furthermore, the invention is defined only by the scope of the claims. Throughout the specification, similar reference numerals denote similar elements.

[0043] Unless otherwise specified, all terms used herein (including technical and scientific terms) are intended to have the meaning understood by one of skill in the art. Furthermore, unless clearly and specifically defined, terms defined in common dictionaries should not be interpreted anomalously or excessively.

[0044] The technical terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit the invention. In this specification, singular terms may include plural forms unless otherwise specified. It should also be understood that, when used in this specification, the terms “comprises” and / or “comprising” indicate the presence of the mentioned component, but do not exclude the presence or addition of one or more other components.

[0045] Preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings.

[0046] Figure 1 This is an assembly diagram of a secondary battery 1 according to an embodiment of the present invention. Figure 2 This is a cross-sectional view of a bag film laminate according to an embodiment of the present invention.

[0047] According to an embodiment of the present invention, since the toughness is increased by improving the tensile strength and elongation of the pouch film laminate 135, the formability is improved when the pouch film laminate 135 is molded to prepare the pouch-type battery casing 13. Furthermore, since the pouch film laminate has excellent puncture strength, it can more effectively protect the internal electrode components even if it is subjected to significant external pressure or damaged by being punctured by a sharp object.

[0048] Therefore, according to an embodiment of the present invention, the pouch battery housing 13 is a pouch battery housing 13 in which an electrode assembly 10 formed by a positive electrode, a separator, and a negative electrode is housed, and includes a pouch film laminate 135, the pouch film laminate 135 including: a sealing layer 1351, the sealing layer 1351 being formed of a first polymer as the innermost layer; a surface protective layer 1353, the surface protective layer 1353 being formed of a second polymer as the outermost layer; and a gas barrier layer 1352, the gas barrier layer 1352 being laminated between the surface protective layer 1353 and the sealing layer 1351 and being formed of an aluminum alloy film having a thickness of 60 μm to 100 μm and a grain size of 10 μm to 13 μm.

[0049] A secondary battery 1 according to an embodiment of the present invention includes: an electrode assembly 10 formed by stacking a positive electrode, a separator, and a negative electrode; and a pouch-type battery housing 13 housing the electrode assembly 10, wherein the battery housing 13 includes a pouch film laminate 135, the pouch film laminate 135 including: a sealing layer 1351, the sealing layer 1351 being formed of a first polymer as the innermost layer; a surface protective layer 1353, the surface protective layer 1353 being formed of a second polymer as the outermost layer; and a gas barrier layer 1352, the gas barrier layer 1352 being laminated between the surface protective layer 1353 and the sealing layer 1351 and being formed of an aluminum alloy film having a thickness of 60 μm to 100 μm and a grain size of 10 μm to 13 μm.

[0050] The electrode assembly 10 is formed by sequentially stacking a positive electrode, a separator, and a negative electrode. First, a slurry in which electrode active materials, binders, and plasticizers are mixed is applied to a positive electrode current collector and a negative electrode current collector to prepare the positive and negative electrodes. After forming the electrode assembly 10 with a predetermined shape by stacking the positive and negative electrodes on both sides of the separator, the electrode assembly 10 is inserted into the battery housing 13, and the battery housing 13 is sealed after an electrolyte solution is injected.

[0051] Specifically, the electrode assembly 10 includes two types of electrodes (such as positive and negative electrodes) and a separator disposed between the electrodes to insulate them from each other. The electrode assembly 10 includes stacked, jelly roll, and stacked folded types. Both types of electrodes (i.e., positive and negative electrodes) have structures in which an active material slurry is applied to an electrode current collector in the form of a metal foil or mesh, including aluminum and copper. The active material slurry is typically formed by stirring granular active material, conductive material, and binder in a solvent-containing state. The solvent can be removed in subsequent processes.

[0052] like Figure 1As shown, the electrode assembly 10 includes electrode tabs 11. The electrode tabs 11 are connected to each of the positive and negative electrodes of the electrode assembly 10 and protrude outward from one side of the electrode assembly 10, thus becoming a path through which electrons can move between the interior and exterior of the electrode assembly 10. The current collector of the electrode assembly 10 consists of a portion to which an electrode active material is applied and a distal end thereon (i.e., an uncoated portion) to which no electrode active material is applied. Each electrode tab 11 can be formed by cutting the uncoated portion or by attaching individual conductive members to the uncoated portion via ultrasonic welding or the like. Figure 1 As shown, the electrode tabs 11 may protrude side by side from one side of the electrode assembly 10 in the same direction, but are not limited thereto, and may protrude in different directions from each other.

[0053] Electrode leads 12 are connected to electrode contacts 11 of electrode assembly 10 via spot welding or similar methods. Furthermore, a portion of the electrode lead 12 is surrounded by an insulating portion 14. The insulating portion 14 is confined at a sealing portion 134, where the first housing 131 and the second housing 132 of the battery housing 13 are thermally fused, thereby bonding the electrode lead 12 to the battery housing 13. Additionally, the insulating portion 14 prevents the flow of electricity generated from the electrode assembly 10 through the electrode lead 12 to the battery housing 13 and maintains the seal of the battery housing 13. Therefore, the insulating portion 14 can be made of a non-conductive material. Generally, a relatively thin insulating strip that is easy to attach to the electrode lead 12 is widely used as the insulating portion 14, but the invention is not limited to this; various components can be used as long as they insulate the electrode lead 12.

[0054] One end of the electrode lead 12 is connected to the electrode contact 11, and the other end of the electrode lead 12 protrudes to the outside of the battery casing 13. That is, the electrode lead 12 includes a positive electrode lead 121 and a negative electrode lead 122. One end of the positive electrode lead 121 is connected to the positive electrode contact 111 and extends in the direction protruding from the positive electrode contact 111, and one end of the negative electrode lead 122 is connected to the negative electrode contact 112 and extends in the direction protruding from the negative electrode contact 112. Figure 1 As shown, the other ends of both the positive electrode lead 121 and the negative electrode lead 122 protrude to the outside of the battery casing 13. Accordingly, the power generated in the electrode assembly 10 can be supplied to the outside. Furthermore, since the positive electrode contact 111 and the negative electrode contact 112 are formed to protrude in each direction, the positive electrode lead 121 and the negative electrode lead 122 can also extend in each direction.

[0055] The positive electrode lead 121 and the negative electrode lead 122 can be made of different materials. That is, the positive electrode lead 121 can be made of the same material as the positive current collector, namely aluminum (Al), and the negative electrode lead 122 can be made of the same material as the negative current collector, namely copper (Cu) or copper coated with nickel (Ni). Since the portion of the electrode lead 12 that protrudes to the outside of the battery casing 13 becomes a terminal portion, it is electrically connected to an external terminal.

[0056] The battery casing 13 is formed by molding a bag made of a flexible material. The case where the battery casing 13 is a bag will be described below. The battery casing 13 houses the electrode assembly 10, such that a portion of the electrode leads 12, i.e., the terminal portion, is exposed and then sealed. Figure 1 As shown, the battery housing 13 includes a first housing 131 and a second housing 132. A cup-shaped portion 133 is formed in the second housing 132 to provide a receiving space 1331 capable of accommodating the electrode assembly 10. The first housing 131 covers the receiving space 1331 from the top, such that the electrode assembly 10 does not separate from the outside of the battery housing 13. In this case, as... Figure 1 As shown, a cup-shaped portion 133 with a receiving space 1331 can also be formed in the first housing 131 to receive the electrode assembly 10 from the top. For example... Figure 1 As shown, the first housing 131 and the second housing 132 can be prepared by connecting one side of them to each other, but the invention is not limited thereto. The first housing 131 and the second housing 132 can be prepared in various ways, for example, the first housing 131 and the second housing 132 can be separated from each other and manufactured separately.

[0057] When the electrode lead 12 is connected to the electrode tab 11 of the electrode assembly 10 and the insulating portion 14 is formed on a portion of the electrode lead 12, the electrode assembly 10 is accommodated in the receiving space 1331 provided in the cup-shaped portion 133 of the second housing 132, and the first housing 131 covers the space from the top. Then, an electrolyte is injected into it, and the sealing portions 134 formed on the edges of the first housing 131 and the second housing 132 are sealed. The electrolyte can move lithium ions generated by the electrochemical reaction of the electrodes during the charging and discharging of the secondary battery 1, wherein the electrolyte may include a non-aqueous organic electrolyte as a mixture of lithium salt and high-purity organic solvent, or a polymer electrolyte using a polymer. The pouch-type secondary battery 1 can be prepared by the above method.

[0058] Figure 2 This is a cross-sectional view of the bag film laminate 135 according to an embodiment of the present invention.

[0059] The battery casing 13 of the pouch-type secondary battery 1 according to an embodiment of the present invention can be manufactured by drawing the pouch film laminate 135. That is, the battery casing 13 is prepared by drawing the pouch film laminate 135 to form a cup-shaped portion 133 using a stamping press or the like. According to an embodiment of the present invention, as Figure 2 As shown, the bag film laminate 135 includes a sealant layer 1351, a gas barrier layer 1352, and a surface protection layer 1353, and may further include a drawing assistance layer 1354 if necessary.

[0060] The sealing layer 1351 is formed of a first polymer and is formed as the innermost layer to directly contact the electrode assembly 10. Here, the innermost layer refers to the layer positioned at the end of the gas barrier layer 1352 in the direction in which the electrode assembly 10 is positioned. When the bag film laminate 135 having the laminated structure described above is drawn using a press or similar method, a portion of the bag film laminate 135 is elongated to form a cup-shaped portion 133, which includes a bag-shaped receiving space 1331. Then, when the electrode assembly 10 is received in the receiving space 1331, an electrolyte solution is injected. Subsequently, if the first housing 131 and the second housing 132 come into contact with each other and thermal compression is applied to the sealing portion 134, the sealing layers 1351 bond together to seal the bag. In this case, the sealing layer 1351 must be insulating because it is in direct contact with the electrode assembly 10, and must be corrosion resistant because it is also in contact with the electrolyte solution. Furthermore, since it is necessary to completely seal the interior of the battery casing 13 to prevent material movement between the interior and exterior, it must have high sealing performance. That is, the sealing portions 134 where the sealing layers 1351 are bonded to each other must have excellent bonding strength. Generally, the first polymer used to prepare the sealing layer 1351 may include at least one material selected from the group consisting of: polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aromatic polyamide, nylon, polyester, poly(p-phenylenebenzobisoxazole), polyarylate, polytetrafluoroethylene, and glass fiber. In particular, polyolefin-based resins such as polypropylene (PP) or polyethylene (PE) are mainly used. Polypropylene (PP) is mainly used to prepare the sealing layer 1351 because it has excellent mechanical properties such as tensile strength, rigidity, surface hardness, abrasion resistance, and heat resistance, and chemical properties such as corrosion resistance. Furthermore, the sealing layer may be composed of cast polypropylene, acid-modified polypropylene, or a polypropylene-butene-ethylene terpolymer. Here, the acid-treated polypropylene may be maleic anhydride polypropylene (MAH PP). Additionally, the sealing layer 1351 may have a single-layer structure formed from any one of the materials or a composite layer structure having two or more of these materials formed as layers.

[0061] The thickness of the sealing layer 1351 can be 0.6 to 1.2 times, preferably 0.7 to 1.1 times, and more preferably 0.8 to 1.1 times, the thickness of the gas barrier layer (described below). If the thickness of the sealing layer is less than 0.6 times the thickness of the gas barrier layer, the sealing durability may decrease, while if the thickness of the sealing layer is greater than 1.2 times the thickness of the gas barrier layer, the formability may decrease due to the excessive increase in the total thickness of the bag. Furthermore, to ensure sufficient insulation, it is preferable that the thickness of the sealing layer 1351 is 0.8 times or greater than the thickness of the gas barrier layer.

[0062] Specifically, the thickness of the sealing layer 1351 can be in the range of 30 μm to 90 μm, preferably 50 μm to 90 μm, and more preferably 70 μm to 90 μm. When the thickness of the sealing layer 1351 is less than 30 μm, the seal durability may decrease, for example, internal failure may occur during sealing. When the thickness of the sealing layer 1351 is greater than 90 μm, the formability may decrease and the battery energy density (energy per volume) may decrease due to the excessive increase in bag thickness. Furthermore, to ensure sufficient insulation, it is preferable that the thickness of the sealing layer 1351 is 70 μm or greater. This is because when the sealant thickness is small, the dielectric breakdown voltage of the bag film laminate may decrease, degrading the insulation. Furthermore, when using a bag film laminate with poor insulation to prepare the battery, the failure rate may increase.

[0063] The gas barrier layer 1352 is laminated between the surface protective layer 1353 and the sealing layer 1351 to ensure the mechanical strength of the bag, prevent the introduction and release of gas or moisture from outside the secondary battery 1, and prevent electrolyte solution leakage.

[0064] The gas barrier layer 1352 is made of an aluminum alloy thin film, and according to embodiments of the present invention, the gas barrier layer 1352 can be particularly formed of an aluminum alloy thin film having a thickness of 60 μm to 100 μm and a grain size of 10 μm to 13 μm. The aluminum alloy thin film is lightweight while ensuring mechanical strength above a predetermined level, complementing the electrochemical properties provided by the electrode assembly 10 and the electrolyte solution, and ensuring heat dissipation.

[0065] Specifically, the aluminum alloy film according to embodiments of the present invention may have a thickness of 60 μm to 100 μm, for example 70 μm to 90 μm, and a grain size of 10 μm to 13 μm, preferably 10.5 μm to 12.5 μm, and more preferably 11 μm to 12 μm. When the thickness and grain size of the aluminum alloy film meet the above ranges, the forming depth can be increased without pinholes or cracks occurring during cup forming.

[0066] Typically, the gas barrier layer 1352 is formed to a thickness of 30 μm to 50 μm. However, when the thickness of the gas barrier layer is 30 μm to 50 μm, there are limitations: even if the bag film laminate 135 is stretched and molded, increasing the molding depth of the cup-shaped portion 133 or molding the outer wall of the cup-shaped portion 133 to a near-vertical state, there are also limitations in reducing the radius of curvature of the rounded corners of the cup-shaped portion 133. In addition, due to the low puncture strength, there is a problem that the internal electrode assembly 10 is easily damaged when the battery casing is subjected to external impact.

[0067] To address this issue in this invention, the gas barrier layer 1352 is formed with a thickness of 60 μm to 100 μm, particularly 70 μm to 100 μm. When the thickness of the gas barrier layer meets this range, the formability of the gas barrier layer 1352 is improved, allowing the cup-shaped portion 133 to be formed deeper during the stretching of the bag film laminate 135, and also reducing the radius of curvature of the edge of the cup-shaped portion 133. Furthermore, due to the increased volume of the accommodating space 1331, more electrodes and separators can be stacked within the electrode assembly 10, increasing the energy efficiency relative to volume. However, if the thickness of the gas barrier layer 1352 is greater than 100 μm, the total thickness of the bag may increase excessively, potentially reducing the energy density of the secondary battery 1 relative to volume.

[0068] Furthermore, given that the thickness of the gas barrier layer meets the above-mentioned range, the improved puncture strength of the bag film laminate 135 allows it to more effectively protect the internal electrode assembly 10 even if it is subjected to significant external pressure or damaged by a sharp object. Here, "excellent puncture strength" means high strength when puncturing a hole in the bag film laminate 135.

[0069] However, while increasing the thickness of the aluminum alloy film may increase the forming depth, it also leads to sealing durability issues due to pinholes or cracks occurring in the film after forming. Therefore, as a result of extensive research, the inventors of this application discovered that using an aluminum alloy film with a grain size of 10 μm to 13 μm can suppress the occurrence of pinholes or cracks even with increased forming depth, leading to the present invention. According to the inventors' research, when the grain size of the aluminum alloy film is greater than 13 μm, the strength of the film decreases, increasing the likelihood of cracks or pinholes during forming. Conversely, when the grain size is less than 10 μm, the reduced flexibility of the film limits the improvement of formability.

[0070] Grain size varies depending on the composition and processing method of the aluminum alloy film, and can be measured by observing a cross-section in the thickness direction of the aluminum alloy film using a scanning electron microscope (SEM). Specifically, in this invention, a cross-sectional SEM image of the aluminum alloy film in the thickness direction is obtained using a scanning electron microscope, the maximum diameter of 30 random grains observed in the SEM image is measured, and their average value is then evaluated as the grain size.

[0071] The aluminum alloy film according to the invention may include metallic elements other than aluminum, for example, at least one selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg) and zinc (Zn).

[0072] The iron (Fe) content of the aluminum alloy film can be in the range of 1.2 wt% to 1.7 wt%, preferably 1.3 wt% to 1.7 wt%, and more preferably 1.3 wt% to 1.45 wt%. When the iron (Fe) content of the aluminum alloy film is less than 1.2 wt%, the strength of the aluminum alloy film may decrease, leading to cracks and pinholes during molding. When the iron (Fe) content of the aluminum alloy film is greater than 1.7 wt%, there are limitations in improving formability due to the reduced flexibility of the aluminum alloy film.

[0073] Furthermore, the silicon (Si) content of the aluminum alloy thin film can be in the range of 0.2 wt% or less, preferably from 0.05 wt% to 0.2 wt%, and more preferably from 0.08 wt% to 0.19 wt%. When the silicon content is greater than 0.2 wt%, the formability may decrease.

[0074] Specifically, the aluminum alloy film according to the present invention can be an aluminum alloy with alloy number AA8021.

[0075] Figure 3 This is a graph showing the iron and silicon content of aluminum alloy AA8079, which is mainly used in batteries and is conventionally used in battery pouches, and aluminum alloy AA8021, which is used in this invention.

[0076] like Figure 3As shown, alloy number AA8079 comprises 0.6 wt% to 1.2 wt% iron and 0.05 wt% to 0.3 wt% silicon. Generally, when aluminum alloys contain a large amount of iron, their mechanical strength is improved, while when they contain a small amount of iron, their flexibility is improved. For aluminum alloy number AA8079, which contains relatively little iron, flexibility may be improved when it is used to prepare the gas barrier layer 1352; however, due to the potential reduction in strength, there may be limitations in formability.

[0077] In comparison, such as Figure 3 As shown, alloy number AA8021 comprises 1.2 wt% to 1.7 wt%, particularly 1.3 wt% to 1.7 wt% of iron, and 0.05 wt% to 1.9 wt%, particularly 0.08 wt% to 0.19 wt% of silicon. When the gas barrier layer 1352 is prepared from the aluminum alloy with alloy number AA8021, the tensile strength, elongation rate, and puncture strength are improved due to the relatively large amount of iron included.

[0078] Figure 4 The tensile strength (Rm), elongation (A), and grain size of aluminum alloys AA8079 and AA8021 are shown.

[0079] like Figure 4 As shown, AA8079 has low tensile strength and elongation, which limits its formability. Due to its relatively large grain size of 13 μm to 21 μm, internal stress is less dispersed during stretching, resulting in an increased number of pinholes.

[0080] In contrast, AA8021 exhibits excellent formability due to its high tensile strength and elongation, and has a relatively small grain size of 10 μm to 13 μm. As a result, internal stress can be more dispersed during stretching, and thus, pinholes can be effectively suppressed.

[0081] When tensile force is applied to a material, the relationship between tensile strength and elongation can be represented as a graph. In this case, if the vertical axis of the graph represents tensile strength and the horizontal axis represents elongation, then the area under the graph represents the toughness of the corresponding material. Toughness refers to the degree of resistance to material failure; the higher the toughness, the more the material can be stretched before it breaks. In the case of preparing the gas barrier layer 1352 using aluminum alloy with alloy number AA8021, the improved tensile strength and elongation result in increased toughness and improved formability.

[0082] The surface protective layer 1353 is made of a second polymer and is formed as the outermost layer to protect the secondary battery 1 from external friction and impact while electrically insulating the electrode assembly 10 from the outside. Here, the outermost layer refers to the layer positioned at the end of the gas barrier layer 1352 on a square opposite to the direction in which the electrode assembly 10 is positioned. The second polymer used to prepare the surface protective layer 1353 can be at least one material selected from the group consisting of: polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aromatic polyamide, nylon, polyester, poly(p-phenylenebenzobisoxazole), polyarylate, polytetrafluoroethylene, and glass fiber. In particular, it is preferable to primarily use polymers with abrasion resistance and heat resistance, such as polyethylene terephthalate (PET). The surface protective layer 1353 can have a single-layer structure made of any one material or a composite layer structure having two or more of these materials formed as layers.

[0083] According to an embodiment of the present invention, the thickness of the surface protective layer 1353 can be in the range of 6 μm to 25 μm. If the thickness of the surface protective layer 1353 is less than 6 μm, there is a problem of reduced external insulation. In contrast, if the thickness of the surface protective layer 1353 is greater than 25 μm, the energy density of the secondary battery 1 relative to its volume may actually decrease because the total thickness of the bag may increase.

[0084] Although PET is inexpensive, has excellent durability, and excellent electrical insulation properties, it has poor adhesion to aluminum (which is typically used as the gas barrier layer 1352), and the two materials behave differently when stretched under stress. Therefore, if the surface protective layer 1353 and the gas barrier layer 1352 are directly adhered, they may delaminate during stretching. As a result, the formability may be reduced because the gas barrier layer 1352 may not be stretched uniformly.

[0085] According to an embodiment of the present invention, the battery casing 13 may further include a stretching aid layer 1354, which is made of a third polymer and laminated between the surface protective layer 1353 and the gas barrier layer 1352. The stretching aid layer 1354 is laminated between the surface protective layer 1353 and the gas barrier layer 1352 to prevent delamination of the surface protective layer 1353 and the gas barrier layer 1352 during stretching. The third polymer used to prepare the stretching aid layer 1354 may include at least one material selected from the group consisting of: polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aromatic polyamide, nylon, polyester, poly(p-phenylenebenzobisoxazole), polyarylate, polytetrafluoroethylene, and glass fiber. Specifically, since nylon resin readily adheres to the polyethylene terephthalate (PET) of the surface protective layer 1353 and exhibits behavior similar to that of the aluminum alloy of the gas barrier layer 1352 when stretched, it is preferable to primarily use nylon resin as the third polymer. The stretching aid layer 1354 may have a single-layer structure made of any one material or a composite layer structure having two or more of these materials formed as layers.

[0086] As described above, according to embodiments of the present invention, the moldability of the gas barrier layer 1352 is improved because it has a thickness of approximately 60 μm to approximately 100 μm. In this case, to similarly improve the moldability of the stretching aid layer 1354, the stretching aid layer 1354 may have a thickness of 20 μm to 50 μm, and particularly preferably, a thickness of 25 μm to 38 μm. If the thickness of the stretching aid layer 1354 is less than 20 μm, it may be damaged during stretching because it may not match the improved moldability of the gas barrier layer 1352. In contrast, if the thickness is greater than 50 μm, the volume of the secondary battery 1 may increase and the energy density may decrease because the total thickness of the bag may increase.

[0087] The pouch film laminate according to the invention can have a total thickness of 180 μm or greater, for example, 180 μm to 210 μm. When the thickness of the pouch film laminate is 180 μm or greater, the cup forming depth can be further increased compared to the conventional case. Excessive total thickness of the pouch film laminate is undesirable because it increases the overall volume of the secondary battery.

[0088] The bag film laminate according to the invention exhibits excellent tensile strength and elongation by comprising an aluminum alloy film having a specific thickness and grain size. Specifically, the bag film laminate according to the invention can have a tensile strength of 200 N / 15 mm to 300 N / 15 mm, preferably 220 N / 15 mm to 270 N / 15 mm, and more preferably 220 N / 15 mm to 250 N / 15 mm, measured while stretching at a stretching speed of 50 mm / min after the bag film laminate has been cut into 15 mm × 80 mm dimensions, and can have an elongation of 105% to 150%, preferably 105% to 140%, and more preferably 105% to 130%. As described above, due to the high tensile strength and elongation of the bag film laminate according to the invention, optionally, cracking is less likely to occur even when the forming depth is large during cup forming.

[0089] Furthermore, the bag film laminate according to the invention has excellent puncture strength by comprising an aluminum alloy film having a specific thickness and grain size. Specifically, the bag film laminate according to the invention can have a puncture strength of 30 N or greater, for example, 30 N to 40 N.

[0090] The invention will be described in more detail below with reference to specific embodiments.

[0091] Example 1

[0092] A surface protective layer, a stretching aid layer, and a gas barrier layer are formed by sequentially bonding a nylon resin with a width of 266 cm, a length of 50 m, and a thickness of 25 μm, and a polyethylene terephthalate (PET) with a width of 266 cm, a length of 50 m, and a thickness of 12 μm to one surface of an aluminum (Al) alloy with the alloy number AA8021, which has a width of 266 cm, a length of 50 m, and a thickness of 80 μm, using a dry lamination method with a urethane adhesive.

[0093] Next, cast polypropylene (CPP) is melted at high temperature and then co-extruded onto the other surface of an aluminum (Al) alloy film to form a 60 μm thick sealing layer, thereby preparing the bag film laminate. The total thickness of the bag film laminate is 183 μm.

[0094] Example 2

[0095] The bag film laminate was prepared in the same manner as in Example 1, except that the sealing layer was formed to a thickness of 80 μm. The total thickness of the bag film laminate was 203 μm.

[0096] Comparative Example 1

[0097] The bag film laminate was prepared in the same manner as in Example 1, except that: an aluminum alloy film with a thickness of 40 μm and alloy number AA8021 was used as the gas barrier layer, a nylon film with a thickness of 15 μm was used as the stretching aid layer, and the sealing layer was formed to a thickness of 80 μm. The total thickness of the bag film laminate was 153 μm.

[0098] Comparative Example 2

[0099] The bag film laminate was prepared in the same manner as in Example 1, except that a 50 μm thick aluminum alloy film with alloy number AA8021 was used as the gas barrier layer. The total thickness of the bag film laminate was 153 μm.

[0100] Comparative Example 3

[0101] The bag film laminate was prepared in the same manner as in Example 1, except that an 80 μm thick aluminum alloy film (alloy number AA8079) was used as the gas barrier layer. The total thickness of the bag film laminate was 183 μm.

[0102] Comparative Example 4

[0103] The bag film laminate was prepared in the same manner as in Example 2, except that an 80 μm thick aluminum alloy film (alloy number AA8079) was used as the gas barrier layer. The total thickness of the bag film laminate was 203 μm.

[0104] Comparative Example 5

[0105] The bag film laminate was prepared in the same manner as in Example 1, except that: an aluminum alloy film with a thickness of 40 μm and alloy number AA8079 was used as the gas barrier layer, a nylon film with a thickness of 15 μm was used as the stretching aid layer, and the sealing layer was formed to a thickness of 80 μm. The total thickness of the bag film laminate was 153 μm.

[0106] [Table 1]

[0107]

[0108] Experimental Example 1: Grain Size Measurement

[0109] The grain size was measured by observing cross-sections in the thickness direction of the AA8021 and AA8079 aluminum alloy films used as gas barrier layers in Example 1 and Comparative Example 3, respectively, using a scanning electron microscope (SEM). Specifically, the grain size was measured by calculating the average value of 30 grains observed in the cross-sectional SEM images of the aluminum alloy films in the thickness direction obtained using a scanning electron microscope.

[0110] SEM images of AA8021 aluminum alloy and AA8079 aluminum alloy are shown in... Figure 5 The results of measuring the grain size based on the SEM images shown are as follows: the grain size of AA8021 is 11.6 μm, and the grain size of AA8079 is 16.8 μm.

[0111] Experimental Example 2: Formability Evaluation

[0112] After cutting the bag film laminates prepared in Examples 1 and 2 and Comparative Examples 1 to 5 into 90 mm × 150 mm dimensions, molding was performed in a battery casing molding apparatus having a molding part with dimensions of 32 mm wide × 55 mm while varying the molding depth. The molding depth at the crack location in each sample was recorded. Here, the corners and edges of the stamping press and the molding part of the battery casing molding apparatus were chamfered. The corners of the stamping press had a curvature of 2 mm, and its edges had a curvature of 1 mm. The corners of the molding part had a curvature of 2.3 mm, and its edges had a curvature of 1 mm. Furthermore, the clearance between the stamping press and the molding part was 0.3 mm. The measurement results are shown in Table 2 below.

[0113] [Table 2]

[0114]

[0115] As listed in Table 2, no cracks occurred in the bag film laminates of Examples 1 and 2 according to the present invention, and they could be molded to a depth of 15.0 mm or greater. However, for the bag film laminates of Comparative Examples 1 to 5, in which the thickness of the barrier layer and / or the grain size are outside the scope of the present invention, cracks occurred at a molding depth of less than 15.0 mm. Therefore, it can be confirmed that the moldability of the bag film laminate is improved while satisfying the barrier layer thickness and grain size of the present invention. If a battery casing is prepared using the bag film laminate prepared according to the examples of the present invention, a receiving space with a depth of 30 mm or greater can be obtained because a cup-shaped portion is formed in both the second casing and the first casing. Therefore, since a thicker electrode assembly can be accommodated, the energy density of the secondary battery relative to its volume can be increased.

[0116] Experimental Example 3: Evaluation of Tensile Strength and Elongation

[0117] Five samples of each of the bag film laminates prepared in Examples 1 and 2, and Comparative Examples 1 to 5, were cut into identical 15 mm × 80 mm sizes. Each sample was then fixed to the lower clamp of a tensile strength tester (manufacturer: Shimadzu, model: AGX-V). Furthermore, after fixing each sample to a point 30 mm from the upper end using the upper clamp, the sample was elongated while the upper clamp was moved away from the lower clamp at a speed of 50 mm / min. The tensile strength and elongation were then measured before the bag film laminate fractured. The measurement results are shown in Tables 3 and 4 below.

[0118] [Table 3]

[0119]

[0120] [Table 4]

[0121]

[0122] Figure 6 This is a graph showing the test results of tensile strength and elongation of the bag film laminates of Embodiment 1, Comparative Example 1, and Comparative Example 2 according to the present invention. (Refer to...) Figure 6 As shown in Tables 3 and 4, it can be confirmed that the bag film laminates of Examples 1 and 2 have better tensile strength and elongation compared with the bag film laminates of Comparative Examples 1 to 5.

[0123] In a graph relating tensile strength and elongation, the area below the graph represents the toughness of the corresponding material, where, for example... Figure 6 As shown, it can be understood that the image area of ​​the bag film laminate of Embodiment 1 according to the present invention is larger than the image area of ​​the bag film laminates according to Comparative Example 1 and Comparative Example 2, which shows that the bag film laminate of Embodiment 1 according to the present invention has excellent toughness.

[0124] Experimental Example 4: Evaluation of Puncture Strength

[0125] After cutting ten samples of each of the bag film laminates prepared in Examples 1 and 2 and Comparative Examples 1 to 5 into identical 90 mm × 80 mm dimensions, each sample was horizontally fixed to the fixture of a puncture strength tester (manufacturer: Shimadzu, model: AGX-V). A probe with a diameter of 1.0 mm and a tip curvature of 0.5 mm was vertically mounted above the mounted sample. The puncture strength of each sample was then measured by placing the probe on each sample. The measurement results are shown in Table 5 below.

[0126] [Table 5]

[0127]

[0128] Figure 7 This is a graph showing the test results of the puncture strength of the bag film laminates of Embodiment 1, Comparative Example 1, and Comparative Example 2 according to the present invention. (Refer to...) Figure 7 As confirmed by Table 5, the bag film laminates of Examples 1 and 2 have better puncture strength compared to the bag film laminates of Comparative Examples 1 to 5. That is, even if they are subjected to greater external pressure or damaged by being punctured by a sharp object, the bag film laminate according to the present invention can more effectively protect the internal electrode assembly.

[0129] Experimental Example 5: Insulation Evaluation

[0130] After the bag film laminates prepared in Examples 1 and 2 were each cut into identical 90 mm × 150 mm pieces and stored in a vacuum oven at 60 degrees Celsius for 24 hours, the dielectric breakdown voltage was measured in a drying chamber. Specifically, a 5 t thick aluminum film was placed on both sides of the bag film laminate. The (+) electrode of the measuring device was connected to the gas barrier layer of the bag film laminate, and the (-) electrode was connected to the aluminum film in contact with the sealing layer. The voltage applied while a leakage current of 0.5 Ma or greater was measured at a rate of 100 V / s was evaluated as the dielectric breakdown voltage. The measurement results are shown in Table 6 below.

[0131] [Table 6]

[0132]

[0133] Referring to Table 6, it can be confirmed that the dielectric breakdown voltage of the bag film laminate of Example 2 with a sealing layer thickness of 80 μm is higher than that of the bag film laminate of Example 1 with a sealing layer thickness of 60 μm, wherein the surface has better insulation when the sealing layer thickness is 80 μm.

[0134] Those skilled in the art will understand that various changes in form and detail may be made without departing from the spirit and scope of the invention as defined by the following claims. Accordingly, it is to be understood that the invention has been described by way of example rather than limitation. Therefore, the scope of the invention is defined by the following claims rather than the foregoing detailed description, and it is to be interpreted that all changes or variations derived from the meaning, scope, and equivalent concepts of the appended claims are within the scope of the invention.

[0135] [Symbol Explanation]

[0136] 1: Secondary battery; 10: Electrode assembly

[0137] 11: Electrode contact piece 12: Electrode lead

[0138] 13: Battery casing 14: Insulation part

[0139] 111: Positive terminal connector; 112: Negative terminal connector

[0140] 121: Positive lead; 122: Negative lead

[0141] 131: First shell 132: Second shell

[0142] 133: Cup-shaped part; 134: Sealing part

[0143] 135: Bag film laminate; 1331: Reception space

[0144] 1351: Sealing layer; 1352: Gas barrier layer

[0145] 1353: Surface protective layer; 1354: Tensile auxiliary layer

Claims

1. A pouch-type battery casing for housing an electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode. The pouch-type battery housing includes a pouch film laminate, which comprises: A sealing layer, wherein the sealing layer is formed of a first polymer as the innermost layer; A surface protective layer, wherein the surface protective layer is formed of a second polymer as the outermost layer; and A gas barrier layer is laminated between the surface protective layer and the sealing layer and is formed of an aluminum alloy film having a thickness of 60 μm to 100 μm and a grain size of 10 μm to 13 μm.

2. The pouch-type battery casing according to claim 1, wherein the aluminum alloy film contains 1.2% to 1.7% by weight of iron.

3. The pouch-type battery casing according to claim 1, wherein the aluminum alloy film contains 1.3% to 1.7% by weight of iron.

4. The pouch-type battery casing according to claim 1, wherein the aluminum alloy film contains 0.2% by weight or less of silicon.

5. The pouch-type battery casing according to claim 2, wherein the aluminum alloy film has a grain size of 10.5 μm to 12.5 μm.

6. The pouch-type battery casing according to claim 1, wherein the aluminum alloy film comprises aluminum alloy with alloy number AA8021.

7. The pouch-type battery housing according to claim 1, wherein the gas barrier layer has a thickness of 70 μm to 90 μm.

8. The pouch-type battery casing according to claim 1, wherein the thickness of the sealing layer is 0.6 to 1.2 times the thickness of the gas barrier layer.

9. The pouch-type battery housing according to claim 1, wherein the sealing layer has a thickness of 30 μm to 90 μm.

10. The pouch-type battery casing of claim 1, wherein the first polymer comprises polypropylene (PP).

11. The pouch-type battery housing according to claim 1, wherein the surface protective layer has a thickness of 6 μm to 25 μm.

12. The pouch-type battery casing according to claim 1, wherein the second polymer comprises polyethylene terephthalate (PET).

13. The pouch-type battery housing according to claim 1, further comprising a stretching aid layer made of a third polymer and laminated between the surface protective layer and the gas barrier layer.

14. The pouch-type battery housing according to claim 13, wherein the stretching auxiliary layer has a thickness of 20 μm to 50 μm.

15. The pouch-type battery housing of claim 13, wherein the third polymer comprises nylon.

16. The pouch-type battery housing according to claim 1, wherein the pouch film laminate has a total thickness of 180 μm or greater.

17. The pouch-type battery casing according to claim 1, wherein the pouch film laminate has a tensile strength of 200 N / 15 mm to 300 N / 15 mm and an elongation of 105% to 150%, wherein the tensile strength is measured while stretching the pouch film laminate at a stretching speed of 50 mm / min after it has been cut into 15 mm × 80 mm dimensions.

18. The pouch-type battery housing according to claim 1, wherein the pouch film laminate has a puncture strength of 30N or greater.

19. A pouch-type secondary battery, comprising: An electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode; and a pouch-type battery casing that houses the electrode assembly, The pouch-type battery housing includes a pouch film laminate, which comprises: A sealing layer, wherein the sealing layer is formed of a first polymer as the innermost layer; A surface protective layer, wherein the surface protective layer is formed of a second polymer as the outermost layer; and A gas barrier layer is laminated between the surface protective layer and the sealing layer and is formed of an aluminum alloy film having a thickness of 60 μm to 100 μm and a grain size of 10 μm to 13 μm.

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