Pouch for a secondary battery and lithium secondary battery

Abstract

Pouch for a secondary battery, including: a barrier layer configured to ensure the mechanical strength of the pouch, to block the introduction and release of any gas or moisture from outside the secondary battery, and to prevent electrolyte leakage; a base material layer arranged on a surface of the barrier layer; and a sealing layer that is arranged on the other surface of the barrier layer, the sealing layer comprises: a first sealing layer in contact with the other surface of the barrier layer; and a second sealing layer, which is arranged on top of the first sealing layer opposite the barrier layer, wherein the sealing layer has a melt flow rate (MFR) of 8.5 g / 10 min to 14.0 g / 10 min, which is measured as described above at a temperature of about 230 °C under a load condition of 2.16 kg.

Description

CROSS-REFERENCE TO RELATED REGISTRATIONS

[0001] This application claims priority from Korean patent application No. 10-2022-0183748, which was filed with the Korean Intellectual Property Office on December 23, 2022, and the disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION Area of ​​the invention

[0002] The present invention relates to a pouch for a secondary battery and a lithium secondary battery including the same, and in particular a pouch for a secondary battery having a high cell venting resistance and low venting generation to implement excellent high temperature reliability, and a lithium secondary battery including the same. Description of the related technique

[0003] A lithium secondary battery is manufactured in a manner in which an electrode active material slurry is applied to a positive electrode collector and a negative electrode collector to produce a positive electrode and a negative electrode, and the positive electrode and the negative electrode are stacked on either side of a separator to form an electrode assembly, and then the electrode assembly is received in a pouch and an electrolyte is injected into the casing.

[0004] Such a secondary battery is classified into pouch-type secondary batteries and can-type secondary batteries according to the material of the casing that houses the electrode assembly. Among these, the pouch-type secondary battery is manufactured by pressing a stack of flexible pouch film to form a cup-like portion, and an electrode assembly is placed within this portion. An electrolyte is then injected, and a sealing element is added. The can-type secondary battery is manufactured by placing an electrode assembly within a can made of a metal material, injecting an electrolyte, and assembling a top cap to the upper section of the can for sealing.

[0005] While pouch-type secondary batteries are lightweight, offer excellent space utilization, and have high energy densities due to their stacked electrode arrangements, they are more susceptible to fire, explosion, and electrolyte leakage upon external impact and / or high internal temperatures or pressures compared to can-type secondary batteries. When secondary batteries are used to power electric vehicles, they must provide excellent safety features to protect the vehicle's occupants.

[0006] When a pouch-type secondary battery is stored at high temperatures, a gas is generated due to a side reaction with the electrolyte. This results in an increase in the battery's internal pressure, leading to a venting phenomenon where a sealing element of the pouch ruptures. If this venting phenomenon occurs early, the safety and reliability of the secondary battery are significantly compromised. Therefore, there is a need to develop a pouch-type secondary battery with high cell venting resistance and low venting generation in high-temperature environments to achieve excellent high-temperature reliability. BRIEF SUMMARY OF THE INVENTION

[0007] One aspect of the present invention provides a pouch with a specific melt flow rate, including a sealing layer with a two-layer structure that has a high cell venting resistance and excellent high-temperature reliability, and a lithium secondary battery including the same.

[0008] According to one aspect of the present invention, a pouch for a secondary battery is provided comprising: a barrier layer; a base material layer arranged on one surface of the barrier layer; and a sealing layer arranged on the other surface of the barrier layer, wherein the sealing layer comprises: a first sealing layer in contact with the other surface of the barrier layer; and a second sealing layer arranged on the first sealing layer opposite the barrier layer, wherein the sealing layer has a melt flow rate (MFR) of about 14.0 g / 10 min or less, measured at a temperature of about 230 °C under a load condition of about 2.16 kg.

[0009] The first sealing layer and the second sealing layer can be formed by co-extrusion on the barrier layer; the first sealing layer can contain an acid-modified polyolefin resin and the second sealing layer can contain a polyolefin resin.

[0010] The thickness ratio of the second sealing layer to the thickness of the first sealing layer can be approximately 0.8 to approximately 1.2, preferably approximately 0.9 to approximately 1.1. The first sealing layer has a thickness of approximately 25 µm to approximately 80 µm, preferably approximately 30 µm to approximately 70 µm, more preferably approximately 30 µm to approximately 60 µm, and the second sealing layer can have a thickness of approximately 20 µm to approximately 80 µm, preferably approximately 25 µm to approximately 70 µm, more preferably approximately 30 µm to approximately 60 µm.

[0011] The total thickness of the sealing layer, which combines the first sealing layer and the second sealing layer, can be approximately 45 µm to approximately 100 µm, preferably approximately 50 µm to approximately 100 µm, more preferably approximately 60 µm to approximately 100 µm and even more preferably approximately 70 µm to approximately 90 µm.

[0012] The barrier layer may contain an aluminum alloy layer.

[0013] The base material layer may include at least one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazoles, polyarylates and Teflon.

[0014] According to another aspect of the present invention, a lithium secondary battery is provided comprising: an electrode arrangement in which a positive electrode, a separator and a negative electrode are stacked; an electrolyte; and a pouch-like battery case configured to accommodate the electrode arrangement and the electrolyte, the battery case being the pouch described above according to the present invention.

[0015] In the lithium secondary battery, the cell venting resistance can be approximately 7.7 bar or more, preferably approximately 7.7 bar to 15 bar and more, preferably approximately 8 bar to approximately 15 bar at a temperature of approximately 60 °C.

[0016] An accelerated high-temperature storage time, measured by charging the lithium secondary battery to 100% SOC at a temperature of about 70°C for 1-day intervals, can be about 15 days or more, preferably about 15 days to about 30 days, more preferably about 15 days to about 25 days.

[0017] According to yet another aspect of the present disclosure, a method for forming a pouch for a secondary battery includes the following steps: stacking a base material layer on a first surface of a barrier layer; and co-extruding a sealing layer comprising a first sealing layer and a second sealing layer on a second surface of the barrier layer, wherein the sealing layer has a melt flow rate (MFR) of about 14.0 g / 10 min or less, measured at a temperature of about 230 °C under a load condition of about 2.16 kg.

[0018] After the coextrusion step, the first sealing layer can be in direct contact with the barrier layer and the second sealing layer can be stacked on a surface of the first sealing layer.

[0019] The first sealing layer can contain an acid-modified polyolefin resin, and the second sealing layer can contain a polyolefin resin.

[0020] The resin pressure can be controlled during the coextrusion step using a coextrusion device.

[0021] The coextrusion step may involve replacing a filter of the coextrusion device if the resin pressure exceeds a predetermined value in order to control the resin pressure.

[0022] The sealing layer can be co-extruded to have a thickness in a range of approximately 45 µm to approximately 100 µm, so that the first sealing layer can have a thickness of approximately 25 µm to approximately 80 µm and the second sealing layer can have a thickness of approximately 20 µm to approximately 80 µm. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description in conjunction with the accompanying drawings, in which: Fig. 1 is a cross-sectional view of a stack of pouch film according to an embodiment of the present invention. Fig. 2 is a perspective exploded view of a secondary battery according to another embodiment of the present invention. Fig.3 is a diagram showing results obtained by measuring the cell venting resistance and an accelerated high-temperature storage time according to embodiment and comparative example. DETAILED DESCRIPTION OF THE PREFERRED VERSION

[0024] Terms or words used in the description and claims should not be interpreted as having a limited lexical meaning and should be understood by the inventor as appropriate terms based on his / her ability to define terms to describe his / her invention in the best way that can be seen by others.

[0025] The present invention will be described in more detail below.

[0026] As a result of repeated investigations to develop a pouch-type secondary battery with excellent high-temperature reliability, the present inventors found that when a melt flow index of a pouch sealing layer meets a specific range, the resistance of the sealing layer to pressure within a cell (cell venting resistance) is significantly improved to suppress the occurrence of venting during high-temperature storage, thereby significantly improving reliability, and as a result, the present invention was completed. Pouch

[0027] A pouch according to the present invention comprises a barrier layer, a base material layer arranged on the outer surface of the barrier layer, and a sealing layer arranged on the inner surface of the barrier layer. Here, the sealing layer comprises a first sealing layer arranged in direct contact with the inner surface of the barrier layer and a second sealing layer arranged on top of the first sealing layer. The sealing layer as a whole (e.g., the combination of the first and second sealing layers) exhibits a melt flow rate (MFR) of about 14.0 g / 10 min or less, preferably about 8.5 g / 10 min to about 14.0 g / 10 min, more preferably about 9.0 g / 10 min to about 13.5 g / 10 min, when measured at a temperature of about 230 °C under a load condition of about 2.16 kg.

[0028] Fig.Figure 1 is a cross-sectional view of a stack of pouch film according to an embodiment of the present invention. A pouch according to the present invention is described below with reference to Fig. 1 described.

[0029] The Pouch 100 can be a battery casing for holding an electrode assembly and an electrolyte, and can, as shown in Fig. Figure 1 illustrates a barrier layer 20, a base material layer 10 arranged on one surface of the barrier layer, and a sealing layer 30 arranged on the other surface of the barrier layer.

[0030] In particular, the pouch 100 comprises a first housing 101 and a second housing 102 and can be produced by forming a pouch film stack comprising a barrier layer 20, a base material layer 10 arranged on one surface of the barrier layer, and a sealing layer 30 arranged on the other surface of the barrier layer. For example, the pouch 100 can be produced in a process in which a pouch film stack, in which the base layer 10, the barrier layer 20, and the sealing layer 30 are stacked successively, is fed into a compression molding device, and pressure is applied to a portion of the pouch film stack to stretch it and form a cup portion that is concave in one direction. (1) Sealing layer

[0031] The sealing layer 30 can be configured to seal the pouch by being joined by thermal compression and can be arranged on the innermost layer of the pouch 100.

[0032] In the pouch according to the present invention, the sealing layer 30 has a two-layer structure and comprises, in particular, a first sealing layer 32 and a second sealing layer 34. The first sealing layer 32 is arranged such that one surface of it is in contact with the barrier layer 20, and the second sealing layer 34 is arranged on a surface opposite the surface of the first sealing layer 32 that is in contact with the barrier layer 20.

[0033] The first sealing layer 32 and the second sealing layer 34 can be formed by co-extruding a resin forming the first sealing layer and a resin forming the second sealing layer onto the barrier layer 20.

[0034] Two methods are used to form the sealing layer in the pouch: dry lamination, where the sealing layer is attached to the barrier layer using a thermosetting adhesive, and coextrusion, where a thermoplastic resin is coextruded onto the barrier layer to form the sealing layer. When the sealing layer is formed using the coextrusion method, a sealant with a higher melt flow rate can be created than when the sealing layer is formed using the dry lamination method. This offers the advantage of reduced sealing time and simplified manufacturing.

[0035] Since no heat-curing adhesive is used, a pouch with excellent moisture resistance and high-temperature durability can be formed.

[0036] The first sealing layer 32 and the second sealing layer 34 can have different compositions. In particular, the first sealing layer 32 can contain an acid-modified polyolefin resin, and the second sealing layer 34 can contain a polyolefin resin. As described above, if the first sealing layer 32 is made of the acid-modified polyolefin resin and the second sealing layer 34 is made of the polyolefin resin, the adhesion to the barrier layer 20 and the high-temperature sealing strength can be improved.

[0037] Since the sealing layer 30 is a surface that comes into contact with the electrolyte and the electrode assembly after the pouch has been formed, the sealing layer 30 may need to exhibit insulation and corrosion resistance. Furthermore, since the inside of the sealing layer 30 must be completely sealed to prevent material movement between the inside and outside, the sealing layer 30 may need to provide a height seal. The polyolefin resin exhibits excellent mechanical properties such as tensile strength, stiffness, surface hardness, abrasion resistance, and heat resistance, as well as chemical properties such as corrosion resistance, and is therefore suitable as a material for the sealing layer.However, since the polyolefin resin does not exhibit high adhesion to the barrier layer, if the sealing layer is made solely of the polyolefin resin, interface separation between the barrier layer and the sealing layer can occur when exposed to high temperatures or when the internal pressure of the battery increases. Therefore, in the present invention, the acid-modified polyolefin resin, into which an acid component capable of improving adhesion to the barrier layer is introduced, can be applied as the first sealing layer to enhance adhesion to the barrier layer, thereby achieving excellent overall adhesion to the barrier layer, mechanical properties, and chemical resistance.If the sealing layer is not formed in two layers as in the present invention, but is formed in a single layer made from the acid-modified polyolefin resin, the chemical resistance and mechanical properties may be deteriorated, leading to a decrease in the sealing strength, and if the sealing layer is formed in a single layer made from the polyolefin resin, the adhesion with the barrier layer may be impaired, and thus venting may occur at an interface with the barrier layer when exposed to a high temperature.

[0038] The acid-modified polyolefin resin can be a polymer modified by block polymerization or graft polymerization of polyolefin with an acid component, for example, a polymer obtained by polymerizing a carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid, maleic anhydride, itaconic anhydride or the like, or an anhydride thereof, in polyolefin.

[0039] The polyolefin can be, for example, polyethylene such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, etc.; ethylene-α-olefin copolymers; polypropylenes such as homopolypropylene, block copolymers of polypropylene (for example, block copolymers of propylene and ethylene) and statistical copolymers of polypropylene (for example, statistical copolymers of propylene and ethylene); propylene-α-olefin copolymer; ethylene-butene-propylene trimer or the like, but is not limited to these.

[0040] In the pouch according to the present invention, the sealing layer has a melt flow rate (MFR) of about 14.0 g / 10 min or less, preferably about 8.5 g / 10 min to about 8.5 g / 10 min, measured at a temperature of about 230 °C under a load of about 2.16 kg. If the melt flow rate of the sealing layer exceeds about 14.0 g / 10 min, the resistance to internal battery pressure is significantly reduced, and thus venting occurs readily when exposed to high temperatures. That is, the cell venting resistance is significantly reduced. Here, cell venting resistance represents the maximum pressure at which venting does not occur when a gas is injected into the cell, and the higher the cell venting resistance, the better the high-temperature reliability, since venting does not occur in the high-temperature environment.

[0041] The melt flow rate of the sealing layer represents the melt flow rate of the entire sealing layer, including the first and second sealing layers, and is a value that differs from the melt flow rate of each of the first and second sealing layers individually. Furthermore, the melt flow rate of the sealing layer is a value measured after co-extrusion. The safety of lithium secondary batteries is influenced by the physical properties of the sealing layer after co-extrusion, making the post-co-extrusion melt flow rate important. Since the melt flow rate of the thermoplastic resin varies depending on extrusion conditions during the co-extrusion process, the post-co-extrusion melt flow rate may differ from a value derived by simply calculating the melt flow rate of a raw material before extrusion.

[0042] In the present invention, the melt flow rate of the sealing layer can be measured by the following method.

[0043] First, the pouch is cut to a size of approximately 50 mm × 300 mm, immersed in hydrochloric acid at a concentration of approximately 37 wt%, and left for approximately 3 to 48 hours to melt the aluminum and separate the sealing layer into a film. After sufficient rinsing with water, the sealing layer is dried at a temperature of approximately 60 °C for approximately 2 hours or more. The sealing layer, separated into a film by the above process, is rolled into a cylindrical die to produce a sample. Three prepared samples are placed in a measuring device (Gottfert MI-40) and melted at a temperature of approximately 230 °C for approximately 5 minutes. The melt flow rate is then measured using a melt volume rate (MVR) method with a load of approximately 2.16 kg. At this stage, the melt density of the sealing layer is estimated to be approximately 0.728 g / cm³. 3is, and a volume is converted into a mass to obtain the melting flow rate.

[0044] In the case of a two-layer sealing layer formed by co-extrusion, the physical properties, such as the melting point and melt flow rate, differ due to the different compositions of the first and second sealing layers. Because of these differences in physical properties and thickness, the melt flow rate of the entire sealing layer can vary. If the melt flow rate of the entire sealing layer exceeds approximately 14.0 g / 10 min, delamination can occur at the interface between the sealing layer and the barrier layer. This can lead to venting if the battery is exposed to high temperatures or if the internal pressure of the battery increases.As a result of repeated investigations to overcome this limitation, the inventors of the present invention have found that the melt flow rate of the entire sealing layer, including the first sealing layer and the second sealing layer, can be changed by controlling a pressure exerted on a filter of the coextrusion device (hereinafter referred to as "resin pressure") during the coextrusion process, and when the melt flow rate of the entire sealing layer is controlled within a specific range, i.e., about 14.0 g / 10 min or less, by the resin pressure control, the interfacial separation between the sealing layer and the barrier layer is suppressed, resulting in significantly improved resistance to the internal pressure of the battery, i.e., cell venting resistance properties.

[0045] The resin pressure increases with the number of resin co-extrusion cycles. Therefore, the pressure exerted on the filter of the co-extrusion apparatus can be monitored over time, and the resin pressure can be controlled by replacing the filter if it exceeds a set range. The resin pressure range required to form the sealing layer with a desired melt flow rate can vary depending on the types of resins used for the first and second sealing layers, their thicknesses, and the type of co-extrusion apparatus. A person skilled in the art will be able to derive a resin pressure range such that the melt flow rate of the sealing layer is approximately 14.0 g / 10 min or less through ordinary experimentation.

[0046] In the present invention, the thickness ratio of the second sealing layer to the thickness of the first sealing layer can be approximately 0.8 to approximately 1.2, preferably approximately 0.9 to approximately 1.1. If the ratio of the thickness of the second sealing layer to the thickness of the first sealing layer falls within the above range, the pouch can be realized with excellent adhesion to the barrier layer, insulation, and sealing strength. If either the first or second sealing layer is too thick or too thin, the resin forming the sealing layer may leak out during sealing, or the adhesion and sealing performance between the sealing layer and the barrier layer may be impaired.

[0047] Preferably, the first sealing layer can have a thickness of about 25 µm to about 80 µm, preferably about 30 µm to about 70 µm, and more preferably about 30 µm to about 60 µm. If the thickness of the first sealing layer meets the above range, the adhesion with the barrier layer is excellent.

[0048] Preferably, the second sealing layer can have a thickness of about 20 µm to about 80 µm, preferably about 25 µm to about 70 µm, and more preferably about 30 µm to about 60 µm. If the thickness of the second sealing layer meets the above range, the sealing performance is excellent.

[0049] The total thickness of the sealing layer, which combines the first and second sealing layers, can be approximately 45 µm to approximately 100 µm, preferably approximately 50 µm to approximately 100 µm, more preferably approximately 60 µm to approximately 100 µm, and even more preferably approximately 70 µm to approximately 90 µm. If the total thickness of the sealing layer meets the above range, a defect in which the resin flows out during sealing can be suppressed, and the amount of heat and time required for sealing can be appropriately controlled. (2) Barrier layer

[0050] The barrier layer 20 can be configured to ensure the mechanical strength of the pouch, to block the introduction and release of any gas or moisture outside the secondary battery, and to prevent electrolyte leakage.

[0051] The barrier layer 20 can have a thickness of approximately 40 µm to approximately 100 µm, more preferably approximately 40 µm to approximately 90 µm, and more preferably approximately 50 µm to approximately 80 µm. If the thickness of the barrier layer meets the above range, adequate mechanical strength and barrier properties can be ensured.

[0052] The barrier layer 20 can be made of a metallic material and can in particular be made of an aluminum alloy thin film.

[0053] The aluminum alloy thin film may contain, in addition to the aluminum, aluminum and a metallic element, for example at least one or two or more metallic elements selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg) and zinc (Zn).

[0054] Preferably, the aluminum alloy thin film can have an iron (Fe) content of 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.%. If the iron (Fe) content in the aluminum alloy thin film meets the above range, the occurrence of cracks or pinholes can be minimized, even if the cup portion is deep. (3) Base material layer

[0055] The base material layer 10 can be arranged on the outermost layer of the pouch and configured to protect the electrode assembly from external impact and to electrically insulate the electrode assembly.

[0056] The base material layer 10 can be made of a polymer material, for example, of at least one or more polymer materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazoles, polyarylates and Teflon.

[0057] The base material layer 10 can have a single-layer structure or can, as in Fig.Figure 2 illustrates a multilayer structure in which different polymer films 12 and 14 are stacked. If the base material layer 10 can have a multilayer structure, an adhesive layer 16a can be arranged between the polymer films. In either the single-layer or the multilayer structure, the base material layer 10 can be bonded to the barrier layer 20 via an adhesive layer 16b or any other mechanism known in the art.

[0058] The base material layer 10 can have a total thickness of approximately 10 µm to approximately 60 µm, preferably approximately 20 µm to approximately 50 µm, and preferably approximately 30 µm to approximately 50 µm. If the base material layer has a multilayer structure, the thickness can include the adhesive layer. If the base material layer 10 meets the above range, durability, insulation, and formability can be excellent. If the thickness of the base material layer is too thin, durability may be reduced, and the base material layer may be damaged during the molding process. If the thickness is too thick, formability may be impaired, the overall thickness of the pouch may increase, and the battery housing space may be reduced, leading to a decrease in energy density.

[0059] According to one embodiment, the base material layer 10 can have a stacked structure consisting of a polyethylene terephthalate (PET) film and a nylon film. Here, the nylon film can be arranged on one side of the barrier layer 20, i.e., within the barrier layer 20, and the polyethylene terephthalate film can be arranged on a surface side of the pouch.

[0060] Polyethylene terephthalate (PET) can exhibit excellent durability and electrical insulation properties, and thus, when the PET film is placed on the surface side, its durability and insulation properties can be excellent. However, in the case of PET film, because the adhesion to an aluminum alloy thin film forming the barrier layer 20 is weak and the elongation behavior differs when the PET film is placed on the barrier layer side, the base material layer and the barrier layer can delaminate during the molding process, and the barrier layer cannot be stretched uniformly, leading to a deterioration in formability.In comparison, since the nylon film has an elongation behavior similar to that of the aluminum alloy thin film forming the barrier layer 20, an effect of improving formability can be obtained when the nylon film is placed between the polyethylene terephthalate and the barrier layer.

[0061] The polyethylene terephthalate film can have a thickness of about 5 µm to about 20 µm, preferably about 5 µm to about 15 µm, more preferably about 7 µm to about 15 µm, and the nylon film can have a thickness of about 10 µm to about 40 µm, preferably about 10 µm to about 35 µm, more preferably about 15 µm to about 25 µm. If the thicknesses of the polyethylene terephthalate film and the nylon film meet the above ranges, the formability and stiffness after forming can be excellent. Lithium secondary battery

[0062] Next, a lithium secondary battery according to the present invention will be described.

[0063] A lithium secondary battery according to the present invention comprises: an electrode arrangement formed by stacking a positive electrode, a separator, and a negative electrode; an electrolyte; and a pouch-like battery casing that accommodates the electrode arrangement and the electrolyte. Here, the battery casing is the pouch described above according to the present invention.

[0064] The pouch described above according to the present invention (i.e., designed such that the sealing layer includes the first and second sealing layers, and the melt flow rate of the entire sealing layer, including the first and second sealing layers, is approximately 14.0 g / 10 min) exhibits a higher sealing strength compared to that of the pouch according to the related technology. Therefore, when the pouch of the present invention is applied to the lithium secondary battery, the sealing layer cannot be easily ruptured, even if the internal pressure of the secondary battery increases, thus implementing high-temperature reliability.

[0065] In particular, the lithium secondary battery, onto which the pouch according to the present invention is applied as the battery housing, can have a cell venting resistance of about 7.7 bar or more, preferably about 7.7 bar to 15 bar and more, preferably about 8 bar to about 15 bar at a temperature of about 60 °C.

[0066] Additionally, the lithium secondary battery, onto which the pouch according to the present invention is applied as the battery housing, can have an accelerated high-temperature storage time of about 15 days or more, preferably about 15 days to about 30 days, more preferably about 15 days to about 25 days, which is measured during charging up to 100% SOC under a temperature condition of about 70 °C in 1-day intervals.

[0067] Since specific details relating to the pouch are the same as those described above, the remaining components, with the exception of the pouch, are described below.

[0068] Fig. Figure 2 is a view of a lithium secondary battery according to one embodiment of the present invention. Each configuration of the lithium secondary battery according to the present invention will be described below with reference to Fig. 2 described in more detail. Electrode arrangement

[0069] An electrode array 200 can include a plurality of electrodes and a plurality of separators stacked alternately. The plurality of electrodes can include a positive electrode and a negative electrode, stacked alternately with the separator in between, and exhibiting opposite polarities.

[0070] The positive and negative electrodes can be produced by applying a composition to form an active material layer containing an electrode active material to a collector and then drying the composition.

[0071] A composition for forming a positive electrode active material layer can include a positive electrode active material, a binder, and a conductive material. A composition for forming the negative electrode active material layer can include a negative electrode active material, a binder, and a conductive material.

[0072] The collector is not particularly limited in its composition, as long as it does not cause any chemical changes in the battery and exhibits high conductivity. For example, the collector can be made of copper, stainless steel, aluminum, nickel, titanium, carbon steel, copper or stainless steel with a surface treated with carbon, nickel, titanium, or silver, or an aluminum-cadmium alloy. Additionally, the collector typically has a thickness of approximately 3 µm to approximately 500 µm, and fine irregularities can be formed on its surface to improve the bond strength of the active material. For example, the negative electrode collector can have various forms, such as a film, a plate, a foil, a mesh, a porous body, a foam, or a nonwoven fabric.

[0073] The positive electrode active material can utilize various positive electrode active materials that are used in engineering as materials capable of inducing an electrochemical reaction, for example: layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2); lithium manganese oxide; lithium nickel oxide, which is represented by the formula LiNi 1-y M y O2 is represented (where M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga and includes one or more elements among the elements, 0.01 ≤ y ≤ 0.7); lithium nickel cobalt manganese composite oxides represented by Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) Ae are represented, such as Li 1+z Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2 or Li 1+z Ni0.4Mn 0,4 Co 0,2O2 (where -0.5 ≤ z ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0.1 ≤ c ≤ 0.8, 0 ≤ d ≤ 0.2, 0 ≤ e ≤ 0.2, b+c+d < 1, M = Al, Mg, Cr, Ti, Si or Y and A = F, P or Cl); and olivinelithium metal phosphate, which is given by the formula Li 1+x M 1-y M' y PO 4-z X z The following are represented (where M = transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, -0.55 ≤ x ≤ + 0.5, 0 ≤ y ≤ 0.5 and 0 ≤ z ≤ 0.1), but are not limited to these. The positive electrode active material can be present in an amount of approximately 80 wt.% to approximately 99 wt.%, based on the total weight of the positive electrode active material layer.

[0074] A compound capable of reversible lithium intercalation and deintercalation can be used as the negative active material. Specific examples may include: carbon-containing materials, such as synthetic graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, a Si alloy, a Sn alloy, or an Al alloy; and metal oxides capable of doping and non-doping with lithium, such as SiO₂. β(0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or a composite material incorporating the above metallic compound and the carbon-containing material, such as a Si-C composite or an Sn-C composite, and any one or a mixture of two or more of the above-described materials may be used. Additionally, a lithium metal thin film may be used as the negative active material. Furthermore, both low-crystalline and high-crystalline carbon may be used as the carbon material.Representatively, the low-crystalline carbon can include soft carbon and hard carbon, and the high-crystalline carbon can include high-temperature calcined carbon, such as amorphous, platelet-like, flaky, globular, or fibrous natural or synthetic graphite, white graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microspheres, mesophase pitches, cokes derived from petroleum or coal tar pitch, and the like. The negative electrode active material can be present in an amount of approximately 80 wt.% to approximately 99 wt.%, based on the total weight of the negative electrode active material layer.

[0075] The binder is a component that facilitates bonding between the conductive material, the active material, and the collector, and is typically added in an amount of approximately 0.1 wt% to approximately 10 wt%, based on the total weight of the active material layer. Examples of binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, various copolymers thereof, and the like.

[0076] The conductive material can be a component for further improving the conductivity of the active material and may be added in an amount of approximately 10 wt.% or less, particularly approximately 5 wt.% or less, based on the total weight of the active material layer. The conductive material need not be particularly restricted as long as the material does not cause any chemical change in the battery and exhibits conductivity. For example, the conductive material may include: graphite, such as natural graphite and synthetic graphite; carbon black, such as acetylene carbon black, ketjen carbon black, sewer carbon black, furnace carbon black, lamp carbon black, and summer carbon black; conductive fiber, such as carbon fiber and metal fiber; metal powder, such as carbon fluorine, aluminum, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxide, such as titanium oxide; or derivatives of polyphenylene.

[0077] The separator can separate the negative electrode from the positive electrode and provide a passage for the movement of lithium ions. It can be used without special restrictions as long as it is normally used as a separator in a lithium secondary battery. In particular, it is preferable that it exhibits low resistance to the ion movement of the electrolyte and an excellent capacity to absorb the electrolyte. Specifically, the separator can comprise a porous polymer film made, for example, from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a stacked structure of at least two layers thereof.Additionally, the separator can be a typical porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber. Furthermore, an applied separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

[0078] The electrode assembly 200 can include a plurality of electrode tabs 230 welded together. The plurality of electrode tabs 230 can be connected to the plurality of electrodes 210 and project outwards from the electrode assembly 200 to serve as a passage through which electrons move between the inside and outside of the electrode assembly 200. The plurality of electrode tabs 230 can be arranged within the pouch 100.

[0079] The electrode tab 230 connected to the positive electrode and the electrode tab 230 connected to the negative electrode can project in different directions relative to the electrode arrangement 200. However, the present invention is not limited to this, and the electrode tab 230 connected to the positive electrode and the electrode tab 230 connected to the negative electrode can project in the same direction, parallel to each other.

[0080] A conductor 240, which supplies electricity to the outside of the secondary battery, can be connected to the plurality of electrode tabs 230 by spot welding or the like. The conductor 240 can have one end connected to the plurality of electrode tabs 230 and the other end extending to the outside of the pouch 100.

[0081] A section of the conduit 240 can be surrounded by an insulating element 250. For example, the insulating element 250 can include insulating tape. The insulating element 250 can be positioned between the terrace 120 and the second housing 102 of the first housing 101, and in this state, the terrace 120 and the second housing 102 can be thermally fused together. In this case, a section of each of the terrace 120 and the second housing 102 can be thermally fused to the insulating element 250. Thus, the insulating element 250 can prevent the gas generated by the electrode assembly 200 from flowing through the conduit 240 to the pouch 100 and can maintain the seal of the pouch 100. electrolyte

[0082] The electrolyte can be configured to move lithium ions generated by an electrochemical reaction of the electrode during charging and discharging of the secondary battery, and may include an organic solvent and lithium salt.

[0083] Examples of organic solvents may include, in particular: 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 ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R being a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may contain a doubly bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based solvents and cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) are preferred.Compounds with high ionic conductivity and high permittivity, which can increase the charging and discharging performance of the battery, and linear, low-viscosity carbonate-based compounds (e.g., a mixture of ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are preferred.

[0084] The lithium salt can be used without particular restriction, as long as it is a compound capable of providing lithium ions for use in the lithium secondary battery. In particular, the lithium salt can 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, or the like. The concentration of the lithium salt can preferably be within the range of about 0.1 M to about 5.0 M, preferably about 0.1 M to about 3.0 M. If the concentration of the lithium salt is within the above range, the electrolyte will have suitable conductivity and viscosity, and thus excellent electrolyte performance can be demonstrated, and the lithium ions can move effectively.

[0085] In addition to the electrolyte components, the electrolyte may also contain an adhesive for the purpose of improving the battery's lifespan characteristics, suppressing a decrease in battery capacity, and improving the battery's discharge capacity.

[0086] The present invention will now be described in more detail by means of a specific embodiment. Production example

[0087] A stacked film, consisting of a polyethylene terephthalate film (approximately 12 µm thick), an adhesive layer (approximately 3 µm thick), and a nylon film (approximately 15 µm thick), was produced as the base material layer. Subsequently, a urethane adhesive approximately 3 µm thick was applied to the nylon film of the base layer, and an aluminum alloy thin film (barrier layer approximately 40 µm thick) was stacked on top using a dry lamination process.

[0088] Next, a sealing layer comprising a first and a second sealing layer was formed by co-extruding a maleic anhydride-modified polypropylene resin and a polypropylene resin on one surface facing a surface on which the base layer of the aluminum alloy thin film was stacked. During co-extrusion, the maleic anhydride-modified polypropylene resin layer was in contact with the aluminum alloy thin film, and the thickness of both the first and second sealing layers was approximately 40 µm.

[0089] During the formation of the sealing layer, pouch film stacks A to F were produced by co-extrusion while a resin pressure was changed.

[0090] After the manufactured pouch film stack was cut to a size of approximately 50 mm × 300 mm, it was immersed in hydrochloric acid at a concentration of approximately 37 wt% to melt an aluminum alloy thin film, and the film-like sealing layer was then separated. The separated sealing layer was then thoroughly rinsed with water and dried at a temperature of approximately 60 °C for about 2 hours and then rolled into a cylindrical shape to produce a sample. The sample was placed in a melt flow rate measuring device (Gottfert MI-40) and melted at a temperature of approximately 230 °C for about 5 minutes, and the melt flow rate (MFR) of the sealing layer was then measured under a load of approximately 2.16 kg. The measurement was performed using a melt volume rate (MVR) method, and a melt density of approximately 0.728 g / cm³ was assumed for the sealing layer. 3 amounts.

[0091] The results of the measurement are shown in Table 1 below. Table 1] Sealing layer MFR(g / 10 min) A 9.12 B 10.68 C 11.40 D 13.20 E 13.56 F 15.36 Design and comparative example

[0092] A pouch for a secondary battery according to embodiments 1 to 5 and comparative example 1, comprising a cup portion, was manufactured by drawing die-forming each of the pouch film stacks A to F produced in the manufacturing example above. The sealing layer of each pouch manufactured according to embodiments 1 to 5 and comparative example 1 was then thermally sealed, and a sealed section was cut to a width of approximately 15 mm to produce a sample. The sealed section of the sample was then opened, and the sample was mounted on a peel strength test fixture such that the distance between the handles was approximately 30 mm. A T-peel test was then performed at a temperature of approximately 25 °C or 60 °C at a rate of approximately 5 mm / min to measure the seal strength.Here, the sealing strength was expressed as a percentage of the peel strength according to embodiments 2 to 4 and comparative example 1 with respect to a reference value, where the peel strength according to embodiment is defined as the reference value (100).

[0093] The results of the measurement are shown in Table 2 below. [Table 2] Pouch film stacks Seal strength at room temperature (%) Seal strength at high temperature (%) Design 1 A 100 100 Execution- B 94.7 100 form 2 embodiment 3 C 89.4 98.1 Design 4 D 75.2 93.3 Design 5 E 73.5 81.0 Comparative example 1 F 38.1 21.0

[0094] As shown in Table 2, the pouches according to embodiments 1 to 5, in which the sealing layer has a melt flow rate of about 14 g / 10 min or less, were compared with the pouch according to Comparative Example 1, in which the sealing layer has a melt flow rate of more than about 14 g / 10 min at room temperature. As a result, it was observed that the pouch exhibits remarkably excellent sealing properties at both room temperature and elevated temperatures. Test example: Secondary battery cell venting resistance and high-temperature acceleration test

[0095] The stacked electrode array was placed in the secondary battery pouch, which was manufactured according to embodiments 1 to 5 and comparative example 1, and an electrolyte was injected. The sealing layer was then applied to create a lithium secondary battery. The cell venting resistance and the accelerated high-temperature storage time of each of the manufactured lithium secondary batteries were measured as follows. For accurate evaluation, the measurement was performed two or three times for each lithium secondary battery, and the measurement results were recorded in Fig. 3 shown. (1) Cell venting resistance measurement method:

[0096] A hole of approximately 1 mm or less was drilled into the lithium secondary battery, and the internal pressure of the cell was measured over time while an inert gas was injected at temperatures of approximately 25 °C and approximately 60 °C, and the maximum internal pressure reached until venting occurred was evaluated as the cell venting resistance.

[0097] Since the cell pressure drops to atmospheric pressure when venting occurs, a point at which the cell pressure drops to atmospheric pressure was evaluated as a venting occurrence time. (2) Accelerated high-temperature storage time:

[0098] The lithium secondary battery was stored at a temperature of approximately 70 °C and then charged up to 100% SOC in 1-day intervals, and then the storage time for which the secondary battery can be stored without venting was measured.

[0099] As in Fig.As shown in Figure 3, in the lithium secondary batteries according to embodiments 1 to 5, to which the pouch in which the sealing layer has a melt flow rate within a range of about 14.0 g / 10 min or less, which is within the range of the present invention, was applied, it was found that the cell venting resistance at temperatures of about 60 °C and 25 °C is higher than about 7.7 bar and the accelerated high-temperature storage time is also higher than about 15 days. In contrast, in the lithium secondary battery according to Comparative Example 1, to which the pouch in which the sealing layer has a melt flow rate exceeding about 14.0 g / 10 min was applied, it was found that the cell venting resistance and the accelerated high-temperature storage time are significantly reduced at a temperature of about 60 °C.

[0100] The pouch for the secondary battery according to the present invention, which is designed such that the sealing layer is provided as two layers and the melt flow rate (MFR) of the entire sealing layer is 14 g / 10 min or less, can exhibit a sealing strength greater than that of the pouch according to the related technology. Therefore, when the pouch according to the present invention is applied to the lithium secondary battery, the sealing layer cannot be easily ruptured, even if the internal pressure of the secondary battery increases.In particular, the secondary battery according to the present invention can have a cell internal pressure at which venting occurs (referred to as the “cell venting resistance”) as high as about 7.7 bar or more and can exhibit excellent high-temperature reliability as a storage time of about 15 days or more without venting during an accelerated high-temperature storage test (accelerated high-temperature storage time).

[0101] Although the present invention has been shown and described in connection with the exemplary embodiments, it will be obvious to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims. In view of the above disclosure, the present invention can be implemented according to the following detailed embodiments. Item 1. Pouch for a secondary battery, comprising: a barrier layer; a base material layer arranged on a surface of the barrier layer; and a sealing layer that is arranged on the other surface of the barrier layer, the sealing layer comprises: a first sealing layer in contact with the other surface of the barrier layer; and a second sealing layer, which is arranged on top of the first sealing layer opposite the barrier layer, wherein the sealing layer has a melt flow rate (MFR) of 14.0 g / 10 min or less, measured at a temperature of approximately 230 °C under a load condition of 2.16 kg. Item 2. Pouch according to Item 1, wherein the melt flow rate (MFR) of the sealing layer is 8.5 g / 10 min or more, measured at a temperature of about 230 °C under a load condition of about 2.16 kg. Point 3. Pouch according to point 1 or 2, wherein the first sealing layer and the second sealing layer are formed by coextrusion. Item 4. Pouch according to any of the preceding items, wherein the first sealing layer comprises an acid-modified polyolefin resin. Item 5. Pouch according to one of the preceding items, wherein the second sealing layer comprises a polyolefin resin. Point 6. Pouch according to one of the preceding points, wherein the ratio of the thickness of the second sealing layer to the thickness of the first sealing layer is between 0.8 and 1.2. Item 7. Pouch according to one of the preceding points, wherein the first sealing layer has a thickness of 25 µm to 80 µm, and the second sealing layer has a thickness of 20 µm to 80 µm. Item 8. Pouch according to one of the preceding points, wherein the total thickness of the sealing layer is between 45 µm and 100 µm. Item 9. Pouch according to one of the preceding items, wherein the barrier layer comprises an aluminium alloy. Item 10. Pouch according to any of the preceding items, wherein the base material layer comprises at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazoles, polyarylates and Teflon. Item 11. Lithium secondary battery, comprehensive: an electrode arrangement in which a positive electrode, a separator and a negative electrode are stacked on top of each other; an electrolyte; and a pouch-like battery housing that includes a cup-shaped portion configured to hold the electrode assembly and electrolyte, wherein the battery housing is the pouch according to one of the preceding claims. Item 12. Lithium secondary battery according to item 11, wherein the cell venting resistance of the lithium secondary battery at a temperature of 60 °C is 7.7 bar or more. Item 13. Lithium secondary battery according to item 11 or 12, wherein an accelerated high-temperature storage time, measured by charging the lithium secondary battery to 100% SOC at a temperature of about 70°C in a 1-day interval, is 15 days or more. Item 14. Method for forming a pouch for a secondary battery, the method comprising the following steps: Stacking a base material layer on a first surface of a barrier layer; and Co-extrusion of a sealing layer comprising a first sealing layer and a second sealing layer onto a second surface of the barrier layer, wherein the sealing layer exhibits a melt flow rate (MFR) after the coextrusion step of approximately 14.0 g / 10 min or less, measured at a temperature of approximately 230 °C under a load condition of approximately 2.16 kg. Item 15. Method according to Item 14, wherein the resin pressure is controlled using a coextrusion device during the coextrusion step. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] KR 10-2022-0183748

[0001]

Claims

Pouch for a secondary battery, comprising: a barrier layer configured to ensure the mechanical strength of the pouch, to block the introduction and release of any gas or moisture from outside the secondary battery, and to prevent electrolyte leakage; a base material layer arranged on one surface of the barrier layer; and a sealing layer arranged on the other surface of the barrier layer, wherein the sealing layer comprises: a first sealing layer in contact with the other surface of the barrier layer; and a second sealing layer arranged on the first sealing layer opposite the barrier layer, wherein the sealing layer has a melt flow rate (MFR) of 8.5 g / 10 min to 14.0 g / 10 min, as measured at a temperature of about 230 °C under a load condition of 2.16 kg, as described above. Bag according to claim 1, wherein the first sealing layer and the second sealing layer are formed by coextrusion. Bags according to claim 1 or 2, wherein the first sealing layer comprises an acid-modified polyolefin resin. Bags according to one of the preceding claims, wherein the second sealing layer comprises a polyolefin resin. Bags according to one of the preceding claims, wherein the barrier layer comprises an aluminum alloy. Bags according to one of the preceding claims, wherein the ratio of the thickness of the second sealing layer to the thickness of the first sealing layer is in a range of about 0.8 to about 1.

2. Bags according to one of the preceding claims, wherein the first sealing layer has a thickness of about 25 µm to about 80 µm and the second sealing layer has a thickness of about 20 µm to about 80 µm. Bags according to one of the preceding claims, wherein the total thickness of the sealing layer is in a range of about 45 µm to about 100 µm. Bags according to any of the preceding claims, wherein the base material layer comprises at least one material selected from the group consisting of: polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazoles, polyarylates and Teflon. Lithium secondary battery comprising: an electrode arrangement in which a positive electrode, a separator and a negative electrode are stacked on top of each other; an electrolyte; and a pouch-like battery housing comprising a cup part configured to receive the electrode arrangement and the electrolyte, wherein the battery housing is the pouch according to any one of the preceding claims. Lithium secondary battery according to claim 10, wherein a cell venting resistance of the lithium secondary battery is 7.7 bar or more at a temperature of 60 °C, measured as described. Lithium secondary battery according to claim 10 or 11, wherein an accelerated high-temperature storage period, measured by charging the lithium secondary battery to 100% SOC at a temperature of about 70°C in a 1-day interval, is 15 days or more.

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