Exterior material for lithium secondary battery, method for detecting exterior material for lithium secondary battery, and lithium secondary battery

Abstract

An exterior material for a lithium secondary battery according to an embodiment of the present disclosure comprises: an outer layer comprising one or more of a polyester-based resin and a polyamide-based resin; an inner layer including a polyolefin-based resin including a first inner layer, a second inner layer, and a third inner layer; and a barrier layer disposed between the outer layer and the inner layer. The first inner layer is disposed between the barrier layer and the second inner layer. The second inner layer is disposed between the first inner layer and the third inner layer, and has a crystal structure different from that of the first inner layer and that of the third inner layer. The onset temperature of the third inner layer is 100 DEG C or more.

Description

Technical Field

[0001] The present disclosure relates to an exterior material for a lithium secondary battery, a method for detecting an exterior material for a lithium secondary battery, and a lithium secondary battery. Background Art

[0002] With the development of the electronics, communication, and space industries, the demand for lithium secondary batteries as energy power sources has increased rapidly. In particular, as the importance of environmental protection policies is emphasized globally, the market for electric vehicles has grown by leaps and bounds, and research and development on lithium secondary batteries are vigorously underway both in Korea and abroad.

[0003] Lithium secondary batteries can be classified into cylindrical batteries, square batteries, and pouch-type batteries according to their shapes. Pouch-type batteries can sufficiently ensure the energy density of the battery, so pouch-type batteries may be preferred over other types of batteries.

[0004] The pouch-type battery includes a pouch-type exterior material that houses the cell. The pouch-type exterior material forms a sealing portion for separating the inside and outside of the battery. For example, after laminating the sheets of the pouch-type exterior material, it can be heat-sealed to form a sealing portion.

[0005] On the one hand, the sealing portion formed by the pouch-type exterior material needs to have qualified sealing performance for the inside of the battery. To test the sealing performance, various methods are used after forming the sealing portion of the pouch-type exterior material. For example, after forming the sealing portion, the tensile strength is confirmed at the heat-sealed portion, or the time consumed for the sealing portion to be damaged in a high-temperature environment is confirmed to complete the test of the sealing performance. In this case, it may take too much time to judge the sealing performance, and the sealing performance can only be judged after manufacturing the sealing portion, so the process may become overly complicated. Summary of the Invention

[0006] One aspect of the present disclosure provides an exterior material for a lithium secondary battery, a method for detecting an exterior material for a lithium secondary battery, and a lithium secondary battery that improve the sealing predictability and thus can improve the convenience of sealing detection.

[0007] One aspect of the present disclosure provides an exterior material for a lithium secondary battery, a method for detecting an exterior material for a lithium secondary battery, and a lithium secondary battery that improve the sealing performance of the manufactured product and improve the reliability related to the sealing performance.

[0008] It may be that an exterior material for a lithium secondary battery according to an embodiment of the present disclosure includes: an outer layer including one or more of a polyester resin and a polyamide resin; an inner layer including a polyolefin resin, including a first inner layer, a second inner layer, and a third inner layer; and a barrier layer disposed between the outer layer and the inner layer. It may be that the first inner layer is disposed between the barrier layer and the second inner layer. It may be that the second inner layer is disposed between the first inner layer and the third inner layer and may have a crystal structure different from that of the first inner layer and the third inner layer. It may be that the onset temperature of the third inner layer is 100 °C or higher.

[0009] According to an embodiment, it may be that the polyester resin includes one or more of the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), copolyester, and polycarbonate (PC). It may be that the polyamide resin includes one or more of the group consisting of nylon 6, nylon 6.6, nylon 6.10, and m-xylylene adipamide (MXD 6).

[0010] According to an embodiment, it may be that the barrier layer includes a metal or an inorganic compound. It may be that the metal includes one or more of aluminum and a metal. It may be that the inorganic compound includes silicon oxide, aluminum oxide, etc.

[0011] According to an embodiment, it may be that the first inner layer, the second inner layer, and the third inner layer have a thickness ratio of 1:2:1 to 1:3:1.

[0012] According to an embodiment, it may be that the first inner layer includes random polypropylene and maleic acid. It may be that the second inner layer includes impact copolymer polypropylene. It may be that the third inner layer includes random polypropylene.

[0013] It may be that a lithium secondary battery according to an embodiment of the present disclosure includes: the exterior material for a lithium secondary battery; and an electrode assembly disposed within the exterior material for a lithium secondary battery, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0014] It may be that a method for detecting an exterior material for a lithium secondary battery according to an embodiment of the present disclosure includes: a step of measuring the onset temperature of the exterior material for a lithium secondary battery using AFM (Atomic Force Microscope); and a step of determining the sealing performance of the exterior material for a lithium secondary battery based on the onset temperature.

[0015] According to an embodiment, the exterior material for a lithium secondary battery may include: an outer layer including one or more of a polyester resin and a polyamide resin; an inner layer including a polyolefin resin, including a first inner layer, a second inner layer, and a third inner layer; and a barrier layer disposed between the outer layer and the inner layer. The measuring step may include: measuring the starting temperature of the third inner layer.

[0016] According to an embodiment, the measuring step may include: bringing the measurement probe of AFM into contact with a point within 20 μm based on the outer surface of the third inner layer.

[0017] According to an embodiment, the measuring step may include: applying heat to the third inner layer with the measurement probe.

[0018] According to an embodiment, the judging step may include: comparing the starting temperature of the third inner layer with 100 °C as a reference temperature.

[0019] According to an embodiment, the judging step may include: when the starting temperature of the third inner layer is 100 °C or higher, judging that the sealing performance of the lithium secondary battery manufactured using the exterior material for a lithium secondary battery can meet the standard; and when the starting temperature of the third inner layer is lower than 100 °C, judging that it is difficult for the sealing performance of the lithium secondary battery manufactured using the exterior material for a lithium secondary battery to meet the standard.

[0020] According to an embodiment of the present disclosure, there can be provided an exterior material for a lithium secondary battery, a method for detecting an exterior material for a lithium secondary battery, and a lithium secondary battery, which can improve the sealing predictability and thus improve the convenience of seal detection.

[0021] Embodiments of the present disclosure can provide an exterior material for a lithium secondary battery, a method for detecting an exterior material for a lithium secondary battery, and a lithium secondary battery, which can improve the sealing performance of the manufactured product and improve the reliability related to the sealing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram showing a lithium secondary battery according to an embodiment.

[0023] Figure 2 is a schematic cross-sectional view showing an exterior material according to an embodiment.

[0024] Figure 3 is a schematic cross-sectional view showing an exterior material according to another embodiment.

[0025] Figure 4 is a flowchart showing a method for detecting an exterior material for a lithium secondary battery according to an embodiment. Detailed Implementation Modes

[0026] The specific structural and functional descriptions of the embodiments according to the concepts of the present disclosure disclosed in this specification or application are only examples for the purpose of illustrating the embodiments according to the concepts of the present disclosure. The embodiments according to the concepts of the present disclosure can be implemented in various forms and should not be construed as being limited to the embodiments described in this specification or application.

[0027] 1. Outer Packaging Material for Lithium Secondary Battery and Lithium Secondary Battery Comprising the Same For the lithium secondary battery 1 according to an embodiment, the outer packaging material POU for the lithium secondary battery that forms the sealing portion SEL satisfies preset thermal characteristics. The inventors of the present invention confirmed the points that can determine the sealing performance of the lithium secondary battery 1 based on the thermal characteristics of the outer packaging material POU for the lithium secondary battery measured by AFM (Atomic Force Microscope). In this case, while improving the sealing performance of the lithium secondary battery 1, the process for testing the sealing performance can be simplified, thereby saving costs.

[0028] Hereinafter, the outer packaging material for the lithium secondary battery, the detection method of the outer packaging material for the lithium secondary battery, and the lithium secondary battery according to an embodiment will be described with reference to the accompanying drawings.

[0029] Figure 1 is a schematic diagram showing a lithium secondary battery according to an embodiment.

[0030] Figure 2 is a schematic cross-sectional view showing an outer packaging material according to an embodiment.

[0031] Figure 3 is a schematic cross-sectional view showing an outer packaging material according to another embodiment.

[0032] Reference Figures 1 to 3 , the lithium secondary battery 1 according to an embodiment may include: an outer layer 100 including one or more of a polyester resin and a polyamide resin; an inner layer 300 including a polyolefin resin, including a first inner layer 320, a second inner layer 340, and a third inner layer 360; and a barrier layer 200 disposed between the outer layer 100 and the inner layer 300, the first inner layer 320 being disposed between the barrier layer 200 and the second inner layer 340, the second inner layer 340 being disposed between the first inner layer 320 and the third inner layer 360, having a crystal structure different from that of the first inner layer 320 and the third inner layer 360, and the onset temperature of the third inner layer 360 being 100 °C or higher.

[0033] The lithium secondary battery 1 according to an embodiment includes an outer packaging material POU for accommodating an electrode assembly ASM. Figure 1 is a schematic diagram showing a lithium secondary battery according to an embodiment.Figure 2 and Figure 3 is a schematic cross-sectional view showing an exterior material according to an embodiment. Figure 2 may represent the first exterior material POU1. Figure 3 may represent the second exterior material POU2.

[0034] Hereinafter, for convenience of explanation, the exterior material POU is used to refer to the exterior material POU for a lithium secondary battery.

[0035] The exterior material POU may have a laminated structure 10 including an outer layer 100, a barrier layer 200, and an inner layer 300. According to an embodiment, the exterior material POU may include a first exterior material POU1 formed of a single laminated structure 10 and a second exterior material POU2 in which two laminated structures 10 and 10' are combined with each other.

[0036] The outer layer 100 may be disposed on the periphery as compared with the inner layer 300 and the barrier layer 200. According to an embodiment, the outer layer 100 may be combined with the barrier layer 200 by various lamination methods (for example, dry lamination, etc.). According to an embodiment, in order to combine the outer layer 100 and the barrier layer 200, a polyurethane adhesive or the like may be used, but the present disclosure is not limited thereto. According to an embodiment, the outer layer 100 may refer to a protective layer.

[0037] In consideration of the chemical resistance and moldability of the exterior material POU, etc., the outer layer 100 may include various substances. For example, the outer layer 100 may include one or more of polyester resins and polyamide resins. According to an embodiment, the polyester resin may include one or more of the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), copolyester, and polycarbonate (PC). According to an embodiment, the polyamide resin may include one or more of the group consisting of nylon 6, nylon 6.6, nylon 6.10, and m-xylylene adipamide (MXD 6).

[0038] The outer layer 100 may form a peripheral layer in the first exterior material POU1. In the second exterior material POU2, the outer layer 100 may be an upper outer layer 100a, or may be a lower outer layer 100b.

[0039] The barrier layer 200 may be disposed between the outer layer 100 and the inner layer 300. The barrier layer 200 may prevent impurities (such as moisture, gas, etc.) from penetrating into the lithium secondary battery 1 from the outside. The barrier layer 200 may include a metal or an inorganic compound. The metal may include one or more of aluminum and a metal, and the inorganic compound may include silicon oxide, aluminum oxide, etc. According to an embodiment, considering that it is sandwiched between two or more layers, so as to be able to suppress the generation of pinholes due to bending, etc., the barrier layer 200 may preferably include aluminum.

[0040] The barrier layer 200 can form an intermediate layer in the first outer packaging material POU1. In the second outer packaging material POU2, the barrier layer 200 can be an upper barrier layer 200a or a lower barrier layer 200b.

[0041] The inner layer 300 can be disposed more inwardly than the outer layer 100 and the barrier layer 200. The inner layer 300 can include various functional layers. For example, the inner layer 300 can include a first inner layer 320, a second inner layer 340, and a third inner layer 360. According to an embodiment, the layers forming the inner layer 300 can be manufactured using nano-extrusion, air pressure, tandem extrusion, or lamination methods.

[0042] According to an embodiment, the first inner layer 320, the second inner layer 340, and the third inner layer 360 can have a thickness ratio of 1:2:1 to 1:3:1. For example, when the inner layer 300 has a thickness of 80 μm, the first inner layer 320 can be 20 μm, the second inner layer 340 can be 40 μm, and the third inner layer 360 can be 20 μm. However, the present disclosure is not necessarily limited thereto.

[0043] Each layer forming the inner layer 300 can include a polyolefin resin. For example, the polyolefin resin can include one or more of a polyethylene resin and a polypropylene resin.

[0044] According to an embodiment, the first inner layer 320 can include atactic polypropylene and maleic acid, the second inner layer 340 can include impact copolymer polypropylene, and the third inner layer 360 can include atactic polypropylene.

[0045] The first inner layer 320 can be disposed between the barrier layer 200 and the second inner layer 340. The first inner layer 320 includes a polyolefin resin and can also include a material suitable for binding to the barrier layer 200. For example, when the barrier layer 200 includes a metal (such as aluminum), the first inner layer 320 includes a polypropylene resin and can also include maleic acid to have suitable binding properties with the metal. Maleic acid includes two carboxyl groups and one hydroxyl group, and the ratio of such carboxyl and hydroxyl groups can form a structure suitable for binding to metal ions. According to an embodiment, the first inner layer 320 can include atactic polypropylene. The polypropylene resin used to form the first inner layer 320 can be a random copolymer. The random copolymer can include a comonomer, thereby having a structure with improved uniformity.

[0046] The first inner layer 320 can be adjacent to the barrier layer 200 in the first outer packaging material POU1. In the second outer packaging material POU2, the first inner layer 320 can be an upper first inner layer 320a or a lower first inner layer 320b.

[0047] The second inner layer 340 may be disposed between the first inner layer 320 and the third inner layer 360. The second inner layer 340 includes a polyolefin resin, and the polyolefin resin forming the second inner layer 340 may have a structure capable of improving impact resistance. The second inner layer 340 may have a crystal structure different from those of the first inner layer 320 and the third inner layer 360. For example, the second inner layer 340 may include an impact copolymer. The second inner layer 340 may include impact polypropylene. For example, the impact polypropylene, as a nano-composite polypropylene, may include homopolypropylene and a further rubber phase component (e.g., ethylene-propylene rubber, etc.). The impact copolymer may be a block copolymer and is hard against external forces, thereby being able to improve the impact resistance of the outer packaging material POU. According to an embodiment, the second inner layer 340 may refer to the core layer.

[0048] The second inner layer 340 may form the core layer of the inner layer 300 in the first outer packaging material POU1. In the second outer packaging material POU2, the second inner layer 340 may be the upper second inner layer 340a or the lower second inner layer 340b.

[0049] The third inner layer 360 may be disposed on the other surface of the second inner layer 340 where the first inner layer 320 is not disposed. The third inner layer 360 may include a polyolefin resin. For example, the third inner layer 360 may include a polypropylene resin having a random copolymer structure. The third inner layer 360 includes a random copolymer, so that when heat melting is performed to form the sealing portion SEL, an excessively high temperature may not be required.

[0050] The third inner layer 360 may form the sealing portion SEL of the outer packaging material POU. For example, in the region where the outer packaging material POU is sealed, the upper laminate structure 10 and the lower laminate structure 10' are hot-pressed, so that the third inner layer 360a of the upper laminate structure 10 and the third inner layer 360b of the lower laminate structure 10' can be combined with each other, and the sealing portion SEL of the outer packaging material POU can be manufactured.

[0051] The third inner layer 360 may form the innermost layer of the inner layer 300 in the first outer packaging material POU1. In the second outer packaging material POU2, the third inner layer 360 may be the upper third inner layer 360a or the lower third inner layer 360b.

[0052] The second exterior material POU2 may include an upper laminate structure 10 and a lower laminate structure 10'. The upper laminate structure 10 may include an upper outer layer 100a, an upper barrier layer 200a, an upper first inner layer 320a, an upper second inner layer 340a, and an upper third inner layer 360a. The lower laminate structure 10' may include a lower outer layer 100b, a lower barrier layer 200b, a lower first inner layer 320b, a lower second inner layer 340b, and a lower third inner layer 360b.

[0053] To seal the exterior material POU, heat and pressure may be applied in a state where the upper third inner layer 360a and the lower third inner layer 360b are in contact with each other. In this case, the resins (e.g., polypropylene-based resins) of the upper third inner layer 360a and the lower third inner layer 360b may melt and bond to each other. Since the upper third inner layer 360a and the lower third inner layer 360b may have the same resin layer with each other, a uniform sealing portion SEL can be formed by melting.

[0054] As a random copolymer, the third inner layer 360 may include random polypropylene. At this time, the onset temperature of the random polypropylene forming the third inner layer 360 may be 100 °C or higher.

[0055] The onset temperature may be the temperature at which the target substance starts to become soft (or melt) when the temperature of the target substance is raised. According to an embodiment, the onset temperature of the substance forming the third inner layer 360 may be measured by AFM (Atomic Force Microscope).

[0056] For example, after setting a probe capable of dissipating heat in the AFM, the probe may be brought into contact with the target substance, and the temperature of the probe may be uniformly changed (e.g., raised at a uniform rate). In this case, a part of the target substance adjacent to the probe may melt, and by measuring the minute activities occurring as the target substance melts by AFM, the temperature at which the minute activities are observed can be determined as the onset temperature.

[0057] The present inventors have confirmed that when the onset temperature of at least a part of the third inner layer 360 forming the sealing portion SEL is 100 °C or higher during hot melting, the lithium secondary battery 1 thus produced is hermetically sealed successfully.

[0058] That is, the present inventors have confirmed that the hermeticity can be judged by confirming the thermal properties of the partial structure forming the sealing portion SEL in the exterior material POU. For this purpose, by using a structure in which the onset temperature of the third inner layer 360 is 100 °C or higher, the exterior material POU can be specially manufactured, thereby enabling the provision of a lithium secondary battery 1 including an exterior material POU with improved hermeticity and improved reliability of the hermeticity.

[0059] Meanwhile, according to the prior art, it is necessary to use the hot-melt outer packaging material POU to confirm the actual sealing structure and then judge the sealing qualification. However, according to the embodiment, before the hot-melt outer packaging material POU, the thermal properties of the partial structure participating in the sealing / melting can be confirmed, so as to judge the sealing qualification after actual manufacturing. In this case, the process can be simplified, thus saving process costs, and the sealing qualification is determined based on consistent physical properties, so the reliability of the sealing qualification is significantly improved.

[0060] According to an embodiment, a lithium secondary battery 1 including the aforementioned outer packaging material POU is provided. The lithium secondary battery 1 may include a positive electrode CAT, a negative electrode ANO, and a separator SEP.

[0061] According to an embodiment, the lithium secondary battery 1 may include: the aforementioned outer packaging material POU for lithium secondary battery; and an electrode assembly CEL, which is disposed within the outer packaging material POU for lithium secondary battery and includes a positive electrode CAT, a negative electrode ANO, and a separator SEP disposed between the positive electrode CAT and the negative electrode ANO.

[0062] The positive electrode CAT and the negative electrode ANO may include current collectors and active material layers disposed on the current collectors. For example, the positive electrode CAT may include a positive current collector and a positive active material layer, and the negative electrode ANO may include a negative current collector and a negative active material layer.

[0063] The current collector may include any known conductive material within the range that does not cause a chemical reaction within the lithium secondary battery. For example, the current collector may include any one of stainless steel, nickel (Ni), aluminum (Al), titanium (Ti), copper (Cu), and their alloys, and may be provided in various forms such as a film, a sheet, or a foil.

[0064] The active material layer includes an active material. For example, the positive active material layer may include a positive active material, and the negative active material layer may include a negative active material.

[0065] The positive active material may be a material into which and from which lithium ions can be inserted and extracted. The positive active material may be a lithium metal oxide. For example, the positive active material may be one of lithium manganese oxides, lithium nickel oxides, lithium cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, lithium iron phosphate compounds, lithium manganese phosphate compounds, lithium cobalt phosphate compounds, and lithium vanadium phosphate compounds.

[0066] The negative electrode active material can be a material that allows lithium ions to be intercalated and deintercalated. For example, the negative electrode active material can be any one of carbonaceous materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers; lithium alloys; silicon (Si); and tin (Sn). According to an embodiment, the negative electrode active material can be natural graphite or artificial graphite, but is not limited thereto.

[0067] The positive electrode CAT and the negative electrode ANO can each further include a binder and a conductive material.

[0068] The binder can mediate the binding between the current collector and the active material, thereby improving mechanical stability. For example, the binder can be an organic binder or an aqueous binder. For example, the organic binder can be any one of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, and polymethyl methacrylate, and the aqueous binder can be styrene-butadiene rubber (SBR), but is not limited thereto.

[0069] The conductive material can improve the conductivity of the secondary battery. The conductive material can include metal series substances. The conductive material can include conventional carbon series conductive materials. For example, the conductive material can include any one of graphite, carbon black, graphene, and carbon nanotubes, and preferably includes carbon nanotubes.

[0070] The separator SEP is interposed between the positive electrode CAT and the negative electrode ANO. The separator SEP can be configured to prevent electrical short circuit between the positive electrode CAT and the negative electrode ANO and allow ion flow.

[0071] For example, the separator SEP can include polyolefin materials. The separator SEP can include a porous polymer membrane or a porous non-woven fabric. The porous polymer membrane can be composed of a single layer or multiple layers of polyolefin polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. The porous non-woven fabric can include high melting point glass fibers and polyethylene terephthalate fibers. However, it is not limited thereto, and according to an embodiment, it can be a high heat resistance separator including ceramic (Ceramic coated separator).

[0072] The electrode assembly ASM includes a single CEL, and the single CEL includes a positive electrode CAT, a negative electrode ANO, and a separator SEP. A plurality of single CELs may be provided and configured within an exterior material POU. For example, a plurality of single CELs may be provided for winding, lamination, folding, or zigzag stacking.

[0073] 2. Detection Method for Exterior Material of Lithium Secondary Battery According to the embodiment, it is possible to form a sealing portion SEL without heat-melting the exterior material POU, thereby determining the sealing performance of the exterior material POU for a lithium secondary battery.

[0074] Hereinafter, with reference to Figure 4 A detection method for the exterior material POU of a lithium secondary battery according to an embodiment will be described.

[0075] Figure 4 It is a flowchart showing a detection method for the exterior material of a lithium secondary battery according to an embodiment.

[0076] With reference to Figure 4 A detection method for the exterior material POU of a lithium secondary battery may include: a step S100 of measuring the starting temperature of the exterior material of the lithium secondary battery; and a step S200 of determining the sealing performance of the exterior material of the lithium secondary battery based on the starting temperature.

[0077] Specifically, a detection method for the exterior material POU of a lithium secondary battery according to an embodiment may include: a step S100 of measuring the starting temperature of the exterior material POU of the lithium secondary battery using an AFM (Atomic Force Microscope); and a step S200 of determining the sealing performance of the exterior material POU of the lithium secondary battery based on the starting temperature.

[0078] First, prepare an exterior material POU for manufacturing a lithium secondary battery 1. As described above, with reference to Figures 1 to 3 The exterior material POU may have a plurality of laminated structures including a resin structure for heat melting.

[0079] In step S100 of measuring the starting temperature, the starting temperature of the third inner layer 360 of the exterior material POU may be measured using an AFM.

[0080] That is, with reference to Figures 1 to 3When, in the detection method of the outer packaging material POU for a lithium secondary battery according to an embodiment, the outer packaging material POU for a lithium secondary battery may include: an outer layer 100 including one or more of a polyester resin and a polyamide resin; an inner layer 300 including a polyolefin resin, including a first inner layer 320, a second inner layer 340, and a third inner layer 360; and a barrier layer 200 disposed between the outer layer 100 and the inner layer 300, the measuring step S100 may include: a step of measuring the starting temperature of the third inner layer 360.

[0081] According to an embodiment, the measuring step S100 may include: a step of bringing the measuring probe of the AFM into contact with a point within 20 μm based on the outer surface of the third inner layer 360.

[0082] According to an embodiment, the measuring step S100 may include: a step of applying heat to the third inner layer 360 with the measuring probe.

[0083] For example, the measuring probe of the AFM may be brought into contact with a point within 20 μm based on the exposed outer surface of the third inner layer 360. The area within 20 μm based on the outer surface of the third inner layer 360 may at least include the area where the outer packaging material POU is heat-melted to form the sealing portion SEL. Then, heat may be applied to the area where the measuring probe is provided to raise the surrounding temperature, and information (e.g., image data showing the bonding structure) showing the bonding structure of the third inner layer 360 based on the change in the surrounding temperature may be obtained. Thus, the bonding structure can be judged according to the change in temperature. When a specific temperature is reached, as the bonding structure separates, the structure of the third inner layer 360 may become soft. Experimentally, when the bonding structure of the third inner layer 360 becomes soft, the temperature may be specified as the starting temperature of the third inner layer 360.

[0084] Alternatively, according to an experimental example, the starting temperature of the target layer may be determined based on the measurement result of the heat flow of the temperature. For example, the target layer may be heated at a predetermined temperature rate, and the heat flow may be measured to obtain a heat flow chart based on the temperature of the target layer. At this time, when referring to the obtained chart, the temperature at the point where the change amount of the heat flow increases sharply based on the temperature change may be determined as the starting temperature. According to an embodiment, the temperature at the point where the following two tangents intersect may be determined as the starting temperature, that is, the tangent of the chart in the low-temperature region based on a relatively prominent region and the tangent of the chart in the high-temperature region based on a relatively prominent region.

[0085] Next, in the step S200 of judging the sealing performance, the sealing performance in the lithium secondary battery 1 manufactured using the outer packaging material POU may be judged based on the starting temperature measured in the previous step.

[0086] According to an embodiment, the step S200 of determination may include: comparing the starting temperature of the third inner layer 360 with 100°C as a reference temperature.

[0087] According to an embodiment, the step S200 of determination may include: when the starting temperature of the third inner layer 360 is 100°C or higher, determining that the sealing performance of the lithium secondary battery 1 manufactured using the outer packaging material POU for lithium secondary batteries can meet the requirements; and when the starting temperature of the third inner layer 360 is lower than 100°C, determining that it is difficult for the sealing performance of the lithium secondary battery 1 manufactured using the outer packaging material POU for lithium secondary batteries to meet the requirements.

[0088] In this step, the measured starting temperature and the reference temperature can be compared. For example, it can be determined whether the measured starting temperature is 100°C or higher. Those skilled in the art have confirmed that when the starting temperature of the melted area during the hot melting process in the outer packaging material POU is 100°C or higher, qualified sealing performance can be ensured. Thus, it can be determined that when the measured starting temperature is 100°C or higher, the sealing performance of the lithium secondary battery 1 manufactured using this outer packaging material POU can meet the requirements. On the contrary, when the measured starting temperature is lower than 100°C, it can be determined that it is difficult for the sealing performance of the lithium secondary battery 1 manufactured using this outer packaging material POU to meet the requirements. That is, without performing the hot melting process for forming the sealing portion SEL, by grasping the thermal characteristics of the outer packaging material POU, the sealing performance of the final product can be determined.

[0089] Hereinafter, the present disclosure will be further described in detail based on examples and comparative examples. However, the following examples and comparative examples are only examples for further describing the present disclosure in detail, and the present disclosure is not limited to the following examples and comparative examples.

[0090] 3. Examples and Comparative Examples (1)Manufacturing Examples - Examples and Comparative Examples

Example

[0091] 2) Starting Temperature According to the same manufacturing method, a lithium secondary battery 1 according to the embodiment is manufactured, and the content of polypropylene in each of the first inner layer 320, the second inner layer 340, and the third inner layer 360 is adjusted, so that the starting temperatures of the first inner layer 320, the second inner layer 340, and the third inner layer 360 are different from each other.

[0092] For example, the outer packaging material POU according to Embodiments 1 to 4 is manufactured so that the starting temperatures of the third inner layer 360 of the outer packaging materials according to the embodiments are various temperatures of 100°C or higher.

[0093] The starting temperatures of the first inner layer 320, the second inner layer 340, and the third inner layer 360 in each of the embodiments are marked as follows.

[0094] 3) Manufacture of lithium secondary battery According to a conventional method, a ternary lithium nickel cobalt manganese oxide is used as a positive electrode active material, and the active material is coated on an aluminum current collector to manufacture a positive electrode CAT. Artificial graphite is used as a negative electrode active material, and the active material is coated on a copper current collector to manufacture a negative electrode ANO. Then, after a separator SEP including a polyolefin-based material is interposed between the negative electrode ANO and the positive electrode CAT, a non-aqueous electrolyte is injected to manufacture the lithium secondary battery 1 according to the embodiment.

[0095]

Comparative example

[0096] The outer packaging material according to Comparative Example 2 has a structure including the first inner layer 320, the second inner layer 340, and the third inner layer 360, and the starting temperature of the third inner layer 360 is made lower than 100°C, which is different from the outer packaging material POU according to the embodiment in this regard.

[0097] Except for the outer packaging material, the lithium secondary batteries according to Comparative Examples 1 and 2 are manufactured by the same method as in the embodiment.

[0098] (2) Experimental example The sealing performance between the embodiment and the comparative example was compared. In each of the embodiment and the comparative example, the starting temperature at each position of the inner layer 300 of the outer packaging material POU of the lithium secondary battery was measured, and the exhaust pressure generated in the lithium secondary batteries manufactured according to the embodiment and the comparative example was measured in a high-temperature environment (70°C).

[0099] Thus, Table 1 can show the relationship between the starting temperature at each position of the inner layer 300 and the exhaust pressure in the high-temperature environment in each of the embodiment and the comparative example.

[0100] In this experimental example, in order to measure the initial temperature of the exterior materials according to the examples and comparative examples, a measurement probe (model name: VIT-DM-NANOTA-200) was set in the AFM. After the measurement probe was brought into contact with the exterior materials according to the examples and comparative examples respectively, the temperature was raised at a rate of 5 °C / s up to a maximum temperature of 300 °C, and the minute activities of the exterior materials according to the examples and comparative examples were observed and measured, whereby the initial temperatures of the exterior materials according to the examples and comparative examples were judged respectively.

[0101] The method for measuring the exhaust pressure of each of the examples and comparative examples in this experimental example is as follows. In order to measure the exhaust pressure, air was injected into the exterior material POU of the lithium secondary battery at a rate of 0.001 MPa / 2 sec in a high-temperature environment (70 °C), and the internal pressure when air was discharged to the outside of the exterior material POU of the lithium secondary battery was measured, and this internal pressure was measured as the exhaust pressure.

[0102]

Table 1

[0103] Referring to Table 1, it can be confirmed that when the initial temperature of the third inner layer 360 that participates in the sealing and is adjacent to the exterior materials POU is 100 °C or higher, the exhaust pressure in the lithium secondary battery 1 manufactured is measured to be 0.4 MPa or higher. That is, it can be confirmed that when the initial temperature of the third inner layer 360 that participates in the sealing is 100 °C or higher, the sealing performance of the lithium secondary battery 1 meets the standard.

Claims

1. A packaging material for a lithium secondary battery, comprising: An outer layer comprising one or more of a polyester resin and a polyamide resin; An inner layer comprising a polyolefin resin, comprising a first inner layer, a second inner layer and a third inner layer; and a barrier layer disposed between the outer layer and the inner layer, The first inner layer is disposed between the barrier layer and the second inner layer, The second inner layer is disposed between the first inner layer and the third inner layer, and has a crystal structure different from that of the first inner layer and the third inner layer. The starting temperature of the third inner layer is 100° C. or higher.

2. The lithium secondary battery exterior material according to claim 1, wherein The polyester resin includes at least one selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolyester and polycarbonate. The polyamide resin includes at least one selected from the group consisting of nylon 6, nylon 6.6, nylon 6.10 and poly(meta-xylylene adipamide).

3. The lithium secondary battery exterior material according to claim 1, wherein The barrier layer comprises a metal or an inorganic compound, The metal includes one or more of aluminum and metal, The inorganic compound includes silicon oxide, aluminum oxide and the like.

4. The lithium secondary battery exterior material according to claim 1, wherein The first inner layer, the second inner layer, and the third inner layer have a thickness ratio of 1:2:1 to 1:3:

1.

5. The lithium secondary battery exterior material according to claim 1, wherein The first inner layer comprises random polypropylene and maleic acid, The second inner layer comprises impact polypropylene, The third inner layer includes random polypropylene.

6. A lithium secondary battery comprising: The external packaging material for a lithium secondary battery according to claim 1; and The electrode unit cell is disposed in the lithium secondary battery exterior material and includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

7. A method for detecting an outer packaging material for a lithium secondary battery, comprising: The step of measuring the onset temperature of the lithium secondary battery outer packaging material using AFM; and A step of determining the sealing property of the lithium secondary battery exterior material based on the starting temperature.

8. The method for detecting a lithium secondary battery outer packaging material according to claim 7, wherein: The external packaging material for a lithium secondary battery comprises: an outer layer comprising one or more of a polyester resin and a polyamide resin; an inner layer comprising a polyolefin resin, including a first inner layer, a second inner layer and a third inner layer; and a barrier layer disposed between the outer layer and the inner layer. The measuring step includes: a step of measuring the starting temperature of the third inner layer.

9. The method for detecting a lithium secondary battery outer packaging material according to claim 8, wherein: The measuring step includes the step of bringing a measuring probe of an AFM into contact with a point within 20 μm from the outer surface of the third inner layer.

10. The method for detecting a lithium secondary battery outer packaging material according to claim 9, wherein: The measuring step includes a step of applying heat to the third inner layer by the measuring probe.

11. The method for detecting a lithium secondary battery outer packaging material according to claim 8, wherein: The judging step includes the step of comparing the starting temperature of the third inner layer with 100° C. as a reference temperature.

12. The method for detecting a lithium secondary battery outer packaging material according to claim 11, wherein: The steps of determining include: When the starting temperature of the third inner layer is 100° C. or higher, judging that the sealing performance of the lithium secondary battery manufactured by using the lithium secondary battery outer packaging material can reach an acceptable level; and When the starting temperature of the third inner layer is lower than 100° C., it is judged that the sealing property of the lithium secondary battery manufactured by using the lithium secondary battery exterior material is difficult to reach an acceptable level.

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