KR-102960983-B1 - CELL POUCH FILM, SECONDARY BATTERY INLCUDING THE SAME AND METHOD FOR MANUFACTURING THE SECONDARY BATTERY

Abstract

The present specification relates to a film for a cell pouch, a secondary battery including the same, and a method for manufacturing the same. According to the present invention, by controlling the moisture content of the film for a cell pouch, it is possible to achieve excellent moldability, a level of thermal deformation bubbles, and mechanical properties.

Inventors

• 송녹정
• 이창우
• 김용환
• 노광민
• 신성철
• 김유한
• 이두희

Assignees

• 율촌화학 주식회사

Dates

Publication Date

20260508

Application Date

20241217

Priority Date

20240626

Claims (8)

1. A film for a cell pouch comprising at least an outer layer including a nylon film, a barrier layer made of metal, and a sealant layer, The above film for the cell pouch is, (a) The moisture content measured by the [Method for Measuring Moisture Content of Film for Cell Pouch] below is 1250 ppm or less, and, (b) i) the average bubble size measured by the [Method for Evaluating Thermal Deformation Bubble Levels] below is 70 μm or less; and/or ii) the bubble size of all bubbles measured by the [Method for Evaluating Thermal Deformation Bubble Levels] below is 150 μm or less, and includes two or fewer bubbles with a bubble size exceeding 100 μm; and The above nylon film is a film for a cell pouch, wherein i) it has a moisture content of 4,000 ppm to 10,000 ppm, ii) it has a moisture content of 300 μg to 900 μg, or iii) the ratio of the moisture content of the nylon film to the total weight of the film for the cell pouch is 70% to 87%: [Method for Measuring Moisture Content of Films for Cell Pouches] Prepare a sample of a cell pouch film by cutting it into 60 mm × 40 mm lengthwise (Machine direction, MD) × widthwise (Transverse direction, TD). Divide this sample into four equal parts of 15 mm × 40 mm lengthwise (MD) × widthwise (TD). Place the four divided samples into vials and seal them. Place the sealed vials into a moisture measuring device, measure the moisture content vaporizing from the vials at a temperature of 150°C, and verify this as the moisture content of the cell pouch film. The measurement conditions are a temperature of 150°C and a gas flow rate of 50 mL/min. [Method for Evaluating Thermal Deformation Bubble Levels] (1) Cut a film for cell pouch into a width of 200 mm and a length of 100 mm to prepare a specimen. (2) Fold the specimen in half vertically to make it 200mm wide and 50mm long. (3) After that, heat sealing is performed in the transverse direction. The heat sealing temperature is 220℃, the heat sealing pressure is 0.2 MPa, and the heat sealing time is 1.6 seconds. (4) After heat sealing, a 6x15mm punch is used to punch the area of the heat-sealed region where the most heat-deformed bubbles occur, thereby obtaining a sample containing the area where the bubbles occurred. (5) Place the sample obtained by punching onto a slide glass. (6) Flatten the sample using a rubber roller with a total weight of 2.5 kg. (7) Measure an image of the sample using the x10 obj lens of the optical microscope (DM2700M). (8) Using the Leica Application Suite (LAS) program mounted on the optical microscope (DM2700M), the bubble size of all bubbles included in the sample image is measured, and the average bubble size is calculated. At this time, the bubble size is measured by the major axis and including the black shading.
2. In paragraph 1, A film for a cell pouch having a moisture content of 300 ppm to 1250 ppm.
3. In paragraph 2, A film for a cell pouch, wherein the outer layer comprises a polyethylene terephthalate (PET) film and a nylon film, the barrier layer is made of aluminum, and the sealant layer comprises a polypropylene layer.
4. In paragraph 3, A film for a cell pouch, wherein the yield strength of the film is 120 N/15 mm to 152 N/15 mm, and the yield strength is measured using a Universal Testing Machine (UTM) under conditions of a test speed of 50 mm/min and a grip distance of 50 mm.
5. In paragraph 3, A film for a cell pouch, wherein the heat sealing strength of the film for the cell pouch is 128 N/15 mm to 150 N/15 mm, and the heat sealing strength is measured using a Universal Testing Machine (UTM) under conditions of a test speed of 50 mm/min and a grip distance of 50 mm.
6. In paragraph 3, A cell pouch film having a moldability of 16 mm to 19 mm.
7. A secondary battery enclosed in a film for a cell pouch according to any one of paragraphs 1 to 6.
8. A method for manufacturing a secondary battery, comprising the step of outering the secondary battery with a film for a cell pouch according to any one of claims 1 to 6.

Description

Cell pouch film, secondary battery including the same, and method for manufacturing the same The present specification discloses a film for a cell pouch, a secondary battery including the same, and a method for manufacturing the same. Pouch-type batteries, generally used in electric vehicles and the like, have the advantage of being easy to change shape and having a high energy density compared to cylindrical or prismatic batteries. As an outer casing that encloses the battery's electrode group and electrolyte, these cell pouches must satisfy required characteristics such as interlayer adhesion between metal thin films and polymers, thermal fusion strength, electrolyte resistance, airtightness, moisture permeability, and moldability. Korean Registered Patent Publication No. 10-2042252 discloses a battery cell comprising a metal plate for blocking moisture penetration. However, conventional films for cell pouches suffer from problems such as poor formability, poor mechanical properties like yield strength or heat seal strength, or poor appearance due to bubble formation caused by thermal deformation. Therefore, there is a need to develop a film for cell pouches that satisfies all requirements regarding formability, thermal deformation appearance characteristics, and mechanical properties. Meanwhile, to encase the battery body with a pouch film, the innermost layer of the pouch film (e.g., the sealant layer) is typically brought into contact, and then heat-sealed by applying heat and pressure to form a seal. If thermal deformation and/or air bubbles occur beyond a certain level during this heat and pressure sealing process, problems may arise regarding the pouch's sealability, seal retention characteristics, and appearance quality. Therefore, there is a need to research and develop pouch films that minimize thermal deformation and/or air bubble formation during the sealing process. FIG. 1 is a graph showing the change in moisture content according to temperature, relative humidity, and time of a film for a cell pouch according to one embodiment of the present invention. Figure 2 is an image showing the thermal deformation evaluation criteria of a film for a cell pouch according to one embodiment of the present invention. Figure 3 is an image of a film for a cell pouch according to one embodiment evaluated as Level 1 and Level 2 according to the criteria of Table 5. Figure 4 is an image of a film for a cell pouch according to a comparative example evaluated as Level 3 and Level 4 according to the criteria of Table 5. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings. The embodiments of the present invention disclosed in the text are illustrative for illustrative purposes only, and the embodiments of the present invention may be implemented in various forms and should not be interpreted as being limited to the embodiments described in the text. As the present invention is capable of various modifications and may take various forms, the embodiments are not intended to limit the present invention to a specific disclosed form and should be understood to include all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention. In this specification, when a part is described as “comprising” a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Throughout the specification, when a part such as a layer, film, region, plate, etc. is described as being “on” or “above” another part, this may include not only cases where it is immediately above another part, but also cases where there is another part in between. Throughout the specification, terms such as “first,” “second,” etc., may be used to describe various components, but the components should not be limited by these terms. The terms are used solely for the purpose of distinguishing one component from another. In this specification, the term “cell” means a battery and may have the broadest meaning, including all types of batteries such as secondary batteries like lithium-ion batteries and lithium-polymer batteries, or portable storage batteries. In this specification, the term “cell pouch” has the broadest meaning and includes all devices in which cell components, such as an anode, a cathode, and a separator, are impregnated with an electrolyte and housed therein, and which are processed into a pouch or box shape using a laminated film structure that takes into account gas barrier properties, flexibility, electrolyte resistance, and heat sealability to house said cell components. In this specification, “barrier performance” refers to the ability to block water vapor from the outside of the battery. In this specification, “formability” refers to the depth measured after forming a specimen of a film for a cell pouch. If all 10 specimens do not break a