JP-7857484-B2 - Manufacturing method for multilayer separators

Inventors

• リュウ キョン サン
• チェ クワン ホ
• キム ビョン ヒョン
• チョン ジン ヒョン
• キム ヒョン ジュ
• キム ジョン レ

Assignees

• ダブル・スコープコリア カンパニー，リミテッド
• ダブル－スコープ チュンジュ プラント カンパニー リミテッド

Dates

Publication Date

20260512

Application Date

20250917

Priority Date

20220127

Claims (10)

1. A multilayer separator comprising layers derived from a first composition containing a first polyolefin and a second composition containing a second polyolefin, A multilayer separator in which the thickness deviation of the outermost layer, measured by the following formula, is 10% or less. <Formula> Thickness deviation (%) = {(Maximum thickness) - (Minimum thickness)} / (Minimum thickness) × 100 In the above formula, the thickness deviation is determined by a method that includes the steps of: cutting the multilayer separator into 100 mm × 100 mm (MD × TD), dividing it into five equal parts in the vertical direction (MD) to obtain five test pieces having a size of 20 mm × 100 mm (MD × TD); measuring the thickness of the outermost layer at the center of the test piece in the horizontal direction (TD); and calculating the thickness deviation using the above formula based on the maximum and minimum values of the thickness.
2. The multilayer separator according to claim 1, wherein the thickness of the multilayer separator is 1 to 15 μm.
3. The multilayer separator according to claim 1, wherein the perforation strength of the multilayer separator is 600 gf or more.
4. The longitudinal (MD) tensile strength of the aforementioned multilayer separator is 1,300 to 2,000 kgf/cm². 2 The multilayer separator according to claim 1.
5. The lateral (TD) tensile strength of the aforementioned multilayer separator is 3,000 to 6,000 kgf/cm². 2 The multilayer separator according to claim 1.
6. The multilayer separator according to claim 1, wherein the longitudinal (MD) tensile elongation of the multilayer separator is 150 to 450%.
7. The multilayer separator according to claim 1, wherein the lateral (TD) tensile elongation of the multilayer separator is 30 to 100%.
8. The first polyolefin and the second polyolefin each include one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, and two or more combinations or copolymers thereof. The multilayer separator according to claim 1, wherein the weight-average molecular weights of the first polyolefin and the second polyolefin are each 300,000 to 2,000,000.
9. The first or second composition further comprises a hydrophilic polymer, The multilayer separator according to claim 1, wherein the content of the hydrophilic polymer in the first composition or the second composition is 0.1 to 5% by weight.
10. The multilayer separator according to claim 9, wherein the hydrophilic polymer is one selected from the group consisting of ethylene vinyl acetate, ethylene vinyl alcohol, polyvinyl alcohol, polyacrylic acid, polyoxyethylene-polyoxypropylene block copolymer, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl butyral, cellulose derivatives, glycerol, and two or more combinations thereof.

Description

This invention relates to a method for manufacturing a multilayer separator, and more particularly, to a method for manufacturing a multilayer separator that can homogenize the structural properties of each layer constituting the multilayer separator and improve the mechanical properties required for the separator. Lithium-ion batteries are widely used as power sources for various electrical products that require miniaturization and weight reduction, such as smartphones, laptops, and tablet PCs. As their application areas expand to include smart grids and medium- and large-sized batteries for electric vehicles, there is a growing demand for lithium-ion batteries with higher capacity, longer lifespan, and greater stability. Recently, with the increasing energy density of lithium-ion batteries, the load on the batteries has increased, and a high level of safety is required for the separators. This has highlighted the importance of not only the mechanical properties of the separators, but also their heat resistance, which is crucial for ensuring safety. Traditionally, polyolefin-based microporous membranes have been used as separators in lithium-ion batteries. Among these, microporous membranes made of polyethylene resin are known to have excellent shutdown capabilities, where the micropores of the membrane close and interrupt the flow of current when the battery temperature rises. However, even after the shutdown function has activated, the battery temperature may rise further. In this case, the separator may melt down, causing a short circuit inside the battery. This generates a large amount of heat, leading to dangers such as smoke, fire, and explosion. Therefore, it is necessary to suppress the risk of short circuits even at temperatures higher than the shutdown temperature. To achieve both the shutdown and meltdown characteristics of the separator, methods such as blending polyethylene and polypropylene, or laminating a microporous membrane made of polyethylene resin with a microporous membrane made of polypropylene resin, have been proposed. For example, Patent Documents 1 and 2 disclose a method for manufacturing a multilayer separator by co-extruding two or more resin compositions, and disclose that the mechanical strength and heat resistance of the multilayer separator manufactured through this method can be improved in a balanced manner. However, since interlayer lamination is performed by co-extrusion, i.e., stacking is performed, before the formation of the porous structure by stretching, there is a problem that the structural properties of each layer become non-uniform in subsequent film-forming processes such as stretching and extraction. Specifically, as the thickness deviation in different regions of the outermost layer of the multilayer separator increases, the mechanical properties of the separator itself may become non-uniform, and in particular, when assembling a battery using the separator, there is a problem that areas that are significantly thinner than the surrounding areas are easily damaged or fractured. Such problems have become even more noticeable recently in thin-film separators (thickness of about 15 μm or less, preferably about 10 μm or less) used to cope with the trend of battery integration and high capacity. Furthermore, Patent Document 3 discloses a method for manufacturing a multilayer separator by laminating and stacking two or more separators that have been completely formed through extrusion, stretching, extraction, and heat fixing, as shown in Figure 1. However, in this case, sufficient interlayer bonding strength cannot be provided, resulting in the problem of each layer easily delaminating. To improve this, a step of re-stretching and heat fixing can be added after laminating and stacking two or more separators, but this has the problem of reduced productivity and economic efficiency due to the added equipment and process. Korean Patent Publication No. 10-2005-0120689Korean Patent Publication No. 10-2016-0094448Korean Patent Publication No. 10-2008-0028444 This document shows a conventional method for manufacturing a multilayer separator.A method for manufacturing a multilayer separator according to one embodiment of the present invention is shown.This invention provides a method for measuring the thickness deviation of a multilayer separator according to one embodiment of the present invention.A method for manufacturing a multilayer separator according to one comparative example of the present invention is shown. The present invention will be described below. However, the present invention can be realized in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly illustrate the present invention in the drawings, parts unrelated to the description have been omitted, and similar parts have been given similar reference numerals throughout the specification. Throughout the specification, when any part is