CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2018-0126702, filed on Oct. 23, 2018, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The following disclosure relates to a separator for a secondary battery and an electrochemical device using the same.

More particularly, the following disclosure relates to a composite separator having a more excellent cycle life and including a coating layer which does not easily swell in an electrolyte solution.

BACKGROUND

Recently, a secondary battery having high capacity and a large size, which is applied to an electric automobile, or the like, has been developed. As part of that development, an electrode-separator assembly technique in which an electrode and a separator are stacked and integrated has been used.

However, this type of electrode-separator assembly may cause lifting phenomenon or distortion in the preparation or during the use, resulting in a decrease in efficiency, such as failing to achieve a desired high capacity. Also, it is difficult to enlarge the size due to the occurrence of distortion, or the like.

Furthermore, a gap may be formed between an electrode and a separator according to charge and discharge, which is a factor that deteriorates a cycle life. Therefore, it is an important technique to maintain uniformly adhesiveness of an adhesive part in an electrode or a separator.

To solve the above problems, there is a technique used by coating acryl-based resins or modified fluorine-based resins on a surface in contact with an electrode, but these resins are easily swollen or decomposed in an electrolyte solution, resulting in an adverse effect on a battery cycle life.

RELATED ART DOCUMENT

Patent Document

(Patent Document 1) Japanese Patent Publication No. 4414165 (2009.11.27)

SUMMARY

The present invention is intended to solve the above problems, and forms a specialized polyolefin-based latex on the surface of a separator in contact with an electrode surface as an electrode adhesive layer, thereby solving the above problems.

An embodiment of the present invention is directed to providing a composite separator without lifting phenomenon of the electrode surface and the separator surface when heat and pressure are applied in the process of integrating the electrode and the separator.

Another embodiment of the present invention is directed to providing a composite separator capable of maintaining a battery cycle life for a long time without easy swelling or decomposing in an electrolyte solution.

Another embodiment of the present invention is directed to providing a composite separator including a coating layer in which slip properties are improved to improve assemblability between the electrode surface and the separator when a composite separator is manufactured, the composite separator is easily seated on an electrode surface due to slip properties or the like upon assembly, such that no wrinkles occur, and also no distortion or lifting phenomenon occurs between the electrode and the separator.

Another embodiment of the present invention is directed to providing a composite separator that allows the manufacture of a battery having excellent cycle characteristics and capable of achieving a desired high capacity by the above-described advantages.

In one general aspect, there is provided a composite separator including a porous substrate, a heat-resistant coating layer formed on the porous substrate, and an electrode adhesive layer, wherein the electrode adhesive layer includes polyolefin-based organic particles, and a Gurley permeability satisfies the following Equation 1 and a Gurley permeability change rate (ΔP) satisfies the following Equation 2:
G1≤300  [Equation 1]
10%≤ΔP≤50%  [Equation 2]

wherein ΔP=(G2−G1)/G1×100, G2is a Gurley permeability measured according to ASTM D726 in a state where the composite separator is stacked between two TEFLON® (PTFE, Polytetrafluoroethylene, Registered trademark of Dupont Inc.) sheets, the composite separator and the TEFLON® sheets are pressed and fused at 4 MPa and 70° C., and the TEFLON® sheets are then removed, and G1is a Gurley permeability of the composite separator before fusion, where a unit of the Gurley permeability is sec/100 cc.

Other features and aspects will be apparent from the following detailed description and the claims.

