US-12627002-B2 - Separator for electrochemical device and method for manufacturing the same

US12627002B2US 12627002 B2US12627002 B2US 12627002B2US-12627002-B2

Abstract

A separator for an electrochemical device including a heat resistant layer and an adhesive layer and a method for manufacturing the same. The separator uses a heat resistant polymer having a high melting point for a heat resistant layer and shows excellent peel strength between the separator substrate and the heat resistant layer and high adhesion between the separator and an electrode.

Inventors

Seung-Hyun Lee
Dong-Wook Sung
Hyun-Kyung Shin

Assignees

LG ENERGY SOLUTION, LTD.

Dates

Publication Date: 20260512
Application Date: 20230411
Priority Date: 20180130

Claims (15)

1 . A separator for an electrochemical device comprising: a porous substrate; a heat resistant layer formed on at least one surface of the porous substrate; and an adhesive layer formed on a surface of the heat resistant layer opposite the porous substrate, wherein: the heat resistant layer comprises inorganic particles and a heat resistant binder resin, the heat resistant binder resin has a melting point (Tm) of 150° C. or higher, the adhesive layer consists of a fluorinated binder resin and a non-fluorinated binder resin as adhesive binder resins, the non-fluorinated binder resin comprises a (meth)acrylic polymer, the fluorinated binder resin is concentrated at a surface of the adhesive layer and the non-fluorinated binder resin is concentrated near a surface of the heat resistant layer, and the heat resistant layer comprises pores and the non-fluorinated binder resin is partially present in the pores of the heat resistant layer.
2 . The separator for the electrochemical device according to claim 1 , wherein the heat resistant layer comprises the heat resistant binder resin in an amount of 1 wt % to 20 wt % based on 100 wt % of the heat resistant layer.
3 . The separator for the electrochemical device according to claim 2 , wherein the heat resistant binder resin is present in an amount larger than 90 wt % based on 100 wt % of the binder resin present in the heat resistant layer.
4 . The separator for the electrochemical device according to claim 1 , wherein the heat resistant layer comprises a pore path passing through a thickness direction of the heat resistant layer by one pore or by interconnection of two or more open pores, and either or both of the fluorinated binder resin and the non-fluorinated binder resin of the adhesive layer are introduced through at least one pore path so that the heat resistant layer is bound with the surface of the porous substrate.
5 . The separator for the electrochemical device according to claim 1 , which has a shrinkage of 25% or less in a transverse direction (TD) and machine direction (MD), after it is allowed to stand at 150° C. for 30 minutes.
6 . The separator for the electrochemical device according to claim 1 , which has a breakdown voltage of 1.8 kV or higher.
7 . The separator for the electrochemical device according to claim 1 , which shows a peel strength of 20 gf/15 mm or more between the heat resistant layer and the porous substrate.
8 . The separator for electrochemical device according to claim 1 , wherein the heat resistant binder resin comprises polyacetal, polysulfone (PSF), polyethersulfone (PES), polyetherimide (PEI), polyphenylene sulfide (PPS), polyetherether ketone (PEEK), polyarylate (PA), polycarbonate, polyamideimide (PAI), polyimide (PI), polyamide, fully aromatic polyamide (aramid), polyphenylene oxide, polybutylene terephthalate, polyethylene terephthate, polyether sulfone, polyether ketone or a mixture of at least two of them.
9 . The separator for the electrochemical device according to claim 1 , wherein the fluorinated binder resin comprises a polyvinylene fluoride (PVDF)-based polymer resin comprising vinylidene fluoride (VDF) as a unit.
10 . The separator for the electrochemical device according to claim 1 , wherein the fluorinated binder resin comprises a copolymer of vinylidene fluoride (VDF) with a comonomer, and the comonomer comprises hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), hexafluoroisobutylene, perfluorobutyl ethylene, perfluoropropyl vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE), perfluromethyl vinyl ether (PMVE), perfluro-2,2-dimethyl-1,3-dioxole (PDD), perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD) or at least two of them.
11 . A method for manufacturing the separator of claim 1 comprising the steps of: (S 10 ) forming a heat resistant layer on a surface of a porous substrate; (S 20 ) applying a polymer solution for forming an adhesive layer to a surface of the heat resistant layer opposite the porous substrate; and (S 30 ) drying the applied polymer solution to form an adhesive layer, wherein the drying in step (S 30 ) is carried out under a humidifying treatment condition at a relative humidity of 20-50%.
12 . The method for manufacturing the separator according to claim 11 , wherein the polymer solution for forming the adhesive layer comprises a fluorinated binder resin, a non-fluorinated binder resin, a solvent and a non-solvent.
13 . The separator for the electrochemical device according to claim 1 , wherein the adhesive layer has pores having a rectangular finger-like structure, Bernard cell structure, or a mesoporous structure in a thickness direction.
14 . The separator for the electrochemical device according to claim 1 , wherein the non-fluorinated binder resin is present in an amount of 1 wt % to 20 wt % based on 100 wt % of the binder resins in the adhesive layer.
15 . A secondary battery comprising a cathode, an anode and a separator according to claim 1 and the separator is interposed between the cathode and the anode.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a Continuation of application Ser. No. 16/628,499 filed on Jan. 3, 2020, which is the U.S. National Phase of PCT/KR2019/001311, filed Jan. 30, 2019, and which claims priority under 35 U.S.C. § 119(a) to Application No. 10-2018-0011649 filed on Jan. 30, 2018, in the Republic of Korea, the entire contents of all of which are expressly incorporated by reference into the present application. TECHNICAL FIELD The present disclosure relates to a separator for an electrochemical device which has high heat resistance and excellent peel strength between a substrate and a heat resistant layer, and a method for manufacturing the same. BACKGROUND ART As technological development and demand for mobile instruments have been increased, secondary batteries have been increasingly in demand as energy sources. Among such secondary batteries, lithium secondary batteries having high energy density and operating voltage, long cycle life and a low discharge rate have been commercialized and used widely. Such a lithium secondary battery has been developed into a model capable of realizing high voltage and high capacity according to consumers' needs. To realize high capacity, required is a process of optimizing four main elements of a lithium secondary battery, including a positive electrode material, a negative electrode material, a separator and an electrolyte, in a limited space. Among the elements, a separator is an insulating film for electrically insulating a positive electrode and a negative electrode from each other and an important constitutional element in terms of safety of battery. When a secondary battery is overheated to cause thermal runaway or a separator is perforated, there is great concern about explosion. Particularly, a polyolefin-based porous substrate used conventionally as a separator for an electrochemical device shows a severe heat shrinking behavior at a temperature of 100° C. or higher due to its material property and a characteristic during its manufacturing process, including orientation, thereby causing a short-circuit between a positive electrode and a negative electrode. To solve the above-mentioned safety problems of an electrochemical device, there has been suggested an organic/inorganic composite separator having a porous coating layer formed by applying a mixture of inorganic particles with a binder polymer onto at least one surface of a porous substrate having a plurality of pores. In the organic/inorganic composite separator, the inorganic particles in the porous coating layer coated on the polyolefin-based porous substrate functions as a kind of spacer which can retain the physical shape of a porous active layer, and thus can inhibit the polyolefin-based porous substrate from heat shrinking upon overheating of an electrochemical device. In addition, interstitial volumes are present among the inorganic particles to form micropores. To allow the porous coating layer coated on the organic/inorganic composite separator to inhibit heat shrinking of the polyolefin-based porous substrate sufficiently, it is required that the inorganic particles are incorporated sufficiently at least in a predetermined amount. However, as the content of a binder polymer is decreased relatively due to an increase in content of the inorganic particles, adhesion between the porous coating layer and the polyolefin-based porous substrate and adhesion between the porous coating layer and an electrode are degraded. Therefore, the porous coating layer becomes less effective for inhibiting heat shrinking of the polyolefin-based porous substrate. In this case, it is difficult to inhibit a short circuit between a positive electrode and a negative electrode, when a battery is overheated. In addition, the electrode may be spaced apart easily from the separator, resulting in the problems of an increase in ion conductivity and degradation of resistance characteristics. On the other hand, when the content of a binder polymer in the porous coating layer is increased in order to prevent detachment of inorganic particles, the content of inorganic particles is decreased relatively. Thus, the effect of inhibiting heat shrinking of the polyolefin-based porous substrate may be degraded, and the battery performance may also be degraded due to a decrease in porosity in the porous coating layer. DISCLOSURE Technical Problem The present disclosure is directed to providing a separator for an electrochemical device and a method for manufacturing the same. The present disclosure is also directed to providing a separator, which has high peel strength between a separator substrate and a heat resistant layer and excellent adhesion between a separator and an electrode, by using a heat resistant polymer having a high melting point in a heat resistant layer, as well as a method for manufacturing the same. These and other objects and advantages of the present disclosure may be understood from th