JP-7856331-B2 - A cross-linked structure-containing separation membrane for lithium secondary batteries, a method for manufacturing the same, and a lithium secondary battery equipped with the separation membrane.

JP7856331B2JP 7856331 B2JP7856331 B2JP 7856331B2JP-7856331-B2

Inventors

ソン－ジェ・ハン
ジュ－ソン・イ
ソン・シク・ムン
キル－アン・ジュン

Assignees

エルジー・ケム・リミテッド

Dates

Publication Date: 20260511
Application Date: 20220509
Priority Date: 20210507

Claims (19)

A crosslinked structure-containing polyolefin porous support having a crosslinked structure in which polymer chains are directly linked to each other, An inorganic composite void layer comprising an inorganic filler and a first binder polymer, located on at least one surface of the cross-linked structure-containing polyolefin porous support, It comprises a porous adhesive layer located on the inorganic composite void layer and containing a second binder polymer, The crosslinked structure, in which the polymer chains are directly linked, is formed by introducing a photoinitiator containing thioxanthone, a thioxanthone derivative, or two or more of these onto the surface of a porous polyolefin support, wherein the photoinitiator is added to a coating liquid that forms a porous adhesive layer. The aforementioned polyolefin porous support is a crosslinked structure-containing separation membrane for lithium secondary batteries, which does not contain a crosslinked structure in which a photoinitiator and polymer chains are directly linked.
The separation membrane containing a cross-linked structure for lithium secondary batteries according to claim 1, wherein the thermal shrinkage rate in the mechanical direction and the transverse direction, measured after leaving the separation membrane containing the cross-linked structure for lithium secondary batteries at 150°C for 30 minutes, is 20% or less.
The separation membrane containing a cross-linked structure for lithium secondary batteries according to claim 1, wherein the weight ratio of the inorganic filler to the first binder polymer is 95:5 to 99.9:0.1.
The separation membrane containing a cross-linked structure for lithium secondary batteries according to claim 1, wherein the first binder polymer comprises an acrylic polymer, polyacrylic acid, styrene-butadiene rubber, polyvinyl alcohol, or two or more of these.
The separation membrane containing a crosslinked structure for lithium secondary batteries according to claim 1, wherein the second binder polymer comprises polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-tetrafluoroethylene, polyvinylidene fluoride-trifluoroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylhexyl acrylate-methyl methacrylate copolymer, ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, or two or more of these.
The separation membrane containing a crosslinked structure for a lithium secondary battery according to claim 1, wherein the porous adhesive layer has a pattern comprising one or more adhesive portions containing the second binder polymer and one or more plain portions where the adhesive portions are not formed.
The separation membrane containing a cross-linked structure for lithium secondary batteries according to claim 1, wherein the meltdown temperature of the separation membrane containing the cross-linked structure for lithium secondary batteries is 160°C or higher.
The separation membrane containing a cross-linked structure for lithium secondary batteries according to claim 1, wherein the shutdown temperature of the separation membrane containing the cross-linked structure for lithium secondary batteries is 145°C or lower.
(S1) A step of producing an inorganic composite void layer forming slurry containing an inorganic filler, a first binder polymer, and a dispersion medium, (S2) The step of forming an inorganic composite void layer by coating and drying the slurry for forming the inorganic composite void layer on at least one surface of a polyolefin porous support, (S3) A step of coating the upper surface of the inorganic composite void layer with a coating liquid for forming a porous adhesive layer, which includes a second binder polymer, a solvent for the second binder polymer, and a photoinitiator. (S4) The process involves immersing the product obtained in step (S3) in a coagulation solution containing a non-solvent for the second binder polymer, and then drying it to form a porous adhesive layer. A method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries, comprising the step of (S5) irradiating the result of step (S4) with ultraviolet light.
The method for producing a cross-linked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the content of the photoinitiator is 0.015 to 0.3 parts by weight per 100 parts by weight of the polyolefin porous support.
A method for producing a cross-linked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the weight ratio of the inorganic filler to the first binder polymer is 95:5 to 99.9:0.1.
The method for producing a cross-linked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the first binder polymer comprises an acrylic polymer, polyacrylic acid, styrene-butadiene rubber, polyvinyl alcohol, or two or more of these.
The method for producing a cross-linked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the dispersion medium is an aqueous dispersion medium.
The method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the second binder polymer comprises polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-tetrafluoroethylene, polyvinylidene fluoride-trifluoroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylhexyl acrylate-methyl methacrylate copolymer, ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, or two or more of these.
The method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the solvent for the second binder polymer comprises acetone, tetrahydrofuran, methylene chloride, chloroform, trimethyl phosphate, triethyl phosphate, methyl ethyl ketone, toluene, hexane, cyclohexane, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, or two or more of these.
The method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the photoinitiator includes a type II photoinitiator.
The method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the photoinitiator comprises thioxanthone, thioxanthone derivative, benzophenone, benzophenone derivative, or two or more of these.
A method for producing a cross-linked structure-containing separation membrane for lithium secondary batteries according to claim 9, wherein the irradiation amount of ultraviolet light is 10 to 2000 mJ/ cm² .
A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator membrane interposed between the positive electrode and the negative electrode, A lithium secondary battery wherein the separation membrane is a crosslinked structure-containing separation membrane for lithium secondary batteries according to any one of claims 1 to 8.

Description

This application claims priority based on Korean Patent Application No. 10-2021-0059581, filed on May 7, 2021. This invention relates to a cross-linked structure-containing separation membrane for lithium secondary batteries, a method for manufacturing the same, and a lithium secondary battery equipped with the separation membrane. In recent years, interest in energy storage technology has been steadily increasing. As applications expand to include mobile phones, camcorders, laptops, and even electric vehicles, there is a growing demand for higher energy density batteries used as power sources for these electronic devices. Lithium-ion batteries are the type of battery best suited to meet these demands, and research into them is currently very active. Such lithium-ion secondary batteries consist of a positive electrode, a negative electrode, an electrolyte, and a separation membrane. The separation membrane requires both electrical insulation to separate the positive and negative electrodes, and high ionic conductivity to enhance lithium ion permeability based on high porosity. Polyolefin separation membranes are widely used as such separation membranes. However, in the case of polyethylene (PE) separation membranes, a typical polyolefin separation membrane, the low melting point (Tm) means that if the battery temperature rises above the polyethylene melting point in an environment where the battery is misused, a meltdown phenomenon may occur, potentially causing ignition and explosion. Furthermore, due to its material properties and manufacturing process characteristics, the separation membrane may exhibit significant thermal contraction behavior under high temperatures, potentially leading to safety problems such as internal short circuits. Therefore, there is a pressing need for separation membranes that can ensure safety at high temperatures. This figure schematically shows a crosslinked structure-containing separation membrane for lithium secondary batteries according to one embodiment of the present invention.This figure shows the meltdown temperature in the mechanical direction, measured by thermomechanical analysis (TMA) of the separation membranes produced in Example 1, Comparative Example 1, and Comparative Example 2. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and in the claims are not to be interpreted in their usual and dictionary sense, but rather in a sense and concept corresponding to the technical idea of the present invention, in accordance with the principle that the inventor himself may appropriately define the concepts of terms in order to best describe the invention. Therefore, the embodiments described herein and the configurations shown in the drawings represent only one of the most preferred embodiments of the present invention and do not represent the entire technical concept of the invention. It should be understood that, at the time of this application, there may be a variety of equivalents and modifications that can be substituted therewith. In this specification, terms such as "first," "second," etc., are used to distinguish one component from another, and the components are not limited by these terms. A separation membrane containing a crosslinked structure for lithium secondary batteries according to one embodiment of the present invention is A crosslinked structure-containing polyolefin porous support having a crosslinked structure in which polymer chains are directly linked to each other, An inorganic composite void layer comprising an inorganic filler and a first binder polymer, located on at least one surface of the cross-linked structure-containing polyolefin porous support, The material comprises a porous adhesive layer located on the inorganic composite void layer and containing a second binder polymer. Figure 1 is a schematic diagram showing a cross-linked structure-containing separation membrane for lithium secondary batteries according to one embodiment of the present invention. Referring to Figure 1, the crosslinked structure-containing separation membrane 1 for lithium secondary batteries according to one embodiment of the present invention includes a crosslinked structure-containing polyolefin porous support 10. In this specification, "a crosslinked structure in which polymer chains are directly linked" refers to a state in which polymer chains substantially composed of polyolefins, more preferably composed solely of polyolefins, become reactive upon the addition of a photoinitiator, and the polymer chains directly crosslink with each other. Therefore, a crosslinking reaction occurring between crosslinking agents due to the addition of an additional crosslinking agent does not constitute a "crosslinked structure in which polymer chains are directly linked" as defined in this invention. Furthermore, a crosslinking reaction o