# US 12,002,986 B2 · Thin polyethylene separator with reduced compressibility and electrochemical device including the same

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- Number: US 12,002,986 B2
- Document ID: US12002986B2
- Status: Granted
- Kind: B2
- Application number: 16/979,816
- Filed: 2019-06-21
- Published: 2021-02-18
- Granted: 2024-06-04
- Earliest claimed: 2018-06-22
- Assignees: LG Energy Solution, Ltd.
- Applicants: LG Chem, Ltd.
- Inventors: Su-Jin Park; Chan-Jong Kim; Sang-Joon Lee
- Web page: https://patentgrep.com/patent/US12002986B2

## CPC

- H01M 50/411: Organic material
- H01G 9/02: Diaphragms; Separators
- H01G 11/52: Separators
- H01M 10/052: Li-accumulators
- H01M 10/0525: Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
- H01M 50/403: Manufacturing processes of separators, membranes or diaphragms
- H01M 50/409: Separators, membranes or diaphragms characterised by the material
- H01M 50/417: Polyolefins
- H01M 50/443: Particulate material
- H01M 50/446: Composite material consisting of a mixture of organic and inorganic materials
- H01M 50/449: having a layered structure
- H01M 50/451: comprising layers of only organic material and layers containing inorganic material
- H01M 50/457: comprising three or more layers
- H01M 50/489: Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M 50/491: Porosity
- Y02E 60/10: Energy storage using batteries
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01G: CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE (selection of specified materials as dielectric H01B3/00; capacitors having potential barriers H10D1/62, H10K10/10)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A separator for an electrochemical device. The separator includes a porous substrate made of a porous polymer film having an excellent compressibility and permanent strain. The porous substrate has excellent physical strength and durability, and ensures a high breakdown voltage while using a heat resistant layer having a small thickness, and thus shows a low possibility of short-circuit generation. In addition, the separator may further include a heat resistant layer including inorganic particles, on the surface of the porous substrate. It is possible to further improve the compressibility, maximum compressibility and permanent strain characteristics depending on the types of inorganic particles.

## Claims

### Claim 1

A separator for an electrochemical device comprising:
a porous substrate,
wherein the porous substrate comprises polyethylene and polypropylene;
wherein the porous substrate satisfies the following conditions a), b) and c), when the porous substrate is pressurized at 40° C. from 0.04 N to 1 N at a rate of 0.25 N/min and depressurized from 1 N to 0.04 N at the rate of 0.25 N/min:
a) a compressibility of 15% or less when the pressure reaches 1 N,
b) a maximum compressibility of 18% or less within the pressure range of 0.04 N to 1 N, and
c) a permanent strain of 13% or less;
wherein the porous substrate has a porosity of 45% or less; and
wherein the polyethylene has a weight average molecular weight (Mw) of 300,000 to 500,000,
the polyethylene is present in an amount of 80 wt % or more based on 100 wt % of the porous substrate, and the polypropylene is present in the porous substrate in an amount greater than 0 wt % up to 5 wt % based on 100 wt % of the porous substrate.

### Claim 2 (depends on 1)

The separator for an electrochemical device according to claim 1, wherein the porous substrate has a thickness of 5 μm to 20 μm.

### Claim 3 (depends on 1)

The separator for an electrochemical device according to claim 1, wherein the porous substrate has pores formed by removing a pore-forming agent from a mixture of a polymer resin with the pore-forming agent.

### Claim 4 (depends on 1)

The separator for an electrochemical device according to claim 1,
wherein the amount of polypropylene present in the porous substrate ranges from 4.7 wt % to 4.8 wt % based on 100 wt % of the porous substrate.

### Claim 5 (depends on 1)

The separator for an electrochemical device according to claim 1, wherein when a plurality of specimens of the separator are prepared, a percentage of specimens of the separator in which a short-circuit occurs at 75 V or less, is less than 1% based on a total number of specimens of the separator.

### Claim 6 (depends on 1)

The separator for an electrochemical device according to claim 1, which further comprises a heat resistant layer on at least one surface of the porous substrate, wherein the porous substrate satisfies each of the conditions of:
the compressibility of 15% or less,
the maximum compressibility of 17% or less, and
the permanent strain of 12% or less.

### Claim 7 (depends on 1)

The separator for an electrochemical device according to claim 1, which further comprises:
a heat resistant layer on at least one surface of the porous substrate,
wherein the heat resistant layer comprises a binder resin with inorganic particles, and
wherein each inorganic particle comprises at least one of an oxide, or a hydroxide, and
wherein the oxide and hydroxide independently comprise at least one element selected from the group consisting of aluminum, magnesium, silicon, zirconium, calcium, strontium, barium, antimony, tin, zinc and rare earth elements.

### Claim 8

A method for selecting a porous substrate of a separator for an electrochemical device, comprising the steps of:
(S1) preparing a porous substrate comprising polyethylene, and polypropylene, and having thickness of 5 μm to 20 μm;
(S2) measuring compressibility, maximum compressibility and permanent strain of the porous substrate; and
(S3) selecting the porous substrate that satisfies the conditions of:
a) a compressibility of 15% or less,
b) a maximum compressibility of 18% or less, and
c) a permanent strain of 13% or less, and
wherein the polyethylene has a weight average molecular weight (Mw) of 300,000 to 500,000, the polyethylene is present in an amount of 80 wt % or more based on 100 wt % of the porous substrate and the polypropylene is present in the porous substrate in an amount greater than 0 wt % up to 5 wt % based on 100 wt % of the porous substrate.