# US 12,770,973 B2 · Separator for lithium secondary battery and method for manufacturing the same

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- Number: US 12,770,973 B2
- Document ID: US12770973B2
- Status: Granted
- Kind: B2
- Application number: 18/033,735
- Filed: 2021-11-11
- Published: 2023-12-14
- Granted: 2026-10-20
- Earliest claimed: 2020-11-11
- Assignees: LG Chem, Ltd.
- Applicants: LG Chem, Ltd.
- Inventors: Sung Cik Mun; Joo-Sung Lee; Sung-Jae Han
- Web page: https://patentgrep.com/patent/US12770973B2

## CPC

- H01M 50/403: Manufacturing processes of separators, membranes or diaphragms
- C08K 3/013: Fillers, pigments or reinforcing additives
- C09J 9/00: Adhesives characterised by their physical nature or the effects produced, e.g. glue sticks (C09J7/00 takes precedence)
- H01M 10/052: Li-accumulators
- H01M 50/417: Polyolefins
- H01M 50/431: Inorganic material
- H01M 50/44: Fibrous material
- H01M 50/446: Composite material consisting of a mixture of organic and inorganic materials
- H01M 50/451: comprising layers of only organic material and layers containing inorganic material
- H01M 50/461: {with adhesive layers between electrodes and separators}
- H01M 50/491: Porosity
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)
- C09J: ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES (preparation of glue or gelatine C09H)

## Abstract

A separator for a lithium secondary battery, a method of making the same, and a lithium secondary battery including the same is disclosed herein. In some embodiments, a separator for a lithium secondary battery including a porous polyolefin substrate having a tan(δ) of 0.3 or less. The tan(δ) is determined by Formula 1 at a temperature of 230° C. and an angular frequency of 0.1 rad/s: tan(δ)=G″/G′ [Formula 1] wherein G′ is a storage modulus of the polyolefin and G″ is a loss modulus of the polyolefin. The separator has a low viscosity but high elasticity at high temperature, maintains strength at high temperature, and has resistance against external force at high temperature. A lithium secondary battery including the separator has improved safety.

## Claims

### Claim 1

A separator for a lithium secondary battery, comprising:
a porous polyolefin substrate having a tan(δ) of 0.3 or less, wherein tan(δ) is determined by Formula 1 at a temperature of 230° C. and an angular frequency of 0.1 rad/s,
wherein the porous polyolefin substrate has an ‘a’ value of 0.03-0.25 as determined by Formula 2 at a temperature of 230° C. and an angular frequency of 0.1 rad/s:
tan(δ)=G″/G′ {Formula 1}
a=d(log(G′))/d(log(angular frequency)) [Formula 2]
wherein G′ is a storage modulus of the porous polyolefin substrate and G″ is a loss modulus of the porous polyolefin substrate.

### Claim 2 (depends on 1)

The separator for a lithium secondary battery according to claim 1, wherein tan(δ) is 0.1 to 0.3.

### Claim 3 (depends on 1)

The separator for a lithium secondary battery according to claim 1, wherein ‘a’ value is 0.04 to 0.23.

### Claim 4 (depends on 1)

The separator for a lithium secondary battery according to claim 1, wherein the porous polyolefin substrate comprises a plurality of fibrils and pores,
wherein the pores are formed by the fibrils entangling with one another, and
wherein polyolefin chains forming the fibrils are crosslinked directly with one another.

### Claim 5 (depends on 4)

The separator for a lithium secondary battery according to claim 4, wherein the surfaces of fibrils are crosslinked.

### Claim 6 (depends on 1)

The separator for a lithium secondary battery according to claim 1, wherein G′ is 1.0×105 to 1.0×107 Pa.

### Claim 7 (depends on 1)

The separator for a lithium secondary battery according to claim 1, wherein G″ is 1.0×106 Pa or less.

### Claim 8 (depends on 1)

The separator for a lithium secondary battery according to claim 1, wherein the separator has a melt-down temperature of 160° C. or higher.

### Claim 9 (depends on 1)

The separator for a lithium secondary battery according to claim 1, wherein the separator has a porosity of 40% or more.

### Claim 10 (depends on 1)

The separator for a lithium secondary battery according to claim 1, wherein the separator has an air permeability of 500 sec/100 mL or less.

### Claim 11 (depends on 1)

The separator for a lithium secondary battery according to claim 1, further comprising:
an inorganic composite porous layer disposed on at least one surface of the porous polyolefin substrate, wherein the inorganic composite porous layer comprises an inorganic filler and a binder polymer.

### Claim 12 (depends on 1)

The separator for a lithium secondary battery according to claim 1, further comprising:
an inorganic composite porous layer disposed on at least one surface of the porous polyolefin substrate, wherein the inorganic composite porous layer comprises an inorganic filler and a first binder polymer; and
a porous adhesive layer disposed on the inorganic composite porous layer, wherein the porous adhesive layer comprises a second binder polymer.

### Claim 13 (depends on 1)

A method for manufacturing the separator for a lithium secondary battery of claim 1, comprising the steps of:
(S1) preparing a non-crosslinked porous polyolefin substrate;
(S2) applying a photoinitiator composition to the non-crosslinked polyolefin porous substrate, wherein the photoinitiator composition comprises a Type 2 photoinitiator; and
(S3) irradiating the porous polyolefin substrate having the applied photoinitiator composition, wherein the irradiation uses ultraviolet (UV) rays.

### Claim 14 (depends on 13)

The method for manufacturing the separator for a lithium secondary battery according to claim 13, wherein the non-crosslinked porous polymer substrate in step (S1) has a BET specific surface area of 15 m2/g or more.

### Claim 15 (depends on 13)

The method for manufacturing the separator for a lithium secondary battery according to claim 13, wherein the non-crosslinked porous polyolefin substrate of step (S1) has a tan(δ) of 0.5 or more, as determined by Formula 1 at a temperature of 230° C. and an angular frequency of 0.1 rad/s.

### Claim 16 (depends on 13)

The method for manufacturing the separator for a lithium secondary battery according to claim 13, wherein the Type 2 photoinitiator comprises isopropyl thioxanthone (ITX), an isopropyl thioxanthone derivative, thioxanthone (TX), benzophenone (BPO), a benzophenone derivative, 4-hydroxybenzophenone, or combinations thereof.

### Claim 17 (depends on 13)

The method for manufacturing the separator for a lithium secondary battery according to claim 13, wherein the concentration of the Type 2 photoinitiator is 0.01 to 0.3 wt % based on the total weight of the photoinitiator composition.

### Claim 18 (depends on 13)

The method for manufacturing the separator for a lithium secondary battery according to claim 13, wherein the photoinitiator composition in step (S2) further comprises a Type 1 photoinitiator, and
wherein the Type 1 photoinitiator comprises a benzoin-based initiator, a hydroxyketone-based initiator, an aminoketone-based initiator, a phosphine oxide-based initiator, or combinations thereof.

### Claim 19 (depends on 1)

A lithium secondary battery, comprising:
a positive electrode;
a negative electrode; and
the separator of claim 1 interposed between the positive electrode and the negative electrode.