US-20260128465-A1 - SEPARATOR FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY INCLUDING THE SAME

US20260128465A1US 20260128465 A1US20260128465 A1US 20260128465A1US-20260128465-A1

Abstract

The present disclosure relates to a separator for a rechargeable lithium battery and a rechargeable lithium battery including the separator. The separator includes a porous substrate, a first coating layer on a first surface of the porous substrate, and a second coating layer on a second surface of the porous substrate. The first coating layer and the second coating layer include a binder and a filler, the binder of the first coating layer includes a first binder, and the binder of the second coating layer includes a second binder. The first binder and the second binder each include a copolymer of a monomer mixture including a first structural unit including a unit derived from an aromatic based unsaturated monomer, a second structural unit derived from a (meth)acrylic monomer, and a third structural unit derived from a sulfonic acid group-containing monomer.

Inventors

Nam Ju Kim
Jung Seong Lee
Hyeon Seon CHOI
Bae Wook LEE
Jae Yeon Lee
Dong Wan Seo

Assignees

SAMSUNG SDI CO., LTD.

Dates

Publication Date: 20260507
Application Date: 20251106
Priority Date: 20241107

Claims (15)

1 . A separator for a rechargeable lithium battery, the separator comprising: a porous substrate; a first coating layer on a first surface of the porous substrate; and a second coating layer on a second surface of the porous substrate, wherein the first coating layer includes a first binder and a first filler, and the second coating layer includes a second binder and a second filler, the first binder and the second binder each include a copolymer including a first structural unit including a unit derived from an aromatic based unsaturated monomer; a second structural unit derived from a (meth)acrylic monomer containing an alkyl group having 4 or more carbon atoms in the main chain in the ester moiety; and a third structural unit derived from a sulfonic acid group-containing monomer, with respect to 100 mol % of the copolymer, about 5 mol % to about 80 mol % of the first structural unit, about 10 mol % to about 40 mol % of the second structural unit, and about 5 mol % to about 80 mol % of the third structural unit are included, and the first filler and the second filler satisfy the following Expression 1: ( Average ⁢ particle ⁢ size ⁢ ( D ⁢ 50 ) ⁢ of ⁢ second ⁢ filler ) / ( Average ⁢ particle ⁢ size ⁢ ( D ⁢ 50 ) ⁢ of ⁢ first ⁢ filler ) ≥ 3. Expression ⁢ 1
2 . The separator of claim 1 , wherein the first filler has an average particle size D50 of more than 0 nm and less than about 100 nm, and the second filler has an average particle size D50 of about 100 nm or more and about 300 nm or less.
3 . The separator of claim 1 , wherein the first filler is amorphous, and the second filler is cubic.
4 . The separator of claim 1 , wherein the first filler and the second filler have a pH of about 7 or higher.
5 . The separator of claim 1 , wherein the first filler and the second filler each comprise at least one of Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , CeO 2 , MgO, NiO, CaO, GaO, ZnO, ZrO 2 , Y 2 O 3 , SrTiO 3 , BaTiO 3 , Mg(OH) 2 , boehmite, and a combination thereof.
6 . The separator of claim 1 , wherein the first binder and the second binder each have a glass transition temperature in a range of about 60° C. to about 80° C.
7 . The separator of claim 1 , wherein the first binder and the first filler are included in a mass ratio in a range of about 1:10 to about 1:50, and the second binder and the second filler are included in a mass ratio in a range of about 1:10 to about 1:50.
8 . The separator of claim 1 , wherein the unit derived from the aromatic based unsaturated monomer is represented by Chemical Formula 1 below: in Chemical Formula 1, R 1 and R 2 each independently comprises hydrogen or a substituted or unsubstituted C1 to C5 alkyl group, and Ar comprises a substituted or unsubstituted, monocyclic or polycyclic C6 to C20 aryl group, the second structural unit is represented by Chemical Formula 4 below: in Chemical Formula 4, R 7 and R 8 each independently comprises hydrogen or a methyl group, and L 2 comprises a substituted or unsubstituted, straight or branched C4 to C30 alkyl group, and the third structural unit is represented by any one of Chemical Formulas 5 to 7 below: in Chemical Formulas 5 to 7, R 9 , R 10 , R 11 , R 12 , R 13 , and R 14 each independently comprises hydrogen or a C1 to C3 alkyl group, L 3 , L 5 , and L 7 each independently comprises —C(═O)—, —C(═O)O—, —OC(═O)—, —O—, or —C(═O)NH—, L 4 , L 6 , and L 8 each independently comprises a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, and a, b, c, d, e, and f are each independently an integer in a range from 0 to 2, and in Chemical Formula 6, M comprises an alkali metal.
9 . The separator of claim 1 , wherein the first structural unit further comprises a unit derived from a (meth)acrylic monomer containing an alkyl group having 1 to 3 carbon atoms in the main chain in the ester moiety.
10 . The separator of claim 9 , wherein the unit derived from the (meth)acrylic monomer is represented by the following Chemical Formula 3: in Chemical Formula 3, R 5 and R 6 each independently comprises hydrogen or a methyl group, and L 1 comprises a substituted or unsubstituted, straight or branched C1 to C3 alkyl group.
11 . The separator of claim 9 , wherein the unit derived from the aromatic based unsaturated monomer and the unit derived from the (meth)acrylic monomer are included in a molar ratio in a range of about 1:0.5 to about 1:2.
12 . The separator of claim 9 , wherein with respect to 100 mol % of the copolymer, about 5 mol % to about 35 mol % of the structural unit derived from the aromatic based unsaturated monomer, about 5 mol % to about 35 mol % of the structural unit derived from the (meth)acrylic monomer containing an alkyl group having 1 to 3 carbon atoms in the main chain in the ester moiety, about 20 mol % to about 30 mol % of the second structural unit, and about 10 mol % to about 60 mol % of the third structural unit, are included.
13 . The separator of claim 9 , wherein the copolymer comprises: a structural unit derived from an aromatic based unsaturated monomer derived from one or more of styrene, α-methyl styrene, 4-butyl styrene, 4-butoxy styrene, halo styrene, vinyl toluene, and vinyl naphthalene; a structural unit derived from a (meth)acrylic monomer containing an alkyl group having 1 to 3 carbon atoms in the main chain in the ester moiety, which is derived from one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and iso-propyl (meth)acrylate; a second structural unit derived from one or more of 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and isodecyl (meth)acrylate; and a third structural unit derived from at least one of vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethol sulfonic acid, (meth)acrylamido alkane sulfonic acid, sulfoalkyl (meth)acrylate, and a salt thereof.
14 . The separator of claim 1 , wherein the first coating layer and the second coating layer each have a thickness in a range of about 0.1 μm to about 1.5 μm.
15 . A rechargeable lithium battery comprising: a positive electrode; a negative electrode; and the separator according to claim 1 interposed between the positive electrode and the negative electrode.

Description

CROSS-REFERENCE TO RELATED APPLICATION The present application claims priority to Korean Patent Application No. 10-2024-0157092, filed on Nov. 7, 2024 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. BACKGROUND 1. Field of the Disclosure The present disclosure relates to a separator for a rechargeable lithium battery, and a rechargeable lithium battery including the separator. 2. Discussion of Related Art With increasing presence of electronic devices using batteries, such as, e.g., mobile phones, notebook computers, electric vehicles, and the like, the demand for secondary batteries having high energy density and high capacity is increasing. Therefore, improving the performance of rechargeable lithium batteries may be advantageous. A rechargeable lithium battery includes a positive electrode and a negative electrode that contain an active material capable of the intercalation and deintercalation of lithium ions, and produces electrical energy by oxidation and reduction reactions when the lithium ions are intercalated into and deintercalated from the positive electrode and the negative electrode. SUMMARY The present disclosure is directed to providing a separator for a rechargeable lithium battery, which exhibits low membrane resistance when impregnated with an electrolyte. The present disclosure is also directed to providing a separator for a rechargeable lithium battery, which exhibits high electrolyte wettability, desired or improved air permeability, and high adhesion to an electrode plate. The present disclosure is also directed to providing a separator for a rechargeable lithium battery, which exhibits desired or improved heat resistance. The present disclosure is also directed to providing a separator for a rechargeable lithium battery, which exhibits a high capacity retention rate and a low direct current internal resistance (DC-IR) change rate at room temperature and at high temperature. The present disclosure is also directed to providing a rechargeable lithium battery including the above-described separator for a rechargeable lithium battery. One aspect of the present disclosure includes a separator for a rechargeable lithium battery. The separator for a rechargeable lithium battery includes a porous substrate, a first coating layer located on a first surface of the porous substrate, and a second coating layer located on a second surface of the porous substrate. The first coating layer includes a binder and a filler, and the second coating layer includes a binder and a filler. The binder of the first coating layer includes a first binder, and the binder of the second coating layer includes a second binder. The first binder and the second binder each include a copolymer including a first structural unit including a unit derived from an aromatic based unsaturated monomer, a second structural unit derived from a (meth)acrylic monomer containing an alkyl group having 4 or more carbon atoms in the main chain in the ester moiety, and a third structural unit derived from a sulfonic acid group-containing monomer. With respect to 100 mol % of the copolymer, about 5 mol % to about 80 mol % of the first structural unit, about 10 mol % to about 40 mol % of the second structural unit, and about 5 mol % to about 80 mol % of the third structural unit are included. The filler of the first coating layer includes a first filler, and the filler of the second coating layer includes a second filler, and the first filler and the second filler satisfy the following Expression 1: (Average⁢ particle⁢ size⁢ (D⁢50 )⁢ of⁢ second⁢ filler)/(Average⁢ particle⁢ size⁢ (D⁢50)⁢ of⁢ first⁢ filler)≥3.Expression⁢ 1 Another aspect of the present disclosure includes a rechargeable lithium battery. The rechargeable lithium battery includes a positive electrode, a negative electrode, and the above-described separator interposed between the positive electrode and the negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present disclosure may become more apparent to those of ordinary skill in the art by describing example embodiments thereof in detail with reference to the accompanying drawings, in which: FIG. 1 is a scanning electron microscope (SEM) image of an amorphous filler; FIG. 2 is an SEM image of a cubic filler; FIG. 3 is a schematic cross-sectional view of a separator for a rechargeable lithium battery according to an example embodiment; and FIG. 4 to FIG. 7 are schematic cross-sectional views of rechargeable lithium batteries according to example embodiments. DETAILED DESCRIPTION Hereinafter, example embodiments of the present disclosure are described in detail. However, the embodiments are presented as examples, the present disclosure is not limited thereto, and the present disclosure is only defined by the scope of the appended claims. Unless otherwise stated herein, when a par