Composite separator including porous substrate with porous layer including polyacrylic acid metal salt binder and inorganic particles, lithium battery including the same, and method of preparing the same

1 . A composite separator comprising:

a porous substrate; and

a coating layer on at least one surface of the porous substrate,

wherein the coating layer comprises a water-soluble binder and inorganic particles,

the water-soluble binder comprises a polyacrylic acid metal salt,

the polyacrylic acid metal salt has a weight average molecular weight of 300,000 Dalton to 500,000 Dalton, and

the inorganic particles have an average particle diameter (D50) of about 500 nm or more,

wherein the polyacrylic acid metal salt comprises a polyacrylic acid lithium salt,

wherein the polyacrylic acid metal salt comprises an acrylic acid repeating unit substituted with lithium ions and an acrylic acid repeating unit, and a mole ratio of the acrylic acid repeating unit substituted with lithium ions to the acrylic acid repeating unit included the polyacrylic acid metal salt is from 0.3 to about 0.9.

2 . The composite separator of claim 1 , wherein the weight average molecular weight of the polyacrylic acid metal salt is about 300,000 Dalton to about 450,000 Dalton.

3 . The composite separator of claim 1 , wherein the coating layer comprises 0.5 parts by weight to 30 parts by weight of the water-soluble binder based on 100 parts by weight of the inorganic particles.

4 . The composite separator of claim 1 , wherein the average particle diameter (D50) of the inorganic particles is about 500 nm to about 1000 nm.

5 . The composite separator of claim 1 , wherein the inorganic particles comprise at least one selected from TiO 2 , SnO 2 , CaO, ZnO, ZrO 2 , CeO 2 , NiO, MgO, Al 2 O 3 , SiO 2 , Y 2 O 3 , SrTiO 3 , BaTiO 3 , MgF 2 , Mg(OH) 2 , barium sulfate, and boehmite.

6 . The composite separator of claim 1 , wherein a total thickness of the coating layer is 25% or less of a total thickness of the composite separator.

7 . The composite separator of claim 1 , wherein a thickness of the coating layer on one surface of the porous substrate is 1.2 μm or less, and a total thickness of the composite separator is 10.5 μm or less.

8 . The composite separator of claim 1 , wherein the coating layer has a peel strength of about 10 gf/mm to about 30 gf/mm with respect to the porous substrate.

9 . The composite separator of claim 1 , wherein the porous substrate has a pore size of about 0.01 μm to about 2 μm.

10 . The composite separator of claim 1 , wherein the porous substrate has a porosity of about 5% to about 95%.

11 . The composite separator of claim 1 , wherein the porous substrate comprises one or more selected from polyethylene, polypropylene terephthalate, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate.

12 . The composite separator of claim 1 , wherein when treated at 150° C. for 1 hour, the composite separator has a machine direction shrinkage rate and a transverse direction shrinkage rate, each being 3% or less.

13 . The composite separator of claim 1 , wherein the composite separator has a moisture content of about 1 ppm and about 990 ppm when treated at 85° C. for 12 hours.

14 . The composite separator of claim 1 , wherein the coating layer further comprises a wetting agent.

15 . The composite separator of claim 14 , wherein the wetting agent has a weight average molecular weight of about 250 Dalton to about 30,000 Dalton.

16 . The composite separator according to claim 14 , wherein the wetting agent comprises one or more selected from polyvinyl alcohol, polyethylene glycol, sodium dodecyl sulfate, sodium dibutylnaphthalenesulfonate, polyacrylamide, polyethylene glycol fatty acid ester, alkyl polyoxyethylene ether carboxylate, alkyl phenol polyoxyethylene ether, sodium alkylbenzenesulfonate, alkyl phenol polyoxyethylene ether, polyoxyethylene alkyl amine, and polyoxyethylene amide.

17 . A lithium battery comprising:

a positive electrode; a negative electrode; and

the composite separator of claim 1 between the positive electrode and the negative electrode.

18 . A method of manufacturing a composite separator of claim 1 , the method comprising:

providing the porous substrate;

preparing a stacked structure by coating a composition comprising the water-soluble binder, the inorganic particles, and water on one surface or opposite surfaces of the porous substrate; and

drying the stacked structure to form the coating layer on the at least one surface of the porous substrate,

wherein the coating layer comprises the water-soluble binder and the inorganic particles, and the water-soluble binder comprises the polyacrylic acid metal salt, and

the weight average molecular weight of the polyacrylic acid metal salt is about 300,000 Dalton to 450,000 Dalton, and the average particle diameter (D50) of the inorganic particles is about 500 nm or more.