Separator for secondary battery
Provided herein is a separator used for an electrochemical device such as a lithium-ion battery. The separator disclosed herein comprises a porous base material, and a protective porous layer coated on one or both surfaces of the porous base material disclosed herein, wherein the protective porous layer comprises an organic binder and an inorganic filler, and wherein a difference in tensile strength of the separator along the TD direction and MD direction is about 15% or less. Also provided herein is a lithium-ion battery including the separator disclosed herein. The separator disclosed herein is excellent in terms of safety, ion permeability, and cycle characteristics.
1. A secondary-battery separator comprising, a porous base material, and a protective porous layer coated on one or both surfaces of the porous base material, wherein the protective porous layer comprises an organic binder and an inorganic filler, wherein the protective porous layer has a first side adjacent to the porous base material and a second side adjacent to an anode or a cathode, wherein an amount of the organic binder at the first side is greater than an amount of the organic binder at the second side, and wherein a difference in tensile strength of the separator along the TD direction and MD direction is about 15% or less.
2. The secondary-battery separator of claim 1 , wherein the inorganic filler is a whisker material selected from the group consisting of Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 , BaO x , ZnO, CaCO 3 , TiN, AlN, MTiO 3 , K 2 O.nTiO 2 , Na 2 O.mTiO 2 , and combinations thereof, wherein x is 1 or 2; M is Ba, Sr or Ca; n is 1, 2, 4, 6 or 8; and m is 3 or 6.
3. The secondary-battery separator of claim 2 , wherein the whisker material has an average diameter from about 0.05 μm to about 3 μm and a ratio of length to diameter from about 5 to about 300.
4. The secondary-battery separator of claim 1 , wherein the inorganic filler is a particulate material selected from the group consisting of Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 , BaO x , ZnO, CaCO 3 , TiN, AlN, and combinations thereof, wherein x is 1 or 2.
5. The secondary-battery separator of claim 2 , wherein the inorganic filler further comprises a particulate material selected from the group consisting of Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 , BaO x , ZnO, CaCO 3 , TiN, AlN, and combinations thereof, wherein x is 1 or 2.
6. The secondary-battery separator of claim 5 , wherein the protective porous layer is a single-layered structure, and wherein the particulate material and the whisker material are randomly distributed throughout the protective porous layer.
7. The secondary-battery separator of claim 5 , wherein the protective porous layer is a two-layered structure comprising a first layer and a second layer, wherein the first layer is adjacent to the porous base material and the second layer is on and in contact with the first layer, and wherein the particulate material resides in the first layer and the whisker material resides in the second layer.
8. The secondary-battery separator of claim 5 , wherein the protective porous layer is a two-layered structure comprising a first layer and a second layer, wherein the first layer is adjacent to the porous base material and the second layer is on and in contact with the first layer, and wherein greater than 50% of the particulate material resides in the first layer and greater than 50% of the whisker material resides in the second layer, based on the total volume or weight of the inorganic filler.
9. The secondary-battery separator of claim 8 , wherein the average thickness ratio of the second layer to the first layer is from about 1:3 to about 3:1.
10. The secondary-battery separator of claim 8 , wherein the first layer has a first side adjacent to the porous base material and the second layer has a second side adjacent to an anode or a cathode, and wherein an amount of the organic binder at the first side is greater than an amount of the organic binder at the second side.
11. The secondary-battery separator of claim 1 , wherein the porous base material is a non-woven fabric consisting of natural or polymeric fibers, and wherein the polymeric fibers has a melting point of 200° C. or higher.
12. The secondary-battery separator of claim 11 , wherein the polymeric fibers of the porous base material are selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetherether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalate, and combinations thereof.
13. The secondary-battery separator of claim 12 , wherein the polyester is polyethylene terephthalate, polybutylene terephthalate, or a combination thereof.
14. The secondary-battery separator of claim 1 , wherein the organic binder is selected from the group consisting of a polyester, polyamide, polyether, polyimide, polycarboxylate, polycarboxylic acid, polyvinyl compound, polyolefin, rubber, polyvinyl pyrrolidone, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, carboxymethyl cellulose, cyanoethylcellulose, cyanoethylsucrose, polyurethane, nitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), latex, acrylonitrile-styrene-butadiene copolymer, fluorinated polymer, chlorinated polymer, and combinations thereof.
15. The secondary-battery separator of claim 1 , wherein the weight ratio of the inorganic filler to the organic binder is from about 99:1 to about 1:1.
16. The secondary-battery separator of claim 1 , wherein the separator has a thickness from about 1 μm to about 80 μm.
17. The secondary-battery separator of claim 1 , wherein the separator has a porosity from about 40% to about 97%.
18. A lithium battery comprising the separator as claimed in claim 1 .