Separator for electrochemical device and method for producing the same
The present invention provide a separator for an electrochemical device which comprises a wet nonwoven fabric comprising one or more kinds of fibrillated organic fibers which are at least partially fibrillated into a fiber diameter of 1 μm or less, and one or more kinds of unfibrillated organic fibers having a fineness of 0.5 dtex or less, which exhibits excellent heat resistance, electrolyte holding properties, internal short-circuit preventing property, and winding property, which results in a lowered internal resistance and prolonged life of an electrochemical device, and a method for producing the same and an electrochemical device.
1. A separator for an electrochemical device, which comprises:
a wet nonwoven fabric comprising one or more kinds of fibrillated liquid crystalline polymeric fibers which have at least partially a fiber diameter of 0.0004 μm to 1 μm, have a melting point or a thermal decomposition temperature of 250 C to 650° C. and have an average fiber length of 0.3 mm to 2 mm, and
one or more kinds of unfibrillated organic fibers having a fineness of 0.5 dtex or less, wherein the separator has a void rate of 65% to 85% and a maximum pore diameter of 0.9 μm to 6 μm.
2. The separator for an electrochemical device according to claim 1 , wherein the fibrillated liquid crystalline polymeric fibers are fibrillated at least by means of a high-pressure homogenizer.
3. The separator for an electrochemical device according to claim 1 , wherein the liquid crystalline polymeric fibers are totally aromatic polyamide fibers.
4. The separator for an electrochemical device according to claim 1 , wherein the liquid crystalline polymeric fibers are totally aromatic polyester fibers.
5. The separator for an electrochemical device according to claim 1 , which comprises fibrillated cellulose fibers in an amount of 8% or less.
6. The separator for an electrochemical device according to claim 1 , which comprises bacterial cellulose in an amount of 8% or less.
7. The separator for an electrochemical device according to claim 1 , which has Gurley air permeability of 0.5 s/100 ml to 20 s/100 ml.
8. The separator for an electrochemical device according to claim 1 , which has an extract solution conductivity of 3.5 μS/cm to 30 μS/cm.
9. The separator for an electrochemical device according to claim 1 , which has a center plane average surface roughness SRa of 1.7 μm to 20 μm.
10. The separator for an electrochemical device according to claim 1 , which has tensile strength in a longitudinal direction of 1 kg/50 mm or more, and puncture strength of 100 g or more.
11. The separator for an electrochemical device according to claim 1 , which has moisture absorption of lower than 5%, as measured after the separator was dried at any temperature of 150 C to 210 C for one hour or longer, and allowed to stand in an atmosphere of 20 C and 65% RH for 24 hours or longer.
12. The separator for an electrochemical device according to claim 1 , which exhibits heat shrinkage degree of lower than 5%, as measured after being left in an atmosphere of 150 C to 210 C for one hour or longer.
13. The separator for an electrochemical device according to claim 1 , which has a multi-layer structure.
14. The separator for an electrochemical device according to claim 1 , which has a multi-layer structure comprising a relatively higher and lower density layers.
15. The separator for an electrochemical device according to claim 1 , which is thermally treated at 150 C to 250 C.
16. The separator for an electrochemical device according to claim 1 , wherein the wet nonwoven fabric is brought into contact with a roll heated to 150 C to 250 C for the thermal treatment.
17. A separator for an electric double layer capacitor which comprises the separator for an electrochemical device according to claim 1 .
18. A method for producing a separator for an electrochemical device, which comprises a wet nonwoven fabric comprising one or more kinds of fibrillated liquid crystalline polymeric fibers which are at least partially fibrillated into a fiber diameter of 0.0004 μm to 1 μm, and having a melting point or a thermal decomposition temperature of 250 C to 650° C. and an average fiber length of 0.3 mm to 2 mm, one or more kinds of unfibrillated organic fibers having a fineness of 0.5 dtex or less, wherein the separator has a void rate of 65% to 85% and a maximum pore diameter of 0.9 μm to 6 μm, the method comprises preparing a stock slurry having a solid content of 0.001% to 0.5% and a conductivity of 30 μS/cm or less, and carrying out a wet paper-making method.
19. The method for producing a separator for an electrochemical device according to claim 18 , wherein the paper-making is carried out by combining two or more layers.
20. The method for producing a separator for an electrochemical device according to claim 18 , further comprising a thermal treatment at 150 C to 250 C.