Separator for lithium ion secondary battery
A separator, used for a lithium ion secondary battery that produces electromotive force by lithium doping/dedoping, which is composed of a porous film comprising an organic polymer (component A) which can swell in an electrolyte solution to retain it, surrounding a nonwoven fabric which cannot swell in the electrolyte solution, the porous film including an electrolyte solution non-swelling organic polymer with a melting point of 210° C. or above (component B) and an electrolyte solution non-swelling organic polymer with a melting point of 180° C. or below (component C), wherein component B is incorporated in the fiber composing the nonwoven fabric. The separator is highly safe and exhibits low reduction mechanical properties with respect to organic solvents.
1. A separator, used for a lithium ion secondary battery that produces electromotive force by lithium doping/dedoping, said separator
being composed of a porous film comprising an organic polymer (component A) which can swell in an electrolyte solution to retain the electrolyte solution, surrounding a nonwoven fabric which cannot swell in the electrolyte solution, said porous film including an electrolyte solution non-swelling organic polymer with a melting point of 210° C. or above (component B) and an electrolyte solution non-swelling organic polymer with a melting point of 180° C. or below (component C),
wherein component B is incorporated in the fiber composing the nonwoven fabric,
wherein said nonwoven fabric is a nonwoven fabric formed of component B and component C, and
wherein the fiber composing said nonwoven fabric is a core-sheath fiber with component B as the core and component C as the sheath.
2. The separator according to claim 1 , wherein component C is a polyolefin.
3. The separator according to claim 1 , wherein the content of component C is 5–45 wt % with respect to the separator weight.
4. The separator according to claim 1 , wherein component B is at least one component selected from the group consisting of polyesters, aromatic polyamides and polyphenylene sulfide.
5. The separator according to claim 4 , wherein component B is polyethylene terephthalate.
6. The separator according to claim 1 , wherein said nonwoven fabric has an average film thickness of 10–35 μm, a basis weight of 6–20 g/m 2 , a gas permeability (JIS P8117) of no longer than 100 seconds, a MacMullin number at 250° C. of no greater than 10 and a MacMullin number x average film thickness value of no greater than 200 μm, and said separator has an average film thickness of 10–35 μm and a basis weight of 10–25 g/m 2 .
7. The separator according to claim 1 , wherein component A is polyvinylidene fluoride, a polyvinylidene fluoride copolymer or a component consisting mainly thereof.
8. A separator, used for a lithium ion secondary battery that produces electromotive force by lithium doping/dedoping, said separator
being composed a porous film comprising an organic polymer (component A) which can swell in an electrolyte solution to retain the electrolyte solution, surrounding a nonwoven fabric which cannot swell in the electrolyte solution, said porous film including an electrolyte solution non-swelling organic polymer with a melting point of 210° C. or above (component B) and an electrolyte solution non-swelling organic polymer with a melting point of 180° C. or below (component C),
wherein component B is incorporated in the fiber composing the nonwoven fabric, and
wherein said separator contains a filler composed of component C.
9. The separator according to claim 8 , wherein said filler is attached in a laminar manner to the surface of said nonwoven fabric.
10. The separator according to claim 8 , wherein said filler is formed in a laminar manner on the surface of said separator.
11. The separator according to claim 8 , wherein component C is a polyolefin.
12. The separator according to claim 8 , wherein the content of component C is 5–45 wt % with respect to the separator weight.
13. The separator according to claim 8 , wherein component B is at least one component selected from the group consisting of polyesters, aromatic polyamides and polyphenylene sulfide.
14. The separator according to claim 13 , wherein component B is polyethylene terephthalate.
15. The separator according to claim 8 , wherein said nonwoven fabric has an average film thickness of 10–35 μm, a basis weight of 6–20 g/m 2 , a gas permeability (JIS P8117) of no longer than 100 seconds, a MacMullin number at 25° C. of no greater than 10, and a MacMullin number x average film thickness value of no greater than 200 μm, and said separator has an average film thickness of 10–35 μm and a basis weight of 10–25 g/m 2 .
16. The separator according to claim 8 , wherein component A is polyvinylidene fluoride, a polyvinylidene fluoride copolymer or a component consisting mainly thereof.
17. The separator according to claim 1 , wherein said nonwoven fabric further comprises a fiber of polyethylene terephthalate.
18. The separator according to claim 17 , wherein component C is a polyolefin.
19. The separator according to claim 17 , wherein the content of component C is 5–45 wt % with respect to the separator weight.
20. The separator according to claim 17 , wherein said nonwoven fabric has an average film thickness of 10–35 μm, a basis weight of 6–20 g/m 2 , a gas permeability (JIS P8117) of no longer than 100 seconds, a MacMullin number at 25° C. of no greater than 10 and a MacMullin number x average film thickness value of no greater than 200 μm, and said separator has an average film thickness of 10–35 μm and a basis weight of 10–25 g/m 2 .
21. The separator according to claim 17 , wherein component A is polyvinylidene fluoride, a polyvinylidene fluoride copolymer or a component consisting mainly thereof.