Microporous membrane, methods for making such film, and the use of such film as battery separator film

1. A microporous membrane comprising about 0.05% to about 3% by weight of a paraxylylene polymer or copolymer based on the total weight of the inicroporous membrane.

2. The microporous membrane of claim 1 , wherein the paraxylylene polymer or copolymer derived from a repeat unit of the formula:

wherein n is an integer having a value of greater than or equal to 2 and X is a functional group selected from the group consisting of hydrogen, linear or branched substituted or unsubstituted C 1 -C 10 alkyl; linear or branched, substituted or unsubstituted C 1 -C 10 haloalkyl; substituted or unsubstituted C 6 -C 20 aryl, C 6 -C 20 haloaryl and perhaloaryl, linear or branched, substituted or unsubstituted C 2 -C 10 alkenyl, and linear or branched substituted or unsubstituted C 2 -C 10 haloalkenyl groups.

3. The microporous membrane of claim 2 , wherein X is CF 3 .

4. The microporous membrane of claim 2 . wherein X is CH 2 CH 2 (CF 2 ) m CF 3 and m ranges from 1 to 5.

5. The microporous membrane of claim 1 , wherein the paraxylylene polymer or copolymer is derived from a repeat unit of the formula:

wherein n is an integer having a value of greater than or equal to 2 and each X is in dependently selected from hydrogen, chlorine and fluorine.

6. The microporous membrane of claim 1 , wherein the paraxylylene polymer or copolymer is derived from a repeat unit of the formula:

wherein n is an integer having a value of greater than or equal to 2 and X is a functional group selected from the group consisting of amino, cyano, C 2 -C 10 carboxyl, C 2 -C 10 alkoxy, and C 2 -C 10 hydroxyalkyl groups, hydroxyl, nitro, or halide groups.

7. The microporous membrane of claim 6 , wherein X is fluoride or chloride.

8. The microporous membrane of claim 1 , wherein the paraxylylene polymer or copolymer is derived from a repeat unit of the formula:

wherein n is an integer having a value of greater than or equal to 2 and R 1 and R 2 are each functional groups independently selected from the group consisting of hydrogen, hydroxyl, nitro. halide, linear or branched substituted or unsubstituted C 1 -C 10 alkyl; linear or branched. substituted or unsubstituted C 1 -C 10 haloaklyl; substituted or unsubstituted C 6 -C 20 aryl, C 6 -C 20 haloarly and perhaloraryl, linear or branched, substituted or unsubstituted C 2 -C 10 alkenyl, and linear or branched substituted or unsubtituted C 2 -C 10 haloalkenyl groups.

9. The microporous membrane of claim 8 , wherein R 1 and R 2 are phenyl,

10. The microporous membrane of claim 8 , wherein at least one of R 1 and R 2 is fluoride or chloride.

11. The microporous membrane of claim 1 , further comprising a microporous polymeric membrane substrate.

12. The microporous membrane of claim 11 , wherein the substrate comprises at least one of polyethylene or polypropylene.

13. The microporous membrane of claim 12 , wherein the substrate comprises comprising from 1 wt. % to 20 wt. % of polyethylene having an Mw>1.0×10 6 , and 80 wt. % to 99 wt. % of polyethylene having an Mw≦1.0×10 6 , based on the weight of the substrate and the membrane has a shutdown temperature of >145° C.

14. The microporous membrane of claim 13 , wherein the substrate further comprises 5 wt. % to 40 wt. % polypropylene having an Mw>7.5×10 5 , based on the weight of the substrate.

15. The microporous membrane claim of 1 , wherein the concentration of the paraxylylene polymer or copolymer that varies in the thickness direction of the membrane.

16. The microporous membrane of claim 1 , wherein the microporous membrane has a meltdown temperature ranging from 230° C. to 800° C.

17. The microporous membrane of claim 1 , wherein the microporous membrane has one or more of the following properties: i) a normalized air permeability ≦600 sec/100 cm 3 /20 μm; ii) a porosity in the range of from about 25% to about 80%; iii) a normalized pin puncture strength ≦3,000 mN/20 μm; iv) a tensile strength ≧40,000 kPa: v) an electrolytic solution absorption speed ≧2,0, vi) a TD heat shrinkage at 105° C.≦2.5%; and/or vii) a TD heat shrinkage at 130° C.≦15%.

18. A microporous membrane comprising a 0.1 to 5.0 wt. % paraxylylene polymer or copolymer and a 95.0 to 99.9 wt. % of a microporous polyolefin membrane substrate, based on the weight of the membrane, wherein the paraxylylene polymer or copolymer comprises fluorine and the microporous polyolefin substrate comprises 1 wt. % to 20 wt. % of polyethylene having an Mw >1.0×10 6 ; and 80 wt. % to 99 wt. % of polyethylene having an Mw >1.0×10 6 , based on the weight of the substrate, the membrane having a shutdown temperature of >145° C. and an MD/TD shrink ratio measured at 130° C.>0.95 and a TD heat shrinkage at 130° C.≦2.5% and and MD heat shrinkage at 130° C.≦2.5.

19. A battery separator film comprising the microporous membrane of claim 1 .

20. A method for producing a microporous membrane comprising combining at least a first paraxylylene polymer or copolymer and a microporous polymeric membrane substrate, wherein the microporous membrane comprises about 0.05% to about 3% by weight of the paraxylylene polymer or copolymer based on the total weight of the microporous membrane.

21. The method of claim 20 , wherein the paraxylylene polymer or copolymer is formed on the microporous polymeric, substrate by vapor phase deposition.

22. The method of claim 20 , wherein the paraqlylene polymer or copolymer is laminated to the microporous polymeric membrane substrate.

23. The microporous membrane product produced by the method of claim 20 .

24. A battery comprising an anode, a cathode, an electrolyte, and a separator situated between the anode and the cathode, the separator comprising: a microporous polymeric membrane comprising about 0.05% to about 3% by weight of a paraxylylene polymer or copolymer based on the microporous polymeric membrane.

25. The battery of claim 24 , wherein the wherein the paraxylylene polymer or copolymer comprises fluorine or chlorine.