Fluoropolymer film

Abstract

The invention pertains to a process for manufacturing a fluoropolynner film comprising a fluoropolymer hybrid organic/inorganic composite, said process comprising the following steps: (i) providing a mixture of: at least one fluoropolymer [polymer (F)]; at least one metal compound [compound (M)] having formula: X.sub.4-mAY.sub.m wherein m is an integer from 1 to 4, A is a metal selected from the group consisting of Si, Ti and Zr, Y is a hydrolysable group and X is a hydrocarbon group, optionally comprising one or more functional groups; a liquid medium consisting essentially of at least one ionic liquid (IL) and, optionally, at least one additive (A); optionally, at least one electrolytic salt (ES); and optionally, at least one organic solvent (S); (ii) hydrolyzing and/or polycondensing said compound (M) to yield a liquid mixture comprising fluoropolymer hybrid organic/inorganic composite comprising inorganic domains and incorporating said liquid medium; (iii) processing a film from the liquid mixture obtained in step (ii); and (iv) drying and then, optionally, curing the film obtained in step (iii) for obtaining the fluoropolymer film. The invention also pertains to the fluoropolymer film obtained from said process and to use of said fluoropolymer film in electrochemical and photo-electrochemical devices.

Claims

1. A fluoropolymer film comprising a fluoropolymer hybrid organic/inorganic composite, wherein said hybrid is obtained by a process comprising hydrolysing and/or polycondensing a mixture comprising: at least one fluoropolymer [polymer (F)]; at least one compound [compound (M)] having formula:
X.sub.4-mAY.sub.m wherein m is an integer from 1 to 4, A is an element selected from the group consisting of Si, Ti and Zr, Y is a hydrolysable group and X is a hydrocarbon group, optionally comprising one or more functional groups; and a liquid medium consisting of at least one ionic liquid (IL) and, optionally, at least one additive (A) selected from organic carbonates and mixtures thereof.

2. The fluoropolymer film according to claim 1, wherein polymer (F) is a polymer (F-2) comprising recurring units derived from vinylidene fluoride (VDF) and, optionally, from one or more fluorine-containing monomers different from VDF.

3. The fluoropolymer film according to claim 1, wherein polymer (F) comprises recurring units derived from at least one (meth)acrylic monomer [monomer (MA)] having formula (I): ##STR00017## wherein each of R.sub.1, R.sub.2, R.sub.3, equal to or different from each other, is independently a hydrogen atom or a C.sub.1-C.sub.3 hydrocarbon group and R.sub.OH is a C.sub.1-C.sub.5 hydrocarbon moiety comprising at least one hydroxyl group.

4. The fluoropolymer film according to claim 1, said film further comprising at least one electrolytic salt (ES) different from said ionic liquid (IL).

5. A metal-ion secondary battery comprising as polymer electrolyte separator the fluoropolymer film according to claim 1, said fluoropolymer film comprising at least one electrolytic salt (ES) different from said ionic liquid (IL).

6. A metal-ion capacitor comprising as polymer electrolyte separator the fluoropolymer film according to claim 1, said fluoropolymer film comprising at least one electrolytic salt (ES) different from said ionic liquid (IL).

7. A dye-sensitized solar cell comprising as polymer electrolyte separator the fluoropolymer film according to claim 1, said fluoropolymer film comprising at least one electrolytic salt (ES) different from said ionic liquid (IL).

8. A photochromic device comprising as polymer electrolyte separator the fluoropolymer film according to claim 1, said fluoropolymer film comprising at least one electrolytic salt (ES) different from said ionic liquid (IL).

9. An electrochromic device comprising as polymer electrolyte separator the fluoropolymer film according to claim 1, said fluoropolymer film comprising at least one electrolytic salt (ES) different from said ionic liquid (IL).

10. A fuel cell comprising as polymer separator the fluoropolymer film according to claim 1, said fluoropolymer film comprising a liquid medium consisting essentially of at least one protic ionic liquid (IL.sub.p) and, optionally, at least one additive (A) selected from organic carbonates and mixtures thereof.

11. A process for manufacturing the fluoropolymer film according to claim 1, said process comprising: (i) providing a mixture comprising: the at least one fluoropolymer [polymer (F)]; the at least one compound [compound (M)] having formula:
X.sub.4-mAY.sub.m wherein m is an integer from 1 to 4, A is an element selected from the group consisting of Si, Ti and Zr, Y is a hydrolysable group and X is a hydrocarbon group, optionally comprising one or more functional groups; and the liquid medium consisting of at least one ionic liquid (IL) and, optionally, at least one additive (A) selected from the group consisting of organic carbonates and mixtures thereof; (ii) hydrolysing and/or polycondensing said compound (M) to yield a liquid mixture comprising a fluoropolymer hybrid organic/inorganic composite comprising inorganic domains and incorporating said liquid medium; (iii) processing a film from the liquid mixture obtained in step (ii); and (iv) drying and then, optionally, curing the film obtained in step (iii) to obtain the fluoropolymer film.

12. The process according to claim 11, wherein polymer (F) comprises recurring units derived from at least one (meth)acrylic monomer [monomer (MA)] having formula (I): ##STR00018## wherein each of R.sub.1, R.sub.2, R.sub.3, equal to or different from each other, is independently a hydrogen atom or a C.sub.1-C.sub.3 hydrocarbon group and R.sub.OH is a C.sub.1-C.sub.5 hydrocarbon moiety comprising at least one hydroxyl group.

13. The process according to claim 11, wherein the amount of one or more ionic liquids (IL) in the liquid medium is such that the mixture of step (i) comprises at least 1% by weight and at most 95% by weight of ionic liquids (IL) based on the total weight of the polymer (F) and the ionic liquid (IL) in said mixture.

14. The process according to claim 11, wherein the ionic liquid (IL) in the liquid medium is selected from protic ionic liquids (IL.sub.p), aprotic ionic liquids (IL.sub.a) and mixtures thereof.

15. The process according to claim 11, wherein under step (i) the mixture further comprises: at least one organic solvent (S) different from said ionic liquid (IL) and said additive (A).

16. The process according to claim 11, wherein under step (iii) the film is manufactured by casting the liquid mixture onto a support surface, said support surface being made of a composition comprising: at least one polymer (F) having a melting temperature of at least 180 C.; and from 0.1% to 30% by weight of mica.

17. The process according to claim 13, wherein the mixture of step (i) comprises at least 5% by weight and at most 85% by weight of ionic liquids (IL) based on the total weight of the polymer (F) and the ionic liquid (IL) in said mixture.

18. The process according to claim 13, wherein the mixture of step (i) comprises at least 10% by weight and at most 75% by weight of ionic liquids (IL) based on the total weight of the polymer (F) and the ionic liquid (IL) in said mixture.

19. The process according to claim 16, wherein under step (iii) the film is manufactured by casting the liquid mixture onto a support surface, said support surface being made of a composition comprising: at least one polymer (F) having a melting temperature of at least 200 C.; and from 1% to 10% by weight of mica.

Description

EXAMPLE 1: MANUFACTURE OF THE FLUOROPOLYMER FILM WITH VDF/HEA COPOLYMER

(1) The dissolution of VDF/HEA copolymer (0.4 g) was carried out in DMF (4 g) (10% by weight) during one night at room temperature.

(2) An electrolyte solution was formed by the mixture of the electrolytic salt (ES-1) and the ionic liquid (IL-1) with the following relative amount: 0.5 M of LiTFSI in Pyr13TFSI. The electrolyte solution so obtained had an ionic conductivity of 2.410.sup.3 S/cm at 25 C.

(3) The electrolyte solution (1 g) and tetraethoxysilane (TEOS) (0.38 g) were added to the VDF/HEA copolymer solution and stirred during 10 minutes at room temperature. A mixture was obtained containing 27% by volume (32% by weight) of VDF/HEA copolymer, 64% by volume (60% by weight) of the electrolyte solution and 9% by volume (8% by weight) of SiO.sub.2 (equivalent amount of TEOS fully condensated).

(4) 0.64 g of formic acid were then added to the mixture and the mixture was stirred during 2 minutes at room temperature.

(5) The mixture was poured into a mold.

(6) The condensation reaction was followed by weight loss. Then a thermal post-processing at 150 C. during 40 minutes under ambient atmosphere was performed.

(7) The fluoropolymer film so obtained had an ionic conductivity of 3.210.sup.4 S/cm.

(8) No break was observed up to a flexion angle of 175.

EXAMPLE 2: MANUFACTURE OF THE FLUOROPOLYMER FILM WITH SOLEF 6008 VDF HOMOPOLYMER

(9) The same preparation procedure as detailed in Example 1 was followed but the VDF/HEA copolymer was replaced with SOLEF 6008 VDF homopolymer.

(10) The fluoropolymer film so obtained had an ionic conductivity of 2.310.sup.4 S/cm.

(11) A breaking point was observed at a flexion angle of 110.

EXAMPLE 3: MANUFACTURE OF THE FLUOROPOLYMER FILM WITH VDF/HEA COPOLYMER

(12) The same procedure as detailed in Example 1 was followed but using a mixture containing 18.7% by volume (22.1% by weight) of VDF/HEA copolymer, 75% by volume (70.3% by weight) of the electrolyte solution and 6.3% by volume (5.6% by weight) of SiO.sub.2 (equivalent amount of TEOS fully condensated).

(13) The fluoropolymer film so obtained had an ionic conductivity of 4.610.sup.4 S/cm.

(14) A breaking point was observed at an angle of 150.

EXAMPLE 4: MANUFACTURE OF THE FLUOROPOLYMER FILM WITH VDF/HEA COPOLYMER

(15) The same procedure as detailed in Example 1 was followed but using a mixture containing 11.3% by volume (13.9% by weight) of VDF/HEA copolymer, 85% by volume (82.5% by weight) of the electrolyte solution and 3.7% by volume (3.8% by weight) of SiO.sub.2 (equivalent amount of TEOS fully condensated).

(16) The fluoropolymer film so obtained had an ionic conductivity of 1.510.sup.3 S/cm.

EXAMPLE 5: MANUFACTURE OF THE FLUOROPOLYMER FILM WITH VDF/HEA COPOLYMER

(17) The same procedure as detailed in Example 1 was followed but using a mixture containing 35% by volume of VDF/HEA copolymer, 64% by volume of the electrolyte solution and 1% by volume of SiO.sub.2.

(18) The fluoropolymer film so obtained had an ionic conductivity of 1.010.sup.4 S/cm.

(19) No break was observed up to a flexion angle of 175.

EXAMPLE 6: MANUFACTURE OF THE FLUOROPOLYMER FILM WITH VDF/HEA COPOLYMER

(20) The same procedure as detailed in Example 5 was followed but a fluoropolymer film was obtained having a thickness of about 20 m was obtained.

(21) The fluoropolymer film so obtained had an ionic conductivity of 1.210.sup.4 S/cm.

(22) No break was observed upon flexion. The elongation at break of the fluoropolymer film was 155%.

(23) The fluoropolymer film had an optical transparency over 85% between 250 nm and 1000 nm.

COMPARATIVE EXAMPLE 1

(24) The same procedure as detailed in Example 1 was followed but replacing the VDF/HEA copolymer with TEOS and using a mixture containing 64% by volume (60% by weight) of the electrolyte solution and 36% by volume (40% by weight) of SiO.sub.2 (equivalent amount of TEOS fully condensated). A breaking point was observed at an angle of 0.

COMPARATIVE EXAMPLE 2

(25) The same procedure as detailed in Example 1 was followed but replacing the VDF/HEA copolymer with TEOS and using a mixture containing 87.7% by volume of the electrolyte solution and 12.3% by volume of SiO.sub.2 (equivalent amount of TEOS fully condensated).

(26) A breaking point was observed at an angle of 0.

COMPARATIVE EXAMPLE 3

(27) The fluoropolymer film obtained according to Example 1 was subjected to extraction of the ionic liquid (IL-1) by acetonitrile Soxhlet washing. Pore size was characterized by nitrogen adsoption-desorption: BJH calculation led to pore diameters of 2.1 nm.

(28) The resulting material after Soxhlet extraction was not flexible.

EXAMPLE 7: MANUFACTURE OF LI-ION BATTERY

(29) A battery prototype was manufactured consisting of a cylindrical inch stainless steel Swagelok wherein the positive electrode was a LiFePO.sub.4 based electrode, the negative electrode was Lithium metal and the polymer electrolyte separator was the fluoropolymer film obtained according to Example 3. No additional electrolyte solution was added. Galvanostatic curves obtained during cycling at C/5 rate and 23 C. for an electrochemical window of 2-4.2 V demonstrated that the fluoropolymer film of the present invention is advantageously suitable for use in Lithium-ion batteries.

(30) Capacity values were advantageously held constant at 45% during 70 cycles.

(31) Processing of the Fluoropolymer Film

(32) It has been found that by using as support surface an ECTFE polymer having a molar ratio of CTFE and ethylene of 50:50 and containing 3% by weight of mica, said ECTFE polymer having a melting point of 240 C. [polymer (S)], the fluoropolymer film processed under step (iii) of the process of the invention is advantageously easily detached and individualized from said support while leaving its surface advantageously homogeneous and free of defects.

(33) Table 1 here below shows the results of the detachment tests from a support surface of fluoropolymer films having a thickness of about 30 m obtained according to Example 1 of the invention.

(34) TABLE-US-00001 TABLE 1 Support surface Detachment Appearance Polymer (S) Possible Homogeneous Mica Possible but mica breaks Glass Non possible

(35) It has been found that, by using mica as support surface, the fluoropolymer film obtained according to Example 1 is detached but mica breaks.

(36) It has been also found that, by using glass as support surface, the fluoropolymer film obtained according to Example 1, said film containing a relatively high amount of SiO.sub.2 of 9% by volume, is not detached and individualized from said support.

(37) Table 2 here below shows the results of the detachment tests from a support surface of fluoropolymer films having a thickness of about 30 m obtained according to Example 5 of the invention.

(38) TABLE-US-00002 TABLE 2 Support surface Detachment Appearance Polymer (S) Possible Homogeneous Glass Possible

(39) It has been found that, by using glass as support surface, the fluoropolymer film obtained according to Example 5, said film containing a relatively low amount of SiO.sub.2 of 1% by volume, is detached and individualized from said support.