Hybrid fluoropolymer composites

Abstract

The present invention pertains to a fluoropolymer hybrid organic/inorganic composite, to a process for manufacturing said fluoropolymer hybrid organic/inorganic composite and films and membranes thereof and to uses of said fluoropolymer hybrid organic/inorganic composite and films and membranes thereof in various applications.

Claims

1. A process for manufacturing a polymer electrolyte membrane, said process comprising: (i) providing a composition [composition (C1)] comprising: at least one fluoropolymer [polymer (F)] comprising recurring units derived from at least one fluorinated monomer [monomer (F)] and at least one hydrogenated monomer comprising at least one hydroxyl group [monomer (OH)], at least one metal compound [compound (M1)] of formula (I):
X.sub.4-mAY.sub.m(I) wherein m is an integer from 1 to 3, 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 comprising at least one NCO functional group, a liquid medium [medium (L)], an electrolyte medium comprising at least one metal salt [medium (E)], and optionally, at least one metal compound [compound (M2)] of formula (II):
X.sub.4-mAY.sub.m(II) 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 at least one functional group different from the NCO functional group; (ii) reacting at least a fraction of the hydroxyl groups of the monomer (OH) of said polymer (F) with at least a fraction of said compound (M1) and, optionally, at least a fraction of said compound (M2) thereby providing a composition [composition (C2)] comprising at least one grafted fluoropolymer [polymer (F-g)] comprising recurring units derived from at least one fluorinated monomer [monomer (F)] and at least one hydrogenated monomer [monomer (HH)], said monomer (HH) comprising: at least one pendant side chain comprising an end group of formula OC(O)NHZ-AY.sub.mX.sub.3-m (M1-g), wherein m, Y, A, X have the same meaning as defined above and Z is a hydrocarbon group, optionally comprising at least one NCO functional group, and optionally, at least one pendant side chain comprising an end group of formula O-AY.sub.m-1X.sub.4-m (M2-g), wherein m, Y, A, X have the same meaning as defined above; (iii) hydrolysing and/or condensing the end groups of formula OC(O)NHZ-AY.sub.mX.sub.3-m (M1-g) and, optionally, the end groups of formula O-AY.sub.m-1X.sub.4-m (M2-g) of the polymer (F-g) thereby providing a composition [composition (C3)] comprising at least one fluoropolymer hybrid organic/inorganic composite [polymer (F-h)]; (iv) processing into a polymer electrolyte membrane the composition (C3) provided in step (iii); and (v) drying the polymer electrolyte membrane provided in step (iv).

2. The process according to claim 1, wherein the medium (E) comprises at least one metal salt and at least one organic carbonate.

3. The process according to claim 1, wherein the medium (E) comprises at least one metal salt, at least one ionic liquid and, optionally, at least one organic carbonate.

4. The process according to claim 1, wherein the metal salt is selected from the group consisting of MeI, Me(PF.sub.6).sub.n, Me(BF.sub.4).sub.n, Me(ClO.sub.4).sub.n, Me(bis(oxalato)borate).sub.n (Me(BOB).sub.n), MeCF.sub.3SO.sub.3, Me[N(CF.sub.3SO.sub.2).sub.2].sub.n, Me[N(C.sub.2F.sub.5SO.sub.2).sub.2].sub.n, Me[N(CF.sub.3SO.sub.2)(R.sub.FSO.sub.2)].sub.n with R.sub.F being C.sub.2F.sub.5, C.sub.4F.sub.9, CF.sub.3OCF.sub.2CF.sub.2, Me(AsF.sub.6).sub.n, Me[C(CF.sub.3SO.sub.2).sub.3].sub.n, Me.sub.2S.sub.n, wherein Me is a metal, and n is the valence of said metal.

5. The process according to claim 1, wherein under step (i) the polymer (F) is obtainable by polymerization of at least one monomer (F) and at least one monomer (OH).

6. The process according to claim 1, wherein under step (i) the polymer (F) further comprises recurring units derived from at least one hydrogenated monomer [monomer (H)] different from the monomer (OH).

7. The process according to claim 1, wherein under step (i) the monomer (OH) of the polymer (F) is selected from the group consisting of (meth)acrylic monomers of formula (III) and vinylether monomers of formula (IV): ##STR00017## wherein each of R.sub.1, R.sub.2 and 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.X is a C.sub.1-C.sub.5 hydrocarbon moiety comprising at least one hydroxyl group.

8. The process according to claim 1, wherein under step (i) the polymer (F) is selected from the group consisting of: polymers (F-1) comprising recurring units derived from vinylidene fluoride (VDF), at least one monomer (OH) and, optionally, at least one monomer (F) different from VDF, and polymers (F-2) comprising recurring units derived from at least one per(halo)fluoromonomer selected from tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE), at least one monomer (H) selected from ethylene, propylene and isobutylene, and at least one monomer (OH), optionally comprising one or more additional monomers.

9. The process according to claim 8, wherein the polymer (F-1) comprises: (a) at least 60% by moles of vinylidene fluoride (VDF); (b) optionally, from 0.1% to 15% by moles of at least one monomer (F) selected from vinyl fluoride (VF.sub.1), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), perfluoromethylvinylether (PMVE); and (c) from 0.01% to 20% by moles of at least one monomer (OH) of formula (III) as defined in claim 7.

10. The process according to claim 1, wherein the compound (M1) is of formula (I-A):
R.sup.A.sub.4-mA(OR.sup.B).sub.m(I-A) wherein m is an integer from 1 to 3, A is a metal selected from the group consisting of Si, Ti and Zr, R.sup.A, equal to or different from each other and at each occurrence, is a C.sub.1-C.sub.12 hydrocarbon group comprising at least one NCO functional group and R.sup.B, equal to or different from each other and at each occurrence, is a C.sub.1-C.sub.5 linear or branched alkyl group, preferably R.sup.B being a methyl or ethyl group.

11. The process according to claim 1, wherein under step (i) the composition (C) further comprises at least one condensation catalyst.

Description

EXAMPLE 1MANUFACTURE OF A FLUOROPOLYMER FILM

Example 1-A: Preparation of the Solution

(1) The polymer (F-1) (1.5 g) was dissolved in 8.5 g of acetone at 60 C. thereby providing a solution containing 15% by weight of the polymer (F-1). The solution was homogeneous and transparent after homogenization at room temperature and then at 60 C. Then, DBTDL (0.015 g) and TSPI (0.060 g) were added to the solution. The quantity of DBTDL was calculated to be 10% by moles vs. TSPI. TSPI itself was calculated to be 1.1% by moles vs. the polymer (F-1). Once again, the solution was homogenized at 60 C. and then it was left at 60 C. for about 90 min so as to let isocyanate functional groups of TSPI to react with the hydroxyl groups of the polymer (F-1). The solution was then brought to room temperature.

(2) Once again, the solution was homogenized at 60 C. and then brought to room temperature.

Example 1-B: Casting of the Solution

(3) The solution was spread with a constant thickness onto a PET film substrate using a tape casting machine (doctor blade). The thickness was controlled by setting a distance of 150 m between the knife and the PET film.

(4) After evaporation of the solvents from the solution, a film was obtained.

(5) After a few hours, the film was detached from the PET substrate.

(6) The film had a constant thickness, comprised between 10 m and 60 m, depending on its composition.

(7) The film thereby provided was advantageously swollen but not dissolved in DMF.

EXAMPLE 2MANUFACTURE OF A FLUOROPOLYMER FILM

(8) The same procedure under Example 1 was followed but, after homogenization at 60 C., formic acid was added to the solution of Example 1-A. The solution so obtained was homogenized at 60 C. and then brought to room temperature. TEOS was added thereto and the solution thereby provided was held at 60 C. for 30 min. The solution was then brought to room temperature.

(9) The quantity of TEOS was calculated from the weight ratio (m.sub.SiO2/m.sub.polymer (F-1)) assuming total conversion of TEOS into SiO.sub.2.

(10) The quantity of formic acid was calculated from the following equation:
n.sub.formic acid/n.sub.TEOS=7.8

(11) The film thereby provided contained 10% by weight of SiO.sub.2 deriving from TEOS.

(12) The film was advantageously swollen but not dissolved in DMF.

COMPARATIVE EXAMPLE 1

(13) A film was manufactured following the same procedure under Example 1-B but using a solution containing only 15% by weight of the polymer (F-1) in acetone.

(14) The film was dissolved in DMF.

COMPARATIVE EXAMPLE 2

(15) A film was manufactured following the same procedure under Example 1-B but using a solution containing 15% by weight of the polymer (F-1) in acetone to which, after homogenization at 60 C., formic acid was added. The solution so obtained was homogenized at 60 C. and then brought to room temperature. TEOS was added thereto and the solution thereby provided was held at 60 C. for 30 min. The solution was then brought to room temperature.

(16) The film thereby provided contained 10% by weight of SiO.sub.2 deriving from TEOS.

(17) The film was dissolved in DMF.

EXAMPLE 3MANUFACTURE OF A POLYMER ELECTROLYTE MEMBRANE

(18) A polymer electrolyte membrane was manufactured by using the solution of Example 1-A to which an electrolyte medium was added, said electrolyte medium consisting of a mixture of ethylene carbonate (EC) and propylene carbonate (PC) (1/1 by volume) in which LiTFSI (1 mol/L) was dissolved and vinylene carbonate (VC) (2% by weight) was finally added. The membrane thereby provided contained 5% by weight of SiO.sub.2 deriving from TEOS.

(19) The weight ratio [m.sub.electrolyte/(m.sub.electrolyte+m.sub.polymer (F-1))] was 50%.

(20) The membrane thereby provided was advantageously swollen but not dissolved in DMF.

EXAMPLE 4MANUFACTURE OF A POLYMER ELECTROLYTE MEMBRANE

(21) A polymer electrolyte membrane was manufactured by using the solution of Example 2 to which an electrolyte medium was added, said electrolyte medium consisting of a mixture of ethylene carbonate (EC) and propylene carbonate (PC) (1/1 by volume) in which LiTFSI (1 mol/L) was dissolved and vinylene carbonate (VC) (2% by weight) was finally added.

(22) The weight ratio[m.sub.electrolyte/(m.sub.electrolyte+m.sub.polymer (F-1))] was 50%.

(23) The membrane thereby provided contained 5% by weight of SiO.sub.2 deriving from TEOS.

(24) The membrane thereby provided was advantageously swollen but not dissolved in DMF.

EXAMPLE 5MANUFACTURE OF A POLYMER ELECTROLYTE MEMBRANE

(25) A polymer electrolyte membrane was manufactured by using the solution of Example 2 to which an electrolyte medium was added, said electrolyte medium consisting of a mixture of ethylene carbonate (EC) and propylene carbonate (PC) (1/1 by volume) in which LiTFSI (1 mol/L) was dissolved and vinylene carbonate (VC) (2% by weight) was finally added.

(26) The weight ratio[m.sub.electrolyte/(m.sub.electrolyte+m.sub.polymer (F-1))] was 50%.

(27) The membrane thereby provided contained 20% by weight of SiO.sub.2 deriving from TEOS.

(28) The membrane thereby provided was advantageously swollen but not dissolved in DMF.

EXAMPLE 6MANUFACTURE OF A POLYMER ELECTROLYTE MEMBRANE

(29) A polymer electrolyte membrane was manufactured by using the solution of Example 1-A, further containing (Zr(O.sub.nPr).sub.4, to which an electrolyte medium was added, said electrolyte medium consisting of a mixture of ethylene carbonate (EC) and propylene carbonate (PC) (1/1 by volume) in which LiTFSI (1 mol/L) was dissolved and vinylene carbonate (VC) (2% by weight) was finally added.

(30) The weight ratio [m.sub.electrolyte/(m.sub.electrolyte+m.sub.polymer (F-1))] was 50%.

(31) The membrane thereby provided contained 10% by weight of ZrO.sub.2 deriving from Zr(O.sub.nPr).sub.4.

(32) The membrane thereby provided was advantageously swollen but not dissolved in DMF.

EXAMPLE 7MANUFACTURE OF A POLYMER ELECTROLYTE MEMBRANE

(33) A polymer electrolyte membrane was manufactured by using the solution of Example 2 to which an electrolyte medium was added, said electrolyte medium consisting of a mixture of ethylene carbonate (EC) and propylene carbonate (PC) (1/1 by volume) in which LiTFSI (1 mol/L) was dissolved and vinylene carbonate (VC) (2% by weight) was finally added.

(34) The weight ratio[m.sub.electrolyte/(m.sub.electrolyte+m.sub.polymer (F-1))] was 66%.

(35) The membrane thereby provided contained 20% by weight of SiO.sub.2 deriving from TEOS.

(36) The membrane thereby provided was advantageously swollen but not dissolved in DMF.

(37) Ionic conductivity: 0.13 mS/cm

EXAMPLE 8INTEGRITY OF THE POLYMER ELECTROLYTE MEMBRANE

(38) The polymer electrolyte membrane of Example 5 was dried and re-wetted with the same electrolyte. The same amount of electrolyte was impregnated in the re-wetted membrane.

(39) The membrane thereby provided exhibits good mechanical integrity and good flexibility properties in absorbing and desorbing the electrolyte.

EXAMPLE 9MANUFACTURE OF A POLYMER ELECTROLYTE MEMBRANE

(40) A polymer electrolyte membrane was manufactured by using the solution of Example 2 to which an electrolyte medium was added, said electrolyte medium consisting of a mixture of ethylene carbonate (EC) and propylene carbonate (PC) (1/1 by volume) in which LiTFSI (1 mol/L) was dissolved and vinylene carbonate (VC) (2% by weight) was finally added.

(41) The weight ratio [m.sub.electrolyte/(m.sub.electrolyte+m.sub.polymer (F-1))] was 66%.

(42) The membrane thereby provided was advantageously swollen but not dissolved in DMF.

(43) Ionic conductivity: 0.8 mS/cm

(44) The polymer electrolyte membrane of Example 9 was tested in the following battery: anode/polymer electrolyte membrane/cathode.

(45) Cathode: 91.5% LiFePO.sub.4/2% C-NERGY SUPER C65 carbon black/2% VGCF carbon fiber/4.5% SOLEF 5130 PVDF (loading: 3.7 mAh/cm.sup.2).

(46) Anode: 96% TIMREX SLP 30 graphite/2% CMC (carboxymethylcellulose)/2% SBR (Styrene Butadiene Rubber) (loading: 4.3 mAh/cm.sup.2).

(47) Manufacture of the Battery

(48) The polymer electrolyte membrane was treated at 70 C. for 30 min. Both the electrodes were dried for 48 hours under vacuum at 80 C. The electrodes and the membrane were put in an argon environment. Both the electrodes were immersed into an electrolyte medium consisting of a mixture of ethylene carbonate (EC) and propylene carbonate (PC) (1/1 by volume) in which LiTFSI (1 mol/L) was dissolved and vinylene carbonate (VC) (2% by weight) was finally added (30 s) and the excess of the electrolyte medium on the surface of the electrodes was then taken off. The membrane was then placed between the two electrodes in a coin cell. The discharge capacity values of the coin cell so obtained at different discharge rates are set forth in Table 1 here below.

(49) TABLE-US-00001 TABLE 1 Average Discharge Rate [mAh/g] [%] 0.05 Discharge D/20 106.6 100 0.1 Discharge D/10 105.3 99 0.2 Discharge D/5 98.5 92 0.5 Discharge D/2 84.5 79 1 Discharge D 58.9 55 2 Discharge 2D 22.8 21 0.05 Discharge D/20 103.0 97

COMPARATIVE EXAMPLE 3

(50) A polymer electrolyte membrane was manufactured according to Example 2 but without TSPI.

(51) The membrane was dissolved in DMF.

EXAMPLE 10MANUFACTURE OF A POLYMER ELECTROLYTE MEMBRANE

Example 10-A: Preparation of the Solution

(52) The polymer (F-2) (3 g) was dissolved in 27 g of DMF at room temperature thereby providing a solution containing 10% by weight of the polymer (F-2). The solution was homogeneous and transparent after homogenization at room temperature. DBTDL (0.039 g) was then added. The solution was homogenized at room temperature for 15 min and TSPI (0.154 g) was added. The quantity of DBTDL was calculated to be 10% by moles vs. TSPI. TSPI itself was calculated to be 1.1% by moles vs. the polymer (F-2). The solution was stirred at room temperature for about 24 hours so as to let isocyanate functional groups of TSPI to react with the hydroxyl groups of the polymer (F-2).

(53) In the next step, 3.19 g of the solution were mixed with 1 g of an electrolyte medium containing a 0.5 mol/L solution of LiTFSI in PYR13TFSI.

(54) The quantity of the electrolyte medium was fixed to 1 g and the quantity of the polymer (F-2) was calculated accordingly.

(55) The weight ratio [m.sub.electrolyte/(m.sub.electrolyte+m.sub.polymer (F-2)] was set to 76% (i.e. 0.319 g of polymer (F-2)).

(56) After homogenization at room temperature, TEOS was added. Once again, the solution was homogenized at room temperature for 10 min and formic acid was added. The solution was vigorously stirred for 30 sec.

(57) The quantity of TEOS was calculated from the weight ratio (m.sub.SiO2/m.sub.polymer (F-2)) assuming total conversion of TEOS into SiO.sub.2. This ratio was 25%. Thus, the mass of TEOS was 0.29 g.

(58) The quantity of formic acid was calculated from the following equation:
n.sub.formic acid/n.sub.TEOS=2.

(59) Thus, the mass of formic acid was 0.13 g.

Example 10-B: Casting of the Solution

(60) The solution was spread with a constant thickness onto a HALAR 9414 film substrate using a tape casting machine (doctor blade). This casting step was repeated twice with fresh solutions so as to obtain a membrane based on three casting layers. The thickness of the casting was controlled by setting for the first two layers a distance of 40 m and for the third layer a distance of 60 m between the knife and the substrate. After each casting step, the membrane was left at room temperature for 2 hours and dried in the oven at 50 C. for 30 min.

(61) The membrane had a constant thickness of about 30 m.

(62) No dissolution of the membrane in DMF was observed.

COMPARATIVE EXAMPLE 4

(63) A polymer electrolyte membrane was manufactured according to Example 10 but without TSPI.

(64) The membrane was dissolved in DMF.