FR2834651A1 - POROUS MEMBRANE BASED ON A MIXTURE OF A FLUOROPOLYMER AND A SILANE - Google Patents

Abstract

The present invention relates to a porous membrane based on a mixture comprising, by weight, from 0.1 to 30% of at least one silane for 99.9 to 70% of at least one fluorinated polymer, respectively. also the electrochemical generators having a positive electrode, a separator and a negative electrode and wherein at least one electrode or the separator consists of the preceding porous membrane. In order to constitute a separator, the membrane advantageously contains a filler such as, for example, silica, to constitute an electrode that contains either carbon black or metal oxides. The porous membrane of the invention is advantageously a separator in a lithium battery. ion.

Description

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POROUS MEMBRANE BASED ON A MIXTURE OF A FLUOROPOLYMER
AND A SILANE [Field of the invention]
The present invention relates to a porous membrane based on a mixture of a fluoropolymer and a silane. This membrane is useful in electrochemical generators such as for example lithium-ion batteries.

 A lithium-ion battery consists of a positive electrode, a negative electrode, a separator is disposed between and the assembly is filled with an electrolyte. The electrodes of a lithium-ion battery consist of an electroactive layer associated with a layer of metal (the collector). The electroactive layer is a fluorinated polymer (or fluoropolymer) heavily loaded with carbon and / or oxides, the fluoropolymer is also referred to as a binder. This fluorinated polymer ensures the cohesion of the electroactive layer.

 In the production of lithium-ion batteries, the electroactive layer containing either lithium metal oxide charges or carbon and / or graphite charges, with other ingredients for adjusting the electrical performance, is generally carried out by dispersion. fillers in a solvent in the presence of a fluorinated polymeric binder. The dispersion thus obtained is for example deposited on a metal collector by a method of "Cast" (coating), the solvent is then evaporated to obtain a negative or positive electrode depending on the charges used.

 The metal collectors used are generally sheets or grids of copper in the case of the negative electrode and of aluminum in the case of the positive electrode. The polymeric binder ensures the cohesion of the electroactive layer as well as the adhesion to the metal collector. This cohesion and this adhesion are necessary for the good realization of the batteries.

 The performance of the battery is highly dependent on the characteristics of the binder. A good binder makes it possible to produce sufficiently charged layers of electroactive ingredients with respect to the amount of binder required and thus makes it possible to have a high specific capacity. The binder

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 must also be stable with respect to oxidation-reduction reactions during charge and discharge cycles and must also be insensitive to the electrolyte present in the battery. This electrolyte typically contains carbonate type solvents such as propylene carbonate, ethylene, dimethyl ethyl and a lithium salt such as LiPF6 or LiBF4. By way of example, PVDF or VF2 copolymers are materials which possess the characteristics for their use as lithium battery binders.

 Microporous polyolefin separators (essentially PE or PP) are used in liquid electrolyte Li-ion technology, while for Li-ion gel electrolyte batteries, microporous PVDF separators are often used.

 The porous membrane of the invention consists of a mixture of fluoropolymer and silane, also referred to as "silane-modified fluoropolymer" or "silane-modified fluoropolymer". Depending on the charge it contains, it is useful as an electroactive layer or as a separator.

 The porous membrane of the invention is also useful as a separator in non-refillable cells.

[The prior art and the technical problem]
EP 730316 discloses Li-ion battery separators of PVDF homopolymer or copolymer. The separator may be sintered PVDF, open-cell PVDF foam or PVDF deposited in "solvent cast", ie deposited in solution in a solvent and then spread on a surface.

 WO9859384 discloses Li-ion battery separators based on a mixture of PVDF and a filler selected from silicates, inorganic oxides, silica and alumina.

 The separators described in the two preceding patents are such that, under actual conditions of use of a battery (ie inflated in the electrolyte), they withstand a rise in temperature up to 80.degree. C., but little beyond that. they dissolve in the electrolyte. This is enough for the

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 most common applications, but for particularly demanding applications of Li-ion battery, such as very fast charges and discharges (> 5C), the battery undergoes an additional heating which forces to use separators which do not dissolve up to a temperature of 100 C.

 It has now been found that it is sufficient to add about 10% by weight of a silane based on the weight of fluoropolymer in the formulation of the separators described in the foregoing prior art to obtain superior thermomechanical properties. The porosity of the membrane decreases slightly (from 60% to 50% approximately), and thus the conductivity in the electrolyte, but the latter is quite acceptable for the application. The separators of the present invention hold up to 110 C at least, so can meet a more demanding specification.

 This modification of the fluoropolymer with a silane is advantageous not only for the porous membranes used as separators, but also for the porous membranes used as electroactive layers.

 Prior art US 6010628 discloses oxygen permeable and impermeable to water vapor membranes used in electrochemical current generators. These membranes are copolymers of VF2 (vinylidene fluoride) and TFE (tetrafluoroethylene) and one of the faces is covered with a silane which is deposited with a solvent. This has nothing to do with the present invention in which the membrane component is a mixture of a fluoropolymer and a silane.

[Brief description of the invention]
The present invention relates to a porous membrane based on a mixture comprising, by weight, 0.1 to 30% of at least one silane for respectively 99.9 to 70% of at least one fluorinated polymer.

 The invention also relates to electrochemical generators having a positive electrode, a separator and a negative electrode and wherein

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 least one electrode or the separator consists of the preceding porous membrane. To form a separator, the membrane advantageously contains a filler such as, for example, silica, to constitute an electrode that contains either carbon black or metal oxides.

 The porous membrane of the invention is advantageously a separator in a Li-ion battery.

[Detailed description of the invention]
Regarding the fluoropolymer is thus denoted any polymer having in its chain at least one monomer chosen from compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to this vinyl group, at least one atom fluorine, a fluoroalkyl group or a fluoroalkoxy group.

 By way of example of monomer, mention may be made of vinyl fluoride; vinylidene fluoride (VF2); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE); perfluoro (1,3-dioxole); perfluoro (2,2-dimethyl-1,3-dioxole) (DP); the product of formula CF2 = CFOCF2CF (CF3) OCF2CF2X wherein X is SO2F, CO2H, CH20H, CH20CN or CH20PO3H; the product of formula CF2 = CFOCF2CF2S02F; the product of formula F (CF 2) nCH 2 OCOF = CF 2 wherein n is 1,2, 3,4 or 5; the product of formula R 1 CH 2 OCF = CF 2 in which R 1 is hydrogen or F (CF 2) z and z is 1, 2, 3 or 4; the product of formula R30CF = CH2 wherein R3 is F (CF2) z-z is 1,2,3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene.

 The fluoropolymer may be a homopolymer or a copolymer, it may also include non-fluorinated monomers such as ethylene.

Advantageously, the fluoropolymer is PVDF homopolymer or copolymer containing at least 60% by weight of VF2, the comonomer

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 if any is selected from the fluorinated monomers mentioned above and is advantageously HFP. The fluoropolymer may contain plasticizers or additives, for example a well-known plasticizer dibutyl sebacate.

 The fluoropolymer is advantageously a copolymer PVDF containing at least 5% by weight and preferably 5 to 20% of HFP. The advantage of this copolymer is to be easily soluble in acetone which allows an easier implementation.

 As regards the silane, mention may be made, for example, of aminosilanes.

Of the aminosilanes, those having alkoxysilane functions are preferred. Thus denotes any product having an amine function and an alkoxysilane function.

dans laquelle : # R1 désigne un groupe alkyle ayant de 1 à 8 atomes de carbone ou un groupe alkyle ayant de 2 à 8 atomes de carbone et contenant un atome d'oxygène à l'intérieur de sa chaîne, # n vaut 0 ou 1, # R2 désigne H ou un groupe alkyle ayant de 1 à 8 atomes de carbone, # R3 désigne alkyle ayant de 1 à 8 atomes de carbone ou un groupe aryle ou cycloalkyle ou encore un groupe arylalkyle,

#X désigne - N - R' # R5 désigne H ou un groupe alkyle ayant de 1 à 8 atomes de carbone, # p vaut 0 ou 1, # R4 désigne un alkyle ayant de 1 à 8 atomes de carbone, By way of example, mention may be made of the following products of formula (1):

wherein: # R1 denotes an alkyl group having 1 to 8 carbon atoms or an alkyl group having 2 to 8 carbon atoms and containing an oxygen atom within its chain, # n is 0 or 1 , # R2 denotes H or an alkyl group having 1 to 8 carbon atoms, # R3 denotes alkyl having 1 to 8 carbon atoms or an aryl or cycloalkyl group or an arylalkyl group,

#X denotes - N - R '# R5 denotes H or an alkyl group having 1 to 8 carbon atoms, # p is 0 or 1, # R4 denotes an alkyl having from 1 to 8 carbon atoms,

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# q is 0 or 1 with the proviso that if q is 0 then p is 0,
Advantageously, the aminosilane is chosen from aminopropyltriethoxysilane and aminopropyltrimethoxysilane.

 Advantageously, the proportion of silane is 5 to 15% by weight for respectively 95 to 85% of fluoropolymer.

 The silane-modified fluoropolymer is prepared by simple mixing in a solvent, fluoropolymer, silane and optionally fillers. These charges will be described later. The previous solution also called "slurry" is deposited on a plate and the solvent is evaporated. A membrane whose thickness can be between 20 and 500 m is obtained. The porosity is provided either by the nature of the charges or because a product has been incorporated in the slurry which, once the membrane has been formed, is removed with the aid of a specific solvent or by the combination of the two. As an example of a product that can generate porosity, mention may be made of dibutyl phthalate, it can be extracted from the membrane by one or more washings with diethyl ether.

 Porosity can be provided as a non-solvent of the fluoropolymer. For example, the fluoropolymer is dissolved in acetone, a sheet is formed by spreading this sheet on a surface and then this sheet is passed through a butanol bath which is not a solvent of the fluoropolymer and finally the butanol is evaporated. .

 The porosity can be between 1 and 95%. As regards the membrane used as a separator, the porosity is between 25 and 75% and preferably between 40 and 65%.

 This porous membrane containing no fillers can be used as a separator. This porous membrane may also contain fillers, described below. Depending on the nature of the charges, the membrane is either a separator or an electrode.

 As regards the charges, it is necessary to distinguish the mineral fillers that can be used for the separator and those used for the electroactive layers.

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 As regards the mineral fillers which can be used for the separator, mention may be made of silicates, silica, alumina and inorganic oxides. Silica is preferred.

 Lithium metal oxides of the LiMxOy type in which M is a metal are used for producing the electroactive layers of the positive electrodes. Advantageously M is a transition metal such as Mn, Ni, or Co.

 Carbon-based products are used to make electroactive layers of negative electrodes. By way of example of carbon-based products, mention may be made of graphite, carbon black aggregates, carbon fibers and activated carbons. It would not be outside the scope of the invention using several carbon-based products for example; (i) graphite and carbon black aggregates; (ii) graphite, carbon black aggregates and carbon fibers; (iii) carbon black aggregates and carbon fibers; graphite and carbon fibers.

 The carbon products that can be used are described in Handbook of fillers 2nd Edition published by Chem Tec Publishing 1999 page 62 ≈2. 1.22, page 92 ≈2. 1.33 and page 184 ≈2. 2.2. Preferably, it will be possible to use graphites of size between 20 and 50 m. Among the carbon blacks that may be used include black Ketjen EC 600 JD specific surface 1250 m2 / gr, Ketjen EC 300 J. specific surface 800 m2 / gr and the black company M.M.M. sold under the reference Super P characterized by a specific surface area of the order of 57 to 67 m 2 / g (measured by BET nitrogen adsorption method). It will advantageously be possible to use carbon fibers with a length of 150 m.

 As for the proportions of fillers and fluoropolymer modified silane they are, by weight for the membranes used as electroactive layers, 2 to 40% of fluoropolymer modified silane for respectively 98 to 60% of charges. Advantageously 2 to 30% of fluoropolymer modified silane for 98 to 70% of fillers, respectively. As for the membrane used as a separator, the proportions are 20 to 80% of silane-modified fluoropolymer for 80 to 20% of fillers, respectively. In addition to

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 Porosity provided by the charges can be incorporated into the membrane a product that is extracted with a specific solvent once the membrane formed.

[Examples] The following materials were used: The VF2-HFP # 1 copolymer is the KYNARFLEX 2801 grade marketed by ATOFINA. It is characterized by a melt viscosity of 2500 Pa.s at 230 ° C. under a shear of 100 s -1, a melting point of 143 ° C. and a density of 1.78. The proportion of HFP is about 11%.

The VF2-HFP # 2 copolymer is the KYNAR POWERFLEX LBG-1 grade marketed by ATOFINA. It is characterized by a melt viscosity of 2680 Pa.s at 230 ° C. under a shear of 100 s -1, a melting point of 150 ° C. and a density of 1.78.

Example 1 (comparative): Preparation of a silane-free separator.

In an Erlenmayer, 7.5 g of a VF2-HFP copolymer are dissolved in 62.5 ml of acetone (NORMAPUR grade of PROLABO) with magnetic stirring at 40 ° C. for 2 hours. Once the solution has returned to room temperature, 6. 25 g of hydrophobic treated silica powder (grade TS-530 sold by CABOT®) and then 10 g of dibutyl phthalate (marketed by ALDRICH, abbreviated as DBP in the following) are added. . The solution is homogenized by magnetic stirring at room temperature for 5 minutes with vigorous stirring (2000 rpm) in a DISPERMAT multi-blade turbine disperser. The slurry obtained is spread on a thick polyethylene plate, then a film is formed by means of a Doctor Blade manual doctor blade set at 250 μm. The film is dried at room temperature and is peeled off the plate with a spatula. Finally, the DBP is extracted from the membrane by two successive washes in a diethyl ether bath. The membrane as well

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 formed is composed of 54.5% by weight of VF2-HFP copolymer and 45.5% of hydrophobically treated silica. Its thickness is between 50 and 70 m.

Example 2: Preparation of a separator with an amino silane

In an Erlenmayer, 7.5 g of a VF2-HFP copolymer are dissolved in 62.5 ml of acetone (NORMAPUR grade of PROLABO) with magnetic stirring at 40 ° C. for 2 hours (unless otherwise indicated). Once the solution has returned to room temperature, 6. 25 g of hydrophobic treated silica powder (grade TS-530 sold by CABOT) and then 10 g of DBP are added. The solution is homogenized by magnetic stirring at room temperature for 5 minutes with vigorous stirring (2000 rpm) in a DISPERMAT multi-blade turbine disperser. An amount of x% (by weight relative to the weight of fluorinated polymer) of (3-aminopropyl) trimethoxysilane (marketed by ALDRICH, abbreviated amino-silane in the following) is added to the solution and homogenized by magnetic stirring at room temperature during 1 minute. The slurry obtained is spread immediately after (unless otherwise stated) on a thick polyethylene plate, then a film is formed by means of a Doctor Blade manual doctor blade set at 250 m. The film is dried at room temperature and is peeled off the plate with a spatula. Finally, the DBP is extracted from the membrane by two successive washes in a diethyl ether bath. The membrane thus formed has a thickness of between 50 and 70 m.

 The properties of the membranes obtained are then measured, the results are reported in Tables 1 and 2.

Calculation of the porous volume of the membranes.

The membrane formed according to Example 1 or Example 2 is porous on the one hand because of the free volume left by the extraction of DBP and on the other hand because of the porous structure of the silica used. To calculate the pore volume of a membrane, five 16 mm diameter discs are cut

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 in the membrane thanks to a cookie cutter. For each of the disks, its weight and its thickness are measured, then the pore volume is calculated knowing the respective ratio of each of the constituents and their density.

Resistance of the membrane in a bath of carbonate solvents.

In the membrane formed according to Example 1 or Example 2, a disc of 16 mm in diameter is cut by a punch. It is immersed for 2 seconds in a beaker containing a mixture of three carbonate solvents, dimethyl carbonate (marketed by Aldrich, abbreviated DMC in the following), ethylene carbonate (marketed by ALDRICH, abbreviated EC in the following ) and diethyl carbonate (marketed by ALDRICH, abbreviated DEC in the following) in the proportions 40/40/20 by weight. The temperature of the solution is incremented in increments of 5 C. Thus, the maximum temperature of resistance of the membrane is noted since, starting from a certain temperature, it is dissolved in the mixture of carbonate solvents.

Weight loss in the DMC.

In the membrane formed according to Example 1 or Example 2, a disc of 16 mm in diameter is cut by a punch. Its mass is measured. The disc is then immersed in a solution of DMC at 40 ° C. for 16 hours, then extracted and then dried in an oven at 80 ° C. for 1 hour under vacuum. Its mass is again measured to deduce the mass extracted by the DMC.

Measurement of the mechanical properties of the membrane.

In the membrane formed according to Example 1 or Example 2, a rectangle of 100 mm by 15 mm is cut by means of a punch. This is placed between the jaws of a dynamometer INSTRON 4301 equipped with a cell

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 force of 100 N for a stress in tension performed at a speed of 5 mm / min. The elongation and the stress at break are thus noted.

Measurement of the conductivity of the membranes.

In the membrane formed according to Example 1 or Example 2, five discs 16 mm in diameter are cut by a punch. Their thicknesses and their masses are measured. Each disc is then immersed for 16 hours in a propylene carbonate electrolyte solution (sold by ALDRICH, abbreviated PC hereinafter) containing 1 mole of LiClO 4, and then taken out and wiped off with its excess of solvent. The mass of the disc is again measured, which makes it possible to deduce the weight gain of the membrane after impregnation in the electrolyte solution. Each impregnated membrane disk is then placed between two electrodes to measure the electrical resistance, and to deduce the conductivity of the impregnated membrane.

Influence of the amino-silane level on the thermomechanical resistance of the separator.

Separators are produced with the copolymer VF2-HFP # 1 or # 2 and with different levels of amino-silane according to Example 1 or Example 2. For each separator, the pore volume, the thermomechanical resistance in a Carbonate solution, weight loss in DMC, mechanical properties and conductivity are measured as indicated above. The results are summarized in Tables 1 and 2.

The addition of an amino silane in the slurry during the manufacture of the separator makes it possible to improve its thermomechanical properties (increased resistance of at least 20 ° C. in the carbonate solvents) without appreciably affecting its conductivity in the electrolyte, nor its mechanical properties.

Influence of the dissolution temperature on the thermomechanical resistance of the separator.

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Separators are produced with copolymer VF2-HFP # 2 and with 10% amino silane according to Example 2 with two different dissolution procedures for PVDF: either 2 hours at 40 ° C. or 20 minutes at 55 ° C. For each separator, the pore volume, the thermomechanical resistance in a carbonate solution and the weight loss in the DMC are measured as indicated above. The results are collated in Table 3.

The improvement of the thermomechanical properties of the separator by adding an amino silane in the slurry during its manufacture is further increased by 20 C with better dissolution of the PVDF.

Influence of the slurry waiting time on the thermomechanical resistance of the separator.

Separators are produced with copolymer VF2-HFP # 2 and with 10% amino silane according to Example 2 with dissolution of 20 minutes at 55 ° C.

After adding the amino-silane, the slurry is either used immediately, or used after 30 minutes or after 2 hours. For each separator, the pore volume, the thermomechanical resistance in a carbonate solution and the weight loss in the DMC are measured as indicated above. The results are collated in Table 4.

The improvement of the thermomechanical properties of the separator by adding an amino silane in the slurry during its manufacture is not affected by the aging of the slurry.

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Table 1

<tb> Membrane <SEP> Type <SEP> of <SEP> AminoSilane <SEP><SEP> Rate <SEP><SEP> Maximum Temperature <SEP><SEP> Loss of <SEP> SEP <Weight> in <SEP> the <SEP> Elongation <SEP> to <SEP> the <SEP> Constraint <SEP> to <SEP> la
<tb> copolymer <SEP> ratio <SEP> to <SEP> reached <SEP> in <SEP><SEP> solution <SEP> DMC <SEP> to <SEP> 40 C <SEP> / <SEP> 16 <SEP> h <SEP> h <SEP> rupture <SEP> rupture <SEP> (MPa)
<tb> polymer <SEP> fluorinated <SEP> carbonate
####
######
######
######
<tb># 5 <SEP># 2 <SEP> 10 <SEP>% <SEP> 95 C <SEP> 10 <SEP>% <SEP> nm <SEP> nm
<Tb>

# 6 <SEP># 2 <SEP> 15 <SEP>% <SEP> 100 C <SEP> nm <SEP> nm <SEP> nm
<Tb>

# 7 <SEP># 2 <SEP> 25 <SEP>% <SEP> 110 C <SEP> 6 <SEP>% <SEP> 40 <SEP>% <SEP> 1.8
<Tb>
nm means: not measured.

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Table 2

<tb> Membrane <SEP> Type <SEP> of <SEP> Aminosilane <SEP><SEP> Rate <SEP><SEP> Porous Volume <SEP> of <SEP><SEP> Weight <SEP> Weight <SEP> in <SEP> Conductivity <SEP> in
<tb> copolymer <SEP> ratio <SEP> to <SEP> polymer <SEP> the <SEP> membrane <SEP> PC <SEP> + <SEP> 1 <SEP> M <SEP> LiCI04 <SEP> PC <SEP > + <SEP> 1 <SEP> M <SEP> LiCI04 <SEP> (mS / cm)
<tb> fluorinated
<tb># 1 <SEP># 1 <SEP> 0 <SEP>% <SEP> 51 <SEP>% <SEP> 125 <SEP>% <SEP> 1.4
<tb># 2 <SEP># 2 <SEP> 0 <SEP>% <SEP> 62 <SEP>% <SEP> 145 <SEP>% <SEP> 2.4 <SEP>
<tb># 3 <SEP># 2 <SEP> 5 <SEP>% <SEP> 55 <SEP>% <SEP> nm <SEP> nm
<Tb>

# 4 <SEP># 1 <SEP> 10 <SEP>% <SEP> 41 <SEP>% <SEP> 95 <SEP>% <SEP> 0.45 <SEP>
<tb># 5 <SEP># 2 <SEP> 10 <SEP>% <SEP> 48 <SEP>% <SEP> 135 <SEP>% <SEP> 1.2
<tb># 6 <SEP># 2 <SEP> 15 <SEP>% <SEP> 46 <SEP>% <SEP> nm <SEP> nm
<Tb>

# 7 <SEP># 2 <SEP> 25 <SEP>% <SEP> 41 <SEP>% <SEP> 77 <SEP>% <SEP> 0.6 <SEP>
<Tb>

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Table 3

<tb> Membrane <SEP> Type <SEP> of <SEP> AminoSilane <SEP> Rate <SEP> by <SEP><SEP><SEP><SEP> Volume <SEP><SEP> Max SEP> Temperature <SEP> achieved <SEP> Loss <SEP> of <SEP> weight <SEP> in <SEP> la
<tb> copolymer <SEP> ratio <SEP> to <SEP> polymer <SEP> dissolving <SEP> of <SEP><SEP> membrane <SEP> in <SEP><SEP> solution <SEP> carbonate <SEP > DMC <SEP> to <SEP> 40 C <SEP> / <SEP> 16 <SEP> h
<tb> fluorinated
<Tb>

#5 #2 10 % 2 h / 40 C 48 % 95 C 10 %

# 5 # 2 10% 2 h / 40 C 48% 95 C 10%

###### > 9 <SEP>%
<Tb>
Table 4

<tb> Membrane <SEP> Type <SEP> of <SEP> Aminosilane <SEP> Rate <SEP> Porous <SEP> Volume <SEP> of <SEP> The <SEP> Maximum <SEP> Temperature <SEP> Elongation <SEP> to <SEP> the <SEP> Constraint <SEP> to <SEP>
<tb> copolymer <SEP> with <SEP> ratio <SEP> at <SEP> membrane <SEP> reached <SEP> in <SEP> the <SEP> solution <SEP> rupture <SEP> rupture <SEP> (MPa)
<tb> polymer <SEP> fluorinated <SEP> carbonate
<tb># 8 <SEP># 2 <SEP> 10 <SEP>% <SEP> 58 <SEP>% <SEP> 120 C <SEP> 300 <SEP>% <SEP> 3
<tb># 9 <SEP># 2 <SEP> 10 <SEP>% <SEP> 59 <SEP>% <SEP> 120 C <SEP> 450 <SEP>% <SEP> 3.6
<tb># 10 <SEP># 2 <SEP> 10 <SEP>% <SEP> 61 <SEP>% <SEP> 120 C <SEP> 600 <SEP>% <SEP> 4.6
<Tb>

Claims (12)

A porous membrane based on a mixture comprising, by weight, 0.1 to 30% of at least one silane for respectively 99.9 to 70% of at least one fluorinated polymer.  The membrane of claim 1 wherein the fluoropolymer is PVDF homopolymer or copolymer containing at least 60% by weight of VF2.  The membrane of claim 2 wherein the fluoropolymer is a copolymer PVDF containing at least 5% by weight of HFP.  Membrane according to any one of the preceding claims wherein the silane is an aminosilane having alkoxysilane functions.  A membrane according to any one of the preceding claims wherein the proportion of silane is 5 to 15% by weight for respectively 95 to 85% of fluoropolymer.  Membrane according to any one of the preceding claims wherein the porosity is between 1 and 95%.  Membrane according to any one of the preceding claims comprising a mineral filler selected from silicates, silica, alumina and inorganic oxides.  The membrane of claim 7 wherein the inorganic filler is silica. <Desc / Clms Page number 17>  Membrane according to any one of Claims 1 to 6, comprising lithium metal oxides of the LiMxOy type in which M is a metal.  A membrane according to any one of claims 1 to 6 comprising at least one carbon product selected from graphite, carbon black aggregates, carbon fibers and activated carbons.  Electrochemical generators having a positive electrode, a separator and a negative electrode and in which the separator is constituted by the membrane according to any one of claims 1 to 8.  Electrochemical generators having a positive electrode, a separator and a negative electrode and in which at least one electrode consists of the membrane according to claim 9 or 10.