Method for manufacturing an all-solid-state electrolyte for secondary batteries

Abstract

The present invention relates to a method for preparing a solid-state electrolyte in the form of a film, the method comprising the steps of: providing a solution C comprising at least one fluorinated polymer A1, at least one organic solvent A2, at least one alkali metal salt B1 and at least one plasticiser B2; depositing the solution C on a support D to form a film; drying the resulting film; characterised in that the at least one organic solvent A2 has a donor number greater than 4 kcal / mol and a saturated vapour pressure of less than 24 kPa at 20°C; and in that the at least one plasticiser B2 comprises at least one ionic liquid.

Description

[0001] Process for manufacturing an all-solid electrolyte for secondary batteries

[0002] Technical field

[0003] The present invention relates generally to the field of electrical energy storage in all-solid-state batteries, in particular in Li-ion type secondary batteries. More specifically, the invention relates to a solid electrolyte and a method for manufacturing a film therefrom. This film is intended for an application as an all-solid-state battery separator or electrolyte, in particular for Li-ion batteries. The invention also relates to an all-solid-state battery comprising such a separator and / or such a non-porous film.

[0004] Technological background of the invention

[0005] A secondary battery such as Li-ion comprises at least one negative electrode or anode coupled with a copper current collector, one positive electrode or cathode coupled with an aluminum current collector, a separator and an electrolyte. The electrolyte consists of an alkali metal salt, generally a lithium salt, mixed with a solvent which is a mixture of organic carbonates, chosen to optimize the transport and dissociation of ions. A high dielectric constant promotes the dissociation of ions, and therefore, the number of ions available in a given volume, while a low viscosity is favorable to ionic diffusion which plays a key role, among other parameters, in the charging and discharging rates of the electrochemical system. Secondary batteries such as lithium-ion batteries conventionally use liquid electrolytes composed of solvent(s), alkali metal salt(s) such as lithium salts and additive(s).These electrolytes have good ionic conductivity but are prone to leakage or ignition if the battery is damaged.

[0006] The use of solid electrolytes overcomes these difficulties. However, solid electrolytes are generally less conductive than liquid electrolytes. The challenge with solid electrolytes is to combine high ionic conductivity, good electrochemical stability, and sufficient temperature resistance. Ionic conductivity must be equivalent to that of liquid electrolytes. Electrochemical stability must allow the electrolyte to be used with cathode materials that can operate at high voltages (> 4.5 V). Similarly, the solid electrolyte must operate at least up to 80°C.

[0007] Furthermore, sufficient mechanical strength must be achieved at the separator level. In particular, the latter must prevent the formation of dendrites during charge / discharge cycles. In general, the solid electrolyte must demonstrate greater safety, but this cannot be at the expense of other performance characteristics. Finally, from an implementation point of view, the solid electrolyte must be able to be handled (stretched) and rolled.

[0008] Polyvinylidene fluoride (PVDF) and its derivatives are of interest as the main constituent material of the separator due to their electrochemical stability and their high dielectric constant, which promotes ion dissociation and therefore conductivity. The P(VDF-HFP) copolymer (vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer) has been studied as a gelled membrane because it has a lower crystallinity than PVDF. Therefore, the interest of these P(VDF-HFP) copolymers is that they allow greater swelling to be achieved and thus promote conductivity.

[0009] However, solid or quasi-solid electrolytes with a polymer matrix are generally complex to manufacture and require several steps: dissolution, addition of co-components, homogenization, deposition and drying. For each of these steps, controlling the dry extract as well as the homogeneity of the "slurry" is essential to achieve the best possible performance and ensure that they are homogeneous throughout the manufactured object.

[0010] WO 2020126750 describes solid electrolyte compositions comprising a mixture of fluoropolymer and an isocyanate compound to form a crosslinked network. The film is prepared in the presence of acetone. However, processing a film in the presence of acetone does not allow a homogeneous film to be obtained due to the low vapor pressure of acetone, which impacts the ionic conductivity of the film and the final performance of the battery. In addition, low vapor pressure creates process safety issues.

[0011] There is therefore a need to develop new solid electrolytes which present a good compromise between ionic conductivity, electrochemical stability and temperature resistance, and which are suitable for simplified implementation, compatible with an industrial application.

[0012] The invention therefore aims to remedy at least one of the drawbacks of the prior art, namely to prepare a film of homogeneous solid electrolytes exhibiting good performance.

[0013] Summary of the invention

[0014] According to a first aspect, the present invention relates to a method for preparing a solid electrolyte in the form of a film comprising the steps of:

[0015] Providing a solution C comprising at least one fluorinated polymer Al, at least one organic solvent A2, at least one alkali metal salt B1 and at least one plasticizer B2;

[0016] Deposition of said solution C on a support D to form a film,

[0017] Drying of the film thus obtained; characterized in that said at least one organic solvent A2 has a donor number greater than 4 kcal / mol and a saturated vapor pressure less than 24 kPa at 20°C; ; and in that said at least one plasticizer B2 comprises at least one ionic liquid.

[0018] The use of an organic solvent A2 as defined in the present application makes it possible to prepare a homogeneous film which improves the ionic conductivity and the final performance of the battery. According to a preferred embodiment, solution C is obtained according to the following steps:

[0019] Preparation of a solution A comprising said at least one fluorinated polymer Al and said at least one organic solvent A2;

[0020] Preparation of a solution B comprising at least one alkali metal salt B1 and at least one plasticizer B2;

[0021] Mix solutions A and B to obtain solution C.

[0022] According to a preferred embodiment, said at least one organic solvent A2 has a flash point above -15°C.

[0023] According to a preferred embodiment, said at least one organic solvent A2 has a saturated vapor pressure greater than 7 Pa at 20°C. This makes it possible to evaporate the solvent more easily and thus avoid an excessively high solvent content in the film obtained by the process of the invention. According to a preferred embodiment, said at least one organic solvent A2 has a mass water content of less than 5000 ppm. Limiting the water content makes it possible to avoid the degradation of certain components used in the process.

[0024] According to a preferred embodiment, said at least one fluorinated polymer Al comprises monomeric units derived from vinylidene fluoride and optionally monomeric units derived from a monomer selected from the group consisting of vinyl fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methylvinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propylvinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFO CF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R 1 CH2OCF=CF2in which R 1is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

[0025] According to a preferred embodiment, said at least one fluorinated polymer Al is a homopolymer of vinylidene fluoride or a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from a monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene or a mixture thereof.

[0026] According to a preferred embodiment, said at least one alkali metal salt B1 is selected from the group consisting of LiCF3SO3, LiPF6, LiCIO4, LiBF4, LiB(C2O4)2, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F3)2, LiN(SO2C2F5)2, LiN(SO2F)(SO2CF3), LiN(SO2F)(SO2C2F5), LiN(SO2CF3)(SO2C2F5), LiAsF6, LiBF2C2O4, UNO3, LiPF3(CF2CF3)3, LiBETI, LiTDI, NaTDI, KTDI, NaCIO4, KCIO4, NaPF6, KPF6, NaBF4, KBF4, NaAsF6, KAsF6, NaCF3SO3, KCF3SO3, NaN(CF3SO2)2, KN(CF3SO2)2, NaN(SO2C2F5)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2C2F5), NaN(SO2CF3) (SO2C2F5), KN(SO2C2F5)2, KN(SO2F)(SO2CF3), KN(SO2F)(SO2C2F5), KN(SO2CF3)(SO2C2F5), OR a mixture of these.

[0027] According to a preferred embodiment, said at least one plasticizer B2 is an ionic liquid which comprises an anion selected from the group consisting of tetrafluoroborate (BF4-), bis(oxalato)borate BOB-, hexafluorophosphate (PF6-), hexafluoroarsenate (AsF6-), triflate or trifluoromethylsulfonate (CF3SO3-), bis(fluorosulfonyl)imide (FSI-), bis-(trifluoromethanesulfonyl)imide (TFSI-), nitrate (NO3-), 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI-), an acrylate or a methacrylate; and a cation selected from the group consisting of ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and mixtures thereof;or said at least one plasticizer B2 is a mixture of at least one ionic liquid and at least one solvent SI with a boiling point above 100°C selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, trans-4,5-difluoro-1,3-dioxolan-2-one, ethylene carbonate, propylene carbonate, (2-cyanoethyl)triethoxysilane, 3-methoxypropionitrile, sulfolane, and polyethylene glycol dimethyl ethers.;

[0028] According to a preferred embodiment, said film has a porosity of less than 10%.

[0029] According to a preferred embodiment, said film has a thickness varying by less than 20% over its entire length.

[0030] According to another aspect, the present invention provides a composition for the preparation of a solid electrolyte comprising at least one fluoropolymer Al, at least one organic solvent A2, at least one alkali metal salt B1 and at least one plasticizer B2 comprising at least one ionic liquid characterized in that said at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of 7 Pa to 24 kPa at 20°C, a flash point greater than -15°C and a mass water content less than 5000 ppm. According to a preferred embodiment, said at least one fluoropolymer Al is as defined in the present application, said at least one alkali metal salt B1 is as defined in the present application, and said at least one plasticizer B2 is as defined in the present application.

[0031] According to another aspect, the present invention provides a film comprising from 15 to 70% by weight of at least one fluoropolymer Al, from 10 to 80% by weight of plasticizer(s) B2 comprising at least one ionic liquid, from 2 to 30% by weight of alkali metal salt(s) Bl, and from 1 ppb to 5000 ppm of water.

[0032] According to a preferred embodiment, said film also comprises from 1 ppb to 15% of said at least one organic solvent A2 as defined in the present application.

[0033] According to a preferred embodiment, said film consists of from 15 to 70% by weight of at least one fluorinated polymer Al, from 10 to 80% by weight of plasticizer(s) B2 comprising at least one ionic liquid, from 2 to 30% by weight of alkali metal salt(s) Bl, from 1 ppb to 15% of said at least one organic solvent A2 and from 1 ppb to 5000 ppm of water; the sum of the constituents being equal to 100.

[0034] According to a preferred embodiment, said film has an ionic conductivity of 0.01 to 5 mS / cm, preferably of 0.05 to 5 mS / cm, advantageously of 0.5 to 5 mS / cm at 25°C, measured by electrochemical impedance spectroscopy.

[0035] According to a preferred embodiment, said film is obtained by the method according to the present invention.

[0036] According to a preferred embodiment, said film has a thickness varying by less than 20% over its entire length.

[0037] According to a preferred embodiment, said film has a porosity of less than 10%.

[0038] According to another aspect, the present invention provides a separator for a Li-ion rechargeable battery, comprising the film according to the present invention.

[0039] According to another aspect, the present invention provides an electrochemical device selected from the group consisting of batteries, capacitor, electrochemical double layer electric capacitor, and membrane electrode assembly (MEA) for fuel cell or an electrochromic device, said device comprising a film according to the present invention.

[0040] According to another aspect, the present invention provides an all-solid-state battery comprising an anode, a cathode and a separator, wherein said separator comprises the film according to the present invention.

[0041] According to another aspect, the present invention provides an all-solid-state battery comprising an anode, a cathode and a separator, wherein the anode and / or the cathode comprises a film according to the present invention. Brief description of the figures

[0042] Fig. 1 shows the evolution of the mass of a film as a function of the coating length.

[0043] Fig. 2 shows the evolution of the thickness of a film as a function of the coating length.

[0044] Detailed description of the invention

[0045] The invention is now described in more detail and in a non-limiting manner in the following description.

[0046] According to a first aspect of the present invention, a method for preparing a solid electrolyte in the form of a film is provided. Said method comprises a step of providing a solution C comprising at least one fluorinated polymer Al, at least one organic solvent A2, at least one alkali metal salt B1 and at least one plasticizer B2. Preferably, said at least one plasticizer B2 comprises at least one ionic liquid. This solution C is deposited on a support D to form a film. Preferably, said method also comprises a step of drying said film to remove said at least one organic solvent A2 used during the preparation.

[0047] Thus, preferably, the method according to the present invention comprises the steps of:

[0048] Providing a solution C comprising said at least one fluorinated polymer Al, said at least one organic solvent A2, said at least one alkali metal salt B1 and said at least one plasticizer B2;

[0049] Deposition of said solution C on a support D to form a film,

[0050] Drying of the film thus obtained.

[0051] Preferably, solution C is obtained by mixing two separate solutions A and B. Solution A comprises said at least one fluorinated polymer Al and said at least one organic solvent A2. Solution B comprises said at least one alkali metal salt B1 and said at least one plasticizer B2. Solution B may also comprise an organic solvent. The latter may be said organic solvent A2 or any other organic solvent capable of solubilizing said alkali metal salt B1 and / or said plasticizer B2. Solutions A and B are then mixed to obtain solution C.

[0052] According to a preferred embodiment, the step of preparing said solution A is carried out at a temperature between 15°C and 90°C, preferably between 15°C and 60°C.

[0053] According to a preferred embodiment, the step of preparing said solution B is carried out at a temperature between 15°C and 90°C, preferably between 15°C and 60°C.

[0054] According to a preferred embodiment, the step of depositing said solution C on the support D is carried out at a temperature of between 15°C and 100°C, preferably between 15°C and 90°C. The step of drying the film can be carried out at a temperature of 20°C to 120°C, preferably of 20°C to 90°C, in particular of 40°C to 80°C. This step is generally carried out under extraction.

[0055] Fluorinated polymer Al

[0056] Said fluorinated polymer Al comprising monomeric units containing at least one fluorine atom. According to a preferred embodiment, said fluorinated polymer Al contains 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 fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

[0057] Preferably, said fluorinated polymer Al contains at least monomeric units derived from a monomer selected from the group consisting of vinyl fluoride; vinylidene fluoride (VDF); 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) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R 1 CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof.

[0058] In particular, said fluorinated polymer Al comprises at least monomeric units derived from vinylidene fluoride. The fluorinated polymer Al may be a homopolymer or a copolymer. The copolymer may also comprise non-fluorinated monomers.

[0059] According to one embodiment, the fluorinated polymer Al is a vinylidene fluoride homopolymer.

[0060] According to an alternative embodiment, the fluorinated polymer Al is a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from at least one other comonomer copolymerizable with vinylidene fluoride. The comonomers compatible with vinylidene fluoride may be halogenated (fluorinated, chlorinated or brominated) or non-halogenated.Thus, said fluorinated polymer Al comprises monomeric units derived from vinylidene fluoride and monomeric units derived from a monomer selected from the group consisting of vinyl fluoride; 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) (PDD); the monomer of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the monomer of formula CF2=CFOCF2CF2SO2F; the monomer of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the monomer of formula R. 1 CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the monomer of formula R 2OCF=CH2in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. Trifluoropropenes include 3,3,3-trifluoropropene. Tetrafluoropropenes include 2, 3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene. Pentafluoropropenes include 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene. Chlorofluoroethylene may refer to either 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. Chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0061] Preferably, the fluoropolymer Al is a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from a monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene and hexafluoropropylene or a mixture thereof. In the fluoropolymer Al, the mass content of the vinylidene fluoride units is at least 50%, preferably at least 60%, more preferably greater than 70% and advantageously greater than 80%.

[0062] In particular, the fluorinated polymer Al is a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from hexafluoropropylene; preferably the mass content of the monomeric units derived from vinylidene fluoride is at least 50%, preferably at least 60%, more preferably greater than 70% and advantageously greater than 80%.

[0063] More particularly, the fluorinated polymer Al is a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from hexafluoropropylene; the mass content of the vinylidene fluoride units is greater than 65% and the mass content of the hexafluoropropylene units is less than 35%.

[0064] According to one embodiment, the fluoropolymer Al consists of a mixture of a vinylidene fluoride homopolymer (PVDF) and at least one VDF copolymer, with a mass content of PVDF homopolymer ranging from 0.1 to 20% based on the weight of said mixture.

[0065] According to one embodiment, said fluorinated polymer Al consists of a mixture of a PVDF homopolymer and a P(VDF-HFP) copolymer.

[0066] According to one embodiment, said fluorinated polymer Al consists of a mixture of two VDF copolymers of different structures.

[0067] According to a particular embodiment, the fluorinated polymer Al is functionalized in whole or in part, which allows it to improve adhesion to metal. Thus, said fluorinated polymer Al may comprise monomer units carrying at least one of the functions selected from the group consisting of carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups such as glycidyl, amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, phosphonic; preferably at least one carboxylic acid or hydroxyl function.

[0068] The function is introduced by a chemical reaction which may be grafting, or a copolymerization of the monomeric units bearing a fluorine atom with a monomer bearing at least one of said functional groups and a vinyl function capable of copolymerizing with the fluorinated monomer, according to techniques well known to those skilled in the art.

[0069] According to one embodiment, the functional group carries a carboxylic acid function which is a (meth)acrylic acid type group chosen from acrylic acid, methacrylic acid, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, hydroxyethylhexyl(meth)acrylate and acryloyloxy propylsuccinate.

[0070] According to one embodiment, the units carrying the carboxylic acid function further comprise a heteroatom chosen from oxygen, sulfur, nitrogen and phosphorus.

[0071] According to one embodiment, the functionality is introduced via the transfer agent used during the synthesis process. The transfer agent is a polymer with a molar mass less than or equal to 20,000 g / mol and carrying functional groups chosen from the groups: carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups (such as glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, phosphonic. An example of a transfer agent of this type is acrylic acid oligomers. According to a preferred embodiment, the transfer agent is an acrylic acid oligomer with a molar mass less than or equal to 20,000 g / mol.

[0072] The content of functional groups in PVDF is at least 0.01 mol%, preferably at least 0.1 mol%, and at most 15 mol%, preferably at most 10 mol%.

[0073] The PVDF preferably has a high molecular weight. By high molecular weight, as used herein, is meant a PVDF having a melt viscosity greater than 100 Pa.s, preferably greater than 500 Pa.s, more preferably greater than 1000 Pa.s, according to ASTM D-3835 measured at 232°C and 100 sec-1.

[0074] The PVDF homopolymers and VDF copolymers used in the invention can be obtained by known polymerization methods such as emulsion or suspension polymerization.

[0075] According to one embodiment, they are prepared by an emulsion polymerization process in the absence of fluorinated surfactant.

[0076] Polymerization of PVDF results in a latex generally having a solids content of 10 to 60% by weight, preferably 10 to 50%, and having a weight average particle size of less than 1 micrometer, preferably less than 1000 nm, preferably less than 800 nm, and more preferably less than 600 nm. The weight average particle size is generally at least 20 nm, preferably at least 50 nm, and advantageously the average size is in the range of 100 to 400 nm. The polymer particles may form agglomerates having a weight average size of 1 to 30 micrometers, and preferably 2 to 10 micrometers. The agglomerates may break into discrete particles during formulation and application to a substrate.

[0077] In some embodiments, the PVDF homopolymer and VDF copolymers are composed of bio-based VDF. The term "bio-based" means "derived from biomass." This improves the ecological footprint of the polymer. The bio-based VDF may be characterized by a renewable carbon content, i.e., carbon of natural origin and originating from a biomaterial or biomass, of at least 1 atomic % as determined by the 14C content according to standard NF EN 16640. The term "renewable carbon" indicates that the carbon is of natural origin and originates from a biomaterial (or biomass), as indicated below.According to certain embodiments, the bio-carbon content of the VDF may be greater than 5%, preferably greater than 10%, preferably greater than 25%, preferably greater than or equal to 33%, preferably greater than 50%, preferably greater than or equal to 66%, preferably greater than 75%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98%, preferably greater than 99%, advantageously equal to 100%. Organic solvent A2.

[0078] Said organic solvent A2 makes it possible to solubilize said fluorinated polymer Al. Thus, said organic solvent A2 has a donor number greater than 4 kcal / mol. Preferably, said organic solvent has a donor number greater than 5 kcal / mol. The donor index, or donor number, of a solvent represents the value -AH, AH being the enthalpy of the interaction between the solvent and antimony pentachloride (according to the method described in Journal of Solution Chemistry, vol. 13, no. 9, 1984).

[0079] According to a preferred embodiment, said organic solvent A2 has a donor number greater than 6 kcal / mol, advantageously greater than 7 kcal / mol, preferably greater than 8 kcal / mol, more preferably greater than 9 kcal / mol, in particular greater than 10 kcal / mol.

[0080] According to a preferred embodiment, said organic solvent A2 has a donor number of less than 30 kcal / mol, advantageously less than 29 kcal / mol, preferably less than 28 kcal / mol, more preferably less than 27 kcal / mol, in particular less than 26 kcal / mol, more particularly less than 25 kcal / mol, preferably less than 24 kcal / mol, advantageously less than 23 kcal / mol, preferably less than 22 kcal / mol, more preferably less than 21 kcal / mol, particularly preferably less than 20 kcal / mol.

[0081] Thus, according to a preferred embodiment, said organic solvent A2 has a donor number greater than 6 kcal / mol, advantageously greater than 7 kcal / mol, preferably greater than 8 kcal / mol, more preferably greater than 9 kcal / mol, in particular greater than 10 kcal / mol; and less than 30 kcal / mol, advantageously less than 29 kcal / mol, preferably less than 28 kcal / mol, more preferably less than T1 kcal / mol, in particular less than 26 kcal / mol, more particularly less than 25 kcal / mol, preferably less than 24 kcal / mol, advantageously less than 23 kcal / mol, preferably less than 22 kcal / mol, more preferably less than 21 kcal / mol, particularly preferably less than 20 kcal / mol.

[0082] According to a particular embodiment, said organic solvent A2 has a donor number of between 5 and 30 kcal / mol, advantageously between 5 and 25 kcal / mol, preferably between 10 and 20 kcal / mol.

[0083] In order to also allow the preparation of a homogeneous film, i.e. a homogeneous thickness over the entire length of the coating, the use of a specific organic solvent A2 or organic solvent mixture A2 is preferred. The use of an organic solvent having a saturated vapor pressure as explained in the different embodiments below makes it possible to improve the quality of the film produced. Said organic solvent A2 has a saturated vapor pressure of less than 24 kPa at 20°C. According to a preferred embodiment, said organic solvent A2 has a saturated vapor pressure of less than 23 kPa, advantageously less than 22 kPa, preferably less than 21 kPa, more preferably less than 20 kPa at 20°C, in particular less than 18 kPa at 20°C, more particularly less than 16 kPa at 20°C, preferably less than 14 kPa at 20°C, advantageously less than 12 kPa at 20°C.

[0084] According to a preferred embodiment, said organic solvent A2 has a saturated vapor pressure greater than 7 Pa, advantageously greater than 8 Pa, preferably greater than 9 Pa, more preferably greater than 10 Pa at 20°C, in particular greater than 25 Pa, more particularly greater than 50 Pa, preferably greater than 100 Pa, advantageously more preferably greater than 500 Pa at 20°C. This makes it possible to avoid a residual content of the solvent that is too high in the film produced.

[0085] Thus, said organic solvent A2 has a saturated vapor pressure of less than 24 kPa at 20°C. According to a preferred embodiment, said organic solvent A2 has a saturated vapor pressure of less than 23 kPa, advantageously less than 22 kPa, preferably less than 21 kPa, more preferably less than 20 kPa at 20°C, in particular less than 18 kPa at 20°C, more particularly less than 16 kPa at 20°C, preferably less than 14 kPa at 20°C, advantageously more preferably less than 12 kPa at 20°C; and said organic solvent A2 has a saturated vapor pressure greater than 7 Pa, advantageously greater than 8 Pa, preferably greater than 9 Pa, more preferably greater than 10 Pa at 20°C, in particular greater than 25 Pa, more particularly greater than 50 Pa, preferably greater than 100 Pa, advantageously more preferably greater than 500 Pa at 20°C.

[0086] According to a preferred embodiment, said at least one organic solvent A2 has a flash point above -15°C, advantageously above -14°C, preferably above -13°C, in particular above -12°C. Preferably, said at least one organic solvent A2 has a flash point below 90°C, advantageously below 85°C, preferably below 80°C, in particular below 75°C. Thus, said at least one organic solvent A2 may have a flash point above -15°C, advantageously above -14°C, preferably above -13°C, in particular above -12°C;and less than 90°C, advantageously less than 85°C, preferably less than 80°C, in particular less than 75°C. The flash point corresponds to the lowest temperature at which a combustible body emits sufficient vapor to form, with the ambient air, a gaseous mixture which ignites under the effect of a heat energy source but not sufficiently for combustion to sustain itself. The flash point as defined herein is the flash point measured in a closed cup. According to a particular embodiment, said at least one organic solvent A2 has: a donor number greater than 6 kcal / mol, advantageously greater than 7 kcal / mol, preferably greater than 8 kcal / mol, more preferably greater than 9 kcal / mol, in particular greater than 10 kcal / mol;and less than 30 kcal / mol, advantageously less than 29 kcal / mol, preferably less than 28 kcal / mol, more preferably less than Tl kcal / mol, in particular less than 26 kcal / mol, more particularly less than 25 kcal / mol, preferably less than 24 kcal / mol, advantageously less than 23 kcal / mol, preferably less than 22 kcal / mol, more preferably less than 21 kcal / mol, particularly preferably less than 20 kcal / mol; a saturated vapor pressure of less than 23 kPa, advantageously less than 22 kPa, preferably less than 21 kPa, more preferably less than 20 kPa at 20°C, in particular less than 18 kPa at 20°C, more particularly less than 16 kPa at 20°C, preferably less than 14 kPa at 20°C, advantageously less than 12 kPa at 20°C;and greater than 7 Pa, advantageously greater than 8 Pa, preferably greater than 9 Pa, more preferably greater than 10 Pa at 20°C, in particular greater than 25 Pa, more particularly greater than 50 Pa, preferably greater than 100 Pa, advantageously more preferably greater than 500 Pa at 20°C; a flash point greater than -15°C, advantageously greater than -14°C, preferably greater than -13°C, in particular greater than -12°C; and less than 90°C, advantageously less than 85°C, preferably less than 80°C, in particular less than 75°C.;

[0087] Furthermore, said at least one organic solvent A2 preferably has a mass water content of less than 5000 ppm, advantageously less than 4000 ppm, preferably less than 3000 ppm, more preferably less than 2000 ppm, in particular less than 1000 ppm, more particularly less than 500 ppm, preferably less than 100 ppm, advantageously less than 50 ppm, preferably less than 10 ppm. Preferably, said at least one organic solvent A2 has a mass water content of greater than 1 ppb, more preferably greater than 10 ppb, in particular greater than 100 ppb. The low water content in said solvent prevents deterioration of the other constituents present.Said organic solvent A2 may be chosen in particular from esters, carbonates, nitriles or dinitriles, ethers or diethers, ketones provided that it has a donor number as provided in the present application and the saturated vapor pressure as described in the present application; and preferably the flash point as described in the present application. Combinations of these may also be used as organic solvent.

[0088] By way of non-limiting example, the following may be mentioned as organic solvent A2 according to the present invention: N,N-dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone, 2-butanone, 1,2-dimethoxyethane, 1,3-dioxolane, 2,3-butanedione, 2-methylpentan-3-one, 2-methyltetrahydrofuran, 2-pentanone, methyl cyanide, 3,3-dimethyl-2-butanone, 3-methyl-2-butanone, 3-pentanone, butyl acetate, cyclohexanone, cyclopentanone, 4-methylpentan-2-one, dibutyl ether, 1,4-dioxane, dipropyl ether, ethyl acetate, ethyl butanoate or methyl propanoate, tetrahydrofuran, N-butyl-2-pyrrolidone or a mixture thereof;in particular 2- butanone, 1,2-dimethoxyethane, 1,3-dioxolane, 2,3-butanedione, 2-methylpentan-3-one, 2- methyltetrahydrofuran, 2-pentanone, methyl cyanide, 3,3-dimethyl-2-butanone, 3-methyl-2- butanone, 3-pentanone, butyl acetate, cyclohexanone, cyclopentanone, 4-methylpentan-2- one, dibutyl ether, 1,4-dioxane, dipropyl ether, ethyl acetate, ethyl butanoate or methyl propanoate, or a mixture thereof.;

[0089] Alkali metal salt B1

[0090] Said alkali metal salt is selected from the group consisting of LiCF3SO3, LiPF6, LiCIO4, Li BF4, LiB(C2O4)2, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F3)2, LiN(SO2C2F5)2, LiN(SO2F)(SO2CF3), LiN(SO2F)(SO2C2F5), LiN(SO2CF3)(SO2C2F5),LiAsF6, LiBF2C2O4, LiNO3, LiPF3(CF2CF3)3, LiBETI, LiTDI, NaTDI, KTDI, NaCIO4, KCIO4, NaPF6, KPF6, NaBF4, KBF4, NaAsF6, KAsF6, NaCF3SO3, KCF3SO3, NaN(CF3SO2)2, KN(CF3SO2)2, NaN(SO2C2F5)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2C2F5), NaN(SO2CF3)(SO2C2F5), KN(SO2C2F5)2, KN(SO2F)(SO2CF3), KN(SO2F)(SO2C2F5), KN(SO2CF3)(SO2C2F5), or a mixture thereof. Preferably, said alkali metal salt is selected from the group consisting of LiCF3SO3, LiPF6, LiCIO4, LiBF4, LiB(C2O4)2, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F3)2, LiN(SO2C2F5)2, LiN(SO2F)(SO2CF3), LiN(SO2F)(SO2C2F5), LiN(SO2CF3)(SO2C2F5), LiAsF6, LiBF2C2O4, LiNO3, LiPF3(CF2CF3)3, LiBETI, LiTDI, or a mixture thereof.

[0091] Plasticizer B2

[0092] According to a preferred embodiment, said plasticizer B2 comprises at least one ionic liquid.

[0093] An ionic liquid is a salt that is liquid at room temperature, meaning it has a melting point below 100°C under atmospheric pressure. It is formed by the combination of an organic cation and an anion whose ionic interactions are weak enough not to form a solid.

[0094] Examples of organic cations include ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and mixtures thereof. According to one embodiment, this cation may comprise a C1-C30 alkyl group, such as 1-butyl-1-methylpyrrolidinium, 1-ethyl-3-methylimidazolium, N-methyl-N-propylpyrrolydinium or N-methyl-N-butylpiperidinium.

[0095] According to one embodiment, the anions associated with them are chosen from: imides, in particular bis(fluorosulfonyl)imide and bis(trifluoromethanesulfonyl)imide; borates; phosphates; phosphinates and phosphonates, in particular alkylphosphonates; amides, in particular dicyanamide; aluminates, in particular tetrachloroaluminate; halides (such as bromide, chloride, iodide anions); cyanates; acetates (CH3COO-), in particular trifluoroacetate; sulfonates, in particular methanesulfonate (CH3SO3-), trifluoromethanesulfonate; and sulfates, in particular hydrogen sulfate; an acrylate or a methacrylate.

[0096] According to one embodiment, the anions are chosen from tetrafluoroborate (BF4-), bis(oxalato)borate (BOB-), hexafluorophosphate (PF6-), hexafluoroarsenate (AsF6-), triflate or trifluoromethylsulfonate (CF3SO3-), bis(fluorosulfonyl)imide (FSI-), bis-(trifluoromethanesulfonyl)imide (TFSI-), nitrate (NO3-), 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI-), an acrylate or a methacrylate.

[0097] According to one embodiment, said anion of the ionic liquid is chosen from TDI-, FSI-, TFSI-, PF6-, BF4-, NO3-, BOB-, CH2=CHCOO-, According to one embodiment, said anion of the ionic liquid is FSI-.

[0098] According to one embodiment, said plasticizer B2 is a mixture of at least two ionic liquids chosen from those described above.

[0099] According to one embodiment, said plasticizer B2 is a mixture of at least one ionic liquid and at least one solvent SI with a boiling point greater than 100°C, preferably greater than 110°C, more preferably greater than 125°C, in particular greater than 150°C, more particularly greater than 160°C. According to one embodiment, said solvent SI is chosen from:

[0100] - vinylene carbonate (VC) (CAS: 872-36-6),

[0101] - fluoroethylene carbonate or 4-fluoro-1,3-dioxolan-2-one (FEC or F1EC) (CAS: 114435-02-8),

[0102] - trans-4,5-difluoro-l,3-dioxolan-2-one (F2EC) (CAS: 171730-81-7),

[0103] - ethylene carbonate (EC) (CAS: 96-49-1), - propylene carbonate (PC) (CAS: 108-32-7),

[0104] - (2-cyanoethyl)triethoxysilane (CAS: 919-31-3),

[0105] - 3-methoxypropionitrile (CAS: 110-67-8),

[0106] - sulfolane (CAS: 126-33-0),

[0107] - triethyl phosphate (TEP) (CAS: 78-40-0),

[0108] - b-Butyrolactone (CAS: 96-48-0),

[0109] - ethers such as polyethylene glycol dimethyl ethers, including diethylene glycol dimethyl ether (EG2DME), triethylene glycol dimethyl ether (EG3DME), and tetraethylene glycol dimethyl ether (EG4DME).

[0110] Plasticizers provide improved properties of conductivity, electrochemical stability, thermal stability, electrode compatibility, and capacity retention compared to conventional liquid electrolytes.

[0111] Examples of plasticizer B2 according to the invention are the following mixtures:

[0112] - l-ethyl-3-methylimidazolium-FSI and EC,

[0113] - l-ethyl-3-methylimidazolium-FSI and tetraethylene glycol dimethyl ether,

[0114] - l-ethyl-3-methylimidazolium-FSI and EC and FEC,

[0115] - 1-butyl-l-methylpyrrolidinium-FSI and tetraethylene glycol dimethyl ether, - 1-butyl-l-methylpyrrolidinium-FSI and EC and FEC,

[0116] - N-propyl-N-methylpyrrolidinium and tetraethylene glycol dimethyl ether

[0117] - l-ethyl-3-methylimidazolium-TFSI and FEC,

[0118] - l-ethyl-3-methylimidazolium-FSI,

[0119] - 1-butyl-l-methylpyrrolidinium-FSI.

[0120] According to one embodiment, in the mixture of at least one ionic liquid and a solvent SI, the mass ratio between the ionic liquids and the solvents forming said plasticizer B2 varies from 10:0.1 to 0.1:10.

[0121] Support D

[0122] Said film prepared from solution C is deposited on a support D. According to a preferred embodiment, the support D can be removed after the film drying step to obtain a self-supporting film. In this case, the support D can be, by way of non-limiting example, polyethylene terephthalate, polypropylene, aluminum or aluminum coated with a polymer layer. According to an alternative embodiment, the support D is a fibrous reinforcement. This makes it possible to maintain the film prepared from solution C. Generally, when the support is a fibrous reinforcement, it is not removed. The fibrous reinforcement is made of any material (porous membrane, woven or non-woven) making it possible to improve the mechanical properties. It can be, in a non-limiting manner, a polypropylene non-woven, a polyethylene terephthalate non-woven, a polyvinylidene fluoride non-woven or a microporous polypropylene membrane.

[0123] Composition

[0124] According to another aspect, the present invention provides a composition for the preparation of a solid electrolyte. Said composition corresponds to said solution C used in the above method. Preferably, said composition comprises said at least one fluoropolymer Al, said at least one organic solvent A2, said at least one alkali metal salt B1 and said at least one plasticizer B2; and said at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of 7 Pa to 24 kPa at 20°C, and preferably a flash point greater than -15°C and a mass water content less than 5000 ppm based on the total weight of the composition.

[0125] Advantageously, said composition comprises from 0.75% to 18% by weight of said at least one fluorinated polymer Al, from 75% to 95% by weight of said at least one organic solvent A2, from 0.1% to 7.5% by weight of said at least one alkali metal salt B1 and from 0.5% to 20% by weight of said at least one plasticizer B2 and a mass content of water of less than 5000 ppm based on the total weight of the composition; and said at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of 7 Pa to 24 kPa at 20°C, and preferably a flash point greater than -15°C.

[0126] Preferably, said composition comprises from 0.75% to 18% by weight of said at least one fluorinated polymer Al, from 75% to 95% by weight of said at least one organic solvent A2, from 0.1% to 7.5% by weight of said at least one alkali metal salt B1 and from 0.5% to 20% by weight of said at least one plasticizer B2 and a mass water content greater than 1 ppb and less than 5000 ppm based on the total weight of the composition; and said at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of 7 Pa to 24 kPa at 20°C, and preferably a flash point greater than -15°C.

[0127] In particular, said composition comprises from 2.25% to 18% by weight of said at least one fluorinated polymer Al, from 75% to 85% by weight of said at least one organic solvent A2, from 0.3% to 7.5% by weight of said at least one alkali metal salt B1 and from 1.5% to 20% by weight of said at least one plasticizer B2 and a mass content of water of less than 5000 ppm based on the total weight of the composition; and said at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of 7 Pa to 24 kPa at 20°C, and preferably a flash point greater than -15°C.

[0128] More particularly, said composition comprises from 2.25% to 18% by weight of said at least one fluorinated polymer Al, from 75% to 85% by weight of said at least one organic solvent A2, from 0.3% to 7.5% by weight of said at least one alkali metal salt B1 and from 1.5% to 20% by weight of said at least one plasticizer B2 and a mass water content greater than 1 ppb and less than 5000 ppm based on the total weight of the composition; and said at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of 7 Pa to 24 kPa at 20°C, and preferably a flash point greater than -15°C.

[0129] Said organic solvent A2 may be as described above. Fluorinated polymer Al may be as described above. Said alkali metal salt B1 may be as described above. Said plasticizer B2 may be as described above.

[0130] Furthermore, said composition may have a mass water content of less than 5000 ppm, advantageously less than 4000 ppm, preferably less than 3000 ppm, more preferably less than 2000 ppm, in particular less than 1000 ppm, more particularly less than 500 ppm, preferably less than 100 ppm, advantageously less than 50 ppm, preferably less than 10 ppm based on the total weight of the composition. Preferably, said composition may have a mass water content of greater than 1 ppb, more preferably greater than 10 ppb, preferably greater than 100 ppb based on the total weight of the composition, in particular greater than 1 ppm.

[0131] According to a preferred embodiment, said composition has a solution viscosity of 100 to 50,000 cP at 10 s-1 at room temperature.

[0132] Movie

[0133] According to another aspect, the present invention provides a film, preferably non-porous, i.e. having a porosity of less than 10%, more preferably less than 5%, in particular less than 1%. The porosity of the film is obtained according to the following calculation described in the publication of M.CAI, Nature Communications, 10, 2019, 4597:

[0134] ^ER ~ denseER p = — — where V E R represents the actual volume of the film and is calculated by multiplying the film surface area with the film thickness. VdenseER represents the volume occupied by each of the constituents without any porosity and is calculated according to the following formula: is the sum of the volume occupied by each constituent of the film.

[0135] According to a preferred embodiment, said film comprises from 15 to 70% by weight of said at least one fluoropolymer Al, from 10 to 80% by weight of said plasticizer(s) B2, from 2 to 30% by weight of said alkali metal salt(s) B1, from 1 ppb to 5000 ppm of water based on the total weight of said film. The contents expressed here relate to the film without taking into account the support D, i.e. after removal thereof. Preferably, said film also comprises from 1 ppb to 15% of said at least one organic solvent A2. Said film may comprise from 20 to 70% of said at least one fluoropolymer Al, advantageously from 25 to 70% of said at least one fluoropolymer Al, preferably from 30 to 70% of said at least one fluoropolymer Al.

[0136] Thus, preferably, said film consists of from 15 to 70% by weight of said at least one fluoropolymer Al, from 10 to 80% by weight of said plasticizer(s) B2, from 2 to 30% by weight of said alkali metal salt(s) B1, from 1 ppb to 15% of said at least one organic solvent A2 and from 1 ppb to 5000 ppm of water based on the total weight of said film; the sum of the constituents being equal to 100. More preferably, said film consists of from 20 to 70% by weight of said at least one fluoropolymer Al, from 10 to 80% by weight of said plasticizer(s) B2, from 2 to 30% by weight of said alkali metal salt(s) B1, from 1 ppb to 15% of said at least one organic solvent A2 and from 1 ppb to 5000 ppm of water based on the total weight of said film; the sum of the constituents being equal to 100.

[0137] According to a preferred embodiment, in this film, the content of organic solvent A2 as defined in the present application is from 1 ppb to 10%, more preferably from 1 ppb to 5%, in particular from 1 ppb to 1%, more particularly from 1 ppb to 5000 ppm. More preferably, in this film, the content of organic solvent A2 as defined in the present application is from 10 ppb to 15%, advantageously from 10 ppb to 10%, preferably from 10 ppb to 5%, more preferably from 10 ppb to 1%, in particular from 10 ppb to 5000 ppm. In particular, in this film, the content of organic solvent A2 as defined in the present application is from 100 ppb to 15%, advantageously from 100 ppb to 10%, preferably from 100 ppb to 5%, more preferably from 100 ppb to 1%, in particular from 100 ppb to 5000 ppm.

[0138] Furthermore, in this film, the mass content of water is less than 5000 ppm, advantageously less than 4000 ppm, preferably less than 3000 ppm, more preferably less than 2000 ppm, in particular less than 1000 ppm, more particularly less than 500 ppm, preferably less than 100 ppm, advantageously less than 50 ppm, preferably less than 10 ppm; and the mass content of water is greater than 1 ppb, more preferably greater than 10 ppb, in particular greater than 100 ppb, more particularly greater than 1 ppm.

[0139] Advantageously, the film contains little or no solvent and has high ionic conductivity. Advantageously, the film is self-supporting, i.e., it can be handled without the aid of a support. Advantageously, the film is capable of being wound, i.e., it can be handled so that it can be wound onto a reel.

[0140] According to an alternative embodiment, when the film contains a fibrous reinforcement, the mass ratio between the film and the fibrous reinforcement is from 1.5 to 9.

[0141] According to one embodiment, said film has a thickness of 5 to 60 μm, preferably of 5 to 30 μm, more preferably of 7 μm to 20 μm.

[0142] Advantageously, said film has a thickness varying by less than 20% over its entire length, preferably by less than 15% over its entire length, in particular by less than 10% over its entire length.

[0143] According to one embodiment, the film according to the invention has an ionic conductivity ranging from 0.01 to 5 mS / cm, preferably from 0.05 to 5 mS / cm, advantageously from 0.5 to 5 mS / cm, at 25°C. The conductivity is measured by electrochemical impedance spectroscopy. According to one embodiment, the non-porous film is placed between two gold electrodes in a sealed conductivity cell under an inert atmosphere (CESH, Biology) and an electrochemical impedance spectroscopy is carried out between 1 Hz and 1 MHz with an amplitude of 10 mV. The resistance R of the film is then determined by linear regression of the curve -lm(Z) = f (Re(Z)). The conductivity o is then given by the following relationship: where / is the film thickness and S its surface area. For each composition, the conductivity value at a given temperature is obtained by averaging at least two measurements made on different samples.

[0144] Advantageously, the film according to the invention has good electrochemical stability over the temperature range from -20°C to 80°C.

[0145] Advantageously, the film retains its properties up to 80°C and does not ignite below 130°C.

[0146] According to one embodiment, the film according to the invention has a mechanical strength characterized by an elastic modulus, measured at 1 Hz and 23°C by dynamic mechanical analysis, greater than 0.1 MPa, preferably greater than 1 MPa, even more preferably greater than 10 MPa. Another subject of the invention is a separator for an all-solid-state battery consisting, in whole or in part, of said film. In this case, the presence of said lithium salt may be optional.

[0147] The invention also relates to an electrochemical device selected from the group: batteries, capacitor, electrochemical double-layer electric capacitor, and membrane-electrode assembly (MEA) for fuel cell or an electrochromic device, said device comprising a separator as described.

[0148] Another object of the invention is an all-solid-state battery, for example a Li-ion battery, or Li-S or Li-air batteries, comprising a negative electrode, a positive electrode and a separator, wherein said separator comprises a film as described above.

[0149] According to one embodiment, said battery comprises a lithium metal anode.

[0150] The invention also relates to an all-solid-state battery comprising such a film according to the present invention, preferably non-porous.

[0151] Examples

[0152] The following examples illustrate in a non-limiting manner the scope of the invention.

[0153] Measuring the thickness of a polymer electrolyte film

[0154] 20 mm diameter pellets are cut from the polymer electrolyte film to measure the mass and thickness of each pellet. The mass of the pellets is measured using a Mettler Toledo XPE105 balance with a readability of up to 0.01 mg. The thickness of the pellets is measured using a Mitutoyo IDH0530 digimatic comparator with an accuracy of 0.5 μm. These pellets are sampled every 10 cm along the length of the coating. The mass and thickness of these pellets are shown in Figure 1.

[0155] Example 1 (comparative): Production of a film in the presence of acetone

[0156] 5.91 g of P(VDF-HFP) (poly(vinylidene fluoride)-co-hexafluoropropylene) were dissolved in 30 g of acetone (donor number = 17 kcal / mol; saturation vapor pressure = 24.7 kPa at 20°C) at room temperature in a Thinky ARE250 planetary mixer. 0.47 g of LiFSI (lithium bis(fluorosulfonyl)amide) is further dissolved in 5.48 g of EMIM-FSI (1-ethyl-3-methylimidazolium bis(fluorosulfonyl imide). This latter solution is added to the P(VDF-HFP) solution and then mixed. The final solution is coated onto an aluminum foil 13 μm thick and 30 cm wide using a coating machine with a doctor blade set at 200 μm from the aluminum foil and a coating speed of 0.5 m / min. The coating is dried in an oven at 25°C for 2 h to evaporate the acetone. A polymer electrolyte film approximately 1.50 m long and 10 cm wide is thus obtained.

[0157] As can be seen in Fig. 1, acetone is not a suitable solvent for the preparation of flexible electrolyte films because the film thickness and mass is not homogeneous along the coating length, there is a variation of about 40% in the film thickness and mass between the start and the end of the coating (over lm50 of length).

[0158] Example 2 (invention): Production of a film in the presence of 2-butanone

[0159] 5.91 g of P(VDF-HFP) (poly(vinylidene fluoride)-co-hexafluoropropylene) were dissolved in 30 g of 2-butanone (Donor number = 17.4 kcal / mol; saturation vapor pressure of 10.3 kPa at 20°C) at room temperature in a Thinky ARE250 planetary mixer. 0.47 g of LiFSI (lithium bis(fluorosulfonyl)amide) is further dissolved in 5.48 g of EMIM-FSI (1-ethyl-3-methylimidazolium bis(fluorosulfonyl imide). This latter solution is added to the P(VDF-HFP) solution and then mixed. The final solution is coated onto an aluminum foil 13 μm thick and 30 cm wide using a coating machine with a doctor blade set at 200 μm from the aluminum foil and a coating speed of 0.5 m / min. The coating is dried in an oven at 25°C for 2 hours to evaporate the acetone. A polymer electrolyte film approximately 1.5 m long and 10 cm wide is thus obtained.

[0160] 2-Butanone is a suitable solvent for the preparation of flexible electrolyte films because the film thickness and mass is relatively homogeneous along the entire coating length (approximately 10% variation as shown in Figure 1 and Figure 2) unlike a solvent such as acetone (approximately 50% variation over the coating length).

Claims

Claims 1. A method of preparing a solid electrolyte in the form of a film comprises the steps of: Providing a solution C comprising at least one fluorinated polymer Al, at least one organic solvent A2, at least one alkali metal salt B1 and at least one plasticizer B2; Deposition of said solution C on a support D to form a film, Drying of the film thus obtained; characterized in that said at least one organic solvent A2 has a donor number greater than 4 kcal / mol and a saturated vapor pressure less than 24 kPa at 20°C; and in that said at least one plasticizer B2 comprises at least one ionic liquid.

2. Method according to the preceding claim, characterized in that solution C is obtained according to the following steps: Preparation of a solution A comprising said at least one fluorinated polymer Al and said at least one organic solvent A2; Preparation of a solution B comprising said at least one alkali metal salt B1 and said at least one plasticizer B2; Mix solutions A and B to obtain solution C.

3. Method according to any one of the preceding claims, characterized in that said at least one organic solvent A2 has a flash point above -15°C.

4. Method according to any one of the preceding claims, characterized in that said at least one organic solvent A2 has a saturated vapor pressure greater than 7 Pa at 20°C.

5. Method according to any one of the preceding claims, characterized in that said at least one organic solvent A2 has a mass water content of less than 5000 ppm.

6. Method according to any one of the preceding claims, characterized in that said at least one fluorinated polymer Al comprises monomeric units derived from vinylidene fluoride and optionally monomeric units derived from a monomer selected from the group consisting of vinyl fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methylvinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propylvinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R 1CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof.

7. Method according to any one of the preceding claims, characterized in that said at least one fluorinated polymer Al is a homopolymer of vinylidene fluoride or a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from a monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene or a mixture thereof.

8. Method according to any one of the preceding claims, characterized in that said at least one alkali metal salt B1 is selected from the group consisting of UCF3SO3, LiPF6, IJCIO4, LiBF4, LiB(C2O4)2, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F3)2, LiNfSC^Fsh, LiN(SO2F)(SO2CF3), LiN(SO2F)(SO2C2F5), LiN(SO2CF3) (SO2C2F5), LiBF2C2O4, LiNO3, LiPF3(CF2CF3)3, LiBETI, LiTDI, NaTDI, KTDI, NaCIO4, KCIO4, NaPF6, KPF6, NaBF4, KBF4, NaAsF6, KAsF6, NaCF3SO3, KCF3SO3, NaN(CF3SO2)2, KN(CF3SO2)2, NaN(SO2C2F5)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2C2F5), NaN(SO2CF3)(SO2C2F5) , KN(SO2C2F5)2, KN(SO2F)(SO2CF3), KN(SO2F)(SO2C2F5), KN(SO2CF3)(SO2C2F5), OR a mixture thereof.

9. Method according to any one of the preceding claims, characterized in that said at least one plasticizer B2 is an ionic liquid which comprises an anion selected from the group consisting of tetrafluoroborate (BF4-), bis(oxalato)borate BOB-, hexafluorophosphate (PF6-), hexafluoroarsenate (AsF6-), triflate or trifluoromethylsulfonate (CF3SO3-), bis(fluorosulfonyl)imide (FSI-), bis-(trifluoromethanesulfonyl)imide (TFSI-), nitrate (NO3-), 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI-), an acrylate or a methacrylate; and a cation selected from the group consisting of ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and mixtures thereof; or said at least one plasticizer B2 is a mixture of at least one ionic liquid and at least one solvent SI with a boiling point above 100°C selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, trans-4,5-difluoro-1,3-dioxolan-2-one, ethylene carbonate, propylene carbonate, (2-cyanoethyl)triethoxysilane, 3-methoxypropionitrile, sulfolane, and polyethylene glycol dimethyl ethers.

10. Method according to any one of the preceding claims, characterized in that said film has a porosity of less than 10%.

11. Method according to any one of the preceding claims, characterized in that said film has a thickness varying by less than 20% over its entire length.

12. Composition for the preparation of a solid electrolyte comprising at least one fluorinated polymer Al, at least one organic solvent A2, at least one alkali metal salt B1 and at least one plasticizer B2 comprising at least one ionic liquid characterized in that said at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of 7 Pa to 24 kPa at 20°C, a flash point greater than -15°C and a mass water content less than 5000 ppm.

13. Composition according to the preceding claim, characterized in that said at least one fluorinated polymer Al is as defined in claim 6 or 7, said at least one alkali metal salt B1 is as defined in claim 8, and said at least one plasticizer B2 is as defined in claim 9.

14. Film comprising from 15 to 70% by weight of at least fluoropolymer Al, from 10 to 80% by weight of plasticizer(s) B2 comprising at least one ionic liquid, from 2 to 30% by weight of alkali metal salt(s) Bl, and from 1 ppb to 5000 ppm of water based on the total weight of said film.

15. Film according to the preceding claim, characterized in that it comprises from 1 ppb to 15% of said at least one organic solvent A2 as defined in any one of the preceding claims 1 to 5.

16. Film according to the preceding claim 14 or 15 characterized in that it consists of from 15 to 70% by weight of at least one fluorinated polymer Al, from 10 to 80% by weight of plasticizer(s) B2 comprising at least one ionic liquid, from 2 to 30% by weight of alkali metal salt(s) Bl, from 1 ppb to 15% of said at least one organic solvent A2 and from 1 ppb to 5000 ppm of water based on the total weight of said film; the sum of the constituents being equal to 100.

17. Film according to any one of the preceding claims 14 to 16, characterized in that it has an ionic conductivity of 0.01 to 5 mS / cm, preferably of 0.05 to 5 mS / cm, advantageously of 0.5 to 5 mS / cm at 25°C, measured by electrochemical impedance spectroscopy.

18. Film according to any one of the preceding claims 14 to 17, characterized in that it is obtained by the process according to any one of claims 1 to 11.

19. Film according to any one of the preceding claims 14 to 18, characterized in that it has a thickness varying by less than 20% over its entire length.

20. Film according to any one of the preceding claims 14 to 19, characterized in that it has a porosity of less than 10%.

21. Separator for a Li-ion rechargeable battery, comprising the film according to one of claims 14 to 20.

22. An electrochemical device selected from the group consisting of batteries, capacitor, electrochemical double layer electric capacitor, and membrane electrode assembly (MEA) for a fuel cell or an electrochromic device, said device comprising a film according to one of claims 14 to 20.

23. An all-solid-state battery comprising an anode, a cathode and a separator, wherein said separator comprises the film according to one of claims 14 to 20.

24. All-solid-state battery comprising an anode, a cathode and a separator, wherein the anode and / or the cathode comprises a film according to one of claims 14 to 20.

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