Method for manufacturing all-solid electrolyte for secondary battery

Abstract

The invention relates to a method for producing a solid electrolyte in the form of a film, comprising the following steps: 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 plasticizer B2; depositing the solution C on a carrier D to form a film; drying the resulting film; characterized in that the at least one organic solvent A2 has a donor number of greater than 4 kcal / mol and a saturated vapor pressure of less than 24 kPa at 20 DEG C; and the at least one plasticizer B2 comprises at least one ionic liquid.

Description

Technical Field

[0001] The present invention generally relates to the field of storing electrical energy in all-solid-state batteries, particularly in lithium-ion secondary batteries. More specifically, the present invention relates to solid electrolytes and methods for producing membranes therefrom. The membranes are intended for use as all-solid-state battery separators or electrolytes, notably for lithium-ion batteries. The present invention also relates to all-solid-state batteries comprising such separators and / or such non-porous membranes. Background Art

[0002] Secondary batteries such as lithium-ion batteries include at least one negative electrode or anode coupled to a copper current collector, a positive electrode or cathode coupled to an aluminum current collector, a separator, and an electrolyte. The electrolyte is composed of an alkali metal salt (usually a lithium salt) mixed with a solvent, and the solvent is a mixture of organic carbonates, which is selected to optimize the transport and dissociation of ions. High dielectric constant promotes the dissociation of ions and therefore promotes the number of ions available in a given volume, while low viscosity promotes ion diffusion, which plays an important role in the charge and discharge rate of the electrochemical system in addition to other parameters. Secondary batteries (such as lithium-ion batteries) typically use a liquid electrolyte consisting of a solvent, an alkali metal salt (such as a lithium salt) and an additive. These electrolytes have good ionic conductivity, but are prone to leaking or catching fire if the battery is damaged.

[0003] The use of solid electrolytes makes it possible to overcome these difficulties. However, the conductivity of solid electrolytes is generally lower than that of liquid electrolytes. The difficulty of solid electrolytes lies in reconciling high ionic conductivity, good electrochemical stability and satisfactory thermal stability. The ionic conductivity must be comparable to that of liquid electrolytes. The electrochemical stability must enable the electrolyte to be used with cathode materials that can operate at high voltages (>4.5 V). Similarly, solid electrolytes must at least operate at a maximum temperature of 80°C.

[0004] Furthermore, satisfactory mechanical strength must be achieved at the separator. The latter must, in particular, prevent the formation of dendrites during the charge / discharge cycle. Generally, solid electrolytes must exhibit improved safety, but this cannot be achieved at the expense of other performance qualities. Finally, from an implementation point of view, solid electrolytes must be able to be handled (stretched) and rolled up.

[0005] Poly(vinylidene fluoride) (PVDF) and its derivatives are advantageous as the main constituent materials of the separator due to their electrochemical stability and their high dielectric constant, which promotes ion dissociation and thus conductivity. The copolymer P(VDF-HFP) (a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP)) has been studied as a gel membrane because it has a lower crystallinity than PVDF. For this reason, the advantage of these P(VDF-HFP) copolymers is that they can achieve greater swelling and thus improve conductivity.

[0006] However, solid or nearly solid electrolytes with a polymer matrix are often complex to manufacture and require several steps: dissolution, addition of co-components, homogenization, deposition, and drying. For each of these steps, the dry extract and the homogeneity of the slurry must be controlled in order to achieve the best possible performance and ensure its uniformity throughout the manufactured object.

[0007] WO 2020 / 126 750 describes a solid electrolyte composition comprising a mixture of a fluoropolymer and an isocyanate compound to form a cross-linked network. The membrane is prepared in the presence of acetone. However, due to the low vapor pressure of acetone, using the membrane in the presence of acetone does not provide a uniform membrane, which affects the ionic conductivity of the membrane and the final performance of the battery. In addition, the low vapor pressure leads to process safety issues.

[0008] Therefore, there is a need to develop new solid electrolytes that have a good compromise between ionic conductivity, electrochemical stability, and thermal stability and are suitable for simplified use compatible with industrial applications.

[0009] It is therefore an object of the present invention to remedy at least one of the disadvantages of the prior art, namely to produce a homogeneous solid electrolyte membrane having good performance qualities. Summary of the Invention

[0010] According to a first aspect, the present invention relates to a method for preparing a solid electrolyte in the form of a membrane, comprising the following steps:

[0011] - providing a solution C comprising at least one fluoropolymer A1, at least one organic solvent A2, at least one alkali metal salt B1 and at least one plasticizer B2;

[0012] - depositing the solution C on a support D to form a film;

[0013] - drying the film thus obtained;

[0014] Characterized in that the at least one organic solvent A2 has a donor number greater than 4 kcal / mol and a saturated vapor pressure at 20° C. less than 24 kPa; and the at least one plasticizer B2 comprises at least one ionic liquid.

[0015] The use of an organic solvent A2 as defined in this patent application allows the preparation of homogeneous membranes, which improves the ionic conductivity and the final performance qualities of the battery.

[0016] According to a preferred embodiment, solution C is obtained according to the following steps:

[0017] - preparing a solution A comprising said at least one fluoropolymer A1 and said at least one organic solvent A2;

[0018] - preparing a solution B comprising at least one alkali metal salt B1 and at least one plasticizer B2;

[0019] - Mix solutions A and B to obtain solution C.

[0020] According to a preferred embodiment, the at least one organic solvent A2 has a flash point higher than -15°C.

[0021] According to a preferred embodiment, the at least one organic solvent A2 has a saturated vapor pressure at 20° C. greater than 7 Pa. This makes it easier to evaporate the solvent, thus avoiding an excessive solvent content in the film obtained via the process of the invention.

[0022] According to a preferred embodiment, the at least one organic solvent A2 has a mass content of water of less than 5000 ppm. Limiting the water content helps to prevent degradation of certain components used in the process.

[0023] According to a preferred embodiment, the at least one fluoropolymer A1 comprises monomer units derived from vinylidene fluoride and optional monomer units derived from monomers selected from:

[0024] 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); products of the formula CF2=CFOCF2CF(CF3)OCF2CF2X, where X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; products of the formula CF2=CFOCF2CF2SO2F; products of the formula F(CF2)nCH2OCF=CF2, where n is 1, 2, 3, 4 or 5; products of the formula R 1 The product of CH2OCF=CF2, where R 1is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; Formula R 2 OCF=CH2 product, where R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); 3,3,3-trifluoropropene, and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

[0025] According to a preferred embodiment, the at least one fluoropolymer A1 is a homopolymer of vinylidene fluoride or a copolymer comprising monomer units derived from vinylidene fluoride and monomer units derived from a monomer selected from trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene or mixtures thereof.

[0026] According to a preferred embodiment, the at least one alkali metal salt B1 is selected from the group consisting of LiCF3SO3, LiPF6, LiClO4, 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), LiBETI, LiTDI, NaTDI, KTDI, NaClO4, KClO4, NaPF6, KPF6, NaBF4, KBF4, NaAsF6, KAsF6, NaCF3SO3, KCF3SO3, NaN(CF3SO2)2, KN(CF3SO2)2, NaN(SO2C2F5)2, NaN(SO2F)(SO2C F3), NaN(SO2F)(SO2C2F5), NaN(SO2CF3)(SO2C2F5), KN(SO2C2F5)2, KN(SO2F)(SO2CF3), KN(SO2F)(SO2C2F5), KN(SO2CF3)(SO2C2F5), or mixtures thereof.

[0027] According to a preferred embodiment, the at least one plasticizer B2 is an ionic liquid comprising an anion selected from tetrafluoroborate (BF4-), bis(oxalate)borate BOB-, hexafluorophosphate (PF6-), hexafluoroarsenate (AsF6-), trifluoromethanesulfonate or trifluoromethylsulfonate (CF3SO3-), bis(fluorosulfonyl)imide (FSI-), bis(trifluoromethanesulfonyl)imide (TFSI-), nitrate (NO3-), 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI-), acrylate or methacrylate; and an anion selected from The plasticizer B2 is a cation selected from ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidine, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium and mixtures thereof; or the at least one plasticizer B2 is a mixture of at least one ionic liquid and at least one solvent S1 having a boiling point greater than 100° C., the solvent S1 being selected from vinylene carbonate, fluoroethylene carbonate, trans-4,5-difluoro-1,3-dioxolane-2-one, ethylene carbonate, propylene carbonate, (2-cyanoethyl)triethoxysilane, 3-methoxypropionitrile, cyclopentane and polyethylene glycol dimethyl ether.

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

[0029] According to a preferred embodiment, the membrane has a thickness that varies less than 20% over its entire length.

[0030] According to another aspect, the present invention provides a composition for preparing a solid electrolyte, comprising at least one fluoropolymer A1, 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 the at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of from 7 Pa to 24 kPa at 20°C, a flash point greater than -15°C, and a water mass content of less than 5000 ppm.

[0031] According to a preferred embodiment, the at least one fluoropolymer A1 is as defined in the present patent application, the at least one alkali metal salt B1 is as defined in the present patent application, and the at least one plasticizer B2 is as defined in the present patent application.

[0032] According to another aspect, the present invention provides a membrane comprising 15 to 70 wt.% of at least one fluoropolymer A1, 10 to 80 wt.% of one or more plasticizers B2, 2 to 30 wt.% of one or more alkali metal salts B1, and 1 ppb to 5000 ppm of water.

[0033] According to a preferred embodiment, the membrane further comprises from 1 ppb to 15% of said at least one organic solvent A2 as defined in the present patent application.

[0034] According to a preferred embodiment, the membrane is composed of 15% to 70% by weight of at least one fluoropolymer A1, 10% to 80% by weight of one or more plasticizers B2 comprising at least one ionic liquid, 2% to 30% by weight of one or more alkali metal salts B1, 1 ppb to 15% of the at least one organic solvent A2, and 1 ppb to 5000 ppm of water; the sum of said components being equal to 100.

[0035] According to a preferred embodiment, the membrane has an ionic conductivity measured by electrochemical impedance spectroscopy at 25° C. comprised between 0.01 and 5 mS / cm, preferably between 0.05 and 5 mS / cm, advantageously between 0.5 and 5 mS / cm.

[0036] According to a preferred embodiment, the membrane is obtained via the process according to the invention.

[0037] According to a preferred embodiment, the membrane has a thickness that varies less than 20% over its entire length.

[0038] According to a preferred embodiment, the membrane has a porosity of less than 10%.

[0039] According to another aspect, the present invention provides a separator for a Li-ion rechargeable battery comprising a membrane according to the present invention.

[0040] According to another aspect, the present invention provides an electrochemical device selected from a battery, a capacitor, an electrochemical double layer capacitor and a membrane electrode assembly (MEA) for a fuel cell, or an electrochromic device, comprising a membrane 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 separator comprises a membrane according to the present invention.

[0042] 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 membrane according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Represents the evolution of the film mass as a function of the coating length.

[0044] Figure 2 Represents the evolution of the film thickness as a function of the coating length. DETAILED DESCRIPTION

[0045] The invention will now be described in more detail 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 film form is provided. The method comprises providing a solution C comprising at least one fluoropolymer A1, at least one organic solvent A2, at least one alkali metal salt B1, and at least one plasticizer B2. Preferably, the at least one plasticizer B2 comprises at least one ionic liquid. Solution C is deposited on a support D to form a film. Preferably, the method further comprises drying the film to remove the at least one organic solvent A2 used during preparation.

[0047] Therefore, preferably, the method according to the present invention comprises the following steps:

[0048] - providing a solution C comprising said at least one fluoropolymer A1, said at least one organic solvent A2, said at least one alkali metal salt B1 and said at least one plasticizer B2;

[0049] - depositing the solution C on a support D to form a film;

[0050] - Drying the film thus obtained.

[0051] Preferably, solution C is obtained by mixing two different solutions, A and B. Solution A comprises the at least one fluoropolymer A1 and the at least one organic solvent A2. Solution B comprises the at least one alkali metal salt B1 and the at least one plasticizer B2. Solution B may further comprise an organic solvent. The organic solvent may be the organic solvent A2 or any other organic solvent capable of dissolving the alkali metal salt B1 and / or the plasticizer B2. Solutions A and B are then mixed to obtain solution C.

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

[0053] According to a preferred embodiment, the step of preparing said solution B is carried out at a temperature of 15°C to 90°C, preferably 15°C to 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 ranging from 15°C to 100°C, preferably from 15°C to 90°C.

[0055] The membrane drying step can be carried out at a temperature of 20 to 120° C., preferably 20 to 90° C., in particular 40 to 80° C. This step is usually carried out under extraction.

[0056] Fluoropolymer A1

[0057] The fluoropolymer A1 comprises monomer units containing at least one fluorine atom. According to a preferred embodiment, the fluoropolymer A1 contains in its chain at least one monomer selected from compounds containing a vinyl group capable of opening for polymerization and containing at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group directly attached to the vinyl group.

[0058] Preferably, the fluoropolymer A1 contains at least monomer units derived from the following monomers: 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); products of the formula CF2=CFOCF2CF(CF3)OCF2CF2X, where X is SO2F, CO2H, CH2OH, CH2OCN, or CH2OPO3H; products of the formula CF2=CFOCF2CF2SO2F; products of the formula F(CF2)nCH2OCF=CF2, where n is 1, 2, 3, 4, or 5; products of the formula R 1 The product of CH2OCF=CF2, where R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; Formula R 2 OCF=CH2 product, where R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropylene, tetrafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropylene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropylene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

[0059] In particular, the fluoropolymer A1 comprises at least monomer units derived from vinylidene fluoride. The fluoropolymer A1 may be a homopolymer or a copolymer. The copolymer may also contain non-fluorinated monomers.

[0060] According to one embodiment, the fluoropolymer A1 is a vinylidene fluoride homopolymer.

[0061] According to an alternative embodiment, the fluoropolymer A1 is a copolymer comprising monomer units derived from vinylidene fluoride and monomer units derived from at least one other comonomer copolymerizable with vinylidene fluoride. The comonomer compatible with vinylidene fluoride may be halogenated (fluorinated, chlorinated or brominated) or non-halogenated.

[0062] Thus, the fluoropolymer A1 comprises monomer units derived from vinylidene fluoride and monomer units derived from monomers 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); monomers of the formula CF2=CFOCF2CF(CF3)OCF2CF2X, where X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; monomers of the formula CF2=CFOCF2CF2SO2F; monomers of the formula F(CF2)nCH2OCF=CF2, where n is 1, 2, 3, 4 or 5; monomers of the formula R 1 CH2OCF=CF2 monomer, where R 1 is hydrogen or F(CF2)m and the value of m is 1, 2, 3 or 4; Formula R 2 OCF=CH2 monomer, where R 2 is F(CF2)p and p is 1, 2, 3, or 4; perfluorobutylethylene (PFBE); trifluoropropylene, tetrafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropylene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropylene, and 2-trifluoromethyl-3,3,3-trifluoro-1-propene, or mixtures thereof. Among the trifluoropropylenes, 3,3,3-trifluoropropylene may be mentioned. Among the tetrafluoropropylenes, 2,3,3,3-tetrafluoropropylene or 1,3,3,3-tetrafluoropropylene may be mentioned. Among the pentafluoropropylenes, 1,1,3,3,3-pentafluoropropylene or 1,2,3,3,3-pentafluoropropene may be mentioned. Chlorofluoroethylene may represent 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. The chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0063] Preferably, fluoropolymer A1 is a copolymer comprising monomer units derived from vinylidene fluoride and monomer units derived from a monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, and hexafluoropropylene, or a mixture thereof. Fluoropolymer A1 contains vinylidene fluoride units in an amount of at least 50% by mass, preferably at least 60% by mass, more preferably greater than 70% by mass, and advantageously greater than 80% by mass.

[0064] In particular, the fluoropolymer A1 is a copolymer comprising monomer units derived from vinylidene fluoride and monomer units derived from hexafluoropropylene; preferably, the mass content of monomer units derived from vinylidene fluoride is at least 50%, preferably at least 60%, more preferably greater than 70% and advantageously greater than 80%.

[0065] More specifically, the fluorine-containing polymer A1 is a copolymer comprising monomer units derived from vinylidene fluoride and monomer 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%.

[0066] According to one embodiment, the fluoropolymer A1 consists of a mixture of vinylidene fluoride homopolymer (PVDF) and at least one VDF copolymer, wherein the mass content of the PVDF homopolymer ranges from 0.1% to 20% based on the weight of the mixture.

[0067] According to one embodiment, the fluoropolymer A1 consists of a mixture of a PVDF homopolymer and a P(VDF-HFP) copolymer.

[0068] According to one embodiment, the fluoropolymer A1 consists of a mixture of two VDF copolymers having different structures.

[0069] According to a particular embodiment, the fluoropolymer A1 is fully or partially functionalized, which helps improve its adhesion to metals. Thus, the fluoropolymer A1 may comprise monomer units bearing at least one of the following functional groups: carboxylic acid, carboxylic anhydride, carboxylic ester, epoxy (such as glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenol, ester, ether, siloxane, sulfonic acid, sulfuric acid, phosphoric acid, and phosphonic acid; preferably at least one carboxylic acid or hydroxyl functional group.

[0070] According to techniques known to those skilled in the art, the functional groups are introduced by a chemical reaction which can be the grafting or copolymerization of a monomer unit containing a fluorine atom with a monomer containing at least one of said functional groups and a vinyl functional group capable of copolymerizing with the fluorine-containing monomer.

[0071] According to one embodiment, the functional group carries a carboxylic acid function which is a (meth)acrylic type group chosen from acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate and acryloyloxypropyl succinate.

[0072] According to one embodiment, the unit carrying a carboxylic acid function additionally comprises heteroatoms selected from oxygen, sulfur, nitrogen and phosphorus.

[0073] According to one embodiment, the functionality is introduced via a transfer agent used during the synthesis process. A transfer agent is a polymer having a molar mass of less than or equal to 20,000 g / mol and containing functional groups selected from the group consisting of carboxylic acid, carboxylic anhydride, carboxylic ester, epoxy (e.g., glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenol, ester, ether, siloxane, sulfonic acid, sulfuric acid, phosphoric acid, or phosphonic acid. Acrylic acid oligomers are examples of this type of transfer agent. According to a preferred embodiment, the transfer agent is an acrylic acid oligomer having a molar mass of less than or equal to 20,000 g / mol.

[0074] The content of functional groups in PVDF is at least 0.01 mol %, preferably at least 0.1 mol % and not more than 15 mol %, preferably not more than 10 mol %.

[0075] PVDF preferably has a high molecular weight. As used herein, the term "high molecular weight" refers to a PVDF having a molecular weight of 100 s at 232°C according to ASTM D-3835. -1 PVDF having a melt viscosity of greater than 100 Pa.s, preferably greater than 500 Pa.s, more preferably greater than 1000 Pa.s, measured at 400°C.

[0076] The PVDF homopolymer and VDF copolymer used in the present invention can be obtained by known polymerization methods, such as emulsion polymerization or suspension polymerization.

[0077] According to one embodiment, they are prepared by an emulsion polymerization process in the absence of fluorinated surfactants.

[0078] The polymerization of PVDF produces latex, and this latex has by weight from 10% to 60%, preferably from 10% to 50% solids content generally, and has less than 1 micron, preferably less than 1000 nm, preferably less than 800 nm and more preferably less than the weight average particle size of 600nm.The weight average size of particle is generally at least 20 nm, preferably at least 50 nm, and advantageously average size is in the scope of 100-400 nm.Polymer particles can form agglomerates, and their weight average size is 1 to 30 microns, preferably 2 to 10 microns.Agglomerates can be broken into discrete particles during preparation and being applied on substrate.

[0079] According to certain embodiments, the PVDF homopolymer and the VDF copolymer are composed of bio-based VDF. The term "bio-based" means "produced from biomass". This makes it possible to improve the ecological footprint of the polymer. Bio-based VDF can be characterized by a content of renewable carbon (i.e. carbon derived from natural sources of biomaterials or biomass) of at least 1 atomic %, as determined by standard NF EN 16640. 14The term "renewable carbon" means that the carbon is of natural origin and is derived from biological materials (or from biomass), as shown below. According to certain embodiments, the biochar content of VDF can 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%, and advantageously equal to 100%.

[0080] Organic solvent A2

[0081] The organic solvent A2 helps dissolve the fluoropolymer A1. Therefore, the organic solvent A2 has a donor number greater than 4 kcal / mol. Preferably, the organic solvent has a donor number greater than 5 kcal / mol. The donor number or donor index of a solvent is expressed as -ΔH value, where ΔH is the enthalpy of interaction between the solvent and antimony pentachloride (according to the method described in Journal of Solution Chemistry, Vol. 13, No. 9, 1984).

[0082] According to a preferred embodiment, the 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 and in particular greater than 10 kcal / mol.

[0083] According to a preferred embodiment, the donor number of the organic solvent A2 is 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, in a preferred manner less than 24 kcal / mol, in an advantageous preferred manner less than 23 kcal / mol, in a preferred manner less than 22 kcal / mol, in a more preferred manner less than 21 kcal / mol, and in a particularly preferred manner less than 20 kcal / mol.

[0084] Therefore, according to a preferred embodiment, the donor number of the organic solvent A2 is 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 27 kcal / mol, in particular less than 26 kcal / mol, more particularly less than 25 kcal / mol, in a preferred manner less than 24 kcal / mol, in an advantageous and preferred manner less than 23 kcal / mol, in a preferred manner less than 22 kcal / mol, in a more preferred manner less than 21 kcal / mol, in a particularly preferred manner less than 20 kcal / mol.

[0085] According to a particular embodiment, the donor number of the organic solvent A2 is between 5 and 30 kcal / mol, advantageously between 5 and 25 kcal / mol, preferably between 10 and 20 kcal / mol.

[0086] In order to also allow the preparation of a uniform film, i.e. a uniform thickness over the entire length of the coating, it is preferred to use a specific A2 organic solvent or A2 organic solvent mixture. The use of an organic solvent having a saturated vapor pressure as explained in the various embodiments below makes it possible to improve the quality of the produced film.

[0087] The organic solvent A2 has a saturated vapor pressure of less than 24 kPa at 20° C. According to a preferred embodiment, the organic solvent A2 has a saturated vapor pressure of less than 23 kPa at 20° C., advantageously less than 22 kPa, preferably less than 21 kPa, more preferably less than 20 kPa, 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.

[0088] According to a preferred embodiment, the organic solvent A2 has a saturated vapor pressure at 20° C. of greater than 7 Pa, advantageously greater than 8 Pa, preferably greater than 9 Pa, more preferably greater than 10 Pa, particularly greater than 25 Pa, more particularly greater than 50 Pa, preferably greater than 100 Pa, advantageously preferably greater than 500 Pa. This helps prevent excessively high residual solvent content in the produced film.

[0089] Therefore, the organic solvent A2 has a saturated vapor pressure of less than 24 kPa at 20° C. According to a preferred embodiment, the organic solvent A2 has a saturated vapor pressure of less than 23 kPa at 20° C., advantageously less than 22 kPa, preferably less than 21 kPa, more preferably less than 20 kPa, 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 preferably less than 12 kPa at 20° C.; and the organic solvent A2 has a saturated vapor pressure of greater than 7 Pa at 20° C., 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 preferably greater than 500 Pa at 20° C.

[0090] According to a preferred embodiment, the flash point of the at least one organic solvent A2 is higher than -15°C, advantageously higher than -14°C, preferably higher than -13°C, in particular higher than -12°C. Preferably, the flash point of the at least one organic solvent A2 is lower than 90°C, advantageously lower than 85°C, preferably lower than 80°C, in particular lower than 75°C. Thus, the flash point of the at least one organic solvent A2 may be higher than -15°C, advantageously higher than -14°C, preferably higher than -13°C, in particular higher than -12°C; and lower than 90°C, advantageously lower than 85°C, preferably lower than 80°C, in particular lower than 75°C. The flash point corresponds to the lowest temperature at which a combustible body emits sufficient vapor to form a gaseous mixture with the ambient air, which gaseous mixture ignites under the action of a heat source, but is insufficient for the combustion to sustain itself. The flash point defined here is the flash point measured in a closed cup.

[0091] According to a particular embodiment, the at least one organic solvent A2 has:

[0092] a donor number of 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 27 kcal / mol, in particular less than 26 kcal / mol, more particularly less than 25 kcal / mol, preferably less than 24 kcal / mol, advantageously preferably 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;

[0093] a saturated vapor pressure of less than 23 kPa at 20°C, advantageously less than 22 kPa, preferably less than 21 kPa, more preferably less than 20 kPa, 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 preferably less than 12 kPa at 20°C; and greater than 7 Pa at 20°C, advantageously greater than 8 Pa, preferably greater than 9 Pa, more preferably greater than 10 Pa, in particular greater than 25 Pa at 20°C, more particularly greater than 50 Pa, preferably greater than 100 Pa, advantageously preferably greater than 500 Pa at 20°C;

[0094] a flash point above -15°C, advantageously above -14°C, preferably above -13°C, in particular above -12°C; and below 90°C, advantageously below 85°C, preferably below 80°C, in particular below 75°C.

[0095] Furthermore, the at least one organic solvent A2 preferably has a water content by mass 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, and preferably less than 10 ppm. Preferably, the at least one organic solvent A2 has a water content by mass of greater than 1 ppb, more preferably greater than 10 ppb, and in particular greater than 100 ppb. A low water content in the solvent prevents degradation of other components present.

[0096] Described organic solvent A2 can be notably selected from ester, carbonate, nitrile or dinitrile, ether or diether, or ketone, provided that it has the donor number as provided in this patent application and the saturated vapor pressure as described in this patent application, and preferably the flash point as described in this patent application. Also can use these combinations as organic solvent.

[0097] As organic solvent A2 according to the present invention, mention may be made, by way of non-limiting examples, of the following: N,N-dimethylformamide, dimethyl sulfoxide, 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. esters, ethyl butyrate or methyl propionate, tetrahydrofuran, N-butyl-2-pyrrolidone or mixtures 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 butyrate or methyl propionate, or mixtures thereof.

[0098] Alkali metal salt B1

[0099] The alkali metal salt is selected from the following: LiCF3SO3, LiPF6, LiClO4, LiBF4, LiB(C2O4)2, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F3)2, LiN(SO2C2F5)2, LiN(SO2F)(SO 2CF3), LiN(SO2F)(SO2C2F5), LiN(SO2CF3)(SO2C2F5), LiAsF6, LiBF2C2O4, LiNO3, LiPF3(CF2CF3)3, LiBETI, LiTDI, NaTDI, KTDI, NaClO4, KClO4, 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 mixtures thereof. Preferably, the alkali metal salt is selected from the following: LiCF3SO3, LiPF6, LiClO4, 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.

[0100] Plasticizer B2

[0101] According to a preferred embodiment, the plasticizer B2 comprises at least one ionic liquid.

[0102] An ionic liquid is a salt that is liquid at ambient temperature, that is to say it has a melting point at atmospheric pressure of less than 100° C. It is formed by a combination of organic cations and anions whose ionic interactions are weak enough not to form a solid.

[0103] As examples of organic cations, the following may be mentioned: cations of ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidine, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium and mixtures thereof. According to one embodiment, the cation may comprise C1-C 30Alkyl, for example 1-butyl-1-methylpyrrolidinium, 1-ethyl-3-methylimidazolium, N-methyl-N-propylpyrrolidinium or N-methyl-N-butylpiperidinium.

[0104] According to one embodiment, the anions associated therewith are chosen from: imides, in particular bis(fluorosulfonyl)imide and bis(trifluoromethanesulfonyl)imide; borates; phosphates; phosphinates and phosphonates, notably alkylphosphonates; amides, notably dicyanamide; aluminates, notably tetrachloroaluminate; halide anions (e.g. bromide, chloride or iodide anions); cyanates; acetates (CH3COO-), notably trifluoroacetate; sulfonates, notably methanesulfonates (CH3SO3-) or trifluoromethanesulfonates; and sulfates, notably hydrogensulfates; acrylates or methacrylates.

[0105] According to one embodiment, the anion is selected from tetrafluoroborate (BF4-), bis(oxalato)borate (BOB-), hexafluorophosphate (PF6-), hexafluoroarsenate (AsF6-), trifluoromethanesulfonate or trifluoromethylsulfonate (CF3SO3-), bis(fluorosulfonyl)imide (FSI-), bis(trifluoromethanesulfonyl)imide (TFSI-), nitrate (NO3-) and 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI-), acrylate or methacrylate.

[0106] According to one embodiment, the anion of the ionic liquid is selected from TDI-, FSI-, TFSI-, PF6-, BF4-, NO3-, BOB- and CH2=CHCOO-. According to one embodiment, the anion of the ionic liquid is FSI-.

[0107] According to one embodiment, the plasticizer B2 is a mixture of at least two ionic liquids selected from those mentioned above.

[0108] According to one embodiment, the plasticizer B2 is a mixture of at least one ionic liquid and at least one solvent S1 having a boiling point above 100° C., preferably above 110° C., more preferably above 125° C., in particular above 150° C., more in particular above 160° C. According to one embodiment, the solvent S1 is selected from:

[0109] -vinylene carbonate (VC) (CAS: 872-36-6),

[0110] -Fluoroethylene carbonate or 4-fluoro-1,3-dioxolane-2-one (FEC or F1EC) (CAS: 114435-02-8),

[0111] - trans-4,5-difluoro-1,3-dioxolane-2-one (F2EC) (CAS: 171730-81-7),

[0112] -ethylene carbonate (EC) (CAS: 96-49-1),

[0113] -propylene carbonate (PC) (CAS: 108-32-7),

[0114] -(2-Cyanoethyl)triethoxysilane (CAS: 919-31-3),

[0115] -3-Methoxypropionitrile (CAS: 110-67-8),

[0116] -Sulfolane (CAS: 126-33-0),

[0117] -Triethyl phosphate (TEP) (CAS: 78-40-0),

[0118] -b-Butyrolactone (CAS: 96-48-0),

[0119] - ethers, such as polyethylene glycol dimethyl ethers, in particular diethylene glycol dimethyl ether (EG2DME), triethylene glycol dimethyl ether (EG3DME) and tetraethylene glycol dimethyl ether (EG4DME).

[0120] Plasticizers make it possible to obtain improved properties in terms of conductivity, electrochemical stability, thermal stability, compatibility with electrodes, and capacity retention compared to conventional liquid electrolytes.

[0121] Examples of plasticizers B2 according to the invention are the following mixtures:

[0122] -1-ethyl-3-methylimidazolium FSI and EC,

[0123] -1-ethyl-3-methylimidazolium FSI and tetraethylene glycol dimethyl ether,

[0124] -1-ethyl-3-methylimidazolium FSI and EC and FEC,

[0125] -1-butyl-1-methylpyrrolidinium FSI and tetraethylene glycol dimethyl ether,

[0126] -1-butyl-1-methylpyrrolidinium FSI and EC and FEC,

[0127] -N-propyl-N-methylpyrrolidinium and tetraethylene glycol dimethyl ether,

[0128] -1-ethyl-3-methylimidazolium TFSI and FEC,

[0129] -1-ethyl-3-methylimidazolium FSI,

[0130] -1-Butyl-1-methylpyrrolidinium FSI.

[0131] According to one embodiment, in the mixture of at least one ionic liquid and solvent S1, the mass ratio of ionic liquid to solvent forming said plasticizer B2 is from 10:0.1 to 0.1:10.

[0132] Carrier D

[0133] The 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 polyethylene terephthalate, polypropylene, aluminum or aluminum coated with a polymer layer, as non-limiting examples.

[0134] According to alternative embodiment, carrier D is fiber-reinforced material.This allows the film prepared by solution C to remain in place.Usually, when carrier is fiber-reinforced material, it is not removed.Fiber-reinforced material is made up of any material (porous membrane, woven fabric or nonwoven fabric) of the mechanical property that allows improvement.In a non-limiting manner, this can be polypropylene nonwoven fabric, polyethylene terephthalate nonwoven fabric, polyvinylidene fluoride nonwoven fabric or polypropylene microporous membrane.

[0135] Composition

[0136] According to another aspect, the present invention provides a composition for preparing a solid electrolyte. The composition corresponds to the solution C used in the above method. Preferably, the composition comprises the at least one fluoropolymer A1, the at least one organic solvent A2, the at least one alkali metal salt B1, and the at least one plasticizer B2; and the 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 a flash point preferably greater than -15°C, and a water content by mass of less than 5000 ppm based on the total weight of the composition.

[0137] Advantageously, the composition comprises 0.75% to 18% by weight of the at least one fluoropolymer A1, 75% to 95% by weight of the at least one organic solvent A2, 0.1% to 7.5% by weight of the at least one alkali metal salt B1 and 0.5% to 20% by weight of the 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 the 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 higher than -15° C.

[0138] Preferably, the composition comprises 0.75% to 18% by weight of the at least one fluoropolymer A1, 75% to 95% by weight of the at least one organic solvent A2, 0.1% to 7.5% by weight of the at least one alkali metal salt B1 and 0.5% to 20% by weight of the at least one plasticizer B2, and a mass content of water greater than 1 ppb and less than 5000 ppm based on the total weight of the composition; and the 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 higher than -15° C.

[0139] In particular, the composition comprises 2.25% to 18% by weight of the at least one fluoropolymer A1, 75% to 85% by weight of the at least one organic solvent A2, 0.3% to 7.5% by weight of the at least one alkali metal salt B1 and 1.5% to 20% by weight of the 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 the 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 higher than -15° C.

[0140] More particularly, the composition comprises 2.25% to 18% by weight of the at least one fluoropolymer A1, 75% to 85% by weight of the at least one organic solvent A2, 0.3% to 7.5% by weight of the at least one alkali metal salt B1 and 1.5% to 20% by weight of the at least one plasticizer B2, and a mass content of water greater than 1 ppb and less than 5000 ppm, based on the total weight of the composition; and the 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 higher than -15° C.

[0141] The organic solvent A2 can be as described above. The fluorine-containing polymer A1 can be as described above. The alkali metal salt B1 can be as described above. The plasticizer B2 can be as described above.

[0142] Furthermore, the composition may have a water content by mass 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 less than 10 ppm, based on the total weight of the composition. Preferably, the composition may have a water content by mass of greater than 1 ppb, more preferably greater than 10 ppb, preferably greater than 100 ppb, in particular greater than 1 ppm, based on the total weight of the composition.

[0143] According to a preferred embodiment, the composition is -1 The invention has a solution viscosity of 100 to 50 000 cP.

[0144] membrane

[0145] According to another aspect, the present invention provides a membrane, preferably a non-porous membrane, i.e., a membrane having a porosity of less than 10%, more preferably less than 5%, and in particular less than 1%. The porosity of the membrane is obtained according to the following calculation described in the publication of M. Cai, Nature Communications, 10, 2019, 4597:

[0146] Where V ER Represents the actual volume of the membrane as calculated by multiplying the membrane surface area by the membrane thickness. denseER represents the volume that each component would occupy in the absence of any porosity and is calculated according to the following formula:

[0147] V denseER is the sum of the volumes occupied by each component of the membrane.

[0148] According to a preferred embodiment, the film comprises 15% to 70% by weight of the at least one fluoropolymer A1, 10% to 80% by weight of the plasticizer B2, 2% to 30% by weight of the alkali metal salt B1, and 1 ppb to 5000 ppm of water, based on the total weight of the film. The contents expressed herein relate to the film without considering the carrier D, i.e. after its removal. Preferably, the film also comprises 1 ppb to 15% of the at least one organic solvent A2. The film may comprise 20% to 70% of the at least one fluoropolymer A1, advantageously 25% to 70% of the at least one fluoropolymer A1, preferably 30% to 70% of the at least one fluoropolymer A1.

[0149] Thus, preferably, the membrane consists of 15% to 70% by weight of the at least one fluoropolymer A1, 10% to 80% by weight of the plasticizer B2, 2% to 30% by weight of the alkali metal salt B1, 1 ppb to 15% of the at least one organic solvent A2, and 1 ppb to 5000 ppm of water, based on the total weight of the membrane; the sum of said components being equal to 100. More preferably, the membrane consists of 20% to 70% by weight of the at least one fluoropolymer A1, 10% to 80% by weight of the plasticizer B2, 2% to 30% by weight of the alkali metal salt B1, 1 ppb to 15% of the at least one organic solvent A2, and 1 ppb to 5000 ppm of water, based on the total weight of the membrane; the sum of said components being equal to 100.

[0150] According to a preferred embodiment, the content of organic solvent A2 as defined in the present patent application in the film is from 1 ppb to 10%, more preferably from 1 ppb to 5%, in particular from 1 ppb to 1%, and more particularly from 1 ppb to 5000 ppm. More preferably, the content of organic solvent A2 as defined in the present patent application in the film 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%, and in particular from 10 ppb to 5000 ppm. In particular, the content of organic solvent A2 as defined in the present patent application in the film 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%, and in particular from 100 ppb to 5000 ppm.

[0151] In addition, in the membrane, 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 preferably 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.

[0152] Advantageously, the membrane contains little or no solvent and has high ionic conductivity. Advantageously, the membrane is self-supporting, meaning it can be handled without the aid of a support. Advantageously, the membrane is rollable, meaning it can be handled so that it can be rolled onto a reel.

[0153] According to an alternative embodiment, when the membrane comprises a fibrous reinforcement, the mass ratio between the membrane and the fibrous reinforcement is from 1.5 to 9.

[0154] According to one embodiment, the thickness of the film is from 5 μm to 60 μm, preferably from 5 μm to 30 μm, more preferably from 7 μm to 20 μm.

[0155] Advantageously, the membrane has a thickness that varies 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.

[0156] According to one embodiment, the membrane according to the invention has an ionic conductivity in the range of 0.01 to 5 mS / cm, preferably 0.05 to 5 mS / cm, advantageously 0.5 to 5 mS / cm at 25°C. The electrical conductivity is measured by electrochemical impedance spectroscopy. According to one embodiment, the non-porous membrane is placed between two gold electrodes in a sealed conductivity cell under an inert atmosphere (CESH, Biologic), and electrochemical impedance spectroscopy is performed between 1 Hz and 1 MHz with an amplitude of 10 mV. The resistance R of the membrane is then determined by linear regression of the curve -Im(Z)=f(Re(Z)). The electrical conductivity (conductivity) σ is then given by the following relationship:

[0157] where l is the thickness of the film and S is its surface area. For each composition, the conductivity value at a given temperature is obtained by taking the average of at least two measurements performed on different samples.

[0158] Advantageously, the membrane according to the invention has good electrochemical stability within a temperature range extending from -20°C to 80°C.

[0159] Advantageously, the membrane maintains its properties up to 80°C and does not ignite below 130°C.

[0160] According to one embodiment, the membrane according to the invention has a mechanical strength characterized by an elastic modulus measured by dynamic mechanical analysis at 1 Hz and 23° C. greater than 0.1 MPa, preferably greater than 1 MPa, more preferably greater than 10 MPa.

[0161] Another subject of the invention is a separator for all-solid-state batteries, consisting entirely or partly of said membrane. In this case, the presence of said lithium salt may be optional.

[0162] The present invention also relates to an electrochemical device selected from a battery, a capacitor, an electrochemical double layer capacitor and a membrane electrode assembly (MEA) for a fuel cell, or an electrochromic device, said device comprising the described separator.

[0163] Another subject of the present invention is an all-solid-state battery, such as a Li-ion battery, or a Li-S or Li-air battery, comprising a negative electrode, a positive electrode and a separator, wherein the separator comprises a membrane as described above.

[0164] According to one embodiment, the battery comprises a lithium metal anode.

[0165] The present invention also relates to an all-solid-state battery comprising such a membrane according to the invention, preferably a non-porous membrane.

[0166] Example

[0167] The following examples illustrate the scope of the present invention in a non-limiting manner.

[0168] Measuring the thickness of polymer electrolyte membranes

[0169] 20 mm diameter pellets were cut from the polymer electrolyte membrane to measure the mass and thickness of each pellet. The mass of the pellets was measured using a Mettler Toledo XPE105 balance with a reading accuracy of 0.01 mg. The thickness of the pellets was measured using a Mitutoyo IDH0530 digimatic comparator with a precision of 0.5 μm. These pellets were collected every 10 cm along the length of the coating. The mass and thickness of these pellets were as follows: Figure 1 shown.

[0170] Example 1 (Comparative): Membrane Preparation in the Presence of Acetone

[0171] 5.91 g of P(VDF-HFP) (poly(vinylidene fluoride)-co-hexafluoropropylene) was dissolved in 30 g of acetone (donor number = 17 kcal / mol; saturated vapor pressure = 24.7 kPa at 20°C) in a Thinky ARE 250 planetary mixer at room temperature. Separately, 0.47 g of LiFSI (lithium bis(fluorosulfonyl)amide) was dissolved in 5.48 g of EMIM-FSI (1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide). The latter solution was added to the P(VDF-HFP) solution and then mixed. The final solution was applied to a 13 μm thick, 30 cm wide aluminum strip using a coater with a doctor blade positioned 200 μm from the strip at a coating speed of 0.5 m / min. The coating was dried in an oven at 25°C for 2 hours to evaporate the acetone. A polymer electrolyte membrane of about 1.50 m in length and 10 cm in width was thus obtained.

[0172] from Figure 1It can be seen in Figure 5 that acetone is not a suitable solvent for preparing flexible electrolyte membranes because the thickness and quality of the membrane are not uniform along the length of the coating, with a variation of about 40% between the beginning and the end of the coating (over a length of 1.50 m).

[0173] Example 2 (Invention): Film Production in the Presence of 2-Butanone

[0174] 5.91 g of P(VDF-HFP) (poly(vinylidene fluoride)-co-hexafluoropropylene) was dissolved in 30 g of 2-butanone (donor number = 17.4 kcal / mol; saturated vapor pressure of 10.3 kPa at 20°C) in a Thinky ARE 250 planetary mixer at room temperature. Separately, 0.47 g of LiFSI (lithium bis(fluorosulfonyl)amide) was dissolved in 5.48 g of EMIM-FSI (1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide). The latter solution was added to the P(VDF-HFP) solution and then mixed. The final solution was applied to a 13 μm thick, 30 cm wide aluminum strip at a coating speed of 0.5 m / min using a coater with a doctor blade set at 200 μm from the aluminum strip. The coating was dried in an oven at 25°C for 2 hours to evaporate the acetone. A polymer electrolyte membrane of about 1.50 m in length and 10 cm in width was thus obtained.

[0175] 2-Butanone is a suitable solvent for preparing flexible electrolyte membranes because the thickness and quality of the membrane are relatively uniform along the length of the coating (e.g. Figure 1 and Figure 2 As shown, about 10% variation) as opposed to solvents such as acetone (about 50% variation along the length of the coating).

Claims

1. A method for preparing a solid electrolyte in the form of a membrane, comprising the following steps: - providing a solution C comprising at least one fluoropolymer A1, at least one organic solvent A2, at least one alkali metal salt B1 and at least one plasticizer B2; - depositing the solution C on a support D to form a film; - drying the film thus obtained; It is characterized by The at least one organic solvent A2 has a donor number greater than 4 kcal / mol and a saturated vapor pressure at 20° C. less than 24 kPa; and the at least one plasticizer B2 comprises at least one ionic liquid.

2. The method according to the preceding claim, characterized in that Solution C was obtained according to the following steps: - preparing a solution A comprising said at least one fluoropolymer A1 and said at least one organic solvent A2; - preparing 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. The method according to any one of the preceding claims, characterized in that The at least one organic solvent A2 has a flash point above -15°C.

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

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

6. The method according to any one of the preceding claims, characterized in that The at least one fluoropolymer A1 comprises monomer units derived from vinylidene fluoride and optional monomer units derived from monomers 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); products of the formula CF2=CFOCF2CF(CF3)OCF2CF2X, where X is SO2F, CO2H, CH2OH, CH2OCN, or CH2OPO3H; products of the formula CF2=CFOCF2CF2SO2F; products of the formula F(CF2)nCH2OCF=CF2, where n is 1, 2, 3, 4, or 5; products of the formula R 1 The product of CH2OCF=CF2, where R 1 is hydrogen or F(CF2)m and the value of m is 1, 2, 3 or 4; Formula R 2 OCF=CH2 product, where R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropylene, tetrafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropylene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropylene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

7. The method according to any one of the preceding claims, characterized in that The at least one fluoropolymer A1 is a homopolymer of vinylidene fluoride or a copolymer comprising monomer units derived from vinylidene fluoride and monomer units derived from a monomer selected from trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene or a mixture thereof.

8. The method according to any one of the preceding claims, characterized in that The at least one alkali metal salt B1 is selected from the group consisting of: LiCF3SO3, LiPF6, LiClO4, 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), LiBETI, LiTDI, NaTDI, KTDI, NaCl O4, KClO4, 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 mixtures thereof.

9. The method according to any one of the preceding claims, characterized in that The at least one plasticizer B2 is an ionic liquid comprising an anion selected from tetrafluoroborate (BF4-), bis(oxalato)borate BOB-, hexafluorophosphate (PF6-), hexafluoroarsenate (AsF6-), trifluoromethanesulfonate or trifluoromethylsulfonate (CF3SO3-), bis(fluorosulfonyl)imide (FSI-), bis(trifluoromethanesulfonyl)imide (TFSI-), nitrate (NO3-), 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI-), acrylate or methacrylate; and an anion selected from ammonium, sulfonium, Cations of pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidine, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium and mixtures thereof; or the at least one plasticizer B2 is a mixture of at least one ionic liquid and at least one solvent S1 having a boiling point greater than 100° C., the solvent S1 being selected from vinylene carbonate, fluoroethylene carbonate, trans-4,5-difluoro-1,3-dioxolane-2-one, ethylene carbonate, propylene carbonate, (2-cyanoethyl)triethoxysilane, 3-methoxypropionitrile, cyclopentane and polyethylene glycol dimethyl ether.

10. The method according to any one of the preceding claims, characterized in that The membrane has a porosity of less than 10%.

11. The method according to any one of the preceding claims, characterized in that The film has a thickness that varies less than 20% throughout its length.

12. A composition for preparing a solid electrolyte, comprising at least one fluoropolymer A1, 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: The at least one organic solvent A2 has a donor number greater than 4 kcal / mol, a saturated vapor pressure of 7 to 24 kPa at 20° C., a flash point greater than −15° C., and a water content by mass less than 5000 ppm.

13. Composition according to the preceding claim, characterized in that The at least one fluoropolymer A1 is as defined in claim 6 or 7 , the at least one alkali metal salt B1 is as defined in claim 8 , and the at least one plasticizer B2 is as defined in claim 9 .

14. A membrane comprising, based on the total weight of the membrane, 15 to 70 wt% of at least one fluoropolymer A1, 10 to 80 wt% of one or more plasticizers B2 comprising at least one ionic liquid, 2 to 30 wt% of one or more alkali metal salts B1, and 1 ppb to 5000 ppm of water.

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

16. Membrane according to claim 14 or 15, characterized in that The membrane consists of 15% to 70% by weight of at least one fluoropolymer A1, 10% to 80% by weight of one or more plasticizers B2 comprising at least one ionic liquid, 2% to 30% by weight of one or more alkali metal salts B1, 1 ppb to 15% of the at least one organic solvent A2, and 1 ppb to 5000 ppm of water, based on the total weight of the membrane; the sum of the components being equal to 100.

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

18. Membrane 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. The membrane according to any one of claims 14 to 18, characterized in that The film has a thickness that varies less than 20% throughout its length.

20. The membrane according to any one of claims 14 to 19, characterized in that The membrane has a porosity of less than 10%.

21. A separator for a lithium ion rechargeable battery comprising the membrane according to any one of claims 14 to 20.

22. An electrochemical device selected from a battery, a capacitor, an electrochemical double layer capacitor and a membrane electrode assembly (MEA) for a fuel cell, or an electrochromic device, comprising a membrane according to any one of claims 14 to 20.

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

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

Images