Solid electrolyte for na-ion and k-ion battery

Abstract

The invention relates to a solid electrolyte composition which can be used to manufacture a film offering a very good compromise between ion conductivity, electrochemical stability, high-temperature stability and mechanical strength. This composition can be used in a separator or an electrode of Na-ion or K-ion batteries.

Description

[0001] DESCRIPTION

[0002] TITLE: SOLID ELECTROLYTE FOR NA-ION AND K-ION BATTERIES

[0003] FIELD OF INVENTION

[0004] The present invention relates generally to the field of electrical energy storage in secondary Na-ion and K-ion batteries. More specifically, the invention concerns a solid electrolyte composition exhibiting a very good compromise between ionic conductivity, electrochemical stability, high-temperature stability, and mechanical strength.

[0005] TECHNICAL BACKGROUND

[0006] Demand for lithium-ion batteries has increased in recent years due to their use in a wide variety of electronic devices, such as mobile phones and electric vehicles. However, lithium-based compounds are relatively expensive, and natural lithium sources are unevenly distributed and difficult to access, being located in only a small number of countries. Alternatives to lithium have been sought, and sodium-ion batteries have been developed for this purpose. Sodium is indeed very abundant and evenly distributed throughout the Earth's crust. It is also advantageously non-toxic and more economical.

[0007] A battery comprises at least one negative electrode or anode coupled to a copper current collector, one positive electrode or cathode coupled to an aluminum current collector, a separator, and an electrolyte. The electrolyte consists of an alkali metal salt mixed with a solvent chosen to optimize ion transport and dissociation. A high dielectric constant promotes ion dissociation, and therefore the number of ions available in a given volume, while low viscosity favors ion diffusion, which plays a crucial role, among other parameters, in the charging and discharging rates of the electrochemical system.

[0008] Rechargeable or secondary batteries are more advantageous than primary (non-rechargeable) batteries because the associated electrochemical reactions that occur at the positive and negative electrodes of the battery are reversible. The electrodes of secondary cells can be regenerated multiple times by applying an electric current. Numerous advanced electrode systems have been developed for storing electrical energy. Simultaneously, considerable effort has been devoted to developing electrolytes capable of enhancing the performance of electrochemical cells.

[0009] Located between the two electrodes, the separator acts as a mechanical and electronic barrier and an ionic conductor. Several categories of separators exist: dry polymer membranes, gelled polymer membranes, and micro- or macroporous separators impregnated with liquid electrolyte. The separator market is dominated by the use of polyolefins (Celgard). 9 or Hipore 9 ) produced by extrusion and / or stretching. The separators must simultaneously exhibit low thickness, optimal affinity for the electrolyte, and sufficient mechanical strength. Among the most interesting alternatives to polyolefins, polymers with better affinity for standard electrolytes have been proposed to reduce the internal resistance of the system, such as poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVDF), and poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-co-HFP)).

[0010] Liquid electrolytes composed of solvent(s), alkali metal salt(s) and additive(s) have good ionic conductivity but are liable to leak or catch fire if the battery is damaged.

[0011] The use of solid electrolytes overcomes these difficulties by avoiding the use of flammable liquid components. The advantage of solid or semi-solid electrolytes is also that they allow the use of metallic sodium or potassium at the negative electrode, preventing the formation of dendrites that can cause short circuits during cycling. The use of metallic sodium or potassium results in increased energy density compared to insertion or alloy negative electrodes.

[0012] However, solid electrolytes are generally less conductive than liquid electrolytes. The challenge with solid electrolytes is to achieve a balance between high ionic conductivity, good electrochemical stability, and sufficient temperature resistance. The ionic conductivity must be equivalent to that of liquid electrolytes.

[0013] There is still a need to develop new solid electrolytes that offer a good compromise between ionic conductivity, electrochemical stability and temperature resistance, and that are suitable for simplified implementation, compatible with industrial application.

[0014] The invention therefore aims to remedy at least one of the drawbacks of the prior art, namely to offer a solid electrolyte composition with performance at least equivalent to that of a liquid electrolyte.

[0015] The invention also relates to a film or gel consisting of said composition having good mechanical strength, ionic conductivity and electrochemical stability properties.

[0016] The invention also aims to provide at least one method for manufacturing this film.

[0017] Another object of the invention is a separator, particularly for a secondary Na-ion or K-ion battery, consisting, in whole or in part, of said film. This separator can also be used in a battery, a capacitor, an electrochemical double-layer capacitor, a membrane-electrode assembly (MEA) for a fuel cell, or an electrochromic device. Another object of the invention aims to provide an electrode containing said solid electrolyte composition.

[0018] Finally, the invention aims to provide rechargeable Na-ion or K-ion secondary batteries comprising said separator or said electrode.

[0019] SUMMARY OF THE INVENTION

[0020] According to a first aspect, the present invention relates to a solid electrolyte composition comprising, preferably consisting of: a) at least one fluoropolymer PI, b) at least one ionic liquid, and c) at least one sodium or potassium salt. In a preferred embodiment, said composition also comprises at least one plasticizer. In a preferred embodiment, said at least one fluoropolymer PI has a melt viscosity of between 0.1 and 50 kP, advantageously between 0.5 and 45 kP, preferably between 1 and 45 kP, more preferably between 5 and 45 kP, in particular between 10 and 45 kP, more particularly between 15 and 45 kP, measured according to ASTM D-3835 method measured at 232°C and 100 seconds. 1 .

[0021] According to a preferred embodiment, said fluorinated polymer PI comprises repeating units from a monomer Mla selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(l,3-dioxole); perfluoro(2,2-dimethyl-l,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 the formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of the formula R 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture of these.

[0022] According to a preferred embodiment, said fluorinated polymer PI comprises repeating units from the monomer Mla and repeating units from a monomer Mlb or repeating units from a non-fluorinated monomer Mlc or a mixture of repeating units from said monomer Mlb and Mlc; said monomer Mla being vinylidene fluoride; said monomer Mlb selected from the group consisting of vinyl fluoride, trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(l,3-dioxole); perfluoro(2,2-dimethyl-l,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=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R; 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof; said non-fluorinated monomer Mlc being selected from the group consisting of a monomer of formula R 1 R 2 C=C(R 3 )((X 1 ) P HORN 4 ) in which the R substituents 1 , R 2 and R 3 are independently selected from the group consisting of H, CO2H and Ci-C5alkyl; R 4is selected from the group consisting of - NHC(CH3)2CH2C(O)CH3OU -OR 5 with R 5 selected from the group consisting of H and Ci-Ci8alkyl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2, -OC(O)R groups 6 , - C(O)OR 6 or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; R 6 being selected from the group consisting of Ci-C6alkyl or C6-Ci2aryl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2 group(s); p is 0 or 1; X 1 is selected from the group consisting of — [-C(O)OC(R 7 (R s )C(R 9 (R 10 )-] w i- and a C1-C10 alkyl hydrocarbon group optionally bearing one or more -OH, -CO2H or ester group(s); with wl being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R 7 , R8 , R 9 , R 10 are independently of each other, independently for each wl unit, selected from the group consisting of H and C1-C5 alkyl.

[0023] According to a preferred embodiment, said at least one PI polymer comprises repeating units from a monomer Mla being vinylidene fluoride and repeating units from a monomer Mlb selected from the group consisting of trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, hexafluoropropene and tetrafluoroethylene, or a mixture thereof.

[0024] According to a preferred embodiment, said polymer PI comprises repeating units from monomer Mla and repeating units from monomer Mlb; said monomer Mla being vinylidene fluoride and said monomer Mlb being hexafluoropropene; said polymer PI having a mass content of hexafluoropropene greater than or equal to 1%, advantageously greater than or equal to 3%, preferably greater than or equal to 8%, and less than or equal to 45%, advantageously less than or equal to 40%, preferably less than or equal to 35%, more preferably less than or equal to 30%, in particular less than or equal to 25%, more particularly less than 20% on the basis of the total weight of said polymer PI.

[0025] According to a preferred embodiment, said at least one ionic liquid comprises an anion selected from bis(oxalato)borate BOB', hexafluorophosphate (PF6), hexafluoroarsenate (AsF6), triflate or trifluoromethylsulfonate (CF3SO3), bis(fluorosulfonyl)imide (FSI), bis-(trifluoromethanesulfonyl)imide (TFSI), nitrate (NO3) and 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) and preferably, said ionic liquid comprises a cation selected from the list: ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and mixtures thereof.

[0026] According to a preferred embodiment, said at least one plasticizer having a boiling point above 150°C, preferably said plasticizer is selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, sulfolane, trans-4,5-difluoro-1,3-dioxolan-2-one, ethylene carbonate, propylene carbonate, (2-cyanoethyl)triethoxysilane, 3-methoxypropionitrile, polyethylene glycol dimethyl ethers and triethyl phosphate.

[0027] According to a preferred embodiment, said sodium or potassium salt is selected from the group consisting of NaCF3SO3, NaPF6, NaB(C2O4)2, NaN(SO2F)2, NaN(SO2CF3)2, NaN(SO2C2F3)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2CF2CF3), NaN(SO2CF3)(SO2CF2CF3), NaAsF6, NaBF2C2O4, NaNO3, NaPF3(CF2CF3)3, NaTDI, KCF3SO3, KPF6, KB(C2O4)2, KN(SO2F)2, KN(SO2CF3)2, KN(SO2C2F3)2, KN(SO2CF2CF3)2, KN(SO2F)(SO2CF3), KN(SO2F)(SO2CF2CF3), KN(SO2CF3)(SO2CF2CF3), KAsFe, KBF2C2O4, KNO3, KPF3(CF2CF3)3 and KTDI or a mixture of these.

[0028] According to a preferred embodiment, said composition comprises, preferably consists of: a) 10 to 60% by weight of fluoropolymer PI, b) 10 to 80% by weight of ionic liquid(s) and optionally of at least one plasticizer and c) 2 to 30% by weight of sodium or potassium salt(s), based on the total weight of the composition, preferably the sum of the three components a), b) and c) is 100%.

[0029] According to another aspect, the present invention relates to a non-porous film comprising, preferably consisting of, the solid electrolyte composition according to the present invention.

[0030] According to a preferred embodiment, said film has a solvent content (or solvents) with a boiling point below 150°C of less than 1% by weight, advantageously less than 0.1%, preferably less than 100 ppm, in particular less than 10 ppm.

[0031] 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.

[0032] According to another aspect, the present invention relates to a solvent-based method for preparing the film according to the present invention, said method comprising the following steps:

[0033] - solubilize said at least one PI fluorinated polymer at room temperature in a solvent selected from: n-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl formamide, methyl ethyl ketone, ethyl acetate, cyclopentanone and acetone;

[0034] - dissolve said at least one sodium or potassium salt in said ionic liquid and optionally said plasticizer, to obtain a sodium or potassium salt solution;

[0035] - mix the solutions of fluorinated polymer PI and sodium or potassium salt,

[0036] - place the resulting mixture onto a surface,

[0037] - dry at a temperature below 60°C.

[0038] According to another aspect, the present invention relates to a method for preparing the film according to the present invention by extrusion, said method comprising the following steps:

[0039] - mix said fluoropolymer PI and optionally said plasticizer at room temperature,

[0040] - introduce the resulting mixture into an extruder heated to 120-180°C,

[0041] - Add the sodium or potassium salt dissolved in the ionic liquid, and homogenize.

[0042] - extrude the mixture through a flat die, advantageously 300 µm thick,

[0043] - calender to obtain a film, preferably with a thickness of 5 to 50 µm.

[0044] According to another aspect, the present invention relates to a method for preparing the film according to the present invention by hot pressing, said method comprising the following steps: - mixing said fluorinated polymer PI, ionic liquid(s), plasticizer(s) and sodium or potassium salt(s) and optionally said at least one plasticizer,

[0045] - homogenize the said mixture,

[0046] - to place the said mixture between the two metal plates of a heated press,

[0047] - Apply a pressure of 5 to 10 kN for 1 to 5 minutes at 100-150°C to obtain a film,

[0048] - Cool the film to room temperature.

[0049] According to another aspect, the present invention relates to a separator for rechargeable Na-ion or K-ion battery, comprising the film according to the present invention.

[0050] According to another aspect, the present invention relates to an electrochemical device selected from the group: batteries, capacitor, electrochemical double-layer electrical capacitor, and membrane-electrode assembly (MEA) for fuel cell or an electrochromic device, said device comprising a separator according to the present invention.

[0051] According to another aspect, the present invention relates to a secondary Na-ion or K-ion battery comprising an anode, a cathode and a separator, in which said separator comprises the film according to the present invention.

[0052] In another aspect, the present invention relates to an electrode comprising an active material, a solid electrolyte composition according to the present invention, and optionally a conductive material. In a preferred embodiment, said active material is selected from the group consisting of: an active material for the cathode selected from the group consisting of an active material which may have the formula Na x M y 02 or K x M y O2 with M comprising at least one metal or a mixture of metals, x is between 0 and 1, y is between 0 and 1; or of the formula NaFePC, Na 3 2(PO4)3, NaMnPO4, NaCoPO4, NaTi2(PO4)3, Na2FeP2O7, Na2MnP2O7, Na2CoP2O7, Na7V3(P2O7)4, KFePO4, K3V2(PO4)3, KMnPO4, KCoPO4, KTi2(PO4)3, K2FeP2O7, K2MnP2O7, K2CoP2O7, K7V3(P2O7)4; an active material for anode selected from the group consisting of graphite, soft carbon, hard carbon, sodium metal, potassium metal, sodium alloy, potassium alloy, Na2Ti3O7, Na4Ti5O2, NaTi2(PO4)3, FeSe2, SnO2, FES, Sn, Sn3P4, phosphorus, Fe2O3, MoS2, SnS2, NiS2, Sb, K2Ti3O7, K2Ti4O9, K4Ti5O 12 , K2Ti8O 17 , KTi2(PO4)3.

[0053] The present invention overcomes the drawbacks of the prior art. More specifically, it provides a solid electrolyte composition suitable for use in a separator or electrode. For example, in the separator, this solid electrolyte composition is in the form of a film exhibiting high ionic conductivity, good electrochemical stability, temperature resistance, and sufficient mechanical strength to allow for easy handling of the separator. Like liquid electrolytes, the solid electrolyte according to the invention can be used in a battery with a graphite or hard carbon anode. However, its resistance to dendrite growth on the anode surface also allows for the use of a sodium metal or potassium metal anode, thus increasing energy density.

[0054] DESCRIPTION OF METHODS OF IMPLEMENTING THE INVENTION

[0055] The invention is now described in more detail and in a non-limiting manner in the following description. According to a first aspect, the invention relates to a solid electrolyte composition comprising: a) at least one PI fluorinated polymer, b) at least one ionic liquid, and c) at least one sodium or potassium salt.

[0056] According to a preferred embodiment, the invention relates to a solid electrolyte composition consisting of: a) at least one PI fluorinated polymer, b) at least one ionic liquid, and c) at least one sodium or potassium salt.

[0057] According to various embodiments, the film comprises the following characteristics, possibly in combination. The stated contents are expressed by weight, unless otherwise indicated. The stated concentration ranges include the limits, unless otherwise indicated.

[0058] Component a)

[0059] Said fluorinated polymer PI comprises in its chain at least repeating units derived from a fluorinated monomer Mla selected 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.Preferably, said fluorinated polymer PI comprises repeating units from a monomer Mla selected from the group consisting of vinyl fluoride, vinylidene fluoride, 1,2-difluoroethylene, hexafluoropropylene, trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(l,3-dioxole); perfluoro(2,2-dimethyl-l,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=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R. 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2is F(CF2)p and p is 1, 2, 3, or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene, and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof. Examples of trifluoropropene include 3,3,3-trifluoropropene. Examples of tetrafluoropropene include 2,3,3,3-tetrafluoropropene and 1,3,3,3-tetrafluoropropene. Examples of pentafluoropropene include 1,1,3,3,3-pentafluoropropene and 1,2,3,3,3-pentafluoropropene. Chlorofluoroethylene can refer to either 1-chloro-l-fluoroethylene or l-chloro-2-fluoroethylene. The 1-chloro-l-fluoroethylene isomer is preferred. Chlorotrifluoropropene is preferably l-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0060] In said fluorinated polymer PI, the mass percentage of repeating units Mla is at least 50%, preferably at least 60%, more preferably greater than 70% and advantageously greater than 80%, on the basis of the total weight of said fluorinated polymer PI.

[0061] In particular, said fluorinated polymer PI comprises at least repeating units derived from a monomer Mla being vinylidene fluoride. Preferably, in said fluorinated polymer PI, when the fluorinated monomer Mla is vinylidene fluoride, the mass percentage of vinylidene fluoride repeating units in said fluorinated polymer PI is at least 50%, preferably at least 60%, more preferably greater than 70%, and advantageously greater than 80%, based on the total weight of said fluorinated polymer PI.

[0062] The fluorinated polymer PI can be a homopolymer or a copolymer of vinylidene fluoride.

[0063] According to a particular embodiment, the PI fluorinated polymer is a vinylidene fluoride homopolymer.

[0064] According to another particular embodiment, the fluorinated polymer PI is a polymer comprising repeating units from a monomer Mla being vinylidene fluoride and repeating units from a fluorinated monomer Mlb copolymerizable with vinylidene fluoride, or repeating units from a non-fluorinated monomer Mlc or a mixture of the two.

[0065] According to one embodiment, said fluorinated polymer PI comprises repeating units from a monomer Mla being vinylidene fluoride and repeating units from a fluorinated monomer Mlb selected from the group consisting of vinyl fluoride, 1,2-difluoroethylene, hexafluoropropylene (HFP), trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(l,3-dioxole); perfluoro(2,2-dimethyl-l,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of the formula CF2=CFOCF2CF2SO2F; the product of the formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of the formula R 1 CH2OCF=CF2 in which R 1is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, pentafluoropropene, bromotrifluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof. Preferably, the fluorinated polymer PI comprises repeating units from a monomer Mla being vinylidene fluoride and repeating units from a fluorinated monomer Mlb selected from the group consisting of vinyl fluoride, 1,2-difluoroethylene, tetrafluoroethylene, trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, perfluoro(alkyl vinyl)ethers such as perfluoro(methyl vinyl)ether, perfluoro(ethyl vinyl)ether or perfluoro(propyl vinyl)ether; perfluoro(l,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole); 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=CF2 in which n is 1, 2, 4 or 5; the product of formula R'CH2OCF=CF2 in which R' is hydrogen or F(CF2)z and z is 1, 2, 3 or 4; the product of formula R"OCF=CH2 in which R" is F(CF2)z and z is 1, 2, 3 or 4; or a mixture thereof. In particular, the fluorinated polymer PI comprises repeating units from a monomer Mla being vinylidene fluoride and repeating units from a fluorinated monomer Mlb selected from the group consisting of 1,2-difluoroethylene, trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene and hexafluoropropylene or a mixture thereof.

[0066] The said PI polymer may be a copolymer of vinylidene fluoride and at least one monomer Mlb. The mass content of said at least one monomer Mlb may be greater than or equal to 1%, advantageously greater than or equal to 3%, preferably greater than or equal to 8%, and less than or equal to 45%, advantageously less than or equal to 40%, preferably less than or equal to 35%, based on the total weight of said PI polymer.

[0067] The said PI polymer may be a copolymer of vinylidene fluoride and hexafluoropropene. The mass content of hexafluoropropene may be greater than or equal to 1%, advantageously greater than or equal to 3%, preferably greater than or equal to 8%, and less than or equal to 45%, advantageously less than or equal to 40%, preferably less than or equal to 35%, more preferably less than or equal to 30%, in particular less than or equal to 25%, more particularly less than 20% on the basis of the total weight of said PI polymer.

[0068] Preferably, said fluorinated PI polymer comprises repeating units from a monomer Mla being vinylidene fluoride and repeating units from a fluorinated monomer Mlb selected from the group consisting of trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, hexafluoropropene and tetrafluoroethylene or a mixture thereof.

[0069] The said PI polymer may in particular be a copolymer of vinylidene fluoride and trifluoroethylene, a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and chlorotrifluoroethylene, a terpolymer of vinylidene fluoride, chlorotrifluoroethylene and tetrafluoroethylene, a terpolymer of vinylidene fluoride, chlorotrifluoroethylene and trifluoroethylene, a terpolymer of vinylidene fluoride, trifluoroethylene and hexafluoropropene, a terpolymer of vinylidene fluoride, tetrafluoroethylene and 1,1-chlorofluoroethylene or a terpolymer of vinylidene fluoride, hexafluoropropene and tetrafluoroethylene. In the PI polymer, the molar content of vinylidene fluoride may be at least 10 mol%, advantageously at least 20 mol%, preferably at least 30 mol%, more preferably at least 40 mol%, in particular at least 50 mol%, more particularly at least 55 mol%.Preferably, the molar content of vinylidene fluoride can be between 55 and 99 mol%, advantageously between 55 and 95 mol%, preferably between 60 and 90 mol%, in particular between 60 and 90 mol%.

[0070] In the PI polymer, the molar content of trifluoroethylene may be at least 1 mol%, advantageously at least 5 mol%, preferably at least 7 mol%, more preferably at least 10 mol%, in particular at least 12 mol%, more particularly at least 15 mol%. Preferably, the molar content of trifluoroethylene may be between 15 and 50%, advantageously between 17 and 45 mol%, preferably between 20 and 40 mol%, in particular between 20 and 35 mol%, more particularly between 20 and 30 mol%.

[0071] In the PI polymer, the molar content of chlorotrifluoroethylene may be at least 0.5 mol%, advantageously at least 1 mol%, preferably at least 2 mol%, more preferably at least 3 mol%, in particular at least 4 mol%, more particularly at least 5 mol%. Preferably, the molar content of chlorotrifluoroethylene may be between 1 and 20%, advantageously between 2 and 17 mol%, preferably between 3 and 15 mol%, in particular between 4 and 15 mol%, more particularly between 5 and 12 mol%.

[0072] In the PI polymer, the molar content of tetrafluoroethylene may be at least 1 mol%, advantageously at least 5 mol%, preferably at least 7 mol%, more preferably at least 10 mol%, in particular at least 15 mol%, more particularly at least 20 mol%. Preferably, the molar content of tetrafluoroethylene may be between 1 and 60%, advantageously between 2 and 55 mol%, preferably between 5 and 50 mol%, in particular between 7 and 45 mol%, more particularly between 10 and 40 mol%.

[0073] In the PI polymer, the molar content of 1,1-chlorofluoroethylene may be at least 0.5 mol%, advantageously at least 1 mol%, preferably at least 2 mol%, more preferably at least 3 mol%, in particular at least 4 mol%, more particularly at least 5 mol%. Preferably, the molar content of 1,1-chlorofluoroethylene may be between 1 and 20%, advantageously between 2 and 17 mol%, preferably between 3 and 15 mol%, in particular between 4 and 15 mol%, more particularly between 5 and 12 mol%.

[0074] In a copolymer of vinylidene fluoride and trifluoroethylene, the molar content of vinylidene fluoride may be between 60 and 99 mol%, advantageously between 65 and 95 mol%, preferably between 65 and 90 mol%, more preferably between 68 and 85 mol%, particularly between 70 and 82 mol%, and more particularly between 73 and 82 mol%; and the molar content of trifluoroethylene may be between 1 and 40 mol%, advantageously between 5 and 35 mol%, preferably between 10 and 35 mol%, more preferably between 15 and 32 mol%, particularly between 18 and 30 mol%, and more particularly between 18 and 27 mol%. In the most preferred proportions, the copolymer possesses ferroelectric and ferroelectric relaxor properties.

[0075] In a copolymer of vinylidene fluoride and tetrafluoroethylene, the molar content of vinylidene fluoride may be between 40 and 99 mol%, advantageously between 45 and 95 mol%, preferably between 50 and 90 mol%, more preferably between 55 and 85 mol%; and the molar content of tetrafluoroethylene may be between 1 and 60 mol%, advantageously between 5 and 55 mol%, preferably between 10 and 50 mol%, more preferably between 15 and 45 mol%.

[0076] In a copolymer of vinylidene fluoride and chlorotrifluoroethylene, the molar content of vinylidene fluoride may be between 60 and 99 mol%, advantageously between 65 and 98 mol%, preferably between 65 and 97 mol%, more preferably between 70 and 96 mol%, in particular between 75 and 95 mol%; and the molar content of trifluoroethylene may be between 1 and 40 mol%, advantageously between 2 and 35 mol%, preferably between 3 and 35 mol%, more preferably between 4 and 30 mol%, in particular between 5 and 25 mol%.

[0077] In a terpolymer of vinylidene fluoride, chlorotrifluoroethylene and tetrafluoroethylene, the molar content of vinylidene fluoride may be between 20 and 98 mol%, advantageously between 35 and 90 mol%, preferably between 50 and 90 mol%; and the molar content of tetrafluoroethylene may be between 1 and 50 mol%, advantageously between 5 and 50 mol%, preferably between 5 and 40 mol%; and the molar content of chlorotrifluoroethylene may be between 1 and 30 mol%, advantageously between 1 and 15 mol%, preferably between 1 and 12 mol%.

[0078] In a terpolymer of vinylidene fluoride, chlorotrifluoroethylene, and trifluoroethylene, the molar content of vinylidene fluoride may be from 20 to 98 mol%, advantageously from 35 to 90 mol%, preferably from 50 to 90 mol%; and the molar content of trifluoroethylene may be from 1 to 50 mol%, advantageously from 5 to 50 mol%, preferably from 5 to 40 mol%; and the molar content of chlorotrifluoroethylene may be from 1 to 30 mol%, advantageously from 1 to 15 mol%, preferably from 1 to 12 mol%. In the most preferred proportions, the copolymer possesses ferroelectric and ferroelectric relaxor properties.

[0079] In a terpolymer of vinylidene fluoride, trifluoroethylene and hexafluoropropene, the molar content of vinylidene fluoride may be between 20 and 98 mol%, advantageously between 35 and 90 mol%, preferably between 50 and 90 mol%; and the molar content of trifluoroethylene may be between 1 and 50 mol%, advantageously between 5 and 50 mol%, preferably between 5 and 40 mol%; and the molar content of hexafluoropropene may be between 1 and 30 mol%, advantageously between 1 and 15 mol%, preferably between 1 and 12 mol%.

[0080] In a terpolymer of vinylidene fluoride, tetrafluoroethylene and 1,1-chlorofluoroethylene, the molar content of vinylidene fluoride may be between 20 and 98 mol%, advantageously between 35 and 90 mol%, preferably between 50 and 90 mol%; and the molar content of tetrafluoroethylene may be between 1 and 50 mol%, advantageously between 5 and 50 mol%, preferably between 5 and 40 mol%; and the molar content of 1,1-difluoroethylene may be between 1 and 30 mol%, advantageously between 1 and 15 mol%, preferably between 1 and 12 mol%.

[0081] In a terpolymer of vinylidene fluoride, trifluoroethylene, and 1,1-chlorofluoroethylene, the molar content of vinylidene fluoride may be from 20 to 98 mol%, advantageously from 35 to 90 mol%, preferably from 50 to 90 mol%; and the molar content of trifluoroethylene may be from 1 to 50 mol%, advantageously from 5 to 50 mol%, preferably from 5 to 40 mol%; and the molar content of 1,1-chlorofluoroethylene may be from 1 to 30 mol%, advantageously from 2 to 15 mol%, preferably from 4 to 12 mol%. In the most preferred proportions, the copolymer possesses ferroelectric and ferroelectric relaxor properties.

[0082] In a terpolymer of vinylidene fluoride, hexafluoropropene and tetrafluoroethylene, the molar content of vinylidene fluoride may be between 20 and 98 mol%, advantageously between 35 and 90 mol%, preferably between 50 and 90 mol%; and the molar content of tetrafluoroethylene may be between 1 and 50 mol%, advantageously between 5 and 50 mol%, preferably between 5 and 40 mol%; and the molar content of hexafluoropropene may be between 1 and 30 mol%, advantageously between 1 and 15 mol%, preferably between 1 and 12 mol%.

[0083] The fluorinated polymer PI may also comprise repeating units derived from a monomer Mla, being vinylidene fluoride, and repeating units derived from a non-fluorinated monomer Mlc of formula R 1 R 2 C=C(R 3 )((X 1 ) P HORN 4 ) in which the R substituents 1 , R 2 and R 3are independently selected from the group consisting of H, CO2H and Ci-C5alkyl; R 4 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -OR 5 with R 5 selected from the group consisting of H and Ci-Cis alkyl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2, -OC(O)R group(s) 6 , -C(O)OR 6 OR a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; R 6 being selected from the group consisting of Ci-C6alkyl or C6-Ci2aryl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2 group(s); p is 0 or 1; X 1 is selected from the group consisting of — [-C(O)OC(R 7 (R s )C(R 9 (R 10 )-] wi- and an alkyl hydrocarbon group Ci-Cio optionally bearing one or more -OH, -CO2H or ester group(s); with wl being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R 7 , R 8 , R 9 , R 10are independently of each other, independently for each wl unit, selected from the group consisting of H and Ci-C5 alkyl. Said heterocycle may be saturated, unsaturated, or aromatic. Said heterocycle may be monocyclic or bicyclic. Said heterocycle may be a pyrrole, pyrrolidine, pyridine, piperidine, pyrimidine, pyrazine, 1,4-dihydropyridine, indole, oxindole, isatin, quinoline, isoquinoline, quinazoline, imidazoline, pyrazolidine, 2-pyrrolidone, delta-lactam, succinimide, 2-imidazolidinone, or 4-imidazolidinone ring. Said heterocycle may be substituted by one or more Ci-C5 alkyl groups. As mentioned above, the Ci-Cis alkyl is optionally substituted by said heterocycle. The latter can be linked to the alkyl chain by the nitrogen atom or any other atom forming the heterocycle. Preferably the heterocycle is 2-pyrrolidone, delta-lactam, succinimide, 2-imidazolidinone, 4-imidazolidinone.The said non-fluorinated monomer Mlc can have the formula R. 1 R 2 C=C(R 3 )((X 1 ) P HORN 4 ) in which the R substituents 1 , R 2 and R 3 are independently selected from the group consisting of H, CO2H and Ci-C5alkyl; R 4 is -OR 5 with R 5 selected from the group consisting of H and C1-C15 alkyl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2, -OC(O)R groups 6 , -C(O)OR 6 R 6 being selected from the group consisting of Ci-C6alkyl or C6-Ci2aryl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2 group(s); p is 0 or 1; X 1 is selected from the group consisting of — [-C(O)OC(R 7 (R s )C(R 9 (R 10 )-] wi- and an alkyl hydrocarbon group Ci-Cio optionally bearing one or more -OH, -CO2H or ester group(s); with wl being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R 7 , R 8 , R 9 , R 10 are independently of each other, independently for each wl unit, selected from the group consisting of H and Ci-C5 alkyl. Preferably, said non-fluorinated monomer Mlc may be of formula R 1 R 2 C=C(R 3 )((X 1 ) P HORN 4 ) in which the R substituents 1 , R 2 and R 3 are independently selected from the group consisting of H, CO2H and Ci-C5alkyl; R 4 is -OR 5 with R 5 selected from the group consisting of H and Ci-Cio alkyl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2, -OC(O)R group(s)6 , -C(O)OR 6 R 6 being selected from the group consisting of Ci-C6alkyl or C6-Ci2aryl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2 group(s); p is 0 or 1; X 1 is selected from the group consisting of -[- C(O)OC(R 7 (R 8 )C(R 9 (R 10 )-] w i- and an alkyl hydrocarbon group Ci-Cio optionally bearing one or more -OH, -CO2H or ester group(s); with wl being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R 7 , R 8 , R 9 , R 10 are independently of each other, independently for each wl unit, selected from the group consisting of H and Ci-C5alkyl. More preferably, said non-fluorinated monomer Mlc may have the formula R 1 R 2 C=C(R 3 )(HORN 4 ) in which the R substituents1 , R 2 and R 3 are independently selected from the group consisting of H, CO2H and Ci-C5alkyl; R 4 is -OR 5 with R 5 selected from the group consisting of H and Ci-Cio alkyl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2, -OC(O)R group(s) 6 , -C(O)OR 6 R 6 being selected from the group consisting of Ci-C6alkyl or C6-Ci2aryl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2 group(s). In particular, said non-fluorinated monomer Mlc may have the formula R 1 R 2 C=C(R 3 )(HORN 4 ) in which the R substituents 1 , R 2 and R 3 are independently selected from the group consisting of H, CO2H and Ci-C3alkyl; R 4 is -OR 5 with R 5selected from the group consisting of H and Ci-C5 alkyl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2, -OC(O)R group(s) 6 , -C(O)OR 6 R 6being selected from the group consisting of Ci-C6alkyl or C6-Ci2aryl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2 group(s). More specifically, said non-fluorinated monomer Mlc may be acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-dodecyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, diacetone acrylamide, lauryl acrylate, n-octyl acrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, methyl acrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, methacrylate n-butyl, isobutyl methacrylate, t-butyl methacrylate, n-dodecyl methacrylate,amyl methacrylate, isoamyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, n-octyl methacrylate, ureido methacrylate, monomers of formula CHz^HfCOzCHzCHjCOzH), CHz^HfCOzCHzCHz-O- OJ-CHzCHzCOzH), CH2=CH(CO2CH2CH2CH2-OC(O)-CH2CH2CO2H), ; CH2=CH(CO2CH(CH3)CH2-OC(O)-

[0084] CH2CH2CO2H) ; CH2=CH(CO2CH2CH2-OC(O)-C6H4CO2H) ; CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H); and mixtures thereof. Among these, said non-fluorinated monomer Mlc with an alkyl group having from 1 to 8 carbon atoms is preferred, and an alkyl group having from 1 to 5 carbon atoms is more preferable. Said fluorinated polymer PI may comprise one or more repeating units derived from said non-fluorinated monomer Mlc as defined herein.

[0085] According to another embodiment, said fluorinated polymer PI comprises repeating units from a monomer Mla being vinylidene fluoride, repeating units from a fluorinated monomer Mlb, repeating units from a non-fluorinated monomer Mlc; said monomers Mlb and Mlc being as defined above.For example, said fluorinated polymer PI comprises repeating units from a monomer Mla being vinylidene fluoride, repeating units from a fluorinated monomer Mlb being hexafluoropropene and repeating units from a non-fluorinated monomer Mlc selected from the group consisting of acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, hydroxypropyl methacrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, methyl acrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, the monomers of formula CH2=CH(CO2CH2CH2CC>2H), CH2=CH(CO2CH2CH2-O- C(O)-CH2CH2CO2H), CH2=CH(CO2CH2CH2CH2-OC(O)-CH2CH2CO2H), CH2=CH(CO2CH(CH3)CH2-OC(O)- CH2CH2CO2H),CH2=CH(CO2CH2CH2-OC(O)-C6H4CO2H), CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H); and mixtures of these.

[0086] According to a particular embodiment, the fluorinated PI polymer can be functionalized in whole or in part, thereby improving its adhesion to metal. Thus, said fluorinated PI polymer can comprise repeating units bearing 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.

[0087] The functional group is introduced by a chemical reaction, which may be grafting or copolymerization of the fluorinated monomer with another monomer (for example, the non-fluorinated monomer Mlc bearing at least one of the aforementioned functional groups and a vinyl group capable of copolymerizing with the fluorinated monomer, according to techniques well known to those skilled in the art). In one embodiment, the functional group bears a carboxylic acid group, which is a (meth)acrylic acid type group selected from acrylic acid, methacrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate, and acryloyloxy propylsuccinate. The units bearing the carboxylic acid group further comprise a heteroatom selected from oxygen, sulfur, nitrogen, and phosphorus.In one embodiment, the functionality can be introduced via the transfer agent used in the synthesis process. The transfer agent is a polymer with a molecular mass of 20,000 g / mol or less and bearing functional groups selected from the following: 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, and phosphonic groups. An example of such a transfer agent is acrylic acid oligomers. In a preferred embodiment, the transfer agent is an acrylic acid oligomer with a molecular mass of 20,000 g / mol or less. Alternatively, the functional group can be introduced by an oligomeric or polymeric compound comprising said functional group and mixed with the fluorinated polymer PI.The oligomeric or polymeric compound may be impregnated in, mixed with, or intimately blended with the fluorinated polymer PI. In this case, the functional group may be derived from a (meth)acrylic acid compound selected from acrylic acid, methacrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate, and acryloyloxy propylsuccinate. For example, the functional group may be an oligomer or a polymer comprising repeating units derived from a monomer selected from the group consisting of acrylic acid, methacrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate, and acryloyloxy propylsuccinate.According to one embodiment, the oligomer or polymer has a weight-average molecular weight less than or equal to 100,000 g / mol, advantageously less than 80,000 g / mol, preferably less than 60,000 g / mol, more preferably less than 40,000 g / mol, and in particular less than 20,000 g / mol. The weight-average molecular weight is determined by GPC using a Waters 2695e instrument coupled with a Wyatt NEON refractometer equipped with two PL Gel mixed C columns and a guard column (7.8 mm LD x 30 cm, 5 µm) under the following conditions: Temperature: 35°C; flow rate: 1.0 mL / min; injection volume: 100 µL. Samples are prepared at a concentration of 1 mg / mL in THF. Twelve samples of poly(methylmethacrylate) with a molecular mass ranging from 535 to 2,210,000 g / mol are used as calibration standards. This oligomer or polymer is preferably added during the production process of the fluorinated polymer PI.The functional group content of PVDF is at least 0.01 mol%, preferably at least 0.1 mol%, and at most 15 mol%, preferably at most 10 mol%.

[0088] Said PI fluorinated polymer preferably has a high molecular weight. By high molecular weight, as used here, is meant a PI fluorinated polymer 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 method measured at 232°C and 100 sec-1.

[0089] Preferably, said at least one fluoropolymer PI has a melt viscosity of between 0.1 and 50 kP, advantageously between 0.5 and 45 kP, preferably between 1 and 45 kP, more preferably between 5 and 45 kP, in particular between 10 and 45 kP, more particularly between 15 and 45 kP, measured according to ASTM D-3835 method measured at 232°C and 100 sec. 1 .

[0090] The fluorinated PI polymer used in the invention can be obtained by known polymerization methods such as emulsion or suspension polymerization. In a preferred embodiment, the fluorinated PI polymer is prepared by an emulsion polymerization process in the presence of a non-fluorinated surfactant. Thus, the fluorinated PI polymer may comprise between 10 ppm and 2 wt% of a non-fluorinated surfactant comprising polyethylene glycol or polypropylene glycol units. Preferably, the non-fluorinated surfactant has an HLB value of 1 to 20, in particular an HLB value of 1 to 5 or 10 to 15. In particular, the non-fluorinated surfactant comprises at least one polyethylene glycol segment and at least one polypropylene glycol segment, and has an HLB value of 1 to 5 and a weight-average molecular weight of 5000 to 10000 g·mol⁻¹.Alternatively, said surfactant comprises at least one segment of polyethylene glycol and at least one segment of polypropylene glycol, and has an HLB value of 10 to 15 and a weight average molecular weight of 500 to 2500 g.mol-1.

[0091] According to a preferred embodiment, said PI fluorinated polymer is prepared by a suspension polymerization process.

[0092] The fluorinated polymer (PI) may be in the form of 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 with a weight-average size of 1 to 30 micrometers, and preferably 2 to 10 micrometers. The agglomerates may break down into discrete particles during formulation and application to a substrate.

[0093] The fluoropolymer PI can be in powder form. This is obtained from latex which is subjected, for example, to a drying step and optionally to granulation.

[0094] In certain embodiments, the vinylidene fluoride contained in the fluorinated PI polymer is bio-based. The term "bio-based" means "derived from biomass." This improves the polymer's environmental footprint. The bio-based fluorinated PI polymer can be characterized by a renewable carbon content—that is, carbon of natural origin from a biomaterial or biomass—of at least 1 atomic percent, 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 comes from a biomaterial (or biomass), as described below.In some 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%. In one embodiment, said PI polymer is a statistical polymer. This type of polymer has the advantage of exhibiting a homogeneous distribution of the comonomer(s) along the vinylidene fluoride chains.

[0095] According to another embodiment, said PI polymer is a so-called "heterogeneous" polymer, which is characterized by a non-homogeneous distribution of a monomer along the VDF chains, due to the synthesis process described by the applicant, for example, in US document 6187885 or in US document 10570230. A heterogeneous polymer has two (or more) distinct phases, with a phase rich in homopolymer PVDF and a polymer phase rich in one of the monomers.

[0096] A heterogeneous polymer can consist of discrete, discontinuous copolymer domains of comonomer-rich phases, homogeneously distributed within a continuous PVDF-rich phase. This is referred to as a non-continuous structure. Alternatively, a heterogeneous polymer can have two (or more) continuous phases that are intimately bonded and cannot be physically separated. This is referred to as a co-continuous structure.

[0097] According to a particular embodiment, said heterogeneous polymer comprises two or more co-continuous phases comprising: a) 25 to 50 percent by weight of a first co-continuous phase comprising 90-100 percent by weight of vinylidene fluoride monomer motifs and 0 to 10 percent by weight of motifs of other fluoromonomers, and b) more than 50% by weight to 75% by weight of a second co-continuous phase comprising 65 to 95% by weight of vinylidene fluoride monomer motifs and an effective amount of one or more comonomers, such as hexafluoropropylene and perfluorovinyl ether, to cause phase separation of the second co-continuous phase from the first continuous phase.The heterogeneous polymer can be manufactured by forming an initial polymer rich in VDF monomer units, typically exceeding 90% by weight of VDF, preferably exceeding 95% by weight, and, in a preferred embodiment, a PVDF homopolymer. A co-monomer is then added to the reactor at a late stage of polymerization to produce a copolymer. The VDF-rich polymer and copolymer will form distinct phases, resulting in an intimate heterogeneous copolymer.

[0098] Component b)

[0099] The second component of the solid electrolyte composition of the invention is at least an ionic liquid.

[0100] 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 association of an organic cation and an anion whose ionic interactions are weak enough not to form a solid.

[0101] Examples of organic cations include ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and mixtures thereof. In one embodiment, this cation may comprise a C1-C30 alkyl group, such as 1-butyl-1-methylpyrrolidinium, 1-ethyl-3-methylimidazolium, N-methyl-N-propylpyrrolidinium, or N-methyl-N-butylpiperidinium.

[0102] 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 alkyl-phosphonates; 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.

[0103] According to one embodiment, the anions are chosen from bis(oxalato)borate (BOB), hexafluorophosphate (PF6), hexafluoroarsenate (AsF6), triflate or trifluoromethylsulfonate (CF3SO3'), bis(fluorosulfonyl)imide (FSI), bis-(trifluoromethanesulfonyl)imide (TFSI), nitrate (NO3) and 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI).

[0104] According to one embodiment, said anion of the ionic liquid is chosen from TDI', FSI', TFSI', PF6', NO3' and BOB'.

[0105] According to one embodiment, said anion of the ionic liquid is the FSI'.

[0106] Plasticizer

[0107] The said solid electrolyte composition may also include at least one plasticizer. Preferably, said at least one plasticizer forms a mixture with said at least one ionic liquid.

[0108] Component b) of the solid electrolyte composition of the invention also contains a plasticizer. Advantageously, the plasticizer is a solvent with a high boiling point (above 150°C). In one embodiment, the plasticizer is selected from:

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

[0110] - fluoroethylene carbonate or 4-fluoro-l,3-dioxolan-2-one (FEC or F1EC) (CAS: 114435-02-8),

[0111] - trans-4,5-difluoro-1,3-dioxolan-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, including diethylene glycol dimethyl ether (EG2DME), triethylene glycol dimethyl ether (EG3DME), and tetraethylene glycol dimethyl ether (EG4DME). Mixtures of at least one ionic liquid and at least one plasticizer provide improved conductivity, electrochemical stability, thermal stability, electrode compatibility, and capacitance retention compared to conventional liquid electrolytes.

[0120] Examples of component b) according to the invention are the following mixtures:

[0121] - l-ethyl-3-methylimidazolium-FSI and EC,

[0122] - l-ethyl-3-methylimidazolium-FSI and tetraethylene glycol dimethyl ether,

[0123] - l-ethyl-3-methylimidazolium-FSI and EC and FEC,

[0124] 1-butyl-l-methylpyrrolidinium-FSI and tetraethylene glycol dimethyl ether,- 1-butyl-l-methylpyrrolidinium-FSI and EC and FEC,

[0125] - N-propyl-N-methylpyrrolidinium and tetraethylene glycol dimethyl ether

[0126] - l-ethyl-3-methylimidazolium-TFSI and FEC,

[0127] - l-ethyl-3-methylimidazolium-FSI,

[0128] - 1-butyl-l-methylpyrrolidinium-FSI.

[0129] According to one embodiment, in the mixture, the mass ratio between the ionic liquids and the plasticizers forming compound b) varies from 10 to 0.1 to 0.1 to 10.

[0130] The presence of a plasticizer helps to improve the mechanical strength of said solid electrolyte composition and to prevent leakage of one of its constituents.

[0131] Component c)

[0132] Said sodium or potassium salt is selected from the group consisting of NaCF3SO3, NaPF6, NaCIO4, NaBF4, NaB(C2O4)2, NaN(SO2F)2, NaN(SO2CF3)2, NaN(SO2C2F3)2, NaN(SO2CF2CF3)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2CF2CF3), NaN(SO2CF3)(SO2CF2CF3), NaAsF6, NaBF2C2O4, NaNO3, NaPF3(CF2CF3)3, NaTDI, KCF3SO3, KPF6, KCIO4, KBF4, KB(C2O4)2, KN(SO2F)2, KN(SO2CF3)2, KN(SO2C2F3)2, KN(SO2CF2CF3)2, KN(SO2F)(SO2CF3), KN(SO2F)(SO2CF2CF3), KN(SO2CF3)(SO2CF2CF3), KAsFe, KBF2C2O4, KNO3, KPF3(CF2CF3)3 and KTDI or a mixture of these.

[0133] According to one embodiment, the sodium or potassium salt is selected from: NaCF3SO3, NaPF6, NaB(C2O4)2, NaN(SO2F)2, NaN(SO2CF3)2, NaN(SO2C2F3)2, NaN(SO2CF2CF3)2, NaAsF6, NaBF2C2O4, NaNO3, NaPF3(CF2CF3)3, NaTDI, KCF3SO3, KPF6, KB(C2O4)2, KN(SO2F)2, KN(SO2CF3)2, KN(SO2C2F3)2, KN(SO2CF2CF3)2, KAsF6, KBF2C2O4, KNO3, KPF3(CF2CF3)3 and KTDI, or a mixture thereof. Improved electrochemical stability can be achieved with the salts mentioned herein.

[0134] Solid electrolyte composition

[0135] The said solid electrolyte composition may also include inorganic particles selected from the group consisting of: BaTiO3, Pb(Zr,Ti)O3, Pbi. x There x Zr y O3(0 <x<l, 0<y<l), PbMg3Nb 2 / 3 O3, PbTiO3, hafnie (HfO, HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, Y2O3, bohemite (γ-AlO2(OH)), Al2O3, TiO2, SiC, ZrO2, SiO2, boron silicate, BaSO4, nano-clays, sodium lanthanum zirconium oxide), sodium aluminum titanium phosphate (e.g., Na3PO4, sodium titanate oxide, or mixtures thereof). The mass content of inorganic particles may be between 10 and 95% based on the total weight of said inorganic particles and said PI polymer.

[0136] The anion present in said sodium or potassium salt may be the same as that present in said ionic liquid. The anion present in said sodium or potassium salt may be different from that present in said ionic liquid.

[0137] According to one embodiment, the solid electrolyte composition comprises: a) 10 to 60% by weight of fluorinated polymer PI, b) 10 to 80% by weight of ionic liquid(s) and optionally at least one plasticizer, and c) 2 to 30% by weight of sodium or potassium salt(s); based on the total weight of the composition, preferably the sum of the three components a), b) and c) is 100%.

[0138] According to one embodiment, the solid electrolyte composition consists of: a) 10 to 60% by weight of PI fluorinated polymer, b) 10 to 80% by weight of ionic liquid(s) and optionally of at least one plasticizer, and c) 2 to 30% of sodium or potassium salt(s); based on the total weight of the composition, the sum of the three components a), b) and c) is 100%.

[0139] According to one embodiment, the solid electrolyte composition comprises:

[0140] - 30 to 50% by weight of fluoropolymer PI,

[0141] - 40 to 70% by weight of ionic liquid(s) and optionally at least one plasticizer, and

[0142] - 3 to 10% by weight of sodium or potassium salt(s); based on the total weight of the composition, preferably the sum of the three components a), b) and c) is 100%.

[0143] According to one embodiment, the composition of the solid electrolyte consists of:

[0144] - 30 to 50% by weight of fluoropolymer PI,

[0145] - 40 to 70% by weight of ionic liquid(s) and optionally at least one plasticizer, and

[0146] - 3 to 10% by weight of sodium or potassium salt(s); based on the total weight of the composition, preferably the sum of the three components a), b) and c) is 100%.

[0147] Within the compositions presented above, the percentages in the different constituents can be adapted according to the intended application, i.e. separator or electrode.

[0148] The said solid electrolyte composition may be in the form of a non-porous film, particularly when intended for use in a separator. The invention also relates to a non-porous film consisting of said solid electrolyte composition. Advantageously, the film is solvent-free and exhibits high ionic conductivity. Advantageously, the film is self-supporting, meaning it can be handled without support. Advantageously, the film is windable, meaning it can be handled so that it can be wound onto a reel.

[0149] According to one embodiment, the film has a thickness of 5 to 50 µm, preferably from 7 to 30 µm. According to another 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 ionic conductivity of the films is measured at 25°C by electrochemical impedance spectroscopy in a button cell, where the film is placed between two stainless steel electrodes. The resistance R of the film is obtained by extrapolating (with a linear model) the quasi-linear portion of the low-frequency scattering tail of the impedance spectra. The resistance R is taken where the extrapolated curve intersects the X-axis of the Nyquist plot. Consequently, the ionic conductivity o is obtained using the equation o=d / (RxA), where d is the film thickness and A is the area of ​​the stainless steel electrode.

[0150] Advantageously, the film according to the invention exhibits good electrochemical stability over the temperature range from -20°C to 80°C.

[0151] Advantageously, the film according to the invention has a solvent content (or solvents) with a boiling point below 150°C of less than 1% by weight, advantageously less than 0.1%, preferably less than 100 ppm, in particular less than 10 ppm.

[0152] Advantageously, the film retains its properties up to 80°C and does not ignite below 130°C.

[0153] According to one embodiment, the film according to the invention has a mechanical strength characterized by an elastic modulus, measured at 1Hz and 23°C by dynamic mechanical analysis, greater than 0.1 MPa, preferably greater than 1 MPa.

[0154] The invention also aims to provide at least one method for manufacturing this film.

[0155] In one embodiment, the film of the solid electrolyte composition is manufactured by a solvent-based process. The fluorinated polymer PI is solubilized at room temperature in a solvent selected from: n-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl formamide, methyl ethyl ketone, acetonitrile, and acetone. At least one sodium or potassium salt is dissolved in the ionic liquid / plasticizer mixture to obtain a sodium or potassium salt solution. The two solutions are mixed. The resulting mixture is then deposited onto a support (for example, a glass plate) and dried at a temperature below 60°C under vacuum overnight. A perfectly homogeneous and transparent self-supporting film is obtained.

[0156] According to one embodiment, the film of the solid electrolyte composition is manufactured by extrusion. The fluorinated polymer PI and the plasticizer are mixed at room temperature. This mixture is fed into an extruder heated to 100-200°C. Sodium or potassium salt dissolved in the ionic liquid is then added. After homogenization, the mixture is extruded through a flat die 300 µm thick. The thickness is adjusted to the desired value by drawing the film.

[0157] According to one embodiment, the film of the solid electrolyte composition is manufactured by hot pressing. The mixture of fluorinated polymer PI, ionic liquid(s), plasticizer(s), and sodium or potassium salt(s) is homogenized and then deposited between the two metal plates of a heated press. A pressure of 5 to 10 kN is then applied for 1 to 5 minutes at 100-150°C to obtain a film. The resulting film is then cooled to room temperature. Another object of the invention is a separator for a secondary Na-ion or K-ion battery consisting, in whole or in part, of said film.

[0158] The invention also relates to an electrochemical device selected from the group: batteries, capacitor, electrochemical double-layer electrical capacitor, and membrane-electrode assembly (MEA) for fuel cell or an electrochromic device, said device comprising a separator as described.

[0159] Another object of the invention is a secondary sodium or potassium-based battery comprising a negative electrode, a positive electrode and a separator, in which said separator comprises a film as described above.

[0160] The solid electrolyte composition can also be used in an electrode as a catholyte or anolyte. In this case, the solid electrolyte composition is located within the electrode's porosity. The invention therefore also relates to an electrode comprising an active material, a solid electrolyte composition according to the present invention, and optionally a conductive material. The electrode may also contain a binder. This binder facilitates the adhesion of the active material to the current collector.

[0161] The said active material may be selected from the group consisting of: an active material for cathode selected from the group consisting of an active material which may be of formula Na x M y 02 or K x M y 02 with M comprising at least one metal or mixture of metals, x is between 0 and 1, y is between 0 and 1; or of formula NaFePC , Na3V2(PO4)3, NaMnPC , NaCoPC , NaTi2(PO4)3, Na2FeP2O7, Na2MnP2O7, Na2CoP2O7, Na7V3(P2O7)4, KFePO4, K3V2(PO4)3, KMnPO4, KCoPO4, KTi2(PO4)3, K2FeP2O7, K2MnP2O7, K2CoP2O7, K7V3(P2O7)4; an active material for anode selected from the group consisting of graphite, soft carbon, hard carbon, sodium metal, potassium metal, sodium alloy, potassium alloy, Na2Ti3O7, Na4Ti5O2, NaTi2(PO4)3, FeSe2, SnO2, FES, Sn, Sn3P4, phosphorus, Fe2O3, MoS2, SnS2, NiS2, Sb, K2Ti3O7, K2Ti4O9, K4Ti5O 12 , K2Ti8O 17 , KTi2(PO4)3.

[0162] Advantageously, the active material for the cathode can have the formula Na x M y 02 or K x M y 02 with M selected from the group consisting of Ti, V, Cr, Mn, Fe, Mg, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Au, Pt, Ir, Os, W, Ta, Al, Y, Ca, Li, Rb, Cs, Ce, Mo, Ba, Sc, B and Hf or a mixture thereof; x is between 0 and 1; y is between 0 and 1. Preferably, M is selected from the group consisting of Cr, Mn, Fe, Mg, Co, Ni, Cu, Zn, Zr, Nb, Mo and Hf. In particular, M is selected from the group consisting of Ni, Mn, Fe, Co, Cu, Zn, Mg.

[0163] Another object of the invention is a secondary sodium or potassium-based battery comprising a negative electrode, a positive electrode and a separator, wherein at least one of the electrodes comprises said solid electrolyte composition.

[0164] EXAMPLES

[0165] The following examples illustrate, without limitation, the scope of the invention. 1. Preparation of a solid electrolyte for a Na-ion battery separator by solvent extraction

[0166] 2.0 g of P(VDF-HFP) (poly(vinylidene fluoride)-co-hexafluoropropylene) (containing 11% HFP by weight) are dissolved in 10 g of acetone. Separately, 2.80 g of EMIM-FSI (l-ethyl-3-methylimidazolium bis(fluorosulfonyl imide)) and 0.20 g of NaFSI (sodium bis(fluorosulfonyl)amide) are dissolved in 5 g of acetone. This latter solution is added to the P(VDF-HFP) solution and mixed. The resulting solution is then applied as a film using a squeegee and allowed to dry at room temperature overnight. A transparent, self-supporting film of 15–20 µm is obtained.

[0167] 2. Preparation of a solid electrolyte for a Na-ion battery separator by extrusion

[0168] A mixture of 5.7 g of P(VDF-HFP) (containing 15% HFP by weight) and 4 g of EG4DME (tetraethylene glycol dimethyl ether) is prepared and introduced into a 15 mL micro-extruder (with material recirculation) heated to 100–150°C. Next, a mixture of 0.57 g of NaFSI dissolved in 4 g of EMIM-FSI is added. The mixture is homogenized, and a rod is extruded and pressed at 120°C. This yields a transparent, self-supporting film approximately 30 µm thick.

[0169] 3. Measurement of the conductivity of a solid separator

[0170] According to the process of Example 1, an SI film composed of 40 wt% P(VDF-HFP) (containing 11 wt% HFP), 28 wt% EG4DME, 28 wt% EMIM-FSI, and 4 wt% NaFSI, and an S2 film composed of 40 wt% P(VDF-HFP) (containing 11 wt% HFP), 56 wt% EMIM-FSI, and 4 wt% NaFSI, are prepared. The ionic conductivity of the films is measured at 25°C by electrochemical impedance spectroscopy in a button cell, where the film is placed between two stainless steel electrodes. The resistance R of the film is obtained by extrapolating (with a linear model) the quasi-linear portion of the low-frequency scattering curve of the impedance spectra. The resistance R is taken where the extrapolated curve intersects the X-axis of the Nyquist diagram. Consequently, the ionic conductivity a is obtained using the equation o=d / (RxA), where d is the film thickness and A is the area of ​​the stainless steel electrode.We obtain a conductivity of 0.83 mS / cm at 25°C for the SI film and 1.38 mS / cm at 25°C for the 52 film.

Claims

DEMANDS 1. Solid electrolyte composition comprising, preferably consisting of: a) at least one fluorinated polymer PI, b) at least one ionic liquid, and c) at least one sodium or potassium salt.

2. Solid electrolyte composition according to the preceding claim characterized in that it also comprises at least one plasticizer.

3. A solid electrolyte composition according to any one of the preceding claims, characterized in that said at least one PI fluoropolymer has a melt viscosity of between 0.1 and 50 kP, advantageously between 0.5 and 45 kP, preferably between 1 and 45 kP, more preferably between 5 and 45 kP, in particular between 10 and 45 kP, more particularly between 15 and 45 kP, measured according to ASTM D-3835 method measured at 232°C and 100 sec. 1 .

4. Solid electrolyte composition according to any one of the preceding claims characterized in that said fluorinated polymer PI comprises repeating units derived from a monomer Mla selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, 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 the formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of the formula R 1 CH2OCF=CF2 in which R 1is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture of these.

5. A solid electrolyte composition according to any one of the preceding claims, characterized in that said fluorinated polymer PI comprises repeating units derived from monomer Mla and repeating units derived from monomer Mlb or repeating units derived from non-fluorinated monomer Mlc or a mixture of repeating units derived from said monomer Mlb and Mlc; said monomer Mla being vinylidene fluoride; said monomer Mlb selected from the group consisting of vinyl fluoride, trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, 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 the formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of the formula R 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof; said non-fluorinated monomer Mlc being selected from the group consisting of a monomer of formula R 1 R 2 C=C(R 3 )((X 1 ) P HORN 4 ) in which the R substituents 1 , R 2 and R 3 are independently selected from the group consisting of H, CO2H and Ci-C5alkyl; R 4 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -OR 5 with R 5 selected from the group consisting of H and Ci-Ci8alkyl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2, -OC(O)R groups 6 , -C(O)OR 6or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; R 6 being selected from the group consisting of Ci-C6alkyl or C6-Ci2aryl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H2 group(s); p is 0 or 1; X 1 is selected from the group consisting of — [-C(O)OC(R 7 (R s )C(R 9 (R 10 )-] w i- and an alkyl hydrocarbon group Ci-Cio optionally bearing one or more -OH, -CO2H or ester group(s); with wl being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R 7 , R 8 , R 9 , R 10 are independently of each other, independently for each wl unit, selected from the group consisting of H and Ci-C5alkyl.

6. A solid electrolyte composition according to any one of the preceding claims, characterized in that said at least one PI polymer comprises repeating units derived from a monomer Mla, being vinylidene fluoride, and repeating units derived from a monomer Mlb selected from the group consisting of trifluoroethylene, 1,1-chlorofluoroethylene, chlorotrifluoroethylene, hexafluoropropene and tetrafluoroethylene, or a mixture thereof.

7. A solid electrolyte composition according to any one of the preceding claims, characterized in that said PI polymer comprises repeating units derived from the monomer Mla and repeating units derived from a monomer Mlb; said monomer Mla being vinylidene fluoride and said monomer Mlb being hexafluoropropene; said polymer PI having a mass content of hexafluoropropene greater than or equal to 1%, advantageously greater than or equal to 3%, preferably greater than or equal to 8%, and less than or equal to 45%, advantageously less than or equal to 40%, preferably less than or equal to 35%, more preferably less than or equal to 30%, in particular less than or equal to 25%, more particularly less than 20% on the basis of the total weight of said polymer PI.

8. Solid electrolyte composition according to any one of the preceding claims, characterized in that said at least one ionic liquid comprises an anion selected from bis(oxalato)borate BOB', hexafluorophosphate (PF6), hexafluoroarsenate (AsF6), triflate or trifluoromethylsulfonate (CF3SO3), bis(fluorosulfonyl)imide (FSI), bis- (trifluoromethanesulfonyl)imide (TFSI), nitrate (NO3) and 4,5-dicyano-2- (trifluoromethyl)imidazole (TDI); and preferably said ionic liquid comprises a cation selected from the list: ammonium, sulfonium, pyridinium, pyrrolidinium, imidazolium, imidazolinium, phosphonium, guanidinium, piperidinium, thiazolium, triazolium, oxazolium, pyrazolium, and mixtures thereof.

9. Solid electrolyte composition according to any one of the preceding claims 2 to 8 characterized in that said at least one plasticizer has a boiling point above 150°C, preferably said plasticizer is selected from the group consisting of: vinylene carbonate, fluoroethylene carbonate, sulfolane, trans-4,5-difluoro-1,3-dioxolan-2-one, ethylene carbonate, propylene carbonate, (2-cyanoethyl)triethoxysilane, 3-methoxypropionitrile, polyethylene glycol dimethyl ethers and triethyl phosphate.

10. Solid electrolyte composition according to any one of the preceding claims, wherein said sodium or potassium salt is selected from the group consisting of NaCF3SO3, NaPF6, NaB(C2O4)2, NaN(SO2F)2, NaN(SO2CF3)2, NaN(SO2C2F3)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2CF2CF3), NaN(SO2CF3)(SO2CF2CF3), NaAsF6, NaBF2C2O4, NaNO3, NaPF3(CF2CF3)3, NaTDI, KCF3SO3, KPF6, KB(C2O4)2, KN(SO2F)2, KN(SO2CF3)2, KN(SO2C2F3)2, KN(SO2CF2CF3)2, KN(SO2F)(SO2CF3), KN(SO2F)(SO2CF2CF3), KN(SO2CF3)(SO2CF2CF3), KASF6, KBF2C2O4, KNO3, KPF3(CF2CF3)3 and KTDI or a mixture of these.

11. Solid electrolyte composition according to any one of the preceding claims comprising, preferably consisting of: a) 10 to 60% by weight of fluoropolymer PI, b) 10 to 80% by weight of ionic liquid(s) and optionally of at least one plasticizer and c) 2 to 30% by weight of sodium or potassium salt(s); based on the total weight of the composition, preferably the sum of the three components a), b) and c) is 100%.

12. Non-porous film comprising, preferably consisting of, the solid electrolyte composition according to any one of the preceding claims 1 to 11.

13. Film according to the preceding claim, having a solvent content(s) with a boiling point below 150°C of less than 1% by weight, advantageously less than 0.1%, preferably less than 100 ppm, in particular less than 10 ppm.

14. Film according to any one of the preceding claims 12 or 13, having 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.

15. A process for preparing the film according to any one of the preceding claims 12 to 14 by solvent means, said process comprising the following steps: - solubilize said at least one PI fluorinated polymer at room temperature in a solvent selected from: n-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl formamide, methyl ethyl ketone, ethyl acetate, cyclopentanone and acetone; - dissolve said at least one sodium or potassium salt in said ionic liquid and optionally said plasticizer, to obtain a sodium or potassium salt solution; - mix the solutions of fluorinated polymer PI and sodium or potassium salt, - place the resulting mixture onto a surface, - dry at a temperature below 60°C under vacuum overnight.

16. A method for preparing the film according to any one of claims 12 to 14 by extrusion, said method comprising the following steps: - mix said fluoropolymer PI and optionally said plasticizer at room temperature, - introduce the resulting mixture into an extruder heated to 100-200°C, - Add the sodium or potassium salt dissolved in the ionic liquid, and homogenize. - extrude the mixture through a flat die, advantageously 300 µm thick - calender to obtain a film, preferably with a thickness of 5 to 50 µm.

17. A method for preparing the film according to any one of claims 12 to 14 by hot pressing, said method comprising the following steps: - mix said fluorinated polymer PI, ionic liquid(s), plasticizer(s) and sodium or potassium salt(s) and optionally said at least one plasticizer, - homogenize the said mixture, - to place the said mixture between the two metal plates of a heated press, - Apply a pressure of 5 to 10 kN for 1 to 5 minutes at 100-150°C to obtain a film, - Cool the film to room temperature.

18. Separator for rechargeable Na-ion or K-ion battery, comprising the film according to any one of claims 12 to 14.

19. Electrochemical device selected from the group: batteries, capacitor, electrochemical double-layer electrical capacitor, and membrane-electrode assembly (MEA) for fuel cell or electrochromic device, said device comprising a separator according to the preceding claim.

20. Secondary Na-ion or K-ion battery comprising an anode, a cathode and a separator, wherein said separator comprises the film according to any one of claims 12 to 14.

21. Electrode comprising an active material, a solid electrolyte composition according to any one of the preceding claims 1 to 11 and optionally a conductive material.

22. Electrode according to the preceding claim characterized in that said active material is selected from the group consisting of: an active material for a cathode selected from the group consisting of an active material which may be of formula Na x M y 02 or K x M y O2 with M comprising at least one metal or a mixture of metals, x is between 0 and 1, y is between 0 and 1; or of the formula NaFePC, Na 3 2 (PO4)3, NaMnPO4, NaCoPO4, NaTi2(PO4)3, Na2FeP2O7, Na2MnP2O7, Na2CoP2O7, Na7V3(P2O7)4,KFePO4, K3V2(PO4)3, KMnPO4, KCoPO4, KTi2(PO4)3, K2FeP2O7, K2MnP2O7, K2CoP2O7, K7V3(P2O7)4; an active material for anode selected from the group consisting of graphite, soft carbon, hard carbon, sodium metal, potassium metal, sodium alloy, potassium alloy, Na2Ti3O7, Na4Ti5O2, NaTi2(PO4)3, FeSe2, SnO2, FES, Sn, Sn3P4, phosphorus, Fe2O3, MoS2, SnS2, NiS2, Sb, K2Ti3O7, K2Ti4O9, K4Ti5O 12 , K2Ti8O 17, KTi2(PO4)3.