Cathode binders for sodium-ion batteries

Abstract

The present invention relates to an electrode composition comprising at least one binder and at least one active material for the preparation of a sodium-ion battery electrode.

Description

Title of the invention: Cathode binders for sodium-ion battery Technical field

[0001] The present invention relates generally to the field of electrical energy storage in rechargeable secondary batteries of the Na-ion type. More specifically, the present invention relates to an electrode composition for a Na-ion battery. Technological background of the invention

[0002] The demand for lithium-ion batteries has increased in recent years due to their application in a wide variety of electronic devices such as mobile phones and electric vehicles. However, lithium-based compounds are relatively expensive and natural sources of lithium are unevenly distributed and difficult to access because they are located in a small number of countries. Alternatives to lithium have been sought. To this end, sodium-ion batteries have been developed. Sodium is in fact very abundant and distributed evenly in the Earth's crust. It is advantageously non-toxic and economically more attractive.

[0003] However, the oxidation-reduction potential of the Na+ / Na couple is -2.71 V compared to the standard hydrogen electrode (ESH) and is therefore higher than that of the Li+ / Li couple whose potential is -3.05 V compared to the standard hydrogen electrode, for a triple molar mass. These specificities make sodium-ion batteries less energy dense. New active cathode materials of the oxide type make it possible to bridge this gap between these two technologies by increasing the voltage and the specific capacity. Unfortunately, these new materials have the disadvantage of being basic and therefore poorly suited to the binders conventionally used in the solvent-based cathode manufacturing process for lithium batteries. For example, US2024079577 discloses a sodium-ion battery comprising a cathode prepared from a cathode material, PVDF and carbon black.

[0004] However, the development of high energy density Na-ion batteries, and therefore competitive with Li-ion batteries, requires the use of these oxide-type active materials which have the best energy densities. There are many oxide-type active materials for sodium ion on the market or in development but all have a high pH in water. This high pH reflects the presence of basic species on the surface of the active material particles.

[0005] There is therefore a need for new electrode binders compatible with the active materials used in sodium-ion batteries and allowing for optimal rheological properties for the application of a coating to a current collector by all coating methods known to those skilled in the art.

[0006] The applicant surprisingly found that the presence, in the electrode composition, of compounds having acid functions in a particular content made it possible to manufacture high-performance electrodes for sodium-ion batteries. Summary of the invention

[0007] According to a first aspect, the present invention relates to a positive electrode composition of a Na-ion battery comprising a binder composition and at least one active material; said binder composition comprising at least one fluorinated polymer PI; characterized in that said binder composition has a total molar content of acid functional groups greater than 1.40 mol% based on the total binder composition.

[0008] The applicant has found that a binder composition in which the molar content of acid functional groups was greater than 1.40 mol% made it possible to prepare high-performance electrodes for sodium-ion batteries. The binder composition may comprise said fluorinated polymer PI alone or in combination with an acrylic polymer P2 or an additive C or a mixture thereof as defined in the present application.

[0009] According to a preferred embodiment, said at least one active material has a pH greater than 12; said pH being determined according to the protocol described in the present application.

[0010] According to a preferred embodiment, said at least one active material is of formula NaxMyO2; M comprising at least one transition metal or a mixture of transition metals; x is between 0 and 1; y is between 0 and 1.

[0011] According to a preferred embodiment, said fluoropolymer PI comprises repeating units derived from a monomer Mla selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, 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)OCF2CF2 X 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 R1CH2OCF=CF2 in which R1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R2OCF=CH 2 in which R2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE);trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethyl; lene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro- 1-propene or a mixture thereof.

[0012] According to a preferred embodiment, said fluoropolymer PI comprises repeating units derived from the monomer Mla and repeating units derived from a monomer Mlc and optionally repeating units derived from a monomer Mlb; said monomer Mla being vinylidene fluoride; said monomer Mlb selected from the group consisting of vinyl fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF 2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF 2 in which n is 1, 2, 3, 4 or 5;the product of formula R1CH2OCF=CF2 in which R1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R2OCF=CH2 in which R2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutyl ene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof; said monomer Mlc being selected from the group consisting of formula R1R2C=C(R3)((X1)PC(O)R4) in which the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and Ci-C5 alkyl;R4 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -OR5 with R5 selected from the group consisting of H and CrCi8 alkyl optionally substituted with one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)R6, -C(O)O-R6 or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; R6 being selected from the group consisting of C1-C6 alkyl or C6-C12 aryl optionally substituted with one or more groups -OH, -CO2H, -SO3H, -PO3H; p is 0 or 1; X1 is selected from the group consisting of -[-C(O)OC(R7)(R8)C(R9)(R10)-]wi- and a C1-C10 alkyl hydrocarbon group optionally carrying 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; R7, R8, R9, R10 are independently of each other, ; independently for each wl unit, selected from the group consisting of H and C1-C5 alkyl.

[0013] According to a preferred embodiment, said binder composition comprises an acrylic polymer P2 and the latter comprises repeating units derived from one or more monomer(s) M2a of formula RaRbC=C(Rc)((X2)p C(O)Rd) in which the substituents Ra, Rb and Rc are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; Rd is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -ORd with Rd selected from the group consisting of H and CrCi8 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)Rd, -C(O)O-Rd or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; Rd being selected from the group consisting of C1-C6 alkyl or C6-C12 aryl optionally substituted by one or more group(s) -OH, -CO2H, -SO3H, -PO3H; p' is 0 or 1;X2 is selected from the group consisting of -[-C(O)OC(Re)(Rf)C(Rs)(Rh)-]w2- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w2 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; Re, Rf, Rs, Rh are independently of each other, independently for each w2 unit, selected from the group consisting of H and C1-C5 alkyl. ;

[0014] According to a preferred embodiment, said binder composition has a total molar content of acid functional groups greater than 1.41 mol%, advantageously greater than 1.42 mol%, preferably greater than 1.43 mol%, more preferably greater than 1.44 mol%, in particular greater than 1.45 mol%, more particularly 1.46 mol%, preferably greater than 1.47 mol%, advantageously more than 1.48 mol%, preferably more than 1.49 mol%, particularly preferably more than 1.50 mol% based on the total binder composition.

[0015] According to a preferred embodiment, said acid functional groups are selected from the group consisting of CO2H, SO3H and PO3H or a mixture thereof.

[0016] According to a preferred embodiment, said binder composition comprises an additive C comprising one or more acid functional groups selected from the group consisting of CO2H, SO3H and PO3H or a mixture thereof.

[0017] According to a preferred embodiment, said electrode composition has an angle δ greater than or equal to 45° measured at a strain rate of 1% at a frequency oscillation of 1 Hz and at a temperature of 23°C, the angle ô corresponds to a phase shift angle between the real and imaginary parts G' and G' ' of the viscoelastic modulus.

[0018] According to a preferred embodiment, said fluorinated polymer PI comprises repeating units derived from a monomer Mla as defined in the present application and repeating units derived from a monomer Ml c as defined in the present application and has a molar content of acid functional groups greater than 1.40 mol%; preferably the monomer Mla is vinylidene fluoride.

[0019] According to a preferred embodiment, said fluoropolymer PI is a homopolymer of vinylidene fluoride and said composition also comprises said acrylic polymer P2 as defined in the present application or said additive C as defined in the present application.

[0020] According to another aspect, the present invention relates to a positive electrode comprising a current collector and a positive electrode composition according to the present invention; said positive electrode composition being deposited on at least one of the faces of said current collector.

[0021] According to another aspect, the present invention relates to a sodium-ion secondary battery comprising an electrode according to the present invention.

[0022] According to a preferred embodiment, said battery also comprises an electrolyte salt selected from the group consisting of NaCF3SO3, NaPF6, NaC104, NaBF4, NaB(C2O4)2, NaN(SO2F)2, NaN(SO2CF3)2, NaN(SO2C2F3)2, NaN(SO2C2F5)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2C2F5), NaN(SO2CF3)(SO2C2F5), NaAsF6, NaBF2 C2O4, NaNO3, NaPF3(CF2CF3)3, NaBETI, NaTDI, or a mixture thereof.

[0023] According to another aspect, the present invention relates to the use of a fluorinated polymer PI as a binder for the preparation of a positive electrode of a sodium-ion battery, said fluorinated polymer PI has a molar content of acid functional groups greater than 1.40 mol%.

[0024] According to a preferred embodiment, said fluorinated polymer PI is as defined in the present application.

[0025] According to a preferred embodiment, said acid functional groups are selected from the group consisting of CO2H, SO3H and PO3H or a mixture thereof.

[0026] According to another aspect, the present invention relates to a binder composition for the positive electrode of a sodium-ion battery comprising a fluorinated polymer PI as defined in the present application and optionally an acrylic polymer P2 as defined in the present application or an additive C as defined in the present application or a mixture of the two; said binder composition having a molar content in acid functional groups greater than 1.40 mol% based on the total binder composition. Detailed Description of the Present Invention

[0027] According to a first aspect of the present invention, an electrode composition is provided, in particular a positive electrode composition. Said positive electrode composition comprises a binder composition and at least one active material. Considering the basic nature of the active material used at the cathode of a sodium-ion battery, the binder composition used to adhere the active material to the current collector must contain a minimum content of acid functional groups. Thus, said binder composition has a total molar content of acid functional groups greater than 1.40 mol% based on the total binder composition. The binder composition may comprise several components, each of which may provide a certain content of acid functional groups up to at least 1.40 mol% in the binder composition. As mentioned above, the binder composition preferably comprises at least one PI fluoropolymer.Said binder composition may also comprise an acrylic polymer P2 or an additive C or a mixture of both. Said polymer PI, said acrylic polymer P2 and said additive C are described below.

[0028] Preferably, said binder composition has a total molar content of acid functional groups greater than 1.41 mol%, advantageously greater than 1.42 mol%, preferably greater than 1.43 mol%, more preferably greater than 1.44 mol%, in particular greater than 1.45 mol%, more particularly 1.46 mol%, preferably greater than 1.47 mol%, advantageously more than 1.48 mol%, preferably more than 1.49 mol%, particularly preferably more than 1.50 mol% based on the total binder composition.In particular, said binder composition has a total molar content of acid functional groups greater than 1.51 mol%, advantageously greater than 1.52 mol%, preferably greater than 1.53 mol%, more preferably greater than 1.54 mol%, in particular greater than 1.55 mol%, more particularly 1.56 mol%, preferably greater than 1.57 mol%, advantageously more than 1.58 mol%, preferably more than 1.59 mol% based on the total binder composition. The total molar content of acid functional groups can be determined by standard techniques such as NMR.

[0029] Fluorinated polymer PI

[0030] According to a preferred embodiment, said fluorinated polymer PI comprises in its chain repeating units of at least one fluorinated monomer Mla chosen from compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to this vinyl group, at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.

[0031] Preferably, said fluoropolymer PI comprises repeating units derived from a monomer Mla selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, 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 formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R1CH2OCF=CF2 in which R1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R2OCF=CH2 in which R2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE);trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. Trifluoropropenes include 3,3,3-trifluoropropene. Tetrafluoropropenes include 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene. Pentafluoropropenes include 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene. Chlorofluoroethylene may refer to either 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. The chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene. ;

[0032] More preferably, said fluorinated polymer PI may be a homopolymer or a copolymer of the monomer Mla. The comonomer of the monomer Mla may be the monomer Mlb or the monomer Mlc as described below or a mixture of the two.

[0033] In particular, said fluoropolymer PI comprises at least repeating units derived from a monomer Mla being vinylidene fluoride. The fluoropolymer PI may be a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride.

[0034] When said fluoropolymer PI is a homopolymer of the monomer Mla, for example vinylidene fluoride, the latter is preferably combined with said acrylic polymer P2 or said additive C according to the present invention to form the binder composition according to the present invention. In this case, said acrylic polymer P2 or said additive C carry acid functional groups to form said binder composition according to the present invention having a molar content of acid functional groups greater than 1.4 mol%.

[0035] When said fluoropolymer PI is a copolymer of the monomer Mla, for example vinylidene fluoride, it comprises repeating units derived from a monomer Mla, for example vinylidene fluoride, and repeating units derived from a fluoromonomer Ml b or repeating units derived from a monomer Ml c or a mixture thereof. In said fluoropolymer PI, when it is a copolymer as described herein, the mass content of repeating units derived from the monomer Mla, preferably vinylidene fluoride, may be at least 50%, advantageously at least 60%, preferably greater than 70%, more preferably greater than 80%, in particular greater than 90%, more particularly greater than 95%.

[0036] Said fluorinated polymer PI may comprise repeating units derived from a fluorinated monomer Mlb. Said fluorinated monomer Mlb is different from the monomer Mla. Said fluorinated monomer Mlb is preferably selected from the group consisting of vinyl fluoride, trifluoroethylene, 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)OCF2CF 2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF 2 in which n is 1, 2, 3, 4 or 5; the product of formula R1CH2OCF=CF2 in which R1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4;the product of formula R2OCF=CH2 in which R2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutyl ene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. Preferably, the fluoropolymer PI comprises repeating units derived from a monomer Mla being vinylidene fluoride and repeating units derived from a fluorinated monomer Mlb selected from the group consisting of vinyl fluoride; trifluoroethylene; chlorotrifluoroethylene; 1,2-difluoroethylene, tetrafluoroethylene; 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-l,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=CFOCF; 2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 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; trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. In particular, the fluoropolymer PI comprises repeating units derived from a monomer Mla being vinylidene fluoride and repeating units derived from a fluorinated monomer Mlb selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene and hexafluoropropylene or a mixture thereof.Preferably, when it contains it, said fluoropolymer PI comprises from 1% to 40%, preferably from 1% to 30%, in particular from 2% to 20% by weight of repeating units derived from said monomer M 1b based on the total weight of said fluoropolymer PI.

[0037] Said fluorinated polymer PI may comprise repeating units derived from a monomer Ml c. Said monomer Mlc may carry acid functional groups. In this case, said monomer Mlc may be of formula R1R2C=C(R3)((X1)PC(O)R4) in which the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R4 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -OR5 with Rd' selected from the group consisting of H and CrCi8 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)R6, -C(O)O-R6 or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; R6 being selected from the group consisting of C1-C6 alkyl or C6-Ci2 aryl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H; p is 0 or 1;X1 is selected from the group consisting of -[-C(O)OC(R7)(R8)C(R9)(R10)-]wr and a C1-C10 alkyl hydrocarbon group optionally carrying 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; R7, R8, R9, R10 are independently of each other, independently for each wl unit, selected from the group consisting of H and C1-C5 alkyl. Said heterocycle may be saturated or 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, deltalactam, succinimide, 2- ring; imidazolidinone, 4-imidazolidinone. Said heterocycle may be substituted by one or more C1-C5 alkyl groups. As mentioned above, the CrCi8 alkyl is optionally substituted by said heterocycle. The latter may 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.

[0038] Advantageously, said monomer M le may be of formula ')PC(O)R4) wherein the substituents R1, R2 and R3 are independently selected from the group consisting of H, CO2H and C1-C5 alkyl; R4 is -OR5 with R5 selected from the group consisting of H and C1-C5 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)R6, -C(O)O-R6 or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; R6 being selected from the group consisting of C1-C6 alkyl or C6-C12 aryl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H; p is 0 or 1; X1 is selected from the group consisting of -[-C(O)OC(R7)(R8)C(R9)(R10)-]wr and a C1-C10 alkyl hydrocarbon group optionally carrying 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;R7, R8, R9, R10 are independently of each other, independently for each wl unit, selected from the group consisting of H and C1-C5 alkyl.;

[0039] Preferably, said monomer M le may be of formula R1R2C=C(R3)((X1)PC(O)R 4) in which the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R4 is -OR5 with R5 selected from the group consisting of H and C1-C5 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)R 6, -C(O)O-R6; R6 being selected from the group consisting of C1-C5 alkyl or C6-C10 aryl optionally substituted by one or more groups -OH, -CO 2H, -SO3H, -PO3H; p is 0 or 1; X1 is selected from the group consisting of -[-C(O)OC(R7)(R8)C(R9)(R10)-]w i- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5;R7, R8, R9, R10 are independently of each other, independently for each wl unit, selected from the group consisting of H and C1-C5 alkyl.;

[0040] More preferably, said monomer M le may be of formula R'R^^CR3 )((X')PC(O)R4) in which the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl; R4 is -OR5 with R5 selected from the group consisting of H and C1-C10 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)R6, -C(O)O-R6; R6 being selected from the group consisting of C1-C5 alkyl or C6 aryl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H; p is 0 or 1; X1 is selected from the group consisting of -[-C(O)OC(R7)(R8)C(R9)(R10)-]wr and a C1-C5 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with wl being an integer from 1 to 5;R7, R8, R9, R10 are independently of each other, independently for each wl unit, selected from the group consisting of H and CrC3 alkyl. ;

[0041] In particular, said monomer M le may be of formula R'R2C=C(R3)(C(O)R4 ) in which the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and CrC3 alkyl; R4 is -OR5 with R5 selected from the group consisting of H and CrCi 0 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)R6, -C(O)O-R6; R6 being selected from the group consisting of C1-C5 alkyl or C6 aryl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO 3H.

[0042] According to a particularly preferred embodiment, said monomer M le 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, methacrylate propyl, n-butyl methacrylate, 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 CH2=CH(CO2CH2CH2CO2H), CH2=CH(CO2CH2CH2-OC(O)-CH2CH2CO2H), CH2=CH(CO2CH2CH2CH2-OC(O)-CH2CH2CO2H),CH2=CH(CO2CH(CH3)CH2-OC(O)-CH2CH2CO2H),CH2=CH(CO , 2CH2CH2-OC(O)-C6H4CO2H), CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2 H); and mixtures thereof. Among these, said monomer M le 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 fluoropolymer PI may comprise one or more repeating units derived from said monomer M le as defined herein. Preferably, when containing, said polymer PI comprises from 0.01% to 10%, preferably from 0.05% to 5%, in particular from 0.1% to 5% by weight of repeating units derived from said monomer M le based on the total weight of said polymer PI.

[0043] In particular, said fluoropolymer PI comprises at least 50%, preferably at least 60%, more preferably at least 70%, in particular at least 80%, more particularly at least 90%, preferably at least 95% by weight of repeating units derived from a monomer Mla being, preferably, vinylidene fluoride, and from 0.01% to 5% by weight of repeating units derived from a monomer Mlc as defined above, based on the total weight of said polymer PI; in particular said monomer M le is selected from the group consisting of 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, n-butyl methacrylate, 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 CH2=CH(CO2CH2CH2CO2H), CH2=CH(CO2CH2CH2-OC(O)-CH2CH2CO2H), CH2=CH(CO2CH2CH2CH2-OC(O)-CH2CH2CO2H), CH2=CH(CO2 CH(CH3)CH2-OC(O)-CH2CH2CO2H),CH2=CH(CO2CH2CH2-OC(O)-C6H4CO2H), CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H); and mixtures thereof. ,

[0044] According to another embodiment, said fluorinated polymer PI comprises repeating units derived from a monomer Mla being vinylidene fluoride, repeating units derived from a fluorinated monomer Mlb, repeating units derived from a monomer Ml c; said monomers Mlb and Ml c being as defined above in the proportions as defined above.

[0045] Said monomer Mlc may be distributed in the chain of the fluorinated polymer PI in a random manner. Preferably, at least 50%, preferably at least 60%, of the repeating units from the monomer Mlc are randomly distributed in the chain of the fluoropolymer PI, i.e. located between two repeating units from the monomer Mla, for example vinylidene fluoride.

[0046] As explained above, said fluoropolymer PI may contain acid functional groups. The acid functional groups are preferably selected from the group consisting of CO2H, SO3H, PO3H. According to a preferred embodiment, the molar content of acid functional groups in said fluoropolymer PI is greater than 0.1 mol%, advantageously greater than 0.25 mol%, preferably greater than 0.5 mol%, more preferably greater than 0.75 mol%, in particular greater than 1.0 mol%. Preferably, the molar content of acid functional groups in said fluoropolymer PI is greater than 1.1 mol%, advantageously greater than 1.2 mol%, preferably greater than 1.3 mol%, more preferably greater than 1.40 mol%, in particular greater than 1.45 mol%, more particularly greater than 1.50 mol%.In particular, the molar content of acid functional groups in said fluorinated polymer PI is greater than 1.51 mol%, advantageously greater than 1.52 mol%, preferably greater than 1.53 mol%, more preferably greater than 1.54 mol%, in particular greater than 1.55 mol%, more particularly 1.56 mol%, preferably greater than 1.57 mol%, advantageously greater than 1.58 mol%, preferably greater than 1.59 mol%.

[0047] When said fluorinated polymer PI has a molar content of acid functional groups of less than 1.4 mol%, the binder composition according to the present invention comprises other constituents carrying acid functional groups in order to achieve the molar content defined in the present application.

[0048] According to one embodiment, the average particle size of said PI polymer is between 10 and 1000 nm. According to another embodiment, the average particle size is between 1 pm and 200 pm, preferably from 1 pm to 100 pm. The average particle size is determined by laser granulometry. A particle size analyzer of the Malvern INSITEC System type is used for the measurement. This is carried out in a dry process by laser diffraction on a powder with a focal length of 100 mm.

[0049] According to certain embodiments, the vinylidene fluoride contained in said fluoropolymer PI is biosourced. The term “biosourced” means “derived from biomass”. This makes it possible to improve the ecological footprint of the polymer. The biosourced VDF can be characterized by a renewable carbon content, i.e. carbon of natural origin and originating from a biomaterial or biomass, of at least 1 atomic % as determined by the 14C content according to standard NF EN 16640. The term “renewable carbon” indicates that the carbon is of natural origin and comes from a biomaterial (or biomass), as indicated below. According to certain embodiments, the bio-carbon content of the VDF may be greater than 5%, preferably greater than 10%, preferably greater than 25%, preferably greater than or equal to 33%, preferably greater than 50%, preferably greater than or equal to 66%, preferably greater than 75%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98%, preferably greater than 99%, advantageously equal to 100%.

[0050] Preparation of the PI polymer

[0051] According to a preferred embodiment, said fluoropolymer PI is prepared by a suspension or emulsion polymerization process forming a latex which can optionally be dried to result in a fluoropolymer PI in powder form. The polymerization step uses the monomer Mla and optionally the monomer Mlb and / or Mlc as defined above.

[0052] The polymerization step can be carried out at a temperature above 40°C, preferably at a temperature of 40°C to 120°C, in particular of 40°C to 90°C.

[0053] The polymerization step may be carried out at a pressure of 10 to 120 bara, advantageously at a pressure of 15 bara to 110 bara, preferably at a pressure of 20 bara to 110 bara, in particular 40 to 110 bara. During the polymerization reaction, the pressure used is higher than the critical pressure of the monomer Mla. In particular, when the monomer Mla is vinylidene fluoride, the pressure applied during the polymerization reaction is higher than its critical pressure. The pressure may be maintained by the continuous addition of the monomer Mla or water or an aqueous solution of said monomer Mlc.

[0054] Preferably, said monomer Ml c is added, in said reactor, in the form of an aqueous solution. According to a preferred embodiment, said monomer Ml c is added, in said reactor, continuously in order to guarantee a random (homogeneous) distribution thereof in said polymer PI.

[0055] Said process is preferably carried out in the presence of an initiator. The initiator may be one or a combination of several of the initiators known in the art to be useful in the dispersion polymerization of halogenated monomers. Suitable non-limiting classes of initiators include persulfate salts, peroxides, and redox systems. Examples of persulfate salts are sodium persulfate, potassium persulfate, or ammonium persulfate. The amount of persulfate salt added to the reaction mixture based on the total weight of monomer added to the reaction mixture is typically about 0.005 to about 1.0 wt. %. Organic peroxides that are useful include dialkyl peroxides, alkyl hydroperoxides, peroxyesters, and peroxydicarbonates. A suitable example of a dialkyl peroxide is di-tert-butyl peroxide. Examples of suitable peroxy esters include tert-amyl peroxypivalate, tert-butyl peroxypivalate, and succinic acid peroxide. Examples of suitable peroxydicarbonate initiators include di-n-propyl peroxydicarbonate and diisopropyl peroxydicarbonate, which are typically added to the reaction mixture in an amount based on the total weight of monomer added to the reaction mixture of about 0.05 to about 2.5 wt%. The initiator may comprise a redox system. By "redox system" is meant a system comprising an oxidizing agent, a reducing agent, and optionally a promoter acting as an electron transfer medium. The promoter is a component which, in different oxidation states, is capable of reacting with both the oxidizing agent and the reducing agent, thereby accelerating the overall reaction.Oxidizing agents include, for example, persulfate salts; peroxides, such as hydrogen peroxide; hydroperoxides, such as tert-butyl hydroperoxide and cumene hydroperoxide; and oxidizing metal salts such as, for example, ferric sulfate and potassium permanganate. Examples of reducing agents include sodium formaldehyde sulfoxylate; sodium or potassium sulfite, bisulfite, or metabisulfite; ascorbic acid; oxalic acid; and reduced metal salts. Typical promoters include transition metal salts such as ferrous sulfate. In redox systems, the oxidizing agent and reducing agent are typically used in an amount of about 0.01 to about 0.5 wt.% based on the total weight of monomer added to the reaction mixture.The promoter, if used, is typically employed in an amount of about 0.005 to about 0.025% by weight based on the total weight of monomer added to the reaction mixture.

[0056] Said method can be carried out in the presence of a phase transfer agent. This can be a dispersant, preferably when the method is carried out in suspension. The dispersant can be polyvinyl alcohol (PVA) or a compound comprising a cellulose unit such as methylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose. Said phase transfer agent can be a surfactant, preferably when the method is carried out in emulsion. For example, said surfactant comprises a polyethylene glycol segment and a polypropylene glycol segment. Preferably, said surfactant has an HLB value of 1 to 20, in particular an HLB value of 1 to 5 or 10 to 15. In particular, said surfactant comprising a polyethylene glycol segment and a polypropylene glycol segment has an HLB value of 1 to 5 and a weight-average molecular weight of 2500 to 10000 g.mol-1.Alternatively, said surfactant comprising a polyethylene glycol segment and a polypropylene glycol segment, has an HLB value of 10 to 15 and a weight average molecular weight of 500 to 2500 g.mol-1. .

[0057] A paraffin antifoulant is optionally used in the polymerization. Any long-chain saturated hydrocarbon wax or oil may be used. The oil or wax is added to the reactor prior to formation of the fluoropolymer, in an amount sufficient to minimize adhesion of polymers to the reactor components. This amount is generally proportional to the interior surface area of ​​the reactor and may vary from about 1 to about 40 mg / cm2 of interior surface area of ​​the reactor. If a paraffin wax or hydrocarbon oil is used as the antifoulant, the amount used is generally about 5 mg / cm2 of interior surface area of ​​the reactor.

[0058] The polymerization reaction mixture may optionally contain a buffering agent to maintain a controlled pH during the polymerization reaction. The pH is generally controlled in the range of 3 to 8. The buffering agent may be added at the beginning, at different points or throughout the polymerization. Suitable exemplary buffering agents are phosphate buffers and acetate buffers, which are well known to those skilled in the art.

[0059] Molecular weight regulators, also known as chain transfer agents, may optionally be used to adjust the molecular weight profile of the product. They may be added in a single portion at the beginning of the reaction, gradually, or continuously throughout the reaction. The amount of molecular weight regulator added to the polymerization reaction is generally from about 0.05 to about 5% by weight, more generally from about 0.1 to about 2% by weight based on the total weight of monomer added to the reaction mixture. Oxygenated compounds such as alcohols, carbonates, ketones, esters, and ethers may serve as molecular weight regulators. Examples of suitable oxygenated compounds include isopropyl alcohol, acetone, ethyl acetate, and diethyl carbonate.Other classes of molecular weight regulators include halogenated compounds such as chlorocarbons, hydrochlorocarbons, hydrofluorocarbons, chlorofluorocarbons, and hydrochlorofluorocarbons. Particular examples of halogenated molecular weight regulators include 1-fluoroethane, trichlorofluoromethane, and 1,1-dichloro-2,2,2-trifluoroethane. Certain hydrocarbons can be used as molecular weight regulators, such as hydrocarbons that contain two to five carbon atoms, with ethane and propane as particular examples.

[0060] The PI polymer obtained at the end of the reaction can be washed and dried to form a powder. Alternatively, the PI polymer obtained at the end of the reaction can be washed and used in the form of a latex.

[0061] Acrylic polymer P2

[0062] The binder composition may also comprise an acrylic polymer P2. The presence of this acrylic polymer P2 may make it possible to adjust the molar content of acid functional groups in the binder composition to reach the required threshold.

[0063] Preferably, said acrylic polymer P2 comprises repeating units derived from one or more monomer(s) M2a of formula RaRbC=C(Rc)((X2)p C(O)R d) in which the substituents Ra, Rb and Rc are independently of one another selected from the group consisting of H, CO2H and Ci-C5 alkyl; Rd is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -ORd with Rd selected from the group consisting of H and CrCi8 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)Rd, -C(O)O-Rd or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; Rd being selected from the group consisting of C1-C6 alkyl or C6-C12 aryl optionally substituted by one or more group(s) -OH, -CO2H, -SO3H, -PO3H; p' is 0 or 1;X2 is selected from the group consisting of -[-C(O)OC(Re)(Rf)C(Rs)(Rh)-]w 2- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO 2H or ester group(s); with w2 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5;Re, Rf, Rs, Rh are independently of each other, independently for each w2 unit, selected from the group consisting of H and C1-C5 alkyl. Said heterocycle may be saturated or 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, deltalactam, succinimide, 2-imidazolidinone, 4-imidazolidinone ring. Said heterocycle may be substituted by one or more C1-C5 alkyl groups. As mentioned above, C1-C18 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. ;

[0064] Advantageously, said monomer M 2a may be of formula RaRbC=C(Rc)((X2 )p C(O)Rd) in which the substituents Ra, Rb and Rc are independently of one another selected from the group consisting of H, CO2H and Ci-C5 alkyl; Rd is -ORd with Rd selected from the group consisting of H and CrCi8 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)Rd , -C(O)O-Rd or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; Rd being selected from the group consisting of C1-C6 alkyl or C6-C12 aryl optionally substituted by one or more -OH, -CO2H, -SO3H, -PO3H group(s); p' is 0 or 1; X2 is selected from the group consisting of -[-C(O)OC(Re)(Rf)C(Rs)(Rh)-]w 2- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w2 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; Re, Rf, Rs, Rh are independently of each other, independently for each w2 unit, selected from the group consisting of H and C1-C5 alkyl.

[0065] Preferably, said monomer M 2a may be of formula RaRbC=C(Rc)((X2)p C(O)Rd) in which the substituents Ra, Rb and Rc are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; Rd is -ORd with Rd selected from the group consisting of H and C1-C1 5 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO 3H, -OC(O)Rd, -C(O)O-Rd; Rd being selected from the group consisting of C1-C1 5 alkyl or C6-C1 0 aryl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H; p' is 0 or 1; X2 is selected from the group consisting of -[-C(O)OC(Re)(Rf)C(Rs)(Rh)-]w 2- and a Cr Cio alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w2 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5;Re, Rf, Rs, Rh are independently of each other, independently for each w2 unit, selected from the group consisting of H and C1-C5 alkyl. ;

[0066] More preferably, said monomer M 2a may be of formula RaRbC=C(Rc )((X2)PC(O)Rd) in which the substituents Ra, Rb and Rc are independently of each other selected from the group consisting of H, CO2H and Ci-C3 alkyl; Rd is -ORd with Rd selected from the group consisting of H and Ci-Ci 0 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO 3H, -OC(O)Rd , -C(O)O-Rd; Rd being selected from the group consisting of CrC 5 alkyl or C6 aryl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H; p' is 0 or 1; X2 is selected from the group consisting of -[-C(O)OC(Re)(Rf)C(Rs)(Rh)-]w 2- and a C1-C5 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w2 being an integer from 1 to 5; Re, Rf, Rs, Rh are independently one of the others, independently for each w2 unit, selected from the group consisting of H and C1-C3 alkyl.

[0067] In particular, said monomer M 2a may be of formula RaRbC=C(Rc)((X2)p C(O)R d) in which the substituents Ra, Rb and Rc are independently of each other selected from the group consisting of H, CO2H and CrC3 alkyl; Rd is -ORd with Rd selected from the group consisting of H and CrCi 0 alkyl optionally substituted by one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)Rd , -C(O)O-Rd; Rd being selected from the group consisting of C1-C5 alkyl or C6 aryl optionally substituted by one or more groups -OH, -CO2H, -SO3 H, -PO3H.

[0068] According to a particularly preferred embodiment, said monomer M 2a 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, n-butyl methacrylate, 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 CH2=CH(CO2CH2CH2CO2H), CH2=CH(CO2CH2CH2-OC(O)-CH2CH2CO2H), CH2=CH(CO2CH2CH2CH2-OC(O)-CH2CH2CO2H),CH2=CH(CO2CH(CH3)CH2-OC(O)-CH2CH2CO2H),CH2=CH(CO2CH 2CH2-OC(O)-C6H4CO2H), CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H); and mixtures thereof. Among these, said monomer M 2a with an alkyl group having 1 to 8 carbon atoms is preferred, and an alkyl group having 1 to 5 carbon atoms is more preferable. Said acrylic polymer P 2 may comprise one or more monomers M 2a as defined herein.

[0069] The polymer P2 may be in the form of a salt or partially salified. The salt may be a lithium, sodium, potassium, calcium or magnesium salt.

[0070] Additive C

[0071] The binder composition may also comprise an additive C. The presence of this additive C may make it possible to adjust the molar content of acid functional groups in the binder composition to reach the required threshold. Said additive C is a hydrocarbon compound. Said additive C comprises one or more functional groups acid selected from the group consisting of CO2H, SO3H and PO3H or a mixture thereof. Preferably, said additive C has a molar mass of less than 500 g / mol.By way of non-limiting example, said additive C is selected from the group consisting of tartaric acid, citric acid, oxalic acid, malonic acid, maleic acid, citraconic acid, succinic acid, adipic acid, phthalic acid, terephthalic acid, itaconic acid, acrylic acid, CH2=CH(CO2CH2CH2CO2H), CH2 =CH(CO2CH2CH2-OC(O)-CH2CH2CO2H), CH2=CH(CO2CH2CH2CH2-OC(O)-CH 2CH2CO2H),CH2=CH(CO2CH(CH3)CH2-OC(O)-CH2CH2CO2H),CH2=CH(CO2CH 2CH2-OC(O)-C6H4CO2H) and CH2=CH(CC)2CH2CH2CH2CH(CC)2H)CH2CH2CC)2^^ PSS (polystyrene sulfonic acid), polyphosphoric acid, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, dodecanesulfonic acid, para-toluenesulfonic acid, camphor-10-sulfonic acid, methanephosphonic acid, phenylphosphonic acid, octadecylphosphonic acid and ethylphosphonic acid.Preferably, said additive C is selected from the group consisting of tartaric acid, citric acid, oxalic acid, malonic acid, maleic acid, citraconic acid, succinic acid, adipic acid, phthalic acid, terephthalic acid, itaconic acid, acrylic acid, methane sulfonic acid, ethane sulfonic acid, propane sulfonic acid, butane sulfonic acid, pentane sulfonic acid, hexane sulfonic acid, dodecane sulfonic acid, para toluene sulfonic acid, camphor-10-sulfonic acid, methane phosphonic acid, phenyl phosphonic acid, octadecyl phosphonic acid and ethyl phosphonic acid. Additive C may be in the form of a salt or partially salified. The salt may be a lithium, sodium, potassium, calcium or magnesium salt.

[0072] Active ingredient

[0073] As mentioned above, said electrode composition also comprises an active material. Said active material preferably has at least a pH greater than 12. The protocol for measuring the pH of the active material is described below.

[0074] According to a preferred embodiment, said at least one active material is of formula NaxMy02; M comprising at least one metal or a mixture of metals; x is between 0 and 1; y is between 0 and 1. Advantageously, M is 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. 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.

[0075] Thus, the active material used in the positive electrode of a sodium-ion battery is selected from the group consisting of:

[0076] Nao.95Nio.3i7Mn0.3i7Mgo.i58Tio.2o802, Nao.677Nio.3ooMno.6ooMgo.o33Tio.o6702, Nao.68Cuo.34Mn o.6e02, Na7 / 9Cu2 / 9Fei / 9Mn2 / 3O2, Nao.9oCuo.22Feo.3oMno.4802, NaNii / 3Fei / 3Mni / 3O2, NaxMnO 2, Na0.67Nii / 3Mn2 / 3O2, NaFeo.5Coo.502, NaxFei / 2Mni / 2O2, NaxCrO2, NaNio.25Feo.5Mno.2502, Na2 / 3Mgo.28Mn0.7202, Nao.46Coo.5Mno.502, Nao.67Nio.15Feo.7Mno.65O7, NaxFeO2, NaFeo.3Nio.7 O2, NaLio.o5(Nio.25Feo.25Mn0.5)o.9502, Na0.7Fe0.4Mn0.4Co0.7O7, Nao.g7Feo.5Mno.5O7, Nao.7(Feo,5 Mn0.5)o.8Co0.202, NaxCoO2, NaxNiO2, Nai / 3Nii / 3Mn2 / 3O2, Nao.67Nio.7Mgo.1Mno.7O7, Na7 / 3Ni i / 3-xZnxMn2 / 3O2, Nao.7Mno.6Nio.3Coo.i02, Nao.7Mno.65Nio.i5Feo.202, Nao.85Lio.i7Nio.2iMno.6402, NaxTiO2, NaNio.5Tio.5O2, NaxVO2, NaxV2O5, Na1+xV3O8.

[0077] The active material used in a positive electrode can also be of formula Nai+aNixMnyFezAmBnO2 in which -0.35 <a<0,20, 0,08<x<0,5, 0,05<y<0,48, 0,03<z<0,4, 0,03<m<0,24, 0,001<n<0,06, x+y+z+m+n=l ; avec A sélectionné parmi le groupe consistant en Ti, Zn, Co, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, F, P et Cu, ou un mélange de ceux-ci ; B sélectionné parmi le groupe consistant en Ti, Co, Al, Zr, Y, Ca, Li, Rb, Cs, W, Ce, Mo, Ba, Mg, Ta, Nb, V, Sc, Sr, B, F, P et Cu, ou un mélange de ceux-ci.

[0078] Conducting agent

[0079] Said electrode composition may also comprise a conductive agent. The conductive agent in the electrode is composed of one or more materials that can improve conductivity. Some examples include carbon blacks such as acetylene black, Ketjen black; carbon fibers, such as carbon nanotube, carbon nanofiber, vapor-grown carbon fiber; metal powders such as SUS powder, and aluminum powder.

[0080] Preparation of the electrode composition

[0081] In a preferred embodiment, the electrode composition has the following mass composition:

[0082] a. 50% to 99.95% of active material, preferably 50% to 99%,

[0083] b. 0% to 25% of conductive agent, preferably 0.5% to 25%,

[0084] c. 0.05% to 25% of said binder composition according to the invention, preferably 0.5% at 25%,

[0085] d. 0% to 5% of at least one additive selected from the group consisting of a plasticizer, an ionic liquid, a dispersing agent for a conductive additive, and a flow aid;

[0086] the sum of all these percentages being 100%.

[0087] According to a preferred embodiment, said electrode composition has an angle δ greater than or equal to 45° measured at a strain rate of 1% at an oscillation frequency of 1 Hz and at a temperature of 23°C, the angle δ corresponds to a phase shift angle between the real and imaginary parts G' and G” of the viscoelastic modulus. When the electrode composition has a delta greater than or equal to 45°, this makes it easier to prepare the electrode by coating, i.e. the spreading of the electrode composition on the current collector.

[0088] According to another preferred embodiment, said electrode composition has a viscosity of between 2000 and 7000 cP, measured according to the protocol described below. Preferably, said electrode composition has a viscosity of between 2000 and 6900 cP, advantageously between 2000 and 6800 cP, preferably between 2000 and 6700 cP, more preferably between 2000 and 6600 cP, in particular between 2000 and 6500 cP, more particularly between 2100 and 6500 cP, preferably between 2200 and 6500 cP, advantageously preferably between 2300 and 6500 cP, preferably preferably between 2400 and 6500 cP, particularly preferably between 2500 and 6500 cP.

[0089] Said electrode composition may be prepared by mixing the constituents, for example in powder form, in the required proportions. Alternatively, the constituents may be mixed in the form of an aqueous solution or an organic solution (i.e., in the presence of an organic solvent), in the required proportions and then the solution may be dried to obtain a powder or used as such. Said organic solvent is not specifically limited and is chosen so as to solubilize said binder composition.Said organic solvent may be, in a non-limiting manner, n-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), triethylphosphite (TEP), acetone, cyclopentanone, tetrahydrofuran, methyl ethylketone (MEK), methyl isobutyl ketone (MiBK), ethyl acetate (EA), butyl acetate (BA), ethylene carbonate (EC), propylene carbonate. (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), gamma-butyrolactone and N-butylpyrrolidone; and mixtures thereof. .

[0090] A method of preparing the dry coated electrode comprises the following steps:

[0091] - mixing the active material in powder form, the binder composition according to the present invention, and optionally the conductive agent in powder form, the additive in powder form or both to form said electrode composition according to the present invention;

[0092] - depositing said electrode composition on said current collector for make an electrode, and

[0093] - optionally consolidation of said electrode by a treatment thermomechanical.

[0094] Said dry coated electrode is thus prepared according to a “solvent-free” process, i.e. one which does not require a step of evaporation of residual solvent after the deposition step because all the constituents are mixed in the dry state, in powder form, and the deposition is also carried out without solvent. A thermomechanical treatment refers to the application of mechanical pressure to the electrode at a given temperature. Such a thermomechanical treatment can be carried out, for example, by a calendering machine comprising rollers which can be heated or a plate press which can also be heated.

[0095] As solvent-free mixing processes of the various constituents of the electrode composition before the deposition phase on the collector, the following may be mentioned, without being exhaustive: mixing by stirring, mixing by air jet, high shear mixing, mixing by V-mixer, mixing by screw mass mixer, mixing by double cone, mixing by drum, conical mixing, mixing by double Z-arm, mixing in a fluidized bed, mixing in a planetary mixer, mixing by mechanical fusion, mixing by extrusion, mixing by calendering, mixing by grinding.

[0096] According to one embodiment, after the powder mixing step, the electrode is manufactured by a solvent-free spraying process, by depositing the electrode composition on the metal substrate, by a pneumatic spraying process, by electrostatic spraying, by dipping in a fluidized powder bed, by spraying, by electrostatic screen printing, by deposition with rotating brushes, by deposition with rotating addition rollers, by calendering.

[0097] According to one embodiment, the consolidation of the electrode after a deposition process on the metal substrate by solvent-free spraying (pneumatic spraying process, by electrostatic spraying, by dipping in a fluidized powder bed, by sprinkling, by electrostatic screen printing, by deposition with rotating brushes, by deposition with rotating addition rollers) is carried out by a calendering process. This process consists of applying pressure to the electrode using two optionally heated rollers. The consolidation step is optional. Its implementation depends on the technique used to deposit the constituents on the electrode. Thus, when the deposition step has been implemented by calendering, this consolidation step is optional because calendering allows the deposition and consolidation of the electrode simultaneously.

[0098] According to one embodiment, after the powder mixing step, the electrode is manufactured by a two-step solvent-free process. A first step consists of manufacturing a self-supporting film from the premixed formulation with a thermomechanical process such as extrusion, calendering or thermocompression. In a second step, the self-supporting film is laminated onto the metal substrate by a process combining temperature and pressure such as calendering or thermocompression.

[0099] According to one embodiment, after the powder mixing step, the electrode is manufactured by a solvent-free process using a calendering process which makes it possible to carry out the film-forming and transfer step of the coating onto the current collector in a single step, i.e. without going through a step of manufacturing a self-supporting film. To do this, the calender used has several rollers (at least three). The powder obtained after the mixing step is introduced between the first two rollers, which are most often heated and have differential rotation speeds to shear the powder. The coating formed and remaining stuck on the fastest roller is then directly laminated onto the current collector with a third roller. The electrode thus obtained can be subsequently passed through a calender to adjust its porosity or thickness if necessary.

[0100] The positive electrode thus obtained comprises a current collector and a positive electrode composition according to the present invention; said positive electrode composition being deposited on at least one of the faces of said current collector.

[0101] Use

[0102] According to another aspect of the present invention, a Na-ion battery is provided. Preferably, the Na-ion battery comprises a positive electrode, a negative electrode and a separator. Said positive electrode is an electrode according to the present invention. Preferably, said Na-ion battery also comprises an electrolyte salt selected from the group consisting of NaCF3SO3, NaPF6, NaC104, NaBF4, NaB(C2O4)2, NaN(SO2F)2, NaN(SO2CF3)2, NaN(SO2C2F3)2, NaN(SO2C2F5)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2C2F5), NaN(SO2CF3)(SO2C2F5), NaAsF6, NaBF2 C2O4, NaNO3, NaPF3(CF2CF3)3, NaBETI, NaTDI, or a mixture thereof. Examples Preparation of the electrode composition

[0103] In the examples below, the binder composition is a copolymer of vinylidene fluoride and acrylic acid. In binder composition 1, the binder composition is Solef® 5130 (copolymer of vinylidene fluoride and acrylic acid) comprising 1 mol% of acid functional groups. Binder compositions 2, 3, 4 and 5 are copolymers of vinylidene fluoride and acrylic acid having respectively 1.4 mol%, 1.5 mol%, 1.6 mol% and 2.4 mol% of acid functional groups.

[0104] The manufacture of an electrode composition is carried out according to the following steps: a solution of a binder composition at 7% by mass in N-methyl-2-pyrrolidone is prepared until the binder in question is completely dissolved. Then, Super P C65 carbon black (supplier Timcal) is added to this solution. The solution is mixed using a mechanical stirrer. Then an active material of the oxide type Na0j66Feoj5Mnoj502 is added. This active material has a pH of 12.6. N-methyl-2-pyrrolidone can then be added to adjust the final dry extract. An electrode composition with a final dry extract of between 40 and 90% is obtained. The dry composition of the electrode composition is 96% by weight of active material, 2% by weight of binder and 2% by weight of carbon black.

[0105] Measurement of the viscosity of the electrode composition applicable to a metal support

[0106] The viscosity of the electrode compositions was measured at 23°C, using a TA HR 10 rheometer. The ink is deposited between 2 parallel plates (diameter of 40mm) separated by 500 pm (=gap of 500 pm). The viscosity values ​​are obtained at different shear rates ranging from 0.1s-1 to 100 s-1. The value of 10s-1 is mentioned in the table below.

[0107] Measurement of the delta of the electrode composition applicable on a metal support

[0108] The dynamic viscosity of the electrode formulations was measured @ 23°C, using a TA HR 10 rheometer. The ink is deposited between 2 parallel plates (diameter of 40mm) separated by 500 pm (=gap of 500 pm). The dynamic viscosity values ​​are obtained at different stress rates ranging from 0.1% to 100% at an oscillation frequency of 1Hz. The delta is then calculated according to the formula known to those skilled in the art. The delta value at 1% is taken as a comparison between the different compositions. Measurement of the pH of the active ingredient

[0109] The pH of the active ingredient is measured using a potentiometric probe previously calibrated with pH standards = 4, 7 and 10. 1 g of active ingredient is suspended in 10 g of demineralized water. The suspension is stirred using a magnetic bar for 15 min before taking the pH.

[0110] The rheological properties of the different electrode compositions are detailed in Table 1 below. [YES] [Tables 1] Electrode composition ABCDE Binder composition 1(*) 2 3 4 5 %mol of acid functional groups 1 1.4 1.5 1.6 2.4 Viscosity t=0 (cp) 10540 18370 3752 4124 3891 Dry extract (%) 52 52 52 52 52 Delta t=0 (°) 14 12 45 47 53 Coating deposit (visual inspection)* * 0 0 1 1 1

[0112] (*) Corresponds to the product Solef® 5130 / ** when coating was not possible on the collector, a score of 0 is given; when coating was possible on the collector, a score of 1 was given

[0113] It has been found that to obtain an electrode composition capable of being correctly applied to a current collector, a viscosity between 2000 and 7000 cP and / or a delta greater than 45° are necessary. As demonstrated in the present application, binder compositions 3, 4 and 5 having a molar content of acid functional groups greater than 1.4 mol% make it possible to achieve the best results and therefore present a very good compromise for preparing homogeneous and high-performance electrodes. Binder compositions 1 and 2 having a molar content of acid functional groups less than 1.4 mol% result in electrode compositions (A and B) having a viscosity too high to allow coating thereof on the current collector. The binder composition according to the invention therefore makes it possible to solve the existing problems for the preparation of electrodes in a sodium-ion battery.

Claims

Claims

1. A positive electrode composition of a Na-ion battery comprising a binder composition and at least one active material; said binder composition comprising at least one fluorinated polymer PI characterized in that said binder composition has a total molar content of acid functional groups greater than 1.40 mol% based on the total binder composition.

2. Positive electrode composition according to the preceding claim, characterized in that said at least one active material has a pH greater than 12; said pH being determined according to the protocol described in the description.

3. Positive electrode composition according to any one of the preceding claims, characterized in that said at least one active material is of formula NaxMyO2; M comprising at least one transition metal or a mixture of transition metals; x is between 0 and 1; y is between 0 and 1.

4. A positive electrode composition according to any one of the preceding claims, characterized in that said fluoropolymer PI comprises repeating units derived from a monomer Mla selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, 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 formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R1CH2OCF=CF2 in which R1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4;the product of formula R2OCF=CH2 in which R2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof.;

5. A positive electrode composition according to any one of the preceding claims, characterized in that said fluoropolymer PI comprises repeating units derived from the monomer Mla and repeating units derived from a monomer Mlc and optionally repeating units derived from a monomer Mlb; said monomer Mla being vinylidene fluoride; said monomer Mlb selected from the group consisting of vinyl fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2 H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2 =CFOCF2CF2SO2F;the product of formula F(CF2)nCH2OCF=CF 2 in which n is 1, 2, 3, 4 or 5; the product of formula R'CH2 OCF=CF2 in which R1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R2OCF=CH2 in which R2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof; said monomer Mlc being selected from the group consisting of formula R1 R2C=C(R3)((X1)PC(O)R4) in which the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and Ci-C5 alkyl;R4 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -OR5 with R5 selected from the group consisting of H and CrCi8 alkyl optionally substituted with one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)R6, -C(O)O-R6 or a five or ten membered heterocycle comprising at least one nitrogen atom in its ring chain; R6 being selected from the group consisting of C1-C6 alkyl or C6-Ci2 aryl optionally substituted with one or more groups -OH, -CO2H, -SO3H, -PO3H; p is 0 or; 1; X1 is selected from the group consisting of -[-C(O)OC(R7)(R8)C(R9)(R1O)-]W i- and a CrCio alkyl hydrocarbon group optionally carrying one or more -OH, -CO 2H 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; R7, R8, R9, R10 are independently of each other, independently for each wl unit, selected from the group consisting of H and Cr C5 alkyl.

6. A positive electrode composition according to any one of the preceding claims characterized in that said binder composition comprises an acrylic polymer P2 and the latter comprises repeating units derived from one or more monomer(s) M2a of formula RaRbC=C(Rc)((X2)p C(O)Rd) in which the substituents Ra, Rb and Rc are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; Rd is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -ORd with Rd selected from the group consisting of H and CrCi8 alkyl optionally substituted with one or more groups -OH, -CO2H, -SO3H, -PO3H, -OC(O)Rd, -C(O)O-Rd or a five or ten membered heterocycle comprising at least one nitrogen atom in its ring chain; Rd being selected from the group consisting of C1-C6 alkyl or C6-Ci2 aryl optionally substituted with one or more groups -OH, -CO2H, -SO3H, -PO3H;p' is 0 or 1; X2 is selected from the group consisting of -[-C(O)OC(R e)(Rf)C(Rs)(Rh)-]w 2- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO 2H or ester group(s); with w2 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; Re, Rf, Rs, Rh are independently of each other, independently for each unit w2, selected from the group consisting of H and Cr C5 alkyl.;

7. Positive electrode composition according to any one of the preceding claims, characterized in that said binder composition has a total molar content of acid functional groups greater than 1.41 mol%, advantageously greater than 1.42 mol%, preferably greater than 1.43 mol%, more preferably greater than 1.44 mol%, in particular greater than 1.45 mol%, more particularly 1.46 mol%, preferably greater than 1.47 mol%, advantageously more preferably greater than 1.48 mol%, preferably more preferably greater than 1.49 mol%, particularly more preferably greater than 1.50 mol% based on the total binder composition.

8. A positive electrode composition according to any one of the preceding claims characterized in that said acid functional groups are selected from the group consisting of CO2H, SO3H and PO3H or a mixture thereof.

9. A positive electrode composition according to any one of the preceding claims characterized in that said binder composition comprises an additive C comprising one or more acid functional groups selected from the group consisting of CO2H, SO3H and PO3H or a mixture thereof.

10. Positive electrode composition according to any one of the preceding claims, characterized in that it has an angle d greater than or equal to 45° measured at a strain rate of 1% at an oscillation frequency of 1 Hz and at a temperature of 23°C, the angle ô corresponds to a phase shift angle between the real and imaginary parts G' and G” of the viscoelastic modulus.

11. Positive electrode composition according to any one of the preceding claims, characterized in that said fluoropolymer PI comprises repeating units derived from a monomer Mla as defined in claim 4 and repeating units derived from a monomer Ml c as defined in claim 5 and has a molar content of acid functional groups greater than 1.40 mol%; preferably the monomer Mla is vinylidene fluoride.

12. Positive electrode composition according to any one of the preceding claims 1 to 10 characterized in that said fluoropolymer PI is a homopolymer of vinylidene fluoride and said binder composition also comprises said acrylic polymer P2 as defined in claim 6 or said additive C as defined in claim 9.

13. A positive electrode comprising a current collector and a positive electrode composition according to any one of preceding claims; said positive electrode composition being deposited on at least one of the faces of said current collector.

14. A sodium-ion secondary battery comprising an electrode according to the preceding claim.

15. Battery according to the preceding claim characterized in that it also comprises an electrolyte salt selected from the group consisting of NaCF3SO3, NaPF6, NaC104, NaBF4, NaB(C2O4)2 , NaN(SO2F)2, NaN(SO2CF3)2, NaN(SO2C2F3)2, NaN(SO2C2F5)2, NaN(SO2F)(SO2CF3), NaN(SO2F)(SO2C2F5), NaN(SO2CF3)(SO2C2F5 ), NaAsF6, NaBF2C2O4, NaNO3, NaPF3(CF2CF3)3, NaBETI, NaTDI, or a mixture thereof.

16. Use of a fluorinated polymer PI as a binder for the preparation of a positive electrode of a sodium-ion battery, said fluorinated polymer PI has a molar content of acid functional groups greater than 1.40 mol%.

17. Use according to the preceding claim, characterized in that said fluorinated polymer PI is as defined in claim 4, 5 or 11.

18. 11. Use according to any one of the preceding claims 16 or 17 characterized in that said acid functional groups are selected from the group consisting of CO2H, SO3H and PO3H or a mixture thereof.

19. A binder composition for a positive electrode of a sodium-ion battery comprising a fluorinated polymer PI as defined in claim 4 or claim 5 or claim 11 and optionally an acrylic polymer P2 as defined in claim 6 or an additive C as defined in claim 9 or a mixture of both; said binder composition having a molar content of acid functional groups greater than 1.40 mol% based on the total binder composition.