Cathode binders for sodium-ion battery

Abstract

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

Description

[0001] sodium-ion battery Technical field 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 The demand for lithium-ion batteries has increased in recent years with regard 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 homogeneously in the Earth's crust.It is advantageously non-toxic and economically more interesting. 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 oxide cathode materials 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.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. There is therefore a need for new electrode binders compatible with the active materials used in sodium-ion batteries and allowing optimal rheological properties for the application of a coating on a current collector by all the coating methods known to those skilled in the art.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 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 fluoropolymer P1 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. The applicant 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 fluoropolymer P1 alone or in combination with an acrylic polymer P2 or an additive C or a mixture thereof as defined in the present application. If the binder composition comprises said fluoropolymer P1 but not said acrylic polymer P2 or said additive C or a mixture thereof; said total molar content of acid functional groups of said binder composition corresponds to the molar content of acid functional groups of said fluoropolymer P1. 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. According to a preferred embodiment, said at least one active material is of formula Na. x M yO2; 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. According to a preferred embodiment, said fluoropolymer P1 comprises repeating units derived from a monomer M1a 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=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R 1 CH2OCF=CF2in which R 1is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2is 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.According to a preferred embodiment, said fluoropolymer P1 comprises repeating units derived from monomer M1a and repeating units derived from a monomer M1c and optionally repeating units derived from a monomer M1b; said monomer M1a being vinylidene fluoride; said monomer M1b 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, 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. 1CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof; said monomer M1c being selected from the group consisting of of formula R 1 R 2 C=C(R 3 )((X 1 ) p HORN 4 ) in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3or –OR 5 with R 5 selected from the group consisting of H and C1-C18 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 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 C1-C6alkyl or C6-C 12 aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; 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 )-] w1 - and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R 7 , R 8 , R 9 , R 10are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl. According to a preferred embodiment, said binder composition comprises an acrylic polymer P2 and this comprises repeating units derived from one or more monomer(s) M2a of formula R a R b C=C(R c )((X 2 ) p’ HORN d ) in which the substituents R a , R b and R c are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R d is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3or –OR d’ with R d’ selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R d’’ , -C(O)OR d’’or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; R d’’ being selected from the group consisting of C1-C6alkyl or C6-C 12 aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; p' is 0 or 1; X 2 is selected from the group consisting of –[-C(O)OC(R e )(R f )C(R g )(R h )-] w2 - and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R e , R f , R g , R hare independently of each other, independently for each w2 unit, selected from the group consisting of H and C1-C5alkyl. 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 preferably greater than 1.48 mol%, preferably more preferably greater than 1.49 mol%, particularly preferably greater than 1.50 mol% based on the total binder composition. According to a preferred embodiment, said acid functional groups are selected from the group consisting of CO2H, SO3H and PO3H2 or a mixture thereof; preferably CO2H.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 PO3H2 or a mixture thereof. 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.According to a preferred embodiment, said fluoropolymer P1 comprises repeating units derived from a monomer M1a as defined in claim 4 and repeating units derived from a monomer M1c as defined in claim 5 and has a molar content of acid functional groups greater than 1.40 mol%; preferably the monomer M1a is vinylidene fluoride and in particular the molar content of acid functional groups of said fluoropolymer P1 is less than 5.0 mol%. According to a preferred embodiment, said fluoropolymer P1 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.According to another aspect, the present invention relates to a positive electrode comprising a current collector and a positive electrode composition according to any one of the preceding claims; said positive electrode composition being deposited on at least one of the faces of said current collector. According to another aspect, the present invention relates to a sodium-ion secondary battery comprising an electrode according to the present invention. According to a preferred embodiment, said battery also comprises an electrolyte salt selected from the group consisting of NaCF3SO3, NaPF6, NaClO4, 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.According to another aspect, the present invention relates to the use of a fluoropolymer P1 as a binder for the preparation of a positive electrode of a sodium-ion battery, said fluoropolymer P1 has a molar content of acid functional groups greater than 1.40 mol%. According to a preferred embodiment, said fluoropolymer P1 is as defined in the present application. According to a preferred embodiment, said acid functional groups are selected from the group consisting of CO2H, SO3H and PO3H2 or a mixture thereof.According to another aspect, the present invention relates to a binder composition for a positive electrode of a sodium-ion battery comprising a fluoropolymer P1 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 both; said binder composition having a molar content of acid functional groups greater than 1.40 mol% based on the total binder composition. Detailed description of the present invention 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.Given 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 fluoropolymer P1. Said binder composition may also comprise an acrylic polymer P2 or an additive C or a mixture of both. Said polymer P1, said acrylic polymer P2 and said additive C are described below.Preferably, said binder composition consists of said fluoropolymer P1 and optionally said acrylic polymer P2 or said additive C or a mixture of both. 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 preferably greater than 1.48 mol%, preferably more preferably greater than 1.49 mol%, particularly preferably greater 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 preferably greater than 1.58 mol%, preferably more preferably greater than 1.59 mol% based on the total binder composition. Preferably, said binder composition has a total molar content of acid functional groups less than 15 mol%, advantageously less than 12 mol%, preferably less than 10 mol%, more preferably less than 8 mol%, in particular less than 5 mol%, more particularly less than 4 mol%.The total molar content of acid functional groups in the binder composition corresponds to the sum of the molar contents of acid functional groups in polymer P1, and optionally in polymer P2 or additive C if the latter two are present in the binder composition. Thus, if the binder composition comprises polymer P1 but not polymer P2 or additive C, the total molar content of acid functional groups in the binder composition corresponds to the molar content of acid functional groups in polymer P1. For example, if polymer P1 contains CO2H acid functional groups, the molar content of acid functional groups corresponds to the molar content of CO2H groups in polymer P1. This is calculated by standard NMR techniques.If the binder composition comprises polymer P1 and polymer P2, each having acid functional groups as defined in the present invention, the total molar content of acid functional groups corresponds to the sum of the molar contents of acid functional groups of polymer P1 and polymer P2. Individually, polymers P1 and P2 may therefore have a molar content of acid functional groups of less than 1.40 mol% but the sum of the molar contents of each of them is greater than 1.40 mol%. The total molar content of acid functional groups can be determined by standard techniques such as NMR.Fluorinated polymer P1 According to a preferred embodiment, said fluoropolymer P1 comprises in its chain repeating units of at least one fluoro monomer M1a 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.Preferably, said fluoropolymer P1 comprises repeating units derived from a monomer M1a 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=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R. 1 CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2is 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. Among the trifluoropropenes, mention may be made of 3,3,3-trifluoropropene. Among the tetrafluoropropenes, mention may be made of 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene. Among the pentafluoropropenes, mention may be made of 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene. Chlorofluoroethylene may denote either 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. Chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene. More preferably, said fluoropolymer P1 may be a homopolymer or a copolymer of the monomer M1a.The comonomer of monomer M1a may be monomer M1b or monomer M1c as described below or a mixture of both. In particular, said fluoropolymer P1 comprises at least repeating units derived from a monomer M1a being vinylidene fluoride. The fluoropolymer P1 may be a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride. When said fluoropolymer P1 is a homopolymer of monomer M1a, 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%.When said fluoropolymer P1 is a copolymer of the monomer M1a, for example vinylidene fluoride, it comprises repeating units derived from a monomer M1a, for example vinylidene fluoride, and repeating units derived from a fluoromonomer M1b or repeating units derived from a monomer M1c or a mixture thereof. In said fluoropolymer P1, when it is a copolymer as described herein, the mass content of repeating units derived from the monomer M1a, 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%. Said fluoropolymer P1 may comprise repeating units derived from a fluoromonomer M1b. Said fluoromonomer M1b is different from the monomer M1a.Said fluoro monomer M1b 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)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R. 1 CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2is 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. Preferably, the fluoropolymer P1 comprises repeating units derived from a monomer M1a being vinylidene fluoride and repeating units derived from a fluoromonomer M1b 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(1,3-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=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R'CH2OCF=CF2in which R' is hydrogen or F(CF2)z and z is 1, 2, 3 or 4; the product of formula R''OCF=CH2in 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 P1 comprises repeating units derived from a monomer M1a being vinylidene fluoride and repeating units derived from a fluoromonomer M1b 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 P1 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 M1b based on the total weight of said fluoropolymer P1. Said fluoropolymer P1 may comprise repeating units derived from a monomer M1c. Said monomer M1c may carry acid functional groups. In this case, said monomer M1c may be of formula R, 1 R 2 C=C(R 3 )((X 1 ) p HORN 4 ) in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3or –OR 5 with R d ' selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 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 C1-C6alkyl or C6-C 12 aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; 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 )-] w1 - and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R 7 , R 8 , R 9 , R 10are independently of each other, independently for each w1 unit, selected from the group consisting of H and C1-C5alkyl. 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 with one or more C1-C5alkyl groups. As mentioned above, the C1-C 18alkyl 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. Advantageously, said monomer M1c may be of formula R 1 R 2 C=C(R 3 )((X 1 ) p HORN 4 ) in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R 4 is –OR 5 with R 5 selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 6 , -C(O)OR 6 or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; R 6being selected from the group consisting of C1-C6alkyl or C6-C 12 aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; 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 )-] w1 - and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R 7 , R 8 , R 9 , R 10 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl. Preferably, said monomer M1c may be of formula R 1 R 2 C=C(R 3 )((X 1 ) p HORN 4 ) in which the substituents R 1 , R 2and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R 4 is –OR 5 with R 5 selected from the group consisting of H and C1-C 15 alkyl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 6 , -C(O)OR 6 ; R 6 being selected from the group consisting of C1-C5alkyl or C6-C 10 aryl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2; 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 )-] w1 - and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R 7 , R8 , R 9 , R 10 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl. More preferably, said monomer M1c may be of formula R 1 R 2 C=C(R 3 )((X 1 ) p HORN 4 ) in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl; R 4 is –OR 5 with R 5 selected from the group consisting of H and C1-C 10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 6 , -C(O)OR 6 ; R 6 being selected from the group consisting of C1-C5alkyl or C6aryl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2; p is 0 or 1; X 1is selected from the group consisting of –[-C(O)OC(R 7 )(R 8 )C(R 9 )(R 10 )-] w1 - and a C1-C5alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 5; R 7 , R 8 , R 9 , R 10 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C3alkyl. In particular, said monomer M1c may be of formula R 1 R 2 C=C(R 3 )(HORN 4 ) in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C3alkyl; R 4 is –OR 5 with R 5 selected from the group consisting of H and C1-C 10alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 6 , -C(O)OR 6 ; R 6being selected from the group consisting of C1-C5alkyl or C6aryl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2. According to a particularly preferred embodiment, said monomer M1c 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, methacrylic 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(CO2CH2CH2-OC(O)-C6H4CO2H), CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H); and mixtures thereof. Of these, said monomer M1c 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 fluoropolymer P1 may comprise one or more repeating units derived from said monomer M1c as defined herein. Preferably, when it contains it, said polymer P1 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 M1c based on the total weight of said polymer P1. In particular, said fluoropolymer P1 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 M1a being, preferably, vinylidene fluoride, and from 0.01% to 5% by weight of repeating units derived from a monomer M1c as defined above, based on the total weight of said polymer P1; in particular said monomer M1c 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, methacrylic 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(CO2CH2CH2-OC(O)-C6H4CO2H), CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H); and mixtures thereof. According to another embodiment,said fluoropolymer P1 comprises repeating units derived from a monomer M1a being vinylidene fluoride, repeating units derived from a fluoromonomer M1b, repeating units derived from a monomer M1c; said monomers M1b and M1c being as defined above in the proportions as defined above. Said monomer M1c may be distributed in the chain of the fluoropolymer P1 in a random manner. Preferably, at least 50%, preferably at least 60%, of the repeating units derived from the monomer M1c are distributed randomly in the chain of the fluoropolymer P1, that is to say located between two repeating units derived from the monomer M1a, for example vinylidene fluoride. As explained above, said fluoropolymer P1 may contain acid functional groups. The acid functional groups are preferably selected from the group consisting of CO2H, SO3H, PO3H2, preferably CO2H. According to a preferred embodiment,the molar content of acid functional groups in said fluoropolymer P1 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 P1 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 fluoropolymer P1 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%. Preferably, the molar content of acid functional groups in said fluoropolymer P1 is less than 15.0 mol%, advantageously less than 12.0 mol%, preferably less than 10.0 mol%, more preferably less than 8.0 mol%, in particular less than 5.0 mol%, more particularly less than 4.5 mol%, preferably less than 4.0 mol%. In particular, the molar content of acid functional groups in said fluoropolymer P1 is between 1.4 mol% and 5.0 mol%, preferably between 1.45 mol% and 4.5 mol%; preferably the acid functional groups are CO2H. When said fluoropolymer P1 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 bearing acid functional groups in order to achieve the molar content defined in the present application. According to one embodiment, the average particle size of said polymer P1 is between 10 and 1000 nm. According to another embodiment, the average particle size is between 1 µm and 200 µm, preferably from 1 µm to 100 µm. 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 the dry process by laser scattering on a powder with a focal length of 100 mm. According to certain embodiments,The vinylidene fluoride contained in said fluoropolymer P1 is bio-based. The term "bio-based" means "derived from biomass". This improves the ecological footprint of the polymer. The bio-based 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 originates from a biomaterial (or biomass), as indicated below. According to 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%. Preparation of polymer P1 According to a preferred embodiment, said fluoropolymer P1 is prepared by a suspension or emulsion polymerization process forming a latex which can optionally be dried to result in a fluoropolymer P1 in powder form. The polymerization step uses the monomer M1a and optionally the monomer M1b and / or M1c as defined above. 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. The polymerization step can 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 M1a. In particular, when the monomer M1a is vinylidene fluoride, the pressure applied during the polymerization reaction is higher than its critical pressure. The pressure can be maintained by the continuous addition of the monomer M1a or of water or of an aqueous solution of said monomer M1c. Preferably, said monomer M1c is added, in said reactor, in the form of an aqueous solution. According to a preferred embodiment, said monomer M1c is added, in said reactor,continuously in order to ensure a random (homogeneous) distribution thereof in said polymer P1. 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 from about 0.005 to about 1.0 wt.%. Organic peroxides which 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 oxidant 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. Said process can be carried out in the presence of a phase transfer agent. This can be a dispersant, preferably when the process 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 process 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. 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 fluoropolymer formation in an amount sufficient to minimize polymer adhesion 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 reactor surface area. If a paraffin wax or hydrocarbon oil is used as an antifoulant, the amount used is generally about 5 mg / cm2 of interior reactor surface area. 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 various 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. 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 wt. %, more generally from about 0.1 to about 2 wt. % 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 being particular examples. The resulting polymer P1 can be washed and dried to form a powder. Alternatively, the polymer P1 obtained at the end of the reaction can be washed and used in the form of a latex.Acrylic polymer P2 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 achieve the required threshold. Preferably, said acrylic polymer P2 comprises repeating units derived from one or more monomer(s) M2a of formula R. a R b C=C(R c )((X 2 ) p’ HORN d ) in which the substituents R a , R b and R c are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R d is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3or –OR d’ with R d’ selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R d’’ , -C(O)OR d’’or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; R d’’ being selected from the group consisting of C1-C6alkyl or C6-C 12 aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; p' is 0 or 1; X 2 is selected from the group consisting of –[-C(O)OC(R e )(R f )C(R g )(R h )-] w2 - and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R e , R f , R g , R hare independently of each other, independently for each w2 unit, selected from the group consisting of H and C1-C5alkyl. 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 with one or more C1-C5alkyl groups. As mentioned above, the C1-C 18alkyl 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. Advantageously, said monomer M2a may be of formula R a R b C=C(R c )((X 2 ) p’ HORN d ) in which the substituents R a , R b and R c are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R d is -OR d’ with R d’ selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R d’’ , -C(O)OR d’’ or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; R d’’being selected from the group consisting of C1-C6alkyl or C6-C 12 aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; p' is 0 or 1; X 2 is selected from the group consisting of –[-C(O)OC(R e )(R f )C(R g )(R h )-] w2 - and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R e , R f , R g , R h are independently of each other, independently for each unit w2, selected from the group consisting of H and C1-C5alkyl. Preferably, said monomer M2a may be of formula R a R b C=C(R c )((X 2 ) p’ HORN d ) in which the substituents R a , R band R c are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R d is –OR d’ with R d’ selected from the group consisting of H and C1-C 15 alkyl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R d’’ , -C(O)OR d’’ ; R d’’ being selected from the group consisting of C1-C5alkyl or C6-C 10 aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; p' is 0 or 1; X 2 is selected from the group consisting of –[-C(O)OC(R e )(R f )C(R g )(R h )-] w2 - and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R e , Rf , R g , R h are independently of each other, independently for each unit w2, selected from the group consisting of H and C1-C5alkyl. More preferably, said monomer M2a may be of formula R a R b C=C(R c )((X 2 ) p’ HORN d ) in which the substituents R a , R b and R c are independently of each other selected from the group consisting of H, CO2H and C1-C3alkyl; R d is –OR d’ with R d’ selected from the group consisting of H and C1-C 10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R d’’ , -C(O)OR d’’ ; R d’’ being selected from the group consisting of C1-C5alkyl or C6aryl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2; p' is 0 or 1; X 2is selected from the group consisting of –[-C(O)OC(R e )(R f )C(R g )(R h )-] w2 - and a C1-C5alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w2 being an integer from 1 to 5; R e , R f , R g , R h are independently of each other, independently for each unit w2, selected from the group consisting of H and C1-C3alkyl. In particular, said monomer M2a may be of formula R a R b C=C(R c )((X 2 ) p’ HORN d ) in which the substituents R a , R b and R c are independently of each other selected from the group consisting of H, CO2H and C1-C3alkyl; R d is –OR d’ with R d’ selected from the group consisting of H and C1-C 10alkyl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R d’’ , -C(O)OR d’’ ; R d’’being selected from the group consisting of C1-C5alkyl or C6aryl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2. According to a particularly preferred embodiment, said monomer M2a 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, methacrylic 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(CO2CH2CH2-OC(O)-C6H4CO2H), CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H); and mixtures thereof. Among these, said monomer M2a 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 P2 may comprise one or more monomers M2a as defined herein. 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. Additive C 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 achieve the required threshold. Said additive C is a hydrocarbon compound. Said additive C comprises one or more acid functional groups selected from the group consisting of CO2H, SO3H and PO3H2 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)-CH2CH2CO2H), CH2=CH(CO2CH(CH3)CH2-OC(O)-CH2CH2CO2H),CH2=CH(CO2CH2CH2-OC(O)-C6H4CO2H) and CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H), PSS (polystyrene sulfonic acid), polyphosphoric 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. 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, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, dodecanesulfonic acid, para toluenesulfonic 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. Active material As mentioned above, said electrode composition also comprises an active material. Said active material preferably has at least one pH greater than 12. The protocol for measuring the pH of the active material is described below. According to a preferred embodiment, said at least one active material is of formula Na, x M yO2; 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. Thus, the active material used in a positive electrode of a sodium-ion battery is selected from the group consisting of: Na 0.95 Neither 0.317 Mn 0.317 Mg 0.158 You 0.208 O2, Na 0.677 Neither 0.300 Mn 0.600 Mg 0.033 You 0.067 O2, Na 0.68 Cu 0.34 Mn 0.66 O2, Na 7 / 9 Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2, Na 0.90 Cu 0.22 Fe 0.30 Mn 0.48O2, NaNi 1 / 3 Feb 1 / 3 Mr 1 / 3 O2, Na x MnO2, Na 0.67 Ni 1 / 3 Mr 2 / 3 O2, NaFe 0.5 Co 0.5 O2, Na x Feb 1 / 2 Mr 1 / 2 O2, Na x CrO2, NaNi 0.25 Feb 0.5 Mr 0.25 O2, Na 2 / 3 Mg 0.28 Mr 0.72 O2, Na 0.46 Co 0.5 Mr 0.5 O2, Na 0.67 Ni 0.15 Feb 0.2 Mr 0.65 O2, Na x FeO2, NaFe 0.3 Ni 0.7 O2, NaLi 0.05 (Ni 0.25 Feb 0.25 Mr 0.5 ) 0.95 O2, Na 0.7 Feb 0.4 Mr 0.4 Co 0.2 O2, Na 0.97 Feb 0.5 Mr 0.5 O2, Na 0.7 (Fe 0.5 Mr 0.5 ) 0.8 Co 0.2 O2, Na x CoO2, Na x NiO2, Na 1 / 3 Ni 1 / 3 Mr 2 / 3 O2, Na 0.67 Ni 0.2 Mg 0.1 Mr 0.7 O2, Na 2 / 3 Ni 1 / 3−x Zn x Mr 2 / 3 O2, Na0.7 Mn 0.6 Neither 0.3 Co 0.1 O2, Na 0.7 Mn 0.65 Neither 0.15 Fe 0.2 O2, Na 0.85 Li 0.17 Neither 0.21 Mn 0.64 O2, Na x TiO2, NaNi 0.5 You 0.5 O2, Na x VO2, Na x V2O5, Na 1+x V3O8. The active material used in a positive electrode can also be of formula Na 1+a Neither x Mn y Fe z HAS m B nO2 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=1 ; 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. Agent conducteur Ladite composition d’électrode peut également comprendre un agent conducteur. L’agent conducteur dans l’électrode est composé d’un ou plusieurs matériaux qui peuvent améliorer la conductivité. Certains exemples comprennent des noirs de carbone tels que le noir d’acétylène, le noir de Ketjen ; desfibres de carbone, telles qu’un nanotube de carbone, une nanofibre de carbone, unefibre de carbone par croissance en phase vapeur ; des poudres métalliques telles qu’une poudre SUS, et une poudre d’aluminium.Preparation of the electrode composition In a preferred embodiment, the electrode composition has the following mass composition: a. 50% to 99.95% of active material, preferably 50% to 99%, b. 0% to 25% of conductive agent, preferably 0.5% to 25%, c. 0.05% to 25% of said binder composition according to the invention, preferably 0.5% to 25%, d. 0% to 5% of at least one additive selected from the group consisting of a plasticizer, an ionic liquid, a dispersing agent for conductive additive, and a flow aid; the sum of all these percentages being 100%. 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. spreading the electrode composition on the current collector. 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.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.Ledit solvant organique peut être de manière non limitative n-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), triethylphosphite (TEP), acétone, cyclopentanone, tetrahydrofurane, 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 ; et les mélanges de ceux-ci.A method for preparing the dry-coated electrode comprises the following steps: - 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; - depositing said electrode composition on said current collector to manufacture an electrode, and - optionally consolidating said electrode by a thermomechanical treatment. Said dry-coated electrode is thus prepared according to a "solvent-free" process, i.e. one which does not require a residual solvent evaporation step 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 with heatable rollers or a plate press that can also be heated. Solvent-free mixing processes for the various components of the electrode composition before the deposition phase on the collector include, but are not limited to: stirring mixing, air jet mixing, high shear mixing, V-mixer mixing, screw mass mixer mixing, double cone mixing, drum mixing, conical mixing, double Z-arm mixing, fluidized bed mixing, planetary mixer mixing, mechanical melt mixing, extrusion mixing, calendering mixing, and milling mixing.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. 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 spraying, by electrostatic screen printing, by deposition with rotating brushes, by deposition with rotating addition rollers) is carried out by a calendering process.This method consists of applying pressure to the electrode using two possibly 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. 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 the manufacture of 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 on the metal substrate by a process combining temperature and pressure such as calendering or thermocompression.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 filming step and transfer 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, most often heated and having different 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.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. Use 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, NaClO4, 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.Examples Preparation of the electrode composition 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. 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 ingredient of the Na oxide type is added. 0,66Fe 0,5 Mn 0,5O2. This active ingredient 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 ingredient, 2% by weight of binder and 2% by weight of carbon black. Measurement of the viscosity of the electrode composition applicable on a metal support 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 (40mm diameter) separated by 500 µm (=gap of 500 µm). 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.Delta measurement of the electrode composition applicable on a metal support 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 (40mm diameter) separated by 500 µm (=gap of 500 µm). The dynamic viscosity values ​​at different stress rates ranging from 0.1% to 100% at an oscillation frequency of 1Hz are obtained. 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 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.The rheological properties of the various electrode compositions are detailed in Table 1 below. [Table 1] Electrode composition ABCDE Binder composition 1(*) 2 3 4 5 %mol of functional groups 1 1.4 1.5 1.6 2.4 acid Viscosity t=0 (cp) 10540 18370 3752 4124 3891 Solids content (%) 52 52 52 52 52 Delta t=0 (°) 14 12 45 47 53 Coating deposition (visual inspection)** 0 0 1 1 1 (*) Corresponds to the Solef® 5130 product / ** 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 It was 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 that is 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. 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 fluoropolymer P1 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 Na x M yO2; 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. Positive electrode composition according to any one of the preceding claims, characterized in that said fluoropolymer P1 comprises repeating units derived from a monomer M1a 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=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R 1CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

5. Positive electrode composition according to any one of the preceding claims characterized in that said fluoropolymer P1 comprises repeating units derived from monomer M1a and repeating units derived from a monomer M1c and optionally repeating units derived from a monomer M1b; said monomer M1a being vinylidene fluoride; said monomer M1b 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, CO2H, CH2OH, CH2OCN or CH2OPO3H;the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R; 1 CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof; said monomer M1c being selected from the group consisting of of formula R 1 R 2 C=C(R 3 )((X 1 ) p HORN 4 ) in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R 4is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3or –OR 5 with R 5 selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, - PO3H2, -OC(O)R 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 C1-C6 alkyl or C6-C12 aryl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2; 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 )-] w1 - and a hydrocarbon group C1-C 10alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R 7 , R 8 , R 9 , R 10 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl.

6. Positive electrode composition according to any one of the preceding claims characterized in that said binder composition comprises an acrylic polymer P2 and this comprises repeating units derived from one or more monomer(s) M2a of formula R a R b C=C(R c )((X 2 ) p’ HORN d ) in which the substituents R a , R b and R c are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R dis selected from the group consisting of – NHC(CH3)2CH2C(O)CH3 or –OR d’ with R d’ selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R d’’ , -C(O)OR d’’ or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its cyclic chain; R d’’ being selected from the group consisting of C1-C6alkyl or C6-C 12 aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; p' is 0 or 1; X 2 is selected from the group consisting of –[-C(O)OC(R e )(R f )C(R g )(R h )-] w2 - and a C1-C hydrocarbon group 10alkyl optionally carrying one or more -OH, -CO2H or ester(s) 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; R e , R f , R g , R h are independently of each other, independently for each w2 unit, selected from the group consisting of H and C1-C5alkyl.

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 preferred greater than 1.49 mol%, particularly preferred 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 PO3H2 or a mixture thereof; preferably CO2H.

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 PO3H2 or a mixture thereof. 10.Positive electrode composition according to any one of the preceding claims, characterized in that it 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.

11. Positive electrode composition according to any one of the preceding claims, characterized in that said fluoropolymer P1 comprises repeating units derived from a monomer M1a as defined in claim 4 and repeating units derived from a monomer M1c as defined in claim 5 and has a molar content of acid functional groups greater than 1.40 mol%; preferably the monomer M1a is vinylidene fluoride and in particular the molar content of acid functional groups of said fluoropolymer P1 is less than 5.0 mol%. 12.Positive electrode composition according to any one of the preceding claims 1 to 10, characterized in that said fluoropolymer P1 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. Positive electrode comprising a current collector and a positive electrode composition according to any one of the preceding claims; said positive electrode composition being deposited on at least one of the faces of said current collector.

14. 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, NaClO4, 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 fluoropolymer P1 as a binder for the preparation of a positive electrode of a sodium-ion battery, said fluoropolymer P1 has a molar content of acid functional groups greater than 1.40 mol%. 17.Use according to the preceding claim, characterized in that said fluoropolymer P1 is as defined in claim 4, 5 or 11.

18. 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 PO3H2 or a mixture thereof.

19. Binder composition for the positive electrode of a sodium-ion battery comprising a fluoropolymer P1 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 the two; said binder composition having a molar content of acid functional groups greater than 1.40 mol% based on the total binder composition.

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