Binder for an electrode, electrode formulation for a li-ion battery, and process for manufacturing a solvent-free electrode

Abstract

The present invention relates to a binder for a dry-coated electrode of a secondary battery, comprising a fluorinated polymer A and an acrylic polymer B, characterized in that said binder is in the form of a powder.

Description

[0001] Title: Binder electrode, electrode formulation Li-ion battery and solvent-free electrode manufacturing process

[0002] Technical field

[0003] The present invention relates generally to the field of electrical energy storage in Li-ion type lithium storage batteries. More specifically, the invention relates to a binder for a dry-coated electrode for a Li-ion battery. Another subject of the invention is a method for preparing an electrode using said binder. The invention also relates to lithium-ion batteries manufactured by incorporating said electrode.

[0004] Technological background of the invention

[0005] An elementary cell of a Li-ion storage battery or a lithium battery comprises an anode (for discharge), and a cathode (also for discharge) generally composed of a lithium insertion compound of the metal oxide type, such as LiMn2O4, LiCoO2 or LiNiO2, between which is inserted an electrolyte which conducts the lithium ions.

[0006] Rechargeable or secondary cells are more advantageous than primary (non-rechargeable) cells because the associated chemical reactions that take place at the positive and negative electrodes of the battery are reversible. Secondary cell electrodes can be regenerated multiple times by applying an electrical charge. Many advanced electrode systems have been developed to store an electrical charge. In parallel, much effort has been devoted to developing electrolytes capable of improving the capabilities of electrochemical cells.

[0007] For their part, the electrodes generally comprise at least one current collector on which is deposited, in the form of a film, a composite material consisting of a material called active material because it has electrochemical activity compared to lithium, a polymer which acts as a binder, plus one or more electronically conductive additives which are generally carbon black or acetylene black, and possibly a surfactant.

[0008] Binders are classified as inactive components since they do not directly contribute to cell capacity. However, their key role in electrode processing and their considerable influence on the electrochemical performance of electrodes have been widely described. The main relevant physical and chemical properties of binders are thermal stability, chemical and electrochemical stability, tensile strength (strong adhesion and cohesion), and flexibility. The main objective of using a binder is to form stable networks of the solid electrode components, i.e., active materials and conductive agents (cohesion). In addition, the binder must ensure close contact of the composite electrode to the current collector (adhesion).

[0009] The current manufacturing process for lithium-ion battery electrodes, the "slurry" process, uses a solvent. This process involves preparing an ink by mixing an active material, a conductive filler, and a polymer binder in a solvent. This ink is then deposited on a current collector, and the solvent is evaporated. A large portion of the energy consumed by this process comes from the solvent evaporation step. A strong trend in the lithium-ion battery field is to reduce manufacturing costs, which involves limiting costs related to energy consumption for manufacturing.

[0010] Compared to the conventional wet-suspension electrode manufacturing process, dry (solvent-free) manufacturing processes are simpler; these processes eliminate volatile organic compound emissions and offer the possibility to manufacture electrodes with larger thicknesses (> 120 μm), with higher energy density of the final energy storage device. The change in production technology will have little impact on the active material of the electrodes, however, the polymer additives responsible for the mechanical integrity of the electrodes must be adapted to the new manufacturing conditions. US 2019 / 0305316 discloses dry-processed electrode films comprising a microparticulate non-fibrillable binder having certain particle sizes and a method of obtaining a film flexible enough to be handled for roll-to-roll processing using fibrillable binders.However, fibrillated binders require additional shearing in addition to the dispersion of the components. This is energy-consuming and destructive to the active materials. Also known from US 2020 / 0313193 are electrode films by dry processing comprising an elastic polymeric binder in which the dry electrode film is self-supporting and comprises at most an insubstantial amount of polytetrafluoroethylene. US 2020 / 0313193 primarily discloses polyethylene, as the elastic polymeric binder, which is not electrochemically stable enough for use in both a cathode and an anode of lithium-ion secondary batteries. The adhesion of the coating to the current collector achieved with a solvent-free process is often lower than that achieved with a slurry process.To improve adhesion to the current collector, one solution is to use a current collector covered with a conductive coating that provides adhesion to the current collector and ensures electronic transfer between the current collector and the electrode coating. However, this solution is expensive and brings a significant additional cost.

[0011] Therefore, there is a need for a binder with good electrochemical resistance, providing good adhesion to the metal current collector via a solvent-free manufacturing process. It is also essential that the said binder has a high affinity with the other ingredients of the solvent-free formulation so that during pressing this binder provides intimate cohesion.

[0012] Summary of the invention

[0013] According to a first aspect, the present invention relates to a binder for a dry-coated electrode of a secondary battery comprising a fluoropolymer A and an acrylic polymer B, characterized in that said binder is in the form of a powder.

[0014] The binder according to the present invention comprising two types of polymers, i.e. a fluoropolymer and an acrylic-based polymer, makes it possible to improve adhesion to the current collector. The use of the binder in powder form allows solvent-free use from the phase of mixing the constituents to the phases of deposition on the current collector and consolidation. In addition, the use of a binder in powder form for the manufacture of the electrode makes it possible to avoid the need for grinding or dispersion steps after mixing with the active materials and the conductive agents.

[0015] According to a preferred embodiment, said binder has a particle size distribution with a D90 less than or equal to 750 pm.

[0016] According to a preferred embodiment, said acrylic polymer B has a pH between 1.5 and 4.0 measured in water at room temperature.

[0017] According to a preferred embodiment, said acrylic polymer B comprises at least 20% by weight of monomeric units containing a -CO2H functional group based on the total weight of said acrylic polymer B.

[0018] According to a preferred embodiment, the fluoropolymer A contains at least monomeric units derived from a monomer selected from the group consisting of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SC>2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2OCF=CH2 in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof.

[0019] According to a preferred embodiment, said fluoropolymer A comprises monomeric units derived from vinylidene fluoride and optionally monomeric units of a monomer selected from the group consisting of vinyl fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R 1 CH2OCF=CF2 in which R 1is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof.

[0020] According to a preferred embodiment, the fluoropolymer A is a homopolymer of vinylidene fluoride or a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from a monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene or a mixture thereof. According to a preferred embodiment, said fluoropolymer A comprises monomeric units carrying at least one of the functions selected from the group consisting of carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups such as glycidyl, amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, phosphonic.

[0021] According to a preferred embodiment, the acrylic polymer B has a glass transition temperature less than or equal to 230°C.

[0022] According to a preferred embodiment, the acrylic polymer B has a number-average molar mass greater than or equal to 3000 g.mol-1.

[0023] According to a preferred embodiment, the acrylic polymer B comprises monomeric units carrying a carboxylic acid or carboxylic acid anhydride functional group and monomeric units carrying a carboxylic acid ester functional group.

[0024] According to a preferred embodiment, the acrylic polymer B comprises monomeric units of formula R 1 R 2 C=C(R 3 )CO2H in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H and C1-C5alkyl, and monomeric units of formula R 4 R5 C=C(R 6 )HORN 7 in which the substituents R 4 , R 5 and R 6 are independently of each other selected from the group consisting of H and C1-C5 alkyl and R 7 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 or -OR' with R' selected from the group consisting of Ci-Cis alkyl optionally substituted with one or more -OH groups or a five or six-membered heterocycle comprising at least one nitrogen atom in its ring chain.

[0025] According to a preferred embodiment, the mass rate of acrylic polymer B relative to the fluorinated polymer A is from 1 to 70%.

[0026] According to another aspect, the present invention provides a method of preparing the binder, according to the present invention, characterized in that it comprises a step of:

[0027] Mixture of said polymer A in latex form and said polymer B in the form of an aqueous solution or latex, and

[0028] Drying of the mixture obtained, preferably by atomization or co-atomization,

[0029] Optionally, grinding of the dried mixture obtained in the previous step.

[0030] According to another aspect, the present invention provides a dry coated electrode comprising the binder according to the present invention, a dry active material and optionally a conductive agent. According to a preferred embodiment, the electrode has the following mass composition: a. 50% to 99.9% of active material, preferably 50% to 99%, b. 25% to 0% of conductive agent, preferably 25% to 0.5%, c. 25% to 0.05% of binder according to the present invention, preferably 25% to 0.5%, 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%.

[0031] According to a preferred embodiment, said conductive agents are composed of one or more materials among 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.

[0032] According to a preferred embodiment, for a positive electrode, said active material is selected from the group consisting of: LiCoO2, Li(Ni, Co, AI)O2, Li(l+ x), NiaMnbCoc (x represents a real number of 0 or more, a = 0.8, 0.6, 0.5, or 1 / 3, b = 0.1, 0.2, 0.3, or 1 / 3, c = 0.1, 0.2, or 1 / 3), LiNiO2, LiMn2O4, LiCoMnO4, Li3NiMn3O3, Li3Fe2(PO4)3, Li3V2(PO4)3, a Li Mn spinel substituted by a different element having a composition represented by Lil+xMn2-x- yMyO4, M representing at least one metal selected from Al, Mg, Co, Fe, Ni, and Zn, x and y independently representing a real number between 0 and 2, lithium titanate LixTiOy - x and y independently representing a real number between 0 and 2, and a lithium metal phosphate having a composition represented by UMPO4, M representing Fe, Mn, Co, or Ni.

[0033] According to a preferred embodiment, for a negative electrode, said active material is chosen from the group consisting of: a lithium alloy, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy and Li4TiO12.

[0034] According to another aspect, the present invention provides a method for preparing the dry-coated electrode according to the present invention, comprising a thermomechanical treatment step carried out at a temperature Tl between Tf - 50°C < Tl < Tg + 50°C when Tg > Tf or at a temperature Tl between Tg - 50°C < Tl < Tf + 50°C when Tf > Tg with Tf being the melting temperature of the fluoropolymer A and Tg being the glass transition temperature of the acrylic polymer B. According to a preferred embodiment, the present invention provides a Li-ion battery comprising a positive electrode, a negative electrode and a separator, at least one electrode being a dry-coated electrode according to the present invention.

[0035] Detailed description of the invention

[0036] According to a first aspect, a binder for a dry-coated electrode of a secondary battery is provided. Preferably, said binder comprises a mixture of at least two polymers. Thus, said binder comprises a fluoropolymer A and an acrylic polymer B.

[0037] Preferably, said binder is in the form of a powder. In particular, said powder has a particle size distribution with a D90 of less than or equal to 750 pm, advantageously less than or equal to 700 pm, preferably less than or equal to 650 pm, more preferably less than or equal to 600 pm, in particular less than or equal to 550 pm, more particularly less than or equal to 500 pm.Advantageously, said powder has a particle size distribution with a D90 of less than or equal to 450 pm, preferably less than or equal to 400 pm, more preferably less than or equal to 350 pm, in particular less than or equal to 300 pm, more particularly less than or equal to 250 pm, preferably less than or equal to 200 pm, advantageously less than or equal to 150 pm, preferably less than or equal to 100 pm, particularly preferably less than or equal to 50 pm. The D90 is the particle size at 90. emepercentile (by volume) of the cumulative particle size distribution. This parameter is determined by laser particle size analysis. A Malvern INSITEC System particle size analyzer is used for the measurement. This is carried out dry by laser diffraction on a powder with a focal length of 100 mm. This applies to all D90s described in this specification.

[0038] According to a preferred embodiment, the mass content of acrylic polymer B relative to the fluorinated polymer A is from 1 to 70%, advantageously from 2 to 60%, preferably from 3 to 50%, more preferably from 4 to 40%, in particular from 5 to 30%.

[0039] Fluorinated polymer A

[0040] According to a preferred embodiment, said fluoropolymer A contains in its chain at least one monomer chosen from compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to this vinyl group, at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.Preferably, said fluoropolymer A contains at least monomeric units derived from a monomer selected from the group consisting of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN OR CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R. 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2OCF=CH2 in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. Trifluoropropenes include 3,3,3-trifluoropropene. Tetrafluoropropenes include 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene. Pentafluoropropenes include 1,1,3,3,3-pentafluoropropene or 1, 2, 3,3,3-pentafluoropropene. Chlorofluoroethylene can refer to either 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. Chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0041] In particular, said fluorinated polymer A comprises at least monomeric units derived from vinylidene fluoride. The fluorinated polymer A may be a homopolymer or a copolymer. The copolymer may also comprise non-fluorinated monomers.

[0042] According to one embodiment, the fluoropolymer A is a vinylidene fluoride homopolymer.

[0043] According to an alternative embodiment, the fluorinated polymer A is a polymer comprising units derived from vinylidene fluoride, and is preferably chosen from polyvinylidene fluoride homopolymer and copolymers comprising vinylidene fluoride units and units derived from at least one other comonomer copolymerizable with vinylidene fluoride.

[0044] Thus, said fluoropolymer A comprises monomeric units derived from vinylidene fluoride and monomeric units derived from a monomer selected from the group consisting of vinyl fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SC>2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2OCF=CH2 in which R 2 is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-l-propene or a mixture thereof.

[0045] According to a preferred embodiment, the fluoropolymer A is a copolymer comprising vinylidene fluoride (VDF) units and units derived from one or more monomers 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=CFOCF2CF2SC>2F; 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-l-propene or a mixture thereof.;

[0046] Preferably, the fluoropolymer A is a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from a monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene and hexafluoropropylene or a mixture thereof. In the fluoropolymer A, the mass content of the vinylidene fluoride units is at least 50%, preferably at least 60%, more preferably greater than 70% and advantageously greater than 80%.

[0047] According to a particular embodiment, the fluoropolymer A is functionalized in whole or in part, which allows it to improve adhesion to metal. Thus, said fluoropolymer A may comprise monomer units carrying at least one of the functions selected from the group consisting of carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups such as glycidyl, amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, phosphonic; preferably at least one carboxylic acid or hydroxyl function.

[0048] The function is introduced by a chemical reaction which may be grafting, or a copolymerization of the fluorinated monomer with a monomer carrying at least one of said functional groups and a vinyl function capable of copolymerizing with the fluorinated monomer, according to techniques well known to those skilled in the art.

[0049] According to one embodiment, the functional group carries a carboxylic acid function which is a (meth)acrylic acid type group chosen from acrylic acid, methacrylic acid, methyl acrylic acid, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, hydroxyethylhexyl(meth)acrylate and acryloyloxy propylsuccinate.

[0050] According to one embodiment, the units carrying the carboxylic acid function further comprise a heteroatom chosen from oxygen, sulfur, nitrogen and phosphorus.

[0051] According to one embodiment, the functionality is introduced via the transfer agent used during the synthesis process. The transfer agent is a polymer with a molar mass less than or equal to 20,000 g / mol and carrying functional groups chosen from the groups: carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups (such as glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, phosphonic. An example of a transfer agent of this type is acrylic acid oligomers. According to a preferred embodiment, the transfer agent is an acrylic acid oligomer with a molar mass less than or equal to 20,000 g / mol. The molar mass of the transfer agent is determined according to a method as described below for acrylic polymer B.

[0052] The functional group content of the PVDF is at least 0.01 mol%, preferably at least 0.1 mol%, and at most 15 mol%, preferably at most 10 mol%. The PVDF preferably has a high molecular weight. By high molecular weight, as used herein, is meant a PVDF having a melt viscosity greater than 100 Pa.s, preferably greater than 500 Pa.s, more preferably greater than 1000 Pa.s, according to ASTM D-3835 method measured at 232°C and 100 sec-1.

[0053] The PVDF homopolymers and VDF copolymers used in the invention can be obtained by known polymerization methods such as emulsion or suspension polymerization.

[0054] According to one embodiment, they are prepared by an emulsion polymerization process in the absence of fluorinated surfactant.

[0055] Polymerization of PVDF results in a latex generally having a solids content of 10 to 60% by weight, preferably 10 to 50%, and having a weight average particle size of less than 1 micrometer, preferably less than 1000 nm, preferably less than 800 nm, and more preferably less than 600 nm. The weight average particle size is generally at least 20 nm, preferably at least 50 nm, and advantageously the average size is in the range of 100 to 400 nm. The polymer particles may form agglomerates having a weight average size of 1 to 30 micrometers, and preferably 2 to 10 micrometers. The agglomerates may break into discrete particles during formulation and application to a substrate.

[0056] In some embodiments, the PVDF homopolymer and VDF copolymers are composed of bio-based VDF. The term "bio-based" means "derived from biomass." This improves the ecological footprint of the polymer. The bio-based VDF may be characterized by a renewable carbon content, i.e., carbon of natural origin and originating from a biomaterial or biomass, of at least 1 atomic % as determined by the 14C content according to standard NF EN 16640. The term "renewable carbon" indicates that the carbon is of natural origin and originates from a biomaterial (or biomass), as indicated below.According to certain embodiments, the bio-carbon content of the VDF may be greater than 5%, preferably greater than 10%, preferably greater than 25%, preferably greater than or equal to 33%, preferably greater than 50%, preferably greater than or equal to 66%, preferably greater than 75%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98%, preferably greater than 99%, advantageously equal to 100%.

[0057] Acrylic Polymer B As mentioned above, said binder also comprises an acrylic polymer B.

[0058] Preferably, said acrylic polymer B has a pH of between 1.5 and 4.0, advantageously between 1.6 and 3.9, preferably between 1.7 and 3.8, more preferably between 1.8 and 3.7, in particular between 1.9 and 3.6, more particularly between 2.0 and 3.5, measured in water at room temperature.

[0059] Preferably, said acrylic polymer B comprises at least 20% by weight of monomeric units containing a -CO2H functional group based on the total weight of said acrylic polymer B.

[0060] Preferably, said acrylic polymer B has a glass transition temperature of less than or equal to 230°C. Advantageously, said acrylic polymer B has a glass transition temperature of less than or equal to 220°C, preferably less than 200°C, more preferably less than 180°C, in particular less than 160°C, more particularly less than or equal to 150°C.

[0061] According to a preferred embodiment, the acrylic polymer B has a number-average molar mass greater than or equal to 3000 g.mol-1, advantageously greater than or equal to 10000 g.mol-1, preferably greater than or equal to 50000 g.mol-1, more preferably greater than or equal to 100000 g.mol-1, in particular greater than or equal to 150000 g.mol-1. The molecular or molar mass is determined by Size Exclusion Chromatography (SEC). A test portion of the polymer solution corresponding to 90 mg of dry matter is introduced into a 10 mL flask. Mobile phase, supplemented with 0.04% dimethylformamide (DMF), is added up to a total mass of 10 g. The composition of this mobile phase is as follows: NaHCOs: 0.05 mol / L, NaNOs: 0.1 mol / L, triethanolamine: 0.02 mol / L, NaNs 0.03% by mass.The CES system consists of a Waters 510 isocratic pump with a flow rate set at 0.8 mL / min, a Waters 717+ autosampler, an oven containing a 6 cm long, 40 mm inner diameter Waters Guard Column Ultrahydrogel precolumn, followed by a 30 cm long, 7.8 mm inner diameter Waters Ultrahydrogel linear column. Detection is performed using a Waters RI 410 differential refractometer. The oven is heated to 60°C and the refractometer is heated to 45°C. The CES system is calibrated with a series of sodium polyacrylate standards supplied by Polymer Standards Service with a peak molecular weight between 1000 g / mol and 1.10. 6g / mol and a polydispersity index between 1.4 and 1.7. The calibration curve is linear and takes into account the correction obtained using the flow marker: dimethylformamide (DMF). Preferably, the acrylic polymer B comprises monomeric units carrying a carboxylic acid or carboxylic acid anhydride functional group and optionally monomeric units carrying a carboxylic acid ester functional group. The use of an acrylic polymer B with this type of functional group according to the present invention makes it possible to improve adhesion to the current collector.

[0062] According to a preferred embodiment, the acrylic polymer B comprises: monomeric units M1 derived from a monomer of formula R 1 R 2 C=C(R 3 )CO2H in which the substituents R 1 , R 2 and R 3are independently of each other selected from the group consisting of H and C1-C5 alkyl, preferably H and C1-C3 alkyl, in particular H or CH3; and optionally monomeric units M2 derived from a monomer of formula R 4 R 5 C=C(R 6 )HORN 7 in which the substituents R 4 , R 5 and R 6 are independently of each other selected from the group consisting of H and C1-C5 alkyl and R 7 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3 OR -OR' with R' selected from the group consisting of Ci-Cis alkyl optionally substituted with one or more -OH groups or a five or six-membered heterocycle comprising at least one nitrogen atom in its ring chain.

[0063] The combined presence of carboxylic acid and carboxylic acid ester functions makes it possible to both improve adhesion to the current collector and also to obtain deformable polymer particles compatible with fluoropolymer A.

[0064] 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, the C1-C18alkyl is optionally substituted by said heterocycle. The latter may be linked to the alkyl chain by the nitrogen atom or any other atoms forming the heterocycle. Preferably the heterocycle is 2-pyrrolidone, deltalactam, succinimide, 2-imidazolidinone, 4-imidazolidinone.

[0065] Preferably, said acrylic polymer B is based on an alkyl acrylate monomer M2 of formula R 4 R 5 C=C(R 6 )HORN7 in which the substituents R 4 , R 5 and R 6 are independently of each other selected from the group consisting of H and C1-C5alkyl; R 7 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3or -OR' with R' selected from the group consisting of C1-C18alkyl optionally substituted with one or more -OH group(s) a five or ten membered heterocycle comprising at least one nitrogen atom in its ring chain. Preferably, the heterocycle is as defined above, in particular the heterocycle is 2-pyrrolidone, deltalactam, succinimide, 2-imidazolidinone, 4-imidazolidinone. In the present application, the term alkyl includes linear and branched alkyls.

[0066] According to a preferred embodiment, the substituent R' is selected from the group consisting of methyl, ethyl, propyl, n-butyl, isobutyl, t-butyl, n-dodecyl, amyl, isoamyl, hexyl, 2-ethylhexyl, lauryl, n-octyl, hydroxybutyl, hydroxypropyl, ethyl substituted by a ureido group, hydroxyethyl.

[0067] In particular, said acrylic polymer B comprises monomeric units M2 of formula R 4 R 5 C=C(R 6 )HORN 7 in which the substituents R 4 and R 5 are H; R 6 is H or CH3; R 7 is -OR' with R' selected from the group consisting of methyl, ethyl, propyl, n-butyl, isobutyl, t-butyl, n-dodecyl, amyl, isoamyl, hexyl, 2-ethylhexyl, lauryl, n-octyl, hydroxypropyl, hydroxybutyl, 2-pyrrolidone, deltalactam, succinimide, 2-imidazolidinone, 4-imidazolidinone ethyl substituted with a ureido group, hydroxyethyl.

[0068] Thus, said acrylic polymer B comprises monomeric units M2 derived from 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 acrylate, methyl acrylic acid, methyl methacrylate or ureido methacrylate. The term "acrylate" herein includes acrylates and methacrylates.

[0069] In particular, said acrylic polymer B comprises monomeric units Ml of formula R 1 R 2 C=C(R 3 )CO2H in which the substituents R 1 and R 2 are H; and R 3 is H or CH3.

[0070] Optionally, the acrylic polymer B may also comprise monomeric units M3 derived from an unsaturated monomer copolymerizable with the monomers of formula R 1 R 2 C=C(R 3 )CO2H and monomers of formula R 4 R 5 C=C(R 6 )HORN 7 as defined above. Advantageously, the monomeric units M3 derived may be derived from a monomer of formula (R^R^CfR 10 )^ 11 ^ 12 ), (R 8 )(R 9 )C=C(R 10 )(P(O)(OR 13 )(GOLD 14 )),

[0071] (R 8 )(R 9 )C=C(R 10 )(C(O)NH(R 17 -R 18 )) OR (R 8 )(R 9 )C=C(R 10 )(C(O)N(R 15 -R 16 )(R 17 -R 18 )) in which the substituents R 8 , R 9 and R 10are independently of each other selected from the group consisting of H and C1-C5alkyl; R 11 , R 15 and R 17 are independently of each other selected from the group consisting of C1-C18alkyl, C6-C18aryl, C4-C18cycloalkyl, C1-C18fluoroalkyl, Cg-Cis fluoroaryl, C4-C18fluorocycloalkyl, propylene glycol oligomers, ethylene glycol oligomers, hexafluoropropylene oxide oligomers and tetrafluoroethylene oxide oligomers; R 12 , R 16 and R 18 are independently of each other selected from the group consisting of CO2H, COOM, OH, CONH2, CON(R 19 )2, SO3H, SO3M with R 19 being C1-C5 alkyl, M is NH4 + , NR 19 4 + , N / A + or K + ; R 13 and R 14are independently of each other selected from the group consisting of H, C1-C1s alkyl, C8-C1s aryl, C4-C18cycloalkyl, C1-C1s fluoroalkyl, C8-C1s fluoroaryl, C4-C18fluorocycloalkyl, propylene glycol oligomers, ethylene glycol oligomers, hexafluoropropylene oxide oligomers, tetrafluoroethylene oxide oligomers, an alkali cation, NH4 + and NR 19 4 + .

[0072] Preferably, the monomeric units M3 may be derived from a monomer selected from the group consisting of fumaric acid, crotonic acid, itaconic acid, vinyl acetate, vinyl neodecanoate, acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide, N,N-dialkylmethacrylamide, diacetone acrylamide, 2-hydroxyethyl acrylate, N-dialkylaminoethyl acrylate, glycidyl acrylate, n-dodecyl acrylate, fluoroalkyl acrylate, dialkylaminoethyl methacrylate, fluoroalkyl methacrylate, 2-hydroxyethyl methacrylate, n-octyl methacrylate, t-butyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, maleic anhydride, and alkenyl glycidyl ether compounds such as, for example, allyl glycidyl ether, 1,3-butadiene, isoprene, divinyl benzene, acrylonitrile, methacrylonitrile. Of these, itaconic acid, fumaric acid, N-methylolacrylamide, N-methylolmethacrylamide, diacetone acrylamide, acrylamido-2-methylpropane sulfonic acid, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and allyl glycidyl ether, 1,3-butadiene and acrylonitrile are preferred. These compounds may be used alone or as a mixture of two or more.

[0073] According to a preferred embodiment, said acrylic polymer B comprises at least 30% by weight, advantageously at least 40% by weight, preferably at least 50% by weight of monomeric units Ml based on the weight of said acrylic polymer B. According to another embodiment, said acrylic polymer B comprises at least 90% by weight, advantageously at least 95% by weight, preferably at least 99% by weight, in particular 100% by weight of monomeric units Ml based on the weight of said acrylic polymer B.

[0074] According to a preferred embodiment, said acrylic polymer B comprises at least 1%, advantageously at least 5% by weight, preferably at least 10% by weight, more preferably at least 20% by weight, in particular at least 30% by weight, more particularly at least 40% by weight of monomeric units M2 based on the weight of said acrylic polymer B. According to an alternative embodiment, the acrylic polymer B may not contain monomeric units M2.

[0075] According to a particular embodiment, the acrylic polymer B comprises less than 30% by weight, advantageously less than 20% by weight, preferably less than 10% by weight, in particular less than 5% by weight, more particularly less than 1% by weight of monomeric units M3 based on the weight of said acrylic polymer B. According to an alternative embodiment, the acrylic polymer B may not contain monomeric units M3.

[0076] The acrylic polymer B used in the invention can be obtained by polymerization of the monomers according to known polymerization methods such as emulsion or suspension polymerization.

[0077] According to another aspect, the present invention provides a method for preparing said binder according to the present invention. According to a preferred embodiment, said method comprises a step of:

[0078] Mixture of said polymer A in latex form and said polymer B in the form of an aqueous solution or latex, and

[0079] Drying of the mixture obtained in the previous step, preferably by atomization or co-atomization,

[0080] Optionally, grinding of the dried mixture obtained in the previous step.

[0081] The drying step may be carried out by atomization or co-atomization, preferably at a temperature of 100°C to 220°C. The powder may also be obtained by grinding techniques, such as cryo-grinding, where the mixture is brought to a temperature below room temperature, for example by means of liquid nitrogen, before grinding. At the end of the powder manufacturing step, namely after the drying step, the particle size may be adjusted and optimized by selection or screening methods and / or by grinding. Preferably, said binder has a pH of between 1.5 and 4.0, advantageously between 1.6 and 3.9, preferably between 1.7 and 3.8, more preferably between 1.8 and 3.7, in particular between 1.9 and 3.6, more particularly between 2.0 and 3.5, measured in water at room temperature.

[0082] According to another aspect, the present invention provides a dry coated electrode. The dry coated electrode comprises said binder according to the present invention, a conductive agent and a dry active material.

[0083] In a preferred embodiment, the dry coated electrode has the following mass composition: a. 50% to 99.9% active material, preferably 50% to 99%, b. 25% to 0% conductive agent, preferably 25% to 0.5%, c. 25% to 0.05% of said binder, preferably 25% to 0.5%, 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%.

[0084] The conductive agents in the dry-coated electrode are 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.

[0085] Active materials are materials that are capable of storing and releasing lithium ions.

[0086] In a preferred embodiment, said electrode is a negative electrode. In particular, for a negative electrode, said active material is selected from the group consisting of a lithium alloy, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy and Li4TiO12. The shape of the negative electrode active material is not particularly limited but is preferably particulate.

[0087] In another preferred embodiment, said electrode is a positive electrode. Preferably, for a positive electrode, said active material is selected from the group consisting of LiCoO2, Li(Ni, Co, AI)O2, Li(l+ x), NiaMnbCoc (x represents a real number of 0 or more, a = 0.8, 0.6, 0.5, or 1 / 3, b = 0.1, 0.2, 0.3, or 1 / 3, c = 0.1, 0.2, or 1 / 3), LiNiO2, LiMn2O4, LiCoMnO4, Li3NiMn3O3, Li3Fe2(PO4)3, Li3V2(PO4)3, a Li Mn spinel substituted by a different element having a composition represented by Lil+xMn2-x-yMyO4, M representing at least one metal selected from Al, Mg, Co, Fe, Ni, and Zn, x and y independently representing a real number between 0 and 2, lithium titanate LixTiOy - x and y independently representing a real number between 0 and 2, and a lithium metal phosphate having a composition represented by UMPO4, M representing Fe, Mn, Co, or Ni.

[0088] In addition, the surface of each of the materials described above can be coated. The coating material is not particularly limited as long as it has lithium ion conductivity and contains a material capable of being maintained as a coating layer on the surface of the active material. Examples of the coating material include LiNbO3, Li4Ti5O12, and Li3PO4.

[0089] The shape of the positive electrode active material is not particularly limited but is preferably particulate.

[0090] According to another aspect of the present invention, a method for preparing the dry coated electrode is provided. Said method comprises a thermomechanical treatment step carried out at a temperature Tl between Tf - 50°C < Tl < Tg + 50°C when Tg > Tf or at a temperature Tl between Tg - 50°C < Tl < Tf + 50°C when Tf > Tg with Tf being the melting temperature of the fluoropolymer A and Tg being the glass transition temperature of the acrylic polymer B.

[0091] Said method of preparing the dry coated electrode comprises the following steps:

[0092] - mixing the active material, said binder according to the present invention in powder form as described above, and the conductive agent using a process which provides an electrode formulation applicable to a metal substrate by a “solvent-free” process;

[0093] - depositing said electrode formulation on a substrate by a solvent-free process to obtain a Li-ion battery electrode, and

[0094] - consolidation of said electrode by a thermomechanical treatment carried out at a temperature Tl between Tf - 50°C < Tl < Tg + 50°C when Tg > Tf or at a temperature Tl between Tg - 50°C < Tl < Tf + 50°C when Tf > Tg with Tf being the melting temperature of the fluorinated polymer A and Tg being the glass transition temperature of the acrylic polymer B.

[0095] A “solventless” process is one that does not require a residual solvent evaporation step after the deposition step.

[0096] A thermomechanical treatment refers to the application Tl between Tf - 50°C < Tl < Tg + 50°C when Tg > Tf or at a temperature Tl between Tg - 50°C < Tl < Tf + 50°C when Tf > Tg with Tf being the melting temperature of the fluoropolymer A and Tg being the glass transition temperature of the acrylic polymer B, with mechanical pressure. Such a thermomechanical treatment can be carried out for example by a calendering machine having rollers that can be heated or a plate press that can also be heated.

[0097] Solvent-free mixing processes for the various constituents of the electrode formulation 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 melting mixing, extrusion mixing, calendering mixing, grinding mixing.

[0098] According to one embodiment, after the powder mixing step, the electrode is manufactured by a solvent-free spraying process, by depositing the formulation 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.

[0099] 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.

[0100] 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 thermo-compression. 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 thermo-compression.

[0101] 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 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 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.

[0102] The mass ratio of conductive agents to active material is preferably 0 to 10%, more preferably 0 to 7%.

[0103] The mass ratio of binder to active material is preferably 0.1 to 10%, more preferably 0.5 to 7%.

[0104] According to one embodiment, the electrode components are all mixed at once according to conventional methods, resulting in an electrode formulation.

[0105] In one embodiment, the electrode components are sequentially mixed according to conventional methods, resulting in an electrode formulation. In one embodiment, said electrode formulation is applied to a substrate by electrostatic screen printing. Some examples of the substrate are current collectors such as metal foil and metal mesh, polymer films, or a solid electrolyte layer of a solid-state battery.

[0106] The preferred thickness of an electrode is 0.1 pm to 1000 pm, preferably 0.1 pm to 300 pm.

[0107] According to another aspect of the present invention, a Li-ion battery is provided. Preferably, the Li-ion battery comprises a positive electrode, a negative electrode and a separator, at least one electrode being a dry-coated electrode according to the present invention.

[0108] The following examples illustrate the present invention without limiting it.

[0109] pH measurement method

[0110] A Mettler Toledo SevenEasy or equivalent pH meter and an Electrode In Lab Routine Pro are used. Before calibration, the electrode is checked for cleanliness. If necessary, clean the electrode with warm soapy water. Ensure that the pH electrode is always kept filled with KCl filling solution. The device is calibrated with pH 10, 7 and 4 buffer solutions. To calibrate, the electrode is immersed in the pH 10 buffer solution and pressed Cal. Once the pH has stabilized, repeat the operation with the pH 7 and then 4 buffer. Rinse with distilled water and dry the electrode between each buffer. The electrode is pre-prepared before measurement by soaking in a 0.1M HCl solution for one to two hours and then rinsed with deionized water. To measure the pH, dip the electrode into the product to be tested and stir for a few seconds. Leave the measurement to stabilize for 15 minutes and read the value displayed by the pH meter.The measurement is made at room temperature.

[0111] Calculation of the glass transition temperature

[0112] The glass transition temperatures shown here are calculated using the Fox equation. The Fox equation is an equation used to predict the glass transition temperature of random copolymers:

[0113] 1 / Tg,copo = i coi / Tg,i

[0114] Tg,copo is the glass transition temperature of the copolymer,

[0115] Tg,i are those of the homopolymers i corresponding to each comonomer, coi are the mass fractions of the monomers i composing this copolymer. The mass fractions are expressed without unit. The glass transition temperatures are expressed in degrees Kelvin. The temperature is then converted to degrees Celsius.

[0116] Synthesis of acrylic polymer B

[0117] Several acrylic polymers B have been prepared

[0118] Polymer Bl

[0119] In a 1000ml glass reactor equipped with mechanical stirring and oil bath heating, 416g of deionized water and 3.2g of 97% sodium dodecyl sulfate were weighed. In a first container equipped with a magnetic stirrer bar, 150g of deionized water, 1.06g of 97% sodium dodecyl sulfate, 0.7g of dial lyphtha latate, 163g of ethyl acrylate, 116g of methacrylic acid were weighed. This mixture was kept under constant stirring throughout the polymerization. In a second container, a solution consisting of 0.7g of ammonium persulfate, 10g of deionized water was prepared. In a third container, a solution consisting of 0.1g of sodium metabisulfite and 10g of deionized water was prepared. The reactor was heated to 76°C. The contents of the second and third containers were introduced into it, then the contents of the first container were introduced, still under stirring, using a peristaltic pump into the reactor over 120 minutes at 76°C.The dispersion was heated at 78°C for 60 min. A dispersion containing 28% dry matter was obtained. The particles have a median diameter measured by DDL of 100 nm. The pH of the aqueous dispersion is 3.1.

[0120] Polymer B-2

[0121] Polymer B-2 was prepared according to the process described in patent WO2011 / 1611511A1. It consists of 57.7% ethyl acrylate, 40.9% methacrylic acid, 0.3% diallyl phthalate and 1.1% AMPS. The resulting dispersion contained 25.8% dry matter. The particles have a median diameter measured by DDL of 187 nm. The pH of the aqueous dispersion is 3.0.

[0122] Polymer B-3

[0123] Polymer B-3 is produced according to the process described in patent WO2011 / 161508A1.

[0124] It consists of 67.2% ethyl acrylate, 32% acrylic acid, 0.25% diallyl phthalate and 0.55% AMPS. The resulting dispersion contained 19.8% dry matter. The particles have a median diameter measured by DDL of 191 nm. The pH of the aqueous dispersion is 2.1.

[0125] Polymer B-4

[0126] In a 1000ml reactor equipped with an oil bath heater and mechanical stirring, 875g of deionized water and 100g of acrylic acid were weighed. The mixture was heated to 72°C with stirring. A solution consisting of 0.35g of ammonium persulfate and 10g of deionized water was added. The temperature rose to 90°C in 15 min and then maintained at 90°C for 90 min. The final solution thus obtained was cooled and 50% sodium hydroxide was added until a pH of 2.5 was obtained. This gave an aqueous solution of polyacrylic acid with a pH of 2.5.

[0127] Polymer B-5

[0128] In a 1000ml reactor equipped with an oil bath heater and mechanical stirring, 300g of isopropyl alcohol and 2g of AZDN were weighed. The mixture was brought to reflux with isopropanol (approximately 81°C). In a container, 200g of acrylic acid and 80g of butyl acrylate were weighed. The monomer mixture was then added using a peristaltic pump over 130 minutes to the reactor, which was still heated and was refluxing. Reflux was maintained for 60 minutes. The isopropanol was then distilled off, gradually replacing it with deionized water during the distillation. The polymer has a number-average molar mass of approximately 7,000g / mol.

[0129] Polymer B-6

[0130] In a 1000ml reactor equipped with an oil bath heater and mechanical stirring, 463g of deionized water and 0.68g of copper sulfate pentahydrate were weighed. The mixture was heated to 96°C. In a first container, 330g of methacrylic acid and 63g of deionized water were weighed. In a second container, 20g of 35% hydrogen peroxide and 54g of deionized water were weighed. The contents of both containers were then added over 120 minutes using two peristaltic pumps. The pumps were rinsed with bi-exchanged water. The temperature was maintained at 96°C for 90 minutes. The mixture was cooled to room temperature. An aqueous solution of pH 2.5 was obtained. The resulting polymer has a number-average molar mass of 10,000g / mol.

[0131] Polymer B-7

[0132] In a 1000ml glass reactor equipped with mechanical stirring and oil bath heating, 460g of deionized water and 3.5g of 97% sodium dodecyl sulfate were weighed. In a first container equipped with a magnetic stirrer bar, 150g of deionized water, 1.1g of 97% sodium dodecyl sulfate, 200g of ethyl acrylate, and 117g of methacrylic acid were weighed. This mixture was kept under constant stirring throughout the polymerization. In a second container, a solution consisting of 1g of ammonium persulfate and 10g of deionized water was prepared. In a third container, a solution consisting of 0.1g of sodium metabisulfite and 10g of deionized water was prepared. The reactor was heated to 76°C. The contents of the second and third containers are introduced into it, then the contents of the first container are introduced under stirring using a peristaltic pump into the reactor in 120 minutes at 76°C. The pump is rinsed with deionized water.The temperature is maintained at 78°C for 60 min. The polymer is then cooled. A dispersion containing 30% dry matter was obtained. The particles have a median diameter measured by DDL of 95 nm. The pH of the aqueous dispersion is 2.8.

[0133] Polymer A We have an aqueous dispersion of PVDF polymer in the form of a latex with a pH of 3.6, a solids content of 24.1% and a particle size of 145nm. PVDF is a copolymer of vinylidene fluoride and hexafluoropropylene characterized by a melting temperature of 148°C measured by DSC (differential scanning calorimetry).

[0134] Aqueous formulations are produced according to the following process:

[0135] Polymer A is weighed into a container and acrylic polymer B is introduced over 10 minutes while stirring using a mechanical stirrer. The stirring time after introduction of the acrylic polymer is 10 minutes.

[0136] Example 1

[0137] 73.31g of polymer A are weighed and 27.14g of polymer Bl are added. A stable aqueous dispersion of pH 2.9, dry extract 25% and measured particle diameter of 128nm is obtained.

[0138] Example 2

[0139] We weigh 66.22g of polymer A and add 34.55g of polymer B-2.

[0140] A stable aqueous dispersion of pH 2.7, dry extract 23% and measured particle diameter of 270nm is obtained.

[0141] Example 3

[0142] We weigh 70.8g of polymer A and add 29.24g of polymer B-3.

[0143] A stable aqueous dispersion of pH 2.5, dry extract 24% and measured particle diameter of 174nm is obtained.

[0144] Example 4

[0145] Weigh 57.8g of polymer A and add 59g of polymer B-4. A viscous aqueous dispersion of pH 2.7, dry extract 16% and measured particle diameter of 150nm is obtained.

[0146] Example 5

[0147] 213.7g of polymer A are weighed and 48.7g of polymer B-5 are added. An aqueous dispersion with a pH of 2.2, a dry extract of 24.6% and a measured particle diameter of 160nm is obtained.

[0148] Example 6 195.5g of polymer A are weighed and 60.3g of polymer B-6 are added. An aqueous dispersion of pH 2, dry extract 26.1% and measured particle diameter of 155nm is obtained.

[0149] Example 7

[0150] 75.7g of polymer A are weighed and 25.5g of polymer B-7 are poured onto it. An aqueous dispersion with a pH of 3.3, a dry extract of 26.4% and a measured particle diameter of 135nm is obtained.

[0151] Each aqueous formulation containing a dry ratio of 70% PVDF and 30% acrylic polymer is placed in a crystallizer and dried for 24 hours in an oven at 110°C. In each case, homogeneous powders are obtained which are ground using an electric knife mill such as a coffee grinder in a first step, then cryogenically ground using a ball mill in a second step. The powders obtained are particularly homogeneous and can be very easily compressed in order to obtain polymeric layers on metal surfaces, using for example presses or calendering machines. This original process therefore makes it possible to carry out dry coating on aluminum-type supports, which makes it possible to produce cathodes without the presence of toxic solvents such as NMP or even to avoid aqueous processes which require particularly expensive drying and complex formulations requiring difficult control of rheology.The same type of solventless process can be used for anode manufacturing.

[0152] Preparing an electrode

[0153] Lithium-ion graphite battery anodes were produced using a solvent-free process. The graphite used is Actilion GHDR 15-4 graphite marketed by IMERYS. The anodes consist of 95% graphite by weight and 5% polymer binder by weight according to the invention. Each electrode is prepared according to the following protocol. The graphite and polymer binder powder are weighed and placed in a 250ml metal pot. The graphite / binder formulation is mixed for 1 minute and 30 minutes using a Minimix vibrating mixer marketed by MERRIS. Once mixed, the powdered formulation is deposited by sprinkling onto an 18pm thick copper current collector. The deposited quantity is between 15 and 20mg / cm 2on a surface of 10x5 cm 2 . Once the deposition step is completed, the electrode is consolidated using a table calender (model CA3 / 200-SP marketed by SUMET Gmbh). The temperature and roller speed are set at 110°C and 0.1 m / min respectively. The compression force is controlled to apply a force per unit length of 44 N / mm. To prevent the electrode from sticking to the upper roller, a sheet of temperature-resistant silicone paper is inserted between the coating and the upper roller.

[0154] Example 8 (according to the invention)

[0155] Anode based on graphite and the mixture of Example 1

[0156] Example 9 (according to the invention)

[0157] Anode based on graphite and the mixture of example 2

[0158] Example 10 (according to the invention)

[0159] Anode based on graphite and the mixture of Example 4

[0160] Example 11 (according to the invention)

[0161] Anode based on graphite and the mixture of Example 7

[0162] Example 12 (comparative example)

[0163] Anode based on graphite and polymer A powder.

[0164] Membership Assessment:

[0165] Adhesion is considered to be zero if the coating spontaneously delaminates at the end of the consolidation stage.

[0166] Table 1: Results of adhesion assessment on copper All electrode coatings with a binder of the invention exhibit adhesion with cohesive failure in the coating. The level of adhesion achieved is sufficient to allow handling of the electrode. In contrast, the coating with a pure PVDF binder exhibits no adhesion; the coating spontaneously detaches from the copper after the calendering step.

Claims

Claims 1. Binder for a dry-coated electrode of a secondary battery comprising a fluorinated polymer A and an acrylic polymer B, characterized in that said binder is in the form of a powder.

2. Binder according to the preceding claim, characterized in that it has a particle size distribution with a D90 less than or equal to 750 pm.

3. Binder according to any one of the preceding claims, characterized in that said acrylic polymer B comprises at least 20% by weight of monomeric units containing a -CO2H functional group based on the total weight of said acrylic polymer B.

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

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

6. Binder according to any one of the preceding claims, characterized in that the fluoropolymer A is a homopolymer of vinylidene fluoride or a copolymer comprising monomeric units derived from vinylidene fluoride and monomeric units derived from a monomer selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene or a mixture thereof.

7. Binder according to any one of the preceding claims, characterized in that said fluoropolymer A comprises monomer units carrying at least one of the functions selected from the group consisting of carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups such as glycidyl, amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, phosphonic.

8. Binder according to any one of the preceding claims, characterized in that the acrylic polymer B has a glass transition temperature less than or equal to 230°C.

9. Binder according to any one of the preceding claims, characterized in that the acrylic polymer B has a number-average molar mass greater than or equal to 3000 g.mol-1.

10. Binder according to any one of the preceding claims, characterized in that the acrylic polymer B comprises monomeric units carrying a carboxylic acid or carboxylic acid anhydride functional group and monomeric units carrying a carboxylic acid ester functional group.

11. Binder according to any one of the preceding claims, characterized in that the acrylic polymer B comprises monomeric units of formula R 1 R 2 C=C(R 3 )CO2H in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H and C1-C5alkyl, and monomeric units of formula R 4 R 5 C=C(R 6 )HORN 7 in which the substituents R 4 , R 5 and R 6 are independently of each other selected from the group consisting of H and C1-C5alkyl and R7 is selected from the group consisting of -NHC(CH3)2CH2C(O)CH3or -OR' with R' selected from the group consisting of Ci-Cis alkyl optionally substituted with one or more -OH groups or a five or six-membered heterocycle comprising at least one nitrogen atom in its ring chain.

12. Binder according to any one of the preceding claims, characterized in that said acrylic polymer B has a pH of between 1.5 and 4.0 measured in water at room temperature.

13. Binder according to any one of the preceding claims, characterized in that the mass content of acrylic polymer B relative to the fluorinated polymer A is from 1 to 70%.

14. Process for preparing the binder according to any one of the preceding claims, characterized in that it comprises a step of: Mixture of said polymer A in latex form and said polymer B in the form of an aqueous solution or latex, and Drying of the mixture obtained, preferably by atomization or co-atomization, Optionally, grinding of the dried mixture obtained in the previous step.

15. A dry coated electrode comprises the binder of any one of claims 1 to 13, a dry active material and optionally a conductive agent.

16. Dry coated electrode according to the preceding claim, having the following mass composition: a. 50% to 99.9% of active material, preferably 50% to 99%, b. 25% to 0% of conductive agent, preferably 25% to 0.5%, c. 25% to 0.05% of binder according to any one of the preceding claims 1 to 13, preferably 25% to 0.5%, 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%.

17. A dry coated electrode according to any one of claims 15 and 16, said conductive agents being composed of one or more of 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.

18. A dry coated electrode according to any one of claims 15 to 17, wherein, for a positive electrode, said active material is selected from the group consisting of: LiCoO2, Li(Ni, Co, AI)O2, Li(l+ x), NiaMnbCoc (x represents a real number of 0 or more, a = 0.8, 0.6, 0.5, or 1 / 3, b = 0.1, 0.2, 0.3, or 1 / 3, c = 0.1, 0.2, or 1 / 3), LiNiO2, LiMn2O4, LiCoMnO4, Li3NiMn3O3, Li3Fe2(PO4)3, Li3V2(PO4)3, a Li Mn spinel substituted by a different element having a composition represented by Lil+xMn2-x-yMyO4, M representing at least one metal selected from Al, Mg, Co, Fe, Ni, and Zn, x and y independently representing a real number between 0 and 2, lithium titanate LixTiOy - x and y independently representing a real number between 0 and 2, and a lithium metal phosphate having a composition represented by LÎMPO4, M representing Fe, Mn, Co, or Ni.

19. A dry coated electrode according to any one of claims 15 to 17, wherein, for a negative electrode, said active material is selected from the group consisting of: a lithium alloy, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy and Li4TiO12.

20. Process for the preparation of the dry-coated electrode according to any one of claims 15 to 19, comprising a thermomechanical treatment step carried out at a temperature Tl between Tf - 50°C < Tl < Tg + 50°C when Tg > Tf or at a temperature Tl between Tg - 50°C < Tl < Tf + 50°C when Tf > Tg with Tf being the melting temperature of the fluoropolymer A and Tg being the glass transition temperature of the acrylic polymer B.

21. A Li-ion battery comprising a positive electrode, a negative electrode and a separator, at least one electrode being a dry-coated electrode according to any one of claims 15 to 19.

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