FR3146374A1 - Electrode binder, electrode formulation for Li-ion battery and electrode manufacturing method - Google Patents

Abstract

The present invention relates to a binder for an electrode of a secondary battery comprising a fluorinated polymer A and an acrylic polymer B, characterized in that said acrylic polymer B comprises monomeric units containing one or more CO2-Li+ functional group(s) and said acrylic polymer B has a lithiation rate of at least 30%.

Description

Electrode binder, electrode formulation for Li-ion battery and electrode manufacturing method

The present invention relates generally to the field of electrical energy storage in lithium storage batteries of the Li-ion type. More specifically, the invention relates to a binder for an electrode. 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.

Technological background of the invention

An elementary cell of a Li-ion storage battery or a lithium battery comprises an anode (on discharge), and a cathode (also on discharge) generally composed of a lithium insertion compound of the metal oxide type, such as LiMn ₂ O ₄ , LiCoO ₂ or LiNiO ₂ , between which is inserted an electrolyte which conducts the lithium ions.

Rechargeable or secondary cells are more advantageous than primary (non-rechargeable) cells since 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 the development of electrolytes capable of improving the capabilities of electrochemical cells.

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 with respect 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.

Binders are classified as inactive components since they do not directly contribute to the 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 purpose of using a binder is to form stable networks of the solid components of the electrodes, i.e., active materials and conductive agents (cohesion). In addition, the binder must ensure the close contact of the composite electrode to the current collector (adhesion).

The current manufacturing process for lithium-ion battery electrodes, the “slurry” process, uses a solvent. This process consists of 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.

Dry (solvent-free) manufacturing processes are also known. These processes eliminate volatile organic compound emissions and offer the possibility of manufacturing electrodes with greater thicknesses (>120 µm), with a higher energy density of the final energy storage device. US 2019/0305316 discloses dry processing 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, fibrillable binders require additional shear in addition to the dispersion of the components. This is energy intensive and destructive to the active materials. Also known from US 2020/0313193 are dry-processed electrode films comprising an elastic polymeric binder, wherein 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.

There is a need for a binder that provides good electrochemical resistance, provides good adhesion to the metal current collector via a solvent-free manufacturing process and improves the conductivity of the electrode. It is also important that the binder has a high affinity with the other ingredients of the solvent-free formulation so that during pressing, the binder provides intimate cohesion.

According to a first aspect, the present invention relates to a binder comprising a fluorinated polymer A and an acrylic polymer B , characterized in that said acrylic polymer B comprises monomeric units containing one or more functional group(s) CO ₂ ^- Li ⁺ and said acrylic polymer B has a lithiation rate of at least 30%.

The binder according to the present invention comprises two types of polymers, i.e. a fluorinated polymer and an acrylic-based polymer having CO ₂ ^- Li ⁺ functional groups while having a high lithiation rate. Said binder makes it possible to improve the adhesion to the current collector and the conductivity of the electrode containing the binder. Said binder can be used in the preparation of an electrode via a slurry or solvent-free process.

According to a preferred embodiment, said acrylic polymer B has a pH between 2.0 and 10.0 measured at room temperature.

According to a preferred embodiment, said acrylic polymer B also comprises at least 5 mol% of monomeric units containing a functional group –CO ₂ H or carboxylic acid anhydride.

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 (VF ₃ ); 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 CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ X in which X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ =CFOCF ₂ CF ₂ SO ₂ F; the product of formula F(CF ₂ )nCH ₂ OCF=CF ₂ in which n is 1, 2, 3, 4 or 5; the product of formula R ¹ CH ₂ OCF=CF ₂ in which R ¹ is hydrogen or F(CF ₂ )m and m is 1, 2, 3 or 4; the product of formula R ² OCF=CH ₂ in which R ² is F(CF ₂ )p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

According to a preferred embodiment, said fluorinated polymer A comprises monomeric units derived from vinylidene fluoride and optionally monomeric units of a monomer selected from the group consisting of vinyl fluoride; trifluoroethylene (VF ₃ ); 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 CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ X in which X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ =CFOCF ₂ CF ₂ SO ₂ F; the product of formula F(CF ₂ )nCH ₂ OCF=CF ₂ in which n is 1, 2, 3, 4 or 5; the product of formula R ¹ CH ₂ OCF=CF ₂ in which R ¹ is hydrogen or F(CF ₂ )m and m is 1, 2, 3 or 4; the product of formula R ² OCF=CH ₂ in which R ² is F(CF ₂ )p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

According to a preferred embodiment, the fluorinated polymer 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 fluorinated polymer 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.

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

According to a preferred embodiment, the acrylic polymer B comprises monomeric units containing one or more CO ₂ ^- Li ⁺ functional group(s), monomeric units bearing one or more carboxylic acid or carboxylic acid anhydride functional group(s) and monomeric units bearing one or more carboxylic acid ester functional group(s).

According to a preferred embodiment, the acrylic polymer B comprises monomeric units M0 derived from a monomer of formula R ¹ R ² C=C(R ³ )((X ¹ ) _n -CO ₂ ^- Li ⁺ ) in which the substituents R ¹ , R ² and R ³ are independently of one another selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl, monomeric units M1 derived from a monomer of formula R ¹ R ² C=C(R ³ )((X ² ) _n -CO ₂ H) in which the substituents R ¹ , R ² and R ³ are independently of one another selected from the group consisting of H, CO _{2 H and C 1 -C 5 alkyl optionally substituted by a CO 2} H or CO 2 R' group with R' being C ₁ -C ₅ alkyl, CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl, ; X ¹ and X ² being independently of each other a C ₁ -C ₁₀ alkyl hydrocarbon group optionally carrying one or more hydroxyl group(s); n is 0 or 1; and monomeric units M2 derived from a monomer of formula R ⁴ R ⁵ C=C(R ⁶ )C(O)R ⁷ in which the substituents R ⁴ , R ⁵ and R ⁶ are independently of each other selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl; and R ⁷ is selected from the group consisting of –NHC(CH ₃ ) ₂ CH ₂ C(O)CH ₃ or –OR' with R' selected from the group consisting of C ₁ -C ₁₈ 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.

According to a preferred embodiment, said acrylic polymer B in solution in water has a pH between 2.0 and 10.0 measured at room temperature.

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

According to a preferred embodiment, said acrylic polymer B also comprises a divalent cation.

According to another aspect, the present invention provides an electrode comprising the binder according to the present invention, a conductive agent and an active material.

According to a preferred embodiment, the 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 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%.

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 a carbon nanotube, a carbon nanofiber, a vapor-grown carbon fiber; metal powders such as a SUS powder, and an aluminum powder.

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(1+ 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 Li1+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 LiMPO4, M representing Fe, Mn, Co, or Ni.

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

According to another aspect, the present invention provides a method for preparing a dry coated electrode comprising:

- the mixture in powder form of said binder according to the present invention, of an active material and optionally of a conductive agent;

- depositing the mixture obtained in the previous step on a current collector to obtain an electrode;

- consolidation of said electrode by a thermomechanical treatment step carried out at a temperature T1 between Tf – 50°C < T1 < Tg + 50°C when Tg > Tf or at a temperature T1 between Tg – 50°C < T1 < 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.

According to another aspect, the present invention provides a method for preparing an electrode by solvent-based route comprising the steps of:

- mixing in the presence of a solvent of said binder according to the present invention, of an active material and optionally of a conductive agent;

- depositing the mixture obtained in the previous step on a current collector to obtain an electrode;

- drying of said electrode.

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 an electrode according to the present invention.

Detailed description of the invention

According to a first aspect, an electrode binder 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.

Preferably, said binder is in the form of a powder. The use of the binder in powder form allows solvent-free implementation from the phase of mixing the constituents to the phases of deposits 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 having to resort to grinding or dispersion steps after mixing with the active materials and the conductive agents. In particular, said powder has a particle size distribution with a D90 of less than or equal to 750 µm, advantageously less than or equal to 700 µm, preferably less than or equal to 650 µm, more preferably less than or equal to 600 µm, in particular less than or equal to 550 µm, more particularly less than or equal to 500 µm. D90 is the particle size at the 90th percentile (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 in a dry process by laser diffraction on a powder with a focal length of 100 mm. Advantageously, said powder has a particle size distribution with a D90 of less than or equal to 450 µm, preferably less than or equal to 400 µm, more preferably less than or equal to 350 µm, in particular less than or equal to 300 µm, more particularly less than or equal to 250 µm, preferably less than or equal to 200 µm, advantageously less than or equal to 150 µm, preferably less than or equal to 100 µm, particularly preferably less than or equal to 50 µm.

According to a preferred embodiment, said fluorinated polymer 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 CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ X in which X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ =CFOCF ₂ CF ₂ SO ₂ F; the product of formula F(CF ₂ )nCH ₂ OCF=CF ₂ in which n is 1, 2, 3, 4 or 5; the product of formula R ¹ CH ₂ OCF=CF ₂ in which R ¹ is hydrogen or F(CF ₂ )m and m is 1, 2, 3 or 4; the product of formula R ² OCF=CH ₂ in which R ² is F(CF ₂ )p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

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.

According to one embodiment, the fluorinated polymer A is a vinylidene fluoride homopolymer.

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.

Thus, said fluorinated polymer 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 CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ X in which X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ =CFOCF ₂ CF ₂ SO ₂ F; the product of formula F(CF ₂ )nCH ₂ OCF=CF ₂ in which n is 1, 2, 3, 4 or 5; the product of formula R ¹ CH ₂ OCF=CF ₂ in which R ¹ is hydrogen or F(CF ₂ )m and m is 1, 2, 3 or 4; the product of formula R ² OCF=CH ₂ in which R ² is F(CF ₂ )p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

In 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 CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ X in which X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ =CFOCF ₂ CF ₂ SO ₂ F; the product of formula F(CF ₂ )nCH ₂ OCF=CF ₂ in which n is 1, 2, 3, 4 or 5; the product of formula R'CH ₂ OCF=CF ₂ in which R' is hydrogen or F(CF ₂ )z and z is 1, 2, 3 or 4; the product of formula R''OCF=CH ₂ in which R'' is F(CF ₂ )z and z is 1, 2, 3 or 4; perfluorobutylethylene; 3,3,3-trifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

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%.

According to a particular embodiment, the fluorinated polymer A is functionalized in whole or in part, which allows it to improve adhesion to metal. Thus, said fluorinated polymer A can 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.

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.

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, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, hydroxyethylhexyl(meth)acrylate and acryloyloxy propylsuccinate.

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

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 of less than or equal to 20,000 g/mol and bearing 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 of less than or equal to 20,000 g/mol.

The functional group content of PVDF is at least 0.01 mol%, preferably at least 0.1 mol%, and at most 15 mol%, preferably at most 10 mol%.

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 measured at 232°C and 100 sec-1.

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

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

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 up into discrete particles during formulation and application to a substrate.

In some embodiments, the PVDF homopolymer and VDF copolymers are comprised 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%.

As mentioned above, said binder also comprises an acrylic polymer B.

Said acrylic polymer B comprises monomeric units containing one or more CO ₂ ^- Li ⁺ functional group(s). Preferably, said acrylic polymer B has a lithiation rate of at least 30%. The lithiation rate corresponds to the ratio between the number of moles of -CO ₂ ^- Li ⁺ groups and the number of moles of carboxylic groups and -CO ₂ ^- Li ⁺ groups in said acrylic polymer B. In particular, said acrylic polymer has a lithiation rate of at least 35%, advantageously at least 40%, preferably at least 50%. Said acrylic polymer B having a lithiation rate as expressed herein makes it possible to improve the conductivity of an electrode containing said binder.

Preferably, said acrylic polymerB in solution in water has a pH between 2.0 and 10.0, advantageously between 2.5 and 9.0, preferably between 3.0 and 8.0 measured at room temperature.

Preferably, said acrylic polymer B comprises at least 5%, advantageously at least 10%, preferably at least 15%, in particular at least 20% by moles of monomeric units containing a functional group –CO ₂ H or carboxylic acid anhydride. The presence of carboxylic groups or carboxylic acid anhydride also improves adhesion to the current collector.

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.

Preferably, the acrylic polymer B comprises monomeric units containing one or more CO ₂ ^- Li ⁺ functional group(s), monomeric units carrying one or more carboxylic acid or carboxylic acid anhydride functional group(s) and monomeric units carrying one or more carboxylic acid ester functional group(s).

The use of an acrylic polymer B with this type of functional group according to the present invention makes it possible to improve the adhesion to the current collector on which said binder according to the present invention is deposited and the conductivity of the electrode containing a binder according to the present invention.

• des unités monomériquesM0issues d’un monomère de formule R¹R²C=C(R³)((X¹)_n-CO₂ ^-Li⁺) dans laquelle les substituants R¹, R²et R³sont indépendamment les uns des autres sélectionnés parmi le groupe consistant en H, CO₂H et C₁-C₅alkyle optionnellement substitué par un groupement CO₂H ou CO₂R’ avec R’ étant C₁-C₅alkyle,
• des unités monomériquesM1issues d’un monomère de formule R¹R²C=C(R³)((X²)_n-CO₂H) dans laquelle les substituants R¹, R²et R³sont indépendamment les uns des autres sélectionnés parmi le groupe consistant en H, CO₂H et C₁-C₅alkyle optionnellement substitué par un groupement CO₂H ou CO₂R’ avec R’ étant C₁-C₅alkyle, ; X¹et X²étant indépendamment l’un de l’autre un groupement hydrocarbure C₁-C₁₀alkyle optionnellement porteur d’un ou plusieurs groupement(s) hydroxyle(s) ; n est 0 ou 1 ; et
• optionnellement des unités monomériquesM2issues d’un monomère de formule R⁴R⁵C=C(R⁶)C(O)R⁷dans laquelle les substituants R⁴, R⁵et R⁶sont indépendamment les uns des autres sélectionnés parmi le groupe consistant en H, CO₂H et C₁-C₅alkyle optionnellement substitué par un groupement CO₂H ou CO₂R’ avec R’ étant C₁-C₅alkyle ; et R⁷est sélectionné parmi le groupe consistant en –NHC(CH₃)₂CH₂C(O)CH₃ou –OR’ avec R’ sélectionné parmi le groupe consistant en C₁-C₁₈alkyle optionnellement substitué par un ou plusieurs groupement(s) –OH ou un hétérocycle à cinq ou six chainons comprenant au moins un atome d’azote dans sa chaine cyclique.

According to a preferred embodiment, the acrylic polymer B comprises:

• monomeric units M0 derived from a monomer of formula R ¹ R ² C=C(R ³ )((X ¹ ) _n -CO ₂ ^- Li ⁺ ) in which the substituents R ¹ , R ² and R ³ are independently of each other selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl,
• monomeric units M1 derived from a monomer of formula R ¹ R ² C=C(R ³ )((X ² ) _n -CO ₂ H) in which the substituents R ¹ , R ² and R ³ are independently of each other selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl, ; X ¹ and X ² being independently of each other a C ₁ -C ₁₀ alkyl hydrocarbon group optionally carrying one or more hydroxyl group(s); n is 0 or 1; and
• optionally monomeric units M2 derived from a monomer of formula R ⁴ R ⁵ C=C(R ⁶ )C(O)R ⁷ in which the substituents R ⁴ , R ⁵ and R ⁶ are independently selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl; and R ⁷ is selected from the group consisting of –NHC(CH ₃ ) ₂ CH ₂ C(O)CH ₃ or –OR' with R' selected from the group consisting of C ₁ -C ₁₈ alkyl optionally substituted by one or more –OH groups or a five or six membered heterocycle comprising at least one nitrogen atom in its ring chain.

The combined presence of lithium carboxylate, carboxylic acid and carboxylic acid ester functions makes it possible to improve adhesion to the current collector, the conductivity performance of the electrode and also to obtain deformable polymer particles compatible with the fluorinated polymer A.

In particular, the monomeric units M 0 are derived from a monomer of formula R ¹ R ² C=C(R ³ )((X ¹ ) _n -CO ₂ ^- Li ⁺ ) in which the substituents R ¹ and R ² are independently of each other H or CO ₂ H; and R ³ is H, CH ₂ CO ₂ H or CH ₃ ; X ¹ is a C ₁ -C ₅ alkyl hydrocarbon group optionally carrying one or more hydroxyl groups; n is 0 or 1. More particularly, the monomeric units M 0 are derived from a monomer of formula R ¹ R ² C=C(R ³ )((X ¹ ) _n -CO ₂ ^- Li ⁺ ) in which the substituents R ¹ and R ² are independently of each other H or CO ₂ H; and R ³ is H, CH ₂ CO ₂ H or CH ₃ ; X ¹ is a C ₁ -C ₃ alkyl hydrocarbon group optionally carrying one or more hydroxyl groups; n is 0 or 1. Preferably, the monomeric units M 0 are derived from a monomer of formula R ¹ R ² C=C(R ³ )(CO ₂ ^- Li ⁺ ) in which the substituents R ¹ and R ² are independently of each other H or CO ₂ H; and R ³ is H, CH ₂ CO ₂ H or CH ₃ .

In particular, monomeric unitsM1 are derived from a monomer of formula R¹R²C=C(R³)((X²)_n-CO₂H) in which the substituents R¹and R²are independently H or CO₂H; and R³is H, CH₂CO₂H or CH₃; X²is a hydrocarbon group C₁-C₅alkyl optionally carrying one or more hydroxyl groups; n is 0 or 1. More particularly, the monomeric unitsM1 are derived from a monomer of formula R¹R²C=C(R³)((X²)_n-CO₂H) in which the substituents R¹and R²are independently H or CO₂H; and R³is H, CH₂CO₂H or CH₃; X²is a hydrocarbon group C₁-C₃alkyl optionally carrying one or more hydroxyl groups; n is 0 or 1. Preferably, the monomeric unitsM1 are derived from a monomer of formula R¹R²C=C(R³)(CO₂H) in which the substituents R¹and R²are independently H or CO₂H; and R³is H, CH₂CO₂H or CH₃. According to a preferred embodiment, said acrylic polymerBcomprises at least 5%, advantageously at least 10%, preferably at least 15%, in particular at least 20%, more particularly at least 30%, preferably at least 40%, particularly preferably at least 50% by moles of monomeric unitsM 1.

Preferably, said acrylic polymer B comprises monomeric units M 2 of formula R ⁴ R ⁵ C=C(R ⁶ )C(O)R ⁷ in which the substituents R ⁴ , R ⁵ and R ⁶ are independently of each other selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl; R ⁷ is selected from the group consisting of –NHC(CH ₃ ) ₂ CH ₂ C(O)CH ₃ or –OR' with R' selected from the group consisting of C ₁ -C ₁₈ alkyl optionally substituted by one or more –OH group(s) a five or ten membered heterocycle comprising at least one nitrogen atom in its cyclic chain. 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 C ₁ -C ₅ alkyl groups. As mentioned above, the C ₁ -C ₁₈ alkyl 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, delta-lactam, succinimide, 2-imidazolidinone, 4-imidazolidinone. In the present application, the term alkyl includes linear and branched alkyls. 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. In particular, said acrylic polymer B comprises monomeric units M 2 of formula R ⁴ R ⁵ C=C(R ⁶ )C(O)R ⁷ in which the substituents R ⁴ and R ⁵ are H; R ⁶ is H or CH ₃ ; 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. Thus, said acrylic polymer B comprises monomeric units M 2 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.

According to a preferred embodiment, said acrylic polymer B comprises at least 1%, advantageously at least 5%, preferably at least 10%, in particular at least 25%, more particularly at least 20% by mole of monomeric units M 2 .

Optionally, acrylic polymerBmay also include monomeric unitsM3from an unsaturated monomer copolymerizable with the monomers of formula R¹R²C=C(R³)((X²)_n-CO₂H), R¹R²C=C(R³)((X¹)_n-CO₂ ^-Li⁺) and monomers of formula R⁴R⁵C=C(R⁶)HORN⁷ as defined above. Advantageously, the monomeric unitsM3issues can be derived from a monomer of formula (R⁸)(R⁹)C=C(R¹⁰)(R¹¹-R¹²), (R⁸)(R⁹)C=C(R¹⁰)(P(O)(OR¹³)(GOLD¹⁴)), (R⁸)(R⁹)C=C(R¹⁰)(C(O)NH(R^{1 7}-R¹⁸)) or (R⁸)(R⁹)C=C(R¹⁰)(C(O)N(R¹⁵-R¹⁶)(R^{1 7}-R¹⁸)) in which the substituents R⁸, R⁹and R¹⁰are independently selected from the group consisting of H and C₁-C₅alkyl; R¹¹, R¹⁵and R¹⁷are independently of each other selected from the group consisting of C₁-C₁₈alkyl, C₆-C₁₈aryl, C₄-C₁₈cycloalkyl, C₁-C₁₈fluoroalkyl, C₆-C₁₈fluoroaryl, C₄-C₁₈fluorocycloalkyl, propylene glycol oligomers, ethylene glycol oligomers, hexafluoropropylene oxide oligomers and tetrafluoroethylene oxide oligomers; R¹², R¹⁶and R¹⁸are independently selected from the group consisting of CO₂H, COOM, OH, CONH₂, CON(R¹⁹)₂, SO₃H, SO₃M with R¹⁹being C₁-C₅alkyl, M is NH₄ ⁺, NR¹⁹ ₄ ⁺, N / A⁺or K⁺; R¹³and R¹⁴are independently selected from the group consisting of H, C₁-C₁₈alkyl, C₆-C₁₈aryl, C₄-C₁₈cycloalkyl, C₁-C₁₈fluoroalkyl, C₆-C₁₈fluoroaryl, C₄-C₁₈fluorocycloalkyl, propylene glycol oligomers, ethylene glycol oligomers, hexafluoropropylene oxide oligomers, tetrafluoroethylene oxide oligomers, an alkali cation, NH₄ ⁺and NR¹⁹ ₄ ⁺. Preferably, the monomeric unitsM3may 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, methacrylate n-octyl, 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. Among these, itaconic acid, fumaric acid, N-methylolacrylamide, N-methylolmethacrylamide, diacetone acrylamide, acrylamido-2-methylpropanesulfonic acid, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate and allyl glycidyl ether, 1,3-butadiene and acrylonitrile are preferred. These compounds can be used alone or in a mixture of two or more. Preferably, the acrylic polymerBcomprises less than 30%, advantageously less than 20% by mole of monomeric unitsM3 .

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. The acrylic polymer B thus obtained is then brought into contact with a solution or dispersion of lithium hydroxide in order to obtain the monomers comprising -CO ₂ Li groups. The concentration of LiOH is adapted to the desired content of -CO ₂ Li groups.

According to a preferred embodiment, said acrylic polymer B also comprises a divalent cation. Said divalent cation may be Ca ²⁺ , Mg ²⁺ , Ba ²⁺ , Cu ²⁺ or Zn ²⁺ or a mixture thereof. Preferably, said divalent cation may be Ca ²⁺ or Zn ²⁺ or a mixture thereof. Said divalent cation is preferably linked to a carboxylate group CO ₂ ^- of said acrylic polymer B . Said divalent cation may be added in the form of a solution or dispersion of hydroxide of said cation. This is added to the acrylic polymer B simultaneously or not with the solution or dispersion of LiOH mentioned above. The presence of this divalent cation makes it possible to improve the efficiency of the battery comprising said acrylic polymer B . The molar ratio between the divalent cation and the lithium is from 0.01 to 1, preferably from 0.05 to 0.5.

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%.

• Mélange dudit polymère fluoréAsous forme de latex et dudit polymère acryliqueBsous forme d’une solution aqueuse ou de latex, et
• Optionnellement, séchage du mélange obtenu à l’étape précédente, de préférence par atomisation ou co-atomisation,
• Optionnellement broyage du mélange séché obtenu à l’étape précédente.

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

• Mixture of said fluorinated polymer A in the form of latex and said acrylic polymer B in the form of an aqueous solution or latex, and
• Optionally, drying the mixture obtained in the previous step, preferably by atomization or co-atomization,
• Optionally, grinding the dried mixture obtained in the previous step.

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 cryogenic 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 processes and/or by grinding. The drying and grinding steps are carried out when said binder is put into the form of a powder.

Alternatively, said fluorinated polymer A and said acrylic polymer B may be mixed in the presence of an organic solvent or a mixture of water and organic solvent.

According to another aspect, the present invention provides an electrode. The electrode comprises said binder according to the present invention, a conductive agent and an active material.

In a preferred embodiment, the 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 according to the 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%.

The conductive agents in the electrode are composed of one or more materials that can enhance the 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.

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

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, lithium metal, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy and Li ₄ TiO ₁₂ . The shape of the negative electrode active material is not particularly limited but is preferably particulate.

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 LiCoO ₂ , Li(Ni, Co, AI)O ₂ , Li(1+ 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), LiNiO ₂ , LiMn ₂ O ₄ , LiCoMnO ₄ , Li ₃ NiMn ₃ O ₃ , Li ₃ Fe ₂ (PO ₄ ) ₃ , Li ₃ V ₂ (PO ₄ ) ₃ , a Li Mn spinel substituted by a different element having a composition represented by Li1+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 LiMPO4, M representing Fe, Mn, Co, or Ni.

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 LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , and Li ₃ PO ₄ .

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

According to another aspect of the present invention, a method of preparing the dry coated electrode is provided.

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

- 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;

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

- consolidation of said electrode by a thermomechanical treatment step carried out at a temperature T1 between Tf – 50°C < T1 < Tg + 50°C when Tg > Tf or at a temperature T1 between Tg – 50°C < T1 < 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.

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

Thermomechanical treatment can be carried out, for example, by a calendering machine with rollers that can be heated or a plate press that can also be heated.

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

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.

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.

In 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.

According to one embodiment, after the powder mixing step, the electrode is manufactured by a solvent-free process using a calendering process that makes it possible to carry out the film-forming and coating transfer step on 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 rolled 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 mass ratio of conductive agents to active material is preferably 0 to 10%, more preferably 0 to 7%.

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

In one embodiment, the electrode components are all mixed at once using 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.

The preferred thickness of an electrode is 0.1 µm to 1000 µm, preferably 0.1 µm to 300 µm.

According to another aspect, the present invention provides a method of preparing an electrode by solvent-based route comprising the steps of:

- mixing in the presence of a solvent of said binder according to the present invention, of an active material and optionally of a conductive agent;

- depositing the mixture obtained in the previous step on a current collector to obtain an electrode;

- drying of said electrode.

In this method, said solvent may be water or an organic solvent or a mixture of both. Said organic solvent may be selected from the group consisting of n-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), triethylphosphite (TEP), acetone, cyclopentanone, tetrahydrofuran, methyl ethylketone (MEK), methyl isobutyl ketone (MiBK), ethyl acetate (EA), butyl acetate (BA), ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), gamma-butyrolactone and N-butylpyrrolidone; and mixtures thereof.

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 an electrode according to the present invention.

Examples

The following examples illustrate the present invention without limiting it.

pH measurement method

A Mettler Toledo SevenEasy pH meter or equivalent and an Electrode In Lab Routine Pro are used. Before calibration, ensure that the electrode is clean. 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, dip the electrode in the pH 10 buffer solution and press Cal, once the pH has stabilized repeat the operation with the pH 7 then 4 buffer. Rinse with distilled water and dry the electrode between each buffer. The electrode is prepared beforehand before measurement by soaking in a 0.1M HCl solution for one to two hours then rinsed with deionized water. To measure the pH, dip the electrode in the product to be tested and shake for a few seconds. Allow the measurement to stabilize for 15 minutes and read the value displayed by the pH meter. The measurement is taken at room temperature.

Polymer B

In a 1000 ml glass reactor equipped with mechanical stirring and oil bath heating, 416 g of deionized water and 3.2 g of 97% sodium dodecyl sulfate were weighed. In a first container equipped with a magnetic bar stirrer, 150 g of deionized water, 1.06 g of 97% sodium dodecyl sulfate, 0.7 g of diallylphthalate, 163 g of methyl methacrylate, 116 g of methacrylic acid were weighed. This mixture was stirred constantly throughout the polymerization. In a second container, a solution consisting of 0.7 g of ammonium persulfate, 10 g of deionized water was prepared. In a third container, a solution was prepared consisting of 0.1 g of sodium metabisulfite and 10 g of deionized water. 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 stirring, using a peristaltic pump into the reactor over 120 min at 76°C. The dispersion was heated to 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. To this solution, a dispersion of 20% lithium hydroxide in water was added so as to obtain a lithiation rate of 35%.

Polymer A

An aqueous dispersion of PVDF polymer is available in the form of a latex with a pH of 3.6, a dry extract of 24.1% and whose particle sizes are 145 nm. PVDF is a copolymer of vinylidene fluoride and hexafluoropropylene characterized by a melting temperature of 148 ° C measured by DSC (differential scanning calorimetry).

Aqueous formulations are produced using the following process:

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

Example 1

70.11 g of polymer A are weighed and 30.04 g of polymer B are added. The aqueous formulation containing in dry ratio 70% by mass of PVDF and 30% of acrylic polymer is placed in a crystallizer and dried for 24 hours in an oven at 110 ° C. A homogeneous powder is obtained which is ground using an electric knife mill of the coffee grinder type in a first step, then cryogenically ground using a ball mill in a second step. The powder obtained is particularly homogeneous and can be very easily compressed in order to obtain polymeric layers on metal surfaces, using for example a press or calendering machines. This process therefore makes it possible to carry out dry coating on aluminium-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 solvent-free process can be used for the manufacture of anodes.

Claims (20)

Binder comprising a fluorinated polymer A and an acrylic polymer B , characterized in that said acrylic polymer B comprises monomeric units containing one or more functional group(s) CO ₂ ^- Li ⁺ and said acrylic polymer B has a lithiation rate of at least 30% . Binder according to any one of the preceding claims, characterized in that said acrylic polymer B also comprises at least 5 mol% of monomeric units containing a functional group –CO ₂ H or carboxylic acid anhydride. 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 CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ X in which X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ =CFOCF ₂ CF ₂ SO ₂ F; the product of formula F(CF ₂ )nCH ₂ OCF=CF ₂ in which n is 1, 2, 3, 4 or 5; the product of formula R ¹ CH ₂ OCF=CF ₂ in which R ¹ is hydrogen or F(CF ₂ ) _m and m is 1, 2, 3 or 4; the product of formula R ² OCF=CH ₂ in which R ² is F(CF ₂ ) _p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. 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 CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ X in which X is SO ₂ F, CO ₂ H, CH ₂ OH, CH ₂ OCN or CH ₂ OPO ₃ H; the product of formula CF ₂ =CFOCF ₂ CF ₂ SO ₂ F; the product of formula F(CF ₂ )nCH ₂ OCF=CF ₂ in which n is 1, 2, 3, 4 or 5; the product of formula R ¹ CH ₂ OCF=CF ₂ in which R ¹ is hydrogen or F(CF ₂ )m and m is 1, 2, 3 or 4; the product of formula R ² OCF=CH ₂ in which R ² is F(CF ₂ )p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. Binder according to any one of the preceding claims, characterized in that the fluorinated polymer 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. Binder according to any one of the preceding claims, characterized in that said fluorinated polymer HAScomprises 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. 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. Binder according to any one of the preceding claims, characterized in that the acrylic polymer B comprises monomeric units containing one or more CO ₂ ^- Li ⁺ functional group(s), monomeric units carrying one or more carboxylic acid or carboxylic acid anhydride functional group(s) and monomeric units carrying one or more carboxylic acid ester functional group(s). Binder according to any one of the preceding claims, characterized in that the acrylic polymer B comprises monomeric units M0 derived from a monomer of formula R ¹ R ² C=C(R ³ )((X ¹ ) _n -CO ₂ ^- Li ⁺ ) in which the substituents R ¹ , R ² and R ³ are independently of each other selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl, monomeric units M1 derived from a monomer of formula R ¹ R ² C=C(R ³ )((X ² ) _n -CO ₂ H) in which the substituents R ¹ , R ² and R ³ are independently of each other selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl; X ¹ and X ² being independently of each other a C ₁ -C ₁₀ alkyl hydrocarbon group optionally carrying one or more hydroxyl group(s); n is 0 or 1; and optionally monomeric units M2 derived from a monomer of formula R ⁴ R ⁵ C=C(R ⁶ )C(O)R ⁷ in which the substituents R ⁴ , R ⁵ and R ⁶ are independently of each other selected from the group consisting of H, CO ₂ H and C ₁ -C ₅ alkyl optionally substituted by a CO ₂ H or CO ₂ R' group with R' being C ₁ -C ₅ alkyl; and R ⁷ is selected from the group consisting of –NHC(CH ₃ ) ₂ CH ₂ C(O)CH ₃ or –OR' with R' selected from the group consisting of C ₁ -C ₁₈ 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. Binder according to any one of the preceding claims, characterized in that said acrylic polymer B in solution in water has a pH of between 2.0 and 10.0 measured at room temperature. 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%. Binder according to any one of the preceding claims, characterized in that said acrylic polymer B also comprises a divalent cation. Electrode comprising said binder according to any one of claims 1 to 12, a conductive agent and an active material. Electrode according to the preceding claim having the following mass composition:
a. 50% to 99% active material,
b. 25% to 0.5% conductive agent,
c. 25% to 0.05% of binder according to any one of the preceding claims 1 to 12, 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%. An electrode according to any one of claims 13 and 14, said conductive agent 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. An electrode according to any one of claims 13 to 15, wherein, for a positive electrode, said active material is selected from the group consisting of: LiCoO2, Li(Ni, Co, AI)O2, Li(1+ 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 Li1+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 LiMPO4, M representing Fe, Mn, Co, or Ni. An electrode according to any one of claims 13 to 15, wherein, for a negative electrode, said active material is selected from the group consisting of a lithium alloy, lithium metal, a metal oxide, a carbon material such as graphite or hard carbon, silicon, a silicon alloy and Li4TiO12. A process for the preparation of a dry coated electrode comprising:
- the mixture in powder form of said binder according to any one of claims 1 to 12, of an active material and optionally of a conductive agent;
- depositing the mixture obtained in the previous step on a current collector to obtain an electrode;
- consolidation of said electrode by a thermomechanical treatment step carried out at a temperature T1 between Tf – 50°C < T1 < Tg + 50°C when Tg > Tf or at a temperature T1 between Tg – 50°C < T1 < 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. Process for the preparation of an electrode by solvent-based means comprising the steps of:
- mixing in the presence of a solvent of said binder according to any one of claims 1 to 12, of an active material and optionally of a conductive agent;
- depositing the mixture obtained in the previous step on a current collector to obtain an electrode;
- drying of said electrode. A Li-ion battery comprising a positive electrode, a negative electrode and a separator, at least one electrode being an electrode according to any one of claims 13 to 17.