LIANT POLYMERE FLUORE

Abstract

The present invention relates generally to the field of electrical energy storage in secondary Li-ion batteries. More specifically, the invention concerns a binder in powder form based on a homogeneous mixture of fluorinated polymers. The invention also relates to several methods for preparing said binder. Finally, the invention relates to an electrode comprising said binder, as well as to secondary Li-ion batteries comprising at least one such electrode.

Description

Title of the invention: FLUORIDE POLYMER BINDER FIELD OF INVENTION

[0001] The present invention relates generally to the field of electrical energy storage in secondary Li-ion batteries. More specifically, the invention relates to a binder in powder form based on an intimate mixture of fluorinated polymers. The invention also relates to several methods for preparing said binder. Finally, the invention relates to an electrode comprising said binder, as well as to energy storage devices comprising at least one such electrode, such as secondary Li-ion batteries and supercapacitors. TECHNICAL BACKGROUND

[0002] A Li-ion battery comprises at least one negative electrode or anode coupled to a copper current collector, one positive electrode or cathode coupled to an aluminum current collector, a separator, and an electrolyte. The electrolyte consists of a lithium salt, generally lithium hexafluorophosphate, mixed with a solvent that is a mixture of organic carbonates, chosen to optimize ion transport and dissociation. A high dielectric constant promotes ion dissociation, and therefore the number of ions available in a given volume, while low viscosity is favorable to ion diffusion, which plays an essential role, among other parameters, in the charging and discharging rates of the electrochemical system.

[0003] For their part, the electrodes generally include at least one current collector on which is deposited, in the form of a film, a composite material which consists of: a material called active because it has an electrochemical activity towards 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.

[0004] Binders are considered inactive components because 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 extensively 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 components of the electrodes, i.e., the active materials and the conductive agents (cohesion). In addition, the binder must ensure close contact with the electrode composite towards the current collector (adhesion).

[0005] Polyvinylidene fluoride (PVDF) is the most commonly used binder in lithium-ion batteries due to its excellent electrochemical stability, good adhesion, and strong bonding to electrode and current collector materials. However, PVDF can only be dissolved in certain organic solvents such as N-methylpyrrolidone (NMP), which is volatile, flammable, explosive, and highly toxic, leading to serious environmental problems. The use of organic solvents requires significant investment in production, recycling, and purification facilities.

[0006] Compared to the conventional method of manufacturing electrodes in wet suspension, dry (solvent-free) manufacturing processes are simpler; these processes eliminate the emission of volatile organic compounds, and offer the possibility of manufacturing electrodes with higher thicknesses (>120pm), with a higher energy density of the final energy storage device.

[0007] Polytetrafluoroethylene (PTFE) is a material of choice for the manufacture of dry electrodes due to its ability to fibrillate at room temperature. Fibrillation of PTFE improves the mechanical properties of the electrode and increases its cohesion. However, PTFE has two limitations: it does not always allow for sufficient adhesion to the cathode (on aluminum foil) and must be combined with other binders; at the anode, there is a reduction reaction of PTFE, which severely limits its use.

[0008] Document WO 2015 / 161289 describes an energy storage device having a cathode, an anode, and a separator between the anode and the cathode, wherein at least one of the electrodes comprises a composite binding material based on polytetrafluoroethylene (PTFE). The PTFE composite binding material may comprise PTFE and at least one of the following materials: polyvinylidene fluoride (PVDF), PVDF copolymer, and poly(ethylene oxide) (PEO). Example 6 describes a manufacturing process for forming the cathode electrode film, said process comprising first mixing activated carbon with powdered PVDF in a mass ratio of 2:1 for 10 minutes, followed by a spray milling step under a pressure of about 80 psi, then adding a powder mixture comprising NMC, activated carbon and carbon black, and finally adding PTFE and mixing for 10 minutes.

[0009] The disadvantage of this type of composite binder is the lack of durable cohesion, namely that even if an initial homogeneous mixture of several types of particles is obtained, these particles are not attached to each other and are therefore subject to settling phenomena during storage or transport, and thus to a loss of homogeneity over time.

[0010] There is still a need to develop new electrode binders for Li-ion batteries that are suitable for dry (solvent-free) electrode manufacturing.

[0011] The invention therefore aims to provide compositions and manufacturing methods of binders and films, based on solid particles, for battery electrodes.

[0012] Another object of the present invention is to provide an electrode which has a relatively low mass ratio of binder in order to increase the active charge rate in the cathode in order to maximize the capacity of the batteries.

[0013] The invention also aims to provide a method for manufacturing electrodes for Li-ion batteries using said compositions, by a solvent-free deposition technique on a metallic substrate. Finally, the invention relates to an electrode obtained by this method.

[0014] Finally, the invention aims to provide energy storage devices comprising at least one such electrode such as Li-ion secondary batteries and supercapacitors comprising at least one such electrode. Summary of the invention

[0015] The present invention relates to a binder usable in a lithium-ion battery. It is a composite binder formed from an intimate mixture of two fluorinated polymers, PTFE and PVDF.

[0016] The invention relates firstly to a fluorinated polymer binder for lithium-ion battery, consisting of a mixture of a PTFE phase formed of PTFE particles having a size ranging from 10 nm to 1 pm, and a PVDF phase formed of PVDF particles having a size ranging from 10 nm to 1 pm, said binder being in powder form.

[0017] According to one embodiment, PVDF is selected from poly(vinylidene fluoride) homopolymers and copolymers of vinylidene difluoride with at least one comonomer selected from the list: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, 1,1,3,3,3-pentafluoropropene, 1,2,3,3,3-pentafluoropropene, perfluoropropylvinyl ether, perfluoromethylvinyl ether, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene, chlorotrifluoropropene, ethylene, and mixtures thereof.

[0018] The invention also relates to different methods of manufacturing said binder.

[0019] According to one embodiment, said binder is prepared by coating PVDF latex and PTFE, the process comprising the following steps:

[0020] a. mixing a PVDF latex with a PTFE latex, b. Add water to the PVDF and PTFE latex mixture to bring it back the dry extract has a content between 10 and 50% by weight of polymer, c. coatomize the mixture thus obtained to obtain a composite powder formed of PTFE particles and PVDF particles.

[0021] According to one embodiment, said binder is prepared by polymerization of PVDF in the presence of a PTFE seed.

[0022] According to one embodiment, said binder is prepared by polymerization of PTFE in the presence of a PVDF seed.

[0023] Another object of the invention is a Li-ion battery electrode comprising an active charge for the anode or cathode, an electronic conductive charge, and a fluorinated polymer binder as described above. The Applicant has demonstrated that it is possible to manufacture electrodes for lithium-ion batteries containing a binder mass percentage equal to or greater than 1% and equal to or less than 5%; this represents a smaller quantity of binder compared to a technique that does not allow for the intimate combination of the two types of binders, which results in the need to increase the quantity of binder used to obtain equivalent handling, flexibility, and adhesion properties. Reducing the quantity of binder makes it possible to increase the active charge percentage in the cathode and thus increase its charging capacity.

[0024] The invention also relates to a method for manufacturing a Li-ion battery electrode, by a solvent-free route.

[0025] Another object of the invention is a secondary Li-ion battery comprising a negative electrode, a positive electrode and a separator, in which at least one electrode is such as described above.

[0026] The present invention overcomes the drawbacks of the prior art. More specifically, it provides a technology that makes it possible to:

[0027] - improve the ability of the electrode material to be handled, for a rate less binder in the electrode;

[0028] - control the distribution of the binder and the conductive filler on the surface of the filler active;

[0029] - ensure the cohesion and mechanical integrity of the electrode, by guaranteeing a good film formation or consolidation of formulations which can be difficult to achieve for solvent-free processes;

[0030] - improve the homogeneity of the electrode composition in thickness and width of the electrode;

[0031] - decrease the overall binder content in the electrode, which, in the case of processes without known solvents, remains superior compared to a standard "slurry" process,

[0032] - improve the mechanical strength of self-supporting films of electrode formulations. This means that in the case of the solvent-free electrode manufacturing process goes through an intermediate manufacturing phase of a self-supporting film of the formulation before assembly on the current collector, the formulation allows to obtain sufficient mechanical behavior for the handling and winding / unwinding phases.

[0033] DESCRIPTION OF WAYS TO EMBODI THE INVENTION

[0034] The invention is now described in more detail and in a non-limiting manner in the following description.

[0035] According to a first aspect, the invention relates to a fluorinated polymer binder for lithium-ion battery, consisting of a mixture of a polytetrafluoroethylene (PTFE) phase, and a polyvinylidene fluoride (PVDF) phase.

[0036] Characteristically, said binder is in the form of a powder consisting of a mixture of primary PTFE particles having a size ranging from 10 nm to 1 pm, and primary PVDF particles having a size ranging from 10 nm to 1 pm.

[0037] According to various embodiments, said electrode comprises the following characteristics, possibly combined. The indicated contents are expressed by weight, unless otherwise stated.

[0038] According to one embodiment, said PTFE particles have a size ranging from 50 nm to 500 nm, preferably from 100 nm to 300 nm.

[0039] According to one embodiment, said PVDF particles have a size ranging from 50 nm to 500 nm, preferably from 100 nm to 300 nm.

[0040] Primary particles are defined here as particles having a size less than 1 pm.

[0041] The size of the polymer particles is expressed as the volume-average diameter (Dv50). Dv50 is the particle diameter at the fiftieth percentile of the cumulative particle size distribution. This parameter can be measured by laser granulometry.

[0042] The mass ratio in the binder between PVDF and PTFE varies from 10:90 to 90:10.

[0043] According to one embodiment, the binder is fibrillizable, due to the presence of the PTFE.

[0044] PVDF

[0045] The fluorinated polymer used in the invention, generically designated by the abbreviation PVDF, is a vinylidene difluoride-based polymer.

[0046] According to one embodiment, PVDF is a homopolymer poly(vinylidene fluoride) or a mixture of homopolymers of vinylidene fluoride.

[0047] According to one embodiment, PVDF is a homopolymer poly(vinylidene fluoride) or a copolymer of vinylidene difluoride with at least one comonomer compatible with vinylidene difluoride.

[0048] The comonomers compatible with vinylidene difluoride can be halogenated (fluorinated, chlorinated or brominated) or non-halogenated.

[0049] Examples of suitable fluorinated comonomers are: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoropropenes and in particular 3,3,3-trifluoropropene, tetrafluoropropenes and in particular 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropenes and in particular 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene, perfluoroalkylvinyl ethers and in particular those of general formula Rf-O-CF-CF2, Rf being an alkyl group, preferably at Cl to C4 (preferred examples being perfluoropropylvinyl ether and perfluoromethylvinyl ether).

[0050] The fluorinated comonomer may contain a chlorine or bromine atom. In particular, it may be selected from bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene, and chlorotrifluoropropene. Chlorofluoroethylene may 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.

[0051] The VDF copolymer may also include non-halogenated monomers such as ethylene, and / or acrylic or methacrylic comonomers.

[0052] The fluorinated polymer preferably contains at least 50 mole percent of vinylidene difluoride.

[0053] According to one embodiment, PVDF is a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (P(VDF-HFP)), having a weight percentage of hexafluoropropylene monomer units of 2 to 23%, preferably 4 to 15% by weight relative to the weight of the copolymer.

[0054] According to one embodiment, PVDF is a mixture of a homopolymer poly(vinylidene fluoride) and a VDF-HFP copolymer.

[0055] According to one embodiment, PVDF is a copolymer of vinylidene fluoride and tetrafluoroethylene (TFE).

[0056] According to one embodiment, PVDF is a copolymer of vinylidene fluoride and

[0057] chlorotrifluoroethylene (CTFE).

[0058] In one embodiment, PVDF is a VDF-TFE-HFP terpolymer. In another embodiment, PVDF is a VDF-TrFE-TFE terpolymer (TrFE being trifluoroethylene). In these terpolymers, the mass content of VDF is at least 10%, the comonomers being present in varying proportions.

[0059] According to one embodiment, PVDF is a mixture of two or more VDF-HFP copolymers.

[0060] According to one embodiment, the PVDF comprises monomer units bearing at minus one of the following functional 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. The functional group is introduced by a chemical reaction which may be grafting, or copolymerization of the fluorinated monomer with a monomer bearing at least one of the 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.

[0061] According to one embodiment, the functional group carries a carboxylic acid function which is a (meth)acrylic acid type group selected from acrylic acid, methacrylic acid, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate and hydroxyethylhexyl(meth)acrylate.

[0062] According to one embodiment, the units bearing the carboxylic acid function further comprise a heteroatom selected from oxygen, sulfur, nitrogen and phosphorus.

[0063] 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 bearing functional groups selected from among the following: carboxylic acid, carboxylic acid anhydride, carboxylic acid esters, epoxy groups (such as glycidyl), amide, hydroxyl, carbonyl, mercapto, sulfide, oxazoline, phenolic, ester, ether, siloxane, sulfonic, sulfuric, phosphoric, and phosphonic groups. An example of such a transfer agent is acrylic acid oligomers.

[0064] 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%.

[0065] The PVDF preferably has a high molecular weight. By high molecular weight, as used here, is meant a PVDF having a molten viscosity greater than 100 Pa·s, preferably greater than 500 Pa·s, more preferably greater than 1000 Pa·s, advantageously greater than 2000 Pa·s. The viscosity is measured at 232°C, at a shear rate of 100 s⁻¹ using a capillary rheometer or a parallel-plate rheometer, according to ASTM D3825. Both methods give similar results.

[0066] The homopolymer PVDFs and VDF copolymers used in the invention can be obtained by polymerization methods known as emulsion polymerization.

[0067] According to one embodiment, they are prepared by an emulsion polymerization process in the absence of a fluorinated surfactant.

[0068] The 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 10 nm, preferably at least 50 nm, and advantageously the weight-average size is in the range of 100 to 400 nm. The polymer particles may form agglomerates, called secondary particles, whose weight-average size is less than 5000 µm, preferably less than 1000 µm, advantageously between 1 and 80 micrometers, and preferably between 2 and 50 micrometers. Agglomerates can break down into discrete particles during formulation and application to a substrate.

[0069] In certain embodiments, homopolymer PVDF and VDF copolymers are composed of bio-based VDF. The term "bio-based" means "derived from biomass." This improves the membrane's environmental footprint. Bio-based VDF can be characterized by a renewable carbon content, i.e., carbon of natural origin from a biomaterial or biomass, of at least 1 atomic percent as determined by the 14C content according to standard NF EN 16640. The term "renewable carbon" indicates that the carbon is of natural origin and comes from a biomaterial (or biomass), as described below.According to certain embodiments, the bio-carbon content of 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%.

[0070] PTFE

[0071] The fluorinated polymer used in the invention, generically designated by the abbreviation PTFE, is a tetrafluoroethylene (TFE) based polymer.

[0072] According to one embodiment, PTFE is a poly(tetrafluoroethylene) homopolymer or a mixture of tetrafluoroethylene homopolymers.

[0073] According to one embodiment, PTFE is a poly(tetrafluoroethylene) homopolymer or a copolymer of tetrafluoroethylene with at least one comonomer compatible with tetrafluoroethylene, such as vinylidene fluoride or hexafluoropropylene.

[0074] According to one embodiment, the polytetrafluoroethylene which forms part of the binder according to the invention, in a mixture with PVDF, is a polymer obtained by polymerization of TFE in emulsion, under conditions known to man of job.

[0075] According to one embodiment, the TFE can be copolymerized with at least one other monomer, such as vinylidene fluoride or hexafluoropropylene.

[0076] The polymerization of PTFE 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 10 nm, preferably at least 50 nm, and advantageously the average size is in the range of 100 to 400 nm.

[0077] According to one embodiment, the PTFE used in the invention has a high molecular weight, preferably greater than 100,000 g / mol

[0078] The invention also relates to different manufacturing processes of the fluorinated polymer binder.

[0079] Coatomization

[0080] According to one embodiment, said binder is prepared by coatomization of the PVDF and PTFE latexes described above.

[0081] Atomization (or coatomization) is known in itself. For a general description of this technology, see, for example, the chapter "Drying" by P.Y. McCormick, in "Encyclopedia of Polymer Science and Engineering", Volume 5, pp. 187-203, Wiley International Sciences, 1990. During the preparation of the binder in powder form, the fluorinated polymers are always in the form of particles smaller than 1 µm.

[0082] According to one embodiment, an aqueous dispersion is prepared by stirring the mixture of fluorinated polymer latex (PVDF latex and PTFE latex, as described above) to reduce the dry extract to a content of between 10 and 50% by mass of PVDF + PTFE polymers. This aqueous dispersion is then atomized, preferably in the presence of a siloxane-modified polyether antifoaming agent, to produce a composite powder that can then be used in the preparation of electrodes.

[0083] At the end of the powder manufacturing step, the particle size can be adjusted and optimized by selection or sieving methods.

[0084] Polymerization of PVDF in the presence of a PTFE seed (PVDF shell / PTFE core)

[0085] According to one embodiment, said binder is prepared by polymerization of PVDF in the presence of a PTFE seed.

[0086] According to one embodiment, in the reactor used for the emulsion polymerization of TFE monomers and for obtaining PTFE in latex form, one Water is added to obtain a dry extract ranging from 10 to 50%, to which vinylidene fluoride and a polymerization initiator are added. At the end of the polymerization reaction, a stable latex is obtained with a particle size in the range of 200 to 400 nm (Dv50). The PVDF:PTFE mass composition of this latex varies from 10:90 to 90:10. The solids content obtained is between 10 and 60%.

[0087] According to one embodiment, PTFE latex is obtained in a first reactor, it is transferred to another reactor possibly after a storage time, then the polymerization of PVDF is started.

[0088] Polymerization of PTFE in the presence of a PVDF seed (PTFE shell / PVDF core)

[0089] According to one embodiment, said binder is prepared by polymerization of PTFE in the presence of a PVDF seed.

[0090] According to one embodiment, water is added to the reactor used for the emulsion polymerization of VDF monomers and the production of PVDF in latex form to obtain a dry extract ranging from 10 to 50%, to which tetrafluoroethylene and a polymerization initiator are added. At the end of the polymerization reaction, a stable latex is obtained with a particle size in the range of 200 to 400 nm (Dv50). The PVDF:PTFE mass composition of this latex varies from 10:90 to 90:10. The solids content obtained is between 10 and 60%.

[0091] According to one embodiment, PVDF latex is obtained in a first reactor, it is transferred to another reactor possibly after a storage time, then the polymerization of PTFE is started.

[0092] Another object of the invention is a Li-ion battery electrode comprising an active charge for anode or cathode, an electronic conductive charge, and a fluorinated polymer binder as described above.

[0093] In the electrode material, PTFE is fibrillated. The extent of fibrillation and the quality of the fibrils formed influence certain properties of the electrode, such as its flexibility and handling. The fibrils are visible by scanning electron microscopy (SEM).

[0094] The active materials at the negative electrode are generally lithium metal, graphite, graphene, silicon / carbon composites, silicon, CFX type fluorinated graphites with x between 0 and 1 and LiTi50i2 type titanates.

[0095] The active materials at the positive electrode are generally of the type LiM02, of the type LiMPO4, of the type Li2MPO3F, of the type Li2MSiO4 where M is Co, Ni, Mn, Fe or a combination thereof, of the type LiMn2O4, of the type S8, and of lithium polysulfides represented by the formula Li2Sn with n >1.

[0096] The conductive fillers are selected from carbon blacks, graphites, natural or synthetic, carbon fibers, carbon nanotubes, fibers and metallic powders and conductive metal oxides. Preferably, they are chosen from carbon blacks, graphites, natural or synthetic, carbon fibers and carbon nanotubes.

[0097] A mixture of these conductive fillers can also be made. In particular, the use of carbon nanotubes in association with another conductive filler such as carbon black can have the advantages of reducing the proportion of conductive fillers in the electrode and reducing the proportion of polymer binder due to a lower specific surface area compared to carbon black.

[0098] According to one embodiment, a polymeric dispersant, which is separate from said binder, is used in a mixture with the conductive filler to break down any agglomerates present and aid its dispersion in the final formulation with the polymeric binder and the active filler. The polymeric dispersant is selected from poly(vinylpyrrolidone), poly(phenylacetylene), poly(meta-phenylene vinylidene), polypyrrole, poly(para-phenylene benzobisoxazole), poly(vinyl alcohol), and mixtures thereof.

[0099] The mass composition of the electrode is:

[0100] - 50% to 99% active load, preferably from 50% to 99%, - 25% to 0.05% conductive charge, preferably 25% to 0.5%, - 10 to 0.5% polymer binder, preferably 6 to 1%, - 0 to 5% of at least one additive chosen from the list: plasticizer, ionic liquid, dispersing agent for conductive fillers, and flow agent for the formulation,

[0101] the sum of all these percentages being 100%.

[0102] The invention also relates to a solvent-free manufacturing process for a Li-ion battery electrode, said process comprising the following steps:

[0103] - mixture of the active filler, the polymer binder, the conductive filler and the possible additives using a process that makes it possible to obtain an electrode formulation applicable to a metallic support by a solvent-free process;

[0104] - deposition of said electrode formulation onto the metallic substrate by a process called "solvent-free", to obtain a Li-ion battery electrode, and

[0105] - the consolidation of said electrode by a heat treatment (application of a temperature up to 50°C above the polymer melting temperature, without mechanical pressure), and / or thermo-mechanical treatment such as calendering or thermo-compression.

[0106] A "solvent-free" process is understood to mean a process which does not require a residual solvent evaporation step downstream of the deposition step.

[0107] Another embodiment of the process for manufacturing an electrode comprises the following steps:

[0108] - mixing of the active charge, the polymer binder and the conductive charge using of a process which makes it possible to obtain an electrode formulation whose constituents are mixed homogeneously;

[0109] - manufacturing a self-supporting film of the formulation using a thermo process mechanical processes such as extrusion, calendering or thermo-compression;

[0110] - deposition of the self-supporting film onto the metallic substrate by a calendering process or thermo-compression, and

[0111] - the consolidation of said electrode by a heat treatment and / or thermo mechanical processes such as calendering, for example, with the latter step being optional if the previous step already allows a sufficient level of adhesion and / or porosity to be achieved.

[0112] As solvent-free mixing processes for the different constituents of the electrode formulation, the following may be mentioned without being exhaustive: stirring, 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, mechano-fusion mixing, extrusion mixing, calendering mixing, grinding mixing.

[0113] As another mixing method, we can mention mixing methods using a liquid as Skin such as spray drying (co-atomization or "spray drying") or a method of spraying a liquid containing the binder and / or the conductive filler onto a bed of fluidized powder of the active filler.

[0114] The metal supports for the electrodes are generally made of aluminum for the cathode and copper for the anode. The metal supports may be surface-treated and have a conductive primary layer 5 µm thick or more. The supports may also be woven or nonwoven carbon fiber.

[0115] The consolidation of said electrode is carried out by heat treatment by passing it through an oven, under an infrared lamp, in a calender with heated rollers or in a heated platen press. Another alternative consists of a two-step process.

[0116] First, the electrode undergoes heat treatment in a furnace, under an infrared lamp, or in contact with unpressurized heated plates. Then, a compression step at room temperature or while hot is carried out using a calender or a platen press. This step allows the electrode's porosity to be adjusted and improves adhesion to the metallic substrate.

[0117] The invention also relates to a Li-ion battery electrode manufactured by the process described above.

[0118] According to one embodiment, said electrode is an anode.

[0119] According to one embodiment, said electrode is a cathode.

[0120] Another object of the invention is a secondary Li-ion battery comprising a negative electrode, a positive electrode and a separator, in which at least one electrode is such as described above.

[0121] Another object of the invention is a supercapacitor comprising at least one such electrode.

[0122] EXAMPLES

[0123] The following examples illustrate, in a non-limiting manner, the scope of the invention.

[0124] Sample 1 - Preparation of a PTFE latex

[0125] Water, an initiator, a chain transfer agent, a non-fluorinated emulsifier, and ethylene tetrafluoride are introduced into a reactor. Polymerization is carried out at a temperature of 68°C and under a pressure of 3000 kPa. After 180 min, a latex containing 29% solids is obtained. The primary particle size is 250 nm (D50).

[0126] Sample 2 - Preparation of a PTFE powder

[0127] The latex from sample 1 is then spray-dried to obtain a PTFE powder.

[0128] Sample 3 - Preparation of a PVDF latex

[0129] Water, an initiator, a chain transfer agent, a non-fluorinated emulsifier, and vinylidene fluoride are introduced into a reactor. Polymerization is carried out at a temperature of 85°C and under a pressure of 9000 kPa. After 180 min, a latex containing 37% solids is obtained. The size of the primary particle is 225 nm (D50).

[0130] Sample 4 - Preparation of a PVDF powder

[0131] The latex corresponding to sample 3 is spray-dried to obtain a PVDF powder

[0132] Sample 5 - Preparation of a mixture of PVDF and PTFE powders

[0133] In a Henschel FM10 type powder mixer for 2 minutes, 750g of PTFE powder corresponding to sample 2 and 250g of PVDF powder corresponding to sample 4 are introduced. Agitation is carried out for 2min at a rotation speed such that the speed at the end of the blades is 20 ms'.

[0134] Sample 6 - Preparation of a PTFE / PVDF composite binder by coatomization

[0135] The PTFE latex corresponding to sample 1 (1.034 kg) and the latex of PVDF corresponding to sample 3 (0.27 kg) and 0.696 kg of water were added to bring the dry extract to 20% PVDF + PTFE polymer. An antifoaming agent (Byk 019) was also added. The addition was carried out under moderate stirring in a 5-liter container (10 rpm) at room temperature (20°C). The resulting aqueous dispersion was easily pumpable. The PTFE latex / PVDF latex mixture thus prepared was then pumped under moderate stirring (10 rpm) and then coatomized using the operating conditions. following ratories:

[0136] Coatomizer inlet temperature: 175°C

[0137] Coatomizer outlet temperature: 55°C

[0138] Compressed air: 220 kPa

[0139] Coatomization of PVDF latex particles and PTFE particles allows the preparation of 400 g of PVDF / PTFE composite powder. This composite powder contains 25% by mass of PVDF and 75% by mass of PTFE. The size of the secondary particles thus formed is 23 µm (D50).

[0140] Sample 7 - Preparation of a core-shell structure, PTFE core / PVDF shell

[0141] Water, an initiator, a chain transfer agent, a non-fluorinated emulsifier, and ethylene tetrafluoride are introduced into a reactor. Polymerization is carried out at a temperature of 68°C and under a pressure of 3000 kPa. The total reaction volume is 2 L. After 180 min, a latex containing 29% solids is obtained. The latex thus obtained is then reduced to a 20% dry extract by adding water (900 g). The temperature is then increased to 90°C and the pressure is increased to 4500 kPa by continuously adding VF2 to the reactor. The addition of potassium persulfate initiator allows the polymerization of a PVDF shell around the PTFE core to begin. After 60 minutes of polymerization, a stable latex is obtained with a particle size of 280 nm (D50). The mass composition is 75% PTFE and 25% PVDF. The solids content obtained is 25%.The total quantity consumed was 193 g of VF2.

[0142] Sample 8 - Preparation of a core-shell structure, PVDF core / PTFE shell

[0143] Water, an initiator, a chain transfer agent, a non-fluorinated emulsifier, and PVDF are introduced into a reactor. Polymerization is carried out at a temperature of 90°C and under a pressure of 4500 kPa. The total reaction volume is 2 L. After 180 min, a latex containing 37% solids is obtained, with a primary particle size D50 of 225 nm. The latex thus obtained is then reduced to a 15% dry extract by the addition of water (2933 g). The temperature is then lowered to 70°C and the pressure is reduced to 3000 kPa by the continuous addition of TFE to the reactor. The addition of potassium persulfate initiator allows the polymerization of a PTFE shell around the PVDF core to begin. After 200 minutes of polymerization, a stable latex is obtained with a particle size of 338 nm (D50). The mass composition is 75% PTFE and 25% PVDF.The solids content obtained is 37.5%.

[0144] Conventional electrode formulation: active material, conductive filler such as carbon black (but also graphene, carbon nanotubes, carbon fibers obtained by vapor-phase growth (VGCF)), and PVDF binder. Electrode manufacturing process

[0145] The active ingredient / conductive filler binder mixture is prepared in two steps. First, an active filler is mixed with a conductive filler using a solvent-free process. In a second step, the binder is mixed with the pre-mixed active and conductive fillers. A Henschel FM 10 high-speed paddle mixer was used for 2 minutes at a rotational speed such that the velocity at the blade tips was 20 m / s.

[0146] The composition is then prepared as a self-supporting film by compression using a heated parallel-plate press. To do this, the formulation is deposited onto a silicone film to obtain a basis weight of 25 mg / cm². A second silicone paper film is then deposited on the surface of the deposit. The assembly, consisting of the first layer of silicone paper, the formulation, and the second layer of silicone paper, is then compressed at 200°C under 700 kPa for 5 minutes. After the compression step, the assembly is removed from the press and allowed to cool to room temperature. A self-supporting film is obtained after removing the silicone paper layers. Subsequently, the self-supporting film is compressed onto the aluminum current collector under the same conditions as the self-supporting film was produced.

[0147] The film and final cathode preparation conditions were adjusted to obtain a thickness of 75 µm and a porosity of 32–34%, calculated indirectly based on the surface weight divided by the theoretical weight per unit area. Film handling was measured.

[0148] An elongation-to-break test is performed on the film, and a classification is established to determine its handling properties. The classification ranges from H0 (immediate breakage) to H3 (elongation at break greater than 3%). Adhesion measurement

[0149] A 180° peel test is performed using a dynamometer on specimens cut to lengths of 15 cm and widths of 25 mm. Double-sided adhesive tape is used to evaluate the peel force. One side of the tape is attached to the electrode, and the other side is attached to a rigid metal support a few millimeters thick. The rigid support is fixed in the lower jaw of the dynamometer, while the end of the electrode is fixed in the upper jaw. The peel force is determined by applying tension at a speed of approximately 100 to 200 mm / min. This allows for the following classification – the values ​​are indicative only, as they depend on the measuring instrument, the peel force, the peel speed, and the adhesive supplier.

[0150] The ranking varies from A0 (no membership) to A4 (excellent membership).

[0151] Measurement of flexibility - empirical test (described in US document 2002 / 0168569)

[0152] Test specimens 5 cm long and at least 2 cm wide are cut from the electrodes. These specimens are then wrapped around a 1 mm diameter metal rod or folded over themselves. The surface is then visually inspected to identify any cracks and establish the following classification

[0153] The classification varies from F0 (very poor flexibility) to F4 (excellent flexibility).

[0154] [Tables 1]

Claims

Claims

1. Fluorinated polymer binder for lithium-ion battery, consisting of a mixture of a polytetrafluoroethylene (PTFE) phase formed from primary PTFE particles having a size ranging from 10 nm to 1 pm, and a polyvinylidene fluoride (PVDF) phase formed from primary PVDF particles having a size ranging from 10 nm to 1 pm, said binder being in powder form.

2. Binder according to claim 1, wherein the PTFE particles have a size ranging from 50 nm to 500 nm, preferably from 100 nm to 300 nm.

3. Binder according to one of claims 1 or 2, wherein the PVDF particles have a size ranging from 50 nm to 500 nm, preferably from 100 nm to 300 nm.

4. Binder according to one of claims 1 to 3, in which the PVDF is chosen from poly(vinylidene fluoride) homopolymers and copolymers of vinylidene difluoride with at least one comonomer chosen from the list: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, 1,1,3,3,3-pentafluoropropene, 1,2,3,3,3-pentafluoropropene, perfluoropropylvinylether, perfluoromethylvinylether, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene, chlorotrifluoropropene, ethylene, and mixtures thereof.

5. A method of manufacturing the binder according to one of claims 1 to 4, by coatomization of PVDF and PTFE latex, said method comprising the following steps: a. mixing a PVDF latex with a PTFE latex, b. adding water to the mixture of PVDF and PTFE latexes to bring the dry extract to a content between 10 and 50% by weight of polymer, c. coatomizing the mixture thus obtained to obtain a composite powder formed of PTFE particles and PVDF particles.

6. Method of manufacturing the binder according to any one of claims 1 to 4, by polymerization of PVDF in the presence of a PTFE seed.

7. Method of manufacturing the binder according to any one of claims 1 to 4, by polymerization of PTFE in the presence of a PVDF seed.

8. A Li-ion battery electrode comprising an active filler for anode or cathode, an electronically conductive filler, and a fluoropolymer binder according to any one of claims 1 to 4.

9. Electrode according to claim 8, in which said active filler is chosen from lithium metal, graphite, silicon / carbon composites, silicon, graphene, fluorinated graphites of type CFx with x between 0 and 1 and titanates of type LiTi50i2 for a negative electrode.

10. An electrode according to claim 8, wherein said active filler is selected from active materials of the LiM02 type, of the LiMPO4 type, of the Li2MPO3F type, of the Li2MSiO4 type where M is Co, Ni, Mn, Fe or a combination thereof, of the LiMn2O4 type> of the S8 type, and lithium polysulfides represented by the formula Li2Sn with n >1, for a positive electrode.

11. Electrode according to one of claims 8 to 10, in which the conductive fillers are chosen from carbon blacks, graphites, natural or synthetic, carbon fibers, carbon nanotubes, metal fibers and powders, conductive metal oxides, or mixtures thereof.

12. Electrode according to one of claims 8 to 11, having the following mass composition: - 50% to 99% of active filler, preferably from 50 to 99%, - 25% to 0.05% of conductive filler, preferably from 25 to 0.5%, - 10 to 0.5% of polymer binder, preferably from 6 to 1%, - 0 to 5% of at least one additive chosen from the list: plasticizer, ionic liquid, dispersing agent for the conductive fillers, and flow agent for the formulation, the sum of all these percentages being 100%.

13. A method of manufacturing the Li-ion battery electrode according to one of claims 8 to 12, said method comprising the following steps: - mixing the active filler, the polymer binder and the conductive filler using a method which makes it possible to obtain an electrode formulation applicable on a metal support by a solvent-free method; - depositing said electrode formulation on the metal substrate by

14. a solvent-free process for obtaining a Li-ion battery electrode, and - consolidating said electrode by thermal and / or thermo-mechanical treatment. Li-ion secondary battery comprising an anode, a cathode and a separator, wherein at least one of the electrodes has the composition according to one of claims 8 to 12.

15. Supercapacitor comprising at least one electrode according to one of claims 8 to 12.