Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/362—Composites
  • H01M4/366—Composites as layered products
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
  • C08F214/18—Monomers containing fluorine
  • C08F214/22—Vinylidene fluoride
  • C08F214/222—Vinylidene fluoride with fluorinated vinyl ethers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L27/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers
  • C08L27/02—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L27/12—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08L27/16—Homopolymers or copolymers or vinylidene fluoride
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0402—Methods of deposition of the material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/134—Electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/381—Alkaline or alkaline earth metals elements
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/381—Alkaline or alkaline earth metals elements
  • H01M4/382—Lithium
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/621—Binders
  • H01M4/622—Binders being polymers
  • H01M4/623—Binders being polymers fluorinated polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2203/00—Applications
  • C08L2203/20—Applications use in electrical or conductive gadgets
  • C08L2203/206—Applications use in electrical or conductive gadgets use in coating or encapsulating of electronic parts
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
  • C08L2205/025—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group containing two or more polymers of the same hierarchy C08L, and differing only in parameters such as density, comonomer content, molecular weight, structure
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates generally to the field of electrical energy storage in secondary lithium batteries of the Li-ion type. More specifically, the invention relates to an anode for a Li-ion secondary battery, said anode comprising a protective film based on fluorinated copolymer (s). The invention also relates to the processes for preparing this anode. The invention finally relates to a secondary Li-ion battery comprising an anode according to the invention.
• Lithium-ion batteries include flammable liquid electrolytes based on solvents and lithium salts. Faced with the growing use of this type of batteries in the field of electronic consumer products such as computers, tablets or mobile phones (smartphones), but also in the field of transport with in particular electric vehicles, the improvement safety and reducing the manufacturing cost of these lithium batteries have become major challenges. These batteries use graphite anodes in which Li ions are inserted during charging. The compound that forms is CeLi, equivalent to Li for 72 g of graphite.
• Interfaces can be stabilized by means of additives, or deposits can be cured by agents acting as screens or by blocking growth mechanically with ceramics. Stabilization of the Li anode would be of interest, both for batteries based on solvent / salt pairs, as on batteries based on solid polymer electrolytes (SPEs, for Solid Polymer Electrolyte), without liquid solvent, thus avoiding the use of flammable liquid components as in conventional Li-ion batteries and allowing the production of finer and possibly more flexible batteries.
• SPEs solid polymer electrolytes
• a protective layer can form during battery operation to form a SEI (Solid Electrolyte Interface).
• This interface is an ionic conductor formed by a mixture of LLSe and P2S5 (denoted LSPS), complexed to lead to a single polymeric species in dimethoxyethane (DME).
• DME dimethoxyethane
• the additive is reduced on the surface of the Li metal, and gives a dense layer of Ü3PS 4 .
• the amorphous nature of this material is critical for good protection.
• the SEI is uniform and compact without a high density of defects.
• the two aforementioned methods are complicated to implement.
• the microspheres must have a large homogeneity in size and crosslinking to avoid fragile areas where the dendrites could exert pressure.
• the structure of LÎ3PS 4 must also be well controlled to provide the best protection. This control is not easy. In addition, this structure is very sensitive to humidity and oxygen and its handling is delicate.
• Document KR201 10082289 describes a Li-ion battery in which a polymer film containing a lithium powder is placed between an electrode and a separator. Said film is prepared by applying a solution, in which the lithium metal is dispersed in a solution of polymeric binder, on the electrode, followed by a drying step.
• the binder solution is prepared by dissolving at least one of the following polymers in a non-aqueous solvent: a fluorine-based polymer, an acrylic polymer, an SBR (styrene-butadiene) rubber and a polyacrylonitrile-based polymer.
• the invention therefore aims to remedy at least one of the drawbacks of the prior art, namely the formation of dendrites, which is particularly noticeable in the case of high charge / discharge speeds.
• the invention also aims to provide methods for manufacturing these stabilized anodes by depositing a film of fluorinated copolymer. Finally, the invention aims to provide secondary Li-ion batteries comprising stabilized anodes.
• the invention relates firstly to a negative electrode (or anode) for a lithium-ion battery, comprising a current collector and a layer of active material of negative electrode covered with a film of fluorinated copolymer (s).
• fluorinated copolymer includes the copolymers and terpolymers described below.
• said film comprises at least one of the following copolymers:
• VDF-TFE a copolymer comprising vinylidene fluoride and tetrafluoroethylene units of formula P (VDF-TFE), or
• the terpolymer comprising units of vinylidene fluoride, trifluoroethylene and chlorotrifluoroethylene of formula P (VDF-TrFE-CTFE),
• the terpolymer comprising units of vinylidene fluoride, trifluoroethylene and chlorotrifluoroethylene of formula P (VDF-TrFE-CTFE),
• the terpolymer comprising units of vinylidene fluoride, trifluoroethylene and hexafluoropropylene of formula P (VDf-TrFE-HFP),
• the terpolymer comprising units of vinylidene fluoride, of tetrafluoroethylene and of 1,1-chlorofluoroethylene of formula P (VDF-TFE-CFE),
• the terpolymer comprising units of vinylidene fluoride, tetrafluoroethylene and chlorotrifluoroethylene of formula P (VDF-TFE-CTFE),
• the terpolymer comprising units of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene of formula P (VDf-TFE-HFP).
• said anode comprises the following characters, where appropriate combined.
• said film comprises a mixture of copolymer P (VDF-TrFE) with the copolymer P (VDF-TFE).
• said film comprises a mixture of copolymer P (VDF-TrFE) with one of the abovementioned terpolymers.
• said film comprises a mixture of copolymer P (VDF-TFE) with one of the abovementioned terpolymers.
• said film comprises a mixture of two terpolymers chosen from those listed above.
• the active material of the negative electrode is an alkali metal. According to one embodiment, the active material of negative electrode is lithium. According to one embodiment, said film has a thickness ranging from 1 to 14 mih, preferably from 1 to 10 mih, and more preferably between 2 and 10 miti, limits included.
• said film has a density ranging from 1.2 to 2 g / cm 3 .
• the invention also relates to a method of manufacturing a negative electrode comprising a layer of active material of negative electrode covered with a film of fluorinated copolymer (s) as described above.
• This method comprises a step of depositing or forming a film of fluorinated copolymer (s) on the surface of said active negative electrode material.
• the film is formed in the solvent route, by evaporation of the solvent from a solution of fluorinated copolymer (s).
• the film is deposited in the dry process consisting in preparing a fluorinated film on a suitable support and in transferring this fluorinated film onto the layer of active material of negative electrode.
• Another object of the invention is a secondary Li-ion battery comprising said negative electrode, a positive electrode and an electrolyte.
• Another object of the invention is the use of a copolymer chosen from:
• copolymer comprising vinylidene fluoride and trifluoroethylene units of formula P (VDF-TrFE),
• copolymer comprising vinylidene fluoride and tetrafluoroethylene units of formula P (VDF-TFE), and
• a fluorinated terpolymer chosen from: the terpolymer comprising vinylidene fluoride, trifluoroethylene and chlorofluoroethylene units of formula P (VDF-TrFE-CFE), the terpolymer comprising vinylidene fluoride, trifluoroethylene and chlorotrifluoroethylene units of formula P (VDF-TrFE-CTFE), the terpolymer comprising vinylidene fluoride, trifluoroethylene and hexafluoropropylene units of formula P (VDf-TrFE-HFP), the terpolymer comprising vinylidene fluoride, tetrafluoroethylene and of chlorofluoroethylene of formula P (VDF-TFE-CFE), the terpolymer comprising units of vinylidene fluoride, of tetrafluoroethylene and of chlorotrifluoroethylene of formula P (VDF-TFE-CTFE), and the terpolymer comprising units of
• the present invention overcomes the drawbacks of the state of the art. It more particularly provides a stabilized anode thanks to the presence of a film of fluorinated copolymer (s) deposited on the surface of the active material of the negative electrode, said film inhibiting the formation of dendrites within the active material of negative electrode. It is particularly suitable for the manufacture of lithium-ion secondary batteries of which said active material of negative electrode is lithium. The stability of this electrode improves the performance and lifespan of the batteries.
• the invention relates to a negative electrode for a lithium-ion battery, comprising a current collector and a layer of active material of negative electrode covered with a film of fluorinated copolymer (s).
• said film comprises at least one copolymer comprising vinylidene fluoride and trifluoroethylene units of formula P (VDF-TrFE), or a copolymer comprising vinylidene fluoride and tetrafluoroethylene units of formula P (VDF-TFE) ), or a fluorinated terpolymer chosen from: the terpolymer comprising vinylidene fluoride, trifluoroethylene and 1, 1-chlorofluoroethylene units of formula P (VDF-TrFE-CFE), the terpolymer comprising vinylidene fluoride units, trifluoroethylene and chlorotrifluoroethylene of formula P (VDF-TrFE-CTFE), the terpolymer comprising units of vinylidene
• the negative electrode active material can be an alkali metal, an alkaline earth metal or a member of the boron group.
• the active negative electrode material claimed in the present invention is an alkali metal.
• said anode comprises the following characters, where appropriate combined.
• said active material of negative electrode is lithium.
• said film has a thickness ranging from 1 to 14 mih, preferably from 1 to 10 micrometers, and more preferably from 2 to 10 pm, limits included.
• the thickness of the fluorinated film must be limited, to avoid creating an interface impedance detrimental to a power operation of the battery. With films that are too thick, the diffusion of lithium is slowed down.
• said fluorinated film has a density ranging from 1.2 to 2 g / cm 3 .
• said fluorinated film is a porous film with a pore size of between 100 nm and 1 ⁇ m.
• the presence of the fluorinated film on the layer of active material of negative electrode makes it possible to prevent or at least to greatly reduce the formation of lithium dendrites.
• the targeted copolymers or terpolymers are naturally polar: FE phase (Ferroelectric for copolymers) and / or RFE phase (Ferroelectric Relaxer for terpolymers), which are close to the Beta phase obtained for PVDF under very specific conditions (for example, by film stretching or dissolution in specific solvents and slow evaporation or addition of additives, solutions which are not compatible with industrially applicable processes).
• the Applicant thinks that the polarity of the fluorinated film obtained from the copolymers and terpolymers described is sufficient to allow orientation of the lithium cations in a plane parallel to the collector and to the Li metal film, rather than in a perpendicular direction which would favor the formation of dendrites.
• the invention is therefore based on the use of a fluorinated copolymer or terpolymer or their mixture, in the form of a film deposited on the surface of an active material of a negative electrode.
• fluorinated is meant a polymer comprising -F groups.
• the copolymers and terpolymers are relaxant ferroelectric or ferroelectric polymers.
• Ferroelectric copolymers or terpolymers have a large hysteresis of the polarization curve (charge vs applied field) with a high coercive field (typically of the order of 20 V / pm, even 50 V / miti) and a high remanent polarization (typically around 60 mC / m 2 ).
• the terpolymers or copolymers relaxants have a weak coercive field (typically less than 10 V / pm), a weak remanent polarization (typically less than 20 mC / m 2 ) or even zero, a polarization at high saturation (typically of the order of 60 mC / m 2 or even 70 mC / m 2 ) and a maximum dielectric permittivity as a function of the temperature depending on the frequency of the electric field.
• a weak coercive field typically less than 10 V / pm
• a weak remanent polarization typically less than 20 mC / m 2
• a polarization at high saturation typically of the order of 60 mC / m 2 or even 70 mC / m 2
• a maximum dielectric permittivity as a function of the temperature depending on the frequency of the electric field.
• Another advantage is that of the higher permittivity of the copolymers and especially of the terpolymers which makes it possible to obtain a more marked polarization at the interface with lithium and a more marked dissociation of the electrolytes.
• the relative dielectric permittivity at 23 ° C. and 1 kHz of the copolymers and terpolymers is greater than 10.
• the maximum dielectric permittivity as a function of the temperature is at least 30 or even 40.
• the relative dielectric permittivity can be measured by dielectric spectroscopy.
• the Curie temperature of the copolymer P is between 50 and 140 ° C.
• the Curie temperature of the polymers of the invention can be measured by differential scanning calorimetry or by dielectric spectroscopy.
• the proportion of units from trifluoroethylene is less than 55 mol.% And more than 18 mol% relative to the sum of the units from fluoride of vinylidene and trifluoroethylene.
• the proportion of units derived from tetrafluoroethylene is less than 60 mol.% And greater than 10 mol% relative to the sum of the units derived from vinylidene fluoride and tetrafluoroethylene.
• copolymers and terpolymers of the invention can be produced using any known method, such as emulsion polymerization, microemulsion polymerization, suspension polymerization and solution polymerization.
• emulsion polymerization emulsion polymerization
• microemulsion polymerization emulsion polymerization
• suspension polymerization emulsion polymerization
• solution polymerization emulsion polymerization
• the use of the process described in document WO 2010/1 16105 is particularly preferred. This process makes it possible to obtain terpolymers of high molecular weight and of suitable structuring.
• the average molar mass by weight which in the context of this application is also designated by “molecular weight” (Mw), of the terpolymer, is from 200,000 to 1,500,000 g / mol, preferably of 250,000 to 1,000,000 g / mol, and more particularly from 300,000 to 700,000 g / mol.
• Mw molecular weight
• the latter can be adjusted by modifying certain process parameters, such as the temperature in the reactor, or by adding a transfer agent.
• the molecular weight distribution can be estimated by SEC (size exclusion chromatography) with dimethylformamide (DMF) as eluent, with a set of 3 columns of increasing porosity.
• the stationary phase is a styrene-DVB gel.
• the detection process is based on a measurement of the refractive index, and the calibration is carried out with polystyrene standards.
• the sample is dissolved in 0.5 g / L in DMF and filtered through a 0.45 ⁇ m nylon filter.
• the molecular weight can also be evaluated by measuring the melt flow index (MFI) at 230 ° C under a load of 10 kg according to ASTM D1238 (ISO 1133).
• MFI melt flow index
• the MFI is between 0.1 and 100, preferably between 0.5 and 50 and more particularly between 1 and 10.
• the molecular weight can also be characterized by a measurement of the viscosity in solution according to ISO standard 1628.
• Methyl ethyl ketone (MEK) is a preferred solvent for terpolymers for the determination of the viscosity index.
• the molar composition of the terpolymers of the invention can be determined by various means.
• a person skilled in the art thus has a range of methods or a combination of methods allowing him to determine without ambiguity and with the necessary precision the composition of the terpolymers of the invention.
• the molar ratio of the VDF units to the TrFE or TFE units in the terpolymers is from 85/15 to 30/70, and preferably from 75/25 to 40/60.
• the proportion of units derived from the CFE, HFP or CTFE monomer is from 1 to 15 mol.%, More preferably from 1 to 12 mol.%, Relative to the totality of the units of a terpolymer.
• the fluorinated copolymer or terpolymer may contain an additional unit, introduced during radical polymerization, between 0.1 and 10 mol%, preferably between 0.2 and 8 mol% and particularly between 0.5 and 5 mol%.
• This additional unit makes it possible to improve certain particular properties of the film, such as adhesion with the introduction of functional units of the acid, alcohol, glycidyl, phosphonate type such as trifluoromethacrylic acid, without degrading its electroactive properties.
• the fluorinated copolymer or terpolymer can be functionalized. That is to say chemically modified after the polymerization step to introduce chemical functions along the polymer chain allowing, for example, the crosslinking of the film, for example with a terpolymer carrying azide functions, or improving the adhesion of the film on the electrode, for example with a terpolymer carrying associative functions such as imidazolidinyl, triazolyl, triazinyl, bisureyl, ureido-pyrimidyl groups.
• copolymers of formula P (VDF-TrFE) or P (VDF-TFE) are compatible with the terpolymers listed above and having a Curie temperature different from that of the terpolymer.
• compatible is meant that the mixture of the two polymers forms a homogeneous phase with a single glass transition temperature.
• the fluorinated film deposited on said active negative electrode material is formed from a mixture of copolymer and terpolymer, these are present in a mass ratio of 50:50 to 1: 99, preferably from 45:55 to 1:99, more preferably from 40:60 to 5:95.
• said film also comprises compatible polymers of the acrylic and / or methacrylic type. These have the effect of stabilizing the film, facilitating adhesion or allowing crosslinking.
• the invention relates to a method of manufacturing a negative electrode comprising a layer of active material of negative electrode covered with a film of fluorinated copolymer (s) as described above.
• This method comprises a step of depositing or forming a film of fluorinated copolymer (s) on the surface of said active negative electrode material.
• the film is deposited in the solvent route.
• the solvent method consists in dissolving the fluorinated copolymers and / or the fluorinated terpolymers in a solvent or a mixture of solvents which do not damage the anode, in particular if it is made of Li metal. Indeed, many solvents, including ketones or esters, damage the Li metal by chemical reaction.
• copolymers and terpolymers based on vinylidene fluoride and trifluoroethylene are soluble in a large number of solvents. Unlike homopolymer PVDF, they easily crystallize in the polar phase (ferroelectric or ferroelectric relaxers) from solutions. They thus allow in a simple, rapid and inexpensive manner to produce deposits inhibiting the formation of dendrites.
• the solvents used in the invention are chosen from the group consisting of carbonates, carbamates, nitriles, amides, sulfoxides (such as dimethyl sulfoxide), sulfolane, nitromethane, 1, 3-dimethyl-2- imidazolidinone, 1, 3-dimethyl-3,4,5,6-tetrahydro-2 (1, H) -pyrimidinone, 3-methyl-2-oxazolidinone, and mixtures thereof.
• nitriles mention may, for example, be made of acetonitrile, pyruvonitrile, propionitrile, methoxypropionitrile, dimethylaminopropionitrile, butyronitrile, isobutyronitrile, valeronitrile, pivalonitrile, isovaleronitrile, glutaronitrile, methoxyglutaronitrile, 2-methylglutaronitrile, 3-methylglutaronitrile, adiponitrile, malononitrile, and mixtures thereof.
• cyclic carbonates such as, for example, ethylene carbonate (EC) (CAS: 96-49-1), propylene carbonate (PC) (CAS: 108-32-7) , butylene carbonate (BC) (CAS: 4437-85-8), dimethyl carbonate (DMC) (CAS: 616-38-6), diethyl carbonate (DEC) (CAS: 105-58-8 ), methyl ethyl carbonate (EMC) (CAS: 623-53-0), diphenyl carbonate (CAS 102-09-0), methyl phenyl carbonate (CAS: 13509-27-8), carbonate dipropyl (DPC) (CAS: 623-96-1), methyl propyl carbonate (MPC) (CAS: 1333-41 -1), ethyl propyl carbonate (EPC), carbonate vinylene (VC)
• EC ethylene carbonate
• PC propylene carbonate
• BC butylene carbonate
• DMC dimethyl carbonate
• DEC diethyl
• These solvents advantageously have a dielectric constant greater than or equal to 1, over a temperature range between 0 and 100 ° C., preferably between 10-80 ° C. and advantageously between 15-70 ° C.
• the measurement of dielectric permittivity can be carried out at by means of a LCR meter Sefelec LCR 819, which makes it possible to measure a capacity which is proportional to the permittivity.
• the step of depositing in the form of a film the solution of copolymer and / or terpolymer and solvent (s) on the active material of negative electrode is followed by a step of evaporation of the solvent (drying of the film). After drying, according to one embodiment, said film has a thickness ranging from 2 to 14 mih, preferably from 2 to 10 micrometers, limits included.
• the film is deposited in the dry process consisting in preparing a fluorinated film on a suitable support and in transferring this fluorinated film onto the layer of active material of negative electrode.
• the fluorinated film is transferred by any mechanical process, which can be by means of a roller or by lamination, followed by pressing with a thermal contribution not exceeding 100 ° C.
• the solution contains crosslinking co-agents such as bi or polyfunctional (meth) acrylic monomers in terms of reactive double bonds; bi or polyfunctional primary amines; bi or polyfunctional compounds carrying azide functions; organic peroxides; bi or polyfunctional allylic compounds.
• the method according to the invention comprises a step of crosslinking the film thermally, between 30 and 200 ° C, preferably between 50 and 180 ° C and especially between 60 and 160 ° C; or radiative, preferably with ultraviolet radiation and particularly with a wavelength between 250 and 405 nm.
• the latter is insoluble in some or all of the solvents which can be used to make the solution giving the crosslinked film a particular advantage since the use of the electrolyte is no longer limited by the solubility of the film.
• Another object of the invention is a secondary Li-ion battery comprising said negative electrode, a positive electrode and an electrolyte.
• the samples were heated to 100 ° C and kept at this temperature for 3 minutes to clear their thermal past. Then, the products were cooled to -80 ° C and then reheated to 200 ° C at a speed of between 5 ° C / min and 20 ° C / min.
• a button cell battery is mounted with a metal Li anode, a 25 ⁇ m thick PP separator and a cathode containing 2% PVDF, 5% Ketjen Black and 93% NMC 11 1 (LiNio, 33Mno, 33Coo, 3202 ).
• the electrolyte is 1 M LiFSI in an EMC / EC mixture (7/3 in vol.).
• a solution of copolymer P (VDF-TrFE) with a molar composition of 80% VDF and 20% TrFE is prepared in a 3/7 EC / EMC mixture by volume. Then deposited on a sheet of metal Li in glove box a sufficient amount of liquid to obtain after drying a film of 4 microns. Relatively rapid evaporation of the copolymer solution is carried out.
• a button cell is mounted with the Li anode treated with the fluorinated copolymer, a 25 ⁇ m thick PP separator and a cathode containing 2% PVDF, 5% Ketjen Black and 93% of NMC 1 1 1 (LiNio, 33Mno, 33Coo, 3202).
• the electrolyte is LiFSI 1 M in EMC / EC mixture (7/3 in vol.).
• the cycling is carried out at 2 C in charge and discharge between 3 and 4.2 volts for 300 cycles.
• the two button cells are removed in a glove box and the Li anodes examined by scanning electron microscopy (SEM).
• SEM scanning electron microscopy
• the untreated anode of Comparative Example 1 comprises dendrites whose surface density is much higher and the length between a few nm and around 1 micron.
• a solution of terpolymer P (VDF-TrFE-CTFE) in dimethoxyethane is prepared.
• the molar ratio of VDF units to TrFE units is 67% and the molar proportion of CTFE is 8%.
• a quantity of liquid is then deposited on a sheet of Li metal in a glove box sufficient to obtain, after drying, a film of 4 non-porous films. Relatively rapid evaporation of the copolymer solution is carried out.
• a button cell is mounted with the Li anode treated with the fluorinated terpolymer, a 25 ⁇ m thick PP separator and a cathode containing 2% PVDF, 5% Ketjen Black and 93% NMC 1 1 1 (LiNio , 33Mno, 33Coo, 3202).
• the electrolyte is 1 M LiFSI in an EMC / EC mixture (7/3 in vol.).
• the button cell of Example 4 is removed in a glove box and the Li anode examined by scanning electron microscopy (SEM).
• SEM scanning electron microscopy
• the anode treated with the fluorinated terpolymer of Example 4 has very few beginnings of dendrites whose size is less than 12- 13 nm and a very low surface density. Examination shows that the terpolymer appears to be more effective than the copolymer of Example 2.
• a solution of copolymer P (VDF-TrFE) with a molar composition of 80% in VDF and 20% in 1, 3-dioxolane is prepared. It is then deposited on a glass support, allowed to dry for the time necessary to get rid of the solvent, then the film of fluorinated copolymer is peeled off, which is applied mechanically in a glove box to a Li metal strip. A pressure of 1 MPa is applied to the assembly at a temperature of 60 ° C. and a fluoropolymer film-Li anode composite is handled.
• a button cell is mounted with the Li anode treated with the fluorinated copolymer, a 25 mm thick PP separator and a cathode containing 2% PVDF, 5% Ketjen Black and 93% NMC 1 1 1 (LiNio , 33Mno, 33Coo, 3202).
• the electrolyte is 1 M LiFSI in an EMC / EC mixture (7/3 in vol.). The cycling is carried out at 2 C in charge and discharge between 3 and 4.2 volts for 100 cycles.
• the button cell is disassembled in a glove box and the Li anode examined by scanning electron microscopy (SEM).
• SEM scanning electron microscopy

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