Classifications

• • 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
  • H01M4/13—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
  • H01M4/386—Silicon or alloys based on silicon
• • 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
  • H01M4/387—Tin or alloys based on tin
• • 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
• • 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
• • 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
  • H01M4/624—Electric conductive fillers
  • H01M4/625—Carbon or graphite
• • 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
• • 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
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

• the invention relates to an electrode composite material, it also relates to battery electrodes made of said material and lithium batteries comprising such electrodes.
• the invention applies to the field of storage of electrical energy in batteries and more particularly in lithium secondary batteries Li-ion type. Technological background of the invention
• the electrode composite materials comprise an active element, that is to say an element capable of exhibiting an electrochemical activity with respect to a metal, as well as a binder and a conductive additive.
• the active element used most conventionally is graphite and cobalt oxide for the positive electrode.
• lithium batteries for the negative electrode silicon Si or tin Sn.
• Li-ion battery is meant a battery which comprises at least one negative electrode or anode, a positive electrode or cathode, a separator, and an electrolyte.
• the electrolyte consists of a lithium salt, usually lithium hexafluorophosphate, mixed with a solvent that is a mixture of organic carbonates, chosen to optimize the transport and dissociation of ions.
• a high dielectric constant favors the dissociation of ions, and therefore the number of ions available in a given volume, whereas a low viscosity will be favorable for the ionic diffusion which plays a key role, among other parameters, in the charging and discharging speeds of the electrochemical system.
• a lithium battery electrode comprises a current collector on which is deposited a composite material which comprises a lithium-active element, a polymer which acts as a binder and which is generally a copolymer of fluoride. vinylidene, and an electrically conductive additive that is usually carbon black.
• Li-ion batteries are used especially in mobile phones, computers and light tools.
• Li-ion batteries have the highest energy density of all rechargeable systems and are therefore widely considered as a source of electrical energy in streetcars, electric vehicles and hybrid vehicles of the future, particularly those that would allow plug-in hybrid charging.
• the new negative electrode active elements have significantly higher capacities than the graphite which reaches 372 mAh / g, this theoretically allows to have the same capacity in a smaller volume or to have in the same volume, a capacity more big.
• the theoretical capacity of Si is 4200 mAh / g, while that of Sn is 1400 mAh / g.
• the capacity after 30 cycles, for four Sn-Sb-Cu tested alloys varies from 100 to 450 mAh / g with a positive influence of the Sb content; on the other hand, the capacitance as a function of the current density decreases all the more as the Sb content is high (no value reaches 400 mAh / g at 2 mA / cm 2 ).
• a method using an alloy is claimed in US Patent Application No. 2008 000 3503 of January 3, 2008 to Canon Kabushiki Kaisha; the objective is to prepare a silicon and tin composite covered with a protective layer of W, Ti, Mo, Nb or V oxides.
• a conductive additive to be selected from mesoporous carbons, nanotubes or carbon is added.
• JP-A-2002-8652 discloses a negative electrode prepared by depositing fine Si particles on a graphite powder and then producing a carbon coating. Nevertheless, these electrodes present problems of loss of electrical contact over time.
• the 20 micron silicon particles are dispersed in THF with carbon nanotubes and PVC. After ultrasonification, the suspension is dried and the solid treated at 900 ° C. under argon. After 20 cycles, the capacity is only 650 mAh / g of electrode for composites incorporating up to 30% of nanotubes; it is necessary to reach a content of 35% of nanotubes to obtain a capacity of 750 mAh / g of electrode at the twentieth cycle. When 500 nm diameter silicon particles are used instead of the 20 micron particles, the value then reaches 970 mAh / g of electrode at the twentieth cycle. It is not clear, however, whether the decrease in the size of the silicon particles is accompanied by a decrease in the density of the electrode. And the capacity is not stable in cycling.
• Matshushita Electric Industrial which describes a negative electrode.
• the problem solved in this document D1 is also the obtaining of a negative electrode for battery having a high capacity maintenance during the charging and discharging cycles.
• an active material capable of forming a reversible alloy with lithium comprising at least one metal and at least one semiconductor.
• the results are improved when the electrode substrate is conductive and porous, and the active material fills the pores of the substrate.
• the electrode thus comprises an active material comprising both a metal (such as Ti) and a semi-metal (semiconductor such as Si); a conductive material such as carbon nanotubes (CNTs) and a porous conductive substrate.
• This document describes a method of manufacturing a negative electrode for rechargeable battery. According to this method, a mixture of conductive material containing fibrous carbon, a polymer and a dispersion medium is produced; to which is added an active material containing silicon.
• the use as conductive material of NTC or NFC is exemplified.
• the teaching provided by this document is similar to that described above for the document WO 2004/049473 and does not solve the problem.
• the present invention provides an electrode composite material for the manufacture of negative electrodes for batteries so that the batteries have a capacity maintenance as high as possible to the cycling.
• the electrode material allows the batteries to have low internal resistance and charge and discharge kinetics as high as possible.
• the invention also proposes an industrial process for manufacturing the electrode composite material, the electrodes obtained and the batteries incorporating said electrodes.
• the technical problem solved is, in particular but not exclusively, the realization of a composite material active against lithium, capable of forming reversibly alloys.
• the material makes it possible to manufacture negative electrodes of Li-ion batteries.
• the negative electrodes can be incorporated in a battery having a maintenance capacity as high as possible to cycling, a low internal resistance and load kinetics and discharge as strong as possible.
• carbon nanotubes NTC is meant one or more hollow tubes with one or more graphitic plane walls or sheets of graphene, coaxial, or graphene sheet wound on itself. This or these tubes, usually “open” (ie open at one end) resemble several grid tubes arranged coaxially; in cross section the CNT is in the form of concentric rings. The external diameter of the CNT is from 2 to 50 nm.
• SWNT single-walled carbon nanotubes
• MWNT multi-walled carbon nanotubes
• carbon nanofibers or NFC fibrils solid fibers of graphitic carbon, with a diameter of
• NFCs are in the form of a disk.
• the length / diameter ratio is much greater than 1, typically greater than 100.
• the conductive material comprises a mixture of CNT and NFC as in the present invention.
• NTCs are used alone as a conductive element.
• the conductive material is at least one of carbon nanotube and carbon nanofiber"
• the CNTs are alone.
• the range of values for the diameter given in paragraph [0080] corresponds to the diameter of the CNTs.
• the invention more particularly relates to an electrode composite material comprising a conductive additive, mainly characterized in that the conductive additive is a mixture of conductive additives containing at least carbon nanofibers
• NFC carbon nanotubes
• CNTs carbon nanotubes
• the mixture may comprise other conductive additives chosen from graphite, carbon black such as acetylene black and SP carbon.
• Carbon nanofibers have a diameter ranging from 50 to 200 nm and a form factor that can go from 10 to 1000 and carbon nanotubes, have a diameter of between 0.4 and 20 nm and a form factor of 20 to 1000.
• the composite material according to the invention also comprises a so-called active element, that is to say an element operating on the principle of insertion (Li + ), conversion, displacement, and dissolution-recrystallization, for the electrode that contains said active element.
• active element that is to say an element operating on the principle of insertion (Li + ), conversion, displacement, and dissolution-recrystallization, for the electrode that contains said active element.
• the composite material comprises an active element capable of making reversible alloys with lithium, for example silicon (Si) or tin (Sn).
• the invention also relates to an electrode comprising said composite material.
• the electrode may be the negative electrode for electrochemical devices such as lithium batteries.
• the subject of the invention is the use of such an electrode in a non-aqueous electrolyte secondary battery, as well as the secondary battery (Li-ion) comprising the electrode comprising said composite material.
• charging and discharging of the battery takes place in a range of 0 to 1.1 lithium atoms inserted per silicon atom.
• the invention also relates to the manufacture of secondary batteries with nonaqueous electrolyte, as well as secondary lithium batteries comprising an electrode comprising said composite material.
• the composite material is usable in a non-aqueous electrolyte secondary battery having excellent capacitance characteristics and cycling under high current density.
• the invention also relates to a method of manufacturing an electrode composite material comprising: the preparation of a suspension containing a binder P1, at least NFC carbon nanofibers conferring electronic conductivity, at least NTC carbon nanotubes conferring electronic conductivity, an M1 electrode active element capable of reversibly forming a alloy with lithium, a volatile solvent Sl,
• the invention relates to the use of the method of manufacturing a composite material for the manufacture of electrodes for electrochemical devices of the lithium battery type.
• the substrate film can be used directly as an electrode.
• the invention applies to the use of the method for the manufacture of secondary battery with non-aqueous electrolyte, comprising an electrode comprising the composite material thus obtained.
• FIG. graphical form the rheological characteristics of a dispersion obtained according to the process of the invention
• FIGS. 2 and 3 represent scanning electron microscopic photographs of the composite material according to the invention with respectively a magnification of 3000 and 5000
• FIG. 4 represents curves of evolution of capacitance Q as a function of the number of cycles for several samples, one of which is made of composite material according to the invention
• FIG. 5 represents the evolution of the capacitance Q for an electrode made according to example 2.
• the electrode composite material proposed according to the invention comprises a mixture of conductive additives containing at least carbon nanofibers (NFC) and at least carbon nanotubes (CNTs).
• the two conductive additives NFC and NTC are different from the conductive additives used in the state of the art, such as SP carbon or graphite, by their very high form factor. This is defined by the largest dimension ratio on the smallest dimension of the particles. This ratio is of the order of 30 to 1000 for nanofibers and nanotubes, against 3 to 10 for SP carbon and graphite.
• a conductive additive a mixture of conductive additives containing at least carbon nanofibers (NFC) and at least carbon nanotubes (CNTs), that carbon nanofibers and carbon nanotubes in the electrode composite material, complementary roles with respect to maintaining the cycling capacity, which give a negative electrode based on an active element capable of reversibly forming alloys with lithium an excellent stability in cycling at high levels of active element in the electrode composite material.
• NFC carbon nanofibers
• CNTs carbon nanotubes
• the carbon nanofibers which are easily dispersed because of their large diameter, form a continuous structure capable of ensuring the transport of electrons from the current collector through the entire volume of the composite material.
• This structure can preserve its integrity despite variations in the volume of the particles of the active element due to the very long length of the carbon nanofibers.
• Carbon nanotubes are more difficult to disperse. Nevertheless, thanks to the method according to the invention, it is possible to distribute them in the electrode composite material in such a way that they form a mesh around the particles of the active element and thus play a complementary role to that of the nanofibres. .
• they ensure the distribution to the particles of the active element of the electrons brought from the current collector by the carbon nanofibers.
• they because of their length and their flexibility, they form electric bridges between the particles of the active element fractured by the repetition of their expansions and voluminal contractions.
• the applicant has found that the usual conductive additives (SP carbon and graphite), with their low form factor, are significantly less effective than carbon nanofibers to ensure the maintenance during the cycling of electron transport from the collector current. Indeed, with this type of conductive additives, the electrical paths are formed by the juxtaposition of grains and the contacts between them are easily broken due to the volume expansion of the particles of the active element.
• the conductive additive mixture may further comprise one or more other conductive additives consisting of graphite, carbon black such as acetylene black, SP carbon.
• the electrode composite material comprises an active element with respect to lithium.
• these metals M or metal alloys are chosen from Sn, Sb, Si.
• the composite material also comprises at least one polymeric binder.
• the polymeric binder is chosen from polysaccharides, modified polysaccharides, latices, polyelectrolytes, polyethers, polyesters, polyacrylic polymers, polycarbonates, polyimines, polyamides, polyacrylamides, polyurethanes, polyepoxides, polyphosphazenes, polysulfones, halogenated polymers.
• the composite material has a submicron and micron structure that can be observed on a sample by scanning electron microscopy
• Carbon nanofibers and carbon nanotubes have fibrillar morphology. Carbon nanofibers are different from carbon nanotubes by their larger diameter, 100 nm to 200 nm on average for the first against 10 to 20 nm average for the second.
• the length of the carbon nanofibers is generally of the order of 10-30 ⁇ m and the length of the carbon nanotubes is generally of the order of 5-
• the method according to the invention for the preparation of an electrode composite material comprises: - the preparation of a suspension containing a polymer P1, at least NFC carbon nanofibers conferring electronic conductivity, at least carbon nanotubes NTC imparting electronic conductivity, optionally a third conductive additive C1, an electrode active element M1 capable of reversibly forming an alloy with lithium, a volatile solvent S1, developing a film from the suspension obtained.
• This film can optionally be densified by applying a pressure (between 0.1 and 10 tons).
• a pressure between 0.1 and 10 tons.
• the polymer P1 is introduced in the pure state or in the form of a solution in a volatile solvent; the NFC + NTC mixture is introduced in the pure state or in the form of a suspension in a volatile solvent.
• the polymer P 1 can be chosen from polysaccharides, modified polysaccharides, latices, polyelectrolytes, polyethers, polyesters, polyacrylic polymers, polycarbonates, polyimines, polyamides, polyacrylamides, polyurethanes, polyepoxides and polyphosphazenes. polysulfones, halogenated polymers.
• halogenated polymer there may be mentioned homopolymers and copolymers of vinyl chloride, vinylidene fluoride, vinylidene chloride, ethylene tetrafluoride, chlorotrifluoroethylene, and copolymers of vinylidene fluoride and of hexafluoropropylene (PVdF-HFP).
• Water-soluble polymers P 1 are particularly preferred.
• carboxymethyl cellulose and hydroxypropyl methyl cellulose
• polyethers such as homopolymers and copolymers of ethylene oxide
• polyacrylic polymers such as homopolymers and copolymers of acrylamide, acrylic acid, homopolymers and copolymers of maleic acid, homopolymers and copolymers of maleic anhydride, homopolymers and copolymers of acrylonitrile, homopolymers and copolymers of vinyl acetate and vinyl alcohol, homopolymers and pyrrolidone vinyl copolymers
• polyelectrolytes such as homopolymers and copolymers of vinyl sulfonic acid, phenyl sulfonic acid, homopolymers and copolymers allylamine, diallyldimethylammonium, vinylpyridine, aniline, ethylenimine.
• aqueous dispersions of polymers known as latex based on vinyl acetate, acrylic, nitrile rubber, polychloroprene, polyurethane, acrylic styrene and styrene butadiene may be mentioned.
• copolymer is meant in the present text, a polymer compound obtained from at least two different monomers.
• Polymer blends are also interesting. There may be mentioned mixtures of carboxymethyl cellulose with styrene-butadiene latex, acrylic, and nitrile rubber.
• the volatile solvent S1 is an organic solvent or water or a mixture of organic solvent and water.
• Organic solvents include N-methyl pyrrolidone and dimethyl sulfoxide.
• Solvent S 1 is preferably water. Its pH can be adjusted by addition of an acid or a base.
• the solvent S1 may contain a surfactant.
• a surfactant There may be mentioned 4- (1,1,3,3-tetramethylbutyl) phenylpolyethylene glycol (marketed under the trade name Triton® X100).
• Compound C1 may consist of graphite, carbon black such as acetylene black, SP carbon. Commercial conductive additives meet this requirement. These include in particular compounds Ensagri Super S ® or Super P® sold by Chemetals.
• the active element M1 may be chosen in particular from the compounds that react with lithium during charging of the Li-ion battery, for example: M metals or alloys of metals M a M b M c ... forming an alloy with Lithium type Li x M has M b M c .
• the preparation of the suspension can be carried out in a single step or in two successive steps.
• a first embodiment consists in preparing a dispersion containing the carbon nanotubes and optionally all or part of the polymer P1, and then adding to this dispersion the other constituents of the composite material, this new suspension being used for the preparation of the final film.
• a second embodiment consists in preparing a dispersion containing the carbon nanotubes and optionally all or part of the polymer P1 in a solvent, adding the active element M1, removing the solvent to obtain a powder and then forming a new suspension. by adding Sl and the remainder of the constituents of the composite material to this powder, this new suspension being used for the preparation of the final film.
• the preparation of a dispersion of carbon nanotubes is advantageous because it allows the formation of a more homogeneous composite material film.
• the film can be obtained from the suspension by any conventional means, for example extrusion, spreading (tap casting) or spraying (spray drying) on a substrate followed by drying.
• a metal sheet capable of serving as a collector for the electrode for example a copper or nickel sheet or grid treated with an anti-corrosion coating.
• the substrate film thus obtained can be used directly as an electrode.
• the composite material according to the invention is useful for the elaboration of electrodes for electrochemical devices, in particular in lithium batteries.
• Another object of the invention is constituted by a composite electrode constituted by the material according to the invention.
• a lithium battery comprises a negative electrode constituted by lithium metal, a lithium alloy or a lithium insertion compound and a positive electrode, the two electrodes being separated by a solution of a salt whose cation contains at least one lithium ion, for example LiPF ⁇ , LiAsFe, LiClO 4 , LiBF 4 , LiC 4 BO 8 , Li (C 2 F 5 SO 2 ) 2 N, Li [(C 2 F 5 ) 3 PF 3 ], LiCF 3 SO 3 , LiCH 3 SO 3 , and LiN (SO 2 CF 3 ) 2 , LiN (FSO 2) 2, ...
• a salt whose cation contains at least one lithium ion
• the negative electrode may be a composite electrode according to the invention containing a negative electrode active element as defined above.
• the positive electrode When the positive electrode is constituted by a lithium insertion compound, it may also consist of a material according to the invention in which the active element is a positive electrode active element as defined above.
• the nanotubes have an average diameter of 20 nm, an estimated length of a few microns and their chemical composition shows that they contain about 7% of mineral ash from the synthesis process.
• the carbon nanofibers have an average diameter of 150 nm and an estimated length of 15 ⁇ m. They come from SHOWA DENKO company.
• CMC is used here to allow the incorporation and dispersion of carbon nanotubes in water.
• CMC is a polyelectrolyte which, thanks to the presence of cellulosic units, can establish van der Waals bonds with carbon nanotubes and adsorb to their surface, thus promoting their wetting with water, and thanks to the presence of ionizable carboxylate groups ensures good dispersion of the nanotubes according to an electrostatic repulsion mechanism.
• the conditions of the dispersion are 15 h at 700 rpm, a 12.5 ml crushing bowl containing 3 beads of 10 mm diameter, 1 ml of deionized water, 32 mg of nanotubes, and 4 mg of CMC.
• Figure 1 gives the rheological characteristics of the dispersion after 15 hours of grinding.
• optimum electrochemical performances are obtained when the storage module G 'reaches a value of 800 Pa in the frequency range 0.1 to 10 Hz.
• the silicon particles (320 mg), the carbon nanofibers (16 mg) and the remaining CMC (28 mg) are added, and the mixture is mixed by co-grinding. 500 rpm for 30 minutes.
• the composite material constitutes 28.57% by weight of the suspension. The rest is deionized water.
• the electrode is prepared by coating the suspension containing the composite on a 25 ⁇ m thick copper current collector.
• the height of the doctor blade of the coating machine is set at 100 ⁇ m.
• the electrode is dried first at room temperature and then 3h at 55 ° C under vacuum.
• the amount of silicon deposited per cm 2 of current collector is 1.70 mg and the thickness of the electrode 15 ⁇ m.
• Figures 2 and 3 represent scanning electron microscope (SEM) photographs of the obtained composite material, respectively with a magnification of 3000 and 50000. It appears that the composite material according to the invention consists of silicon particles, nanotubes of carbon and nanofibers of carbons. The latter are differentiated from the first by their larger diameter, 150 nm on average against 20 nm on average, and their greater length.
• CMC is present in the form of a very thin layer on the surface of all other materials.
• the carbon nanofibers form a continuous structure capable of supplying the electron collector throughout the volume of the composite material from the current collector.
• the carbon nanotubes form a mesh around the silicon particles. It appears that the method according to the invention allows a very homogeneous distribution of the two conductive additives.
• the electrode (a) thus obtained was mounted in a battery having as a positive electrode a lithium metal foil laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte consisting of a 1M LiPF solution. 6 dissolved in EC / DMC 1: 1.
• the cycling performance was measured and compared to that of similar batteries in which the negative electrode is an electrode whose initial composition is: - (b) 80% Si, 8% CMC, 12% SP carbon;
• the cycling was carried out with a constant specific capacity limited to 950 mAh / g in the 0-1 V vs potential range. Li + / Li. It was driven in galvanostatic mode at a current I of 150 mA / g which corresponds to a regime of C / 6 (duration of 6.33 hours of each charge and discharge). This mode of cycling leads to a constant capacity as long as the end-of-reaction potential is greater than OV, then to a capacity which decreases as a function of the number of cycles when the end-of-reaction potential becomes equal to OV.
• FIG. 4 represents the evolution of the capacity Q (in mAh / g) as a function of the number of cycles N.
• the correspondence between the two curves and the samples is as follows: Curve - • - • -: sample a according to the Invention Curve f: Comparative Sample B Curve O: Comparative Sample C Curve: Comparative Sample
• the comparison of the cycling curves shows a substantial improvement in cycling capacity only when the composite material constituting the electrode contains the mixture of the two conductive additives claimed by the invention: carbon nanotubes and carbon nanofibers.
• the capacity restored at the hundredth cycle is 900 mAh / g of silica, ie 720 mAh / g of electrode.
• the volume capacity of the electrode is approximately 630 mAh / cm 3, which is to be compared with the volume capacity of commercial graphite anodes equal to approximately 500 mAh / cm 3 ("Nano-and-bulk-silicon-based insertion anodes for lithium- ion secondary cell ", U. Kasavajjula et al., J.
• Example 2 is obtained with an electrode according to the invention and a battery prepared as in Example 1.
• the amount of silicon deposited per cm 2 of current collector is 1.80 mg.
• the mixture of CNT and NFC is preferably within the following limits: bound 1: 9% carbon nanofibers + 3% carbon nanotubes terminal 2: 3% carbon nanofibers + 9% carbon nanotubes.
• Example 3 is given to illustrate the results within these limits: Example 3
• the silicon particles, the carbon nanofibers and the remainder of the CMC are added, and the whole is mixed by co-grinding at 500 rpm for 30 minutes.
• the composite material constitutes 28.57% by mass of the suspension.
• the rest is deionized water.
• the electrodes are prepared by coating the suspension containing the composite on a 25 ⁇ m thick copper current collector.
• the height of the doctor blade of the coating machine is set at 100 ⁇ m.
• the electrodes are first dried at room temperature and then 3h at 55 ° C under vacuum.
• the electrodes thus obtained were mounted in a battery having, as a positive electrode, a lithium metal sheet laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte constituted by a 1M LiPF ⁇ solution dissolved in EC / DMC 1: 1.
• the cycling was carried out with a constant specific capacity limited to 950 mAh / g in the 0-1 V vs potential range. Li + / Li. It was driven in galvanostatic mode at a current I of 150 mA / g which corresponds to a regime of C / 6 (duration of 6.33 hours of each charge and discharge). This mode of cycling leads to a constant capacity as long as the end-of-reaction potential is greater than OV, then to a capacity which decreases as a function of the number of cycles when the end-of-reaction potential becomes equal to OV.
• VCF Vapor growth carbon fiber
• MWNT Multi Walled Carbon Nanotubes
• the fibrous carbon content is preferably greater than 3 and less than 12 parts per 100 parts of active material.
• the amount provided for in the present invention is greater than the upper limit of this range, ie 12 parts of conductive additive for 80 parts (equivalent to 15 parts per 100 parts) of active material.
• the content of fibrous carbon is greater than 12 parts per 100 parts of active material (ie 9.6% by weight in the electrode).
• the cycling stability is worse as illustrated in Example 4 below.
• the composite material of this example consists of 83% by weight of silicon particles of 1 to 10 ⁇ m
• the silicon particles, the carbon nanofibers and the remainder of the CMC are added, and the whole is mixed by co-grinding at 500 rpm for 30 minutes.
• the composite material constitutes 28.57% by weight of the suspension.
• the rest is deionized water.
• the electrodes are prepared by coating the suspension containing the composite on a 25 ⁇ m thick copper current collector.
• the height of the doctor blade of the coating machine is set at 100 ⁇ m.
• the electrodes are first dried at room temperature and then 3h at 55 ° C under vacuum.
• the electrodes thus obtained were mounted in a battery having, as positive electrode, a lithium metal foil laminated on a nickel current collector, a fiberglass separator, a liquid electrolyte consisting of a 1M LiPF ⁇ solution dissolved in EC / DMC 1: 1.
• the cycling was carried out with a constant specific capacity limited to 950 mAh / g in the 0-1 V vs potential range. Li + / Li. It was driven in galvanostatic mode at a current I of 150 mA / g which corresponds to a regime of C / 6 (duration of 6.33 hours of each charge and discharge). This mode of cycling leads to a constant capacity as long as the end-of-reaction potential is greater than 0V, then to a capacity which decreases as a function of the number of cycles when the end-of-reaction potential becomes equal to 0V.
• the service life increases to 88 in number of cycles instead of 120 if we choose 12 parts for 80 parts of active material as can be seen in the previous table.

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