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
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/362—Composites
• • 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
  • H01M4/64—Carriers or collectors
  • H01M4/66—Selection of materials
  • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
• • 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
• • 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
• • 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
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/581—Chalcogenides or intercalation compounds thereof
  • H01M4/5815—Sulfides
• • 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
  • H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
  • H01M4/602—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
  • H01M4/621—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
• • 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
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • 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
  • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
• • 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 invention relates to the field of lithium / sulfur batteries and more particularly an active material formulation for the manufacture of a cathode having improved performance and an accumulator comprising said active material.
• the invention also relates to a process for preparing such a formulation.
• Li / S storage batteries or Li / S batteries are seen as promising alternatives to Li-ion batteries.
• the interest for this type of battery comes in particular from the high density of potential energy of sulfur.
• sulfur has the advantages of being abundant, lightweight, low cost and non-toxic, which allows for the development of Li / S batteries on a large scale.
• the discharge and charge mechanism of a Li / S battery is based on the reduction / oxidation of sulfur at the cathode (S + 2e _ ⁇ S 2 ) and the oxidation / reduction of lithium at the anode ( Li ⁇ Li + + e).
• the cathode and the anode must be generally good electronic conductors.
• sulfur has relatively slow discharge regimes and being an electrical insulator, it is necessary to confer a conductive character.
• the mixture of the active ingredient and the conductive additive can be done in different ways.
• the mixing can be done during the preparation of the electrode.
• the sulfur is then mixed with the conductive additive and optionally a binder by mechanical stirring, before forming the electrode. Thanks to this homogenization step, the carbonaceous additive is supposed to be distributed around the sulfur particles, and thus create a percolating network.
• a grinding step can also be used and allows for a more intimate mix materials. However, this additional step may result in destruction of the porosity of the electrode.
• Another way of mixing the active ingredient with the carbonaceous additive is to grind the sulfur and the carbonaceous additive in the dry process, so as to coat the carbon sulfur.
• the carbonaceous additive is a carbon nanotube
• the introduction of carbon nanotubes into the formulations raises some problems. Indeed, they are difficult to handle and disperse, because of their small size, their powderiness and, possibly, when they are obtained by chemical vapor deposition (CVD), their entangled structure generating otherwise strong interactions of Van Der Waals between them.
• CVD chemical vapor deposition
• the low dispersion of the nanotubes limits the efficiency of the charge transfer between the positive electrode and the electrolyte and thus the performance of the Li / S battery despite the addition of a mass of conductive material.
• an active material could also be obtained by contacting carbon nanotubes (hereinafter referred to as CNTs) with a sulfur-containing material in a molten stream, for example in a compounding device, thus forming a improved active material, usable for the preparation of an electrode (WO2016 / 102865).
• CNTs carbon nanotubes
• sulfur-containing material for example in a compounding device
• the sulfur material is associated with carbon nanofillers such as CNTs, graphene or carbon black in a mixing tool at the melting temperature of the sulfur material.
• carbon nanofillers such as CNTs, graphene or carbon black
• Li-S batteries continue to suffer from a relatively rapid decrease in capacity during cycling.
• cycling capacity is multifactorial. It involves the formation of several lithium polysulfides during the discharge that dissolve in the electrolyte and escape from the cathode. Capacity decline also occurs through passivation effects and insoluble sulphide formation, amplified by volume changes during discharge, which causes mechanical stresses and loss of contact with the current collector.
• MWNT or GNF gives better electrochemical properties but the improvement remains limited, since after 50 cycles the capacity is only 130 mAh / g with carbon blacks, 250 mAh / g with carbon blacks plus GNF and 300 mAh / g with carbon blacks plus MWNT for initial capacities of about 700 mAh / g.
• nanotubes with other carbon black carbon type fillers, graphene or graphene oxide.
• a nanostructured Li 2 S-carbon composite obtained by dry-ball milling micron Li 2 S powder in the presence of carbon blacks is used with carbon nanotubes and a simple electrochemical activation method to improve the carbon nanotubes. use and reversibility of the electrodes in the presence of nanotubes.
• carbon nanotubes and carbon nanofibers have also been combined in order to produce electrodes comprising a sulfur infiltration in micropores ( ⁇ 2 nm) and thus making it possible to increase the capacity and the stability of the cycling ( Linchao Zeng et al., Free-standing porous carbon nanofiber-sulfur composite for Li-S flexible battery cathode, 2014, Vol.6, 9579-9587).
• the object of the invention is to propose a formulation for the manufacture of an electrode exhibiting improved cycling stability.
• the invention further aims to provide a method for preparing a formulation for the manufacture of an electrode, said method being fast and simple to implement, and which increases the load capacity. and discharging the battery incorporating this active material.
• the invention relates to an active material formulation comprising a sulfur material and an electrically conductive composition comprising carbon nanotubes and at least one other carbonaceous filler selected from carbon nanofibers and carbon fibers.
• the invention relates to an active material formulation comprising a sulfur-containing material and an electrically conductive composition characterized in that the electrically conductive composition comprises carbon nanotubes and carbon fibers.
• the performance of the batteries can be improved by the use of an electrical conductive composition according to the invention.
• the active ingredient for Li-S cathodes is generally based on sulfur and carbon. Generated according to the methods of the prior art, it generally has a stability to cycling and in particular a low dimensional stability. Indeed, the active ingredient may be damaged during charging and discharging cycles resulting in degradation of the performance of the battery incorporating said active material.
• the Applicant has developed a new formulation to increase the performance of the batteries, including allowing improved cycling stability.
• the formulation according to the invention can be used as a cathode active material of a lithium / sulfur accumulator.
• an active material comprising a conductive composition containing at least carbon nanotubes, in combination with carbon nanofibers and / or carbon fibers, preferably in combination with carbon fibers, which can be homogeneously dispersed and form a network by the three-dimensional nanotubes in the mass of a sulfur-containing material, this active material making it possible to increase the stability and the charging and discharging capacity of the battery incorporating this active material.
• additives of the carbon nanotube type have the advantage of also conferring a beneficial adsorbent effect for the active ingredient by limiting its dissolution in the electrolyte and thus promoting better cyclability.
• the addition of a second population of carbonaceous additives, such as carbon fibers, and possibly a third population of carbonaceous additives, coarser than nanotubes makes it possible to benefit from a synergy of stability of the conductive network in the mass of the cathode especially when it is thick (for example beyond 100 pm).
• nanofibers and more carbon fibers, of larger diameter can play the role of main paths of conduction while the nanotubes play the role of secondary conductors over shorter distances where dispersion quality is less problematic.
• the electrically conductive composition comprises carbon nanotubes, carbon nanofibers, and carbon fibers. The best performances are obtained with the combination of these three carbon charges.
• the electrical conductive composition further comprises another carbonaceous filler selected from: carbon blacks, acetylene blacks, graphites, graphenes, activated carbons, and mixtures thereof.
• the sulfurized material and the electrically conductive composition have a mass ratio of between 1/4 and 50/1.
• the level of carbon nanotubes is at least 20% by weight of the conductive composition.
• At least a portion of the nanofibers, nanotubes and / or carbon fibers is covered by an intrinsically conductive polymer.
• at least a portion of the nanotubes and / or carbon fibers is covered by an intrinsically conductive polymer.
• At least a portion of the nanofibers, nanotubes and / or carbon fibers is covered by an ionically conductive ceramic material.
• at least a portion of the nanotubes and / or carbon fibers is covered by an ionically conductive ceramic material.
• the sulfurized material has an S8 content of less than 10% by weight of the sulfur material.
• the invention further relates to a process for preparing the formulation of active material according to the invention, comprising a step of contacting the sulfurized material with the electrical conductive composition.
• the contacting step is selected from: mixing the sulfurized material with the electrical conductive composition at a temperature greater than or equal to the melting temperature of the sulfurized material, sublimation of the sulfurized material on the electrical conductive composition, the deposition of liquid phase of the sulfurized material on the electrical conductive composition.
• the method comprises a step of forming a Sulfur-Carbon composite, said prior step of forming the Sulfur-Carbon composite comprising a melting of a sulfur-containing material and mixing of the molten sulfur material and carbonaceous fillers, preferably in a device compounding.
• the presence in the formulation of a sulfur-carbon composite obtained by the molten route makes it possible to improve the performance of the cathode since such a composite is more efficient than a Sulfur-carbon composite obtained for example by co-grinding sulfur and carbon. carbon.
• the Sulfur-Carbon composite can be obtained by melting a sulfur-containing material and kneading the molten sulfur material and the carbon nanofillers.
• the method comprises a grinding step of the sulfur-carbon composite, said grinding step being able to be carried out in a ball mill (horizontal and vertical cage), a cavitator, a jet mill, a fluidized bed jet mill, a liquid phase mill, screw disperser, brush mill, hammer mill, ball mill, or other methods of micronization.
• the method comprises the following steps:
• the invention further relates to a catholyte comprising the formulation of active material according to the invention and a binder.
• a catholyte comprising the formulation of active material according to the invention and a binder.
• the catholyte further comprises at least one additive selected from: a rheology modifier, an ionic conductor, another carbonaceous electrical conductor, an electrolyte and an electron donor element.
• the invention further relates to the use of the formulation according to the invention for the manufacture of a cathode. More particularly, the invention further relates to a cathode prepared from the formulation of active material according to the invention or a catholyte according to the invention.
• the formulation of active material according to the invention makes it possible to improve the electronic conductivity of the electrode formulation, the mechanical integrity of the electrode and therefore the operation over time of the battery.
• the invention further relates to a lithium / sulfur accumulator comprising a cathode according to the invention.
• the formation of active material has a better combination of a sulfur-donor material, with a 3D network of carbonaceous fillers to facilitate the access of sulfur to electrochemical reactions, which can contribute to a good maintenance of the battery operation during time.
• FIG. 1 is a diagrammatic representation of a process for preparing an active ingredient formulation according to the invention. The dotted steps are optional.
• FIG. 2 is a schematic representation of a preferred grinding method according to the invention. rDescription of the invention!
• the term “active material” compounds that can provide effective electrical transfer from the current collector of the electrode and offer active interfaces to electrochemical reactions during operation of the battery. More particularly, this corresponds to the compounds with which the lithium ions are likely to react, and of which the lithium ions are likely to be released.
• the active material corresponds to the sulfur material.
• the term “formulation of active material” a mixture of different substances including the active ingredient.
• sulfur material is meant a sulfur donor compound, selected from native sulfur (or elemental), sulfur-containing organic compounds or polymers and sulfur-containing inorganic compounds.
• elemental sulfur or “elemental sulfur” is meant sulfur particles in crystalline form S8 or in amorphous form. More particularly, this corresponds to elemental sulfur particles having no sulfur associated with carbon from the carbonaceous feeds.
• electrical conductive composition a composition comprising compounds or structures capable of conducting an electric current.
• catholyte is meant a composition comprising the components which form a cathode.
• carbonaceous filler By “carbonaceous filler”, it is possible to designate a filler comprising at least one element of the group formed by carbon nanotubes, carbon nanofibers, carbon fibers, carbon blacks, acetylene blacks and graphites. , graphenes and activated carbons.
• the term “filler” is generally used to denote a carbonaceous filler whose smallest dimension is between 0.1 and 20 ⁇ m, preferably between 0.1 and 15 ⁇ m, more preferably between 0.1 and 10 ⁇ m, more preferably more preferred between 0.2 and 10 ⁇ m.
• nanofiller is usually used to denote a carbonaceous filler whose smallest dimension is between 0.1 and 200 nm, preferably between 0.1 and 100 nm, more preferably between 0.1 and 50 nm, measured by diffusion. light.
• solvent a substance, liquid or supercritical at its temperature of use, which has the property of dissolving, diluting or extracting other substances without chemically modifying them and without itself changing .
• Liquid phase solvent is a solvent in the liquid state.
• Sulfur-Carbon Composite an assembly of at least two immiscible components whose properties are complementary, said immiscible components comprising a sulfur-containing material and a carbonaceous filler.
• compounding device an apparatus conventionally used in the plastics industry, for the melt blending of thermoplastic polymers and additives in order to produce composites.
• the sulfurized material and the carbonaceous fillers are mixed using a high-shear device, for example a co-rotating twin-screw extruder or a co-rotating machine.
• the melt generally comes out of the apparatus in an agglomerated solid physical form, for example in the form of granules.
• substantially constant within the meaning of the invention corresponds to a value varying from less than 20% relative to the value compared, preferably less than 10%, even more preferably less than 5%.
• an active material formulation which can be used for the manufacture of an electrode, comprising a sulfur-containing material and an electrically conductive composition comprising carbon nanotubes and at least one other carbonaceous filler selected. among carbon nanofibers and carbon fibers.
• the electrical conductive composition comprises carbon nanotubes and carbon fibers.
• the electrical conductive composition can then further comprise carbon nanofibers.
• such a formulation is able to maintain a nearly constant capacity even after a large number of charge / discharge cycles and thus preserve the capacity of a Li-S battery over time.
• the electrical conductive composition must comprise carbon nanotubes in combination with one and / or the other carbon nanofibers and carbon fibers.
• the electrical conductive composition comprises carbon nanotubes and carbon fibers.
• the electrical conductive composition comprises carbon nanotubes, carbon nanofibers and carbon fibers.
• the combination of at least these three carbonaceous feeds gives the best results of maintaining the cycling capacity.
• at least two populations of carbonaceous fillers in the form of fibrils provide a better dimensional stability of the cathode to the volume changes between charge and discharge.
• the conductive composition may comprise from 1 to 99% of carbon nanotubes and from 1 to 99% of carbon fibers.
• the electrical conductive composition comprises at least 20% of single-walled, double-walled or multi-walled carbon nanotubes, preferably at least 30% of carbon nanotubes, more preferably at least 40% of carbon nanotubes. and even more preferably at least 50% of carbon nanotubes.
• the sulfur-containing material and the electrical conductive composition preferably have a mass ratio of between 1/4 and 50/1. More preferably, the sulfurized material and the electrically conductive composition have a mass ratio of between 2/1 and 20/1, and even more preferably between 4/1 and 15/1.
• the carbon nanotubes may be of the single-walled type (SWNT), double-walled carbon nanotubes (DWNT) in English terminology. -Saxonne) or multiple walls (MWNT, "multi-walled carbon nanotubes” in English terminology), preferably they are multi-walled.
• the carbon nanotubes used according to the invention usually have a mean diameter ranging from 0.1 to 100 nm, preferably from 0.1 to 50 nm, more preferably from 1 to 30 nm, or even from 10 to 15 nm, and advantageously a length of 0.1 micron or more and advantageously from 0.1 to 20 microns, preferably from 0.1 to 10 microns.
• the length / diameter ratio of the carbon nanotubes, or form factor is advantageously greater than 10 and most often greater than 100.
• Their specific surface area is for example between 50 and 300 m 2 / g, advantageously between 100. and 300 m 2 / g, and their apparent density may especially be between 0.01 and 0.5 g / cm 3 and more preferably between 0.07 and 0.2 g / cm 3 .
• MWNT may for example comprise from 5 to 25 walls or sheets and more preferably from 7 to 20 sheets.
• Carbon nanotubes are obtained in particular by chemical vapor deposition (CCVD), for example according to the method described in WO06 / 082325. They can be obtained from renewable raw material, in particular of plant origin, as described in the patent application EP1980530.
• CVD chemical vapor deposition
• nanotubes are under the trade name Graphistrength® ® C100 from Arkema. These nanotubes can be purified and / or treated (for example oxidized) and / or milled and / or functionalized.
• the grinding of the nanotubes can be carried out cold or hot, carried out according to known techniques used in devices such as ball mills, hammers, grinders, knives, gas jet or any other grinding system likely to reduce the size of the entangled network of nanotubes. It is preferred that the grinding is carried out according to a gas jet grinding technique and in particular in an air jet mill.
• the purification of the crude or milled nanotubes can be carried out by washing with a sulfuric acid solution, so as to rid them of any residual mineral and metal impurities, such as for example the catalyst originating from them. process of preparation.
• the weight ratio of nanotubes to sulfuric acid can be between 1: 2 and 1: 3.
• the purification operation may also be carried out at a temperature ranging from 90 to 120 ° C, for example for a period of 5 to 10 hours. This operation may advantageously be followed by rinsing steps with water and drying the purified nanotubes.
• Oxidizing acids such as nitric acid, in addition to the removal of a large part of the mineral materials, will create polar surface functions by surface oxidation of the outer layer.
• the nanotubes may alternatively be purified by high temperature heat treatment, typically greater than 1000 ° C.
• the carbon nanotubes may be previously compacted before being subjected to a heat treatment, according to the method described in the application WO2018 / 178929.
• the oxidation of the nanotubes is advantageously carried out by putting them in contact with a solution of sodium hypochlorite containing from 0.5 to 15% by weight of NaOCI and preferably from 1 to 10% by weight of NaOCI. for example in a weight ratio of nanotubes to sodium hypochlorite ranging from 1: 0.1 to 1: 1.
• the oxidation is advantageously carried out at a temperature below 60 ° C. and preferably at room temperature, for a duration ranging from a few minutes to 24 hours. This oxidation operation may advantageously be followed by filtration and / or centrifugation, washing and drying steps of the oxidized nanotubes.
• raw carbon nanotubes which may be crushed, that is to say nanotubes which are neither oxidized nor purified nor functionalized and which have not undergone any other chemical treatment and / or thermal.
• the level of carbon nanotubes may be between 1 and 99% by weight of the electrical conductive composition.
• the electrical conductive composition comprises more than 20% of carbon nanotubes and more preferably 40% or more of carbon nanotubes. For example, it comprises between 25% and 75% of carbon nanotubes.
• the carbon nanofibers or carbon nanofibrils that can be used in the present invention are also nanofilaments produced by chemical vapor deposition (CCVD) from a carbon source decomposed on a catalyst comprising a transition metal (Fe, Ni, Co, Cu), in the presence of hydrogen, at temperatures of 500 to 1200 ° C, such as carbon nanotubes.
• CCVD chemical vapor deposition
• these two carbonaceous charges are differentiated by their structure, because carbon nanofibers consist of zones more or less organized graphitics (or turbostratic stacks) whose planes are inclined at variable angles with respect to the axis of the fiber.
• These stacks may take the form of platelets, fish bones or stacked cups to form structures generally ranging in diameter from 50 nm to 500 nm or more.
• Examples of usable carbon nanofibers have in particular a diameter of 100 to 200 nm, for example about 150 nm, advantageously a length of 5 to 100 microns and preferably a length of 5 to 75 microns. It is possible to use, for example, VGCF nanofibers from SHOWA DENKO.
• the carbon nanofibers contained in the electrical conductive composition preferably have a form factor, that is to say the ratio between the length and the diameter, between 10 and 2000.
• the electrical conductive composition comprises more than 20% carbon nanofibers and more preferably 40% or more carbon nanofibers.
• it contains between 25% and 75% of carbon nanofibers.
• the carbon fibers that can be used in the present invention are solid or partially porous carbon fibers, at least partially graphitized, having diameters preferably between 200 nm and 20 ⁇ m, preferably between 500 nm and 20 ⁇ m. and even more preferably a diameter of from 500 nm to 8 microns.
• the preference is for ex-cellulose fibers or pitch with reduced diameter ( ⁇ 5 ⁇ m), which will be more favorable to avoid excessive thickness and electrode architecture defects.
• the carbon fibers contained in the electrical conductive composition preferably have a form factor, that is to say the ratio between the length and the diameter, of between 5 and 1000.
• the carbon fibers that can be used in the present invention advantageously have a specific density of between 1.3 and 1.9 g / cm 3 .
• the conductive composition comprises more than 20% of carbon fibers and more preferably 40% or more of carbon fibers.
• the conductive composition contains between 25% and 75% of carbon fibers.
• the conductive composition comprises at least 20% of carbon fibers, preferably at least 30% of carbon fibers and more preferably 40% of carbon fibers.
• the electrical conductive composition comprises more than 20% of carbon nanotubes and more than 20% of another carbonaceous filler selected from: carbon nanofibers and carbon fibers. Even more preferably, the electrical conductive composition comprises more than 20% of carbon nanotubes, more than 20% of carbon nanofibers and more than 20% of carbon fibers.
• carbon nanotubes, carbon nanofibers and / or carbon fibers may be subject to a surface treatment.
• an intrinsically conductive polymer such as polyaniline, polythiophene, polypyrrole, etc.
• at least a portion of the nanofibers of carbon, carbon nanotubes and / or carbon fibers is covered by an ionically conductive ceramic material.
• the active material formulation may further comprise another carbonaceous filler selected from : carbon blacks, acetylene blacks, graphites, graphenes, activated carbons, and mixtures thereof, preferably graphenes.
• graphene is meant a plane graphite sheet, isolated and individualized, but also, by extension, an assembly comprising between one and a few tens of sheets and having a flat structure or more or less wavy.
• This definition therefore includes FLG (Few Layer Graphene or Graphene NanoRibbons or Graphene NanoRibbons), NGP (Nanosized Graphene Plates), CNS (Carbon NanoSheets or nano-graphene sheets), and Graphene NanoRibbons. nano-ribbons of graphene).
• the graphene used according to the invention is not subjected to an additional step of chemical oxidation or functionalization.
• the graphene used according to the invention is obtained by chemical vapor deposition or CVD, preferably in a process using a powdery catalyst based on a mixed oxide. It is typically in the form of particles having a thickness of less than 50 nm, preferably less than 15 nm, more preferably less than 5 nm and less than one micron side dimensions, preferably 10 nm at less than 1000 nm, more preferably 50 to 600 nm, or even 100 to 400 nm. Each of these particles generally contains from 1 to 50 sheets, preferably from 1 to 20 sheets and more preferably from 1 to 10 sheets, or even from 1 to 5 sheets which are capable of being separated from each other in the form of independent sheets, for example example during an ultrasound treatment.
• the sulfurized material may be elemental sulfur, or a sulfur molecule such as a sulfur-containing organic compound or polymer, or a sulfur-containing inorganic compound, or a mixture thereof in all proportions.
• the sulfur-containing inorganic compounds that can be used as sulfur-containing materials are, for example, anionic alkali metal polysulfides, preferably lithium polysulfides represented by the formula Li 2 S n (with n greater than or equal to 1).
• the sulfur material comprises elemental sulfur.
• the sulfur can be used as it is, or the sulfur can be previously purified by different techniques such as refining, sublimation, or precipitation.
• the sulfur, or more generally the sulfurized material can also be subjected to a preliminary grinding and / or sieving step in order to reduce the size of the particles and to tighten their distribution.
• the particle size of the powder can vary widely.
• the sulfur-containing inorganic compounds that can be used as sulfur-containing materials are, for example, anionic alkali metal polysulfides, preferably lithium polysulfides represented by the formula Li 2 S n (with n> 1).
• the sulfur-containing organic compounds or polymers may be chosen from organic polysulfides, organic polythiolates including, for example, functional groups such as dithioacetal, dithiocetal or trithioorthocarbonate, aromatic polysulfides, polyethers, polysulphides, acid salts, and the like.
• organosulfur compounds are described in particular in document WO 2013/155038.
• the sulfur material is an aromatic polysulfide.
• aromatic polysulfides have the following general formula (I):
• R 1 to R 8 represent, identically or differently, a hydrogen atom, a radical -OH or -OM + , or a saturated or unsaturated carbon chain containing from 1 to 20 carbon atoms, or a group -OR 10, with Rio which may be an alkyl, arylalkyl, acyl, carboalkoxy, alkyl ether, silyl or alkylsilyl radical containing from 1 to 20 carbon atoms.
• M represents an alkaline or alkaline earth metal
• n and n ' are two integers, identical or different, each being greater than or equal to 1 and less than or equal to 8,
• p is an integer from 0 to 50
• A is a nitrogen atom, a single bond, or a saturated or unsaturated carbon chain of 1 to 20 carbon atoms.
• Ri, R 4 and R 7 are OM + radicals
• R2, R5 and Re are hydrogen atoms
• R 3 , Re and Rg are saturated or unsaturated carbon chains containing 1 to 20 carbon atoms, preferably 3 to 5 carbon atoms, the average value of n and n 'is about 2,
• the average value of p is between 1 and 10, preferably between 3 and 8.
• - A is a single bond linking the sulfur atoms to the aromatic rings.
• poly (alkyl phenol) polysulfides of formula (I) are known and can be prepared for example in two steps:
• R is a tert-butyl or tert-pentyl radical.
• the sulfurized material used in the formulation of active material according to the invention may have different values of melting enthalpy.
• This enthalpy of fusion (DH fus ) may preferably be between 70 and 100 J. g -1 .
• the sulfurized material for example in the elemental state or in the form of polysulfide, can be characterized by a melting enthalpy measured during a phase transition (fusion) by differential scanning calorimetry between 80 ° C. and 130 ° C (DSC - "Differential scanning calorimetry" in Anglo-Saxon terminology).
• the sulfur-containing material has an S8 content of less than 10% by weight of the sulfur-containing material.
• the S8 content can be measured by DSC.
• the invention in another aspect, relates to a process for preparing the active ingredient formulation.
• This method comprises a step of contacting the sulfurized material with the electrical conductive composition.
• the contacting step according to the invention can be carried out by many means.
• the contacting step is selected from: mixing the sulfurized material with the electrical conductive composition at a temperature greater than or equal to the melting temperature of the sulfurized material, sublimation of the sulfurized material on the electrically conductive composition and depositing the sulfur-containing material in the liquid phase on the electrical conductive composition, the sulfur-containing material then being solubilized in a suitable solvent.
• the present invention provides a method for obtaining an active material formulation having a better combination of a sulfur donor material, with carbonaceous feed particles to facilitate access of sulfur to electrochemical reactions, which can contribute to a good maintenance of the battery operation over time.
• the active material according to the invention may take the form of a solid state finished product comprising a mixture of particles comprising the electrically conductive composition dispersed in the mass of the sulfur-containing material and this in a homogeneous manner.
• the active material advantageously has a density greater than 1, 4 g / cm 3 , determined according to the standard NF EN ISO 1183-1.
• the density is generally less than 2 g / cm 3 .
• the process for preparing the active material formulation comprises a step of forming a Sulfur-Carbon composite, said step of forming the Sulfur-Carbon composite comprising a melting of a sulfur-containing material and mixing. molten sulfur material and carbonaceous fillers. Such a step allows the formation of a homogeneous mixture.
• the melting of the mixture is limited by the density difference between the carbonaceous fillers (0.05 - 0.5 g / cm 3 ) and the sulfur (2 g / cm 3 ), it is necessary to add an intense mechanical energy to achieve this mixture, which can be between 0.05 kWh / kg and 1 kWh / kg of active material, preferably between 0.2 and 0.5 kWh / kg of active ingredient.
• the carbonaceous charges are thus dispersed homogeneously throughout the mass, and are not found only on the surface of the sulfur particles.
• a compounding device ie an apparatus conventionally used in the plastics industry for the melt blending of thermoplastics and additives in order to produce composites.
• the Sulfur-Carbon composite is obtained by a manufacturing process comprising a step of melting the sulfur-containing material and kneading the molten sulfur material and carbonaceous fillers.
• This melting and kneading step may advantageously be carried out by a compounding device.
• the process 100 according to the invention can comprise preliminary stages of formation of the Sulfur-Carbon composite, said stages of formation of the carbon Sulfur composite comprising:
• a step 120 for introducing an additive optionally, a step 120 for introducing an additive
• a compounding device is preferably used, that is to say an apparatus conventionally used in the plastics industry for the melt blending of thermoplastic polymers and additives in order to to produce composites.
• the active ingredient according to the invention can thus be prepared according to a process also comprising the recovery 150 of the Sulfur-Carbon composite obtained in agglomerated solid physical form.
• the introduction step 110 is implemented in a compounding apparatus.
• the sulfurized material and the carbonaceous fillers are mixed using a high-shear device, for example a co-rotating twin-screw extruder or a co-kneader.
• the melt generally comes out of the apparatus in solid physical form agglomerated, for example in the form of granules, or in the form of rods which, after cooling, are cut into granules.
• co-kneaders examples include the BUSS® MDK co-kneaders and those of the BUSS® MKS or MX series marketed by the company BUSS AG, all of which consist of a screw shaft provided with fins. , disposed in a heating sleeve optionally consisting of several parts and whose inner wall is provided with kneading teeth adapted to work with the fins to produce a shear of the material.
• the shaft is rotated, and is provided with an oscillation movement in the axial direction by a motor.
• co-kneaders may be equipped with a granule manufacturing system, adapted for example to their outlet orifice, which may consist of an extrusion screw or a pump.
• the co-kneaders that can be used according to the invention preferably have an L / D screw ratio ranging from 7 to 22, for example from 10 to 20, while the co-rotating extruders advantageously have an L / D ratio ranging from 15 to 56, for example from 20 to 50.
• the active material formulation further comprises at least one additive chosen from: a rheology modifier, a binder, an ionic conductor, another electrical carbon conductor, an electrolyte, an electron donor element or their association.
• the method may comprise a step 120 for introducing at least one additive.
• the additive (s) may be incorporated into the active ingredient formulation by melt, for example in step 120.
• the sulfurized material and the electrically conductive composition then represent from 50% to 99% by weight, preferably from 60% to 95% by weight relative to the total weight of the active material formulation.
• a rheology modifier or an additive which reduces the viscosity of the sulfur in the molten state, in order to reduce the self-heating of the mixture in the compounding device.
• additives are described in application WO 2013/178930. Examples that may be mentioned include dimethyl sulphide, diethyl sulphide, dipropyl sulphide, dibutyl sulphide, their trisulphide homologues, their tetrasulfide homologues, their pentasulfide homologues, their hexasulfide homologues, alone or in mixtures of two. or more of them in all proportions.
• the amount of rheology modifier additive is generally between 0.01% to 5% by weight, preferably from 0.1% to 3% by weight relative to the total weight of the active ingredient formulation.
• the formulation of active material may comprise a binder, especially a polymeric binder.
• Polymeric binders may also provide some dimensional plasticity or flexibility of the electrode formed from the active material.
• these binders are introduced before or during the compounding step.
• an important role of the binder is also to ensure a homogeneous dispersion of the active material and for example Sulfur-Carbon composite particles.
• polymeric binders may be employed in the formulation according to the invention and they may be chosen, for example, from: halogenated polymers, preferably fluorinated polymers, functional polyolefins, polyacrylonitriles, polyurethanes, polyacrylic acids and their derivatives, polyvinyl alcohols and polyethers, and a mixture thereof in all proportions.
• halogenated polymers preferably fluorinated polymers, functional polyolefins, polyacrylonitriles, polyurethanes, polyacrylic acids and their derivatives, polyvinyl alcohols and polyethers, and a mixture thereof in all proportions.
• PVDF polyvinylidene fluoride
• PVDF polyvinylidene fluoride
• PVDF polyvinylidene fluoride
• PVDF polyvinylidene fluoride
• PTFE polytetrafluoroethylene
• HFP hexafluoropropylene
• VF3 polytetrafluoroethylene
• TFE trifluoroethylene
• CTFE chlorotrifluoroethylene
• FEP fluoroethylene / propylene copolymers
• FEP copolymers of ethylene with either fluoroethylene / propylene (FEP), either tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE); perfluoropropyl vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE), 2,3,3,3-tetrafluoropropene, and copolymers of ethylene with perfluoromethylvinyl ether (PMVE), or mixtures
• polyethers examples include alkylene polyoxides such as POE ethylene polyoxides, polyalkylene glycols such as polyethylene glycols PEG, polypropylene glycols PPG, polytetramethylene glycols (PTMG), polytetramethylene ether glycols (PTMEG), etc.
• alkylene polyoxides such as POE ethylene polyoxides
• polyalkylene glycols such as polyethylene glycols PEG, polypropylene glycols PPG, polytetramethylene glycols (PTMG), polytetramethylene ether glycols (PTMEG), etc.
• the polymeric binders may also be selected from block copolymers of these polymers such as a PEO / PPO / PEO block copolymer. More preferably, the polymeric binder is PVDF or POE. POE is sometimes used in acetonitrile or isopropanol, as is PTFE suspended in ethanol or water. The most common polymer is polyvinylidene fluoride (PVDF), used in solution in N-methyl-2-pyrrolidone (NMP). This polymer is chemically stable vis-à-vis the organic electrolyte, but also electrochemically in the potential window of Li / S accumulators. It does not dissolve in organic solvents, swells very little, and therefore allows the electrode to maintain its morphology and its mechanical behavior in cycling.
• PVDF polyvinylidene fluoride
• NMP N-methyl-2-pyrrolidone
• the possible binders are also those of the family of polysaccharides such as carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), etc ...
• the binder is PVDF, POE or CMC.
• the amount of binder is generally less than 20% by weight relative to the active material formulation and is preferably between 5% and 15% by weight.
• the active ingredient formulation may comprise an ionic conductor having a favorable interaction on the surface of the sulfur or the sulfur molecule in order to increase the ionic conductivity of the active ingredient.
• ionic conductors that may be mentioned in a nonlimiting manner are organic lithium salts, for example imidazolate salts. of lithium. Mention may also be made of alkylene polyoxides which, in addition to their binder function, can bring ionic conductivity properties to the active material.
• the active ingredient formulation may also comprise another electrical conductor, advantageously a carbon-based electrical conductor, such as carbon black, graphite or graphene, generally in proportions ranging from 1 to 10% relative to the sulfur molecule.
• a carbon-based electrical conductor such as carbon black, graphite or graphene
• the carbon black is used as the electrical conductor.
• the active ingredient formulation may include an electron donor element to enhance electronic interchange and regulate polysulfide length during charging, thereby optimizing charge / discharge cycles of the battery.
• electron donor elements it is advantageous to use an element, in the form of a powder or in the form of a salt, of columns IVa, Va and Via of the periodic table, preferably chosen from Se, Te, Ge, Sn, Sb, Bi. , Pb, Si or As.
• These compounds can generally be added in proportions ranging from 1 to 10% by weight relative to the weight of sulfur-containing material.
• the active ingredient formulation may further comprise an electrolyte salt preferably selected from: (Bis) trifluoromethanesulfonate lithium imide (LiTFSI), lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), bis (fluorosulfonyl) lithium imide (LiFSI), lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (UCIO4), lithium trifluoromethylsulfonate (CF3SO3U), lithium trifluoroacetate (CF3COO), dilithium dodecafluorododecaborate (U2B12F12), bis (oxalate) borate lithium (UBC4O8) and lithium tetrafluoroborate (LiBF 4 ). More preferably, the electrolyte liquid solvent comprises LiTFSI.
• LiTFSI lithium 2-trifluoromethyl-4,5-dicyanoimidazole
• LiFSI bis (fluorosulfonyl
• the compounding step 130 is carried out at a temperature above the melting temperature of the sulfur-containing material.
• the compounding temperature can range from 120 ° C to 150 ° C.
• the compounding temperature is a function of the specifically used material whose melting temperature is generally mentioned by the material supplier.
• the residence time will also be adapted to the nature of the sulfur material.
• the method may comprise a kneading step 140 of the molten sulfur material and the carbonaceous fillers.
• the kneading can be implemented by any mixing, kneading or extrusion device known to those skilled in the art and compatible with the formulation of active material, especially with the temperature during the compounding step.
• the mixture of particles can then be milled, during a milling step 160, to obtain a powder having no particles larger than 100 microns, preferably no particles larger than 25 microns so to facilitate the process of manufacturing the electrode.
• the carbonaceous fillers are mixed with the sulfur-containing molecule (s), in particular with sulfur, preferably in the melt.
• the grinding step can be carried out in the solid state, in other words in a dry state.
• the grinding step of the Sulfur-Carbon composite may, for example, be carried out in a ball mill (horizontal and vertical cage), a cavitator, a jet mill, a fluidized bed jet mill, a liquid phase mill, screw disperser, brush mill, hammer mill, ball mill, or other methods of micronization.
• the inventors have developed a process for preparing a formulation for the manufacture of an electrode from a Sulfur-Carbon composite capable of improving the load and discharge capacity and the to improve the interfaces by grinding in a solvent in the liquid phase comprising, for example, electrolyte salts and / or solid electrolytes.
• a solvent in the liquid phase comprising, for example, electrolyte salts and / or solid electrolytes.
• the creation of favorable interfaces in the grinding stage can make it possible to improve the performance of the active ingredient formulation. More particularly, grinding in the presence of an electrolyte makes it possible to obtain the catholyte directly. The latter can then be used to form the cathode.
• the improved grinding method according to the invention comprises the following steps:
• Obtention 240 following said grinding step, of an active ingredient formulation in the form of a solid-liquid dispersion, comprising the sulfur-carbon composite in the form of particles of less than 50 ⁇ m median diameter D50.
• the method according to the invention comprises an introduction step 210 in a grinding device of a solvent in the liquid phase.
• the amount of solvent used makes it possible to form a solid-liquid dispersion having a solids content by weight of less than 90%, preferably less than 80%, more preferably between 30% and 60%.
• the solvent used during the grinding step can be a solvent that can be evaporated before the manufacture of the electrode.
• the solvent is preferably selected from liquid phase solvents having a boiling point of less than 300 ° C, preferably less than or equal to 200 ° C, more preferably less than or equal to 115 ° C, even more preferably less than or equal to 100 ° C.
• the solvent can be evaporated after the milling step without causing a modification of the carbon-sulfur composite.
• the solvent in the liquid phase used in the invention may for example comprise at least one protonic or aprotonic solvent, said protonic or aprotonic solvent being selected from: water, alcohols, ethers, esters, lactones, N- Methyl-2-pyrrolidone and dimethylsulfoxide.
• liquid phase solvent used is water or an alcohol and the solvent is removed via a freeze-drying step.
• the solvent in the liquid phase is degassed before its introduction into the grinding device.
• the method according to the invention comprises an introduction step 220 in the grinding device of a composite sulfur-carbon.
• the sulfur-carbon composite comprises at least one sulfur-containing material and carbonaceous fillers.
• the Sulfur-Carbon composite, before the grinding step, can be in the form of solids, or solids, having a median diameter D50 greater than 50 pm.
• the Sulfur-Carbon composite used during the grinding step can be obtained by several processes and has a shape and dimensions defined by its production line.
• the Sulfur-Carbon composite is obtained by a method of manufacturing comprising a step of melting a sulfur-containing material and mixing the molten sulfur material and the carbonaceous fillers, preferably in the presence of an intense mechanical energy. This melting and kneading step may advantageously be carried out by a compounding device.
• the Sulfur-Carbon composite is generally in agglomerated physical form, for example in the form of granules. In this case, the shape of the granules will depend on the diameter of the die holes and the speed of the knives.
• the granules may for example have at least one dimension between 0.5 mm and several millimeters.
• the sulfur-carbon composite is in the form of solids such as granules or particles having a median diameter D50 greater than 100 ⁇ m, preferably greater than 200 ⁇ m and more preferably greater than 500 ⁇ m. pm.
• the sulfur-carbon composite advantageously used in the context of the invention, comprises percolated carbonaceous feedstocks in a molten sulfur matrix, and the carbonaceous feedstocks are distributed homogeneously throughout the mass of the sulfur-containing material, which can be visualized for example by electron microscopy.
• the mixture sulfur material / carbonaceous charge is of morphology adapted to an optimization of the operation of a Li / S battery electrode.
• the carbonaceous charges are thus dispersed homogeneously throughout the mass of the particles, and are not found only on the surface of the sulfur particles.
• the active ingredient according to the invention namely an active material based on this Sulfur-Carbon composite, can thus ensure efficient electricity transfer from the current collector of the electrode and offer the active interfaces to the reactions. electrochemical when operating the battery.
• the method according to the invention comprises a grinding step 230.
• the grinding in the liquid state has the advantage of not creating too much porosity in the active material obtained.
• the powder obtained has a higher density than powders obtained with conventional methods.
• the grinding step may for example be carried out in a ball mill (horizontal and vertical cage), a cavitator, a jet mill, a fluidized bed jet mill, a liquid phase mill, a disperser a brush mill, a hammer mill, a ball mill, or other methods of micronizing solid materials.
• the grinding step is generally conducted over a period of 30 minutes or more. Preferably, the grinding step is conducted for a period of 1 hour or more, more preferably at least 2 hours.
• the method according to the invention may comprise two stages of successive grindings, carried out on two different grinding devices.
• the grinding step is generally conducted at a temperature below the boiling point of the solvent in the liquid phase.
• the grinding step is conducted at a temperature below the melting point of the sulfur material.
• the grinding step is preferably conducted at a temperature below 300 ° C, more preferably at a temperature below 200 ° C, even more preferably at a temperature of 110 ° C or less.
• the grinding step is preferably conducted at a temperature above 0 ° C. More preferably, it is conducted at a temperature above 10 ° C.
• the grinding step is conducted at a temperature between 1 ° C and 300 ° C, preferably between 5 ° C and 200 ° C and more preferably between 5 ° C and 110 ° C.
• a temperature between 1 ° C and 300 ° C, preferably between 5 ° C and 200 ° C and more preferably between 5 ° C and 110 ° C.
• the grinding step will probably generate a heating of the mixture caused by the friction generated by the grinding step.
• self-heating is accepted up to the desired temperature, and then the process may comprise a step of cooling the mixture, in particular to remain at a temperature below the boiling point of the solvent in the liquid phase used.
• the grinding step may be followed by a step of mixing the solid-liquid dispersion with additives, which may be other components of the electrode, preferably by liquid means.
• the method according to the invention comprises a step 240 for obtaining a formulation in the form of a solid-liquid dispersion generated during the grinding stage.
• this formulation comprises the sulfur-carbon composite in the form of particles of less than 50 ⁇ m median diameter D 50 and advantageously less than 10% by number of the particles of the dispersion are elemental sulfur particles.
• the formulation in the form of a solid-liquid dispersion as defined according to the invention makes it possible to increase the specific capacity of the electrode, and to increase the charge capacity and discharge of the electrode.
• the formulation according to the invention can thus ensure an efficient transfer of electricity from the current collector of the electrode and offer the active interfaces to the electrochemical reactions during operation of the battery.
• the method according to the invention may comprise a drying step 250.
• the drying step 250 makes it possible to generate an active material formulation in the form of a powder.
• the active ingredient formulation, obtained from the solid-liquid dispersion then advantageously has a moisture content of less than 100 ppm.
• This drying step may for example be performed via an atomization step.
• This active ingredient powder has common advantages with the formulation namely improved performance due to a low level of elemental sulfur and / or low oxidation.
• This powder can then be formulated with conventional additives and used in the dry process.
• the formulation of active ingredient in powder form according to the invention comprises particles having an intimate mixture of carbonaceous charges dispersed in the mass of the sulfur-containing material and that in a homogeneous manner.
• the formulation of active material advantageously has a density greater than 1, 6 g / cm 3 , determined according to the standard NF EN ISO 1183-1.
• the formulation of active material according to the invention preferably in the form of a powder as characterized above, and advantageously having a porosity of less than 20% and / or a density greater than 1.6 g / cm 3 , can be used to prepare an electrode, in particular a cathode, of Li / S battery.
• the active material generally represents about 20 to 95% by weight, preferably 35 to 80% by weight relative to the complete formulation of the electrode.
• the melting enthalpy of the sulfur-containing material in the sulfur-carbon composite forming the active material according to the invention is lower than the melting enthalpy of the sulfur-containing material found in formulations or active materials formed according to methods of the prior art.
• the sulfur-containing material of the sulfur-carbon composite has a melting enthalpy, as measured by differential scanning calorimetry between 80 ° C. and 130 ° C. (eg 5 ° C./min under nitrogen flow), at least 10% less than the melting enthalpy of the sulfur-containing material used for forming the Sulfur-Carbon composite, more preferably at least 15% less and more preferably at least 20% less.
• the sulfur-containing material of the Sulfur-carbon composite exhibits a melting enthalpy, as measured by differential scanning calorimetry between 80 ° C. and 130 ° C (eg 5 ° C / min under nitrogen flow), less than 60 J. g 1 , preferably less than 55 J. g 1 and more preferably less than 50 J. g 1 .
• the invention relates to a catholyte comprising a formulation of active material according to the invention and a binder.
• the binder is selected in particular from: acrylic polymers, methacrylic polymers fluorinated polymers, polyethers, polyesters, polysaccharides such as cellulose and its derivatives including CMC, functional polyolefins, polyethylene imines, polyacrylonitriles, polyurethanes, polyvinyl alcohols, polyvinylpyrrolidones, copolymers thereof and mixtures thereof.
• the catholyte further comprises at least one additive selected from: a rheology modifier, an ionic conductor, another carbonaceous electrical conductor, an electrolyte and an electron donor element.
• the catholyte may comprise one or more of each of these additives. These additives have already been described previously, thus, the catholyte according to the invention may comprise the additives described above, especially the preferred additives.
• the electrolyte is preferably selected from L1NO2, LiFSI, LiTFSI,
• the electrolyte comprises LiFSI, LiTFSI and / or LiTDI.
• at least a portion of the electrolyte may be a solid electrolyte or ionic conductive ceramic.
• the carbonaceous electrical conductor is preferably selected from carbon blacks, acetylene blacks, graphites, graphene, carbon nanofibers, carbon fibers, activated carbons, intrinsically conductive polymers and mixtures thereof. Indeed, there are fibers and / or nanofibres, preferably carbon fibers, in the formulation of active material according to the invention, but there is a possibility of adding again such fibers or nanofibers in the catholyte .
• the catholyte according to the invention may comprise a liquid solvent capable of solubilizing at least one electrolyte salt, also called liquid electrolyte solvent.
• the electrolyte liquid solvent may for example be selected from: a monomer, an oligomer, a polymer and a mixture thereof.
• the solvent in the liquid phase comprises at least one compound selected from: water, an amide, a carbonate ester, an ether, a sulfone, a fluorinated compound, toluene and dimethylsulfoxide.
• the amide is preferably N-methyl-2-pyrrolidone (NMP) or N, N-dimethylformamide (DMF).
• the electrolyte liquid solvent is preferably a solvent suitable for lithium-sulfur batteries, in this case it is not necessary to implement an evaporation step after the grinding step and this allows the direct formulation of the cathode.
• the liquid phase solvent comprises at least one compound selected from: a carbonate ester, an ether, a sulfone, a fluorinated compound and toluene.
• the carbonate esters can be used as liquid electrolyte solvents.
• the ethers make it possible in particular to obtain a good solubilization of lithium polysulfides and although having dielectric constants generally lower than carbonates, ether-type solvents offer relatively high ionic conductivities and a capacity to solvate lithium ions.
• the electrolyte liquid solvent is an ether such as 1,3-dioxolane (DIOX) or 1,2-dimethoxyethane (DME) or a carbonate ester such as dimethyl carbonate (DMC). ) or propylene carbonate (PC).
• ether such as 1,3-dioxolane (DIOX) or 1,2-dimethoxyethane (DME)
• DME 1,2-dimethoxyethane
• a carbonate ester such as dimethyl carbonate (DMC).
• PC propylene carbonate
• the electrolyte liquid solvent may also comprise a combination of solvents.
• it may include an ether and a carbonate ester. This can reduce the viscosity of a mixture having a high molecular weight carbonate ester.
• the electrolyte liquid solvent is selected from: 1,3-dioxolane (DIOX), 1,2-dimethoxyethane (DME), ethylene carbonate (EC), diethyl carbonate (DEC) ), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropylcarbonate, tetrahydrofuran (THF), 2-methyltetrahydrofuran, methylpropylpropionate, ethylpropylpropionate, methyl acetate, diglyme (2-methoxyethyl ether), tetraglyme, diethylene glycol dimethyl ether (diglyme, DEGDME), polyethylene glycol dimethyl ether (PEGDME), tetraethylene glycol dimethyl ether (TEGDME), ethylene carbonate, carbonate propylene, butyrolactone, dioxolane, hexamethylphosphoamide, pyridine, di
• the electrolyte liquid solvent is selected from: tetrahydrofuran, 2-methyltetrahydrofuran, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate, methylpropylpropionate, ethylpropylpropionate, methyl acetate, dimethoxyethane, 1,3-dioxolane, diglyme (2-methoxyethyl ether), tetraglyme, ethylene carbonate, propylene carbonate, butyrolactone, dioxolane, hexamethyl phosphoamide, pyridine, dimethylsulfoxide, tributyl phosphate, trimethyl phosphate, N-tetraethylsulfamide, sulfone and mixtures thereof.
• solvents may also be used, for example sulfones, fluorinated compounds or toluene.
• the solvent is a sulfone or a mixture of sulfones.
• sulfones are dimethylsulfone and sulfolane.
• Sulfolane can be used as a solvent singly or in combination, for example, with other sulfones.
• the electrolyte liquid solvent comprises lithium trifluoromethanesulfonate and sulfolane.
• the invention also relates to the use of the active material formulation as described above in an electrode, in particular in a Li / S battery cathode.
• the active material according to the invention makes it possible to improve the electronic conductivity of the electrode formulation, the mechanical integrity of the electrode and therefore the operation over time of the battery.
• the invention relates to the use of the formulation according to the invention for the manufacture of an electrode, in particular a cathode.
• the formulation in the form of a particulate mixture, can be deposited on the current collector.
• the active ingredient formulation can be applied to the current collector in the form of a suspension in a solvent (for example water or an organic solvent).
• a solvent for example water or an organic solvent.
• the solvent can then be removed, for example by drying, and the resulting structure wedged to form a composite structure, which can be cut into the desired shape to form a cathode.
• the cathode comprises 1 to 5% by weight of PEO and 1 to 5% by weight of a binder selected from gelatin, a cellulose (for example carboxymethylcellulose) and / or a rubber (for example styrene-butadiene rubber).
• a binder selected from gelatin, a cellulose (for example carboxymethylcellulose) and / or a rubber (for example styrene-butadiene rubber).
• binders can improve the life of the cell.
• the use of such binders can also reduce the total amount of binder, for example to levels of 10% by weight of the total weight of the cathode, or less.
• the cathode described herein can be used in a lithium-sulfur cell.
• the present invention provides a lithium / sulfur accumulator, or lithium-sulfur cell, comprising a cathode as described above.
• the lithium / sulfur accumulator may also comprise an anode comprising a lithium metal or lithium metal alloy and an electrolyte.
• the electrolyte may be a solid electrolyte or comprise at least one lithium salt and at least one organic solvent.
• a separator can be positioned between the cathode and the anode.
• a separator when assembling the cell, a separator can be placed in the cathode and a lithium anode placed on the separator. The electrolyte can then be introduced into the assembled cell to wet cathode and separator. Alternatively, the electrolyte may be applied to the separator, for example, by coating or spraying before the lithium anode is placed on the separator.
• the separator is generally composed of a porous polyolefin membrane (polyethylene, polypropylene). This element is only used in combination with a liquid electrolyte, the polymer or gelled electrolytes already ensuring by themselves the physical separation of the electrodes.
• the separator may comprise any suitable porous substrate or membrane that allows the ions to move between the electrodes of the cell.
• the separator must be positioned between the electrodes to prevent direct contact between the electrodes.
• the porosity of the substrate must be at least 30%, preferably at least 50%, for example greater than 60%.
• Suitable separators comprise a lattice formed of a polymeric material. Suitable polymers include polypropylene, nylon and polyethylene. Nonwoven polypropylene is particularly preferred. It is possible to use a multilayer separator.
• the separator may comprise carbonaceous fillers.
• the separator may be Li-Nafion.
• the cell comprises an electrolyte.
• the electrolyte is present or disposed between the electrodes, which allows the charge to be transferred between the anode and the cathode.
• the electrolyte wets the pores of the cathode as well as, for example, the pores of the separator.
• the organic solvents that can be used in the electrolyte are those described above as electrolyte liquid solvents.
• the temperature setpoints within the co-kneader were as follows: Zone 1: 140 ° C .; Zone 2: 130 ° C; Screw: 120 ° C.
• the mixture consisting of 87.5% by weight of sulfur and 12.5% by weight of nanotubes, is in the form of granules obtained by the overhead cut cooled by air.
• the temperature setpoints within the co-kneader were as follows: Zone 1: 140 ° C .; Zone 2: 130 ° C; Screw: 120 ° C.
• the mixture consisting of 87.5% by weight of sulfur and 10% by weight of nanotubes and 2.5% by weight of nanofibers, is in the form of granules obtained by the cooled head cut. by air.
• Example 2 was repeated but using a conductive agent consisting of 60% of nanotubes Graphistrength ® C100 and 40% nanofibers VGCF H. The other parameters are not changed.
• Example 2 was repeated but using a conductive agent consisting of 40% of nanotubes Graphistrength ® C100 and 60% nanofibers VGCF H. The other parameters are not changed.
• Example 2 was repeated but using a conductive agent consisting of 20% of nanotubes Graphistrength ® C100 and 80% nanofibers VGCF H. The other parameters are not changed.
• Example 7 Example 2 is repeated but using a conductive agent consisting of 100% nanofibres VGCF H. The other parameters are not changed.
• a composite is prepared with a conductive agent content equal to 20% (12% nanotubes and 8% nanofibers) and a sulfur content equal to 80%. The other parameters are not changed.
• a composite is prepared with a conductive agent content of 20% (12% nanotubes and 8% ex-viscose carbon fibers) and a sulfur content equal to 80%. The other parameters are not changed.
• a composite is prepared with the composition Sulfur 87.5% - Nanotubes 7.5% and Nanofibers 5%
• a formulation is produced with 80% sulfur, 10% carbon nanotubes, 5% VGCF H nanofibers and 5% ex viscose carbon fibers.
• the cathode formulations are applied to the electrode via a paste in a solvent and then drying and pressing.
• the capacity of the cathode of the test cell is between 1, 5 and 3 mAh / cm 2 .
• the test cells were put under charging / discharging conditions.
• the performances of the cathode were evaluated after 150 cycles and are reported in the table below. o Table 1
• the stability is still substantially increased when the conductive composition comprises more than 20% of carbon nanofibers and more preferably 40% or more of carbon nanofibers.
• the performances are also improved as evidenced by Examples 3 and 9.
• the presence of carbon fibers makes it possible to ensure a performance after 150 cycles which is much greater than a composition comprising only NTC.
• the cycling stability is improved when the electrical conductive composition comprises at least 20% carbon fibers and even more so when the electrical conductive composition comprises at least 40% carbon fibers.
• the stability is still substantially increased when the conductive composition comprises more than 20% carbon nanotubes and more preferably 40%. % or more of carbon nanotubes.
• the reduction in the amount of nanotubes in favor of an increase in carbon nanofibers decreases the performance after 150 cycles.
• the performance is identical regardless of the amount of nanotubes relative to the amount of carbon nanofibers.
• the performance is improved even after 150 cycles.
• this performance is improved when the amount of nanotubes and carbon fibers increases.
• the performance is improved particularly when the composition comprises more than 20% of carbon fibers.

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• 2018
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