STATE OF THE ART

A lithium sulfur battery (hereinafter referred to as Li / O battery) is composed of a positive electrode (cathode) of elemental sulfur or other sulfur electroactive material, a negative electrode (anode) made of metallic lithium or a metal alloy based on lithium and an organic liquid electrolyte.

Typically, the positive electrode is prepared from an active material comprising elemental sulfur Ss (hereinafter referred to as native sulfur), and optionally various additives, mixed with a solvent and a binder thus forming a paste which is applied on a current collector and then dried in order to remove the solvent. The formed composite structure is optionally subjected to a compression step and then cut to the desired size of the cathode.

The Li / S battery is obtained by depositing a separator on the cathode and a lithium anode is deposited on the separator. An electrolyte usually comprising at least one lithium salt dissolved in a solvent is then introduced into the battery.

The Li / S batteries are the subject of much research since the 2000s and are approached as promising alternatives to conventional Li-ion batteries. The advantage of this type of battery has a high capacity mass storage of the sulfur electrode, to achieve energy densities up to 500 Wh.kg "1 . In addition, the native sulfur presents significant advantages of being abundant, low cost and non-toxic, which allows to consider the development of Li / S batteries at scale.

The discharge mechanism and charging a Li / S battery is based on the reduction / oxidation of sulfur to the cathode (S + 2e " <→ S 2" ) and the oxidation / reduction lithium to the anode (Li → Li + + e " ).

During the discharge, Ss sulfur molecules are reduced and form lithium polysulfides chains of the general formula Li 2 S n (n> 2), solubilized in the organic electrolyte. The last step of reducing the sulfur is in the lithium sulfide forming Li 2 O which precipitates in the organic electrolyte and deposited on the anode. Reverse electrochemical reactions occur in load.

To allow electrochemical reactions to occur rapidly to the electrodes, the cathode and the anode must be generally good electronic conductor. However, the sulfur is an electronic insulator (σ = 5.10 "30 S · cm " 1 of at 25 ° C), the discharge conditions are relatively slow.

Different ways of improvement to overcome this low electronic conductivity of the active material are contemplated, including the addition of an electronically conductive additive such as conductive carbon material. However, in the cathode reaction kinetics is limited if the sulfur / additive mixture is not optimum or if the additive content is too low.

Among the conductive additives, carbon black, activated carbon, carbon fibers or carbon nanotubes are generally used. Carbon black is conventionally used.

The blend of active material and conductive additive can be done in different ways.

For example, the mixture can be done directly in the preparation of the electrode. The sulfur is then mixed with the additive conductor and binder by mechanical mixing, before forming the electrode. With this homogenization step, the carbon-containing additive is assumed to be distributed around the sulfur particles, and thus create a percolating network. A grinding step may also be employed and provides a more intimate mixture of materials. However, this additional step can lead to destruction of the porosity of the electrode.

Another way of mixing the active material with the carbon-containing additive comprises grinding sulfur, and carbonaceous additive in dry, so as to coat the carbon with sulfur.

In the same vein, the carbon may be deposited around the sulfur particles by vapor deposition. Conversely, a heart-shell structure may also be prepared from carbon black on which is deposited a layer of sulfur, for example by precipitation of sulfur on the carbon black nanoparticles.

For example, in FR 2,948,233, there is described a conductive composite material obtained from a chemical treatment and sulfur atoms, introduced into a sealed reactor without external control of the pressure inside of the reactor, at a temperature between 115 ° C and 400 ° C, for a time sufficient to melt the sulfur and reach equilibrium. This material is in the form of sulfur particles coated with carbon having a low surface area. Carbon introduction method in sulfur, described in this document, however, is applicable only to carbon nanofillers without shape factor or aggregation, and does not lead to carbonaceous nanofillers homogeneously dispersed in the mass sulfur.

The document US 2013/0161557) discloses a process for preparing an electrode active material for a lithium battery of sulfur rare earths. The method leads to a composite material comprising molten sulfur absorbed in carbon nanotubes at high temperature and under vacuum. This composite material is then subjected to various treatments including solubilization in an alcohol, grinding, drying, calcination, so as to form an electrode active material. The process described in this document is relatively complex to work with.

Unlike carbon black, additives of carbon nanotubes like (CNTs) have the advantage of also conferring a beneficial effect for the adsorbent active material limiting its dissolution in the electrolyte and thus promoting better cyclability.

For example, in the article Electrochimica Acta 51 (2006), ppl33-1335, W. Zheng et al describes the preparation of a composite sulfur / carbon nanotube (CNT) by mixing at high temperature for a long spunlaid residence time. However, the cycling tests with this material were made only on 60 cycles, which does not show that the carbon nanotubes are homogeneously dispersed in the mass of sulfur to obtain an effect on the duration life of the electrode.

The introduction of CNTs in formulations constituting the electrodes still raises many problems. Indeed CNTs are difficult to handle and disperse, because of their small size, powdering and eventually when obtained by chemical vapor deposition (CVD), their entangled structure generating further strong interactions Van Der Waals between their molecules. The low dispersion of the CNTs limit the efficiency of charge transfer between the positive electrode and the electrolyte and thus the performance of Li / S battery despite the addition of the conductive material.

Therefore, it would be advantageous for the formulator to have an active material comprising CNTs well dispersed in sulfur, and generally in a sulfur-containing material in the form of ready to use active material that can be used directly in a formulation for the manufacture of a Li electrode / S in order to effectively increase its electronic conductivity.

The Applicant has now found that an active material comprising uniformly dispersed carbon nanotubes in the mass of a sulfur-containing material such as sulfur increases the conductive fillers interfaces / sulfur, thereby increasing load capacity and discharging of the battery incorporating this active ingredient.

The Applicant has also discovered that this active material can be obtained by contacting the CNT with a melt-in sulfur material for example in a compounding device, thus forming an improved active material, usable for the preparation of an electrode.

It is also apparent that this invention could also be applied to other carbonaceous nanofillers that CNT, particularly carbon nanofibers and graphene, or mixtures thereof in all proportions.

SUMMARY OF THE INVENTION

The invention relates to an active material for the manufacture of an electrode comprising:

- a sulfur-containing material;

from 1 to 25% by weight of carbonaceous nanofillers homogeneously dispersed in the mass of the sulfur material.

According to one embodiment, the electrode active material comprises 5 to 25% by weight of carbonaceous nanofillers homogeneously dispersed in the mass of the sulfur material.

The invention also relates to an electrode active material comprising:

- a sulfur-containing material;

from 1 to 25% by weight of carbonaceous nanofillers homogeneously dispersed in the mass of the sulfur material,

characterized in that it has a porosity less than 40%>.

The invention also relates to an electrode active material comprising:

- a sulfur-containing material;

from 1 to 25% o by weight of carbon nanofillers homogeneously dispersed in the mass of the sulfur material,

characterized in that it has a density greater than 1, 6 g / cm 3 .

According to one embodiment of the invention, said active material is obtained by a melt route, in particular with a mechanical energy which may be between 0.05 kWh and kWh per 1 kg of active compound, preferably between 0.2 and 0 , 5 kWh / kg active ingredient.

By "nanofiller carbon" means a carbonaceous filler whose smallest dimension is between 0, 1 and 200 nm, preferably between 0, 1 and 160 nm, more preferably between 0, 1 and 50 nm, as measured by light scattering,

By "nanofiller carbonaceous" may designate a feed comprising at least one member of the group consisting of carbon nanotubes, carbon nanofibers and graphene, or a mixture thereof in any proportions. Preferably, the carbonaceous nanofillers include at least carbon nanotubes.

By "sulfur-containing material" is meant a sulfur donor compound selected from native sulfur (or basic) compounds or sulfur-containing organic polymers and inorganic sulfur compounds.

According to a preferred embodiment of the invention, the sulfur-containing material comprises at least native sulfur, the sulfur-containing material being only native sulfur, or in admixture with at least one other sulfur-containing material.

The active ingredient according to the invention comprises carbonaceous nanofillers well percolated in a molten matrix sulfur, and carbonaceous nanofillers are homogeneously distributed throughout the bulk of the sulfur material, which can be visualized for example by electron microscopy. The sulfur material mixture / nano filler is morphology suitable for optimizing the operation of a Li / S battery electrode.

The active ingredient according to the invention may thus provide efficient power transfer from the current collector of the electrode and deliver the active interfaces to the electrochemical reactions during operation of the battery.

Thus, the present invention provides an active material having improved combination of a sulfur donor material with carbon particles to facilitate nanofillers sulfur access to electrochemical reactions. In addition, incorporating the electrode active material according to the invention provides good support of the operation of the battery over time.

According to one embodiment of the invention, the active ingredient further comprises at least one additive selected from a rheology modifier, a binder, an ion conductor, a carbon electrical conductor, an electron-donor element or combination thereof. As carbonaceous nanofillers, the / additives are incorporated into the active material by the molten route.

Another aspect of the invention is the use of the active material as described above in an electrode, particularly a Li / S battery cathode. The active ingredient according to the invention allows to improve the electronic conductivity of the electrode formulation.

BREVE DESCRIPTION DES FIGURES

Figure 1 shows the distribution of the particle size of the powder obtained in Example 1 according to the invention.

2 shows SEM morphology of the electrode active material obtained in Example 1 according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is now described in more detail and not limited to the following description.

The carbon nanofillers

According to the invention, carbonaceous nanofillers may be carbon nanotubes, carbon nano fiber, graphene, or a mixture thereof in any proportions. Preferably, the carbon nano-filler are carbon nanotubes alone or mixed with at least one other carbon nanofiller.

Carbon nanotubes (CNTs) used in the composition of the active material may be of the single-walled type, double-walled or multi-walled, preferably multi-wall (MWNT)

Carbon nanotubes used according to the invention usually have an average diameter ranging from 0.1 to 200 nm, preferably from 0.1 to 100 nm, more preferably from 0.4 to 50 nm, and more preferably 1 30 nm, or 10 to 15 nm, and advantageously a length of more than 0.1 μιη and preferably from 0.1 to 20 μιη, preferably from 0.1 to 10 μιη, for example about 6 μιη. Their length / diameter ratio is advantageously greater than 10 and most often greater than 100. Their specific surface area is for example between 100 and 300 m 7 G, preferably between 200 and 300 m 7 G, and their apparent density may in particular 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 15 layers and more preferably from 7 to 10 sheets.

Carbon nanotubes may be obtained by chemical vapor deposition, for example by the process described in WO 06/082325. Preferably, they are obtained from renewable raw materials, especially of plant origin, as described in the patent application EP 1980530.

These nanotubes can be treated or not.

An example of crude carbon nanotubes is especially the trade name Graphistrength® ® Cl 00 from Arkema.

These nanotubes can be purified and / or treated (eg oxidized) and / or ground and / or functionalized.

The grinding of the nanotubes can be in particular carried out in hot or cold and be performed according to known techniques implemented in devices such as ball mills, hammer, grinding wheels, knives, gas jet or any other system grinding may reduce the size of the entangled network of nanotubes. It is preferred that the milling step is performed in a grinding technique gas jet and in particular in an air jet mill.

The purification of raw or milled nanotubes may be carried out by washing with a sulfuric acid solution, so as to rid them of any residual mineral and metallic impurities, such as iron from their method of preparation . The weight ratio of the nanotubes to sulfuric acid may in particular be between 1: 2 and 1: 3. The purification operation can 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 water rinsing and drying steps of the purified nanotubes. The nanotubes may alternatively be purified by high temperature heat treatment, typically greater than 1000 ° C.

Oxidation of nanotubes is advantageously carried out by bringing the latter into contact with a sodium hypochlorite solution containing from 0.5 to 15% by weight NaOCl and preferably 1 to 10% by weight of NaOCl, e.g. in a weight ratio of the nanotubes to sodium hypochlorite ratio of 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 period of a few minutes to 24 hours. This oxidation operation may advantageously be followed by steps of filtration and / or centrifugation, washing and drying of the oxidized nanotubes.

The functionalization of the nanotubes can be achieved by grafting of reactive moieties such as vinyl monomers on the surface of nanotubes.

preferably used in the present invention, crude carbon nanotubes optionally ground, that is to say of the nanotubes which are neither oxidized nor purified nor functionalized and have not undergone any other chemical and / or thermal.

The carbon nanofibers used as carbonaceous nanofillers in the present invention are, like carbon nanotubes, nanowires produced by chemical vapor deposition (CVD) from a carbon source which is decomposed on a catalyst comprising a metal transition (Fe, Ni, Co, Cu), in the presence of hydrogen, at temperatures from 500 to 1200 ° C. However, these two carbonaceous fillers differ in their structure, since the carbon nanofibers are composed of graphitic areas more or less organized (or turbostratic stacks) whose planes are inclined at varying angles to the axis of the fiber. These stacks can take the form of flakes of

Examples of usable carbon nanofibers have in particular a diameter of 100 to 200 nm, for example about 150 nm and advantageously a length of 100 to 200 μιη. One can use eg VGCF nanofibers ® SHOWA DENKO.

By graphene, describes 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 or more or less corrugated structure. This definition encompasses FLG (Few Layer Graphene or poorly stacked graphene), the NGP (nanosized Graphene Plates or nanoscale graphene plates), CNS (Carbon NanoSheets or nano-graphene sheets), the GNR (Graphene NanoRibbons or nano-graphene ribbons). But exclude the nanotubes and nanofibers atoms, which are respectively constituted by the winding of one or more graphene sheets coaxially and turbostratic stacking of the layers. It is further preferred that graphene used according to the

Graphene used according to the invention is obtained by chemical vapor deposition or CVD, preferably by a method using a powdery catalyst of a mixed oxide. It arises, typically in particulate form having a thickness of less than 50 nm, preferably less than 15 nm, more preferably less than 5 nm and lateral dimensions less than one micron, preferably from 10 nm less than 1000 nm, more preferably from 50 to 600 nm, or from 100 to 400 nm. Each of these particles generally contains from 1 to 50 layers, preferably 1 to 20 layers and more preferably from 1 to 10 layers, or from 1 to 5 sheets which are likely to be disengaged from each other in the form of independent layers, eg during

The sulfur material

The sulfur-containing material may be native sulfur, sulfur compound or organic polymer, or a sulfur-containing inorganic compound, or a mixture thereof in any proportions.

Different sources of native sulfur are commercially available. The particle size of sulfur powder may vary within wide limits. Sulfur can be used as such, or the sulfur may first be purified according to various techniques such as refining, sublimation, or precipitation. Sulfur, or more generally the sulfur-containing material may also be subjected to a preliminary step of grinding and / or sieving in order to reduce the particle size and narrow distribution.

Sulfur-containing inorganic compounds 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 (n> 1).

The compounds or usable sulfur-containing organic polymers as sulfur-containing materials can be chosen from organic polysulfides, organic polythiolates including for example, functional groups such as dithioacetal, dithioketal or trithio-orthocarbonate, aromatic polysulfides, polyether polysulfides, salts polysulfides acids, thiosulfonates [-S (0) 2 -S-], thiosulfinates [-S (0) S-], thiocarboxylates [-C (0) S-], the dithiocarboxylates [-RC (S ) -S-], the thiophosp haste, thiophosphonates, thiocarbonates, polysulfides organometallic or mixtures thereof.

Examples of such organo sulfur compounds are described in WO 2013/155038.

According to a particular embodiment of the invention, the sulfur-containing material is an aromatic polysulfide.

Poly aromatic sulfides have the general formula (I):

in which :

- Ri to R9 identically or differently, a hydrogen atom, -OH or -0 " M + , or a saturated or unsaturated carbon chain having 1 to 20 carbon atoms, or a group -OR10, with Rio can be alkyl, arylalkyl, acyl, carboalkoxy, alkyl ether, silyl, alkyl silyl having 1 to 20 carbon atoms.

- M represents an alkali or alkaline metal earthy

- n and n 'are two integers, which are identical or different, each being greater than or equal to 1 and less than or equal to 8,

- p is an integer between 0 and 50,

- and A is a nitrogen atom, a single bond, or a saturated or unsaturated carbon chain of 1 to 20 carbon atoms.

Preferably, in formula (I):

Ri, R 4 and R 7 are radicals 0 " M + ,

R2, R5 and Rs are hydrogen atoms,

R3, and R9 5 are saturated or unsaturated carbon chains having 1 to 20 carbon atoms, preferably 3 to 5 carbon atoms, the average value of n and n 'is approximately 2,

the average value of p is between 1 and 10, preferably between 3 and 8. (These mean values ​​are calculated by those skilled in the art from proton NMR data and by weight sulfur assay).

- A is a single bond linking the sulfur atoms in the aromatic rings.

Such polysulfides poly (alkylphenol) of formula (I) are known and can be prepared for example in two stages:

1) reacting the monochloride or sulfur dichloride with an alkyl phenol, at a temperature between 100 and 200 ° C, according to the following reaction:

(II)

Compounds of formula (II) are in particular marketed by the Company

Arkema under the name Vultac ® .

2) reacting the compound (II) with a metal compound containing the metal M, such as for example an oxide, a hydroxide, an alkoxide or a dialkylamide of this metal to obtain radicals 0 " M + .

According to a more preferred embodiment, R is tert-butyl or tert-pentyl.

According to another preferred variant of the invention, a mixture of compounds of formula (I) wherein two of the R groups present on each aromatic unit are carbon chains having at least one tertiary carbon by which R is linked to the aromatic nucleus .

The Active Ingredient

The amount of carbonaceous nanofillers in the active material is 1 25% by weight, preferably 10 to 15% by weight, eg 12 to 14%> by poidi relative to the total weight of the active ingredient.

The active ingredient according to the invention is a finished product in the solid state comprising an intimate mixture of particles, carbonaceous nanofiller are dispersed in the mass of the sulfur material and it homogeneously.

The active material preferably has a density greater than 1.6 g / cm 3 , determined according to standard NF EN ISO 1183-1. The density is generally less than 2 g / cm 3 .

It has also advantageously a porosity less than 40%, most preferably less than 20% porosity. The porosity can be determined from the difference between the theoretical density and the measured density.

The active material of such an electrode as defined according to the invention allows to increase the specific capacity of the electrode which is denser, and increase the load capacity and discharge of the electrode.

The homogeneous mixture of particles can then be milled to obtain a powder having no particles larger than 100 μιη, preferably having no particles larger than 50 μιη to facilitate the electrode manufacturing process.

Carbonaceous nanofillers such as CNTs are mixed with the sulfur-containing material, in particular with sulfur, preferably in the melt route. However, fusion of the mixture is limited by the difference in density between the CNT (0.1 g / cm 3 ) and sulfur (2 g / cm 3 ), it is generally necessary to add an intense mechanical energy to achieve this mixture may be between 0.05 kWh / kg and 1 kWh / kg of active compound, preferably between 0.2 and 0.5 kWh / kg active ingredient. The carbon nano-filler are thus homogeneously dispersed throughout the mass of the particles, and are not found only on the surface of sulfur particles as described in FR 2948233.

To do this, use is preferably a compounding device, that is to say an apparatus conventionally used in the plastics industry for the mixture to melt thermoplastic polymers and additives in order to produce composites.

The active ingredient according to the invention can thus be prepared by a process comprising the steps of:

(A) introducing into a compounding device, at least one sulfur-containing material and carbonaceous nanofillers,

(B) melting of the sulfur-containing material;

(C) kneading the melted and carbonaceous nanofillers sulfur material;

(D) recovering the resulting mixture in a solid physical form agglomerated;

(E) grinding the mixture in powder form.

In an apparatus for compounding, the sulfur-containing material and carbonaceous nanofillers are mixed using a high shear device, for example a twin co-rotating screws or co-kneader. The molten material generally exits the apparatus in an agglomerated solid physical form, for example in granular form, or the form of rods which, after cooling, are cut into pellets.

Examples of suitable co-mixers are the co-mixers BUSS ® MDK

46 and those of the series BUSS ® MKS or MX, sold by the company BUSS AG, which are constituted by a screw shaft provided with vanes arranged in a heating sheath optionally consisting of several parts and whose inner wall is provided with kneading teeth adapted to cooperate with the vanes to produce a shearing of the kneaded material. The shaft is driven in rotation and provided with an oscillating movement in the axial direction, by a motor. These co-kneaders may be equipped with a pellet manufacturing system, adapted for example to their outlet, which may consist of an extrusion screw or a pump.

The co-kneaders used preferably have a screw ratio L / D of from 7 to 22, eg 10 to 20, while the co-rotating extruders advantageously have an L / D of from 15 to 56, e.g. 20 to 50.

The compounding step is carried out at a temperature above the melting point of the sulfur material. In the case of sulfur, the compounding temperature may range from 120 ° C to 150 ° C. In the case of other types of sulfur-containing material, the compounding temperature is dependent on the specific material used whose melting temperature is generally referred to by the supplier of the material. The residence time will also be adapted to the nature of the sulfur material.

This method allows to disperse efficiently and homogeneously a significant amount of carbon nanofillers in the sulfur material, despite the density difference between the components of the active material.

According to one embodiment of the invention, the active ingredient further comprises at least one additive selected from a rheology modifier, a binder, an ion conductor, a carbon electrical conductor, an electron-donor element or combination thereof. These additives are preferably introduced during compounding step, so as to obtain a homogeneous active substance.

In this embodiment, the sulfur-containing material and carbonaceous nanofillers then represent from 20% to 100% by weight, preferably from 20% to 80% by weight relative to the total weight of the active ingredient.

In particular, it is possible to add, during mixing, during compounding step, a rheology modifier additive of the sulfur in the molten state, to reduce rautoéchauffement the mixture in the compounding device. Such additives having a fluidizing effect on the liquid sulfur are described in WO 2013/178930. There may be mentioned as examples the dimethyl sulfide, diethyl sulfide, dipropyl sulfide, dibutyl sulfide, dimethyl disulfide, diethyl disulfide, dipropyl disulfide, dibutyl disulfide, homologues trisulfide, tetrasulfide their counterparts pentasulfides their counterparts, their counterparts hexasulfures, alone or in mixtures of two or more of them in all proportions.

The amount of rheology additive is generally between 0.01) 5%> by weight, preferably from 0.1% to 3% by weight relative to the total weight of the active ingredient.

The active material may include a binder including a binder polymer, selected for example among halogenated polymers, preferably fluoropolymers, functional polyolefins, polyacrylonitriles, polyurethanes, polyacrylic acids and their derivatives, polyvinyl alcohols and polyethers or a mixture thereof in any proportions.

There may be mentioned as examples of fluorinated polymers, poly (vinylidene fluoride) (PVDF), preferably in shape, poly (trifluoroethylene) (PVF3), polytetrafluoroethylene (PTFE), polyvinylidene fluoride copolymers with either hexafluoropropylene (HFP) or trifluoroethylene (VF3), or tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE), fluoroethylene / propylene copolymers (FEP), copolymers of ethylene with either fluoroethylene / propylene (FEP) or tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE); perfluoropropyl vinyl ether (PPVE), the perfluoroethyl vinyl ether (PEVE), the 2,3,3,3-tetrafluoropropene, and ethylene copolymers with perfluorométhylvinyl ether (PMVE) or mixtures thereof.

There may be mentioned as examples of polyethers, polyalkylene oxides such as polyethylene oxide PEO, polyalkylene glycols such as polyethylene glycols PEG, PPG polypropylene glycols, polytetramethylene glycols (PTMG), polytetramethylene ether glycol (PTMEG), etc.

Preferably, the binder is PVDF or a POE.

The active material may include an ionic conductor having a favorable interaction with the surface of the sulfur material in order to increase the ionic conductivity of the active material. Examples of ionic conductors include without limitation organic salts of lithium, for example lithium imidazolate salts or lithium sulphites. It may also be made of alkylene oxides which, besides their binding function, can provide ionic conductivity properties to the active ingredient.

The active material may comprise an electrical conductor, preferably a carbonaceous electric conductor, such as carbon black, graphite or graphene, generally in proportions ranging from 1 to 10% with respect to the sulfur material. Preferably, carbon black is used as an electrical conductor.

The active material may comprise an electron-donor element to improve the electronic exchange and regulate the length polysulfides during charge, which optimizes the cycles of charging / discharging the battery.

As electron donor elements, use may advantageously be an element, in powder form or in salt form, columns IVa, Va and Via of the periodic table, preferably selected from Se, Te, Ge, Sn, Sb, Bi , Pb, Si or As.

The active ingredient according to the invention is advantageously in the form of a powder comprising particles having an average size less than 150 μιη, preferably less than 100 μιη, a dso median diameter between 1 and 60 μιη, preferably between 10 and 60 μιη, more preferably between 20 and 50 μιη, a median diameter less than 100 do μιη, preferably a diameter less than DIØØ 50μιη, these characteristics being determined by laser diffraction.

For this powder morphology, use is generally a mill type apparatus hammer brushes mill, ball mill, a jet mill, or other methods for micronization of solid materials.

The active ingredient according to the invention, preferably in powder form as characterized above, and preferably having a porosity of less than 20% and / or a density greater than 1.6 g / cm 3 , can be used to prepare a battery electrode Li / S, it is generally of the order of 20 to 95% by weight, preferably 35 to 80% by weight based on the complete formulation of the electrode.

The invention is illustrated by the following examples, which are not intended to limit the scope of the invention defined by the appended claims.

EXPERIMENTAL

Example 1 Preparation of an active substance S / NTC

CNTs (Graphistrength ® Cl 00 ARKEMA) and solid sulfur (50-800 μπι) were introduced into the first feed hopper of a co -malaxeur BUS S ® MDK 46 (L / D = 11), equipped with an extrusion screw of recovery and a granulating device.

The temperature setpoints in the co-kneader were as follows: Zone 1: 140 ° C; Zone 2: 130 ° C; Screw: 120 ° C.

On leaving the die, the mixture consisting of 87.5% by weight of sulfur and 12.5%) by weight of CNT is in the form of granules obtained by the cutting head, cooled by air.

The granules were then milled in a hammer mill, the cooling being carried out by nitrogen.

Observation under a scanning electron microscope (SEM) showed that CNTs were well dispersed in sulfur.

The granules were ground in a high speed brushes mill (12000- 14000 rpm), the cooling being carried out with liquid nitrogen at -30 ° C on the granules introduced in the mill feed screw. The powder was sieved using a cylindrical 80μιη grid. The particle size distribution determined by laser diffraction on a Malvern type of apparatus is illustrated in Figure 1. The larger particles size is less than 100 μιη, and the median diameter dso is between 20 and 50 μιη.

Sieving the powder was performed in a second test using a grid of 50 cylindrical μιη. The distribution of the particle size indicates that the DIØØ diameter is less than 50 μιη. The morphology of the electrode active material thus obtained is shown in Figure 2.

This powder consists of 87.5% by weight of sulfur and 12.5% ​​by weight of CNT is an active ingredient used for the preparation of an electrode for Li / S battery.

Example 2 Preparation of an active substance S / DMDS / NTC

CNTs (Graphistrength ® Cl 00 ARKEMA) and solid sulfur (50-800 μπι) were introduced into the first hopper of a Buss co-kneader ® MDK 46 (L / D = 1 1), equipped with an extrusion screw of recovery and a granulating device.

Dimethyl disulfide (DMDS), liquid was injected in the st zone of the co-kneader.

The temperature setpoints in the co-kneader were as follows: Zone 1: 140 ° C; Zone 2: 130 ° C; Screw: 120 ° C.

On leaving the die, the masterbatch consisting of 83% by weight of sulfur, 2%) by weight of DMDS and 15% by weight of CNT is in the form of granules obtained by the cutting head, cooled by a jet of water.

The granules obtained were dried to a moisture content <100 ppm.

The dry granules were then ground in a hammer mill, the cooling being carried out by nitrogen.

There was obtained a powder having a median diameter D50 between 30 and 60 μιη, used for the preparation of a Li / S battery electrode.

EXAMPLE 3 Preparation of an active substance S / disulfide poly (t-butyl phenol) / NTC

CNTs (Graphistrength ® Cl 00 from Arkema) and solid sulfur (50-800 μπι) were introduced into the first hopper of a Buss co-kneader ® MDK 46 (L / D = 11) equipped a recovery extrusion screw and a granulating device.

Dimethyl disulfide (DMDS), liquid was injected in the st zone of the co-kneader.

Poly disulfide (tert-butyl phenol) sold under the name VULTAC- TB7 ® Arkema was premixed with a Li salt, sold under the name LOA (Lithium 4,5-dicyano-2- (trifluoromethyl) imidazole) by Arkema then introduced into the first hopper by means of a 3- eme dispenser.

The temperature setpoints in the co-kneader were as follows: Zone 1: 140 ° C; Zone 2: 130 ° C; Screw: 120 ° C.

On leaving the die, the mixture is in the form of granules obtained by the cutting head, cooled by a water jet.

The granules obtained were dried to a moisture content <100 ppm. The dry granules were then ground in a hammer mill, the cooling being carried out by nitrogen.

77% of a powder was obtained by weight of sulfur, 2% by weight

DMDS and 15% by weight of CNTs, 5% VULTAC- TB7 ® , 1% LOA, used for the preparation of a Li / S battery electrode.

Example 4 Preparation of an active substance S / POE / L12S / NTC

CNTs (Graphistrength ® Cl 00 from Arkema) and solid sulfur (50-800 μπι) were introduced into the first hopper of a Buss co-kneader ®

MDK 46 (L / D = 11) equipped with an extrusion screw of recovery and a granulating device.

The polyethylene oxide POLYOX ® WSR N-60K (produced by Dow) was pre-mixed with the Li 2 S supplied SIGMA. This mixture is introduced into the era hopper by the 3rd dose inhaler.

The temperature setpoints in the co-kneader were as follows: Zone 1: 140 ° C; Zone 2: 130 ° C; Screw: 120 ° C.

On leaving the die, the mixture consisting by weight of 70% sulfur, 15% CNT, 10% Polyox ® WSR N-60K, and 5% of Li 2 O is in the form of granules obtained by the dimmer of rush, cut by the treadmill without contact with water.

The dry granules were then ground in a hammer mill, the cooling being carried out by nitrogen.

There was obtained a powder consisting by weight of 70%> of sulfur, 15% of CNTs, 10% Polyox ® WSR N-60K, and 5% of Li 2 S comprising particles having an average size less than 150 μιη, a median diameter D50 and D90 adapted so that the powder is used as a cathode active material for Li / S battery.

EXAMPLE 5 Evaluation of the active ingredient

Active material evaluation tests were carried out in a battery model Li / S containing:

1) Anode metal Li, thickness 100 μιη;

2) A separator / membrane (20 μιη)

3) Electrolyte base sulfolane with 1M Li +

4) cathode based on a sulfur formulation supported by a collector Al cathode Two formulations were tested:

reference formulation comprising 70 wt% sulfur, 10%> of carbon black and 20% PEO (POLYOX ® WSR N-60K), representative of the prior art.

Formulation comprising 80% by weight of active material of Example 1, 5% carbon black and 15% POE.

The cathode formulation was applied to the electrode via a pulp in a solvent and then drying.

The capacity of the cathode of the test cell is between 1.5 and 3 mAh / cm 2 .

The test cells were under conditions of charge / discharge.

cathode performance was evaluated after 150 cycles:

cathode prepared from the reference formulation: 78% relative to the initial capacity

cathode prepared from the formulation comprising the active material according to the invention: 88% relative to the initial capacity

These results confirm that the active material of the invention having carbon nanofillers improves the life and therefore the effectiveness of a Li / S battery.

CLAIMS

1. Active material for manufacturing an electrode comprising:

- a sulfur-containing material;

from 1 to 25% by weight of carbonaceous nanofillers homogeneously dispersed in the mass of the sulfur material.

2. electrode active material comprising:

- a sulfur-containing material;

from 1 to 25% by weight of carbonaceous nanofillers homogeneously dispersed in the mass of the sulfur material,

characterized in that it has a porosity less than 40%.

3. electrode active material comprising:

- a sulfur-containing material;

from 1 to 25% o by weight of carbon nanofillers homogeneously dispersed in the mass of the sulfur material,

characterized in that it has a density greater than 1.6 g / cm 3 .

4. Active ingredient according to any one of the preceding claims, characterized in that the carbonaceous nanofillers are carbonaceous fillers of which the smallest dimension is between 0.1 and 200 nm, preferably between 0.1 and 160 nm, more preferably between 0.1 and 50 nm, as measured by light scattering.

5. Active ingredient according to any one of the preceding claims, characterized in that the carbonaceous nanofillers are chosen from carbon nanotubes, carbon nano fiber, graphene, or a mixture thereof in any ratio, preferably carbonaceous nanofillers are carbon nanotubes.

6. Active ingredient according to any one of the preceding claims, characterized in that it is obtained by a melt route.

7. Active substance according to claim 6 characterized in that it implements a mechanical energy of between 0.05 kWh and kWh per 1 kg of active material.

8. Active substance according to any one of the preceding claims, characterized in that the sulfur-containing material is a sulfur compound sulfur donor selected from native sulfur, the compounds or sulfur-containing organic polymers, or inorganic sulfur compounds, or a mixture of these in all proportions.

9. active material according to claim 8, characterized in that the sulfur-containing inorganic compounds are anionic alkali metal polysulfides, preferably lithium polysulfides represented by the formula Li 2 S n , with n> 1.

10. Active ingredient according to claim 8, characterized in that the sulfur material is selected from organic polysulfides, organic polythiolates particular including functional groups such as dithioacetal, dithioketal or trithio-orthocarbonate, aromatic polysulfides, polyether polysulphides, the polysulfides acid salts, thiosulfonates [-S (0) 2 -S-], thiosulfinates [-S (0) S-], thiocarboxylates [-C (0) S-], the dithiocarboxylates [ -RC (S) -S-], thiophosphates, thiophosphonates, thiocarbonates, polysulfides organometallic or mixtures thereof.

11. Active ingredient according to claim 10, characterized in that the sulfur material is an aromatic polysulfide having the general formula (I):

in which :

- Ri to R9 identically or differently, a hydrogen atom, -OH or -0 " M + , or a saturated or unsaturated carbon chain having 1 to 20 carbon atoms, or a group -OR10, with Rio can be alkyl, arylalkyl, acyl, carboalkoxy, alkyl ether, silyl, alkyl silyl having 1 to 20 carbon atoms.

- M represents an alkali or alkaline metal earthy

- n and n 'are two integers, which are identical or different, each being greater than or equal to 1 and less than or equal to 8,

- p is an integer between 0 and 50,

- and A is a nitrogen atom, a single bond, or a saturated or unsaturated carbon chain of 1 to 20 carbon atoms.

12. Active ingredient according to any one of the preceding claims, characterized in that the sulfur-containing material comprises at least native sulfur.

13. Active ingredient according to any one of the preceding claims, characterized in that it further comprises at least one additive selected from a rheology modifier, a binder, an ion conductor, a carbon electrical conductor, a donor element electrons or their association.

14. Active ingredient according to claim 13, characterized in that the rheology modifier is dimethyl sulfide, diethyl sulfide, dipropyl sulfide, dibutyl sulfide, dimethyl disulfide, diethyl disulfide, disulfide dipropyl disulfide, dibutyl trisulfides their counterparts, their counterparts tetrasulfides, pentasulfides their counterparts, their counterparts hexasulfures, alone or as mixtures of two or more of them in any proportion.

15. Active ingredient according to claim 13, characterized in that the binder is selected from halogenated polymers, preferably fluoropolymers, functional polyolefins and polyethers, or a mixture thereof in any proportions.

16. Active ingredient according to claim 13, characterized in that the binder is a fluorinated polymer selected from poly (vinylidene fluoride) (PVDF), preferably in shape, poly (trifluoroethylene) (PVF3), polytetrafluoroethylene ( PTFE), polyvinylidene fluoride copolymers with either hexafluoropropylene (HFP) or trifluoroethylene (VF3), or tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE), fluoroethylene / propylene copolymers (FEP), copolymers ethylene with either fluoroethylene / propylene (FEP) or tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE); perfluoropropyl vinyl ether (PPVE), the perf uoroéthyl vinyl ether (PEVE), 2,3,3,3 tetrafluoroethane uoropropène, and ethylene copolymers with perfluorométhylvinyl ether (PMVE) or mixtures thereof.

17. Active ingredient according to claim 13, characterized in that the binder is a polyether selected from polyalkylene oxides or polyalkylene glycols.

18. Active ingredient according to claim 13, characterized in that the ionic conductor is an organic salt of lithium such as a lithium imidazolate salt, lithium sulfite, or a polyalkylene oxide.

19. Active ingredient according to claim 13 characterized in that the carbon is electrically conductive carbon black, graphite or graphene.

20. Active ingredient according to claim 13, characterized in that the electron-donor element is an element, in powder form or in salt form, columns IVa, Va and Via of the periodic table, preferably selected from Se , Te, Ge, Sn, Sb, Bi, Pb, Si or As.

21. Active ingredient according to any one of the preceding claims, characterized in that the sulfur-containing material and carbonaceous nanofillers represent from 20% to 100% by weight relative to the total weight of the active ingredient.

22. Active ingredient according to any one of the preceding claims, characterized in that it is in powder form comprising particles having an average size less than 150 μιη, a dso median diameter between 10 and 60 and a median diameter μιη do less than 100 μιη.

23. Use of the active substance according to any preceding claim in an electrode.