EP3740984A1

EP3740984A1 - Formulation in the form of a solid-liquid dispersion for the fabrication of a cathode for an li/s battery and process for preparing said formulation

Info

Publication number: EP3740984A1
Application number: EP19705553.6A
Authority: EP
Inventors: Alexander Korzhenko; Patrick Delprat; Christophe VINCENDEAU
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2018-01-16
Filing date: 2019-01-16
Publication date: 2020-11-25
Also published as: CN111602273A; WO2019141941A1; FR3076952B1; US20200350560A1; JP7057443B2; JP2021511646A; KR20200095549A; KR102544853B1; FR3076952A1

Abstract

The invention relates to a formulation, in the form of a solid-liquid dispersion, for the fabrication of a cathode, comprising a liquid-phase solvent, a sulfur-carbon composite, in the form of particles having a median diameter D50 of less than 50 µm, and less than 10% by number of the particles of the dispersion are particles of sulfur in the elemental state.

Description

FORMULATION IN THE FORM OF A SOLID-LIQUID DISPERSION FOR THE MANUFACTURE OF A CATHODE FOR LI / S BATTERY AND METHOD OF

PREPARATION OF THIS FORMULATION

The invention relates to the field of lithium / sulfur storage batteries and more particularly a formulation in the form of a solid-liquid dispersion for the manufacture of a cathode having improved performance and an accumulator comprising said material. active. The invention also relates to a process for preparing such a formulation. previous art]

[0002] For some ten years, the very rapid increase in the development of emerging applications such as electric vehicles or the storage of renewable energy has provoked a growing demand for high performance batteries. Lithium / sulfur (Li / S) storage batteries are touted as promising alternatives to Li-ion batteries. The interest for this type of battery comes from the strong specific storage capacity of sulfur. In addition, sulfur has the advantages of being abundant, low cost and non-toxic, which allows the development of Li / S batteries on a large scale.

A lithium / sulfur accumulator (also referred to in the literature and indifferently thereafter Li / S battery) consists of a positive electrode (cathode) comprising an electroactive sulfur material on which can be deposited a separator, a negative electrode (anode) based on lithium, as well as an electrolyte. The electrolyte generally comprises at least one lithium salt dissolved in a solvent.

The discharge mechanism and charge 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). To enable electrochemical reactions to occur rapidly at the electrodes, the cathode and the anode must be generally good electronic conductors. Since sulfur is an electrical insulator, the discharge regimes are relatively slow.

Different improvement ways to overcome this low electrical conductivity of sulfur have been considered, including the addition of an electronic conductive additive such as a conductive carbonaceous material. The mixture of the active ingredient and the conductive additive can be done in different ways. For example, the mixing can be done directly 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 employed and allows for a more intimate mixing of the 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 Applicant has discovered that 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).

In this case, 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. This makes it possible to produce a Sulfur-Carbon composite that can take the form of compact granules. These granules are then milled under an inert atmosphere so as to obtain a powder that can be used for the manufacture of the cathode.

Nevertheless, the Applicant has observed that despite an intimate mixture within this powder between the sulfurized material and the carbon nanofillers, the performance is not at the level of performance to be theoretically obtained by such materials. There is therefore a need for improved formulations to increase the efficiency of accumulators obtained from a sulfur-carbon composite.

It has also been proposed a sulfur / carbon composite material for lithium / sulfur cells in which the sulfur is used to impregnate a carbon structure grafted with a polymer network (CN103247799). Nevertheless, such a material requires several manufacturing steps including a step of grafting nanofibre carbon and does not increase the load capacity and discharge of the battery incorporating the active ingredient but seems rather to increase the cyclic stability. It has also been proposed to manufacture batteries based on a sulfur / carbon composite comprising an yttrium oxide (US20130161557), zirconium-titanium phosphates (CN106654216) or organosulfur compounds (WO2013155038). Nevertheless, none of these documents are concerned with the preparation of a formulation in the form of a solid-liquid dispersion comprising CNTs well dispersed in a sulfur-containing material while minimizing the content of elemental sulfur particles, and by therefore allowing a high capacity. [001 1] Thus, it would be advantageous for a manufacturer to have a formulation comprising NTCs well dispersed in a sulfur-containing material, said formulation having been prepared under conditions ensuring optimal performance of the active ingredient without degradation of its properties. to increase the efficiency of the cathode and in particular the charging and discharging capacity of the battery incorporating this active ingredient.

rTechnical problem!

The invention therefore aims to overcome the disadvantages of the prior art. In particular, the object of the invention is to propose a formulation for the manufacture of an electrode having an increased capacitance as well as improved performances.

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, with a reduced number of steps, and allowing to increase the specific capacity of said active ingredient. Brief description of the invention

For this purpose, the invention relates to a formulation, in the form of a solid-liquid dispersion, for the manufacture of a cathode, comprising:

a solvent in the liquid phase,

a Sulfur-Carbon composite in the form of particles of less than 50 μm median diameter D 50, preferably in the form of particles with a median diameter D 50 of between 10 μm and 50 μm, and

less than 10% by number of the particles of the dispersion are particles of sulfur in the elemental state.

The performance of the batteries can be improved by the use of a composite sulfur-carbon. In this context, the Applicant has discovered that the active material for Li-S cathodes based on Sulfur-carbon composite generated according to the methods of the prior art exhibited degraded performance and in particular a reduced mass capacity. Indeed, the composite Sulfur-Carbon can suffer damage during its preparation resulting in degradation of the performance of the battery incorporating said Sulfur-Carbon composite and in particular a reduction in the specific capacity. These damages include, in particular, oxidation of the sulfur-containing material and the presence of elemental sulfur particles in the active material. Thus, the Applicant has developed a new process for generating a new formulation capable of increasing the performance of the batteries, in particular by having a low content of sulfur particles in the elemental state. The formulation according to the invention can be used as a cathode active material of a lithium / sulfur accumulator.

[0017] According to other optional features of the formulation:

more than 95% by number of the particles of the dispersion are Sulfur-Carbon composite particles. Indeed, the formulation according to the invention has the advantage of having very few particles of elemental sulfur and most of the particles present in the formulation are Sulfur-Carbon composite particles.

it has a solids content of less than 90%. Thus, the formulation has a significant portion of solvent in the liquid phase. The solids content corresponds to the percentage by weight of a dry extract relative to the weight of the formulation. Preferably, the solids content is between 30% and 60%;

the solvent in the liquid phase comprises at least one compound having a boiling point of less than 300 ° C., preferably less than 200 ° C., more preferably less than 115 ° C. In particular, all compounds forming the solvent in the liquid phase have a boiling point of less than 115 ° C. Indeed, in the case where the solvent is to be evaporated, it is desirable that the boiling point of the solvent is not too high so as not to alter the sulfur-carbon composite.

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 advantageously selected from N, N-dimethylformamide and N-methyl-2-pyrrolidone. Such compounds are capable of solubilizing at least one electrolyte salt and more particularly allow the constitution of a solvent suitable for lithium-sulfur batteries.

it furthermore comprises a solid electrolyte, preferably a solid electrolyte of ceramic type. Preferably, the solid electrolyte is present in the form of particles of less than 50 μm median diameter D50.

it comprises less than 15% by weight of polymeric binder. Preferably, it comprises less than 10% by weight of polymeric binder. - It has a Brookfield viscosity greater than 100 mPa-S ^-1 . Preferably, it has a Brookfield viscosity of greater than 1,000 mPa.s.sup.- ¹ , more preferably greater than 5,000 mPa.s.sup.- ¹ , and even more preferably greater than 10,000 mPa.s.sup.- ¹ .

the Sulfur-Carbon composite is obtained by molten route. 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 mixing the molten sulfur material and the carbon nanofillers.

the sulfur-carbon composite comprises a sulfur-containing material and from 0.01 to 50% by weight of carbon nanofillers.

The invention further relates to a process for preparing a formulation for the manufacture of an electrode comprising:

a prior step of forming the Sulfur-Carbon composite, said prior step of forming the Sulfur-Carbon composite comprising a melting of a sulfur-containing material and kneading of the molten sulfur material and carbon nanofillers,

the introduction into a grinding device of a solvent in the liquid phase and of a Sulfur-Carbon composite, said Sulfur-Carbon composite comprising at least one sulfur-containing material and carbon nanofillers,

the implementation of a grinding step, and

- Obtaining, following said grinding step, an active material in the form of a solid-liquid dispersion, comprising the Sulfur-carbon composite in the form of particles of less than 50 pm of median diameter D50.

Indeed, as detailed below, the Applicant has discovered that when performing a dry grinding under an inert atmosphere according to the methods of the prior art, the composite Sulfur-Carbon, and more particularly the material sulfur, could suffer damage, resulting in degradation of the performance of the battery incorporating said composite and in particular a reduction in the mass capacity. These damages include, in particular, oxidation of sulfur and the presence in the formulation of elemental sulfur particles. The preparation process according to the invention makes it possible to increase the performance, in particular by reducing the oxidation of the sulfur-containing material and the formation of sulfur particles in the elemental state. In addition, during this process, the interfaces are preserved from contact with oxygen by introducing into the grinding device a solvent in the liquid phase. In addition, such a method has lower risks than dry milling and can, therefore, be performed under less restrictive operating conditions.

According to other optional features of the method:

a host polymer is introduced into the grinding device, preferably before carrying out the grinding step. The presence of a host polymer during the grinding stage makes it possible to favor the interfaces between the sulfur-carbon composite and the host polymer and thus makes it possible to obtain a higher performance active material, such as the mass capacity,. In addition, more viscous electrolytes (based on more viscous solvents) also result in a reduced shuttle mechanism and an increase in battery life and a reduction in capacity reduction associated with irreversible active material losses.

- The method further comprises a step of introducing into the mill of at least one electrolyte salt preferably selected from: lithium trifluoromethanesulfonate, (bis) trifluoromethanesulfonate lithium imide, 2-trifluoromethyl-4,5-dicyanoimidazole lithium, lithium bis (fluorosulfonyl) imide, lithium hexafluorophosphate, lithium perchlorate, lithium trifluoromethylsulfonate, lithium trifluoroacetate, dilithium dodecafluorododecaborate, lithium bis (oxalate) borate, and lithium tetrafluoroborate. The presence of a salt during the grinding stage makes it possible to favor the interfaces between the Sulfur-Carbon composite and the salt, and makes it possible to obtain a higher performance active material, such as the specific mass capacity,.

a solid electrolyte, preferably a ceramic solid electrolyte, is introduced into the grinding device, preferably before carrying out the grinding step. The presence of a solid electrolyte during the grinding stage makes it possible to favor the interfaces between the Sulfur-Carbon composite and the solid electrolyte, and makes it possible to obtain a higher performance active substance, such as the mass capacity,.

the grinding step is carried out in a ball mill, a cavitator, a jet mill, a fluidized bed jet mill, a liquid phase mill, a screw disperser, a brush mill, a hammer mill , or a ball mill. - The grinding step is conducted at a temperature above 0 ° C and below the boiling point of the solvent in the liquid phase. Preferably, the grinding step is conducted at a temperature greater than 0 ° C and less than or equal to 1 10 ° C. The control of the grinding temperature makes it possible to reduce the risks of degradation of the performances of the carbon-sulfur composite during the grinding stage.

the grinding step is followed by a step of evaporation of the solvent and addition of an electrolyte, preferably a liquid electrolyte.

the prior step of forming the Sulfur-Carbon composite comprises the addition of a mechanical energy of between 0.05 kWh / kg and 1 kWh / kg of solid material. The solid material corresponding in particular to sulfur material and carbon nanofillers.

the preliminary step of forming the Sulfur-Carbon composite comprises the following sub-steps:

introduction into a device for compounding at least one sulfur-containing material, and carbon nanofillers,

- Implementation of a compounding step so as to allow the melting of the sulfur material, and

- Mixing of molten sulfur material and carbon nanofillers.

the enthalpy of melting of the sulfur-containing material of the Sulfur-Carbon composite is at least 10% less than the enthalpy of melting of the sulfur-containing material introduced into the compounding device.

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 manufactured from the formulation according to the invention.

The invention further relates to a lithium / sulfur accumulator comprising a cathode according to the invention.

Other advantages and features of the invention will appear on reading the following description given by way of illustrative and non-limiting example, with reference to the appended figures which represent:

FIG. 1, a schematic representation of steps implemented in accordance with the invention during the process for preparing an active material according to the invention. Dotted steps are optional. FIG. 2, a schematic representation of sub-steps implemented in accordance with the invention during the optional prior step of forming the Sulfur-Carbon composite.

[Description of the invention

In the following description, the term "solid-liquid dispersion" a mixture of a liquid in which are immersed small solid particles. The liquid may be an aqueous phase or an oil; the solid particles are essentially sulfur-carbon composite particles. The solid-liquid dispersion may be used by spreading, extrusion or injection, and then undergo physical (evaporation) or chemical (reaction) transformation to pass the dispersion to the solid state. Within the solid-liquid dispersion the solid particles are separated from the liquid continuous phase by interfaces, which increase the free energy of the dispersion relative to a system in which all the solid would be collected in a single homogeneous domain. Interfaces play a very important role. In addition, during the implementation of a solid-liquid dispersion in a battery, the interfaces play a vital role in the performance of said battery.

By "host polymer" is meant a polymer which in combination with a salt can form a polymer electrolyte. The host polymer may be a host polymer capable of forming a solid polymer electrolyte or gelled polymer electrolyte.

The term "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 itself change . "Liquid phase solvent" is a solvent in the liquid state.

By "Sulfur-Carbon Composite" is meant an assembly of at least two immiscible components whose properties are complementary, said immiscible components comprising a sulfur-containing material and a carbonaceous nanocharge.

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

By "carbon nanobond" is meant a charge comprising at least one element of the group consisting of carbon nanotubes, carbon nanofibres and graphene, or a mixture thereof in all proportions. Preferably, the carbon nanofillers comprise at least carbon nanotubes. The term "nanoburden" is usually used to denote a carbon charge 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, measured by light scattering.

"Sulfur in the elemental state" means 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 carbon nanofillers.

By "compounding device" is meant, according to the invention, an apparatus conventionally used in the plastics industry, for the melt blending of thermoplastic polymers and additives in order to produce composites. In this apparatus, the sulfur-containing material and the carbon nanofillers 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.

The invention is now described in more detail and without limitation in the description which follows. In the rest of the description, the same references are used to designate the same elements.

As shown in the examples, the inventors have discovered that the methods used previously, from the state of the art, to prepare a Sulfur-Carbon composite powder can cause a reduction in the performance of the active ingredient. Indeed, during the dry grinding step, the different forces acting on the Sulfur-Carbon composite, especially at the moment of impact, causes the formation of elemental sulfur particles, that is to say particles having no Sulfur-Carbon mixture and thus not participating in the performance of a battery using such a powder. This grinding also causes a sharp reduction in the density of the powder obtained after grinding.

In addition, in the presence of oxygen, the sulfur tends to oxidize and this is accentuated when are engaged in large friction forces such as those exerted during grinding steps. Thus, during the grinding under an inert atmosphere of Sulfur-Carbon composite granules, the traces of oxygen present can lead to partial oxidation of the sulfur material composing the composite and thus a reduction in the performance of the active material. Sulfur oxidation will reduce the performance of Lithium / Sulfur accumulators.

Thus, the inventors have developed a method for preparing a formulation for the manufacture of an electrode from a Sulfur-Carbon composite capable of reducing the formation of sulfur particles in the elemental state and to preserve the interfaces of the sulfur-containing material with oxygen contact. Advantageously, the improvement of the interfaces and the reduction of the level of sulfur particles in the elemental state are also possible by carrying out grinding in a liquid phase solvent comprising host polymers, electrolyte salts and / or solid electrolytes. As will be detailed later on, the creation of favorable interfaces at the grinding stage may make it possible to improve the performance of the active ingredient. More particularly, grinding in the presence of an electrolyte makes it possible to obtain the catholite directly. The latter can then be used to form the cathode.

As shown in FIG. 1, the method according to the invention comprises the following steps:

Introduction 210 in a device for grinding a solvent in the liquid phase, Introduction 230 in the grinding device of a sulfur-carbon composite, said sulfur-carbon composite comprising at least one sulfur-containing material and carbon nanofillers,

- Implementation 250 of a grinding step,

- Obtaining 260, following said grinding step, an active material in the form of a solid-liquid dispersion, comprising the Sulfur-carbon composite in the form of particles of less than 50 pm median diameter D50.

The steps 210, 220, 230, 240, prior to the milling step 250 are presented in a certain order in FIG. 1. Nevertheless, in the context of the invention, the order of introduction of the substances into the mill may be modified without this being considered as being another invention.

Solvent phase introduction

As shown in Figure 1, the method according to the invention comprises an introduction step 210 in a grinding device of a solvent in the liquid phase.

Preferably, 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. In this case, 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 1 15 ° C , still way more preferred less than or equal to 100 ° C. Thus, the solvent can be evaporated after the milling step without causing a modification of the carbon-sulfur composite.

In this context, the solvent in the liquid phase used in the invention may for example comprise at least one protonic or aprotonic solvent, said protonic or aprotic solvent being selected from: water, alcohols, ethers, esters, lactones, N- Methyl-2-pyrrolidone and DMSO.

Alternatively, the solvent in the liquid phase used is water or an alcohol and the solvent is removed via a lyophilization step.

In addition, preferably, the solvent in the liquid phase is degassed before its introduction into the grinding device.

However, as mentioned, the creation of the grinding stage of favorable interfaces can improve the performance of the active material used for electrode manufacture. Indeed, a grinding in the electrolyte makes it possible to directly obtain the catholite and the catholite can then be used directly for the manufacture of an electrode without requiring an evaporation step.

Thus, the process according to the invention may comprise a step 220 for introducing into the mill at least one electrolyte salt. Preferably, the process according to the invention may comprise a step 220 for introducing into the mill at least one electrolyte salt preferably selected from: lithium trifluoromethanesulfonate (LiTF), lithium bisulfide (Bis) trifluoromethanesulfonate (LiTFSI), lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), lithium bis (fluorosulfonyl) imide (LiFSI), lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (UCIO4), lithium trifluoromethylsulfonate (CF3SO3U) ), Lithium trifluoroacetate (CF3COOU), dilithium dodecafluorododecaborate (U2B12F12), lithium bis (oxalate) borate (LiBCe) and lithium tetrafluoroborate (UBF4). More preferably, the electrolyte liquid solvent comprises LiTFSI.

When an electrolyte salt is added to the mill, the solvent in the liquid phase is preferably 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. In particular, 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 selected from N-methyl-2-pyrrolidone (NMP) or N, N-dimethylformamide (DMF). The electrolyte liquid solvent is preferably a solvent adapted to 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. Thus, preferably, 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.

Thus, preferably, the electrolyte liquid solvent is selected from 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).

The electrolyte liquid solvent may also comprise a combination of solvents. For example, it may include an ether and a carbonate ester. This can reduce the viscosity of a mixture having a high molecular weight carbonate ester.

Preferably, 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, dimethylsulfoxide, tributylphosphate, trimethylphosphate, N-tetraethylsulfamide, sulfone and mixtures thereof.

More preferably, 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. Other solvents may also be used, for example sulfones, fluorinated compounds or toluene.

Preferably, the organic solvent is a sulfone or a mixture of sulfones. Examples of sulfones are dimethylsulfone and sulfolane. The sulfolane may be used as a single solvent or in combination with, for example, other sulfones. In one embodiment, the electrolyte liquid solvent comprises lithium trifluoromethanesulfonate and sulfolane.

During operation of the battery, the liquid electrolytes may cause dissolution of the active material, and promote the diffusion of the latter to the negative electrode. Thus, an alternative is the use of polymer electrolytes comprising an electrolyte salt and a host polymer, said host polymer for limiting the diffusion of the active ingredient. Thus, in addition to the use of a liquid solvent, the process according to the invention may comprise the incorporation of a host polymer.

The host polymer may be a host polymer capable of forming a solid polymer electrolyte or a gelled polymer electrolyte. A solid polymer electrolyte is a solid electrolyte at room temperature, preferably consisting of a mixture of polymers and lithium salts. This type of electrolyte can be used without a separator because it offers a positive and negative physical separation of the electrodes. Nevertheless, the operation of the battery must be conducted at a temperature higher than the ambient temperature, to allow the electrolyte to be in the molten state and thus to conduct sufficiently the lithium ions (T> 65 ° C for the POE ). A gelled electrolyte is an electrolyte in which a polymer is mixed with a lithium salt, but also with a solvent or a mixture of organic solvents. The salt and the solvent (s) are trapped in the polymer, which is then said plasticized. Like the polymer electrolyte, the gelled electrolyte also acts as a separator of the positive and negative electrodes, and is therefore not coupled to a conventional liquid electrolyte separator. On the other hand, the difference lies in the cycling temperature, since this type of electrolyte membrane operates at ambient temperature.

The host polymers may for example be polyethers, polyesters or polyfluoroes. Preferably, the polymeric electrolytes are selected from: polyethylene glycol (PEO), polyethylene glycol-dimethoxyethane, tetraethyleneglycol dimethoxyethane, poly (vinylidene fluoride-co-hexafluoropropylene), poly (methylmethacrylate). When they are added during the grinding step, such polymers allow the production of active material capable of increasing the coulombic efficiency for several cycles and / or the conductivity due to a confinement of the active ingredient to the positive electrode.

In addition, the method according to the invention may also comprise a step of introducing a solid electrolyte, preferably a ceramic solid electrolyte into the mill. In this context, the grinding step in the presence of the solid electrolyte will also increase the performance of the active material in comparison with an addition subsequent to the grinding step, for example during the manufacture of the electrode . Preferably, the process according to the invention comprises a co-grinding of the sulfur-carbon composite and the ceramic solid electrolyte. Thus, a solid electrolyte, preferably a ceramic solid electrolyte, is added to the grinding device, advantageously before carrying out the grinding step. The solid electrolyte may be added as a pre-milled powder.

The ceramic solid electrolyte may advantageously comprise lithium, germanium and / or silicon.

[0062] Preferably, the ceramic solid electrolyte is selected from: U2SP2S5, Li ₂ S- P2S5-U, Li ₂ S-P2S5-LiBH 4, and Li ₂ _S-P2S5-GeS2, or other formulations of the ceramic U2S-X-P2S5 family (with x sulphide, oxide, selenide or halide). Also, the ceramic electrolyte may be composed of heterogeneous metal sulfides, in the amorphous (vitreous) or crystalline state. The ceramic compounds based on metal oxide may also be used. More preferably, the ceramic solid electrolyte is selected from the Li ₂ S-X-P2S5 type formulations.

In an optional step 240, other salts or additives may also be added to the formulation of liquid or polymeric electrolytes, to give them particular properties. For example, the process may comprise the addition of additives selected from:

nitrogen-containing additives such as lithium nitrate (UNO ₃ ) which is very effective in suppressing the shuttle mechanism due to the passivation of the lithium surface, or nitromethane (CH 3 NO 2)),

organic polysulfide compounds of general formula P2S _X such as phosphorus pentasulfide (P2S5), capable of limiting the irreversible deposition of Li ₂ S on the lithium metal electrode,

one or more electrical conductors, advantageously a carbon-based electrical conductor, such as carbon black, graphite or graphene, generally in proportions ranging from 1 to 10% by weight relative to the sulfurized material. Preferably, the carbon black is used as an electrical conductor, and / or

- One or more electron donor elements to improve the electronic exchanges and regulate the length of the polysulfides during charging, which optimizes the charge / discharge cycles of the battery. As 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.

Polymeric binders may also allow to bring a certain dimensional plasticity or flexibility of the electrode formed from the active material. In addition, an important role of the binder is also to ensure a homogeneous dispersion of the Sulfur-Carbon composite particles. It should not be swollen when in contact with organic solvents, and preferably be dissolved in non-toxic solvents. Different 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, or a mixture thereof in all proportions.

Examples of fluorinated polymers that may be mentioned are polyvinylidene fluoride (PVDF), preferably in the α form, poly (trifluoroethylene) (PVF 3), polytetrafluoroethylene (PTFE), copolymers of vinylidene fluoride with either hexafluoropropylene (HFP), trifluoroethylene (VF3), tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE), 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 thereof.

As examples of polyethers, mention may be made of alkylene polyoxides such as ethylene polyoxides (POE), polypropylene oxide (PPO), polyalkylene glycols such as polyethylene glycols (PEG), polypropylene glycols (PPG), polytetramethylene glycols (PTMG), polytetramethylene ether glycols (PTMEG), etc.

A polymeric binder may preferably be selected from the following compounds: poly (vinylidene difluoride) ((PVDF)), polypyrrole, polyvinylpyrrolidone, polyethyleneimine, polyethylene oxide (PEO), poly (propylene oxide) (PPO), polyvinyl alcohol, poly (acrylamide-co-diallyldimethylammonium chloride), polytetrafluoroethylene (PTFE), poly (acrylonitrile-methyl methacrylate), carboxymethylcellulose (CMC), gelatin and mixtures thereof. The polymeric binders may also be selected from block copolymers of such polymers such as PEO / PPO / PEO block copolymer.

More preferably, the polymeric binder is PVDF or POE.

The POE is sometimes used in acetonitrile or isopropanol, as well as PTFE suspended in ethanol or water. The most common polymer remains poly (vinylidene 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.

The amount of binder is generally less than 20% by weight relative to the formulation or active material and is preferably between 5% and 15% by weight.

Introduction of the Sulfur-Carbon composite

As shown in Figure 1, the method according to the invention comprises an introduction step 230 in the grinding device of a composite sulfur-carbon.

The sulfur-carbon composite comprises at least one sulfur-containing material and carbon nanofillers.

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 .mu.m.

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. Advantageously, the Sulfur-Carbon composite is obtained by a manufacturing process comprising a step of melting a sulfur-containing material and kneading the molten sulfur material and carbon nanofillers. This melting and kneading step may advantageously be carried out by a compounding device. The Sulfur-Carbon composite is generally in physical form agglomerated, 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.

Thus, preferably, the Sulfur-Carbon composite is in the form of solids such as granules or particles having a median diameter D50 greater than 100 μm, preferably greater than 200 μm and more preferably greater than 500 μm. pm. The sulfur-carbon composite, advantageously used in the context of the invention, comprises carbon nanofillers percolated in a molten sulfur matrix, and the carbon nanofillers are distributed homogeneously throughout the mass of the sulfur-containing material, which can be visualized for example by electron microscopy. The sulfur material / nanofiller mixture is of morphology adapted to an optimization of the operation of a Li / S battery electrode. The carbon nanofillers are thus homogeneously dispersed throughout the mass of the particles, and are not found only on the surface of the sulfur particles as described in document FR 2 948 233.

The active material 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 amount of carbon nanofillers in the Sulfur-Carbon composite represents from 1 to 25% by weight, preferably from 10 to 15% by weight, for example from 12 to 14% by weight, relative to the total weight of the active ingredient.

Etaoe de brovaae:

As shown in Figure 1, the method according to the invention comprises a milling step 250.

The grinding in the liquid state has the advantage of not creating too much porosity in the active material obtained. Thus, the powder obtained has a higher density than powders obtained with conventional methods.

The grinding step can for example be carried out in a ball mill (horizontal and vertical cage), a cavity, 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.

Advantageously, the method according to the invention may comprise two successive grinding stages, 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. Advantageously, the grinding step is Conducting at a temperature below the melting temperature of the grinding sulfur material is preferably carried out at a temperature below 300 ° C, more preferably at a temperature below 200 ° C, more preferably at a temperature of less than 200 ° C. less than or equal to 1 10 ° C.

In addition, unlike processes of the prior art, the grinding step is preferably conducted at a temperature above 0 ° C. More preferably, it is conducted at a temperature above 10 ° C.

Thus, 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 1 10 ° C. When the expression "between" is used, it must be understood that the boundaries are included. The grinding step will probably generate a heating of the mixture caused by the friction generated by the grinding step. Thus, 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.

After grinding and obtaining a solid-liquid dispersion, preferably homogeneous, it is necessary to determine during a step 265, if the solvent in liquid phase used during grinding can be integrated into a accumulator. If this is the case and for example an electrolyte salt has been added in a step 220, then a catholite is obtained.

In the opposite case, the grinding step may be followed by a step of evaporation of the solvent in the liquid phase. This evaporation step 270 is especially necessary when the solvent used during the grinding is not a solvent capable of solubilizing electrolytes or more specifically if it is not suitable for the formulation of a catholite.

In the case of evaporation of the solvent, the process according to the invention also comprises a step 280 of adding an electrolyte, for example a liquid electrolyte. Preferably, there is saturation of the active ingredient by the electrolyte.

If necessary, 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.

Obtaining a formulation

As shown in FIG. 1, the process according to the invention comprises a step 260 for obtaining a formulation in the form of a solid-liquid dispersion generated during the grinding step. In addition, this formulation comprises the Sulfur-Carbon composite in the form of particles of less than 50 μm 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.

According to another aspect, the invention relates to a formulation in the form of a solid-liquid dispersion for the manufacture of an electrode, comprising a solvent in the liquid phase and a Sulfur-Carbon composite in the form of a solid-liquid dispersion.

In addition, less than 10% by number of the particles of the dispersion are elemental sulfur particles, for example less than 5% by number, preferably less than 1% and even more preferably less than 0.5%. The elemental sulfur particles in the dispersion may, for example, be enumerated by scanning electron microscopy.

Sulfur particles in the elemental state do not absorb the electronic radiation with respect to Sulfur-carbon composite particles comprising carbon nanofillers. Thus, on the image generated by scanning electron microscopy, the sulfur particles in the elemental state will be represented as white or light particles, especially in backscattered electron imaging mode. Conversely, Sulfur-Carbon composite particles will be represented as gray or black particles. Thus, the light particles can be enumerated and compared to the total amount of particles.

Preferably, the solid-liquid dispersion has a solids content of less than 90% by weight, more preferably less than 80%, even more preferably between 30% and 60% by weight.

[0097] Preferably, the formulation has a viscosity greater than 100 mPa.s-1. The viscosity is more particularly a Brookfield viscosity and can be measured using a rotary viscometer during one or more measurements at 10 rpm at 25 ° C. according to standard NF EN ISO 2555.

Preferably, the solvent in the liquid phase is selected from: water, an amide, a carbonate ester, an ether, a sulfone, a fluorinated compound, toluene, dimethylsulfoxide and mixtures thereof in all proportions. As has been mentioned, the creation of favorable interfaces at the grinding stage can make it possible to improve the performance of the formulation and more particularly of the active material that can be used for the manufacture of electrodes. In addition, the solvent in the liquid phase comprises at least one compound having a boiling point below 300 ° C.

Preferably, the formulation further comprises a solid electrolyte, preferably a solid electrolyte of the ceramic type.

The solid-liquid dispersion may comprise particles, immersed in a liquid, having a median diameter D50 generally less than 50 μm, for example between 1 and 50 μm, preferably between 10 and 50 μm, preferably between 10 and 20 pm.

Advantageously, the sulfur-carbon composite has been obtained by molten route, preferably with a mechanical energy of between 0.05 kWh and 1 kWh per kg of Sulfur-carbon composite. For example, the Sulfur-Carbon composite can be obtained by melting a sulfur-containing material and kneading the molten sulfur material and carbon nanofillers. Preferably, the Sulfur-Carbon composite comprises a sulfur-containing material, and from 0.01 to 50% by weight, preferably from 1 to 30% by weight, and more preferably from 5 to 25% by weight of carbon nanofillers. dispersed in the sulfur material.

Thus, the present invention provides a formulation comprising particles having a better combination of a sulfur donor material, with carbon nanofillers particles to facilitate access of sulfur to electrochemical reactions. In addition, the electrode incorporating the formulation according to the invention and more particularly the active ingredient according to the invention provides a good maintenance of the battery operation over time. The formulation according to the invention is advantageously in the form of a solid-liquid dispersion comprising Sulfur-Carbon composite particles having an average size of less than 150 μm, preferably less than 100 μm, a median diameter dso of between 1 and 50 μm, preferably between 10 and 50 μm, more preferably between 20 and 50 μm, and a median diameter dgo less than 100 μm. The particle size distribution is evaluated by the laser diffraction method.

The formulation according to the invention has the advantage of being used in the form of a paste that can be directly applied to a surface so as to form an electrode, in particular a cathode. Nevertheless, the formulation according to the invention can also be used in powder form while retaining the advantages associated with the low oxidation of sulfur and the low level of elemental sulfur particles.

[00104] Thus, according to another aspect, the invention relates to a method for manufacturing an active substance in the form of a powder comprising a step of drying the formulation according to the invention so as to generate an active ingredient in the form of a powder. The active material, 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 active substance in the form of powder according to the invention comprises particles having an intimate mixture of carbon nanofillers 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, 6 g / cm ³ , determined according to the standard NF EN ISO 1 183-1.

It also advantageously has a porosity of less than 20%, which can be determined from the difference between the theoretical density and the measured density. The 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 a electrode, in particular a cathode, 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 active ingredient in powder form according to the invention has a higher density than the densities observed with the methods of the prior art. Thus, preferably, the active ingredient in powder form according to the invention advantageously has a density greater than 1 g / cm ³ , preferably greater than 1.1 g / cm ³ , determined following compression of a cubic centimeter of powder at a pressure of 100 MPa

In addition, the enthalpy of melting 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. Thus, preferably, the sulfur-containing material of the carbon-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), at least 10% lower than the melting enthalpy of the sulfur material used for forming the Sulfur-Carbon composite, more preferably at least 15% less and more preferably at least 20% less. It would not be departing from the scope of the invention, in the case where the Sulfur-Carbon composite does not contain any enthalpy of melting of the sulfur-containing material between 80 ° C. and 130 ° C., that is to say the case where he is amorphous.

[001] Advantageously, 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 .

Process for preparing the composite

[001 1 1] The sulfur-carbon composite can be advantageously obtained by a melt process. A process for preparing a sulfur-carbon composite that is particularly advantageous in the context of the invention is described in document WO2016 / 102865.

[001] For optimal formation of the Sulfur-Carbon composite, carbon nanofillers such as CNTs are mixed with the sulfur-containing material, in particular with sulfur, in a molten state. For this, it is generally 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 active material comprising in particular carbon nanofillers and sulfur material. The carbon nanofillers are thus homogeneously dispersed throughout the mass of the particles, and are not found only on the surface of the sulfur particles as described in document FR 2 948 233.

[001 13] Advantageously, 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 carbon nanofillers. This melting and kneading step may advantageously be carried out by a compounding device. Thus, as shown in FIG. 2, the process according to the invention may comprise preliminary stages of formation of the Sulfur-Carbon composite, said stages of formation of the carbon Sulfur composite comprising: introduction into a device for compounding at least one sulfur-containing material, and carbon nanofillers,

the implementation of a step 130 of compounding so as to allow the melting of the sulfur-containing material, and

the kneading 140 of the molten sulfur material and the carbon nanofillers.

[001 14] For this purpose, 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 to produce composites. The active ingredient according to the invention can thus be prepared according to a process comprising the following steps:

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

(b) melting the sulfur material;

(c) mixing the molten sulfur material and the carbon nanofillers;

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

In a compounding apparatus, the sulfur material and the carbon nanofillers 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.

[001 16] Examples of suitable co-kneaders are co-Buss kneaders ^® 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 fins, disposed in a heating sleeve optionally consisting of several parts and whose inner wall is provided with kneading teeth adapted to cooperate with the fins to produce a shear of the kneaded material. The shaft is rotated and provided with oscillation movement in the axial direction by a motor. These 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 usable co-kneaders 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 15. 56, for example from 20 to 50.

The compounding step is carried out at a temperature greater than the melting point of the sulfur-containing material. In the case of sulfur, the temperature of Compounding can range from 120 ° C to 150 ° C. In the case of other types of sulfur material, 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.

This method makes it possible to disperse efficiently and homogeneously a large amount of carbon nanofillers in the sulfurized material, despite the difference in density between the constituents of the active material.

Examples of co-kneaders that can be used according to the invention are the BUSS 'MDK 46 co-kneaders and those of the BUSS' MKS or MX series, marketed by the company BUSS AG, all of which consist of a tree. screw provided with fins, has in a heating sleeve optionally consists of several parts and whose inner wall is provided with mixing teeth adapted to cooperate with the fins to produce shearing of the kneaded material. The shaft is rotated and provided with oscillation movement in the axial direction by a motor. These co-kneaders may be equipped with a granule manufacturing system, adapted for example to their outlet orifice, which may be constituted by 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.

To achieve optimal dispersion of the carbon nanofillers in the sulfurized material in the compounding device, it is necessary to apply a large mechanical energy, which is preferably greater than 0.05 kWh / kg of material.

The compounding step is carried out at a temperature above the melting temperature of the sulfur material. In the case of elemental sulfur, the compounding temperature can range from 120 ° C to 150 ° C. In the case of other types of sulfur material, the compounding temperature is a function of the specifically used material whose melting temperature is generally mentioned by the supplier of the material. The residence time will also be adapted to the nature of the sulfur material.

The Soufré material

According to a preferred embodiment of the invention, the sulfur-containing material comprises at least native sulfur, the sulfur-containing material being native sulfur alone, or in admixture with at least one other sulfur-containing material. The sulfurized material may be native sulfur, a sulfur-containing organic compound or polymer, or a sulfur-containing inorganic compound, or a mixture thereof in all proportions.

[00125] Different sources of native sulfur are commercially available. The particle size of the sulfur powder can vary widely. 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 sulfur-containing inorganic compounds that can be used as sulfur-containing materials are, for example, anionic polysulfides of alkali metal, preferably lithium polysulfides represented by the formula Li ₂ S _n (with n> 1).

The sulfur-containing organic compounds or polymers that can be used as sulfur-containing materials may be chosen from organic polysulfides, organic polythiolates including, for example, functional groups such as dithioacetal, dithioketal or trithioorthocarbonate, aromatic polysulfides, polyether-polysulfides, salts of polysulfide acids, thiosulfonates [-S (O) ₂ -S-], thiosulfinates [-S (O) -S-], thiocarboxylates [- C (O) -S-], dithiocarboxylates [- RC (S) -S-], thiophosphates, thiophosphonates, thiocarbonates, organometallic polysulfides, or mixtures thereof.

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

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

The aromatic polysulfides have the following general formula (I):

in which :

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,

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 FO 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.

(These average values are calculated by those skilled in the art from proton NMR data and by weight assay of sulfur).

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

Such poly (alkyl phenol) polysulfides of formula (I) are known and can be prepared for example in two steps:

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

Compounds of formula (II) are in particular marketed by Arkema under the name Vultac ^®.

2) reaction of the compound (II) with a metal derivative containing the metal M, such as for example an oxide, a hydroxide, an alcoholate or a dialkylamide of this metal to obtain OM ⁺ radicals.

In a more preferred embodiment, R is a tert-butyl or tert-pentyl radical. According to another preferred variant of the invention, use is made of a mixture of compounds of formula (I) in which 2 radicals R present on each aromatic unit are carbon chains comprising at least one tertiary carbon through which R is connected. to the aromatic nucleus.

The sulfurized material used to form the sulfur-carbon composite according to the invention may have different melting enthalpy values. This melting enthalpy (DH _fUS ) may preferably be between 70 and 100 J. g ^-1 . Indeed, the sulfurized material, for example in the elemental state or in the form of aromatic 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 English terminology). Following the implementation of the process according to the invention, and in particular the incorporation of the carbon nanofillers in molten _mode , there is a decrease in the enthalpy value (DH _fUS ) of the composite with respect to the enthalpy value of the sulfur material of origin.

The carbon nanocharqes

According to the invention, the carbon nanofillers may be carbon nanotubes, carbon nanofibers, graphene, or a mixture thereof in all proportions. Preferably, the carbon nanofillers are carbon nanotubes (CNTs), alone or mixed with at least one other carbon nanocharge. In fact, unlike carbon black, the NTC type additives 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 CNTs used in the composition of the active ingredient may be single-walled, double-walled or multi-walled, preferably multi-walled (MWNT) type.

The carbon nanotubes used according to the invention usually have a mean diameter ranging from 0.1 to 200 nm, preferably from 0.1 to 100 nm, more preferably from 0.4 to 50 nm, and better still , from 1 to 30 nm, indeed from 10 to 15 nm, and advantageously a length of more than 0.1 μm and advantageously from 0.1 to 20 μm, preferably from 0.1 to 10 μm, for example from approximately 6 pm. 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 nf / g, advantageously between 200 and 300 nf / g, and their apparent density may notably be included. between 0.01 and 0.5 g / cm ³ and more preferably between 0.07 and 0.2 g / cm ³ . The MWNT can for example comprise from 5 to 15 sheets and more preferably from 7 to 10 sheets.

Carbon nanotubes are obtained in particular by chemical vapor deposition, for example according to the method described in WO06 / 082325. Preferably, they are obtained from renewable raw material, in particular of plant origin, as described in the patent application EP1980530.

These nanotubes may or may not be treated.

[00140] An example of crude carbon nanotubes is especially the trade name Graphistrength® ^® C100 from Arkema.

These nanotubes can be purified and / or treated (for example oxidized) and / or crushed and / or functionalized.

The grinding of the nanotubes may in particular be performed cold or hot and be carried out according to known techniques used in devices such as ball mills, hammers, grinders, knives, gas jet or any another grinding system capable of reducing the size of the entangled network of nanotubes. It is preferred that this grinding step is performed 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 iron from their process of preparation. The weight ratio of the nanotubes to the sulfuric acid may especially 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. The nanotubes may alternatively be purified by high temperature heat treatment, typically greater than 1000 ° C.

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.

The functionalization of the nanotubes can be carried out by grafting reactive units such as vinyl monomers on the surface of the nanotubes. Crude nanotubes, optionally milled nanotubes, that is to say nanotubes which are neither oxidized nor purified nor functionalized and undergo any other chemical and / or thermal treatment, are preferably used in the present invention. .

The carbon nanofibers that can be used as carbon nanofillers in the present invention are, like the carbon nanotubes, nanofilaments produced by chemical vapor deposition (or CVD) from a carbon source which is decomposed on a catalyst comprising a transition metal (Fe, Ni, Co, Cu), in the presence of hydrogen, at temperatures of 500 to 1200 ° C. However, these two carbonaceous charges are differentiated by their structure, because carbon nanofibers consist of more or less organized graphitic zones (or turbostratic stacks) whose planes are inclined at variable angles with respect to the axis of the fiber. These stacks can take the form of platelets, fish bones or stacked cups to form structures generally ranging in diameter from 100 nm to 500 nm or more.

Examples of usable carbon nanofibers have in particular a diameter of 100 to 200 nm, for example approximately 150 nm, and advantageously a length of 100 to 200 μm. It is possible to use, for example, VGCF ^® nanofibers from SHOWA DENKO.

By graphene is meant a planar 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). On the other hand, it excludes carbon nanotubes and nanofibers, which consist respectively of the winding of one or more sheets of graphene in a coaxial manner and of the turbostratic stacking of these sheets. It is furthermore preferred that 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 leaves, preferably from 1 to 20 leaves and more preferably from 1 to 10 leaves, or even from 1 to 5 leaves which are likely to be disconnected from each other in the form of independent sheets, for example during an ultrasound treatment.

Additives for the formation of the Sulfur-Carbon composite

According to one embodiment of the invention, the sulfur-carbon composite further comprises at least one additive selected from a rheology modifier, a binder, an ionic conductor, a carbonaceous electrical conductor, an electron donor element or their association. Like the carbon nanofillers, the additive (s) are incorporated by melting.

According to one embodiment of the invention, the sulfur-carbon composite further comprises at least one additive selected from a rheology modifier, a binder, an ionic conductor, a carbonaceous electrical conductor, an electron donor element or their association. These additives are advantageously introduced during the compounding step, so as to obtain a homogeneous sulfur-carbon composite. Thus, preferably, a rheology modifier is added to the compounding device, preferably prior to performing the compounding step.

In particular, it is possible to add, during mixing, during the compounding step, an additive modifying the rheology of sulfur in the molten state, in order to reduce the self-heating of the mixture in the process. compounding device. Such additives having a fluidifying effect on liquid sulfur are described in application WO 2013/178930. Examples that may be mentioned include dimethyl sulphide, diethyl sulphide, dipropyl sulphide, dibutyl sulphide, dimethyl disulphide, diethyl disulphide, dipropyl disulphide, dibutyl disulphide, and the like. trisulfides, their tetrasulfide counterparts, their pentasulfide counterparts, their hexasulfide counterparts, alone or as mixtures of two or more of them in all proportions.

The amount of rheology modifier additive is generally from 0.01% to 5% by weight, preferably from 0.1% to 3% by weight relative to the total weight of the carbon-sulfur composite.

The sulfur-carbon composite may comprise a binder, especially a polymeric binder. Thus, it is also possible to add during the formation of the sulfur-carbon composite a polymeric binder as defined above. Indeed, it has already been discussed the introduction of a polymeric binder during the preparation of the liquid-solid dispersion. Nevertheless, such additives can also be advantageously added during the preparation of the sulfur-carbon composite.

The sulfur-carbon composite may comprise an ionic conductor, as defined above, having a favorable interaction with the surface of the sulfur-containing material in order to increase the ionic conductivity of the said composite. The carbon-sulfur composite may comprise an electrical conductor and / or an electron donor element to improve the electronic exchanges and regulate the length of the polysulfides during charging, which optimizes the charging / discharging cycles of the drums. These compounds can generally be added in proportions ranging from 1 to 10% by weight relative to the weight of sulfur-containing material.

According to another aspect, the invention relates to the use of the formulation according to the invention for the manufacture of an electrode, in particular a cathode.

For this, the formulation, in the form of a particulate mixture, can be deposited on the current collector.

The solid-liquid dispersion, or particulate mixture, can be applied to the current collector in the form of a suspension in 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.

Thus, the cathode of the present invention comprises a sulfur-carbon composite comprising a sulfur-containing material. The sulfurized material, or electroactive sulfur material, can form from 70 to 90% by weight of the total weight of the Sulfur-Carbon composite. For example, the sulfurized material may form from 80 to 85% by weight of the total weight of the Sulfur-Carbon composite. The sulfur material may include elemental sulfur, sulfur-based organic compounds, sulfur-containing inorganic compounds, and sulfur-containing polymers. Other examples include the anionic polysulfides of alkali metals, preferably lithium polysulfides represented by the formula L1-S (with n & l). In a preferred embodiment, elemental sulfur is used. The electroactive sulfur material can form from 50 to 80% by weight of the total weight of the cathode, for example from 60 to 70% by weight of the total weight of the cathode. The cathode may comprise 70 to 95% by weight of Sulfur-Carbon composite particles, for example 75 to 90% by weight of Sulfur Carbon composite particles.

The cathode may further comprise a binder for bonding together the Sulfur-Carbon composite particles and the carbon black to form the cathodic composition deposited on the current collector. The cathode may comprise from 2 to 10% by weight of binder based on the total weight of the binder, Sulfur-Carbon composite particles and carbon charge conductive particles. The polymeric binder may be selected from the polymeric binders described above. In a preferred embodiment, the binder is gelatin, a cellulose (for example carboxymethylcellulose) or a rubber, for example a styrene-butadiene rubber. In a more preferred embodiment, the binder comprises PEO and at least one of gelatin, cellulose (e.g. carboxymethylcellulose) and rubber (e.g., styrene-butadiene rubber).

In one embodiment, 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). Such binders can improve the life of the cell. The use of such binders can also reduce the total amount of binder, e.g. at levels of 10% by weight of the total weight of the cathode or less.

The cathode described here can be used in a lithium-sulfur cell.

According to another aspect, 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.

[00169] Optionally, a separator can be positioned between the cathode and the anode. For example, 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 the cathode and the 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. When a separator is present in the cell of the present invention, 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.

[00170] As discussed above, 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. Preferably, 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 examples below illustrate the invention but are not limiting in nature.

rExemplesl

EXAMPLE 1 Active Ingredient Produced on BUSS Mixer MDK-46-1 L / D.

[00171] 10% of NTC (Graphistrength ^® C100 from Arkema), 5% carbon black (ENSACO 350G 5%) and 85% of solid sulfur (50- 800 microns) are introduced into the first feed hopper of a BUSS ^® MDK 46 co-kneader (L / D = 1 1).

The temperature setpoints within the co-kneader are as follows: Zone 1: 140 ° C .; Zone 2: 130 ° C.

At the exit of the die, the Sulfur-Carbon composite, or masterbatch, consisting of 85% by weight of sulfur, 10% by weight of NTC and 5% by weight of carbon black is in the form of granules. obtained by cutting in the head, cooled by a jet of water.

The granules obtained, of dimension close to 2 - 3 mm, are pre-milled in the wet state in a ceramic ball mill.

The paste obtained was diluted with additional water to obtain a solids content of 60%. The mixture is then placed in a vertical ball mill (cage).

After 1 hour of grinding, a homogeneous pasty substance, solid-liquid dispersion type, was obtained.

EXAMPLE 2 Comparison of the active ingredient prepared by the dry route (comparative) or according to the method of the invention (wet process) The granules obtained, of dimension close to 2 - 3 mm, according to Example 1 were milled by two methods:

Sample A (comparative): Air jet grinding under nitrogen. The powder obtained is characterized by D 50 = 15 μm, D 90 = 35 μm.

Sample B: Grinding done as described in Example 1. The particles obtained, in solid-liquid dispersion, are characterized by D 50 = 15 μm and D 90 = 40 μm, the grinding time was extended by 2 h. At this stage, an enumeration of the elemental sulfur particles in the liquid-solid dispersion can be carried out, for example by scanning electron microscopy so as to observe a very small proportion of sulfur particles in the elemental state by compared to other particles of the dispersion. This dispersion then underwent an evaporation step to obtain a powder.

Table 1 below shows the results of measuring the density of the active ingredient (powder).

Table 1

This table represents the density, or density, of the powders obtained by these two grinding methods. The density of the powders was characterized by the method of measurement of apparent density. Briefly, the powders from both milling methods were compacted uni-axially, using a press, in a cylinder with an applied pressure of 20 kg / cm ² .

The active material obtained after the grinding step according to the sample B is denser, less porous and therefore has an advantage for the architecture of a cathode with higher energy density.

In addition, the Sulfur-Carbon composite was analyzed by the differential scanning calorimetry method using a Mettler apparatus. The temperature rise method is 5 ° C per minute under nitrogen flow and the heat of fusion is measured between 80 ° C and 130 ° C.

The melting enthalpy value (DH _fus ) obtained for the Sulfur-Carbon composite is 45 J. g ^-1 and brought to the amount of sulfur-containing material in the Sulfur-Carbon composite that corresponds to 52.9 J g ^-1 . By way of comparison and measured under the same conditions, the material The sulfur content at the origin of the composite has a melting enthalpy value of 71 J. g ^-1 . This corresponds to a 25% reduction in the melting enthalpy value of the sulfur-containing material.

Thus, the process according to the invention causes a modification of the melting enthalpy of the sulfur-containing material.

Example 3 Manufacture of a Li / S Battery with the Active Ingredient Prepared by the Dry Way (Comparative) or According to the Process of the Invention (Wet Way)

The active material obtained by grinding in the form of solid-liquid dispersion (sample B), was used to make a Li / S battery model containing:

1) Metal Li anode, thickness 100 μm;

2) HDPE separator / membrane (20 μm)

3) Sulfolane Electrolyte with 1M LiTFSI (3M)

4) Cathode based on a support by the collector Aluminum, with sulfur formulation supported by an aluminum collector: 80% (Sulfur / NTC / carbon black), 20% Polyethylene Oxide (PEO).

The cathode formulation was applied and homogenized in a planetary mixer for 3 hours.

The 5000 mP viscosity ink was applied to the aluminum collector. Drying was carried out in the oven ventilated at 130 ° C for 15 min. Then the electrode was packaged in a vacuum cabinet for 24 hours. The capacity of the cathode is 3.4 mAh / cm ² .

[00187] Three button cells were then put in the charging / discharging conditions. The performances of the cathode are 0.5C. Efficacy was evaluated after 50 cycles.

Example 4: Improved interfaces

The granules obtained in Example 1, of dimension close to 2 - 3 mm, are added with a Sulfolane-based electrolyte with 1 M LiTFSI and then pre-milled in the wet state in a ball mill. ceramic.

The paste obtained was diluted with additional electrolyte to obtain a solids content of 60%. The mixture is then placed in a vertical ball mill (cage).

After 1 hour of grinding, a homogeneous pasty substance, of solid-liquid dispersion type, was obtained.

Example 5: Manufacture of a Na-S Battery The active substance obtained by grinding in the form of a solid-liquid dispersion (sample B), was used to make a Na-S battery model containing:

1) Anode based on sodium metal,

2) 1,2-Dimethoxyethane-NaCF ₃ S03-NaNO3 base electrolyte

3) Cathode based on a support by the aluminum collector, with sulfur formulation supported by an aluminum collector: 80% of (Sulfur / NTC, 90/10), 10% of polyvinylidene fluoride and 10% of black of carbon as an electrical conductor.

The viscosity ink 5000 mP.s was applied to the aluminum collector. Drying was carried out in the oven ventilated at 130 ° C for 15 min. Then the electrode was packaged in a vacuum cabinet for 24 hours.

Example 6: Manufacture of a solid Li-S battery

The active substance obtained by grinding in the form of a solid-liquid dispersion (sample B), was used to make a Na-S battery model containing:

1) Metal Li Anode, 100 μm thick,

2) Solid electrolyte based on U2S-P2S5

3) Cathode based on a support by the collector Aluminum, with sulfur formulation supported by an aluminum collector: 80% (Sulfur / NT C / carbon black, 85/10/5), 20% Polyethylene Oxide (PEO).

Claims

claims

1. Formulation, in the form of a solid-liquid dispersion, for the manufacture of a cathode, comprising:

a solvent in the liquid phase,

2. Formulation according to claim 1, characterized in that more than 95% by number of the particles of the dispersion are Sulfur-Carbon composite particles.

3. Formulation according to one of claims 1 or 2, characterized in that it has a solids content of less than 90%.

4. Formulation according to any one of claims 1 to 3, characterized in that the solvent in the liquid phase comprises at least one compound having a boiling point below 300 ° C.

5. Formulation according to any one of claims 1 to 4, characterized in that 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.

6. Formulation according to any one of claims 1 to 5, characterized in that it further comprises a solid electrolyte, preferably a solid electrolyte ceramic type.

7. Formulation according to any one of claims 1 to 6, characterized in that it comprises less than 15% by weight of polymeric binder.

8. Formulation according to any one of claims 1 to 7, characterized in that it has a Brookfied viscosity greater than 100 mPa.s ¹ .

9. Formulation according to any one of claims 1 to 8, characterized in that the sulfur-carbon composite is obtained by molten route.

10. Formulation according to claim 9, characterized in that the sulfur-carbon composite is obtained by melting a sulfur-containing material and kneading the molten sulfur material and carbon nanofillers.

1 1. Formulation according to any one of Claims 1 to 10, characterized in that the sulfur-carbon composite comprises a sulfur-containing material and from 0.01 to 50% by weight of carbon nanofillers.

A process for preparing a formulation for the manufacture of an electrode comprising:

a prior step (100) for forming the Sulfur-Carbon composite, said prior step of forming the Sulfur-Carbon composite comprising a melting of a sulfur-containing material and a kneading of the molten sulfur material and the carbon nanofillers,

the introduction (210) in a grinding device of a solvent in the liquid phase and a Sulfur-Carbon composite, said Sulfur-Carbon composite comprising at least one sulfur-containing material and carbon nanofillers,

the implementation of a step (250) of grinding, and

obtaining (260), following said grinding step, a formulation in the form of a solid-liquid dispersion comprising the Sulfur-Carbon composite in the form of particles of less than 50 μm of median diameter D50 and less 10% by number of the particles of the dispersion are elemental sulfur particles.

13. Preparation process according to claim 12, characterized in that a host polymer is introduced into the grinding device, preferably before carrying out the grinding step.

14. A method of preparation according to one of claims 12 or 13, characterized in that the method further comprises a step (220) of introduction into the mill of at least one electrolyte salt preferably selected from: trifluoromethanesulfonate Lithium, (Bis) trifluoromethanesulfonate lithium imide, lithium 2-trifluoromethyl-4,5-dicyanoimidazole, lithium bis (fluorosulfonyl) imide, lithium hexafluorophosphate, lithium perchlorate, lithium trifluoromethylsulfonate, trifluoroacetate of lithium lithium, dilithium dodecafluorododecaborate, lithium bis (oxalate) borate, and lithium tetrafluoroborate.

15. Preparation process according to any one of claims 12 to 14, characterized in that a solid electrolyte, preferably a solid electrolyte ceramic type, is introduced into the grinding device, preferably before the implementation of the grinding step.

16. Preparation process according to any one of claims 12 to 15, characterized in that the grinding step is conducted in a ball mill, a cavitator, a jet mill, a fluidized bed jet mill, a liquid phase mill, screw disperser, brush mill, hammer mill or ball mill.

17. Preparation process according to any one of claims 12 to 16, characterized in that the grinding step is conducted at a temperature above 0 ° C and below the boiling point of the solvent in the liquid phase.

18. Preparation process according to any one of claims 12 to 17, characterized in that the grinding step is followed by a step of evaporating the solvent and adding an electrolyte, preferably a liquid electrolyte.

19. Preparation process according to any one of claims 12 to 18, characterized in that the preliminary step of forming the Sulfur-carbon composite comprises the addition of a mechanical energy of between 0.05 kWh / kg and 1 kWh / kg of solid matter.

20. Preparation process according to claim 12, characterized in that the prior step of forming the Sulfur-Carbon composite comprises the following substeps:

introduction (1 10) into a device for compounding at least one sulfur-containing material, and carbon nanofillers,

implementing a compounding step (130) so as to allow the melting of the sulfur-containing material, and

mixing (140) the molten sulfur material and the carbon nanofillers.

21. Use of the formulation according to any one of claims 1 to 1 1 for the manufacture of a cathode.

22. Cathode manufactured from a formulation according to any one of claims 1 to 1 1.

Lithium / sulfur accumulator comprising a cathode according to claim 22.