阅读说明：本技术 用于锂-硫电池的活性材料配制物和制备方法 (Active material formulation for lithium-sulfur battery and preparation method ) 是由 A.科尔兹亨科 D.普利 于 2019-02-19 设计创作，主要内容包括：本发明涉及包含含硫材料和导电组合物的活性材料配制物,其特征在于所述导电组合物包含碳纳米管和碳纤维。本发明还涉及制备活性材料配制物的方法以及还涉及包含所述配制物的阴极电解质、包含所述阴极电解质的阴极和包含所述阴极的电池。(The invention relates to an active material formulation comprising a sulphur-containing material and an electrically conductive composition, characterized in that the electrically conductive composition comprises carbon nanotubes and carbon fibres. The invention also relates to a method for preparing the active material formulation and also to a catholyte comprising the formulation, a cathode comprising the catholyte and a battery comprising the cathode.)

1. An active material formulation comprising a sulphur-based material and an electrically conductive composition, characterised in that the electrically conductive composition comprises carbon nanotubes and carbon fibres.

2. The active material formulation of claim 1, wherein the conductive composition further comprises carbon nanofibers.

3. The active material formulation of any one of claims 1 and 2, wherein the electrically conductive composition further comprises an additional carbon-based filler selected from the group consisting of: carbon black, acetylene black, graphite, graphene, activated carbon, and mixtures thereof.

4. The active material formulation of any one of claims 1 to 3, wherein a mass ratio of the sulfur-based material and the conductive composition is between 1/4 and 50/1.

5. The active material formulation of any one of claims 1 to 4, wherein the carbon nanotube content is at least 20 wt% of the conductive composition.

6. Active material formulation according to any one of the preceding claims, wherein at least a part of the carbon nanofibres, carbon nanotubes and/or carbon fibres are covered with an intrinsically conductive polymer.

7. The active material formulation of any one of claims 1 to 5, wherein at least a portion of the carbon nanofibers, carbon nanotubes and/or carbon fibers are covered with an ion conducting ceramic material.

8. Active material formulation according to any one of claims 1 to 7, characterized in that the S8 content of the sulphur-based material is less than 10% by weight of the sulphur-based material.

9. A catholyte comprising the active material formulation of any one of claims 1 to 8 and a binder.

10. The catholyte according to claim 9, further comprising at least one additive selected from the group consisting of: rheology modifiers, ionic conductors, other carbon-based electrical conductors, electrolytes and electron donating elements.

11. A method of making an active material formulation as claimed in any one of claims 1 to 8 comprising the step of contacting a sulphur-based material with a conductive composition.

12. The method of claim 11, wherein the contacting step is selected from the group consisting of: the sulfur-based material is mixed with the conductive composition at a temperature greater than or equal to the melting point of the sulfur-based material, the sulfur-based material is sublimated on the conductive composition, and the sulfur-based material is liquid-phase deposited on the conductive composition.

13. A method of preparation according to claim 11, characterized in that it comprises a step of forming a sulfur-carbon composite, said preliminary step of forming a sulfur-carbon composite comprising melting a sulfur-based material and blending the molten sulfur-based material and a carbon-based filler, preferably in a compounding device.

14. Preparation process according to any one of claims 11 to 13, characterized in that it comprises a step of grinding the sulfur-carbon composite, which can be carried out in a tank mill (horizontal and vertical caged), cavitator, jet mill, fluid bed jet mill, liquid phase mill, screw disperser, brush mill, hammer mill, ball mill, or by other micronization methods.

15. Preparation process according to one of claims 11 to 14, characterized in that it comprises the following steps:

-introducing (210) a liquid phase solvent and introducing (220) a sulphur-carbon composite into the grinding device, the sulphur-carbon composite comprising at least one sulphur-based material and a carbon-based filler,

-carrying out a grinding step (230),

-producing (240), after the grinding step, a formulation in the form of a solid-liquid dispersion comprising the sulphur-carbon composite,

-optionally carrying out a drying step (250).

16. A cathode prepared from the catholyte of claim 9 or 10.

17. A lithium/sulfur battery comprising the cathode of claim 16.

Background

The development of rechargeable batteries with high energy density is of great technical and commercial interest. There are many kinds of systems such as portable electronic systems equipped with Li-ion batteries, hybrid vehicles equipped with Ni-MH batteries, or other technologies.

Lithium/sulfur (Li/S) batteries or Li/S cells are contemplated as promising alternatives to lithium ion batteries. The interest in this type of cell comes in particular from the high potential density of sulfur. In addition, sulfur has the advantages of being abundant, inexpensive, and non-toxic, which makes large-scale development of Li/S batteries conceivable.

The mechanism for discharging and charging Li/S cells is based on the reduction/oxidation of sulfur at the cathode

And oxidation/reduction of lithium at the anodeIn order for the electrochemical reaction to occur rapidly at the electrodes, the cathode and anode must be generally good electronic conductors. However, the mechanism of sulfur discharge (regiomes) is relatively slow and, since it is an electrical insulator, it is necessary to impart its conductive properties.

Various improved approaches aimed at overcoming the low electronic conductivity of sulfur have been envisaged, in particular the addition of electron conducting additives (conductive additives), such as carbon-based conductive materials.

The mixing of the active material and the conductive additive may be performed in various ways. For example, mixing may be performed during preparation of the electrode. The sulfur is then mixed with the conductive additive and optionally the binder by mechanical agitation before shaping the electrode. By this homogenization step, it is assumed that the carbon-based additive is distributed around the sulphur particles, thereby creating a percolating network. A milling step may also be employed and may enable a more intimate mixing of the materials. However, this additional step may destroy the porosity of the electrode. Another way of mixing the active material with the carbon-based additive comprises (consists in) grinding the sulphur and the carbon-based additive by a dry route in order to coat the sulphur with carbon. However, when the carbon-based additive is carbon nanotubes, the introduction of carbon nanotubes into the formulation presents some problems. This is because they prove difficult to handle and disperse, due to their small size, their powdered state and possibly their wound structure further creating strong van der waals interactions between them when they are obtained by Chemical Vapor Deposition (CVD). The low dispersion of the nanotubes limits the charge transfer efficiency between the positive electrode and the electrolyte (electrolyte) and thus limits the performance of the Li/S cell despite the addition of a mass of conductive material.

The applicant has found that active materials can also be obtained by contacting carbon nanotubes (hereinafter referred to as CNTs) by a melt route with a sulphur-based material, for example in a compounding device, to form an improved active material that can be used for the preparation of electrodes (WO 2016/102865).

In this case, the sulfur-based material is combined with a carbon-based nanofiller (e.g. CNT, graphene or carbon black) in a blending tool at the melting point of the sulfur-based material. This enables the production of sulfur-carbon composites that can be in the form of compacted pellets. These pellets are then milled under an inert atmosphere to obtain a powder that can be used to make cathodes.

Despite the advantages of Li-S batteries, and the ability of these novel processes to form more uniform active materials, Li-S batteries continue to suffer from relatively rapid decreases in cycling capacity.

The decrease in the circulation capacity is multifactorial. It is notably involved in the formation of several lithium polysulfides during discharge, which become dissolved in the electrolyte and escape from the cathode. The reduction in capacity also occurs via passivation effects and the formation of insoluble sulfides, amplified by volume changes during discharge, which cause mechanical tensions and loss of contact with the current collector.

Various methods have been proposed to improve the cycle. For example, the effect of MWNT (multiwalled nanotubes) and Graphite Nanofibers (GNF) on the cathode performance of Li-S batteries has been investigated (Kim Jong-Hwa et al, Materials Science Forum, 2005, 486-. MWNTs or GNFs were added to the electrodes as additives consisting of 60% sulfur, 20% acetylene black, 5% MWNTs or GNFs and 15% PEO (polyethylene oxide) dissolved in acetonitrile.

The addition of MWNTs or GNFs provides better electrochemical properties, but the improvement remains limited because, for an initial capacity of about 700mAh/g, after 50 cycles, the capacity is only: 130mAh/g (with carbon black), 250mAh/g (with carbon black plus GNF) and 300mAh/g (with carbon black plus MWNT).

Solutions based on the combination of nanotubes with additional carbon-based fillers (such as carbon black, graphene or graphene oxide) have also been proposed. For example, micrometer sized Li by dry ball milling in the presence of carbon black₂Li obtained from S powder₂S-carbon nanostructured composites are used with carbon nanotubes and a simple electrochemical activation process to improve the use and reversibility of the electrode in the presence of the nanotubes.

Methods including carbon nanotubes and carbon nanofibers have also been proposed for the purpose of improving battery performance. However, these methods described in CN106450191 show that performance is only maintained at relatively low cycle times. The method described in CN107221660 comprising a combination of carbon nanofibers and nanotubes shows for its part that the presence or absence of carbon nanofibers in the presence of carbon nanotubes produces similar results.

Another method taught in US 2011/0165462 also discloses the use of nanotubes in combination with carbon nanofibers having a diameter of less than 100nm to make electrodes by rolling up a sheet. These techniques allow the formation of dendrites for improving the performance of the battery to be tolerated.

Finally, carbon nanotubes and carbon nanofibers have also been combined to make electrodes that include sulfur penetration into micropores (<2nm) and thereby allow for improved capacity and cycling stability (Linchao Zeng et al, Free-standing pore carbon fibers-sulfur composite for flexible Li-S battery cathode,2014, Vol.6, 9579-9587).

Despite the cycle improvements obtained with the prior art methods, there is still a need for active material formulations for further improving the cycle stability of Li/S electrodes.

In addition, there is a need for active material formulations for improving the charge and discharge capacity of batteries incorporating the active materials.

Technical problem

It is therefore an object of the present invention to overcome the disadvantages of the prior art. In particular, the object of the present invention is to propose a formulation for manufacturing an electrode with improved cycling stability.

It is also an object of the present invention to propose a process for preparing a formulation for manufacturing an electrode, which is fast and easy to carry out and which enables the charge and discharge capacity of a battery incorporating the active material to be improved.

Disclosure of Invention

To this end, the invention relates to an active material formulation comprising a sulphur-based material and an electrically conductive composition comprising carbon nanotubes and at least one further carbon-based filler selected from carbon nanofibers and carbon fibers.

Preferably, the present invention relates to an active material formulation comprising a sulphur-based material and an electrically conductive composition, characterized in that the electrically conductive composition comprises carbon nanotubes and carbon fibres.

The performance of the battery can be improved by using the conductive composition according to the present invention. The active materials used in Li-S cathodes are generally based on sulfur and carbon. The method according to the prior art results in a generally poor cycle stability and in particular a poor dimensional stability. In particular, the active material may suffer damage during charge and discharge cycles, with the result that the performance of a battery incorporating the active material deteriorates.

Accordingly, applicants have developed novel formulations for improving battery performance, particularly by enabling improved cycling stability. The formulations according to the invention can be used as cathode active materials for lithium/sulfur batteries.

Specifically, the applicant has found that an active material comprising a conductive composition containing at least carbon nanotubes in combination with carbon nanofibers and/or carbon fibers, preferably in combination with carbon fibers, can be uniformly dispersed in a bulk (bulk) of a sulfur-based material and form a three-dimensional nanotube network, which active material makes it possible to improve the stability and charge and discharge capacity of a battery incorporating the active material. Unlike carbon black, carbon nanotube type additives have the advantage of also imparting a beneficial adsorption effect on the active material by limiting its dissolution in the electrolyte and thus promoting better cycle performance (cyclability). Furthermore, the addition of a second group of carbon-based additives (such as carbon fibers) and optionally a third group of carbon-based additives (which are coarser than the nanotubes) allows to benefit from the synergistic effect of the stability of the conductive network in the bulk of the cathode, especially when said cathode is thick (for example more than 100 μm).

The advantage of combining the two types of materials is that the nanofibers and even the larger diameter carbon fibers can act as the primary conducting path, while the nanotubes act as secondary conductors over a shorter distance (where dispersion quality issues are less).

According to other optional features of the active material formulation:

-the electrically conductive composition comprises carbon nanotubes, carbon nanofibers and carbon fibers. The best performance is obtained with a combination of these three carbon-based fillers.

-the conductive composition further comprises an additional carbon-based filler selected from the group consisting of: carbon black, acetylene black, graphite, graphene, activated carbon, and mixtures thereof.

-the mass ratio of the sulfur-based material to the conductive composition is between 1/4 and 50/1.

-the carbon nanotubes content is at least 20% by weight of the conductive composition.

At least a portion of the carbon nanofibers, carbon nanotubes and/or carbon fibers are covered with an intrinsically conductive polymer. In particular, at least a portion of the carbon nanotubes and/or carbon fibers are covered with an intrinsically conductive polymer.

At least a portion of the carbon nanofibers, carbon nanotubes and/or carbon fibers are covered with an ion conducting ceramic material. In particular, at least a portion of the carbon nanotubes and/or carbon fibers are covered with an ion conducting ceramic material.

-the S8 content of the sulphur-based material is less than 10 wt% of the sulphur-based material.

The present invention also relates to a method for preparing an active material formulation according to the present invention comprising the step of contacting a sulfur-based material with a conductive composition.

According to other optional features of the method:

-the contacting step is selected from: the sulfur-based material is mixed with the conductive composition at a temperature greater than or equal to the melting point of the sulfur-based material, the sulfur-based material is sublimated on the conductive composition, and the sulfur-based material is liquid-phase deposited on the conductive composition.

-the process comprises a preliminary step of forming a sulphur-carbon composite comprising melting a sulphur-based material and blending the molten sulphur-based material and a carbon-based filler, preferably in a compounding device. The presence of the sulfur-carbon composite obtained by the melt route in the formulation 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 (comilling) of sulfur and carbon. The sulfur-carbon composite may be obtained by melting a sulfur-based material and blending the molten sulfur-based material and a carbon-based nanofiller.

The process comprises a step of grinding the sulfur-carbon composite, which may be carried out in a tank mill (horizontal and vertical caged), cavitator, jet mill, fluid bed jet mill, liquid phase mill, screw disperser, brush mill, hammer mill, ball mill, or by other micronization processes.

-the method comprises the steps of:

introducing into the milling device: a liquid phase solvent and

sulphur-carbon composite comprising at least one sulphur-based material and a carbon-based filler,

o carrying out a grinding step,

o producing a formulation in the form of a solid-liquid dispersion comprising said sulfur-carbon composite, after said grinding step, and

optionally performing a drying step.

Carrying out the grinding in the presence of a solvent in the liquid phase makes it possible to improve the properties of the formulation with respect to dry grinding under an inert atmosphere according to the methods of the prior art.

The invention also relates to a catholyte comprising an active material formulation according to the invention and a binder. Such a catholyte is able to maintain a substantially constant capacity even after multiple charge/discharge cycles and is therefore able to maintain the capacity of a lithium-sulphur battery over time.

According to other optional features, the catholyte further comprises at least one additive selected from: rheology modifiers, ionic conductors, other carbon-based electrical conductors, electrolytes and electron donating elements.

The invention also relates to the use of the formulation according to the invention for the manufacture of cathodes. More particularly, the invention also relates to cathodes prepared from the active material formulations according to the invention or from the catholyte according to the invention. The active material formulation according to the invention makes it possible to improve the electronic conductivity of the electrode formulation, the mechanical integrity of the electrode and thus the operation of the battery over time.

The invention also relates to a lithium/sulphur battery comprising a cathode according to the invention. The active material formulation has a better combination of sulfur donating materials with a 3D network of carbon based fillers to promote sulfur insertion (access) electrochemical reactions, which can contribute to a good maintenance of the operation of the cell over time.

Further advantages and characteristics of the invention will become apparent from reading the following description, given by way of illustrative and non-limiting example, with reference to the accompanying drawings, which depict:

FIG. 1: schematic representation of a process for preparing an active material formulation according to the present invention. The step with dotted lines is optional.

-figure 2: schematic representation of a preferred grinding method (process ) according to the present invention.

Detailed Description

In the subsequent part of the description, the term "active material" refers to a compound (compound) capable of ensuring efficient electrical transmission from the current collector of the electrode and capable of providing an active interface for the electrochemical reaction during operation of the battery. More particularly, this corresponds to a compound which is capable of reacting with lithium ions and of releasing lithium ions therefrom. Thus, preferably, in the context of the present invention, the active material corresponds to a sulphur-based material. Thus, for the purposes of the present invention, the term "active material formulation" means a mixture of different substances, including in particular the active material.

The term "sulfur-based material" means a sulfur-providing compound selected from natural (or elemental, elemental) sulfur, sulfur-based organic compounds or polymers, and sulfur-based inorganic compounds.

The term "elemental sulfur" or "elemental sulfur" means sulfur particles in the form of crystalline S8 or in amorphous form. More particularly, this corresponds to the sulphur particles in elemental form, which do not include any sulphur associated (associated) with the carbon derived from the carbon-based filler.

The term "conductive composition" means a composition that includes a compound or structure capable of conducting an electrical current.

The term "catholyte" means a composition comprising the components forming the cathode.

The term "carbon-based filler" may denote a filler comprising at least one element from the group consisting of carbon nanotubes, carbon nanofibers, carbon fibers, carbon black, acetylene black, graphite, graphene and activated carbon. The term "filler" generally denotes a carbon-based filler, the smallest dimension of which is between 0.1 and 20 μm, preferably between 0.1 and 15 μm, more preferably between 0.1 and 10 μm and even more preferably between 0.2 and 10 μm. The term "nanofiller" generally denotes carbon-based fillers having a minimum dimension of between 0.1 and 200nm, preferably between 0.1 and 100nm and more preferably between 0.1 and 50nm, as measured by light scattering.

The term "solvent" means a substance that is liquid or supercritical (state) at its working temperature and has the property of dissolving, diluting or extracting other substances without chemically modifying them and without itself being modified. A "liquid phase solvent" is a solvent in liquid form.

The term "sulfur-carbon composite" means an aggregate of at least two immiscible components whose properties are complementary to each other, including a sulfur-based material and a carbon-based filler.

According to the invention, the term "compounding device" refers to the equipment conventionally used in the plastics industry for melt mixing thermoplastic polymers and additives to produce composite materials. In this apparatus, the sulfur-based material and the carbon-based filler are mixed by means of a high shear device, such as a co-rotating twin screw extruder or co-kneader. The molten material typically exits the apparatus in an agglomerated solid physical form (e.g., in the form of pellets).

For the purposes of the present invention, the expression "substantially constant" corresponds to a value that varies by less than 20%, preferably by less than 10% and even more preferably by less than 5%, with respect to the comparison value.

The invention will now be described in more detail and in a non-limiting manner in the following description. In the following description, the same reference numerals are used to designate the same elements (components).

As presented in the examples, the inventors have developed a combination of a sulfur-based material with a specific conductive composition that allows for improved retention of cycling capacity and dimensional stability.

Accordingly, the inventors have developed active material formulations that can be used to fabricate electrodes comprising a sulfur-based material and a conductive composition comprising carbon nanotubes and at least one additional carbon-based filler selected from carbon nanofibers and carbon fibers. Preferably, the conductive composition comprises carbon nanotubes and carbon fibers. The conductive composition may further comprise carbon nanofibers. As presented in the examples, such formulations are able to maintain nearly constant capacity even after multiple charge/discharge cycles and thus are able to maintain the capacity of a lithium-sulfur battery over time.

The inventors have determined that the conductive composition must include carbon nanotubes in combination with one and/or the other from among carbon nanofibers and carbon fibers. Preferably, the conductive composition comprises carbon nanotubes and carbon fibers.

However, they also show that preferably the conductive composition comprises carbon nanotubes, carbon nanofibers and carbon fibers. In particular, the combination of at least these three carbon-based fillers provides the best results in terms of maintaining the circulation capacity. In particular, the carbon-based filler in the form of at least two groups of fibrils ensures a better dimensional stability of the cathode with respect to volume changes between charging and discharging.

The conductive composition may include 1% to 99% carbon nanotubes and 1% to 99% carbon fibers. In particular, the conductive composition comprises at least 20% of carbon nanotubes of the single-walled, double-walled or multi-walled type, preferably at least 30% of carbon nanotubes, more preferably at least 40% of carbon nanotubes and even more preferably at least 50% of carbon nanotubes.

Further, the mass ratio of the sulfur-based material to the conductive composition is preferably between 1/4 and 50/1. More preferably, the mass ratio of the sulfur-based material and the conductive composition is between 2/1 and 20/1 and even more preferably between 4/1 and 15/1.

According to the present invention, the carbon nanotubes may be single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), or multi-walled carbon nanotubes (MWNTs); it is preferably multi-walled. The carbon nanotubes used according to the invention generally have an average diameter in the range 0.1 to 100nm, preferably 0.1 to 50nm, more preferably 1 to 30nm, or even 10 to 15nm, and a length advantageously of 0.1 micron or more and advantageously of 0.1 to 20 microns, preferably of 0.1 to 10 microns.

The length/diameter ratio, or aspect ratio, of the carbon nanotubes is advantageously greater than 10 and generally greater than 100. The specific surface area is, for example, between 50 and 300m²A/g, advantageously between 100 and 300m²Is between/g and its apparent density may be in particular between 0.01 and 0.5g/cm³And more preferably between 0.07 and 0.2g/cm³In the meantime. MWNTs may comprise, for example, 5 to 25 walls and more preferably 7 to 20 sheets (sheets).

Carbon nanotubes are obtained in particular by Chemical Vapor Deposition (CVD), for example according to the method described in WO 06/082325. Preferably, it is obtained from renewable starting materials, in particular plant sources, as described in patent application EP 1980530.

An example of carbon nanotubes is under the trade nameC100 is found in Arkema corporation. These nanotubes may be purified and/or treated (e.g., oxidized) and/or milled and/or functionalized. The grinding of the nanotubes can be carried out under cold or hot conditions and can be carried out according to known techniques, in equipment such as ball mills, hammer mills, edge mills (edge runner mills), knife mills or gas jet mills or any other grinding system capable of reducing the size of the entangled network of nanotubes. The grinding is preferably carried out according to the gas jet grinding technique and in particular in an air jet mill.

Raw or milled nanotubes can be purified by washing with a sulfuric acid solution to free them from possible residual mineral and metal impurities, such as catalysts originating from their preparation. The weight ratio of nanotubes to sulfuric acid may be between 1:2 and 1: 3. The purification operation can also be carried out at a temperature ranging from 90 ℃ to 120 ℃, for example for a duration ranging from 5 to 10 hours. This operation may advantageously be followed by a step of washing with water and drying the purified nanotubes.

It is obvious that any other relatively strong acid may also be suitably used. An oxidizing acid, such as nitric acid, in addition to removing most of the mineral material, also produces polar surface functional groups by surface oxidation of the outer layer.

As a variant, the nanotubes can be purified by high temperature heat treatment (typically above 1000 ℃). Alternatively, the carbon nanotubes may be pre-compacted according to the method described in patent application WO2018/178929, before being subjected to a thermal treatment.

The oxidation of the nanotubes is advantageously carried out by contacting them with a sodium hypochlorite solution containing 0.5 to 15% by weight of NaOCl and preferably 1 to 10% by weight of NaOCl, 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 lower than 60 ℃ and preferably at room temperature, for a duration ranging from a few minutes to 24 hours. This oxidation operation may advantageously be followed by steps of filtering and/or centrifuging, washing and drying the oxidized nanotubes.

Raw, optionally milled nanotubes, that is to say nanotubes which have neither been oxidised nor purified, nor functionalized and have not undergone any further chemical and/or thermal treatment, are preferably used in the present invention.

The carbon nanotube content can be between 1 wt% and 99 wt% of the conductive composition. Advantageously, and as presented in the examples, the conductive composition comprises more than 20% carbon nanotubes and more preferably 40% or more carbon nanotubes. For example, it comprises between 25% and 75% carbon nanotubes.

Like carbon nanotubes, carbon nanofibers or carbon nanofibrils useful in the present invention are also nanowires produced by decomposition of a carbon-based source on a catalyst comprising a transition metal (Fe, Ni, Co, Cu) by Chemical Vapor Deposition (CVD) in the presence of hydrogen at a temperature of 500 to 1200 ℃. However, the structure of these two carbon-based fillers differs, since the carbon nanofibers are composed of more or less organized graphitic regions (or turbine layer stacks), the planes of which are inclined at variable angles with respect to the axis of the fiber. These stacks may take the form of sheets, fish bones or stacked discs to form structures having diameters typically in the range of 50nm to 500nm or even larger. Examples of carbon nanofibers that can be used are in particular 100 to 200nm in diameter, for example about 150nm, and advantageously 5 to 100 microns in length and preferably 5 to 75 microns in length. For example, VGCF nanofibers from Showa Denko may be used.

Therefore, the aspect ratio (i.e., the ratio between the length and the diameter) of the carbon nanofibers contained in the conductive composition is preferably between 10 and 2000.

Advantageously, and as presented in the examples, the conductive composition comprises more than 20% carbon nanofibers and more preferably 40% or more carbon nanofibers. For example, it comprises between 25% and 75% carbon nanofibers.

The carbon fibers useful in the present invention are filled or partially porous carbon fibers, which are at least partially graphitized, preferably between 200nm and 20 μm in diameter, preferably between 500nm and 20 μm and even more preferably in the range of 500nm to 8 μm in diameter. Among the family of carbon fibers, pre-cellulose (ex-cellulose) or pitch (pitch) fibers with reduced diameter (<5 μm) are preferred, which may be more advantageous to avoid excessive thickness and electrode structural defects.

The aspect ratio (i.e. the ratio between the length and the diameter) of the carbon fibres contained in the conductive composition is preferably between 5 and 1000.

Furthermore, the specific density of the carbon fibers useful in the present invention is advantageously between 1.3 and 1.9g/cm³In the meantime.

Advantageously, and as presented in the examples, the conductive composition comprises more than 20% carbon fibers and more preferably 40% or more carbon fibers. For example, it comprises between 25% and 75% carbon fibres. In particular, the conductive composition comprises at least 20% carbon fibres, preferably at least 30% carbon fibres and more preferably 40% carbon fibres.

More preferably, the conductive composition comprises greater than 20% carbon nanotubes and greater than 20% of other carbon-based fillers selected from the group consisting of: carbon nanofibers and carbon fibers. Even more preferably, the conductive composition comprises greater than 20% carbon nanotubes, greater than 20% carbon nanofibers, and greater than 20% carbon fibers.

In order to improve the electrical properties of the carbon nanotubes, carbon nanofibers and/or carbon fibers, they may be subjected to a surface treatment. Thus, advantageously, at least a portion of the carbon nanofibers, carbon nanotubes and/or carbon fibers are covered with an intrinsically conductive polymer, such as polyaniline, polythiophene, polypyrrole and the like. Alternatively, at least a portion of the carbon nanofibers, carbon nanotubes, and/or carbon fibers are covered with an ion conducting ceramic material.

Although good results have been obtained with carbon nanotubes and at least one additional carbon-based filler selected from carbon nanofibers and carbon fibers, the active material formulation may also comprise an additional carbon-based filler selected from the group consisting of: carbon black, acetylene black, graphite, graphene, activated carbon, and mixtures thereof, with graphene being preferred.

The term "graphene" denotes a flat, separate and individualized sheet of graphite, but also, by extension, an aggregate comprising between one and several tens of sheets and having a flat or more or less corrugated structure. This definition thus covers FLG (Few layers of (Few Layer) graphene), NGP (nano-sized graphene plates), CNS (carbon nanosheets) and (graphene nanoribbons). On the other hand, it excludes carbon nanotubes and nanofibers, which consist of coaxially wound one or more graphene sheets and a stack of turbine layers of these sheets, respectively. Further, the graphene used according to the present invention is preferably not subjected to an additional step of chemical oxidation or functionalization.

The graphene used according to the invention is obtained by chemical vapour deposition or CVD, preferably according to a process using a powdered catalyst based on mixed oxides. Characterized in the form of particles having a thickness of less than 50nm, preferably less than 15nm and more preferably less than 5nm, and a lateral dimension of less than 1 micron, preferably from 10nm to less than 1000nm, more preferably from 50 to 600nm, or even from 100 to 400 nm. Each of these particles generally contains from 1 to 50 lamellae, preferably from 1 to 20 lamellae and more preferably from 1 to 10 lamellae, or even from 1 to 5 lamellae, which can be separated from each other in the form of separate lamellae, for example during sonication.

The sulfur-based material may be elemental sulfur or sulfur-based molecules, such as sulfur-based organic compounds or polymers, or sulfur-based inorganic compounds, or mixtures thereof in all proportions. Sulfur-based inorganic compounds which can be used as sulfur-based materials are, for example, alkali metal anionic polysulfides, preferably of the formula Li₂S_n(wherein n is 1 or more). Preferably, the sulphur-based material comprises elemental sulphur.

Natural sulfur from various sources is commercially available. The sulphur may be used as such or the sulphur may have been purified beforehand according to different techniques, such as refining, sublimation or precipitation. Sulfur or, more generally, sulfur-based materials may also be subjected to a preliminary step of milling and/or screening to reduce the particle size and narrow its distribution. The particle size (particle size) of the powder can vary within wide limits.

Sulfur-based inorganic compounds which can be used as sulfur-based materials are, for example, alkali metal anionic polysulfides, preferably of the formula Li₂S_n(wherein n.gtoreq.1) or a salt thereof.

The sulfur-based organic compound or polymer may be selected from: organic polysulfides, organic polythiolates, including, for example, functional groups such as dithioacetals, dithioketals or trithiocarbonates, aromatic polysulfides, polyethers, polysulfides, salts of polysulfidic acids (polysulfidic acids), thiosulfonates [ -S (O) z-S- ], thiosulfinates [ -S (O) -S- ], thiocarboxylates [ -C (O) -S- ], dithiocarboxylates [ -RC (S) -S- ], thiophosphates, thiophosphonates, thiocarbonates, organometallic polysulfides or mixtures thereof.

Examples of such organosulfur compounds are described in particular in WO 2013/155038.

According to a particular embodiment of the invention, the sulphur-based material is an aromatic polysulphide.

Aromatic polysulfides for the following general formula (I):

wherein:

-R₁to R₉Which may be the same or different, represent a hydrogen atom, -OH or-O^-M⁺A radical, a saturated OR unsaturated carbon-based chain comprising 1 to 20 carbon atoms OR a radical-OR₁₀Wherein R is₁₀Can be an alkyl, arylalkyl, acyl, carboxyalkoxy, alkylether, silyl or alkylsilyl group comprising from 1 to 20 carbon atoms,

-M represents an alkali metal or an alkaline earth metal,

n and n', which may be identical or different, are two integers each 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-based chain of 1 to 20 carbon atoms.

Preferably, in formula (I):

-R₁、R₄and R₇Is a group O^-M⁺，

-R₂、R₅And R₈Is a hydrogen atom, and is a hydrogen atom,

-R₃、R₆and R₉Is a saturated or unsaturated carbon-based chain comprising from 1 to 20 carbon atoms, preferably from 3 to 5 carbon atoms,

n and n' have an average value of about 2,

the average value of p is between 1 and 10, preferably between 3 and 8. (these average values are calculated by the person skilled in the art from proton NMR data and by gravimetric sulfur analysis).

-a is a single bond linking the sulfur atom to the aromatic ring.

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

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

the compounds of the formula (II) are especiallySold by Arkema corporation.

2) Reaction of the compound (II) with a metal derivative containing the metal M, for example an oxide, hydroxide, alkoxide or dialkylamide of this metal, to give the group O^-M⁺。

According to a more preferred variant, R is a tert-butyl or tert-amyl group.

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

The sulfur-based material used in the active material formulation according to the present invention may have various heat of fusion values. The heat of fusion (. DELTA.H)_fus) May preferably be between 70 and 100J.g^-1In the meantime. In particular, the sulfur-based material (e.g., in elemental or polysulfide form) may be characterized by a heat of fusion measured by Differential Scanning Calorimetry (DSC) between 80 ℃ and 130 ℃ during the phase change (melting). After implementation of the preparation method according to the invention, and in particular after incorporation of the carbon-based filler by the melting route, the enthalpy value (Δ H) of the composite material with respect to that of the original sulfur-based material_fus) And decreases.

Further, it is preferable that the S8 content of the sulfur-based material is less than 10 wt% of the sulfur-based material. The S8 content can be measured by DSC.

According to another aspect, the present invention relates to a method for preparing an active material formulation. The method includes the step of contacting a sulfur-based material with a conductive composition.

The contacting step according to the present invention may be performed in a variety of ways. Preferably, the contacting step is selected from: the method includes mixing a sulfur-based material with a conductive composition at a temperature greater than or equal to a melting point of the sulfur-based material, subliming the sulfur-based material onto the conductive composition, and liquid phase depositing the sulfur-based material onto the conductive composition, the sulfur-based material being subsequently dissolved in a suitable solvent.

The present invention provides a method for obtaining an active material formulation with a better combination of a sulfur donating material with particles of a carbon based filler to promote sulfur insertion into the electrochemical reaction, which can contribute to a good maintenance of the operation of the battery over time. The active material according to the present invention may take the form of a solid finished product comprising a mixture of particles, which includes the conductive composition dispersed in a uniform manner in the bulk of the sulfur-based material. In this case, the density of the active material is advantageously greater than 1.4g/cm³Measured according to standard NF EN ISO 1183-1. The density is generally less than 2g/cm³. The porosity is also advantageously less than 40%, preferably less than 20%. The porosity can be determined from the difference between the theoretical density and the measured density.

Preferably, the method for preparing the active material formulation comprises the step of forming a sulfur-carbon composite, said preliminary step of forming the sulfur-carbon composite comprising melting the sulfur-based material and blending the molten sulfur-based material and the carbon-based filler. Such a step enables the formation of a homogeneous mixture.

However, melting (melting) of the mixture is limited to carbon-based fillers (0.05-0.5 g/cm)³) And sulfur (2 g/cm)³) The density difference between them, and therefore it is necessary to add a strong mechanical energy to carry out the mixing, which may be between 0.05 and 1kWh/kg of active material, preferably between 0.2 and 0.5kWh/kg of active material. Thus, it is possible to provideCarbon-based fillers are uniformly dispersed throughout the bulk (through the bulk) and are found not only at the surface of the sulfur-based particles. For this purpose, it is preferred to use compounding units, i.e.equipment conventionally used in the plastics industry for melt blending of thermoplastics and additives to produce composite materials. A process for the preparation of a sulphur-carbon composite via the (by) melt route, which is particularly advantageous in the context of the present invention, is described in WO 2016/102865.

Advantageously, the sulfur-carbon composite is obtained via a manufacturing process comprising the steps of: melting the sulfur-based material and blending the molten sulfur-based material and the carbon-based filler. This melting and blending step can advantageously be carried out by means of a compounding device. Thus, as represented in fig. 1, the method 100 according to the invention may comprise a preliminary step of forming a sulfur-carbon composite, said step of forming a sulfur-carbon composite comprising:

-introducing 110 at least one sulphur-based material and a carbon-based filler into a compounding device,

-optionally, a step 120 of introducing additives,

-performing a compounding step 130 to melt the sulphur-based material, and

blending 140 the molten sulphur-based material and the carbon-based filler.

For this purpose, it is preferred to use compounding devices, i.e. the equipment conventionally used in the plastics industry for melt blending of thermoplastic polymers and additives to produce composite materials. Thus, the active material according to the present invention may be prepared according to a process that also includes recovery 150 of the sulfur-carbon composite obtained in an agglomerated solid physical form.

The introduction step 110 is performed in a compounding device. The sulfur-based material and the carbon-based filler are mixed using a high shear device, such as a co-rotating twin screw extruder or co-kneader. The molten material typically exits the apparatus in an agglomerated solid physical form, for example, in the form of pellets or in the form of rods (which are cut into pellets after cooling).

Examples of co-kneaders which can be used are those sold by Buss AGMDK co-kneader andco-kneaders of the MKS or MX series, all comprising a screw shaft with flights (flight), said screw shaft being located in a heating barrel, optionally containing several sections, the inner wall of which is provided with kneading teeth suitable to work together with the flights to shear said material. The shaft is rotationally driven and is provided with an oscillating movement in the axial direction by a motor. These co-kneaders can be equipped with a system for producing pellets, for example adapted to their outlet orifice, which can comprise an extrusion screw or a pump. The screw length-to-diameter ratio L/D of the cokneaders which can be used according to the invention is preferably from 7 to 22, for example from 10 to 20, while the L/D ratio of the corotating extruders is advantageously from 15 to 56, for example from 20 to 50.

Preferably, the active material formulation further comprises at least one additive selected from the group consisting of: rheology modifiers, binders, ionic conductors, other carbon-based electrical conductors, electrolytes, electron donating elements, or combinations thereof. Thus, the method may include a step 120 of introducing at least one additive. As with the carbon-based filler, the additive(s) may be incorporated into the active material formulation by a melt route, such as during step 120.

These additives are advantageously introduced before or during the compounding step, so as to obtain a homogeneous (homogeneous) formulation of the active material. In this embodiment, the sulfur-based material and the conductive composition then represent 50 to 99 wt.%, preferably 60 to 95 wt.%, relative to the total weight of the active material formulation.

In particular, rheology modifiers, i.e. additives that lower the rheology of the sulfur in molten form, can be added during mixing, before or during the compounding step, to reduce self-heating of the mixture in the compounding device. Such additives are described in patent application WO 2013/178930. Examples that may be mentioned include: dimethyl sulfide, diethyl sulfide, dipropyl sulfide, dibutyl sulfide, trisulfide homologues thereof, tetrasulfide homologues thereof, pentasulfide homologues thereof, hexasulfide homologues thereof, alone or as a mixture of two or more of the above in any ratio.

The amount of rheology modifying additive is generally between 0.01% and 5% by weight, preferably 0.1% to 3% by weight, relative to the total weight of the active material formulation.

The active material formulation may comprise a binder, in particular a polymeric binder. The polymeric binder may also provide a certain amount of dimensional plasticity or flexibility to the electrodes formed from the active material. Advantageously, these binders are introduced before or during the compounding step. In addition, an important role of the binder is also to ensure uniform dispersion of the active material and, for example, the sulfur-carbon composite particles. A variety of polymeric binders may be used in the formulations according to the invention and they may be selected, for example, from: halogenated polymers, preferably fluoropolymers, functional polyolefins, polyacrylonitriles, polyurethanes, polyacrylic acids and derivatives thereof, polyvinyl alcohols and polyethers, and mixtures thereof in any proportion.

Examples of fluoropolymers that may be mentioned include: poly (vinylidene fluoride) (PVDF), preferably in the alpha form, poly (trifluoroethylene) (PVF3), Polytetrafluoroethylene (PTFE), copolymers of vinylidene fluoride with 1 Hexafluoropropylene (HFP) or trifluoroethylene (VF3) or Tetrafluoroethylene (TFE) or Chlorotrifluoroethylene (CTFE), fluoroethylene/propylene (FEP) copolymers, copolymers of ethylene with fluoroethylene/propylene (FEP) or Tetrafluoroethylene (TFE) or Chlorotrifluoroethylene (CTFE), perfluoropropyl vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE), 2,3,3, 3-tetrafluoropropene and copolymers of ethylene with perfluoromethyl vinyl ether (PMVE), or mixtures thereof.

Examples of polyethers which may be mentioned include: poly (alkylene oxides) such as poly (ethylene oxide) (PEO), polyalkylene glycols such as polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), polytetramethylene ether glycol (PTMEG), and the like.

The polymeric binder may also be selected from block copolymers of these polymers, such as copolymers containing PEO/PPO/PEO blocks. More preferably, the polymer binder is PVDF or POE. POE is sometimes used in acetonitrile or isopropanol, and as such PTFE is in suspension in ethanol or water. The most common polymer is still poly (vinylidene fluoride) (PVDF), which is used in a solution of N-methyl-2-pyrrolidone (NMP). The polymer is chemically stable with respect to the organic electrolyte and also electrochemically stable in the potential window of a Li/S battery. It is insoluble in organic solvents, hardly swellable, and therefore enables the electrode to retain its morphology and mechanical strength during cycling.

Possible binders may also be binders of the polysaccharide family, such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC) and the like. Preferably, the binder is PVDF, PEO or CMC.

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

The active material formulation may include an ionic conductor that has a favorable interaction with the surface of the sulfur or sulfur-based molecule to increase the ionic conductivity of the active material. Examples of ionic conductors that may be mentioned include, in a non-limiting manner, organic lithium salts, such as lithium imidazolium salts. Mention may also be made of poly (alkylene oxides) which, in addition to their role as binders, can also provide ionic conductivity properties to the active material.

The active material formulation may also comprise other electrical conductors, advantageously carbon-based electrical conductors, such as carbon black, graphite or graphene, typically in proportions that may range from 1% to 10% relative to the sulfur-based molecule. Preferably, carbon black is used as the electrical conductor. The active material formulation may contain an electron donating element to improve electron exchange during discharge and adjust the length of the polysulfide, which optimizes the charge/discharge cycle of the battery. Elements from groups IVa, Va and VIa of the periodic table of the elements in powder form or in salt form can advantageously be used As electron-donating elements, preferably selected from Se, Te, GeSn, Sb, Bi, Pb, Si or As.

These compounds may be generally added in proportions that may range from 1 to 10% by weight relative to the weight of the sulfur-based material.

The active material formulation may further include an electrolyte saltPreferably, it is selected from: lithium (bis) trifluoromethanesulfonate imide (LiTFSI), lithium 2-trifluoromethyl-4, 5-dicyanoimidazolate (littdi), lithium bis (fluorosulfonyl) imide (LiFSI), lithium hexafluorophosphate (LiPF)₆) Lithium perchlorate (LiClO)₄) Lithium trifluoromethanesulfonate (CF)₃SO₃Li), lithium trifluoroacetate (CF)₃COOLi), lithium dodecafluorododecaborate (Li)₂B₁₂F₁₂) Lithium bis (oxalato) borate (LiBC)₄O₈) And lithium tetrafluoroborate (LiBF)₄). More preferably, the electrolyte liquid solvent comprises LiTFSI.

The compounding step 130 is performed at a temperature above the melting point of the sulfur-based material. In the case of elemental sulfur, the compounding temperature range may be 120 ℃ to 150 ℃. In the case of other types of sulfur-based materials, the compounding temperature depends on the particular material used, the melting point of which is usually provided by the supplier of the material. The residence time will also be adapted to the properties of the sulphur-based material.

This approach allows for efficient (effective) and uniform dispersion of large amounts of carbon-based filler in the sulfur-based material despite the density differences between the ingredients of the active material formulation.

In order to achieve an optimal dispersion of the carbon-based filler in the sulphur-based material in the compounding device, a large amount of mechanical energy must be applied, which is preferably greater than 0.05kWh/kg of material.

In the case of compounding in an extruder, the active material formulation is advantageously obtained in the form of extrudates, the diameter of which may be between 0.5 and 5 mm.

The method may include the step 140 of blending the molten sulfur-based material and the carbon-based filler. The blending can be carried out by any kneading, blending or extrusion device known to those skilled in the art and compatible with the active material formulation, especially with the temperature during the compounding step.

Then, during the milling step 160, the mixture of particles may be milled to obtain a powder free of any particles having a size greater than 100 microns, preferably free of particles having a size greater than 25 microns, to facilitate the electrode manufacturing process. The carbon-based filler is mixed with the sulfur-based molecule(s), in particular with sulfur, preferably via (via) the melt route. The grinding step may be carried out in solid state, in other words in dry form.

The step of grinding the sulfur-carbon composite material may be performed, for example, in a tank mill (horizontal and vertical caged), cavitator, jet mill, fluidized bed jet mill, liquid phase mill, screw disperser, brush mill, hammer mill, ball mill, or by other methods of micronizing solid materials.

Further, the inventors have developed a method of preparing a formulation for manufacturing an electrode from a sulfur-carbon composite, which is capable of improving charge and discharge capacity and improving an interface by performing milling in a liquid-phase solvent including, for example, an electrolyte salt and/or a solid electrolyte. As will be described in detail below, creating a favorable interface from the milling step may allow for improved performance of the active material formulation. More particularly, the milling in the presence of the electrolyte makes it possible to obtain the catholyte directly. The catholyte may then be used to form a cathode.

As represented in fig. 2, the improved grinding method (process) according to the invention comprises the following steps:

introducing 210 a solvent in liquid phase into the milling device,

introducing 220 a sulfur-carbon composite into the grinding device, the sulfur-carbon composite comprising at least one sulfur-based material and a carbon-based filler,

-carrying out a grinding step 230 of the material,

-after said grinding step, producing an active material formulation in the form of a 240 solid-liquid dispersion comprising a sulphur-carbon composite in the form of particles having a median diameter D50 of less than 50 μm.

Steps 210 and 220 prior to grinding step 230 are presented in a certain order in fig. 2. However, in the context of the present invention, the order of introduction of the substances into the mill may vary and this is not to be considered as another invention.

As presented in fig. 2, the method according to the invention comprises a step 210 of introducing a liquid phase solvent into the milling device.

Preferably, the amount of solvent used is such that a solid-liquid dispersion can be formed with a solids weight content of less than 90%, preferably less than 80%, more preferably between 30% and 60%.

The solvent used during the milling step may be one that can be evaporated off prior to the manufacture of the electrode. In this case, the solvent is preferably chosen from liquid-phase solvents having a boiling point of less than 300 ℃, preferably less than or equal to 200 ℃, more preferably less than or equal to 115 ℃, even more preferably less than or equal to 100 ℃. Thus, the solvent may be evaporated after the milling step without denaturing the carbon-sulfur composite.

In this case, the liquid-phase solvent used in the present invention may comprise, for example, at least one protic or aprotic solvent selected from: water, alcohols, ethers, esters, lactones, N-methyl-2-pyrrolidone and dimethyl sulfoxide.

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

Further, preferably, the liquid-phase solvent is degassed before being introduced into the milling device.

As presented in fig. 2, the method according to the invention comprises a step 220 of introducing the sulfur-carbon composite into a milling apparatus.

The sulfur-carbon composite includes at least one sulfur-based material and a carbon-based filler.

Prior to the milling step, the sulfur-carbon composite may be in the form of a solid, or a solid material (form), having a median diameter D50 of greater than 50 μm.

The sulfur-carbon composite used during the grinding step can be obtained by several methods and has a form and dimensions defined by its production path. Advantageously, the sulfur-carbon composite is obtained by a manufacturing process comprising the following steps: melting the sulfur-based material and blending the molten sulfur-based material and the carbon-based filler, preferably in the presence of strong mechanical energy. This melting and blending step can advantageously be carried out with a compounding device. The sulfur-carbon composite is typically in an agglomerated physical form, such as in the form of pellets. In this case, the form of the pellets will depend on the diameter of the holes of the die and the speed of the knife. For example, at least one dimension of the pellets may be between 0.5mm and several millimeters.

Thus, preferably the sulphur-carbon composite is in solid form, such as pellets or granules having a median diameter D50 of greater than 100 μm, preferably greater than 200 μm and more preferably greater than 500 μm.

Advantageously, the sulphur-carbon composite used in the context of the present invention comprises a carbon-based filler infiltrated in a molten sulphur-based matrix, and the carbon-based filler is uniformly distributed throughout the bulk of the sulphur-based material (bulk sulphur-based material), which can be visualized, for example, by electron microscopy. The sulfur-based material/carbon-based filler mixture has a morphology suitable for optimizing the operation of the Li/S battery electrode. Thus, the carbon-based filler is uniformly dispersed throughout the bulk of the particle (a large number of particles), not just found at the surface of the sulfur-based particles.

The active material according to the present invention, i.e., the active material based on the sulfur-carbon composite, may thus provide efficient electrical transmission from the current collector of the electrode and provide an active interface for the electrochemical reaction during operation of the battery.

As represented in fig. 2, the method according to the invention comprises a grinding step 230.

The advantage of milling in the liquid state is that it does not produce too high a porosity in the obtained active material. Thus, the obtained powder has a higher density than the powder obtained by the conventional method.

The grinding step may be carried out, for example, in a tank mill (horizontal and vertical caged), cavitator, jet mill, fluidized bed jet mill, liquid phase mill, screw disperser, brush mill, hammer mill, ball mill, or by other methods of micronizing solid materials.

The milling step is typically carried out over a period of 30 minutes or more. Preferably, the milling step is carried out for 1 hour or more, more preferably at least 2 hours.

Advantageously, the method according to the invention may comprise two successive grinding steps carried out on two different grinding devices.

The trituration step is typically carried out at a temperature below the boiling point of the liquid phase solvent. Advantageously, the grinding step is carried out at a temperature below the melting point of the sulphur-based material. The grinding step is preferably carried out at a temperature lower than 300 ℃, more preferably at a temperature lower than 200 ℃, even more preferably at a temperature lower than or equal to 110 ℃.

Furthermore, in contrast to the prior art processes, the grinding step is preferably carried out at a temperature above 0 ℃. More preferably, it is carried out at a temperature higher than 10 ℃.

Thus, the grinding step is carried out at a temperature between 1 ℃ and 300 ℃, preferably between 5 ℃ and 200 ℃ and more preferably between 5 ℃ and 110 ℃. When the term "between. The grinding step may result in heating of the mixture due to friction caused by the grinding step. Thus, self-heating up to the desired temperature may be acceptable, and the process may then include the step of cooling the mixture, particularly to maintain it at a temperature below the boiling point of the liquid phase solvent used.

If this is necessary, the milling 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 a liquid route.

As presented in fig. 2, the method according to the invention comprises a step 240 of obtaining the formulation in the form of a solid-liquid dispersion produced during the grinding step. Furthermore, the formulation comprises a sulphur-carbon composite in the form of particles having a median diameter D50 of less than 50 μm, and advantageously less than 10% by number of the particles of the dispersion are sulphur particles in elemental form.

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, as well as to increase the charge and discharge capacity of the electrode. Thus, the formulations according to the present invention can provide efficient electrical transmission from the current collector of the electrode and provide an active interface for the electrochemical reaction during operation of the cell.

As represented in fig. 2, the method according to the invention comprises a drying step 250. The drying step 250 enables the production of active material formulations in powder form. The active material formulations obtained from solid-liquid dispersions then advantageously have a moisture content of less than 100 ppm.

This drying step can be carried out, for example, by an atomization step. The active material powder has the common advantage with the formulation, namely improved properties through low content of sulphur in elemental form and/or low oxidation. This powder can then be formulated with conventional additives and used in the dry route.

The active material formulation in powder form according to the present invention comprises particles exhibiting an intimate mixture of carbon-based filler dispersed in a homogeneous manner in a bulk (bulk) of the sulfur-based material. The density of the active material formulation is advantageously greater than 1.6g/cm³Measured according to standard NF EN ISO 1183-1.

It also advantageously has a porosity of less than 20%, which can be determined by the difference between the theoretical density and the measured density. The active material formulation according to the invention, preferably in powder form as characterized previously, advantageously has a porosity of less than 20% and/or greater than 1.6g/cm³Can be used for preparing electrodes, in particular cathodes, of Li/S batteries. The active material typically comprises about 20 to 95 wt%, preferably 35 to 80 wt%, relative to the total formulation of the electrode.

Furthermore, the heat of fusion of the sulfur-based material in the sulfur-carbon composite forming the active material according to the present invention is lower than the heat of fusion of the sulfur-based material seen in formulations or active materials formed according to prior art methods. Thus, preferably, the heat of fusion of the sulfur-carbon composite's sulfur-based material, as measured by differential scanning calorimetry between 80 ℃ and 130 ℃ (e.g., 5 ℃/minute under a stream of nitrogen), is at least 10% less, more preferably at least 15% less, and more preferably at least 20% less than the heat of fusion of the sulfur-carbon composite-forming material. It would not depart from the scope of the present invention if the sulfur-carbon composite did not have the heat of fusion of the sulfur-based material between 80 ℃ and 130 ℃, i.e., in the case where it was amorphous.

Advantageously, the heat of fusion of the sulfur-based material of the sulfur-carbon composite measured by differential scanning calorimetry between 80 ℃ and 130 ℃ (e.g., 5 ℃/min under a stream of nitrogen) is less than 60J.g^-1Preferably less than 55J.g^-1And more preferably less than 50J.g^-1。

According to another aspect, the present invention relates to a catholyte comprising an active material formulation according to the present invention and a binder.

Preferably, the binder is chosen in particular from: acrylic polymers, methacrylic polymers, fluoropolymers, polyethers, polyesters, polysaccharides, such as cellulose and its derivatives, in particular CMC, functional polyolefins, polyethyleneimine, polyacrylonitrile, polyurethane, polyvinyl alcohol, polyvinylpyrrolidone, copolymers thereof, and mixtures thereof.

The catholyte further comprises at least one additive selected from the group consisting of: rheology modifiers, ionic conductors, other carbon-based electrical conductors, electrolytes and electron donating elements. The catholyte may comprise one or more of each of these additives. These additives have been previously described; the catholyte according to the present invention may therefore comprise the previously described additives, especially preferred additives.

The electrolyte is preferably selected from LiNO₂LiFSI, LiTFSI, LiTDI and other Li salts, and mixtures thereof. More preferably, the electrolyte comprises LiFSI, LiTFSI and/or LiTDI. Further, at least a portion of the electrolyte may be an ion conducting ceramic or a solid electrolyte.

The carbon-based electrical conductor is preferably selected from: carbon black, acetylene black, graphite, graphene, carbon nanofibers, carbon fibers, activated carbon, intrinsically conductive polymers, and mixtures thereof. In particular, fibers and/or nanofibers, preferably carbon fibers, are present in the active material formulation according to the invention, but such fibers or nanofibers may also be added to the catholyte again.

Furthermore, the catholyte according to the present invention may comprise a liquid solvent capable of dissolving at least one electrolyte salt, also referred to as electrolyte liquid solvent. For example, the electrolyte liquid solvent may be selected from: monomers, oligomers, polymers and mixtures thereof. In particular, the liquid-phase solvent comprises at least one compound selected from: water, amides, carbonates, ethers, sulfones, fluorine-containing compounds, toluene and dimethyl sulfoxide. The amide is preferably N-methyl-2-pyrrolidone (NMP) or N, N-Dimethylformamide (DMF).

The electrolyte liquid solvent is preferably a solvent suitable for use in a lithium-sulfur battery; in this case, it is not necessary to perform an evaporation step after the milling step, and this allows the cathode to be formulated directly. Thus, preferably, the liquid-phase solvent comprises at least one compound selected from the group consisting of: carbonates, ethers, sulfones, fluorine-containing compounds and toluene.

Carbonates can be used as electrolyte liquid solvents. Ethers in particular allow good dissolution of lithium polysulphides to be obtained and, although ether type solvents generally have a lower dielectric constant than carbonates, provide relatively high ionic conductivity and the ability to solvate lithium ions.

Thus, preferably, the electrolyte liquid solvent is an ether, such as 1, 3-Dioxolane (DIOX) or 1, 2-Dimethoxyethane (DME), or a carbonate ester such as dimethyl carbonate (DMC) or Propylene Carbonate (PC).

The electrolyte liquid solvent may also include a combination of solvents. For example, it may comprise ethers and carbonates. This may allow the viscosity of mixtures comprising high molecular weight carbonates to be reduced.

Preferably, the electrolyte liquid solvent is selected from: 1, 3-Dioxolane (DIOX), 1, 2-Dimethoxymethane (DME), Ethylene Carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), propyl methyl carbonate, Tetrahydrofuran (THF), 2-methyl tetrahydrofuran, methyl propyl propionate, ethyl propyl propionate, methyl acetate, diglyme (2-methoxyethyl ether), tetraglyme, diglyme (diglyme, DEGDME), polyethylene glycol dimethyl ether (PEGDME), Tetraglyme (TEGDME), ethylene carbonate, propylene carbonate, butyrolactone, dioxolane, hexamethylphosphoramide, pyridine, dimethyl sulfoxide, tributyl phosphate, trimethyl phosphate, N-tetraethylsulfamide, sulfone, and mixtures thereof.

More preferably, the electrolyte liquid solvent is selected from: tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl propionate, ethyl propyl propionate, methyl acetate, dimethoxyethane, 1, 3-dioxolane, diethylene glycol dimethyl ether (2-methoxyethyl ether), tetraethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, butyrolactone, dioxolane, hexamethylphosphoramide, pyridine, dimethyl sulfoxide, tributyl phosphate, trimethyl phosphate, N-tetraethylsulfamide, sulfone, and mixtures thereof.

Other solvents such as sulfones, fluorine containing compounds, or toluene may also be used.

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

The invention also relates to the use of the active material formulation as described previously in an electrode, in particular in a Li/S battery cathode. The active material according to the invention makes it possible to improve the electronic conductivity of the electrode formulation, the mechanical integrity of the electrode and thus the operation of the battery over time.

Thus, 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.

To this end, the formulation in the form of a particulate (particulate) mixture may be deposited on a current collector.

The active material formulation may be applied to the current collector as a suspension in a solvent (e.g., water or an organic solvent). The solvent may then be removed, for example by drying, and the resulting structure is blocked to form a composite structure, which may be cut into a desired shape to form a cathode.

In one embodiment, the cathode comprises 1 to 5 wt.% PEO and 1 to 5 wt.% binder selected from gelatin, cellulose (e.g., carboxymethyl cellulose), and/or rubber (e.g., styrene butadiene rubber). Such binders may improve the life of the battery. The use of such a binder may also allow the total amount of binder to be reduced, for example to a level of 10 wt% or less of the total weight of the cathode.

The cathodes described herein can be used in lithium-sulfur batteries.

According to another aspect, the invention provides a lithium/sulphur battery, or lithium-sulphur battery, comprising a cathode as described above.

The lithium/sulfur battery may also include an anode comprising lithium metal or an alloy of lithium metal and an electrolyte.

The electrolyte may be a solid electrolyte or may comprise at least one lithium salt and at least one organic solvent.

Optionally, a separator may be disposed between the cathode and the anode. For example, during assembly of the battery, a separator may be placed in the cathode, and a lithium anode placed on the separator. An electrolyte may then be introduced into the assembled cell to wet the cathode and separator. As a variant, 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 generally includes a porous film of polyolefin (polyethylene, polypropylene). This element is used only in combination with a liquid electrolyte, since the polymer electrolyte or gel-like electrolyte itself already ensures physical separation of the electrodes. When present in a battery of the invention, the separator may comprise any suitable porous membrane or substrate that allows ions to move between the electrodes of the battery. The membrane must be located 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 more than 60%. Suitable membranes include lattices formed from polymeric materials. Suitable polymers include polypropylene, nylon, and polyethylene. Non-woven polypropylene is particularly preferred. A multilayer separator may be used. The separator may include a carbon-based filler. The separator may be Li-Nafion.

As described above, the battery contains an electrolyte. An electrolyte is present or disposed between the electrodes, which allows charge to be transferred between the anode and the cathode. Preferably, the electrolyte wets the pores of the cathode and also wets the pores of, for example, the separator. The organic solvents that can be used in the electrolyte are those described above as electrolyte liquid solvents.

The examples which follow illustrate the invention without, however, limiting it in any way.