Improvement of the shaping properties of a solid sulfide electrolyte for the preparation of all-solid batteries prepared by dry process

Abstract

Improvement of the shaping properties of a solid sulfide electrolyte for the preparation of all-solid-state batteries prepared by the dry process. The present invention relates to a solvent-free process for the preparation of an electrode, or a solid electrolyte layer, comprising the following steps: (a) preparation of a mixture comprising a solid sulfide electrolyte, a fluoropolymer, and fumed silica; and (b) shaping the mixture into a film. The invention also relates to a solvent-free formulation for a solid electrode or electrolyte layer. Figure for abstract: none

Description

Title of the invention: Improvement of the shaping properties of a solid sulfide electrolyte for the preparation of all-solid batteries prepared by the dry process. FIELD OF THE INVENTION

[0001] The present invention relates to the field of energy storage, and more specifically to batteries, particularly lithium batteries. More particularly, the present invention relates to a solvent-free process for preparing an electrode, or a solid electrolyte layer (“SEL” acronym for “Solid Electrolyte Layer”), as well as a formulation suitable for use in such a process, such that they improve the film-forming of formulations comprising the components of the electrode or the SEL. BACKGROUND OF THE INVENTION

[0002] The operation of lithium batteries is based on the reversible exchange of lithium ions between a positive electrode and a negative electrode, separated by a separator containing an electrolyte, with lithium being inserted into the negative electrode during charging operation.

[0003] All-solid-state technology is based on replacing the liquid electrolyte with a non-flammable and more thermally stable solid electrolyte, thus offering increased safety. In all-solid-state batteries, a layer of solid electrolyte acts as a separator, and solid electrolyte particles are present at the cathode and possibly at the anode. The solid electrolyte may, in particular, be a sulfide electrolyte.

[0004] The conventional method for producing solid positive or negative electrodes containing a sulfide electrolyte involves creating a composition in the form of an ink comprising this solid sulfide electrolyte, an active ingredient, a binder, optionally a carbon additive, and a solvent. This ink is then coated onto a strip and dried. The conventional method for preparing SEL involves creating a composition comprising this solid sulfide electrolyte, a binder, and a solvent.

[0005] Given the high reactivity of the solid sulfide electrolyte with a large number of substances, particularly polar solvents, preparing all-solid electrodes based on sulfide electrolyte using a liquid process can lead to significant material degradation problems, resulting in a loss of sulfide electrolyte properties and consequently reduced battery performance. One way to overcome this problem is to produce electrodes without using solvents (dry process). In addition to this non-reactivity, there is a reduction in equipment size (no need for lengthy electrodes). energy-intensive furnace) and production cost (no solvent extraction and recycling step) are observed.

[0006] However, the rheological behavior of the sulfide electrolyte differs between the liquid and dry forms. In the liquid form, the presence of a solvent allows for good dispersion of the sulfide electrolyte in the mixture with the other materials, notably by localizing itself at the interface between the different electrolyte particles, thus breaking up the electrolyte agglomerates. In the dry form, due to the absence of a dispersing medium, the intrinsic properties of the electrolyte powder govern the behavior of the electrolyte (and therefore its ability to disperse well) during its mixing with the various components of the electrode formulation. Generally speaking, the smaller the particle size of a solid electrolyte powder, the greater its specific surface area and the easier it is for it to conduct ionically (beneficial for improving battery performance), but the more difficult it will be to disperse without a solvent.In some cases, it can even be accompanied by a strong compaction property, further reducing its ability to disperse properly without solvent. This phenomenon then leads to problems in large-scale electrode manufacturing, particularly during dry forming steps (uneven weights, material deficiencies in some areas, inhomogeneities in mixtures), especially during a forming step such as calendering, and consequently, battery performance problems.

[0007] Thus, there is a need for the provision of a process to overcome the problems of dispersion and compaction which can be encountered with solid sulfide electrolytes when preparing an electrode, or a layer of solid electrolyte by dry means. BRIEF DESCRIPTION OF THE INVENTION

[0008] The present invention relates to a solvent-free method for preparing an electrode, or a layer of solid electrolyte, comprising the following steps: (a) preparation of a mixture comprising: - a solid sulfide electrolyte, - a fluoropolymer, and - fumed silica; (b) shaping the mixture into a film.

[0009] According to one embodiment, the solid sulfide electrolyte has an average particle size (d50) measured by laser granulometry of less than 10 pm, preferably less than 7 pm.

[0010] Advantageously, the solid sulfide electrolyte is a Li6PS5X type electrolyte, with X = Cl, Br or I, or mixtures thereof.

[0011] According to one embodiment, the fumed silica has a specific surface area (BET) of 175 to 225 m2 / g.

[0012] According to one embodiment, the fluoropolymer is selected from the group consisting of polytetrafluoroethylene (PTFE) and its co-polymers, such as chlorofluoroethylene, perfluoroalkoxy (PFA), polychlorotrifluoroethylene (PCTFE or PTFCE), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene or poly(ethylene-co-tetrafluoroethylene) (ETFE), tetrafluoroethylene perfluoromethyl vinyl ether (MFA), preferably PTFE.

[0013] According to one embodiment, the mixture further comprises a co-binder, preferably selected from the group consisting of thermoplastic polyurethane (TPU), poly(vinylidene fluoride) (PVDF) or its copolymers, cellulose and its derivatives, poly(oxyethylene) (POE), standard or modified cellulose, poly(styrene-butadiene-styrene) (SBS), poly(styrene-ethylene-butadiene-styrene) (SEBS), thermoplastic elastomers (TPE), vulcanized thermoplastics (TPV), polyamides, thermoplastic copolyesters (TPC), polystyrene-β-poly(ethylene-butylene)-β-polystyrene (SEBS), butadiene-acrylonitrile copolymers also known as "nitrile rubbers" (NBR), hydrogenated butadiene-acrylonitrile copolymers, also known as "hydrogenated nitrile rubbers" (HNBR), elastomers, thermoplastics and ethylene-acrylate terpolymers.

[0014] Preferably, the shaping is carried out by calendering, advantageously using a roller calender whose rollers have identical or different rotation speeds.

[0015] According to one embodiment, the mixture comprises from 0.1 to 5%, preferably from 1 to 3.5%, by weight of fumed silica relative to the total weight of the mixture.

[0016] According to one embodiment, the process further comprises, before step (b), a step of fibrillation of the mixture.

[0017] The invention also relates to a solvent-free formulation for an electrode, or solid electrolyte layer comprising: - a solid sulfide electrolyte, - a fluoropolymer, and - fumed silica.

[0018] According to one embodiment, the formulation further comprises an active material and, optionally, an electronically conductive material when it is a formulation for a positive electrode.

[0019] The invention further relates to an electrode or solid electrolyte layer comprising the formulation described above and to an electrochemical element comprising at least one such electrode and / or such a solid electrolyte layer.

[0020] The invention also relates to the use of fumed silica in a solvent-free process for preparing an electrode, or an electrolyte layer, based on solid sulfide electrolyte to facilitate the shaping into a film of formulations comprising the components of the electrode or the solid electrolyte layer.

[0021] Other aspects of the invention are as described below. FIGURES

[0022] [Fig.1] Fig.1 represents a photograph of a solid electrolyte layer formulated according to example 1 (outside the invention) and shaped by calendering.

[0023] [Fig.2] Fig.2 shows a photograph of a solid electrolyte layer of formulation according to example 2 (according to the invention) and shaping by calendering. DETAILED DESCRIPTION OF THE INVENTION

[0024] The inventors discovered that adding fumed silica (also known as smoked silica) to the constituents of a solid sulfide electrolyte electrode or electrolyte layer formulation during their preparation without any solvent (dry process) solves the problems mentioned above. In fact, the addition of fumed silica allows, in particular, the production of continuous and homogeneous films by calendering without degrading the ionic conductivity of the resulting films: the latter remains satisfactory.

[0025] The use of fumed silica in a solvent-free preparation process for an electrode, or a solid electrolyte layer, therefore makes it easier to shape the formulations comprising the components of the electrode or the SEL into a film.

[0026] Thus, the present invention relates to a solvent-free method for preparing an electrode, or a solid electrolyte layer, comprising the following steps:

[0027] (a) preparation of a mixture comprising: - a solid sulfide electrolyte, - a fluoropolymer, and - fumed silica; and

[0028] (b) shaping the mixture into a film.

[0029] The process is solvent-free in that it does not use any organic or aqueous solvent, which would necessitate a drying step. By eliminating the use of any solvent, problems related to reactivity between the solid sulfide electrolyte and solvent residues can be avoided. The mixture is therefore a powdered mixture. This powdered mixture is formed by a dry process, that is, without the presence of any solvent or liquid.

[0030] The preparation of the mixture in powder form can be carried out by simply mixing the components, typically in powder form, under agitation. This can notably be done with a planetary mixer. The mixture preparation step is typically conducted at a temperature below 100°C. According to a particular embodiment, the mixture preparation step can be carried out in several distinct steps.

[0031] The mixture comprises a solid sulfide electrolyte, a fluoropolymer as a binder, and fumed silica. It may further comprise additional ingredients, such as an active material, a conductive element, a co-binder, particularly depending on the intended use (electrode or solid electrolyte layer).

[0032] The solid sulfide electrolyte, the fluoropolymer, the fumed silica and any additional ingredients may be as described below.

[0033] The mixture can then be fibrillated. The mixture subjected to fibrillation may include the additional ingredients.

[0034] Fibrillation refers to a mixture under mechanical stress aimed at fibrillating the fluoropolymer binder.

[0035] Fibrillation can typically be achieved by extrusion with an extruder, or by mixing with an internal mixer or a planetary mixer. The fibrillation of the fluoropolymer can be total or partial.

[0036] The term "extrusion" refers to a thermomechanical process by which the mixture is forced through a sleeve under the action of pressure and heat.

[0037] The extrusion step can be adapted according to several parameters, such as the mixing temperature, the type of screw profile of the extruder, the type of die of the extruder, the rotation speed and / or the length of the screws.

[0038] In some embodiments, fibrillation can be carried out with a single- or twin-screw type extruder, preferably a co-rotating twin-screw extruder.

[0039] The screw profile used in the extruder is generally of the shear type to fibrillate the fluoropolymer within the extruder. The screw profile may contain one or more mixing zones. The number of mixing zones typically depends on the number of feed zones. The position of the mixing zones in the extruder generally depends on the number of material feed zones. A mixing zone may be added after each material feed zone.

[0040] The screw rotation speed is the same along its entire length. It is generally recommended to rotate it between 100 rpm and 1000 rpm, particularly between 100 and 750 rpm. The screw rotation speed is generally adjusted according to the desired material flow rate at the extruder outlet. The lower the screw rotation speed, the lower the output flow rates. Note that lower rotation speeds result in longer residence times in the extruder. In such a case, if the flow rate If the material input is high, there is a risk of clogging the extruder. In the case of high screw rotation speeds, output flow rates may fluctuate if the input material flow rates are too low.

[0041] The fibrillation step can advantageously be carried out at a temperature ranging from 40°C, or preferably 60°C, to the degradation temperature of the fluoropolymer, particularly when a co-binder is present between the melting temperature of the co-binder and the melting temperature of the fluoropolymer under the extrusion conditions, it being understood that the degradation and / or melting temperatures of the fluoropolymer under the extrusion conditions may be reduced due to the mechanical stresses exerted. By way of illustration, for PTFE, the degradation temperature is approximately 350°C (under shear) and the melting temperature is approximately 330°C (this value may vary depending on the grade of PTFE), it being understood that, due to the stresses exerted, the extrusion temperature is preferably below 260°C.

[0042] In the case where fibrillation is carried out by an internal mixer, the same conditions as those described for extrusion can be implemented.

[0043] The mixture obtained at the end of the fibrillation step is typically in the form of granules, an agglomerated powder or a solvent-free paste.

[0044] In one embodiment, the mixture obtained at the end of the fibrillation step may be subjected to a grinding step before the shaping step.

[0045] The shaping of the mixture into a film is carried out starting from the mixture, which may be fibrillated. This shaping is typically achieved by calendering, for example, using a heated roller calender, typically having a different roller speed, or an external roller mixer. Problems with solvent-free formulations for electrodes or solid electrolyte layers arise particularly during such a shaping step. The present inventors have thus observed that solvent-free formulations (or "powder formulations" or "dry formulations") for electrodes or solid electrolyte layers are not suitable for dry shaping in the absence of fumed silica.

[0046] More specifically, a heterogeneous densification phenomenon has been observed in a mixture in the form of an agglomerated powder containing a solid sulfide electrolyte and formed into a film, particularly for formulations containing solid sulfide electrolyte with specific surface areas of at least 5-10 m² / g. This phenomenon is significantly amplified as the specific surface area of ​​the solid sulfide electrolyte increases. Furthermore, this phenomenon is favored when the force levels applied to the adjacent rollers of the calender are high and can be encountered even for forces as low as 20 N.

[0047] Similarly, the shear rate applied to form such a mixture from powder into a film plays a role in the occurrence of this heterogeneous densification phenomenon: film heterogeneity problems appear at high shear rates. The shear rate is defined as the speed difference between two adjacent rollers of a calender. The greater the speed difference between the rollers, the greater the shear rate applied to the material. Thus, the aforementioned heterogeneous densification phenomena can be amplified as the shear rate increases (sometimes even above a shear rate of 85%).It is worth mentioning that if the shear rate applied to a powder mixture containing a solid sulfide electrolyte is too low (a level that depends on the grade of solid electrolyte and its specific surface area), it is possible that no film may be produced.

[0048] Finally, although the temperature of shaping the powder and the rollers can sometimes have a beneficial effect on the behavior of the powder, these parameters can sometimes worsen the compaction phenomenon.

[0049] Solvent-free formulations for electrode, or solid electrolyte layer, according to the invention, comprising a solid sulfide electrolyte, a fluoropolymer, and fumed silica, make it possible to remedy all of the aforementioned problems encountered.

[0050] Following the shaping step, the film thus obtained can then be deposited either on a current collector to form an electrode or, for a SEL, be deposited on a support such as a liner to then be transferred onto an electrode or directly onto a negative or positive electrode.

[0051] The process according to the invention therefore typically includes a step of depositing the film thus obtained. Solid sulfide electrolyte#

[0052] The term “solid sulfide electrolyte” refers to solid sulfur-based electrolytes typically used for the manufacture of all-solid-state batteries.

[0053] The solid sulfide electrolyte used in the context of the present invention typically has an average particle size (d50) measured by laser granulometry of less than 10 pm, preferably less than 7 pm. According to one embodiment, the solid sulfide electrolyte has an average particle size (d50) ranging from 0.1 pm to 10 pm, preferably from 0.3 pm to 7 pm, more preferably from 0.3 pm to 5 pm, and even more preferably from 0.3 pm to 3 pm.

[0054] The average particle size (d50) is understood to be the diameter (equivalent spherical diameter) for which 50% by volume of the particles (primary particles, i.e. particles isolated from each other and therefore not agglomerated) of the sample have a diameter less than or equal to said diameter d50.

[0055] By way of example, the solid sulfide electrolyte may be chosen from: • sulfide electrolytes of the halide or chalcogenide family; • the set of phases [(Li2S)y (Li2O)t(P2S5)i_y_t](i_z)(LiX)z, with X representing one or more halogen elements; 0 <y<l; 0<z<l; 0<t< 1 ; • compounds having an argyrodite structure such as Li6PS5X, with X = Cl, Br or I or mixtures thereof, or Li7P3Sn; • sulfide electrolytes having the crystallographic structure equivalent to the compound LiioGeP2Si2 including for example substitutions, dopings and / or vacancies; • Li3PS4.

[0056] Preferably, the solid sulfide electrolyte is a Li6PS5X type electrolyte, with X = Cl, Br or I or mixtures thereof. Pyrogenated silica

[0057] The fumed silica is preferably fumed silica.

[0058] The fumed silica used in the present invention presents typically a specific surface area (BET) of 175 to 225 m2 / g.

[0059] Preferably, the fumed silica is a hydrophilic fumed silica having a specific surface area (BET) of 175 to 225 m2 / g. The specific surface area is measured by absorption of a gas (nitrogen) using the BET method (Brunauer, Emett and Teller).

[0060] Preferably, the fumed silica used in the context of the present invention typically has an average particle size (d50) measured by laser granulometry of less than 1 pm, preferably between 1 nm and 100 nm, more preferably between 2 nm and 80 nm.

[0061] The average particle size (d50) is understood to be the diameter (equivalent spherical diameter) for which 50% by volume of the particles (primary particles, i.e. particles isolated from each other and therefore not agglomerated) of the sample have a diameter less than or equal to said diameter d50.

[0062] Examples of pyrogenated silica useful in the context of the present invention include, but are not limited to, Aerosil® 200 from Evonik or Cabosil® from Cabot.

[0063] The mixture generally comprises from 0.1 to 5%, preferably from 1 to 3.5%, by weight of fumed silica relative to the total weight of the mixture. Fluoropolymer

[0064] The term "fluoropolymer" refers to a fluorinated polymer whose repeating unit is a fluorocarbon, comprising multiple carbon-fluorine bonds. The fluoropolymer is used as a binder.

[0065] The fluoropolymer is preferably selected from the group consisting of polytetrafluoroethylene (PTFE) and its co-polymers, such as chlorofluoroethylene, perfluoroalkoxy (PFA), polychlorotrifluoroethylene (PCTFE or PTFCE), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene or poly(ethylene-co-tetrafluoroethylene) (ETFE), tetrafluoroethylene perfluoromethyl vinyl ether (MFA).

[0066] Preferably, the fluoropolymers are of the fibrillable type. The term "fibrillable" refers to types of fluoropolymers that are capable of fibrillating, that is, that can form a network of fibers in the mixture. These types of fluoropolymers can be of different shapes and / or grades.

[0067] Preferably, the fluoropolymer is PTFE.

[0068] Preferably, the PTFE used in the context of the present invention has Typically, the average particle size (d50) measured by laser granulometry is less than 700 pm, preferably between 200 pm and 650 pm. In this case, it typically refers to the average size of secondary particles (secondary particles, i.e., agglomerates of primary particles).

[0069] The average particle size (d50) is understood to be the diameter (equivalent spherical diameter) for which 50% by volume of the particles in the sample have a diameter less than or equal to said diameter d50. Additional ingredients

[0070] The mixture may include a co-binder.

[0071] The term "co-binder" refers to a material that provides the electrode with cohesion between its various components and ensures its mechanical stability on the current collector, and / or provides the electrode with a certain degree of flexibility for its implementation in the cell. More specifically, the co-binder ensures cohesion between the different components. The co-binder can be amorphous or semi-crystalline.

[0072] The co-binder is preferably selected from the group consisting of thermoplastic polyurethane (TPU), poly(vinylidene fluoride) (PVDF) or its copolymers, cellulose and its derivatives, poly(oxyethylene) (POE), standard or modified cellulose, poly(styrene-butadiene-styrene) (SBS), poly(styrene-ethylene-butadiene-styrene) (SEBS), thermoplastic elastomers (TPE), vulcanized thermoplastics (TPV), polyamides, thermoplastic copolyesters (TPC), polystyrene-β-poly(ethylene-butylene)-β-polystyrene (SEBS), butadiene-acrylonitrile copolymers also known as "nitrile rubbers" (NBR), hydrogenated butadiene-acrylonitrile copolymers also known as "hydrogenated nitrile rubbers" (HNBR), the Elastomers, thermoplastics and ethylene-acrylate terpolymers. More specifically, the co-binder is chosen from HNBR, POE, PVDF and its copolymers, cellulose and its derivatives.

[0073] In the preparation of an electrode, the mixture typically includes an active electrode material. The active electrode material can be chosen from among electrochemically active materials. It depends in particular on the type of electrode (positive or negative), the nature of the solid sulfide electrolyte, and / or the type of battery considered.

[0074] The active material of the positive electrode is not particularly limited. It can be chosen from the following groups or mixtures thereof:

[0075] - nickel-manganese-cobalt (NMC) type compounds, in particular oxides lamellar with a high nickel content;

[0076] - nickel-cobalt-aluminium (NCA) type compounds.

[0077] Preferably, the active material of the positive electrode used in the context of the present invention typically has an average particle size (d50) measured by laser particle size analysis of 1 µm to 15 µm. In this case, it typically refers to the average size of secondary particles (secondary particles, i.e., agglomerates of primary particles).

[0078] The average particle size (d50) is understood to be the diameter (equivalent spherical diameter) for which 50% by volume of the particles in the sample have a diameter less than or equal to said diameter d50.

[0079] According to one embodiment, particularly in the context of the preparation of a positive electrode, the ratio of the average particle size between the active material and the solid sulfide electrolyte (d50 of the active material particles / d50 of the solid sulfide electrolyte particles) is between 1 and 5.

[0080] The active material used in the context of the present invention may be monocrystalline or polycrystalline. In such an embodiment, the solid sulfide electrolyte to be used in the context of the present invention may be judiciously adapted according to the nature of the active material.

[0081] In the context of preparing a positive electrode, the mixture may include a conductive element. It may be chosen from electronically conductive materials, such as graphite, carbon black, more particularly activated or unactivated carbon black, acetylene black, soot, graphene, carbon fibers, carbon nanotubes or a mixture thereof.

[0082] In the context of preparing an electrode, the mixture may further include one or more additives chosen from lubricants such as oils or waxes or graphite.

[0083] The mixture may also include a carbon additive. This additive is distributed within the electrode so as to form an electronic percolating network between the active material and the current collector. When present, the carbon additive may comprise up to approximately 10% by weight.

[0084] In the context of preparing a solid electrolyte layer, the mixture generally comprises, relative to the total weight of the mixture, from 75 to 99%, preferably from 85 to 99%, by weight of solid sulfide electrolyte; from 0.1 to 10%, preferably from 0.1 to 3%, by weight of fluoropolymer, preferably PTFE; 0.1 to 5%, preferably 1 to 3%, by weight of fumed silica; and optionally 1 to 10%, preferably 1 to 3% by weight, of co-binder.

[0085] In the preparation of an electrode, the mixture generally comprises, relative to the total weight of the mixture, from 45 to 95%, preferably from 55 to 90% active ingredient; from 5 to 50%, preferably from 8 to 35%, by weight of solid sulfide electrolyte; from 0.1 to 5%, preferably from 0.5 to 3.5%, of fluoropolymer, preferably PTFE; from 0.1 to 5%, preferably from 0.5 to 3.5%, by weight of fumed silica; optionally from 0.5 to 5%, preferably from 0.5 to 3.5% by weight, of co binding; and optionally from 0.01 to 5%, preferably from 0.1 to 3.5% by weight, of electronic conductor.

[0086] The present invention also relates to mixtures useful in the process of the invention. Thus, the present invention also relates to a powder formulation for preparing an electrode, or solid electrolyte layer, the formulation comprising: a solid sulfide electrolyte, a fluoropolymer, and fumed silica.

[0087] The formulations may further include additional ingredients as previously described.

[0088] The components of the formulations of the invention (nature and proportions) may be as previously described.

[0089] The formulations are useful for the preparation of electrodes or solid electrolyte layers.

[0090] Thus, the present invention also relates to electrodes or electrolyte layers comprising a formulation according to the invention.

[0091] The electrode can consist of a conductive support used as a current collector which is coated with the formulation according to the invention in a shaped form.

[0092] The term "negative electrode" refers to the electrode functioning as the anode when the battery is discharging, and as the cathode when the battery is charging. The anode is defined as the electrode where an electrochemical oxidation reaction (electron emission) takes place, while the cathode is the site of reduction. The term "negative electrode" also refers to the electrode from which electrons are released and from which cations (Li+) are released during discharge.

[0093] The term "positive electrode" refers to the electrode where electrons enter, and where discharged cations (Li+) arrive.

[0094] The term "current collector" refers to an element such as a pad, plate, sheet or other, made of conductive material, connected to the positive or negative electrode, and ensuring the conduction of the flow of electrons between the electrode and the terminals of the battery.

[0095] The current collector is preferably a two-dimensional conductive support such as a solid or perforated metal strip.

[0096] In the case of the positive electrode, the current collector is typically an aluminum strip, which can be covered with a coating comprising a carbon additive.

[0097] The present invention also relates to an electrochemical element comprising at least one electrode and / or solid sulfide electrolyte layer comprising a formulation according to the invention.

[0098] The expression "electrochemical element" refers to an elementary electrochemical cell consisting of the assembly "positive electrode / solid electrolyte layer / negative electrode", allowing the electrical energy supplied by a chemical reaction to be stored and released in the form of a current.

[0099] Electrochemical elements can be adapted to different battery technologies and types of electrolytes.

[0100] The present invention also relates to an electrochemical module comprising the stacking of at least two elements according to the invention, each element being electrically connected with one or more other element(s).

[0101] The term “module” therefore refers here to the assembly of several electrochemical elements, the assemblies being able to be in series and / or parallel.

[0102] The present invention also relates to a battery comprising one or more modules according to the invention.

[0103] The term “battery” or accumulator refers to the assembly of one or more modules according to the invention. EXAMPLES Material

[0104] Solid sulfide electrolyte

[0105] Pyrogenated silica: Aerosil® 200 supplied by Evonik

[0106] Fluoropolymer type binder: PTFE supplied by Chemours.

[0107] Example 1 (outside the scope of the invention): Preparation of a solid electrolyte layer

[0108] A formulation for SEL was prepared by mixing a solid sulfide electrolyte (99% by weight) and a fluoropolymer binder (1% by weight). The mixing was carried out in a planetary mixer to ensure homogeneous distribution of the different components. The introduction of the different components into this mixer can be done either all at once or in several stages.

[0109] The assembly was then fibrillated.

[0110] The assembly was then calendered in a heated 2-roll calender (between 80 and 130°C).

[0111] During the shaping of the formulation by calendering, a discontinuous film characterized by missing material areas and areas of non-homogeneous basis weights was obtained ([Fig.1]).

[0112] Example 2 (according to the invention): Preparation of a solid electrolyte layer

[0113] A formulation for SEL was prepared by mixing a solid sulfide electrolyte (97% by weight), a fluoropolymer binder (1% by weight), and fumed silica (2% by weight). The mixture was prepared in a paddle mixer to ensure homogeneous distribution of the components. The introduction of the components into this mixer can be done either all at once or in several stages.

[0114] The assembly was then fibrillated.

[0115] The assembly was then calendered in a heated 2-roll calender (between 80 and 130°C).

[0116] During the shaping of the formulation by calendering, a continuous film of homogeneous density was obtained ([Fig.2]).

[0117] The film obtained exhibits satisfactory ionic conductivity.

Claims

Demands

1. A solvent-free process for preparing an electrode, or a solid electrolyte layer, comprising the following steps: (a) preparing a mixture comprising: - a solid sulfide electrolyte, - a fluoropolymer, and - fumed silica; (b) shaping the mixture into a film.

2. A method according to claim 1 wherein the solid sulfide electrolyte has an average particle size (d50) measured by laser granulometry of less than 10 pm, preferably less than 7 pm.

3. A process according to claim 1 or 2 wherein the solid sulfide electrolyte is a Li6PS5X type electrolyte, with X = Cl, Br or I, or mixtures thereof.

4. A process according to any one of claims 1 to 3 wherein the fumed silica has a specific surface area (BET) of 175 to 225 m2 / g.

5. A process according to any one of claims 1 to 4 wherein the fluoropolymer is selected from the group consisting of polytetrafluoroethylene (PTFE) and its co-polymers, such as chlorofluoroethylene, perfluoroalkoxy (PFA), polychlorotrifluoroethylene (PCTFE or PTFCE), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene or poly(ethylene-co-tetrafluoroethylene) (ETFE), tetrafluoroethylene perfluoromethyl vinyl ether (MFA), preferably PTFE.

6. A process according to any one of claims 1 to 5, wherein the mixture further comprises a co-binder, preferably the co-binder being selected from the group consisting of thermoplastic polyurethane (TPU), poly(vinylidene fluoride) (PVDF) or its copolymers, cellulose and its derivatives, poly(oxyethylene) (POE), standard or modified cellulose, poly(styrene-butadiene-styrene) (SBS), poly(styrene-ethylene-butadiene-styrene) (SEBS), thermoplastic elastomers (TPE), vulcanized thermoplastics (TPV), polyamides, thermoplastic copolyesters (TPC), polystyrene-β-poly(ethylene-butylene)-β-polystyrene

7.

8.

9.

10.

11.

12.

13.

14. (SEBS), butadiene-acrylonitrile copolymers also known as "nitrile rubbers" (NBR), hydrogenated butadiene-acrylonitrile copolymers, also known as "hydrogenated nitrile rubbers" (HNBR), elastomers, thermoplastics and ethylene-acrylate terpolymers. A method according to any one of claims 1 to 6 in which the shaping is carried out by calendering. A process according to any one of claims 1 to 7 wherein the mixture comprises from 0.1 to 5%, preferably from 1 to 3.5%, by weight of fumed silica relative to the total weight of the mixture. A process according to any one of claims 1 to 8 further comprising, prior to step (b), a fibrillation step of the mixture. A solvent-free formulation for an electrode, or a solid electrolyte layer comprising: - a solid sulfide electrolyte, - a fluoropolymer, and - fumed silica. Formulation according to claim 10 further comprising an active substance and optionally an electronically conductive material when it is a formulation for a positive electrode. Electrode or solid electrolyte layer comprising a formulation according to claim 10. Electrochemical element comprising at least one electrode and / or a solid electrolyte layer according to claim 12. Use of fumed silica in a solvent-free preparation process of a solid sulfide electrolyte electrode or electrolyte layer to facilitate film forming of formulations comprising the components of the solid electrolyte electrode or layer.

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