Method for solution synthesis of lithium argyrodite particles

Abstract

The present invention relates to a method for synthesis of particles of lithium argyrodite of formula Li7-(a+b)PS6-(a+b+c)OcXaQb, where X and Q are two different halogenated elements selected from F, Cl, Br, I; O is an oxygen atom, where 1≤a+b<2, c is between 0 and 0.25, limits included, a and b not being simultaneously zero, from a lithium reagent Li2Sx, where x is between 1 and 8, a phosphorus reagent Rp selected from P2S5, P4S10, P4S9 and P4S9+n, where n is between 0 and 1, and a halogenated compound selected from LiX and PSX3; and an optional phosphorus-containing or halogen-containing oxygenated reagent selected from P2O5, LiCIO4, LiBrO4, LilO4, by formation of an intermediate solvate-complex compound Li3PS4 solvent, centrifugation, redispersion of the centrifuged phase in an anhydrous solvent, then filtration and washing of the intermediate compound, drying and heat treatment.

Description

[0001]Method for the synthesis in solution of lithium argyrodite particles Technical field The present invention relates to the field of electrochemical energy storage via lithium batteries, more particularly all-solid-state batteries using an inorganic phase of the argyrodite type as solid electrolyte. The invention relates more particularly to the preparation in solution of argyrodite phases and aims to propose a relevant method in terms of product quality, preparation time and industrial extrapolation. Prior art The development of industrializable methods for the preparation of argyrodite phases having good ionic conduction properties is essential for the development of all-solid-state batteries. Furthermore, in order to be viable, these preparation methods must be able to be extrapolated to the industrial scale at an acceptable cost.Initially, argyrodite phases were obtained by solid-state fusion-quenching preparation methods, as described for example in patent applications and patents US 20170222257A1, US8075865 BB, US09899701 B2. These are time-consuming and difficult to extrapolate to the industrial scale. More recently, preparation methods by mechanosynthesis have been described and generally make it possible to obtain smaller micrometric particles than by fusion-quenching methods with good conductivity. These methods are now the majority and involve grinding sequences lasting several days, followed by a high-temperature heat treatment, as described in particular in patent applications and patents US11264642 BB, CN113097560 A, US11245131 BB, US11699809 B2, as well as in the publication Phys. Status Solidi A208, No. 8 (2011).Wet milling methods are also described and allow to reduce the milling time and the particle size, as described in patent applications WO2022162085 A, CN113410513 A, CN109638347 A, US11258057 BB. Mechanosynthesis techniques require equipment, for example planetary mills, which are not extrapolable to the industrial scale. Alternative preparation methods in solution have also been described. For example, the authors of ACS Energy Lett. 2019, 4, 265−270 describe the method of preparing lithium argyrodite (LiPSX) via the formation of an intermediate compound Li3PS4∙2THF in a tetrahydrofuran THF solvent (24h at room temperature) and then adding a solution comprising LiX (I, Br and Cl) and Li2S in ethanol. After stirring for 1 night, the solution is evaporated under reduced pressure and then dried under reduced pressure at 140°C for 20 hours.Finally, the powder is densified by pressing and annealed at 550°C / 6h under reduced pressure. Other patents and patent applications describe the preparation of argyrodites via reaction of Li2S, P2S5 and LiX in a polar solvent at room temperature (US10777846 BB; US20210242493 A1, CN114455613 A, US10777846 BB). The solvents can be, for example, alcohols, carbonates, esters, ethers, nitriles or mixtures. After evaporation under reduced pressure of the solvent (25-50°C for 1 to 3h), a powder is recovered and preferably dried under reduced pressure (several drying sequences can be used). This is then heat treated between 350°C and 550°C for 1 to 5 hours.Other methods of preparation in solution have been developed to attempt to accelerate the reaction kinetics, in particular by varying the operating conditions, such as temperature, pressure, stirring method and solvent combination, see in particular patent application WO2021 / 099625 which proposes cooling to -80°C, or patent US10879559 which combines two solvents: a polar solvent and a saturated or unsaturated hydrocarbon. Summary of the invention Surprisingly, the Applicant has discovered that it is possible to prepare lithium argyrodite particles in solution according to a particular method not involving expensive equipment or steps, with short reaction times, therefore extrapolable to the industrial scale. The invention relates to a process for the synthesis of lithium argyrodite particles of formula Li. 7‐(a+b) PS 6‐(a+b+c) O c X a Q bwith X and Q two distinct halogenated elements chosen from F, Cl, Br, I; O the oxygen atom, with 1≤a+b<2, c between 0 and 0.25, limits included, a and b not being simultaneously zero, from a lithium reagent Li2S x with x between 1 and 8, a phosphorus reagent Rp chosen from P2S5, P4S 10 , P4S9 and P4S 9+nwith n between 0 and 1, and a halogenated compound chosen from LiX and PSX3; and an optional phosphorus-containing or halogenated oxygenated reagent chosen from P2O5, LiClO4, LiBrO4, LiIO4 comprising at least the following steps under an inert atmosphere: A) Contacting the lithium reagent and the halogenated compound and the optional halogenated oxygenated reagent, previously suspended in at least one first polar solvent (solvent 1), with a suspension containing at least the phosphorus-containing reagent and the optional phosphorus-containing oxygenated reagent in at least one second polar solvent (solvent 2, of identical or different nature) at a temperature between 50 and 150°C and formation in suspension under reflux of an intermediate compound in the form of a solvato-complex Li3PS4∙solvent in a mixture with the other solid reagents Li2Sx and LiX and the optional oxygenated reagent,the solvent 1 / solvent 2 volume ratio being between 1 and 4, preferably between 0.5 and 1.5, the relative proportions of the different reagents being chosen stoichiometrically with respect to the formula Li, 7‐(a+b) PS 6‐(a+b+c) O c X a Q b of the final compound in the form of lithium argyrodite particles; B) Centrifugation, redispersion of the centrifuged phase in a third anhydrous solvent, of the same or different nature as said first and second solvents, then filtration and washing of said intermediate compound; C) Drying at a temperature between 25°C and 150°C for a period of between 1 hour and 10 hours. D) Heat treatment at a temperature between 300 and 600°C and a period of between 1 and 10 hours. According to one embodiment, we have 1≤a+b≤1.8, in particular 1≤a+b≤1.6, and preferably 1≤a+b≤1.5. According to a first embodiment, in step A): A1) the lithium reagent Li2Sx, preferably Li2S, the halogenated compound (LiX or PSX3, preferably LiX) and the optional halogenated oxygenated reagent can be dispersed with stirring in a first polar solvent (solvent 1) at a mass concentration of lithium reagent Li2S xin the solvent of between 10 g / L and 100 g / L, preferably between 30 g / L and 70 g / L and a mass concentration of halogenated compound LiX or PSX3 in the solvent of between 1 g / L and 100 g / L, preferably between 5 g / L and 80 g / L, and a mass concentration of halogenated oxygenated reagent of between 0.1 and 10 g / L, and the suspension obtained can be heated between 25°C and 50°C, preferably between 30°C and 40°C; A2) then the phosphorus reagent Rp can be dispersed with stirring in a second polar solvent (solvent 2), at a mass concentration of phosphorus reagent in the solvent of between 10 g / L and 100 g / L, preferably between 30 g / L and 80 g / L, even more preferably between 35 g / L and 70 g / L, the suspension obtained being heated between 50°C and 150°C, preferably between 90°C and 110°C; A3) the solution of lithium reagent and halogenated compound can be gradually added,preferably Li2S and LiX, in the suspension of phosphorus reagent, preferably P2S5, activated at temperature for a period of between 1 min and 6 min, preferably between 2 and 4 min and the resulting suspension is kept stirring at reflux for a period of between 1 and 24 hours, preferably between 2 and 8 hours under an inert atmosphere. In a second embodiment, in step A): A1) a first part of the lithium reagent Li2Sx, preferably Li2S, and the phosphorus reagent, preferably P2S5, can be dispersed with stirring in a first polar solvent (solvent 1) at a mass concentration of lithium reagent (preferably Li2S) in the solvent of between 3 g / L and 30 g / L, preferably between 5 g / L and 20 g / L and a mass concentration of phosphorus reagent (preferably P2S5) in the solvent of between 10 g / L and 100 g / L, preferably between 30 g / L and 80 g / L,even more preferably between 35 g / L and 70 g / L, and the suspension obtained can be heated between 25°C and 50°C, preferably between 30°C and 40°C, to form a solution; A2) a second part of the lithium reagent Li2Sx and the halogenated compound LiX or PSX3 can be dispersed with stirring in a second polar solvent (solvent 2) at a mass concentration of lithium reagent Li2S, x in the solvent between 10 g / L and 80 g / L, preferably between 5 g / L and 70 g / L and a mass concentration of halogenated compound LiX or PSX 3 between 1 g / and 100 g / L, preferably between 5 g / L and 80 g / L and the suspension obtained can be heated between 50°C and 150°C, preferably between 90°C and 110°C; A3) then the solution of lithium reagent and phosphorus reagent (preferably Li2S and P2S5) can be gradually added to the suspension of lithium reagent and halogenated compound (preferably Li2S + LiX), for a period of between 1 min and 6 min, preferably between 2 and 4 min and the resulting suspension can be kept stirring at reflux for a period of between 1 and 24 h, preferably between 2 and 8 h under an inert atmosphere.Said intermediate compound in the form of a solvato-complex can be recovered in the form of a wet powder by centrifugation at a speed of between 1000 and 10,000 rpm for a period of between 5 and 30 min, redispersion in a third anhydrous solvent, then washing on a frit with an identical or different anhydrous solvent. The drying of step C) can be carried out under reduced pressure of between 10. ‐2 and 10 ‐3 mbar at a temperature between 40°C and 80°C for a period between 2h and 6h. The drying of step C) can be followed by a heat treatment step D) carried out in a crossed-bed reactor under an inert gas flow or under reduced pressure between 10-2 and 10-3 mbar. The inert gas can be argon or nitrogen or a mixture of the two and the gas flow rate can be between 1 L / g / h and 15 L / g / h, preferably between 8 and 12 L / h / g. The Li2S reagent xcan be pretreated before suspension by mechanical grinding in a dry process or in solution, by dissolution-precipitation in a solvent. The polar solvent, whether the first solvent (solvent 1) or the second solvent (solvent 2), can be chosen from cyclic or linear ethers, esters, nitriles, alcohols, thiols. The synthesis process according to the invention in which X=Cl, a =1, b=0, c=0 makes it possible to obtain an argyrodite phase Li6PS5Cl. The synthesis process according to the invention in which X=Cl, a =1.5, b=0, c=0 makes it possible to obtain an argyrodite phase Li 5,5 PS4.5Cl 1,5 The synthesis process according to the invention in which X=Cl Q=Br, a =0.5, b=0.5, c=0 makes it possible to obtain an argyrodite phase Li6PS5Cl 0,5 Br 0,5 The invention also relates to an argyrodite phase Li6PS5Cl, an argyrodite phase Li 5,5 PS4.5Cl 1,5, Li6PS5Cl 0,5 Br 0,5, in particular as obtained by the process according to the invention. The invention also relates to the use of these phases to form part of a solid electrolyte, in particular with a view to making electrochemical devices of the battery type, and these devices integrating them. List of figures Figure 1 represents a block diagram of the synthesis steps according to the invention. Figure 2 represents the Raman spectrum of the Li6PS5Cl phase obtained in example 1. Figure 3 represents the diffractogram of the Li6PS5Cl phase obtained in example 1. Figure 4 represents the SEM image of the Li6PS5Cl particles obtained in example 1. The Raman spectra are expressed as RAMAN displacement in cm ‐1on the abscissa and in arbitrary units (au) on the ordinate. SEM means Scanning Electron Microscope. The diffractogram represents, on the ordinate, arbitrary units (au). Description of the embodiments The present invention relates to a new method for preparing argyrodite phases of formula Li 7‐(a+b) PS 6‐(a+b+c) O c X a Q b with X and Q two distinct halogenated elements chosen from F, Cl, Br, I; O the oxygen atom, with 1≤a+b<2, c between 0 and 0.25, limits included, a and b not being simultaneously zero, said synthesis method allowing short reaction times and the possibility of being extrapolated to an industrial scale. When c=0 the argyrodite phase is of formula Li 7‐(a+b) PS 6‐(a+b) X a Q b.Reagents The reagents used in the argyrodite synthesis process according to the invention are as follows. For the lithium reagent, the reagents are preferably Li2S, Li2S x with x between 2 and 8. Throughout the description, for the sake of simplification, the lithium reagent is referred to as Li2S x with x between 1 and 8. For the phosphorus reagent, the reagents are preferably P2S5, P4S 10 , P4S9 and P4S 9+nwith n between 0 and 1. For the phosphorus-containing oxygenated reagent, the reagent is preferably P2O5. For the halogenated compound type reagent, the reagents are preferably LiX with X= F, Cl, Br and I and / or PSX3 with X= F, Cl, Br and I. For the halogenated oxygenated reagent, the reagents are preferably LiClO4, LiBrO4 and LiIO4. All the preparation methods for obtaining the reagents described in the present application are suitable for the method for preparing the argyrodite phases according to the invention. Advantageously, the Li2S reagent xcan be pretreated. In the case of Li2S, the pretreatment may be mechanical (planetary) grinding in the dry or solution process or dissolution-precipitation in ethanol, or any other method known to those skilled in the art. Polar solvents are used for the dispersion and / or activation of the reagents. Advantageously, one or more solvents may be used in combination for the dispersion and activation of the reagents, in particular: - for the dispersion of the lithium reagent and the halogenated compound, preferably Li2S and LiX (solvent 1): cyclic or linear ethers (e.g. THF and dimethoxyethane, dioxane, dioxolane, dibutyl ether, anisole)), esters (alkyl acetate, e.g. butyl acetate, ethyl acetate, tert-butyl acetate, methyl acetate; isobutylisobutyrate, dimethyl glutarate, diethyl glutarate, ethyl benzoate, methyl benzoate), nitriles (e.g. acetonitrile,propionitrile, butanenitrile, benzonitrile), thiols (e.g. propanethiol, butanethiol, pentanethiol, thiophenyl), ‐ for activation of the phosphorus reagent, e.g. P2S5 (Solvent 2): cyclic or linear ethers (e.g. THF and dimethoxyethane, dioxane, dioxolane, dibutyl ether, anisole)), esters (alkyl acetate, e.g. butyl acetate, ethyl acetate, tert-butyl acetate, methyl acetate; isobutylisobutyrate, dimethyl glutarate, diethyl glutarate, ethyl benzoate, methyl benzoate), nitriles (e.g. acetonitrile, propionitrile, butanenitrile, benzonitrile), thiols (e.g. propanethiol, butanethiol, pentanethiol, thiophenyl), alcohols (e.g. methanol, ethanol, isopropanol, tert-butanol), amines (butylamine, pyridine, ethylenediamine, piperidine) Solvent 3, called washing solvent, is preferably chosen from polar, apolar or aprotic solvents, and is not an alcohol. It may be,for example tetrahydrofuran THF or acetonitrile ACN. All solvents are preferably anhydrous. As indicated in the solvent lists above, according to one embodiment of the invention, solvents 1 and 2 may be identical. According to another preferred embodiment of the invention, they are chosen to be of different natures. A possible choice is, for example, to combine a solvent 1 in THF and a solvent 2 in butyl acetate,or to combine a solvent 1 in THF and a solvent 2 in isobutyl isobutyrate. The preparation method comprises at least four steps. All manipulations are carried out under an inert atmosphere. ^ A step of formation in suspension under reflux of the intermediate compound Li3PS4∙solvent (solvato-complex) in the presence of the other solid reagents (for example Li2S and LiX). ^ A step of washing by centrifugation and filtration ^ A step of drying preferably under reduced pressure ^ A step of heat treatment, The relative proportions of the different reagents are chosen by the person skilled in the art in a stoichiometric manner, depending on the formula of the final argyrodite compound targeted. Advantageously, for each reagent: the mass concentration of Li2S, xin the solvent may be between 30 g / L and 70 g / L, the mass concentration of the phosphorus reagent, for example P2S5 in the solvent may be between 35 g / L and 70 g / L, the mass concentration of LiCl in the solvent may be between 5 g / L and 30 g / L, the mass concentration of LiBr in the solvent may be between 15 g / L and 55 g / L, the mass concentration of LiI in the solvent may be between 30 g / L and 80 g / L, the mass concentration of PSCl3 in the solvent may be between 1 g / L and 20 g / L, the mass concentration of LiClO4 in the solvent may be between 0.1 g / L and 5 g / L, the mass concentration of LiBrO4 in the solvent may be between 0.1 g / L and 5 g / L, the mass concentration of LiIO4 in the solvent may be between 0.5 g / L and 10 g / L, the mass concentration of P2O5 in the solvent can be between 0.1 g / L and 5 g / L.Without limitation, the method is described below for Li2S and LiX reagents, as well as P2S. 5.First step: The first step can be carried out in two alternative ways. Figure 1 (top) shows the different stages of formation of the argyrodite phase compound according to the first embodiment. Figure 1 (bottom) shows the different stages of formation of the argyrodite phase compound according to a second embodiment. In Figure 1, (1) corresponds to suspension, (2) to reflux, (3) to reflux, (4) to washing and (5) to heat treatment. For the upper part of Figure 1, block (1) corresponds to the suspension of the Li and P reagents and possibly also a phosphorus oxygenated reagent, and block (2) to the reflux of the Li and X reagents and possibly a halogenated oxygenated reagent.For the lower part of Figure 1, block (1) corresponds to the suspension of the Li and X reagents and possibly a halogenated oxygenated reagent, and block (2) corresponds to the refluxing of the P reagents and possibly a phosphorus oxygenated reagent. The steps below are described with reference to Figure 1. Step 1: formation in suspension (reflux) of the intermediate compound The synthesis method according to the invention makes it possible to overcome the kinetic limitation of the formation of the intermediate compound by activating the phosphorus reagent, for example P2S5. Indeed, this is in the form of an adamantate P4S type cage. 10, limiting the reaction with Li2S. Activation of the P2S5 reagent consists of heating the adamantate cage to dedimerize it. In order to promote a rapid reaction, the lithium and halogenated compound reagents, here Li2S and LiX, previously suspended, are added hot to the suspension containing the phosphorus reagent P2S5. ^ Step 1.1 The first phase allows the lithium reagent Li2S and the halogenated compound LiX to be dispersed in a first polar solvent (solvent 1), for example in a Schlenck flask, to form a suspension. The dispersion is advantageously carried out in an ultrasonic bath between 25°C and 50°C, preferably between 30°C and 40°C for a period of between 1 min and 120 min, preferably between 10 and 50 min. The mass concentration of Li2S in the solvent is between 10 g / L and 100 g / L, preferably between 30 g / L and 70 g / L.The mass concentration of LiX is between 1 g / and 100 g / L, preferably between 5 g / L and 35 g / L when X= Cl, preferably between 10 g / L and 60 g / L when X= Br and preferably between 20 g / L and 80 g / L when X= I. ^ Step 1.2 The second phase allows the P2S5 reagent to be dispersed in a second polar solvent (solvent 2, which can be of the same nature as solvent 1) in a three-necked flask equipped with a water condenser. The suspension is heated between 50 °C and 150 °C, preferably between 90 °C and 110 °C with stirring. The mass concentration of P2S5 in the solvent is between 10 g / L and 100 g / L, preferably between 30 g / L and 80 g / L, even more preferably between 35 g / L and 70 g / L. ^ Step 1.3 The suspension of Li2S + LiX is advantageously transferred into a device allowing the progressive addition of P2S to the suspension. 5 activated, for example a dropping funnel, to be added dropwise into the temperature-activated P2S5 suspension. The suspension addition time is between 1 min and 6 min, preferably between 2 and 4 min. The resulting suspension is maintained at reflux at a temperature between 50 and 150°C (preferably at 100°C) for a time between 1 and 24 h, preferably between 2 and 8 h under an inert atmosphere. The inert atmosphere can be dynamic (constant flow) or static and the nature of the gas can be argon or nitrogen or a mixture of the two. The molar ratio Li2S / P2S5 is between 3 and 6, preferably between 4 and 5. The molar ratio LiX / P2S5 is between 0.5 and 3.5, preferably between 1 and 3. The volume ratio solvent 1 / solvent 2 is between 0.1 and 4, preferably between 0.5 and 1.5.According to the second embodiment of step 1, which is described with reference to Figure 1 below, as an example for Li2S and LiX reagents, as well as P2S5: ^ Alternative step 1.1 The first sub-step makes it possible to disperse a first part of the lithium reagent Li2S and the phosphorus reagent P2S5 in a first polar, preferably aprotic, solvent (solvent 1), for example in a Schlenck flask, to form a solution. The mass concentration of Li2S in the solvent is between 3 g / L and 30 g / L, preferably between 5 g / L and 20 g / L. The mass concentration of P2S5 in the solvent is between 10 g / L and 100 g / L, preferably between 30 g / L and 80 g / L, even more preferably between 35 g / L and 70 g / L. ^ Step 1.2 alternative The second sub-step allows a second part of the lithium reagent Li2S and the halogenated compound LiX to be dispersed in a second polar solvent (solvent 2, which may be of the same nature as solvent 1), for example in a three-necked flask equipped with a water condenser, to form a suspension. The suspension is heated between 50°C and 150°C, preferably between 90°C and 110°C, with stirring. The mass concentration of Li2S in the solvent is between 10 g / L and 80 g / L, preferably between 20 g / L and 70 g / L. The mass concentration of LiX is between 1 g / L and 100 g / L, preferably 5 g / L and 35 g / L when X= Cl, preferably between 10 g / L and 60 g / L when X= Br, and preferably between 20 g / L and 80 g / L when X= I. ^ Step 1.3 alternative Finally, the solution of Li2S and P2S5 is advantageously transferred into a device allowing the gradual addition of Li2S and LiX into the suspension, for example in a dropping funnel, to be added dropwise into the suspension of Li2S + LiX. The addition time of the solution of Li2S and P2S5 is between 1 min and 6 min, preferably between 2 and 4 min. The resulting suspension is maintained at reflux at a temperature between 50 and 150°C (preferably 100°C) for a time between 1 and 24 h, preferably between 2 and 8 h under an inert atmosphere. The inert atmosphere can be dynamic (constant flow) or static and the nature of the gas can be argon or nitrogen or a mixture of the two. The molar ratio Li2S / P2S5 is between 3 and 6, preferably between 4 and 5. The molar ratio LiX / P2S5 is between 0.5 and 3.5, preferably between 1 and 3.The solvent 1 / solvent 2 volume ratio is between 0.1 and 4, preferably between 0.5 and 1.5. Step 2: washing the intermediate compound (solvato-complex) At the end of the reaction, the intermediate compound which is a mixture of a solvato-complex Li3PS4∙solvent with the other solid reagents Li2S. x and LiX and the optional oxygenated reagent, is in the form of a suspension in the mixture of solvents. Said intermediate compound is recovered by centrifugation, advantageously at a speed of between 1000 and 10000 rpm for a period of between 5 and 30 min (here 10000 rpm for 20 min) and redispersed in a third anhydrous solvent (of the same nature as previously or different) before being washed, advantageously on frit with an identical or different anhydrous solvent, to obtain a wet powder. Step 3: Drying The powder obtained is dried, preferably under reduced pressure (typically between 10 ‐2and 10 ‐3mbar), at a temperature between 25°C and 150°C, preferably between 40°C and 80°C for a period of 1 h to 10 h, preferably between 2 h and 6 h. Step 4: Heat treatment A heat treatment is carried out, preferably in a crossed-bed reactor under inert gas flow or under reduced pressure (typically between 10-2 and 10-3 mbar). The nature of the inert gas can be argon or nitrogen or a mixture of the two. The gas flow rate is between 1 L / g / h and 15 L / g / h, preferably between 8 and 12 L / h / g. This configuration allows efficient removal of the solvent. The treatment temperature is advantageously between 300°C and 600°C for a period of between 1 hour and 10 hours. The treatment conditions depend on the nature of the phase to be treated. SEM images are taken with a scanning electron microscope (SEM) (Supra 40 model sold by Zeiss®). The accelerating voltage is 2kV.RAMAN analysis is useful for determining the phases present by observing, in particular, the RAMAN absorption wavelengths of PS43-tetrahedra, which are at the origin of the good ionic conductivity of thiophosphates. Raman spectra are acquired on a Renishaw spectrometer equipped with a confocal lens and a 532 nm laser. The sample is previously conditioned in sealed cells. The spectra were acquired with the following parameters: power 3.9 mW and time 100 s. XRD analysis is used to check that the characteristic crystalline structure of argyrodites is obtained. Diffractograms are acquired on a Brucker D4 diffractometer (40 kV, 40 mA) with a copper anode (Kα1 = 1.54060 Å; Kα2 = 1.54439 Å). The sample is previously conditioned between two Kapton sheets sealed with vacuum grease.The ionic conductivity of the samples is measured by electrochemical impedance spectroscopy between two blocking electrodes in a thermostatically controlled cell (model ASC-T sold by Sphere Energy®). The solid electrolyte is directly densified to 4 ton / cm2 between the two electrodes. The impedance measurement is carried out with a Biologic® MTZ-35 impedance meter between 30 MHz and 1 Hz with an amplitude of 10 mV relative to a voltage of 0 V and a temperature of 30 °C. Examples Example 1: Preparation of the Li6PS5Cl phase according to the invention In a Schlenck tube 0.45 g of Li2S and 2.17 g of P2S5 are dispersed in 50 mL of tetrahydrofuran THF. The tube is then placed under ultrasound for 30 min at 35 °C and the resulting solution is transferred into a dropping funnel. In a three-necked flask, 1.70 g of Li2S and 0.85 g of LiCl are weighed and dispersed in 50 mL of butyl acetate BA. The suspension of Li2S and LiCl is heated to 100 °C in a reflux assembly.The Li2S and P2S5 solution is then added dropwise over 3 min into the Li2S and LiCl solution. After stirring for 4 h at a temperature maintained at 100°C, the flask is allowed to cool to room temperature. The suspension is then centrifuged at 10,000 rpm for 20 min. The precipitate is redispersed in tetrahydrofuran (THF) before being washed on a frit with THF, resulting in a wet white powder. This is then dried under reduced pressure at 50°C for 5 h. The resulting powder is then annealed at 550°C for 4 h under an argon flow rate of 10 L / h / g. The resulting powder is characterized by Raman spectroscopy (Figure 2), X-ray diffraction (Figure 3), scanning electron microscopy (Figure 4) and impedance spectroscopy. Figure 2 shows the Raman spectrum of the phase obtained with the vibration peak at 424 cm‐1 characteristic of the PS43‐ units of lithium argyrodite phases.Figure 3 confirms that the crystal structure of the obtained phase corresponds mainly to the structure of lithium argyrodite. Figure 4 shows the Li6PS5Cl particles obtained before heat treatment. The measured ionic conductivity is 0.9. mS / cm at 30°C. Example 2: Preparation of the Li6PS5Cl phase 0,5 Br 0.5according to the invention In a Schlenck tube 0.41 g of Li2S and 1.98 g of P2S5 are dispersed in 50 mL of tetrahydrofuran THF. The tube is then placed under ultrasound for 30 min at 35°C and then the resulting solution is transferred into a dropping funnel. In a three-necked flask, 1.6 g of Li2S, 0.38 g of LiCl and 0.78 g of LiBr are weighed and dispersed in 50 mL of butyl acetate BA. The suspension of Li2S, LiCl and LiBr is heated to 100°C in a reflux assembly. The solution of Li2S and P2S5 is then added dropwise over 3 min into the solution of Li2S, LiCl and LiBr. After 4 hours of stirring at a temperature maintained at 100°C, the flask is allowed to cool to room temperature. The suspension is then centrifuged at 10,000 rpm for 20 min. The precipitate is redispersed in tetrahydrofuran (THF) before being washed on a frit with THF, resulting in a wet white powder.This is then dried under reduced pressure at 50°C for 5 h. The powder obtained is then annealed at 550°C for 4 h under an argon flow rate of 10 L / h / g. The powder obtained is characterized by Raman spectroscopy (Figure 2), X-ray diffraction (Figure 3) and impedance spectroscopy. Figure 2 shows the Raman spectrum of the phase obtained with the vibration peak at 425 cm. ‐1 PS4 unit features 3‐ lithium argyrodite phases. Figure 3 confirms that the crystal structure of the phase obtained corresponds mainly to the structure of lithium argyrodite. The measured ionic conductivity is 1.8 mS / cm at 30°C Example 3: Preparation of the Li phase 5.5 PS 4.5 Cl 1,5according to the invention In a Schlenck tube 0.44 g of Li2S and 2.15 g of P2S5 are dispersed in 50 mL of tetrahydrofuran THF. The tube is then placed under ultrasound for 30 min at 35°C and then the resulting solution is transferred into a dropping funnel. In a three-necked flask, 0.44 g of Li2S and 1.23 g of LiCl are weighed and dispersed in 50 mL of butyl acetate BA. The suspension of Li2S and LiCl is heated to 100°C in a reflux assembly. The solution of Li2S and P2S5 is then added dropwise over 3 min into the solution of Li2S and LiCl. After 4 hours of stirring at a temperature maintained at 100°C, the flask is allowed to cool to room temperature. The suspension is then centrifuged at 10,000 rpm for 20 min. The precipitate is redispersed in tetrahydrofuran (THF) before being washed on a frit with THF, obtaining a wet white powder. This is then dried under reduced pressure at 50°C for 5 h.The obtained powder is then annealed at 550°C for 4 h under an argon flow rate of 10 L / h / g. The obtained powder is characterized by Raman spectroscopy (Figure 2), X-ray diffraction (Figure 3) and impedance spectroscopy. Figure 2 shows the Raman spectrum of the obtained phase with the vibration peak at 426 cm. ‐1 PS4 unit features 3‐lithium argyrodite phases. Figure 3 confirms that the crystal structure of the phase obtained corresponds mainly to the structure of lithium argyrodite. The measured ionic conductivity is 2.5 mS / cm at 30°C. In a Schlenck tube, 0.44 g of Li2S, 2.06 g of P2S5 and 0.07 g of P2O5 are dispersed in 50 mL of tetrahydrofuran THF. The tube is then placed under ultrasound for 30 min at 35°C and the resulting solution is transferred into a dropping funnel. In a three-necked flask, 0.44 g of Li2S and 1.23 g of LiCl are weighed and dispersed in 50 mL of butyl acetate BA. The suspension of Li2S and LiCl is heated to 100°C in a reflux flask. The Li2S and P2S5 solution is then added dropwise over 3 min into the Li2S and LiCl solution. After stirring for 4 hours at a temperature maintained at 100°C, the flask is allowed to cool to room temperature. The suspension is then centrifuged at 10,000 rpm for 20 min.The precipitate is redispersed in tetrahydrofuran (THF) before being washed on a frit with THF, obtaining a wet white powder. This is then dried under reduced pressure at 50°C for 5 h. The powder obtained is then annealed at 550°C for 4 h under an argon flow rate of 10 L / h / g. The powder obtained is characterized by Raman spectroscopy (Figure 2), X-ray diffraction (Figure 3) and impedance spectroscopy. Figure 2 shows the Raman spectrum of the phase obtained with the vibration peak at 424 cm. ‐1 PS4 unit features 3‐ lithium argyrodite phases. Figure 3 confirms that the crystal structure of the phase obtained corresponds mainly to the structure of lithium argyrodite. The measured ionic conductivity is 1.3 mS / cm at 30°C. Table 1 Example Ionic conductivity (mS / cm) at 30°C 1 0.9 Li6PS5Cl 2 1.8 Li6PS5Cl 0,5 Br 0.5 3 2.5 Li 5.5 PS 4.5Cl 1,5 4 1.3 Li6PS 4.875 O 0,125 Cl 1,5 We see that the ionic conductivities of these 4 examples are close to or greater than 1 mS / cm, therefore interesting conductivity levels for electrolyte applications, particularly for batteries.

Claims

Claims 1. Procédé de synthèse de particules d’argyrodite de lithium de formule Li 7‐(a+b) PS 6‐(a+b+c) O c X a Q b with X and Q two distinct halogenated elements chosen from F, Cl, Br, I; O the oxygen atom, with 1≤a+b<2, c between 0 and 0.25, limits included, a and b not being s imultanément nuls, à partir d’un réactif lithium Li2Sx avec x compris entre 1 et 8, un réactif phosphorus Rp chosen from P2S5, P4S 10 , P4S9 and P4S 9+n with n between 0 and 1, and a halogenated compound chosen from LiX and PSX3; and an optional oxygenated phosphorus or halogenated reagent chosen p armi P2O5, LiClO4, LiBrO4, LiIO4 comprenant au moins les étapes suivantes sous atmosphère inert: A) Contacting the lithium reagent and the halogenated compound and the possible oxygenated reagent h alogéné, préalablement mis en suspension dans au moins un premier solvant polaire (solvant 1), avec une suspension contenant au moins le réactif phosphore et l’éventuel phosphorus-containing oxygenated reagent in at least one second polar solvent (solvent 2), of nature i dentique ou différente à une température comprise entre 50 et 150°C et formation en suspension sous reflux d’un composé intermédiaire sous forme d’un solvato‐complexe Li3PS4∙solvant en mélange avec les autres réactifs solides Li2Sx et LiX et l’éventuel réactif oxygéné, le ratio volumique solvant 1 / solvant 2 étant compris entre 1 et 4 préférentiellement entre 0,5 et 1,5, les proportions relatives des différents réactifs étant choisies de manière stœchiométrique par rapport à la formule Li7‐(a+b)PS6‐(a+b+c)OcXaQb du final compound in the form of lithium argyrodite particles; B) Centrifugation, redispersion of the centrifuged phase in a third anhydrous solvent, of the same or different nature as that of said first and second solvents, then filtration and washing of said intermediate compound; C) Drying preferably under reduced pressure, at a temperature between 25°C and 150°C for a period of between 1 hour and 10 hours. D ) Traitement thermique à une température comprise entre 300 et 600°C et une durée between 1 and 10 hours.

2. Procédé de synthèse de particules d’argyrodites selon la revendication 1, dans lequel à step A): A 1) on disperse sous agitation le réactif lithium Li2Sx, de préférence Li2S, le composé halogéné LiX ou PSX3, de préférence LiX, et l’éventuel réactif oxygéné halogéné dans un premier solvant polaire (solvant 1) à une concentration massique de réactif lithium Li2Sx dans le solvent between 10 g / L and 100 g / L, preferably between 30 g / L and 70 g / l and a mass concentration of halogenated compound LiX or PSX3 in the solvent between 1 g / L and 100 g / L, preferably between 5 g / L and 80 g / L, and a mass concentration of d e réactif oxygéné halogéné comprise entre 0,1 et 10 g / L, et on chauffe la suspension obtained between 25°C and 50°C, preferably between 30°C and 40°C; A 2) puis on disperse sous agitation le réactif phosphore Rp dans un deuxième solvant polaire (solvant 2), à une concentration massique réactif phosphore dans le solvant est comprise entre 10 g / L et 100 g / L préférentiellement entre 30 g / L et 80 g / L, encore plus preferably between 35 g / L and 70 g / L, the suspension obtained being heated between 50°C and 150°C, preferably between 90°C and 110°C; A 3) on ajoute progressivement la solution de réactif lithium et de composé halogéné, de preferably Li2S and LiX, in the suspension of phosphorus reagent, preferably P2S5, activated at temperature for a period of between 1 min and 6 min, preferably between 2 and 4 min and the resulting suspension is kept stirring at reflux for a period of between 1 and 24, preferably between 2 and 8 h under an inert atmosphere.

3. Procédé de synthèse de particules d’argyrodites selon la revendication 1, dans lequel à step A): A 1) on disperse sous agitation une première partie du réactif lithium Li2Sx, de préférence Li2S, et the phosphorus reagent, preferably P2S 5, in a first polar solvent (solvent 1) at a mass concentration of lithium reagent, preferably Li2S, in the solvent of between 3 g / L and 30 g / L, preferably between 5 g / L and 20 g / l and a mass concentration of r éactif phosphore, de préférence P2S5 , dans le solvant comprise entre 10 g / L et 100 g / L, preferably between 30 g / L and 80 g / L, even more preferably between 35 g / L and 70 g / L, and the suspension obtained is heated between 25°C and 50°C, preferably between 30°C and 40°C, to form a solution; A 2) on disperse sous agitation une deuxième partie du réactif lithium Li2Sx et le composé halogéné LiX ou PSX3 dans un deuxième solvant polaire (solvant 2) à une concentration massique de réactif lithium Li2Sx dans le solvant comprise entre 10 g / L et 80 g / L, préférentiellement entre 5 g / L et 70 g / L et une concentration massique de composé halogenated LiX or PSX 3 between 1 g / and 100 g / L, preferably between 5 g / L and 80 g / L and the suspension obtained is heated between 50°C and 150°C, preferably between 90°C and 110°C; A3) puis on ajoute progressivement la solution de réactif lithium et de réactif phosphore , de preferably Li2S and P2S5, in the suspension of lithium reagent and halogenated compound, preferably Li2S + LiX, for a period of between 1 min and 6 min, preferably between 2 and 4 min, and the resulting suspension is kept stirring at reflux for a period of between 1 and 24 h, preferably between 2 and 8 h, under an inert atmosphere.

4. Procédé de synthèse selon l’une des revendications 1 à 3, dans lequel ledit composé intermediate in the form of solvato-complex is recovered in the form of wet powder by c entrifugation à une vitesse comprise entre 1000 et 10 000 tours / min pendant une durée between 5 and 30 min, redispersion in an anhydrous solvent, then washing on a frit with an identical or different anhydrous solvent.

5. Synthesis process according to any one of claims 1 to 4, in which the drying of step C) is carried out under reduced pressure between 10 ‐2 and 10 ‐3 mbar at a temperature between 40°C and 80°C for a period between 2h and 6h.

6. Synthesis process according to one of claims 1 to 5, in which the drying of step C) is followed by a step D) of heat treatment carried out in a crossed-bed reactor under a flow of inert gas or under reduced pressure between 10 ‐2 and 10 ‐3 7. Synthesis process according to claim 6, wherein the inert gas is argon or nitrogen o u un mélange des deux, et le débit du gaz est compris entre 1 L / g / h et 15 L / g / h preferably between 8 and 12 L / h / g.

8. Synthesis process according to one of the preceding claims, in which the Li2S reagent xis pretreated before suspension by mechanical grinding in a dry process or in solution, by dissolution-precipitation in a solvent.

9. Synthesis process according to one of the preceding claims, in which the polar solvent, whether the first solvent (solvent 1) or the second solvent (solvent 2), is chosen from cyclic or linear ethers, esters, nitriles, alcohols, thiols.

10. Synthesis process according to one of claims 1 to 9, in which X=Cl, a =1, b=0, c=0 and an argyrodite phase Li6PS5Cl is obtained.

11. Synthesis process according to one of claims 1 to 9, in which X=Cl, a =1.5, b=0, c=0 and an argyrodite phase Li 5,5 PS4.5Cl 1,5 .

12. Synthesis process according to one of claims 1 to 9, in which X=Cl Q=Br, a =0.5, b=0.5, c=0 and an argyrodite phase Li6PS5Cl is obtained. 0,5 Br 0,5 .

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