Method for preparing lithium argyrodite

Abstract

The present invention relates to a novel process for preparing lithium argyrodite, as well as to the products obtained by said process and their use, in particular as solid electrolytes.

Description

[Technical field]

[0001] The present invention relates to a process for the preparation of lithium argyrodite, as well as to the products obtained and the use of said products, in particular as solid electrolytes. [Background technology]

[0002] Lithium batteries are used to power portable electronic devices and electric vehicles due to their high energy and power density. Traditional lithium batteries utilize a liquid electrolyte consisting of lithium salts dissolved in an organic solvent. Organic solvents are flammable, which creates a safety issue in the aforementioned system. When lithium dendrites form and pass through the liquid electrolyte medium, they can cause short circuits and generate heat, which can lead to accidents that can cause serious injuries.

[0003] Non-flammable inorganic solid electrolytes offer a solution to safety concerns, and their mechanical stability helps inhibit the formation of lithium dendrites, preventing self-discharge and heating problems and extending battery life.

[0004] Solid sulfide electrolytes are advantageous for lithium battery applications due to their high ionic conductivity and mechanical properties. These electrolytes can be pelletized and attached to electrode materials by cold pressing, eliminating the need for high temperature assembly steps. Eliminating the high temperature sintering step removes one of the challenges to using lithium metal anodes in lithium batteries.

[0005] Therefore, new solid sulfide electrolytes are needed.

[0006] Argyrodites have been known for a long time and are derived from the argyrodite Ag8GeS6 first described in 1886 by C. Winkler, whose analysis led to the discovery of germanium. The argyrodite family consists of over 100 crystalline solids, including, for example, solid compounds in which silver is replaced by copper, germanium by gallium or phosphorus, and sulfur by selenium. Thus, Nitsche, Kuhs, Krebs, Evain, Boucher, Pfitzner, and Nilges have described compounds such as Cu9GaS6, Ag7PSe6, and Cu8GaS5Cl, among others, whose solid structures are derived from argyrodite.

[0007] As reported in the literature, most lithium argyrodites, especially most Li6PS5Cl, are prepared by dry or wet mechanochemical routes.

[0008] All solution routes proposed in the literature so far mostly start with preformed Li3PS4 dissolved in ethanol, followed by the introduction of Li2S and LiCl, or involve the dissolution of preformed Li6PS5Cl.

[0009] Therefore, there is a need for a completely solution route to prepare sulfide-based solid electrolytes. Summary of the Invention

[0010] The object of the present invention is to provide a sulfide-based solid electrolyte with argyrodite structure, preferably prepared by a faster and easier to construct synthetic route compared to the aforementioned methods.

[0011] The object of the present invention is to provide a novel process for the preparation of lithium argyrodite in solution, which preferably has improved productivity and allows control of the morphology of the product obtained.

[0012] The invention therefore relates to at least one step of preparing a solution S1 at a temperature T1 comprised between −200° C. and 10° C., preferably between −110° C. and 0° C., said solution S1 comprising a solvent and (PS4) 3- At least P species in the form of + Li species in the form of X - and residual sulfur in the form of polysulfides, followed by removing at least a portion of the solvent from the solution to obtain Li6PS5X, wherein X is a halogen.

[0013] The present invention also relates to Li6PS5X, where X is a halogen, accessible by the method of the present invention. The present invention also relates to the use of such Li6PS5X as a solid electrolyte. The present invention also relates to a solid electrolyte comprising such Li6PS5X, and an electrochemical device comprising Li6PS5X according to the present invention. The present invention also relates to an all-solid-state battery comprising the solid electrolyte of the present invention, and a vehicle comprising an all-solid-state battery.

[0014] definition Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises, comprising, includes, including" are understood to mean the inclusion of a stated element or method step or group of elements or method steps, but not the exclusion of any other element or method step or group of elements or method steps. According to a preferred embodiment, the words "comprise" and "include" and variations thereof mean "consisting only of".

[0015] As used herein, the singular forms "a," "an," and "the" include plural embodiments unless the context clearly indicates otherwise. The term "and / or" includes the meaning of "and," "or," and also all other possible combinations of the elements associated with this term.

[0016] The term "between" should be understood to be inclusive of the points.

[0017] Ratios, concentrations, amounts, and other numerical data may be presented in a range format in this specification. Such range formats are used merely for convenience and brevity, and should be understood to be interpreted flexibly to include not only the numerical values ​​explicitly recited as the range endpoints, but also to include all individual numerical values ​​or subranges contained within the range as if each numerical value and subrange were explicitly recited. For example, a temperature range of about 120°C to about 150°C should be interpreted to include not only the explicitly recited endpoints of about 120°C to about 150°C, but also the subranges such as 125°C to 145°C, 130°C to 150°C, and individual amounts within the stated range, such as subquantities, e.g., 122.2°C, 140.6°C, and 141.3°C.

[0018] The term "electrolyte" refers in particular to ions, e.g. Li + An electrolyte is a substance through which charges can move but through which electrons cannot be conducted. + A "solid electrolyte" according to the present invention is a material that serves to electrically insulate the cathode and anode of a battery while allowing ions such as Li to pass through the electrolyte. + By "solid matter" we mean any type of material that can move around in.

[0019] The term "electrochemical device" refers in particular to devices that generate and / or store electrical energy, for example, by electrochemical and / or electrostatic processes. Electrochemical devices can include electrochemical cells, such as batteries, in particular solid-state batteries. Batteries can be primary (i.e., for single or "disposable" use) or secondary (i.e., rechargeable) batteries.

[0020] As used herein, the terms "vehicle" or "vehicular" or other similar terms generally include passenger cars, buses, trucks, various commercial vehicles, water vehicles such as various boats and ships, motor vehicles such as airplanes, and also hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen vehicles, and other alternative fuel vehicles (e.g., fuels obtained from resources other than petroleum). The hybrid vehicle referred to herein is a vehicle having two or more different power sources, for example, a vehicle having both gasoline and electricity as power sources.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The method of the present invention is based on the preparation of a homogeneous solution containing ionic species. Therefore, no suspension is included.

[0022] Therefore, all species involved in the preparation of Li6PS5X are dissolved in the solvent and are in the form of the ionic species described above.

[0023] An essential feature of the method of the present invention is the temperature T1 defined above. Therefore, the method of the present invention is carried out at a low temperature, particularly to stabilize the (PS4) 3- species in the solution and, as a result, to obtain the solution S1 at the required temperature.

[0024] After the solution S1 is prepared, a step of removing at least a part of the solvent is then carried out. Thereafter, Li6PS5X is obtained as a solid, preferably as a powder.

[0025] Preferably, the term "at least a part of the solvent" refers to at least 50% by weight, preferably at least 60% by weight of the solvent.

[0026] (PS4) 3- The P species in the form of are preferably obtained from precursors selected from the group consisting of P2S5, P4S 10 , P4S9, and P4S 9+x (0 < x < 1).

[0027] Li + The Li species in the form is preferably obtained from a precursor selected from the group consisting of Li2S and LiHS.

[0028] X - The X species in the form is preferably obtained from a precursor selected from the group consisting of LiF, LiCl, LiBr, and LiI.

[0029] The remaining sulfur in the form of polysulfide is preferably P2S5, P4S 10 , P4S9, P4S 9+x (0 < x < 1), and is obtained from a precursor selected from the group consisting of Li2S, S, and LiHS.

[0030] According to one embodiment, the solution S1 defined above is obtained by mixing lithium sulfide, phosphorus sulfide, and a halogen compound in a solvent at a temperature in the range of -200°C to 10°C, preferably -110°C to 0°C.

[0031] According to this embodiment, all species (Li, P, halogen, and S) are preferably added together into the solvent at temperature T1.

[0032] According to another embodiment, the solution S1 defined above comprises the following steps: - Mixing lithium sulfide and a halogen compound in a solvent to obtain a precursor solution; and - Adding phosphorus sulfide to the precursor solution at a temperature included in the range of -200°C to 10°C, preferably -110°C to 0°C, to obtain the solution S1; is obtained by performing.

[0033] According to this embodiment, the solution S1 is prepared in two steps, and the first step thereof includes the mixing of lithium and a halogen compound.

[0034] The method of the present invention is easy to carry out, especially easier than the methods of the prior art. For example, lithium sulfide can be used as it is, even if it is obtained by carbo-reduction. In fact, the lithium sulfide obtained from the carbo-reduction containing residual carbon is used directly in the solvent for the preparation of solution S1, after having undergone a filtration step to remove the carbon. This makes an intermediate lithium sulfide separation step unnecessary.

[0035] Preferably, the step of removing at least a portion of the solvent from solution S1 is carried out at a temperature comprised between 30° C. and 200° C., preferably between 30° C. and 185° C., for example between 30° C. and 100° C. According to one embodiment, this temperature may be comprised between 35° C. and 65° C.

[0036] The step of removing the solvent can be carried out by conventional means, particularly by solvent evaporation.

[0037] This preferred temperature range for solvent removal is advantageous in that secondary reactions are not promoted at such temperature values.

[0038] The preparation of solution S1 can be carried out in an inert atmosphere, under vacuum, or under a flow of H2S.

[0039] The method of the invention may comprise an additional step of heat treatment of Li6PS5X, in particular after the step of removing the solvent. Preferably, after removal of the solvent, Li6PS5X is then heat treated at a temperature comprised between 150° C. and 700° C., preferably at about 550° C.

[0040] Such an additional step therefore advantageously consists in a heat treatment of the solid Li6PS5X obtained after the solvent removal step.

[0041] Preferably, the solvent used in the method of the invention is capable of dissolving Li6PS5X, lithium sulfide, phosphorus sulfide and halogen compounds, as mentioned above, which results in a homogeneous solution S1 as defined above.

[0042] According to a preferred embodiment, the solvent is an aliphatic alcohol. Most preferably, the solvent is selected from the group consisting of ethanol, methanol, and mixtures thereof.

[0043] The temperature T1 is comprised between -200°C and 10°C, preferably between -110°C and 0°C, most preferably between -110°C and -10°C, in particular between -100°C and -50°C, in particular between -90°C and -70°C. For example, T1 is about -80°C.

[0044] According to a particular embodiment, the temperature used during the step of removing at least a portion of the solvent from the solution S1 is comprised between 35°C and 65°C, the temperature T1 is comprised between -110°C and -10°C, preferably between -100°C and -50°C.

[0045] In particular, during the preparation of solution S1, the temperature T1 remains constant.

[0046] Advantageously, the method according to the invention allows for much less, or even no, global and local deviations relative to the stoichiometry.

[0047] Lithium sulfide is generally a compound that contains one or more sulfur atoms and one or more lithium atoms, or one or more sulfur-containing ionic groups and one or more lithium-containing ionic groups. In certain preferred embodiments, lithium sulfide may be composed of sulfur and lithium atoms.

[0048] Phosphorus sulfides are compounds that typically contain one or more sulfur atoms and one or more phosphorus atoms, or one or more sulfur-containing ionic groups and one or more phosphorus-containing ionic groups. In certain preferred embodiments, phosphorus sulfides may be composed of sulfur and phosphorus atoms. Examples of phosphorus sulfides include, but are not limited to, P2S5, P4S3, P4S 10 , P4S4, P4S5, P4S6, P4S7, P4S8, and P4S9.

[0049] A halogen compound is a compound that contains one or more halogen atoms, such as F, Cl, Br, or I, through a chemical bond (e.g., ionic or covalent bond) to other atoms that make up the compound. In certain preferred embodiments, the halogen compound may contain one or more F, Cl, Br, I, or a combination thereof, and one or more metal atoms. In another preferred embodiment, the halogen compound may contain one or more F, Cl, Br, I, or a combination thereof, and one or more non-metal atoms. Non-limiting examples may suitably include metal halides such as LiF, LiBr, LiCl, LiI, NaF, NaBr, NaCl, NaI, KaF, KBr, KCl, KI, etc. In certain preferred embodiments, the halogen compound suitable for use in the solid electrolyte of the all-solid-state Li-ion battery may contain one or more halogen atoms and Li.

[0050] Preferably, the lithium sulfide may include or is lithium sulfide Li2S, and the phosphorus sulfide may include or is phosphorus pentasulfide P2S5.

[0051] The halogen compound defined above may be selected from the group consisting of LiCl, LiBr, LiI, LiF, and combinations thereof. Preferably, said halogen compound is LiCl.

[0052] Solution S1 contains at least 50 mol % Li sulfide based on the total moles of lithium sulfide added to the solvent. + Li species in the form of, preferably at least 80 mol % Li + and more preferably at least 95 mol % Li + The Li species may be in the form

[0053] Solution S1 is (PS4) 3- and (P2S7) 4- The P species may be in the form of:

[0054] Solution S1 contains at least 50 mol % (PS4) relative to the total molar amount of phosphorus sulfide added to the solvent. 3-P species in the form, preferably at least 80 mol % (PS4) 3- More preferably at least 95 mol % of P species in the form of (PS4) 3- or even at least 99 mol % of P species in the form (PS4) 3- The P species may be in the form

[0055] Solution S1 contains at least 50 mol % of X based on the total molar amount of halogen compounds added to the solvent. - X species in the form, preferably at least 80 mol % X - and more preferably at least 95 mol % of X - The X species may be in the form

[0056] The present invention also relates to Li6PS5X, where X is a halogen, which is accessible by the process defined above. Preferably, it also relates to Li6PS5Cl, which is accessible by the process defined above.

[0057] The present invention also relates to the use of Li6PS5X, preferably Li6PS5Cl, as defined above as a solid electrolyte.The present invention also relates to a solid electrolyte, in particular a sulfide-based solid electrolyte, comprising Li6PS5X, preferably Li6PS5Cl, as defined above, for lithium-ion batteries.

[0058] The present invention also relates to an electrochemical device comprising the Li6PS5X defined above. The present invention also relates to an all-solid-state battery, such as an all-solid-state lithium secondary battery, comprising the solid electrolyte defined above, and to a vehicle comprising the all-solid-state battery defined above.

[0059] Typically, a lithium all-solid-state battery includes a positive electrode active material layer including a positive electrode active material, a negative electrode active material layer including a negative electrode active material, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer. At least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer includes a solid electrolyte including Li6PS5X, preferably Li6PS5Cl, as defined above. [Brief description of the drawings]

[0060] [Figure 1] NMR data of Li6PS5Cl before annealing (Example 1). The asterisk corresponds to PS4 3-. [Diagram 2] NMR data of Li6PS5Cl before annealing (Example 1). The asterisks correspond to Li in Li6PS5Cl. [Diagram 3] 31P solution NMR of Example 1 in reaction medium (solution S1) + 10% DMSO-d6. The asterisk corresponds to PS4 3- solvated by ethanol molecules. [Figure 4] 1 shows XRD data after synthesis (Example 1). [Diagram 5] NMR data for Li6PS5Cl after annealing at 550 °C (Example 2). The stars correspond to PS4 3-, the circles correspond to PO4 3-, the squares correspond to partially oxidized thiophosphate, and the other signals are artifacts (spinning side bands). [Figure 6] NMR data for Li6PS5Cl after annealing at 550° C. (Example 2). The stars correspond to Li in Li6PS5Cl and the circles correspond to Li in Li3PO4. [Figure 7] 4 shows XRD data after annealing at 550° C. (Example 2). [Figure 8] 1 shows conductivity measurement of Example 2. [Figure 9] NMR31P data Li6PS5Cl (Example 3). The asterisk corresponds to PS4 3-, and the hexagon corresponds to P2S7 4-. [Figure 10] 6Li NMR data Li6PS5Cl (Example 3). The asterisks correspond to Li in Li6PS5Cl and the triangles correspond to Li2S. [Figure 11] 31P solution NMR of reaction medium (solution S1) + 10% DMSO-d6 (Example 3). The stars correspond to PS4 3- solvated by ethanol molecules. [Figure 12] 1 is XRD data of the powder of Example 3. [Figure 13]1 is XRD data of the powder of Example 4. EXAMPLES

[0061] The following examples serve to illustrate the invention but do not have a limiting character.

[0062] X-ray diffraction: XRD diffractograms of powders were acquired on an XRD goniometer in Bragg Brentano geometry using a Cu X-ray tube (Cu Kalpha with wavelength 1.5406 Å). The setup can be used in various optical configurations, i.e. with variable or fixed divergence slits, or Soller slits. Primary filtering devices such as Panalytical monochromators or Bragg Brentano HD optics can also be used. If a variable divergence slit is used, the typical irradiation area is 10 mm × 10 mm. The sample holder is loaded on a spinner and the rotation speed during acquisition is typically 60 rpm. The tube settings were operated at 40 kV / 30 mA for variable slit acquisition and 45 kV / 40 mA for fixed slit acquisition with incident Bragg Brentano HD optics. The acquisition steps were 0.017° per step. The angular range is typically 5°-90° over 2 theta. Total acquisition times were typically more than 30 min.

[0063] The powder is covered with a Kapton film to prevent reaction with moisture in the air.

[0064] Conductivity measurement: Conductivities were obtained on pellets using a uniaxial press operating at 500 MPa.

[0065] The measurements are carried out under a load of 40 MPa, using two carbon paper foils as current collectors in a pressure cell from MTI (BATTE-CELL-0067 EQ-PSC-15-P).

[0066] The impedance spectra are acquired with a Biologic VMP3 device and the temperature control is ensured by a Binder climatic chamber. A duration of 2 hours is set to allow the temperature to equilibrate between two measurements.

[0067] Impedance spectroscopy is acquired in PEIS mode (25 points per 10 measurements, averaging 50 measurements per frequency point) with an amplitude of 10 mV and a frequency range of 1 MHz to 1 kHz.

[0068] liquid phase NMR 31 P solution NMR spectra were recorded on a Bruker 300 MHz spectrometer equipped with a QNP Z-GRD Z8352 / 107 probe. The relaxation time was 7 s. 1 Decoupled from H.

[0069] solid phase NMR Solid-state NMR spectra were recorded on a Bruker Avance 400 spectrometer equipped with a high-speed DVT4 probe. 31 P and 6 Li measurements were performed by magic angle spinning (MAS) at a rate of 10 kHz in single pulse mode with relaxation time D1 according to the experiment (see examples below). 7 Li measurements were performed in static single pulse mode with a relaxation time D1 = 120 s. 31 The P NMR reference was 85% H3PO4. 6 The reference for Li NMR is 5 mol L -1 The LiCl solution was

[0070] Example 1 LiCl (229 mg, Sigma-Aldrich) and Li2S (620 mg, Albemarle) were weighed into a 100 mL Schlenk flask in an Ar-filled glove box with oxygen and moisture levels both below 1 ppm. The flask was then removed from the glove box and connected to a N2 / vacuum line. 35 mL of absolute ethanol (Merck Seccosolv®, water content <50 ppm) was added to the flask via a glass syringe. The resulting mixture was stirred under an inert atmosphere (N2). Complete dissolution of the reactants took approximately 20 min.

[0071] P2S5 (600 mg, Sigma-Aldrich, 99% purity) was weighed into a 100 mL 3-neck flask equipped with a dropping funnel. After cooling to -80 °C for 30 min using a dry ice / acetone bath, the above Li / S / Cl solution was transferred to the dropping funnel and added rapidly. P2S5 dissolved within about 10 min to a clear yellow solution.

[0072] The solution was then stirred for 6 hours while the temperature was kept at -80° C. No further changes were observed. 31 Samples of 600 μL of the reaction medium were taken after 1, 3 and 6 h for P NMR monitoring (Bruker 300 MHz spectrometer equipped with a QNP Z-GRD Z8352 / 107 probe). The solvent was then slowly removed under primary vacuum, initially at room temperature, then the temperature was raised to 50 °C when the solution was concentrated to about 60% of its initial volume and left at this value overnight. The product obtained was a pale yellow powder. It was characterized by powder X-ray diffraction (Panalytical), solid phase 31 P, 1 H, and 6 Li MAS NMR and solid phase 7 It was characterized by Li static NMR (Bruker NEO400 spectrometer equipped with a 4 mm BL4 probe).

[0073] Example 2 One end of a quartz tube, 250 mm long, 10 mm inner diameter, and 1.1 mm wall thickness, was closed using a propane and oxygen fueled torch. The tube was placed in an Ar filled glove box with both oxygen and moisture levels below 1 ppm and filled with 250 mg of material prepared according to Example 1. A valved PVC hose adapter was then attached to the tube, removed from the glove box, and connected to a vacuum line via a valve. The system was evacuated. When the vacuum reached 1 mbar, the tube was sealed using a propane / oxygen torch. The sealed tube was heated in a muffle furnace at 2°C / min to 550°C and held at this value for 5 hours. After cooling to 30°C, it was transferred into an Ar filled glove box and cut with a tungsten carbide cutter to recover the product as a grey powder. The powder was analyzed by X-ray diffraction, solid phase 31 P, 6 Li, and 1 H MAS NMR and solid-state static 7 It was characterized by Li NMR.

[0074] The lithium ion conductivity was measured by impedance spectroscopy on pellets of this material, which is σ=1.3×10 at 30 °C. -3 S.cm -1 and the activation energy is 0.43 eV.

[0075] Example 3 (Comparative) LiCl (229 mg, Sigma-Aldrich) and Li2S (620 mg, Albemarle) were weighed into a 100 mL Schlenk flask in an Ar-filled glove box with oxygen and moisture levels both below 1 ppm. The flask was then connected to a N2 / vacuum line and 35 mL of absolute ethanol (Merck Seccosolv®, water content <50 ppm) was added. The mixture was stirred under an inert atmosphere (N2).

[0076] P2S5 (600 mg, Sigma-Aldrich, 99% purity) was weighed into a 100 mL Schlenk flask equipped with a dropping funnel. The above Li / S / Cl solution was then transferred to the dropping funnel and added rapidly. P2S5 dissolved within about 10 min to a clear yellow solution. Then, 31 P NMR spectra were recorded on 600 μL of the reaction medium.

[0077] The solution was then stirred at room temperature (22 °C) for 2 hours. No further changes were observed. After this time, another 600 μL sample of the solution was taken and 31 It was characterized by P NMR. 31 As seen in the P solution NMR (Figure 11), the solution contains a large amount of impurities / by-products, especially the signal at 114 ppm. The solvent was then removed under vacuum, initially at room temperature, then the temperature was increased to 45°C when the solution was concentrated to about 60% of its initial volume, and finally to 80°C when most of the ethanol was gone, and held at this value for another 3.5 hours. The resulting product was a white paste. This paste was then heated to 100°C on a vacuum line for 3.5 hours, reducing it to a white powder. The resulting powder was 31 Contains large amounts of impurities / by-products as seen by P solid-state NMR (Figure 9).

[0078] Example 4 In an Ar-filled glovebox with oxygen and moisture levels both below 1 ppm, LiCl (344 mg, Sigma-Aldrich), Li2S (930 mg, Albemarle), and elemental sulfur (135 mg, AnalR NORMAPUR®, VWR Chemicals) were weighed together into a 100 mL Schlenk flask. 30 g of absolute ethanol (VWR, water content less than 30 ppm) was added to the mixture. The flask was then removed from the glovebox and connected to a N2 / vacuum line. The resulting mixture was stirred at 0° C. (water / ice bath) under an inert atmosphere (N2). Complete dissolution of the reactants took approximately 15 min. A deep yellow solution was obtained, which was then stirred at 0° C. for an additional 20 min.

[0079] P2S5 (600 mg, Sigma-Aldrich, 99% purity) was weighed into a 100 mL Schlenk flask. The flask was cooled to -15°C using a sodium chloride / ice bath for 30 min, then the above Li / S / Cl solution was added rapidly via Teflon cannula. P2S5 dissolved within 5 min to give a deep yellow solution.

[0080] The solution was stirred for 3 hours 45 minutes while maintaining the temperature between -15°C and -10°C. The reaction medium was then placed under dynamic primary vacuum and the temperature was raised to 180°C (silicone oil bath on a hot plate) to remove the solvent. A temperature of 180°C was reached after 30 minutes and held at this value for a further 2 hours. The product obtained was a dry grey powder. This powder was characterized by X-ray diffraction and solution chromatography. 31 It was characterized by P NMR.

[0081] The lithium ion conductivity was measured by impedance spectroscopy of pellets of this material, which is σ=1×10 at 30 °C. -4 S.cm -1 and the activation energy is 0.42 eV.

Claims

1. At least one step of preparing a solution S1 at a temperature T1 comprised between −200° C. and 10° C., said solution S1 comprising a solvent and (PS ４ ) ３－ At least P species in the form of ＋ and Li species in the form of X － and the remaining sulfur in the form of polysulfides, followed by removing at least a portion of the solvent from the solution S1 to obtain Li ６ P.S. ５ Li ６ P.S. ５ A process for preparing X, wherein X is a halogen.

2. 2. The method according to claim 1, wherein said solution S1 is obtained by mixing lithium sulfide, phosphorus sulfide and a halogen compound in said solvent at a temperature comprised between -200°C and 10°C.

3. The solution S1 is - mixing lithium sulfide and a halogen compound in said solvent to obtain a precursor solution; and - adding phosphorus sulfide to said precursor solution, at a temperature comprised between -200°C and 10°C, to obtain said solution S1; The method of claim 1 , wherein the compound is obtained from

4. The method according to any one of claims 1 to 3, wherein the step of removing at least a portion of the solvent from S1 is carried out at a temperature comprised between 30°C and 200°C.

5. The preparation of solution S1 may be carried out in an inert atmosphere, under vacuum, or under H ２ The process according to any one of claims 1 to 4, carried out under a S flow.

6. Li ６ P.S. ５ Method according to any one of the preceding claims, in which X is subsequently heat treated at a temperature comprised between 150°C and 700°C.

7. The solvent is Li ６ P.S. ５ The method according to any one of claims 1 to 6, wherein X, lithium sulfide, phosphorus sulfide, and a halogen compound are soluble.

8. The method according to any one of claims 1 to 7, wherein the solvent is an aliphatic alcohol.

9. The method according to any one of claims 1 to 8, wherein the solvent is selected in the group consisting of ethanol, methanol, and mixtures thereof.

10. The method according to any one of claims 1 to 9, wherein the temperature T1 is comprised between -110°C and 0°C.

11. The method according to any one of claims 2 to 10, wherein the halogen compound is selected in the group consisting of LiCl, LiBr, LiI, and LiF.

12. The solution S1 contains at least 50 mol % of Li with respect to the total molar amount of lithium sulfide added to the solvent. ＋ The method of any one of claims 1 to 11, comprising Li species in the form

13. The solution S1 has at least 50 mol % (PS ４ ) ３－ The method of any one of claims 1 to 12, comprising P species in the form

14. The solution S1 contains at least 50 mol % of X based on the total molar amount of halogen compounds added to the solvent. － The method of any one of claims 1 to 13, comprising species X in the form

15. 15. The method according to any one of the preceding claims, wherein the temperature T1 is comprised between -100°C and -50°C and the step of removing at least a portion of the solvent from the solution S1 is carried out at a temperature comprised between 35°C and 65°C.

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