Process for preparing a powder of lithium sulfide

Abstract

The present disclosure relates to a process for preparing a powder of lithium sulfide (Li2S powder), comprising the steps of: a) providing a powder of lithium hydroxide, or a powder of lithium carbonate presenting a residual water content below 5 wt %; b) reacting such LiOH powder or Li2CO3 powder with H2S present in a reagent gas (RG1) to obtain Li2S powder, optionally carbon dioxide and water vapor, wherein reagent gas (RG1) comprises H2S, a gas (G) selected from the list consisting of H2, CH4, C2H6, C3H8, and mixtures thereof and optionally an inert carrier gas (CG) different from (G); wherein reacting is performed in a fixed bed reactor, a fluidized bed reactor, a stirred reactor or a mobile bed reactor.

Description

DescriptionPROCESS FOR PREPARING A POWDER OF LITHIUM SULFIDECross-reference to related application

[0001] This application claims priority to European application No. 24315298.0 filed on June 19, 2024, the whole content of this application being incorporated herein by reference for all purposes:Technical field

[0002] The present disclosure relates to a process for preparing a powder of lithium sulfide (Li2S powder) comprising the steps of: a) providing a powder of lithium hydroxide (LiOH powder A), or a powder of lithium carbonate (Li2COs powder A’) presenting a residual water content below 5 wt %; b) reacting such LiOH powder A or Li2COs powder A’ with H2S present in a reagent gas (RG1 ) to obtain Li2S powder, optionally carbon dioxide and water vapor, wherein reagent gas (RG1 ) comprises H2S, a gas (G) selected from the list consisting of H2, CH4, C2H6, C3H8, and mixtures thereof and optionnally an inert carrier gas (CG) different from (G); wherein reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) is performed in at least one fixed bed reactor, at least one fluidized bed reactor, at least one stirred reactor or at least one mobile bed reactor, with the proviso that if reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) is performed in a mobile bed reactor, powder and reagent gas (RG1 ) flow in the same direction. The present disclosure also relates to the powder of lithium sulfide (Li2S powder ) obtained from such a process, its use to manufacture sulfide solid electrolytes and its use as cathode active material in a rechargeable lithium battery.

[0003] Lithium ion batteries are widely used as power supplies notably for appliances. In such secondary batteries, an organic solvent is used as an organic liquid electrolyte and lithium ions migrate from one electrode to the other, depending on whether the battery is charging or discharging.

[0004] Because the solvent used as an electrolyte is flammable, all-solid-state lithium ion batteries not using organic solvent are very attractive. Such all-solid-state lithium ion batteries are formed by solidifying the whole battery using a solid electrolyte, for example containing Li, P, S, and a halogen.

[0005] One of the starting materials to prepare such a solid electrolyte is lithium sulfide (Li2S). The technical features (e.g. purity, particle size and porosity) of such starting material is crucial to obtain a high purity solid electrolyte. Different methods have been disclosed in the art for the manufacture of Li2S generally involving raw materials such as LiOH or Li2COs as lithium source and H2S as sulfur source.

[0006] In some examples the manufacture of Li2S is performed in solution, e.g. in an organic solvent, and is therefore a gas-liquid reaction between gaseous H2S stream and LiOH or Li2COs in solution. However, it appears to be advantageous, environmental and economically, to perform a gas-solid reaction between gaseous H2S stream and LiOH or Li2COs solid particles at least because it requires less effluent management.

[0007] The overall equilibrated reaction between LiOH and H2S can be represented by the following reaction scheme 1 :(scheme 1 )

[0008] Besides, the reaction between Li2COs and H2S can be represented by the following reaction scheme 2:(scheme 2)

[0009] For example, US 2020 / 165129 A1 (Albemarle) relates to a Li2S powder and its preparation, such powder having an average particle size between 250 and 1500 pm and BET surface areas between 1 and 100 m2 / g. The preparationmethod consists in: a) heating lithium hydroxide monohydrate with an average particle size in the 150-2,000 pm range in a temperature-controlled unit to a reaction temperature between 150°C-450°C in the absence of air, flowing an inert gas over or through it, until the residual water of crystallization content of the formed lithium hydroxide is less than 5 wt.% and b) overflowing or traversing the anhydrous lithium hydroxide formed in the first stage by a sulfur source.

[0010] In some embodiments, the sulfur source is gaseous H2S of the maximum purity. Indeed, it should contain less than 300 ppm of gaseous impurities that may react e.g. with lithium sulfide. For obtaining lithium sulfide, a constant hydrogen sulfide stream of either pure H2S or a mixture of H2S and an inert carrier gas is introduced in a reactor filled with lithium hydroxide.

[0011] Using H2S of such high purity represents an important additional cost to the process.

[0012] WO 2023 / 280797 A1 (Rhodia Operations) discloses a process for obtaining a powder of lithium sulfide having a d50 of less than 10pm by reacting a powder of lithium hydroxide having a d50 of less than 10pm with a sulfide reactant that can be gaseous H2S. Nothing is said about water content or about any other substance present in H2S gas.

[0013] EP 2698856 A1 (Mitsui Mining & Smelting Co., Ltd) discloses a method for producing lithium sulfide powder by reacting a powder of lithium carbonate with a gas containing sulfur, like gaseous H2S, in a dry state. Again, nothing is said about water content or about any other substance present in H2S gas.

[0014] US 2017 / 368515 A1 (Idemitsu Kosan Co., Ltd.) discloses a method for producing a lithium sulfide in the absence of solvent, through the reaction of lithium hydroxide and a flow rate of hydrogen sulfide into a reaction container at a temperature ranging from 140°C to 230°C. The water content of the hydrogen sulfide involved in the reaction is preferably 50 ppm or less. Therefore drying of H2S to such an extent represents an important additional cost to the process. An apparatus including a reaction container for allowing lithium hydroxide powder to be in contact with a hydrogen sulfide gas equippedwith a stirring blade and heating systems is also disclosed. Finally, nothing is said about any other substance present in H2S gas.

[0015] JP2015174787 A2 (Toray Fine Chemicals Co., Ltd) discloses a manufacturing method of Li2S through gas-solid reaction between gaseous H2S stream and particles of lithium carbonate Li2COs at 650°C. Although the purity of hydrogen sulfide is said to be more preferably 95% or more, nothing is said about water content or about any other substance present in H2S. Moreover, exemplified hydrogen sulfide raw material, is provided by Sumitomo Seika Co., Ltd., has a purity of 99.99% and contains, according to the manufacturer, less than 2 mg / L of water.

[0016] JP2018087133 A2 (Toray Fine Chemicals Co., Ltd) discloses a manufacturing method of Li2S through gas-solid reaction between gaseous H2S stream and particles of lithium carbonate LiOH at 400°C. Although the purity of hydrogen sulfide is said to be more preferably 95% ore more, nothing is said about water content or about any other substance present in H2S. Moreover, exemplified hydrogen sulfide raw material, is provided by Sumitomo Seika Co., Ltd., has a purity of 99.99% and contains, according to the manufacturer, less than 2 mg / L of water.

[0017] Finally, JP2017141129 A2 (Furukawa Co., Ltd.) discloses a method for manufacturing Li2S by the reaction between lithium hydroxide and gaseous hydrogen sulfide stream that may contain dilution gas such as nitrogen or argon, in absolute pressure of less than 0.101 MPa at a temperature of 130°C or more. In this method, for example, particulate LiOH is placed on a porous sheet in a reaction vessel at a temperature of 300°C and hydrogen sulfide is introduced with a flow rate of 10 L / min from a gas introduction pipe. Exhausted gas containing the water generated by the reaction between LiOH and H2S, and unreacted H2S can be recycled after water removal. However, nothing is said about any other substance present in H2S gas.

[0018] Summary

[0019] From prior art Li2S is generally manufactured through a gas-solid reaction between a reagent gas comprising H2S and LiOH or Li2COs solid particles athigh temperature. The reagent gas generally comprises H2S, optionally an inert carrier gas and / or traces of water.

[0020] As can be seen from scheme 1 and scheme 2 management of water is a key issue to generate good conversion of LiOH or Li2COs and avoid reverse reaction leading back to LiOH from Li2S. Presence of water may also lead to the formation of LiSH.

[0021] The presence of water also reduces the overall kinetic of the desired reaction, thus rendering the process less efficient.

[0022] As can be understood from the patent documents cited above, water management is generally solved through using extremely dry H2S gas sources which is not a cost efficient way of proceeding.

[0023] Therefore, there is a need for a process wherein Li2S of high purity can be produced.

[0024] There is a need for an efficient process which allows recovering high purity Li2S having a very low amount of residual LiOH.

[0025] There is a need for an efficient process which allows recovering high purity Li2S having a very low amount of LiSH.

[0026] There is a need for an efficient process which allows high kinetic of the reaction of Li2S formation.

[0027] Finally, there is a need for Li2S powder of high purity with low amount of residual LiOH and low amount of LiSH.

[0028] Hence, the Applicant faced the problem of providing a new process for the manufacture of Li2S powder that can solve the above mentioned issues.

[0029] The present invention relates to a process for preparing a powder of lithium sulfide (Li2S powder), comprising the steps of: a) providing a powder of lithium hydroxide (LiOH powder A), or a powder of lithium carbonate (Li2COs powder A’) presenting a residual water content below 5 wt %; b) reacting such LiOH powder A or Li2COs powder A’ with H2S present in a reagent gas (RG1 ) to obtain Li2S powder, optionally carbon dioxide and water vapor,wherein reagent gas (RG1 ) comprises H2S, a gas (G) selected from the list consisting of H2, CH4, C2H6, C3H8, and mixtures thereof and optionally an inert carrier gas (CG) different from (G); wherein reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) is performed in at least one fixed bed reactor, at least one fluidized bed reactor, at least one stirred reactor or at least one mobile bed reactor, with the proviso that if reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) is performed in a mobile bed reactor, powder and reagent gas (RG1 ) flow in the same direction.

[0030] The present disclosure also relates to the powder of lithium sulfide (Li2S powder) obtained from such a process.

[0031] The present invention also relates to a Li2S powder obtainable by the process as above explained characterized in that it contains less than 0.2 wt % of residual LiOH as measured by solid state proton NMR and has a solid state proton NMR spectrum showing a peak signal at -2.0 ± 0.2 ppm that corresponds to less than 0.005 wt % of equivalent LiOH.

[0032] The present invention also relates to the use of the Li2S powder according to the invention to manufacture sulfide solid electrolyte for use in a rechargeable lithium battery.

[0033] The present invention also relates to the use of the Li2S powder according to the invention as cathode active material in a rechargeable lithium battery.Disclosure of the invention

[0034] The present invention relates to a process for obtaining a powder of lithium sulfide powder (Li2S powder), such powder having high purity which makes it well-suited to be used to prepare battery components such as sulfide solid electrolytes or to be used as cathode active material in a rechargeable lithium battery.

[0035] The process of the present invention for the manufacture of said Li2S powder advantageously comprises the steps of:a) providing a powder of lithium hydroxide (LiOH powder A), or a powder of lithium carbonate (U2CO3 powder A’) presenting a residual water content below 5 wt %; b) reacting such LiOH powder A or Li2COs powder A’ with H2S present in a reagent gas (RG1 ) to obtain Li2S powder, optionally carbon dioxide and water vapor, wherein reagent gas (RG1 ) comprises H2S, a gas (G) selected from the list consisting of H2, CH4, C2H6, CsHs, and mixtures thereof and optionally an inert carrier gas (CG) different from (G); wherein reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) is performed in at least one fixed bed reactor, at least one fluidized bed reactor, at least one stirred reactor or at least one mobile bed reactor, with the proviso that if reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) is performed in a mobile bed reactor, powder and reagent gas (RG1 ) flow in the same direction.

[0036] Advantageously, the process of the present invention is solvent free. In other words, no solvent is added to the reactor during the reaction under step b). This is advantageous because the step for removing the solvent adds to the complexity of the industrial process, as well as to its overall cost.

[0037] It is understood that the process according to the present invention may be carried out in the presence of a very low amount of solvent, that-is-to-say an amount of solvent less than 5 wt.%, based on the total weight of the reaction mixture. Preferably, according to this embodiment, the amount of solvent is less than 4 wt.%, less than 3 wt.%, less than 2 wt.%, less than 1 wt.%, less than 0.5 wt.%, less than 0.1 wt.%, less than 0.01 wt.%, or less than 0.001 wt.% of solvent, based on the total weight of the reaction mixture. The total weight of the reaction mixture is obtained by adding the weight of the reactants.

[0038] In the process of the present invention the powder of lithium hydroxide (LiOH powder A), or the powder of lithium carbonate (Li2COs powder A’) provided in step a) presents a residual water content below 5 wt %.

[0039] In some embodiments, the residual water content of the LiOH powder A or the U2CO3 powder A’ is less than 4 wt.%, less than 3 wt.%, less than 2 wt.%, less than 1 wt.% or even less than 0.1 wt.% based on the total weight of the LiOH powder. In some embodiments, the residual water content of the LiOH powder A ot the Li2COs powder A’ is more than 0.001 wt.%, or more than 0.01 wt.%.

[0040] Accordingly when LiOH is used as raw material, LiOH powder A of step a) can be obtained by heating powder of lithium hydroxide monohydrate (LiOH.H2O) at a temperature generally equal to or less than 400°C, preferably equal to or less than 300°C, and more preferably equal to or less than 200°C, in order to obtain the LiOH powder A.

[0041] In some embodiment, the LiOH powder A is prepared by heating a powder of lithium hydroxide monohydrate (LiOH.H2O) presenting a residual water content above 5 wt.%, at a temperature equal to or less than 180°C, in order to obtain a powder of lithium hydroxide presenting a residual water content below 5 wt.% (LiOH powder A).

[0042] According to this embodiment, the step of heating is performed at a temperature equal to or less than 180°C. Such temperature may for example be less than 170°C, less than 160°C, less than 150°C, less than 140°C, less than 130°C, less than 120°C, less than 110°C and even less than 100°C. The heating step can for example take place at a temperature of 80°C.

[0043] Preferably, such heating step is performed in the absence of air. The heating step advantageously takes place under vacuum and / or by flowing an inert gas over or through the powder. Inert gas can be nitrogen, argon or mixtures thereof.

[0044] Generally the pressure does not exceed 3 bars during the heating step; often it does not exceed 1.3 bars. Good results were obtained at atmospheric pressure.

[0045] In some embodiments the heating step is conducted under vacuum.

[0046] The time duration of the heating step is not limited and can be as long as needed to reach the expected residual amount of water. For example, the heating step can last between 1 and 24 hours.

[0047] Good results were obtained by drying LiOH.FhO at 200°C during 3 hours by flowing nitrogen over or through the powder.

[0048] In some embodiments the powder of lithium hydroxide monohydrate (LiOH.FhO) presenting a residual water content above 5 wt.% is ground before being heated.

[0049] Any type of equipment can be used to perform such grinding. Reference can for example be made to rotor-stator grinders, planetary ball mills or attritors.

[0050] The time duration of the grinding step is not limited and can be as long as needed to reach the expected dso-value. For example, the grinding step can last between 1 and 24 hours.

[0051] Generally dso-value of the LiOH powder A ranges from 100 pm to 600 pm, preferably from 200 pm to 400 pm. Generally, doo-value is below 1000 pm.

[0052] The particle size distribution can be measured by laser diffraction from a dispersion of the powder in para-xylene.

[0053] dx-value denotes the value which is determined with regard to the distribution by volume of the sizes of the particles for which x% of the particles have a size less than or equal to this value dx. Thus, for example, with respect to dio, 10% of the particles have a size which is less than dio. For example again, with respect to doo, 90% of the particles have a size which is less than doo. dso corresponds to the median value of the distribution by volume.

[0054] When Li2COs is used as raw material, Li2COs powder A’ of step a) is obtained by heating powder of lithium carbonate Li2COs presenting a residual water content above 5 wt.%, at a temperature generally of less than 400°C, preferably less than 300°C, more preferably less than 200°C and even more preferably less than 180°C, in order to obtain a powder of lithium carbonate presenting a residual water content below 5 wt.% (Li2COs powder A’).

[0055] Li2COs powder A’ of step a) is prepared by heating a powder of lithium carbonate Li2COs presenting a residual water content above 5 wt.%, at a temperature of less than 180°C, in order to obtain a powder of lithium carbonate presenting a residual water content below 5 wt.% (Li2COs powder A’).

[0056] Preferably, such heating step is performed in the absence of air. The heating step advantageously takes place under vacuum and / or by flowing an inert gas over or through the powder.

[0057] Generally the pressure does not exceed 3 bars during the heating step; often it does not exceed 1.3 bars. Good results were obtained at atmospheric pressure.

[0058] The time duration of the heating step is not limited and can be as long as needed to reach the expected residual amount of water. For example, the heating step can last between 1 and 24 hours.

[0059] Generally dso-value of the Li2COs powder A’ ranges from 100 pm to 600 pm, preferably from 200 pm to 400 pm. Generally, dgo-value is below 1000 pm.

[0060] In some embodiments the powder of lithium carbonate presenting a residual water content above 5 wt.% is ground before being heated as above described for LiOH, H2O.

[0061] Preparing LiOH powder A or Li2COs powder A’ having a residual water content below 5 wt % can be performed by batch using equipment well know by the person having ordinary skill in the art.

[0062] Just for the sake of example it can be performed in a reactor equiped with a stirring blade and heating equipment, in which particles are dried with water removal.

[0063] Preparing LiOH powder A or Li2COs powder A’ having a residual water content below 5 wt % can be performed continuously using equipment well known by the person having ordinary skill in the art.

[0064] Just for the sake of example it can be performed in a rotary kiln or in a tubular reactor equipped with an Archimedean screw, in which particles are conveyed and dried in a continuous and dried in a continuous flow, with water removal.

[0065] The second step b) of the process consists in reacting such LiOH powder A or Li2COs powder A’ with H2S present in a reagent gas (RG1 ) to obtain Li2S powder, optionally carbon dioxide and water vapor, wherein reagent gas (RG1 ) comprises H2S, a gas (G) selected from the list consisting of H2, CH4, C2H6,CsHs, and mixtures thereof and optionally an inert carrier gas (CG) different from (G).

[0066] The inventors have found that surprisingly and advantageously using reagent gas (RG1 ) comprising H2S and a gas (G) selected from the list consisting of H2, CH4, C2H6, C3H8, and mixtures thereof at a given content of optional inert carrier gas (CG) different from (G) has a significant impact on the kinetic of the reaction between LiOH powder A or U2CO3 powder A’ and hydrogen sulfide and thus on the kinetic of formation of l_i2S .

[0067] Accordingly, at a given inert gas (CG) content a faster reaction rate is observed when (RG1 ) comprises H2S and a gas (G) than when (RG1 ) comprises H2S and no gas (G). This faster reaction rate is accompanied by a higher purity of the l_i2S powder obtained by the process according to the present invention.

[0068] Faster reaction rates can be demonstrated by Temperature Programmed Sulfiding (TPS) experiments using different reagent gas and LiOH powder A or Li2COs powder A’. Some examples will be detailed below.

[0069] Step b) generally takes place at a temperature at least 20°C below the melting point of the considered LiOH powder A or Li2COs powder A’.

[0070] When LiOH powder A is used as raw material, step b) generally takes place at a temperature ranging from 100 to 450°C, preferably ranging from 100 to 400°C. In some embodiments, the temperature ranges from 150°C to 350°C, or from 180°C to 300°C. Good results were obtained at 400°C.

[0071] When LiOH powder A is used as raw material, Li2S powder and water vapor are obtained in step b).

[0072] Melting point of the considered LiOH powder A can be found in the literature or can be measured by any well known technique such as Differential Scanning calorimetry (DSC).

[0073] When Li2COs powder A’ is used as raw material, step b) generally takes place at a temperature ranging from 200 to 700°C, sometimes at a temperature ranging from 300°C to 650°C, often ranging from 400°C to 600°C.

[0074] When Li2COs powder A’ is used as raw material, Li2S powder, carbon dioxide and water vapor are obtained in step b).

[0075] Melting point of the considered U2CO3 powder A’ can be found in the literature or can be measured by any well known technique such as Differential Scanning calorimetry (DSC).

[0076] In second step b) hydrogen sulfide is used as a sulfur source and more particularly gaseous hydrogen sulfide (H2S) is reacted with LiOH powder A or Li2COs powder A’.

[0077] The overall equilibrated reaction between LiOH and H2S can be represented by the following reaction scheme 1 :(scheme 1 )

[0078] Besides, the reaction between Li2COs and H2S can be represented by the following reaction scheme 2:(scheme 2)

[0079] Generally, the reagent gas (RG1 ) according to the invention comprises H2S in an amount ranging from 30 % to 99.9 % in volume and the gas (G) in an amount ranging from 0.1 % to 20 % in volume with regard to the total of the volume of the reagent gas (RG1 ).

[0080] In some other embodiments, the reagent gas (RG1 ) according to the invention comprises H2S in an amount ranging from 40 % to 70 % in volume and the gas (G) in an amount ranging from 1 % to 20 % in volume with regard to the total of the volume of the reagent gas (RG1 ).

[0081] Still in some other embodiments, the reagent gas (RG1 ) according to the invention comprises H2S in an amount ranging from 50 % to 70 % in volume and the gas (G) in an amount ranging from 5 % to 15 % in volume with regard to the total of the volume of the reagent gas (RG1 ).

[0082] In some embodiments, when the amount of H2S and of the gas (G) is below 100 % in volume of the reagent gas (RG1 ), the complement is provided by the inert carrier gas (CG) to reach 100 % in volume of the reagent gas (RG1 ).

[0083] Good results were obtained with the reagent gas (RG1 ) consisting of 60 % in volume of H2S, 10 % in volume of gas (G) and 30 % in volume of inert carrier gas (CG).

[0084] Good results were also obtained with the reagent gas (RG1 ) consisting of 60 % in volume of H2S, 5 % in volume of gas (G) and 35 % in volume of inert carrier gas (CG).

[0085] Generally, the gas (G) is selected from the list consisting of H2, CH4, C2H6, C3H8, and mixtures thereof. In some preferred embodiments, the gas (G) is H2.

[0086] Generally, inert carrier gas (CG) can be nitrogen, argon or mixtures thereof. In some preferred embodiments, the inert carrier gas (CG) is nitrogen.

[0087] For example, good results were obtained with the reagent gas (RG1 ) consisting of 60 % in volume of H2S, 10 % in volume of H2 and 30 % in volume of N2.

[0088] For example, good results were obtained with the reagent gas (RG1 ) consisting of 60 % in volume of H2S, 5 % in volume of H2 and 35 % in volume of N2.

[0089] In some embodiments, the reagent gas (RG1 ) according to the invention is essentially composed or consists of H2S in an amount ranging from 80 % to 99.9 % in volume and the gas (G) in an amount ranging from 0.1 % to 20 % in volume with regard to the total of the volume of the reagent gas (RG1 ).

[0090] By essentially composed is meant that the reagent gas (RG1 ) comprises less than 1.5 % in volume, preferably less than 1 % in volume, more preferably less than 0.5 % in volume, of a gas different from H2S and (G) with regard to the total of the volume of the reagent gas (RG1 ).

[0091] Generally, the reagent gas (RG1 ) comprises water in an amount of at most 5.0 wt%. In some embodiments, the reagent gas (RG1 ) comprises water in an amount ranging from 0.5 to 5.0 wt%; in some other embodiments the reagent gas (RG1 ) comprises water in an amount ranging from 1.0 to 4.0 wt%; still in some other embodiments the reagent gas (RG1 ) comprises water in an amount ranging from 1 .5 to 3.5 wt%.

[0092] Advantageously and surprisingly, the process of the present invention does not require extremely dried reagent gas (RG1 ) as it is generally recommended in the prior art. This is advantageous because the step of drying reagent gas (RG1 ), or of its components, increases the cost of the overall process.

[0093] In step b), reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) to obtain l_i2S powder is performed in at least one fixed bedreactor, at least one fluidized bed reactor, at least one stirred reactor or at least one mobile bed reactor, with the proviso that if reacting LiOH powder A or U2CO3 powder A’ with H2S present in the reagent gas (RG1 ) is performed in a mobile bed reactor, powder and reagent gas (RG1 ) flow in the same direction. In other terms, step b) is not carried out in a reactor wherein said LiOH powder A or said Li2COs powder A’ flows counter-currently to said reagent gas (RG1 ).

[0094] Preparing Li2S powder according to the invention can be performed by batch using equipment well known by the person having ordinary skill in the art.

[0095] Therefore in step b), reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) to obtain Li2S powder is performed in at least one fixed bed reactor, at least one fluidized bed reactor or at least one stirred powder reactor.

[0096] In the present invention a fixed bed reactor is, for example, a container where the reagent gas (RG1 ) flows through the bed of powder A or powder A’ which is held between two porous surfaces or that the flow rate of reagent gas (RG1 ) is not enough for the gas to lift the particles and get a fluidized bed.

[0097] In the present invention a fluidized bed reactor is, for example, a container where the reagent gas (RG1 ) that flows through the bed of powder A or powder A’ which is spread on a porous surface, can lift and carry the particles that make up the powder. In the batch process said particles are not transported out of the reactor by the reagent gas; in fact the gravity center of the whole particles is stationary.

[0098] Fixed bed and fluidized bed are described in JP2017141129 A2 (Furukawa Co., Ltd.) which discloses a method for manufacturing Li2S by the reaction between lithium hydroxide and gaseous hydrogen sulfide stream. In this method, particulate LiOH is placed on a porous sheet in a reaction vessel at a given temperature and hydrogen sulfide is introduced from the bottom with different flow rates via a gas introduction pipe. When the flow rate is low, it is not enough for the gas to lift the particles and the bed is fixed. When the flow rate is enough for the gas to lift the particles then the bed is fluidized.

[0099] Stirred reactor suitable for the process according to the invention can be any reactor where LiOH powder A or U2CO3 powder A’ can be in contact with reagent gas (RG1 ) under stirring and heating at the required temperature.

[0100] Just for the sake of example, preparing l_i2S powder according to the invention can be performed in a stirred reactor as described in US 2017 / 368515 A1 (Idemitsu Kosan Co., Ltd.). Indeed US 2017 / 368515 A1 discloses a method for producing a lithium sulfide via the reaction of lithium hydroxide and a flow rate of hydrogen sulfide using an apparatus including a reaction container for allowing lithium hydroxide powder to be in contact with a hydrogen sulfide gas equipped with a stirring blade and heating systems.

[0101] Still for the sake of example, a stirred reactor can be a rotary kiln or a paddle dryer allowing stirring a LiOH powder A or Li2COs powder A’ in the presence of reagent gas (RG1 ) flow.

[0102] Preparing Li2S powder according to the invention can be performed continuously using equipment well known by the person having ordinary skill in the art.

[0103] Therefore in step b), reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) to obtain Li2S powder can be performed in at least one mobile bed reactor, with the proviso that powder A or powder A’ and reagent gas (RG1 ) flow in the same direction.

[0104] Powder A or powder A’ and reagent gas (RG1 ) flowing in the same direction means that powder A or powder A’ flows with reagent gas (RG1 ) stream, in other terms that powder A or powder A’ flows in co-current with reagent gas (RG1 ) flow.

[0105] Just for the sake of example a mobile bed reactor can be a rotary kiln or a tubular reactor equipped with an Archimedean screw, in which powder A or powder A’ is conveyed in a continuous flow while reagent gas (RG1 ) flows in the same direction.

[0106] Alternatively, in the present invention a mobile bed reactor can be a fluidized bed reactor, for example, a container where the reagent gas (RG1 ) that flows through the bed of powder A or powder A’ which is spread on a porous surface,can lift, carry and transport out of the reactor the particles that make up the powder. In that case the gravity center of the whole particles is not stationary but flows with the reagent gas (RG1 ).

[0107] The reaction of step b) generally takes place at a pressure below 10 bars (1 MPa), preferably at pressure below 5 bars (0.5 MPa), more preferably at pressure below 2 bars (0.2 MPa), even more preferably at pressure below 1.5 bars (0.15 MPa). Good results were obtained at 1 bar (0.1 Mpa).

[0108] In step b) the reagent gas (RG1 ) is generally introduced in the reactor through at least one inlet pipe and flows over or through LiOH powder A or Li2COs powder A’ present in the reactor.

[0109] In the process according to the invention the reagent gas (RG1 ) is generally introduced with a gas hour velocity (GHSV) ranging from 50 IT1to 1000 tr1

[0110] Water vapor obtained in step b) is preferably removed from the reactor. Therefore, step b) comprises extracting unreacted H2S, unreacted gas (G), formed water vapor, optionally formed carbon dioxide and optionally present inert carrier gas from the reactor via at least one outlet pipe as an extracted gas (RG2). Accordingly, extracted gas (RG2) comprises unreacted H2S, unreacted gas (G), water vapor, optionally formed carbon dioxide and optionally present inert carrier gas.

[0111] Generally, in step b) introduction of the reagent gas (RG1 ) and extraction of extracted gas (RG2) are conducted in a single gas stream going through the reactor from inlet pipe as reagent gas (RG1 ) to outlet pipe as extracted gas (RG2).

[0112] In some embodiments the unreacted H2S, and unreacted gas (G) comprised in extracted gas (RG2) are recycled and are reintroduced in the process according to the invention. Any technique well known by the person having ordinary skill in the art can be used for this purpose .

[0113] The inventors have found that the process according to the invention allows to prepare with high reaction rate highly pure l_i2S powder.

[0114] It has been found surprisingly that the l_i2S powder of the present invention, despite the fact that it is produced using reagent gas (RG1 ) comprising H2S, agas (G) selected from the list consisting of H2, CH4, C2H6, C3H8, and mixtures thereof is a very pure material presenting low amount of LiOH and LiSH.

[0115] Indeed, it has been found that advantageously the l_i2S powder of the invention, i.e. is produced using reagent gas (RG1 ) comprising H2S, a gas (G) selected from the list consisting of H2, CH4, C2H6, C3H8, and mixtures thereof, is characterized by a lower amount of residual LiOH as well as a lower amount of LiSH than the Li2S powder of the prior art prepared using H2S in the absence of any gas (G).

[0116] Accordingly, the Li2S powder of the invention generally contains less than 0.2 wt %, preferably less than 0.15 wt %, more preferably less than 0.1 wt % of residual LiOH as measured by solid state proton NMR.

[0117] In addition, the Li2S powder of the invention generally contains less than 0.005 wt %, preferably less than 0.003 wt %, more preferably less than 0.002 wt % expressed in equivalent LiOH of a compound (I) to which is assigned the peak signal at -2.0 ± 0.2 ppm in solid state proton NMR.

[0118] Therefore, the Li2S powder of the invention has a solid state proton NMR spectrum showing a peak signal at -2.0 ± 0.2 ppm that corresponds to less than 0.005 wt %, preferably less than 0.003 wt %, more preferably less than 0.002 wt % of equivalent LiOH.

[0119] The peak signal at -2.0 ± 0.2 ppm cannot be assigned to LiOH; without being bound to any theory it is assumed that the compound (I) is LiSH.

[0120] Accordingly an object of the present invention is a process as above described, wherein the Li2S powder obtained contains less than 0.2 wt % of residual LiOH as measured by solid state proton NMR and has a solid state proton NMR spectrum showing a peak signal at -2.0 ± 0.2 ppm that corresponds to less than 0.005 wt %of equivalent LiOHpreferably less than 0.003 wt% .

[0121] Still another object of the invention is a Li2S powder obtainable by the process as above explained characterized in that : it contains less than 0.2 wt % of residual LiOH as measured by protonNMR,it has a solid state proton NMR spectrum showing a peak signal at -2.0 ± 0.2 ppm that corresponds to less than 0.005 wt % of equivalent LiOH, more preferably less than 0.003 wt %.

[0122] Moreover, generally the l_i2S powder of the invention is characterized in that it has a purity as measured by XRD of more than 99 wt %.

[0123] Solid state proton NMR and XRD methods used to determine the purity of l_i2S powders are detailed in the experimental part below.

[0124] Finally, the l_i2S powder of the present invention generally contains less than 0.08 wt % of carbon residues as measured by C / S elemental analysis.

[0125] The l_i2S powder of the present invention is composed of free flowing particles having relatively large particle size, dust-free and therefore easy to handle in a subsequent process for technical and safety reasons.

[0126] Generally, the l_i2S powder of the present invention is characterized by a specific surface area ranging from 2 to 20 m2 / g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method.

[0127] The l_i2S powder of the present invention is characterized by its dso-value, as measured by laser diffraction in para-xylene ranging from 20 pm to 500 pm.

[0128] The l_i2S powder of the present invention is characterized by its dgo-value, as measured by laser diffraction in para-xylene of less than 1000 pm.

[0129] In some embodiments, the l_i2S powder according to the invention is characterized in that it has a specific surface area generally ranging from 2 to 20 m2 / g, for example from 3 to 10 m2 / g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method, it has a dso- value generally ranging from 20 pm to 500 pm as measured by laser diffraction in para-xylene, and it has a dgo-value generally of less than 1000 pm as measured by laser diffraction in para-xylene.

[0130] It has also been found that surprisingly the l_i2S powder of the present invention is less reactive to ambient moisture. Indeed, the l_i2S powder is such that it releases less than 400 ml / g of H2S when exposed to a relative humidity of 30- 40% at 23°C during 60 minutes. This is particularly advantageous since it appears that l_i2S powder of the present invention is more stable during storageor transportation than l_i2S powder obtained using reagent gas comprising H2S and no additional gas (G).

[0131] Such l_i2S powder having the above described features may notably be produced by the process of the present invention.

[0132] Accordingly an object of the present invention is a process as above described, wherein the l_i2S powder obtained, containing less than 0.2 wt % of residual LiOH as measured by solid state proton NMR and having a solid state proton NMR spectrum showing a peak signal at -2.0 ± 0.2 ppm that corresponds to less than 0.005 wt %of equivalent LiOH, preferably less than 0.003 wt%, is further characterized in that it exhibits at least one, preferably all, of the following features: it has a purity of more than 99 wt % as measured by XRD, it contains less than 0.08 wt % of carbon residues as measured by C / S elemental analysis, it has a specific surface area ranging from 2 to 20 m2 / g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method, it has a dso-value ranging from 20 pm to 500 pm, as measured by laser diffraction in para-xylene, it has a dgo-value of less than 1000 pm, as measured by laser diffraction in para-xylene.

[0133] Still another object of the invention is the Li2S powder containing less than 0.2 wt % of residual LiOH as measured by proton NMR, having a solid state proton NMR spectrum showing a peak signal at -2.0 ± 0.2 ppm that corresponds to less than 0.005 wt % of equivalent LiOH, more preferably less than 0.003 wt % characterized in that it exhibits at least one, preferably all, of the following features: it has a purity of more than 99 wt % as measured by XRD, it contains less than 0.08 wt % of carbon residues as measured by C / S elemental analysis, it has a specific surface area ranging from 2 to 20 m2 / g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method,it has a dso-value ranging from 20 pm to 500 pm, as measured by laser diffraction in para-xylene, it has a dgo-value of less than 1000 pm, as measured by laser diffraction in para-xylene.

[0134] It has been found that the l_i2S powder according to the present invention is suitable to be used to manufacture sulfide solid electrolytes for rechargeable lithium batteries. Thus, another object of the present invention is related to the use of the l_i2S powder according to the present invention to manufacture sulfide solid electrolytes for rechargeable lithium batteries.

[0135] It has been found that the l_i2S powder according to the present invention is suitable to be used as cathode active material (positive electrode), combined with liquid, polymer or solid electrolyte. Particularly it is suitable to prepare all solid state cells based on sulfide electrolytes, acting as the positive active electrode material. Thus, another object of the present invention is related to the use of the l_i2S powder according to the present invention as active material in a rechargeable lithium battery.Figures

[0136] Figure 1 : solid state1H NMR spectrum of l_i2S made from the process according to the invention

[0137] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0138] The invention will be now described with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.Examples

[0139] Materials

[0140] LiOH-F was obtained from Altichem (dso = 300-350 pm).H2S was obtained from Air Liquide (purity > 99.5 vol.%).

[0141] Drying of LiOH and sulfidation

[0142] Approximately 126 grams of LiOH, 1 H2O obtained from Altichem were weighted and introduced into a quartz fixed bed reactor equipped with a heating system. The powder was exposed to a N2 flow and the temperature was raised up to 200 °C to remove water. H2O was recovered as a condensate downstream. Once there was no more H2O collected, the temperature was raised up to 400 °C. After the temperature was stabilized, the reagent gas composition comprising H2S, N2 and in some experiments H2 was introduced in the reactor via an inlet pipe and the gas hour space velocity (GHSV) was kept at 300 IT1. The gas flows were controlled by mass flow controllers. The sulfidation reaction started as soon as H2S gets in contact with the LiOH powder. The sulfidation reaction was followed by weighting condensed water collected after unreacted gas and formed water vapor were extracted via an outlet pipe. Furthermore, the endothermic reaction was followed by measuring the temperature in the bed powder. The sulfidation reaction was stopped when no more H2O or no more endotherm icity was detected. Finally, the reactor was cooled down under N2 flow and the Li2S powder recovered. Characteristics of the different samples are reported in table 2.

[0143] The reagent gas composition was 60 vol % of H2S and 40 vol % of N2 for comparative example 1 . The reagent gas composition was 60 vol % of H2S, 5 vol % of H2 and 35 vol % of N2 for example 2, 60 vol % of H2S, 10 vol % of H2 and 30 vol % of N2 for example 3, and 60 vol % of H2S, 2 vol % of H2 and 38 vol % of N2 for example 4.

[0144] XRD Analysis

[0145] The XRD diffractograms of the powders were acquired on a XRD goniometer (Malvern-Panalytical Aeris) in the Bragg Brentano geometry, with a Cu X Ray tube (Cu Kalpha wavelength of 1 .5406 A). Tube settings were operating at 40 kV / 15 mA, 600 W). The setup was used with fixed slits and Soller slits of 0.02 rad. A filtering device on the primary side may also be used, like a nickel filter, a monochromator or a Bragg Brentano HD optics from Panalytical. The sample holder was loaded on a spinner; rotation speed was typically 60 rpm during theacquisition. Acquisition step was 0.0108° per step. Angular range was typically 10° to 90° in two theta or larger. Total acquisition time was typically 30 min or longer. Measurements were made in a dry room.

[0146] The quantification of residual LiOH in l_i2S was made by the preparation of different mixtures of l_i2S (Lorad, 200 mesh) and LiOH (Sigma Aldrich). Three different mixtures were prepared (1 , 5 and 10 wt. % of LiOH in Li2S). Firstly, LiOH was milled in a ball-milling jar (Pulverisette 7, FRITSCH) with 5 mm Zirconium beads (2 cycles of 30 min at 400 rpm with a break time of 15 min). Then, the pre-milled LiOH and Li2S were weighed and mixed manually in a dry room (Dew Point < -40 °C). The obtained diffractograms were all normalized on

[0100] peak of Li2S at 27.06 °. After analyzing the prepared standards, a calibration plot was obtained by taking into consideration the ratios between the integrated areas of the

[0100] Li2S peak (between 26 and 28 °) and the integrated areas of the

[0100] LiOH peak (between 32 and 33 °). Measurements on experimental Li2S allow to determine XRD purity (wt %) from the calibration curve. Results are reported in table 2.

[0147] Carbon analysis

[0148] Carbon analysis was performed in a C / S analyzer (Horiba EMIA 320). Standards with 0.0059, 0.0012 and 0.0455 wt. % of carbon were used to calibrate the instrument. 200 mg of Li2S samples were mixed with Lecocel, iron and tin beads (as combustion accelerators) in alumina crucibles and then introduced in the combustion chamber.

[0149] Particle Size Distribution measurement

[0150] The Particle Size Distribution (PSD) of the powders was evaluated using laser diffraction measurement. For this purpose, the powder was stirred in paraxylene. The solution was introduced in a Malvern Mastersizer 3000. Data was treated with the optical model of Fraunhofer.

[0151] Specific surface area of the particles by BET method

[0152] Specific surface area of the particles was measured by nitrogen gas adsorption according to the Brunauer-Emet-Teller (BET) method described in “TheJournal of the American Chemical Society”, vol. 60, page 309, February 1938The instrument used was a Micromeritics® TriStar 3000. The samples were pretreated in vacuum at 160 °C for 2 hours prior to analysis. The specific surface area was calculated by considering the P / P° range between 0.05 and 0.2. At least 6 points were selected within this range of P / P° in order to obtain a good correlation coefficient.

[0153] Evaluation of LiOH content by solid state1H NMR

[0154] 1H NMR spectrum was recorded on l_i2S sample to determine H containing impurities. The Avance spectrometer 400 from Broker was used with a high speed probe with a magic-angle spinning of 10 kHz and in one pulse sequence (D1 = 600 s). The calibration standard is H2O (5=4.8ppm).

[0155] Different peaks were attributed to different species as reported in Table 1 .Table 1 : Chemical species identified by solid state1H NMR* It is assumed that compound (I) is LiSH.

[0156] The quantification of LiOH was made by the integration of the whole1H signal i.e. from -34 ppm to 34 ppm after substraction of the probe signal, thereby giving an LiOH equivalent content. In this regard, other H impurities might be present and the value of LiOH can be overestimated. A calibration plot was prepared by analyzing different mixtures of LiOH (Sigma Aldrich) and LiCI (Sigma Aldrich). LiCI was chosen as an inert sample in order to avoid the presence of residual LiOH in the sample. For this purpose, 0.5, 1 , 2, 5 and 10 wt. % LiOH in LiCI mixtures were prepared in a glovebox (moisture level < 5 ppm, O2 level < 5 ppm). Then, for each mixture the whole1H signal was integrated after substraction of the probe signal and the calibration plot was obtained as a straight line passing through the origin. All the signals arenormalized by the sample mass introduced in the NMR rotor. This way, the technique can be considered as semi-quantitative. Results regarding residual LiOH contents are reported in table 2.

[0157] Evaluation of compound (I) content by solid state1H NMR

[0158] The quantification of the compound (I) was made by the integration of the1H peak signal assigned to the compound (I) at -2.0 ppm. For this purpose the integration was made from the chemical shift of the peak + 0.5 ppm to the chemical shift of the peak - 0.5 ppm, i.e. from -1.5 ppm to -2.5 ppm as represented on figure I. No deconvolution was applied. Compound (I) content was calculated as LiOH equivalent using the calibration plot described above. Results are reported in table 2.

[0159] Table 2: Characteristics of Li2S powders prepared using different reagent gas compositionsIt is clear from the results presented in table 2 that the residual LiOH present in the product obtained by the process according to the invention, i.e. using a reagent gas composition comprising H2S and H2, is reduced when compared with product obtained by the process using a reagent gas composition comprising H2S but no H2. The same trend is observed for the compound (I) content expressed in wt % of equivalent LiOH.

[0160] Temperature Programmed Sulfiding (TPS)

[0161] Temperature programmed sulfiding (TPS) is a common characterization technique to evaluate sulfiding conditions of different materials. For example, Bonne et al. in Journal of Catalysis, 154(1), 115-123 (1995), describe the study of the sulfidation with H2S of vanadium oxide using TPS and Zeuthen et al. in Applied Catalysis, 68, 117-130 (1991), describe the study of the sulfidation with H2S of Ni-Me / alumina catalysts by TPS.

[0162] The temperature programmed experiments were carried out in a fixed-bed reactor. 200 mg of LiOH were used. Prior to TPS experiments, the reactor was flushed with nitrogen for 10 min at 60 ml / min. A linear temperature rate of 1.2 K / min was used throughout. A thermocouple was located close to the powder bed and the powder was heated from room temperature (20-30 °C) up to 450 °C. The various gasses used were introduced via a mass flow controller. The effluent gas products were analyzed by gas chromatography with a temperature conductivity detector (TCD). The gas flow used was 60 ml / min, and the gas concentration could be varied using mixtures of H2S, H2 and N2.

[0163] The parameters considered to evaluate TPS experiences were:Tpeak (°C) = Temperature at which the sulfidation rate was maximum Tx (°C) = Temperature at which x % of conversion of LiOH was reached.X (%) = conversion

[0164] Conversion X (%) was calculated as explained below considering the reaction scheme: 2 LiOH + H2S — Li2S +2 H2OX (%) = n H2S consumed / (1 / 2 n LiOH) * 100 where n LiOH is the initial number of moles of LiOH introduced in the reactor;>2 n LiOH is the theoretical equivalent of H2S needed to fully convert initial LiOH introduced in the reactor into Li2S; and n H2S consumed is determined experimentally from integration of TPS signal. According to this method, the lower the Tx, the faster is the sulfidation of LiOH

[0165] Table 3 shows the impact of H2 on the sulfidation behavior of LiOH.Table 3: Tx (°C) depending on the reagent gas composition

[0166] According to the results presented in table 3, in the conditions of the process according to the invention, i.e. using a reagent gas composition comprising H2S and H2, the reaction of sulfidation of LiOH takes place at lower temperatures and thus at higher rate than in the conditions of a process using a reagent gas composition comprising H2S but no H2.

[0167] To conclude, the inventors have found that stable, highly pure l_i2S powders can be obtained with high reaction rates using a reagent gas comprising H2S and H2. Indeed, resulting l_i2S powders obtained by the process according to the invention contain much less impurities such as LiOH and compound (I) which is assumed to be LiSH.

[0168] This is advantageous since such impurities are generally detrimental to subsequent use of Li2S in demanding applications such as the manufacture of sulfide solid material e.g. for use as solid electrolyte, or such as cathode active material for lithium batteries.

Claims

ClaimsClaim 1 . A process for preparing a powder of lithium sulfide (l_i2S powder), comprising the steps of: a) providing a powder of lithium hydroxide (LiOH powder A), or a powder of lithium carbonate (Li2COs powder A’) presenting a residual water content below 5 wt %; b) reacting such LiOH powder A or Li2COs powder A’ with H2S present in a reagent gas (RG1 ) to obtain Li2S powder, optionally carbon dioxide and water vapor, wherein reagent gas (RG1 ) comprises H2S, a gas (G) selected from the list consisting of H2, CH4, C2H6, C3H8 and mixtures thereof and optionally an inert carrier gas (CG) different from (G); wherein reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) to obtain Li2S powder is performed in at least one fixed bed reactor, at least one fluidized bed reactor, at least one stirred powder reactor or at least one mobile bed reactor, with the proviso that if reacting LiOH powder A or Li2COs powder A’ with H2S present in the reagent gas (RG1 ) to obtain Li2S powder is performed in a mobile bed reactor, powder and reagent gas (RG1 ) flow in the same direction.Claim 2. The process according to claim 1 , wherein the step b) of reacting LiOH powder A with reagent gas (RG1 ) is performed at a temperature ranging from 100°C to 450°C, preferably at a temperature ranging from 100°C to 400°C, .Claim 3. The process according to claim 1 , wherein the step b) of reacting Li2COs powder A’ with reagent gas (RG1 ) is performed at a temperature ranging from 200°C to 700°C.Claim 4. The process according to any one of claims 1 to 3, wherein the reagent gas (RG1 ) comprises H2S in an amount ranging from 30 % to 99.9 % in volume and the gas (G) in an amount ranging from 0.1 % to 20 % in volume with regard to the total of the volume of the reagent gas (RG1 ).Claim 5. The process according to any one of claims 1 to 4, wherein the reagent gas (RG1 ) comprises water in an amount of at most 5.0 wt%.Claim 6. The process according to any one of claims 1 to 5, wherein the gas (G) is H2.Claim 7. The process according to any one of claims 1 to 6, wherein the inert carrier gas (CG) is selected from nitrogen, argon and mixtures therof.Claim 8. The process according to any one of the preceding claims, wherein to perform reacting LiOH powder A or Li2COs powder A’ with H2S present in a reagent gas (RG1 ) to obtain l_i2S powder as in step b) the reagent gas (RG1 ) is introduced in the reactor through at least one inlet pipe; flows over or through LiOH powder A or Li2COs powder A’ present in the reactor, and wherein unreacted H2S, obtained water vapor, optionally obtained carbon dioxide and optionally present inert carrier gas are extracted from the reactor via at least one outlet pipe as an extracted gas (RG2).Claim 9. The process according to claim 8, wherein the reagent gas (RG1 ) is introduced with gas hour space velocity (GHSV) ranging from 50h’1to 1000h’1.Claim 10. The process according to any one of the preceding claims, wherein the Li2S powder obtained contains less than 0.2 wt % of residual LiOH as measured by solid state proton NMR and has a solid state proton NMR spectrum showing a peak signal at -2.0 ± 0.2 ppm that corresponds to less than 0.005 wt % of equivalent LiOH, preferably less than 0.003 wt %.Claim 11 . The process according to claim 10, wherein Li2S powder obtained further exhibits at least one, preferably all, of the following features :it has a purity of more than 99 wt % as measured by XRD, it contains less than 0.08 wt % of carbon residues as measured by C / S elemental analysis it has a specific surface area ranging from 2 to 20 m2 / g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method, it has a dso-value ranging from 20 pm to 500 pm, as measured by laser diffraction in para-xylene, it has a dgo-value of less than 1000 pm, as measured by laser diffraction in para-xylene.Claim 12. l_i2S powder obtainable by the process according to any one of claims 1 to 11 characterized in that it contains less than 0.2 wt % of residual LiOH as measured by solid state proton NMR and has a solid state proton NMR spectrum showing a peak signal at -2.0 ± 0.2 ppm that corresponds to less than 0.005 wt % of equivalent LiOH, preferably less than 0.003 wt %.Claim 13. Li2S powder according to claim 12 further characterized in that it exhibits at least one, preferably all, of the following features: it has a purity of more than 99 wt % as measured by XRD, it contains less than 0.08 wt % of carbon residues as measured by C / S elemental analysis, it has a specific surface area ranging from 2 to 20 m2 / g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method, it has a dso-value ranging from 20 pm to 500 pm, as measured by laser diffraction in para-xylene, it has a dgo-value of less than 1000 pm, as measured by laser diffraction in para-xylene.Claim 14. Use of the lithium sulfide powder according to claim 12 or 13 to manufacture solid sulfide electrolytes.Claim 15. Use of the lithium sulfide powder according to claim 12 or 13 as cathode active material in a rechargeable lithium battery

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