EP4676877A1 - Process for preparing a powder of lithium sulfide - Google Patents

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 (LiOH powder A), or a powder of lithium carbonate (Li₂CO₃ powder A') presenting a residual water content below 5 wt %; b) reacting such LiOH powder A or Li₂CO₃ 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, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas and optionally an inert carrier. The present disclosure also relates to the powder of lithium sulfide obtained from such process and to the use of such Li₂S powder to prepare a solid compound of formula (I): Li_aPS_bX_c (I) wherein - X represents at least one halogen element; - a represents a number from 3.0 to 6.0; - b represents a number from 3.5 to 5.0; and - c represents a number from 0 to 3.0.

Description

Description

PROCESS FOR PREPARING A POWDER OF LITHIUM SULFIDE

Cross-reference to related patent applications

[0001 ] This application claims priority filed on 10 March 2023 in Europe with Nr. 23305328.9, 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 (U2S 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, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas and optionally an inert carrier gas. The present disclosure also relates to the powder of lithium sulfide (Li2S powder ) obtained from such process and to the use of such Li2S powder to prepare a solid compound of formula (I):

LiaPSbXc (I) wherein

- X represents at least one halogen element;

- a represents a number from 3.0 to 6.0;

- b represents a number from 3.5 to 5.0; and

- c represents a number from 0 to 3.0.

It finally relates to the use of the lithium sulfide powder as cathode active material in a rechargeable lithium battery.

Background [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 battery 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 solid electrolyte is lithium sulfide (U2S). 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 sulur 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, environementally 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 :

2 LiOH + H₂

²S Li₂S + 2 H₂O , . „ (scheme 1 )

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

Li₂

²CO

[0009] For example, US 2020/165129 A1 (Albemarle) relates to a U2S 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 preparation method 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 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 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.

[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 extend represents important additional cost to the process.

[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 in H2S. However, examplified 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 in H2S. However, examplified 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. More specifically, the exhausted gas, comprising water and H2S, is passed through a column packed with a dehydrating agent such as zeolite. The water content acceptable for this recycled H2S reactant gas to be reinjected in the process is not specified. However, the use of a dehydrating agent suggests a highly dried gas with a very low amount of water and represents an important additional cost to the process. Finally, examplified hydrogen sulfide raw material, has a purity of 99% and is provided by Sumitomo Seika Co., Ltd as in the previously cited document. Therefore, the use of H2S with very low content of water, typically less than 2 mg/L, is teached by Furukawa Co., Ltd.

Summary

[0018] The Applicant noticed that the commercially available U2S is of high cost because its manafacture requires H2S in excess. Said excess has to be neutralized leading to by products such as Na2S when neutralization is made through a scrubber containing NaOH.

[0019] Therefore, there is a need for a process wherein H2S can be recycled and can be reintroduced in said process.

[0020] Since the reaction between gaseous H2S and LiOH is equilibrated (see scheme 1 above), there is a need to displace the equilibrium using H2S containing low amount of water to allow suitable kinetics and to avoid l_i2S giving back LiOH.

[0021 ] Water has to be removed from H2S in an economically advantageous way which does not require the use of any dessicant material. Similarly, H2S has to be dried in an economically advantageous way which does requires expensive cooling facilities e.g. requiring low temperature coolant for water condensation.

[0022] Since the reaction between gaseous H2S and LiOH is equilibrated (see scheme 1 above), there is a need for an efficient process which allows recovering high purity U2S having very low amount of residual LiOH.

[0023] The Applicant is aware that U2S suffers from poor stability during storage, especially when exposed to ambient moisture.

[0024] There is a need for Li2S powder which remains stable when exposed to moisture during storage or transportation.

[0025] Hence, the Applicant faced the problem of providing a new process for the manufacture of Li2S powder that can solve the above mentioned issues.

[0026] 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 (U2CO3 powder A’) presenting a residual water content below 5 wt %; b) reacting such LiOH powder A or U2CO3 powder A’ with H2S present in a reagent gas (RG1 ) to obtain U2S powder, optionally carbon dioxide and water vapor; wherein reagent gas (RG1 ) comprises H2S, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas and optionally an inert carrier gas. [0027] The present invention also relates to a l_i2S powder obtainable by the process as above explained characterized in that : it has a specific surface area ranging from 2 to 15 m²/g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method, it has a dso-value ranging from 100 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, it contains less than 1 wt % of residual LiOH as measured by XRD and/or by proton NMR, it contains less than 0.08 wt % of carbon residues as measured by C/S elemental analysis, and it releases less than 400 ml/g of H₂S when exposed to a relative humidity of 30-40% at 23°C during 60 minutes.

[0028] The present invention also relates to the use of the l_i2S powder according to the invention as cathode active material in a rechargeable lithium battery.

[0029] The present invention also relates to a method for preparing a solid compound of formula (I): LiaPSbXc (I) wherein

X represents at least one halogen element; a represents a number from 3.0 to 6.0; b represents a number from 3.5 to 5.0; and c represents a number from 0 to 3.0, said method comprising the use of the l_i2S powder disclosed above.

[0030] The present invention also relates to a compound of formula (I), in particular a compound of formula (II), obtainable by the method described herein LiaPSbXc (I) Li7-yPS6-yXy (II); wherein y is a number such as 1 < y < 2.

Disclosure of the invention [0031 ] The present invention relates to a process for obtaining a powder of lithium sulfide powder (l_i2S powder), such powder having certain specific technical features which makes it well-suited to be used to prepare battery components such as lithium sulfide solid electrolyte, including lithium argyrodites.

[0032] The process of the present invention for the manufacture of said l_i2S powder advantagesouly comprises 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 U2CO3 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, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas and optionally an inert carrier gas.

[0033] Advantageously, the process of the present invention is solvent and/or diluent free. In other words, no solvent and/or diluent is added to the reaction vessel 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.

[0034] 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.

[0035] 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 %. [0036] 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.%.

[0037] 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.

[0038] 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).

[0039] 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.

[0040] 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.

[0041 ] 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.

[0042] Good results were obtained by drying LiOH.H2O at 200°C during 3 hours by flowing nitrogen over or through the powder.

[0043] In some embodiments the powder of lithium hydroxide monohydrate (LiOH.H2O) presenting a residual water content above 5 wt.% is ground before being heated. [0044] 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.

[0045] 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.

[0046] Generally dso-value of the LiOH powder A ranges from 100 pm to 600 pm, preferably from 200 pm to 400 pm. Generally, dgo-value is below 1000 pm.

[0047] The particle size distribution can be measured by laser diffraction from a dispersion of the powder in para-xylene.

[0048] 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 d_x. 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 dgo, 90% of the particles have a size which is less than dgo. dso corresponds to the median value of the distribution by volume.

[0049] 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’).

[0050] 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’).

[0051 ] 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.

[0052] 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. [0053] 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.

[0054] 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.

[0055] 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 U2S powder, optionally carbon dioxide, and water vapor; wherein reagent gas (RG1 ) comprises H2S, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas and optionally an inert carrier gas.

[0056] 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’.

[0057] When LiOH powder A is used as raw material, step b) generally takes place at a temperature ranging from 100 to 400°C, preferably ranging from 150°C to 350°C, more preferably ranging from 180°C to 300°C. Good results were obtained at 200°C.

[0058] When LiOH powder A is used as raw material, Li2S powder and water vapor are obtained in step b).

[0059] Melting point of the considered LiOH powder A can be found in the literature or can be measured by any well know technique such as Differential Scanning calorimetry (DSC).

[0060] 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.

[0061 ] When Li2COs powder A’ is used as raw material, U2S powder, carbon dioxide and water vapor are obtained in step b).

[0062] Melting point of the considered Li2COs powder A’ can be found in the literature or can be measured by any well know technique such as Differential Scanning calorimetry (DSC). [0063] 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 U2CO3 powder A’.

[0064] The overall equilibrated reaction between LiOH and H2S can be represented by the following reaction scheme 1 :

2 LiOH + H₂

²S Li₂S + 2 H₂O , . „ (scheme 1 )

[0065] Generally, the molar ratio between H2S and LiOH ranges from 0.5 to 2.5, preferably from 0.5 to 2, more preferably from 0.5 to 1.5. Good results were obtained with a molar ratio of 1 .25 i.e. 2.5 equivalent of H2S compared to what is theoretically required to transform LiOH to Li2S.

[0066] Besides, the reaction between Li2COs and H2S can be represented by the following reaction scheme 2:

Li₂

²CO

[0067] Generally, the molar ratio between H2S and Li2COs ranges from 1 to 5, preferably from 1 to 4, more preferably from 1 to 3.

[0068] Generally, H2S is present in a reagent gas (RG1 ) which comprises H2S, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas and optionally an inert carrier gas.

[0069] In some embodiments, the reagent gas (RG1 ) comprises water in an amount ranging from 1 .0 to 4.0 wt%; in some other embodiments the reagent gas (RG1 ) comprises water in an amount ranging from 1 .5 to 3.5 wt%.

[0070] Still in some other embodiments, the reagent gas (RG1 ) is essentially composed or consists of gaseous H2S and of water vapor in an amount ranging from 0.5 to 5.0 wt%; preferably ranging from 1 to 4 wt%; more preferably ranging from 1 .5 to 3.5 wt%.

[0071 ] By essentially composed is meant that although the reagent gas (RG1 ) comprises essentially gaseous H2S and water vapor, it may comprise any additional gas in an amount not exceeding 5 wt %; for example not exceeding 4 wt %; or not exceeding 3 wt %; or not exceeding 2 wt %; or not exceeding 1 wt %. Just for the sake of example and without limitation, the additional gas may be an inert gas such as nitrogen or argon.

[0072] Advantageously and surprisingly, the process of the present invention does not require extremely dried H2S gas as it is generally recommended in the prior art. This is adavantageous because the step of drying hydrogen sulfide increases the cost of the overall process. This is surprising because it is generally admitted that extremely dried H2S gas is required to displace the equilibrium represented in scheme 1 towards the formation of l_i2S and thus to obtain l_i2S with low amount of LiOH. The inventors have found that using reagent gas comprising water vapor in an amount ranging from 0.5 to 5.0 wt% has only moderate impact on the kinetic of the reaction between LiOH powder A or Li2COs powder A’ and hydrogen sulfide.

[0073] The reaction generally takes place in a vessel allowing LiOH powder A or Li2COs powder A’ to be in contact with the reagent gas (RG1 ) comprising gaseous H2S. The reaction vessel generally includes a stirring blade. The vessel may be a vertical reactor in which the reactants are positioned at the bottom of the vessel. Other types of reactors may also be used, for example lateral reactor such as dryers or extruders. The reactor is preferably sealed. The capacity of the reactor is not limited. The reaction may takes place at a pressure under or above atmospheric pressure, for example a pressure of 0.05 MPa or a pressure of 1 MPa can be used. Generally, pressure ranges from 0.05 MPa to 1 MPa. Good results were obtained at 0.1 Mpa. The reactor is equipped with at least one heating mean. The heating mean keeps the temperature of an inner wall of the reactor in contact with the raw materials. The reactor may be equipped with additional heating means, for example a second heating mean, which may be located at the upper part of the reactor. The reactor is also equipped with means to inject the reagent gas (RG1 ) comprising the gaseous H2S.

[0074] In step b) the reagent gas (RG1 ) is generally introduced in the vessel through an inlet pipe and flows over or through LiOH powder A or Li2COs powder A’ present in the vessel. [0075] Step b) preferably takes place while stirring the LiOH powder A or I 2CO3 powder A’. In this case, the vessel is equipped with a stirring blade or a conveying stirrer which is positioned as close as possible to the bottom of the reactor and/or as close as possible to the walls, for example with a d/D > 0.9 (d is the size of the stirring blade and D is the internal diameter of the vessel).

[0076] Generally, the powder is stirred with a stirring blade working from 50 to 300 r.p.m., typically from 100 to 200 r.p.m..

[0077] Water vapor obtained in step b) is preferably removed from the vessel. Therefore, step b) comprises extracting unreacted H2S, formed water vapor, optionally formed carbon dioxide and optionally present inert carrier gas from the vessel via an outlet pipe as an extracted gas (RG2). Accordingly, extracted gas (RG2) comprises H₂S, water vapor, optionally formed carbon dioxide and optionally present inert carrier gas.

[0078] 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 reaction vessel from inlet pipe as reagent gas (RG1 ) to outlet pipe as extracted gas (RG2).

[0079] Advantageously the unreacted H2S comprised in extracted gas (RG2) can be recycled and can be reintroduced in the process according to the invention. Indeed, because the process of the present invention does not require extremely dried H2S gas, as it is generally recommended in the prior art, unreacted H2S gas can be easily and economically recycled.

[0080] For this purpose, the process according to the invention comprises a step c) wherein water is removed from the extracted gas (RG2) to give a reagent gas (RG3), wherein the reagent gas (RG3) comprises H2S, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas, optionally carbon dioxide and optionally an inert carrier gas.

[0081 ] This step c) can be achieved merely by placing a condenser on the gas discharge line of the vessel, where water that is in the gaseous state becomes liquid (condensed) and collected outside of the vessel. Accordingly, water is removed from extracted gas (RG2) by cooling said extracted gas (RG2) and condensing of water.

[0082] Through the regulation of the temperature of cooling and of the gas flow in the condenser, the person of ordinary skill in the art can easily and economically remove water from extracted gas (RG2) to obtain a reagent gas (RG3) comprising H2S, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas, optionally carbon dioxide and optionally an inert carrier gas.

[0083] When extracted gas (RG2) comprises H2S, water, carbon dioxide and optionally an inert carrier gas, it can be freed from carbon dioxide either before or after performing water removal as previously described. Carbon dioxide can be removed from extracted gas (RG2) by trapping, using techniques well known to the skilled person.

[0084] Since reagent gas (RG3) comprises H₂S, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas, and optionally an inert carrier gas i.e. reagent gas (RG3) has similar water content as reagent gas (RG1 ), said reagent gas (RG3) can be introduced in the vessel to react with unreacted LiOH powder or Li2COs powder.

[0085] In some embodiments, the reagent gas (RG3) is essentially composed or consists of gaseous H2S and of water in an amount ranging from 0.5 to 5.0 wt%; preferably ranging from 1 to 4 wt%; more preferably ranging from 1.5 to 3.5 wt%. This is typically the case when initially introduced reagent gas (RG1 ) is essentially composed or consists of gaseous H2S and of water in an amount ranging from 0.5 to 5.0 wt%.

[0086] The process of the present invention may be continuous or it may be batch- wise.

[0087] The present invention also relates to l_i2S powder characterized in that it has a specific surface area generally ranging from 2 to 15 m²/g, for example from 3 to 10 m²/g , sometimes from 4 to 9 m²/g, often from 6 to 9 m²/g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method, it has a dso-value generally ranging from 100 pm to 500 pm, sometimes from from 200 pm to 500 pm, often from 300 pm to 450 pm as measured by laser diffraction in para-xylene, and it has a dgo-value generally of less than 1000 pm, sometimes of less than 700 pm, as measured by laser diffraction in para-xylene.

[0088] The l_i2S powder of the present invention is characterized by a specific surface area ranging from 2 to 15 m²/g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method.

[0089] The l_i2S powder of the present invention is characterized by its dso-value, as measured by laser diffraction in para-xylene ranging from 100 pm to 500 pm.

[0090] 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.

[0091 ] The l_i2S powder of the present invention is composed of free flowing particles having relatively large particle size, dust-free and therefor easy to handle in a subsequent process for technical and safety reasons.

[0092] It has been found surprisingly that the l_i2S powder of the present invention, despite the fact that it is produced using H2S comprising 0.5 to 5.0 wt % of water, is a very pure material. Indeed, according to prior art, this highly pure l_i2S powder is generally obtained using highly dried H2S.

[0093] It is surprising since l_i2S powder is composed of relatively large particles having a dso-value ranging from 100 pm to 500 pm and that one may expect the presence of unreacted LiOH in the core of the particles. Generally, the l_i2S powder of the invention is characterized in that it contains less than 1 wt % of residual LiOH as measured by XRD and/or by proton NMR, or/and in that it contains less than 0.08 wt % of carbon residues as measured by C/S elemental analysis.

[0094] Preferably, the U2S powder of the invention is characterized in that it contains less than 0.5 wt %, more preferably less than 0.25 wt % of residual LiOH as measured by XRD and/or by proton NMR.

[0095] It has also been found surprisingly that the Li2S powder of the present invention is less reactive to ambiant moisture. Indeed, the Li2S 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 storage or transportation than l_i2S powder obtained using highly dried H2S.

[0096] Such l_i2S powder having the above described features may notably be produced by the process of the present invention.

[0097] Another object of the invention is thus a l_i2S powder obtainable by the process as above explained characterized in that : it has a specific surface area ranging from 2 to 15 m²/g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method, it has a dso-value ranging from 100 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, it contains less than 1 wt % of residual LiOH as measured by XRD and/or by proton NMR, it contains less than 0.08 wt % of carbon residues as measured by C/S elemental analysis, and it releases less than 400 ml/g of H₂S when exposed to a relative humidity of 30-40% at 23°C during 60 minutes.

[0098] 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 Li2S powder according to the present invention as active material in a rechargeable lithium battery

[0099] It has been found that the l_i2S powder according to the present invention is particularly suitable to prepare solid sulfide compounds of formula (I) below.

[00100] Therefore another object of the present invention relates to a method for preparing a solid compound of formula (I):

LiaPSbXc (I) wherein

- X represents at least one halogen element;

- a represents a number from 3.0 to 6.0;

- b represents a number from 3.5 to 5.0; and

- c represents a number from 0 to 3.0, said method comprising the steps of i) obtaining a composition by admixing the starting materials including the lithium sulfide powder obtainable by the process descried herein, optionally in one or more solvents; ii) applying a mechanical treatment to the composition obtained in step i); iii) optionally removing at least a portion of the one or more solvents from the composition obtained on step ii), so that to obtain a solid precursor; iv) optionally pressing the solid precursor from step iii) into pellets; v) heating the obtained precursor obtained in step iii) e.g. in the form of pellets, to a temperature in the range of from 350°C to 580°C, under an inert atmosphere, for a time period ranging from 1 to 12 hours, thereby forming the solid material particles; and vi) optionally treating the solid material obtained in step v) to the desired particle size distribution.

[00101 ] The starting materials of step i) generally comprise at least lithium sulfide (Li 2S) and phosphorus sulfide (P2S5). In some embodiments the starting materials of step i) comprises lithium sulfide (I 2S), phosphorus sulfide (P2S5) and a compound of formula LiX wherein X represents at least one halogen element.

[00102] The solvent of step i) is generally selected among aliphatic hydrocarbons (for instance hexane, heptane, octane or nonane, preferably heptane) and aromatic hydrocarbons (for instance benzene, toluene, ethylbenzene, xylenes or liquid naphthenes, preferably xylenes). More preferably, the carbonated solvent (S) is selected from the group consisting of xylene, para-xylene, heptane, octane, and mixtures thereof. [00103] Still, another object of the present invention relates to the use of the lithium sulfide powder according to the present invention to prepare a solid compound of formula (I):

LiaPSbXc (I) wherein

- X represents at least one halogen element;

- a represents a number from 3.0 to 6.0;

- b represents a number from 3.5 to 5.0; and

- c represents a number from 0 to 3.0.

[00104] Finally, another object of the present invention relates to the use of the lithium sulfide powder according to the present invention to prepare a solid compound of formula (II):

Li7-yPS6-yXy (II) wherein y is a number such as 1 < y < 2; preferably such as 1 .2 < y < 1 .6

[00105] 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.

[00106] The present invention will be now described in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the disclosure.

Figures

[00107] Figure 1 : Scanning Electron Microscopy of l_i2S according to the present invention, magnification X100.

Figure 2: Scanning Electron Microscopy of l_i2S according to the present invention, magnification X8000.

Examples

[00108] XRD Analysis

[00109] The XRD d iff ractog rams 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 the acquisition. 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 dry room.

[00110] 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 [100] 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 [100] Li2S peak (between 26 and 28 °) and the integrated areas of the [100] LiOH peak (between 32 and 33 °). Measurements on experimental Li₂S allow to determine XRD purity (wt %) from calibration curve.

[00111 ] Carbon analysis

[00112] 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.

[00113] Particle Size Distribution measurement

[00114] The Particle Size Distribution (PSD) of the powders was evaluated using laser diffraction measurement. For this purpose, the powder was stirred in para- xylene. The solution was filtered on a 800 pm sieve and introduced in a Malvern Mastersizer 3000. Data was treated with the optical model of Fraunhofer.

[00115] Specific surface area of the particles by BET method

[00116] Specific surface area of the particles was measured by nitrogen gas adsorption according to the Brunauer-Emet-Teller (BET) method described in “The journal of the American Chemical Society”, vol. 60, page 309, February 1938.

The instrument used was a Micromeritics® TriStar 3000. The samples were pretreated in vacuum at 200 °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.

[00117] Determination of H2S emission

[00118] The preparation of the sample is carried out in a dry Ar glove-box (moisture level < 5 ppm, O2 level < 5 ppm). The sample (between 350 and 700 mg of powder) is placed in an open circular holder with a circular surface of 4.02 cm². Then, the holder is placed on a zirconia pot where it can be isolated from the atmosphere. The zirconia pot is transferred from the dry-argon glove box to a room air operated one that is used for the H2S quantification test. Relative humidity is set at 35% at room temperature (23°C) (corresponding to a Dew Point of 6.7°C). Humidity is measured by a Dew Point probe from Mitchell Instruments (EA2-TX-100). Humidity within the glove-box can be controlled by the inlet of pre-dried compressed air. The atmosphere within the glove-box is homogenized by means of two fans. Once the atmosphere is stable, the zirconia pot is opened, exposing the sample to the controlled humid atmosphere. H2S quantification is carried out by a Sensorcon sensor (Industrial Pro - H2S Pro). The experiment is carried out for 60 minutes at the end of which the zirconia pot is again closed.

[00119] Evaluation of LiOH content by solid state ¹H NMR

[00120] 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 = 10 s). The calibration standard is H₂O (5=4.8ppm). The quantification of LiOH was made by the integration of the whole ¹H signal. In this regard, other H impurities might be present and the value of LiOH can be overestimated. Firstly, a calibration plot was performed 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. 0.1 , 0.2, 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, the whole ¹H signal was integrated and the calibration plot was obtained.

[00121 ] Materials

[00122] Dry LiOH was obtained from Sigma (dso = 400-475 pm) and UOH-H2O from Chengdu (dso = 300-350 pm).

H2S was obtained from Air Liquide (purity > 99.5 vol.%).

[00123] Sulfidation set-up

[00124] The reaction was performed in a 200mL stirred quartz reactor that can operate under an inert atmosphere and at high temperature.

The reactor was equipped with gas inlet and outlet, an agitator and counterblades. The reactor was equiped with a system allowing heating the reactor and the lid of the reactor. The temperature was measured by a probe placed in the powder introduced in the reactor. A pump connected to the reactor made possible the introduction of the reagent gas by an inlet pipe. An outlet pipe was connected to a Dean-Starck apparatus to recover water generated by the reaction and further to a scrubber containing NaOH to neutralize unreacted H2S. The reactor was inerted with nitrogen, applying cycles of purge under vacuum followed by refill with nitrogen.

[00125] Drying of LiOH

[00126] LiOH powder or LiOH-H₂O was placed in the reactor at a temperature set at 200 °C under a flow of dry nitrogen during 3 h. The mechanical stirring was set at 100 r.p.m.

[00127] Sulfidation with dry H2S (comparative example 1) [00128] 3 moles of LiOH powder were placed into the reactor. The reactor was inerted with 3 cycles of purge under vacuum followed by refill with nitrogen. Then, mechanical stiring was set at 100 r.p.m. and temperature at 200°C.

Dry H2S, after passing through molecular sieves, was introduced in the reactor via an inlet pipe at a flow rate of 10NL/h until reaching 2.5 equivalent with regards to LiOH present.

Unreacted H2S and formed water vapor were extracted via an outlet pipe and condensed water was collected via a Dean-Starck apparatus while H2S was neutralized in a scrubber containing NaOH.

[00129] Sulfidation with wet H2S (example 1)

[00130] Wet H2S was prepared by bubbling dry H2S in a vessel containing water set at defined temperature. By taking a molar ratio H2O/H2S of 50/50 at equilibrium state between gas phase and liquid phase, the theoretical dew curve gives a relationship between the temperature of the vessel and water amount in H2S gas . The values are reported in table 1 below.

[00131 ] Table 1 : water content in the gas phase as function of the temperature of the vessel

[00132] 3 moles of LiOH powder were placed into the reactor. The reactor was inerted with 3 cycles of purge under vacuum followed by refill with nitrogen. Then, mechanical stiring was set at 100 r.p.m. and temperature at 200°C.

Wet H2S containing 2.25 wt % of water was introduced in the reactor via an inlet pipe at a flow rate of 10NL/h until reaching 2.5 equivalent with regards to LiOH present.

Unreacted H2S and formed water vapor were extracted via an outlet pipe and condensed water was collected via a Dean-Starck apparatus while H2S was neutralized in a scrubber containing NaOH. [00133] During sulfidation with dry or wet H2S, the advancement of the reaction was monitored through the recovery of formed water in the Dean-Starck apparatus. In both cases, the reaction reached a plateau and was almost completed when 1.5 equivalent of H2S had been introduced. In both cases, the reaction was completed after 2.5 equivalent of H2S had been introduced, thereby showing that the kinetic was not impaired by the presence of water in H2S.

[00134] The products recovered after sulfidation with 2.5 equivalents of H2S according to the invention have the special morphology as shown by Scanning Electron Microscopy pictures on figures 1 and 2. The powder is composed of dense and faceted blocks with a rather rough surface where can be observed platelets.

[00135] The products recovered after sulfidation with 2.5 equivalents of H2S have the characteristics reported in table 2.

[00136] Table 2: l_i2S recovered from reaction of LiOH with dry or wet H2S

* Ex.1 and C. Ex. 1 obtained from LiOH provided by Sigma Aldrich; similar results were obtained with LiOH, H2O beforehand dried as above described.

** From C/S elemental analysis.

[00137] Results presented in table 2 show that, despite Li2S powders obtained with wet H2S have significantly larger particle size than Li2S powders obtained with dry H2S, their LiOH content remains below the LiOH content of the latest. This trend was also verified by XRD experiments.

[00138] Results presented in table 2 also show that Li2S powders obtained with wet H2S and Li2S powders obtained with dry H2S have similar very low C content.. [00139] Finally, results presented in table 2 show that l_i2S powders obtained with wet H2S are significantly less reactive to moisture than l_i2S powders obtained with dry H2S, since they produce much less H2S when exposed to moisture.

[00140] To conclude, the inventors have found that stable, highly pure l_i2S powders can be obtained using H2S gas comprising a moderate amount of water i.e. comprised in the range of from 0.5 wt % to 5 wt %. Indeed, below this range resulting l_i2S powders are more reactive to moisture and thus produce more H2S when exposed to the latter. Besides, above this range resulting l_i2S powders contain much more impurities such a LiOH which is detrimental to subsequent use in demanding application such as the manufacture of solid sulfide material e.g. for use as solid electrolyte for lithium batteries.

Claims

Claims

Claim 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, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas and optionnally an inert carrier gas.

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 400°C, preferably at a temperature ranging from 150°C to 350°C, more preferably ranging from 180°C to 300°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 ) is essentially composed or consists of gaseous H2S and of water in an amount ranging from 0.5 to 5.0 wt%; preferably ranging from 1 to 4 wt%; more preferably ranging from 1 .5 to 3 wt%.

Claim 5. The process according to any one of the preceding claims, wherein in step b) the reagent gas (RG1 ) is introduced in a vessel through an inlet pipe; flows over or through LiOH powder A or Li2COs powder A’ present in the vessel, and wherein unreacted H2S, obtained water vapor, optionally obtained carbon dioxide and optionally present inert carrier gas are extracted from the vessel via an outlet pipe as an extracted gas (RG2).

Claim 6. The process according to claim 5, comprising a step c) wherein water and optionally carbon dioxide are removed from the extracted gas (RG2) to give reagent gas (RG3), wherein reagent gas (RG3) comprises H2S, water in an amount ranging from 0.5 to 5.0 wt% of the total weight of the reagent gas and optionally an inert carrier gas.

Claim 7. The process according to claim 6, wherein water is removed from extracted gas (RG2) by cooling said extracted gas (RG2) and condensing of water.

Claim 8. The process according to claim 6 or 7, wherein reagent gas (RG3) obtained by water and optionally carbon dioxide removal from extracted gas (RG2) is introduced in the vessel to react with unreacted LiOH or Li2COs powder.

Claim 9. The process according to any one of claims 6 to 8, wherein the reagent gas (RG3) is essentially composed or consists of gaseous H2S and of water in an amount ranging from 0.5 to 5.0 wt%; preferably ranging from 1 to 4 wt%; more preferably ranging from 1 .5 to 3.5 wt%.

Claim 10. The process according to any one of the preceding claims, wherein l_i2S powder is such that :

- it has a specific surface area ranging from 2 to 15 m²/g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method,

- it has a dso-value ranging from 100 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 paraxylene,

- it contains less than 1 wt % of residual LiOH as measured by XRD and/or by proton NMR,

- it contains less than 0.08 wt % of carbon residues as measured by C/S elemental analysis, and - it releases less than 400 ml/g of H2S when exposed to a relative humidity of 30- 40% at 23°C during 60 minutes.

Claim 11. l_i₂S powder obtainable by the process of any one of claims 1-10 characterized in that :

- it has a specific surface area ranging from 2 to 15 m²/g as measured by nitrogen gas adsorption according to Brunauer-Emmet-Teller (BET) method,

- it has a dso-value ranging from 100 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 paraxylene,

- it contains less than 1 wt % of residual LiOH as measured by XRD and/or by proton NMR,

- it contains less than 0.08 wt % of carbon residues as measured by C/S elemental analysis, and

- it releases less than 400 ml/g of H2S when exposed to a relative humidity of 30- 40% at 23°C during 60 minutes.

Claim 12. A method for preparing a solid compound of formula (I):

LiaPSbXc (I) wherein

- X represents at least one halogen element;

- a represents a number from 3.0 to 6.0;

- b represents a number from 3.5 to 5.0; and

- c represents a number from 0 to 3.0, said process comprising the steps of

- mixing the starting materials, in dry or slurry state, including the lithium sulfide powder according to claim 11 , to provide a mixture,

- optionally drying said mixture,

- optionally pressing the resulting dried mixture into pellets, and - heating the mixture, optionally dried, or the pellets to a temperature comprised between 350°C and 550°C for a time period of at least 2 hours.

Claim 13. Use of the lithium sulfide powder according to claim 11 to prepare a solid compound of formula (I):

LiaPSbXc (I) wherein

- X represents at least one halogen element;

- a represents a number from 3.0 to 6.0;

- b represents a number from 3.5 to 5.0; and

- c represents a number from 0 to 3.0.

Claim 14. The use according to claim 13, wherein the solid compound responds to formula (II):

Li7-yPS6-yXy (II) wherein y is a number such as 1 < y < 2; preferably such as 1.2 < y < 1.6.

Claim 15. Use of the lithium sulfide according to claims 11 as cathode active material in a rechargeable lithium battery.