Synthesis process for Li3PS4 thiophosphate particles

Abstract

The present invention relates to a process for synthesizing Li3PS4 thiophosphate particles from a solvato-complex formed between Li3PS4 and a first solvent S1. The process comprises: a) a step of dispersing the solvato-complex between Li3PS4 and the first solvent S1 in a second, non-complexing solvent S2. This second solvent S2 is miscible with the first solvent S1 and has: - a logarithm of the water / octanol partition coefficient logP equal to or greater than 1.1, - a molecular density equal to or greater than 0.869 g / cm³, - a dipole moment less than or equal to 2.32 D, so as to precipitate Li3PS4 thiophosphate particles; b) a step of separating the Li3PS4 thiophosphate particles precipitated in step a); c) a step of drying the Li3PS4 thiophosphate particles separated in step b). Figure 1 to be published

Description

Title of the invention: Process for the synthesis of Li3PS thiophosphate particles 4 technical field

[0001] The present invention relates to the field of electrochemical energy storage via lithium batteries, more particularly via all-solid-state batteries using an inorganic thiophosphate phase as a solid electrolyte. The invention relates more particularly to the preparation of thiophosphate-based materials, including the operation of crystallizing them, at least partially. Previous technique

[0002] The development of industrializable methods for preparing thiophosphate phases with good ionic conduction properties is essential for the growth of all-solid-state batteries. Furthermore, to be viable, these preparation methods must be scalable to industrial production at an acceptable cost and reaction time.

[0003] Another parameter to consider for the implementation of all-solid-state batteries is the size of the solid electrolyte particles, particularly during the formulation of composite cathodes. Indeed, in order to maximize battery cell performance, it is desirable to promote contact between the cathode's active material particles and the solid electrolyte particles. Electrolyte particles smaller than the active material particles are preferably chosen, specifically two to three times smaller. See Adv. Energy Mater. 2020, 10, 1902881 for further information. Thus, for an active material with a particle size centered on 12 pm, the solid electrolyte particle size is preferably chosen to be no more than 6 pm. However, the particle size is often linked to the particle preparation process.

[0004] It is then possible to consider reducing their size after synthesis by post-treatment.

[0005] Initially, thiophosphate phases were obtained by solid-state preparation methods by melt-quenching, as described, for example, in patents JP3433173 and JP5270825. These methods are time-consuming and difficult to extrapolate to an industrial scale. More recently, mechanosynthesis preparation methods have been described and generally allow for obtaining micrometer-sized particles smaller than those produced by melt-quenching methods, with good conductivity. However, the grinding times are on the order of several tens of hours (see US patent 8993176 and the publication Adv. Energy Mater. 2021-2101111) or require additional heat treatment, such as described in patents EP3740996 and JP2017208324. Grinding methods in the presence of one or more solvents have also been developed to reduce the grinding time to a few hours and further reduce the particle size, as described in patents CN106329002, JP2021082409, WO2022162085, CN114678586.

[0006] Mechanical grinding with or without solvent has thus been used to reduce particle size after preparation, as reported in Materials 63 (2023) 102985. Submicrometer particle sizes can be achieved by this method, and grinding times can be reduced by adding solvent. However, such post-synthesis grinding remains energy-intensive and time-consuming, especially in the presence of solvent, which subsequently requires drying.

[0007] An alternative preparation method has also been described in several studies (see the following publications and patents: J. Am. Chem. Soc. 2013, 135, 975-978, US8597838; CN106505247; Chem. Lett. 2015, 44, 884-886; ACS Appl. Mater. Interfaces 2018, 10, 15). This method is based on the reaction of Li2S with P2S5 suspended in a polar aprotic solvent for periods ranging from overnight to several days at temperatures between ambient and 50°C. After washing, an intermediate compound called the solvato-complex is recovered and then dried under reduced pressure. This compound is then thermally decomposed, leading to the amorphous Li3PS4 phase or the [3-Li3PS4.In the case of the Li3PS4 phase, the ionic conductivities obtained by reaction in tetrahydrofuran (THF) are between 0.074 mS / cm and 0.16 mS / cm at 25°C, and the particles obtained have a rod-like morphology and sizes of several tens of microns. The reaction times are long and the sizes of the particles obtained are large, potentially too large for at least some of the applications targeted in the present invention.

[0008] Furthermore, the need for heat treatment entails several drawbacks. The first relates to the handling of the product, which must be carried out under an inert atmosphere to prevent its degradation. The second is the energy expended and the cost of the heat treatment (heating and controlled atmosphere).

[0009] Other methods of preparation in solution have been developed, notably by manipulating operating conditions such as temperature, pressure, stirring method, and solvent combinations. Examples include combining solvents with different polarities (as described in US patent 10439198), sequencing the mixture of precursors with different solvents (as described in CN patent 110444806), and heating the reaction medium by microwaves with autogenous pressure (as described in US patent 11325096). Despite Although interesting advances, all these methods require heat treatment to decompose the solvato-complex and obtain the phase of interest.

[0010] US patent 11325096 describes a microwave-activated solvothermal method for preparing Li3PS4. The amorphous Li3PS4 phase is thus obtained after a 3-hour reaction at 100 °C in the THF. Other scientific authors describe various mechanical agitation methods using grinding beads or vibrating systems, for example, Solid State Ionics 285 (2016) 2-5; ACS Appl. Energy Mater. 2021, 4, 2275-2281; Heliyon 5 (2019) e02760; Powder Technology 387 (2021) 415-420, methods which are difficult to industrialize.

[0011] An alternative has also been described in patent CN113471519, which consists of directly preparing the Li2S reagent with a reduced particle size via a preparation method involving the reaction of LiEt3BH with elemental sulfur in THF. The reaction then takes place in a colloidal suspension and yields [3-Li3PS4] phase particles with a particle size of 30 nm. Although the use of LiEt3BH allows for rapid formation of the solvato-complex and the production of small particles, the resulting ionic conductivity is low, the cost of the LiEt3BH reagent is very high compared to the Li2S reagent, and the process still requires heat treatment.

[0012] The invention aims to develop an improved process for synthesizing Li3PS4 thiophosphate particles, particularly from a solvato-complex, a process that overcomes the aforementioned drawbacks and, in particular, limits the need for heat treatments and / or allows for better control of the size and / or morphology of the particles obtained. Summary of the invention

[0013] The invention relates firstly to a process for synthesizing Li3PS4 thiophosphate particles from a solvato-complex formed between Li3PS4 and a first solvent SI, said process comprising: a) a step of dispersing the solvato-complex between Li3PS4 and the first solvent SI in a second non-complexing solvent S2, said second solvent S2 being miscible with the first solvent SI and exhibiting - a logarithm of the water / octanol partition coefficient logP equal to or greater than 1.1, - a molecular density equal to or greater than 0.869 g / cm3, - a dipole moment less than or equal to 2.32 D, so as to precipitate thiophosphate particles Li3PS4 b) a step of separating the Li3PS4 thiophosphate particles precipitated in step a) c) a drying step of the Li3PS4 thiophosphate particles separated in step b).

[0014] For the purposes of this invention, "a solvato-complex formed between Li3PS4 and a first solvent SI" means a defined solid compound in which a defined amount of solvent is associated with the Li3PS4 compound and is an integral part of the crystalline phase of the complex. A relevant example of a solvato-complex is the Li3PS4-2THF compound.

[0015] In the context of the present invention, a “non-complexing” solvent is understood to mean that the second solvent S2 does not form a new solvato-complex solid phase with molecules of this solvent that would be integrated into the structure of the solvato-complex.

[0016] As is known, the preparation of a Li3PS4-xSolvent solvato-complex involves, for example, dispersing the Li2S reactants with P2S5 in a polar aprotic solvent. After the reaction, the precipitate formed is washed with a solvent and then dried to obtain a powder.

[0017] Surprisingly, the inventors thus discovered that it was possible to isolate thiophosphate particles from a solvato-complex after synthesis by simply suspending the solvato-complex in a specific solvent meeting the criteria stated above: with such a solvent, it is possible to extract the solvent molecules from the solvato-complex, without reforming another solvato-complex with the molecules of this other solvent, and thus forming the Li3PS4 phase of interest without heat treatment (apart from simple drying).

[0018] In the context of the present invention, "absence of heat treatment" means the absence of treatment of the dried solvato-complex, which would go beyond a temperature of 140 °C, and which would be necessary to decompose the solvato-complex, remove the structural solvent and at least partially crystallize the phase.

[0019] This represents a considerable gain in terms of the duration and simplification of the thiophosphate synthesis process, and in terms of energy expenditure and industrial equipment required to implement this process. The process according to the invention eliminates the need for a heat treatment aimed at the high-temperature decomposition of the solvent contained in the solvato-complex: this first solvent is no longer extracted by the effect of high heat, but by the action of another, carefully chosen solvent, which will not replace it.

[0020] The second solvents S2 according to the invention are miscible with the solvent SI of the solvato-complex and preferably have a sufficiently low polarity so as not to interact strongly with the Li3PS4 phase.

[0021] With the process according to the invention, thiophosphate particles of controllable size are obtained, and in particular, particles of sufficiently small size are obtained without the need for additional post-synthesis treatment such as grinding. It has also been noted that the size distribution of the resulting particles could be quite narrow. Finally, the morphology of the particles can also be controlled and / or chosen.

[0022] Preferably, the process according to the invention is free of any heat treatment subsequent to the drying step c).

[0023] Preferably, step a) of dispersion can be carried out at a temperature between 5°C and 120°C, in particular between 15 and 40°C or between 20 and 25°C, in particular for a period of between 30 minutes and 48 hours, preferably between 2 hours and 30 hours or between 20 hours and 25 hours.

[0024] Preferably, in the dispersion step a), the initial mass concentration of the solvato-complex between Li3PS4 and the first solvent S1 in the second solvent S2 can be between 10 g / L and 100 g / L, in particular between 30 g / L and 60 g / L or between 45 g / L and 55 g / L.

[0025] According to one embodiment of the invention, step a) can be repeated several times. This can prove advantageous, since the driving force of the crystallization of the Li3PS4 phase relies at least in part on a concentration gradient of the solvent molecules to be extracted (the first solvent SI) between the structure of the solvato-complex and the extraction solvent (the second solvent S2).

[0026] Preferably, step b) of separating the Li3PS4 thiophosphate particles can be carried out by centrifugation or filtration.

[0027] Preferably step c) of drying the separated Li3PS4 thiophosphate particles can be carried out at a temperature between 10 and 100°C, in particular between 15°C and 30°C.

[0028] Preferably, step c) of drying the separated Li3PS4 thiophosphate particles can be carried out under reduced pressure, in particular at a pressure between 102 mbar and 101 mbar, i.e. between 1 and 10 Pa.

[0029] Preferably, step c) of drying the separated Li3PS4 thiophosphate particles can be carried out for a period of 1 hour to 10 hours, in particular between 2 and 6 hours or between 4 and 6 hours.

[0030] Advantageously, the second solvent S2 can be selected from esters, nitriles, ethers, ketones, thiols, nitriles, aromatics, in particular phenolic and / or halogenated aromatics. In particular, it can be selected from at least one of the following solvents: anisole, butyronitrile, isobutylisobutyrate, benzonitrile, propanethiol, triphenol, benzothiophene, dibenzothiophene, benzene, toluene, ortho-xylene, meta-xylene, para-xylene, phenol, chlorobenzene, fluorobenzene, bromobenzene, naphthalene, dibenzofuran, ethyl benzoate, methyl benzoate.

[0031] Advantageously, the first solvent SI can be chosen from any other solvent suitable for making a solvato-complex. Thus, the solvent S1 can be chosen from at least one of the following solvents: acetone, tetrahydrofuran THF, acetonitrile ACN, butyl acetate, t-butyl acetate, dimethoxyethane, dimetoxyethane, dioxolane, dioxane, ethyl acetate, ethylenediamine, isobutyronitrile, proprionitrile, ethyl propioniate, thiolane.

[0032] The invention also relates to the process described above, which includes a preliminary operation of preparing the solvato-complex: According to the invention, the solvato-complex between Li3PS4 and the first solvent SI can result from a direct synthesis between a reagent comprising lithium Li and a reagent comprising phosphorus P in the first solvent SI.

[0033] It can also result from an indirect synthesis, starting from a solvato-complex between Li3PS4 and a third solvent S3, followed by solvent exchange in the solvato-complex with the first solvent SI. The solvent S3 can, for example, be THF or acetonitrile.

[0034] Thus, the process according to the invention may comprise, according to a first embodiment, prior to the dispersion step a), a preparation step aO) of the solvato-complex between Li3PS4 and the first solvent SI, said step aO) comprising - the dispersion of a first reagent Li2S and a second reagent P2S5 in the first solvent S1 - then the separation of the solvato-complex formed, notably by centrifugation or filtration, - then optionally washing the separate solvato-complex, in particular with the first solvent S1 - then optionally the drying of the separate solvato-complex and optionally washed.

[0035] According to one embodiment, the filtered solvato-complex can optionally be subjected to a washing step with a solvent, in particular the same solvent as that composing the solvato-complex, and then dried.

[0036] According to another embodiment, the separated solvato-complex can be washed with the second solvent S2, this washing being able to constitute at least in part / being able to continue in step a) of dispersion of the solvato-complex between Li3PS4 and the first solvent SI in the second solvent S2. The drying step of the previous embodiment is then avoided.

[0037] Step aO) can be directly followed by step a) (or even replace it at least in part as indicated above). Steps aO) and a) can also be separated in time, with intermediate storage of the solvato-complex obtained in step aO) before its treatment by dispersion according to step a).

[0038] In step aO), before the dispersion of the first reagent Li2S and the second reagent P2S5 in the first solvent SI, a mixing operation of the two reagents Li2S and P2S5 in solid form, preferably in powder form, can be provided.

[0039] In step aO) a pretreatment of at least one of the two reactants, or of both reactants if they are mixed, can be carried out before dispersion in the first solvent SI, said pretreatment being chosen from at least one of the following treatments: mechanical grinding in dry or solution, dissolution-precipitation in a solvent, thermal dehydration treatment.

[0040] The step aO) of the solvato-complex according to this first variant can be designated under the term preparation by direct synthesis (between Li2S and P2S5).

[0041] According to a second embodiment, the solvato-complex can be prepared in a preliminary step aO') by an indirect synthesis, which involves starting from a solvato-complex with a solvent (which may be called the third solvent S3), and carrying out an exchange between this solvent and the first solvent SI. This third solvent S3 preferably does not meet the criteria indicated above concerning the second solvent S2, just like the first solvent SI. This third solvent S3 can be chosen, for example, from tetrahydrofuran THF and acetonitrile ACN, and is naturally different from the first solvent SI.

[0042] With the process according to the invention, lithium thiophosphate Li3PS 4 and / or [3-Li3PS4.

[0043] The invention also relates to dried Li3PS 4 thiophosphate particles obtained by the process described above, which are partly crystalline and partly amorphous, for example in the form of a glass-ceramic type material, or which are predominantly or substantially or entirely crystalline.

[0044] "Majorly" means a proportion of at least 50% (in particular by weight) and "substantially" means a proportion of at least 80 or 90 or 95 or 99% (in particular by weight).

[0045] The particles according to the invention may have a truncated octahedral type morphology, with in particular a larger size of between 1 and 5 pm, preferably with a dispersion of at most ± 1 pm or at most ± 10 or 20%.

[0046] The particles according to the invention may have a rod-like morphology, in particular with a length between 10 and 20 pm and a width between 3 and 7 pm, with a dispersion that may be + / - 5 pm or + / - 3 pm

[0047] The particles according to the invention may advantageously have an ionic conductivity at room temperature of at least 0.01 mS.cm1, in particular between 0.01 mS.cm1 and 0.5 mS.cm1 or between 0.1 mS.cm1 and 0.3 or 0.2 mS.cm'.

[0048] The invention also relates to any solid electrolyte comprising the Li3PS4 thiophosphate particles described above or obtained by the process described above.

[0049] The invention also relates to any electrochemical system comprising at least one electrolyte or an electrode comprising such an electrolyte, in particular of the battery type.

[0050] The invention also relates to any electrical machine associated with at least one such battery-type electrochemical system so that said system can supply it with electricity. This may, in particular, be an electrical machine installed in a land, sea, or air vehicle and forming part of its powertrain, or an electrical machine for static applications.

[0051] Various non-limiting embodiments for producing the solvato-complex are detailed below. This solvato-complex is to be considered an intermediate product in the complete synthesis of thiophosphate particles, which is the desired final product of the present invention. It is understood that the process may start from this solvato-complex or also incorporate the preliminary operations for obtaining this solvato-complex.

[0052] Further details on methods of preparing the solvato-complex can be found in patent application FR23 / 14782 filed on December 21, 2023, to which reference will be made where appropriate. In this text and thereafter, the term "intermediate product" refers to the solvato-complex described above.

[0053] The process for synthesizing thiophosphate particles Li3PS4 can be carried out from a Li2S reagent and a phosphorus P2S5 reagent, said process comprising at least the following steps under an inert atmosphere: A) Contacting the Li2S reagent, previously suspended in at least one first polar solvent (“solvent 1”), with a suspension containing at least the phosphorus reagent P2S5 in at least one second polar solvent (“solvent 2”), of the same or different nature as the first solvent, at a temperature between 50 and 150°C and formation in suspension under reflux of an intermediate compound in the form of a solvato-complex Li3PS4-solvent, the molar ratio Li2S / P2S5 being between 1 and 4, preferably between 2 and 3 and the volume ratio solvent 1 / solvent 2 being between 0.1 and 4, preferably between 0.5 and 1.5. B) Centrifugation, redispersion of the centrifuged phase in a third anhydrous solvent, which may be identical or different from said first and second solvents (solvent 1 and solvent 2), then filtration and washing of said intermediate compound.

[0054] These steps may be followed by the following steps: C) Drying of said washed intermediate compound at a temperature between 25°C and 150°C for a period of 1 hour to 10 hours; D) Optional heat treatment of said intermediate compound dried at a temperature between 80°C and 300°C for a duration between 1 and 10 hours.

[0055] According to a first embodiment of the invention, in step A): A1) the Li2S reagent can be dispersed under stirring in a first polar solvent (“solvent 1”) at a mass concentration of Li2S reagent in the solvent between 10 g / L and 100 g / L, preferably between 30 g / L and 50 g / L, and the resulting suspension heated between 25 °C and 50 °C, preferably between 30 °C and 40 °C; A2) then the phosphorus reagent P2S5 can be dispersed under stirring in a second polar solvent (“solvent 2”), at a mass concentration of P2S5 in the solvent is between 10 g / L and 100 g / L preferably between 40 g / L and 80 g / L even more preferably between 50 g / L and 70 g / L, the resulting suspension being heated between 50 °C and 150 °C preferably between 90 °C and 110 °C; A3) the Li2S reagent suspension can be gradually added to the phosphorus reagent suspension, preferably P2S5, activated at temperature for a period of between 1 min and 6 min, preferably between 2 and 4 min, and the resulting suspension can be maintained under reflux stirring at a temperature between 50 and 150°C for a time between 1 and 24 h, preferably between 2 and 8 h under an inert atmosphere.

[0056] According to a second embodiment of the invention, in step A): A1) a first part of the Li2S reagent and the phosphorus reagent P2S5 can be dispersed under stirring in a first polar solvent (“solvent 1”) at a mass concentration of Li2S reagent in the solvent of between 3 g / L and 30 g / L, preferably between 5 g / L and 20 g / L and a mass concentration of phosphorus reagent (preferably P2S5) in the solvent of between 10 g / L and 100 g / L, preferably between 40 g / L and 80 g / L, even more preferably between 50 g / L and 70 g / L to form a solution; A2) then a second part of the Li2S reagent can be dispersed under stirring in a second polar solvent (“solvent 2”) at a mass concentration of Li2S reagent in the solvent between 10 g / L and 80 g / L, preferably between 15 g / L and 50 g / L, and the resulting suspension heated between 50 °C and 150 °C, preferably between 90 °C and 110 °C; A3) The Li2S and P2S5 phosphorus reagent solution can be gradually added to the Li2S reagent suspension over a period of 1 to 6 minutes, preferably 2 to 4 minutes, and the resulting suspension can be maintained under agitation under reflux at a temperature between 50 and 150°C for a time between 1 and 24 h preferably between 2 and 8 h under an inert atmosphere.

[0057] Said intermediate compound in the form of a solvato-complex can be recovered in the form of a wet powder by centrifugation at a speed of between 1000 and 10000 rpm for a period of between 5 and 30 minutes, redispersion in a third solvent, then washing on sintered material with an identical or different anhydrous solvent, said third solvent being an anhydrous solvent of the same or different nature as said first and second solvents.

[0058] The drying of step c) can be carried out under reduced pressure between 102 and 103 mbar, at a temperature between 40°C and 80°C for a duration between 2h and 6h.

[0059] The inert gas can be argon or nitrogen or a mixture of both and the gas flow rate can be between 1 L / g / h and 15 L / g / h preferably between 8 and 12 L / h / g.

[0060] The Li2S reagent can be pretreated before suspension by mechanical grinding in dry or solution mode, by dissolution-precipitation in a solvent or by thermal dehydration treatment.

[0061] The polar solvent, whether it is the first solvent (solvent 1) or the second solvent (solvent 2), can be chosen from cyclic or linear ethers, esters, nitriles, thiols. List of figures

[0062] [Fig.1] Fig. 1 represents the Raman spectrum of the [3-Li3PS4] phases obtained according to different examples of implementation of the invention. [Fig.2] Figure 2 shows the diffractogram of the [3-Li3PS4] phases obtained according to different examples of implementation of the invention after post-processing. [Fig.3] Figure 3 represents the SEM (Scanning Electron Microscope) image of the Li3PS4 particles obtained in example 1. [Fig.4] Figure 4 represents the SEM image of the Li3PS4 particles obtained in example 2. [Fig. 5] Figure 5 represents the SEM image of the [3-Li3PS4] particles obtained in example 3. [Fig.6] Figure 6 represents a distribution graph of the size of the Li3PS4 particles obtained in Example 1. [Fig.7] Figure 7 represents a distribution graph of the size of the Li3PS4 particles obtained in Example 3. Description of the implementation methods

[0063] The present invention relates to a new method for preparing Li3PS4 thiophosphate phases that are at least partially crystallized (or amorphous).

[0064] The present invention relates to a new process for preparing ion-conducting alkali sulfide phases of Li3PS4 from a solvato-complex formed between Li3PS4 and a first solvent called SL

[0065] The set of steps of the process according to the invention makes it possible to obtain particles with a submicrometer size and a well-defined morphology, while maintaining a satisfactory ionic conductivity for the intended application, from an intermediate compound called a solvato-complex.

[0066] Certain non-limiting methods of preparing said intermediate solvato-complex are also part of the invention, but the invention applies to any solvato-complex of Li3PS4-xSolvent structure, regardless of its method of obtaining.

[0067] In general, "xSolvent" in this text means that, for one mole of Li3PS4, there are x mole(s) of solvent in the solvato-complex, the value of x depending on the solvato-complex (and therefore on the solvent).

[0068] The embodiment examples below describe the complete synthesis process, with the preparation of the solvato-complex, then the process of obtaining thiophosphate particles from said complex.

[0069] Reagents For the preparation of Li3PS4 thiophosphate phases, the reagents used in the synthesis process according to the invention are: - a Li2S reagent and - a phosphorus reagent P2S5

[0070] All preparation methods for obtaining the reagents are suitable for the Li3PS4 phase preparation method described in the present invention.

[0071] The preparation of a Li3PS4-xSolvent solvato-complex is known to involve dispersing the Li2S reactants with P2S5 in a polar aprotic solvent. After reaction, the precipitate formed is washed with a solvent and then dried to obtain a powder. Method for calculating the descriptors

[0072] The second solvents S2 according to the invention are described by three descriptors used in the approaches called "Quantitative Structure Activity Relationships (QSAR)" [Karelson M. Molecular Descriptors in QSAR / QSPR, John Wiley & Sons, Inc.: New York (2000)]. These three descriptors are available in databases or calculated by molecular modeling methods according to the procedure described below.

[0073] To calculate these descriptors, it is necessary to have a realistic representation of the molecules at the atomic scale. By realistic representation, we understand a structure close to that measured by an experimental characterization technique. Calculation methods in theoretical chemistry provide such representations. As examples of these methods, we can cite, without excluding any other technique not mentioned, force field calculation methods (COMPASS II, Dreiding, UFF, etc.), those based on the density theory of the electronic functional (PBE, BLYP, B3LYP, etc.; commonly referred to as DFT by its acronym in English) and ab initio methods based on the approximate solution of the Schrödringer equation (Hartree-Fock, methods that apply perturbation theory such as MP2, methods based on the calculation of several Slater determinants, etc.).Artificial intelligence or machine learning methods can also provide the information needed to calculate the descriptors. All these approaches provide a three-dimensional structure of the molecules characterized by a set of coordinates in a Cartesian coordinate system.

[0074] A person skilled in the art chooses the most appropriate method according to the complexity of the molecule and the computing resources available to them. The expected impact of the choice of method on the subsequent calculations is on the order of 10%. In the case of the present invention, the thresholds defined for the three descriptors were calculated from geometric structures obtained from geometry optimization calculations using the COMPASS II force field method [Sun, H.; Jin, Z.; Yang, C.; Akkermans, RLC; Robertson, SH; Spenley, NA; Miller, S.; Todd, SM, "COMPASS II: extended coverage for polymer and drug-like molecule databases", J. Mol. Mode., 22(2), 1-10 (2016)], implemented in the Forcite software of the Materials Studio suite from the publisher Dassault Systèmes BIOVIA.

[0075] The molecular structures thus obtained are used to calculate the three descriptors in question, which characterize the molecules of the present invention: - The logP descriptor is calculated according to the method described in the publication [Ghose, AK; Crippen, GMJ Comput. Chem., 7, 565-577 (1986)]. In the context of the present invention, we used the QSAR AlogP spatial descriptor from Materials Studio (Dassault Systèmes BIOVIA) which corresponds to this value. - Molecular density is calculated as the ratio between the sum of the masses of the atoms constituting the molecule and its Van der Waals volume, which is obtained from tabulated data known to a person skilled in the art. In the context of this invention, the QSAR spatial descriptors implemented in Materials Studio (Dassault Systèmes BIOVIA) were used. - The total dipole moment of the molecules is calculated by performing the vector sum of the characteristic dipole moments of each bond within the molecules. The dipole moments of each bond are calculated from the molecular structures and the partial charge of the atoms. The partial charge of the atoms can be obtained either from an ab initio or DFT calculation, or by applying a force field method, or from an artificial intelligence or machine learning method. In the context of the present invention, we used the QSAR spatial descriptors implemented in Materials Studio (Dassault Systèmes BIOVIA) and the atomic charges from the COMPASS II force field method [Sun, H.; Jin, Z.; Yang, C.; Akkermans, RLC; Robertson, SH; Spenley, NA; Miller, S.; Todd, SM, "COMPASS II: extended coverage for polymer and drug-like molecule databases", J. Mol. Model., 22(2), 1-10 (2016)].

[0076] Preparation method: The crystallization method described in the invention comprises three steps: - A step of dispersing the solvato-complex Li3PS4-Xsolvent in a non-complexing solvent - A separation step, for example by centrifugation or filtration - A drying step, preferably under reduced pressure.

[0077] The term "crystallization" should be understood as meaning that the thiophosphate particles obtained are at least partially crystallized: either completely, or partially, predominantly, and they may therefore also contain amorphous portions. This can result in a glass-ceramic type particle structure.

[0078] Step 1: Crystallization at room temperature, example of implementation

[0079] The first step consists of dispersing the solvato-complex Li3PS4-Xsolvent, the solvent being a first solvent SI, in a non-complexing solvent, called the second solvent S2, in a Schlenck-type flask to form a suspension. The dispersion is stirred at a temperature between 5°C and 120°C, preferably between 15°C and 40°C and even more preferably between 20°C and 25°C for a period of between 30 min and 48 hours, preferably between 2 hours and 30 hours, and even more preferably between 20 hours and 25 hours. The mass concentration of Li3PS4 •Xsolvent in the solvent is between 10 g / L and 100 g / L, preferably between 30 g / L and 60 g / L, and between 45 g / L and 55 g / L more preferably.

[0080] This step can be repeated several times. Indeed, the driving force of the crystallization of the Li3PS4 phase is based on a concentration gradient of the solvent molecules to be extracted between the structure of the solvato-complex and the extraction solvent.

[0081] This operation can be carried out directly after the synthesis of the Li3PS4-Xsolvent solvato-complex, during the washing step. This eliminates the drying step of the Li3PS4-Xsolvent solvato-complex.

[0082] This step can be carried out discontinuously, in batch mode, as described above. The contacting of the solvato-complex and the second non-complexing solvent S2 can also be carried out continuously (continuous stirred tank reactor, bed reactor, etc.).

[0083] Step 2: Separation of the thiophosphate phase

[0084] The second step consists of separating the at least partially crystallized thiophosphate phase from the second non-complexing solvent S2. Any liquid / solid separation method is suitable, preferably by centrifugation.

[0085] Step 3: Drying

[0086] The powder is dried under reduced pressure at a temperature between 10°C and 100°C, preferably between 15°C and 30°C, for a period of 1 hour to 10 hours, preferably between 4 hours and 6 hours.

[0087] Materials and methods: The SEM images in figures 3 to 5 were taken with a scanning electron microscope (SEM) (Supra 40 model marketed by Zeiss®). The accelerating voltage was 2 kV.

[0088] Raman analysis of [Fig. 1] is useful for determining the phases present, particularly by observing the wavenumber Raman shifts of the vibrations of the PS43 tetrahedra responsible for the high ionic conductivity of the thiophosphate phases. Raman spectra are acquired using a Renishaw spectrometer equipped with a confocal lens and a 532 nm laser. The sample is first conditioned in a sealed cell.

[0089] XRD analysis of [Fig. 2] allows the crystallographic structure of the material obtained to be determined. The analyses are performed on a Brucker D4 diffractometer (40 kV, 40 mA) with a copper anode (Kal = 1.54060 Å; Ka2 = 1.54439 Å) at room temperature. The samples are prepared with a transmission sample holder between two Kapton© sheets sealed with vacuum grease. The [3-Li3PS4] structure is indexed with PDF reference number 04-010-1784.

[0090] The ionic conductivity of the samples is measured by electrochemical impedance spectroscopy between two blocking electrodes in a temperature-controlled cell (ASC-T model sold by Sphere Energy®). The solid electrolyte is directly densified to 4 tonnes / cm² between the two electrodes. The impedance measurement is performed with a Biologie® MTZ-35 impedance meter between 30 MHz and 1 Hz with an amplitude of 10 mV relative to a voltage of 0 V and a temperature of 30 °C. Examples

[0091] Example 1 according to the invention: Preparation of the [3-Li3PS4] phase in anisole

[0092] - Formation of the Li3PS4-2THF solvato-complex: the first solvent S1 is therefore here the tetrahydrofuran THF.

[0093] The Li3PS4-2THF solvato-complex is prepared according to the following protocol. The reagents Li2S (3.818 g) and P2S5 (6.498 g) are mixed and ground in a mortar until a homogeneous powder is obtained. The resulting powder is then dispersed in a flask with 200 mL of THF. After 24 hours of stirring at room temperature, the suspension is filtered and the resulting powder is washed with THF. The powder is then dried under reduced pressure between 10⁻¹ and 10² mbar (less than or equal to 0.1 mbar) for 4 hours at room temperature.

[0094] This preparation is preferably carried out in a dry and / or inert atmosphere.

[0095] - Crystallization of the [3-Li3PS4] phase

[0096] In a flask, 2 g of the previously obtained Li3PS4-2THF solvato-complex are weighed and dispersed in 40 mL of anisole, which thus acts as the second solvent S2. After 24 hours of stirring at room temperature, the suspension is centrifuged at 10,000 rpm for 20 minutes. The recovered powder is then washed with anisole by centrifugation and subsequently dried under reduced pressure (less than or equal to 0.1 mbar) at room temperature for 4 hours.

[0097] Example 2 according to the invention: Preparation of the [3-Li3PS4] phase in butyronitrile

[0098] The only difference from example 1 is that anisole is replaced by butyronitrile to play the role of the second solvent S2.

[0099] Example 3 according to the invention: Preparation of the [3-Li3PS4] phase in propanethiol

[0100] The only difference from example 1 is that anisole is replaced by propanethiol to play the role of the second solvent S2.

[0101] Example 4: comparative example

[0102] The only difference from example 1 is that anisole is replaced by dioxolane to play the role of the second solvent S2.

[0103] The powders are characterized by Raman spectroscopy, X-ray diffraction, scanning microscopy and impedance spectroscopy.

[0104] Figure 1 represents the Raman spectrum of the phases obtained according to these four examples (each curve is identified by the solvent S2 used in each of the examples), with the Raman shift expressed in cm⁴ on the x-axis and the intensity in arbitrary units on the y-axis.

[0105] It is observed that these spectra display the vibrational peak at 421 cm⁴, characteristic of the PS⁴³ units of the Li₃PS⁴ phase for Examples 1 (anisole), 2 (butyronitrile), and 3 (propanethiol). Furthermore, the broad peak located at 173 cm⁻¹ indicates the formation of the phase crystalline [3-Li3PS4 (Adv. Energy Mater. 2021, 2101111). In the case of comparative example 4 (dioxolane), the shift of the peak of the PS43 units to 430 cm 1 and the absence of the peak of the [3] structure indicates that the PS43 units are still solvated in a solvato-complex.

[0106] Figure 2 shows the diffractograms of the four phases obtained, identified according to the nature of the second solvent S2, with the angle 2θ in degrees on the abscissa and the intensity in au on the ordinate. She confirms that the phases obtained have the structure [3-Li3PS4 with no visible trace of Li2S in the three examples 1,2,3. In contrast, the diffractogram of comparative example 4 shows the presence of a new structure which does not correspond to the [3] structure. This confirms that the choice of the second solvent S2 is crucial for the formation of the [3-Li3PS4] phase that we want to obtain.

[0107] The descriptors of several solvents were calculated according to the method described above and are presented in Table 1. The conformity results show that the conformity rule is in agreement with the examples presented above. Indeed, the solvents used in Examples 1, 2, and 3 conform to the invention, whereas the solvent in comparative Example 4 (dioxolane) does not conform because its partition coefficient with water is less than 1.1.

[0108] Table 1 below shows examples of second solvents S2 that conform and do not conform to the invention according to the three selection criteria retained.

[0109] [Tables] Solvent Partition coefficient logP Molecular density (g / cm³) Dipole moment (D) Compliance Acetone 0.4 0.898 2.60 no Acetonytrile 0.2 0.899 2.29 no Anisole 1.8 0.988 1.66 yes Butyl acetate 1.1 0.939 1.09 no Butyronitrile 1.2 0.869 2.31 yes Dimethoxyethane -0.2 0.933 0.00 no Dioxolane 0.0 1.078 2.24 no Dioxane -0.3 1.033 0.00 no Ethyl acetate 0.2 0.981 1.09 no Ethylenediamine -1.4 0.875 0.99 no Isobutyronitrile 1.4 0.871 2.33 no Isobutylisobutyrate 2.3 0.919 1.08 yes Proprionitrile 0.8 0.879 2.31 no Benzonitrile 2.1 1.018 2.22 yes Ethyl propionate 0.8 0.964 1.09 no Propanethiol 1.1 0.944 1.03 yes Thiolane 0.8 1.011 1.26 no t-Butyl acetate 0.7 0.948 1.26 no Thiophenol 2.0 1.082 0.93 yes Benzothiophene 2.1 1.083 1.26 yes Dibenzothiophene 3.5 1.133 1.17 yes Benzene 2.0 0.928 0.00 yes Toluene 2.5 0.914 0.13 yes o-Xylene 3.0 0.908 0.21 yes m-Xylene 3.0 0.907 0.13 yes p-Xylene 3.0 0.906 0.00 yes Phenol 1.8 1.024 1.52 yes Chlorobenzene 2.6 1.151 1.20 yes Fluorobenzene 2.2 1.083 1.99 yes Bromobenzene 2.8 1.531 0.94 yes Naphthalene 3.0 1.000 0.00 yes Dibenzofuran 3.1 1.098 1.92 yes Ethyl Benzoate 2.1 1.039 0.95 yes Methyl benzoate e 1.8 1.061 0.90 yes

[0110] The SEM images of examples 1, 2 and 3 are shown in figures 3, 4 and 5 respectively. The particles from examples 1 and 3 have a truncated octahedral morphology with a monodisperse distribution, of respectively 2.1 + 1.0 pm (see [Fig.6]) and 2.0 ± 0.9 pm (see [Fig.7]). The particles from example 2 have a rod-like morphology with lengths between 10 and 20 pm and widths of 5 pm.

[0111] We can thus see that the choice of the second solvent S2, the extraction solvent, influences the morphology and / or size of the particles obtained.

[0112] The ionic conductivities of the [3-Li3PS4] phases obtained are presented in Table 2 below for examples 1 to 3. The ionic conductivity of comparative example 4 is negligible, due to its solvato-complex structure.

[0113] [Tables2] Example Second Solvent S2 Conductivity (mS / cm) at 30°C 1 Anisole 0.140 2 Butyronitrile 0.032 3 Propanethiol 0.096

[0114] From this table, it can be verified that the ionic conductivities of the particles of the examples according to the invention are satisfactory, that of example 1 with S2 in anisole being remarkably high.

Claims

Demands

1. A process for the synthesis of Li3PS4 thiophosphate particles, from a solvato-complex formed between Li3PS4 and a first solvent SI, said process comprising: a) a step of dispersing the solvato-complex between Li3PS4 and the first solvent S1 in a second non-complexing solvent S2, said second solvent S2 being miscible with the first solvent SI and having - a logarithm of the water / octanol distribution coefficient logP equal to or greater than 1.1, - a molecular density equal to or greater than 0.869 g / cm3, - a dipole moment less than or equal to 2.32 D, so as to precipitate Li3PS4 thiophosphate particles; b) a step of separating the Li3PS4 thiophosphate particles precipitated in step a); c) a step of drying the Li3PS4 thiophosphate particles separated in step b).

2. A method according to the preceding claim, characterized in that step a) of dispersion is carried out at a temperature between 5°C and 120°C, in particular between 15 and 40°C or between 20 and 25°C, in particular for a period of between 30 minutes and 48 hours, preferably between 2 hours and 30 hours or between 20 hours and 25 hours.

3. A process according to any one of the preceding claims, characterized in that, in the dispersion step a), the initial mass concentration of the solvato-complex between Li3PS4 and the first solvent S1 in the second solvent S2 is between 10 g / L and 100 g / L, in particular between 30 g / L and 60 g / L or between 45 g / L and 55 g / L.

4. A method according to any one of the preceding claims, characterized in that step a) is repeated several times.

5. A method according to any one of the preceding claims, characterized in that step b) of separation of the thiophosphate particles Li3PS4 is carried out by centrifugation or filtration.

6. A process according to any one of the preceding claims, characterized in that step c) of drying the separated Li3PS4 thiophosphate particles is carried out at a temperature between 10 and 100°C, in particular between 15°C and 30°C.

7. A process according to any one of the preceding claims, characterized in that step c) of drying the separated Li3PS4 thiophosphate particles is carried out under reduced pressure, in particular at a pressure between 1 and 10 Pa.

8. A process according to any one of the preceding claims, characterized in that step c) of drying the separated Li3 PS4 thiophosphate particles is carried out for a period of 1 hour to 10 hours, in particular between 2 hours and 6 hours.

9. A process according to any one of the preceding claims, characterized in that the second solvent S2 is selected from esters, nitriles, ethers, ketones, thiols, nitriles, aromatics, in particular phenolic and / or halogenated aromatics, and in particular from at least one of the following solvents: anisole, butyronitrile, isobutylisobutyrate, benzonitrile, propanethiol, triphenol, benzothiophene, dibenzothiophene, benzene, toluene, ortho-xylene, meta-xylene, para-xylene, phenol, chlorobenzene, fluorobenzene, bromobenzene, naphthalene, dibenzofuran, ethyl benzoate, methyl benzoate.

10. A process according to any one of the preceding claims, characterized in that the first solvent SI is selected from at least one of the following solvents: acetone, tetrahydrofuran THF, acetonitrile ACN, butyl acetate, t-butyl acetate, dimethoxyethane, dimetoxyethane, dioxolane, dioxane, ethyl acetate, ethylenediamine, isobutyronitrile, proprionitrile, ethyl propioniate, thiolane.

11. A process according to any one of the preceding claims, characterized in that the solvato-complex between Li3PS4 and the first solvent SI results from a direct synthesis between a reagent comprising lithium Li and a reagent comprising phosphorus P in the first solvent SI, or from an indirect synthesis from a solvato-complex between Li3PS4 and a third solvent S3 and then exchange of solvents in the solvato-complex with the first solvent SI.

12. A process according to any one of the preceding claims, characterized in that it comprises, prior to the dispersion step a), a preparation step a0 of the solvato-complex between Li3PS4 and the first solvent SI, said step a0 comprising - the dispersion of a first reagent Li2S and a second reagent P2S5 in the first solvent S1 - then the separation of the solvato-complex formed, in particular by centrifugation or filtration, - then optionally the washing of the separated solvato-complex, in particular with the first solvent S1 - then optionally the drying of the separated and optionally washed solvato-complex.

13. A process according to the preceding claim, characterized in that, in step a0) of preparation of the solvato-complex, the filtered solvato-complex is washed with solvent S2, this washing constituting at least in part / continuing in step a) of dispersion of the solvato-complex between Li3PS4 and the first solvent S1 in the second solvent S2.

14. A process according to any one of claims 12 or 13, characterized in that, in step a0), prior to the dispersion of the first reagent Li2S and the second reagent P2S5 in the first solvent SI, a mixing operation of the two reagents Li2S and P2S5 in solid form, preferably in powder form, is carried out.

15. A process according to any one of claims 12 to 14, characterized in that, in step a0), a pretreatment is carried out on at least one of the two reactants, or on both reactants if they are mixed, before dispersion in the first solvent SI, said pretreatment being selected from at least one of the following treatments: mechanical grinding in dry or solution, dissolution-precipitation in a solvent, thermal dehydration treatment.

16. Dried Li3PS4 thiophosphate particles obtained by the process according to any one of the preceding claims, characterized in that they are partly crystalline and partly amorphous, for example of glass-ceramic type, or in that they are substantially or entirely crystalline.

17. Particles according to the preceding claim, characterized in that they have a truncated octahedral type morphology, with in particular a larger size of between 1 and 5 pm, preferably with a dispersion of at most + / - 1 pm or at most + / - 10 or 20%, or of rod type, with in particular a length of between 10 and 20 pm and a width of between 3 and 7 pm.

18.

19.

20. Particles according to one of claims 16 or 17, characterized in that their ionic conductivity is at least 0.01 mS.cm'. Solid electrolyte comprising Li3PS4 thiophosphate particles according to any one of claims 16 to 18. Electrochemical system comprising at least one electrode having an electrolyte according to the preceding claim.

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