Method for the synthesis of sodium or lithium thiophosphate particles in solution

Abstract

The present invention relates to a method for synthesizing thiophosphate particles Li3PS4 or Na3PS4 from a reagent A2S and a phosphorus reagent P2S5, with A chosen from Li or Na, comprising at least the following steps under an inert atmosphere: A) Contacting the reagent A2S, 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 at temperature and formation in suspension under reflux of an intermediate compound in the form of a solvato-complex A3PS4 solvent; B) Centrifugation, redispersion in a solvent, then filtration and washing of said intermediate compound; C) Drying of said intermediate compound; D) Optional heat treatment. Figure 3 to be published

Description

Title of the invention: Method for the synthesis in solution of sodium or lithium thiophosphate particles Technical field

[0001] The present invention relates to the field of electrochemical energy storage via lithium or sodium batteries, more particularly all-solid-state batteries using an inorganic phase of the thiophosphate type as solid electrolyte. The invention relates more particularly to the preparation in solution of thiophosphate phases and aims to propose a relevant method in terms of product quality, preparation time and industrial extrapolation. Prior art

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

[0003] Initially, the thiophosphate phases were obtained by solid-state preparation methods by melting-quenching, as described for example in patents JP3433173 B2 and JP5270825 B2. The latter are time-consuming and difficult to extrapolate to the industrial scale. More recently, preparation methods by mechanosynthesis have been described and generally make it possible to obtain smaller micrometric particles than by melting-quenching methods with good conductivity. However, the grinding times are of the order of several tens of hours [US8993176 BB; Adv. Energy Mater. 2021 2101111] or require additional heat treatment [EP3740996 A1; JP2017208324 A2]. Grinding methods in the presence of one or more solvents have also been developed to reduce the grinding time to a few hours and enhance the reduction in particle sizes [CN106329002; JP2021082409 A2; WO2022162085 A; CN114678586 B],

[0004] An alternative preparation method has also been described by several studies [J. Am. Chem. Soc. 2013, 135, 975-978, US8597838 BB; CN106505247 A; Chem. Lett. 2015, 44, 884-886; ACS Appl. Mater. Interfaces 2018, 10, 15]. This is based on the reaction of Li2S or Na2S with P2S5 suspended in an aprotic polar solvent for periods ranging from overnight to several days with temperatures between room temperature and 50°C. After washing, an intermediate compound called solvato-complex is recovered and then dried under reduced pressure. This compound is then thermally decomposed leading to the amorphous Li3PS4 phase, the [3-Li3PS4 phase or the cubic or tetragonal Na3PS4 phase. 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. In the case of the Na3PS4 phase obtained by reaction in acetonitrile (ACN), the ionic conductivity is 0.0844 mS / cm at room temperature and the size of the primary particles is 200 nm but the latter are agglomerated.

[0005] Other methods of preparation in solution have been developed to attempt to overcome these limitations, in particular by varying the operating conditions such as temperature, pressure, stirring method and combination of solvents.

[0006] US patent 11325096 BB describes a method for preparing Li3PS4 of the solvothermal type activated by microwaves. The amorphous Li3PS4 phase is thus obtained after 3 h of reaction at 100 °C in THF. Other scientific authors describe different methods of mechanical agitation by adding grinding balls, vibrating system, for example Solid State lonics 285 (2016) 2-5; ACS Appl. Energy Mater. 2021, 4, 2275-2281; Heliyon 5 (2019) e02760; Powder Technology 387 (2021) 415-420, which are difficult to industrialize.

[0007] An improvement to the method for preparing Li3PS4 and Na3PS4 described in the literature consists of combining several solvents, for example non-polar and polar (US 10439198 BB), but this method implies that the reaction medium is cooled before adding the second solvent and the reaction times are longer.

[0008] An alternative has also been described in patent CN113471519 B which consists of directly preparing the Li2S reagent with a reduced size via a preparation method involving the reaction of LiEt3BH with elemental sulfur in THF. The reaction then takes place in colloidal suspension and makes it possible to obtain [3-Li3PS4 phase particles with a particle size of 30 nm. However, the use of LiEt3BH is dangerous because it is a very flammable compound which easily decomposes into H2 and BEt3 (pyrophoric compound) and is very sensitive to humidity and air. Although the use of LiEt3BH allows rapid formation of the solvato-complex and the obtaining of small-sized particles, the ionic conductivity is low and the cost of the LiEt3BH reagent is very high compared to the Li2S reagent. Summary of the invention

[0009] Surprisingly, the Applicant has discovered that it is possible to prepare lithium and sodium thiophosphates in solution according to a particular method not involving expensive equipment or steps, nor dangerous precursors, with short reaction times, therefore extrapolable to the industrial scale and thus to obtain thiophosphate phases of satisfactory conductivity.

[0010] The invention relates to a method for synthesizing thiophosphate particles Li3PS4 or Na3PS4 from a reagent A2S and a phosphorus reagent P2S5 with A chosen from Li or Na, comprising at least the following steps under an inert atmosphere: A) Contacting the reagent A2S, 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 from that of the first solvent, at a temperature of between 50 and 150°C and formation in suspension under reflux of an intermediate compound in the form of a solvato-complex A3PS4-solvent, the molar ratio A2S / P2S5 being between 3 and 6, preferably between 4 and 5 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 to or different from said first and second solvents (solvent 1 and solvent 2), then filtration and washing of said intermediate compound; C) Drying 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 dried intermediate compound at a temperature between 80°C and 300°C and a duration between 1 and 10 hours.

[0011] According to a first embodiment of the invention, in step A): Al) the A2S reagent can be dispersed with stirring in a first polar solvent (solvent 1) at a mass concentration of A2S reagent in the solvent of between 10 g / L and 100 g / L, preferably between 50 g / L and 70 g / l and the suspension obtained can be heated between 25°C and 50°C, preferably between 30°C and 40°C; A2) then the phosphorus reagent P2S5 can be dispersed with stirring in a second polar solvent (solvent 2), at a mass concentration of 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, the suspension obtained being heated between 50°C and 150°C, preferably between 90°C and 110°C; A3) the suspension of reagent A2S can be gradually added to the suspension of phosphorus reagent, preferably P2S5, activated by temperature for a period of between 1 min and 6 min, preferably between 2 and 4 min and the resulting suspension can be kept stirring at reflux at a temperature of between 50 and 150°C for a period of between 1 and 24 h, preferably between 2 and 8 h under an inert atmosphere.

[0012] According to a second embodiment of the invention, in step A): Al) a first part of the reagent A2S and the phosphorus reagent P2S5 can be dispersed with stirring in a first polar solvent (solvent 1) at a mass concentration of reagent A2S 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 A2S reagent can be dispersed with stirring in a second polar solvent (solvent 2) at a mass concentration of A2S reagent in the solvent of between 10 g / L and 80 g / L, preferably between 15 g / L and 50 g / L, and the suspension obtained can be heated between 50°C and 150°C, preferably between 90°C and 110°C; A3) the solution of reagents A2S and phosphorus P2S5 can be gradually added to the suspension of reagent A2S for a period of between 1 min and 6 min, preferably between 2 and 4 min, and the resulting suspension can be kept stirring at reflux at a temperature of between 50 and 150°C for a period of between 1 and 24 h, preferably between 2 and 8 h, under an inert atmosphere.

[0013] 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 min, redispersion in a third solvent, then washing on a frit with an identical or different anhydrous solvent, said third solvent being an anhydrous solvent of the same or different nature as that of said first and second solvents.

[0014] The drying of step c) can be carried out under reduced pressure of between 102 and 103 mbar, at a temperature of between 40°C and 80°C for a duration of between 2 h and 6 h.

[0015] The drying of step c) can be followed by a step d) of heat treatment carried out in a crossed bed reactor under a flow of inert gas or under reduced pressure of between 102 and 103 mbar, at a temperature between 180°C and 300°C and a duration between 1 and 4 hours.

[0016] The inert gas may be argon or nitrogen or a mixture of the two and the gas flow rate may be between 1 L / g / h and 15 L / g / h, preferably between 8 and 12 L / h / g.

[0017] The A2S reagent can be pretreated before suspension by mechanical grinding in a dry or solution process, by dissolution-precipitation in a solvent or by a thermal dehydration treatment.

[0018] The polar solvent, whether the first solvent (solvent 1) or the second solvent (solvent 2), can be chosen from cyclic or linear ethers, esters, nitriles, thiols.

[0019] In one embodiment, A = Li and the synthesis method makes it possible to obtain a lithium thiophosphate phase Li3PS4 or [3-Li3PS4 .

[0020] In another embodiment, A=Na and the synthesis method makes it possible to obtain a sodium thiophosphate phase Na3PS4. List of figures [Fig 1]

[0021] [Fig.l] represents a block diagram of the synthesis steps according to the invention. [Fig 2]

[0022] [Fig.2] represents the Raman spectrum of the Li3PS4 phase obtained in example 1. [Fig 3]

[0023] [Fig.3] represents the SEM image of the amorphous Li3PS4 particles obtained in example 1. [Fig 4]

[0024] [Fig.4] represents the Raman spectrum of the [3-Li3PS4] phase obtained in example 2. [Fig 5]

[0025] [Fig.5] represents the diffractogram of the [3-Li3PS4] phase obtained in example 2. [Fig 6]

[0026] [Fig.6] represents the SEM image of the particles [3-Li3PS4 obtained in example 2. [Fig 7]

[0027] [Fig.7] represents the Raman spectrum of the [3-Li3PS4] phase obtained in example 3. [Fig 8]

[0028] [Fig.8] represents the diffractogram of the phase [3-Li3PS4 obtained in example 3. [Fig 9]

[0029] [Fig.9] represents the SEM image of the particles [3-Li3PS4 obtained in example 3. [Fig 10]

[0030] [Fig. 10] represents the diffractogram of the t-Na3PS4 phase obtained in example 4. [Fig 11]

[0031] [Fig. 11] represents the SEM image of the t-Na3PS4 particles obtained in Example 4. Description of the embodiments

[0032] The present invention relates to a new method for preparing thiophosphate phases Li3PS4 or Na3PS4, crystallized or amorphous.

[0033] The present invention relates to a new method for preparing ion-conducting alkali sulfide phases A3PS4, in particular sodium or lithium (Na3PS4 and Li3PS4). All the steps of the process according to the invention make it possible to obtain a shorter formation time for the intermediate compound (solvato-complex) than the synthesis of the prior art, particles with a submicrometric size and a well-defined morphology, while maintaining satisfactory ionic conductivity for the intended application. Reagents#

[0034] For the preparation of thiophosphate phases A3PS4 (Na3PS4 and Li3PS4) the reagents used in the synthesis process according to the invention are: - an A2S reagent with A chosen from Li, Na; and - a phosphorus reagent P2S5.

[0035] All preparation methods for obtaining the reagents are suitable for the method for preparing the A3PS4 phases described in the present invention.

[0036] Pre-processing of A 2 S_:

[0037] The commercial A2S reagent can be used directly or pretreated. In the case of Li2S, the pretreatment can be mechanical (planetary) grinding in a dry or solution process or dissolution-precipitation in ethanol. In the case of Na2S, a dehydration heat treatment can be carried out. These methods are known to those skilled in the art. Solvents

[0038] The solvents used are advantageously polar solvents, preferably aprotic:

[0039] Solvent 1: cyclic or linear ethers (e.g. THF and dimethoxyethane (DME)), esters (alkyl acetate, e.g. butyl acetate), nitriles (e.g. acetonitrile), thiols (e.g. propanethiol)

[0040] Solvent 2: cyclic or linear ethers (e.g. THF and dimethoxyethane), esters (alkyl acetate, e.g. butyl acetate; isobutylisobutyrate, dimethyl glutarate, diethyl glutarate), nitriles (e.g. acetonitrile), thiols (e.g. propanethiol).

[0041] All solvents are anhydrous.

[0042] The preparation method according to the invention comprises at least three steps, then an optional heat treatment step. All manipulations are carried out under an inert atmosphere. • A step of formation in suspension under reflux of the intermediate compound (solvato-complex) of formula A3PS4-fast solvent. • A washing step by centrifugation and filtration • A drying step, preferably under reduced pressure; • An optional decomposition step by heat treatment, depending on the desired phase.

[0043] First step: The first step can be carried out in two alternative ways.

[0044] [Fig. 1] shows the different stages of formation of the compound of phase A3 PS4 according to a first embodiment (at the top), and according to a second embodiment (at the bottom).

[0045] The synthesis method according to the invention makes it possible to overcome the kinetic limitation of the formation of the intermediate compound by activating the phosphorus reagent P2S5. Indeed, this is in the form of an adamantate cage P4Si0, limiting the reaction with A2S (A=Li or Na). The activation of the P2S5 reagent consists of heating the adamantate cage to dedimerize it. In order to promote a rapid reaction, the previously suspended A2S reagent is added hot to the suspension containing the phosphorus reagent P2S5. • Step 1.1

[0046] The first sub-step makes it possible to disperse the A2S reagent in a polar solvent, preferably aprotic (solvent 1), for example in a Schlenck type flask, to form a suspension. The dispersion is advantageously carried out in an ultrasonic bath between 25°C and 50°C, preferably between 30°C and 40°C for a period of between 1 min and 120 min, preferably between 10 and 50 min. The mass concentration of A2S in the solvent is between 10 g / L and 100 g / L, preferably between 30 g / L and 70 g / L, more preferably between 30 g / L and 50 g / l when A = Li and more preferably between 50 g / L and 70 g / L when A = Na. • Step 1.2

[0047] The second phase makes it possible to disperse the P2S5 reagent in a polar solvent, preferably aprotic (solvent 2, which may be of the same nature as solvent 1) in a three-necked flask equipped with a water condenser. The suspension is heated between 50°C and 150°C, preferably between 90°C and 110°C, with stirring. The mass concentration of P2S5 in the solvent is between 10 g / L and 100 g / L, preferably between 40 g / L and 80 g / L, even more preferably between 50 g / L and 70 g / L. • Step 1.3

[0048] The A2S suspension is advantageously transferred into a device allowing the gradual addition of activated P2S5 into the suspension, for example a dropping funnel, to be added dropwise into the temperature-activated P2S5 suspension. The time for adding the A2S suspension is between 1 min and 6 min, preferably between 2 and 4 min. The resulting suspension is maintained at reflux at a temperature between 50 and 150°C (preferably 100°C). for a time between 1 and 24 h, preferably between 2 and 8 h under an inert atmosphere. The inert atmosphere can be dynamic (constant flow) or static and the nature of the gas can be argon or nitrogen or a mixture of the two. The molar ratio A2S / P2S5 is between 1 and 4, preferably between 2 and 3, and the volume ratio solvent 1 / solvent 2 is between 0.1 and 4, preferably between 0.5 and 1.5.

[0049] According to the second embodiment of step 1, which can be described with reference to [Fig.l] below: • Alternative step 1.1

[0050] The first sub-step makes it possible to disperse the A2S reagent and the P2S5 reagent in an aprotic polar solvent (solvent 1) in a Schlenck-type flask to form a solution. The mass concentration of A2S in the solvent is between 3 g / L and 30 g / L, preferably between 10 g / L and 20 g / l when A = Li and preferably between 10 g / L and 30 g / L when A = Na. The 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. • Alternative step 1.2

[0051] The second sub-step makes it possible to disperse the A2S reagent in a polar solvent, preferably aprotic (solvent 2, which may be of the same nature as solvent 1), for example in a three-necked flask equipped with a water cooler, to form a suspension. The suspension is heated between 50°C and 150°C, preferably between 90°C and 110°C, with stirring. The mass concentration of A2S in the solvent is between 5 g / L and 50 g / L, preferably between 15 g / L and 40 g / L when A=Li and preferably between 20 g / L and 50 g / L when A=Na. • Alternative step 1.3

[0052] Finally, the solution of A2S and P2S5 is advantageously transferred into a device allowing the gradual addition of A2S into the suspension, for example into a dropping funnel, to be added dropwise into the temperature-activated suspension of A2S. The time for adding the solution of A2S and P2S5 is between 1 min and 6 min, preferably between 2 and 4 min. The resulting suspension is maintained at reflux at a temperature between 50 and 150°C (preferably 100°C) for a time between 1 and 24 h, preferably between 2 and 8 h under an inert atmosphere. The inert atmosphere can be dynamic (constant flow) or static and the nature of the gas can be argon or nitrogen or a mixture of the two. The A2S / P2S5 molar ratio is between 1 and 4, preferably between 2 and 3, and the solvent 1 / solvent 2 volume ratio is between 0.1 and 4, preferably between 0.5 and 1.5.

[0053] Step 2: washing of the intermediate compound (solvato-complex)

[0054] At the end of the reaction, the intermediate compound which is an A3PS 4-solvent solvato-complex is in the form of a suspension in the solvent mixture. Said intermediate compound is recovered by centrifugation, advantageously at a speed of between 1000 and 10000 revolutions per min for a duration of between 5 and 30 min (here 10000 revolutions per min for 20 min) and redispersed in a solvent (of the same nature as previously or different) before being washed, advantageously on frit with an identical or different solvent, to obtain a wet powder. Step 3#: Drying

[0055] The powder obtained is dried, preferably under reduced pressure (typically between 102 and 103 mbar), at a temperature between 25°C and 150°C, preferably between 40°C and 80°C for a period of 1 hour to 10 hours, preferably between 2 hours and 6 hours.

[0056] The structure obtained depends on the solvents used and on the nature and the initial size distribution and crystallinity of the A2S reagent. Step 4#: Heat treatment (optional)

[0057] A heat treatment may be carried out, preferably in a flow-through bed reactor under inert gas flow or under reduced pressure (typically between 102 and 103 mbar). The nature of the inert gas may be argon or nitrogen or a mixture of the two. The gas flow rate is between 1 L / g / h and 15 L / g / h, preferably between 8 and 12 L / h / g. This configuration allows efficient removal of the solvent. The treatment temperature is advantageously between 80 and 300°C, preferably between 180°C and 300°C for a duration of between 1 h and 10 h, preferably between 1 h and 4 h. The treatment conditions depend on the nature of the phase to be treated. Characterization techniques

[0058] The SEM images are taken with a scanning electron microscope (SEM) (Supra 40 model sold by Zeiss®). The acceleration voltage is 2kV.

[0059] RAMAN analysis is useful for determining the phases present by observing, in particular, the RAMAN absorption wavelengths of the PS43 tetrahedra, which are at the origin of the good ionic conductivity of the thiophosphates. The acquisition of the Raman spectra is carried out on a Renishaw spectrometer equipped with a confocal lens and a 532 nm laser. The sample is previously conditioned in sealed cells. The spectra were acquired with the following parameters: power 3.9 mW and time 100 s.

[0060] DRX analysis makes it possible to check that the characteristic crystalline structure of thiophosphate is obtained. The diffractograms are acquired on a Brucker D4 diffractometer (40 kV, 40 mA) with a copper anode (Kal = 1.54060 Â ; Ka2 = 1.54439 Â). The sample is previously conditioned between two Kapton sheets sealed with vacuum grease.

[0061] The ionic conductivity of the samples is measured by electrochemical impedance spectroscopy between two blocking electrodes in a thermostated cell (model ASC-T sold by Sphere Energy®). The solid electrolyte is directly densified to 4 ton / cm2 between the two electrodes. The impedance measurement is carried out with a 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 at the same pressure. Examples

[0062] Example 1: Preparation of the amorphous Li3PS4 phase according to the invention

[0063] In a Schlenck tube, 1.912 g of Li2S are weighed and dispersed in 50 mL of THF (tetrahydrofuran). The tube is then placed under ultrasound for 30 min at 35°C and the resulting suspension is transferred into a dropping funnel. In a three-necked flask, 3.33 g of P2S5 are weighed and dispersed in 50 mL of butyl acetate BA. The P2S5 suspension is heated to 100°C in a reflux assembly. The Li2S suspension is then added dropwise over 3 min into the P2S5 solution. After 4 h of stirring, the flask is allowed to cool to room temperature. The suspension is then centrifuged at 10,000 rpm for 20 min. The precipitate is redispersed in THF before being washed on a frit with THF, obtaining a wet white powder. This is then dried under reduced pressure at 50°C for 4 h to obtain the amorphous Li3PS4 phase.

[0064] The powder is characterized by Raman spectroscopy, scanning electron microscopy and impedance spectroscopy. [Fig.2] shows the Raman spectrum of the obtained phase with the vibration peak at 421 cm 1 characteristic of the PS43 units of the Li3PS 4 phase. In addition, the two broad peaks located between 100 and 300 cm 1 indicate the formation of an amorphous phase. The SEM image in [Fig.3] shows the morphology of the obtained particles. These have a 1D rod-like morphology with lengths ranging from 2 to 20 microns and thicknesses ranging from 300 to 500 nm. The measured ionic conductivity is 0.11 mS / cm at 30°C.

[0065] Example 2: Preparation of the [3-Li3PS4] phase according to the invention

[0066] In a Schlenck tube, 1.912 g of Li2S are weighed and dispersed in 50 mL of acetonitrile ACN. The tube is then placed under ultrasound for 30 min at 35°C and then the resulting suspension is transferred into a dropping funnel. In a three-necked flask, 3.33 g of P2S5 are weighed and dispersed in 50 mL of butyl acetate BA. The P2S5 suspension is heated to 100°C in a reflux assembly. The Li2S suspension is then added dropwise over 3 min into the P2S5 solution. After 6 h of stirring, the flask is allowed to cool to room temperature. The suspension is then centrifuged at 10,000 rpm for 20 min. The precipitate is redispersed in ACN before being washed on a frit with ACN, obtaining a wet white powder. This is then dried under reduced pressure at 50°C for 4 h to obtain the intermediate compound Li3PS4ACN. The latter is then annealed at 200°C for 2 h under a flow of argon (100 / h / g) to obtain the phase [3-Li3PS4.

[0067] The powder is characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy and impedance spectroscopy. [Fig.4] shows the Raman spectrum of the obtained phase with the vibration peak at 421 cm 1 characteristic of the PS43 units of the Li3PS4 phase. The presence of the vibration peak at 173 cm 1 corresponds to the vibrations of the PS43 units in the crystalline structure [3-Li3PS4. The diffractogram in [Fig.5] confirms the formation of the phase [3-Li3PS4. The SEM image in [Fig.6] shows the morphology of the obtained particles. These are faceted and have a morphology of truncated octahedrons with two vertices, combined with 2D platelets. They have a thickness of about ten to a hundred nanometers and a width of about one micron. The measured ionic conductivity is 0.017 mS / cm at 30°C.

[0068] Example 3: Preparation of the [3-Li3PS4] phase from submicronic Li2S according to the invention

[0069] The Li2S is pretreated by dissolution precipitation in ethanol and then dried. Amorphous particles of submicron size are obtained and then used. In a Schlenck tube, 1.912 g of submicron Li2S are weighed and dispersed in 50 mL of acetonitrile ACN. The tube is then placed under ultrasound for 30 min at 35°C and then the resulting suspension is transferred into a dropping funnel. In a three-necked flask, 3.33 g of P2S5 are weighed and dispersed in 50 mL of butyl acetate BA. The P2S5 suspension is heated to 100°C in a reflux assembly. The Li2S suspension is then added dropwise over 3 min into the P2S5 solution. After 6 h of stirring, the flask is allowed to cool to room temperature. The suspension is then centrifuged at 10,000 rpm for 20 min. The precipitate is redispersed in ACN before being washed on a frit with ACN, obtaining a wet white powder.This is then dried under reduced pressure at 50°C for 4 h to obtain the dried intermediate compound Li3PS4ACN. The latter is then annealed at 200°C for 2 h under a flow of argon (100 / h / g) to obtain the phase [3-Li3PS4 .

[0070] The powder is characterized by Raman spectroscopy ([Fig.7]), X-ray diffraction ([Fig.8]), scanning electron microscopy ([Fig.9]) and impedance spectroscopy. [Fig.7] shows the Raman spectrum of the phase obtained with the vibration peak at 421 cm1 characteristic of PS43 units of the Li3PS4 phase. In addition, the presence of the vibration peak at 173 cm 1 corresponds to the vibrations of PS43 units in the [3-Li3PS4] crystal structure. The diffractogram in [Fig.8] confirms the formation of the [3-Li3PS4] phase. The SEM image in [Fig.9] shows particles with a size of about 2 pm. The measured ionic conductivity is 0.104 mS / cm at 30°C.

[0071] [Tables 1] Example Phase Conductivity (mS / cm) at 30° Ç 1 Li 3 PS 4 amorphous 0.11 2 B-Li 3 PS 4 0.017 3 B-Li 3 PS 4 0.104 4 Na3PS4 0.0002

[0072] Example 4: Preparation of the Na3PS4 phase according to the invention

[0073] In a Schlenck tube, 2.52 g of Na2S are weighed and dispersed in 50 mL of acetonitrile ACN. The tube is then placed under ultrasound for 30 min at 35°C and then the resulting suspension is transferred into a dropping funnel. In a three-necked flask, 2.53 g of P2S5 are weighed and dispersed in 50 mL of butyl acetate BA. The P2S5 suspension is heated to 100°C in a reflux assembly. The Na2S suspension is then added dropwise over 6 min into the P2S5 solution. After 16 h of stirring, the flask is allowed to cool to room temperature. The suspension is then centrifuged at 10,000 rpm for 20 min. The precipitate is redispersed in ACN before being washed on a frit with ACN, resulting in a wet white powder. This is then dried under reduced pressure at 50°C for 5 h to obtain the Na3PS4 phase. The powder is then heated under argon at 290°C for 4 h to obtain the crystalline Na3PS4 phase.

[0074] The powder is characterized by X-ray diffraction, scanning electron microscopy and impedance spectroscopy. The diffractogram in [Fig. 10] shows the formation of the tetragonal phase Na3PS4. The SEM image in [Fig. 11] shows particles with sizes less than one micrometer. The measured ionic conductivity is 0.0002 mS / cm at 30°C.

Claims

Claims

1. Process for the synthesis of Li3PS4 or Na3 PS4 thiophosphate particles from a reagent A2S and a phosphorus reagent P2S5> with A chosen from Li or Na, comprising at least the following steps under an inert atmosphere: A. Contacting the reagent A2S, 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), the first and second solvents being of identical or different nature, at a temperature between 50 and 150°C and formation in suspension under reflux of an intermediate compound in the form of a solvato-complex A3PS4-solvent, the molar ratio A2S / P2S5 being between 3 and 6, preferably between 4 and 5 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, of the same or different nature as that of said first and second solvents, then filtration and washing of said intermediate compound; C. Drying 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 dried intermediate compound at a temperature between 80°C and 300°C and a duration between 1 and 10 hours.

2. Process for the synthesis of thiophosphate particles according to claim 1, wherein in step A): Al) the A2S reagent is dispersed with stirring in a first polar solvent (solvent 1) at a mass concentration of A2S reagent in the solvent of between 10 g / L and 100 g / L, preferably between 50 g / L and 70 g / l and the suspension obtained is heated between 25°C and 50°C, preferably between 30°C and 40°C; A2) then the phosphorus reagent P2S5 is dispersed with stirring in a second polar solvent (solvent 2), at a concentration mass 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 suspension obtained being heated between 50°C and 150°C, preferably between 90°C and 110°C; A3) the suspension of reagent A2S is gradually added to the suspension of phosphorus reagent, preferably P2S5, activated in temperature for a period of between 1 min and 6 min, preferably between 2 and 4 min, and the resulting suspension is kept stirring at reflux at a temperature of between 50 and 150°C for a period of between 1 and 24 h, preferably between 2 and 8 h, under an inert atmosphere.

3. A method for synthesizing thiophosphate particles according to claim 1, wherein in step A): Al) a first portion of the A2S reagent and the phosphorus reagent P2S5 are dispersed with stirring in a polar solvent (solvent 1) at a mass concentration of A2S 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 reagent A2S is dispersed with stirring in a polar solvent (solvent 2) at a mass concentration of reagent A2S in the solvent of between 10 g / L and 80 g / L, preferably between 15 g / L and 50 g / L, and the suspension obtained is heated between 50°C and 150°C, preferably between 90°C and 110°C;A3) the solution of reagents A2S and phosphorus P2S5 is gradually added to the suspension of reagent A2S for a period of between 1 min and 6 min, preferably between 2 and 4 min, and the resulting suspension is kept stirring at reflux at a temperature of between 50 and 150°C for a period of between 1 and 24 h, preferably between 2 and 8 h, under an inert atmosphere.;

4. A synthesis process according to one of claims 1 to 3, wherein said intermediate compound in solvato-complex form is recovered in the form of wet powder by centrifugation at a speed between 1000 and 10000 rpm for a period between 5 and 30 min, redispersion in a third anhydrous solvent, then washing on frit with an identical or different anhydrous solvent.

5. Synthesis process according to any one of claims 1 to 4 in which the drying of step c) is carried out under reduced pressure of between 102 and 103 mbar at a temperature of between 40°C and 80°C for a duration of between 2 h and 6 h.

6. Synthesis process according to one of claims 1 to 5, in which the drying of step C) is followed by a step D) of heat treatment carried out in a crossed-bed reactor under a flow of inert gas or under reduced pressure of between 102 and 103 mbar, at a temperature of between 180°C and 300°C and a duration of between 1 and 4 hours.

7. Synthesis process according to claim 6, wherein the inert gas is argon or nitrogen or a mixture of the two and the gas flow rate is between 1 L / g / h and 15 L / g / h, preferably between 8 and 12 L / h / g.

8. Synthesis process according to one of the preceding claims, in which the A2S reagent is pretreated before suspension by mechanical grinding in a dry process or in solution, by dissolution-precipitation in a solvent or by a dehydration heat treatment.

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

10. Synthesis process according to one of the preceding claims in which A = Li and a lithium thiophosphate phase Li3PS 4 or [3-Li3PS4.

11. Synthesis process according to one of claims 1 to 9 in which A=Na and a sodium thiophosphate phase Na3PS4 is obtained.

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