SYNTHESIS METHOD

Abstract

Process for synthesizing a material, the process including the steps consisting in: a) providing a plurality of powders including: at least one powder including lithium, at least one powder including, for more than 95.0% of its mass, a transition metal chosen from titanium, cobalt, manganese, nickel, niobium, tin, iron and mixtures thereof, and at least one powder including, for more than 95.0% of its mass, a chalcogen element chosen from sulfur, selenium, tellurium and mixtures thereof, b) preparing a particulate mixture by mixing all the powders of the plurality or by mixing one of the powders of the plurality with a milled material obtained by milling a particulate assembly formed by mixing at least two of the other powders of the plurality, and milling the particulate mixture to form the material.

Claims

1. Process for synthesizing a material, the process including the steps consisting in: a) providing a plurality of powders including: at least one powder including lithium, referred to as lithiated powder, at least one powder including, for more than 95.0% of its mass, a transition metal chosen from titanium, cobalt, manganese, nickel, niobium, tin, iron and mixtures thereof, referred to as TM powder, and at least one powder including, for more than 95.0% of its mass, a chalcogen element chosen from sulfur, selenium, tellurium and mixtures thereof, referred to as chalcogen powder, b) preparing a particulate mixture by mixing all the powders of the plurality or by mixing one of the powders of the plurality with a milled material obtained by milling a particulate assembly formed by mixing at least two of the other powders of the plurality, and c) milling the particulate mixture to form the material, the material obtained at the end of step c) having a crystallographic structure of NaCl type.

2. Process according to claim 1, in which the amounts of lithiated powder, of TM powder and of chalcogen powder are determined so that, at the end of the milling step c), the material has the formula (I)
Li.sub.xM.sub.yA.sub.z, with M being a transition metal chosen from titanium, manganese, cobalt, nickel, niobium, tin, iron and mixtures thereof, A being a chalcogen element chosen from sulfur, tellurium, selenium and mixtures thereof, the stoichiometric coefficients x, y and z being such that 1.0<x4.0; 0<y2.0; and 1.0z4.0.

3. Process according to claim 1, in which the lithiated powder includes lithium and, for less than 90% of its mass, chalcogen element.

4. Process according to claim 1, in which the transition metal is titanium or manganese or cobalt or nickel or niobium or tin or iron.

5. Process according to claim 1, in which the plurality of powders includes first and second TM powders that are different from each other.

6. Process according to claim 2, in which, the transition metal of the first TM powder is titanium and the transition metal of the second TM powder is chosen from cobalt, manganese, nickel, niobium, tin, iron and mixtures thereof.

7. Process according to claim 6, in which the amounts of first and second TM powders are chosen such that the material obtained at the end of the milling step c) has the formula Li.sub.x(Ti.sub.bM.sub.1-b).sub.yA.sub.z, M being chosen from cobalt, manganese, nickel, niobium, tin, iron and mixtures thereof, the coefficient b being such that 0<b<1.

8. Process according to claim 1, in which the chalcogen element is sulfur or selenium or tellurium.

9. Process according to claim 2, in which the plurality of powders includes first and second chalcogen powders that are different from each other.

10. Process according to claim 9, in which the chalcogen element of the first chalcogen powder is sulfur and the chalcogen element of the second chalcogen powder is chosen from selenium, tellurium and mixtures thereof.

11. Process according to claim 10, in which the amounts of first and second chalcogen powders are chosen such that the material obtained at the end of the milling step c) has the formula Li.sub.xM.sub.y(A.sub.cS.sub.1-c).sub.z, A being chosen from tellurium, selenium and mixtures thereof, the coefficient c being such that 0<c<1.

12. Process according to claim 2, in which 1.9<x<3.1, and/or 0.9<y<1.1, and/or 2.0<z<3.5.

13. Process according to claim 1, in which the TM powder includes, for more than 99.9% of its mass, lithium sulfide particles, the chalcogen powder includes, for more than 99.9% of its mass, sulfur particles, and the TM powder includes, for more than 99.9% of its mass, titanium particles, and the amounts of said powders are determined such that the material obtained at the end of step c) has the formula Li.sub.2TiS.sub.3.

14. Process according to claim 1, in which, in step c), the milling of the particulate mixture is performed in a wet medium in a solvent.

15. Process according to claim 14, in which, in step c), the solvent used is chosen from hexane, cyclohexane, a mixture of heptane, acetone and ethanol and mixtures thereof.

Description

[0083] Other advantages of the invention will emerge on reading the examples that follow and by means of the attached drawing, in which:

[0084] FIG. 1 contains diffractograms obtained by X-ray diffraction of materials of formula Li.sub.2TiS.sub.3 obtained via the process according to the invention and according to the prior art, in which the diffraction intensity, in arbitrary units, is expressed as a function of the diffraction angle 2, and

[0085] FIG. 2 is a graph representing the change in the potential, in V vs Li+/Li, as a function of the capacity, in mAh/g, during the first charging/discharging cycle, of a battery including the material of formula Li.sub.2TiS.sub.3 obtained via the process of the prior art and via the process of the invention.

EXAMPLES

[0086] The nonlimiting examples that follow are given for the purpose of illustrating the invention.

[0087] The following starting materials are used to perform the following examples: [0088] powder of lithium sulfide Li.sub.2S particles, sold under the reference 213241-10G by the company Sigma Aldrich, [0089] powder of titanium sulfide TiS.sub.2 particles, sold under the reference 333492-10G by the company Sigma Aldrich, [0090] powder of titanium Ti particles, including by mass at least 99.98% of titanium, the particles having a size of less than 44 m, sold by the company Sigma Aldrich, and [0091] powder of sulfur S flakes, including by mass at least 99.99% of sulfur, sold by the company Sigma Aldrich.

[0092] Moreover, the X-ray diffraction analysis were performed using a Brker brand D8 Advance diffractometer.

Comparative Example 1

[0093] 0.44 g of lithium sulfide powder and 1.06 g of titanium sulfide powder are placed in a 50 ml zirconia jar containing 285 zirconia beads with a diameter equal to 5 mm. No solvent is added. The jar is then closed by means of a lid and mounted on a Retsch brand planetary ball mill of reference PM 100. The bowl is filled and emptied in a glovebox filled with argon. Milling is then performed for a time of 20 hours, the spin speed of the mill being set at 510 rpm.

[0094] A powder of Li.sub.2TiS.sub.3 particles is thus obtained.

[0095] A composition including, as mass percentages, 10% of Super P C65 carbon sold by the company Timcal, 10% of polyvinylidene difluoride (PVDF) as binder, and 80% of the Li.sub.2TiS.sub.3 particle powder is then prepared in a glovebox under an argon atmosphere. 0.400 ml of N-methyl-2-pyrrolidone (NMP) is added to the composition. The composition is then mixed for 5 minutes at 25 C. An ink is thus obtained. A thickness of 100 m of the ink is coated using a doctor blade onto an aluminum foil. The ink is dried under an argon atmosphere for 24 hours at 70 C. An electrode is then cut out of the ink-covered aluminum foil which has dried. The electrode is in the form of a pellet 14 mm in diameter. It is pressed under a pressure of 100 kN and finally dried under vacuum at 60 C. for 48 hours.

[0096] A battery in the form of a button cell in CR2032 format is manufactured and includes the electrode forming the cathode and a lithium metal (Li) counterelectrode forming the anode, with a diameter of 16 mm. A separator in the form of a pellet 16 mm in diameter, constituted of a Viledon brand membrane of reference FS 2207-2-DA WA and a Celgard 2400 membrane, is placed between the electrode and the counterelectrode. The electrodes, counterelectrode and separator are immersed in a volume of 150 M of a liquid electrolyte LP100 constituted of a solvent formed, by mass, of one part of ethyl carbonate, one part of propylene carbonate and three parts of dimethyl carbonate, in which is dissolved a lithium hexafluorophosphate (LiPF.sub.6) salt at a concentration of 1 mol/l.

[0097] The battery is subjected to 1 cycle formed of galvanostatic charging followed by galvanostatic discharging, imposed at 25 C. between a potential of 1.5 V and 3.0 V vs Li.sup.+/Li at a regime of C/10.

[0098] The battery cycling system is of Arbin Instruments brand.

Example 2

[0099] 0.40 g of lithium sulfide powder, 0.42 g of titanium powder and 0.56 g of sulfur powder are placed in a 50 ml zirconia jar containing 285 zirconia beads with a diameter equal to 5 mm. High-purity hexane (greater than 99.9%) is poured into the jar until the zirconia beads are covered. The jar is then closed by means of a lid and mounted on a Retsch brand planetary ball mill of reference PM 100. The mill is placed in a glovebox filled with argon. Milling is then performed for a time of 32 hours, the spin speed of the mill being set at 510 rpm.

[0100] A powder of Li.sub.2TiS.sub.3 particles is thus obtained.

[0101] An electrode and a battery are manufactured according to the same procedure as that described in Example 1, replacing the powder of Example 1 with the powder of Example 2.

[0102] X-ray diffraction analyses of the Li.sub.2TiS.sub.3 powders of Examples 1 and 2 confirm that the constituent materials of these powders have a crystallographic structure of NaCl type, as is confirmed by the respective diffractograms 5 and 10 shown in FIG. 1.

[0103] Moreover, diffractograms 15 and 20 of the starting Li.sub.2S and TiS.sub.2 powders are shown in FIG. 1. After milling, no trace of Li.sub.2S or of TiS.sub.2 is detected for Comparative Example 1 and no trace of Li.sub.2S is detected for Example 2, which means that all the constituents of the particulate mixtures have reacted during the milling to form lithium titanium sulfide.

[0104] Moreover, the powders of Comparative Example 1 and of Comparative Example 2 both have a crystallographic structure of NaCl type, as is illustrated by their respective diffractograms 5 and 10.

[0105] FIG. 2 represents the change during the first cycle of charging 25.sub.1-2 and discharging 30.sub.1-2 of the potential 35 of the positive electrode including the materials of Examples 1 and 2, respectively, as a function of the specific capacity 40 of the material. Curves 25.sub.1, 30.sub.1 correspond to Comparative Example 1 and curves 25.sub.2, 30.sub.2 correspond to Example 2 according to the invention.

[0106] Needless to say, the invention is not limited to the embodiments of the product and to the implementations of the process presented in the present description.

[0107] Moreover, unless otherwise indicated, an inequality of the type A less than B, also worded as A<B, is strictly considered. This is likewise the case for an inequality of the type A greater than B, also worded as A>B. In other words, the equality between A and B is excluded.