Method for producing inorganic compounds

Abstract

The present arrangement provides compounds (I) A.sub.aM.sub.m(YO4).sub.yZ.sub.z(I) that are obtained from precursors of the constituent elements by a method having steps that can include dispersion of the precursors in a liquid support having one or more ionic liquids made up of a cation and an anion the electric charges of which balance out to give a suspension of the precursors in the liquid. The suspension is heated to a temperature of 25 to 380 C. and the ionic liquid and the inorganic oxide of formula (I) are separated from the reaction of the precursors.

Claims

1. A process for preparing an inorganic oxide of formula (I) A.sub.aM.sub.m(YO.sub.4).sub.yZ.sub.z (I) in which: A represents at least one element chosen from alkali metals, alkaline-earth metals, a dopant element and a space; M represents (T.sub.1-t,T.sub.t), T representing one or more transition metals and T representing at least one element chosen from Mg, Ca, Al and rare-earths, 0 t<1; Y represents at least one element chosen from S, Se, P, As, Si, Ge and Al; Z represents at least one element chosen from F, O and OH; a, m, y and z are stoichiometric coefficients and are real, zero or positive numbers, with the following conditions: a, m, t, y and z are such that the electrical neutrality of the inorganic oxide of formula (I) is respected, a0; m>0; y>0 z0; starting with precursors of the constituent elements of the inorganic oxide of formula (I), said process comprises the following steps: i) dispersion of said precursors in a support liquid consisting essentially of one or more ionic liquids formed from a cation and an anion whose electrical charges equilibrate, to obtain a suspension of said precursors in said liquid, said precursors having no solubility in said liquid support ii) heating of said suspension to a temperature from 25 to 380 C., iii) separation of said ionic liquid and of the inorganic oxide of formula (I) derived from the reaction between said precursors.

2. The process as claimed in claim 1, wherein the precursors of an alkali metal A are selected from the group consisting of the salts of thermolabile anions; the salts of volatile organic acids; and the salts of acids that can decompose when hot.

3. The process as claimed in claim 2, wherein said precursors are selected fro the group consisting of Li.sub.2CO.sub.3, LiHCO.sub.3, LiOH, Li.sub.2O.sub.2, LiNO.sub.3, LiCH.sub.3CO.sub.2, LiCHO.sub.2, Li.sub.2C.sub.2O.sub.4, Li.sub.3C.sub.6H.sub.5O.sub.7, Na.sub.2CO.sub.3, NaOH, Na.sub.2O.sub.2, NaNO.sub.3, NaCH.sub.3CO.sub.2, NaCHO.sub.2, Na.sub.2C.sub.2O.sub.4, Na.sub.3C.sub.6H.sub.5O.sub.7, K.sub.2CO.sub.3, KOH, K.sub.2O.sub.2, KO.sub.2 KNO.sub.3, KCH.sub.3CO.sub.2, KCHO.sub.2, K.sub.2C.sub.2O.sub.4, K.sub.3C.sub.6H.sub.5O.sub.7 and hydrates thereof.

4. The process as claimed in claim 1, wherein the precursors of a transition metal M are selected from the group consisting of the salts of volatile inorganic acids, the salts of volatile organic acids, the salts of acids that can decompose when hot, and the salts of inorganic acids.

5. The process as claimed in claim , wherein the precursors of the oxyanions YO.sub.4 are chosen from the corresponding acids thermolabile ammonium, amine, imidazole or pyridine salts.

6. The process as claimed claim 1, wherein the oxyanion YO.sub.4 precursors are selected from the group consisting of AHSO.sub.4 and A.sub.2SO.sub.4, in which A represents an alkali metal.

7. The process as claimed in claim 6, wherein the oxyanion YO.sub.4 precursors are selected from the group consisting of LiHSO.sub.4 and Li.sub.2SO.sub.4.

8. The process as claimed in claim 1, wherein the amount of precursors present in the ionic liquid during step i) is from 0.01% to 85% by mass.

9. The process as claimed in claim 1, wherein the oxides of formula (I) are selected from the group consisting of the fluorosulfates A.sub.aM.sub.mSO.sub.4F and sulfates.

10. The process as claimed in claim 1, wherein the cations of the ionic liquid are selected from the group consisting of the cations of the following formulae: ##STR00002## in which: the radicals R.sup.4-R.sup.17, R.sup.27, R.sup.24 , R.sup.28, R.sup.29 , R.sup.37, R.sup.34, R.sup.39, R.sup.43 and R.sup.46 to R.sup.57, independently of each other, represent a C.sub.1-C.sub.24 alkyl, C.sub.1-C.sub.24 arylalkyl or (C.sub.1-C.sub.24)alkylaryl radical; the radicals R.sup.18 to R.sup.22, R.sup.23, R.sup.25,R.sup.26,R.sup.30 to R.sup.33, R.sup.35, R.sup.36, R.sup.38, R.sup.40 to R.sup.42, R.sup.44, and R.sup.45 represent a hydrogen atom, a C.sub.1-C.sub.24 alkyl radical, an aryl radical, a C.sub.1-C.sub.24 oxaalkyl radical or a radical [(CH).sub.2].sub.mQ in which Q represents OH, CN, C(O)OR.sup.58, C(O)NR.sup.59R.sub.60,NR.sup.61R.sup.62 or a 1-imidazoyl, 3-imidazoyl or 4-imidazoyl radical and m is a positive integer between 0 and 12 inclusive; the radicals R.sup.8 to R.sup.16 may also denote a (C.sub.1-C.sub.20)alkylaryl radical or a group NR.sup.63R.sup.64, R.sup.58 to R.sup.64, independently of each other, represent a hydrogen atom or a C.sub.1 -C.sub.20 alkyl, aryl or C.sub.1-C.sub.20 oxaalkyl radical.

11. The process as claimed in claim 1, wherein the anions of the ionic liquids are selected from the group consisting of: Cl, Br, I, RSO.sub.3.sup.31 , ROSO.sub.3.sup., [RPO.sub.2].sup., [R(RO)PO.sub.2].sup., [(RO).sub.2PO.sub.2].sup., BF.sub.4.sup., R.sub.fBF.sub.3.sup., PF.sub.6.sup., R.sub.fPF.sub.5.sup., (R.sub.f).sub.2PF.sub.4.sup., (R.sub.f).sub.3PF.sub.3.sup., R.sub.fCO.sub.2.sup., R.sub.fSO.sub.3.sup., [(R.sub.fSO.sub.2).sub.2N].sup., [(R.sub.fSO.sub.2).sub.2CH].sup., [(R.sub.fSO.sub.2).sub.2C(CN)].sup., [R.sub.fSO.sub.2C(CN).sub.2].sup., [(R.sub.fSO.sub.2).sub.3C].sup.31 , N(CN).sub.2.sup., C(CN).sub.3.sup., [(C.sub.2O.sub.4).sub.2B].sup.in which: R and R, which may be identical or different, represent a C.sub.1-C.sub.24 alkyl, aryl or (C.sub.1-C.sub.24)alkylaryl radical, R.sub.f is a fluoro radical chosen from C.sub.nF.sub.2n+1 in which 0n8, CF.sub.3OCF.sub.2, HCF.sub.2CF.sub.2 and C.sub.6F.sub.5.

12. The process as claimed in claim 1, wherein the ionic liquid contains one or more carbon precursors chosen from simple carbohydrates and polymerized carbohydrates.

13. The process as claimed in claim 1, wherein the heating step ii) is continued d beyond 380 C.

14. The process as claimed in clan wherein the heating step is performed under an inert atmosphere, at atmospheric pressure.

15. The process as claimed in claim 1, wherein the duration of the heating step ii) ranges from 10 minutes to 200 hours.

16. The process as claimed in claim 2, wherein the precursors of an alkali metal A are selected from the group consisting of carbonates, hydrogen carbonates, hydroxides, peroxides and nitrates; acetates and formates; oxalates, malonates and citrates.

17. The process as claimed in claim 4, wherein the precursors of a transition metal M are selected from the group consisting of nitrates and carbonates, acetates and formates, oxalates, malonates and citrates, and sulfates, chlorides and bromides.

18. The process as claimed in claim 5, wherein the precursors of the oxyanions YO.sub.4 are chosen from H.sub.2SO.sub.4; thermolabile ammonium, amine, imidazole or pyridine salts.

19. The process as claimed in claim 12, wherein the ionic liquid contains one or more carbon precursors chosen from sugars and starch and cellulose.

Description

(1) The present invention is illustrated by the following embodiment examples, to which it is not, however, limited.

(2) In the examples, unless otherwise mentioned, FeSO.sub.4.H.sub.2O was prepared from FeSO.sub.4.7H.sub.2O by heating under vacuum at 200 C., or by heating FeSO.sub.4.7H.sub.2O in the ionic liquid EMI-TFSI at 250 C. for 2 hours.

(3) FIGS. 1-2 represent the X-ray diffraction diagram of the material LiFePO.sub.4 obtained, respectively, in Examples 1-2.

(4) FIGS. 3 to 4 represent the X-ray diffraction diagram for the materials Na.sub.2FePO.sub.4F of Examples 5 and 6.

(5) FIGS. 5 to 9 represent the X-ray diffraction diagram for the materials Na.sub.2MnPO.sub.4F, Na.sub.2Fe.sub.0.95Mn.sub.0.5PO.sub.4, LiFePO.sub.4F, NaFeSO.sub.4F, LiTiPO.sub.4F obtained, respectively, in Examples 7 to 11.

(6) FIGS. 10a and 10b concern a lithium cell, and FIGS. 11a and 11b concern a sodium cell containing the material of the invention according to Example 5 (figures a) and the material according to the invention of Example 6 (figures b). In each of the figures, the variation of the potential P (in V) is given as a function of the content x of alkali metal during the first two cycles. The insert represents the change in capacitance C (in mAh/g) as a function of the number of cycles N.

(7) FIG. 12 represents the image obtained by SEM for the material LiFeSO.sub.4F of Example 13.

(8) FIG. 13a represents the TEM image, more particularly the corresponding SAED diagram, for the material LiFeSO.sub.4F of Example 13, and FIG. 13b represents the EDS spectrum, which shows the presence of F. The intensity is given on the y-axis (in arbitrary units) as a function of the energy E (in keV) on the x-axis.

(9) FIG. 14 represents the X-ray diffraction diagram, and, in the form of an insert, the structure of the material LiFeSO.sub.4F of Example 13.

(10) FIG. 15 represents the diagram obtained during the characterization by TGA coupled with mass spectrometry, of the material LiFeSO.sub.4F of Example 13.

(11) FIG. 16 represents the change in the X-ray diffraction diagram during the increase in temperature for a material LiFeSO.sub.4F.

(12) FIG. 17 represents the X-ray diffraction diagram for an equimolar mixture of anhydrous FeSO.sub.4 and of LiF before heat treatment (FIG. 17a) and after heat treatment in air at 450 C. for 15 minutes (FIG. 17b).

(13) FIGS. 18 to 21 represent the X-ray diffraction diagram for Examples 15 to 18, respectively.

(14) FIGS. 22 and 23 represent the X-ray diffraction diagram and the diagram obtained during TGA characterization of the material LiCoSO.sub.4F of Example 19.

(15) FIG. 24 represents the change in X-ray diffraction diagram during the increase in temperature, for a sample of LiCoSO.sub.4F.

(16) FIGS. 25 and 26 represent, respectively, the X-ray diffraction diagram and the diagram obtained during characterization by TGA of the material LiNiSO.sub.4F of Example 20.

(17) FIG. 27 represents the change in the X-ray diffraction diagram during the increase in temperature, for a sample of LiNiSO.sub.4F.

(18) FIGS. 28 and 29 represent the X-ray diffraction diagrams, respectively, for the solid solution Fe.sub.0.5Mn.sub.0.5SO.sub.4.H.sub.2O of Example 21 and for the compound FeSO.sub.4F of Example 22.

(19) FIGS. 30 to 32 correspond to a compound of Example 16. In FIG. 30, the main curve represents the variation in potential as a function of the level of insertion x of lithium, during cell cycling at a regime of C/10, and the insert represents the change in capacitance of the cell as a function of the cycle number N. FIG. 31 represents the variation in potential as a function of the level of insertion x of lithium, during cell cycling at a regime of C/2. FIG. 32 represents the variation in capacitance as a function of the cycling regime R.

(20) In the X-ray diffraction diagrams, the intensity I (in arbitrary units) is given on the y-axis, and the wavelength 2 is given on the x-axis.

EXAMPLE 1

Synthesis of LiFePO4 in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

(21) In this example, the synthesis of LiFePO.sub.4 was performed by precipitation in a 50 ml round-bottomed flask.

(22) To 1 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (or EMI-TFSI) (supplied by the company Solvionic) containing 2 ml of 1,2-propanediol and 0.5 g of urea were added 0.524 g of 99% LiH.sub.2PO.sub.4 (Aldrich) and 1 g of FeCl.sub.2.4H.sub.2O. After stirring for 10 minutes, the mixture (suspension) was brought to a temperature of 180 C. with a temperature increase rate of 1 C./minute. The temperature was maintained at 180 C. for 10 hours, and the reaction medium was then cooled to room temperature. After recovery by filtration, the powder of LiFePO.sub.4 is washed with 5 ml of acetone, and then with twice 50 ml of distilled water, and finally with 5 ml of acetone, and is dried in an oven at 60 C. 1 g of LiFePO.sub.4 is obtained in a yield of 95%.

(23) The compound thus obtained was then analyzed by X-ray diffraction (XR) with a copper cathode. The corresponding diffractogram is shown in the attached FIG. 1. It shows that the inorganic oxide LiFePO.sub.4 is a single phase of orthorhombic structure. The morphology of the LiFePO.sub.4 thus obtained is as follows:

(24) SG: Pnma (62)

(25) a=10.33235 (5) ; b=6.00502 (6) ; c=4.69804 (3)

(26) The ionic liquid used for the synthesis of the oxide LiFePO.sub.4 was then recovered and washed with 50 ml of water, then with twice 50 ml of a hydrochloric acid solution at a concentration of 2 mol/l, and finally with 50 ml of water, and then dried on a Rotavapor.

EXAMPLE 2

Synthesis of LiFePO4 in the Ionic Liquid EMI-TFSI

(27) The synthesis of LiFePO.sub.4 was performed by precipitation in a 50 ml round-bottomed flask. 0.524 g of 99% LiH.sub.2PO.sub.4 (Aldrich) and 0.908 g of Fe(C.sub.2O.sub.4).2H.sub.2O were added to 15 ml of EMI-TFSI. After stirring for 10 minutes, the suspension was brought to a temperature of 250 C. with a temperature increase rate of 1 C/minute. The temperature of the reaction medium was maintained at 250 C. for 24 hours, and the medium was then cooled to room temperature. After recovery by filtration, the LiFePO.sub.4 powder was washed with 50 ml of acetone, then with twice 50 ml of water and finally with 50 ml of acetone and dried in an oven at 60 C. 1.53 g of LiFePO.sub.4 were obtained in a yield of 97%.

(28) The compound thus obtained was analyzed by X-ray diffraction with a copper cathode. The corresponding diffractogram is shown in the attached FIG. 2. It shows that the inorganic oxide LiFePO.sub.4 is a single phase that has the same orthorhombic structure as the sample obtained according to Example 1.

(29) The ionic liquid was recovered in the same manner as in Example 1.

EXAMPLE 3

Synthesis of LiFePO4 in EMI-TFSI in the Presence of Traces of 1-tetradecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

(30) The synthesis of LiFePO.sub.4 was performed in a bomb, 510.sup.3 mol of LiH.sub.2PO.sub.4 and 510.sup.3 mol of Fe(C.sub.2O.sub.4).2H.sub.2O were added to 10 ml of EMI-TFSI containing traces of 1-tetradecyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide (used as surfactant to modify the form of the particles). After stirring, the reaction mixture was brought to a temperature of 250 C. with a temperature increase rate of 1 C./minute. The temperature of the reaction medium was maintained at 250 C. for 24 hours, and the medium was then cooled to room temperature. After recovery, washing and drying as indicated above in Example 2, the expected product was obtained. Analysis by X-ray diffraction showed a single phase of LiFePO.sub.4.

EXAMPLE 4

Synthesis of LiFePO4 in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-triflate) containing traces of 1-tetradecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

(31) The synthesis of LiFePO.sub.4 was performed in a bomb. 510.sup.3 mol of LiH.sub.2PO.sub.4 and 510.sup.3 mol of Fe(C.sub.2O.sub.4).2H.sub.2O were added to 10 ml of EMI-triflate containing traces of 1-tetradecyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide (used as surfactant to modify the form of the particles). After stirring, the reaction mixture was brought to a temperature of 250 C. with a temperature increase rate of 1 C./min. The temperature of the reaction medium was maintained at 250 C. for 24 hours, and the medium was then cooled to room temperature. After recovery, washing and drying as indicated above in Example 2, the expected product was obtained. Analysis by X-ray diffraction showed a single phase of LiFePO.sub.4.

EXAMPLE 5

Synthesis of Na2FePO4F from FeF2 and Na3PO4

(32) 1 g of an FeF.sub.2/Na.sub.3PO.sub.4 equimolar mixture (obtained by grinding for 10 minutes) was introduced into 5 ml of 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide. The mixture was heated at 270 C. for 48 hours and then allowed to cool to room temperature. The powder recovered after filtration is washed with 20 ml of acetone to remove the traces of ionic liquid, rinsed rapidly with cold water to remove the traces of NaF formed during the synthesis, washed with 20 ml of acetone, and then dried in an oven at 60 C.

(33) FIG. 3 shows the X-ray diffractogram of the compound obtained according to the reaction scheme FeF.sub.2+Na.sub.3PO.sub.4.fwdarw.Na.sub.2FePO.sub.4F+NaF. It shows that said compound is a single orthorhombic phase whose parameters are: SG: P b c n (60); a=5.20681 (4) ; b=13.58217 (2) ; c=11.69389 (2) .

(34) The compound Na.sub.2FePO.sub.4F is obtained in the form of particles with a mean size of 20 to 50 nm.

EXAMPLE 6

Preparation of Na2FePO4F from FeF2, FeCl2 and Na3PO4

(35) The procedure of Example 5 was repeated, using 1 g of an equimolar mixture of FeF.sub.2, FeCl.sub.2 and Na.sub.3PO.sub.4 as mixture of precursors.

(36) FIG. 4 shows the X-ray diffractogram of the compound obtained according to the reaction scheme FeF.sub.2+FeCl.sub.2+Na.sub.3PO.sub.4.fwdarw.Na.sub.2FePO.sub.4F+NaCl. It shows that said compound is a single orthorhombic phase whose parameters are: SG: P b c n (60); a=5.22576 (4) ; b=13.86986 (2) ; c=11.79141 (2) .

(37) The compound Na.sub.2FePO.sub.4F is obtained in the form of particles with a mean size of 1 to 3 m.

EXAMPLE 7

Synthesis of Na2MnPO4F from MnF2 and Na3PO4

(38) The procedure of Example 1 was repeated, using 1 g of an equimolar mixture of MnF.sub.2/Na.sub.3PO.sub.4 as mixture of precursors.

(39) FIG. 5 shows the X-ray diffractogram of the compound obtained according to the reaction scheme MnF.sub.2+Na.sub.3PO.sub.4.fwdarw.Na.sub.2MnPO.sub.4F+NaCl. It shows that said compound is a single monoclinic phase whose parameters are: SG: P 121/N1 (14); a=13.69172 (4) ; b=5.30686 (2) ; c=13.70873 (4) ; =119.67074.

EXAMPLE 8

Synthesis of Na2Fe0.95Mn0.05PO4F from FeF2, FeCl2, MnF2 and Na3PO4

(40) The procedure of Example 6 was repeated, using 1 g of an equimolar mixture of 0.5FeF.sub.2, 0.45 FeCl.sub.2, 0.05MnF.sub.2 and Na.sub.3PO.sub.4 as mixture of precursors, and by modifying the washing.

(41) The powder formed and recovered by filtration is washed with acetone to remove the traces of ionic liquid, and then twice with 20 ml of methanol to remove the NaCl formed during the synthesis, and then with 20 ml of acetone and finally dried in an oven at 60 C.

(42) FIG. 6 shows the X-ray diffractogram of the compound obtained according to the reaction scheme
0.5FeF.sub.2+0.45FeCl.sub.2+0.05MnCl.sub.2+Na.sub.3PO.sub.4.fwdarw.Na.sub.2Fe.sub.0.95Mn.sub.0.05PO.sub.4F+NaCl

(43) FIG. 6 shows that said compound is a single orthorhombic phase whose parameters are: SG: P b c n (60); a=5.24863 (4) ; b=13.85132 (3) ; c=1.1.79877 (4) .

EXAMPLE 9

Synthesis of LiFePO4F from FeF3 and Li3PO4

(44) 1 g of an FeF.sub.3/Li.sub.3PO.sub.4 equimolar mixture (obtained by grinding for 30 minutes) was introduced into 5 ml of 1-butyl-3-methylimidazolium trifluoromethanesulfonate. The mixture was heated at 260 C. for 48 hours, and then allowed to cool to room temperature. The powder recovered after filtration was washed with 20 ml of acetone to remove the traces of ionic liquid, rinsed rapidly with cold water to remove the traces of LiF formed during the synthesis, washed with 20 ml of acetone and then dried in an oven at 60 C.

(45) The X-ray diffractogram shown in FIG. 7 is that of the compound obtained according to the reaction scheme FeF.sub.3+Li.sub.3PO.sub.4.fwdarw.LiFePO.sub.4F+2LiF. It shows that said compound is a single triclinic phase of space group P-1(2) whose parameters are: a=5.15616 , b=5.31041 , c=7.48189 , =67.22507, =67.33746, =81.74728, V=174.303 .sup.3.

EXAMPLE 10

Synthesis of NaFeSO4F from FeSO4.7H2O and NaF

(46) A mixture of 5 ml of EMI-TFSI and 2.808 g of FeSO.sub.4.7H.sub.2O is placed in an open Parr bomb and heated to 230 C. After 5 hours of heating, the mixture is cooled to room temperature, 0.42 g of NaF is added and the Parr bomb is then closed. After 10 minutes of magnetic stirring, the mixture is heated at 250 C. for 24 hours. After cooling to room temperature, the recovered powder is washed twice with 20 ml of acetone and then dried in an oven at 60 C. The X-ray diffraction diagram, shown in FIG. 8, shows the formation of a new crystalline phase in an monoclinic lattice, of space group P2.sub.1/c with the lattice parameters: a=6.6798(2) , b=8.7061(2) , c=7.19124(18), =113.517(2) and V=383.473(18) .sup.3.

EXAMPLE 11

Synthesis of LiTiPO4F

(47) The synthesis is performed in a Parr bomb at 260 C. The limiting factor in the synthesis of LiTiPO.sub.4F is the reaction temperature. To have a complete reaction with standard ionic liquids, temperatures above 300 C. are required. However, fluorinated materials decompose at and above 280 C. The use of an ionic liquid protected with a CH.sub.3 group in position 2 in the presence of an OH (hydroxyl) group makes it possible to reduce the reaction temperature by increasing the solubility of the precursors.

(48) 1 g of an equimolar mixture of TiF.sub.3 and Li.sub.3PO.sub.4 prepared by grinding for 30 minutes is added to 5 ml of 1,2-dimethyl(3-hydroxypropyl)imidazolium bis(trifluoromethanesulfonyl)imide. After stirring for 20 minutes, the mixture is heated at 260 C. for 48 hours and then cooled to room temperature. The powder recovered by filtration is washed with 20 ml of acetone to remove the traces of ionic liquid, rinsed with cold water to remove the traces of LiF formed during the synthesis, washed with 20 ml of acetone and then dried in an oven at 60 C.

(49) FIG. 9 shows the X-ray diffractogram of the compound LiTiPO.sub.4F obtained according to the reaction scheme TiF.sub.3+Li.sub.3PO.sub.4.fwdarw.LiTiPO.sub.4F+2LiF. It shows that said compound is a single triclinic phase of space group P-1(2) whose parameters are: a=5.24979 , b=5.31177 , c=7.43029 ; =68.07435, =68.01394, =83.37559 V=178.161 .sup.3.

(50) The compound is in the form of nanometric particles.

EXAMPLE 12

(51) The performance qualities of the compounds obtained via the process described in Examples 5 and 6 were evaluated.

(52) Each of the materials was used as cathode material, on the one hand, in a lithium electrochemical cell, and, on the other hand, in a sodium electrochemical cell. Cycling was performed at a regime of C/15, in which an electron is exchanged in 15 hours.

(53) The lithium cell comprises: an anode formed from a sheet of lithium metal; an electrolyte formed from a 1M solution of LiPF.sub.6 in a 1/1 by mass mixture of ethyl carbonate and dimethyl carbonate.

(54) The sodium cell comprises: an anode formed by sodium metal applied to a steel disk; an electrolyte formed by a 1M solution of NaClO.sub.4 in propylene carbonate.

(55) FIGS. 10a and 10b concern the lithium cells, and FIGS. 11a and 11b concern the sodium cells. The figures a concern the material of the invention according to Example 5, and the figures b concern the material according to the invention of Example 6.

(56) In each of the figures, the variation of the potential P (in V) is given as a function of the content x of alkali metal over the first two cycles (for the compound (Li,Na).sub.xFePO.sub.4F in FIG. 10, for the compound Na.sub.xFePO.sub.4F in FIG. 11). The insert represents the change in capacitance C (in mAh/g) as a function of the cycling regime R.

EXAMPLE 13

Preparation of LiFeSO4F

(57) Synthesis

(58) In a preliminary step, FeSO.sub.4.7H.sub.2O was subjected to heat treatment in EMI-TFSI at 250 C. for 10 hours, and then at 280 C. for 24 hours. The monohydrate FeSO.sub.4.H.sub.2O formed is recovered by centrifugation, washed with ethyl acetate and then dried under vacuum at 100 C.

(59) 0.85 g of FeSO.sub.4.H.sub.2O thus obtained and 0.148 g of LiF (1/1.14 mole ratio) were mixed together in a mortar, the mixture was introduced into a Parr bomb and 5 ml of ethylmethylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) were added. The mixture was stirred for 20 minutes at room temperature, the phases were allowed to settle for 2 hours, and the mixture was then heated at 300 C. for two hours, in the open bomb, without stirring.

(60) After cooling the reaction mixture to room temperature, the powder obtained was separated out by centrifugation, washed 3 times with 20 ml of dichloromethane and then dried in an oven at 60 C.

(61) The product obtained is in the form of a pale green powder. It was subjected to various analyses.

(62) SEM Analysis

(63) FIG. 12 shows the image obtained by SEM and shows that the powder is in the form of aggregates formed from micrometric particles.

(64) TEM Analysis

(65) FIG. 13a shows the TEM image, more particularly the corresponding SAED diagram, and shows that the particles are formed from numerous crystallites. FIG. 13b shows the EDS spectrum, which shows the presence of F. The intensity is given on the y-axis (in arbitrary units) as a function of the energy E keV) on the x-axis.

(66) X-Ray Diffraction

(67) FIG. 14 shows the X-ray diffraction diagram, and, in the form of an insert, the structure of the compound obtained. This structure comprises independent FeO.sub.4F.sub.2 octahedra, SO.sub.4 tetrahedra with tunnels in which are located the Li.sup.+ ions,

(68) Thermogravimetric Analysis (TGA)

(69) FIG. 15 shows the diagram obtained during characterization of the compound by TGA coupled with mass spectrometry. The top curve (which bears the values 1.14%, 0.07%, etc.) corresponds to the TGA analysis, the middle curve (which bears the values 458.5 C. and 507.4 C.) corresponds to the differential scanning calorimetry (DSC), and the bottom curve (bearing the references m48 and m64) corresponds to the mass spectrometry. These curves show that a 23.41% loss of weight takes place between 400 C. and 700 C., corresponding to a loss of SO.sub.2, which, under electron impact in the mass spectrometers, becomes partially fragmented to SO. The undulations in the TGA and DSC curve for temperatures above 350 C. indicate the start of thermal instability of the compound.

(70) The DSC and TGA analyses thus show that it is not possible to obtain LiFeSO.sub.4F via a ceramic-route process performed at temperatures above 400 C. as described in US-2005/0163699.

(71) To confirm this fact, a sample of the product obtained in the present example was heated in air for 30 minutes as in US 2005/0163699, FIG. 16 shows the change in the X-ray diffraction diagram during the temperature increase. The lines that are visible at 500 C. are attributed to the compounds existing at this temperature, with reference to the JCPDS file numbers corresponding to the identified materials, as follows: * Fe.sub.2O.sub.3 (79-1741) | Fe.sub.2O.sub.3 (25-1402) Li.sub.2SO.sub.4 (32-064)+FeF.sub.3.3H.sub.2O (32-0464) LiHSO.sub.4 (31-0721)

COMPARATIVE EXAMPLE 14

(72) An equimolar mixture of anhydrous FeSO.sub.4 and of LiF was prepared and heated in air at 450 C. for 15 minutes.

(73) FIG. 17 shows the X-ray diffraction diagram for the starting reagent mixture (FIG. 17a) and for the product obtained after the heat treatment (FIG. 17b). The peaks corresponding, respectively, to FeSO.sub.4 and to LiF are visible in FIG. 17a, whereas FIG. 17b shows peaks corresponding, respectively, to LiF, Li.sub.2SO.sub.4, Fe.sub.2O.sub.3 and Li.sub.2S.sub.2O.sub.7.

(74) This example confirms that the ceramic-route treatment of a precursor mixture of Fe and of S, and of a precursor of F does not give the compound LiFeSO.sub.4F, contrary to what is asserted in US 2005/0163699.

EXAMPLE 15

Synthesis of LiFeSO4F from FeSO4.7H2O and LiF in EMI-TFSI

(75) A mixture of 1.404 g of FeSO.sub.4.7H.sub.2O and 0.149 g of LiF prepared in a mortar was placed in a PTFE flask containing 3 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), the mixture was subjected to magnetic stiffing for 20 minutes at room temperature, the stiffing was stopped, 2 ml of ionic liquid (EMI-TFSI) were then added, and the mixture was maintained at room temperature for 30 minutes without stirring. The whole was then placed in an oven at 200 C., the oven temperature was increased by 10 C. every 20 minutes up to 275 C., maintained at this value for 12 hours and then allowed to cool slowly.

(76) The powder formed during the heat treatment was separated from the ionic liquid by centrifugation, washed three times with 10 ml of dichloromethane and then dried in an oven at 60 C.

(77) The refinement of the X-ray diffraction spectrum performed with a copper cathode (shown in FIG. 18) shows the presence of two phases LiFeSO.sub.4F and FeSO.sub.4.H.sub.2O in equivalent proportions.

(78) Phase 1: LiFeSO.sub.4F

(79) Triclinic, space group: P-1 (2) A=5.1819(5) , b=5.4853(4) , c=7.2297(4) , =106.4564(3), =107.134(6), =97.922(5) V=182.761(4) .sup.3.
Phase 2: FeSO.sub.4.H.sub.2O Triclinic, space group: P-1(2) A=5.178(7) , b=5.176(7) , c=7.599(7) ; =107.58(6), =107.58(8), =93.34(6) V=182.56(4) .sup.3.

(80) This example shows that the use of iron sulfate heptahydrate does not make it possible to obtain a triclinic monophase compound.

EXAMPLE 16

Synthesis of LiFeSO4F starting with FeSO4.H2O and LiF in EMI-TFSI

(81) A mixture of 0.85 g of FeSO.sub.4.H.sub.2O and 0.149 g of LiF (1/1.14 mole ratio) prepared in a mortar was introduced into a PTFE flask containing 3 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), the mixture was subjected to magnetic stirring for 20 minutes at room temperature, the stirring was stopped, 2 ml of ionic liquid (EMI-TFSI) were then added, and the mixture was maintained at room temperature for 30 minutes without stirring. The whole was then introduced into an oven at 200 C., and the oven temperature was increased by 10 C. every 20 minutes up to 275 C., maintained at this value for 12 hours and then allowed to cool slowly.

(82) The powder formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane and then dried in an oven at 60 C.

(83) The refinement of the X-ray diffraction spectrum produced with a copper cathode (shown in FIG. 19) shows the presence of a single LiFeSO.sub.4F phase, the lattice parameters of which are as follows: Triclinic, space group: P-1 (2) a=5.1827(7) , b=5.4946(6) , c=7.2285(7) , =106.535(7), =107.187(6), =97.876(5) V=182.95(4) .sup.3.

EXAMPLE 17

Synthesis of LiFeSO4F Starting with FeSO4.H2O and LiF

(84) A mixture of 0.85 g of FeSO.sub.4.H.sub.2O and 0.149 g of LiF (1/1.14 mole ratio) prepared in a mortar was placed in an autoclave containing 3 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), the mixture was subjected to magnetic stirring for 30 minutes at room temperature, the stirring was stopped, 2 ml of ionic liquid (EMI-TFSI) were then added and the mixture was maintained at room temperature for 30 minutes without stirring. After closing the autoclave under argon, the whole was placed in an oven at 200 C., and the temperature of the oven was increased by 10 C. every 20 minutes up to 280 C., maintained at this value for 48 hours and then allowed to cool slowly.

(85) The powder formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane and then dried in an oven at 60 C.

(86) The product obtained is in the form of a whitish powder. The color slightly different than that of the sample of Example 1 denotes a tendency towards non-stoichiometry of the phases, according to the operating conditions.

(87) The refinement of the X-ray diffraction spectrum produced with a copper cathode (shown in FIG. 20) shows the presence of a single LiFeSO.sub.4F phase, the lattice parameters of which are as follows: Triclinic, space group: P-1 (2) a=5.1782(4) , b=5.4972(4) , c=7.2252(4) , =106.537(4), =107.221(4), =97.788(3) V=182.82(4) .sup.3.

EXAMPLE 18

Synthesis of LiFeSO4F Starting with FeSO4.H2O and LiF in 1-butyl-3-methylimidazolium trifluoromethanesulfonate (triflate)

(88) A mixture of 0.85 g of FeSO.sub.4.H.sub.2O and 0.149 g of LiF (1/1.14 mole ratio) prepared in a mortar was introduced into an autoclave containing 3 ml of 1-butyl-3-methylimidazolium trifluoromethanesulfonate (triflate), the mixture was subjected to magnetic stirring for 30 minutes at room temperature, the stirring was stopped, 2 ml of ionic liquid EMI-Tf were then added and the mixture was maintained at room temperature for 30 minutes without stirring. After closing the autoclave under argon, the whole was placed in an oven at 200 C., and the temperature of the oven was increased by 10 C. every 20 minutes up to 270 C., maintained at this value for 48 hours and then allowed to cool slowly.

(89) The powder formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane and then dried in an oven at 60 C.

(90) The refinement of the X-ray diffraction spectrum produced with a cobalt cathode (shown in FIG. 21) shows the presence of an LiFeSO.sub.4F phase (representing about 50% by mass) and two anhydrous FeSO.sub.4 phases. Phase 1: LiFeSO.sub.4F, triclinic, space group: P-1(2) Phase 2: orthorhombic, space group Cmcm (63) Phase 3: orthorhombic, space group Pbnm (62)

(91) Comparison of this example with the preceding example shows that the use of a hydrophobic ionic liquid (EMI-TFSI) makes it possible to obtain a monophase LiFeSO.sub.4F compound, whereas the hydrophilic ionic liquid used in the present example dehydrates the FeSO.sub.4.H.sub.2O before the reaction. The result is a partial reaction, and as such the final product is a mixture.

EXAMPLE 19

Synthesis of LiCoSO4F Starting with CoSO4.H2O and LiF in EMI-TFSI

(92) The precursor CoSO.sub.4.H.sub.2O used was prepared from CoSO.sub.4.7H.sub.2O by heating under vacuum at 160 C. for 2 hours.

(93) A mixture of 0.86 g of CoSO.sub.4.H.sub.2O and 0.149 g of LiF (1/1.13 mole ratio) prepared in a mortar was placed in a PTFE flask containing 5 and of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), the mixture was subjected to magnetic stirring for 20 minutes at room temperature, and the stirring was stopped. The flask was then closed under argon, and the reaction mixture was maintained at room temperature for 30 minutes without stirring. The whole was then introduced into an oven at 250 C., the temperature of the oven was increased by 5 C. every 10 minutes up to 275 C., maintained at this value for 36 hours and then allowed to cool slowly.

(94) The powder formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of ethyl acetate, and then dried in an oven at 60 C.

(95) The refinement of the X-ray diffraction spectrum produced with a cobalt cathode (shown in FIG. 22) shows the presence of a single phase of triclinic lattice (P-1) LiCoSO.sub.4F, whose lattice parameters are as follows: a=5.1719(6) , b=5.4192(6) , c=7.1818(7) , =106.811(7), =107.771(7), =97.975 (5) V=177.71(3) .sup.3.

(96) The curve obtained by thermogravimetric analysis is shown in FIG. 23. It shows a loss of weight at and above 400 C., which is proof that the compound LiCoSO.sub.4F is decomposed. It therefore cannot be obtained via a solid-phase process using higher temperatures.

(97) To confirm this fact, a sample of the product obtained in the present example was heated in air for 30 minutes as in US 2005/0163699. FIG. 24 shows the change in the X-ray diffraction diagram during the temperature increase. The arrows denote the zones in which the peaks corresponding to decomposition products are present. It thus appears that the compound begins to decompose at 375 C. The abbreviation RT given to the right of the bottom curve means room temperature.

EXAMPLE 20

Synthesis of LiNiSO4F Starting with NiSO4.H2O and LiF in EMI-TFSI

(98) The monohydrate NiSO.sub.4.H.sub.2O used as precursor was prepared from NiSO.sub.4.7H.sub.2O by heating under vacuum at 240 C. for 2 hours.

(99) A mixture of 0.86 g of NiSO.sub.4.H.sub.2O and 0.149 g of LiF (1/1.13 mole ratio) prepared in a mortar was placed in a PTFE flask containing 5 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), the mixture was subjected to magnetic stirring for 20 minutes at room temperature, and the stirring was stopped. The flask was then closed under argon and the reaction mixture was maintained at room temperature for 30 minutes without stirring. The whole was then placed in an oven at 250 C., and the temperature of the oven was increased up to 285 C. over 2 hours, maintained at this value for 36 hours, and then allowed to cool slowly.

(100) The powder formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of ethyl acetate and then dried in an over at 60 C.

(101) The X-ray diffraction diagram produced with a cobalt cathode (shown in FIG. 25) shows that the compound obtained contains more than 90.95% of a phase similar to that of LiFeSO.sub.4F or LiCoSO.sub.4F. The lattice parameters of this phase are as follows: Triclinic, space group: P-1 (2) a=5.173(1) , b=5.4209(5) , c=7.183(1) , =106.828(9), =107.776(8), =97.923 (8) V=177.85(5) .sup.3.

(102) The curve obtained by thermogravimetric analysis is shown in FIG. 26. It shows a weight loss at and above 380 C., which is proof that the compound LiNiSO.sub.4F has decomposed. It therefore cannot be obtained via a solid-phase process using higher temperatures.

(103) To confirm this fact, a sample of the product obtained in the present example was heated in air for 30 minutes as in US 2005/0163699, FIG. 27 shows the change in the X-ray diffraction diagram during the temperature increase. The arrows denote the areas in which the peaks corresponding to decomposition products are present. It thus appears that the compound begins to decompose at 375 C. The abbreviation RT given to the right of the bottom curve means room temperature.

EXAMPLE 21

Solid Solution of LiFe1yMnySO4F

(104) A compound LiFe.sub.1yMn.sub.ySO.sub.4F was prepared from LiF and from a solid solution Fe.sub.1yMn.sub.ySO.sub.4.H.sub.2O as precursor.

(105) Preparation of the Precursor

(106) 1-y mol of FeSO.sub.4.7H.sub.2O and y mol of MnSO.sub.4.H.sub.2O were dissolved in 2 ml of water degassed beforehand with argon to avoid oxidation of the Fe(II), followed by addition of 20 ml of ethanol. The powder formed by precipitation during the addition of the ethanol was recovered by centrifugation, washed twice with 20 ml of ethanol and then heated at 200 C. under vacuum for 1 hour.

(107) Several samples were prepared, by varying the value of y.

(108) The samples were analyzed by X-ray diffraction. The diffractogram of the sample y=0.5 obtained is shown in FIG. 28. It shows that it is a solid solution Fe.sub.0.5Mn.sub.0.5SO.sub.4.H.sub.2O whose lattice parameters are as follows: Triclinic; space group: P-1 (2) a=5.2069 , b=5.2056 , c=7.6725 , =107.7196, =107.4498, =93.08 V=1186.56 .sup.3.
Preparation of the Solid Solution LiFe.sub.1yMn.sub.ySO.sub.4F

(109) The synthesis was performed via the ionothermal route in an autoclave at 270 C., for various samples of precursors.

(110) A mixture of 0.85 g of Fe.sub.0.5Mn.sub.0.5SO.sub.4.H.sub.2O and 0.149 g of LiF (1/1.14 mole ratio) prepared in a mortar was placed in an autoclave containing 3 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), the mixture was subjected to magnetic stirring for 20 minutes at room temperature, the stirring was stopped, 2 ml of ionic liquid (EMI-TFSI) were then added and the mixture was maintained at room temperature for 30 minutes without stirring. After closing the autoclave under argon, the whole was placed in an oven at 200 C., and the temperature of the oven was increased by 10 C. every 20 minutes up to 270 C., maintained at this value for 48 hours and then allowed to cool slowly.

(111) The powder formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane and then dried in an oven at 60 C.

(112) The X-ray diffraction shows the formation of the solid solution LiFe.sub.1yMn.sub.ySO.sub.4F at low values of y (especially for y<0.1) and the formation of mixed phases for higher values of y (especially for y>0.25).

EXAMPLE 22

Preparation of FeSO4F

(113) The compound is prepared by chemical delithiation with NO.sub.2OF.sub.4 in acetonitrile at room temperature. The X-ray diffraction spectrum shown in FIG. 29 shows that the compound crystallizes in a lattice whose parameters are: triclinic, space group: P-1 (2) A=5.0682 , b=5.0649 , c=7.255 69.36, =68.80, =88.16 V=161.52.sup.3.

EXAMPLE 23

Electrochemical Tests

(114) Samples of compound LiFeSO.sub.4F, prepared according to Example 16, were tested as positive electrode material in a Swagelok cell in which the electrode is a lithium foil, the two electrodes being separated by a polypropylene separator soaked with a 1M solution of LiPF.sub.6 in a 1/1 ethylene carbonate/dimethyl carbonate EC-DMC mixture. To produce a positive electrode, 80 mg of LiFeSO.sub.4F (in the form of particles with a mean diameter of 1 m) and 20 mg of carbon were mixed together by mechanical grinding in a SPEX 1800 mill for 15 minutes. An amount of mixture corresponding to 8 mg of LiFeSO.sub.4F per cm.sup.2 was applied to an aluminum current collector.

(115) In FIG. 30, the main curve shows the variation in potential as a function of the degree of insertion of lithium, during the cell cycling at a regime of C/10, and the insert shows the change in capacitance of a cell during the succession of cycles at a regime of C/10, N being the number of cycles.

(116) FIG. 31 shows the variation in potential as a function of the degree of insertion of lithium, during cell cycling at a regime of C/2.

(117) FIG. 32 shows the variation in capacitance of a cell as a function of the cycling regime R.

(118) It is thus seen that the capacitance remains at 90% at a regime of 0.5 C, and at 67% at a regime of C/10.