# Patent

## Title
Fluorosulphates useful as electrode materials

## Abstract

A material is made up of particles of an optionally-doped fluorosulphate. The fluorosulphate has a distorted Tavorite type structure of formula (A1−aA′a)x(Z1−bZ′b)z(SO4)sFf (I) where A=Li or Na, A′ 0 a hole or at least one doping element, Z=at least one element selected from Fe, Co and Ni, Z′=a hole or at least one doping element, the indices a, b, x, z, s, and f are selected to assure the electroneutrality of the compound and a≧0, b≧0, x≧0, z>0, s>0, f>0, the respective quantities a and b of dopant A and Z′ being such that the Tavorite type structure is preserved. The material is obtained from the precursors thereof by an ionothermal route or ceramic route in a closed reactor. The material is of particular use as an active electrode material.

## Background
RELATED APPLICATIONS
This application is a National Phase application of PCT/FR2009/052040, filed on Oct. 23, 2009, which in turn claims the benefit of priority from French Patent Application Nos. 08 05875, filed on Oct. 23, 2008; 09 53529, filed on May 28, 2009; and 09 55233, filed on Jul. 27, 2009, the entirety of which are incorporated herein by reference.
The present invention relates to a fluorinated material that can be used as an electrode active material, and also to a process for the production thereof.
PRIOR ART
Lithium batteries are known which use an insertion compound as a basis for the operation of the positive electrode, such as LixCoO2, 0.4≦x≦1 which is used pure or in solid solution with nickel and manganese and aluminum. The main obstacles to the generalization of this type of electrochemistry are the rarity of cobalt and the excessively positive potential of the transition oxides, with, as consequences, safety problems for the battery.
LixTMmZyP1−sO4 compounds (“oxyanions”) are also known in which TM is chosen from Fe, M and Co, and Z represents one or more elements that have a valence between 1 and 5 and that may be substituted into the sites of the transition metals or of the lithium. These compounds exchange only the lithium and have only a very low electronic and ionic conductivity. These handicaps may be overcome by the use of very fine particles (such as nanoparticles and by the deposition of a carbon coating by pyrolysis of organic compounds. The drawbacks associated with the use of nanoparticles are a low tap density which results in a loss of specific energy, and this problem is further aggravated by the deposition of carbon. Furthermore, the deposition of carbon takes place at high temperature, under reducing conditions. In practice, it is difficult to use transition elements other than FeII and MnII, the elements CoII and NiII being readily reduced to the metallic state. The same applies for FeIII, MnIII, CrIII, VIII and VIV which are advantageous dopants for increasing the ionic or electronic conductivity.
Other compounds have been proposed, especially compounds corresponding to the general formula AaMb(SO4)cZd in which A represents at least one alkali metal. Z represents at least one element chosen from F and OH, and M represents at least one divalent or trivalent metal cation. L. Sebastian et al., [J. Mater. Chem. 2002, 374-377] describe the preparation of LiMgSO4F via a ceramic route, and also the crystallographic structure of said compound which is isotypic of the structure of tavorite LiFeOHPO4. The authors mention the high ionic conduction of this compound, and suggest that the compounds LiMSO4F in which M is Fe, Co or Ni, which would be isostructural, appear to be significant for the redox insertion/extraction of lithium involving MII/MIII oxidation states. The authors also specify that the preparation of the compounds of Fe, Ni or Co via a ceramic route is in progress, but no subsequent publication regarding these compounds has been made.
Moreover, US-2005/0163699 describes the preparation, via a ceramic route, of the aforementioned compounds AaMb(SO4)cZd. The technique is illustrated by concrete examples regarding compounds in which M is Ni, Fe, Co, Mn, (MnMg), (FeZn), or (FeCo). These compounds are prepared, via a ceramic route, from LiF, precursor of Li, and from the sulfate of the M element or elements. Among these compounds, the most advantageous are the compounds that contain Fe, since besides their relatively low cost, they are capable, on the basis of structural and chemical considerations (especially the ionocovalence of the bonds), of exhibiting advantageous electrochemical properties over a range of potential that is desirable for guaranteeing a reliable use for large-volume applications. For reasons of inductive effect, the sulfates should have higher potentials from the phosphates, regardless of their structure. Examples for preparing compounds containing various metallic elements are described, but no electrochemical property is reported. Thus, example 2 describes the preparation of an LiFeSO4F compound via a ceramic method at 600° C. which wives a non-homogenous compound, then 500° C. where the compound is red/black, or else at 400° C. in air where the compound is red. This method is capable of enabling the reduction of the SO42− group by Fe2+ in the absence of oxygen according to: SO42−+Fe2+SO2+2O2−2Fe3+. The red color observed in the compounds obtained at the various temperatures is due to the O2+/Fe3+ association in a crystal lattice such as the oxide Fe2O3. It is furthermore known that the compounds of FeII oxidize in air from 200° C. giving FeIII, and the preparation from example 2 at 400° C. in air confirms it. The compounds containing iron that are prepared via a ceramic route starting from LiF and iron sulfate according to US-2005/0163699 do not therefore consist of LiFeSO4F. Similarly, it appears that the compounds in which M is Co, Ni are not stable at the temperatures used during the recommended preparation via a ceramic route. It is not therefore plausible that the compounds described in US-2005/0163699 have actually been obtained.
INVENTION
The objective of the present invention is to provide a novel electrode material having an improved electrochemical activity close to the theoretical capacity (that is to say a material capable of inserting one alkali metal ion per fluorinated oxyanion unit), and also a process that makes it possible to produce said material in a reliable, rapid and economical manner.
The material of the present invention consists of particles of a fluorosulfate which has a distorted tavorite-type structure and which corresponds to the following formula (I):

(A1−aA′a)x(Z1−bZ′b)z(SO4)sFf  (I)

in which:

    
    
        A represents Li or Na;
        A′ represents a vacancy or at least one dopant element;
        Z represents at least one element chosen from Fe, Co and Ni;
        Z′ represents a vacancy or at least one dopant element;
        the indices a, b, x, z, s, and f are chosen so as to ensure the electroneutrality of the compound, and a≧0, b≧0, x≧0, z>0, s>0, f>0;
        the respective amounts a and b of dopant A and Z′ are such that the tavorite-type structure is preserved.
    
    


The tavorite structure comprises ZO4F2 octahedra centered about Z connected by apical fluorines forming chains along the c axis. The octahedra all have F atoms in the trans position, but they are divided into two different types. The chains are connected together via isolated. SO4 tetrahedra, thus creating a three-dimensional structure and defining tunnels along the [100], [010] and [101] axis, the A1−aA′a element of a compound (I) lodging in said tunnels (3D diffusion).
When A is Li, the distorted tavorite-type structure of compound (I) has a triclinic lattice of space group P−1. When A is Na, the distorted tavorite-type structure of compound (I) has a monoclinic lattice (P21/C).



FIGS. 1 and 2 are schematic representations respectively of the distorted tavorite-type structure having a triclinic lattice and having a monoclinic lattice.
FIG. 3 is a comparative view of the triclinic lattice on the left and the monoclinic lattice on the right.
FIG. 4 represents the image obtained by SEM for the LiFeSO4F material from example 1.
FIG. 5a represents the TEM image, more particularly the corresponding SAED diagram, for the LiFeSO4F material from example 1 and FIG. 5b 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.
FIG. 6 represents the X-ray diffraction diagram and, in the form of an insert, the structure of the LiFeSO4F material from example 1.
FIG. 7 represents the diagram obtained during the characterization by TGA coupled with a mass spectrometry of the LiFeSO4F material from example 1.
FIG. 8 represents the change in the X-ray diffraction diagram during the increase in the temperature, for a sample of LiFeSO4F.
FIG. 9 represents the X-ray diffraction diagram for the FeSO4+LiF mixture FIG. 9a) and for the material obtained after the heat treatment (FIG. 9b).
FIGS. 10, 11, 12 and 13 represent the X-ray diffraction diagram of the LiFeSO4F material obtained respectively in examples 2, 3, 4 and 5.
FIGS. 14 and 15 represent the X-ray diffraction diagram and the diagram obtained during the characterization by TGA of the LiCoSO4F material from example 6.
FIG. 16 represents the change in the X-ray diffraction diagram during the increase in the temperature, for a sample of LiCoSO4F.
FIGS. 17 and 18 respectively represent the X-ray diffraction diagram and the diagram obtained during the characterization by TGA of the LiNiSO4F material from example 7.
FIG. 19 represents the change in the X-ray diffraction diagram during the increase in the temperature, for a sample of LiNiSO4F.
FIGS. 20 and 21 represent the X-ray diffraction diagram respectively of the material Fe0.5Mn0.5SO4.H2O from example 8 and of the material NaFeSO4F from example 9.
FIGS. 22 and 23 represent the X-ray diffraction diagram of the LiFeSO4F material obtained respectively in examples 10 and 11.
FIG. 24 represents, on the left, the X-ray diffraction diagram of the LiFeSO4F material obtained, in example 12 and, on the right, an SEM micrograph of said material.
FIGS. 25, 26 and 27 represent the X-ray diffraction diagram respectively of the NaFeSO4F material from example 13, of the NaCoSO4F material from example 14 and of the FeSO4F material from example 15.
FIGS. 28a, b and c relate to several samples of LiFeSO4F prepared according to example 3. FIG. 28a represents the variation in the potential (in V) as a function of the insertion rate x of lithium and (in the form of an insert) the variation in the capacity C (in mAh/g) as a function of the number of cycles N at a C/10 regime. FIG. 28b represents the variation in the potential (in V) as a function of the insertion rate x of lithium at a C/2 regime. FIG. 28c represents the variation in the capacity as a function of the regime R.
FIG. 29 represents the variation in the potential P (in V) as a function of the insertion rate x of lithium (left-hand curve) and the variation of the capacity C (in mAh/g) as a function of the number of cycles N (right-hand curve) for the LiFeSO4 material from example 12.
FIG. 30 represents the variation in the potential P (in V) as a function of the insertion rate x of lithium for the NaFeSO4F material from example 13.



In all the X-ray diffraction diagrams, the intensity I (in arbitrary units) is given on the y-axis, and the wavelength 2θ is given on the x-axis.
In the TGA diagrams, % TG indicates the weight loss as a function of the temperature T (in ° C.) and optionally DSC indicates the amount of energy in (mW).
A compound according to the invention is in the form of grains, the dimension of which is less than 100 μm, or even less than 1.00 nm.
When A′ is a dopant element, A′ may be an alkali metal different from A, an alkaline-earth metal or a 3d metal, in particular Ti, V, Cr, Mn, Fe, Mn, Co or Cu. Generally, the “a” content of dopant A′ is preferably less than 0.25%, that is to say a<0.25.
When Z′ is a dopant element, Z′ may be a metal chosen from alkali metals, Mn, Mg, Co, Sc, Ti, V, Cr, Zn, Al, Ga, Zr, Nb and Ta in at least one of their degrees of oxidation. Generally, the “b” content of dopant Z′ is preferably less than 25%, that is to say b<0.25. Particularly advantageous Z′ dopants are Mn, Mg, Zn, Ti and Al.
Compounds according to the invention that are particularly preferred are those which correspond to the formulae Li(Z1−bZ′b)SO4F and Na(Z1−bZ′b)zSO4F, in particular LiFeSO4F, LiCoSO4F, LiNiSO4F, and their solid solutions, NaFeSO4F, NaCoSO4F, NaNiSO4F and their solid solutions, and also the solid solutions Li(Z1−bMnb)SO4F and Na(Z1−bZ′b)SO4F in which Z is Fe, Co or Ni, b≦0.2.
One particular category of compounds (I) comprises the compounds in which the (Z1−bZ′b) group represents more than one element. These are compounds in which Z represents more than one element chosen from Fe, Co and Ni, and also compounds in which b≠0, the two cases possibly being combined.
A compound (I) in which x=0, that is to say a compound of formula (Z1−bZ′b)z(SO4)sFf, in particular a compound ZSO4F, more particularly FeSO4F is advantageous because it makes it possible to construct primary electrochemical generators in the charged state with a lithium anode and a liquid or gel type electrolyte, or secondary generators, in particular with polymer electrolytes.
A material (I) according to the invention in which x>0 may be obtained from precursors of the elements which form it, via a ceramic route or via an ionothermal route.
The precursor of A or of A′ may be chosen from inorganic acid salts (such as carbonates and hydrogen carbonates, hydroxides, peroxides and nitrates), volatile organic acid salts (such as acetates and formates), heat-decomposable acid salts (such as oxalates, malonates and citrates), fluorides and sulfates. Among such precursors, Li2CO3, LiHCO3, LiOH, Li2O, Li2O2, LiNO3, LiCH3CO2, LiCHO2, Li2C2O4, Li3C6H5O7, Na2CO3, NaOH, Na2O2, NaNO3, NaCH3CO2, NaCHO2, Na2C2O4, Na3C6H5O7, and hydrates thereof are preferred in particular. The precursors of Li or Na that provide at least two constituents of the final product such as fluorides and sulfates are particularly preferred, especially LiF, NaF, LiHSO4 and the sulfates Li2SO4, Na2SO4 and NaHSO4 in hydrated form.
The precursor of a Z or Z′ element is preferably chosen from the sulfates of Z or of Z′ that have a tavorite-type structure and that will make it possible to obtain the tavorite-type structure of compound (I).
When the precursors of A, of A′, of Z or of Z′ do not provide any F or S elements, or provide an insufficient amount with respect to the stoichiometry of compound (I) to be prepared, it is possible to add precursors providing solely one or several F or S elements.
The precursors of the oxyanion SO42− may be chosen from the acid H2SO4, and its thermolabile ammonium, amine, imidazole or pyridine salts such as, for example, NH4HSO4, (NH4)2SO4, (C3H5)HSO4, (C5H6)2SO4 and (C3H5)2SO4, (C5H6)HSO4.
The precursors of S may also be chosen from the salts of Mg or Ca. By way of example, mention may be made of the compounds A′′(HSO4)2, and A′′SO4, A′′HPO4, and A′′2P2O7, A′′(PO3)2 in which A′′ represents an alkaline-earth metal (Mg, Ca).
The fluoride ion precursors may be chosen from ammonium fluorides (NH4F.nHF), imidazolium fluorides (C3H5N2F.nHF) or pyridinium fluorides (C5H6NF.nHF) 0≦n≦5. Of course, it is possible to use several precursors for the same element.
In one particularly preferred embodiment, the precursor of Z and, where appropriate, the precursor of Z′ are chosen from the sulfates of the Z and/or Z elements. The precursor of A and, where appropriate, the precursor of A′ are chosen from the fluorides of the A an/or A′ elements. Preferably, use is made of sulfates in hydrate form, in particular in monohydrate form. It has been observed that, surprisingly, the use of a sulfate monohydrate precursor that has a distorted tavorite-type structure makes it possible to retain the more or less distorted tavorite-type structure during the reaction with the fluoride.
The reaction is topotactic due to the structural relationship between ZSO4.H2O and the corresponding Li and Na phases, based on maintaining the general arrangement of the SO4 tetrahedra and ZO4F2 octahedra in the structural framework.
The monohydrate ZSO4.H2O may be obtained from ZSO4.7H2O either by heating under vacuum at a temperature between 150° C. and 450° C. (for example 200° C.), or by heating in an ionic liquid (for example 2 hours at 270° C. in EMI-TFSI).
The compounds (I) in which the (Z1−bZ′b) group represents more than one element are preferably prepared by using, as a precursor of Z and Z′, a solid solution of sulfate, preferably in hydrate form.
In one particular embodiment, a process that aims to prepare an Fe1−bZ′bSO4.H2O precursor comprises the following steps:

    
    
        dissolving 1-b moles of FeSO4.nH2O and b moles of Z′SO4.nH2O in water previously degassed by argon or nitrogen to avoid the oxidation of Fe(II), b≦0.25 and n≦7;
        adding an alcohol (for example ethanol or isopropanol) to give rise to the precipitation of Fe1−bZ′bSO4.nH2O;
        recovering (for example by centrifuging) the powder which is formed; and
        washing with alcohol, then heating at a temperature between 150 and 250° C. (for example at 200° C.) under vacuum for 1 hour.
    
    


The preparation of a precursor in which Z represents Fe and Co or Fe and Ni may be carried out in the same manner by choosing CoSO4.nH2O or NiSO4.nH2O for Z′SO4.nH2O, b then being less than 1.
A compound of the invention may be obtained by a synthesis process at temperatures of less than 330° C. via an ionothermal route.
The process via the ionothermal route comprises the following steps:

    i) dispersing said precursors in a support liquid comprising at least one ionic liquid consisting of a cation and of an anion, the electric charges of which are balanced, in order to obtain a suspension of said precursors in said liquid;
    ii) heating said suspension to a temperature of 25 to 330° C.;
    iii) separating said ionic liquid and the inorganic oxide of formula (I) resulting from the reaction between said precursors.


The sulfate monohydrate precursor may be prepared previously, or prepared in situ in the ionic liquid, during a preliminary step.
The expression “ionic liquid” is understood to mean a compound that contains only anions and cations, the charges of which are balanced, and which is liquid at the temperature of the reaction for formation of the compounds of the invention, either pure, or as a mixture with an additive.
The amount of precursors present within the ionic liquid during step i) is preferably from 0.01% to 85% by weight, and more preferably from 5 to 60% by weight.
The respective amounts of the various precursors depend on the stoichiometry of the compound (I) to be prepared. Their determination is within the scope of the person skilled in the art, since the reactions are stoichiometric. Preferably, an excess of fluoride, preferably of the order of 5 to 25%, is used.
According to one preferred embodiment of the invention, the cation of ionic liquid is chosen from the cations of the following formulae:




in which:

    
    
        the R4-R7, R17, R27, R24, R28, R29, R37, R34, R39, R43 and R46 to R57 radicals, independently of one another, represent a C1-C24 alkyl, C1-C24 arylalkyl or (C1-C24)alkylaryl radical;
        the R8—R16 radicals have the meaning given for R4 or they each represent a (C1-C20)alkylaryl radical or an NR63R64 group;
        the R18 to R22, R23, R25, R26, R30 to R33, R35, R36, R38, R40 to R42, R44 and R45 radicals represent a hydrogen atom, a C1-C24 alkyl, an or C1-C24 oxaalkyl radical or a —[(CH)2]nQ radical in which Q represents —OH, —CN, —C(═O)OR58, —C(═O)NR59R60, —NR61R62, —CH(OH)CH2OH, or else a 1-imidazoyl, 3-imidazoyl or 4-imidazoyl radical, and 0≦n≦12; and
        R58 to R64, independently of one another, represent a hydrogen atom, a C1-C20 alkyl, aryl or C1-C20 oxaalkyl radical.
    
    


Very particularly preferred are the imidazolium cations in which R23═H or CH3, R24═CH3, R25═R26═H, and R27═C2H5, C3H7, C4H9, C5H11, C6H13, C8H17, (CH2)3OH, (CH2)3CN, (CH2)4OH, or (CH2)4CN, and the imidazolium cations in which R23═H or CH3, R24═C4H9, R25═R26═H, R27═(CH2)2OH, (CH2)2CN, (CH2)3OH, (CH2)3CN, (CH2)4OH, (CH2)4CN, or CH2CH(OH)CH2OH.
The anion of an ionic liquid is preferably chosen from Cl, Br, I, RSO3−, ROSO3−, [RPO2]−, [R(R′O)PO2]−, [(RO)2PO2]−, BF4−, RfBF3−, PF6−, RfPF5−, (Rf)2PF4−, (Rf)3PF3−, RfCO2−, RfSO3−, [(RfSO2)2N]−, [(RfSO2)2CH]−, [(RfSO2)2C(CN)]−, [RfSO2C(CN)2]−, [(RfSO2)3C]−, N(CN)2−, C(CN)3−, [(C2O4)2B]− in which:

    
    
        R and R′, which are identical or different, each represent a C1-C24 alkyl, aryl or (C1-C24)alkylaryl radical; and
    
    


Rf is a fluoro radical chosen from CnF2n+1 in which 0≦n≦8, CF3OCF2, HCF2CF2 and C6F5.
When the cation of the ionic liquid is an imidazolium cation, it is desirable for the C2 carbon of the imidazolium cation to be protected by an alkyl group, preferably having 1 to 4 carbon atoms, due to the fact that the precursor of the A element is a fluoride. Otherwise, the acid proton borne by the C2 carbon would give rise to the decomposition of the cation of the ionic liquid.
An ionic liquid having a high hydrophobic character favors the reaction between the precursor of A (AF) and the hydrated ZSO4 precursor. It makes it possible to carry out the synthesis in an open reactor. A hydrophilic ionic liquid is less favorable, and it necessitates carrying out the synthesis in a sealed reactor under pressure.
1-Butyl-3-methylimidazolium trifluoromethanesulfonate (BMI-triflate), and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) are particularly preferred. EMI-TFSI, which is more hydrophobic than BMI-triflate, is particularly preferred.
According to one preferred embodiment of the invention, the temperature for heating the suspension during step ii) is between 100° C. and 330° C., and more preferably still between 150 and 280° C.
The heating step ii) is preferably carried out under an inert atmosphere, at atmospheric pressure. Indeed, one of the main advantages of the process in accordance with the invention is to not require a pressurized chamber due to the lack of volatility of the ionic liquid(s).
The heating may be carried out by various means, in particular by heating in an oven, or by microwave heating. It may be carried out continuously, in a heated chamber in which the ionic liquid and the precursors of the compound (I) flow, with a residence time that enables the reaction to be complete.
The duration of the heating step ii) generally varies from 10 minutes to 200 hours, preferably from 3 to 48 hours.
The separation of compound (I) during step iii) may be carried out by any technique known to a person skilled in the art such as, for example, by extraction with a solvent of the ionic liquid or by centrifugation, and removal of the possible by-products via an alcohol, a nitrile, a ketone or a chloroalkane having 1 to 6 carbon atoms.
At the end of the synthesis, the compound (I) may be washed, with an organic solvent such as, for example, acetone, acetonitrile or ethyl acetate, then used without further purification.
Likewise at the end of the synthesis, the ionic liquid may be recovered, optionally diluted by dichloromethane, chloroform, dichloroethane, methyl ethyl ketone, a pentanone, esters including ethyl acetate and ethyl formate, and washed, preferably with water and/or an acid solution such as, for example, an aqueous solution of hydrochloric acid, of sulfuric acid or sulfamic acid. After washing and drying (for example using Rotavapor®) or under primary vacuum, the ionic liquid may thus be used for a new synthesis, which is very advantageous from an economical viewpoint.
The process for preparing, a material (I) via a ceramic route uses the same precursors as the process by the ionothermal route. It consists in bringing powders of precursors into contact and in subjecting the mixture to a heat treatment. It is characterized in that:

    
    
        the SO4, Z and, where appropriate, Z′ elements are provided by a single precursor in the form of a hydrated sulfate;
        the F, A and, where appropriate A′ elements are each provided by a fluoride;
        the heat treatment is carried out in a sealed reactor.
    
    


The sulfate hydrate is preferably in (Z1−bZ′b)SO4.H2O precursor monohydrate form.
The precursors are used in stoichiometric amounts, or with an excess of fluoride preferably of the order of 5 to 25%.
The mixture of powder is preferably pelleted via compression before being introduced into the reactor.
The heat treatment is carried out under temperature and pressure conditions that depend on the volume of the reactor (made of steel or made of quartz for example) and on the amount of precursors introduced into the reactor. The proportion of tavorite phase and of parasitic phases depends on the “mass of precursors treated/volume of the sealed reactor” ratio. It is noted that a higher confinement favors the production of a single tavorite phase. The determination of the conditions suitable for each particular case is within the scope of the person skilled in the art.
A material (I) according to the invention in which x=0, for example the compound FeSO4F, may be obtained by electrochemical oxidation or by chemical oxidation of LiFeSO4F in the presence of NO2BF4 or (CF3CO2)2ICC6H5. It has a triclinic structure, space group P−1 with the following lattice parameters a=5.0683(7) (Å), b=5.0649(19) (Å), c=7.2552(19) (Å), α=69.36(3), β=68.80(3), γ=88.16(2), and V=161.52(8) (Å3).
A compound (I) may be used in various applications as a function of the elements that form it. By way of example, the compounds (I) of the invention may be used as active material for the manufacture of electrodes in batteries and electrochromic systems, as ceramics, as magnetic materials for storing information, as pigment, or in a photovoltaic cell as a light-absorbing material with a better result than that obtained with the aid of conventionally used TiO2.
When a compound according to the invention is used as an electrode material, the electrode may be prepared by depositing onto a current collector a composite material obtained by mixing, via manual milling or via mechanical milling (for example via milling for around 10 minutes using an SPEX 1800 mill), a mixture comprising a compound of the invention and carbon. The percentage by weight of compound (I) relative to the “compound (I)+carbon” composite material may be from 50 to 99%, more particularly from 80 to 95%.
The composite material used for producing an electrode may also contain an additional compound, the compound (I)/additional compound weight ratio being greater than 5%. The additional compound may be, for example, a material with an olivine structure such as an LiMPO4 material in which M represents at least one of the elements Fe, Co and Ni, or an oxide LiCoO2 or LiNiO2.
The amount of material deposited on the current collector is preferably such that the amount of compound according to the invention is between 0.1 and 200, preferably from 1 to 50 mg per cm2. The current collector may consist of a grid or sheet of aluminum, of titanium, of graphite paper or of stainless steel.
An electrode according to the invention may be used in an electrochemical cell comprising a positive electrode and a negative electrode separated by an electrolyte. The electrode according to the invention forms the positive electrode.
The negative electrode may consist of metallic lithium or of one of its alloys, or of a transition metal oxide that forms, via reduction, a nanoscale dispersion in lithium oxide, or of a double nitride of lithium and of a transition metal. The negative electrode may also consist of a material capable of reversibly inserting Li+ ions at potentials of less than 1.6 V. As examples of such materials, mention may be made of low-potential oxides that have the general formula Li1+y+x/3Ti2−x/3O4 (0≦x≦1, 0≦y≦1), Li4+x′Ti5O120≦x′≦3, carbon and carbon-based products resulting from the pyrolysis of organic materials, and also dicarboxylates.
The electrolyte advantageously comprises at least one lithium or sodium salt in solution in a polar aprotic liquid solvent, in a solvating polymer optionally plasticized by a liquid solvent or an ionic liquid, or in a gel consisting of a liquid solvent gelled by addition of a solvating or non-solvating polymer.
The present invention is illustrated by the following exemplary embodiments, to which it is not however limited.
Unless otherwise mentioned, FeSO4.H2O was prepared from FeSO4.7H2O by heating under vacuum at 200° C., or by heating FeSO4.7H2O in the EMI-TFSI ionic liquid at 250° C. for 2 hours.
EXAMPLE 1
In a preliminary step, FeSO4.7H2O was subjected to a heat treatment in EMI-TFSI at 250° C. for 10 h, then at 280° C. for 24 h. The FeSO4.H2O monohydrate formed is recovered by centrifugation, washed with ethyl acetate, then dried under vacuum at 100° C.
In a mortar, 0.85 g of FeSO4.H2O thus obtained and 0.148 g of LiF (1/1.14 molar ratio) were mixed, and the mixture was introduced into a Parr® bomb calorimeter and 5 ml of ethylmethylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) were added. The mixture was stirred for 20 min at room temperature, left to settle for 2 h, then heated at 300° C. for two hours, in the open bomb calorimeter, without stirring.
After cooling the reaction mixture to room temperature, the powder obtained was separated by centrifugation, washed 3 times with 20 ml of dichloromethane, then dried in an oven at 60° C.
The product obtained is in the form of a pale green-colored powder. It was subjected to various analyses.
SEM Analyses
FIG. 4 represents the image obtained by SEM and shows that the powder is in the form of agglomerates consisting of micron-sized particles.
TEM Analysis
FIG. 5a represents the TEM image, more particularly the corresponding SAED diagram, and it shows that the particles consist of numerous crystallites. FIG. 5b 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.
X-Ray Diffraction
FIG. 6 represents the X-ray diffraction diagram and, in the form of an insert, the structure of the compound obtained. This structure comprises independent FeO4F2 octahedra (denoted by “2”), SO4 tetrahedra (denoted by “1”) with tunnels in which the Li+ ions (denoted by “3”) are found.
Thermogravimetric Analysis (TGA)
FIG. 7 represents the diagram obtained during the characterization of the compound by TGA coupled with mass spectrometry. The upper curve (which is labeled with −1.14%, 0.07%, etc.) corresponds to the TGA analysis, the middle curve (which is labeled with 458.5° C. and 507.4° C.) corresponds to the differential scanning calorimetry (DSC) and the lower curve (labeled with m48 and m64) corresponds to the mass spectrometry. These curves show that a weight loss of 23.41% occurs between 400° C. and 700° C., corresponding to a departure of SO2 which, under the electron impact in the mass spectrometers, partially fragments to SO. The irregularities in the TGA and DSC curve for is temperatures above 350° C. indicate the beginning of thermal instability of the compound.
The DSC and TGA analyses thus show that it is not possible to obtain LiFeSO4F by a process via a ceramic route carried out at temperatures above 400° C. as described in US-2005/0163699.
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. 8 represents the change in the X-ray diffraction diagram during the increase in the temperature. RT denotes room temperature. The lines visible at 500° C. are attributed to the compounds that exist at this temperature, with reference to the numbers of the JCPDS files corresponding to the materials identified as follows:
* Fe2O3 (79-1741)
| Fe2O3 (25-1402)
 Li2SO4 (32-064)+FeF3.3H2O (32-0464)
● LiHSO4 (31-0721)
COMPARATIVE EXAMPLE 1
An equimolar mixture of anhydrous FeSO4 and of LiF was prepared, and it was heated in air at 450° C. for 15 minutes.
FIG. 9 represents the X-ray diffraction diagram for the mixture of starting reactants (FIG. 9a) and for the product obtained after the heat treatment at 450° C. for 15 min (FIG. 9b). The peaks that correspondent respectively to FeSO4 and to LiF are visible in FIG. 9a, whereas FIG. 9b shows peaks corresponding respectively to LiF, Li2SO4, Fe2O3 and Li2S2O7.
This example confirms that the treatment, via a ceramic route, of a mixture of precursor of Fe and of S, and of a precursor of F does not give the compound LiFeSO4F under the conditions described in US-2005/0163699.
EXAMPLE 2
Synthesis of LiFeSO4F from FeSO4.7H2O and LiF in EMI-TFSI
Introduced into a PTFE flask containing 3 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) was a mixture of 1.404 g of FeSO4.7H2O and 0.149 g of LiF prepared in a mortar, the mixture was subjected to magnetic stirring for 20 minutes at room temperature, the stirring was stopped, then 2 ml of ionic liquid (EMI-TFSI) were added, and the mixture was kept without stirring at room temperature for 30 minutes. The whole assembly was then introduced into an oven at 200° C., the temperature of the oven was increased, by 10° C. every 20 minutes up to 275° C., kept at this value for 12 hours, then left to cool slowly.
The powder that was formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane, then dried in an oven at 60° C.
The refinement of the X-ray diffraction spectrum carried out with a copper cathode (represented in FIG. 10) shows the presence of two phases, LiFeSO4F and FeSO4.H2O, in equivalent proportions.
Phase 1: LiFeSO4F
Triclinic, space group: P−1 (2)
A=5.1819(5) Å, b=5.4853(4) Å, c=7.2297(4) Å,
α=106.4564(3)°, β=107.134(6)°, γ97.922(5)°
V=182.761(4) Å3.
Phase 2: FeSO4.H2O
Triclinic, space group: P−1 (2)
A=5.178(7) Å, b=5.176(7) Å, c=7.599(7) Å;
α=107.58(6)°, β=107.58(8)°, γ=93.34(6)°
V=182.56(4) Å3.
EXAMPLE 3
Synthesis of LiFeSO4F from FeSO4.7H2O and LiF in EMI-TFSI
Introduced into a PTFE flask containing 3 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) was a mixture of 0.85 g of FeSO4.H2O and 0.149 g of LiF (1/1.14 molar ratio) prepared in a mortar, the mixture was subjected to magnetic stirring for 20 minutes at room temperature, the stirring was stopped, then 2 ml of ionic liquid (EMI-TFSI) were added, and the mixture was kept without stirring at room temperature for 30 minutes. The whole assembly was then introduced into an oven at 200° C., the temperature of the oven was increased by 10° C. every 20 minutes up to 275° C., kept at this value for 12 hours, then left to cool slowly.
The powder that was formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane, then dried in an oven at 60° C.
The refinement of the X-ray diffraction spectrum carried out with a copper cathode (represented in FIG. 11) shows the presence of a single, LiFeSO4F phase, the lattice parameters of which are as follows:
Triclinic, space group: P−1 (2)
a=5.1827(7) Å, b=5.4916(6) Å, c=7.2285(7) Å,
α=106.535(7)°, β=107.187(6)°, γ97.876(5)°
V=182.95(4) Å3.
The comparison of examples 2 and 3 shows that the use of a sulfate monohydrate is more favorable than the use of a sulfate heptahydrate, insofar as the first mentioned makes it possible to obtain a single phase, whereas the second gives a mixture.
EXAMPLE 4
Synthesis of LiFeSO4F from FeSO4.H2O and LiF
The synthesis of LiFeSO4F is carried out via an ionothermal route in an autoclave at 280° C.
Introduced into an autoclave containing 3 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) was a mixture of 0.85 g of FeSO4.H2O and 0.149 g of LiF (1/1.14 molar ratio) prepared in a mortar, the mixture was subjected to magnetic stirring for 30 minutes at room temperature, the stirring was stopped, then 2 ml of ionic liquid (EMI-TFSI) were added, and the mixture was kept without stirring at room temperature for 30 minutes. After sealing the autoclave under argon, the whole assembly was then introduced into an oven at 200° C., the temperature of the oven was increased by 10° C. every 20 minutes up to 280° C. kept at this value for 48 hours, then left to cool slowly.
The powder that was formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane, then dried in an oven at 60° C.
The product obtained is in the form of a whitish powder. The slightly different color from that of the sample from example 1 denotes an aptitude for the non-stoichiometry of the phases, according to the operating conditions.
The refinement of the X-ray diffraction spectrum carried out with a copper cathode (represented in FIG. 12) shows the presence of a single, LiFeSO4F phase, the lattice parameters of which are as follows:
Triclinic, space group: P−1 (2)
a=5.1782(4) Å, b=5.4972(4) Å, c=7.2252(4) Å,
α=106.537(4)°, β=107.221(4)°, γ=97.788(3)°
V=182.82(4) Å3.
EXAMPLE 5
Synthesis of LiFeSO4F from FeSO4.H2O and LiF in 1-butyl-3-methylimidazolium trifluoromethanesulfonate (triflate)
The synthesis of LiFeSO4F is carried out via an ionothermal route in an autoclave at 270° C.
Introduced into an autoclave containing 3 ml of 1-butyl-3-methylimidazolium trifluoromethanesulfonate (triflate) was a mixture of 0.85 g of FeSO4.H2O and 0.149 g of LiF (1/1.14 molar ratio) prepared in a mortar, the mixture was subjected to magnetic stirring for 30 minutes at room temperature, the stirring was stopped, then 2 ml of ionic liquid (EMI-Tf) were added, and the mixture was kept without stirring at room temperature for 30 minutes. After sealing the autoclave under argon, the whole assembly was then introduced into an oven at 200° C., the temperature of the oven was increased, by 10° C. every 20 minutes up to 270° C., kept at this value for 48 hours, then left to cool slowly.
The powder that was formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane, then dried in an oven at 60° C.
The refinement of the X-ray diffraction spectrum carried out with a cobalt cathode (represented in FIG. 13) shows the presence of an LiFeSO4F phase (representing around 50% by weight), and two “anhydrous FeSO4” phases.
Phase 1: LiFeSO4F, Triclinic, space group P−1 (2)
Phase 2: orthorhombic, space group Cmcm (63)
Phase 3: orthorhombic, space group Pbnm (62)
The comparison of examples 4 and 5 shows that the use of a hydrophobic ionic liquid is more favorable than the use of a hydrophilic ionic liquid, insofar as the first mentioned makes it possible to obtain a single phase, whereas the second gives a mixture.
EXAMPLE 6
Synthesis of LiCoSO4F from CoSO4.H2O and LiF in EMI-TFSI
The CoSO4.H2O precursor used was prepared from CoSO4.H2O by heating under vacuum at 160° C. for 2 hours.
Introduced into a PTFE flask containing 5 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) was a mixture of 0.86 g of CoSO4.H2O and 0.149 g of LiF (1/1.13 molar ratio) prepared in a mortar, the mixture was subjected to magnetic stirring for 20 minutes at room temperature and the stirring was stopped. The flask was then sealed under argon, and the reaction mixture was kept without stirring at room temperature for 30 minutes. The whole assembly 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., kept at this value for 36 hours, then left to cool slowly.
The powder that was formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of ethyl acetate, then dried in an oven at 60° C.
The refinement of the X-ray diffraction spectrum carried out with a cobalt cathode (represented in FIG. 14) shows the presence of a single, LiCoSO4F phase, the lattice parameters of which are as follows:
a=5.1719(6) Å, b=5.4192(6) Å, c=7.1818(7) Å,
α=106.811(7)°, β=107.771(7)°, γ=97.975 (5)°
V=177.71(3) Å3.
The curve obtained by thermogravimetric analysis is represented in FIG. 15. It shows a loss of weight starting from 400° C., prove that the compound LiCoSO4F is decomposed. It cannot therefore be obtained by a process in the solid phase using higher temperatures.
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 represents the change in the X-ray diffraction diagram during the increase in the temperature. RT denotes room temperature. The arrows denote the zones in which the peaks corresponding to decomposition products are found. It thus appears that the compound begins to decompose at 375° C. The label “RT” given on the right of the lower curve signifies “room temperature”.
EXAMPLE 7
Synthesis of LiNiSO4F from NiSO4.H2O and LiF in EMI-TFSI
The NiSO4.H2O monohydrate used as precursor was prepared from NiSO4.7H2O by heating under vacuum at 240° C. for 2 hours.
Introduced into a PTFE flask containing 5 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) was a mixture of 0.86 g of NiSO4.H2O and 0.149 g of LiF (1/1.13 molar ratio) prepared in a mortar, the mixture was subjected to magnetic stirring for 20 minutes at room temperature and the stirring was stopped. The flask was then sealed under argon, and the reaction mixture was kept without stirring at room temperature for 30 minutes. The whole assembly was then introduced into an oven at 250° C., the temperature of the oven was increased up to 285° C. over 2 hours, kept at this value for 36 hours, then left to cool slowly.
The powder that was formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of ethyl acetate, then dried in an oven at 60° C.
The X-ray diffraction diagram produced with a cobalt cathode (represented in FIG. 17) shows that the compound obtained contains more than 90.95% of a phase similar to that of LiFeSO4F or LiCoSO4F. The lattice parameters of this phase are as follows:
Triclinic, space group: P−1 (2)
a=5.173(1) Å, b=5.4209(5) Å, c=7.183(1) Å,
α=106.828(9)°, β=107.776(8)°, γ=97.923 (8)°
V=177.85(5) Å3.
The curve obtained by thermogravimetric analysis is represented in FIG. 18. It shows a loss of weight starting from 380° C., proof that the compound LiNiSO4F is decomposed. It cannot therefore be obtained by a process in the solid phase using higher temperatures.
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. 19 represents the change in the X-ray diffraction diagram during the increase in the temperature. The arrows denote the zones in which the peaks corresponding to decomposition products are found. It thus appears that the compound begins to decompose at 375° C. The label “RT” given on the right of the lower curve signifies “room temperature”.
EXAMPLE 8
LiFe1−yMnySO4F Solid Solution
An LiFe1−yMnySO4F compound was prepared from LiF and from a Fe1−yMnySO4.H2O solid solution as precursor.
Preparation of the Precursor
1-y mol of FeSO4.7H2O and y mol of MnSO4.H2O were dissolved in 2 ml of water previously degassed under argon to prevent the oxidation of Fe(II), then 20 ml of ethanol was added. The powder which formed by precipitation during the addition of ethanol was recovered by centrifugation, washed twice with 20 ml of ethanol, then heated at 200° C. under vacuum for 1 hour.
Several samples were prepared, varying the value of y.
The samples were analyzed by X-ray diffraction. The diffraction diagram of the “y=0.5” sample obtained, is represented in FIG. 20. It shows that it is the Fe0.5Mn0.5SO4.H2O solid solution, the lattice parameters of which are as follows:
Triclinic, space group: P−1 (2)
a=5.2069 Å, b=5.2056 Å, c=7.6725 Å,
α=107.7196°, β=107.4498°, γ=93.08°
V=186.56 Å3.
Preparation of the LiFe1−yMnySO4F Solid Solution
The synthesis is carried out via an ionothermal route in an autoclave at 270° C., for various precursor samples.
Introduced into an autoclave containing 3 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) was a mixture of 0.85 g of Fe0.5Mn0.5SO4.H2O and 0.149 g of LiF (1/1.14 molar ratio) prepared in a mortar, the mixture was subjected to magnetic stirring for 20 minutes at room temperature, the stirring was stopped, then 2 ml of ionic liquid (EMI-TFSI) were added, and the mixture was kept without stirring at room temperature for 30 minutes. After sealing the autoclave under argon, the whole assembly was then introduced into an oven at 200° C., the temperature of the oven was increased by 10° C. every 20 minutes up to 270° C., and kept at this value for 48 hours, then left to cool slowly.
The powder that was formed during the heat treatment was separated from the ionic liquid by centrifugation, washed 3 times with 10 ml of dichloromethane, then dried in an oven at 60° C.
The X-ray diffraction shows the formation of LiFe1−yMnySO4F solid solution at low values of y (in particular for y<0.1) and the formation of mixed phases for the higher values of y (in particular for y>0.25).
EXAMPLE 9
Synthesis of NaFeSO4F from FeSO4.7H2O and NaF
A mixture of 5 ml of EMI-TFSI and 2.808 g of FeSO4.7H2O was introduced into an open Parr® bomb calorimeter, and heated at 230° C. After heating for 5 h, the mixture was cooled to room temperature, then 0.42 g of NaF was added before sealing the Parr® bomb calorimeter. After 10 minutes of magnetic stirring, the mixture was heated at 250° C. for 24 hours. After cooling to room temperature, the powder recovered was washed twice with 20 ml of acetone, then dried in an oven at 60° C. The X-ray diffraction diagram, represented in FIG. 21, shows the formation of a new phase having a monoclinic distorted tavorite-type structure having the space group P21/C.
In the examples, FeO4.H2O and CoSO4.H2O were prepared by heating FeSO4.7H2O and CoSO4.7H2O respectively and applying primary vacuum at 200° C. for 1 hour.
EXAMPLE 10
Synthesis of LiFeSO4F
In a mortar, 0.850 g of FeSO4.H2O monohydrate was mixed manually with 0.145 g of LiF, which corresponds to a 10% excess of LiF relative to the stoichiometric amounts. The powder was pelleted under a 10 tonne load, then the pellet was introduced into a Parr bomb calorimeter that was assembled in a dry box using argon as the carrier gas. The bomb calorimeter was then placed in an oven, the temperature of which was brought to 280° C. over 5 hours and maintained at this value for 60 hours. The oven was then rapidly cooled, the pellet was recovered and milled in order to characterize it via XRD.
The XRD diagram is represented in FIG. 22. It shows that the product obtained is a 95% single-phase product.
EXAMPLE 11
Synthesis of LiFeSO4F from FeSO4.H2O and LiF at 280° C. (Effect of the Internal Pressure)
A mixture of FeSO4.H2O/LiF powders in a 1/1.14 molar ratio was prepared, and a pellet was prepared by compressing 1 g of powder mixture under a 10 tonne load. The pellet was introduced into a Parr bomb calorimeter that was assembled in a dry box using argon as the carrier gas. The Parr bomb calorimeter was then subjected to a heat treatment according to the following scheme: 1 h at 250° C., 1 h at 260° C., 1 h at 270° C., 60 h at 280° C., slow cooling. The oven was then rapidly cooled, the pellet was recovered and it was milled in order to characterize it by XRD (CuKα).
This procedure was carried out, on the one hand, in a Parr bomb calorimeter of 25 ml and, on the other hand, in a Parr bomb calorimeter of 50 ml.
The XRD diagrams are represented in FIG. 23. The upper curve corresponds to the implementation in the 25 ml Parr bomb calorimeter and the lower curve corresponds to the implementation in the 50 ml Parr bomb calorimeter. The diagrams show that the formation of the LiFeSO4F phase characteristic of the lines identified by the sign * and of impurities. The level of impurities is lowest in the 25 ml bomb calorimeter, namely around 5%.
EXAMPLE 12
Synthesis of LiFeSO4F Starting from FeSO4.H2O and LiF at 290° C.
A mixture of 0.850 g of FeSO4H2O and 0.2 g of LiF was prepared by mechanical milling for 10 min in an SPEX-800 mill, then the mixture was pelleted under a 10 tonne load and the pellet obtained was placed in a 25 ml Parr bomb calorimeter that was sealed under argon. The following heat treatment was then applied: 1 h at 250° C., 1 h at 260° C., 1 h at 270° C., 48 h at 290° C., slow cooling. The oven was then rapidly cooled, the pellet was recovered and it was milled in order to characterize it by XRD (CuKα). FIG. 24 represents the XR diffraction diagram (left-hand section) and a scanning electron microscopy photo (right-hand section). The XRD diagram shows the formation of a pure LiFeSO4F phase, crystallized in a triclinic lattice, of space group P−1, with the following lattice parameters: a=5.1865(11) (Å), b=5.4863(9) (Å), c=7.2326(12) (Å), α=106.49(1), β=107.153(9), γ=97.888 (8), and a volume V=182.99(6) Å3. The scanning electron microscopy photo shows agglomerates of small nanoscale particles that are very varied in size (400 nm to 800 nm).
EXAMPLE 13
Synthesis of NaFeSO4F
In a mortar, 0.850 mg of FeSO4.H2O monohydrate was mixed manually with 24545 mg of NaF, which corresponds to a 10% excess of NaF relative to the stoichiometric amounts. The powder was pelleted under a pressure of 10 000 psi, then the pellet was introduced into a Parr bomb calorimeter that was assembled in a dry box using argon as the carrier gas. The bomb calorimeter was then placed in an oven, the temperature of which was brought to 290° C. over 5 hours and maintained at this value for 80 hours. The oven was then rapidly cooled, the pellet was recovered and milled in order to characterize it via XRD. The XRD diagram is represented in FIG. 25. It shows that the compound obtained is NaFeSO4F and crystallizes into a monoclinic lattice (space group P21/c) with the following parameters: a=6.6798(2) (Å), b=8.7061(2) (Å), c=7.19124(18) (Å), b=113.517(2) (Å) and V=383.473 (Å3).
EXAMPLE 14
Synthesis of NaCoSO4F
In a mortar, 0.855 mg of CoSO4.H2O monohydrate was mixed manually with 245 ma of NaF, which corresponds to a 10% excess of NaF relative to the stoichiometric amounts. The powder was pelleted under a pressure of 10 000 psi, then the pellet was introduced into a Parr bomb calorimeter that was assembled in a thy box using argon as the carrier gas. The bomb calorimeter was then placed in an oven, the temperature of which was brought to 300° C. over 5 hours and maintained at this value for 1 week. The oven was then rapidly cooled, the pellet was recovered and milled in order to characterize it via XRD. The XRD diagram is represented in FIG. 26. It shows the predominant presence of the NCoSO4F phase which crystallizes in the space group P21/c with the lattice parameters a=6.645(2) Å, b=8.825(2) Å, c=7.162(2) Å, β=112.73(3) and V=387.38(3) Å3.
EXAMPLE 15
Preparation of FeSO4F
The compound was prepared by chemical delithiation of LiFeSO4F with NO2OF4 in acetonitrile at room temperature. The X-ray diffraction spectrum represented in FIG. 27 shows that the compound crystallizes into a lattice, the parameters of which are:
Triclinic, space group: P−1 (2)
A=5.0682 Å, b=5.0649 Å, c=7.255 Å
α=69.36°, β=68.80°, γ=88.16°
V=161.52 Å3.
EXAMPLE 18
Electrochemical Tests
Samples of compound LiFeSO4F, prepared according to example 3, were tested as a 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 by a 1M solution of LiPF6 in a 1/1 ethylene carbonate/dimethyl carbonate EC-DMC mixture. To produce a positive electrode, 80 mg of LiFeSO4F (in the form of particles having a mean diameter of 1 μm) and 20 mg of carbon were mixed by mechanical milling in an SPEX 1800 mill for 15 minutes. An amount of mixture corresponding to 8 mg of LiFeSO4F per cm2 was applied to an aluminum current collector.
In FIG. 28a, the main curve represents the variation of the potential as a function of the insertion rate of lithium, during the cycling of the cell at a C/10 regime, and the insert represents the change in the capacity of a cell during the succession of cycles at a C/10 regime, N being the number of cycles.
FIG. 28b represents the variation of the potential as a function of the insertion rate of lithium, during the cycling of the cell at a C/2 regime.
FIG. 28c represents the variation of the capacity of a cell as a function of the cycling regime R.
It thus appears that the capacity remains at 90% at a C/2 regime and at 67% at a C/10 regime.
EXAMPLE 19
Electrochemical Test
An LiFeSO4F sample prepared according to example 12 was subjected to an electrochemical test. An LiFeSO4F (ceramic)/carbon (acetylene black) composite material in an 85/15 weight proportion was prepared by mechanical milling for 15 min in an SPEX® mill. This composite material was applied to an aluminum current collector and it was mounted in a cell in which the negative anode is a lithium foil and the electrolyte is a commercial electrolyte of LP30 type. The cell thus obtained was cycled in the potential window [2.5 V-4.5 V] under a C/5 regime (1 electron exchanged over 5 hours). The results of the electrochemical tests are represented in FIG. 29, in which the left-hand curve represents the variation of the potential as a function of the lithium ion content in the fluorosulfate, and the right-hand curve represents the variation of the capacity as a function of the number of cycles. It appears that the material electrochemical activity is centered in the vicinity of 3.6 V, with a reversible capacity of around 80 mAh/g which is stable at least in the first 5 cycles.
EXAMPLE 20
Electrochemical Test
An NaFeSO4F sample prepared according to example 13 was tested under the conditions of example 19. The cycling curve is represented in FIG. 30. It shows that the material has an electrochemical activity similar to that of the corresponding material prepared in an ionic liquid medium. In particular, the phase the reactivity with respect to Li is limited to 0.2 Li per formula unit, irrespective of the preparation process.

## Claims

1. A process for preparing a material, having particles of a fluorinated compound which has a distorted tavorite structure and which corresponds to the following formula (I):


(A1−aA′a)x(Z1−bZ′b)z(SO4)sFf  (I)

in which
A represents Li or Na;
A′ represents a vacancy or at least one dopant element;
Z represents at least one element chosen from Fe, Co and Ni;
Z′ represents a vacancy or at least one dopant element;
the indices a, b, x, z, s, and f are chosen so as to ensure the etectroneutrality of the compound, and 1≧a≧0, 1>b≧0, x≧0, z>0, s>0, f>0;
the respective amounts a and b of dopant A and Z′ are such that the tavorite structure is preserved, wherein said method comprises the steps of:


dispersing precursors of the elements which form said material of formula (I) in a support liquid comprising at least one ionic liquid consisting of a cation and of an anion, the electric charges of which are balanced, in order to obtain a suspension of said precursors in said liquid;
ii) heating said suspension to a temperature of 25 to 330° C.;
iii) separating said ionic liquid and the material of formula (I) resulting from the reaction between said precursors.

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

3. The process as claimed in claim 1, wherein the precursor of A or A′ is chosen from inorganic acid salts, volatile organic acid salts, heat-decomposable acid salts, fluorides and sulfates.

4. The process as claimed in claim 1, wherein the precursor of a Z or Z′ element is chosen from the sulfates of Z or of Z′ that have a tavorite structure.

5. The process as claimed in claim 1, wherein the precursor of Z and, where appropriate, of Z′ is a monohydrate ZSO4.H2O or Z′SO4.H2O or a mixed monohydrate Z1−bZ′bSO4.H2O, and the precursor of A and, where appropriate, of A′ is a fluoride.

6. The process as claimed in claim 5, wherein an excess of fluoride of 5% to 25% is used.

7. The process as claimed in claim 1, wherein the ionic liquid is 1-butyl-3-methylimidazolium trifluoromethanesulfonate or 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

8. The process as claimed in claim 1, wherein the heating step ii) is carried out under an inert atmosphere, at atmospheric pressure.

9. The process as claimed in claim 1, wherein A′ is an alkali et different from A, an alkaline-earth metal or a 3d metal.

10. The process as claimed in claim 1, wherein Z′ is a metal chosen from alkali metals, Mn, Mg, Ca, Sc, Ti, V, Cr, Zn, Al, Ga, Sn, Zr, Nb and Ta in at least one of their degrees of oxidation.

11. The process as claimed in claim 1, wherein said material corresponds to one of the formulae Li(Z1−bZ′b)zSO4F and Na(Z1−bZ′b)zSO4F.

12. The process as claimed in claim 1, wherein said material corresponds to the formula (Z1−bZ′b)z(SO4)sFf.