The subject-matter of the present invention is ionic compositions having a high ionic conductivity, comprising a salt in which the anionic charge is delocalized, and their uses, in particular as electrolyte.
It is known and particularly advantageous to introduce ionic groups into organic molecules or polymers having various functions. This is because the coulombic forces correspond to the strongest available interactions at the molecular level and the ionic groups modify in the most pronounced way the molecules to which they are attached. Mention may be made of dyes, which are rendered soluble in water using sulfonate or carboxylate functional groups.
However, the groups of this type, —CO2 − 1/mMm+ or —SO3 − 1/mMm+, are not dissociated and they do not induce solubility in solvents other than water or some very polar protic solvents, such as light alcohols, which greatly restrict the scope of their use.
Furthermore, salts of the compounds 1/mMm+ C−(SO2RF)3, in which RF is a perfluorinated group and Mm+ a cation with the valency m, are known which are soluble and dissociated in organic aprotic media or in solvating polymers. However, it is considered that the existence of at least two perfluoroalkylsulfonyl groups (in particular the existence of fluorine atoms on the carbon atom α to each of the sulfonyl groups), which exert a large attractant power on the electrons of the anionic charge, is a necessary condition for the solubility and dissociation properties to be obtained.
Surprisingly, the inventors have found that the excellent solubility and dissociation properties of the —C(SO2RF)3 ionic groups are retained when a single sulfone group has fluorine atoms on atoms adjacent to the sulfur atom, allowing an extremely wide choice of functional molecules. In just as unexpected a way, it was found that it is possible, with the same properties being obtained, to omit the —SO2— group attached to the nonperfluorinated group, provided that the group attached directly to the carbon has a Hammett parameter σ+ of greater than 0.55. By way of comparison, the Hammett parameter σ+ of an —SO2— group connected to a nonperfluorinated group is 3.5 and 4.55 for a CF3SO2— group.
The subject-matter of the present invention is an ionic composition comprising at least one ionic compound in solution in a solvent, the said ionic compound comprising an anionic part associated with at least one cationic part Mm+ in a number sufficient to ensure the electronic neutrality of the combination. The said composition is characterized in that it has a conductivity of greater than 10−5 S.cm−1 at a temperature of between −30° C. and 150° C., in that Mm+ is a proton, a hydronium, a hydroxonium, a nitrosonium NO+, an ammonium —NH4 + or a cation having the valency m chosen from metal cations, organic cations and organometallic cations, and in that the anionic part corresponds to one of the formulae XF—SOx—C−(Z) (Z′), XF—SOx—C−(YR) (Y′R′) or XF—SOx—C−—(Z) (YR) in which:
x is 2 (sulfonyl group) or 1 (sulfinyl group);
XF represents a monovalent or multivalent radical chosen from the group consisting of linear, branched or cyclic perhalogenated radicals of the alkyl, alkylaryl, oxa-alkyl, aza-alkyl, thia-alkyl, alkenyl, oxa-alkenyl, aza-alkenyl, thia-alkenyl or dialkylazo type or from the group consisting of organic radicals in which the carbon α to the SOx group carries at least one F atom, it being understood that a multivalent XF radical is connected to more than one —SOxC— group ;
Z and Z′ represent, independently of one another, a monovalent or multivalent electron-withdrawing radical, it being understood that a multivalent Z or Z′ radical can form part of a ring or be connected to several —C−SOx—XF groups;
Y or Y′ represent a sulfonyl, sulfinyl, carbonyl or phosphonyl group;
R is a monovalent or multivalent organic radical and R′ is H or a monovalent or multivalent organic radical, R and R′ being other than a perfluoroalkyl when x=2 ; it Being understood that each of the substituents R, R′, Z or Z′ can form part of an aromatic or nonaromatic ring or of a polymer, and that each of the substituents XF, R, R′, Z or Z′ can be connected to a substituent XF, R, R′, Z or Z′ carried by the same anionic center C− or by another anionic center.
In the ionic compound of a composition of the present invention, the cation can be a metal cation chosen from alkali metal cations, alkaline earth metal cations, transition metal cations, in the divalent or trivalent state, and rare earth cations. Mention may be made, by way of example, of Na+, Li+, K+, Sm3+, La3+, Ho3+, Sc3+, Al3+, Y3+, Yb3+, Lu3+ or Eu3+.
The cation can also be an organometallic cation, in particular a metallocenium. Mention may be made, by way of example, of the cations derived from ferrocene, from titanocene, from zirconocene, from an indenocenium or from a metallocenium arene, the cations of transition metals complexed by ligands of phosphine type optionally possessing a chirality, or the organometallic cations possessing one or more alkyl or aryl groups covalently attached to an atom or a group of atom, such as the methylzinc, phenylmercury, trialkyltin or trialkyllead cations. The organometallic cation can form part of a polymer chain.
The cation of the salt of a composition of the invention can be an organic cation chosen from the group consisting of the R″3O+(onium), NR″4 +(ammonium), R″C (NHR″2)2 +(amidinium), C(NHR″2)3 +(guanidinium), C5R″6N+(pyridinium), C3R″5N2 +(imidazolium), C2R″4N3 +(triazolium), C3R″7N2 +(imidazolinium), SR″3 +(sulfonium), PR″4 +(phosphonium), IR″2 +(iodonium) or (C6R″5)3C+(carbonium) cations, the R″ radicals independently representing H or a nonperfluorinated organic radical. The organic radicals R″, which are identical or different, are preferably chosen from the group consisting of:
the proton, alkyl, alkenyl, oxa-alkyl, oxa-alkenyl, aza-alkyl, aza-alkenyl, thia-alkyl, thia-alkenyl, optionally hydrolyzable sila-alkyl or optionally hydrolyzable sila-alkenyl radicals and dialkylazo radicals, it being possible for the said radicals to be linear, branched or cyclic
cyclic or heterocyclic radicals optionally comprising at least one side chain comprising heteroatoms, such as nitrogen, oxygen or sulfur;
aryls, arylalkyls, alkylaryls and alkenylaryls, optionally comprising heteroatoms in the aromatic nucleus or in a substituent;
groups comprising several condensed or noncondensed, aromatic or heterocyclic nuclei, optionally comprising at least one nitrogen, oxygen, sulfur or phosphorus atom. When an onium cation carries at least two R″ radicals other than H, these radicals can together form an aromatic or nonaromatic ring, optionally encompassing the center carrying the cationic charge.
A cationic onium group can be polycationic, for example when an R″ substituent is a divalent substituent connected to two cationic centers. Mention may be made, by way of example, of the cation of the following compound:
When the cationic part of the ionic compound is an onium cation, it can be provided either in the form of an independent cationic group which is only bonded to the anionic part via the ionic bond between the positive charge of the cation and the negative charge of the anionic part. In this case, the cationic part can form part of a repeat unit of a polymer.
An onium cation can also form part of one of the RH
, R or R′ radicals. In this case, the ionic compound constitutes a zwitterion. Mention may be made, by way of example, of the following compound:
The onium cation can be chosen so as to introduce, into the salt, substituents which make it possible to confer specific properties on the said salt. For example, the M+ cation can be a cationic heterocycle of aromatic nature comprising at least one quaternized nitrogen atom in the ring. Mention may be made, by way of example, of the imidazolium, triazolium, pyridinium and 4-(dimethylamino)pyridinium ions, the said cations optionally carrying a substituent on the carbon atoms of the ring. Among these cations, those which give a salt with a melting point of less than 150° C. are advantageous, because they give ionic compositions which have a protonic conduction. A particularly preferred composition with protonic conduction comprises a salt in which the cation is formed by addition of a proton to the nitrogen of an imidazoline, of an imidazole or of a triazole, as well as the corresponding nitrogenous base, in a proportion of 0.5 to 10 by molar ratio.
A salt in which the cation is a cationic group possessing an —N═N— or —N═N+ linkage, a sulfonium group, an iodonium group or an areneferrocenium cation which is substituted or unsubstituted, optionally incorporated in a polymeric backbone, is advantageous insofar as it can be activated by a source of actinic energy of appropriate wavelength. Mention may be made, as specific examples of such salts, of substituted or unsubstituted phenacyldialkylsulfonium, trialkylaryl-sulfonium, triarylsulfonium, dialkylaryliodonium and diaryliodonium salts. The abovementioned cations can form part of a polymer chain.
The M cation of a salt can incorporate a 2,2′[Azobis(2-2′-imidazolinio-2-yl)propane]2+ or 2,2′-Azobis(2-amidiniopropane)2+ group. The salt is then capable of releasing, under the action of heat or of ionizing radiation, radicals which make it possible to initiate polymerization or crosslinking reactions or, generally, chemical reactions involving free radicals. Furthermore, this salt is readily soluble in polymer and monomer organic solvents, even of low polarity, in contrast to the derivatives of the anions of Cl− type commonly associated with the abovementioned cations. Furthermore, they exhibit a negligible vapor pressure, in contrast to the other radical initiators of peroxide or azo type, which is a considerable advantage in the processing of polymers as thin films, poor polymerization or crosslinking of the surface of the film being the consequence of the volatility of the initiator.
In an embodiment of the invention, XF
is a perhalogenated alkyl radical preferably having from 1 to 12 carbon atoms or a perhalogenated alkylaryl radical preferably having from 6 to 9 carbon atoms. A heteroatom, such as O, N or S, can be present between two carbon atoms or at the end of the radical. Mention may be made, by way of examples, of the following compounds:
An XF substituent can also be a radical chosen from the group consisting of RHCF2—, RHCF2CF2—, RHCF2CF(CF3)— and CF3C(RH)F—, in which RH represents a nonperhalogenated organic radical.
An R, R′ or RH
substituent can be chosen from alkyl, alkenyl, oxa-alkyl, oxa-alkenyl, aza-alkyl, aza-alkenyl, thia-alkyl, thia-alkenyl and dialkylazo radicals having from 1 to 24 carbon atoms, or from aryl, arylalkyl, alkylaryl or alkenylaryl radicals having from 5 to 24 carbon atoms, it being possible for the said radicals optionally to be completely or partially fluorinated, R and R′ being other than a perfluorosalkyl when XF
is a perfluoroalkylsufonyl. A few examples are given hereinbelow by way of illustration.
Two R and R′ substituents can together form a divalent radical connected to a Y group and a Y′ group. A compound example is given hereinbelow
An R, R′ or RH
substituent can be chosen from alkyl or alkenyl radicals having from 1 to 12 carbon atoms and optionally comprising at least one O, N or S heteroatom in the main chain or in a side chain and/or optionally carrying a hydroxyl group, a carbonyl group, an amine group, an alkoxysilane group or a carboxyl group. When two substituents together form a divalent radical, this divalent radical can carry a heteroatom in a side chain and optionally form part of a ring. Mention may be made, by way of example, of
Two R and R′ radicals can together form a biradical connected, at each of its ends, to an —SO2
anionic group. A polyionic compound is thus obtained, such as, for example:
An R, R′ or RH substituent can be a polymer radical, for example an oligo(oxyalkylene) radical. The salt of the composition of the invention is then provided in the form of a polymer carrying an [(R′,Y′) (XFSOx) CY—]− M+ ionic group, where R is a polymer radical, or in the form of a polymer carrying an [(RY) (R′,Y′)C—SOx—]− group, where RH is a polymer radical.
An R or R′ substituent can be a repeat unit of a polymer. The salt of the composition of the invention is then provided in the form of a polymer in which at least a portion of the repeat units carry a side group to which is attached an (XF
ionic group. Mention may be made, as an example, of a poly(oxyalkylene), a polyaniline or a poly(furan-vinylene), in which at least some oxyalkylene units carry an [(R′,Y′) (XF
or [(RY) (R′,Y′)C—SOx
substituent. Mention may also be made of a polystyrene in which at least some styrene units carry an [(R′,Y′) (XF
) CY—]−, M +
substituent, for example a [styrenyl-(R′,Y′) (XF
A specific category of salts, which salts can be used in a composition according to the invention, comprises the compounds in which an R, R′ or RH substituent possesses at least one anionic ionophoric group and/or at least one cationic ionophoric group. The anionic group can, for example, be a carboxylate functional group (—CO2 −), a sulfonate functional group (—SO3 −), a disulfonimide functional group (—SO2NSO2 −) or a sulfonamide functional group (—SO2N═). The cationic ionophoric group can, for example, be an iodonium, sulfonium, oxonium, ammonium, amidinium, guanidinium, pyridinium, imidazolium, imidazolinium, triazolium, phosphonium or carbonium group. The cationic ionophoric group can entirely or partially act as the M cation.
When an R, R′ or RH substituent comprises at least one ethylenic unsaturated and/or one condensable group and/or one group dissociable by the thermal route, by the photochemical route or by ionic dissociation, the compounds of the invention are reactive compounds which can be subjected to polymerizations, crosslinkings or condensations, optionally with other monomers. They can also be used to attach ionophoric groups to polymers carrying the appropriate reactive functional group.
An R, R′ or RH substituent can comprise a mesomorphic group or a chromophoric group or a self-doped electronic conducting polymer or a hydrolyzable alkoxysilane.
An R, R′ or RH substituent can comprise a group capable of scavenging free radicals, for example a hindered phenol or a quinone.
An R, R′ or RH substituent can also comprise a dissociating dipole, for example an amide functional group, a sulfonamide functional group or a nitrile functional group.
An R, R′ or RH substituent can also comprise a redox couple, for example a disulfide group, a thioamide group, a ferrocene group, a phenothiazine group, a bis(dialkylaminoaryl) group, a nitroxide group or an aromatic imide group.
An R, R′ or RH substituent can also comprise a complexing ligand.
An R, R′ or RH, RY or R′Y substituent can be an optically active group (for example an amino acid) or an optically or biologically active polypeptide.
When a compound of the present invention corresponds to the formula XF—SOx—C—(Z) (Z′) or XF—SOx—C—(Z) (YR), Z or Z′ can be chosen from the group consisting of —CN, —NO2, —SCN, —N3, —CF3, R′FCH2—(R′F being a perfluorinated radical), CF2═CFO—, CF2═CF—S—, CF2═CF—, —C2F4H, fluoroalkyloxy or perfluoroalkyloxy radicals, fluoroalkylthioxy radicals and perfluoroalkylthioxy radicals. Z or Z′ can also be a radical comprising one or more aromatic nuclei optionally comprising at least one nitrogen, oxygen, sulfur or phosphorus atom, it being possible for the said nuclei optionally to be condensed nuclei and/or it being possible for the said nuclei optionally to carry at least one substituent chosen from the group consisting of halogens, —OCnF2n+1, —OC2F4H, —SCnF2n+1, —SC2F4H, —O—CF═CF2, —SCF═CF2, —CN, —NO2, —SCN, —N3, —CF3, CF3CH2—, aza, thia and oxa radicals, perfluoroalkyl radicals, fluoroalkyloxy radicals, fluoroalkylthioxy radicals, alkyl, alkenyl, oxa-alkyl, oxa-alkenyl, aza-alkyl, aza-alkenyl, thia-alkyl or thia-alkenyl radicals, polymer radicals, and radicals possessing at least one cationic ionophoric group and/or at least one anionic ionophoric group;
it being understood that a Z or Z′ substituent can be a monovalent radical, a portion of a multivalent radical connected to several XF—SOx—C− groups, or a segment of a polymer, and that two Z and Z′ substituents can together form a multivalent group comprising a nucleus or several optionally condensed aromatic nuclei, including or not including the carbon carrying the anionic charge.
A Z substituent can also represent a repeat unit of a polymer. In this case, the ionic composition of the invention comprises a polymer in which at least some repeat units carry a −CSO 2XF ionic group. The Z substituent of an anionic group and the Z′ substituent of a neighboring anionic group can also form a biradical. In this case, the ionic composition of the invention comprises a polymer in which the C− anionic center forms part of the backbone of the polymer, the XFSO2 group being found as a side substituent.
The solvent of the ionic composition of the invention can be an aprotic liquid solvent, a polar polymer or one of their mixtures.
The aprotic liquid solvent is chosen, for example, from linear ethers and cyclic ethers, esters, nitrites, nitro derivatives, amides, sulfones, sulfolanes, alkylsulfamides and partially halogenated hydrocarbons. The particularly preferred solvents are diethyl ether, dimethoxyethane, glyme, tetrahydrofuran, dioxane, dimethyltetrahydrofuran, methyl or ethyl formate, propylene or ethylene carbonate, alkyl carbonates (in particular dimethyl carbonate, diethyl carbonate and methyl propyl carbonate), butyrolactone, acetonitrile, benzonitrile, nitromethane, nitrobenzene, dimethylformamide, diethyl-formamide, N-alkylpyrrolidones (in particular N-methyl-pyrrolidone), dimethyl sulfone, tetramethylene sulfone and tetraalkylsulfonamides having from 5 to 10 carbon atoms.
An ionic composition of the invention can comprise a polar polymer solvent chosen from crosslinked or noncrosslinked solvating polymers carrying or not carrying grafted ionic groups. A solvating polymer is a polymer which comprises solvating units comprising at least one heteroatom chosen from sulfur, oxygen, nitrogen and fluorine. Mention may be made, as an example of solvating polymers, of polyethers with a linear, comb or block structure, forming or not forming a network, based on poly(ethylene oxide) or copolymers comprising the ethylene oxide or propylene oxide or allyl glycidyl ether unit, polyphosphazenes, crosslinked networks based on poly(ethylene glycol) crosslinked by isocyanates or networks obtained by polycondensation and carrying groups which make possible the incorporation of crosslinkable groups. Mention may also be made of block copolymers in which some blocks carry functional groups which have redox properties. Of course, the above list is not limiting and any polymer exhibiting solvating properties can be used.
An ionic composition of the present invention can simultaneously comprise an aprotic liquid solvent chosen from the abovementioned aprotic liquid solvents and a polar polymer solvent comprising units comprising at least one heteroatom chosen from sulfur, nitrogen, oxygen and fluorine. The composition can comprise from 2 to 98% of liquid solvent. Mention may be made, as example of such a polar polymer, of polymers which mainly comprise units derived from acrylonitrile, from vinylidene fluoride, from N-vinylpyrrolidone or from methyl methacrylate. The proportion of aprotic liquid in the solvent can vary from 2% (corresponding to a plasticized solvent) to 98% (corresponding to a gelled solvent).
An ionic composition of the present invention can additionally comprise a salt used conventionally in the prior art for the preparation of an ionically conducting material. Mention may be made, among the salts which can be added to an ionic composition according to the invention, of perfluoroalkanesulfonates, bis(perfluoroalkylsulfonyl)imides, bis(perfluoroalkylsulfonyl)methanes and tris(perfluoro-alkylsulfonyl)methanes.
Of course, an ionic composition of the invention can additionally comprise the additives conventionally used in ionically conducting materials and in particular inorganic or organic fillers in the form of a powder or of fibers.
Generally, a compound Q1C(M) (Q2) (Q3) in which Q1, Q2 and Q3 represent RY, R′Y′, Z, Z′ or XFSOx can be prepared by the reaction of a compound possessing a leaving group L with a precursor of the final compound, according to the following reaction scheme:
L represents a leaving group such as F, Cl, Br, imidazolyl, triazolyl or RSO3—. E represents an electrophilic group, such as M. For example, E can be H, Li, Na, K, a substituted or unsubstituted ammonium, MgL, Si(R7)3 or Sn(R8)3, R7 and R8 representing an alkyloxy radical.
A compound XF—SOx—C−(Z) (Z′) can be prepared by the reaction of a compound possessing a leaving group L with a precursor of the final compound, according to the following reaction scheme:
L+E (M)C(Z) (Z′)
C (Z) (Z′) (M)+LE
The compounds EC(M) (Q2)(Q3) can be prepared by a similar method according to the reaction scheme
EC (M) (Q2
)+LE in which Q2
, E, M and L have the meaning indicated above.
In an alternative form, where Q represents XFSOx—, the reaction can involve sulfur in the +2 or +4 oxidation state, according to the following reaction scheme:
C (M) (Q2
An ionic composition of the present invention of the polymer type can be prepared by dissolving the solvating polymer and an ionic compound carrying a −CSO xXF group in a common solvent, such as acetonitrile, and then evaporating the solvent. The procedure can also be employed which consists in dissolving an ionic compound in a volatile solvent, in then dissolving this ionic composition and a solvating polymer in a common solvent and in evaporating the volatile solvent, the ionic composition being chosen so as to give a predetermined ionic compound/repeat unit ratio. An ionic composition of the present invention of the gell type can be obtained either by incorporating a liquid solvent in a polymer composition or by dissolving the ionic compound in a solvent in which the polymer can also be dissolved under warm conditions.
The salts of the ionic compositions of the present invention comprise at least one ionophoric group to which are attached substituents which can be highly varied. Bearing in mind the large choice possible for the substituents, the salts make it possible to induce properties of ionic conduction in the majority of organic media, liquids or polymers, possessing a polarity, even a low polarity. The applications are significant in the field of electrochemistry, in particular of the storage of energy in primary or secondary generators, in supercapacitors, in fuel cells and in electroluminescent diodes. When the composition according to the invention comprises a polymer salt (introduced directly into the composition or obtained in situ by polymerization of a monomer salt), it exhibits the properties listed above with the advantage of having an immobile anionic charge.
An ionic composition according to the invention can be used as electrolyte of an electrochemical device.
In this case, the salt is preferably chosen from the compounds for which the cation is ammonium or a cation derived from a metal, in particular of lithium or potassium, zinc, calcium or rare earth metals, or an organic cation, such as a substituted ammonium, an imidazolium, a triazolium, a pyridinium or a 4-(dimethylamino)pyridinium, the said cations optionally carrying a substituent on the carbon atoms of the ring. The electrolyte thus obtained exhibits a high conductivity and a high solubility in the solvents, due to the weak interactions between the positive charge and the negative charge. Its range of electrochemical stability is broad and it is stable in both reducing and oxidizing media. Mention may be made, among the salts which can be used in an ionic composition of the invention, of those which have an organic cation and a melting point of less than 150° C., in particular imidazolium, triazolium, pyridinium or 4-(dimethylamino)pyridinium salts. Mention may be made, by way of example, of the following salts:
These salts exhibit a high intrinsic conductivity when they are in the molten phase. They can therefore be used with a minimum, indeed even zero, amount of solvent in forming an ionically conducting composition.
A composition of the invention in which the anion of the salt comprises a perhalogenated alkyl XF substituent having from 1 to 12 carbon atoms or a perhalogenated alkylaryl substituent having from 6 to 9 carbon atoms is particularly advantageous as electrolyte insofar as the weak interactions between the fluorine atoms of the chain result in high solubilities and a high conductivity, even in the case where the other substituents of the salt comprise groups having a tendency to give strong interactions, for example conjugated aromatic radicals or zwitterions.
A compound of the invention in which XF is chosen from the RHCF2—, RHCF2CF2—, RHCF2CF (CF3)— or CF3C (RH) F— radicals makes it possible to very specifically adapt the properties of the ionically conducting material by appropriately choosing the RH substituent. In particular, it makes it possible to enjoy, with a reduced number of fluorine atoms, dissociation and solubility properties peculiar to the anionic charges of perfluorinated systems. These groups are readily accessible from industrial products, such as tetrafluoroethylene or tetrafluoropropylene. The reduced amount of fluorine renders these compound less sensitive to reduction by highly electropositive metals, such as aluminum, magnesium or, especially, lithium.
An ionic composition of the invention can be used as electrolyte in an electrochemical generator. Another subject-matter of the present invention is therefore an electrochemical generator comprising a negative electrode and a positive electrode separated by an electrolyte, characterized in that the electrolyte is an ionic composition as defined above. According to a specific embodiment, such a generator comprises a negative electrode composed of metallic lithium or of one of its alloys, optionally in the form of a nanometric dispersion in lithium oxide, or of a double lithium and transition metal nitride, or of an oxide of low potential having the general formula Li1+y+x/3Ti2-x/3O4 (0≦×≦1, 0≦y≦1), or of carbon and carbonaceous products resulting from the pyrolysis of organic matter. According to another embodiment, the generator comprises a positive electrode chosen from vanadium oxides VOx, (2≦×≦2.5), LiV3O8, LiyNi1-xCoxO2, (0≦×≦1; 0≦y≦1), manganese spinels LiyMn1-xMxO2, (M=Cr, Al, V, Ni, 0≦×≦0.5; 0≦y≦2), organic polydisulfides, FeS, FeS2, iron sulfate Fe2(SO4)3, iron and lithium phosphates and phosphosilicates of olivine structure, or their products of substitution of the iron by manganese, used alone or as mixtures. The collector of the positive electrode is preferably made of aluminum.
Use will preferably be made, as electrolyte of an electrochemical generator, of an ionic composition comprising an alkali metal salt. Preference is very particularly given to lithium salts, optionally as a mixture with a potassium salt.
The salts in which the R and R′ substituents represent an alkyl, an aryl, an alkylaryl or an aralkyl preferably having from 6 to 20 carbon atoms constitute good candidates for the ionic compositions intended to be used as electrolyte of an electrochemical generator. However, specific properties can be obtained by choosing other substituents. When the salt has at least one R, R′ or XF substituent comprising a mesomorphic group or an ethylenic unsaturation and/or a condensable group and/or a group dissociable by the thermal route, by the photochemical route or by ionic dissociation, the ionic composition readily forms polymers or copolymers which are polyelectrolytes, either intrinsic, when the polymer carries solvating groups, or by addition of a polar solvent of liquid or polymer type or by mixing with such a solvent. These compositions of the polyelectrolyte type have a conductivity solely due to the cations.
When the salt of the ionic composition used as electrolyte carries at least one R, R′ or RH
substituent which is a self-doped electronic conducting polymer, the stability of the electrolyte is improved with respect to external agents and the conductivity is stable all the time, even at high temperatures. On contact with metals, such a composition gives very weak interfacial resistances. Its use as electrolyte makes it possible to protect from corrosion, in particular ferrous metals or aluminum, in particular when the aluminum is used as collector of the cathode of the generator. Mention may be made, by way of example, of:
When the salt of the ionic composition used as electrolyte comprises an R, R′ or RH substituent which comprises a redox couple (for example a disulfide, a thioamide, a ferrocene, a phenothiazine, a bis (dialkylaminoaryl) group, a nitroxide or an aromatic imide), the electrolyte has redox shuttle properties of use as charge equalization and protection component of the electrochemical generator.
The use of a salt carrying at least one R, R′ or RH substituent which represents an alkyl, an aryl, an alkylaryl or an arylalkyl makes it possible to induce properties of mesogenic type in the electrolyte of the generator. Alkyls having from 6 to 20 carbon atoms or arylalkyl, in particular those comprising the biphenyl entity which form liquid crystal phases, are particularly preferred. The conduction properties of the nematic, cholesteric or discotic liquid crystal phases thus constituted are to reduce the mobility of the anions of the electrolyte, in particular in polymer electrolytes, without affecting the mobility of the cations. This distinctive feature is important for electrochemical generators involving lithium cations.
When a composition according to the invention is intended to be used as electrolyte of a lithium generator, the solvent is advantageously chosen from conventionally used polar aprotic liquid solvents. It can also be chosen from crosslinked or noncrosslinked solvating polar polymer solvents carrying or not carrying grafted ionic groups. Use may also be made, as solvent, of a gel obtained by mixing a liquid solvent and a polymer solvent. A poly(ethylene oxide) and a copolymer of ethylene oxide or of propylene oxide and of a crosslinkable monomer, such as allyl glycidyl ether and methyl glycidyl ether, are particularly advantageous.
An ionic composition of the invention can also be used for the preparation of the cathode of a lithium generator. The material of the cathode then comprises an ionic composition of the invention, in which the salt is an electronic conducting polymer. Mention may be made, by way of example of such a salt, of:
An ionic composition of the present invention can also be used as electrolyte of a supercapacitor. Another subject-matter of the present invention is consequently a supercapacitor using at least one carbon electrode with a high specific surface or one electrode comprising a redox polymer, in which the electrolyte is an ionic composition according to the present invention.
The cation of the salt of the ionic composition used as electrolyte of a supercapacitor is preferably an ammonium NH4 +, a metal cation or an organic cation comprising a quaternized nitrogen atom. The preferred cations are Li, K, Ca, rare earths and the imidazolium, triazolium, pyridinium or 4-(dimethylamino)pyridinium ions.
The salt of the ionic composition of the invention used as electrolyte of a supercapacitor is advantageously chosen from the salts in which R, R′ and XF have a low atom number, preferably of less than 3. The compounds in which R and R′ represent —CH3 or —N(CH3)2 and XF represents CF3— are particularly preferred. It can be advantageous to add a small proportion of ionic compounds in which R and/or R′ are long alkyl chains (n≧8) in order to act as surfactant and to improve the penetration of the liquid into the micropores of the carbon of the carbon electrode.
The solvents are preferably chosen from those which have a low viscosity and which confer a high conductivity to the composition, for example acetonitrile, alkyl carbonates, or the ethylene carbonate and dimethoxyethane mixture.
An ionic composition according to the present invention can be used as electrolyte of a fuel cell. For this specific application, the salt of the electrolyte is advantageously chosen from the XF—SOx—C−-(Z) (Z′) or XF—SOx—C−(Z) (YR) salts, the first ones mentioned being preferred.
The cation of the compound used in the electrolyte of a fuel cell is preferably a hydronium, an ammonium, a metal cation or an organic cation comprising a quaternized nitrogen atom (as partial replacement for hydronium). The preferred cations are H+, H3O+, Li+, K+, Ca++ or the imidazolium, triazolium, pyridinium and 4-(dimethylamino)pyridinium ions.
The Z or Z′ substituents of the ionic compound are preferably chosen from —ΦOCnF2n+1, —ΦOC2F4H, —ΦSCnF2n+1and —ΦSC2F4H, —ΦOCF═CF2, —ΦSCF═CF2, —C2F4H and CF2═CF—, n being an integer from 1 to 8. Such a salt is a precursor of stable monomers and polymers, in particular stable with respect to oxygen. The electrolyte thus exhibits high stability, even at temperatures of greater than 80° C., when the salt is a polymer.
An ionic composition of the present invention can be used as electrolyte in photoelectrochemical systems, in particular systems with conversion of light to electricity, and in systems for modulating light of electrochromic type. A photoelectrochemical device in which the electrolyte is an ionic composition according to the invention is another subject-matter of the present invention.
It is advantageous to use, as electrolyte, an ionic composition in which the cation of the salt is H+, H3O+, Na+, K+, NH4 +, an imidazolium, a triazolium, a pyridinium or a 4-(dimethylamino)pyridinium. When the electrophotochemical device is a system for converting light to electricity or a system for modulating light of the electrochromic type, it is advantageous to use, in the electrolyte, a salt which carries at least one R, R′ or RH substituent comprising a redox couple, such as a disulfide, a thioamide, a ferrocene, a phenothiazine, a bis(dialkylaminoaryl) group, a nitroxide or an aromatic imide. The electrolyte thus exhibits redox shuttle properties of use in ensuring the passage of current without polarization. When the cation of the ionic compound is an imidazolium, a triazolium, a pyridinium or a 4-(dimethylamino)pyridinium, the ionic compound is molten at room temperature and exhibits a high ionic conductivity of greater than 10−3 S.cm−1. A composition comprising the said salt, the corresponding base (imidazole, triazole, pyridine or 4-(dimethylamino)pyridine) and a poly(ethylene oxide), preferably of high mass or crosslinkable, constitutes an anhydrous protonic conducting polymer.
For an electrochromic device comprising dyes, use is made, as electrolyte, of a composition according to the invention in which the salt is a compound having molten salt properties and which additionally comprises supplementary dyes which change color on passing from the oxidized state to the reduced state and vice versa.
An ionic composition according to the invention can also be used as electroactive dye or electrolyte in a device for optical display. In this specific use, it is advantageous to choose, for R, R′ or RH, an alkyl, an aryl, an alkylaryl or an arylalkyl which makes it possible to induce properties of mesogenic type in the ionic composition. Alkyls having from 6 to 20 carbon atoms or arylalkyl, in particular those comprising the biphenyl entity which form liquid crystal phases are particularly preferred.
An ionic composition of the present invention can also be used for the p or n doping of an electronically conducting polymer and this use constitutes another subject-matter of the present invention. The anions of the salt of the ionic composition of the invention can act as countercharge to polycationic conjugated polymers, such as polyacetylene, polyprrole, polythiophene, polyparaphenylene, polyquinolines and their alternating copolymers with acetylene (ex. polyparaphenylenevinylene) and their derivatives of substitution by alkyl, alkoxy or aryl groups and the like. optionally, the polymerization or the doping are carried out by the electrochemical route starting from the ionic compositions or by exchange of the anions of an already doped polymer by the anions of the ionic compositions.
The anionic charge carried by one of the XF—SOx—C−(Z) (Z′), XF—SOx—C−(YR) (Y′R′) or XF—SOx—C−(Z) (YR) anions exerts a stabilizing effect on the electronic conductors of conjugated polymer type and the use of a composition comprising a salt carrying at least one Z, Z′, R or R′ substituent comprising a long alkyl chain makes it possible to render these polymers soluble in the usual organic solvents, even in the doped state. The grafting of these charges to the polymer itself gives polymers, the overall charge of which is cationic, which are soluble in organic solvents and which exhibit, in addition to their stability, corrosion-resistant properties with respect to metals, aluminum and ferrous metals. Another subject-matter of the present invention is electronically conducting materials comprising an ionic composition of the present invention in which the cationic part of the salt is a polycation composed of a “p”-doped conjugated polymer. The preferred salts for this application are those in which one of the Z, Z′, R or R′ substituents comprises at least one alkyl chain having from 6 to 20 carbon atoms. Mention may be made, by way of example, of the compounds in which R or R′ is an alkyl radical. Mention may be also be made of the compounds in which XF is RHCF2—, RHCF2CF2—, RHCF2CF(CF3)— or CF3C(RH)F—, in which compounds RH— represents an alkyl radical. Mention may additionally be made of the compounds in which Z represents an aromatic nucleus carrying an alkyl radical.
It has been observed that the strong dissociation of the ionic species of the compounds of the invention is reflected by stabilization of the carbocations, in particular of those in which there exists conjugation with oxygen or nitrogen and, surprisingly, by a high activity of the protonated form of the compounds of the invention with regard to some monomers. Another subject-matter of the present invention is therefore the use of an ionic composition as photochemical or thermochemical initiator source of Brönsted acid catalyst of polymerization or of crosslinking of monomers or of prepolymers capable of reacting by the cationic route, as catalyst for various chemical reactions or as catalyst for the modification of polymers. Preference is very particularly given, as catalyst for the chemical modification of polymers, to the compositions in which the cation of the salt is a proton, an oxonium, Li, Mg, Cu, a rare earth, trimethylsilyl, a ferrocene, a zirconocene or a zirconoindocene.
The process for the polymerization or for the crosslinking of monomers or of prepolymers capable of reacting by the cationic route is characterized in that use is made of an ionic composition of the invention as photoinitiator, source of acid catalyzing the polymerization reaction. The ionic compositions according to the invention in which the cation of the salt is a group possessing an —N═N+
or —N═N— linkage, a sulfonium group, an iodonium group or an areneferrocenium cation which is substituted or unsubstituted, optionally incorporated in a polymeric backbone, are preferred. The compositions comprising a 2,2′[Azobis(2-2′-imidazolinio-2-yl)propane]2+
or 2,2′-Azobis (2-amidiniopropane)2+
salt are particularly suited as photothermal initiators. The compositions comprising an iodonium salt are particularly suited as photochemical initiator. Mention may be made, by way of example of salts, of:
The choice of the XF substituent, on the one hand, and of the R, R′ or Z substituents, on the other hand, is made so as to enhance the compatibility of the salt with the solvents used for the reaction of the monomers or of the prepolymers and according to the properties desired for the final polymer. For example, the choice of unsubstituted alkyl radicals provides solubility in not very polar media. The choice of radicals comprising an oxa group or a sulfone will provide solubility in polar media. The radicals including a sulfoxide group, a sulfone group, a phosphine oxide group or a phosphonate group, obtained respectively by addition of oxygen to sulfur or phosphorus atoms, can confer, on the polymer obtained, improved properties as regards adhesion, gloss or resistance to oxidation or to UV radiation. The monomers and the prepolymers which can be polymerized or crosslinked using the photoinitiators of the present invention are those which can be subjected to cationic polymerization.
Mention may be made, among the monomers, of monomers which comprise a cyclic ether functional group, a cyclic thioether functional group or a cyclic amine functional group, vinyl compounds (more particularly vinyl ethers), oxazolines, lactones and lactams.
Mention may be made, among the prepolymers, of the compounds in which epoxy groups are carried by an aliphatic chain, an aromatic chain or a heterocyclic chain, for example glycidic ethers of bisphenol A ethoxylated by 3 to 15 ethylene oxide units, siloxanes possessing side groups of the epoxycyclohexene-ethyl type which are obtained by hydrosilylation of copolymers of dialkyl-, alkylaryl- or diarylsiloxane with methylhydrosiloxane in the presence of vinylcyclohexene oxide, condensation products of the sol-gel type obtained from triethoxy- or trimethoxysilapropylcyclohexene oxide, or urethanes incorporating the reaction products of butanediol monovinyl ether and of an alcohol with a functionality of greater than or equal to 2 with an aliphatic or aromatic di- or triisocyanate.
The polymerization process according to the invention consists in mixing at least one monomer or prepolymer capable of polymerizing by the cationic route and at least one ionic composition of the invention and in subjecting the mixture obtained to actinic radiation or P radiation. The reaction mixture is preferably subjected to the radiation after having been put into the form of a thin layer having a thickness of less than 5 mm, preferably into the form of a thin film having a thickness of less than or equal to 500 μm. The duration of the reaction depends on the thickness of the sample and on the power of the source at the active wavelength λ. It is defined by the rate of forward progression past the source, which is between 300 m/min and 1 cm/min. Layers of final material having a thickness of greater than 5 mm can be obtained by repeating the operation several times, which operation consists in spreading a layer and in treating it with the radiation.
The amount of composition acting as photochemical initiator used is generally between 0.01 and 15% by weight with respect to the weight of monomer or of prepolymer, preferably between 0.1 and 10% by weight.
An ionic composition of the present invention comprising a very low, indeed even zero, amount of solvent can be used as photochemical initiator, in particular when it is desired to polymerize liquid monomers in which the salt of the ionic composition used as photochemical initiator is soluble or readily dispersible. This form of use is particularly advantageous because it makes it possible to eliminate the problems related to solvents (toxicity, inflammability).
An ionic composition of the present invention can also be used as photochemical or thermochemical initiator in the form of a homogeneous solution in a solvent which is inert with respect to polymerization, which solution is ready for use and readily dispersible, in particular in the case where the medium to be polymerized or to be crosslinked exhibits a high viscosity.
Mention may be made, as example of inert solvent, of volatile solvents, such as acetone, methyl ethyl ketone and acetonitrile. Mention may also be made of nonvolatile solvents, such as, for example, propylene carbonate, γ-butyrolactone, ether-esters of mono-, di- or triethylene or -propylene glycols, ether-alcohols of mono-, di- or triethylene or -propylene glycols, diethers of mono-, di- or triethylene glycol and diethers of mono-, di- or propylene glycol, and plasticizers, such as esters of phthalic acid or of citric acid.
In order to irradiate the reaction mixture, the radiation can be chosen from ultraviolet radiation, visible radiation, X-rays, γ-rays and β radiation. When ultraviolet light is used as actinic radiation, it can be advantageous to add, to the photochemical or thermochemical initiator of the invention, photosensitizers intended to make possible efficient photolysis with less energetic wavelengths than those corresponding to the absorption maximum of the photochemical or thermochemical initiator, such as those emitted by industrial devices (λ≈300 nm for mercury vapor lamps, in particular).
Among the various types of radiation mentioned, ultraviolet radiation is particularly preferred. On the one hand, its use is more convenient than the use of the other types of radiation mentioned. On the other hand, the photochemical initiators are generally directly sensitive to UV rays and the photosensitizers become increasingly efficient as the difference in energy (δλ) decreases.
The ionic compounds of the invention can also be employed in combination with initiators of radical type which are generated thermally or by the action of actinic radiation. It is thus possible to polymerize or to crosslink mixtures of monomers or of prepolymers comprising functional groups with different modes of polymerization, for example monomers or prepolymers polymerizing by the radical route and monomers or prepolymers polymerizing by the cationic route. This possibility is particularly advantageous in creating interpenetrating networks having physical properties different from those which would be obtained by simple mixing of the polymers resulting from the corresponding monomers.
Another subject-matter of the invention is the use of the ionic compositions of the invention in reactions for the chemical amplification of photoresists for microlithography. During such a use, a film of a material comprising a polymer and an ionic composition of the invention is subjected to irradiation. The irradiation leads to the formation of the acid by replacement of the cation M by a proton, which catalyzes the decomposition or the conversion of the polymer. After decomposition or conversion of the polymer on the parts of the film which have been irradiated, the monomers formed or the converted polymer are removed and there remains an image of the unexposed parts. For this specific application, it is advantageous to use a composition of the invention which is provided in the form of a polymer comprised essentially of styrenyl repeat units carrying an XF—SOx—C− ionic substituent in which the cationic part is an iodonium or a sulfonium. These compounds make it possible to obtain, after photolysis, products which are not volatile and therefore neither corrosive nor odorous when sulfides are produced from the decomposition of the sulfonium. Mention may in particular be made, among polymers which can thus be modified in the presence of a compound of the invention, of polymers comprising ester units or aryl tert-alkyl ether units, for example poly(phthalaldehydes), polymers of bisphenol A and of a diacid, poly(tert-butoxycarbonyloxystyrene), poly(tert-butoxy-α-methyl-styrene), poly(di-tert-butyl fumarate-co-allyltrimethyl-silane) and polyacrylates of a tertiary alcohol, in particular poly(tert-butyl acrylate). Other polymers are described in J. V. Crivello et al., Chemistry of Materials, 8, 376-381 (1996).
In the salts of the compositions of the present invention, the ion pairs exhibit a very strong dissociation, which makes possible the expression of the intrinsic catalytic properties of the Mm+ cation, the active orbitals of which are readily exposed to the substrates of the reaction, in various media. The majority of the important reactions of organic chemistry can thus be carried out under conditions which are not very restrictive, with excellent yields and the ability to separate the catalyst from the reaction mixture. The demonstration of asymmetric induction by the use of an ionic composition according to the invention comprising a salt which carries a chiral group is particularly significant because of its generality and its ease of implementation. It should be noted that chiralperfluorinated molecules [(RFSO2)3C]−1/mMm+ are unknown and would only exhibit a negligible optical activity, due to the low polarizability of the perfluorinated groups. Another subject-matter of the present invention is consequently the use of the compositions of the invention as catalysts in Friedel-Craft reactions, Diels-Alder reactions, aldol reactions, Michael additions, allylation reactions, pinacol coupling reactions, glycosilation reactions, ring opening reactions of oxetanes, methathesis reactions of alkenes, polymerizations of Ziegler-Natta type, polymerizations of the methathesis type by ring opening and polymerizations of the methathesis type of acyclic dienes. The preferred ionic compositions of the invention for use as catalyst for the above reactions are those in which the cation of the salt is chosen from H, lithium, magnesium, transition metals in the divalent or trivalent state, rare earths, platinoids and their organometallic couples, in particular metallocenes. Compositions comprising a salt having an optically active R, R′ or Z substituent are particularly effective in enantioselective catalysis.
The compositions of the invention can also be used as solvent for carrying out chemical, photochemical, electrochemical or photoelectrochemical reactions. For this specific use, preference is given to the ionic compositions in which the salt has a cation of the imidazolium, triazolium, pyridinium or 4-(dimethylamino)pyridinium type, the said cation optionally carrying a substituent on the carbon atoms of the ring, and an anion in which the substituents have a low number of carbon atoms, preferably of less than or equal to 4. Preference is very especially given, among these salts, to those which have a melting point of less than 150° C., more particularly of less than 100° C. The amount of solvent can then be minimized. Use may also be made of a composition comprising a salt of a solvated metal cation, for example solvated by a polyethylene glycol preferably having a mass of less than 1000.
Dyes of cationic type (cyanines) are increasingly frequently used as sensitizers for photographic films, for the optical storage of information (write-accessible optical disks) or for lasers. The tendency of these conjugated molecules to stack together when they are in solid phases limits their use, as a result of variations in the optical properties in comparison with the isolated molecule. The use of ionic compositions of the invention for the manufacture of cationic dyes, the counterions of which, optionally attached to this same molecule, correspond to the functionalities of the invention, makes it possible to reduce the phenomena of aggregation, including in polymer solid matrices, and to stabilize these dyes. Another subject-matter of the present invention is the use of an ionic composition according to the invention as cationic dye composition. The particularly preferred ionic compositions for this application are those which comprise a salt in which the negative charge or charges of the XF
(Z) (Z′), XF
(YR) (Y′R′) or XF
(Z) (YR) anionic group are either attached to the dye molecule or constitute the counterion of the positive charges of the dye. Mention may be made, by way of example of such compounds, of the following compounds: