EP0603370A1 - Oxirane and dioxolane copolymers, process for their preparation and ionic conduction materials containing same - Google Patents

Abstract

The present invention relates to copolymers, their method of preparation and their use for the production of ionically conductive materials. A copolymer according to the invention consists of monomer units corresponding to the formula -CH2-O-CHR-CH2-O- (I) and monomer units corresponding to the formula -CH2-CHR'-O- (II) in which: R represents a hydrogen atom, a linear or branched alkyl radical containing from 1 to 8 carbon atoms or a CH3(-O-CH2-CH2)nO-CH2- radical, in which 1 n 10; R′ represents an aliphatic radical having an unsaturation which can be polymerized by the radical route and which is inert under the conditions of cationic polymerization. The copolymers can be obtained by cationic polymerization of the appropriate oxirane and dioxolane. Application to the production of ionically conductive materials.

Description

 Oxirane and dioxoiane copolymers, their preparation process and ionically conductive materials containing them.

The present invention relates to copolymers, their preparation process and their use for the preparation of ionically conductive materials.

Polymer electrolytes obtained by disso¬ lution of a salt in a solvating polymer comprising hetero atoms are known. Such electrolytes, the solvent of which is a polyethylene oxide or an ethylene oxide copolymer, are described, for example, in EP-A-13199 (M. Armand, M. Duclot). These polymer electrolytes have many applications, in particular in the field of electrochemical generators, light modulation systems (M. Armand et al, EP-87401555), sensors, for example for selective membranes or reference (A. Hammou et al, FR-86.09602).

Polyethylene oxide is a semi-crystalline polymer which forms with salts stoichiometric complexes. The amorphous conductive phases of these complexes only exist above a eutectic temperature generally between 40 ° C and 65 "C depending on the nature of the complexed salts. Good conductivities at ordinary temperature are only obtained with macromolecular systems with little or no crystallinity. Numerous studies have been carried out to improve the conduction properties of these materials. They have resulted, for example, in the formation of oxide-based copolymers. ethylene (M. Armand et al, FR-83.09886). The copolymerization of ethylene oxide with other epoxides such as propylene oxide or ethyl glycidyl ether significantly reduces the crystallinity of the material, however, the statistical introduction of defects results in a notable loss of the solvating and dissociating power of the regular polyethylene oxide sequence The preparation of copolymers having high macromolecular masses es, supé¬ EXTERIORFEATURES 10 ^5, and good mechanical properties, requires high purity reagents and reproducible control of the co-introduced monomèreε rate is difficult because of the difference in reactivity between ethylene oxide and its counterparts.

By polycondensation of oligooxyethylene glycols (M _w ≈ 200 - 1000) with dichloromethane, amorphous polymers having good conductivity but poor mechanical strength were obtained [CV Nicholas, DJ Wilson, C. Booth & RJM Gilles, Brit . Polym. J. 2 _. 0 289 (1988)]. In addition, these materials, which are based on polyethylene oxide, do not have reactive functions and therefore cannot be crosslinked.

Dioxoiane homopolymers are also known which are very crystalline and which have melting temperatures close to 55 "C. The conductivity of the poly-dioxolane / salt complexes at temperatures below 25 ° C. is therefore poor. Furthermore, it is difficult to obtain by cationic polymerization of dioxoiane high-mass polymers, the mechanical properties of the electrolytes prepared from these homopolymers are therefore poor at temperatures above 80 ° C. The purpose of the present invention is to provide materials with ion conduction comprising a solid polymer electrolyte and having both good conductivity and good mechanical strength.

To this end, the present invention relates to a family of crosslinkable copolymers having a low crystallinity.

The invention also relates to a process for the preparation of said copolymers.

Finally, the subject of the invention is materials with ionic conduction, the solvent of which consists essentially of the abovementioned copolymer.

A copolymer according to the invention consists of monomer units corresponding to the formula -CH ₂ -0-CHR-CH ₂ -0- (I) and monomer units corresponding to the formula -CH ₂ -CHR'-0- ( II) in which:

- R represents a hydrogen atom, a linear or branched al yl radical containing from 1 to 8 carbon atoms or a CH ₃ (-0-CH ₂ -CH ₂ ) _n -0-CH ₂ - radical, in which 1 <n <10; - R 'represents an aliphatic radical having an unsaturation which can be polymerized by the radical route and which is inert under the cationic polymerization conditions.

Among the radicals R, H and CH ₃ are very particularly preferred.

The radical R ′ may be chosen from those which comprise ethylenic unsaturation, such as for example the alkenyl radiophiles CH ₂ = CH- (CH ₂ ) _q - in which 1 <q <6 and the radicals CH ₃ - ( CH ₂ ) _y -CH = CH- (CH ₂ ) _X - in which 0 <x + y <5 and 0 <x; among these radicals, there may be mentioned by way of example the radical -CH ₂ -CH ₂ -CH = CH ₂ . R 'can also be chosen from allyloxyalkylene radicals having from 4 to 8 carbon atoms; by way of example, mention may be made of -CH ₂ -0 -CH ₂ -CH = CH ₂ . R ′ can also be chosen from acryloxyalkylene radicals and methacryloxyalkylene radicals, among which - CH ₂ -0-CO-CH = CH and -CH ₂ -0-CO-C (CH ₃ ) = CH ₂ are particularly favorite.

The monomer units (I) and the monomer units (II) constituting a copolymer of the present invention are derived respectively from a dioxoiane and an oxirane.

Preferably, when the copolymers of the present invention are intended to be used as solvent for materials with ionic conduction, the ratio p / (p + m) is between approximately 3% and approximately 30%, more particularly between approximately 5% and approximately 10%, p representing the number of monomer units (II) and m representing the number of monomer units (I) constituting a copolymer of the present invention. The copolymer thus obtained has long blocks (40 to 60 monomer units) of polydioxolane and short blocks of oxirane. However, the overall distribution of the monomer units exhibits a statistical trend.

The copolymers of the present invention can be obtained by cationic polymerization of oxirane

1 1 i 1 0-CH -CHR 'and dioxoiane CH -0-CHR-CH -0 suitable. Different polymerization initiators can be used, among which mention may be made of BF3 (OC2H5) ₂ , C5H5COX ¹ or C6H5CH2 ¹ in which X ¹ represents SbF ₆ , PF ₆ , AsF ₆ , BF, SbF ₆ or CF ₃ SO ₃ , SbFg being particularly preferred, or pCl- ^c 6 ^H ₄ ^N 2 ^γ1 ' ^γl representing PF ₆ or BF ₄ .

The cationic polymerization can be carried out in bulk, the dioxoiane then serving simultaneously as solvent and comonomer. The cationic polymerization can also be carried out in a concentrated solution of monomers in an aprotic solvent. Among these solvents, mention may be made of dichloromethane and nitromethane.

It is particularly advantageous to add the initiator first to the dioxoiane, and then to introduce only the oxirane in order to avoid polymerization of the only oxirane molecules which are more reactive with respect to the cationic polymerization initiator than dioxoiane molecules. The addition of the oxirane can be carried out at once, several times discontinuously, or continuously throughout the duration of the polymerization. The last two modes of addition are preferred because the copolymers obtained give, after crosslinking, a higher rate of insolubles. The copolymers according to the present invention, in which the p / (p + m) ratio is between 3% and 30%, are particularly useful for the preparation of materials with ionic conduction.

The ion-conducting materials of the present invention essentially consist of an easily dissociable salt and a polymer obtained by crosslinking of a copolymer according to the present invention, preferably a copolymer in which the ratio p / (p + m) is between approximately 3% and approximately 30%, more particularly between approximately 5% and approximately 10%. The use of this particular category of copolymers makes it possible to limit the number of crosslinking points which would stiffen the polymer obtained by crosslinking.

The salt introduced into the copolymer before crosslinking or in the crosslinked polymer is chosen from the salts usually used for solid materials with ionic conduction. By way of example, mention may be made of the salts (l / nM) ⁺ X ^~ , M representing a metal cation, an organic cation of the ammonium, amidiniu or guanidinium type; n being valence cation M; X representing an anion with delocalized electronic charge, for example Br ~, ClO ^ -, AsF ₆ ~, R _F S0 ₃ ^~ , (R _F S0 ₂ ) ₂ N ^~ , (R _F Sθ ₂ ) ₃ C ^~ , R _F representing a perfluoroalkyl or perfluoroaryl group. The salt can also be chosen from the salts corresponding to the formula (l / nM) ⁺ [(RpS0 ₂ ) 2CY] "in which Y represents an electron-attracting group chosen from -CΞN and the groups RZ- in which Z represents a carbonyl group, a sulfonyl group or a phosphonyl group and R represents a monovalent organic group, M represents a metal having the valence n or an organic group which may exist in cationic form, Rp represents a perfluoroalkyl or perfluoroaryl group. Such compounds can be prepared by reacting a compound (1 / nM) ⁺ [(RpS0 ₂ ) CH] "with a compound YX in the presence of a nucleotic aprotic base Nu, X representing a halogen or a pseudo-halogen. These salts and their preparation process are described in FR91.13789 filed on 8.11.1991, which will be referred to for more details. The lithium salts are particularly preferred, more especially (CF ₃ S0 ₂ ) 2 ^N ~ ^L i ^{+ and} (CF3SO2) 3C ~ Li ⁺ . Mixtures of salts can be used.

Of course, the ionically conductive materials of the present invention may also contain additives usually used in ionically conductive materials such as plasticizers or stabilizers, depending on the final properties sought.

In a first embodiment, an ionically conductive material is obtained by dissolving the copolymer, the salt and the initiator in a common solvent. The amount of initiator used is advantageously from 2 to 5% by weight relative to the copolymer. The solvent is chosen from volatile solvents; by way of example of such a solvent, mention may be made of acetonitrile, tetrahydrofuran and acetone. The viscous solution obtained is degassed, then spread on an appropriate support, for example a PTFE plate. After evaporation of the solvent, the film obtained is brought to a temperature between 70 ° C. and 120 ° C. depending on the initiator used, for 4 hours. L ¹ cross-linking initiator can be chosen by example among benzoyl peroxide, azobis isobutyronitrile (AIBN) or dicumylperoxide (Dicup). Benzoyl peroxide is particularly preferred.

In another embodiment, the crosslinking of the copolymer in solution in a solvent similar to that described above is carried out first, in the absence of salt, and a membrane is produced in the same manner as above. is lying. The salt is then introduced into the membrane as follows: a very concentrated solution of the salt in acetonitrile is produced, it is made to absorb by the membrane, then the solvent is evaporated. The amount of salt introduced is determined by the difference between the initial weight of the membrane and its final weight.

In a third embodiment, the crosslinking of a copolymer of the present invention is carried out in solution in an appropriate solvent using a radical polymerization initiator, in the presence of a monomer carrying an ionic group and a group crosslinkable by radical route. Such a monomer can be chosen from those which correspond to the general formula (1) ACFX ² -S0 ₂ Z ² in which:

- A represents one of the groups R ¹ R ² N-C0-, R ³ -0-CF ₂ - or

R3-;

- Z ² represents an ionic group; - X ² represents F, Cl, H or R _F ;

- the radicals R ¹ , R ² and R ³ , which are identical or different, are chosen from non-perfluorinated organic radicals comprising a function which can be polymerized by the radical route;

- R _F is chosen from perfluoroalkyl radicals and perfluoroaryl radicals.

The ionic group Z ² is advantageously chosen from l / mM ^ -O] ^" , l / mM" * [- NS0 ₂ Q] ^" , l / mM ^ f-CH (S0Q)] ~ and l / mM ^{m +} [- C (S0 ₂ Q) ₂ ] ^~ , Q representing -R _F or -CFX-A and M "representing an ion of a metal having the valence m, chosen from alkali metals, alkaline earth metals, transition metals and rare earths, or ammonium, amidinium or guanidinium ions.

When A represents a group R ¹ R ² N-CO-, the monomers (1) can be prepared by reaction of an acid fluoride sulfonyl acetic F-COCFX-S0 ₂ F with an amine R ¹ R ² NH in the presence of a base.

When A represents a group R ³ -0-CF2 ~, the monomers (1) can be obtained from the sulfonylacetic acid fluoride by a three-step process: reaction of the sulfonylacetic acid fluoride with a fluoride M 'F; bringing the perfluoroalkoxide obtained into contact with a reagent R ³ Y to obtain the compound R ³ 0-CF-CFX-SO ₂ F; reaction of this compound with the appropriate reagent to replace the fluorine of the SO ₂ F group with an ionic group chosen from l / mM ^ CO] -, l / mM ⁺ [-NS0 ₂ R _F ] ~, 1 / mM "[- CH (S0 ₂ R _F )] ^" or

When group A is R ³ -, the monomers (1) are obtained from the sulfonylacetic acid fluoride by a three-step process. In a first step, the sulfonylacetic acid fluoride is treated with water, which causes hydrolysis followed by decarboxylation. The compound obtained has on the α carbon a proton having an acidic character allowing the formation of a carbion which gives rise, during a second step, to a nucleophilic substitution reaction in the presence of a base. . In a third step, the compound obtained is reacted with the appropriate reagent to replace the fluorine of the SO ₂ F group with an ionic group. Such monomers are described in FR92.02027 deposited on February 21, 1992, to which reference will be made for more details. Among the aforementioned monomers, those which are monomers derived from perhalogenated sultones are particularly interesting. The ion conduction materials obtained, consisting of a crosslinked polymer and a salt, can be used as solid polymer electrolyte in an electrochemical cell. They are particularly useful for electrochemical generators, rechargeable or not. They are also useful in other electrochemical systems such as electrochromic systems, light modulation systems, for the development of selective membranes or reference membranes in membrane sensors. The present invention is illustrated by the following examples given by way of illustration but not limitation.

EXAMPLE 1 37 g of dioxoiane were dissolved in dichloromethane so as to obtain a solution of 5 moles / liter. To this solution, maintained under argon at -20 ° C, was added 1.12 g of benzoyl hexafluoroanti onate in solution in dichloromethane (0.034 mol / liter), then 4.312 g of 1,2-epoxy-hexene -5 in the form of a 0.44 mol / liter solution in dichloromethane, in 0.2 cm ³ fractions every 20 min. The polymerization is considered to be complete after two hours.

Analysis by gas chromatography shows the total disappearance of the epoxy-hexene and the consumption of about 90% of the dioxoiane. The respective proportions of the two monomers in the copolymer obtained, determined by the magnetic resonance spectra H1 recorded in CD ₃ CN, are 12% for 1 epoxy-hexene and 88% for dioxoiane.

After deactivation of the macromolecular chains by addition of a solution of sodium ethanolate in ethanol at a concentration 5 times higher than that of the initiator, the copolymer obtained is purified by dissolution in tetrahydrofuran and precipitation in pentane. The precipitate is filtered, then dried under vacuum at 40 ° C. The molar masses, expressed in polystyrene equivalent, were determined by analysis by steric exclusion chromatography carried out in THF using a set of three columns of Ultrastyragel® (marketed by the company Micropore) having respectively a porosity of 500 , 10 ³ and 10 ⁴ Â. They are: Mp = 68,000 g / mole and Mn = 19,000 g / mole.

Analysis by differential scanning calorimetry (DSC) of the sample shows the presence of two melting peaks at 29 "C and 40 ° C. After fusion and quenching of the sample, the thermogram no longer shows phase crystal and the measured glass transition temperature is 209 K. EXAMPLE 2

4 g of the copolymer obtained in Example 1 are dissolved in acetonitrile, and 80 mg of benzoyl peroxide are added thereto. The solution is spread on a support, and degassed. After evaporation of the solvent, a membrane is obtained which is brought to 70 ° C. for 4 hours, then washed with Soxhlet at

1 acetonitrile for 24 hours. It was thus found that 90% of the copolymer was effectively crosslinked. The thermogram

DSC no longer reveals a melting peak and the glass transition temperature measured is 217 K.

The incorporation into this membrane of lithium bis (trifluorosulfonyl) imide (with an oxygen / lithium concentration ratio of 14) makes it possible to obtain a stable polymer electrolyte up to the temperature of 250 ° C., as evidenced by the thermogravimetric analysis carried out under helium, said polymer electrolyte being perfectly amorphous in the temperature range explored (200 to 450 K) with a glass transition temperature of 235 K.

The conductivity is 2.10 ^-6 S / cm at 5 ° C, 4.10 ^"5 S / cm at 25 ° C and reaches 10 ~ ³ S / cm at 70 ° C. The range of electrochemical stability compared to lithium is 4.5 volts.

EXAMPLE 3

1.5 g of the copolymer obtained in Example 1 were dissolved in 5 ml of acetonitrile; 0.205 g of (CF ₃ S0 ₂ ) 2 ^NL i (O / Li = 30) and 0.06 g of AIBN were added. After degassing, the viscous solution is poured into a glass ring placed on a 10 cm ² PTFE plate. After evaporation of the solvent, the membrane is maintained at 75 ° C for 5 hours to complete the crosslinking. The film obtained has a conductivity of 6.10 ^-6 S / cm at 5 ° C, 9.10 ^"5 S / cm at 30 ° C and 2.10" ³ S / cm at 65 ° C.

EXAMPLE 4 In a solution in acetonitrile of 2 g of a dioxolane / epoxy-1,2,2-hexene-5 copolymer comprising 7% by mole of epoxy hexene and having a mass Mn = 17,000 g / mole, added 1.17 g of monomer (CH ₂ = CH-CH ₂ ) 2NCO-C (CF ₃ ) F-S0 ₃ Li and 0.100 g of benzoyl peroxide. The viscous solution obtained was poured into a glass ring placed on a 10 cm ² PTFE plate. After evaporation of the solvent, the membrane is maintained at 70 ° C for 4 hours to complete the crosslinking. A film having good mechanical strength is obtained. After washing the film with acetonitrile in Soxhlet, the analysis of the washing extracts shows that all the salt introduced has been incorporated into the crosslinked polymer. DCS analysis shows the absence of crystalline phase. The glass transition temperature measured is -61 ° C.

There was thus obtained a grafted anion electrolyte with a conductivity of 10 ~ ⁶ S / cm at 25 ° C, 10 ~ ⁴ S / cm at 70 ° C.

EXAMPLE 5 An electrochemical generator was developed comprising a negative lithium electrode, an ionically conductive material according to the invention as an electrolyte, and a composite positive electrode.

The negative electrode consisted of a layer of lithium having a thickness of 50 μm deposited on a polypropylene film of 8 μm metallized by a layer of 100 nm of nickel. The electrolyte was obtained in the following manner. A copolymer analogous to that used in Example 4 was brought to 40 ° C., and then added thereto without using a solvent 3% by weight of benzoyl peroxide and 35% by weight of salt (CF3SO2) 2 ^NIj i ^le O / Li atomic ratio being 14. The mixture was spread on a 30 μm polypropylene film. After heating for 4 hours at 80 ° C., a film with a thickness of 55 μm was detached from the support and placed on the lithium electrode in a glove box under an atmosphere of aron. The positive electrode used was constituted by a composite material containing 45% by volume of lithium manganite of spinel structure LiMn ₂ 0 ₄ in grains of approximately 8 μ, 5% by volume of acetylene black and 50% by volume d 'a material obtained by incorporating the salt (CF3Sθ2) 2 ^NIj i in a copolymer similar to that used for the electrolyte but not crosslinked, in an amount of 35% by weight of salt relative to the copolymer. The various constituents were mixed at 50 ° C., without the addition of solvent, and the mixture was then spread on a current collector similar to that of the negative electrode.

There was thus obtained a flexible generator 190 μm thick having an emf of 3 volts and a flow rate of 400 μA / cm ² at 50 ° C for a voltage of 2.8 volts.

Claims

1. Copolymer consisting of monomer units corresponding to the formula - (CH2-O-CHR-CH ₂ -0) - (I) and monomeric units corresponding to the formula ~ (CH ₂ -CHR'-O ) - (II), in which:

- R represents a hydrogen atom, an alkyl radical, linear or branched, comprising from 1 to 8 carbon atoms, a radical CH ₃ (-0-CH ₂ -CH ₂ ) _n -0-CH ₂ -, with 1 <n <10; - R 'represents an aliphatic radical having an unsaturation which can be polymerized by a radical and inert route under the conditions of cationic polymerization.

2. Copolymer according to claim 1, characterized in that R 'is a radical CH ₂ = CH- (CH ₂ ) _q - with 1 <q <6, or a radical CH ₃ - (CH ₂ ) _y -CH = CH - (CH ₂ ) _χ -, with 0 <x + y <5 and 0 <x.

3. Copolymer according to claim 1, characterized in that R 'is an allyloxy alkylene radical having from 4 to 8 carbon atoms.

4. Copolymer according to claim 1, characterized in that R 'is an acryloxyalkylene radical or a methacryloxyalkylene radical.

5. Copolymer according to claim 1, characterized in that R 'is chosen from -CH ₂ -CH ₂ -CH = CH ₂ , -CH ₂ -0-CH ₂ -CH = CH ₂ , -CH ₂ -0-CO -CH = CH ₂ or -CH ₂ -0-CO-C (CH ₃ ) = CH ₂ .

6. Copolymer according to claim 1, characterized in that R is H or CH.

7. Copolymer according to claim 1, characterized in that 0.03 <p / m + p <0.3, p representing the number of monomer units (II) and m the number of monomer units (I) killing the copolymer.

8. Copolymer according to claim 7, characterized in that 0.05 <w / m + p <0.1.

9. A method of preparing a copolymer according to claim 1, characterized in that it consists in carrying out a polymerization of a dioxoiane monomer corresponding to the formula CH -O-CHR-CH -0 and of a monomer corresponding to the formula 0-CH ₂ -CΗR 'in the presence of a cationic polymerization initiator.

10. Method according to claim 9, characterized in that the polymerization is carried out in bulk.

11. Method according to claim 9, characterized in that the monomers are dissolved in a common solvent chosen from aprotic solvents.

12. Method according to one of claims 9 to 11, characterized in that the polymerization initiator is chosen from BF ₃ (OC ₂ H5) 2, CgHsCOX ¹ or in which X ¹ represents SbF6, PF5, AsF ₆ , BF ₄ , SbF ₆ , CF ₃ SO ₃ , or pCl-C ₆ H ₄ N ₂ Y ¹ , Y ¹ representing PF ₆ or BF.

13. Ionically conductive material, containing a salt and a polymer solid solvent, characterized in that the polymer solvent consists essentially of at least one polymer obtained by crosslinking a copolymer according to claim 1.

14. Material according to claim 13, characterized in that the copolymer is chosen from those for which the ratio p / (m + p) is between approximately 3% and approximately 30%.

15. Material according to claim 13, characterized in that the salt is chosen from the salts (l / n) M ⁺ X ~, M representing a metallic cation, an organic cation of the ammonium, amidinium or guanidinium type; n being the valence of the cation M; X representing an anion with delocalized electronic charge, for example Br ^~ , CIO /, -, AsFg ^" , R _F S0 ₃ -, (R _F S0 ₂ ) ₂ N ~, (R _F S0 ₂ ) ₃ C ^~ or (R _F Sθ ₂ ) ₂ CY ~, R _F representing a perfluoroalkyl or perfluoroaryl group and Y representing an electron attractor group.

16. Material according to claim 13, characterized in that the copolymer is crosslinked in the presence of a monomer comprising an ionic group and a group which can be polymerized by the radical route.